The food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is carcinogenic in the male Fischer-344 rat, affecting principally the colon. PhIP-DNA adducts may play a role in the initiation of the carcinogenic process. We have evaluated the formation and persistence of PhIP-DNA adducts in the colon, circulating white blood cells (WBC) and several other non-target organs of the male Fischer-344 rat. Young adult male animals were given a single dose of PhIP (50 mg/kg) by gavage. Animals were killed 1, 2, 6, 12, 16 or 20 days after dosing (4 animals/time point) and their liver, lungs, stomach, small intestine, cecum, colon, kidneys, WBC, heart and spleen were removed for isolation of DNA and assay of PhIP-DNA adducts by 32P-postlabeling. For interorgan comparisons of cell turnover, rats were given a single i.p. dose of [methyl-3H]thymidine, after which DNA was isolated at the same time intervals as for adduct analysis and its sp. act. (d.p.m. 3H/100 micrograms) was determined. In all organs up to three adducts could be isolated and the adduct pattern was the same in each case. On day 1, total adduct levels were highest in the colon (the target organ), followed by the spleen, cecum, small intestine, stomach, liver, kidneys, lungs, WBC and heart. Rates of adduct removal were similar in the colon, spleen, cecum, liver, lungs, stomach and small intestine, with day 16 and day 20 levels falling to < 16% of those on day 1; rates of removal were slower in the heart and kidneys (52.0 and 30.3% of day 1 values remaining on day 16 respectively). Adducts in WBC increased at first (day 2) and decreased thereafter to virtually non-detectable levels on days 16 and 20. Heart adducts on days 2-12 increased slightly or remained as high as those on day 1, then decreased to lower levels on days 16 and 20 (53.0 and 28.7% of day 1 levels respectively). There was no preferential removal or persistence of any individual adduct in WBC or in any of the organs. On days 1 and 2, the sp. act. of intestinal DNA (small intestine, cecum and colon) was > 30-fold higher than that in several other organs, including the liver. These sp. act. decreased to the low sp. act. of the liver on day 20. It is concluded that the rates of adduct removal from the intestines are more likely to be related to cell turnover of epithelial cells than to enzymatic repair.(ABSTRACT TRUNCATED AT 400 WORDS)

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The food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is carcinogenic in the CDF1 mouse liver, lungs and stomach. IQ is activated to its ultimate carcinogenic form by N-hydroxylation, catalyzed principally by hepatic microsomal cytochrome P450IA2, and further esterification, resulting in the formation of N-(deoxyguanosin-8-yl)-IQ and other adducts. The furanoterpenoid 4-ipomeanol (IPO) is a naturally occurring pneumotoxin which exerts its specific toxicity in Clara cells of the lung after activation by microsomal cytochrome P450. Because IPO is activated in the liver by a cytochrome P450IA2 enzyme, we evaluated IPO as a possible chemopreventive agent by assessing its ability to inhibit IQ-DNA adduct formation in the CDF1 mouse. Mice were put on an AIN-76A diet with or without 0.075% IPO from day 0 to 54. IQ (0.01%) was added to the diets from day 22 to 41 and animals were killed (four animals/time point) on days 42, 44, 46, 48, 50 and 54. Blood (for white blood cell isolation), liver, lungs, stomach, small intestine, cecum, colon, kidneys, spleen and heart were collected for analysis of IQ-DNA adducts by 32P-post-labeling. During the 12 day period after cessation of IQ exposure (days 42-54) IQ-DNA adduct formation was significantly inhibited in the liver (33.6-46.4%), lungs (29.9-58.6%), stomach (33.2-51.5%) and white blood cells (24.5-63.7%), but not in the other organs. Except in the colon, adduct removal from organs during days 42-54 was relatively slow (36.0-81.9% of day 42 levels remaining on day 54, 9.4-16.7% in the colon), but the presence of IPO in the diet did not influence the rate of adduct removal. Measurement of hepatic microsomal ethoxyresorufin deethylase, an activity specific for cytochrome P450IA isozymes, showed that the enzyme could be inhibited (14.1-68.1%) by IPO (0.05-10.0 mM) in vitro. It is concluded that IPO inhibits IQ-DNA adduct formation in target organs of the CDF1 mouse and that IPO may act by inhibiting N-hydroxylation of IQ. It is therefore possible that IPO may be a candidate chemopreventive agent against IQ-induced carcinogenesis.

The genotoxic effect of an environmental chemical may be estimated from the concentration of its DNA adducts in peripheral white blood cells (WBCs). The food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is carcinogenic in the Fischer-344 rat, affecting principally the liver, small intestine and large intestine. In the present study we have determined whether DNA adducts of IQ are present in circulating WBCs of rats after single or multiple oral doses of IQ and how these adducts are related to those in internal organs. Male Fischer-344 rats received IQ as an oral dose (5 or 50 mg/kg, starting on day 0) by daily gavage (1, 8 or 15 days of treatment). Using 32P-postlabeling assays, IQ-DNA adducts were isolated and quantitated in organs and WBCs on days 1, 8 and 15. Adduct patterns in WBCs were qualitatively similar to those in the organs and adduct formation was highest in the liver, followed by the lungs, kidneys, stomach, large intestine, WBC and small intestine. Accumulation of adducts occurred in all organs and in WBCs in a dose- and time-dependent manner. For all organs, IQ-DNA adduct formation was strongly correlated with those in WBCs. It is concluded that IQ-DNA adducts in WBCs are qualitatively and quantitatively directly related to those in internal organs, independent of the target organ specificity of the carcinogenic effect of IQ.