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

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.

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.

Exosomes secreted by adipose mesenchymal stem cells overexpressing circPIP5K1C exert

BACKGROUND

Erectile dysfunction (ED) seriously affects men's normal life, and obstructive sleep apnoea (OSA) has been diagnosed as a causative factor. Currently, exosomes secreted by adipose mesenchymal stem cells (ADSC) have been used in the non-clinical experimental treatment of ED disease with prominent efficacy due to the advantages of high stability and no immune exclusion.

METHODS

In this study, chronic intermittent hypoxia (CIH) exposure was used to induce ED-corresponding phenotypes in Sprague Dawley (SD) rats as well as in cavernous smooth muscle cells (CCSMCs). ED symptoms were treated using exosomes secreted by ADSCs overexpressing circPIP5K1C (EXO-circ) injected into the rat corpus cavernosum.

RESULTS

EXO-circ has the effect of ameliorating ED induced by CIH exposure in rats, the mechanism of which is to promote the expression of the downstream target gene SMURF1 after adsorption of miR-153-3p through the sponge so that SMURF1 and PFKFB3 occur protein-protein binding and ubiquitination degradation of PFKFB3 appears to inhibit the occurrence of spongiotic smooth muscle cells glycolysis, and to restore the function of the smooth muscle.

CONCLUSIONS

These findings show that EXO-circ have a promising therapeutic potential in OSA-induced ED.

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.

Targeting heme in sickle cell disease: new perspectives on priapism treatment

Men with sickle cell disease (SCD) frequently experience priapism, defined as prolonged, painful erections occurring without sexual arousal or desire. This urological emergency can lead to penile fibrosis and permanent erectile dysfunction if not treated adequately. Due to its complex pathophysiology, there is currently no effective preventative treatment for this condition. Recent studies have highlighted the dysfunction of the nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) pathway in erectile tissues as a critical mechanism in developing priapism in SCD. Additionally, further research indicates that intravascular hemolysis promotes increased smooth muscle relaxation in the corpus cavernosum and that excess heme may significantly contribute to priapism in SCD. Pharmacological treatments should ideally target the pathophysiological basis of the disease. Agents that reduce excess free heme in the plasma have emerged as potential therapeutic candidates. This review explores the molecular mechanisms underlying the excess of heme in SCD and its contribution to developing priapism. We discuss pharmacological approaches targeting the excess free heme in the plasma, highlighting it as a potential therapeutic target for future interventions in managing priapism.

Sickle Cell Disease in Brazil: Current Management

Sickle cell disease (SCD) comprises inherited red blood cell disorders due to a mutation in the β-globin gene (c20A > T, pGlu6Val) and is characterized by the presence of abnormal hemoglobin, hemoglobin S, hemolysis, and vaso-occlusion. This mutation, either in a homozygous configuration or in compound states with other β-globin mutations, leads to polymerization of hemoglobin S in deoxygenated conditions, causing modifications in red blood cell shape, particularly sickling. Vaso-occlusive crisis (VOC) is the hallmark of the disease, but other severe complications may arise from repeated bouts of VOCs. SCD is considered a global health problem, and its incidence has increased in some areas of the world, particularly the Americas and Africa. Management of the disease varies according to the region of the world, mainly due to local resources and socioeconomic status. This review aimed to describe more recent data on SCD regarding available treatment options, especially in Brazil. New treatment options are expected to be available to all patients, particularly crizanlizumab, which is already approved in the country.

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.

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.

Mouse models of sickle cell disease: Imperfect and yet very informative

The root cause of sickle cell disease (SCD) has been known for nearly a century, however, few therapies to treat the disease are available. Over several decades of work, with advances in gene editing technology and after several iterations of mice with differing genotype/phenotype relationships, researchers have developed humanized SCD mouse models. However, while a large body of preclinical studies has led to huge gains in basic science knowledge about SCD in mice, this knowledge has not led to the development of effective therapies to treat SCD-related complications in humans, thus leading to frustration with the paucity of translational progress in the SCD field. The use of mouse models to study human diseases is based on the genetic and phenotypic similarities between mouse and humans (face validity). The Berkeley and Townes SCD mice express only human globin chains and no mouse hemoglobin. With this genetic composition, these models present many phenotypic similarities, but also significant discrepancies that should be considered when interpreting preclinical studies results. Reviewing genetic and phenotypic similarities and discrepancies and examining studies that have translated to humans and those that have not, offer a better perspective of construct, face, and predictive validities of humanized SCD mouse models.

