Markers of platelet apoptosis: methodology and applications

Perturbation of calcium homeostasis invokes eryptosis-like cell death in enucleated bone marrow stem cells

Enucleated cells, also known as cytoplasts, are valuable tools with a wide range of applications. However, their potential for bio-engineering is greatly restricted by the short lifespan. We postulated that the enucleation process damages the integrity of the plasma membrane and thus activates a cell death program(s). The results showed that a tiny hole was generated transiently on the plasma membrane when the nucleus was spun off, while force-gated ion channels were activated in response to the pulling by the nucleus. Influx of extracellular calcium stimulated the opening of calcium channels and the release of calcium from endoplasmic reticulum and mitochondria. Long lasting calcium transient increased protein phosphorylation and activated caspase 9 and calpain proteinase activities. Subsequently, mitochondria membrane permeability and Reactive Oxygen Species (ROS) levels were significantly elevated, which eventually led to eryptosis-like cell death. When extracellular calcium was maintained at optimal concentration, the lifespan of enucleated cells was extended; however, huge amounts of vacuoles appeared in the cytoplasm, possibly derived from enlarged autophagosomes. Inhibition of vacuolation by inhibitors of autophagy or in co-culture with primary muscle cells did not rescue cells dying from the paraptosis-like pathway. These results offer valuable insights for further investigation into the intricate mechanisms underlying enucleated cell death.

Effect of platelet dynamic changes on disseminated intravascular coagulation and prognosis in severe heatstroke patients

OBJECTIVE

This study aimed to investigate the dynamic changes in the platelets of patients with severe heatstroke and the impact of these changes on the occurrence of disseminated intravascular coagulation (DIC) and prognosis in them.

METHODS

This retrospective cohort study conducted at two tertiary hospitals recruited 264 patients with severe heatstroke. Logistic regression was used to analyze the association between platelet counts and DIC. The receiver operating characteristic (ROC) curve was used to evaluate the predictive performance of platelets count for DIC occurrence. We used mediation effect to analysis the role of DIC as a mediating variable to mediate the relationship between platelet count decrease after 24 hours and death.

RESULTS

There were 214 patients with lower platelet counts compared to admission (107 × 109/L[69,168] vs.171 × 109/L[126,215], p < 0.001). The DIC patients had lower platelet counts than the non-DIC patients when measured in the emergency department and after 24 hours. The platelet count decrease after 24 hours was a risk factor for DIC (odds ratio [OR] = 2.710, 95% confidence interval [CI] = 1.069-6.869). The results of the ROC curve revealed that the predictive performance of the platelet count after 24 hours (area under the curve [AUC] = 0.8685, 95% CI = 0.8173-0.9197) was significantly better than that of the platelet count measured in the emergency department (AUC = 0.7080, 95% CI = 0.6345-0.7815). Mediation analyses showed that PLT decrease after 24 hours did not directly lead to death, but can indirectly cause death by inducing the development of DIC.

CONCLUSIONS

Decreased platelet count is an independent risk factor for DIC in patients with severe heatstroke. Although the platelet counts measured in the emergency department and after 24 hours show a good predictive performance for DIC occurrence, the prediction performance of the latter is better.

Hump-Nosed Pit Viper (Hypnale hypnale) Venom-Induced Irreversible Red Blood Cell Aggregation, Inhibition by Monovalent Anti-Venom and N-Acetylcysteine

Envenomation by the Hypnale hypnale in the Western Ghats of India (particularly in the Malabar region of Kerala) and the subcontinent island nation of Sri Lanka is known to inflict devastating mortality and morbidity. Currently, H. hypnale bites in India are devoid of anti-venom regimens. A detailed characterization of the venom is essential to stress the need for therapeutic anti-venom. Notably, the deleterious effects of this venom on human blood cells have largely remained less explored. Therefore, in continuation of our previous study, in the present study, we envisioned investigating the effect of venom on the morphological and physiological properties of red blood cells (RBCs). The venom readily induced deleterious morphological changes and, finally, the aggregation of washed RBCs. The aggregation process was independent of the ROS and the intracellular Ca2+ ion concentration. Confocal and scanning electron microscopy (SEM) images revealed the loss of biconcave morphology and massive cytoskeletal disarray. Crenation or serrated plasma membrane projections were evenly distributed on the surface of the RBCs. The venom did not cause the formation of methemoglobin in washed RBCs but was significantly induced in whole blood. Venom did not affect glucose uptake and Na+/K+ -ATPase activity but inhibited glucose 6 phosphate dehydrogenase activity and decreased the fluidity of the plasma membrane. Venom-induced RBC aggregates exhibited pro-coagulant activity but without affecting platelet aggregation. In pre-incubation or co-treatment studies, none of the bioactive compounds, such as melatonin, curcumin, fisetin, berberine, and quercetin, sugars such as mannose and galactose, and therapeutic polyvalent anti-venoms (Bharat and VINS) were inhibited, whereas only N-acetylcysteine and H. hypnale monovalent anti-venom could inhibit venom-induced deleterious morphological changes and aggregation of RBCs. In post-treatment studies, paradoxically, none of the bioactives and anti-venoms, including N-acetylcysteine and H. hypnale monovalent anti-venom, reversed the venom-induced RBC aggregates.

Preanalytical conditions for multiparameter platelet flow cytometry

Background

Flow cytometry is an important technique for understanding multiple aspects of blood platelet biology. Despite the widespread use of the platform for assessing platelet function, the optimization and careful consideration of preanalytical conditions, sample processing techniques, and data analysis strategies should be regularly assessed. When set up and designed with optimal conditions, it can ensure the acquisition of robust and reproducible flow cytometry data. However, these parameters are rarely described despite their importance.

Objectives

We aimed to characterize the effects of several preanalytical variables on the analysis of blood platelets by multiparameter fluorescent flow cytometry.

Methods

We assessed anticoagulant choice, sample material, sample processing, and storage times on 4 distinct and commonly used markers of platelet activation, including fibrinogen binding, expression of CD62P and CD42b, and phosphatidylserine exposure.

Results

The use of suboptimal conditions led to increases in basal platelet activity and reduced sensitivities to stimulation; however, the use of optimal conditions protected the platelets from artifactual stimulation and preserved basal activity and sensitivity to activation.

Conclusion

The optimal preanalytical conditions identified here for the measurement of platelet phenotype by flow cytometry suggest a framework for future development of multiparameter platelet assays for high-quality data sets and advanced analysis.

An Overview of Two Old Friends Associated with Platelet Redox Signaling, the Protein Disulfide Isomerase and NADPH Oxidase

Oxidative stress participates at the baseline of different non-communicable pathologies such as cardiovascular diseases. Excessive formation of reactive oxygen species (ROS), above the signaling levels necessary for the correct function of organelles and cells, may contribute to the non-desired effects of oxidative stress. Platelets play a relevant role in arterial thrombosis, by aggregation triggered by different agonists, where excessive ROS formation induces mitochondrial dysfunction and stimulate platelet activation and aggregation. Platelet is both a source and a target of ROS, thus we aim to analyze both the platelet enzymes responsible for ROS generation and their involvement in intracellular signal transduction pathways. Among the proteins involved in these processes are Protein Disulphide Isomerase (PDI) and NADPH oxidase (NOX) isoforms. By using bioinformatic tools and information from available databases, a complete bioinformatic analysis of the role and interactions of PDI and NOX in platelets, as well as the signal transduction pathways involved in their effects was performed. We focused the study on analyzing whether these proteins collaborate to control platelet function. The data presented in the current manuscript support the role that PDI and NOX play on activation pathways necessary for platelet activation and aggregation, as well as on the platelet signaling imbalance produced by ROS production. Our data could be used to design specific enzyme inhibitors or a dual inhibition for these enzymes with an antiplatelet effect to design promising treatments for diseases involving platelet dysfunction.

Gamma irradiation induces a pro-apoptotic state in longer stored platelets, without progressing to an overt apoptosis by day 7 of storage

BACKGROUND

Although gamma-irradiation to platelet products is a standard method to prevent the risk of TA-GVHD in vulnerable recipients, it induces some proteomic and redox changes, of which irradiation-induced ROS increments may potentiate platelet mitochondrial dysfunction. However, whether these changes cause platelet apoptosis, or affect their viability during storage, is the main subject of this study.

