METABOLISM OF BENZIDINE-BASED DYES AND THE APPEARANCE OF MUTAGENIC METABOLITES IN URINE OF RATS AFTER ORAL OR INTRAPERITONEAL ADMINISTRATION

The azo reduction and acetylation in vitro and the mutagenic activation in vivo of 3 azo dyes were studied. In the presence of rat liver 9000 g supernatant benzidine was released from direct black 38 and direct brown 95, whereas hardly any benzidine was produced during incubation of direct blue 6. Incubation of benzidine with isolated rat hepatocytes resulted in the appearance of diacetylbenzidine. No diacetylbenzidine was formed during incubation of benzidine with rat liver 9000 g supernatant, unless the cofactor for the acetylation reaction, acetyl CoA, was added to the incubation medium. Isolated rat hepatocytes were capable to produce diacetylbenzidine from direct black 38, direct blue 6 or direct brown 95 without supplementation with acetyl CoA. Administration of benzidine, direct black 38 or direct brown 95 to rats resulted in the appearance of mutagenicity in urine. For direct black 38 significantly higher mutagenicity values were found in urine after oral administration than after i.p. treatment. Such differences were not observed for benzidine and direct brown 95. Rat liver has a considerable capacity to reduce azo compounds. For some compounds, like direct black 38, extrahepatic enzymes, most likely present in the intestinal flora, may also play a substantial role in the azo cleavage.