Endogenous reactive oxygen species content and modulation of tyrosine phosphorylation during sperm capacitation

Effects of Reactive Oxygen and Nitrogen Species on Male Fertility

Significance: In recent decades, male fertility has been severely reduced worldwide. The causes underlying this decline are multifactorial, and include, among others, genetic alterations, changes in the microbiome, and the impact of environmental pollutants. Such factors can dysregulate the physiological levels of reactive species of oxygen (ROS) and nitrogen (RNS) in the patient, generating oxidative and nitrosative stress that impairs fertility. Recent Advances: Recent studies have delved into other factors involved in the dysregulation of ROS and RNS levels, such as diet, obesity, persistent infections, environmental pollutants, and gut microbiota, thus leading to new strategies to solve male fertility problems, such as consuming prebiotics to regulate gut flora or treating psychological conditions. Critical Issues: The pathways where ROS or RNS may be involved as modulators are still under investigation. Moreover, the extent to which treatments can rescue male infertility as well as whether they may have side effects remains, in most cases, to be elucidated. For example, it is known that prescription of antioxidants to treat nitrosative stress can alter sperm chromatin condensation, which makes DNA more exposed to ROS and RNS, and may thus affect fertilization and early embryo development. Future Directions: The involvement of extracellular vesicles, which might play a crucial role in cell communication during spermatogenesis and epididymal maturation, and the relevance of other factors such as sperm epigenetic signatures should be envisaged in the future.

Dibutyl phthalate disrupts glycogen synthase kinase 3α essential for sperm motility

To unravel the toxic mechanism of phthalate ester plasticizer endocrine disruptor in spermatozoa, we examined the effect of dibutyl phthalate (DBP) on the stability and inhibitory phosphorylation of glycogen synthase kinase 3α (GSK3α), a protein kinase crucial for sperm motility in mice. In DBP-treated spermatozoa, reactive oxygen species (ROS) and lipid peroxide were significantly increased. In computer-assisted sperm analysis, DBP at concentrations of 10 - 100 μg/mL significantly decreased total motility and progressive motility of spermatozoa. On western blots, DBP decreased p-GSK3α(Ser21) and increased p-GSK3α(Tyr279) in spermatozoa. Similarly, hydrogen peroxide decreased p-GSK3α(Ser21) but not p-GSK3α(Tyr279) in spermatozoa. Immunofluorescent labeling demonstrated that DBP markedly decreased immunoreactivities of GSK3α and p-GSK3α(Ser21) but increased immunoreactivity of p-GSK3α(Tyr279) in spermatozoa. DBP at a concentration of 100 μg/mL significantly increased phosphatase activity in spermatozoa. Calyculin A, a protein phosphatase 1 and 2 A inhibitor, markedly increased p-GSK3α(Ser21) and sperm motility and attenuated a DBP-induced decrease of p-GSK3α(Ser21) and sperm motility. On western blot, 1-100 μg/mL DBP decreased GSK3α in spermatozoa. On immunoprecipitation western blot, DBP at 10 - 100 μg/mL increased polyubiquitinated sperm proteins including GSK3α. The MG115, proteasome inhibitor attenuated degradation of GSK3α in DBP-treated spermatozoa. Hydrogen peroxide at 10 μM increased polyubiquitinated sperm proteins, suggesting that DBP may increase ubiquitination of GSK3α via ROS induction. Together, DBP may decrease the cellular amount of GSK3α through the ubiquitin-proteasome pathway and p-GSK3α(Ser21) through ROS generation and activation of protein phosphatases, impairing sperm motility.

SUMO1 and Defective Spermatozoa Correlate with Endogenous Hydrogen Peroxide and Live Birth Outcome in Intrauterine Insemination Cycles for Unexplained Infertility

