Nutrient chapter

Paracetamol

Paracetamol, also called acetaminophen. An analgesic and antipyretic that is only weakly anti-inflammatory, does not inhibit platelet function and does not injure the gastric mucosa, and is a weak inhibitor of both cyclooxygenases in isolated enzyme preparations. Its mechanism remains contested: it acts as a reducing cosubstrate at the peroxidase site so that its potency falls as ambient hydroperoxide rises, which would account for the tissue pattern; a proposed third cyclooxygenase does not translate beyond the dog; and in rodents it is deacetylated and conjugated with arachidonic acid to AM404, which carries the analgesia but not the effect on body temperature. It is recorded as an entity distinct from NAPQI, the metabolite that causes the liver injury, and from AM404, and is not linked to either as a family. Species, exposure and limitations are retained in each linked claim.

32 recorded mechanisms · 5 availability situations · 1 preserved sources. Draft and verified records are labeled separately.

Read recorded mechanisms Open recursive mind map

The mechanisms

What the sources say this nutrient does, one relationship at a time. Plain wording comes first; the technical statement follows.

The potency of acetaminophen against both purified ovine cyclooxygenase-1 and human cyclooxygenase-2 was increased approximately 30-fold by the presence of glutathione peroxidase and glutathione, giving half-maximal inhibitory concentrations of 33 and 980 micromolar respectively, acetaminophen was found to be a good reducing agent of both enzymes, and the results are consistent with a mechanism in which it reduces the active oxidized form of the enzyme to the resting form, so that inhibition would be more effective under conditions of low peroxide concentration, consistent with the known tissue selectivity.
Paracetamol → Cyclooxygenase-1 (PTGS1) source_derived_draftungraded
Experimental context and source evidence
evidence_span
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experimental_model
Purified ovine cyclooxygenase-1 and human cyclooxygenase-2 assayed with and without a peroxide-removing system
exposure
Acetaminophen with and without glutathione peroxidase and glutathione
limitations
Adding a peroxide-removing system is the manipulation that reveals the mechanism, because it changes potency thirtyfold without changing the drug. Purified enzyme, so the concentrations are not tissue concentrations.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Sheep and human enzyme
plain_language
Take the peroxide away and the same drug becomes thirty times stronger, which is the whole mechanism in one experiment.
primary_references
[apap-p11370851] Mechanism of acetaminophen inhibition of cyclooxygenase isoforms. (2001). https://pubmed.ncbi.nlm.nih.gov/11370851/ DOI: 10.1006/abbi.2000.2232
tissue_or_cell_type
Purified cyclooxygenase
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 77–88
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified ovine cyclooxygenase-1 and human cyclooxygenase-2 assayed with and without a peroxide-removing system · source_derived_draft · unverified_draft
### apap-potency-depends-on-peroxide The potency of acetaminophen against both purified ovine cyclooxygenase-1 and human cyclooxygenase-2 was increased approximately 30-fold by the presence of glutathione peroxidase and glutathione, giving half-maximal inhibitory concentrations of 33 and 980 micromolar respectively, acetaminophen was found to be a good reducing agent of both enzymes, and the results are consistent with a mechanism in which it reduces the active oxidized form of the enzyme to the resting form, so that inhibition would be more effective under conditions of low peroxide concentration, consistent with the known tissue selectivity. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Take the peroxide away and the same drug becomes thirty times stronger, which is the whole mechanism in one experiment. organism: Sheep and human enzyme tissue_or_cell_type: Purified cyclooxygenase experimental_model: Purified ovine cyclooxygenase-1 and human cyclooxygenase-2 assayed with and without a peroxide-removing system limitations: Adding a peroxide-removing system is the manipulation that reveals the mechanism, because it changes potency thirtyfold without changing the drug. Purified enzyme, so the concentrations are not tissue concentrations. exposure: Acetaminophen with and without glutathione peroxidase and glutathione evidence_span: {"source_cache": "artifacts/paracetamol-research/11370851.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "4eeda4b163828f2cc2a4341c4810df6bf6c683d6165eeb09479104f185e52ca4", "start_char": 0, "end_char": 1086, "text_sha256": "4eeda4b163828f2cc2a4341c4810df6bf6c683d6165eeb09479104f185e52ca4"} [apap-p11370851] Mechanism of acetaminophen inhibition of cyclooxygenase isoforms. (2001). https://pubmed.ncbi.nlm.nih.gov/11370851/ DOI: 10.1006/abbi.2000.2232
Complete structured claim and evidence
Acetaminophen inhibited prostaglandin H synthase activity with a half-maximal inhibitory concentration of 4.3 micromolar in interleukin-1-alpha-stimulated human umbilical vein endothelial cells against 1,870 micromolar in the platelet with 2 micromolar arachidonic acid as substrate, and this difference is not caused by isoform selectivity because acetaminophen inhibits purified ovine prostaglandin H synthase-1 and murine recombinant synthase-2 equally.
Paracetamol → Selectivity of a drug between cell types rather than between enzyme isoforms source_derived_draftungraded
Experimental context and source evidence
availability_state
biomarker_context Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/12011469.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d", "start_char": 0, "end_char": 1561, "text_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d"}
experimental_model
Interleukin-1-alpha-stimulated human endothelial cells and human platelets compared, with hydroperoxide addition
exposure
Acetaminophen with 2 micromolar arachidonic acid, and with prostaglandin G2, 12-hydroperoxyeicosatetraenoic acid or tert-butyl hydroperoxide added back
limitations
The decisive record of the chapter: it measures a 435-fold difference between two human cell types, shows it is not isoform selectivity, and reverses it by adding the peroxide back.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
The same drug is four hundred times weaker in a platelet than in an inflamed blood vessel, and it is not because the enzymes differ.
primary_references
[apap-p12011469] Determinants of the cellular specificity of acetaminophen as an inhibitor of prostaglandin H(2) synthases. (2002). https://pubmed.ncbi.nlm.nih.gov/12011469/ DOI: 10.1073/pnas.102588199
tissue_or_cell_type
Endothelium and platelets
trigger_kind
biomarker_context Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 90–101
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Interleukin-1-alpha-stimulated human endothelial cells and human platelets compared, with hydroperoxide addition · source_derived_draft · unverified_draft
### apap-four-hundred-fold-cell-difference Acetaminophen inhibited prostaglandin H synthase activity with a half-maximal inhibitory concentration of 4.3 micromolar in interleukin-1-alpha-stimulated human umbilical vein endothelial cells against 1,870 micromolar in the platelet with 2 micromolar arachidonic acid as substrate, and this difference is not caused by isoform selectivity because acetaminophen inhibits purified ovine prostaglandin H synthase-1 and murine recombinant synthase-2 equally. Condition category: biomarker_context nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The same drug is four hundred times weaker in a platelet than in an inflamed blood vessel, and it is not because the enzymes differ. organism: Human tissue_or_cell_type: Endothelium and platelets experimental_model: Interleukin-1-alpha-stimulated human endothelial cells and human platelets compared, with hydroperoxide addition limitations: The decisive record of the chapter: it measures a 435-fold difference between two human cell types, shows it is not isoform selectivity, and reverses it by adding the peroxide back. exposure: Acetaminophen with 2 micromolar arachidonic acid, and with prostaglandin G2, 12-hydroperoxyeicosatetraenoic acid or tert-butyl hydroperoxide added back evidence_span: {"source_cache": "artifacts/paracetamol-research/12011469.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d", "start_char": 0, "end_char": 1561, "text_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d"} [apap-p12011469] Determinants of the cellular specificity of acetaminophen as an inhibitor of prostaglandin H(2) synthases. (2002). https://pubmed.ncbi.nlm.nih.gov/12011469/ DOI: 10.1073/pnas.102588199
Complete structured claim and evidence
Increasing the peroxide product of the cyclooxygenase, prostaglandin G2, by elevating the concentration of either enzyme or substrate reverses the inhibitory action of acetaminophen, as does adding prostaglandin G2 itself, 0.3 micromolar 12-hydroperoxyeicosatetraenoic acid which is a major product of the platelet completely reverses the action on synthase-1, and inhibition in endothelial cells is abrogated by tert-butyl hydroperoxide, supporting the hypothesis that hydroperoxide concentration contributes to the cellular selectivity.
Ambient cellular hydroperoxide concentration → Paracetamol source_derived_draftungraded
Experimental context and source evidence
availability_state
biomarker_context Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/12011469.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d", "start_char": 0, "end_char": 1561, "text_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d"}
experimental_model
Interleukin-1-alpha-stimulated human endothelial cells and human platelets compared, with hydroperoxide addition
exposure
Acetaminophen with 2 micromolar arachidonic acid, and with prostaglandin G2, 12-hydroperoxyeicosatetraenoic acid or tert-butyl hydroperoxide added back
limitations
The decisive record of the chapter: it measures a 435-fold difference between two human cell types, shows it is not isoform selectivity, and reverses it by adding the peroxide back.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
Put the peroxide back and the drug stops working, which is why the platelet is untouched.
primary_references
[apap-p12011469] Determinants of the cellular specificity of acetaminophen as an inhibitor of prostaglandin H(2) synthases. (2002). https://pubmed.ncbi.nlm.nih.gov/12011469/ DOI: 10.1073/pnas.102588199
tissue_or_cell_type
Endothelium and platelets
trigger_kind
biomarker_context Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 103–114
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Interleukin-1-alpha-stimulated human endothelial cells and human platelets compared, with hydroperoxide addition · source_derived_draft · unverified_draft
### apap-peroxide-reverses-it Increasing the peroxide product of the cyclooxygenase, prostaglandin G2, by elevating the concentration of either enzyme or substrate reverses the inhibitory action of acetaminophen, as does adding prostaglandin G2 itself, 0.3 micromolar 12-hydroperoxyeicosatetraenoic acid which is a major product of the platelet completely reverses the action on synthase-1, and inhibition in endothelial cells is abrogated by tert-butyl hydroperoxide, supporting the hypothesis that hydroperoxide concentration contributes to the cellular selectivity. Condition category: biomarker_context nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Put the peroxide back and the drug stops working, which is why the platelet is untouched. organism: Human tissue_or_cell_type: Endothelium and platelets experimental_model: Interleukin-1-alpha-stimulated human endothelial cells and human platelets compared, with hydroperoxide addition limitations: The decisive record of the chapter: it measures a 435-fold difference between two human cell types, shows it is not isoform selectivity, and reverses it by adding the peroxide back. exposure: Acetaminophen with 2 micromolar arachidonic acid, and with prostaglandin G2, 12-hydroperoxyeicosatetraenoic acid or tert-butyl hydroperoxide added back evidence_span: {"source_cache": "artifacts/paracetamol-research/12011469.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d", "start_char": 0, "end_char": 1561, "text_sha256": "7e599890f658a63c52471fbc7e6853d7db6a5ecbe892241a39c8a633b3ab2d0d"} [apap-p12011469] Determinants of the cellular specificity of acetaminophen as an inhibitor of prostaglandin H(2) synthases. (2002). https://pubmed.ncbi.nlm.nih.gov/12011469/ DOI: 10.1073/pnas.102588199
Complete structured claim and evidence
Relatively low concentrations of acetaminophen from 20 to 200 micromolar stimulate prostaglandin H synthase activity in ram seminal vesicle microsomes whereas concentrations above 10 millimolar inhibit the conversion of arachidonic acid to prostaglandin G2, both activities apparently involving reduction of oxidized complexes of the enzyme and roughly correlating with the electrochemical half-wave oxidation potentials of a series of hydroxyacetanilides, consistent with common intermediate enzyme forms for both cyclooxygenase and hydroperoxidase catalysed reactions of which one is reduced at low drug concentrations to stimulate and another at higher concentrations to inhibit.
Paracetamol → Cyclooxygenase-1 (PTGS1) source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/3124965.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502", "start_char": 0, "end_char": 2236, "text_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502"}
experimental_model
Ram seminal vesicle microsomal prostaglandin H synthase with product identification by cooxidation
exposure
Acetaminophen from 20 micromolar to above 10 millimolar, with glutathione, ascorbate and indomethacin
limitations
Shows that the drug both stimulates and inhibits the same enzyme depending on concentration, and that the enzyme makes NAPQI from it. A microsomal preparation at concentrations far above therapeutic.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Sheep
plain_language
At low concentrations the drug feeds the enzyme and at high concentrations it stalls it, both by handing over electrons.
primary_references
[apap-p3124965] Acetaminophen and analogs as cosubstrates and inhibitors of prostaglandin H synthase. (1988). https://pubmed.ncbi.nlm.nih.gov/3124965/ DOI: 10.1016/0009-2797(88)90101-9
tissue_or_cell_type
Seminal vesicle microsomes
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 116–127
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Ram seminal vesicle microsomal prostaglandin H synthase with product identification by cooxidation · source_derived_draft · unverified_draft
### apap-stimulates-then-inhibits Relatively low concentrations of acetaminophen from 20 to 200 micromolar stimulate prostaglandin H synthase activity in ram seminal vesicle microsomes whereas concentrations above 10 millimolar inhibit the conversion of arachidonic acid to prostaglandin G2, both activities apparently involving reduction of oxidized complexes of the enzyme and roughly correlating with the electrochemical half-wave oxidation potentials of a series of hydroxyacetanilides, consistent with common intermediate enzyme forms for both cyclooxygenase and hydroperoxidase catalysed reactions of which one is reduced at low drug concentrations to stimulate and another at higher concentrations to inhibit. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: At low concentrations the drug feeds the enzyme and at high concentrations it stalls it, both by handing over electrons. organism: Sheep tissue_or_cell_type: Seminal vesicle microsomes experimental_model: Ram seminal vesicle microsomal prostaglandin H synthase with product identification by cooxidation limitations: Shows that the drug both stimulates and inhibits the same enzyme depending on concentration, and that the enzyme makes NAPQI from it. A microsomal preparation at concentrations far above therapeutic. exposure: Acetaminophen from 20 micromolar to above 10 millimolar, with glutathione, ascorbate and indomethacin evidence_span: {"source_cache": "artifacts/paracetamol-research/3124965.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502", "start_char": 0, "end_char": 2236, "text_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502"} [apap-p3124965] Acetaminophen and analogs as cosubstrates and inhibitors of prostaglandin H synthase. (1988). https://pubmed.ncbi.nlm.nih.gov/3124965/ DOI: 10.1016/0009-2797(88)90101-9
Complete structured claim and evidence
Using acetaminophen as a probe, at low concentrations it is converted in a cooxidation reaction with arachidonic acid to the dimer 4,4-dihydroxy-3,3-biacetanilide and other polymeric products, and the electrophilic metabolite N-acetyl-p-benzoquinone imine was detected directly and indirectly by its reaction with glutathione to form 3-S-glutathionylacetaminophen; the same products were formed by the synthase with hydrogen peroxide in reactions not inhibited by indomethacin, and formation of all products was inhibited by ascorbic acid and butylated hydroxyanisole.
Cyclooxygenase-1 (PTGS1) → N-Acetyl-p-benzoquinone imine / NAPQI source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/3124965.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502", "start_char": 0, "end_char": 2236, "text_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502"}
experimental_model
Ram seminal vesicle microsomal prostaglandin H synthase with product identification by cooxidation
exposure
Acetaminophen from 20 micromolar to above 10 millimolar, with glutathione, ascorbate and indomethacin
limitations
Shows that the drug both stimulates and inhibits the same enzyme depending on concentration, and that the enzyme makes NAPQI from it. A microsomal preparation at concentrations far above therapeutic.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Sheep
plain_language
The prostaglandin enzyme can itself turn the drug into the liver-damaging metabolite.
primary_references
[apap-p3124965] Acetaminophen and analogs as cosubstrates and inhibitors of prostaglandin H synthase. (1988). https://pubmed.ncbi.nlm.nih.gov/3124965/ DOI: 10.1016/0009-2797(88)90101-9
tissue_or_cell_type
Seminal vesicle microsomes
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 129–140
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Ram seminal vesicle microsomal prostaglandin H synthase with product identification by cooxidation · source_derived_draft · unverified_draft
