Cardiopulmonary complications of sickle cell disease: role of nitric oxide and hemolytic anemia

Double-edged functions of hemopexin in hematological related diseases: from basic mechanisms to clinical application

It is now understood that hemolysis and the subsequent release of heme into circulation play a critical role in driving the progression of various diseases. Hemopexin (HPX), a heme-binding protein with the highest affinity for heme in plasma, serves as an effective antagonist against heme toxicity resulting from severe acute or chronic hemolysis. In the present study, changes in HPX concentration were characterized at different stages of hemolytic diseases, underscoring its potential as a biomarker for assessing disease progression and prognosis. In many heme overload-driven conditions, such as sickle cell disease, transfusion-induced hemolysis, and sepsis, endogenous HPX levels are often insufficient to provide protection. Consequently, there is growing interest in developing HPX therapeutics to mitigate toxic heme exposure. Strategies include HPX supplementation when endogenous levels are depleted and enhancing HPX's functionality through modifications, offering a potent defense against heme toxicity. It is worth noting that HPX may also exert deleterious effects under certain circumstances. This review aims to provide a comprehensive overview of HPX's roles in the progression and prognosis of hematological diseases. It highlights HPX-based clinical therapies for different hematological disorders, discusses advancements in HPX production and modification technologies, and offers a theoretical basis for the clinical application of HPX.

Cardiovascular consequences of sickle cell disease

Sickle cell disease (SCD) is an inherited blood disorder caused by a single point mutation within the beta globin gene. As a result of this mutation, hemoglobin polymerizes under low oxygen conditions causing red blood cells to deform, become more adhesive, and increase in rigidity, which affects blood flow dynamics. This process leads to enhanced red blood cell interactions with the endothelium and contributes to vaso-occlusion formation. Although traditionally defined as a red blood cell disorder, individuals with SCD are affected by numerous clinical consequences including stroke, painful crisis episodes, bone infarctions, and several organ-specific complications. Elevated cardiac output, endothelium activation along with the sickling process, and the vaso-occlusion events pose strains on the cardiovascular system. We will present a review of the cardiovascular consequences of sickle cell disease and show connections with the vasculopathy related to SCD. We will also highlight biophysical properties and engineering tools that have been used to characterize the disease. Finally, we will discuss therapies for SCD and potential implications on SCD cardiomyopathy.

Hepatitis C virus (HCV) infection among patients with sickle cell disease at the Korle-Bu teaching hospital

Background

Hepatitis C virus (HCV) infection is a blood borne infection that remains potentially transmissible through blood transfusions. Sickle cell disease (SCD) is a common inheritable haemoglobinopathy in Ghana that requires multiple blood transfusions as part of its management. The SCD patient is therefore at a high risk of HCV infection; however, data on the occurrence of HCV in SCD patients has not been documented in Ghana. This study sought to determine the prevalence and genotypes of HCV infection in SCD patients.

Materials and methods

This was a cross-sectional study which enrolled 141 sickle-cell disease patients from the Ghana Institute for Clinical Genetics, Korle-Bu Teaching Hospital (KBTH). Patient information was obtained through a structured questionnaire. Aliquots of the plasma obtained was used for both serology with Advanced Quality Rapid Anti-HCV Test Strip and molecular testing by RT-PCR with primers targeting the HCV core gene. The amplified DNA were purified and subjected to phylogenetic analysis to characterize HCV genotypes.

Results

Twelve (9%) out of the 141 patients were sero-positive for HCV total antibodies. HCV RNA was amplified from 8 (6%) out of the total number of patients’ samples. One of the 12 sero-positives was HCV RNA positive. Five (63%) out of the 8 HCV RNA positive samples were successfully sequenced. The phylogenetic tree constructed with the study and GenBank reference sequences, clustered all five study sequences into HCV genotype 1.

Conclusion

The HCV seroprevalence of 9% among sickle cell disease patients is higher than reported for the general Ghanaian population which is 3%. Genotype 1 is the common HCV genotype infecting SCD patients. Sickle cell disease is likely to be a high-risk group for HCV inapparent infections in Ghana as seroprevalence does not correlate with viremia. However, even with higher seroprevalence, the group must be given priority in resource allocation for preventive, diagnostic and therapeutic strategies.

Murine models of sickle cell disease and beta-thalassemia demonstrate pulmonary hypertension with distinctive features

Sickle cell anemia and β-thalassemia intermedia are very different genetically determined hemoglobinopathies predisposing to pulmonary hypertension. The etiologies responsible for the associated development of pulmonary hypertension in both diseases are multi-factorial with extensive mechanistic contributors described. Both sickle cell anemia and β-thalassemia intermedia present with intra and extravascular hemolysis. And because sickle cell anemia and β-thalassemia intermedia share features of extravascular hemolysis, macrophage iron excess and anemia we sought to characterize the common features of the pulmonary hypertension phenotype, cardiac mechanics, and function as well as lung and right ventricular metabolism. Within the concept of iron, we have defined a unique pulmonary vascular iron accumulation in lungs of sickle cell anemia pulmonary hypertension patients at autopsy. This observation is unlike findings in idiopathic or other forms of pulmonary arterial hypertension. In this study, we hypothesized that a common pathophysiology would characterize the pulmonary hypertension phenotype in sickle cell anemia and β-thalassemia intermedia murine models. However, unlike sickle cell anemia, β-thalassemia is also a disease of dyserythropoiesis, with increased iron absorption and cellular iron extrusion. This process is mediated by high erythroferrone and low hepcidin levels as well as dysregulated iron transport due transferrin saturation, so there may be differences as well. Herein we describe common and divergent features of pulmonary hypertension in aged Berk-ss (sickle cell anemia) and Hbb^th/3+ (intermediate β-thalassemia) mice and suggest translational utility as proof-of-concept models to study pulmonary hypertension therapeutics specific to genetic anemias.

Relationship Between Disease Severity and Resting Electrocardiograms of Adults With Sickle Cell Anemia in a Tertiary Institution in Southern Nigeria

Introduction

Sickle cell anemia (SCA) in adults has many clinical manifestations. These manifestations are due to effects of recurrent hemolysis, anemia, and ischemia-reperfusion injury on various organs, including the heart. These factors determine the severity of the disease.

Objectives

The aim of the study was to assess the severity of SCA using a scoring system consisting of clinical and laboratory parameters. In addition, the study aimed to determine the electrocardiographic abnormalities in the adult SCA population.

Study design

This was a cross-sectional, observational study conducted in the medical outpatient clinic of Irrua Specialist Teaching Hospital, Irrua, Nigeria.

