Delivering cholesterol or cholestanol to bull sperm membranes improves cryosurvival

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.

Sperm characteristics of cryopreserved Prochilodus lineatus semen after adding cholesterol-loaded cyclodextrin

The experiment evaluated the effect of adding cholesterol-loaded cyclodextrin (CLC) to Prochilodus lineatus fish (Curimata) semen on post-thaw sperm quality. Twelve adult fish were used for sperm collection after induced spermiation with carp pituitary gland. The semen was diluted and treated with CLC in concentrations of 0 (control), 0.5, 1.0, 2.0, 3.0, and 4.0 mg for 120 × 106 spermatozoa/ml, loaded in 0.5 ml straws, packaged and placed in dry vapor vessel cylinders for 24 h before being submerged in liquid nitrogen for storage. The samples were thawed in a water bath at 60 °C for 8 s, and the sperm parameters evaluated were motility, activation duration, longevity, plasma membrane integrity, and morphology. Data were tested for normal distribution and ANOVA, followed by Friedman test (P < 0.05). Spermatozoa treated with CLC displayed higher motility than the control (P < 0.05). The duration of sperm activation was longer in sperm treated with 0.5, 1.0, and 2.0 mg of CLC than in control (P < 0.05). The membrane integrity was higher in sperm treated with 0.5, 1.0, 2.0, and 3.0 mg of CLC than in control and four mg-treated samples (P < 0.05). The sperm longevity and morphology alterations did not differ between treatments (P > 0.05). Adding 0.5, 1.0, or 2.0 mg of CLC in Prochilodus lineatus semen before cryopreservation improves sperm motility and membrane integrity.

The association of resveratrol and AFPI did not enhance the cryoresistance of ram sperm

Cryoprotectants are required to reduce damage caused to the cells due to low temperatures during the cryopreservation. Antifreeze proteins (AFP) have a well-known role in cell membrane protection, while resveratrol is a potent antioxidant. This study assessed the effect of the association of resveratrol concentrations and AFP I in a ram semen extender. Pooled semen of four rams was allocated into six treatments in a factorial arrangement: (CONT, only the semen extender); only AFP I (ANT: 0.1 µg/mL of AFP I), only resveratrol, one treatment with two levels (10 µM/mL or 50 µM/mL of resveratrol); and two treatments with the interactions, with one AFP I and one of the two levels of resveratrol (0.1 µg/mL of AFP I with 10 µM/mL resveratrol; 0.1 µg/mL of AFP I with 50 µM/mL resveratrol). No interaction between factors was observed on sperm kinetics, plasma membrane integrity, hypo-osmotic test, and mitochondrial activity parameters. There was a high probability (P = 0.06) of reducing sperm cells with functional membrane percentage in the hypo-osmotic test and increasing the percentage of sperm with high mitochondrial activity (P = 0.07) was observed in AFP presence. An interaction of AFP and resveratrol was observed in non-capacitated sperm (P = 0.009), acrosomal reaction (P = 0.034), and sperm binding (P = 0.04). In conclusion, the association of resveratrol and AFP did not improve the quality of frozen-thawed semen and even promoted deleterious effects compared to their single addition in the semen extender. The supplementation of 50 µM/mL of resveratrol improved the outcomes of frozen-thawed ram sperm, being a potential cryoprotectant.

"Fine feathers make fine birds" - The mammalian sperm plasma membrane lipid composition and effects on assisted reproduction

The sperm plasma membrane is important in modulating many sperm functions. The sperm membrane is composed of a complex mixture of lipids including phospholipids, glycolipids and sterols. There are differences of sperm membrane composition among mammalian species with two groups differing in the most abundant polyunsaturated fatty acid (PUFA), either docosahexaenoic (ω-3 PUFA) or docosapentaenoic acid (ω-6 PUFA). During testicular and epididymal maturation, composition of the sperm plasma membrane evolves with spermatozoa gaining the capacity for fertilization. The importance of fatty acid metabolism for complete spermatogenesis has been elucidated using gene knockout mice. During epididymal transit cholesterol content decreases and PUFA content increases, conferring more fluidity properties to the sperm membrane. The relatively lesser content of antioxidant enzymes and the relatively larger content of PUFA make the spermatozoa particularly susceptible to lipid peroxidation during sperm preservation. In numerous studies, there was adding of PUFA and antioxidants to the diet of animals or to semen extenders with the aim to improve sperm membrane integrity. This review highlights the current knowledge on the sperm membrane composition and effects on sperm function in mammalian domestic animals.