### apap-the-enzyme-makes-napqi Using acetaminophen as a probe, at low concentrations it is converted in a cooxidation reaction with arachidonic acid to the dimer 4,4-dihydroxy-3,3-biacetanilide and other polymeric products, and the electrophilic metabolite N-acetyl-p-benzoquinone imine was detected directly and indirectly by its reaction with glutathione to form 3-S-glutathionylacetaminophen; the same products were formed by the synthase with hydrogen peroxide in reactions not inhibited by indomethacin, and formation of all products was inhibited by ascorbic acid and butylated hydroxyanisole. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The prostaglandin enzyme can itself turn the drug into the liver-damaging metabolite. organism: Sheep tissue_or_cell_type: Seminal vesicle microsomes experimental_model: Ram seminal vesicle microsomal prostaglandin H synthase with product identification by cooxidation limitations: Shows that the drug both stimulates and inhibits the same enzyme depending on concentration, and that the enzyme makes NAPQI from it. A microsomal preparation at concentrations far above therapeutic. exposure: Acetaminophen from 20 micromolar to above 10 millimolar, with glutathione, ascorbate and indomethacin evidence_span: {"source_cache": "artifacts/paracetamol-research/3124965.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502", "start_char": 0, "end_char": 2236, "text_sha256": "dcc85a1ab66984973092042b5553f43fbbe5eb10b674614c9b1fa991b3969502"} [apap-p3124965] Acetaminophen and analogs as cosubstrates and inhibitors of prostaglandin H synthase. (1988). https://pubmed.ncbi.nlm.nih.gov/3124965/ DOI: 10.1016/0009-2797(88)90101-9
Complete structured claim and evidence
Reduction of prostaglandin H synthase compound II to native enzyme by phenol proceeded with a second-order rate constant of 5.3 x 10(5) per molar per second and by hydroquinone at 2.1 x 10(6), rapid scan spectra also showed reduction of compound I to compound II by both so that reduction of both compounds is a one-electron process, and the results suggest the tyrosyl radical detected in the presence of oxidizing agents is formed by intramolecular electron transfer from the tyrosyl residue to the porphyrin pi-cation radical and tends to disappear in the presence of sufficient reducing substrate.
A reducing cosubstrate of the peroxidase → Prostaglandin H synthase compound II source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/1727638.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "028284c7b657c213a3052d362a0a5d050b1678d9ab3c5403b8e68d3631494c0c", "start_char": 0, "end_char": 1789, "text_sha256": "028284c7b657c213a3052d362a0a5d050b1678d9ab3c5403b8e68d3631494c0c"}
experimental_model
Rapid scan spectrometry and transient state kinetics of prostaglandin H synthase compound II reduction
exposure
Phenol and hydroquinone as reducing cosubstrates, with indomethacin
limitations
Measures the reduction step directly with rate constants rather than inferring it from inhibition. It uses phenol and hydroquinone rather than paracetamol, which is recorded on the claim.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Enzyme
plain_language
A phenol hands the enzyme one electron at a time, and enough of it makes the radical the enzyme needs disappear.
primary_references
[apap-p1727638] Reduction of prostaglandin H synthase compound II by phenol and hydroquinone, and the effect of indomethacin. (1992). https://pubmed.ncbi.nlm.nih.gov/1727638/ DOI: 10.1016/0003-9861(92)90070-d
tissue_or_cell_type
Purified prostaglandin H synthase
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 142–153
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Rapid scan spectrometry and transient state kinetics of prostaglandin H synthase compound II reduction · source_derived_draft · unverified_draft
### apap-one-electron-reduction Reduction of prostaglandin H synthase compound II to native enzyme by phenol proceeded with a second-order rate constant of 5.3 x 10(5) per molar per second and by hydroquinone at 2.1 x 10(6), rapid scan spectra also showed reduction of compound I to compound II by both so that reduction of both compounds is a one-electron process, and the results suggest the tyrosyl radical detected in the presence of oxidizing agents is formed by intramolecular electron transfer from the tyrosyl residue to the porphyrin pi-cation radical and tends to disappear in the presence of sufficient reducing substrate. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: A phenol hands the enzyme one electron at a time, and enough of it makes the radical the enzyme needs disappear. organism: Enzyme tissue_or_cell_type: Purified prostaglandin H synthase experimental_model: Rapid scan spectrometry and transient state kinetics of prostaglandin H synthase compound II reduction limitations: Measures the reduction step directly with rate constants rather than inferring it from inhibition. It uses phenol and hydroquinone rather than paracetamol, which is recorded on the claim. exposure: Phenol and hydroquinone as reducing cosubstrates, with indomethacin evidence_span: {"source_cache": "artifacts/paracetamol-research/1727638.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "028284c7b657c213a3052d362a0a5d050b1678d9ab3c5403b8e68d3631494c0c", "start_char": 0, "end_char": 1789, "text_sha256": "028284c7b657c213a3052d362a0a5d050b1678d9ab3c5403b8e68d3631494c0c"} [apap-p1727638] Reduction of prostaglandin H synthase compound II by phenol and hydroquinone, and the effect of indomethacin. (1992). https://pubmed.ncbi.nlm.nih.gov/1727638/ DOI: 10.1016/0003-9861(92)90070-d
Complete structured claim and evidence
Higher concentrations of eugenol were required to inhibit iron-reconstituted prostaglandin H synthase than the manganese-reconstituted enzyme which retains cyclooxygenase but not peroxidase activity, inhibition was highly dependent on arachidonic acid concentration, adding 10 micromolar prostaglandin G2 did not prevent the inhibitory effects, and other phenolic compounds including guaiacol, butylated hydroxyanisole and acetaminophen inhibited the manganese enzyme similarly, demonstrating that these compounds specifically inhibit the cyclooxygenase component in addition to or independent of their effect on peroxide tone, which the authors suggest is due to competition with arachidonic acid for the active site.
Paracetamol → Prostaglandin H synthase reconstituted with manganese protoporphyrin, retaining cyclooxygenase but little peroxidase activity source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/2511429.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8dbe8c6f23fc857be6bba07e2a518c59f8dc76c9f8625c25ba84030c43f6e636", "start_char": 0, "end_char": 1593, "text_sha256": "8dbe8c6f23fc857be6bba07e2a518c59f8dc76c9f8625c25ba84030c43f6e636"}
experimental_model
Prostaglandin H synthase apoenzyme reconstituted with manganese or iron protoporphyrin
exposure
Eugenol, guaiacol, butylated hydroxyanisole and acetaminophen against both reconstituted forms, with prostaglandin G2 added
limitations
The manganese-reconstituted enzyme retains cyclooxygenase but little peroxidase activity, which is what lets this study separate the two proposed sites. Its conclusion is the opposite of the peroxide-tone account.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Enzyme
plain_language
In an enzyme stripped of its peroxidase the drug still works, which argues it also competes at the other site.
primary_references
[apap-p2511429] Mechanism of inhibition of prostaglandin H synthase by eugenol and other phenolic peroxidase substrates. (1989). https://pubmed.ncbi.nlm.nih.gov/2511429/ DOI: 10.1016/s0026-895x(25)09658-0
tissue_or_cell_type
Reconstituted prostaglandin H synthase
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 155–166
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Prostaglandin H synthase apoenzyme reconstituted with manganese or iron protoporphyrin · source_derived_draft · unverified_draft
### apap-maybe-the-cox-site-instead Higher concentrations of eugenol were required to inhibit iron-reconstituted prostaglandin H synthase than the manganese-reconstituted enzyme which retains cyclooxygenase but not peroxidase activity, inhibition was highly dependent on arachidonic acid concentration, adding 10 micromolar prostaglandin G2 did not prevent the inhibitory effects, and other phenolic compounds including guaiacol, butylated hydroxyanisole and acetaminophen inhibited the manganese enzyme similarly, demonstrating that these compounds specifically inhibit the cyclooxygenase component in addition to or independent of their effect on peroxide tone, which the authors suggest is due to competition with arachidonic acid for the active site. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: In an enzyme stripped of its peroxidase the drug still works, which argues it also competes at the other site. organism: Enzyme tissue_or_cell_type: Reconstituted prostaglandin H synthase experimental_model: Prostaglandin H synthase apoenzyme reconstituted with manganese or iron protoporphyrin limitations: The manganese-reconstituted enzyme retains cyclooxygenase but little peroxidase activity, which is what lets this study separate the two proposed sites. Its conclusion is the opposite of the peroxide-tone account. exposure: Eugenol, guaiacol, butylated hydroxyanisole and acetaminophen against both reconstituted forms, with prostaglandin G2 added evidence_span: {"source_cache": "artifacts/paracetamol-research/2511429.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8dbe8c6f23fc857be6bba07e2a518c59f8dc76c9f8625c25ba84030c43f6e636", "start_char": 0, "end_char": 1593, "text_sha256": "8dbe8c6f23fc857be6bba07e2a518c59f8dc76c9f8625c25ba84030c43f6e636"} [apap-p2511429] Mechanism of inhibition of prostaglandin H synthase by eugenol and other phenolic peroxidase substrates. (1989). https://pubmed.ncbi.nlm.nih.gov/2511429/ DOI: 10.1016/s0026-895x(25)09658-0
Complete structured claim and evidence
Salicylate inhibits prostaglandin H synthase-1 and -2 with a potency inversely related to ambient hydroperoxide concentrations and its inhibition of synthase-1 was prevented by 12-hydroperoxyeicosatetraenoic acid, but unlike typical phenolic inhibitors such as acetaminophen, salicylate was ineffective as a reducing cosubstrate for the peroxidase activity, implicating the cyclooxygenase site as its target; 12-HPETE does not prevent inhibition of the manganese-reconstituted enzyme by salicylate, indicating that reversal by hydroperoxides depends on electron transfer between the cyclooxygenase and peroxidase active sites.
Salicylate / salicylic acid → Paracetamol source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/12538810.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "23bbb8a6c280cfcae85e304695c2a93f2c748c804befc1e006f415f4f8dfaed0", "start_char": 0, "end_char": 1592, "text_sha256": "23bbb8a6c280cfcae85e304695c2a93f2c748c804befc1e006f415f4f8dfaed0"}
experimental_model
Prostaglandin H synthase inhibition by salicylate compared with phenolic inhibitors, using manganese-reconstituted enzyme
exposure
Salicylate and benzoic acid analogues, with 12-hydroperoxyeicosatetraenoic acid and prostaglandin G2
limitations
Recorded here because it separates paracetamol from salicylate mechanistically while showing both are peroxide-sensitive. The work is on salicylate, which is stated on the claim.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Enzyme
plain_language
Two drugs that both stop working when peroxide is high, reaching that point by different routes.
primary_references
[apap-p12538810] Inhibition of prostaglandin H2 synthases by salicylate is dependent on the oxidative state of the enzymes. (2003). https://pubmed.ncbi.nlm.nih.gov/12538810/ DOI: 10.1124/jpet.102.042853
tissue_or_cell_type
Prostaglandin H synthase
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 168–179
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Prostaglandin H synthase inhibition by salicylate compared with phenolic inhibitors, using manganese-reconstituted enzyme · source_derived_draft · unverified_draft
### apap-salicylate-is-not-a-cosubstrate Salicylate inhibits prostaglandin H synthase-1 and -2 with a potency inversely related to ambient hydroperoxide concentrations and its inhibition of synthase-1 was prevented by 12-hydroperoxyeicosatetraenoic acid, but unlike typical phenolic inhibitors such as acetaminophen, salicylate was ineffective as a reducing cosubstrate for the peroxidase activity, implicating the cyclooxygenase site as its target; 12-HPETE does not prevent inhibition of the manganese-reconstituted enzyme by salicylate, indicating that reversal by hydroperoxides depends on electron transfer between the cyclooxygenase and peroxidase active sites. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Two drugs that both stop working when peroxide is high, reaching that point by different routes. organism: Enzyme tissue_or_cell_type: Prostaglandin H synthase experimental_model: Prostaglandin H synthase inhibition by salicylate compared with phenolic inhibitors, using manganese-reconstituted enzyme limitations: Recorded here because it separates paracetamol from salicylate mechanistically while showing both are peroxide-sensitive. The work is on salicylate, which is stated on the claim. exposure: Salicylate and benzoic acid analogues, with 12-hydroperoxyeicosatetraenoic acid and prostaglandin G2 evidence_span: {"source_cache": "artifacts/paracetamol-research/12538810.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "23bbb8a6c280cfcae85e304695c2a93f2c748c804befc1e006f415f4f8dfaed0", "start_char": 0, "end_char": 1592, "text_sha256": "23bbb8a6c280cfcae85e304695c2a93f2c748c804befc1e006f415f4f8dfaed0"} [apap-p12538810] Inhibition of prostaglandin H2 synthases by salicylate is dependent on the oxidative state of the enzymes. (2003). https://pubmed.ncbi.nlm.nih.gov/12538810/ DOI: 10.1124/jpet.102.042853
Complete structured claim and evidence
Paracetamol and salicylate are weak inhibitors of both isolated cyclooxygenase-1 and -2 but potent inhibitors of prostaglandin synthesis in intact cells if low concentrations of arachidonic acid are available, the effects of both being overcome by increased hydroperoxide levels; at low arachidonic acid concentrations cyclooxygenase-2 is the major isoenzyme involved when both are present, so these drugs may selectively inhibit synthesis involving cyclooxygenase-2 because the lower flux through that pathway produces less prostaglandin G2 than the pathway involving cyclooxygenase-1, and the authors propose the class name peroxide sensitive analgesic and antipyretic drugs.
Ambient cellular hydroperoxide concentration → The ratio of cyclooxygenase-1 to cyclooxygenase-2 inhibitory potency source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/15035793.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "f72415969de66bea6c0588049cbe1fd1a4b23195c0e2f5a60293eaf99a0f641e", "start_char": 0, "end_char": 1279, "text_sha256": "f72415969de66bea6c0588049cbe1fd1a4b23195c0e2f5a60293eaf99a0f641e"}
experimental_model
Review of the mechanism of paracetamol and salicylate as peroxide-sensitive inhibitors
exposure
Paracetamol and salicylate at low arachidonic acid concentrations
limitations
A review proposing a drug class rather than a new measurement. Its argument that apparent cyclooxygenase-2 selectivity arises from flux rather than binding is the useful part.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human and enzyme
plain_language
The apparent preference for the second enzyme may be nothing to do with binding it, and everything to do with how much peroxide each pathway makes.
primary_references
[apap-p15035793] Mechanisms of action of paracetamol and related analgesics. (2003). https://pubmed.ncbi.nlm.nih.gov/15035793/ DOI: 10.1163/156856003322699573
tissue_or_cell_type
Cyclooxygenase
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 181–192
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Review of the mechanism of paracetamol and salicylate as peroxide-sensitive inhibitors · source_derived_draft · unverified_draft
### apap-apparent-selectivity-from-flux Paracetamol and salicylate are weak inhibitors of both isolated cyclooxygenase-1 and -2 but potent inhibitors of prostaglandin synthesis in intact cells if low concentrations of arachidonic acid are available, the effects of both being overcome by increased hydroperoxide levels; at low arachidonic acid concentrations cyclooxygenase-2 is the major isoenzyme involved when both are present, so these drugs may selectively inhibit synthesis involving cyclooxygenase-2 because the lower flux through that pathway produces less prostaglandin G2 than the pathway involving cyclooxygenase-1, and the authors propose the class name peroxide sensitive analgesic and antipyretic drugs. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The apparent preference for the second enzyme may be nothing to do with binding it, and everything to do with how much peroxide each pathway makes. organism: Human and enzyme tissue_or_cell_type: Cyclooxygenase experimental_model: Review of the mechanism of paracetamol and salicylate as peroxide-sensitive inhibitors limitations: A review proposing a drug class rather than a new measurement. Its argument that apparent cyclooxygenase-2 selectivity arises from flux rather than binding is the useful part. exposure: Paracetamol and salicylate at low arachidonic acid concentrations evidence_span: {"source_cache": "artifacts/paracetamol-research/15035793.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "f72415969de66bea6c0588049cbe1fd1a4b23195c0e2f5a60293eaf99a0f641e", "start_char": 0, "end_char": 1279, "text_sha256": "f72415969de66bea6c0588049cbe1fd1a4b23195c0e2f5a60293eaf99a0f641e"} [apap-p15035793] Mechanisms of action of paracetamol and related analgesics. (2003). https://pubmed.ncbi.nlm.nih.gov/15035793/ DOI: 10.1163/156856003322699573
Complete structured claim and evidence
A third distinct cyclooxygenase isozyme, COX-3, made from the cyclooxygenase-1 gene but retaining intron 1 in its messenger RNA, was described as expressed in canine cerebral cortex and as an approximately 5.2 kilobase transcript most abundant in human cerebral cortex and heart, the retained intron introducing an insertion of 30 to 34 amino acids into the hydrophobic signal peptide; canine COX-3 expressed in insect cells possessed glycosylation-dependent cyclooxygenase activity and was selectively inhibited by analgesic and antipyretic drugs such as acetaminophen, phenacetin, antipyrine and dipyrone, so that inhibition of COX-3 could represent a primary central mechanism by which these drugs decrease pain and possibly fever.
