Platelet P2Y(12) receptor influences the vessel wall response to arterial injury and thrombosis

Pharmacotherapeutic options for coronary thrombosis treatment: where are we today?

INTRODUCTION

Advances in pharmacotherapy for coronary thrombosis treatment and prevention have transformed the clinical outcomes of patients with coronary artery disease but increased the complexity of therapeutic decision-making. Improvements in percutaneous coronary intervention techniques and stent design have reduced the incidence of thrombotic complications, which consequently has increased the challenge of adequately powering clinical trials of novel antithrombotic strategies for efficacy outcomes. Knowledge of the pathophysiology of coronary thrombosis and the characteristics of antithrombotic drugs can help with therapeutic decisions.

AREAS COVERED

This review covers the pathophysiology of coronary thrombosis and the mechanisms of action of drugs developed for its treatment, provides an overview of the key issues in decision-making, and highlights key areas for further work in order to guide clinicians on how to individualize risk management and address gaps in the evidence base.

EXPERT OPINION

Individualization of antithrombotic therapy regimens has become a vital part of optimizing risk management in people with coronary thrombosis. A critical appraisal of the strengths and limitations of available drugs and the evidence supporting the use of different antithrombotic combinations is intended to provide direction to clinicians and point the way toward further improvements in pharmacotherapy for coronary thrombosis treatment and prevention.

Chromosome Y Haplogroup R Was Associated with the Risk of Premature Myocardial Infarction with ST-Elevation: Data from the CholeSTEMI Registry

Cardiovascular disease (CVD) is the leading cause of death worldwide, with coronary artery disease (CAD) being one of its main manifestations. Both environmental and genetic factors are widely known to be related to CAD, such as smoking, diabetes mellitus, dyslipidemia, and a family history of CAD. However, there is still a lack of information about other risk factors, especially those related to genetic mutations. Sex represents a classic CAD risk factor, as men are more likely to suffer CAD, but there is lack of evidence with regard to sex-specific genetic factors. We evaluated the Y chromosome haplogroups in a cohort of young Spanish male patients who suffered from STEMI. In this cohort, haplogroup R was significantly more frequent in STEMI patients.

Loss of α4A- and β1-tubulins leads to severe platelet spherocytosis and strongly impairs hemostasis in mice

Native circulating blood platelets present with a discoid flat morphology maintained by a submembranous peripheral ring of microtubules, named marginal band. The functional importance of this particular shape is still debated, but it was initially hypothesized to facilitate platelet interaction with the injured vessel wall and to contribute to hemostasis. The importance of the platelet discoid morphology has since been questioned on the absence of clear bleeding tendency in mice lacking the platelet-specific β1-tubulin isotype, which exhibits platelets with a thinner marginal band and an ovoid shape. Here, we generated a mouse model inactivated for β1-tubulin and α4A-tubulin, an α-tubulin isotype strongly enriched in platelets. These mice present with fully spherical platelets completely devoid of a marginal band. In contrast to the single knockouts, the double deletion resulted in a severe bleeding defect in a tail-clipping assay, which was not corrected by increasing the platelet count to normal values by the thrombopoietin-analog romiplostim. In vivo, thrombus formation was almost abolished in a ferric chloride-injury model, with only a thin layer of loosely packed platelets, and mice were protected against death in a model of thromboembolism. In vitro, platelets adhered less efficiently and formed smaller-sized and loosely assembled aggregates when perfused over von Willebrand factor and collagen matrices. In conclusion, this study shows that blood platelets require 2 unique α- and β-tubulin isotypes to acquire their characteristic discoid morphology. Lack of these 2 isotypes has a deleterious effect on flow-dependent aggregate formation and stability, leading to a severe bleeding disorder.

Pleiotropic effects of clopidogrel

Clopidogrel is a widely prescribed prodrug with anti-thrombotic activity through irreversible inhibition of the P2Y₁₂ receptor on platelets. It is FDA-approved for the clinical management of thrombotic diseases like unstable angina, myocardial infarction, stroke, and during percutaneous coronary interventions. Hepatic clopidogrel metabolism generates several distinct metabolites. Only one of these metabolites is responsible for inhibiting the platelet P2Y₁₂ receptor. Importantly, various non-hemostatic effects of clopidogrel therapy have been described. These non-hemostatic effects are perhaps unsurprising, as P2Y₁₂ receptor expression has been reported in multiple tissues, including osteoblasts, leukocytes, as well as vascular endothelium and smooth muscle. While the "inactive" metabolites have been commonly thought to be biologically inert, recent findings have uncovered P2Y₁₂ receptor-independent effects of clopidogrel treatment that may be mediated by understudied metabolites. In this review, we summarize both the P2Y₁₂ receptor-mediated and non-P2Y₁₂ receptor-mediated effects of clopidogrel and its metabolites in various tissues.

The role of P2Y12 receptor inhibition in ischemic stroke on microglia, platelets and vascular smooth muscle cells

P2Y12 receptors on platelets have long been the main target of antiplatelet drugs. However, a growing number of studies have revealed that P2Y12 receptor activation on microglia and vascular smooth muscle cells (VSMCs) also aggravates ischemic stroke injury. The proliferation and migration of VSMCs in the vascular wall have important influence on the early lesion of atherosclerosis, which may lead to the origin of cerebral ischemic attack of atherosclerosis. Blockage of cellular P2Y12 receptors could inhibit microglial activation, block formation of platelet-leukocyte aggregates, reduce proinflammatory cytokine levels and suppress migration and proliferation of VSMCs, implying that apart from anti-thrombotic effect, P2Y12 inhibitors have additional neuroprotective, anti-inflammatory and anti-atherosclerotic therapeutic benefits against ischemic stroke. In this review, we will summarize recent advances in studies on P2Y12 receptors and emphatically introduce their significance in microglia, platelets and VSMCs after ischemic stroke, discussing how to exert the beneficial effects of P2Y12 inhibition.

The role of P2Y receptors in regulating immunity and metabolism

P2Y receptors are G protein-coupled receptors whose physiological agonists are the nucleotides ATP, ADP, UTP, UDP and UDP-glucose. Eight P2Y receptors have been cloned in humans: P2Y1R, P2Y2R, P2Y4R, P2Y6R, P2Y11R, P2Y12R, P2Y13R and P2Y14R. P2Y receptors are expressed in lymphoid tissues such as thymus, spleen and bone marrow where they are expressed on lymphocytes, macrophages, dendritic cells, neutrophils, eosinophils, mast cells, and platelets. P2Y receptors regulate many aspects of immune cell function, including phagocytosis and killing of pathogens, antigen presentation, chemotaxis, degranulation, cytokine production, and lymphocyte activation. Consequently, P2Y receptors shape the course of a wide range of infectious, autoimmune, and inflammatory diseases. P2Y12R ligands have already found their way into the therapeutic arena, and we envision additional ligands as future drugs for the treatment of diseases caused by or associated with immune dysregulation.

