Binding of phosphatidylserine-positive microparticles by PBMCs classifies disease severity in COVID-19 patients

Infection with SARS-CoV-2 is associated with thromboinflammation, involving thrombotic and inflammatory responses, in many COVID-19 patients. In addition, immune dysfunction occurs in patients characterised by T cell exhaustion and severe lymphopenia. We investigated the distribution of phosphatidylserine (PS), a marker of dying cells, activated platelets and platelet-derived microparticles (PMP), during the clinical course of COVID-19. We found an unexpectedly high amount of blood cells loaded with PS+ PMPs for weeks after the initial COVID-19 diagnosis. Elevated frequencies of PS+ PMP+ PBMCs correlated strongly with increasing disease severity. As a marker, PS outperformed established laboratory markers for inflammation, leucocyte composition and coagulation, currently used for COVID-19 clinical scoring. PS+ PMPs preferentially bound to CD8+ T cells with gene expression signatures of proliferating effector rather than memory T cells. As PS+ PMPs carried programmed death-ligand 1 (PD-L1), they may affect T cell expansion or function. Our data provide a novel marker for disease severity and show that PS, which can trigger the blood coagulation cascade, the complement system, and inflammation, resides on activated immune cells. Therefore, PS may serve as a beacon to attract thromboinflammatory processes towards lymphocytes and cause immune dysfunction in COVID-19.

Levels of procoagulant microparticles expressing phosphatidylserine contribute to bleeding phenotype in patients with inherited thrombocytopenia

Inherited thrombocytopenia is a heterogeneous group of hereditary disorders with varying bleeding tendencies, not simply related to platelet count. Platelets transform into different subpopulations upon stimulation, including procoagulant platelets and platelet microparticles (PMPs), which are considered critical for haemostasis. We aimed to investigate whether abnormalities in PMP and procoagulant platelet function were associated with the bleeding phenotype of inherited thrombocytopenia patients. We enrolled 53 inherited thrombocytopenia patients. High-throughput sequencing of 36 inherited thrombocytopenia related genes was performed in all patients and enabled a molecular diagnosis in 57%. Bleeding phenotype was evaluated using the ISTH bleeding assessment tool, dividing patients into bleeding (n = 27) vs. nonbleeding (n = 26). Unstimulated and ADP, TRAP or collagen-stimulated PMP and procoagulant platelet functions were analysed by flow cytometry using antibodies against granulophysin (CD63), P-selectin (CD62P), activated GPIIb/IIIa (PAC-1) and a marker for phosphatidylserine expression (lactadherin). Procoagulant platelets were measured in response to collagen stimulation. An in-house healthy reference level was available. Overall, higher levels of activated platelets, PMPs and procoagulant platelets were found in nonbleeding patients compared with the reference level. Nonbleeding patients had higher proportions of phosphatidylserine and PMPs compared with bleeding patients and the reference level, in response to different stimulations. Interestingly, this finding of high proportions of phosphatidylserine and PMPs was limited to PMPs, and not present in procoagulant platelets or platelets. Our findings indicate that nonbleeding inherited thrombocytopenia patients have compensatory mechanisms for improved platelet subpopulation activation and function, and that generation of phosphatidylserine expressing PMPs could be a factor determining bleeding phenotype in inherited thrombocytopenia.

Extracellular vesicle-associated procoagulant activity is highest the first 3 hours after trauma and thereafter declines substantially: A prospective observational pilot study

BACKGROUND

Trauma patients have high concentrations of circulating extracellular vesicles (EVs) following injury, but the functional role of EVs in this setting is only partly deciphered. We aimed to describe in detail EV-associated procoagulant activity in individual trauma patients during the first 12 hours after injury to explore their putative function and relate findings to relevant trauma characteristics and outcome.

METHODS

In a prospective observational study of 33 convenience recruited trauma patients, citrated plasma samples were obtained at trauma center admission and 2, 4, 6, and 8 hours thereafter. We measured thrombin generation from isolated EVs and the procoagulant activity of phosphatidylserine (PS)-exposing EVs. Correlation and multivariable linear regression analyses were used to explore associations between EV-associated procoagulant activity and trauma characteristics as well as outcome measures.

RESULTS

EV-associated procoagulant activity was highest in the first 3 hours after injury. EV-associated thrombin generation normalized within 7 to 12 hours of injury, whereas the procoagulant activity of PS-exposing EVs declined to a level right above that of healthy volunteers. Increased EV-associated procoagulant activity at admission was associated with higher New Injury Severity Score, lower admission base excess, higher admission international normalized ratio, prolonged admission activated partial thromboplastin time, higher Sequential Organ Failure Assessment score at day 0, and fewer ventilator-free days.

CONCLUSION

Our data suggest that EVs have a transient hypercoagulable function and may play a role in the early phase of hemostasis after injury. The role of EVs in trauma-induced coagulopathy and posttraumatic thrombosis should be studied bearing in mind this novel temporal pattern.

LEVEL OF EVIDENCE

Prognostic/epidemiologic, level V.

Does endurance training improve red blood cell aging and hemorheology in moderate-trained healthy individuals?

OBJECTIVE

To examine the impact of a 6-week endurance training on red blood cell (RBC) aging and deformability of healthy participants to detect possible improved hemorheological and performance-related adaptations.

METHODS

A total of 31 participants (17 females and 14 males) performed a 6-week moderate training protocol (three 1-h running sessions per week at 70% of maximal heart rate). Blood was sampled before and after the training. RBCs from each participant were fractioned according to density and age into 4 RBC subfractions. Subfractions were examined for changes of RBC properties, including aging distribution, RBC deformability, RBC microparticles, and phosphatidylserine concentrations. RBC and plasma nitrite levels were measured as indicators of nitric oxide metabolism.

RESULTS

Aerobic performance, peak oxygen consumption, ventilatory thresholds, velocity at the aerobic-anaerobic threshold, and lactate at exhaustion improved after training. The relative amount of both young RBCs and old RBCs increased, and the amount of the main RBC fraction decreased. Phosphatidylserine externalization and RBC-derived microparticles decreased. Overall deformability expressed as shear stress required to achieve half-maximum deformation to theoretical maximal elongation index at infinite shear stress improved in unfractioned RBCs (p < 0.001). Nitrite decreased in total (p = 0.001), young (p < 0.001), main (p < 0.001), and old (p = 0.020) aged RBCs and in plasma (p = 0.002), but not in very old RBCs.

CONCLUSION

These results indicate that non-endurance-trained healthy participants benefit from a regular moderate running training program because performance-related parameters improve and a younger RBC population with improved RBC properties is induced, which might support oxygen supply in the microcirculation.

Serum Metabolomics of Early Postoperative Cognitive Dysfunction in Elderly Patients Using Liquid Chromatography and Q-TOF Mass Spectrometry

Postoperative cognitive dysfunction (POCD) is a common postoperative complication observed in elderly patients. However, the diagnosis of POCD is not very satisfactory as no specific biomarkers have been classified. It is necessary to identify new diagnostic markers to better understand the pathogenesis of POCD. We performed liquid chromatography with a time-of-flight mass spectrometer- (LC/Q-TOF-MS-) based metabolomics study to investigate POCD. A total of 40 metabolites were differentially expressed between POCD and non-POCD patients. In this study, we investigated whether phosphatidylserine (PS) (17:2/0:0), with an area under the curve value of 0.966, was a potential sensitive and specific biomarker for the diagnosis and prognosis of POCD. Pathway analysis showed that fatty acid metabolism, lipid metabolism, and carnitine metabolism were significantly altered in POCD. Network analysis indicated that nitric oxide signaling, PI3K-AKT signaling, mTOR signaling, and mitochondrial dysfunction were related to the pathogenesis of POCD. This study showed that metabolic profiling was meaningful when studying the diagnosis and pathogenesis of POCD.

The emerging roles of eryptosis in liver diseases

Erythrocytes undergo programmed cell death, similar to apoptosis, known as eryptosis. This process is a result of several factors including hyperosmolarity, oxidative stress, and exposure to xenobiotics, and is characterized by the breakdown of membrane phospholipid asymmetry, the clustering of band 3, and the generation of red blood cell-derived microparticles. Under pathological conditions, the liver is the primary site of erythrocyte clearance and plays an important role in iron recycling. Phosphatidylserine exposure and band-3 clustering on eryptotic erythrocytes represent mainly pro-phagocytic signals. Further, the percentage of eryptotic erythrocytes is enhanced in the circulating blood of patients with hepatic failure, hyperbilirubinemia, and nonalcoholic steatohepatitis. In this review, we concentrate on recent progress regarding the pathophysiological roles of eryptosis in liver diseases.

Platelets Drive Thrombus Propagation in a Hematocrit and Glycoprotein VI-Dependent Manner in an In Vitro Venous Thrombosis Model

OBJECTIVE

The objective of this study was to measure the role of platelets and red blood cells on thrombus propagation in an in vitro model of venous valvular stasis.

APPROACH AND RESULTS

A microfluidic model with dimensional similarity to human venous valves consists of a sinus distal to a sudden expansion, where for sufficiently high Reynolds numbers, 2 countercurrent vortices arise because of flow separation. The primary vortex is defined by the points of flow separation and reattachment. A secondary vortex forms in the deepest recess of the valve pocket characterized by low shear rates. An initial fibrin gel formed within the secondary vortex of a tissue factor-coated valve sinus. Platelets accumulated at the interface of the fibrin gel and the primary vortex. Red blood cells at physiological hematocrits were necessary to provide an adequate flux of platelets to support thrombus growth out of the valve sinus. A subpopulation of platelets that adhered to fibrin expose phosphatidylserine. Platelet-dependent thrombus growth was attenuated by inhibition of glycoprotein VI with a blocking Fab fragment or D-dimer.