METHODS

PLT-rich plasma PC was split into two bags, one kept as control while other was subjected to gamma-irradiation. Within 7-days storage, cytosolic and mitochondrial levels of cytochrome c and pro-apoptotic molecules of Bak and Bax were evaluated by western-blotting. Intraplatelet active caspase (using FAM-DEVD-FMK) and PS-exposure were detected by flowcytometry. Caspase activity in platelet lysate was also confirmed by immunofluorescence detection of Caspase-3/7 Substrate N-Ac-DEVD-N'-MC-R110 while platelet viability was evaluated with MTT assays.

RESULTS

Cytosolic cytochrome c gradually increased while its mitochondrial content steadily declined during 7 days of storage. In a contrary trend, reverse patterns were observed for Bak and Bax expressions. Gamma-irradiated platelets showed higher release of mitochondrial cytochrome c that reflected by higher cytosolic cytochrome c levels on day 7 of storage. Concurrently mitochondrial pro-apoptotic Bak and Bax proteins increased on day 7 in irradiated products. However, gamma-irradiation didn't significantly increase caspase activity or PS-exposure, nor did it decrease platelet viability.

CONCLUSION

Here, consistent with studies on "gamma-irradiation-induced oxidative stress", we showed that gamma-ray also increases platelet pro-apoptotic signals during storage, although not strongly enough to affect platelet viability by overt apoptosis induction. Conclusively, whether supplementing ROS scavengers or antioxidants to irradiated platelets can improve their quality during storage may be of interest for future research.

Identification of thrombopoiesis inducer based on a hybrid deep neural network model

Thrombocytopenia is a common haematological problem worldwide. Currently, there are no relatively safe and effective agents for the treatment of thrombocytopenia. To address this challenge, we propose a computational method that enables the discovery of novel drug candidates with haematopoietic activities. Based on different types of molecular representations, three deep learning (DL) algorithms, namely recurrent neural networks (RNNs), deep neural networks (DNNs), and hybrid neural networks (RNNs+DNNs), were used to develop classification models to distinguish between active and inactive compounds. The evaluation results illustrated that the hybrid DL model exhibited the best prediction performance, with an accuracy of 97.8 % and Matthews correlation coefficient of 0.958 on the test dataset. Subsequently, we performed drug discovery screening based on the hybrid DL model and identified a compound from the FDA-approved drug library that was structurally divergent from conventional drugs and showed a potential therapeutic action against thrombocytopenia. The novel drug candidate wedelolactone significantly promoted megakaryocyte differentiation in vitro and increased platelet levels and megakaryocyte differentiation in irradiated mice with no systemic toxicity. Overall, our work demonstrates how artificial intelligence can be used to discover novel drugs against thrombocytopenia.

Shear-Mediated Platelet Microparticles Demonstrate Phenotypic Heterogeneity as to Morphology, Receptor Distribution, and Hemostatic Function

Objective

Implantable cardiovascular therapeutic devices (CTD) including stents, percutaneous heart valves and ventricular assist devices, while lifesaving, impart supraphysiologic shear stress to platelets resulting in thrombotic and bleeding device-related coagulopathy. We previously demonstrated that shear-mediated platelet dysfunction is associated with downregulation of platelet GPIb-IX-V and αIIbβ3 receptors via generation of platelet-derived microparticles (PDMPs). Here, we test the hypothesis that shear-generated PDMPs manifest phenotypical heterogeneity of their morphology and surface expression of platelet receptors, and modulate platelet hemostatic function.

Approach and Results

Human gel-filtered platelets were exposed to continuous shear stress and sonication. Alterations of platelet morphology were visualized using transmission electron microscopy. Surface expression of platelet receptors and PDMP generation were quantified by flow cytometry. Thrombin generation was quantified spectrophotometrically, and platelet aggregation in plasma was measured by optical aggregometry. We demonstrate that platelet exposure to shear stress promotes notable alterations in platelet morphology and ejection of several distinctive types of PDMPs. Shear-mediated microvesiculation is associated with the differential remodeling of platelet receptors with PDMPs expressing significantly higher levels of both adhesion (α _IIb β ₃ , GPIX, PECAM-1, P-selectin, and PSGL-1) and agonist-evoked receptors (P ₂ Y ₁₂ & PAR1). Shear-mediated PDMPs have a bidirectional effect on platelet hemostatic function, promoting thrombin generation and inhibiting platelet aggregation induced by collagen and ADP.

Conclusions

Shear-generated PDMPs demonstrate phenotypic heterogeneity as to morphologic features and defined patterns of surface receptor alteration, and impose a bidirectional effect on platelet hemostatic function. PDMP heterogeneity suggests that a range of mechanisms are operative in the microvesiculation process, contributing to CTD coagulopathy and posing opportunities for therapeutic manipulation.

Water-Soluble Tomato Concentrate, a Potential Antioxidant Supplement, Can Attenuate Platelet Apoptosis and Oxidative Stress in Healthy Middle-Aged and Elderly Adults: A Randomized, Double-Blinded, Crossover Clinical Trial

Increased oxidative stress and platelet apoptotic in middle-aged and elderly adults are important risk factors for atherosclerotic cardiovascular disease (ASCVD). Therefore, it is of great significance to control the oxidative stress and platelet apoptosis in middle-aged and elderly adults. Previous acute clinical trials have shown that water-soluble tomato concentrate (WSTC) from fresh tomatoes could exert antiplatelet benefits after 3 h or 7 h, but its effects on platelet apoptosis and oxidative stress are still unknown, especially in healthy middle-aged and elderly adults. This current study aimed to examine the efficacies of WSTC on platelet apoptosis and oxidative stress in healthy middle-aged and elderly adults via a randomized double-blinded placebo-controlled crossover clinical trial (10 weeks in total). A total of 52 healthy middle-aged and elderly adults completed this trial. The results showed that WSTC could increase the serum total antioxidant capacity levels (p < 0.05) and decrease the serum malondialdehyde levels (p < 0.05) after a 4-week WSTC supplementation in healthy middle-aged and elderly adults. Platelet endogenous reactive oxygen species generation (p < 0.05), mitochondrial membrane potential dissipation (p < 0.05) and phosphatidylserine exposure (p < 0.05) were attenuated. In addition, our present study also found that WSTC could inhibit platelet aggregation and activation induced by collagen or ADP after intervention (p < 0.05), while having no effects on adverse events (p > 0.05). The results suggest that WSTC can inhibit oxidative stress and its related platelet apoptosis, which may provide a basis for the primary prevention of WSTC in ASCVD.

Challenges in Platelet Functions in HIV/AIDS Management

The interest in platelet functions in HIV/AIDS is due to the high incidence of microvascular thrombosis in these individuals. A lot of laboratory data have been generated regarding platelet functions in this population. The tests demonstrate platelet hyperactivity but decreased aggregation, though results are inconsistent depending on the study design. Antiretroviral treatments currently in use display complex interactions. Many studies on platelet functions in these patients have been for research purposes, but none have found utility in guiding drug treatment of thrombosis.

A guide to molecular and functional investigations of platelets to bridge basic and clinical sciences

Platelets have been shown to be associated with pathophysiological process beyond thrombosis, demonstrating critical additional roles in homeostatic processes, such as immune regulation, and vascular remodeling. Platelets themselves can have multiple functional states and can communicate and regulate other cells including immune cells and vascular smooth muscle cells, to serve such diverse functions. Although traditional platelet functional assays are informative and reliable, they are limited in their ability to unravel platelet phenotypic heterogeneity and interactions. Developments in methods such as electron microscopy, flow cytometry, mass spectrometry, and 'omics' studies, have led to new insights. In this Review, we focus on advances in platelet biology and function, with an emphasis on current and promising methodologies. We also discuss technical and biological challenges in platelet investigations. Using coronavirus disease 2019 (COVID-19) as an example, we further describe the translational relevance of these approaches and the possible 'bench-to-bedside' utility in patient diagnosis and care.

