Long-term oral phosphodiesterase 5 inhibitor therapy alleviates recurrent priapism

Resveratrol attenuates the priapism phenotype in sickle cell mice by restoring NO-cGMP-PDE5 signaling and reducing NADPH oxidase 2 expression

The pathogenesis of priapism in sickle cell disease (SCD) is closely linked to oxidative stress and reduced bioavailability of nitric oxide (NO) in penile tissue. Resveratrol, a potent natural antioxidant, has demonstrated protective effects in various vascular disorders. To evaluate the therapeutic effects of resveratrol on priapism, oxidative stress markers, and NO-cGMP signaling in the penile tissue of transgenic SCD mice. Male wild-type (C57BL/6) and transgenic SCD mice were treated with resveratrol (100 mg/kg/day, gavage) or vehicle for 2 weeks. Functional studies were conducted on CC strips mounted in organ baths to assess relaxation responses to acetylcholine (ACh), sodium nitroprusside (SNP), and nitrergic stimulation (electrical field stimulation, EFS). The oxidative stress markers (NOX-2, 4-HNE, and 3-NT), cGMP levels, and the mRNA expression of endothelial nitric oxide synthase (eNOS) and phosphodiesterase type 5 (PDE5) were evaluated. Resveratrol treatment decreased exaggerated ACh-, SNP-, and EFS-induced relaxation responses in SCD mice. It also reduced oxidative stress markers (NOX-2, 4-HNE, and 3-NT) and normalized eNOS and PDE5 mRNA expression in the CC of SCD mice. Additionally, cGMP levels in the CC were significantly increased by resveratrol treatment. These effects were specific to SCD mice and not observed in wild-type mice. In conclusion, resveratrol reduces oxidative stress and restores NO-cGMP signaling in the penile tissue, reducing the exaggerated cavernosal relaxation characteristic of priapism in SCD. These findings highlight resveratrol as a promising therapeutic candidate for managing priapism in patients with SCD.

Current evidence on the management of ischaemic priapism post-shunting: a narrative review

When ischaemic priapism becomes unresponsive to aspiration-irrigation and shunting, poor outcomes for priapism resolution and functional recovery are expected. This study reviews the strategies to improve the outcomes for priapism patients after shunting, based on a comprehensive literature-search on PubMed, Cochrane Library, and EMBASE. Erectile dysfunction is common after shunting, particularly in cases of pre-existing erectile dysfunction, older age, recurrent priapism, or necrosis detected by magnetic resonance imaging. Distal shunts are typically adopted as first-line options. Systemic anticoagulation may prevent thrombus-formation, which may lead to recurrence of ischaemic priapism. Both selective and non-selective phosphodiesterase type 5 inhibitors may enhance erectile function recovery and prevent priapism recurrence. A repeat penile blood gas analysis can help determine whether there has been a conversion to non-ischaemic priapism if shunts fail. Proximal shunts and the penoscrotal decompression can be considered when distal shunting does not result in complete detumescence. Early malleable penile prosthesis implantation is an option after shunting failure. Use of vacuum erection device regimens should be encouraged after shunting to minimize penile fibrosis, especially when late penile prosthesis implantation is needed due to erectile dysfunction previously unresponsive to medical management. More evidence is needed to achieve consensus regarding the optimal management of ischaemic priapism after shunting, and surgical innovation should continue to refine the current techniques.

Idiopathic recurrent ischemic priapism: a review of current literature and an algorithmic approach to evaluation and management

BACKGROUND

Stuttering priapism is characterized by recurrent, self-limited episodes of penile erection lasting from a few minutes to a maximum of three hours, often resolving spontaneously. These episodes can occur with or without sexual stimulation. If not treated promptly and effectively, stuttering priapism can severely impact a patient's quality of life, leading to significant psychological distress and anxiety related to sexual performance. Although it has been associated with various hematological disorders and pharmacological treatments, many cases of stuttering priapism remain idiopathic, meaning they have no identifiable cause. Currently, no conclusive randomized clinical trials exist on the management of idiopathic stuttering priapism. This study aims to review the existing literature on the pathophysiology and management of idiopathic stuttering priapism and propose an algorithm to assist physicians in its evaluation and treatment.

RESULTS

A systematic literature review was conducted using the PubMed database, focusing on the terms "idiopathic," "stuttering," "ischemic," and "priapism." The search identified 23 relevant references published between 1991 and 2022. The selection and analysis of these studies adhered to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and results were described qualitatively. Recent research into the effectiveness, sustainability, tolerability, and side effects of various treatments for idiopathic stuttering priapism has enhanced the understanding of its underlying molecular mechanisms. Various treatments, targeting different mechanisms, have been identified that can potentially reduce the frequency and severity of episodes and improve patient outcomes.

CONCLUSION

Current research predominantly addresses the acute treatment of idiopathic stuttering priapism rather than strategies to alter the disease's overall course. The limited number of treatment reviews, case reports, and the low level of evidence available, combined with the absence of randomized clinical trials, prevent the establishment of a consensus on treatment protocols. As a result, idiopathic stuttering priapism remains under-recognized and under-treated. This review proposes a management framework to help clinicians access and apply the available literature effectively, minimizing the reliance on extensive case reports and review articles.

Sympathetic hypoactivity leads to hypocontractility of the corpus cavernosum in sickle cell mice: a mechanism contributing to priapism

Priapism, a prevalent complication in sickle cell disease (SCD) patients, manifests as prolonged and painful erections unrelated to sexual arousal. The detailed mechanisms contributing to this condition, especially regarding sympathetic function in the corpus cavernosum that maintains penile flaccidity, remain to be elucidated. In this study, it was hypothesized that the pathways of the sympathetic nervous system would be down-regulated, thereby contributing to the development of ischemic priapism in sickle cell disease. This study aimed to investigate the contractions induced by stimulation of sympathetic terminals and the expression of tyrosine hydroxylase in the corpora cavernosa of Berkeley SCD mice. C57BL/6 mice (wild-type, WT) and Berkeley SCD mice were used. A total of 22 mice were used in this study, with 11 allocated to the WT group and 11 to the SCD group. Mice corpus cavernosum was dissected free and mounted in 7-mL organ baths containing Krebs solution. Noradrenergic contractions were obtained using electrical-field stimulation (4-32 Hz) in corpus cavernosum strips from WT and SCD mice. Measurements of tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expressions in cavernosal tissues were also measured by western blot. The neurogenic contractions were significantly lower (P < 0.05) in the SCD group compared to WT group at all tested frequencies. The protein expression of both total tyrosine hydroxylase and tyrosine hydroxylase phosphorylated at Ser-31 was significantly decreased by approximately 46.28% (P = 0.01) and 55.32% (P = 0.03) in cavernosal tissues from the SCD group compared to the control group, respectively. In conclusion, sympathetic hypoactivity characterized by the downregulation of tyrosine hydroxylase contributes to the hypocontractility of the corpus cavernosum in Berkeley SCD mice. This suggests an impairment in the mechanism responsible for maintaining penile flaccidity, potentially predisposing to erections without sexual stimulation, similar to those observed in ischemic priapism. Pharmacological treatments aiming to restore sympathetic tone in the penis might hold promise for addressing ischemic priapism in SCD.

