Selection of Nonapoptotic Spermatozoa As a New Tool for Enhancing Assisted Reproduction Outcomes: An In Vitro Model1

Sperm selection using magnetic activated cell sorting (MACS) in assisted reproduction: a systematic review and meta-analysis

PURPOSE

To determine whether the use of Magnetic Activated Cell Sorting (MACS) as a sperm selection technique improves ART success rates in couples undergoing assisted reproduction treatment.

METHODS

Systematic review and meta-analysis of prospective randomized trials. Two reviewers conducted study selection and data extraction independently.

RESULTS

Five studies (prospective randomized trials) that comprised 499 patients were included. Sperm selection using MACS resulted in statistically significant differences in pregnancy rates when compared with density gradient centrifugation and swim-up techniques (RR=1.50, 95 % CI 1.14-1.98). No differences were found between the groups according to the implantation (RR=1.03, 95 % CI 0.80-1.31) and miscarriage (RR=2.00, 95 % CI 0.19-20.90) rates.

CONCLUSIONS

MACS appears to be a safe and efficient method to select functional sperm with consistently good results. This technique may improve pregnancy rates when used to complement standard sperm selection methods in ART.

Comparison of the DNA Fragmentation and the Sperm Parameters after Processing by the Density Gradient and the Swim up Methods

INTRODUCTION

The swim up and the density-gradient centrifugation are the two main techniques which are used to separate the viable motile sperm fraction in the assisted reproductive technology. However, there are several published studies about these methods, but there is no sufficient evidence for recommending the superiority of one of them. This study was designed to study the efficiency of the swim-up and the density gradient techniques to recover the spermatozoa with a high degree of motility, a normal morphology and a low level of DNA fragmentation.

MATERIAL AND METHODS

A total of 35 semen samples were included in the study. The semen samples were collected, one part of the semen was spread on a slide and the remainder was prepared by using the swim-up or the density gradient techniques. The recovered spermatozoa were evaluated for concentration, motility, and normal morphology. A comet assay was carried out to assay the DNA fragmentation in all the samples.

RESULTS

There were significant differences in the sperm parameters between the density gradient and the swim up techniques. Also, the swim-up technique showed a significantly higher level of DNA fragmentation as compare to the density gradient technique.

CONCLUSION

The results of this study demonstrated several benefits of the gradients method in the separation of normal and motile spermatozoa with healthy DNA, in comparison to the swim up method.

Sperm selection for ICSI using annexin V

Annexin-V magnetic-activated cell sorting (MACS) is a new tool to optimize sperm selection in assisted reproduction. The technique is based on the binding of superparamagnetic Annexin-microbeads to externalized phosphatidylserine at the outer leaflet of the plasma membrane of sperm with activated apoptosis signaling or membrane damage. The combination of Annexin-V MACS and density gradient centrifugation was demonstrated to enhance clinical pregnancy rates in ICSI cycles. This chapter focuses on the practical details of Annexin-V MACS.

Processes involved in assisted reproduction technologies significantly increase sperm DNA fragmentation and phosphatidylserine translocation

Sperm preparation techniques in assisted reproduction technologies (ART) are potential generators of exogenous stresses that cause additional DNA damage. DNA fragmentation tests, such as the sperm chromatin structure assay, involve freezing sperm samples in the absence of cryoprotectant. Thermal, oxidative stress (OS) and freezing are detrimental to sperm DNA fragmentation and phosphatidylserine (PS) translocation. The primary aim of this study was to subject mature sperm to environmental insults that normally occur during ART. We tested the hypotheses that OS, thermal stress and freeze-thawing caused sperm nuclear and membrane damage and that a positive correlation exists between PS translocation and DNA fragmentation. Sperm DNA integrity deteriorates in semen samples from men with advancing age and a sperm concentration of <15 m ml(-1) . The significant increase in sperm DNA fragmentation at 37 °C after merely 1 h is important clinically as semen liquefaction and short-term sperm storage in an ART cycle involve incubating samples at this temperature. Freezing without a cryoprotectant significantly increases the level of sperm nuclear damage, so it is important not to freeze neat semen prior to DNA fragmentation testing. This study highlights the importance of minimising the production of exogenous stresses during sperm preparation in ART.

