Persistence and repair of bifunctional DNA adducts in tissues of laboratory animals exposed to 1,3-butadiene by inhalation

1,3-Butadiene (BD) is an important industrial and environmental chemical classified as a human carcinogen. The mechanism of BD-mediated cancer is of significant interest because of the widespread exposure of humans to BD from cigarette smoke and urban air. BD is metabolically activated to 1,2,3,4-diepoxybutane (DEB), which is a highly genotoxic and mutagenic bis-alkylating agent believed to be the ultimate carcinogenic species of BD. We have previously identified several types of DEB-specific DNA adducts, including bis-N7-guanine cross-links (bis-N7-BD), N⁶-adenine-N7-guanine cross-links (N⁶A-N7G-BD), and 1,N⁶-dA exocyclic adducts. These lesions were detected in tissues of laboratory rodents exposed to BD by inhalation (Goggin et al. (2009) Cancer Res.69, 2479 -2486). In the present work, persistence and repair of bifunctional DEB-DNA adducts in tissues of mice and rats exposed to BD by inhalation were investigated. The half-lives of the most abundant cross-links, bis-N7G-BD, in mouse liver, kidney, and lungs were 2.3-2.4 days, 4.6-5.7 days, and 4.9 days, respectively. The in vitro half-lives of bis-N7G-BD were 3.5 days (S,S isomer) and 4.0 days (meso isomer) due to their spontaneous depurination. In contrast, tissue concentrations of the minor DEB adducts, N7G-N1A-BD and 1,N⁶-HMHP-dA, remained essentially unchanged during the course of the experiment, with an estimated t_1/2 of 36-42 days. No differences were observed between DEB-DNA adduct levels in BD-treated wild type mice and the corresponding animals deficient in methyl purine glycosylase or the Xpa gene. Our results indicate that DEB-induced N7G-N1A-BD and 1,N⁶-HMHP-dA adducts persist in vivo, potentially contributing to mutations and cancer observed as a result of BD exposure.