Removal of DNA adducts of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the male Fischer-344 rat.

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)