Complement activation in sickle cell disease: Dependence on cell density, hemolysis and modulation by hydroxyurea therapy

Current and emerging drug treatment strategies to tackle sickle cell anemia

INTRODUCTION

Since its discovery in the early 1900s, sickle cell disease (SCD) has contributed significantly to the scientific understanding of hemoglobin and hemoglobinopathies. Despite this, now almost a century later, optimal medical management and even curative options remain limited. Encouragingly, in the last decade, there has been a push toward advancing the care for individuals with SCD and a diversifying interest in options to manage this disorder.

AREAS COVERED

Here, we review the current state of disease modifying therapies for SCD including fetal hemoglobin inducers, monoclonal antibodies, anti-inflammatory modulators, and enzyme activators. We also discuss current curative strategies with specific interest in transformative gene therapies.

EXPERT OPINION

SCD is a chronic, progressive disease that despite a century of clinical description, only now is seeing a growth and advance in therapeutic options to improve the lifespan and quality of life for individuals with SCD. We anticipate newly designed and even repurposed therapies that may work as a single agent or combination agents to tackle the progression of SCD. The vast majority of individuals living with SCD are unlikely to receive gene therapy, therefore improved disease management is critical even for those that may ultimately chose to pursue a potentially curative strategy.

Spontaneous Extradural Hematoma in a Sickle Cell Anemia Patient with Hyperinflammation and Thrombotic Microangiopathy Successfully Treated with Eculizumab: A Case Report and Review of the Literature

BACKGROUND

 The event of extradural hematoma in the absence of head trauma is a rare central nervous system complication of sickle cell disease. We report here a case of spontaneous extradural hematoma in a patient being treated for sickle cell vasoocclusive crisis complicated by hyperinflammation and thrombotic microangiopathy. The significance of inflammation as an integral component of the pathomechanism of vasoocclusive crisis in patients with sickle cell disease and the role of heme in activating the complement system's alternative pathway are highlighted in this case report.

CASE PRESENTATION

 A teenage patient with sickle cell disease developed a spontaneous right parietal extradural hematoma while receiving treatment for sickle cell vasoocclusive crisis. The concurrent events of hyperinflammation, disseminated intravascular coagulation, hyperhemolysis syndrome, thrombotic microangiopathy, and refractory postoperative bleeding complicated this patient's clinical course after surgical evacuation of extradural hematoma. This patient was subsequently treated with eculizumab and improved in the days following.

CONCLUSION

 Treatment with the anti-C5 monoclonal antibody eculizumab, which targets and inhibits terminal complement system activation, reversed the deleterious cascade of events in this patient with sickle cell disease.

Effects of hydroxyurea on fertility in male and female sickle cell disease patients. A systemic review and meta-analysis

BACKGROUND

Evidence supports the benefits of hydroxyurea (HU) in adults with sickle cell disease (SCD), but reservations remain due to long-term concerns of fertility. Retrospective analysis of clinical records of SCD patients (haemoglobin SS genotype) have identified gender-related differences in disease progression. This could inform risk stratification during SCD at diagnosis with the possibility to guide therapeutic decisions.

METHODS

This systemic review and meta-analysis evaluated fertility parameters in both children (aged ≥ 6 years) and adults with SCD receiving HU therapy. Studies were sourced from PubMed and EMBASE from inception to July 2023. A total of 160 potentially relevant articles were identified.

RESULTS

Four studies were included that evaluated the effects of HU on sperm parameters in males. A further 4 studies assessed anti-mullerian hormone (AMH) levels and ovarian reserves in females. Differences from baseline values were used to identify compromised fertility. Amongst males, HU treatment negatively impacted the concentration of spermatozoa (MD = -15.48 million/mL; 95% CI: [-20.69, -10.26]; p< 0.001), which continued following treatment cessation (MD = -20.09 million/mL; 95% CI: [-38.78, -1.40]; P = 0.04). HU treatment also led to lower total sperm counts (MD = -105.87 million; 95% CI: [-140.61, -71.13]; P< 0.001) which persisted after treatment (MD = -53.05 million; 95% CI: [-104.96, -1.14]; P = 0.05). Sperm volume, initial forward motility and morphology were unaffected by HU treatment. In females, HU treatment decreased the mean AMH levels 1.83 (95% CI [1.42, 2.56]. A total of 18.2.% patients treated with HU showed reduced ovarian reserves.

INTERPRETATION & CONCLUSIONS

This systemic review and meta-analysis suggest that the use of HU for SCD impacts seminal fluid parameters in males and can diminish AMH levels and ovarian reserves in females.

Neutrophils in sickle cell disease: Exploring their potential role as a therapeutic target

Factors influencing the activation of neutrophils in SCD and the potential neutrophil-mediated ameliorating effects of therapies in SCD.

Multiomics Signatures of Coagulopathy in a Polytrauma Swine Model Contrasted with Severe Multisystem Injured Patients

Trauma-induced coagulopathy (TIC) is a leading contributor to preventable mortality in severely injured patients. Understanding the molecular drivers of TIC is an essential step in identifying novel therapeutics to reduce morbidity and mortality. This study investigated multiomics and viscoelastic responses to polytrauma using our novel swine model and compared these findings with severely injured patients. Molecular signatures of TIC were significantly associated with perturbed coagulation and inflammation systems as well as extensive hemolysis. These results were consistent with patterns observed in trauma patients who had multisystem injuries. Here, intervention using resuscitative endovascular balloon occlusion of the aorta following polytrauma in our swine model revealed distinct multiomics alterations as a function of placement location. Aortic balloon placement in zone-1 worsened ischemic damage and mitochondrial dysfunction, patterns that continued throughout the monitored time course. While placement in zone-III showed a beneficial effect on TIC, it showed an improvement in effective coagulation. Taken together, this study highlights the translational relevance of our polytrauma swine model for investigating therapeutic interventions to correct TIC in patients.