Relationship between fertilization rate and early apoptosis in sperm population of infertile individuals

Integrity of the sperm membrane, of which phosphatidyl serine (PS) plays a central role, is essential for fertilization. The externalisation of PS (EPS) occurs during capacitation and the acrosome reaction. EPS, from the inner to the outer membrane, is considered as a sign of early apoptosis. Therefore, EPS may have a dual function in sperm. This study has evaluated the relationship between EPS and fertilization, embryo quality and pregnancy outcomes in couples who were candidates for ICSI. Semen samples were collected from 43 ICSI candidates and assessed according to World Health Organization guidelines for semen parameters. EPS was assessed by Annexin V and propidium iodide (PI) staining. Protamine deficiency was assessed by chromomycin A3 (CMA3) staining. A significant positive correlation was observed between the percentages of fertilization and annexin-positive PI-negative (An(+)PI(-)) sperm. There was a significant negative correlation between the percentages of protamine-deficient sperm with the percentage of fertilization. In addition, the percentage of An(+)PI(-) sperm in individuals with fertilization rates higher and lower than 50% significantly differed. The percentage of annexin-positive PI-positive (An(+)PI(+)) sperm in semen of the partners of pregnant women significantly differed from the partners of nonpregnant women. In conclusion, if An(+)PI(-) is a sign of capacitation and An(+)PI(+) is a sign of apoptosis, the results suggest that semen samples with a higher ability to undergo capacitation have a higher chance to result in successful fertilization post-ICSI. The presence of a high percentage of apoptotic sperm in the insemination sample before capacitation may reduce the chances of pregnancy.

Sperm DNA damage: how relevant is it clinically?

PURPOSE OF REVIEW

The true impact of the current sperm DNA fragmentation testing needs further scrutiny to assess whether clinically meaningful information is conveyed.

RECENT FINDINGS

Various studies have suggested different or no threshold values with assorted tests for the percentage of DNA fragmentation in the ejaculated sperm above which natural conception, fertilization or embryo development and/or clinical pregnancy rates are compromised. Current DNA fragmentation assessment methods provide very little specific information on the nature and severity of the DNA damage detected. Although sperm DNA fragmentation is associated with lower pregnancy rates through natural conception or intrauterine insemination, it does not seem to affect intracytoplasmic sperm injection outcome. Although animal studies demonstrated adverse reproductive effects of sperm DNA fragmentation, any conclusive evidence in humans is yet to be demonstrated. It is not clear whether interventions aimed at enrichment of sperm with decreased DNA fragmentation are effective in preventing the potential adverse effects of sperm DNA fragmentation in humans. Major concern about the use of sperm DNA integrity tests as prognostic parameters is that the direct evaluation of DNA fragmentation in individual sperm fertilizing the oocyte is not possible.

SUMMARY

The lack of consensus in defining a clinically relevant standard DNA fragmentation test with a meaningful cut-off level brings challenges in implementing the routine use of sperm DNA integrity assessment in daily practice.

Relationship Between Apoptotic-Like Changes in Stored Boar Semen and DNA Fragmentation in Preimplantation Embryos

The aim of this experiment was to study the relationship between apoptotic-like changes in spermatozoa and DNA fragmentation in embryos obtained after insemination with fresh and stored semen. The ejaculates collected from three boars (five ejaculates from the same boar) were extended in Biosolwens Plus extender and stored for five days at 15-17°C. Semen, both fresh (Day 0) and stored (Day 5) used for insemination was analysed to detect apoptotic-like changes using fluorescence method: an assay to assess early changes in the membrane integrity of the sperm using the YO-PRO-1 fluorophore. After 5.5 days of insemination embryos were flushed out of the uterus and DNA fragmentation using TUNEL was analysed. In the fresh semen an average of 2.7, 3.7 and 6.2% of apoptotic sperm was observed in boar nos. 1, 2 and 3, respectively. After five days of storage the percentage of apoptotic sperm significantly increased up to 8.0, 15.7 and 23.2% in each analysed boar. The TUNEL index was 7.1% in the morphologically normal expanded blastocysts obtained after insemination with stored semen, and approximately 1.7% after insemination with fresh semen. A greater number of degenerated embryos and higher incidence of DNA fragmentation in the morphologically normal blastocysts were observed after insemination with stored semen which consists of higher percentage of apoptotic sperm compared to results from insemination with fresh semen.

Apoptotic sperm biomarkers and their correlation with conventional sperm parameters and male fertility potential

PURPOSE

To investigate the relationship between sperm apoptotic biomarkers and patient clinical characteristics, conventional sperm parameters and fertility potential.

MATERIAL AND METHODS

Sperm analysis, phospholipid asymmetry, mitochondrial membrane potential (MMP) and DNA denaturation were assessed in 142 males of infertile couples. Seventy-three couples were allocated to the natural conception group, and 55 couples underwent IVF or ICSI.

