The Effect of Oral Phosphodiesterase-5 Inhibitors on Sperm Parameters: A Meta-analysis and Systematic Review

Protective effects of tadalafil and N-acetyl cysteine therapy on cisplatin-induced testicular toxicity

PURPOSE

To investigate whether tadalafil (TAD) and N-acetyl cysteine (NAC) can prevent cisplatin (CIS)-induced testicular toxicity.

METHODS

Forty Wistar-Albino rats were divided into five groups: Control group, CIS group, TAD group, NAC group and TAD + NAC group. All groups were compared regarding body and testicular weights, testicular volumes, blood testosterone levels, testicular tissue malondialdehyde (MDA) levels, histopathological features, and testicular Cosentino and Johnsen scores.

RESULTS

There was no significant difference between the groups regarding body weights and Johnsen scores. It was observed that TAD and NAC affected the apoptotic index, and Cosentino scores were lower in these groups than in the control group. This effect was most prominent in the TAD + NAC group. The CIS treatment led to a decrease in serum testosterone levels. While testosterone levels were higher in the TAD Group, no statistically significant difference was found between the groups. Combination therapy and NAC did not affect blood testosterone levels.

CONCLUSIONS

Cisplatin has adverse effects on the testicular tissue. The histopathological changes caused by this agent can be prevented by TAD + NAC combination therapy.

Antirheumatic drugs in reproduction, pregnancy, and lactation: a systematic literature review informing the 2024 update of the EULAR recommendations

OBJECTIVES

This study aimed to summarise and update evidence to inform the 2024 update of the European Alliance of Associations for Rheumatology recommendations for the use of antirheumatic drugs in reproduction, pregnancy, and lactation.

METHODS

A systematic literature review (SLR) was performed, including keywords on reproduction, adverse pregnancy outcomes (APOs), and lactation. Two appraised SLRs were the basis for the SLR on drug safety in men. If sufficient data were available, a meta-analysis was performed on maternal drug exposure and the risk of APOs.

RESULTS

Of 6680 screened articles, 255 were included in the final analysis. In pregnancy, most evidence was available for biologic disease-modifying antirheumatic drugs (bDMARDs). Meta-analyses with adjusted risk estimates did not reveal APOs or serious infant infections to be associated with tumour necrosis factor inhibitor (TNFi) use. Data on non-TNFi bDMARDs did not raise concerns. In bDMARD-exposed infants, no serious adverse effects to rotavirus live vaccination were reported. Safety of Bacille Calmette-Guérin vaccination in TNFi-exposed infants could be a concern in the first 6 months of life. Regarding oral glucocorticoids, the SLR and meta-analysis using adjusted risk estimates found a dose-dependent association with an increased risk of preterm birth. Nonsteroidal anti-inflammatory drug use could reversibly reduce fecundability. Concerning lactation, available data on various bDMARDs was reassuring. In male patients, available evidence on methotrexate and most other drugs did not reveal adverse effects on sperm quality or birth outcomes. Cyclophosphamide remains the only drug that causes a dose-dependent irreversible infertility.

CONCLUSIONS

This SLR provides up-to-date evidence to guide the 2024 update of the European Alliance of Associations for Rheumatology recommendations for the use of antirheumatic drugs in reproduction, pregnancy, and lactation.

Evaluation of the acute effects of single-dose TPN171 on semen quality in healthy Chinese male volunteers

AIMS

TPN171 is a novel phosphodiesterase type 5 inhibitor for the treatment of erectile dysfunction. This study aimed to assess the immediate impact of a single dose of TPN171 (10 mg) on semen quality in healthy male Chinese volunteers. Additionally, the study investigated the exposure of TPN171 in seminal plasma and observed the safety of TPN171 in the participants.

METHODS

Eighteen healthy male volunteers were enrolled in this double-blind, randomized, placebo-controlled, 2-period, 2-sequence, crossover study. Semen samples were collected to compare semen parameters between the TPN171 and placebo groups. The concentrations of TPN171 were measured in seminal plasma and blood plasma to calculate the ratio of TPN171 concentration in seminal plasma to that in blood plasma, along with the exposure level and percentage of TPN171 in the seminal plasma.

