Inhibition Of Platelet Activation Research Articles

IL-37 Attenuates Platelet Activation and Thrombosis Through IL-1R8 Pathway.

IL-37 (interleukin-37), a natural suppressor of innate inflammatory and immune responses, is increased in patients with myocardial infarction. Platelets play an important role in the progress of myocardial infarction, but the direct effects of IL-37 on platelet activation and thrombosis, as well as the underlying mechanisms, still remain unclear. We evaluated the direct effects of IL-37 on agonists-induced platelet activation and thrombus formation, as well as revealed the underlying mechanisms using platelet-specific IL-1R8 (IL-1 receptor 8)-deficient mice. Using myocardial infarct model, we explored the effects of IL-37 on microvascular obstruction and myocardial injury. IL-37 directly inhibited agonists-induced platelet aggregation, dense granule ATP release, P-selectin exposure, integrin αIIbβ3 activation, platelet spreading, and clot retraction. IL-37 inhibited thrombus formation in vivo in a FeCl3-injured mesenteric arteriole thrombosis mouse model and ex vivo in a microfluidic whole-blood perfusion assay. Mechanistic studies using platelet-specific IL-1R8-deficient mice revealed that IL-37 bound to platelet IL-1R8 and IL-18Rα, and IL-1R8 deficiency impaired the inhibitory effects of IL-37 on platelet activation. Using PTEN (phosphatase and tensin homolog)-specific inhibitor and PTEN-deficient platelets, we found that IL-37 combined with IL-1R8 to enhance PTEN activity, inhibit Akt (protein kinase B), mitogen-activated protein kinases, and spleen tyrosine kinase pathways, as well as decrease the generation of reactive oxygen species to regulate platelet activation. Exogenous IL-37 injection suppressed microvascular thrombosis to protect against myocardial injury in wild-type mice but not in platelet-specific IL-1R8-deficient mice after permanent ligation of the left anterior descending coronary. Finally, a negative correlation between plasma IL-37 concentration and platelet aggregation was observed in patients with myocardial infarction. IL-37 directly attenuated platelet activation, thrombus formation, and myocardial injury via IL-1R8 receptor. Accumulated IL-37 in plasma inhibited platelet activation to ameliorate atherothrombosis and infarction expansion, and thus may have therapeutic advantages as potential antiplatelet drugs.

Platelets and Cardioprotection: The Role of Nitric Oxide and Carbon Oxide

Nitric oxide (NO) and carbon monoxide (CO) represent a pair of biologically active gases with an increasingly well-defined range of effects on circulating platelets. These gases interact with platelets and cells in the vessels and heart and exert fundamentally similar biological effects, albeit through different mechanisms and with some peculiarity. Within the cardiovascular system, for example, the gases are predominantly vasodilators and exert antiaggregatory effects, and are protective against damage in myocardial ischemia-reperfusion injury. Indeed, NO is an important vasodilator acting on vascular smooth muscle and is able to inhibit platelet activation. NO reacts with superoxide anion (O2(-•)) to form peroxynitrite (ONOO(-)), a nitrosating agent capable of inducing oxidative/nitrative signaling and stress both at cardiovascular, platelet, and plasma levels. CO reduces platelet reactivity, therefore it is an anticoagulant, but it also has some cardioprotective and procoagulant properties. This review article summarizes current knowledge on the platelets and roles of gas mediators (NO, and CO) in cardioprotection. In particular, we aim to examine the link and interactions between platelets, NO, and CO and cardioprotective pathways.

Decreased plasma exposure of clopidogrel active metabolite in rats after long-term treatment with clopidogrel.

Clopidogrel (Clop) is oxidized by cytochrome P450s (CYPs) to an active thiol metabolite, Clop-AM, to inhibit platelet activation and aggregation. As an irreversible inhibitor of CYP2B6 and CYP2C19, clopidogrel may inhibit its own metabolism after long-term administration. The study compared the pharmacokinetic profiles of clopidogrel and its metabolites in rats receiving a single or a 2 week administration of Clop. The mRNA and protein levels of hepatic clopidogrel-metabolizing enzymes and their enzymatic activities were analyzed to explore their contribution to any altered plasma exposure of Clop and its metabolites. The results showed that long-term treatment with clopidogrel significantly decreased the AUC(0-t) and Cmax values of Clop-AM in rats, accompanied with markedly impaired catalytic activities of Clop-metabolizing CYPs including CYP1A2, CYP2B6, CYP2C9, CYP2C19, and CYP3A4. It suggests that consecutive administration of Clop to rats decreases hepatic CYPs activities, which may, in turn, inhibit clopidogrel metabolism and then reduce Clop-AM plasma exposure. Therefore, long-term treatment with clopidogrel has the potential to reduce its anti-platelet activity and to increase the risk of drug-drug interaction.

