Eryptotic Cells Research Articles

Eicosapentaenoic Acid Triggers Phosphatidylserine Externalization in the Erythrocyte Membrane through Calcium Signaling and Anticholinesterase Activity

Hemolysis and eryptosis contribute to anemia encountered in patients undergoing chemotherapy. Eicosapentaenoic acid (EPA) is an omega-3 dietary fatty acid that has anticancer potential by inducing apoptosis in cancer cells, but its effect on the physiology and lifespan of red blood cells (RBCs) is understudied. Human RBCs were exposed to anticancer concentrations of EPA (10–100 μM) for 24 h at 37 °C. Acetylcholinesterase (AChE) activity and hemolysis were measured by colorimetric assays whereas annexin-V-FITC and forward scatter (FSC) were employed to identify eryptotic cells. Oxidative stress was assessed by H2DCFDA and intracellular Ca2+ was measured by Fluo4/AM. EPA significantly increased hemolysis and K+ leakage, and LDH and AST activities in the supernatants in a concentration-dependent manner. EPA also significantly increased annexin-V-FITC-positive cells and Fluo4 fluorescence and decreased FSC and AChE activity. A significant reduction in the hemolytic activity of EPA was noted in the presence extracellular isosmotic urea, 125 mM KCl, and polyethylene glycol 8000 (PEG 8000), but not sucrose. In conclusion, EPA stimulates hemolysis and eryptosis through Ca2+ buildup and AChE inhibition. Urea, blocking KCl efflux, and PEG 8000 alleviate the hemolytic activity of EPA. The anticancer potential of EPA may be optimized using Ca2+ channel blockers and chelators to minimize its toxicity to off-target tissue.

Linolenic acid stimulates eryptosis and hemolysis through oxidative stress and CK1α/MLKL: protective role of melatonin, urea, and polyethylene glycol

Anticancer medications cause anemia in patients through ill-defined mechanisms, including hemolysis and eryptosis. Although α-linolenic acid (ALA) possesses anticancer properties against a variety of cancer cells, there is a dearth of evidence regarding how it modulates red blood cell (RBC) physiology. RBCs from healthy donors were subjected to anticancer concentrations of ALA (2.5, 5, 10, 20, 40, 80, and 100 μM) at 37 °C for 24 h, and colorimetric tests were used to determine hemolysis and acetylcholinesterase (AChE) activity. Meanwhile, flow cytometry was employed to identify eryptotic cells using annexin-V-FITC and forward scatter (FSC), Fluo4/AM to detect Ca2+, and H2DCFDA to assess oxidative stress. ALA significantly increased hemolysis and eryptosis in a concentration-dependent manner, along with elevated Fluo4 and DCF fluorescence, and erythrocyte sedimentation rate, and reduced FSC and AChE activity. Moreover, the addition of D4476, necrosulfonamide, melatonin, isosmotic urea, and polyethylene glycol 8000 – but not sucrose – significantly inhibited ALA toxicity. In conclusion, ALA stimulates hemolysis and eryptosis through Ca2+ buildup, oxidative stress, anticholinesterase activity, casein kinase 1α (CK1α), and mixed lineage kinase domain-like protein (MLKL). The anticancer activity of ALA may be potentiated by the use of Ca2+ channel blockers and chelators, antioxidants, and CK1α and MLKL inhibitors to ameliorate its toxicity to RBCs.

Internalization of nano- and micro-plastics in human erythrocytes leads to oxidative stress and estrogen receptor-mediated cellular responses