Effect of cholestanol and cholesterol-loaded cyclodextrin on stallion sperm function and capacitation post-cryopreservation

Cryopreservation of stallion semen is less efficient than other species such as bovine. This is mainly because of the greater susceptibility of stallion sperm to the freezing damage that generates oxidative stress and plasma membrane injury, resulting in DNA fragmentation and cell death. These data suggest the need to develop new strategies of sperm cryopreservation that can improve the efficiency of this technique in stallions by reducing or preventing membrane damage and cell death. The present study aimed to evaluate the effect of adding membrane stabilizers to the freezing medium and assess the quality and in vitro capacitation of stallion sperm after thawing. Semen samples from three stallions frozen with membrane stabilizers (cholesterol-loaded cyclodextrin and cholestanol-loaded cyclodextrin) were evaluated in two experiments: i) sperm quality and functional analysis after thawing, and ii) sperm quality and functional analysis after 4 h of post-thaw incubation in capacitating conditions. Plasma membrane integrity, mitochondrial membrane potential, membrane lipid disorder, intracellular Ca²⁺, tyrosine phosphorylation, acrosome reaction, DNA damage, sperm motility, and binding to the zona pellucida were assessed. The results showed that cholesterol-loaded cyclodextrin was the stabilizer that most efficiently reduced the membrane disruption and post-thaw cell damage. In addition, this stabilizer made it possible to obtain in vitro capacitated sperm showing higher plasma membrane integrity, mitochondrial membrane potential, sperm motility, binding to the zona pellucida and better response to in vitro capacitating conditions.

Application of High Hydrostatic Pressure (HHP) to Improve Cryopreservation of Young Bull Semen

The objective of the study was to determine the effect of high hydrostatic pressure (HHP) on quality of cryopreserved semen of young bulls. Semen for this study was collected from 8 bulls aged between 13 and 18 months at monthly intervals, from June to September. After collection, semen was diluted in a commercial Bioxcell® extender (one part at 1:1 and a second part to give a sperm concentration of 20 million/0.2 mL), filled into straws and treated with HHP at 30 MPa for 90 min. After HHP treatment, pre-diluted semen (1:1) was diluted to a sperm concentration 20 million/0.2 mL and filled into straws. In addition, part of the semen diluted to a concentration of 20 million/0.2 mL was not treated with HHP (control). All of it was held at +4°C and frozen in a freezer after 2.5-h equilibration. Semen was thawed in a water bath at 38°C and subjected to estimation of the percentage of motile sperm both subjectively and using a computer-assisted semen analyzer and cytometric assessment of sperm cell membrane integrity. Subjective motility and fast progressive motility were significantly higher with pre-diluted (1:1) and HHP treated semen compared to control (P<0.05). No significant differences were observed in percentage of membraneintact spermatozoa between control and experimental groups. Additionally, the influence of HHP on the sperm of individual bulls was assessed. In bull number 2, the HHP treatment after semen pre-dilution significantly improved progressive motility from 54.1 to 63.4 percent (P<0.05). In bull number 4, the HHP treatment after semen pre-dilution significantly improved subjective motility, rapid motility and progressive motility by 12.5, 16.8 and 16.3 percent, respectively (P<0.05). No effect was seen for 6 bulls. It is concluded that for some bulls, the application of HHP before semen freezing may improve the cryopreservation outcome. However, this requires further research in this area, also to determine the fertilizing capacity of bull semen exposed to high hydrostatic pressure.

Desmosterol Incorporation Into Ram Sperm Membrane Before Cryopreservation Improves in vitro and in vivo Fertility

Pregnancy rates in ewes are markedly low after cervical insemination with frozen-thawed sperm. Sensitivity of ram sperm to freeze-thawing is related to the lipid composition of the membrane, particularly to its low sterol content. Recently, we proved that sterol content of ram sperm can be increased by treatment with methyl-β-cyclodextrin-sterol complexes and we provided mechanistic based evidence on the differential behavior of cholesterol and desmosterol in the ram sperm membrane. In the present study, we evaluated the role of increasing cholesterol and desmosterol content of ram sperm before cryopreservation, on the extent and distribution of sterols, cryocapacitation status, acrosome integrity, DNA damage associated with apoptosis and fertility competence in vitro and in vivo of post-thawed sperm. After freeze-thawing, similar levels of sterol content were evidenced in control sperm cells and in those pre-incubated with either cholesterol or desmosterol. Still, moderately higher levels of sterols were registered in treated sperm compared to the control, indicating no physiological excess of sterols after thawing or sterol losses that exceed the control. Live cell imaging of fluorescent cholesterol evidenced the presence of sperm sub-populations differentially affected by freeze-thawing. Similar unimodal frequency profiles were observed between sterol-enriched groups, while the control exhibited a sub-population of sperm compatible with low sterol content. Tyrosine phosphorylation was significantly lower when ram sperm incorporated cholesterol compared to the control. No difference in this capacitation parameter was found between the latter and desmosterol-enriched sperm. The percentage of sperm with damaged acrosomes post-thawing, assessed by a fluorescent lectin, was reduced in sperm that incorporated sterols before freezing, irrespective of the sterol class. These results suggest that sterols exert a stabilizing effect on the acrosome. No differences were found in levels of apoptotic DNA fragmentation among experimental groups. As to fertility trials, desmosterol-enriched sperm gave rise to higher rates of in vitro activated oocytes by heterologous fertilization and to significantly lower pregnancy loss in vivo. Our research provides new insights on sterol incorporation into ram sperm prior to cryopreservation, in particular on the additional benefit of incorporating desmosterol as a strategy to improve fertility outcome.

