Local Platelet Activation Research Articles

Cardiomyocyte-derived C-type natriuretic peptide diminishes myocardial ischaemic injury by promoting revascularisation and limiting fibrotic burden

BackgroundC-type natriuretic peptide (CNP) is a significant player in the maintenance of cardiac and vascular homeostasis regulating local blood flow, platelet and leukocyte activation, heart structure and function, angiogenesis and metabolic balance. Since such processes are perturbed in myocardial infarction (MI), we explored the role of cardiomyocyte-derived CNP, and pharmacological administration of the peptide, in offsetting the pathological consequences of MI. MethodsWild type (WT) and cardiomyocyte-restricted CNP null (cmCNP-/-) mice were subjected to left anterior descending coronary artery (LADCA) ligation and acute effects on infarct size and longer-term outcomes of cardiac repair explored. Heart structure and function were assessed by combined echocardiographic and molecular analyses. Pharmacological administration of CNP (0.2 mg/kg/day; s.c.) was utilized to assess therapeutic potential. ResultsCompared to WT littermates, cmCNP-/- mice had a modestly increased infarct size following LADCA ligation but without significant deterioration of cardiac structural and functional indices. However, cmCNP-/- animals exhibited overtly worse heart morphology and contractility 6 weeks following MI, with particularly deleterious reductions in left ventricular ejection fraction, dilatation, fibrosis and revascularization. This phenotype was largely recapitulated in animals with global deletion of natriuretic peptide receptor (NPR)-C (NPR-C-/-). Pharmacological administration of CNP rescued the deleterious pathology in WT and cmCNP-/-, but not NPR-C-/-, animals. Conclusions and implicationsCardiomyocytes synthesize and release CNP as an intrinsic protective mechanism in response to MI that reduces cardiac structural and functional deficits; these salutary actions are primarily NPR-C-dependent. Pharmacological targeting of CNP may represent a new therapeutic option for MI.

Qihuang Zhuyu formula alleviates coronary microthrombosis by inhibiting PI3K/Akt/αIIbβ3-mediated platelet activation

BackgroundCoronary microembolism (CME) is commonly seen in the peri-procedural period of Percutaneous Coronary Intervention (PCI), where local platelet activation and endothelial cell inflammation crosstalk may lead to micro thrombus erosion and rupture, with serious consequences. Qihuang Zhuyu Formula (QHZYF) is a Chinese herbal compound with high efficacy against coronary artery disease, but its antiplatelet mechanism is unclear. Hypothesis/PurposeThis study aimed to elucidate the effects and mechanisms of QHZYF on sodium laurate-induced CME using network pharmacology and in vitro and in vivo experiments. MethodsWe employed high-performance liquid chromatography mass spectrometry to identify the main components of QHZYF. Network pharmacology analysis, molecular docking and surface plasmon resonance (SPR) were utilized to predict the primary active components, potential therapeutic targets, and intervention pathways mediating the effects of QHZYF on platelet activation. Next, we pretreated a sodium laurate-induced minimally invasive CME rat model with QHZYF. In vivo experiments were performed to examine cardiac function in rats, to locate coronary arteries on heart sections to observe internal microthrombi, to extract rat Platelet-rich plasma (PRP) for adhesion assays and CD62p and PAC-1 (ITGB3/ITGA2B) flow assays, and to measure platelet-associated protein expression in PRP. In vitro clot retraction and Co-culture of HUVECs with PRP were performed and the gene pathway was validated through flow cytometry and immunofluorescence. ResultsCombining UPLC-Q-TOF/MS technology and database mining, 78 compounds were finally screened as the putative and representative compounds of QHZYF, with 75 crossover genes associated with CME. QHZYF prevents CME mainly by regulating key pathways of the inflammation and platelets, including Lipid and atherosclerosis, Fluid shear stress, platelet activation, and PI3K-Akt signaling pathways. Five molecules including Calyson, Oroxin A, Protosappanin A,Kaempferol and Geniposide were screened and subjected to molecular docking and SPR validation in combination with Lipinski rules (Rule of 5, Ro5). In vivo experiments showed that QHZYF not only improved myocardial injury but also inhibited formation of coronary microthrombi. QHZYF inhibited platelet activation by downregulating expression of CD62p receptor and platelet membrane protein αIIbβ3 and reduced the release of von Willebrand Factor (vWF), Ca2+ particles and inflammatory factor IL-6. Further analysis revealed that QHZYF inhibited the activation of integrin αIIbβ3, via modulating the PI3K/Akt pathways. In in vitro experiments, QHZYF independently inhibited platelet clot retraction. Upon LPS induction, the activation of platelet membrane protein ITGB3 was inhibited via the PI3K/Akt pathway, revealing an important mechanism for attenuating coronary microthrombosis. We performed mechanistic validation using PI3K inhibitor LY294002 and Akt inhibitor MK-2206 to show that QHZYF inhibited platelet membrane protein activation and inflammation to improved coronary microvessel embolism by regulating PI3K/Akt/αIIbβ3 pathways, mainly by inhibiting PI3K and Akt phosphorylation. ConclusionQHZYF interferes with coronary microthrombosis through inhibition of platelet adhesion, activation and inflammatory crosstalk, thus has potential in clinical anti-platelet applications. Calyson, Oroxin A, Protosappanin A, Kaempferol and Geniposide may be the major active ingredient groups of QHZYF that alleviate coronary microthrombosis.

