Increased platelet reactivity and circulating monocyte-platelet aggregates in patients with stable coronary artery disease

Biomarkers of platelet activation in acute coronary syndromes

The most convincing evidence for the participation of platelets in arterial thrombosis in humans comes from studies of platelet activation in patients with acute coronary syndromes (ACS) and from trials of antiplatelet drugs. Both strongly support the concept that repeated episodes of platelet activation over the thrombogenic surface of a vulnerable plaque may contribute to the risk of death from coronary causes. However, the relation of in vivo platelet activation and adverse clinical events to results of platelet function tests remains largely unknown. A valuable marker of in vivo platelet activation should be specific, unaltered by pre-analytical artefacts and reproducibly measured by easily performed methods. This article describes current biomarkers of platelet activation in ACS, reviews their advantages and disadvantages, discusses their potential pitfalls, and demonstrates emerging data supporting the positive clinical implications of monitoring in vivo platelet activation in the setting of ACS.

Improved accuracy and reproducibility of enumeration of platelet-monocyte complexes through use of doublet-discriminator strategy

BACKGROUND

Platelet-monocyte complex (PMC) formation is a marker of in vivo platelet activation and may be readily measured by flow cytometry. Due to the high frequency of free platelets relative to monocytes and PMCs, false-positive identification through coincidence remains a significant technical problem.To overcome this problem, we evaluated the use of a doublet-discriminator strategy (DDM) to allow faster sample acquisition whilst significantly reducing aberrant coincidence.

METHODS

Fourteen healthy volunteers and 20 patients with coronary artery disease (CAD) gave arterial and/or peripheral venous blood samples (NaCit). Whole blood was labelled in duplicate with anti-CD61 and anti-CD14 using a standard lyse/wash protocol. One of each paired sample was serially diluted before analysis; the second was analyzed at full concentration but using FL1-width to exclude co-incident platelet and monocyte events. Control experiments were performed with ex vivo thrombin activated samples.

RESULTS

With the DDM use PMC frequencies in the peripheral blood of healthy individuals and in CAD patients fell significantly [6.27% ± 1.77 (mean ± sd) to 2.57% ± 0.99 (P = 0.02)] and from 16.04% (± 11.26) to 7.66% (± 5.18) (P < 0.01), respectively. DDM use significantly reduced the percentage of PMCs in the ex vivo thrombin activated samples (P < 0.05).

CONCLUSIONS

Use of DDM effectively reduces the coincidence and enumerates true PMC in the samples of normal individuals and in patients with CAD and in ex vivo thrombin activated samples.

Effects of P2Y(1) receptor antagonism on the reactivity of platelets from patients with stable coronary artery disease using aspirin and clopidogrel

BACKGROUND AND PURPOSE

P2Y(1) is a purine receptor that triggers platelet aggregation. Its inhibition was studied in patients with stable coronary artery disease (CAD) receiving standard anti-platelet therapy.

EXPERIMENTAL APPROACH

Blood samples from 10 patients on aspirin therapy (ASA, 80 mg·day(-1) ) were withdrawn before and 24 h after the administration of 450 mg clopidogrel (ASA/C) and were anti-coagulated with citrate or hirudin/PPACK in the presence or absence of the P2Y(1 ) inhibitor MRS2179 (M, 100 µM). Platelet responses to ADP (2.5 µM) and TRAP (2.5 µM), and collagen-induced thrombosis under flow conditions were analysed.

KEY RESULTS

Compared with ASA, ASA + M strongly inhibited ADP-induced peak platelet aggregation (88%), late aggregation (84%), P-selectin expression (85%) and α(IIb) β(3) activation (62%) (28%, 65%, 70% and 51% inhibition, respectively, for ASA/C vs. ASA). ASA + M also inhibited platelet/monocyte and platelet/neutrophil conjugate formation by 69% and 71% (57% and 59% for ASA/C vs. ASA). In TRAP-activated blood, ASA + M unexpectedly inhibited α(IIb) b(3) activation by 30%. In blood perfused in collagen-coated glass capillaries (shear rate of 1500 s(-1) ), ASA/C prevented thrombus growth beyond 5 min in relation to thrombus fragments embolization. ASA + M with or without clopidogrel completely prevented thrombus formation. Finally, ex vivo addition of MRS2179 and ASA to the blood of healthy donors markedly blocked thrombus formation on collagen in flow conditions, in contrast to ASA plus the P2Y(12) inhibitor 2-MeSAMP.

CONCLUSIONS AND IMPLICATIONS

Through particularly efficient complementarities with ASA to inhibit platelet activation and thrombus formation, the inhibition of P2Y(1) in the blood of patients with CAD appears to play a more important role than previously anticipated.

Roles of Mac-1 and glycoprotein IIb/IIIa integrins in leukocyte-platelet aggregate formation: stabilization by Mac-1 and inhibition by GpIIb/IIIa blockers

Circulating platelet-leukocyte hetero-aggregates play an important role in acute cardiovascular events and hypersensitivity reactions. The association involves the receptor families of selectins and integrin. The objective of this study was to investigate the role of CD11b/CD18 integrin (Mac-1) in hetero-aggregate formation and search for a counter-receptor on platelets ready to interact with Mac-1. As a model of leukocytes, Mac-1 presenting Chinese hamster ovary (CHO) cells were used to evaluate the role of Mac-1 in hetero-aggregate formation. The amount of CHO cell-bound active and inactive platelets was measured by flow cytometry, while the counter-receptors on platelets were identified via using blocking antibodies. We observed significant platelet adhesion on Mac-1-bearing cells when platelet-rich plasma or activated platelets were present. Inactive platelets did not adhere to Mac-1-bearing cells. Addition of fibrinogen, a ligand of Mac-1 significantly increased platelet binding. CD40L was demonstrated to act similarly on Mac-1. Inhibition of platelet GpIIb/IIIa completely abolished CHO cell-platelet aggregation. In our study, we have shown for the first time that Mac-1 mediates the formation of hetero-aggregates without selectin tethering when Mac-1 ligands such as fibrinogen or CD40L are present and blockers of platelet GpIIb/IIIa are able to diminish this interaction.