Whole Blood miR-210, miR-122, miR-223 Expression Levels and Their Relationship With Iron Status Parameters and Hypercoagulability Indices in Children With Iron Deficiency Anemia

MicroRNAs have the potential to regulate systemic and cellular iron homeostasis at multiple points. In iron deficiency anemia (IDA), hypoxia, platelet reactivity, and potentially microRNAs play a role in the development of hypercoagulability. A total of 57 children diagnosed with IDA between October 2016 and October 2017 and 48 healthy children were included in this cross-sectional study. Blood count parameters, serum iron, transferrin saturation, ferritin level, maximum clot firmness (MCF), and clot formation time index, which are indicators of hypercoagulability in rotational thromboelastometry test, of the IDA and control groups obtained in our previous study were recorded. miR-210, miR-122, and miR-223 levels were analyzed. There was no difference in the miR-210, miR-122, and miR-223 levels between the IDA and control groups. Patients with hemoglobin (Hb) <8 g/dL had higher miR-210 levels than patients with Hb>8 g/dL (P<0.05). There was a negative correlation between miR-210 and Hb and ferritin levels, a positive correlation between miR-122 and ferritin levels, and a negative correlation between miR-223 and MCF index. In IDA, there is a close relationship between the severity of anemia and miR-210, and miR-210 expression is slightly increased in those with severe anemia. miR-210 and miR-122 collectively play a role in maintaining the iron balance. The correlation between miR-223, a platelet function regulator, and the MCF index, suggested that miR-223 has a role in the development of hypercoagulability in IDA.

Carotid Stent Restenosis and Thrombosis in Rabbits: The Effect of Antiplatelet Agents

BACKGROUND

The purpose of the study was the comparative assessment of ticagrelor and clopidogrel effects on carotid post-balloon injury (PBI) and on post carotid artery stenting (CAS) rate of in-stent restenosis (ISR) and in-stent thrombosis in atherosclerotic rabbits.

METHODS

Forty-eight New Zealand white rabbits on high-fat diet were randomized into 4 groups: A1: PBI and clopidogrel (30 mg/kg/d), A2: PBI and ticagrelor (21 mg/kg twice daily), B1: PBI, CAS, and clopidogrel (30 mg/kg/d), B2: PBI, CAS, and ticagrelor (21 mg/kg twice daily). All rabbits received orally aspirin (10 mg/kg/d) and interventions were performed in their right carotid arteries (RCAs). Optical coherence tomography (OCT) and carotid angiography were performed at end point, while platelet aggregation and lipid profile were measured. After euthanasia both carotids were obtained for histological examination.

RESULTS

In B1 group, 3 rabbits presented thrombotic total occlusion of the stents, while none such episode was observed in B2 group. The neointimal areas in RCAs, calculated by OCT, did not differ between A1 and A2 groups, and between B1 and B2 groups (P > .05). From the histological findings, the intima/(media + intima) percentage (%) in RCAs of balloon-injured rabbits did not present any difference between groups (P = .812). Similarly, the immunohistochemically determined accumulation of endothelial cells and macrophages on vascular walls was equivalent between groups (P > .05).

CONCLUSION

Following carotid balloon injury and stenting, clopidogrel and ticagrelor did not show any differential effects on the extent of neointimal formation and ISR in atherosclerotic rabbits receiving aspirin. Three thrombotic stent occlusions were noted in the clopidogrel treatment group, but this finding was not statistically significant.

Immobilisation of an anti-platelet adhesion and anti-thrombotic drug (EP224283) on polydopamine coated vascular stent promoting anti-thrombogenic properties

Current vascular drug-eluting stents based on immuno-proliferative drugs would reduce the rate of in-stent restenosis (ISR) but may be associated with a higher risk of acute stent thrombosis due to non-selective activity. In this paper, we aimed to develop a polydopamine (PDA) coated chromium‑cobalt (CoCr) stent functionalised with EP224283 (Endotis Pharma SA), which combines both a GPIIbIIIa antagonist (tirofiban moiety) and a factor Xa inhibitor (idraparinux moiety) to reduce acute stent thrombosis. PDA-coated chromium‑cobalt (CoCr) samples were first immersed in a polyethylenimine (PEI, pH 8.5) solution to increase amine function density (36.0 ± 0.1 nmol/cm²) on the CoCr surface. In a second step, avidin was grafted onto CoCr-PDA-PEI through the biotin linkage (strategy 1) or directly by coupling reactions (strategy 2). The HABA titration proved the fixation of biotin onto CoCr-PDA-PEI surface with a density of 0.74 nmol/cm². The fixation of avidin was demonstrated by water contact angle (WCA) and surface plasmon resonance (SPR). SEM micrograph shows the flexibility of the thin layer coated onto the stent after balloon inflation. Independently of the strategy, a qualitative SEM analysis showed a reduction in platelet activation when the molecule EP224283 was immobilised on avidin. In parallel, the measurement of anticoagulant activity (anti-Xa) revealed a higher anti-factor Xa activity (2.24 IU/mL vs. 0.09 IU/mL in control) when EP224283 was immobilised on avidin. Interestingly, after seven days of degradation, the anticoagulant activity was persistent in both strategies and looked more important with the strategy 2 than in strategy 1. Throughout this work, we developed an innovative vascular stent through the immobilisation of EP224283 onto CoCr-PDA-PEI-(avidin) system, which provides a promising solution to reduce ISR and thrombosis after stent implantation.

Ticagrelor versus clopidogrel in patients undergoing implantation of paclitaxel-eluting stent in the femoropopliteal district: A randomized pilot study using frequency-domain optical coherence tomography

OBJECTIVES

Aim of this study was to evaluate different response in platelet reactivity and vessel healing using high-resolution frequency-domain optical coherence tomography (FD-OCT) in patients with femoropopliteal artery disease treated with ZILVER PTX drug eluting stents (DES), and randomly assigned to clopidogrel or ticagrelor for 12 months.

BACKGROUND

The optimal antithrombotic regimen for long-term management of patients with peripheral artery disease (PAD) after revascularization is poorly defined and often extrapolated from trials performed on patients undergoing percutaneous coronary intervention.

METHODS

In this single center randomized trial 40 patients with femoropopliteal artery disease treated with ZILVER PTX DES stents, were randomized to Ticagrelor (T) + Aspirin for 3 months, subsequently continuing Ticagrelor alone for another 9 months or Clopidogrel (C) + Aspirin for 3 months, subsequently continuing Clopidogrel alone for 9 months. Platelet reactivity via the P2Y12 pathway was evaluated at baseline and at 3 months follow-up, angiographic and FD-OCT follow-up along the entire stented segment was performed at 12 months.

RESULTS

No significant difference between T and C group was found concerning net percentage volume obstruction (29.7% ± 17.6% vs. 31.2% ± 10.7%; p = 0.78). FD-OCT at 12 months showed a high percentage of uncovered stent struts in both groups: 24.2% ± 32.8% in the T group vs 15.3% ± 15.8% in the C group (p = 0.4). Mean values of platelet reactivity units (PRU) at 3 month follow-up were 81 ± 72 in the T group and 200 ± 61 in the C group (p < 0.001).

