IN VITRO SULFOXIDATION OF THIOETHER COMPOUNDS BY HUMAN CYTOCHROME P450 AND FLAVIN-CONTAINING MONOOXYGENASE ISOFORMS WITH PARTICULAR REFERENCE TO THE CYP2C SUBFAMILY
- 1 March 2004
- journal article
- Published by Elsevier in Drug Metabolism and Disposition
- Vol. 32 (3) , 333-339
- https://doi.org/10.1124/dmd.32.3.333
Abstract
Cytochrome P450 (P450) and flavin-containing monooxygenase (FMO) enzymes are major catalysts involved in the metabolism of xenobiotics. The sulfoxidation of the thioether pesticides, phorate, disulfoton, sulprofos, and methiocarb, was investigated. Using pooled human liver microsomes (HLMs), thioether compounds displayed similar affinities; however, phorate and disulfoton displayed higher intrinsic clearance rates than either sulprofos or methiocarb. The sulfoxidation of thioethers by HLMs was found to be predominantly P450-driven (85-90%) compared with FMO (10-15%). Among 16 cDNA-expressed human P450 isoforms and 3 human FMO isoforms examined, the following isoforms and their polymorphisms had the highest rates for sulfoxidation, as follows: phorate, CYP1A2, 3A4, 2B6, 2C9*1, 2C18, 2C19, 2D6*1, and FMO1; disulfoton, CYP1A2, 3A4, 2B6, 2C9*1, 2C9*2, 2C18, 2C19, 2D6*1, and FMO1; sulprofos, CYP1A1, 1A2, 3A4, 2C9*1, 2C9*2, 2C9*3, 2C18, 2C19, 2D6*1, and FMO1; methiocarb, CYP1A1, 1A2, 3A4, 2B6, 2C9*1, 2C19, 2D6*1, and FMO1. Among these isoforms, members of the CYP2C subfamily often had the highest affinities and clearance rates. Moreover, sulfaphenazole, a CYP2C9 competitive inhibitor, inhibited disulfoton sulfoxidation by CYP2C9 (IC50 0.84 microM) as well as in HLMs. Ticlopidine, a CYP2C19 mechanism-based inhibitor, inhibited disulfoton sulfoxidation by CYP2C19 (IC50 after coincubation, 43.5 microM; IC50 after preincubation, 4.3 microM) and also in HLMs. Our results indicate that current models of the substrate binding site of the CYP2C subfamily would not effectively predict thioether pesticide metabolism. Thus, the substrate specificity of CYP2Cs is more extensive than is currently believed, and some reevaluation of structure-activity relationships may be required.Keywords
This publication has 33 references indexed in Scilit:
- Clinical relevance of genetic polymorphisms in the human CYP2C subfamilyBritish Journal of Clinical Pharmacology, 2001
- Ticlopidine as a Selective Mechanism-Based Inhibitor of Human Cytochrome P450 2C19Biochemistry, 2001
- Synthesis of Sulfaphenazole Derivatives and Their Use as Inhibitors and Tools for Comparing the Active Sites of Human Liver Cytochromes P450 of the 2C SubfamilyJournal of Medicinal Chemistry, 2001
- Engineering Microsomal Cytochrome P450 2C5 to Be a Soluble, Monomeric EnzymePublished by Elsevier ,2000
- Physiological factors affecting protein expression of flavin-containing monooxygenases 1, 3 and 5Xenobiotica, 1998
- Ticlopidine inhibition of phenytoin metabolism mediated by potent inhibition of CYP2C19*Clinical Pharmacology & Therapeutics, 1997
- A convenient method to discriminate between cytochrome P450 enzymes and flavin-containing monooxygenases in human liver microsomesArchives of Toxicology, 1996
- Differential Developmental and Tissue‐Specific Regulation of Expression of the Genes Encoding Three Members of the Flavin‐Containing Monooxygenase Family of Man, FMO1, FMO3 and FMO4European Journal of Biochemistry, 1996
- Stereoselective sulfoxidation of the pesticide methiocarb by flavin‐containing monooxygenase and cytochrome P450‐dependent monooxygenases of rat liver microsomes. Anticholinesterase activity of the two sulfoxide enantiomersJournal of Biochemical Toxicology, 1995
- Characterization of cDNAs, mRNAs, and proteins related to human liver microsomal cytochrome P-450 S-mephenytoin 4-hydroxylaseBiochemistry, 1988