Showing papers in "Thrombosis and Haemostasis in 2009"

Cell-derived microparticles in haemostasis and vascular medicine

Abstract: Considerable interest for cell-derived microparticles has emerged, pointing out their essential role in haemostatic response and their potential as disease markers, but also their implication in a wide range of physiological and pathological processes. They derive from different cell types including platelets - the main source of microparticles - but also from red blood cells, leukocytes and endothelial cells, and they circulate in blood. Despite difficulties encountered in analyzing them and disparities of results obtained with a wide range of methods, microparticle generation processes are now better understood. However, a generally admitted definition of microparticles is currently lacking. For all these reasons we decided to review the literature regarding microparticles in their widest definition, including ectosomes and exosomes, and to focus mainly on their role in haemostasis and vascular medicine.

Impact of proton pump inhibitors on the antiplatelet effects of clopidogrel

Abstract: Patients receiving dual antiplatelet treatment with aspirin and clopidogrel are commonly treated with proton pump inhibitors (PPIs). Attenuating effects on platelet response to clopidogrel have been reported solely for the PPI omeprazole. PPIs differ in their metabolisation properties as well as their potential for drug-drug interactions. The aim of this study was to investigate the impact of different PPIs (pantoprazole, omeprazole, esomeprazole) on platelet response to clopidogrel in patients with previous coronary stent placement under chronic clopidogrel treatment. In a cross-sectional observational study, consecutive patients under clopidogrel maintenance treatment (n=1,000) scheduled for a control coronary angiography were enrolled. Adenosine diphosphate (ADP)-induced platelet aggregation (in AU*min) was measured with multiple electrode platelet aggregometry (MEA). From the entire study population, 268 (26.8%) patients were under PPI treatment at the time point of platelet function testing (pantoprazole, n=162; omeprazole, n=64; esomeprazole, n=42). Platelet aggregation (median [interquartile range]) was significantly higher in patients with omeprazole treatment (295.5 [193.5–571.2] AU*min) compared to patients without PPI treatment (220.0 [143.8–388.8] AU*min; p=0.001). Platelet aggregation was similar in patients with pantoprazole (226.0 [150.0–401.5] AU*min) or esomeprazole (209.0 [134.8–384.8] AU*min) treatment compared to patients without PPI treatment (p=0.69 and p=0.88, respectively). Attenuating effects of concomitant PPI treatment on platelet response to clopidogrel were restricted to the use of omeprazole. No attenuating effects on platelet response to clopidogrel were observed for pantoprazole or esomeprazole. Specifically designed and randomized clinical studies are needed to define the impact of concomitant PPI treatment on adverse events after percutaneous coronary intervention.

Mechanisms of platelet activation: need for new strategies to protect against platelet-mediated atherothrombosis.

Abstract: Platelets are central mediators of haemostasis at sites of vascular injury, but they also mediate pathologic thrombosis. Activated platelets stimulate thrombus formation in response to rupture of an atherosclerotic plaque or endothelial cell erosion, promoting atherothrombotic disease. They also interact with endothelial cells and leukocytes to promote inflammation, which contributes to atherosclerosis. Multiple pathways contribute to platelet activation, and current oral antiplatelet therapy with aspirin and a P2Y12 adenosine diphosphate (ADP) receptor antagonist target the thromboxane A2 and ADP pathways, respectively. Both can diminish activation by other factors, but the extent of their effects depends upon the agonist, agonist strength, and platelet reactivity status. Although these agents have demonstrated significant clinical benefit, residual morbidity and mortality remain high. Neither agent is effective in inhibiting thrombin, the most potent platelet activator. This lack of comprehensive inhibition of platelet function allows continued thrombus formation and exposes patients to risk for recurrent thrombotic events. Moreover, bleeding risk is a substantial limitation of antiplatelet therapy, because these agents target platelet activation pathways critical for both protective haemostasis and pathologic thrombosis. Novel antiplatelet therapies that provide more complete inhibition of platelet activation without increasing bleeding risk could considerably decrease residual risk for ischemic events. Inhibition of the protease-activated receptor (PAR)-1 platelet activation pathway stimulated by thrombin is a novel, emerging approach to achieve more comprehensive inhibition of platelet activation when used in combination with current oral antiplatelet agents. PAR-1 inhibition is not expected to increase bleeding risk, as this pathway does not interfere with haemostasis.

