Rapid and reproducible characterization of sickling during automated deoxygenation in sickle cell disease patients

Computing Sickle Erythrocyte Health Index on quantitative phase imaging and machine learning

Sickle cell disease (SCD) is a genetic disorder characterized by abnormal hemoglobin and deformation of red blood cells (RBCs), leading to complications and reduced life expectancy. This study developed an in vitro assessment, the Sickle Erythrocyte Health Index, using quantitative phase imaging (QPI) and machine learning to model the health of RBCs in people with SCD. The health index combines assessment of cell deformation, sickle-shaped classification, and membrane flexibility to evaluate erythrocyte health. Using QPI and image processing, the percentage of sickle-shaped cells and membrane flexibility were quantified. Statistically significant differences were observed between individuals with and without SCD, indicating the impact of underlying pathophysiology on erythrocyte health. Additionally, sodium metabisulfite led to an increase in sickle-shaped cells and a decrease in flexibility in the sickle cell blood samples. Based on these findings, two approaches were used to calculate the Sickle Erythrocyte Health Index: one using hand-crafted features and one using learned features from deep learning models. Both indices showed significant differences between non-SCD and SCD groups and sensitivity to changes induced by sodium metabisulfite. The Sickle Erythrocyte Health Index has important clinical implications for SCD management and could be used by providers when making treatment decisions. Further research is warranted to evaluate the clinical utility and applicability of the Sickle Erythrocyte Health Index in diverse patient populations.

A novel composition of endogenous metabolic modulators improves red blood cell properties in sickle cell disease

The most common forms of sickle cell disease (SCD) are sickle cell anemia (SCA; HbSS) and HbSC disease. In both, especially the more dense, dehydrated and adherent red blood cells (RBCs) with reduced deformability are prone to hemolysis and sickling, and thereby vaso-occlusion. Based on plasma amino acid profiling in SCD, a composition of 10 amino acids and derivatives (RCitNacQCarLKHVS; Axcella Therapeutics, USA), referred to as endogenous metabolic modulators (EMMs), was designed to target RBC metabolism. The effects of ex vivo treatment with the EMM composition on different RBC properties were studied in SCD (n = 9 SCA, n = 5 HbSC disease). Dose-dependent improvements were observed in RBC hydration assessed by hemocytometry (MCV, MCHC, dense RBCs) and osmotic gradient ektacytometry (Ohyper). Median (interquartile range [IQR]) increase in Ohyper compared to vehicle was 4.9% (4.0%-5.5%), 7.5% (6.9%-9.4%), and 12.8% (11.5%-14.0%) with increasing 20×, 40×, and 80X concentrations, respectively (all p < 0.0001). RBC deformability (EImax using oxygen gradient ektacytometry) increased by 8.1% (2.2%-12.1%; p = 0.0012), 9.6% (2.9%-15.1%; p = 0.0013), and 13.3% (5.7%-25.5%; p = 0.0007), respectively. Besides, RBC adhesion to subendothelial laminin decreased by 43% (6%-68%; p = 0.4324), 58% (48%-72%; p = 0.0185), and 71% (49%-82%; p = 0.0016), respectively. Together, these results provide a rationale for further studies with the EMM composition targeting multiple RBC properties in SCD.

Voxelotor improves red blood cell functionality in children with sickle cell anaemia: An ancillary study of the HOPE-KIDS 1 trial

INTRODUCTION

Sickle haemoglobin (HbS) polymerisation perturbs red blood cell (RBC) rheology and drives sickle cell disease (SCD) pathophysiology. Voxelotor is an HbS polymerisation inhibitor that increases haemoglobin (Hb)-oxygen affinity.

METHODS/RESULTS

In this 48-week, prospective, single-centre translational study, 10 children aged 4-11 years with SCD were treated with voxelotor. Improvements in RBC deformability were observed using osmotic/oxygen gradient ektacytometry, with increases in minimal and maximal elongation index and reductions in point of sickling. Increased Hb and reduced markers of haemolysis were also observed.

CONCLUSION

These findings suggest that voxelotor treatment is associated with reduced RBC sickling and haemolysis in children with SCD.

Oxygen gradient ektacytometry-derived biomarkers are associated with acute complications in sickle cell disease

ABSTRACT

We investigated the potential of the point of sickling (PoS; the pO2 tension at which red cells start to sickle), determined by oxygen gradient ektacytometry to serve as a biomarker associated with the incidence of acute sickle cell disease-related complications in 177 children and 50 adults. In the pediatric cohort, for every 10 mmHg increase in PoS reflecting a greater likelihood of sickling, the likelihood of an individual experiencing >1 type of acute complication increased; the adjusted odds ratio (aOR) was 1.65. For every 0.1 increase in minimum elongation index (EImin; reflecting improved red blood cell deformability at hypoxia), the aOR was 0.50. In the adult cohort, for every 10 mmHg increase in PoS, we found an aOR of 3.00, although this was not significant after correcting for multiple testing. There was a trend for an association between higher PoS and greater likelihood of vaso-occlusive episodes (VOEs; children aOR, 1.35; adults aOR, 2.22). In children, only EImin was associated with VOEs (aOR, 0.68). When data of both cohorts were pooled, significant associations with PoS and/or EImin were found for all acute complications, independently and when >1 type of acute complication was assessed. These findings indicate that oxygen gradient ektacytometry generates novel biomarkers and provides a rationale for further development of these biomarkers in the assessment of clinical severity, evaluation of novel therapies, and as surrogate clinical trial end points. These biomarkers may be useful in assessing efficacy of novel therapies like pyruvate kinase activators, voxelotor, and L-glutamine.