Paracetamol → COX-3 / COX-1b, a cyclooxygenase-1 transcript retaining intron 1 source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/12242329.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "0c00962f9e58da9af386335ac3312d5c260d637270d80481a6f55d0ebec67a78", "start_char": 0, "end_char": 1711, "text_sha256": "0c00962f9e58da9af386335ac3312d5c260d637270d80481a6f55d0ebec67a78"}
experimental_model
Cloning and expression of cyclooxygenase-1-derived transcripts from canine cerebral cortex in insect cells
exposure
Canine COX-3 compared with murine cyclooxygenase-1 and -2 against acetaminophen, phenacetin, antipyrine and dipyrone
limitations
The paper that proposed the answer. Its activity data are for the canine protein expressed in insect cells; the human claim is about messenger RNA abundance, not about an active protein.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Dog and human
plain_language
A third form of the enzyme was reported in dog brain, and it was the one this drug blocked.
primary_references
[apap-p12242329] COX-3, a cyclooxygenase-1 variant inhibited by acetaminophen and other analgesic/antipyretic drugs: cloning, structure, and expression. (2002). https://pubmed.ncbi.nlm.nih.gov/12242329/ DOI: 10.1073/pnas.162468699
tissue_or_cell_type
Cerebral cortex
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 194–205
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Cloning and expression of cyclooxygenase-1-derived transcripts from canine cerebral cortex in insect cells · source_derived_draft · unverified_draft
### apap-cox3-proposed A third distinct cyclooxygenase isozyme, COX-3, made from the cyclooxygenase-1 gene but retaining intron 1 in its messenger RNA, was described as expressed in canine cerebral cortex and as an approximately 5.2 kilobase transcript most abundant in human cerebral cortex and heart, the retained intron introducing an insertion of 30 to 34 amino acids into the hydrophobic signal peptide; canine COX-3 expressed in insect cells possessed glycosylation-dependent cyclooxygenase activity and was selectively inhibited by analgesic and antipyretic drugs such as acetaminophen, phenacetin, antipyrine and dipyrone, so that inhibition of COX-3 could represent a primary central mechanism by which these drugs decrease pain and possibly fever. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: A third form of the enzyme was reported in dog brain, and it was the one this drug blocked. organism: Dog and human tissue_or_cell_type: Cerebral cortex experimental_model: Cloning and expression of cyclooxygenase-1-derived transcripts from canine cerebral cortex in insect cells limitations: The paper that proposed the answer. Its activity data are for the canine protein expressed in insect cells; the human claim is about messenger RNA abundance, not about an active protein. exposure: Canine COX-3 compared with murine cyclooxygenase-1 and -2 against acetaminophen, phenacetin, antipyrine and dipyrone evidence_span: {"source_cache": "artifacts/paracetamol-research/12242329.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "0c00962f9e58da9af386335ac3312d5c260d637270d80481a6f55d0ebec67a78", "start_char": 0, "end_char": 1711, "text_sha256": "0c00962f9e58da9af386335ac3312d5c260d637270d80481a6f55d0ebec67a78"} [apap-p12242329] COX-3, a cyclooxygenase-1 variant inhibited by acetaminophen and other analgesic/antipyretic drugs: cloning, structure, and expression. (2002). https://pubmed.ncbi.nlm.nih.gov/12242329/ DOI: 10.1073/pnas.162468699
Complete structured claim and evidence
Acetaminophen has potent antipyretic and analgesic actions but very weak anti-inflammatory activity, and when administered to humans it reduces levels of prostaglandin metabolites in urine but does not reduce synthesis of prostaglandins by blood platelets or by the stomach mucosa; because it is a weak inhibitor in vitro of both cyclooxygenase-1 and -2 the possibility exists that it inhibits a so far unidentified form, and in animal studies cyclooxygenase in homogenates of different tissues varies in sensitivity to its inhibitory action, which may be evidence that there are more than two isoforms.
Paracetamol → Platelet thromboxane A2 production in vitro source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/11113024.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "f3d9785240d2bc30e79775035576d3b017471500c110d627653e6fd80e820eee", "start_char": 0, "end_char": 1012, "text_sha256": "f3d9785240d2bc30e79775035576d3b017471500c110d627653e6fd80e820eee"}
experimental_model
Review of the evidence for an unidentified cyclooxygenase form, written before COX-3 was cloned
exposure
Acetaminophen compared against its effects on urinary prostaglandin metabolites and on platelet and gastric prostaglandin synthesis
limitations
A review that states the puzzle precisely before an answer existed. The human observations it collects are the clinical signature any mechanism has to explain.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human and animal
plain_language
It lowers prostaglandins measured in urine while leaving the platelet and the stomach alone, and that is the puzzle every account has to solve.
primary_references
[apap-p11113024] Mechanism of action of acetaminophen: is there a cyclooxygenase 3? (2000). https://pubmed.ncbi.nlm.nih.gov/11113024/ DOI: 10.1086/317520
tissue_or_cell_type
Platelets, gastric mucosa and tissue homogenates
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 207–218
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Review of the evidence for an unidentified cyclooxygenase form, written before COX-3 was cloned · source_derived_draft · unverified_draft
### apap-the-puzzle-stated Acetaminophen has potent antipyretic and analgesic actions but very weak anti-inflammatory activity, and when administered to humans it reduces levels of prostaglandin metabolites in urine but does not reduce synthesis of prostaglandins by blood platelets or by the stomach mucosa; because it is a weak inhibitor in vitro of both cyclooxygenase-1 and -2 the possibility exists that it inhibits a so far unidentified form, and in animal studies cyclooxygenase in homogenates of different tissues varies in sensitivity to its inhibitory action, which may be evidence that there are more than two isoforms. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: It lowers prostaglandins measured in urine while leaving the platelet and the stomach alone, and that is the puzzle every account has to solve. organism: Human and animal tissue_or_cell_type: Platelets, gastric mucosa and tissue homogenates experimental_model: Review of the evidence for an unidentified cyclooxygenase form, written before COX-3 was cloned limitations: A review that states the puzzle precisely before an answer existed. The human observations it collects are the clinical signature any mechanism has to explain. exposure: Acetaminophen compared against its effects on urinary prostaglandin metabolites and on platelet and gastric prostaglandin synthesis evidence_span: {"source_cache": "artifacts/paracetamol-research/11113024.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "f3d9785240d2bc30e79775035576d3b017471500c110d627653e6fd80e820eee", "start_char": 0, "end_char": 1012, "text_sha256": "f3d9785240d2bc30e79775035576d3b017471500c110d627653e6fd80e820eee"} [apap-p11113024] Mechanism of action of acetaminophen: is there a cyclooxygenase 3? (2000). https://pubmed.ncbi.nlm.nih.gov/11113024/ DOI: 10.1086/317520
Complete structured claim and evidence
The 98 base pair intron 1 of the cyclooxygenase-1 gene remains unprocessed in rat COX-1b messenger RNA, causing a frameshift mutation and a 127 amino acid open reading frame with no sequence similarity with known cyclooxygenases, and transfection of COS-7 cells produced a protein of the expected size which was also detected in rat tissues with highest expression in heart, kidney and neuronal tissue, but rat COX-1b does not have cyclooxygenase activity and does not have any effect on the inhibition of prostaglandin production by acetaminophen, leading the authors to propose the name cyclooxygenase variant protein instead.
Intron 1 of the cyclooxygenase-1 gene → A frameshift arising from retention of an unprocessed intron source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/15650114.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "1661f4d2b21244e0fc16b9a3b947cf4d09d39be35367ed263cce441f43a60563", "start_char": 0, "end_char": 1473, "text_sha256": "1661f4d2b21244e0fc16b9a3b947cf4d09d39be35367ed263cce441f43a60563"}
experimental_model
Cloning and sequencing of rat COX-1b from cerebral endothelial cells with transfection and antibody generation
exposure
Rat COX-1b complementary DNA transfected into COS-7 cells, assayed for activity and for effect on acetaminophen inhibition
limitations
Tests the proposal in a second species by building the protein and asking whether it works. The protein is detected in rat tissue, so the finding is that it exists and is not a cyclooxygenase.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Rat
plain_language
In the rat the retained intron shifts the reading frame, so what is made is a different protein altogether and not an enzyme.
primary_references
[apap-p15650114] Cloning and characterization of cyclooxygenase-1b (putative cyclooxygenase-3) in rat. (2005). https://pubmed.ncbi.nlm.nih.gov/15650114/ DOI: 10.1124/jpet.104.079533
tissue_or_cell_type
Cerebral endothelial cells
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 220–231
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Cloning and sequencing of rat COX-1b from cerebral endothelial cells with transfection and antibody generation · source_derived_draft · unverified_draft
### apap-frameshift-makes-a-different-protein The 98 base pair intron 1 of the cyclooxygenase-1 gene remains unprocessed in rat COX-1b messenger RNA, causing a frameshift mutation and a 127 amino acid open reading frame with no sequence similarity with known cyclooxygenases, and transfection of COS-7 cells produced a protein of the expected size which was also detected in rat tissues with highest expression in heart, kidney and neuronal tissue, but rat COX-1b does not have cyclooxygenase activity and does not have any effect on the inhibition of prostaglandin production by acetaminophen, leading the authors to propose the name cyclooxygenase variant protein instead. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: In the rat the retained intron shifts the reading frame, so what is made is a different protein altogether and not an enzyme. organism: Rat tissue_or_cell_type: Cerebral endothelial cells experimental_model: Cloning and sequencing of rat COX-1b from cerebral endothelial cells with transfection and antibody generation limitations: Tests the proposal in a second species by building the protein and asking whether it works. The protein is detected in rat tissue, so the finding is that it exists and is not a cyclooxygenase. exposure: Rat COX-1b complementary DNA transfected into COS-7 cells, assayed for activity and for effect on acetaminophen inhibition evidence_span: {"source_cache": "artifacts/paracetamol-research/15650114.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "1661f4d2b21244e0fc16b9a3b947cf4d09d39be35367ed263cce441f43a60563", "start_char": 0, "end_char": 1473, "text_sha256": "1661f4d2b21244e0fc16b9a3b947cf4d09d39be35367ed263cce441f43a60563"} [apap-p15650114] Cloning and characterization of cyclooxygenase-1b (putative cyclooxygenase-3) in rat. (2005). https://pubmed.ncbi.nlm.nih.gov/15650114/ DOI: 10.1124/jpet.104.079533
Complete structured claim and evidence
Prostanoid production by rat aorta, heart, lung and whole blood was inhibited by all drugs tested with the order of potency SC560 greater than naproxen greater than acetaminophen greater than or equal to rofecoxib while in brain and cerebellum no differences among drug potencies were found, Western blotting using a commercially available antibody raised against canine COX-3 failed to detect any immunoreactive proteins, and the authors conclude that cyclooxygenase-1 and -2 are the functional forms present in the rat tissues tested, that acetaminophen is not a selective inhibitor of cyclooxygenase activities in the central nervous system, and that expression of an active cyclooxygenase protein from COX-3 messenger RNA in the rat is apparently impossible.
COX-3 / COX-1b, a cyclooxygenase-1 transcript retaining intron 1 → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/15148345.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c", "start_char": 0, "end_char": 1940, "text_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c"}
experimental_model
Comparison of acetaminophen, rofecoxib, naproxen and SC560 across rat aorta, heart, lung, brain, cerebellum and whole blood
exposure
Four drugs of differing isoform selectivity, with transcript and protein detection including an anti-canine-COX-3 antibody
limitations
Tests the proposal functionally across tissues and looks for the protein directly. A rat study, and a negative Western blot is weaker evidence than a positive one.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Rat
plain_language
Nobody could find the protein, and in brain the drug showed no special selectivity at all.
primary_references
[apap-p15148345] Cyclooxygenases 1, 2, and 3 and the production of prostaglandin I2: investigating the activities of acetaminophen and cyclooxygenase-2-selective inhibitors in rat tissues. (2004). https://pubmed.ncbi.nlm.nih.gov/15148345/ DOI: 10.1124/jpet.103.063875
tissue_or_cell_type
Multiple tissues
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 233–244
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Comparison of acetaminophen, rofecoxib, naproxen and SC560 across rat aorta, heart, lung, brain, cerebellum and whole blood · source_derived_draft · unverified_draft
### apap-no-cox3-protein-found Prostanoid production by rat aorta, heart, lung and whole blood was inhibited by all drugs tested with the order of potency SC560 greater than naproxen greater than acetaminophen greater than or equal to rofecoxib while in brain and cerebellum no differences among drug potencies were found, Western blotting using a commercially available antibody raised against canine COX-3 failed to detect any immunoreactive proteins, and the authors conclude that cyclooxygenase-1 and -2 are the functional forms present in the rat tissues tested, that acetaminophen is not a selective inhibitor of cyclooxygenase activities in the central nervous system, and that expression of an active cyclooxygenase protein from COX-3 messenger RNA in the rat is apparently impossible. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Nobody could find the protein, and in brain the drug showed no special selectivity at all. organism: Rat tissue_or_cell_type: Multiple tissues experimental_model: Comparison of acetaminophen, rofecoxib, naproxen and SC560 across rat aorta, heart, lung, brain, cerebellum and whole blood limitations: Tests the proposal functionally across tissues and looks for the protein directly. A rat study, and a negative Western blot is weaker evidence than a positive one. exposure: Four drugs of differing isoform selectivity, with transcript and protein detection including an anti-canine-COX-3 antibody evidence_span: {"source_cache": "artifacts/paracetamol-research/15148345.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c", "start_char": 0, "end_char": 1940, "text_sha256": "6ca43f39a9bb4cbc398f4f7f6e3401854f6c100b72fb7fdf952ee49486438d3c"} [apap-p15148345] Cyclooxygenases 1, 2, and 3 and the production of prostaglandin I2: investigating the activities of acetaminophen and cyclooxygenase-2-selective inhibitors in rat tissues. (2004). https://pubmed.ncbi.nlm.nih.gov/15148345/ DOI: 10.1124/jpet.103.063875
Complete structured claim and evidence
Although COX-3 might have cyclooxygenase activity in canines and that activity might be inhibited by acetaminophen, its low expression level and the kinetics indicate unlikely clinical relevance, and in rodents and humans COX-3 encodes proteins with completely different amino acid sequences than cyclooxygenase-1 or -2 and without cyclooxygenase activity, so it is improbable that it plays a role in prostaglandin-mediated fever and pain in these species.
COX-3 / COX-1b, a cyclooxygenase-1 transcript retaining intron 1 → Reduction of a raised body temperature source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/15879007.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "857ae81119eac4c47a63027afa15fde1b0099c377c0d444e13da087ea71dec86", "start_char": 0, "end_char": 807, "text_sha256": "857ae81119eac4c47a63027afa15fde1b0099c377c0d444e13da087ea71dec86"}
experimental_model
Critical review of the COX-3 literature
exposure
Evaluation of the expression levels, kinetics and species differences of the proposed isoform
limitations
A review rather than new data. It states the species-specific reason the proposal fails and the reason it would not matter even where the protein is active.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Dog, rodent and human
plain_language
Even in the dog the amounts are too small to matter, and in people the protein is not an enzyme.
primary_references
[apap-p15879007] Acetaminophen and the cyclooxygenase-3 puzzle: sorting out facts, fictions, and uncertainties. (2005). https://pubmed.ncbi.nlm.nih.gov/15879007/ DOI: 10.1124/jpet.105.085431
tissue_or_cell_type
Cyclooxygenase variants
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 246–257
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Critical review of the COX-3 literature · source_derived_draft · unverified_draft
### apap-unlikely-in-any-species Although COX-3 might have cyclooxygenase activity in canines and that activity might be inhibited by acetaminophen, its low expression level and the kinetics indicate unlikely clinical relevance, and in rodents and humans COX-3 encodes proteins with completely different amino acid sequences than cyclooxygenase-1 or -2 and without cyclooxygenase activity, so it is improbable that it plays a role in prostaglandin-mediated fever and pain in these species. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Even in the dog the amounts are too small to matter, and in people the protein is not an enzyme. organism: Dog, rodent and human tissue_or_cell_type: Cyclooxygenase variants experimental_model: Critical review of the COX-3 literature limitations: A review rather than new data. It states the species-specific reason the proposal fails and the reason it would not matter even where the protein is active. exposure: Evaluation of the expression levels, kinetics and species differences of the proposed isoform evidence_span: {"source_cache": "artifacts/paracetamol-research/15879007.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "857ae81119eac4c47a63027afa15fde1b0099c377c0d444e13da087ea71dec86", "start_char": 0, "end_char": 807, "text_sha256": "857ae81119eac4c47a63027afa15fde1b0099c377c0d444e13da087ea71dec86"} [apap-p15879007] Acetaminophen and the cyclooxygenase-3 puzzle: sorting out facts, fictions, and uncertainties. (2005). https://pubmed.ncbi.nlm.nih.gov/15879007/ DOI: 10.1124/jpet.105.085431
Complete structured claim and evidence
