Human platelets synthesize and express functional tissue factor

Activation of AMPK in platelets promotes the production of offspring

Platelets are terminally differentiated anucleated cells, but they still have cell-like functions and can even produce progeny platelets. However, the mechanism of platelet sprouting has not been elucidated so far. Here, we show that when platelet-rich plasma(PRP) was cultured at 37°C, platelets showed a spore phenomenon. The number of platelets increased when given a specific shear force. It is found that AMP-related signaling pathways, such as PKA and AMPK are activated in platelets in the spore state. Meanwhile, the mRNA expression levels of genes, such as CNN3, CAPZB, DBNL, KRT19, and ESPN related to PLS1 skeleton proteins also changed. Moreover, when we use the AMPK activator AICAR(AI) to treat washed platelets, cultured platelets can still appear spore phenomenon. We further demonstrate that washed platelets treated with Forskolin, an activator of PKA, not only platelet sprouting after culture but also the AMPK is activated. Taken together, these data demonstrate that AMPK plays a key role in the process of platelet budding and proliferation, suggesting a novel strategy to solve the problem of clinical platelet shortage.

Update on Tissue Factor Detection in Blood in 2024: A Narrative Review

Tissue factor (TF) is a transmembrane protein essential for hemostasis. Different forms of active TF circulate in the blood, either as a component of blood cells and extracellular vesicles (EVs) or as a soluble plasma protein. Accumulating experimental and clinical evidence suggests that TF plays an important role in thrombosis. Many in-house and commercially available assays have been developed to measure TF-dependent procoagulant activity or antigen in blood and have shown promising results for the prediction of disease outcomes or the occurrence of thrombosis events in diseases such as cancer or infectious coagulopathies. This review addresses the different assays that have been published for measuring circulating TF antigen and/or activity in whole blood, cell-free plasma, and EVs and discusses the main preanalytical and analytical parameters that impact results and their interpretation, highlighting their strengths and limitations. In the recent decade, EVTF assays have been significantly developed. Among them, functional assays that use a blocking anti-TF antibody or immunocapture to measure EVTF activity have higher specificity and sensitivity than antigen assays. However, there is still a high variability between assays. Standardization and automatization are prerequisites for the measurement of EVTF in clinical laboratories.

Inflammation, Sepsis, and the Coagulation System

Sepsis has been a major health problem for centuries and it is still the leading cause of hospital deaths. Several studies in the past decades have identified numerous biochemical abnormalities in severe cases, and many of these studies provide evidence of the perturbation of the hemostatic system. This can result in complications, such as disseminated intravascular coagulation that can lead to multiorgan failure. Nevertheless, large clinical studies have demonstrated that the simple approach of inhibiting the coagulation processes by any means fails to provide significant improvement in the survival of septic patients. A cause of this failure could be the fact that in sepsis the major clinical problems result not primarily from the presence of the infective agent or enhanced coagulation but from the complex dysregulated systemic host response to pathogens. If this overt reaction is not fully deciphered, appropriate interference is highly unlikely and any improvement by conventional therapeutic interventions would be limited. Cellular activation in sepsis can be targeted by novel approaches like inhibition of the heterotypic cellular interactions of blood cells by targeting surface receptors or posttranscriptional control of the hemostatic system by noncoding ribonucleic acid (RNA) molecules. Stable RNA molecules can affect the expression of several proteins. Thus, it can be anticipated that modulation of microRNA production would result in a multitude of effects that may be beneficial in septic cases. Here, we highlight some of the recent diagnostic possibilities and potential novel routes of the dysregulated host response.

Haemostatic Gene Expression in Cancer-Related Immunothrombosis: Contribution for Venous Thromboembolism and Ovarian Tumour Behaviour

Ovarian cancer (OC) is the deadliest gynaecological malignancy. Identifying new prognostic biomarkers is an important research field. Haemostatic components together with leukocytes can drive cancer progression while increasing the susceptibility to venous thromboembolism (VTE) through immunothrombosis. Unravelling the underlying complex interactions offers the prospect of uncovering relevant OC prognostic biomarkers, predictors of cancer-associated thrombosis (CAT), and even potential targets for cancer therapy. Thus, this study evaluated the expression of F3, F5, F8, F13A1, TFPI1, and THBD in peripheral blood cells (PBCs) of 52 OC patients. Those with VTE after tumour diagnosis had a worse overall survival (OS) compared to their counterparts (mean OS of 13.8 ± 4.1 months and 47.9 ± 5.7 months, respectively; log-rank test, p = 0.001). Low pre-chemotherapy F3 and F8 expression levels were associated with a higher susceptibility for OC-related VTE after tumour diagnosis (χ2, p < 0.05). Regardless of thrombogenesis, patients with low baseline F8 expression had a shorter progression-free survival (PFS) than their counterparts (adjusted hazard ratio (aHR) = 2.54; p = 0.021). Among those who were not under platelet anti-aggregation therapy, low F8 levels were also associated with a shorter OS (aHR = 6.16; p = 0.006). Moving forward, efforts should focus on external validation in larger cohorts.

Sepsis-Induced Coagulopathy: A Comprehensive Narrative Review of Pathophysiology, Clinical Presentation, Diagnosis, and Management Strategies

Physiological hemostasis is a balance between pro- and anticoagulant pathways, and in sepsis, this equilibrium is disturbed, resulting in systemic thrombin generation, impaired anticoagulant activity, and suppression of fibrinolysis, a condition termed sepsis-induced coagulopathy (SIC). SIC is a common complication, being present in 24% of patients with sepsis and 66% of patients with septic shock, and is often associated with poor clinical outcomes and high mortality. 1 , 2 Recent preclinical and clinical studies have generated new insights into the molecular pathogenesis of SIC. In this article, we analyze the complex pathophysiology of SIC with a focus on the role of procoagulant innate immune signaling in hemostatic activation--tissue factor production, thrombin generation, endotheliopathy, and impaired antithrombotic functions. We also review clinical presentations of SIC, the diagnostic scoring system and laboratory tests, the current standard of care, and clinical trials evaluating the efficacies of anticoagulant therapies.

Platelet protein synthesis, regulation, and post-translational modifications: mechanics and function

Dogma had been firmly entrenched in the minds of the scientific community that the anucleate mammalian platelet was incapable of protein biosynthesis since their identification in the late 1880s. These beliefs were not challenged until the 1960s when several reports demonstrated that platelets possessed the capacity to biosynthesize proteins. Even then, many still dismissed the synthesis as trivial and unimportant for at least another two decades. Research in the field expanded after the 1980s and numerous reports have since been published that now clearly demonstrate the potential significance of platelet protein synthesis under normal, pathological, and activating conditions. It is now clear that the platelet proteome is not a static entity but can be altered slowly or rapidly in response to external signals to support physiological requirements to maintain hemostasis and other biological processes. All the necessary biological components to support protein synthesis have been identified in platelets along with post-transcriptional processing of mRNAs, regulators of translation, and post-translational modifications such as glycosylation. The last comprehensive review of the subject appeared in 2009 and much work has been conducted since that time. The current review of the field will briefly incorporate the information covered in earlier reviews and then bring the reader up to date with more recent findings.

