DNA adduct formation in mouse tissues in relation to serum levels of benzo(a)pyrene-diol-epoxide after injection of benzo(a)pyrene or the diol-epoxide

Abstract

Previous studies have shown that the carcinogenic metabolite of benzo(a)pyrene [B(a)P], B(a)P-7,8-diol-9,10-epoxide (BPDE), is transported in serum after B(a)P injection in mice. It is possible that serum transport is an important source of carcinogenic metabolite and results in DNA adduct formation in tissues. This possibility was studied by comparing the time course for BPDE appearance in serum with that for BPDE/DNA adduct formation after B(a)P i.p. injection (2, 20, or 200 mg/kg) into female C57BL/6 x C3H F1 mice. Additionally, BPDE was injected i.v. (8.25 nmol), and its disappearance from serum and adduction of tissue DNA were followed. BPDE serum levels and DNA adduct levels were measured by 32P-postlabeling analysis. Results indicate that, after a 200-mg B(a)P/kg i.p. injection, BPDE/DNA adduct levels rose sharply in liver, lung, kidney, stomach, and spleen through 5 h and then more gradually through 24 h. Adduct levels were similar in all tissues at 24 h. BPDE levels in serum reached a plateau within 2.5 h and remained constant thereafter (10 to 11 nM). B(a)P levels in serum fell steadily from 1980 nM at 1 h to 350 nM by 24 h. Levels of serum BPDE and DNA adducts showed a similar dose dependency at 10- and 100-fold lower B(a)P i.p. doses. After BPDE i.v. injection, BPDE levels in serum decreased to 0.16% of the initial level within 5 min. By this time, BPDE/DNA adducts were at peak levels in all tissues assayed. Lung adduct levels were 10 to 100 times greater than those in the other tissues. These results support a role for serum transport of BPDE in the production of DNA adducts after B(a)P since BPDE was available in serum throughout the time course for DNA adduct formation. Further, injected BPDE rapidly formed DNA adducts and this occurred primarily in the lung, which had the greatest access to the transported carcinogen.