In vitro acetaminophen elicited a 4.4-fold selectivity toward cyclooxygenase-2 inhibition with half-maximal inhibitory concentrations of 113.7 micromolar for cyclooxygenase-1 and 25.8 micromolar for cyclooxygenase-2, following a single oral 1000 milligram dose maximal ex vivo inhibitions were 56% for cyclooxygenase-1 and 83% for cyclooxygenase-2, plasma concentrations remained above the in vitro cyclooxygenase-2 value for at least 5 hours, and ex vivo values compared favourably with in vitro ones; acetaminophen inhibited cyclooxygenase-2 by more than 80%, comparable to non-steroidal anti-inflammatory drugs and selective inhibitors, but the greater than 95% cyclooxygenase-1 blockade relevant for suppression of platelet function was not achieved, and in view of its substantial cyclooxygenase-2 inhibition the cardiovascular warnings defined for selective inhibitors should also be considered.
Paracetamol → Cyclooxygenase-2 (PTGS2) source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/17884974.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "e2856e9fc1c319219fd3d3cb145f70bb1157f7ca0baa0221594c9583cf7ddc23", "start_char": 0, "end_char": 1857, "text_sha256": "e2856e9fc1c319219fd3d3cb145f70bb1157f7ca0baa0221594c9583cf7ddc23"}
experimental_model
Ex vivo and in vitro human whole blood cyclooxygenase assays in five volunteers given a single oral dose
exposure
1000 milligrams oral acetaminophen, with coagulation-induced thromboxane B2 and lipopolysaccharide-induced prostaglandin E2 as isoform indices
limitations
Measures both isoform indices in dosed people and relates them to plasma concentration. Five volunteers and a single dose.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
In people it blocks the second enzyme as hard as a proper anti-inflammatory does, and never blocks the first enough to touch platelets.
primary_references
[apap-p17884974] Acetaminophen (paracetamol) is a selective cyclooxygenase-2 inhibitor in man. (2008). https://pubmed.ncbi.nlm.nih.gov/17884974/ DOI: 10.1096/fj.07-8506com
tissue_or_cell_type
Whole blood
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 259–270
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Ex vivo and in vitro human whole blood cyclooxygenase assays in five volunteers given a single oral dose · source_derived_draft · unverified_draft
### apap-four-fold-cox2-selective-in-man In vitro acetaminophen elicited a 4.4-fold selectivity toward cyclooxygenase-2 inhibition with half-maximal inhibitory concentrations of 113.7 micromolar for cyclooxygenase-1 and 25.8 micromolar for cyclooxygenase-2, following a single oral 1000 milligram dose maximal ex vivo inhibitions were 56% for cyclooxygenase-1 and 83% for cyclooxygenase-2, plasma concentrations remained above the in vitro cyclooxygenase-2 value for at least 5 hours, and ex vivo values compared favourably with in vitro ones; acetaminophen inhibited cyclooxygenase-2 by more than 80%, comparable to non-steroidal anti-inflammatory drugs and selective inhibitors, but the greater than 95% cyclooxygenase-1 blockade relevant for suppression of platelet function was not achieved, and in view of its substantial cyclooxygenase-2 inhibition the cardiovascular warnings defined for selective inhibitors should also be considered. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: In people it blocks the second enzyme as hard as a proper anti-inflammatory does, and never blocks the first enough to touch platelets. organism: Human tissue_or_cell_type: Whole blood experimental_model: Ex vivo and in vitro human whole blood cyclooxygenase assays in five volunteers given a single oral dose limitations: Measures both isoform indices in dosed people and relates them to plasma concentration. Five volunteers and a single dose. exposure: 1000 milligrams oral acetaminophen, with coagulation-induced thromboxane B2 and lipopolysaccharide-induced prostaglandin E2 as isoform indices evidence_span: {"source_cache": "artifacts/paracetamol-research/17884974.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "e2856e9fc1c319219fd3d3cb145f70bb1157f7ca0baa0221594c9583cf7ddc23", "start_char": 0, "end_char": 1857, "text_sha256": "e2856e9fc1c319219fd3d3cb145f70bb1157f7ca0baa0221594c9583cf7ddc23"} [apap-p17884974] Acetaminophen (paracetamol) is a selective cyclooxygenase-2 inhibitor in man. (2008). https://pubmed.ncbi.nlm.nih.gov/17884974/ DOI: 10.1096/fj.07-8506com
Complete structured claim and evidence
Acetaminophen inhibited lipopolysaccharide-induced whole blood prostaglandin E2 and thromboxane B2 production with half-maximal inhibitory concentrations of 44 and 94 micromolar, at therapeutic concentrations of 100 and 300 micromolar it reduced prostaglandin E2 more than thromboxane B2, but in isolated monocytes both were maximally reduced by only 60%, and at the same concentrations it caused a similar and incomplete inhibition of platelet prostaglandin E2 and thromboxane B2 during whole blood clotting, so that in the presence of plasma the drug almost completely suppressed inducible prostaglandin E2 biosynthesis through effects on both cyclooxygenase-2 and inducible prostaglandin E synthase.
Paracetamol → Inducible prostaglandin E synthase source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/12598417.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "e5796a25a03c77d12e8376a60aa094e481bd0c2ab58b29ddcb70027ab477b267", "start_char": 0, "end_char": 1894, "text_sha256": "e5796a25a03c77d12e8376a60aa094e481bd0c2ab58b29ddcb70027ab477b267"}
experimental_model
Human whole blood and isolated monocytes and platelets with parallel prostaglandin E2 and thromboxane B2 measurement
exposure
Acetaminophen at therapeutic plasma concentrations of 100 and 300 micromolar, in whole blood and in isolated cells
limitations
The whole blood against isolated cell comparison shows plasma components matter, and measuring two prostanoids in parallel separates the synthase from the downstream synthase. Ex vivo only.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
In whole blood it nearly abolishes the inflammatory prostaglandin; in isolated cells it manages only sixty per cent.
primary_references
[apap-p12598417] Effects of acetaminophen on constitutive and inducible prostanoid biosynthesis in human blood cells. (2003). https://pubmed.ncbi.nlm.nih.gov/12598417/ DOI: 10.1038/sj.bjp.0705078
tissue_or_cell_type
Monocytes and platelets
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 272–283
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human whole blood and isolated monocytes and platelets with parallel prostaglandin E2 and thromboxane B2 measurement · source_derived_draft · unverified_draft
### apap-plasma-changes-the-answer Acetaminophen inhibited lipopolysaccharide-induced whole blood prostaglandin E2 and thromboxane B2 production with half-maximal inhibitory concentrations of 44 and 94 micromolar, at therapeutic concentrations of 100 and 300 micromolar it reduced prostaglandin E2 more than thromboxane B2, but in isolated monocytes both were maximally reduced by only 60%, and at the same concentrations it caused a similar and incomplete inhibition of platelet prostaglandin E2 and thromboxane B2 during whole blood clotting, so that in the presence of plasma the drug almost completely suppressed inducible prostaglandin E2 biosynthesis through effects on both cyclooxygenase-2 and inducible prostaglandin E synthase. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: In whole blood it nearly abolishes the inflammatory prostaglandin; in isolated cells it manages only sixty per cent. organism: Human tissue_or_cell_type: Monocytes and platelets experimental_model: Human whole blood and isolated monocytes and platelets with parallel prostaglandin E2 and thromboxane B2 measurement limitations: The whole blood against isolated cell comparison shows plasma components matter, and measuring two prostanoids in parallel separates the synthase from the downstream synthase. Ex vivo only. exposure: Acetaminophen at therapeutic plasma concentrations of 100 and 300 micromolar, in whole blood and in isolated cells evidence_span: {"source_cache": "artifacts/paracetamol-research/12598417.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "e5796a25a03c77d12e8376a60aa094e481bd0c2ab58b29ddcb70027ab477b267", "start_char": 0, "end_char": 1894, "text_sha256": "e5796a25a03c77d12e8376a60aa094e481bd0c2ab58b29ddcb70027ab477b267"} [apap-p12598417] Effects of acetaminophen on constitutive and inducible prostanoid biosynthesis in human blood cells. (2003). https://pubmed.ncbi.nlm.nih.gov/12598417/ DOI: 10.1038/sj.bjp.0705078
Complete structured claim and evidence
Prostaglandin E-like activity in cisternal cerebrospinal fluid was usually undetectable or low at normal body temperature and increased, often many-fold, during pyrogen fever irrespective of the route of pyrogen administration, and the antipyretic drugs indomethacin, paracetamol and aspirin injected intraperitoneally during the fever brought down temperature and returned the activity to low levels, with chromatography placing the activity in the zone of the E series prostaglandins, supporting the theory that pyrogens produce fever by increasing prostaglandin synthesis in the preoptic anterior hypothalamic area and that antipyretics of the aspirin type act by inhibiting that synthesis.
Paracetamol → Prostaglandin E-like activity in cisternal cerebrospinal fluid source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/4588122.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "274f00794352ea4d44e1ef2c2cf46a094d9a03752d7c485a2d6222e519534aa9", "start_char": 0, "end_char": 2254, "text_sha256": "274f00794352ea4d44e1ef2c2cf46a094d9a03752d7c485a2d6222e519534aa9"}
experimental_model
Cisternal cerebrospinal fluid sampled from unanaesthetised cats during fever and after antipyretics
exposure
Shigella dysenteriae pyrogen given into the third ventricle, cisterna magna or intravenously, with indomethacin, paracetamol and aspirin
limitations
Bioassay on a stomach strip rather than direct measurement, and prostaglandin E-like activity rather than identified prostaglandin E2. It is the record that connects fever to central prostaglandin and to this drug.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Cat
plain_language
Fever raises a prostaglandin in the fluid round the brain, and this drug brings both down together.
primary_references
[apap-p4588122] Effect of pyrogen and antipyretics on prostaglandin acitvity in cisternal c.s.f. of unanaesthetized cats. (1973). https://pubmed.ncbi.nlm.nih.gov/4588122/ DOI: 10.1113/jphysiol.1973.sp010346
tissue_or_cell_type
Cerebrospinal fluid and hypothalamus
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 285–296
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Cisternal cerebrospinal fluid sampled from unanaesthetised cats during fever and after antipyretics · source_derived_draft · unverified_draft
### apap-antipyresis-follows-central-prostaglandin Prostaglandin E-like activity in cisternal cerebrospinal fluid was usually undetectable or low at normal body temperature and increased, often many-fold, during pyrogen fever irrespective of the route of pyrogen administration, and the antipyretic drugs indomethacin, paracetamol and aspirin injected intraperitoneally during the fever brought down temperature and returned the activity to low levels, with chromatography placing the activity in the zone of the E series prostaglandins, supporting the theory that pyrogens produce fever by increasing prostaglandin synthesis in the preoptic anterior hypothalamic area and that antipyretics of the aspirin type act by inhibiting that synthesis. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Fever raises a prostaglandin in the fluid round the brain, and this drug brings both down together. organism: Cat tissue_or_cell_type: Cerebrospinal fluid and hypothalamus experimental_model: Cisternal cerebrospinal fluid sampled from unanaesthetised cats during fever and after antipyretics limitations: Bioassay on a stomach strip rather than direct measurement, and prostaglandin E-like activity rather than identified prostaglandin E2. It is the record that connects fever to central prostaglandin and to this drug. exposure: Shigella dysenteriae pyrogen given into the third ventricle, cisterna magna or intravenously, with indomethacin, paracetamol and aspirin evidence_span: {"source_cache": "artifacts/paracetamol-research/4588122.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "274f00794352ea4d44e1ef2c2cf46a094d9a03752d7c485a2d6222e519534aa9", "start_char": 0, "end_char": 2254, "text_sha256": "274f00794352ea4d44e1ef2c2cf46a094d9a03752d7c485a2d6222e519534aa9"} [apap-p4588122] Effect of pyrogen and antipyretics on prostaglandin acitvity in cisternal c.s.f. of unanaesthetized cats. (1973). https://pubmed.ncbi.nlm.nih.gov/4588122/ DOI: 10.1113/jphysiol.1973.sp010346
Complete structured claim and evidence
Acetaminophen, following deacetylation to its primary amine, is conjugated with arachidonic acid in the brain and the spinal cord to form the potent TRPV1 agonist N-arachidonoylphenolamine, and this conjugation is absent in mice lacking the enzyme fatty acid amide hydrolase; AM404 also inhibits purified cyclooxygenase-1 and -2 and prostaglandin synthesis in lipopolysaccharide-stimulated macrophages and acts on the endogenous cannabinoid system, identifying fatty acid conjugation as a novel pathway for drug metabolism.
Paracetamol → AM404 / N-arachidonoylphenolamine source_derived_draftungraded
Experimental context and source evidence
availability_state
machinery_impairment Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/15987694.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8da7599ee6674ced34346ae03fae0e421bcc5c1f53b0cb879145d7a511502001", "start_char": 0, "end_char": 1093, "text_sha256": "8da7599ee6674ced34346ae03fae0e421bcc5c1f53b0cb879145d7a511502001"}
experimental_model
Brain and spinal cord metabolite identification in wild-type and fatty acid amide hydrolase knockout mice
exposure
Acetaminophen, with the conjugation step tested by genetic deletion of the conjugating enzyme
limitations
Identifies a previously unknown route of drug metabolism and proves the enzyme by knockout. The downstream activities are measured on purified enzyme and cell lines rather than in the treated animal.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse
plain_language
The brain takes the drug apart and builds the pieces into something new, and that something is what acts.
primary_references
[apap-p15987694] Conversion of acetaminophen to the bioactive N-acylphenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system. (2005). https://pubmed.ncbi.nlm.nih.gov/15987694/ DOI: 10.1074/jbc.m501489200
tissue_or_cell_type
Brain and spinal cord
trigger_kind
machinery_impairment Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 298–309
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Brain and spinal cord metabolite identification in wild-type and fatty acid amide hydrolase knockout mice · source_derived_draft · unverified_draft
### apap-faah-builds-am404 Acetaminophen, following deacetylation to its primary amine, is conjugated with arachidonic acid in the brain and the spinal cord to form the potent TRPV1 agonist N-arachidonoylphenolamine, and this conjugation is absent in mice lacking the enzyme fatty acid amide hydrolase; AM404 also inhibits purified cyclooxygenase-1 and -2 and prostaglandin synthesis in lipopolysaccharide-stimulated macrophages and acts on the endogenous cannabinoid system, identifying fatty acid conjugation as a novel pathway for drug metabolism. Condition category: machinery_impairment nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The brain takes the drug apart and builds the pieces into something new, and that something is what acts. organism: Mouse tissue_or_cell_type: Brain and spinal cord experimental_model: Brain and spinal cord metabolite identification in wild-type and fatty acid amide hydrolase knockout mice limitations: Identifies a previously unknown route of drug metabolism and proves the enzyme by knockout. The downstream activities are measured on purified enzyme and cell lines rather than in the treated animal. exposure: Acetaminophen, with the conjugation step tested by genetic deletion of the conjugating enzyme evidence_span: {"source_cache": "artifacts/paracetamol-research/15987694.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8da7599ee6674ced34346ae03fae0e421bcc5c1f53b0cb879145d7a511502001", "start_char": 0, "end_char": 1093, "text_sha256": "8da7599ee6674ced34346ae03fae0e421bcc5c1f53b0cb879145d7a511502001"} [apap-p15987694] Conversion of acetaminophen to the bioactive N-acylphenolamine AM404 via fatty acid amide hydrolase-dependent arachidonic acid conjugation in the nervous system. (2005). https://pubmed.ncbi.nlm.nih.gov/15987694/ DOI: 10.1074/jbc.m501489200
Complete structured claim and evidence
The antinociceptive effect of acetaminophen at an oral dose lacking hypolocomotor activity was absent in fatty acid amide hydrolase and TRPV1 knockout mice in the formalin, tail immersion and von Frey tests, that dose did not affect global brain contents of prostaglandin E2 or endocannabinoids, intracerebroventricular injection of AM404 produced a TRPV1-mediated antinociceptive effect in the formalin test, and pharmacological inhibition of brain TRPV1 by intracerebroventricular capsazepine abolished the antinociceptive effect of oral acetaminophen.
Human transient receptor potential vanilloid 1 / TRPV1 → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
Experimental context and source evidence
availability_state
machinery_impairment Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/20862299.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2cb3934d80d1a7a6632c49f2007cb6e203b3851706a4ffeb43fda2bb655fa8f2", "start_char": 0, "end_char": 1701, "text_sha256": "2cb3934d80d1a7a6632c49f2007cb6e203b3851706a4ffeb43fda2bb655fa8f2"}