RESULTS

DNA denaturation correlated positively with age and negatively with testicular volume (TV). MMP correlated negatively with BMI and FSH and positively with TV. Normal viable sperm correlated positively with TV and negatively with age, BMI and FSH. DNA denaturation was associated with a significantly lower natural pregnancy rate (OR 5.4, 95% CI:1.3-22, p = 0.011).

CONCLUSION

Sperm apoptosis is related to male age, BMI, testicular volume and FSH. Among the apoptotic markers, only DNA denaturation has been found to predict natural pregnancy better than conventional sperm parameters.

Density gradient centrifugation before or after magnetic-activated cell sorting: which technique is more useful for clinical sperm selection?

PURPOSE

Although, at present, the selection of sperm prior to ICSI is based on motility and morphology, undetectable anomalies, and more importantly damaged DNA are overlooked. In this regard, novel sperm selection procedures have gained much interest. For instance, sperm has been selected by Magnetic-Activated Cell Sorting (MACS) based on early apoptotic marker, the externalization of phosphatidylserine (EPS). Review of the literature has revealed that the efficiency of this technique has been mainly evaluated post Density Gradient Centrifugation (DGC). Therefore, there is a need to prove the efficiency of this technique independent of DGC. In addition, considering the fact that DGC induces EPS due to capacitation and acrosome reaction, therefore, the role of MACS before DGC(MACS-DGC) and MACS after DGC (DGC-MACS) should be assessed.

METHODS

Semen samples from fifteen infertile men were divided into three separate fractions: control, DGC, and MACS. To carry out DGC-MACS, DGC samples were further divided into two fractions and MACS was carried on the second fractions. Similarly to carry out MACS-DGC, the MACS samples were further divided into two fractions and DGC was carried on the second fractions. Percentages of sperm with normal morphology, DNA fragmentation, protamine deficiency, EPS and caspase-3 activity were determined in each fraction.

RESULTS

DGC is more efficient than MACS in separating intact sperm only in terms of normal morphology, DNA and chromatin integrity but not for active caspase. However, a combination of these procedures was more efficient than a single procedure to separate intact sperm for the aforementioned parameters. Comparison of the combined procedures showed only higher efficiency to separate active caspase in the MACS-DGC group.

CONCLUSION

Based on these results, we propose MACS-DGC rather than DGC-MACS to be implemented in clinical settings.

Sperm preparation: state-of-the-art--physiological aspects and application of advanced sperm preparation methods

For assisted reproduction technologies (ART), numerous techniques were developed to isolate spermatozoa capable of fertilizing oocytes. While early methodologies only focused on isolating viable, motile spermatozoa, with progress of ART, particularly intracytoplasmic sperm injection (ICSI), it became clear that these parameters are insufficient for the identification of the most suitable spermatozoon for fertilization. Conventional sperm preparation techniques, namely, swim-up, density gradient centrifugation and glass wool filtration, are not efficient enough to produce sperm populations free of DNA damage, because these techniques are not physiological and not modeled on the stringent sperm selection processes taking place in the female genital tract. These processes only allow one male germ cell out of tens of millions to fuse with the oocyte. Sites of sperm selection in the female genital tract are the cervix, uterus, uterotubal junction, oviduct, cumulus oophorus and the zona pellucida. Newer strategies of sperm preparation are founded on: (i) morphological assessment by means of 'motile sperm organelle morphological examination (MSOME)'; (ii) electrical charge; and (iii) molecular binding characteristics of the sperm cell. Whereas separation methods based on electrical charge take advantage of the sperm's adherence to a test tube surface or separate in an electrophoresis, molecular binding techniques use Annexin V or hyaluronic acid (HA) as substrates. Techniques in this category are magnet-activated cell sorting, Annexin V-activated glass wool filtration, flow cytometry and picked spermatozoa for ICSI (PICSI) from HA-coated dishes and HA-containing media. Future developments may include Raman microspectrometry, confocal light absorption and scattering spectroscopic microscopy and polarization microscopy.

Effect of the MACS technique on rabbit sperm motility

Magnetic-activated cell sorting (MACS) separates apoptotic spermatozoa by the use of annexin V-conjugated nanoparticles which bind to phosphatidylserine that is externalized on the outer leaflet of the sperm plasma membrane. This technique yields two fractions: annexin V-negative (AnV−) and annexin V-positive (AnV+). The aim of the study was to evaluate the effect of MACS application on the motility parameters of rabbit spermatozoa. Rabbit semen samples collected separately from 4 bucks (I, II, III, and IV) were filtered and separated in a MACS system. The semen samples from a control (untreated) group, AnV− and AnV+ fraction were evaluated using CASA system. The experiment was replicated 4 times for each buck. The AnV+ sperm had significantly lower concentration than the AnV− fractions and the control samples (P<0.05 for bucks I, II, III, but not IV). We observed that the proportion of apoptotic spermatozoa in the semen of NZW bucks is about 20%. There was no significant difference in the percentage of motile and progressively motile spermatozoa between the AnVfractions and control samples. In conclusion, the MACS technique has no harmful effect on the rabbit sperm concentration and motility.