CONCLUSIONS

A 3-step process regulated by hemodynamics was necessary for robust thrombus propagation: First, immobilized tissue factor initiates coagulation and fibrin deposition within a low flow niche defined by a secondary vortex in the pocket of a model venous valve. Second, a primary vortex delivers platelets to the fibrin interface in a red blood cell-dependent manner. Third, platelets adhere to fibrin, activate through glycoprotein VI, express phosphatidylserine, and subsequently promote thrombus growth beyond the valve sinus and into the bulk flow.

Apoptotic-like mitochondrial events associated to phosphatidylserine exposure in blood platelets induced by local anaesthetics

Phosphatidylserine exposure in platelets is required for normal haemostasis and is also a hallmark of apoptosis. It results from activation of a phospholipid scramblase, which has been shown to be differently stimulated by Ca2+-influx and during apoptosis, thus suggesting that mitochondria may be involved in phosphatidylserine exposure in platelets. It is also well known that local anaesthetics can expose phosphatidylserine in platelets and affect the mitochondrial metabolism in other cells. Thus, the present study was undertaken to evaluate the specific involvement of mitochondria in phosphatidylserine exposure in platelets. For this purpose, we stimulated phosphatidylserine exposure by local anaesthetics and avoided any external Ca2+-influx by performing all experiments in the absence of added Ca2+. We report that phosphatidylserine exposure, induced by the lipophilic local anaesthetics dibucaine and tetracaine, was accompanied by depolarization of the mitochondrial membrane, cytochrome c release, calpain-processing of caspases 9 and 3 to active enzymes, as well as a prolonged increase in both cytosolic and mitochondrial Ca2+ concentrations. In contrast, in the absence of extracellular Ca2+, the Ca2+-ionophore A23187 induced a smaller transient increase in both cytosolic and mitochondrial Ca2+ concentrations, but did not induce any other phenomena, nor phosphatidylserine exposure. However, phosphatidylserine exposure and depolarization induced by dibucaine still occurred in spite of inhibition of intracellular Ca2+ elevation. Thus we conclude that phosphatidylserine exposure in platelets is associated with mitochondrial apoptotic-like events. Therefore, we propose that mitochondria engagement in an apoptotic pathway in platelets could lead to PS exposure without the participation of Ca2+.

Farnesoid X Receptor and Liver X Receptor Ligands Initiate Formation of Coated Platelets

OBJECTIVES

The liver X receptors (LXRs) and farnesoid X receptor (FXR) have been identified in human platelets. Ligands of these receptors have been shown to have nongenomic inhibitory effects on platelet activation by platelet agonists. This, however, seems contradictory with the platelet hyper-reactivity that is associated with several pathological conditions that are associated with increased circulating levels of molecules that are LXR and FXR ligands, such as hyperlipidemia, type 2 diabetes mellitus, and obesity.

APPROACH AND RESULTS

We, therefore, investigated whether ligands for the LXR and FXR receptors were capable of priming platelets to the activated state without stimulation by platelet agonists. Treatment of platelets with ligands for LXR and FXR converted platelets to the procoagulant state, with increases in phosphatidylserine exposure, platelet swelling, reduced membrane integrity, depolarization of the mitochondrial membrane, and microparticle release observed. Additionally, platelets also displayed features associated with coated platelets such as P-selectin exposure, fibrinogen binding, fibrin generation that is supported by increased serine protease activity, and inhibition of integrin αIIbβ3. LXR and FXR ligand-induced formation of coated platelets was found to be dependent on both reactive oxygen species and intracellular calcium mobilization, and for FXR ligands, this process was found to be dependent on cyclophilin D.

CONCLUSIONS

We conclude that treatment with LXR and FXR ligands initiates coated platelet formation, which is thought to support coagulation but results in desensitization to platelet stimuli through inhibition of αIIbβ3 consistent with their ability to inhibit platelet function and stable thrombus formation in vivo.

Inner Mitochondrial Membrane Disruption Links Apoptotic and Agonist-Initiated Phosphatidylserine Externalization in Platelets

OBJECTIVE

Phosphatidylserine exposure mediates platelet procoagulant function and regulates platelet life span. Apoptotic, necrotic, and integrin-mediated mechanisms have been implicated as intracellular determinants of platelet phosphatidylserine exposure. Here, we investigate (1) the role of mitochondrial events in platelet phosphatidylserine exposure initiated by these distinct stimuli and (2) the cellular interactions of the procoagulant platelet in vitro and in vivo.

APPROACH AND RESULTS

Key mitochondrial events were examined, including cytochrome c release and inner mitochondrial membrane (IMM) disruption. In both ABT-737 (apoptotic) and agonist (necrotic)-treated platelets, phosphatidylserine externalization was temporally correlated with IMM disruption. Agonist stimulation resulted in rapid cyclophilin D-dependent IMM disruption that coincided with phosphatidylserine exposure. ABT-737 treatment caused rapid cytochrome c release, eventually followed by caspase-dependent IMM disruption that again closely coincided with phosphatidylserine exposure. A nonmitochondrial and integrin-mediated mechanism has been implicated in the formation of a novel phosphatidylserine-externalizing platelet subpopulation. Using image cytometry, this subpopulation is demonstrated to be the result of the interaction of an aggregatory platelet and a procoagulant platelet rather than indicative of a novel intracellular mechanism regulating platelet phosphatidylserine externalization. Using electron microscopy, similar interactions between aggregatory and procoagulant platelets are demonstrated in vitro and in vivo within a mesenteric vein hemostatic thrombus.

CONCLUSIONS

Platelet phosphatidylserine externalization is closely associated with the mitochondrial event of IMM disruption identifying a common pathway in phosphatidylserine-externalizing platelets. The limited interaction of procoagulant platelets and integrin-active aggregatory platelets identifies a potential mechanism for procoagulant platelet retention within the hemostatic thrombus.

Thrombin generation and cell-dependent hypercoagulability in sickle cell disease

Essentials Sickle cell disease is increasingly being recognized as a chronic hypercoagulable state. Thrombin generation is elevated in the whole blood, but not the plasma of sickle cell patients. Whole blood thrombin generation inversely correlates to erythrocyte phosphatidylserine exposure. Acquired protein S deficiency is likely explained by binding of protein S to sickle red cells. Click to hear Dr Hillery discuss coagulation and vascular pathologies in mouse models of sickle cell disease.

SUMMARY

Introduction Sickle cell disease (SCD) is a hypercoagulable state with chronic activation of coagulation and an increased incidence of thromboembolic events. However, although plasma pre-thrombotic markers such as thrombin-anithrombin complexes and D-dimer are elevated, there is no consensus on whether global assays of thrombin generation in plasma are abnormal in patients with SCD. Based on our recent observation that normal red blood cells (RBCs) contribute to thrombin generation in whole blood, we hypothesized that the cellular components in blood (notably phosphatidylserine-expressing erythrocytes) contribute to enhanced thrombin generation in SCD. Methods Whole blood and plasma thrombin generation assays were performed on blood samples from 25 SCD patients in a non-crisis 'steady state' and 25 healthy race-matched controls. Results Whole blood thrombin generation was significantly elevated in SCD, whereas plasma thrombin generation was paradoxically reduced compared with controls. Surprisingly, whole blood and plasma thrombin generation were both negatively correlated with phosphatidylserine exposure on RBCs. Plasma thrombin generation in the presence of exogenous activated protein C or soluble thrombomodulin revealed deficiencies in the protein C/S anticoagulant pathway in SCD. These global changes were associated with significantly lower plasma protein S activity in SCD that correlated inversely with RBC phosphatidylserine exposure. Conclusion Increased RBC phosphatidylserine exposure in SCD is associated with acquired protein S deficiency. In addition, these data suggest a cellular contribution to thrombin generation in SCD (other than RBC phosphatidylserine exposure) that explains the elevated thrombin generation in whole blood.

A TMEM16F point mutation causes an absence of canine platelet TMEM16F and ineffective activation and death-induced phospholipid scrambling

BACKGROUND

TMEM16F is an ion channel and calcium-dependent lipid scramblase that mediates phosphatidylserine (PS) exposure on the plasma membrane. Two disparate disease phenotypes are associated with TMEM16F loss-of-function mutations: a rare bleeding disorder (Scott syndrome) and skeletal malformations due to aberrant bone mineralization in a TMEM16F knockout mouse. We therefore undertook comparative studies of TMEM16F expression in canine Scott syndrome (CSS), an autosomal recessive platelet defect.

OBJECTIVES

To define anoctamin proteins and scramblase response of CSS platelets and to determine whether TMEM16F is the CSS disease gene.

METHODS

CSS TMEM16F cDNA and gene were sequenced and mutation detection was performed in CSS pedigrees. Platelet fractions from CSS dogs were isolated for proteomic and immunologic characterization of TMEM16F. Annexin V was used as a flow cytometric marker of induced platelet PS externalization.