RESULTS

The administration of a single 10-mg dose of TPN171 did not result in statistically significant effects on sperm motility, count, density, morphology, viscosity or volume in healthy male Chinese volunteers. The ratio of TPN171 concentration in seminal plasma to that in blood plasma was 0.72, with the amount of TPN171 in the seminal plasma measured at 78.5 ng. The percentage of exposure to the administered dose (10 mg) was 0.00085%. No adverse events were reported in the TPN171 group.

CONCLUSION

The findings indicate that a single oral dose of 10 mg TPN171 did not induce acute effects on semen quality in healthy male Chinese volunteers. The exposure of seminal plasma to TPN171 was <0.001% of the administered dose.

CLINICAL TRIAL REGISTRATION NUMBER

NCT05585931.

Phosphodiesterase Type 5 Inhibitors in Male Reproduction: Molecular Mechanisms and Clinical Implications for Fertility Management

Phosphodiesterases, particularly the type 5 isoform (PDE5), have gained recognition as pivotal regulators of male reproductive physiology, exerting significant influence on testicular function, sperm maturation, and overall fertility potential. Over the past several decades, investigations have expanded beyond the original therapeutic intent of PDE5 inhibitors for erectile dysfunction, exploring their broader reproductive implications. This narrative review integrates current evidence from in vitro studies, animal models, and clinical research to clarify the roles of PDEs in effecting the male reproductive tract, with an emphasis on the mechanistic pathways underlying cyclic nucleotide signaling, the cellular specificity of PDE isoform expression, and the effects of PDE5 inhibitors on Leydig and Sertoli cell functions. Although certain findings suggest potential improvements in sperm motility, semen parameters, and a more favorable biochemical milieu for spermatogenesis, inconsistencies in study design, limited sample sizes, and inadequate long-term data temper definitive conclusions. Addressing these gaps through standardized protocols, larger and more diverse patient cohorts, and explorations of mechanistic biomarkers could pave the way for incorporating PDE5 inhibitors into evidence-based fertility treatment strategies. In the future, such targeted approaches may inform individualized regimens, optimize male reproductive outcomes, and refine the clinical application of PDE5 inhibitors as part of comprehensive male fertility management.

An overview of conventional and investigational phosphodiesterase 5 inhibitors for treating erectile dysfunction and other conditions

INTRODUCTION

There is a rising concern about developing innovative, efficacious PDE5I molecules that provide better safety, efficacy, and tolerability with less adverse effects. Innovative PDE5I with dual targets have also been defined in the literature. Additionally, some of PDE5I are able to selectively inhibit other enzymes such as histone deacetylase, acetylcholine esterase, and cyclooxygenase or act as nitric oxide donors. This review presents knowledge concerning the advanced trends and perspectives in using PDE5I in treatment of ED and other conditions.

AREAS COVERED

Pre-clinical and early clinical trials that investigated the safety, efficacy, and tolerability of novel PDE5I such as Udenafil, Mirodenafil, Lodenafil, Youkenafil, Celecoxib, and TPN729 in treatment of ED and other conditions.

EXPERT OPINION

Preclinical and limited early clinical studies of the new molecules of PDE5I have demonstrated encouraging results; however, safety, efficacy, and tolerability are still issues that necessitate further long-term multicenter clinical studies to ensure justification of their uses in treatment of ED and other conditions. Progress in molecular delivery techniques and tailored patient-specific management and additional therapeutic technology will dramatically improve care for ED and other conditions. The dream of ED and many other conditions becoming more effectively managed may be feasible in the near future.

A drug target for erectile dysfunction to help improve fertility, sexual activity, and wellbeing: mendelian randomisation study

OBJECTIVE

To investigate the association of genetically proxied (using a surrogate biomarker) inhibition of phosphodiesterase 5 (PDE5), an established drug target for erectile dysfunction, with fertility, sexual behaviour, and subjective wellbeing.

DESIGN

Two sample cis-mendelian randomisation study.

SETTING

Summary data on genetic associations obtained from the International Consortium for Blood Pressure and UK Biobank.

PARTICIPANTS

Individuals of European ancestry from the International Consortium for Blood Pressure (n=757 601) for estimating PDE5 inhibition (using the surrogate biomarker of diastolic blood pressure reduction), and UK Biobank (n=211 840) for estimating the fertility, sexual behaviour, and subjective wellbeing outcomes in male participants.

INTERVENTION

Genetically proxied PDE5 inhibition.

MAIN OUTCOME MEASURES

Number of children fathered, number of sexual partners, probability of never having had sexual intercourse, and subjective wellbeing.

