Erythroid adhesion molecules in sickle cell disease: effect of hydroxyurea

Genetic modulation of anemia severity, hemolysis level, and hospitalization rate in Angolan children with Sickle Cell Anemia

BACKGROUND

Sickle Cell Anemia (SCA) is a genetic disease caused by the c.20 A > T mutation in HBB gene, generally characterized by sickle erythrocytes, chronic hemolytic anemia, and vaso-occlusive events. This study aimed to investigate genetic modulators of anemia severity, chronic hemolytic rate, and clinical manifestations in pediatric SCA patients from Angola, where the disease is a severe public health problem.

METHODS AND RESULTS

The study was conducted on 200 SCA children living in Luanda or Caxito province. Their clinical phenotype was collected from patients' hospital records. Hematological and biochemical phenotypes were characterized in steady state condition. Twelve polymorphic regions in VCAM1, CD36 and NOS3 genes were genotyped using PCR, RFLP, and Sanger sequencing. CD36 gene promoter variants showed a significant impact on anemia severity. Particularly, the rs1413661_C allele was associated with lower hemoglobin levels, and increased number of hospitalizations and transfusions. This is the first report associating this SNP with SCA phenotypic heterogeneity. Moreover, the rs1041163_C allele in VCAM1 was associated with lower LDH levels; inversely the rs2070744_C allele in NOS3 was related with higher LDH levels and number of hospitalizations, being a risk factor for increased hemolytic rate.

CONCLUSION

This study highlights, for the first time in the Angolan population, the importance of the genetic modifiers of vascular cell adhesion and nitric oxide metabolism in SCA pediatric phenotypic variability.

Oxidative stress activates red cell adhesion to laminin in sickle cell disease

Vaso-occlusive crises are the hallmark of sickle cell disease (SCD). They are believed to occur in two steps, starting with adhesion of deformable low-dense red blood cells (RBCs), or other blood cells such as neutrophils, to the wall of post-capillary venules, followed by trapping of the denser RBCs or leukocytes in the areas of adhesion because of reduced effective lumen-diameter. In SCD, RBCs are heterogeneous in terms of density, shape, deformability and surface proteins, which accounts for the differences observed in their adhesion and resistance to shear stress. Sickle RBCs exhibit abnormal adhesion to laminin mediated by Lu/BCAM protein at their surface. This adhesion is triggered by Lu/BCAM phosphorylation in reticulocytes but such phosphorylation does not occur in mature dense RBCs despite firm adhesion to laminin. In this study, we investigated the adhesive properties of sickle RBC subpopulations and addressed the molecular mechanism responsible for the increased adhesion of dense RBCs to laminin in the absence of Lu/BCAM phosphorylation. We provide evidence for the implication of oxidative stress in post-translational modifications of Lu/BCAM that impact its distribution and cis-interaction with glycophorin C at the cell surface activating its adhesive function in sickle dense RBCs.

Ex Vivo Activation of Red Blood Cell Senescence by Plasma from Sickle-Cell Disease Patients: Correlation between Markers and Adhesion Consequences during Acute Disease Events

BACKGROUND: Blood transfusion remains a key treatment for managing occlusive episodes and painful crises in sickle-cell disease (SCD). In that clinical context, red blood cells (RBCs) from donors and transfused to patients, may be affected by plasma components in the recipients’ blood. Senescence lesion markers appear on the red cells after transfusion, shortening the RBC lifespan in circulation. In the specific context of SCD, senescence signals can also trigger the occlusive painful events, typical of the disease. This work follows through our previous data that described a RBC senescence process, rapidly detected after challenge with SCD pathological plasmas. In this clinical context, we wanted here to further explore the characteristics and physiologic consequences of AA RBC lesions associated with senescence, as lesions caused by RBCs after transfusion may have adverse consequences for SCD patients. METHODS: Plasma samples from SCD patients, with acute symptoms (n = 20) or steady-state disease (n = 34) were co-incubated with donor AA RBCs from blood units for 24 to 48 h. Specific markers signing RBC senescence were quantified after the incubation with SCD plasma samples. The physiologic in-flow adhesion was investigated on senescent RBCs, an in vitro technic into biochips that mimic adherence of RBCs during the occlusive events of SCD. RESULTS: Senescence markers on AA RBCs, together with their in-flow adhesion to the plasma-bridging protein thrombospondin, were associated with the clinical status of the SCD patients from whom plasma was obtained. In these experiments, the highest values were obtained for SCD acute plasma samples. Adhesion of senescent RBCs into biochips, which is not reversed by a pre-treatment with recombinant Annexin V, can be reproduced with the use of chemical agents acting on RBC membrane channels that regulate either Ca²⁺ entry or modulating RBC hydration. CONCLUSION: We found that markers on red cells are correlated, and that the senescence induced by SCD plasma provokes the adhesion of RBCs to the vessel wall protein thrombospondin. In-flow adhesion of senescent red cells after plasma co-incubations can be reproduced with the use of modulators of RBC membrane channels; activating the Piezo1 Ca²⁺ mechanosensitive channel provokes RBC adhesion of normal (non-senescent) RBCs, while blocking the Ca²⁺-dependent K⁺ Gardos channel, can reverse it. Clinically modulating the RBC adhesion to vascular wall proteins might be a promising avenue for the treatment of painful occlusive events in SCD.