experimental_model
Formalin, tail immersion and von Frey tests in fatty acid amide hydrolase and TRPV1 knockout mice with intracerebroventricular injection
exposure
Oral acetaminophen at a dose lacking hypolocomotor activity, with intracerebroventricular AM404 and capsazepine
limitations
Two separate knockouts and a central antagonist all point the same way, and the dose was chosen to avoid sedation confounding the pain tests. Brain prostaglandin E2 was unchanged at that dose, which is a notable negative.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse
plain_language
Remove the channel and the painkiller stops working, while putting the metabolite straight into the brain works.
primary_references
[apap-p20862299] TRPV1 in brain is involved in acetaminophen-induced antinociception. (2010). https://pubmed.ncbi.nlm.nih.gov/20862299/ DOI: 10.1371/journal.pone.0012748
tissue_or_cell_type
Brain
trigger_kind
machinery_impairment Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 311–322
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Formalin, tail immersion and von Frey tests in fatty acid amide hydrolase and TRPV1 knockout mice with intracerebroventricular injection · source_derived_draft · unverified_draft
### apap-analgesia-needs-trpv1 The antinociceptive effect of acetaminophen at an oral dose lacking hypolocomotor activity was absent in fatty acid amide hydrolase and TRPV1 knockout mice in the formalin, tail immersion and von Frey tests, that dose did not affect global brain contents of prostaglandin E2 or endocannabinoids, intracerebroventricular injection of AM404 produced a TRPV1-mediated antinociceptive effect in the formalin test, and pharmacological inhibition of brain TRPV1 by intracerebroventricular capsazepine abolished the antinociceptive effect of oral acetaminophen. Condition category: machinery_impairment nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Remove the channel and the painkiller stops working, while putting the metabolite straight into the brain works. organism: Mouse tissue_or_cell_type: Brain experimental_model: Formalin, tail immersion and von Frey tests in fatty acid amide hydrolase and TRPV1 knockout mice with intracerebroventricular injection limitations: Two separate knockouts and a central antagonist all point the same way, and the dose was chosen to avoid sedation confounding the pain tests. Brain prostaglandin E2 was unchanged at that dose, which is a notable negative. exposure: Oral acetaminophen at a dose lacking hypolocomotor activity, with intracerebroventricular AM404 and capsazepine evidence_span: {"source_cache": "artifacts/paracetamol-research/20862299.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2cb3934d80d1a7a6632c49f2007cb6e203b3851706a4ffeb43fda2bb655fa8f2", "start_char": 0, "end_char": 1701, "text_sha256": "2cb3934d80d1a7a6632c49f2007cb6e203b3851706a4ffeb43fda2bb655fa8f2"} [apap-p20862299] TRPV1 in brain is involved in acetaminophen-induced antinociception. (2010). https://pubmed.ncbi.nlm.nih.gov/20862299/ DOI: 10.1371/journal.pone.0012748
Complete structured claim and evidence
Systemic 4-aminophenol and 4-hydroxy-3-methoxybenzylamine led to dose-dependent formation of AM404 and of arvanil and olvanil respectively in the mouse brain, the order of potency of these lipid metabolites as TRPV1 activators being arvanil equal to olvanil much greater than AM404, both parent amines displayed antinociceptive activity in rodent pain tests, formation of these metabolites and the antinociceptive effects were substantially reduced or disappeared in fatty acid amide hydrolase null mice, activity was lost in TRPV1 null mice, intracerebroventricular capsazepine eliminated the effects, and in the rat, inhibition of fatty acid amide hydrolase, TRPV1, cannabinoid CB1 receptors and spinal 5-HT3 or 5-HT1A receptors and chemical deletion of bulbospinal serotonergic pathways all prevented the action, giving a pharmacological profile identical to that previously reported for paracetamol.
4-aminophenol → AM404 / N-arachidonoylphenolamine source_derived_draftungraded
Experimental context and source evidence
evidence_span
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experimental_model
Metabolite formation and antinociception for 4-aminophenol and a vanillylamine analogue across knockouts and pharmacological blockade
exposure
Systemic 4-aminophenol and 4-hydroxy-3-methoxybenzylamine, with fatty acid amide hydrolase, TRPV1, cannabinoid and serotonergic manipulations
limitations
The broadest test of the route: it reconstructs the whole chain from metabolite formation to descending pathway, and shows the profile of the metabolite matches that of the parent drug.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse and rat
plain_language
Every step of the proposed chain was cut in turn, and cutting any of them stopped the painkilling.
primary_references
[apap-p23940628] Fatty acid amide hydrolase-dependent generation of antinociceptive drug metabolites acting on TRPV1 in the brain. (2013). https://pubmed.ncbi.nlm.nih.gov/23940628/ DOI: 10.1371/journal.pone.0070690
tissue_or_cell_type
Brain and spinal cord
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 324–335
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Metabolite formation and antinociception for 4-aminophenol and a vanillylamine analogue across knockouts and pharmacological blockade · source_derived_draft · unverified_draft
### apap-the-whole-chain Systemic 4-aminophenol and 4-hydroxy-3-methoxybenzylamine led to dose-dependent formation of AM404 and of arvanil and olvanil respectively in the mouse brain, the order of potency of these lipid metabolites as TRPV1 activators being arvanil equal to olvanil much greater than AM404, both parent amines displayed antinociceptive activity in rodent pain tests, formation of these metabolites and the antinociceptive effects were substantially reduced or disappeared in fatty acid amide hydrolase null mice, activity was lost in TRPV1 null mice, intracerebroventricular capsazepine eliminated the effects, and in the rat, inhibition of fatty acid amide hydrolase, TRPV1, cannabinoid CB1 receptors and spinal 5-HT3 or 5-HT1A receptors and chemical deletion of bulbospinal serotonergic pathways all prevented the action, giving a pharmacological profile identical to that previously reported for paracetamol. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Every step of the proposed chain was cut in turn, and cutting any of them stopped the painkilling. organism: Mouse and rat tissue_or_cell_type: Brain and spinal cord experimental_model: Metabolite formation and antinociception for 4-aminophenol and a vanillylamine analogue across knockouts and pharmacological blockade limitations: The broadest test of the route: it reconstructs the whole chain from metabolite formation to descending pathway, and shows the profile of the metabolite matches that of the parent drug. exposure: Systemic 4-aminophenol and 4-hydroxy-3-methoxybenzylamine, with fatty acid amide hydrolase, TRPV1, cannabinoid and serotonergic manipulations evidence_span: {"source_cache": "artifacts/paracetamol-research/23940628.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "cc9d85547497bfdf88095aaeccf5a11cb9198140ebb35523d5da1b85f76e0a44", "start_char": 0, "end_char": 2208, "text_sha256": "cc9d85547497bfdf88095aaeccf5a11cb9198140ebb35523d5da1b85f76e0a44"} [apap-p23940628] Fatty acid amide hydrolase-dependent generation of antinociceptive drug metabolites acting on TRPV1 in the brain. (2013). https://pubmed.ncbi.nlm.nih.gov/23940628/ DOI: 10.1371/journal.pone.0070690
Complete structured claim and evidence
In thermal, mechanical and chemical pain tests the specific cannabinoid receptor 1 antagonist AM-251 abolished the analgesic action of acetaminophen, which was also lost in cannabinoid receptor 1 knockout mice, yet acetaminophen was shown unable to bind to those receptors demonstrating an indirect involvement, inhibition of fatty acid amide hydrolase suppressed the effect, and the antinociceptive activity of a cannabinoid receptor 1 agonist was itself inhibited by lesion of bulbospinal serotonergic pathways and by spinal 5-HT receptor antagonists, leading the authors to propose a sequence of metabolism to AM404, indirect cannabinoid receptor involvement, reinforcement of serotonergic bulbospinal pathways and action at spinal serotonergic receptors.
Human cannabinoid receptor 1 / CB1 / CNR1 → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/18485596.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f", "start_char": 0, "end_char": 1545, "text_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f"}
experimental_model
Thermal, mechanical and chemical pain tests in cannabinoid receptor 1 knockout mice with receptor binding and pathway lesions
exposure
Acetaminophen with AM-251, cannabinoid receptor 1 deletion, fatty acid amide hydrolase inhibition and serotonergic pathway lesion
limitations
The binding experiment is what makes the receptor involvement indirect rather than direct, which is the substantive point. The proposed sequence is the authors’ synthesis.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse
plain_language
The drug needs the cannabinoid receptor but never touches it, which is what a metabolite doing the work looks like.
primary_references
[apap-p18485596] Endocannabinoid and serotonergic systems are needed for acetaminophen-induced analgesia. (2008). https://pubmed.ncbi.nlm.nih.gov/18485596/ DOI: 10.1016/j.pain.2008.03.030
tissue_or_cell_type
Brain and spinal cord
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 337–348
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Thermal, mechanical and chemical pain tests in cannabinoid receptor 1 knockout mice with receptor binding and pathway lesions · source_derived_draft · unverified_draft
### apap-cb1-needed-but-not-bound In thermal, mechanical and chemical pain tests the specific cannabinoid receptor 1 antagonist AM-251 abolished the analgesic action of acetaminophen, which was also lost in cannabinoid receptor 1 knockout mice, yet acetaminophen was shown unable to bind to those receptors demonstrating an indirect involvement, inhibition of fatty acid amide hydrolase suppressed the effect, and the antinociceptive activity of a cannabinoid receptor 1 agonist was itself inhibited by lesion of bulbospinal serotonergic pathways and by spinal 5-HT receptor antagonists, leading the authors to propose a sequence of metabolism to AM404, indirect cannabinoid receptor involvement, reinforcement of serotonergic bulbospinal pathways and action at spinal serotonergic receptors. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The drug needs the cannabinoid receptor but never touches it, which is what a metabolite doing the work looks like. organism: Mouse tissue_or_cell_type: Brain and spinal cord experimental_model: Thermal, mechanical and chemical pain tests in cannabinoid receptor 1 knockout mice with receptor binding and pathway lesions limitations: The binding experiment is what makes the receptor involvement indirect rather than direct, which is the substantive point. The proposed sequence is the authors’ synthesis. exposure: Acetaminophen with AM-251, cannabinoid receptor 1 deletion, fatty acid amide hydrolase inhibition and serotonergic pathway lesion evidence_span: {"source_cache": "artifacts/paracetamol-research/18485596.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f", "start_char": 0, "end_char": 1545, "text_sha256": "9bd927cbceffd6cf3a23e34bb0a6ce1584f989173a383745a97b82222f89798f"} [apap-p18485596] Endocannabinoid and serotonergic systems are needed for acetaminophen-induced analgesia. (2008). https://pubmed.ncbi.nlm.nih.gov/18485596/ DOI: 10.1016/j.pain.2008.03.030
Complete structured claim and evidence
In rats using the hot plate test the analgesic effect of paracetamol was prevented by two antagonists at cannabinoid CB1 receptors, AM281 and SR141716A, at doses that prevent the analgesic activity of the cannabinoid CB1 agonist HU210, suggesting that paracetamol-induced antinociception involves the cannabinoid system.
AM251, a cannabinoid receptor 1 antagonist → Antinociception in thermal, mechanical and chemical pain tests source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/16438952.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f", "start_char": 0, "end_char": 509, "text_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f"}
experimental_model
Hot plate test in rats with two cannabinoid receptor antagonists
exposure
Paracetamol with AM281 and SR141716A at doses that prevent the action of a cannabinoid agonist
limitations
A short report with the antagonist doses anchored to a positive control. One pain test in one species.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Rat
plain_language
Two different blockers of the cannabinoid receptor each stopped the painkiller working.
primary_references
[apap-p16438952] The analgesic activity of paracetamol is prevented by the blockade of cannabinoid CB1 receptors. (2006). https://pubmed.ncbi.nlm.nih.gov/16438952/ DOI: 10.1016/j.ejphar.2005.12.015
tissue_or_cell_type
Whole animal
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 350–361
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Hot plate test in rats with two cannabinoid receptor antagonists · source_derived_draft · unverified_draft
### apap-two-antagonists-block-it In rats using the hot plate test the analgesic effect of paracetamol was prevented by two antagonists at cannabinoid CB1 receptors, AM281 and SR141716A, at doses that prevent the analgesic activity of the cannabinoid CB1 agonist HU210, suggesting that paracetamol-induced antinociception involves the cannabinoid system. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Two different blockers of the cannabinoid receptor each stopped the painkiller working. organism: Rat tissue_or_cell_type: Whole animal experimental_model: Hot plate test in rats with two cannabinoid receptor antagonists limitations: A short report with the antagonist doses anchored to a positive control. One pain test in one species. exposure: Paracetamol with AM281 and SR141716A at doses that prevent the action of a cannabinoid agonist evidence_span: {"source_cache": "artifacts/paracetamol-research/16438952.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f", "start_char": 0, "end_char": 509, "text_sha256": "8fe3f4535ff4a14c2e417850a583722fc34262e925952ff2fdd9fe244c7e218f"} [apap-p16438952] The analgesic activity of paracetamol is prevented by the blockade of cannabinoid CB1 receptors. (2006). https://pubmed.ncbi.nlm.nih.gov/16438952/ DOI: 10.1016/j.ejphar.2005.12.015
Complete structured claim and evidence
Cerebrospinal fluid and blood were collected from 26 adult male patients between 10 and 211 minutes after intravenous administration of 1 gram of paracetamol, AM404 was detected in 17 of the 26 evaluable cerebrospinal fluid samples at 5 to 40 nanomoles per litre and paracetamol was measurable within 10 minutes with a maximum measured concentration of 60 micromoles per litre at 206 minutes, the first report of AM404 in human cerebrospinal fluid after paracetamol, although the measured concentrations were far below the previously documented half-maximal inhibitory concentration for this metabolite.
Paracetamol → AM404 / N-arachidonoylphenolamine source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/29238213.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "3f8c752d7c1931585f2ce5bc6059b45b103e73fbc7e067912b0d2c60e8541165", "start_char": 0, "end_char": 1557, "text_sha256": "3f8c752d7c1931585f2ce5bc6059b45b103e73fbc7e067912b0d2c60e8541165"}
experimental_model
Cerebrospinal fluid and blood sampled from 26 adult male patients after intravenous paracetamol
exposure
1 gram intravenous paracetamol, with AM404 measured by liquid chromatography-tandem mass spectrometry
limitations
The first human demonstration that the metabolite reaches the central nervous system, and simultaneously the strongest quantitative objection to its importance, since the concentrations found are far below the reported potency of the compound.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
The metabolite really is in human brain fluid, at about a thousandth of the concentration it is thought to need.
primary_references
[apap-p29238213] First evidence of the conversion of paracetamol to AM404 in human cerebrospinal fluid. (2017). https://pubmed.ncbi.nlm.nih.gov/29238213/ DOI: 10.2147/jpr.s143500
tissue_or_cell_type
Cerebrospinal fluid
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 363–374
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Cerebrospinal fluid and blood sampled from 26 adult male patients after intravenous paracetamol · source_derived_draft · unverified_draft
### apap-am404-in-human-csf-but-low Cerebrospinal fluid and blood were collected from 26 adult male patients between 10 and 211 minutes after intravenous administration of 1 gram of paracetamol, AM404 was detected in 17 of the 26 evaluable cerebrospinal fluid samples at 5 to 40 nanomoles per litre and paracetamol was measurable within 10 minutes with a maximum measured concentration of 60 micromoles per litre at 206 minutes, the first report of AM404 in human cerebrospinal fluid after paracetamol, although the measured concentrations were far below the previously documented half-maximal inhibitory concentration for this metabolite. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The metabolite really is in human brain fluid, at about a thousandth of the concentration it is thought to need. organism: Human tissue_or_cell_type: Cerebrospinal fluid experimental_model: Cerebrospinal fluid and blood sampled from 26 adult male patients after intravenous paracetamol limitations: The first human demonstration that the metabolite reaches the central nervous system, and simultaneously the strongest quantitative objection to its importance, since the concentrations found are far below the reported potency of the compound. exposure: 1 gram intravenous paracetamol, with AM404 measured by liquid chromatography-tandem mass spectrometry evidence_span: {"source_cache": "artifacts/paracetamol-research/29238213.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "3f8c752d7c1931585f2ce5bc6059b45b103e73fbc7e067912b0d2c60e8541165", "start_char": 0, "end_char": 1557, "text_sha256": "3f8c752d7c1931585f2ce5bc6059b45b103e73fbc7e067912b0d2c60e8541165"} [apap-p29238213] First evidence of the conversion of paracetamol to AM404 in human cerebrospinal fluid. (2017). https://pubmed.ncbi.nlm.nih.gov/29238213/ DOI: 10.2147/jpr.s143500
Complete structured claim and evidence
