Tissue factor and thrombin in sickle cell anemia

COVID-19 and Sickle Cell Disease: Two Independent Risk Factors for Venous Thromboembolism

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been widely documented as a multi-systemic illness and associated with an increased incidence of thromboses. Likewise, sickle cell disease (SCD) is a hematologic disease responsible for widespread effects on the vasculature and is also associated with elevated thrombotic risk. In this review, we examine the incidence rates of venous thromboembolism (VTE) in SCD and COVID-19 independently and review the mechanisms of coagulopathy associated with both diseases. We describe the possible associations and commonalities between VTE mechanisms, as both diseases cause widespread inflammation that influences each tenet of Virchow's triad. We also discuss current anticoagulation guideline recommendations for the prevention of VTE events in each of these diseases. We report on current literature to date describing rates of VTE in SCD-COVID-19 patients and outline prospective areas of research to further understand the possible synergistic influence of coagulopathy in these patients. The association between SCD and COVID-19 remains a largely under-researched area of coagulopathy in current hematology and thrombotic literature, and our report lays out potential future prospects in the field.

Mitochondrial reactive oxygen species scavenging attenuates thrombus formation in a murine model of sickle cell disease

BACKGROUND

Sickle cell disease (SCD) is characterized by hemolysis-associated platelet dysfunction that leads to increased risk of thrombosis and plays a role in the high morbidity and mortality of the disease. The mechanisms by which hemolysis induces platelet activation remain unclear. We recently demonstrated that patients with SCD showed increased platelet mitochondrial reactive oxygen species (mtROS) production that correlates with markers of hemolysis and platelet activation. Experiments in isolated platelets demonstrated that mtROS stimulated platelet activation. However, the role of hemolysis-induced mtROS in thrombus formation in vivo remains unclear.

OBJECTIVES

Here, we hypothesize that scavenging of mtROS attenuates the propensity for thrombosis in mouse models of hemolysis.

METHODS

We used models of hemolysate infusion into wildtype mice as well as the Berkley transgenic mouse model of SCD, a chronic mode of hemolysis, to test the effect of hemolysis on platelet mtROS production and thrombosis.

RESULTS

We show that infusion of hemolysate in wildtype mice induces platelet mtROS production and decreases time to vessel occlusion in a model of ferric chloride-induced carotid artery thrombosis. Increased mtROS and propensity for thrombosis was also observed in the Berkley transgenic mouse model of SCD. Notably, treatment with mtROS scavengers decreased platelet mtROS levels and attenuated the propensity for thrombus formation in both models.

CONCLUSIONS

These data demonstrate that mtROS significantly contribute to the mechanism of hemolysis-induced thrombosis in vivo and suggest a potential role for mitochondrially targeted antioxidant therapy in hemolysis and SCD-related thrombosis.

The Evolving Pharmacotherapeutic Landscape for the Treatment of Sickle Cell Disease

Sickle cell disease (SCD) is an extremely heterogeneous disease that has been associated with global morbidity and early mortality. More effective and inexpensive therapies are needed. During the last five years, the landscape of the pharmacotherapy of SCD has changed dramatically. Currently, 54 drugs have been used or under consideration to use for the treatment of SCD. These fall into 3 categories: the first category includes the four drugs (Hydroxyurea, L-Glutamine, Crizanlizumab tmca and Voxelotor) that have been approved by the United States Food and Drug Administration (FDA) based on successful clinical trials. The second category includes 22 drugs that failed, discontinued or terminated for now and the third category includes 28 drugs that are actively being considered for the treatment of SCD. Crizanlizumab and Voxelotor are included in the first and third categories because they have been used in more than one trial. New therapies targeting multiple pathways in the complex pathophysiology of SCD have been achieved or are under continued investigation. The emerging trend seems to be the use of multimodal drugs (i.e. drugs that have different mechanisms of action) to treat SCD similar to the use of multiple chemotherapeutic agents to treat cancer.