This study aimed to investigate the correlation between hydrogen peroxide (H2O2), small ubiquitin-like modifier molecules (SUMO), and pregnancy outcomes in couples with unexplained infertility (UI) undergoing intrauterine insemination (IUI) treatment. We prospectively collected semen samples from 56 couples with UI and divided the spermatozoa into motile and immotile fractions by density gradient centrifugation (DSC). Immunofluorescence staining was used to examine the immunostaining and localization of nuclear pore complex (NPC), SUMO1, and SUMO2/3 in spermatozoa. We detected H2O2 levels by chemiluminescence methods. We found that H2O2 levels correlated with NPC (neck) (r = 0.400) and NPC (tail) (r = 0.473) in motile sperm fractions. In immotile fractions, H2O2 positively correlated with NPC (tail) (r = 0.431) and SUMO1 (neck) (r = 0.282). Furthermore, the positive NPC (tail) group had a significantly lower live birth rate than the negative NPC group (17.9% = 5/28 vs. 42.9% = 12/28). In conclusion, H2O2 positively correlated with SUMO1 (neck) and NPC (tail) in human spermatozoa. The DSC may partially eliminate defective spermatozoa (positive NPC staining); however, if defective spermatozoa remain in the motile fraction, this scenario is associated with a low live birth rate following IUI treatment.

Protective effects of melatonin against the toxic effects of environmental pollutants and heavy metals on testicular tissue: A systematic review and meta-analysis of animal studies

BACKGROUND

Environmental pollution and infertility are two modern global challenges that agonize personal and public health. The causal relationship between these two deserves scientific efforts to intervene. It is believed that melatonin maintains antioxidant properties and may be utilized to protect the testicular tissue from oxidant effects caused by toxic materials.

METHODS

A systematic literature search was conducted in PubMed, Scopus, and Web of Science to identify the animal trial studies that evaluated melatonin therapy's effects on rodents' testicular tissue against oxidative stress caused by heavy metal and non-heavy metal environmental pollutants. Data were pooled, and standardized mean difference and 95% confidence intervals were estimated using the random-effect model. Also, the risk of bias was assessed using the Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) tool. (PROSPERO: CRD42022369872).

RESULTS

Out of 10039 records, 38 studies were eligible for the review, of which 31 were included in the meta-analysis. Most of them showed beneficial effects of melatonin therapy on testicular tissue histopathology. [20 toxic materials were evaluated in this review, including arsenic, lead, hexavalent chromium, cadmium, potassium dichromate, sodium fluoride, cigarette smoke, formaldehyde, carbon tetrachloride (CCl4), 2-Bromopropane, bisphenol A, thioacetamide, bisphenol S, ochratoxin A, nicotine, diazinon, Bis(2-ethylhexyl) phthalate (DEHP), Chlorpyrifos (CPF), nonylphenol, and acetamiprid.] The pooled results showed that melatonin therapy increased sperm count, motility, viability and body and testicular weights, germinal epithelial height, Johnsen's biopsy score, epididymis weight, seminiferous tubular diameter, serum testosterone, and luteinizing hormone levels, testicular tissue Malondialdehyde, glutathione peroxidase, superoxide dismutase, and glutathione levels. On the other hand, abnormal sperm morphology, apoptotic index, and testicular tissue nitric oxide were lower in the melatonin therapy arms. The included studies presented a high risk of bias in most SYRCLE domains.

CONCLUSION

In conclusion, our study demonstrated amelioration of testicular histopathological characteristics, reproductive hormonal panel, and tissue markers of oxidative stress. Melatonin deserves scientific attention as a potential therapeutic agent for male infertility.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/PROSPERO, identifier CRD42022369872.

KCNQ1 Potassium Channel Expressed in Human Sperm Is Involved in Sperm Motility, Acrosome Reaction, Protein Tyrosine Phosphorylation, and Ion Homeostasis During Capacitation

Potassium channels are involved in membrane hyperpolarization and ion homeostasis regulation during human sperm capacitation. However, the types of potassium channels in human sperm remain controversial. The voltage-gated ion channel KCNQ1 is ubiquitously expressed and regulates key physiological processes in the human body. In the present study, we investigated whether KCNQ1 is expressed in human sperm and what role it might have in sperm function. The expression and localization of KCNQ1 in human sperm were evaluated using Western blotting and indirect immunofluorescence. During capacitation incubation, human sperm were treated with KCNQ1- specific inhibitor chromanol 293B. Sperm motility was analyzed using a computer-assisted sperm analyzer. The acrosome reaction was studied using fluorescein isothiocyanate-conjugated Pisum sativum agglutinin staining. Protein tyrosine phosphorylation levels and localization after capacitation were determined using Western blotting and immunofluorescence. Intracellular K⁺, Ca²⁺, Cl⁻, pH, and membrane potential were analyzed using fluorescent probes. The results demonstrate that KCNQ1 is expressed and localized in the head and tail regions of human sperm. KCNQ1 inhibition reduced sperm motility, acrosome reaction rates, and protein tyrosine phosphorylation but had no effect on hyperactivation. KCNQ1 inhibition also increased intracellular K⁺, membrane potential, and intracellular Cl⁻, while decreasing intracellular Ca²⁺ and pH. In conclusion, the KCNQ1 channel plays a crucial role during human sperm capacitation.

