Elevated plasma endothelin-1 levels in sickle cell anemia: relationships to oxygen saturation and left ventricular hypertrophy

Sickle cell disease iPSC-derived sensory neurons exhibit increased excitability and sensitization to patient plasma

ABSTRACT

Individuals living with sickle cell disease (SCD) experience severe recurrent acute and chronic pain. Challenges to gaining mechanistic insight into pathogenic SCD pain processes include differential gene expression and function of sensory neurons between humans and mice with SCD, and extremely limited availability of neuronal tissues from patients with SCD. Here, we used induced pluripotent stem cells (iPSCs), derived from patients with SCD, differentiated into sensory neurons (SCD iSNs) to begin to overcome these challenges. We characterize key gene expression and function of SCD iSNs to establish a model to investigate intrinsic and extrinsic factors that may contribute to SCD pain. Despite similarities in receptor gene expression, SCD iSNs show pronounced excitability using patch clamp electrophysiology. Furthermore, we find that plasma taken from patients with SCD during acute pain associated with a vaso-occlusive event increases the calcium responses to the nociceptive stimulus capsaicin in SCD iSNs compared with those treated with paired plasma from patients with SCD at steady state baseline or healthy control plasma samples. We identified high levels of the polyamine spermine in baseline and acute pain states of plasma from patients with SCD, which sensitizes SCD iSNs to subthreshold concentrations of capsaicin. Together, these data identify potential intrinsic mechanisms within SCD iSNs that may extend beyond a blood-based pathology.

Bosentan attenuates sickle cell disease erythrocyte HbS polymerization and impaired deformability induced by endothelin-1

The effects of endothelin-1 (ET-1) on erythrocytes from sickle cell disease (SCD) patients have been described, but mechanisms of ET-1 regarding primary erythrocyte functions remain unknown. ET-1 is a vasoconstrictor peptide produced by endothelial cells, and the expression of ET-1 is increased in SCD. The present study used ex vivo experiments with sickle cell erythrocytes, ET-1, and bosentan, a dual antagonist of ETA and ETB receptors. We performed a hemoglobin S (HbS) polymerization assay with three concentrations of ET-1 (1, 20, and 50 pg/mL) and bosentan (100 nmol/L). ET-1 increased HbS polymerization at all concentrations, and this effect was suppressed by bosentan. For the deformability assay, red blood cells (RBCs) were incubated on a Sephacryl column with the same concentrations of ET-1 and bosentan. ET-1 decreased deformability, and this effect was reversed by bosentan. To observe erythrocyte adhesion, ET-1 and bosentan were incubated with RBCs in thrombospondin-coated 96-well plate, which demonstrated that ET-1 decreased adhesion but that bosentan enhanced adhesion. We also assessed erythrocyte apoptosis and observed decreased eryptosis induced by ET-1, and these effects were inhibited bosentan. Thus, these findings demonstrated that ET-1 modulates HbS polymerization, erythrocyte deformability, adhesion to thrombospondin, and eryptosis, and these effects were suppressed or enhanced by bosentan.

Sickle cell disease patient plasma sensitizes iPSC-derived sensory neurons from sickle cell disease patients

Individuals living with sickle cell disease (SCD) experience severe recurrent acute and chronic pain. In order to develop novel therapies, it is necessary to better understand the neurobiological mechanisms underlying SCD pain. There are many barriers to gaining mechanistic insight into pathogenic SCD pain processes, such as differential gene expression and function of sensory neurons between humans and mice with SCD, as well as the limited availability of patient samples. These can be overcome by utilizing SCD patient-derived induced pluripotent stem cells (iPSCs) differentiated into sensory neurons (SCD iSNs). Here, we characterize the key gene expression and function of SCD iSNs to establish a model for higher-throughput investigation of intrinsic and extrinsic factors that may contribute to increased SCD patient pain. Importantly, identified roles for C-C Motif Chemokine Ligand 2 (CCL2) and endothelin 1 (ET1) in SCD pain can be recapitulated in SCD iSNs. Further, we find that plasma taken from SCD patients during acute pain increases SCD iSN calcium response to the nociceptive stimulus capsaicin compared to those treated with paired SCD patient plasma at baseline or healthy control plasma samples. Together, these data provide the framework necessary to utilize iSNs as a powerful tool to investigate the neurobiology of SCD and identify potential intrinsic mechanisms of SCD pain which may extend beyond a blood-based pathology.

PPARγ increases HUWE1 to attenuate NF-κB/p65 and sickle cell disease with pulmonary hypertension

Sickle cell disease (SCD)-associated pulmonary hypertension (PH) causes significant morbidity and mortality. Here, we defined the role of endothelial specific peroxisome proliferator-activated receptor γ (PPARγ) function and novel PPARγ/HUWE1/miR-98 signaling pathways in the pathogenesis of SCD-PH. PH and right ventricular hypertrophy (RVH) were increased in chimeric Townes humanized sickle cell (SS) mice with endothelial-targeted PPARγ knockout (SSePPARγKO) compared with chimeric littermate control (SSLitCon). Lung levels of PPARγ, HUWE1, and miR-98 were reduced in SSePPARγKO mice compared with SSLitCon mice, whereas SSePPARγKO lungs were characterized by increased levels of p65, ET-1, and VCAM1. Collectively, these findings indicate that loss of endothelial PPARγ is sufficient to increase ET-1 and VCAM1 that contribute to endothelial dysfunction and SCD-PH pathogenesis. Levels of HUWE1 and miR-98 were decreased, and p65 levels were increased in the lungs of SS mice in vivo and in hemin-treated human pulmonary artery endothelial cells (HPAECs) in vitro. Although silencing of p65 does not regulate HUWE1 levels, the loss of HUWE1 increased p65 levels in HPAECs. Overexpression of PPARγ attenuated hemin-induced reductions of HUWE1 and miR-98 and increases in p65 and endothelial dysfunction. Similarly, PPARγ activation attenuated baseline PH and RVH and increased HUWE1 and miR-98 in SS lungs. In vitro, hemin treatment reduced PPARγ, HUWE1, and miR-98 levels and increased p65 expression, HPAEC monocyte adhesion, and proliferation. These derangements were attenuated by pharmacological PPARγ activation. Targeting these signaling pathways can favorably modulate a spectrum of pathobiological responses in SCD-PH pathogenesis, highlighting novel therapeutic targets in SCD pulmonary vascular dysfunction and PH.

