Stallion Sperm Cryopreservation Using Various Permeating Agents: Interplay Between Concentration and Cooling Rate

Evaluation of equine semen frozen in extenders free of egg yolk using two different freezing curves

A chemically defined cryopreservation extender that maintains seminal parameters is relevant. Fifteen ejaculates from 5 stallions (n= 5; r=3) were diluted in 5 extenders: 1) EDTA-glucose based extender with egg-yolk and dimethylformamide (EY); 2) commercial equine extender (CE); 3) CE with dimethylformamide (CE-3); 4) bovine commercial extender with liposomes (OP); 5) bovine commercial extender with soybean lecithin (BIO), and frozen using a slow and a rapid temperature descent curve. Post-thaw evaluations were: sperm kinematic parameters, viability and acrosome status, membrane lipoperoxidation and DNA fragmentation. Sperm data were analysed using an ANOVA or Friedman test (results mean ± SD). Paired comparison between the two freezing curves was analysed using the Wilcoxon test. Total and progressive motility were significantly higher (P<0.05) in the EY and CE-3 samples using the slow curve, whereas for the fast curve, total and progressive motility were significantly higher (P<0.05) in the EY samples compared to all the extenders and the samples frozen in CE-3 were significantly higher than the remaining extenders (P<0.05). The percentages of live acrosome intact sperm and of live non-peroxidized sperm were significantly higher (P<0.05) in the EY extender when using either of the freezing curves and in turn, were significantly higher (P<0.05) in samples frozen in CE-3 compared to the remaining extenders. Intact DNA was significantly lower (P<0.05) in the BIO extender, using the rapid curve. To conclude, the commercial equine extender with 3% dimethylformamide, without egg-yolk, could be a suitable alternative for extenders with egg-yolk.

l-carnitine enhances the kinematics and protects the sperm membranes of chilled and frozen-thawed Peruvian Paso horse spermatozoa

l-carnitine (LC) transports fatty acids to the mitochondria for energy production, reducing lipid availability for peroxidation through β-oxidation. This research examines the effect of LC supplementation to two skimmed milk-based extenders on the cryosurvival of chilled (5°C) and frozen-thawed Peruvian Paso horse spermatozoa .An initial experiment determined the optimal LC concentration (0, 1, 5, 10, 25, and 50 mM) when added to INRA-96® and UHT (skimmed milk + 6% egg yolk) extenders, using nine ejaculates from three stallions chilled for up to 96 h. Subsequently, the effect of 25 mM LC supplementation (the optimal concentration) on chilling (INRA-96) and freezing (INRA-Freeze®) extenders was evaluated using eight pooled samples from sixteen ejaculates (2 ejaculates/pool) from four stallions. Results indicated that all LC concentrations produced significantly higher values (P<0.05) for kinematic variables (total [TM] and progressive motilities, curvilinear [VCL] and straight-line [VSL] velocity, and beat-cross frequency [BCF]), and the integrity of plasma/acrosome membranes (IPIA) compared to non-supplemented chilled sperm samples for up to 96 h with both extenders. Moreover, the use of 25 mM LC was more efficient (P<0.05) in preserving the post-chilled values of velocity, BCF, and IPIA for the long term than lower LC concentrations (1-10 mM). Post-thaw values of total motility, the amplitude of lateral head displacement (ALH), and IPIA were significantly improved (P<0.05) when INRA-Freeze extender was supplemented with 25 mM LC. In conclusion, supplementation of l-carnitine to skimmed milk-based extenders enhanced kinematic variables and protected the membrane integrity in chilled and frozen-thawed Peruvian Paso horse spermatozoa.

