Identification and quantitation of benzo[ a]pyrene-derived DNA adducts formed at low adduction level in mice lung tissue

Abstract

The two major metabolic pathways of benzo[ a]pyrene (BP) that lead to DNA lesions are monooxygenation that results in diolepoxides (BPDE) and one-electron oxidation that yields a BP radical cation. These pathways result in formation of stable and depurinating DNA adducts, respectively. Most in vivo animal studies with BP, however, have employed dosage/DNA adduct levels several orders of magnitude higher than the DNA damage level expected from environmentally relevant exposures. Presented are results of experiments in which A/J strain mice were intraperitoneally exposed to 50-μg/g doses of BP. It is shown that non-line-narrowed fluorescence and fluorescence line-narrowing spectroscopies possess the selectivity and sensitivity to distinguish between helix-external, base-stacked, and intercalated conformations of DNA–BPDE adducts formed in lung tissue. Concentrations measured by 32P postlabeling 2 and 3 days after intraperitoneal injection were 420–430 and 600–830 amol BPDE-type adducts per μg DNA. The external and base-stacked conformations are attributed mainly to (+)- trans-anti-BPDE-N 2dG and the intercalated conformations to (+)- cis-anti adducts. A stable adduct derived from 9-OH-BP-4,5-epoxide was also detected at a concentration about a factor of 10 lower than the above concentrations. The DNA supernatants were analyzed for the presence of depurinating BP-derived adducts by capillary electrophoresis laser-induced fluorescence and high-performance liquid chromatography mass spectrometry.