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

Paternal Age Amplifies Cryopreservation-Induced Stress in Human Spermatozoa

The global fall in male fertility is a complicated process driven by a variety of factors, including environmental exposure, lifestyle, obesity, stress, and aging. The availability of assisted reproductive technology (ART) has allowed older couples to conceive, increasing the average paternal age at first childbirth. Advanced paternal age (APA), most often considered male age ≥40, has been described to impact several aspects of male reproductive physiology. In this prospective cohort study including 200 normozoospermic patients, 105 of whom were ≤35 years (non-APA), and 95 of whom were ≥42 years (APA), we assessed the impact of paternal age on different endpoints representative of sperm quality and cryopreservation tolerance. Non-APA patients had superior fresh semen quality; DNA fragmentation was notably increased in APA as compared to non-APA individuals (21.7% vs. 15.4%). Cryopreservation further increased the DNA fragmentation index in APA (26.7%) but not in non-APA patients. Additionally, APA was associated with increased mtDNAcn in both fresh and frozen/thawed sperm, which is indicative of poorer mitochondrial quality. Cryopreservation negatively impacted acrosome integrity in both age groups, as indicated by reduced incidences of unreacted acrosome in relation to fresh counterparts in non-APA (from 71.5% to 57.7%) and APA patients (from 75% to 63%). Finally, cryopreservation significantly reduced the phosphorylation status of proteins containing tyrosine residues in sperm from young males. Therefore, the present findings shed light on the effects of paternal age and cryopreservation on sperm quality and serve as valuable new parameters to improve our understanding of the mechanisms underlying sperm developmental competence that are under threat in current ART practice.

Zinc Cations Uniquely Stabilize Cell Membrane for Cell Cryopreservation

We report, for the first time, merely using a small amount of (0.039% w/w) Zn(II) instead of very high concentration (25%-50% w/w) of conventional cryoprotective agents (CPAs), i.e., glycerol, during the cryopreservation of red blood cells (RBCs) can lead to a comparable post-thaw recovery rate of ∼95% while avoiding the tedious gradient washout process for the removal of CPA afterward. The result is remarkable, since Zn(II) does not have the ice-controlling ability reported to be critical for CPA. It benefits from its moderate interaction with lipid molecules, facilitating the formation of small and dynamic lipid clusters. Consequently, the membrane fluidity is maintained, and the cells are resilient to osmotic and mechanical stresses during cryopreservation. This study first reports the ion-specific effect on stabilizing the cell membrane; meanwhile, reversibly tuning the structure of biological samples against injuries during the cooling and rewarming provides a new strategy for cryopreservation.

Ejaculatory Abstinence Affects the Sperm Quality in Normozoospermic Men-How Does the Seminal Bacteriome Respond?

This study was designed to describe bacterial profiles of ejaculates collected following a long and short ejaculatory abstinence set in the context of changes in the conventional, oxidative, and immunological characteristics of semen. Two specimens were collected in succession from normozoospermic men (n = 51) following 2 days and 2 h, respectively. Semen samples were processed and analyzed according to the World Health Organization (WHO) 2021 guidelines. Afterwards, sperm DNA fragmentation, mitochondrial function, levels of reactive oxygen species (ROS), total antioxidant capacity, and oxidative damage to sperm lipids and proteins were evaluated in each specimen. Selected cytokine levels were quantified using the ELISA method. Bacterial identification by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry revealed that samples collected following two days of abstinence presented with a higher bacterial load and diversity, and a greater prevalence of potentially uropathogenic bacteria including Escherichia coli, Staphylococcus aureus and Enterococcus faecalis. Only staphylococci and Escherichia coli remained present in specimens obtained after 2 h of abstinence. Whilst all samples accomplished the criteria set by WHO, a significantly higher motility (p < 0.05), membrane integrity (p < 0.05), mitochondrial membrane potential (p < 0.05), and DNA integrity (p < 0.0001) were detected following 2 h of ejaculatory abstinence. On the other hand, significantly higher ROS levels (p < 0.001), protein oxidation (p < 0.001), and lipid peroxidation (p < 0.01) accompanied by significantly higher concentrations of tumor necrosis factor alpha (p < 0.05), interleukin-6 (p < 0.01), and interferon gamma (p < 0.05) were observed in specimens collected after two days of abstinence. It may be summarized that shorter ejaculatory abstinence does not compromise sperm quality in normozoospermic men, while it contributes to a decreased occurrence of bacteria in semen which is accompanied by a lower probability of damage to spermatozoa by ROS or pro-inflammatory cytokines.

NADPH oxidase 5 activation; a novel approach to human sperm cryoinjury

Sperm cryopreservation leads to various structural and functional damages, some of which induce by oxidative stress. The reactive oxygen species (ROS) generates by mitochondria and membrane NADPH oxidases (NOXs). Among the NOXs, only NOX5 has been identified in the cell membrane of human sperm. This study was designed to clarify the possible role of NOX5 on sperm cryoinjury. Forty human semen samples were washed and randomly divided into fresh and cryopreserved groups. Each group was divided into 4 subgroups containing Ham's F10 (control), 0.1% DMSO (vehicle), 100 nM of PMA (phorbol 12-myristate 13-acetate) and 1 µM of DPI (diphenyleneiodonium), as NOX5 activator and inhibitor. The samples of cryopreserved groups were preserved in liquid nitrogen for 1 month. The sperm kinematics, membrane integrity, ROS production, apoptosis rate, mitochondrial membrane potential (MMP), intracellular ATP and calcium concentration [Ca²⁺]_i were evaluated. The percent of sperm with intact membrane and motile sperm reduced significantly after thawing (p ≤ 0.01). The ROS production (p ≤ 0.01) and the apoptotic rate increased, MMP dissipated, and the percentage of live cells with high [Ca²⁺]_i decreased significantly in the cryopreserved control group relative to the fresh control group. DPI, in contrast to PMA, improved sperm progressive motility (p ≤ 0.01), membrane integrity in fresh and cryopreserved groups and reduced the ROS amount in cryopreserved group (p ≤ 0.01). Apoptotic rate, [Ca²⁺]_i, ATP, and MMP did not change with DPI and PMA in cryopreserved groups. We conclude that NOX5 activity in fresh sperm is low, and it increases during cryopreservation. NOX5 inhibition improves the cryopreserved sperm quality.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

