Concentration-dependent Sildenafil citrate (Viagra) effects on ROS production, energy status, and human sperm function

New Insights on Sperm Function in Male Infertility of Unknown Origin: A Multimodal Approach

The global trend of rising (male) infertility is concerning, and the unidentifiable causes in half of the cases, the so-called unknown origin male infertility (UOMI), demands a better understanding and assessment of both external/internal factors and mechanisms potentially involved. In this work, it was our aim to obtain new insight on UOMI, specifically on idiopathic (ID) and Unexplained male infertility (UMI), relying on a detailed evaluation of the male gamete, including functional, metabolic and proteomic aspects. For this purpose, 1114 semen samples, from males in couples seeking infertility treatment, were collected at the Reproductive Medicine Unit from the Centro Hospitalar e Universitário de Coimbra (CHUC), from July 2018-July 2022. Based on the couples' clinical data, seminal/hormonal analysis, and strict eligibility criteria, samples were categorized in 3 groups, control (CTRL), ID and UMI. Lifestyle factors and anxiety/depression symptoms were assessed via survey. Sperm samples were evaluated functionally, mitochondrially and using proteomics. The results of Assisted Reproduction Techniques were assessed whenever available. According to our results, ID patients presented the worst sperm functional profile, while UMI patients were similar to controls. The proteomic analysis revealed 145 differentially expressed proteins, 8 of which were specifically altered in ID and UMI samples. Acrosin (ACRO) and sperm acrosome membrane-associated protein 4 (SACA4) were downregulated in ID patients while laminin subunit beta-2 (LAMB2), mannose 6-phosphate isomerase (MPI), ATP-dependent 6-phosphofructokinase liver type (PFKAL), STAR domain-containing protein 10 (STA10), serotransferrin (TRFE) and exportin-2 (XPO2) were downregulated in UMI patients. Using random forest analysis, SACA4 and LAMB2 were identified as the sperm proteins with a higher chance of distinguishing ID and UMI patients, and their function and expression variation were in accordance with the functional results. No alterations were observed in terms of lifestyle and psychological factors among the 3 groups. These findings obtained in an experimental setting based on 3 well-defined groups of subjects, might help to validate new biomarkers for unknown origin male infertility (ID and UMI) that, in the future, can be used to improve diagnostics and treatments.

Ameliorative effect of hesperidin against high dose sildenafil-induced liver and testicular oxidative stress and altered gene expression in male rats

BACKGROUND

The clinical use of sildenafil citrate (Viagra), a drug used to treat erectile dysfunction, is limited because of its many side effects on tissues. In this context, we aimed to investigate the protective effects of hesperidin, a citrus flavonoid, on hepatic and testicular damage induced by a high dose of sildenafil citrate in male rats. Rats were randomly divided into four groups. The first group was used as the control group. The second group was orally administered sildenafil citrate at a high dose of 75 mg/kg thrice a week. In the third group, hesperidin was administered orally at a dose of 50 mg/kg/day. The fourth group was administered 75 mg/kg sildenafil citrate three times a week with 50 mg/kg hesperidin daily. The experiment lasted for 28 days.

RESULTS

In the sildenafil-treated groups, blood indices were altered, liver function tests were deranged, and serum testosterone levels were reduced. In the liver and testicular tissue, sildenafil citrate treatment resulted in significant reductions in catalase and total antioxidant capacity; as well as increased malondialdehyde, reactive oxygen species, and nitrous oxide levels. In addition, sildenafil citrate treatment caused abnormal histopathological patterns in both the liver and the testes. Liver vascular endothelial growth factor and testicular steroidogenic acute regulatory protein gene expression were upregulated.

CONCLUSIONS

Hesperidin attenuated the harmful effects of intensive sildenafil citrate treatment on liver and testicular functions, alleviated oxidative stress and normalized blood indices. Therefore, hesperidin could be protective against sildenafil citrate-induced oxidative damage that may develop over the long term.

