Enhanced levels of soluble VCAM-1 in sickle cell patients and their specific increment during vasoocclusive crisis

Association of biomarkers of endothelial function, coagulation activation and kidney injury with persistent albuminuria in sickle cell anaemia

Persistent albuminuria (PA) is common in sickle cell anaemia (SCA). With the association of chronic kidney disease (CKD) with increased mortality, biomarkers that predict its development or progression are needed. We evaluated the association of select biomarkers with PA in adults with SCA using Kruskal-Wallis rank-sum test and logistic regression models, with adjustment for multiple testing. Of 280 subjects, 100 (35.7%) had PA. Median plasma levels of soluble vascular cell adhesion molecule-1 (VCAM-1) (1176.3 vs. 953.4 ng/mL, false discovery rate [FDR] q-value <0.003), thrombin-antithrombin complex (5.5 vs. 4.7 ng/mL, FDR q-value = 0.04), and urinary angiotensinogen (AGT) (12.2 vs. 5.3 ng/mg, FDR q-value <0.003), urinary nephrin (30.6 vs. 27.2 ng/mg, FDR q-value = 0.04), and urinary kidney injury molecule-1 (KIM-1) (0.8 vs. 0.5 ng/mg, FDR q-value <0.003), normalized to urine creatinine, were significantly higher in subjects with PA. In multivariable analysis, only urinary AGT (odds ratio = 1.058, FDR q-value <0.0001) remained a significant predictor of PA. In addition, soluble VCAM-1 (FDR q-value <0.0001), D-dimer (FDR q-value <0.0001), urinary AGT (FDR q-value <0.0001), KIM-1 (FDR q-value <0.0001), and nephrin (FDR q-value <0.0001) were significantly associated with urine albumin-creatinine ratio in multivariable analyses. Longitudinal studies to evaluate the predictive capacity of biomarkers for the development and progression of CKD in SCA are warranted.

Can we use biomarkers to identify those at risk of acute pain from sickle cell disease?

INTRODUCTION

Acute pain episodes, also known as vaso-occlusive crises (VOC), are a major symptom of sickle cell disease (SCD) and lead to frequent hospitalizations. The diagnosis of VOC can be challenging, particularly in adults with SCD, 50% of whom have chronic pain. Several potential biomarkers have been proposed for identifying individuals with VOC, including elevation above the baseline of various vascular growth factors, cytokines, and other markers of inflammation. However, none have been validated to date.

AREAS COVERED

We summarize prospective biomarkers for the diagnosis of acute pain in SCD, and how they may be involved in the pathophysiology of a VOC. Previous and current strategies for biomarker discovery, including the use of omics techniques, are discussed.

EXPERT OPINION

Implementing a multi-omics-based approach will facilitate the discovery of objective and validated biomarkers for acute pain.

Inflammatory status in pediatric sickle cell disease: Unravelling the role of immune cell subsets

Introduction: The mutation of the beta-globin gene that causes sickle cell disease (SCD) results in pleiotropic effects, such as hemolysis and vaso-occlusive crisis that can induce inflammatory mechanisms with deleterious consequences on the organism. Moreover, SCD patients display an increased susceptibility to infections. Few studies are currently available that evaluate a wide immunological profile in a pediatric population. This study proposes an evaluation of the immune profile in subjects with SCD in a pediatric population through a detailed analysis by flow cytometry. Methods and Materials: Peripheral blood samples from 53 pediatric patients with SCD (mean age 9.8 years, interquartile range 9 years) were obtained and then analyzed by flow cytometry, in order to evaluate changes in the immune populations compared to 40 healthy donors (mean age 7.3 years, interquartile range 9.5 years). Results: Our data showed an increase in neutrophils (with a reduction in the CD62L + subpopulation) and monocytes (with a decrease in HLA-DRlow monocytes) with normal values of lymphocytes in SCD patients. In the lymphocyte subpopulations analysis we observed lower values of CD4⁺ T cells (with higher number of memory and central memory T lymphocytes) with increased frequency of CD8⁺ T cells (with a predominant naive pattern). Moreover, we observed higher values of CD39⁺ Tregs and lower HLA-DR+ and CD39^- T cells with an increased Th17, Th1-17 and Th2 response. Conclusion: We observed immunological alterations typical of an inflammatory status (increase in activated neutrophils and monocytes) associated with a peculiar Treg pattern (probably linked to a body attempt to minimize inflammation intrinsic to SCD). Furthermore, we highlighted a T helper pathway associated with inflammation in line with other studies. Our data showed that immunological markers may have an important role in the understanding the pathophysiology of SCD and in optimizing targeted therapeutic strategies for each patient.

The oral ferroportin inhibitor vamifeport improves hemodynamics in a mouse model of sickle cell disease

Sickle cell disease (SCD) is an inherited hemolytic anemia caused by a single point mutation in the β-globin gene of hemoglobin that leads to synthesis of sickle hemoglobin (HbS) in red blood cells (RBCs). HbS polymerizes in hypoxic conditions, leading to intravascular hemolysis, release of free hemoglobin and heme, and increased adhesion of blood cells to the endothelial vasculature, which causes painful vaso-occlusion and organ damage. HbS polymerization kinetics are strongly dependent on the intracellular HbS concentration; a relatively small reduction in cellular HbS concentration may prevent HbS polymerization and its sequelae. We hypothesized that iron restriction via blocking ferroportin, the unique iron transporter in mammals, might reduce HbS concentration in RBCs, thereby decreasing hemolysis, improving blood flow, and preventing vaso-occlusive events. Indeed, vamifeport (also known as VIT-2763), a clinical-stage oral ferroportin inhibitor, reduced hemolysis markers in the Townes model of SCD. The RBC indices of vamifeport-treated male and female Townes mice exhibited changes attributable to iron-restricted erythropoiesis: decreased corpuscular hemoglobin concentration mean and mean corpuscular volume, as well as increased hypochromic and microcytic RBC fractions. Furthermore, vamifeport reduced plasma soluble VCAM-1 concentrations, which suggests lowered vascular inflammation. Accordingly, intravital video microscopy of fluorescently labeled blood cells in the microvasculature of Townes mice treated with vamifeport revealed diminished adhesion to the endothelium and improved hemodynamics. These preclinical data provide a strong proof-of-concept for vamifeport in the Townes model of SCD and support further development of this compound as a potential novel therapy in SCD.

Integrin VLA-4 as a PET imaging biomarker of hyper-adhesion in transgenic sickle mice

In sickle cell disease (SCD), very late antigen-4 (VLA-4 or integrin α4β1) mediates the adhesion of reticulocytes to inflamed, proinflammatory endothelium, a key process in promoting vaso-occlusive episodes (VOEs). We hypothesized that a radionuclide tracer targeting VLA-4 could be harnessed as a positron emission tomography (PET) imaging biomarker of VOEs. We tested the VLA-4 peptidomimetic PET tracer 64Cu-CB-TE1A1P-PEG4-LLP2A (64Cu-LLP2A) for imaging hyper-adhesion-associated VOEs in the SCD Townes mouse model. With lipopolysaccharide (LPS)-induced VOEs, 64Cu-LLP2A uptake was increased in the bone marrow of the humeri and femurs, common sites of VOEs in SCD mice compared with non-SCD mice. Treatment with a proven inhibitor of VOEs (the anti-mouse anti-P-selectin monoclonal antibody [mAb] RB40.34) during LPS stimulation led to a reduction in the uptake of 64Cu-LLP2A in the humeri and femurs to baseline levels, implying blockade of VOE hyper-adhesion. Flow cytometry with Cy3-LLP2A demonstrated an increased percentage of VLA-4-positive reticulocytes in SCD vs non-SCD mice in the bone and peripheral blood after treatment with LPS, which was abrogated by anti-P-selectin mAb treatment. These data, for the first time, show in vivo imaging of VLA-4-mediated hyper-adhesion, primarily of SCD reticulocytes, during VOEs. PET imaging with 64Cu-LLP2A may serve as a valuable, noninvasive method for identifying sites of vaso-occlusion and may provide an objective biomarker of disease severity and anti-P-selectin treatment efficacy in patients with SCD.

