Platelet function in acute myocardial infarction treated with direct angioplasty

[Clinical pharmacology of current antiplatelet drugs]

Dual antiplatelet therapy with low-dose acetylsalicylic acid (ASA) and an inhibitor of the P2Y12 adenosine diphosphate (ADP) receptor is the standard treatment for patients presenting with acute coronary syndrome (ACS) or undergoing elective coronary interventions according to the current guidelines published by the European Society of Cardiology (ESC). New generation P2Y12 inhibitors, such as prasugrel and ticagrelor exert stronger and more consistent inhibition of the P2Y12 receptor. In clinical studies enrolling patients with ACS these drugs decreased the incidence of ischemic events compared to the standard therapy with clopidogrel and ASA; however, this beneficial effect was associated with an increase in bleeding events. Alternative therapeutic approaches via addition of drugs with different modes of action showed an overall reduction of ischemic events but also failed to uncouple this beneficial effect from an increased bleeding risk.

Cangrelor: an emerging therapeutic option for patients with coronary artery disease

OBJECTIVES

To perform a systematic up-to-date review and critical discussion of potential clinical applications of cangrelor based on its pharmacologic properties and the main findings from randomized clinical studies.

METHODS

A database search (PubMed, CENTRAL and Google Scholar) by two independent investigators, including proceedings from scientific sessions of ACC, AHA, ESC, TCT and EuroPCR, from January 1998 through December 2013.

RESULTS

Cangrelor is a potent, intravenous, direct-acting P2Y12 antagonist with rapid onset and quickly reversible action. In contrast to ticagrelor, cangrelor's interaction with thienopiridines requires termination of cangrelor infusion before switching to clopidogrel or prasugrel. According to randomized trials, a cangrelor-clopidogrel combination is relatively safe and more effective than the standard clopidogrel regimen in both urgent and elective percutaneous coronary intervention (PCI) settings, with the advantage of this drug combination fully evident when the universal definition of myocardial infarction is applied. In contrast to available antiplatelet drugs with delayed onset and offset of action, its favorable properties make cangrelor a desirable agent for ad hoc elective PCI, high risk acute coronary syndromes treated with immediate coronary stenting and for bridging those surgery patients who require periprocedural P2Y12 inhibition. Current evidence on cangrelor therapy is limited by the lack of adequately powered studies assessing cangrelor co-administration either with prasugrel or ticagrelor, suboptimal design of some of the trials favoring cangrelor, potentially attenuated benefits with modern stent design, and finally, by the lack of survival advantage.

CONCLUSIONS

With its pharmacokinetic and pharmacodynamic advantages, allowing consistent and strong P2Y12 inhibition, and with its rapid onset and swift reversal of action devoid of need for an antidote, cangrelor might improve clinical outcomes in clopidogrel-treated patients by reducing ischemic events, while maintaining a favorable safety profile. However, further studies, addressing the safety and efficacy of cangrelor on top of novel oral P2Y12 inhibitors, are warranted.

Microparticles in health and disease

Microparticles (MPs), small membrane-derived vesicles, are derived from many cell types and released into the circulation. Microparticles can express antigens, and contain cell surface proteins, cytoplasmic contents, and nuclear components from their cell of origin that determines their composition, characterization, and transfer of biologic information. Certain prompts for this release include shear stress, complement activation, proapoptotic stimulation, cellular damage, or agonist interaction with cell surface receptors. Release can be physiologic or pathologic and is associated with proinflammatory and procoagulant effects and has been implicated in thrombotic states. Microparticles also contribute to systemic inflammation and cardiovascular, hematologic, and oncologic disease states. The study of MPs in human medicine is rapidly advancing and extends into the physiology of health, the pathophysiology of disease, and the role of MPs in transfusion medicine. In veterinary medicine, published work on MPs has been limited to the area of inherited disorders, blood storage, and leukoreduction (LR). Microparticle research is still in its infancy, and this review should be seen as a snapshot of what is currently known. As research continues important limitations, including variations in preanalytic variables such as collection, storage, or centrifugation, and limitations of quantitation are coming to the forefront. Correlation of quantitation of MPs with assays of activity will hopefully shed light on the true nature of MPs in health and disease. This review will focus on the role of cellular exocytic vesiculation in health, disease, and transfusion medicine.

Platelet-function testing in patients undergoing neurovascular procedures: caught between a rock and a hard place

In the context of neurointerventional procedures, clopidogrel hyper-responsiveness has been associated with hemorrhage; on the other hand, clopidogrel resistance has been associated with thromboembolism. This might seem to make a compelling argument in favor of routine platelet testing. Our reading of the literature leads us to conclude that routine platelet testing in neurointerventional procedures is not, unfortunately, ready for prime time.