Management of Antithrombotic Therapy in Atrial Fibrillation Patients Presenting with Acute Coronary Syndrome and/or Undergoing Percutaneous Coronary Intervention/ Stenting

Abstract: There remains uncertainty over optimal antithrombotic management strategy for patients with atrial fibrillation (AF) presenting with an acute coronary syndrome and/or undergoing percutaneous coronary intervention/stenting. Clinicians need to balance the risk of stroke and thromboembolism against the risk of recurrent cardiac ischaemia and/or stent thrombosis, and the risk of bleeding. This consensus document comprehensively reviews the published evidence and presents a consensus statement on a ‘best practice’ antithrombotic therapy guideline for the management of antithrombotic therapy in such AF patients.

How much is too much? Interleukin-6 and its signalling in atherosclerosis

Abstract: The importance of inflammation as a driver of pathology is no longer confined to autoimmune and infectious diseases In line with convincing experimental data as well as abundant clinical findings the current view of atherosclerosis points to inflammation as a critical regulator of atherosclerotic plaque formation and progression leading to the fatal clinical endpoints myocardial infarction, stroke or sudden cardiac death The underlying mechanisms have been a matter of intense research during the last decades In this regard, the interleukin-6 (IL-6) cytokines and their signalling events have been shown to contribute to both, atherosclerotic plaque development and plaque destabilisation via a variety of mechanisms These involve the release of other pro-inflammatory cytokines, oxidation of lipoproteins by phospholipases, stimulation of acute phase protein secretion, the release of prothrombotic mediators, and the activation of matrix metalloproteinases Moreover, the formation of reactive oxygen species generated by vascular enzyme systems may play a critical role in the regulation of IL-6 indicating a cross talk between vasoactive substances ie angiotensin II or adrenalin and pro-inflammatory cytokines such as IL-6 In this review we will summarise and discuss the underlying molecular and cellular mechanisms how IL-6 as an early and central regulator of inflammation contributes to atherosclerosis and how this knowledge can be integrated into the clinical context

Prophylactic fibrinogen infusion reduces bleeding after coronary artery bypass surgery. A prospective randomised pilot study.

Abstract: It has been suggested that preoperative fibrinogen plasma concentration is independently associated to postoperative blood loss after cardiac surgery. Theoretically, prophylactic infusion of fibrinogen concentrate may thus reduce postoperative bleeding, but this has not previously been investigated. Twenty elective coronary artery bypass graft (CABG) patients with preoperative plasma fibrinogen levels

Fibrin network structure and clot mechanical properties are altered by incorporation of erythrocytes.

Abstract: Although many in vitro fibrin studies are performed with plasma, in vivo clots and thrombi contain erythrocytes, or red blood cells (RBCs). To determine the effects of RBCs on fibrin clot structure and mechanical properties, we compared plasma clots without RBCs to those prepared with low (2 vol%), intermediate (5-10 vol%), or high (> or =20 vol%) numbers of RBCs. By confocal microscopy, we found that low RBC concentrations had little effect on clot structure. Intermediate RBC concentrations caused heterogeneity in the fiber network with pockets of densely packed fibers alongside regions with few fibers. With high levels of RBCs, fibers arranged more uniformly but loosely around the cells. Scanning electron micrographs demonstrated an uneven distribution of RBCs throughout the clot and a significant increase in fiber diameter upon RBC incorporation. While permeability was not affected by RBC addition, at 20% or higher RBCs, the ratio of viscous modulus (G'') to elastic modulus (G') increased significantly over that of a clot without any RBCs. RBCs triggered variability in the fibrin network structure, individual fiber characteristics, and overall clot viscoelasticity compared to the absence of cells. These results are important for understanding in vivo clots and thrombi.

Bleeding with anticoagulation therapy - who is at risk, and how best to identify such patients.

Abstract: Anticoagulation with vitamin K antagonists (VKAs) has been shown to be effective in the prevention and treatment of thrombotic complications in various clinical settings, including atrial fibrillation (AF), venous thromboembolism (VTE), acute coronary syndromes and after invasive cardiac procedures. Bleeding is the most important complication of VKAs and a major concern for both physicians and patients. The occurrence of bleeding during treatment is not only important for the treated subjects, but also for a correct and complete use of this therapy in all the subjects who have a clear clinical indication for anticoagulation. This review analyses the treatment- and person-associated risk factors for bleeding during VKAs and their combination in clinical prediction rules that have been proposed in the attempt to identify those patients at higher risk for bleeding. The clinical prediction rules may help physicians stratify patients into categories of risk and thus to evaluate their individual risk/benefit ratio of starting or prolonging an anticoagulant treatment.

Heparin, heparan sulfate and heparanase in inflammatory reactions.