Mn porphyrins as a novel treatment targeting sickle cell NOXs to reverse and prevent acute vaso-occlusion in vivo

In sickle cell disease (SCD), adhesion of sickle red blood cells (SSRBCs) and activated leukocytes in inflamed venules affects blood rheology, causing vaso-occlusive manifestations and vital reduction in microvascular blood flow. Recently, we found that NADPH oxidases (NOXs) create a vicious feedback loop within SSRBCs. This positive feedback loop mediates SSRBC adhesion to the endothelium. We show for the first time the therapeutic effectiveness of the redox-active manganese (Mn) porphyrins MnTnBuOE-2-PyP5+ (MnBuOE; BMX-001) and MnTE-2-PyP5+ (MnE; BMX-010, AEOL10113) to treat established vaso-occlusion in a humanized sickle mouse model of an acute vaso-occlusive crisis using intravital microscopy. These Mn porphyrins can suppress SSRBC NOX activity. Subcutaneous administration of only 1 dose of MnBuOE or MnE at 0.1 to 2 mg/kg after the inflammatory trigger of vaso-occlusion, or simultaneously, reversed and reduced leukocyte and SSRBC adhesion, diminished leukocyte rolling, restored blood flow, and increased survival rate. Furthermore, MnBuOE and MnE administered to sickle mice subcutaneously at 0.1 to 1 mg/kg for 28 days (except on weekends) did not exacerbate anemia, which seemed to be due to downregulation of both SSRBC reactive oxygen species production and exposure of the eryptotic marker phosphatidylserine. In addition, Mn porphyrins ameliorated leukocytosis, venous blood gases, endothelial activation, and organ oxidative damage. Our data suggest that Mn porphyrins, likely by repressing NOX-mediated adhesive function of SSRBCs and activated leukocytes, could represent a novel, safe therapeutic intervention to treat or prevent the establishment of acute pain crises. These NOX-targeted antioxidants merit further assessment in SCD clinical trials.

Sickle cell vaso-occlusion: The dialectic between red cells and white cells

The pathophysiology of sickle cell anemia, a hereditary hemoglobinopathy, has fascinated clinicians and scientists alike since its description over 100 years ago. A single gene mutation in the HBB gene results in the production of abnormal hemoglobin (Hb) S, whose polymerization when deoxygenated alters the physiochemical properties of red blood cells, in turn triggering pan-cellular activation and pathological mechanisms that include hemolysis, vaso-occlusion, and ischemia-reperfusion to result in the varied and severe complications of the disease. Now widely regarded as an inflammatory disease, in recent years attention has included the role of leukocytes in vaso-occlusive processes in view of the part that these cells play in innate immune processes, their inherent ability to adhere to the endothelium when activated, and their sheer physical and potentially obstructive size. Here, we consider the role of sickle red blood cell populations in elucidating the importance of adhesion vis-a-vis polymerization in vaso-occlusion, review the direct adhesion of sickle red cells to the endothelium in vaso-occlusive processes, and discuss how red cell- and leukocyte-centered mechanisms are not mutually exclusive. Given the initial clinical success of crizanlizumab, a specific anti-P selectin therapy, we suggest that it is appropriate to take a holistic approach to understanding and exploring the complexity of vaso-occlusive mechanisms and the adhesive roles of the varied cell types, including endothelial cells, platelets, leukocytes, and red blood cells.

The Sickle Cell Pro-Inflammatory Response to Interval Testing Study (SPRINTS) in children and young adults with sickle cell anemia - Study design and methodological strategies

The impact of sickle cell anemia (SCA) and its complications on physical functioning and cardiopulmonary/aerobic fitness in affected individuals is significant. Although limited data support the safety of maximal cardiopulmonary exercise testing (CPET) for children and adults with SCA, the safety of submaximal moderate and high intensity, and longer duration, exercise in this population is not clear. The Sickle Cell Pro-Inflammatory Response to Interval Testing Study (SPRINTS) is a multicenter, randomized, prospective trial. SPRINTS leverages unique collaborations between investigators in pediatric hematology and exercise science to evaluate the impact of exercise intensity on the acute phase inflammatory response to exercise and changes in airway dynamics in children and young adults with SCA. Here we describe the study design and methodological strategies employed in SPRINTS, including an exercise challenge that mimics real-life patterns of childhood physical activity, characterized by multiple moderate and high intensity brief bouts of exercise interspersed with rest periods. Primary outcomes comprise pre- and post-exercise biomarkers of inflammation and endothelial dysfunction and spirometry. Secondary outcomes include assessment of physical activity and functioning, genomic studies and near-infrared spectroscopy measurements to assess tissue oxygenation status during exercise. SPRINTS aims to enroll 70 subjects with SCA and 70 matched, healthy controls. We anticipate that data from SPRINTS will address gaps in our understanding of exercise responses and safety in SCA and support the future development of evidence-based, exercise prescription guidelines in this population.

Pathologic angiogenesis in the bone marrow of humanized sickle cell mice is reversed by blood transfusion

Sickle cell disease (SCD) is a monogenic red blood cell (RBC) disorder with high morbidity and mortality. Here, we report, for the first time, the impact of SCD on the bone marrow (BM) vascular niche, which is critical for hematopoiesis. In SCD mice, we find a disorganized and structurally abnormal BM vascular network of increased numbers of highly tortuous arterioles occupying the majority of the BM cavity, as well as fragmented sinusoidal vessels filled with aggregates of erythroid and myeloid cells. By in vivo imaging, sickle and control RBCs have significantly slow intravascular flow speeds in sickle cell BM but not in control BM. In sickle cell BM, we find increased reactive oxygen species production in expanded erythroblast populations and elevated levels of HIF-1α. The SCD BM exudate exhibits increased levels of proangiogenic growth factors and soluble vascular cell adhesion molecule-1. Transplantation of SCD mouse BM cells into wild-type mice recapitulates the SCD vascular phenotype. Our data provide a model of SCD BM, in which slow RBC flow and vaso-occlusions further diminish local oxygen availability in the physiologic hypoxic BM cavity. These events trigger a milieu that is conducive to aberrant vessel growth. The distorted neovascular network is completely reversed by a 6-week blood transfusion regimen targeting hemoglobin S to <30%, highlighting the plasticity of the vascular niche. A better insight into the BM microenvironments in SCD might provide opportunities to optimize approaches toward efficient and long-term hematopoietic engraftment in the context of curative therapies.