High on-treatment platelet reactivity and P2Y12 antagonists in clinical trials

Dual antiplatelet therapy with aspirin and clopidogrel in patients undergoing percutaneous coronary intervention (PCI) and in patients with acute coronary syndromes (ACS) has substantially decreased the rate of cardiovascular events. Within the past decade, the variability in pharmacodynamic response as well as the moderate antiplatelet efficacy of clopidogrel has raised major concerns, since high on-clopidogrel platelet reactivity has consistently been associated with increased risk for ischaemic events in PCI patients. The variability in response could be linked to genetic polymorphisms impacting on activity of cytochrome P450 enzymes as well as clinical and demographic variables, but, taken together, factors identified so far can explain only up to approximately 12% of this variability in adenosine diphosphate-induced platelet aggregation on clopidogrel. Regulatory agencies as well as major cardiac societies suggest the use of other anti-platelet medications or alternative dosing strategies for clopidogrel in patients with reduced effectiveness of clopidogrel. This review will focus on the current status of alternate strategies for more sufficient suppression of high platelet reactivity.

Randomized comparison of new dual-antiplatelet therapy (aspirin, prasugrel) and triple-antiplatelet therapy (aspirin, clopidogrel, cilostazol) using P2Y12 point-of-care assay in patients with STEMI undergoing primary PCI

BACKGROUND

Both new dual antiplatelet therapy (DAT; aspirin and prasugrel) and triple antiplatelet therapy (TAT; aspirin, clopidogrel and cilostazol) are more potent than classic DAT (aspirin and clopidogrel). We compared the antiplatelet efficacy between new DAT and TAT in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary coronary percutaneous coronary intervention (PCI).

METHODS

Forty patients who were eligible for primary PCI were prospectively randomized to DAT group (n=20) or TAT group (n=20) immediately after hospital arrival. The primary end point was P2Y12 reaction unit (PRU) determined with the VerifyNow P2Y12 point-of-care assay at the time of discharge.

RESULTS

PRU value at discharge was significantly lower in patients receiving DAT compared with that of TAT (84.5 ± 44.7 vs. 128.4 ± 74.9, p=0.032). Percent platelet inhibition was significantly higher for DAT compared with TAT at discharge (72.1 ± 12.2 vs. 57.5 ± 23.5, p=0.020). Inter-patient variability of PRU values at discharge was significantly smaller in patient taking DAT compared with TAT (p=0.026).

CONCLUSION

A new DAT is more potent antiplatelet therapy than TAT in patients with STEMI undergoing primary PCI.

Platelet-Derived Microparticles and Platelet Function Profile in Children With Congenital Heart Disease

Platelet microparticles (PMPs) and function profile in children with congenital heart disease (CHD) have not been widely explored. We investigated platelet aggregation, flow cytometric platelet surface receptors (P-selectin and glycoprotein (GP) IIb/IIIa) and PMPs in 23 children with cyanotic CHD (CCHD), 30 children with acyanotic CHD (ACHD) and 30 healthy controls correlating these variables to hematological and coagulation parameters including von Willebrand factor antigen (vWF Ag) as a marker of endothelial dysfunction. Hemoglobin, hematocrit (HCT), d-dimer, and vWF Ag were significantly higher in CCHD than ACHD group. Platelet MPs and P-selectin expression were increased in patients than controls, particularly in CCHD and positively correlated to HCT, d-dimer, and vWF Ag while platelet count, aggregation, and GP IIb/IIIa expression were decreased in CCHD compared with ACHD group and negatively correlated to HCT. The overproduction of PMPs and platelet activation with suppressed aggregation may be implicated in the pathogenesis of coagulation/hemostatic abnormalities in children with CCHD.

The dimeric platelet collagen receptor GPVI-Fc reduces platelet adhesion to activated endothelium and preserves myocardial function after transient ischemia in mice

Platelets play a critical role in the pathophysiology of reperfusion, sepsis, and cardiovascular diseases. In a multiple step process, they adhere to activated endothelium and release proinflammatory cytokines thereby promoting the inflammatory process. Glycoprotein VI (GPVI) is the major collagen receptor on the platelet surface and triggers platelet activation and primary hemostasis. Activation of GPVI leads to stable platelet adhesion and degranulation of platelet granules. However, GPVI is critically involved in platelet adhesion to activated endothelium without exposure of subendothelial matrix. Earlier studies show that the soluble GPVI-Fc binds to collagen and protects mice from atherosclerosis and decreases neointima proliferation after arterial injury. Here, we show for the first time that recombinant GPVI-Fc binds to activated endothelium mainly via vitronectin and prevents platelet/endothelial interaction. Administration of GPVI-Fc reduced infarct size and preserved cardiac function in a mouse model of myocardial infarction. This process was associated with reduced GPVI-induced platelet degranulation and release of proinflammatory cytokines in vitro and in vivo. Taken together, administration of GPVI-Fc offers a novel strategy to control platelet-mediated inflammation and to preserve myocardial function following myocardial infarction.

