Molecular analysis of erection regulatory factors in sickle cell disease associated priapism in the human penis

The endocannabinoid system's genetic polymorphisms in sickle cell anemia patients

Sickle cell anemia (SCA) is a monogenic blood disease with complex and multifactorial pathophysiology. The endocannabinoid system (ECS) could be a candidate for modulating SCA complications, such as priapism, as it has demonstrated an essential role in hematopoiesis, platelet aggregation, and immune responses. We evaluated the association of ECS-related single nucleotide polymorphisms (SNP) (FAAH rs324420, MAGL rs604300, CNR1 rs7766029, and CNR2 rs35761398) with priapism in a Brazilian SCA cohort. The study involved 138 SCA patients (n = 80 with priapism and n = 58 without priapism). SCA was detected with HPLC, and the Hb SS genotype was confirmed with PCR-RE. Alpha thalassemia mutations were detected with Multiplex-PCR, and SNP genotyping was performed using TaqMan genotyping assays. We observed a lower frequency of -α3.7kb-thalassemia mutation in patients with priapism than in patients without this complication (p < 0.001), and in adjusted multivariate analyses TT-CC genotype of CNR2 rs35761398 was associated with a lower chance of developing priapism (OR = 0.386 [0.175-0.854], p = 0.019) and a lower risk of it over time (HR = 0.634 [0.402-0.987], p = 0.049). The SCA ischemic priapism is related to unbalanced vasodilation/vasoconstriction pathways, such as decreased RhoA/Rho-kinase (ROCK) signaling. Since activating the type 2 cannabinoid receptor (CB2) decreases RhoA activation, we suggest a novel approach to SCA priapism involving CB2.

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.

The effect of red blood cell disorders on male fertility and reproductive health

Male infertility is defined as a failure to conceive after 12 months of unprotected intercourse owing to suspected male reproductive factors. Non-malignant red blood cell disorders are systemic conditions that have been associated with male infertility with varying severity and strength of evidence. Hereditary haemoglobinopathies and bone marrow failure syndromes have been associated with hypothalamic-pituitary-gonadal axis dysfunction, hypogonadism, and abnormal sperm parameters. Bone marrow transplantation is a potential cure for these conditions, but exposes patients to potentially gonadotoxic chemotherapy and/or radiation that could further impair fertility. Iron imbalance might also reduce male fertility. Thus, disorders of hereditary iron overload can cause iron deposition in tissues that might result in hypogonadism and impaired spermatogenesis, whereas severe iron deficiency can propagate anaemias that decrease gonadotropin release and sperm counts. Reproductive urologists should be included in the comprehensive care of patients with red blood cell disorders, especially when gonadotoxic treatments are being considered, to ensure fertility concerns are appropriately evaluated and managed.

Soluble guanylate cyclase stimulators and activators: new horizons in the treatment of priapism associated with sickle cell disease

Priapism, defined as a prolonged and often painful penile erection occurring without sexual stimulation or desire, is a common complication in sickle cell disease (SCD), affecting up to 48% of male patients. This condition presents significant clinical challenges and can lead to erectile dysfunction if not properly managed. Current pharmacological treatments for SCD-related priapism are primarily reactive rather than preventative, highlighting a gap in effective medical intervention strategies. A critical factor in developing priapism is the reduced basal bioavailability of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in erectile tissues. New prevention strategies should ideally target the underlying pathophysiology of the disease. Compounds that stimulate and activate soluble guanylate cyclase (sGC) emerge as potential therapeutic candidates since these compounds have the property of inducing cGMP production by sGC. This review explores the potential of sGC stimulators and activators in treating priapism associated with SCD. We discuss the advantages of these agents in the face of the challenging pathophysiology of SCD. Additionally, the review underscores the impact of intravascular hemolysis and oxidative stress on priapism pathophysiology in SCD, areas in which sGC stimulators and activators may also have beneficial therapeutic effects.

Novel erectile analyses revealed augmentable penile Lyve-1, the lymphatic marker, expression

Purpose

The pathophysiology of penis extends to erectile dysfunction (ED) to conditions including sexually transmitted diseases (STDs) and cancer. To date, there has been little research evaluating vascular drainage from the penis. We aimed to evaluate penile blood flow in vivo and analyze its possible relationship with the lymphatic maker.

