Influence of Different Combinations of Permeable and Nonpermeable Cryoprotectants on the Freezing Capacity of Equine Sperm

Freezing Hu ram semen: influence of different penetrating cryoprotectants and egg yolk level on the post-thaw quality of sperm

OBJECTIVE

The Hu sheep is a renowned breed known for its high reproductive rate. It is in estrus all year round, and its breeding population is gradually expanding. However, the current techniques for cryopreserving semen have limited effectiveness, which hinders the continuous development of this species. The purpose of this study is to explore the effects of different penetrating cryoprotectants (CPAs) and egg yolk (EY) concentrations on the cryopreservation of Hu ram semen to determine the most effective combination.

METHODS

In this study, the effects of glycerol (GLY), ethylene glycol (EG), dimethylacetamide, dimethyl sulfoxide, different proportions of GLY and EG, EY on sperm quality after thawing were investigated by detecting sperm total motility (TM), progressive motility (PM), straight-line velocity, curvilinear velocity, average path velocity, amplitude of lateral head displacement, wobble movement coefficient, average motion degree, functional integrity (plasma membrane integrity, acrosome integrity) and reactive oxygen species (ROS) level.

RESULTS

When GLY and EG were added together, compared to other concentration groups, 6% GLY significantly (p<0.05) increased TM, PM, plasma membrane integrity, and acrosome integrity of thawed sperm. Additionally, it significantly (p<0.05) decreased the ROS level of sperm. In this study, the TM, PM, and membrane integrity of the 6% EG were significantly (p<0.05) higher than those of the control, 1% GLY+5% EG and 6% GLY+6% EG groups. Compared to other concentration groups, 20% EY significantly (p<0.05) improved the TM, PM, and plasma membrane integrity of thawed sperm. However, the integrity of the acrosome increased with the higher concentration of EY.

CONCLUSION

In conclusion, the post-thawed Hu ram semen diluted with a diluent containing 6% GLY and 20% EY exhibited higher quality compared to the other groups.

A brief review of the methodology and cryoprotectants in selected fish and mammalian species

Cryopreservation is a valuable technique used to assist in the genetic improvement of cultured stocks and provide a continuous supply of good-quality semen for artificial insemination. Conserving semen by cryopreservation serves several purposes (e.g. artificial reproductive technologies and species conservation) and is also used in the clinical treatment of human infertility. However, the lifespan of cryopreserved semen is influenced by a range of factors, including storage temperature, cooling rate, chemical composition of the extender, the concentration of cryoprotectant, reactive oxygen species, seminal plasma composition and hygienic control. The choice of cryoprotectant is a vital factor underlying the success of animal semen cryopreservation. In this regard, extensive research has been carried out on various cryoprotectants, such as egg yolk, dimethyl sulfoxide, methanol, ethylene glycol and dimethylacetamide. Recent studies have also described the use of a range of new cryoprotectants for cryopreservation, including compounds of plant origin (soy), amino acids, antifreeze proteins, carbohydrates and cyclodextrins. Moreover, semen cryopreservation and storage require the use of liquid nitrogen or ultralow refrigeration methods for both long- and short-term storage. This review summarizes the general methods used for freezing semen and discusses the use of traditional and newly emerging cryoprotectants (permeable and non-permeable) for the cryopreservation of semen in selected fish and mammalian species.

Novel Apoplastic Antifreeze Proteins of Deschampsia antarctica as Enhancer of Common Cell Freezing Media for Cryobanking of Genetic Resources, a Preliminary Study

Antifreeze proteins (AFPs) are natural biomolecules found in cold-adapted organisms that lower the freezing point of water, allowing survival in icy conditions. These proteins have the potential to improve cryopreservation techniques by enhancing the quality of genetic material postthaw. Deschampsia antarctica, a freezing-tolerant plant, possesses AFPs and is a promising candidate for cryopreservation applications. In this study, we investigated the cryoprotective properties of AFPs from D. antarctica extracts on Atlantic salmon spermatozoa. Apoplastic extracts were used to determine ice recrystallization inhibition (IRI), thermal hysteresis (TH) activities and ice crystal morphology. Spermatozoa were cryopreserved using a standard cryoprotectant medium (C+) and three alternative media supplemented with apoplastic extracts. Flow cytometry was employed to measure plasma membrane integrity (PMI) and mitochondrial membrane potential (MMP) postthaw. Results showed that a low concentration of AFPs (0.05 mg/mL) provided significant IRI activity. Apoplastic extracts from D. antarctica demonstrated a cryoprotective effect on salmon spermatozoa, with PMI comparable to the standard medium. Moreover, samples treated with apoplastic extracts exhibited a higher percentage of cells with high MMP. These findings represent the first and preliminary report that suggests that AFPs derived from apoplastic extracts of D. antarctica have the potential to serve as cryoprotectants and could allow the development of novel freezing media.