Vasculopathy in Sickle Cell Disease: From Red Blood Cell Sickling to Vascular Dysfunction

Sickle cell disease (SCD) is a hereditary disorder that leads to the production of an abnormal hemoglobin, hemoglobin S (HbS). HbS polymerizes in deoxygenated conditions, which can prompt red blood cell (RBC) sickling and leaves the RBCs more rigid, fragile, and prone to hemolysis. SCD patients suffer from a plethora of complications, ranging from acute complications, such as characteristic, frequent, and debilitating vaso-occlusive episodes to chronic organ damage. While RBC sickling is the primary event at the origin of vaso-occlusive processes, other factors that can further increase RBC transit times in the microcirculation may also be required to precipitate vaso-occlusive processes. The adhesion of RBC and leukocytes to activated endothelium and the formation of heterocellular aggregates, as well as increased blood viscosity, are among the mechanisms involved in slowing the progress of RBCs in deoxygenated vascular areas, favoring RBC sickling and promoting vascular occlusion. Chronic inflammatory processes and oxidative stress, which are perpetuated by hemolytic events and ischemia-reperfusion injury, result in this pan cellular activation and some acute events, such as stroke and acute chest syndrome, as well as chronic end-organ damage. Furthermore, impaired vasodilation and vasomotor hyperresponsiveness in SCD also contribute to vaso-occlusive processes. Treating SCD as a vascular disease in addition to its hematological perspective, the present article looks at the interplay between abnormal RBC physiology/integrity, vascular dysfunction and clinical severity in SCD, and discusses existing therapies and novel drugs in development that may ameliorate vascular complications in the disease. © 2021 American Physiological Society. Compr Physiol 11:1785-1803, 2021.

Association of Left Ventricular Hypertrophy with Hemoglobin Levels in Nonanemic and Anemic Populations

<b><i>Introduction:</i></b> It is established that anemia leads to adaptive changes in cardiac geometry including left ventricular hypertrophy (LVH). However, published data are still scarce regarding the association of LVH with normal-range hemoglobin levels. <b><i>Objective:</i></b> To evaluate the association between hemoglobin level and LVH in subjects with or without anemia. <b><i>Methods:</i></b> The study included 48,034 Korean men and women who received echocardiography during their medical health checkup. They were divided into 4 groups according to their hemoglobin concentration (g/dL) in men (&#x3c;14, 14–14.9, 15–15.9, and ≥16) and women (&#x3c;12, 12–12.9, 13–13.9, and ≥15). Multivariate logistic regression analysis was used to calculate adjusted ORs and 95% CI for LVH in each group compared with the group with the lowest hemoglobin. Subgroup analysis was conducted for subjects within normal hemoglobin levels. <b><i>Results:</i></b> There was an inverse relationship between hemoglobin levels and LVH, where unadjusted and adjusted ORs and 95% CI for LVH decreased with increasing hemoglobin levels in both men and women. In subgroup analysis, this inverse relationship was also observed in subjects with hemoglobin in the nonanemic range. <b><i>Conclusion:</i></b> The decrease in hemoglobin was significantly associated with the increased probability of LVH, and this association was found even in nonanemic subjects.

Peroxisome Proliferator-Activated Receptor γ Regulates the V-Ets Avian Erythroblastosis Virus E26 Oncogene Homolog 1/microRNA-27a Axis to Reduce Endothelin-1 and Endothelial Dysfunction in the Sickle Cell Mouse Lung

Pulmonary hypertension (PH), a serious complication of sickle cell disease (SCD), causes significant morbidity and mortality. Although a recent study determined that hemin release during hemolysis triggers endothelial dysfunction in SCD, the pathogenesis of SCD-PH remains incompletely defined. This study examines peroxisome proliferator-activated receptor γ (PPARγ) regulation in SCD-PH and endothelial dysfunction. PH and right ventricular hypertrophy were studied in Townes humanized sickle cell (SS) and littermate control (AA) mice. In parallel studies, SS or AA mice were gavaged with the PPARγ agonist, rosiglitazone (RSG), 10 mg/kg/day, or vehicle for 10 days. In vitro, human pulmonary artery endothelial cells (HPAECs) were treated with vehicle or hemin for 72 hours, and selected HPAECs were treated with RSG. SS mice developed PH and right ventricular hypertrophy associated with reduced lung levels of PPARγ and increased levels of microRNA-27a (miR-27a), v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1), endothelin-1 (ET-1), and markers of endothelial dysfunction (platelet/endothelial cell adhesion molecule 1 and E selectin). HPAECs treated with hemin had increased ETS1, miR-27a, ET-1, and endothelial dysfunction and decreased PPARγ levels. These derangements were attenuated by ETS1 knockdown, inhibition of miR-27a, or PPARγ overexpression. In SS mouse lung or in hemin-treated HPAECs, activation of PPARγ with RSG attenuated reductions in PPARγ and increases in miR-27a, ET-1, and markers of endothelial dysfunction. In SCD-PH pathogenesis, ETS1 stimulates increases in miR-27a levels that reduce PPARγ and increase ET-1 and endothelial dysfunction. PPARγ activation attenuated SCD-associated signaling derangements, suggesting a novel therapeutic approach to attenuate SCD-PH pathogenesis.