Sildenafil aggravates adriamycin-induced testicular toxicity in rats; a preliminary investigation

Male reproductive toxicity is a well-established side effect of the chemotherapeutic drug adriamycin (ADR). Sildenafil (SIL) is a phosphodiesterase inhibitor known to enhance the chemosensitivity of cancer cells to ADR. However, there is a scarcity of information on the effect of SIL on ADR-induced testicular toxicity. In this study, SIL (5, 10, or 20 mg/kg/day) was administered to male rats for 7 days, followed by a single intraperitoneal injection of ADR (20 mg/kg) on day 7. Control rats received either ADR, SIL, or normal saline for 7 days. Epididymal sperm were collected from the testes to assess the effects on sperm quality, quantity, and serum testosterone concentration was also determined. ADR treatment caused a decrease in sperm motility and elevated the percentage of sperms with tail defects which worsened in combination with SIL (20 mg/kg). Furthermore, ADR alone or in combination with SIL dose-dependently increased total sperm abnormalities. SIL (20 mg/kg) plus ADR also decreased sperm count and lowered testosterone level compared to ADR-only rats. In conclusion, exposure of rats to SIL before ADR treatment has the potential to worsen ADR-induced testicular toxicity.

Mitochondria-Targeted Compounds to Assess and Improve Human Sperm Function

Significance: Currently 10%-15% of couples in reproductive age face infertility issues. More importantly, male factor contributes to 50% of these cases (either alone or in combination with female causes). Among various reasons, impaired sperm function is the main cause for male infertility. Furthermore, mitochondrial dysfunction and oxidative stress due to increased reactive oxygen species (ROS) production, particularly of mitochondrial origin, are believed to be the main contributors. Recent Advances: Mitochondrial dysfunction, particularly due to increased ROS production, has often been linked to impaired sperm function/quality. For decades, different methods and approaches have been developed to assess mitochondrial features that might correlate with sperm functionality. This connection is now completely accepted, with mitochondrial functionality assessment used more commonly as a readout of sperm functionality. More recently, mitochondria-targeted compounds are on the frontline for both assessment and therapeutic approaches. Critical Issues: In this review, we summarize the current methods for assessing key mitochondrial parameters known to reflect sperm quality as well as therapeutic strategies using mitochondria-targeted antioxidants aiming to improve sperm function in various situations, particularly after sperm cryopreservation. Future Directions: Although more systematic research is needed, mitochondria-targeted compounds definitely represent a promising tool to assess as well as to protect and improve sperm function. Antioxid. Redox Signal. 37, 451-480.

Mitochondrial Functional Assessment in Mammalian Gametes Using Fluorescent Probes

A positive relationship between mitochondrial functionality and gamete quality, ultimately contributing to fertilization success and normal embryo development has been established for some years now. Both mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) production are major indicators of mitochondrial function, and the need for accurate biomarkers mirroring gamete quality highlights the importance of a precise assessment of mitochondrial quality and function. In this chapter, we discuss the use of some mitochondrial fluorescent probes coupled to flow cytometry and/or fluorescence microscopy to specifically assess mitochondrial ROS production and MMP in both sperm and oocytes. Furthermore, as the distribution/aggregation of mitochondria in the oocyte is of interest to determine its quality, a detailed protocol is also given. These methodologies are easy, accurate and can be safely applied in research- and/or clinical-based contexts.

Fluorescent probes for the detection of reactive oxygen species in human spermatozoa

Reactive oxygen species (ROS) production is a by-product of mitochondrial activity and is necessary for the acquisition of the capacitated state, a requirement for functional spermatozoa. However, an increase in oxidative stress, due to an abnormal production of ROS, has been shown to be related to loss of sperm function, highlighting the importance of an accurate detection of sperm ROS, given the specific nature of this cell. In this work, we tested a variety of commercially available fluorescent probes to detect ROS and reactive nitrogen species (RNS) in human sperm, to define their specificity. Using both flow cytometry (FC) and fluorescence microscopy (FM), we confirmed that MitoSOX™ Red and dihydroethidium (DHE) detect superoxide anion (as determined using antimycin A as a positive control), while DAF-2A detects reactive nitrogen species (namely, nitric oxide). For the first time, we also report that RedoxSensor™ Red CC-1, CellROX^® Orange Reagent, and MitoPY1 seem to be mostly sensitive to hydrogen peroxide, but not superoxide. Furthermore, mean fluorescence intensity (and not percentage of labeled cells) is the main parameter that can be reproducibly monitored using this type of methodology.

An acute oral administration of Sildenafil in asthenozoospermic patients improves sperm motility after density gradient centrifugation

Objective:

Investigate the possible effect of an acute sildenafil dose in asthenozoospermic patients.

