Sildenafil therapy in patients with sickle cell disease and pulmonary hypertension

An official American Thoracic Society clinical practice guideline: diagnosis, risk stratification, and management of pulmonary hypertension of sickle cell disease

BACKGROUND

In adults with sickle cell disease (SCD), an increased tricuspid regurgitant velocity (TRV) measured by Doppler echocardiography, an increased serum N-terminal pro-brain natriuretic peptide (NT-pro-BNP) level, and pulmonary hypertension (PH) diagnosed by right heart catheterization (RHC) are independent risk factors for mortality.

METHODS

A multidisciplinary committee was formed by clinician-investigators experienced in the management of patients with PH and/or SCD. Clinically important questions were posed, related evidence was appraised, and questions were answered with evidence-based recommendations. Target audiences include all clinicians who take care of patients with SCD.

RESULTS

Mortality risk stratification guides decision making. An increased risk for mortality is defined as a TRV equal to or greater than 2.5 m/second, an NT-pro-BNP level equal to or greater than 160 pg/ml, or RHC-confirmed PH. For patients identified as having increased mortality risk, we make a strong recommendation for hydroxyurea as first-line therapy and a weak recommendation for chronic transfusions as an alternative therapy. For all patients with SCD with elevated TRV alone or elevated NT-pro-BNP alone, and for patients with SCD with RHC-confirmed PH with elevated pulmonary artery wedge pressure and low pulmonary vascular resistance, we make a strong recommendation against PAH-specific therapy. However, for select patients with SCD with RHC-confirmed PH who have elevated pulmonary vascular resistance and normal pulmonary capillary wedge pressure, we make a weak recommendation for either prostacyclin agonist or endothelin receptor antagonist therapy and a strong recommendation against phosphodiesterase-5 inhibitor therapy.

CONCLUSIONS

Evidence-based recommendations for the management of patients with SCD with increased mortality risk are provided, but will require frequent reassessment and updating.

Sildenafil, a PDE5 inhibitor, in the treatment of pulmonary hypertension

Pulmonary hypertension is a devastating disorder, characterized by vascular proliferation, intimal hypertrophy and vasoconstriction. In this disorder, alterations in the nitric oxide pathway have borne out to be important in not only vascular proliferation, but also in the maintenance of vascular tone. After synthesis by soluble guanylate cyclase, cGMP effects vasodilation via protein kinase G and other mediators, and is hydrolyzed by phosphodiesterases (PDEs). PDE5 is abundantly expressed in the mammalian lung and its inhibition by sildenafil has been demonstrated to improve pulmonary vascular physiology in vitro and in vivo animal models of pulmonary hypertension. Recent human data has confirmed the efficacy of sildenafil in therapy for humans with pulmonary arterial hypertension. The following review will discuss the underlying basic science supporting the use of sildenafil, as well as human evidence supporting the critical role of this drug in therapy of patients with pulmonary hypertension.

Regular long-term red blood cell transfusions for managing chronic chest complications in sickle cell disease

BACKGROUND

Sickle cell disease can cause severe vaso-occlusive crises and dysfunction of most organ systems. The two most common chronic chest complications due to sickle cell disease are pulmonary hypertension and chronic sickle lung disease. These complications can lead to morbidity (such as reduced exercise tolerance) and increased mortality.

OBJECTIVES

The aim of this review is to find out whether trials involving people with sickle cell disease that compare regular long-term blood transfusion regimens with an alternative treatment or no treatment show differences in the following:1. the incidence of chronic chest complications (chronic sickle lung disease or pulmonary hypertension);2. the 'severity' or progression of established chronic chest complications;3. the mortality associated with chronic chest complications; and4. unacceptable adverse events.

SEARCH METHODS

We searched the Group's Haemoglobinopathies Trials Register. Specific websites were also searched for information of ongoing or newly completed trials. The search included the reference lists of any randomised controlled trials identified using the above methods.Date of the most recent search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register: 22 July 2013.

SELECTION CRITERIA

We included randomized controlled trials. Trials that used quasi-randomized methods were to be included if sufficient evidence existed that the treatment and control groups were similar at baseline. Trials were eligible for inclusion if they investigated regular red blood cell transfusion regimens (either simple top-up or exchange transfusions) aimed at reducing the incidence, mortality, or objective measures of severity or progression of chronic chest complications (chronic sickle lung and pulmonary hypertension) among men or women of any age and with one of four common sickle cell disease genotypes, ie Hb SS, Sß(0), SC, or Sß(+). These interventions would be compared to an alternative treatment with the same aim or to no treatment.

DATA COLLECTION AND ANALYSIS

No studies matching the selection criteria were found.

MAIN RESULTS

No studies matching the selection criteria were found.

AUTHORS' CONCLUSIONS

There is a need for randomized controlled trials looking at the role of long-term transfusion therapy in pulmonary hypertension and chronic sickle lung disease. Due to the chronic nature of the conditions, such trials should aim to use a combination of objective and subjective measures to assess participants during an extended 'steady state' baseline, and after the intervention.

Transthoracic echocardiography and 6-minute walk test in Kuwaiti sickle cell disease patients

OBJECTIVE

The aim of this study was to investigate cardiac abnormalities in Kuwaiti sickle cell disease (SCD) patients using markers such as tricuspid regurgitant jet velocity (TRJV), pulmonary artery systolic pressure (PASP), and the 6-minute walk (6MW) test and correlate these findings with clinical, hematological, and biochemical parameters.

MATERIALS AND METHODS

Seventy-three patients with SCD and 70 matched controls were studied. The cardiac status was investigated using transthoracic echocardiography in 57 patients; the 6MW test was carried out in patients and controls. Complete blood counts and hemolytic parameters were assessed.

