P-254: The Effects of Zinc in Vitrification Medium on In vitro Maturation of Oocytes Derived from Vitrified-Warmed Mouse Ovary

Background: Cryopreservation of ovarian tissue is an important option for preserving the fertility of cancer patients undergoing chemotherapy and radiotherapy. Researchers have used different cryoprotectants and various techniques to improve the cryopreservation of ovaries However, despite significant recent progress, the efficiency of ovary cryopreservation is still low. Zinc is essential for many biological processes, including proper functioning of gametes. Reserches describe major changes in the zinc physiology of the mammalian oocyte as it matures and initiates embryonic development. In this study, the effects of zinc in vitrification medium on in vitro maturation of oocytes derived from vitrified-warmed mouse ovary were examined. Materials and Methods: In this experimental study, the ovaries of 2-4 week-old NMRI mice randomly assigned to following groups :V0(vitrified-warmed ovaries without any zinc in vitrification solution ),V1,V2 ,V3 (vitrified warmed ovaries with 100,150and 200 μg/dl zinc concentration in vitrification solution,N-v (none vitrified ovaries). Ovaries in the vitrified groups were frozen sequentially by immersion into two vitrification solutions VS1: 7.5% ethylene glycol (EG) + 7.5% DMSO in holding medium (α-MEM + 20% FBS) for 7minutes and VS2: 15% EG + 15% DMSO for 3 minutes in holding medium and vitrified by straw and were keeped in LN2 tank for a week. After one week, the ovaries were thawed at temprature room in 1.0,0.5 and 0.25 M sucrose, vitrified ovaries as well as non-vitrified ovaries were serially sectioned and examined histologically. Immature oocytes were isolated mechanically from ovaries,they were put in maturation medium and evaluated for in vitro maturation (IVM) . Results: The results show that the presence of zinc in vitrification solution is effective and can reduce the traumatic effects of vitrification on ovarian tissues. In addition viability of oocyte and oocyte maturation rate was higher in the presence of 200μM zinc concentration in comparison to other vitrified-warmed groups, nevertheless it was lower than non vitrified group(ANOVA, p-value <0.05). Conclusion: Zinc supplementation of vitrification medium has a positive effect on the in vitro maturation of oocyte.