Liposomes as an alternative to egg yolk in stallion freezing extender

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

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

Lipidomics random forest algorithm of seminal plasma is a promising method for enhancing the diagnosis of necrozoospermia

BACKGROUND

Despite the clear clinical diagnostic criteria for necrozoospermia in andrology, the fundamental mechanisms underlying it remain elusive. This study aims to profile the lipid composition in seminal plasma systematically and to ascertain the potential of lipid biomarkers in the accurate diagnosis of necrozoospermia. It also evaluates the efficacy of a lipidomics-based random forest algorithm model in identifying necrozoospermia.

METHODS

Seminal plasma samples were collected from patients diagnosed with necrozoospermia (n = 28) and normozoospermia (n = 28). Liquid chromatography-mass spectrometry (LC-MS) was used to perform lipidomic analysis and identify the underlying biomarkers. A lipid functional enrichment analysis was conducted using the LION lipid ontology database. The top 100 differentially significant lipids were subjected to lipid biomarker examination through random forest machine learning model.

RESULTS

Lipidomic analysis identified 46 lipid classes comprising 1267 lipid metabolites in seminal plasma. The top five enriched lipid functions as follows: fatty acid (FA) with ≤ 18 carbons, FA with 16-18 carbons, monounsaturated FA, FA with 18 carbons, and FA with 16 carbons. The top 100 differentially significant lipids were subjected to machine learning analysis and identified 20 feature lipids. The random forest model identified lipids with an area under the curve > 0.8, including LPE(20:4) and TG(4:0_14:1_16:0).

CONCLUSIONS

LPE(20:4) and TG(4:0_14:1_16:0), were identified as differential lipids for necrozoospermia. Seminal plasma lipidomic analysis could provide valuable biochemical information for the diagnosis of necrozoospermia, and its combination with conventional sperm analysis may improve the accuracy and reliability of the diagnosis.

A soy lecithin nanoparticles-based extender effectively cryopreserves Holstein bull sperm

Plant-based semen extenders, typically derived from soybean lecithin, are easier to modulate more and consistent in their composition than animal-based extenders. As large lecithin particles can, however, reduce effectiveness and solubility in bull semen extenders, sonication was used to create nano-lecithin (NL) particles of soybean lecithin. The objective was to determine the effects of lecithin type and concentration on the quality of frozen-thawed bovine sperm. We hypothesized that reducing the size of lecithin improves its interactions with the sperm and enhances the parameters that favor its motility, viability and fertility. Semen was collected from six mature Holstein bulls and ejaculates meeting minimum standards were pooled. Eight Tris-based extenders that contained 1, 2, 3, or 4 % of either conventional lecithin (L1-L4) or NL (NL1-NL4), plus two control extenders (one animal-based extender containing 20 % egg yolk [EY] and a commercial lecithin-based extender [BioXcell®]) were compared. Among soybean lecithin-based extenders, NL3 had the highest total and progressive sperm motility, and average path, straight-line and curvilinear sperm velocity, and was comparable to EY. Additionally, sperm mitochondrial activity was the highest in NL3, whereas sperm viability was highest in EY, NL3, and L4. Following in vitro fertilization of in vitro-matured bovine oocyes, NL3 had cleavage and hatching rates comparable to BioXcell®, but a lower blastocyst rate than EY. Overall, NL3 performed better than the other extenders for most end points, with efficiency comparable to EY. We, therefore, concluded that reducing lecithin particle size to a nano level improves sperm cryopreservation with optimal performance with 3 % NL.

Sperm Cryopreservation Today: Approaches, Efficiency, and Pitfalls

The cryopreservation of human spermatozoa has been an option for patients undergoing chemo or radiotherapies since the late 1950s. Presently, there are different techniques for the cryopreservation of spermatozoa. The most commonly used techniques are programmable slow freezing and freezing on liquid nitrogen vapors, while the use of vitrification is still not accepted as clinically relevant. Although there have been many improvements, the ideal technique for achieving better post-thaw sperm quality continues to be a mystery. A major obstacle during cryopreservation is the formation of intracellular ice crystals. Cryodamage generated by cryopreservation causes structural and molecular alterations in spermatozoa. Injuries can happen because of oxidative stress, temperature stress, and osmotic stress, which then result in changes in the plasma membrane fluidity, motility, viability, and DNA integrity of the spermatozoa. To prevent cryodamage as much as possible, cryoprotectants are added, and in some clinical trial cases, even antioxidants that may improve post-thaw sperm quality are added. This review discusses cryopreservation techniques, cryodamage on molecular and structural levels, and cryoprotectants. It provides a comparison of cryopreservation techniques and describes recent advances in those techniques.