Methodology

Sixty SCA patients who were older than 18 years old were recruited for this study between February 2017 and January 2018. Sixty healthy individuals matched for age and sex were recruited to serve as controls. Patients who were pregnant or having an acute crises were excluded from the study. Each participant had an electrocardiogram and a SCA severity score was calculated using their clinical history and complete blood count. Data analysis was carried out using the IBM Statistical Package for Social Sciences Statistics® software, version 21 (IBM SPSS Statistics for Windows, Armonk, NY) and statistical significance assigned to p-values less than 0.05.

Results

Severity scores for SCA ranged between 7 and 24, with a mean score of 14.5 ± 4.04. Out of the 60 patients, 14 (23.3%), 39 (65%), and seven (11.7%) participants met criteria for mild, moderate, and severe disease, respectively. Tachycardia, prolonged QTc, and the presence of ST-segment and T-wave abnormalities were significantly associated with severe SCA (p = 0.024, p = 0.027, and p = 0.018, respectively). There was positive correlation between SCA severity scores and P-wave duration (r = 0.327, p = 0.011), QRS dispersion (r = 0.298, p = 0.021), QTc interval (r = 0.332, p = 0.010), and QTc dispersion (r = 0.320, p = 0.013).

Conclusion

This study demonstrated that moderate and severe forms of SCA are common in our region. Tachycardia, left atrial abnormality, prolonged corrected QT interval, and the presence of ST-segment and T-wave changes are electrocardiographic findings associated with more severe forms of the disease. These abnormalities are significant etiologies of cardiac morbidity and mortality in SCA.

Vasculo-toxic and pro-inflammatory action of unbound haemoglobin, haem and iron in transfusion-dependent patients with haemolytic anaemias

Increasing evidence suggests that free haem and iron exert vasculo‐toxic and pro‐inflammatory effects by activating endothelial and immune cells. In the present retrospective study, we compared serum samples from transfusion‐dependent patients with β‐thalassaemia major and intermedia, hereditary spherocytosis and sickle cell disease (SCD). Haemolysis, transfusions and ineffective erythropoiesis contribute to haem and iron overload in haemolytic patients. In all cohorts we observed increased systemic haem and iron levels associated with scavenger depletion and toxic ‘free’ species formation. Endothelial dysfunction, oxidative stress and inflammation markers were significantly increased compared to healthy donors. In multivariable logistic regression analysis, oxidative stress markers remained significantly associated with both haem‐ and iron‐related parameters, while soluble vascular cell adhesion molecule 1 (sVCAM‐1), soluble endothelial selectin (sE‐selectin) and tumour necrosis factor α (TNFα) showed the strongest association with haem‐related parameters and soluble intercellular adhesion molecule 1 (sICAM‐1), sVCAM‐1, interleukin 6 (IL‐6) and vascular endothelial growth factor (VEGF) with iron‐related parameters. While hereditary spherocytosis was associated with the highest IL‐6 and TNFα levels, β‐thalassaemia major showed limited inflammation compared to SCD. The sVCAM1 increase was significantly lower in patients with SCD receiving exchange compared to simple transfusions. The present results support the involvement of free haem/iron species in the pathogenesis of vascular dysfunction and sterile inflammation in haemolytic diseases, irrespective of the underlying haemolytic mechanism, and highlight the potential therapeutic benefit of iron/haem scavenging therapies in these conditions.

The Worst Things in Life are Free: The Role of Free Heme in Sickle Cell Disease

Hemolysis is a pathological feature of several diseases of diverse etiology such as hereditary anemias, malaria, and sepsis. A major complication of hemolysis involves the release of large quantities of hemoglobin into the blood circulation and the subsequent generation of harmful metabolites like labile heme. Protective mechanisms like haptoglobin-hemoglobin and hemopexin-heme binding, and heme oxygenase-1 enzymatic degradation of heme limit the toxicity of the hemolysis-related molecules. The capacity of these protective systems is exceeded in hemolytic diseases, resulting in high residual levels of hemolysis products in the circulation, which pose a great oxidative and proinflammatory risk. Sickle cell disease (SCD) features a prominent hemolytic anemia which impacts the phenotypic variability and disease severity. Not only is circulating heme a potent oxidative molecule, but it can act as an erythrocytic danger-associated molecular pattern (eDAMP) molecule which contributes to a proinflammatory state, promoting sickle complications such as vaso-occlusion and acute lung injury. Exposure to extracellular heme in SCD can also augment the expression of placental growth factor (PlGF) and interleukin-6 (IL-6), with important consequences to enthothelin-1 (ET-1) secretion and pulmonary hypertension, and potentially the development of renal and cardiac dysfunction. This review focuses on heme-induced mechanisms that are implicated in disease pathways, mainly in SCD. A special emphasis is given to heme-induced PlGF and IL-6 related mechanisms and their role in SCD disease progression.

Surfactant protein D as a marker for pulmonary complications in pediatric patients with sickle cell disease: Relation to lung function tests

BACKGROUND

Surfactant protein D (SP-D) is considered a candidate biomarker for lung integrity and for disease progression.

AIM

We determined the level of SP-D in children and adolescents with SCD and assessed its possible relation to pulmonary complications and lung function.

METHODS

Serum SP-D levels were assessed in 50 SCD patients compared with 30 healthy controls. High-resolution computerized tomography (HRCT) of the chest was done. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁ ), FEV₁ /FVC% and forced expiratory flow rate during 25-75% of expiration (FEF25-75%) were determined.

RESULTS

SP-D was significantly higher in SCD patients than controls, particularly patients with sickle cell anemia than those with sickle β-thalassemia. SP-D levels were significantly associated with increasing severity of interstitial lung disease. The highest SP-D levels were observed among patients with restrictive lung disease followed by mixed type then obstructive lung disease. SP-D was positively correlated to HbS and serum ferritin while negatively correlated to duration of hydroxyurea treatment and parameters of pulmonary functions. ROC curve analysis revealed that SP-D cutoff value 720 ng/mL could significantly detect the presence of abnormal pulmonary function among SCD patients with 82% sensitivity and 88% specificity. Logistic regression analysis showed that SP-D is an independent factor related to abnormal pulmonary function in SCD.

CONCLUSIONS

SP-D may be a promising biomarker for screening of SCD patients for risk of later pulmonary complications.

Does sickle cell disease have a psychosomatic component? A particular focus on anxiety and depression

Sickle cell disease, an early-age genetic condition, encompasses a range of blood disorders with severe complications. This disease is characterized by the synthesis of abnormal hemoglobin molecules, which tend to polymerize due to their low solubility upon deoxygenation in the peripheral capillary beds, resulting in sickle-like red blood cells. Sickled cells lose their normal functioning and hemodynamic properties, leading to chronic fatigue as well as to episodes of painful crises. Over the last two decades, a growing body of clinical evidence has pointed out that these somatic complaints can give rise to neuropsychiatric disorders, among which anxiety and depression are the most common, that worsen the health-related quality of life in patients. At first glance, this somatic influence may be unsurprising, as both anxiety and depressive signs are prevalent in almost all chronic diseases. However, in the case of a genetic condition such as sickle cell disease whose somatic disturbances are predetermined, the fact that mood disorders can increase fatigue and pain through a psychosomatic component has attracted increasing attention. In this review, we address the hypothesis of a psychosomatic component in patients with sickle cell disease by underlining the most relevant clinical studies that have highlighted the existence of a bidirectional link between physical and psychological sequelae, which are reported to be relieved not only by pharmacological cotreatments but also by the concomitant application of cognitive behavioral therapy.

