Effects of superoxide dismutase on mouse in vitro fertilization and embryo culture system

We recently found that, for mouse embryos fertilized in vivo, the two-cell block could be attenuated by adding superoxide dismutase (SOD), a scavenger of superoxide radicals, to the culture medium. In this study, we evaluated the effects of SOD on the process of fertilization and on the further development of the embryos fertilized in vitro.

We performed incubation of mouse epididymal spermatozoa, in vitro fertilization, and further cultivation in Biggers-Whitten-Whittingham's medium supplemented with various concentrations of Cu.Zn-SOD.

High concentrations (2000 micrograms/ml or more) of SOD prevented loss of motility in mouse sperm over time. The addition of SOD (less than 2000 micrograms/ml) to the basic medium showed no significant difference in the fertilization rate. Also, no significant difference was observed in the rate of polyspermy or parthenogenesis between the basic and the SOD-supplemented media. However, 18% of the two-cell-stage embryos developed to the expanded blastocyst stage in the 500 micrograms/ml SOD-supplemented medium, while no blastocysts were found in the basic medium. Furthermore, the addition of SOD 7 hr after insemination increased the expanded blastocyst rate (28%).

These results indicate that the addition of SOD exerts a protecting effect from oxidative stress both on sperm viability and on the development of embryos fertilized in vitro as well as in vivo, while its addition showed no effect on the process of fertilization.