Shorter abstinence decreases sperm deoxyribonucleic acid fragmentation in ejaculate

OBJECTIVE

To evaluate the relationship between duration of sexual abstinence and sperm selection on sperm DNA fragmentation (SDF).

DESIGN

Prospective study based on normozoospermic individuals.

SETTING

Fertility and IVF unit and university unit for research.

PATIENT(S)

Two cohorts of normozoospermic individuals: 21 men (aged 25-35 years) attending a clinic and with clearly adverse female factors; and a group of 12 selected donors (aged 20-25 years).

INTERVENTION(S)

SDF assessment using the sperm chromatin the dispersión test (Halosperm) in two cohorts of normozoospermic men.

MAIN OUTCOME MEASURE(S)

SDF assessment after 24 hours of abstinence with recurrent ejaculation (one every 24 hours) using neat sperm samples; and SDF assessment before and after sperm selection with abstinence of 3 hours.

RESULT(S)

Lower baseline levels of SDF were observed after shorter periods of abstinence between ejaculations (24 hours and 3 hours) than those recommended. This effect is much more marked after quick repetitive ejaculation (3 hours of abstinence) and sperm selection.

CONCLUSION(S)

The present results challenge the role of abstinence in current male infertility treatments and suggest that SDF can be efficiently reduced by a biological practice consisting of short-term recurrent ejaculation coupled with effective sperm selection.

Effects of advanced selection methods on sperm quality and ART outcome: a systematic review

BACKGROUND

Current routine semen preparation techniques do not inclusively target all intrinsic sperm characteristics that may impact the fertilization potential. In order to address these characteristics, several methods have been recently developed and applied to sperm selection. The objective of this study was to systematically review the literature describing these advanced sperm selection methods focusing on their anticipated benefits on sperm quality and assisted reproductive technique (ART) outcome.

METHODS

Systematic literature review was conducted by means of a Medline literature search. Sperm quality parameters assessed included: motility, morphology, viability, DNA integrity, apoptosis and maturity. ART outcomes assessed included: fertilization, embryo quality, pregnancy, abortion and live birth rates.

RESULTS

A total of 44 studies were identified describing four advanced sperm selection methods based on: (i) surface charge (electrophoresis and zeta potential), (ii) apoptosis (magnetic cell sorting and glass wool), (iii) membrane maturity (hyaluronic acid binding) and (iv) ultramorphology (high magnification). Selection of high-quality sperm including improvements in DNA integrity, resulted from the application of these methods. Fertilization and pregnancy rates showed improvement following some of the advanced sperm selection techniques.

CONCLUSIONS

While some of the advanced sperm selection methods are of value in specific clinical ART settings, others are in need of further evaluation. More clinical studies on safety and efficacy are needed before the implementation of advanced sperm selection methods could be universally recommended in ART.

Clinical management of male infertility in assisted reproduction: ICSI and beyond

The advent of in vitro fertilization and its augmentation with intracytoplasmic sperm injection (ICSI) has allowed a large number of couples suffering from moderate to severe male infertility, and also presenting with female pathologies, to achieve their reproductive dreams. Notwithstanding the existence of fundamental questions about the pathophysiological mechanisms leading to sperm dysfunction, and still unanswered concerns about health risks following ICSI, it appears that overall ICSI is safe and here to stay. Although on one hand ICSI possibly hampered advances of the knowledge in some areas of gamete biology and interaction, on the other it definitely gave impulse to studies designed to unveil the sperm contributions during and beyond fertilization, including the normalcy of the DNA/chromatin as well as molecular mechanisms of genetic/epigenetic control and nuclear organization status. In all, almost entering the fourth decade of assisted reproductive technologies, we should continue monitoring the safety of the technique and long-term development of offspring, whereas at the same time prioritizing areas of research addressing these fundamental questions.