Chronic Pain Does Not Impact Baseline Circulating Cytokine Levels in Adults with Sickle Cell Disease

Chronic pain affects 50% of adults with sickle cell disease (SCD). Although inflammation is thought to contribute to the pathogenesis of chronic pain, no studies have examined the differences in circulating cytokines between patients with SCD with and without chronic pain. We performed an observational cohort study using blood and urine samples from adults with SCD with and without chronic pain at their usual state of health. We tested the hypothesis that, compared to those without chronic pain, those with chronic pain would have significantly higher baseline circulating proinflammatory cytokines. A total of 61 adults with SCD, 40 with chronic pain and 21 without chronic pain were tested. When SCD patients with chronic pain were compared to those without chronic pain, no significant differences in cytokine levels were noted. The variables most associated with the diagnosis of chronic pain in this population were opioid dose and subject age.

Cross-sectional analysis of adhesion in individuals with sickle cell disease using a standardized whole blood adhesion bioassay to VCAM-1

Sickle cell disease (SCD) is characterized by frequent and unpredictable vaso-occlusive episodes (VOEs) that lead to severe pain, organ damage, and early death. Lack of reliable biomarkers that objectively define VOEs remains a critical barrier to improving the care for SCD patients. VOEs result from a complex interplay of cell-cell interactions that promote micro-vascular occlusion. Earlier studies demonstrated that sickle erythrocytes are more adherent than non-sickle erythrocytes and established a direct link between adhesion and frequency of VOEs. We developed a standardized, flow-based adhesion bioassay to assess the adhesive properties of SCD blood samples. The current study provides a cross-sectional analysis of steady state adhesion in SCD patients presenting at monthly out-patient hematology visits. Steady state adhesion varied from patient-to-patient. Adhesion positively correlated with reticulocyte percent and WBC count although there was no significant relationship between adhesion and platelets or hemoglobin in this study. Additionally, steady state adhesion indices were significantly lower in SCD subjects receiving hydroxyurea therapy when compared to the untreated group. The well-plate based microfluidic flow adhesion bioassay described in this report may provide a platform to identify SCD subjects with severe disease phenotypes, predict impending VOEs, and monitor response to current and developing therapies.

Inhaled steroids associated with decreased macrophage markers in nonasthmatic individuals with sickle cell disease in a randomized trial

Inhaled mometasone was shown to improve pain scores and decrease soluble vascular cell adhesion molecule (sVCAM) concentration in a randomized controlled trial of nonasthmatic patients with sickle cell disease. We sought to explore potential changes in systemic inflammation as a mechanism underlying this effect. Serum samples from 41 trial participants (15 placebo- and 26 mometasone-treated) were analyzed using a 92 inflammatory marker panel at baseline and after 8 weeks of mometasone therapy. Individual marker analysis and correlation analysis were conducted. Adjusted for age, the mometasone-treated group decreased the concentration of CXCL9, CXCL11, CD40, IL-10, and IL-18 relative to placebo-treated participants. Hierarchical clustering and correlation analysis identified additional evidence for a decrease in cytokines linking to macrophage signaling and migration. There was no statistically significant change in markers of asthma and allergy, indicating that the improvement was unlikely mediated by modulation of occult reactive airway disease. This analysis of inflammatory markers suggests that decrease in macrophage activity may be involved in the mediation of the clinical benefit seen with use of inhaled mometasone in nonasthmatic patients with sickle cell disease.Trial registration: clinicaltrials.gov identifier: NCT02061202.

Correlation Between Soluble Endothelial Adhesion Molecules and Nitric Oxide Metabolites in Sickle Cell Disease

Nitric Oxide (NO) and soluble adhesion molecules are promising biomarkers, which predict endothelial dysfunction in sickle cell disease (SCD). Several studies have investigated the relationship between NO (as well as its metabolites) and endothelial adhesion molecules in SCD. However, these studies were done mainly in the developed world, and it is difficult to extrapolate the findings to SCD populations in other geographical regions such as Africa due to significant disparities in the results. The aim of the current study was to determine the correlation between levels of nitric oxide metabolites (NOx) and adhesion molecules in SCD patients in a tertiary hospital in Ghana. A case control cross-sectional study involving 100 SCD (made up of HbSS and HbSC patients) and 60 healthy controls was conducted. Concentrations of NOx and soluble endothelial adhesion molecules (ICAM-1, VCAM-1 and E-selectin) were measured in all the study participants (n = 160) by the Griess reagent system and enzyme-linked immunosorbent assay (ELISA). Correlation analysis was performed to determine a possible link between the variables. Levels of soluble adhesion molecules were higher in the HbSS patients. Correlation of NOx with ICAM-1 almost approached significance (r = 0.565, p = 0.058) in the HbSS patients. There were no correlations between NOx and E-selectin in both HbSS and HbSC patients. There were no significant correlations between NOx and VCAM-1 in all the study participants (p > 0.05). Of the soluble adhesion molecules, ICAM-1 showed a significant positive correlation with VCAM-1 in the HbSC patients. There were no significant differences between the adhesion molecules and the age of participants in the various study groups. Whether or not a significant correlation exists between NOx and soluble adhesion molecules may not depend on the sickle cell genotype. The expression of adhesion molecules may not depend on age.

Inflammation in sickle cell disease

The primary β-globin gene mutation that causes sickle cell disease (SCD) has significant pathophysiological consequences that result in hemolytic events and the induction of the inflammatory processes that ultimately lead to vaso-occlusion. In addition to their role in the initiation of the acute painful vaso-occlusive episodes that are characteristic of SCD, inflammatory processes are also key components of many of the complications of the disease including autosplenectomy, acute chest syndrome, pulmonary hypertension, leg ulcers, nephropathy and stroke. We, herein, discuss the events that trigger inflammation in the disease, as well as the mechanisms, inflammatory molecules and cells that propagate these inflammatory processes. Given the central role that inflammation plays in SCD pathophysiology, many of the therapeutic approaches currently under pre-clinical and clinical development for the treatment of SCD endeavor to counter aspects or specific molecules of these inflammatory processes and it is possible that, in the future, we will see anti-inflammatory drugs being used either together with, or in place of, hydroxyurea in those SCD patients for whom hematopoietic stem cell transplants and evolving gene therapies are not a viable option.

Levels of Soluble Endothelium Adhesion Molecules and Complications among Sickle Cell Disease Patients in Ghana

BACKGROUND

Soluble adhesion molecules are involved in the gathering and joining of inflammatory cells to vascular endothelium. Therefore, they serve as potential markers of endothelial dysfunction in vascular diseases including sickle cell disease (SCD). In Ghana, there are scarcely any report on the levels of adhesion molecules among SCD patients. The current study aimed to determine plasma levels of ICAM-1, VCAM-1 and E-Selectin as markers of endothelial dysfunction in SCD patients in steady state, complications and controls.

METHODOLOGY

This was a cross-sectional study involving 60 HbAA controls, 46 HbSS steady state, 57 HbSS VOC, 18 HbSC VOC, 21 HbSS with leg ulcer and 11 HbSS with priapism. Blood samples were collected from all the study subjects (n = 213) and processed into plasma. The plasma levels of VCAM-1, ICAM-1 and E-Selectin concentrations of SCD patients and controls were measured using a double sandwich ELISA technique. Demographic information was also collected from the study subjects.