RESULTS

A TMEM16F splice site mutation segregated with the CSS trait and TMEM16F protein was undetectable in CSS platelet membranes; however, a second anoctamin, TMEM16K, was found. Proteomic analyses revealed a network of 32 proteins that differentially cosegregated with platelet plasma membrane TMEM16F. CSS platelets had profoundly impaired scramblase response to pharmacologic and physiologic agents that increase intraplatelet calcium and conditions that induce apoptotic and necrotic cell death.

CONCLUSIONS

CSS platelets represent a TMEM16F-null mutant model that demonstrates a central role for TMEM16F in mediating platelet PS externalization in response to activating and death signals. Platelet TMEM16F may prove a novel drug target for modulating platelet procoagulant activity and extending platelet life span.

Desmopressin treatment improves platelet function under flow in patients with postoperative bleeding

BACKGROUND

Patients undergoing major cardiothoracic surgery are subjected to dilution, owing to massive fluid infusion and blood component transfusion. These patients may experience bleeding perioperatively, and are frequently treated with the endothelium-activating agent desmopressin.

OBJECTIVES

To investigate the effect of desmopressin administration on von Willebrand factor (VWF)-dependent coagulant and platelet functions under flow conditions.

PATIENTS/METHODS

Blood from 16 patients with postoperative bleeding was obtained before and after desmopressin treatment (0.3 μg kg(-1) body weight), and assessed for coagulant properties and platelet function. Furthermore, VWF antigen levels and multimer composition were determined in both samples.

RESULTS

Desmopressin treatment did not change thrombin generation in plasma or whole blood thromboelasticity. Also coagulation factor levels (other than factor VIII) and coagulation times were unchanged, suggesting that desmopressin treatment did not have a major effect on the coagulant activity. On the other hand, desmopressin treatment raised the already high plasma levels of VWF from a median of 116 IU mL(-1) (interquartile range [IQR] 102-154 IU mL(-1) ) to a median of 160 IU mL(-1) (IQR 126-187 IU mL(-1) ) (P = 0.007), owing to accumulation of the high molecular weight VWF multimers. Furthermore, desmopressin treatment caused an increase in collagen-dependent thrombus formation and platelet phosphatidylserine exposure. Markers of thrombus formation correlated with the plasma levels of VWF. In vitro control experiments confirmed a major contribution of VWF to thrombus formation and procoagulant activity under conditions of blood dilution.

CONCLUSIONS

Desmopressin treatment of patients with bleeding complications after cardiothoracic surgery induces the release of high molecular weight VWF multimers, which enhance platelet activation and thrombus formation under flow conditions.

The prediction of type 2 diabetes in women with previous gestational diabetes mellitus using lipidomics

AIMS/HYPOTHESIS

The risk of developing diabetes is greater for women with previous gestational diabetes mellitus (GDM). In the general population, plasma lipidomic analysis can identify individuals at risk of developing type 2 diabetes. The aim of this study was to determine whether circulating lipid levels 12 weeks following a GDM pregnancy were associated with an increased risk of developing type 2 diabetes.

METHODS

Plasma lipid profiles containing >300 lipids were measured in 104 normal glucose-tolerant women 12 weeks following an index GDM pregnancy using electrospray-ionisation tandem mass spectrometry. Women were assessed for 10 years for development of overt type 2 diabetes.

RESULTS

Among the 104 women with previous GDM, 21 (20%) developed diabetes during the median follow-up period of 8.5 years. Three lipid species, the cholesteryl ester species CE 20:4, the alkenylphosphatidylethanolamine species PE(P-36:2) and the phosphatidylserine species PS 38:4, were independently and positively associated with the development of type 2 diabetes. In a clinical model of prediction of type 2 diabetes that included age, BMI, and levels of pregnancy fasting glucose, postnatal fasting glucose, triacylglycerol and total cholesterol, the addition of these three lipid species resulted in an improvement in the net reclassification index of 22.3%.

CONCLUSIONS/INTERPRETATION

The lipid species CE 20:4, PE(P-36:2) and PS 38:4 were significant risk factors for the development of type 2 diabetes in women with a previous history of GDM. This report is the first to use plasma lipidomic analysis to identify individual lipids as potential biomarkers for the prediction of type 2 diabetes in women with a history of GDM.

A simple flow cytometry method improves the detection of phosphatidylserine-exposing extracellular vesicles

BACKGROUND

Plasma contains cell-derived extracellular vesicles (EVs), which participate in physiopathological processes and have potential applications as disease biomarker. However, the enumeration of EVs faces major problems, due to their sub-micrometer size and to intrinsic limitations in methods of characterization, mainly flow cytometry (FCM).

OBJECTIVES

Our objective is to enumerate EVs in plasma, by taking as the prototype the population of phosphatidylserine (PS)-exposing EVs, which constitute one of the major EV populations and are responsible for thrombotic disorders.

METHODS

The concentration of PS-exposing EVs in platelet-free plasma (PFP) of healthy subjects was measured by FCM using either light scattering or fluorescence as the trigger and fluorescent Annexin-5 (Anx5) as the specific label. In addition, PS-exposing EVs were enumerated by electron microscopy (EM) after labeling with Anx5 gold nanoparticles and sedimentation on EM grids.

RESULTS

We show that about 50× more Anx5-positive EVs are detected by FCM when detection is triggered on fluorescence as compared with light scattering. By fluorescence triggering, concentrations of 22 000-30 000 Anx5-positive EVs per μL PFP were determined, using two different flow cytometers. The limit of detection of the fluorescence triggering method was estimated at about 1000-2500 Anx5 molecules. Results from EM suggest that EVs down to 100-150 nm diameter are detected by fluorescence triggering.

CONCLUSION

This study presents a simple method for enumerating EVs. We believe that this method is applicable in a general context and will improve our understanding of the roles of EVs in pathophysiological situations, which will open avenues for the development of EV-based diagnosis assays.

Platelets interact with Coxsackieviruses B and have a critical role in the pathogenesis of virus-induced myocarditis

BACKGROUND

To further understand the role of platelets in the pathogenesis of viral infections we explored platelet interaction with Coxsackieviruses B (CVB) 1 and 3. CVB is a group of viruses that cause the majority of human enterovirus-related viral myocarditis; their receptor (CAR) is expressed on the platelet surface and there is a well-characterized CVB3-induced myocarditis murine model.

METHODS

Human platelets were infected with CVB1 and 3 and viruses were detected in pellets and in supernatants. C57BL/6J mice with or without platelet depletion were inoculated with CVB3 and peripheral blood and heart samples collected at different times post-infection.

RESULTS

CVB1 and 3 RNA and a capsid protein were detected in infected platelets. Despite the fact that titration assays in Vero cells showed increasing infectivity titers over time, supernatants and pellets from infected platelets showed similar levels, suggesting that platelets were not susceptible to a replicative infectivity cycle. CVB binding was CAR-independent and resulted in P-selectin and phosphatidylserine (PS) exposure. CVB3-infected mice showed a rapid thrombocytopenia that correlated with an increase in platelet PS exposure and platelet-leukocyte aggregates without modification of platelet P-selectin expression or von Willebrand factor levels. Mortality, viremia, heart viral titers and myocarditis were significantly higher in platelet-depleted than normal animals. Type I IFN levels were not changed but IgG levels were lower in infected and platelet-depleted mice.

CONCLUSIONS

Our data reveal that platelets play a critical role in host survival and immune response against CVB3 infection.

Erythrocytic phosphatidylserine exposure and hemostatic alterations in β-thalassemia intermediate patients

INTRODUCTION

Hypercoagulable state is one of the common findings in beta-thalassemia intermedia (β-TI), particularly in splenectomized patients, with infrequent blood transfusion. Abnormality of the red blood cells (RBC) membrane due to oxidative damage is suggestive of possible etiologies. Membrane lipid peroxidation increases the exposure of phosphatidylserine (PS) that plays a role in the activation of coagulation factors V and X, subsequently initiating thrombosis. Our aim of this study was to find the probable correlation of the alteration of the PS on the RBC outer membrane with the hypercoagulable state in the β-TI patients.

MATERIALS AND METHODS

Our cross-sectional study was conducted on 39 splenectomized β-TI patients and 38 age-matched healthy controls. The mean age was 37 years. Analysis of the PS exposure on the RBCs was performed by fluorescein isothiocyanate (FITC) conjugated AV protein. Measurement of the coagulation factors X, V and antithrombin III (AT-III) was performed. We also checked the D-dimer levels. Analysis was performed by SPSS16.

RESULTS

Fluorescence of FITC-Annexin V labeling on patients RBCs were higher than healthy controls; (2.8 ± 2.2%) of the patients versus (0.4 ± 0.18%) in the control group and was statistically significant (P < 0.05). Mean levels of factor X and AT-III of the patients as compared with the control group decreased and showed significant difference (P < 0.05).

CONCLUSIONS

Circulation of thalassemic RBCs, which abnormally possess PS on RBC membrane outer surface, suggests the possibility of the gradual consumption of the coagulation factors in the presence of a chronic coagulability state.