Modulation of platelet activation in chronic kidney disease patients on erythropoiesis-stimulating agents

BACKGROUND

Clinical trials demonstrate either no benefit or increased risk of cardiovascular events and mortality in patients with chronic kidney disease (CKD) targeted for higher hemoglobin levels, who are treated with erythropoiesis-stimulating agents (ESAs). The mechanism underlying this observation remains unexplained.

METHODS AND RESULTS

We assessed platelet activation by measuring soluble P-selectin (sPsel), CD40 ligand (CD40L), and circulating microparticles (CMP) in patients with CKD. Higher hemoglobin levels were associated with increased Psel levels in patients on ESAs but not in ESA-naïve anemic and nonanemic patients. Psel positively correlated with CMP and CD40L in both anemic and nonanemic patients. Multivariate linear regression analysis revealed an association between increased Psel levels and hemoglobin concentration in patients receiving ESAs.

CONCLUSIONS

Anemic CKD patients on ESAs demonstrate increased levels of markers of platelet activation. These observations suggest a potentially complex interplay between platelet activation, impaired kidney function, and treatment of CKD anemia with ESAs.

Chinese herb and formulas for promoting blood circulation and removing blood stasis and antiplatelet therapies

Atherothrombosis, which directly threatens people's health and lives, is the main cause of morbidity and mortality all over the world. Platelets play a key role in the development of acute coronary syndromes (ACSs) and contribute to cardiovascular events. Oral antiplatelet drugs are a milestone in the therapy of cardiovascular atherothrombotic diseases. In recent years, many reports have shown the possibility that “resistance” to oral anti-platelet drugs and many adverse reactions, such as serious bleeding risk, which provides an impetus for developing new anti-platelet drugs possesses highly efficiency and fewer adverse effects. Study on the blood stasis syndrome and promoting blood circulation and removing blood stasis is the most active field of research of integration of traditional and western medicine in China. Blood-stasis syndrome and platelet activation have close relationship, many Chinese herb and formulas for promoting blood circulation and removing blood stasis possess definite anti-platelet effect. This paper covers the progress of anti-platelet mechanism of Chinese herb and formulas for promoting blood circulation and removing blood stasis and is to be deeply discussed in further research.

The role of dermcidin isoform 2: a two-faceted atherosclerotic risk factor for coronary artery disease and the effect of acetyl salicylic Acid on it

Hypertension and diabetes mellitus are considered to be two major atherosclerotic risk factors for coronary artery disease (CAD). A stress-induced protein identified to be dermcidin isoform 2 of Mr. 11 kDa from blood plasma of hypertensive persons when injected (0.1 μM) in rabbits increased the systolic pressure by 77% and diastolic pressure by 45% over the controls within 2 h. Ingestion of acetyl salicylic acid (150 mg/70 kg) by these subjects reduced systolic (130 mm Hg) and diastolic pressures (80 mm Hg) with reduction of plasma dermcidin level to normal ranges (9 nM). The protein was found to be a potent activator of platelet cyclooxygenase and inhibited insulin synthesis. Aspirin was found to reduce hypertension by reduction of plasma dermcidin level, neutralized the effect of cyclooxygenase, and restored the pancreatic insulin synthesis through NO synthesis. These results indicated that dermcidin could be a novel atherosclerotic risk factor for its hypertensive and diabetogenic effects.

Hemoconcentration and hemostasis during acute stress: interacting and independent effects

BACKGROUND

Acute psychological stress can produce significant hemoconcentration as well as prothrombotic changes in blood, both of which may have potentially harmful effects on the cardiovascular system. It is unclear whether these effects are independent or have influence on each other.

PURPOSE

This review discusses research investigating the effects of acute psychological stress on hemoconcentration and hemostasis and explores future directions for psychohematology research. Physiology, associations with cardiovascular disease, and relationships between acute psychological stress are discussed independently for hemoconcentration and hemostasis, followed by an examination of the effects of stress-hemoconcentration on hemostasis.

CONCLUSIONS

Traditional methods of adjusting for stress-hemoconcentration effects (e.g., calculated plasma volume or hematocrit level corrections) may not be appropriate when examining stress-induced changes in hemostasis. The effects of acute stress on hemostasis should be examined in conjunction with hemoconcentration.

Darbepoetin enhances endothelium-dependent vasomotor function in patients with stable coronary artery disease only after preceding ischaemia/reperfusion

Vasoprotective effects of erythropoietin in animal models are mediated by endothelium-derived NO and/or mobilization of EPCs (endothelial progenitor cells) and may be enhanced by ischaemia: whether they are present in humans is unknown. We examined whether the erythropoietin analogue darbepoetin improves FMD (flow-mediated dilatation), a measure of endothelium-derived NO, and whether this is influenced by preceding I/R (ischaemia/reperfusion). A total of 36 patients (50–75 years) with stable coronary artery disease were randomized to receive a single dose of darbepoetin (300 μg) or saline placebo. FMD was measured at the brachial artery using high-resolution ultrasound. CD133+/CD34+/VEGFR2+ (vascular endothelial growth factor receptor 2) circulating EPCs were enumerated by flow cytometry. Measurements were made immediately before darbepoetin/placebo and at 24 h, 72 h and 7 days. At 24 h, FMD was repeated after 20 min of I/R of the upper limb. A further group of 11 patients was studied according to the same protocol, all receiving darbepoetin, with omission of forearm I/R at 24 h. Immunoreactive erythropoietin peaked at 24 h and remained elevated at approximately 50-fold of baseline at 72 h. FMD did not differ significantly between groups at 24 h (before I/R). At 72 h (48 h after I/R), FMD was greater (by 2.3±0.5% in the darbepoetin compared with the placebo group, a 66% increase over baseline; P<0.001) and greater than FMD at the same time point without preceding I/R (P<0.01). Increases in CD133+/CD34+/VEGFR2+ cells after darbepoetin did not differ according to the presence or absence of preceding I/R. Preceding I/R is required for darbepoetin to enhance endothelial function, possibly by increasing expression of the erythropoietin receptor and by a mechanism likely to involve Akt/NO rather than circulating EPCs.