Crucial roles of red blood cells and platelets in whole blood thrombin generation

Red blood cells (RBCs) and platelets contribute to the coagulation capacity in bleeding and thrombotic disorders. The thrombin generation (TG) process is considered to reflect the interactions between plasma coagulation and the various blood cells. Using a new high-throughput method capturing the complete TG curve, we were able to compare TG in whole blood and autologous platelet-rich and platelet-poor plasma to redefine the blood cell contributions to the clotting process. We report a faster and initially higher generation of thrombin and shorter coagulation time in whole blood than in platelet-rich plasma upon low concentrations of coagulant triggers, including tissue factor, Russell viper venom factor X, factor Xa, factor XIa, and thrombin. The TG was accelerated with increased hematocrit and delayed after prior treatment of RBC with phosphatidylserine-blocking annexin A5. RBC treatment with ionomycin increased phosphatidylserine exposure, confirmed by flow cytometry, and increased the TG process. In reconstituted blood samples, the prior selective blockage of phosphatidylserine on RBC with annexin A5 enhanced glycoprotein VI-induced platelet procoagulant activity. For patients with anemia or erythrocytosis, cluster analysis revealed high or low whole-blood TG profiles in specific cases of anemia. The TG profiles lowered upon annexin A5 addition in the presence of RBCs and thus were determined by the extent of phosphatidylserine exposure of blood cells. Profiles for patients with polycythemia vera undergoing treatment were similar to that of control subjects. We concluded that RBC and platelets, in a phosphatidylserine-dependent way, contribute to the TG process. Determination of the whole-blood hypo- or hyper-coagulant activity may help to characterize a bleeding or thrombosis risk.

Effects of the interactions between platelets with other cells in tumor growth and progression

It has been confirmed that platelets play a key role in tumorigenesis. Tumor-activated platelets can recruit blood cells and immune cells to migrate, establish an inflammatory tumor microenvironment at the sites of primary and metastatic tumors. On the other hand, they can also promote the differentiation of mesenchymal cells, which can accelerate the proliferation, genesis and migration of blood vessels. The role of platelets in tumors has been well studied. However, a growing number of studies suggest that interactions between platelets and immune cells (e.g., dendritic cells, natural killer cells, monocytes, and red blood cells) also play an important role in tumorigenesis and tumor development. In this review, we summarize the major cells that are closely associated with platelets and discuss the essential role of the interaction between platelets with these cells in tumorigenesis and tumor development.

The severity and duration of Hypoglycemia affect platelet-derived protein responses in Caucasians

Objective

Severe hypoglycemia is associated with increased cardiovascular death risk, and platelet responses to hypoglycemia (hypo) have been described. However, the impact of deep transient hypo (deep-hypo) versus prolonged milder hypo (mild-hypo) on platelet response is unclear.

Research Design and methods

Two hypo studies were compared; firstly, mild-hypo in 18-subjects (10 type-2-diabetes (T2D), 8 controls), blood glucose to 2.8mmoL/L (50 mg/dL) for 1-hour; secondly deep-hypo in 46-subjects (23 T2D, 23 controls), blood glucose to < 2.2mmoL/L (< 40 mg/dL) transiently. Platelet-related protein (PRP) responses from baseline to after 1-hour of hypo (mild-hypo) or at deep-hypo were compared, and at 24-hours post-hypo. Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement was used to determine PRP changes for 13 PRPs.

Results

In controls, from baseline to hypo, differences were seen for four PRPs, three showing increased %change in deep-hypo (Plasminogen activator inhibitor-1(PAI-1), CD40 ligand (CD40LG) and Protein-S), one showing increased %change in mild-hypo (von Willebrand factor (vWF)); at 24-hours in controls, %change for Protein-S remained increased in deep-hypo, whilst % change for vWF and plasminogen were increased in mild-hypo. In T2D, from baseline to hypo, differences were seen for 4 PRPs, three showing increased %change in deep-hypo (PAI-1, platelet glycoprotein VI and Tissue factor), one showing increased %change in mild-hypo (CD40LG); at 24-hours in T2D, %change for CD40LG remained increased, together with vWF, in deep-hypo.

Conclusion

Both mild-hypo and deep-hypo showed marked PRP changes that continued up to 24-hours, showing that both the severity and duration of hypoglycemia are likely important and that any degree of hypoglycemia may be detrimental for increased cardiovascular risk events through PRP changes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01639-w.

Activated Platelets and Platelet-Derived Extracellular Vesicles Mediate COVID-19-Associated Immunothrombosis

Activated platelets and platelet-derived extracellular vesicles (EVs) have emerged as central players in thromboembolic complications associated with severe coronavirus disease 2019 (COVID-19). Platelets bridge hemostatic, inflammatory, and immune responses by their ability to sense pathogens via various pattern recognition receptors, and they respond to infection through a diverse repertoire of mechanisms. Dysregulated platelet activation, however, can lead to immunothrombosis, a simultaneous overactivation of blood coagulation and the innate immune response. Mediators released by activated platelets in response to infection, such as antimicrobial peptides, high mobility group box 1 protein, platelet factor 4 (PF4), and PF4⁺ extracellular vesicles promote neutrophil activation, resulting in the release of neutrophil extracellular traps and histones. Many of the factors released during platelet and neutrophil activation are positively charged and interact with endogenous heparan sulfate or exogenously administered heparin via electrostatic interactions or via specific binding sites. Here, we review the current state of knowledge regarding the involvement of platelets and platelet-derived EVs in the pathogenesis of immunothrombosis, and we discuss the potential of extracorporeal therapies using adsorbents functionalized with heparin to deplete platelet-derived and neutrophil-derived mediators of immunothrombosis.

Controversial Role of the Immune Checkpoint OX40L Expression on Platelets in Breast Cancer Progression

In conventional T cells, OX40 has been identified as a major costimulating receptor augmenting survival and clonal expansion of effector and memory T cell populations. In regulatory T cells, (Treg) OX40 signaling suppresses cellular activity and differentiation. However, clinical trials investigating OX40 agonists to enhance anti-tumor immunity, showed only limited success so far. Here we show that platelets from breast cancer patients express relevant levels of OX40L and platelet OX40L (pOX40L) inversely correlates with platelet-expressed immune checkpoint molecules GITRL (pGITRL) and TACI (pTACI). While high expression of pOX40L correlates with T and NK cell activation, elevated pOX40L levels identify patients with higher tumor grades, the occurrence of metastases, and shorter recurrence-free survival (RFS). Of note, OX40 mRNA levels in breast cancer correlate with enhanced expression of anti-apoptotic, immune-suppressive, and tumor-promoting mRNA gene signatures. Our data suggest that OX40L on platelets might play counteracting roles in cancer and anti-tumor immunity. Since pOX40L reflects disease relapse better than the routinely used predictive markers CA15-3, CEA, and LDH, it could serve as a novel biomarker for refractory disease in breast cancer.

A rapid, sensitive, and specific assay to measure TF activity based on chromogenic determination of thrombin generation

BACKGROUND

Most tissue factor (TF) activity assays are based on measurement of factor X (FX) activation by TF in the presence of factor VII (FVII)/FVIIa. This requires long incubation, which may result in TF-independent activity of FX and inaccurate measurement of TF activity.

AIM

To develop a sensitive and specific TF activity assay, which does not register a non-specific TF activity, using commercial coagulation factors.

METHODS

Tissue factor activity was measured based on the ability of TF to accelerate the activation of FX by FVIIa in the presence of factor V (FV)/Va, prothrombin, and phospholipids. Following 4 min incubation at 37°C, TF activity was quantified in test samples of different nature by thrombin generation using a chromogenic substrate.

