Generation and Export of Red Blood Cell ATP in Health and Disease

Pyruvate Kinase Function Correlates With Red Blood Cell Properties and Clinical Manifestations in Sickle Cell Disease

Pyruvate kinase (PK) is a key enzyme involved in the final step of glycolysis, essential to produce adenosine triphosphate (ATP). Relatively decreased red blood cell (RBC) PK activity (reflected by a lower PK/hexokinase [HK] ratio) and PK thermostability (PK activity after exposure to heat) were recently identified as pathophysiological features of sickle cell disease (SCD). In this study, we investigated whether impaired PK function is associated with sickle RBC properties and SCD-related clinical manifestations. This study included 97 non-transfused patients with SCD (88 HbSS, 9 HbS/β0 thalassemia). PK thermostability was correlated with RBC parameters such as reticulocyte count (r = -0.402, p < 0.0001) and hemoglobin F (r = 0.394, p < 0.0001), and indicators of impaired functional properties of sickle RBCs, such as the point of sickling (r = -0.417, p < 0.0001), oxygen affinity (r = 0.408, p < 0.001) and RBC adhesion to laminin (r = -0.322, p = 0.024). Additionally, a low PK/HK ratio correlated with decreased PK thermostability (r = 0.308, p = 0.002), decreased RBC deformability (r = 0.268, p = 0.009), and elevated 2,3-diphosphoglycerate levels (r = -0.244, p = 0.016). Multivariate Poisson regression analysis demonstrated that reduced PK thermostability and PK/HK ratio were associated with a higher incidence of SCD-related clinical complications. For every 10-unit decrease in PK thermostability and 1-unit decrease in PK/HK ratio, the incidence of SCD-related clinical complications increased by 11% (p = 0.012) and 10% (p = 0.019), respectively. Altogether, these findings indicate that impaired PK function is related to compromised sickle RBC properties and SCD-related clinical manifestations. This supports the relevance and underlines the potential of PK activation therapy.

Targeting sickle cell pathobiology and pain with novel transdermal curcumin

Several comorbidities of sickle cell disease (SCD) originate from red blood cell (RBC) instability, chronic inflammation, and oxidative stress. Development of scalable, cost-effective therapeutics suitable for chronic administration to prevent, attenuate, and perhaps reverse the consequences of RBC instability is needed. Curcumin has many of these attributes as a safe compound with antisickling, antiinflammatory, and antioxidant properties, but its translational potential has been constrained due to limited bioavailability from oral administration. The present study demonstrates the rapid and high bioavailability of a novel topical/transdermal (TD) curcumin gel formulation in the plasma and blood cells and its effectiveness in humanized sickle cell mice in: (i) ameliorating features of sickle cell pain hypersensitivity and axonal injury; (ii) reducing multiple manifestations of RBC instability including evidence of decreased hemolysis (reduced lactate dehydrogenase levels), enhanced RBC ATP levels along with decreased oxidative damage; (iii) decreasing multiple proinflammatory cytokines including interleukin-6, monocyte chemoattractant protein-1, granulocyte-macrophage colony-stimulating factor, and activation, normal T cell expressed and secreted protein in skin secretome; and (iv) reducing mast cell degranulation and activation. Our data suggest that an easy-to-use novel TD curcumin gel formulation has the potential to ameliorate chronic pain, improve RBC stability, and reduce inflammatory consequences of SCD.

Safety and efficacy of mitapivat in sickle cell disease (RISE UP): results from the phase 2 portion of a global, double-blind, randomised, placebo-controlled trial

BACKGROUND

Sickle cell disease, a debilitating, inherited haemolytic anaemia with premature morbidity and mortality, affects millions globally. Mitapivat, a first-in-class, oral, allosteric activator of pyruvate kinase, improves red blood cell survival by increasing ATP and diminishes sickling by decreasing 2,3-diphosphoglycerate. We aimed to evaluate the efficacy and safety of mitapivat in patients with sickle cell disease.