Abstract: Heparan sulfate (HS) proteoglycans at the cell surface and in the extracellular matrix of most animal tissues are essential in development and homeostasis, and are implicated in disease processes. Emerging evidence demonstrates the important roles of HS in inflammatory reactions, particularly in the regulation of leukocyte extravasation. Heparin, a classical anticoagulant, exhibits anti-inflammatory effects in animal models and in the clinic, presumably through interference with the functions of HS, as both polysaccharides share a high similarity in molecular structure. Apart of regulation during biosynthesis, the structures of HS and heparin are significantly modulated by heparanase, an endoglycosidase that is upregulated in a number of inflammatory conditions. Exploring the physiological roles of HS and heparin and the mode of heparanase action in modulating their functions during inflammation responses is of importance for future studies.

Driving Rho GTPase activity in endothelial cells regulates barrier integrity.

Abstract: In the past decade understanding of the role of the Rho GTPases RhoA, Rac1 and Cdc42 has been developed from regulatory proteins that regulate specific actin cytoskeletal structures – stress fibers, lamellipodia and filopodia – to complex integrators of cytoskeletal structures that can exert multiple functions depending on the cellular context. Fundamental to these functions are three-dimensional complexes between the individual Rho GTPases, their specific activators (GEFs) and inhibitors (GDIs and GAPs), which greatly outnumber the Rho GTPases themselves, and additional regulatory proteins. By this complexity of regulation different vasoactive mediators can induce various cytoskeletal structures that enable the endothelial cell (EC) to respond adequately. In this review we have focused on this complexity and the consequences of Rho GTPase regulation for endothelial barrier function. The permeability inducers thrombin and VEGF are presented as examples of G-protein coupled receptor- and tyrosine kinase receptor-mediated Rho GTPase activation, respectively. These mediators induce complex but markedly different networks of activators, inhibitors and effectors of Rho GTPases, which alter the endothelial barrier function. An interesting feature in this regulation is that Rho GTPases often have both barrier-protecting and barrier-disturbing functions. While Rac1 enforces the endothelial junctions, it becomes part of a barrier-disturbing mechanism as activator of reactive oxygen species generating NADPH oxidase. Similarly RhoA is protective under basal conditions, but becomes involved in barrier dysfunction after activation of ECs by thrombin. The challenge and promise lies in unfolding this complex regulation, as this will provide leads for new therapeutic opportunities.

The genetics of venous thromboembolism: a meta-analysis involving ~120,000 cases and 180,000 controls.

Abstract: We conducted a systematic and comprehensive meta-analysis on all candidate genes to assess their genetic contribution to the aetiology of venous thromboembolism (VTE) (pulmonary embolism and deep venous thrombosis) in all ethnic groups. Electronic databases were searched until and including January 2008 for any candidate gene investigated in VTE. Odds ratios (OR) and 95% confidence intervals (CI) were determined for each gene disease association using fixed and random effect models. Our meta-analyses included approximately 126,525 cases and 184,068 controls derived from 173 case-control studies, which included 21 genes (28 polymorphisms). Statistically significant associations with VTE were identified for factor V G1691A (OR 9.45; 95% CI 6.72-13.30, p < 0.0001), factor V A4070G (OR 1.24; 95% CI 1.02-1.52, p = 0.03), prothrombin G20210A, (OR 3.17; 95% CI 2.19-3.46, p < 0.00001), prothrombin G11991A, (OR 1.17; 95% CI 1.07-1.27, p = 0.0007), PAI-1 4G/5G, (OR 1.62; 95% CI 1.22-2.16, p = 0.0008), alpha-fibrinogen Thr312Ala (OR 1.37; 95% CI 1.14-1.64, p = 0.0008), all in Caucasian populations. MTHFR/ C677T in Chinese/Thai populations (OR 1.57; 95% CI 1.23-2.00, p = 0.0003), and ACE I/D in African American populations (OR 1.5; 95% CI 1.03-2.18, p = 0.03) were found to be significantly associated with VTE. Factor XIII Val34Leu (OR 0.80; 95% CI 0.68-0.94, p = 0.007) and beta-fibrinogen 455 G/A (OR 0.84; 95% CI 0.72-0.97, p = 0.02) both showed significantly protective effects. Our work supports a genetic aetiology to VTE disease and provides reliable risk estimates.