RESULTS

Reticulocytes, bilirubin, and lactate dehydrogenase were significantly higher (p < 0.0001) in patients, while hemoglobin (Hb) and haptoglobin were lower (p < 0.0001) than in controls. The mean fetal Hb among patients was 15.85 ± 8.7%. Of the 57 patients, 14 (24.5%) and 15 (26%) had mild tricuspid and mitral regurgitation, respectively. The mean ejection fraction, TRJV, and PASP were 63.9 ± 6.3%, 1.7 ± 0.5 m/s, and 23.0 ± 7.3 mm Hg, respectively. Three (5.2%) patients had mildly raised TRJV (2.6-2.97 m/s, normal range <2.5 m/s) while 8 (14%) had high PASP (mean 35.3 ± 5.1 mm Hg, normal range <30 mm Hg). Hb, hematocrit, and reticulocytes were different (p = 0.010, p = 0.006, and p = 0.011, respectively) between patients with normal and high PASP. All 3 patients who had a high TRJV had a high PASP, and 2 of these patients died during follow-up. The systolic and diastolic blood pressure, oxygen saturation before and after the 6MW test, and distance walked were lower (p = 0.006, p = 0.000, p = 0.002, p = 0.000, and p = 0.000, respectively) in patients compared to controls.

CONCLUSION

Raised PASP was common in Kuwaiti SCD patients while raised TRJV was not.

[Cardiopulmonary complications in sickle cell anemia]

Sickle cell anemia, considered the most prevalent genetic disease among African Americans, is a disease with autosomal recessive inheritance pattern, characterized by the production of hemoglobin S. This abnormal protein polymerizes and facilitates the formation of fibrillar aggregates that alters the erythrocyte morphology. The stiffness of the red blood cells hinders the adequate transit across microcirculation, leading to hemolysis and increased blood viscosity, which ease thrombogenesis and vascular occlusion, resulting in tissue ischemia and microinfarcts. This disease has a high rate of morbidity and mortality, especially in the first three years of life, when a rapid diagnosis and appropriate treatment are essential. Cardiovascular complications such as heart failure and pulmonary hypertension may develop independently, and each one contributes to increased mortality, being the combination of both risk factors, an important aggravating factor for prognosis and a determinant indicator of mortality.

Pulmonary hypertension associated with chronic hemolytic anemia and other blood disorders

Pulmonary hypertension (PH) has emerged as a major complication of several hematologic disorders, including hemoglobinopathies, red cell membrane disorders, chronic myeloproliferative disorders, and splenectomy. With the exception of sickle cell disease, there are a limited number of studies systematically evaluating the prevalence of PH using the gold standard right heart catheterization in these disorders. The cause of the PH in patients with hematologic disorders is multifactorial, and a thorough diagnostic evaluation is essential. More importantly, there are virtually no high-quality data on the safety and efficacy of PH-targeted therapy in this patient population.

Hematological and hemorheological determinants of the six-minute walk test performance in children with sickle cell anemia

The six-minute walk test is a well-established submaximal exercise reflecting the functional status and the clinical severity of sickle cell patients. The aim of the present cross-sectional study was to investigate the biological determinants of the six-minute walk test performance in children with sickle cell anemia. Hematological and hemorheological parameters, pulmonary function and the six-minute walk test performance were determined in 42 children with sickle cell anemia at steady state. The performance during the six-minute walk test was normalized for age, sex and height and expressed as percentage of the predicted six-minute walk distance. We showed that a high level of anemia, a low fetal hemoglobin expression and low red blood cell deformability were independent predictors of a low six-minute walk test performance. This study describes for the first time the impact of blood rheology in the six-minute walk test performance in children with sickle cell anemia.

Pulmonary hypertension in β thalassaemia

Pulmonary hypertension is one of the leading causes of morbidity and mortality in patients with haemolytic disorders and is a frequent finding in echocardiographic screening of patients with β thalassaemia. Substantial progress has been made in understanding of the multifactorial pathophysiology of pulmonary hypertension in β thalassaemia. Haemolysis, reduced nitric oxide bioavailability, iron overload, and hypercoagulopathy are among the main pathogenetic mechanisms. Various disease-directed therapeutic methods, such as transfusion, chelation, and splenectomy, have important roles in the development of pulmonary hypertension in β thalassaemia. Studies investigating the prevalence of pulmonary hypertension in β thalassaemia are mostly based on echocardiographic findings, and are thus limited by the scarcity of information derived from right heart catheterisation. Invasive pulmonary haemodynamic data are needed to clarify the true prevalence of pulmonary hypertension in β thalassaemia, to better understand the underlying pathophysiology and risk factors, and to define the optimum therapy for this devastating complication.

Myocardial infarction in sickle cell disease: use of translational imaging to diagnose an under-recognized problem

Sickle cell disease (SCD) is an inherited disorder in which microvascular occlusion causes complications across multiple organ systems. The precise incidence of myocardial ischemia and infarction (MI), potentially under-recognized microvascular disease-related complications, remains unknown. The absence of typical atherosclerotic lesions seen in other patients with MI suggests a microvascular mechanism of myocardial injury. Cardiac magnetic resonance (CMR) can demonstrate microvascular disease, making it an appealing modality to assess symptomatic SCD patients. We demonstrate in several dramatic instances how CMR is uniquely able to depict cardiac microvascular obstruction in patients with SCD and chest pain, without which the possibility of myocardial injury would almost certainly be otherwise neglected. Much remains unknown regarding ischemic heart disease in patients with SCD including prevalence, detection, and management. Further work to define evaluation and management algorithms for chest pain in SCD and to develop risk assessment tools may reduce sudden cardiac death in this population.

Misclassification of pulmonary hypertension in adults with sickle hemoglobinopathies using Doppler echocardiography

OBJECTIVE

To compare the diagnostic utility of Doppler echocardiography-derived tricuspid regurgitant jet velocity (TRV) ≥ 2.5 m/s to right heart catheterization (RHC) in defining pulmonary hypertension (PH) in adult patients with sickle cell disease (SCD).