Correlation of skin carotenoid levels with embryo development and pregnancy result of in vitro fertilization cycles for couples with unexplained infertility

Oxidative stress-related DNA damage is a significant pathology for male subfertility and unexplained infertility (UI). Antioxidant supplement by food or nutrition may benefit sperm function of UI couples. However, the role of antioxidant status on fertilization outcome and embryo development for UI couples is not clear. A total of 63 semen samples from UI couples undergoing in vitro fertilization (IVF) treatment (26 pregnant cycles and 37 nonpregnant cycles) were recruited for this prospective observational study. The reactive oxygen species (ROS) levels of sperm cells are detected by a chemiluminescence assay. Total antioxidant capacity (TAC) of seminal plasma is evaluated according to an antioxidant assay kit. The skin carotenoid status in the male partners of UI couples is measured by resonance Raman spectroscopy to determine the antioxidant potential from dietary supplement. The skin carotenoid status (23,115 ± 6,831 vs. 19,432 ± 5,242 Raman intensity, p = .0329 by Mann-Whitney U test) and day 3 good embryo rates (49.6 ± 27.1% vs. 26.8 ± 23.1%, p = .002 by Mann-Whitney U test) are higher in pregnant cycles compared to those in nonpregnant cycles. The local antioxidant capacity (seminal TAC) is closely correlated with fertilization rates (r = .35, p = .005). In contrast, skin carotenoid status is intimately associated with good embryo rates in IVF cycles (r = .34, p = .007). In conclusion, the skin carotenoid status of male partners of UI couples may benefit embryo development and the subsequent pregnancy outcome of IVF treatment. Further investigation about the effect and mechanism of nutritional supplement on embryo development in IVF cycles for UI couples is deserved.

Human Sperm Capacitation Involves the Regulation of the Tyr-Phosphorylation Level of the Anion Exchanger 1 (AE1)

Bicarbonate uptake is one of the early steps of capacitation, but the identification of proteins regulating anion fluxes remains elusive. The aim of this study is to investigate the role of sperm solute carrier 4 (SLC4) A1 (spAE1) in the capacitation process. The expression, location, and tyrosine-phosphorylation (Tyr-P) level of spAE1 were assessed. Thereby, it was found that 4,4′-Diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS), an SLC4 family channel blocker, inhibited capacitation in a dose-dependent manner by decreasing acrosome reaction (ARC% 24.5 ± 3.3 vs. 64.9 ± 4.3, p < 0.05) and increasing the percentage of not viable cells (NVC%), comparable to the inhibition by I-172, a cystic fibrosis transmembrane conductance regulator (CFTR) blocker (AR% 30.5 ± 4.4 and NVC% 18.6 ± 2.2). When used in combination, a synergistic inhibitory effect was observed with a remarkable increase of the percentage of NVC (45.3 ± 4.1, p < 0.001). spAE1 was identified in sperm membrane as a substrate for Tyr-protein kinases Lyn and Syk, which were identified as both soluble and membrane-bound pools. spAE1-Tyr-P level increased in the apical region of sperm under capacitating conditions and was negatively affected by I-172 or DIDS, and, to a far greater extent, by a combination of both. In conclusion, we demonstrated that spAE1 is expressed in sperm membranes and it is phosphorylated by Syk, but above all by Lyn on Tyr359, which are involved in sperm viability and capacitation.