Methods:

We ran this experimental, descriptive, prospective and non-blinded study in 32 patients diagnosed with asthenozoospermia according to the WHO criteria, after two consecutive semen analyses (samples 1 and 2), and we asked them to provide a new semen sample two weeks after the initial exams (sample 3). One hour prior to the semen collection, we gave the patients 100mg oral sildenafil. Samples 2 and 3 were allowed to liquefy and density gradients centrifugation was performed. We assessed sperm motility by Computer-assisted sperm analysis (CASA).

Results:

There were no significant differences between the samples obtained before (sample2) or after sildenafil administration (sample3). However, a single oral 100 mg sildenafil dose in asthenozoospermic patients increase the percentage of motile sperm recovered after density gradient centrifugation.

Conclusions:

An acute administration of sildenafil enhances sperm recovery after density gradient centrifugation in asthenozoospermic patients, and it may produce more available mobile sperm to perform intra uterine insemination or to improve the chances of success in this procedure. This approach may be used as an alternative strategy in assisted reproductive programs. Sildenafil was well tolerated and no patient was withdrawn from the study due to adverse events attributed to sildenafil.

Comparative effect of administration and discontinuation of sildenafil and/or clomipramine on the hepatic, cardiac and testicular tissues of male rats

In this study, we examined the adverse consequences of prolonged treatment with sildenafil and/or clomipramine (CLO) on the hepatic, cardiac and testicular tissues of rats. Additionally, we investigated the potential effects of treatment discontinuation. To this end, 60 adult male rats were randomly assigned into six groups and were orally treated with 4.5 mg sildenafil /kg BW (SLD) and 9 mg/ kg BW (SHD), 2.25 mg CLO/kg BW (CLO), 4.5 mg sildenafil/kg BW + 2.25 mg CLO/kg BW (SLD-CLO) and 9 mg sildenafil/kg BW + 2.25 mg CLO/kg BW (SHD-CLO) while the control rats received 0.5 ml distilled water for 8 weeks. Then, five rats from each group were sacrificed and the other five rats were left untreated for another four weeks to recover from the drug treatment. Long-term administration of sildenafil and/or CLO led to oxidative stress, inflammation and structural changes in the liver, heart and testis, reduction in sperm count and motility, an increase in abnormalities, and a reduction in serum testosterone, FSH and LH levels. All tested parameters returned to the normal state following the four-week discontinuation of sildenafil. Additionally, all the alterations caused by long-term administration of CLO, SLD-CLO and SHD-CLO were significantly improved during the recovery period.

Phosphodiesterase Inhibitors (PDE Inhibitors) and Male Reproduction

The nonspecific PDE inhibitors, particularly the methylxanthines: caffeine, pentoxifylline (PTX), and theophylline, are known to stimulate sperm motility in vitro and have been used to treat sperm prior to insemination. The in vivo effects are less dramatic. A beneficial effect of caffeine, which is a constituent of some medications, remains controversial. Very high doses of caffeine do have negative effects on fertility endpoints in men and experimental species. The specific PDE5 inhibitors, particularly sildenafil and tadalafil, are prescribed for erectile dysfunction, as well as pulmonary hypertension, lower urinary tract symptoms, and premature ejaculation. PDE5 is expressed throughout the contractile tissues of the male reproductive tract, generally increasing contractility. Some PDE5 inhibitors tend to increase circulating testosterone levels somewhat. For short-term exposure consistent with use prior to intercourse, there appears to be minimal effects on semen quality. Several large, randomized controlled trials (RCTs) in healthy men have not found adverse effects of long-term use of these drugs on semen quality. RCTs in infertile men have demonstrated a modest increase in semen quality. Animal studies at human equivalent doses (HED) have produced similar results in young males, but a study in aging male rats found progressive decreases in epididymal sperm quality accompanied by consistent degeneration of the seminal tubules suggesting that studies in older men might be warranted. A concerning study in mice found lower fertilization rates in males treated with HED of sildenafil and mated the next day to untreated females than for control males. Fertility studies in humans are needed.

