Individual variability in response to a single sickling event for normal, sickle cell, and sickle trait erythrocytes

Sickle cell trait and multisystem trauma: an unaddressed urgent knowledge gap

Sickle cell trait (SCT) has historically been considered a benign condition, but SCT-positive patients have increased baseline risk of venous thromboembolism and chronic kidney disease, as well as increased risk of sickled erythrocytes in settings of hypoxia, acidosis, and hypovolemia. Multisystem traumatic injuries are a common clinical scenario, in which hypoxia, acidosis, and hypovolemia occur; however, little is known about how SCT-positive status impacts outcomes in multisystem trauma. We conducted a scoping literature review to investigate what was known about SCT in the setting of multisystem trauma. In the 110+ years that sickle cell hemoglobinopathies have been known, only three studies have ever examined the relationship between SCT and multisystem traumas. All three articles were case reports. None of the articles intentionally measured the association between SCT and multisystem trauma outcomes; they only incidentally captured information on SCT. Our article then examines historical reasons why so little research has studied the pathophysiology of the multisystem trauma in patients with SCT. Among the reasons is that historical and logistical factors have long prevented patients from knowing their SCT-status: historical discriminations against SCT-positive patients in the 1960s and 1970s delayed federal mandating of SCT newborn screening until 2006, whereas difficulties communicating known SCT-status to afflicted children also contributed to lack of patient knowledge. In light of our findings, we offer specific calls to action for the trauma surgery research community: (1) consider testing for SCT in trauma patients that have unexpected complications, particularly venous thromboembolism, rhabdomyolysis, or renal failure and (2) support research to understand how SCT impacts multisystem trauma outcomes. We also offer specific guidelines about how to ‘proceed with caution’ in implementation of these goals in light of the troubled history of SCT testing and policy in the USA.

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.

Can red blood cell function assays assess response to red cell-modifying therapies?

BACKGROUND

Red blood cell (RBC)-modifying therapies have provided new opportunities for patients with sickle cell disease, although the absence of validated biomarkers of RBC function is a barrier to FDA approval and clinical adoption. Flow Adhesion (FA) and Mechanical Fragility (MF) biomarkers objectively stratify individuals with SCD into pro-adhesive vs pro-hemolytic phenotypes respectively, which may potentially help predict therapeutic responses.

OBJECTIVE

A Phase 3 clinical trial to determine the effectiveness of vepoloxamer, an RBC-modifying therapy in sickle cell disease (SCD), failed to meet its primary clinical outcome. The aim of this study was to determine whether standardized flow adhesion and mechanical fragility bioassays could differentiate cellular level "responders" from "non-responders" to vepoloxamer treatment.

METHODS

Standardized biomarkers of RBC function (adhesion and mechanical fragility) were utilized in this study to assess the effect of veploxamer on blood samples collected from SCD subjects and to determine whether our assays could differentiate cellular-level "responders" from "non-responders" to vepoloxamer treatment. A Wilcoxon signed-rank test was used to test for differences in adhesion in response to varying vepoloxamer treatments and a Wilcoxon Mann-Whitney test was used to assess differences in mechanical fragility, pre- and post-vepoloxamer treatment. A p-value<0.05 was considered significant.

RESULTS

In this study, we report that in vitro treatment with vepoloxamer reduced adhesion by >75%in 54%of patient samples and induced changes in the membranes of sickle erythrocytes (SSRBCs) making sickle cells behave more like normal erythrocytes (AARBCs) in terms of their resistance to hemolysis.

CONCLUSION

This study demonstrates that the standardized flow adhesion and mechanical fragility biomarkers described here may be useful tools to predict clinical responders to RBC-modifying therapies.

Trends in the Development of Diagnostic Tools for Red Blood Cell-Related Diseases and Anemias

In the recent years, the progress in genetic analysis and next-generation sequencing technologies have opened up exciting landscapes for diagnosis and study of molecular mechanisms, allowing the determination of a particular mutation for individual patients suffering from hereditary red blood cell-related diseases or anemia. However, the huge amount of data obtained makes the interpretation of the results and the identification of the pathogenetic variant responsible for the diseases sometime difficult. Moreover, there is increasing evidence that the same mutation can result in varying cellular properties and different symptoms of the disease. Even for the same patient, the phenotypic expression of the disorder can change over time. Therefore, on top of genetic analysis, there is a further request for functional tests that allow to confirm the pathogenicity of a molecular variant, possibly to predict prognosis and complications (e.g., vaso-occlusive pain crises or other thrombotic events) and, in the best case, to enable personalized theranostics (drug and/or dose) according to the disease state and progression. The mini-review will reflect recent and future directions in the development of diagnostic tools for red blood cell-related diseases and anemias. This includes point of care devices, new incarnations of well-known principles addressing physico-chemical properties, and interactions of red blood cells as well as high-tech screening equipment and mobile laboratories.

Peripheral Vaso-Occlusive Events Following Trauma in Patients With Sickle Cell Trait

Sickle cell trait (SCT) is a common hemoglobin variant, particularly in patients of African descent. Patients with SCT have an increased risk of adverse ocular events following trauma with subsequent elevated intraocular pressure (IOP). The authors describe three cases of young males with peripheral vaso-occlusive events following ocular trauma with subsequent elevated IOP. These cases demonstrate the importance of careful peripheral exams in young patients with SCT following trauma. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:e84-e87.].