Low nitric oxide level is implicated in sickle cell disease and its complications in Ghana

BACKGROUND

Nitric oxide (NO) plays a fundamental role in maintaining normal vasomotor tone. Recent clinical and experimental data suggest that NO may play a role in the pathogenesis and therapy of sickle cell disease (SCD). The aim of this study was to determine NO metabolites (NOx) in SCD patients at steady state and in vaso-occlusive crisis (VOC), as well as those with hemolytic clinical sub-phenotype that includes leg ulcers and priapism.

METHODOLOGY

This was a case-control cross-sectional study conducted on a total of 694 subjects including 148 comparison group HbAA, 208 HbSS SCD patients in steady state, 82 HbSC SCD patients in steady state, 156 HbSS SCD patients in VOC, 34 HbSC SCD patients in VOC, 34 HbSS SCD patients in post VOC, 21 HbSS SCD patients with leg ulcer and 11 HbSS SCD patients with priapism, with age ranging from 15 to 65 years. Laboratory diagnosis of SCD was done at the Sickle Cell Clinic of the Korle-Bu Teaching Hospital. Plasma nitric oxide metabolites were measured using Griess reagent system by ELISA method.

RESULTS

Mean NOx of 59.66±0.75 µMol/L in the comparison group was significantly different from those in steady state (P=0.02). During VOC, there was a significant reduction in mean NOx levels to 6.08±0.81 µMol/L (P<0.001). Mean NOx levels were however, significantly higher (50.97±1.68 µMol/L) (P<0.001) in the immediate postcrisis period. The mean NOx levels in the leg ulcer (21.70±1.18 µMol/L) (P<0.001) and priapism (28.97±1.27 µMol/L) (P<0.001) patients were significantly low as compared to the SCD patients in the steady state and comparison group.

CONCLUSION

This study presents the first report on plasma NOx levels in SCD complication in Ghanaian SCD patients and confirms reduced plasma NOx levels in SCD patients in general.

Novel Sickle Cell Disease Therapies: Targeting Pathways Downstream of Sickling

Sickle cell disease is an inherited hemoglobinopathy characterized by hemolytic anemia, frequent painful episodes, poor quality of life, end organ damage and a shortened lifespan. Although the seminal event is the polymerization of the abnormal hemoglobin, the downstream pathophysiology of vaso-occlusion results from heterotypic interactions between the altered, adhesive sickle cell RBCs, neutrophils, endothelium, and platelets. Ischemia reperfusion injury, hemolysis and oxidant damage all contribute to heightened inflammation and activation of the hemostatic system. These downstream targets are the focus of emerging treatments with considerable potential to ameliorate disease manifestations. This review summarizes the progress on development of these agents.

Airway inflammation in sickle cell disease-A translational perspective

Asthma and sickle cell disease (SCD) are common chronic conditions in children of African ancestry that are characterized by cough, wheeze, and obstructive patterns on pulmonary function. Pulmonary function testing in children with SCD has estimated a prevalence of obstructive lung disease ranging from 13% to 57%, and airway hyper-responsiveness of up to 77%, independent of a diagnosis of asthma. Asthma co-existing with SCD is associated with increased risk of acute chest syndrome (ACS), respiratory symptoms, pain episodes, and death. However, there are inherent differences in the pathophysiology of SCD and asthma. While classic allergic asthma in the general population is associated with a T-helper 2 cell (Th-2 cells) pattern of cell inflammation, increased IgE levels and often positive allergy testing, inflammation in SCD is associated with different inflammatory pathways, involving neutrophilic and monocytic pathways, which have been explored to a limited extent in mouse models and with a dearth of human studies. The current review summarizes the existent literature on sickle cell related airway inflammation and its cross roads with allergic asthma-related inflammation, and discusses the importance of further elucidating and understanding these common and divergent inflammatory pathways in human studies to facilitate development of targeted therapy for children with SCD and pulmonary morbidity.

Sleep-disordered breathing in patients with sickle cell disease

Sickle cell disease is one of the most common hereditary hemoglobinopathies worldwide, and its vaso-occlusive and hemolytic crises cause considerable patient morbidity. A growing body of evidence has shown that sleep-disordered breathing, and in particular, obstructive sleep apnea, occurs at high frequency in the sickle cell population, and that there is significant overlap in the underlying pathophysiology of these two conditions. Through a variety of mechanisms including nocturnal hypoxemia and increased oxidative stress, production of pro-inflammatory cytokines, and endothelial dysfunction, sickle cell anemia and sleep-disordered breathing potentiate each other's clinical effects and end-organ complications. Here, we will review the shared pathophysiologic mechanisms of these conditions and discuss their clinical sequelae. We will also examine the results of studies that have been carried out with clinical intervention of nocturnal hypoxemia in patients with sickle cell disease in the attempts to overcome the complications of the disease. Finally, we will propose the areas of investigation that merit further investigations in future in patients with sickle cell disease and sleep-disordered breathing.

Sickle cell disease: a malady beyond a hemoglobin defect in cerebrovascular disease

INTRODUCTION

Sickle cell disease (SCD) is a devastating monogenic disorder that presents as a multisystem illness and affects approximately 100,000 individuals in the United States alone. SCD management largely focuses on primary prevention, symptomatic treatment and targeting of hemoglobin polymerization and red blood cell sickling. Areas covered: This review will discuss the progress of SCD over the last few decades, highlighting some of the clinical (mainly cerebrovascular) and psychosocial challenges of SCD in the United States. In addition, focus will also be made on the evolving science and management of this inherited disease. Expert commentary: Until recently hydroxyurea (HU) has been the only FDA approved therapy for SCD. However, advancing understanding of SCD pathophysiology has led to multiple clinical trials targeting SCD related thrombo-inflammation, abnormal endothelial biology, increased oxidant stress and sickle cell mutation. Yet, despite advancing understanding, available therapies are limited. SCD also imposes great psychosocial challenges for the individual and the affected community, which has previously been under-recognized. This has created a pressing need for complementary adjuvant therapies with repurposed and novel drugs, in addition to the establishment of comprehensive clinics focusing on both the medical treatment and the psychosocial issues associated with SCD.

