Superoxide anion production by human spermatozoa as a part of the ionophore-induced acrosome reaction process

Genotoxic and cytotoxic effects of aflatoxin on the reproductive system: Focus on cell cycle dynamics and apoptosis in testicular tissue

Aflatoxins (AFs) are inevitable environmental contaminants that are detrimental to human and animal health. AFs interfere with metabolic processes, metabolizing into different hydroxylated derivatives in the liver, as well as mechanistically induce ROS accumulation, S-phase arrest, DNA damage, and cell apoptosis. Chronic consumption of aflatoxin-contaminated foods can adversely affect the male reproductive system, cause testicular damage, prevent testosterone synthesis, decline sperm quality, and cause infertility. Oxidative stress is the fundamental pathogenesis of aflatoxin-induced reproductive toxicity. The overproduction of reactive oxygen substances can cause testicular failure and disturb the process of spermatogenesis. Mitochondria are susceptible to being impaired by oxidative stress, and its damage is associated with infertility. AFs also disturb the process of spermatogenesis by disrupting the regulation of genes related to the progression of the cell cycle such as cyclins and inducing genes related to apoptosis, thereby weakening fertility and negatively affecting the testicular endocrine potential by suppressing androgen synthesis. Additionally, AFs downregulate ERα expression, potentially negatively impacting spermatogenesis by enhancing the apoptotic mechanism. In this review, we provide new insights into the genotoxic and cytotoxic effects of AFB1 on the male reproductive system with a focus on the cell cycle and apoptosis destruction of testicular tissue.

Lactate-induced spontaneous acrosomal exocytosis as a method to study acrosome function in stallion sperm

Evaluation of acrosome function in stallion sperm is mostly based on the use of inducers of acrosomal exocytosis (AE), such as the calcium ionophore A23187 or progesterone. Recently, it has been reported that incubation of stallion sperm under presumed capacitating conditions (i.e., medium formulated with calcium, bicarbonate, and bovine serum albumin) using a lactate-only containing medium (Lac-MW) results in a high rate of spontaneous AE in viable sperm (AE/Viable). In the current study, we developed an alternative assay of acrosome function for stallion sperm following the incubation of sperm in a medium formulated only with lactate as an energy substrate (Lac-MW). In Experiment 1, freshly ejaculated stallion sperm was incubated with 10 μM A23187, Lac-MW, or Control, for up to 6 h under capacitating conditions. The percentages of motile sperm, viable sperm, total AE (Total AE), and AE in viable sperm (AE/Viable) were compared among treatment groups. Incubation in Lac-MW, but not with Control or A23187, resulted in a time-dependent increase in the percentage of AE/Viable, as determined by flow cytometry, particularly at 4 and 6 h of incubation (P < 0.05). In Experiment 2, freshly ejaculated sperm was incubated in Lac-MW for up to 6 h, and the occurrence of protein tyrosine phosphorylation and AE/Viable were determined. At 4h and 6h of incubation in Lac-MW, ∼40% of the sperm displayed a protein tyrosine phosphorylation immunofluorescence pattern that coincides with that recently associated with stallion sperm capacitation (i.e., immunofluorescence signal at the acrosome and midpiece). In Experiment 3, the rate of AE/Viable sperm was compared among freshly ejaculated, cool-stored, and frozen/thawed stallion sperm. Except at 2h incubation in Lac-MW, differences in mean AE/Viable among fresh, cool-stored, and frozen/thawed sperm were not observed (P > 0.05). In Experiment 4, the relationship between Total AE (A23187), or AE/Viable (Lac-MW), and in vivo fertility of 5 stallions was determined. A linear relationship was observed between mean AE/Viable and the per-cycle (r = 0.93; P < 0.05) and seasonal (r = 0.66; P < 0.05) pregnancy rates of five stallions used for artificial insemination with cool-stored semen. In Experiment 5, frozen/thawed sperm from subfertile Thoroughbred (TB) stallions, known to carry the susceptibility genotype for Impaired Acrosomal Exocytosis (IAE; FKBP6 A/A-A/A) was evaluated following incubation in Lac-MW. Sperm from subfertile TB stallions with IAE had lower mean AE/Viable, at both 4h and 6h incubation in Lac-MW, when compared to that of fertile control stallions (P < 0.05). Overall, the Lac-MW model validated in the current study may be a useful complementary assay to evaluate the ability of stallion sperm to physiologically undergo AE and to study stallion fertility potential. This acrosome function assay can be used to evaluate fresh, cool-stored, or frozen/thawed stallion sperm, and describes a strong linear relationship with in vivo-fertility of stallions used in artificial insemination programs.

Integration of omics studies indicates that species-dependent molecular mechanisms govern male fertility

BACKGROUND

Comparative and comprehensive omics studies have recently been conducted to provide a comprehensive understanding of the biological mechanisms underlying infertility. However, because these huge omics datasets often contain irrelevant information, editing strategies for summarizing and filtering the data are necessary prerequisite steps for identifying biomarkers of male fertility. Here, we attempted to integrate omics data from spermatozoa with normal and below-normal fertility from boars and bulls, including transcriptomic, proteomic, and metabolomic data. Pathway enrichment analysis was conducted and visualized using g:Profiler, Cytoscape, EnrichmentMap, and AutoAnnotation to determine fertility-related biological functions according to species.

RESULTS

In particular, gamete production and protein biogenesis-associated pathways were enriched in bull spermatozoa with below-normal fertility, whereas mitochondrial-associated metabolic pathways were enriched in boar spermatozoa with normal fertility. These results indicate that below-normal fertility may be determined by aberrant regulation of protein synthesis during spermatogenesis, and the modulation of reactive oxygen species generation to maintain capacitation and the acrosome reaction governs boar sperm fertility.

CONCLUSION

Overall, this approach demonstrated that distinct molecular pathways drive sperm fertility in mammals in a species-dependent manner. Moreover, we anticipate that searching for species-specific signaling pathways may aid in the discovery of fertility-related biomarkers within large omics datasets.