Glycoprotein IIb-IIIa inhibitors

Platelets play a pivotal role in the pathogenesis of coronary artery disease and myocardial infarction. Therefore, great interests have been focused in the last decades on improvement in antiplatelet therapies, that currently are regarded as main pillars in the prevention and treatment of coronary artery disease, with special attention to glycoprotein IIb-IIIa (GP IIb-IIIa) receptors, that mediates the final stage of platelet activation. GP IIb-IIIa inhibitors, especially abciximab, have been shown to improve clinical outcome in patients undergoing primary angioplasty for STEMI. Upstream administration cannot routinely recommended, but may potentially be considered among high-risk patients within the first 4 h from symptoms onset. In case of periprocedural administration of antithrombotic therapy, Bivalirudin should be considered, especially in patients at high risk for bleeding complications. Among high-risk patients with acute coronary syndromes, an early invasive strategy with selective downstream administration of GP IIb-IIIa inhibitors is the strategy of choice, whereas bivalirudin should be considered in patients at high risk for bleeding complications. Among patients with unstable angina GP IIb-IIIa inhibitors should be considered only in case of evidence of intracoronary thrombus or in case of thrombotic complications (as provisional use). Further, randomized trials are certainly needed in the era of new oral antiplatelet therapies, and with strategies to prevent bleeding complications such as larger use of radial approach, mechanical closure devices, bivalirudin, or postprocedural protamine administration to promote early sheat removal.

Adhesive interaction between peripheral blood mononuclear cells and activated platelets in the presence of anti-human leukocyte antigen Class I alloantibody causes production of IL-1β and IL-8

BACKGROUND

Activated platelets form heterogeneous aggregates of platelets and monocytes, which are involved in a variety of inflammatory disorders. Some anti-human leukocyte antigen (HLA) Class I antibodies have been shown to activate platelets.

MATERIALS AND METHODS

Human leukocyte antigen-A2-positive or HLA-A2-negative platelets were incubated with HLA-A2-negative peripheral blood mononuclear cells (PBMNCs) in the presence of anti-HLA-A2 serum at 37°C. The binding of platelets to monocytes was analysed by flow cytometry. The levels of IL-1 β and IL-8 in the culture supernatant were determined by ELISA.

RESULTS

Anti-HLA-A2 serum increased the formation of aggregates between monocytes and HLA-A2-positive platelets, but not HLA-A2-negative platelets, in a dose-dependent manner. Antiserum also increased the number of platelets bound to monocytes in a time-dependent manner. The addition of anti-P-selectin glycoprotein ligand (PSGL-1) mAb almost completely inhibited the formation of platelet-monocyte aggregates as well as the number of platelets bound to monocytes. When HLA-A2-positive or HLA-A2-negative platelets were incubated with HLA-A2-negative PBMNCs in the presence of anti-HLA-A2, the level of IL-1β and IL-8 in the supernatant of coculture was significantly higher in HLA-A2-positive platelets than in HLA-A2-negative platelets. The addition of anti-PSGL-1 mAb partially but significantly inhibited the production of both IL-1β and IL-8.

CONCLUSIONS

The activation of platelets with anti-HLA Class I alloantibody caused the formation of platelet-monocyte aggregates, followed by the production of IL-1β and IL-8, in a cognate antigen-antibody manner. The adhesive interaction of P-selectin and PSGL-1 at least partially contributed to these phenomena.

Monocyte and macrophage dynamics during atherogenesis

Vascular inflammation is associated with and in large part driven by changes in the leukocyte compartment of the vessel wall. Here, we focus on monocyte influx during atherosclerosis, the most common form of vascular inflammation. Although the arterial wall contains a large number of resident macrophages and some resident dendritic cells, atherosclerosis drives a rapid influx of inflammatory monocytes (Ly-6C(+) in mice) and other monocytes (Ly-6C(-) in mice, also known as patrolling monocytes). Once in the vessel wall, Ly-6C(+) monocytes differentiate to a phenotype consistent with inflammatory macrophages and inflammatory dendritic cells. The phenotype of these cells is modulated by lipid uptake, Toll-like receptor ligands, hematopoietic growth factors, cytokines, and chemokines. In addition to newly recruited macrophages, it is likely that resident macrophages also change their phenotype. Monocyte-derived inflammatory macrophages have a short half-life. After undergoing apoptosis, they may be taken up by surrounding macrophages or, if the phagocytic capacity is overwhelmed, can undergo secondary necrosis, a key event in forming the necrotic core of atherosclerotic lesions. In this review, we discuss these and other processes associated with monocytic cell dynamics in the vascular wall and their role in the initiation and progression of atherosclerosis.

Gene expression profiling reveals multiple differences in platelets from patients with stable angina or non-ST elevation acute coronary syndrome

INTRODUCTION

Platelets play a key role in coronary artery disease. They have the capacity of protein synthesis through translation of megakaryocyte-derived mRNAs, which may influence pathophysiological functions. The present study aimed to prove the concept that platelets from patients with non-ST elevation acute coronary syndrome (NSTE-ACS) have differential mRNA expression profiles, in the hypothesis that this may influence their thrombogenicity.

MATERIALS AND METHODS

Gene expression profiles were determined in RNA pools from resting platelets of patients with stable angina (SA, n = 14) or NSTE-ACS (n = 15) using a glass microarray platform. Validation was done by real-time PCR and immunoblot analyses in independent sets of individual samples (26 SA and 17 NSTE-ACS patients, in total). Parallel comparison with healthy subjects was performed to relate the relative abundance of validated genes in CAD patients to a control expression level.

