Towards whole sheep ovary cryopreservation

Area of Science:

• Reproductive biology
• Cryobiology
• Veterinary science

Background:

• Cryopreservation of ovarian tissue is crucial for fertility preservation in young women undergoing treatments that may cause infertility.
• Developing simple and efficient cryopreservation methods is essential for maximizing success rates.

Purpose of the Study:

• To investigate the outcomes of rapid cooling for whole sheep ovaries using VS4 cryoprotectant.
• To assess the viability of ovarian follicles following a specific rapid cooling and rewarming protocol.

Main Methods:

• Whole sheep ovaries were perfused with VS4 cryoprotectant via the ovarian artery.
• Ovaries underwent rapid cooling by quenching in liquid nitrogen (estimated cooling rate >300°C/min).
• Rewarming involved two stages: slow warming in liquid nitrogen vapor followed by rapid thawing in a 45°C water bath.

Main Results:

• Differential scanning calorimetry (DSC) indicated that VS4 would vitrify, but ovarian cortex fragments did not fully vitrify, forming approximately 18.4% ice.
• Post-warming, a dye exclusion test revealed 61.4% viability in small follicles.
• Histological analysis showed 48% of primordial follicles remained normal.

Conclusions:

• The rapid cooling and rewarming protocol using VS4 resulted in partial preservation of ovarian follicles in sheep ovaries.
• Complete vitrification of the ovarian cortex was not achieved, suggesting that improved conditions may enhance follicle survival rates.
• Further research is needed to optimize cryopreservation conditions for complete tissue vitrification and improved fertility preservation outcomes.