Zebrafish thrombocytes: functions and origins

Platelets play an important role in mammalian hemostasis. Thrombocytes of early vertebrates are functionally equivalent to mammalian platelets. A substantial amount of research has been done to study platelet function in humans as well as in animal models. However, to date only limited functional genomic studies of platelets have been performed but are low throughput and are not cost-effective. Keeping this in mind we introduced zebrafish, a vertebrate genetic model to study platelet function. We characterized zebrafish thrombocytes and established functional assays study not only their hemostatic function but to also their production. We identified a few genes which play a role in their function and production. Since we introduced the zebrafish model for the study of hemostasis and thrombosis, other groups have adapted this model to study genes that are associated with thrombocyte function and a few novel genes have also been identified. Furthermore, transgenic zebrafish with GFP-tagged thrombocytes have been developed which helped to study the production of thrombocytes and their precursors as well as their functional roles not only in hemostasis but also hematopoiesis. This paper integrates the information available on zebrafish thrombocyte function and its formation.

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.

Platelet-derived microparticles during and after acute coronary syndrome

As microparticles are shedded upon platelet activation, and may be used to assess platelet function, we measured plasma concentrations of platelet-derived microparticles (PMPs) during and after an acute coronary syndrome (ACS). Fifty-one patients with ACS were investigated at admission, within 24 hours (before coronary angiography), and six months later. Sixty-one sex- and age-matched healthy controls were investigated once. PMPs were defined as particles <1.0 μm in size, negative to phalloidin (labels cell-fragments), and positive to CD61. Exposure of phosphatidylserine (PS+), CD62P and CD142 were also measured. Plasma concentrations of PS+PMPs exposing CD61, CD62P and CD142 were elevated 2.5, 6.0-, and 5.0-fold at admission (p<0.001 for all, compared to controls; aspirin only), decreased significantly 24 hours later following initiation of treatment with clopidogrel and subcutaneous anticoagulation (p<0.001 for all), and decreased even further six months later (p<0.01 for all). However, PS+PMPs exposing CD62P or CD142 were still between 1.2-and 2.3-fold higher than in controls (p<0.001 for both). The pattern for PS-PMPs during and after the ACS was very similar to that for PS+PMPs although the numbers were approximately 1/3 lower. In conclusion, PMP concentrations follow the pattern of platelet activation during and after an ACS. Decreased concentrations are observed after initiation of antithrombotic treatment, but PMP exposing CD62P or CD142 are still elevated after six months. Flow cytometric measurements of PMP in frozen-thawed samples enable studies of platelet function in larger clinical trials.

Validation of flow cytometric detection of platelet microparticles and liposomes by atomic force microscopy

BACKGROUND

Platelet microparticles (PMPs) are a promising prognostic marker for thrombotic disorders because of their release during platelet activation. The use of flow cytometry for the enumeration of PMPs in plasma has generated controversy due to their size, which is below the stated detection limits of conventional flow cytometry instruments. The potential impact of this is an underestimation of PMP counts.

OBJECTIVES/METHODS

To address this possibility, we used a combination of fluorescence-activated cell sorting (FACS) and atomic force microscopy (AFM) to determine the size distribution of PMPs present in plasma from acute myocardial infarction (AMI) patients and normal volunteers, and PMPs generated by expired platelet concentrates and washed platelets treated with agonists such as thrombin and calcium ionophore (A23187).

RESULTS

According to AFM image analysis, there was no statistically significant difference in height or volume distributions in PMPs from thrombin-activated, calcium ionophore-activated, expired platelet concentrates and plasma from healthy volunteers and AMI patients. Based on volume, expired platelets released the greatest proportion of exosomes (< 1.0 × 10(-22) L(3) in volume) in relation to the entire PMP population (29.7%) and the smallest proportion of exosomes was observed in AMI patient plasma (1.8%). Moreover, AFM imaging revealed that PMPs from expired platelets exhibited smooth surfaces compared with other PMP types but this was not statistically significant.

CONCLUSIONS

We confirm that flow cytometry is capable of analyzing PMPs from plasma by using AFM to perform nanoscale measurements of individual PMP events isolated by FACS. This method also provided the first quantitative nanoscale images of PMP ultrastructure.

Low molecular weight heparin versus unfractionated heparin in patients with acute non-ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention with drug-eluting stents

BACKGROUND

Whether low molecular weight heparin (LMWH) enoxaparin is equivalent to unfractionated heparin (UFH) in patients with non-ST-segment elevation myocardial infarction (NSTEMI) undergoing percutaneous coronary intervention (PCI) with drug-eluting stents (DES) remains unclear.

METHODS

A total of 2397 NSTEMI patients who underwent PCI with DES received either LMWH [n=1178, subcutaneous enoxaparin 1 mg/kg, b.i.d., initiated after the patient's arrival and continued until 3-5 days after PCI plus reduced dose of UFH (50-70 U/kg) during PCI] or UFH (n=1219, 24,000U/day infusion, initiated after the patient's arrival and continued until at least 48 h after PCI). The bleeding events and clinical outcomes during in-hospital and at 8 months were compared.

