The cryoprotective effect of low-density lipoproteins in extenders on bull spermatozoa following freezing–thawing

Evaluation of Chicken Egg Yolk Plasma and Low-Density Lipoprotein Alone or Enriched with Ewe or Cow Skim Milk in Tris-Citric Acid-Based Diluent for Cryostorage of Ram Semen

The main purpose of the current study was to find suitable and optimum levels of protectants among chicken egg yolk plasma (CEYP) and low-density lipoproteins (LDLs), alone or supplemented with ewe or cow skim milk, for cryopreservation of ram semen. In Experiments 1 and 2, the CEYP (28%) freezing extender was enriched with ewe or cow milk (2.5%, 5%, 10%, or 20%; v/v), respectively. In Experiments 3 and 4, the semen extender was prepared by varying the amounts of fresh or lyophilized LDL (lyo-LDL), respectively. Finally, ewe or cow skim milk was added to the freshly extracted LDL extender and the quality of frozen-thawed semen was examined (Experiments 5 and 6). Kinematics of spermatozoa (assessed using a computer-assisted sperm analysis system), viability, functionality of the plasma membrane, and levels of malondialdehyde (MDA) and total antioxidant capacity (TAC) were evaluated. Results revealed that addition of ewe or cow skim milk (5%, 10%, or 20%; v/v) to the CEYP diluent enhanced kinematics, viability, and membrane integrity of spermatozoa compared with the control (p < 0.05). Moreover, fresh LDL diluent was more effective than lyo-LDL in the cryosurvival of ram spermatozoa. In addition, enrichment of fresh LDL diluent with ewe or cow skim milk improved different variables of spermatozoa compared with the control (p < 0.05). Levels of MDA and TAC were not affected by adding ewe or cow milk to the diluents (p > 0.05). In conclusion, enrichment of fresh LDL extenders with ewe or cow milk also is proposed as an approach to preserve ram semen quality against cold shock and cryodamage injuries.

Post-thaw quality of ram sperm frozen with different concentrations of low-density lipoproteins associated with non-enzymatic antioxidants

The cryopreservation reduces ram sperm quality, decreasing the pregnancy rate of ewes inseminated with thawed sperm. Hence, we aimed to improve the post-thaw quality of ram sperm replacing egg yolk on Tris-Glucose extender with different concentrations of LDL (2 or 8%), associated with the addition of 10 mM non-enzymatic antioxidants (ascorbic acid, hydroxytoluene butylate, ascorbyl palmitate, and trehalose). Semen samples were collected from six rams, split into different treatments, and frozen. After thawing, kinematic (CASA), structural (propidium iodide and carboxyfluorescein diacetate) and functional (hypoosmotic test) sperm membrane integrity was assessed. Total motility, VCL, and LIN were also assessed in thawed samples during 3 h of incubation (38 °C). The results showed that hydroxytoluene butylate at 10 mM in Tris-Glucose extender with 8% LDL improved velocity parameters immediately post-thaw compared with Tris-Glucose egg yolk extender, as well as prevented the reduction of total motility and VCL after incubation. There was no benefit of adding ascorbic acid and trehalose. Moreover, for the first time, it was shown the motility impairment promoted by ascorbyl palmitate to ram sperm.

Gamma-oryzanol supplemented in extender enhances the quality of semen cryopreservation and alters proteomic profile in Thai swamp buffalo

