{"id":"87dd6060-3d68-51d7-bf0f-55b6a03bdc98","stable_key":"8c946991-97f0-55ee-8df0-00e67621962f:nad-plus-serum-processing","predicate":"changes","statement":"NAD+ restored XRCC1 recruitment in NAD-depleted MCF-7 cells more readily in fetal-bovine-serum-containing medium than serum-free or heat-inactivated-serum conditions; precursor metabolism and rescue also depended on incubation time.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"6561caed-beff-5307-85b1-28ab271c56b8","mechanism_event_label":"The material outside a cell can determine whether an added precursor works.","subject":{"id":"bd52455b-d684-5585-8084-a55f62174b7c","slug":"fetal-bovine-serum-nad-processing","display_name":"NAD precursor processing by fetal bovine serum","entity_type_key":"cellular_process"},"object":{"id":"a3282ce5-a1dc-5ccb-a0bb-cf90d2652d96","slug":"human-nad-dependent-xrcc1-recruitment","display_name":"NAD-dependent XRCC1 recruitment and PAR signaling in human cells","entity_type_key":"cellular_process"},"evidence_count":1,"mechanism_event":{"id":"6561caed-beff-5307-85b1-28ab271c56b8","stable_key":"8c946991-97f0-55ee-8df0-00e67621962f:nad-plus-serum-processing-event","event_type":"observed_relationship","label":"The material outside a cell can determine whether an added precursor works.","description":"NAD+ restored XRCC1 recruitment in NAD-depleted MCF-7 cells more readily in fetal-bovine-serum-containing medium than serum-free or heat-inactivated-serum conditions; 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medium comparison, NMR precursor stability and six- versus 24-hour exposure.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Serum components are not individually identified by this result; do not assign the effect to human CD73 or infer direct uptake.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"NAD+ collection; molecular form, preparation, species, exposure and manipulation remain explicit.","comparator":null,"unit":null,"notes":"","entity":{"slug":"nad-plus","display_name":"NAD+","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"The material outside a cell can determine whether an added precursor works.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Extracellular NAD+ enhances PARP-dependent DNA repair capacity independently of CD73 activity. · 2020 · https://pubmed.ncbi.nlm.nih.gov/31959836/ · DOI 10.1038/s41598-020-57506-9","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"42255081-dbed-504f-80ff-d8def2b8d67c","evidence_kind":"source_excerpt","locator":"Lines 364-370","start_line":364,"end_line":370,"excerpt":"## nad-plus-serum-processing\nThe material outside a cell can determine whether an added precursor works.\nNAD+ restored XRCC1 recruitment in NAD-depleted MCF-7 cells more readily in fetal-bovine-serum-containing medium than serum-free or heat-inactivated-serum conditions; precursor metabolism and rescue also depended on incubation time.\nModel: Human cells; medium comparison, NMR precursor stability and six- versus 24-hour exposure.\nLimitations: Serum components are not individually identified by this result; do not assign the effect to human CD73 or infer direct uptake.\nEvidence access: Primary full text\nExtracellular NAD+ enhances PARP-dependent DNA repair capacity independently of CD73 activity. · 2020 · https://pubmed.ncbi.nlm.nih.gov/31959836/ · DOI 10.1038/s41598-020-57506-9","model_system":"Human cells; medium comparison, NMR precursor stability and six- versus 24-hour exposure.","directness":"reported_statement","verification_status":"source_derived_draft","notes":"Original curation paraphrase; evidence access and experimental limitations specified.","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"f59aa302-d463-5462-876f-e21e64861eac","stable_key":"import-8c946991-97f0-55ee-8df0-00e67621962f","title":"NAD+: compartmental supply, consumption and cross-nutrient mechanisms (2026-09-19)","document_type":"imported_text","citation_label":"AI-assisted research curation; 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