RESULTS

The TF activity assay proved high sensitivity (low fM range) and specificity, assessed by neutralization of TF activity by anti-TF antibody and the use of FVIIai. TF activity was detected in extracellular vesicles (EVs) derived from HAP1-TF+cells, while no activity was measured in EVs from HAP1-TF/KO cells. The assay was applicable for measurement of TF activity on the surface of live endothelial cells and monocytes activated in vitro, and cell lysates. Infusion of low dose lipopolysaccharide (2 ng/kg bodyweight endotoxin) caused a transient 8-fold increase (peaked at 4 h) in TF activity in EVs isolated from plasma of healthy volunteers.

CONCLUSION

Our assay provides a fast, sensitive, and specific measurement of TF activity. It reliably quantifies TF activity on cell surface, cell lysate, and isolated EVs. The assay can be used for laboratory and clinical research.

Disseminated intravascular coagulation and its immune mechanisms

Disseminated intravascular coagulation (DIC) is a syndrome triggered by infectious and noninfectious pathologies characterized by excessive generation of thrombin within the vasculature and widespread proteolytic conversion of fibrinogen. Despite diverse clinical manifestations ranging from thrombo-occlusive damage to bleeding diathesis, DIC etiology commonly involves excessive activation of blood coagulation and overlapping dysregulation of anticoagulants and fibrinolysis. Initiation of blood coagulation follows intravascular expression of tissue factor or activation of the contact pathway in response to pathogen-associated or host-derived, damage-associated molecular patterns. The process is further amplified through inflammatory and immunothrombotic mechanisms. Consumption of anticoagulants and disruption of endothelial homeostasis lower the regulatory control and disseminate microvascular thrombosis. Clinical DIC development in patients is associated with worsening morbidities and increased mortality, regardless of the underlying pathology; therefore, timely recognition of DIC is critical for reducing the pathologic burden. Due to the diversity of triggers and pathogenic mechanisms leading to DIC, diagnosis is based on algorithms that quantify hemostatic imbalance, thrombocytopenia, and fibrinogen conversion. Because current diagnosis primarily assesses overt consumptive coagulopathies, there is a critical need for better recognition of nonovert DIC and/or pre-DIC states. Therapeutic strategies for patients with DIC involve resolution of the eliciting triggers and supportive care for the hemostatic imbalance. Despite medical care, mortality in patients with DIC remains high, and new strategies, tailored to the underlying pathologic mechanisms, are needed.

Platelets after burn injury - hemostasis and beyond

Burn injuries are common and often life-threatening trauma. With this trauma comes an interruption of normal hemostasis, with distinct impacts on platelets. Our interest in the relationships between burn injury and platelet function stems from two key perspectives: platelet function is a vital component of acute responses to injury, and furthermore the incidence of cardiovascular disease (CVD) is higher in burn survivors compared to the general population. This review explores the impact of burn injury on coagulation, platelet function, and the participation of platelets in immunopathology. Potential avenues of further research are explored, and consideration is given to what therapies may be appropriate for mediating post-burn thrombopathology.

Neutrophil-Derived Protein S100A8/A9 Alters the Platelet Proteome in Acute Myocardial Infarction and Is Associated With Changes in Platelet Reactivity

Supplemental Digital Content is available in the text.

Objective:

Platelets are central to acute myocardial infarction (MI). How the platelet proteome is altered during MI is unknown. We sought to describe changes in the platelet proteome during MI and identify corresponding functional consequences.

Approach and Results:

Platelets from patients experiencing ST-segment–elevation MI (STEMI) before and 3 days after treatment (n=30) and matched patients with severe stable coronary artery disease before and 3 days after coronary artery bypass grafting (n=25) underwent quantitative proteomic analysis. Elevations in the proteins S100A8 and S100A9 were detected at the time of STEMI compared with stable coronary artery disease (S100A8: FC, 2.00; false discovery rate, 0.05; S100A9: FC, 2.28; false discovery rate, 0.005). During STEMI, only S100A8 mRNA and protein levels were correlated in platelets (R=0.46, P=0.012). To determine whether de novo protein synthesis occurs, activated platelets were incubated with 13C-labeled amino acids for 24 hours and analyzed by mass spectrometry. No incorporation was confidently detected. Platelet S100A8 and S100A9 was strongly correlated with neutrophil abundance at the time of STEMI. When isolated platelets and neutrophils were coincubated under quiescent and activated conditions, release of S100A8 from neutrophils resulted in uptake of S100A8 by platelets. Neutrophils released S100A8/A9 as free heterodimer, rather than in vesicles or extracellular traps. In the community-based Bruneck study (n=338), plasma S100A8/A9 was inversely associated with platelet reactivity—an effect abrogated by aspirin.

Conclusions:

Leukocyte-to-platelet protein transfer may occur in a thromboinflammatory environment such as STEMI. Plasma S100A8/A9 was negatively associated with platelet reactivity. These findings highlight neutrophils as potential modifiers for thrombotic therapies in coronary artery disease.

Proteomics and enriched biological processes in Antiphospholipid syndrome: A systematic review

Identification of differentially expressed proteins in antiphospholipid syndrome (APS) is a developing area of research for unique profiles of this pathology. Advances in technologies of mass spectrometry brings improvements in proteomics and results in assessment of soluble or cellular proteins which could be candidates for clinical biomarkers of primary APS. The use of blood as a source of proteins ease the acquisition of samples for proteomics analyses and later for disease diagnosis. We performed a systematic review to explore the proteomics studies carried out in circulating released proteins (serum, plasma) or cellular proteins (monocytes and platelets) of APS patients. The study groups differentiate among clinical APS cases with the aim to translate molecular findings to disease stratification and to improve APS diagnosis and prognosis. These studies also include the unravelling of new autoantibodies in non-criteria APS or how post-translational protein modifications provides clues about the pathological mechanisms of antigen-autoantibody recognition. Herein, we identified 82 proteins that were dysregulated in APS across eleven studies. Enrichment analysis revealed its connection to cellular activation and degranulation that eventually leads to thrombosis as the main biological process highlighted by these studies. Validation of APS-relevant proteins by functional and mechanistic studies will be essential for patient stratification and the development of targeted therapies for every clinical subtype of APS.

Effect of heparanase inhibitor on tissue factor overexpression in platelets and endothelial cells induced by anti-β2-GPI antibodies

BACKGROUND

Anti-phospholipid syndrome (APS) is characterized by arterial and/or venous thrombosis and pregnancy morbidity associated with the presence of "anti-phospholipid antibodies." Thrombosis may be the result of a hypercoagulable state related to activation of endothelial cells and platelets by anti-β2-glycoprotein I (β2-GPI) antibodies. Anti-β2-GPI antibodies induce a proinflammatory and procoagulant phenotype in these cells that, after activation, express tissue factor (TF), the major initiator of the clotting cascade, playing a role in thrombotic manifestations. Moreover, TF expression may also be induced by heparanase, an endo-β-D-glucuronidase, that generates heparan sulfate fragments, regulating inflammatory responses.

OBJECTIVES

In this study we analyzed, in human platelets and endothelial cells, the effect of a new symmetrical 2-aminophenyl-benzazolyl-5-acetate derivative (RDS3337), able to inhibit heparanase activity, on signal transduction pathways leading to TF expression triggered by anti-β2-GPI.

METHODS

Platelets and endothelial cells were incubated with affinity purified anti-β2-GPI after pretreatment with RDS3337. Cell lysates were analyzed for phospho-interleukin-1 receptor-associated kinase 1 (IRAK1), phospho-p65 nuclear factor kappa B (NF-κB) and TF by western blot. In addition, platelet activation and secretion by ATP release dosage were evaluated.