Nitric Oxide Resistance in Priapism Associated with Sickle Cell Disease: Mechanisms, Therapeutic Challenges, and Future Directions

Patients with sickle cell disease (SCD) display priapism, a prolonged penile erection in the absence of sexual arousal. The current pharmacological treatments for SCD-associated priapism are limited and focused on acute interventions rather than prevention. Thus, there is an urgent need for new drug targets and preventive pharmacological therapies for this condition. This review focuses on the molecular mechanisms linked to the dysfunction of the NO-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) pathway implicated in SCD-associated priapism. In murine models of SCD, reduced nitric oxide (NO)-cGMP bioavailability in the corpus cavernosum is associated with elevated plasma hemoglobin levels, increased reactive oxygen species levels that inactive NO, and testosterone deficiency that leads to endothelial nitric oxide synthase downregulation. We discuss the consequences of the reduced cGMP-dependent PDE5 activity in response to these molecular changes, highlighting it as the primary pathophysiological mechanism leading to excessive corpus cavernosum relaxation, culminating in priapism. We also further discuss the impact of intravascular hemolysis on therapeutic approaches, present current pharmacological strategies targeting the NO-cGMP-PDE5 pathway in the penis, and identify potential pharmacological targets for future priapism therapies. In men with SCD and priapism, PDE5 inhibitor therapy and testosterone replacement have shown promising results. Recent preclinical research reported the beneficial effect of treatment with haptoglobin and NO donors. SIGNIFICANCE STATEMENT: This review discusses the molecular changes that reduce NO-cGMP bioavailability in the penis in SCD and highlights pharmacological targets and therapeutic strategies for the treatment of priapism, including PDE5 inhibitors, hormonal modulators, NO donors, hydroxyurea, soluble guanylate cyclase stimulators, haptoglobin, hemopexin, and antioxidants.

What is the effectiveness of surgical and non-surgical therapies in the treatment of ischemic priapism in patients with sickle cell disease? A systematic review by the EAU Sexual and Reproductive Health Guidelines Panel

Sickle cell disease (SCD) is an inherited hemoglobin disorder characterized by the occlusion of small blood vessels by sickle-shaped red blood cells. SCD is associated with a number of complications, including ischemic priapism. While SCD accounts for at least one-third of all priapism cases, no definitive treatment strategy has been established to specifically treat patients with SC priapism. The aim of this systematic review was to assess the efficacy and safety of contemporary treatment modalities for acute and stuttering ischemic priapism associated with SCD. The primary outcome measures were defined as resolution of acute priapism (detumescence) and complete response of stuttering priapism, while the primary harm outcome was as sexual dysfunction. The protocol for the review has been registered (PROSPERO Nr: CRD42020182001), and a systematic search of Medline, Embase, and Cochrane controlled trials databases was performed. Three trials with 41 observational studies met the criteria for inclusion in this review. None of the trials assessed detumescence, as a primary outcome. All of the trials reported a complete response of stuttering priapism; however, the certainty of the evidence was low. It is clear that assessing the effectiveness of specific interventions for priapism in SCD, well-designed, adequately-powered, multicenter trials are strongly required.

Treatment of Refractory Ischemic Priapism: A Case Report and Literature Review

Recurrent priapism is a rare and poorly known entity. It is defined by recurrent episodes of painful erections that last less than four hours. The etiology is similar to that of ischemic priapism. Episodes lasting more than four hours require immediate intervention to prevent penile fibrosis and subsequent erectile dysfunction. A 42-year-old male with no significant chronic-degenerative history was referred to our medical center from his second-level medical unit after a 56-hour history of ischemic priapism with the persistence of tumescence despite medical and surgical treatment. Upon interrogation, the patient reported stuttering (recurrent) episodes of painful erections lasting approximately three to four hours, not associated with sexual activity or arousal, in the past two years, with spontaneous resolution. He denied the use of psychotropics or drugs for erectile dysfunction. As a palliative measure, a left saphenous-cavernous (Grayhack) bypass was performed, with a 90% decrease in tumescence and total resolution of pain during the first 12 hours. There is little information and treatment recommendations for patients with recurrent priapism, and even less for patients who are refractory to conventional medical and surgical treatment. Recurrent or stuttering priapism is a condition with a low incidence and a pathophysiology compatible with low-flow priapism. It is difficult to treat and has a poor prognosis in terms of erectile function. Likewise, it is mostly associated with the use of psychotropic drugs such as cocaine and marijuana, medications for erectile dysfunction such as phosphodiesterase inhibitors, prostaglandin E1 analogues, and hematological malignancies such as sickle cell anemia and multiple myeloma. The aim of this article is to share our experience with a patient refractory to multiple medical and surgical treatments.

Priapism in Lymphoproliferative Disorders: A Systematic Review

Priapism is defined as a persistent penile erection lasting more than 4 h. We searched the literature for reviews, case reports, and series for patients with lymphoproliferative disorders who developed priapism. The search involved all the lymphoproliferative disorders included in the revised 2016 World Health Organization classification of lymphoid neoplasms including chronic lymphocytic leukemia, multiple myeloma, Waldenström macroglobulinemia, and lymphomas. A total of 16 articles were found. The search included cases up to 4^th January 2021. Priapism was seen most commonly as the first manifestation of lymphoproliferative disorders, rarely seen after treatment or after diagnosis.

Update on Treatment Options for Stuttering Priapism

Purpose of Review

There is a paucity of peer-reviewed evidence to guide medical management of stuttering priapism. The purpose of this review is to summarize the current understanding regarding the pathophysiology of priapism and management options for stuttering priapism.

Recent Findings

Conducting large-scale, randomized, placebo-controlled trials that elucidate the optimal treatment of stuttering priapism is challenging. Therefore, recent treatment guidelines are based upon small case series, retrospective studies, and expert opinions. Nonetheless, multiple compounds from various drug classes have shown promise in treating stuttering priapism, and a few pharmacotherapies such as Crizanlizumab are currently under active investigation.

Summary

Stuttering priapism is an under-investigated disorder with a complex pathophysiology. Currently, there is no wildly adopted universal therapeutic strategy. Further research is warranted to identify the appropriate treatment of stuttering priapism and to determine the long-term side effects of current pharmacotherapies.

Stuttering Priapism in a Dog—First Report

Simple Summary

A 5-year-old recently castrated male Doberman dog presented for prolonged erection of one week’s duration with associated pain and dysuria. This was the fourth episode within a year. Each episode was associated with an unusual event, which was stressful for the dog. Castration performed two months prior to the final episode did not prevent recurrence. Due to tissue necrosis, penile amputation and urethrostomy had to be performed. To our knowledge, this case is the first report of a stuttering priapism in a dog. Stuttering priapism, also called recurrent or intermittent priapism, is a particular type of ischemic priapism described in humans that is characterized by repeated episodes of prolonged erections.

Abstract

A 5-year-old recently castrated male Doberman dog presented for prolonged erection of one week’s duration with associated pain and dysuria. This was the fourth episode within a year. Each episode was associated with an unusual event, which was stressful for the dog. Castration performed two months prior to the final episode did not prevent recurrence. Due to tissue necrosis, penile amputation and urethrostomy had to be performed. The dog recovered fully. Prolonged erection that persists beyond or that is unrelated to sexual stimulation is called “priapism”. This term refers to the Greek god Priapus, a god of fertility, memorialized in sculptures for his giant phallus. In humans, depending on the mechanism involved, priapism is classified as nonischemic or ischemic. Because prognosis and treatment are different, priapism must be determined to be nonischemic or ischemic. Nonischemic priapism is a rare condition observed when an increase in penile arterial blood flow overwhelms the capacity of venous drainage; it is often associated with penile trauma, and does not require medical intervention. Ischemic priapism is associated with decreased venous return. In humans, ischemic priapism accounts for 95% of cases, the majority of which are idiopathic. Ischemic priapism is a urological emergency; simple conservative measures such as aspiration of blood from the corpora cavernosa and intracavernosal injection of an adrenergic agent are often successful. Stuttering priapism, also called recurrent or intermittent priapism, is a particular form of ischemic priapism reported in humans that is characterized by repetitive episodes of prolonged erections. Management consists of treating each new episode as an episode of acute ischemic priapism, and preventing recurrence with oral medications such as dutasteride and/or baclofen, gabapentin, or tadalafil. To the authors’ knowledge, this case is the first report of stuttering priapism in a dog.