Evaluation of the expression of red blood cell CD36, interleukin-6 and interleukin-8 in sickle cell anemia pediatric patients

Sickle cell anemia (SCA) is a complex multisystem disease characterized by acute and chronic inflammation, with alterations in inflammatory cytokines and adhesion molecules. This case-control study was carried out to assess the levels of CD36, immature reticulocytes, interleukin (IL)-6 and IL8 in SCA patients (in crisis and the steady state) and healthy controls. It included 90 children who were 2-18 years old; 60 with SCA and 30 healthy controls. Complete blood count, total reticulocyte count, reticulocyte subpopulations, immature reticulocyte fraction (IRF), percentage of CD36-positive red blood cells (RBCs), IL-6 and IL-8 levels were evaluated. The total white blood cell (WBC) and neutrophil counts, CD36-positive RBCs percentage, IRF, IL-6 and IL-8 levels were significantly higher in crises than in the steady state (P < 0.05). We also found that patients with SCA had significantly higher reticulocyte, WBC and neutrophil counts, fetal hemoglobin, CD36-positive RBCs percentage, IRF, and IL-6 and IL-8 levels than healthy children (P < 0.05). A significant positive linear correlation was reported between IL-6 and neutrophils during crises (Spearman correlation coefficient = 0.397, P = 0.03). These findings suggest that the levels of adhesion molecules and inflammatory markers and IRF, as evidenced by CD36-positive RBCs, IL-6 and IL-8, are elevated in SCA patients, both during steady state and crises, although these elevations are more marked during crises. Further knowledge about these cytokines and adhesion molecules will help in understanding the pathogenesis and improve therapy of SCA.

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.

A comprehensive review of hydroxyurea for β-haemoglobinopathies: the role revisited during COVID-19 pandemic

Background

Hydroxyurea is one of the earliest drugs that showed promise in the management of haemoglobinopathies that include β-thalassaemia and sickle cell disease. Despite this, many aspects of hydroxyurea are either unknown or understudied; specifically, its usefulness in β-thalassaemia major and haemoglobin E β-thalassaemia is unclear. However, during COVID-19 pandemic, it has become a valuable adjunct to transfusion therapy in patients with β-haemoglobinopathies. In this review, we aim to explore the available in vitro and in vivo mechanistic data and the clinical utility of hydroxyurea in β-haemoglobinopathies with a special emphasis on its usefulness during the COVID-19 pandemic.

Main body

Hydroxyurea is an S-phase-specific drug that reversibly inhibits ribonucleoside diphosphate reductase enzyme which catalyses an essential step in the DNA biosynthesis. In human erythroid cells, it induces the expression of γ-globin, a fetal globin gene that is suppressed after birth. Through several molecular pathways described in this review, hydroxyurea exerts many favourable effects on the haemoglobin content, red blood cell indices, ineffective erythropoiesis, and blood rheology in patients with β-haemoglobinopathies. Currently, it is recommended for sickle cell disease and non-transfusion dependent β-thalassaemia. A number of clinical trials are ongoing to evaluate its usefulness in transfusion dependent β-thalassaemia. During the COVID-19 pandemic, it was widely used as an adjunct to transfusion therapy due to limitations in the availability of blood and logistical disturbances. Thus, it has become clear that hydroxyurea could play a remarkable role in reducing transfusion requirements of patients with haemoglobinopathies, especially when donor blood is a limited resource.

Conclusion

Hydroxyurea is a well-tolerated oral drug which has been in use for many decades. Through its actions of reversible inhibition of ribonucleoside diphosphate reductase enzyme and fetal haemoglobin induction, it exerts many favourable effects on patients with β-haemoglobinopathies. It is currently approved for the treatment of sickle cell disease and non-transfusion dependent β-thalassaemia. Also, there are various observations to suggest that hydroxyurea is an important adjunct in the treatment of transfusion dependent β-thalassaemia which should be confirmed by randomised clinical trials.

[>Femoral bone infarction revealing compound heterozygous SC sickle cell disease in a Moroccan patient]

La double hétérozygotie SC est considérée comme un syndrome drépanocytaire majeur; en effet, son évolution peut être marquée par des complications sévères voire irréversibles, tel que l´infarctus osseux. Notre observation rapporte la découverte d´une hétérozygotie composite SC chez un patient de 17 ans à la suite de gonalgies intenses et met ainsi en exergue le retard diagnostic de cette maladie, et soulève la nécessité de mise en place d´une politique de dépistage précoce afin d´améliorer la prise en charge et le pronostic des sujets atteints.