RESULTS

IRAK phosphorylation and consequent NF-κB activation, as well as TF expression triggered by anti-β2-GPI treatment were significantly prevented by previous pretreatment with RDS3337. In the same vein, pretreatment with RDS3337 prevented platelet aggregation and ATP release triggered by anti-β2-GPI antibodies.

CONCLUSION

These findings support the view of heparanase involvement in a prothrombotic state related to APS syndrome, suggesting a novel target to regulate overexpression of procoagulant protein(s).

Added Value of Blood Cells in Thrombin Generation Testing

The capacity of blood to form thrombin is a critical determinant of coagulability. Plasma thrombin generation (TG), a test that probes the capacity of plasma to form thrombin, has improved our knowledge of the coagulation system and shows promising utility in coagulation management. Although plasma TG gives comprehensive insights into the function of pro- and anticoagulation drivers, it does not measure the role of blood cells in TG. In this literature review, we discuss currently available continuous TG tests that can reflect the involvement of blood cells in coagulation, in particular the fluorogenic assays that allow continuous measurement in platelet-rich plasma and whole blood. We also provide an overview about the influence of blood cells on blood coagulation, with emphasis on the direct influence of blood cells on TG. Platelets accelerate the initiation and velocity of TG by phosphatidylserine exposure, granule content release and surface receptor interaction with coagulation proteins. Erythrocytes are also major providers of phosphatidylserine, and erythrocyte membranes trigger contact activation. Furthermore, leukocytes and cancer cells may be important players in cell-mediated coagulation because, under certain conditions, they express tissue factor, release procoagulant components and can induce platelet activation. We argue that testing TG in the presence of blood cells may be useful to distinguish blood cell-related coagulation disorders. However, it should also be noted that these blood cell-dependent TG assays are not clinically validated. Further standardization and validation studies are needed to explore their clinical usefulness.

Platelet-expressed immune checkpoint regulator GITRL in breast cancer

Owing to their key role in several diseases including cancer, activating and inhibitory immune checkpoint molecules are increasingly exploited as targets for immunotherapy. Recently, we demonstrated that platelets, which largely influence tumor progression and immune evasion, functionally express the ligand of the checkpoint molecule GITR. This immunoreceptor modulates effector functions of T cells and NK cells with its function varying dependent on cellular context and activation state. Here, we provide a comparative analysis of platelet-derived GITRL (pGITRL) in breast cancer patients and healthy volunteers. The levels of pGITRL were found to be higher on platelets derived from cancer patients and appeared to be specifically regulated during tumor progression as exemplified by several clinical parameters including tumor stage/grade, the occurrence of metastases and tumor proliferation (Ki67) index. In addition, we report that pGITRL is upregulated during platelet maturation and particularly induced upon exposure to tumor-derived soluble factors. Our data indicate that platelets modulate the GITR/GITRL immune checkpoint in the context of malignant disease and provide a rationale to further study the GITR/GITRL axis for exploitation for immunotherapeutic intervention in cancer patients.

Hemostatic changes by thrombopoietin-receptor agonists in immune thrombocytopenia patients

Thrombopoietin receptor agonist (TPO-RA) treatment increases the thrombosis rate in immune thrombocytopenia (ITP). We hypothesize that TPO-RAs influence platelet function, global and secondary hemostasis and/or fibrinolysis. A systematic review was performed. If possible, data were compared between responders (relevant increase in platelet count), and non-responders. Twelve observational studies with 305 patients were included (responders (127/150 (85%))). There were indications that TPO-RA treatment enhanced platelet function, with respect to platelet-monocyte aggregates, soluble P-selectin, GPVI expression, and adhesion under flow. Studies addressing global and secondary hemostasis and fibrinolysis were scarce. Overall, no changes were found during TPO-RA treatment, apart from an accelerated clot formation and conflicting data on levels of plasminogen activator inhibitor (PAI)-1. The parameters that increased have previously been associated with thrombosis in other patient groups, and might contribute to the increased rate of thrombosis observed in TPO-RA-treated ITP patients.

Mechanisms and biomarkers of cancer-associated thrombosis

Cancer-associated thrombosis is a leading cause of non-cancer death in cancer patients and is comprised of both arterial and venous thromboembolism (VTE). There are multiple risk factors for developing VTE, including cancer type, stage, treatment, and other medical comorbidities, which suggests that the etiology of thrombosis is multifactorial. While cancer-associated thrombosis can be treated with anticoagulation, benefits of therapy must be balanced with the increased bleeding risks seen in patients with cancer. Although risk models exist for primary and recurrent VTE, additional predictors are needed to improve model performance and discrimination of high-risk patients. This review will outline the diverse mechanisms driving thrombosis in cancer patients, as well as provide an overview of biomarkers studied in thrombosis risk and important considerations when selecting candidate biomarkers.

Biotech-Educated Platelets: Beyond Tissue Regeneration 2.0

The increasing discoveries regarding the biology and functions of platelets in the last decade undoubtedly show that these cells are one of the most biotechnological human cells. This review summarizes new advances in platelet biology, functions, and new concepts of biotech-educated platelets that connect advanced biomimetic science to platelet-based additive manufacturing for tissue regeneration. As highly responsive and secretory cells, platelets could be explored to develop solutions that alter injured microenvironments through platelet-based synthetic biomaterials with instructive extracellular cues for morphogenesis in tissue engineering beyond tissue regeneration 2.0.

Platelet "-omics" in health and cardiovascular disease

The importance of platelets for cardiovascular disease was established as early as the 19th century. Their therapeutic inhibition stands alongside the biggest achievements in medicine. Still, certain aspects of platelet pathophysiology remain unclear. This includes platelet resistance to antiplatelet therapy and the contribution of platelets to vascular remodelling and extends beyond cardiovascular disease to haematological disorders and cancer. To address these gaps in our knowledge, a better understanding of the underlying molecular processes is needed. This will be enabled by technologies that capture dysregulated molecular processes and can integrate them into a broader network of biological systems. The advent of -omics technologies, such as mass spectrometry proteomics, metabolomics and lipidomics; highly multiplexed affinity-based proteomics; microarray- or RNA-sequencing-(RNA-seq)-based transcriptomics, and most recently ribosome footprint-based translatomics, has enabled a more holistic understanding of platelet biology. Most of these methods have already been applied to platelets, and this review will summarise this information and discuss future developments in this area of research.

Platelets as a 'natural factory' for growth factor production that sustains normal (and pathological) cell biology

Platelets have attracted substantial attention in the current decade owing to their unexpected pleiotropic properties and conflicted functions. In fact, platelets participate in both health (hemostasis) and disease (thrombotic diseases). Much of the plasticity of platelets comes from the fact that platelets are the reservoir and the 'natural factory' of growth factors (GFs), with pivotal functions in wound repair and tissue regeneration. By combining the platelets' plasticity and biotechnological processes, PlateInnove Biotechnology optimized the production of GFs in nanoparticle biointerfacing by platelet content, which opens an avenue of possibilities.