The endothelin B receptor plays a crucial role in the adhesion of neutrophils to the endothelium in sickle cell disease

Although the primary origin of sickle cell disease is a hemoglobin disorder, many types of cells contribute considerably to the pathophysiology of the disease. The adhesion of neutrophils to activated endothelium is critical in the pathophysiology of sickle cell disease and targeting neutrophils and their interactions with endothelium represents an important opportunity for the development of new therapeutics. We focused on endothelin-1, a mediator involved in neutrophil activation and recruitment in tissues, and investigated the involvement of the endothelin receptors in the interaction of neutrophils with endothelial cells. We used fluorescence intravital microscopy analyses of the microcirculation in sickle mice and quantitative microfluidic fluorescence microscopy of human blood. Both experiments on the mouse model and patients indicate that blocking endothelin receptors, particularly ET_B receptor, strongly influences neutrophil recruitment under inflammatory conditions in sickle cell disease. We show that human neutrophils have functional ET_B receptors with calcium signaling capability, leading to increased adhesion to the endothelium through effects on both endothelial cells and neutrophils. Intact ET_B function was found to be required for tumor necrosis factor α-dependent upregulation of CD11b on neutrophils. Furthermore, we confirmed that human neutrophils synthesize endothelin-1, which may be involved in autocrine and paracrine pathophysiological actions. Thus, the endothelin-ET_B axis should be considered as a cytokine-like potent pro-inflammatory pathway in sickle cell disease. Blockade of endothelin receptors, including ET_B, may provide major benefits for preventing or treating vaso-occlusive crises in sickle cell patients.

Endothelin receptor antagonists in sickle cell disease: A promising new therapeutic approach

Sickle cell disease (SCD) is a genetic hematologic disorder that is characterized by a variety of potentially life threatening acute and chronic complications. Currently, hydroxyurea is the only clinically approved pharmacological therapy for the treatment of SCD, and the continued prevalence of severe disease complications underscores the desperate need for the development of new therapeutic agents. Central features of the sickle cell disease milieu, including hypoxia, oxidative stress, and thrombosis, are established enhancers of endothelin-1 (ET-1) synthesis. This conceptual connection between ET-1 and SCD was confirmed by multiple studies that demonstrated markedly elevated plasma and urinary levels of ET-1 in SCD patients. Direct evidence for the involvement of ET-1 signaling in the development of SCD pathologies has come from studies using endothelin receptor antagonists in SCD mice. This review summarizes recent studies that have implicated ET-1 signaling as a mechanistic contributor to renal, vascular, pulmonary, and nociceptive complications of sickle cell disease and discusses the potential for the use of ET receptor antagonists in the treatment of SCD.

Abnormal Regulation of Microvascular Tone in a Murine Model of Sickle Cell Disease Assessed by Contrast Ultrasound

BACKGROUND

Microvascular dysregulation, abnormal rheology, and vaso-occlusive events play a role in the pathophysiology of sickle cell disease (SCD). The aim of this study was to test the hypothesis that abnormalities in skeletal muscle perfusion in a murine model of SCD could be parametrically assessed by quantitative contrast-enhanced ultrasound perfusion imaging.

METHODS

A murine model of moderate SCD without anemia produced by homozygous β-globin deletion replaced by human βs-globin transgene (NY1DD-/-; n = 18), heterozygous transgene replacement (NY1DD+/-; n = 19), and C57Bl/6 control mice (n = 14) was studied. Quantitative contrast-enhanced ultrasound of the proximal hindlimb skeletal muscle was performed at rest and during contractile exercise (2 Hz). Time-intensity data were analyzed to measure microvascular blood volume (MBV), microvascular blood transit rate (β), and microvascular blood flow. Erythrocyte deformability was measured by elongation at various rotational shears.

RESULTS

At rest, muscle MBV was similar between strains, whereas β was significantly (P = .0015, analysis of variance) reduced to a similar degree in NY1DD-/- and NY1DD+/- compared with wild-type mice (0.24 ± 0.10, 0.16 ± 0.07, and 0.34 ± 0.14 sec(-1), respectively), resulting in a reduction in microvascular blood flow. During contractile exercise, there were no groupwise differences in β (1.43 ± 0.67, 1.09 ± 0.42, and 1.36 ± 0.49 sec(-1) for NY1DD-/-, NY1DD+/-, and wild-type mice, respectively) or in microvascular blood flow or MBV. Erythrocyte deformability at high shear stress (≥5 Pa) was mildly reduced in both transgenic groups, although it was not correlated with blood flow or β.

CONCLUSIONS

Contrast-enhanced ultrasound in skeletal muscle revealed a lower microvascular blood transit rate in the NY1DD model of SCD and sickle trait but no alterations in MBV. The abnormality in microvascular blood transit rate was likely due to vasomotor dysfunction, because it was abrogated by contractile exercise and at rest was only weakly related to erythrocyte deformability.

Coronary artery dilation and left ventricular hypertrophy do not predict morbidity in children with sickle cell disease

BACKGROUND

Little is known about the clinical significance of coronary artery dilation (CAD) and left ventricular hypertrophy (LVH) in patients with sickle cell disease (SCD).

PROCEDURE

In a retrospective cohort, we studied the prevalence of CAD and LVH in 101 children with SCD in comparison to 93 healthy African-American patients without SCD. Hospital days, number of admissions, and intensive care unit admission after the echocardiogram were assessed as measures of morbidity.