One-year safety and efficacy of mitapivat in sickle cell disease: follow-up results of a phase 2, open-label study

Targeting the primary pathogenic event of sickle cell disease (SCD), the polymerization of sickle hemoglobin (HbS), may prevent downstream clinical events. Mitapivat, an oral pyruvate kinase (PK) activator, has therapeutic potential by increasing adenosine triphosphate (ATP) and decreasing 2,3-diphosphoglycerate (2,3-DPG), a glycolytic red blood cell (RBC) intermediate. In the previously reported 8-week dose-finding period of this phase 2, investigator-initiated, open-label study, mitapivat was well tolerated and showed efficacy in SCD. Here, the 1-year fixed-dose extension period is reported in which 9 of 10 included patients (90%) aged ≥16 years with SCD (HbSS, HbS/β0, or HbS/β+) continued with mitapivat. Mostly mild treatment-emergent adverse events (AEs) (most commonly, transaminase increase and headache) were still reported. Apart from the reported nontreatment-related serious AE (SAE) of a urinary tract infection in the dose-finding period, 1 nontreatment-related SAE occurred in the fixed-dose extension period in a patient who died of massive pulmonary embolism due to COVID-19. Importantly, sustained improvement in Hb level (mean increase, 1.1 ± 0.7 g/dL; P = .0014) was seen, which was accompanied by decreases in markers of hemolysis. In addition, the annualized rate of vaso-occlusive events reduced significantly from a historic baseline of 1.33 ± 1.32 to 0.64 ± 0.87 (P = .0489) when combining the dose-finding period and fixed-dose extension period. Cellularly, the ATP:2,3-DPG ratio and Hb-oxygen affinity significantly increased and RBC sickling (point of sickling) nonsignificantly reduced. Overall, this study demonstrated 1-year safety and efficacy of treatment with mitapivat in SCD, supporting further evaluation in ongoing phase 2/3 study (RISE UP, NCT05031780). This trial was registered at https://www.clinicaltrialsregister.eu/ as NL8517 and EudraCT 2019-003438-18.

Metabolic signatures of cardiorenal dysfunction in plasma from sickle cell patients as a function of therapeutic transfusion and hydroxyurea treatment

Metabolomics studies in sickle cell disease (SCD) have been so far limited to tens of samples, owing to technical and experimental limitations. To overcome these limitations, we performed plasma metabolomics analyses on 596 samples from patients with SCD enrolled in the WALK-PHaSST study (clinicaltrials gov. Identifier: NCT00492531). Clinical covariates informed the biological interpretation of metabolomics data, including genotypes (hemoglobin [Hb] SS, hemoglobin SC), history of recent transfusion (HbA%), response to hydroxyurea treatment (fetal Hb%). We investigated metabolic correlates to the degree of intravascular hemolysis, cardiorenal function, as determined by tricuspid regurgitation velocity (TRV), estimated glomerular filtration rate (eGFR), and overall hazard ratio (unadjusted or adjusted by age). Recent transfusion events or hydroxyurea treatment were associated with elevation in plasma-free fatty acids and decreases in acyl-carnitines, urate, kynurenine, indoles, carboxylic acids, and glycine- or taurine-conjugated bile acids. High levels of these metabolites, along with low levels of plasma S1P and L-arginine were identified as top markers of hemolysis, cardiorenal function (TRV, eGFR), and overall hazard ratio. We thus uploaded all omics and clinical data on a novel online portal that we used to identify a potential mechanism of dysregulated red cell S1P synthesis and export as a contributor to the more severe clinical manifestations in patients with the SS genotype compared to SC. In conclusion, plasma metabolic signatures - including low S1P, arginine and elevated kynurenine, acyl-carnitines and bile acids - are associated with clinical manifestation and therapeutic efficacy in SCD patients, suggesting new avenues for metabolic interventions in this patient population.

Metabolic signatures of cardiorenal dysfunction in plasma from sickle cell patients, as a function of therapeutic transfusion and hydroxyurea treatment

Metabolomics studies in sickle cell disease (SCD) have been so far limited to tens of samples, owing to technical and experimental limitations. To overcome these limitations, we performed plasma metabolomics analyses on 596 samples from patients with sickle cell sickle cell disease (SCD) enrolled in the WALK-PHaSST study. Clinical covariates informed the biological interpretation of metabolomics data, including genotypes (hemoglobin SS, hemoglobin SC), history of recent transfusion (HbA%), response to hydroxyurea treatment (HbF%). We investigated metabolic correlates to the degree of hemolysis, cardiorenal function, as determined by tricuspid regurgitation velocity (TRV), estimated glomerular filtration rate (eGFR), and overall hazard ratio (unadjusted or adjusted by age). Recent transfusion events or hydroxyurea treatment were associated with elevation in plasma free fatty acids and decreases in acyl-carnitines, urate, kynurenine, indoles, carboxylic acids, and glycine- or taurine-conjugated bile acids. High levels of these metabolites, along with low levels of plasma S1P and L-arginine were identified as top markers of hemolysis, cardiorenal function (TRV, eGFR), and overall hazard ratio. We thus uploaded all omics and clinical data on a novel online portal that we used to identify a potential mechanism of dysregulated red cell S1P synthesis and export as a contributor to the more severe clinical manifestations in patients with the SS genotype compared to SC. In conclusion, plasma metabolic signatures - including low S1P, arginine and elevated kynurenine, acyl-carnitines and bile acids - are associated with clinical manifestation and therapeutic efficacy in SCD patients, suggesting new avenues for metabolic interventions in this patient population.

The need for multimodal health data modeling: a practical approach for a federated-learning healthcare platform

Federated learning initiatives in healthcare are being developed to collaboratively train predictive models without the need to centralize sensitive personal data. GenoMed4All is one such project, with the goal of connecting European clinical and -omics data repositories on rare diseases through a federated learning platform. Currently, the consortium faces the challenge of a lack of well-established international datasets and interoperability standards for federated learning applications on rare diseases. This paper presents our practical approach to select and implement a Common Data Model (CDM) suitable for the federated training of predictive models applied to the medical domain, during the initial design phase of our federated learning platform. We describe our selection process, composed of identifying the consortium's needs, reviewing our functional and technical architecture specifications, and extracting a list of business requirements. We review the state of the art and evaluate three widely-used approaches (FHIR, OMOP and Phenopackets) based on a checklist of requirements and specifications. We discuss the pros and cons of each approach considering the use cases specific to our consortium as well as the generic issues of implementing a European federated learning healthcare platform. A list of lessons learned from the experience in our consortium is discussed, from the importance of establishing the proper communication channels for all stakeholders to technical aspects related to -omics data. For federated learning projects focused on secondary use of health data for predictive modeling, encompassing multiple data modalities, a phase of data model convergence is sorely needed to gather different data representations developed in the context of medical research, interoperability of clinical care software, imaging, and -omics analysis into a coherent, unified data model. Our work identifies this need and presents our experience and a list of actionable lessons learned for future work in this direction.