Platelet-based coagulation: different populations, different functions

Platelets in a thrombus interact with (anti)coagulation factors and support blood coagulation. In the concept of cell-based control of coagulation, three different roles of platelets can be distinguished: control of thrombin generation, support of fibrin formation, and regulation of fibrin clot retraction. Here, we postulate that different populations of platelets with distinct surface properties are involved in these coagulant functions. Platelets with elevated Ca(2+) and exposed phosphatidylserine control thrombin and fibrin generation, while platelets with activated α(IIb) β(3) regulate clot retraction. We review how coagulation factor binding depends on the platelet activation state. Furthermore, we discuss the ligands, platelet receptors and downstream intracellular signaling pathways implicated in these coagulant functions. These insights lead to an adapted model of platelet-based coagulation.

P2Y12 protects platelets from apoptosis via PI3k-dependent Bak/Bax inactivation

BACKGROUND

Platelet ADP receptor P2Y(12) is well studied and recognized as a key player in platelet activation, hemostasis and thrombosis. However, the role of P2Y(12) in platelet apoptosis remains unknown.

OBJECTIVES

To evaluate the role of the P2Y(12) receptor in platelet apoptosis.

METHODS

We used flow cytometry and Western blotting to assess apoptotic events in platelets treated with ABT-737 or ABT-263, and stored at 37°C, combined with P2Y(12) receptor antagonists or P2Y(12) -deficient mice.

RESULTS

 P2Y(12) activation attenuated apoptosis induced by ABT-737 in human and mouse platelets in vitro, evidenced by reduced phosphatidylserine (PS) exposure, diminished depolarization of mitochondrial inner transmembrane potential (ΔΨm) and decreased caspase-3 activation. Through increasing the phosphorylation level of Akt and Bad, and changing the interaction between different Bcl-2 family proteins, P2Y(12) activation inactivated Bak/Bax. This antiapoptotic effect could be abolished by P2Y(12) antagonism or PI3K inhibition. We also observed the antiapoptotic effect of P2Y(12) activation in platelets stored at 37°C. P2Y(12) activation improved the impaired activation responses of apoptotic platelets stressed by ABT-737. In platelets from mice dosed with ABT-263 in vivo, clopidogrel or deficiency of P2Y(12) receptor enhanced apoptosis along with increased Bak/Bax activation.

CONCLUSIONS

This study demonstrates that P2Y(12) activation protects platelets from apoptosis via PI3k-dependent Bak/Bax inactivation, which may be physiologically important to counter the proapoptotic challenge. Our findings that P2Y(12) blockade exaggerates platelet apoptosis induced by ABT-263 (Navitoclax) also imply a novel drug interaction of ABT-263 and P2Y(12) antagonists.

Procoagulant and prothrombotic effects of the herbal medicine, Dipsacus asper and its active ingredient, dipsacus saponin C, on human platelets

BACKGROUND

In spite of the growing popularity of herbal medicines and natural food supplements, their effects on cardiovascular homeostasis remain largely unknown, especially regarding pro-thrombotic risks.

OBJECTIVE

In the present study, 21 herbal tea extracts were screened for the procoagulant activities on platelets, an important promoter of thrombosis to examine if herbal medicines or natural products may have prothrombotic risks. We discovered that Dipsacus asper (DA), known to have analgesic and anti-inflammatory effects, potently induced procoagulant activities in platelets. We tried to identify the active ingredient and elucidate the underlying mechanism.

RESULTS

Among 10 major ingredients of DA, dipsacus saponin C (DSC) was identified as a key active ingredient in DA-induced procoagulant activities. DSC-induced procoagulant activities were achieved by the exposure of phosphatidylserine (PS) and PS-bearing microparticle generation that were caused by the alteration in the activities of phospholipid translocases: scramblase and flippase. These events were initiated by increased intracellular calcium and ATP depletion. Notably, DSC induced a series of apoptotic events including the disruption of mitochondrial membrane potential, translocation of Bax and Bak, cytochrome c release and caspase-3 activation. The key roles of apoptotic pathway and caspase activation were demonstrated by the reversal of DSC-induced PS exposure and procoagulant activities with the pretreatment of caspase inhibitors. Interestingly, EGTA reversed DSC-induced procoagulant activities and apoptotic events suggesting that an intracellular calcium increase may play a central role. These results were also confirmed in vivo where platelets of the rats exposed to DSC or DA exhibited PS exposure. Most importantly, DSC or DA administration led to increased thrombus formation.

CONCLUSION

These results demonstrate that herbal medicines or natural products such as DA or DSC might have prothrombotic risks through procoagulant activation of platelets.

Relationship between clotting activity and phosphatidylserine expression on erythrocyte membranes in polycythemia vera patients with the JAK2 V617F mutation

INTRODUCTION

Polycythemia vera (PV) accompanies the clinical course of thrombosis. Phosphatidylserine (PS) expression on the plasma membrane has been known to be one of place where the coagulation system activates. We studied the relationship between clotting factor activity and PS expression on the erythrocyte membrane in patients with erythrocytosis.

METHODS

The coagulation test and PS expression in 23 patients with erythrocytosis were measured. PS expression was determined indirectly by measuring annexin V binding to erythrocytes using fluorescence activated cell sorter analysis (FACS).

RESULTS

The activity of clotting factors (II, V, VII, VIII, von Willebrand factor, IX, X) was significantly lower in PV than in the mutation-negative erythrocytosis. There was a significant correlation between reduced activity of clotting factors such as V, X, and IX and increased PS expression of the erythrocyte membrane.

CONCLUSION

Increased expression of PS on the erythrocyte membrane may reduce the activities of clotting factors in PV patients with JAK2 V617F mutation.

Increased expression of endothelial-platelet dysfunctional pathway in patients with arterial erectile dysfunction

AIM

Pathophysiological externalization of specific substances belonging to the vessel wall (after endothelial injury), usually not in contact with the blood (subintimal area) is the signal which is captured by surface receptor platelet's results in their adhesion. There are no studies that have so far examined the expression of these receptors in patients with arterial erectile dysfunction (ED). The aim of this study was to assess by flow cytometry, serum concentration of apoptotic endothelial microparticles (EMPa) and vitronectin receptor (VR) in a selected series of patients with arterial ED and without apparent other sistemic arterial involvement.

METHODS

Evaluated consecutively 50 selected patients with arterial ED-based (mean IIEF-5 score of 6.3±0.3 and mean peak systolic velocity of 24.5±0.6 cm/s). Evaluation of EMPa and VR was conducted using a flow cytometer. The events CD45neg-CD144pos-annexinVpos were defined EMPa, while events CD51pos-CD61pos-CD41neg were defined VR.

RESULTS

Patients with arterial ED had a serum baseline concentrations of circulating EMPa (12.2±2.2% vs. 1.8±0.4%) and VR (7.4±1.2% vs. 1.2±0.2%) significantly higher than control group.

CONCLUSION

The present study shows that patients with arterial ED had an increased expression of endothelial apoptosis and initial platelet adhesion.

Red blood cell phosphatidylserine exposure is responsible for increased erythrocyte adhesion to endothelium in central retinal vein occlusion

BACKGROUND

Retinal vein occlusion (RVO) is a common cause of permanent loss of vision. The pathophysiology is uncertain, although enhanced erythrocyte aggregation and blood hyperviscosity have been observed. Increased red blood cell (RBC) adhesion has been associated with vascular complications in several diseases, such as sickle cell anemia, diabetes mellitus or polycythemia vera.

OBJECTIVES

To measure RBC adhesion to endothelial cells in RVO and to explore the molecular basis of the adhesion process.

PATIENTS AND METHODS

We assessed RBC adhesion to endothelial cells and adhesion molecule expression among 32 patients with RVO. Patients with disease known to alter RBC adhesion were excluded (n = 8), and further investigation was conducted in 20 patients with central retinal vein occlusion (CRVO) and four patients with retinal artery occlusion (RAO), compared with 25 normal subjects.

RESULTS

Under static conditions, adhesion of CRVO RBC was increased (135 ± 7 × 10(2) mm(-2)) compared with RAO RBC (63 ± 5 × 10(2) mm(-2)) (P < 0.01) and normal control RBC (37 ± 3 × 10(2) mm(-2)) (P < 0.001). Under flow conditions, CRVO RBC adhered in greater numbers than normal RBC (P < 0.001). Phosphatidylserine (PS) expression on CRVO RBC was 2.4-fold higher than controls and correlated with RBC adhesion (P = 0.001). In static conditions, specific antibodies against PS receptor and annexin V inhibited RBC adhesion. In flow conditions, the inhibitory effect was in the same range with antibodies but was 2-fold higher with annexin V.

CONCLUSION

Increased CRVO RBC adhesion is mediated by PS RBC and endothelial PS receptor. This phenomenon may be one of the factors responsible for CRVO.

Activation of mononuclear phagocytes and its relationship to asplenia and phosphatidylserine exposing red blood cells in hemoglobin E/β-thalassemia patients

Aged or abnormal red blood cells with exposed phosphatidylserine (PSRBCs) are cleared from the circulation by splenic macrophages. In asplenic patients, other mononuclear phagocytic cells in tissues and in circulation may function in this capacity. To better understand these changes and the relationship among splenic status, PS-RBCs, blood monocytes, and serum tumor necrosis factor (TNF-α), a product of mononuclear phagocyte activation, patients with hemoglobin E/β-thalassemia (E/β-Thal) were studied. Whole blood of 20 nonsplenectomized, 20 splenectomized E/β-Thal patients, and 20 healthy subjects was assayed for PS-RBCs; for monocytes, activated monocytes, and monocyte response to lipopolysaccharide stimulation; and serum was assayed for TNF-α. Asplenic E/β-Thal patients had significantly increased (P < 0.05) amounts of PS-RBCs, monocytes, activated monocytes, and levels of serum TNF-α. The amount of PS-RBCs correlated with levels of serum TNF-α, but the amount of activated monocytes did not correlate with either the amount of PS-RBCs or levels of serum TNF-α. Monocyte response to lipopolysaccharide stimulation in asplenic patients was not as efficient as in the other patients or in normals (77 vs. 404, and 304 folds increment, respectively). The results suggest that splenectomy in E/β-Thal patients led to an increased amount of PSRBCs and activation in the mononuclear phagocytic system.