Plastic material versatility has resulted in a substantial increase in its use in several sectors of our everyday lives. Consequently, concern regarding human exposure to nano-plastics (NPs) and micro-plastics (MPs) has recently increased. It has been shown that plastic particles entering the bloodstream may adhere to the erythrocyte surface and exert adverse effects following erythrocyte aggregation and adhesion to blood vessels. Here, we explored the effects of polystyrene nano-plastics (PS-NPs) and micro-plastics (PS-MPs) on human erythrocytes. Cellular morphology, binding/internalization of PS-NPs and PS-MPs, oxidative stress parameters, as well as the distribution and anion exchange capability of band 3 (anion exchanger 1; SLC4A1) have been analyzed in human erythrocytes exposed to 1 μg/mL PS-NPs or PS-MPs for 3 and 24 h, respectively. The data obtained showed significant modifications of the cellular shape after exposure to PS-NPs or PS-MPs. In particular, a significantly increased number of acanthocytes, echinocytes and leptocytes were detected. However, the percentage of eryptotic cells (<1 %) was comparable to physiological conditions. Analytical cytology and confocal microscopy showed that PS-NPs and PS-MPs bound to the erythrocyte plasma membrane, co-localized with estrogen receptors (Erα/ERβ), and were internalized. An increased trafficking from the cytosol to the erythrocyte plasma membrane and abnormal distribution of ERs were also observed, consistent with ERα-mediated binding and internalization of PS-NPs. An increased phosphorylation of ERK1/2 and AKT kinases indicated that an activation of the ER-modulated non-genomic pathway occurred following exposure to PS-NPs and PS-MPs. Interestingly, PS-NPs or PS-MPs caused a significant production of reactive oxygen species, resulting in an increased lipid peroxidation and protein sulfhydryl group oxidation. Oxidative stress was also associated with an altered band 3 ion transport activity and increased oxidized haemoglobin, which led to abnormal clustering of band 3 on the plasma membrane. Taken together, these findings identify cellular events following the internalization of PS-NPs or PS-MPs in human erythrocytes and contribute to elucidating potential oxidative stress-related harmful effects, which may affect erythrocyte and systemic homeostasis.

Aortic Valve Stenosis Causes Accumulation of Extracellular Hemoglobin and Systemic Endothelial Dysfunction.

Whether aortic valve stenosis (AS) can adversely affect systemic endothelial function independently of standard modifiable cardiovascular risk factors is unknown. We therefore investigated endothelial and cardiac function in an experimental model of AS mice devoid of standard modifiable cardiovascular risk factors and human cohorts with AS scheduled for transcatheter aortic valve replacement. Endothelial function was determined by flow-mediated dilation using ultrasound. Extracellular hemoglobin (eHb) concentrations and nitric oxide (NO) consumption were determined in blood plasma of mice and humans by ELISA and chemiluminescence. This was complemented by measurements of aortic blood flow using 4-dimensional flow acquisition by magnetic resonance imaging and computational fluid dynamics simulations. The effects of plasma and red blood cell (RBC) suspensions on vascular function were determined in transfer experiments in a murine vasorelaxation bioassay system. In mice, the induction of AS caused systemic endothelial dysfunction. In the presence of normal systolic left ventricular function and mild hypertrophy, the increase in the transvalvular gradient was associated with elevated eryptosis, increased eHb, and increased plasma NO consumption; eHb sequestration by haptoglobin restored endothelial function. Because the aortic valve orifice area in patients with AS decreased, postvalvular mechanical stress in the central ascending aorta increased. This was associated with elevated eHb, circulating RBC-derived microvesicles, eryptotic cells, lower haptoglobin levels without clinically relevant anemia, and consecutive endothelial dysfunction. Transfer experiments demonstrated that reduction of eHb by treatment with haptoglobin or elimination of fluid dynamic stress by transcatheter aortic valve replacement restored endothelial function. In patients with AS and subclinical RBC fragmentation, the remaining circulating RBCs before and after transcatheter aortic valve replacement exhibited intact membrane function, deformability, and resistance to osmotic and hypoxic stress. AS increases postvalvular swirling blood flow in the central ascending aorta, triggering RBC fragmentation with the accumulation of hemoglobin in the plasma. This increases NO consumption in blood, thereby limiting vascular NO bioavailability. Thus, AS itself promotes systemic endothelial dysfunction independent of other established risk factors. Transcatheter aortic valve replacement is capable of limiting NO scavenging and rescuing endothelial function by realigning postvalvular blood flow to near physiological patterns. URL: https://www.clinicaltrials.gov; Unique identifiers: NCT05603520 and NCT01805739.

Eriocitrin Disrupts Erythrocyte Membrane Asymmetry through Oxidative Stress and Calcium Signaling and the Activation of Casein Kinase 1α and Rac1 GTPase.