How I treat sickle cell disease in pregnancy

ABSTRACT

Fifty years ago, people with sickle cell disease (SCD) were discouraged from becoming pregnant, but now, most should be supported if they choose to pursue a pregnancy. They and their providers, however, should be aware of the physiological changes of pregnancy that aggravate SCD and pregnancy's unique maternal and fetal challenges. Maternal problems can arise from chronic underlying organ dysfunction such as renal disease or pulmonary hypertension; from acute complications of SCD such as acute anemia, vaso-occlusive crises, and acute chest syndrome; and/or from pregnancy-related complications such as preeclampsia, sepsis, severe anemia, thromboembolism, and the need for cesarean delivery. Fetal problems include alloimmunization, opioid exposure, fetal growth restriction, preterm delivery, and stillbirth. Before and during pregnancy, in addition to the assessment and care that every pregnant patient should receive, patients with SCD should be evaluated and treated by a multidisciplinary team with respect to their unique maternal and fetal issues.

High-throughput complement component 4 genomic sequence analysis with C4Investigator

The complement component 4 gene loci, composed of the C4A and C4B genes and located on chromosome 6, encodes for complement component 4 (C4) proteins, a key intermediate in the classical and lectin pathways of the complement system. The complement system is an important modulator of immune system activity and is also involved in the clearance of immune complexes and cellular debris. C4A and C4B gene loci exhibit copy number variation, with each composite gene varying between 0 and 5 copies per haplotype. C4A and C4B genes also vary in size depending on the presence of the human endogenous retrovirus (HERV) in intron 9, denoted by C4(L) for long-form and C4(S) for short-form, which affects expression and is found in both C4A and C4B. Additionally, human blood group antigens Rodgers and Chido are located on the C4 protein, with the Rodger epitope generally found on C4A protein, and the Chido epitope generally found on C4B protein. C4A and C4B copy number variation has been implicated in numerous autoimmune and pathogenic diseases. Despite the central role of C4 in immune function and regulation, high-throughput genomic sequence analysis of C4A and C4B variants has been impeded by the high degree of sequence similarity and complex genetic variation exhibited by these genes. To investigate C4 variation using genomic sequencing data, we have developed a novel bioinformatic pipeline for comprehensive, high-throughput characterization of human C4A and C4B sequences from short-read sequencing data, named C4Investigator. Using paired-end targeted or whole genome sequence data as input, C4Investigator determines the overall gene copy numbers, as well as C4A, C4B, C4(Rodger), C4(Ch), C4(L), and C4(S). Additionally, C4Ivestigator reports the full overall C4A and C4B aligned sequence, enabling nucleotide level analysis. To demonstrate the utility of this workflow we have analyzed C4A and C4B variation in the 1000 Genomes Project Data set, showing that these genes are highly poly-allelic with many variants that have the potential to impact C4 protein function.

Complement involvement in sickle cell disease

Sickle Cell Disease (SCD) is a hereditary blood disorder characterized by the presence of abnormal hemoglobin, leading to the formation of sickle-shaped red blood cells, causing vaso-occlusion. Inflammation is a key component of the pathophysiology of SCD, contributing to the vascular complications and tissue damage. This review is centered on exploring the role of the inflammatory complement system in the pathophysiology of SCD. Our goal is to offer a comprehensive summary of the existing evidence regarding complement activation in patients with SCD, encompassing both steady-state conditions and episodes of vaso-occlusive events. Additionally, we will discuss the proposed mechanisms by which the complement system may contribute to tissue injury in this pathology. Finally, we will provide an overview of the available evidence concerning the effectiveness of therapeutic interventions aimed at blocking the complement system in the context of SCD and discuss the perspective of complement inhibition.

Cold exposure induces vaso-occlusion and pain in sickle mice that depend on complement activation

Vaso-occlusive pain episodes (VOE) cause severe pain in patients with sickle cell disease (SCD). Vaso-occlusive events promote ischemia/reperfusion pathobiology that activates complement. We hypothesized that complement activation is linked to VOE. We used cold to induce VOE in the Townes sickle homozygous for hemoglobin S (HbSS) mouse model and complement inhibitors to determine whether anaphylatoxin C5a mediates VOE. We used a dorsal skinfold chamber to measure microvascular stasis (vaso-occlusion) and von Frey filaments applied to the plantar surface of the hind paw to assess mechanical hyperalgesia in HbSS and control Townes mice homozygous for hemoglobin A (HbAA) mice after cold exposure at 10°C/50°F for 1 hour. Cold exposure induced more vaso-occlusion in nonhyperalgesic HbSS mice (33%) than in HbAA mice (11%) or HbSS mice left at room temperature (1%). Cold exposure also produced mechanical hyperalgesia as measured by paw withdrawal threshold in HbSS mice compared with that in HbAA mice or HbSS mice left at room temperature. Vaso-occlusion and hyperalgesia were associated with an increase in complement activation fragments Bb and C5a in plasma of HbSS mice after cold exposure. This was accompanied by an increase in proinflammatory NF-κB activation and VCAM-1 and ICAM-1 expression in the liver. Pretreatment of nonhyperalgesic HbSS mice before cold exposure with anti-C5 or anti-C5aR monoclonal antibodies (mAbs) decreased vaso-occlusion, mechanical hyperalgesia, complement activation, and liver inflammatory markers compared with pretreatment with control mAb. Anti-C5 or -C5aR mAb infusion also abrogated mechanical hyperalgesia in HbSS mice with ongoing hyperalgesia at baseline. These findings suggest that C5a promotes vaso-occlusion, pain, and inflammation during VOE and may play a role in chronic pain.

Hypercoagulability in Sickle Cell Disease: A Thrombo-Inflammatory Mechanism

Sickle cell disease (SCD) is a group of inherited disorders characterized by the presence of abnormal hemoglobin S. Patients with SCD suffer from frequent episodes of anemia, chronic hemolysis, pain crisis, and vaso-occlusion. Additionally, SCD is associated with diverse and serious clinical complications, including thrombosis, which can lead to organ failure, increased morbidity, and eventually, mortality. SCD is known to be a hypercoagulable condition, and the cause of hypercoagulability is multifactorial, with the molecular basis of hemoglobin S being the main driver. The presence of hemoglobin S induces sickling of the RBCs and their subsequent hemolysis, as well as oxidative stress. Both of these processes can alter the hemostatic system, through the activation of platelets, coagulation system, and fibrinolysis, as well as depletion of coagulation inhibitors. These changes can also induce the formation of microvesicles and expression of tissue factor, leading to activation of WBCs, endothelial cell damage, and inflammatory response. Understanding the various factors that drive hypercoagulability as a thrombo-inflammatory mechanism in SCD can help provide explanations for the pathogenesis and other complications of the disease.