Boar sperm protein tyrosine phosphorylation in the presence of egg yolk soluble and low density lipoprotein fractions during cooling

Increased protein tyrosine phosphorylation and the appearance of a phosphorylated protein of 32 kD (p32) are reported among the capacitation-like changes in cryopreserved boar sperm. Egg yolk freezing extenders are composed by two fractions: insoluble granules and soluble plasma, which contains the low density lipoproteins (LDL) proposed as responsible for the egg yolk cryoprotective action. The aim of this work was to analyze the effects of complete egg yolk and its insoluble, soluble and LDL fractions on boar sperm quality and protein tyrosine phosphorylation after the first stage of a standard cryopreservation protocol. Semen samples in Androstar^® Plus diluent were centrifuged and resuspended in the different egg yolk extenders. Temperature was decreased from 17 °C to 5 °C and sperm quality, protein tyrosine phosphorylation and protein pattern were analyzed. Results showed that complete egg yolk as well as soluble and LDL egg yolk fractions maintained sperm quality after temperature decrease. Cooling without any lipid component or in the presence of the insoluble fraction, significantly reduced sperm motility. About sperm protein tyrosine phosphorylation analysis, the p32 band appeared before treatments or after cooling in Androstar^® Plus diluent. Complete egg yolk and its insoluble fraction interfered with sperm tyrosine phosphorylation even after cells were extensively washed. Analysis of extenders revealed a high amount of tyrosine phosphorylated proteins in the insoluble fraction, which may have co-precipitate with sperm in experiments. Samples submitted to temperature decrease from 17 °C to 5 °C in the presence of soluble and LDL egg yolk fractions in Androstar^® Plus diluent did not show any change in the p32 band associated with sperm capacitation. However, a tyrosine-phosphorylated protein of 33 kD present in clarified egg yolk was also observed in sperm treated with this extender. Protein transference from plasma and LDL egg yolk extenders was also observed in sperm protein profile. Results suggested that soluble and LDL fractions might have a protective action preventing sperm protein tyrosine phosphorylation during cooling from 17 °C to 5 °C. Further studies are needed to expand the knowledge of the LDL protection mechanism as well as to determine the possible benefits of clarified egg yolk in freezing protocols.

Effect of cholesterol loaded cyclodextrin on semen cryopreservation of Aksaray Malakli shepherd dogs of different ages

The objective of the study was to determine the effect of cholesterol-loaded cyclodextrin (CLC) on the quality parameters of semen from Aksaray Malakli Shepherd dogs of different age groups. Forty-eight male dogs were divided into 3 groupings according to their ages (young age (Y): ≤3 years, n: 20; middle age (M): 4-6 years, n: 20; old age (O): ≥7 years; n: 8). The sperm-rich portion of the ejaculate from each dog was divided into four aliquots and extended with either tris as a control (C) or tris loaded with 0.5, 1.0, and 1.5 mg/120 × 10⁶ CLC as low (L), intermediate (I), and high (H) doses, respectively. Following equilibration for at least half an hour, the straws were frozen in nitrogen vapor and then stored in liquid nitrogen at least for 48 h. Later, the frozen straws were thawed in a water bath for spermatological evaluation. Significant differences were observed between different age groups in terms of the spermatological parameters (p < 0.05). The evidence suggests that increasing age is associated with poor in-vitro spermatological parameters and CLC was able to protect the acrosome integrity from cryo-damage during the freeze-thawing process. Better semen freezability characteristics were obtained at young ages, considering the overall parameters.