Role of antioxidants in fertility preservation of sperm - A narrative review

Male fertility is affected by multiple endogenous stressors, including reactive oxygen species (ROS), which greatly deteriorate the fertility. However, physiological levels of ROS are required by sperm for the proper accomplishment of different cellular functions including proliferation, maturation, capacitation, acrosomal reaction, and fertilization. Excessive ROS production creates an imbalance between ROS production and neutralization resulting in oxidative stress (OS). OS causes male infertility by impairing sperm functions including reduced motility, deoxyribonucleic acid damage, morphological defects, and enhanced apoptosis. Several in-vivo and in-vitro studies have reported improvement in quality-related parameters of sperm following the use of different natural and synthetic antioxidants. In this review, we focus on the causes of OS, ROS production sources, mechanisms responsible for sperm damage, and the role of antioxidants in preserving sperm fertility.

Inhibition of Mitochondrial Uncoupling Proteins Arrests Human Spermatozoa Motility without Compromising Viability

Mitochondrial uncoupling proteins (UCPs) are central in the regulation of mitochondrial activity and reactive oxygen species (ROS) production. High oxidative stress is a major cause of male infertility; however, UCPs expression and function in human spermatozoa are still unknown. Herein, we aimed to assess the expression and function of the different homologs (UCP1-6) in human spermatozoa. For this purpose, we screened for the mRNA expression of all UCP homologs. Protein expression and immunolocalization of UCP1, UCP2, and UCP3 were also assessed. Highly motile spermatozoa were isolated from human normozoospermic seminal samples (n = 16) and incubated with genipin, an inhibitor of UCPs (0, 0.5, 5, and 50 µM) for 3 h at 37 °C. Viability and total motility were assessed. Mitochondrial membrane potential and ROS production were evaluated. Media were collected and the metabolic profile and antioxidant potential were analyzed by ¹H-NMR and FRAP, respectively. The expression of all UCP homologs (UCP1-6) mRNA by human spermatozoa is herein reported for the first time. UCP1-3 are predominant at the head equatorial segment, whereas UCP1 and UCP2 are also expressed at the spermatozoa midpiece, where mitochondria are located. The inhibition of UCPs by 50 µM genipin, resulting in the UCP3 inhibition, did not compromise sperm cell viability but resulted in irreversible total motility loss that persisted despite washing or incubation with theophylline, a cAMP activator. These effects were associated with decreased mitochondrial membrane potential and lactate production. No differences concerning UCP3 expression, however, were observed in spermatozoa from normozoospermic versus asthenozoospermic men (n = 6). The inhibition of UCPs did not increase ROS production, possibly due to the decreased mitochondrial activity and genipin antioxidant properties. In sum, UCPs are major regulators of human spermatozoa motility and metabolism. The discovery and characterization of UCPs' role in human spermatozoa can shed new light on spermatozoa ROS-related pathways and bioenergetics physiology.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

A stallion spermatozoon's journey through the mare's genital tract: In vivo and in vitro aspects of sperm capacitation

Conventional in vitro fertilization is not efficacious when working with equine gametes. Although stallion spermatozoa bind to the zona pellucida in vitro, these gametes fail to initiate the acrosome reaction in the vicinity of the oocyte and cannot, therefore, penetrate into the perivitelline space. Failure of sperm penetration most likely relates to the absence of optimized in vitro fertilization media containing molecules essential to support stallion sperm capacitation. In vivo, the female reproductive tract, especially the oviductal lumen, provides an environmental milieu that appropriately regulates interactions between the gametes and promotes fertilization. Identifying these 'fertilization supporting factors' would be a great contribution for development of equine in vitro fertilization media. In this review, a description of the current understanding of the interactions stallion spermatozoa undergo during passage through the female genital tract, and related specific molecular changes that occur at the sperm plasma membrane is provided. Understanding these molecular changes may hold essential clues to achieving successful in vitro fertilization with equine gametes.

Therapeutic Effects of Xianlu Oral Solution on Rats with Oligoasthenozoospermia through Alleviating Apoptosis and Oxidative Stress

Idiopathic oligoasthenozoospermia (iOAZS) is one of the major causes of male infertility, and the ideal therapies for iOAZS have not been established yet. Traditional Chinese medicine (TCM), including Xianlu oral solution (XL), has been widely used as an adjunct treatment for male infertility in the clinic. However, the underlying mechanisms of XL treatment on iOAZS are still not known. Here, we found that XL treatment has therapeutic effects on ornidazole (ORN)-induced OAZS model rats through the amelioration of testis tissues spermatogenesis and the improvement of sperm concentration and motility. Moreover, XL treatment ameliorated the serum hormone levels, mitochondrial membrane potential, apoptosis status, and oxidative stress status in the testis tissues of iOAZS model rats. These findings identify a potential mechanism underlying the therapeutic effects of Xianlu oral solution on iOAZS, and Xianlu oral solution may be used as a traditional Chinese medicine (TCM) therapy for male infertility caused by iOAZS in clinical practice.

Roles of Oxidative Stress in the Male Reproductive System: Potential of Antioxidant Supplementation for Infertility Treatment

The decline of fertility in modern society is a serious worldwide concern, and the reasons behind it are complex and difficult to unveil. The fact that a big percentage of infertility cases remain diagnosed as idiopathic, turn the strategies to treat such conditions very limited. Nevertheless, one must agree that keeping the oxidative balance of the reproductive tissues should be one of the first lines of treatment for infertile patients. As reported, 30-80% of male infertile individuals present high levels of prooxidant species in the seminal fluid. Thus, antioxidant therapies, which consist of dietary supplementation therapy with one or more antioxidant compound, remain the first step in the treatment of male infertility. Nevertheless, the efficacy of such therapies is variable between individuals. The most common prescribed antioxidants are carnitines and vitamins C and E, but recently phytochemical quercetin has emerged as a potential compound for the treatment of oxidative stress in the male reproductive system. Although there are several animals' evidence about the great potential of quercetin for the treatment of infertility, clinical trials on this subject remain scarce.