Neutrophil-Platelet Interactions as Novel Treatment Targets in Cardiovascular Disease.

Neutrophils and platelets are among the most abundant cell types in peripheral blood and characterized by high plasticity and a readily available reservoir of surface proteins and secretable granule contents. Receptor-mediated activation and granule release predispose both cell types for rapid responses to various stimuli. While neutrophils provide the first line of defense to microbial infections and platelets are known for their aggregatory functions in hemostasis and thrombosis, research of the past decade has highlighted that both cell types jointly shape local and systemic immune responses and clot formation alike. Concomitant activation of neutrophils and platelets has been observed in a variety of cardiovascular diseases, including arterial and venous thrombosis, atherosclerosis as well as myocardial infarction and ischemia-reperfusion injury. In this review, we describe the mechanisms by which neutrophils and platelets interact physically, how release of granule contents and soluble molecules by either cell type affects the other and how this mutual activation supports the efficacy of immune responses. We go on to describe how activated platelets contribute to host defense by triggering neutrophil extracellular trap (NET) formation in a process termed immunothrombosis, which in turn promotes local platelet activation and coagulation. Further, we review current evidence of hazardous overactivation of either cell type and their respective role in cardiovascular disease, with a focus on thrombosis, myocardial infarction and ischemia-reperfusion injury, and describe how neutrophils and platelets shape thromboinflammation in COVID-19. Finally, we provide an overview of therapeutic approaches targeting neutrophil-platelet interactions as novel treatment strategy in cardiovascular disease.

Platelet Activation In Situ in Breasts at High Risk of Cancer: Relationship with Mammographic Density and Estradiol.

High mammographic density in postmenopausal women is an independent risk factor for breast cancer by undetermined mechanisms. No preventive therapy for this risk group is available. Activated platelets release growth factors that modulate the microenvironment into a protumorigenic state. Estrogens may affect the risk of breast cancer and platelet function. Whether platelets are activated in situ in breast cancer or in normal breast tissue at high risk of breast cancer and the association to estradiol remains elusive. To investigate whether platelets are activated in situ in breast cancers and in dense breast tissue of postmenopausal women and explore correlations between estradiol, released platelet factors, and inflammatory proteins. Sampling of in vivo proteins was performed using microdialysis in a total of 71 women: 10 with breast cancer, 42 healthy postmenopausal women with different breast densities, and 19 premenopausal women. Our data demonstrate increased levels of coagulation factors in dense breast tissue similar to that found in breast cancers, indicating excessive platelet activation. Premenopausal breasts exhibited similar levels of coagulation factors as postmenopausal dense breasts. Out of 13 coagulations factors that were upregulated in dense breasts, 5 exhibited significant correlations with estradiol, both locally in the breast and systemically. In breast tissue, positive correlations between coagulation factors and key inflammatory proteins and matrix metalloproteinases were detected. Breast density, not estradiol, is the major determinant of local platelet activation. Inactivation of platelets may be a therapeutic strategy for cancer prevention in postmenopausal women with dense breasts.