Using Cryo-ET to distinguish platelets during pre-acute myeloid leukemia from steady state hematopoiesis

Early diagnosis of acute myeloid leukemia (AML) in the pre-leukemic stage remains a clinical challenge, as pre-leukemic patients show no symptoms, lacking any known morphological or numerical abnormalities in blood cells. Here, we demonstrate that platelets with structurally abnormal mitochondria emerge at the pre-leukemic phase of AML, preceding detectable changes in blood cell counts or detection of leukemic blasts in blood. We visualized frozen-hydrated platelets from mice at different time points during AML development in situ using electron cryo-tomography (cryo-ET) and identified intracellular organelles through an unbiased semi-automatic process followed by quantitative measurement. A large proportion of platelets exhibited changes in the overall shape and depletion of organelles in AML. Notably, 23% of platelets in pre-leukemic cells exhibit abnormal, round mitochondria with unfolded cristae, accompanied by a significant drop in ATP levels and altered expression of metabolism-related gene signatures. Our study demonstrates that detectable structural changes in pre-leukemic platelets may serve as a biomarker for the early diagnosis of AML.

Effect of local anesthetics on platelet physiology and function

Local anesthetics are often used at the site of injury or mixed with platelet-rich plasma to reduce pain when treating orthopedic and sports-related injuries. Local anesthetics have been shown to have deleterious effects on stromal cells, but their impact on platelets has not been investigated. In this study, we aimed to assess the effects of lidocaine, bupivacaine, and ropivacaine on platelet health. Based on the deleterious effects of local anesthetics on nucleated cells, we hypothesized that these compounds would affect platelet viability, intracellular physiology, and function. Platelet preparations were derived from randomly selected donors and exposed to lidocaine 1%, bupivacaine 0.75%, ropivacaine 0.5%, and saline at 1:1 and 1:3 ratios. Platelet morphology, viability, intracellular calcium, production of radical oxygen species (ROS), apoptosis, and adhesion were assessed via fluorescent microscopy and flow cytometry. Bupivacaine resulted in increased ROS production, calcium dysregulation, apoptosis, and reduced platelet adhesion. By contrast, ropivacaine and lidocaine were similar to saline in most assays, except for a low degree of mitochondrial stress as evidenced by increased ROS production. Ultimately, bupivacaine 0.75% was harmful to platelets as evidenced by reduced platelet viability, adhesion, and increased apoptosis, whereas lidocaine 1% and ropivacaine 0.5% were relatively safe at the 1:1 and 1:3 dilutions. Clinical significance: Lidocaine 1% and ropivacaine 0.5% can be used at up to a 1:1 ratio with platelet preparations to reduce the pain and discomfort of PRP procedures while maintaining platelet therapeutic potential.

T cell-mediated autoimmunity in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. In addition to anti-platelet autoantibodies, CD8⁺ T cells have been implicated as a mechanism of platelet destruction. The current evidence for the existence of platelet-specific CD8⁺ T cells in ITP is inconclusive. The purpose of this review is to summarize the studies that investigated CD8⁺ T cells in ITP and to review the methods that have been used to detect autoreactive CD8⁺ T cells in other autoimmune diseases.

Multidimensional flow cytometry reveals novel platelet subpopulations in response to prostacyclin

BACKGROUND

Robust platelet activation leads to the generation of subpopulations characterized by differential expression of phosphatidylserine (PS). Prostacyclin (PGI2 ) modulates many aspects of platelet function, but its influence on platelet subpopulations is unknown.

OBJECTIVES AND METHODS

We used fluorescent flow cytometry coupled to multidimensional fast Fourier transform-accelerated interpolation-based t-stochastic neighborhood embedding analysis to examine the influence of PGI2 on platelet subpopulations.

RESULTS

Platelet activation (SFLLRN/CRP-XL) in whole blood revealed three platelet subpopulations with unique combinations of fibrinogen (fb) binding and PS exposure. These subsets, PSlo /fbhi (68%), PShi /fblo (23%), and PShi /fbhi (8%), all expressed CD62P and partially shed CD42b. PGI2 significantly reduced fibrinogen binding and prevented the majority of PS exposure, but did not significantly reduce CD62P, CD154, or CD63 leading to the generation of four novel subpopulations, CD62Phi /PSlo /fblo (64%), CD62Phi /PSlo /fbhi (22%), CD62Phi /PShi /fblo (3%), and CD62Plo /PSlo /fblo (12%). Mechanistically this was linked to PGI2 -mediated inhibition of mitochondrial depolarization upstream of PS exposure. Combining phosphoflow with surface staining, we showed that PGI2 -treated platelets were characterized by both elevated vasodilator-stimulated phosphoprotein phosphorylation and CD62P. The resistance to cyclic AMP signaling was also observed for CD154 and CD63 expression. Consistent with the functional role of CD62P, exposure of blood to PGI2 failed to prevent SFLLRN/CRP-XL-induced platelet-monocyte aggregation despite reducing markers of hemostatic function.

CONCLUSION

The combination of multicolor flow cytometry assays with unbiased computational tools has identified novel platelet subpopulations that suggest differential regulation of platelet functions by PGI2 . Development of this approach with increased surface and intracellular markers will allow the identification of rare platelet subtypes and novel biomarkers.

Pediatric immune thrombocytopenia: apoptotic markers may help in predicting the disease course

BACKGROUND

In all, 15-30% of pediatric immune thrombocytopenia (ITP) patients will remain chronically thrombocytopenic at 1 year post diagnosis. All attempts to classify patients at diagnosis have proven unsuccessful. We hypothesized that a different pathophysiology is responsible for non-chronic versus chronic pediatric ITP. We aimed to examine differences in the apoptotic markers' presentation at diagnosis between non-chronic and chronic patients.

METHODS

Blood samples were collected from 42 pediatric patients with newly diagnosed ITP prior to initiation of treatment. We incubated patients' sera with control platelets and compared the results among three research groups: healthy controls, chronic ITP, and non-chronic ITP patients. We measured apoptotic markers phosphatidylserine (PS) exposure and mitochondrial inner membrane potential (ΔΨm) by flow cytometry and the level of human apoptotic proteins by Human Apoptosis Array.

RESULTS

We found increased platelet PS exposure and decreased ΔΨm in response to all ITP patients' sera compared to control subjects. Human Apoptotic Array revealed an increased expression of five apoptotic proteins: BIM, CD40, IGFBP2, P21, and SMAC, following sera incubation of non-chronic pediatric ITP patients, compared to chronic patients' sera, at diagnosis.

CONCLUSIONS

Our data contribute to knowledge on apoptosis markers that may aid in predicting the prognosis of children with ITP.

IMPACT

The key message of our article is that children with chronic ITP have a different apoptotic profile compared to non-chronic ITP. Addition to existing literature: This is the first study comparing apoptotic markers between children with chronic ITP to non-chronic ITP.

IMPACT

Our findings indicate that, in the future, apoptotic markers may help to classify ITP patients into non-chronic versus chronic ones, at diagnosis.

Guidelines for Regulated Cell Death Assays: A Systematic Summary, A Categorical Comparison, A Prospective

Over the past few years, the field of regulated cell death continues to expand and novel mechanisms that orchestrate multiple regulated cell death pathways are being unveiled. Meanwhile, researchers are focused on targeting these regulated pathways which are closely associated with various diseases for diagnosis, treatment, and prognosis. However, the complexity of the mechanisms and the difficulties of distinguishing among various regulated types of cell death make it harder to carry out the work and delay its progression. Here, we provide a systematic guideline for the fundamental detection and distinction of the major regulated cell death pathways following morphological, biochemical, and functional perspectives. Moreover, a comprehensive evaluation of different assay methods is critically reviewed, helping researchers to make a reliable selection from among the cell death assays. Also, we highlight the recent events that have demonstrated some novel regulated cell death processes, including newly reported biomarkers (e.g., non-coding RNA, exosomes, and proteins) and detection techniques.

