Possible mechanism of Sudan III-induced prevention of chemical carcinogenesis in rats.

The effect of treatment of rats with Sudan III on the ability of the liver to transform benzo(a)pyrene (BP) to a mutagen was investigated to elucidate a possible mechanism of the Sudan III-induced prevention of chemical carcinogenesis (Huggins et al., Proc. Natl. Acad. Sci., 75:4524-4527, 1978) using a modified Ames mutagenesis test system. Preincubation of BP with liver 9000 x g supernatant (S-9) from rats treated with Sudan III markedly increased the mutagenicity of BP in the conventional Ames method. The increase in number of revertant colonies was proportional to the aryl hydrocarbon hydroxylase activity of the S-9 fractions used (r greater than 0.9). This azo dye was found to induce both cytochrome P-448 which is an activating enzyme of procarcinogens and the activities of UDP glucuronyl transferase and glutathione-S-transferase (GST), which are detoxifying enzymes of active carcinogenic intermediates. The addition of anti-cytochrome P-448 antibody or the cofactors for UDP glucuronyl transferase and glutathione-S-transferase to the liver S-9 preincubation mixture with BP caused a marked decrease in BP mutagenicity when liver S-9 fractions from Sudan III-treated rats were used. The decrease obtained by the addition of the cofactors was proportional to the induced levels of the UDP glucuronyl transferase or glutathione-S-transferase. It was concluded that Sudan III-induced prevention of chemical carcinogenesis is due to an accelerated elimination of the carcinogen by the induction of both cytochrome P-448 and detoxifying enzymes with a limited increase in levels of active metabolic intermediates.