Characterization of hprt mutations following l,2-epoxy-3-butene exposure of human TK6 cells

1,3-Butadiene (BD) is an indirect-acting mutagen that is bioactivated in laboratory animals to at least two mutagenic metabolites, 1,2-expoxy-3-butene (EB) and 1,2,3,4-diepoxybutane (DEB). In the present study, the cytotoxicity, mutagenicity and mutational spectrum at hprt were determined after EB-exposure of human TK6 lymphoblastoid cells (TK6 cells). EB was cytotoxic at concentrations ranging from 200 to 1000 microM x 24 h; at 400 microM x 24 h, the cell survival relative to unexposed controls was approximately 10%. Exposure of TK6 cells to EB (400 microM x 24 h) resulted in a 5-9-fold increase in the hprt mutant frequency. Molecular characterization of EB-induced hprt mutants indicated that 78% of the mutations at hprt were single base substitutions. A significant (P < 0.05) increase in A:T-->T:A transversions was observed compared with spontaneous hprt mutants isolated during these studies. All of the A:T-->T:A transversions in EB-induced mutants occurred with the A in the non-transcribed strand. These data indicate that a primary mode of genotoxicity induced by EB in human TK6 cells is the induction of single base substitutions.