Effects of three epoxides, ethylene oxide, propylene oxide and epichlorohydrin, on cell cycle progression and cell death in human diploid fibroblasts

Ethylene oxide (EtO), propylene oxide (PO), and epichlorohydrin (ECH) stron gly influenced the G(1)/S progression in human diploid fibroblasts, VH-IO. However, these epoxides did not affect substantially the G(2)/M progression . It was found that G(1) arrest is induced by these epoxides 6-18 h after t he treatment at doses above 5, 3, and 0.5 mMh for EtO, PO, and ECH, respect ively. An inhibitory effect on DNA synthesis was also demonstrated at the s ame doses within the same time interval. On the contrary, the epoxides tran siently stimulated DNA synthesis 3-18 h after the treatment with the lower doses (below 5, 3, and 0.5 mMh for EtO, PO, and ECH, respectively). This ef fect was manifested both as an elevated rate of DNA synthesis and as an inc rease in the number of cells in S-phase. Among the three studied epoxides E tO was the most effective one: the increases of the rate of DNA synthesis a nd of cells in S-phase were 35 and 55%, respectively. All the epoxides test ed induced significant decrease of intracellular level of reduced glutathio ne (GSH) shortly after cell exposure. While low and moderate doses induced a transient decrease in GSH level, the high doses induced its irreversible depletion. The extensive GSH depletion was, related to cell death. Morpholo gical examination of cell nuclei indicated that epoxide-treated cells die v ia necrosis. This conclusion is supported by the lack of such features of t he apoptosis as chromatin condensation and the occurrence of so called 'apo ptotic bodies'. The absence of nucleosomal fragmentation of DNA and an incr ease of the permeability of the plasma membrane after the epoxide treatment also indicated a necrotic form of cell death. ECH is about ten times more toxic than the two other epoxides, and it causes almost 100% necrosis at do se of 3.0 mMh. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.