Sperm cryopreservation: A review on current molecular cryobiology and advanced approaches

The cryopreservation of spermatozoa was introduced in the 1960s as a route to fertility preservation. Despite the extensive progress that has been made in this field, the biological and biochemical mechanisms involved in cryopreservation have not been thoroughly elucidated to date. Various factors during the freezing process, including sudden temperature changes, ice formation and osmotic stress, have been proposed as reasons for poor sperm quality post-thaw. Little is known regarding the new aspects of sperm cryobiology, such as epigenetic and proteomic modulation of sperm and trans-generational effects of sperm freezing. This article reviews recent reports on molecular and cellular modifications of spermatozoa during cryopreservation in order to collate the existing understanding in this field. The aim is to discuss current freezing techniques and novel strategies that have been developed for sperm protection against cryo-damage, as well as evaluating the probable effects of sperm freezing on offspring health.

Cryopreservation media differentially affect sperm motility, morphology and DNA integrity

INTRODUCTION

Human sperm freezing is very widely used for male fertility preservation. This procedure consists in adding cryoprotectants to the spermatozoa followed by cooling and storing the spermatozoa at a subzero temperature. Many standardized cryopreservation media are available on the market. However, these media differ in their chemical composition and there are no sufficient data to optimize their classification. Therefore, the aim of this study was to compare five commercially available sperm cryopreservation media, which have not been compared together, in terms of motility, morphology and DNA integrity.

MATERIALS AND METHODS

One-hundred semen samples were obtained from 10 fertile participants and 90 infertile men. Each sample was evaluated before freezing for motility, morphology and DNA fragmentation index (DFI). Then, it was equally divided into five aliquots. Each aliquot was cryopreserved using one of the five media (A, B, C, D, and E). The same parameters were re-evaluated after the addition of the cryopreservation media in the fertile group, and after sperm thawing in fertile and infertile groups.

RESULTS

The results showed that the five selected cryopreservation media had negative effects on sperm motility and morphology per se. In the infertile group, the cryosurvival factor was significantly lower in cryomedium A when compared to the four other media (p < 0.001). In addition, a significantly higher percentage of sperm with coiled tail was detected in cryomedium E compared to cryomedium A (p < 0.05) and to cryomedium B (p < 0.001) after thawing, in the infertile group. Furthermore, the sperm DFI was significantly higher in cryomedia A (p < 0.001), B (p < 0.001), C (p < 0.01), D (p < 0.01) and E (p < 0.05) compared to that of the fresh semen derived from infertile participants.

CONCLUSION

This study indicates that the recovery rate of competent spermatozoa, after cryopreservation, is still critical in infertile men. Therefore, frozen semen sample should be used only when necessary.

Minimal volume vitrification of epididymal spermatozoa results in successful in vitro fertilization and embryo development in mice

This study compared three cryopreservation protocols on sperm functions, IVF outcomes, and embryo development. Epididymal spermatozoa cryopreserved using slow-cooling (18% w/v raffinose, RS-C) were compared with spermatozoa vitrified using 0.25 M sucrose (SV) or 18% w/v raffinose (RV). The motility, vitality, and DNA damage (TUNEL assay) of fresh control (FC) spermatozoa were compared with post-thawed or warmed RS-C, RV, and SV samples. Mouse oocytes (n = 267) were randomly assigned into three groups for insemination: RV (n = 102), RS-C (n = 86), and FC (n = 79). The number and the proportion of two-cell embryos and blastocysts from each treatment were assessed. Sperm motility (P < 0.01) and vitality (P < 0.05) were significantly reduced after vitrification compared with slow-cooled spermatozoa. However, DNA fragmentation was significantly reduced in spermatozoa vitrified using sucrose (15 ± 1.8% [SV] vs 26 ± 2.8% [RV] and 27 ± 1.2% [RS-C]; P < 0.01). Although the number of two-cell embryos produced by RS-C, RV, and FC spermatozoa was not significantly different, the number of blastocysts produced from two-cell embryos using RV spermatozoa was significantly higher than FC spermatozoa (P = 0.0053). This simple, small volume vitrification protocol and standard insemination method allows successful embryo production from small numbers of epididymal spermatozoa and may be applied clinically to circumvent the need for ICSI, which has the disadvantage of bypassing sperm selection.

Chapter 6 Technology of Aseptic Cryoprotectant-Free Vitrification of Human ICSI Spermatozoa

The aim of this chapter was to describe the standardized aseptic technology of permeable cryoprotectant-free vitrification of human spermatozoa in capillaries (for ICSI or IVF in microvolume). Spermatozoa, vitrified by this technology, are free from seminal plasma owing to swim-up procedure preceding vitrification and are free from permeable cryoprotectants. They are ready for further use immediately after warming without any additional treatment.

Long-Time Cooling before Cryopreservation Decreased Translocation of Phosphatidylserine (Ptd-L-Ser) in Human Ovarian Tissue

Objectives

To translocation (externalization) of phosphatidylserine lead at least the five negative effects observed during cells cryopreservation: hypoxia, increasing of intracellular Ca²⁺, osmotic disruption of cellular membranes, generation of reactive oxygen species (ROS) and lipid peroxidation. The aim of this study was to test the intensiveness of the phosphatidylserine translocation immediately after thawing and after 45 d xenografting of human ovarian tissue, which was either frozen just after operative removal from patient or cooled before cryopreservation to 5°C for 24 h and then frozen.