Classification of red cell dynamics with convolutional and recurrent neural networks: a sickle cell disease case study

The fraction of red blood cells adopting a specific motion under low shear flow is a promising inexpensive marker for monitoring the clinical status of patients with sickle cell disease. Its high-throughput measurement relies on the video analysis of thousands of cell motions for each blood sample to eliminate a large majority of unreliable samples (out of focus or overlapping cells) and discriminate between tank-treading and flipping motion, characterizing highly and poorly deformable cells respectively. Moreover, these videos are of different durations (from 6 to more than 100 frames). We present a two-stage end-to-end machine learning pipeline able to automatically classify cell motions in videos with a high class imbalance. By extending, comparing, and combining two state-of-the-art methods, a convolutional neural network (CNN) model and a recurrent CNN, we are able to automatically discard 97% of the unreliable cell sequences (first stage) and classify highly and poorly deformable red cell sequences with 97% accuracy and an F1-score of 0.94 (second stage). Dataset and codes are publicly released for the community.

Using Transfer Learning to Train a Binary Classifier for Lorrca Ektacytometery Microscopic Images of Sickle Cells and Healthy Red Blood Cells

Multiple blood images of stressed and sheared cells, taken by a Lorrca Ektacytometery microscope, needed a classification for biomedical researchers to assess several treatment options for blood-related diseases. The study proposes the design of a model capable of classifying these images, with high accuracy, into healthy Red Blood Cells (RBCs) or Sickle Cells (SCs) images. The performances of five Deep Learning (DL) models with two different optimizers, namely Adam and Stochastic Gradient Descent (SGD), were compared. The first three models consisted of 1, 2 and 3 blocks of CNN, respectively, and the last two models used a transfer learning approach to extract features. The dataset was first augmented, scaled, and then trained to develop models. The performance of the models was evaluated by testing on new images and was illustrated by confusion matrices, performance metrics (accuracy, recall, precision and f1 score), a receiver operating characteristic (ROC) curve and the area under the curve (AUC) value. The first, second and third models with the Adam optimizer could not achieve training, validation or testing accuracy above 50%. However, the second and third models with SGD optimizers showed good loss and accuracy scores during training and validation, but the testing accuracy did not exceed 51%. The fourth and fifth models used VGG16 and Resnet50 pre-trained models for feature extraction, respectively. VGG16 performed better than Resnet50, scoring 98% accuracy and an AUC of 0.98 with both optimizers. The study suggests that transfer learning with the VGG16 model helped to extract features from images for the classification of healthy RBCs and SCs, thus making a significant difference in performance comparing the first, second, third and fifth models.

OcclusionChip: A functional microcapillary occlusion assay complementary to ektacytometry for detection of small-fraction red blood cells with abnormal deformability

Red blood cell (RBC) deformability is a valuable hemorheological biomarker that can be used to assess the clinical status and response to therapy of individuals with sickle cell disease (SCD). RBC deformability has been measured by ektacytometry for decades, which uses shear or osmolar stress. However, ektacytometry is a population based measurement that does not detect small-fractions of abnormal RBCs. A single cell-based, functional RBC deformability assay would complement ektacytometry and provide additional information. Here, we tested the relative merits of the OcclusionChip, which measures RBC deformability by microcapillary occlusion, and ektacytometry. We tested samples containing glutaraldehyde-stiffened RBCs for up to 1% volume fraction; ektacytometry detected no significant change in Elongation Index (EI), while the OcclusionChip showed significant differences in Occlusion Index (OI). OcclusionChip detected a significant increase in OI in RBCs from an individual with sickle cell trait (SCT) and from a subject with SCD who received allogeneic hematopoietic stem cell transplant (HSCT), as the sample was taken from normoxic (pO2:159 mmHg) to physiologic hypoxic (pO2:45 mmHg) conditions. Oxygen gradient ektacytometry detected no difference in EI for SCT or HSCT. These results suggest that the single cell-based OcclusionChip enables detection of sickle hemoglobin (HbS)-related RBC abnormalities in SCT and SCD, particularly when the HbS level is low. We conclude that the OcclusionChip is complementary to the population based ektacytometry assays, and providing additional sensitivity and capacity to detect modest abnormalities in red cell function or small populations of abnormal red cells.

The oral ferroportin inhibitor vamifeport improves hemodynamics in a mouse model of sickle cell disease

Sickle cell disease (SCD) is an inherited hemolytic anemia caused by a single point mutation in the β-globin gene of hemoglobin that leads to synthesis of sickle hemoglobin (HbS) in red blood cells (RBCs). HbS polymerizes in hypoxic conditions, leading to intravascular hemolysis, release of free hemoglobin and heme, and increased adhesion of blood cells to the endothelial vasculature, which causes painful vaso-occlusion and organ damage. HbS polymerization kinetics are strongly dependent on the intracellular HbS concentration; a relatively small reduction in cellular HbS concentration may prevent HbS polymerization and its sequelae. We hypothesized that iron restriction via blocking ferroportin, the unique iron transporter in mammals, might reduce HbS concentration in RBCs, thereby decreasing hemolysis, improving blood flow, and preventing vaso-occlusive events. Indeed, vamifeport (also known as VIT-2763), a clinical-stage oral ferroportin inhibitor, reduced hemolysis markers in the Townes model of SCD. The RBC indices of vamifeport-treated male and female Townes mice exhibited changes attributable to iron-restricted erythropoiesis: decreased corpuscular hemoglobin concentration mean and mean corpuscular volume, as well as increased hypochromic and microcytic RBC fractions. Furthermore, vamifeport reduced plasma soluble VCAM-1 concentrations, which suggests lowered vascular inflammation. Accordingly, intravital video microscopy of fluorescently labeled blood cells in the microvasculature of Townes mice treated with vamifeport revealed diminished adhesion to the endothelium and improved hemodynamics. These preclinical data provide a strong proof-of-concept for vamifeport in the Townes model of SCD and support further development of this compound as a potential novel therapy in SCD.