Blood rheology biomarkers in sickle cell disease

Sickle cell disease (SCD) is the most common inherited blood disorder, affecting approximately 100,000 patients in the U.S. and millions more worldwide. Patients with SCD experience a wide range of clinical complications, including frequent pain crises, stroke, and early mortality, all originating from a single-point mutation in the β-globin subunit. The RBC changes resulting from the sickle mutation lead to a host of rheological abnormalities that diminish microvascular blood flow, and produce severe anemia due to RBC hemolysis, and ischemia from vaso-occlusion initiated by sticky, rigid sickle RBCs. While the pathophysiology and mechanisms of SCD have been investigated for many years, therapies to treat the disease are limited. In addition to RBC transfusion, there are only two US Food and Drug Administration (FDA)-approved drugs to ameliorate SCD complications: hydroxyurea (HU) and L-glutamine (Endari™). The only curative therapy currently available is allogeneic hematopoietic stem cell transplantation (HSCT), which is generally reserved for individuals with a matched related donor, comprising only 10–15% of the total SCD population. Potentially curative advanced gene therapy approaches for SCD are under investigation in ongoing clinical trials. The ultimate goal of any curative treatment should be to repair the hemorheological abnormalities caused by SCD, and thus normalize blood flow and prevent clinical complications. Our mini-review highlights a set of key hemorheological biomarkers (and the current and emerging technologies used to measure them) that may be used to guide the development of novel curative and palliative therapies for SCD, and functionally assess outcomes.

Impact statement

Severe impairment of blood rheology is the hallmark of SCD pathophysiology, and one of the key factors predisposing SCD patients to pain crises, organ damage, and early mortality. As novel therapies emerge to treat or cure SCD, it is crucial that these treatments are functionally evaluated for their effect on blood rheology. This review describes a comprehensive panel of rheological biomarkers, their clinical uses, and the technologies used to obtain them. The described technologies can produce highly sensitive measurements of the ability of current treatments to improve blood rheology of SCD patients. The goal of curative therapies should be to achieve blood rheology biomarkers measurements in the range of sickle cell trait individuals (HbAS). The use of the panel of rheological biomarkers proposed in this review could significantly accelerate the development, optimization, and clinical translation of novel therapies for SCD.

Erythrocyte cAMP in Determining Frequency of Acute Pain Episodes in Sickle Cell Disease Patients from Odisha State, India

Vaso-occlusive crisis (VOC) occurs more frequently during stress in sickle cell disease patients. Epinephrine released during stress increases adhesion of sickled red blood cells (RBCs) to endothelium and to leukocytes, a process mediated through erythrocyte cyclic adenosine monophosphate (cAMP). Increased adhesion of sickled RBCs retards blood flow through the capillaries and promotes vaso-occlusion. Therefore, we examined the association of RBC-cAMP levels with frequency of acute pain episodes in sickle cell disease subjects. Using a case control study design, we measured RBC-cAMP levels, fetal hemoglobin (Hb F), α-thalassemia (α-thal) and other hematological parameters at baseline (sham treated) and after stimulation with epinephrine. The cases consisted of sickle cell disease subjects with three or more acute pain episodes in the last 12 months, and those without a single acute pain episode in the last 12 months were considered as controls. Significantly higher cAMP values were found in cases than the controls, in both sham treated (p < 0.001) and epinephrine treated RBCs (p < 0.001) by Wilcoxon Rank Sum test. However, significant association of cAMP values was observed both on univariate [odds ratio (OR): 4.8, 95% confidence interval (95% CI): 1.51-15.19, p < 0.008) and multivariate logistic regression analyses only in epinephrine treated (OR: 5.07, 95% CI: 1.53-16.82, p < 0.008) but not in sham-treated RBCs. In the covariates, Hb F consistently showed protective effects in univariate as well as in multivariate analyses. Frequent acute pain episodes are associated with higher cAMP levels than those with less frequent pain episodes, only after stimulation with epinephrine but not with baseline level.

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.

Real-life experience with hydroxyurea in sickle cell disease: A multicenter study in a cohort of patients with heterogeneous descent

We conducted the first nation-wide cohort study of sickle cell disease (SCD) in Italy, a Southern European country exposed to intense recent flux migration from endemic areas for SCD. We evaluate the impact of hydroxyurea on a total of 652 pediatric and adult patients from 33 Reference Centers for SCD (mean age 24.5±15years, 51.4% males). Hydroxyurea median treatment duration was 7years (range: <1year to 29years) at a mean therapeutic dose of 18±4.7mg/kg/day. Hydroxyurea was associated with a significant increase in mean total and fetal hemoglobin and a significant decrease in mean hemoglobin S, white blood and platelet counts, and lactate dehydrogenase levels. Hydroxyurea was associated with a significant reduction in the incidence of acute chest syndrome (-29.3%, p<0.001), vaso-occlusive crisis (-34.1%, p<0.001), hospitalization (-53.2%, p<0.001), and bone necrosis (-6.9%, p<0.001). New silent cerebral infarction (SCI) occurred during treatment (+42.4%, p<0.001) but not stroke (+0.5%, p=0.572). These observations were generally consistent upon stratification for age, descent (Caucasian or African), genotype (βS/βS, βS/β⁰ or βS/β⁺) and duration of treatment (< or ≥10years). There were no new safety concerns observed compared to those commonly reported in the literature. Our study, conducted on a large population of patients with different descent and compound state supports the benefits of hydroxyurea therapy as a treatment option. Registered at clinical trials.gov (NCT02709681).

