Long-term tolerability of phosphodiesterase-5 inhibitors in pulmonary hypertension of sickle cell disease

Pulmonary Hypertension in Sickle Cell Disease: Novel Findings of Gene Polymorphisms Related to Pathophysiology

Pulmonary hypertension (PH) is a progressive and potentially fatal complication of sickle cell disease (SCD), affecting 6-10% of adult SCD patients. Various mechanisms and theories have been evaluated to explain the pathophysiology of this disease. However, questions remain, particularly regarding the clinical heterogeneity of the disease in terms of symptoms, complications, and survival. Beyond the classical mechanisms that have been thoroughly investigated and include hemolysis, nitric oxide availability, endothelial disorders, thrombosis, and left heart failure, attention is currently focused on the potential role of genes involved in such processes. Potential candidate genes are investigated through next-generation sequencing, with the transforming growth factor-beta (TGF-β) pathway being the initial target. This field of research may also provide novel targets for pharmacologic agents in the future, as is already the case with idiopathic PH. The collection and processing of data and samples from multiple centers can yield reliable results that will allow a better understanding of SCD-related PH as a part of the disease's clinical spectrum. This review attempts to capture the most recent findings of studies on gene polymorphisms that have been associated with PH in SCD patients.

Pulmonary hypertension in sickle cell disease

Sickle cell disease (SCD) is a complex genetic disorder that has long challenged both patients and healthcare professionals. One of its chronic and debilitating complications is pulmonary hypertension (PH). SCD-associated PH is often post-capillary, secondary to left heart disease. It can also sometimes be pre-capillary with multiple and often interrelated mechanisms including obstructive remodeling of the pulmonary vascular bed secondary to hemolysis, endothelial dysfunction, thrombosis, hypoxia, or associated risk factors like portal hypertension. Screening symptomatic patients with echocardiographic signs of PH is crucial to determine those who should undergo right heart catheterization, the cornerstone exam to diagnose and categorize patients with PH. The workup following the diagnosis relies on identifying the cause of PH to personalize treatment. Ongoing efforts are made to treat this complex condition, starting with treating the underlying disease with hydroxyurea or chronic blood exchange transfusion. Robust data on the efficacy of PAH-specific therapies are lacking in this specific population. Initiation of such therapies must be made by an expert center after a case-by-case assessment of the benefit-risk ratio according to the phenotype and the mechanisms involved in the development of PH. Efforts are also poured into studying the interventional and medical therapies used on chronic thromboembolic PH for patients presenting with a thrombotic form. The management of those patients requires a multidisciplinary approach, with conjoint efforts from PH and SCD specialists.

The Role of Inflammation in The Cellular and Molecular Mechanisms of Cardiopulmonary Complications of Sickle Cell Disease

Cardiopulmonary complications remain the major cause of mortality despite newer therapies and improvements in the lifespan of patients with sickle cell disease (SCD). Inflammation has been identified as a major risk modifier in the pathogenesis of SCD-associated cardiopulmonary complications in recent mechanistic and observational studies. In this review, we discuss recent cellular and molecular mechanisms of cardiopulmonary complications in SCD and summarize the most recent evidence from clinical and laboratory studies. We emphasize the role of inflammation in the onset and progression of these complications to better understand the underlying pathobiological processes. We also discuss future basic and translational research in addressing questions about the complex role of inflammation in the development of SCD cardiopulmonary complications, which may lead to promising therapies and reduce morbidity and mortality in this vulnerable population.

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.

The different facets of sickle cell disease-related pulmonary hypertension

PURPOSE OF REVIEW

Sickle cell disease (SCD), one of the most common genetic diseases in the world, is characterized by repeated episodes of hemolysis and vaso-occlusion. Hemolytic anemia is a risk factor for the development of pulmonary hypertension, and currently SCD-related pulmonary hypertension is classified as World Health Organization group 5 pulmonary hypertension. Patients with SCD-related pulmonary hypertension have unique hemodynamics, multiple comorbidities, and distinct phenotypes that may contribute to the development of pulmonary hypertension.

RECENT FINDINGS

SCD-related pulmonary hypertension is defined as a mean pulmonary artery pressure >20 mmHg, a pulmonary artery occlusion pressure ≤15 mmHg and relatively low pulmonary vascular resistance (>2 Wood units) rather than the traditional definition of ≥3 Wood units, an important distinction due to a baseline high-cardiac output state in the setting of chronic anemia and low vascular resistance. Diastolic dysfunction is frequently identified in this patient population and right heart catheterization is essential to determine if combined pre- and postcapillary pulmonary hypertension is present. Thromboembolism is common among patients with SCD, and screening for chronic thromboembolic pulmonary hypertension is essential. Data regarding advanced therapies are limited. Primary treatment options include targeting correction of their primary hemoglobinopathy as well as aggressive management of underlying comorbid conditions.

SUMMARY

SCD-related pulmonary hypertension is common among patients with SCD and is associated with increased mortality. A high index of suspicion is warranted during evaluation to identify all potential factors that may be contributing to disease.