CONCLUSIONS

Significantly higher platelet reactivity remains in patients treated with clopidogrel as compared to ticagrelor 3 months after PTA and stent implantation. Ticagrelor does not reduce neointimal proliferation in patients treated with DES in the femoropopliteal district as compared with clopidogrel. A large amount of uncovered stent struts at 12-month follow-up was found in these patients regardless of the antiplatelet treatment assumed.

Impacts of CYP2C19 Polymorphism and Clopidogrel Dosing on in-Stent Restenosis: A Retrospective Cohort Study in Chinese Patients

Objective

This retrospective cohort study is to analyze the impacts of CYP2C19 polymorphism and clopidogrel dosing on in-stent restenosis (ISR) after coronary stenting.

Methods

Totally, 111 patients were included, who underwent percutaneous coronary intervention (PCI) with drug-eluting stent. Patients received clopidogrel treatment after the intervention on the background treatment with aspirin, based on the genotypes: 75 mg clopidogrel once each day for subjects without CYP2C19 loss-of-function (LOF) alleles (n=51; EM), 75 mg clopidogrel once each day (n=27; IM75) or twice each day (n=33; IM150) for subjects with one CYP2C19 LOF allele. ISR at 3-18 months after coronary stenting was assessed.

Results

ISR rate was significantly higher in the IM75 group (40.7%) than the EM group (11.8%). ISR rate in the IM150 group was lower than the IM75 group (6.1% vs 40.7%), and comparable to that in the EM group. Multivariate logistic regression showed that both CYP2C19 genotype and clopidogrel dosing were associated with the risk of ISR after adjusting the relevant confounding factors. ISR risk was higher in the IM patients than the EM patients. Patients with clopidogrel dose of 75 mg once each day had significantly higher risk of ISR than those with the dose of 75 mg twice each day.

Conclusion

Increased dose of clopidogrel may reduce the risk of ISR after PCI in CYP2C19 LOF allele(s) carriers. The presence of CYP2C19 LOF allele(s) increases the risk of ISR after stenting, which could be counteracted by the increased dose of clopidogrel.

Platelet Oxidative Stress and its Relationship with Cardiovascular Diseases in Type 2 Diabetes Mellitus Patients

Enhanced platelet activation and thrombosis are linked to various cardiovascular diseases (CVD). Among other mechanisms, oxidative stress seems to play a pivotal role in platelet hyperactivity. Indeed, upon stimulation by physiological agonists, human platelets generate and release several types of reactive oxygen species (ROS) such as O2 -, H2O2 or OH-, further amplifying the platelet activation response via various signalling pathways, including, formation of isoprostanes, Ca2+ mobilization and NO inactivation. Furthermore, excessive platelet ROS generation, incorporation of free radicals from environment and/or depletion of antioxidants induce pro-oxidant, pro-inflammatory and platelet hyperaggregability effects, leading to the incidence of cardiovascular events. Here, we review the current knowledge regarding the effect of oxidative stress on platelet signaling pathways and its implication in CVD such as type 2 diabetes mellitus. We also summarize the role of natural antioxidants included in vegetables, fruits and medicinal herbs in reducing platelet function via an oxidative stress-mediated mechanism.

Human Y Chromosome Exerts Pleiotropic Effects on Susceptibility to Atherosclerosis

Supplemental Digital Content is available in the text.

The male-specific region of the Y chromosome (MSY) remains one of the most unexplored regions of the genome. We sought to examine how the genetic variants of the MSY influence male susceptibility to coronary artery disease (CAD) and atherosclerosis.

Genetic deletion of ADP-activated P2Y12 receptor ameliorates lithium-induced nephrogenic diabetes insipidus in mice

AIM

Therapeutic use of lithium in bipolar disorder is limited by the development of nephrogenic diabetes insipidus (NDI). We reported that pharmacological blockade of P2Y₁₂ receptor (R) with clopidogrel or prasugrel significantly ameliorated lithium-induced NDI in rodents. Using mice genetically lacking P2Y₁₂ -R we evaluated whether the observed amelioration is mediated through P2Y₁₂ -R METHODS: P2ry12^-/- mouse line (C57/BL6) was rederived from cryopreserved embryos of the knockout (KO) mice generated by Deltagen Inc. Syngeneic wild type (WT) mice obtained by heterozygous crossing were inbred. Groups of adult WT and KO mice were fed lithium-added (40 mmol LiCl/kg food) or regular diet, and euthanized after 2 or 4 weeks. Twenty-four hour urine samples and terminal blood and kidney samples were analyzed.

RESULTS

At both time points, lithium-induced polyuria and decrease in aquaporin-2 (AQP2) protein abundance in the kidney medulla were less marked in KO vs WT mice. Immunofluorescence microscopy revealed that lithium-induced alterations in the cellular disposition of AQP2 protein in the medullary collecting ducts of WT mice were blunted in KO mice. Serum lithium, sodium and osmolality were similar in both genotypes after lithium treatment. After 2 weeks, lithium induced marked increases in urinary excretion of Na, K, and arginine vasopressin in WT mice but not in KO mice.

CONCLUSION

Taken together, our data show that similar to pharmacological blockade, deletion of P2Y₁₂ -R significantly ameliorates lithium-induced NDI, without reducing serum lithium levels. Hence, targeting P2Y₁₂ -R with currently available drugs in the market offers a novel and safer method for treating NDI.

Absence of transforming growth factor beta 1 in murine platelets reduces neointima formation without affecting arterial thrombosis

Platelet degranulation at the site of vascular injury prevents bleeding and may affect the chronic vascular wound healing response. Transforming Growth Factor (TGF)-β1 is a major component of platelet α-granules known to accumulating in thrombi. It was our aim to determine the role of TGFβ1 released from activated platelets for neointima formation following arterial injury and thrombosis. Mice with platelet-specific deletion of TGFβ1 (Plt.TGFβ-KO) underwent carotid artery injury. Immunoassays confirmed the absence of active TGFβ1 in platelet releasates and plasma of Plt.TGFβ-KO mice. Whole blood analyses revealed similar haematological parameters, and tail cut assays excluded major bleeding defects. Platelet aggregation and the acute thrombotic response to injury in vivo did not differ between Plt.TGFβ-KO and Plt.TGFβ-WT mice. Morphometric analysis revealed that absence of TGFβ1 in platelets resulted in a significant reduction of neointima formation with lower neointima area, intima-to-media ratio, and lumen stenosis. On the other hand, the media area was enlarged in mice lacking TGFβ1 in platelets and contained increased amounts of proteases involved in latent TGFβ activation, including MMP2, MMP9 and thrombin. Significantly increased numbers of proliferating cells and cells expressing the mesenchymal markers platelet-derived growth factor receptor-β or fibroblast-specific protein-1, and the macrophage antigen F4/80, were observed in the media of Plt.TGFβ-KO mice, whereas the medial smooth muscle-actin-immunopositive area and collagen content did not differ between genotypes. Our findings support an essential role for platelet-derived TGFβ1 for the vascular remodelling response to arterial injury, apparently independent from the role of platelets in thrombosis or haemostasis.