Impella 5.5 Versus Centrimag: A Head-to-Head Comparison of Device Hemocompatibility

Despite growing use of mechanical circulatory support, limitations remain related to hemocompatibility. Here, we performed a head-to-head comparison of the hemocompatibility of a centrifugal cardiac assist system-the Centrimag, with that of the latest generation of an intravascular microaxial system-the Impella 5.5. Specifically, hemolysis, platelet activation, microparticle (MP) generation, and von Willebrand factor (vWF) degradation were evaluated for both devices. Freshly obtained porcine blood was recirculated within device propelled mock loops for 4 hours, and alteration of the hemocompatibility parameters was monitored over time. We found that the Impella 5.5 and Centrimag exhibited low levels of hemolysis, as indicated by minor increase in plasma free hemoglobin. Both devices did not induce platelet degranulation, as no alteration of β-thromboglobulin and P-selectin in plasma occurred, rather minor downregulation of platelet surface P-selectin was detected. Furthermore, blood exposure to shear stress via both Centrimag and Impella 5.5 resulted in a minor decrease of platelet count with associated ejection of procoagulant MPs, and a decrease of vWF functional activity (but not plasma level of vWF-antigen). Greater MP generation was observed with the Centrimag relative to the Impella 5.5. Thus, the Impella 5.5 despite having a lower profile and higher impeller rotational speed demonstrated good and equivalent hemocompatibility, in comparison with the predicate Centrimag, with the advantage of lower generation of MPs.

Protocatechuic Acid Protects Platelets from Apoptosis via Inhibiting Oxidative Stress-Mediated PI3K/Akt/GSK3β Signaling

Oxidative stress plays crucial roles in initiating platelet apoptosis that facilitates the progression of cardiovascular diseases (CVDs). Protocatechuic acid (PCA), a major metabolite of anthocyanin cyanidin-3-O-β-glucoside (Cy-3-g), exerts cardioprotective effects. However, underlying mechanisms responsible for such effects remain unclear. Here, we investigate the effect of PCA on platelet apoptosis and the underlying mechanisms in vitro. Isolated human platelets were treated with hydrogen peroxide (H₂O₂) to induce apoptosis with or without pretreatment with PCA. We found that PCA dose-dependently inhibited H₂O₂-induced platelet apoptosis by decreasing the dissipation of mitochondrial membrane potential, activation of caspase-9 and caspase-3, and decreasing phosphatidylserine exposure. Additionally, the distributions of Bax, Bcl-xL, and cytochrome c mediated by H₂O₂ in the mitochondria and the cytosol were also modulated by PCA treatment. Moreover, the inhibitory effects of PCA on platelet caspase-3 cleavage and phosphatidylserine exposure were mainly mediated by downregulating PI3K/Akt/GSK3β signaling. Furthermore, PCA dose-dependently decreased reactive oxygen species (ROS) generation and the intracellular Ca²⁺ concentration in platelets in response to H₂O₂. N-Acetyl cysteine (NAC), a ROS scavenger, markedly abolished H₂O₂-stimulated PI3K/Akt/GSK3β signaling, caspase-3 activation, and phosphatidylserine exposure. The combination of NAC and PCA did not show significant additive inhibitory effects on PI3K/Akt/GSK3β signaling and platelet apoptosis. Thus, our results suggest that PCA protects platelets from oxidative stress-induced apoptosis through downregulating ROS-mediated PI3K/Akt/GSK3β signaling, which may be responsible for cardioprotective roles of PCA in CVDs.

Protective effect of L-carnitine on platelet apoptosis during storage of platelet concentrate

BACKGROUND

Platelet apoptosis is considered as one of the important factors involved in platelet storage lesion (PSL) and affect the quality of platelets during storage. The beneficial effect of L-carnitine (LC) on platelet apoptosis during platelet concentrates (PCs) storage has not been fully investigated. The aim of this study was to evaluate the effects of LC on platelets of PC regarding their apoptosis markers during storage.

METHODS

Ten PCs from healthy donors were investigated in this study. PCs were prepared by platelet rich plasma (PRP) method and stored at 22±2°C with gentle agitation during storage. The effects of LC (15mM) on the platelet apoptosis were assessed by analyzing different indicative presence or absence of LC. Sampling was performed to evaluate apoptosis markers during platelet storage.

RESULTS

The results indicated significantly higher mitochondrial membrane potential for LC-treated platelets than the untreated on the days 2 and 5 of storage (P_day2=0.001, P_day5=0.001). Phosphatidylserine (PS) exposure significantly increased on the untreated compared with LC-treated platelets on the second and third days of storage (P_day2=0.014, P_day3=0.012). Also, active caspase 3 was lower in the LC- treated platelets than the control group on the day 5 of storage (P_day5=0.004). Cytosolic cytochrome C was so significantly lower in LC-treated compared to the untreated platelets during storage time (P_day2=0.002, P_day3=0.001, Pday5=0.001).

CONCLUSION

The results of this study indicate that the use of LC as an additive solution in platelets may be useful to reduce PSL by decreasing platelet apoptosis via mitochondrial pathway and increase platelet quality during storage.

Antimalarial drugs impact chemical messenger secretion by blood platelets

Background

Advances in antimalarial drug development are important for combating malaria. Among the currently identified antimalarial drugs, it is suggested that some interact directly with the malarial parasites while others interact indirectly with the parasites. While this approach leads to parasite elimination, little is known about how these antimalarial drugs impact immune cells that are also critical in malarial response.

Methods

Herein, the effects of two common antimalarial drugs, chloroquine and quinine, on platelets were explored at both the bulk level, using high performance liquid chromatography, and the single cell level, using carbon-fiber microelectrode amperometry, to characterize any changes in chemical messenger secretion.

Results

The data reveal that both drugs cause platelet activation and reduce the number of platelet exocytosis events as well as delay fusion pore opening and closing.

Conclusions

This work demonstrates how chloroquine and quinine quantitatively and qualitatively impact in vitro platelet function.

General significance

Overall, the goal of this work is to promote understanding about how antimalarial drugs impact platelets as this may affect antimalarial drug development as well as therapeutic approaches to treat malarial infection.

•

Antimalarial drugs impact platelet function by inducing activation.

•

Single cell electrochemistry reveals changes in platelet function.

•

It is important to consider platelet behaviors beyond aggregation to understand the side effects of antimalarial drugs.

Role of Platelet Mitochondria: Life in a Nucleus-Free Zone

Platelets are abundant, small, anucleate circulating cells, serving many emerging pathophysiological roles beyond hemostasis; including active critical roles in thrombosis, injury response, and immunoregulation. In the absence of genomic DNA transcriptional regulation (no nucleus), platelets require strategic prepackaging of all the needed RNA and organelles from megakaryocytes, to sense stress (e.g., hyperglycemia), to protect themselves from stress (e.g., mitophagy), and to communicate a stress response to other cells (e.g., granule and microparticle release). Distinct from avian thrombocytes that have a nucleus, the absence of a nucleus allows the mammalian platelet to maintain its small size, permits morphological flexibility, and may improve speed and efficiency of protein expression in response to stress. In the absence of a nucleus, platelet lifespan of 7–10 days, is largely determined by the mitochondria. The packaging of 5–8 mitochondria is critical in aerobic respiration and yielding metabolic substrates needed for function and survival. Mitochondria damage or dysfunction, as observed with several disease processes, results in greatly attenuated platelet survival and increased risk for thrombovascular events. Here we provide insights into the emerging roles of platelets despite the lack of a nucleus, and the key role played by mitochondria in platelet function and survival both in health and disease.

