Microparticles in sickle cell disease

Blood rheology and vascular function in sickle cell trait and sickle cell disease: From pathophysiological mechanisms to clinical usefulness

Sickle cell disease (SCD) is an autosomal recessive disorder. Although the molecular mechanisms at the origin of SCD have been well characterized, its clinical expression is highly variable. SCD is characterized by blood rheological abnormalities, increased inflammation and oxidative stress, and vascular dysfunction. Individuals with only one copy of the mutated β-globin gene have sickle cell trait (SCT) and are usually asymptomatic. The first part of this review focuses on the biological responses of SCT carriers during exercise and on the effects of combined SCT and diabetes on vascular function, several biomarkers and clinical complications. The second part of the review focuses on SCD and shows that the magnitude of red blood cell (RBC) rheological alterations is highly variable from one patient to another, and this variability reflects the clinical and hematological variability: patients with the less deformable RBCs have high hemolytic rate and severe anemia, and are prone to develop leg ulcers, priapism, cerebral vasculopathy, glomerulopathy or pulmonary hypertension. In contrast, SCD patients characterized by the presence of more deformable RBCs (but still rigid) are less anemic and may exhibit increased blood viscosity, which increases the risk for vaso-occlusive events. Several genetic and cellular factors may modulate RBC deformability in SCD: co-existence of α-thalassemia, fetal hemoglobin level, oxidative stress, the presence of residual mitochondria into mature RBCs, the activity of various non-selective cationic ion channels, etc. The last part of this review presents the effects of hydroxyurea and exercise training on RBC rheology and other biomarkers in SCD.

Vascular pathophysiology of sickle cell disease

Sickle cell disease (SCD) is an hereditary disorder characterized by the production of an abnormal hemoglobin called hemoglobin S (HbS). HbS may polymerize in deoxygenated conditions, which leads to red blood cell (RBC) sickling. Sickled RBCs are more rigid and fragile, and prone to lysis. SCD patients exhibit various acute and/or chronic complications, which may affect several organs. The clinical presentation of SCD is highly variable from one patient to another and cannot be only explained by RBC sickling. Increased blood viscosity, caused by the presence of RBCs with abnormal deformability and aggregation, may increase vascular resistance and increase the risk of acute and chronic vascular complications. Chronic hemolysis results in decreased nitric oxide (NO) bioavailability which may compromise vasodilation and participate to the development of chronic vasculopathy. Furthermore, chronic hemolysis is responsible for increased inflammation and oxidative stress, which affect the vascular system and may promote the adhesion of circulating cells to endothelial cells. Extracellular vesicles and especially RBC microparticles (massively released in the context of SCD) are also at the origin of vascular damages and increased white blood cells adhesion to the endothelium, which may trigger vaso-occlusive crisis and other vascular-related complications. This review highlights the fact that SCD should not only be considered as a hematological disorder but also as a vascular disease.

Association of Circulating Procoagulant Microvesicles with Painful Vaso-Occlusive Crisis in Sickle Cell Disease

Introduction

Thrombotic complication is one of the features of sickle cell disease (SCD), characterized by appearance of phosphatidylserine on the outer membrane of sickle-shaped red blood cells and most abundantly on membrane protrusions called microvesicles (MVs). However, the exact mechanism by which MVs may enhance coagulant activity in SCD patients has not been fully addressed. The aim of this study was to further investigate the procoagulant activity of circulating MVs in sickle cell crises.

Materials and Methods

Subjects included in this cross-sectional study were 47 patients with SCD and 25 normal subjects with written informed consent obtained from all the participants. MV analysis was conducted by using CD61, CD235α, and Annexin-V monoclonal antibodies. The coagulant activity of MVs was determined by an ELISA-based procoagulant activity assay.

Results

The majority of MVs were originated from platelets (CD61+) and erythrocytes (CD235+). These MVs demonstrated significantly enhanced levels during the painful crisis when compared with the steady-state period (p < 0.001) and controls (p < 0.001). Also, the procoagulant activity of MVs was significantly higher in crisis compared to those of steady state (p < 0.001) and positively correlated with the number of Annexin-V+ MVs (p < 0.001). Significant correlations were found between erythrocyte-derived MVs with hemolysis marker (r = 0.51, p < 0.001) and the hemoglobin level (r = -0.63, p < 0.001).