Platelet Volume Indices in Patients with Acute Coronary Syndrome

Background & Aims: Acute coronary syndrome is one of the leading causes of morbidity and mortality in the world and platelet hyperactivity with local platelet activation plays a crucial role in its genesis. As there is discrepancy regarding the significance of deranged platelet parameters, we aimed to study the role of platelet volume indices in the spectrum of coronary artery syndrome and to correlate them clinically.
 Study Design: The study was conducted by collecting the data of patients with Myocardial infarction from the Cardiac care unit registry along with their clinical history and investigations. Stable coronary artery cases were collected from the Catheterization Lab and compared with Age and Sex matched controls. All CBCs of the above groups were processed by a 5-part counter and the data generated was transferred to a master chart for statistical analysis.
 Place and Duration of study: The study was conducted in the Central Laboratory & Department of Pathology at D.Y. Patil Hospital, Navi Mumbai, India in collaboration with the Cardiac Care Unit and Catheterisation Lab of the hospital for a period of two years.
 Methods: A total of 122 cases were studied and grouped into 5 groups according to presentation and the platelet volume indices of these were compared with 38 matched controls and statistically analysed.
 Results: Mean Platelet Volume and Platelet Distribution Width of patients with ST elevation Myocardial Infarction (STEMI) and Non ST elevation Myocardial Infarction(NSTEMI) were increased marginally in number when compared to Stable Coronary Artery Disease(SCAD) and Control group, however this was not statistically significant. Platelet Large Cell Ratio (PLCR) was significantly raised in STEMI cases only (P = 0.09), so it may prove to be a better marker for the disease (P = 0.09). Platelet counts in various groups when compared with controls gave inconsistent results i.e SCAD vs Control significantly decreased (P = 0.07) and STEMI vs Control significantly increased (P = 0.01).
 Conclusion: The platelet volume indices in suspected acute coronary syndrome cases showed various changes, but present data failed to be diagnostically significant. However this data may later help to characterise further relationship between Acute coronary syndrome and platelet function in subsequent studies.

Non-physiologic closing of bi-leaflet mechanical heart prostheses requires a new tri-leaflet valve design

Mechanical heart valve prostheses are based on older designs without changes during the last 40 years. Today, there is an unmet need for less thrombogenic mechanical prostheses. Analysis of the relationship between flow characteristics and thromboembolic complications is possible using numerical and biomolecular flow studies that have shown that the reverse rather than the forward flow is responsible for local platelet activation and thrombosis. After peak flow, leaflets experience flow deceleration and the leaflets are still widely open when the flow becomes zero. The closure of the valve starts with the onset of reverse flow. Therefore, the valve closes extremely fast with most of the leaflet traveling angle occurring in <10 ms with excessively high reverse flow velocities. The pivoting spaces, so-called “Hot Spots” should be eliminated to prevent pathologic shear stress that result in thrombosis. A novel tri-leaflet valve combines favorable hemodynamics with the durability of mechanical heart valve. This valve closes within 60 ms, much slower than bi-leaflet valves and similar to the closing mode of a tissue valve. Micro-particle image velocimetry did not show critical regions of flow stagnation and zones of excessive shear in the pivoting region suggesting low potential for thrombogenic events that should allow to avoid long-term anticoagulation.

Platelet Activation Is Limited during Transcatheter Aortic Valve Implantation in Patients on Aspirin Monotherapy and without per Procedural Clinical Complications.

