Lipid dynamics in the plasma membrane of fresh and cryopreserved human spermatozoa

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.

Influence of alpha linolenic acid on the motility, viability, antioxidant activity and fertility of frozen-thawed New Zealand white rabbit buck semen

Freezing and thawing processes result in production and accumulation of high concentrations of reactive oxygen species that are detrimental to spermatozoal motility and fertility. Therefore, supplementation of exogenous source of antioxidants to freezing diluent is crucial. The aim of the present study was to investigate for the first time whether supplementation of semen diluent with alpha linolenic acid (ALA) can improve motility, viability, membrane integrity, antioxidant status and fertility of post-thaw rabbit spermatozoa. Semen was collected and pooled from fifteen New Zealand white rabbit bucks. Semen samples were diluted with a tris-citrate-glucose (TCG) extender supplemented with ALA (0, 50, 75 and 100 μmol). Then, extended rabbit semen was cooled at 5°C and cryopreserved in liquid nitrogen. After thawing, spermatozoal quality parameters (individual motility %, viability %, osmotic resistance %, and acrosome integrity %), antioxidant activity (SOD, CAT, and GSH activities), lipid peroxidation (malondialdehyde) and fertility (conception and kindling rates) were evaluated. Results revealed that supplementation of rabbit semen extender with 50 μmol ALA significantly (P<0.05) increased spermatozoal characteristics including motility (56.54%), viability (60.01%), acrosome status (72.66%) and membrane integrity (59.13%). The activity of semen antioxidant enzymes (SOD, CAT, and GSH) showed a significant improvement with a marked decrease in lipid peroxidation. Moreover, the conception (73.30%) and kindling (70.00%) rates were significantly (P<0.05) higher in does inseminated with thawed semen treated with 50 μmol ALA in comparison with other concentrations (0, 75 and 100 μmol). In summary, supplementation of rabbit semen extender with 50 μmol ALA improved motility, viability, membrane integrity, acrosome integrity, antioxidant enzymes activity and fertility of post-thaw rabbit spermatozoa. Our findings suggested that higher concentrations of ALA are detrimental to post-thaw characteristics of New Zealand white rabbit buck spermatozoa. To achieve better results, the semen freezing extender should be supplemented with ALA at lower concentrations, especially 50 μmol.

Effects of extender type on the quality of post-thaw giant panda (Ailuropoda melanoleuca) semen

Sperm cryopreservation is an essential approach for assisted reproduction and genetic resources conservation in captive giant pandas. Cryopreservation, however, leads to a significant decrease in sperm quality and, consequently, a low fertilization rate. Therefore, it is mandatory to disclose more suitable and efficient freezing strategies for sperm cryopreservation. In the present study, we compared for the first time the performance of two commercial freeze extender (INRA96 versus TEST) freezing methods on post-thawed semen quality. Semen cryopreserved with the INRA96 showed better total motility (73.00 ± 4.84% vs 57.56 ± 3.60%, P < 0.001), membrane integrity (60.92 ± 2.27% vs 40.53 ± 2.97%, P < 0.001) and acrosome integrity (90.39 ± 2.74% vs 84.26 ± 4.27%, P < 0.05) than stored with TEST. There was no significant difference in DNA integrity after thawing between the two extenders (95.69 ± 3.60% vs 94.26 ± 4.84%). In conclusion, the INRA96 method showed to be better for giant panda sperm cryopreservation and should therefore be recommended for use in order to increase success of artificial insemination.

Effects of Gangliosides on Spermatozoa, Oocytes, and Preimplantation Embryos

Gangliosides are sialic acid-containing glycosphingolipids, which are the most abundant family of glycolipids in eukaryotes. Gangliosides have been suggested to be important lipid molecules required for the control of cellular procedures, such as cell differentiation, proliferation, and signaling. GD1a is expressed in interstitial cells during ovarian maturation in mice and exogenous GD1a is important to oocyte maturation, monospermic fertilization, and embryonic development. In this context, GM1 is known to influence signaling pathways in cells and is important in sperm-oocyte interactions and sperm maturation processes, such as capacitation. GM3 is expressed in the vertebrate oocyte cytoplasm, and exogenously added GM3 induces apoptosis and DNA injury during in vitro oocyte maturation and embryogenesis. As a consequence of this, ganglioside GT1b and GM1 decrease DNA fragmentation and act as H2O2 inhibitors on germ cells and preimplantation embryos. This review describes the functional roles of gangliosides in spermatozoa, oocytes, and early embryonic development.