Phosphatidylserine exposure and other apoptotic-like events in Bernard-Soulier syndrome platelets

In the Bernard-Soulier syndrome (BSS), the giant platelets are said to have increased phosphatidylserine (PS) surface exposure in the resting state and shortened survival in the circulation. When normal platelets are activated, they undergo many biochemical and morphological changes, some of which are apoptotic. Herein, we investigated apoptotic-like events in BSS platelets upon activation, specifically, PS exposure, microparticle (MP) formation, cell shrinkage, and loss of mitochondrial inner membrane potential (DeltaPsi(m)). Platelets from two unrelated BSS patients were examined in whole blood; agonists used were collagen, thrombin, PAR1- or PAR4-activating peptides (APs), or combinations of collagen with thrombin, and the PAR-APs. Flow cytometry was used to measure PS exposure (annexin A5 binding), platelet-derived MPs (forward scatter; events <0.75 microm size), and DeltaPsi(m) (TMRM fluorescence). PS exposure was increased on resting and activated BSS platelets, and this was independent of the platelet size. MP formation by BSS platelets was generally enhanced. Cell shrinkage occurred on activation to form smaller, PS-exposing platelets in BSS and controls. A proportion of PS-exposing BSS and control platelets exhibited DeltaPsi(m) loss, but unlike controls, there was also loss of DeltaPsi(m) in the BSS platelets not exposing PS. Thus, BSS platelets undergo apoptotic-like events upon activation, with PS exposure and MP formation being enhanced. These events may play a role in the shortened survival in BSS, as well as affecting thrombin generation.

Specific binding of hypochlorite-oxidized HDL to platelet CD36 triggers proinflammatory and procoagulant effects

OBJECTIVE

Oxidative stress and systemic inflammation negatively affect several protective functions of high density lipoproteins (HDL) and oxidative modification of HDL by the inflammation-derived oxidant hypochlorite converts HDL into a potent platelet agonist. Therefore it was the aim of this work to clarify if these platelet-activating effects result from specific binding of hypochlorite-oxidized HDL (hyp-OxHDL) to the platelet surface and to identify responsible receptors.

METHODS

Binding and functional studies were performed with hyp-OxHDL in absence and presence of (potential) competitors in normal and CD36-deficient human platelets. Platelet aggregation was quantified by light transmission aggregometry. Surface expression of CD62P, phosphatidylserine and CD40L was quantified by flow cytometry.

RESULTS

Binding studies reveal that hyp-OxHDL show specific and saturable high-affinity binding to the platelet surface. Hyp-OxHDL trigger platelet aggregation and in a dose dependent way provoke the release of significant amounts of CD40L as well as phosphatidylserine on the platelet surface. Blocking specific binding of hyp-OxHDL to the platelet surface interferes with the ability of hyp-OxHDL to stimulate human platelets. CD36-deficient human platelets show markedly reduced binding of hyp-OxHDL. Upon addition of hypochlorite-oxidized HDL, CD36-deficient platelets do not aggregate and completely fail to release CD40L or phosphatidylserine.

CONCLUSIONS

From these results we conclude that specific binding of hyp-OxHDL to platelet CD36 is essential for the proinflammatory and procoagulant effects of hyp-OxHDL shown within this work. The contribution of other receptors besides CD36 to specific binding of hyp-OxHDL to the platelet membrane appears to be minimal, at best.

RGD-ligand mimetic antagonists of integrin alphaIIbbeta3 paradoxically enhance GPVI-induced human platelet activation

BACKGROUND

The integrin alpha(IIb)beta(3) is the major mediator of platelet aggregation and has, therefore, become an important target of antithrombotic therapy. Antagonists of alpha(IIb)beta(3), for example abciximab, tirofiban and eptifibatide, are used in the treatment of acute coronary syndromes. However, in addition to effective blockade of the integrin, binding of can induce conformational changes in the integrin and can also induce integrin clustering. This class effect of RGD-ligand mimetics might, therefore, underlie paradoxical platelet activation and thrombosis previously reported.

OBJECTIVES

To examine the components of signaling pathways and functional responses in platelets that may underlie this phenomenon of paradoxical platelet activation.

METHODS

We assessed the effect of lotrafiban, and other alpha(IIb)beta(3) antagonists including the clinically used drug tirofiban, on tyrosine phosphorylation of key signaling proteins in platelets by immunoblotting and also platelet functional outputs such as cytosolic calcium responses, phosphatidylserine exposure (pro-coagulant activity) and dense granule release.

RESULTS

In all cases, no effect of alpha(IIb)beta(3) antagonists were observed on their own, but these integrin antagonists did lead to a marked potentiation of glycoprotein VI (GPVI)-associated FcR gamma-chain phosphorylation, activation of Src family kinases and Syk kinase. This correlated with increased dense granule secretion, cytosolic calcium response and exposure of phosphatidylserine on the platelet surface. P2Y(12) antagonism abolished the potentiated phosphatidylserine exposure and dense granule secretion but not the cytosolic calcium response.

CONCLUSIONS

These data provide a mechanism for enhancement of platelet activity by alpha(IIb)beta(3) inhibitors, but also reveal a potentially important signaling pathway operating from the integrin to GPVI signaling.

Effect of iron chelators on labile iron and oxidative status of thalassaemic erythroid cells

BACKGROUND/AIMS

Iron accumulation in vital organs such as heart and liver is a major pathology in beta-thalassaemia. It may also affect mature RBCs and developing erythroid precursors. The cellular damage is mainly caused by the labile iron pool (LIP) and is mediated by reactive oxygen species (ROS). We have previously shown that thalassaemic RBCs and their precursors have more LIP and ROS than their normal counterparts. We now report the effect of clinically relevant iron chelators on these parameters.

METHODS

RBCs, reticulocytes and cultured erythroid precursors derived from patients with beta-thalassaemia were studied for LIP and oxidative stress parameters by flow-cytometry.

RESULTS

In vitro treatment with deferiprone, deferasirox and deferoxamine reduced the cytosolic LIP in RBCs and reticulocytes, and both the cytosolic and mitochondrial LIP in cultured erythroid precursors. This was associated with reduced oxidative stress (ROS and external phosphatidylserine). While the effect of deferiprone and deferasirox was fast (within 10 min), deferoxamine affected these parameters after 24 h, suggesting a slower rate of entry.

CONCLUSION

The chelators studied reduce the LIP and the oxidative status of thalassaemic RBC and their precursors. Whether these effects directly improve ineffective erythropoiesis and RBC survival remains to be shown.

Testosterone and estradiol-17 beta dependent phospholipid biosynthesis in ovariectomized catfish, Heteropneustes fossilis (Bloch)

Effect of cumulative doses (7, 14 and 28 mg kg(-1) body weight) of testosterone (T) and estradiol-17 beta (E2) on total phospholipids (TP), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE) in tissues were investigated during the gonadal recrudescence, in prespawning phase of the annual reproductive cycle in intact and ovariectomized freshwater catfish, Heteropneustes fossilis. After ovariectomy, the hepatic levels of TP and PE were elevated and remained unaffected for PC, PS and PE when compared with control. In general, T and E2 were stimulatory fora specific class ofphospholipid in tissues of intact and ovariectomized catfish. These effects were higher at 14 and 28 mg kg(-1) body weight in ovariectomized catfish whereas 7 mg kg(-1) body weight of T and E2 have pronounced effect in intact ovaries. In conclusion, the various phospholipid biosynthesis were under T and E2 dependent. Among the phospholipid, the PC was the main constituent and was sex steroid dependent biosynthesis during prespawning phase.

Multimerin 1 binds factor V and activated factor V with high affinity and inhibits thrombin generation

Multimerin 1 (MMRN1) is a polymeric, factor V (FV) binding protein that is stored in platelet and endothelial cell secretion granules but is undetectable in normal plasma. In human platelet alpha-granules, FV is stored complexed to MMRN1, predominantly by noncovalent binding interactions. The FV binding site for MMRN1 is located in the light chain, where it overlaps the C1 and C2 domain membrane binding sites essential for activated FV (FVa) procoagulant function. Surface plasmon resonance (SPR), circular dichroism (CD) and thrombin generation assays were used to study the binding of FV and FVa to MMRN1, and the functional consequences. FV and FVa bound MMRN1 with high affinities (K(D): 2 and 7 nM, respectively). FV dissociated more slowly from MMRN1 than FVa in SPR experiments, and CD analyses suggested greater conformational changes in mixtures of FV and MMRN1 than in mixtures of FVa and MMRN1. SPR analyses indicated that soluble phosphatidylserine (1,2-Dicaproylsn-glycero-3-phospho-L-serine) competitively inhibited both FV-MMRN1 and FVa-MMRN1 binding. Furthermore, exogenous MMRN1 delayed and reduced thrombin generation by plasma and platelets, and it reduced thrombin generation by preformed FVa. Exogenous MMRN1 also delayed FV activation, triggered by adding tissue factor to plasma, or by adding purified thrombin or factor Xa to purified FV. The high affinity binding of FV to MMRN1 may facilitate the costorage of the two proteins in platelet alpha-granules. As a consequence, MMRN1 release during platelet activation may limit platelet dependent thrombin generation in vivo.