Transcatheter aortic valve implantation (TAVI) is an established treatment option for symptomatic patients with severe aortic valve stenosis (AS). During and early after the procedure, both ischemic events (predominantly stroke) and bleedings remain prevalent. The optimal antithrombotic regimen is still debated. Single- versus dual-antiplatelet therapy is associated with a lower rate of severe bleeding, without difference in thrombotic complications. Although platelets have been empirically targeted, little is known on their contribution to these events primarily related to embolization of thrombotic material and tissue-derived debris from the wounded aortic valve and large vessels. The objective of this study was to assess local platelet activation in blood sampled in the ascending aorta immediately before and within minutes postimplantation. A series of 18 patients with AS on monotherapy with aspirin successfully underwent TAVI with the self-expandable Medtronic CoreValve by transfemoral route. No clinical thrombotic complication occurred at 30-day follow-up. Compared with patients with stable coronary artery disease unscathed of AS and similarly treated by low-dose aspirin, AS patients displayed a chronic state of platelet activation before TAVI, assessed in venous blood using various biomarkers. However, per procedure, in aortic blood, no change occurred between the two time points in the plasma levels of serotonin or 12-lipoxgenase products, or membrane exposure of granule markers CD62-P and CD63. Our results suggest that local acute platelet activation is limited during TAVI on monotherapy with aspirin.

Interfering with local fibrotic platelet activation significantly inhibits fibrosis in multiple animal models: suggestions of the importance of the platelet-wound healing axis for fibrosis

Interfering with local fibrotic platelet activation significantly inhibits fibrosis in multiple animal models: suggestions of the importance of the platelet-wound healing axis for fibrosis

Development of Synthetic Platelet‐Activating Hydrogel Matrices to Induce Local Hemostasis

Several hemostatic strategies rely on the use of blood components such as fibrinogen and thrombin, which suffer from high cost and short shelf‐life. Here, a cost‐effective synthetic biomaterial is developed for rapid local hemostasis. Instead of using thrombin, thrombin‐receptor‐agonist‐peptide‐6 (TRAP6) is covalently engineered in polyvinyl alcohol (PVA) hydrogels. Soluble PVA‐TRAP6 is first prepared by covalent attachment of cysteine‐containing TRAP6 onto the backbone of PVA‐norbornenes (PVA‐NB) through photoconjugation. Cytotoxicity studies using C2C12 myoblasts indicate that PVA‐NB and PVA‐TRAP6 are nontoxic. Thromboelastography reveals that hemostatic activity of TRAP6 is retained in conjugated form, which is comparable to free TRAP6 solutions with equal concentrations. A 0.1% PVA‐TRAP6 solution can shorten the clotting time (CT) to ca. 45% of the physiological CT. High platelet‐activating efficiency is further confirmed by platelet aggregation assay and flow cytometry (FACS). For potential clinical applications, TRAP6‐presenting hydrogel particulates (PVA‐TRAP6‐P) are developed for local platelet activation and hemostasis. PVA‐TRAP6‐P is prepared by biofunctionalization of photopolymerized PVA‐NB hydrogel particulates (PVA‐NB‐P) with TRAP6. It is demonstrated that PVA‐TRAP6‐P can effectively shorten the CT to ca. 50%. FACS shows that PVA‐TRAP6‐P can activate platelets to a comparable extent as soluble TRAP6 control. Altogether, PVA‐TRAP6‐P represents a promising class of biomaterials for safe hemostasis and wound healing.

Systemic Platelet Dysfunction Is the Result of Local Dysregulated Coagulation and Platelet Activation in the Brain in a Rat Model of Isolated Traumatic Brain Injury

Coagulopathy after severe traumatic brain injury (TBI) has been extensively reported. Clinical studies have identified a strong relationship between diminished platelet-rich thrombus formation, responsiveness to adenosine diphosphate agonism, and severity of TBI. The mechanisms that lead to platelet dysfunction in the acute response to TBI are poorly understood. The development of a rodent model of TBI that mimics the coagulopathy observed clinically has recently been reported. Using immunohistochemical techniques and thromboelastography platelet mapping, the current study demonstrated that the expression of coagulation (tissue factor and fibrin) and platelet activation (P-selectin) markers in the injured brain paralleled the alteration in systemic platelet responsiveness to the agonists, adenosine diphosphate and arachodonic acid. Results of this study demonstrate that local procoagulant changes in the injured brain have profound effects on systemic platelet function.

