Oxidative Stress-Induced Membrane Shedding from RBCs is Ca Flux-Mediated and Affects Membrane Lipid Composition

What Should Be Responsible for Eryptosis in Chronic Kidney Disease?

BACKGROUND

Renal anemia is an important complication of chronic kidney disease (CKD). In addition to insufficient secretion of erythropoietin (EPO) and erythropoiesis disorders, the impact of eryptosis on renal anemia demands attention. However, a systemic analysis concerning the pathophysiology of eryptosis has not been expounded.

SUMMARY

The complicated conditions in CKD patients, including oxidative stress, osmotic stress, metabolic stress, accumulation of uremic toxins, and iron deficiency, affect the normal skeleton structure of red blood cells (RBCs) and disturbs ionic homeostasis, causing phosphatidylserine to translocate to the outer lobules of the RBC membrane that leads to early elimination and/or shortening of the RBC lifespan. Inadequate synthesis of RBCs cannot compensate for their accelerated destruction, thus exacerbating renal anemia. Meanwhile, EPO treatment alone will not reverse renal anemia. A variety of eryptosis inhibitors have so far been found, but evidence of their effectiveness in the treatment of CKD remains to be established.

KEY MESSAGES

In this review, the pathophysiological processes and factors influencing eryptosis in CKD were elucidated. The aim of this review was to underline the importance of eryptosis in renal anemia and determine some promising research directions or possible therapeutic targets to correct anemia in CKD.

Intertwined associations between oxidative and nitrosative stress and endocannabinoid system pathways: Relevance for neuropsychiatric disorders

The endocannabinoid system (ECS) appears to regulate metabolic, cardiovascular, immune, gastrointestinal, lung, and reproductive system functions, as well as the central nervous system. There is also evidence that neuropsychiatric disorders are associated with ECS abnormalities as well as oxidative and nitrosative stress pathways. The goal of this mechanistic review is to investigate the mechanisms underlying the ECS's regulation of redox signalling, as well as the mechanisms by which activated oxidative and nitrosative stress pathways may impair ECS-mediated signalling. Cannabinoid receptor (CB)1 activation and upregulation of brain CB2 receptors reduce oxidative stress in the brain, resulting in less tissue damage and less neuroinflammation. Chronically high levels of oxidative stress may impair CB1 and CB2 receptor activity. CB1 activation in peripheral cells increases nitrosative stress and inducible nitric oxide (iNOS) activity, reducing mitochondrial activity. Upregulation of CB2 in the peripheral and central nervous systems may reduce iNOS, nitrosative stress, and neuroinflammation. Nitrosative stress may have an impact on CB1 and CB2-mediated signalling. Peripheral immune activation, which frequently occurs in response to nitro-oxidative stress, may result in increased expression of CB2 receptors on T and B lymphocytes, dendritic cells, and macrophages, reducing the production of inflammatory products and limiting the duration and intensity of the immune and oxidative stress response. In conclusion, high levels of oxidative and nitrosative stress may compromise or even abolish ECS-mediated redox pathway regulation. Future research in neuropsychiatric disorders like mood disorders and deficit schizophrenia should explore abnormalities in these intertwined signalling pathways.

Sickle cell vaso-occlusion: The dialectic between red cells and white cells

The pathophysiology of sickle cell anemia, a hereditary hemoglobinopathy, has fascinated clinicians and scientists alike since its description over 100 years ago. A single gene mutation in the HBB gene results in the production of abnormal hemoglobin (Hb) S, whose polymerization when deoxygenated alters the physiochemical properties of red blood cells, in turn triggering pan-cellular activation and pathological mechanisms that include hemolysis, vaso-occlusion, and ischemia-reperfusion to result in the varied and severe complications of the disease. Now widely regarded as an inflammatory disease, in recent years attention has included the role of leukocytes in vaso-occlusive processes in view of the part that these cells play in innate immune processes, their inherent ability to adhere to the endothelium when activated, and their sheer physical and potentially obstructive size. Here, we consider the role of sickle red blood cell populations in elucidating the importance of adhesion vis-a-vis polymerization in vaso-occlusion, review the direct adhesion of sickle red cells to the endothelium in vaso-occlusive processes, and discuss how red cell- and leukocyte-centered mechanisms are not mutually exclusive. Given the initial clinical success of crizanlizumab, a specific anti-P selectin therapy, we suggest that it is appropriate to take a holistic approach to understanding and exploring the complexity of vaso-occlusive mechanisms and the adhesive roles of the varied cell types, including endothelial cells, platelets, leukocytes, and red blood cells.