RESULTS

Enoxaparin group had similar incidences of cardiac death, total death, and total major adverse cardiac events (MACE) at 8 months compared with UFH group. The incidences of major and minor bleeding events were also similar between the two groups. Multivariable Cox regression analysis showed that enoxaparin group had similar incidences of cardiac death [adjusted odds ratio (OR) 1.16, 95% confidence interval (CI) 0.64-2.10, p=0.620], total death (adjusted OR 1.08, 95% CI 0.66-1.76, p=0.760), and total MACE (adjusted OR 0.94, 95% CI 0.69-1.28, p=0.692) at 8 months as compared with UFH group.

CONCLUSIONS

Enoxaparin with reduced dose of UFH only during PCI as an adjunctive antithrombotic therapy in NSTEMI patients undergoing PCI with DES was safe and showed comparable 8-month clinical outcomes as compared with UFH alone.

High on treatment platelet reactivity

The addition of clopidogrel to aspirin for patients undergoing percutaneous coronary intervention (PCI) had significantly reduced cardiovascular events. However, despite dual antiplatelet therapy ischaemic events still occur, especially stent thrombosis, which is associated with a high mortality rate. Inter-individual response to clopidogrel is highly variable. It was shown that 4-46% could be considered as high on treatment platelet reactivity (HTPR). Recent studies had demonstrated a relationship between HTPR and ischaemic events in the setting of PCI. Actually the assessment of platelet reactivity in routine practice and its interpretation to make a decision is a debatable issue.

The PPAR-Platelet Connection: Modulators of Inflammation and Potential Cardiovascular Effects

Historically, platelets were viewed as simple anucleate cells responsible for initiating thrombosis and maintaining hemostasis, but clearly they are also key mediators of inflammation and immune cell activation. An emerging body of evidence links platelet function and thrombosis to vascular inflammation. peroxisome proliferator-activated receptors (PPARs) play a major role in modulating inflammation and, interestingly, PPARs (PPARβ/δ and PPARγ) were recently identified in platelets. Additionally, PPAR agonists attenuate platelet activation; an important discovery for two reasons. First, activated platelets are formidable antagonists that initiate and prolong a cascade of events that contribute to cardiovascular disease (CVD) progression. Dampening platelet release of proinflammatory mediators, including CD40 ligand (CD40L, CD154), is essential to hinder this cascade. Second, understanding the biologic importance of platelet PPARs and the mechanism(s) by which PPARs regulate platelet activation will be imperative in designing therapeutic strategies lacking the deleterious or unwanted side effects of current treatment options.

Pharmacological prevention of peri-, and post-procedural myocardial injury in percutaneous coronary intervention

In recent years, percutaneous coronary intervention (PCI) has become a well-established technique for the treatment of coronary artery disease. PCI improves symptoms in patients with coronary artery disease and it has been increasing safety of procedures. However, peri- and post-procedural myocardial injury, including angiographical slow coronary flow, microvascular embolization, and elevated levels of cardiac enzyme, such as creatine kinase and troponin-T and -I, has also been reported even in elective cases. Furthermore, myocardial reperfusion injury at the beginning of myocardial reperfusion, which causes tissue damage and cardiac dysfunction, may occur in cases of acute coronary syndrome. Because patients with myocardial injury is related to larger myocardial infarction and have a worse long-term prognosis than those without myocardial injury, it is important to prevent myocardial injury during and/or after PCI in patients with coronary artery disease. To date, many studies have demonstrated that adjunctive pharmacological treatment suppresses myocardial injury and increases coronary blood flow during PCI procedures. In this review, we highlight the usefulness of pharmacological treatment in combination with PCI in attenuating myocardial injury in patients with coronary artery disease.

Clopidogrel response variability and the advent of personalised antiplatelet therapy. A bench to bedside journey

Platelet-mediated thrombosis is a dreaded clinical event and is the primary cause of acute coronary syndromes and post-percutaneous intervention (PCI) ischaemic events. There has been a long standing interest in the ex vivo quantification of platelet reactivity to assess the risk of thrombosis. Early studies demonstrated platelet activation and heightened platelet reactivity in acute coronary syndromes and after PCI. However, a demonstration that heightened reactivity actually precipitated the ischaemic event was lacking. Our knowledge of platelet receptor physiology and the advent of novel inhibitors have significantly advanced the field. The P2Y12 receptor has been shown to play a pivotal role in the amplification of platelet activation by multiple agonists and its inhibition has resulted in improved clinical outcomes. The most widely used drug to block P2Y12 receptor, clopidogrel is associated with resistance in selected patients and these patients have been shown to be at increased risk for post-PCI ischaemic event occurrence in multiple studies. Importantly, a threshold of high platelet reactivity has been demonstrated, and beyond this threshold ischaemic events occur precipitously. Based on the current evidence, it is rational to quantify the intensity of the ADP-P2Y12 interaction in the patient at the greatest risk for thrombosis-the PCI patient. However, there is only evidence from small clinical trials demonstrating the clinical efficacy of changing an antiplatelet regimen based on an ex vivo platelet function measurement. Moreover, there are numerous patients with vulnerable coronary anatomy that have not yet experienced plaque rupture; the prognostic role of a measurement of platelet reactivity in the latter group has never been studied. Large-scale trials are ongoing that will investigate the role of personalised antiplatelet therapy in the PCI patient.

