Mutagenic activation of aflatoxin B1 by P-450 HFLa in human fetal livers

The genotoxic and mutagenic activation of promutagens by human fetal livers was measured by the induction of umu gene expression in Salmonella typhimurium TA1535/pSk1002. Liver homogenates of human fetuses were the most active for the mutagenic activation of aflatoxin B1 (AFB1), followed by 2-amino-3-methylimidazo(4,5-f)quinoline (IQ), and to a lesser extent by 2-amino-6-methyldipyrido(1,2-a:3',2'-d)imidazole (Glu-P-1). The amounts of P-450 HFLa immunochemically determined in human fetal livers correlated highly with the induction of umu gene expression by AFB1 (r = 0.98, n = 5). P-450 HFLa catalyzed the mutagenic activation of AFB1 in a reconstituted system: cytochrome b5 markedly stimulated the activation. Anti-P-450 HFLa antibodies inhibited the mutagenic activation of AFB1 in a dose-dependent manner. These results strongly support the idea that P-450 HFLa is responsible for the mutagenic activation of AFB1 in human fetal livers.