RESULTS

Microarray analysis identified 45 transcripts with a significant ≥ ± 2.0-fold difference in expression between NSTE-ACS and SA platelet pools. Thus, gene expression profiles at least partially discriminate unstable from stable CAD. Validation confirmed a significant over-expression of 3 genes in NSTE-ACS at both mRNA and protein level. In particular, the glycoprotein Ib β-polypeptide (GP1BB) was increased in NSTE-ACS also in comparison with healthy subjects.

CONCLUSION

This study provides evidence that NSTE-ACS platelets are potentially preconditioned to a higher degree of reactivity on the transcriptional level. Our data suggest that a different composition of the mRNA pool might mediate an increased platelet prothrombotic potential in NSTE-ACS patients.

Lipoxin A₄ inhibits porphyromonas gingivalis-induced aggregation and reactive oxygen species production by modulating neutrophil-platelet interaction and CD11b expression

Porphyromonas gingivalis is an etiological agent that is strongly associated with periodontal disease, and it correlates with numerous inflammatory disorders, such as cardiovascular disease. Circulating bacteria may contribute to atherogenesis by promoting CD11b/CD18-mediated interactions between neutrophils and platelets, causing reactive oxygen species (ROS) production and aggregation. Lipoxin A₄ (LXA₄) is an endogenous anti-inflammatory and proresolving mediator that is protective of inflammatory disorders. The aim of this study was to investigate the effect of LXA₄ on the P. gingivalis-induced activation of neutrophils and platelets and the possible involvement of Rho GTPases and CD11b/CD18 integrins. Platelet/leukocyte aggregation and ROS production was examined by lumiaggregometry and fluorescence microscopy. Integrin activity was studied by flow cytometry, detecting the surface expression of CD11b/CD18 as well as the exposure of the high-affinity integrin epitope, whereas the activation of Rac2/Cdc42 was examined using a glutathione S-transferase pulldown assay. The study shows that P. gingivalis activates Rac2 and Cdc42 and upregulates CD11b/CD18 and its high-affinity epitope on neutrophils, and that these effects are diminished by LXA₄. Furthermore, we found that LXA₄ significantly inhibits P. gingivalis-induced aggregation and ROS generation in whole blood. However, in platelet-depleted blood and in isolated neutrophils and platelets, LXA₄ was unable to inhibit either aggregation or ROS production, respectively. In conclusion, this study suggests that LXA₄ antagonizes P. gingivalis-induced cell activation in a manner that is dependent on leukocyte-platelet interaction, likely via the inhibition of Rho GTPase signaling and the downregulation of CD11b/CD18. These findings may contribute to new strategies in the prevention and treatment of periodontitis-induced inflammatory disorders, such as atherosclerosis.

Platelet reactivity in diabetic patients subjected to acute exercise stress test

BACKGROUND

Previous studies have reported ambiguous results regarding the effect of acute exercise on platelet reactivity in healthy and cardiac patients.

OBJECTIVES

We aimed to assess platelet reactivity among diabetic patients before and immediately after an acute exercise stress test.

METHODS

Patients (controls: mean age 53.1 ± 12.1 years; four males; body mass index 27.0 ± 5.7 kg/m(2); HbA(1c) 6.0 ± 1.1%, n = 8) and diabetic patients (52.9 ± 11.3; six males; body mass index 30.7 ± 2.2 kg/m(2); HbA(1c) 7.8 ± 1.7%, n = 8) referred for diagnostic nuclear exercise stress test were recruited. Blood samples obtained at rest and immediately post-exercise were stimulated with adenosine diphosphate (ADP), collagen and arachidonic acid. Expression of CD41 (pan-platelet marker) and CD62p (platelet stimulation marker) were measured by flow cytometry. Aspirin responsiveness was measured using VerifyNow.

RESULTS

Although peak systolic blood pressure was significantly higher in the diabetics compared with nondiabetics (186.3 ± 25.4 vs. 157.1 ± 19.1, respectively, P = .028), peak exercise heart rate was similar (156.5 ± 8.3 vs. 155.5 ± 12.1 for diabetics and nondiabetics, respectively). No differences were observed between groups for aspirin resistance. Platelet stimulation with ADP exhibited significantly lower CD62p-positive cell population (%) in the diabetic patients both prior to and following the exercise stress test (P = .03). In addition, although not significant, platelet stimulation was higher post-exercise in the diabetic patients (6.3 ± 4.7% vs. 12.0 ± 5.6%, for pre- and post-exercise, respectively, P = .2) with no difference in controls (9.2 ± 5.5% vs. 8.9 ± 5.9%).

CONCLUSION

Platelet stimulation in diabetic patients is blunted and might be explained by the prolonged exposure of platelets to multiple diabetic risk factors.

The role of monocytes in atherosclerotic coronary artery disease

Inflammation plays a key role in the pathogenesis of atherosclerosis. The more we discover about the molecular pathways involved in atherosclerosis, the more we perceive the importance of monocytes in this process. Circulating monocytes are components of innate immunity, and many pro-inflammatory cytokines and adhesion molecules facilitate their adhesion and migration to the vascular endothelial wall. In addition to the accumulation of lipids and formation of atherogenic 'foam' cells, monocytes may promote atherosclerotic plaque growth by production of inflammatory cytokines, matrix metalloproteinases, and reactive oxidative species. However, the contribution of monocytes to atherogenesis is not only limited to tissue destruction. Monocyte subsets are also involved in intraplaque angiogenesis and tissue reparative processes. The aim of this overview is to discuss the mechanisms of monocyte activation, the pivotal role and importance of activated monocytes in atherosclerotic coronary artery disease, their implication in the development of acute coronary events, and their potential in cardiovascular reparative processes such angiogenesis.