RESULTS

Genetically proxied PDE5 inhibition was associated with male participants having 0.28 (95% confidence interval 0.16 to 0.39) more children (false discovery rate corrected P<0.001). This association was not identified in female participants. No evidence was found of an association between genetically proxied PDE5 inhibition and number of sexual partners, probability of never having had sexual intercourse, or self-reported wellbeing in male participants.

CONCLUSIONS

The findings of this study provide genetic support for PDE5 inhibition potentially increasing the number of children fathered by male individuals. Absence of this association in female participants supports increased propensity for sustained and robust penile erections as a potential underlying mechanism. Further studies are required to confirm this, however, and these findings should not promote indiscriminate use of PDE5 inhibitors, which can also have harmful adverse effects.

Oral phosphodiesterase type 5 inhibitors and male reproductive potential: an overview

BACKGROUND

Phosphodiesterase type 5 inhibitors (PDE5Is), due to their efficacy and tolerable profile for more than 2 decades,are considered a good addition to the available treatments in patients with erectile dysfunction (ED).

AIM

We sought to assess the possible influence of oral PDE5Is on male human reproduction.

METHODS

A literature review was performed in several databases, including the PubMed/Medline database, Scopus, Cochrane Library, EMBASE, Academic Search Complete, and Egyptian Knowledge Bank databases. The keywords/search terms were "PDE5Is," "sildenafil," "vardenafil," "tadalafil," or "avanafil," combining and crossing them with "male infertility," "semen," "reproductive hormones," or "sperm."

RESULTS

Overall, 101 articles were selected. After removal of duplicates and animal studies, 75 articles were finally subjected to review covering the different items related to male human reproduction, including effects of PDE5Is on different parameters of semen or reproductive hormones, as uses of PDE5Is in cases related to distinctive male factor infertility, such as ED, temporary ED, or ejaculatory failure alongside assisted reproduction (AR) procedures, and ejaculatory dysfunction in spinal cord lesions. We found 26 articles that addressed the direct effects of PDE5Is on semen and reproductive hormonal profiles, 16 in vivo studies and 10 in vitro studies. Oral PDE5Is have in general a stimulatory effect on sperm motility, while other semen parameters and reproductive hormonal profiles showed varied outcomes. Such effects are more pronounced with a long-term daily regimen than with an on-demand regimen. However, it seems that the best-controlled studies suggested no change in the sperm quality of male reproductive potential.

CONCLUSION

Oral PDE5Is have in general stimulatory effects on sperm motility, while other semen parameters and hormone profiles showed varied results. In addition, oral PDE5Is have played a useful role in conditions related to distinctive male factor infertility, such as ED, temporary ED, ejaculatory failure alongside AR, and ejaculatory dysfunction in spinal cord lesions.

Is tadalafil associated with decreased risk of major adverse cardiac events or venous thromboembolism in men with lower urinary tract symptoms?

Purpose

To evaluate the association of tadalafil, a phosphodiesterase-5 inhibitor (PDE5I), with major adverse cardiac events (MACE) or venous thromboembolism (VTE) in men with lower urinary tract symptoms (LUTS).

Methods

Data was obtained from the TriNetX Research Network, ICD-10 codes were used to identify men with LUTS, MACE, and VTE. In addition, demographic characteristics and use of tadalafil or alpha-blocker was evaluated. Then, unbalanced and balanced association analyses was performed to assess the relation between tadalafil and/or alpha-blocker use with MACE/VTE.

Results

After participant selection, analysis included 821,592 men that did not use an alpha blocker or tadalafil, 5,004 men that used tadalafil but no alpha blocker, 327,482 men that used an alpha blocker but no tadalafil, and 6,603 men that used both an alpha blocker and tadalafil. On balanced analysis, tadalafil was independently associated with a decreased risk of MACE/VTE within a 3-year time period (OR = 0.59, 95%CI 0.49–0.70, p < 0.0001). Among men with a history of alpha blocker use, tadalafil use was also independently associated with a decreased risk of MACE or VTE, both before and after controlling for potentially confounding variables (OR = 0.57, 95%CI: 0.50–0.66; p < 0.0001).

Conclusions

In our study, tadalafil was associated with a decreased risk of MACE/VTE in men with LUTS with and without a history of alpha blocker use. It is time to perform further long-term prospective randomized studies to further analyze the cardiovascular effects of PDE5Is as combination treatment with alpha blockers in the management of LUTS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00345-022-04005-3.