Bull Semen Obtained on Beef Farms by Electroejaculation: Sperm Quality in the First Two Hours of Storing with Different Extenders and Holding Temperatures

Sperm quality decreases over time, so bull semen may need to be preserved after field collection. However, the effect of handling such semen samples from commercial farms and placing them in very short-term storage has not been elucidated. Therefore, ejaculate from 25 bulls from 1 dairy and 14 beef cattle farms were collected under farm conditions and evaluated for semen quality during the first two hours after collection. Two commercial extenders (AndroMed^® and BIOXcell^®) and two different storage temperatures (5 °C and room temperature) were used to evaluate the influence on semen quality and sperm kinetics in ejaculates grouped into three evaluation times, based on time since collection (Time 1: <75 min, n = 7; Time 2: 75-105 min, n = 11; and Time 3: 105-120 min, n = 7). Classical semen parameters, sperm motion kinetics by CASA and colony-forming units were assessed. The differences between both extenders in curvilinear and straight-line velocities (VCL and VSL) for the different time groups (Time 2 and Time 3) were statistically significant for p < 0.05. AndroMed^® showed lower VSL, straightness and linearity in sperm compared to BIOXcell^® (p < 0.05). In conclusion, AndroMed^® induced more curvilinear movement, while BIOXcell^® stimulated straighter motility.

Determining the Optimal Dosage of Lecithin Nanoliposome in Rooster Semen Freezing Medium and Fertility Potential

Introduction: Lecithin nanoliposome (nano-LPO), with its cryoprotective properties, is considered to enhance the performance of a traditional semen cryoprotectant. Objective: To determine the optimal dose of lecithin nano-LPO added to the rooster semen extender. Materials and Methods: Semen samples collected weekly from eight broiler breeder roosters were mixed and aliquoted into five equal subsamples, during the five successive weeks. The subsamples were then diluted with a semen extender containing 0%, 0.5%, 1%, 1.5%, or 2% of lecithin nano-LPO. Post-thawed semen quality attributes, including sperm motility and velocity parameters, plasma membrane functionality, mitochondrial membrane potential (MMP), apoptosis-like changes, and fertility potential, were evaluated. Results: Total motility and velocity parameters, including curvilinear velocity (VCL), straight-line velocity (VSL), average path velocity μm/s (VAP), straightness (STR), linearity (LIN), lateral head displacement (ALH), and wobble (WOB) were quadratically (p < 0.01) influenced by graded levels of lecithin nano-LPO, such that the highest values were obtained when 1% of lecithin nano-LPO was used. Treatments had no significant effect on plasma membrane functionality; however, MMP (p < 0.08) and percentages of live and dead spermatozoa (p < 0.05) quadratically responded to increasing levels of lecithin nano-LPO, where the best outcome was found when about 1% of lecithin nano-LPO was used in the semen extender. The percentage of apoptotic spermatozoa cubically responded to increasing levels of lecithin nano-LPO (p ≤ 0.07). No significant trend of fertility rate was found in response to addition of lecithin nano-LPO levels. Conclusions: Supplementing an extender with 1.10% of lecithin nano-LPO is shown to be the optimal dose associated with the most improvement in post-thawed rooster sperm velocity measurements.

PUFA-rich phospholipid classes and subclasses of ram spermatozoa are unevenly affected by cryopreservation with a soybean lecithin-based extender