Microfluidic methods to advance mechanistic understanding and translational research in sickle cell disease

Sickle cell disease (SCD) is caused by a single point mutation in the β-globin gene of hemoglobin, which produces an altered sickle hemoglobin (HbS). The ability of HbS to polymerize under deoxygenated conditions gives rise to chronic hemolysis, oxidative stress, inflammation, and vaso-occlusion. Herein, we review recent findings using microfluidic technologies that have elucidated mechanisms of oxygen-dependent and -independent induction of HbS polymerization and how these mechanisms elicit the biophysical and inflammatory consequences in SCD pathophysiology. We also discuss how validation and use of microfluidics in SCD provides the opportunity to advance development of numerous therapeutic strategies, including curative gene therapies.

Hypoxia and hemorheological properties in older individuals

Hypoxia is caused by insufficient oxygen availability for the organism leading to reduced oxygen delivery to tissues and cells. It has been regarded as a severe threat to human health and it is indeed implicated in pathophysiological mechanisms involved in the development and progression of many diseases. Nevertheless, the potential of controlled hypoxia interventions (i.e. hypoxia conditioning) for improving cardio-vascular health is gaining increased attention. However, blood rheology is often a forgotten factor for vascular health while aging and hypoxia exposure are both suspected to alter hemorheological properties. These changes in blood rheology may influence the benefits-risks balance of hypoxia exposure in older individuals. The benefits of hypoxia exposure for vascular health are mainly reported for healthy populations and the combined impact of aging and hypoxia on blood rheology could therefore be deleterious in older individuals. This review discusses evidence of hypoxia-related and aging-related changes in blood viscosity and its determinants. It draws upon an extensive literature search on the effects of hypoxia/altitude and aging on blood rheology. Aging increases blood viscosity mainly through a rise in plasma viscosity, red blood cell (RBC) aggregation and a decrease in RBC deformability. Hypoxia also causes an increase in RBC aggregation and plasma viscosity. In addition, hypoxia exposure may increase hematocrit and modulate RBC deformability, depending on the hypoxic dose, i.e, beneficial effect of intermittent hypoxia with moderate dose vs deleterious effect of chronic continuous or intermittent hypoxia or if the hypoxic dose is too high. Special attention is directed toward the risks vs. benefits of hemorheological changes during hypoxia exposure in older individuals, and its clinical relevance for vascular disorders.

The ektacytometric elongation Index (EI) of erythrocytes, validation of a prognostic, rheological biomarker for patients with sickle cell disease

OBJECTIVES

Validation of the measurement of erythrocyte deformability as a useful prognostic, rheological biomarker for patients with sickle cell disease (SCD).

METHODS

The degree of reduced deformability was based on the value of the maximum elongation index (EI_max ) of the deformability curve of an osmotic gradient ektacytometer. The performance of this technique was analytically and clinically validated by analysing 200 normal subjects and 100 patients with well-documented thalassemia's and Hb variants in relation to their clinical condition.

RESULTS

In this study, we show that EI_max is a reproducible parameter with a small inter-individual coefficient of (Biological) variation (CV)=1.6% and a small intra-individual CV=3.5%. We demonstrate that loss of deformability correlates with the clinical condition and the various mutations underlying sickle cell disease and thalassemia. For SCD patients, a strongly reduced EI_max with a cut-off =0.360 is a signal for future vaso-occlusive (VOC) events requiring hospitalisation with a specificity=85%, sensitivity=80%, PPV=81% and NPV=84% based on a ROC curve (AUC=0.89).

CONCLUSION

This study validated the clinical utility of EI_max as a prognostic marker for future clinical problems in individual high-risk SCD patients. In addition, EI_max may help to achieve an adequate personal transfusion policy for an optimal blood flow in anaemic patients with SCD.

Technologies for measuring red blood cell deformability

Human red blood cells (RBCs) are approximately 8 μm in diameter, but must repeatedly deform through capillaries as small as 2 μm in order to deliver oxygen to all parts of the body. The loss of this capability is associated with the pathology of many diseases, and is therefore a potential biomarker for disease status and treatment efficacy. Measuring RBC deformability is a difficult problem because of the minute forces (∼pN) that must be exerted on these cells, as well as the requirements for throughput and multiplexing. The development of technologies for measuring RBC deformability date back to the 1960s with the development of micropipette aspiration, ektacytometry, and the cell transit analyzer. In the past 10 years, significant progress has been made using microfluidics by leveraging the ability to precisely control fluid flow through microstructures at the size scale of individual RBCs. These technologies have now surpassed traditional methods in terms of sensitivity, throughput, consistency, and ease of use. As a result, these efforts are beginning to move beyond feasibility studies and into applications to enable biomedical discoveries. In this review, we provide an overview of both traditional and microfluidic techniques for measuring RBC deformability. We discuss the capabilities of each technique and compare their sensitivity, throughput, and robustness in measuring bulk and single-cell RBC deformability. Finally, we discuss how these tools could be used to measure changes in RBC deformability in the context of various applications including pathologies caused by malaria and hemoglobinopathies, as well as degradation during storage in blood bags prior to blood transfusions.