Synthesis and hyperpolarisation of eNOS substrates for quantification of NO production by 1H NMR spectroscopy

Hyperpolarization enhances the intensity of the NMR signals of a molecule, whose in vivo metabolic fate can be monitored by MRI with higher sensitivity. SABRE is a hyperpolarization technique that could potentially be used to image nitric oxide (NO) production in vivo. This would be very important, because NO dysregulation is involved in several pathologies, including cardiovascular ones. The nitric oxide synthase (NOS) pathway leads to NO production via conversion of l-arginine into l-citrulline. NO is a free radical gas with a short half-life in vivo (≈5s), therefore direct NO quantification is challenging. An indirect method - based on quantifying conversion of an l-Arg- to l-Cit-derivative by 1H NMR spectroscopy - is herein proposed. A small library of pyridyl containing l-Arg derivatives was designed and synthesised. In vitro tests showed that compounds 4a-j and 11a-c were better or equivalent substrates for the eNOS enzyme (NO2- production=19-46μM) than native l-Arg (NO2- production=25μM). Enzymatic conversion of l-Arg to l-Cit derivatives could be monitored by 1H NMR. The maximum hyperpolarization achieved by SABRE reached 870-fold NMR signal enhancement, which opens up exciting future perspectives of using these molecules as hyperpolarized MRI tracers in vivo.

Hemoglobin induced cell trauma indirectly influences endothelial TLR9 activity resulting in pulmonary vascular smooth muscle cell activation

It is now well established that both inherited and acquired forms of hemolytic disease can promote pulmonary vascular disease consequent of free hemoglobin (Hb) induced NO scavenging, elevations in reactive oxygen species and lipid peroxidation. It has recently been reported that oxidative stress can activate NFkB through a toll-like receptor 9 (TLR9) mediated pathway; further, TLR9 can be activated by either nuclear or mitochondrial DNA liberated by stress induced cellular trauma. We hypothesis that Hb induced lipid peroxidation and subsequent endothelial cell trauma is linked to TLR9 activation, resulting in IL-6 mediated pulmonary smooth muscle cell proliferation. We examined the effects of Hb on rat pulmonary artery endothelial and smooth muscle cells (rPAEC and rPASMC, respectively), and then utilized TLR9 and IL6 inhibitors, as well as the Hb and heme binding proteins (haptoglobin (Hp) and hemopexin (Hpx), respectively) to further elucidate the aforementioned mediators. Further, we explored the effects of Hb in vivo utilizing endothelial cell (EC) specific myeloid differentiation primary response gene-88 (MyD88) and TLR9 null mice. Our data show that oxidized Hb induces lipid peroxidation, cellular toxicity (5.5 ± 1.7 fold; p≤0.04), increased TLR9 activation (60%; p = 0.01), and up regulated IL6 expression (1.75±0.3 fold; p = 0.04) in rPAEC. Rat PASMC exhibited a more proliferative state (13 ± 1%; p = 0.01) when co-cultured with Hb activated rPAEC. These effects were attenuated with the sequestration of Hb or heme by Hp and Hpx as well as with TLR9 an IL-6 inhibition. Moreover, in both EC-MyD88 and TLR9 null mice Hb-infusion resulted in less lung IL-6 expression compared to WT cohorts. These results demonstrate that Hb-induced lipid peroxidation can initiate a modest TLR9 mediated inflammatory response, subsequently generating an activated SMC phenotype.

Clinical Predictive Value of Cystatin C in Pediatric Sickle Cell Disease: A Marker of Disease Severity and Subclinical Cardiovascular Dysfunction

BACKGROUND

Patients with sickle cell disease (SCD) are at high risk of renal dysfunction and cardiovascular morbidity. The association between cystatin C and renal function is well known, however, cystatin C has recently emerged as a strong predictor of cardiovascular events and adverse outcomes in patients with and without kidney disease, mostly related to both inflammation and atherosclerosis.

AIM

To determine cystatin C levels in 53 children and adolescents with SCD compared to 40 age- and sex-matched healthy controls and assess its relation to markers of hemolysis, iron overload, sickle vasculopathy, and carotid intima-media thickness (CIMT).

METHODS

Patients with SCD in steady state were studied, focusing on hydroxyurea therapy, hematological profile, serum ferritin, high-sensitivity C-reactive protein (hs-CRP), urinary albumin-creatinine ratio (UACR), and serum cystatin C. Echocardiography and CIMT were assessed using high-resolution ultrasound. Heart disease was defined by systolic left ventricle dysfunction (shortening fraction <30% or ejection fraction <55%).

RESULTS

Carotid IMT was significantly higher in patients with SCD compared to controls ( P < .001). Patients with SCD having nephropathy, heart disease, or history of frequent sickling crisis (≥3 attacks/y) had significantly higher cystatin C levels than those without ( P < .05). Patients with SCD treated with hydroxyurea had lower cystatin C levels than untreated patients ( P = .039). High-sensitivity C-reactive protein, UACR, ejection fraction, and CIMT were independently related to cystatin C in multiple regression analysis. The cutoff values of cystatin C for detection of renal or cardiovascular complications were determined.

CONCLUSION

Cystatin C may be considered a biological marker for vascular dysfunction and subclinical atherosclerosis in SCD.

Sickle red cells as danger signals on proinflammatory gene expression, leukotriene B4 and interleukin-1 beta production in peripheral blood mononuclear cell

This study tested the hypothesis that sickle red blood cell (SS-RBC) induce Toll-like receptors (TLR) and Nod-like receptor family, pyrin domain containing 3 (NLRP3)- inflammasome expression in peripheral blood mononuclear cells (PBMC). TLR and NLRP3 inflammasome could contribute to the maintenance of the inflammatory status in sickle cell anemia (SCA) patients, since SS-RBC act as danger signals activating these pathways. In this study, first, we evaluated TLR (2, 4, 5 and 9), NLRP3, Caspase-1, interleukin (IL)-1β and IL-18 expression in PBMC freshly isolated from SCA patients (SS-PBMC) in comparison with PBMC from healthy individuals (AA-PBMC). In the second moment, we investigated whether SS-RBC could interfere with the expression of these molecules in PBMC from healthy donor, in the absence or presence of hydroxyurea (HU) in vitro. TLRs and NLRP3 inflammasome expression were investigated by qPCR. IL-1β, Leukotriene-B4 (LTB4) and nitrite production were measured in PBMC (from healthy donor) culture supernatants. TLR2, TLR4, TLR5, NLRP3 and IL-1β were highly expressed in SS-PBMC when compared to AA-PBMC. Additionally, SS-RBC induced TLR9, NLRP3, Caspase-1, IL-1β and IL-18 expression and induced IL-1β, LTB4 and nitrite production in PBMC cultures. HU did not prevent TLR and NLRP3 inflammasome expression, but increased TLR2 and IL-18 expression and reduced nitrite production. In conclusion, our data suggest that TLR and inflammasome complexes may be key inducers of inflammation in SCA patients, probably through SS-RBC; also, HU does not prevent NLRP3 inflammasome- and TLR-dependent inflammation, indicating the need to develop new therapeutic strategies to SCA patients that act with different mechanisms of those observed for HU.