Associations between endothelial dysfunction and clinical and laboratory parameters in children and adolescents with sickle cell anemia

Background

Hematological changes can drive damage of endothelial cells, which potentially lead to an early endothelial dysfunction in patients with sickle cell anemia (SCA). An association may exist between endothelial dysfunction and several clinical manifestations of SCA. The present study aims to evaluate the links between changes in endothelial function and clinical and laboratory parameters in children and adolescents with SCA.

Methods

This study included 40 children and adolescents with stable SCA as well as 25 healthy children; aged 6–18 years. All study subjects were evaluated for endothelial function using Doppler ultrasonography. In addition, a number of laboratory assays were performed, including reticulocyte and leukocyte counts as well as measurement of circulating levels of total bilirubin, C-reactive protein (CRP), glucose, lipoproteins and peripheral oxyhemoglobin saturation. These parameters were also compared between SCA patients who were undertaking hydroxyurea (HU) and those who were not.

Results

Flow-mediated vasodilation (FMD) values were found to be reduced in SCA patients compared with those detected in healthy controls. SCA individuals with lower FMD values exhibited higher number of hospital admissions due to vaso-occlusive events. Additional analyses revealed that patients who had decreased FMD values exhibited higher odds of acute chest syndrome (ACS) episodes. A preliminary analysis with limited number of individuals failed to demonstrate significant differences in FMD values between SCA individuals who were treated with HU and those who were not.

Conclusions

Children and adolescents with SCA exhibit impaired endothelial function. Reductions in FMD values are associated with ACS. These findings underline the potential use of FMD as screening strategy of SCA patients with severe prognosis at early stages.

From the Cradle to the Grave: The Role of Macrophages in Erythropoiesis and Erythrophagocytosis

Erythropoiesis is a highly regulated process where sequential events ensure the proper differentiation of hematopoietic stem cells into, ultimately, red blood cells (RBCs). Macrophages in the bone marrow play an important role in hematopoiesis by providing signals that induce differentiation and proliferation of the earliest committed erythroid progenitors. Subsequent differentiation toward the erythroblast stage is accompanied by the formation of so-called erythroblastic islands where a central macrophage provides further cues to induce erythroblast differentiation, expansion, and hemoglobinization. Finally, erythroblasts extrude their nuclei that are phagocytosed by macrophages whereas the reticulocytes are released into the circulation. While in circulation, RBCs slowly accumulate damage that is repaired by macrophages of the spleen. Finally, after 120 days of circulation, senescent RBCs are removed from the circulation by splenic and liver macrophages. Macrophages are thus important for RBCs throughout their lifespan. Finally, in a range of diseases, the delicate interplay between macrophages and both developing and mature RBCs is disturbed. Here, we review the current knowledge on the contribution of macrophages to erythropoiesis and erythrophagocytosis in health and disease.

Sickle cell disease biochip: a functional red blood cell adhesion assay for monitoring sickle cell disease

Sickle cell disease (SCD) afflicts millions of people worldwide and is associated with considerable morbidity and mortality. Chronic and acute vaso-occlusion are the clinical hallmarks of SCD and can result in pain crisis, widespread organ damage, and early movtality. Even though the molecular underpinnings of SCD were identified more than 60 years ago, there are no molecular or biophysical markers of disease severity that are feasibly measured in the clinic. Abnormal cellular adhesion to vascular endothelium is at the root of vaso-occlusion. However, cellular adhesion is not currently evaluated clinically. Here, we present a clinically applicable microfluidic device (SCD biochip) that allows serial quantitative evaluation of red blood cell (RBC) adhesion to endothelium-associated protein-immobilized microchannels, in a closed and preprocessing-free system. With the SCD biochip, we have analyzed blood samples from more than 100 subjects and have shown associations between the measured RBC adhesion to endothelium-associated proteins (fibronectin and laminin) and individual RBC characteristics, including hemoglobin content, fetal hemoglobin concentration, plasma lactate dehydrogenase level, and reticulocyte count. The SCD biochip is a functional adhesion assay, reflecting quantitative evaluation of RBC adhesion, which could be used at baseline, during crises, relative to various long-term complications, and before and after therapeutic interventions.

Score Predicting Acute Chest Syndrome During Vaso-occlusive Crises in Adult Sickle-cell Disease Patients

Background

Vaso-occlusive crisis (VOC), hallmark of sickle-cell disease (SCD), is the first cause of patients' Emergency-Room admissions and hospitalizations. Acute chest syndrome (ACS), a life-threatening complication, can occur during VOC, be fatal and prolong hospitalization. No predictive factor identifies VOC patients who will develop secondary ACS.

Methods

This prospective, monocenter, observational study on SS/S-β₀thalassemia SCD adults aimed to identify parameters predicting ACS at Emergency-Department arrival. The primary endpoint was ACS onset within 15 days of admission. Secondary endpoints were hospitalization duration, morphine consumption, pain evaluation, blood transfusion(s) (BT(s)), requiring intensive care and mortality.