High glucose concentrations per se do not adversely affect human sperm function in vitro

Diabetes mellitus (DM) represents one of the greatest concerns to global health and it is associated with diverse clinical complications, including reproductive dysfunction. Given the multifactorial nature of DM, the mechanisms that underlie reproductive dysfunction remain unclear. Considering that hyperglycemia has been described as a major effector of the disease pathophysiology, we used anin vitroapproach to address the isolated effect of high glucose conditions on human sperm function, thus avoiding otherin vivoconfounding players. We performed a complete and integrated analysis by measuring a variety of important indicators of spermatozoa functionality (such as motility, viability, capacitation status, acrosomal integrity, mitochondrial superoxide production and membrane potential) in human sperm samples after incubation withd- andl-glucose (5, 25, or 50 mM) for 24 and 48 h. No direct effects promoted by 25 or 50 mMd-glucose were found for any of the parameters assessed (P>0.05), except for the acrosome reaction, which was potentiated after 48 h of exposure to 50 mMd-glucose (P<0.05). Interestingly, non-metabolizablel-glucose drastically increased superoxide production (P<0.05) and suppressed sperm motility (P<0.05) and capacitation (P<0.05) after 24 h of treatment, whereas mitochondrial membrane potential (P<0.05), acrosomal integrity (P<0.01) and viability (P<0.05) were later decreased. The overall results suggest that high glucose levelsper sedo not influence human sperm functionin vitro, which stresses the importance of other factors involved in DM pathology. Nevertheless, the absence of metabolizable glucose contributes to a severe impairment of sperm function and thus compromises male fertility.

Free Portuguese abstract: A Portuguese translation of this abstract is freely available athttp://www.reproduction-online.org/content/150/1/77/suppl/DC1.

In vitro exposure to the organochlorine p,p'-DDE affects functional human sperm parameters

Although no information exists regarding the levels of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) on reproductive fluids of heavily exposed populations, they are possibly quite high given the serum levels reported so far. In these populations altered semen quality has been reported, although the direct effects of this DDT metabolite on crucial sperm parameters remain largely unexplored. With this in mind, a long-term in vitro incubation that better mimics the putative continuous exposure of spermatozoa to p,p'-DDE in the female reproductive tract in vivo was used. Before compromising sperm viability, continuous p,p'-DDE exposure remarkably decreased sperm motility, possibly due to the combined reduction in the proportion of sperm with high mitochondrial membrane potential and cellular ATP levels, all of which were clearly more affected at 50 and 100 μM p,p'-DDE. Moreover, 25 μM p,p'-DDE was also able to promote a decline in sperm with high MMP, however without significantly affecting motility. On the other hand, p,p'-DDE at the highest concentration strongly inhibited the process of capacitation following 24h of incubation. In conclusion, human sperm function is affected by continuous high p,p'-DDE exposure which may ultimately compromise male fertility. Given our previously findings that showed a non-regulated Ca(2+) entry in the presence of p,p'-DDE, we suggest that this organochlorine may promote mitochondrial Ca(2+) overload which may culminate in a general mitochondrial dysfunction and cellular ATP depletion, thus affecting sperm fertilizing potential. Our findings suggest a broader understanding of the non-genomic mechanism of p,p'-DDE action in human sperm.

Stimulation of human damaged sperm motility with hydrogen molecule

Background

Sperm motility is a critical factor in male fertility. Low motility can be caused by a variety factors including abnormal spermatogenesis, oxidative damage, or depletion of intracellular ATP. Recent findings indicate that hydrogen molecule (H₂) selectively reduces toxic reactive oxygen species. In this study, we investigated the effects of H₂ on human sperm motility in vitro.

Methods

Experimentally damaged sperm suspensions from patients left at room temperature for > 5 days or frozen immediately after ejaculation were used. After exposure with H₂, their forward motility was measured with a counting chamber. A time-lapse movie was recorded to analyze sperm swimming speed. Mitochondria were stained with a membrane potential-sensitive dye.

Results

H₂ treatment significantly improved the rate of forward motility, whereas treatment with nitrogen gas did not. While treatment for 30 min was sufficient to improve motility, it did not affect sperm swimming speed. After 24 h, retreatment with H₂ increased the motility again. H₂ treatment also increased mitochondrial membrane potential. Forward motility of low motile frozen-thawed sperm from patients significantly improved with cleavage medium containing H₂.

Conclusions

Our results illustrated that H₂ treatment stimulates low sperm motility. H₂ is a new promising tool for male infertility treatments.