RESULTS

Levels of all soluble proteins (ICAM-1, VCAM-1 and E-Selectin) were significantly higher in HbSS steady-state patients compared to non-SCD controls (p < 0.001). Generally, SCD patients with complications had relatively higher levels of the soluble proteins compared to those in the steady-state. Of the SCD patients with complications, those with vaso-occlusion crisis (HbSS VOC) had relatively higher levels of ICAM-1, VCAM-1 and E-Selectin at (62.42 ng/mL &plusmn; 26.09), (634.99 ng/mL &plusmn; 324.31) and (236.77 ng/mL &plusmn; 114.40) respectively; Conclusion: Although levels of adhesion molecules were high in all the SCD patients with complications, those with vaso-occlusive crisis had higher levels. This might reflect an ongoing endothelial dysfunction in these patients. SCD patients with vaso-occlusive crisis presents with a more severe pathophysiology condition.

HO-1hi patrolling monocytes protect against vaso-occlusion in sickle cell disease

Patients with sickle cell disease (SCD) suffer from intravascular hemolysis associated with vascular injury and dysfunction in mouse models, and painful vaso-occlusive crisis (VOC) involving increased attachment of sickle erythrocytes and activated leukocytes to damaged vascular endothelium. Patrolling monocytes, which normally scavenge damaged cells and debris from the vasculature, express higher levels of anti-inflammatory heme oxygenase 1 (HO-1), a heme degrading enzyme. Here, we show that HO-1-expressing patrolling monocytes protect SCD vasculature from ongoing hemolytic insult and vaso-occlusion. We found that a mean 37% of patrolling monocytes from SCD patients express very high levels of HO-1 (HO-1^hi) vs 6% in healthy controls and demonstrated that HO-1^hi expression was dependent on uptake of heme-exposed endothelium. SCD patients with a recent VOC episode had lower numbers of HO-1^hi patrolling monocytes. Heme-mediated vaso-occlusion by mouse SCD red blood cells was exacerbated in mice lacking patrolling monocytes, and reversed following transfer of patrolling monocytes. Altogether, these data indicate that SCD patrolling monocytes remove hemolysis-damaged endothelial cells, resulting in HO-1 upregulation and dampening of VOC, and that perturbation in patrolling monocyte numbers resulting in lower numbers of HO-1^hi patrolling monocyte may predispose SCD patients to VOC. These data suggest that HO-1^hi patrolling monocytes are key players in VOC pathophysiology and have potential as therapeutic targets for VOC.

Application of phospho-CyTOF to characterize immune activation in patients with sickle cell disease in an ex vivo model of thrombosis

Sickle cell disease (SCD) is a genetic disease caused by mutations in the beta globin gene, and inflammation plays a key role in driving many aspects of disease pathology. Early immune activation is believed to be associated with hemodynamic stresses and thrombus formation as cells traffic through blood vessels. We applied an extracorporeal perfusion system to model these effects ex vivo, and combined this with a phospho-CyTOF workflow to comprehensively evaluate single-cell signatures of early activation across all major circulating immune subsets. These approaches showed immune activation following passage through the perfusion chamber, most notably in monocytes, which exhibited platelet aggregation and significantly elevated expression of multiple phospho-proteins. Overall, these studies outline a robust and broadly applicable workflow to leverage phospho-CyTOF to characterize immune activation in response to ex vivo or in vivo perturbations and may facilitate identification of novel therapeutic targets in SCD and other inflammatory diseases.

Inhaled steroids reduce pain and sVCAM levels in individuals with sickle cell disease: A triple-blind, randomized trial

Clinical and preclinical data demonstrate that altered pulmonary physiology (including increased inflammation, increased blood flow, airway resistance, and hyper-reactivity) is an intrinsic component of Sickle Cell Disease (SCD) and may contribute to excess SCD morbidity and mortality. Inhaled corticosteroids (ICS), a safe and effective therapy for pulmonary inflammation in asthma, may ameliorate the altered pulmonary physiologic milieu in SCD. With this single-center, longitudinal, randomized, triple-blind, placebo controlled trial we studied the efficacy and feasibility of ICS in 54 nonasthmatic individuals with SCD. Participants received once daily mometasone furoate 220 mcg dry powder inhalation or placebo for 16 weeks. The primary outcome was feasibility (the number who complete the trial divided by the total number enrolled) with prespecified efficacy outcomes including daily pain score over time (patient reported) and change in soluble vascular cell adhesion molecule (sVCAM) levels between entry and 8-weeks. For the primary outcome of feasibility, the result was 96% (52 of 54, 95% CI 87%-99%) for the intent-to-treat analysis and 83% (45 of 54, 95% CI 71%-91%) for the per-protocol analysis. The adjusted treatment effect of mometasone was a reduction in daily pain score of 1.42 points (95%CI 0.61-2.21, P = 0.001). Mometasone was associated with a reduction in sVCAM levels of 526.94 ng/mL more than placebo (95% CI 50.66-1003.23, P = 0.03). These results support further study of ICS in SCD including multicenter trials and longer durations of treatment. www.clinicaltrials.gov (NCT02061202).

Simvastatin reduces vaso-occlusive pain in sickle cell anaemia: a pilot efficacy trial

Sickle cell anaemia (SCA) is a progressive vascular disease characterized by episodic vaso-occlusive pain. Despite the broad impact of inflammation on acute and chronic clinical manifestations of SCA, no directed anti-inflammatory therapies currently exist. Statins are cholesterol-lowering agents shown to confer protection from vascular injury by suppressing inflammation. We previously documented a reduction in soluble biomarkers of inflammation in patients with sickle cell disease treated with simvastatin. To determine the potential clinical efficacy of simvastatin, we treated 19 SCA patients with single daily dose simvastatin for 3 months and assessed changes from baseline in the frequency and intensity of diary-reported pain and levels of circulating nitric oxide metabolites (NOx), high sensitivity C-reactive protein (hs-CRP), vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), ICAM-3, E-selectin, and vascular endothelial growth factor (VEGF). Treatment with simvastatin resulted in a significant reduction in the frequency of pain (P = 0·0003), oral analgesic use (P = 0·003) and circulating hs-CRP (P = 0·003), soluble (s)E-selectin (P = 0·01), sICAM-1 (P = 0·02), sICAM-3 (P = 0·02) and sVEGF (P = 0·01). Simvastatin had no effect on pain intensity or levels of NOx, sP-selectin and sVCAM-1. The observed reductions in pain rate and markers of inflammation were greatest in subjects receiving hydroxycarbamide (HC), suggesting a synergistic effect of simvastatin. These results provide preliminary clinical data to support a larger trial of simvastatin in SCA.

Longitudinal Analysis of Patient Specific Predictors for Mortality in Sickle Cell Disease

Introduction

White Blood Cell (WBC) count, %HbF, and serum creatinine (Cr), have been identified as markers for increased mortality in sickle cell anemia (SCA) but no studies have examined the significance of longitudinal rate of change in these or other biomarkers for SCA individuals.

Methods

Clinical, demographic and laboratory data from SCA patients seen in 2002 by our hospital system were obtained. Those who were still followed in 2012 (survival cohort) were compared to those who had died in the interim (mortality cohort). Patients lost to follow-up were excluded. Age adjusted multivariable Cox proportional hazards models were constructed to assess hazard ratios of mortality risk associated with the direction and degree of change for each variable.