METHODS

This is a retrospective chart review of adults with SCD who had a TRV ≥ 2.5 m/s and RHC. A TRV ≥ 2.5 m/s is suggestive of PH. Pulmonary arterial hypertension (PAH) was defined as a mean pulmonary artery pressure (mPAP) ≥ 25 mm Hg and pulmonary capillary wedge pressure ≤ 15 mm Hg. Pulmonary venous hypertension was defined as an mPAP ≥ 25 mm Hg and pulmonary capillary wedge pressure >15 mm Hg.

RESULTS

Twenty-five patients with SCD met the inclusion criteria. Nine of the 25 (36%) patients had an mPAP ≥ 25 mm Hg. Of these 9, 3 (33%) had PAH and 6 (66%) had pulmonary venous hypertension. Patients with PH did not have a higher TRV (3.1 ± 0.68 vs 2.70 ± 0.16 m/s; P = 0.12), but they did have higher cardiac outputs (10.4 ± 2.7 vs 7.81 ± 1.85 L/min; P = 0.012. The specificity of TRV equal to 2.51 m/s in diagnosing PH was 18.8%. At a TRV of 2.88 m/s, the specificity increased to 81%.

CONCLUSIONS

In adults with SCD, a TRV of 2.5 m/s lacks specificity for use as a screening tool in the diagnosis of PH. Using a TRV of ≥ 2.88 m/s allows the TRV to be used as a screening tool and reduces the false-positive rate and need for unnecessary RHC.

Atherosclerosis in sickle cell disease - a review

Acute, vaso-occlusive crises are the most common and earliest clinical manifestations of sickle cell disease. Recent thoughts about development of atherosclerosis as a result of this disease are presented. Current insights into the pathogenesis of atherosclerosis in sickle cell disease are reviewed, in particular the role of endothelial dysfunction, homocysteine and platelets. Common and uncommon sites of atherosclerosis are described. Radiological assessment and potential therapeutic agents to slow the progression of atherosclerosis are discussed. Finally, treatment of atherosclerosis in certain sites is evaluated and reviewed.

Cardiovascular abnormalities in sickle cell disease

Sickle cell disease is characterized by recurrent episodes of ischemia-reperfusion injury to multiple vital organ systems and a chronic hemolytic anemia, both contributing to progressive organ dysfunction. The introduction of treatments that induce protective fetal hemoglobin and reduce infectious complications has greatly prolonged survival. However, with increased longevity, cardiovascular complications are increasingly evident, with the notable development of a progressive proliferative systemic vasculopathy, pulmonary hypertension (PH), and left ventricular diastolic dysfunction. Pulmonary hypertension is reported in autopsy studies, and numerous clinical studies have shown that increased pulmonary pressures are an important risk marker for mortality in these patients. In epidemiological studies, the development of PH is associated with intravascular hemolysis, cutaneous leg ulceration, renal insufficiency, iron overload, and liver dysfunction. Chronic anemia in sickle cell disease results in cardiac chamber dilation and a compensatory increase in left ventricular mass. This is often accompanied by left ventricular diastolic dysfunction that has also been a strong independent predictor of mortality in patients with sickle cell disease. Both PH and diastolic dysfunction are associated with marked abnormalities in exercise capacity in these patients. Sudden death is an increasingly recognized problem, and further cardiac investigations are necessary to recognize and treat high-risk patients.

Pulmonary complications of sickle cell disease

Sickle cell disease (SCD) is a common monogenetic disorder with high associated morbidity and mortality. The pulmonary complications of SCD are of particular importance, as acute chest syndrome and pulmonary hypertension have the highest associated mortality rates within this population. This article reviews the pathophysiology, diagnosis, and treatment of clinically significant pulmonary manifestations of SCD, including acute chest syndrome, asthma, and pulmonary hypertension in adult and pediatric patients. Clinicians should be vigilant in screening and treating such comorbidities to improve patient outcomes.

Pathology of sickle cell disease

Sickle cell disease (SCD) is a hereditary chronic hemolytic anemia with numerous clinical consequences. Intravascular sickling of red blood cells leads to multiorgan dysfunction. Although the pathophysiology of SCD has been well studied, there remains a lack of effective treatment. Refinements in overall care have improved quality of life; however, premature death is still not uncommon. SCD usually presents in childhood and is common in areas where malaria is (or was) common. The association with malaria is apparently of benefit to the individual because these individuals tend to contract a milder form of the disease. This review highlights the spectrum of pathology seen in people with SCD, with an emphasis on the pathogenesis of sudden death.

Regular long-term red blood cell transfusions for managing chronic chest complications in sickle cell disease

BACKGROUND

Sickle cell disease can cause severe vaso-occlusive crises and dysfunction of most organ systems. The two most common chronic chest complications due to sickle cell disease are pulmonary hypertension and chronic sickle lung disease. These complications can lead to morbidity (such as reduced exercise tolerance) and increased mortality.

OBJECTIVES

The aim of this review is to find out whether trials involving people with sickle cell disease that compare regular long-term blood transfusion regimens with an alternative treatment or no treatment show differences in the following:1. the incidence of chronic chest complications (chronic sickle lung disease or pulmonary hypertension); 2. the 'severity' or progression of established chronic chest complications; 3. the mortality associated with chronic chest complications; and 4. unacceptable adverse events.

SEARCH STRATEGY

We searched the Group's Haemoglobinopathies Trials Register. Specific websites were also searched for information of ongoing or newly completed trials. The search included the reference lists of any randomised controlled trials identified using the above methods.Date of the most recent search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register: 18 April 2011.