Findings

Among 250 VOCs included, 247 were analyzed. Forty-four (17.8%) ACSs occurred within 15 (median [IQR] 3 [2, 3]) days post-admission based on auscultation abnormalities; missing chest radiographs excluded three patients. Comparing ACS to VOC, respectively, median hospital stay was longer 9 [7–11] vs 4 [3–7] days (p < 0.0001), 7/41 (17%) vs 1/203 (0.5%) required intensive care (p < 0.0001), and 20/41 (48.7%) vs 6/203 (3%) required BTs (p < 0.0001). No patient died. The multivariate model retained reticulocyte and leukocyte counts, and spine and/or pelvis pain as being independently associated with ACS; the resulting ACS-predictive score's area under the ROC was 0.840 [95% CI 0.780–0.900], 98.8% negative-predictive value and 39.5% positive-predictive value for the real ACS incidence.

Interpretation

The ACS-predictive score is simple, easily applied and could change VOC management and therapeutic perspectives. Assessed ACS risk could lead to earlier discharges or close monitoring and rapid medical intensification to prevent ACS.

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Acute chest syndrome is a threatening complication.

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Acute chest syndrome often occurs during a vaso occlusive crisis.

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Our study provides a predictive score of acute chest syndrome.

Dynamic deformability of sickle red blood cells in microphysiological flow

In sickle cell disease (SCD), hemoglobin molecules polymerize intracellularly and lead to a cascade of events resulting in decreased deformability and increased adhesion of red blood cells (RBCs). Decreased deformability and increased adhesion of sickle RBCs lead to blood vessel occlusion (vaso-occlusion) in SCD patients. Here, we present a microfluidic approach integrated with a cell dimensioning algorithm to analyze dynamic deformability of adhered RBC at the single-cell level in controlled microphysiological flow. We measured and compared dynamic deformability and adhesion of healthy hemoglobin A (HbA) and homozygous sickle hemoglobin (HbS) containing RBCs in blood samples obtained from 24 subjects. We introduce a new parameter to assess deformability of RBCs: the dynamic deformability index (DDI), which is defined as the time-dependent change of the cell's aspect ratio in response to fluid flow shear stress. Our results show that DDI of HbS-containing RBCs were significantly lower compared to that of HbA-containing RBCs. Moreover, we observed subpopulations of HbS containing RBCs in terms of their dynamic deformability characteristics: deformable and non-deformable RBCs. Then, we tested blood samples from SCD patients and analyzed RBC adhesion and deformability at physiological and above physiological flow shear stresses. We observed significantly greater number of adhered non-deformable sickle RBCs than deformable sickle RBCs at flow shear stresses well above the physiological range, suggesting an interplay between dynamic deformability and increased adhesion of RBCs in vaso-occlusive events.

Splenic Dendritic Cells Survey Red Blood Cells for Missing Self-CD47 to Trigger Adaptive Immune Responses

Sheep red blood cells (SRBCs) have long been used as a model antigen for eliciting systemic immune responses, yet the basis for their adjuvant activity has been unknown. Here, we show that SRBCs failed to engage the inhibitory mouse SIRPα receptor on splenic CD4(+) dendritic cells (DCs), and this failure led to DC activation. Removal of the SIRPα ligand, CD47, from self-RBCs was sufficient to convert them into an adjuvant for adaptive immune responses. DC capture of Cd47(-/-) RBCs and DC activation occurred within minutes in a Src-family-kinase- and CD18-integrin-dependent manner. These findings provide an explanation for the adjuvant mechanism of SRBCs and reveal that splenic DCs survey blood cells for missing self-CD47, a process that might contribute to detecting and mounting immune responses against pathogen-infected RBCs.

Red cell adhesion in human diseases

PURPOSE OF REVIEW

This review discusses the unexpected role of red blood cell (RBC) adhesiveness in the pathophysiology of two red cell diseases, hereditary spherocytosis and polycythemia vera, and two 'nonerythroid' disorders, central retinal vein occlusion and Gaucher disease. These pathologies share common clinical manifestations, that is vaso-occlusion and/or thrombotic events.

RECENT FINDINGS

Recently, the direct involvement of RBC adhesion to the vascular endothelium has been demonstrated in the occurrence of vaso-occlusive events, in particular in sickle cell disease (SCD). Several erythroid adhesion molecules and their ligands have been identified that belong to different molecular classes (integrins, Ig-like molecules, lipids...) and are activated by a variety of signaling pathways. Among these, the laminin receptor, Lutheran/basal cell adhesion molecule, which is activated by phosphorylation, appears to play a central role in several pathologies.

SUMMARY

RBC adhesiveness might be involved in complications such as the vaso-occlusive crisis in SCD, thrombosis in polycythemia vera, splenic sequestration in hereditary spherocytosis, occlusions in central retinal vein occlusion and bone infarcts in Gaucher disease. Characterization of this pathological process at the cellular and molecular levels should prove useful to develop new therapeutic approaches based on the blockade of RBC abnormal interactions with vascular endothelium and/or circulating blood cells.