RESULTS

Multivariable analysis of echocardiographic measures of LVH and CAD did not predict subsequent intensive care unit admission, hospital days/year or number of hospital admissions/year during a median follow-up time of 6.1 years. LVH as measured by left ventricular mass index was present in 46% of children with SCD and was inversely related to age (P = 0.0004). Height-indexed dimensions in children with SCD demonstrated that the prevalence of dilation was 49% for the left main coronary artery (LMCA), 29% for the left anterior descending (LAD), and 6% for the right coronary artery (RCA). LMCA dilation was related to relative wall thickness (P = 0.006), inversely to age (P < 0.0006) and weakly to disease severity as determined by hemoglobin (P = 0.03). CAD and LVH were not related to a clinical history of vaso-occlusive pain episode, acute chest syndrome, or cerebrovascular accident.

CONCLUSION

LVH and CAD are common findings in children with SCD; however, they are not associated with need for subsequent hospital or intensive care unit admission.

Modulation of pain in pediatric sickle cell disease: understanding the balance between endothelin mediated vasoconstriction and apelin mediated vasodilation

Children with sickle cell disease (SCD) have painful vaso-occlusive episodes (VOEs), which often reoccur across the individual's lifespan. Vaso-constrictive and vaso-dilatory molecules have been hypothesized to play a role in VOEs. Endothelin-1 (ET-1) is a potent vasoconstrictor that is released during VOEs and is correlated with pain history. Apelin is a vaso-dilatory peptide that also has a modulatory role in pain processing. We hypothesize that the ratio between vaso-dilatory and vaso-constrictive tone in children with SCD may be a marker of pain sensitization and vaso-occlusion. Plasma endothelin and apelin levels were measured in 47 children with SCD. Procedural pain and baseline pain were assessed via child- and caregiver-reports and observational distress. Pain history was assessed using retrospective chart review. Plasma apelin was related to age, with decreased levels in older children. The ratio between apelin and ET-1 was negatively correlated to observational baseline pain. The ratio between apelin and Big ET was negatively correlated to caregiver ratings of baseline pain and positively correlated to history of VOEs, which is possibly due to hydroxyurea treatment. These results suggest that an imbalance in the apelin and endothelin systems may contribute to an increasing number of VOEs and baseline pain in children with SCD.

Heme-bound iron activates placenta growth factor in erythroid cells via erythroid Krüppel-like factor

In adults with sickle cell disease (SCD), markers of iron burden are associated with excessive production of the angiogenic protein placenta growth factor (PlGF) and high estimated pulmonary artery pressure. Enforced PlGF expression in mice stimulates production of the potent vasoconstrictor endothelin-1, producing pulmonary hypertension. We now demonstrate heme-bound iron (hemin) induces PlGF mRNA >200-fold in a dose- and time-dependent fashion. In murine and human erythroid cells, expression of erythroid Krüppel-like factor (EKLF) precedes PlGF, and its enforced expression in human erythroid progenitor cells induces PlGF mRNA. Hemin-induced expression of PlGF is abolished in EKLF-deficient murine erythroid cells but rescued by conditional expression of EKLF. Chromatin immunoprecipitation reveals that EKLF binds to the PlGF promoter region. SCD patients show higher level expression of both EKLF and PlGF mRNA in circulating blood cells, and markers of iron overload are associated with high PlGF and early mortality. Finally, PlGF association with iron burden generalizes to other human diseases of iron overload. Our results demonstrate a specific mechanistic pathway induced by excess iron that is linked in humans with SCD and in mice to markers of vasculopathy and pulmonary hypertension. These trials were registered at www.clinicaltrials.gov as #NCT00007150, #NCT00023296, #NCT00081523, and #NCT00352430.

Left ventricular systolic function in sickle cell anemia: a meta-analysis

BACKGROUND

We sought to evaluate whether patients with sickle cell anemia (SCA) have left ventricular (LV) systolic dysfunction.

METHODS AND RESULTS

We conducted a Medline, Embase, Ebscohost, and Google scholar literature search articles published before April 2010. All studies that compared any measure of LV function (eg, ejection fraction [EF], fractional shortening [FS], or cardiac index [CI]) between normal control subjects and SCA (hemoglobin SS) patients were included. Among 57 studies that qualified for review, 19 studies including 841 SCA patients and 554 control subjects met the inclusion criteria. There were no significant differences in either LVEF (Hedge g = 0.15; 95% confidence interval -0.84 to 1.14; P = .76) or FS (P = .28) between SCA patients and control subjects. CI was significantly higher (P < .001) and LV end-systolic stress-volume index (load independent) was significantly lower (P < .001) in SCA patients. All LV systolic measures inversely correlated with age (all P < .001). LV end-systolic and -diastolic dimensions were significantly higher in SCA patients and increased with age.

CONCLUSIONS

SCA patients have similar load-dependent but lower load-independent measures of LV systolic function than control subjects. SCA is associated with LV dilation. LV structural and functional abnormalities appear to be age dependent with progressive LV dilation and impairment over time.

Pulmonary complications of sickle cell disease

The pulmonary complications of sickle cell disease are a major cause of morbidity and mortality in affected patients. The acute chest syndrome (ACS) is a leading cause of death in patients with sickle cell disease and has a multifactorial etiology. Hydroxyurea (HU), stem cell transplantation (SCT) and chronic transfusions are known to prevent the recurrence of ACS. Careful management of patients admitted for pain crises and surgery including use of incentive spirometry is critical in preventing this complication. Pulmonary hypertension is well known to be associated with sickle cell disease and patients with pulmonary hypertension have increased mortality. Asthma is also commonly seen in patients with sickle cell disease and is associated with a more complicated course. Chronic lung disease develops in a significant proportion of patients with sickle cell disease.