Hemolysis and eryptosis result in the premature elimination of circulating erythrocytes and thus contribute to chemotherapy-related anemia, which is extremely prevalent in cancer patients. Eriocitrin (ERN), a flavanone glycoside in citrus fruits, has shown great promise as an anticancer agent, but the potential toxicity of ERN to human erythrocytes remains unstudied. Erythrocytes were exposed to anticancer concentrations of ERN (10-100 μM) for 24 h at 37 °C, and hemolysis and associated markers were quantified using colorimetric assays. Eryptosis was assessed by flow cytometric analysis to detect phosphatidylserine (PS) exposure by annexin-V-FITC, intracellular Ca2+ using Fluo4/AM, and oxidative stress with 2-,7-dichlorodihydrofluorescin diacetate (H2DCFDA). ERN was also tested against specific signaling inhibitors and anti-hemolytic agents. ERN caused significant, concentration-dependent hemolysis at 20-100 μM. ERN also significantly increased the percentage of eryptotic cells characterized by Ca2+ elevation and oxidative stress. Furthermore, the hemolytic activity of ERN was significantly ameliorated in the presence of D4476, NSC23766, isosmotic urea and sucrose, and polyethylene glycol 8000 (PEG). In whole blood, ERN significantly elevated MCV and ESR, with no appreciable effects on other peripheral blood cells. ERN promotes premature erythrocyte death through hemolysis and eryptosis characterized by PS externalization, Ca2+ accumulation, membrane blebbing, loss of cellular volume, and oxidative stress. These toxic effects, mediated through casein kinase 1α and Rac1 GTPase, can be ameliorated by urea, sucrose, and PEG. Altogether, these novel findings are relevant to the further development of ERN as an anticancer therapeutic.

Tamoxifen induces eryptosis through calcium accumulation and oxidative stress.

Chemotherapy-related anemia is a major obstacle in anticancer therapy. Tamoxifen (TAM) is an antiestrogen prescribed for breast cancer patients with hemolytic potential and apoptotic properties in nucleated cells. However, the eryptotic activity of TAM has hitherto escaped the efforts of investigators. RBCs from apparently healthy volunteers were treated with 1-50μM of TAM for 24h at 37°C. Hemoglobin leakage and LDH, AST, and AChE activities were photometrically determined while K+, Na+, and Mg2+ were detected by ion-selective electrode. Flow cytometry was used to identify eryptotic cells by annexin-V-FITC, intracellular Ca2+ by Fluo4/AM, sell size and morphology by FSC and SSC signals, respectively, and oxidative stress by H2DCFDA. Whole blood was also exposed to 30μM of TAM for 24h at 37°C to examine the toxicity of TAM to WBCs and platelets. TAM caused Ca2+-independent, dose-responsive hemolysis accompanied by K+, LDH, and AST leakage without improving the mechanical stability of RBCs in hypotonic environments. TAM treatment also increased the proportion of cells positive for annexin-V-FITC, Fluo4, and DCF, along with diminished FSC and SSC signals and AChE activity. Notably, TAM toxicity was aggravated by sucrose but abrogated by vitamin C, PEG 8000, and urea. Moreover, TAM exhibited distinct cytotoxic profiles against leukocytes and platelets. TAM-induced eryptosis is characterized by breakdown of membrane asymmetry, inhibition of AChE activity, Ca2+ accumulation, cell shrinkage, and oxidative stress. Vitamin C, PEG 8000, and urea may hold promise to subvert the undesirable toxic effects of TAM on RBCs.

Stimulation of Hemolysis and Eryptosis by α-Mangostin through Rac1 GTPase and Oxidative Injury in Human Red Blood Cells.

Chemotherapy-related anemia is prevalent in up to 75% of patients, which may arise due to hemolysis and eryptosis. Alpha-mangostin (α-MG) is a polyphenolic xanthonoid found in the mangosteen tree (Garcinia mangostana) whose antitumor medicinal properties are well-established. Nevertheless, the potential toxic effects of α-MG on red blood cells (RBCs) have, as of yet, not been as well studied. RBCs were exposed to 1-40 μM of α-MG for 24 h at 37 °C. Hemolysis and related markers were measured using colorimetric assays, eryptotic cells were identified through Annexin-V-FITC, Ca2+ was detected with Fluo4/AM, and oxidative stress was assessed through H2DCFDA using flow cytometry. The toxicity of α-MG was also examined in the presence of specific signal transduction inhibitors and in whole blood. α-MG at 10-40 μM caused dose-dependent hemolysis with concurrent significant elevation in K+, Mg2+, and LDH leakage, but at 2.5 μM it significantly increased the osmotic resistance of cells. A significant increase was also noted in Annexin-V-binding cells, along with intracellular Ca2+, oxidative stress, and cell shrinkage. Moreover, acetylcholinesterase activity was significantly inhibited by α-MG, whose hemolytic potential was significantly ameliorated by the presence of BAPTA-AM, vitamin C, NSC23766, and isosmotic sucrose but not urea. In whole blood, α-MG significantly depleted intracellular hemoglobin stores and was selectively toxic to platelets and monocytes. α-MG possesses hemolytic and eryptotic activities mediated through Ca2+ signaling, Rac1 GTPase activity, and oxidative injury. Also, α-MG leads to accelerated cellular aging and specifically targets platelet and monocyte populations in a whole blood milieu.