Garcinol A Novel Inhibitor of Platelet Activation and Apoptosis

Garcinol, an anti-inflammatory and anti-carcinogenic polyisoprenylated benzophenone isolated from Garcinia plants, stimulates tumor cell apoptosis and suicidal erythrocyte death, but supports the survival of hepatocytes and neurons. The present study explored whether the substance influences platelet function and/or apoptosis. To this end, we exposed murine blood platelets to garcinol (33 µM, 30 min) without and with activation by collagen-related peptide (CRP) (2-5 µg/mL) or thrombin (0.01 U/mL); flow cytometry was employed to estimate cytosolic Ca²⁺-activity ([Ca²⁺]_i) from Fluo-3 fluorescence, platelet degranulation from P-selectin abundance, integrin activation from αIIbβ3 integrin abundance, caspase activity utilizing an Active Caspase-3 Staining kit, phosphatidylserine abundance from annexin-V-binding, relative platelet volume from forward scatter, and aggregation utilizing staining with CD9-APC and CD9-PE. As a result, in the absence of CRP and thrombin, the exposure of the platelets to garcinol did not significantly modify [Ca²⁺]_i, P-selectin abundance, activated αIIbβ3 integrin, annexin-V-binding, cell volume, caspase activity, and aggregation. Exposure of platelets to CRP or thrombin was followed by a significant increase of [Ca²⁺]_i, P-selectin abundance, αIIbβ3 integrin activity, annexin-V-binding, caspase activity, and aggregation, as well as significant cell shrinkage. All effects of CRP were strong and significant; those of thrombin were only partially and slightly blunted in the presence of garcinol. In conclusion, garcinol blunts CRP-induced platelet activity, apoptosis and aggregation.

Platelet factor 4-containing immune complexes induce platelet activation followed by calpain-dependent platelet death

Heparin-induced thrombocytopenia (HIT) is a complication of heparin therapy sometimes associated with thrombosis. The hallmark of HIT is antibodies to the heparin/platelet factor 4 (PF4) complex that cause thrombocytopenia and thrombosis through platelet activation. Despite the clinical importance, the molecular mechanisms and late consequences of immune platelet activation are not fully understood. Here, we studied immediate and delayed effects of the complexes formed by human PF4 and HIT-like monoclonal mouse anti-human-PF4/heparin IgG antibodies (named KKO) on isolated human platelets in vitro. Direct platelet-activating effect of the KKO/PF4 complexes was corroborated by the overexpression of phosphatidylserine (PS) and P-selectin on the platelet surface. The immune platelet activation was accompanied by a decrease of the mitochondrial transmembrane potential (ΔΨm), concurrent with a significant gradual reduction of the ATP content in platelets, indicating disruption of energy metabolism. A combination of PS expression and mitochondrial depolarization induced by the PF4-containing immune complexes observed in a substantial fraction of platelets was considered as a sign of ongoing platelet death, as opposed to a subpopulation of activated live platelets with PS on the plasma membrane but normal ΔΨm. Both activated and dying platelets treated with KKO/PF4 formed procoagulant extracellular microvesicles bearing PS on their surface. Scanning and transmission electron microscopy revealed dramatic morphological changes of KKO/PF4-treated platelets, including their fragmentation, another indicator of cell death. Most of the effects of KKO/PF4 were prevented by an anti-FcγRII monoclonal antibody IV.3. The adverse functional and structural changes in platelets induced by the KKO/PF4 complexes were associated with strong time-dependent activation of calpain, but only trace cleavage of caspase 3. The results indicate that the pathogenic PF4-containing HIT-like immune complexes induce direct prothrombotic platelet activation via FcγRIIA receptors followed by non-apoptotic calpain-dependent death of platelets, which can be an important mechanism of thrombocytopenia during HIT development.

Effects and Mechanisms of Vitamin C Post-Conditioning on Platelet Activation after Hypoxia/Reoxygenation

Background

Platelet activation occurs upon ischemia/reperfusion and is related to the generation of reactive oxygen species (ROS) during this process. Vitamin C (VC) is a powerful antioxidant. VC scavenges ROS, reduces platelet activation, and attenuates reperfusion injury. However, the effects of VC on platelets undergoing hypoxia/reoxygenation (H/R) remain unclear.

Objectives

Herein, we evaluated the effects of VC on platelets in vitro following H/R and the related mechanisms.

Method

Fresh platelets were collected from 67 volunteers at the Blood Center of Hebei Province. Platelets were diluted with saline to a concentration of 2.00 × 10¹¹/L. Aggregation and the curve slope were evaluated within 4 h with a whole-blood impedance analyzer. To determine the optimal experimental time, platelets were treated with hypoxia or reoxygenation for different times, and impedance aggregometry was carried out by measuring changes in electrical impedance induced by arachidonic acid (0.5 mM) and adenosine diphosphate (10 µM), thereby establishing the H/R model. Three antioxidants (VC, melatonin, and probucol) were used to treat platelets after H/R, and impedance aggregometry was used to determine their effects on platelet aggregation. The influence of VC on apoptosis-related indicators was detected. ROS and the mitochondrial membrane potential were observed by inverted fluorescence microscopy and flow cytometry, respectively. Related protein levels were detected by Western blotting.

Results

ROS scavengers inhibited platelet activation and aggregation in a concentration-dependent manner. VC post-conditioning scavenged ROS, downregulated cytochrome C, Bax, and caspase-9 proteins, and upregulated Bcl-2 protein. These effects collectively blocked platelet apoptosis and inhibited platelet aggregation.

Conclusions

VC inhibited platelet aggregation by blocking apoptosis. Thus, VC may have applications in the treatment of platelet-related diseases.

Changes in platelet Bax levels contribute to impaired platelet response to thrombin after cardiopulmonary bypass: prospective observational clinical and laboratory investigations

Background

Anucleate platelets can undergo apoptosis in response to various stimuli, as do nucleated cells. Cardiopulmonary bypass (CPB) causes platelet dysfunction and can also activate platelet apoptotic pathways. We therefore evaluated time-dependent changes in blood platelet Bax (a pro-apoptotic molecule) levels and platelet dysfunction after cardiac surgery.

Methods

We assessed blood samples obtained from subjects having on-pump or off-pump coronary artery bypass graft surgery ( n =20 each). We also evaluated the in vitro effects of platelet Bax increase in eight healthy volunteers.

Results

Thrombin-induced platelet calcium mobilisation and platelet-surface glycoprotein Ib (GPIb) expression were lowest at weaning from CPB and did not recover on postoperative day one. On-pump surgery increased platelet expression of Bax, especially the oligomerised form, along with translocation of Bax from the cytosol to mitochondria and platelet-surface tumour necrosis factor-alpha (TNF-α)-converting enzyme (TACE) expression. In contrast, mitochondrial cytochrome c expression was reduced. While similar in direction, the magnitude of the observed changes was smaller in patients having off-pump surgery. In vitro , a cell-permeable Bax peptide increased platelet Bax expression to the same extent seen during bypass and produced similar platelet changes. These apoptotic-like changes were largely reversed by Bcl-xL pre-administration, and were completely reversed by combined application of inhibitors that stabilise outer mitochondrial membrane permeability and TACE.

Conclusions

CPB increases platelet Bax expression, which contributes to reduced platelet-surface GPIb expression and thrombin-induced platelet calcium changes. These changes in platelet apoptotic signalling might contribute to platelet dysfunction after CPB.

Clinical trial registration

UMIN Clinical Trials Registry (number UMIN000006033).

Para-tertiary butyl catechol (PTBC), an industrial antioxidant induces human platelet apoptosis

The catecholic derivative para-tertiary butyl catechol (PTBC) is a conventional antioxidant and polymerization inhibitor, which exhibits melanocytotoxic effects and contact dermatitis often leading to occupational leucoderma or vitiligo. Although numerous industrial workers will be in constant exposure to PTBC and its chances of getting entry into blood are most expected, its effect on blood components is still undisclosed. As platelets play a prominent role in dermatitis, inflammation, and immunity, in this study we have evaluated the effect of PTBC on human platelets in vitro. Exposure of platelets to PTBC showed increased reactive oxygen species (ROS), intracellular calcium, cardiolipin oxidation, mitochondrial permeability transition pore (MPTP) formation, activation of caspases, phosphatidylserine (PS) externalization and decreased mitochondrial membrane potential. In addition, there was a significant decrease in cellular glutathione level, increased γ-glutamyltransferase (GGT) activity and cell death. These findings demonstrate that PTBC could induce toxic effects on blood components, which is often ignored field of research. Since dermal exposure of humans to toxic chemicals covers an important issue in various industries, there is a need of such work to understand and update the long-term toxicities induced by PTBC usage in industrial sectors and public domain.