Novel Antiplatelet Activity of Ginsenoside Re Through the Inhibition of High Shear Stress-Induced Platelet Aggregation.

Bleeding is one of the most serious side effects of antiplatelet drugs. Efforts have been made to find new antiplatelet agents without bleeding complications. Shear-induced platelet aggregation (SIPA) occurs only under pathological conditions and is a promising target for overcoming bleeding problems. This work demonstrates that the ginsenoside Re selectively inhibits platelet aggregation induced by high shear stress. Human platelets were exposed to high shear stress using microfluidic chip technology, and aggregation, activation, and phosphatidylserine (PS) exposure were measured. The Von Willebrand Ristocetin Cofactor (vWF:RCo) assay and western blot were used to evaluate the effect of the vWF-GPⅠb/PI3K/Akt signal pathway. The coagulation and bleeding risk were evaluated by measuring the coagulation parameters PT, APTT, TT, and thromboelastography. The 3-dimensional morphology of platelet aggregates was observed by a microscopic 3-dimensional imaging. Re was a potent inhibitor of SIPA, with an IC 50 of 0.071 mg/mL. It effectively blocked shear stress-induced platelet activation without any significant toxicity. It was highly selective against SIPA, effectively inhibiting vWF-GPIb and the downstream PI3K/Akt signaling pathway. Most importantly, Re did not affect normal blood coagulation and did not increase the risk of bleeding. In conclusion, Re inhibits platelet activation through the inhibition of the vWF-GPIb/PI3K/Akt pathway. Thus, it might be considered as a new antiplatelet drug in the prevention of thrombosis without increasing the risk of bleeding.

Evaluation of the Efficacy and Safety of Antiplatelet Therapeutics in Rabbits.

Hemostasis is a multifactorial process that involves vasoconstriction of blood vessels, activation of the coagulation cascade, and platelet aggregation. Inappropriate activation of hemostatic processes can result in thrombosis and tissue ischemia. In patients at risk for thrombotic events, antiplatelet therapeutic agents inhibit platelet activation, thereby reducing the incidence of pathologic clot formation. Platelets are activated by several endogenous chemical mediators, including adenosine diphosphate, thrombin, and thromboxane. These activation pathways serve as attractive drug targets. The protocols described in this article are designed to evaluate the preclinical efficacy and safety of novel antiplatelet therapeutics in rabbits. Here, we provide two protocols for blood collection, two for determining platelet activation, and one for assessing bleeding safety. Together, these protocols can be used to characterize the efficacy and safety of antiplatelet agents for hemostasis. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Blood collection via the central ear artery Alternative Protocol 1: Blood collection via the jugular vein Basic Protocol 2: Platelet aggregation assessment via light transmission aggregometry Alternative Protocol 2: Platelet activation assessment via flow cytometry Basic Protocol 3: Determination of tongue bleeding time.

Role of GPR56 in Platelet Activation and Arterial Thrombosis.

The adhesion G protein-coupled receptor GPR56 mediates cell-cell and cell-extracellular matrix interactions. To examine the function of GPR56 in platelet activation and arterial thrombosis, we generated GPR56-knockout mice and evaluated GPR56 expression in human and mouse platelets. The results revealed that the levels of the GPR56 N-terminal fragment were significantly higher on the first day after myocardial infarction than on the seventh day in the plasma of patients with ST-segment-elevation myocardial infarction. Next, we investigated the effects of GPR56 on platelet function in vitro and in vivo. We observed that collagen-induced aggregation and adenosine triphosphate release were reduced in Gpr56 -/- platelets. Furthermore, P-selectin expression on the Gpr56 -/- platelet surface was also reduced, and the spreading area on immobilized collagen was decreased in Gpr56 -/- platelets. Furthermore, collagen-induced platelet activation in human platelets was inhibited by an anti-GPR56 antibody. Gpr56 -/- mice showed an extended time to the first occlusion in models with cremaster arteriole laser injury and FeCl3-induced carotid artery injury. GPR56 activated the G protein 13 signaling pathway following collagen stimulation, which promoted platelet adhesion and thrombus formation at the site of vascular injury. Thus, our study confirmed that GPR56 regulated the formation of arterial thrombosis. Inhibition of the initial response of GPR56 to collagen could significantly inhibit platelet activation and thrombus formation. Our results provide new insights for research into antiplatelet drugs.