Left ventricular hypertrophy and diastolic dysfunction in children with sickle cell disease are related to asleep and waking oxygen desaturation

Premature death and cardiac abnormalities are described in individuals with sickle cell disease (SCD), but the mechanisms are not well characterized. We tested the hypothesis that cardiac abnormalities in children with SCD are related to sleep-disordered breathing. We enrolled 44 children with SCD (mean age, 10.1 years; range, 4-18 years) in an observational study. Standard and tissue Doppler echocardiography, waking oxygen saturation averaged over 5 minutes, and overnight polysomnography were obtained in participants, each within 7 days. Eccentric left ventricular (LV) hypertrophy was present in 46% of our cohort. After multivariable adjustment, LV mass index was inversely related to average asleep and waking oxygen saturation. For every 1% drop in the average asleep oxygen saturation, there was a 2.1 g/m(2.7) increase in LV mass index. LV diastolic dysfunction, as measured by the E/E' ratio, was present in our subjects and was also associated with low oxygen saturation (sleep or waking). Elevated tricuspid regurgitant velocity (> or = 2.5 m/sec), a measure of pulmonary hypertension, was not predicted by either oxygen saturation or sleep variables with multivariable logistic regression analysis. These data provide evidence that low asleep and waking oxygen saturations are associated with LV abnormalities in children with SCD.

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.

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.

Heart failure: epidemiologic update

Heart failure is a disease of epidemic proportions in the United States affecting almost 6 million people. This heart failure overview includes a brief description of the etiology of this extremely prevalent coronary artery disease. Myocardial (ventricular) remodeling is described as being either physiological or pathological. Patients must initially be taught that heart failure is a chronic and ongoing disease to comprehend the need for lifestyle changes and management of life problems. Because adherence is a key determinate of clinical outcomes, promoting patient adherence with medications is a major focus for clinicians working with patients with heart failure. Various diagnostic tests are explained as well as the treatment of heart failure. Treatment includes pharmacologic, nonpharmacologic, and surgical interventions. Although there have been substantial advances in care and management, this information is important for healthcare service professionals to know because the number of people diagnosed with heart failure continues to increase each year.

Endothelin receptor antagonism prevents hypoxia-induced mortality and morbidity in a mouse model of sickle-cell disease

Patients with sickle-cell disease (SCD) suffer from tissue damage and life-threatening complications caused by vasoocclusive crisis (VOC). Endothelin receptors (ETRs) are mediators of one of the most potent vasoconstrictor pathways in mammals, but the relationship between vasoconstriction and VOC is not well understood. We report here that pharmacological inhibition of ETRs prevented hypoxia-induced acute VOC and organ damage in a mouse model of SCD. An in vivo ultrasonographic study of renal hemodynamics showed a substantial increase in endothelin-mediated vascular resistance during hypoxia/reoxygenation-induced VOC. This increase was reversed by administration of the dual ETR antagonist (ETRA) bosentan, which had pleiotropic beneficial effects in vivo. It prevented renal and pulmonary microvascular congestion, systemic inflammation, dense rbc formation, and infiltration of activated neutrophils into tissues with subsequent nitrative stress. Bosentan also prevented death of sickle-cell mice exposed to a severe hypoxic challenge. These findings in mice suggest that ETRA could be a potential new therapy for SCD, as it may prevent acute VOC and limit organ damage in sickle-cell patients.

Pulmonary hypertension associated with sickle cell disease: pathophysiology and rationale for treatment

Approximately one third of patients with sickle cell disease (SCD) have pulmonary hypertension (PH), which increases their risk of death. Endothelin (ET)-1 is elevated in SCD and appears to play a key role in many of the pathologic processes in this disease, including PH, suggesting that endothelin receptor antagonists such as bosentan may be effective in treating patients with SCD, particularly those with PH. Other possible treatments include sildenafil, epoprostenol, and oral arginine. Data from controlled clinical trials are needed to establish the most effective treatment of patients with PH associated with SCD.

Protective effects of phosphodiesterase-4 (PDE-4) inhibition in the early phase of pulmonary arterial hypertension in transgenic sickle cell mice

Pulmonary arterial hypertension (PAH) is one of the leading causes of morbidity and mortality in adult patients with sickle cell disease (SCD). Here, we developed a model to study the early stage of PAH in SCD. We exposed wild-type and transgenic sickle cell SAD (Hbb(s)/Hbb(s)) mice to hypoxia (8% O(2)) for 7 days. Prolonged hypoxia in SAD mice only induced 1) increased neutrophil count in both bronchoalveolar lavage (BAL) and peripheral circulation; 2) increased BAL IL1beta, IL10, IL6, and TNF-alpha; and 3) up-regulation of the genes endothelin-1, cyclo-oxygenase-2, angiotensin-converting-enzyme, and IL-1beta, suggesting that amplified inflammatory response and activation of the endothelin-1 system may contribute to the early phase of PAH in SCD. Since phosphodiesterases (PDEs) are involved in pulmonary vascular tone regulation, we evaluated gene expression of phosphodiesterase-4 (PDE-4) isoforms and of PDE-1, -2, -3, -7, -8, which are the main cyclic-adenosine-monophosphate hydrolyzing enzymes. In SAD mouse lungs, prolonged hypoxia significantly increased PDE-4 and -1 gene expressions. The PDE-4 inhibitor, rolipram, prevented the hypoxia-induced PDE-4 and -1 gene up-regulation and interfered with the development of PAH, most likely through modulation of both vascular tone and inflammatory factors. This finding supports a possible therapeutic use of PDEs inhibitors in the earlier phases of PAH in SCD.

