Lipopolysaccharide Compromises Human Sperm Function by Reducing Intracellular cAMP

In Vitro Effects of Lipopolysaccharide on Rabbit Sperm: Toll-like Receptor 4 Expression, Motility, and Oxidative Status

Lipopolysaccharide (LPS)-induced inflammation impairs sperm function; however, its impact on ejaculated rabbit sperm remains unexplored. This dose-response study aims to determine the LPS concentration that negatively affects sperm motility in vitro, while also providing the first identification of TLR4 localization on rabbit spermatozoa. Additionally, it evaluates malondialdehyde (MDA) levels in seminal plasma as an indicator of oxidative stress. Sperm motility was analyzed using computer-assisted sperm analysis (CASA) after incubation with increasing LPS concentrations (0, 50, 100, 200, 400, 600, and 800 µg/mL) at multiple time points (0, 1, 2, and 4 h). LPS doses ≥ 400 µg/mL significantly reduced progressive and non-progressive motility, as well as curvilinear velocity (all p < 0.001), while increasing the proportion of static spermatozoa (p < 0.05). Receiver operating characteristic (ROC) analysis identified 300 µg/mL as the threshold dose for motility decline. Immunofluorescence revealed TLR4 localization in the midpiece of sperm tails, with weak labeling in control samples and a marked increase after 4 h of incubation with 400 μg/mL LPS. MDA levels were assessed using the thiobarbituric acid reactive substances (TBARS) assay with a colorimetric kit, showing no significant effect of LPS treatment. No correlation was found between MDA and other semen parameters. ccThese findings identify TLR4 on rabbit sperm for the first time and establish a threshold LPS dose for future in vitro studies.

Bacterial Vaginosis Toxins Impair Sperm Capacitation and Fertilization

Study question

What effect do toxins produced by bacterial vaginosis (BV) bacteria have on sperm function?

Summary answer

Bacterial vaginosis toxins dysregulate sperm capacitation and intracellular calcium homeostasis and impair the ability of sperm to fertilize oocytes.

What is known already

In bacterial vaginosis, which is linked to infertility, overgrowth of Prevotella and Gardnerella in the vagina is accompanied by elevated concentrations of the toxins lipopolysaccharide (LPS) and vaginolysin (VLY).

Study design size duration

This was a laboratory study in which human semen samples were collected from consenting healthy donors with normal semen parameters. Mouse sperm samples were obtained from the caudal epididymis.

Participants/materials setting methods

Motile mouse and human sperm were isolated via swim-up and treated under non-capacitating or capacitating conditions. LPS from Escherichia coli was commercially available. VLY was produced by cloning the Gardnerella VLY protein in the ClearColi expression system. Mouse sperm were pre-incubated in in vitro fertilization medium with LPS or VLY and then co-cultured with ovulated cumulus-oocyte complexes. The effects of LPS and VLY on sperm motility and hyperactivation were assessed with computer-assisted sperm analysis. Effects on viability were assessed by Hoechst staining. Acrosomal exocytosis was assessed in sperm from transgenic Acr-eGFP mice and in human sperm stained with Pisum sativum agglutinin FITC. Intracellular calcium dynamics were assessed by staining sperm with the calcium-sensitive dye Fluo-4 AM and fluorescent imaging several sperm at the single-cell level. The effects of LPS on sperm from CatSper knock-out mice were assessed. Additionally, sperm were treated with a toll-like receptor 4 antagonist and further exposed to LPS.

Main results and the role of chance

Exposure of mouse sperm to LPS or VLY significantly decreased in vitro fertilization ( P < 0.05). Under capacitating conditions, both toxins initially increased mouse and human sperm hyperactivation, then significantly decreased sperm motility ( P < 0.05), hyperactivation ( P < 0.05), and acrosomal exocytosis ( P < 0.01). These changes were accompanied by a rapid and irreversible increase in intracellular calcium concentration. Effects of LPS, but not VLY, were prevented by polymyxin-B, which aggregates LPS. The LPS-induced intracellular calcium increase required external calcium but not the calcium channel CatSper and was inhibited by the Toll-like receptor 4 antagonist.

Limitations reasons for caution

First, the commercially available LPS we used was isolated from Escherichia coli , rather than from the BV-associated bacteria Prevotella bivia . Second, we did not quantify the absolute sperm intracellular calcium concentration before or after LPS or VLY treatment. Third, all of our experiments were in vitro .