Materials and Methods

We established an in vivo system designed to assess the dynamic blood outflow from the corpus cavernosum (CC) by dye injection. To analyze lymphatic characteristics in the CC, the expression of Lyve-1, the key lymphatic endothelium marker, was examined by the in vitro system and lipopolysaccharide (LPS) injection to mimic the inflammatory conditions.

Results

A novel cavernography methods enable high-resolution morphological and functional blood drainage analysis. The expression of Lyve-1 was detected along the sinusoids. Furthermore, its prominent expression was also observed after penile LPS injection and in the erectile condition.

Conclusions

The current in vivo system will potentially contribute to the assessment of penile pathology from a novel viewpoint. In addition, current analyses revealed inducible Lyve-1 expression for LPS injection and the erection state, which requires further analyses on penile lymphatic system.

Hydroxyurea does not reverse functional alterations of the nitric oxide-cGMP pathway associated with priapism phenotype in corpus cavernosum from sickle cell mouse

Sickle cell disease (SCD) is a genetic disorder that has been associated with priapism. The role of hydroxyurea, a common SCD therapy, in influencing the nitric oxide (NO)-cGMP pathway and its effect on priapism is unclear. To investigate the effect of hydroxyurea treatment on smooth muscle relaxation of corpus cavernosum induced by stimulation of the NO-cGMP pathway in SCD transgenic mice and endothelial NO synthase gene-deficient (eNOS-/-) mice, which are used as model of priapism associated with the low bioavailability of endothelial NO. Four-month-old wild-type (WT, C57BL/6), SCD transgenic, and eNOS-/- male mice were treated with hydroxyurea (100 mg/Kg/day) or its vehicle (saline) daily for three weeks via intraperitoneal injections. Concentration-response curves for acetylcholine (ACh), sodium nitroprusside (SNP), and electrical field stimulation (EFS) were generated using strips of mice corpus cavernosum. The SCD mice demonstrated an amplified CC relaxation response triggered by ACh, EFS, and SNP. The corpus cavernosum relaxation responses to SNP and EFS were found to be heightened in the eNOS-/- group. However, the hydroxyurea treatment did not alter these escalated relaxation responses to ACh, EFS, and SNP in the corpus cavernosum of the SCD group, nor the relaxation responses to EFS and SNP in the eNOS-/- group. In conclusion, hydroxyurea is not effective in treating priapism associated with SCD. It is likely that excess plasma hemoglobin and reactive oxygen species, which are reported in SCD, are reacting with NO before it binds to GCs in the smooth muscle of the corpus cavernosum, thus preventing the restoration of baseline NO/cGMP levels. Furthermore, the downregulation of eNOS in the penis may impair the pharmacological action of hydroxyurea at the endothelial level in SCD mice. This study emphasize the urgency for exploring alternative therapeutic avenues for priapism in SCD that are not hindered by high plasma hemoglobin and ROS levels.

Intravascular hemolysis leads to exaggerated corpus cavernosum relaxation: Implication for priapism in sickle cell disease

Patients with sickle cell disease (SCD) display priapism. Clinical studies have shown a strong positive correlation between priapism and high levels of intravascular hemolysis in men with SCD. However, there are no experimental studies that show that intravascular hemolysis promotes alterations in erectile function. Therefore, we aimed to evaluate the corpus cavernosum smooth muscle relaxant function in a murine model that displays intravascular hemolysis induced by phenylhydrazine (PHZ), as well as the role of intravascular hemolysis in increasing the stress oxidative in the penis. Corpus cavernosum strips were dissected free and placed in organ baths. Acetylcholine and electrical field stimulation (EFS)-induced corpus cavernosum relaxations in vitro were obtained. Increased corpus cavernosum relaxant responses to acetylcholine and EFS were observed in the PHZ group. Protein expression of heme oxygenase-1 increased in the corpus cavernosum of the PHZ group, but PDE5 protein expression was not modified. Preincubation with the heme oxygenase inhibitor 1 J completely reversed the increased relaxant responses to acetylcholine and EFS in PHZ mice. Protein expression of NADPH oxidase subunit gp91phox, 3-nitrotyrosine, and 4-hydroxynonenal increased in the corpus cavernosum of the PHZ group, suggesting a state of oxidative stress. Basal cGMP production was lower in the PHZ group. Our results show that intravascular hemolysis promotes increased corpus cavernosum smooth muscle relaxation associated with increased HO-1 expression, as well as increased oxidative stress associated with upregulation of gp91phox expression. Moreover, our study supports clinical studies that point to a strong positive correlation between priapism and high levels of intravascular hemolysis in men with SCD.

