title: Genotoxic and mutagenic activation of aflatoxin B1 by constitutive forms of cytochrome P-450 in rat liver microsomes.
abstract: Cytochrome P-450-mediated activation of aflatoxin B1 (AFB1) to genotoxic and mutagenic products which subsequently cause induction of an umu gene expression in Salmonella typhimurium TA1535/pSK1002 has been studied in a rat liver microsomal or reconstituted monooxygenase system. Liver microsomes from male Sprague-Dawley rats had a 1.5-fold higher activity to catalyze AFB1 than did those from female rats. In addition, the activation was not increased in liver microsomes from rats pretreated with phenobarbital, 3-methylcholanthrene, a polychlorinated biphenyl mixture, or dexamethasone, suggesting that the constitutive forms of cytochrome P-450 have important roles for the activation of AFB1 in rat liver microsomes. Using 15 forms of cytochrome P-450 purified from liver microsomes of untreated and phenobarbital- and 3-methylcholanthrene-treated rats, three isozymes from untreated male rats and one isozyme from untreated female rats were found to have high reactivities in metabolizing AFB1 to genotoxic products. Cytochrome P-450 forms isolated from inducer-treated rats were relatively less active. The close correlation between induction of umu gene expression and mutagenicity with Ames/S. typhimurium TA98 system by activated metabolites of AFB1 in the reconstituted monooxygenase system suggested that the constitutive forms of cytochrome P-450 had major roles for genotoxic and mutagenic activation of AFB1 in rat liver microsomes.
mesh_terms: D016604:Aflatoxin B1; D000348:Aflatoxins / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004249:DNA Damage; D005260:Female; D005798:Genes, Bacterial / Q000187:drug effects*; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009152:Mutagenicity Tests; D009153:Mutagens / Q000378:metabolism*; D009154:Mutation; D010105:Oxygenases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012486:Salmonella typhimurium / Q000235:genetics; D012727:Sex Characteristics
chemical_list: D000348:Aflatoxins; D009153:Mutagens; D003577:Cytochrome P-450 Enzyme System; D016604:Aflatoxin B1; D010105:Oxygenases