L-amino acid oxidase 1 in sperm is associated with reproductive performance in male mice and bulls

Sperm quality is an important indicator of male fertility, and a suitable biomarker enables the selection of high-quality spermatozoa. We previously found that L-amino acid oxidase encoded by the L-amino acid oxidase 1 (Lao1) gene exerts biological roles in the mammary gland and brain by converting specific L-amino acids into keto acids, ammonia, and hydrogen peroxide (H2O2). Here, we describe the role of Lao1 in male reproduction. Lao1-deficient (Lao1-/-) male mice generated fewer pregnant embryos and pups as well as lower ratios of fertilized oocytes and even ovulated number was not different, suggesting that male subfertility caused the smaller litters. We found that LAO1 expressed in acrosomes is associated with high malformation ratios and low viability of Lao1-/- sperm. Wild-type (WT) sperm produced more H2O2 than Lao1-/- sperm, and 10 μM H2O2 restored knockout (KO) sperm viability in vitro. In addition, the sperm ratio of induced acrosome reaction was higher in WT than in Lao1-/- sperm incubated with the calcium ionophore A23187. Moreover, LAO1 expression was abundant in bovine sperm with high fertilization ratios. We concluded that LAO1 localized in the sperm acrosome influences sperm viability and morphology as well as the acrosome reaction, and that LAO1-deficient sperm might cause male subfertility. Thus, LAO1 might serve as a novel marker for selecting high-quality spermatozoa, especially for livestock reproduction.

Mitochondrial Functionality in Male Fertility: From Spermatogenesis to Fertilization

Mitochondria are structurally and functionally distinct organelles that produce adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS), to provide energy to spermatozoa. They can also produce reactive oxidation species (ROS). While a moderate concentration of ROS is critical for tyrosine phosphorylation in cholesterol efflux, sperm–egg interaction, and fertilization, excessive ROS generation is associated with male infertility. Moreover, mitochondria participate in diverse processes ranging from spermatogenesis to fertilization to regulate male fertility. This review aimed to summarize the roles of mitochondria in male fertility depending on the sperm developmental stage (from male reproductive tract to female reproductive tract). Moreover, mitochondria are also involved in testosterone production, regulation of proton secretion into the lumen to maintain an acidic condition in the epididymis, and sperm DNA condensation during epididymal maturation. We also established the new signaling pathway using previous proteomic data associated with male fertility, to understand the overall role of mitochondria in male fertility. The pathway revealed that male infertility is associated with a loss of mitochondrial proteins in spermatozoa, which induces low sperm motility, reduces OXPHOS activity, and results in male infertility.

The Impact of Di-2-Ethylhexyl Phthalate on Sperm Fertility

A growing number of studies point to reduced fertility upon chronic exposure to endocrine-disrupting chemicals (EDCs) such as phthalates and plasticizers. These toxins are ubiquitous and are often found in food and beverage containers, medical devices, as well as in common household and personal care items. Animal studies with EDCs, such as phthalates and bisphenol A have shown a dose-dependent decrease in fertility and embryo toxicity upon chronic exposure. However, limited research has been conducted on the acute effects of these EDCs on male fertility. Here we used a murine model to test the acute effects of four ubiquitous environmental toxins: bisphenol A (BPA), di-2-ethylhexyl phthalate (DEHP), diethyl phthalate (DEP), and dimethyl phthalate (DMP) on sperm fertilizing ability and pre-implantation embryo development. The most potent of these toxins, di-2-ethylhexyl phthalate (DEHP), was further evaluated for its effect on sperm ion channel activity, capacitation status, acrosome reaction and generation of reactive oxygen species (ROS). DEHP demonstrated a profound hazardous effect on sperm fertility by producing an altered capacitation profile, impairing the acrosome reaction, and, interestingly, also increasing ROS production. These results indicate that in addition to its known chronic impact on reproductive potential, DEHP also imposes acute and profound damage to spermatozoa, and thus, represents a significant risk to male fertility.

Follicle-Stimulating Hormone Treatment and Male Idiopathic Infertility: Effects on Sperm Parameters and Oxidative Stress Indices according to FSHR c. 2039 A/G and c. -29 G/A Genotypes

Scientific evidence shows that the administration of follicle-stimulating hormone (FSH) to infertile patients with normal serum FSH concentrations improves sperm parameters in oligozoospermic men. The aim of this study was to evaluate the effects of highly purified urofollitropin (hpFSH) on conventional and bio-functional sperm parameters and on oxidative stress indices in patients with idiopathic infertility. We also evaluated the response to hpFSH on these parameters in relationship to FSHR c. 2039 A/G and FSHR c. -29 G/A genotypes. A prospective longitudinal study was conducted on 42 patients with idiopathic male infertility, 23 of whom underwent to FSHR c. 2039 A/G and FSHR c. -29 G/A genotyping. Each patient was asked to collect two semen samples before and after administration of 150 IU hpFSH three times a week for 16 weeks. Patients were divided into responders or non-responders based on whether their total sperm count had at least doubled or was less than double at the end of treatment, respectively. Responders showed a significantly higher semen volume, sperm concentration, spermatids, and leukocytes. Non-responders had a significant decrease of the percentage of spermatozoa in early apoptosis after hpFSH administration. Oxidative stress indexes did not differ significantly after FSH administration in both groups. Conventional and bio-functional sperm parameters did not differ in patients with FSHR c. 2039 GG and AA genotypes, and FSHR c. -29 GG genotype both before and after FSH administration. The FSHR c. 2039 and FSHR -29 G/A genotypes and allelic distribution did not differ between responders and non-responders. FSH showed to be capable of ameliorating sperm parameters in about half patients treated, therefore it may be helpful in patients with idiopathic infertility.