SELECTION CRITERIA

We included randomized controlled trials. Trials that used quasi-randomized methods were to be included if sufficient evidence existed that the treatment and control groups were similar at baseline. Trials were eligible for inclusion if they investigated regular red blood cell transfusion regimens (either simple top-up or exchange transfusions) aimed at reducing the incidence, mortality, or objective measures of severity or progression of chronic chest complications (chronic sickle lung and pulmonary hypertension) among men or women of any age and with one of four common sickle cell disease genotypes, ie Hb SS, Sß(0), SC, or Sß(+). These interventions would be compared to an alternative treatment with the same aim or to no treatment.

DATA COLLECTION AND ANALYSIS

No studies matching the selection criteria were found.

MAIN RESULTS

No studies matching the selection criteria were found.

AUTHORS' CONCLUSIONS

There is a need for randomized controlled trials looking at the role of long-term transfusion therapy in pulmonary hypertension and chronic sickle lung disease. Due to the chronic nature of the conditions, such trials should aim to use a combination of objective and subjective measures to assess participants during an extended 'steady state' baseline, and after the intervention.

Mild haemorheological changes induced by a moderate endurance exercise in patients with sickle cell anaemia

The levels and duration of physical activity that can be considered as completely safe in patients with sickle cell anaemia (SCA) is unknown. The present study compared the haemorheological and haematological profile, cell density distribution and basic biochemistry between a group of 17 patients with SCA and 21 healthy subjects before and after a 20 min duration submaximal cycling exercise at the same absolute workload. Blood was sampled at rest and 3 min after the end of exercise for measurement of biological parameters. Exercise did not affect the haematocrit and blood viscosity in the two groups. Plasma viscosity was not different between the two groups at rest and similarly increased with exercise. The proportion of intermediary dense cells (with density between 1·11 and 1·12 g/ml) decreased with exercise in the SCA group resulting in an increase in the proportion of red blood cells with a density >1·12 g/ml. No change was observed in the control group. The present study suggests that mild-moderate exercise is not very harmful for SCA patients. The haemorheological and haematological changes were very mild, except for the formation of dense cells but no clinically significant signs of medical complication were present in any of the patients.

Hospitalization for pain in patients with sickle cell disease treated with sildenafil for elevated TRV and low exercise capacity

In adults with sickle cell disease (SCD), an increased tricuspid regurgitation velocity (TRV) by Doppler echocardiography is associated with increased morbidity and mortality. Although sildenafil has been shown to improve exercise capacity in patients with pulmonary arterial hypertension, it has not been evaluated in SCD. We therefore sought to determine whether sildenafil could improve exercise capacity in SCD patients with increased TRV and a low exercise capacity. A TRV ≥ 2.7 m/s and a 6-minute walk distance (6MWD) between 150 and 500 m were required for enrollment in this 16-week, double-blind, placebo-controlled sildenafil trial. After 74 of the screened subjects were randomized, the study was stopped early due to a higher percentage of subjects experiencing serious adverse events in the sildenafil arm (45% of sildenafil, 22% of placebo, P = .022). Subject hospitalization for pain was the predominant cause for this difference: 35% with sildenafil compared with 14% with placebo (P = .029). There was no evidence of a treatment effect on 6MWD (placebo-corrected effect -9 m; 95% confidence interval [95% CI] -56-38; P = .703), TRV (P = .503), or N-terminal pro-brain natriuretic peptide (P = .410). Sildenafil appeared to increase hospitalization rates for pain in patients with SCD. This study is registered at www.clinicaltrials.gov as NCT00492531.

Inhibition of phosphodiesterase 9A reduces cytokine-stimulated in vitro adhesion of neutrophils from sickle cell anemia individuals

OBJECTIVE

Leukocyte adhesion to vessel walls may initiate vaso-occlusion in sickle cell anemia (SCA); however, the extent to which inflammation participates in this mechanism is not understood. This in vitro study investigated whether inflammatory molecules, commonly augmented in SCA, can affect neutrophil adhesive properties and whether cyclic guanosine monophosphate (cGMP)-elevating agents can inhibit such adhesion.

SUBJECTS AND METHODS

Effects of Interleukin 8 (IL-8), tumor necrosis factor-α (TNF-α), granulocyte macrophage-colony stimulating factor (GM-CSF) cytokines, BAY 73-6691 [phosphodiesterase (PDE)-9A-inhibitor], and BAY 41-2271 (guanylate-cylase stimulator) on the adhesive properties of neutrophils from healthy control (CON) and steady-state SCA individuals were determined using static-adhesion assays.

RESULTS

SCA neutrophils demonstrated increased adhesive properties, compared to CON neutrophils; IL-8, TNF-α and GM-CSF increased CON neutrophil adhesion and further increased SCA neutrophil adhesion to fibronectin (FN). The PDE9A inhibitor, BAY-73-6691, significantly reduced basal CON neutrophil and SCA neutrophil adhesion; this was accompanied by decreased SCA neutrophil surface expressions of the L-selectin and CD11b adhesion molecules. BAY-73-6691 also significantly reduced cytokine-stimulated CON neutrophil and SCA neutrophil adhesion to FN; however, this was not accompanied by alterations in adhesion-molecule presentation.

CONCLUSIONS

The chronic inflammatory nature of SCA may contribute to leukocyte adhesive functions in SCA. Furthermore, elevation of leukocyte cGMP may be an interesting approach for inhibition of leukocyte adhesion to the vessel wall, even in the presence of inflammatory stimuli.