#3658 PERITONEAL INFLAMMATION INDUCES SYSTEMIC ERYPTOSIS IN PERITONEAL DIALYSIS-ASSOCIATED PERITONITIS

Abstract Background and Aims Eryptosis is stress-induced RBC (Red Blood Cell) death mechanism. Our preliminary data show that there is a significative increased of eryptosis during peritoneal dialysis-associated peritonitis. Furthremore, there is an elevation of local and systemic inflammatory mediators. The aim of this study was to evaluate the relationship between systemic eryptosis levels in peritonitis and specific peritonitis biomarkers in peritonitis effluent (PDE), such as Peritoneal White Blood cell count (pWBC), peritoneal NGAL (pNGAL) and peritoneal cytokines levels. Method We enrolled 22 PD patients with peritonitis and 17 healthy subjects. PD-related peritonitis was defined according to the Guidelines of the International Society of Peritoneal Dialysis. At the time of diagnosis, blood samples were collected for eryptosis and peritoneal effluent were taken to evaluate pWBC, pNGAL and cytokines. All eryptotic measurements were made in freshly isolated RBCs. PS avidly binds AnnexinV, which is thus employed to identify eryptotic cells. Thus, PS exposure at RBC surface was estimated from FITC-AnnexinV binding using flow cytometric analyses. Results 13/22 patients were treated with continuous ambulatory PD (CAPD) and 9 with automated PD (APD). The median length of PD treatment was 28.1 months and the range was: minimum: 3 – maximum: 124.9 months. The percentage of AnnexinV-binding RBCs was significantly higher in PD patients with peritonitis than in CTR (PD patients with peritonitis: 7.7; IQR 4.3-14.2, versus CTR: 0.8; IQR 0.7-1.3; p&amp;lt;0.001) (Figure 1). WBC, NGAL and cytokines levels in PDE are reported in Table 2. We observed important correlation between eriptosis levels and peritoneal biomarkers (Figure 2). Conclusion In conclusion, we investigated a potential connection between systemic eryptosis and peritoneal biomarkers involved in peritonitis. The presented results revealed that upregulated inflammatory markers could be the cause of high levels of systemic eryptosis during PD-related peritonitis.

Ion Transport in Eryptosis, the Suicidal Death of Erythrocytes.

Erythrocytes are among the most abundant cells in mammals and are perfectly adapted to their main functions, i.e., the transport of O2 to peripheral tissues and the contribution to CO2 transport to the lungs. In contrast to other cells, they are fully devoid of organelles. Similar to apoptosis of nucleated cells erythrocytes may enter suicidal death, eryptosis, which is characterized by the presentation of membrane phosphatidylserine on the cell surface and cell shrinkage, hallmarks that are also typical of apoptosis. Eryptosis may be triggered by an increase in the cytosolic Ca2+ concentration, which may be due to Ca2+ influx via non-selective cation channels of the TRPC family. Eryptosis is further induced by ceramide, which sensitizes erythrocytes to the eryptotic effect of Ca2+. Signaling regulating eryptosis further involves a variety of kinases including AMPK, PAK2, cGKI, JAK3, CK1α, CDK4, MSK1/2 and casein kinase. Eryptosis-dependent shrinkage is induced by K+ efflux through Ca2+-activated K+ channel KCa3.1, the Gardos channel. Eryptotic cells are phagocytosed and may adhere to endothelial cells. Eryptosis may help prevent hemolysis since defective erythrocytes usually undergo eryptosis followed by rapid clearance from circulating blood. Excessive eryptosis stimulated by various diseases and xenobiotics may result in anemia and/or impaired microcirculation. This review focuses on the significance and mechanisms of eryptosis as well as on the ion fluxes involved. Moreover, a short summary of further ion transport mechanisms of the erythrocyte membrane is provided.

