Oral phosphodiesterase type 5 inhibitors alleviate recurrent priapism complicating thalassemia intermedia: a case report

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.

PDE5 inhibitors and male reproduction: Is there a place for PDE5 inhibitors in infertility clinics or andrology laboratories?

The objective of this review study is to evaluate the therapeutic role of PDE5 inhibitors (PDE5is) in the amelioration of oligoasthenospermia in infertile males. PDE5is have a beneficial influence on the secretory function of the Leydig and Sertoli cells, the biochemical environment within the seminiferous tubule, the contractility of the testicular tunica albuginea, and the prostatic secretory function. In several studies, the overall effect of sildenafil and vardenafil increased quantitative and qualitative sperm motility. Furthermore, some studies indicate that PDE5is influence positively the sperm capacity to undergo capacitation under biochemical conditions that are known to induce the sperm capacitation process. Additional research efforts are necessary in order to recommend unequivocally the usage of sildenafil, vardenafil, or avanafil for the alleviation of male infertility.

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.

Renoprotective Effect of Vardenafil and Avanafil in Contrast-Induced Nephropathy: Emerging Evidence from an Animal Model

The potential renoprotective effects of vardenafil (VAR) have been evaluated in a very limited number of studies using acute kidney injury animal models other than contrast-induced nephropathy (CIN) with promising results, while avanafil (AVA) has not been evaluated in this respect before. The purpose of this study was to evaluate for the first time the potential renoprotective effect of VAR and AVA in a rat model of CIN. Twenty-five male Wistar rats were equally assigned into five groups: control, CIN, CIN+N-acetyl cysteine (NAC) (100 mg/kg/day) as a positive control, CIN+VAR (10 mg/kg/day) and CIN+AVA (50 mg/kg/day). CIN was induced by dehydration, inhibition of prostaglandin and nitric oxide synthesis as well as exposure to the contrast medium (CM). Serum Cr (sCr) levels were measured at 24 and 48 h after CIN induction. At 48 h of CM exposure, animals were sacrificed. Matrix metalloproteinase (MMP) 2 (MMP-2) and MMP-9, kidney injury molecule 1 (KIM-1) and cystatin-C (Cys-C) were measured on renal tissue. Histopathological findings were evaluated on kidney tissue. All treatment groups had close to normal kidney appearance. sCr levels subsided in all treatment groups compared to CIN group at 48 h following CIN induction. A significant decline in the levels of MMP-2, MMP-9, KIM-1 and Cys-C compared to CIN group was observed. These results provide emerging evidence that VAR and AVA may have the potential to prevent CIN.

Thalassemia and Priapism: A Literature Review of a Rare Association

Thalassemia is a hematologic disorder caused by genetic mutation resulting in impaired hemoglobin chain production. Patients with thalassemia commonly experience complications such as anemia, blood transfusion-related issues, hepatic or cardiac involvement, and psychosocial impacts. Rarely, priapism has been associated with thalassemia as an initial presentation or subsequently occurring at any time in the disease course. Our literature review summarizes the reported cases of thalassemia-associated priapism and delves into underlying mechanisms of its pathophysiology and appropriate management.

Using cyproterone acetate to treat recurrent ischemic priapism in a patient with sickle cell anemia as a comorbidity: a case report

Introduction

The management of recurrent ischemic priapism is unclear in contemporary practice. Yet, if left untreated, the condition may evolve into an acute ischemic priapism and in some cases result in erectile dysfunction. This report documents the results of successful management of recurrent ischemic priapism using cyproterone acetate in a 30-year-old Saudi man with sickle cell anemia as a comorbidity.

Case presentation

A 30-year-old Saudi man denoted visited the emergency room with a painful erection which had lasted for more than four hours. The patient has sickle cell anemia and a family history of sickle cell disease. He is married and has two children. His first priapism case occurred when he was 7 years old. At the age of 15, the condition recurred, and the patient’s doctor prescribed cyproterone acetate 50 mg twice daily for 5 days. The doctor had told him that whenever he was experiencing priapism, he should adhere to this regimen for 5 days. The doctor could not find any guidelines for the prescription of cyproterone acetate.

Conclusion

Priapism cases represent a significant challenge in therapeutic management because of the elevated risk of structural damage to the penis. The fact that there lacks a clinically approved standard approach to managing the condition make it difficult for physicians to effectively manage the condition. Management of the condition is further complicated by existence of comorbidities such as sickle cell anemia. This patient’s case demonstrates that cyproterone acetate prescription is a great preventative strategy that limits priapism recurrences.