METHODS

We report results from the phase 2, 12-week, double-blind period of RISE UP, a global, phase 2/3, double-blind, randomised, placebo-controlled trial. The phase 2 part of the study was conducted at 32 clinical study sites across 13 countries. Patients aged 16 years or older with a confirmed diagnosis of sickle cell disease (any genotype), baseline haemoglobin of 5·5-10·5 g/dL (inclusive), and two to ten sickle cell pain crises within 12 months before providing informed consent, were randomly assigned 1:1:1 to receive oral mitapivat 50 mg, 100 mg, or placebo twice daily, in this portion of the study which is now complete. Randomisation was performed using a permuted-block method and concealed with an interactive response system; patients, investigators, and individuals assessing outcomes were masked to treatment assignment. Primary efficacy and safety endpoints were haemoglobin response (≥1·0 g/dL increase from baseline in average haemoglobin concentration from week 10 through week 12), and type, severity, and relationship to study drug of adverse and serious adverse events. Efficacy and safety endpoints were evaluated in the full analysis set (all randomly assigned patients) and safety analysis set (all patients who received at least one dose of study drug), respectively. This study is registered with ClinicalTrials.gov as part of an ongoing phase 2/3 study (NCT05031780).

FINDINGS

Between Jan 19, 2022, and April 25, 2023, 79 patients were randomly assigned (51 [65%] female, 28 [35%] male; 46 [58%] Black or African American, 26 [33%] White, five [6%] multiracial, two [3%] Asian); 26 received mitapivat 50 mg, 26 received mitapivat 100 mg, and 27 received placebo, twice daily. Both treatment groups showed a statistically significant haemoglobin response rate versus placebo (12 [46%] of 26 patients in the mitapivat 50 mg group and 13 [50%] of 26 patients in the mitapivat 100 mg group, versus one [4%] of 27 patients in the placebo group; two-sided p=0·0003 and p=0·0001, respectively). Mitapivat was generally well tolerated. Serious adverse events were reported in two (8%) of 26 patients in the mitapivat 50 mg group, four (15%) of 26 patients in the mitapivat 100 mg group, and three (11%) of 27 patients in the placebo group; grade 3 or worse adverse events occurred in three (12%), five (19%), and two (7%) patients, respectively. No serious or grade 3 or worse adverse events were considered treatment related and there were no treatment-related deaths. The most common grade 3 or worse adverse events were infections and infestations, and included one patient in the placebo group with an infected skin ulcer, one patient in the mitapivat 50 mg group with meningitis and one with pelvic inflammatory disease, and one patient each with malaria, pneumonia, and tonsillitis in the mitapivat 100 mg group.

INTERPRETATION

Mitapivat, through its dual effect of increasing ATP and decreasing 2,3-diphosphoglycerate, could provide clinical benefit to patients with sickle cell disease. These results support continued evaluation of mitapivat in the phase 3 portion of the study.

FUNDING

Agios Pharmaceuticals.

Biopreservation and reversal of oxidative injury during blood storage by a novel curcumin-based gel formulation

Blood storage lesion induces cytosolic and membrane changes driven in part by hemoglobin (Hb) oxidation reactions within red blood cells (RBCs). A novel gel formulation containing the antioxidant curcuminoids in a biocompatible solvent system was used to deliver curcumin into RBCs. Incubation of peroxide treated RBCs stored in PBS with curcumin gel led to a reduction in prooxidant ferrylHb and recovery in ATP. Curcumin treatment prevented band 3 tyrosine (Y359 and Y21) phosphorylation. RBCs stored in AS-3 solutions for 28, 35, 42 and 49 days, following a single-dose of 100µM curcuminoids at each time points, caused reduction in protein carbonylation and considerable recovery in ATP levels. Proteomic analysis revealed minimal changes in the proteomic landscape in 35 days. However, a downregulation in fibrinogen was observed in the treated samples which may reduce RBC aggregation. Additionally, we used a guinea pig model where the circulation of infused aged RBCs can be extended (approximately 10%) when treated with curcumin gel at the start of storage. Our data therefore provide mechanistic insights and supportive animal data into benefits of treating stored RBCs with a novel curcuminoid formulation based on the biopreservation of RBC membrane integrity, redox balance, and increased longevity in circulation.