Effect of Melatonin and Caffeine Supplementation to Freezing Medium on Cryosurvival of Peruvian Paso Horse Sperm Using a Two-Step Accelerating Cooling Rate

This research examined the antioxidant and cryoprotective effects of melatonin (ME) and caffeine (CAF) supplementation in freezing medium on the cryosurvival of Peruvian Paso horse sperm using a two-step accelerating cooling rate. Twenty ejaculates from four adult and fertile stallions were recovered, initially diluted with INRA-96®, and finally frozen with INRA-Freeze® with either no supplementation (as control), 1 μM ME, or 2 mM CAF using a two-ramp freezing system content inside a cryogenic-box and liquid nitrogen vapors. The sperm kinematic parameters and integrity of the plasma and acrosomal membranes of fresh semen and cryopreserved samples were evaluated using the CASA system (SCA-Evolution® 2018) and PI/fluorescein isothiocyanate-conjugated peanut (Arachis hypogaea) agglutinin double fluorescent test, respectively. The oxidative stress of post-thaw sperm samples was also assessed using the CellRox Deep Red fluorescence test. The results showed that curvilinear velocity and average-path velocity were greater (p < 0.05) after freezing with CAF than the control group. In addition, there were significance differences (p < 0.01) between stallions (1-4) in post-thaw kinematic parameters regardless of ME or CAF addition. Both ME and CAF improved (p < 0.05) the proportion of sperm with intact plasma membranes and intact acrosomes. Nevertheless, neither CAF nor ME improved the oxidative stress after the cryopreservation process.

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.

Influence of Two Widely Used Solvents, Ethanol and Dimethyl Sulfoxide, on Human Sperm Parameters

To study mechanisms involved in fertility, many experimental assays are conducted by incubating spermatozoa in the presence of molecules dissolved in solvents such as ethanol (EtOH) or dimethyl sulfoxide (DMSO). Although a vehicle control group is usually included in such studies, it does not allow to evaluate the intrinsic effect of the solvent on sperm parameters and its potential influence on the outcome of the experiment. In the present study, we incubated human spermatozoa for 4 h in a capacitation medium in the absence or the presence of different concentrations of EtOH and DMSO (0.1, 0.5, 1.0, and 2.0%) to assess the impact of these solvents on sperm motility, vitality, capacitation, and acrosome integrity. The presence of statistically significant relationships between increasing solvent concentrations and the investigated parameters was assessed using linear mixed models. A significant effect was observed with both solvents for total and progressive sperm motilities. We also evaluated the effect of time for these parameters and showed that the influence of the solvents was stable between 0 and 4 h, indicating an almost direct impact of the solvents. While EtOH did not influence sperm vitality and acrosome integrity, a significant effect of increasing DMSO concentrations was observed for these parameters. Finally, regarding capacitation, measured via phosphotyrosine content, although a dose-dependent effect was observed with both solvents, the statistical analysis did not allow to precisely evaluate the intensity of the effect. Based on the results obtained in the present study, and the corresponding linear mixed models, we calculated the concentration of both solvents which would result in a 5% decline in sperm parameters. For EtOH, these concentrations are 0.9, 0.7, and 0.3% for total motility, progressive motility, and capacitation, respectively, while for DMSO they are 1.5, 1.1, >2, 0.3 and >2% for total motility, progressive motility, vitality, capacitation, and acrosome integrity, respectively. We recommend using solvent concentrations below these values to dissolve molecules used to study sperm function in vitro, to limit side effects.

Dimethylformamide Preserves the Integrity of Cryopreserved Goat Semen in a Soybean Lecithin-Based Extender

This study investigated the cryoprotectant effects of dimethylformamide (DMF), ethylene glycol (EG), and dimethyl sulfoxide (DMSO) as substitutes for glycerol (GLY) in a soybean lecithin (SL)-based extender in the cryopreservation of buck sperm. In this study, the semen of three Saanen bucks was individually extended in SL supplemented with 5% GLY (control), DMF, EG, or DMSO. After this, the extended semen was cryopreserved and two straws from each group were thawed (37°C for 30 seconds), pooled, and analyzed for sperm motion parameters, plasma membrane integrity (PMI), acrosomal integrity (ACI), and high mitochondrial membrane potential (HMMP). Samples were analyzed after 15 minutes (T0) and after 2 hours of incubation at 37°C (T2). The results revealed higher values of motility (total and progressive) and sperm motion parameters for DMF than the other cryoprotectants (p < 0.0001). PMI and HMMP did not differ (p > 0.05) between GLY and DMF, but ACI was higher (p < 0.01) for DMF compared with GLY. Based on these results, DMF and GLY samples were used in heterologous in vitro fertilization assays by using bovine oocytes (n = 337) obtained from a slaughterhouse. No differences (p > 0.05) were observed between GLY and DMF for unfertilized (GLY: 38.8%; DMF: 25.33%), pronucleus (GLY: 25.68%; DMF: 27.92%), and cleavage rates (GLY: 35.52%; DMF: 46.75%). Based on these results, it is concluded that DMF preserves sperm motion characteristics and ACI better than GLY, EG, and DMSO, and it is the penetrating cryoprotectant of choice for the cryopreservation of buck sperm in SL extender.