Modification of membrane cholesterol and desmosterol in chicken spermatozoa improves post-thaw survival and prevents impairment of sperm function after cryopreservation

During cryopreservation, spermatozoa are subjected to cryodamage that leads to a decline in fertilisation ability. Due to the complex nature of this process, the initial trigger for cryodamage remains unknown. Recently, we demonstrated that cryopreservation induces early apoptotic changes characterised by phosphatidylserine (PS) translocation via sterol loss from the plasma membrane of chicken spermatozoa. This led us to hypothesise that sterol incorporation into membranes minimises cryodamage, thereby improving the quality of cryopreserved chicken spermatozoa. In the present study, treating spermatozoa with 1.5 mg mL−1 cholesterol- and 3 mg mL−1 desmosterol-loaded cyclodextrin (CLC and DLC respectively) increased post-thaw survival and motility. These effects appeared to be highly dependent the amount of sterol loaded into the spermatozoa. Localisation experiments confirmed the incorporation of exogenous cholesterol into the sperm head region. Detection of PS translocation showed that elevation of these sterols inhibited early apoptotic changes, thereby enhancing post-thaw survival. Furthermore, CLC and DLC treatment suppressed spontaneous acrosome reaction after cryopreservation, preserving the ability of spermatozoa to undergo acrosome reactions in response to physiological stimulation. These results demonstrate that loading sterols into chicken spermatozoa before cryopreservation enhances their quality by inhibiting early apoptotic changes and spontaneous acrosome reactions. The present study provides new mechanistic insight into cryodamage in chicken spermatozoa.

Free cholesterol and cholesterol esters in bovine oocytes: Implications in survival and membrane raft organization after cryopreservation

Part of the damage caused by cryopreservation of mammalian oocytes occurs at the plasma membrane. The addition of cholesterol to cell membranes as a strategy to make it more tolerant to cryopreservation has been little addressed in oocytes. In order to increase the survival of bovine oocytes after cryopreservation, we proposed not only to increase cholesterol level of oocyte membranes before vitrification but also to remove the added cholesterol after warming, thus recovering its original level. Results from our study showed that modulation of membrane cholesterol by methyl-β-cyclodextrin (MβCD) did not affect the apoptotic status of oocytes and improved viability after vitrification yielding levels of apoptosis closer to those of fresh oocytes. Fluorometric measurements based on an enzyme-coupled reaction that detects both free cholesterol (membrane) and cholesteryl esters (stored in lipid droplets), revealed that oocytes and cumulus cells present different levels of cholesterol depending on the seasonal period. Variations at membrane cholesterol level of oocytes were enough to account for the differences found in total cholesterol. Differences found in total cholesterol of cumulus cells were explained by the differences found in both the content of membrane cholesterol and of cholesterol esters. Cholesterol was incorporated into the oocyte plasma membrane as evidenced by comparative labeling of a fluorescent cholesterol. Oocytes and cumulus cells increased membrane cholesterol after incubation with MβCD/cholesterol and recovered their original level after cholesterol removal, regardless of the season. Finally, we evaluated the effect of vitrification on the putative raft molecule GM1. Cholesterol modulation also preserved membrane organization by maintaining ganglioside level at the plasma membrane. Results suggest a distinctive cholesterol metabolic status of cumulus-oocyte complexes (COCs) among seasons and a dynamic organizational structure of cholesterol homeostasis within the COC. Modulation of membrane cholesterol by MβCD improved survival of bovine oocytes and preserved integrity of GM1-related rafts after vitrification.

Effect of seminal plasma from high- and low-fertility bulls on cauda epididymal sperm function

The aim of this study was to characterise the effect of seminal plasma (SP) from bulls of high or low fertility on sperm function. First, the effect of SP on the motility of fresh cauda epididymal spermatozoa (CES) and frozen–thawed ejaculated spermatozoa was assessed (Experiment 1a). Seminal plasma was then collected from bulls of known high and low fertility. Pooled CES were incubated in the SP from each bull, diluted and assessed for motility and viability on Days 1, 2, 3 and 5 after packaging as fresh semen (Experiment 1b). Also assessed were motility, kinematics, viability and mitochondrial membrane potential after thawing (Experiment 1c) as well as hypotonic resistance (Experiment 2) and fertilisation potential using in vitro fertilisation (Experiment 3). Seminal plasma increased the motility of CES (P < 0.05); however, there was no effect of SP on the motility and viability of fresh CES or on CES post-thaw motility, viability and mitochondrial membrane potential (P > 0.05). The hypotonic resistance of CES was reduced by SP (P < 0.05), irrespective of whether the SP was from high- or low-fertility bulls. Seminal plasma from high- or low-fertility bulls had no effect on cleavage or blastocyst rates (P > 0.05). In conclusion, SP affects the physiological function of CES but there is no difference between SP from high- or low-fertility bulls.