Association of antioxidant defense system with semen attributes vis a vis fertility in exotic and indigenous chicken breeds

The present study was designed to ascertain the association of antioxidant defense system with semen attributes and fertility in RIR (Rhode Island Red), PR (Punjab Red), RIR x local cross, Aseel and Kadaknath breeds. Based on sperm attributes, roosters of each breed were divided into two group i.e. G-I (exhibiting >50% sperm attributes) and G-II (exhibiting <50% sperm attributes). Motility, viability, membrane-, acrosome-, DNA-integrity and fertility differed significantly (p < 0.05) among the breeds, representing maximum in PR roosters and least in Aseel roosters. Values of sperm attributes and fertility rate were also significantly (p < 0.05) higher in G-I compared to G-II roosters in exotic as well as indigenous breeds. MDA content differed significantly (p < 0.05) in spermatozoa of five breeds. It indicated a least oxidant stress in PR and highest in Aseel. MDA concentration was significantly (P < 0.05) higher in G-II (28.36 ± 2.40-96.0 ± 6.4) than G-I (13.65 ± 1.81-52.22 ± 6.4) roosters in all breeds. Antioxidant enzyme activity varied significantly (p < 0.05) among the breeds and groups within the breeds. Significantly (p < 0.05) higher activity of four enzymes was evident in G-II as compared to G-I roosters irrespective of the breed. A moderate to strong negative correlation was perceived among LPO, SOD, GPX, catalase, GRE and sperm attributes/fertility rate. A moderate to strong positive correlation (0.21-0.92) among LPO and antioxidant enzymes revealed that with the increase in LPO, antioxidant enzymes increase too and vice versa in all breeds. Likewise, positive correlation between sperm attributes and fertility revealed that higher sperm attributes contribute to the high fertility of roosters. This is one of the first reports on complete set of antioxidant enzymes and oxidative stress in relation to sperm attributes and fertility in different five chicken breeds. A complete antioxidant enzyme system seems to modulate the oxidative stress, sperm attributes and fertility. It may be possible to use LPO as a fertility marker to select the roosters for breeding purpose in the chicken breeds.

Dietary Cholesterol and Lipid Overload: Impact on Male Fertility

Lipid metabolic disorders due to poor eating habits are on the rise in both developed and developing countries, with a negative impact of the "Western diet" on sperm count and quality. Dietary lipid imbalance can involve cholesterol, fatty acids, or both, under different pathophysiological conditions grouped under the term dyslipidemia. The general feature of dyslipidemia is the development of systemic oxidative stress, a well-known deleterious factor for the quality of male gametes and associated with infertility. Sperm are particularly rich in polyunsaturated fatty acids (PUFA), an important characteristic associated with normal sperm physiology and reproductive outcomes, but also targets of choice for oxidative thrust. This review focuses on the effects of dietary cholesterol or different fatty acid overload on sperm composition and function in both animals and humans. The links between oxidative stress induced by dyslipidemia and sperm dysfunction are then discussed, including possible preventive or therapeutic strategies to preserve gamete quality, longevity when stored in cryobanking, and male fertility.

Effect of Vitamin E and Polyunsaturated Fatty Acids on Cryopreserved Sperm Quality in Bos taurus Bulls Under Testicular Heat Stress

Taurine bulls are highly susceptible to heat stress, leading to increased oxidative stress (OS) and impaired sperm viability. Polyunsaturated fatty acids (PUFAs) supplementation can be an alternative to improve semen quality, which also results in more sperm susceptibility to lipid peroxidation. Moreover, this deleterious effect can be exacerbated in animals affected by heat stress. Vitamin E is a key antioxidant that counteracts lipid peroxidation of sperm membrane caused by OS. Thus, combining PUFAs with vitamin E may improve sperm quality. In this context, this study aimed to evaluate the effect of interaction between PUFAs and vitamin E on sperm quality in Bos taurus bulls under testicular heat stress. Sixteen taurine bulls under testicular heat stress were randomly assigned in four groups: Control, Vitamin E, PUFA, and PUFA + Vitamin E. All groups lasted for 60 days. Samples were cryopreserved/thawed and analyzed for motility variables (CASA), membrane and acrosome integrity, mitochondrial activity, susceptibility to oxidative stress, DNA integrity, and sperm-binding capacity. Results showed that vitamin E had a beneficial effect on some sperm characteristics, whereas PUFA supplementation had an adverse effect when the two treatments were evaluated separately. Finally, the association between PUFAs and vitamin E did not improve sperm quality.

Biochemical alterations in the oocyte in support of early embryonic development

Notwithstanding the enormous reproductive potential encapsulated within a mature mammalian oocyte, these cells present only a limited window for fertilization before defaulting to an apoptotic cascade known as post-ovulatory oocyte aging. The only cell with the capacity to rescue this potential is the fertilizing spermatozoon. Indeed, the union of these cells sets in train a remarkable series of events that endows the oocyte with the capacity to divide and differentiate into the trillions of cells that comprise a new individual. Traditional paradigms hold that, beyond the initial stimulation of fluctuating calcium (Ca2+) required for oocyte activation, the fertilizing spermatozoon plays limited additional roles in the early embryo. While this model has now been drawn into question in view of the recent discovery that spermatozoa deliver developmentally important classes of small noncoding RNAs and other epigenetic modulators to oocytes during fertilization, it is nevertheless apparent that the primary responsibility for oocyte activation rests with a modest store of maternally derived proteins and mRNA accumulated during oogenesis. It is, therefore, not surprising that widespread post-translational modifications, in particular phosphorylation, hold a central role in endowing these proteins with sufficient functional diversity to initiate embryonic development. Indeed, proteins targeted for such modifications have been linked to oocyte activation, recruitment of maternal mRNAs, DNA repair and resumption of the cell cycle. This review, therefore, seeks to explore the intimate relationship between Ca2+ release and the suite of molecular modifications that sweep through the oocyte to ensure the successful union of the parental germlines and ensure embryogenic fidelity.

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.