Evaluation of the procoagulant potential of endothelial microparticles CD144 (VE-Cadherin) positive in coronary syndrome patients

Background Apoptotic microparticles are responsible for almost all tissue factor activity of the plaque lipid core. We hypothesized that elevated levels of procoagulant microparticles could also circulate in the peripheral blood of patients with recent clinical signs of plaque disruption and thrombosis. The present study included 60 acute coronary syndrome (ACS) adult patients. Group I included 30 patients with diabetes mellitus who presented with ACS. Group II included 30 nondiabetic patients complaining of ACS and 25 healthy individuals as controls. ACS patients were further classified according to laboratory and radiological findings (troponin test and ECG) as follows: group A included 16 ST-segment elevation myocardial infarction (STEMI) patients, group B included 19 non-ST-segment elevation myocardial infarction (NSTEMI) patients, and group C included 25 patients with unstable angina. Traditional laboratory investigations and special laboratory assessments of CD144 fluorescein isothiocyanate by flow cytometry were performed.Results The present study found highly elevated CD144 percentages in diabetic ACS patients compared with healthy controls (P≤0.0001(, and highly elevated creatine kinase-MB (CK-MB), fasting sugar, total cholesterol, triglyceride, HDL, and LDL (P = 0.0001, 0.0001, 0.0002, 0.0002, 0.0001, and 0.0001, respectively). In contrast, nondiabetic ACS patients had significantly elevated CD144, CK-MB, total cholesterol, triglyceride, HDL, and LDL (P = 0.0001, 0.0001, 0.0001, 0.0021, 0.0001, and 0.0021, respectively), whereas fasting sugar and HbA1c did not change significantly. However, the patients in group B (NSTEMI) had significantly elevated CD144% in comparison with patients with unstable angina (group C) ( P = 0.05), but patients with group A (STEMI) had significantly elevated CK-MB compared with patients with unstable angina (group C) (P = 0.02).Conclusion The high levels of circulating microparticles of endothelial origin are increased in diabetic patients with coronary artery disease, suggesting an important role for endothelial injury in the prediction of ACS. Hyperglycemia in ACS is associated with enhanced local thrombin generation and platelet activation, as well as unfavorably altered clot features in patients with and without a previous history of diabetes.

A brief review of the past and future of platelet P2Y12 antagonist

ADP plays a pivotal role in localized platelet activation and recruitment, and, with that, in the maintenance of thrombus integrity, making it a suitable target for the control of intravascular thrombosis. The limited distribution of one of its receptors, the P2Y12 receptor, primarily to platelets makes it an especially attractive pharmacologic target. For the last several decades the thienopyridine family of P2Y12 antagonists have provided the vast majority of clinical data confirming the clinical benefit of selective P2Y12 inhibition. Recently, new thienopyridine plus nonthienopyridine P2Y12 antagonists have become available or are being studied that will further improve our treatment of patients with coronary disease.

Management of peripheral arterial interventions with mono or dual antiplatelet therapy—the MIRROR study: a randomised and double-blinded clinical trial

To investigate the influence of dual antiplatelet therapy vs. aspirin alone on local platelet activation and clinical endpoints in patients with PAD treated with endovascular therapy. Patients received either 500 mg aspirin and 300 mg clopidogrel before intervention followed by a daily dose of 100 mg aspirin and 75 mg clopidogrel for 6 months, or the same doses of aspirin plus placebo instead of clopidogrel. Primary endpoints were local concentrations of platelet activation markers β-thromboglobulin and CD40L, and the rate of patient's resistant to clopidogrel. Secondary endpoints included the clinical development 6 months after the intervention. Eighty patients, 40 in each group, were enrolled. The median peri-interventional concentration of β-TG was 224.5 vs. 365.5 (P = 0.03) in the clopidogrel and placebo group. The concentration of CD40L was 127 and 206.5 (P = 0.05). Thirty per cent of patients who had received clopidogrel were resistant. Two clopidogrel and eight placebo patients required TLR (P = 0.04). The clopidogrel patients who needed revascularisation were both resistant to clopidogrel. Minor bleeding complications occurred in one clopidogrel and two placebo patients. Dual antiplatetet therapy reduces peri-interventional platelet activation and improves functional outcome without higher bleeding complications. An individual tailored dual antiplatelet therapy seems desirable for endovascularly treated patients with PAD.