Comparison of Membrane Characteristics between Freshly Ejaculated and Cryopreserved Sperm in the Chicken

Cryopreserved sperm undergoes serious damage which affects its fertilizing ability. Despite progress in understanding the nature of functional deterioration in mammalian sperm, little is known about the mechanism involved in the induction of functional damage in avian sperm. Cellular membranes are considered the primary site of cryodamage to sperm. Membrane rafts are specific membrane regions enriched in sterols, ganglioside GM1, and functional proteins and they play important roles in the regulation of diverse functions exerted in mammalian sperm during fertilization. Several reports investigating cryopreservation-induced membrane changes in mammalian sperm have suggested that cryopreservation induces a compositional alteration of membrane rafts via a loss of membrane sterols, leading to impaired fertilizing ability. Recently, we demonstrated that membrane rafts are present in chicken sperm. Therefore, we investigated a possible mechanism for the induction of functional damage in cryopreserved chicken sperm, with particular attention to cryopreservation-induced compositional changes in membrane rafts. Sterol quantification showed that loss of sterols from sperm membranes occurred following cryopreservation. Biochemical analyses of detergent-insoluble membranes showed that the lipid and protein compositions of membrane rafts were altered dramatically by cryopreservation. To determine the physiological role of these changes, we examined external translocation of phosphatidylserine (PS), representing an early apoptotic change, and found that cryopreservation induced apoptotic changes in chicken sperm. Furthermore, methyl-β-cyclodextrin-induced loss of sterols from the plasma membranes stimulated PS translocation that was not accompanied with caspase-3 activation, which plays an important role downstream of the apoptotic cascade. Based on the results obtained in this study, we discuss a new mechanism for reduction of the fertilizing ability in avian sperm after cryopreservation.

Evaluation of cholesterol- treated dromedary camel sperm function by heterologous IVF and AI

Cholesterol (cholesterol-loaded cyclodextrins: CLC) treatment of dromedary camel sperm prior to freezing enhances cryosurvival. The present study first validated the efficacy of a heterologous zona-free goat oocyte assay (n=115 oocytes) to evaluate camel sperm function in vitro (Experiment 1: n=6 bulls), then examined the effects of CLC treatment (1.5mg/mL CLC; CLC+) versus no treatment (0 CLC) of fresh (Experiment 2: n=4 bulls) and frozen-thawed (Experiment 3: n=5 bulls) camel sperm to penetrate, de-condense and form pro-nuclei in in vitro-matured goat oocytes. Finally, the ability of fresh 0 CLC and CLC+ sperm to fertilize in vivo was studied by artificially inseminating super-ovulated females (n=7-9 per treatment) and examining embryo production (Experiment 4: n=4-5 bulls/treatment). Camel spermatozoa penetrated (60%) and formed pro-nuclei (33%) in goat oocytes demonstrating the utility of this heterologous system for assessing sperm function in vitro. For fresh spermatozoa, 0 CLC-treated sperm performed better than their CLC+ counterparts for all parameters measured (P<0.05). In contrast, cryopreservation resulted in a sharp decline in sperm-oocyte interaction in 0 CLC aliquots but remained unaltered in CLC+ aliquots demonstrating a protective effect of cholesterol treatment. There was no difference between treatments in the in vitro fertilizing ability of frozen-thawed sperm or in the numbers of embryos retrieved following AI with fresh 0 CLC or CLC+ sperm. We conclude that although CLC treatment of dromedary camel sperm improves sperm motility it fails to confer an advantage to them in terms of improved in vitro sperm-oocyte interaction or in vivo fertilization under the conditions tested.

Modification of membrane cholesterol and its impact on frozen-thawed chicken sperm characteristics

This study was conducted to determine the changes in chicken sperm plasma membranes fluidity and polarity as lipid packing arrangement induced by cholesterol-loaded cyclodextrin (CLC) and 2-hydroxypropyl-β-cyclodextrin (HBCD) and how sperm cryopreservation outcomes are improved by these changes. Treatment with 2 mg HBCD supported the highest (P < 0.01) percentage of viable spermatozoa compared with the control and CLCs groups after cryopreservation. The percentage of post-thaw progressive and rapid sperm motility was highest in 2 mg HBCD (P < 0.01). After thawing, sperm treated with 1 or 2 mg CLC showed the highest anisotropy at 5, 21, 25 and 40°C (P < 0.01). At 25°C, the lowest anisotropy was observed in the thawed semen from the control group. The highest value (P < 0.01) of generalized polarization (GP) (0.5) at 5°C was observed in the 1 mg CLC treated sample. After 2 h of incubation, the highest percentage of viable spermatozoa was observed in the HBCD group in relation to the other treatments (P < 0.01). Exposure to 1 mg or 2 mg of CLC significantly decreased the percentage of live spermatozoa after thawing (P < 0.01). In conclusion, HBCD appears to play a role in the modification of sperm membranes, increasing their fluidity and preventing them against membrane phase transition to gel, thus minimizing freezing-thaw sperm damage. HBCD treatment enhances chicken sperm viability and motility after cryopreservation and subsequent storage. This novel procedure may be useful for improving the technology for cryopreservation of fowl spermatozoa.