The Redox Balance and Membrane Shedding in RBC Production, Maturation, and Senescence

Membrane shedding in the form of extracellular vesicles plays a key role in normal physiology and pathology. Partial disturbance of the membrane-cytoskeleton linkage and increased in the intracellular Ca content are considered to be mechanisms underlying the process, but it is questionable whether they constitute the primary initiating steps. Homeostasis of the redox system, which depends on the equilibrium between oxidants and antioxidants, is crucial for many cellular processes. Excess oxidative power results in oxidative stress, which affects many cellular components, including the membrane. Accumulating evidence suggests that oxidative stress indirectly affects membrane shedding most probably by affecting the membrane-cytoskeleton and the Ca content. In red blood cells (RBCs), changes in both the redox system and membrane shedding occur throughout their life-from birth-their production in the bone marrow, to death-aging in the peripheral blood and removal by macrophages in sites of the reticuloendothelial system. Both oxidative stress and membrane shedding are disturbed in diseases affecting the RBC, such as the hereditary and acquired hemolytic anemias (i.e., thalassemia, sickle cell anemia, and autoimmune hemolytic anemia). Herein, I review some data-based and hypothetical possibilities that await experimental confirmation regarding some aspects of the interaction between the redox system and membrane shedding and its role in the normal physiology and pathology of RBCs.

Oxidative stress, eryptosis and anemia: a pivotal mechanistic nexus in systemic diseases

The average lifespan of circulating erythrocytes usually exceeds hundred days. Prior to that, however, erythrocytes may be exposed to oxidative stress in the circulation which could cause injury and trigger their suicidal death or eryptosis. Oxidative stress activates Ca²⁺ -permeable nonselective cation channels in the cell membrane, thus, stimulating Ca²⁺ entry and subsequent cell membrane scrambling resulting in phosphatidylserine exposure and activation of Ca²⁺ -sensitive K⁺ channels leading to K⁺ exit, hyperpolarization, Cl^- exit, and ultimately cell shrinkage due to loss of KCl and osmotically driven water. While the mechanistic link between oxidative stress and anemia remains ill-defined, several diseases such as diabetes, hepatic failure, malignancy, chronic kidney disease and inflammation have been identified to display both increased oxidative stress as well as eryptosis. Recent compelling evidence suggests that oxidative stress is an important perpetrator in accelerating erythrocyte loss in different systemic conditions and an underlying mechanism for anemia associated with these pathological states. In the present review, we discuss the role of oxidative stress in reducing erythrocyte survival and provide novel insights into the possible use of antioxidants as putative antieryptotic and antianemic agents in a variety of systemic diseases.

Epoetin beta pegol for treatment of anemia ameliorates deterioration of erythrocyte quality associated with chronic kidney disease

Background

Epoetin beta pegol (continuous erythropoietin receptor activator; C.E.R.A.) is currently widely used for the treatment of anemia associated with chronic kidney disease (CKD). Therapeutic control of anemia is assessed by monitoring haemoglobin (Hb) levels. However, certain qualitative aspects of erythrocytes are also impaired in CKD, including loss of deformability and shortened life-span. Therefore, monitoring Hb alone could potentially fail to reveal pathological changes in erythrocytes. Focusing on erythrocyte quality in CKD may lead to more effective anemia therapy with C.E.R.A.