Unraveling Potential Causative Components for the Deleterious Effect of Atmospheric Fine Particulate Matter on Red Blood Cells

Atmospheric fine particulate matter (PM2.5) poses threats to the cardiovascular system. Red blood cells (RBCs) are the most abundant cells in blood, which are actively involved in multiple hematological diseases, such as blood clot formation and thrombosis. Exploring how PM2.5 with spatiotemporal heterogeneity influences the hematological system by targeting RBCs would help gain insights into the deleterious effects of PM2.5 and provide clues for finding the causative components therein. Herein, the PM2.5 samples collected from 3 urban sites in Beijing (i.e., Chaoyang, Shunyi, and Yanqing districts) during 4 seasons of 2022 were studied for their toxicities to mouse RBCs, and the main contributing components were further explored through chemical analysis and correlation measure. The results showed that exposure to PM2.5 samples decreased adenosine triphosphate (ATP) levels and increased phosphatidylserine (PS) externalization of RBCs, causing cell morphological deformity. The Pearson correlation analysis showed that the aromaticity of the dissolved organic matter (DOM) in PM2.5 samples was positively correlated with PS exposure of RBCs, showing that the lignin-like compounds were the potential contributors. The negative correlation of zeta potentials of PM2.5 samples with PS exposure of RBCs showed the particle-derived bioactivities of this airborne pollutant. The simulative test based on artificial nanomaterials of carbon black (CB) and oxidized CB (OCB) confirmed the crucial role of particulate carbon in PM2.5-induced effects on RBCs, and soot with a certain oxidation degree was, thus, recognized as another contributor, given its ubiquitous existence in PM2.5 samples. This study, for the first time, revealed PM2.5-induced PS exposure of RBCs, and the causative components of DOM and soot were unraveled. Considering the inevitable contact of airborne PM2.5 with RBCs in the blood circulatory system, the findings obtained herein would help bridge the gap between PM2.5 exposure and the risk of cardiovascular diseases, like thrombogenesis.

Erythronecroptosis: an overview of necroptosis or programmed necrosis in red blood cells

Necroptosis is considered a programmed necrosis that requires receptor-interacting protein kinase 1 (RIPK1), receptor-interacting protein kinase 3 (RIPK3), and pore-forming mixed lineage kinase domain-like protein (MLKL) to trigger a regulated cell membrane lysis. Membrane rupture in necroptosis has been shown to fuel innate immune response due to release of damage-associated molecular patterns (DAMPs). Recently published studies indicate that mature erythrocytes can undergo necroptosis as well. In this review, we provide an outline of multiple cell death modes occurring in erythrocytes, discuss possible immunological aspects of diverse erythrocyte cell deaths, summarize available evidence related to the ability of erythrocytes to undergo necroptosis, outline key involved molecular mechanisms, and discuss the potential implication of erythrocyte necroptosis in the physiology and pathophysiology. Furthermore, we aim to highlight the interplay between necroptosis and eryptosis signaling in erythrocytes, emphasizing specific characteristics of these pathways distinct from their counterparts in nucleated cells. Thus, our review provides a comprehensive summary of the current knowledge of necroptosis in erythrocytes. To reflect critical differences between necroptosis of nucleated cells and necroptosis of erythrocytes, we suggest a term erythronecroptosis for necroptosis of enucleated cells.