Agonist-Evoked Increases in Intra-Platelet Zinc Couple to Functional Responses

Background  Zinc (Zn ²⁺ ) is an essential trace element that regulates intracellular processes in multiple cell types. While the role of Zn ²⁺ as a platelet agonist is known, its secondary messenger activity in platelets has not been demonstrated.

Objectives  This article determines whether cytosolic Zn ²⁺ concentrations ([Zn ²⁺ ] _i ) change in platelets in response to agonist stimulation, in a manner consistent with a secondary messenger, and correlates the effects of [Zn ²⁺ ] _i changes on activation markers.

Methods  Changes in [Zn ²⁺ ] _i were quantified in Fluozin-3 (Fz-3)-loaded washed, human platelets using fluorometry. Increases in [Zn ²⁺ ] _i were modelled using Zn ²⁺ -specific chelators and ionophores. The influence of [Zn ²⁺ ] _i on platelet function was assessed using platelet aggregometry, flow cytometry and Western blotting.

Results  Increases of intra-platelet Fluozin-3 (Fz-3) fluorescence occurred in response to stimulation by cross-linked collagen-related peptide (CRP-XL) or U46619, consistent with a rise of [Zn ²⁺ ] _i . Fluoresence increases were blocked by Zn ²⁺ chelators and modulators of the platelet redox state, and were distinct from agonist-evoked [Ca ²⁺ ] _i signals. Stimulation of platelets with the Zn ²⁺ ionophores clioquinol (Cq) or pyrithione (Py) caused sustained increases of [Zn ²⁺ ] _i , resulting in myosin light chain phosphorylation, and cytoskeletal re-arrangements which were sensitive to cytochalasin-D treatment. Cq stimulation resulted in integrin α _IIb β ₃ activation and release of dense, but not α, granules. Furthermore, Zn ²⁺ -ionophores induced externalization of phosphatidylserine.

Conclusion  These data suggest that agonist-evoked fluctuations in intra-platelet Zn ²⁺ couple to functional responses, in a manner that is consistent with a role as a secondary messenger. Increased intra-platelet Zn ²⁺ regulates signalling processes, including shape change, α _IIb β ₃ up-regulation and dense granule release, in a redox-sensitive manner.

Apoptosis of Platelets Inhibited By Herba Sarcandrae Extract through the Mitochondria Pathway

The purpose of the present study is to decode the underlying mechanism of Herba Sarcandrae that indicated antipurpuric effect and to unveil one of its primary components, flavonoids, which play an important role. An immune mediated bone marrow failure (BMF) model in mouse was established by infusion thymus suspension cells after radiation in vivo. Platelets isolated in vitro were prepared from normal mice and BMF mice, respectively. The expressions of PS, P-selectin, PAC-1, Bax, Bad, Bid, and caspase-9 were examined by flow cytometry, and alteration of morphology of platelets under different conditions was observed. Our results indicated that the number of platelets was increased by addition of total flavonoids, and some of apoptotic markers such as Bax, Bad, Bid, and Caspase-9 were downregulated. In addition, the phosphatidylserine (PS) exposure on platelets was inhibited by total flavonoids, and the expressions of PAC-1 and P-selectin were decreased. In conclusion, it is suggested that the total flavonoids of Herba Sarcandrae may inhibit the excessive platelet apoptosis through mitochondrial pathway. In addition, activation of platelets may be also involved in mediating apoptosis of platelets.

How to Avoid False-Negative and False-Positive Diagnoses of Platelet Apoptosis: Illustrative Experimental and Clinically Relevant Cases

Platelets may selectively execute apoptosis (PL-Apo), activation (PL-Act), and both or no responses when exposed to different chemical agents, shear stresses, and stored under blood banking conditions. Appropriate diagnosis of PL-Apo is an important issue of platelet physiology investigations. However, in diagnosing PL-Apo, there is a risk of a false-negative or false-positive diagnosis. The goal of the current review is to present recommendations that may help to avoid incorrect PL-Apo diagnosis. Analyzing reported studies, we recommend (1) using platelet-rich plasma rather than isolated platelets to minimize artificial stimulation of PL-Apo during platelet isolation, (2) using established optimal conditions for stimulation of PL-Apo and/or PL-Act, (3) using a panel of PL-Apo and PL-Act markers, and (4) appropriate positive and negative controls for quantification of PL-Apo and PL-Act responses.

Evaluation of platelet activation in leukocyte-depleted platelet concentrates during storage

Structural and functional changes in platelets during storage can lead to the loss of platelet reactivity and response. Our aim was to evaluate leukocyte-depleted platelet concentrates on storage days 0, 3 and 5, obtained by in-line filtration. In non-filtered platelet concentrates (NF-PC) group, 180 whole blood units were collected with quadruple blood bags and then compared to another group of 180 whole blood units (leukocyte-depleted platelet concentrates [LD-PC]), collected in Imuflex Whole Blood Filter Saving Platelets (WB-SP) bags with an integrated leukoreduction filter, with regard to the platelet quality and characteristics. The efficacy of the two techniques for platelet concentrate preparation was evaluated by white blood cell (WBC) and platelet count on day 0. The partial pressure of oxygen (pO2), pH, platelets positive for P-selectin (CD62P), CD63, cluster of differentiation 42b (CD42b), phosphatidylserine (PS), and mitochondrial membrane potential (MMP) were analyzed during the storage in both groups. A significantly lower WBC count and higher platelet count was observed in LD-PC compared to NF-PC group, indicating the overall efficacy of the first technique. During the 5-day storage, pH and pO2 decreased in both groups. In LD-PC group, higher pH, increased pO2 and decreased platelet surface expression of CD62P, CD63 and PS were observed compared to NF-PC group. In both groups, the percentage of CD42b positive platelets and MMP did not change significantly during the 5-day period. The assessment of different markers of platelet activation may be an effective tool in evaluating the quality of platelets during storage. A better understanding of platelet activation may provide new insights for developing a novel therapeutic approach in the manipulation of platelet aggregation.

Drug-induced thrombocytopenia: Focus on platelet apoptosis

Thrombocytopenia is a serious and potentially fatal complication of drug therapy that results either from a decrease in bone marrow platelet production or the excessive destruction of circulating platelets. Although multiple mechanisms are responsible for deregulated platelet clearance, the role of programmed platelet death (apoptosis) in drug-induced thrombocytopenia has been relatively under-investigated until recently. Here we review apoptotic signaling pathways in platelets, with a focus on current data that provide mechanistic insights into drug-induced apoptosis and thrombocytopenia.

A large scale Plasmodium vivax- Saimiri boliviensis trophozoite-schizont transition proteome

Plasmodium vivax is a complex protozoan parasite with over 6,500 genes and stage-specific differential expression. Much of the unique biology of this pathogen remains unknown, including how it modifies and restructures the host reticulocyte. Using a recently published P. vivax reference genome, we report the proteome from two biological replicates of infected Saimiri boliviensis host reticulocytes undergoing transition from the late trophozoite to early schizont stages. Using five database search engines, we identified a total of 2000 P. vivax and 3487 S. boliviensis proteins, making this the most comprehensive P. vivax proteome to date. PlasmoDB GO-term enrichment analysis of proteins identified at least twice by a search engine highlighted core metabolic processes and molecular functions such as glycolysis, translation and protein folding, cell components such as ribosomes, proteasomes and the Golgi apparatus, and a number of vesicle and trafficking related clusters. Database for Annotation, Visualization and Integrated Discovery (DAVID) v6.8 enriched functional annotation clusters of S. boliviensis proteins highlighted vesicle and trafficking-related clusters, elements of the cytoskeleton, oxidative processes and response to oxidative stress, macromolecular complexes such as the proteasome and ribosome, metabolism, translation, and cell death. Host and parasite proteins potentially involved in cell adhesion were also identified. Over 25% of the P. vivax proteins have no functional annotation; this group includes 45 VIR members of the large PIR family. A number of host and pathogen proteins contained highly oxidized or nitrated residues, extending prior trophozoite-enriched stage observations from S. boliviensis infections, and supporting the possibility of oxidative stress in relation to the disease. This proteome significantly expands the size and complexity of the known P. vivax and Saimiri host iRBC proteomes, and provides in-depth data that will be valuable for ongoing research on this parasite’s biology and pathogenesis.