Conclusion

The numbers of platelet- and erythrocyte-derived MVs are related to painful crisis, and their quantification in SCD may be helpful for identifying cases at increased risk of thrombotic complications.

Multi-Organ Morphological Findings in a Humanized Murine Model of Sickle Cell Trait

Sickle cell disease (SCD) is caused by the homozygous beta-globin gene mutation that can lead to ischemic multi-organ damage and consequently reduce life expectancy. On the other hand, sickle cell trait (SCT), the heterozygous beta-globin gene mutation, is still considered a benign condition. Although the mechanisms are not well understood, clinical evidence has recently shown that specific pathological symptoms can also be recognized in SCT carriers. So far, there are still scant data regarding the morphological modifications referable to possible multi-organ damage in the SCT condition. Therefore, after genotypic and hematological characterization, by conventional light microscopy and transmission electron microscopy (TEM), we investigated the presence of tissue alterations in 13 heterozygous Townes mice, one of the best-known animal models that, up to now, was used only for the study of the homozygous condition. We found that endothelial alterations, as among which the thickening of vessel basal lamina, are ubiquitous in the lung, liver, kidney, and spleen of SCT carrier mice. The lung shows the most significant alterations, with a distortion of the general tissue architecture, while the heart is the least affected. Collectively, our findings contribute novel data to the histopathological modifications at microscopic and ultrastructural levels, underlying the heterozygous beta-globin gene mutation, and indicate the translational suitability of the Townes model to characterize the features of multiple organ involvement in the SCT carriers.

Emerging functional microfluidic assays for the study of thromboinflammation in sickle cell disease

PURPOSE OF REVIEW

This review briefly summarizes the significant impact of thromboinflammation in sickle cell disease in relation to recent advances in biomarkers that are used in functional microfluidic assays.

RECENT FINDINGS

Sickle cell disease (SCD) is an inherited hemoglobinopathy that affects 100 000 Americans and millions worldwide. Patients with SCD exhibit chronic haemolysis, chronic inflammation and thrombosis, and vaso-occlusion, triggering various clinical complications, including organ damage and increased mortality and morbidity. Recent advances in functional microfluidic assays provide direct biomarkers of disease, including abnormal white blood cell and red blood cell adhesion, cell aggregation, endothelial degradation and contraction, and thrombus formation.

SUMMARY

Novel and emerging functional microfluidic assays are a promising and feasible strategy to comprehensively characterize thromboinflammatory reactions in SCD, which can be used for personalized risk assessment and tailored therapeutic decisions.

Annexin V- and tissue factor+ microparticles as biomarkers for predicting deep vein thrombosis in patients after joint arthroplasty

OBJECTIVE

Venous thromboembolism (VTE) is a common and severe complication of joint arthroplasty. Microparticles (MPs) containing phosphatidylserine (PS) and tissue factor (TF) can trigger coagulation in VTE. This study aims to measure and compare MP levels in joint arthroplasty patients with and without VTE.

METHODS

This prospective cohort study enrolled 181 patients who underwent joint arthroplasty. Ultrasound examination was used to diagnose VTE on preoperative day 0 and postoperative day 6. MPs were analysed using transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and flow cytometry. The levels of platelet-derived microparticles (PMPs), endothelial cell-derived microparticles (EMPs), granulocyte-derived microparticles (GMPs), red cell-derived microparticles (RMPs), monocyte-derived microparticles (MMPs), Annexin V⁺ MPs (AV⁺ MPs), and tissue factor⁺ MPs (TF⁺ MPs) derived from five kinds of MPs were measured on day 0 (before surgery), 1, 2, 3, 4, 5, and 6 after surgery.

RESULTS

The levels of AV^-TF⁺ EMPs and AV^-TF⁺ MMPs were significantly increased in patients with VTE on postoperative day 5 compared to those without VTE (P=0.031 and P=0.031, respectively).

