title: Hydrogen peroxide supports human and rat cytochrome P450 1A2-catalyzed 2-amino-3-methylimidazo[4,5-f]quinoline bioactivation to mutagenic metabolites: significance of cytochrome P450 peroxygenase.
abstract: We show that the naturally occurring hydroperoxide hydrogen peroxide is highly effective in supporting the cytochrome P450 1A2 peroxygenase-catalyzed metabolic activation of the heterocyclic aromatic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) to genotoxic metabolites. Mutagenicity was assessed by the Ames assay with Salmonella typhimurium strain YG1012 and an activation system consisting of hydroperoxides plus either 3-methylcholanthrene-induced rat liver microsomes (rP4501A) or human P450 1A2-containing microsomes (hP4501A2). The mutagenic response was dependent on the concentration of microsomal protein, IQ, and hydroperoxides. The addition of hydrogen peroxide or tert-butyl hydroperoxide to rP4501A greatly enhanced the yield of histidine prototrophic (His+) revertants. This increase was inhibited, in a concentration-dependent manner, by alpha-naphthoflavone, a P450 1A inhibitor. Hydrogen peroxide was the most effective peroxygenase cofactor, particularly with hP4501A2 (K(m) = 0.1 mM). The hydroperoxide-supported activation of IQ produced reactive intermediates which bound to 2'-deoxyguanosine; LC/MS analysis of the adducts revealed the same major (protonated) adduct at m/z = 464.4 as previously reported for the DNA adduct formed (in vivo or in vitro) by the mixed function-catalyzed bioactivation system. None of the peroxidase-catalyzed IQ metabolites (nitro-, azo-, or azoxy-IQ) were detected. In conclusion, hydrogen peroxide in the physiological/pathological concentration range may be able to support the metabolic activation of arylamines to genotoxic products through the cytochrome P450 peroxygenase pathway.
authors.affiliation: Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: M R
authors.initials: MR
authors.lastname: Anari
authors.forename: P D
authors.initials: PD
authors.lastname: Josephy
authors.forename: T
authors.initials: T
authors.lastname: Henry
authors.forename: P J
authors.initials: PJ
authors.lastname: O'Brien
mesh_terms: D000818:Animals; D001711:Biotransformation / Q000187:drug effects; D002384:Catalysis; D019388:Cytochrome P-450 CYP1A2 / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000502:physiology*; D009152:Mutagenicity Tests; D009153:Mutagens / Q000378:metabolism / Q000493:pharmacokinetics*; D011804:Quinolines / Q000378:metabolism / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012486:Salmonella typhimurium / Q000187:drug effects
chemical_list: D009153:Mutagens; D011804:Quinolines; C071417:2-nitro-3-methylimidazo(4,5-f)quinoline; C029216:2-amino-3-methylimidazo(4,5-f)quinoline; D006861:Hydrogen Peroxide; D006899:Mixed Function Oxygenases; C022333:peroxygenase; D019388:Cytochrome P-450 CYP1A2; C036989:2-amino-3,4-dimethylimidazo(4,5-f)quinoline