Hemostatic Testing in Critically Ill Infants and Children

Children with critical illness frequently manifest imbalances in hemostasis with risk of consequent bleeding or pathologic thrombosis. Traditionally, plasma-based tests measuring clot formation by time to fibrin clot generation have been the "gold standard" in hemostasis testing. However, these tests are not sensitive to abnormalities in fibrinolysis or in conditions of enhanced clot formation that may lead to thrombosis. Additionally, they do not measure the critical roles played by platelets and endothelial cells. An added factor in the evaluation of these plasma-based tests is that in infants and young children plasma levels of many procoagulant and anticoagulant proteins are lower than in older children and adults resulting in prolonged clot generation times in spite of maintaining a normal hemostatic "balance." Consequently, newer assays directly measuring thrombin generation in plasma and others assessing the stages hemostasis including clot initiation, propagation, and fibrinolysis in whole blood by viscoelastic methods are now available and may allow for a global measurement of the hemostatic system. In this manuscript, we will review the processes by which clots are formed and by which hemostasis is regulated, and the rationale and limitations for the more commonly utilized tests. We will also discuss selected newer tests available for the assessment of hemostasis, their "pros" and "cons," and how they compare to the traditional tests of coagulation in the assessment and management of critically ill children.

Platelet HIF-2α promotes thrombogenicity through PAI-1 synthesis and extracellular vesicle release

Oxygen-compromised environments, such as high altitude, are associated with platelet hyperactivity. Platelets confined within the relatively impervious core of an aggregate/thrombus have restricted access to oxygen, yet they continue to perform energy-intensive procoagulant activities that sustain the thrombus. Studying platelet signaling under hypoxia is, therefore, critical to our understanding of the mechanistic basis of thrombus stability. We report here that hypoxia-inducible factor (HIF)-2α is translated from pre-existing mRNA and stabilized against proteolytic degradation in enucleate platelets exposed to hypoxia. Hypoxic stress, too, stimulates platelets to synthesize plasminogen-activator inhibitor-1 (PAI-1) and shed extracellular vesicles, both of which potentially contribute to the prothrombotic phenotype associated with hypoxia. Stabilization of HIF-α by administering hypoxia-mimetics to mice accelerates thrombus formation in mesenteric arterioles. In agreement, platelets from patients with chronic obstructive pulmonary disease and high altitude residents exhibiting thrombogenic attributes have abundant expression of HIF-2α and PAI- 1. Thus, targeting platelet hypoxia signaling could be an effective anti-thrombotic strategy.

Wisdom of artificial crowds feature selection in untargeted metabolomics: An application to the development of a blood-based diagnostic test for thrombotic myocardial infarction

INTRODUCTION

Heart disease remains a leading cause of global mortality. While acute myocardial infarction (colloquially: heart attack), has multiple proximate causes, proximate etiology cannot be determined by a blood-based diagnostic test. We enrolled a suitable patient cohort and conducted a non-targeted quantification of plasma metabolites by mass spectrometry for developing a test that can differentiate between thrombotic MI, non-thrombotic MI, and stable disease. A significant challenge in developing such a diagnostic test is solving the NP-hard problem of feature selection for constructing an optimal statistical classifier.

OBJECTIVE

We employed a Wisdom of Artificial Crowds (WoAC) strategy for solving the feature selection problem and evaluated the accuracy and parsimony of downstream classifiers in comparison with traditional feature selection techniques including the Lasso and selection using Random Forest variable importance criteria.

MATERIALS AND METHODS

Artificial Crowd Wisdom was generated via aggregation of the best solutions from independent and diverse genetic algorithm populations that were initialized with bootstrapping and a random subspaces constraint.

RESULTS/CONCLUSIONS

Strong evidence was observed that a statistical classifier utilizing WoAC feature selection can discriminate between human subjects presenting with thrombotic MI, non-thrombotic MI, and stable Coronary Artery Disease given abundances of selected plasma metabolites. Utilizing the abundances of twenty selected metabolites, a leave-one-out cross-validation estimated misclassification rate of 2.6% was observed. However, the WoAC feature selection strategy did not perform better than the Lasso over the current study.

Tissue Factor: An Essential Mediator of Hemostasis and Trigger of Thrombosis

Tissue factor (TF) is the high-affinity receptor and cofactor for factor (F)VII/VIIa. The TF-FVIIa complex is the primary initiator of blood coagulation and plays an essential role in hemostasis. TF is expressed on perivascular cells and epithelial cells at organ and body surfaces where it forms a hemostatic barrier. TF also provides additional hemostatic protection to vital organs, such as the brain, lung, and heart. Under pathological conditions, TF can trigger both arterial and venous thrombosis. For instance, atherosclerotic plaques contain high levels of TF on macrophage foam cells and microvesicles that drives thrombus formation after plaque rupture. In sepsis, inducible TF expression on monocytes leads to disseminated intravascular coagulation. In cancer patients, tumors release TF-positive microvesicles into the circulation that may contribute to venous thrombosis. TF also has nonhemostatic roles. For instance, TF-dependent activation of the coagulation cascade generates coagulation proteases, such as FVIIa, FXa, and thrombin, which induce signaling in a variety of cells by cleavage of protease-activated receptors. This review will focus on the roles of TF in protective hemostasis and pathological thrombosis.

Increased number of tissue factor protein expressing thrombocytes in canine idiopathic immune mediated hemolytic anemia

Dogs suffering from canine idiopathic immune mediated hemolytic anemia (cIIMHA) are at great risk of dying particularly in the first two weeks after the diagnosis is made. This high mortality risk may be associated with the development of thromboembolism (TE) and/or disseminated intravascular coagulation (DIC) resulting in organ failure. The exact mechanism of the development of TE and/or DIC in cIIMHA is still undetermined. Therefore, this study investigates the presence of tissue factor (TF) in thrombocytes of dogs suffering from cIIMHA, using OptiPrep™ for the isolation of blood cells and immunocytochemistry (ICC) to visualize TF on thrombocytes. The normalised TF quantity, acquired with 'colour deconvolution' (ImageJ plug in), revealed that in cIIMHA dogs the fraction TF positive thrombocytes was statistically significant higher (P < 0.001; mean 0.79; n = 7) compared to the fraction TF positive thrombocytes of the healthy dogs (mean 0.43; n = 9). We further have indications that the fraction of TF positive thrombocytes decreases with time and therapy, but that the progression rate differs individually. Since cIIMHA dogs have more thrombocytes that are TF-positive compared to healthy dogs, this may explain the increased risk to develop TE and DIC. Furthermore, it seems that the number of TF-positive thrombocytes in cIIMHA dogs remains high during the first two weeks of the disease, the time when the animals are at greatest health risk.

Platelets, inflammation and anti-inflammatory effects of antiplatelet drugs in ACS and CAD

Platelets play a pivotal role in chronic inflammation leading to progression of atherosclerosis and acute coronary events. Recent discoveries on novel mechanisms and platelet-dependent inflammatory targets underpin the role of platelets to maintain a chronic inflammatory condition in cardiovascular disease. There is strong and clinically relevant crosslink between chronic inflammation and platelet activation. Antiplatelet therapy is a cornerstone in the prevention and treatment of acute cardiovascular events. The benefit of antiplatelet agents has mainly been attributed to their direct anti-aggregatory impact. Some anti-inflammatory off-target effects have also been described. However, it is unclear whether these effects are secondary due to inhibition of platelet activation or are caused by direct distinct mechanisms interfering with inflammatory pathways. This article will highlight novel platelet associated targets that contribute to inflammation in cardiovascular disease and elucidate mechanisms by which currently available antiplatelet agents evolve anti-inflammatory capacities, in particular by carving out the differential mechanisms directly or indirectly affecting platelet mediated inflammation. It will further illustrate the prognostic impact of antiplatelet therapies by reducing inflammatory marker release in recent cardiovascular trials.