Results

359 SCA patients were identified. Baseline higher levels of WBC, serum creatinine and hospital admissions were associated with increased mortality, as were alkaline phosphatase and aspartate aminotransaminase levels. Lower baseline levels of %HbF were also associated with increased mortality. When longitudinal rates of change for individuals were assessed, increases in Hb or WBC over patient baseline values were associated with greater mortality risk (HR 1.54, p = 0.02 and HR 1.16, p = 0.01 with negative predictive values of 87.8 and 94.4 respectively), while increasing ED use was associated with decreased mortality (HR 0.84, p = 0.01). We did not detect any increased mortality risk for longitudinal changes in annual clinic visits or admissions, creatinine or %HbF.

Conclusions

Although initial steady state observations can help predict survival in SCA, the longitudinal course of a patient may give additional prognostic information.

New strategies for the treatment of pulmonary hypertension in sickle cell disease : the rationale for arginine therapy

Nitric oxide (NO) is inactivated in sickle cell disease (SCD), while bioavailability of arginine, the substrate for NO synthesis, is diminished. Impaired NO bioavailability represents the central feature of endothelial dysfunction, and is a key factor in the pathophysiology of SCD. Inactivation of NO correlates with the hemolytic rate and is associated with erythrocyte release of cell-free hemoglobin and arginase during hemolysis. Accelerated consumption of NO is enhanced further by the inflammatory environment of oxidative stress that exists in SCD. Based upon its critical role in mediating vasodilation and cell growth, decreased NO bioavailability has also been implicated in the pathogenesis of pulmonary arterial hypertension (PHT). Secondary PHT is a common life-threatening complication of SCD that also occurs in most hereditary and chronic hemolytic disorders. Aberrant arginine metabolism contributes to endothelial dysfunction and PHT 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 PHT. Decompartmentalization of hemoglobin into plasma consumes endothelial NO and thus drives a metabolic requirement for arginine, whose bioavailability is further limited by arginase activity. New treatments aimed at maximizing both arginine and NO bioavailability through arginase inhibition, suppression of hemolytic rate, or oral arginine supplementation may represent novel therapeutic strategies.

Crises in Sickle Cell Disease

In spite of significant strides in the treatment of sickle cell disease (SCD), SCD crises are still responsible for high morbidity and early mortality. While most patients initially seek care in the acute setting for a seemingly uncomplicated pain episode (pain crisis or vaso-occlusive crisis), this initial event is the primary risk factor for potentially life-threatening complications. The pathophysiological basis of these illnesses is end-organ ischemia and infarction combined with the downstream effects of hemolysis that results from red blood cell sickling. These pathological changes can occur acutely and lead to a dramatic clinical presentation, but are frequently superimposed over a milieu of chronic vasculopathy, immune dysregulation, and decreased functional reserve. In the lungs, acute chest syndrome is a particularly ominous lung injury syndrome with a complex pathogenesis and potentially devastating sequelae, but all organ systems can be affected. It is, therefore, critical to understand the SCD patients' susceptibility to acute complications and their risk factors so that they can be recognized promptly and managed effectively. Blood transfusions remain the mainstay of therapy for all severe acute crises. Recommendations and indications for the safest and most efficient implementation of transfusion strategies in the critical care setting are therefore presented and discussed, together with their pitfalls and potential future therapeutic alternatives. In particular, the importance of extended phenotypic red blood cell matching cannot be overemphasized, due to the high prevalence of severe complications from red cell alloimmunization in SCD.

The acute phase inflammatory response to maximal exercise testing in children and young adults with sickle cell anaemia

Although individuals with sickle cell anaemia (SCA) have elevated baseline inflammation and endothelial activation, the acute phase response to maximal exercise has not been evaluated among children with SCA. We measured the acute phase response to maximal exercise testing for soluble vascular cell adhesion molecule (sVCAM) as well as interleukin 6 (IL6), total white blood cell (WBC) count, C-reactive protein (CRP) and D-dimer in a cohort of children with SCA and matched controls at baseline, immediately after, and 30, 60 and 120 min following exercise. Despite higher baseline levels of all biomarkers except CRP, the acute phase response from baseline to immediately after exercise was significantly greater in subjects versus controls for CRP (2·1 vs. 0·2 mg/l, P = 0·02) and D-dimer (160 vs. 10 μg/l, P < 0·01) only. Similar between-group trends were observed over time for all biomarkers, including sVCAM, IL6, total WBC, CRP and D-dimer. Lower fitness, defined by peak oxygen consumption (VO2 ), was independently associated with greater acute phase responses to exercise for sVCAM. Our results suggest maximal exercise may not be associated with any greater escalation of endothelial activation or inflammation in SCA and provide preliminary biomarker evidence for the safety of brief, high-intensity physical exertion in children with SCA.

Elevated Steady State WBC and Platelet Counts Are Associated with Frequent Emergency Room Use in Adults with Sickle Cell Anemia

INTRODUCTION

Sickle cell anemia has many sequelae that result in emergency department (ED) use, but a minority of patients with sickle cell disease are frequent utilizers and make up the majority of ED visits. If patients who are likely to be frequent ED can be identified in steady state, they can be treated with disease modifying agents in an attempt to reduce ED use frequency. We sought to identify steady state markers for frequent ED use.

METHODS

We identified all patients with SS/Sβ0 seen at our facilities in 2012. Health care utilization over the entire year was calculated and ED visit numbers categorized as either 0-1, 2-5, or 6 or more visits a year. Steady state and acutely active laboratory parameters were collected and analyzed using analysis of variance models and odds ratios.

RESULTS

432 adult sickle cell patients were identified, ages 18-87, 54% female, and 38% had been prescribed hydroxyurea. Of the 432 patients,192 had 0-1 visits in the year, 144 had 2-5 visits in the year, and 96 had >6 visits for a total of 2259 visits. Those who had >6 visits accounted for 1750 (77%) of the total visits for the year. When steady state laboratory markers were examined, each additional 50x10(9)/L platelets was associated with 22% greater risk (p < .001); each 1x10(9)/L of WBC was associated with 11% greater risk (p = .003), and each 1g/dL Hb was associated with 23% lower risk (p = .007) of >6 ED visits/year. We did not observe a relationship between baseline HbF, LDH or reticulocyte count with >6 ED visits.

CONCLUSION

Patients with elevated white blood cell counts, elevated platelet counts, and low hemoglobin levels exhibited higher risk for frequent ED utilization and could be candidates for early and aggressive therapy with disease modifying agents.

Monocytosis is associated with hemolysis in sickle cell disease

BACKGROUND

The clinical relevance of monocytosis in sickle cell disease (SCD) is uncertain. The purpose of this study was to explore the association of monocyte counts with clinical and laboratory variables in SCD.

DESIGN AND METHODS

This cross-sectional study was performed using a cohort of adult patients with SCD and control subjects without SCD. Complete blood counts, markers of hemolysis, coagulation activation, endothelial injury, and other laboratory studies were obtained in patients with SCD. Clinical complications were ascertained at the time of evaluation and tricuspid regurgitant jet velocity was determined by Doppler echocardiography.

RESULTS

One hundred and fifty-seven patients with SCD and 24 healthy, African-American, control subjects were evaluated. The absolute monocyte count was increased in SCD patients compared with healthy controls (0.6 × 10(9)/l vs. 0.4 × 10(9)/l, P = 0.0025), with higher counts in HbSS/HbSβ(0) thalassemia compared with HbSC/HbSβ(+) thalassemia. In univariate analyses, absolute monocyte count was correlated with reticulocyte count, absolute neutrophil count, indirect bilirubin, lactate dehydrogenase, and inversely correlated with hemoglobin in SCD patients. Furthermore, monocyte count was correlated with soluble vascular cell adhesion molecule-1 (VCAM-1) in HbSS/HbSβ(0) thalassemia patients. No significant associations were observed between absolute monocyte count and evaluated clinical complications. In multivariable analyses, reticulocyte count and absolute neutrophil count were significantly associated with absolute monocyte count.