Experimental thermal lesions induce beta-thromboglobulin release from activated platelets

Time courses of beta-thromboglobulin release, and protein extravasation after thermal inflammation of human skin was compared to neurogenic inflammation induced by histamine iontophoresis. Beta-TG and protein levels were sampled by intradermal microdialysis. Three microdialysis membranes were inserted at each stimulation site. The collected samples were measured photometrically for protein by the Coomassie blue method and for beta-TG by ELISA. Heat stimuli of 40 °C and 47 °C, and histamine iontophoresis were inflicted directly above the membranes. In vitro recovery rates of beta-TG and bovine albumin were measured using a latex chamber. Recovery rates at a continuous flow rate of 3 μl/min for bovine albumin ranged between 20% and 35%; those for beta-TG ranged between 14% and 17%. Heat stimulation at 40 °C showed a slight but insignificant increase of beta-TG during the stimulation period. Temperatures of 47 °C produced a significant, long-lasting increase of beta-TG, whereas histamine iontophoresis did not. Protein extravasation corresponded with beta-TG release; a long-lasting significant increase during and after the burn lesion, and only an initial increase of protein extravasation during the 40 °C heat stimulus. Long lasting heat stimuli to the skin induced beta-TG release from platelets, whereas histamine iontophoresis although provoking protein extravasation and neurogenic flare, did not. Using microdialysis techniques we detected beta-TG release during an inflammatory response. We conclude that local platelet activation is induced by the heating stimulus. Platelet mediators, such as beta-TG might contribute to the subsequent inflammatory process which is also characterized by mechanical and heat hyperalgesia.

Combination Antithrombotic Therapies

Atherothrombosis is the major pathophysiological process responsible for the occurrence of severe ischemic events in patients with cardiovascular diseases. In the United States, atherothrombosis strongly influenced mortality in 2004: One in 2.8 deaths was due to CVD, 1 in 5 deaths to coronary heart disease, and 1 in 17 deaths to stroke.1 Because cardiovascular disease is a progressive and systemic disease, long-term antithrombotic therapies that effectively target the entire arterial vasculature and modulate the key components responsible for thrombus generation are essential to improve patient outcomes. Because platelet activation is determined by multiple receptor-mediated signaling pathways, clinical studies have evaluated the efficacy of multidrug administration in the prevention of atherothrombotic complications.2,3 The major concern with these therapies is the critical balance between anti-ischemic effect and bleeding risk. This review summarizes our understanding of the role of combination antiplatelet therapies in the treatment and prevention of atherothrombosis. Platelet activation and aggregation play a pivotal role in the generation of occlusive thrombus at the site of coronary arterial plaque rupture. In addition, platelets influence various endothelial and inflammatory responses during the initiation and progression of atherosclerosis. Under normal conditions, anucleate circulating platelets are in a quiescent state. Healthy vascular endothelium prevents adhesion and activation of platelets by producing antithrombotic factors such as CD39 (ectoADPase), prostaglandin I2, nitric oxide, heparin, matrix metalloproteinase-9, protein S, and thrombomodulin.3,4 Endothelial activation and denudation and frank atherosclerotic plaque rupture expose the subendothelial matrix and release prothrombotic factors during acute coronary syndromes (ACS) and percutaneous interventions. These processes result in localized platelet adhesion and platelet activation. After adhesion to the exposed subendothelial matrix, platelets are activated by shear and the soluble agonists thromboxane A2 (TxA2), ADP, and thrombin. TxA2 is produced from arachidonic acid, which originates from membrane phospholipids and …

Elevated levels of 8-iso-prostaglandin F2α in acute coronary syndromes are associated with systemic and local platelet activation