Exploration de l’hémolyse associée à la drépanocytose et perspectives thérapeutiques spécifiques

Sickle Cell Anemia is a disease with a strong vascular tropism. Beyond anemia, the pathophysiological mechanisms responsible for hemolysis, directly affect both acute and chronic vascular damages, thus resulting in a systemic disease. Understanding the different types of hemolysis underline the need for novel specific biomarkers. Targeted therapeutic approaches for these pathophysiological pathways are necessary to improve Sickle Cell patients' prognosis. Finally, given its complexity, Sickle Cell Disease is often used as a "proof of concept" for other pathologies. It seems likely that the rapidly evolving knowledge in this field will also benefit other diseases. © 2023 Société nationale française de médecine interne (SNFMI). Published by Elsevier Masson SAS. All rights reserved.

Hemolysis is associated with altered heparan sulfate of the endothelial glycocalyx and with local complement activation in thrombotic microangiopathies

The complement system plays a key role in the pathophysiology of kidney thrombotic microangiopathies (TMA), as illustrated by atypical hemolytic uremic syndrome. But complement abnormalities are not the only drivers of TMA lesions. Among other potential pathophysiological actors, we hypothesized that alteration of heparan sulfate (HS) in the endothelial glycocalyx could be important. To evaluate this, we analyzed clinical and histological features of kidney biopsies from a monocentric, retrospective cohort of 72 patients with TMA, particularly for HS integrity and markers of local complement activation. The role of heme (a major product of hemolysis) as an HS-degrading agent in vitro, and the impact of altering endothelial cell (ECs) HS on their ability to locally activate complement were studied. Compared with a positive control, glomerular HS staining was lower in 57 (79%) patients with TMA, moderately reduced in 20 (28%), and strongly reduced in 37 (51%) of these 57 cases. Strongly reduced HS density was significantly associated with both hemolysis at the time of biopsy and local complement activation (C3 and/or C5b-9 deposits). Using primary endothelial cells (HUVECs, Glomerular ECs), we observed decreased HS expression after short-term exposure to heme, and that artificial HS degradation by exposure to heparinase was associated with local complement activation. Further, prolonged exposure to heme modulated expression of several key genes of glycocalyx metabolism involved in coagulation regulation (C5-EPI, HS6ST1, HS3ST1). Thus, our study highlights the impact of hemolysis on the integrity of endothelial HS, both in patients and in endothelial cell models. Hence, acute alteration of HS may be a mechanism of heme-induced complement activation.

Molecular and cellular effects of in vivo chronic intravascular hemolysis and anti-inflammatory therapeutic approaches

Intravascular hemolysis (IVH) occurs in numerous inherited and acquired disorders, including sickle cell disease (SCD), malaria and sepsis. These diseases display unique symptoms, but often share complications, such as vasomotor dysfunction and pulmonary hypertension. Consequently, in vivo models are needed to study the effects of continuous intravascular hemolytic processes, independently of the molecular or extrinsic alteration that leads to erythrocyte destruction. We gave twice-weekly low-dose phenylhydrazine (LDPHZ) to C57BL/6 J mice for 4 weeks, and measured parameters indicative of anemia, hemoglobin-clearance pathways, inflammation and iron turnover, comparing these to those of a murine model of SCD, which displays associated IVH. LDPHZ administration provoked discreet anemia in mice and significant reticulocytosis, in association with hemoglobin/heme-clearance pathway protein depletion. Mice subjected to chronic hemolysis displayed elevated leukocyte counts and plasma levels of interleukin (IL)-1β, TNF-α, IL-6, soluble ICAM-1, endothelin-1 and anti-inflammatory IL-10, closely emulating alterations indicative of systemic inflammatory and endothelial activation in SCD, and confirming chronic IVH in itself as a serious complication. Discreet accelerations in hepatic and splenic iron turnover also occurred in LDPHZ mice, without alterations in liver damage markers. Examining the effects of two therapies on hemolysis-induced inflammation, the administration of hydroxyurea (and to a lesser extent, l-glutamine) significantly abrogated hemolytic inflammation in mice, without apparent inhibition of hemolysis. In conclusion, the isolation of chronic IVH, a common disease mechanism, using this model, may allow the study of hemolysis-specific sequelae at the cellular and systemic level, and the investigation of candidate agents that could potentially counter hemolytic inflammation.

Clinical Complications and Their Management

The diversity of disease-related complications among patients with β-thalassemia is complicated by the wide spectrum of genotypes and clinical risk factors. The authors herein present the different complications seen in patients with β-thalassemia, the pathophysiology underlying these complications and their management.

Thrombo-Inflammation in COVID-19 and Sickle Cell Disease: Two Faces of the Same Coin

People with sickle cell disease (SCD) are at greater risk of severe illness and death from respiratory infections, including COVID-19, than people without SCD (Centers for Disease Control and Prevention, USA). Vaso-occlusive crises (VOC) in SCD and severe SARS-CoV-2 infection are both characterized by thrombo-inflammation mediated by endothelial injury, complement activation, inflammatory lipid storm, platelet activation, platelet-leukocyte adhesion, and activation of the coagulation cascade. Notably, lipid mediators, including thromboxane A2, significantly increase in severe COVID-19 and SCD. In addition, the release of thromboxane A2 from endothelial cells and macrophages stimulates platelets to release microvesicles, which are harbingers of multicellular adhesion and thrombo-inflammation. Currently, there are limited therapeutic strategies targeting platelet-neutrophil activation and thrombo-inflammation in either SCD or COVID-19 during acute crisis. However, due to many similarities between the pathobiology of thrombo-inflammation in SCD and COVID-19, therapies targeting one disease may likely be effective in the other. Therefore, the preclinical and clinical research spurred by the COVID-19 pandemic, including clinical trials of anti-thrombotic agents, are potentially applicable to VOC. Here, we first outline the parallels between SCD and COVID-19; second, review the role of lipid mediators in the pathogenesis of these diseases; and lastly, examine the therapeutic targets and potential treatments for the two diseases.