Proteomic and functional characterisation of platelet microparticle size classes

Abstract: Activated platelets release large lipid-protein complexes termed microparticles. These platelet microparticles (PMP) are composed of vesicular fragments of the plasma membrane and α-granules. PMP facilitate coagulation, promote platelet and leukocyte adhesion to the subendothelial matrix, support angiogenesis and stimulate vascular smooth muscle proliferation. Objectives: PMP were separated into 4 size classes to facilitate identification of active protein and lipid components. PMP were obtained from activated human platelets and separated into 4 size classes by gel filtration chromatography. Proteins were identified using 2-dimensional, liquid chromatography tandem mass spectrometry. Functional effects on platelets were determined using the PFA-100→ and on endothelial cells by measuring transendothelial cell electrical resistance. PMP size classes differed significantly in their contents of plasma membrane receptors and adhesion molecules, chemokines, growth factors and protease inhibitors. The two smallest size classes (3 and 4) inhibited collagen/adenosine-diphosphate-mediated platelet thrombus formation, while fractions 2 and 4 stimulated barrier formation by endothelial cells. Heat denaturation blocked the effect of fraction 4 on endothelial cell function, but not fraction 2 implying that the active component in fraction 4 is a protein and in fraction 2 is a heat-stable protein or lipid but not sphingosine-1-phosphate. Proteomic and functional analysis of PMP size fractions has shown that PMP can be separated into different size classes that differ in protein components, protein/lipid ratio, and functional effects on platelets and endothelial cells. This analysis will facilitate identification of active components in the PMP and clarify their involvement in diseases such as atherosclerosis and cancer.

Point-of-care versus central laboratory coagulation testing during haemorrhagic surgery. A multicenter study.

Abstract: Delay in collecting coagulation test results from a central laboratory is one of the critical issues to efficiently control haemostasis during surgery. The aim of this multicenter study was to compare the performance of a point-of-care (POC) device (Coagu- ChekTM Pro DM) with the central laboratory-based coagulation testing during haemorrhagic surgery. For this purpose, 93 patients undergoing major surgical procedure were prospectively included in three centers. Blood was drawn from all patients before surgical incision and from most patients during surgical procedure after a blood loss of 25% or more was observed. When expressed in activity percentage, POC-based prothrombin time (PT) was in good agreement with central laboratory test result with coefficient of correlation in the range from 0.711 to 0.960 in the three centers. Comparison was less conclusive when PT was expressed in seconds or as the patient-to-control ratio and for activated partial thromboplastin time, with significantly shorter clotting times and lower ratios obtained on the POC device. On-site PT (in activity percentage) monitoring would have induced no significant change in fresh frozen plasma (FFP) transfusion in patients when compared to central laboratory monitoring. Test results were obtained in less than 5 minutes when performed using the POC device versus a median turnaround time of 88 minutes (range: 29–235 minutes) when blood collection tubes were sent to the central laboratory. These results suggest that, in providing a rapid answer, POC-based monitoring of PT (in percentage) using the CoaguChek device could be validly used in patients undergoing haemorrhagic surgical procedures.

VIDAS D-dimer in combination with clinical pre-test probability to rule out pulmonary embolism. A systematic review of management outcome studies.

Abstract: Clinical outcome studies have shown that it is safe to withhold anticoagulant therapy in patients with suspected pulmonary embolism (PE) who have a negative D-dimer result and a low pretest probability (PTP) either using a PTP model or clinical gestalt. It was the objective of the present study to assess the safety of the combination of a negative VIDAS D-dimer result in combination with a non-high PTP using the Wells or Geneva models to exclude PE. A systematic literature search strategy was conducted using MEDLINE, EMBASE, the Cochrane Register of Controlled Trials and all EBM Reviews. Seven studies (6 prospective management studies and 1 randomised controlled trial) reporting failure rates at three months were included in the analysis. Non-high PTP was defined as "unlikely" using the Wells' model, or "low/intermediate" PTP using either the Geneva score, the Revised Geneva Score, or clinical gestalt. Two reviewers independently extracted data onto standardised forms. A total of 5,622 patients with low/intermediate or unlikely PTP were assessed using the VIDAS D-dimer. PE was ruled out by a negative D-dimer test in 2,248 (40%, 95% confidence intervals [CI] 38.7 to 41.3%) of them. The three-month thromboembolic risk in patients left untreated on the basis of a low/intermediate or unlikely PTP and a negative D-dimer test was 3/2,166 (0.14%, 95% CI 0.05 to 0.41%). In conclusion, the combination of a negative VIDAS D-dimer result and a non-high PTP effectively and safely excludes PE in an important proportion of outpatients with suspected PE.

C-reactive protein and venous thromboembolism. A prospective investigation in the ARIC cohort.

