The impact of reactive oxygen species on bovine sperm fertilizing ability and oocyte maturation

The objective of this study was to examine the effects of reactive oxygen species (ROS) on bovine sperm function and on the developmental competence of in vitro-matured bovine oocytes. In a first series of experiments, spermatozoa were exposed to ROS generated through the use of the hypoxanthine-xanthine oxidase system +/- catalase prior to the conduct of in vitro fertilization (IVF). Reactive oxygen species exposure reduced significantly (P < 0.001) the rates of oocyte penetration (control: 56% +/- 4 SEM; ROS: 16 +/- 2-23% +/- 7 SEM), and this effect was reversed by adding catalase (ROS+catalase: 67% +/- 0.3 SEM). During IVF, addition of superoxide dismutase (SOD: 1, 10, or 100 U/ml) had no effect on penetration rates. However, increasing concentrations of catalase (0.1 or 1 mg/ml) reduced these rates significantly (control: 70% +/- 3 SEM; treated: 45% +/- 5 and 1% +/- 1 SEM; P < 0.001). In a second series of experiments, when oocytes were matured in vitro in the presence of exogenous antioxidants (SOD: 10, 100, or 1000 U/ml; beta-mercaptoethanol: 0.01, 0.1, or 0.5 mM; ascorbic acid: 0.05 mg/ml), the developmental competence of the oocytes after IVF was not significantly improved. On the other hand, presumed production of ROS using the hypoxanthine-xanthine system at the beginning of the in vitro maturation period did improve subsequent developmental competence of the oocytes under some conditions and when catalase was present (control: 14% +/- 4 SEM and treated: 23% +/- 9 and 27% +/- 8 SEM; P < 0.05). These observations demonstrate that ROS may be beneficial to gamete function under specific conditions.