Phosphodiesterase (PDE) 5 inhibitors sildenafil, tadalafil and vardenafil impact cAMP-specific PDE8 isoforms-linked second messengers and steroid production in a mouse Leydig tumor cell line

Type 5 phosphodiesterase (PDE5) blockade by inhibitors (PDE5i) results in intracellular cyclic guanosine monophosphate (cGMP) increase and smooth muscle relaxation and are used for the treatment of men erectile dysfunction. Although they have high specificity for PDE5, these inhibitors are suspected to cross-interact also with cyclic adenosine monophosphate (cAMP)-specific PDEs, inducing the intracellular accumulation of this cyclic nucleotide and related testosterone increase, positively impacting male reproductive parameters. However, the link between the use of PDE5i and the activation of cAMP-mediated steroidogenesis is still unclear. We have investigated whether three PDE5i, sildenafil, tadalafil and vardenafil, cross-interacts with the high affinity cAMP-specific enzymes type 8A and 8B PDEs (PDE8A and PDE8B), in live, transfected mouse Leydig tumor (mLTC1) and human embryonic kidney (HEK293) cell lines in vitro. The PDE5i-induced production of cAMP-dependent testosterone and its precursor progesterone was evaluated as well. We have developed PDE8A/B biosensors and modified cyclic nucleotides confirming enzyme binding to cAMP, but not to cGMP, in our cell models. cAMP binding to PDE8A/B was displaced upon cell treatment with PDE5i, revealing that sildenafil, tadalafil and vardenafil have similar effectiveness in live cells, in vitro. The cross-interaction between PDE5i and PDE8A/B supports the gonadotropin-enhanced intracellular cAMP increase, occurring together with cGMP increase, as well as steroid synthesis. Indeed, we found that Leydig cell treatment by PDE5i increases progesterone and testosterone production triggered by gonadotropins. We demonstrated that PDE5i may interact with the cAMP-specific PDE8A and PDE8B, possibly inducing intracellular cAMP and sex steroid hormone increase. These findings support clinical data suggesting that PDE5i might increase testosterone levels in men.

Effect of Multiple Sclerosis and Its Treatments on Male Fertility: Cues for Future Research

Multiple sclerosis is a chronic disease that may lead to different types of symptoms and disabilities. with the better quality of life and decreased disability due to early diagnosis and the availability of disease-modifying therapies (DMTs), the treating physician is increasingly asked to counsel patients on its effects on fertility and reproduction. In particular, reproductive issues are still scarcely studied and discussed in men. Among the still open questions are the following: (a) Does multiple sclerosis cause infertility per sè? (b) Is multiple sclerosis correlated with conditions that increase the risk of infertility? (c) Do DMTs or other therapies for multiple sclerosis impact gonadal function in men? The aim of this review is to provide an overview on the available literature data about the reproductive issues unique to men with multiple sclerosis, underlining the numerous areas where evidence is lacking and, therefore, the priorities for future research.

The Effect of Phosphodiesterase-type 5 Inhibitors on Erectile Function: An Overview of Systematic Reviews

Background: Multiple systematic reviews explore the effect of phosphodiesterase type 5 (PDE5) inhibitors on erectile dysfunction (ED), with each study addressing specific outcomes. However, physicians and policymakers require a holistic approach of this topic.

Objective: To summarize the current evidence regarding the efficacy and safety of PDE5 inhibitors for the management of ED through an overview of systematic reviews.

Methods: Studies were identified by searching PubMed, Web of Science, Cochrane Library and Scopus databases, as well as sources of grey literature until June 12, 2021 (PROSPERO: CRD42020216754). We considered systematic reviews, meta-analyses or network meta-analyses of randomized trials that provided outcomes about the efficacy and safety of any approved PDE5 inhibitor (avanafil, sildenafil, tadalafil and vardenafil). We constructed forest plots for meta-analytic effects regarding the change in erectile function, adverse events and dropouts after administration of PDE5 inhibitors in the general population and in specific patient groups.