Abstract: The role of inflammation in the causation of venous thromboembolism (VTE) is uncertain. In 10,505 participants of the Atherosclerosis Risk in Communities (ARIC) Study, we assessed the association of the systemic inflammation marker, elevated C-reactive protein (CRP), with incidence of VTE (n=221) over a median of 8.3 years of follow-up. Adjusted for age, race, and sex, the hazard ratios of VTE across quintiles of CRP were 1.0, 1.61, 1.16, 1.56, and 2.31 (p for trend p<0.0007). For CRP above the upper 10 percentile (≥8.55 mg/L), compared with the lowest 90% of CRP values, the hazard ratio of VTE was 2.07 (95% CI 1.47, 2.94). Further adjustment for baseline hormone replacement therapy, diabetes, and body mass index attenuated the hazard ratios only slightly. For example, the adjusted hazard ratio of VTE was 1.76 (95% CI 1.23, 2.52) for CRP above versus below the 90th percentile. In conclusion, this prospective, populationbased study suggests elevated CRP is independently associated with increased risk of VTE.

Anti-cancer properties of low-molecular-weight heparin: Preclinical evidence

Abstract: Malignant conditions are frequently associated with a hypercoaguable state, with recurrent thrombosis due to the impact of cancer cells and chemotherapy or radiotherapy on the coagulation cascade. Heparin and, its pharmacokinetically improved versions, low-molecular-weight heparins (LMWH) are effective in the prevention and treatment of thromboembolic events in cancer patients. There are several lines of preclinical evidence suggesting potential benefits of LMWH in hypercoagulation and thrombosis as well as in various processes involved in tumour growth and metastasis. Tinzaparin is a LMWH produced by controlled enzymatic depolymerisation of unfractionated heparin. The efficacy of tinzaparin has been documented in several clinical trials across various conditions and in special patient populations. The main objective of this review is to present the existing knowledge on the preclinical anti-cancer properties of tinzaparin and other LMWH. The evidence for tinzaparin, as well as other LMWH, regarding interference with cancer-induced hypercoagulation, cancer cell proliferation, degradation of extracellular matrix, angiogenesis, selectin-mediated binding of platelet and cancer cells, chemokine signalling, tumour progression, and metastasis are reviewed. Certain clinical trials suggest improved survival of cancer patients with deep venous thrombosis treated with LMWH versus unfractionated heparin and when added to the promising preclinical anti-cancer properties of LMWH this warrants further investigations in prospective, randomised, controlled clinical trials in cancer patients. The benefits of LMWH in cancer might at least in part, be independent from its anti-coagulant activities, but may still be partially dependent on its anti-coagulant activities.

Genetic fusion to albumin improves the pharmacokinetic properties of factor IX

Abstract: Haemophilia B is a X-chromosome linked disease characterised by a deficiency of functionally active coagulation Factor IX (FIX). Patients with severe haemophilia B at risk of recurrent bleeding are treated approximately twice a week in a prophylactic setting by application of FIX concentrates. To increase convenience and compliance of the therapy it is desirable to reduce the dosing frequency by improving the pharmacokinetic properties of FIX. Here a concept of rFIX (recombinant factor IX) albumin fusion proteins (rIX-FPs) with cleavable linker peptides derived from the FIX activation sequence is presented. Constructs of the genetic fusion of FIX to albumin via cleavable linkers were expressed in mammalian cells and characterised after purification. In vitro activation studies with FXIa demonstrated that cleavage of the linker and the activation peptide proceeded comparably well. In a clotting assay the rIX-FPs with cleavable linker showed a 10- to 30-fold increase in the molar specific clotting activity compared to fusion proteins with non-cleavable linkers. Furthermore, in-vivo recovery, terminal half-life and the AUC of rIX-FPs in rats and rabbits as determined by FIX antigen measurements were significantly increased compared to rFIX (BeneFIX®). In FIX deficient (FIX-/-) mice the in-vivo recovery and the AUC were also significantly increased. The efficacy in reducing bleeding time was shown in FIX-/- mice by a tail tip bleeding model. The results suggest that rIX-FPs with a cleavable linker between FIX and albumin are a promising concept that may support the use of the albumin fusion technology to extend the half-life of FIX.

Prasugrel compared with high-dose clopidogrel in acute coronary syndrome. The randomised, double-blind ACAPULCO study.