Reconstructing sickle cell disease: a data-based analysis of the "hyperhemolysis paradigm" for pulmonary hypertension from the perspective of evidence-based medicine

The "hyperhemolytic paradigm" (HHP) posits that hemolysis in sickle disease sequentially and causally establishes increased cell-free plasma Hb, consumption of NO, a state of NO biodeficiency, endothelial dysfunction, and a high prevalence of pulmonary hypertension. The basic science underpinning this concept has added an important facet to the complexity of vascular pathobiology in sickle disease, and clinical research has identified worrisome clinical issues. However, this critique identifies and explains a number of significant concerns about the various HHP component tenets. In addressing these issues, this report presents: a very brief history of the HHP, an integrated synthesis of mechanisms underlying sickle hemolysis, a review of the evidentiary value of hemolysis biomarkers, an examination of evidence bearing on existence of a hyperhemolytic subgroup, and a series of questions that should naturally be applied to the HHP if it is examined using critical thinking skills, the fundamental basis of evidence-based medicine. The veracity of different HHP tenets is found to vary from true, to weakly supported, to demonstrably false. The thesis is developed that the HHP has misidentified the mechanism and clinical significance of its findings. The extant research questions identified by these analyses are delineated, and a conservative, evidence-based approach is suggested for application in clinical medicine.

Pulmonary hypertension, tricuspid regurgitant velocity screening, and the nitric oxide pathway

Chronic pulmonary complications, including pulmonary hypertension (PH), are common in sickle cell disease (SCD), especially in adults with sickle cell anemia (SCA). The underlying pathophysiology is complex and variable, involving multiple biological systems. Recent emphasis has been placed on the pleotropic biological factor nitric oxide (NO). An elevated tricuspid regurgitant velocity (TRV) appears to have limitations in specificity in SCA, but may indicate the presence of PH, a diagnosis confirmed by right heart catheterization. TRV has been used in recent clinical trials to identify or define subjects with PH for enrollment into PH-specific interventions; these include sildenafil, which enhances NO-induced vasorelaxation. Results from a controlled trial show no benefit and an unexpected increase in adverse events, emphasizing the biological complexities of SCA. Management remains principally supportive, includes recognition and treatment of comorbidities, and may incorporate individualized PH-specific strategies (despite recent trials) based on appropriate diagnostic testing. Ultimately, therapy is likely to be multimodal and tailored to the processes identified to be the most contributory in a given individual. Based on the relative prevalence of the conditions, routine screening for asthma in children with SCD and by Doppler echocardiography to measure TRV as an initial screen for PH in adults with SCA may be warranted. Data are limited regarding the clinical utility of screening in other forms of SCD and the pediatric population. This article offers an individual perspective on practical and challenging clinical considerations.

Sickle-cell disease

Sickle-cell disease is one of the most common severe monogenic disorders in the world. Haemoglobin polymerisation, leading to erythrocyte rigidity and vaso-occlusion, is central to the pathophysiology of this disease, although the importance of chronic anaemia, haemolysis, and vasculopathy has been established. Clinical management is basic and few treatments have a robust evidence base. One of the main problems of sickle-cell disease in children is the development of cerebrovascular disease and cognitive impairment, and the role of blood transfusion and hydroxycarbamide for prevention of these complications is starting to be understood. Recurrent episodes of vaso-occlusion and inflammation result in progressive damage to most organs, including the brain, kidneys, lungs, bones, and cardiovascular system, which becomes apparent with increasing age. Most people with sickle-cell disease live in Africa, where little is known about this disease; however, we do know that the disorder follows a more severe clinical course in Africa than for the rest of the world and that infectious diseases have a role in causing this increased severity of sickle-cell disease. More work is needed to develop effective treatments that specifically target pathophysiological changes and clinical complications of sickle-cell disease.

Pulmonary complications of hemoglobinopathies

Hemoglobinopathies are diseases caused by genetic mutations that result in abnormal, dysfunctional hemoglobin molecules or lower levels of normal hemoglobin molecules. The most common hemoglobinopathies are sickle cell disease (SCD) and the thalassemias. In SCD, an abnormal hemoglobin alters the erythrocyte, causing a chronic hemolytic anemia, which can lead to pulmonary parenchymal damage and impaired vascular function. Pulmonary complications of SCD include the acute chest syndrome (ACS), reactive airways disease, pulmonary hypertension (PH), and pulmonary fibrosis. Episodes of ACS and the development of PH both increase the risk of death in patients with SCD. Both α and β thalassemia are characterized by impaired production of hemoglobin subunits, and severity of disease varies widely. Although screening studies suggest that PH is a common complication for patients with thalassemia, its impact on survival is unknown. Understanding the pathogenesis, diagnostic options, and prevention and treatment strategies for such complications is critical for clinicians who care for these patients. In this review, we discuss the mechanisms and clinical presentation of pulmonary complications associated with hemoglobinopathies, with a focus on recent advances in pathogenesis and treatment.

Effect of oral arginine supplementation on exhaled nitric oxide concentration in sickle cell anemia and acute chest syndrome

INTRODUCTION

Decreased exhaled nitric oxide levels (FE(NO)) have been described in patients with sickle cell disease (SCD) and a history of acute chest syndrome (ACS) when compared with non-ACS controls. Oral arginine supplementation has been shown to increase FE(NO) in healthy participants, but its effect in SCD patients is not known.

OBJECTIVE

To determine the effect of oral arginine intake on FENO in sickle cell patients with and without history of ACS, and in healthy controls.

HYPOTHESIS

No differences in the FE(NO) increase were seen in SCD patients with a history of ACS (ACS+) compared with healthy controls (HC) and SCD patients without history of ACS (ACS-).

MATERIALS AND METHODS

ACS+ (n=6), ACS- (n=9), and HC (n=7) patients were studied. At baseline, and after the administration of escalating doses of oral L-arginine (0.1, 0.2, and 0.4 g/kg), serial measurements were made of the following: FE(NO), plasma concentrations of arginine, ornithine, citrulline, aspartate, glutamate, arginine/ornithine ratio, nitrite, nitrate, heart rate (HR), respiratory rate (RR), blood pressure (BP), oxygen saturation (SpO2), forced expiratory volume in 1 second (FEV1), and forced vital capacity (FVC).