Evaluation of α-linolenic acid for freezability and in vivo fertility of Nili Ravi (Bubalus bubalis) buffalo semen

Alpha linolenic acid (ALA) is integral component of cell membrane that protects the cell in stressful events and involves in many metabolic pathways. It was hypothesized that ALA have the ability to protect the structural and functional integrity of buffalo spermatozoa during freeze-thawing. Therefore, study was designed to evaluate ALA supplementation (0, 5, 10 and 20 ng/mL) in extender on freezability and in vivo fertility of buffalo bull spermatozoa. Semen from three adult Nili-Ravi buffalo bulls of similar age was collected with artificial vagina (42 °C) for five weeks (replicates; N = 30). Qualified semen ejaculates (>1 mL volume, >60% motility; >0.5 billion/mL concentration) were diluted with tris-citric acid extender containing 0.0 (control), 5.0, 10.0 and 20.0 ng/mL ALA at 37 °C and cryopreserved following established protocol. Sperm motility and plasma membrane integrity were recorded higher (P < 0.05) in extender containing 5.0 ng/mL of ALA compared to control. Nevertheless, sperm viability, live dead ratio and chromatin integrity were observed higher (P < 0.05) in all experimental extenders with ALA compared to control. The number of abnormal sperm reduced significantly in all experimental extenders having ALA. A total of 539 artificial inseminations were performed with the best evolved extender having ALA (5.0 ng/mL; 272 inseminations) and control (267 inseminations). In vivo fertility rates of buffalo semen were recorded higher (P < 0.05) with extender containing ALA (5.0 ng/mL) (58%) compared to control (46%). In conclusion, supplementing 5.0 ng/mL ALA in extender improved the post-thaw quality and in vivo fertility of cryopreserved Nili-Ravi buffalo bull semen.

Role of Membrane Lipid Fatty Acids in Sperm Cryopreservation

Lipid is an important constituent of cell membrane. Membrane lipid composition of spermatozoa has been correlated to different function. Many researchers have related membrane lipid with survival success after cryopreservation or cold shock. Sperm maturation and acrosome reactions are natural phenomenon, but cryopreservation or cold shock is not. Therefore, sperm cells are not programmed for such change and undergo stress. So the change in membrane lipid composition due to cold shock or cryopreservation may be looked upon as response of spermatozoa to a certain stressed condition. A significant body of research worked on the relationship between membrane lipid and fatty acid composition and ability of cell to tolerate adverse change in temperature. However, as the approach of different research groups was different, it is very difficult to compare the changes. Studies have been done with different species, ejaculated/seminal or epididymal sperm. Lipid analyses have been done with whole cell membrane isolated by different methods. Fatty acids estimated were from whole cell, plasma membrane, head membrane, or phospholipids. The cryopreservation condition, media composition, and diluents/cryoprotectants were also different. At this onset a comprehensive review is needed to cover changes of sperm membrane lipid composition of different species under different cryopreservation conditions.

Protective effects of exogenous gangliosides on ROS-induced changes in human spermatozoa

This article summarizes the available evidence on the efficacy of gangliosides to reduce the degree of reactive oxygen species (ROS)-mediated damage. The antioxidative efficacy of exogenous gangliosides in protecting different cells encouraged us to examine their ability to protect human spermatozoa. Gangliosides are sialic acid-containing glycosphingolipids with strong amphiphilic character due to the bulky headgroup made of several sugar rings with sialic acid residues and the double-tailed hydrophobic lipid moiety. The amphiphilicity of gangliosides allows them to exist as micelles in aqueous media when they are present at a concentration above their critical micellar concentration. The protective effect of ganglioside micelles on spermatozoa is believed to stem from their ability to scavenge free radicals and prevent their damaging effects. In our study, we particularly focused our attention on the protective effect of ganglioside micelles on DNA in human spermatozoa exposed to cryopreservation. The results indicate that ganglioside micelles can modulate the hydrophobic properties of the sperm membrane to increase tolerance to DNA fragmentation, thus protecting the DNA from cryopreservation-induced damage. Further actions of ganglioside micelles, which were documented by biochemical and biophysical studies, included (i) the modulation of superoxide anion generation by increasing the diffusion barrier for membrane events responsible for signal translocation to the interior of the cell; (ii) the inhibition of iron-catalysed hydroxyl radical formation due to the iron chelation potential of gangliosides; and (iii) inhibition of hydrogen peroxide diffusion across the sperm membrane.

Spermatozoa and seminal plasma fatty acids as predictors of cryopreservation success

There is a lack of information about the importance of fatty acid composition of the human sperm membranes and seminal plasma in the cryopreservation procedure. Our aims were to study the possible relationships between the fatty acid composition of human spermatozoa or seminal fluid before freezing, and the sperm quality, measured in terms of viability and motility, before and after freezing-thawing. A further objective of this study was to determine whether the antioxidant capacity (TAC) of the seminal plasma is related to fatty acid (FA) composition and to success of the cryopreservation process. Polyunsaturated fatty acids (PUFA), ω3 PUFAs and docosahexaenoic acid (DHA) in spermatozoa were significantly positively correlated with sperm viability and motility parameters before and after freezing. An inverse relationship was found for monounsaturated (MUFA), ratio ω6/ω3, ratio saturated saturated fatty acids/PUFA (SFA/PUFA) with the seminal parameters. Seminal plasma fatty acid composition was not related to viability. However, motility parameters before and after freezing were related to stearic acid (C18:0) and DHA. TAC in seminal plasma was directly related to PUFA, w3 and DHA. On the other hand, SFA, C22:0, C24:0 and MUFA in seminal plasma were inversely related to the antioxidant capacity. TAC was directly correlated with motion parameters after thawing, We described a significant correlation between the fatty acid composition of the human spermatozoa or seminal plasma and the sperm parameters of the samples after thawing. PUFA, W3 and specially DHA are directly correlated with sperm motility and viability after freezing/thawing, and MUFA was inversely correlated. This means that in the future the fatty acid composition could be used as a predictor of the capacity of cryopreservation. On the other hand, we could design further procedures to modify the lipid composition or/and antioxidant capacity of ejaculate to make it more resistant to the cryopreservation process.

