Correlation between cytotoxic effect of hydrogen peroxide and the yield of DNA strand breaks in cells of different species.

The rate of loss of reproductive capacity produced by hydrogen peroxide was shown to be 6-times faster for human fibroblasts than for Chinese hamster fibroblasts. Mouse fibroblasts exhibited an intermediate response. The explanation for that does not lie in the different capacities of these cells to destroy H2O2. The kinetics of repair of single-strand breaks although slightly different for the three cell lines also does not provide a full explanation for the different sensitivity. What was shown to correlate well with the killing effect was the yield of strand breaks produced by H2O2 in the DNA of cells from the three species. A similar H2O2 concentration produced 5-10-times more strand breaks in human DNA than in hamster DNA and 2-4-times more than in mouse DNA. This ratio holds for different cell lines from human and hamster and thus seems to be species-specific. Based on our previous findings we propose that this difference may lie in the amount of chromatin-bound iron and the level of superoxide ion in these cells.