Results: We included 23 studies with 154,796 participants and a total of 258 meta-analytic effects. Sildenafil 25 mg [Weighted Mean Difference (WMD): 13.08, 95% Confidence Interval (CI): 10.1-16.06] seemed to be statistically superior to all interventions in improving erectile function compared to placebo, but studies with low-dose sildenafil are lacking. Moreover, comparing among different PDE5 inhibitors, sildenafil 50 mg or sildenafil 100 mg were considered the most effective compounds in the general population. The latter derived, however, predominantly from indirect comparisons among different PDE5 inhibitors. Still, sildenafil 100 mg was associated with more treatment-related adverse events and dropouts. Interestingly, low-dose daily tadalafil may be more effective than high-dose on-demand tadalafil (WMD: 1.24, 95% CI: 0.03-2.44). Furthermore, testosterone and PDE5 inhibitors in patients with ED and hypogonadism seem to further improve symptoms, while the addition of a-blockers in patients with urinary symptoms treated with PDE5 inhibitors does not provide additional benefits (WMD: −0.8, 95% CI: −1.65-0.06).

Conclusion: Although the efficacy and safety of PDE5 inhibitors, compared to placebo, is well-documented, the existing evidence comparing different PDE5 inhibitors is low. Therefore, high-quality, head-to-head, trials comparing different PDE5 inhibitors are necessary to determine their ideal dosage and formulation based on their safety and efficacy profile.

Systematic Review Registration: PROSPERO, identifier [CRD42020216754].

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.

Male Sexual Dysfunctions in the Infertile Couple-Recommendations From the European Society of Sexual Medicine (ESSM)

INTRODUCTION

Sexual dysfunctions (SDs) have been frequently reported among male partners of infertile couples due to psychogenic, relational and/or organic issues related with the inability to conceive. Likewise, male infertility (MI) could be a consequence of sexual dysfunctions.

AIM

To review the evidence on the prevalence and treatment of male SDs in men of infertile couples and provide clinical recommendations on behalf of the European Society of Sexual Medicine (ESSM).

METHODS

The MEDLINE database was searched in September 2019 for randomized clinical trials (RCTs), meta-analyses and open-label prospective or retrospective studies investigating the presence of erectile dysfunction (ED) and/or ejaculatory dysfunctions (EjDs) and/or low sexual desire (LSD) in conjunction with infertility.

MAIN OUTCOME MEASURE

The panel provided statements on: (i) Prevalence and association between SDs and MI; (ii) Treatment of male SDs in men of infertile couples.

RESULTS

ED has been reported in 9% to 62% of male partners of infertile couples, with severe impairment observed in only 1% to 3% of ED cases. Moreover, worse semen parameters have been associated with greater ED severity. Phosphodiesterase type 5 inhibitors (PDE5is) can be safely used to treat ED among patients seeking fatherhood. Male partners of infertile couples are at higher risk of premature ejaculation (PE). Retrograde ejaculation (RE) and anejaculation are a cause of MI and can be managed with electroejaculation (EEJ) or penile vibratory stimulation (PVS) or, alternatively, with oral treatments, however the latter with limited documented success. Low sexual desire has been reported by one third of men of infertile couples.

CONCLUSION

ED could significantly affect male partners of infertile couple; PDE5is should be suggested to ensure an effective and satisfactory sexual relationship of the couple. Anejaculation and RE should be considered as a possible cause of MI and treated accordingly. Low sexual desire is frequently reported among men of infertile couple and could be a symptom of other systemic conditions or psychological distress. Capogrosso P, Jensen CFS, Rastrelli G, et al. Male Sexual Dysfunctions in the Infertile Couple-Recommendations From the European Society of Sexual Medicine (ESSM). J Sex Med 2021;9:100377.

Effect of Phosphodiesterase-5 Inhibitors on the Treatment of Male Infertility: A Systematic Review and Meta-Analysis

Purpose

Male infertility is a worldwide problem with limitations in the treatment. Phosphodiesterase-5 inhibitors (PDE5is) is the first choice for the treatment of erectile dysfunction, more and more studies show that it has a certain effect on male infertility in recent years. But there was currently no high quality of systematic review to evaluate the effects of PDE5is on semen quality.

Materials and Methods

We retrieved the electronic databases of MEDLINE, PubMed, Web of Science, EMBASE, etc. Related randomized controlled trials (RCTs) were collected and selected up to May 20, 2020. We have searched literature with terms “male infertility”, “phosphodiesterase-5 inhibitors”, “PDE5i”, “Tadalafil”, “Sildenafil”, “Vardenafil”, “Udenafil”, “Avanafil”, “semen”, and “sperm”. Mean value and its standard deviation were used to perform quantitative analysis. All statistical analyses were conducted by RevMan 5.3 and Stata software.