Phosphoinositide 3-kinase signalling pathway involvement in a truncated apoptotic cascade associated with motility loss and oxidative DNA damage in human spermatozoa

Human spermatozoa are characterized by poor functionality and abundant DNA damage that collude to generate the high incidences of male infertility and miscarriage seen in our species. Although apoptosis has been suggested as a possible cause of poor sperm quality, the ability of these cells to enter an apoptotic state and the factors that might trigger such an event are unresolved. In the present study we provide evidence that the commitment of these cells to apoptosis is negatively regulated by PI3K (phosphoinositide 3-kinase)/AKT. If PI3K activity is inhibited, then spermatozoa default to an apoptotic cascade characterized by rapid motility loss, mitochondrial reactive oxygen species generation, caspase activation in the cytosol, annexin V binding to the cell surface, cytoplasmic vacuolization and oxidative DNA damage. However, the specialized physical architecture of spermatozoa subsequently prevents endonucleases activated during this process from penetrating the sperm nucleus and cleaving the DNA. As a result, DNA fragmentation does not occur as a direct result of apoptosis in spermatozoa as it does in somatic cells, even though oxidative DNA adducts can clearly be detected. We propose that this unusual truncated apoptotic cascade prepares spermatozoa for silent phagocytosis within the female tract and prevents DNA-damaged spermatozoa from participating in fertilization.

Not all sperm are equal: functional mitochondria characterize a subpopulation of human sperm with better fertilization potential

Human sperm samples are very heterogeneous and include a low amount of truly functional gametes. Distinct strategies have been developed to characterize and isolate this specific subpopulation. In this study we have used fluorescence microscopy and fluorescence-activated cell sorting to determine if mitochondrial function, as assessed using mitochondrial-sensitive probes, could be employed as a criterion to obtain more functional sperm from a given ejaculate. We first determined that mitochondrial activity correlated with the quality of distinct human samples, from healthy donors to patients with decreased semen quality. Furthermore, using fluorescence-activated cell sorting to separate sperm with active and inactive mitochondria we found that this was also true within samples. Indeed, sperm with active mitochondria defined a more functional subpopulation, which contained more capacitated and acrosome intact cells, sperm with lower chromatin damage, and, crucially, sperm more able to decondense and participate in early development using both chemical induction and injection into mature bovine oocytes. Furthermore, cell sorting using mitochondrial activity produced a more functional sperm subpopulation than classic swim-up, both in terms of improvement in a variety of functional sperm parameters and in statistical significance. In conclusion, whatever the true biological role of sperm mitochondria in fertilization, mitochondrial activity is a clear hallmark of human sperm functionality.

Apoptotic-like changes in the spermatozoa of fresh and stored boar semen and the quality of embryos produced in vivo

The aim of this study was to determine the apoptotic-like changes in the spermatozoa of fresh and stored boar semen and to investigate the relationship between this phenomenon and the quality of embryos produced in vivo. The experiments were divided into two series. In the first series, ten ejaculates were collected from five boars, which were crossbreeds of the Polish Landrace and Large White breeds. The semen was stored as a liquid until Day A (the day on which sperm motility decreased to 30%). Three fluorescence methods were used to evaluate semen quality: an assay to assess the early changes in sperm membrane integrity using the fluorophore YO-PRO-1, an assay for phosphatidylserine (PS) translocation across the plasma membrane using fluorescein-labeled annexin-V and the mitochondrial-specific probe JC-1 (5,5',6,6'-tetrachloro-1,1',3,3' tetraethylbenzimidazolylcarbocyanine iodide) for measuring changes in mitochondrial membrane potential. Our results showed that liquid preservation of boar semen causes apoptotic-like changes in the sperm, and a significant increase in both: apoptotic sperm (YO-PRO-1(+)/PI(-)) and early apoptotic sperm (annexin-V(+)/PI(-)) were observed between Day 0 (fresh semen) and Day A only in semen from three of the five boars. In the second series of experiments, the semen from boar nos. 1, 2, and 3 was selected for insemination of superovulated gilts. The fertilizing capacity of fresh and stored semen with different levels of apoptotic spermatozoa was measured based on the morphology and the number of cells of embryos that were obtained after insemination with this semen. Our studies indicated no significant differences in the fertilization rate of gilts after insemination with fresh and stored semen with increased levels of apoptotic spermatozoa. After insemination with stored semen, a significantly greater number of degenerated embryos were observed, but the morphologically normal blastocysts obtained after insemination with either fresh or stored semen had a similar number of nuclei.

Implication of apoptosis in sperm cryoinjury

Apoptosis is an ongoing physiological phenomenon that has been documented to play a role in male infertility, if deregulated. Caspase activation, externalization of phosphatidylserine, alteration of mitochondrial membrane potential and DNA fragmentation are markers of apoptosis found in ejaculated human spermatozoa. These markers appear in excess in subfertile men and functionally incompetent spermatozoa. Sperm cryopreservation is a widely used procedure in the context of assisted reproductive techniques. Cryopreservation and thawing is a procedure that inflicts irreversible injury on human spermatozoa. The damage is manifested by a decrease in recovery of viable spermatozoa with optimum fertilization potential. This review describes the implication of apoptosis as one of the possible mechanisms involved in sperm cryoinjury. Evidence shows significant increase in some apoptosis markers following cryopreservation and thawing. On the other hand, the increase in sperm DNA fragmentation following cryopreservation and thawing requires further investigation. Specific technical measures should be applied to minimize the induction of apoptosis in human spermatozoa during cryopreservation and thawing. These include standardization of freezing protocols and cryoprotectant use. Selection of non-apoptotic spermatozoa may also prove to be of benefit.