The role of platelets in atherothrombosis

Platelets have evolved highly specialized adhesion mechanisms that enable cell-matrix and cell-cell interactions throughout the entire vasculature irrespective of the prevailing hemodynamic conditions. This unique property of platelets is critical for their ability to arrest bleeding and promote vessel repair. Platelet adhesion under conditions of high shear stress, as occurs in stenotic atherosclerotic arteries, is central to the development of arterial thrombosis; therefore, precise control of platelet adhesion must occur to maintain blood fluidity and to prevent thrombotic or hemorrhagic complications. Whereas the central role of platelets in hemostasis and thrombosis has long been recognized and well defined, there is now a major body of evidence supporting an important proinflammatory function for platelets that is linked to host defense and a variety of autoimmune and inflammatory diseases. In the context of the vasculature, experimental evidence indicates that the proinflammatory function of platelets can regulate various aspects of the atherosclerotic process, including its initiation and propagation. The mechanisms underlying the proatherogenic function of platelets are increasingly well defined and involve specific adhesive interactions between platelets and endothelial cells at atherosclerotic-prone sites, leading to the enhanced recruitment and activation of leukocytes. Through the release of chemokines, proinflammatory molecules, and other biological response modulators, the interaction among platelets, endothelial cells, and leukocytes establishes a localized inflammatory response that accelerates atherosclerosis. These inflammatory processes typically occur in regions of the vasculature experiencing low shear and perturbed blood flow, a permissive environment for leukocyte-platelet and leukocyte-endothelial interactions. Therefore, the concept has emerged that platelets are a central element of the atherothrombotic process and that future therapeutic strategies to combat this disease need to take into consideration both the prothrombotic and proinflammatory function of platelets.

Circulating microparticles in cardiovascular disease: implications for atherogenesis and atherothrombosis

The complex and multifactorial nature of atherogenesis and development of atherothrombotic complications involves numerous interactions between various cell types inside the vascular wall (e.g. macrophages and smooth muscle cells) and in the blood (e.g. leukocytes and platelets). One relatively recent advance in this area is the discovery of circulating microparticles and their role in endothelial damage, platelet activation, hypercoagulability and regulation of inter-cellular interactions. Microparticles are small anucleoid phospholipid vesicles released from different cells, such as platelets, erythrocytes, leukocytes and endothelial cells. Microparticles carry surface proteins and include cytoplasmic material of the parental cells responsible for the exertion of microparticle-mediated biological effects. About 25% of the procoagulant activity of stimulated platelet suspensions is associated with microparticles released upon platelet activation and their surface may be approximately 50-100-fold more procoagulant than the surface of activated platelets per se. The available lines of evidence indicate that shedding of microparticles from the parental cells is not just a passive process accompanying cellular dysfunction and apoptosis, but a tightly regulated mechanism implicated in the interactions between various cell types. The role of microparticles as biological messengers is supported by their differential and specific involvement in the pathophysiology of different cardiovascular disorders, including atherogenesis and thrombosis.

Cellular phenotype switching and microvesicles

Cell phenotype alteration by cell-derived vesicles presents a new aspect for consideration of cell fate. Accumulating data indicates that vesicles from many cells interact with or enter different target cells from other tissues, altering their phenotype toward that of the cell releasing the vesicles. Cells may be changed by direct interactions, transfer of cell surface receptors or epigenetic reprogramming via transcriptional regulators. Induced epigenetic changes appear to be stable and result in significant functional effects. These data force a reconsideration of the cellular context in which transcription regulates the proliferative and differentiative fate of tissues and suggests a highly plastic cellular system, which might underlay a relatively stable tissue system. The capacity of marrow to convert to non-hematopoietic cells related to vesicle cross-communication may underlie the phenomena of stem cell plasticity. Additionally, vesicles have promise in the clinical arenas of disease biomarkers, tissue restoration and control of neoplastic cell growth.

Platelet interactions as therapeutic targets for prevention of atherothrombosis

Physiologically, platelets perform important tasks to maintain the homeostasis of the vascular wall and the surrounding environment. In pathologic conditions, however, platelets contribute to the formation of atherosclerotic plaques as well as to atherothrombotic events (i.e., acute myocardial infarction). This review aims to elucidate the role of platelets in atherogenesis and atherothrombosis and to provide an insight into current and future strategies for platelet inhibition.