Purinergic P2Y6 receptors: A new therapeutic target of age-dependent hypertension

Aging has a remarkable effect on cardiovascular homeostasis and it is known as the major non-modifiable risk factor in the development of hypertension. Medications targeting sympathetic nerve system and/or renin-angiotensin-aldosterone system are widely accepted as a powerful therapeutic strategy to improve hypertension, although the control rates remain unsatisfactory especially in the elder patients with hypertension. Purinergic receptors, activated by adenine, uridine nucleotides and nucleotide sugars, play pivotal roles in many biological processes, including platelet aggregation, neurotransmission and hormone release, and regulation of cardiovascular contractility. Since clopidogrel, a selective inhibitor of G protein-coupled purinergic P2Y₁₂ receptor (P2Y₁₂R), achieved clinical success as an anti-platelet drug, P2YRs has been attracted more attention as new therapeutic targets of cardiovascular diseases. We have revealed that UDP-responsive P2Y₆R promoted angiotensin type 1 receptor (AT1R)-stimulated vascular remodeling in mice, in an age-dependent manner. Moreover, the age-related formation of heterodimer between AT1R and P2Y₆R was disrupted by MRS2578, a P2Y₆R-selective inhibitor. These findings suggest that P2Y₆R is a therapeutic target to prevent age-related hypertension.

Biomarkers Associated with Ischemic Stroke in Diabetes Mellitus Patients

Diabetes is an established risk factor for ischemic stroke, but the associated molecular mechanisms remain to be fully elucidated. This study investigated the role of plasma and platelet microRNAs and their targeting proteins in the activation of platelets and their association with the occurrence of ischemic stroke in patients with type 2 diabetes mellitus (T2DM). Results showed that the expressions of platelet and plasma miR-144 and miR-223 were significantly altered in T2DM patients with or without ischemic stroke compared to that in healthy controls, but these changes were more significant in T2DM patients with ischemic stroke. The expressions of P2Y12 and IRS-1 as well as phosphorylation levels of IRS-1, PI3K, and Akt in platelets were significantly altered in T2DM patients with or without ischemic stroke. The expression of platelet miR-144 and miR-223 significantly correlated with their plasma levels, P2Y12 and IRS-1 expression, blood glucose concentration, and platelet activation rate. High glucose concentration significantly elevated P-selectin, miR-144 and P2Y12 expression and significantly reduced miR-223 and IRS-1 expression in UT-7 cells. Overexpression of miR-223 and blocking of miR-144 expression significantly normalized the effects of high glucose concentration in UT-7 cells. In conclusion, hyperglycemia may activate platelets through miR-144 and miR-223 to downregulate IRS-1 and upregulate P2Y12 expression in the platelets of T2DM patients through an IRS-1-PI3K-Akt signaling. Low platelet and plasma miR-223 expression in addition to high platelet and plasma miR-144 expression are risk factors for ischemic stroke in T2DM patients.

Effects of P2Y12 receptor antagonists beyond platelet inhibition--comparison of ticagrelor with thienopyridines

The effect and clinical benefit of P2Y12 receptor antagonists may not be limited to platelet inhibition and the prevention of arterial thrombus formation. Potential additional effects include reduction of the pro-inflammatory role of activated platelets and effects related to P2Y12 receptor inhibition on other cells apart from platelets. P2Y12 receptor antagonists, thienopyridines and ticagrelor, differ in their mode of action being prodrugs instead of direct acting and irreversibly instead of reversibly binding to P2Y12 . These key differences may provide different potential when it comes to additional effects. In addition to P2Y12 receptor blockade, ticagrelor is unique in having the only well-documented additional target of inhibition, the equilibrative nucleoside transporter 1. The current review will address the effects of P2Y12 receptor antagonists beyond platelets and the protection against arterial thrombosis. The discussion will include the potential for thienopyridines and ticagrelor to mediate anti-inflammatory effects, to conserve vascular function, to affect atherosclerosis, to provide cardioprotection and to induce dyspnea.

Prevention of occlusive arterial thrombus formation by a single loading dose of prasugrel suppresses neointimal hyperplasia in mice

The present study examined the effects of prasugrel in a mouse model of thrombosis-induced neointimal hyperplasia. Following carotid artery injury by application of ferric chloride solution, thrombus formation was assessed on Day 1 and neointimal thickening was assessed on Day 21. Single administrations of prasugrel at 0.3-3mg/kg (p.o.) resulted in a dose-related and sustained inhibition of ADP-induced platelet aggregation through 24h. Single and multiple (1 and 3 weeks) administration of prasugrel (3mg/kg loading and 1mg/kg/day maintenance doses) resulted in a marked inhibition of neointimal thickening in the injured artery. In the dose-response study, a single administration of prasugrel at 0.3-3mg/kg (p.o.) dose-relatedly inhibited thrombus formation and neointimal thickening on Days 1 and 21, respectively. The degree of neointimal hyperplasia in the injured artery correlated significantly with the thrombus indices, time to occlusion and patency rate. To explore possible mechanisms of inhibition of neointimal hyperplasia by prasugrel, mRNA expression levels of inflammatory and fibrosis markers were determined in injured arteries. Prasugrel treatment resulted in reduced MCP-1, ICAM-1 and TGF-β mRNA levels on Day 2 (24h after the injury) and Day 8 (1 week after the injury) in the target arteries. In conclusion, we found that a single oral loading dose of prasugrel markedly prevented neointimal hyperplasia by inhibiting platelet activation and thrombus formation and was associated with inhibition of the expression of inflammatory and fibrosis markers, including MCP-1, ICAM-1 and TGF-β, in the injured arteries.

Purinergic Receptors in Thrombosis and Inflammation

Under various pathological conditions, including thrombosis and inflammation, extracellular nucleotide levels may increase because of both active release and passive leakage from damaged or dying cells. Once in the extracellular compartment, nucleotides interact with plasma membrane receptors belonging to the P2 purinergic family, which are expressed by virtually all circulating blood cells and in most blood vessels. In this review, we focus on the specific role of the 3 platelet P2 receptors P2Y1, P2Y12, and P2X1 in hemostasis and arterial thrombosis. Beyond platelets, these 3 receptors, along with the P2Y2, P2Y6, and P2X7 receptors, constitute the main P2 receptors mediating the proinflammatory effects of nucleotides, which play important roles in various functions of circulating blood cells and cells of the vessel wall. Each of these P2 receptor subtypes specifically contributes to chronic or acute vascular inflammation and related diseases, such as atherosclerosis, restenosis, endotoxemia, and sepsis. The potential for therapeutic targeting of these P2 receptor subtypes is also discussed.

Endogenously generated omega-3 fatty acids attenuate vascular inflammation and neointimal hyperplasia by interaction with free fatty acid receptor 4 in mice

Background

Omega‐3 polyunsaturated fatty acids (ω3 PUFAs) suppress inflammation through activation of free fatty acid receptor 4 (FFAR4), but this pathway has not been explored in the context of cardiovascular disease. We aimed to elucidate the involvement of FFAR4 activation by ω3 PUFAs in the process of vascular inflammation and neointimal hyperplasia in mice.