Pulmonary platelet thrombi and vascular pathology in acute chest syndrome in patients with sickle cell disease

A growing body of evidence suggests a role for platelets in sickle cell disease (SCD). Despite the proinflammatory, occlusive nature of platelets, a role for platelets in acute chest syndrome (ACS), however, remains understudied. To provide evidence and potentially describe contributory factors for a putative link between ACS and platelets, we performed an autopsy study of 20 SCD cases—10 of whom died from ACS and 10 whose deaths were not ACS‐related. Pulmonary histopathology and case history were collected. We discovered that disseminated pulmonary platelet thrombi were present in 3 out of 10 of cases with ACS, but none of the matched cases without ACS. Those cases with detected thrombi were associated with significant deposition of endothelial vWF and detection of large vWF aggregates adhered to endothelium. Potential clinical risk factors were younger age and higher platelet count at presentation. However, we also noted a sharp and significant decline in platelet count prior to death in each case with platelet thrombi in the lungs. In this study, neither hydroxyurea use nor perimortem transfusion was associated with platelet thrombi. Surprisingly, in all cases, there was profound pulmonary artery remodeling with both thrombotic and proliferative pulmonary plexiform lesions. The severity of remodeling was not associated with a severe history of ACS, or hydroxyurea use, but was inversely correlated with age. We thus provide evidence of undocumented presence of platelet thrombi in cases of fatal ACS and describe clinical correlates. We also provide novel correlates of pulmonary remodeling in SCD. Am. J. Hematol. 91:173–178, 2016. © 2015 The Authors. American Journal of Hematology Published by Wiley Periodicals, Inc.

Soluble Fas/FasL ratio as a marker of vasculopathy in children and adolescents with sickle cell disease

OBJECTIVES

Sickle cell disease (SCD) is characterized by chronic inflammation due to ischemic tissue damage, accentuated during acute complications. Fas and its ligand (FasL) are members of tumor necrosis factor receptor superfamily and a major pathway for induction of apoptosis. Fas/FasL interactions may be related to augmentation of inflammatory response. We assessed the levels of sFas and sFasL in 35 children and adolescents with SCD compared with 35 healthy controls in relation to hemolysis, iron overload, sickle vasculopathy including kidney disease.

METHODS

SCD patients, in steady state and asymptomatic for pulmonary hypertension, were studied stressing on hydroxyurea therapy, serum ferritin, urinary albumin creatinine ratio (UACR), high-sensitivity C-reactive protein (hs-CRP) and sFas/sFasL levels.

RESULTS

sFas/sFasL ratio was significantly higher in patients compared with controls. sFas/sFasL ratio was elevated in patients with pulmonary hypertension, nephropathy and those who had history of frequent sickling crisis or serum ferritin ⩾2500. SCD patients treated with hydroxyurea had lower sFas/sFasL ratio than untreated patients. sFas/sFasL ratio was positively correlated to transfusion index, white blood cells, hs-CRP, serum ferritin and UACR. The cutoff value of sFas/sFasL at 8.75pg/mL could differentiate SCD patients with and without nephropathy while the cutoff value at 22pg/mL could differentiate SCD patients with and without pulmonary hypertension risk with high sensitivity and specificity.

CONCLUSION

sFas/sFasL ratio may be considered as a marker for vascular dysfunction in SCD patients and is related to inflammation, iron overload and albuminuria level. Thus, it may be a reliable method to assess renal impairment in SCD.

Conjunctival and pulmonary hemodynamic properties in sickle cell disease subjects with and without pulmonary hypertension

Conjunctival microvascular hemodynamic alterations were reported for the first time in sickle cell subjects with and without pulmonary hypertension. Assessment of the conjunctival microcirculation using noninvasive imaging may improve understanding of microvascular hemodynamic alterations that occur due to pulmonary hypertension in sickle cell disease.

Citrulline Supplementation Improves Organ Perfusion and Arginine Availability under Conditions with Enhanced Arginase Activity

Enhanced arginase-induced arginine consumption is believed to play a key role in the pathogenesis of sickle cell disease-induced end organ failure. Enhancement of arginine availability with l-arginine supplementation exhibited less consistent results; however, l-citrulline, the precursor of l-arginine, may be a promising alternative. In this study, we determined the effects of l-citrulline compared to l-arginine supplementation on arginine-nitric oxide (NO) metabolism, arginine availability and microcirculation in a murine model with acutely-enhanced arginase activity. The effects were measured in six groups of mice (n = 8 each) injected intraperitoneally with sterile saline or arginase (1000 IE/mouse) with or without being separately injected with l-citrulline or l-arginine 1 h prior to assessment of the microcirculation with side stream dark-field (SDF)-imaging or in vivo NO-production with electron spin resonance (ESR) spectroscopy. Arginase injection caused a decrease in plasma and tissue arginine concentrations. l-arginine and l-citrulline supplementation both enhanced plasma and tissue arginine concentrations in arginase-injected mice. However, only the citrulline supplementation increased NO production and improved microcirculatory flow in arginase-injected mice. In conclusion, the present study provides for the first time in vivo experimental evidence that l-citrulline, and not l-arginine supplementation, improves the end organ microcirculation during conditions with acute arginase-induced arginine deficiency by increasing the NO concentration in tissues.

Endothelial nitric oxide synthase gene intron 4 VNTR polymorphism in sickle cell disease: relation to vasculopathy and disease severity

BACKGROUND

Impaired NO bioavailability represents the central feature of endothelial dysfunction, and is a common denominator in the pathogenesis of vasculopathy in sickle cell disease (SCD). Evidence indicates the contribution of 4a allele of endothelial NO synthase (eNOS) gene to cardiac and renal diseases. We studied the 27-base pair tandem repeat polymorphism in intron 4 of eNOS gene in 51 patients with SCD compared with 55 healthy controls and evaluated its role in disease severity and hemolysis-associated complications.

PROCEDURE

Transfusion history, vaso-occlusive crisis, thrombotic events, urinary albumin excretion, and echocardiography were assessed. Analysis of eNOS intron 4 gene polymorphism was performed by polymerase chain reaction.

RESULTS

The distribution of eNOS alleles and genotypes was similar between patients with SCD and controls. Compared with bb genotype, the frequency of eNOS4a allele (aa and ab genotypes) was significantly higher in patients with elevated tricuspid regurgitant velocity (TRV) (P = 0.009), nephropathy (P = 0.006), or history of cerebral stroke (P = 0.029). Logistic regression analysis revealed that eNOS4a allele was an independent risk factor for elevated TRV (P < 0.001). Patients with SCD and eNOS4a allele had higher lactate dehydrogenase, serum ferritin, D-Dimer, and von Willebrand factor antigen (P < 0.05).

