The food-borne
mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-
b]pyridine (
PhIP) induces
tumors in colon of male rats and has been implicated in the etiology of human
cancers, particularly
colorectal cancer. This study was conducted to examine: (1) the biliary and/or circulatory transport of
N-hydroxy-PhIP and its N-
glucuronides, N-sulfonyloxy-
PhIP and
N-acetoxy-PhIP; (2) their role as proximate and ultimate carcinogenic metabolites of
PhIP; (3) the potential role of
glutathione in modulating
PhIP-DNA adduct formation.
PhIP-
DNA adducts, measured by the 32P-postlabeling method, were highest in the pancreas (361 adducts/10(8)
nucleotides or 100%), followed by colon (56%), lung (28%), heart (27%) and liver (2%), at 24 h after a single oral dose of
PhIP (220 mumol/kg) to male rats. In each tissue examined, we observed two major adducts, each of which accounted for 35-45% of the total, and one minor adduct, which represented about 10-20% of the total. One of the major adducts was identified as N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-
b]pyridine by chromatographic comparisons with an authentic standard. The major urinary metabolites of
PhIP in these rats were 4'-hydroxy-PhIP and its
glucuronide and
sulfate conjugates, followed by
N-hydroxy-PhIP N3-glucuronide,
N-hydroxy-PhIP N2-glucuronide and unchanged
PhIP. In bile duct-ligated rats, the urinary excretion of the
N-OH-PhIP N3-glucuronide was increased two-fold, but there was no effect on
PhIP-DNA adduct formation in the colon, heart, lung, pancreas or liver.
2,6-Dichloro-4-nitrophenol, which strongly inhibits arylsulfo-
transferase-mediated
DNA binding in vivo, had no effect on
PhIP-DNA adduct levels in liver or in extrahepatic tissues. Pretreatment of rats with
buthionine sulfoximine, which results in hepatic
glutathione depletion, caused a five-fold increase in adduct formation in the liver.
Intravenous administration (10 mumol/kg) of
N-hydroxy-PhIP and
N-acetoxy-PhIP each led to high levels of
PhIP-
DNA adducts in each of the extrahepatic tissues examined. Adduct levels ranged from two- to six-fold higher (for
N-hydroxy-PhIP) and four- to 28-fold higher (for
N-acetoxy-PhIP) as compared to that after an i.v. dose of the parent compound, indicating that these two bioactivated derivatives of
PhIP are sufficiently stable to be transported through the circulation to extrahepatic tissues.(ABSTRACT TRUNCATED AT 400 WORDS)