Implication of apoptosis in sperm cryoinjury

Apoptosis is an ongoing physiological phenomenon that has been documented to play a role in male infertility, if deregulated. Caspase activation, externalization of phosphatidylserine, alteration of mitochondrial membrane potential and DNA fragmentation are markers of apoptosis found in ejaculated human spermatozoa. These markers appear in excess in subfertile men and functionally incompetent spermatozoa. Sperm cryopreservation is a widely used procedure in the context of assisted reproductive techniques. Cryopreservation and thawing is a procedure that inflicts irreversible injury on human spermatozoa. The damage is manifested by a decrease in recovery of viable spermatozoa with optimum fertilization potential. This review describes the implication of apoptosis as one of the possible mechanisms involved in sperm cryoinjury. Evidence shows significant increase in some apoptosis markers following cryopreservation and thawing. On the other hand, the increase in sperm DNA fragmentation following cryopreservation and thawing requires further investigation. Specific technical measures should be applied to minimize the induction of apoptosis in human spermatozoa during cryopreservation and thawing. These include standardization of freezing protocols and cryoprotectant use. Selection of non-apoptotic spermatozoa may also prove to be of benefit.Apoptosis, also termed selective cell death, is a phenomenon that affects cell viability. The process has been documented in human spermatozoa and is implicated in the failure of fertilization following assisted reproductive techniques. There are several markers of apoptosis that present in ejaculated human spermatozoa, especially in those from infertile men. Freezing and thawing of human spermatozoa is commonly used nowadays in conjunction with assisted reproductive techniques such as intrauterine insemination and IVF. Sperm freezing is also used to preserve fertility in men undergoing cancer treatment or before undergoing vasectomies. Therefore, it is important to ensure that frozen–thawed spermatozoa will maintain its fertilizing capability. Despite recent methodological advances, freezing exerts detrimental effects on spermatozoa that lead to significant decreases in sperm viability and motility and ultimately in fertilization potential. The process of freezing and thawing increases the amount of apoptotic spermatozoa, which in turn is expected to decrease the success rates of assisted reproductive techniques. Therefore, current protocols for sperm freezing and thawing should be carefully evaluated to ensure minimizing the extent of apoptosis induction. The integration of novel techniques that isolate non-apoptotic spermatozoa also increases sperm survival following freezing and thawing.