Persistence of benzo(a)pyrene metabolite:DNA adducts in lung and liver of mice.

The persistence of benzo(a)pyrene (BP) metabolite:DNA adducts has been studied in lung and liver of A/HeJ and C57BL/6J mice after a dose of BP (6 mg/mouse) which induces pulmonary adenomas in A/HeJ mice but not in C57BL/6J mice. BP is not a hepatic carcinogen in either strain. Following p.o. administration of [3H]BP, animals were killed at times ranging from 10 hr to 28 days, and BP metabolite:DNA adducts were analyzed by high-pressure liquid chromatography. The major adduct identified in each tissue was the (+)-7 beta-8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene:deoxyguanosine adduct. A 7 beta, 8 alpha-dihydroxy-9 beta,10 beta,epoxy-7,8,9, 10-tetrahydrobenzo(a)pyrene:deoxyguanosine adduct, a (-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene:deoxyguanosine adduct, and an unidentified adduct were also observed. The disappearance of (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydro-BP adduct in A/HeJ mice followed first-order kinetics over the time period examined, with a half-life of 18 and 9 days in lung and liver, respectively. The decay of this adduct in C57BL/6J mice was biphasic in both tissues. Our data on cell turnover suggest that there is active removal of adducts in liver, but that normal DNA turnover can account for the partial or possibly total observed disappearance of adducts in lung. These results suggest that the tissue specificity for BP-induced neoplasia in A/HeJ mice may be related to the relative persistence of adducts and high cell turnover rates in lung. In contrast, the results on formation and persistence of adducts and cell turnover do not provide an explanation for the strain difference in susceptibility to BP-induced pulmonary adenomas. It was also shown that the rates of removal of BP metabolite:DNA adducts in A/HeJ mice are not significantly different at a 500-fold lower BP dose.