1,3-Butadiene-Induced Adenine DNA Adducts Are Genotoxic but Only Weakly Mutagenic When Replicated in <i>Escherichia coli</i> of Various Repair and Replication Backgrounds

The adverse effects of the human carcinogen 1,3-butadiene (BD) are believed to be mediated by its DNA-reactive metabolites such as 3,4-epoxybut-1-ene (EB) and 1,2,3,4-diepoxybutane (DEB). The specific DNA adducts responsible for toxic and mutagenic effects of BD, however, have yet to be identified. Recent <i>in vitro</i> polymerase bypass studies of BD-induced adenine (BD-dA) adducts show that DEB-induced <i>N</i>⁶,<i>N</i>⁶-DHB-dA (DHB = 2,3-dihydroxybutan-1,4-diyl) and 1,<i>N</i>⁶-γ-HMHP-dA (HMHP = 2-hydroxy-3-hydroxymethylpropan-1,3-diyl) adducts block replicative DNA polymerases but are bypassed by human polymerases η and κ, leading to point mutations and deletions. In contrast, EB-induced <i>N</i>⁶-HB-dA (HB = 2-hydroxy-3-buten-1-yl) does not block DNA synthesis and is nonmutagenic. In the present study, we employed a newly established <i>in vivo</i> lesion-induced mutagenesis/genotoxicity assay via next-generation sequencing to evaluate the <i>in vivo</i> biological consequences of <i>S</i>-<i>N</i>⁶-HB-dA, <i>R,R</i>-<i>N</i>⁶,<i>N</i>⁶-DHB-dA, <i>S</i>,<i>S</i>-<i>N</i>⁶,<i>N</i>⁶-DHB-dA, and <i>R</i>,<i>S</i>-1,<i>N</i>⁶-γ-HMHP-dA. In addition, the effects of AlkB-mediated direct reversal repair, MutM and MutY catalyzed base excision repair, and DinB translesion synthesis on the BD-dA adducts in bacterial cells were investigated. BD-dA adducts showed the expected inhibition of DNA replication <i>in vivo</i> but were not substantively mutagenic in any of the genetic environments investigated. This result is in contrast with previous <i>in vitro</i> observations and opens the possibility that <i>E. coli</i> repair and bypass systems other than the ones studied here are able to minimize the mutagenic properties of BD-dA adducts