direct-black-3 and direct-blue-6

The role of the rat intestinal flora in the azo reduction of some benzidine-based dyes was studied in vitro and in vivo. The formation of benzidine was measured after anaerobic incubation of direct black 38, direct blue 6 and direct brown 95 in the presence of caecal bacteria in vitro. Benzidine was absorbed from the intestinal tract much better than the parent compounds. Oral administration of direct black 38 or direct brown 95 to Wistar rats results in the urinary excretion of mutagens. After oral administration of these dyes to germ-free Wistar rats no mutagenicity was observed in urine. The present results show that after oral administration, reduction by the intestinal flora should be considered as the first essential step in the biotoxification of benzidine-based dyes.

Topics: Administration, Oral; Animals; Azo Compounds; Benzidines; Biological Transport; Chromatography, High Pressure Liquid; Intestinal Mucosa; Male; Mutagens; Rats; Rats, Inbred Strains

The azo reduction and acetylation in vitro and the mutagenic activation in vivo of three 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 coenzyme A, 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 coenzyme A. 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 intraperitoneal treatment. Such differences were not observed for benzidine and direct brown 95. The results demonstrate that rat liver has a considerable capacity to reduce azo compounds. Nevertheless, 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.

Topics: Acetylation; Administration, Oral; Animals; Azo Compounds; Carcinogens; Coloring Agents; Glucuronidase; In Vitro Techniques; Injections, Intraperitoneal; Liver; Mutagens; Oxidation-Reduction; Rats; Rats, Inbred Strains

Topics: Animals; Azo Compounds; Benzidines; Body Weight; Chemical and Drug Induced Liver Injury; Coloring Agents; Dose-Response Relationship, Drug; Female; Liver; Liver Neoplasms; Male; Mice; Naphthalenesulfonates; Neoplasms, Experimental; Rats; Rats, Inbred F344; Time Factors