Evaluation of left ventricular diastolic function in pediatric sickle cell disease patients

Although cardiac involvement is common in adult sickle cell disease (SCD) patients, it is unknown when cardiac dysfunction appears in the course of SCD. Diastolic function has not been comprehensively analyzed in children with SCD. Thus, our aim was to evaluate diastolic function in pediatric SCD patients. Echocardiograms were performed in 156 (73 SC and 81 control) patients. Left ventricular and left atrial volumes, left ventricular mass, mitral inflow, and tissue Doppler indices (TDI) were obtained. The right ventricular pressures (RVP) were calculated. For each SCD patient, mean hemoglobin (Hb), fetal hemoglobin (HbF) levels, and blood transfusion encounters were recorded. Data were analyzed using t-test, univariate and multivariate regression, and Spearman correlation analyses. SCD patients had significantly larger left ventricular and atrial volumes than controls. Mitral inflow velocities were significantly higher in the SCD group. Of 73 SCD subjects, 32 had left ventricular dilatation, 11 had hypertrophy, and 25 had elevated RVP. Left ventricular size was inversely related to Hb, but unrelated to HbF or age. The early mitral inflow velocity was correlated negatively with Hb and positively with left ventricular sizes. TDI indices did not differ between the SCD and control groups. They were unrelated to Hg, HgF, transfusion history, or ventricular size; however, Doppler indices of left ventricular stiffness were increased in SCD patients. Pediatric SCD patients demonstrate increased left ventricular stiffness, and a significant percentage of them have left ventricular hypertrophy. There are strong positive relations between left ventricular hypertrophy and right ventricular pressure in these patients. TDI should be employed in the evaluation of SCD patients.

Changes in echocardiographic variables of left ventricular size and function in a model of canine normovolemic anemia

The objective of this study was to document changes in echocardiographic variables of left ventricular size and function noninvasively during acute normovolemic anemia. This model was developed as a pilot study with the purpose of providing baseline information to investigate the pathophysiology, and more specifically the effect on the heart, of canine babesiosis-induced anemia. The study group comprised of 11 mature healthy Beagle dogs that weighed between 9 and 15 kg. Severe normovolemic anemia was induced over a 3-4-day period by serial bleeding while maintaining normovolemia by autotransfusing plasma and infusing crystalloids. The dogs were then allowed to recover. Preanemic (mean Hct 46.7%, standard deviation [SD] 2.4%) echocardiographic variables of left ventricular performance (Fractional shortening, ejection fraction, end-systolic and end-diastolic ventricular volumes, cardiac index, and heart rate) were compared with those in the severely (mean Hct 15.3%, SD 1.1%), moderately (Hct mean 24.7%, SD 1.5%), and mildly (mean Hct 33.5%, SD 2.5%) anemic states, and between the anemic states. With the exception of end diastolic volume, there was a statistically significant (P < 0.05) increase in all variables in the severely anemic state vs. the preanemic and the mild and moderate anemic states. In concordance with previous invasive models, a hyperdynamic state of the left ventricle develops in response to experimentally induced acute canine normovolemic anemia in the conscious dog. Echocardiography has promise as a noninvasive technique of evaluating the cardiac changes in dogs having canine babesiosis.

Hypoxic adaptation during development: relation to pattern of neurological presentation and cognitive disability

Children with acute hypoxic-ischaemic events (e.g. stroke) and chronic neurological conditions associated with hypoxia frequently present to paediatric neurologists. Failure to adapt to hypoxia may be a common pathophysiological pathway linking a number of other conditions of childhood with cognitive deficit. There is evidence that congenital cardiac disease, asthma and sleep disordered breathing, for example, are associated with cognitive deficit, but little is known about the mechanism and whether there is any structural change. This review describes what is known about how the brain reacts and adapts to hypoxia, focusing on epilepsy and sickle cell disease (SCD). We prospectively recorded overnight oxyhaemoglobin saturation (SpO2) in 18 children with intractable epilepsy, six of whom were currently or recently in minor status (MS). Children with MS were more likely to have an abnormal sleep study defined as either mean baseline SpO2 <94% or >4 dips of >4% in SpO2/hour (p = .04). In our series of prospectively followed patients with SCD who subsequently developed acute neurological symptoms and signs, mean overnight SpO2 was lower in those with cerebrovascular disease on magnetic resonance angiography (Mann-Whitney, p = .01). Acute, intermittent and chronic hypoxia may have detrimental effects on the brain, the clinical manifestations perhaps depending on rapidity of presentation and prior exposure.

Urinary endothelin-1 as a marker of renal damage in sickle cell disease

BACKGROUND

Sickle cell disease (SCD) affects the kidney by acute mechanisms as well as by insidious renal medullary/papillary necrosis, resulting in tubular defects, which increase the risk of dehydration and subsequent sickle crisis. Hypoxia has been reported to stimulate endothelin-1 (ET-1) synthesis by endothelial cells and also in the renal tubule.

METHODS

This case-control study measured ET-1 in urine as a marker of its renal synthesis in asymptomatic SCD patients. Baseline plasma and urinary ET-1 levels were measured and followed during a water deprivation study and a subsequent administration of desmopressin.

RESULTS

Urine and plasma levels of ET-1 were elevated in patients with SCD, compared with carefully matched African-French and African controls, and urine ET-1 excretion was associated with a marked urine-concentrating defect. Moreover, urinary ET-1 output was correlated with microalbuminuria in SCD patients.

CONCLUSIONS

ET-1 is known to antagonize the tubular effects of vasopressin and to promote renal scarring; increased renal production of ET-1 could produce nephrogenic diabetes insipidus and dehydration in SCD patients through a combination of fibrosis and functional resistance to vasopressin. This study provides a rationale for trials with endothelin receptor antagonists in sickle cell disease nephropathy.