MAIN RESULTS

At baseline, FE(NO) did not differ among the groups. ACS- and ACS+ groups were deficient in arginine, and had decreased FEV1, FVC, and SaO2 when compared with HC patients. After arginine supplementation, FE(NO), arginine, ornithine, citrulline, nitrite, and the arginine/ornithine ratio increased similarly in all groups. Changes from baseline for HR, BP, SpO2, RR, FEV1, and FVC were minimal and similar in all groups.

CONCLUSIONS

In contrast to our earlier study, ACS+ patients had similar FE(NO) values when compared with ACS- and HC patients. All SCD patients were arginine deficient at baseline and showed impairment in respiratory physiology when compared with HC patients. After arginine supplementation, FE(NO) concentration increased in all groups to a similar degree, and lung function and physiologic parameters were minimally affected. The physiologic significance of alterations in FE(NO) in SCD patients and its relationship to ACS predilection requires further delineation.

The critical roles of platelet activation and reduced NO bioavailability in fatal pulmonary arterial hypertension in a murine hemolysis model

Pulmonary arterial hypertension (PAH) is suspected to be a strong mortality determinant of hemolytic disorders. However, direct contribution of acute intravascular hemolysis to fatal PAH has not been investigated. The roles of nitric oxide (NO) insufficiency and platelet activation in hemolysis-associated fatal PAH have been suspected but not been experimentally studied. We recently generated a unique intravascular hemolysis mouse model in which the membrane toxin, intermedilysin (ILY), exclusively lyses the erythrocytes of transgenically expressing human CD59 mice (ThCD59(RBC)), thereby inducing ILY-dose-dependent massive hemolysis. Using this murine hemolysis model, we found that the acute increase in pulmonary arterial pressure leading to right ventricle failure caused sudden death. Reduced NO bioavailability and massive platelet activation/aggregation leading to the formation of massive thrombosis specifically in the pulmonary microvasculature played the critical roles in pathogenesis of acute hemolysis-associated fatal PAH. Therapeutic interventions enhancing NO bioactivity or inhibiting platelet activation prevented sudden death or prolonged survival time via the suppression of the acute increase in pulmonary arterial pressure and improvement of right ventricle function. These findings further highlight the importance of the inhibition of platelet activation and the enhancement of NO bioavailability for the treatment and prevention of hemolysis-associated (fatal) PAH.

Pulmonary hypertension in hemolytic disorders: pulmonary vascular disease: the global perspective

The inherited hemoglobin disorders sickle cell disease and thalassemia are the most common monogenetic disorders worldwide. Pulmonary hypertension is one of the leading causes of morbidity and mortality in adult patients with sickle cell disease and thalassemia, and hemolytic disorders are potentially among the most common causes of pulmonary hypertension. The pathogenesis of pulmonary hypertension in hemolytic disorders is likely multifactorial, including hemolysis, impaired nitric oxide (NO) bioavailability, chronic hypoxemia, chronic thromboembolic disease, chronic liver disease, and asplenia. In contrast to patients with traditional forms of pulmonary arterial hypertension, patients with hemolytic disorders have a mild-to-moderate degree of elevation in mean pulmonary pressures, with mild elevations in pulmonary vascular resistance. The hemodynamic etiology of pulmonary hypertension in these patients is multifactorial and includes pulmonary arterial hypertension, pulmonary venous hypertension, and pulmonary hypertension secondary to a hyperdynamic state. Currently, there are limited data on the effects of any specific treatment modality for pulmonary hypertension in patients with hemolytic disorders. It is likely that maximization of treatment of the primary hemoglobinopathy in all patients and treatment with selective pulmonary vasodilators and antiproliferative agents in patients with pulmonary arterial hypertension would be beneficial. However, there is still a major need for large multinational trials of novel therapies for this patient population.

Sickle-cell anemia and pulmonary hypertension

PURPOSE

To provide nurse practitioners (NPs) information about sickle-cell disease (SCD) and pulmonary hypertension (PHTN) as a complication. A case study is presented to illustrate the diagnosis of PHTN in a patient with SCD. Clinical manifestations, diagnosis, and interventions for both SCD and PHTN are also discussed.

DATA SOURCE

A literature search to support this case review was conducted in PubMed and SCOPUS using key search words. Specific information for the case study was obtained from a patient in a primary care setting.

CONCLUSION

Pulmonary hypertension is frequently diagnosed secondary to hemoglobinopathies such as SCD. Patients with sickle-cell anemia, a lifelong hereditary hemoglobinopathy, are now surviving into adulthood because of the advances made in treatment. About one third of these patients develop pulmonary hypertension, a complication that carries a 40% mortality rate. Delayed diagnosis can affect the patient's quality of life. Timely diagnosis and referral is imperative, but only if the advanced practitioner is able to recognize this common complication.

IMPLICATIONS FOR PRACTICE

Many patients with SCD are seen in primary care practices. Such is the situation for the patient in this case study. Familiarity with pulmonary hypertension secondary to SCD can increase the awareness of NPs of this potential consequence and initiate early diagnostic evaluation.

Pulmonary hypertension and nitric oxide depletion in sickle cell disease

During the past decade a large body of experimental and clinical studies has focused on the hypothesis that nitric oxide (NO) depletion by plasma hemoglobin in the microcirculation plays a central role in the pathogenesis of many manifestations of sickle cell disease (SCD), particularly pulmonary hypertension. We have carefully examined those studies and believe that the conclusions drawn from them are not adequately supported by the data. We agree that NO depletion may well play a role in the pathophysiology of other hemolytic states such as paroxysmal nocturnal hemoglobinuria, in which plasma hemoglobin concentrations are often at least an order of magnitude greater than in SCD. Accordingly, we conclude that clinical trials in SCD designed to increase the bioavailability of NO or association studies in which SCD clinical manifestations are related to plasma hemoglobin via its surrogates should be viewed with caution.

