title: Human variation and CYP enzyme contribution in benfuracarb metabolism in human in vitro hepatic models.
abstract: Human responses to the toxicological effects of chemicals are often complicated by a substantial interindividual variability in toxicokinetics, of which metabolism is often the most important factor. Therefore, we investigated human variation and the contributions of human-CYP isoforms to in vitro metabolism of benfuracarb. The primary metabolic pathways were the initial sulfur oxidation to benfuracarb-sulfoxide and the nitrogen-sulfur bond cleavage to carbofuran (activation). The Km, Vmax, and CL(int) values of carbofuran production in ten individual hepatic samples varied 7.3-, 3.4-, and 5.4-fold, respectively. CYP2C9 and CYP2C19 catalyzed benfuracarb sulphur oxidation. Carbofuran formation, representing from 79% to 98% of the total metabolism, was catalyzed predominantly by CYP3A4. The calculated relative contribution of CYP3A4 to carbofuran formation was 93%, while it was 4.4% for CYP2C9. The major contribution of CYP3A4 in benfuracarb metabolism was further substantiated by showing a strong correlation with CYP3A4-selective markers midazolam-1'-hydroxylation and omeprazole-sulfoxidation (r=0.885 and 0.772, respectively). Carbofuran formation was highly inhibited by the CYP3A inhibitor ketoconazole. Moreover, CYP3A4 marker activities were relatively inhibited by benfuracarb. These results confirm that human CYP3A4 is the major enzyme involved in the in vitro activation of benfuracarb and that CYP3A4-catalyzed metabolism is the primary source of interindividual differences.
authors.affiliation: Center for Arctic Medicine, Thule Institute, University of Oulu, Finland; Pharmacology and Toxicology Unit, Institute of Biomedicine, P.O. Box 5000, FI-90014 University of Oulu, Oulu, Finland. Electronic address: khaled.megahed@oulu.fi.
authors.forename: Khaled
authors.initials: K
authors.lastname: Abass
authors.forename: Petri
authors.initials: P
authors.lastname: Reponen
authors.forename: Sampo
authors.initials: S
authors.lastname: Mattila
authors.forename: Arja
authors.initials: A
authors.lastname: Rautio
authors.forename: Olavi
authors.initials: O
authors.lastname: Pelkonen
mesh_terms: D000328:Adult; D001572:Benzofurans / Q000378:metabolism* / Q000633:toxicity; D001711:Biotransformation; D051544:Cytochrome P-450 CYP3A / Q000502:physiology; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D005260:Female; D006801:Humans; D007306:Insecticides / Q000378:metabolism*; D007527:Isoenzymes / Q000502:physiology; D007654:Ketoconazole / Q000494:pharmacology; D008297:Male; D053858:Metabolic Networks and Pathways; D008862:Microsomes, Liver / Q000378:metabolism*; D008875:Middle Aged; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity
chemical_list: D001572:Benzofurans; D007306:Insecticides; D007527:Isoenzymes; D015091:beta-Alanine; C096128:benfuracarb; D003577:Cytochrome P-450 Enzyme System; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D007654:Ketoconazole
keywords: Benfuracarb; CYP assignment; Cytochrome P450s; Human variability; Metabolism; Risk assessment