Paracetamol induced hypothermia to the same extent in cannabinoid receptor 1 and TRPV1 knockout mice as in wild-type mice and to the same extent in mice pretreated with the antagonists AM251 or SB366791 as in controls, AM404 failed to induce hypothermia at pharmacological doses, inhibition of fatty acid amide hydrolase did not prevent the development of hypothermia and paracetamol induced hypothermia in fatty acid amide hydrolase knockout mice to the same extent as in wild-type mice, so paracetamol induces hypothermia independent of cannabinoids and TRPV1 and AM404 does not mediate this response.
AM404 / N-arachidonoylphenolamine → Hypothermia induced by paracetamol below normal body temperature source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/21628499.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "784e57af3594f8d46b3b9fa70cdbc69451f9c2d424253c3b69b216d7cc541613", "start_char": 0, "end_char": 1809, "text_sha256": "784e57af3594f8d46b3b9fa70cdbc69451f9c2d424253c3b69b216d7cc541613"}
experimental_model
Body temperature after paracetamol in cannabinoid receptor 1 and TRPV1 knockout mice with antagonists and fatty acid amide hydrolase manipulation
exposure
300 milligrams per kilogram paracetamol in knockouts and after AM251 or SB366791, with AM404 given directly
limitations
Applies the same knockout logic used for analgesia to a different endpoint and gets the opposite answer, which is why both are recorded. Hypothermia below normal is not the same endpoint as antipyresis in fever.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse
plain_language
The same knockouts that abolish the painkilling leave the temperature drop completely untouched.
primary_references
[apap-p21628499] Paracetamol-induced hypothermia is independent of cannabinoids and transient receptor potential vanilloid-1 and is not mediated by AM404. (2011). https://pubmed.ncbi.nlm.nih.gov/21628499/ DOI: 10.1124/dmd.111.038638
tissue_or_cell_type
Whole body temperature
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 376–387
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Body temperature after paracetamol in cannabinoid receptor 1 and TRPV1 knockout mice with antagonists and fatty acid amide hydrolase manipulation · source_derived_draft · unverified_draft
### apap-hypothermia-is-a-different-mechanism Paracetamol induced hypothermia to the same extent in cannabinoid receptor 1 and TRPV1 knockout mice as in wild-type mice and to the same extent in mice pretreated with the antagonists AM251 or SB366791 as in controls, AM404 failed to induce hypothermia at pharmacological doses, inhibition of fatty acid amide hydrolase did not prevent the development of hypothermia and paracetamol induced hypothermia in fatty acid amide hydrolase knockout mice to the same extent as in wild-type mice, so paracetamol induces hypothermia independent of cannabinoids and TRPV1 and AM404 does not mediate this response. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The same knockouts that abolish the painkilling leave the temperature drop completely untouched. organism: Mouse tissue_or_cell_type: Whole body temperature experimental_model: Body temperature after paracetamol in cannabinoid receptor 1 and TRPV1 knockout mice with antagonists and fatty acid amide hydrolase manipulation limitations: Applies the same knockout logic used for analgesia to a different endpoint and gets the opposite answer, which is why both are recorded. Hypothermia below normal is not the same endpoint as antipyresis in fever. exposure: 300 milligrams per kilogram paracetamol in knockouts and after AM251 or SB366791, with AM404 given directly evidence_span: {"source_cache": "artifacts/paracetamol-research/21628499.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "784e57af3594f8d46b3b9fa70cdbc69451f9c2d424253c3b69b216d7cc541613", "start_char": 0, "end_char": 1809, "text_sha256": "784e57af3594f8d46b3b9fa70cdbc69451f9c2d424253c3b69b216d7cc541613"} [apap-p21628499] Paracetamol-induced hypothermia is independent of cannabinoids and transient receptor potential vanilloid-1 and is not mediated by AM404. (2011). https://pubmed.ncbi.nlm.nih.gov/21628499/ DOI: 10.1124/dmd.111.038638
Complete structured claim and evidence
AM404 was a potent inhibitor of T-cell-receptor-mediated T-cell activation, specifically inhibiting interleukin-2 and tumour necrosis factor alpha gene transcription and tumour necrosis factor alpha synthesis in stimulated Jurkat T cells in a fatty acid amide hydrolase independent way, inhibiting both the binding to DNA and the transcriptional activity of endogenous nuclear factor of activated T cells without affecting early steps such as calcium mobilization or dephosphorylation, and without interfering with the pathways leading to AP-1 or nuclear factor kappa B activation.
AM404 / N-arachidonoylphenolamine → Nuclear factor of activated T cells signalling source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/17196940.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "adb730eafbac5bf2eeb05418523f3f943b2b4f0ffb83e8e80cdc97c6f0ce27e9", "start_char": 0, "end_char": 1544, "text_sha256": "adb730eafbac5bf2eeb05418523f3f943b2b4f0ffb83e8e80cdc97c6f0ce27e9"}
experimental_model
Jurkat T cells stimulated through the T-cell receptor with transcription factor reporter assays
exposure
AM404 applied to CD3 and CD28-stimulated cells, with fatty acid amide hydrolase independence tested
limitations
Identifies a target of the metabolite that has nothing to do with pain. Cell line work at concentrations that are not related here to those reached in a person.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human cells
plain_language
The metabolite also switches off a transcription factor that immune cells use, by a route unrelated to the enzyme that made it.
primary_references
[apap-p17196940] The acetaminophen-derived bioactive N-acylphenolamine AM404 inhibits NFAT by targeting nuclear regulatory events. (2007). https://pubmed.ncbi.nlm.nih.gov/17196940/ DOI: 10.1016/j.bcp.2006.12.001
tissue_or_cell_type
T lymphocytes
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 389–400
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Jurkat T cells stimulated through the T-cell receptor with transcription factor reporter assays · source_derived_draft · unverified_draft
### apap-am404-blocks-nfat AM404 was a potent inhibitor of T-cell-receptor-mediated T-cell activation, specifically inhibiting interleukin-2 and tumour necrosis factor alpha gene transcription and tumour necrosis factor alpha synthesis in stimulated Jurkat T cells in a fatty acid amide hydrolase independent way, inhibiting both the binding to DNA and the transcriptional activity of endogenous nuclear factor of activated T cells without affecting early steps such as calcium mobilization or dephosphorylation, and without interfering with the pathways leading to AP-1 or nuclear factor kappa B activation. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The metabolite also switches off a transcription factor that immune cells use, by a route unrelated to the enzyme that made it. organism: Human cells tissue_or_cell_type: T lymphocytes experimental_model: Jurkat T cells stimulated through the T-cell receptor with transcription factor reporter assays limitations: Identifies a target of the metabolite that has nothing to do with pain. Cell line work at concentrations that are not related here to those reached in a person. exposure: AM404 applied to CD3 and CD28-stimulated cells, with fatty acid amide hydrolase independence tested evidence_span: {"source_cache": "artifacts/paracetamol-research/17196940.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "adb730eafbac5bf2eeb05418523f3f943b2b4f0ffb83e8e80cdc97c6f0ce27e9", "start_char": 0, "end_char": 1544, "text_sha256": "adb730eafbac5bf2eeb05418523f3f943b2b4f0ffb83e8e80cdc97c6f0ce27e9"} [apap-p17196940] The acetaminophen-derived bioactive N-acylphenolamine AM404 inhibits NFAT by targeting nuclear regulatory events. (2007). https://pubmed.ncbi.nlm.nih.gov/17196940/ DOI: 10.1016/j.bcp.2006.12.001
Complete structured claim and evidence
After intraperitoneal acetaminophen, tissue glutathione was reduced more in mice than in rats and more in liver than in kidney without appearance of oxidized glutathione in either tissue, covalent binding of tritiated metabolites to tissue protein was likewise greater in mice than rats and greater in liver than kidney, prior 3-methylcholanthrene produced far greater induced changes in liver than kidney suggesting the reactive metabolite forms by slightly different mechanisms in each organ, and at doses below those causing demonstrable acute toxicity the duration of covalent binding was longer for renal papilla than for renal cortex or liver.
Paracetamol → Tissue reduced glutathione content source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/660552.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7041ada7ee2ce923645d1103db3a3dccc3febcf138c5095e24aa96cdbc04e9e3", "start_char": 0, "end_char": 1309, "text_sha256": "7041ada7ee2ce923645d1103db3a3dccc3febcf138c5095e24aa96cdbc04e9e3"}
experimental_model
Tissue glutathione and covalent binding of tritiated metabolites in CD-1 mice and Sprague-Dawley rats
exposure
Intraperitoneal acetaminophen, with and without prior 3-methylcholanthrene induction
limitations
Compares two organs and two species in the same design. The authors note the covalent binding measurement is extremely sensitive to trace radiochemical impurity, which is an honest caution about the method.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse and rat
plain_language
The drug empties the cell of its protective thiol and then sticks to proteins, most of all in mouse liver.
primary_references
[apap-p660552] Covalent binding of metabolites of acetaminophen to kidney protein and depletion of renal glutathione. (1978). https://pubmed.ncbi.nlm.nih.gov/660552/ DOI: 10.1016/s0022-3565(25)31316-9
tissue_or_cell_type
Liver, kidney cortex and renal papilla
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 402–413
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Tissue glutathione and covalent binding of tritiated metabolites in CD-1 mice and Sprague-Dawley rats · source_derived_draft · unverified_draft
### apap-binding-tracks-glutathione-loss After intraperitoneal acetaminophen, tissue glutathione was reduced more in mice than in rats and more in liver than in kidney without appearance of oxidized glutathione in either tissue, covalent binding of tritiated metabolites to tissue protein was likewise greater in mice than rats and greater in liver than kidney, prior 3-methylcholanthrene produced far greater induced changes in liver than kidney suggesting the reactive metabolite forms by slightly different mechanisms in each organ, and at doses below those causing demonstrable acute toxicity the duration of covalent binding was longer for renal papilla than for renal cortex or liver. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The drug empties the cell of its protective thiol and then sticks to proteins, most of all in mouse liver. organism: Mouse and rat tissue_or_cell_type: Liver, kidney cortex and renal papilla experimental_model: Tissue glutathione and covalent binding of tritiated metabolites in CD-1 mice and Sprague-Dawley rats limitations: Compares two organs and two species in the same design. The authors note the covalent binding measurement is extremely sensitive to trace radiochemical impurity, which is an honest caution about the method. exposure: Intraperitoneal acetaminophen, with and without prior 3-methylcholanthrene induction evidence_span: {"source_cache": "artifacts/paracetamol-research/660552.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7041ada7ee2ce923645d1103db3a3dccc3febcf138c5095e24aa96cdbc04e9e3", "start_char": 0, "end_char": 1309, "text_sha256": "7041ada7ee2ce923645d1103db3a3dccc3febcf138c5095e24aa96cdbc04e9e3"} [apap-p660552] Covalent binding of metabolites of acetaminophen to kidney protein and depletion of renal glutathione. (1978). https://pubmed.ncbi.nlm.nih.gov/660552/ DOI: 10.1016/s0022-3565(25)31316-9
Complete structured claim and evidence
Leflunomide given 4 hours after a hepatotoxic dose of acetaminophen afforded significant protection from liver necrosis by serum alanine aminotransferase and histopathology at 8 and 24 hours, and the mechanism was not inhibition of cytochrome-P450-catalysed bioactivation or suppression of innate immunity but inhibition of acetaminophen-induced phosphorylation of c-Jun N-terminal protein kinase, preventing downstream Bcl-2 and Bcl-XL inactivation and protecting from mitochondrial permeabilization and cytochrome c release, while also preventing induction of inducible nitric oxide synthase and formation of peroxynitrite; protection was still obtained when given 8 hours after the dose.
c-Jun N-terminal kinase → Hepatic necrosis source_derived_draftungraded
Experimental context and source evidence
availability_state
biomarker_context Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/17366662.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7c7eb70728aa75fa3ac54f70703ce08d7a540b3a2a7da7e4797f27a6b1312dbb", "start_char": 0, "end_char": 1791, "text_sha256": "7c7eb70728aa75fa3ac54f70703ce08d7a540b3a2a7da7e4797f27a6b1312dbb"}
experimental_model
Male C57BL/6 mice given a hepatotoxic dose followed by leflunomide at 4 or 8 hours
exposure
750 milligrams per kilogram acetaminophen intraperitoneally, rescued with 30 milligrams per kilogram leflunomide
limitations
A rescue given hours after the dose, which separates the injury pathway from the bioactivation step. A mouse model at a dose far above therapeutic.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Mouse
plain_language
The damage is done by a signalling kinase hours later, not by the chemistry of the metabolite alone, which is why a late rescue works.
primary_references
[apap-p17366662] Mitochondrial protection by the JNK inhibitor leflunomide rescues mice from acetaminophen-induced liver injury. (2007). https://pubmed.ncbi.nlm.nih.gov/17366662/ DOI: 10.1002/hep.21475
tissue_or_cell_type
Liver
trigger_kind
biomarker_context Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 415–426
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Male C57BL/6 mice given a hepatotoxic dose followed by leflunomide at 4 or 8 hours · source_derived_draft · unverified_draft
### apap-jnk-not-bioactivation Leflunomide given 4 hours after a hepatotoxic dose of acetaminophen afforded significant protection from liver necrosis by serum alanine aminotransferase and histopathology at 8 and 24 hours, and the mechanism was not inhibition of cytochrome-P450-catalysed bioactivation or suppression of innate immunity but inhibition of acetaminophen-induced phosphorylation of c-Jun N-terminal protein kinase, preventing downstream Bcl-2 and Bcl-XL inactivation and protecting from mitochondrial permeabilization and cytochrome c release, while also preventing induction of inducible nitric oxide synthase and formation of peroxynitrite; protection was still obtained when given 8 hours after the dose. Condition category: biomarker_context nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The damage is done by a signalling kinase hours later, not by the chemistry of the metabolite alone, which is why a late rescue works. organism: Mouse tissue_or_cell_type: Liver experimental_model: Male C57BL/6 mice given a hepatotoxic dose followed by leflunomide at 4 or 8 hours limitations: A rescue given hours after the dose, which separates the injury pathway from the bioactivation step. A mouse model at a dose far above therapeutic. exposure: 750 milligrams per kilogram acetaminophen intraperitoneally, rescued with 30 milligrams per kilogram leflunomide evidence_span: {"source_cache": "artifacts/paracetamol-research/17366662.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7c7eb70728aa75fa3ac54f70703ce08d7a540b3a2a7da7e4797f27a6b1312dbb", "start_char": 0, "end_char": 1791, "text_sha256": "7c7eb70728aa75fa3ac54f70703ce08d7a540b3a2a7da7e4797f27a6b1312dbb"} [apap-p17366662] Mitochondrial protection by the JNK inhibitor leflunomide rescues mice from acetaminophen-induced liver injury. (2007). https://pubmed.ncbi.nlm.nih.gov/17366662/ DOI: 10.1002/hep.21475
Complete structured claim and evidence
Acetaminophen overdose is the leading cause of acute liver failure in Canada and around the world with approximately 4,500 hospitalisations each year in Canada and about 6% of those hospitalised developing liver injury including acute liver failure that may require transplant or lead to death, and on the Rumack-Matthew nomogram derived from patients not treated with antidote a serum concentration above 200 milligrams per litre at 4 hours carries a 60% incidence of severe hepatotoxicity and 5% mortality rising to 90% and 24% at 300 milligrams per litre, with treatment by N-acetylcysteine required above 140 milligrams per litre at 4 hours.
Paracetamol → Acute liver failure source_derived_draftungraded
Experimental context and source evidence
availability_state
biomarker_context Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/36191122.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "859db1958aeb26b75a34a32e4dd1c4713dc7db413717cefe62a3659856db7568", "start_char": 0, "end_char": 3325, "text_sha256": "859db1958aeb26b75a34a32e4dd1c4713dc7db413717cefe62a3659856db7568"}
experimental_model
Review of point-of-care testing and antidote guidance for acute overdose
exposure
Serum acetaminophen concentration interpreted against the Rumack-Matthew nomogram
limitations
A health-technology review rather than primary research. The nomogram figures it quotes are derived from patients not treated with antidote, which is stated.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
Above a concentration that can be read off a chart, the liver fails in most people unless the antidote is given.
primary_references
[apap-p36191122] Point-of-Care Testing and N-Acetylcysteine for Acute Acetaminophen Overdose (2021). https://pubmed.ncbi.nlm.nih.gov/36191122/
tissue_or_cell_type
Liver
trigger_kind
biomarker_context Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 428–439
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Review of point-of-care testing and antidote guidance for acute overdose · source_derived_draft · unverified_draft