Abstract: Compared with the approved dose regimen of clopidogrel (300-mg loading dose [LD], 75-mg maintenance dose [MD]), prasugrel has been demonstrated to reduce ischaemic events in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI). In ACS, antiplatelet effects of a prasugrel MD regimen have not been previously compared with either a higher clopidogrel MD or after switching from a higher clopidogrel LD. The objective of this study was to evaluate the antiplatelet effect of a prasugrel 10-mg MD versus a clopidogrel 150-mg MD in patients with ACS who had received a clopidogrel 900-mg LD. Patients with non-ST elevation ACS, treated with aspirin and a clopidogrel 900-mg LD, were randomised within 24 hours post-LD to receive a prasugrel 10-mg or clopidogrel 150-mg MD. After 14 days of the initial MD, subjects switched to the alternative treatment for 14 days. The primary endpoint compared maximum platelet aggregation (MPA, 20 µM adenosine diphosphate [ADP]) between prasugrel and clopidogrel MDs for both periods. Responder analyses between treatments were performed using several platelet-function methods. Of 56 randomised subjects, 37 underwent PCI. MPA was 26.2% for prasugrel 10 mg and 39.1% for clopidogrel 150 mg (p<0.001). The prasugrel MD regimen reduced MPA from the post-900-mg LD level (41.2% to 29.1%, p=0.003). Poor response ranged from 0% to 6% for prasugrel 10 mg and 4% to 34% for clopidogrel 150 mg. Thus, in ACS patients a prasugrel 10-mg MD regimen resulted in significantly greater platelet inhibition than clopidogrel at twice its approved MD or a 900-mg LD.

Plasma leakage in dengue haemorrhagic fever.

Abstract: Dengue viruses (DENV), a group of four serologically distinct but related flaviviruses, are the cause of one of the most important emerging viral diseases. DENV infections result in a wide spectrum of clinical disease including dengue haemorrhagic fever (DHF), a viral haemorrhagic disease characterised by bleeding and plasma leakage. The characteristic feature of DHF is the transient period of plasma leakage and a haemorrhagic tendency. DHF occurs mostly during a secondary DENV infection. Serotype cross-reactive antibodies and mediators from serotype cross-reactive Dengue-specific T cells have been implicated in the pathogenesis. A complex interaction between virus, host immune response and endothelial cells likely impacts the barrier integrity and functions of endothelial cells leading to plasma leakage. Recently the role of angiogenic factors and the role of dengue virus on endothelial cell transcription and functions have been studied. Insights into the mechanisms that confer protection or cause disease are critical in the development of prophylactic and therapeutic modalities for this important disease.

Vulnerable atherosclerotic plaque metalloproteinases and foam cell phenotypes.

Abstract: Plaque rupture underlies most myocardial infarctions. Plaques vulnerable to rupture have thin fibrous caps, an excess of macrophages over vascular smooth muscle cells, large lipid cores, and depletion of collagen and other matrix proteins form the cap and lipid core. Production of matrix metalloproteinases from macrophages is prominent in human plaques, and studies in genetically modified mice imply a causative role for metalloproteinases in plaque vulnerability. Recent in-vitro studies on human monocyte-derived macrophages and on foam-cell macrophages generated in vivo suggest the existence of several macrophage phenotypes with distinct patterns of metalloproteinase expression. These phenotypes could play differing roles in cap, core and aneurysm formation.

Hantavirus regulation of endothelial cell functions.

Abstract: Hantaviruses cause two vascular permeability-based diseases and primarily infect endothelial cells which form the primary fluid barrier of the vasculature. Since hantavirus infections are not lytic, the mechanisms by which hantaviruses cause haemorrhagic fever with renal syndrome (HFRS) or Hantavirus Pulmonary Syndrome (HPS) are indeterminate. HPS is associated with acute pulmonary oedema and HFRS with moderate haemorrhage and renal sequelae, perhaps reflecting the location of vast microvascular beds and endothelial cell reservoirs available for hantavirus infection. Endothelial cells regulate capillary integrity, and hantavirus infection provides a primary means for altering vascular permeability that contributes to pathogenesis. The central importance of endothelial cells in regulating oedema, vascular repair, angiogenesis, immune cell recruitment, platelet deposition as well as gas exchange and solute delivery suggest that a multitude of inputs and cellular responses may be influenced by hantavirus infection and contribute to pathogenic changes in vascular permeability. Here we focus on understanding hantavirus interactions with endothelial cells which are linked to vascular permeability, and provide insight into the contribution of endothelial cell responses in hantavirus pathogenesis.

Coagulation assessment by rotation thrombelastometry in normal pregnancy.

Abstract: We analysed changes in coagulation during normal pregnancy with a novel point-of-care device based on thrombelastometry (ROTEM®). We compared the results obtained with those of standard coagulation tests in 104 patients: 20 non-pregnant women (controls) and 84 women in the first (T1, n=17), second (T2, n=9) and third (T3, n=58) trimesters of pregnancy. We measured the clotting time (CT), the maximum clot firmness (MCF), the early clot amplitude at 5 and 15 minutes (CA5, CA15) and the clot lysis index (CLI30) with four tests containing specific reagents. (a) The INTEM® test involving ellagic acid activated the intrinsic pathway and (b) the EXTEM® test using tissue factor triggered the extrinsic pathway; (c) The FIBTEM® test based on a platelet inhibitor (cytochalasin D) evaluated the contribution of fibrinogen to clot formation and (d) the APTEM® test was similar to the EXTEM but was based on inhibition in vitro of fibrinolysis by aprotinin. CT and CLI30 were not significantly modified during pregnancy whereas MCF, CA5 and CA15 (INTEM, EXTEM, FIBTEM) increased significantly between the second and third trimesters (e.g. median [interquartile range]: MCF-FIBTEM, 13 [11–16] mm vs. 19 [17–23] mm, respectively, in controls and T3, p