Results

There were a total of 1,121 participants in the nine included studies. There was a statistically significant improvement treated with PDE5is compared with sham therapy, which including sperm concentration (mean difference [MD]=1.96, 95% confidence interval [CI]=1.70–2.21, p<0.001; MD=3.22, 95% CI=1.96–4.48, p<0.001), straight progressive motility (%) Grade A (MD=3.71, 95% CI=2.21–5.20, p<0.001), sperm motility (MD=8.09, 95% CI=7.83–8.36, p<0.001), morphologically normal spermatozoa (%) (MD=0.67, 95% CI=0.20–1.15, p=0.005; MD=1.27, 95% CI=0.02–2.52, p=0.05), sperm abnormalities (%) (MD=−0.64, 95% CI=−0.81–−0.47, p<0.001), and progressive motile sperm (MD=5.34, 95% CI=3.87–6.81, p<0.001).

Conclusions

In this meta-analysis of nine RCTs, treatment with PDE5is could improve some indicators of male sperm.

Effect of phosphodiesterase type 5 inhibitors on sperm motility and acrosome reaction: An in vitro study

Purpose

Phosphodiesterase type 5 (PDE5) inhibitors are effective treatments for erectile dysfunction, and several recent studies have reported positive effects of PDE5 inhibitors on semen parameters as well. However, the data are still controversial. We investigated the effect of PDE5 inhibitors on sperm function by analyzing sperm motility and acrosome reaction.

Materials and Methods

This study included young healthy men who underwent fertility evaluation; 32 cases were finally included. Men were excluded if they used a PDE5 inhibitor within 2 weeks or if they had insufficient semen volume (≤2 mL), leukocytospermia, or a genitourinary infection. Changes in sperm motility and acrosome reaction were determined after in vitro exposure to the maximal semen concentration of oral intake of sildenafil (100 mg) or tadalafil (20 mg).

Results

Mean age of the participants was 35.4±4.9 years, mean sperm concentration was 68.7±32.4 ×10⁶/mL, and mean sperm motility was 50.38%±8.41%. All three groups (control, sildenafil, tadalafil) experienced trends of decreased average sperm motility over time, but these changes were not significant. There were no significant differences between the three groups in the acrosome reaction after 120 minutes of drug exposure, either. The maximal semen concentration of oral intake of sildenafil (100 mg) or tadalafil (20 mg) did not substantially affect sperm motility or acrosome reaction.

Conclusions

Our results suggest that on-demand use of a PDE5 inhibitor is safe and useful for the male partner of an infertile couple; however, further studies are warranted for daily PDE5 inhibitor use.

Phosphodiesterase 5 (PDE5): Structure-function regulation and therapeutic applications of inhibitors

Phosphodiesterase 5 (PDE5) is one of the most well-studied phosphodiesterases (PDEs) that specifically targets cGMP typically generated by nitric oxide (NO)-mediated activation of the soluble guanylyl cyclase. Given the crucial role of cGMP generated through the activation of this cellular signaling pathway in a variety of physiologically processes, pharmacological inhibition of PDE5 has been demonstrated to have several therapeutic applications including erectile dysfunction and pulmonary arterial hypertension. While they are designed to inhibit PDE5, the inhibitors show different affinities and specificities against all PDE subtypes. Additionally, they have been shown to induce allosteric structural changes in the protein. These are mostly attributed to their chemical structure and, therefore, binding interactions with PDE catalytic domains. Therefore, understanding how these inhibitors interact with PDE5 and the structural basis of their selectivity is critically important for the design of novel, highly selective PDE5 inhibitors. Here, we review the structure of PDE5, how its function is regulated, and discuss the clinically available inhibitors that target phosphodiesterase 5, aiming to better understand the structural bases of their affinity and specificity. We also discuss the therapeutic indications of these inhibitors and the potential of repurposing for a wider range of clinical applications.

Is there a role for phosphodiesterase inhibitors in the treatment of male subfertility?