Wider implications of the findings

These studies suggest that BV-associated toxins contribute to infertility by, in part, impairing sperm capacitation and reducing their fertilizing ability.

Study funding/competing interests

This work was supported by the National Institutes of Health (grant #R01 HD069631). The authors declare that they have no conflict of interest.

Gallic acid mitigates lipopolysaccharide-induced testicular inflammation via regulation of the NF-κB and PK2/PKR1 pathway

Genital tract infections are common causes of male infertility, and most of diagnosed men are asymptomatic. This study examined the effect of gallic acid (GA) against lipopolysaccharide (LPS)-induced testicular inflammation. Thirty-two Spraque Dawley, 2.5-3 month-old male rats were separated into four groups (n = 8). Control group; saline at 3 ml/kg, and in the GA group; GA was dissolved in saline, by gavage at 100 mg/kg for 14 days. LPS group; LPS 5 mg/kg as a single dose was given intraperitoneal on the 11th day. LPS + GA group; GA was given for 14 days and LPS 5 mg/kg on the 11th day. After 72 h of LPS injection, all samples were collected. Semen analysis, biochemical assays, histological evaluations, and immunohistochemical or Western blot analyses for nuclear factor-kappa B (NF-κB) and Prokineticin 2/prokineticin receptor 1(PK2/PKR1) pathways were performed. There was a significant decrease in body and testicular weight, sperm parameters, serum testosterone level, mean seminiferous tubule diameter, germinal epithelial thickness, and Johnsen score in the LPS group compared to control and GA groups. However, a significant increase was found in interstitial space width, percentage of abnormal sperm, NF-κB and PK2 immunoreactivities, and expression of PK2 and PKR1 proteins. In the LPS + GA group, GA administration was observed to significantly prevent these adverse effects. In conclusion, the inhibitory effects of GA on the NF-κB and PK2/PKR1 pathways not only suppressed the inflammatory response but also restored impaired sperm parameters and testicular structure. These findings indicate GA's potential for treating testicular inflammation and protecting male reproductive health.

Antimicrobial peptides and proteins as alternative antibiotics for porcine semen preservation

BACKGROUND

Antimicrobial resistance (AMR) is nowadays a major emerging challenge for public health worldwide. The over- and misuse of antibiotics, including those for cell culture, are promoting AMR while also encouraging the research and employment of alternative drugs. The addition of antibiotics to the cell media is strongly recommended in sperm preservation, being gentamicin the most used for boar semen. Because of its continued use, several bacterial strains present in boar semen have developed resistance to this antibiotic. Antimicrobial peptides and proteins (AMPPs) are promising candidates as alternative antibiotics because their mechanism of action is less likely to promote AMR. In the present study, we tested two AMPPs (lysozyme and nisin; 50 and 500 µg/mL) as possible substitutes of gentamicin for boar semen preservation up to 48 h of storage.

RESULTS

We found that both AMPPs improved sperm plasma membrane and acrosome integrity during semen storage. The highest concentration tested for lysozyme also kept the remaining sperm parameters unaltered, at 48 h of semen storage, and reduced the bacterial load at comparable levels of the samples supplemented with gentamicin (p > 0.05). On the other hand, while nisin (500 µg/mL) reduced the total Enterobacteriaceae counts, it also decreased the rapid and progressive sperm population and the seminal oxidation-reduction potential (p < 0.05).

CONCLUSIONS

The protective effect of lysozyme on sperm function together with its antimicrobial activity and inborn presence in body fluids, including semen and cervical mucus, makes this enzyme a promising antimicrobial agent for boar semen preservation.