The Importance of Oxidative Stress in Determining the Functionality of Mammalian Spermatozoa: A Two-Edged Sword

This article addresses the importance of oxidative processes in both the generation of functional gametes and the aetiology of defective sperm function. Functionally, sperm capacitation is recognized as a redox-regulated process, wherein a low level of reactive oxygen species (ROS) generation is intimately involved in driving such events as the stimulation of tyrosine phosphorylation, the facilitation of cholesterol efflux and the promotion of cAMP generation. However, the continuous generation of ROS ultimately creates problems for spermatozoa because their unique physical architecture and unusual biochemical composition means that they are vulnerable to oxidative stress. As a consequence, they are heavily dependent on the antioxidant protection afforded by the fluids in the male and female reproductive tracts and, during the precarious process of insemination, seminal plasma. If this antioxidant protection should be compromised for any reason, then the spermatozoa experience pathological oxidative damage. In addition, situations may prevail that cause the spermatozoa to become exposed to high levels of ROS emanating either from other cells in the immediate vicinity (particularly neutrophils) or from the spermatozoa themselves. The environmental and lifestyle factors that promote ROS generation by the spermatozoa are reviewed in this article, as are the techniques that might be used in a diagnostic context to identify patients whose reproductive capacity is under oxidative threat. Understanding the strengths and weaknesses of ROS-monitoring methodologies is critical if we are to effectively identify those patients for whom treatment with antioxidants might be considered a rational management strategy.

Is corifollitropin alfa effective in controlled ovarian stimulation among all poor ovarian responders? A retrospective comparative study

Several studies have compared the effectiveness of corifollitropin alfa versus daily gonadotropins in poor ovarian responders (PORs) undergoing controlled ovarian stimulation (COS), showing conflicting results in terms of IVF outcomes. Given the heterogeneity of patients included in the classification of POR according to 'Bologna criteria', the aim of this study was to evaluate the impact of corifollitropin alfa in two different categories of POR distinguished according to patients' antral follicle count (AFC). We retrospectively evaluated 104 infertile POR, split into two groups according to AFC (Group A ≤ 5; Group B > 5) and subgroups according to the ovarian stimulation regimen (corifollitropin alfa plus daily gonadotropins (Subgroup 1) versus daily gonadotropins alone (Subgroup 2)). Outcome measures were total oocytes, MII oocytes, total embryos, follicular output rate (FORT), implantation rate (IR), clinical pregnancy rate (CPR), miscarriage rate (MR), and live birth rate (LBR). Subgroup A1 experienced a lower number of total oocytes, MII oocytes, total embryos, and FORT (p < .05) in comparison to Subgroup A2, while no difference was found when comparing Subgroups B1 and B2. No difference was found between subgroups even in terms of IR, CPR, MR, and LBR. In conclusion, corifollitropin alfa may be as effective as daily gonadotropins in POR with AFC > 5 undergoing COS, while it might be inferior to daily gonadotropins in POR with AFC ≤ 5.

Effect of addition of melatonin on liquid storage of ram semen at 4°C

Adding a certain amount of antioxidants to semen extender has been shown to improve semen quality. The aim of present study was to elucidate whether the supplementation of melatonin to the Tris-based extender (CTR) could enhance the quality of ram spermatozoa during storage at 4°C. Ram semen samples were collected and diluted with CTR extender containing different concentrations (0, 0.05 (M 0.05), 0.1 (M 0.1), 0.2 (M 0.2) or 0.4 (M 0.4) mM) of melatonin. Sperm routine indicators, mitochondrial activity, total antioxidant capacity (T-AOC) and malondialdehyde (MDA) content were analysed in control and melatonin treatment groups. The higher per cent of motility, plasma membrane integrity, mitochondrial activity and T-AOC activity was observed in M 0.05, M 0.1 and M 0.2 groups compared to control group at 5 days of storage (p < 0.05), while lower percentage of MDA content was observed among these groups (p < 0.05). In addition, there were no significant differences in acrosome integrity among the control and M 0.05, M 0.1 and M 0.2 groups during the experiment. The above results show that the addition of 0.05, 0.1, 0.2 mM of melatonin is beneficial to the preservation of ram semen during liquid storage at 4°C mainly through antioxidative stress.