Recent advances in donkey sperm vitrification

Artificial insemination (AI) with cryopreserved semen is an important tool to preserve endangered species, including European donkey breeds. Sperm vitrification is an alternative method to conventional freezing using high cooling rates and non-permeable cryoprotectant agents (CPAs). In donkeys, sperm vitrification was firstly developed in spheres by directly dropping the sperm (30 µl) into the liquid nitrogen. The vitrification media contained a combination of sucrose and bovine serum albumin as non-permeable CPAs and resulted in better sperm parameters after warming than extenders containing glycerol. Thereafter, sperm vitrification was optimized using an aseptic protocol, which consists of volumes up to 160 µl vitrified at 300 million sperm/ml using 0.25-ml straws with outer covers, obtaining similar sperm parameters as conventional freezing for total motility (52.7 ± 15.6% versus. 58.2 ± 16.1%), progressive motility (44.3 ± 15.0% versus. 44.7 ± 18.2%) and plasma membrane integrity (49.2 ± 11.2% versus. 55.4 ± 9.0%), respectively. In order to vitrify larger volumes of sperm, a procedure using 0.5-ml straws was evaluated; however, this methodology failed when compared to conventional freezing or other vitrification protocols, obtaining poor sperm quality after warming. Recently, a new methodology was developed for warming 0.25-ml straws in a water bath and after AI using the vitrified sperm, the uterine inflammatory response solved faster, and pregnancy rates were greater (22%) than frozen semen (10%) but not statistically different. In conclusion, all these findings confirm that sperm vitrification can be performed in donkeys as an alternative to conventional freezing for AI in jennies.

high-throughput droplet vitrification of stallion sperm using permeating cryoprotective agents

Stallion sperm is typically cryopreserved using low cooling rates and low concentrations of cryoprotective agents (CPAs). The inevitable water-to-ice phase transition during cryopreservation is damaging and can be prevented using vitrification. Vitrification requires high cooling rates and high CPA concentrations. In this study, the feasibility of stallion sperm vitrification was investigated. A dual-syringe pump system was used to mix sperm equilibrated in a solution with a low concentration of CPAs, with a solution containing a high CPA concentration, and to generate droplets of a defined size (i.e., ~20 μL) that were subsequently cooled by depositing on an aluminum alloy block placed in liquid nitrogen. Mathematical modeling was performed to compute the heat transfer and rate of cooling. The minimum CPA concentration needed for vitrification was determined for various CPAs (glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide) and combinations thereof, while effects of droplet size and carrier solution were also identified. Sperm vitrification was eventually done using a glycerol/propylene glycol (1/1) mixture at a final concentration of 45% in buffered saline supplemented with 3% albumin and polyvinylpyrrolidon, while warming was done in standard diluent supplemented with 100 mM sucrose. The sperm concentration was found to greatly affect sperm membrane integrity after vitrification-and-warming, i.e., was found to be 21 ± 12% for 10 × 10⁶ sperm mL^-1 and 54 ± 8% for 1 × 10⁶ sperm mL^-1. However, an almost complete loss of sperm motility was observed. In conclusion, successful sperm vitrification requires establishing the narrow balance between droplet size, sperm concentration, CPA type and concentration, and exposure time.