Cryopreservation is known to affect spermatozoa structure and function. Ram sperm are among the most highly sensitive mammalian gametes to freezing, due to their lipid composition, which limit their efficiency in artificial insemination programs. The aim of this study was to investigate the effects of cryopreservation with a chemically defined soybean lecithin-based extender on ram spermatozoa functionality on the one hand, and quantifiable changes in lipid and fatty acid profile on the other. Freeze-thawing decreased sperm quality, as indicated by post-thaw parameters related to membrane integrity, mitochondrial viability and sperm motility. The most relevant lipid change after cryopreservation was a remarkable loss of all glycerophospholipids containing 22:6n-3. Species of sphingomyelin with very long chain polyunsaturated fatty acids (VLC-PUFA), that are exclusively located in the sperm head, where responsible of its reduction after cryostorage. Freezing caused a reduction in mitochondrial function, which was confirmed by significantly decreased of mitochondrial membrane potential and by the generation of 4-HNE. Mitochondria damage was accompanied by a loss in cardiolipin with 18:2n-6 and phosphatidylethanolamine with 20:4n-6, two well-known lipids that are critical components for mitochondrial membrane functionality. Loss of sterols after cryopreservation occurred along with a decrease in the order of sperm membrane lipids. Our research provides new insights on deleterious effects of cryopreservation on PUFA-rich phospholipids of ram sperm and highlight their importance as biomarkers of ultrastructural, biochemical and functional damage that ram spermatozoa undergo after freezing-thawing.

INRA96 Supplemented With Phospholipids Liposomes, A Promising Approach for Stallion Sperm Chilling

Among biotechnologies of reproduction in the equine species, artificial insemination remains the most used technology especially for cooled transported sperm. Although the use of INRA96 extender has demonstrated its efficiency for long-term sperm storage at 4°C or 15°C, some stallions ("bad coolers") are excluded from such technology. Some years ago, we demonstrated that liposomes produced from egg yolk (EY) phospholipids could be an alternative to egg yolk plasma in stallion freezing extenders. To develop a new extender for sperm chilling, we evaluated the protective effect of liposomes produced from EY phospholipids on stallion sperm storage at 4°C. The sperm of stallions from two studs was diluted in INRA96 extender (as control) or an experimental extender (EE) composed of INRA96 supplemented with liposomes of EY phospholipids. After 24H (D1), 72H (D3), and 6 days (D6) or 7 days (D7), motility parameters were evaluated using Computer Assisted Semen Analyzer. Our results demonstrated that total and progressive motility decreased significantly after dilution and storage in INRA96 between D1 and D3 (P < .05) while no significant decrease was observed between D1 and D3 with EE. Regarding VAP parameter, no significant difference was observed between extenders except at D7 in stud 2. Moreover, total and progressive motility were maintained at a significantly higher level (D3, D6, D7) when sperm was stored in EE compared to INRA96. These promising results demonstrate that the supplementation of INRA96 extender with egg-yolk phospholipids liposomes allows a higher protection to stallion sperm cells.

Effects of different ultrastructures of lecithin on cryosurvival of goat spermatozoa

This study was to evaluate the effects of two different ultrastructures of lecithin including nanoparticles (NPE mostly nanomicelles) and lecithin nanoliposome (NLE) with egg yolk extender (EYE) on goat sperm cryopreservation. Semen samples were collected from 6 goats, then pooled, diluted and then frozen. Motility and motion parameters, plasma membrane integrity and functionality, morphology, apoptosis status (Annexin V-PI), acrosome integrity, DNA fragmentation and in vitro fertilisation were assessed. Total motility and most motion parameters were higher in EYE (p < .05) compared with the two lecithin extenders, while there were no significant differences between NLE and NPE. NLE and NPE had higher values for viable spermatozoa (Annexin V-PI) (p < .05) compared with EYE. The highest value for dead spermatozoa was observed in EYE (p = .08). A higher percentage of DNA fragmentation (p < .05) was detected in EYE compared with NPE. Plasma membrane integrity and functionality, morphology, acrosome integrity and fertility of spermatozoa indicated no significant differences between extenders. Data suggested that ultrastructural changes of lecithin (micelles versus. liposome) could not improve the sperm cryosurvival of goat spermatozoa. Moreover, we cannot also claim that lecithin-based diluent supplies better protection compared with the egg yolk in goat.

High-speed centrifugation of extender of freeze-thaw boar semen

In semen cryopreservation, egg yolk is still widely used as a non-penetrating cryoprotectant. Much has been developed in the search for alternatives for this biological product. This work aimed to evaluate the processed egg yolk through ultracentrifugation and/or sonication in the cryopreservation of swine semen. Twenty-seven semen doses were purchased from a commercial boar stud and processed for cryopreservation using egg yolk lactose 11% (control) extender, processed using two different methods: high-speed centrifugation and sonication. Then, they were submitted to freeze-thawing protocol and were assessed for kinematic and cell structural parameters. Samples in which extenders underwent centrifugation had better results in velocity parameters, meanwhile those that only sonication was performed had poorest results in this parameter. The preservation of the membrane and mitochondria structure had better results when the diluent was only centrifuged in comparison with the other treatments. Therefore, centrifugation of extender containing egg yolk is important for better cryopreservation of swine semen.