Intracytoplasmic sperm injection (ICSI) is frequently used to overcome severe deficits in semen quality. Concerns, however, are arising over its increasing use for non-male factor infertility. Moreover, increased risk of cardiovascular disease, congenital abnormalities, aneuploidies and childhood cancers have all been reported in the literature in relation to ICSI and it is possible that the quality of sperm chosen for injection may be an important factor in these unwanted outcomes. Given the wider adoption of ICSI to treat beyond the requirements of male infertility alone, research focussed on alternative methods to diagnose and treat the infertile couple is gaining increasing attention. This review focuses on the information available to date on the use of non-selective phosphodiesterase inhibitors (PDEI), specifically pentoxifylline (PF), caffeine (CF) and theophylline (TP) to stimulate sperm motility, thereby potentially reducing the need for ICSI in certain patient groups who may benefit from either expectant management or from a less stressful, minimally invasive and inexpensive treatment such as intrauterine insemination (IUI). The review focuses firstly on the mechanism of action of PDEI followed by treatment effects on sperm parameters such as motility and hyperactivated motility and sperm DNA integrity. Specific clinical implications are discussed that outline the potential role of PDEI in clinical practice and highlights areas in need of further research.

The Role of the Urologist in a Reproductive Endocrinology and Infertility Practice

With male factor infertility accounting for up to 50% of infertility cases, demand for male fertility services has increased. Integrating a reproductive urologist within a fertility center allows for treatment of both partners simultaneously with easier, more convenient access to a comprehensive male evaluation and any indicated interventions. A joint practice allows urologists to collaborate more closely with reproductive endocrinologists, which can, in turn, improve clinical care and research endeavors. This full-service, streamlined approach translates to optimized care for the infertile couple and allows for emphasis of male partner health.

Established and emerging therapeutic uses of PDE type 5 inhibitors in cardiovascular disease

PDE type 5 inhibitors (PDE5Is), such as sildenafil, tadalafil and vardenafil, are a class of drugs used to prolong the physiological effects of NO/cGMP signalling in tissues through the inhibition of cGMP degradation. Although these agents were originally developed for the treatment of hypertension and angina, unanticipated side effects led to advances in the treatment of erectile dysfunction and, later, pulmonary arterial hypertension. In the last decade, accumulating evidence suggests that PDE5Is may confer a wider range of clinical benefits than was previously recognised. This has led to a broader interest in the cardiovascular therapeutic potential of PDE5Is, in conditions such as hypertension, myocardial infarction, stroke, peripheral arterial disease, chronic kidney disease and diabetes mellitus. Here, we review the pharmacological properties and established licensed uses of this class of drug, along with emerging therapeutic developments and possible future indications.

Effect of phosphodiesterase-5 inhibitors (PDE5is) on the treatment of male infertility: A protocol for systematic review and meta-analysis

BACKGROUND

Male infertility is a worldwide problem with limitations in the treatment. Phosphodiesterase-5 inhibitors (PDE5is) is the first choice for the treatment of erectile dysfunction (ED), but more and more studies show that it has a certain effect on male infertility in recent years. The literatures of PDE5is related to male infertility have shown inconsistent results, and there is currently no high quality of systematic review to evaluate the effects of PDE5is on semen quality in male infertility patients.

METHODS

The electronic databases of MEDLINE, PubMed, Web of Science, EMBASE, Clinicaltrials.org, China National Knowledge Infrastructure Database (CNKI), Wan fang Database, China Biology Medicine Database (CBM), VIP Science Technology Periodical Database, Chinese Clinical Trial Registry and Cochrane Library were retrieved. Grey literature will be searched in Open Grey. Related Randomized controlled trials (RCTs) were collected and selected before October 20, 2019. We will search English literature and Chinese literature with search terms "male infertility", "phosphodiesterase-5 inhibitors", "PDE5i", "Tadalafil", "Sildenafil", "Vardenafil", "Udenafil", "Avanafil", "semen" and "sperm". Sperm concentration, motility and morphology, sperm DNA fragmentation index, number of per ejaculate, sperm viability and adverse events will be evaluated. RevMan 5.3 and Stata 14.0 will be used for Systematic review and Meta-analysis. This protocol reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) statement, and we will report the systematic review by following the PRISMA statement.

CONCLUSION AND DISSEMINATION

Efficacy and safety of PDE5is on male sperm quality in infertile men will be assessed. The results will be published in a public issue journal to provide evidence-based medical evidence for urologists and andrologists to make clinical decisions.

REGISTRATION INFORMATION

PROSPERO CRD42019142980.