Rho GTPase Signaling in Platelet Regulation and Implication for Antiplatelet Therapies.

Platelets play a vital role in regulating hemostasis and thrombosis. Rho GTPases are well known as molecular switches that control various cellular functions via a balanced GTP-binding/GTP-hydrolysis cycle and signaling cascade through downstream effectors. In platelets, Rho GTPases function as critical regulators by mediating signal transduction that drives platelet activation and aggregation. Mostly by gene targeting and pharmacological inhibition approaches, Rho GTPase family members RhoA, Rac1, and Cdc42 have been shown to be indispensable in regulating the actin cytoskeleton dynamics in platelets, affecting platelet shape change, spreading, secretion, and aggregation, leading to thrombus formation. Additionally, studies of Rho GTPase function using platelets as a non-transformed model due to their anucleated nature have revealed valuable information on cell signaling principles. This review provides an updated summary of recent advances in Rho GTPase signaling in platelet regulation. We also highlight pharmacological approaches that effectively inhibited platelet activation to explore their possible development into future antiplatelet therapies.

Commentary on 'Identification and characterization of select oxysterols as ligands for GPR17'.

Commentary on 'Identification and characterization of select oxysterols as ligands for GPR17'.

PLATELET SUPPRESSION BY TIROFIBAN AMELIORATES PULMONARY COAGULATION AND FIBRINOLYSIS ABNORMALITIES IN THE LUNGS OF MOUSE ANTIBODY-MEDIATED TRANSFUSION-RELATED ACUTE LUNG INJURY.

This study aimed to explore the ameliorating effects of the platelet surface glycoprotein IIb/IIIa receptor antagonist tirofiban on coagulation and fibrinolytic abnormalities in a mouse model of antibody-mediated transfusion-associated acute lung injury (ALI). This is important because ALI is a major cause of death attributable to the occurrence of adverse transfusion reactions. No information on a definite diagnosis or pathological mechanism exists, and targeted treatment options are not available. In this study, wild-type male Balb/c mice aged 8 to 10 weeks were randomly divided into the TRALI model, blank control, tirofiban intervention, and isotype control groups. After different treatment exposures, the mice were observed for 2 h before being killed, and lung tissue samples were collected. To explore the intervention effect of tirofiban, the degree of lung injury was quantified by estimating the lung wet/dry ratio, rectal temperature, survival rate, total protein, and myeloperoxidase and via hematoxylin-eosin staining. Furthermore, the coagulation, anticoagulation, and fibrinolysis assays were measured by automatic coagulation instrument and enzyme-linked immunosorbent assay kits, and the fluorescence densities of platelets and fibrin were quantified using immunofluorescence to analyze the effects of tirofiban on the platelet and fibrin interactions of TRALI. Compared with the TRALI model group, the lung injury indices in the tirofiban intervention group decreased significantly, and survival rates also improved. Furthermore, the level of coagulation and fibrinolytic abnormalities were obviously lower than those in the TRALI model group. In conclusion, our findings suggest that tirofiban might interfere with TRALI by inhibiting platelet activation and improving coagulation and fibrinolytic abnormalities.

Toll-Like Receptor 4-Dependent Platelet-Related Thrombosis in SARS-CoV-2 Infection.

