Effects of superoxide dismutase on development following the implantation stage in mice.

Abstract

To examine the effects of superoxide dismutase on embryonic development after the implantation stage, mouse blastocysts were cultured under low-(5%), standard- (20%), and high-oxygen (40%) conditions with or without superoxide dismutase (SOD), which is a potent scavenger of superoxide radicals. Under 5% O2 conditions, the rates of formation of two germ cell layers and egg cylinder were 61.5% and 43.6%, respectively. These rates did not differ significantly from values determined in embryos cultured under 20% O2 conditions (69.7% and 51.3%, respectively). However, under 40% O2 conditions, the respective two germ cell layers and egg cylinder rates of formation were significantly lower than those under 5% and 20% O2 conditions (31.7% and 27.2%). Addition of 5μg/ml SOD resulted in no significant difference in formation rates of two germ cell layers (71.3%) and egg cylinder (52.9%) from those of the SOD-free group (61.3% and 45.2%). However, both rates were significantly decreased at SOD concentrations of 10μg/ml or greater. Microscopic examination of the morphology of cultured embryos showed that the degeneration of the inner cell mass (ICM) occurred follwing its migration from the trophetoderm and direct exposure to medium supplemented with 500μg/ml SOD. These results indicate that excessive oxidative stress exerts adverse effects on embryonic development after implantation. Embryos which are exposed to such stress after the implantation stage are in turns more resistant to these effects than those observed at the pronuclear stage, which is known to proliferate under 5% O2 conditions. Moreover, it is suggested that higher concentrations of SOD in the medium may diminish the concentration of superoxide anion radicals in ICM during differentiation, thus causing the degeneration of ICM.