CONCLUSION

AV^-TF⁺ MPs may indicate the development of VTE and serve as predictive markers in joint arthroplasty patients.

Autologous blood extracellular vesicles and specific CD4+ T-cell co-activation

Extracellular vesicles (EVs), which are generated by cell membrane budding in diverse cells, are present in variable numbers in the blood. An immunoregulatory role has been demonstrated principally for heterologous EVs, but the function of the EVs present naturally in blood remains unknown. We hypothesize that these autologous EVs might also modulate the phenotype and function of immune system cells, especially CD4⁺ T lymphocytes (TLs), as previously described for heterologous EVs. Several membranes and soluble immunoregulatory molecules were studied after the treatment of CD4⁺ TLs with autologous EVs. No direct activation was detected with autologous EVs, contrasting with the findings for heterologous EVs. However, following treatment with autologous EVs, a soluble form of CD27 (sCD27) was detected. sCD27 is strongly associated with lymphoproliferation. Autologous EVs have been shown to increase TL proliferation only after T-cell receptor (TcR) engagement due to polyclonal or specific-antigen stimulation. Our results therefore suggest that the EVs present in the blood have an immunomodulatory role different from that of heterologous EVs. These findings should be taken into account in future studies, particularly those focusing on infectious diseases, autotransfusion or doping practices.

Multiple inducers of endothelial NOS (eNOS) dysfunction in sickle cell disease

A characteristic aspect of the robust, systemic inflammatory state in sickle cell disease is dysfunction of endothelial nitric oxide synthase (eNOS). We identify 10 aberrant endothelial cell inputs, present in the specific sickle context, that are known to have the ability to cause eNOS dysfunction. These are: endothelial arginase depletion, asymmetric dimethylarginine, complement activation, endothelial glycocalyx degradation, free fatty acids, inflammatory mediators, microparticles, oxidized low density lipoproteins, reactive oxygen species, and Toll‐like receptor 4 signaling ligands. The effect of true eNOS dysfunction on clinical testing using flow‐mediated dilation can be simulated by two known examples of endothelial dysfunction mimicry (hemoglobin consumption of NO; and oxidation of smooth muscle cell soluble guanylate cyclase). This lends ambiguity to interpretation of such clinical testing. The presence of these multiple perturbing factors argues that a therapeutic approach targeting only a single injurious endothelial input (or either example of mimicry) would not be sufficiently efficacious. This would seem to argue for identifying therapeutics that directly protect eNOS function or application of multiple therapeutic approaches.

Azithromycin Reduces Markers of Vascular Damage in Pediatric Patients With Sickle Cell Disease

Background

Immunomodulatory effects of macrolides in chronic inflammation are well known. In this study, we tested our hypothesis that azithromycin (AZT) can decrease inflammation in pediatric patients with sickle cell disease (SCD).

Methods

The use of AZT as an anti-inflammatory agent was evaluated in double-blind, placebo-controlled, cross-over study for 8 weeks of treatment with 8 weeks of washout. Blood samples were collected before (PRE) and after (POST) each 8-week treatment period. Repeated measures analysis of variance (ANOVA) with post hoc multiple comparison procedures and Chi-square test were used for statistical analysis of the data. Complete blood count, distribution of the lymphocyte subsets, and plasma levels of markers of vascular damage were analyzed.

Results

A significant decrease in the number of leucocytes and granulocytes was observed in AZT group following treatment. An opposite dynamic was observed in placebo group; numbers of granulocytes significantly increased at POST interval. All markers of vascular damage were reduced in AZT group at POST interval with overall significance (P = 0.026). The most prominent significant changes were observed in levels of myeloid-related protein 8/14 (MRP8/14), lipocalin A (NGAL), matrix metalloproteinases (MMP) 9, and insulin-like growth factor-binding protein (IGFBP) 4. Plasma level of C-reactive protein (CRP) was significantly decreased in AZT group as well.

Conclusions

Data suggested that AZT may be beneficial in management of microvascular injury in SCD.