Methods

A CKD rat model was induced by uninephrectomy followed by anti-Thy1.1 antibody injection. From 5 weeks after the operation, C.E.R.A. (0.6 μg/kg) or vehicle was administered every 2 weeks. Erythrocyte deformability was quantified with ektacytometry and erythrocyte turnover was estimated by biotin labeling. Intracellular calcium level was assessed by Fluo-3/AM.

Results

Erythrocyte deformability progressively declined in CKD rats. Furthermore, erythrocyte turnover in the circulation drastically accelerated in CKD rats. With administration of C.E.R.A. at a dose sufficient to adequately control Hb, deterioration of erythrocyte deformability and turnover in CKD rats were significantly improved. Intracellular calcium, which plays a pivotal role in the mediation of erythrocyte quality, was significantly increased in CKD and was normalized by C.E.R.A. treatment.

Conclusion

C.E.R.A. treatment exerted a favorable effect not only on anemia but also on the improvement of erythrocyte quality. C.E.R.A. administered for the treatment of CKD-associated anemia may confer therapeutic benefits on erythrocytes.

Impaired embryonic development in glucose-6-phosphate dehydrogenase-deficient Caenorhabditis elegans due to abnormal redox homeostasis induced activation of calcium-independent phospholipase and alteration of glycerophospholipid metabolism

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a commonly pervasive inherited disease in many parts of the world. The complete lack of G6PD activity in a mouse model causes embryonic lethality. The G6PD-deficient Caenorhabditis elegans model also shows embryonic death as indicated by a severe hatching defect. Although increased oxidative stress has been implicated in both cases as the underlying cause, the exact mechanism has not been clearly delineated. In this study with C. elegans, membrane-associated defects, including enhanced permeability, defective polarity and cytokinesis, were found in G6PD-deficient embryos. The membrane-associated abnormalities were accompanied by impaired eggshell structure as evidenced by a transmission electron microscopic study. Such loss of membrane structural integrity was associated with abnormal lipid composition as lipidomic analysis revealed that lysoglycerophospholipids were significantly increased in G6PD-deficient embryos. Abnormal glycerophospholipid metabolism leading to defective embryonic development could be attributed to the increased activity of calcium-independent phospholipase A₂ (iPLA) in G6PD-deficient embryos. This notion is further supported by the fact that the suppression of multiple iPLAs by genetic manipulation partially rescued the embryonic defects in G6PD-deficient embryos. In addition, G6PD deficiency induced disruption of redox balance as manifested by diminished NADPH and elevated lipid peroxidation in embryos. Taken together, disrupted lipid metabolism due to abnormal redox homeostasis is a major factor contributing to abnormal embryonic development in G6PD-deficient C. elegans.

Cell-derived microparticles after exercise in individuals with G6PD Viangchan

Glucose-6-phospate dehydrogenase (G6PD) deficient cells are sensitive to oxidative damage leading to the formation of microparticles (MPs). Therefore, we examined the concentration of MPs and changes in the antioxidant balance after an acute strenuous exercise (SEx) and moderate-intensity exercise (MEx). Eighteen healthy females (18-24 years) with G6PD normal and eighteen age-matched females with G6PD Viangchan (871G>A) were tested by running on a treadmill at their maximal oxygen uptake for SEx and at 75% of their maximal heart rate for MEx. It was found that SEx triggered the release of total microparticles (TTMPs) above baseline levels and remained significantly higher 45 minutes after the exercise in G6PD normal individuals. However, SEx-induced increase in TTMPs was significantly higher in G6PD Viangchan as compared to G6PD normal. In contrast, MEx did not to alter the release of TTMPs in both G6PD normal and Viangchan. Moreover, TTMPs concentrations were inversely correlated with G6PD activity (r =-0.82, P <  0.05) but positively correlated with MDA concentrations (r = 0.74, P <  0.05). Using cell specific antibodies, we determined that MPs were mainly derived from platelets and erythrocytes. Altogether, the present study indicates that G6PD Viangchan may participate in MEx without higher MPs concentration and oxidative stress compared with G6PD normal.