A role of phosphatidylserine externalization in clearance of erythrocytes exposed to stress but not in eliminating aging populations of erythrocyte in mice

Age dependent changes in phosphatidylserine (PS) externalization were studied in mouse erythrocytes of different age groups (range 1-55 days) by using a newly developed double in vivo biotinylation (DIB) technique. Around 3-4% of the erythrocytes freshly released in the circulation were PS(+) but this proportion fell rapidly to 1% or less and did not increase at later time points. Blocking erythrocyte clearance from the circulation by in vivo depletion of macrophages (by treatment with clodronate loaded liposomes) for up to 7 days did not result in accumulation of PS(+) erythrocytes in the circulation indicating that the low percentage of PS(+) cells within old erythrocytes (age >40 days) was not related to the clearance of PS(+) erythrocytes by macrophages. In vitro treatment with stress inducing agents like deoxyglucose or Ca(++)/calcium ionophore resulted in a marked induction of PS externalization in mouse erythrocytes and this effect was most prominent in the youngest erythrocyte population (age <10 days). Kinetics of clearance of different age groups of stress exposed erythrocytes after intravenous infusion into recipient mice indicated that the young erythrocytes were cleared at fastest rate from the circulation as compared to erythrocytes of older age groups. Within young erythrocytes exposed to stress, PS(+) erythrocytes were preferentially cleared. Taken together our results suggest that PS externalization is unlikely to have a role in the removal of old erythrocytes from blood circulation but may have a role in the clearance of stressed and damaged young erythrocytes in blood circulation.

The active metabolite of prasugrel inhibits adenosine diphosphate- and collagen-stimulated platelet procoagulant activities

BACKGROUND

Prasugrel is a novel antiplatelet prodrug of the same thienopyridine class as clopidogrel and ticlopidine. Metabolism of prasugrel generates the active metabolite R-138727, an antagonist of the platelet P2Y(12) adenosine diphosphate (ADP) receptor, leading to inhibition of ADP-mediated platelet activation and aggregation. ADP also enhances the platelet response to collagen, and these two agonists contribute to the generation of platelet procoagulant activity. We therefore examined whether R-138727 inhibits ADP- and collagen-triggered platelet procoagulant activities.

METHODS AND RESULTS

As shown by whole blood flow cytometry, R-138727 inhibited surface phosphatidylserine expression on ADP plus collagen-stimulated platelets and tissue factor (TF) expression on ADP-, collagen-, and ADP plus collagen-stimulated monocyte-platelet aggregates. R-138727 reduced monocyte-platelet aggregate formation, thereby further inhibiting TF expression. ADP, collagen, and ADP plus collagen accelerated the kinetics of thrombin generation in recalcified whole blood and R-138727 significantly inhibited this acceleration. Clot strength in a modified thromboelastograph system was also inhibited by R-138727 (IC50 0.7 +/- 0.1 microM).

CONCLUSIONS

In addition to its previously known inhibitory effects on platelet activation and aggregation, the active metabolite of prasugrel, R-138727, inhibits platelet procoagulant activity in whole blood (as determined by phosphatidylserine expression on platelets and TF expression on monocyte-platelet aggregates), resulting in the functional consequences of delayed thrombin generation and impaired clot development.

Differential effects of dialysis and ultrafiltrate from individuals with CKD, with or without diabetes, on platelet phosphatidylserine externalization

Individuals with chronic kidney disease (CKD) and/or diabetes mellitus (DM) are at increased risk of cardiovascular events and have elevated externalization of phosphatidylserine (PS; which propagates thrombus formation) in a small subpopulation of platelets. The purpose of this study was to examine the effect of 1) removing uremic toxins by hemodialysis on PS externalization in patients with either CKD or CKD and DM and 2) ultrafiltrate (UF) from these individuals on PS externalization in healthy platelets. PS externalization was quantified by a fluorescence-activated cell sorter using annexin V in platelet-rich plasma. PS externalization was elevated threefold in CKD patients and returned to basal values during 3-h hemodialysis. In contrast, it was elevated fivefold in individuals with CKD and DM and was still threefold above control after 3-h treatment. UF significantly increased PS externalization in a small subpopulation of platelets from healthy controls. The effect of UF from individuals with CKD and DM was significantly greater than that from patients with CKD alone, and the responses were partially inhibited by the protein kinase Cδ (PKCδ) inhibitor rottlerin and the 5-hydroxytryptamine (5-HT)2A/2Creceptor antagonist ritanserin. The data suggest that uremic toxins present in UF mediate PS externalization in a small subpopulation of platelets, at least in part, via the 5-HT2A/2Creceptor and PKCδ and demonstrate that DM further enhances platelet PS externalization in CKD patients undergoing hemodialysis. This may explain, at least in part, the additional increase in vascular damage observed in CKD patients when DM is present.

Influence of pH on stored human platelets

BACKGROUND

During storage at room temperature, platelets (PLTs) undergo several changes, a process known as PLT storage lesion. The pH is one of the variables changing and has been suggested to be a good surrogate marker for the quality of PLT concentrates. It is unknown whether the pH decrease as such induces the PLT storage lesion or that the deterioration of the PLTs results in the pH decrease. In this study, the responses of PLTs to applied pH values were investigated.

STUDY DESIGN AND METHODS

PLTs were washed three times in PLT additive solution (PAS-IIIM) and were resuspended in PAS-IIIM buffers with or without 30 percent plasma with different pH values over a range from 6.0 to 7.5 (at 37 degrees C). The PLTs were stored in 50-mL culture flasks at 22 degrees C.

RESULTS

During 3 days of storage in 100 percent additive solution (AS), the extracellular pH did not affect in vitro quality measures. Both at the lower and at the higher end of the pH range, we observed an increased glycolytic flux, accelerated at Day 6. Also in the presence of 30 percent plasma, the effect of extracellular pH was very limited, but all variables indicated better PLT quality with stable values up to Day 6 of storage.

CONCLUSIONS

We conclude that PLTs stored in 100 percent AS are able to cope with high and low pH values without a strong deterioration within 3 days. PLTs stored in 30 percent plasma-70 percent AS are more capable in dealing with different pH values than PLTs stored in AS and remained stable for 6 days. We suggest that the pH decrease is a result of the PLT storage lesion and not the cause.

Investigation on the early events of apoptosis in senescent erythrocytes with special emphasis on intracellular free calcium and loss of phospholipid asymmetry in chronic renal failure

BACKGROUND

The pathophysiological link between increased blood concentrations of factors responsible for the derangement and erythrocyte membrane functions in chronic renal failure (CRF) patients are not thoroughly elucidated. We studied the erythrocyte characteristics and phospholipid asymmetry loss in CRF patients with different grades of uremia and also examined the involvement of intracellular free Ca(2+) in early events of apoptosis in uremic erythrocytes.

METHODS

The studied population consisted of 90, age and sex matched control subjects (Group I) and 238 CRF cases divided into 3 groups (Group II, III and IV) according to urea concentrations and complexity of secondary complications. Erythrocyte membrane fluidity determined by binding of MC540. Intracellular free Ca(2+) concentration was determined by the 2-wavelength method by using fluorescent calcium-sensitive probe FURA-2AM. Measurement of erythrocyte phosphatidylserine exposure by flow cytometry using Annexin V-FITC.

RESULTS

Cholesterol shedding increased with increasing severity of uremic complications. Erythrocytes from Group II show mild echinocyte or formation of spicules on the erythrocyte membrane surface whereas in Group III and IV they were echinocytic. Binding of MC540 was significantly higher with progression of uremic complications. Surface charge of uremic erythrocyte membrane was significantly reduced when compared with control subjects. Intracellular free Ca(2+) was positively correlated with binding of MC540 and surface hydrophobicity. The phosphatidylserine exposure of erythrocytes was significantly higher (p<0.001) in uremic patients when compared with controls.

CONCLUSIONS

Phosphatidylserine (PS) exposure erythrocytes were significantly increased in uremic patients when compared with controls. Uremic complications predisposes to membrane damages in erythrocytes.

Thrombin induces apoptotic events through the generation of reactive oxygen species in human platelets

BACKGROUND

Thrombin is a major physiological platelet agonist that activates a number of cell functions including aggregation. Platelet stimulation with thrombin has been shown to result in the development of apoptotic events, including activation of caspases-3 and -9, cytochrome c release and phosphatidylserine (PS) exposure; however, the mechanism underlying the activation of apoptosis remains unclear.

OBJECTIVES

In the present study, we aim to investigate whether endogenously generated reactive oxygen species upon thrombin stimulation is required for the activation of apoptosis in human platelets.

METHODS

Changes in the mitochondrial membrane potential were registered using the dye JC-1; caspase-3 and -9 activity was determined from the cleavage of their respective specific fluorogenic substrates; PS externalization was estimated using annexin V-fluorescein isothicyanate and cytochrome c release was detected by Western blotting in samples from the mitochondrial and cytosolic fractions.