Haptoglobin treatment contributes to regulating nitric oxide signal and reduces oxidative stress in the penis: A preventive treatment for priapism in sickle cell disease

Background: In sickle cell disease (SCD), reduced bioavailability of endothelial NO and cGMP results in reduced expression of phosphodiesterase type 5 (PDE5), thus impairing the penile erection control mechanism and resulting in prolonged penile erection (priapism). In SCD, reduced NO bioavailability is associated with excess plasma hemoglobin due to intravascular hemolysis and increased oxidative stress. Haptoglobin is the plasma protein responsible for reducing plasma hemoglobin levels, but in SCD, haptoglobin levels are reduced, which favors the accumulation of hemoglobin in plasma. Therefore, we aimed to evaluate the effects of haptoglobin treatment on functional and molecular alterations of erectile function, focusing on the contractile and relaxant mechanisms of corpus cavernosum (CC), as well as oxidative stress.

Methods: SCD mice were treated with haptoglobin (400 mg/kg, subcutaneous) or vehicle of Monday, Wednesday and Friday for a period of 1 month. Corpus cavernosum strips were dissected free and placed in organ baths. Cumulative concentration-response curves to the acetylcholine, sodium nitroprusside, phenylephrine and KCL, as well as to electrical field stimulation (EFS), were obtained in CC. Protein expressions of eNOS, phosphorylation of eNOS at Ser-1177, nNOS, PDE5, ROCK1, ROCK2, gp91^phox, 3-nitrotyrosine, and 4-HNE were measured by western blot in CC.

Results: Increased CC relaxant responses to acetylcholine, sodium nitroprusside and electrical-field stimulation were reduced by haptoglobin in SCD mice. Reduced CC contractile responses to phenylephrine and KCl were increased by haptoglobin in SCD mice. Haptoglobin prevented downregulated eNOS, p-eNOS (Ser-1177), PDE5, and ROCK2 protein expressions and reduced protein expressions of reactive oxygen species markers, NADPH oxidase subunit gp91phox, 3-nitrotyrosine and 4-HNE in penises from SCD mice. Haptoglobin treatment did not affect ROCK1 and nNOS protein expressions in penises from SCD mice. Basal cGMP production was lower in the SCD group, which was normalized by haptoglobin treatment.

Conclusion: Treatment with haptoglobin improved erectile function due to up-regulation of eNOS-PDE5 expression and down-regulation of the gp91phox subunit of NADPH oxidase and oxidative/nitrosative stress in the penises of SCD mice. Treatment with haptoglobin also increased contractile activity due to up-regulation of ROCK2. Therefore, haptoglobin treatment may be an additional strategy to prevent priapism in SCD.

Resveratrol-nitric oxide donor hybrid effect on priapism in sickle cell and nitric oxide-deficient mouse

Background

Children and adult with sickle cell disease (SCD) display priapism associated with low nitric oxide (NO) bioavailability and oxidative stress in penis.

Aim

This study aimed to evaluate the effects of hybrid compound RVT-FxMe, derived from resveratrol bearing a NO-donor subunit, on two murine model that display priapism phenotype, SCD transgenic mice and endothelial NO synthase gene-deficient (eNOS^-/-) mice.

Methods

Wild-type, SCD, and eNOS^-/- mice were treated with RVT-FxMe (25 mg/kg/d, 2 weeks).

Outcomes

Hematological parameters, concentration-response curves to acetylcholine (ACh) and sodium nitroprusside (SNP), as well as to electrical field stimulation (EFS), were obtained in mice corpus cavernosum strips.

Results

Corpus cavernosum relaxations to SNP and EFS were increased in eNOS^-/- group, which were normalized by RVT-FxMe treatment. SCD mice exhibited an excessive CC relaxant response induced by ACh, EFS and SNP RVT-FxMe treatment did not change the increased relaxant responses to ACh, EFS and SNP in corpus cavernosum from SCD group.