Induction of Eryptosis in Red Blood Cells Using a Calcium Ionophore.

Eryptosis, erythrocyte programmed cell death, occurs in a number of hematological diseases and during injury to erythrocytes. A hallmark of eryptotic cells is the loss of compositional asymmetry of the cell membrane, leading to the translocation of phosphatidylserine to the membrane outer leaflet. This process is triggered by increased intracellular concentration of Ca2+, which activates scramblase, an enzyme that facilitates bidirectional movement of phospholipids between membrane leaflets. Given the importance of eryptosis in various diseased conditions, there have been efforts to induce eryptosis in vitro. Such efforts have generally relied on the calcium ionophore, ionomycin, to enhance intracellular Ca2+ concentration and induce eryptosis. However, many discrepancies have been reported in the literature regarding the procedure for inducing eryptosis using ionomycin. Herein, we report a step-by-step protocol for ionomycin-induced eryptosis in human erythrocytes. We focus on important steps in the procedure including the ionophore concentration, incubation time, and glucose depletion, and provide representative result. This protocol can be used to reproducibly induce eryptosis in the laboratory.

Computerized Morphometric Analysis of Eryptosis.

Eryptosis is the suicidal destruction-process of erythrocytes, much like apoptosis of nucleated cells, in the course of which the stressed red cell undergoes cell-shrinkage, vesiculation and externalization of membrane phosphatidylserine. Currently, there exist numerous methods to detect eryptosis, both morphometrically and biochemically. This study aimed to design a simple but sensitive, automated computerized approach to instantaneously detect eryptotic red cells and quantify their hallmark morphological characteristics. Red cells from 17 healthy volunteers were exposed to normal Ringer and hyperosmotic stress with sodium chloride, following which morphometric comparisons were conducted from their photomicrographs. The proposed method was found to significantly detect and differentiate normal and eryptotic red cells, based on variations in their structural markers. The receiver operating characteristic curve analysis for each of the markers showed a significant discriminatory accuracy with high sensitivity, specificity and area under the curve values. The software-based technique was then validated with RBCs in malaria. This model, quantifies eryptosis morphometrically in real-time, with minimal manual intervention, providing a new window to explore eryptosis triggered by different stressors and diseases and can find wide application in laboratories of hematology, blood banks and medical research.

Eryptosis (quasi-apoptosis) the human red blood cells. Its role in medicinal therapy

In the course of circulation erythrocytes can test damages, which compromises their integrity and thus triggers suicidal erythrocyte death or eryptosis. This mechanism is characterised by cell shrinkage, cell membrane blebbing, and cell membrane phospholipid scrambling after phosphatidylserine exposure on the cell surface that is identified by macrophages, which engulf and degrade the eryptotic cells. The term eryptosis also includes typical mechanisms, which contribute to the triggering of this process, such as oxidative stress, Ca2+ entry with an increase in cytosolic Ca2+ activity and the activation of p38 kinase, which is a kinase expressed in human erythrocytes and activated after hyperosmotic shock. Enhanced eryptosis has been observed in several clinical conditions such as diabetes, renal insufficiency, haemolytic uremic syndrome, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anaemia, beta-thalassemia, glucose-6-phosphate dehydrogenase (G6PD)-deficiency, hereditary spherocytosis, paroxysmal nocturnal haemoglobinuria, Wilson’s disease, myelodysplastic syndrome, and phosphate depletion. Therefore, eryptosis may be considered as a useful mechanism of removal of defective erythrocytes to prevent haemolysis. Moreover, the clearance of infected erythrocytes in diseases such as malaria may counteract parasitemia. Indeed it is known that sickle-cell trait, beta-thalassemia trait, G6PD-deficiency and iron deficiency confer some protection against a severe course of malaria. Importantly, strategies to control Plasmodium infection by inducing eryptosis are not expected to generate resistance of the pathogen, as the proteins involved in suicidal death of the host cell are not encoded by the pathogen and thus cannot be modified by mutations of its genes. However, excessive eryptosis could compromise microcirculation and lead to anemia. Besides, adhesion of eryptosis erythrocytes to a vascular wall also can lead to microcirculation infringement.Thus, modern representations about eryptosis expand our knowledge about the programmed death of blood cells and is more directed to create new therapeutic schemes of treatment of patients.

