Effects of partially replacing glycerol with cholesterol-loaded cyclodextrin on protamine deficiency, in vitro capacitation and fertilization ability of frozen-thawed Yanbian Yellow cattle sperm

Polyvinyl alcohol addition to freezing extender can improve the post-thaw quality, longevity and in vitro fertility of ram epididymal spermatozoa

Recovering and cryopreserving epididymal spermatozoa are suitable methods for preserving the genetic potential of livestock and endangered species. Regarding encouraging reports on the use of polyvinyl alcohol (PVA) in cryopreserving various cell types, we conducted this study to examine the impact of PVA on the post-thaw quality, longevity, and in vitro fertility of ram epididymal sperm. In the first experiment, ram epididymal spermatozoa were frozen in extenders containing 6 % glycerol and 0, 0.5, 1, 2, 5, 10, or 15 mg/ml of PVA. Polyvinyl alcohol at concentrations of 0.5, 1, and 2 mg/ml improved the motility and functional membrane integrity (FMI) of the sperm compared with the control group (P < 0.05). In the second experiment, we investigated whether PVA could partially substitute glycerol in the freezing extender. PVA was added at 0, 0.5, 1, and 2 mg/ml to the extenders containing 1 % or 2 % glycerol. After thawing, the sperm motility parameters of the group containing 1 mg/ml PVA and 2 % glycerol were significantly higher than those of the un-supplemented groups (P < 0.05). In the third experiment, the effect of PVA on the post-thaw sperm longevity were examined. Sperm were frozen in 3 extenders: one containing 6 % glycerol and 1 mg/ml PVA (Gly6P1), another containing 2 % glycerol and 1 mg/ml PVA (Gly2P1), and a control extender with 6 % glycerol. After thawing, the quality of the sperm was evaluated. Sperm were then diluted in human tubal fluid (HTF) and incubated at 37 °C for 3 h. Afterwards, the quality of the sperm was evaluated once more. The presence of PVA in the freezing extender improved motility parameters and FMI. Additionally, PVA-containing groups had lower proportions of capacitated and acrosome reacted sperm compared with the control group (P < 0.05). The Gly6P1 group performed better than the other two groups (P < 0.05). In the fourth experiment, sperm from the Gly6P1 and Control groups were used in the IVF process immediately after thawing (T0) and after a 3-h incubation at 37 °C in HTF (T3). Cleavage, blastocyst and hatching rates in both groups were similar at T0, but they were lower in the Control group at T3 (P < 0.05). In conclusion, PVA as an additive to the freezing extender significantly improves post-thaw motility, viability, acrosome integrity, longevity, and fertile lifespan of ram epididymal spermatozoa.

Sperm cryopreservation: current status and future developments

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.