The blood-epididymis barrier and inflammation

The blood-epididymis barrier (BEB) is a critical structure for male fertility. It enables the development of a specific luminal environment that allows spermatozoa to acquire both the ability to swim and fertilize an ovum. The presence of tight junctions and specific cellular transporters can regulate the composition of the epididymal lumen to favor proper sperm maturation. The BEB is also at the interface between the immune system and sperm. Not only does the BEB protect maturing spermatozoa from the immune system, it is also influenced by cytokines released during inflammation, which can result in the loss of barrier function. Such a loss is associated with an immune response, decreased sperm functions, and appears to be a contributing factor to post-testicular male infertility. Alterations in the BEB may be responsible for the formation of inflammatory conditions such as sperm granulomas. The present review summarizes current knowledge on the morphological, physiological and pathological components associated with the BEB, the role of immune function on the regulation of the BEB, and how disturbance of these factors can result in inflammatory lesions of the epididymis.

Protection of common carp (Cyprinus carpio L.) spermatozoa motility under oxidative stress by antioxidants and seminal plasma

The protective influence of seminal plasma and the antioxidants catalase (CAT), superoxide dismutase (SOD), and glutathione (GTH) on quality parameters, oxidative stress indices, and antioxidant activity was studied in common carp (Cyprinus carpio) spermatozoa exposed to the xanthine-xanthine oxidase (X-XO) system. Fish spermatozoa were incubated for 5 and 20 min at 4 °C with X-XO concentrations of 1 mM X-0.1 U/mL, 0.6 mM X-0.05 U/mL, 0.3 mM X-0.025 U/mL, and 0.1 mM X-0.0125 U/mL. A dose-dependent reduction in spermatozoa motility and velocity was observed at concentrations of 0.1 mM X-0.0125 U/mL to 1 mM X-0.1 U/mL XO. Increase in spermatozoa motility parameters was recorded following treatment with antioxidants and seminal plasma. The level of the oxidative stress indices lipid peroxidation (LPO) and carbonyl derivatives of proteins (CP) was significantly reduced after addition of CAT, SOD, or GTH along with seminal plasma. Significant differences in SOD, glutathione reductase, and glutathione peroxidase activity were seen in spermatozoa incubated with, compared to that without, seminal plasma at all studied X-XO concentrations. The data demonstrated that CAT, SOD, or GTH in combination with SP can reduce reactive oxygen species stress in fish spermatozoa and improve spermatozoa quality.

Biomonitoring of polycyclic aromatic hydrocarbons from coke oven emissions and reproductive toxicity in nonsmoking workers

The objective of the cross-sectional study was to assess whether exposure to polycyclic aromatic hydrocarbons (PAHs) from coke oven emissions contributed to alteration of semen quality and sperm DNA integrity in nonsmoking workers. Nonsmoking coke oven workers from a steel plant in Taiwan served as the exposure groups (topside-oven workers for the high exposure group and side-oven workers for the low exposure group), and administrators and security personnel in the plant served as the control. An exposure assessment was conducted to determine both particulate and gaseous phase of PAH levels and urinary 1-hydroxypyrene (1-OHP) levels. Semen quality was analyzed according to WHO guidelines. DNA fragmentation and bulky DNA adducts were measured to assess sperm DNA integrity. There was no significant difference in sperm concentrations, vitality, and DNA fragmentation between the exposed group and the control. The high exposure group experienced significantly lower percentages of normal morphology as compared with the control (p=0.0001). Bulky DNA adducts were detected in the exposed group that were significant higher than the control (p=0.04). Exposure to PAHs from coke-oven emissions could contribute to increased levels of bulky DNA adducts in sperm.

Reactive oxygen and nitrogen species in normal physiological processes

Abstract Reactive oxygen species (ROS) and reactive nitrogen species have generally been considered as being highly reactive and cytotoxic molecules. Besides their noxious effects, ROS participate in physiological processes in a carefully regulated manner. By way of example, microbicidal ROS are produced in professional phagocytes, ROS function as short-lived messengers having a role in signal transduction and, among other processes, participate in the synthesis of the iodothyronine hormones, reproduction, apoptosis and necrosis. Because of their ability to mediate a crosstalk between key molecules, their role might be dual (at least in some cases). The levels of ROS increase from a certain age, being associated with various diseases typical of senescence. The aim of this review is to summarize the recent findings on the physiological role of ROS. Other issues addressed are an increase in ROS levels during ageing, and the possibility of the physiological nature of this process.

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.

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.

Generation of superoxide anion by equine spermatozoa as detected by dihydroethidium

Low-level production of the superoxide anion (O2*-) is an important signal transduction event in sperm function including capacitation; however, excessive production of O2*- can be detrimental to sperm function. The objective of this study was to assess dihydroethidium (DHE) as a probe for O2*- in equine spermatozoa. Ejaculated spermatozoa were separated by centrifugation over a Percoll gradient (40:80), and loaded with DHE (2.0 microM) as well as with calcein-acetoxymethylester (CAM, 7.8 nM) to determine cell viability. In Experiment 1, cells were incubated with the xanthine-xanthine oxidase (X, 0.1 mM; XO, 0.01 U/mL) generating system for the production of O2*-, with or without the addition of superoxide dismutase (SOD, 150 U/mL) or the SOD mimetic, Tiron (0.1, 1.0 or 5.0 mM) for 1h. Changes in fluorescence of DHE were determined for the live cell population (calcein-positive cells) by flow cytometry. The DHE fluorescence increased with the X-XO incubation; this increase was inhibited by SOD or Tiron, indicating that DHE is specific for O2*- detection. In Experiment 2, spermatozoa were loaded with DHE/CAM, treated with calcium ionophore A23187 (0, 0.8, or 8.0 microM), and incubated for 15 min. Cell fluorescence was again determined by flow cytometry. Calcium ionophore A23187 increased O2*- production in a dose-dependent manner. In Experiment 3, cells were loaded with DHE/CAM, treated with NADPH (0.0, 0.25, 0.5, or 1 mM) with or without 0.5% Triton X-100, and incubated for 15 min prior to flow cytometry. Cells treated with NADPH with or without 0.5% Triton X-100 did not have O2*- levels that were significantly different from the control. In Experiment 4, spermatozoa loaded with DHE/CAM were incubated under capacitating conditions (1.2 mM dibutryl-cAMP+1.0 mM caffeine) or in control media for 3h. Although O2*- generation increased over time in control and capacitated treatments, spermatozoa incubated under capacitating conditions had higher O2*- production than those incubated in control media. Therefore, DHE was a useful probe for the detection of O2*- in equine spermatozoa and elevation in intracellular calcium as well as capacitation in vitro were associated with increased generation of O2*-.

