Journal
TOXICOLOGY LETTERS
Volume 132, Issue 1, Pages 65-70Publisher
ELSEVIER IRELAND LTD
DOI: 10.1016/S0378-4274(02)00068-1
Keywords
cytochrome P450; flavin monooxygenase; hydroxy-imidacloprid; imidacloprid insecticide; metabolism; recombinant human liver monooxygenases
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Many metabolites of imidacloprid (IMI) have been identified, but the enzymatic basis for their formation has not been reported. This study with individual recombinant cytochrome P450 (CYP450) isozymes from human liver shows that the principal organoextractable NADPH-dependent metabolites are the 5-hydroxy (major) and olefin (minor) derivatives from hydroxylation and desaturation of the imidazolidine moiety and the nitrosoimine (major), guanidine (minor) and urea (trace) derivatives from reduction and cleavage of the nitroimine substituent. Isozymes selective for imidazolidine oxidation in order of decreasing overall activity are CYP3A4 > CYP2C19 or CYP2A6 > CYP2C9, while those selective for nitroimine reduction are CYP1A2, CYP2B6, CYP2D6 and CYP2E1. Three flavin monooxygenase isozymes (FMO1, FMO3, and FMO5) with NADPH are not active as assayed. These observations establish site specificity in IMI metabolism by CYP450 isozymes and that a single enzyme (CYP3A4) both oxidizes and reduces IMI at the imidazolidine and nitroimine moieties, respectively. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.
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