Astaxanthin Prevents Human Papillomavirus L1 Protein Binding in Human Sperm Membranes

Astaxanthin (Asta), red pigment of the carotenoid family, is known for its anti-oxidant, anti-cancer, anti-diabetic, and anti-inflammatory properties. In this study, we evaluated the effects of Asta on isolated human sperm in the presence of human papillomavirus (HPV) 16 capsid protein, L1. Sperm, purified by gradient separation, were treated with HPV16-L1 in both a dose and time-dependent manner in the absence or presence of 30 min-Asta pre-incubation. Effects of HPV16-L1 alone after Asta pre-incubation were evaluated by rafts (CTB) and Lyn dislocation, Tyr-phosphorylation (Tyr-P) of the head, percentages of acrosome-reacted cells (ARC) and endogenous reactive oxygen species (ROS) generation. Sperm membranes were also analyzed for the HPV16-L1 content. Results show that HPV16-L1 drastically reduced membrane rearrangement with percentage of sperm showing head CTB and Lyn displacement decreasing from 72% to 15.8%, and from 63.1% to 13.9%, respectively. Accordingly, both Tyr-P of the head and ARC decreased from 68.4% to 10.2%, and from 65.7% to 14.6%, respectively. Asta pre-incubation prevented this drop and restored values of the percentage of ARC up to 40.8%. No alteration was found in either the ROS generation curve or sperm motility. In conclusion, Asta is able to preserve sperm by reducing the amount of HPV16-L1 bound onto membranes.

Alterations in oxidative responses and post-translational modification caused by p,p´-DDE in Mus spretus testes reveal Cys oxidation status in proteins related to cell-redox homeostasis and male fertility

The major derivate of DDT, 1,1-dichloro-2,2-bis (p-chlorophenyl) ethylene (p,p´-DDE), is a persistent pollutant previously associated with oxidative stress. Additionally, p,p´-DDE has been linked to several metabolic alterations related to sexual function in rodents. In this study, we analysed the effects of a non-lethal p,p´-DDE dose to Mus spretus mice in testes, focusing on oxidative damage to biomolecules, defence mechanisms against oxidative stress and post-translational protein modifications. No increase in lipid or DNA oxidation was observed, although antioxidative enzymatic defences and redox status of glutathione were altered in several ways. Global protein carbonylation and phosphorylation were significantly reduced in testes from p,p´-DDE-exposed mice; however, the total redox state of Cys thiols did not exhibit a defined pattern. We analysed the reversible redox state of specific Cys residues in detail with differential isotopic labelling and a shotgun labelling-based MS/MS proteomic approach for identification and quantification of altered peptides. Our results show that Cys residues are significantly affected by p,p´-DDE in several proteins related to oxidative stress and/or male fertility, particularly those participating in fertilization, sperm capacitation and blood coagulation. These molecular changes could explain the sexual abnormalities previously described in p,p´-DDE exposed organisms.

Melatonin Scavenger Properties against Oxidative and Nitrosative Stress: Impact on Gamete Handling and In Vitro Embryo Production in Humans and Other Mammals

Oxidative and nitrosative stress are common problems when handling gametes in vitro. In vitro development in mammalian embryos is highly affected by culture conditions, especially by reactive oxygen species (ROS) and reactive nitrogen species (RNS), because their absence or overproduction causes embryo arrest and changes in gene expression. Melatonin in gamete co-incubation during in vitro fertilization (IVF) has deleterious or positive effects, depending on the concentration used in the culture medium, demonstrating the delicate balance between antioxidant and pro-oxidant activity. Further research is needed to better understand the possible impact of melatonin on the different IVP steps in humans and other mammals, especially in seasonal breeds where this neuro-hormone system highly regulates its reproduction physiology.

Effects of Synthetic Serum Supplementation in Sperm Preparation Media on Sperm Capacitation and Function Test Results

Albumin supplementation of culture media induces sperm capacitation in assisted reproduction technique cycles. Synthetic serum supplementation is clinically used to replace albumin for preventing transmission of infectious agents. However, the effects of synthetic serum supplementation on sperm capacitation have rarely been investigated. Spermatozoa from 30 men with normal basic semen analysis results were collected, divided into five aliquots, and cultured in capacitating conditions in four combinations of two synthetic serum supplements, serum substitute supplement (SSS) and serum protein substitute (SPS), and two fertilization media, Quinns Advantage™ Fertilization (QF) and human tubular fluid (HTF) media. Reactive oxygen species (ROS) levels in spermatozoa were measured through chemiluminescence. Furthermore, acrosome reaction and western blotting for tyrosine phosphorylation were used to evaluate sperm capacitation. HTF+SSS had significantly higher ROS levels than QF+SPS did (11,725 ± 1,172 versus 6,278 ± 864 relative light units). In addition, the spermatozoa cultured in QF+SPS had lower motility, acrosome reaction rates, and tyrosine phosphorylation levels compared with those cultured in HTF+SSS. In conclusion, the effects of synthetic serum supplementation on sperm capacitation varied according to the combination of media. These differences may lead to variations in spermatozoon ROS levels, thus affecting sperm function test results.