Reactive oxygen species (ROS) exert an adverse effect on sperm quality during the freezing process. Gamma-oryzanol is an effective antioxidant and has the ability to inhibit lipoperoxidation in various cells. Therefore, this study aims to investigate the effect of gamma-oryzanol supplementation in extender on post-thawed motility and proteomic profiles of swamp buffalo spermatozoa. Each ejaculate of an individual bull was divided into four equal aliquots. Gamma-oryzanol was supplemented at 0 (control), 0.1, 0.25, and 0.5 mM in tris-citrate egg yolk extender. The parameters of sperm motility were evaluated using computer assisted semen analyzer (CASA). The results showed that the progressive motility was significantly higher in 0.5 mM of gamma-oryzanol supplementation group when compared with the control group (p < 0.05), but no significant differences were observed among the treatments. In addition, a proteomic approach was applied to analyze the differentially expressed proteins in post-thawed sperm with or without gamma-oryzanol supplementation in extender. We confirmed that 2-phospho-d-glycerate hydro-lyase (ENO1), glutathione s-transferase mu 1 (GSTM1), phospholipid hydroperoxide glutathione peroxidase (GPX4), outer dense fiber protein 2 (ODF2), tektin-4 (TEKT4), tubulin beta-4B chain (TUBB4B), and ATP synthase subunit beta (ATP5B) were up-regulated in 0.5 mM of gamma-oryzanol supplementation group, which might be associated with the improved post-thawed motility observed in this treatment group. These results demonstrate the beneficial effect of gamma-oryzanol on post-thawed survival of swamp buffalo spermatozoa and help advance the understanding about molecular metabolism of sperm in this species.

Low concentrations of 3-O-methylglucose improve post thaw recovery in cryopreserved bovine spermatozoa

A number of studies have explored the use of membrane permeable (usually metabolizable) and membrane impermeable saccharides to protect cells in general, and sperm in particular during cryopreservation. Critical concentrations for protective levels of sugars frequently range between 50 mmol/L and 500 mmol/L, where efficacy is attributed to the sugar's membrane stabilizing and glass forming attributes and colligative effects that reduce intra- and extracellular salt concentrations during freezing. Many studies on bull sperm have demonstrated that both permeating and non-permeating sugars have negligible positive effects on post-thaw viability. Recently, however, a non-metabolizable sugar, 3-O-Methylglucose (3-OMG), was shown to protect hepatocytes during liver cryopreservation at 0.1-0.3 mol/L. Because glucose is readily transported into sperm, we hypothesized that 3-OMG could be a new class of cryoprotectant to explore in bull sperm. Here we present positive results demonstrating that 3-OMG improves post thaw viability in bull sperm, and that this effect is not likely due to improved glass forming capabilities. In particular, in experiment 1, 3-OMG was added to the Tris-egg yolk-glycerol base media at levels from 0 mmol/L to 200 mmol/L. Semen from four bulls was collected and diluted with one of the cryopreservation media, cooled, and frozen following industry standard practices. Motility and mitochondrial activity were negatively impacted when concentration of 3-OMG was more than 25 mmol/L. Therefore, we explored lower concentrations in experiment 2, where semen from eight bulls was used to evaluate concentrations 5 mmol/L, 15 mmol/L and 25 mmol/L of 3-OMG compared with control. Motility and progressive motility in 5 mmol/L 3-OMG and in the control were significantly higher than 15 mmol/L and 25 mmol/L 3-OMG, whereas mitochondrial activity and acrosome integrity in 5 mmol/L 3-OMG were significantly better than the control freezing medium. In experiment 3, to evaluate whether the improved effects of 3-OMG are due to its non-metabolizing property, or due to colligative effects, we compared post-thaw viability in semen from four bulls cryopreserved with 5 mmol/L glucose, sucrose, or 3-OMG. Motility and progressive motility was significantly improved in 3-OMG compared to glucose or sucrose groups which were comparable to the EY control. In conclusion, 3-OMG at a concentration of 5 mmol/L in Tris-egg yolk-glycerol medium improves the post thaw motility, progressive motility and viability of bull sperm. The mechanism of action is not understood but because the efficacy is maximal at low concentrations, it is not likely due to improved intra- or extracellular glass forming abilities and may demonstrate a different protective mechanism than was shown in hepatocytes.