CONCLUSIONS

We suggest that eNOS intron 4 gene polymorphism is related to endothelial dysfunction and vasculopathy in SCD and could provide utility for prediction of increased susceptibility to vascular complications.

Pulmonary hypertension in well-transfused thalassemia major patients

The risk for pulmonary hypertension (PH) in thalassemia major (TM) patients remains controversial. We report echocardiography results from 60 TM patients: we evaluated the association between tricuspid regurgitation velocities (TRV), iron stores, and serologic markers of hemolysis and arginine dysregulation. Patients were enrolled from August 2004 until May 2009. All parameters were inversely weighted by the number of exams. TRV was comparable between sexes and it was uncorrelated with age. At the first exam, TR velocities at the upper limits of normal (2.5-2.7m/s) were observed in 8 patients. An abnormal TRV (2.9m/s) was found in 1 patient. Borderline increases in TRV were associated with a reduced global arginine bioavailability (R=-0.399 P=0.005), increased anemia (hemoglobin: R=-0.219 P=0.0461), cardiac index (R=0.223 P=0.0481), and diastolic dysfunction (E/A: R=0.289 P=0.0088; E/E': R=0.223 P=0.0453), but not hemolysis, iron overload and systolic function evaluated by Magnetic Resonance Imaging, and splenectomy. Well-transfused TM patients have a lower risk for PH than thalassemia intermedia patients. However, they do have vascular stressors that raise their lifetime PH risk to levels higher than for the general population. Consequently, we support recommendations for annual echocardiographic screening and cardiac catheterization for persistent TRV above 3m/s.

The crossroads of iron with hypoxia and cellular metabolism. Implications in the pathobiology of pulmonary hypertension

The pathologic hallmark of pulmonary arterial hypertension (PAH) is pulmonary vascular remodeling, characterized by endothelial cell proliferation, smooth muscle hypertrophy, and perivascular inflammation, ultimately contributing to increased pulmonary arterial pressures. Several recent studies have observed that iron deficiency in patients with various forms of PAH is associated with worsened clinical outcome. Iron plays a key role in many cellular processes regulating the response to hypoxia, oxidative stress, cellular proliferation, and cell metabolism. Given the potential importance of iron supplementation in patients with the disease and the broad cellular functions of iron, we review its role in processes that pertain to PAH.

The role of phosphodiesterase inhibitors in the management of pulmonary vascular diseases

Phosphodiesterase inhibitors (PDE) can be used as therapeutic agents for various diseases such as dementia, depression, schizophrenia and erectile dysfunction in men, as well as congestive heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, other inflammatory diseases, diabetes and various other conditions. In this review we will concentrate on one type of PDE, mainly PDE5 and its role in pulmonary vascular diseases.

Echocardiography-derived tricuspid regurgitant jet velocity is an important marker for the progression of sickle-cell disease

BACKGROUND

Although echocardiography-derived tricuspid regurgitant jet velocity (TRV) is associated with increased mortality in sickle-cell disease (SCD), it is unclear whether increased TRV is a marker of multiorgan disease due to systemic vasculopathy or related to increased pulmonary artery systolic pressure with episodes of multiple acute chest syndrome (ACS).

METHODS

Our study analyzed 148 consecutive patients with transthoracic echocardiography with TRV data, who came to our adult SCD Clinic at the Wake Forest Baptist Medical Center. For our analysis, we took TRV ≥ 2.5 m/s as elevated. Patients were followed on average for 9 years.

RESULTS

TRV ≥ 3 m/s was significantly associated with increased mortality (p < 0.001), thromboembolism (p < 0.001), hospitalization for ACS (p < 0.001), supraventricular arrhythmia (p = 0.028), right ventricular (RV) dilation, decreased hemoglobin and increased creatinine. Patients with a progressive increase in TRV during follow-up had increased mortality (36.7 vs. 8.6%, p = 0.007) and increased ACS (45 vs. 5.7%, p < 0.001). Death was independently associated with TRV ≥ 3 m/s (p = 0.023), ACS (p = 0.001) and increased RV basal diameter (p = 0.003).

CONCLUSIONS

TRV is an important global marker for the severity and progression of SCD, and carries a significant prognostic implication.

Thrombosis in paroxysmal nocturnal hemoglobinuria

The most frequent and feared complication of paroxysmal nocturnal hemoglobinuria (PNH) is thrombosis. Recent research has demonstrated that the complement and coagulation systems are closely integrated with each influencing the activity of the other to the extent that thrombin itself has recently been shown to activate the alternative pathway of complement. This may explain some of the complexity of the thrombosis in PNH. In this review, the recent changes in our understanding of the pathophysiology of thrombosis in PNH, as well as the treatment of thrombosis, will be discussed. Mechanisms explored include platelet activation, toxicity of free hemoglobin, nitric oxide depletion, absence of other glycosylphosphatidylinositol-linked proteins such as urokinase-type plasminogen activator receptor and endothelial dysfunction. Complement inhibition with eculizumab has a dramatic effect in PNH and has a major impact in the prevention of thrombosis as well as its management in this disease.

Antisickling fetal hemoglobin reduces hypoxia-inducible factor-1α expression in normoxic sickle mice: microvascular implications

Chronic inflammation is a salient feature of sickle cell disease (SCD) and transgenic-knockout sickle (BERK) mice. Inflammation is implicated in the activation of hypoxia-inducible factor-1α (HIF-1α) under normoxic conditions. We hypothesize that, in SCD, inflammation coupled with nitric oxide (NO) depletion will induce expression of HIF-1α, a transcription factor with wide-ranging effects including activation of genes for vasoactive molecules. To this end, we have examined the expression of HIF-1α in normoxic BERK mice expressing exclusively human α- and β(S)- globins, and evaluated the effect of fetal hemoglobin (HbF) in BERK mice (i.e., <1.0%, 20%, and 40% HbF). HbF exerts antisickling and anti-inflammatory effects. Here, we show that HIF-1α is expressed in BERK mice under normoxic conditions, accompanied by increased expression of its vasoactive biomarkers such as VEGF, heme oxygenase-1 (HO-1), and serum ET-1 levels. In BERK mice expressing HbF, HIF-1α expression decreases concomitantly with increasing HbF, commensurately with increased NO bioavailability, and shows a strong inverse correlation with plasma NO metabolites (NOx) levels. Reduced HIF-1α expression is associated with decreased HO-1, VEGF, and ET-1. Notably, arteriolar dilation, enhanced volumetric blood flow, and low blood pressure in normoxic BERK mice all show a trend toward normalization with the introduction of HbF. Also, arginine treatment reduced HIF-1α, as well as VEGF expression in normoxic BERK mice, supporting a role of NO bioavailability in HIF-1α activation. Thus HIF-1α expression in normoxic sickle mice is likely a consequence of chronic inflammation, and HbF exerts an ameliorating effect by decreasing sickling, increasing NO bioavailability, and reducing inflammation.

