title: Inhibition of fipronil and nonane metabolism in human liver microsomes and human cytochrome P450 isoforms by chlorpyrifos.
abstract: Previous studies have established that chlorpyrifos (CPS), fipronil, and nonane can all be metabolized by human liver microsomes (HLM) and a number of cytochrome P450 (CYP) isoforms. However, metabolic interactions between these three substrates have not been described. In this study the effect of either coincubation or preincubation of CPS with HLM or CYP isoforms with either fipronil or nonane as substrate was investigated. In both co- and preincubation experiments, CPS significantly inhibited the metabolism of fipronil or nonane by HLM although CPS inhibited the metabolism of fipronil more effectively than that of nonane. CPS significantly inhibited the metabolism of fipronil by CYP3A4 as well as the metabolism of nonane by CYP2B6. In both cases, preincubation with CPS caused greater inhibition than coincubation, suggesting that the inhibition is mechanism based.
authors.affiliation: Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC 27695, USA.
authors.forename: Hyun
authors.initials: H
authors.lastname: Joo
authors.forename: Kyoungju
authors.initials: K
authors.lastname: Choi
authors.forename: Randy L
authors.initials: RL
authors.lastname: Rose
authors.forename: Ernest
authors.initials: E
authors.lastname: Hodgson
mesh_terms: D000473:Alkanes / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004390:Chlorpyrifos / Q000494:pharmacology*; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006801:Humans; D007306:Insecticides / Q000494:pharmacology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology*
chemical_list: D000473:Alkanes; D065607:Cytochrome P-450 Enzyme Inhibitors; D007306:Insecticides; D007527:Isoenzymes; D011720:Pyrazoles; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating; D004390:Chlorpyrifos; C082360:fipronil; C017573:nonane