Tissue Factor: An Essential Mediator of Hemostasis and Trigger of Thrombosis

Tissue factor (TF) is the high-affinity receptor and cofactor for factor (F)VII/VIIa. The TF-FVIIa complex is the primary initiator of blood coagulation and plays an essential role in hemostasis. TF is expressed on perivascular cells and epithelial cells at organ and body surfaces where it forms a hemostatic barrier. TF also provides additional hemostatic protection to vital organs, such as the brain, lung, and heart. Under pathological conditions, TF can trigger both arterial and venous thrombosis. For instance, atherosclerotic plaques contain high levels of TF on macrophage foam cells and microvesicles that drives thrombus formation after plaque rupture. In sepsis, inducible TF expression on monocytes leads to disseminated intravascular coagulation. In cancer patients, tumors release TF-positive microvesicles into the circulation that may contribute to venous thrombosis. TF also has nonhemostatic roles. For instance, TF-dependent activation of the coagulation cascade generates coagulation proteases, such as FVIIa, FXa, and thrombin, which induce signaling in a variety of cells by cleavage of protease-activated receptors. This review will focus on the roles of TF in protective hemostasis and pathological thrombosis.

Rheumatoid Arthritis in Sickle-Cell Population: Pathophysiologic Insights, Clinical Evaluation and Management

The advent of hydroxyurea and advanced medical care, including immunizations has led to improved survival among patients with Sickle Cell Disease (SCD). This prolonged survival however, introduces a chronic inflammatory disorder, Rheumatoid Arthritis (RA), which presents at a relatively older age and is rarely reported among SCD patients. In this review, we highlight the epidemiological association of SCD-RA and discuss the underlying common pathogenetic mechanisms, such as endothelial dysfunction, the role of inflammatory cytokines and oxidative stress. We also point to the difficulties in ascertaining the clinical diagnosis of RA in SCD patients. Finally, we provide rationale for therapeutic options available for RA and the challenges in the management of these patients with agents that are known to increase the risk of infection and immunosuppression such as steroids, disease modifying anti-rheumatic drugs and biologics.

Coagulation disorders and their cutaneous presentations: Pathophysiology

Hypercoagulable states are inherited or acquired predispositions to venous or arterial thromboses that are best understood in the context of the coagulation cascade. Dermatologists can play a critical role in diagnosing and treating patients with hypercoagulable states because cutaneous symptoms may be a presenting manifestation, thereby reducing morbidity and mortality related to these conditions. This review focuses on the epidemiology and pathophysiology of hypercoagulable states, while the accompanying article iterates the basic clinical features, diagnostic testing, and management of patients who have these conditions.

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

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

Emerging drugs for sickle cell anemia

INTRODUCTION

The search for effective therapeutic interventions for sickle cell disease (SCD) has been an ongoing endeavor for over 50 years. During this period, only hydroxyurea (HU), which received US FDA approval in February 1998, was identified as an effective therapeutic agent in preventing or ameliorating the frequency of vaso-occlusive crises, acute chest syndrome and the need for blood transfusion. Approximately 25% of patients with sickle cell anemia (SCA), however, do not respond to HU and some patients experiencing serious side effects of this chemotherapeutic agent. Nevertheless, the success of HU opened the sluice gates to identify other effective drug therapies. The objective of this review is to describe the emerging drug therapies for SCA.

AREAS COVERED

In this review, we describe the pathophysiology of SCD and provide an in-depth analysis of the current and new pharmacologic therapies in the field. Literature searches involved multiple databases including Medline In-Process & Other Non-Indexed Citations, MEDLINE, Embase, Cochrane Database of Systematic Reviews, and Scopus.

EXPERT OPINION

SCA is a heterogeneous disease that has caused tremendous global morbidity and early mortality. More effective, individualized and inexpensive therapies are needed. New therapies targeting multiple pathways in its complex pathophysiology are under investigation.

Vaso-occlusion in sickle cell disease: pathophysiology and novel targeted therapies

Recurrent and unpredictable episodes of vaso-occlusion are the hallmark of sickle cell disease. Symptomatic management and prevention of these events using the fetal hemoglobin-reactivating agent hydroxyurea are currently the mainstay of treatment. Discoveries over the past 2 decades have highlighted the important contributions of various cellular and soluble participants in the vaso-occlusive cascade. The role of these elements and the opportunities for therapeutic intervention are summarized in this review.

Vaso-occlusion in sickle cell disease: pathophysiology and novel targeted therapies

Recurrent and unpredictable episodes of vaso-occlusion are the hallmark of sickle cell disease. Symptomatic management and prevention of these events using the fetal hemoglobin-reactivating agent hydroxyurea are currently the mainstay of treatment. Discoveries over the past 2 decades have highlighted the important contributions of various cellular and soluble participants in the vaso-occlusive cascade. The role of these elements and the opportunities for therapeutic intervention are summarized in this review.