Human megakaryocytes confer tissue factor to a subset of shed platelets to stimulate thrombin generation

Tissue factor (TF), the main activator of the blood coagulation cascade, has been shown to be expressed by platelets. Despite the evidence that both megakaryocytes and platelets express TF mRNA, and that platelets can make de novo protein synthesis, the main mechanism thought to be responsible for the presence of TF within platelets is through the uptake of TF positive microparticles. In this study we assessed 1) whether human megakaryocytes synthesise TF and transfer it to platelets and 2) the contribution of platelet-TF to the platelet hemostatic capacity. In order to avoid the cross-talk with circulating microparticles, we took advantage from an in vitro cultured megakaryoblastic cell line (Meg-01) able to differentiate into megakaryocytes releasing platelet-like particles. We show that functionally active TF is expressed in human megakaryoblasts, increased in megakaryocytes, and is transferred to a subset of shed platelets where it contributes to clot formation. These data were all confirmed in human CD34pos- derived megakaryocytes and in their released platelets. The effect of TF silencing in Meg-megakaryoblasts resulted in a significant reduction of TF expression in these cells and also in Meg-megakaryocytes and Meg-platelets. Moreover, the contribution of platelet-TF to the platelet hemostatic capacity was highlighted by the significant delay in the kinetic of thrombin formation observed in platelets released by TF-silenced megakaryocytes. These findings provide evidences that TF is an endogenously synthesised protein that characterises megakaryocyte maturation and that it is transferred to a subset of newly-released platelets where it is functionally active and able to trigger thrombin generation.

Platelet-neutrophil interactions as drivers of inflammatory and thrombotic disease

Neutrophils are well known for their role in infection and inflammatory disease and are first responders at sites of infection or injury. Platelets have an established role in hemostasis and thrombosis and are first responders at sites of vascular damage. However, neutrophils are increasingly recognized for their role in thrombosis, while the immunemodulatory properties of platelets are being increasingly studied. Platelets and neutrophils interact during infection, inflammation and thrombosis and modulate each other’s functions. This review will discuss the consequences of platelet–neutrophil interactions in infection, thrombosis, atherosclerosis and tissue injury and repair.

Analysis of factor XIa, factor IXa and tissue factor activity in burn patients

INTRODUCTION

An elevated procoagulant activity observed in trauma patients is, in part, related to tissue factor (TF) located on blood cells and microparticles. However, analysis of trauma patient plasma indicates that there are other contributor(s) to the procoagulant activity. We hypothesize that factor (F)XIa and FIXa are responsible for an additional procoagulant activity in burn patients.

METHODS

Multiple time-point plasma samples from 56 burn patients (total number of samples was 471; up to 20 time-points/patient collected in 3 weeks following admission) were evaluated in a thrombin generation assay using inhibitory antibodies to TF, FIXa and FXIa.

RESULTS

Due to the limited volume of some samples, not all were analyzed for all three proteins. At admission, 10 of 53 patients (19%) had active TF, 53 of 55 (96%) had FXIa and 48 of 55 (87%) had FIXa in their plasma. 34 patients of 56 enrolled (61%) showed TF activity at one or more time-points. All patients had FXIa and 96% had FIXa at one or more time-points. Overall, TF was observed in 99 of 455 samples analyzed (22%), FXIa in 424 of 471 (90%) and FIXa in 244 of 471 (52%). The concentration of TF was relatively low and varied between 0 and 2.1pM, whereas that of FXIa was higher, exceeding 100pM in some samples. The majority of samples with FIXa had it at sub-nanomolar concentrations. No TF, FXIa and FIXa activity was detected in plasma from healthy individuals.

CONCLUSIONS

For the first time reported, the majority of plasma samples from burn patients have active FXIa and FIXa, with a significant fraction of them having active TF. The concentration of all three proteins varies in a wide range.

Human platelet interaction with E. coli O111 promotes tissue-factor-dependent procoagulant activity, involving Toll like receptor 4

Platelets have a major role in clotting activation and contribute to the innate immune response during systemic infections. Human platelets contain tissue factor (TF) and express functional Toll-like receptor 4 (TLR4). However, the role of TLR4 in triggering the procoagulant properties of platelets, upon challenge with bacteria, is yet unknown. Our hypothesis is that E. coli O111-TLR4 interaction activates platelets and elicits their procoagulant activity. We demonstrated that the strain, but not ultrapure LPS, increased surface P-selectin expression, platelet dependent TF procoagulant activity (TF-PCA) and prompted a faster thrombin generation (TG). Blockade of TLR4 resulted in decreased platelet activation, TF-PCA and TG, revealing the participation of this immune receptor on the procoagulant response of platelets. Our results provide a novel mechanism by which individuals with bacterial infections would have an increased incidence of blood clots. Furthermore, the identification of platelet TF and TLR4 as regulators of the effect of E. coli O111 might represent a novel therapeutic target to reduce the devastating consequences of the hemostatic disorder during sepsis.

The association between P selectin glycoprotein ligand 1 gene variable number of tandem repeats polymorphism and risk of thrombosis in Behçet's disease

OBJECTIVES

Behçet's disease (BD) has been recognized as an unclassified type of vasculitis with an accompanying tendency to thrombosis. No disease-specific pathology has been demonstrated so far to explain the prothrombotic state, and this predisposition is considered to be associated with endothelial activation/dysfunction. P-selectin glycoprotein ligand-1 (PSGL-1) variable number of tandem repeat (VNTR) polymorphism has an impact on the protein length, and heterozygosity affect of the PSGL-1 to P-selectin interaction, which has been found to be associated with an increased risk of thrombosis in patients with antiphospholipid syndrome. We aimed to analyze the association of PSGL-1 gene polymorphism, in a group of BD patients with and without thrombosis.

METHODS

The study group consisted of 136 BD patients (112 male, 24 female) with thrombosis, 120 BD patients without thrombosis (54 male, 66 female) during at least 5 years disease course, and 190 healthy controls (103 male, 87 female) All patients fulfilled the International Study Group criteria for classification of BD. Genotyping for the PSGL-1 gene exon 2 VNTR polymorphism was carried out with the amplification of genomic DNA and running of the polymerase chain reaction product on agarose gel electrophoresis.

RESULTS

The frequency of heterozygous genotypes (AB+AC+BC) was greater in BD patients with thrombosis compared to BD patients without thrombosis (33.1% vs. 20.8%, P = 0.028, odds ratio = 1.85). However, the increased frequency of heterozygous genotypes in BD patients with thrombosis did not reach a statistically significant level compared to healthy controls (33.1% vs. 32.6%).

CONCLUSIONS

PSGL-1 VNTR polymorphism may have limited contribution to the thrombotic tendency in patients with BD.

Correlation between factor (F)XIa, FIXa and tissue factor and trauma severity

BACKGROUND

It has been observed that trauma patients often display elevated procoagulant activity that could be caused, in part, by tissue factor (TF). We previously observed that trauma patients with thermal, blunt, and penetrating injuries have active FIXa and FXIa in their plasma. In the current study, we evaluated the effect of injury severity, with or without accompanying shock, on the frequency and concentration of TF, FIXa, and FXIa in plasma from trauma patients.

METHODS

Eighty trauma patients were enrolled and divided equally into four groups based on their Injury Severity Score and base deficit:Blood was collected at a 0 time-point (first blood draw upon arrival at hospital) and citrate plasma was prepared, frozen, and stored at -80 °C. FXIa, FIXa, and TF activity assays were based on a response of thrombin generation to corresponding monoclonal inhibitory antibodies.