An update on the management algorithms of priapism during the last decade

Priapism is a persistent penile erection lasting longer than 4 hours, that needs emergency management. This disorder can induce irreversible erectile dysfunction. There are three subtypes of priapism: ischemic, non-ischemic, and stuttering priapism. If the patient has ischemic priapism (IP) of less than 24-hours (h) duration, the initial management should be a corporal blood aspiration followed by instillation of phenylephrine into the corpus cavernosum. If sympathomimetic fails or the patient has IP from 24 to 48h, surgical shunts should be performed. It is recommended that distal shunts should be attempted first. If distal shunt failed, proximal, venous shunt, or T-shunt with tunneling could be performed. If the patient had IP for 48 to 72h, proximal and venous shunt or T-shunt with tunneling is indicated, if those therapies failed, a penile prosthesis should be inserted. Non-ischemic priapism (NIP) is not a medical emergency and many patients will recover spontaneously. If the NIP does not resolve spontaneously within six months or the patient requests therapy, selective arterial embolization is indicated. The goal of the management of a patient with stuttering priapism (SP) is the prevention of future episodes. Phosphodiesterase type 5 (PDE5) inhibitor therapy is considered an effective tool to prevent stuttering episodes but it is not validated yet. The management of priapism should follow the guidelines as the future erectile function is dependent on its quick resolution. This review briefly discusses the types, pathophysiology, and diagnosis of priapism. It will discuss an updated approach to treat each type of priapism.

Medical treatment of recurrent ischaemic priapism: a review of current molecular therapeutics and a new clinical management paradigm

OBJECTIVES

To examine the current molecular therapeutics in the medical treatment of recurrent ischemic priapism (RIP). To propose a stepwise clinical management paradigm for the treatment of RIP.

METHODS

We performed a literature search using the PubMed database for the terms 'recurrent ischemic priapism' and 'stuttering priapism' up until December 2020. We assessed pre-clinical and clinical studies regarding medical management of RIP and molecular pathophysiology. Case series and randomized trials were evaluated by study quality and patient outcomes to determine a potential clinical management scheme.

RESULTS

Recent research has fostered an improved understanding of the underlying molecular pathophysiology of RIP that has paved the way forward for developing new therapeutic agents. Medications targeting neurovascular, hormonal and haematological mechanisms associated with RIP show great promise towards remedying this condition. A host of therapeutic agents operating across different mechanistic directions may be implemented according to a clinical management scheme to potentially optimize RIP outcomes.

CONCLUSION

RIP remains a medically neglected condition with current management focused on treating the acute condition rather than modulating the course of disease. Continued research into the molecular mechanisms of RIP and standardized clinical pathways can improve the quality of care for patients suffering from this condition.

Essential thrombocythemia with (type2) calreticulin presented as stuttering priapism case report and review of literature

Priapism is a rare presentation and complication of ET that might be underreported. In ET, priapism can present as an ischemic or stuttering type. These patients are more likely to be anemic and have a high platelet count.

The management of stuttering priapism

INTRODUCTION

Stuttering priapism is a variation of ischemic priapism, generally transient and self-limiting, occurring during sleep and lasting less than 3-4 hours. It may progress to episodes of complete ischemic priapism in approximately one third of cases, necessitating emergent intervention.

EVIDENCE ACQUISITION

This review aims to provide an up-to-date picture of the pathophysiology and management of stuttering priapism. A search using Medline and EMBASE for relevant publications using the terms "priapism", "stuttering", "diagnosis", "treatment", "fibrosis", was performed.

EVIDENCE SYNTHESIS

Stuttering priapism shares its etiologies with ischemic priapism and a large number of diseases or clinical situations have risk association for developing the disorder. The most common causes are sickle cell disease or other hematologic and coagulative dyscrasias especially in children. In the adult population, idiopathic priapism occurring without any discernible cause is considered to be the most common form in adults. The medical management of priapism represents a therapeutic challenge to urologists. Unfortunately, although numerous medical treatment options have been reported, the majority are through small trials or anecdotal reports. Understanding the underlying pathophysiology and understanding the current and emerging future agents and therapeutic options are mandatory in order to provide the best solution for each patient.

CONCLUSIONS

The goal of management of priapism is to achieve detumescence of the persistent erection in order to preserve erectile function. To achieve successful management, urologists should address this emergency clinical condition. In the present article, we review the diagnosis and clinical management of the three types of priapism.

The Role of Phosphodiesterase Inhibitors in the Management of Cavernositis With Multifocal Abscesses: A Report of Case Series

Introduction

Cavernositis is a rare acute infection of the corporal bodies of the penis. It might result in corporal cavernosal abscesses, fibrosis, and subsequently erectile dysfunction if the treatment is inadequate. Previous reports advocate penile aspiration when cavernosal abscesses were significantly present.

Aim

We report 2 cases of cavernositis treated by the standard antimicrobial therapy in addition to the daily use of phosphodiesterase type 5 inhibitors (iPDE-5).

Methods

We include 2 patients who fulfill the criteria for the diagnosis of cavernositis. They were diagnosed clinically based on history and physical examination. Patient 1 had multifocal abscesses on initial penile contrast-enhanced magnetic resonance imaging (MRI). This patient showed rapid clinical improvement with the addition of phosphodiesterase inhibitor (PDEi) to the antimicrobial therapy without the need for surgical drainage of the abscesses. Patient 2 had persistent infection despite 3 weeks of oral second-generation cephalosporin (Cefuroxime). But he showed significant clinical improvement after being started on PDEi in conjunction with the current antimicrobial therapy. Follow-up after 3 months by clinical examination and penile magnetic resonance imaging in both patients showed normal erectile function with no scarring.

Conclusion

PDEi have promising results on disease progression and outcomes. It synergizes the effect of antimicrobial therapy and can potentially reduce the residual corporal fibrosis and erectile dysfunction. However, large studies are required to validate and generalize this treatment approach.

Bakhsh A, Daqqaq T, Alhasan A, et al. The Role of Phosphodiesterase Inhibitors in the Management of Cavernositis With Multifocal Abscesses: A Report of Case Series. Sex Med 2020;8:318–322.

Mechanisms underlying priapism in sickle cell disease: targeting and key innovations on the preclinical landscape

Introduction: Priapism is prolonged penile erection in the absence of sexual arousal or desire and is a devastating condition affecting millions of patients with sickle cell disease (SCD) globally. Available drug treatments for SCD-related priapism remain limited and have been primarily reactive rather than preventive. Hence, there is an unmet need for new drug targets and pharmacologic therapies.Areas covered: We examine the molecular mechanisms underlying SCD-associated priapism evaluated mostly in animal models. In mouse models of SCD, molecular defects of priapism operating at the cavernous tissue level include reduced tonic NO/cGMP signaling, elevated oxidative/nitrosative stress, vascular adhesion molecule derangements, excessive adenosine and opiorphin signaling, dysregulated vasoconstrictive RhoA/ROCK signaling, and testosterone deficiency. We discuss the consequences of downregulated cGMP-dependent phosphodiesterase type 5 (PDE5) activity in response to these molecular signaling derangements, as the main effector mechanism causing unrestrained cavernous tissue relaxation that results in priapism.Expert opinion: Basic science studies are crucial for understanding the underlying pathophysiology of SCD-associated priapism. Understanding the molecular mechanisms could unearth new therapeutic targets for this condition based on these mechanisms. Treatment options should aim to improve deranged erection physiology regulatory signaling to prevent priapism and potentially restore or preserve erectile function.