Quercetin-modulated erythrocyte membrane sodium-hydrogen exchanger during human aging: correlation with ATPase's

CONTENT

Quercetin uptake by erythrocytes is rapid. The sodium-hydrogen exchanger (NHE) is a secondary active transporter, regulating intracellular pH, Na(+) concentration and cell volume.

OBJECTIVE

The aim of present study was to investigate NHE as a function of human age and effect of quercetin on its activity. The NHE activity was correlated with erythrocytes ATPases.

MATERIALS AND METHODS

We analyzed normal, healthy subjects of both sexes (20-82 years). NHE activity was estimated in terms of amiloride-sensitive H+-efflux from acid-loaded cells.

RESULTS

A significant age-dependent increase in NHE activity was observed during aging in humans. Concentration (10(-3 )M to 10(-8 )M)-dependent in vitro treatment with quercetin causes inhibition of NHE activity. The Na(+)/K(+) -ATPase (r = 0.8882) and Ca(2+)-ATPase (r = 0.9540) activities positively correlated with it.

DISCUSSION AND CONCLUSION

The present data show an additional mechanism where dietary flavonoids may exerts beneficial effect during aging.

Oxidative stress in paroxysmal nocturnal hemoglobinuria and other conditions of complement-mediated hemolysis

The complement (C') system and redox status play important roles in the physiological functioning of the body, such as the defense system, but they are also involved in various pathological conditions, including hemolytic anemia. Herein, we review the interaction between the C' and the redox systems in C'-mediated hemolytic anemias, paroxysmal nocturnal hemoglobinuria (PNH) and autoimmune hemolytic anemia, including acute hemolytic transfusion reaction. Blood cells in these diseases have been shown to have increased oxidative status, which was further elevated by interaction with activated C'. The results suggest that oxidative stress, in conjunction with activated C', may cause the underlying symptoms of these diseases, such as intra- and extravascular hemolysis and thrombotic complications. Antioxidants ameliorate oxidative stress by preventing generation of free radicals, by scavenging and preventing their accumulation, and by correcting their cellular damage. Antioxidants have been shown to reduce the oxidative stress and inhibit hemolysis as well as platelet activation mediated by activated C'. This raises the possibility that treatment with antioxidants might be considered as a potential therapeutic modality for C'-mediated hemolytic anemias. Currently, eculizumab, a humanized monoclonal antibody that specifically targets the C' protein C5, is the main treatment modality for PNH. However, because antioxidants are well tolerated and relatively inexpensive, they might be considered as potential adjuvants or an alternative therapeutic modality for PNH and other C'-mediated hemolytic anemias.

Intra-Colonial Functional Differentiation-Related Modulation of the Cellular Membrane in a Pocilloporid Coral Seriatopora caliendrum

Scleractinian corals have displayed phenotypic gradients of polyps within a single genotypic colony, and this has profound implications for their biology. The intrinsic polymorphism of membrane lipids and the molecular interactions involved allow cells to dynamically organize their membranes to have physicochemical properties appropriate for their physiological requirements. To gain insight into the accommodation of the cellular membrane during ontogenetic shifts, intra-colony differences in the glycerophosphocholine profiling of a pocilloporid coral, Seriatopora caliendrum, were characterized using a previously validated method. Specifically, several major polyunsaturated phosphatidylcholines showed higher levels in the distal tissue of coral branches. In contrast, the corresponding molecules with 1-2-degree less unsaturation and plasmanylcholines were expressed more highly in the proximal tissue. The lipid profiles of these two colonial positions also contrasted sharply with regard to the saturated, monounsaturated, and lyso-glycerophosphocholine ratios. Based on the biochemical and biophysical properties of these lipids, the associated modulation of cellular membrane properties could be related to the physiological requirements, including coral growth and aging, of the functionally differentiated polyps. In this study, the metabolic regulation of membrane lipids involved in the functional differentiation of polyps within a S. caliendrum colony was identified.