Assessment of Blood Biophysical Properties Using Pressure Sensing with Micropump and Microfluidic Comparator

To identify the biophysical properties of blood samples consistently, macroscopic pumps have been used to maintain constant flow rates in a microfluidic comparator. In this study, the bulk-sized and expensive pump is replaced with a cheap and portable micropump. A specific reference fluid (i.e., glycerin solution [40%]) with a small volume of red blood cell (RBC) (i.e., 1% volume fraction) as fluid tracers is supplied into the microfluidic comparator. An averaged velocity (<Ur>) obtained with micro-particle image velocimetry is converted into the flow rate of reference fluid (Qr) (i.e., Qr = CQ × Ac × <Ur>, Ac: cross-sectional area, CQ = 1.156). Two control variables of the micropump (i.e., frequency: 400 Hz and volt: 150 au) are selected to guarantee a consistent flow rate (i.e., COV < 1%). Simultaneously, the blood sample is supplied into the microfluidic channel under specific flow patterns (i.e., constant, sinusoidal, and periodic on-off fashion). By monitoring the interface in the comparator as well as Qr, three biophysical properties (i.e., viscosity, junction pressure, and pressure-induced work) are obtained using analytical expressions derived with a discrete fluidic circuit model. According to the quantitative comparison results between the present method (i.e., micropump) and the previous method (i.e., syringe pump), the micropump provides consistent results when compared with the syringe pump. Thereafter, representative biophysical properties, including the RBC aggregation, are consistently obtained for specific blood samples prepared with dextran solutions ranging from 0 to 40 mg/mL. In conclusion, the present method could be considered as an effective method for quantifying the physical properties of blood samples, where the reference fluid is supplied with a cheap and portable micropump.

Shear-Stress-Gradient and Oxygen-Gradient Ektacytometry in Sickle Cell Patients at Steady State and during Vaso-Occlusive Crises

Oxygen gradient ektacytometry (oxygenscan) measures the changes in red blood cell (RBC) deformability in normoxia and during deoxygenation. We investigated the changes in RBC deformability, measured by both oxygenscan and classical shear-stress-gradient ektacytometry, in 10 patients with sickle cell disease (SCD) during vaso-occlusive crisis (VOC) versus steady state. Oxygenscan and shear-stress-gradient ektacytometry parameters were also measured in 38 SCD patients at steady state on two different occasions. Shear-stress-gradient ektacytometry parameters, maximal RBC deformability at normoxia and the minimum RBC deformability during deoxygenation were lower during VOC compared to steady state. The oxygen partial pressure at which RBCs started to sickle (PoS) was not significantly affected by VOC, but the results were very heterogeneous: the PoS increased in 5 in 10 patients and decreased in 4 in 10 patients. Both oxygenscan and shear-stress-gradient ektacytometry parameters remained unchanged in patients at steady state between two sets of measurements, performed at 17 ± 8 months intervals. In conclusion, the present study showed that both oxygen gradient ektacytometry and shear-stress-gradient ektacytometry are sensitive to disease activity in SCD, and that both techniques give comparable results; however, the oxygen-dependent propensity of RBCs to sickle was highly variable during VOC.

Etavopivat, a Pyruvate Kinase Activator in Red Blood Cells, for the Treatment of Sickle Cell Disease

Etavopivat is an investigational, oral, small molecule activator of erythrocyte pyruvate kinase (PKR) in development for the treatment of sickle cell disease (SCD) and other hemoglobinopathies. PKR activation is proposed to ameliorate the sickling of SCD red blood cells (RBC) through multiple mechanisms, including reduction of 2,3-diphosphoglycerate (2,3-DPG), which consequently increases hemoglobin (Hb)-oxygen affinity; increased binding of oxygen reduces HbS polymerization and sickling. In addition, PKR activation increases adenosine triphosphate (ATP) produced via glycolytic flux, which helps preserve membrane integrity and RBC deformability. We evaluated the pharmacodynamic response to etavopivat in non-human primates (NHP) and in healthy human subjects, and the effects in RBC from patients with SCD after ex vivo treatment with etavopivat. A single dose of etavopivat decreased 2,3-DPG in NHP and healthy subjects. Hb-oxygen affinity was significantly increased in healthy subjects after 24 hours. Following daily dosing of etavopivat over 5 consecutive days in NHP, ATP was increased by 38% from baseline. Etavopivat increased Hb-oxygen affinity and reduced sickling in RBC collected from SCD patients with either HbSS or HbSC disease. Collectively, these results demonstrate the ability of etavopivat to decrease 2,3-DPG and increase ATP, resulting in increased Hb-oxygen affinity and improved sickle RBC function. Etavopivat is currently being evaluated in clinical trials for the treatment of SCD. ClinicalTrials.gov identifier: NCT03815695 Significance Statement Etavopivat-a small molecule activator of the glycolytic enzyme erythrocyte pyruvate kinase -decreased 2,3-diphosphoglycerate in red blood cells (RBC) from non-human primates and healthy subjects and significantly increased hemoglobin (Hb)-oxygen affinity in healthy subjects. Using ex vivo RBC from donors with sickle cell disease (SCD) (HbSS or HbSC genotype), etavopivat increased Hb-oxygen affinity and reduced sickling under deoxygenation. Etavopivat shows promise as a treatment for SCD, that potentially might reduce vaso-occlusion and improve anemia.

Priming With Red Blood Cells Allows Red Blood Cell Exchange for Sickle Cell Disease in Low-Weight Children

Red blood cell exchanges are frequently used to treat and prevent cerebrovascular complications in patients with sickle cell anemia (SCA). However, the low weight of young children represents serious concerns for this procedure. The Spectra Optia device can perform automatic priming using red blood cells (RBCs) (RCE/RBC-primed) which could allow RBC exchanges (RCE) to be performed in young children without hypovolemic complications, but this method requires evaluation. We prospectively analyzed the clinical safety of the RCE/RBC-primed procedure in 12 SCA low-weight children under either a chronic RCE program or emergency treatment over 65 sessions. We monitored grade 2 adverse events (AEs) such as a decrease in blood pressure, increase in heart rate, fainting sensation, or transfusion reactions and identified the critical times during the sessions in which AEs could occur. Post-apheresis hematocrit (Hct) and a fraction of cell remaining (FCR) values were compared to the expected values. We also compared the impact of automatic RCE (n = 7) vs. RCE/RBC-primed (n = 8) on blood viscosity and RBC rheology. A low incidence of complications was observed in the 65 RCE sessions with only seven episodes of transient grade 2 AEs. Post-apheresis Hct and FCR reached expected values with the RCE/RBC-primed method. Both the automatic and priming procedures improved RBC deformability and decreased the sickling tendency during deoxygenation. Blood rheological features improved in both RCE/RBC-primed and automatic RCE without priming conditions. The RCE/RBC-primed procedure provides blood rheological benefits, and is safe and efficient to treat, notably in young children with SCA in prophylactic programs or curatively when a SCA complication occurs.

