Butadiene diolepoxide- and diepoxybutane-derived DNA adducts at N7-guanine: a high occurrence of diolepoxide-derived adducts in mouse lung after 1,3-butadiene exposure

Butadiene (BD) is a high production volume chemical and is known to be tumorigenic in rodents. BD is metabolized to butadiene monoepoxide (BMO), diepoxybutane (DEB) and butadiene diolepoxide (BDE). These epoxides are genotoxic and alkylate DNA both in vitro and in vivo, mainly at the N7 position of guanine. In this study, a ³²P-post-labeling/thin-layer chromatography (TLC)/high-pressure liquid chromatography (HPLC) assay for BDE and DEB adducts at the N7 of guanine was developed and was used in determining the enantiomeric composition of the adducts and the organ dose of BD exposure in lung. Exposure of 2′-deoxyguanosine (dGuo), 2′-deoxyguanosine-5′-phosphate (5′-dGMP) and 2′-deoxyguanosine-3′-phosphate (3′-dGMP) to racemic BDE followed by neutral thermal hydrolysis gave two products (products 1 and 2) that were identified by MS and UV and NMR spectroscopy as a diastereomeric pair of N7-(2,3,4-trihydroxybutan-1-yl)-guanines. Exposure of dGuo nucleotides to RR/SS DEB (also referred to as dl DEB) followed by thermal depurination resulted in a single product coeluting with the BDE product 1. If the reaction mixture of BDE and 5′-dGMP was analyzed by HPLC before hydrolysis of the glycosidic bond, four major nucleotide alkylation products (A, B, C and D) with identical UV sepectra were detected. The products were isolated and hydrolyzed, after which A and C coeluted with product 1 and B and D coeluted with the product 2. The major adduct of DEB-exposed 5′-dGMP was N7-(2-hydroxy-3,4-epoxy-1-yl)-dGMP (product E). A ³²P-post-labeling assay was used to detect BDE- and DEB-derived N7-dGMP adducts in DNA. Levels of adducts increased with a dose of BDE and DEB and exhibited a half life of 30 ± 3 (r = 0.98) and 31 ± 4 h (r = 0.95), respectively. Incubation of DEB-modified DNA at 37°C at neutral pH for up to 142 h did not lead to an increase of N7-(2,3,4-trihydroxybutan-1-yl)-dGMP in the DNA. These observations led to the conclusion that the N7-(2,3,4-trihydroxybutan-1-yl)-dGMP adducts in DNA can be used as a marker of BDE exposure and that N7-(2-hydroxy-3,4-epoxy-1-yl)-dGMP adducts are related to DEB exposure. Dose-related levels of BDE- and DEB-derived adducts were detected in lungs of mice inhaling butadiene. Most of the N7-dGMP adducts (73%; product D) were derived from the 2R-diol-3S-epoxide of 1,3-butadiene. The data presented in this paper indicate that in vivo, 98% of N7-dGMP alkylation after BD exposure is derived from BDE, and ~2% of the adducts were derived from DEB and BMO.