Sperm cryopreservation: current status and future developments

Abstract

The cryopreservation of spermatozoa is an important reproductive technology for the preservation of fertility in man and animals. Since the serendipitous discovery of glycerol as an effective cryoprotectant in 1947, sperm cryopreservation has undergone many changes in terms of the freezing methods employed, the rates at which samples are frozen and thawed, and the media used to preserve sperm functionality and DNA integrity. An extensive literature survey has been conducted addressing the cryoprotectants employed for both animal and human semen and the freezing protocols utilised. The results indicate that glycerol remains the dominant cryoprotective agent, usually incorporated into a balanced salt solution containing energy substrates, buffers, osmolytes and protein in the form of human serum albumin (human) or skimmed milk (animal). Realisation that some of the damage observed in cryostored cells involves the generation of reactive oxygen species during the thawing process, has prompted many studies to assess the relative merits of incorporating antioxidants into the cryopreservation media. However, in the absence of systematic comparisons, there is currently no consensus as to which antioxidant combination might be the most effective. Utilising our fundamental understanding of cryodamage to optimise cryopreservation protocols for each species will be important in the future.

Exploring how sucrose-colloid selection improves the fertilizing ability of chicken sperm after cryopreservation with glycerol

“…Indeed, centrifugal force may impact sperm membrane integrity ( Varisli et al, 2009 ), however, our objective is to recover a sufficient amount of sperm for insemination while preserving their fertilization ability. It is impossible to ignore the need for a significantly larger quantity of retrieved sperm compared to what is used for in vitro fertilization ( Morrell et al, 2016 ; Hungerford et al, 2023 ). Therefore, the centrifugation step should aim to achieve a balance between ensuring optimal sperm recovery and minimizing damage to the sperm membranes.…”

A Pilot Analysis of Whole Transcriptome of Human Cryopreserved Sperm

“…The sperm cryopreservation procedure needs to be improved in the future. Possible strategies to prevent gamete damage and new approaches to sperm cryopreservation include vitrification [75]; pre-cryopreservation selection of motile spermatozoa [76]; addition of antioxidant to cryoprotectants with the aim of mitigating the possible toxic effects of reactive oxygen species generated during the freezing/thawing [77]; addition of growth factors [78]; lyophilization of sperm which would avoid the use of liquid nitrogen, allowing easy storage, packaging, and transfer of the samples [79]; and use of alternative devices for low sperm number [80]. Although vitrification seems to be the most promising approach, since it is superior to conventional freezing methods in sperm preservation with regard to motility [75], there is currently no validation of these innovations in clinical settings and we are far from defining the optimal mixture of cryoprotectants and the best freezing procedure.…”

Addition of Vitamin C Mitigates the Loss of Antioxidant Capacity, Vitality and DNA Integrity in Cryopreserved Human Semen Samples

“…An explanation for such mixed responses to different doses of vitamin C can possibly be found in this compound's pro-oxidant action. As a powerful reducing agent, vitamin C is able to reduce trace amounts of transition metals, such as iron and copper, that can participate in Fenton-like reactions which lead to ROS generation and increased oxidative damage [16,50,51]. The levels of redox-active iron and copper in human semen are variable and in some cases, may be sufficient to promote Fenton chemistry and enhance rather than suppress the induction of oxidative stress [52,53].…”

“…Spermatozoa are particularly vulnerable to cryoinjury because of the lipid composition of their plasma membranes and their limited capacity for active repair [11]. In this context, it has become apparent that spermatozoa suffer from many different kinds of disruption as a consequence of cryopreservation, including osmotic stress, oxidative stress, and the physical damage induced by ice-crystal formation [14,16]. Given the importance of these pathophysiological mechanisms, numerous attempts have been made to improve cryopreservation outcomes by incorporating a variety of reagents into the cryodiluent to counteract these stressors.…”