Materials and Methods

Ovarian fragments from twelve patients were divided into small pieces in form of cortex with medulla, and randomly divided into the following four groups. Pieces of Group 1 (n=30) were frozen immediately after operation, thawed and just after thawing their quality was analyzed. Group 2 pieces (n=30) after operation were cooled to 5°C for 24 h, then frozen after 24 h pre-cooling to 5°C, thawed and just after thawing their quality was analyzed. Group 3 pieces (n=30) were frozen immediately after operation without pre-cooling, thawed, transplanted to SCID mice and then, after 45 d of culture their quality was analyzed. Group 4 pieces (n=30) were frozen after 24 h pre-cooling to 5°C, thawed, transplanted to SCID mice and then, after 45 d their quality was analyzed. The effectiveness of the pre-freezing cooling of tissuewas evaluated by the development of follicles (histology) and by intensiveness of translocation of phosphatidylserine (FACS with FITC-Annexin V and Propidium Iodide).

Results

For groups 1, 2, 3 and 4 the mean densities of follicles per 1 mm³ was 19.0, 20.2, 12.9, and 12.2, respectively (P_{1-2, 3-4} >0.1). For these groups, 99%, 98%, 88% and 90% preantral follicles, respectively were morphologically normal (P_{1-2, 3-4} >0.1). The FACS analysis showed significantly decreased intensiveness of translocation of phosphatidylserine after pre-cooling of frozen tissue (46.3% and 33.6% in Groups 2 and 4, respectively), in contrast with tissue frozen without pre-cooling (77.1% and 60.2 % in Groups 1 and 3, respectively, P_{1, 3-2, 4} <0.05).

Conclusions

Long time (24 h) cooling of ovarian tissue to 5°C before cryopreservation decreased translocation of phosphatidylserine that evidences about increases the viability of the cells in the tissue after thawing.

Density gradient centrifugation prior to cryopreservation and hypotaurine supplementation improve post-thaw quality of sperm from infertile men with oligoasthenoteratozoospermia

STUDY QUESTION

Can selection of spermatozoa by density gradient centrifugation prior to cryopreservation and/or hypotaurine supplementation improve the post-thaw quality of sperm from infertile men with oligoasthenoteratozoospermia?

SUMMARY ANSWER

Sperm selection by density gradient centrifugation before freezing and supplementation of the media by hypotaurine is beneficial for the cryopreservation of semen samples of patients with oligoasthenoteratozoospermia.

WHAT IS KNOWN ALREADY

Sperm from men with oligoasthenoteratozoospermia are more susceptible than normal to cryoinjury. Density gradient centrifugation before sperm freezing may allow the selection of a subpopulation of spermatozoa more resistant to cryopreservation. Hypotaurine is an antioxidant with a protective effect on sperm functions.

STUDY DESIGN, SIZE, DURATION

The experiment was carried out according to a factorial design involving two binary factors resulting in four treatment combinations which were randomly allocated in oligoasthenoteratozoospermia sperm samples from 64 patients recruited between January 2009 and June 2010.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen was provided by 64 men undergoing evaluation for infertility at the Centre for Reproductive Medicine of the University Hospital in Clermont-Ferrand, France, between January 2009 and June 2010. Four treatment combinations were tested: sperm freezing before selection without (F-S/H-; n = 16) and with hypotaurine supplementation (F-S/H+; n = 16); sperm selection before freezing without (S-F/H-; n = 16) and with hypotaurine supplementation (S-F/H+; n = 16). Measurements of sperm recovery rates and markers of apoptosis (externalization of phosphatidylserine (PS), mitochondrial membrane potential and DNA fragmentation) were compared in recovered spermatozoa after each procedure.

MAIN RESULTS AND THE ROLE OF CHANCE

Higher recovery rates of progressive and total motile spermatozoa were observed when sperm selection was performed before freezing (P < 0.05). The protective effect of hypotaurine was only observed on the percentage of live spermatozoa with PS externalization among total live spermatozoa (AN+ PI-/((AN+ PI-) + (AN- PI-)) when the sperm selection by density gradient centrifugation was performed before freezing (S-F/H+ versus S-F/H-: 6.8 ± 1.09 versus 11.8 ± 2.03%, P = 0.04). The percentage of mitochondrial membrane potential (DiOC6(3) (high)) spermatozoa was higher (P = 0.001) when sperm selection was done before freezing compared with procedures in which sperm selection was done after sperm freezing with (S-F/H+ versus F-S/H+: 58.1 ± 3.50 versus 46.7 ± 5.48%) or without (S-F/H- versus F-S/H-: 57.0 ± 5.18 versus 35.4 ± 4.99%) hypotaurine supplementation. The percentages of TUNEL+ spermatozoa were significantly lower (P = 0.001) when sperm selection was done before sperm freezing compared with procedures in which sperm selection was done after sperm freezing with (S-F/H+ versus F-S/H+: 38.6 ± 9.59 versus 55.7 ± 5.88%) or without hypotaurine supplementation (S-F/H- versus F-S/H-: 37.2 ± 7.91 versus 71.0 ± 5.66%).

LIMITATIONS, REASONS FOR CAUTION

The ICSI outcomes were not assessed and the fertility of the spermatozoa remains unknown.

WIDER IMPLICATIONS OF THE FINDINGS

Sperm selection by density gradient centrifugation before freezing and hypotaurine supplementation could improve the cryopreservation of sperm from oligoasthenoteratozoospermic men and make a larger number of functional spermatozoa available for ICSI.

STUDY FUNDING/COMPETING INTERETS(S)

This work was supported by a hospital grant (Projet Hospitalier Recherche Clinique, CHU Clermont Ferrand, France). None of the authors has any conflict of interest to declare.