Cellular and Molecular Consequences of Stallion Sperm Cryopreservation: Recent Approaches to Improve Sperm Survival

Cryopreservation of stallion semen does not achieve the post-thaw quality or fertility results observed in other species like cattle. There are many reasons for this, but the membrane composition and intracellular changes in stallion sperm predispose them to low resistance to the cooling, freezing, and subsequent thawing process. Damage to the sperm results from different processes activated during cryopreservation, including oxidative stress, apoptosis, and structural modifications in the sperm membrane that increase the deleterious effect on sperm. In addition, significant individual variability is observed among stallions in the ability of sperm to survive the freeze-thaw process. Recent advances in genomics, transcriptomics, proteomics, metabolomics, and epigenetics are making it possible to advance our understanding of the cellular and molecular processes involved in the cryopreservation process, opening new possibilities for improvement. This review addresses the ongoing research on stallion semen cryopreservation, focusing on the cellular and molecular consequences of this procedure in stallions and discusses the new tools currently available to increase the tolerance of equine spermatozoa to freeze-thaw.

Freezability and Fertility Rates of Stallion Semen Supplemented With Trehalose in Lactose Extender

Cryopreservation of stallion semen is often associated with poor post-thaw sperm quality. One of the reason for this diminished quality is osmotic stress that spermatozoa experiences during freezing and thawing process. The aim of the present study was to evaluate the cryoprotective effect of trehalose on stallion sperm quality and field fertility rates subjected to cooling and freeze-thawing process. Semen samples were collected from six Marwari breed stallions, divided into three different treatments in a final concentration of 150 × 106 sperm/mL by using Lactose based extender containing 0, 50, and 150 mM of trehalose then subjected to cryopreservation after equilibration. Sperm motility, acrosome integrity, plasma membrane integrity, mitochondrial membrane potential, DNA integrity and oxidative stress related parameters of the stallion spermatozoa were analyzed at fresh, prefreeze and post thaw stages. Thirty (30) reproductively healthy mares were inseminated with frozen-thawed semen either supplemented with (treatment) or without (control) trehalose to evaluate the field fertility. Results of the current study indicated that, the extender containing 50 mM trehalose has enhanced the functional plasma membrane, acrosomal, DNA integrities and augmented the mitochondrial membrane potential. Trehalose supplementation to the semen extender not only ameliorated the semen quality parameters, but also protected the stallion sperm from oxidative stress by reducing the levels of reactive oxygen species (ROS) and lipid peroxidation (LPO). The inclusion of 50 mM trehalose in semen extender resulted in significantly (P < .05) increased post-thaw progressive motility and viability compared to the control group. Mares inseminated with frozen-thawed semen supplemented with 50 mM trehalose tended to have better pregnancy rates than controls (non-significant [P < .05]) although a larger fertility trial is required to determine if this effect reaches the level of significance. In conclusion, addition of 50 mM trehalose yielded in better quality stallion semen after cooling and post-thawing in terms of reducing the oxidative stress and enhancing the motility, integrities of acrosome, plasma membrane, mitochondrial potential and DNA.