Substitution of egg yolk by a cyclodextrin-cholesterol complex allows a reduction of the glycerol concentration into the freezing medium of equine sperm

The aim of this work was to completely replace the egg yolk a classical diluent for freezing equine semen by a cyclodextrin-cholesterol complex. At the same time, the reduction in the glycerol content used for cryopreservation and the incubation time between sperm and the freezing media were evaluated. Horse ejaculates were frozen with four different freezing extenders: a frozen reference medium (IF) containing egg yolk and 2.5% glycerol and media without egg yolk but supplemented with 1.5 mg 2-hydroxypropyl-beta-cyclodextrin cholesterol (HPβCD-C) complex and containing either 1% (G1), 2% (G2) or 3% glycerol (G3). Three incubation times (90, 120 and 180 min) at 4 °C between the fresh semen and the different media were tested before freezing. Viability and motility analyses were performed with computer assisted semen analysis (CASA). Results showed that the freezing media containing the HPβCD-C complex with 1%, 2% and 3% glycerol significantly improve the 3 in vitro parameters of post thawing semen quality (viability, progressive and total mobilities) compared to IF. The best improvement of the parameters was obtained with G1 medium and the longest contact time. The substitution of egg yolk by HPβCD-C complex allows the decrease of protein charge of the medium while favouring the cholesterol supply to membrane spermatozoa offering it a better resistance to osmotic imbalance and a better tolerance to the glycerol toxicity. Our results highlight that the egg yolk of an extender for the freezing of horse semen can be completely substituted by HPβCD-C complex.

Características do sêmen a fresco e descongelado de garanhões da raça Nordestina

RESUMO: Este estudo descreveu as características seminais, da membrana plasmática e do acrossoma de espermatozoide congelado/descongelado de 19 ejaculados de garanhões da raça Nordestina. Os aspectos analisados incluíram os parâmetros físicos do sêmen fresco; a motilidade e a longevidade do sêmen diluído e descongelado; a morfologia espermática, integridade funcional e estrutural da membrana plasmática do espermatozoide e a habilidade de ligação do espermatozoide à membrana perivitelina da gema do ovo de galinha do sêmen descongelado. As variáveis foram avaliadas pela ANOVA com post hoc teste de Student Newman-Keuls (P<0,05). A MT e a MP foram maiores (P<0,05) no sêmen diluído do que no descongelado. A percentagem média de defeitos maiores, menores e totais foi muito inferior ao limite recomendado pelo CBRA. A porcentagem de reativos ao HOST foi de 14,21±1,12% e a porcentagem média de membranas íntegras detectadas pelo teste supravital de 62,22±9,06% e pela sonda SYBR-14 de 81,47±26,90. O número médio de espermatozoides ligados à MPV após a descongelação do sêmen foi de 230,39±57,09. A MT e MP no tempo 0 min do TTR foi superior (P<0,05) em relação a 150 min, não diferindo nos tempos 10 min e 30 min. Os resultados demonstram que a utilização dos testes laboratoriais adicionais ajudam no processo de avaliação das amostras, possibilitando a obtenção de informações mais confiáveis e precisas. Embora a criopreservação tenha provocado queda na motilidade seminal, o uso de diluidor contendo amidas minimizou os danos osmóticos nas células espermáticas e manteve a integridade morfológica, funcional e estrutural da membrana plasmática do espermatozoide. Estes resultados são um referencial em estudos futuros uma vez que, inexistem dados comparativos nesta raça.

Heat shock protein A8 stabilizes the bull sperm plasma membrane during cryopreservation: Effects of breed, protein concentration, and mode of use

Heat shock protein A8 (HSPA8) is a highly conserved member of the Hsp70 family, which is expressed in oviductal cells, translocated into oviductal fluid, and becomes attached to the sperm surface during sperm transport. Previous research has shown that HSPA8 supports mammalian sperm viability during in vitro incubation at both 5 °C and body temperature. The present series of experiments was designed to explore the possibility that bovine recombinant HSPA8 might therefore protect bull spermatozoa during cryopreservation through its beneficial effects on the sperm plasma membrane. Soy-based cryopreservation media were used in these experiments. The effects of HSPA8 addition before freezing were examined at concentrations ranging from 0.2 to 6.4 μg/mL, whereas the effects of postthaw HSPA8 addition were tested between 0.2 and 12.8 μg/mL. When bull spermatozoa (from beef and dairy breeds) were frozen in the presence of HSPA8, beneficial but complex effects on postthaw viability were observed. Low HSPA8 concentrations (0.2 and 0.4 μg/mL) resulted in significantly reduced postthaw sperm viability, but concentrations above 0.8 μg/mL improved plasma membrane integrity. If HSPA8 was added to spermatozoa after thawing, outcomes were also biphasic and beneficial effects on viability were only seen if the HSPA8 concentration exceeded 3.2 μg/mL. Beneficial effects were significantly more apparent with beef rather than dairy breeds. When HSPA8 was used in combination with cholesterol-loaded cyclodextrin, spermatozoa from the beef breeds showed significantly lower apoptotic effects. This was not observed with the dairy breeds.

