Mutagenicity of butadiene and its epoxide metabolites: I. Mutagenic potential of 1,2-epoxybutene, 1,2,3,4-diepoxybutane and 3,4-epoxy-1,2-butanediol in cultured human lymphoblasts.

The mutagenic potential of the epoxide metabolites of butadiene (BD) was measured at the tk and hprt loci in TK6 human lymphoblastoid cells. TK6 cells were exposed for 24 h to 0-400 microM 1,2-epoxybutene (EB), 0-800 microM 3,4-epoxy-1,2-butanediol (EBD), or 0-6 microM 1,2,3,4-diepoxybutane (DEB). Treated cells were allowed to grow for several days and then seeded in medium containing either 6-thioguanine or trifluorothymidine to select for hprt- or tk-/- mutants, respectively. All three metabolites were mutagenic at both loci, with DEB exhibiting activity at concentrations approximately 100-fold lower than EB or EBD. At the hprt locus, an induced mutation frequency of 5 x 10(-6) (approximately twice background hprt- frequency) was produced by treatment with 3.5 microM DEB, 150 microM EB and 450 microM EBD. At the tk locus, a similar increase in mutation frequency (total tk-/- frequency) was produced by treatment with 1.0 microM DEB, 100 microM EB and 350 microM EBD. Each epoxide tested was capable of inducing slow growth tk-/- mutants. This mutant phenotype, as shown previously by others, results from large alterations in the tk region which completely remove the active tk allele. In addition, Southern blot analysis revealed that approximately half of DEB-induced hprt- mutants displayed loss of wild-type hprt restriction fragments. No statistically significant increase in the fraction of hprt deletions among EB mutants was observed. The ability of DEB to induce deletions may be related to its ability to form DNA-DNA and DNA-protein cross-links.