MUTAGENICITY OF BUTADIENE AND ITS EPOXIDE METABOLITES .1. 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) w as measured at the tk and hprt loci in TK6 human lymphoblastoid cells. TK6 cells were exposed for 24 h to 0-400 mu M 1,2-epoxybutene (EB), 0 -800 mu M 3,4-epoxy-1,2-butanediol (EBD), or 0-6 mu M 1,2,3,4-diepoxyb utane (DEB). Treated cells were allowed to grow for several days and t hen seeded in medium containing either 6-thioguanine or trifluorothymi dine to select for hprt(-) or tk(-/-) mutants, respectively. Ah 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 5x10(-6) (approximately t wice background hprt(-) frequency) was produced by treatment with 3.5 mu M DEB, 150 mu M EB and 450 mu M EBD. At the tk locus, a similar inc rease in mutation frequency (total tk(-/-) frequency) was produced by treatment with 1.0 mu M DEB, 100 mu M EB and 350 mu M EBD. Each epoxid e tested was capable of inducing slow growth tk(-/-) mutants. This mut ant phenotype, as shown previously by others, results from large alter ations in the tk region which completely remove the active tk allele. In addition, Southern blot analysis revealed that approximately half o f DEB-induced hprt(-) mutants displayed loss of wild-type hprt restric tion 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 DN A-protein cross-links.