The effect of diet on 2,6-dinitrotoluene hepatocarcinogenesis.

Pectin-induced changes in microflora have been shown to elevate the covalent binding of 2,6-dinitrotoluene (2,6-DNT)-related materials to total rat hepatic macromolecules. Therefore, the effect of diets varying in pectin content on the induction of foci and hepatic tumors induced by 2,6-DNT was studied in male F344 rats. 2,6-DNT (3.0-3.5 and 0.6-0.7 mg/kg/day) was incorporated into NIH-07 (NIH), an open formula cereal-based diet high in pectin content, AIN-76A (AIN), a purified pectin-free diet, or AIN-76A supplemented with 5% pectin (AP). Hepatic foci were scored after histochemical staining for gamma-glutamyl transpeptidase (GGT), canalicular adenosine triphosphatase or glucose-6-phosphatase following administration of test diets for 3, 6 and 12 months. The number of foci per cm3 of liver increased in a dose- and time-department manner following incorporation of 2,6-DNT into test diets with NIH greater than AP greater than AIN. In the NIH diet, 2,6-DNT did not alter the phenotypic distribution of foci. Animals fed control or 2,6-DNT-containing AIN and AP diets had few or no GGT foci throughout the study. Hepatocellular carcinomas and neoplastic nodules were observed only in rats fed NIH containing 2,6-DNT. The concentrations of 2,6-DNT-related material covalently bound to hepatic macromolecules after a single oral dose of radiolabeled 2,6-DNT given after 12 months on the diets increased in control rats and in rats receiving low dose 2,6-DNT in the diet with AIN less than AP less than NIH. These studies show that the carcinogenicity of 2,6-DNT differs depending on whether rats are fed an NIH or AIN (+/- pectin) diet. The results suggest that diet-induced alterations in the covalent binding of 2,6-DNT are not the sole factor in determining the carcinogenic response to 2,6-DNT. Furthermore, unidentified contaminants in cereal-based diets may influence foci and tumor production in rat liver during carcinogen treatment.