The Effects of 5% Oxygen Condition and Superoxide Dismutase (SOD) on the in - vitro Development of Preimplantation Mouse Embryos

Abstract

Objective: In the human body the embryo initially gmws in the fallopian tube which is maintained in an 3-8% O2 concentration environment, and various substances such as growth factors and antioxidants present in tbe tubal fluid assists in maintaining a healthy environment for embryo development. But in IVF programs embryo cultures are conducted in incubators with 21.9% O2 and 5% CO2 condition, and such high oxygen concentrations have been reported to increase the production of oxygen free radicals within the embryo and is detrimental to the growth and development of the embryo. The objective of this study, therefore, is to determine the culture conditions which will decrease oxygen free radical production and thereby minimize the injury to the embryo. Methods: Six to eight week old ICR strain mice embryos were cultured in 5% or 21.9% O2 conditions and in culture media to which inaement concentrations of superoxide dismutase (SOD) had been and the H2O2 concentration within the embryo, embryo developmental rate, and degree of fragmentation of the embryos was investigated. Results: The control gmup embryos which were cultured in 21.9% O2 condition without addition of SOD showed developmental arrest at the 2-cell stage or fragmentation, while those cultured in 21.9% O2 condition with addition of SOD showed development to the blastocyst stage with deaeased fragmentation. In particular, the blastulation and fragmentation rates were the lowest in the group to which 500 IU/ml of SOD was added, but in the 5% O2 enviranment group many embryos reached the blastocyst stage and with no difference in frapnentation with or without addition of SOD. The HO relative intensity (120.5+-20.2) within the embryos cultured in 21.9% O2 environment without SOD was significantly higher than that (56.8+-10.8) of group with SOD (p<0.05). As showing that in the 5% O2 environment group without SOD it was 43.8+-7.8 and in the group with SOD it was 37.3+-5.4, the H2O2 concentration within embryos cultured in 5% 02 condition was significantly lower those that of 21,9% 02 environment regardless of SOD addition (p<0.05). Conclusion: The optimal oxygen concentration in incubator for mice embryo cultures is that which is similar to the 5% 0 concentration in vivo. When 20% 02 incubators are routinely used, the addition of SOD to the culture media will decrease the H2O2 concentration within the embryos with subsequent improvement in development. The optimal concentration which should be used is thought to be 500 IU/ml. It is suggested that the use of the above method in human IVF-ET programs will lead to improved embryo quality and enhanced pregnancy rates.