Exercise capacity and haemodynamics in patients with sickle cell disease with pulmonary hypertension treated with bosentan: results of the ASSET studies

Doppler-defined pulmonary hypertension (PH) in sickle cell disease (SCD) is associated with 40% mortality at 40 months. To assess the effect of bosentan in SCD-PH, two randomized, double-blind, placebo-controlled, 16-week studies were initiated. Safety concerns are particularly relevant in SCD due to comorbid conditions. ASSET-1 and -2 enrolled patients with pulmonary arterial hypertension (PAH) and pulmonary venous hypertension (PH), respectively. Haemodynamics and 6-min walk distance (6MWD) were obtained at baseline and week 16. The studies were terminated due to slow site initiation and patient enrolment (n = 26). Bosentan appeared to be well tolerated. Although sample sizes were limited, in ASSET-1 at baseline, 6MWD correlated with cardiac output (CO; P = 0.006) with non-significant inverse correlations between 6MWD and pulmonary vascular resistance (PVR; P = 0.07) and between 6MWD and right atrial pressure (P = 0.08). In ASSET-2 at baseline, there was a non-significant correlation between 6MWD and CO (P = 0.06). Due to limited sample sizes, efficacy endpoints were not analysed. However, in both studies, non-significant increases in CO were observed with bosentan compared to placebo. Similarly, non-significant decreases in PVR were observed with bosentan. Limited data in SCD-PH suggest that a low 6MWD predicts a low CO. Standard-dose bosentan appears to be well tolerated. Further investigation is warranted. Clinicaltrials.gov registration numbers NCT00310830, NCT00313196, NCT00360087.

Pulmonary hypertension in hemolytic anemias

Pulmonary hypertension (PH) has been reported with nearly all forms of the inherited as well as the acquired hemolytic anemias. Recent research investigating the pathophysiology of PH in sickle cell disease and thalassemia has helped elucidate the central role of hemolysis-mediated endothelial dysfunction in the development of PH in these populations. Although the most appropriate treatment of PH in patients with hemolytic anemia is not clearly defined, the associated significant increased risk of death underscores the need for randomized clinical trials in this area.

Investigational drugs in sickle cell anemia

Sickle cell anemia is one of the most common autosomal recessive diseases in the world. Patients with sickle cell anemia have variable penetrance and it is hard to predict the risk and timing of complications. It is characterized by a point mutation in the beta-globin gene (GAG --> GTG) and the production of hemoglobin S. The latter leads to decreased deformability of the red blood cells (RBCs) that adhere to endothelia cells culminating in vascular occlusion and its sequelae of tissue ischemia and organ damage. Moreover, sickled RBCs undergo intravascular hemolysis and accelerated erythropoesis. The hallmarks of this disease are shortened RBC survival and vaso-occlusive crises. For the past ten years, the pathophysiology of this disease has been better elucidated and has led to significant improvements in the standard of care. Vaso-occlusion is now understood to be a complex event that involves abnormal interactions between RBCs, leukocytes, endothelial cells and the coagulation pathways. The field of translational research in sickle cell anemia has expanded greatly and has led to new clinical trials with new therapeutic agents and strategies. In this paper, we review the drugs that are now being investigated in the treatment of sickle cell anemia.

Non-congenital heart disease associated pediatric pulmonary arterial hypertension

Recognition of causes of pulmonary hypertension other than congenital heart disease is increasing in children. Diagnosis and treatment of any underlying cause of pulmonary hypertension is crucial for optimal management of pulmonary hypertension. This article discusses the available knowledge regarding several disorders associated with pulmonary hypertension in children: idiopathic pulmonary arterial hypertension (IPAH), pulmonary capillary hemangiomatosis, pulmonary veno-occlusive disease, hemoglobinopathies, hepatopulmonary syndrome, portopulmonary hypertension and HIV. Three classes of drugs have been extensively studied for the treatment of IPAH in adults: prostanoids (epoprostenol, treprostinil, iloprost, beraprost), endothelin receptor antagonists (bosentan, sitaxsentan, ambrisentan), and phosphodiesterase inhibitors (Sildenafil, tadalafil). These medications have been used in treatment of children with pulmonary arterial hypertension, although randomized clinical trial data is lacking. As pulmonary vasodilator therapy in certain diseases may be associated with adverse outcomes, further study of these medications is needed before widespread use is encouraged.

Endothelin receptor antagonists for pulmonary hypertension in adult patients with sickle cell disease

Pulmonary Hypertension is a serious complication of sickle cell disease (SCD), with high morbidity and mortality. Endothelin (ET)-1, a potent vasoconstrictor elevated in SCD, acts through the ET receptors (ETR), ETR-A and ETR-B. Bosentan and ambrisentan are ETR blockers used in primary pulmonary hypertension. We report on the use of ETR blocking agents in a cohort of 14 high-risk SCD adult patients with pulmonary hypertension. Patients underwent right heart catheterization, 6-min walk test, echocardiogram, physical examination and blood work-up before starting ETR blockers. Eight patients received ETR blockers as initial therapy; six patients were already taking sildenafil. Over more than 6 months of therapy, sequential measurements of 6-min walk distance increased significantly (baseline 357 +/- 22 to 398 +/- 18 m at 5-6 months, P < 0.05). Downward trends were observed for amino-terminal brain natriuretic peptide and tricuspid regurgitant velocity. Pulmonary artery mean pressures decreased in three patients that had repeat right heart catheterization (44-38 mmHg). Adverse events were: increased serum alanine aminotransferase (2), peripheral oedema (4), rash (1), headache (3), decreased haemoglobin (2). Therapy was stopped in two patients who were switched then to the other ETR blocker agent. These data suggest preliminary evidence for the benefit of bosentan and ambrisentan in pulmonary hypertension in SCD.