CONCLUSIONS

Monocytosis is associated with hemolysis and inflammation in SCD. We suggest that hemolysis and the resultant erythropoietic response contribute to monocyte activation.

Increased erythrocyte adhesion to VCAM-1 during pulsatile flow: Application of a microfluidic flow adhesion bioassay

Sickle cell disease (SCD) is characterized by microvascular occlusion mediated by adhesive interactions of sickle erythrocytes (SSRBCs) to the endothelium. Most in vitro flow adhesion assays measure SSRBC adhesion during continuous flow, although in vivo SSRBC adhesive interactions occur during pulsatile flow. Using a well-plate microfluidic flow adhesion system, we demonstrate that isolated SSRBCs adhere to vascular cell adhesion molecule (VCAM-1) at greater levels during pulsatile versus continuous flow. A significant increase in adhesive interactions was observed between all pulse frequencies 1 Hz to 2 Hz (60-120 beats/min) when compared to non-pulsatile flow. Adhesion of isolated SSRBCs and whole blood during pulsatile flow was unaffected by protein kinase A (PKA) inhibition, and exposure of SSRBCs to pulsatile flow did not affect the intrinsic adhesive properties of SSRBCs. The cell type responsible for increased adhesion of whole blood varied from patient to patient. We conclude that low flow periods of the pulse cycle allow more adhesive interactions between sickle erythrocytes and VCAM-1, and sickle erythrocyte adhesion in the context of whole blood may better reflect physiologic cellular interactions. The microfluidic flow adhesion bioassay used in this study may have applications for clinical assessment of sickle erythrocyte adhesion during pulsatile flow.

Genetic variation in CD36, HBA, NOS3 and VCAM1 is associated with chronic haemolysis level in sickle cell anaemia: a longitudinal study

Chronic haemolysis stands out as one of the hallmarks of sickle cell anaemia, a clinically heterogeneous autosomal recessive monogenic anaemia. However, the genetic architecture of this sub-phenotype is still poorly understood. Here, we report the results of an association study between haemolysis biomarkers (serum LDH, total bilirubin and reticulocyte count) and the inheritance of 41 genetic variants of ten candidate genes in a series of 99 paediatric SS patients (median current age of 9.9 yr) followed up in two general hospitals in Greater Lisboa area (median follow-up per patient of 5.0 yr). Although in a large number of tests a seemingly significant (i.e. P < 0.05) association was observed, the following ones were confirmed upon correction for multiple comparisons: (i) an increased serum LDH level was associated with haplotype 7 within VCAM1 gene; (ii) a lower total bilirubin was associated with the 3.7-kb deletion at HBA gene, rs2070744_T allele at NOS3 gene, and haplotype 9 within VCAM1 promoter; and (iii) a diminished reticulocyte count was associated with the 3.7-kb deletion at HBA, whereas an increased count was associated with rs1984112_G allele at CD36 gene. On the whole, our findings suggest a complex genetic architecture for the sickle cell anaemia haemolysis process involving multiple pathways, namely control of vascular cell adhesion, NO synthesis and erythrocyte volume and haemoglobinisation.

Asthma management in sickle cell disease

Asthma is a common comorbid factor in sickle cell disease (SCD). However, the incidence of asthma in SCD is much higher than expected compared to rates in the general population. Whether "asthma" in SCD is purely related to genetic and environmental factors or rather is the consequence of the underlying hemolytic and inflammatory state is a topic of recent debate. Regardless of the etiology, hypoxemia induced by bronchoconstriction and inflammation associated with asthma exacerbations will contribute to a cycle of sickling and subsequent complications of SCD. Recent studies confirm that asthma predisposes to complications of SCD such as pain crises, acute chest syndrome, and stroke and is associated with increased mortality. Early recognition and aggressive standard of care management of asthma may prevent serious pulmonary complications and reduce mortality. However, data regarding the management of asthma in SCD is very limited. Clinical trials are needed to evaluate the effectiveness of current asthma therapy in patients with SCD and coincident asthma, while mechanistic studies are needed to delineate the underlying pathophysiology.

Spatiotemporal dysfunction of the vascular permeability barrier in transgenic mice with sickle cell disease

Sickle cell disease (SCD) is characterized by chronic intravascular hemolysis that generates excess cell-free hemoglobin in the blood circulation. Hemoglobin causes multiple endothelial dysfunctions including increased vascular permeability, impaired reactivity to vasoactive agonists, and increased adhesion of leukocytes to the endothelium. While the adhesive and vasomotor defects of SCD associated with cell-free hemoglobin are well defined, the vascular permeability phenotype remains poorly appreciated. We addressed this issue in two widely used and clinically relevant mouse models of SCD. We discovered that the endothelial barrier is normal in most organs in the young but deteriorates with aging particularly in the lung. Indeed, middle-aged sickle mice developed pulmonary edema revealing for the first time similarities in the chronic permeability phenotypes of the lung in mice and humans with SCD. Intravenous administration of lysed red blood cells into the circulation of sickle mice increased vascular permeability significantly in the lung without impacting permeability in other organs. Thus, increased vascular permeability is an endothelial dysfunction of SCD with the barrier in the lung likely the most vulnerable to acute inflammation.

How I treat acute chest syndrome in children with sickle cell disease

Acute chest syndrome describes new respiratory symptoms and findings, often severe and progressive, in a child with sickle cell disease and a new pulmonary infiltrate. It may be community-acquired or arise in children hospitalized for pain or other complications. Recognized etiologies include infection, most commonly with atypical bacteria, and pulmonary fat embolism (PFE); the cause is often obscure and may be multifactorial. Initiation of therapy should be based on clinical findings. Management includes macrolide antibiotics, supplemental oxygen, modest hydration and often simple transfusion. Partial exchange transfusion should be reserved for children with only mild anemia (Hb > 9 g/dL) but deteriorating respiratory status. Therapy with corticosteroids may be of value; safety, efficacy and optimal dosing strategy need prospective appraisal in a clinical trial. On recovery, treatment with hydroxyurea should be discussed to reduce the likelihood of recurrent episodes.

Pleiotropic effects of intravascular haemolysis on vascular homeostasis

The breakdown of senescent or defective red blood cells releases red cell contents, especially haemoglobin, which scavenges nitric oxide (NO) and decomposes to haem and free iron. These are potent oxidants, all of which have promoted the evolution of inducible and vasculoprotective compensatory pathways to rapidly clear and detoxify haemoglobin, haem and iron. Chronic haemolytic red cell disorders as diverse as sickle cell disease, thalassaemia, unstable haemoglobinopathy, cytoskeletal defects and enzymopathies have been linked to a clinical constellation of pulmonary hypertension, priapism, leg ulceration and possibly cerebrovascular disease and thrombosis. Besides free haemoglobin, haemolysis has been associated with extracellular arginase that limits substrate availability to NO synthase, endogenous inhibitors of NO synthase activity, and inappropriate activation of haemostatic pathways. This article reviews the haemolytic disorders that have been reported to manifest vascular complications, and explores the speculative possibility that haemolysis mediates some of the vascular complications of inflammation and diabetes.