Concentration of Glutathione and Expression of Glutathione Peroxidases 1 and 4 in Fresh Sperm Provide a Forecast of the Outcome of Cryopreservation of Human Spermatozoa

Oxidative stress imbalance potentially leads to damage of the structure of the cell and macromolecules such as plasma membrane components, proteins, and DNA. The plasma membrane of the sperm cell, which has high levels of polyunsaturated fatty acids, renders it particularly sensitive to free radical-mediated attacks. The freezing and subsequent thawing of sperm is a physically stressful process carried out during routine procedures in assisted reproduction techniques, which results in a highly variable and unpredictable reduction in the number of motile sperm cells. Subsequently, oxidative status can positively or negatively affect the motility, viability, and fertilizing capacity of thawed sperm. These effects are counteracted by various oxidative defense enzymes and anti-oxidants such as glutathione peroxidase isoforms GPx1 and GPx4, glutathione reductase (GR), and cellular glutathione (reduced) (GSH). In this way, oxidative status could represent a predictive marker of sperm quality following the freeze-thaw process. This study was based on 56 human sperm samples. We observed direct positive and negative relationships between the postthaw motile sperm recovery rate and GPx1 and GPx4 expression and activity, on the one hand, and GSH concentrations, on the other. No correlation was found between this recovery rate and GR or basic semen parameters. Predictive values clearly demonstrate that, among the molecules analyzed, the most accurate diagnoses result when analyses are conducted for GPx1 and GPx1 messenger RNA expression, GPx1 and GPx4 enzymatic activity, and GSH concentration. In conclusion, a reserve of glutathione, together with GPx expression, is necessary to eliminate free radicals using GSH or a like structural protein and seems to be essential for a good postthaw recovery. These molecules can be employed as indicators of postthaw sperm quality.

Novel Approaches to the Cryopreservation of Human Spermatozoa: History and Development of the Spermatozoa Vitrification Technology

Cryobiology is very intensively applied in reproductive and veterinary medicine for preservation of gametes, embryos and reproductive tissues. Sub-zero temperatures combined with appropriate cryoprotective agents preserve the physiological and reproductive functions of the cells making long-term storage possible without loss of viability. With the use of cryoprotective agents it has become possible to develop cryopreservation techniques, such as the slow conventional freezing and vitrification that are in use in the present times. In slow controlled-rate conventional freezing extracellular ice crystals are formed whereas in vitrification no ice crystals are formed. Glass formation is compatible with the survival of the cell and the preservation of its intracellular structures provided the type(s) and concentrations of cryoprotectant used are not chemo- or osmotoxic. However, irrespective of the type of cooling method employed the cryosurvival of cells and tissues is influenced by the size and maturity of cells, amounts of intracellular water, quality and quantity of intracellular lipids, type of cells, their function and morphology. The intracellular milieu of cryopreserved cells and tissues remain less understood. The application of nanotechnology may help reveal and help advance our knowledge of the cryobiological principles involved in cryosurvival. At this moment the methods of cryopreservation that merit further investigation are vitrification and lyophilization. Vitrification is cheap if reagents are prepared in-house and the procedure can be performed rapidly. It has been successfully applied for gametes and embryos (of different stages of development), and reproductive cells/tissues, somatic cells and stem cells. However, vitrification is more demanding technically and requires operation and storage at sub-zero temperatures. On the other hand lyophilization deserves further investigation because it is a cheaper form of cryopreservation that may enable cryostorage at less demanding temperatures of 4°C and may even allow transport at ambient temperature. These possibilities are explored in this review.

A comparison of cryopreservation methods: Slow-cooling vs. rapid-cooling based on cell viability, oxidative stress, apoptosis, and CD34+ enumeration of human umbilical cord blood mononucleated cells

BACKGROUND

The finding of human umbilical cord blood as one of the most likely sources of hematopoietic stem cells offers a less invasive alternative for the need of hematopoietic stem cell transplantation. Due to the once-in-a-life time chance of collecting it, an optimum cryopreservation method that can preserve the life and function of the cells contained is critically needed.

METHODS

Until now, slow-cooling has been the routine method of cryopreservation; however, rapid-cooling offers a simple, efficient, and harmless method for preserving the life and function of the desired cells. Therefore, this study was conducted to compare the effectiveness of slow- and rapid-cooling to preserve umbilical cord blood of mononucleated cells suspected of containing hematopoietic stem cells. The parameters used in this study were differences in cell viability, malondialdehyde content, and apoptosis level. The identification of hematopoietic stem cells themselves was carried out by enumerating CD34+ in a flow cytometer.

RESULTS

Our results showed that mononucleated cell viability after rapid-cooling (91.9%) was significantly higher than that after slow-cooling (75.5%), with a p value = 0.003. Interestingly, the malondialdehyde level in the mononucleated cell population after rapid-cooling (56.45 μM) was also significantly higher than that after slow-cooling (33.25 μM), with a p value < 0.001. The apoptosis level in rapid-cooling population (5.18%) was not significantly different from that of the mononucleated cell population that underwent slow-cooling (3.81%), with a p value = 0.138. However, CD34+ enumeration was much higher in the population that underwent slow-cooling (23.32 cell/μl) than in the one that underwent rapid-cooling (2.47 cell/μl), with a p value = 0.001.

CONCLUSIONS

Rapid-cooling is a potential cryopreservation method to be used to preserve the umbilical cord blood of mononucleated cells, although further optimization of the number of CD34+ cells after rapid-cooling is critically needed.

Effect of sperm DNA fragmentation on pregnancy outcome depends on oocyte quality

OBJECTIVE

To quantify the effect of sperm DNA fragmentation (SDF) on reproductive outcome by evaluating the most statistically significant bias factors using logistic regression.

DESIGN

Prospective blind observational cohort study.

SETTING

University affiliated private IVF unit.

PATIENT(S)

Two hundred ten male partners of couples undergoing in vitro fertilization (IVF) or first intracytoplasmic sperm injection (ICSI) cycles with fresh or thawed sperm with the women's own or donated oocytes.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

SDF determined before and after swim-up (n=420), odds ratio calculated of the effect of an increase of one unit of SDF on pregnancy, and stratified regression analysis performed to evaluate the confusion effect of oocyte quality, sperm origin, and the fertilization procedure.

RESULT(S)

The effect of SDF on pregnancy was not affected by sperm origin (fresh or thawed) or fertilization procedure when measured both before and after swim-up. When oocytes from infertile patients were employed, SDF had a statistically significant negative impact on chance of pregnancy. For every 10% increase in SDF, the probability of not achieving pregnancy increased by 1.31. When donated oocytes were employed, SDF did not have a statistically significant effect.

CONCLUSION(S)

The effect of SDF on the probability of pregnancy can be calculated independent of the fertilization procedure or sperm origin. Oocyte quality conditions the extent of the negative impact of SDF on pregnancy; this can be overcome when good quality oocytes are employed.