Development of novel phosphodiesterase 5 inhibitors for the therapy of Alzheimer's disease

Nitric oxide (NO) is a gaseous molecule that plays a multifactorial role in several cellular processes. In the central nervous system, the NO dual nature in neuroprotection and neurotoxicity has been explored to unveil its involvement in Alzheimer's disease (AD). A growing body of research shows that the activation of the NO signaling pathway leading to the phosphorylation of the transcription factor cyclic adenine monophosphate responsive element binding protein (CREB) (so-called NO/cGMP/PKG/CREB signaling pathway) ameliorates altered neuroplasticity and memory deficits in AD animal models. In addition to NO donors, several other pharmacological agents, such as phosphodiesterase 5 (PDE5) inhibitors have been used to activate the pathway and rescue memory disorders. PDE5 inhibitors, including sildenafil, tadalafil and vardenafil, are marketed for the treatment of erectile dysfunction and arterial pulmonary hypertension due to their vasodilatory properties. The ability of PDE5 inhibitors to interfere with the NO/cGMP/PKG/CREB signaling pathway by increasing the levels of cGMP has prompted the hypothesis that PDE5 inhibition might be used as an effective therapeutic strategy for the treatment of AD. To this end, newly designed PDE5 inhibitors belonging to different chemical classes with improved pharmacologic profile (e.g. higher potency, improved selectivity, and blood-brain barrier penetration) have been synthesized and evaluated in several animal models of AD. In addition, recent medicinal chemistry effort has led to the development of agents concurrently acting on the PDE5 enzyme and a second target involved in AD. Both marketed and investigational PDE5 inhibitors have shown to reverse cognitive defects in young and aged wild type mice as well as transgenic mouse models of AD and tauopathy using a variety of behavioral tasks. These studies confirmed the therapeutic potential of PDE5 inhibitors as cognitive enhancers. However, clinical studies assessing cognitive functions using marketed PDE5 inhibitors have not been conclusive. Drug discovery efforts by our group and others are currently directed towards the development of novel PDE5 inhibitors tailored to AD with improved pharmacodynamic and pharmacokinetic properties. In summary, the present perspective reports an overview of the correlation between the NO signaling and AD, as well as an outline of the PDE5 inhibitors used as an alternative approach in altering the NO pathway leading to an improvement of learning and memory. The last two sections describe the preclinical and clinical evaluation of PDE5 inhibitors for the treatment of AD, providing a comprehensive analysis of the current status of the AD drug discovery efforts involving PDE5 as a new therapeutic target.

Phosphodiesterase inhibitors say NO to Alzheimer's disease

Phosphodiesterases (PDEs) consisted of 11 subtypes (PDE1 to PDE11) and over 40 isoforms that regulate levels of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), the second messengers in cell functions. PDE inhibitors (PDEIs) have been attractive therapeutic targets due to their involvement in diverse medical conditions, e.g. cardiovascular diseases, autoimmune diseases, Alzheimer's disease (AD), etc. Among them; AD with a complex pathology is a progressive neurodegenerative disorder which affect mostly senile people in the world and only symptomatic treatment particularly using cholinesterase inhibitors in clinic is available at the moment for AD. Consequently, novel treatment strategies towards AD are still searched extensively. Since PDEs are broadly expressed in the brain, PDEIs are considered to modulate neurodegenerative conditions through regulating cAMP and cGMP in the brain. In this sense, several synthetic or natural molecules inhibiting various PDE subtypes such as rolipram and roflumilast (PDE4 inhibitors), vinpocetine (PDE1 inhibitor), cilostazol and milrinone (PDE3 inhibitors), sildenafil and tadalafil (PDE5 inhibitors), etc have been reported showing encouraging results for the treatment of AD. In this review, PDE superfamily will be scrutinized from the view point of structural features, isoforms, functions and pharmacology particularly attributed to PDEs as target for AD therapy.

New Nitric Oxide Donor NCX 1443: Therapeutic Effects on Pulmonary Hypertension in the SAD Mouse Model of Sickle Cell Disease

Nitric oxide (NO) donors may be useful for treating pulmonary hypertension (PH) complicating sickle cell disease (SCD), as endogenous NO is inactivated by hemoglobin released by intravascular hemolysis. Here, we investigated the effects of the new NO donor NCX1443 on PH in transgenic SAD mice, which exhibit mild SCD without severe hemolytic anemia. In SAD and wild-type (WT) mice, the pulmonary pressure response to acute hypoxia was similar and was abolished by 100 mg/kg NCX1443. The level of PH was also similar in SAD and WT mice exposed to chronic hypoxia (9% O2) alone or with SU5416 and was similarly reduced by daily NCX1443 gavage. Compared with WT mice, SAD mice exhibited higher levels of HO-1, endothelial NO synthase, and PDE5 but similar levels of lung cyclic guanosine monophosphate. Cultured pulmonary artery smooth muscle cells from SAD mice grew faster than those from WT mice and had higher PDE5 protein levels. Combining NCX1443 and a PDE5 inhibitor suppressed the growth rate difference between SAD and WT cells and induced a larger reduction in hypoxic PH severity in SAD than in WT mice. By amplifying endogenous protective mechanisms, NCX1443 in combination with PDE5 inhibition may prove useful for treating PH complicating SCD.

Daily use of phosphodiesterase type 5 inhibitors as prevention for recurrent priapism

Summary Objective: The pathogenesis of recurrent priapism is currently being investigated based on the regulation of the phosphodiesterase 5 (PDE5) enzyme. We explored the daily use of PDE5 inhibitors to treat and prevent priapism recurrences. Method: We administered PDE5 inhibitors using a long-term therapeutic regimen in seven men with recurrent priapism, with a mean age of 29.2 years (range 21 to 35 years). Six men (85.7%) had idiopathic priapism recurrences and one man (24.3%) had sickle cell disease-associated priapism recurrences. Tadalafil 5 mg was administered daily. The mean follow-up was 6.6 months (range 3 to 12 months). Results: Daily long-term oral PDE5 inhibitor therapy alleviated priapism recurrences in all patients. Five (71.4%) had no episodes of priapism and two (28.6%) referred decrease in their episodes of priapism. All patients referred improvement in erectile function. Conclusion: These findings suggest the hypothesis that PDE5 dysregulation exerts a pathogenic role for both sickle cell disease-associated priapism and for idiopathic priapism, and that it offers a molecular target for the therapeutic management of priapism. These preliminary observations suggest that continuous long-term oral PDE5 inhibitor therapy may treat and prevent recurrent priapism.

Contemporary best practice in the evaluation and management of stuttering priapism

Stuttering priapism is rare and under-investigated clinical entity. Although it shares similarities with ischaemic priapism, by definition, stuttering priapism has distinct characteristics that advocate for a different management in the clinical setting. Therefore, the management of stuttering priapism aims primarily to prevent recurrence rather than the resolution of spontaneous attacks. A multimodal approach and the individualization of each case are essential because of the diversity of the condition and the plethora of proposed therapeutic strategies. Understanding the underlying pathophysiology and familiarity with contemporary, past and emerging future agents and therapeutic options are required in order to provide an optimal solution for each patient. In addition, patient counselling and the option to combine therapeutic strategies and challenge second-line therapies are essential weapons in the armament of the urologist. Although further clinical trials and studies are mandatory in order to obtain solid data and provide recommendations, all therapeutic options are analysed, with specific interest in the potential advantages and disadvantages. A structured evaluation procedure is also described.

The Case Report of Priapus and a Modern Approach to an Ancient Affliction

INTRODUCTION

Priapism, taking its name from God Priapus, is total or partial erection lasting longer than 4 hours independent of sexual stimulus and can result in erectile dysfunction. There are three subtypes of priapism.

AIM

To review the three subtypes of priapism, their pathophysiology, current treatment options, and complications.

METHODS

The literature including priapism guidelines, review articles, and current trial studies was reviewed and the priapism type of God Priapus was investigated according to the mythology.