C3-dependent effector functions of complement

C3 is the central effector molecule of the complement system, mediating its multiple functions through different binding sites and their corresponding receptors. We will introduce the C3 forms (native C3, C3 [H₂ O], and intracellular C3), the C3 fragments C3a, C3b, iC3b, and C3dg/C3d, and the C3 expression sites. To highlight the important role that C3 plays in human biological processes, we will give an overview of the diseases linked to C3 deficiency and to uncontrolled C3 activation. Next, we will present a structural description of C3 activation and of the C3 fragments generated by complement regulation. We will proceed by describing the C3a interaction with the anaphylatoxin receptor, followed by the interactions of opsonins (C3b, iC3b, and C3dg/C3d) with complement receptors, divided into two groups: receptors bearing complement regulatory functions and the effector receptors without complement regulatory activity. We outline the molecular architecture of the receptors, their binding sites on the C3 activation fragments, the cells expressing them, the diversity of their functions, and recent advances. With this review, we aim to give an up-to-date analysis of the processes triggered by C3 activation fragments on different cell types in health and disease contexts.

Extracellular Vesicle Size Reveals Cargo Specific to Coagulation and Inflammation in Pediatric and Adult Sickle Cell Disease

Aberrant coagulation in sickle cell disease (SCD) is linked to extracellular vesicle (EV) exposure. However, there is no consensus on the contributions of small EVs (SEVs) and large EVs (LEVs) toward underlying coagulopathy or on their molecular cargo. The present observational study compared the thrombin potential of SEVs and LEVs isolated from the plasma of stable pediatric and adult SCD patients. Further, EV lipid and protein contents were analyzed to define markers consistent with activation of thrombin and markers of underlying coagulopathy. Results suggested that LEVs-but not SEVs-from pediatrics and adults similarly enhanced phosphatidylserine (PS)-dependent thrombin generation, and cell membrane procoagulant PS (18:0;20:4 and 18:0;18:1) were the most abundant lipids found in LEVs. Further, LEVs showed activated coagulation in protein pathway analyses, while SEVs demonstrated high levels of cholesterol esters and a protein pathway analysis that identified complement factors and inflammation. We suggest that thrombin potential of EVs from both stable pediatric and adult SCD patients is similarly dependent on size and show lipid and protein contents that identify underlying markers of coagulation and inflammation.

Development of curative therapies for sickle cell disease

Recent advances in managing Sickle Cell Disease (SCD) significantly improved patient survival and quality of life. Disease-modifying drug therapies such as hydroxyurea, L-glutamine, voxelotor, and crizanlizumab reduce pain crises and severe complications. Allogeneic hematopoietic stem cell transplantation using matched-sibling donors is currently the only standard curative option; however, only a small proportion of patients have such donors. Cord blood and haploidentical transplantation with a modified conditioning regimen have expanded the allogeneic donor pool, making the therapy available to more patients. Gene therapy is a promising cure that is currently undergoing clinical trials and different approaches have demonstrated efficacy. Multidisciplinary expertise is needed in developing the best treatment strategy for patients with SCD.

MASP-2 and MASP-3 inhibitors block complement activation, inflammation, and microvascular stasis in a murine model of vaso-occlusion in sickle cell disease

Patients with sickle cell disease (SCD) have ongoing hemolysis that promotes endothelial injury, complement activation, inflammation, vaso-occlusion, ischemia-reperfusion pathophysiology, and pain. Complement activation markers are increased in SCD in steady-state and further increased during vaso-occlusive crisis (VOC). However, the mechanisms driving complement activation in SCD have not been completely elucidated. Ischemia-reperfusion and heme released from hemoglobin during hemolysis, events that characterize SCD pathophysiology, can activate the lectin pathway (LP) and alternative pathway (AP), respectively. Here we evaluated the role of LP and AP in Townes sickle (SS) mice using inhibitory monoclonal antibodies (mAb) to mannose binding lectin (MBL)-associated serine protease (MASP)-2 or MASP-3, respectively. Townes SS mice were pretreated with MASP-2 mAb, MASP-3 mAb, isotype control mAb, or PBS before they were challenged with hypoxia-reoxygenation or hemoglobin. Pretreatment of SS mice with MASP-2 or MASP-3 mAb, markedly reduced Bb fragments, C4d and C5a in plasma and complement deposition in the liver, kidneys, and lungs collected 4 hours after challenge compared to control mAb-treated mice. Consistent with complement inhibition, hepatic inflammation markers NF-ĸB phospho-p65, VCAM-1, ICAM-1, and E-selectin were significantly reduced in SS mice pretreated with MASP-2 or MASP-3 mAb. Importantly, MASP-2 or MASP-3 mAb pretreatment significantly inhibited microvascular stasis (vaso-occlusion) induced by hypoxia-reoxygenation or hemoglobin. These studies suggest that the LP and the AP are both playing a role in promoting inflammation and vaso-occlusion in SCD. Inhibiting complement activation via the LP or the AP might inhibit inflammation and prevent VOC in SCD patients.

Exploring the Complex Network of Heme-Triggered Effects on the Blood Coagulation System

Excess labile heme, occurring under hemolytic conditions, displays a versatile modulator in the blood coagulation system. As such, heme provokes prothrombotic states, either by binding to plasma proteins or through interaction with participating cell types. However, despite several independent reports on these effects, apparently contradictory observations and significant knowledge gaps characterize this relationship, which hampers a complete understanding of heme-driven coagulopathies and the development of suitable and specific treatment options. Thus, the computational exploration of the complex network of heme-triggered effects in the blood coagulation system is presented herein. Combining hemostasis- and heme-specific terminology, the knowledge available thus far was curated and modeled in a mechanistic interactome. Further, these data were incorporated in the earlier established heme knowledge graph, "HemeKG", to better comprehend the knowledge surrounding heme biology. Finally, a pathway enrichment analysis of these data provided deep insights into so far unknown links and novel experimental targets within the blood coagulation cascade and platelet activation pathways for further investigation of the prothrombotic nature of heme. In summary, this study allows, for the first time, a detailed network analysis of the effects of heme in the blood coagulation system.

