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

We show that the naturally occurring hydroperoxide hydrogen peroxide i s highly effective in supporting the cytochrome P450 1A2 peroxygenase- catalyzed metabolic activation of the heterocyclic aromatic amine 2-am ino-3-methylimidazo[4,5-f]quinoline (IQ) to genotoxic metabolites. Mut agenicity was assessed by the Ames assay with Salmonella typhimurium s train YG1012 and an activation system consisting of hydroperoxides plu s either 3-methylcholanthrene-induced rat liver microsomes (rP4501A) o r human P450 1A2-containing microsomes (hP4501A2). The mutagenic respo nse was dependent on the concentration of microsomal protein, IQ, and hydroperoxides. The addition of hydrogen peroxide or tert-butyl hydrop eroxide to rP4501A greatly enhanced the yield of histidine prototrophi c (His(+)) revertants. This increase was inhibited, in a concentration -dependent manner, by (alpha)-naphthoflavone, a P4501A inhibitor. Hydr ogen peroxide was the most effective peroxygenase cofactor, particular ly with hP4501A2 (K-m = 0.1 mM). The hydroperoxide-supported activatio n of IQ produced reactive intermediates which bound to 2'-deoxyguanosi ne; LC/MS analysis of the adducts revealed the same major (protonated) adduct at mit = 464.4 as previously reported for the DNA adduct forme d (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 p hysiological/pathological concentration range may be able to support t he metabolic activation of arylamines to genotoxic products through th e cytochrome P450 peroxygenase pathway.