Disruption of erythrocyte membrane asymmetry by triclosan is preceded by calcium dysregulation and p38 MAPK and RIP1 stimulation

Triclosan (TCS) is a broad-spectrum antimicrobial used in personal care products, household items, and medical devices. Owing to its apoptotic potential against tumor cells, TCS has been proposed for the treatment of malignancy. A major complication of chemotherapy is anemia, which may result from direct erythrocyte hemolysis or premature cell death known as eryptosis. Similar to nucleated cells, eryptotic cells lose membrane asymmetry and Ca2+ regulation, and undergo oxidative stress, shrinkage, and activation of a host of kinases. In this report, we sought to examine the hemolytic and eryptotic potential of TCS and dissect the underlying mechanistic scenarios involved there in. Hemolysis was spectrophotometrically evaluated by the degree of hemoglobin release into the medium. Flow cytometry was utilized to detect phosphatidylserine (PS) exposure by annexin-V binding, intracellular Ca2+ by Fluo-3/AM fluorescence, and oxidative stress by 2-,7-dichlorodihydrofluorescin diacetate (DCFH2-DA). Incubation of cells with 10–100 μM TCS for 1–4 h induced time- and dose-dependent hemolysis. Moreover, TCS significantly increased the percentage of eryptotic cells as evident by PS exposure (significantly enhanced annexin-V binding). Interestingly, TCS-induced eryptosis was preceded by elevated intracellular Ca2+ levels but was not associated with oxidative stress. Cotreatment of erythrocytes with 50 μM TCS and 50 μM SB203580 (p38 MAPK inhibitor), or 300 μM necrostatin-1 (receptor-interacting protein 1 (RIP1) inhibitor) significantly ameliorated TCS-induced PS externalization. We conclude that TCS is cytotoxic to erythrocytes by inducing hemolysis and stimulating premature death at least in part through Ca2+ mobilization, and p38 MAPK and RIP1 activation.

Effects of Plant Sterols or β-Cryptoxanthin at Physiological Serum Concentrations on Suicidal Erythrocyte Death.

The eryptotic and hemolytic effects of a phytosterol (PS) mixture (β-sitosterol, campesterol, stigmasterol) or β-cryptoxanthin (β-Cx) at physiological serum concentration and their effect against oxidative stress induced by tert-butylhydroperoxide (tBOOH) (75 and 300 μM) were evaluated. β-Cryptoxanthin produced an increase in eryptotic cells, cell volume, hemolysis, and glutathione depletion (GSH) without ROS overproduction and intracellular Ca2+ influx. Co-incubation of both bioactive compounds protected against β-Cx-induced eryptosis. Under tBOOH stress, PS prevented eryptosis, reducing Ca2+ influx, ROS overproduction and GSH depletion at 75 μM, and hemolysis at both tBOOH concentrations. β-Cryptoxanthin showed no cytoprotective effect. Co-incubation with both bioactive compounds completely prevented hemolysis and partially prevented eryptosis as well as GSH depletion induced by β-Cx plus tBOOH. Phytosterols at physiological serum concentrations help to prevent pro-eryptotic and hemolytic effects and are promising candidate compounds for ameliorating eryptosis-associated diseases.

Eryptosis: Ally or Enemy.

Prior to senescence, erythrocytes may experience injury, which compromises their integrity and thus triggers suicidal erythrocyte death or eryptosis. This mechanism is characterised by cell shrinkage, cell membrane blebbing, and cell membrane phospholipid scrambling after phosphatidylserine exposure on the cell surface that is identified by macrophages, which engulf and degrade the eryptotic cells. The term eryptosis also includes typical mechanisms, which contribute to the triggering of this process, such as oxidative stress, Ca2+ entry with an increase in cytosolic Ca2+ activity ([Ca ]i) and the activation of p38 kinase, which is a kinase expressed in human erythrocytes and activated after hyperosmotic shock. Enhanced eryptosis has been observed in several clinical conditions such as diabetes, renal insufficiency, haemolytic uremic syndrome, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anaemia, beta-thalassemia, glucose-6-phosphate dehydrogenase-(G6PD) deficiency, hereditary spherocytosis, paroxysmal nocturnal haemoglobinuria, Wilson's disease, myelodysplastic syndrome, and phosphate depletion. Therefore, eryptosis may be considered as a useful mechanism of removal of defective erythrocytes to prevent haemolysis. Moreover, the clearance of infected erythrocytes in diseases such as malaria may counteract parasitemia. Indeed it is known that sickle-cell trait, beta-thalassemia trait, glucose-6-phosphate dehydrogenase (G6PD)- deficiency and iron deficiency confer some protection against a severe course of malaria. Importantly, strategies to control Plasmodium infection by inducing eryptosis are not expected to generate resistance of the pathogen, as the proteins involved in suicidal death of the host cell are not encoded by the pathogen and thus cannot be modified by mutations of its genes. However, excessive eryptosis could compromise microcirculation and lead to anemia.