Inactivation of Mst/Nrf2/Keap1 signaling flexibly mitigates MAPK/NQO-HO1 activation in the reproductive axis of experimental fluorosis

Fluoride induced reprotoxicity through oxidative stress-mediated reproductive cell death. Hence, the current study evaluated the importance of the MST/Nrf2/MAPK/NQO-HO1 signaling pathway in fluorosis-induced reproductive toxicity. For this purpose, the reproductive toxicity of sodium fluoride (NaF) at physiological, biochemical, and intracellular levels was evaluated. In-vivo, NaF at 100 mg/L instigated physiological dysfunction, morphological, stereological, and structural injuries in the gut-gonadal axis of fluorosis mice through weakening the antioxidant signaling, Nrf2/HO-1/NQO1signaling pathway, causing the gut-gonadal barrier disintegrated via oxidative stress-induced inflammation, mitochondrial damage, apoptosis, and autophagy. Similar trends were also observed in-vitro in the isolated Leydig cells (LCs) challenging with 20 mg/L NaF. Henceforth, activating the cellular antioxidant signaling pathway, Nrf2/HO-1/NQO1, inactivating autophagy and apoptosis, or attenuating lipopolysaccharide (LPS) can be the theoretical basis and valuable therapeutic targets for coping with NaF-induced reproductive toxicity.

Paternal immune activation by Poly I:C modulates sperm noncoding RNA profiles and causes transgenerational changes in offspring behavior

Paternal pre-conceptual environmental experiences, such as stress and diet, can affect offspring brain and behavioral phenotypes via epigenetic modifications in sperm. Furthermore, maternal immune activation due to infection during gestation can reprogram offspring behavior and brain functioning in adulthood. However, the effects of paternal pre-conceptual exposure to immune activation on the behavior and physiology of offspring (F1) and grand-offspring (F2) are not currently known. We explored effects of paternal pre-conceptual exposure to viral-like immune activation on F1 and F2 behavioral and physiological phenotypes using a C57BL/6J mouse model. Males were treated with a single injection (intraperitoneal) of the viral mimetic polyinosinic:polycytidylic acid (Poly I:C: 12 mg/kg) then bred with naïve female mice four weeks after the Poly I:C (or 0.9% saline control) injection. The F1 offspring of Poly I:C treated fathers displayed increased depression-like behavior in the Porsolt swim test, an altered stress response in the novelty-suppressed feeding test, and significant transcriptomic changes in their hippocampus. Additionally, the F1 male offspring of Poly I:C treated F0 males showed significantly increased immune responsivity after a Poly I:C immune challenge (12 mg/kg). Furthermore, the F2 male grand-offspring took longer to enter and travelled significantly shorter distances in the light zone of the light/dark box. An analysis of the small noncoding RNA profiles in sperm from Poly I:C treated males and their male offspring revealed significant effects of Poly I:C on the sperm microRNA content at the time of conception and on the sperm PIWI-interacting RNA content of the male offspring. Notably, eight miRNAs with an FDR < 0.05 (miR-141-3p, miR-126b-5p, miR-669o-5p, miR-10b-3p, miR-471-5p, miR-463-5p, miR-148b-3p, and miR-181c-5p) were found to be significantly downregulated in the sperm of Poly I:C treated males. Collectively, we demonstrate that paternal pre-conceptual exposure to a viral immune challenge results in both intergenerational and transgenerational effects on brain and behavior that may be mediated by alterations in the sperm small noncoding RNA content.

Human Male Genital Tract Microbiota

The human body is vastly colonised by microorganisms, whose impact on health is increasingly recognised. The human genital tract hosts a diverse microbiota, and an increasing number of studies on the male genital tract microbiota suggest that bacteria have a role in male infertility and pathological conditions, such as prostate cancer. Nevertheless, this research field remains understudied. The study of bacterial colonisation of the male genital tract is highly impacted by the invasive nature of sampling and the low abundance of the microbiota. Therefore, most studies relied on the analysis of semen microbiota to describe the colonisation of the male genital tract (MGT), which was thought to be sterile. The aim of this narrative review is to present the results of studies that used next-generation sequencing (NGS) to profile the bacterial colonisation patterns of different male genital tract anatomical compartments and critically highlight their findings and their weaknesses. Moreover, we identified potential research axes that may be crucial for our understanding of the male genital tract microbiota and its impact on male infertility and pathophysiology.

Bacteriospermia - A formidable player in male subfertility

Bacterial colonization of male reproductive tissues, cells, and fluids, and the subsequent impact of bacteria on the sperm architecture, activity, and fertilizing potential, has recently gained increased attention from the medical and scientific community. Current evidence strongly emphasizes the fact that the presence of bacteria in semen may have dire consequences on the resulting male fertility. Nevertheless, the molecular basis underlying bacteriospermia-associated suboptimal semen quality is sophisticated, multifactorial, and still needs further understanding. Bacterial adhesion and subsequent sperm agglutination and immobilization represent the most direct pathway of sperm-bacterial interactions. Furthermore, the release of bacterial toxins and leukocytic infiltration, associated with a massive outburst of reactive oxygen species, have been repeatedly associated with sperm dysfunction in bacteria-infested semen. This review serves as a summary of the present knowledge on bacteriospermia-associated male subfertility. Furthermore, we strived to outline the currently available methods for assessing bacterial profiles in semen and to outline the most promising strategies for the prevention and/or management of bacteriospermia in practice.