Cryopreservation of Semen from Domestic Livestock: Bovine, Equine, and Porcine Sperm

In modern livestock breeding, cryopreserved semen is routinely used for artificial insemination. Sperm cryopreservation allows for long-term storage of insemination doses and secures reproduction at a desired time point. In order to cryopreserve semen, it needs to be carefully processed to preserve its vital functions after thawing. In this chapter, we describe the processes involved in cryopreservation of bull, stallion, and boar sperm. These include preparation of diluents, dilution of sperm in primary and freezing extender, slow cooling from room temperature to 5 °C, packaging of insemination doses in straws, freezing at a defined cooling rate in liquid nitrogen vapor, cryogenic storage, and thawing. Two-step dilution approaches, with commonly used diluents, are presented, namely, TRIS-egg yolk (TEY) extender for bull sperm, skim milk (INRA-82) extender for stallion sperm, and lactose-egg yolk (LEY) extender for boar sperm. Furthermore, simple methods are presented for cooling and freezing of sperm at defined cooling rates.

Ice Inhibition for Cryopreservation: Materials, Strategies, and Challenges

Cryopreservation technology has developed into a fundamental and important supporting method for biomedical applications such as cell-based therapeutics, tissue engineering, assisted reproduction, and vaccine storage. The formation, growth, and recrystallization of ice crystals are the major limitations in cell/tissue/organ cryopreservation, and cause fatal cryoinjury to cryopreserved biological samples. Flourishing anti-icing materials and strategies can effectively regulate and suppress ice crystals, thus reducing ice damage and promoting cryopreservation efficiency. This review first describes the basic ice cryodamage mechanisms in the cryopreservation process. The recent development of chemical ice-inhibition molecules, including cryoprotectant, antifreeze protein, synthetic polymer, nanomaterial, and hydrogel, and their applications in cryopreservation are summarized. The advanced engineering strategies, including trehalose delivery, cell encapsulation, and bioinspired structure design for ice inhibition, are further discussed. Furthermore, external physical field technologies used for inhibiting ice crystals in both the cooling and thawing processes are systematically reviewed. Finally, the current challenges and future perspectives in the field of ice inhibition for high-efficiency cryopreservation are proposed.

Principles Underlying Cryopreservation and Freeze-Drying of Cells and Tissues

Cryopreservation and freeze-drying can be used to preserve cells or tissues for prolonged periods. Vitrification, or ice-free cryopreservation, is an alternative to cryopreservation that enables cooling cells to cryogenic temperatures in the absence of ice. The processing pathways involved in (ice-free) cryopreservation and freeze-drying of cells and tissues, however, can be very damaging. In this chapter, we describe the principles underlying preservation of cells for which freezing and drying are normally lethal processes as well as for cells that are able to survive in a reversible state of suspended animation. Freezing results in solution effects injury and/or intracellular ice formation, whereas drying results in removal of (non-freezable) water normally bound to biomolecules, which is generally more damaging. Cryopreservation and freeze-drying require different types of protective agents. Different mechanistic modes of action of cryoprotective and lyoprotective agents are described including minimizing ice formation, preferential exclusion, water replacement, and vitrification. Furthermore, it is discussed how protective agents can be introduced into cells avoiding damage due to too large cell volume excursions, and how knowledge of cell-specific membrane permeability properties in various temperature regimes can be used to rationally design (ice-free) cryopreservation and freeze-drying protocols.

Cryopreservation as a Key Element in the Successful Delivery of Cell-Based Therapies-A Review

Cryopreservation is a key enabling technology in regenerative medicine that provides stable and secure extended cell storage for primary tissue isolates and constructs and prepared cell preparations. The essential detail of the process as it can be applied to cell-based therapies is set out in this review, covering tissue and cell isolation, cryoprotection, cooling and freezing, frozen storage and transport, thawing, and recovery. The aim is to provide clinical scientists with an overview of the benefits and difficulties associated with cryopreservation to assist them with problem resolution in their routine work, or to enable them to consider future involvement in cryopreservative procedures. It is also intended to facilitate networking between clinicians and cryo-researchers to review difficulties and problems to advance protocol optimization and innovative design.

Rosiglitazone in the thawing medium improves mitochondrial function in stallion spermatozoa through regulating Akt phosphorylation and reduction of caspase 3

BACKGROUND

The population of stallion spermatozoa that survive thawing experience compromised mitochondrial functionality and accelerated senescence, among other changes. It is known that stallion spermatozoa show very active oxidative phosphorylation that may accelerate sperm senescence through increased production of reactive oxygen species. Rosiglitazone has been proven to enhance the glycolytic capability of stallion spermatozoa maintained at ambient temperature.