Methods and Results

We used mice with disruption of FFAR4 (Ffar4^−/−), along with a strain that synthesizes high levels of ω3 PUFAs (fat‐1) and a group of crossed mice (Ffar4^−/−/fat‐1), to elucidate the role of FFAR4 in vascular dysfunction using acute and chronic thrombosis/vascular remodeling models. The presence of FFAR4 in vascular‐associated cells including perivascular adipocytes and macrophages, but not platelets, was demonstrated. ω3 PUFAs endogenously generated in fat‐1 mice (n=9), but not in compound Ffar4^−/−/fat‐1 mice (n=9), attenuated femoral arterial thrombosis induced by FeCl₃. Neointimal hyperplasia and vascular inflammation in the common carotid artery were significantly curtailed 4 weeks after FeCl₃ injury in fat‐1 mice (n=6). This included greater luminal diameter and enhanced blood flow, reduced intima:media ratio, and diminished macrophage infiltration in the vasculature and perivascular adipose tissue compared with control mice. These effects were attenuated in the Ffar4^−/−/fat‐1 mice.

Conclusions

These results indicate that ω3 PUFAs mitigate vascular inflammation, arterial thrombus formation, and neointimal hyperplasia by interaction with FFAR4 in mice. Moreover, the ω3 PUFA–FFAR4 pathway decreases inflammatory responses with dampened macrophage transmigration and infiltration.

Platelets are relevant mediators of renal injury induced by primary endothelial lesions

Several studies have suggested a prominent (pro)inflammatory and harmful role of platelets in renal disease, and newer work has also demonstrated platelet release of proangiogenic factors. In the present study, we investigated the role of platelets in a mouse model of selective endothelial cell injury using either platelet depletion or the pharmacological P2Y12 receptor blocker clopidogrel as an interventional strategy. The concanavalin A/anti-concanavalin A model was induced in left kidneys of C57bl/6J wild-type mice after initial platelet depletion or platelet-inhibiting therapy using clopidogrel. FACS analysis of glycoprotein IIb/IIIa/P-selectin double-positive platelets and platelet-derived microparticles demonstrated relevant platelet activation after the induction of selective endothelial injury in mice. Enhanced platelet activation persisted for 5 days after disease induction and was accompanied by increased amounts of circulating platelet-derived microparticles as potential mediators of a prolonged procoagulant state. By immunohistochemistry, we detected significantly reduced glomerular injury in platelet-depleted mice compared with control mice. In parallel, we also saw reduced endothelial loss and a consequently reduced repair response as indicated by diminished proliferative activity. The P2Y12 receptor blocker clopidogrel demonstrated efficacy in limiting platelet activation and subsequent endothelial injury in this mouse model of renal microvascular injury. In conclusion, platelets are relevant mediators of renal injury induced by primary endothelial lesions early on, as demonstrated by platelet depletion as well as platelet inhibition via the P2Y12 receptor. While strategies to prevent platelet-endothelial interactions have shown protective effects, the contribution of platelets during renal regeneration remains unknown.

ADP-induced bladder contractility is mediated by P2Y12 receptor and temporally regulated by ectonucleotidases and adenosine signaling

Purinergic signaling comprises one key pathway in modulating bladder smooth muscle (BSM) contractility, disorders of which become highly prevalent with aging. ADP was first observed to modulate BSM contractility >40 yr ago, yet the underlying molecular mechanism still remains unclear. Here, we demonstrate, using myography, that ADP and ADPβS dose-dependently induce mouse BSM contraction, and ADP-induced BSM contraction is blocked by a selective P2Y12 receptor (P2Y12R) antagonist, PSB 0739 (25 μM), but is unaffected by P2Y1 and P2Y13 receptor antagonists. P2Y12R in BSM exhibits distinct pharmacological properties that are different from P2Y12R in platelets. After an immediate contraction, prolonged exposure to ADP causes BSM to become refractory to further ADP-mediated contraction. However, in mice lacking ectonucleotidases Entpd1 (ATP→ADP→AMP) or Nt5e (AMP→adenosine), or by inhibiting adenosine signaling, the refractory response was altered, resulting in repeated BSM contractions in response to repeated ADP (0.1-1 mM) stimulation. Our data indicate that P2Y12R undergoes slow desensitization; ADP-P2Y12 signaling is tightly regulated by Entpd1/Nt5e activity and adenosine receptors; and ADP-adenosine signaling play an important role in modulating P2X-mediated BSM contraction. The identification of P2Y12R in BSM, and the current clinical availability of P2Y12R inhibitors, such as clopidogrel, offers potentially novel treatment strategies for bladder contractility disorders.

Detection of platelet microRNA expression in patients with diabetes mellitus with or without ischemic stroke

AIMS

The objective of this study was to investigate the role of plasma and platelet microRNAs in the occurrence of ischemic stroke in patients with diabetes mellitus.

METHODS

miR-223, miR-146a, miR-495, and miR-107 expression in the plasma and platelets, blood glucose concentration, and platelet activation rate were measured in patients with diabetes mellitus and ischemic stroke, diabetes mellitus only, ischemic stroke only, and healthy controls. Platelet activity was measured by flow cytometric measurement of P-selectin expression, while miRNA was measured by real-time PCR.

RESULTS

The expressions of platelet and plasma miR-223 and miR-146a were significantly downregulated in patients with ischemic stroke and diabetes mellitus or diabetes mellitus only, but not in patients with ischemic stroke only compared to healthy controls. The expressions of platelet and plasma miR-495 and miR-107 showed no significant differences among these four groups. The expression of platelet miR-223 and miR-146a significantly correlated with plasma miR-223 and miR-146a levels, blood glucose concentration, and platelet activation rate.

CONCLUSIONS

Hyperglycemia may downregulate the expressions of miR-223 and miR-146a, leading to subsequent platelet activation in patients with diabetes mellitus. Low platelet and plasma miR-223 and miR-146a expression is a risk factor for ischemic stroke in Chinese diabetes mellitus patients.

miRNAs and lncRNAs in vascular injury and remodeling

Vascular injury, remodeling, as well as angiogenesis, are the leading causes of coronary or cerebrovascular disease. The blood vessel functional imbalance trends to induce atherosclerosis, hypertension, and pulmonary arterial hypertension. As several genes have been identified to be dynamically regulated during vascular injury and remodeling, it is becoming widely accepted that several types of non-coding RNA, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), are involved in regulating the endothelial cell and vascular smooth muscle cell (VSMC) behaviors. Here, we review the progress of the extant studies on mechanistic, clinical and diagnostic implications of miRNAs and lncRNAs in vascular injury and remodeling, as well as angiogenesis, emphasizing the important roles of miRNAs and lncRNAs in vascular diseases. Furthermore, we introduce the interaction between miRNAs and lncRNAs, and highlight the mechanism through which lncRNAs are regulating the miRNA function. We envisage that continuous in-depth research of non-coding RNAs in vascular disease will have significant implications for the treatment of coronary or cerebrovascular diseases.