Infrared imaging of nitric oxide-mediated blood flow in human sickle cell disease

Vascular dysfunction is an important pathophysiologic manifestation of sickle cell disease (SCD), a condition that increases risk of pulmonary hypertension and stroke. We hypothesized that infrared (IR) imaging would detect changes in cutaneous bloodflow reflective of vascular function. We performed IR imaging and conventional strain gauge plethysmography in twenty-five adults with SCD at baseline and during intra-arterial infusions of an endothelium-dependent vasodilator acetylcholine (ACh), an endothelium-independent vasodilator sodium nitroprusside (SNP), and a NOS inhibitor L-NMMA. Skin temperature measured by IR imaging increased in a dose-dependent manner to graded infusions of ACh (+1.1°C, p<0.0001) and SNP (+0.9°C, p<0.0001), and correlated with dose-dependent increases in forearm blood flow (ACh: +19.9 mL/min/100 mL, p<0.0001; r(s)=0.57, p=0.003; SNP: +8.6 mL/min/100 mL, p<0.0001; r=0.70, p=0.0002). Although IR measurement of skin temperature accurately reflected agonist-induced increases in blood flow, it was less sensitive to decreases in blood flow caused by NOS inhibition. Baseline forearm skin temperature measured by IR imaging correlated significantly with baseline forearm blood flow (31.8±0.2°C, 6.0±0.4 mL/min/100 mL; r=0.58, p=0.003), and appeared to represent a novel biomarker of vascular function. It predicted a blunted blood flow response to SNP (r=-0.61, p=0.002), and was independently associated with a marker of pulmonary artery pressure, as well as hemoglobin level, diastolic blood pressure, homocysteine, and cholesterol (R(2)=0.84, p<0.0001 for the model). IR imaging of agonist-stimulated cutaneous blood flow represents a less cumbersome alternative to plethysmography methodology. Measurement of baseline skin temperature by IR imaging may be a useful new marker of vascular risk in adults with SCD.

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.

Free hemoglobin induction of pulmonary vascular disease: evidence for an inflammatory mechanism

Cell-free hemoglobin (Hb) exposure may be a pathogenic mediator in the development of pulmonary arterial hypertension (PAH), and when combined with chronic hypoxia the potential for exacerbation of PAH and vascular remodeling is likely more pronounced. We hypothesized that Hb may contribute to hypoxia-driven PAH collectively as a prooxidant, inflammatory, and nitric oxide (NO) scavenger. Using programmable micropump technology, we exposed male Sprague-Dawley rats housed under room air or hypoxia to 12 or 30 mg per day Hb for 3, 5, and 7 wk. Blood pressure, cardiac output, right ventricular hypertrophy, and indexes of pulmonary vascular remodeling were evaluated. Additionally, markers of oxidative stress, NO bioavailability and inflammation were determined. Hb increased pulmonary arterial (PA) pressure, pulmonary vessel wall stiffening, and right heart hypertrophy with temporal and dose dependence in both room air and hypoxic cohorts. Hb induced a modest increase in plasma oxidative stress markers (malondialdehyde and 4-hydroxynonenal), no change in NO bioavailability, and increased lung ICAM protein expression. Treatment with the antioxidant Tempol attenuated Hb-induced pulmonary arterial wall thickening, but not PA pressures or ICAM expression. Chronic exposure to low plasma Hb concentrations (range = 3-10 μM) lasting up to 7 wk in rodents induces pulmonary vascular disease via inflammation and to a lesser extent by Hb-mediated oxidation. Tempol demonstrated a modest effect on the attenuation of Hb-induced pulmonary vascular disease. NO bioavailability was found to be of minimal importance in this model.

Vascular endothelial dysfunction in β-thalassemia occurs despite increased eNOS expression and preserved vascular smooth muscle cell reactivity to NO

Aims

The hereditary β-thalassemia major condition requires regular lifelong blood transfusions. Transfusion-related iron overloading has been associated with the onset of cardiovascular complications, including cardiac dysfunction and vascular anomalies. By using an untransfused murine model of β-thalassemia major, we tested the hypothesis that vascular endothelial dysfunction, alterations of arterial structure and of its mechanical properties would occur despite the absence of treatments.

Methods and Results

Vascular function and structure were evaluated ex vivo. Compared to the controls, endothelium-dependent vasodilation with acetylcholine was blunted in mesenteric resistance arteries of β-thalassemic mice while the endothelium-independent vasodilator (sodium nitroprusside) produced comparable vessel dilation, indicating endothelial cell impairment with preserved smooth muscle cell reactivity to nitric oxide (NO). While these findings suggest a decrease in NO bioavailability, Western blotting showed heightened expression of aortic endothelial NO synthase (eNOS) in β-thalassemia. Vascular remodeling of the common carotid arteries revealed increased medial elastin content. Under isobaric conditions, the carotid arteries of β-thalassemic mice exhibited decreased wall stress and softening due to structural changes of the vessel wall.

Conclusions

A complex vasculopathy was identified in untransfused β-thalassemic mice characterized by altered carotid artery structure and endothelial dysfunction of resistance arterioles, likely attributable to reduced NO bioavailability despite enhanced vascular eNOS expression.

Hematopoietic stem cell function in a murine model of sickle cell disease

Previous studies have shown that the sickle environment is highly enriched for reactive oxygen species (ROS). We examined the oxidative effects of sickle cell disease on hematopoietic stem cell function in a sickle mouse model. In vitro colony-forming assays showed a significant decrease in progenitor colony formation derived from sickle compared to control bone marrow (BM). Sickle BM possessed a significant decrease in the KSL (c-kit⁺, Sca-¹⁺, Lineage⁻) progenitor population, and cell cycle analysis showed that there were fewer KSL cells in the G₀ phase of the cell cycle compared to controls. We found a significant increase in both lipid peroxidation and ROS in sickle-derived KSL cells. In vivo analysis demonstrated that normal bone marrow cells engraft with increased frequency into sickle mice compared to control mice. Hematopoietic progenitor cells derived from sickle mice, however, demonstrated significant impairment in engraftment potential. We observed partial restoration of engraftment by n-acetyl cysteine (NAC) treatment of KSL cells prior to transplantation. Increased intracellular ROS and lipid peroxidation combined with improvement in engraftment following NAC treatment suggests that an altered redox environment in sickle mice affects hematopoietic progenitor and stem cell function.