The Deleterious Effects of Oxidative and Nitrosative Stress on Palmitoylation, Membrane Lipid Rafts and Lipid-Based Cellular Signalling: New Drug Targets in Neuroimmune Disorders

Oxidative and nitrosative stress (O&NS) is causatively implicated in the pathogenesis of Alzheimer's and Parkinson's disease, multiple sclerosis, chronic fatigue syndrome, schizophrenia and depression. Many of the consequences stemming from O&NS, including damage to proteins, lipids and DNA, are well known, whereas the effects of O&NS on lipoprotein-based cellular signalling involving palmitoylation and plasma membrane lipid rafts are less well documented. The aim of this narrative review is to discuss the mechanisms involved in lipid-based signalling, including palmitoylation, membrane/lipid raft (MLR) and n-3 polyunsaturated fatty acid (PUFA) functions, the effects of O&NS processes on these processes and their role in the abovementioned diseases. S-palmitoylation is a post-translational modification, which regulates protein trafficking and association with the plasma membrane, protein subcellular location and functions. Palmitoylation and MRLs play a key role in neuronal functions, including glutamatergic neurotransmission, and immune-inflammatory responses. Palmitoylation, MLRs and n-3 PUFAs are vulnerable to the corruptive effects of O&NS. Chronic O&NS inhibits palmitoylation and causes profound changes in lipid membrane composition, e.g. n-3 PUFA depletion, increased membrane permeability and reduced fluidity, which together lead to disorders in intracellular signal transduction, receptor dysfunction and increased neurotoxicity. Disruption of lipid-based signalling is a source of the neuroimmune disorders involved in the pathophysiology of the abovementioned diseases. n-3 PUFA supplementation is a rational therapeutic approach targeting disruptions in lipid-based signalling.

Differences in Rat and Human Erythrocytes Following Blood Component Manufacturing: The Effect of Additive Solutions

BACKGROUND

Small animal models have been previously used in transfusion medicine studies to evaluate the safety of blood transfusion products. Although there are multiple studies on the effects of blood banking practices on human red blood cells (RBCs), little is known about the effect of blood component manufacturing on the quality of rat RBCs.

METHODS

Blood from Sprague-Dawley rats and human volunteers (n = 6) was collected in CPD anticoagulant, resuspended in SAGM or AS3, and leukoreduced. In vitro quality was analyzed, including deformability, aggregation, microvesiculation, phosphatidylserine (PS) expression, percent hemolysis, ATP, 2,3-DPG, osmotic fragility, and potassium concentrations.

RESULTS

Compared to human RBCs, rat RBCs had decreased deformability, membrane rigidity, aggregability, and microvesiculation after component manufacturing process. Rat RBCs in SAGM showed higher hemolysis compared to human RBCs in SAGM (rat 4.70 ± 0.83% vs. human 0.34 ± 0.07%; p = 0.002). Rat RBCs in AS3 had greater deformability and rigidity than in SAGM. The number of microparticles/µl and the percentage PS expression were lower in rat RBCs in AS3 than in rat RBCs in SAGM. Hemolysis was also significantly lower in AS3 compared to SAGM (2.21 ± 0.68% vs. 0.87 ± 0.39%; p = 0.028).

CONCLUSION

Rat RBCs significantly differ from human RBCs in metabolic and membrane-related aspects. SAGM, which is commonly used for human RBC banking, causes high hemolysis and is not compatible with rat RBCs.