Actual Role of Platelet Glycoprotein IIb/IIIa Receptor Inhibitors as Adjunctive Pharmacological Therapy to Primary Angioplasty in Acute Myocardial Infarction: In the Light of Recent Randomized Trials and Observational Studies with Bivalirudin

Strategies for preventing ischemic complications during percutaneous coronary interventions (PCI) in the setting of acute myocardial infarction (AMI) have focused on the platelet surface-membrane glycoprotein (GP) IIb/IIIa receptor. The platelet GP IIb/IIIa receptor inhibitors, by blocking the final common pathway of platelet aggregation, have become a breakthrough in the management of acute coronary syndromes. Current adjuvant pharmacological therapy of AMI with aspirin, clopidogrel, unfractionated heparin (UH), and platelet GP IIb/IIIa inhibitors provides useful therapeutic benefits. Although the use of more potent antithrombin and antiplatelet agents during PCI in AMI has reduced the rate of ischemic complications, in parallel, the rate of bleeding has increased. Several studies have reported an association between bleeding after PCI and an increase in morbidity and mortality. Therefore, investigational studies have focused in pharmacological agents that would reduce bleeding complications without compromising the rate of major adverse cardiovascular events. Based on the results of several randomized trials, abciximab with UH, aspirin and clopidogrel have become a standard adjunctive therapy with primary PCI for AMI. However, some of the trials were done before the use of stents and the widespread use of thienopyridines. In addition, GP IIb/IIIa inhibitors use have been associated with thrombocytopenia, high rates of bleeding, and the need for transfusions, which increase costs, length of hospital stay, and mortality. On the other hand, in the stent era, bivalirudin, a semi-synthetic direct thrombin inhibitor, has recently been shown to provide similar efficacy with less bleeding compared with unfractionated heparin plus platelet GP IIb/IIIa inhibitors in AMI patients treated with primary PCI. The impressive results of this recent randomized trial and other observational studies make a strong argument for the use of bivalirudin rather than heparin plus GP IIb/IIIa inhibitors for the great majority of patients with AMI treated with primary PCI. However, some controversial results and limitations in the studies with bivalirudin exert some doubts in the future widespread use of this drug.

Low-molecular-weight heparin versus unfractionated heparin in acute ST-segment elevation myocardial infarction patients undergoing primary percutaneous coronary intervention with drug-eluting stents

BACKGROUND

Whether low-molecular-weight heparin (LMWH) is superior to unfractionated heparin (UFH) in acute ST-segment elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI) with drug-eluting stents (DESs) remains unclear.

METHODS

A total of 3,372 STEMI patients who underwent primary PCI with DESs received either LMWH (n = 1,531 patients, subcutaneous enoxaparin 1 mg/kg, bid for 3-5 days plus reduced dose of UFH [50 U/kg] during PCI) or UFH alone (n = 1,841 patients, intravenous bolus injection of 5,000 U, followed by 24,000 U/d infusion for at least 48 hours). The bleeding events and clinical outcomes during in-hospital and at 8 months were compared.

RESULTS

The incidences of major and minor bleeding events were similar between the 2 groups. Multivariable Cox regression analysis showed that LMWH group had lower incidences of cardiac death (adjusted odds ratio [OR] 0.55, 95% CI 0.39-0.77, P < .001), total death (adjusted OR 0.50, 95% CI 0.37-0.68, P < .001), and total major adverse cardiac events (adjusted OR 0.77, 95% CI 0.62-0.95, P = .017) at 8 months as compared with UFH group. Similar results were obtained across different subgroups including different DESs, age, and sex.

CONCLUSIONS

The LMWH enoxaparin combined with reduced dose of UFH (50 U/kg) administration as an adjunctive antithrombotic therapy in STEMI patients undergoing primary PCI with DESs seems to be safe and efficacious. However, randomized clinical trials are needed to confirm this conclusion.

Comparative Anticoagulant and Platelet Modulatory Effects of Enoxaparin and Sulodexide

Sulodexide represents a novel antithrombotic agent with multiple sites of action on blood coagulation and vascular processes. The purpose of this study was to compare sulodexide and enoxaparin on anticoagulant effects, tissue factor (TF)-induced activation of platelets, inhibition of microparticle generation and to investigate their effect on heparin-induced platelet aggregation (HIPA). Sulodexide was compared with enoxaparin at equigravimetric concentrations. When compared to enoxaparin, sulodexide produced a stronger anticoagulant effect in the prothrombin time (PT), activated partial thromboplastin time (APTT), Heptest, and thrombin time (TT) assays. In addition, sulodexide had a stronger inhibitory effect on TF-mediated microparticle generation (IC50 = 2.8 μg/ mL), P-selectin expression (IC50 = 4.8 μg/ml), and platelet aggregate formation (IC50 = 8.5 μg/mL) compared to higher IC50 values with enoxaparin. Sulodexide and enoxaparin exhibited a similar effect on heparin-induced thrombocytopenia (HIT) antibody-mediated platelet activation HIPA assays. These results suggest that sulodexide is a relatively stronger anticoagulant agent than enoxaparin. Sulodexide is subcutaneously absorbed. Its ability to inhibit TF-mediated platelet activation may contribute to the observed therapeutic effects of sulodexide in microvascular vasculopathy such as diabetic nephropathy. These results also suggest that inhibition of TF activation of platelets by sulodexide may be independent of its anticoagulant effects. These results warrant further investigation of sulodexide in additional preclinical and clinical studies.