The Current Trends in Using Nanoparticles, Liposomes, and Exosomes for Semen Cryopreservation

Cryopreservation is an essential tool to preserve sperm cells for zootechnical management and artificial insemination purposes. Cryopreservation is associated with sperm damage via different levels of plasma membrane injury and oxidative stress. Nanoparticles are often used to defend against free radicals and oxidative stress generated through the entire process of cryopreservation. Recently, artificial or natural nanovesicles including liposomes and exosomes, respectively, have shown regenerative capabilities to repair damaged sperm during the freeze-thaw process. Exosomes possess a potential pleiotropic effect because they contain antioxidants, lipids, and other bioactive molecules regulating and repairing spermatozoa. In this review, we highlight the current strategies of using nanoparticles and nanovesicles (liposomes and exosomes) to combat the cryoinjuries associated with semen cryopreservation.

In vitro assessment of egg yolk-, soya bean lecithin- and liposome-based extenders for cryopreservation of dairy bull semen

The study was conducted to compare the effect of four commercially available extenders (Triladyl®- egg yolk-based; Andromed® and Bioxcell®-plant based and Optixcell®-liposome-based) on post-thaw sperm quality and functionality variables evaluated using computer-assisted sperm analysis and flow cytometry. A total of 30 ejaculates from five bulls were analysed. With use of Triladyl®, sperm had a greater post-thaw total motility than with use of Bioxell® and Optixcell® but there was no difference as compared with use of Andromed® with the greatest (P < 0.05) percentage of progressively motile cells. With use of Optixcell®, there was a greater (P < 0.05) percentage of sperm with an intact membrane than with use of Triladyl® and Bioxcell®, but values were similar with use of Andromed®. Acrosome damage in semen preserved with use of Optixcell® was less than with use of Bioxcell® and Andromed®. With use of Optixcell®, there was a greater percentage of viable spermatozoa with a lesser lipid disruption (P < 0.05) when compared with the other extenders. Production of peroxides was greater for sperm cryopreserved with use of Triladyl® and Optixcell® while less superoxide was produced in the samples cryopreserved with the egg yolk-based extender. Optixcell® appears to be a promising alternative to replace traditional egg yolk extenders. With use of Optixcell®, however, there were greater peroxide concentrations after thawing. With use of Andromed®, there were similar results as with use of Optixcell®, therefore, it could be an effective substitute for egg-yolk based media due to the greater proportion of highly and progressively motile spermatozoa at thawing.

Effect of cumulus cell removal and sperm pre-incubation with progesterone on in vitro fertilization of equine gametes in the presence of oviductal fluid or cells

In spite of many attempts to establish an in vitro fertilization (IVF) technique in the equine, no efficient conventional IVF technique is available. The presence of oviductal fluid or oviductal cells during IVF helps to improve embryo production in vitro but is not sufficient to reach high fertilization rates. Thus, our aim was to perform equine IVF either after sperm pre-incubation with oviductal fluid or in the presence of oviductal cells, and to evaluate the effect of cumulus removal from the oocyte or sperm pre-incubation with progesterone. In experiments 1 and 2, IVF was performed in the presence of porcine oviduct epithelial cells. The removal of cumulus cells from equine oocytes after in vitro maturation tended to increase the percentage of fertilization when fresh sperm was used (1/33 vs. 4/31, p > 0.05) but had no effect when frozen sperm was used (1/32 vs. 1/32). Equine sperm pre-incubation with progesterone did not significantly influence the fertilization rate when fresh or frozen sperm was used (2/14 vs. 2/18 for fresh, 1/29 vs. 1/25 for frozen). In experiments 3 and 4, IVF was performed after pre-incubation of sperm with porcine oviductal fluid. The removal of cumulus cells tended to increase the percentage of fertilization when fresh sperm was used (1/24 vs. 3/26, p > 0.05). Sperm pre-incubation with progesterone did not significantly influence the fertilization rate when fresh or frozen sperm was used (2/39 vs. 2/36 for fresh, 2/37 vs. 1/46 for frozen), but two 3-4 cell stage zygotes were obtained with fresh sperm pre-incubated with progesterone. This is an encouraging result for the setting up of an efficient IVF procedure in equine.

