Characterization of a microsomal fraction from rat small intestine for metabolic activation of some promutagens

Atrazine treatment potentiates excretion of mutagenic urine in 2,6-dinitrotoluene-treated Fischer 344 rats

Atrazine (ATZ), an s-triazine herbicide, is a widespread environmental contaminant. The hepatocarcinogenic component of technical grade dinitrotoluene, 2,6-dinitrotoluene (2,6-DNT, 19.5%), is a byproduct of trinitrotoluene synthesis and is found at production sites. This study explores the effect of ATZ treatment on the bioactivation of the promutagen, 2,6-DNT. Male Fischer 344 rats (5 weeks old) were administered 50 mg/kg of ATZ by gavage for 5 weeks. At 1, 3, and 5 weeks, both DMSO-control and ATZ-pretreated rats were treated p.o. with 75 mg/kg of 2,6-DNT and were housed in metabolism cages for urine collection. Sulfatase- and beta-glucuronidase-treated, concentrated urine was bioassayed for urinary mutagens in a microsuspension modification of the Salmonella assay with and without metabolic activation. No significant change in mutagen excretion was observed in ATZ-treated rats; however, an elevation in direct-acting urine mutagens from rats receiving ATZ and 2,6-DNT at weeks 1 (359 +/- 68 vs. 621 +/- 96 revertants/ml) and 5 (278 +/- 46 vs. 667 +/- 109 revertants/ml) of treatment was observed. The increase in production of urinary mutagens was accompanied by an elevation in small intestinal nitroreductase activity. Increases in large intestinal nitroreductase and beta-glucuronidase were observed after 5 weeks. There was no apparent effect of ATZ following 5 weeks of treatment on the production of 2,6-DNT-derived hepatic DNA adducts. ATZ treatment modifies intestinal enzymes responsible for promutagen bioactivation, and potentiates the excretion of mutagenic urine in 2,6-DNT-treated animals.

The metabolic disposition of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in the induced mouse

The toxicokinetics of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a member of the aminoimidazoazaarene family of mutagens, was studied in C57BL/6 male mice after ip and gavage exposure to a single dose of 100 mg/kg body weight. Twenty-four hr after administration of the dose, 39% of the [14C]PhIP had been found in the urine of the animals exposed ip and 12% had been found in the faeces. By comparison, at 24 hr, gavage-exposed animals had excreted 31% of the administered radioactivity in the urine and 30% in the faeces. Significantly higher levels of labelled compounds could be detected in the blood of animals dosed ip than in that of those dosed by gavage at 6 and 12 hr after dosing. Tissue concentrations of labelled compound were highest in the liver and gastro-intestinal tract of the ip group and the large intestine of the gavage group. Considerable radioactivity was also detected in the contents of the large and small intestine of the ip group suggesting biliary excretion of PhIP. Peak tissue concentrations were found 6-12 hr after administration of the dose by both routes. High-performance liquid chromatography of urine demonstrated the presence of 11 metabolites while only two major metabolites were found in the faeces, one of which was not present in the urine. None of the metabolites appeared to be formed by simple N-acetylations or N-demethylations of PhIP. No differences were seen in the metabolite profiles between the ip and the gavage groups, but significant differences were seen in the kinetics of PhIP excretion between animals dosed by these two routes. These data indicate that the toxicokinetics of PhIP metabolism differ depending on the route of administration and should be considered when performing animal studies to assess the significance of human dietary PhIP consumption.

Metabolism of the food-borne mutagen/carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in the rat: assessment of biliary metabolites for genotoxicity

The absorption and kinetics of excretion of [14C]2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline (MeIQx) was studied in male Sprague-Dawley rats. Within 72 hr of an oral dose of [14C]MeIQx (20 mg/kg) 33-56% of the radioactivity was excreted in the urine and 37-75% of the radioactivity in the faeces, which accounted for greater than 99% of the dose. Only low levels of radioactivity remained in the body. Radioactivity, when expressed per gram of tissue, was highest in the liver and kidney with smaller amounts detected in the lung and both the small and large intestines. Between 25 and 50% of a dose of MeIQx was recovered in the bile within 24 hr. Biliary metabolites were excreted over a long period of time with one radioactive fraction rapidly excreted at 2-3 hr and a second fraction excreted at 10-12 hr. The metabolites present in bile were assessed for genotoxicity using Salmonella typhimurium TA98 with or without hepatic S-9 activation and were found to be present as detoxified products. The residual mutagenic activity present in bile was attributed primarily to unmetabolized MeIQx.