Inhibition of the plasma SCUBE1, a novel platelet adhesive protein, protects mice against thrombosis

OBJECTIVE

Signal peptide-CUB-EGF domain-containing protein 1 (SCUBE1), a secreted and surface-exposed glycoprotein on activated platelets, promotes platelet-platelet interaction and supports platelet-matrix adhesion. Its plasma level is a biomarker of platelet activation in acute thrombotic diseases. However, the exact roles of plasma SCUBE1 in vivo remain undefined.

APPROACH AND RESULTS

We generated new mutant (Δ) mice lacking the soluble but retaining the membrane-bound form of SCUBE1. Plasma SCUBE1-depleted Δ/Δ mice showed normal hematologic and coagulant features and expression of major platelet receptors, but Δ/Δ platelet-rich plasma showed impaired platelet aggregation in response to ADP and collagen treatment. The addition of purified recombinant SCUBE1 protein restored the aggregation of platelets in Δ/Δ platelet-rich plasma and further enhanced platelet aggregation in +/+ platelet-rich plasma. Plasma deficiency of SCUBE1 diminished arterial thrombosis in mice and protected against lethal thromboembolism induced by collagen-epinephrine treatment. Last, antibodies directed against the epidermal growth factor-like repeats of SCUBE1, which are involved in trans-homophilic protein-protein interactions, protected mice against fatal thromboembolism without causing bleeding in vivo.

CONCLUSIONS

We conclude that plasma SCUBE1 participates in platelet aggregation by bridging adjacent activated platelets in thrombosis. Blockade of soluble SCUBE1 might represent a novel antithrombotic strategy.

The effects of novel, bioresorbable scaffolds on coronary vascular pathophysiology

Percutaneous coronary intervention (PCI) has rapidly evolved over the past 30 years as technology has sought to improve clinical outcomes by addressing pathophysiologic complications arising from the intervention. Stents were designed to resolve the drawbacks of balloon angioplasty by providing radial support to prevent vessel recoil, by sealing coronary dissections, and by preventing abrupt vessel closure. The conceptualization of an ideal drug-eluting fully bioresorbable scaffold (BRS), whether metallic or polymeric, would theoretically address the adverse aspects of permanent metallic stents. In this review of the literature, we will discuss the impact these novel fully BRS platforms have on vascular pathophysiology following PCI.

Argatroban for preventing occlusion and restenosis after extracranial artery stenting

BACKGROUND/AIMS

Restenosis following extracranial artery stenting is a limitation that affects long-term outcomes. Effective and satisfying pharmacological strategies in preventing restenosis have not been established. This study aimed to evaluate whether argatroban, a direct thrombin inhibitor, could reduce the risk of in-stent restenosis after extracranial artery stenting.

METHODS

One hundred and fourteen patients hospitalized between August 2010 and August 2011 were enrolled. Patients were randomly assigned to argatroban (n = 58) and blank control groups (n = 56). The patients in the argatroban arm were treated with 10 mg of intravenous argatroban twice daily 2 days before and 3 days after the stenting procedures. Patients were followed for 12 months after the procedure. During follow-up, restenosis and target revascularization were analyzed. Recurrent cerebrovascular and cardiovascular events and deaths were also compared between the groups.

RESULTS

One patient in the stenting group withdrew immediately after the procedure due to unsuccessful stenting. Restenosis occurred in 4 patients (7.4%) in the argatroban group and in 11 patients (21.6%) in the control group during the 6- to 9-month angiographic follow-up period (p = 0.032). Nine months after the procedures, argatroban-treated patients had a trend towards a lower incidence of target revascularization compared with the controls (5.4 vs. 13.7%, p = 0.188). No major bleeding events or other adverse events occurred in the argatroban group.

CONCLUSION

This pilot clinical trial is the first that uses argatroban to prevent restenosis in ischemic cerebrovascular disease, and suggests that intravenous administration of argatroban is effective and safe in preventing restenosis after extracranial artery stenting. Larger randomized controlled clinical trials are warranted.

Vessel wall, not platelet, P2Y12 potentiates early atherogenesis

AIMS

Platelets have a fundamental role in atherothrombosis, but their role in early atherogenesis is unclear. The P2Y12 receptor is responsible for amplifying and sustaining platelet activation and P2Y12 inhibition is crucial in modulating the vessel wall response to injury. We therefore examined the role of platelet vs. vessel wall P2Y12 in early atherogenesis and considered the use of P2Y12 antagonists ticagrelor and clopidogrel in modulating this process.

METHODS AND RESULTS

ApoE(-/-) and ApoE(-/-)P2Y12 (-/-) male mice underwent bone marrow transplantation and were fed a western diet for 4 weeks before assessing atherosclerotic burden. Compared with ApoE(-/-) controls, platelet P2Y12 deficiency profoundly reduced platelet reactivity but had no effect on atheroma formation, whereas vessel wall P2Y12 deficiency significantly attenuated atheroma in the aortic sinus and brachiocephalic artery (both P < 0.001). ApoE(-/-) and ApoE(-/-)P2Y12 (-/-) male mice fed western diet plus either twice-daily doses of ticagrelor (100 mg/kg) or daily clopidogrel (20 mg/kg) for 4 weeks exhibited no significant reduction in atheroma compared with control mice fed mannitol. Attenuated P-selectin expression confirmed platelet P2Y12 inhibition in drug-treated mice.

CONCLUSIONS

Despite its major contribution to platelet reactivity, platelet P2Y12 has no effect on early atheroma formation, whereas vessel wall P2Y12 is important in this process. Ticagrelor and clopidogrel effectively reduced platelet reactivity but were unable to inhibit early atherogenesis, demonstrating that these P2Y12 inhibitors may not be effective in preventing early disease.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Lower mortality following pulmonary adverse events and sepsis with ticagrelor compared to clopidogrel in the PLATO study

In the PLATelet inhibition and patient Outcomes (PLATO) study of patients with acute coronary syndromes, ticagrelor reduced mortality compared to clopidogrel but the mechanisms for this mortality reduction remain uncertain. We analysed adverse events (AEs) consistent with either pulmonary infection or sepsis, and subsequent mortality, in 18,421 PLATO patients treated with ticagrelor or clopidogrel. AEs occurring within 7 days of last dose of study medication were defined as “on-treatment”. Serial measurements of blood leukocyte counts, C-reactive protein and interleukin-6 were performed. Fewer on-treatment pulmonary AEs occurred in the ticagrelor compared to the clopidogrel group (275 vs. 331 respectively; p = 0.019), with fewer deaths following these AEs (33 vs. 71; p < 0.001), particularly in those who remained on study medication three days after AE onset (10 vs. 43; p < 0.001). There were fewer deaths attributed to sepsis in the ticagrelor group (7 vs. 23; p = 0.003). Leukocyte counts were lower in the clopidogrel group during treatment (p < 0.0001 at 1, 3 and 6 months) but not at 1 month post-discontinuation. C-reactive protein increased more at discharge in the ticagrelor group (28.0 ± 38.0 vs. 26.1 ± 36.6 mg/l; p < 0.001) and interleukin-6 remained higher during the first month of treatment with ticagrelor. We conclude that the mortality risk following pulmonary AEs and sepsis in acute coronary syndrome patients appears to be lower during ticagrelor compared to clopidogrel therapy. Further work should assess whether ticagrelor and clopidogrel have differential effects on immune signalling.