Erythroid Adhesion Molecules in Sickle Cell Anaemia Infants: Insights Into Early Pathophysiology

Sickle cell anaemia (SCA) results from a single mutation in the β globin gene. It is seldom symptomatic in the first semester of life. We analysed the expression pattern of 9 adhesion molecules on red blood cells, in a cohort of 54 SCA and 17 non-SCA very young infants of comparable age (median 144 days, 81-196). Haemoglobin F (HbF) level was unsurprisingly elevated in SCA infants (41.2% ± 11.2) and 2-4 fold higher than in non-SCA infants, yet SCA infants presented significantly decreased Hb level and increased reticulocytosis. Cytometry analysis evidenced a specific expression profile on reticulocytes of SCA infants, with notably an increased expression of the adhesion molecules Lu/BCAM, ICAM-4 and LFA-3, both in percentage of positive cells and in surface density. No significant difference was found on mature red cells. Our findings demonstrate the very early onset of reticulocyte membrane modifications in SCA asymptomatic infants and allow an insight into the first pathological changes with the release of stress reticulocytes expressing a distinctive profile of adhesion molecules.

Cytotoxicity and DNA damage in the neutrophils of patients with sickle cell anaemia treated with hydroxyurea

Hydroxyurea (HU) is the most important advance in the treatment of sickle cell anaemia (SCA) for preventing complications and improving quality of life for patients. However, some aspects of treatment with HU remain unclear, including their effect on and potential toxicity to other blood cells such as neutrophils. This study used the measurement of Lactate Dehydrogenase (LDH) and Methyl ThiazolTetrazolium (MTT) and the comet assay to investigate the cytotoxicity and damage index (DI) of the DNA in the neutrophils of patients with SCA using HU.In the LDH and MTT assays, a cytoprotective effect was observed in the group of patients treated, as well as an absence of toxicity. When compared to patients without the treatment, the SS group (n=20, 13 women and 07 men, aged 18-69 years), and the group of healthy individuals (AA) used as a control group (n=52, 28 women and 24 men, aged 19-60 years), The SSHU group (n=21, 11 women and 10 men, aged 19-63 years) showed a significant reduction (p<0.001) in LDH activity and an increase in the percentage of viable cells by the MTT (p<0.001). However, the SSHU group presented significantly higher DI values (49.57±6.0 U/A) when compared to the AA group (7.43 ± 0,94U/A) and the SS group (22.73 ±5.58 U/A) (p<0.0001), especially when treated for longer periods (>20 months), demonstrating that despite the cytoprotective effects in terms of cell viability, the use of HU can induce DNA damage in neutrophils.

Hydroxycarbamide decreases sickle reticulocyte adhesion to resting endothelium by inhibiting endothelial lutheran/basal cell adhesion molecule (Lu/BCAM) through phosphodiesterase 4A activation

Vaso-occlusive crises are the main acute complication in sickle cell disease. They are initiated by abnormal adhesion of circulating blood cells to vascular endothelium of the microcirculation. Several interactions involving an intricate network of adhesion molecules have been described between sickle red blood cells and the endothelial vascular wall. We have shown previously that young sickle reticulocytes adhere to resting endothelial cells through the interaction of α4β1 integrin with endothelial Lutheran/basal cell adhesion molecule (Lu/BCAM). In the present work, we investigated the functional impact of endothelial exposure to hydroxycarbamide (HC) on this interaction using transformed human bone marrow endothelial cells and primary human pulmonary microvascular endothelial cells. Adhesion of sickle reticulocytes to HC-treated endothelial cells was decreased despite the HC-derived increase of Lu/BCAM expression. This was associated with decreased phosphorylation of Lu/BCAM and up-regulation of the cAMP-specific phosphodiesterase 4A expression. Our study reveals a novel mechanism for HC in endothelial cells where it could modulate the function of membrane proteins through the regulation of phosphodiesterase expression and cAMP-dependent signaling pathways.

Influence of the Clinical Status on Stress Reticulocytes, CD 36 and CD 49d of SSFA 2 Homozygous Sickle Cell Patients Followed in Abidjan

Background and Objectives. Interactions between sickle cells involving CD 49d, CD36, and the vascular endothelium may initiate vasoocclusion leading to acute painful episodes and multiple organ failure. Materials and Methods. We selected 60 SS patients who had never been treated by hydroxyurea. We performed a total blood count. We identified with immunophenotyping by flow cytometry total reticulocytes their distribution according to the degree of maturity (mature, intermediate, very immature) and CD 36(+) and CD 49d(+) antigens. Stress reticulocytes corresponded to the sum of intermediate and immature cells. Results. Subjects in crisis had more total reticulocytes and very immature reticulocytes than subjects in stationary phase (P < 0.05). During the crisis, total CD 36(+) reticulocytes (214 870 ± 107 584/ μ L versus 148 878 ± 115 024/ μ L; P < 0.05) and the very immature CD 36(+) reticulocytes (28.9 ± 7.9% versus 23.0 ± 6.4%; P < 0.05) increased. The clinical status had no impact on CD 49d(+) reticulocytes. Conclusion. The rates of stress reticulocytes in general and those expressing CD 49d and CD 36 were very high. The clinical status had an influence on CD 36(+) reticulocytes. The expression of adhesion molecules is only one of the parameters involved in sickle cell disease crisis.