Comparative study on risk factors and early outcome of symptomatic distal versus proximal deep vein thrombosis: Results from the OPTIMEV study

Abstract: There is a lack of consensus on the value of detecting and treating symptomatic isolated distal deep-vein thrombosis (DVT) of the lower limbs. In our study, we compared the risk factors and outcomes in patients with isolated symptomatic distal DVT with those with proximal symptomatic DVT. We analysed the data of patients with objectively confirmed symptomatic isolated DVT enrolled in the national (France), multicenter, prospective OPTIMEV study. This sub-study outcomes were recurrent venous thromboembolism, major bleeding and death at three months. Among the 6141 patients with suspicion of isolated DVT included between November 2004 and January 2006, DVT was confirmed in 1643 patients (26.8%). Isolated distal DVT was more frequent than proximal DVT (56.8% vs. 43.2%, respectively; p=0.01). Isolated distal DVT was significantly more often associated with transient risk factors (recent surgery, recent plaster immobilisation, recent travel), whereas proximal DVT was significantly more associated with more chronic states (active cancer, congestive heart failure or respiratory insufficiency, age >75 years). Most patients (96.8%) with isolated distal DVT received anticoagulant therapies. There was no difference in the percentage of recurrent venous thromboembolism and major bleeding in patients with proximal DVT and isolated distal DVT. However, the mortality rate was significantly higher (p<0.01) in patients with proximal DVT (8.0%) than in those with isolated distal DVT (4.4%). Symptomatic isolated distal DVT differs from symptomatic proximal DVT both in terms of risk factors and clinical outcome. Whether these differences should influence the clinical management of these two events remains to be determined.

The inflammatory response as a target to reduce myocardial ischaemia and reperfusion injury

Abstract: Acute myocardial infarction is the leading cause of morbidity and mortality in the adult population of developed and developing nations. Although the prompt restoration of antegrade blood flow in the infarct-related coronary artery is the mean therapy for improving survival, reperfusion itself may cause damage to ischaemic myocardial tissue. This event is well known as “reperfusion injury”. Crucial mediators for cardiac damage in the reperfusion phases are oxidative stress, inflammation and leukocyte infiltration. Already approved and novel therapies might directly reduce these inflammatory processes. Treatments modulating chemokine secretion and activity should be considered as very promising approaches to reduce myocardial reperfusion injury.

The role of monocytes in thrombotic disorders. Insights from tissue factor, monocyte-platelet aggregates and novel mechanisms.

Abstract: Although, the main physiological role of monocytes is attributed to innate immunity (that is, phagocytosis) and the development of tissue macrophages and dendritic cells, the pathophysiological role of these goes far behind these (simplistic) limits. Indeed, monocytes constitute a major source of blood tissue factor, a key element of the extrinsic coagulation cascade. Monocytes actively bind to platelets, thus forming very prothrombotic monocyte-platelet aggregates. Additionally, these cells link inflammation and the procoagulant state observed in various prothrombotic conditions. However, monocytes are also crucial for successful thrombus recanalisation. In this article, we review the available data on potential mechanisms that link monocytes with thrombosis-related processes.

Shiga toxins, glycosphingolipid diversity, and endothelial cell injury

Abstract: Shiga toxin (Stx)-producing Escherichia coli (STEC) cause an enteric illness that results in a spectrum of outcomes ranging from asymptomatic carriage to uncomplicated diarrhea, bloody diarrhea, and the postdiarrheal haemolytic uremic syndrome (HUS), which leads to renal and other organ microvascular thrombosis. Binding of Stx to the glycosphingolipid (GSL) globotriaosylceramide (Gb3Cer/CD77) on endothelial cells followed by receptor-mediated endocytosis is the linchpin in STEC-mediated disease. Only GSLs that associate strongly with lipid rafts appear to carry Stxs retrogradely from the plasma membrane through the Golgi apparatus to the endoplasmic reticulum where they are translocated to the cytosol and exert their toxic function. Thus, the biophysical features of the lipid moiety of GSL receptors may influence its incorporation into certain membrane domains and thereby affect toxin destination. Consequently, a detailed structural analysis of Stx-binding GSLs is required to illuminate the molecular causes that may underlie the different Stx susceptibilities of endothelial cells derived from various vascular beds. Solid phase overlay binding assays of thin-layer chromatography (TLC)-separated GSL preparations employing specific antibodies and/or Stxs in conjunction with anti-Stx-antibodies are commonly used for the identification of Stx-binding GSLs. Such GSL-profiling combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) represents a convenient strategy to structurally characterize Stx-receptors from any biological sources such as primary cells, cell lines, or organs. This approach may be helpful to gain insights into Stx-induced impairment of target cells that is suggested to originate at least partly from the structural heterogeneity of the cellular ligands of Stxs.