RESULTS

Treatment of platelets with thrombin stimulates mitochondrial membrane potential depolarization and endogenous generation of H(2)O(2) . Platelet exposure to exogenous H(2)O(2) results in cytochrome c release and activation of caspases-9. In addition, H(2)O(2) induces the activation of caspase-3 and PS exposure by a mechanism dependent on cytochrome c release and caspase-9 activation. Finally, thrombin-evoked development of apoptotic events was impaired by treatment with catalase.

CONCLUSION

Our results indicate that thrombin-induced apoptosis is likely mediated by endogenous generation of H(2)O(2) in human platelets.

Adenosine protects against suicidal erythrocyte death

Suicidal death of erythrocytes or eryptosis is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the erythrocyte surface. The cell membrane scrambling is triggered by an increase in cytosolic Ca(2+) activity and activation of protein kinase C (PKC). Phosphatidylserine exposure fosters adherence of affected erythrocytes to the vascular wall. Thus, microcirculation in ischemic tissues may be impaired by the appearance of eryptotic erythrocytes. Ischemia leads to release of adenosine, which in most tissues leads to vasodilation and protects against cell injury. The present experiments explored whether adenosine influences mechanisms underlying eryptosis. Erythrocyte phosphatidylserine exposure was estimated from annexin V binding, cell volume from forward scatter and cytosolic Ca(2+) activity from Fluo3 fluorescence. Glucose depletion (for 24 or 48 h) significantly increased annexin binding and decreased forward scatter, effects partially reversed by adenosine. The protective effect of adenosine reached statistical significance (s.d.) at > =30 microM. Low Cl(-) solution (Cl(-) exchanged by gluconate for 24 h) similarly increased annexin binding and decreased forward scatter, effects again reversed by adenosine (s.d. at > or =10 and 30 microM, respectively). Similarly, phosphatase inhibitor okadaic acid (OA, 1 microM) and PKC activator phorbol 12-myristate-13-acetate (PMA, 3 microM) significantly enhanced annexin binding and decreased forward scatter. Adenosine significantly blunted the effects of OA and PMA on annexin V binding (s.d. at > or =30 and 10 microM, respectively) and the effect of OA on forward scatter (s.d. at > or =10 microM). In conclusion, adenosine inhibits eryptosis by a mechanism presumably effective downstream of PKC. The effect may participate in the maintenance of microcirculation in ischemic tissue.

The role of erythrocytes phosphatidylserine exposure in anemia in peritoneal dialysis patients

BACKGROUND

An increased red blood cell (RBC) phosphatidylserine (PS) exposure in uremic patients was found that could promote macrophage recognition and decrease RBC survival time. Furthermore, a reduced red cell life span was found to contribute anemia in patients with renal failure. It is therefore possible to hypothesize that increased PS externalization of RBC may influence renal anemia. The present study preliminarily explored the role of erythrocytes' PS exposure in anemia in uremic patients.

METHOD

Erythrocyte PS exposure was measured in 67 stable patients on continuous ambulatory peritoneal dialysis (CAPD). An investigation was conducted in the relationship between the level of erythrocyte PS exposure and hemoglobin concentration. A flow-cytometric assay based on FITC-Annexin V was used to measure the PS exposure of erythrocytes.

RESULTS

An inverse correlation was found between the percentage of PS-positive RBCs and hemoglobin concentration (r = -0.2601, p < 0.05). Logistic regression analysis revealed that the percentage of PS-positive RBCs was identified as a risk factor for anemia (Hazards ratio = -0.421, p < 0.05).

CONCLUSION

This study found that elevated PS exposure in erythrocytes might be a risk factor for anemia and contribute to the development of anemia in peritoneal dialysis patients.

P2X(7) receptor activation causes phosphatidylserine exposure in human erythrocytes

Activation of cation channels causes erythrocyte phosphatidylserine (PS) exposure and cell shrinkage. Human erythrocytes express the P2X(7) receptor, an ATP-gated cation channel. The two most potent P2X(7) agonists, BzATP and ATP, stimulated PS exposure in human erythrocytes. Other nucleotides also induced erythrocyte PS exposure with an order of agonist potency of BzATP>ATP>2MeSATP>ATPgammaS; however neither ADP nor UTP had an effect. ATP induced PS exposure in erythrocytes in a dose-dependent fashion with an EC(50) of approximately 75 microM. BzATP- and ATP-induced erythrocyte PS exposure was impaired by oxidised ATP, as well as in erythrocytes from subjects who had inherited loss-of-function polymorphisms in the P2X(7) receptor. ATP-induced PS exposure in erythrocytes was not significantly altered in the presence of EGTA excluding a role for extracellular Ca(2+). These results show that P2X(7) activation by extracellular ATP can induce PS exposure in erythrocytes.

In vivo effects of lead on erythrocytes following chronic exposure through drinking water

More than 95% of lead, a environmental heavy metal, entering into blood accumulates in erythrocytes suggesting erythrocytes as an important target of lead toxicity. Recent studies reported that erythrocytes could contribute to blood coagulation via phosphatidylserine (PS) exposure in erythrocytes. However, in vivo effects of chronic lead exposure especially by drinking water on procoagulant activity of erythrocytes have not been studied yet. In the present study, we investigated the effects of chronic exposure of lead by drinking water on erythrocytes in rats. Groups of 40 male rats were provided with drinking water containing various concentrations of lead for 4 weeks and complete blood cell count, procoagulant activities of erythrocytes and platelets were evaluated with basic inspections on body weight and food/ water consumption. The administration of lead containing drinking water increased the blood lead level (BLL) in a dose-dependent manner up to 22.39 +/- 2.26 microg/dL. Water consumption was significantly decreased while food consumption or body weight gain was not affected. In contrast to the "previous findings with acute lead exposure, chronic lead exposure failed to increase PS exposure in erythrocytes with statistical significance although some trends of enhancement were observed. It implies that a certain adaptation might have happened in body during repeated exposure to lead, resulting in attenuation of PS exposure. With this study, we believe that a valuable information was provided for the study on the toxicological significance and the risk assessment of lead contaminated drinking water.

Stimulation of erythrocyte phosphatidylserine exposure by paclitaxel

Side effects of cytostatic treatment include development of anemia resulting from either decreased generation or accelerated clearance of circulating erythrocytes. Recent experiments revealed a novel kind of stress-induced erythrocyte death, i.e. eryptosis, which is characterized by enhanced cytosolic Ca(2+) levels, increased ceramide formation and exposure of phosphatidylserine at the cell surface. The present study explored whether cytostatic treatment with paclitaxel (Taxol) triggers eryptosis. Blood was drawn from cancer patients before and after infusion of 175 mg/m2 Taxol. The treatment significantly decreased the hematocrit and significantly increased the percentage of annexin-V-binding erythrocytes in vivo (by 37%). In vitro incubation of human erythrocytes with 10 microM paclitaxel again significantly increased annexin-V-binding (by 129%) and augmented the increase of annexin-V-binding following cellular stress. The enhanced phosphatidylserine exposure was not dependent on caspase-activity but paralleled by erythrocyte shrinkage, increase of cytosolic Ca(2+) activity, ceramide formation and activation of calpain. Phosphatidylserine exposure was similarly induced by docetaxel but not by carboplatin or doxorubicin. Moreover, eryptosis was triggered by the Ca(2+) ionophore ionomycin (10 microM). In mice, ionomycin-treated eryptotic erythrocytes were rapidly cleared from circulating blood and sequestrated into the spleen. In conclusion, our data strongly suggest that paclitaxel-induced anemia is at least partially due to induction of eryptosis.

Rescued mice with Hb E transgene-developed red cell changes similar to human beta-thalassemia/HbE disease

A novel C57BL/6 transgenic murine model of HbE has been developed, and the heterotetrameric ((m)alpha2(h)beta(E)2) hemoglobin shows significant complementation of mild thalassemia phenotype in double heterozygous (beta(m+)beta(m-), beta(hE)) and homozygous knockout (beta(m-)beta(m-), beta(hE)) mice with 100% heterotetrameric hemoglobin. Lethal homozygous beta-thalassemic mice rescued by HbE transgenes mimic beta-thalassemia/HbE phenotype in human. Although anemia was not pronounced, other hematologic parameters were abnormally similar to beta-knockout mice. Flow cytometric study revealed a highly oxidative status in the red cells, but there were no marked changes in PS red cells and RBC vesicles. RBC life span and half-time of rescued red cells were shortened, indicating a rapid RBC destruction.

Alpha-tocopherol modulates phosphatidylserine externalization in erythrocytes: relevance in phospholipid transfer protein-deficient mice

OBJECTIVE

The aim of the present study was to assess the effect of alpha-tocopherol, the main vitamin E isomer on phosphatidylserine (PS) exposure at the surface of circulating erythrocytes, and to determine consequences on erythrocyte properties.