Anemia as a risk factor for cardiovascular disease

In the present review we examine the physiologic response to chronic anemia and describe potential adverse effects of anemia on myocardial and large arterial remodeling. We present observational data demonstrating that anemia is a risk factor for cardiovascular disease (CVD) outcomes in patients with chronic kidney disease and patients with heart failure. We also present data that have evaluated the relationship of level of hematocrit to CVD outcomes in patients with ischemic heart disease and in patients in the general population. The results from the latter studies have been inconclusive and have been limited by lack of knowledge of the cause of anemia. This is potentially important because iron deficiency anemia may, in fact, improve endothelial function. We conclude that additional randomized controlled trials of treatment of anemia are needed in chronic kidney disease and patients with heart failure; however, further exploration of the cause of anemia and the effect of different types of anemia on various CVD outcomes are needed in patients with ischemic heart disease and patients in the general population.

Hematocrit and left ventricular mass: the Framingham Heart study

OBJECTIVES

The goal of this study was to investigate the relationship between hematocrit (Hct) and left ventricular mass index (LVMI) and LV hypertrophy (LVH) in subjects without known hypertension or cardiovascular disease in the Framingham Heart study.

BACKGROUND

Anemia may be an independent risk factor for cardiovascular disease in the general population. One potential explanation for this finding could be an association between Hct with LVMI or LVH.

METHODS

Linear and logistic regression analyses were used to evaluate the association between Hct with LVMI and LVH. All analyses were stratified by gender and further according to menopausal status in women.

RESULTS

There were 1,376 men and 1,769 women who met the inclusion criteria. The mean Hct and LVMI were 46.5% and 41.9%, and 127.3 and 95.8 g/m, respectively, in men and women. After adjustment for confounders, each 3% lower Hct was associated with a 2.6 g/m higher mean LVMI in men, and a 1.8 g/m higher mean LVMI in postmenopausal women (p < 0.05). There was a significant quadratic relationship between Hct and LVMI in premenopausal women (p < 0.01). Subjects in the lowest quartile of Hct (compared with the rest of the sample) had an adjusted odds ratio of LVH of 2.0 (95% confidence interval [CI] 1.3 to 3.0) in men and 1.4 (95% CI 0.8 to 2.4) in postmenopausal women.

CONCLUSIONS

In a sample without known hypertension or cardiovascular disease, a lower Hct is associated with echocardiographically determined LVH in men and a small but significantly higher LVMI in men and postmenopausal women. The clinical importance of these findings remains unknown.

Cytokines in sickle cell disease

Sickle red cells express adhesion molecules including integrin alpha4beta1, CD36, band 3 protein, sulfated glycolipid, Lutheran protein, phosphatidylserine and integrin-associated protein. The proadhesive sickle cells may bind to endothelial cell P-selectin, E-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), CD36 and integrins leading to its activation. Monocytes also activate endothelium by releasing proinflammatory cytokines like tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta). Sickle monocytes also express increased surface CD11b and cytoplasmic cytokines TNFalpha and IL-1beta indicating activated state. Polymorphonuclear leukocytes (PMNs) are also activated with reduced L-selectin expression, enhanced CD64 expression and elevated levels of sL-selectin, sCD16 and elastase resulting in increased adhesiveness to the endothelium. Platelets are also activated and secrete thrombospondin (TSP) and cytokine IL-1. They also form platelet- monocytes aggregates causing endothelial cell P-selectin expression. Endothelial cell activation by these multiple mechanisms leads to a loss of vascular integrity, expression of leukocyte adhesion molecules, change in the surface phenotype from antithrombotic to prothrombotic, excessive cytokine production and upregulation of HLA molecules. Furthermore, contraction of these activated endothelial cells leads to exposure of extracellular matrix proteins, such as TSP, laminin, and fibronectin and their participation in adhesive interactions with bridging molecules from the plasma such as von Willebrand factor (vWf) released from endothelial cells, ultimately culminating in vasoocclusion and local tissue ischemia, the pathognomonic basis of vasoocclusive crisis.

Sickle cell crisis and endothelin antagonists

Sickle cell crisis may be more complex than a vaso-occlusive event in response to hypoxia. Endothelin-1 (ET-1) is a potent vasoconstrictor and mitogen secreted in response to hypoxia. ET-1 contributes to the vaso-occlusion and inflammation in sickle cell crisis. ET-1 antagonists may be useful in the prevention and treatment of crisis.

Pathophysiological-based approaches to treatment of sickle cell disease

Sickle hemoglobin (HbS), as a result of its polymer-related and oxidant effects, damages the sickle erythrocyte, provokes inflammation, and causes endothelial injury. All these elements cause the phenotype of sickle cell disease. Novel treatments inhibit HbS polymerization by inducing fetal hemoglobin expression, prevent or repair erythrocyte dehydration by slowing cellular potassium and water loss, and replace HbS-producing erythroid progenitors by stem cell transplantation. Future treatment prospects include gene therapy, interruption of the interaction of sickle cells with the endothelium, inhibition of oxidative damage, and protection of an injured endothelium.