Impact of caspase activation in human spermatozoa

Caspases are central components in the apoptosis signaling cascade. The family of cysteine proteases transduces and enhances the apoptosis signal, and activation of effector caspases results in controlled cellular degradation. Although initially the presence of caspases in spermatozoa was controversially discussed in recent years, many studies demonstrated their activation in male germ cells. Activated apoptosis signaling results in decreased fertilizing capacity of the sperm. This review presents the current knowledge on the role of caspases in human sperm. Techniques of caspase monitoring are highlighted. With regard to the high impact of caspases on the sperm fertilizing potential, physiological and pathological settings of caspase activation and inactivation are discussed. Finally, the effects of depletion of caspase-positive sperm are shown with various standard and molecular sperm preparation methods.

Sperm DNA fragmentation: mechanisms of origin, impact on reproductive outcome, and analysis

OBJECTIVE

To review the mechanisms responsible for DNA fragmentation in human sperm, including those occurring during spermatogenesis and transport through the reproductive tract. The mechanisms examined include: apoptosis in the seminiferous tubule epithelium, defects in chromatin remodeling during the process of spermiogenesis, oxygen radical-induced DNA damage during sperm migration from the seminiferous tubules to the epididymis, the activation of sperm caspases and endonucleases, damage induced by chemotherapy and radiotherapy, and the effect of environmental toxicants. The different tests currently used for sperm DNA fragmentation analysis and the factors that determine the predictive value of sperm DNA fragmentation testing and their implications in the diagnosis and treatment of infertility are also discussed. Finally, we also scrutinize how the presence in the embryonic genome of DNA strand breaks or modifications of DNA nucleotides inherited from the paternal genome could impact the embryo and offspring. In particular we discuss how abnormal sperm could be dealt with by the oocyte and how sperm DNA abnormalities, which have not been satisfactorily repaired by the oocyte after fertilization, may interfere with normal embryo and fetal development.

CONCLUSION(S)

Sperm DNA can be modified through various mechanisms. The integrity of the paternal genome is therefore of paramount importance in the initiation and maintenance of a viable pregnancy both in a natural conception and in assisted reproduction. The need to diagnose sperm at a nuclear level is an area that needs further understanding so that we can improve treatment of the infertile couple.

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.

Markers of oxidative stress and sperm chromatin integrity

Oxidative stress (OS) is an imbalance between the amount of reactive oxygen species (ROS) produced and the ability of the antioxidants to scavenge these. OS has been established as a major etiological cause of male infertility. High levels of ROS are harmful and cause damage to sperm nuclear DNA. Evaluation of OS-related damage to spermatozoa is therefore highly relevant in assisted reproductive techniques (ART) such as intracytoplasmic sperm injection (ICSI). ICSI is an effective therapy for severe male factor infertility that bypasses the majority of reproductive tract deficiencies. Despite the controversial findings in the existing literature, there is now enough evidence to show that sperm DNA damage is detrimental to reproductive outcomes. In addition to impairment of fertility, such damage might increase the transmission of genetic diseases to the offspring. Standardization of protocols to assess ROS, antioxidant status, and DNA damage is very important for implementation of these tests in clinical practice. Estimation of seminal ROS levels and extent of sperm DNA damage, especially in an infertile male, may help develop new therapeutic strategies and improve the success of ART.

Mitochondria in mammalian sperm physiology and pathology: a review

While, for a long time, the role of mitochondria in sperm physiology and pathology has been largely ignored, recent research points out the mitochondria as a major organelle with key roles in sperm function both under physiological and biotechnological conditions. This paper briefly reviews these novel findings regarding the role of mitochondria in sperm, paying special attention to the most practical, readily applicable, aspects of the topic such as their role as a major source of the sublethal damage that sperm experiments after cryopreservation.

