Multiparameter Flow Cytometry Assay for Analysis of Nitrosative Stress Status in Human Spermatozoa

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.

The characterization of CellROX™ probes could be a crucial factor in ram sperm quality assessment

Several authors have demonstrated that low levels of reactive oxygen species (ROS) are necessary for the physiological functions of sperm, such as capacitation, hyperactivation, acrosomal reaction and fertilization. However, high levels of ROS are associated with oxidative stress and detrimental effects on fertility. Consequently, deep characterization of ROS presence using different fluorescent probes could be crucial. In this sense, the study of intracellular ROS localization and the relationships between ROS and other conventional parameters could improve the characterization of sperm quality for semen preservation protocols in rams. In this work, a multiparametric study was carried out by analyzing four experimental groups of ram sperm with different initial qualities: fresh semen (from both breeding and nonbreeding seasons), frozen-thawed semen and, a positive control group treated with hydrogen peroxide (300 μM) as a marker of extreme damage. Sperm analyses, including viability, apoptosis, lipid peroxidation, motility and kinetic parameters, were applied to compare several experimental groups with different sperm qualities. After that, the signals from two different ROS probes: CellROX™ Deep Red (CRDR) and Green (CRG), were examined by flow cytometry (percentage of cells that express ROS) and fluorescence microscopy (intracellular ROS location). Comparing conventional parameters, fresh samples from the breeding season showed the highest sperm quality, while the positive control samples showed the worst sperm quality. Concerning the ROS probes, the CRDR levels were higher in fresh samples from the breeding season than in the positive control and cryopreserved samples. Surprisingly, CRG presented its highest level (P < 0.05) in the positive control group treated with peroxide by flow cytometry. CRDR and CRG presented opposite labeling patterns that were corroborated by fluorescence microscopy, which determined that the probes localized in different parts of sperm. CRDR was found in the sperm mitochondrial region, while CRG was observed in the cell nucleus, suggesting that ROS localization is an important factor. Finally, our study indicates that CRDR is correlated with proper viability and sperm motility, and could be associated with high mitochondrial activity, while CRG is associated with sperm damage.

FeTPPS, a Peroxynitrite Decomposition Catalyst, Ameliorates Nitrosative Stress in Human Spermatozoa

Excessive levels of reactive nitrogen species (RNS), such as peroxynitrite, promote nitrosative stress, which is an important cause of impaired sperm function. The metalloporphyrin FeTPPS is highly effective in catalyzing the decomposition of peroxynitrite, reducing its toxic effects in vivo and in vitro. FeTPPS has significant therapeutic potential in peroxynitrite-related diseases; however, its effects on human spermatozoa under nitrosative stress have not been described. This work aimed to evaluate the in vitro effect of FeTPPS against peroxynitrite-mediated nitrosative stress in human spermatozoa. For this purpose, spermatozoa from normozoospermic donors were exposed to 3-morpholinosydnonimine, a molecule that generates peroxynitrite. First, the FeTPPS-mediated peroxynitrite decomposition catalysis was analyzed. Then, its individual effect on sperm quality parameters was evaluated. Finally, the effect of FeTPPS on ATP levels, motility, mitochondrial membrane potential, thiol oxidation, viability, and DNA fragmentation was analyzed in spermatozoa under nitrosative stress conditions. The results showed that FeTPPS effectively catalyzes the decomposition of peroxynitrite without affecting sperm viability at concentrations up to 50 μmol/L. Furthermore, FeTPPS mitigates the deleterious effects of nitrosative stress on all sperm parameters analyzed. These results highlight the therapeutic potential of FeTPPS in reducing the negative impact of nitrosative stress in semen samples with high RNS levels.

Animal board invited review: An update on the methods for semen quality evaluation in swine - from farm to the lab

Pig breeding is mainly conducted through artificial insemination with liquid-stored semen. It is, therefore, crucial to ensure that sperm quality is over the standard thresholds, as reduced sperm motility, morphology or plasma membrane integrity are associated with reduced farrowing rates and litter sizes. This work aims to summarise the methods utilised in farms and research laboratories to evaluate sperm quality in pigs. The conventional spermiogram consists in the assessment of sperm concentration, motility and morphology, which are the most estimated variables in farms. Yet, while the determination of these sperm parameters is enough for farms to prepare seminal doses, other tests, usually carried out in specialised laboratories, may be required when boar studs exhibit a decreased reproductive performance. These methods include the evaluation of functional sperm parameters, such as plasma membrane integrity and fluidity, intracellular levels of calcium and reactive oxygen species, mitochondrial activity, and acrosome integrity, using fluorescent probes and flow cytometry. Furthermore, sperm chromatin condensation and DNA integrity, despite not being routinely assessed, may also help determine the causes of reduced fertilising capacity. Sperm DNA integrity can be evaluated through direct (Comet, transferase deoxynucleotide nick end labelling (TUNEL) and its in situ nick variant) or indirect tests (Sperm Chromatin Structure Assay, Sperm Chromatin Dispersion Test), whereas chromatin condensation can be determined with Chromomycin A3. Considering the high degree of chromatin packaging in pig sperm, which only have protamine 1, growing evidence suggests that complete decondensation of that chromatin is needed before DNA fragmentation through TUNEL or Comet can be examined.