The effect of age on the expression of apoptosis biomarkers in human spermatozoa

OBJECTIVE

To evaluate the impact of age on the expression of apoptotic biomarkers in human spermatozoa.

DESIGN

Cross sectional, prospective study.

SETTING

Academic centers.

PATIENT(S)

Healthy volunteers with proven fertility, stratified by age (n = 25, range: 20-68 years).

INTERVENTION(S)

Examination of serum hormone levels and basic semen parameters, and assessment of early (plasma membrane translocation of phosphatidylserine) and late (DNA fragmentation) sperm apoptotic markers by flow cytometry (using Annexin-V binding and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling).

MAIN OUTCOME MEASURE(S)

Apoptosis markers.

RESULT(S)

Advancing male age was significantly and positively correlated with Annexin-V binding results. Although not significant, there was a clear trend for increased DNA fragmentation in the older groups. The age threshold for these observations appears to be 40 years. Advancing male age was positively correlated with FSH and sex hormone-binding globulin (SHBG) levels, and negatively correlated with sperm concentration.

CONCLUSION(S)

Advancing male age is associated with the expression of early apoptotic markers as evidenced by significantly increased plasma membrane translocation of phosphatidylserine, as well as with a more subtle proportion of sperm carrying DNA fragmentation. This study confirmed that male age is also associated with a decline in sperm concentration.

Sperm proteins in teleostean and chondrostean (sturgeon) fishes

Sperm proteins in the seminal plasma and spermatozoa of teleostean and chondrostean have evolved adaptations due to the changes in the reproductive environment. Analysis of the composition and functions of these proteins provides new insights into sperm motility and fertilising abilities, thereby creating possibilities for improving artificial reproduction and germplasm resource conservation technologies (e.g. cryopreservation). Seminal plasma proteins are involved in the protection of spermatozoa during storage in the reproductive system, whereas all spermatozoa proteins contribute to the swimming and fertilising abilities of sperm. Compared to mammalian species, little data are available on fish sperm proteins and their functions. We review here the current state of the art in this field and focus on relevant subjects that require attention. Future research should concentrate on protein functions and their mode of action in fish species, especially on the role of spermatozoa surface proteins during fertilisation and on a description of sturgeon sperm proteins.

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.

Effects of cryopreservation on human sperm deoxyribonucleic acid integrity

OBJECTIVE

To evaluate the effect of cryopreservation on sperm motility and viability and to assess sperm DNA fragmentation and oxidation in men undergoing infertility investigation before and after cryopreservation in liquid nitrogen.

DESIGN

Analysis of cryopreservation effects on sperm DNA integrity.

SETTING

Laboratory of Histology-Embryology of medicine faculty, Sfax, Tunisia.

PATIENT(S)

Fifteen semen samples from men undergoing infertility investigation.

INTERVENTION(S)

Neat semen samples were cryopreserved in liquid nitrogen using a commercial freezing medium (SpermFreeze, Fertipro, Belgium) according to the manufacturer's instructions. Samples were thawed at room temperature.

MAIN OUTCOME MEASURE(S)

Sperm DNA fragmentation was assessed using terminal deoxynucleotidyl transferase (Tdt) mediated dUTP nick end labeling and sperm DNA oxidation was determined using a fluorescent assay (OxyDNA test) for the detection of 8-oxoguanine. Evaluation of DNA fragmentation and oxidation rates was carried out before and after cryopreservation using flow cytometry.

RESULT(S)

A significant decrease in sperm motility and viability was observed after cryostorage. In addition, sperm DNA fragmentation and DNA oxidative damage increased significantly after cryopreservation/thaw.

CONCLUSION(S)

Cryopreservation has deleterious effects on sperm DNA by inducing DNA fragmentation and oxidation but the mechanisms underlying such damages need to be elucidated by further investigations.

Study of apoptosis-related markers in ram spermatozoa

Certain features of capacitated or frozen-thawed spermatozoa have been considered to be an apoptosis-like phenomenon, and, it has been suggested that the presence of apoptotic sperm in seminal doses could be one of the reasons for poor fertility. The objective of this study was to determine whether phosphatidylserine (PS) translocation, caspase activity and DNA fragmentation, which are considered to be apoptotic markers in somatic cells, occur in ram sperm. Fresh ejaculates and sperm samples in different physiological state (cold-shocked, in vitro capacitated and acrosome-reacted (AR)) were compared. Simultaneous staining with 6-carboxifluorescein diacetate (6-CFDA) and Annexin V-Cy3.18 (AnnV) revealed four different sperm subpopulations in ejaculates. The main subpopulation was composed of viable cells without PS exposure (CFDA+/AnnV-). A total of 40.8% of sperm showed inverted PS, with two levels of alteration: CFDA+/AnnV+ in midpiece ("type I AnnV+"), and in acrosome and midpiece ("type II AnnV+"). The fewest subpopulation contained non-viable cells showing Annexin labelling in the entire cell (CFDA-/AnnV+). Labeling of caspases-3 and -7 by immunocytochemistry revealing different sperm subtypes depending on their localization in apical, equatorial, post-acrosomal regions and tail. The results obtained by western-blot showed, for the first time to our knowledge, that caspase-like proteins are present in fresh ram semen as both inactive and active forms. The proportion of sperm with fragmented DNA [terminal transferase-mediated dUDP nick end-labeling (TUNEL)-positive] were found rarely (2.7+/-0.5%) in all fresh ejaculates involved in this study. The analysis of total activity of both caspases by a fluorometric method showed a decrease in vitro capacitated and acrosome-reacted samples as well as in cryoinjured samples. However, the percentage of TUNEL-positive sperm demonstrating DNA fragmentation was significantly increased after in vitro induced capacitation and acrosome reaction, as well as after cold-shock although this augment was not significant. PS exposure is not totally dependent on caspases in ram spermatozoa as the addition of a caspase inhibitor prevented the increase in PS inversion due to incubation in capacitating conditions but not to the ionophore-induced acrosome reaction or cold-shock.