### apap-the-nomogram-and-the-antidote Acetaminophen overdose is the leading cause of acute liver failure in Canada and around the world with approximately 4,500 hospitalisations each year in Canada and about 6% of those hospitalised developing liver injury including acute liver failure that may require transplant or lead to death, and on the Rumack-Matthew nomogram derived from patients not treated with antidote a serum concentration above 200 milligrams per litre at 4 hours carries a 60% incidence of severe hepatotoxicity and 5% mortality rising to 90% and 24% at 300 milligrams per litre, with treatment by N-acetylcysteine required above 140 milligrams per litre at 4 hours. Condition category: biomarker_context nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Above a concentration that can be read off a chart, the liver fails in most people unless the antidote is given. organism: Human tissue_or_cell_type: Liver experimental_model: Review of point-of-care testing and antidote guidance for acute overdose limitations: A health-technology review rather than primary research. The nomogram figures it quotes are derived from patients not treated with antidote, which is stated. exposure: Serum acetaminophen concentration interpreted against the Rumack-Matthew nomogram evidence_span: {"source_cache": "artifacts/paracetamol-research/36191122.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "859db1958aeb26b75a34a32e4dd1c4713dc7db413717cefe62a3659856db7568", "start_char": 0, "end_char": 3325, "text_sha256": "859db1958aeb26b75a34a32e4dd1c4713dc7db413717cefe62a3659856db7568"} [apap-p36191122] Point-of-Care Testing and N-Acetylcysteine for Acute Acetaminophen Overdose (2021). https://pubmed.ncbi.nlm.nih.gov/36191122/
Complete structured claim and evidence
Acetaminophen produced a biphasic response in the N-acyl ethanolamide and PPAR alpha system, with decreased PPAR alpha expression after 6 hours followed by a generalised increase of system components including PPAR alpha, NAPE-PLD and fatty acid amide hydrolase and of the N-acyl ethanolamides after 24 hours, confirmed in mice where gene expression of PPAR alpha and fatty acid amide hydrolase fell at 6 hours and rose by 24 hours, repeated administration decreased both and increased liver N-acyl ethanolamides with complete restoration after 15 days of rest, immunohistochemistry in a human case of acetaminophen hepatotoxicity confirmed the decrements, and damage-related alterations after repeated administration were aggravated in PPAR alpha-deficient mice.
Paracetamol → The N-acyl ethanolamide and PPAR alpha anti-inflammatory system source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/29056914.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2ca7517052bab3c774f315af85f3aa8cdf810e43dc44444724bff46e2f1bdab3", "start_char": 0, "end_char": 2081, "text_sha256": "2ca7517052bab3c774f315af85f3aa8cdf810e43dc44444724bff46e2f1bdab3"}
experimental_model
Human HepG2 cells and mice given acute and repeated doses, with PPAR-alpha-deficient animals and a human case
exposure
0.5 to 20 millimolar in cells and 750 milligrams per kilogram in mice, acute and repeated over four days
limitations
Follows a lipid signalling system across cells, mice, knockouts and one human case. The biphasic time course is the informative part and complicates any single-timepoint reading.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human cells, mouse and human
plain_language
The same lipid system that makes the painkilling metabolite is knocked down by an overdose and then rebounds, and animals lacking it fare worse.
primary_references
[apap-p29056914] Acetaminophen-Induced Liver Injury Alters the Acyl Ethanolamine-Based Anti-Inflammatory Signaling System in Liver. (2017). https://pubmed.ncbi.nlm.nih.gov/29056914/ DOI: 10.3389/fphar.2017.00705
tissue_or_cell_type
Liver
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 441–452
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human HepG2 cells and mice given acute and repeated doses, with PPAR-alpha-deficient animals and a human case · source_derived_draft · unverified_draft
### apap-the-lipid-brake-fails-then-rebounds Acetaminophen produced a biphasic response in the N-acyl ethanolamide and PPAR alpha system, with decreased PPAR alpha expression after 6 hours followed by a generalised increase of system components including PPAR alpha, NAPE-PLD and fatty acid amide hydrolase and of the N-acyl ethanolamides after 24 hours, confirmed in mice where gene expression of PPAR alpha and fatty acid amide hydrolase fell at 6 hours and rose by 24 hours, repeated administration decreased both and increased liver N-acyl ethanolamides with complete restoration after 15 days of rest, immunohistochemistry in a human case of acetaminophen hepatotoxicity confirmed the decrements, and damage-related alterations after repeated administration were aggravated in PPAR alpha-deficient mice. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: The same lipid system that makes the painkilling metabolite is knocked down by an overdose and then rebounds, and animals lacking it fare worse. organism: Human cells, mouse and human tissue_or_cell_type: Liver experimental_model: Human HepG2 cells and mice given acute and repeated doses, with PPAR-alpha-deficient animals and a human case limitations: Follows a lipid signalling system across cells, mice, knockouts and one human case. The biphasic time course is the informative part and complicates any single-timepoint reading. exposure: 0.5 to 20 millimolar in cells and 750 milligrams per kilogram in mice, acute and repeated over four days evidence_span: {"source_cache": "artifacts/paracetamol-research/29056914.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "2ca7517052bab3c774f315af85f3aa8cdf810e43dc44444724bff46e2f1bdab3", "start_char": 0, "end_char": 2081, "text_sha256": "2ca7517052bab3c774f315af85f3aa8cdf810e43dc44444724bff46e2f1bdab3"} [apap-p29056914] Acetaminophen-Induced Liver Injury Alters the Acyl Ethanolamine-Based Anti-Inflammatory Signaling System in Liver. (2017). https://pubmed.ncbi.nlm.nih.gov/29056914/ DOI: 10.3389/fphar.2017.00705
Complete structured claim and evidence
Three aspirin-sensitive asthmatic subjects with a history of reactions underwent double-blind placebo-controlled challenges and reacted to 1000 milligrams of acetaminophen with a greater than 20% fall in forced expiratory volume in one second, two were desensitized to aspirin and then rechallenged with 1000 milligrams of acetaminophen without reaction, and two were desensitized to acetaminophen achieving refractoriness to 1500 but not 2000 milligrams, so cross sensitivity was documented at large challenge doses and the cross desensitization suggests similar mechanisms are responsible for reactions to aspirin, non-steroidal anti-inflammatory drugs and acetaminophen.
Paracetamol → A fall in forced expiratory volume in one second source_derived_draftungraded
Experimental context and source evidence
availability_state
biomarker_context Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/2666482.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9c731e77d65955b683aa03e7df1252729e11b1fb8bed714b9138f22c725eac2b", "start_char": 0, "end_char": 1081, "text_sha256": "9c731e77d65955b683aa03e7df1252729e11b1fb8bed714b9138f22c725eac2b"}
experimental_model
Double-blind placebo-controlled oral challenge and desensitisation in three aspirin-sensitive asthmatic subjects
exposure
1000 to 2000 milligram acetaminophen challenges, with aspirin desensitisation and acetaminophen desensitisation
limitations
Three subjects, selected for a history of reacting, so the frequency of cross-reactivity cannot be read from it. The cross-desensitisation result is what identifies the shared mechanism.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
Desensitise the patient to aspirin and they stop reacting to paracetamol, so it is the same mechanism at work.
primary_references
[apap-p2666482] Cross sensitivity with acetaminophen in aspirin-sensitive subjects with asthma. (1989). https://pubmed.ncbi.nlm.nih.gov/2666482/ DOI: 10.1016/0091-6749(89)90174-7
tissue_or_cell_type
Airway
trigger_kind
biomarker_context Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 454–465
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Double-blind placebo-controlled oral challenge and desensitisation in three aspirin-sensitive asthmatic subjects · source_derived_draft · unverified_draft
### apap-cross-desensitisation-shows-shared-mechanism Three aspirin-sensitive asthmatic subjects with a history of reactions underwent double-blind placebo-controlled challenges and reacted to 1000 milligrams of acetaminophen with a greater than 20% fall in forced expiratory volume in one second, two were desensitized to aspirin and then rechallenged with 1000 milligrams of acetaminophen without reaction, and two were desensitized to acetaminophen achieving refractoriness to 1500 but not 2000 milligrams, so cross sensitivity was documented at large challenge doses and the cross desensitization suggests similar mechanisms are responsible for reactions to aspirin, non-steroidal anti-inflammatory drugs and acetaminophen. Condition category: biomarker_context nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: Desensitise the patient to aspirin and they stop reacting to paracetamol, so it is the same mechanism at work. organism: Human tissue_or_cell_type: Airway experimental_model: Double-blind placebo-controlled oral challenge and desensitisation in three aspirin-sensitive asthmatic subjects limitations: Three subjects, selected for a history of reacting, so the frequency of cross-reactivity cannot be read from it. The cross-desensitisation result is what identifies the shared mechanism. exposure: 1000 to 2000 milligram acetaminophen challenges, with aspirin desensitisation and acetaminophen desensitisation evidence_span: {"source_cache": "artifacts/paracetamol-research/2666482.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "9c731e77d65955b683aa03e7df1252729e11b1fb8bed714b9138f22c725eac2b", "start_char": 0, "end_char": 1081, "text_sha256": "9c731e77d65955b683aa03e7df1252729e11b1fb8bed714b9138f22c725eac2b"} [apap-p2666482] Cross sensitivity with acetaminophen in aspirin-sensitive subjects with asthma. (1989). https://pubmed.ncbi.nlm.nih.gov/2666482/ DOI: 10.1016/0091-6749(89)90174-7
Complete structured claim and evidence
Of 256 patients with a history of recent pseudoallergic skin reactions caused by non-steroidal anti-inflammatory drugs who underwent elective oral challenges, 48 or 19% reacted to acetaminophen or nimesulide, with similar proportions among those with chronic urticaria at 23% and otherwise normal subjects with a history of aspirin-induced urticaria at 19% while pyrazolone-intolerant patients showed the lowest number at 4%, aspirin intolerance was a risk factor for acetaminophen or nimesulide induced urticaria with a relative risk of 5.4, a history of anaphylactoid reactions carried a relative risk of 5.7, and atopy raised reactivity to nimesulide from 9 to 23%.
Paracetamol → Urticaria and angioedema source_derived_draftungraded
Experimental context and source evidence
availability_state
biomarker_context Imported condition classification; unverified.
evidence_span
{"source_cache": "artifacts/paracetamol-research/10400483.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7ea713edb6955db38992c5372794d93c0d52f841d3f8897817286f7f66d28605", "start_char": 0, "end_char": 2662, "text_sha256": "7ea713edb6955db38992c5372794d93c0d52f841d3f8897817286f7f66d28605"}
experimental_model
Elective oral challenges in 256 patients with a history of pseudoallergic skin reactions to non-steroidal anti-inflammatory drugs
exposure
Increasing doses of acetaminophen and nimesulide across three patient groups
limitations
A large challenge series that puts a rate on the cross-reactivity and identifies risk factors. Patients were selected for a history of reacting, so the rates apply to that population and not to the general one.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
One patient in five who reacts to aspirin also reacts to paracetamol, so it is not automatically the safe substitute.
primary_references
[apap-p10400483] Risk factors for acetaminophen and nimesulide intolerance in patients with NSAID-induced skin disorders. (1999). https://pubmed.ncbi.nlm.nih.gov/10400483/ DOI: 10.1016/s1081-1206(10)63166-3
tissue_or_cell_type
Skin
trigger_kind
biomarker_context Imported condition classification; unverified.
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 467–478
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Elective oral challenges in 256 patients with a history of pseudoallergic skin reactions to non-steroidal anti-inflammatory drugs · source_derived_draft · unverified_draft
### apap-twenty-percent-cross-react Of 256 patients with a history of recent pseudoallergic skin reactions caused by non-steroidal anti-inflammatory drugs who underwent elective oral challenges, 48 or 19% reacted to acetaminophen or nimesulide, with similar proportions among those with chronic urticaria at 23% and otherwise normal subjects with a history of aspirin-induced urticaria at 19% while pyrazolone-intolerant patients showed the lowest number at 4%, aspirin intolerance was a risk factor for acetaminophen or nimesulide induced urticaria with a relative risk of 5.4, a history of anaphylactoid reactions carried a relative risk of 5.7, and atopy raised reactivity to nimesulide from 9 to 23%. Condition category: biomarker_context nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: One patient in five who reacts to aspirin also reacts to paracetamol, so it is not automatically the safe substitute. organism: Human tissue_or_cell_type: Skin experimental_model: Elective oral challenges in 256 patients with a history of pseudoallergic skin reactions to non-steroidal anti-inflammatory drugs limitations: A large challenge series that puts a rate on the cross-reactivity and identifies risk factors. Patients were selected for a history of reacting, so the rates apply to that population and not to the general one. exposure: Increasing doses of acetaminophen and nimesulide across three patient groups evidence_span: {"source_cache": "artifacts/paracetamol-research/10400483.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "7ea713edb6955db38992c5372794d93c0d52f841d3f8897817286f7f66d28605", "start_char": 0, "end_char": 2662, "text_sha256": "7ea713edb6955db38992c5372794d93c0d52f841d3f8897817286f7f66d28605"} [apap-p10400483] Risk factors for acetaminophen and nimesulide intolerance in patients with NSAID-induced skin disorders. (1999). https://pubmed.ncbi.nlm.nih.gov/10400483/ DOI: 10.1016/s1081-1206(10)63166-3
Complete structured claim and evidence
Of 237 challenges with various non-steroidal anti-inflammatory drugs and paracetamol in 101 intolerant patients, 19 challenges were positive and 2 patients developed anaphylactic shock, with a ratio of positive to total challenges of 7 of 83 for paracetamol, 2 of 49 for imidazole-hydroxybenzoate and 0 of 30 for nimesulide, and the authors conclude that a positive history of intolerance to a given drug is sufficient reason to contraindicate its use even for diagnostic challenge, which should be restricted to assessing tolerability of alternatives.
Paracetamol → Urticaria and angioedema source_derived_draftungraded
Experimental context and source evidence
evidence_span
{"source_cache": "artifacts/paracetamol-research/7506185.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b38b08631ecb8137b8297b631b8dab0a4378d5445e29c557e3586b546e0e874f", "start_char": 0, "end_char": 1590, "text_sha256": "b38b08631ecb8137b8297b631b8dab0a4378d5445e29c557e3586b546e0e874f"}
experimental_model
Oral challenge series in 112 and then 284 patients intolerant of non-steroidal anti-inflammatory drugs
exposure
Challenges with aspirin, dipyrone, paracetamol, imidazole-hydroxybenzoate and nimesulide
limitations
Provides the denominator that the case reports lack, and records two anaphylactic shocks during challenge, which is why the authors restrict the procedure.
nutrient_topic
Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. · Paracetamol
organism
Human
plain_language
About one in twelve challenges with paracetamol was positive in people already intolerant of these drugs.
primary_references
[apap-p7506185] Oral challenge with alternative nonsteroidal antiinflammatory drugs (NSAIDs) and paracetamol in patients intolerant to these agents. (1993). https://pubmed.ncbi.nlm.nih.gov/7506185/ DOI: 10.2165/00003495-199300461-00065
tissue_or_cell_type
Whole body
Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22) · lines 480–491
AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Oral challenge series in 112 and then 284 patients intolerant of non-steroidal anti-inflammatory drugs · source_derived_draft · unverified_draft
### apap-seven-in-eighty-three Of 237 challenges with various non-steroidal anti-inflammatory drugs and paracetamol in 101 intolerant patients, 19 challenges were positive and 2 patients developed anaphylactic shock, with a ratio of positive to total challenges of 7 of 83 for paracetamol, 2 of 49 for imidazole-hydroxybenzoate and 0 of 30 for nimesulide, and the authors conclude that a positive history of intolerance to a given drug is sufficient reason to contraindicate its use even for diagnostic challenge, which should be restricted to assessing tolerability of alternatives. Condition category: normal nutrient_topic: Paracetamol research collection; topical membership is not evidence of a direct clinical effect, and the drug is recorded separately from the metabolites NAPQI and AM404. plain_language: About one in twelve challenges with paracetamol was positive in people already intolerant of these drugs. organism: Human tissue_or_cell_type: Whole body experimental_model: Oral challenge series in 112 and then 284 patients intolerant of non-steroidal anti-inflammatory drugs limitations: Provides the denominator that the case reports lack, and records two anaphylactic shocks during challenge, which is why the authors restrict the procedure. exposure: Challenges with aspirin, dipyrone, paracetamol, imidazole-hydroxybenzoate and nimesulide evidence_span: {"source_cache": "artifacts/paracetamol-research/7506185.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b38b08631ecb8137b8297b631b8dab0a4378d5445e29c557e3586b546e0e874f", "start_char": 0, "end_char": 1590, "text_sha256": "b38b08631ecb8137b8297b631b8dab0a4378d5445e29c557e3586b546e0e874f"} [apap-p7506185] Oral challenge with alternative nonsteroidal antiinflammatory drugs (NSAIDs) and paracetamol in patients intolerant to these agents. (1993). https://pubmed.ncbi.nlm.nih.gov/7506185/ DOI: 10.2165/00003495-199300461-00065
Complete structured claim and evidence