Oxygen gradient ektacytometry does not predict pain in children with sickle cell anaemia

The loss of red blood cell (RBC) deformability in sickle cell anaemia (SCA) is considered the primary factor responsible for episodes of acute pain and downstream progressive organ dysfunction. Oxygen gradient ektacytometry (Oxygenscan) is a recently commercialised functional assay that aims to describe the deformability of RBCs in SCA at differing oxygen tensions. So far, the Oxygenscan has been evaluated only by a small number of research groups and the validity and clinical value of Oxygenscan-derived biomarkers have not yet been fully established. In this study we examined RBC deformability measured with the Oxygenscan in 91 children with SCA at King's College Hospital in London. We found a significant correlation between Oxygenscan-derived biomarkers and well-recognised modifiers of disease severity in SCA: haemoglobin F and co-inherited α-thalassaemia. We failed, however, to find any independent predictive value of the Oxygenscan in the clinical outcome measure of pain, as well as other important parameters such as hydroxycarbamide treatment. Although the Oxygenscan remains an intriguing tool for basic research, our results question whether it provides any additional information in predicting the clinical course in children with SCA, beyond measuring known markers of disease severity.

Interleukin-1 receptor antagonism leads to improved anaemia in a murine model of sickle cell disease and is associated with reduced ex vivo platelet-mediated erythrocyte sickling

Sickle cell disease (SCD) is associated with haemolytic anaemia and secondary activation of leucocytes and platelets, which in turn may further exacerbate haemolysis. As cytokine signalling pathways may participate in this cycle, the present study investigated whether pharmacological blockade of the interleukin-1 receptor (IL-1R) would mitigate anaemia in a murine model of SCD. Within 2 weeks of treatment, reduced markers of haemolysis were observed in anakinra-treated mice compared to vehicle-treated mice. After 4 weeks of anakinra treatment, mice showed increased numbers of erythrocytes, haemoglobin, and haematocrit, along with reduced reticulocytes. Blood from anakinra-treated mice was less susceptible to ex vivo erythrocyte sickling and was resistant to exogenous IL-1β-mediated sickling. Supernatant generated from IL-1β-treated platelets was sufficient to promote erythrocyte sickling, an effect not observed with platelet supernatant generated from IL-1R^-/- mice. The sickling effect of IL-1β-treated platelet supernatant was inhibited by a transforming growth factor-β (TGF-β) neutralising antibody, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibition, and superoxide scavengers, but replicated by recombinant TGF-β. In conclusion, pharmacological IL-1R antagonism leads to improved anaemia in a murine SCD model. IL-1β stimulation of platelets promotes erythrocyte sickling. This effect may be mediated by platelet-derived TGF-β-induced reactive oxygen species generation though erythrocyte NADPH oxidase.

Rheological Impact of GBT1118 Cessation in a Sickle Mouse Model

In sickle cell disease (SCD), higher whole blood viscosity is a risk factor for vaso-occlusive crisis, avascular necrosis, and proliferative retinopathy. Blood viscosity is strongly impacted by hemoglobin (Hb) levels and red blood cell (RBC) deformability. Voxelotor is a hemoglobin S (HbS) polymerization inhibitor with anti-sickling properties that increases the Hb affinity for oxygen, thereby reducing HbS polymerization. In clinical trials, voxelotor increased Hb by an average of 1g/dl, creating concern that this rise in Hb could increase viscosity, particularly when the drug was cleared. To investigate this potential rebound hyperviscosity effect, we treated SCD mice with GBT1118, a voxelotor analog, and stopped the treatment to determine the effect on blood viscosity and RBC deformability under a range of oxygen concentrations. GBT1118 treatment increased Hb, improved RBC deformability by increasing the elongation index under normoxic (EImax) and hypoxic conditions (EImin), and decreased the point of sickling (PoS) without increasing blood viscosity. The anti-sickling effects and improvement of RBC deformability balanced the effect of increased Hb such that there was no increase in blood viscosity. Forty-eight hours after ceasing GBT1118, Hb declined from the rise induced by treatment, viscosity did not increase, and EImin remained elevated compared to control animals. Hb and PoS were not different from control animals, suggesting a return to native oxygen affinity and clearance of the drug. RBC deformability did not return to baseline, suggesting some residual rheological improvement. These data suggest that concerns regarding viscosity rise above pre-treatment levels upon sudden cessation of voxelotor are not warranted.

Comparisons of oxygen gradient ektacytometry parameters between sickle cell patients with or without α-thalassaemia

The present study tested the impact of α-thalassaemia on oxygen gradient ektacytometry in sickle cell anaemia (SCA). Three SCA groups were compared: (i) no α-thalassaemia (four α-genes, n = 62), (ii) silent α-thalassaemia (three α-genes, n = 35) and (iii) homozygous α-thalassaemia (two α-genes, n = 12). Red blood cell (RBC) deformability measured in normoxia was not different between the three groups. The lowest RBC deformability reached at low oxygen partial pressure (pO₂ ) was greater and the pO₂ at which RBC started to sickle was lower in the two α-genes group compared to the other groups. Our present study showed an effect of α-thalassaemia on oxygen gradient ektacytometry in SCA.