Platelet CD40L mediates thrombotic and inflammatory processes in atherosclerosis

CD40 ligand (CD40L), identified as a costimulatory molecule expressed on T cells, is also expressed and functional on platelets. We investigated the thrombotic and inflammatory contributions of platelet CD40L in atherosclerosis. Although CD40L-deficient (Cd40l(-/-)) platelets exhibited impaired platelet aggregation and thrombus stability, the effects of platelet CD40L on inflammatory processes in atherosclerosis were more remarkable. Repeated injections of activated Cd40l(-/-) platelets into Apoe(-/-) mice strongly decreased both platelet and leukocyte adhesion to the endothelium and decreased plasma CCL2 levels compared with wild-type platelets. Moreover, Cd40l(-/-) platelets failed to form proinflammatory platelet-leukocyte aggregates. Expression of CD40L on platelets was required for platelet-induced atherosclerosis as injection of Cd40l(-/-) platelets in contrast to Cd40l(+/+) platelets did not promote lesion formation. Remarkably, injection of Cd40l(+/+), but not Cd40l(-/-), platelets transiently decreased the amount of regulatory T cells (Tregs) in blood and spleen. Depletion of Tregs in mice injected with activated Cd40l(-/-) platelets abrogated the athero-protective effect, indicating that CD40L on platelets mediates the reduction of Tregs leading to accelerated atherosclerosis. We conclude that platelet CD40L plays a pivotal role in atherosclerosis, not only by affecting platelet-platelet interactions but especially by activating leukocytes, thereby increasing platelet-leukocyte and leukocyte-endothelium interactions.

M118, a novel low-molecular weight heparin with decreased polydispersity leads to enhanced anticoagulant activity and thrombotic occlusion in ApoE knockout mice

Heparin and low-molecular weight heparin (LMWH) are complex, heterogeneous polysaccharides used in the treatment of arterial and venous thrombosis. M118 is a novel LMWH with low polydispersity and pronounced anti-Xa and anti-thrombin (IIa) activity as compared to current LMWHs. To determine if M118 is effective in preventing thrombosis in the setting of a vascular plaque, apolipoprotein E knockout mice fed a high fat diet were injected with M118, enoxaparin, unfractionated heparin, or saline control and examined for arterial thrombosis using a rose bengal laser induced carotid artery injury model. M118 significantly increased the time to occlusion as compared to control and unfractionated heparin but not compared to enoxaparin although fewer M118 treated animals had any vascular occlusion present at the time of protocol completion. Platelet-neutrophil aggregates were studied by flow cytometry and were found to be decreased with M118 as compared to enoxaparin. This is the first published report examining M118, a novel LMWH designed to have low polydispersity and enhanced anticoagulant activity. In an animal model of vascular plaque, M118 is a potent inhibitor of arterial thrombosis and, despite lower in vivo anti-Xa and anti-IIa activity levels, M118 was superior to UFH in the prevention of arterial thrombosis.

Expression of EMMPRIN (CD147) on circulating platelets in vivo

BACKGROUND AND OBJECTIVES

EMMPRIN (CD147) is a matrix metalloproteinase inducer present on leukocytes and recently identified on platelets in vitro. We examined platelet CD147 expression in vivo and in correlation with markers of platelet activation and coronary artery disease (CAD).

PATIENTS/METHODS

This prospective observational study involved 70 subjects (55 patients with CAD and 15 controls). Platelet CD62P expression, PAC-1 expression, platelet-leukocyte aggregates and CD147 (both platelet and leukocyte) expression were assessed by flow cytometry, and soluble CD62P expression was assessed by enzyme-linked immunosorbent assay. A full blood count and high-sensitivity C-reactive protein test were performed.

RESULTS

CD147 was expressed on 20.45% +/- 1.63% (mean +/- standard error of the mean) of circulating platelets, whereas CD62P and PAC-1 were expressed on 0.87% +/- 0.12% and 0.90% +/- 0.27% of platelets, respectively. Platelet CD147 expression correlated with CD62P expression (r = 0.359, P = 0.002), PAC-1 expression (r = 0.428, P < 0.001), leukocyte CD147 expression (monocyte, r = 0.416, P = 0.001; granulocyte, r = 0.434, P < 0.001), C-reactive protein level and neutrophil/lymphocyte ratio (NLR). CAD patients had significantly higher CD147 mean fluorescence intensity than controls on circulating platelets (2.41 +/- 0.14 vs. 2.87 +/- 0.09, P = 0.014), monocytes (8.57 +/- 1.20 vs. 12.3 +/- 0.57, P = 0.006) and granulocytes (4.30 +/- 0.65 vs. 6.50 +/- 0.34, P = 0.005). Age adjustment eliminated the association between platelet CD147 expression and CAD, but the association between leukocyte CD147 expression and CAD persisted. According to multivariate analysis, the independent predictors of platelet CD147 expression were monocyte CD147 expression, NLR and age.

CONCLUSIONS

Platelet CD147 expression is evident in vivo and correlates moderately with traditional platelet activation markers and leukocyte CD147 expression. Platelet CD147 expression shows a stronger association with age, and leukocyte CD147 expression a stronger association with clinical CAD, suggesting differences in the regulation of platelet and leukocyte CD147 expression in vivo.

Platelet activation in essential hypertension: implications for antiplatelet treatment

Essential hypertension is associated with increased risk of arterial thrombotic disease. Among other factors, enhanced platelet activity contributes significantly to this phenomenon. An increased level of circulating monocyte-platelet aggregates (MPAs) represents one of the most robust markers of platelet activation; furthermore, these aggregates are also believed to contribute to the pathophysiology of atherothrombotic disease. Putative mechanisms that contribute to platelet activation in essential hypertension include endothelial dysfunction, neurohumoral (sympathetic and renin-angiotensin systems) overactivity, decreased platelet nitric oxide (NO) biosynthesis, and platelet degranulation secondary to increased shear. Current recommendations are that hypertensive patients receive aspirin therapy only if their calculated cardiovascular risk is high and their blood pressure (BP) is adequately controlled. By contrast, the use of antiplatelet treatment in low-risk hypertensive patients is not established and merits further investigation. Moreover, the place of alternative antiplatelet agents other than aspirin, such as clopidogrel, is unclear at present. Some experimental evidence suggests that clopidogrel may confer an additive protective effect over and above aspirin in hypertensive patients, by virtue of effects on the evolution of the atherosclerotic process. This now needs to be investigated in long-term clinical outcome studies.