MAIN OUTCOME MEASURES

All three types of priapism were reviewed for etiology, diagnosis, and management. Medical and surgical treatment options were reviewed in relation to the current literature. Special emphasis concerned current treatment strategies and controversial surgical topics.

RESULTS

Ischemic priapism is the most common type, constituting 95% of all cases, and is an emergency. First-line treatments are blood aspiration and intracavernosal sympathomimetic drug injections. If these fail, then surgical shunt operations are recommended. A T-shunt combined with corporal tunneling is the currently popular option. Immediate penile prosthesis implantation is recommended for patients who present 48 to 72 hours after the onset of a priapism episode. High-flow priapism is caused by irregular arterial cavernosal blood flow, which usually occurs after a blunt perineal trauma. Antiandrogens and selective arterial embolization are the treatment options. Stuttering priapism is repetitive, self-limiting ischemic priapism and frequent in patients with sickle cell anemia. Ketoconazole is safe, cheap, and effective and appears to be a logical and suitable current treatment option to prevent further episodes, which is the primary treatment goal of stuttering priapism.

CONCLUSION

Priapism is a relatively common condition but not well known by clinicians. The lack and delay of treatment result in irreversible complications such as erectile dysfunction. Each type of priapism should be diagnosed and treated correctly with caution.

Clinical and preclinical treatment of urologic diseases with phosphodiesterase isoenzymes 5 inhibitors: an update

Phosphodiesterase isoenzymes 5 inhibitors (PDE5-Is) are the first-line therapy for erectile dysfunction (ED). The constant discoveries of nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) cell-signaling pathway for smooth muscle (SM) control in other urogenital tracts (UGTs) make PDE5-Is promising pharmacologic agents against other benign urological diseases. This article reviews the literature and contains some previously unpublished data about characterizations and activities of PDE5 and its inhibitors in treating urological disorders. Scientific discoveries have improved our understanding of cell-signaling pathway in NO/cGMP-mediated SM relaxation in UGTs. Moreover, the clinical applications of PDE5-Is have been widely recognized. On-demand PDE5-Is are efficacious for most cases of ED, while daily-dosing and combination with testosterone are recommended for refractory cases. Soluble guanylate cyclase (sGC) stimulators also have promising role in the management of severe ED conditions. PDE5-Is are also the first rehabilitation strategy for postoperation or postradiotherapy ED for prostate cancer patients. PDE5-Is, especially combined with α-adrenoceptor antagonists, are very effective for benign prostatic hyperplasia (BPH) except on maximum urinary flow rate (Q max ) with tadalafil recently proved for BPH with/without ED. Furthermore, PDE5-Is are currently under various phases of clinical or preclinical researches with promising potential for other urinary and genital illnesses, such as priapism, premature ejaculation, urinary tract calculi, overactive bladder, Peyronie's disease, and female sexual dysfunction. Inhibition of PDE5 is expected to be an effective strategy in treating benign urological diseases. However, further clinical studies and basic researches investigating mechanisms of PDE5-Is in disorders of UGTs are required.

Useful Implications of Low-dose Long-term Use of PDE-5 Inhibitors

INTRODUCTION

Phosphodiesterase type 5 (PDE-5) hydrolyzes cyclic guanylate monophosphate (cGMP) specifically to 5' GMP, promoting successful corporeal vascular relaxation and penile erection during sexual stimulation. Oral PDE-5 inhibitors such as sildenafil, vardenafil, tadalafil, and avanafil have provided noninvasive, effective, well-tolerated treatment for erectile dysfunction (ED) patients and, at the same time, stimulated both academic and clinical interests. Lately, some oral PDE-5 inhibitors were released as low-dose preparations with the concept of potential daily administration and long-term use.

AIM

To highlight the possible potential implications of low-dose long-term use of PDE-5 inhibitors.

METHOD

A systematic review was carried out until December 2015 based on a search of all concerned articles in MEDLINE, medical subjects heading (MeSH) databases, Scopus, The Cochrane Library, EMBASE, and CINAHL databases without language restriction. Key words used to assess the outcome and estimates for concerned associations were: PDE-5 inhibitors; erectile dysfunction; low-dose; long-term; sildenafil; tadalafil; vardenafil; avanafil.

MAIN OUTCOME MEASURES

Demonstrating different implications for low-dose long-term use of PDE-5 inhibitors.

RESULTS

Low-dose and/or long-term use of PDE-5 inhibitors was shown to put forth beneficial sound effects in different medical implications with potentials that could be extended for different utilities. These implications included sexual, urogenital, cardiovascular, pulmonary, cutaneous, gastrointestinal, and reproductive, as well as neurological disorders. However, it is evident that most potential appliances were carried out experimentally on preclinical studies with off-label indications.

CONCLUSION

Making use of and exploring low-dose and/or long-term use of several PDE-5 inhibitors for their possible implications seem to be valuable in different medical disorders. Increased knowledge of the drug characteristics, comparative treatment regimens, optimal prescribing patterns, and well-designed clinical trials are needed before these agents can be recommended for use.

Clinical Management of Priapism: A Review

Priapism is defined as a persistent and painful erection lasting longer than four hours without sexual stimulation. Based on episode history and pathophysiology, priapism is classified into three subtypes: ischemic (low-flow), non-ischemic (high-flow), and stuttering priapism. Ischemic priapism is characterized by a persistent, painful erection with remarkable rigidity of the corpora cavernosa caused by a disorder of venous blood outflow from this tissue mass, and is similar to penile compartment syndrome. Stuttering priapism is characterized by a self-limited, recurrent, and intermittent erection, frequently occurring in patients with sickle cell disease. Non-ischemic priapism is characterized by a painless, persistent nonsexual erection that is not fully rigid and is caused by excess arterial blood flow into the corpora cavernosa. Because ischemic and non-ischemic priapism differ based on emergency status and treatment options, appropriate discrimination of each type of priapism is required to initiate adequate clinical management. The goal of management of priapism is to achieve detumescence of the persistent penile erection and to preserve erectile function after resolution of the priapism. To achieve successful management, urologists should address this emergency clinical condition. In the present article, we review the diagnosis and clinical management of the three types of priapism.

Case Report: Conversion of a Low-Flow to High-Flow Priapism

Priapism is defined as an erection lasting for more than 4 hours and can be grouped into 3 distinct subtypes: ischemic (low-flow), stuttering and non-ischemic (high-flow). Herein, we present an interesting case of conversion from a low-flow to high-flow priapism after a distal shunting procedure. This is a rare phenomenon that has a paucity of documented cases. Diagnosis requires prompt clinical suspicion and confirmatory testing including penile cavernosal blood gases and Doppler ultrasound.

[Priapism: Current diagnostics and therapy]

Priapism is characterized by involuntary persistent penile erection after or independent of sexual stimulation. The diagnostic clarification, including patient history, physical findings, duplex ultrasonography and analysis of blood gases is decisive for the underlying pathophysiology and the appropriate therapeutic procedure. Non-hypoxic and non-acidotic blood gas parameters enable a conservative approach, hypoxic, hypercarbic and acidotic parameters may lead to fibrosis of the corpora cavernosa and, in turn, to a loss of penile function. Low-flow or ischemic (veno-occlusive) priapism is an emergency situation and can lead to irreversible erectile dysfunction within 4 h. Treatment consists of blood aspiration and possibly intracavernosal injection of sympathomimetic drugs. A distal shunt is necessary in the case of treatment failure (in rare cases a proximal shunt). Management of recurrent priapism (stuttering) includes self-injection of sympathomimetic drugs and preventive long-term administration of erection inhibitory and erection promoting substances. This concept still needs to be validated. High-flow or non-ischemic priapism does not necessitate immediate treatment measures and should be kept under observation. In cases of a detectable fistula selective artery embolization is often a successful option.