Effect of cholesterol-loaded cyclodextrin on cryosurvival and fertility of cryopreserved carp (Cyprinus carpio) sperm

Addition of cholesterol-loaded cyclodextrin (CLC) to the diluents of mammalian semen increased stability and rigidity of phospholipid hydrocarbon chains of plasma membrane during sperm cryopreservation process. CLC has been tested successfully as cryoprotectant in various livestock sperm cryopreservation protocols but its efficacy for cryopreserving of fish sperm has not previously been tested. In the present study, different cholesterol loaded cyclodextrin concentrations were evaluated for the cryopreservation of carp (Cyprinus carpio) sperm. Sexually mature fish were induced to spermiation and ovulation with Ovopel. The extenders were prepared by using 300 mM glucose and 10% DMSO supplemented with different concentrations of CLC (0.5, 1.0, 1.5, 2.0, 2.5, and 3.0mg per 120×10(6) spermatozoa) and without CLC (control). The pooled semen was diluted separately at a ratio of 1:3 (v/v) by using CLC extenders. Diluted semen placed into 0.25 ml straws were equilibrated at 4°C for 15 min and frozen in liquid nitrogen vapor. Fertilization was conducted using a ratio of 1×10(5) spermatozoa/egg. Fresh sperm with no treatment showed the greatest sperm motility, duration of motility, viability, and fertilization results compared to the other tested cryopreserved and control groups (p<0.05). Supplementation of 1.5 mg CLC to the extender showed the best cryoprotective effect for sperm motility, duration of motility, and viability against freezing damage in comparison to extenders containing 2.5 mg, 3.0 mg CLC, and control group (p<0.05). Cryopreserved sperm containing 1.5 mg CLC provided greater result in term of fertilization success when compared to other extenders containing 0.5, 2.5, and 3.0 mg CLC or control (p<0.05). The amount of CLC effected post-thaw sperm quality and fertility as a dose-dependent manner. It is concluded that treatment of cholesterol-loaded cyclodextrin for carp sperm cryopreservation significantly improves cell cryosurvival and fertilization.

Membrane modification strategies for cryopreservation

Cell membranes can be modified using cyclodextrins loaded with lipids or unilamellar liposomes. Lipid choice can greatly influence the organization of the targeted membrane and result in a cell that is more capable of surviving cryopreservation due to altered membrane-phase transition properties or membrane reorganization that may alter the normal physiologic processes of the treated cell. The protocols described here explain the preparation of the cyclodextrins and liposomes, impact of the amount and type of lipids, and general principles for treating cells using either of these technologies.

Use of cholesterol-loaded cyclodextrin in donkey semen cryopreservation improves sperm viability but results in low fertility in mares

The use of cholesterol-loaded cyclodextrin (CLC) on semen cryopreservation has been related with better sperm viability in several species; however, the effect on fertility is not known in donkey semen. Ejaculates (n = 25) from five donkeys were diluted in S-MEDIUM with 0, 1, 2 or 3 mg of CLC/120 × 10(6) spermatozoa. Semen was frozen, and thawed samples were evaluated by computer-assisted sperm analyser system (CASA), supravital test, hyposmotic swelling test and fluorescent dyes to assess the integrity of sperm membranes. Mares (n = 60) were inseminated with frozen-thawed semen treated with the doses of 0 or 1 mg CLC. Percentages of sperm with progressive motility and with functional plasma membrane were greater (p < 0.05) in the CLC-treated groups than in the control. Percentages of intact plasma membrane and intact plasma membrane and acrosome detected by fluorescent dyes were also greater (p < 0.05) in CLC-treated groups. Although no difference (p > 0.05) in conception rates was detected between groups (control, 3/30, 10%; CLC-treated, 1/30, 3.3%), fertility was low for artificial insemination programs in mares. Therefore, we firstly demonstrated that frozen semen treated with CLC in S-MEDIA extender before freezing improves the in vitro sperm viability, but semen treated or not with CLC in S-MEDIUM extender results in a very low conception rate in mares inseminated with thawed donkey semen.