Low Density Lipoprotein - important player in increasing cryoprotective efficiency of soybean lecithin-based bull semen extenders

Currently, considering cryopreservation of bull semen, there is no clear consensus over the comparability of cryoprotective efficacy of extenders with soybean lecithin and those based on egg yolk. The objective of this study was to prove the use of Low Density Lipoprotein (LDL) extracted from hen-egg yolk as an enhancing factor for soybean lecithin-based extenders. In total, 35 ejaculates of (seven bulls x five ejaculates per bull) were collected and cryopreserved at a commercial insemination centre. The effect of the LDL addition to the extenders AndroMed^® and Bioxcell^® was tested in a 6% (v/v) concentration on spermatozoa after thawing. Modified extender composition effects were assessed on sperm functional parameters motility, plasma membrane, mitochondrial membrane potential and acrosomal integrity after thawing by CASA, flow cytometry and fluorescent microscopy, respectively. Based on kinematic parameters determined from CASA, k-means cluster analysis was used to classify individual spermatozoon into specific subpopulations (fast, medium fast and slow). A subpopulation of fast spermatozoa was increased in the presence of LDL in both selected extenders (P < 0.05). Moreover, the positive effect of LDL on sperm motility was confirmed by decreasing the percentage of sperm in slow subpopulation (P < 0.05). The effect of LDL addition on the incidence of spermatozoa with intact plasma membrane was not demonstrated in any case of extender used (P > 0.05). The percentage of sperm with intact acrosome was improved when LDL was added to Bioxcell^® extender (P < 0.05). On the other hand, addition of LDL to AndroMed^® extender improved mitochondrial intactness after thawing (P < 0.05). In conclusion, our results showed that adding LDL to selected soybean lecithin-based extenders considerably ameliorated the functional parameters of spermatozoa after thawing and thus this lipoprotein could represent an improving agent for soybean lecithin-based extender for bull semen cryopreservation.

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.

Cryopreservation and egg yolk medium alter the proteome of ram spermatozoa

Cryopreservation causes significant lethal and sub-lethal damage to spermatozoa. In order to improve freezing outcomes, a comprehensive understanding of sub-lethal damage is required. Cryopreservation induced changes to sperm proteins have been investigated in several species, but few have employed currently available state of the art, data independent acquisition mass spectrometry (MS) methods. We used the SWATH LC-MS method to quantitatively profile proteomic changes to ram spermatozoa following exposure to egg yolk and cryopreservation. Egg yolk contributed 15 proteins to spermatozoa, including vitellogenins, apolipoproteins and complement component C3. Cryopreservation significantly altered the abundance of 51 proteins. Overall, 27 proteins increased (e.g. SERPINB1, FER) and 24 proteins decreased (e.g. CCT subunits, CSNK1G2, TOM1L1) in frozen thawed ram spermatozoa, compared to fresh spermatozoa. Chaperones constituted 20% of the proteins lost from spermatozoa following cryopreservation. These alterations may interfere with both normal cellular functioning and the ability of frozen thawed spermatozoa to appropriately respond to stress. This is the first study to apply SWATH mass spectrometry techniques to characterise proteins contributed by egg yolk based freezing media and to profile cryopreservation induced proteomic changes to ram spermatozoa.

SIGNIFICANCE

This study profiles changes to the sperm proteome induced by exposure to egg yolk based media and the process of cryopreservation, and the biological consequences are discussed.

Influence of selected factors on bovine spermatozoa cold shock resistance

The objectives of this study were to determine the effects of sire, extender, and addition of Low Density Lipoprotein (LDL) to extenders used on the percentage rate of spermatozoa survival after cold shock. Two groups of extenders were compared: without LDL addition (control variants) and LDL enriched (experimental variants). Three extenders were used: AndroMed®, Bioxcell®, and Triladyl®. Experimental variants included 4–8% LDL addition into the AndroMed® and Bioxcell® extenders, and 6–10% LDL addition into the Triladyl® extender. In total, 12 samples of fresh semen were collected from 4 bulls during a period of 8 weeks. Bovine spermatozoa cold shock resistance (1 ± 1 °C, 10 min) was evaluated by the percentage rate of live sperm using eosin-nigrosine staining immediately and after heat incubation (37 ± 1 °C, 120 min). The results showed the effect of sire as important and individual differences between selected sires in their sperm resistance against cold shock were confirmed. AndroMed® and Bioxcell® were found to be providing better protection of bull semen to cold shock compared to Triladyl® due to lower decline of live sperm proportion. Our results detected a positive effect of LDL addition on sperm resistance against cold shock, especially on lower decrease of live sperm percentage rate after 120 min of the heat test (P < 0.05). Further studies are needed to assess the optimal concentration of LDL in various kinds of extenders as well to state ideal time and temperature conditions for ensuring LDL reaction with sperm.