Astaxanthin Improves Human Sperm Capacitation by Inducing Lyn Displacement and Activation

Astaxanthin (Asta), a photo-protective red pigment of the carotenoid family, is known for its multiple beneficial properties. In this study, the effects of Asta on isolated human sperm were evaluated. Capacitation involves a series of transformations to let sperm acquire the correct features for potential oocyte fertilization, including the generation of a controlled amount of reactive oxygen species (ROS), cholesterol depletion of the sperm outer membrane, and protein tyrosine phosphorylation (Tyr-P) process in the head region. Volunteers, with normal spermiogram values, were divided in two separate groups on the basis of their ability to generate the correct content of endogenous ROS. Both patient group (PG) and control group (CG) were analysed for Tyr-phosphorylation (Tyr-P) pattern and percentages of acrosome-reacted cells (ARC) and non-viable cells (NVC), in the presence or absence of Asta. In addition, the involvement of ROS on membrane reorganization and the presence of Lyn, a Src family kinase associated with lipid rafts, were investigated. Results show that Lyn is present in the membranes of human sperm, mainly confined in midpiece in resting conditions. Following capacitation, Lyn translocated to the head concomitantly with raft relocation, thus allowing the Tyr-P of head proteins. Asta succeeded to trigger Lyn translocation in PG sperm thus bypassing the impaired ROS-related mechanism for rafts and Lyn translocation. In this study, we showed an interdependence between ROS generation and lipid rafts and Lyn relocation leading the cells to undergo the successive acrosome reaction (AR). Asta, by ameliorating PG sperm functioning, may be utilised to decrease male idiopathic infertility.

Oligomycin A-induced inhibition of mitochondrial ATP-synthase activity suppresses boar sperm motility and in vitro capacitation achievement without modifying overall sperm energy levels

Incubation of boar spermatozoa in a capacitation medium with oligomycin A, a specific inhibitor of the F0 component of the mitochondrial ATP synthase, induced an immediate and almost complete immobilisation of cells. Oligomycin A also inhibited the ability of spermatozoa to achieve feasible in vitro capacitation (IVC), as measured through IVC-compatible changes in motility patterns, tyrosine phosphorylation levels of the acrosomal p32 protein, membrane fluidity and the ability of spermatozoa to achieve subsequent, progesterone-induced in vitro acrosome exocytosis (IVAE). Both inhibitory effects were caused without changes in the rhythm of O2 consumption, intracellular ATP levels or mitochondrial membrane potential (MMP). IVAE was accompanied by a fast and intense peak in O2 consumption and ATP levels in control spermatozoa. Oligomycin A also inhibited progesterone-induced IVAE as well as the concomitant peaks of O2 consumption and ATP levels. The effect of oligomycin on IVAE was also accompanied by concomitant alterations in the IVAE-induced changes on intracellular Ca(2+) levels and MMP. Our results suggest that the oligomycin A-sensitive mitochondrial ATP-synthase activity is instrumental in the achievement of an adequate boar sperm motion pattern, IVC and IVAE. However, this effect seems not to be linked to changes in the overall maintenance of adequate energy levels in stages other than IVAE.

Human spermatozoa possess an IL4I1 l-amino acid oxidase with a potential role in sperm function