SARS-CoV-2 is associated with an increased risk of venous and arterial thrombosis, but the underlying mechanism is still unclear. We performed a cross-sectional analysis of platelet function in 25 SARS-CoV-2 and 10 healthy subjects by measuring Nox2 (NADPH oxidase 2)-derived oxidative stress and thromboxane B2, and investigated if administration of monoclonal antibodies against the S protein (Spike protein) of SARS-CoV-2 affects platelet activation. Furthermore, we investigated in vitro if the S protein of SARS-CoV-2 or plasma from SARS-CoV-2 enhanced platelet activation. Ex vivo studies showed enhanced platelet Nox2-derived oxidative stress and thromboxane B2 biosynthesis and under laminar flow platelet-dependent thrombus growth in SARS-CoV-2 compared with controls; both effects were lowered by Nox2 and TLR4 (Toll-like receptor 4) inhibitors. Two hours after administration of monoclonal antibodies, a significant inhibition of platelet activation was observed in patients with SARS-CoV-2 compared with untreated ones. In vitro study showed that S protein per se did not elicit platelet activation but amplified the platelet response to subthreshold concentrations of agonists and functionally interacted with platelet TLR4. A docking simulation analysis suggested that TLR4 binds to S protein via three receptor-binding domains; furthermore, immunoprecipitation and immunofluorescence showed S protein-TLR4 colocalization in platelets from SARS-CoV-2. Plasma from patients with SARS-CoV-2 enhanced platelet activation and Nox2-related oxidative stress, an effect blunted by TNF (tumor necrosis factor) α inhibitor; this effect was recapitulated by an in vitro study documenting that TNFα alone promoted platelet activation and amplified the platelet response to S protein via p47phox (phagocyte oxidase) upregulation. The study identifies 2 TLR4-dependent and independent pathways promoting platelet-dependent thrombus growth and suggests inhibition of TLR4. or p47phox as a tool to counteract thrombosis in SARS-CoV-2.

Ticagrelor reduces doxorubicin-induced pyroptosis of rat cardiomyocytes by targeting GSK-3β/caspase-1.

Doxorubicin (Dox) is a widely used clinical drug whose cardiotoxicity cannot be ignored. Pyroptosis (inflammatory cell death) has gradually gained attention in the context of Dox-induced cardiotoxicity. In addition to the inhibition of platelet activation by ticagrelor, little is known about its other pharmacological effects. Glycogen synthase kinase 3β (GSK-3β) has been shown to contribute to the pathological process of pyroptosis, but whether it is related to the potential role of ticagrelor is unclear. In this study, we investigated the effects of ticagrelor on Dox-induced pyroptosis in cardiomyocytes. Rats were treated with ticagrelor (7.5 mg/kg, i.g.) 1 h before intravenous injection of Dox (2.5 mg/kg), once every 3 days, six times in total. Hearts were collected for histochemical analysis and western blot detection 8 weeks after the last administration. Ticagrelor was shown to significantly improve cardiac function by inhibiting GSK-3β/caspase-1/GSDMD activation. In vitro experiments were conducted using rat cardiac myocytes (RCMs) and rat embryonic cardiac-derived H9c2 cells. Pretreatment with ticagrelor (10 μm) significantly inhibited Dox (1 μm)-induced hypertrophy and reversed the upregulation of GSDMD-NT expression. We showed that ticagrelor suppressed the activation of Akt caused by Dox in the heart tissue as well as in RCMs/H9c2 cells caused by Dox. When GSK-3β expression was absent in H9c2 cells, the inhibitory effect of ticagrelor on Dox-induced caspase-1/GSDMD activation was weakened. These data showed that ticagrelor reduced Dox-induced pyroptosis in rat cardiomyocytes by targeting GSK-3β/caspase-1.

Arterial Baroreflex Dysfunction Promotes Neuroinflammation by Activating the Platelet CD40L/Nuclear Factor Kappa B Signaling Pathway in Microglia and Astrocytes