Effects of Antifreeze Protein Type I and Glycerol in Diluents on Cryopreserved Goat Epididymal Sperm

The effect of antifreeze protein (AFP) as a cryoprotectant used in different concentrations of glycerol on post-thaw quality of epididymal sperm was investigated. Sperm were isolated from 50 testicles, obtained from 25 healthy mature goat bucks, with progressive motility >80%, and total morphological abnormalities <10% were pooled in each replication. The semen samples were diluted with Tris-citrate-fructose-soybean lecithin extender containing different concentration of AFP [0 μg/mL (A0), 5 μg/mL (A5), 10 μg/mL (A10)]. Each concentration of AFP was added in an extender containing either 7% (G7) or 5% (G5) glycerol. Post-thaw total and progressive motility were found to be higher (p < 0.05) in groups A5G5 and A5G7. Plasma membrane integrity, sperm acrosome integrity, DNA integrity, acrosome intact sperm, and mitochondrial membrane potential were found to be higher (p < 0.05) in groups A5G5 and A10G5. Sperm viability was found to be higher (p < 0.05) in group A5G5, while lipid peroxidation was recorded lower (p < 0.05) in groups A5G5 and A5G7. Regarding the apoptosis occurrence, the results demonstrate higher (p < 0.05) live post-thawed spermatozoa for groups containing 5 μg/mL AFP with 5% and 7% glycerol in addition to the lowest (p < 0.05) value for groups containing 0 μg/mL AFP with 5% and 7% glycerol. Based on these results, the present study concludes that the addition of 5 μg/mL AFP in combination with 5% glycerol in freezing extender improves the post-thaw quality, structure, and function parameters for buck spermatozoa.

An Investigation of Equine Sperm Quality Following Cryopreservation at Low Sperm Concentration and Repeated Freeze-Thawing

Stallion spermatozoa are typically cryopreserved at 200 to 300 million sperm/ml; however recent advances such as intracytoplasmic sperm injection (ICSI) requires only one spermatozoon, wasting many, after thawing a whole straw. Cryopreserving at concentrations less than the current standard or refreezing thawed spermatozoa could maximize the use of genetically valuable animals and reduce waste. This investigation aimed to identify if lowering the sperm concentration for cryopreservation affected post-thaw quality after one and two freeze-thaw cycles. Nine ejaculates were collected from three fertile, "good freezer" stallions (post-thaw motility ≥35%) for experiment 1. Each ejaculate was split into eight treatments: five, 10, 20, 50, 100, 200, 300, 400 million sperm/ml and cryopreserved. Post-thaw: motility, viability, acrosome integrity and oxidative stress were assessed. Experiment 2, straws from experiment 1 (300 million sperm/ml) were thawed, diluted to 20 million sperm/ml or left undiluted (control) and refrozen. Post-thaw motility and viability were assessed. In experiment 1 sperm concentration did not affect post-thaw total motility (TM), progressive motility (PM) or viability at 50 to 400 million sperm/ml (P > .05). Whilst sperm concentrations of five to 20 million/ml did differ (post-thaw TM and PM). Both refreezing and reducing spermatozoa concentration, decreased TM, PM and viability (P < .05) after two freeze-thaw cycles. These results suggest cryopreserving at sperm concentrations as low as 50 million/ml maintains spermatozoa quality in good freezer stallions. Spermatozoa maintained some motility and viability when initially cryopreserved at 20 million sperm/ml and after two freeze-thaw cycles but research should investigate more optimal conditions.

Effect of tempol and straw size on rooster sperm quality and fertility after post-thawing

The aim of the present study was to investigate the effects of tempol and straw size on rooster sperm post-thaw quality and fertility. Rooster semen was cryopreserved in Lake extender containing 0 (control), 5, 10, 15 and 20 μM tempol (in two different straw size, 0.25 and 0.5). The percentage of total and progressive sperm motility, VAP and VSL increased in the 10 µM tempol group. Moreover, 10 µM tempol led to lower ROS compared to other groups. The lowest percentage of apoptotic-like changes was detected when the extender was treated with 10 µM of tempol. The minimum ROS was observed in the group treated with 0.5 straw size. Straw size did not have any significantly effect on GPx and SOD activities and TAC of frozen-thawed sperm. The highest significant percentage of fertility and hatching rate were observed in 10 µM of tempol. The results of the present study showed that supplementation of the Lake cryopreservation medium with 10 µM tempol improved cryo-survival. Also, the results of the present study suggested that Lake cryopreservation medium with 0.5-ml straw may perhaps be an appropriate method to improve the quality and fertility post-thawed rooster sperm.