Management of Recurrent Ischemic Priapism 2014: A Complex Condition with Devastating Consequences

INTRODUCTION

The management of recurrent ischemic priapism (RIP) is not clearly defined. Given the rarity of this condition, most treatment options are supported at best by level 3 or 4 evidence.

AIM

In this article, we review the current literature regarding the pathophysiology and management of RIP and discuss the risks and benefits associated with each option, which includes ketoconazole (KTZ), 5-α-reductase inhibitors and other hormonal therapies, phosphodiesterase type 5 (PDE5) inhibitors, intracavernosal sympathomimetic injection, oral sympathomimetic agents, and other investigational therapies.

METHODS

A comprehensive literature review was performed regarding the management options for RIP.

MAIN OUTCOME MEASURE

To examine the pathophysiology of RIP and evaluate the treatment options.

RESULTS

Multiple agents have been investigated to manage RIP. KTZ, finasteride, anti-androgens, gonadotropin-releasing hormone agonists, and estrogen have been shown to be effective in several reports, though some of these agents may have significant hormonal side effects. PDE5 inhibitors currently appear to be well tolerated in this patient population, though evidence of its efficacy is limited. Intracavernosal α-agonist therapy may be used to treat episodes of priapism after they occur. Very limited data suggest terbutaline, oral α-agonists, digoxin, hydroxyurea, and gabapentin may have a role in RIP management.

CONCLUSIONS

An ideal management strategy for RIP should focus on prevention of priapic episodes using an effective, well-tolerated, cost-effective medication. We currently have several proposed options, with varying efficacy rates and side effect profiles. While significant advancements in our understanding and management of stuttering priapism have been made within the past few years, clearly continuing research and clinical studies are needed to guide our management of this disease process. Hoeh MP and Levine LA. Management of recurrent ischemic priapism 2014: A complex condition with devastating consequences. Sex Med Rev 2015;3:24-35.

Subacute Hemolysis in Sickle Cell Mice Causes Priapism Secondary to NO Imbalance and PDE5 Dysregulation

INTRODUCTION

Recent research suggests that priapism in sickle cell disease (SCD) is due to dysregulation of penile erection homeostasis including alteration of nitric oxide synthase (NOS) and phosphodiesterase type 5 (PDE5) activities by excessive levels of reactive oxygen species (ROS) released during hemolysis. It is unknown if subacute exposure to hemolysis is sufficient or if chronic reconditioning of erectile tissues is required for perturbation of homeostatic pathways and whether PDE5 inhibitor (PDE5I) treatment can restore erectile homeostasis in the subacute setting.

AIMS

The aim of this study was to investigate the effects of subacute hemolysis (3-month exposure) on priapism and NO pathway regulation.

METHODS

Mice underwent bone marrow transplantation with either SCD (BM-SS) or wild-type (WT) bone marrow. BM-SS mice were treated with sildenafil 100 mg/kg/day. We measured intracavernous pressure (ICP) measurements with or without cavernous nerve stimulation following bone marrow transplantation to assess for priapism.

MAIN OUTCOME MEASURES

ICP and frequency of erections were assessed. Penile tissues were analyzed for NOS, protein kinase G (PKG), PDE5, and ROS activities.

RESULTS

BM-SS mice demonstrated a priapism phenotype. PDE5I treatment reduced the frequency of erections in BM-SS mice (1.7 ± 1.1 vs. 5.5 ± 2.8 erections per hour, P < 0.05). Penile tissues from BM-SS mice demonstrated decreased NOS, PKG, PDE5 and elevated ROS activities compared with that of control mice. PDE5I treatment increased NOS (11.6 ± 1.3% vs. 7.8 ± 2.3%, P < 0.05) and PDE5 (76.3 ± 9.8% vs. 52.3 ± 11.1%, P < 0.05) activities and decreased ROS activity (137.8 ± 12.1% vs. 199.1 ± 11.3%, P < 0.05) compared with non-PDE5I treated BM-SS mice. PKG activity was increased beyond control levels with PDE5I treatment (158.4 ± 10.3%, P < 0.05).

CONCLUSION

Short-term hemolysis is sufficient to establish a priapism phenotype and results in loss of erectile function. PDE5I treatment ameliorates priapism, in part, because of restored NO balance with decreased ROS generation and increased PDE5 activity.

Nitrergic Mechanisms for Management of Recurrent Priapism

INTRODUCTION

Priapism is a condition involving prolonged penile erection unrelated to sexual interest or desire. The ischemic type, including its recurrent variant, is often associated with both physical and psychological complications. As such, management is of critical importance. Ideal therapies for recurrent priapism should address its underlying pathophysiology.

AIM

To review the available literature on priapism management approaches particularly related to nitrergic mechanisms.

METHODS

A literature review of the pathophysiology and management of priapism was performed using PubMed.

MAIN OUTCOME MEASURE

Publications pertaining to mechanisms of the molecular pathophysiology of priapism.

RESULTS

Nitrergic mechanisms are characterized as major players in the molecular pathophysiology of priapism. PDE5 inhibitors represent an available therapeutic option with demonstrated ability in attenuating these underlying nitrergic derangements. Several additional signaling pathways have been found to play a role in the molecular pathophysiology of priapism and have also been associated with these nitrergic mechanisms.

CONCLUSION

An increasing understanding of the molecular pathophysiology of priapism has led to the discovery of new potential targets. Several mechanism-based therapeutic approaches may become available in the future.

How I treat priapism

Priapism is a disorder of persistent penile erection unrelated to sexual interest or desire. This pathologic condition, specifically the ischemic variant, is often associated with devastating complications, notably erectile dysfunction. Because priapism demonstrates high prevalence in patients with hematologic disorders, most commonly sickle cell disease (SCD), there is significant concern for its sequelae in this affected population. Thus, timely diagnosis and management are critical for the prevention or at least reduction of cavernosal tissue ischemia and potential damage consequent to each episode. Current guidelines and management strategies focus primarily on reactive treatments. However, an increasing understanding of the molecular pathophysiology of SCD-associated priapism has led to the identification of new potential therapeutic targets. Future agents are being developed and explored for use in the prevention of priapism.

Erectile dysfunction after sickle cell disease-associated recurrent ischemic priapism: profile and risk factors

INTRODUCTION

Risk factors associated with erectile dysfunction (ED) that results from recurrent ischemic priapism (RIP) in sickle cell disease (SCD) are incompletely defined.

AIM

This study aims to determine and compare ED risk factors associated with SCD and non-SCD-related "minor" RIP, defined as having ≥2 episodes of ischemic priapism within the past 6 months, with the majority (>75%) of episodes lasting <5 hours.

METHODS

We performed a retrospective study of RIP in SCD and non-SCD patients presenting from June 2004 to March 2014 using the International Index of Erectile Function (IIEF), IIEF-5, and priapism-specific questionnaires.

MAIN OUTCOME MEASURES

Prevalence rates and risk factor correlations for ED associated with RIP.

RESULTS

The study was comprised of 59 patients (40 SCD [mean age 28.2 ± 8.9 years] and 19 non-SCD [15 idiopathic and four drug-related etiologies] [mean age 32.6 ± 11.7 years]). Nineteen of 40 (47.5%) SCD patients vs. four of 19 (21.1%) non-SCD patients (39% overall) had ED (IIEF <26 or IIEF-5 <22) (P = 0.052). SCD patients had a longer mean time-length with RIP than non-SCD patients (P = 0.004). Thirty of 40 (75%) SCD patients vs. 10 of 19 (52.6%) non-SCD patients (P = 0.14) had "very minor" RIP (episodes regularly lasting ≤2 hours). Twenty-eight of 40 (70%) SCD patients vs. 14 of 19 (73.7%) non-SCD patients had weekly or more frequent episodes (P = 1). Of all patients with very minor RIP, ED was found among 14 of 30 (46.7%) SCD patients vs. none of 10 (0%) non-SCD patients (P = 0.008). Using logistic regression analysis, the odds ratio for developing ED was 4.7 for SCD patients, when controlling for RIP variables (95% confidence interval: 1.1-21.0).