Seminal and histopathological alterations in bucks challenged with Mannheimia haemolytica serotype a2 and its LPS endotoxin

Pneumonic mannheimiosis is a widespread respiratory bacterial disease of small ruminants caused by Mannheimia haemolytica serotype A2. The disease is known to affect the respiratory organs of infected animals, but its effect on other vital and reproductive organs has not been fully explored. Previous studies have demonstrated increased serum pro-inflammatory cytokine concentration post-challenge with M. haemolytica A2 and its LPS, indicating systemic inflammation in the host. This study determined the potential tissue changes and alterations of sperm parameters due to infection of M. haemolytica A2 and its LPS endotoxin. In this study, twelve experimental bucks were randomly assigned to three groups of four bucks each: group 1 (control group) were intranasally inoculated with 2 mL of PBS pH 7.0, group 2 received 2 mL of 1.2 × 10⁹ CFU/mL M. haemolytica A2 intranasally, and group 3 received 2 mL of LPS extracted from 1.2 × 10⁹ CFU/mL of M. haemolytica A2 intravenously. Semen samples were collected at pre-determined intervals using an electro-ejaculator and analysed immediately after collection. All experimental bucks were slaughtered via exsanguination on day 60 to collect their vital and reproductive organs at necropsy, and the samples were processed and analysed for histopathological changes. The current study has revealed that bucks challenged with M. haemolytica A2 and its LPS exhibited alterations in semen parameters such as motility, wave pattern, viability, and morphological abnormalities. Mild to moderate histopathological changes of the lung, liver, testis, epididymis, vas deferens, prostate, and lymph nodes were also observed in both challenged groups. Therefore, this study revealed the potential harmful effects of respiratory mannheimiosis on the reproductive organs of the infected bucks and sheds light on the expanse of systemic effects of this disease.

The Impact of Bacteriocenoses on Sperm Vitality, Immunological and Oxidative Characteristics of Ram Ejaculates: Does the Breed Play a Role?

Bacterial contamination of semen is an often overlooked, yet important, factor contributing to decreased sperm vitality. Understanding the impact of bacterial presence on sperm structural integrity and functional activity may assist the development of effective strategies to prevent, or manage, bacteriospermia in the breeding practice. The aim of this study was to describe the bacterial profiles of ram semen (n = 35), and we also focused on the associations between bacteriospermia, sperm structure, and function, as well as oxidative and inflammatory characteristics of semen. For a better insight, the samples were divided into three groups, according to the breeds used in the study: native Wallachian (NW), improved Wallachian (IW), and Slovak dairy (SD) breeds. The results showed a significantly lower motility and membrane integrity in the NW group in comparison to the IW and SD groups, which was accompanied by a significantly higher concentration of leukocytes, increased reactive oxygen species (ROS) generation, and subsequent oxidative insults to the sperm lipids and proteins. Accordingly, the NW group presented with the highest bacterial load, in which Staphylococcus and Escherichia were the predominant representatives. The Pearson correlation analysis uncovered positive relationships amongst the bacterial load and leukocytospermia (r = 0.613), the extent of lipid peroxidation (r = 0.598), protein oxidation (r = 0.514), and DNA fragmentation (r = 0.638). Furthermore, positive correlations were found between the bacterial load and pro-inflammatory molecules, such as the C-reactive protein (r = 0.592), interleukin 1 (r = 0.709), and interleukin 6 (r = 0.474), indicating a possible involvement of the immune response in the process of bacteriospermia. Overall, our data indicate that ram semen quality may be equally affected by the bacterial load and diversity. Furthermore, we can assume that the presence of bacteria in ejaculates triggers inflammatory processes, causes ROS overproduction, and, thereby, contributes to alterations in the sperm structure, while at the same time compromising the fertilization ability of male gametes.