Effects of fermented Crescentia cujete L. on the profile of hematology, clinical chemistry, and circulatory CD4+/CD8+ in Sprague Dawley rats

Background

The calabash (Crescentia cujete L.) is a tropical fruit that offers numerous health benefits. Its fermented calabash (FC) has been found to affect the neurological system positively. However, its impact on hematology, clinical chemistry, and CD4+ and CD8+ levels has yet to be documented.

Aim

Therefore, this study aims to examine the effects of FC on hematology, clinical chemistry, and the levels of CD4+ and CD8+ in the circulatory system using rat models.

Methods

This study used twenty male Sprague Dawley rats. The rats were divided into group 1 (0 mg/kg BW FC), group 2 (50 mg/kg BW FC), group 3 (500 mg/kg BW FC), and group 4 (2,000 mg/kg BW FC). The treatment was administered using a gastric probe once daily for 14 days. On day 15, the blood samples were collected and tested against hematology, clinical chemistry, quality of the erythrocytes, and CD4+/CD8+. The data were then analysed using SPSS with p-value at 0.05.

Results

The conducted study demonstrated that the utilization of FC at varying doses did not have a significant impact on the hematological profile changes (p ≥ 0.05), except for total lymphocytes and a decrease in the neutrophils/lymphocytes (N/L) ratio (p ≤ 0.05). Furthermore, FC did not influence the changes in clinical chemistry, circulatory protein, and electrolyte levels in rat models compared to the control (p ≥ 0.05). The utilization of FC decreased the percentage of hemolysis and elevated the adenosine triphosphate (ATP) concentration (p ≤ 0.05). Additionally, the use of FC led to a significant increase in CD4+ and the ratio of CD4+/CD8+ (p ≤ 0.05), while no significant effect was observed regarding CD8+ (p ≥ 0.05).

Conclusion

The study highlighted FC's beneficial effects on the haemorheology and immune system, specifically on the decrease in the percentage of hemolysis, elevated ATP concentration, number of lymphocytes, ratio N/L, CD4+, and the CD4+/CD8+ ratio, without causing significant changes to the hematological and clinical chemistry profiles in rat models.

Multicenter, phase 1 study of etavopivat (FT-4202) treatment for up to 12 weeks in patients with sickle cell disease

ABSTRACT

Etavopivat is an investigational, once daily, oral, selective erythrocyte pyruvate kinase (PKR) activator. A multicenter, randomized, placebo-controlled, double-blind, 3-part, phase 1 study was conducted to characterize the safety and clinical activity of etavopivat. Thirty-six patients with sickle cell disease (SCD) were enrolled into 4 cohorts: 1 single-dose, 2 multiple ascending doses, and 1 open-label (OL). In the OL cohort, 15 patients (median age 33.0 years [range, 17-55]) received 400 mg etavopivat once daily for 12 weeks; 14 patients completed treatment. Consistent with the mechanism of PKR activation, increases in adenosine triphosphate and decreases in 2,3-diphosphoglycerate were observed and sustained over 12 weeks' treatment. This translated clinically to an increase in hemoglobin (Hb; mean maximal increase 1.6 g/dL [range, 0.8-2.8]), with >1 g/dL increase in 11 (73%) patients during treatment. In addition, the oxygen tension at which Hb is 50% saturated was reduced (P = .0007) with a concomitant shift in point of sickling (P = .0034) to lower oxygen tension in oxygen-gradient ektacytometry. Hemolysis markers (absolute reticulocyte count, indirect bilirubin, and lactate dehydrogenase) decreased from baseline, along with matrix metalloproteinase-9 and erythropoietin. In the OL cohort, adverse events (AEs) were mostly grade 1/2, consistent with underlying SCD; 5 patients had serious AEs. Vaso-occlusive pain episode was the most common treatment-emergent AE (n = 7) in the OL cohort. In this, to our knowledge, the first study of etavopivat in SCD, 400 mg once daily for 12 weeks was well tolerated, resulting in rapid and sustained increases in Hb, improved red blood cell physiology, and decreased hemolysis. This trial was registered at www.ClinicalTrials.gov as #NCT03815695.