Platelet proinflammatory activity in clinically stable patients with CF starts in early childhood

BACKGROUND

Early onset chronic inflammation is present in CF. Platelets may contribute to inflammation by cytokine release and interaction with leukocytes.

METHODS

Parameters of platelet proinflammatory function (soluble CD62P, soluble CD40L, the percentage of platelet-leukocyte aggregates, platelet CD62P) and platelet procoagulatory function (PAC-1-binding to activated integrin alpha(IIb)beta(3) and expression of integrin alpha(IIb)beta(3)=CD41a) were measured in patients and controls.

RESULTS

Levels of sCD62P, sCD40L were increased in CF irrespective of age and activity of inflammation. The number of platelet-leukocyte aggregates was elevated in older CF patients. PAC-1-binding to platelets decreased with growing activity of inflammation. Exocytosis of CD41a upon platelet activation was reduced.

CONCLUSION

In CF, platelet proinflammatory activity is increased at very young age already and might promote inflammation and tissue damage. On the other hand, platelets seem to downregulate the activation of their most important integrin (alpha(IIb)beta(3)) for clot formation.

Relation of endothelial function to residual platelet reactivity after clopidogrel in patients with stable angina pectoris undergoing percutaneous coronary intervention

Platelet reactivity is greater in patients with stable angina and with more extensive peripheral vascular atherosclerosis. We sought to evaluate whether impaired peripheral microcirculatory endothelial function might correlate with platelet reactivity after clopidogrel and therefore predispose to an unfavorable outcome after percutaneous coronary intervention (PCI). In 52 consecutive patients with stable angina undergoing elective PCI, endothelial function was assessed by (1) endothelial peripheral arterial tonometry (measuring the "Endoscore"); (2) the von Willebrandt factor antigen level and ristocetin co-factor activity. Basal platelet reactivity was assessed by soluble P-selectin. Patients then received a 600-mg clopidogrel loading dose > or = 12 hours before PCI. A blood sample was withdrawn 12 hours later, but before PCI, to assess platelet reactivity using the P2Y12 reaction unit and percentage of P2Y12 inhibition with the point-of-care VerifyNow P2Y12 assay. Troponin T was assessed 24 hours after PCI. The Endoscore inversely correlated with von Willebrandt factor antigen activity (r = -0.52, p = 0.0001) and soluble P-selectin concentration (r = -0.36, p = 0.021), suggesting greater platelet reactivity with increased impaired endothelial function. After clopidogrel, the Endoscore correlated directly with the percentage of P2Y12 inhibition (r = 0.36, p = 0.009) and inversely with the P2Y12 reaction unit (r = -0.41, p = 0.002), suggesting greater residual platelet reactivity with more impaired endothelial function. The average Endoscore was significantly lower in patients with troponin T elevation (troponin positive group 0.267 + or - 0.091) than in patients without troponin T elevation (troponin negative group 0.508 + or - 0.041, p = 0.015 vs troponin positive). In conclusion, an impaired endothelial response before clopidogrel was associated with greater platelet reactivity after clopidogrel. This link might explain the unfavorable PCI outcomes in patients with more severe endothelial impairment.

Lipoproteins, platelets and atherothrombosis

Atherosclerosis and thrombosis associated with the rupture of vulnerable plaque are the main causes of cardiovascular events, including acute coronary syndrome. Low-density lipoprotein (LDL) plays a key role in the pathogenesis of atherothrombotic processes. LDLs modify the antithrombotic properties of the vascular endothelium and change vessel contractility by reducing the availability of endothelial nitric oxide and activating proinflammatory signaling pathways. In addition, LDLs also influence the functions and interactions of cells present in atherosclerotic lesions, whether they come from the circulation or are resident in vessel walls. In fact, LDLs entering affected vessels undergo modifications (e.g. oxidation, aggregation and glycosylation) that potentiate their atherogenic properties. Once modified, these intravascular LDLs promote the formation of foam cells derived from smooth muscle cells and macrophages, thereby increasing the vulnerability of atherosclerotic plaque. Moreover, they also increase the thrombogenicity of both plaque and blood, in which circulating tissue factor levels are raised and platelet reactivity is enhanced. This review focuses on the importance of native and modified LDL for the pathogenesis of atherothrombosis. It also discusses current studies on LDL and its effects on the actions of vascular cells and blood cells, particularly platelets, and considers novel potential therapeutic targets.

Monocyte-platelet aggregates and platelet micro-particles in patients with post-hepatitic liver cirrhosis

INTRODUCTION

Monocytes are the cells that play a crucial role in the pathogenesis of liver damage and liver cirrhosis (LC), and as platelets, by connecting hemostasis and inflammatory processes, participate in pathogenesis of chronic liver diseases, we aimed to investigate the presence of monocyte-platelet aggregates and platelet micro-particles (PMPs) and their role in LC.

PATIENTS AND METHODS

The study included 60 patients with post-hepatitic LC and 20 healthy controls. Activated monocytes (CD11b, HLA-DR, CD14, CD16), monocyte-platelet aggregates (CD41/CD14), activated platelets (CD41/CD62) and PMPs were analyzed by flow cytometry. Their relations to the clinical and laboratory data were assessed in the studied group.

RESULTS

Patients with LC had higher levels of activated platelets, activated monocytes and monocyte-platelet aggregations as compared to healthy controls. PMPs percentage showed no significant differences between patients and controls but significantly increased in both patients with no bleeding and patients with splenomegaly compared to patients without. All studied markers showed no significant differences between patients with thrombocytopenia and those with normal platelet counts and also between patients with different disease stages. Positive correlations between monocyte-platelet aggregates and both activated platelets and monocytes were demonstrated. There were significant negative correlations between PMPs and both age and prothrombin time among patients.

CONCLUSIONS

The stage of post-hepatitic LC is not the only factor that affects the level of activated platelets, activated monocytes and monocyte-platelet aggregates. PMPs have no influence on thrombocytopenia but may have the potential to influence the progression of clotting activity in LC.