Clinically relevant enhancement of human sperm motility using compounds with reported phosphodiesterase inhibitor activity

STUDY QUESTION

Can we identify compound(s) with reported phosphodiesterase inhibitor (PDEI) activity that could be added to human spermatozoa in vitro to enhance their motility without compromising other sperm functions?

SUMMARY ANSWER

We have identified several compounds that produce robust and effective stimulation of sperm motility and, importantly, have a positive response on patient samples.

WHAT IS KNOWN ALREADY

For >20 years, the use of non-selective PDEIs, such as pentoxifylline, has been known to influence the motility of human spermatozoa; however, conflicting results have been obtained. It is now clear that human sperm express several different phosphodiesterases and these are compartmentalized at different regions of the cells. By using type-specific PDEIs, differential modulation of sperm motility may be achieved without adversely affecting other functions such as the acrosome reaction (AR).

STUDY DESIGN, SIZE, DURATION

This was a basic medical research study examining sperm samples from normozoospermic donors and subfertile patients attending the Assisted Conception Unit (ACU), Ninewells Hospital Dundee for diagnostic semen analysis, IVF and ICSI. Phase 1 screened 43 commercially available compounds with reported PDEI activity to identify lead compounds that stimulate sperm motility. Samples were exposed (20 min) to three concentrations (1, 10 and 100 µM) of compound, and selected candidates (n = 6) progressed to Phase 2, which provided a more comprehensive assessment using a battery of in vitro sperm function tests.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All healthy donors and subfertile patients were recruited at the Medical Research Institute, University of Dundee and ACU, Ninewells Hospital Dundee (ethical approval 08/S1402/6). In Phase 1, poor motility cells recovered from the 40% interface of the discontinuous density gradient were used as surrogates for patient samples. Pooled samples from three to four different donors were utilized in order to reduce variability and increase the number of cells available for simultaneous examination of multiple compounds. During Phase 2 testing, semen samples from 23 patients attending for either routine diagnostic andrology assessment or IVF/ICSI were prepared and exposed to selected compounds. Additionally, 48 aliquots of prepared samples, surplus to clinical use, were examined from IVF (n = 32) and ICSI (n = 16) patients to further determine the effects of selected compounds under clinical conditions of treatment. Effects of compounds on sperm motility were assessed by computer-assisted sperm analysis. A modified Kremer test using methyl cellulose was used to assess sperm functional ability to penetrate into viscous media. Sperm acrosome integrity and induction of apoptosis were assessed using the acrosomal content marker PSA-FITC and annexin V kit, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

In Phase 1, six compounds were found to have a strong effect on poor motility samples with a magnitude of response of ≥60% increase in percentage total motility. Under capacitating and non-capacitating conditions, these compounds significantly (P ≤ 0.05) increased the percentage of total and progressive motility. Furthermore, these compounds enhanced penetration into a cervical mucus substitute (P ≤ 0.05). Finally, the AR was not significantly induced and these compounds did not significantly increase the externalization of phosphatidylserine (P = 0.6, respectively). In general, the six compounds maintained the stimulation of motility over long periods of time (180 min) and their effects were still observed after their removal. In examinations of clinical samples, there was a general observation of a more significant stimulation of sperm motility in samples with lower baseline motility. In ICSI samples, compounds #26, #37 and #38 were the most effective at significantly increasing total motility (88, 81 and 79% of samples, respectively) and progressive motility (94, 93 and 81% of samples, respectively). In conclusion, using a two-phased drug discovery screening approach including the examination of clinical samples, 3/43 compounds were identified as promising candidates for further study.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study and caution must be taken when extrapolating the results. Data for patients were from one assessment and thus the robustness of responses needs to be established. The n values for ICSI samples were relatively small.

WIDER IMPLICATIONS OF THE FINDINGS

We have systematically screened and identified several compounds that have robust and effective stimulation (i.e. functional significance with longevity and no toxicity) of total and progressive motility under clinical conditions of treatment. These compounds could be clinical candidates with possibilities in terms of assisted reproductive technology options for current or future patients affected by asthenozoospermia or oligoasthenozoospermia.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded primarily by the MRC (DPFS) but with additional funding from the Wellcome Trust, Tenovus (Scotland), University of Dundee, NHS Tayside and Scottish Enterprise. The authors have no competing interests. A patent (#WO2013054111A1) has been published containing some of the information presented in this manuscript.