Clastogenicity of isoamylene oxide to rat lymphocytes in culture

The mutagenic activity of the aliphatic epoxide isoamylene oxide (2-methyl-2,3-epoxybutane) is not readily detectable in the standard Ames test. In this study, the clastogenic potential of isoamylene oxide was evaluated using an in vitro mammalian cell culture system. Approximately 48 h after establishing primary cultures of rat lymphoocyte cultures, the cells were treated for 4 h with various concentrations of isoamylene oxide (50, 166.7, 500, 1666.7 and 5000 μg/ml in the initial assay and 500, 1000, 2000, 3000, 4000, and 5000 μg/ml in the confirmatory assay). The cultures were harvested 24 h after termination of the treatment. Based upon the mitotic indices, cultures treated with the three highest concentrations in both the initial and confirmatory assays were evaluated to estimate the chromosomal aberration frequencies. Isoamylene oxide demonstrated a strong clastogenic activity in this assay: up to 29% aberrant cells (without gaps) were observed at the highest concentration analyzed. The presence of an external metabolic activation system (S9) did not seem to influence the magnitude of the response at the dose levels analyzed.