Cryopreservation of rabbit semen using non-permeable cryoprotectants: effectiveness of different concentrations of low-density lipoproteins (LDL) from egg yolk versus egg yolk or sucrose

This study was designed to identify the most effective non-permeable cryoprotectant (CPA) for the cryopreservation of rabbit semen by comparing the effects of different concentrations of low-density lipoproteins (LDL) on post-thaw sperm quality with those of whole egg yolk or sucrose. In a second experiment, the performance of the non-permeable CPAs identified as most effective was assessed in vivo by determining reproductive performances. Pooled semen samples were diluted to a ratio of 1:1 (v:v) in freezing extender (Tris-citrate-glucose and 16% dimethylsulfoxide as permeable CPA) containing as non-permeable CPAs 6, 8, 10 or 15% LDL from egg yolk, 0.1M sucrose, or 15% egg yolk. The semen was loaded in 0.25mL straws and frozen in liquid nitrogen vapor. After thawing, we determined sperm motility, viability, osmotic resistance, and acrosome and DNA integrity. Our results clearly revealed a significant effect of LDL concentration on semen quality. Also, at an optimal concentration of 10%, motility and acrosome integrity were improved over the values recorded for egg yolk (P<0.05). Based on the in vitro data, 3 groups of does (n=30 each) were inseminated with fresh semen or semen frozen using sucrose or 10% LDL. Sucrose led to a significantly higher conception rate than LDL and reproductive performance was similar to that observed for fresh semen. Our findings indicate the markedly better performance of sucrose in vivo as a non-permeable CPA for the cryopreservation of rabbit semen.

Cryoprotection effectiveness of low concentrations of natural and lyophilized LDL (low density lipoproteins) on canine spermatozoa

The aim of this study was to evaluate the use of low concentrations of natural and lyophilized low density lipoprotein (LDL) from hen's egg yolk for cryopreservation of canine semen. Different ammonium sulphate concentrations were tested to extract LDL from egg yolk. The yolk was centrifuged, and LDL was isolated using 10, 20, 40, 45, or 50% ammonium sulphate solution (ASS). The LDL-rich floating fraction was collected for chemical characterization. Dry matter content was lowest (P<0.05) in the LDL extracted with the 50% ASS. The purification of LDL increased in association with increasing ammonium sulphate concentrations. SDS-PAGE showed that the 50% ASS solution yielded a purer fraction of LDL from egg yolk. For semen cryopreservation, TRIS extender was used replacing 20% egg yolk (control) by natural or lyophilized LDL using 1, 2, and 3% (w/v). Semen was centrifuged (755Xg for 7 min), diluted with one of the extenders, packed into 0.5mL straws (100x106 sperm/mL), and placed in a programmable cryopreservation machine. Thawed semen (37°C/ 30s) was analyzed for sperm motility, morphology, and by the hypoosmotic and epifluorescence tests (CFDA/ PI). Natural LDL extracted with 50% ASS was as effective as whole egg yolk to preserve canine frozen sperm when using low concentrations. The lyophilized LDL, mainly in the two higher concentrations tested (2 and 3%), was unsuitable to maintain the effectiveness of the LDL cryoprotective effect on dog sperm.