Platelet Integrin αIIbβ3 Inhibitor Rescues Progression of Apoptosis in Human Platelets

BACKGROUND Apoptosis plays an important role in the physiology of platelet function. We aimed to detect the effect of the platelet integrin αIIbβ3 inhibitor, tirofiban, on apoptotic events, including mitochondrial inner-membrane potential (ΔΨm), phosphatidylserine (PS) exposure on platelet surface, and the generation of reactive oxygen species (ROS), when washed platelets were stimulated with thrombin. MATERIAL AND METHODS The study included washed platelets from healthy humans, divided into 4 groups: vehicle, and tirofiban (0.05 μg/ml, 0.25 μg/ml, and 0.5 μg/ml). Platelets were pretreated with vehicle or tirofiban and incubated at 37°C with agitation for 6 h and 24 h. Before thrombin addition, the vehicle group divided into 2 equal groups. Except one vehicle group, the other 4 groups were all stimulated with thrombin (1 U/ml) for 30 min at 37°C. Using flow cytometry, we studied the DYm and PS exposure on platelet surfaces, and the generation of ROS in platelets. RESULTS We observed that at the time of 6 h and 24 h, thrombin-stimulated vehicle platelets induced significant depo-larization of ΔΨm, higher PS exposure, and increased ROS production compared with the vehicle group (P<0.01). However, the tirofiban group had significantly more recovery of DYm, PS exposure, and ROS production compared with the thrombin group (P<0.01). CONCLUSIONS The platelet integrin αIIbβ3 inhibitor, tirofiban, inhibits the depolarization of DYm, PS exposure on platelet surface, and ROS production when stimulated with thrombin. These results suggest that αIIbβ3 inhibitor inhibits the initiation of apoptosis in platelets, showing a potential clinical application of tirofiban as an apoptosis inhibitor.

Differences in levels of platelet-derived microparticles in platelet components prepared using the platelet rich plasma, buffy coat, and apheresis procedures

BACKGROUND

There has been an increased interest in platelet-derived microparticles (PMPs) in transfusion medicine. Little is known about PMP status during the preparation of platelet concentrates for transfusion.

AIM

The aim of this study is to compare the PMP levels in platelet components prepared using the buffy coat (BC), platelet-rich plasma platelet concentrate (PRP-PC), and apheresis (AP) processes.

METHODS

Platelet components were prepared using the PRP-PC and BC processes. Apheresis platelets were prepared using the Trima Accel and Amicus instruments. The samples were incubated with annexin A5-FITC, CD41-PE, and CD62P-APC. At day 1 after processing, the PMPs and activated platelets were determined using flow cytometry.

RESULTS

Both the percentage and number of PMPs were higher in platelet components prepared using the Amicus instrument (2.6±1.8, 32802±19036 particles/μL) than in platelet components prepared using the Trima Accel instrument (0.5±0.4, 7568±5298 particles/μL), BC (1.2±0.6, 12,920±6426 particles/μL), and PRP-PC (0.9±0.6, 10731±5514 particles/μL). Both the percentage and number of activated platelets were higher in platelet components prepared using the Amicus instrument (33.2±13.9, 427553±196965 cells/μL) than in platelet components prepared using the Trima Accel instrument (16.2±6.1, 211209±87706 cells/μL), BC (12.9±3.2, 140624±41003 cells/μL), and PRP-PC (21.1±6.3, 265210±86257 cells/μL).

CONCLUSIONS

The study suggests high variability of PMPs and activated platelets in platelet components prepared using different processes. This result may be important in validating the instruments involved in platelet blood collection and processing.

Ex vivo apoptotic and autophagic influence of an estradiol analogue on platelets

Background

Platelets are known contributors to the vascularization, metastasis and growth of tumors. Upon their interaction with cancer cells they are activated resulting in degranulation and release of constituents. Since the apoptotic- and autophagic effects of 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) has been shown to occur in vitro and this compound was designed to bind to carbonic anhydrase II (CAII), the possible occurrence of these cell death mechanisms in platelets as circulatory components, is of importance.

Methods

Scanning electron microscopy was used to assess morphological changes in platelets after exposure to ESE-16. The possible apoptotic- and autophagic effect of ESE-16 in platelets was also determined by means of flow cytometry through measurement of Annexin V-FITC, caspase 3 activity, autophagy related protein 5 levels and light chain 3-I to light chain 3-II conversion.

Results

Scanning electron microscopy revealed no changes in ESE-16-treated platelets when compared to vehicle-treated samples. Apoptosis detection by Annexin V-FITC and measurement of caspase 3 activity indicated that there was no increase in apoptosis when platelets were exposed to ESE-16. The incidence of autophagy by measurement of autophagy related protein 5 levels and light chain 3-I to light chain 3-II conversion showed that exposure to ESE-16 did not cause the incidence of autophagy in platelets.

Conclusion

This is the first ex vivo study reporting on involvement of apoptosis- and autophagy-related targets in platelets after exposure to ESE-16, warranting further investigation in platelets of cancer patients.

Unresolved clinical aspects and safety hazards of blood derived- EV/MV in stored blood components: From personal memory lanes to newer perspectives on the roles of EV/MV in various biological phenomena

Blood cells generate heterogeneous populations of vesicles that are delivered, as small-specialized packages of highly active cell fragments in blood circulation, having almost similar functional activities, as the mother cells. These so called extracellular vesicles are the essential part of an energy-dependent natural apoptotic process; hence their beneficial and harmful biological functions cannot be ignored. Evidence is accumulating, that cellular derived vesicles, originate from all viable cells including: megakaryocytes, platelets, red blood cells, white blood cells and endothelial cells, the highest in proportions from platelets. Shedding can also be triggered by pathological activation of inflammatory processes and activation of coagulation or complement pathways, or even by shear stress in the circulation. Structurally, so called MV/EV appear to be, sometimes inside-out and sometimes outside-in cell fragments having a bilayered phospholipid structure exposing coagulant-active phosphatidylserine, expressing various membrane receptors, and they serve as cell-to-cell shuttles for bioactive molecules such as lipids, growth factors, microRNAs, and mitochondria. Ex vivo processing of blood into its components, embodying centrifugation, processing by various apheresis procedures, leukoreduction, pathogen reduction, and finally storage in different media and different types of blood bags, also have major impacts on the generation and retention of MV content. These artificially generated small, but highly liable packages, together with the original pool of MVs collected from the donor, do exhibit differing biological activities, and are not inert elements and should be considered as a parameter of blood safety in haemovigilance programmes. Harmonization and consensus in sampling protocols, sample handling, processing, and assessment methods, in particular converting to full automation, are needed to achieve consensual interpretations. This review focuses on some of our past personal studies on the role of MV/EV focusing on characterization of platelet storage lesion and platelet therapy that shows the highest transfusion hazards [up to 25%], and loss of 25% platelet efficacy after various leukoreduction and validated platelet pathogen reduction treatments. The planned paths for the future of EV/MV involvement in immunological and viral/ non-viral transfusion hazards are also discussed. Whilst considerable advances made on the characterization of EV/MV, but disparity still exists between various surrogate markers, showing some subtle differences in the levels of MV/ EV & BRMs in platelet preparations, and the clinical outcome showing platelets derived by all current technologies are equivalents in vivo. One possible reason for such a disparity may be relatedto the fact that MVs, being the end products of apoptotic cells, have little specificity and clear rapidly from circulation [<6 h in thrombocytopoenia]. This makes their clinical usefulness rather short lived. The recent findings that pegylating smaller subsets of EV increases its circulatory life from <15 minutes to approximately about one hour is highly promising, in particular, for drug delivery on specific sides. Hence a promising clinical utility of EV/MV continues, as a journey without end, indeed. This manuscript is based mainly on the selected key readings listed below.