Reactive oxygen species (ROS) are known to play an important role in the regulation of human sperm function. In this study, we demonstrate for the first time that human spermatozoa possess interleukin-induced gene 1 (IL4I1), anl-amino acid oxidase (LAAO) which is capable of generating ROS on exposure to aromatic amino acids in the presence of oxygen. The preferred substrates were found to be phenylalanine and tryptophan while the enzyme was located in the acrosomal region and midpiece of these cells. In contrast to equine and bovine spermatozoa, enzyme activity was lost as soon as the spermatozoa became non-viable. On a cell-to-cell basis human spermatozoa were also shown to generate lower levels of hydrogen peroxide than their equine counterparts on exposure to phenylalanine. Stimulation of LAAO activity resulted in the induction of several hallmarks of capacitation including tyrosine phosphorylation of the sperm flagellum and concomitant activation of phospho-SRC expression. In addition, stimulation of LAAO resulted in an increase in the levels of acrosomal exocytosis in both the presence and absence of progesterone stimulation, via mechanisms that could be significantly reversed by the presence of catalase. As is often the case with free radical-mediated phenomena, prolonged exposure of human spermatozoa to phenylalanine resulted in the stimulation of apoptosis as indicated by significant increases in mitochondrial superoxide generation and the activation of intracellular caspases. These results confirm the existence of an LAAO in human spermatozoa with a potential role in driving the redox regulation of sperm capacitation and acrosomal exocytosis.

Contemporary evidence on the physiological role of reactive oxygen species in human sperm function

Reactive oxygen species (ROS) play an important role in male fertility. Overproduction of reactive oxygen species (ROS) has been associated with a variety of male fertility complications, including leukocytospermia, varicocele and idiopathic infertility. The subsequent oxidative insult to spermatozoa can manifest as insufficient energy metabolism, lipid peroxidation and DNA damage, leading to loss of motility and viability. However, various studies have demonstrated that physiological amounts of ROS play important roles in the processes of spermatozoa maturation, capacitation, hyperactivation and acrosome reaction. It is therefore crucial to define and understand the delicate oxidative balance in male reproductive cells and tissues for a better understanding of both positive as well as negative impact of ROS production on the fertilizing ability. This review will discuss the specific physiological roles, mechanisms of action and effects that ROS have on the acquisition of structural integrity and physiological activity of spermatozoa.

Melatonin: shedding light on infertility?--A review of the recent literature

In recent years, the negative impact of oxidative stress on fertility has become widely recognised. Several studies have demonstrated its negative effect on the number and quality of retrieved oocytes and embryos following in-vitro fertilisation (IVF). Melatonin, a pineal hormone that regulates circadian rhythms, has also been shown to exhibit unique oxygen scavenging abilities. Some studies have suggested a role for melatonin in gamete biology. Clinical studies also suggest that melatonin supplementation in IVF may lead to better pregnancy rates. Here we present a critical review and summary of the current literature and provide suggestions for future well designed clinical trials.

Effect of various commercial buffers on sperm viability and capacitation

A wide variety of sperm preparation protocols are currently available for assisted conception. They include density gradient separation and washing methods. Both aim at isolating and capacitating as much motile sperm as possible for subsequent oocyte fertilization. The aim of this study was to examine the effects of four commercial sperm washing buffers on sperm viability and capacitation. Semen samples from 48 healthy donors (normal values of sperm count, motility, morphology, and volume) were analyzed. After separation (density gradient 40/80%), sperm were incubated in various buffers then analysed for reactive oxygen species (ROS) production, viability, tyrosine phosphorylation (Tyr-P), cholera toxin B subunit (CTB) labeling, and the acrosome reaction (AR). The buffers affected ROS generation in various ways resulting either in rapid cell degeneration (when the amount of ROS was too high for cell survival) or the inability of the cells to maintain correct functioning (when ROS were too few). Only when the correct ROS generation curve was maintained, suitable membrane reorganization, evidenced by CTB labeling was achieved, leading to the highest percentages of both Tyr-P- and acrosome-reacted-cells. Distinguishing each particular pathological state of the sperm sample would be helpful to select the preferred buffer treatment since both ROS production and membrane reorganization can be significantly altered by commercial buffers.

Effect of astaxanthin on human sperm capacitation

In order to be able to fertilize oocytes, human sperm must undergo a series of morphological and structural alterations, known as capacitation. It has been shown that the production of endogenous sperm reactive oxygen species (ROS) plays a key role in causing cells to undergo a massive acrosome reaction (AR). Astaxanthin (Asta), a photo-protective red pigment belonging to the carotenoid family, is recognized as having anti-oxidant, anti-cancer, anti-diabetic and anti-inflammatory properties and is present in many dietary supplements. This study evaluates the effect of Asta in a capacitating buffer which induces low ROS production and low percentages of acrosome-reacted cells (ARC). Sperm cells were incubated in the presence or absence of increasing concentrations of Asta or diamide (Diam) and analyzed for their ROS production, Tyr-phosphorylation (Tyr-P) pattern and percentages of ARC and non-viable cells (NVC). Results show that Asta ameliorated both sperm head Tyr-P and ARC values without affecting the ROS generation curve, whereas Diam succeeded in enhancing the Tyr-P level but only of the flagellum without increasing ARC values. It is suggested that Asta can be inserted in the membrane and therefore create capacitation-like membrane alteration which allow Tyr-P of the head. Once this has occurred, AR can take place and involves a higher numbers of cells.