A novel model of atherosclerosis in rabbits using injury to arterial walls induced by ferric chloride as evaluated by optical coherence tomography as well as intravascular ultrasound and histology

This study aim was to develop a new model of atherosclerosis by FeCl₃-induced injury to right common carotid arteries (CCAs) of rabbits. Right CCAs were induced in male New Zealand White rabbits (n = 15) by combination of a cholesterol-rich diet and FeCl₃-induced injury to arterial walls. The right and left CCAs were evaluated by histology and in vivo intravascular ultrasound (IVUS) and optical coherence tomography (OCT) examinations of 24 hours (n = 3), 8 weeks (n = 6), and 12 weeks (n = 6) after injury. Each right CCA of the rabbits showed extensive white-yellow plaques. At eight and 12 weeks after injury, IVUS, OCT, and histological findings demonstrated that the right CCAs had evident eccentric plaques. Six plaques (50%) with evident positive remodeling were observed. Marked progression was clearly observed in the same plaque at 12 weeks after injury when it underwent repeat OCT and IVUS. We demonstrated, for the first time, a novel model of atherosclerosis induced by FeCl₃. The model is simple, fast, inexpensive, and reproducible and has a high success rate. The eccentric plaques and remodeling of plaques were common in this model. We successfully carried out IVUS and OCT examinations twice in the same lesion within a relatively long period of time.

P2Y(12) receptors in platelets and other hematopoietic and non-hematopoietic cells

The P2Y(12) receptor is a Gi-coupled ADP receptor first described in blood platelets where it plays a central role in the complex processes of activation and aggregation. Platelet granules store important amounts of ADP which are released upon stimulation by interaction of platelets with the damaged vessel wall. Therefore, the P2Y(12) receptor is a key player in primary hemostasis and in arterial thrombosis and is an established target of antithrombotic drugs like the thienopyridine compounds ticlopidine, clopidogrel, and prasugrel or the direct, reversible antagonists ticagrelor and cangrelor. Beyond the platelet physiology and pharmacology, recent studies have revealed the expression of the P2Y(12) receptor in other hematopoietic cells including leukocyte subtypes and microglia in the central nervous system as well as in vascular smooth muscle cells. These studies indicate putative roles of the P2Y(12) receptor in inflammatory states and diseases of the brain, lung, and blood vessels. The selective role of P2Y(12) among other P2 receptors as well as the possible impact of P2Y(12) targeting drugs in these processes remain to be evaluated.

Impact of platelet reactivity to adenosine diphosphate before implantation of drug-eluting stents on subsequent adverse cardiac events in patients with stable angina

BACKGROUND

Diverse pharmacological effects of anti-platelet thienopyridines due to individual differences in metabolism have been reported. However, an association between on-treatment platelet reactivity and adverse ischemic events after drug-eluting stent (DES) implantation in Japanese patients has not been fully elucidated.

METHODS AND RESULTS

A total of 450 consecutive patients on dual anti-platelet therapy (aspirin and ticlopidine) with stable angina who underwent DES implantation were enrolled. Adenosine diphosphate (ADP)-induced platelet aggregation was measured before DES implantation using the screen filtration pressure method. The ADP concentration necessary for 50% aggregation was designated as the platelet aggregation threshold index (PATI). A composite primary endpoint of cardiac death, myocardial infarction, target lesion revascularization (TLR), and stent thrombosis occurring within 1 year after stenting, was evaluated. A PATI value <4.8 µmol/L was defined as high on-treatment reactivity to ADP. The composite primary endpoint occurred in 55 patients (12.2%) in the 1-year-period after DES implantation, and the prevalence was 19.0% and 5.1% in groups with high and low on-treatment reactivity to ADP, respectively, showing a significantly higher prevalence in the high reactivity group (P<0.001). The main event was TLR (18.1% vs. 5.1%, P<0.001).

CONCLUSIONS

These data suggested that high on-treatment platelet reactivity to ADP and subsequent occurrence of adverse ischemic events (particularly TLR) were correlated in patients with stable angina who underwent DES implantation.

CD40 is essential in the upregulation of TRAF proteins and NF-kappaB-dependent proinflammatory gene expression after arterial injury

Despite extensive investigations, restenosis, which is characterized primarily by neointima formation, remains an unsolved clinical problem after vascular interventions. A recent study has shown that CD40 signaling through TNF receptor associated factor 6 (TRAF6) plays a key role in neointima formation after carotid artery injury; however, underlying mechanisms are not clearly elucidated. Because neointima formation may vary significantly depending on the type of injury, we first assessed the effect of CD40 deficiency on neointima formation in 2 injury models, carotid artery ligation and femoral artery denudation injury. Compared with wild-type mice, CD40 deficiency significantly reduced neointima formation and lumen stenosis in two different models. Further, we investigated the mechanism by which CD40 signaling affects neointima formation after arterial injury. In wild-type mice, the expression levels of CD40, several TRAF proteins, including TRAF1, TRAF2, TRAF3, TRAF5, and TRAF6, as well as total NF-kB p65 and phospho-NF-kB p65, in the carotid artery were markedly upregulated within 3-7 days after carotid ligation. Deficiency of CD40 abolished the injury-induced upregulation of TRAFs including TRAF6 and NF-kB-p65 in the injured vessel wall. Further, CD40(-/-) mice showed a significant decrease in the recruitment of neutrophils (at 3, 7d) and macrophages (at 7, 21d) into injured artery; this effect was most likely attributed to inhibition of NF-kB activation and marked downregulation of NF-kB-related gene expression, including cytokines (TNFα, IL-1β, IL-6), chemokines (MCP-1), and adhesion molecules (ICAM-1, VCAM-1). Moreover, neutrophil recruitment in a model of thioglycollate-induced peritonitis is impaired in CD40-deficient mice. In vitro data revealed that CD40 deficiency blocked CD40L-induced NF-kB p65 nuclear translocation in leukocytes. Altogether, our data identified for the first time that CD40 is essential in the upregulation of TRAF6, NF-kB activation, and NF-kB-dependent proinflammatory genes in vivo. Our findings firmly established the role for CD40 in neointima formation in 2 distinct injury models.