Arterial baroreflex (ABR) dysfunction has previously been associated with neuroinflammation, the most common pathological feature of neurological disorders. However, the mechanisms mediating ABR dysfunction-induced neuroinflammation are not fully understood. In the present study, we investigated the role of platelet CD40 ligand (CD40L) in neuroinflammation in an in vivo model of ABR dysfunction, and microglia and astrocyte activation in vitro. ABR dysfunction was induced in Sprague‒Dawley rats by sinoaortic denervation (SAD). We used ELSA and immunofluorescence to assess the effect of platelet CD40L on glial cell polarization and the secretion of inflammatory factors. By flow cytometry, we found that rats subjected to SAD showed a high level of platelet microaggregation and upregulation of CD40L on the platelet surface. The promotion of platelet invasion and accumulation was also observed in the brain tissues of rats subjected to SAD. In the animal model and cultured N9 microglia/C6 astrocytoma cells, platelet CD40L overexpression promoted neuroinflammation and activated M1 microglia, A1 astrocytes, and the nuclear factor kappa B (NFκB) signaling pathway. These effects were partially blocked by inhibiting platelet activity with clopidogrel or inhibiting CD40L-mediated signaling. Our results suggest that during ABR dysfunction, CD40L signaling in platelets converts microglia to the M1 phenotype and astrocytes to the A1 phenotype, activating NFκB and resulting in neuroinflammation. Thus, our study provides a novel understanding of the pathogenesis of ABR dysfunction-induced neuroinflammation and indicates that targeting platelet CD40L is beneficial for treating central nervous system (CNS) disorders associated with ABR dysfunction.

Evaluation of Platelet Parameters in Patients With Secondary Failure of Platelet Recovery and Cytomegalovirus Infection After Hematopoietic Stem Cell Transplantation.

To investigate the clinical significance of changes in platelet parameters in patients with secondary failure of platelet recovery (SFPR) and cytomegalovirus (CMV) infection after hematopoietic stem cell transplantation (HSCT). In this retrospective study, 79 patients who had undergone allogeneic HSCT (allo-HSCT), including 40 patients with SFPR and 39 patients without SFPR, were recruited. The evaluated parameters were platelet count (PLT), plateletcrit (PCT), platelet-large cell ratio (P-LCR), mean platelet volume (MPV), platelet distribution width (PDW), the incidence of CMV infection after allo-HSCT, and the correlation of SFPR and CMV infection in patients who had undergone allo-HSCT. The control group included 107 healthy donors. The SFPR group had significantly lower megakaryocyte counts, PLT, and PCT and significantly higher P-LCR, MPV, and PDW than the healthy donor and non-SFPR groups. The incidence of CMV infection was higher in SFPR patients than in non-SFPR patients. Among the patients with SFPR, P-LCR, MPV, and PDW were lower in those with CMV DNA >8000 copies/mL than in those with CMV DNA <8000 copies/mL (P < .05 for all); the CMV viral load was slightly negatively correlated with MPV (P = .0297) and P-LCR (P = .0280). We demonstrate for the first time that the level of platelet activation in SFPR patients, which was closely related to CMV infection, was higher than that in that in non-SFPR patients, and higher CMV load was associated with the inhibition of platelet activation.

Raynaud's Phenomenon: A Brush Up!

Raynaud's Phenomenon: A Brush Up!

Studying the efficacy of antiplatelet drugs on atherosclerosis by optofluidic imaging on a chip.

Vascular stenosis caused by atherosclerosis instigates activation and aggregation of platelets, eventually resulting in thrombus formation. Although antiplatelet drugs are commonly used to inhibit platelet activation and aggregation, they unfortunately cannot prevent recurrent thrombotic events in patients with atherosclerosis. This is partially due to the limited understanding of the efficacy of antiplatelet drugs in the complex hemodynamic environment of vascular stenosis. Conventional methods for evaluating the efficacy of antiplatelet drugs under stenosis either fail to simulate the hemodynamic environment of vascular stenosis characterized by high shear stress and recirculatory flow or lack spatial resolution in their analytical techniques to statistically identify and characterize platelet aggregates. Here we propose and experimentally demonstrate a method comprising an in vitro 3D stenosis microfluidic chip and an optical time-stretch quantitative phase imaging system for studying the efficacy of antiplatelet drugs under stenosis. Our method simulates the atherogenic flow environment of vascular stenosis while enabling high-resolution and statistical analysis of platelet aggregates. Using our method, we distinguished the efficacy of three antiplatelet drugs, acetylsalicylic acid (ASA), cangrelor, and eptifibatide, for inhibiting platelet aggregation induced by stenosis. Specifically, ASA failed to inhibit stenosis-induced platelet aggregation, while eptifibatide and cangrelor showed high and moderate efficacy, respectively. Furthermore, we demonstrated that the drugs tested also differed in their efficacy for inhibiting platelet aggregation synergistically induced by stenosis and agonists (e.g., adenosine diphosphate, and collagen). Taken together, our method is an effective tool for investigating the efficacy of antiplatelet drugs under vascular stenosis, which could assist the development of optimal pharmacologic strategies for patients with atherosclerosis.