Methodological aspects of oxygen gradient ektacytometry in sickle cell disease: Effects of sample storage on outcome parameters in distinct patient subgroups

Sickle cell disease (SCD) is a genetic disorder characterized by the production of an abnormal hemoglobin (Hb), which, under deoxygenation, may polymerize and cause a mechanical distortion of red blood cell (RBC) into a crescent-like shape. Recently a method, using ektacytometry principle, has been developed to assess RBC deformability as a function of oxygen tension (pO2) and is called oxygen gradient ektacytometry (oxygenscan). However, standardization of this test is needed to properly assess the tendency of sickling of RBCs under deoxygenation and to allow comparisons between different laboratories. The study compared the oxygenscan responses during blood storage between distinct populations of SCD patients. Blood from 40 non-transfused homozygous SCD patients (HbSS), 16 chronically transfused HbSS patients, and 14 individuals with compound heterozygous hemoglobin SC disease (HbSC) at steady-state was collected in EDTA tubes. Measurements were performed within 4 hours after collection and after 24 hours of storage at 4°C. We showed that storage affected the minimum RBC deformability reached during deoxygenation (EImin) in both non-transfused HbSS and HbSC patients and the maximum RBC deformability (EImax) measured before deoxygenation (i.e., in normoxia) in the three groups. In contrast, the tendency of RBCs to sickle under deoxygenation (i.e., the point of sickling; PoS) remained rather stable between the two time of measurements. Collectively, since the time between blood sampling and analysis affects some key oxygen gradient ektacytometry-derived parameters we recommend that each laboratory performs oxygenscan measurements at a standardized time point.

Advances in neuroimaging to improve care in sickle cell disease

Sickle cell disease is associated with progressive and increased neurological morbidity throughout the lifespan. In people with sickle cell anaemia (the most common and severe type of sickle cell disease), silent cerebral infarcts are found in more than a third of adolescents by age 18 years and roughly half of young adults by age 30 years, many of whom have cognitive impairment despite having few or no conventional stroke risk factors. Common anatomical neuroimaging in individuals with sickle disease can assess structural brain injury, such as stroke and silent cerebral infarcts; however, emerging advanced neuroimaging methods can provide novel insights into the pathophysiology of sickle cell disease, including insights into the cerebral haemodynamic and metabolic contributors of neurological injury. Advanced neuroimaging methods, particularly methods that report on aberrant cerebral blood flow and oxygen delivery, have potential for triaging patients for appropriate disease-modifying or curative therapies before they have irreversible neurological injury, and for confirming the benefit of new therapies on brain health in clinical trials.

Characterizing bulk rigidity of rigid red blood cell populations in sickle-cell disease patients

In this work, we utilized a parameterization model of ektacytometry to quantify the bulk rigidity of the rigid red blood cell (RBC) population in sickle cell disease (SCD) patients. Current ektacytometry techniques implement laser diffraction viscometry to estimate the RBC deformability in a whole blood sample. However, the diffraction measurement is an average of all cells present in the measured sample. By coupling an existing parameterization model of ektacytometry to an artificially rigid RBC model, we formulated an innovative system for estimating the average rigidity of the rigid RBC population in SCD blood. We demonstrated that this method could more accurately determine the bulk stiffness of the rigid RBC populations. This information could potentially help develop the ektacytometry technique as a tool for assessing disease severity in SCD patients, offering novel insights into the disease pathology and treatment.

Effects of Genotypes and Treatment on Oxygenscan Parameters in Sickle Cell Disease

(1) Background: The aim of the present study was to compare oxygen gradient ektacytometry parameters between sickle cell patients of different genotypes (SS, SC, and S/β⁺) or under different treatments (hydroxyurea or chronic red blood cell exchange). (2) Methods: Oxygen gradient ektacytometry was performed in 167 adults and children at steady state. In addition, five SS patients had oxygenscan measurements at steady state and during an acute complication requiring hospitalization. (3) Results: Red blood cell (RBC) deformability upon deoxygenation (EImin) and in normoxia (EImax) was increased, and the susceptibility of RBC to sickle upon deoxygenation was decreased in SC patients when compared to untreated SS patients older than 5 years old. SS patients under chronic red blood cell exchange had higher EImin and EImax and lower susceptibility of RBC to sickle upon deoxygenation compared to untreated SS patients, SS patients younger than 5 years old, and hydroxyurea-treated SS and SC patients. The susceptibility of RBC to sickle upon deoxygenation was increased in the five SS patients during acute complication compared to steady state, although the difference between steady state and acute complication was variable from one patient to another. (4) Conclusions: The present study demonstrates that oxygen gradient ektacytometry parameters are affected by sickle cell disease (SCD) genotype and treatment.

Automated Oxygen Gradient Ektacytometry: A Novel Biomarker in Sickle Cell Anemia

Sickle cell anemia (SCA) is a hereditary hemoglobinopathy with a variable phenotype. There is no single biomarker that adequately predicts disease severity and can be used to monitor treatment response in patients in clinical trials and clinical care. The use of clinical outcomes, such as vaso-occlusive crises (VOC), requires long and expensive studies, sometimes with inconclusive results. To address these limitations, there are several biomarkers under study to improve the ability to predict complications and assess treatment response in both clinical and research settings. Oxygen gradient ektacytometry, also called as oxygenscan, is an assay that measures the effects of deoxygenation and reoxygenation on red blood cell (RBC) deformability and is gaining popularity in SCA research, because it captures the dynamic sickling capacity of a patient’s RBCs as they are subjected to an oxygen gradient under steady shear stress. We describe here the oxygenscan methodology and evaluate the correlation between oxygenscan parameters and more well-known biomarkers of SCA such as fetal hemoglobin (HbF), F-cells, and dense red blood cells (DRBCs). Our data indicate that the oxygenscan curve is affected by all these parameters and the result incorporates the effects of %HbF, %F-cells, RBC hydration, and RBC membrane deformability.

Mixing commonly used crystalloid solutions with red blood cells in five common additives does not negatively impact hemolysis, aggregometry, or deformability

BACKGROUND

Literature is beginning to challenge the belief that it is unsafe to coinfuse red blood cells (RBCs) with solutions other than isotonic saline. We recently showed that additive-free RBCs tolerated coincubation with Plasma-Lyte or catecholamines dissolved in normal saline (NS), though 5% dextrose in water (D5W) promoted hemolysis. Herein, we evaluate the effect of coincubating crystalloids on additive-preserved RBC hemolysis, aggregation, and membrane deformability.