Evaluation of maize grain and polyunsaturated fatty acid (PUFA) as energy sources for breeding rams based on hormonal, sperm functional parameters and fertility

The objective of the present study was to elucidate the effect of different sources of dietary energy (maize vs polyunsaturated fatty acid (PUFA) on semen functional parameters and fertility of adult rams. Eighteen adult rams were divided into two groups (maize and PUFA, n=9). The main energy source for the rams in the maize group was coarsely ground maize grain, whereas in the PUFA group it was sunflower oil (rich in 18:2 linoleic acid, an omega-6 acid). The ration was fed for a minimum period of 60 days and thereafter semen was collected for evaluation. The proportion of progressive forward motility was significantly (P<0.05) higher in the PUFA group compared with the maize group. Sperm lipid peroxidation as measured by malondialdehyde formation (µM per 1×10(9) spermatozoa) was significantly (P<0.05) higher in the PUFA group compared with the maize group. When the semen was diluted with Tris-egg yolk-citrate buffer and incubated for 24h at 4°C, the proportions of plasmalemma integrity, the sperm subpopulation positive for functional membrane and acrosomal integrities, and mitochondrial membrane potential were significantly (P<0.05) higher in PUFA-fed than in maize-fed animals. The different sources of energy did not influence the serum and seminal plasma IGF-I levels. The cleavage rate (percentage) did not differ significantly between PUFA- (45.4±4.91) and maize- (44.63±6.8) fed animals. In conclusion, PUFA feeding influenced sperm quality by altering or stabilising membrane integrity. The present study indicates that PUFA may improve semen quality but did not improve in vitro fertilisation.

Epididymis cholesterol homeostasis and sperm fertilizing ability

Cholesterol, being the starting point of steroid hormone synthesis, is a long known modulator of both female and male reproductive physiology especially at the level of the gonads and the impact cholesterol has on gametogenesis. Less is known about the effects cholesterol homeostasis may have on postgonadic reproductive functions. Lately, several data have been reported showing how imbalanced cholesterol levels may particularly affect the post-testicular events of sperm maturation that lead to fully fertile male gametes. This review will focus on that aspect and essentially centers on how cholesterol is important for the physiology of the mammalian epididymis and spermatozoa.

Diffusion of active proteins into fish meat to minimize proteolytic degradation

Proteases in fish muscle often cause undesired softening of intact meat pieces during refrigerated storage or slow cooking. Several food-grade proteinaceous inhibitors can overcome this softening if properly delivered to the intracellular sites where proteases are located. Fluorescence recovery after photobleaching (FRAP) and laser scanning confocal microscopy (LSCM) were used to measure the translational diffusion of fluorescein isothiocyanate (FITC)-labeled protease inhibitors into intact muscle fibers of halibut. Diffusion coefficients (D) of alpha-2-macroglobulin (720 kDa), soybean trypsin inhibitor (21 kDa), and cystatin (12 kDa) were measured in both muscle fibers and dilute aqueous solutions. On the time scale of the observation (35 min), cystatin and soybean trypsin inhibitor diffused through the cell membrane (sarcolemma) and sarcoplasm, but at a considerably slower rate (>10-fold difference) than in dilute aqueous solution. alpha-2-Macroglobulin did not diffuse into muscle cells within the time frame of the experiment, but did completely penetrate the cell during overnight exposure. The present study thus shows a clear dependence of D on protein inhibitor size when moving within intact skeletal muscle fibers. Low molecular weight protease inhibitors such as cystatin can be effectively diffused into intact fish muscle cells to minimize proteolytic activity and meat softening.

Removal of spermatozoa with externalized phosphatidylserine from sperm preparation in human assisted medical procreation: effects on viability, motility and mitochondrial membrane potential

BACKGROUND

Externalization of phosphatidylserine (EPS) occurs in apoptotic-like spermatozoa and could be used to remove them from sperm preparations to enhance sperm quality for assisted medical procreation. We first characterized EPS in sperms from infertile patients in terms of frequency of EPS spermatozoa as well as localization of phosphatidylserine (PS) on spermatozoa. Subsequently, we determined the impact of depleting EPS spermatozoa on sperm quality.

METHODS

EPS were visualized by fluorescently-labeled annexin V binding assay. Double staining with annexin V and Hoechst differentiates apoptotic from necrotic spermatozoa. We used magnetic-activated cell sorting using annexin V-conjugated microbeads (MACS-ANMB) technique to remove EPS spermatozoa from sperm prepared by density gradient centrifugation (DGC). The impact of this technique on sperm quality was evaluated by measuring progressive motility, viability, and the integrity of the mitochondrial membrane potential (MMP) by Rhodamine 123.