Treadmill exercise in claudicants on aspirin results in improved antioxidant status but only minimal platelet activation

The consequence of exercise on platelets remains controversial and adverse effects may result from repeated ischaemia reperfusion injury. We investigated platelet activation (platelet P-selectin (PS), and activated glycoprotein (Gp) IIb/IIIa), platelet-monocyte aggregates (PMA) and total plasma antioxidant status (TPAS) in claudicants after exercise. Twenty claudicants, taking 75 mg of aspirin daily, were subjected to repeated treadmill testing (3 km/h, 10% inclination). Blood was sampled before and after exercise. Activated GpIIb/IIIa, PS and PMA were quantified with flow cytometry. TPAS was quantified using a decolourisation assay. Percent positive cells for PS (pre-exercise 3.76% vs. 40 min post-exercise 4.10%; P < 0.05) and platelet-monocyte aggregates (pre-exercise: 25.31% vs. 40 min post-exercise 26.99%; P < 0.05) were significantly higher after exercise. Relative median fluorescence (RMF) for activated GpIIb/IIIa was significantly higher 40 min after exercise (pre-exercise: 3.04 vs. 40 min post-exercise: 4.01; P < 0.05). TPAS was significantly higher post-exercise (pre-exercise: 1.31 mmol/l vs. 1 min post-exercise: 1.40 mmol/l and 40 min post-exercise: 1.38 mmol/l; P < 0.01). Following moderate exercise, 'aspirin treated claudicants' show marginal platelet activation, PMA formation and a favourable improvement in antioxidant status. Further studies are required to assess the effect of additional antiplatelet agents and the significance of platelet-monocyte interactions. The possibility that aspirin contributes to the TPAS changes following exercise needs to be investigated.

Functional interplay between platelet activation and endothelial dysfunction in patients with coronary heart disease

Platelet-monocyte binding and surface P-selectin expression are sensitive markers of platelet activation. Endothelium-derived factors are known to inhibit platelet activation and may confer important anti-atherothrombotic effects. We assessed the relationship between platelet activation and endothelium-dependent vasomotion in patients with coronary heart disease (CHD). Twenty male patients with stable CHD were compared with 20 healthy men. Platelet-monocyte binding and platelet surface expression of P-selectin were assessed using two-colour flow cytometry on whole blood. Forearm blood flow was assessed in patients using venous occlusion plethysmography during intra-arterial infusions of substance P, acetylcholine and sodium nitroprusside. Platelet activation was higher in patients than healthy men (platelet-monocyte binding, 27 +/- 3 vs. 20 +/- 1%; P < 0.05). In patients with CHD, there was an inverse correlation between maximal substance P induced vasodilatation and both platelet-monocyte binding (P = 0.003) and P-selectin expression (P = 0.02). A similar correlation was observed between platelet-monocyte binding and the vasomotor response to acetylcholine (P = 0.08) but not with sodium nitroprusside. In patients with stable coronary heart disease, there is a strong inverse relationship between markers of platelet activation and endothelium-dependent vasomotor function. This may explain the pathophysiological mechanism linking endothelial vasomotor dysfunction and the risk of acute atherothrombotic events.

Platelet activity, reactivity and platelet-leukocyte conjugate formation before and after exhaustive or moderate exercise in patients with IDDM

Diabetes mellitus alters blood coagulation and platelet function which supports the suggestion that diabetes mellitus is a hypercoagulable state. Firstly the aim of the study was to investigate if differences in platelet activity, reactivity and platelet-leukocyte conjugate (PLC) formation can be observed in subjects with IDDM; secondly, if differences can be seen between the diabetic and control group concerning exercise-induced changes in platelet activation and conjugate formation; and thirdly, if different types of exercise lead to different patterns in platelet activation. Sixteen subjects with IDDM and 16 controls underwent a maximal step test and an endurance test (90% IAT, 45 min). Blood samples were taken after 30 min rest, and immediately and 1 h after completion of exercise. CD62P expression and differentiated platelet-leukocyte conjugates (CD45, CD14, CD41) were detected flow-cytometrically with and without stimulation with TRAP-6. The rest values of the platelet-granulocyte (PGC) and platelet-lymphocyte conjugates (PLyC) were higher (P < 0.05) in the diabetics. After exercise, platelet reactivity (CD62P-TRAP; P < 0.05) but not the activity (CD62P-unstimulated), as well as all different conjugates with or without stimulation were increased (P < 0.05) independently from the group. Differences according to the type of exercise were barely observable. IDDM without vascular complications leads to higher PCG and PLyC at rest and to identical increases in differentiated platelet-leukocyte formation after exercise in comparison with matched controls.

Increased leukocyte aggregates are associated with atherosclerosis in patients with hemodialysis

Little data are available on the role of blood rheology in atherosclerosis in hemodialysis (HD) patients. This study sought to assess the relationship between leukocytes conjugated with platelets (leukocyte aggregates [LA]) and atherosclerosis in patients with HD. The present study included 118 patients on HD. As surrogate markers of atherosclerosis, aortic stiffness measured by brachial-ankle pulse wave velocity, and carotid intima-media thickness (IMT) were measured. As an assessment of LA, a method, microchannel array flow analyzer, which makes it possible to directly observe the flow of blood cell elements through the microchannel, was used. We measured a number of LA during 50 microL flow of whole blood through microchannels. In 12 age-matched healthy individuals, a number of LA during 50 microL flow of whole blood was 25.7+/-5.4, whereas in HD patients it was significantly increased up to 48.2+/-16.4 (P<0.001). Flow cytometry demonstrated that LA were predominantly monocytes. Leukocyte aggregates were positively associated with plasma levels of fibrinogen (P<0.01), or serum high-sensitive C-reactive protein (P<0.01). Moreover, LA had highly significant associations with brachial-ankle pulse wave velocity (P<0.001) and IMT (P<0.001). In conclusion, we demonstrated hemorheologically that monocyte-platelet conjugates play an important role in aortic stiffness and IMT in HD patients.