Comparison of in vitro and in vivo fertilizing potential of buffalo bull semen frozen in egg yolk-, soya bean lecithin- and liposome-based extenders

The objective of this study was to compare different extenders for post-thaw in vitro sperm function and in vivo fertility of buffalo semen. Accordingly, sperm of 30 ejaculates extended in egg yolk (TRIS with 20% egg yolk; EY), two soya lecithin-based (SL-1; AndroMed® and SL-2; Bioxcell® ) and a liposome-based extender (LS; OptiXcell® ) were tested. The post-thaw semen was evaluated for computer-assisted sperm analysis (CASA), sperm viability, membrane and acrosome integrity, DNA integrity and acrosome reaction and first service pregnancy rate (FSPR) in a fixed-time artificial insemination programme. Total motility and VCL were the only CASA-based parameters that exhibited significantly higher (p < .05) percentage in LS among these extenders. Post-thaw percentage of acrosome integrity (55.9 ± 1.4, 58.1 ± 2.0, 55.8 ± 2.0, 56.6 ± 2.3) and DNA integrity (68.8 ± 2.0, 69.2 ± 2.3, 71.3 ± 2.1, 69.1 ± 2.1) did not differ (p > .05) in EY, SL-1, SL-2 and LS extender, respectively. However, a variable response in terms of efficacy of different extenders for sperm viability and plasma membrane integrity was observed. Assessment of inducibility of acrosome reaction showed significant differences between extenders (51.9 ± 2.1, 44.3 ± 2.4, 46.1 ± 2.3 and 58.1 ± 3.1%, respectively, for EY, SL-1, SL-2 and LS). Furthermore, field trials revealed significantly higher (p < .05) FSPR of LS-extended semen as compared to that for EY, SL-1 and SL-2 extender (46.3%, 41.2%, 31.2% and 29.7%, respectively). It is concluded that the liposome-based extender is more effective than egg yolk- and soya lecithin-based extenders and may be used for cryopreservation of buffalo semen in the future.

Effect of lecithin nanoliposome or soybean lecithin supplemented by pomegranate extract on post-thaw flow cytometric, microscopic and oxidative parameters in ram semen

This investigation was carried out to study the effect of soybean lecithin 1.5% (wt/vol) (0, 2.5, 5 and 7.5 mg l-1 pomegranate extract (PE)) or PE-loaded lecithin nanoliposome (0, 2.5, 5 and 7.5 mg l-1) to Tris-based extender. Sperm motility (CASA), viability, membrane integrity (HOS test), abnormalities, mitochondrial activity, apoptosis status, lipid peroxidation, total antioxidant capacity (TAC)) and antioxidant activities (GPX, SOD) were investigated following freeze-thawing. No significant differences were detected in motility parameters, viability, membrane integrity, and mitochondria activity after thawing sperm between soybean lecithin and lecithin nanoliposomes. It was shown that PE5 significantly improved sperm total and progressive motility, membrane integrity, viability, mitochondria activity, TAC and reduced lipid peroxidation (malondialdehyde concentration). Moreover, the percentage of apoptotic sperm in PE5 extenders was significantly the lowest among other treatments. Sperm abnormalities, SOD and GPX were not affected by the antioxidant supplements. For apoptotic status, no differences were observed between soybean lecithin and lecithin nanoliposome. We showed that lecithin nanoliposome extender can be a beneficial alternative extender to protect ram sperm during cryopreservation without any adverse effects. It was also observed that regarding pomegranate concentration, PE5 can improve the quality of ram semen after thawing.

Cryopreservation of white-tailed deer (Odocoileus virginianus) semen using soybean-, liposome-, and egg yolk-based extenders

