Protection from oxidative stress by thioredoxin and superoxide dismutase of mouse embryos fertilized in vitro

A low oxygen tension and superoxide dismutase (SOD) have been demonstrated to promote development of embryos in vitro. In this study, we evaluated the effects of thioredoxin (TRX), a powerful protein disulphide reductase, on the development of mouse embryos fertilized in vitro. Moreover, to clarify the difference between the embryo-protecting mechanisms of TRX and SOD, as well as the critical periods of their actions, we carried out experiments in which we transferred embryos among three different media: basic, TRX- and SOD-supplemented. The rates of 4-cell, blastocyst and expanded blastocyst formation in TRX- (53%, 40% and 34% respectively), or SOD- (59%, 29%, 22%) supplemented media were significantly higher than those (28%, 4%, 0%) in the basic medium. The results of the transfer of embryos using basic and TRX-supplemented media indicated an increase in the rate of expanded blastocysts when TRX was applied from 7 to 30 h, and especially from 18 to 24 h after insemination. In contrast, the results of the transfer of embryos using basic and SOD-supplemented media indicated that SOD, which was also most effective when applied from 7 to 30 h after insemination, had some effects after 30 h. These results indicate that TRX and SOD promote the in-vitro development of mouse embryos fertilized in vitro, which suggests that protection of embryos from oxidative stress is a prerequisite for their development in vitro. SOD and TRX provide protection from oxidative stress by different mechanisms.