Mechanisms Underlying the Effects of Chloroquine on Red Blood Cells Metabolism

Chloroquine (CQ) is a 4-aminoquinoline derivative largely employed in the management of malaria. CQ treatment exploits the drug's ability to cross the erythrocyte membrane, inhibiting heme polymerase in malarial trophozoites. Accumulation of CQ prevents the conversion of heme to hemozoin, causing its toxic buildup, thus blocking the survival of Plasmodium parasites. Recently, it has been reported that CQ is able to exert antiviral properties, mainly against HIV and SARS-CoV-2. This renewed interest in CQ treatment has led to the development of new studies which aim to explore its side effects and long-term outcome. Our study focuses on the effects of CQ in non-parasitized red blood cells (RBCs), investigating hemoglobin (Hb) functionality, the anion exchanger 1 (AE1) or band 3 protein, caspase 3 and protein tyrosine phosphatase 1B (PTP-1B) activity, intra and extracellular ATP levels, and the oxidative state of RBCs. Interestingly, CQ influences the functionality of both Hb and AE1, the main RBC proteins, affecting the properties of Hb oxygen affinity by shifting the conformational structure of the molecule towards the R state. The influence of CQ on AE1 flux leads to a rate variation of anion exchange, which begins at a concentration of 2.5 μM and reaches its maximum effect at 20 µM. Moreover, a significant decrease in intra and extracellular ATP levels was observed in RBCs pre-treated with 10 µM CQ vs. erythrocytes under normal conditions. This effect is related to the PTP-1B activity which is reduced in RBCs incubated with CQ. Despite these metabolic alterations to RBCs caused by exposure to CQ, no signs of variations in oxidative state or caspase 3 activation were recorded. Our results highlight the antithetical effects of CQ on the functionality and metabolism of RBCs, and encourage the development of new research to better understand the multiple potentiality of the drug.

Biopreservation and Reversal of Oxidative Injury During Blood Storage by a Novel Curcumin-based Gel Formulation

Blood storage lesion induces cytosolic and membrane changes driven in part by hemoglobin (Hb) oxidation reactions within red blood cells (RBCs). A novel gel formulation containing the antioxidant curcuminoids in a biocompatible solvent system was used to deliver curcumin into RBCs. Incubation of peroxide treated RBCs stored in PBS with curcumin gel led to a reduction in prooxidant ferrylHb and recovery in ATP. Curcumin treatment prevented band 3 tyrosine (Y359 and Y21) phosphorylation. RBCs stored in AS-3 solutions for 28, 35, 42 and 49 days, following a single-dose of 100μM curcuminoids at each time points, caused reduction in protein carbonylation and considerable recovery in ATP levels. Proteomic analysis revealed minimal changes in the proteomic landscape in 35 days. However, a downregulation in fibrinogen was observed in the treated samples which may reduce RBC aggregation. Additionally, we used a guinea pig model where the circulation of infused aged RBCs can be extended (approximately 10%) when treated with curcumin gel at the start of storage. Our data therefore provide mechanistic insights and supportive animal data into benefits of treating stored RBCs with a novel curcuminoid formulation based on the biopreservation of RBC membrane integrity, redox balance, and increased longevity in circulation.

Recent developments in the use of pyruvate kinase activators as a new approach for treating sickle cell disease

ABSTRACT

Pyruvate kinase (PK) is a key enzyme in glycolysis, the sole source of adenosine triphosphate, which is essential for all energy-dependent activities of red blood cells. Activating PK shows great potential for treating a broad range of hemolytic anemias beyond PK deficiency, because they also enhance activity of wild-type PK. Motivated by observations of sickle-cell complications in sickle-trait individuals with concomitant PK deficiency, activating endogenous PK offers a novel and promising approach for treating patients with sickle-cell disease.