Clinical translation

Excess of plasma hemoglobin in SCD may interfere in pharmacological activity of NO donors compounds.

Strength/Limitations

While mechanistic data with promising potential is showed, the current study is not without limitations. RVT-FxMe effects in the mid- and long-term warrant complementary studies.

Conclusion

Treatment with RVT-FxMe reversed the enhanced NO-cGMP-mediated CC relaxations in eNOS^-/- mice, but not in SCD mice; it is likely that excess of plasma hemoglobin in SCD mice act to inactivate NO before it reaches soluble guanylyl cyclase, avoiding restoration of NO bioavailability in penis.

Establishment of mouse line showing inducible priapism-like phenotypes

Purpose

Penile research is expected to reveal new targets for treatment and prevention of the complex mechanisms of its disorder including erectile dysfunction (ED). Thus, analyses of the molecular processes of penile ED and continuous erection as priapism are essential issues of reproductive medicine.

Methods

By performing mouse N-ethyl-N-nitrosourea mutagenesis and exome sequencing, we established a novel mouse line displaying protruded genitalia phenotype (PGP; priapism-like phenotype) and identified a novel Pitpna gene mutation for PGP. Extensive histological analyses on the Pitpna mutant and intracavernous pressure measurement (ICP) and liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI/MS)/MS analyses were performed.

Results

We evaluated the role of phospholipids during erection for the first time and showed the mutants of inducible phenotypes of priapism. Moreover, quantitative analysis using LC-ESI/MS/MS revealed that the level of phosphatidylinositol (PI) was significantly lower in the mutant penile samples. These results imply that PI may contribute to penile erection by PITPα.

Conclusions

Our findings suggest that the current mutant is a mouse model for priapism and abnormalities in PI signaling pathways through PITPα may lead to priapism providing an attractive novel therapeutic target in its treatment.

Testosterone Deficiency in Sickle Cell Disease: Recognition and Remediation

Hypogonadism is common in men with sickle cell disease (SCD) with prevalence rates as high as 25%. Testicular failure (primary hypogonadism) is established as the principal cause for this hormonal abnormality, although secondary hypogonadism and compensated hypogonadism have also been observed. The underlying mechanism for primary hypogonadism was elucidated in a mouse model of SCD, and involves increased NADPH oxidase-derived oxidative stress in the testis, which reduces protein expression of a steroidogenic acute regulatory protein and cholesterol transport to the mitochondria in Leydig cells. In all men including those with SCD, hypogonadism affects physical growth and development, cognition and mental health, sexual function, as well as fertility. However, it is not understood whether declines in physical, psychological, and social domains of health in SCD patients are related to low testosterone, or are consequences of other abnormalities of SCD. Priapism is one of only a few complications of SCD that has been studied in the context of hypogonadism. In this pathologic condition of prolonged penile erection in the absence of sexual excitement or stimulation, hypogonadism exacerbates already impaired endothelial nitric oxide synthase/cGMP/phosphodiesterase-5 molecular signaling in the penis. While exogenous testosterone alleviates priapism, it disadvantageously decreases intratesticular testosterone production. In contrast to treatment with exogenous testosterone, a novel approach is to target the mechanisms of testosterone deficiency in the SCD testis to drive endogenous testosterone production, which potentially decreases further oxidative stress and damage in the testis, and preserves sperm quality. Stimulation of translocator protein within the transduceosome of the testis of SCD mice reverses both hypogonadism and priapism, without affecting intratesticular testosterone production and consequently fertility. Ongoing research is needed to define and develop therapies that restore endogenous testosterone production in a physiologic, mechanism-specific fashion without affecting fertility in SCD men.

TSPO ligand FGIN-1-27 controls priapism in sickle cell mice via endogenous testosterone production

Priapism, a prolonged penile erection in the absence of sexual arousal, is common among patients with sickle cell disease (SCD). Hypogonadism is also common in patients with SCD. While the administration of exogenous testosterone reverses hypogonadism, it is contraceptive. We hypothesized that the stimulation of endogenous testosterone production decreases priapism by normalizing molecular signaling involved in penile erection without decreasing intratesticular testosterone production, which would affect fertility. Treatment of SCD mice with FGIN-1-27, a ligand for translocator protein (TSPO) that mobilizes cholesterol to the inner mitochondrial membrane, resulted in eugonadal levels of serum testosterone without decreasing intratesticular testosterone production. Normalized testosterone levels, in turn, decreased priapism. At the molecular level, TSPO restored phosphodiesterase 5 activity and decreased NADPH oxidase-mediated oxidative stress in the penis, which are major molecular signaling molecules involved in penile erection and are dysregulated in SCD. These results indicate that pharmacologic activation of TSPO could be a novel, targetable pathway for treating hypogonadal men, particularly patients with SCD, without adverse effects on fertility.