Dual pathway inhibition for atherosclerotic cardiovascular disease: Recent advances.

Atherosclerotic cardiovascular disease (ASCVD), which includes coronary artery disease (CAD), cerebrovascular disease, and peripheral arterial disease (PAD) is associated with significant morbidity, mortality, and healthcare costs. Antiplatelet therapy has long been the mainstay of antithrombotic therapy for the prevention of first-ever and recurrent ASCVD events. More recently, however, randomized trials have demonstrated the benefits and cost-effectiveness of a dual pathway inhibition (DPI) strategy in acute and chronic ASCVD. When used in combination, aspirin and low-dose rivaroxaban work synergistically to inhibit platelet activation and thrombin generation, thereby preventing thrombus formation. Among patients with recent acute coronary syndrome (ACS), those with positive cardiac biomarkers or ST-segment elevation myocardial infarction, or a history of heart failure derive the greatest absolute benefits. Among patients with chronic ASCVD, those with involvement of two or more vascular beds, heart failure, chronic kidney disease, or diabetes derive the greatest absolute benefits. Additional trials are underway to assess the impact of DPI therapy in other populations of interest, including patients with ACS at high risk of left ventricular thrombus formation, intracranial atherosclerotic disease with recent transient ischemic attack or stroke, peripheral arterial disease with limiting claudication or post lower extremity revascularization, and advanced chronic kidney disease with ASCVD or risk factors for ASCVD. Further work is required to assess the possible added benefit of combining rivaroxaban with clopidogrel or ticagrelor instead of aspirin.

IRGM/Irgm1 deficiency inhibits neutrophil-platelet interactions and thrombosis in experimental atherosclerosis and arterial injury

BackgroundNeutrophil extracellular traps (NETs) closely link inflammation and thrombosis. The immune-related GTPase family M protein (IRGM) and its ortholog of mouse IRGM1 are positively correlated with plaque rupture during atherosclerosis process. However, whether and how IRGM/IRGM1 affects NETs formation and atherosclerotic thrombosis remains unknown, which will further promote the development of antithrombotic treatment tools. MethodsThe thrombi images, platelet activation makers and NETs makers were detected in the serum of STEMI patients and controls. To futher investigate IRGM/IRGM1 affects NETs formation and atherothrombosis in vivo, ApoE-/-Irgm1+/- and ApoE-/- mice received diets rich in fat and 2.5% FeCl3 was then used to induce experimental arterial thrombosis in an atherosclerosis background. In vitro, PMA and thrombin were used to stimulate neutrophils and platelets, respectively, and the expression of IRGM/IRGM1 were modified. To reveal the molecular mechanisms, MAPK-cPLA2 signals inhibitors were used. ResultsSerum IRGM was positively correlated with PF4 and neutrophil elastase. Subsequently, Irgm1 deficient mice have a longer occlusion time and lower growth rate. In vitro, as expected, IRGM/Irgm1 deficiency inhibits platelet activation and platelet-neutrophil interaction. More importantly, IRGM promoted NETs production through activating MAPK-cPLA2 signals in PMA stimulated neuropils, whereas inhibiting the production of NETs eliminated the difference in platelet activation and thrombosis caused by IRGM/Irgm1 modification in vivo and vitro. Similarly, inhibition of platelet activation also eliminated the influence of IRGM/Irgm1 modification on NETs production. ConclusionsOverall, our data indicate that IRGM/Irgm1 deficiency in neuropils inhibits the intense interaction between neutrophils and platelets, and ultimately inhibits thrombosis.