Oxidative stress is an important causative factor in atherosclerosis. Isoprostanes are derivatives of arachidonate oxidized by reactive oxygen species (ROS). Oxidized lipids are markers of oxidative stress, important mediators of atherosclerosis, and activators of platelets. 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha) is a stable isoprostane and reliable marker of oxidative stress in vivo. The aim of the study was to determine the level of oxidative stress in acute coronary syndromes (ACS) and its correlations with the para meters of hemo stasis. Fourty-nine patients aged 46 to 76 years, including 28 with ACS and 25 with stable coronary artery disease (CAD), were enrolled to the study. The levels of 8-iso-PGF2alpha, soluble CD40 ligand (sCD40L), P-selectin (P-sel), beta-thromboglobulin, and the thrombin-antithrombin complex (TAT) in the plasma of venous blood were determined. A microvascular injury model was also used to evaluate TAT generation and sCD40L levels in blood collected every 60 seconds at the site of standardized microvascular injury. 8-iso-PGF2alpha levels were significantly higher in ACS compared to CAD patients (363.2 +/-45.94 vs. 328.2 -/+31.96 pg/ml, P = 0.011) and correlated with venous plasma levels of P-sel and beta-thromboglobulin in the ACS (r = 0.66; P = 0.0005 and r = 0.62; P = 0.001, respectively) and CAD groups (r = 0.46; P = 0.02 and r = 0.49; P = 0.01, respectively). In the microvascular injury model, the maximum concentrations of sCD40L in the ACS group were associated with plasma 8-iso-PGF2alpha levels (r = 0.50, P = 0.01). No correlations between 8-iso-PGF2alpha and markers of thrombin generation in venous blood and microvascular injury model were observed. Plasma levels of 8-iso-PGF2alpha are significantly higher in ACS compared with stable CAD and correlate with platelet activation.

Platelet functions beyond hemostasis.

Although their central role is in the prevention of bleeding, platelets probably contribute to diverse processes that extend beyond hemostasis and thrombosis. For example, platelets can recruit leukocytes and progenitor cells to sites of vascular injury and inflammation; they release proinflammatory and anti-inflammatory and angiogenic factors and microparticles into the circulation; and they spur thrombin generation. Data from animal models suggest that these functions may contribute to atherosclerosis, sepsis, hepatitis, vascular restenosis, acute lung injury, and transplant rejection. This article represents an integrated summary of presentations given at the Fourth Annual Platelet Colloquium in January 2009. The process of and factors mediating platelet-platelet and platelet-leukocyte interactions in inflammatory and immune responses are discussed, with the roles of P-selectin, chemokines and Src family kinases being highlighted. Also discussed are specific disorders characterized by local or systemic platelet activation, including coronary artery restenosis after percutaneous intervention, alloantibody-mediated transplant rejection, wound healing, and heparin-induced thrombocytopenia.

Early changes in local hemostasis activation following percutaneous coronary intervention in stable angina patients: a comparison between drug-eluting and bare metal stents

Early change in local intracoronary hemostasis following drug-eluting (DES) and bare metal stent (BMS) implantation has never been assessed in stable angina patients. Markers of local platelet activation (soluble glycoprotein V [sGPV] and P-Selectin [CD62P]), coagulation activation (tissue factor [TF], prothrombin fragments 1 + 2 [F1 + 2] and activated factor VII [FVIIa]) and fibrinolysis markers (D-dimers [DD], fibrinogen [FIB], tissue plasminogen activator [t-PA], and plasminogen activator inhibitor type-1 complexes [PAI-1]) were determined in 20 patients with stable angina who underwent percutaneous coronary intervention (PCI). All patients were pretreated with clopidogrel, aspirin, and enoxaparin. Systematic balloon predilation was performed before DES (9 patients) and BMS (11 patients) implantation. All blood samples were drawn 10-20 mm distal to the lesion site. No significant changes in levels of platelet activation markers occurred during PCI. There was a transient significant increase in TF (14%; P = 0.004), in F1 + 2 (40%; P = 0.001), and FVIIa (31%; P = 0.007) following angioplasty. Similarly, a significant 43% increase was observed in DD levels following balloon predilation, associated with an increase of 46%, 60%, and 70% in FIB, t-PA and PAI-1 levels, respectively (all P < 0.0001). All these markers returned to baseline values after stent implantation. No difference was observed between DES and BMS. Early changes in local hemostasis activation following PCI, were related to balloon predilation. Neither DES nor BMS increased markers of platelet activation, coagulation, or fibrinolysis, under dual antiplatelet and anticoagulant pretreatment.

