Effects of Genotype on the Detoxification of 1,3-Butadiene Derived Diepoxide and Formation of Promutagenic DNA-DNA Cross-Links in Human Hapmap Cell Lines.

Smoking is a leading cause of lung cancer, accounting for 81% of lung cancer cases. Tobacco smoke contains over 5000 compounds, of which more than 70 have been classified as human carcinogens. Of the many tobacco smoke constituents, 1,3-butadiene (BD) has a high cancer risk index due to its tumorigenic potency and its abundance in cigarette smoke. The carcinogenicity of BD has been attributed to the formation of several epoxide metabolites, of which 1,2,3,4-diepoxybutane (DEB) is the most toxic and mutagenic. DEB is formed by two oxidation reactions carried out by cytochrome P450 monooxygenases, mainly CYP2E1. Glutathione-S-transferase 1 (GSTT1) facilitates the conjugation of DEB to glutathione as the first step of its detoxification and subsequent elimination via the mercapturic acid pathway. Human biomonitoring studies have revealed a strong association between copy number and urinary concentrations of BD-mercapturic acids, suggesting that it plays an important role in the metabolism of BD. To determine the extent that genotype affects the susceptibility of individuals to the toxic and genotoxic properties of DEB, negative and positive HapMap lymphoblastoid cell lines were treated with DEB, and the extent of apoptosis and micronuclei (MN) formation was assessed. These toxicological end points were compared to the formation of DEB-GSH conjugates and 1,4--(guan-7-yl)-2,3-butanediol (-N7G-BD) DNA-DNA cross-links. negative cell lines were more sensitive to DEB-induced apoptosis as compared to positive cell lines. Consistent with the protective effect of GSH conjugation against DEB-derived apoptosis, positive cell lines formed significantly more DEB-GSH conjugate than negative cell lines. However, genotype did not affect formation of MN or -N7G-BD cross-links. These results indicate that genotype significantly influences BD metabolism and acute toxicity.