Impact of cryopreservation and reactive oxygen species on DNA integrity, lipid peroxidation, and functional parameters in ram sperm

Assisted reproduction using frozen-thawed semen has practical advantages, although cryopreservation is detrimental to sperm fertility in most mammals. We examined the influence of cryopreservation and reactive oxygen species (ROS) on ram sperm DNA stability (using SCSA), lipid peroxidation (LPO), chlortetracycline fluorescence (CTC) patterns, motility and viability. In Experiment 1, DNA integrity, LPO, CTC, motility and viability tests were performed on fresh and cryopreserved sperm after 0, 6, and 24 hr in synthetic oviductal fluid (SOF). In Experiment 2, fresh sperm were incubated in serum-free SOF (SOF-S; 1, 4, and 24 hr) with 0, 50, 150, or 300 microM H2O2 then assayed. Cryopreservation increased the percentage of sperm with a high DNA fragmentation index (%DFI), decreased the percentages of motile and viable sperm at thawing (0 hr), but did not affect LPO. H2O2 (150 or 300 microM) increased %DFI after 24 hr. LPO or sperm viability were not affected by H2O2, although most motility parameters decreased. H2O2 decreased the percentage of chlortetracycline pattern F sperm at 4 hr and increased the percentage of acrosome-reacted sperm (pattern AR) after 1 hr. Pooled data of Experiment 2 showed LPO was positively correlated with SCSA (r = 0.29 to r = 0.59; P < 0.05 to P < 0.01), while most motility parameters and the percentage of viable sperm were negatively correlated with LPO (r = -0.30 to r = -0.38; P < 0.05 to P < 0.01). LPO was positively correlated with the percentage of pattern AR sperm (r = 0.33; P < 0.01). Cryopreservation and H2O2 promote DNA instability in ram sperm, though motility is a more sensitive indicator of oxidative stress than the other parameters investigated.

Activation of Caspases in Human Spermatozoa during Cryopreservation – An Immunoblot Study

Cellular stress to ejaculated spermatozoa such as cryopreservation is known to induce caspase-derived, apoptotic signaling. Therefore, the proenzymes and active forms of caspases 1, 3, 8 and 9 were examined by western blot technique in unfrozen and frozen human spermatozoa of infertility patients and of healthy donors. Twenty-two semen samples derived from healthy donors and 26 semen samples of unselected infertility patients were divided into 3 parts, two of them were cryostored at -196 degrees C with 7% or 14% (v/v, final concentration) of glycerol. The caspases were detected by immunoblots with polyclonal rabbit-anti-caspases-antibodies after 15% sodium dodecyl sulfate-polyacrylgel electrophoresis (SDS-PAGE) under reducing conditions. For evaluation of the differences between amounts of caspase protein the luminol/H(2)O(2) method was applied. A significant increase of activated caspase-1 in donors, of caspase-8 in patients and caspase-9 in patients and donors after cryopreservation were found, whereas, the application of 14% glycerol resulted in higher amounts of activated caspase than did 7% glycerol. Possibly, glycerol may also contribute to activation of caspases via direct toxic effects to mitochondria during cryopreservation of spermatozoa. This finding strongly supports an hypothesis of a higher mitochondria-derived apoptosis-sensitivity of spermatozoa in patients than in healthy donors during cryopreservation. Inactive caspase-3 was reduced subsequent to cryopreservation in patients (p<0.05) and non-significant in donors (p<0.05). Active caspase-3 was detectable in all samples but without significant differences between the three assays. It is concluded that mechanisms associated with apoptotic processes deserve attention in cryopreservation of spermatozoa in order to conserve vital sperm functions after thawing.

Capacitation-like changes in equine spermatozoa following cryopreservation

The primary objective of this study was to assess plasma membrane characteristics and activation of signal transduction pathways in equine spermatozoa during both in vitro capacitation and cryopreservation. Significant plasma membrane restructuring, as assessed by measurement of plasma membrane lipid disorder and phospholipid scrambling, was not observed until after cryopreservation and subsequent thawing (P < 0.05). Although in vitro capacitated cells also displayed increased plasma membrane lipid disorder and phospholipid scrambling (P < 0.05), it appeared that regulation of these events in in vitro capacitated versus cryopreserved equine spermatozoa was not identical. Addition of 5 microM staurosporine to the capacitation media reduced plasma membrane phospholipid scrambling (P < 0.05), but supplementation to the freezing extender prior to cryopreservation did not. Furthermore, progesterone was able to induce a greater degree of acrosomal exocytosis in in vitro capacitated versus frozen/thawed spermatozoa. Expression of phospholipid scramblase, a protein thought to be important in plasma membrane phospholipid scrambling, did not differ between treatments. Comparison of protein tyrosine phosphorylation patterns between in vitro capacitated and cryopreserved cells demonstrated a divergence in signal transduction. Cellular signaling in in vitro capacitated equine spermatozoa appeared to be in part dependent on activation of the cAMP/PKA pathway, whereas signaling in cryopreserved cells seemed to proceed predominantly through alternative pathways. Taken together, these data support the idea that capacitation and "cryocapacitation" are not equivalent processes.

Membranous and structural damage that occur during cryopreservation of human sperm may be time-related events

OBJECTIVE

To evaluate sperm cryopreservation-induced injuries using sperm plasma membrane protein P34H and alpha-tubulin as two different subcellular compartment markers.

DESIGN

Prospective experimental study.

SETTING

Academic hospital research center and fertility clinic.

PATIENT(S)

Semen samples obtained from healthy donors attending the fertility clinic. Sperm samples were either directly processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot experiments (control group) or cryopreserved in liquid nitrogen for different periods of time before being analyzed.

INTERVENTION(S)

SDS-PAGE, Western blotting, and densitometric quantification of P34H and alpha-tubulin before and after cryopreservation.

MAIN OUTCOME MEASURE(S)

Changes in protein quantification between the different groups as a result of sperm cryopreservation.

RESULT(S)

In the 31 sperm samples processed for P34H evaluation, a 50% decrease is observed after sperm cryopreservation as compared to the control group. The alpha-tubulin immunoblotting of 41 sperm samples revealed a 200% increase in the protein detection in the group of cryopreserved sperm as compared to the control group. Contrary to the P34H detection, this change in alpha-tubulin immunodetected levels appears to be related to the cryopreservation period as it increases during storage.