The objectives of the present study were to compare the use of soybean-based (Andromed), liposome-based (Optixcell), and egg yolk-based (Ovine Red, Triladyl, and Biladyl) extenders for cryopreservation of white-tailed deer semen. In experiment 1, ejaculates obtained from six bucks were aliquoted into the following extenders: Andromed, Ovine Red, Triladyl, and Biladyl (containing 4%, 6%, or 8% of glycerol). In experiment 2, ejaculates obtained from eight bucks were divided amongst Andromed, Ovine Red, and Optixcell extenders. Total and progressive sperm motility were assessed for each sample before and after cryopreservation using a computer-automated semen analyzer. In experiment 2, flow cytometry was used for post-thaw assessment of sperm viability (SYBR-14/PI), acrosome integrity (FITC-PNA/PI), and chromatin stability (acridine orange). In experiment 1, both Andromed and Ovine Red extenders exhibited higher post-thaw total motility than Biladyl containing 4% or 6% of glycerol (p<0.05). Andromed also produced higher progressive motility than all other extenders (p<0.01) before and after cryopreservation with no differences amongst the other extenders (p≥0.11). In experiment 2, there were no differences in total and progressive motility between Andromed, Ovine Red, or Optixcell extenders (p≥0.39). Additionally, there were no differences in sperm viability (p=0.18), acrosome integrity in viable sperm (p≥0.10), or DNA fragmentation index (p=0.15). These results demonstrated that soybean (Andromed) and liposome-based (Optixcell) extenders are equally as effective at cryopreserving white-tailed semen as egg yolk-based Ovine Red extender, but are superior to egg yolk-based Biladyl or Triladyl extenders.

The benefits of liposomes for chilling canine sperm for 4 days at 4°C

This study comprises 3 experiments exploring the possible benefits and mechanism of action of liposomes for chilling (4°C) canine sperm over a period of 4 days. In the first experiment, 20 ejaculates collected from 5 Beagle dogs were chilled in an extender containing 6% low density lipoproteins (LDL) (Control), or one of 7 extenders containing different concentrations (2, 4, 6, 8, 10, 15, 20%) of liposomes (LIPO). These ejaculates were chilled over 4 days and motility was assessed daily using a Hamilton Thorne analyzer (HTM-IVOS, 14.0). The 2% LIPO obtained the best results (p=0.038) after four days (72.55% motile spermatozoa and 31.4% progressive spermatozoa). In experiment 2, 10 ejaculates were collected from same 5 dogs and chilled in 6% LDL or 2% LIPO-based extenders. Sperm integrity characteristics were assessed prior to refrigeration and every 48h for four days (D0, D2, and D4). Acrosome integrity was assessed using the FITC-PSA test (Fluorescein IsoThiocyanate-Pisum Sativum Agglutinin), plasma membrane (PM) integrity using both the hypo-osmotic swelling test (HOSt) and SYBR14/Propidium Iodide test (SYBR14/PI), and DNA integrity using the Acridine-Orange test (AO). The 2% LIPO extender provided equivalent preservation of sperm integrity parameters to the reference extender (6% LDL). In experiment 3, a Langmuir-Blodgett trough was used to evaluate the mechanistic interactions between LDL, LIPO, prostatic fluid, and the canine spermatozoal membrane during chilling. Results indicate that LDL and LIPO interact differently with the biomimetic membrane. The most likely conclusion of these findings is that LDL and liposomes employ different protective mechanisms during the chilling (4°C) of canine spermatozoa.

Mode of action of cryoprotectants for sperm preservation

Sperm cryopreservation facilitates storage and transport for use in artificial reproduction technologies. Cryopreservation processing, however, exposes cells to stress resulting in cellular damage compromising sperm function. Cryoprotective agents are needed to minimize cryopreservation injury, but at higher concentration they are toxic to cells. In this review, we describe cryoinjury mechanisms, and modes of action of different types of cryoprotective agents. Furthermore, measures are discussed how to minimize toxic effects caused by adding and removing cryoprotective agents. Cryoprotective agents can be divided into permeating and non-permeating agents. Permeating agents such as glycerol can move across cellular membranes and modulate the rate and extent of cellular dehydration during freezing-induced membrane phase transitions. Permeating protectants provide intracellular protection because they are preferentially excluded from the surface of biomolecules thereby stabilizing the native state. Non-permeating agents can be divided into osmotically active smaller molecules and osmotically inactive macromolecules. Both, permeating and non-permeating protectants form a protective glassy state during freezing preserving biomolecular and cellular structures. Freezing extenders for sperm contain salts, buffer compounds, sugars, proteins and lipids, and typically contain glycerol as the main permeating cryoprotective agent providing intracellular protection. Non-permeating protectants including sugars and proteins are used as bulking agents and to increase the glass transition temperature of the freezing extender. Ultra-heat-treated milk and egg yolk are frequently added as membrane modifying agents to enhance the inherent sperm cryostability. The protocol how to use and add cryoprotectants is a compromise between their beneficial and potentially detrimental effects.

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.

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.