Salpingitis Impairs Bovine Tubal Function and Sperm-Oviduct Interaction

Salpingitis is a common cause for subfertility and infertility both in humans and animals. However, the effects of salpingitis on tubal function and reproductive success are largely unknown. Therefore we set out to investigate the effects of inflammation on sperm and oocyte transport and gameto-maternal interaction in the oviduct using the bovine as a model. For this purpose, oviducts revealing mild (n = 45), moderate (n = 55) and severe (n = 45) inflammation were obtained from cows immediately after slaughter and investigated by live cell imaging, histochemistry and scanning electron microscopy. Our studies showed that endometritis was always correlated with salpingitis. Moderate and severe inflammation caused a significant increase in the thickness of tubal folds (p < 0.05). Severe inflammation was characterized by luminal accumulations of mucus and glycoproteins, increased apoptosis, loss of tight junctions and shedding of tubal epithelial cells. The mean ciliary beat frequency (CBF) in the ampulla was significantly reduced as compared to the controls (p < 0.05). The higher the grade of inflammation, the lower was the CBF (p < 0.001). In severe inflammation, spermatozoa were stuck in mucus resulting in decreased sperm motility. Our results imply that tubal inflammation impairs proper tubal function and leads to reduced sperm fertilizing capacity.

Effects of lipopolysaccharide-induced inflammation on hypoxia and inflammatory gene expression pathways of the rat testis

Background

Bacterial infection and inflammation of the testis impairs fertility, yet an understanding of inflammatory responses of the testis is incomplete. We are interested in identifying gene pathways involved in the detection and clearance of infectious microbes in the male reproductive tract. In previous studies in our lab focused on hypoxia-responsive genes of the testis, preliminary experiments suggested that genes classically categorized as hypoxia genes are also activated during antimicrobial responses. The purpose of this study was to identify hypoxia and inflammatory gene pathways that contribute to antimicrobial protection of the testis and to consider possible cross-talk and interactions between these pathways. Inflammation was induced in Sprague-Dawley rats using P. aeruginosa or E. coli lipopolysaccharide (LPS). Levels of hypoxia-inducible factor-1 (HIF-1α) protein and nuclear factor kappa B (NF-κB) were measured, and hypoxia and inflammatory gene expression patterns in testis were analyzed by gene expression profiling using real-time quantitative PCR arrays.

Results

In LPS-treated rats, HIF-1α protein increased with no change in Hif-1α mRNA. Western Blot analysis also demonstrated no change in NF-κB and inhibitory NFKB alpha (IκBα) protein levels following LPS treatment. Five hypoxia pathway genes (Angptl4, Egr1, Ier3, Pai1, and Glut1), and 11 inflammatory pathway genes (Ccl12, Cc13, Cd14, Cxcl10, Icam1, Il10, Il1b, Il6, Nfkbia, Tlr2, Tnf) up-regulated after 3 h of inflammation. Angptl4, Ccl12, Cc13, Cd14, Egr1, Nfkbia, Tlr2, and Tnf remained elevated at 6 h. Six genes were up-regulated at 6 h only (Bhlhe40, C3, Jak2, Nlrp3, Slc11a1, Tlr1). One gene (Tlr5) was down-regulated after 3 h and no genes at 6 h. Electrophoretic mobility shift assay results suggest a decrease in NF-κB binding activity following LPS treatment.

Conclusions

Testicular HIF-1α is up-regulated following LPS-induced inflammation. In contrast to other tissues, in which HIF-1α is up-regulated through transcriptional activation via NF-κB, we conclude that HIF-1α in the testis is not up-regulated through an increase in Hif-1α mRNA or through NF-κB-dependent mechanisms. Hypoxia pathway genes and genes involved in Toll-like receptor (TLR) and cytokine-mediated signaling comprise major functional categories of up-regulated genes, demonstrating that both hypoxia and classic inflammatory pathways are involved in inflammatory responses of the testis.

Electronic supplementary material

The online version of this article (10.1186/s12610-018-0079-x) contains supplementary material, which is available to authorized users.

[Bacteriospermia: Effects on semen parameters]

OBJECTIVES

Bacteriospermia may result in male hypofertlity. Indeed, 60% of patients treated by Assisted Reproductive Techniques had a local infection or inflammation of genital tract. However, direct effects of bacteriospermia on semen parameters remain controversial. The aim of our work was to explore the effect of bacteriospermia on sperm parameters among patients consulting for hypofertility.