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.

G6PD Deficiency and Priapism: Is There a Link Between the Two Entities?

Glucose 6 phosphate dehydrogenase (G6PD) is called the house keeping enzyme essential for all cells survival. G6PD deficiency is best studied for its role in hemolysis as this enzyme is the only source of nicotinamide adenine dinucleotide phosphate (NADPH) in red blood cells (RBCs) and is the cells defense against reactive oxygen species. We present one of the rare complications of G6PD deficiency in this case where all other causes of priapism were ruled out.

Priapism, hemoglobin desaturation, and red blood cell adhesion in men with sickle cell anemia

Priapism is a serious, but episodic, complication of sickle cell disease (SCD). We had previously reported that subjects with SCD had variable red blood cell (RBC) adhesion to the immobilized sub-endothelial protein laminin (LN). We examined adhesion to LN in a microfluidic device, of RBCs from men with homozygous sickle cell anemia. Adhesion under hypoxic, but not ambient, conditions was greater in men with a history of priapism, with median adhesion of 529 RBCs per 32 mm²/unit area (range 5-5248) rising to 3268 RBCs per 32 mm²/unit area (range 49-18,368, P = 0.004), under ambient and hypoxic conditions, respectively (n = 14). This was not seen in RBCs from men without a history of priapism (median 402 (range 14-785) and 122 (range 31-4112) RBCs per 32 mm²/unit area, ambient and hypoxic conditions, respectively (P = N.S., N = 12)). We also observed an association between hypoxia-enhanced RBC adhesion in vitro and a history of hemoglobin desaturation in vivo independent of priapism. Prolonged Hb desaturation may increase sickle polymer formation and RBC damage, resulting in enhanced RBC adhesion, hemolysis, and endothelial dysfunction. The identification of distinct RBC phenotypes could prompt clinical evaluation for suitability for novel or under-used therapies, like oxygen.

Phenolic analysis and erectogenic function of African Walnut (Tetracarpidium conophorum) seeds: The impact of the seed shell on biological activity

This study investigated the erectogenic potential of African walnut seed (AWS). The extract from AWS cooked with/without shell interacted with phosphodiesterase-5 (PDE-5), arginase, angiotensin-I converting enzymes (ACE), and acetylcholinesterase (AChE); enzymes associated with erectile dysfunction (ED) and Fe²⁺ -induced malonaldehyde (MDA) production in the isolated penile tissue. The results showed that the extracts inhibited the enzymes and MDA production, but Walnut cooked with shell had the highest effect. This agreed with increased phenolic acids and flavonoids, found in the AWS cooked with the shell, compared with that cooked without shell. The inhibition of enzymes and antioxidative potentials could be among the possible mechanisms of actions of AWS in the management/treatment of ED. However, cooking walnut seed with the shell seem to be a contributing factor, as this could prevent possible leaching out of the phytochemicals that could be responsible for these biological effects. PRACTICAL APPLICATIONS: Walnut seed possesses a high content of phenolic compounds and inhibit enzymes relevant to the management of erectile dysfunction. Traditionally, Walnut seed is being cooked with/without the shell and consumed for the purpose of alternative medicine in folklore. Our investigation revealed the possible mechanism underlying the therapeutic effect Walnut seed in the management of ED, but the impact of the shell during cooking contributes to this effect. This result will inform the consumers and food scientist on the importance of cooking Walnut seed with the shell in order to maximize its nutraceutical values.