Extracellular Vesicles in Sickle Cell Disease: Plasma Concentration, Blood Cell Types Origin Distribution and Biological Properties

Prototype of monogenic disorder, sickle cell disease (SCD) is caused by a unique single mutation in the β-globin gene, leading to the production of the abnormal hemoglobin S (HbS). HbS polymerization in deoxygenated condition induces the sickling of red blood cells (RBCs), which become less deformable and more fragile, and thus prone to lysis. In addition to anemia, SCD patients may exhibit a plethora of clinical manifestations ranging from acute complications such as the frequent and debilitating painful vaso-occlusive crisis to chronic end organ damages. Several interrelated pathophysiological processes have been described, including impaired blood rheology, increased blood cell adhesion, coagulation, inflammation and enhanced oxidative stress among others. During the last two decades, it has been shown that extracellular vesicles (EVs), defined as cell-derived anucleated particles delimited by a lipid bilayer, and comprising small EVs (sEVs) and medium/large EVs (m/lEVs); are not only biomarkers but also subcellular actors in SCD pathophysiology. Plasma concentration of m/lEVs, originated mainly from RBCs and platelets (PLTs) but also from the other blood cell types, is higher in SCD patients than in healthy controls. The concentration and the density of externalized phosphatidylserine of those released from RBCs may vary according to clinical status (crisis vs. steady state) and treatment (hydroxyurea). Besides their procoagulant properties initially described, RBC-m/lEVs may promote inflammation through their effects on monocytes/macrophages and endothelial cells. Although less intensely studied, sEVs plasma concentration is increased in SCD and these EVs may cause endothelial damages. In addition, sEVs released from activated PLTs trigger PLT-neutrophil aggregation involved in lung vaso-occlusion in sickle mice. Altogether, these data clearly indicate that EVs are both biomarkers and bio-effectors in SCD, which deserve further studies.

Extracellular Vesicles from Red Blood Cells and Their Evolving Roles in Health, Coagulopathy and Therapy

Red blood cells (RBCs) release extracellular vesicles (EVs) including both endosome-derived exosomes and plasma-membrane-derived microvesicles (MVs). RBC-derived EVs (RBCEVs) are secreted during erythropoiesis, physiological cellular aging, disease conditions, and in response to environmental stressors. RBCEVs are enriched in various bioactive molecules that facilitate cell to cell communication and can act as markers of disease. RBCEVs contribute towards physiological adaptive responses to hypoxia as well as pathophysiological progression of diabetes and genetic non-malignant hematologic disease. Moreover, a considerable number of studies focus on the role of EVs from stored RBCs and have evaluated post transfusion consequences associated with their exposure. Interestingly, RBCEVs are important contributors toward coagulopathy in hematological disorders, thus representing a unique evolving area of study that can provide insights into molecular mechanisms that contribute toward dysregulated hemostasis associated with several disease conditions. Relevant work to this point provides a foundation on which to build further studies focused on unraveling the potential roles of RBCEVs in health and disease. In this review, we provide an analysis and summary of RBCEVs biogenesis, composition, and their biological function with a special emphasis on RBCEV pathophysiological contribution to coagulopathy. Further, we consider potential therapeutic applications of RBCEVs.

Red blood cell alloimmunization and sickle cell disease: a narrative review on antibody induction

The high prevalence of red blood cell (RBC) alloantibodies in people with sickle cell disease (SCD) cannot be debated. Why people with SCD are so likely to form RBC alloantibodies, however, remains poorly understood. Over the past decade, a better understanding of non-ABO blood group antigen variants has emerged; RH genetic diversity and the role this diversity plays in RBC alloimmunization is discussed elsewhere. Outside of antigen variants, the immune systems of people with SCD are known to be different than those of people without SCD. Some of these differences are due to effects of free heme, whereas others are impacted by hyposplenism. Descriptive studies of differences in white blood cell (WBC) subsets, platelet counts and function, and complement activation between people with SCD and race-matched controls exist. Studies comparing the immune systems of alloimmunized people with SCD to non-alloimmunized people with SCD to race-matched controls without SCD have uncovered differences in T-cell subsets, monocytes, Fcγ receptor polymorphisms, and responses to free heme. Studies in murine models have documented the role that recipient inflammation plays in RBC alloantibody formation, with human studies reporting a similar association. Murine studies have also reported the importance of type 1 interferon (IFNα/β), known to play a pivotal role in autoimmunity, in RBC alloantibody formation. The goal of this manuscript is to review existing data on factors influencing RBC alloantibody induction in people with SCD with a focus on inflammation and other immune system considerations, from the bench to the bedside.