Elevated urinary leukotriene E4 levels are associated with hospitalization for pain in children with sickle cell disease

Cysteinyl leukotrienes (CsyLTs) are inflammatory mediators produced by white blood cells. Leukotriene LTE(4) is the stable metabolite of CsyLTs, which can be measured in urine. We tested two hypotheses among children with sickle cell disease (SCD): (1) baseline urinary LTE(4) levels are elevated in children with SCD when compared with controls; and (2) baseline LTE(4) levels are associated with an increased incidence rate of hospitalization for SCD-related pain. Baseline LTE(4) levels were measured in children with SCD (cases) and children without SCD matched for age and ethnicity (controls). Medical records of cases were reviewed to assess the frequency of hospitalization for pain within 3 years of study entry. LTE(4) levels were obtained in 71 cases and 22 controls. LTE(4) levels were higher in cases compared with controls (median LTE(4): 100 vs. 57 pg/mg creatinine, P < 0.001). After adjustment for age and asthma diagnosis, a greater incidence rate of hospitalization for pain was observed among children with SCD in the highest LTE(4) tertile when compared with the lowest (114 vs. 52 episodes per 100 patient-years, P = 0.038). LTE(4) levels are elevated in children with SCD when compared with controls. LTE(4) levels are associated with an increased rate of hospitalizations for pain.

Vascular dysfunction in a murine model of severe hemolysis

Spectrin is the backbone of the erythroid cytoskeleton; sph/sph mice have severe hereditary spherocytosis (HS) because of a mutation in the murine erythroid alpha-spectrin gene. sph/sph mice have a high incidence of thrombosis and infarction in multiple tissues, suggesting significant vascular dysfunction. In the current study, we provide evidence for both pulmonary and systemic vascular dysfunction in sph/sph mice. We found increased levels of soluble cell adhesion molecules in sph/sph mice, suggesting activation of the vascular endothelium. We hypothesized that plasma hemoglobin released by intravascular hemolysis initiates endothelial injury through nitric oxide (NO) scavenging and oxidative damage. Likewise, electron paramagnetic resonance spectroscopy showed that plasma hemoglobin is much greater in sph/sph mice. Moreover, plasma from sph/sph mice had significantly higher oxidative potential. Finally, xanthine oxidase, a potent superoxide generator, is decreased in subpopulations of liver hepatocytes and increased on liver endothelium in sph/sph mice. These results indicate that vasoregulation is abnormal, and NO-based vasoregulatory mechanisms particularly impaired, in sph/sph mice. Together, these data indicate that sph/sph mice with severe HS have increased plasma hemoglobin and NO scavenging capacity, likely contributing to aberrant vasoregulation and initiating oxidative damage.

Microvascular endothelial cells express a phosphatidylserine receptor: a functionally active receptor for phosphatidylserine-positive erythrocytes

Phosphatidylserine (PS)-positive erythrocytes adhere to endothelium and subendothelial matrix components. While thrombospondin mediates these inter-actions, it is unknown whether PS-associated erythrocyte-endothelial adhesion occurs in the absence of plasma ligands. Using ionophore-treated PS-expressing control HbAA erythrocytes, we demonstrate that PS-positive erythrocytes adhered to human lung microendothelial cells in the absence of plasma ligands, that this adhesion was enhanced following endothelial activation with IL-1alpha, TNF-alpha, LPS, hypoxia, and heme, and that this adhesive interaction was selective to erythrocyte PS. We next explored whether microendothelial cells express an adhesion receptor that recognizes cell surface-expressed PS (PSR) similar to that expressed on activated macrophages. We demonstrate constitutive expression of both PSR mRNA and protein that were up-regulated in a time-dependent manner following endothelial activation. While minimal PSR expression was noted on unstimulated cells, endothelial activation up-regulated PSR surface expression. In antibody-blocking studies, using PS-positive erythrocytes generated either artificially via ionophore treatment of control erythrocytes or from patients with sickle cell disease, we demonstrate that PSR was functional, supporting PS-mediated erythrocyte adhesion to activated endothelium. Our results demonstrate the existence of a novel functional adhesion receptor for PS on the microendothelium that is up-regulated by such pathologically relevant agonists as hypoxia, cytokines, and heme.

Adherent leukocytes capture sickle erythrocytes in an in vitro flow model of vaso-occlusion

Recent in vivo studies suggest that adherent leukocytes bind RBCs and contribute to the microvascular pathology that characterizes sickle cell disease (SCD). A parallel-plate flow assay was used: to investigate the capture of RBCs by adherent neutrophils, monocytes, and T-lymphocytes; to examine whether RBC capture is elevated in patients with SCD; and to determine whether hydroxyurea (HU) therapy affects these interactions. Four measures of cell-cell adhesion were used: adhesion of leukocytes to TNF-alpha-treated human umbilical vein endothelial cells (HUVECs), percent of adherent leukocytes that captured RBCs, number of RBCs captured per interacting leukocyte, and duration of RBC capture. Leukocyte subpopulations from sickle patients were more adherent to activated ECs and captured more RBCs per interacting leukocyte than the corresponding subpopulations from healthy controls. While HU did not affect leukocyte adhesion to activated ECs, it reduced the proportion of adherent leukocytes that captured RBCs, as well as the number of RBCs captured per neutrophil. T-lymphocytes demonstrated elevated adhesion in all measures, and may be the leukocyte subpopulation whose behavior is most altered in SCD. Our findings suggest that neutrophils, monocytes, and T-lymphocytes could all be involved in adhesive interactions with autologous RBCs in patients with SCD.

Effects of progressive and maximal exercise on plasma levels of adhesion molecules in athletes with sickle cell trait with or without α-thalassemia

The aim of the study was to examine the effects of exercise on soluble vascular cell adhesion molecule-1 (sVCAM-1) and intercellular adhesion molecule-1 (sICAM-1) in sickle cell trait (SCT) athletes with or without α-thalassemia. Six athletes with SCT, seven athletes with both SCT and α-thalassemia (SCTAT), and seven control athletes (Cont) performed an incremental and maximal test on cycloergometer. Levels of sICAM-1 and sVCAM-1 were assessed at rest, immediately after the end of exercise, and 1, 2, and 24 h after exercise. Although Cont and SCTAT groups exhibited similar basal plasma levels of inflammatory and adhesion molecules, the SCT group had higher sVCAM-1 basal concentrations. Incremental exercise resulted in a significant increase of sVCAM-1 in all subjects, which remained elevated only in the SCT group during the recovery period. In conclusion, as sVCAM-1 increased with exercise and during the recovery period, our findings support the concept that SCT athletes might be at risk for microcirculatory disturbances and adhesive phenomena developing at rest and several hours after exercise. α-Thalassemia might be considered protective among exercising SCT subjects.

