{"id":"7d76c248-e65f-5645-a9ad-ca991deaed30","stable_key":"ea2f0904-ab2c-5d1e-a3d4-3f7ecdd70cd6:caf-probe-confounding","predicate":"confounds","statement":"The NAT2 ratio AFMU/1MX fell to 56.7%, an alternative combined-metabolite NAT2 ratio stayed constant, and a CYP1A2 ratio transiently rose to 167%.","claim_class":"observational","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"13c26236-91e5-58cb-9d64-347343c98953","mechanism_event_label":"A downstream block can make another enzyme’s probe result misleading.","subject":{"id":"cfa51e26-3627-5a5e-9270-89c53f9db01b","slug":"allopurinol","display_name":"Allopurinol","entity_type_key":"small_molecule"},"object":{"id":"1e50dcc0-966a-56e4-8dec-b2d1e262bfe3","slug":"caffeine-metabolite-ratios","display_name":"Caffeine-derived urinary enzyme-phenotyping ratios","entity_type_key":"cellular_process"},"evidence_count":1,"mechanism_event":{"id":"13c26236-91e5-58cb-9d64-347343c98953","stable_key":"ea2f0904-ab2c-5d1e-a3d4-3f7ecdd70cd6:caf-probe-confounding-event","event_type":"observed_relationship","label":"A downstream block can make another enzyme’s probe result misleading.","description":"The NAT2 ratio AFMU/1MX fell to 56.7%, an alternative combined-metabolite NAT2 ratio stayed constant, and a CYP1A2 ratio transiently rose to 167%.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"cfa51e26-3627-5a5e-9270-89c53f9db01b","slug":"allopurinol","display_name":"Allopurinol","entity_type_key":"small_molecule"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"1e50dcc0-966a-56e4-8dec-b2d1e262bfe3","slug":"caffeine-metabolite-ratios","display_name":"Caffeine-derived urinary enzyme-phenotyping ratios","entity_type_key":"cellular_process"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"cf5d980b-0513-5960-88f8-09d7e69b4ef2","slug":"nat2","display_name":"Human arylamine N-acetyltransferase 2 / NAT2","entity_type_key":"protein"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"9b15c13c-a369-5d10-a76a-525e8b19221d","slug":"cyp1a2","display_name":"Human cytochrome P450 1A2","entity_type_key":"protein"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"8de34d8a-46dc-512c-a82f-d169747b496e","slug":"xdh","display_name":"Human xanthine oxidoreductase / XDH","entity_type_key":"protein"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"evidence_access","value_text":"Primary abstract","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Same 21-person caffeine-phenotyping study.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Changed ratios do not prove corresponding changes in NAT2 or CYP1A2 catalytic activity.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Caffeine collection; salts, coffee, species and coexposure contexts retain their identities.","comparator":null,"unit":null,"notes":"","entity":{"slug":"caffeine","display_name":"Caffeine","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"A downstream block can make another enzyme’s probe result misleading.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Xanthine oxidase inhibition by allopurinol affects the reliability of urinary caffeine metabolic ratios as markers for N-acetyltransferase 2 and CYP1A2 activities. · 1999 · https://pubmed.ncbi.nlm.nih.gov/10027663/ · DOI 10.1007/s002280050569","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"cc9feca4-dcdc-5d3f-a2f1-ce99833bc19d","evidence_kind":"source_excerpt","locator":"Lines 244-250","start_line":244,"end_line":250,"excerpt":"## caf-probe-confounding\nA downstream block can make another enzyme’s probe result misleading.\nThe NAT2 ratio AFMU/1MX fell to 56.7%, an alternative combined-metabolite NAT2 ratio stayed constant, and a CYP1A2 ratio transiently rose to 167%.\nModel: Same 21-person caffeine-phenotyping study.\nLimitations: Changed ratios do not prove corresponding changes in NAT2 or CYP1A2 catalytic activity.\nEvidence access: Primary abstract\nXanthine oxidase inhibition by allopurinol affects the reliability of urinary caffeine metabolic ratios as markers for N-acetyltransferase 2 and CYP1A2 activities. · 1999 · https://pubmed.ncbi.nlm.nih.gov/10027663/ · DOI 10.1007/s002280050569","model_system":"Same 21-person caffeine-phenotyping study.","directness":"reported_statement","verification_status":"source_derived_draft","notes":"Original curation paraphrase; evidence access stated with the claim.","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"40a654db-878c-5471-bc6c-88f4f52599c0","stable_key":"import-ea2f0904-ab2c-5d1e-a3d4-3f7ecdd70cd6","title":"Caffeine: receptors, metabolism, nutrient interactions, adaptation and discovery questions (2026-09-18)","document_type":"imported_text","citation_label":"AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text.","file_path":"","sha256":"780d73d4abd45a0284d2cc0c646dbe8432ae347362891a4b98a19a61341a7325","revision_id":"f36ffb0a-d6df-522f-b783-5e30214b9e26","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}