Changes of Platelet Parameters before and after Surgery in Patients with Subarachnoid Hemorrhage

Objective To analyze the clinical application value of platelet parameter changes before and after surgery in patients with subarachnoid hemorrhage in our hospital, and to provide basis for clinical condition observation. Methods A total of 354 patients with subarachnoid hemorrhage who were hospitalized in our hospital from January 2017 to July 2021 were selected, and compared with 217 healthy individuals during the same period. The 4 parameters in platelet venous blood before and after surgery were analyzed: platelet count (Plt), mean platelet volume (MPV), platelet volume (PCT), and platelet distribution density (PDW). Results Before operation: Platelet count (PLT) decreased compared with the normal control group (p&lt;0.01), MPV and PDW were increased compared with the normal control group (p&lt;0.01); PLT increased after operation (p&lt;0.01), but higher than that of the normal control group. Conclusions Early surgical treatment of aneurysmal subarachnoid hemorrhage can seal the ruptured blood vessel, reduce the exposure of endothelial cells, inhibit platelet activation, and reduce the formation of microthrombi.

Heparin and heparin proteoglycan-mimetics activate platelets via PEAR1 and PI3Kβ

BackgroundPlatelet endothelial aggregation receptor 1 (PEAR1) is a single-transmembrane orphan receptor primarily expressed on platelets and endothelial cells. Genetic variants of PEAR1 have repeatedly and independently been identified to be associated with cardiovascular diseases, including coronary artery disease. ObjectivesWe have identified sulfated fucoidans and their mimetics as ligands for PEAR1 and proposed that its endogenous ligand is a sulfated proteoglycan. The aim of this study was to test this hypothesis. MethodsA heparin proteoglycan-mimetic (HPGM) was created by linking unfractionated heparin (UFH) to albumin. The ability of the HPGM, UFH and selectively desulfated heparins to stimulate platelet aggregation and protein phosphorylation was investigated. Nanobodies against the 12th to 13th epidermal growth factor-like repeat of PEAR1 and phosphoinositide 3-kinase (PI3K) isoform-selective inhibitors were tested for the inhibition of platelet activation. ResultsWe show that HPGM, heparin conjugated to an albumin protein core, stimulates aggregation and phosphorylation of PEAR1 in washed platelets. Platelet aggregation was abolished by an anti-PEAR1 nanobody, Nb138. UFH stimulated platelet aggregation in washed platelets, but desulfated UFH did not. Furthermore, HPGM, but not UFH, stimulated maximal aggregation in platelet-rich plasma. However, both HPGM and UFH increased integrin αIIbβ3 activation in whole blood. By using PI3K isoform-selective inhibitors, we show that PEAR1 activates PI3Kβ, leading to Akt phosphorylation. ConclusionOur findings reveal that PEAR1 is a receptor for heparin and HPGM and that PI3Kβ is a key signaling molecule downstream of PEAR1 in platelets. These findings may have important implications for our understanding of the role of PEAR1 in cardiovascular disease.

Humic Acids Inhibit Platelet Activation to Reduce Venous Thromboembolism in Mice.

We aimed to investigate the effects of the natural product humic acids (HA) on platelet activation and development of venous thromboembolism (VTE) in mice and further explore the relevant mechanism. Eight-week C57BL/6 mice were randomly assigned to three groups: sham operation group (n = 7), VTE group (n = 8), and VTE + HA group (n = 10). Thrombi were harvested to hematoxylin-eosin staining to evaluate the thrombolysis and recanalization of the thrombus. In addition, flow cytometry was performed to detect the expression levels of protein disulfide isomerase on endothelial-derived exosomes and glycoprotein IIb/IIIa on the surface of the activated platelets surface in plasma. Furthermore, the protein expression level of glycoprotein IIb/IIIa in thrombus was determined by immunohistochemistry and immunofluorescence. The length of thrombosis in the VTE + HA group was significantly shorter than that in the VTE group (P = 0.040). No significant differences were observed in thrombolysis and recanalization between the VTE + HA group and the VTE group (P > 0.05). The content of protein disulfide isomerase carried by endothelial-derived exosomes was significantly increased in the VTE group (P = 0.008) but significantly reduced by native humic acids (P = 0.012). Compared with the VTE group, the expression of glycoprotein IIb/IIIa on activated platelet surface in the VTE + HA group was significantly decreased (P = 0.002). The concentration of plasmatic P-selectin in the VTE group was significantly higher than that in the VTE + HA group (P < 0.001). We demonstrate that HA possess a pharmacological property that decreases venous thrombus formation in mice. The underlying mechanism is that HA could inhibit the expression of glycoprotein IIb/IIIa on the activated platelets surface by suppressing endothelial-derived exosomes carrying on protein disulfide isomerase, thereby blocking platelet activation.