Phosphodiesterase-5 inhibitors ameliorate structural kidney damage in a rat model of contrast-induced nephropathy

The aim of the study was to investigate the potential of sildenafil and tadalafil to ameliorate structural kidney damage in contrast-induced nephropathy (CIN). A rat model of CIN was developed by dehydration, administration of a nitric oxide inhibitor and a prostaglandin synthesis inhibitor (L-NAME/indomethacin) and contrast media exposure to iopromide. The effect of pre-treatment with sildenafil, tadalafil or N-acetyl cysteine (NAC) for 7 days prior to CIN induction was investigated. All animals were sacrificed at 24 h after CIN induction and both kidneys were collected. Histopathological examination was performed under light microscopy in serial tissue sections stained with hematoxylin and eosin. CIN group showed hydropic changes of the renal tubules (proximal and distal convoluted tubules and Henle's loop), an increased Bowman space with lobulated glomerulus and alteration of macula densa region of distal convolute tubules. The groups pretreated with sildenafil and tadalafil showed nearly normal histological aspects of renal tissue. The group pretreated with NAC showed similar but less intense histopathologic changes compared to CIN group. Sildenafil and tadalafil pre-treatment ameliorates CIN-related structural kidney damage and the protective potential of these agents is superior to NAC.

Current Concepts on the Reno-Protective Effects of Phosphodiesterase 5 Inhibitors in Acute Kidney Injury: Systematic Search and Review

Acute kidney injury (AKI) is associated with increased morbidity, prolonged hospitalization, and mortality, especially in high risk patients. Phosphodiesterase 5 inhibitors (PDE5Is), currently available as first-line therapy of erectile dysfunction in humans, have shown a beneficial potential of reno-protection through various reno-protective mechanisms. The aim of this work is to provide a comprehensive overview of the available literature on the reno-protective properties of PDE5Is in the various forms of AKI. Medline was systematically searched from 1946 to November 2019 to detect all relevant animal and human studies in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. In total, 83 studies were included for qualitative synthesis. Sildenafil is the most widely investigated compound (42 studies), followed by tadalafil (20 studies), icariin (10 studies), vardenafil (7 studies), zaprinast (4 studies), and udenafil (2 studies). Even though data are limited, especially in humans with inconclusive or negative results of only two clinically relevant studies available at present, the results of animal studies are promising. The reno-protective action of PDE5Is was evident in the vast majority of studies, independently of the AKI type and the agent applied. PDE5Is appear to improve the renal functional/histopathological alternations of AKI through various mechanisms, mainly by affecting regional hemodynamics, cell expression, and mitochondrial response to oxidative stress and inflammation.

Sildenafil and tadalafil reduce the risk of contrast-induced nephropathy by modulating the oxidant/antioxidant balance in a murine model

The aim of the study was to evaluate the potential protective role of sildenafil and tadalafil in contrast-induced nephropathy (CIN) by modulating oxidative stress. Thirty Wistar male rats were equally assigned into five groups: sham, CIN, CIN + sildenafil (10 mg/kg bw/day), CIN + tadalafil (5 mg/kg bw/day) and CIN + N-Acetyl Cysteine (NAC) (100 mg/kg bw/day) as a positive control. CIN was induced by 12 h dehydration and administration of indomethacin (10 mg/kg bw), N-ω- nitro-L-arginine methyl ester (10 mg/kg bw), and iopromide (3 g/kg bw iodine). Blood was drawn prior to and 24 h after CIN induction for evaluating renal function and oxidative stress. In the CIN group, total antioxidant capacity (TAC), reduced glutathione (GSH) and catalase (CAT) levels were significantly decreased; and protein carbonyl (PROTC) and thiobarbituric reactive species (TBARS) were significantly increased compared to the sham group. Pre- Sildenafil and tadalafil pre-treatment reduced CIN risk and reversed oxidative stress almost to the sham group levels. These results suggest that PDE5Is can be good candidates for preventing CIN based on their ability to modulate the oxidant/antioxidant balance.

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.

Molecular Profile of Priapism Associated with Low Nitric Oxide Bioavailability

Priapism is a disorder in which prolonged penile erection persists uncontrollably, potentially leading to tissue damage. Priapism commonly afflicts patient populations with severely low nitric oxide (NO) bioavailability. Because NO is a primary mediator of erection, the molecular mechanisms involved in priapism pathophysiology associated with low NO bioavailability are not well-understood. The objective of this study was to identify dysregulated molecular targets and signaling pathways in penile tissue of a mouse model of low NO bioavailability that have potential relevance to priapism. Neuronal plus endothelial NO synthase double knockout mice (NOS1/3^-/-) were used as a model of low NO bioavailability. Priapic-like activity was demonstrated in the NOS1/3^-/- mice relative to wild-type (WT) mice by the measurement of prolonged erections following cessation of electrical stimulation of the cavernous nerve. Penile tissue was processed and analyzed by reverse-phase liquid chromatography tandem mass spectrometry. As a result, 1279 total proteins were identified and quantified by spectral counting, 46 of which were down-regulated and 110 of which were up-regulated in NOS1/3^-/- versus WT (P < 0.05). Ingenuity Pathway Analysis of differentially expressed proteins revealed increased protein kinase A and G-protein coupled receptor signaling in NOS1/3^-/- penises, which represent potential mechanisms contributing to priapism for secondary to low NO bioavailability.