THE SCIENCE AND PRACTICE OF ERECTION PHYSIOLOGY: STORY OF A REVOLUTIONARY GASEOUS MOLECULE

The field of sexual medicine, in reference to the science of the sexual response and the clinical management of sexual dysfunctions, has evolved remarkably in the last 25 years. Erection biology has been central in driving this progress and is measured considerably by the discovery, study, and clinical translation of a simple gaseous molecule, nitric oxide, which is operative in the penis. Nitric oxide functions extraordinarily as a neurotransmitter and molecular signal transducer. It is now well understood to be the principal molecular mediator of penile erection and to be a critical element involved in dysregulatory mechanisms of erection disorders ranging from erectile dysfunction to priapism. It is most familiarly associated with the scientific development of oral medications for treating erectile dysfunction, which has modernized the clinical management of this condition.

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.

The management of the acute ischemic priapism: A state of the art review

OBJECTIVE

To review the current literature on early penile prosthesis implantation in patients with refractory ischemic priapism (IP).

ACQUISITION OF EVIDENCE

A systematic search for the terms "penile prosthesis", "priapism", "impotence", "fibrosis", "downsized prosthesis cylinders", and "patient satisfaction" has been carried out in PubMed, EMBASE, Cochrane, SCOPUS and Science Citation Index databases.

SYNTHESIS OF EVIDENCE

Cavernosal tissue damage in IP is time related. Conservative measures and aspiration with or without intracorporeal instillation of α-adrenergic agonists are usually successful in the early stages. Shunt surgery in patients remains debatable, as the lack of response to aspiration and instillation of α-adrenergic agonists indicates that irreversible changes in the cavernosal smooth muscle are likely to have already occurred. Immediate penile prosthesis implantation in patients with refractory IP settles the priapic episode, maintains the long term rigidity necessary to engage in penetrative sexual intercourse and prevents the otherwise inevitable penile shortening. Although complication rates after penile prosthesis implantation in acute priapism are higher than in virgin cases, they are still lower than after implantation in patients with severe corporal fibrosis due to chronic priapism. Regardless of the complication rates, penile prosthesis implantation in refractory IP should be preferred as it allows the preservation of penile length, which is one of the main factors influencing postoperative patient's satisfaction following surgery.

Testosterone replacement in transgenic sickle cell mice controls priapic activity and upregulates PDE5 expression and eNOS activity in the penis

Sickle cell disease (SCD)-associated priapism is characterized by decreased nitric oxide (NO) signaling and downregulated phosphodiesterase (PDE)5 protein expression and activity in the penis. Priapism is also associated with testosterone deficiency, but molecular mechanisms underlying testosterone effects in the penis in SCD are not known. Given the critical role of androgens in erection physiology and NO synthase (NOS)/PDE5 expression, we hypothesized that testosterone replacement to eugonadal testosterone levels reduces priapism by reversing impaired endothelial (e)NOS activity and molecular abnormalities involving PDE5. Adult male transgenic Berkeley sickle cell (Sickle) and wild-type (WT) mice were implanted with testosterone pellets, which release 1.2 μg testosterone/day for 21 days, or vehicle. After 21 days, animals underwent erectile function assessment followed by collection of blood for serum testosterone measurements, penes for molecular analysis, and seminal vesicles as testosterone-responsive tissue. Serum testosterone levels were measured by radioimmunoassay; protein expressions of PDE5, α-smooth muscle actin, eNOS and nNOS, and phosphorylation of PDE5 at Ser-92, eNOS at Ser-1177, neuronal (n) NOS at Ser-1412, and Akt at Ser-473 were measured by Western blot in penile tissue. Testosterone treatment reversed downregulated serum testosterone levels and increased (p < 0.05) the weight of seminal vesicles in Sickle mice to levels comparable to that of WT mice, indicating restored testosterone levels in Sickle mice. Testosterone treatment reduced (p < 0.05) prolonged detumescence in Sickle mice and normalized downregulated P-PDE5 (Ser-92), PDE5, P-eNOS (Ser-1177), and P-Akt (Ser-473) protein expressions in the Sickle mouse penis. Testosterone treatment did not affect P-nNOS (Ser-1412), eNOS, nNOS, or α-smooth muscle actin protein expressions in the Sickle mouse penis. In conclusion, in the mouse model of human SCD, increasing testosterone to eugonadal levels reduced priapic activity and reversed impaired Akt/eNOS activity and PDE5 protein expression in the penis.

