REJOINING OF DNA STRAND BREAKS INDUCED BY PROPYLENE-OXIDE AND EPICHLOROHYDRIN IN HUMAN-DIPLOID FIBROBLASTS

The repair kinetics of DNA single- and double-strand breaks (SSBs, DSB s) induced with two carcinogenic epoxides, propylene oxide (PO) and ep ichlorohydrin (ECH), was studied in human diploid Fibroblasts. The met hods used were: alkaline DNA unwinding (ADU), the comet assay, and pul sed Field gel electrophoresis (PFGE). About 70% of SSBs, measured by A DU, were rejoined after the treatment with 5 mMh and 10 mMh of PO with in 20 hr, and the half-life was estimated to be similar to 15 hr. On t he other hand, effective rejoining of SSBs after ECH treatment was obs erved only at a dose of 1 mMh (a half-life of similar to 15 hr), where as after 2 mMh treatment, only 26% of SSBs could be rejoined within 20 hr. Furthermore, the use of the comet assay demonstrated that DNA str and breaks were effectively rejoined after PO and ECH treatment at dos es of 5-10 mMh and 0.5-1 mMh, respectively. About 76% and 83% of DSBs induced by 5 and 10 mMh of PO, respectively, were rejoined within 4 hr after the treatment (a half-life of similar to 2.5 hr), with little f urther repair thereafter. At lower dose of ECH (1 mMh) a half-life for DSBs rejoining was estimated to be similar to 2 hr; however, only 29% of DSBs were rejoined within 2 hr at the higher dose of 2 mMh. After 18 hr, the rejoining following treatment with a lower dose was negligi ble. At a higher dose, a rapid accumulation of DSBs was observed, prob ably as the result of cell death and DNA degradation. The results demo nstrate the capability of human diploid fibroblasts to repair DNA SSBs and DSBs at low-to-moderate doses of the epoxides. A weak capacity to rejoin DNA strand breaks induced by higher doses of ECH may be a cons equence of its higher DNA alkylation activity and approximately 10 tim es higher toxicity compared to PO. Environ. Mel. Mutagen. 32:223-228, 1998 (C) 1998 Wiley-Liss, Inc.