METHODS AND RESULTS

In vitro alpha-tocopherol enrichment of isolated erythrocytes significantly decreased PS externalization as assessed by lower Annexin V-fluorescein isothiocyanate labeling. Plasma phospholipid transfer protein (PLTP) transfers vitamin E, and both alpha- and gamma-tocopherol accumulated in circulating erythrocytes from PLTP-deficient homozygous (PLTP-/-) mice as compared with wild-type mice. In agreement with in vitro studies, vitamin E-enriched erythrocytes from PLTP-/- mice displayed fewer externalized PS molecules than wild-type controls (-64%, P<0.05). The perturbation of phospholipid membrane asymmetry from PLTP-/- erythrocytes was accompanied by impairment of their procoagulant properties, with a 20% increase in clotting time as compared with wild-type controls (P<0.05). Less pronounced, however still significant, changes were observed in alpha-tocopherol content, procoagulant properties, and PS externalization in erythrocytes of PLTP-deficient heterozygotes. Finally, whole blood coagulation and circulating level of D-dimer, which reflects increased thrombus formation in vivo, were significantly decreased in PLTP-/- mice compared with wild-type mice.

CONCLUSIONS

Vitamin E modifies PS externalization in circulating erythrocytes, thus modulating in vivo their PS-dependent procoagulant properties.

Changes of phosphatidylserine distribution in human red blood cells during the process of loading sugars

The plasma membrane of red blood cells permits sugars to be loaded into the cytoplasm simply by incubation in a suitable buffer solution containing the sugar. This may provide some hope for the freeze-drying of human red blood cells. However, the effect of the loading process on red blood cells has not been fully investigated. The exposure of phosphatidylserine (PS) on the surface of the cell can be recognized by macrophages and result in shortened circulation in vivo. This study evaluates the effects of the concentration, the incubation time, and the temperature of exposure of human red blood cells to extracellular trehalose or glucose. Exposure of PS was demonstrated by annexin V labeling. It was shown that the efficiency of loading of glucose was significantly greater than that of trehalose. The loading efficiency of both sugars increased with increase in extracellular sugar concentration, prolongation of incubation time, and increase of incubation temperature. The percentages of cells with exposed PS and of damaged cells were dependent on the extracellular sugar concentration, the incubation time, and the temperature. With an extracellular glucose concentration of 0.8M, the percentage of cells with exposed PS was more than 80% and significantly higher than that of red blood cells loaded with trehalose (approximate 20%, P<0.01). As the incubation time was prolonged, the percentage of PS exposure and of damaged cells also increased. After incubation for 5h, the percentage of red cells with exposed PS following loading with glucose was more than 80% and significantly higher than that of cells loaded with trehalose (40%, P<0.01). In addition, the incubation temperature had a major effect on PS exposure. The percentage of cells with PS exposure and the proportion of damaged cells increased with increase of incubation temperature. At 37 degrees C, the percentage of cells with exposed PS and of damaged cells after loading with glucose was more than 80% and significantly higher than that of cells loaded with trehalose (P<0.01). However, when the temperature was below 25 degrees C, the percentage of cells with exposed PS and of damaged cells after loading with glucose or trehalose were both less than 10%. In conclusion, the loading efficiency for glucose was higher than that for trehalose, but the lesser effect of trehalose on exposure of PS suggests that it can maintain the asymmetrical distribution of membrane phospholipids and the intracellular trehalose can increase the osmotic tolerance of cells.

Sulphydryl modifications alter scramblase activity in murine sickle cell disease

Increased oxidant stress has been suggested to play a role in the process of phosphatidylserine (PS) externalization in the red blood cells of sickle cell patients. Inhibition of the ATP-driven translocation from outer to inner monolayer (flippase) by sulphydryl modification has been established. The present study showed that phospholipid scrambling was also sensitive to protein sulphydryl modification. Treatment with N-ethylmaleimide lead to enhanced PS exposure and a lower Ca(++) requirement for scrambling. In contrast, pyridyldithioethylamine treatment inhibited PS exposure. Red blood cells from a murine model for sickle cell disease exhibited a reduced response to both reagents, suggestive of previous sulphydryl modifications to the protein(s) involved in phospholipid scrambling. We conclude that sulphydryl modifications to both scramblase and flippase underlie the enhanced formation of PS-exposing cells in sickle cell disease.

Suicidal death of erythrocytes in recurrent hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia with fragmented erythrocytes, thrombocytopenia, and acute renal failure. Lack of complement inactivating factor H predisposes to the development of atypical HUS. Little is known about mechanisms linking complement activation with loss of erythrocyte integrity during HUS. Recent studies disclosed that increased cytosolic Ca2+ activity and cellular ceramide trigger programmed erythrocyte death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the erythrocyte surface. In the present study, we investigated whether eryptosis occurs during the course of HUS. To this end, erythrocytes from healthy volunteers were exposed to plasma from a patient with severe idiopathic recurrent HUS secondary to factor H depletion. Phosphatidylserine exposure (Annexin binding), cell volume (forward scatter), cytosolic Ca2+ activity (Fluo3 fluorescence), and ceramide formation [anti-ceramide antibody and enzymatic (diacylgycerol kinase) analysis] were determined. Exposure of erythrocytes to plasma from the patient, but not to plasma from healthy individuals, triggered Annexin binding. The effect of plasma on erythrocyte Annexin binding was abolished by plasmapheresis or filtration at 30 kDa. It was paralleled by formation of ceramide and increase of cytosolic Ca2+ activity. Enhanced Annexin binding of erythrocytes from healthy individuals was observed after exposure to plasma from three other patients with HUS. The proeryptotic effect of patient plasma was mimicked by exposure to the Ca2+ ionophore ionomycin, and eryptosis was potentiated in the presence of cell membrane-permeable C6-ceramide. Furthermore, in vitro complement activation similarly triggered erythrocyte phosphatidylserine exposure, an effect which was blunted by the addition of factor H. In conclusion, our present observations disclose a novel, pathophysiological, factor-H dependent mechanism leading to injury of erythrocytes during the course of hemolytic uremic syndrome.

Involvement of the Na+/H+ exchanger in membrane phosphatidylserine exposure during human platelet activation

Platelet membrane phosphatidylserine (PS) exposure that regulates the production of thrombin represents an important link between platelet activation and the coagulation cascade. Here, we have evaluated the involvement of the Na+/H+ exchanger (NHE) in this process in human platelets. PS exposure induced in human platelets by thrombin, TRAP, collagen or TRAP+ collagen was abolished in a Na+ -free medium. Inhibition of the Na+/H+ exchanger (NHE) by 5-(N-Ethyl-N-Isopropyl) Amiloride (EIPA) reduced significantly PS exposure, whereas monensin or nigericin, which mimic or cause activation of NHE, respectively, reproduced the agonist effect. These data suggest a role for Na+ influx through NHE activation in the mechanism of PS exposure. This newly identified pathway does not discount a role for Ca2+, whose cytosolic concentration varies together with that of Na+ after agonist stimulation. Ca2+ deprivation from the incubation medium only attenuated PS exposure induced by thrombin, measured from the uptake of FM1-43 (a marker of phospholipid scrambling independent of external Ca2+). Surprisingly, removal of external Ca2+ partially reduced FM1-43 uptake induced by A23187, known as a Ca2+ ionophore. The residual effect can be attributed to an increase in [Na+]i mediated by the ionophore due to a lack of its specificity. Finally, phosphatidylinositol 4,5-bisphosphate (PIP2), previously reported as a target for Ca2+ in the induction of phospholipid scrambling, was involved in PS exposure through a regulation of NHE activity. All these results would indicate that the mechanism that results in PS exposure uses redundant pathways inextricably linked to the physio-pathological requirements of this process.

Circulating microparticles are elevated in haemophiliacs and non-haemophilic individuals aged <18 years

Platelet and cell stimulation lead to plasma membrane remodelling, resulting in phosphatidylserine (PS) externalisation in the outer leaflet of the membrane, associated with the shedding of PS-rich microparticles (MPs), and contributes to thrombin generation by promoting the assembly of coagulation enzyme complexes. A previous study assessed MP levels in haemophiliacs after haemostatic treatment. To further investigate in vivo membrane remodelling, MP levels and characteristics were studied in 79 haemophiliacs and in 62 non-haemophiliacs. Both groups showed heterogeneity in MP levels, with higher values in individuals <18 years. This finding should be considered when studying MP levels in individuals <18 years.

Erythrocyte adhesion is modified by alterations in cellular tonicity and volume

We tested the hypothesis that dehydration-induced alterations in red blood cell (RBC) membrane organisation or composition contribute to sickle cell adhesion in sickle cell disease (SCD). To examine the role of RBC hydration in adhesion to the subendothelial matrix protein thrombospondin-1 (TSP), normal and sickle RBCs were incubated in buffers of varying tonicity and tested for adhesion to immobilised TSP under flow conditions. Sickle RBCs exhibited a decrease in TSP binding with increasing cell hydration (P<0.005), suggesting that cellular dehydration may contribute to TSP adhesion. Consistent with this hypothesis, normal RBCs showed an increase in TSP adhesion with increasing dehydration (P<0.01). Furthermore, increased TSP adhesion of normal RBCs could also be induced by isotonic dehydration using nystatin-sucrose buffers. Finally, TSP adhesion of both sickle RBCs and dehydrated normal RBCs was inhibited by the anionic polysaccharides, chondroitin sulphate A and high molecular weight dextran sulphate, but not by competitors of CD47-, band 3-, or RBC phosphatidylserine-mediated adhesion. More importantly, we found increased adhesion of nystatin-sucrose dehydrated normal mouse RBCs to kidney capillaries following re-infusion in vivo. In summary, these findings demonstrate that changes in hydration can significantly impact adhesion, causing normal erythrocytes to display adhesive properties similar to those of sickle cells and vice versa.