Intradialytic and postdialytic platelet activation, increased platelet phosphatidylserine exposure and ultrastructural changes in platelets in children with chronic uremia

The present research evaluated the intradialytic and postdialytic changes in platelet factor-4 and beta-thromboglobulin plasma levels by enzyme-linked immunoadsorbent assay method and platelet aggregation by ADP as well as flow cytometric percentage of annexin-V-positive platelets as a measure of phosphatidylserine externalization and ultrastructural examination of platelets in 37 uremic patients on regular hemodialysis and 25 age-matched and sex-matched controls. Platelet factor-4 plasma levels increased, remain consistently high during hemodialysis session (20.24 +/- 3.05 IU/ml after 30 min, P < 0.001 and 23.67 +/- 3.68 IU/ml after 240 min, P < 0.001) and returned to control values (6.10 +/- 1.54 IU/ml) only after 24 h following the end of the session. beta-Thromboglobulin showed a trend similar to that of platelet factor-4. Platelet aggregation by ADP showed reduced function in comparison with controls (69.32 +/- 12.37 versus 91.95 +/- 1.59%, P < 0.001). Flow cytometric percentage of annexin-V-positive platelet was significantly elevated (P < 0.001) in uremic patients when compared with normal controls. Ultrastructural studies of platelets 30 min after starting of dialysis showed degranulation of its granules and at 240 min showed complete degranulation, whereas in the postdialytic phase (12 h after the end of dialysis) refilled alpha-granules started to appear. Positive correlations were found between platelet concentration and platelet factor-4 and beta-thromboglobulin plasma levels during and after dialysis (P < 0.001) and with annexin-V-positive platelets percentage (P < 0.001). In conclusion, activated platelets were found in chronic hemodialysis patients, a finding that may explain why uremic patients often suffer from thrombotic accidents. The platelet activation is associated with exposure of phosphatidylserine on the platelet exterior. Platelet factor-4 and beta-thromboglobulin are released from platelets as a result of a defect in their granules membrane as shown by the electron microscopy, mainly as a consequence of the blood-membrane contact during dialysis, and they return only slowly to control values.

Elevated platelet microparticles in stable coronary artery disease are unrelated to disease severity or to indices of inflammation

Platelet microparticles (PMPs), procoagulant membrane vesicles derived from activated platelets, are elevated in acute myocardial infarction and unstable angina but their relationship to inflammation and indices of coronary artery disease are unclear. We therefore hypothesised that PMPs are related to scores of coronary atheroma and/or coronary stenosis. Our study was completed by comparing PMP data with other platelet markers and with hs-CRP, marking inflammation. We recruited 54 patients attending for coronary angiography, comparing them to 35 age- and sex-matched controls. Peripheral blood was analysed for PMPs, percent platelets positive for CD62P and CD63 (all flow cytometry), soluble P selectin and hsCRP (both immunoassay). Patients exhibited higher PMPs, increased platelet %CD62P, %CD63 and soluble P selectin (all P < 0.01) and hs-CRP (P = 0.0167) than healthy controls. However, analysing only patients with an unequivocal classification, there were no significant (P </= 0.01) correlations with coronary atheroma or coronary stenosis. These findings provide no support for the hypothesis that PMPs are related to the degree of coronary artery disease and therefore may simply be a marker of widespread inappropriate platelet activity.

Temporal pattern of ischemic events in relation to dual antiplatelet therapy in patients with unprotected left main coronary artery stenosis undergoing percutaneous coronary intervention

OBJECTIVES

The aim of this study was to investigate whether there is a temporal pattern of ischemic events in relation to dual antiplatelet therapy in patients with unprotected left main coronary artery (ULMCA) stenosis treated with percutaneous coronary intervention (PCI).

BACKGROUND

Identifying which periods during follow-up of patients with ULMCA stenosis treated with PCI are associated with higher risk of clinical events might help to improve therapeutic strategies.

METHODS

We analyzed data from 15 centers involved in an observational study conducted by the Italian Society of Invasive Cardiology on patients with ULMCA stenosis treated with PCI. Eight hundred ninety-four patients were enrolled.

