Mutagenic potential of adenine N⁶ adducts of monoepoxide and diolepoxide derivatives of butadiene

To determine the biological effects of specific DNA adducts resulting from the interaction of 1,3-butadiene metabolites with DNA, deoxyoligonucleotides have been synthesized with four different adducts at the N⁶ position of adenine, centrally located within the human N-ras codon 61. The adducts are those arising from adduction by either the R or S stereoisomer of the monoepoxide (BDO) or the (R,R) or (S,S) isomer of the diolepoxide (BDE). The diolepoxide can arise from partial hydrolysis of the diepoxide (BDO₂) or from epoxidation of hydrolyzed monoepoxide. These adducted oligonucleotides were used in in vivo and in vitro assays designed both to determine their mutagenic potency and to examine specific interactions with Escherichia coli polymerases. Each adducted oligonucleotide was ligated into a single-stranded vector M13mp7L2 that was subsequently used to transfect E. coli. The resulting mutagenic spectrum for these modified DNAs was stereoisomer specific. Both monoepoxide lesions were nonmutagenic, but the mutagenic spectra for the modified DNAs containing BDE adducts were stereoisomer specific. The mutations generated by adducts of the R,R enantiomer of the diolepoxide were exclusively A → G, whereas adducts of the S,S enantiomer of the diolepoxide yielded exclusively A → C mutations. None of the four modifications resulted in significant blocks to in vivo phage replication, as evidenced by no decrease in plaque-forming ability. Consistent with these data, when each of three purified E. coli polymerases was used to replicate DNAs containing these adducted deoxyoligonucleotides, the individual polymerases appeared to be virtually unaffected, such that all lesions were readily bypassed. Whereas previous animal model studies identified the mutagenic spectrum related to butadiene exposure, these studies begin to establish the specific lesions responsible for mutagenesis. This is the first report of stereoselectivity related to butadiene-induced mutagenesis. (C) 2000 Wiley-Liss, Inc.