Conjugation of Butadiene Diepoxide with Glutathione Yields DNA Adducts in Vitro and in Vivo

Abstract

1,2,3,4-Diepoxybutane (DEB) is reported to be the most potent mutagenic metabolite of 1,3-butadiene, an important industrial chemical and environmental pollutant. DEB is capable of inducing the formation of monoalkylated DNA adducts and DNA–DNA and DNA–protein cross-links. We previously reported that DEB forms a conjugate with glutathione (GSH) and that the conjugate is considerably more mutagenic than several other butadiene-derived epoxides, including DEB, in the base pair tester strain <i>Salmonella typhimurium</i> TA1535 [Cho (2010) Chem. Res. Toxicol. 23, 1544−1546]. In the present study, we determined steady-state kinetic parameters of the conjugation of the three DEB stereoisomers<i>R</i>,<i>R</i>, <i>S</i>,<i>S</i>, and <i>meso</i> (all formed by butadiene oxidation)with GSH by six GSH transferases. Only small differences (<3-fold) were found in the catalytic efficiency of conjugate formation (<i>k</i>_cat/<i>K</i>_m) with all three DEB stereoisomers and the six GSH transferases. The three stereochemical DEB–GSH conjugates had similar mutagenicity. Six DNA adducts (<i>N</i>³-adenyl, <i>N</i>⁶-adenyl, <i>N</i>⁷-guanyl, <i>N</i>¹-guanyl, <i>N</i>⁴-cytidyl, and <i>N</i>³-thymidyl) were identified in the reactions of DEB–GSH conjugate with nucleosides and calf thymus DNA using LC-MS and UV and NMR spectroscopy. <i>N</i>⁶-Adenyl and <i>N</i>⁷-guanyl GSH adducts were identified and quantitated in vivo in the livers of mice and rats treated with DEB ip. These results indicate that such DNA adducts are formed from the DEB–GSH conjugate, are mutagenic regardless of sterochemistry, and are therefore expected to contribute to the carcinogenicity of DEB