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.

Labile Metabolite Profiling in Human Blood Using Phosphorus NMR Spectroscopy

Phosphorus metabolites occupy a unique place in cellular function as critical intermediates and products of cellular metabolism. Human blood is the most widely used biospecimen in the clinic and in the metabolomics field, and hence an ability to profile phosphorus metabolites in blood, quantitatively, would benefit a wide variety of investigations of cellular functions in health and diseases. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy are the two premier analytical platforms used in the metabolomics field. However, detection and quantitation of phosphorus metabolites by MS can be challenging due to their lability, high polarity, structural isomerism, and interaction with chromatographic columns. The conventionally used 1H NMR, on the other hand, suffers from poor resolution of these compounds. As a remedy, 31P NMR promises an important alternative to both MS and 1H NMR. However, numerous challenges including the instability of phosphorus metabolites, their chemical shift sensitivity to solvent composition, pH, salt, and temperature, and the lack of identified metabolites have so far restricted the scope of 31P NMR. In the current study, we describe a method to analyze nearly 25 phosphorus metabolites in blood using a simple one-dimensional (1D) NMR spectrum. Establishment of the identity of unknown metabolites involved a combination of (a) comprehensively analyzing an array of 1D and two-dimensional (2D) 1H/31P homonuclear and heteronuclear NMR spectra of blood; (b) mapping the central carbon metabolic pathway; (c) developing and using 1H and 31P spectral and chemical shift databases; and finally (d) confirming the putative metabolite peaks with spiking using authentic compounds. The resulting simple 1D 31P NMR-based method offers an ability to visualize and quantify the levels of intermediates and products of multiple metabolic pathways, including central carbon metabolism, in one step. Overall, the findings represent a new dimension for blood metabolite analysis and are anticipated to greatly impact the blood metabolomics field.

Molecular insights into hereditary elliptocytosis and pyropoikilocytosis: NGS uncovers multiple potential candidate genes

Hereditary elliptocytosis (HE) and pyropoikilocytosis (HPP) are considered a group of hemolytic anemias (HE/HPP) due to inherited abnormalities of erythrocyte membrane proteins with a worldwide distribution. Most cases are associated with molecular abnormalities linked to spectrin, band 4.1, and ankyrin. The present study aimed to identify significant molecular signatures on a target panel of 8 genes using whole exome sequencing (WES) in 9 Bahraini patients with elliptocytosis. Case selection was based on presence of anemia not associated with iron deficiency or hemoglobinopathy and demonstrating > 50% elliptocytes in blood smears. The c.779 T > C mutation of SPTA1 (Spectrin alpha), which is a known deleterious missense mutation that inhibits normal association of spectrin molecules to form tetramers, was seen in 4 patients in homozygous (n = 1) and heterozygous (n = 3) states. The αLELY abnormality in association with compound heterozygous mutations in SPTA1 was present in 5 patients (2 associated with the SPTA1 c.779 T > C variant; 3 with c.3487 T > G and various other SPTA1 mutations of uncertain/unknown significance). Seven patients had SPTB (Spectrin beta) mutations, predicted as likely benign by in silico analysis. A novel EPB41 (Erythrocyte Membrane Protein Band 4.1) mutation with potential deleterious impact was also seen. Finally, 2 cases showed an InDel (insertion-deletion mutations) abnormality in the gene that codes for the mechanosensitive ion-channel PIEZO (Piezo Type Mechanosensitive Ion Channel Component 1). PIEZO mutations are reported to cause red cell dehydration but have not been previously described in HE/HPP. Results of this study confirm the involvement of previously reported abnormalities in SPTA1 and suggest possible involvement of other candidate genes in a disorder involving polygenic interactions.