The effect of hemolysis on plasma oxidation and nitration in patients with sickle cell disease

This study aimed to determine the effect of haemolysis on plasma oxidation and nitration in sickle cell disease (SCD) patients. Blood was collected from haemoglobin (Hb)A volunteers and homozygous HbSS patients who had not received blood transfusions in the last 3 months. Haemolysis was characterised by low levels of haemoglobin and haptoglobin and high levels of reticulocyte, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), plasma cell-free haemoglobin, bilirubin, total lactate dehydrogenase (LDH) and dominance of LDH-1 isoenzyme. Plasma 8-isoprostane, protein carbonyl and nitrotyrosine levels were measured to evaluate oxidised lipids, oxidised and nitrated proteins, respectively. Plasma nitrite-nitrate levels were also determined to assess nitric oxide (NO) production in both SCD patients and controls. Markers of haemolysis were significantly evident in SCD patients compared to controls. Plasma 8-isoprostane, protein carbonyl and nitrotyrosine levels were markedly elevated in SCD patients compared to controls. Linear regression analysis revealed a significant inverse correlation between haemoglobin and reticulocyte counts and a significant positive correlation of plasma cell-free haemoglobin with protein carbonyl and nitrotyrosine levels. The obtained data shows that increased haemolysis in SCD increases plasma protein oxidation and nitration.

Traditional laboratory measures of cardiovascular risk in hereditary spherocytosis

BACKGROUND

Individuals who have undergone splenectomy may be at an increased risk of arterial and venous thrombosis. We sought to determine if splenectomy affects surrogate laboratory measures of cardiovascular risk in persons with hereditary spherocytosis (HS).

PROCEDURE

We conducted a prospective cross-sectional study of 21 children and 36 adults with HS. Fasting blood samples were collected for complete blood count and plasma lipid panel, homocysteine, lipoprotein (a), C-reactive protein, and fibrinogen. The variables were compared between the groups with and without prior splenectomy by Mann-Whitney tests.

RESULTS

Subjects with prior splenectomy had higher hemoglobin, white blood cell and platelet counts and lower reticulocyte counts and total serum bilirubin concentrations (P < 0.001). Subjects not having had splenectomy had lower than normal levels of total and LDL-cholesterol (LDL-C). Total and LDL-C values were significantly higher, as were fibrinogen and homocysteine concentrations, in the post-splenectomy subjects than in individuals with intact spleen.

CONCLUSION

Various lipid levels and other measures of cardiovascular risk are affected by splenectomy in persons with HS. Further investigations are indicated to more clearly define the balance of the potential benefits of hemolysis and anemia versus the deleterious effects of splenectomy in HS.

Arginase levels and their association with Th17-related cytokines, soluble adhesion molecules (sICAM-1 and sVCAM-1) and hemolysis markers among steady-state sickle cell anemia patients

Sickle cell anemia (SCA) is characterized by a marked endothelial dysfunction, owing to many factors. Arginine metabolism can be related to the inflammatory chronic state presented by patients, playing a key role in their clinical outcome and vascular endothelium. We investigated the serum arginase levels in 50 SCA patients (22 men and 28 women, mean age of 17 +/- 10.5 years) and 28 healthy controls. Serum arginase levels were associated with biochemical hemolysis markers and cytokines involved in Th17 response, as well as levels of soluble intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1). Arginase concentrations were higher in SCA patients, compared with controls (p = 0.005), and were significantly and positively associated with total bilirubin (p = 0.004), indirect bilirubin (p = 0.04), and aspartate aminotransferase (AST; p = 0.039) in the SCA patient group. Moreover, arginase was significantly and positively associated with transforming growth factor-beta (TGF-beta; p = 0.008) among SCA patients. sICAM-1 was significantly and positively associated to reticulocytes (p = 0.014) and AST (p = 0.04). sVCAM-1 was likewise associated with lactate dehydrogenase (p = 0.03). These data suggest a new insight into arginase metabolism, as we show here a shift in arginine catabolism, where TGF-beta may induces the arginase pathway instead of the nitric oxide pathway and a possible involvement of the vascular activation and the serum arginase in chronic hemolysis among SCA patients. Additional studies should be carried out in order to investigate the mechanisms by which TGF-beta participates in the metabolism of arginase in SCA patients.

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.

HLA-G polymorphism influences the susceptibility to HCV infection in sickle cell disease patients

Despite its well known monogenic etiopathogenesis, sickle cell disease (SCD) is characterized by a striking variability of clinical presentation. There is growing evidence that genetic factors may be involved in this variability. Human leukocyte antigen (HLA)-G is a non-classical HLA molecule which was shown to be expressed at sites of inflammation and in inflammatory diseases. Besides its large and highly polymorphic promoter region, the 3' UTR region seems also to play an important role on regulating HLA-G expression. We investigated the influence of the 14 pb (rs1704) and the +3142 (rs1063320) HLA-G polymorphisms in 93 SCD patients in order to evaluate its potential role on clinical parameters. Twenty-one patients presented an HCV infection. Among all SCD patients 16 (22.2%) were homozygous for the +3142C genotype, none of them hepatitis C (HCV) positive. Controlling for blood transfusions in the last year, the C allele represented a dose dependent protection effect for HCV infection (PR = 0.41; 95% CI: 0.24-0.71). The +3142C allele was also underrepresented among patients with history of respiratory-tract infections. Our results support a role of the +3142 polymorphism in the susceptibility to infections, in particular to HCV infection, and suggest a possible interference of the HLA-G molecule in the response to infections, among SCD patients.

Nitric oxide and arginine dysregulation: a novel pathway to pulmonary hypertension in hemolytic disorders

Secondary pulmonary hypertension (PH) is emerging as one of the leading causes of mortality and morbidity in patients with hemolytic anemias such as sickle cell disease (SCD) and thalassemia. Impaired nitric oxide (NO) bioavailability represents the central feature of endothelial dysfunction, and is a major factor in the pathophysiology of PH. Inactivation of NO correlates with hemolytic rate and is associated with the erythrocyte release of cell-free hemoglobin, which consumes NO directly, and the simultaneous release of the arginine-metabolizing enzyme arginase, which limits bioavailability of the NO synthase substrate arginine during the process of intravascular hemolysis. Rapid consumption of NO is accelerated by oxygen radicals that exists in both SCD and thalassemia. A dysregulation of arginine metabolism contributes to endothelial dysfunction and PH in SCD, and is strongly associated with prospective patient mortality. The central mechanism responsible for this metabolic disorder is enhanced arginine turnover, occurring secondary to enhanced plasma arginase activity. This is consistent with a growing appreciation of the role of excessive arginase activity in human diseases, including asthma and pulmonary arterial hypertension. New treatments aimed at improving arginine and NO bioavailability through arginase inhibition, suppression of hemolytic rate, oral arginine supplementation, or use of NO donors represent potential therapeutic strategies for this common pulmonary complication of hemolytic disorders.