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.

Effects of transplantation of umbilical cord blood mononuclear cells into the scrotum on sexual function in elderly mice

Aim: This study investigated the effect of allografting umbilical cord blood mononuclear cells (UCBMCs) into the scrotum on sexual function in male elderly mice. Methods: UCBMCs were injected once into the scrotal sheath cavity of elderly mice. Results: The transplanted UCBMCs survived in the scrotal sheath cavity for 1 month. The mice had significantly increased blood testosterone concentrations, cyclic guanosine monophosphate (cGMP) levels and total nitric oxide synthase (T-NOS) activity in the corpus cavernosum and an increase in the number of mouse matings within 30 min (all p = 0.000). Conclusion: Scrotum-implanted UCBMCs improve the sexual function of male elderly mice through testosterone production and the NOS/cGMP pathway, which may provide an innovative transplantation approach for the treatment of erectile dysfunction.

Epidemiology and treatment of priapism in sickle cell disease

Ischemic priapism is a common but underrecognized morbidity affecting about 33% of adult men with sickle cell disease (SCD). The onset of priapism occurs in the prepubertal period and tends to be recurrent with increasing age. Significantly, priapism is associated with an unrecognized high burden of mental duress and sexual dysfunctions. The diagnosis of priapism is clinical. Many episodes of priapism will resolve spontaneously, but when an episode lasts longer than 4 hours, the episode is considered a urologic emergency requiring quick intervention with either corporal aspiration or shunt surgery. Only 3 randomized clinical trials (stilbesterol, ephedrine or etilefrine, and sildenafil) have been conducted for secondary priapism prevention in SCD. All 3 trials were limited with small sample sizes, selection biases, and inconclusive results after completion. The current molecular understanding of the pathobiology of priapism suggests a relative nitric oxide (NO) deficiency secondary to chronic hemolysis in SCD and associated phosphodiesterase type 5 dysregulation. We posit an increase in NO levels will restore the normal homeostatic relationship between voluntary erection and detumescence. Currently, 2 randomized phase 2 trials (1 double-blind, placebo-controlled trial and 1 open-label, single-arm intervention) are being conducted for secondary priapism prevention in men at high risk for recurrent priapism (NCT03938454 and NCT05142254). We review the epidemiology and pathobiology of priapism, along with mechanistic therapeutic approaches for secondary prevention of priapism in 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.

Development and validation of the sickle cell stress scale-adult

Disease-specific stress can partly explain Sickle Cell Disease (SCD) healthcare utilization. We developed and validated two measures of adult SCD-specific stress for research and clinical care. A large cohort of adults with SCD completed both the 3-item Likert-scale adapted from a previous disease stress measure and a 10-item Likert-scale questionnaire drafted specifically to measure SCD stress. They concurrently completed a psychosocial and health-related quality of life scale battery, then subsequently daily pain diaries. Diaires measured: daily intensity, distress and interference of pain; self-defined vaso-occlusive crises (VOC), opioid use, and types of healthcare utilization for up to 24 weeks. Analyses tested Cronbach's alpha, correlation of the three-item and 10-item stress scales with the concurrent battery, with percentages of pain days, VOC days, opioid use days, and healthcare utilization days, and correlation of baseline stress and 6-month stress for the 10-item scale. Cronbach's alpha was high for both the 3-item (0.73) and 10-item (0.83) SCD stress scales, test-retest correlation of 0.55, expected correlation with the concurrent battery, and correlation with diary-measured healthcare utilization over 6 months. The correlations with the 3-item scale were stronger, but only statistically significant for depression-anxiety. The correlation between the two stress scales was 0.59. Both the 3-item and the 10-item stress scales exhibited good face, construct, concurrent, and predictive validity as well as moderate test-retest reliability. Further scale validation should determine population norms and response to interventions.

Management of Priapism: 2021 Update

Priapism is defined as a persistent penile erection lasting more than 4 hours. Priapism is a rare condition but when present it requires prompt evaluation and definitive diagnosis. Priapism has 2 pathophysiologic subtypes: ischemic and nonischemic. Ischemic priapism accounts for a majority of cases reported. Ischemic priapism is a urologic emergency and requires intervention to alleviate pain and prevent irreversible damage to erectile tissues. This article highlights current guidelines and the contemporary literature on 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.

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.