Erythrocyte pyruvate kinase activation in red cell disorders

PURPOSE OF REVIEW

In red cells, pyruvate kinase is a key enzyme in the final step of glycolytic degradative process, which generates a constant energy supply via ATP production. This commentary discusses recent findings on pyruvate kinase activators as new therapeutic option in hereditary red cell disorders such as thalassemic syndromes or sickle cell disease (SCD).

RECENT FINDINGS

Mitapivat and etavopivat are two oral pyruvate kinase activators. Studies in a mouse model for β thalassemia have shown beneficial effects of mitapivat on both red cell survival and ineffective erythropoiesis, with an amelioration of iron homeostasis. This was confirmed in a proof-of-concept study in patients with nontransfusion-dependent thalassemias. Both mitapivat and etavopivat have been evaluated in mouse models for SCD, showing an increased 2-3DPG/ATP ratio and a reduction in haemolysis as well as in sickling. These data were confirmed in proof-of-concept clinical studies with both molecules carried in patients with SCD.

SUMMARY

Preclinical and clinical evidence indicate that pyruvate kinase activators represent new therapeutic option in hemoglobinopathies or SCD. Other red cell disorders such as hereditary spherocytosis or hereditary anaemias characterized by defective erythropoiesis might represent additional areas to investigate the therapeutic impact of pyruvate kinase activators.

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

The role of SH groups in the regulation of Gardos channels in glucose deficiency

   Background. Disruption of the energy balance of erythrocytes under conditions of a decrease in the glycolysis level can cause a change in the ion permeability of their membrane.   The aim. To study Ca2+-dependent potassium permeability of the erythrocytes membrane in the presence of SH group modifiers under conditions of glucose deficiency.   Materials and methods. The study used precipitated erythrocytes obtained from the blood of 20 male Wistar rats. The change in the Ca2+-dependent potassium conductivity of the erythrocyte membrane was determined using the potentiometric method. The A23187-and redox-induced hyperpolarization responses of erythrocytes were evaluated.   Results. Glucose deficiency in the medium, as well as the use of the glycolysis inhibitor 2-deoxyglucose, led to an increase in the amplitude of A23187-stimulated membrane hyperpolarization by the opening of the Gardos channels. At the same time, the redox-dependent hyperpolarization of the erythrocyte membrane turned out to be insensitive to a decrease in the glucose content in the medium and to the glycolysis inhibition. The effects of SH group modifiers in the normal incubation medium and under glucose deficiency turned out to be multidirectional and depended on the method of stimulation of Gardos channels.   Conclusion. The results obtained indicate that metabolic disorders in erythrocytes under conditions of glucose deficiency lead to a change in the mechanisms of control of Gardos channels with the participation of SH groups of the proteins of these channels or their regulatory proteins.

Homeostasis of extracellular ATP in uninfected RBCs from a Plasmodium falciparum culture and derived microparticles

Plasmodium falciparum, a dangerous parasitic agent causing malaria, invades human red blood cells (RBCs), causing hemolysis and microvascular obstruction. These and other pathological processes of malaria patients are due to metabolic and structural changes occurring in uninfected RBCs. In addition, infection activates the production of microparticles (MPs). ATP and byproducts are important extracellular ligands modulating purinergic signaling within the intravascular space. Here, we analyzed the contribution of uninfected RBCs and MPs to the regulation of extracellular ATP (eATP) of RBCs, which depends on the balance between ATP release by specific transporters and eATP hydrolysis by ectonucleotidases. RBCs were cultured with P. falciparum for 24-48 h prior to experiments, from which uninfected RBCs and MPs were purified. On-line luminometry was used to quantify the kinetics of ATP release. Luminometry, colorimetry and radioactive methods were used to assess the rate of eATP hydrolysis by ectonucleotidases. Rates of ATP release and eATP hydrolysis were also evaluated in MPs. Uninfected RBCs challenged by different stimuli displayed a strong and transient activation of ATP release, together with an elevated rate of eATP hydrolysis. MPs contained ATP in their lumen, which was released upon vesicle rupture, and were able to hydrolyze eATP. Results suggest that uninfected RBCs and MPs can act as important determinants of eATP regulation of RBCs during malaria. The comparison of eATP homeostasis in infected RBCs, ui-RBCs, and MPs allowed us to speculate on the impact of P. falciparum infection on intravascular purinergic signaling and the control of the vascular caliber by RBCs.