RESULTS

At 30-day follow-up, the rate of cardiac mortality and myocardial infarction (MI) was 5.4%. In patients still taking dual antiplatelet therapy, the adjusted incidence rate ratio/10,000 patient-days of the combination of cardiac mortality and MI in the 31- to 180-day interval compared with the 181- to 360-day interval after PCI was 3.64 (p = 0.035). This risk was particularly high in patients with acute coronary syndromes. After stopping clopidogrel, the adjusted incidence rate ratio of cardiac mortality and MI in the 0- to 90-day interval compared with the 91- to 180-day interval was 4.20 (p = 0.009).

CONCLUSIONS

In patients with ULMCA stenosis taking dual antiplatelet therapy there is an increased hazard of cardiac mortality and MI between 31 and 180 days compared with 181 to 360 days. Furthermore, there is an increased hazard of cardiac mortality and MI in the first 90 days after stopping clopidogrel.

Levels and value of platelet activation markers in different subtypes of acute non-cardio-embolic ischemic stroke

INTRODUCTION

Platelet activation and its interaction with leukocytes are important in the pathophysiology of ischemic stroke. This study aimed to evaluate the value of platelet activation and platelet-leukocyte interaction in different subtypes of acute, non-cardio-embolic ischemic stroke.

METHODS

Fifty-four patients with acute, non-cardio-embolic ischemic stroke, including 32 small-vessel and 22 large-vessel diseases, were evaluated. Platelet activation markers (CD62P, CD63, and CD40L) and platelet-leukocyte interaction were measured by flow cytometry at different time points (<48 hours and Days 7, 30, and 90 post-ischemic stroke). Markers were also evaluated in 28 other stroke patients in the convalescent stage (3 to 9 months after acute stroke) and in 28 control subjects.

RESULTS

Patients with ischemic stroke had significantly increased circulating CD62P, CD63, platelet-monocyte interaction, and platelet-lymphocyte interaction in the acute stage compared with the convalescent stage and control groups. Levels of CD62P and CD63 were significantly higher in the large-vessel disease group than in the small-vessel disease group, and differences in CD62P were significant even at one month. The CD40L level in the poor outcome group was significantly higher than that in the good outcome group. Stroke patients with diabetes mellitus and large-vessel disease were associated with poor outcome.

CONCLUSIONS

Patients with large-vessel cerebral infarction elicit higher platelet activation and platelet-leukocyte interaction compared to small-vessel infarction. Further large scale trials are warranted to evaluate the relationship between platelet activation markers and outcome in stroke patients under different anti-platelet therapies, and to clarify optimal treatment.

The role of subintimal angioplasty in the management of arterial disease of the lower limb: the North-East of Scotland experience

INTRODUCTION

The management of occlusive femoropopliteal disease continues to evolve and a definitive strategy remains to be defined. We examine the utility ofsubintimal angioplasty (SIA) in our institution.

METHODS

A retrospective study with predefined end-points, including technical success and primary patency.

RESULTS

61 consecutive cases were identified (claudicants n=29 and critical ischaemia n=32). Sixty-four percent of occlusions were greater than 10 cm with poor run-off (60% with two vessels or less). Technical and physiological success was 95% and 79% respectively, with clinical improvement reported by 72%. At a mean follow-up of 20 months twelve-month primary patency (assessed clinically, with ABPI and selective duplex scanning) was 67% (subgroup analysis: claudicants 83%, criticals 53%, p=0.02) and morbidity 8% with no limb loss or procedure related mortality.

CONCLUSION

SIA is an effective procedure for chronic lower limb ischaemia with acceptable outcome. Our experience correlates well with evidence in the current literature.

Glycoprotein IIb/IIIa antagonists in acute ischaemic stroke: current status and future directions

Glycoprotein (GP) IIb/IIIa receptors on the surface of platelets play a critical role in thrombosis. Intravenous GP IIb/IIIa antagonists abciximab, tirofiban and eptifibatide have demonstrated efficacy in acute coronary syndromes when combined with heparin, aspirin, clopidogrel and percutanous coronary interventions. Results have been less consistent in acute ischaemic stroke. Preclinical data support the potential benefit of these agents both in the microcirculation and in aiding clot lysis. While phase I and II trials of abciximab as the sole agent employing dosages comparable with those used in coronary syndromes were promising, the pivotal phase III trial was abandoned because of an unfavourable benefit-to-risk ratio. New preliminary platelet inhibition measurements from our group suggest that cardiac dosages were likely to be too high for stroke patients. Exploration of lower dosages of abciximab and potentiation with time-limited weight-based heparin along with platelet aggregation inhibition measurement is continuing on a smaller scale. At present, the most common usage of GP IIb/IIIa antagonists in stroke are as adjunctive agents to thrombolysis by intravenous and intra-arterial routes. Substantial progress is likely to require a better understanding of the mechanism of actions and unique pharmacology of GP IIb/IIIa antagonists in ischaemic stroke.