Low-Density Lipoprotein Fraction from Hen’s Egg Yolk Decreases the Binding of the Major Proteins of Bovine Seminal Plasma to Sperm and Prevents Lipid Efflux from the Sperm Membrane1

T, Rossi R. Reproductive biology of Pêga Jackasses: characteristics of sperm-rich fraction collected using the split-ejaculate method

ABSTRACT The aim of this study was to evaluate the physical and morphological characteristics of the sperm-rich fraction of jackass semen. To this end, 130 ejaculates from five Pêga jackasses were collected using an open model artificial vagina. The sperm-rich fraction was collected using the split-ejaculate method and assessed for the number of mounts/ejaculate, for physical and morphological characteristics of the semen and number of doses produced/ejaculate. It was observed that all characteristics evaluated differed among the five jackasses, except for the head defect rates. The mean values obtained for the jackass sperm-rich fraction collected were: number of mounts/ejaculate - 1.27; semen volume - 20.21mL; motility - 84.53%; vigor - 4.46; motility after dilution - 80.10%; sperm concentration/mL - 894.38 x 106; total sperm/ejaculate - 16.14 x 109; number of insemination doses/ejaculate (400x106 motile sptz) - 33.39; number of insemination doses/ejaculate (800 x 106 motile sptz) - 16.69; and percentage of normal sperm - 90.46%. Thus, in the present experiment the split-ejaculate method using an open artificial vagina worked well with the jackasses, and the sperm-rich fraction of the ejaculate of Pêga jackasses had high quality and sperm concentration, allowing its use for semen processing without reducing the number of insemination doses produced per ejaculate.

Fertility and flow cytometry study of frozen-thawed sperm in cryopreservation medium supplemented with soybean lecithin

Semen cryopreservation can provide genetic resources for a large number of females from a small number of superior males. Optimization of cryopreservation media to achieve the highest quality of post-thaw semen is crucial. Soybean lecithin has evaluated as a plant-based cryoprotectant for substitution of egg yolk in ram semen extender. Flow cytometric and fertility assessments were applied following cryopreservation procedure in two experimental groups (SL group: extender containing 1% w/v soybean lecithin and EY group: extender containing 20% v/v egg yolk). The higher percentage of live sperm and the lower percentage of dead sperm were obtained in SL (47.66 ± 1.38, 52.33 ± 1.69, respectively) extender compared to EY (41.16 ± 1.38, 58.83 ± 1.69). For motion characteristics, plasma membrane integrity, acrosome integrity and mitochondria activity, no significant difference was observed between SL and EY extenders. In artificial insemination experiment, there was no significant difference in pregnancy rate, lambing rate and twining rate between SL and EY extenders. It can be concluded that SL extender can be an efficient alternative extender to preserve ram sperm during cryopreservation procedure without adverse effects.

Sequestration of bovine seminal plasma proteins by different assemblies of phosphatidylcholine: A new technical approach

Binder of SPerm (BSP) proteins, the main proteins from bovine seminal plasma, are known to partially intercalate into the outer leaflet of the spermatozoa membrane and bind to choline-containing lipids being present therein. This insertion generates a negative effect on semen quality after cryopreservation by inducing an early-stage capacitation of spermatozoa. The assumption of surface properties exhibited by BSP proteins was checked by tensiometry measurements: BSP proteins are highly surface active. This suggests that BSP proteins can reach the interface covered by phospholipids not only by interactions between one and each other but also due to their own surface activity. The insertion of BSP proteins into the lipid domains outer leaflet of spermatozoa was reproduced on a biomimetic system such as Langmuir monolayers. The insertion of BSP proteins can be performed in the compressible fluid domains which contain choline-bearing lipids. Monolayer films were used as well to study the complexation of BSP proteins by two phospholipid assemblies: low density lipoprotein (LDLs) from egg yolk or liposomes produced from egg phospholipids. Irrespective of the phospholipid structure (lipoprotein or liposome), BSP was hindered to alter the structure of the membrane. Only the overall ratio BSP proteins:phosphatidylcholine was important. The difference between the two sequestering agents lies on their surface properties: LDL have a strong tendency to merge with the outer layer whereas liposomes mainly remain in the bulk on the same time scale.