Evolution of red blood cell membrane complement regulatory proteins and rheology in septic patients: An exploratory study

Background

During sepsis, red blood cell (RBC) deformability is altered. Persistence of these alterations is associated with poor outcome. Activation of the complement system is enhanced during sepsis and RBCs are protected by membrane surface proteins like CD35, CD55 and CD59. In malaria characterized by severe anemia, a study reported links between the modifications of the expression of these RBCs membrane proteins and erythrophagocytosis. We studied the evolution of RBCs deformability and the expression of RBC membrane surface IgG and regulatory proteins in septic patients.

Methods

By flow cytometry technics, we measured at ICU admission and at day 3–5, the RBC membrane expression of IgG and complement proteins (CD35, 55, 59) in septic patients compared to RBCs from healthy volunteers. Results were expressed in percentage of RBCs positive for the protein. RBC shape was assessed using Pearson's second coefficient of dissymmetry (PCD) on the histogram obtained with a flow cytometer technique. A null value represents a perfect spherical shape. RBC deformability was determined using ektacytometry by the elongation index in relation to the shear stress (0.3–50 Pa) applied to the RBC membrane. A higher elongation index indicates greater RBC deformability.

Results

RBCs from 11 septic patients were compared to RBCs from 21 volunteers. At ICU admission, RBCs from septic patients were significantly more spherical and RBC deformability was significantly lower in septic patients for all shear stress ≥1.93 Pa. These alterations of shape and deformability persists at day 3–5. We observed a significant decrease at ICU admission only in CD35 expression on RBCs from septic patients. This low expression remained at day 3–5.

Conclusions

We observed in RBCs from septic patients a rapid decrease expression of CD35 membrane protein protecting against complement activation. These modifications associated with altered RBC deformability and shape could facilitate erythrophagocytosis, contributing to anemia observed in sepsis. Other studies with a large number of patients and assessment of erythrophagocytosis were needed to confirm these preliminary data.

Phosphorus metabolism disorders in erythrocytes and lymphocytes among patients with inflammatory breast cancer, infiltrative stomach and colorectal cancer

Energy and plastic potential dysfunction of erythrocytes and lymphocytes among people with inflammatory breast cancer, infiltrative stomach cancer, and infiltrative colon cancer is characterized by a more aggressive clinical course and poor prognosis. We explored the features of energy metabolism and phosphorus metabolism disorders in the erythrocytes and lymphocytes of patients with inflammatory breast cancer, infiltrative stomach cancer, and infiltrative colon cancer as a predicting factor in the course of the disease. 49 people were examined; the 1^st group had infiltrative stomach cancer (n=17); the 2^nd group had infiltrative colon cancer (n=11); the 3^rd group had inflammatory breast cancer (n=21). Glycerol-3-phosphate dehydrogenase activity was 1.8 times reduced (p≤0.005), and the activity of glyceraldehyde-3-phosphate dehydrogenase in erythrocytes of patients with cancer at the main localization increased 2.5 times, compared with normal. Inflammatory breast cancer patients had a statistically significant decrease (p<0.005) in erythrocytes adenosine triphosphate content by an average of 56.5% compared with the normal ratio, and in cases of patients with gastric and colorectal cancer, a decrease of 67%. Excessive use of phosphorus for energy metabolism and adenosine triphosphate production destroys the balance of energetic and plastic potentials of erythrocytes and lymphocytes in inflammatory breast cancer, infiltrative stomach, and infiltrative colorectal cancers patients.