Contributions of spermatozoa to embryogenesis: assays to evaluate their genetic and epigenetic fitness

During fertilization, spermatozoa contribute genetic and epigenetic factors that affect early embryogenesis. Genetic factors include a haploid genome with intact coding regions and regulatory regions for essential genes. The DNA must contain the proper copy number of essential genes, and cannot have increased single- or double- stranded DNA breaks. Epigenetic factors include a functional centrosome, proper packaging of the chromatin with protamines, modifications of histones, and imprinting of genes. Additionally, the fertilizing spermatozoon provides mRNAs and micro RNAs, which may contribute to the embryonic transcriptome and regulate embryonic gene expression. These epigenetic factors, directly or indirectly, affect the expression of genes in the developing embryo. Each of these contributions represents areas of potential sperm dysfunction, and they are the focus of ongoing research to develop assays which will allow further analysis of their clinical significance. This review briefly describes the current status of research into the genetic and epigenetic contributions of spermatozoa to embryogenesis, and the quest for clinical screening assays. The challenges to validation and clinical application of such testing are also discussed.

Modern andrology: from semen analysis to postgenomic studies of the male gametes

A male factor is implicated in about 50% of couples treated with advanced assisted reproductive techniques (in vitro fertilization [IVF] or intracytoplasmic sperm injection [ICSI]). An important function of spermatozoa is to deliver the paternal genome to the oocyte. However, neither the routine testing of male fertility potential, nor its treatment, addresses the specific mechanisms by which spermatozoal factors may impact reproductive outcome. Recently, a number of screening tests for DNA integrity have been proposed to assess sperm chromatin abnormalities. These include nonspecific DNA strand breaks, numerical abnormalities in spermatozoal chromosome content, and alterations in the epigenetic regulation of the paternal genome. This minireview discusses methods to assess the influence of the paternal genome on reproduction beyond that which can be appreciated by simple quantitative and morphologic evaluation of spermatozoa. Finally, new data on how to select the "best fit" sperm for ICSI will be presented.

Human sperm DNA fragmentation: correlation of TUNEL results as assessed by flow cytometry and optical microscopy

An association between DNA fragmentation in sperm determined by the terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) assay and the incidence of reproductive failure has been reported, either using flow cytometry or optical microscopy. However, the results obtained using each of these two approaches are different. Since there is a relative lack of studies standardizing these two approaches, the direct comparison of the results described in the different articles is difficult at present. To allow the comparison of the TUNEL results obtained using flow cytometry and optical microscopy, we applied these two approaches in a total of 66 human sperm samples. A positive correlation is detected in the TUNEL results as measured by flow cytometry and optical microscopy (Spearman; r = 0.720, P < 0.001). The percentage of TUNEL-positive spermatozoa assessed by flow cytometry is 2.6 times higher than that detected in optical microscopy (39.7% +/- 23.1% versus 15.3% +/- 10.3%). Although there is a good correlation of the TUNEL results obtained by flow cytometry and optical microscopy, the percentages obtained with either technique are different. Therefore, the TUNEL results described in the present work should be valuable to compare the results described in many independent articles, using either optical microscopy or flow cytometry.

Clinical relevance of oxidative stress in male factor infertility: an update

Male factor has been considered a major contributory factor to infertility. Along with the conventional causes for male infertility such as varicocele, cryptorchidism, infections, obstructive lesions, cystic fibrosis, trauma, and tumors, a new, yet important cause has been identified: oxidative stress. Oxidative stress (OS) is a result of the imbalance between reactive oxygen species (ROS) and antioxidants in the body, which can lead to sperm damage, deformity and eventually male infertility. This involves peroxidative damage to sperm membrane and DNA fragmentation at both nuclear and mitochondrial levels. OS has been implicated as the major etiological factor leading to sperm DNA damage. OS-induced DNA damage can lead to abnormalities in the offspring including childhood cancer and achondroplasia. In this article, we discuss the need of ROS in normal sperm physiology, the mechanism of production of ROS and its pathophysiology in relation to male reproductive system. The benefits of incorporating antioxidants in clinical and experimental settings have been enumerated. We also highlight the emerging concept of utilizing OS as a method of contraception and the potential problems associated with it.