Low-density Lipoprotein Improves Motility and Plasma Membrane Integrity of Cryopreserved Canine Epididymal Spermatozoa

Cryopreservation of caudal epididymal spermatozoa is an effective technique to conserve genetic potentials of superior dogs when it is not possible to collect ejaculated spermatozoa. Although hen egg yolk is commonly supplemented into the semen extender, active substances within the egg yolk which protect sperm against cryoinjury remain to be discovered. Among its compositions, low-density lipoprotein (LDL) has been reported to have a cryoprotective property for sperm cryopreservation. However, the effects of LDL on dog epididymal spermatozoa during cryopreservation have not yet been investigated. This study aimed to investigate the effects of LDL on epididymal spermatozoa quality following cryopreservation and thawing. After routine castration of 12 dogs, caudal epididymides from individuals were separated from the testes and cut into a few pieces in a Tris-buffer. Spermatozoa recovered from each sample were examined at once for sperm quality and divided into six groups of extender: no LDL, 20% egg yolk, 4%, 8%, 16%, and 24% LDL, before cryopreservation. The sperm aliquots were then equilibrated and conventionally frozen. After thawing, sperm motility, morphology, plasma membrane integrity, and acrosome integrity were evaluated. The results revealed that 4% LDL and 20% egg yolk yielded significantly higher sperm motility (57.69% and 52.69%, respectively, p<0.05) than other LDLs. In addition, 4% LDL yielded the significantly highest plasma membrane integrity (70.54%, p<0.05). In conclusion, the supplementation of 4% LDL in Tris-glucose extender could be applied for cryopreservation of canine epididymal spermatozoa.

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.

The impact of storage temperature and sperm number on the fertility of liquid-stored bull semen

In Ireland, liquid bull semen is stored at unregulated ambient temperatures, typically at 5×106 spermatozoa per dose, and inseminated within 2.5 days of collection. In Experiment 1, the effect of storage temperature (5, 15, 22, 32°C and fluctuations (Flux) between these temperatures) on progressive motility, viability, acrosomal status, DNA fragmentation and osmotic resistance was assessed. In Experiment 2, the field fertility of liquid semen at 5, 4 and 3×106 spermatozoa per dose, up to Day 2 after collection, was assessed in comparison to frozen-thawed semen at 20×106 spermatozoa per dose (n=35328 inseminations). In Experiment 1, storage at 15°C resulted in the highest progressive motility (PP6 spermatozoa per dose on Day 2 of storage was reduced in comparison to frozen-thawed semen (P<0.01). In conclusion, liquid semen is versatile between storage temperatures of 5 and 22°C, but demonstrates reduced fertility on Day 2 of storage at lower sperm numbers in comparison to frozen-thawed semen.

Effect of egg yolk plasma on dog sperm cryopreservation

This study evaluated the quality of frozen-thawed dog spermatozoon after the inclusion of egg yolk plasma (EYP) instead of whole egg yolk (EY) in the cryopreservation extender and after distinct periods of exposure to EYP. Seven mongrel dogs were used as sperm donors, and EYP was obtained by centrifugation. In Experiment 1, post-thawing sperm motility (MOT) and integrity of membrane (INT) and acrosome (ACR) were superior for spermatozoon extended with 20% EYP T2 than with 20% EY (P < 0.05), although normal sperm morphology (MOR) did not differ (P > 0.05). In Experiment 2, after ejaculates extended with 20% EYP were cooled at 5°C for 2, 6 and 10 h before freezing, MOT, INT and ACR were similar among periods (P > 0.05). Thus, dog spermatozoon extended with 20% EYP can be kept cooled for up to 10 h prior to freezing, achieving post-thawing quality greater than that obtained with the inclusion of EY in freezing extenders.

Effect of different concentrations of trehalose and glycerol on the freezability of ram semen using soybean lecithin-based diluents

This study was conducted to determine the effect of different levels of trehalose and glycerol on ram sperm cryosurvival using lecithin-based diluents. Ejaculates were collected from four rams, pooled after initial evaluation, diluted with Tris-soybean lecithin extender and split into nine equal parts. A total of 0 (T0), 50 (T50) or 100 (T100) mM of trehalose and 3% (G3), 5% (G5) or 7% (G7) of glycerol were added to each part. Sperm motility, viability, plasma membrane integrity and acrosome integrity were evaluated immediately after thawing (0 h), and subsequently after 3 h and 6 h post-thawing incubation at 37°C. Results indicated that there was interaction between trehalose and glycerol on sperm motility. In addition, interaction of trehalose and glycerol with incubation time on sperm motility, viability, plasma membrane integrity and acrosome integrity was not significant (P > 0.05). Sperm motility was greatest in the sperm treated with 100 mM trehalose and 7% glycerol (27%; P < 0.05). The effect of trehalose was significant on viability and plasma membrane integrity of ram spermatozoa (P < 0.05). The main effect of trehalose showed that sperm viability was higher in T100 (47.06%) than T50 (53.96%; P < 0.05). The highest membrane integrity was observed in T100 (47.04%; P < 0.05). Membrane integrity was higher (P < 0.05) in G5 (49.97%) than G3 (41.56%) and there was no difference between G7 (46.86%) and G3 (41.56%; P > 0.05). The best sperm viability and plasma membrane integrity was observed at 0 h (65.75% and 51.58%, respectively). It was concluded that simultaneous use of 7% glycerol and 100 mM trehalose had a desirable effect on motility of ram frozen–thawed 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.

