Sperm DNA fragmentation induced by DNAse I and hydrogen peroxide: an in vitro comparative study among different mammalian species

Abstract

Sperm DNA damage may have adverse effects on reproductive outcome. Sperm DNA breaks can be detected by several tests, which evaluate DNA integrity from different and complementary perspectives and offer a new class of biomarkers of the male reproductive function and of its possible impairment after environmental exposure. The remodeling of sperm chromatin produces an extremely condensed nuclear structure protecting the nuclear genome from adverse environments. This nuclear remodeling is species specific, and differences in chromatin structure may lead to a dissimilar DNA susceptibility to mutagens among species. In this study, the capacity of the comet assay in its two variants (alkaline and neutral) to detect DNA/chromatin integrity has been evaluated in human, mouse, and bull sperm. The hypothesis that chromatin packaging might influence the amount of induced and detectable DNA damage was tested by treating sperm in vitro with DNAse I, whose activity is strictly dependent upon its DNA accessibility. Furthermore, hydrogen peroxide (H2O2) was used to assess whether spermatozoa of the three species showed a different sensitivity to oxidative stress. DNAse I-induced damage was also assessed by the sperm chromatin structure assay and the TUNEL assay, and the performances of these two assays were compared and correlated with the comet assay results. Results showed a different sensitivity to DNAse I treatment among the species with human sperm resulting the most susceptible. On the contrary, no major differences among species were observed after H2O2 treatment. Furthermore, the three tests show a good correlation in revealing sperm with DNA strand breaks.