Management of refractory ischemic priapism: current perspectives

OBJECTIVES

The aim of the present manuscript is to review the current literature on priapism, focusing on the state-of-the-art knowledge of both the diagnosis and the treatment of the refractory ischemic priapism (IP).

METHODS

Pubmed and EMBASE search engines were used to search for words "priapism", "refractory priapism", "penile prosthesis", "diagnosis priapism", "priapism treatment", "penile fibrosis", "priapism therapy". All the studies were carefully examined by the authors and then included in the review.

RESULTS

First-line treatment involves ejaculation, physical exercise and cold shower followed by corporal blood aspiration and injection of α-adrenoceptor agonists. Subsequently, a distal or proximal shunt may be considered. If none of the treatment is effective or the priapism episode lasts >48 hours penile prosthesis implantation could be the only option to solve the priapism and treat the ongoing erectile dysfunction.

CONCLUSION

The management of IP is to achieve detumescence of persistent penile erection and to preserve erectile function after resolution of the priapic episode. On the other hand, penile fibrosis and following shortening should be prevented. Early penile prosthesis implantation in patients with refractory IP is able to solve both the priapic episode and prevent the otherwise certain penile shortening. Penile prosthesis implantation is the actual gold standard of care in cases of refractory IP.

Sympathetic Hyperactivity, Increased Tyrosine Hydroxylase and Exaggerated Corpus Cavernosum Relaxations Associated with Oxidative Stress Plays a Major Role in the Penis Dysfunction in Townes Sickle Cell Mouse

Background

Sickle cell disease patients display priapism that may progress to erectile dysfunction. However, little is known about the pathophysiological alterations of corpus cavernosum in sickle cell disease.

Objective

Thus, this study aimed to evaluate the functional and molecular alterations of sympathetic machinery and nitric oxide—cyclic guanosine monophosphate signaling pathway in Townes transgenic sickle cell disease mice.

Methods

Concentration–response curves to contractile (phenylephrine) and relaxant agents (acetylcholine and sodium nitroprusside) were obtained in corpus cavernosum strips from sickle and C57BL/6 (control) mice. Neurogenic contractions and nitrergic relaxations were obtained using electrical-field stimulation. Measurements of endothelial nitric oxide synthase (eNOS), neuronal nitric oxide synthase (nNOS), phosphodiesterase-5 (PDE5) and α_1A-, α_1B- and α_1D-adrenoceptor mRNA expressions and reactive-oxygen species were performed. Tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expressions in cavernosal tissues were also measured.

Results

The neurogenic contractions were higher in the sickle cell disease group, in association with elevated tyrosine hydroxylase phosphorylated at Ser-31 and total tyrosine hydroxylase protein expression, as well as increased tyrosine hydroxylase mRNA expression. Likewise, phenylephrine-induced contractions were greater in the sickle mice, whereas α_1A-, α_1B- and α_1D-adrenoceptor mRNA expression remained unchanged. Cavernosal relaxations to acetylcholine, sodium nitroprusside and EFS were higher in sickle mice, accompanied by decreased eNOS and nNOS, along with lower PDE5 mRNA expression. An increase of about 40% in reactive-oxygen species generation in corpus cavernosum from sickle mice was also detected.

Conclusion

Our study shows that decreased nitric oxide bioavailability in erectile tissue due to increased oxidative stress leads to both sympathetic hyperactivity and dysregulation of nitric oxide signaling in corpus cavernosum from Townes sickle mice.

Beneficial Effect of the Nitric Oxide Donor Compound 3-(1,3-Dioxoisoindolin-2-yl)Benzyl Nitrate on Dysregulated Phosphodiesterase 5, NADPH Oxidase, and Nitrosative Stress in the Sickle Cell Mouse Penis: Implication for Priapism Treatment