Hyperglycemia Is Associated With Enhanced Thrombin Formation, Platelet Activation, and Fibrin Clot Resistance to Lysis in Patients With Acute Coronary Syndrome

OBJECTIVE—Acute hyperglycemia on admission for acute coronary syndrome worsens the prognosis in patients with and without known diabetes. Postulated mechanisms of this observation include prothrombotic effects. The aim of this study was to evaluate the effect of elevated glucose levels on blood clotting in acute coronary syndrome patients.RESEARCH DESIGN AND METHODS—We studied 60 acute coronary syndrome patients within the first 12 h after pain onset, including 20 subjects with type 2 diabetes, 20 subjects with no diagnosed diabetes but with glucose levels >7.0 mmol/l, and 20 subjects with glucose levels <7.0 mmol/l. We determined generation of thrombin-antithrombin complexes (TATs) and soluble CD40 ligand (sCD40L), a platelet activation marker, at the site of microvascular injury, together with ex vivo plasma fibrin clot permeability and lysis time.RESULTS—The acute coronary syndrome patients with no prior diabetes but elevated glucose levels had increased maximum rates of formation and total production of TATs (by 42.9%, P < 0.0001, and by 25%, P < 0.0001, respectively) as well as sCD40L release (by 16.2%, P = 0.0011, and by 16.3%, P < 0.0001, respectively) compared with those with normoglycemia, whereas diabetic patients had the highest values of TATs and sCD40L variables (P < 0.0001 for all comparisons). Patients with hyperglycemia, with no previously diagnosed diabetes, had longer clot lysis time (by ∼18%, P < 0.0001) similar to that in diabetic subjects, but not lower clot permeability compared with that in normoglycemic subjects.CONCLUSIONS—Hyperglycemia in acute coronary syndrome is associated with enhanced local thrombin generation and platelet activation, as well as unfavorably altered clot features in patients with and without a previous history of diabetes.

Acute Onset Human Atrial Fibrillation Is Associated With Local Cardiac Platelet Activation and Endothelial Dysfunction

The purpose of this study was to determine whether acute onset atrial fibrillation (AF), independent of other risk factors, predisposes to an early prothrombotic state. Several risk factors predispose to the hypercoagulable state in human AF, but whether acute onset AF alone is prothrombotic remains unclear. Patients with paroxysmal AF (n = 22) underwent radiofrequency catheter ablation. All patients presented in sinus rhythm. Baseline blood samples were obtained simultaneously from the femoral vein (systemic sample) and the coronary sinus (local cardiac sample). The AF was induced by burst atrial pacing in 14 patients (AF group). A control group (n = 8) underwent atrial pacing at 120 beats/min. Blood samples were recollected after 15 min. Platelet P-selectin expression (CD62) was measured using flow cytometry. Markers of thrombin generation (thrombin antithrombin complex, prothrombin fragment 1.2), inflammation (C-reactive protein, interleukin-6), and nitric oxide were measured using enzyme-linked immunosorbent assays. Neither local nor systemic platelet activation changed in the control group. In the AF group, local cardiac platelet activation (percent P-selectin [+] platelets) increased significantly (2.2 +/- 0.6% to 2.8 +/- 1.0%, p = 0.007); however, systemic platelet activation did not change. The AF group had increased local thrombin generation (thrombin antithrombin complex: 8.5 +/- 7.6 ng/ml to 33.2 +/- 17.4 ng/ml, p = 0.003; prothrombin fragment 1.2: 95.6 +/- 45.6 micromol/l to 243.8 +/- 120.1 micromol/l, p = 0.003), decreased nitric oxide production (25.2 +/- 10.8 micromol/l to 22.3 +/- 10.0 micromol/l, p < 0.02), and no change in inflammatory markers. Human AF causes local cardiac platelet activation within minutes of onset. The results demonstrate how AF alone, independent of other risk factors, may contribute to the hypercoagulable state.