RESULTS

The frequency and median concentrations of TF were relatively low in non-severe injury groups (17.5% and 0 pM, respectively) but were higher in those with severe injury (65% and 0.5 pM, respectively). Although FXIa was observed in 91% of samples and was high across all four groups, median concentrations were highest (by approximately fourfold) in groups with shock. FIXa was observed in 80% of plasma samples and concentrations varied in a relatively narrow range between all four groups. No endogenous activity was observed in plasma from healthy individuals.

CONCLUSIONS

(1) Frequency and concentration of TF is higher in patients with a higher trauma severity. (2) Concentration of FXIa is higher in patients with shock. (3) For the first time reported, the vast majority of plasma samples from trauma patients contain active FIXa and FXIa.

LEVEL OF EVIDENCE

Prognostic/epidemiological study, level II.

Different Potential of Extracellular Vesicles to Support Thrombin Generation: Contributions of Phosphatidylserine, Tissue Factor, and Cellular Origin

Cells release diverse types of vesicles constitutively or in response to proliferation, injury, inflammation, or stress. Extracellular vesicles (EVs) are crucial in intercellular communication, and there is emerging evidence for their roles in inflammation, cancer, and thrombosis. We investigated the thrombogenicity of platelet-derived EVs, which constitute the majority of circulating EVs in human blood, and assessed the contributions of phosphatidylserine and tissue factor exposure on thrombin generation. Addition of platelet EVs to vesicle-free human plasma induced thrombin generation in a dose-dependent manner, which was efficiently inhibited by annexin V, but not by anti-tissue factor antibodies, indicating that it was primarily due to the exposure of phosphatidylserine on platelet EVs. Platelet EVs exhibited higher thrombogenicity than EVs from unstimulated monocytic THP-1 cells, but blockade of contact activation significantly reduced thrombin generation by platelet EVs. Stimulation of monocytic cells with lipopolysaccharide enhanced their thrombogenicity both in the presence and in the absence of contact activation, and thrombin generation was efficiently blocked by anti-tissue factor antibodies. Our study provides evidence that irrespective of their cellular origin, EVs support the propagation of coagulation via the exposure of phosphatidylserine, while the expression of functional tissue factor on EVs appears to be limited to pathological conditions.

Microvesicles in vascular homeostasis and diseases. Position Paper of the European Society of Cardiology (ESC) Working Group on Atherosclerosis and Vascular Biology

Microvesicles are members of the family of extracellular vesicles shed from the plasma membrane of activated or apoptotic cells. Microvesicles were initially characterised by their pro-coagulant activity and described as "microparticles". There is mounting evidence revealing a role for microvesicles in intercellular communication, with particular relevance to hemostasis and vascular biology. Coupled with this, the potential of microvesicles as meaningful biomarkers is under intense investigation. This Position Paper will summarise the current knowledge on the mechanisms of formation and composition of microvesicles of endothelial, platelet, red blood cell and leukocyte origin. This paper will also review and discuss the different methods used for their analysis and quantification, will underline the potential biological roles of these vesicles with respect to vascular homeostasis and thrombosis and define important themes for future research.

Systems characterization of differential plasma metabolome perturbations following thrombotic and non-thrombotic myocardial infarction

Myocardial infarction (MI) is an acute event characterized by myocardial necrosis. Thrombotic MI is caused by spontaneous atherosclerotic plaque disruption that results in a coronary thrombus; non-thrombotic MI occurs secondary to oxygen supply-demand mismatch. We sought to characterize the differential metabolic perturbations associated with these subtypes utilizing a systems approach. Subjects presenting with thrombotic MI, non-thrombotic MI and stable coronary artery disease (CAD) were included. Whole blood was collected at two acute time-points and at a time-point representing the quiescent stable disease state. Plasma metabolites were analyzed by untargeted UPLC-MS/MS and GC-MS. A weighted network was constructed, and modules were determined from the resulting topology. To determine perturbed modules, an enrichment analysis for metabolites that demonstrated between-group differences in temporal change across the disease state transition was then conducted.

BIOLOGICAL SIGNIFICANCE

We report evidence of metabolic perturbations of acute MI and determine perturbations specific to thrombotic MI. Specifically, a module characterized by elevated glucocorticoid steroid metabolites following acute MI showed greatest perturbation following thrombotic MI. Modules characterized by elevated pregnenolone metabolites, monoacylglycerols, and acylcarnitines were perturbed following acute MI. A module characterized by a decrease in plasma amino acids following thrombotic MI was differentially perturbed between MI subtypes.

Matrix Metalloproteinases and Platelet Function

Platelets contain and release several matrix metalloproteinases (MMPs) and their tissue inhibitors of matrix metalloproteinases (TIMPs), including MMP-1, -2, -3, -9, and -14 and TIMP-1, -2, and -4. Although devoid of a nucleus, platelets also synthesize TIMP-2 upon activation. Platelet-released MMPs/TIMPs, as well as MMPs generated by other cells within the cardiovascular system, modulate platelet function in health and disease. In particular, a normal hemostatic platelet response to vessel wall injury may be transformed into pathologic thrombus formation by the release from platelets and/or by the local generation of some MMPs. Moreover, platelets may localize the production of leukocyte-derived MMPs to sites of vascular damage, contributing to atherosclerosis development and complications and to arterial aneurysm formation. Finally, the interaction between platelets and tumor cells is strongly influenced by MMPs/TIMPs. All these mechanisms are emerging as important in atherothrombosis, inflammatory disease, and cancer growth and dissemination. Increasing knowledge of these mechanisms may open the way to novel therapeutic approaches.

Platelet tissue factor activity and membrane cholesterol are increased in hypercholesterolemia and normalized by rosuvastatin, but not by atorvastatin

BACKGROUND AND AIMS

High plasma LDL-cholesterol (LDL-C) and platelet responses have major pathogenic roles in atherothrombosis. Thus, statins and anti-platelet drugs constitute mainstays in cardiovascular prevention/treatment. However, the role of platelet tissue factor-dependent procoagulant activity (TF-PCA) has remained unexplored in hypercholesterolemia. We aimed to study platelet TF-PCA and its relationship with membrane cholesterol in vitro and in 45 hypercholesterolemic patients (HC-patients) (LDL-C >3.37 mmol/L, 130 mg/dL) and 37 control subjects (LDL-C <3.37 mmol/L). The effect of 1-month administration of 80 mg/day atorvastatin (n = 21) and 20 mg/day rosuvastatin (n = 24) was compared.

METHODS

Platelet TF-PCA was induced by GPIbα activation with VWF-ristocetin.

RESULTS

Cholesterol-enriched platelets in vitro had augmented aggregation/secretion and platelet FXa generation (1.65-fold increase, p = 0.01). HC-patients had 1.5-, 2.3- and 2.5-fold increases in platelet cholesterol, TF protein and activity, respectively; their platelets had neither hyper-aggregation nor endogenous thrombin generation (ETP). Rosuvastatin, but not atorvastatin, normalized platelet cholesterol, TF protein and FXa generation. It also increased slightly the plasma HDL-C levels, which correlated negatively with TF-PCA.

CONCLUSIONS

Platelets from HC-patients were not hyper-responsive to low concentrations of classical agonists and had normal PRP-ETP, before and after statin administration. However, washed platelets from HC-patients had increased membrane cholesterol, TF protein and TF-PCA. The platelet TF-dependent PCA was specifically expressed after VWF-induced GPIbα activation. Rosuvastatin, but not atorvastatin treatment, normalized the membrane cholesterol, TF protein and TF-PCA in HC-patients, possibly unveiling a new pleiotropic effect of rosuvastatin. Modulation of platelet TF-PCA may become a novel target to prevent/treat atherothrombosis without increasing bleeding risks.