RESULTS

Mean percentages of EPS spermatozoa were 14% in DGC sperm. Four subpopulations of spermatozoa were identified: 70% alive, 3% early apoptotic, 16% necrotic and 11% late apoptotic or necrotic. PS were localized on head and/or midpiece or on the whole spermatozoa. MACS efficiently eliminates EPS spermatozoa. MACS combined with DGC allows a mean reduction of 70% in EPS and of 60% in MMP-disrupted spermatozoa with a mean increase of 50% in sperm survival at 24 h.

CONCLUSION

Human ejaculates contain EPS spermatozoa which can mostly be eliminated by DGC plus MACS resulting in improved sperm long term viability, motility and MMP integrity. EPS may be used as an indicator of sperm quality and removal of EPS spermatozoa may enhance fertility potential in assisted medical procreation.

[Male adnexitis]

The term male adnexitis summarizes acute and chronic infections of the male urogenital tract. Chronic infections and inflammatory conditions are difficult to diagnose and the therapy has not been standardized. Therapy and management of complications has been clearly defined for acute urogenital infections. To date, antibiotic treatment in chronic infections and inflammatory conditions is only indicated when pathogenic bacteria can be retrieved from urogenital secretions.The usefulness of treatment with anti-inflammatory drugs is still debatable. One of the major concerns is the effect of urogenital infection on the fertility of the male. Although associations between urogenital infections and infertility have been shown for some entities, a general negative outcome of infectious events on male fertility appears to be unlikely.

Split-sample comparison of directional and liquid nitrogen vapour freezing method on post-thaw semen quality in white rhinoceroses (Ceratotherium simum simum and Ceratotherium simum cottoni)

To increase the quality of cryopreserved sperm in white rhinoceros, the liquid nitrogen vapour (LN vapour) freezing and the multi-thermal gradient directional freezing methods were compared. Sixteen white rhinoceros (Ceratotherium simum sp.) were electro-ejaculated. Semen samples were diluted with cryoextender (Tris, lactose, egg-yolk, DMSO) and aliquoted into straws for LN vapour freezing, and glass hollow tubes for directional freezing. The sperm quality was evaluated before and after freezing by assessing the following parameters: motility, morphologic state, acrosomal integrity and plasma membrane function and integrity (i.e. sperm viability) as defined by the hypo-osmotic swelling. Directional freezing improved the sperm viability by 5.6% (p<0.005), progressive motility score by 34.7% and sperm motility index (SMI) by 8.1% (p<0.005) versus LN vapour freezing. When data was categorized into groups of low (<19%), moderate (20-39%) and high (>40%) percentages of morphologically normal, directional freezing (DF) resulted in 31.4% less abnormal acrosomes for the low quality group as well as 18.7% increase in intact acrosomes and 10.9% increase in motility for the high quality group compared to LN vapour freezing (LN) (p<0.01, p<0.03, p<0.01, respectively). LN showed a significant reduction in sperm head volume (5.7%, p<0.05) compared to the prefreeze; whereas, no significant reduction in head volume was demonstrated after DF. Several additives (xanthenuric acid, cytochalasin D, potassium, EDTA) to the basic cryoextender provided no significant improvement in spermatozoal survival after directional freezing. In conclusion, directional freezing proved to facilitate higher gamete survival compared to LN vapour freezing. This is especially effective in ejaculates of low sperm quality and is important in endangered species where high quality semen donors are often not accessible. These results suggest that directional freezing could be valuable particularly for species with limited freezability of spermatozoa.

Development of vitrified-warmed mouse embryos co-cultured with polarized or non-polarized uterine epithelial cells using sequential culture media

PURPOSE

To our knowledge, little is known about the effect of polarized and non-polarized uterine epithelial cells on cryopreserved embryo growth. This study was, therefore, set up to investigate the effect of these monolayers together with sequential culture media on vitrified-warmed mouse embryos in terms of blastocyst development, blastocyst quality, incidence of apoptosis and related genes expression.

METHODS

Two cell vitrified-warmed mouse embryos were cultured in G-1ver3 medium to the eight-cell stage when they were randomly assigned to three treatment groups of no co-culture (control), non-polarized and polarized mouse uterine epithelial monolayer co-culture. The culture medium was G-2ver3 during the treatment phase. After 96 h on treatment, the significance of differences were evaluated by the one way analysis of variance for continuous data.

RESULTS

In the polarized monolayer group, the hatched blastocyst formation and blastocyst quality improved significantly than other two groups (P < 0.05). Whereas the incidence of apoptosis and related gene expression such as Bax were higher in the blastocysts of control group (P < 0.05). The relative abundance of Bcl-2 mRNA to the beta-tubulin was similar for all treatments.

CONCLUSION

Co-culture system involving polarized uterine epithelial cells and sequential culture media is a promising method for the improvement of vitrified-warmed mouse embryo development.

