Cd. Davis et al., 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, Journal of the National Cancer Institute, 86(14), 1994, pp. 1065-1070
Background: An important class of dietary mutagens and carcinogens are
the heterocyclic arylamine compounds that have been identified in a v
ariety of cooked, protein-containing foods. Among these heterocyclic a
mines, 2-amino-l-methyl-6-phenylimidazo [4,5-b]-pyridine (PhIP) is pot
entially 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 bet
ter assess the significance of breast milk as a route of exposure of t
he newborn to dietary heterocyclic amines, we examined the metabolites
of PhIP in breast milk and in urine of nursing pups. Methods: Lactati
ng 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 fro
m the pups and then analyzed the samples for metabolites of PhIP, usin
g high-pressure liquid chromatography (HPLC). PhlP-DNA adduct levels i
n the tissues of the pups were determined by P-32-postlabeling analysi
s. Results: Three radioactive peaks were observed by HPLC separation o
f 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-glucuro
nide, PhIP-4 '-sulfate, 4 '-hydroxy-PhIP, and N-2-hydroxy-PhIP-N-3-glu
curonide. 4 '-Hydroxy-PhIP and its conjugates contributed approximatel
y 60% of the radioactivity found in the urine. By P-32-postlabeling an
alysis, 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 a
dducts/l0(7) nucleotides. Conclusions: The large percentage of 4 '-hyd
roxy-PhIP and its conjugates in the urine indicates that 5-day-old pup
s detoxify PhIP and further metabolize 4 '-hydroxy-PhIP obtained from
the breast milk. The presence of the glucuronide conjugate of N-hydrox
y-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 p
ups. This conclusion was further supported by the observation that hep
atic S9 fractions from the pups activated PhIP to a mutagen in the Ame
s Salmonella mutagenicity assay and by the presence of PhIP-DNA adduct
s 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.