P2 receptors and platelet function

Following vessel wall injury, platelets adhere to the exposed subendothelium, become activated and release mediators such as TXA(2) and nucleotides stored at very high concentration in the so-called dense granules. Released nucleotides and other soluble agents act in a positive feedback mechanism to cause further platelet activation and amplify platelet responses induced by agents such as thrombin or collagen. Adenine nucleotides act on platelets through three distinct P2 receptors: two are G protein-coupled ADP receptors, namely the P2Y(1) and P2Y(12) receptor subtypes, while the P2X(1) receptor ligand-gated cation channel is activated by ATP. The P2Y(1) receptor initiates platelet aggregation but is not sufficient for a full platelet aggregation in response to ADP, while the P2Y(12) receptor is responsible for completion of the aggregation to ADP. The latter receptor, the molecular target of the antithrombotic drugs clopidogrel, prasugrel and ticagrelor, is responsible for most of the potentiating effects of ADP when platelets are stimulated by agents such as thrombin, collagen or immune complexes. The P2X(1) receptor is involved in platelet shape change and in activation by collagen under shear conditions. Each of these receptors is coupled to specific signal transduction pathways in response to ADP or ATP and is differentially involved in all the sequential events involved in platelet function and haemostasis. As such, they represent potential targets for antithrombotic drugs.

Antiplatelet therapy and vascular disease: an update

Atherosclerosis is a diffuse, systemic disorder of the large and medium-sized arterial vessels, affecting the coronary, cerebral and peripheral circulation. Chronic inflammatory processes are the central pathophysiological mechanism largely driven by lipid accumulation, and provide the substrate for occlusive thrombus formation. The clinical sequelae of acute arterial thrombosis, heart attack and stroke, are the most common causes of morbidity and mortality in the industrialized world. Such acute events are characterized by rupture or erosion of the atherosclerotic plaque leading to acute thrombosis. The atherosclerotic process and associated thrombotic complications are collectively termed atherothrombosis. The platelet is a pivotal mediator of various endothelial, immune, thrombotic and inflammatory responses and therefore a key player in the initiation and progression of atherothrombosis. A robust evidence base supports the clear clinical benefits of antiplatelet agents in the primary and secondary therapy of atherothrombotic disorders. Percutaneous coronary and peripheral interventions have an established central role in the management of atherothrombotic disease and demand a greater understanding of platelet biology. In this article, we provide a clinically orientated overview of the pathophysiology of arterial thrombosis and the evidence supporting the use of the various established antiplatelet therapies, and discuss new and future agents.

Contribution of the P2Y12 receptor-mediated pathway to platelet hyperreactivity in hypercholesterolemia

BACKGROUND

In hypercholesterolemia, platelets demonstrate increased reactivity and promote the development of cardiovascular disease.

OBJECTIVE

This study was carried out to investigate the contribution of the ADP receptor P2Y12-mediated pathway to platelet hyperreactivity due to hypercholesterolemia.

METHODS

Low-density lipoprotein receptor-deficient mice and C57Bl/6 wild-type mice were fed on normal chow and high-fat (Western or Paigen) diets for 8 weeks to generate differently elevated cholesterol levels. P2Y12 receptor-induced functional responses via G(i) signaling were studied ex vivo when washed murine platelets were activated by 2MeSADP and PAR4 agonist AYPGKF in the presence and absence of indomethacin. Platelet aggregation and secretion, α(IIb)β(3) receptor activation and the phosphorylation of extracellular signal-regulated protein kinase (ERK) and Akt were analyzed.

RESULTS

Plasma cholesterol levels ranged from 69 ± 10 to 1011 ± 185 mg dL(-1) depending on diet in mice with different genotypes. Agonist-dependent aggregation, dense and α-granule secretion and JON/A binding were gradually and significantly (P < 0.05) augmented at low agonist concentration in correlation with the increasing plasma cholesterol levels, even if elevated thromboxane generation was blocked. These functional responses were induced via increased levels of G(i) -mediated ERK and Akt phosphorylation in hypercholesterolemic mice vs. normocholesterolemic animals. In addition, blocking of the P2Y12 receptor by AR-C69931MX (Cangrelor) resulted in strongly reduced platelet aggregation in mice with elevated cholesterol levels compared with normocholesterolemic controls.

CONCLUSIONS

These data revealed that the P2Y12 receptor pathway was substantially involved in platelet hyperreactivity associated with mild and severe hypercholesterolemia.

Regulation of functionally active P2Y12 ADP receptors by thrombin in human smooth muscle cells and the presence of P2Y12 in carotid artery lesions

OBJECTIVE

The platelet P2Y12 ADP receptor is a well-known target of thienopyridine-type antiplatelet drugs. This study is the first to describe increased transcriptional expression of a functionally active P2Y12 in response to thrombin in human vascular smooth muscle cells (SMC).

METHODS AND RESULTS

On exposure to thrombin, P2Y12 mRNA was transiently increased, whereas total protein and cell surface expression of P2Y12 were markedly increased within 6 hours and remained elevated over 24 hours. This effect was mediated by activation of nuclear factor κB. Preincubation with thrombin significantly enhanced the efficacy of the P2Y receptor agonist 2-methylthio-ADP to induce interleukin 6 expression and SMC mitogenesis. Effects induced by 2-methylthio-ADP were prevented by RNA interference-mediated knockdown of P2Y12 and a selective P2Y12-antagonist R-138727, the active metabolite of prasugrel. In addition, positive P2Y12 immunostaining was shown in SMC of human carotid artery plaques and was found to colocalize with tissue factor, the rate-limiting factor of thrombin formation in vivo.

CONCLUSIONS

These data suggest that the P2Y12 receptor not only is central to ADP-induced platelet activation but also may mediate platelet-independent responses, specifically under conditions of enhanced thrombin formation, such as local vessel injury and atherosclerotic plaque rupture.

Ticagrelor effectively and reversibly blocks murine platelet P2Y12-mediated thrombosis and demonstrates a requirement for sustained P2Y12 inhibition to prevent subsequent neointima

OBJECTIVE

Our goal was to study the effects of ticagrelor on murine platelet function and thrombosis and characterize the time course of P2Y(12) inhibition required to inhibit neointima formation following vascular injury.

METHODS AND RESULTS

Mice were treated with ticagrelor or vehicle. Platelet aggregation and P-selectin expression were assessed over time, and thrombus formation was assessed in laser-injured cremasteric arterioles of P2Y(12)+/+ and P2Y(12)-/- mice. Neointima formation in FeCl(3)-injured carotid artery was assessed in C57BL/6 mice treated with different regimens of ticagrelor. Ticagrelor inhibited platelet aggregation and P-selectin expression in a dose-dependent, reversible manner. Ticagrelor inhibited thrombus formation to the same extent as seen in P2Y(12)-/- mice. Neointima formation was markedly reduced in mice treated with ticagrelor before and 4 hours after injury (neointima area: control, 39 921±22 749 μm(2), versus ticagrelor, 3705±2600 μm(2); P<0.01), whereas administration of ticagrelor either before injury only or from 4 hours postinjury was ineffective.

CONCLUSIONS

Ticagrelor effectively and reversibly inhibits P2Y(12)-mediated platelet function and thrombosis in mice. P2Y(12) inhibition is required both at the time of and after injury to effectively inhibit neointima formation. Additional studies are warranted to evaluate the role of P2Y(12) inhibition in preventing restenosis.