METABOLISM OF THE FOOD-DERIVED CARCINOGEN 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B] PYRIDINE BY LACTATING FISCHER-344 RATS AND THEIR NURSING PUPS

Background: An important class of dietary mutagens and carcinogens are the heterocyclic arylamine compounds that have been identified in a variety of cooked, protein-containing foods. Among these heterocyclic amines, 2-amino-l-methyl-6-phenylimidazo [4,5-b]-pyridine (PhIP) is potentially the most important carcinogen for human cancer risk. We have recently observed that PhIP-derived radioactivity is excreted into the breast milk of lactating rats administered [H-3]PhIP. Purpose: To better assess the significance of breast milk as a route of exposure of the newborn to dietary heterocyclic amines, we examined the metabolites of PhIP in breast milk and in urine of nursing pups. Methods: Lactating Fischer 344 rats with 5-day-old pups were given a single oral dose of 10 mg/kg of[H-3]PhIP. We collected milk from the dams and urine from the pups and then analyzed the samples for metabolites of PhIP, using high-pressure liquid chromatography (HPLC). PhlP-DNA adduct levels in the tissues of the pups were determined by P-32-postlabeling analysis. Results: Three radioactive peaks were observed by HPLC separation of milk samples: an unidentified early eluting peak, 4 '-hydroxy-PhIP, and PhIP. Four metabolites and the parent compound were found in urine of the pups nursed by dams given radiolabeled PhIP: PhIP4 '-O-glucuronide, PhIP-4 '-sulfate, 4 '-hydroxy-PhIP, and N-2-hydroxy-PhIP-N-3-glucuronide. 4 '-Hydroxy-PhIP and its conjugates contributed approximately 60% of the radioactivity found in the urine. By P-32-postlabeling analysis, PhIP-DNA adducts were detected in spleen, lung, heart, kidney, liver, and stomach of pups at mean levels ranging from 0.06 to 0.55 adducts/l0(7) nucleotides. Conclusions: The large percentage of 4 '-hydroxy-PhIP and its conjugates in the urine indicates that 5-day-old pups detoxify PhIP and further metabolize 4 '-hydroxy-PhIP obtained from the breast milk. The presence of the glucuronide conjugate of N-hydroxy-PhIP in the urine of pups and the lack of detectible conjugate or N-hydroxylamine itself in breast milk suggest that PhIP from breast milk undergoes metabolic activation via N-hydroxytation in 5-day-old rat pups. This conclusion was further supported by the observation that hepatic S9 fractions from the pups activated PhIP to a mutagen in the Ames Salmonella mutagenicity assay and by the presence of PhIP-DNA adducts in the tissues of the pups. Implications: The findings reported here may have carcinogenic and toxicologic implications for the offspring of women who breast-feed and consume a diet rich in cooked meat.