Angiogenic and inflammatory markers of cardiopulmonary changes in children and adolescents with sickle cell disease

Background

Pulmonary hypertension and left ventricular diastolic dysfunction are complications of sickle cell disease. Pulmonary hypertension is associated with hemolysis and hypoxia, but other unidentified factors are likely involved in pathogenesis as well.

Design and Methods

Plasma concentrations of three angiogenic markers (fibroblast growth factor, platelet derived growth factor–BB [PDGF-BB], vascular endothelial growth factor [VEGF]) and seven inflammatory markers implicated in pulmonary hypertension in other settings were determined by Bio-Plex suspension array in 237 children and adolescents with sickle cell disease at steady state and 43 controls. Tricuspid regurgitation velocity (which reflects systolic pulmonary artery pressure), mitral valve E/Edti ratio (which reflects left ventricular diastolic dysfunction), and a hemolytic component derived from four markers of hemolysis and hemoglobin oxygen saturation were also determined.

Results

Plasma concentrations of interleukin-8, interleukin-10 and VEGF were elevated in the patients with sickle cell disease compared to controls (P≤0.003). By logistic regression, greater values for PDGF-BB (P = 0.009), interleukin-6 (P = 0.019) and the hemolytic component (P = 0.026) were independently associated with increased odds of elevated tricuspid regurgitation velocity while higher VEGF concentrations were associated with decreased odds (P = 0.005) among the patients with sickle cell disease. These findings, which are consistent with reports that PDGF-BB stimulates and VEGF inhibits vascular smooth muscle cell proliferation, did not apply to E/Etdi.

Conclusions

Circulating concentrations of angiogenic and pro-Inflammatory markers are altered in sickle cell disease children and adolescents with elevated tricuspid regurgitation velocity, a subgroup that may be at risk for developing worsening pulmonary hypertension. Further studies to understand the molecular changes in these children are indicated.

Bosentan for pulmonary hypertension and other pulmonary diseases: emerging evidence

Endothelin-1 is a potent vasoconstrictor and mitogen that is primarily synthesized and released from vascular endothelial cells. Bosentan is a dual endothelin-receptor antagonist that initially received approval for treatment of WHO group I pulmonary arterial hypertension (PAH) for patients in functional classes III and IV. Analysis of a study conducted in functional class II patients (Endothelin Antagonist Trial in Mildly Symptomatic PAH Patients [EARLY] trial) suggest its efficacy for these less symptomatic patients. In addition, bosentan has demonstrated efficacy in patients with congenital heart disease and Eisenmengers syndrome with right to left shunting and in HIV-related PAH. Studies of bosentan in inoperable or residual chronic thromboembolic pulmonary hypertension suggest possible efficacy. Bosentan appears promising in patients with idiopathic pulmonary fibrosis who do not have pulmonary hypertension. Combinations of bosentan with other PAH therapies such as iloprost and sildenafil may have incremental benefit over monotherapy.

Functional capacity in children and young adults with sickle cell disease undergoing evaluation for cardiopulmonary disease

Although cardiopulmonary disease is associated with decreased functional capacity among adults with sickle cell disease (SCD), its impact on functional capacity in children with SCD is unknown. We evaluated 6-min walk (6MW) distance in 77 children and young adults with SCD undergoing screening for cardiopulmonary disease. Of 30 subjects who also underwent cardiopulmonary exercise testing, we found evidence for decreased exercise capacity in a significant proportion. Exercise capacity was related to baseline degree of anemia and was significantly lower in subjects with a history of recurrent acute chest syndrome. We found that 6MW distance adjusted for weight and body surface area was shorter in subjects with restrictive lung disease but that only 6MW adjusted for weight remained significantly shorter when we controlled for baseline hemoglobin. Exercise capacity was not significantly different in subjects with and without cardiopulmonary disease. We conclude that restrictive lung disease is associated with shorter 6MW distances in children and young adults with SCD, but that variables associated with decreased exercise capacity, other than anemia, remain unclear. Our study underscores the importance of further delineating the direct pathophysiologic processes that contribute to decreased exercise capacity observed among individuals with SCD and cardiopulmonary disease.

Blood donation and blood transfusion: special considerations for African Americans

Unique issues in blood donation and blood transfusion regarding African Americans (AA) in the United States span the donation process, manufacturing of products, and hospital transfusion service. As AAs become a growing population, a constant supply of blood donated by AAs is necessary to support this growth. Nationally, AAs are underrepresented in blood collection, which may be secondary to AAs having higher rates of anemia and other deferrable conditions or unique motivators as well as other barriers to blood donation. When investigating blood transfusion practices, blood utilization for different races and ethnicities is unknown. AAs may receive more red blood cell (RBC) transfusions because they have a higher proportion of diseases that require transfusion. Patients with sickle cell disease are at increased risk of RBC alloimmunization likely due to the predominance of RBC units from white donors in the existing blood supply, but it is not known if all AA recipients experience increased alloimmunization rates compared with whites. In conclusion, there is a need to increase donation by AAs, which can only be achieved by conducting studies to understand racial differences in donor recruitment and to better understand blood utilization and adverse events as a factor of race and ethnicity.

Hemoglobin disorders and endothelial cell interactions

Endothelial damage and inflammation make a significant contribution to the pathophysiology of sickle cell disease (SCD) and the beta-thalassemia syndromes. Endothelial dysfunction and ensuing vasculopathy are implicated in pulmonary hypertension in the hemoglobinopathies and endothelial activation and endothelial-blood cell adhesion, accompanied by inflammatory processes and oxidative stress, are imperative to the vaso-occlusive process in SCD. Herein, we discuss the role that the endothelium plays in all of these processes and the effect that genetic modifiers and hydroxyurea therapy may have upon endothelial interactions. Therapies targeting the endothelium and endothelial interactions may represent a promising approach for treating these diseases.