Thalassemia Major and Priapism: A Case Report of an Adolescent

Priapism is defined as a prolonged pathologic penile erection without sexual stimulation. In children, priapism secondary to sickle cell disease or hematological malignancy is a frequent condition. Appropriate treatment of priapism varies; the treatment is primarily etiological, conservative management. In the present report, we aimed to present a case of asplenic thalassemia major who developed priapism, improved with hydration and ibuprofen treatment. Clinicians should take into account that priapism can be encountered in patients with thalassemia major. To our knowledge this is the second publication reporting the association between thalassemia major and priapism in childhood.

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.

[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.

Priapism, an emerging complication in β-thalassemia intermedia patients

The increase in survival rate of β-thalassemia (β-thal) patients allowed for the appearance and manifestation of several complications in almost every organ system. Priapism in β-thal patients is rarely reported in the literature. We herein report and investigate the occurrence of two cases of priapism in two young patients with β-thal intermedia (β-TI). The potential mechanisms are due to either a cellular mechanism involving a thrombus obstructing the efferent venules of the corpora cavernosa leading to priapism, or a recently elucidated functional mechanism that causes alteration of nitric oxide (NO) response of the penis, ultimately causing priapism. This should incite clinicians for a close follow-up and monitoring of high risk patients who are susceptible to developing priapism.

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.

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.

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.

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.

Priapism in sickle-cell disease: a hematologist's perspective

INTRODUCTION

Priapism is a familiar problem to hematologists, well known for its association with sickle-cell disease (SCD). It also occurs in a variety of other hematological illnesses, nearly all forms of congenital hemolytic anemia, including other hemoglobinopathies and red blood cell membranopathies and enzymopathies.

AIM

Provide urologists with a comprehensive review of priapism in SCD, with an emphasis on the perspective of a practicing hematologist.

METHODS

Medline searches through July 2010 were conducted using the terms priapism, erectile dysfunction, and sickle cell.

MAIN OUTCOME MEASURES

Expert opinion was based on review of the medical literature related to this subject matter.

RESULTS

In men with SCD, large epidemiological studies have linked the risk of priapism to clinical markers of the severity of intravascular hemolysis. Extracellular hemoglobin and arginase released during hemolysis has been implicated in reducing nitric oxide bioavailability, although the relevance of hemolysis to vascular dysfunction has been challenged by some scientists. Consistent with the role of impairment of the nitric oxide axis, mice genetically deficient in nitric oxide production have also been shown to develop priapic activity. Provocative new data indicate that hemolysis-linked dysregulation of adenosine signaling in the penis contributes to priapism in sickle cell mice. Serious questions have arisen regarding the efficacy of mainstays of textbook dogma for treatment of acute severe priapism, including intravenous fluids, alkalinization, and exchange transfusion, and there is increasing acceptance for early aspiration and irrigation of the corpus cavernosum.

CONCLUSION

For patients with sickle cell with recurrent priapism, there is very limited evidence for a medical prophylaxis role for hydroxyurea, etilefrine, pseudoephedrine, leuprolide, sildenafil, and other agents. Recent publications have highlighted nitric oxide and adenosine signal transduction pathways as worthy of additional research. Research and clinical management of sickle-cell priapism is strengthened by multidisciplinary collaboration between hematologists and urologists.

Adenosine deaminase enzyme therapy prevents and reverses the heightened cavernosal relaxation in priapism

INTRODUCTION

Priapism featured with painful prolonged penile erection is dangerous and commonly seen in sickle cell disease (SCD). The preventive approaches or effective treatment options for the disorder are limited because of poor understanding of its pathogenesis. Recent studies have revealed a novel role of excess adenosine in priapism caused by heightened cavernosal relaxation, and therefore present an intriguing mechanism-based therapeutic possibility.

AIM

The aim of this study was to determine the therapeutic effects of adenosine deaminase (ADA) enzyme therapy to lower adenosine in priapism.

METHODS

Both ADA-deficient mice and SCD transgenic (Tg) mice display priapism caused by excessive adenosine. Thus, we used these two distinct lines of mouse models of priapism as our investigative tools. Specifically, we treated both of these mice with different dosages of polyethylene glycol-modified ADA (PEG-ADA) to reduce adenosine levels in vivo. At the end points of the experiments, we evaluated the therapeutic effects of PEG-ADA treatment by measuring adenosine levels and monitoring the cavernosal relaxation.

MAIN OUTCOME MEASURES

Adenosine levels in penile tissues were measured by high-performance liquid chromatography, and cavernosal relaxation was quantified by electrical field stimulation (EFS)-induced corporal cavernosal strip (CCS) assays.

RESULTS

We found that lowering adenosine levels in penile tissues by PEG-ADA treatment from birth in ADA-deficient mice prevented the increased EFS-induced CCS relaxation associated with priapism. Intriguingly, in both ADA-deficient mice and SCD Tg mice with established priapism, we found that normalization of adenosine levels in penile tissues by PEG-ADA treatment relieved the heightened EFS-induced cavernosal relaxation in priapism.

CONCLUSIONS

Our studies have identified that PEG-ADA is a novel, safe, and mechanism-based drug to prevent and correct excess adenosine-mediated increased cavernosal relaxation seen in two independent priapic animal models, and suggested its therapeutic possibility in men suffering from priapism.