The fluidity of Chinese hamster ovary cell and bull sperm membranes after cholesterol addition

Cell plasma membrane fluidity is affected by membrane lipid and protein composition as well as temperature. Altering the cholesterol content of a membrane can change membrane fluidity at different temperatures and this may affect cell survival during cryopreservation. In these experiments, we examined the effect that adding cholesterol to the membranes of Chinese hamster ovary cells (CHO) and bull sperm had on cell plasma membrane fluidity and cell survival when cells were cooled to 5 degrees C or were cryopreserved. Cells were treated with 0, 1.5 or 5.0mg cholesterol-loaded cyclodextrin (CLC), stained with N-((4-(6-phenyl-1,3,5-hexatrienyl)phenyl)propyl)trimethylammonium-p-toluenesulfonate (TMAP-DPH) to evaluate membrane fluidity and with propidium iodide to evaluate cell viability, prior to analysis by flow cytometry at 23, 5 degrees C, and after cryopreservation. CHO cells exhibited a single cell population with all cells having similar membrane fluidity. Membrane fluidity did not change when temperature had been reduced and then returned to 23 degrees C (P<0.05), however, adding cholesterol to the cells induced membranes to become more rigid (P<0.05). Bull sperm samples consisted of two cell subpopulations, one having relatively higher membrane fluidity than the other, regardless of cholesterol treatment or temperature. In addition, cells possessing the highest membrane fluidity did not survive cooling or cryopreservation efficiently. CLC treatment did not significantly alter membrane fluidity after temperature changes, but did maintain higher percentages of spermatozoa surviving cooling to 5 degrees C and cryopreservation (P<0.05). In conclusion, adding cholesterol to cell resulted in detectable membrane fluidity changes in CHO cells and increased survival of bull sperm after cooling to 5 degrees C and after cryopreservation.

Hypochlorous acid-induced stress on human spermatozoa

The fertilising ability of human spermatozoa may be impaired by inflammations of the genital tract, although details of these processes are still unknown. Hypochlorous acid (HOCl), an important product of myeloperoxidase released from stimulated neutrophils, induces a concentration-dependent increase in externalisation of phosphatidylserine in ejaculated human spermatozoa as revealed by fluorescence-activated cell sorting (FACS) analysis. The increase of annexin-V binding cells starts already at about 10(-5) mol/l HOCl, while a formation of lysophosphatidylcholines as detected by matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is only found at HOCl concentrations higher than 10(-4) mol/l. Thus, changes in lipid composition of spermatozoa are unlikely responsible for the phosphatidylcholine (PS)-externalisation. These data gave concomitant evidence that HOCl itself leads to a dramatic damage of the cell membrane. Thus, the neutrophil-derived HOCl contributes to the deterioration of spermatozoa leading to diminished fertilisation ability.

Annexin V binding to plasma membrane predicts the quality of human cryopreserved spermatozoa

Cryopreservation-induced stress may result in membrane injury with consequent decrease of sperm motility and fertilizing capacity. This study has investigated the relationship between human spermatozoa tolerance to cryopreservation and the loss of plasma membrane asymmetry, especially translocation of phosphatidylserine (PS) from the inner to the outer leaflet. The prospective study was performed on semen samples from 31 men. Conventional characteristics of 20 semen were analysed, before and after cryopreservation as well as externalization of PS assessed by annexin V-staining in combination with the propidium iodide which stains dead cells. The fertilizing capacity was evaluated by a zona free hamster egg penetration test in 11 freeze/thaw spermatozoa samples. The percentages of vital annexin V-negative and annexin V-positive spermatozoa in post-thaw samples were significantly lower than in pre-freeze ones (10 +/- 3 vs. 25 +/- 5% and 22 +/- 3 vs. 34 +/- 4% respectively), while the percentages of dead spermatozoa annexin V-negative and annexin V-positive had increased (42 +/- 4 vs. 23 +/- 4% and 23 +/- 4 vs. 16 +/- 2% respectively). The percentages of progressive and total motile spermatozoa were significantly correlated with the percentage of vital annexin V-negative spermatozoa before as well as after cryopreservation. Furthermore, recovery of motile spermatozoa after freeze/thaw was strongly correlated (p < 0.002) with the proportion of vital annexin V-negative spermatozoa in fresh semen. The percentage of penetration of zona-free hamster eggs was correlated (p < 0.02) with the percentage of live annexin V-negative cryopreserved spermatozoa capacitated for 3 h. These findings provide evidence that annexinV-binding staining in combination with PI brings additional information to predict the outcome of cryopreserved ejaculated sperm and may be used as a novel and reliable marker to study the freeze/thaw process.

Deterioration of spermatozoal plasma membrane is associated with an increase of sperm lyso-phosphatidylcholines

Spermatozoa with plasma membranes that lost their asymmetry or permeability for larger molecules can be identified by binding of annexin V to membrane phosphatidylserine (PS). Paramagnetic annexin-V-conjugated microbeads (AN-MB) can be used to eliminate these spermatozoa by magnetic activated cell sorting (MACS). Semen samples of six healthy volunteers with normal spermiogram parameters were divided into two sperm fractions by MACS as a function of bound AN-MB, and their individual lipid compositions were examined by matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS). As a model system, liposomes composed of phosphatidylcholines (PC) from egg yolk were digested by phospholipase A2 (PLA2). The MALDI-TOF mass spectra of organic extracts of both sperm subpopulations differed significantly. The ratio between lyso-phosphatidylcholine LPC 16 : 0 and PC 16 : 0/22 : 6 was approximately 2.5-4.7-fold higher (median 2.9) in the sperm group binding AN-MB than in spermatozoa with intact membrane unable to bind AN-MB. The ratio between LPC 22 : 6 and PC 16 : 0/22 : 6 was also enhanced in the spermatozoa with impaired membrane structure (factor in the range: 1.9-3.9; median 2.6). These alterations corresponded to the effects of PLA2 on artificial phospholipids. It is concluded that spermatozoa with deteriorated membrane and exposed PS are characterized by an increased lyso-phosphatidylcholine content that is likely generated by phospholipases.