A mouse model to study thrombotic complications of thalassemia

Patients with β-thalassemia major and mainly intermedia have an increased risk for developing venous and arterial thrombosis which may be related to circulating pathological red blood cells (RBC) and continuous platelet activation. In the present study we used a modified thalassemic mice model in conjunction with a "real-time" carotid thrombus formation procedure to investigate thrombotic complications of thalassemia. Heterozygous Th3/+ mice, which lack one copy of their β-major and β-minor globin genes, exhibit anomalies in RBC size and shape, chronic anemia and splenomegaly which recapitulate the phenotype of human β-thalassemia intermedia. Flow cytometry measurements showed higher reactive oxygen species generation, indicating oxidative stress, in platelets and RBC of the thalassemic mice compared with wild type mice concomitant with an increase in reduced glutathione content which may represent a compensatory response to oxidative stress, and exposed phosphatidylserine which indicates platelet activation. To elucidate the effect of thalassemia on the development of arterial thrombosis, we studied photochemical-induced real-time thrombus formation in the carotid artery of these mice. The results indicated a significantly shorter "time to occlusion" in the thalassemic mice compared to wild type mice, which was prolonged following in vivo aspirin treatment. We suggest that this mouse model may contribute to our understanding of platelet activation and the hypercoagulable state in thalassemia and lay foundations to screening of anti-platelet drugs as well as anti-oxidants as possible therapeutics for prevention of thrombosis in thalassemia patients.

Eryptosis in lead-exposed workers

Eryptosis is a physiological phenomenon in which old and damaged erythrocytes are removed from circulation. Erythrocytes incubated with lead have exhibited major eryptosis. In the present work we found evidence of high levels of eryptosis in lead exposed workers possibly via oxidation. Blood samples were taken from 40 male workers exposed to lead (mean blood lead concentration 64.8μg/dl) and non-exposed workers (4.2μg/dl). The exposure to lead produced an intoxication characterized by 88.3% less δ-aminolevulinic acid dehydratase (δALAD) activity in lead exposed workers with respect to non-lead exposed workers. An increment of oxidation in lead exposed workers was characterized by 2.4 times higher thiobarbituric acid-reactive substance (TBARS) concentration and 32.8% lower reduced/oxidized glutathione (GSH/GSSG) ratio. Oxidative stress in erythrocytes of lead exposed workers is expressed in 192% higher free calcium concentration [Ca(2+)]i and 1.6 times higher μ-calpain activity with respect to non-lead exposed workers. The adenosine triphosphate (ATP) concentration was not significantly different between the two worker groups. No externalization of phosphatidylserine (PS) was found in non-lead exposed workers (<0.1%), but lead exposed workers showed 2.82% externalization. Lead intoxication induces eryptosis possibly through a molecular pathway that includes oxidation, depletion of reduced glutathione (GSH), increment of [Ca(2+)], μ-calpain activation and externalization of PS in erythrocytes. Identifying molecular signals that induce eryptosis in lead intoxication is necessary to understand its physiopathology and chronic complications.

The osmotic resistance, and zeta potential responses of human erythrocytes to transmembrane modification of Ca2+ fluxes in the presence of the imposed low rate radiation field of 90Sr

PURPOSE

To investigate the effects of the imposed low dose rate ionizing field on membrane stability of human erythrocytes under modulation of transmembrane exchange of Ca(2+).

MATERIALS AND METHODS

Osmotic resistance of human erythrocytes was determined by a measure of haemoglobin released from erythrocytes when placed in a medium containing serial dilutions of Krebs isotonic buffer. The zeta potential as indicator of surface membrane potential was calculated from value of the cellular electrophoretic mobility. The irradiation of erythrocyte suspensions carried out by applying suitable aliquots of (90)Sr in incubation media.

RESULTS

Irradiation of human erythrocytes by (90)Sr (1.5-15.0 μGy·h(-1)) induced a reversible increase of hyposmotic hemolysis and negative charge value on the outer membrane surface as well as changed responses these parameters to modification of Ca(2+) fluxes with calcimycin and nitrendipine.

CONCLUSIONS

Findings indicate that the low dose rate radionuclides ((90)Sr) field modifies both Ca(2+)-mediated, and Ca(2+)-independent cellular signalling regulating mechanical stability of erythrocyte membrane. A direction of that modification presumably depends on the initial structure of membranes, and it is determined by the quality and quantitative parameters of changes in membrane structure caused by concrete operable factors.