Red blood cells mediate the onset of thrombosis in the ferric chloride murine model

Application of ferric chloride (FeCl(3)) to exposed blood vessels is widely used to initiate thrombosis in laboratory mice. Because the mechanisms by which FeCl(3) induces endothelial injury and subsequent thrombus formation are little understood, we used scanning electron and brightfield intravital microscopy to visualize endothelial damage and thrombus formation occurring in situ. Contrary to generally accepted belief, FeCl(3) does not result in appreciable subendothelial exposure within the time frame of thrombosis. Furthermore, the first cells to adhere to FeCl(3)-treated endothelial surfaces are red blood cells (RBCs) rather than platelets. Energy dispersive x-ray spectroscopy demonstrated that ferric ions predominantly localize to endothelial-associated RBCs and RBC-derived structures rather than to the endothelium. With continuing time points, RBC-derived structures rapidly recruit platelets, resulting in large complexes that subsequently enlarge and coalesce, quickly covering the endothelial surface. Further studies demonstrated that neither von Willebrand factor nor platelet glycoprotein Ib-α receptor (GPIb-α) is required for RBCs to adhere to the endothelium, and that deficiency of GPIb-α greatly abrogated the recruitment of platelets to the endothelial-associated RBC material. These findings illuminate the mechanisms of FeCl(3)-mediated thrombosis and reveal a previously unrecognized ability of RBCs to participate in thrombosis by mediating platelet adhesion to the intact endothelial surface.

Abnormal properties of red blood cells suggest a role in the pathophysiology of Gaucher disease

Gaucher disease (GD) is a lysosomal storage disorder caused by glucocerebrosidase deficiency. It is notably characterized by splenomegaly, complex skeletal involvement, ischemic events of the spleen and bones, and the accumulation of Gaucher cells in several organs. We hypothesized that red blood cells (RBCs) might be involved in some features of GD and studied the adhesive and hemorheologic properties of RBCs from GD patients. Hemorheologic analyses revealed enhanced blood viscosity, increased aggregation, and disaggregation threshold of GD RBCs compared with control (CTR) RBCs. GD RBCs also exhibited frequent morphologic abnormalities and lower deformability. Under physiologic flow conditions, GD RBCs adhered more strongly to human microvascular endothelial cells and to laminin than CTR. We showed that Lu/BCAM, the unique erythroid laminin receptor, is overexpressed and highly phosphorylated in GD RBCs, and may play a major role in the adhesion process. The demonstration that GD RBCs have abnormal rheologic and adhesion properties suggests that they may trigger ischemic events in GD, and possibly phagocytosis by macrophages, leading to the appearance of pathogenic Gaucher cells.

Design, synthesis, and pharmacological evaluation of novel hybrid compounds to treat sickle cell disease symptoms. part II: furoxan derivatives

Phthalimide derivatives containing furoxanyl subunits as nitric oxide (NO)-donors (3a-g) were designed, synthesized, and evaluated in vitro and in vivo for their potential uses in the oral treatment of sickle cell disease symptoms. All compounds (3a-g) demonstrated NO-donor properties at different levels. Moreover, compounds 3b and 3c demonstrated analgesic activity. Compound 3b was determined to be a promising drug candidate for the aforementioned uses, and it was further evaluated in K562 culture cells to determine its ability to increase levels of γ-globin expression. After 96 h at 5 μM, compound 3b was able to induce γ-globin expression by nearly three times. Mutagenic studies using micronucleus tests in peripheral blood cells of mice demonstrated that compound 3b reduces the mutagenic profile as compared with hydroxyurea. Compound 3b has emerged as a new leading drug candidate with multiple beneficial effects for the treatment of sickle cell disease symptoms and provides an alternative to hydroxyurea treatment.

Human induced pluripotent stem cells can reach complete terminal maturation: in vivo and in vitro evidence in the erythropoietic differentiation model

BACKGROUND

Human induced pluripotent stem cells offer perspectives for cell therapy and research models for diseases. We applied this approach to the normal and pathological erythroid differentiation model by establishing induced pluripotent stem cells from normal and homozygous sickle cell disease donors.

DESIGN AND METHODS

We addressed the question as to whether these cells can reach complete erythroid terminal maturation notably with a complete switch from fetal to adult hemoglobin. Sickle cell disease induced pluripotent stem cells were differentiated in vitro into red blood cells and characterized for their terminal maturation in terms of hemoglobin content, oxygen transport capacity, deformability, sickling and adherence. Nucleated erythroblast populations generated from normal and pathological induced pluripotent stem cells were then injected into non-obese diabetic severe combined immunodeficiency mice to follow the in vivo hemoglobin maturation.

RESULTS

We observed that in vitro erythroid differentiation results in predominance of fetal hemoglobin which rescues the functionality of red blood cells in the pathological model of sickle cell disease. We observed, in vivo, the switch from fetal to adult hemoglobin after infusion of nucleated erythroid precursors derived from either normal or pathological induced pluripotent stem cells into mice.