Characteristics of the cell membrane fluidity, actin fibers, and mitochondrial dysfunctions of frozen-thawed two-cell mouse embryos

Physical and chemical alterations caused by the freezing and thawing and their effects on survivals/developments in vitro were investigated. Of a total of 452 two-cell mouse embryos, the overall survival rate of the frozen-thawed embryos was 76.1% (344/452). The blastocyst formation of the frozen-thawed embryos was 32.6% (44/136) compared to 74.5% (117/157) in the fresh embryos (P<0.05). The total number of cells in a blastocyst also decreased from 96.0 +/- 19.0 (n=26) in the fresh embryos to 42.0 +/- 11 .34 (n=30) in the frozen-thawed embryos (P<0.05). Fluorescence recovery after photobleaching (FRAP) measurement revealed about 5-fold decrease in the cell membrane fluidity with a characteristic time constant (tau) of 1.46 +/- 0.13 sec (n=5) in the frozen-thawed embryos as opposed to 0.28 +/- 0.04 sec (n=5) in the fresh embryos (P<0.05). The relative amount of H(2)O(2) in an embryo as quantified by the fluorescence intensity of 2',7'-dichlorofluorescein (DCF) showed 62.8 +/- 23.5 (n=24) and 34.2 +/- 14.5 (n=20) in the frozen-thawed embryos and in the fresh embryos, respectively (P<0.05). The distribution of actin filaments in the frozen-thawed embryos revealed an uneven distribution, particularly discontinuities at the "actin band," which contrasted to an even distribution shown in the fresh embryos. Mitochondrial staining by Rhodamine 123 showed that there was no significant difference between the two treatments in the number and in the distribution of viable mitochondria, but a marked aggregation was seen in the arrested embryos. No Annexin V binding was detected in two-cell or four-cell embryos while the binding was positive in the arrested embryos. The mitochondrial membrane potential measured by a membrane potential-sensitive fluorescent probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazol- carbocyanine iodide (JC-1) revealed a marked depolarization in the frozen-thawed embryos. Finally, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-digoxigenin nick end-labeling (TUNEL) was employed to quantify the DNA fragmentation. In 75.0% cells of blastocysts (n=24) in the frozen-thawed embryos, the DNA fragmentation was detected as opposed to 37.0% in the fresh embryos (n=20) (P<0.05). Taken together, it is proposed that during the cryopreservation, two-cell mouse embryos are subjected to physical and chemical alterations, including destruction of the cell membrane integrity, redistribution of actin fibers, mitochondrial depolarizations, and increased reactive oxygen species (ROS) productions, which then may trigger the apoptotic cascade leading to a decrease in the survival rate and in the developmental rate of the embryos.

Cryopreservation alters membrane sulfhydryl status of bull spermatozoa: protection by oxidized glutathione

Cryopreservation induces extensive biophysical and biochemical changes in the membrane of spermatozoa that ultimately decrease the fertility potential of the cells. Sulfhydryl groups of sperm proteins regulate a number of activities of the cells. Qualitative and quantitative analyses of sulfhydryl groups in the sperm membrane were performed by fluorescence microscopy, fluorimetry and electrophoresis. Fluorimetric analysis using 5-iodoacetamidofluoresceine indicated a two-fold increase in the content of sulfhydryl groups in sperm membrane after a freezing/thawing cycle. Electrophoresis of Triton-soluble sperm proteins after labeling with 3-(N-maleimidylpropionyl) biocytin indicated that proteins of 40-65 and 34 kDa range expose more sulfhydryl groups after cooling at 4 degrees C and freezing/thawing. Cryopreservation of spermatozoa changed the distribution pattern of sulfhydryl groups on sperm surface measured with fluorescence microscopy using 5-iodoacetamidofluoresceine. The percentage of spermatozoa labeled at the level of the mid-piece decreased by 50 and 90% after cooling and freezing/thawing, respectively. Spin labeling studies showed a 15% faster rotational diffusion (mobility) of sulfhydryl containing proteins in the membrane of frozen/thawed spermatozoa as compared to that of fresh spermatozoa. Addition of glutathione, reduced (GSH) or oxidized (GSSG), to the cryoprotectant partially prevented the effects of freezing/thawing, such as higher exposure of sulfhydryl groups, changes in the cellular distribution, and enhanced rotational diffusion of sulfhydryl containing proteins of sperm membrane. Addition of GSSG to the cryoprotectant reduced by 35% the loss of motility of spermatozoa undergoing a freezing/thawing cycle. We concluded that cryopreservation perturbs sperm membrane sulfhydryl containing proteins and that these modifications could be partially prevented by the addition of GSSG to the cryopreservation medium.