Cryoprotective effects of low-density lipoproteins, trehalose and soybean lecithin on murine spermatogonial stem cells

Spermatogonial stem cells (SSCs) have the ability to self-renew and offer a pathway for genetic engineering of the male germ line. Cryopreservation of SSCs has potential value for the treatment of male infertility, spermatogonial transplantation, and so on. In order to investigate the cryopreservation effects of different cryoprotectants on murine SSCs, 0.2 M of low-density lipoproteins (LDL), trehalose and soybean lecithin were added to the cryoprotective medium, respectively, and the murine SSCs were frozen at -80°C or -196°C. The results indicated that the optimal recovery rates of murine SSCs in the cryoprotective medium supplemented with LDL, trehalose and soybean lecithin were 92.53, 76.35 and 75.48% at -80°C, respectively. Compared with freezing at -196°C, the optimum temperature for improvement of recovery rates of frozen murine SSCs, cryopreservation in three different cryoprotectants at -80°C, were 17.11, 6.68 and 10.44% respectively. The recovery rates of murine SSCs in the cryoprotective medium supplemented with 0.2 M LDL were significantly higher than that of other cryoprotectants (P < 0.05). Moreover, the recovery rates were demonstrated to be greater at -80°C compared with at -196°C (P < 0.05). In conclusion, 0.2 M of LDL could significantly protect murine SSCs at -80°C. In the freezing-thawing process, LDL is responsible for the cryopreservation of murine SSCs because it can form a protective film at the surface of membranes. However, more research is needed to evaluate and understand the precise role of LDL during the freezing-thawing of SSCs.

Effects of low-density lipoproteins extracted from different avian yolks on boar spermatozoa quality following freezing–thawing

Low-density lipoproteins (LDL) is known to protect boar sperm during freezing–thawing, but little information is known about the effects of LDL extracted from different avian egg yolks on post-thaw boar semen quality. The purpose of this study was to compare and analyze the effects of LDL at various concentrations and different species on boar sperm quality after freezing–thawing. LDL extracted from the yolk of hen egg, duck egg, quail egg, pigeon egg or ostrich egg was added to the extender at the concentrations of 0.06, 0.07, 0.08, 0.09 and 0.1 g/ml, respectively, and their effects on frozen–thawed boar sperm quality were assessed. According to all measured parameters, the results showed that sperm motility, acrosome integrity and plasma membrane integrity were 43.20%, 52.57% and 48.13%, respectively, after being frozen–thawed with 0.09 g/ml LDL extracted from pigeon egg yolk. All these quality parameters were higher than that of other groups (P < 0.05). In conclusion, our results confirmed that LDL extracted from pigeon egg yolk had the best cryoprotective effects on frozen–thawed boar sperm among all of the groups supplemented with LDL from five kinds of avian egg in extender. The optimum concentration of LDL extracted from pigeon egg in boar semen freezing extender was 0.09 g/ml.

The role of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in comparison with whole egg yolk for sperm cryopreservation in rhesus monkeys

Low-density lipoprotein (LDL) extracted from hen egg yolk has recently been considered to be superior to whole egg yolk in sperm cryopreservation of various animal species. Meanwhile, there was a notion that high-density lipoprotein (HDL) in egg yolk may have a negative effect on post-thaw survival. The role of LDL and HDL in sperm cryopreservation of rhesus monkeys has not been explored. The present study evaluates their effect in comparison with egg yolk with or without the addition of permeable cryoprotectant (glycerol) on sperm cryopreservation of rhesus macaques. In addition, various additives intended to change the lipid composition of LDL-sperm membrane complex have also been tested for their effectiveness in preserving post-thaw viability. Our findings indicated that LDL is the main component in egg yolk that is responsible for its protective role for sperm cryopreservation in rhesus monkeys. Regardless of the presence or absence of glycerol, the protective role of LDL is similar to that of egg yolk and we did not observe any superiority in post-thaw survival with LDL when compared to egg yolk. Modifying the lipid composition of LDL-sperm membrane complex with the addition of cholesterol, cholesterol loaded cyclodextrin and phosphatidylcholine also did not yield any improvements in post-thaw survival; while addition of methyl-β-cyclodextrin reduced post-thaw motility. HDL plays a neutral role in sperm cryopreservation of rhesus monkeys. The present study suggests that egg yolk may still hold advantages when compared with LDL as effective components in extenders for sperm cryopreservation in rhesus monkeys.