Utility of magnetic cell separation as a molecular sperm preparation technique

Assisted reproductive techniques (ARTs) have become the treatment of choice in many cases of infertility; however, the current success rates of these procedures remain suboptimal. Programmed cell death (apoptosis) most likely contributes to failed ART and to the decrease in sperm quality after cryopreservation. There is a likelihood that some sperm selected for ART will display features of apoptosis despite their normal appearance, which may be partially responsible for the low fertilization and implantation rates seen with ART. One of the features of apoptosis is the externalization of phosphatidylserine (PS) residues, which are normally present on the inner leaflet of the sperm plasma membrane. Colloidal superparamagnetic microbeads ( approximately 50 nm in diameter) conjugated with annexin V bind to PS and are used to separate dead and apoptotic spermatozoa by magnetic-activated cell sorting (MACS). Cells with externalized PS will bind to these microbeads, whereas nonapoptotic cells with intact membranes do not bind and could be used during ARTs. We have conducted a series of experiments to investigate whether the MACS technology could be used to improve ART outcomes. Our results clearly indicate that integrating MACS as a part of sperm preparation techniques will improve semen quality and cryosurvival rates by eliminating apoptotic sperm. Nonapoptotic spermatozoa prepared by MACS display higher quality in terms of routine sperm parameters and apoptosis markers. The higher sperm quality is represented by an increased oocyte penetration potential and cryosurvival rates. Thus, the selection of nonapoptotic spermatozoa by MACS should be considered to enhance ART success rates.

Conserved molecular portraits of bovine and human blastocysts as a consequence of the transition from maternal to embryonic control of gene expression

The present study investigated mRNA expression profiles of bovine oocytes and blastocysts by using a cross-species hybridization approach employing an array consisting of 15,529 human cDNAs as probe, thus enabling the identification of conserved genes during human and bovine preimplantation development. Our analysis revealed 419 genes that were expressed in both oocytes and blastocysts. The expression of 1,324 genes was detected exclusively in the blastocyst, in contrast to 164 in the oocyte including a significant number of novel genes. Genes indicative for transcriptional and translational control (ELAVL4, TACC3) were overexpressed in the oocyte, whereas cellular trafficking (SLC2A14, SLC1A3), proteasome (PSMA1, PSMB3), cell cycle (BUB3, CCNE1, GSPT1), and protein modification and turnover (TNK1, UBE3A) genes were found to be overexpressed in blastocysts. Transcripts implicated in chromatin remodeling were found in both oocytes (NASP, SMARCA2) and blastocysts (H2AFY, HDAC7A). The trophectodermal markers PSG2 and KRT18 were enriched 5- and 50-fold in the blastocyst. Pathway analysis revealed differential expression of genes involved in 107 distinct signaling and metabolic pathways. For example, phosphatidylinositol signaling and gluconeogenesis were prominent pathways identified in the blastocyst. Expression patterns in bovine and human blastocysts were to a large extent identical. This analysis compared the transcriptomes of bovine oocytes and blastocysts and provides a solid foundation for future studies on the first major differentiation events in blastocysts and identification of a set of markers indicative for regular mammalian development.

DNA damage of human spermatozoa in assisted reproduction: origins, diagnosis, impacts and safety

Sperm DNA contributes half the offspring's genomic material and abnormal DNA can lead to derangements in the reproductive process. Normal sperm genetic material is required for successful fertilization, as well as for further embryo and fetal development that will result in a healthy child. Thus, the damage to sperm DNA is critical in assisted reproductive techniques which are increasingly used to treat infertile couples. There has been improving data about the effects of human sperm DNA damage or fragmentation. As well, increasing knowledge concerning the effects of DNA damage on embryo and fetal development has been attained. This review aims to summarize the present knowledge on the impact of human sperm cell DNA damage on male infertility and outcome in the context of safety.

Molecular glass wool filtration as a new tool for sperm preparation

BACKGROUND

Magnetic-activated cell sorting (MACS) using annexin V-conjugated microbeads in a liquid phase eliminates apoptotic spermatozoa based on the externalization of phosphatidylserine (EPS) residues. The procedure allows the enrichment of a sperm population free of apoptosis markers, giving higher fertilization potential. Our aim was to determine if the annexin V binding principle can be transferred onto a glass wool filter system in order to produce a solid phase filter.

METHODS

Semen samples (n = 42) were subjected to a molecular glass wool filter system using glass surfaces coated with annexin V and compared with aliquots separated by conventional glass wool, as well as with annexin V-MACS. The extent of apoptosis was assessed by measuring levels of activated caspase 3 using fluorescein-labelled inhibitors of caspase, alterations in mitochondrial membrane potential (MMP) using a lipophilic cationic dye, and EPS using a fluorescein isothiocyanate-coupled monoclonal antibody.

RESULTS

Annexin V-negative sperm filtered out by the newly developed molecular glass wool filtration (GWF) system displayed superior quality in terms of high MMP integrity, as well as, to a small extent, caspase 3 activation and EPS.

CONCLUSIONS

The effect of traditional GWF can be further improved by combination with annexin V binding. This newly developed solid phase molecular filter system has been proven to enrich spermatozoa free of apoptosis markers to the same extent as the annexin V magnetic separation technique. The selection of spermatozoa free of apoptosis markers by molecular glass wool filters may enhance the results of IVF.