CONCLUSION(S)

These findings indicate that cryopreservation of human semen induces damages at different cellular levels. Moreover, some cryoinjuries are immediate although others seem to take place over time stored in liquid nitrogen.

A prospective study, using sibling oocytes, examining the effect of 30 seconds versus 90 minutes gamete co-incubation in IVF

BACKGROUND

Traditionally oocytes have been exposed to sperm overnight, for 16-20 h. This long period of co-incubation, however, has been shown to create problems with high levels of reactive oxygen species (ROS), which may affect embryo viability and cause hardening of the zona pellucida. Recently, a positive effect of reducing the co-incubation time to 90-120 min was reported. The objective of this study was to evaluate whether a further reduction of the co-incubation period could benefit the outcome of IVF.

METHODS

In this prospective study, 777 sibling oocytes from 81 women undergoing IVF were divided via alternate allocation to co-incubation for either 30 s (ultrashort co-incubation) (group A) or for 90 min (standard co-incubation) (group B). Endpoints were normal fertilization (two-pronuclear, 2PN), polyspermy (>2PN), embryo quality (EQ), clinical pregnancy (CP) and implantation (IR).

RESULTS

The normal fertilization rates of the two groups were comparable: group A 58.6% versus group B 58.0%. Significantly lower rates of polyspermy were seen in group A compared to group B (2.8 versus 7.2%, P = 0.008). No statistically significant differences in EQ, CP or IR were seen.

CONCLUSION

This is the first study demonstrating the achievement of good fertilization rates in IVF with ultrashort co-incubation. Significantly lower rates of polyspermy were seen in the group with ultrashort compared to the standard co-incubation group. Further studies are, however, needed in order to evaluate whether ultrashort co-incubation has any effect on the outcome of IVF.

Assessment of the cryopreservation of equine spermatozoa in the presence of enzyme scavengers and antioxidants

OBJECTIVE

To evaluate the effect of the addition of enzyme scavengers and antioxidants to the cryopreservation extender on characteristics of equine spermatozoa after freezing and thawing.

SAMPLE POPULATION

2 ejaculates collected from each of 5 stallions.

PROCEDURE

Equine spermatozoa were cryopreserved in freezing extender alone (control samples) or with the addition of catalase (200 U/mL), superoxide dismutase (200 U/mL), reduced glutathione (10 mM), ascorbic acid (10 mM), alpha-tocopherol (25, 50, 100, or 500 microM or 1 mM), or the vehicle for alpha-tocopherol (0.5% ethanol). After thawing, spermatozoal motility was assessed via computer-assisted analysis and DNA fragmentation was assessed via the comet assay. Spermatozoal mitochondrial membrane potential, acrosomal integrity, and viability were determined by use of various specific staining techniques and flow cytometry.

RESULTS

The addition of enzyme scavengers or antioxidants to cryopreservation extender did not improve spermatozoal motility, DNA fragmentation, acrosomal integrity, viability, or mitochondrial membrane potential after thawing. Superoxide dismutase increased DNA fragmentation, likely because of the additional oxidative stress caused by the generation of hydrogen peroxide by this enzyme. Interestingly, the addition of the vehicle for alpha-tocopherol resulted in a significant decrease in live acrosome-intact spermatozoa.

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of antioxidants to the cryopreservation extender did not improve the quality of equine spermatozoa after thawing, which suggests that the role of oxidative stress in cryopreservation-induced damage of equine spermatozoa requires further investigation. Our data suggest that solubilizing alpha-tocopherol in ethanol may affect spermatozoal viability; consequently, water-soluble analogues of alpha-tocopherol may be preferred for future investigations.

Quantitative study of caspase-3 activity in semen and after swim-up preparation in relation to sperm quality

BACKGROUND

There are no studies relating the apoptotic marker caspase-3 in human sperm to different degrees of abnormal sperm concentration, morphology and rapid progressive motility.

METHODS

Semen from 67 males with abnormal semen analyses (n = 61) and normozoospermia (n = 6) were used. In each case, sperm from the neat semen (semen fraction) and after gradient centrifugation and swim-up (swim-up fraction) were incubated with a caspase-3 profluorogenic substrate. Caspase-3 activity was quantified in 119 850 sperm, 67 488 from semen and 52 362 from swim-up fractions. Logistic regression was used to estimate odds ratio (with 99% confidence intervals) for the presence of caspase-3-positive sperm.

RESULTS

In semen fractions, no relationship was found between abnormal semen analysis subgroups and sperm caspase-3 activity. On the contrary, a significantly increased number of sperm with caspase-3 activity was found in the swim-up fractions from samples with poor sperm morphology. When analysis was restricted to single semen analysis defects, a significant increase of caspase-3-positive sperm was found in the semen fractions of cases with asthenozoospermia, and in the swim-up fractions of cases with teratozoospermia.

CONCLUSIONS

Sperm caspase-3 activity seems to be associated with teratozoospermia and asthenozoospermia, thus suggesting that nuclear, mitochondrial and cytoskeletal abnormalities induce caspase-3 activation during spermiogenesis or sperm maturation.

Effects of magnetic-activated cell sorting on sperm motility and cryosurvival rates

OBJECTIVE

To evaluate the effect of magnetic-activated cell sorting in cryopreservation-thawing protocols on sperm motility and cryosurvival rate.

DESIGN

Prospective-controlled study.

SETTING

Andrology department at a university-based medical institution.

PATIENT(S)

Ten healthy volunteer sperm donors.

INTERVENTION(S)

Sperm populations were separated using annexin-V magnetic-activated cell sorting before and after the cryopreservation-thawing process.

MAIN OUTCOME MEASURE(S)

Sperm motility and cryosurvival rate.

RESULT(S)

Annexin-negative sperm separated by magnetic-activated cell sorting had statistically significantly higher motility following cryopreservation-thawing than sperm that were not separated. Similarly, annexin-negative spermatozoa also had higher cryosurvival rate than sperm cryopreserved without magnetic-activated cell sorting and sperm that were annexin-positive.