ADAMTS13 activity in sickle cell disease

Sickle red blood cell (SRBC)-endothelial adhesion plays a central role in sickle cell disease (SCD)-related vaso-occlusion. As unusually large von Willebrand factor (ULVWF) multimers mediate SRBC-endothelial adhesion, we investigated the activity of ADAMTS13, the metalloprotease responsible for cleaving ULVWF multimers, in SCD. ADAMTS13 activity was determined using a quantitative immunoblotting assay. VWF:Ag and VWF:RCo were determined using commercial assays. The high-molecular-weight VWF multimer percentage was determined by employing gel electrophoresis. ADAMTS13 activity was similar among asymptomatic patients (n = 8), patients at presentation with a painful crisis (n = 23), and healthy controls. ADAMTS13/VWF:Ag ratios were lower in patients compared to healthy HbAA controls, with the lowest values at presentation with a painful crisis (P = 0.02). Division of samples in those with VWF:RCo/VWF:Ag ratios < 0.70 and those with ratios >or= 0.70 revealed significantly more samples with ratios >or= 0.70 (P = 0.01) collected during painful crises. ULVWF multimers were detected in 6 patient samples and in 1 control sample. ADAMTS13/VWF:Ag ratios were inversely related to the duration of symptoms at presentation with an acute vaso-occlusive event (r(s)-0.67, P = 0.002). Although SCD is characterized by elevated VWF:Ag levels, no severe ADAMTS13 deficiency was detected in our patients.

Contrasting Roles for Domain 4 of VCAM-1 in the Regulation of Cell Adhesion and Soluble VCAM-1 Binding to Integrin α4β1

Cell adhesion mediated by the interaction between integrin alpha4beta1 and VCAM-1 is important in normal physiologic processes and in inflammatory and autoimmune disease. Numerous studies have mapped the alpha4beta1 binding sites in VCAM-1 that mediate cell adhesion; however, little is known about the regions in VCAM-1 important for regulating soluble binding. In the present study, we demonstrate that 6D VCAM-1 (an alternatively spliced isoform of VCAM-1 lacking Ig-like domain 4) binds alpha4beta1 with a higher relative affinity than does the full-length form of VCAM-1 containing 7 Ig-like extracellular domains (7D VCAM-1). In indirect binding assays, the EC50 of soluble 6D VCAM-1 binding to alpha4beta1 on Jurkat cells (in 1 mM MnCl2) was 2 x 10(-9) M, compared with 7D VCAM-1 at 11 x 10(-9) M. When used in solution to inhibit alpha4beta1 mediated cell adhesion, the IC50 of 6D VCAM-1 was 13 x 10(-9) M, compared with 7D VCAM-1 measured at 150 x 10(-9) M. Removal of Ig-like domains 4, 5, or 6, or simply substituting Asp328 in domain 4 of 7D VCAM-1 with alanine, caused increased binding of soluble 7D VCAM-1 to alpha4beta1. In contrast, cells adhered more avidly to 7D VCAM-1 under shear force, as it induced cell spreading at lower concentrations than did 6D VCAM-1. Finally, soluble 6D VCAM-1 acts as an agonist through alpha4beta1 by augmenting cell migration and inducing cell aggregation. These results indicate that the domain 4 of VCAM-1 plays a contrasting role when VCAM-1 is presented in solution or as a cell surface-expressed adhesive substrate.

Granulocytic adhesive interactions and their role in sickle cell vaso-occlusion

Recent research has high-lighted the importance of leukocytes in sickle cell disease (SCD). Here we summarize evidence to show that the granulocytes may play a role in SCD due to their increased numbers and adhesive properties, facilitating their participation in the vaso-occlusive process.

Histamine increases sickle erythrocyte adherence to endothelium

Complications of sickle cell anaemia include vascular occlusion triggered by the adherence of sickle erythrocytes to endothelium in the postcapillary venules. Adherence can be promoted by inflammatory mediators that induce endothelial cell adhesion molecule expression and arrest flowing erythrocytes. The present study characterised the effect of histamine stimulation on the kinetics of sickle cell adherence to large vessel and microvascular endothelium under physiological flow. Increased sickle cell adherence was observed within minutes of endothelial activation by histamine and reached a maximum value within 30 min. At steady state, sickle cell adherence to histamine-stimulated endothelium was 47 +/- 4 adherent cells/mm(2), 2.6-fold higher than sickle cell adherence to unstimulated endothelial cells. Histamine-induced sickle cell adherence occurred rapidly and transiently. Studies using histamine receptor agonists and antagonists suggest that histamine-induced sickle cell adhesion depends on simultaneous stimulation of the H(2) and H(4) histamine receptors and endothelial P-selectin expression. These data show that histamine release may promote sickle cell adherence and vaso-occlusion. In vivo histamine release should be studied to determine its role in sickle complications and whether blocking of specific histamine receptors may prevent clinical complications or adverse effects from histamine release stimulated by opiate analgesic treatment.

Lactate dehydrogenase as a biomarker of hemolysis-associated nitric oxide resistance, priapism, leg ulceration, pulmonary hypertension, and death in patients with sickle cell disease

Pulmonary hypertension is prevalent in adult patients with sickle cell disease and is strongly associated with early mortality and markers of hemolysis, in particular, serum lactate dehydrogenase (LDH). Intravascular hemolysis leads to impaired bioavailability of nitric oxide (NO), mediated by NO scavenging by plasma oxyhemoglobin and by arginine degradation by plasma arginase. We hypothesized that serum LDH may represent a convenient biomarker of intravascular hemolysis and NO bioavailability, characterizing a clinical subphenotype of hemolysis-associated vasculopathy. In a cohort of 213 patients with sickle cell disease, we found statistically significant associations of steady-state LDH with low levels of hemoglobin and haptoglobin and high levels of reticulocytes, bilirubin, plasma hemoglobin, aspartate aminotransferase, arginase, and soluble adhesion molecules. LDH isoenzyme fractionation confirmed predominance of LD1 and LD2, the principal isoforms within erythrocytes. In a subgroup, LDH levels closely correlated with plasma cell-free hemoglobin, accelerated NO consumption by plasma, and impaired vasodilatory responses to an NO donor. Remarkably, this simple biomarker was associated with a clinical subphenotype of pulmonary hypertension, leg ulceration, priapism, and risk of death in patients with sickle cell disease. We propose that LDH elevation identifies patients with a syndrome of hemolysis-associated NO resistance, endothelial dysfunction, and end-organ vasculopathy.

Levels of soluble endothelium-derived adhesion molecules in patients with sickle cell disease are associated with pulmonary hypertension, organ dysfunction, and mortality

Endothelial cell adhesion molecules orchestrate the recruitment and binding of inflammatory cells to vascular endothelium. With endothelial dysfunction and vascular injury, the levels of endothelial bound and soluble adhesion molecules increase. Such expression is modulated by nitric oxide (NO), and in patients with sickle cell disease (SCD), these levels are inversely associated with measures of NO bioavailability. To further evaluate the role of endothelial dysfunction in a population study of SCD, we have measured the levels of soluble endothelium-derived adhesion molecules in the plasma specimens of 160 adult patients with SCD during steady state. Consistent with a link between endothelial dysfunction and end-organ disease, we found that higher levels of soluble vascular cell adhesion molecule-1 (sVCAM-1) were associated with markers indicating renal dysfunction and hepatic impairment. Analysis of soluble intercellular cell adhesion molecule-1 (sICAM-1), sE-selectin and sP-selectin levels indicated partially overlapping associations with sVCAM-1, with an additional association with inflammatory stress and triglyceride levels. Importantly, increased soluble adhesion molecule expression correlated with severity of pulmonary hypertension, a clinical manifestation of endothelial dysfunction. Soluble VCAM-1, ICAM-1, and E-selectin were independently associated with the risk of mortality in this cohort. Our data are consistent with steady state levels of soluble adhesion molecules as markers of pulmonary hypertension and risk of death.