Effects of supplementation with free radical scavengers on the survival and fertilization rates of mouse cryopreserved oocytes

BACKGROUND: This study was conducted to investigate the effects of supplementation with free radical scavengers on the survival and fertilization rates of freeze-thawed mouse oocytes. METHODS: Superovulated oocytes with cumulus cells were cryopreserved by slow freezing in propanediol combined with a rapid thawing protocol. The cryopreservation medium was supplemented with the antioxidant enzymes superoxide dismutase (SOD) and catalase, and with the nitric oxide (NO) scavenger, haemoglobin (Hb). RESULTS: The addition of 50 IU/ml SOD showed significantly higher survival and fertilization capabilities compared with control (P < 0.01). Oocyte survival was greatly increased by concomitant addition of SOD with 10 IU/ml catalase (P < 0.01). On the other hand, the NO donor (sodium nitroprusside) inhibited survival and fertilization rates (P < 0.05). Significantly decreased survival and fertilization rates were also observed following the addition of high concentrations (10(-3) to 10(-6) nmol/l) of the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). In contrast, significantly better oocyte survival and fertilization rates were detected with low concentrations (10(-7) nmol/l) of L-NAME. Oocyte survival potential was significantly increased by addition of Hb (1 microg/ml, P < 0.05). Moreover, oocyte survival and fertilization rates were significantly promoted by the concomitant addition of SOD with Hb (P < 0.01). CONCLUSIONS: These results suggest that supplementation of free radical scavengers, particularly combinations of SOD with NO scavengers in freezing and thawing media, improved the post-thaw survival and fertilization rates of cryopreserved mouse oocytes.