CONCLUSION(S)

Superparamagnetic annexin V-conjugated microbeads can separate spermatozoa with externalized phosphatidylserine, which is considered one of the early features of late apoptosis. The separation of a distinctive population of nonapoptotic spermatozoa with intact membranes may optimize the cryopreservation-thawing outcome. Magnetic-activated cell sorting using annexin-V microbeads enhances sperm motility and cryosurvival rates following cryopreservation.

Cryopreservation and Thawing Is Associated with Varying Extent of Activation of Apoptotic Machinery in Subsets of Ejaculated Human Spermatozoa1

We investigated the impact of cryopreservation and thawing on levels of caspases-3, -8, and -9 activity, intact mitochondrial membrane potential (Deltapsim), and DNA fragmentation in human spermatozoa. Eleven pools of cryopreserved and eight pools of fresh semen samples were examined. Mature and immature fractions were separated on a two-layer density gradient (47% and 90%) and further subdivided based on the externalization of phosphatidylserine and its binding to annexin V-labeled superparamagnetic microbeads (ANMB). Levels of activated caspases were assessed using fluorescein-labeled inhibitors of caspases (FLICA), Deltapsim using a lipophilic cationic dye, and DNA fragmentation by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay. Cryopreservation was significantly associated with activation of caspases-3, -8, and -9, as well as disruption of the mitochondrial membrane potential but no significant changes were observed in DNA fragmentation. In mature sperm, caspase activation was only detected in the ANMB+ fraction, whereas in immature sperm, both ANMB+ and ANMB- fractions showed activated caspase levels. In ANMB+ immature sperm, apoptosis seemed to be triggered by a surface ligand-receptor mechanism as well as by disruption of mitochondria, whereas in ANMB- immature sperm, apoptosis was induced by activation of caspase-9 following loss of intact Deltapsim. These results demonstrate that selection of annexin V-negative mature spermatozoa might be of clinical relevance for fertility preservation, as this sperm fraction shows no activated apoptosis during the cryopreservation process.

Somatic cell apoptosis markers and pathways in human ejaculated sperm: potential utility as indicators of sperm quality

In this study we extended earlier work to determine whether sperm respond to somatic cell apoptotic stimuli and whether apoptotic phenotypes are significant indicators of human sperm quality. We evaluated ejaculated sperm from fertile donors and subfertile patients following purification of fractions of high and low motility. In unstimulated conditions, caspase enzymatic activity was higher in motile fractions from subfertile patients than in donors, and was higher in low motility fractions from both groups. Staurosporine, but not a Fas ligand or H2O2, significantly increased caspase activity, but only in high motility fractions. Procaspase-3, -7 and -9 and low levels of active caspase-3, -7 and -9 were identified by immunoblot analysis. Apoptosis-inducing factor (AIF) was present in all samples but poly ADP-ribose polymerase-1 (PARP-1) was not detected. Phosphatidylserine translocation was significantly increased only with H2O2 treatment. In ejaculates of both subfertile and fertile men, we demonstrated the presence and activation of several proteins that are key constituents of apoptosis-related pathways in somatic cells, which may serve as markers for sperm quality.

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.

Caspase-independent exposure of aminophospholipids and tyrosine phosphorylation in bicarbonate responsive human sperm cells

Only capacitated sperm cells are able to fertilize egg cells, and this process is triggered by high levels of bicarbonate. Bicarbonate renders the plasma membrane more fluid, which is caused by protein kinase A (PKA)-mediated alterations in the phospholipid (PL) bilayer. We studied exposure of phosphatidylserine (PS) and phosphatidylethanolamine (PE) in human sperm cells. Surface exposure of PS and PE on sperm cell activation in vitro was found to be bicarbonate dependent and restricted to the apical area of the head plasma membrane. The PL scrambling in bicarbonate-triggered human sperm was not related to apoptosis, because the incubated cells did not show any signs of caspases or degeneration of mitochondria or DNA. The PL scramblase (PLSCR) gene family has been implicated in this nonspecific, bidirectional PL movement. A 25-kDa isoform of PLSCR was identified that was homogeneously distributed in human sperm cells. We propose that compartment-dependent activation of PKA is required for the surface exposure of aminophospholipids at the apical plasma membrane of sperm cells. Bicarbonate-induced PL scrambling appears to be an important event in the capacitation process, because the entire intact scrambling sperm subpopulation showed extensive tyrosine phosphorylation, which was absent in the nonscrambling subpopulation. The proportion of live cells with PL scrambling corresponded with that showing capacitation-specific chlortetracyclin staining.

Deterioration of plasma membrane is associated with activated caspases in human spermatozoa

Spermatozoa with deteriorated plasma membranes can be separated by magnetic-activated cell sorting (MACS) after binding superparamagnetic annexin V-conjugated microbeads (ANMBs) to membrane phosphatidylserine (PS). Semen samples from 15 donors and 25 infertile patients were divided into 2 spermatozoal fractions by annexin V-MACS. Activated caspases (aCPs), which mediate degradations of cell quality, were determined by CaspaTag in the 2 subpopulations. Spermatozoa from donors showed lower levels of bound annexin V (3.6% +/- 0.5% vs 11.9% +/- 1.1%; P <.01) and aCPs (21.8% +/- 2.6% vs 43.2% +/- 2.1%; P <.01) than did spermatozoa from infertile patients. MACS resulted in a decrease of spermatozoa with aCPs from 21.8% +/- 2.6% (before separation) to 9.2% +/- 1.4% (in the ANMB-negative fraction) in donors and from 43.2% +/- 2.1% to 18.8% +/- 2.6% in infertile patients (mean +/- SEM; P <.01). Separation effects of the MACS technique were confirmed with flow cytometry using anti-annexin V antibodies and with electron microscopy. ANMB-MACS removes spermatozoa with PS-bound annexin V and produces a higher quality spermatozoal fraction. Spermatozoa with a deteriorated membrane are characterized by an increase in aCPs. A higher percentage of spermatozoa with ANMBs bound to PS and with aCPs were found in infertile patients.