Patients with sickle cell disease (SCD) display priapism, and dysregulated nitric oxide (NO) pathway may contribute to this condition. However, current therapies offered for the prevention of priapism in SCD are few. The 3-(1,3-dioxoisoindolin-2-yl)benzyl nitrate (compound 4C) was synthesized through molecular hybridization of hydroxyurea and thalidomide, which displays an NO-donor property. This study aimed to evaluate the effects of compound 4C on functional and molecular alterations of erectile function in murine models that display low NO bioavailability, SCD transgenic mice, and endothelial NO synthase and neuronal NO synthase double gene-deficient (dNOS^-/) mice, focusing on the dysregulated NO-cGMP- phosphodiesterase type 5 (PDE5) pathway and oxidative stress in erectile tissue. Wild-type, SCD, and dNOS^-/- mice were treated with compound 4C (100 μmol/kg/d, 3 weeks). Intracavernosal pressure in anesthetized mice was evaluated. Corpus cavernosum tissue was dissected free and mounted in organ baths. SCD and dNOS^-/- mice displayed a priapism phenotype, which was reversed by compound 4C treatment. Increased corpus cavernosum relaxant responses to acetylcholine and electrical-field stimulation were reduced by 4C in SCD mice. Likewise, increased sodium nitroprusside-induced relaxant responses were reduced by 4C in cavernosal tissue from SCD and dNOS^-/- mice. Compound 4C reversed PDE5 protein expression and reduced protein expressions of reactive oxygen species markers, NADPH oxidase subunit gp91^phox, and 3-nitrotyrosine in penises from SCD and dNOS^-/- mice. In conclusion, 3-week therapy with the NO donor 4C reversed the priapism in murine models that display lower NO bioavailability. NO donor compounds may constitute an additional strategy to prevent priapism in SCD.

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.

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.

Ischaemic Priapism and Glucose-6-Phosphate Dehydrogenase Deficiency: A Mechanism of Increased Oxidative Stress?

Ischaemic priapism is a devastating urological condition that has the potential to cause permanent erectile dysfunction. The disorder has been associated with numerous medical conditions and the use of pharmacotherapeutic agents. The aetiology is idiopathic in a number of cases. There are two prior case reports of the association of ischaemic priapism and glucose-6-phosphate dehydrogenase (G6PD) deficiency. We report on a third case of priapism associated with G6PD deficiency and review recently described molecular mechanisms of increased oxidative stress in the pathophysiology of ischaemic priapism. The case report of a 32-year old Afro-Caribbean male with his first episode of major ischaemic priapism is described. Screening for common causes of ischaemic priapism, including sickle cell disease was negative. Glucose-6-phosphate dehydrogenase deficiency was discovered on evaluation for priapism. Penile aspiration was performed and erectile function was good post treatment.Glucose-6-phosphate dehydrogenase deficiency is a cause for ischaemic priapism and should be a part of the screening process in idiopathic causes of the disorder. Increased oxidative stress occurs in G6PD deficiency and may lead to priapism.

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.

Fibrotic protein expression profiles in penile tissue of patients with erectile dysfunction

OBJECTIVE

To characterize transforming growth factor beta 1 (TGFβ1) and related signaling pathway proteins in a large cohort of human penile tissue (HPT) samples.

METHODS

HPT was collected from patients undergoing penile prosthesis implantation for erectile dysfunction (ED) and divided into the following 2 groups: postradical prostatectomy ED (RP-ED; n = 57) and organic ED (O-ED; n = 30). HPT from patients undergoing partial penectomy without ED was used as controls (CON; n = 6). Western blot analysis was performed to investigate the protein expressions of TGFβ1, thrombospondin 1 (TSP1; an activator of TGFβ1), fibronectin (an extracellular matrix glycoprotein induced by TGFβ1), and a family of transcriptional factors activated by TGFβ1 (Smad2, phospho-Smad2-serine-465/467 [pSmad2], Smad3, phospho-Smad3-serine-423/425 [pSmad3]).

RESULTS

Expressions of TGFβ1 and TSP1 were significantly higher in RP-ED (P <.05) and O-ED (P <.05) groups compared with that of the CON group and were not different between either ED groups. Expressions of Smad2, pSmad2, Smad3, pSmad3, and fibronectin were similar among all groups. Within the RP-ED group, a subgroup analysis showed that time from RP to penile prosthesis implantation was related to increased expression of pSmad2 (P <.05), and previous history of intracavernosal injection was related to increased expression of TGFβ1 (P <.05).

CONCLUSION

Our results demonstrate that TSP1- and TGFβ1-dependent fibrotic changes occur in penile tissue in patients with ED regardless of etiology. The unchanged expression of the Smad transcriptional factors may be reconciled by a Smad-independent downstream signaling pathway transmitting TGFβ1 signals.

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.