Propylene oxide and epichlorohydrin induce DNA strand breaks in human diploid fibroblasts

The induction of DNA strand breaks in human diploid fibroblasts (VH-10) was demonstrated after in vitro exposure with two carcinogenic epoxides, propylene oxide (PO) and epichlorohydrin (ECH). Alkaline DNA unwinding (ADU), pulsed field gel electropharosis (PFGE), and the comet assay were used to measure DNA single. (SSBs) and double-strand breaks (DSBs). A dose-dependent increase of DNA strand breaks, measured by ADU, was observed in the dose range 2.5-20 mMh of PO and 0.25-2 mMh of ECH. The dose-response of ECH was about five times higher compared with that of PO (211 vs. 41 SSBs. 100 Mbp-1.mMh-1). The induction rates of DSBs, measured by PFGE, were found to be 18 times higher for ECH compared to PO (4.8 and 0.27 DSBs.100 Mbp-1.mMh-1 for ECH and PO, respectively). Using these two methods, the SSBs/ DSBs ratio was estimated to be 148 for PO and 44 for ECH. The data obtained by the comet assay also demonstrated a dose-dependent ability of PO and ECH to induce DNA damage. It was found that ECH was about six times more effective as an inducer of DNA strand breaks compared to PO (200 and 32x100 Mbp-1.mMh-1 for ECH and PO, respectively). The SSBs/DSBs ratios calculated using comet assay and PFGE data were 125 for ECH and 41 for PO. In addition, ECH is about 10 times more toxic than PO with respect to survival. These properties of ECH can at least in part be explained by its higher chemical reactivity connected with a higher rate of DNA alkylation.