CONCLUSIONS

ED is associated with RIP, occurring in nearly 40% of affected individuals overall. SCD patients are more likely to experience ED in the setting of "very minor" RIP episodes and are five times more likely to develop ED compared with non-SCD patients.

Management of priapism: an update for clinicians

Priapism is a prolonged erection that persists beyond or is unrelated to sexual stimulation. It is associated with significant morbidity: psychological, socioeconomic, and physical, including pain and potentially irreversible compromise of erectile function. There are three major types of priapism: ischemic, nonischemic, and stuttering. Establishing the type of priapism is paramount to safely and effectively treating these episodes. Ischemic priapism represents a urological emergency. Its treatment may involve aspiration/irrigation with sympathomimetic injections, surgical shunts, and as a last resort, penile prosthesis implantation. Nonischemic priapism results from continuous flow of arterial blood into the penis, most commonly related to penile trauma. This is not an emergency and may be managed conservatively initially, as most of these episodes are self-limiting. Stuttering priapism involves recurrent self-limiting episodes of ischemic priapism. The primary goal of therapy is prevention, but acute episodes should be managed in accordance with guidelines for ischemic priapism. In this paper we review the diagnosis and treatment of the three priapism variants, as well as discuss future targets of therapy and novel targets on the horizon.

Randomized controlled trial of sildenafil for preventing recurrent ischemic priapism in sickle cell disease

BACKGROUND

Successful preventive therapy for ischemic priapism, a disorder of penile erection with major physical and psychologic consequences, is limited. We conducted a randomized, double-blind, placebo-controlled clinical trial to assess the efficacy and safety of sildenafil by a systematic dosing protocol to prevent recurrent ischemic priapism associated with sickle cell disease.

METHODS

Thirteen patients with sickle cell disease reporting priapism recurrences at least twice weekly were randomized to receive sildenafil 50 mg or placebo daily, unassociated with sleep or sexual activity, for 8 weeks, followed by open-label use of this sildenafil regimen for an additional 8 weeks.

RESULTS

Priapism frequency reduction by 50% did not differ between sildenafil and placebo groups by intention-to-treat or per protocol analyses (P = 1.0). However, during open-label assessment, 5 of 8 patients (62.5%) by intention-to-treat analysis and 2 of 3 patients (66.7%) by per protocol analysis met this primary efficacy outcome. No significant differences were found between study groups in rates of adverse effects, although major priapism episodes were decreased 4-fold in patients monitored "on-treatment."

CONCLUSIONS

Sildenafil use by systematic dosing may offer a strategy to prevent recurrent ischemic priapism in patients with sickle cell disease.

Sildenafil promotes eNOS activation and inhibits NADPH oxidase in the transgenic sickle cell mouse penis

INTRODUCTION

Sickle cell disease (SCD)-associated vasculopathy in the penis is characterized by aberrant nitric oxide and phosphodiesterase (PDE) 5 signaling, and by increased oxidative stress. Preliminary clinical trials show that continuous treatment with PDE5 inhibitor sildenafil unassociated with sexual activity decreases priapic activity in patients with SCD. However, the mechanism of its vasculoprotective effect in the penis remains unclear.

AIMS

We evaluated whether continuous administration of PDE5 inhibitor sildenafil promotes eNOS function at posttranslational levels and decreases superoxide-producing enzyme NADPH oxidase activity in the sickle cell mouse penis.

METHODS

SCD transgenic mice were used as an animal model of SCD. WT mice served as controls. Mice received treatment with the PDE5 inhibitor sildenafil (100 mg/kg/day) or vehicle for 3 weeks. eNOS phosphorylation on Ser-1177 (positive regulatory site), eNOS interactions with heat-shock protein 90 (HSP90) (positive regulator), phosphorylated AKT (upstream mediator of eNOS phosphorylation on Ser-1177), an NADPH oxidase catalytic subunit gp91(phox), and a marker of oxidative stress (4-hydroxy-2-nonenal [HNE]) were measured by Western blot.

MAIN OUTCOME MEASURES

Effect of continuous sildenafil treatment on eNOS posttranslational activation, NADPH oxidase catalytic subunit, and oxidative stress in the penis of the sickle cell mouse.

RESULTS

Continuous treatment with sildenafil reversed (P < 0.05) the abnormalities in protein expressions of P-eNOS (Ser-1177), eNOS/HSP90 interaction, P-AKT, protein expression of gp91(phox), and 4-HNE, in the sickle cell mouse penis. Sildenafil treatment of WT mice did not affect any of these parameters.

CONCLUSION

Our findings that sildenafil enhances eNOS activation and inhibits NADPH oxidase function in the sickle cell mouse penis offers a vasculoprotective molecular basis for the therapeutic effect of sildenafil in the penis in association with SCD.

Prostate cancer risk after anti-androgen treatment for priapism

BACKGROUND

Patients with recurrent ischemic priapism have historically been treated with anti-androgen therapy due to the limited available evidence for more targeted therapies to treat the underlying pathophysiologic mechanisms of this condition. We report a case in which anti-androgen therapy caused significant adverse side effects and likely masked this patient's elevated prostate-specific antigen (PSA) levels, which adversely impacted the timely diagnosis and treatment of his prostate cancer.

CASE REPORT

A 69-year-old man treated with anti-androgens for priapism initially developed unwanted anti-androgenic side effects such as gynecomastia, erectile dysfunction, and decreased libido. After decreasing his anti-androgen dosage and starting a specified regimen of phosphodiesterase type 5 inhibitor therapy, his serum PSA levels were found to be elevated. He was subsequently diagnosed with adenocarcinoma of the prostate and underwent a radical prostatectomy with the pathologic finding of high-grade, locally progressive disease.

CONCLUSION

Anti-androgen therapy carries significant complication risks, including the potential to alter the diagnosis and treatment of prostate cancer. Clinicians administering this therapy for priapism management should be aware of these possible risks.

Sustained nitric oxide (NO)-releasing compound reverses dysregulated NO signal transduction in priapism

We evaluated the therapeutic potential of a sustained nitric oxide (NO)-releasing compound to correct the molecular hallmarks and pathophysiology of priapism, an important but poorly characterized erectile disorder. 1,5-Bis-(dihexyl-N-nitrosoamino)-2,4-dinitrobenzene (C6') and an inactive form of the compound [1,5-bis-(dihexylamino)-2,4-dinitrobenzene (C6)] were tested in neuronal cell cultures and penile lysates for NO release (Griess assay) and biological activity (cGMP production). The effect of local depot C6' or C6 was evaluated in mice with a priapic phenotype due to double neuronal and endothelial NO synthase deletion (dNOS(-/-)) or human sickle hemoglobin transgenic expression (Sickle). Changes in NO signaling molecules and reactive oxygen species (ROS) surrogates were assessed by Western blot. The physiological response after C6' treatment was assessed using an established model of electrically stimulated penile erection. C6' generated NO, increased cGMP, and dose dependently increased NO metabolites. C6' treatment reversed abnormalities in key penile erection signaling molecules, including phosphodiesterase type 5, phosphorylated endothelial nitric oxide synthase, and phosphorylated vasodilator-stimulated phosphoprotein. In Sickle mice, C6' also attenuated the increased ROS markers gp91(phox), 4-hydroxynonenal, and 3-nitrotyrosine. Finally, C6' corrected the excessive priapic erection response of dNOS(-/-) mice. Exogenous sustained NO release from C6' corrects pathological erectile signaling in mouse models of priapism and suggests novel approaches to human therapy.

