Novel technical strategies to optimize cryopreservation of goat semen using cholesterol-loaded cyclodextrin

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.

Soybean lecithin and cholesterol-loaded cyclodextrin in combination to enhances the cryosurvival of dairy goat semen

The objective of the study was to examine the effect of soy lecithin (SL) and cholesterol loaded cryclodestrin (CLC) on cryo-survival of sperm cryopreserved in the presence or absence of seminal plasma in Saanen dairy goats. Tris-based dilutions containing various concentrations of SL (0, 0.5%, 1.0% or 2.0%) and CLC (0, 2.0 g/L, 4.0 g/L or 6.0 g/L CLC) were used to cryopreserve Saanen dairy goat sperm. The quality of frozen-thawed sperm, including progressive motility, viability, acrosome and plasma membrane integrity, as well as fertility were detected. Results found that the optimal combination of the two cryoprotectants was 1.0% SL+4.0 g/L CLC, which significantly increased progressive motility, viability, acrosome and plasma membrane integrity of frozen thawed sperm. The impact of the two cryoprotectants in combination was not affected by the presence of seminal plasma. The conception rates obtained after artificial insemination using sperm cryopreserved with and without seminal plasma were 88.89% and 91.67% (P > 0.05), respectively. The respective values for average number of litter sizes were 1.55 ± 0.17 and 1.56 ± 0.21 (P > 0.05). Therefore, this study improved the cryopreservation efficiency of goat semen, enhanced the sperm cryosurvival, and layed a foundation for the wide application of frozen goat semen.

Oligomeric Proanthocyanidins and Bamboo Leaf Flavonoids Improve the Quality of Bull Semen Cryopreservation

It is important to inhibit oxidative stress to maintain sperm motility during cryopreservation. The present study was performed to investigate the effects of supplementing oligomeric proanthocyanidins (OPC) and bamboo leaf flavonoids (BLF) or their combination as an extender for Simmental bull semen freezing. OPC, BLF, or their combination were added to the frozen diluent of bovine semen. Afterwards, computer-assisted semen analysis (CASA), detection of membrane functionality, acrosome integrity, mitochondrial integrity, CAT, SOD, GSH-PX, MDA, and ROS were conducted. The results showed that adding 50 mg/L OPC or 4 mg/L BLF could improve the quality of frozen sperm. Compared with 50 mg/L OPC alone, the combination of 50mg/L OPC and 2 mg/L BLF significantly increased the kinematic parameters of sperm, and sperm CAT, GSH-PX and SOD levels (p < 0.05), whereas the MDA of sperm was decreased (p < 0.05). These results indicated that compared to the addition of 50 mg/L OPC alone, a combination of 50 mg/L OPC and 2 mg/L BLF could further improve the quality of frozen semen. The results could provide theoretical data support for the development of a new protective agent and are significant for the cryopreservation of bovine semen in the future.

Exogenous cholesterol modulates oxidative stress and freezability of mithun spermatozoa

Effect of cholesterol loaded cyclodextrin (CLC) on improvement of semen quality parameters (SQPs) and deduction of oxidative stresses following cryopreservation in mithun was explored. Total 50 ejaculates were selected out of 105 collected based on preliminary SQPs. Sperm was treated with 1 mg (Gr II) and 2 mg (Gr III) of CLC/ 120×106 spermatozoa and without CLC served as control (Gr I). Diluted semen samples were cryopreserved at ultralow temperature. Frozen thawed samples were evaluated for motility (progressive forward [FPM]; in bovine cervical mucus penetration test [BCMPT] and in computer assisted sperm analyzer [CASA]), viability, total sperm and nuclear abnormality, intactness of plasma membrane and acrosome, intracellular enzymatic leakage and oxidative profile (Malondialdehyde; MDA). Result revealed a significant improvement in motility (FPM, BCMPT and CASA), viability, acrosomal integrity, cholesterol content and reduction of sperm and nuclear abnormalities, leakage of intracellular enzymes and oxidative stressors in 1 mg CLC treated group as compared to control. Moreover, intactness of acrosome and biochemical membrane was protected significantly in extender containing 1 mg CLC. Hence inclusion of mithun spermatozoa with CLC (1 mg/120×106) prior to freezing improved the survivability in cryopreservation. The results clearly indicated the beneficial effects of CLC supplementation on freezability by reducing cryodamage and protecting the spermatozoa integrity.

Possible mechanisms of cholesterol-loaded cyclodextrin action on sperm during cryopreservation

Artificial insemination (AI) with cryopreserved semen has a pivotal role in wider dissemination of germplasm of elite livestock and also for conservation of various endangered species. Cryopreservation allows storage of semen for a prolonged period of time and facilitates greater exchange of genetic material among distant populations. Cryopreservation, however, leads to certain deleterious effects on sperm including premature induction of the acrosome reaction, reduced sperm motility and viability, and impaired sperm DNA integrity and fertility. During cooling procedures, membrane phase transitions take place, which result in micro-domain formation from aggregation of lipids, leading to impaired functions of the sperm membrane, and gap formation between gel and fluid domains. Cyclodextrins are produced by enzymatic degradation of starch and possess a unique feature, that when added alone to sperm cyclodextrins facilitate the removal of cholesterol from the membrane. When preloaded with cholesterol, however, cyclodextrins stimulate the insertion of cholesterol into the sperm membrane due to presence of a hydrophobic core in addition to an outer hydrophilic face. Treating sperm of various species with cholesterol-loaded cyclodextrin improves the quality of sperm during cryopreservation. It is still not clearly known how cholesterol-loaded cyclodextrin functions at sperm cells to enhance the survival during cryopreservation. The present review, therefore, highlights possible mechanisms of cholesterol-loaded cyclodextrin action on sperm during cryopreservation.

Deep insemination with sex-sorted Cashmere goat sperm processed in the presence of antioxidants

Flow cytometrically sex-sorted sperm have been widely used for improving reproductive management in the dairy industry. However, the industrial application of this technology in other domestic species is largely limited by the lower fertility after insemination. The aim of this study was to investigate effects of antioxidant supplementation during the sex-sorting and freezing process on the quality and functions of sorted sperm from Liaoning Cashmere goats. We tested the effects of antioxidant supplementation during sex-sorting and freezing process, including ascorbic acid-2-glucoside AA-2G, glutathione, melatonin and vitamin C (VC), on the quality and functions of sex-sorted fresh and frozen-thawed sperm. Based on these experiments, we performed deep insemination with sex-sorted sperm using our improved strategy, in comparison to unsorted sperm. In Experiment 1, compared with control group and other antioxidants, AA-2G supplementation significantly alleviated the degradation of motility and viability of fresh sperm after sorting and showed the highest percentage of sperm with normal morphology. In addition, AA-2G supplementation showed an evident protection against the sorting process-induced membrane and acrosome damage. In Experiment 2, AA-2G supplementation was most effective in protecting motility, while melatonin supplementation appears to facilitate the degradation of quality of frozen-thawed sex-sorted sperm. In Experiment 3, we performed deep insemination with sperm that were sorted and frozen in the presence of AA-2G and obtained a satisfying pregnancy rate comparable to that from unsorted sperm. The results showed that AA-2G supplementation efficiently protects quality and function of both fresh and frozen-thawed sex-sorted sperm of Cashmere goats, thus obtaining a satisfying pregnancy outcome.