STUDY DESIGN AND METHODS

RBCs were coincubated 5 minutes with plasma, NS, Plasma-Lyte, lactated Ringer's (LR) or D5W (1 mL PRBC +131.3 μL solution). Samples were then assessed for hemolysis (free hemoglobin), aggregation (critical shear stress [mPa]), and membrane deformability (elongation index [EI]). Significance (P ≤ .05) by t test or ANOVA with post-hoc Tukey-Kramer test.

RESULTS

Additive-prepared RBCs coincubated with crystalloid instead of plasma demonstrated: (a) no increase in hemolysis as indicated by plasma free hemoglobin levels that is likely to be clinically relevant; (b) no increase, but in some cases a decrease, in aggregation as indicated by critical shear stress; and (c) in some combinations, a deterioration in deformability. When present, the deformability decrease was likely clinically insignificant in degree, and always returned to normal when the crystalloid was subsequently diluted out with plasma.

CONCLUSION

Our data suggest that additive-prepared RBCs coincubated for 5 minutes with any of four common crystalloids demonstrate no clinically relevant increased lysis, increased aggregation, or decreased deformability.

Inhibition of Band 3 tyrosine phosphorylation: a new mechanism for treatment of sickle cell disease

Many hypotheses have been proposed to explain how a glutamate to valine substitution in sickle haemoglobin (HbS) can cause sickle cell disease (SCD). We propose and document a new mechanism in which elevated tyrosine phosphorylation of Band 3 initiates sequelae that cause vaso-occlusion and the symptoms of SCD. In this mechanism, denaturation of HbS and release of heme generate intracellular oxidants which cause inhibition of erythrocyte tyrosine phosphatases, thus permitting constitutive tyrosine phosphorylation of Band 3. This phosphorylation in turn induces dissociation of the spectrin-actin cytoskeleton from the membrane, leading to membrane weakening, discharge of membrane-derived microparticles (which initiate the coagulation cascade) and release of cell-free HbS (which consumes nitric oxide) and activates the endothelium to express adhesion receptors). These processes promote vaso-occlusive events which cause SCD. We further show that inhibitors of Syk tyrosine kinase block Band 3 tyrosine phosphorylation, prevent release of cell-free Hb, inhibit discharge of membrane-derived microparticles, increase sickle cell deformability, reduce sickle cell adhesion to human endothelial cells, and enhance sickle cell flow through microcapillaries. In view of reports that imatinib (a Syk inhibitor) successfully treats symptoms of sickle cell disease, we suggest that Syk tyrosine kinase inhibitors warrant repurposing as potential treatments for SCD.

Phytocomponents from Anacardium occidentale, Psidium guajava, and Terminalia catappa altered membrane osmotic stability of sickle erythrocytes

Background

The present study identified, quantified, and characterized the combinations of phytocomponents from fractionated leaf extracts of Anacardium occidentale, Psidium guajava, and Terminalia catappa that stabilized sickle erythrocyte membrane against osmotic stress, or otherwise, using standard chromatographic-spectrophotometric techniques, namely GC-MS, FT-IR, and UV-visible systems.

Results

The percentage hemolysis of the control sample, in 0.9 g/100 mL NaCl, was 35.08 ± 11.64%, whereas those of the samples containing 40 mg/100 mL, 60 mg/100 mL, and 80 mg/100 mL of ethylacetate extracts of T. catappa ranged between 31.82 ± 8.32 and 39.18 ± 6.94%. Ethylacetate extract of T. catappa contained comparative high quantities of hexadecanoic acid methyl ester, 9,11-octadecadienoic acid, methyl ester, (E, E)-, trans-13-octadecenoic acid methyl ester, and methyl stearate. FT-IR and UV-visible spectra showed that ethylacetate extract of T. catappa contained aromatic compounds as well as nitro-compounds, phenolics, and esters.

Conclusion

To mention but a few, the combinations of major phytocomponents that stabilized sickle erythrocyte membrane against osmotic stress were hexadecanoic acid, methyl ester, 11-octadecenoic acid, methyl ester, dibutyl phthalate, pentacosane, trans-13-octadecenoic acid, methyl ester, whereas the minor phytocomponents include methyl tetradecanoate, methoxyacetic acid, 3-pentadecyl ester, methyl stearate, hexadecanoic acid, isoxazole, 4,5-dimethyl-.

Blood rheology biomarkers in sickle cell disease

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

Impact statement

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

Rapid and reproducible characterization of sickling during automated deoxygenation in sickle cell disease patients

In sickle cell disease (SCD), sickle hemoglobin (HbS) polymerizes upon deoxygenation, resulting in sickling of red blood cells (RBCs). These sickled RBCs have strongly reduced deformability, leading to vaso‐occlusive crises and chronic hemolytic anemia. To date, there are no reliable laboratory parameters or assays capable of predicting disease severity or monitoring treatment effects. We here report on the oxygenscan, a newly developed method to measure RBC deformability (expressed as Elongation Index ‐ EI) as a function of pO₂. Upon a standardized, 22 minute, automated cycle of deoxygenation (pO₂ median 16 mmHg ± 0.17) and reoxygenation, a number of clinically relevant parameters are produced in a highly reproducible manner (coefficients of variation <5%). In particular, physiological modulators of oxygen affinity, such as, pH and 2,3‐diphosphoglycerate showed a significant correlation (respectively R = ‑0.993 and R = 0.980) with Point of Sickling (PoS_5%), which is defined as the pO₂ where a 5% decrease in EI is observed during deoxygenation. Furthermore, in vitro treatment with antisickling agents, including GBT440, which alter the oxygen affinity of hemoglobin, caused a reproducible left‐shift of the PoS, indicating improved deformability at lower oxygen tensions. When RBCs from 21 SCD patients were analyzed, we observed a significantly higher PoS in untreated homozygous SCD patients compared to treated patients and other genotypes. We conclude that the oxygenscan is a state‐of‐the‐art technique that allows for rapid analysis of sickling behavior in SCD patients. The method is promising for personalized treatment, development of new treatment strategies and could have potential in prediction of complications.