Comprehensive Proteome Profiling of Platelet Identified a Protein Profile Predictive of Responses to An Antiplatelet Agent Sarpogrelate

Sarpogrelate is an antiplatelet agent widely used to treat arterial occlusive diseases. Evaluation of platelet aggregation is essential to monitor therapeutic effects of sarpogrelate. Currently, no molecular signatures are available to evaluate platelet aggregation. Here, we performed comprehensive proteome profiling of platelets collected from 18 subjects before and after sarpogrelate administration using LC-MS/MS analysis coupled with extensive fractionation. Of 5423 proteins detected, we identified 499 proteins affected by sarpogrelate and found that they strongly represented cellular processes related to platelet activation and aggregation, including cell activation, coagulation, and vesicle-mediated transports. Based on the network model of the proteins involved in these processes, we selected three proteins (cut-like homeobox 1; coagulation factor XIII, B polypeptide; and peptidylprolyl isomerase D) that reflect the platelet aggregation-related processes after confirming their alterations by sarpogrelate in independent samples using Western blotting. Our proteomic approach provided a protein profile predictive of therapeutic effects of sarpogrelate.

Platelets are versatile cells: New discoveries in hemostasis, thrombosis, immune responses, tumor metastasis and beyond

Platelets are small anucleate blood cells generated from megakaryocytes in the bone marrow and cleared in the reticuloendothelial system. At the site of vascular injury, platelet adhesion, activation and aggregation constitute the first wave of hemostasis. Blood coagulation, which is initiated by the intrinsic or extrinsic coagulation cascades, is the second wave of hemostasis. Activated platelets can also provide negatively-charged surfaces that harbor coagulation factors and markedly potentiate cell-based thrombin generation. Recently, deposition of plasma fibronectin, and likely other plasma proteins, onto the injured vessel wall has been identified as a new "protein wave of hemostasis" that may occur even earlier than the first wave of hemostasis, platelet accumulation. Although no experimental evidence currently exists, it is conceivable that platelets may also contribute to this protein wave of hemostasis by releasing their granule fibronectin and other proteins that may facilitate fibronectin self- and non-self-assembly on the vessel wall. Thus, platelets may contribute to all three waves of hemostasis and are central players in this critical physiological process to prevent bleeding. Low platelet counts in blood caused by enhanced platelet clearance and/or impaired platelet production are usually associated with hemorrhage. Auto- and allo-immune thrombocytopenias such as idiopathic thrombocytopenic purpura and fetal and neonatal alloimmune thrombocytopenia may cause life-threatening bleeding such as intracranial hemorrhage. When triggered under pathological conditions such as rupture of an atherosclerotic plaque, excessive platelet activation and aggregation may result in thrombosis and vessel occlusion. This may lead to myocardial infarction or ischemic stroke, the major causes of mortality and morbidity worldwide. Platelets are also involved in deep vein thrombosis and thromboembolism, another leading cause of mortality. Although fibrinogen has been documented for more than half a century as essential for platelet aggregation, recent studies demonstrated that fibrinogen-independent platelet aggregation occurs in both gene deficient animals and human patients under physiological and pathological conditions (non-anti-coagulated blood). This indicates that other unidentified platelet ligands may play important roles in thrombosis and might be novel antithrombotic targets. In addition to their critical roles in hemostasis and thrombosis, emerging evidence indicates that platelets are versatile cells involved in many other pathophysiological processes such as innate and adaptive immune responses, atherosclerosis, angiogenesis, lymphatic vessel development, liver regeneration and tumor metastasis. This review summarizes the current knowledge of platelet biology, highlights recent advances in the understanding of platelet production and clearance, molecular and cellular events of thrombosis and hemostasis, and introduces the emerging roles of platelets in the immune system, vascular biology and tumorigenesis. The clinical implications of these basic science and translational research findings will also be discussed.

Characterizing the Mechanistic Pathways of the Instant Blood-Mediated Inflammatory Reaction in Xenogeneic Neonatal Islet Cell Transplantation

Supplemental digital content is available in the text.

Introduction

The instant blood-mediated inflammatory reaction (IBMIR) causes major loss of islets after transplantation and consequently represents the initial barrier to survival of porcine neonatal islet cell clusters (NICC) after xenotransplantation.

Methods

This study used novel assays designed to characterize the various immunologic components responsible for xenogeneic IBMIR to identify initiators and investigate processes of IBMIR-associated coagulation, complement activation and neutrophil infiltration. The IBMIR was induced in vitro by exposing NICC to platelet-poor or platelet-rich human plasma or isolated neutrophils.

Results

We found that xenogeneic IBMIR was characterized by rapid, platelet-independent thrombin generation, with addition of platelets both accelerating and exacerbating this response. Platelet-independent complement activation was observed as early as 30 minutes after NICC exposure to plasma. However, membrane attack complex formation was not observed in NICC histopathology sections until after 60 minutes. We demonstrated for the first time that NICC-mediated complement activation was necessary for neutrophil activation in the xenogeneic IBMIR setting. Finally, using the Seahorse extracellular flux analyzer, we identified substantial loss of islet function (up to 40%) after IBMIR with surviving NICC showing evidence of mitochondrial damage.

Conclusions

This study used novel assays to describe multiple key pathways by which xenogeneic IBMIR causes islet destruction, allowing further refinement of future interventions aimed at resolving the issue of IBMIR in xenotransplantation.

Microparticles in sickle cell anaemia: promise and pitfalls

Blood from patients with sickle cell disease contains microparticles (MP) derived from multiple cell sources, including red cells, platelets, monocytes and endothelial cells. MPs are of great interest because of their disease associations, their status as promising biomarkers, and the intercellular communications they mediate. To illustrate the likelihood of their relevance in sickle cell disease, we discuss the nature of MP, their profiling in sickle disease, some caveats relevant to their detection, their roles in supporting coagulation and the disparate influences they may exert upon the pathobiology of sickle cell disease.

Medicinal Plants with Antiplatelet Activity

Blood platelets play an essential role in the hemostasis and wound-healing processes. However, platelet hyperactivity is associated to the development and the complications of several cardiovascular diseases. In this sense, the search for potent and safer antiplatelet agents is of great interest. This article provides an overview of experimental studies performed on medicinal plants with antiplatelet activity available through literature with particular emphasis on the bioactive constituents, the parts used, and the various platelet signaling pathways modulated by medicinal plants. From this review, it was suggested that medicinal plants with antiplatelet activity mainly belong to the family of Asteraceae, Rutaceae, Fabaceae, Lamiaceae, Zygophyllaceae, Rhamnaceae, Liliaceae, and Zingiberaceae. The antiplatelet effect is attributed to the presence of bioactive compounds such as polyphenols, flavonoids, coumarins, terpenoids, and other substances which correct platelet abnormalities by interfering with different platelet signalization pathways including inhibition of the ADP pathway, suppression of TXA2 formation, reduction of intracellular Ca(2+) mobilization, and phosphoinositide breakdown, among others. The identification and/or structure modification of the plant constituents and the understanding of their action mechanisms will be helpful in the development of new antiplatelet agents based on medicinal plants which could contribute to the prevention of thromboembolic-related disorders by inhibiting platelet aggregation. Copyright © 2016 John Wiley & Sons, Ltd.