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

Hydroxyurea in the management of sickle cell disease-associated priapism: a scoping review

Sickle cell disease (SCD) is an inherited hemolytic-hemoglobinopathy that affects the ability of erythrocytes to deliver oxygen in the body. Hydroxyurea is a pharmacologic agent that has been approved by the Food and Drug Administration (FDA) for the treatment of SCD crises since 1998. It has also been proposed as a therapy for recurrent ischemic priapism (RIP), recurrent prolonged or unwanted erections in the absence of sexual stimulation, which occurs commonly in SCD. The premise behind hydroxyurea's therapeutic effect is that it improves vascular function and hemoglobin metabolism. Its potential role in RIP is to normalize the nitric oxide (NO) signaling pathway, which is fundamental for the regulatory physiology of the erection response. Hydroxyurea has been investigated in diverse research studies, including a recent clinical trial, showing its potential benefit for treating RIP. In this article, we performed a scoping review of the effectiveness of hydroxyurea for the treatment of SCD-associated RIP.

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

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

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

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

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.

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.