Phospholipase C-zeta levels are not correlated with fertilisation rates in infertile couples

In mammals, 'oocyte activation' is triggered by certain proteins, one of which is phospholipase C-zeta. Recent evidence suggests that low expression of phospholipase C-zeta might be associated with male infertility, while a limited number of studies claimed the opposite. This study was designed to test whether quantity of phospholipase C-zeta and in vitro fertilisation rates are correlated or not, assessed by flow cytometry. Semen samples from 43 infertile couples were analysed for the percentage and mean fluorescent intensity (MFI) of phospholipase C-zeta protein. Results were confirmed by immunofluorescent labelling. Patients with a fertilisation rate of 40% or lower were involved in the low fertilisation group, while the high fertilization group consisted of patients with a fertilisation rate of 60% and higher. Quantitative analyses by flow cytometry showed no significant difference among the low fertilisation and high fertilisation groups when phospholipase C-zeta ratio or MFI was considered. No correlation was found between pregnancy rates and phospholipase C-zeta quantity. None of the total fertilisation failure cases were lack of phospholipase C-zeta. In fact, fertilisation was possible even when phospholipase C-zeta levels were very low. Thus, we concluded that phospholipase C-zeta quantity cannot be considered as a diagnostic tool for male infertility.

Oxidative and nitrosative stress in frozen-thawed pig spermatozoa. I: Protective effect of melatonin and butylhydroxytoluene on sperm function

The addition of antioxidants to the cryopreservation medium has been shown to exert a positive effect on the quality of frozen-thawed sperm in different species. The objective of the present study was to evaluate the effects of supplementing the freezing medium with butylhydroxytoluene (BHT) and melatonin (MEL) in frozen-thawed pig spermatozoa. With this purpose, six ejaculates coming from six separate boars were cryopreserved in traditional freezing medium (i.e. lactose/egg-yolk/glycerol; Control) supplemented with 1.0 mM BHT (BHT-1), 2.0 mM BHT (BHT-2), 0.01 μM MEL (MEL-1) and 1.0 μM MEL (MEL-2). We evaluated sperm viability, membrane lipid disorder, acrosome integrity, mitochondrial membrane potential, lipid peroxidation, oxidation of thiol groups, and levels of total reactive oxygen species (ROS), peroxynitrite and superoxide anion (·O₂^-). We also analysed total (TM) and progressive sperm motilities (PM), and kinetic parameters at post-thaw (T0, T30 and T60). The BHT-2 and MEL-2 groups presented higher viability and acrosome integrity, and lower levels of peroxynitrite, ·O₂^- and lipid peroxidation than the control (P < 0.05), whereas MEL-2 diminished the levels of total ROS (P < 0.05). TM and PM were not affected by the treatment, while, LIN and STR shows differences between experimental groups. In conclusion, the addition of BHT and MEL to cryopreservation medium diminishes oxidative and nitrosative stress markers, which has repercussions for the integrity of plasma and acrosomal membranes of frozen-thawed spermatozoa.

Oxidative and nitrosative stress in frozen-thawed pig spermatozoa. II: Effect of the addition of saccharides to freezing medium on sperm function

Saccharides have bioprotective properties, with a high capacity to preserve biological proteins and membranes during sperm cryopreservation. The aim of this study was to evaluate how replacing the lactose of cryopreservation media by sucrose (SUC) or trehalose (TRE) at concentrations of 0.2 M (SUC-1 and TRE-1) and 0.25 M (SUC-2 and TRE-2) affects frozen/thawed pig spermatozoa. The media used were composed of medium A (saccharide/egg yolk) and B (saccharide/egg yolk/glycerol), their osmolality being determined prior to freezing. Cell viability, membrane lipid disorder, acrosome integrity, mitochondrial membrane potential (MMP), lipid peroxidation, thiol group oxidation, total reactive oxygen species (ROS), peroxynitrite and superoxide anion (O₂^●-) were determined through flow cytometry; total motility (TM), progressive motility (PM) and kinetic parameters motility were determined immediately after thawing (T0) and again 30 (T30) and 60 (T60) minutes later. The SUC-2 and TRE-2 groups maintained viability significantly and presented fewer lipid membrane disorders, respectively, both with a significant increase in MMP. The production of O₂^●- and peroxynitrite was lower in the TRE-2 groups compared to the control (P < 0.05). Total motility at T0 was greater in the TRE-2 group (P < 0.05). Sperm kinetics was not affected by the treatment. The use of saccharides SUC and TRE at a concentration of 0.25 M improves sperm quality, so that both non-penetrating cryoprotectants can be utilized in pig sperm freezing media.