The problem of persistent platelet activation in acute coronary syndromes and following percutaneous coronary intervention

Platelets play a central role in the atherosclerotic inflammatory response, thrombotic vascular occlusion, microembolization, vasoconstriction, and plaque progression. Persistent platelet activation poses a serious problem among patients with acute coronary syndromes (ACS) and those who have undergone percutaneous coronary intervention (PCI), placing them at risk for ischemic events and subacute stent thrombosis. Patients undergoing PCI are at risk for further ischemic events because of procedure-related platelet activation as well as the inherent persistent platelet hyperreactivity and enhanced thrombin generation associated with ACS. Persistent platelet activation following an acute coronary event and/or PCI supports incorporating antiplatelet strategies into the standard medical management of such patients. In this clinical setting, antiplatelet therapies are capable of improving outcomes. Aspirin, thienopyridines, and glycoprotein IIb/IIIa inhibitors, the 3 major pharmacologic approaches to persistent platelet activation, target various levels of the hemostatic pathways and thrombus formation.

Regulation of CD40L (CD154) and CD62P (p-selectin) surface expression upon GPIIb-IIIa blockade of platelets from stable coronary artery disease patients

INTRODUCTION

The aim of this study was to further characterize the effect of the antiplatelet agents, aspirin and eptifibatide, on the surface expression of CD40L and CD62P on platelets from patients with stable coronary artery disease.

MATERIALS AND METHODS

Platelet function was evaluated using standard light transmission aggregometry. Measurements of CD62P and CD40L were carried out by flow cytometry and ELISA assays.

RESULTS

All patients had the expected level of platelet aggregation inhibition in response to 20 muM ADP in the presence of increasing eptifibatide concentrations. Platelet activation by adenosine diphosphate (ADP) or thrombin agonist peptide (TRAP) increased CD62P and CD40L surface density in the presence of aspirin by 1.9 - 2.8 -fold. Aspirin treatment did not prevent either CD62P or CD40L expression. Eptifibatide pretreatment at pharmacologically relevant concentrations blocked agonist-induced increases in CD62P platelet surface density. A marked percentage of platelets still expressed low levels of surface CD62P suggesting slight platelet activation even with potent platelet inhibition. Eptifibatide also blocked agonist-induced increases in CD40L surface expression and decreased the percent of platelets positive for surface CD40L. Decreased expression of CD40L was due to an inhibition of CD40L translocation and not caused by enhanced shedding from the surface, as soluble CD40L (sCD40L). Eptifibatide concentrations that effectively blocked platelet aggregation correlated with total inhibition of increased CD62P and CD40L surface density.

CONCLUSION

Blockade of the GPIIb-IIIa receptor on platelets from coronary artery disease patients may have significant bearing on reducing proinflammatory and procoagulant events mediated by CD62P and sCD40L.

Depressive symptoms are associated with soluble P-selectin reactivity to acute exercise in heart failure

BACKGROUND

To determine the effects of depressive symptom severity on the circulating soluble adhesion molecule response to an acute exercise challenge in patients with heart failure (HF) compared with control subjects.

METHODS

Thirty-eight male HF patients and 19 male control subjects (mean age +/- SEM: 55.5 +/- 1.9) completed the Beck Depression Inventory (BDI) before undergoing a moderate 20-minute bicycle exercise at approximately 65% to 70% VO(2peak). Plasma levels of the soluble adhesion molecules P-selectin (sP-selectin) (sCD62P) and soluble intercellular adhesion molecule-1 (sICAM-1) were determined immediately before and after and 10 minutes after exercise.

RESULTS

Higher BDI scores moderated greater increases in sP-selectin levels in response to exercise over time in HF patients as compared with control subjects [F(1.8/84.5) = 3.25, p = .05]. Post hoc testing revealed that in HF patients, but not in control subjects, higher BDI scores were significantly associated with greater increases in sP-selectin levels over time in response to exercise [BDI by exercise interaction: F(1.6/49.6) = 5.67, p = .010]. Also, in HF patients, but not in control subjects, higher BDI scores were associated with higher sP-selectin levels at pre-exercise and postexercise time points [main effect BDI: F(1/31) = 4.86, p = .035].

CONCLUSIONS

Our findings suggest that in male HF patients with increasing depressive symptom severity, levels of the adhesion molecule sP-selectin are higher before and after exercise and have greater increases in response to exercise. This could have implications for acute coronary syndromes associated with exercise and thereby may impact mortality.

Platelet function following acute cerebral ischemia

BACKGROUND

Studies have previously identified increased levels of platelet activation following acute ischemic stroke. In order to evaluate new antiplatelet agents and their combinations, there is a need for accurate measures of platelet activation.

METHODS

Blood was taken from 17 patients within 24 hours of an acute ischemic stroke, and then at 3, 7, 14 and 42 days. For comparison, a group of 18 stable arteriopaths had identical tests performed. Platelet aggregation was measured using a free platelet counting technique, and platelet surface P-selectin and monocyte platelet aggregates (MPAs) were measured using flow cytometry. Soluble P-selectin and D-dimers were measured by an enzyme linked immune assay.

RESULTS

The initial level of MPAs was significantly raised in the stroke patients compared with the stable patients (p = 0.04, 14.2% vs. 9.3%); however, this difference was not significantly higher than later study points (14.2%, 10.1%, 9.3%, 11.9%, 11.3%; days 1, 3, 7, 14 and 42 respectively. Day 1 vs. day 7 p = 0.07 ANOVA). No changes in P-selectin or platelet aggregation were identified. D-dimer levels were significantly higher on day 7 than day 42 (p < 0.01), and fibrinogen levels were elevated on both days 3 and 14 compared with day 42. Fibrinogen levels were not elevated compared with stable patients.

CONCLUSIONS

MPA levels are elevated following an acute ischemic stroke compared to stable patients, but no significant change was seen with other platelet markers. This study suggests MPAs are a more sensitive marker of platelet activation than either P-selectin or aggregation.