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.

In vitro assessment of soybean lecithin and egg yolk based diluents for cryopreservation of goat semen

Soybean lecithin is a suitable plant-based cryoprotectant for freezing ruminant sperm. Optimum level of lecithin was not clear for goat semen cryopreservation. The objective of this study was to investigate the effects of different levels of soybean lecithin in semen extender on post-thaw sperm quality including CASA-motion parameters, viability, plasma membrane integrity and lipid peroxidation. Semen samples were collected from 4 Mahabadi bucks using an artificial vagina. Different concentrations of soy lecithin (SL, 0.5%, 1%, 1.5%, 2% and 2.5% w/v) were compared to 15% (v/v) egg yolk-based extender (TR-EY). No significant difference was observed for sperm progressive motility, viability or plasma membrane integrity in 1.5% SL media (33.8%, 66%, and 62.7%, respectively) and TR-EY medium (35.4%, 67.2%, and 64.9%, respectively). Sperm motion characteristics (VAP, VSL, VCL, ALH and LIN) and rapid spermatozoa were improved with extender containing 1% and 1.5% SL, compared to TR-EY extender. Furthermore, egg yolk produced significantly higher malondialdehyde (4.02±0.21) than other groups. Results suggest that the optimal lecithin concentration in the semen extender was 1.5% and also soy lecithin can substitute for egg yolk during cryopreservation for caprine sperm.

Avaliação de diferentes crioprotetores intra e extracelulares na criopreservação de sêmen de touros

Em um delineamento experimental usando o fatorial 3x2, três crioprotetores internos, glicerol (GLI), etilenoglicol (EG) e dimetilformamida (DMF), e dois externos, gema de ovo (GEMA) e lipoproteína de baixa densidade (LDL), avaliaram-se a motilidade ao descongelamento de GLI-GEMA 53,9±1,96, sendo superior aos demais tratamentos (P<0,05). Na avaliação de morfologia ao descongelamento, não houve diferença (P>0,05) entre os tratamentos EG-GEMA 68,3±1,58, EG-LDL 72,2±2,39 e DMF-GEMA 68,7±1,67 que foram mais altos que os demais (P<0,05). A avaliação de integridade de membrana por fluorescência ao descongelamento GLI-GEMA 34,2±2,28 e EG-GEMA 30,9±1,32 não diferiram entre si (P>0,05), mas foram mais elevados que os demais (P<0,05), enquanto que a HOST dos tratamentos DMF-GEMA 13,6±1,30 e DMF-LDL 9,8±0,78 diferirem entre si (P<0,05) e foram mais baixas que as demais (P<0,05). O uso de etilenoglicol associado à gema de ovo pode ser uma alternativa ao uso de glicerol nos protocolos de congelamento de sêmen de touros.

Soya-lecithin in extender improves the freezability and fertility of buffalo (Bubalus bubalis) bull spermatozoa

Egg yolk is routinely used as a cryoprotectant in semen extenders. However, it may contain cryoprotective antagonists, and there are hygienic risks associated with its use. Proteins of plant origin, like soya-lecithin, lack these hazards. The aim of this study was to use soya-lecithin as a cryoprotectant in extender and to investigate its effects on in vitro quality and in vivo fertility of buffalo semen. Semen from three buffalo bulls was frozen in tris-citric extender containing 5.0%, 10% or 15% soya-lecithin or 20% egg yolk. Sperm motility, plasma membrane integrity and viability were assessed post-dilution, pre-freezing and post-thaw. In Post-dilution and pre-freezing, the values for motility, plasma membrane integrity and viability remained higher (p ≤ 0.05) in extenders containing 10% soya-lecithin and control compared with extender containing 5% and 15% soya-lecithin. However, motility, plasma membrane integrity and viability were higher (p < 0.05) in extender containing 10% soya-lecithin compared with control and extenders containing 5% and 15% soya-lecithin. Semen from two buffalo bulls was frozen in tris-citric extender containing either 10% soya-lecithin or 20% egg yolk. Higher (p < 0.05) fertility rate was recorded in buffaloes inseminated with semen containing 10% soya-lecithin (56%) compared with 20% egg yolk (41.5%). The results suggest that 10% soya-lecithin in extender improves the freezability and fertility of buffalo bull spermatozoa and can be used as an alternate to egg yolk in cryopreservation of buffalo semen.

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.