Spermatozoa from the maned wolf (Chrysocyon brachyurus) display typical canid hyper-sensitivity to osmotic and freezing-induced injury, but respond favorably to dimethyl sulfoxide

We assessed the influences of medium osmolality, cryoprotectant and cooling and warming rate on maned wolf (Chrysocyon brachyurus) spermatozoa. Ejaculates were exposed to Ham's F10 medium (isotonic control) or to this medium plus NaCl (350-1000mOsm), sucrose (369 and 479mOsm), 1M glycerol (1086mOsm) or dimethyl sulfoxide (Me2SO, 1151mOsm) for 10 min. Each sample then was diluted back into Ham's medium and assessed for sperm motility and plasma membrane integrity. Although glycerol and Me2SO had no influence (P>0.05), NaCl and sucrose solutions affected sperm motility (P<0.05), but not membrane integrity. Motility of sperm exposed to <600mOsm NaCl or sucrose was less (P<0.05) than fresh ejaculate, but comparable (P>0.05) to the control. As osmolality of the NaCl solution increased, motility decreased to <5%. In a separate study, ejaculates were diluted in Test Yolk Buffer containing 1M glycerol or Me2SO and cooled from 5°C to -120°C at -57.8°C, -124.2°C or -67.0°C/min, frozen in LN2, thawed in a water bath for 30s at 37°C or 10s at 50°C, and then assessed for motility, plasma- and acrosomal membrane integrity. Cryopreservation markedly (P<0.05) reduced sperm motility by 70% compared to fresh samples. Higher (P<0.05) post-thaw motility (20.0±1.9% versus 13.5±2.1%) and membrane integrity (51.2±1.7% versus 41.5±2.2%) were observed in samples cryopreserved in Me2SO than in glycerol. Cooling rates influenced survival of sperm cryopreserved in glycerol with -57.8°C/min being advantageous (P<0.05). The findings demonstrate that although maned wolf spermatozoa are similar to domestic dog sperm in their sensitivity to osmotic-induced motility damage, the plasma membranes tolerate dehydration, and the cells respond favorably to Me2SO as a cryoprotectant.

Epididymosomes, prostasomes, and liposomes: their roles in mammalian male reproductive physiology

Mammalian spermatozoa are unique cells in many ways, and the acquisition of their main function, i.e. fertilization capacity, is a multistep process starting in the male gonad and ending near the female egg for the few cells reaching this point. Owing to the unique character of this cell, the molecular pathways necessary to achieve its maturation also show some specific characteristics. One of the most striking specificities of the spermatozoon is that its DNA is highly compacted after the replacement of histones by protamines, making the classical processes of transcription and translation impossible. The sperm cells are thus totally dependent on their extracellular environment for their protection against oxidative stress, for example, or for the molecular changes occurring during the transit of the epididymis; the first organ in which post-testicular maturation takes place. The molecular mechanisms underlying sperm maturation are still largely unknown, but it has been shown in the past three decades that extracellular vesicles secreted by the male reproductive tract are involved in this process. This review will examine the roles played by two types of naturally occurring extracellular vesicles, epididymosomes and prostasomes, secreted by the epididymis and the prostate respectively. We will also describe how the use of artificial vesicles, liposomes, contributed to the study of male reproductive physiology.

Pretreatment of Asian elephant (Elephas maximus) spermatozoa with cholesterol-loaded cyclodextrins and glycerol addition at 4°C improves cryosurvival

Asian elephant spermatozoa are sensitive to chilling and do not respond well to cryopreservation. The objectives of the present study were to: (1) determine whether cholesterol content can be modified by preincubation of Asian elephant spermatozoa with cholesterol-loaded cyclodextrin (CLC); and (2) assess the effects of CLC concentration(s), temperature at time of glycerol addition (22°C vs 4°C) and dilution medium on post-thaw sperm survival. Spermatozoa incubated with ≥1.5 mg CLC exhibited increased (P < 0.05) cholesterol concentrations. Pretreatment of spermatozoa with 1.5 mg CLC resulted in improvements (P < 0.05) in all post-thaw parameters. Glycerol addition at 4°C also improved all post-thaw parameters compared with 22°C. Dilution of thawed spermatozoa in an egg yolk-based medium improved (P < 0.05) motility compared with Ham's F-10 culture medium. In summary, our findings indicate that modifying cholesterol content within the plasma membrane improves the cryosurvival of Asian elephant spermatozoa. The development of an improved cryopreservation method that includes modification of membrane cholesterol and the addition of glycerol at 4°C, as reported in the present study, is an important step towards utilisation of cryopreserved spermatozoa in captive management of this species.

Sperm surface changes and physiological consequences induced by sperm handling and storage

Spermatozoa interact with their immediate environment and this contact remodels the sperm surface in preparation for fertilisation. These fundamental membrane changes will be critically covered in this review with special emphasis on the very specific surface destabilisation event, capacitation. This process involves very subtle and intricate modifications of the sperm membrane including removal of suppression (decapacitation) factors and changes in the lateral organisation of the proteins and lipids of the sperm surface. Processing of sperm for assisted reproduction (storage, sex-sorting, etc.) subjects spermatozoa to numerous stressors, and it is possible that this processing overrides such delicate processes resulting in sperm instability and cell damage. To improve sperm quality, novel mechanisms must be used to stabilise the sperm surface during handling. In this review, different types of membrane stress are considered, as well as novel surface manipulation methods to improve sperm stability.