Comparing the Safety and Efficacy of L-Glutamine, Voxelotor, and Crizanlizumab for Reducing the Frequency of Vaso-Occlusive Crisis in Sickle Cell Disease: A Systematic Review

Sickle cell disease (SCD) is a group of inherited red blood cell disorders affecting millions worldwide. The median life expectancy of someone with SCD remains significantly low despite improvements in standards of care and the implementation of hydroxyurea therapy. Notably, a 20-year interval existed (after the implementation of hydroxyurea therapy) prior to the approval of other sickle cell medications, namely, l-glutamine, voxelotor, and crizanlizumab. In this systematic review, these new medications' impact on the occurrences of vaso-occlusive crisis (VOC) events were analyzed and the adverse events of each were noted. Further, a secondary analysis was conducted to determine the effect of combination therapies, whether synergistic, antagonistic, or additive. The systematic review was conducted following the PRISMA 2020 guidelines. The effect-based and dose-effect-based approaches were utilized to determine the combined drugs combination index based on the recommended dosage to achieve an efficacy of 50%. L-glutamine and crizanlizumab were effective in reducing the frequency of VOC (p= 0.0216 and p = 0.02). Voxelotor effect on the reduction of VOC occurrences was not significant, however, its effect on increasing hemoglobin levels was significant (p= <0.001). In all three therapies, pain was the most common adverse event reported by participants. The analysis of combination therapies revealed that voxelotor plus l-glutamine was synergistic, voxelotor plus crizanlizumab was antagonistic, and l-glutamine plus crizanlizumab was additive. Thus, voxelotor plus l-glutamine combination therapy may be more beneficial to sickle cell disease patients. As such, robust combination drug studies for approved therapies used in SCD should be initiated with a specific focus on voxelotor plus l-glutamine. Additionally, the development of medications that lessen the pain burden in sickle cell disease patients should also be prioritized.

Ex Vivo Test for Measuring Complement Attack on Endothelial Cells: From Research to Bedside

As part of the innate immune system, the complement system plays a key role in defense against pathogens and in host cell homeostasis. This enzymatic cascade is rapidly triggered in the presence of activating surfaces. Physiologically, it is tightly regulated on host cells to avoid uncontrolled activation and self-damage. In cases of abnormal complement dysregulation/overactivation, the endothelium is one of the primary targets. Complement has gained momentum as a research interest in the last decade because its dysregulation has been implicated in the pathophysiology of many human diseases. Thus, it appears to be a promising candidate for therapeutic intervention. However, detecting abnormal complement activation is challenging. In many pathological conditions, complement activation occurs locally in tissues. Standard routine exploration of the plasma concentration of the complement components shows values in the normal range. The available tests to demonstrate such dysregulation with diagnostic, prognostic, and therapeutic implications are limited. There is a real need to develop tools to demonstrate the implications of complement in diseases and to explore the complex interplay between complement activation and regulation on human cells. The analysis of complement deposits on cultured endothelial cells incubated with pathologic human serum holds promise as a reference assay. This ex vivo assay most closely resembles the physiological context. It has been used to explore complement activation from sera of patients with atypical hemolytic uremic syndrome, malignant hypertension, elevated liver enzymes low platelet syndrome, sickle cell disease, pre-eclampsia, and others. In some cases, it is used to adjust the therapeutic regimen with a complement-blocking drug. Nevertheless, an international standard is lacking, and the mechanism by which complement is activated in this assay is not fully understood. Moreover, primary cell culture remains difficult to perform, which probably explains why no standardized or commercialized assay has been proposed. Here, we review the diseases for which endothelial assays have been applied. We also compare this test with others currently available to explore complement overactivation. Finally, we discuss the unanswered questions and challenges to overcome for validating the assays as a tool in routine clinical practice.

Protective potential of royal jelly against hydroxyurea -induced hepatic injury in rats via antioxidant, anti-inflammatory, and anti-apoptosis properties

Hydroxyurea (HDU) is a widely used medication for various malignancies, thalassemia, and sickle cell anemia with reported side effects. The current study investigated HDU- induced hepatic injury and the protective potential of the royal jelly (RJ) against this hepatotoxic effect in the light of hepatic oxidative/ antioxidative status, pro-inflammatory cytokine, apoptosis signaling pathway, and histopathology. Sixty albino rats were used (n = 10/group) for 60 days: control, RJ (100 mg/kg body weight, orally), HDU (225 mg/kg body weight, orally), 2HDU (450 mg/kg body weight, orally), and HDU + RJ groups. HDU-treated rats showed significant elevation of liver function tests as aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase, as well as malondialdehyde and nitric oxide (oxidative biomarkers) and significant decreased hepatic antioxidant molecules (reduced glutathione, superoxide dismutase, and glutathione peroxidase), compared to a control group, that more pronounced in the high dose of HDU. In addition, HDU induced significant upregulation of TNF-α and the Caspase-3 apoptotic pathway. Moreover, the liver of HDU treated groups showed various hepatic lesions from mild to severe necrotic changes related to the HDU dose. However, administration of RJ with HDU improved liver function tests, liver histology, and hepatic oxidative/antioxidative status concerning HDU groups. Furthermore, oral RJ administration with HDU significantly lessens the immune-expression area % of TNF-α and Caspase-3. Thus, the royal jelly has antioxidant, anti-inflammatory, and anti-apoptotic properties against HDU- induced hepatic injury and could be, therefore, used as adjuvant therapy in patients with long-term HDU medication.

Autoimmune disease and sickle cell anaemia: 'Intersecting pathways and differential diagnosis'

Sickle cell disease (SCD) is an inherited disorder, which occurs due to a single gene mutation. It has multisystemic manifestations, affecting millions of people worldwide. The effect of SCD on joints and musculature can overlap with clinical features of autoimmune disease (AD). It is therefore difficult for clinical haematologists and physicians treating SCD patients to discriminate between these two conditions clinically. A delay in diagnosis leads to untreated symptoms and treatment differs considerably. An accurate knowledge of clinical findings and laboratory results of AD and SCD can help physicians avoid this. In the review that follows, we examine the existing literature on SCD and AD, and describe the features that may distinguish SCD and autoimmune disease such as systemic lupus erythematosus and rheumatoid arthritis. We aim to guide clinical haematologists and physicians towards a more rapid diagnosis of AD in sickle cell anaemia patients, by correct interpretation of the clinical assessment and commonly available diagnostics.