Availability and dependencies

Each situation shows the normal role first, then what the sources report under a specific condition. A shortfall in the diet, a fault in the machinery, and a low blood reading are kept separate because they are not the same thing.

When the tissue is making its own peroxide

Condition: biomarker_context · A cell with a high ambient hydroperoxide concentration, such as a platelet making 12-hydroperoxyeicosatetraenoic acid or an inflamed tissue.

Normal role: Paracetamol inhibits cyclooxygenase by reducing the oxidised enzyme back to its resting form, which requires the enzyme to be oxidised and not re-oxidised faster than the drug can reduce it.

Recorded consequence: The drug is effectively inert there: the half-maximal inhibitory concentration is 4.3 micromolar in stimulated endothelium against 1,870 micromolar in the platelet, and 0.3 micromolar 12-HPETE completely reverses inhibition.

Scope: Human endothelial cells and platelets

When the enzyme that builds the active metabolite is missing

Condition: machinery_impairment · Genetic deletion of fatty acid amide hydrolase.

Normal role: Paracetamol is deacetylated to 4-aminophenol and then conjugated with arachidonic acid by fatty acid amide hydrolase in brain and spinal cord to form AM404.

Recorded consequence: The conjugation does not occur, AM404 is not formed, and the antinociceptive effect of an oral dose is absent.

Scope: Fatty acid amide hydrolase knockout mice

When the channel the metabolite opens is missing

Condition: machinery_impairment · Genetic deletion of TRPV1, or blockade of brain TRPV1 by intracerebroventricular capsazepine.

Normal role: AM404, formed from paracetamol in the brain, is a potent activator of TRPV1, and activating TRPV1 in the midbrain periaqueductal gray produces antinociception.

Recorded consequence: The antinociceptive effect of an oral dose of paracetamol is absent, while intracerebroventricular AM404 still produces a TRPV1-mediated effect in animals that have the channel.

Scope: TRPV1 knockout mice in formalin, tail immersion and von Frey tests

When the dose exceeds what glutathione can absorb

Condition: biomarker_context · An overdose, which depletes glutathione and leaves NAPQI free to bind protein.

Normal role: A therapeutic dose of paracetamol is almost entirely conjugated, and the small fraction oxidised to NAPQI is trapped by glutathione.

Recorded consequence: Covalent protein binding, c-Jun N-terminal kinase activation, mitochondrial permeabilization and cytochrome c release follow, producing hepatic necrosis; blocking the kinase rescues the liver even 8 hours after the dose, and N-acetylcysteine is the clinical antidote.

Scope: Mouse models at 750 milligrams per kilogram and human overdose management

When an aspirin-sensitive patient takes a large dose

Condition: biomarker_context · A dose large enough to inhibit cyclooxygenase appreciably, around 1000 milligrams or more, in a subject with aspirin-sensitive asthma or aspirin-induced urticaria.

Normal role: Paracetamol is usually recommended as the safe analgesic for patients who react to aspirin, because at ordinary doses it barely inhibits cyclooxygenase in peripheral tissue.

Recorded consequence: Bronchospasm or urticaria can follow, and desensitising the patient to aspirin abolishes the reaction to paracetamol, showing the two act through the same mechanism.

Scope: Double-blind challenge in three aspirin-sensitive asthmatics and challenge series in larger cohorts

The sources

Every document behind this chapter is preserved word for word. Open one to read it in full with its recorded conflicts marked in place.

Paracetamol: the enzyme it reduces rather than blocks, the isoform that turned out not to exist, the metabolite that carries the analgesia, and the metabolite that destroys the liver (2026-09-22)AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · unverified_draftRead preserved source

Recorded disagreements

Where two sources say different things, both are kept and the difference is explained. You can discuss a disagreement or propose a mechanism that might account for it.

Does AM404 carry the effects of paracetamol?For analgesia the case is strong and built from several independent cuts to the same chain: the conjugation does not occur without fatty acid amide hydrolase, the antinociceptive effect of an oral dose is absent in both fatty acid amide hydrolase and TRPV1 knockout mice, central capsazepine abolishes it, cannabinoid receptor 1 antagonists and deletion abolish it while the drug itself does not bind that receptor, and the deacetylated metabolite 4-aminophenol reproduces the entire pharmacological profile of the parent drug. For body temperature the same logic gives the opposite answer: hypothermia is unchanged in cannabinoid receptor 1, TRPV1 and fatty acid amide hydrolase knockout mice, unchanged by either antagonist, and AM404 given directly does not produce it. And in people, although AM404 is now confirmed in cerebrospinal fluid after an intravenous gram, it is present at 5 to 40 nanomoles per litre, which those authors state is far below its documented half-maximal concentration. The reasonable reading is that this drug has at least two mechanisms, that the metabolite route accounts for analgesia in rodents, and that whether it operates at human concentrations is unresolved.Read the recorded disagreement
Does a third cyclooxygenase explain how paracetamol works?A 2002 report described COX-3, a cyclooxygenase-1 transcript retaining intron 1, expressed in canine cerebral cortex and in human cerebral cortex and heart, showed the canine protein had glycosylation-dependent cyclooxygenase activity, and found it selectively inhibited by paracetamol, phenacetin, antipyrine and dipyrone, proposing this as the primary central mechanism. The proposal does not survive translation to other species. In the rat the retained 98 base pair intron causes a frameshift, giving a 127 amino acid protein with no sequence similarity to any cyclooxygenase, no cyclooxygenase activity and no effect on paracetamol inhibition of prostaglandin production. An independent survey across rat tissues found no immunoreactive protein with an anti-canine-COX-3 antibody, found no special potency of paracetamol in brain or cerebellum, and concluded that expression of an active enzyme from this transcript is apparently impossible in the rat. A review adds that even in the dog, expression level and kinetics make clinical relevance unlikely, and that in rodents and humans the encoded proteins are not cyclooxygenases. The records are recorded together because the proposal shaped a decade of writing about this drug; on the evidence here it is a species-specific curiosity rather than the mechanism.Read the recorded disagreement
Does paracetamol act at the peroxidase site or the cyclooxygenase site?The peroxidase account is strongly supported: paracetamol is a good reducing agent of both isoforms, removing peroxide with glutathione peroxidase makes it thirtyfold more potent, and adding hydroperoxide back abolishes inhibition in cells, with 0.3 micromolar 12-hydroperoxyeicosatetraenoic acid enough to reverse it completely. Against that, phenolic compounds including paracetamol still inhibit prostaglandin H synthase reconstituted with manganese protoporphyrin, which retains cyclooxygenase but almost no peroxidase activity, their inhibition depends strongly on arachidonic acid concentration, and adding 10 micromolar prostaglandin G2 did not prevent it; those authors concluded the compounds compete with arachidonate at the cyclooxygenase site in addition to or independent of any effect on peroxide tone. A third record shows the two sites are connected, since cyclooxygenase activity depends on oxidation of an active-site tyrosine by electron transfer from the peroxidase, so a drug that reduces one site can quench the radical at the other. The accounts are not exclusive and no record here measures their relative contribution at a therapeutic concentration.Read the recorded disagreement
Is paracetamol a selective cyclooxygenase-2 inhibitor?Human whole blood gives a clear answer: 4.4-fold selectivity in vitro, and after a single gram, 83% inhibition of the cyclooxygenase-2 index against 56% of the cyclooxygenase-1 index, with those authors concluding the drug functions as a selective cyclooxygenase-2 inhibitor and that the cardiovascular warnings for that class should apply to it. Against that, on purified enzyme the two isoforms are inhibited equally, and the 435-fold difference between endothelial cells and platelets was shown to be cellular rather than isoform selectivity, abolished by adding hydroperoxide back. A third record offers a reconciliation: at the low arachidonate concentrations of intact cells, cyclooxygenase-2 carries the lower flux and so generates less of the hydroperoxide that reverses the drug, which would produce apparent isoform selectivity from a mechanism that has nothing to do with isoform binding. That reconciliation is a proposal rather than a measurement, and the records disagree about what the observed selectivity means even where they agree on what was measured.Read the recorded disagreement

Open questions in this collection

Questions the curators could not answer from the sources in front of them, kept here with the reason each one is still open. These are gaps in this collection, not findings or proof that no one has studied them.

Whether the AM404 route operates at concentrations reached in people.AM404 was confirmed in human cerebrospinal fluid at 5 to 40 nanomoles per litre after an intravenous gram, which those authors state is far below its documented half-maximal concentration, while every functional demonstration of the route is in rodents.
Which of paracetamol’s mechanisms produces which of its effects.The metabolite route accounts for antinociception in rodents and demonstrably does not account for hypothermia, the peroxide-dependent cyclooxygenase account explains the absence of antiplatelet and anti-inflammatory effects, and the cerebrospinal fluid record connects fever to central prostaglandin. No record here apportions the clinical analgesic effect between them.
Whether paracetamol acts at the peroxidase site, the cyclooxygenase site, or both at therapeutic concentrations.Removing peroxide makes it thirtyfold more potent and adding hydroperoxide back abolishes inhibition, but it also inhibits enzyme reconstituted with manganese, which has almost no peroxidase activity, in a manner prostaglandin G2 does not prevent.
Whether the substantial cyclooxygenase-2 inhibition measured in people carries the cardiovascular risk of that drug class.A single oral gram inhibited the cyclooxygenase-2 index by 83% in whole blood, comparable to selective inhibitors, and those authors recommended that the cardiovascular warnings for that class be considered for paracetamol. No record here tests that.
Why paracetamol is recommended as the safe analgesic for aspirin-sensitive patients when about one in five of them reacts to it.Cross-reactivity is dose-dependent, appearing at 1000 milligrams and above in challenge studies, and desensitisation to aspirin abolishes it. No record here establishes a dose at which it is reliably safe in that group.

Chapters are assembled from supplied drafts and curated literature summaries. Statements remain unverified against the primary studies, and the ledger is not medical advice.

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