Erythrocyte Sodium Sensitivity and Eryptosis in Chronic Hemodialysis Patients

Background/Aims: In hemodialysis (HD) patients the endothelial and erythrocyte glycocalyx is impaired which in turn correlates with elevated erythrocyte sodium sensitivity (ESS). Additionally, apoptotic erythrocyte death (eryptosis), characterized by phosphatidylserine (PS) exposure on the cell surface, is increased in this population. We aimed to explore the relationship of ESS and eryptosis. Methods: Blood samples were collected from 11 healthy controls and 20 chronic HD patients before and after midweek HD. ESS was quantified by the salt blood test. PS-exposure, intracellular reactive oxygen species (ROS) of erythrocytes and reticulocytes were assessed by flow cytometry. Results: Compared to controls ESS was significantly higher in HD patients preHD and did not change during treatment. The percentage of eryptotic cells did not differ between controls and patients preHD. However, eryptosis decreased during HD. ESS and eryptosis were uncorrelated, while eryptosis was positively correlated with intracellular ROS and percent reticulocytes. Conclusions: Higher ESS levels in HD patients indicate a pathologic glycocalyx. ESS and eryptosis were not correlated. The decreased eryptosis postHD may possibly be related to dialytic uremic toxin removal, but is likely multifactorial. The relationship between eryptosis and intracellular ROS warrants further research.

Killing me softly – Suicidal erythrocyte death

Similar to nucleated cells, erythrocytes may undergo suicidal death or eryptosis, which is characterized by cell shrinkage, cell membrane blebbing and cell membrane phospholipid scrambling. Eryptotic cells are removed and thus prevented from undergoing hemolysis. Eryptosis is stimulated by Ca2+ following Ca2+ entry through unspecific cation channels. Ca2+ sensitivity is enhanced by ceramide, a product of acid sphingomyelinase. Eryptosis is triggered by hyperosmolarity, oxidative stress, energy depletion, hyperthermia and a wide variety of xenobiotics and endogenous substances. Eryptosis is inhibited by nitric oxide, catecholamines and a variety of further small molecules. Erythropoietin counteracts eryptosis in part by inhibiting the Ca2+-permeable cation channels but by the same token may foster formation of erythrocytes, which are particularly sensitive to eryptotic stimuli. Eryptosis is triggered in several clinical conditions such as iron deficiency, diabetes, renal insufficiency, myelodysplastic syndrome, phosphate depletion, sepsis, haemolytic uremic syndrome, mycoplasma infection, malaria, sickle-cell anemia, beta-thalassemia, glucose-6-phosphate dehydrogenase-(G6PD)-deficiency, hereditary spherocytosis, paroxysmal nocturnal hemoglobinuria, and Wilson's disease. Enhanced eryptosis is observed in mice with deficient annexin 7, cGMP-dependent protein kinase type I (cGKI), AMP-activated protein kinase AMPK, anion exchanger AE1, adenomatous polyposis coli APC and Klotho as well as in mouse models of sickle cell anemia and thalassemia. Eryptosis is decreased in mice with deficient phosphoinositide dependent kinase PDK1, platelet activating factor receptor, transient receptor potential channel TRPC6, janus kinase JAK3 or taurine transporter TAUT. If accelerated eryptosis is not compensated by enhanced erythropoiesis, clinically relevant anemia develops. Eryptotic erythrocytes may further bind to endothelial cells and thus impede microcirculation.