Cell-derived microparticles and sickle cell disease chronic vasculopathy in sub-Saharan Africa: A multinational study

Although most individuals with sickle cell disease (SCD) live in sub-Saharan Africa, the natural history of the disease on this continent remains largely unknown. Intravascular haemolysis results in activation of circulating blood cells and release of microparticles (MPs) that exert pro-inflammatory effects and contribute to vascular damage. We designed a case-control study nested in the CADRE cohort (Coeur-Artère-DRÉpanocytose, clinical trials.gov identifier NCTO3114137) and based on extreme phenotypes, to analyse blood cell-derived MPs in 232 adult SS patients at steady state in Bamako and Dakar. Thirty-six healthy adult controls matched by age and sex were recruited in Bamako. The MPs concentrations were higher in SS patients compared to AA controls with a predominance of erythrocyte- and reticulocyte-derived MPs. These erythroid-derived MPs were significantly lower in patients with retinopathy (P = 0·022). Reticulocyte-derived MPs were significantly negatively and positively associated with a history of priapism (P = 0·020) and leg ulcers (P = 0·041) respectively. We describe for the first time the comparative patterns of plasma MPs in healthy subjects and patients with SCD living in sub-Saharan Africa and exhibiting various complications. Because our present results show no clear pattern of correlation between erythroid MPs and the classical hyper-haemolytic complications, we hypothesise a weak relevance of the hyper-haemolysis versus hyper-viscous paradigm in Africa.

Association Between Nitric Oxide, Oxidative Stress, Eryptosis, Red Blood Cell Microparticles, and Vascular Function in Sickle Cell Anemia

Chronic hemolysis, enhanced oxidative stress, and decreased nitric oxide (NO) bioavailability promote vasculopathy in sickle cell anemia (SCA). Oxidative stress and NO are known to modulate eryptosis in healthy red blood cells (RBCs); however, their role in SCA eryptosis and their impact on the genesis of RBC-derived microparticles (RBC-MPs) remains poorly described. RBC-MPs could play a role in vascular dysfunction in SCA. The aims of this study were to evaluate the roles of oxidative stress and NO in eryptosis and RBC-MPs release, and to determine whether RBC-MPs could be involved in vascular dysfunction in SCA. Markers of eryptosis and oxidative stress, plasma RBC-MPs concentration and arterial stiffness were compared between SCA and healthy (AA) individuals. In-vitro experiments were performed to test: 1) the effects of oxidative stress (antioxidant: n-acetylcysteine (NAC); pro-oxidant: cumene hydroperoxide) and NO (NO donor: sodium nitroprusside (SNP); NO-synthase inhibitor (L-NIO)) on eryptosis, RBC deformability and RBC-MP genesis; 2) the effects of SCA/AA-RBC-MPs on human aortic endothelial cell (HAEC) inflammatory phenotype and TLR4 pathway. Eryptosis, RBC-MPs, oxidative stress and arterial stiffness were increased in SCA. NAC increased RBC deformability and decreased eryptosis and RBC-MPs release, while cumene did the opposite. SNP increased RBC deformability and limited eryptosis, but had no effect on RBC-MPs. L-NIO did not affect these parameters. Arterial stiffness was correlated with RBC-MPs concentration in SCA. RBC-MPs isolated directly from SCA blood increased adhesion molecules expression and the production of cytokines by HAEC compared to those isolated from AA blood. TLR4 inhibition alleviated these effects. Our data show that oxidative stress could promote eryptosis and the release of RBC-MPs that are potentially involved in macrovascular dysfunction in SCA.