The inhibition of spermatic cystine/glutamate antiporter xCT (SLC7A11) influences the ability of cryopreserved stallion sperm to bind to heterologous zonae pellucidae

Sperm are redox-regulated cells, and deregulation of their redox status is considered to affect male fertility and to reduce their fertilizing ability following biotechnological procedures, such as cryopreservation. Cystine (CysS), after incorporation in sperm via SLC7A11 antiporter, has been demonstrated to increase intracellular GSH content, the most important non enzymatic antioxidant. This study was aimed at investigating the role of SLC7A11 antiporter on frozen-thawed stallion sperm ability to respond to in vitro capacitating environment after post-thaw incubation with CysS and/or Sulfasalazine (SS), a specific inhibitor of SLC7A11 antiporter. Viability, motility, immunolocalization of tyrosine phosphorylated proteins and the ability to bind to heterologous zonae pellucidae were evaluated. Thawed sperm from seven stallions (2 ejaculates/stallion) was washed and resuspended in Tyrodes media; each thawed ejaculate was divided in Control (CTR) and 3 samples supplemented with: 0.5 mM Cystine (CysS), 500 μM Sulfasalazine (SS) and 0.5 mM CysS + 500 μM SS (CysS + SS). After 1 h of incubation at 37 °C, samples were washed twice, resuspended in capacitating BWW medium and incubated at 38 °C under 5% CO₂. After 30 and 60 min, sperm motility, viability and tyrosine phosphorylated protein immunolocalization, used as capacitation status index, were evaluated. After 30 min of capacitation, 4 × 10⁵ sperm were co-incubated with denuded pig oocytes in capacitation medium for 30 min for the heterologous binding assay. None of the sperm parameters studied (motility, viability and tyrosine phosphorylation) showed any difference respective to control. The number of sperm bound per oocyte (mean ± SEM) tended to increase in CysS group (44.0 ± 12.3) respect CTR (40.8 ± 10.8) while decreased in SS group (32.4 ± 7.8) (p < 0.01). Moreover, CysS + SS group showed a lower binding rate (32.0 ± 10.0) compared to CysS (p < 0.001). Our results suggest that CysS supplementation of thawed stallion sperm can influence their ability to bind to heterologous zona pellucidae as the inhibition of CysS incorporation by SLC7A11 reduced the number of sperm bound per oocyte. This effect does not seem to be ascribed to a modification of sperm motility, membrane integrity and tyrosine phosphorylation.

Dimethylacetamide alone or in combination with glycerol can be used for cryopreservation of ovine semen

Dimethylacetamide has been included in different extenders for the cryopreservation of semen from species with promising results. The objective of this study was to evaluate the use of dimethylacetamide (DMA) in different concentrations, associated or not with glycerol (GLY), for the cryopreservation of ovine semen, and its effects on in vitro sperm parameters and post-thaw in vivo fertility. Five semen samples of five adult Santa Ines sheep (n=25) were used. The collected ejaculates were divided among the seven treatments for subsequent cryopreservation. The treatments presented different concentrations of DMA and GLY, being divided as G1: GLY 6%; G2: DMA 3%; G3: GLY 5% + DMA 1%; G4: GLY 4% + DMA 2%; G5: GLY 3% + DMA 3%; G6: GLY 2% + DMA 4%; G7: GLY 1% + DMA 5%. %. Post-thawing of the straws, aliquots were evaluated for computerized sperm kinetics (CASA) and plasma membrane integrity, using fluorescent probes and flow cytometry. After the in vitro evaluation of the sperm parameters, in vivo testing was performed by laparoscopic artificial insemination of 72 females. The post-thaw total motility (%) evaluated by CASA were 51.4, 51.4, 50.1, 53.6, 52.3, 52.8 and 46.9, respectively, for the seven groups. And the plasma membrane integrity (%) were 19.7, 28.4, 22.3, 29.4, 24.3, 17.9 and 16.9, respectively. There were no differences (P> 0.05) between the treatments for the parameters of spermatic kinetics and membrane integrity. For females inseminated with semen from the control group (G1, GLY6%), the percentage of pregnant females was 36.1%, a result similar to that obtained with G3 treatment (GLY5% + DMA1%). In conclusion, dimethylacetamide, either alone or in combination with glycerol, can be used for cryopreservation of ovine semen.