Time dependent apoptotic rates in the evolving coronary thrombus mass of myocardial infarction patients

AIM

To study the rate of apoptotic cell death in the process of thrombus evolution after plaque rupture in myocardial infarction.

METHODS

Paraffin embedded thrombosuction aspirates of 63 patients were stained with haematoxylin & eosin (H&E) to assess histologically the age of the thrombi: fresh (intact blood cells; <1day old), lytic (necrosis; 1-5days old) or organized (ingrowth of cells; >5days old). Presence of plaque constituents (atheroma including foam cells, cholesterol crystals calcifications and fibrous cap tissue) was also recorded. Immunohistochemical (double) stains with anti-caspase-3-antibody were used to visualize apoptosis and the cells involved. For the latter caspase-3 antibody was combined with cell-specific markers MPO (granulocytes), CD68 (macrophages), CD34 (endothelial cells), SMA-1 (smooth muscle cells) and a Feulgen stain (DNA). Second, the rate of apoptosis was evaluated in relation to the age of the thrombi. Platelet apoptosis was further evaluated with the use of TEM.

RESULTS

From a total of 63 aspirates, plaque constituents were found in 33 of the aspirates, and in 15 of them lipid rich plaque tissue was the sole component. Age classification of all thrombus containing aspirates (n=48) resulted in 12 fresh (25%), 18 lytic (37.5%) and 18 organized (37.5%) thrombi. Apoptosis was more extensive in lytic thrombi than in fresh or organized thrombi (P<0.0001). Plaque-containing aspirates showed more apoptosis than aspirates without plaque (P<0.05). Immuno staining with caspase-3 antibody in combination with cell-specific markers showed that apoptosis was most extensive in MPO+ granulocytes. Caspase-3-positive platelets (CD61+ anucleate particles) were most abundant in lytic thrombi. Apoptosis in platelets was confirmed by ultrastructure.

CONCLUSION

This study demonstrated a significant association between thrombus age and occurrence of apoptosis of granulocytes and also platelets, with highest rates in (fragile) lytic thrombi. We propose that apoptotic cell death in athero thrombosis could potentially serve as a biomarker for thrombus instability.

Comparison of intraplatelet reactive oxygen species, mitochondrial damage, and platelet apoptosis after implantation of three continuous flow left ventricular assist devices: HeartMate II, Jarvik 2000, and HeartWare

Differences in device design may have an effect on platelet damage and associated clinical complications. We aimed to compare device-specific platelet functionality in 26 heart failure patients supported with three continuous-flow left ventricular assist devices: HeartMate II (n = 8), Jarvik 2000 (n = 9), and HeartWare (n = 9). Intraplatelet reactive oxygen species (ROS) generation, mitochondrial damage, and platelet apoptosis were compared between device types before and after the implantation at every week up to 1 month. Overall, the baseline characteristics, demographics, routine laboratory values were comparable between the three device groups. Intraplatelet ROS, mitochondrial damage, and platelet apoptosis significantly elevated in the HeartWare group in comparison with the other two device groups after implantation. The major bleeding, infections, systemic inflammatory response syndrome, and right ventricular failure were found to be more common among the HeartWare group than others. Intraplatelet ROS and platelet damage levels were returned to baseline in both the HeartMate II and the Jarvik groups, whereas in HeartWare group they remained elevated. The patients with the Jarvik and the HeartMate II experienced less clinical complications and the platelet functionality is not compromised by these devices. Data from this study suggests that the continuous-flow left ventricular assist devices design may exert different effects on platelet function.

Resveratrol preserves the function of human platelets stored for transfusion

Stored platelets undergo biochemical, structural and functional changes that lead to decreased efficacy and safety of platelet transfusions. Not only do platelets acquire markers of activation during storage, but they also fail to respond normally to agonists post-storage. We hypothesized that resveratrol, a cardioprotective antioxidant, could act as a novel platelet storage additive to safely prevent unwanted platelet activation during storage, while simultaneously preserving normal haemostatic function. Human platelets treated with resveratrol and stored for 5 d released less thromboxane B2 and prostaglandin E2 compared to control platelets. Resveratrol preserved the ability of platelets to aggregate, spread and respond to thrombin, suggesting an improved ability to activate post-storage. Utilizing an in vitro model of transfusion and thromboelastography, clot strength was improved with resveratrol treatment compared to conventionally stored platelets. The mechanism of resveratrol's beneficial actions on stored platelets was partly mediated through decreased platelet apoptosis in storage, resulting in a longer half-life following transfusion. Lastly, an in vivo mouse model of transfusion demonstrated that stored platelets are prothrombotic and that resveratrol delayed vessel occlusion time to a level similar to transfusion with fresh platelets. We show resveratrol has a dual ability to reduce unwanted platelet activation during storage, while preserving critical haemostatic function.

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.

An overview of the role of microparticles/microvesicles in blood components: Are they clinically beneficial or harmful?

Blood cells and tissues generate heterogeneous populations of cell-derived vesicles, ranging from approximately 50 nm to 1 µm in diameter. Under normal physiological conditions and as an essential part of an energy-dependent natural process, microparticles (MPs) are continuously shed into the circulation from membranes of all viable cells such as megakaryocytes, platelets, red blood cells, white blood cells and endothelial cells. MP shedding can also be triggered by pathological activation of inflammatory processes and activation of coagulation or complement systems, or even by shear stress in the circulation. Structurally, MPs have a bilayered phospholipid structure exposing coagulant-active phosphatidylserine and expressing various membrane receptors, and they serve as cell-to-cell shuttles for bioactive molecules such as lipids, growth factors, microRNAs, and mitochondria. It was established that ex vivo processing of blood into its components, involving centrifugation, processing by various apheresis procedures, leucoreduction, pathogen reduction, and finally storage in different media and different types of blood bags, can impact MP generation and content. This is mostly due to exposure of the collected blood to anticoagulant/storage media and due to shear stresses or activation, contact with artificial surfaces, or exposure to various leucocyte-removal filters and pathogen-reduction treatments. Such artificially generated MPs, which are added to the original pool of MPs collected from the donor, may exhibit specific functional characteristics, as MPs are not an inert element of blood components. Not surprisingly, MPs' roles and functionality are therefore increasingly seen to be fully relevant to the field of transfusion medicine, and as a parameter of blood safety that must be considered in haemovigilance programmes. Continual advancements in assessment methods of MPs and storage lesions are gradually leading to a better understanding of the impacts of blood collection on MP generation, while clinical research should clarify links of MPs with transfusion reactions and certain clinical disorders. Harmonization and consensus in sampling protocols, sample handling and processing, and assessment methods are needed to achieve consensual interpretations. This review focuses on the role of MPs as an essential laboratory tool and as a most effective player in transfusion science and medicine and in health and disease.

Necrotic platelets provide a procoagulant surface during thrombosis

A subpopulation of platelets fulfills a procoagulant role in hemostasis and thrombosis by enabling the thrombin burst required for fibrin formation and clot stability at the site of vascular injury. Excess procoagulant activity is linked with pathological thrombosis. The identity of the procoagulant platelet has been elusive. The cell death marker 4-[N-(S-glutathionylacetyl)amino]phenylarsonous acid (GSAO) rapidly enters a subpopulation of agonist-stimulated platelets via an organic anion-transporting polypeptide and is retained in the cytosol through covalent reaction with protein dithiols. Labeling with GSAO, together with exposure of P-selectin, distinguishes necrotic from apoptotic platelets and correlates with procoagulant potential. GSAO(+) platelets form in occluding murine thrombi after ferric chloride injury and are attenuated with megakaryocyte-directed deletion of the cyclophilin D gene. These platelets form a procoagulant surface, supporting fibrin formation, and reduction in GSAO(+) platelets is associated with reduction in platelet thrombus size and fibrin formation. Analysis of platelets from human subjects receiving aspirin therapy indicates that these procoagulant platelets form despite aspirin therapy, but are attenuated by inhibition of the necrosis pathway. These findings indicate that the major subpopulation of platelets involved in fibrin formation are formed via regulated necrosis involving cyclophilin D, and that they may be targeted independent of platelet activation.