METHODS

A retrospective comparative study of two groups: a group of 70 patients with bacteriospermia (group 1) and a control group of 70 patients without bacteriospermia (group 2). For these groups, we studied the standard semen parameters (seminal volume and viscosity and spermatozoa count, initial and secondary mobility, vitality and morphology). Comparison of these parameters was made by the Chi² test and the Fisher test.

RESULTS

The mean age of our population was 40.4±6.7 years. There was no significant difference between ejaculate average volume in the 2 groups (group B: 2.78mL versus group A: 2.92mL with P=0.2). Similarly, for the viscosity no difference was noted (P=0,68). The altered parameters in the presence of bacteriospermia were mean concentration and sperm motility (P=0.001 and P=0.049 respectively). The prevalence of secondary asthenospermia was higher in the presence of bacterospermia (P=0.006). No statistically significant differences were observed for morphology and vitality of spermatozoa (P=0.276 and P=0.075 respectively). The leucospermia was associated with bacteriospermia in 10% patients. Ureaplasma urealyticum was the germ most found (45.7%) followed by Streptococcus and Staphylococcacae (20.3% for each), Gram negative rods accounted for 12.9%, while Corynebacterium spp was isolated only in 4,3% patients. U. urealyticum was associated with hypospermia in 33% of cases (P=0.031). Spermatozoa motility was significatively decreased not only in the presence of this bacteria (FT=0.002) but also when cultures were positive for Streptococcus (0.04) and Corynebacterium (P<0.001). Morphological abnormalities were also noticed with Streptococcus with index of teratozoospermia of 46% versus 19% in the 2nd group (P=0.046).

CONCLUSION

Bacteriospermia may impair sperm parameters. The treatment of this affection seems to improve sperm fertilizing potential. In addition, it could prevent contamination of culture media.

Human sperm Toll-like receptor 4 (TLR4) mediates acrosome reaction, oxidative stress markers, and sperm parameters in response to bacterial lipopolysaccharide in infertile men

PURPOSE

To study the role of Toll-like receptor 4 (TLR4) in human spermatozoa and to assess sperm parameters, oxidative stress markers, and acrosome reaction in response to the stimulation of TLR4 by its ligand, the lipopolysaccharide (LPS), as a major endotoxin of Gram-negative bacteria.

METHODS

Our study was carried out in 73 sperm samples from patients undergoing semen analysis for couple infertility investigations. The studied patients were divided into three groups: normozoospermic fertile patients (n = 13), patients with abnormal and leukospermic semen (n = 13), and patients with abnormal and non-leukospermic semen (n = 47). TLR4 expression in human spermatozoa was initially analyzed by western blot. Sperm samples were incubated in the presence of LPS (200 ng/ml) for 18 h. Then, sperm motility and vitality were evaluated by microscopic observation and oxidative stress markers as malondialdehyde (MDA) and carbonyl groups (CG) were spectrophotometrically assessed in neat and selected sperm. A triple-stain technique was also performed to evaluate acrosome reaction in 15 sperm samples from infertile patients.

RESULTS

TLR4 expression was confirmed in human spermatozoa with a molecular weight of 69 kDa. In the normozoospermic group, no significant differences in sperm parameters and oxidative stress markers were shown after incubation with LPS in neat and selected sperms. Regarding samples from the non-leukospermic group, LPS reduced spermatozoa motility and vitality rates in selected sperm (P = 0.003; P = 0.004, respectively). A significant increase of MDA and CG levels was also detected (P = 0.01; P = 0.02, respectively). However, only the MDA levels were significantly increased (P = 0.01) in neat LPS-stimulated sperm. The same results were shown within the leukospermic group. The comparison between the two groups, leukospermic and non-leukospermic, in selected sperms showed a more important LPS effect in the leukospermic group significantly on motility and MDA rates (P = 0.006; P = 0.009, respectively). Furthermore, a significant decrease in reacted spermatozoa rate was detected in response to LPS in selected sperm samples from infertile men (P = 0.03).

CONCLUSIONS

These findings indicate that human spermatozoa express TLR4 and respond to LPS stimulation with alterations in viability, motility, and the acrosome reaction implicating reactive oxygen species (ROS) production in sperm samples from infertile patients.