Cryopreservation of fractionated, highly motile human spermatozoa: effect on membrane phosphatidylserine externalization and lipid peroxidation

INTRODUCTION

This study investigated lipid peroxidation (LPO) and membrane integrity following cryopreservation-thawing.

METHODS

Infertile men (study group) and donors (control group) were examined. Purified populations of highly motile spermatozoa were cryopreserved using TEST-yolk buffer and glycerol (TYB-G) followed by quick thaw. LPO was measured by a spectrophotometric assay, with and without a ferrous ion promoter. Annexin V binding was used to assess membrane translocation of phosphatidylserine (PS).

RESULTS

Pre-freeze LPO was significantly higher in the study than in the control group (P = 0.03). In both groups, LPO measurements after thawing were significantly higher than the pre-freeze samples not exposed to TYB-G (P = 0.002 and P = 0.001 respectively). However, when the pre-freeze samples with TYB-G were compared with the post-thaw samples (all exposed to TYB-G), these differences were not significant. There was a significant increase in PS externalization following cryopreservation in both groups (P = 0.02 and P = 0.003 respectively). In donors, pre-freeze LPO concentrations had a significant positive correlation with thawed spermatozoa depicting PS externalization (r = 0.77, P = 0.04).

CONCLUSION

Although patients had higher basal LPO than donors, LPO did not differ between fresh and cryopreserved-thawed fractionated motile spermatozoa. Freezing-thawing was associated with translocation of PS to the external membrane leaflet.

Production of reactive oxygen species by spermatozoa undergoing cooling, freezing, and thawing

In the present study, we provide evidence for the production of reactive oxygen species (ROS) during cryopreservation of bovine spermatozoa. Cooling and thawing of spermatozoa cause an increase in the generation of superoxide radicals. Although nitric oxide production remains unaltered during sperm cooling from 22-4 degrees C, a sudden burst of nitric oxide radicals is observed during thawing. Increase in lipid peroxidation levels have been observed in frozen/thawed spermatozoa and appears to be associated with a reduction in sperm membrane fluidity as detected by spin labeling studies. The data presented provide strong evidence that oxygen free radicals are produced during freezing and thawing of bovine spermatozoa and suggest that these reactive oxygen species may be a cause for the decrease in sperm function following cryopreservation. Mol. Reprod. Dev. 59: 451-458, 2001.

Lipid dynamics in the plasma membrane of ram and bull spermatozoa after washing and exposure to macromolecules BSA and PVP

Seminal plasma proteins and macromolecules in the external medium have a major influence on the functionality of sperm plasma membranes. In this investigation we have examined their effects on lipid diffusion in the surface membrane of ram and bull spermatozoa as measured by fluorescence recovery after photobleaching (FRAP). Results show that progressive removal of seminal plasma from ram spermatozoa by repeated centrifugation and resuspension in media +/- 4% bovine serum albumin (BSA) or 0.4% polyvinlypyrrolidone (PVP) causes a reduction in lipid diffusion in all regions of the membrane. By contrast, bull sperm membranes respond with an increase in diffusion in all regions. Repeated washing of bull spermatozoa whose membranes were previously immobile (i.e., showed no recovery after FRAP) restored lipid diffusion suggesting an inhibitory effect of seminal plasma proteins. Further analysis by atomic force microscopy revealed a close association between BSA and the plasma membrane. It is concluded that diffusion of lipids in the plasma membrane of ejaculated ram and bull spermatozoa is influenced by seminal plasma proteins and the composition of the suspending medium. Mol. Reprod. Dev. 59:306-313, 2001.

Cryopreservation-thawing of fractionated human spermatozoa and plasma membrane translocation of phosphatidylserine

OBJECTIVE(S)

[1] To evaluate sperm membrane damage during cryopreservation-thawing by the assessment of phosphatidylserine (PS) translocation and [2] to examine the relationship between reactive oxygen species (ROS) and cryopreservation-related alterations.

DESIGN

Prospective cohort study.

SETTING

University-based center.

PATIENT(S)

Men consulting for infertility and fertile donors (controls).

INTERVENTION(S)

Semen processing was performed by density gradient separation followed by cryopreservation and thawing.

MAIN OUTCOME MEASURE(S)

Membrane PS translocation was evaluated with annexin V binding, generation of ROS was detected by chemiluminescence, and motion parameters were assessed by computer analysis.

RESULT(S)

Annexin V binding was detected in the prefreeze fractions with high and low sperm motility. In the patient group, there were significantly higher postthaw levels of annexin V binding in both fractions when compared with prefreezing values. However, such induction of PS translocation was significantly higher in the fractions with high sperm motility. Significantly higher ROS levels were detected in prefreeze samples of the fractions with low sperm motility.

CONCLUSION(S)

In the population of men studied, [1] cryopreservation-thawing was associated with induction of membrane PS translocation; [2] postthaw ROS levels were lower than before freezing; and [3] neither annexin V binding results nor the generation of ROS were able to accurately predict sperm cryosurvival rates.