Avaliação de espermatozoides caprinos congelados em meio à base de água de coco em pó (ACP-101®) ou TRIS

Compararam-se as características cinéticas e morfológicas de espermatozoides caprinos congelados nos meios à base de ACP-101® e TRIS. Os diluentes utilizados foram: ACP-101® (+ 2,5% gema ovo + 7% glicerol) e TRIS (+ 20% gema ovo + 6,8% glicerol). Quarenta e oito ejaculados de quatro bodes foram coletados, avaliados, divididos em duas alíquotas e diluídos nos meios ACP-101® e TRIS, respectivamente, posteriormente congelados e, após 30 dias, descongelados. A avaliação da motilidade espermática por computador foi realizada aos 5, 60 e 120 minutos pós-descongelação. As características de motilidade espermática analisadas foram: motilidade total (MT) (%) e progressiva (MP) (%), velocidades média do trajeto do espermatozoide (VAP) (µm/s) e linear (VSL) (µm/s) e população de espermatozoides rápidos (ER) (%). As avaliações de morfologia espermática quantificaram a porcentagem de espermatozoides normais (N) e as alterações da cabeça (AC), da peça intermediária (API) e do flagelo (AF), aos cinco e 120 minutos pós-descongelação. O diluente TRIS apresentou resultados cinéticos mais elevados que o ACP-101® aos 60 e 120 minutos pós-descongelação. As AC aos 120 minutos pós-descongelação foram mais altas nos espermatozoides congelados em ACP-101®. Conclui-se que o diluente TRIS promoveu maior viabilidade in vitro dos espermatozoides caprinos pós-descongelação.

Effects of extender and equilibration time on post-thaw motility and membrane integrity of cryopreserved Gyr bull semen evaluated by CASA and flow cytometry

The objectives of the present study were to investigate the effects of three equilibration times (0, 2, and 4h) and two extenders (TRIS or Bioxcell) for cryopreservation of bull semen. Semen from 12 Gyr bulls was cryopreserved using an automated freezing machine. There were significant interactions between equilibration times and extenders for sperm motility and membrane integrity. The control treatment (0h equilibration) had the lowest values (P<0.05) for total (MOT) and progressive motilities (PROG), and percentage of sperm with intact plasma and acrosomal membranes (IPIA), with no significant differences between extenders. Extender TRIS had greater cryoprotective action than Bioxcell, with greater MOT, PROG, IPIA at 2 and 4h, as well as the lowest proportion of damaged plasma membrane (DPM, 72.2% vs. 85.8%) for all times. Equilibration for 4h yielded the most desirable (P<0.05) for MOT, PROG, and IPIA, and the least DPM percentage (86.5, 78.0, and 72.6% for 0, 2, and 4h, respectively). Overall, the combination of TRIS and 4h of equilibration was the most desirable semen cryopreservation method, with greatest MOT, PROG, and IPIA (TRIS-T4=26.8%; BIO-T4=18.3%) and the least DPM. In conclusion, based on objective analyses, equilibration during cryopreservation was essential for maintaining motility and integrity of sperm membranes; equilibration for 4h yielded the greatest sperm survival, independent of the extender used.

Proteomic comparison of detergent-extracted sperm proteins from bulls with different fertility indexes

Intrinsic factors such as proteins modulate the fertilising ability of male gametes. We compared detergent-extracted sperm protein composition of bulls with different fertility indexes in order to highlight putative fertility markers of sperm. Frozen semen from 23 Holstein bulls with documented fertility was used. According to their ‘fertility solution’ (SOL), as calculated by the Canadian dairy network, bulls were divided into four groups: high fertility (HF) (SOL>3.0; n=6), medium-HF (2.9>SOL>2.0; n=5), medium-low fertility (−2.8>SOL>−4.9; n=8) and low fertility (LF; SOL<−5.0; n=4), with a SOL=0 being the average. Triton X-100 protein extracts from ejaculated spermatozoa were subjected to two-dimensional difference gel electrophoresis, and polypeptide maps were quantitatively analysed by ImageMaster software. Nine protein spots showed significant differences between the HF and LF groups, and eight of these proteins were identified by liquid chromatography–tandem mass spectrometry. T-complex protein 1 subunits ε and θ (CCT5 and CCT8), two isoforms of epididymal sperm-binding protein E12 (ELSPBP1), proteasome subunit α type-6 and binder of sperm 1 (BSP1) were more expressed in the LF group than in the HF group. On the other hand, adenylate kinase isoenzyme 1 (AK1) and phosphatidylethanolamine-binding protein 1 (PEBP1) were more expressed in the HF group than in the LF group. The presence and expression level of ELSPBP1, BSP1, AK1 and PEBP1 were confirmed by western blot. A linear regression model established that CCT5 and AK1 explained 64% (P<0.001) of the fertility scores. The reported functions of these proteins are in agreement with a putative involvement in defective sperm physiology, where lower or higher levels can jeopardise sperm ability to reach and fertilise the oocyte.