Physiology and Pathophysiology of Eryptosis

Suicidal erythrocyte death (eryptosis) is characterized by cell shrinkage, cell membrane blebbing, and cell membrane phospholipid scrambling with phosphatidylserine exposure at the cell surface. Eryptotic cells adhere to the vascular wall and are rapidly cleared from circulating blood. Eryptosis is stimulated by an increase in cytosolic Ca²⁺ activity, ceramide, hyperosmotic shock, oxidative stress, energy depletion, hyperthermia, and a wide variety of xenobiotics and endogenous substances. Inhibitors of eryptosis include erythropoietin and nitric oxide. Enhanced eryptosis is observed in diabetes, renal insufficiency, hemolytic uremic syndrome, sepsis, mycoplasma infection, malaria, iron deficiency, sickle cell anemia, beta-thalassemia, glucose-6-phosphate dehydrogenase-(G6PD) deficiency, hereditary spherocytosis, paroxysmal nocturnal hemoglobinuria, Wilson’s disease, myelodysplastic syndrome, and phosphate depletion. Eryptosis is further enhanced in gene-targeted mice with deficient annexin 7, cGMP-dependent protein kinase type I (cGKI), AMP-activated protein kinase (AMPK), anion exchanger 1 (AE1), adenomatous polyposis coli (APC), and Klotho, as well as in mouse models of sickle cell anemia and thalassemia. Decreased eryptosis is observed in mice with deficient phosphoinositide-dependent kinase 1 (PDK1), platelet activating factor (PAF) receptor, transient receptor potential channel 6 (TRPC6), janus kinase 3 (JAK3), and taurine transporter (TAUT). Eryptosis may be a useful mechanism to remove defective erythrocytes prior to hemolysis. Excessive eryptosis may, however, compromise microcirculation and lead to anemia.

Dynamic adhesion of eryptotic erythrocytes to endothelial cells via CXCL16/SR-PSOX

Suicidal death of erythrocytes, or eryptosis, is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the cell surface. Eryptosis is triggered by increase of cytosolic Ca2+ activity, which may result from treatment with the Ca2+ ionophore ionomycin or from energy depletion by removal of glucose. The present study tested the hypothesis that phosphatidylserine exposure at the erythrocyte surface fosters adherence to endothelial cells of the vascular wall under flow conditions at arterial shear rates and that binding of eryptotic cells to endothelial cells is mediated by the transmembrane CXC chemokine ligand 16 (CXCL16). To this end, human erythrocytes were exposed to energy depletion (for 48 h) or treated with the Ca2+ ionophore ionomycin (1 μM for 30 min). Phosphatidylserine exposure was quantified utilizing annexin-V binding, cell volume was estimated from forward scatter in FACS analysis, and erythrocyte adhesion to human vascular endothelial cells (HUVEC) was determined in a flow chamber model. As a result, both, ionomycin and glucose depletion, triggered eryptosis and enhanced the percentage of erythrocytes adhering to HUVEC under flow conditions at arterial shear rates. The adhesion was significantly blunted in the presence of erythrocyte phosphatidylserine-coating annexin-V (5 μl/ml), of a neutralizing antibody against endothelial CXCL16 (4 μg/ml), and following silencing of endothelial CXCL16 with small interfering RNA. The present observations demonstrate that eryptotic erythrocytes adhere to endothelial cells of the vascular wall in part by interaction of phosphatidylserine exposed at the erythrocyte surface with endothelial CXCL16.

Inhibition of Suicidal Erythrocyte Death by Xanthohumol

Xanthohumol is a proapoptotic hop-derived beer component with anticancer and antimicrobial activities. Similar to nucleated cells, erythrocytes may undergo suicidal cell death or eryptosis, which is triggered by oxidative stress (tert-butylhydroperoxide, TBOOH) or energy depletion (removal of glucose). The triggers increase cytosolic Ca(2+) concentration, leading to activation of Ca(2+)-sensitive K(+) channels with subsequent cell shrinkage and to cell membrane scrambling with subsequent phosphatidylserine exposure at the erythrocyte surface. Eryptotic cells are cleared from the circulating blood, leading to anemia, and may adhere to the vascular wall, thus impeding microcirculation. The present experiments explored whether xanthohumol influences eryptosis using flow cytometry. Exposure of human erythrocytes to 0.3 mM TBOOH or incubation in glucose-free solution significantly increased Fluo3 fluorescence (Ca(2+) concentration) as well as annexin V-binding (cell membrane scrambling) and decreased forward scatter (cell volume), effects significantly blunted by xanthohumol. In conclusion, xanthohumol is a potent inhibitor of suicidal erythrocyte death in vitro.