Immune Response of Adult Sickle Cell Disease Patients after COVID-19 Vaccination: The Experience of a Greek Center

Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential weapons to control the spread of the coronavirus disease-19 (COVID-19) pandemic and protect immunocompromised patients. With a greater susceptibility to infection, sickle cell disease (SCD) patients are considered as “high risk” patients during the current COVID-19 pandemic. In our study, we try to determine the immune response of adult SCD patients monitored at our center after the first and second dose of the qualified mRNA vaccines available and correlate them to several disease-specific markers, as well as complement activation. The results demonstrate that the levels of neutralizing antibodies (nAbs) against SARS-CoV-2 were adequate for most patients studied after the second dose and there seemed to be a certain association with complement activation. Further studies are critical to determine the durability of this immune response and the potential benefit of a third dose.

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.

Autoimmune Hemolytic Anemia as a Complication of Congenital Anemias. A Case Series and Review of the Literature

Congenital anemias may be complicated by immune-mediated hemolytic crisis. Alloantibodies are usually seen in chronically transfused patients, and autoantibodies have also been described, although they are rarely associated with overt autoimmune hemolytic anemia (AIHA), a serious and potentially life-threatening complication. Given the lack of data on the AIHA diagnosis and management in congenital anemias, we retrospectively evaluated all clinically relevant AIHA cases occurring at a referral center for AIHA, hemoglobinopathies, and chronic hemolytic anemias, focusing on clinical management and outcome. In our cohort, AIHA had a prevalence of 1% (14/1410 patients). The majority were warm AIHA. Possible triggers were recent transfusion, infection, pregnancy, and surgery. All the patients received steroid therapy as the first line, and about 25% required further treatment, including rituximab, azathioprine, intravenous immunoglobulins, and cyclophosphamide. Transfusion support was required in 57% of the patients with non-transfusion-dependent anemia, and recombinant human erythropoietin was safely administered in one third of the patients. AIHA in congenital anemias may be challenging both from a diagnostic and a therapeutic point of view. A proper evaluation of hemolytic markers, bone marrow compensation, and assessment of the direct antiglobulin test is mandatory.

The Benefits of Complement Measurements for the Clinical Practice

The complement cascade is an evolutionary ancient innate immune defense system, playing a major role in the defense against infections. Its function in maintaining host homeostasis on activated cells has been emphasized by the crucial role of its overactivation in ever growing number of diseases, such as atypical hemolytic uremic syndrome (aHUS), autoimmune diseases as systemic lupus erythematosus (SLE), C3 glomerulopathies (C3GN), age-related macular degeneration (AMD), graft rejection, Alzheimer disease, and cancer, to name just a few. The last decade of research on complement has extended its implication in many pathological processes, offering new insights to potential therapeutic targets and asserting the necessity of reliable, sensitive, specific, accurate, and reproducible biomarkers to decipher complement role in pathology. We need to evaluate accurately which pathway or role should be targeted pharmacologically, and optimize treatment efficacy versus toxicity. This chapter is an introduction to the role of complement in human diseases and the use of complement-related biomarkers in the clinical practice. It is a part of a book intending to give reliable and standardized methods to evaluate complement according to nowadays needs and knowledge.

Critical Role of Hemopexin Mediated Cytoprotection in the Pathophysiology of Sickle Cell Disease

Circulating hemopexin is the primary protein responsible for the clearance of heme; therefore, it is a systemic combatant against deleterious inflammation and oxidative stress induced by the presence of free heme. This role of hemopexin is critical in hemolytic pathophysiology. In this review, we outline the current research regarding how the dynamic activity of hemopexin is implicated in sickle cell disease, which is characterized by a pathological aggregation of red blood cells and excessive hemolysis. This pathophysiology leads to symptoms such as acute kidney injury, vaso-occlusion, ischemic stroke, pain crises, and pulmonary hypertension exacerbated by the presence of free heme and hemoglobin. This review includes in vivo studies in mouse, rat, and guinea pig models of sickle cell disease, as well as studies in human samples. In summary, the current research indicates that hemopexin is likely protective against these symptoms and that rectifying depleted hemopexin in patients with sickle cell disease could improve or prevent the symptoms. The data compiled in this review suggest that further preclinical and clinical research should be conducted to uncover pathways of hemopexin in pathological states to evaluate its potential clinical function as both a biomarker and therapy for sickle cell disease and related hemoglobinopathies.

Factor D Inhibition Blocks Complement Activation Induced by Mutant Factor B Associated With Atypical Hemolytic Uremic Syndrome and Membranoproliferative Glomerulonephritis

Complement factor B (FB) mutant variants are associated with excessive complement activation in kidney diseases such as atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy and membranoproliferative glomerulonephritis (MPGN). Patients with aHUS are currently treated with eculizumab while there is no specific treatment for other complement-mediated renal diseases. In this study the phenotype of three FB missense variants, detected in patients with aHUS (D371G and E601K) and MPGN (I242L), was investigated. Patient sera with the D371G and I242L mutations induced hemolysis of sheep erythrocytes. Mutagenesis was performed to study the effect of factor D (FD) inhibition on C3 convertase-induced FB cleavage, complement-mediated hemolysis, and the release of soluble C5b-9 from glomerular endothelial cells. The FD inhibitor danicopan abrogated C3 convertase-associated FB cleavage to the Bb fragment in patient serum, and of the FB constructs, D371G, E601K, I242L, the gain-of-function mutation D279G, and the wild-type construct, in FB-depleted serum. Furthermore, the FD-inhibitor blocked hemolysis induced by the D371G and D279G gain-of-function mutants. In FB-depleted serum the D371G and D279G mutants induced release of C5b-9 from glomerular endothelial cells that was reduced by the FD-inhibitor. These results suggest that FD inhibition can effectively block complement overactivation induced by FB gain-of-function mutations.

Complement in Sickle Cell Disease: Are We Ready for Prime Time?