Does erythropoietin have a role in the treatment of β-hemoglobinopathies?

This review presents the indications and contraindications (pros and cons) for the potential use of erythropoietin (Epo) as a treatment in β-thalassemia and sickle cell anemia (SCA). Its high cost and route of administration (by injection) are obvious obstacles, especially in underdeveloped countries, where thalassemia is prevalent. We believe that from the data summarized in this review, the time has come to define, by studying in vitro and in vivo models, as well as by controlled clinical trials, the rationale for treating patients with various forms of thalassemia and SCA with Epo alone or in combination with other medications.

Effect of sweet grass (Hierochloe odorata) on the physico-chemical properties of liver cell membranes from rats intoxicated with ethanol

Changes in the composition and physicochemical properties of liver cell membranes due to ethanol intoxication are due mainly to reactive oxygen species (ROS). The destructive action of free radicals can be neutralized by administration of antioxidants. The purpose of this study was to investigate the efficacy of sweet grass on the physicochemical and biochemical properties of the rat liver membrane altered by chronic ethanol intoxication. Qualitative and quantitative composition of phospholipids and proteins in the membrane were determined by HPLC. Ethanol increased phospholipid levels and altered the level of integral proteins as determined by decreased phenylalanine, cysteine and lysine. Ethanol significantly enhanced changes in the surface charge density of the liver cell membranes as determined by electrophoresis. Administration of sweet grass to rats intoxicated with ethanol significantly protects lipids and proteins against oxidative modifications. Therefore, sweet grass protects against some of the deleterious membrane changes associated with ethanol exposure.

Ascorbic acid improves membrane fragility and decreases haemolysis during red blood cell storage

BACKGROUND

Changes that occur to red blood cells (RBCs) during routine blood bank storage include decreased deformability, increased haemolysis and oxidative damage. Oxidative injury to the RBC membrane and haemoglobin can affect changes in shape and deformability. Ascorbic acid (AA) is an antioxidant that maintains haemoglobin in a reduced state and minimises RBC oxidative injury. We hypothesised that AA would improve membrane fragility and decrease haemolysis during storage.

METHODS

Whole blood derived, AS-5 preserved, pre-storage leucoreduced RBC units were exposed to either AA or saline control solutions. Several rheological and biochemical parameters were measured serially during storage, including RBC membrane mechanical fragility, percent haemolysis and methaemoglobin levels.

RESULTS

AA exposure significantly reduced mechanical fragility and haemolysis over the entire storage period. The highest two concentrations of AA affected the greatest reductions in mechanical fragility and percent haemolysis. Addition of AA to the RBCs did not significantly alter their biochemical parameters compared to control RBCs incubated with saline.

CONCLUSION

AA reduced RBC membrane fragility and decreased haemolysis during storage without adversely affecting other RBC biochemical parameters. The clinical significance of these findings needs to be determined.

Protection against oxidative stress in beta thalassemia/hemoglobin E erythrocytes by inhibitors of glutathione efflux transporters

In beta thalassemia/hemoglobin E (Hb E), abnormally high levels of oxidative stress account for accelerated senescence and increased destruction of erythrocytes. The present study aimed to investigate the role of glutathione efflux transporters, namely cystic fibrosis transmembrane conductance regulator (CFTR) and multidrug resistance-associated protein 1 (MRP1), in the control of glutathione levels and protection against oxidative challenges in beta thalassemia/Hb E erythrocytes. We found that CFTR protein was expressed in the erythrocytes of beta thalassemia/Hb E patients. Treatments with GlyH-101 (50 µM), a small molecule CFTR inhibitor, and MK571 (50 µM), an MRP1 inhibitor, reduced H₂O₂-induced free radical generation in the erythrocytes by ∼80% and 50%, respectively. Furthermore, combined treatment with GlyH-101 and MK571 completely abolished the induction of reactive oxygen radicals. Increased oxidative stress in the erythrocytes following H₂O₂ challenges was accompanied by a decrease in intracellular level of reduced glutathione (GSH), which was prevented by treatments with GlyH-101 and MK571. CMFDA-based assays revealed that GlyH-101 and MK571 reduced H₂O₂-induced glutathione efflux from the erythrocytes by 87% and 66%, respectively. Interestingly, H₂O₂-induced osmotic tolerance of erythrocytes, a sign of erythrocyte aging, was ameliorated by treatment with GlyH-101. Our study indicates that oxidative stress induces glutathione efflux via CFTR and MRP1 in beta thalassemia/Hb E erythrocytes. Pharmacological inhibition of glutathione efflux represents a potential therapy to delay aging and premature destruction of erythrocytes in beta thalassemia/Hb E.