The Red Blood Cell-Inflammation Vicious Circle in Sickle Cell Disease

Sickle cell disease (SCD) is a genetic disease caused by a single mutation in the β-globin gene, leading to the production of an abnormal hemoglobin called hemoglobin S (HbS), which polymerizes under deoxygenation, and induces the sickling of red blood cells (RBCs). Sickled RBCs are very fragile and rigid, and patients consequently become anemic and develop frequent and recurrent vaso-occlusive crises. However, it is now evident that SCD is not only a RBC rheological disease. Accumulating evidence shows that SCD is also characterized by the presence of chronic inflammation and oxidative stress, participating in the development of chronic vasculopathy and several chronic complications. The accumulation of hemoglobin and heme in the plasma, as a consequence of enhanced intravascular hemolysis, decreases nitric oxide bioavailability and enhances the production of reactive oxygen species (ROS). Heme and hemoglobin also represent erythrocytic danger-associated molecular pattern molecules (eDAMPs), which may activate endothelial inflammation through TLR-4 signaling and promote the development of complications, such as acute chest syndrome. It is also suspected that heme may activate the innate immune complement system and stimulate neutrophils to release neutrophil extracellular traps. A large amount of microparticles (MPs) from various cellular origins (platelets, RBCs, white blood cells, endothelial cells) is also released into the plasma of SCD patients and participate in the inflammation and oxidative stress in SCD. In turn, this pro-inflammatory and oxidative stress environment further alters the RBC properties. Increased pro-inflammatory cytokine concentrations promote the activation of RBC NADPH oxidase and, thus, raise the production of intra-erythrocyte ROS. Such enhanced oxidative stress causes deleterious damage to the RBC membrane and further alters the deformability of the cells, modifying their aggregation properties. These RBC rheological alterations have been shown to be associated to specific SCD complications, such as leg ulcers, priapism, and glomerulopathy. Moreover, RBCs positive for the Duffy antigen receptor for chemokines may be very sensitive to various inflammatory molecules that promote RBC dehydration and increase RBC adhesiveness to the vascular wall. In summary, SCD is characterized by a vicious circle between abnormal RBC rheology and inflammation, which modulates the clinical severity of patients.

Redox Signaling in Sickle Cell Disease

Sickle cell disease (SCD) is characterized by chronic hemolysis and repeated episodes of vascular occlusion leading to progressive organ injury. SCD is characterized by unbalanced, simultaneous pro-oxidant and anti-oxidant processes at the molecular, cellular and tissue levels, with the majority of reactions tipped in favor of pro-oxidant pathways. In this brief review we discuss new findings regarding how oxidized hemin, hemolysis, mitochondrial dysfunction and the innate immune system generate oxidative stress while hemopexin, haptoglobin, heme oxygenase-1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) may provide protection in human and murine SCD. We will also describe recent clinical trials showing beneficial effects of antioxidant therapy in SCD.

Sickle Cell Disease: Advances in Treatment

Background

Sickle cell disease causes significant morbidity and mortality and affects the economic and healthcare status of many countries. Yet historically, the disease has not had commensurate outlays of funds that have been aimed at research and development of drugs and treatment procedures for other diseases.

Methods

This review examines several treatment modalities and new drugs developed since the late 1990s that have been used to improve outcomes for patients with sickle cell disease.

Results

Targeted therapies based upon the pathophysiologic mechanisms of sickle cell disease that result in organ dysfunction and painful episodes include hydroxyurea, L-glutamine, crizanlizumab, and other drugs that are currently on the market or are on the verge of becoming available. These agents have the potential to improve survival and quality of life for individuals with sickle cell disease. Also discussed is stem cell transplantation that, to date, is the only curative approach for this disease, as well as the current status of gene therapy.

Conclusion

These examples demonstrate how the current knowledge of sickle cell disease pathophysiology and treatment approaches intersect. Although interest in sickle cell research has blossomed, many more clinical trials need to be initiated and subjected to more strenuous examination and analysis than have been used in the past.