Sickle cell disease (SCD) is a widely spread inherited hemoglobinopathy that includes a group of congenital hemolytic anemias, all characterized by the predominance of sickle hemoglobin (HbS). Its features are anemia, predisposal to bacterial infections and complications such as vaso-occlusive crisis (VOC) or delayed hemolytic transfusion reaction (DHTR), which lead to increased rate of morbidity and mortality even in the era of hydroxyurea. The interaction between sickle cells, neutrophils, platelets or endothelial cells in small vessels results in hemolysis and has been considered the disease’s main pathophysiological mechanism. Complement activation has been reported in small cohorts of SCD patients, but the governing mechanism has not been fully elucidated. This will be important to predict the patient group that would benefit from complement inhibition. Until now, eculizumab-mediated complement inhibition has shown beneficial effects in DHTR, with limited reports in patients with VOC. In the meantime, several innovative agents are under clinical development Our state-of-the-art review summarizes current data on 1) complement activation in SCD both in steady state and crisis, 2) underlying mechanisms of complement over-activation for the clinician in the context of SCD, 3) actions of hydroxyurea and new therapeutic approaches including indirect involvement in complement activation, and 4) novel paradigms in complement inhibition.

Ex Vivo Complement Activation on Endothelial Cells: Research and Translational Value

The spectrum of human diseases with complement contribution is ever increasing. Tools to study the complement contribution and the potential interest of novel complement inhibitors in clinical practice are lacking. Here we discuss a functional ex vivo assay to monitor complement activation on endothelial cells, which can answer to this need.

Revisiting the interaction of heme with hemopexin

In hemolytic disorders, erythrocyte lysis results in massive release of hemoglobin and, subsequently, toxic heme. Hemopexin is the major protective factor against heme toxicity in human blood and currently considered for therapeutic use. It has been widely accepted that hemopexin binds heme with extraordinarily high affinity of <1 pM in a 1:1 ratio. However, several lines of evidence point to a higher stoichiometry and lower affinity than determined 50 years ago. Here, we re-analyzed these data. SPR and UV/Vis spectroscopy were used to monitor the interaction of heme with the human protein. The heme-binding sites of hemopexin were characterized using hemopexin-derived peptide models and competitive displacement assays. We obtained a K _D value of 0.32 ± 0.04 nM and the ratio for the interaction was determined to be 1:1 at low heme concentrations and at least 2:1 (heme:hemopexin) at high concentrations. We were able to identify two yet unknown potential heme-binding sites on hemopexin. Furthermore, molecular modelling with a newly created homology model of human hemopexin suggested a possible recruiting mechanism by which heme could consecutively bind several histidine residues on its way into the binding pocket. Our findings have direct implications for the potential administration of hemopexin in hemolytic disorders.

Sickle Cell Disease: Role of Oxidative Stress and Antioxidant Therapy

Sickle cell disease (SCD) is the most common hereditary disorder of hemoglobin (Hb), which affects approximately a million people worldwide. It is characterized by a single nucleotide substitution in the β-globin gene, leading to the production of abnormal sickle hemoglobin (HbS) with multi-system consequences. HbS polymerization is the primary event in SCD. Repeated polymerization and depolymerization of Hb causes oxidative stress that plays a key role in the pathophysiology of hemolysis, vessel occlusion and the following organ damage in sickle cell patients. For this reason, reactive oxidizing species and the (end)-products of their oxidative reactions have been proposed as markers of both tissue pro-oxidant status and disease severity. Although more studies are needed to clarify their role, antioxidant agents have been shown to be effective in reducing pathological consequences of the disease by preventing oxidative damage in SCD, i.e., by decreasing the oxidant formation or repairing the induced damage. An improved understanding of oxidative stress will lead to targeted antioxidant therapies that should prevent or delay the development of organ complications in this patient population.

Complement in sickle cell disease and targeted therapy: I know one thing, that I know nothing

Sickle cell disease (SCD) is a common inherited clinical syndrome, characterized by the presence of hemoglobin S. Anemia, susceptibility to infections and episodes of vaso-occlusive crisis (VOC) are among its features. Since SCD complications (VOC or delayed hemolytic transfusion reaction/DHTR) lead to significant morbidity and mortality, a number of studies have addressed their pathophysiology Although SCD pathophysiology has been mainly attributed to the interaction between sickle cells and neutrophils, platelets or endothelial cells in small vessels leading to hemolysis, the role of complement activation has been increasingly investigated. Importantly, complement inhibition with eculizumab has shown beneficial effects in DHTR. Given the unmet clinical need of novel therapeutics in SCD, our review summarizes current understanding of (a) complement system for the clinician, (b) complement activation in SCD both in asymptomatic state and severe clinical manifestations, (c) probable underlying mechanisms of complement activation in SCD, and (d) new therapeutic perspective of complement inhibition.

Complement C3 Deposition on Endothelial Cells Revealed by Flow Cytometry

The three pathways of the complement system converge toward the cleavage of the central complement component C3 into its activated fragments, with C3b being able to bind covalently to the activating surface. The endothelial cells are among the major targets for complement attack in pathological conditions, as the atypical hemolytic uremic syndrome. Therefore, study of complement C3 deposition on endothelial cells by flow cytometry is a sensitive test to measure complement activation. This test can be used as a research or clinical tool to test complement activation induced by patients' sera or to test the functional consequences of newly discovered complement mutations as well as different triggers of endothelial cells injury.

Therapeutic Lessons to be Learned From the Role of Complement Regulators as Double-Edged Sword in Health and Disease

The complement system is an important part of the innate immune system, providing a strong defense against pathogens and removing apoptotic cells and immune complexes. Due to its strength, it is important that healthy human cells are protected against damage induced by the complement system. To be protected from complement, each cell type relies on a specific combination of both soluble and membrane-bound regulators. Their importance is indicated by the amount of pathologies associated with abnormalities in these complement regulators. Here, we will discuss the current knowledge on complement regulatory protein polymorphisms and expression levels together with their link to disease. These diseases often result in red blood cell destruction or occur in the eye, kidney or brain, which are tissues known for aberrant complement activity or regulation. In addition, complement regulators have also been associated with different types of cancer, although their mechanisms here have not been elucidated yet. In most of these pathologies, treatments are limited and do not prevent the complement system from attacking host cells, but rather fight the consequences of the complement-mediated damage, using for example blood transfusions in anemic patients. Currently only few drugs targeting the complement system are used in the clinic. With further demand for therapeutics rising linked to the wide range of complement-mediated disease we should broaden our horizon towards treatments that can actually protect the host cells against complement. Here, we will discuss the latest insights on how complement regulators can benefit therapeutics. Such therapeutics are currently being developed extensively, and can be categorized into full-length complement regulators, engineered complement system regulators and antibodies targeting complement regulators. In conclusion, this review provides an overview of the complement regulatory proteins and their links to disease, together with their potential in the development of novel therapeutics.

