Comparative Studies on Protective Effect of Various Sulfhydryl Compounds Against Cell Death and DNA Strand Breaks Induced by X-Rays in Cultured Mouse L Cells

Ten sulfhydryl (SH) compounds including cysteamine could be divided into three classes according to their radioprotective action and toxicity as measured by colony forming ability in irradiated and unirradiated mouse L cells. Cysteamine, 2-aminoethylisothiuronium bromide hydrobromide (AET) and 2-mercaptopropionylglycine (MPG) were chosen respectively from each class and their protective abilities against the formation of single and double-strand breaks in cellular DNA induced by X-rays were tested. The X-ray-induced single and doublestrand breaks were protected effectively by cysteamine and to a lesser extent by AET, but significant radioprotective action was not observed with MPG. These results are in good agreement with those obtained for cell survival. On the other hand, X-ray-induced single-strand breaks can be rejoined during post-irradiation incubation in SH compound-free medium. However, most of the double-strand breaks were left unrejoined even after prolonged post-irradiation incubation. These results suggest that there is a correlation between protection against cell death and protection against the formation of DNA double-strand breaks.