The identification of [2-C-14]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine metabolites in humans

[2-C-14]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine ([C-14]PhIP), a put ative human carcinogenic heterocyclic amine found in well-done cooked meat, was administered orally to three colon cancer patients undergoing a partia l colonectomy, Forty-eight to seventy-two hours prior to surgery, subjects received a 70-84 mu g dose of C-14. Urine and blood were analyzed by HPLC f or PhIP and PhIP metabolites. Metabolites were identified based on HPLC co- elution with authentic PhIP metabolite standards, mass spectral analysis an d susceptibility to enzymatic cleavage. In two subjects, similar to 90% of the administered [C-14]PhIP dose was eliminated in the urine, whereas in th e other, only 50% of the dose was found in the urine. One subject excreted three times more radioactivity in the first 4 h than did the others. Twelve radioactive peaks associated with PhIP were detected in the urine samples. The relative amount of each metabolite varied by subject, and the amounts of each metabolite within subjects changed over time. In all three subjects the most abundant urinary metabolite was identified as 2-hydroxyamino-1-me thyl-6-phenylimidazo[4,5-b]pyridine-N-2-glucuronide (N-hydroxy-PhIP-N-2-glu curonide), accounting for 47-60% of the recovered counts in 24 h, PhIP acco unted for <1% of the excreted radiolabel in all three patients. Other metab olites detected in the urine at significant amounts were 4-(2-amino-1-methy limidazo[4,5-b]pyrid-6-yl)phenyl sulfate, N-hydroxy-PhIP-N-3-glucuronide an d PhIP-N-2-glucuronide. In the plasma, N-hydroxy-PhIP-N-2-glucuronide accou nted for 60, 18 and 20% of the recovered plasma radioactivity at 1 h post P hIP dose in subjects 1, 2 and 3 respectively. Plasma PhIP was 56-17% of the recovered dose at 1 h post exposure. The relatively high concentration of N-hydroxy-PhIP-N-2-glucuronide and the fact that it is an indicator of bioa ctivation make this metabolite a potential biomarker for PhIP exposure and activation. Determining the relative differences in PhIP metabolites among individuals will indicate metabolic differences that may predict individual susceptibility to carcinogenic risk from this suspected dietary carcinogen .