OBJECTIVES

Thus, we hypothesized that thawed sperm may also benefit from rosiglitazone supplementation.

MATERIALS AND METHODS

Thawed sperm were washed and resuspended in Tyrodes media, and the samples were divided and supplemented with 0 or 75 μM rosiglitazone. After one and two hours of incubation, mitochondrial functionality, Akt phosphorylation and caspase 3 activity were evaluated. Additional samples were incubated in the presence of an Akt1/2 inhibitor, compound C (an AMPK inhibitor) or GW9662 (an antagonist of the PPARγ receptor).

RESULTS

Rosiglitazone maintained Akt phosphorylation and reduced caspase 3 activation (p<0.01), both of which were prevented by incubation in the presence of the three inhibitors. Rosiglitazone also enhanced mitochondrial functionality (P<0.01).

CONCLUSION

We provide the first evidence that the functionality of frozen stallion spermatozoa can be potentially improved after thawing through the activation of pro survival pathways, providing new clues for improving current sperm biotechnology.

Effect of cryoprotectant type and concentration on the vitrification of collared peccary (Pecari tajacu) ovarian tissue

The aim of the present study was to establish a protocol for solid surface vitrification of peccary ovarian tissue by using different cryoprotectants. Ovarian pairs from five adult females were fragmented and two fragments (fresh control group) were immediately subjected to morphological evaluation using classical histology, transmission electron microscopy, and viability analysis using fluorescent probes. The remaining fragments (n = 18) were vitrified using a solid surface method with different concentrations (3 or 6 M) of ethylene glycol (EG), dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF). After 2 weeks, samples were re-warmed and evaluated. A decrease in the percentage of morphologically normal preantral follicles (PFs) was verified for all the groups in comparison to the fresh control (92.0 ± 2.8%); however, if only the primordial follicles are considered, the most effective preservation (P < 0.05) was achieved with the use of EG at 3 M (74.2±7.3%) or DMSO at 6 M (75.0 ± 4.2%). Ultrastructural analysis indicated there were well-preserved PFs in all the groups evaluated, having well-defined membranes, a few vacuoles, and organelles that were uniformly distributed throughout the cytoplasm, mainly round and elongated mitochondria in close association with lipid droplets. Viability was preserved (P <  0.05) with the use of EG at 3 (97%) or 6 (97%) M, DMSO at 3 (100%), and DMF at 6 (97%) M. Solid surface vitrification, therefore, is an effective method for conservation of peccary female germplasm, especially with the use of EG at 3 M, which was highly effective for preservation of both the morphology and viability of PFs.

Freezing of Stallion Semen: In Vitro Evaluation of Motility and Acrosin Activity in Sperm Cells Cryopreserved Using Different Semen Extenders

The work described here aimed to verify the efficiency of different extenders for cryopreservation of equine semen using sperm motility and acrosin activity as spermatic parameters. The semen was fractioned into two equal parts and resuspended in an 11% lactose solution in a 1:1 proportion, where it remained for 20 minutes at room temperature. The semen was centrifuged at 600 g for 10 minutes, and after the second centrifugation, each pellet received the freezing extender (Merck or Zorlesco) and was loaded into 4 mL straws. Each straw was placed in liquid nitrogen vapor steam for 15 minutes and further immersion in liquid nitrogen at -196°C for long-term storage. After thawing, semen samples were initially evaluated for sperm motility, both total and progressive, and acrosin activity. Moreover, semen was incubated at 37°C and further assessed at 60 and 120 minutes in a thermoresistance test (TRT) for sperm motility and acrosin activity. Immediately after thawing, both progressive and total motility, and acrosin activity were lower (p < 0.05) in thawed semen than in fresh semen. During the TRT, total sperm motility and acrosin activity after 60 minutes were lower (p < 0.05) than those obtained after thawing. Similarly, total sperm motility and acrosin activity were lower (p < 0.05) after 120 minutes than at 60 minutes of the TRT. The analysis of motility and acrosin activity allowed the conclusion that both extenders have a similar capacity to preserve the integrity of sperm cells subject to freezing and thawing.