Shedding of phosphatidylserine from developing erythroid cells involves microtubule depolymerization and affects membrane lipid composition

Phosphatidylserine (PS), which is normally localized in the cytoplasmic leaflet of the membrane, flip-flops to the external leaflet during aging of, or trauma to, cells. A fraction of this PS undergoes shedding into the extracellular milieu. PS externalization and shedding change during maturation of erythroid cells and affect the functioning, senescence and elimination of mature RBCs. Several lines of evidence suggest dependence of PS shedding on intracellular Ca concentration as well as on interaction between plasma membrane phospholipids and microtubules (MTs), the key components of the cytoskeleton. We investigated the effect of Ca flux and MT assembly on the distribution of PS across, and shedding from, the membranes of erythroid precursors. Cultured human and murine erythroid precursors were treated with the Ca ionophore A23187, the MT assembly enhancer paclitaxel (Taxol) or the inhibitor colchicine. PS externalization and shedding were measured by flow cytometry and the cholesterol/phospholipids in RBC membranes and supernatants, by ¹H-NMR. We found that treatment with Taxol or colchicine resulted in a marked increase in PS externalization, while shedding was increased by colchicine but inhibited by Taxol. These results indicate that PS externalization is mediated by Ca flux, and PS shedding by both Ca flux and MT assembly. The cholesterol/phospholipid ratio in the membrane is modified by PS shedding; we now show that it was increased by colchicine and A23187, while taxol had no effect. In summary, the results indicate that the Ca flux and MT depolymerization of erythroid precursors mediate their PS externalization and shedding, which in turn changes their membrane composition.

Distribution and shedding of the membrane phosphatidylserine during maturation and aging of erythroid cells

Maturation and aging of erythroid cells are accompanied by extensive remodeling of the membrane and a marked decrease in cell size, processes that are mediated by externalization and shedding of phosphatidylserine (PS). In the present study, we investigated the redistribution of PS in the plasma membrane of erythroid precursors during their maturation and of mature RBCs during senescence, and the involvement of changes in calcium (Ca)-flux in these processes. Maturation was studied by analyzing normal human bone marrow cells as well as cultured human normal erythroid precursors induced by erythropoietin and murine erythroleukemia cells induced by hexamethylene-bisacetamide. Senescence was studied in normal human peripheral RBCs following density fractionation. PS and Ca were determined by flow cytometry using annexin-V and Flu-3, respectively. The outer, inner and shed PS were quantified by a novel two-step binding inhibitory assay. The results indicate a bi-phasic modulation of intracellular Ca and PS externalization/shedding; both of which decreased during maturation and increased during aging. The role of intracellular Ca in PS externalization/shedding was demonstrated by modulating intracellular Ca: Ca was decreased by incubating the cells with an ion chelator (EDTA) or with decreasing concentrations of Ca, whereas treatment with the ionophore A23187 elevated intracellular Ca. The results showed that low Ca resulted in decreased outer and shed PS, whereas high Ca had the opposite effect. The results suggest that PS externalization and shedding are mediated by increased cellular Ca-flux, and that they play an important role in erythroid maturation and RBC senescence.