Seminal malondialdehyde concentration but not glutathione peroxidase activity is negatively correlated with seminal concentration and motility

Objectives: Reactive oxygen species (ROS) induced lipid peroxidation is associated with sperm function. Malondialdehyde (MDA) concentration and glutathione peroxidase (GPx) activity represent the lipid peroxidation and spermicidal antioxidant, respectively. We aimed to evaluate the relationship of MDA and GPx levels with sperm parameters.

Patients and methods: Specimens were divided into two groups: group 1. normospermia (n=20); group 2. oligoasthenospermia (n=31). Seminal MDA concentration was measured by thiobarbituric acid reaction method. Seminal GPx activity was measured by oxidation of reduced nicotinamide-adenine dinucleotide. Seminal MDA levels and GPx activities in both groups were compared.

Results: MDA concentrations in both groups were significantly different (1.52 ± 0.75 vs. 2.25 ± 0.88 nM, p = 0.0021). GPx activities in both groups were non-significantly different (0.48 ± 0.11 vs. 0.47 ± 0.12 U/ml). MDA levels were negatively correlated with the sperm motility (MDA = -0.014 x motility + 2.62, p =0.017) and concentration (MDA = -0.0045 x concentration + 2.23, p = 0.0166). GPx activities were positively but non-significantly correlated with the sperm concentration and sperm motility.

Conclusions: Seminal MDA concentrations are negatively correlated with sperm concentration and motility, which might provide a simple and useful tool in predicting sperm parameters. GPx activity is non-significantly correlated with the seminal quality. Roles of seminal MDA upon spermatogenesis merits further surveys.

Nitric oxide induces acrosome reaction in cryopreserved bovine spermatozoa

The aim of this work was to study the effect of nitric oxide on acrosome reaction (AR) and the participation of protein kinases and reactive oxygen species in the AR of cryopreserved bovine spermatozoa. Spermatozoa were capacitated in Tyrode's albumin lactate pyruvate medium with heparin (10 IU ml(-1)) and then incubated with different concentrations of sodium nitroprusside (SNP) (1-200 micromol l(-1)). Methylene blue and haemoglobin were used to confirm the role of nitric oxide as an inducer of the AR. The participation of protein kinase A (PKA) , protein kinase C (PKC) and protein tyrosine kinase was evaluated using specific inhibitors of these enzymes (H-89, 50 micromol l(-1); bisindolylmaleimide I, 0.1 micromol l(-1) and genistein, 3 micromol l(-1)). The role of hydrogen peroxide or superoxide anion was evaluated by incubation with catalase or superoxide dismutase respectively. AR percentages were determined by the fluorescence technique with chlortetracycline. The highest levels of AR were obtained in capacitated spermatozoa treated with 5-200 micromol l(-1) SNP (24.8 +/- 1.8%). The presence of PKA, PKC and protein tyrosine kinase inhibitors likewise decreased AR percentages. The addition of superoxide dismutase had no effect on the AR level but catalase completely blocked it. These results indicate that nitric oxide induces AR in capacitated spermatozoa involving hydrogen peroxide and the participation of PKA, PKC and protein tyrosine kinase as part of the signal transduction mechanism which lead to the AR in cryopreserved bovine spermatozoa.

Treatment of male infertility

Male factor infertility is a general term that describes a situation in which the inability to conceive is associated with an alteration identified in the male partner. This dysfunction may be associated with low sperm concentration (oligozoospermia), poor sperm motility (asthenozoospermia) or abnormal sperm morphology (teratozoospermia); however, generally, a disturbance of all these variables, oligoasthenoteratozoospermia, is mostly frequent in male subfertility. For many andrological disorders, it is not possible to find a reasonable cause and various uncontrolled treatments have been applied to infertile men, often just on an empirical basis. More recently, after the explosive development of modern assisted reproduction techniques (ARTs), feasible with a single spermatozoon [intracytoplasmic sperm injection (ICSI)], the treatment of male infertility has received new meaning and andrologists are no longer expected to achieve a quantitative increase in sperm number but are instead asked to improve the fertility potential of the single sperm cell in order to achieve better results in both in vitro fertilization and ICSI. Additional prospective studies are needed to better understand the possible role of therapy in ART candidate patients.

Identification of cytochrome-b5 reductase as the enzyme responsible for NADH-dependent lucigenin chemiluminescence in human spermatozoa

Lucigenin-dependent chemiluminescence together with 2-[4-iodophenyl]-3-[4-nitrophenyl]-5-[2,4-disulfophenyl]-2H tetrazolium monosodium salt (WST-1) reduction can be detected following addition of NADH to many cell types, including human sperm suspensions. Although many reports suggest that such a phenomenon is due to reactive oxygen species production, other oxygen detecting metabolite probes, such as MCLA and luminol, do not produce a chemiluminescent signal in this model system. The enzyme responsible for NADH-dependent lucigenin chemiluminescence was purified and identified as cytochrome-b5 reductase. In support of this concept, COS-7 cells overexpressing cytochrome-b5 reductase displayed at least a 3-fold increase in the previously mentioned activity compared with mock-transfected cells. Fractions containing cytochrome-b5 reductase were capable of inducing both lucigenin-dependent chemiluminescence and WST-1 reduction. Oxygen radicals clearly did not mediate the cytochrome b5-mediated activation of these probes in vitro since neither luminol nor MCLA gave a chemiluminescence response in the presence of the enzyme and the cofactor NADH. These results emphasize the importance of the direct NADH-dependent reduction of these putative superoxide-sensitive probes by cytochrome-b5 reductase even though this enzyme does not, on its own accord, produce reactive oxygen species.

