Disposition and metabolism of the food mutagen 2-amino-3,8-dimethylimidazo[4, 5-<i>f</i>]quinoxaline (MeIQx) in rats

The disposition and metabolism of a common food mutagen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), was studied in rats. Five rats of both sexes were given a single oral dose of 14C-labeled MeIQx (3-4 mg/kg body wt). The male rats excreted 36% of the radioactivity and 15% of the mutagenic activity of the dose given in the urine collected during the first 24 h. In the females the corresponding urine contained 41% of the radioactivity and 12% of the mutagenicity. During the next 48 h only 1-3% of the radioactive dose was excreted in urine. The remaining dose was excreted in the feces except of less than 1% that was retained by the tissues after 72 h. The liver and kidney retained more radioactivity than other organs. In a separate study the metabolites of bile, urine and feces of both sexes were investigated. After a single oral dose of 20 mg 14C-labeled MeIQx/kg body wt, three major non-mutagenic metabolites were identified. These were 2-amino-4(or 5)-(beta-D-glucuronopyranosyloxy)-3,8-dimethylimidazo[4,5-f] quinoxaline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxalin-4(or 5)-yl sulfate and N-(3,8-dimethylimidazo[4,5-f]quinoxalin-2-yl) sulfamate. Another two metabolites present in bile, urine and feces were 2-(beta-D-glucuronopyranosylamino)-3,8-dimethylimidazo[4,5-f ] quinoxaline and 2-amino-8-hydroxymethyl-3-methylimidazo[4,5-f]quinoxalin-4 (or 5)yl sulfate. All metabolites were essentially non-mutagenic. Most of the mutagenicity still present in bile, urine and feces could be explained by unchanged MeIQx. Unchanged MeIQx was the most abundant form excreted in urine.