Transgenic sickle mice have vascular inflammation

Inflammation may play an essential role in vaso-occlusion in sickle cell disease. Sickle patients have high white counts and elevated levels of serum C-reactive protein (CRP), cytokines, and adhesion molecules. In addition, circulating endothelial cells, leukocytes, and platelets are activated. We examined 4 transgenic mouse models expressing human alpha- and sickle beta-globin genes to determine if they mimic the inflammatory response seen in patients. These mouse models are designated NY-S, Berk-S(Antilles), NY-S/S(Antilles) (NY-S x Berk-S(Antilles)), and Berk-S. The mean white counts were elevated 1.4- to 2.1-fold (P </=.01) in the Berk-S(Antilles), NY-S/S(Antilles), and Berk-S mice, but not in the NY-S mice compared with controls. Serum amyloid P-component (SAP), an acute-phase response protein with 60% to 70% sequence homology to CRP, was elevated 8.5- to 12.1-fold (P </=.001) in transgenic sickle mice. Similarly, serum interleukin-6 (IL-6) was elevated 1.6- to 1.9-fold (P </=.05). Western blots, confirming immunohistochemical staining, showed vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), and platelet-endothelial cell adhesion molecule (PECAM) were up-regulated 3- to 5-fold (P </=.05) in the lungs of sickle mice. Ribonuclease protection assays (RPAs) demonstrated VCAM mRNA also was elevated in sickle mice 1.2- to 1.4-fold (P </=.01). Nuclear factor kappaB (NF-kappaB), a transcription factor critical for the inflammatory response, was elevated 1.9-fold (P </=.006) in NY-S sickle mouse lungs. We conclude that transgenic sickle mice are good models to study vascular inflammation and the potential benefit of anti-inflammatory therapies to prevent vaso-occlusion in sickle cell disease.

Anemia as a risk factor for cardiovascular disease in The Atherosclerosis Risk in Communities (ARIC) study

OBJECTIVES

We investigated whether the presence of anemia is a risk factor for cardiovascular disease (CVD) outcomes in the general population.

BACKGROUND

Chronic anemia is a risk factor for CVD outcomes in patients with kidney disease and in patients with heart failure, but has not been evaluated as a risk factor in the general population.

METHODS

The Atherosclerosis Risk in Communities (ARIC) study was used to evaluate the relationship of anemia, defined by hemoglobin <13 g/dl in men and <12 g/dl in women, to CVD. Cox proportional hazards regression was used to adjust the relationship between anemia and CVD outcomes for other covariates in the entire study cohort, as well as in subgroups of men, women, African Americans and whites.

RESULTS

A total of 14,410 subjects (6,267 men and 8,143 women) without CVD at baseline had hemoglobin levels measured. Three hundred men (4.8%) and 1,058 women (13.0%) were anemic. During an average follow-up of 6.1 years there was a total of 549 (3.8%) CVD events. The presence of anemia was independently associated with an increased risk of CVD (hazard ratio [95% confidence interval] of 1.41 [1.01, 1.95]) in the entire study cohort. In subgroup analyses the hazard ratios were in the same direction, although not statistically significant in all cases.

CONCLUSIONS

Anemia is an independent risk factor for CVD outcomes in the ARIC cohort, a community cohort of subjects between the ages of 45 and 64 years.

Baseline levels of plasma endothelin-1 (ET-1) and changes during transfusion in thalassemic patients

We studied levels of plasma endothelin-1 (ET-1) in 25 beta-thalassemia/Hb E patients before and after blood transfusion. Baseline ET-1 levels in these patients were significantly higher than in normal controls (10.17 +/- 2.1 pg/mL vs. 8.9 +/- 2.0 pg/mL, P < 0.05). After blood transfusion, levels of plasma ET-1 tend to slightly increase during the first 24 hr but significantly decline at the 7th day to levels (8.01 +/- 1.7 pg/mL) which do not differ from those of controls. This study highlights a different alteration of plasma ET-1 in patients with beta-thalassemia compared to that of patients with sickle-cell anemia.

Developing treatment for sickle cell disease

Sickle cell disease pathophysiology results from sickle haemoglobin polymerisation and its effects on the sickle erythrocyte and the vasculature. Many of the abnormalities of sickle cell disease are secondary to the damage caused by the polymer and the injured red cell. Pharmacological treatment of the disease is focused on the inhibition of sickle haemoglobin polymerisation, prevention or repair of red cell dehydration and interruption of the interaction of sickle cells with the endothelium.

Sickle erythrocytes increase prostacyclin and endothelin-1 production by cultured human endothelial cells under flow conditions

We investigated the effects of sickle erythrocytes on the production of vasotone mediators in endothelial cells (ECs) using an in vitro recirculating flow system. Sickle erythrocytes increased the EC production of two important vasoactivators, prostacyclin and endothelin-1, under venous wall shear stress conditions of 1dyncm2. The presence of interleukin-1 in the perfusion system, as a model for inflammatory cytokine effects, enhanced the overall amounts of released prostacyclin but did not affect the production of endothelin-1. This study demonstrates the effects of sickle erythrocytes on the function and metabolism of ECs under vascular flow environments. The altered production of vasoactivators may contribute to the vasotone instability and vasoocclusive crises in sickle cell anemia.

Exercise in sickle cell anemia: effect on inflammatory and vasoactive mediators

The aim of this study was to determine the response of inflammatory and vasoactive mediators to 3 consecutive days of exercise in African-American women with and without sickle cell anemia (SCA). Circulating inflammatory mediators [C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha)] were measured before, and vasoactive mediators [endothelin-1 (ET-1), nitric oxide metabolites (NOx)] before and after each exercise bout in ten subjects with SCA and ten controls. Exercise did not affect ET-1, IL-6 or CRP concentrations (p >.05). TNFalpha was higher in SCA than controls (p < or = .0005) at all times; however, the response pattern was similar for the groups: no change from day 1 to day 2, but a decrease from day 2 to day 3 (p < or = .05). NOx increased significantly after exercise (p < or = .0001) but returned to baseline by 24 h afterward. On the 3rd day, NOx increased after exercise in SCA but not in the controls (p < or = .05). In conclusion, exercise did not cause a harmful inflammatory response in these individuals with SCA. However, NOx increased after exercise on all 3 days in SCA but appeared attenuated after 2 days in controls.