Sildenafil citrate-restored eNOS and PDE5 regulation in sickle cell mouse penis prevents priapism via control of oxidative/nitrosative stress

Sildenafil citrate revolutionized the practice of sexual medicine upon its federal regulatory agency approval approximately 15 years ago as the prototypical phosphodiesterase type 5 inhibitor indicated for the treatment of male erectile dysfunction. We now provide scientific support for its alternative use in the management of priapism, a clinical disorder of prolonged and uncontrolled penile erection. Sildenafil administered continuously to sickle cell mice, which show a priapism phenotype, reverses oxidative/nitrosative stress effects in the penis, mainly via reversion of uncoupled endothelial nitric oxide synthase to the functional coupled state of the enzyme, which in turn corrects aberrant signaling and function of the nitric oxide/cyclic GMP/protein kinase G/phosphodiesterase type 5 cascade. Priapism tendencies in these mice are reverted partially toward normal neurostimulated erection frequencies and durations after sildenafil treatment in association with normalized cyclic GMP concentration, protein kinase G activity and phosphodiesterase type 5 activity in the penis. Thus, sildenafil exerts pleiotropic effects in the penis that extend to diverse erection disorders.

How I manage priapism due to sickle cell disease

Priapism due to sickle cell disease is a common but less well characterized complication of the disorder. It represents a "medical emergency" with the key determinant of outcome being the duration of penile ischaemia and time to detumescence of <4 h associated with a successful treatment outcome. Management can be outpatient-based and consists of pre-emptive strategies for early stuttering attacks based on prior health education of the association between the 2 disorders, non pharmacological management, outpatient penile aspiration and irrigation with or without instillation of alpha and beta adrenergic agonists for acute episodes and secondary prophylaxis to prevent the high rates of recurrences. The evidence to recommend medical prophylaxis is sparse but based on a consensus of experts and small phase 2 or III clinical trials. A clearer understanding of the molecular mechanism(s) involving normal and dysregulated erectile physiology, scavenger haemolysis and nitric oxide pathway paves way for the use of phosphodiesterase type 5 inhibitors in medical prophylaxis of stuttering attacks. These agents will need to be studied in multi-centre randomized phase III trials before they become standard of care. A multidisciplinary team approach is required to enhance "sexual wellness" and prevent erectile dysfunction in this sexually vulnerable group.

A pathophysiology-based approach to the management of early priapism

Priapism is a rare condition that involves persistent penile erection for greater than 4 h. Distinct variants exist, each with unique characteristics. Ischemic priapism is a painful medical emergency that may occur as a result of veno-occlusion leading to hypoxia and tissue death. Recurrent bouts of ischemic priapism, or stuttering priapism, require treatment for individual attacks as well as long-term prevention. Non-ischemic priapism is associated with trauma and may be managed conservatively. Recent advances into the pathophysiology of priapism have allowed the development of treatment algorithms that specifically target the mechanisms involved. In this review, we outline the basics of smooth muscle contraction and describe how derangement of these pathways results in priapism. A pathophysiological approach to the treatment of priapism is proposed with duration-based algorithms presented to assist in management.

Stuttering priapism: insights into pathogenesis and management

Priapism is defined as a persistent, painful erection that continues beyond, or is unrelated to, sexual stimulation. It may be categorized as either ischemic (low/absent flow) or nonischemic (high flow). Stuttering priapism is a variant of the ischemic type that is characterized by repetitive, transient, painful, self-limiting episodes of priapism. It is associated with various hematological disorders, including sickle cell disease and pharmacological treatments. The consequences of ineffective treatment of priapism are erectile dysfunction and impaired quality of life due to chronic pain and physical disfigurement. Many of the existing medical therapeutic options for treatment of stuttering priapism are nonmechanistic and associated with significant adverse effects. However, the scientific knowledge of stuttering priapism has transitioned in the past few years, from a condition that is poorly understood to one that has borne a burst of evolving molecular science. In this review, the pathophysiology of priapism is discussed, with particular emphasis on new molecular effectors and mechanisms. Novel treatment methods, as well as potential future agents, based on the emerging molecular evidence are discussed.

Unsatisfactory outcomes of prolonged ischemic priapism without early surgical shunts: our clinical experience and a review of the literature

Ischemic priapism is a rare occurrence which can cause severe erectile dysfunction (ED) without timely treatment. This retrospective study reports our experience in treating prolonged ischemic priapism and proposes our further considerations. In this paper, a total of nine patients with prolonged ischemic priapism underwent one to three types of surgical shunts, including nine Winter shunts, two Al-Ghorab shunts and one Grayhack shunt. During the follow-up visit (after a mean of 21.11 months), all patients' postoperative characters were recorded, except one patient lost for death. Six postoperative patients accepted a 25-mg oral administration of sildenafil citrate. The erectile function of the patients was evaluated by their postoperative 5-item version of International Index of Erectile Function Questionnaire (IIEF-5), which were later compared with their premorbid scores. All patients had complete resolutions, and none relapsed. The resolution rate was 100%. Seven patients were resolved with Winter shunts, one with an Al-Ghorab shunt and one with a Grayhack shunt. The mean hospital stay was 8.22 days. There was only one urethral fistula, and the incidence of postoperative ED was 66.67%. Four patients with more than a 72-h duration of priapism had no response to the long-term phosphodiesterase type 5 (PDE-5) inhibitor treatment. These results suggest that surgical shunts are an efficient approach to make the penis flaccid after prolonged priapism. However, the severe ED caused by prolonged duration is irreversible, and long-term PDE-5 inhibitor treatments are ineffective. Thus, we recommend early penile prosthesis surgeries for these patients.

Targeting NADPH oxidase decreases oxidative stress in the transgenic sickle cell mouse penis

INTRODUCTION

Sickle cell disease (SCD) is a state of chronic vasculopathy characterized by endothelial dysfunction and increased oxidative stress, but the sources and mechanisms responsible for reactive oxygen species (ROS) production in the penis are unknown.

AIMS

We evaluated whether SCD activates NADPH oxidase, induces endothelial nitric oxide synthase (eNOS) uncoupling, and decreases antioxidants in the SCD mouse penis. We further tested the hypothesis that targeting NADPH oxidase decreases oxidative stress in the SCD mouse penis.

METHODS

SCD transgenic (sickle) mice were used as an animal model of SCD. Hemizygous (hemi) mice served as controls. Mice received an NADPH oxidase inhibitor apocynin (10 mM in drinking water) or vehicle. Penes were excised at baseline for molecular studies. Markers of oxidative stress (4-hydroxy-2-nonenal [HNE]), sources of ROS (eNOS uncoupling and NADPH oxidase subunits p67(phox) , p47(phox) , and gp91(phox) ), and enzymatic antioxidants (superoxide dismutase [SOD]1, SOD2, catalase, and glutathione peroxidase-1 [GPx1]) were measured by Western blot in penes.

MAIN OUTCOME MEASURES

Sources of ROS, oxidative stress, and enzymatic antioxidants in the SCD penis.

RESULTS

Relative to hemi mice, SCD increased (P<0.05) protein expression of NADPH oxidase subunits p67(phox) , p47(phox) , and gp91(phox) , 4-HNE-modified proteins, induced eNOS uncoupling, and reduced Gpx1 expression in the penis. Apocynin treatment of sickle mice reversed (P<0.05) the abnormalities in protein expressions of p47(phox) , gp91(phox) (but not p67(phox) ) and 4-HNE, but only slightly (P>0.05) prevented eNOS uncoupling in the penis. Apocynin treatment of hemi mice did not affect any of these parameters.

CONCLUSION

NADPH oxidase and eNOS uncoupling are sources of oxidative stress in the SCD penis; decreased GPx1 further contributes to oxidative stress. Inhibition of NADPH oxidase upregulation decreases oxidative stress, implying a major role for NADPH oxidase as a ROS source and a potential target for improving vascular function in the SCD mouse penis.