Lipid peroxide formation in relation to membrane stability of fresh and frozen thawed stallion spermatozoa

In this study we used a new method to detect reactive oxygen species (ROS) induced damage at the level of the sperm plasma membrane in fresh and frozen-thawed stallion sperm. Lipid peroxidation (LPO) in sperm cells was assessed by a fluorescent assay involving the labeling of stallion sperm with the LPO reporter probe C11-BODIPY(581/591). The peroxidation dependent spectral emission shift of this membrane probe could be localized using inverted spectral confocal microscopy and quantified on living and deteriorated sperm cells using flow cytometry. Mass spectrometric analysis of the main endogenous lipid class, phosphatidylcholine (PC), was carried out to determine the formation of hydroxy- and hydroperoxyphosphatidylcholine in fresh sperm cells. Peroxidation as reported by the fluorescent probe corresponded with the presence of hydroxy- and hydroperoxyphosphatidylcholine in the sperm membranes, which are early stage products of LPO. This allowed us to correlate endogenous LPO with localization of this process in the living sperm cells. In absence of peroxidation inducers, only relatively little peroxidation was noted in fresh sperm cells whereas some mid-piece specific probe oxidation was noted for frozen-thawed sperm cells. After induction of peroxidation in fresh and frozen-thawed sperm cells with the 0.1 mM of lipid soluble ROS tert-butylhydrogen peroxide (t-BUT) intense probe oxidation was produced in the mid-piece, whereas the probe remained intact in the sperm head, demonstrating antioxidant activity in the head of fresh sperm cells. At higher levels of t-BUT, probe peroxidation was also noted for the sperm head followed by a loss of membranes there. Frozen-thawed sperm were more vulnerable to t-BUT than fresh sperm. The potential importance of the new assays for sperm assessments is discussed.

Identification of cytochrome P450-reductase as the enzyme responsible for NADPH-dependent lucigenin and tetrazolium salt reduction in rat epididymal sperm preparations

Lucigenin-dependent chemiluminescence and WST-1 reduction can be detected following addition of NADPH to many cell types, including rat epididymal sperm suspensions. Although many reports suggest that such a phenomenon is due to reactive oxygen species production, other probes-such as MCLA and luminol-that are capable of detecting reactive oxygen metabolites do not produce a chemiluminescent signal in this model system. Our aim was to purify and identify the enzyme catalyzing the NADPH-dependent lucigenin and WST-1 reduction from rat epididymal spermatozoa preparations. Here, we show the identity of this enzyme as cytochrome P450-reductase. In support of this, a homogenous preparation of this protein was capable of reducing lucigenin and WST-1 in the presence of NADPH. Moreover, COS-7 cells overexpressing cytochrome P450-reductase displayed a 3-fold increase in the aforementioned activity compared with mock-transfected cells. Immunolocalization studies and biochemical analysis suggest that the majority of the NADPH-lucigenin activity is localized to the epithelial cells present within the epididymis. These results emphasize the importance of the direct NADPH-dependent reduction of superoxide-sensitive probes by cytochrome P450-reductase even though this enzyme does not, on its own accord, produce reactive oxygen species.

Cyclic AMP-dependent tyrosine phosphorylation in tammar wallaby (Macropus eugenii) spermatozoa

Despite considerable advances in our understanding of the molecular mechanisms regulating eutherian sperm function, there is a paucity of such knowledge for the Metatheria. In eutherian spermatozoa, the attainment of functional competence is associated with a redox-regulated, cAMP-mediated tyrosine phosphorylation cascade, activated during capacitation. In this report we investigate whether tammar wallaby (Macropus eugenii) spermatozoa possess a similar signal transduction pathway. Western blot analysis of phosphotyrosine expression in caudal and ejaculated populations of tammar spermatozoa revealed that elevation of intracellular cAMP levels, but not exposure to oxidants or NADPH, induced a dramatic increase in the overall level of tyrosine phosphorylation. Washed, ejaculated spermatozoa exhibited more pronounced increases in tyrosine phosphorylation than unwashed sperm populations. Localisation of tyrosine phosphorylation by immunocytochemistry showed that phosphotyrosine residues were principally located along the tammar sperm flagellum, and occasionally at a small region of the sperm head, adjacent to the acrosome. Associated with the tyrosine phosphorylation of tammar spermatozoa, was a change in sperm head conformation to a T-shaped orientation, further implying the importance of these pathways to normal tammar sperm function. Redox activity, as detected by lucigenin-dependent chemiluminescence, was stimulated by NADPH in caudal sperm preparations but not ejaculated spermatozoa. However, neither sperm population responded to treatment with NADPH with changes in intracellular cAMP or tyrosine phosphorylation. In conclusion, tammar spermatozoa possess the same cAMP-mediated, tyrosine phosphorylation-dependent signal transduction cascade that has been associated with capacitation in eutherian spermatozoa. However in Metatherian spermatozoa we could find no evidence that this pathway was redox regulated.

Reactive oxygen species promote tyrosine phosphorylation and capacitation in equine spermatozoa

The objective of this study was to examine the influence of reactive oxygen species (ROS) on equine sperm capacitation. Motile equine spermatozoa were separated on a discontinuous Percoll gradient, resuspended at 10 x 10(6)ml in Tyrode's medium supplemented with BSA (0.5%) and polyvinyl alcohol (0.5%) and incubated at 39 degrees C for 2h with or without the xanthine (X; 0.1mM)-xanthine oxidase (XO; 0.01 U/ml) system or NADPH (0.25 mM). The importance of hydrogen peroxide or superoxide for capacitation was determined by the addition of catalase (CAT; 150 U/ml) or superoxide dismutase (SOD; 150 U/ml), respectively. Following incubation, acrosomal exocytosis was induced by a 5 min incubation at 39 degrees C with progesterone (3.18 microM), and sperm viability and acrosomal integrity were then determined by staining with Hoechst 33258 and fluoroisothiocyanate-conjugated Pisum sativum agglutin. To examine tyrosine phosphorylation, treatments were subjected to sodium dodecyl sulfate-polyacrylaminde gel electrophoresis (SDS-PAGE) followed by Western blot analysis with the anti-phosphotyrosine antibody (alpha-PY; clone 4G10). Capacitation with the X-XO system or NADPH led to a significant (P<0.0001) increase in live acrosome-reacted spermatozoa compared to controls. The addition of CAT or SOD prevented the increase in live acrosome-reacted spermatozoa associated with X-XO treatment. Incubation with the X-XO system was also associated with a significant (P<0.005) increase in tyrosine phosphorylation when compared to controls, which could be prevented by the addition of CAT but not SOD. This study indicates that ROS can promote equine sperm capacitation and tyrosine phosphorylation, suggesting a physiological role for ROS generation by equine spermatozoa.