CONCLUSIONS

These results demonstrate that human induced pluripotent stem cells: i) can achieve complete terminal erythroid maturation, in vitro in terms of nucleus expulsion and in vivo in terms of hemoglobin maturation; and ii) open the way to generation of functionally corrected red blood cells from sickle cell disease induced pluripotent stem cells, without any genetic modification or drug treatment.

Effect of hydroxyurea on physical fitness indices in children with sickle cell anemia

The current studies aimed at determining physical fitness indices and anthropometrics profiles of children with sickle cell anemia (SCA) after the use of hydroxyurea (HU). Ninety-three male schoolchildren--who participated previously in a similar study before the introduction of HU--comprising 2 groups participated in the studies. Group 1 was 41 children who were suffering from sickle cell disease (SCD) and were on HU for a minimum of 2 years, whereas group 2 was 50 normal healthy controls. Anthropometrics measurement and parameters of physical fitness were assessed in all subjects. All children were also subjected to a minimum of 6-minute running exercise test on a flat motorized treadmill at speed corresponding to 5 km/h. Throughout the test heart rate was monitored and recorded during exercise and for 10 minutes during recovery. Blood hemoglobin (Hb) and HbF% were measured after the use of HU. The mean values of weight, height, and lean body mass were still lower in the SCD children (P < .05) compared with the healthy subjects. However, they had significant decrease in the mean heart rate values and they spent longer time on the treadmill before they got tired compared to their previous performance and were just below the normal controls. Hydroxyurea treatment improved the aerobic exercise tolerance and most of the physical fitness parameters in children with SCD.

Differential modulation of adhesion molecule expression by hydroxycarbamide in human endothelial cells from the micro- and macrocirculation: potential implications in sickle cell disease vasoocclusive events

BACKGROUND

All the cellular partners of the vascular system and especially endothelial cells are involved in the pathophysiology of the vasoocclusive crises associated with sickle cell disease. In sickle cell disease, circulating cells adhere abnormally to endothelial cells in a chronic pro-inflammatory context. Hydroxycarbamide is the only drug with demonstrated efficacy to reduce the frequency of vasoocclusive crises. Here, we investigated the effects of hydroxycarbamide and/or cytokines on the expression of genes related to adhesion events in endothelial cells from three different vascular sites.

DESIGN AND METHODS

Endothelial cells representative of the macro- (HUVEC) or microcirculation (TrHBMEC and HPMEC) were grown in the presence or absence of hydroxycarbamide and/or cytokines (TNFα and IFNγ). Expression of genes encoding adhesion proteins was analyzed by RQ-PCR, ELISA, flow cytometry, in situ ELISA for extracellular matrix proteins, and Western blot.

RESULTS

In cells from the microcirculation, expression of TSP-1, vWF, and PECAM-1 genes was decreased by hydroxycarbamide and/or cytokine treatment at the mRNA level. In the macro-circulation their expression was unaffected or increased. Hydroxycarbamide significantly decreased vWF incorporated in the TrHBMEC extracellular matrix. CD36 mRNA was strongly down-regulated by cytokines in HPMEC, the only cell type in which it is expressed. Hydroxycarbamide decreased soluble PECAM-1 in HUVEC supernatants.

CONCLUSIONS

Our results highlight the heterogeneity of vascular endothelial cell responses to hydroxycarbamide and/or cytokines depending upon their origin. They also suggest that hydroxycarbamide has an anti-adhesogenic effect on endothelial cells, but by mechanisms which could vary according to their macro- or microcirculation and organ origin.

Sickle-cell disease

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

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.

Generation and characterisation of Rhd and Rhag null mice

Mouse Rhd* and Rhag* genes were targeted using insertional vectors; the resulting knockout mice, and double-knockout descendants, were analysed. Rhag glycoprotein deficiency entailed defective assembly of the erythroid Rh complex with complete loss of Rh and intercellular adhesion molecule 4 (ICAM-4), but not CD47, expression. Absence of the Rh protein induced a loss of ICAM-4, and only a moderate reduction of Rhag expression. Double knockout phenotype was similar to that of Rhag targeted mice. Rhd and Rhag deficient mice exhibited neither the equivalent of human Rh(null) haemolytic anaemia nor any clinical or cellular abnormalities. Rhd-/- and Rhag-/- erythrocytes showed decreased basal adhesion to an endothelial cell line resulting from defective ICAM-4 membrane expression. There was no difference in recovery from phenylhydrazine-induced haematopoietic stress for double knockout mice as compared to controls, suggesting that ICAM-4 might be dispensable during stress erythropoiesis. Ammonia and methylammonia transport in erythrocytes was severely impaired in Rhag-/- but only slightly in Rhd-/- animals that significantly expressed Rhag, supporting the view that RhAG and Rhag, but not Rh, may act as ammonium transporters in human and mouse erythrocytes. These knockout mice should prove useful for further dissecting the physiological roles of Rh and Rhag proteins in the red cell membrane.

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.