Influence of reactive oxygen species on human sperm functions and fertilizing capacity including therapeutical approaches

BACKGROUND

Reactive oxygen species (ROS) are an array of molecules including oxygen-centered radicals, which are endowed with one or more unpaired electrons and non-radical oxygen derivatives such as hydrogen peroxide, which behave, to a large extent, like a double-edged sword in human sperm biology. This study aimed to overview the current knowledge of ROS in sperm physiology and pathology, as well as related therapies in spermatozoal dysfunction.

METHODS

We performed this study by searching for keywords from PUBMED, including reactive oxygen species, oxidative stress, sperm function, and antioxidant therapy.

RESULTS AND CONCLUSIONS

Low levels of ROS exert critical function in normal sperm physiology, such as fertilizing ability (acrosome reaction, hyperactivation, capacitation, and chemotaxis) and sperm motility; while increased ROS generation and/or decreased antioxidant capacity leads to the imbalance between oxidation and reduction in living systems, which is called sperm oxidative stress. This condition was widely considered to be a significant contributory factor to sperm DNA damage/apoptosis, lipid peroxidation, and reduced motility, which in turn, increased risk of male factor infertility/subfertility and birth defects. Under the current status quo, numerous subsequent studies have concentrated on antioxidant therapy. Although utility of such a therapeutic strategy significantly improved sperm function and motility in a myriad of experimental and clinical reports, the overall effectiveness still remains controversial mainly due to non-standardized assay to measure the level of ROS and sperm DNA damage, various antioxidant supplementation strategies, and inadequate fertilization and pregnancy data after clinical treatment. Therefore, standardized assessment and evaluation of ROS and total antioxidant capacity in semen should be established to keep ROS in a physiological level and prevent over-treatment of antioxidants toward reductive stress, which should be kept in mind, especially in assisted reproductive procedure. Moreover, the significance of large sample size populations, double-blind randomized, placebo-controlled clinical trials of antioxidant therapies is emphasized in this review to achieve optimal ingredients and dosage of antioxidants for patients with reactive oxygen-induced male fertility/subfertility.

Metabolic substrates exhibit differential effects on functional parameters of mouse sperm capacitation

Although substantial evidence exists that sperm ATP production via glycolysis is required for mammalian sperm function and male fertility, conflicting reports involving multiple species have appeared regarding the ability of individual glycolytic or mitochondrial substrates to support the physiological changes that occur during capacitation. Several mouse models with defects in the signaling pathways required for capacitation exhibit reductions in sperm ATP levels, suggesting regulatory interactions between sperm metabolism and signal transduction cascades. To better understand these interactions, we conducted quantitative studies of mouse sperm throughout a 2-h in vitro capacitation period and compared the effects of single substrates assayed under identical conditions. Multiple glycolytic and nonglycolytic substrates maintained sperm ATP levels and comparable percentages of motility, but only glucose and mannose supported hyperactivation. These monosaccharides and fructose supported the full pattern of tyrosine phosphorylation, whereas nonglycolytic substrates supported at least partial tyrosine phosphorylation. Inhibition of glycolysis impaired motility in the presence of glucose, fructose, or pyruvate but not in the presence of hydroxybutyrate. Addition of an uncoupler of oxidative phosphorylation reduced motility with pyruvate or hydroxybutyrate as substrates but unexpectedly stimulated hyperactivation with fructose. Investigating differences between glucose and fructose in more detail, we demonstrated that hyperactivation results from the active metabolism of glucose. Differences between glucose and fructose appeared to be downstream of changes in intracellular pH, which rose to comparable levels during incubation with either substrate. Sperm redox pathways were differentially affected, with higher levels of associated metabolites and reactive oxygen species generated during incubations with fructose than during incubations with glucose.