Superoxide dismutase content and fatty acid composition in subsets of human spermatozoa from normozoospermic, asthenozoospermic, and polyzoospermic semen samples

Human ejaculated sperm comprised discrete subsets of spermatozoa, with different degrees of maturation. These subpopulations can be isolated through density gradient centrifugation. Sperm from the lowest density layer show the highest content of docosahexaenoic acid and sterols, and produce the highest levels of reactive oxygen species. The main objective of this study was to determine the superoxide dismutase (SOD) content and fatty acid composition of subsets of spermatozoa isolated from normozoospermic, asthenozoospermic, and polyzoospermic semen samples. Four sperm fractions (1-4) were obtained using ISolate gradient centrifugation. Morphology, motion parameters, SOD content, and fatty acid composition were assessed in the original samples and their fractions. Overall, sperm from normozoospermic samples had higher SOD content than those of asthenozoospermic or polyzoospermic samples. Once fractionated in subsets, the sperm SOD content decreased significantly (P < 0.0001) from fraction 1 (top) to 4 (bottom) in all three groups of samples. Fatty acid content as well as the oxidation coefficient followed the same pattern, decreasing from fraction 1 to 4 (F1-F4). Normo- and polyzoospermic samples showed similar amounts of fatty acids, while asthenozoospermic samples mostly revealed increased levels. Normozoospermic samples displayed the lowest unsaturated fatty acid (UFA)/SOD ratio. Spermatozoa from astheno- and polyzoospermic samples, two common seminal pathologies, showed higher UFA and lower SOD content than normal sperm, therefore exhibiting a higher susceptibility to peroxidative damage. F4 from all groups, containing the most mature spermatozoa, displayed the lowest polyunsaturated fatty acid and SOD content of all subsets, suggesting that excessive SOD activity as well as abundant peroxidative targets may both be deleterious to sperm function.

Reactive oxygen species and cryopreservation promote DNA fragmentation in equine spermatozoa

The objective of this study was to examine the effect of reactive oxygen species (ROS) and cryopreservation on DNA fragmentation of equine spermatozoa. In experiment 1, equine spermatozoa were incubated (1 hour, 38 degrees C) according to the following treatments: 1) sperm alone; 2) sperm + xanthine (X, 0.3 mM)-xanthine oxidase (XO, 0.025 U/mL); 3) sperm + X (0.6 mM)-XO (0.05 U/mL); and 4) sperm + X (1 mM)-XO (0.1 U/mL). In experiment 2, spermatozoa were incubated (1 hour, 38 degrees C) with X (1 mM)-XO (0.1 U/mL) and either catalase (200 U/mL), superoxide dismutase (SOD, 200 U/mL), or reduced glutathione (GSH, 10 mM). Following incubation, DNA fragmentation was determined by the single cell gel electrophoresis (comet) assay. In experiment 3, equine spermatozoa were cryopreserved, and DNA fragmentation was determined in fresh, processed, and postthaw sperm samples. In experiment 1, incubation of equine spermatozoa in the presence of ROS, generated by the X-XO system, increased DNA fragmentation (P <.005). In Experiment 2, the increase in DNA fragmentation associated with X-XO treatment was counteracted by the addition of catalase and GSH but not by SOD, suggesting that hydrogen peroxide and not superoxide appears to be the ROS responsible for such damage. In experiment 3, cryopreservation of equine spermatozoa was associated with an increase (P <.01) in DNA fragmentation when compared with fresh or processed samples. This study indicates that ROS and cryopreservation promote DNA fragmentation in equine spermatozoa; the involvement of ROS in cryopreservation-induced DNA damage remains to be determined.

Participation of superoxide anion in the capacitation of cryopreserved bovine sperm

Mammalian spermatozoa must undergo a preparation period known as capacitation to become capable of fertilizing oocytes. Controlled amounts of reactive oxygen species (ROS), such as superoxide anion (O2.-) and hydrogen peroxide (H2O2) have been shown essential for capacitation and acrosome reaction. The presence of an oxidase in the sperm plasma membrane has been suggested. The objective of the present study was to provide evidence for the production of O2.- by capacitating cryopreserved bovine spermatozoa. Percentages of capacitation and acrosome reaction were determined by the chlortetracycline assay. The effect of several nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors on capacitation was also studied. H2O2 production was determined by the fluorometric assay using the p-hydroxyphenylacetic acid-horseradish peroxidase system. Superoxide dismutase (SOD) activity was determined spectrophotometrically at 480 nm. Heparin-dependent capacitation was inhibited by all NADPH oxidase inhibitors tested (p < 0.05). Significant levels of H2O2 were produced during capacitation with heparin; such production was inhibited by diphenyleneiodonium, one of the NADPH oxidase inhibitors. The addition of catalase to the incubation medium failed to modify the capacitation rate; inhibition was only observed when SOD was present (p < 0.05). Endogenous SOD activity was diminished during heparin-dependent capacitation (p < 0.05). Similar levels of acrosome reaction induced by lysophosphatidylcholine were obtained in both heparin and O2.--dependent capacitation. Overall results suggest the participation of a sperm oxidase in bovine sperm capacitation. H2O2, generated by O2.- dismutation, failed to participate in capacitation, although this ROS may have been able to decrease endogenous SOD activity. Exogenous O2.- promotes physiological capacitation in cryopreserved bovine sperm, thus allowing the acquisition of fertilizing capacity.