The molecular basis for the prothrombotic state in sickle cell disease

The genetic and molecular basis of sickle cell disease (SCD) has long since been characterized but the pathophysiological basis is not entirely defined. How a red cell hemolytic disorder initiates inflammation, endothelial dysfunction, coagulation activation and eventually leads to vascular thrombosis, is yet to be elucidated. Recent evidence has demonstrated a high frequency of unprovoked/recurrent venous thromboembolism (VTE) in SCD, with an increased risk of mortality among patients with a history of VTE. Here, we thoroughly review the molecular basis for the prothrombotic state in SCD, specifically highlighting emerging evidence for activation of overlapping inflammation and coagulation pathways, that predispose to venous thromboembolism. We share perspectives in managing venous thrombosis in SCD, highlighting innovative therapies with the potential to influence the clinical course of disease and reduce thrombotic risk, while maintaining an acceptable safety profile.

Thromboinflammatory mechanisms in sickle cell disease - challenging the hemostatic balance

Sickle cell disease (SCD) is an inherited hemoglobinopathy that is caused by the presence of abnormal hemoglobin S (HbS) in red blood cells, leading to alterations in red cell properties and shape, as the result of HbS dexoygenation and subsequent polymerization. SCD pathophysiology is characterized by chronic inflammatory processes, triggered by hemolytic and vaso-occlusive events, which lead to the varied complications, organ damage and elevated mortality seen in individuals with the disease. In association with activation of the endothelium and leukocytes, hemostatic alterations and thrombotic events are well-documented in SCD. Here we discuss the role for inflammatory pathways in modulating coagulation and inducing platelet activation in SCD, due to tissue factor activation, adhesion molecule expression, inflammatory mediator production and the induction of innate immune responses, amongst other mechanisms. Thromboinflammatory pathways may play a significant role in some of the major complications of SCD, such as stroke, venous thromboembolism and possibly acute chest syndrome, besides exacerbating the chronic inflammation and cellular interactions that trigger vaso-occlusion, ischemia-reperfusion processes, and eventually organ damage.

Hemopexin as an Inhibitor of Hemolysis-Induced Complement Activation

Hemopexin is the main plasmatic scavenger of cell-free heme, released in the context of intravascular hemolysis or major cell injury. Heme is indispensable for the oxygen transport by hemoglobin but when released outside of the erythrocytes it becomes a danger-associated molecular pattern, contributing to tissue injury. One of the mechanisms of pro-inflammatory action of heme is to activate the innate immune complement cascade. Therefore, we hypothesized that injection of hemopexin will prevent hemolysis-induced complement activation. Human plasma-derived hemopexin is compatible with the heme clearance machinery of the mice. 100 or 500 mg/kg of hemopexin was injected in C57Bl/6 mice before treatment with phenylhydrazine (inducer of erythrocytes lysis) or with PBS as a control. Blood was taken at different timepoints to determine the pharmacokinetic of injected hemopexin in presence and absence of hemolysis. Complement activation was determined in plasma, by the C3 cleavage (western blot) and in the kidneys (immunofluorescence). Kidney injury was evaluated by urea and creatinine in plasma and renal NGAL and HO-1 gene expression were measured. The pharmacokinetic properties of hemopexin (mass spectrometry) in the hemolytic mice were affected by the target-mediated drug disposition phenomenon due to the high affinity of binding of hemopexin to heme. Hemolysis induced complement overactivation and signs of mild renal dysfunction at 6 h, which were prevented by hemopexin, except for the NGAL upregulation. The heme-degrading capacity of the kidney, measured by the HO-1 expression, was not affected by the treatment. These results encourage further studies of hemopexin as a therapeutic agent in models of diseases with heme overload.

Pro-inflammatory Actions of Heme and Other Hemoglobin-Derived DAMPs

Damage associated molecular patterns (DAMPs) are endogenous molecules originate from damaged cells and tissues with the ability to trigger and/or modify innate immune responses. Upon hemolysis hemoglobin (Hb) is released from red blood cells (RBCs) to the circulation and give a rise to the production of different Hb redox states and heme which can act as DAMPs. Heme is the best characterized Hb-derived DAMP that targets different immune and non-immune cells. Heme is a chemoattractant, activates the complement system, modulates host defense mechanisms through the activation of innate immune receptors and the heme oxygenase-1/ferritin system, and induces innate immune memory. The contribution of oxidized Hb forms is much less studied, but some evidence show that these species might play distinct roles in intravascular hemolysis-associated pathologies independently of heme release. This review aims to summarize our current knowledge about the formation and pro-inflammatory actions of heme and other Hb-derived DAMPs.

Immune mechanisms involved in sickle cell disease pathogenesis: current knowledge and perspectives

Sickle cell disease (SCD) is caused by a single point mutation in the β-chain of the hemoglobin gene that results in the replacement of glutamic acid with valine in the hemoglobin protein. However, recent studies have demonstrated that alterations in several other genes, especially immune related genes, may be associated with complications of SCD. In fact, higher chronic inflammatory status is related to more severe clinical symptoms in SCD patients, suggesting crucial roles of the immune system in SCD physiopathology. Nevertheless, although participation of innate immune cells in SCD pathogenesis has been broadly and extensively described, little is known about the roles of the adaptive immune system in this disease. In addition, the influence of treatments on the immune system of SCD patients and their complications (such as alloimmunization) are not yet completely understood. Thus, we reviewed the current knowledge about the immune mechanisms involved in SCD pathogenesis. We suggest recommendations for future studies to allow for a broader understanding of SCD pathogenesis, helping in the development of new therapies and improvement in the life quality and expectancy of patients.