Dynamics of the mammalian sperm plasma membrane in the process of fertilization

Sexual reproduction requires the fusion of sperm cell and oocyte during fertilization to produce the diploid zygote. In mammals complex changes in the plasma membrane of the sperm cell are involved in this process. Sperm cells have unusual membranes compared to those of somatic cells. After leaving the testes, sperm cells cease plasma membrane lipid and protein synthesis, and vesicle mediated transport. Biophysical studies reveal that lipids and proteins are organized into lateral regions of the sperm head surface. A delicate reorientation and modification of plasma membrane molecules take place in the female tract when sperm cells are activated by so-called capacitation factors. These surface changes enable the sperm cell to bind to the extra cellular matrix of the egg (zona pellucida, ZP). The ZP primes the sperm cell to initiate the acrosome reaction, which is an exocytotic process that makes available the enzymatic machinery required for sperm penetration through the ZP. After complete penetration the sperm cell meets the plasma membrane of the egg cell (oolemma). A specific set of molecules is involved in a disintegrin-integrin type of anchoring of the two gametes which is completed by fusion of the two gamete plasma membranes. The fertilized egg is activated and zygote formation preludes the development of a new living organism. In this review we focus on the involvement of processes that occur at the sperm plasma membrane in the sequence of events that lead to successful fertilization. For this purpose, dynamics in adhesive and fusion properties, molecular composition and architecture of the sperm plasma membrane, as well as membrane derived signalling are reviewed.

Lipid analysis of human spermatozoa and seminal plasma by MALDI-TOF mass spectrometry and NMR spectroscopy - effects of freezing and thawing

In the present study, the applicability of proton NMR spectroscopy and matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) to the analysis of the lipid composition of human spermatozoa and seminal fluids as well as changes after cryopreservation of human spermatozoa was investigated. Whereas NMR spectra primarily indicated a high content of double bonds within the spermatozoa but no marked differences upon cryopreservation, MS detected intense peaks which could be assigned to phosphatidylcholines containing one docosahexaenoic and one palmitic or stearic acid residue (m/z=806 and 834). In contrast, the seminal plasma contained more saturated fatty acids and especially more sphingomyelin (SM). A freezing/thawing cycle markedly influences the lipid composition of spermatozoa. There was a diminution of phosphatidylcholines (16:0, 22:6 and 18:0, 22:6) and SM (16:0) and the appearance of lysophosphatidylcholines (16:0 and 18:0) and ceramide (16:0). These data demonstrate the release or activation of both phospholipase A(2) and sphingomyelinase in human spermatozoa due to the freezing/thawing cycle. These results were finally confirmed by experiments on the action of phospholipases on lipids containing docosahexaenoic acid.

Analysis of DNA fragmentation, plasma membrane translocation of phosphatidylserine and oxidative stress in human spermatozoa

The objectives of this cross-sectional observational study were: (i) to detect DNA damage and plasma membrane translocation of phosphatidylserine in purified sperm populations of high and low motility, and (ii) to analyse their relationship with the endogenous generation of reactive oxygen species. Ejaculates from infertile men were examined following gradient centrifugation. The main outcome measures were: sperm motion parameters (assessed with a computer analyser), generation of reactive oxygen species (measured by chemiluminescence), DNA damage (detected by terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling and monoclonal antibody labelling of single-stranded DNA) and translocation of membrane phosphatidylserine (examined with annexin V staining). DNA fragmentation and membrane translocation of phosphatidyl-serine were observed in the fractions with low and high sperm motility in all patients. The fractions with low sperm motility had significantly higher proportion of cells with DNA damage and production of reactive oxygen species than the fractions with high sperm motility (P < 0.005). DNA fragmentation was significantly and positively correlated with the generation of reactive oxygen species (r = 0.42; P = 0.02).

IN CONCLUSION

(i) spermatozoa from infertile men display translocation of membrane phosphatidylserine as diagnosed by annexin V positive staining; (ii) DNA damage (fragmentation and presence of single-stranded DNA) can be detected in ejaculated spermatozoa from infertile men in fractions with low and high sperm motility, and (iii) there is a relationship between DNA damage and oxidative stress.

Fatty acid composition of spermatozoa and immature germ cells

A great deal of attention has recently been given to the essential role of polyunsaturated fatty acids (PUFA) of sperm membranes. We studied the fatty acid composition of the immature germ cells (IGC) and of the sperm populations separated by Percoll gradient in the ejaculate of normozoospermic patients. Fatty acid pattern was analysed by combined gas chromatography-mass spectrometry on a capillary column. In IGC, differences were found compared with mature spermatozoa, with a higher percentage of saturated fatty acids and of essential fatty acids. On the contrary, the long-chain PUFA were significantly lower in IGC. The highest concentration of n3 PUFA docohexaenoic acid (DHA) was detected in the spermatozoa deriving from 70-100% Percoll layers and a direct linear correlation was found between the increase of DHA and increased percentage of Percoll gradient. An inverse relationship between the percentage of atypical sperm forms in each layer and the percentage of DHA was also observed. This study demonstrates that the human germ cell line can elongate and desaturate essential fatty acids and that the percentage of long-chain PUFA is correlated with the normal morphology of sperm cells.