The multi-functionality of CD40L and its receptor CD40 in atherosclerosis

Abstract: Disrupting the CD40-CD40L co-stimulatory pathway reduces atherosclerosis and induces a stable atherosclerotic plaque phenotype that is low in inflammation and high in fibrosis. Therefore, inhibition of the CD40-CD40L pathway is an attractive therapeutic target to reduce clinical complications of atherosclerosis. The CD40-CD40L dyad is known to interact with other costimulatory molecules, to activate antigen-presenting cells (APC) and to contribute to T-cell priming and B-cell isotype switching. Besides their presence on T-cells and APCs, CD40 and CD40L are also present on macrophages, endothelial cells and vascular smooth muscle cells in the plaque, where they can exert pro-atherogenic functions. Moreover, recent progress indicates the involvement of neutrophil CD40, platelet CD40L and dendritic cell CD40 in atherogenesis. Since systemic CD40-CD40L modulation compromises host defense, more targeted interventions are needed to develop superior treatment strategies for atherosclerosis. We believe that by unravelling the cell-cell CD40-CD40L interactions, inhibition of cell-type specific (signalling components of) CD40(L) that do not compromise the patient’s immune system, will become possible. In this review, we highlight the cell-type specific multi-functionality of CD40-CD40L signalling in atherosclerosis.

Clopidogrel response variability: Current status and future directions

Abstract: Antiplatelet drugs represent the basis of treatment for cardiovascular atherothrombotic disease processes. Clopidogrel selectively inhibits the platelet adenosine diphosphate (ADP) P2Y12 receptor and is accepted as the antiplatelet drug of choice in addition to aspirin for patients with unstable angina and non-ST-segment elevation myocardial infarction (NSTEMI) (1, 2) as well as for patients undergoing percutaneous coronary intervention (PCI) (3–5). Clopidogrel has also shown to improve outcomes in patients with ST-segment elevation myocardial infarction (STEMI) (6, 7). In spite of the clear clinical benefit of clopidogrel therapy as shown in numerous large-scale trials, a considerable number of cardiovascular events continue to occur. Recurrent events despite adjunctive clopidogrel therapy have been, in part, attributed to variability in interindividual response profiles to this antiplatelet agent (8). The present manuscript provides an overview of the current status of knowledge on clopidogrel response variability as well as the possible future strategies to overcome the clinical implications associated with this phenomenon.

Venous thromboembolism in pregnancy: diagnosis, management and prevention

Abstract: A pregnant woman has a two- to five-fold higher risk of venous thromboembolism (VTE) than a non-pregnant woman of the same age and, in developed countries, she is more likely to die from fatal pulmonary embolism (PE) than from obstetric haemorrhage. The increased VTE risk is mediated through normal physiological changes of pregnancy including alterations in haemostasis that favour coagulation, reduced fibrinolysis and pooling and stasis of blood in the lower limbs. Thrombophilia, smoking, obesity, immobility and postpartum factors such as infection, bleeding and emergency surgery (including emergency caesarian section) also increase the risk of pregnancy-related VTE. The diagnosis of VTE can be safely established with acceptable radiation exposure to the fetus using readily available imaging modalities such as ultrasound, ventilation perfusion lung scanning and computed tomographic pulmonary angiography. However, the optimal diagnostic strategies still remain to be determined. If there is no contraindication to anticoagulation, commencing treatment prior to objective confirmation should be strongly considered. For the mother and fetus, effective and safe treatment is readily available with low-molecular-weight heparin (LMWH), but optimal dosing of these agents in pregnancy remains controversial. Emerging data support antepartum LMWH prophylaxis for women with previous VTE if the event was unprovoked or in the presence of thrombophilia. On the other hand, women with prior provoked VTE and no thrombophilia or women with asymptomatic thrombophilia (but a family history of VTE) can safely be managed with antepartum surveillance. Postpartum prophylaxis is recommended for women with prior VTE or thrombophilia (and a family history of VTE).

Clopidogrel response status assessed with Multiplate point-of-care analysis and the incidence and timing of stent thrombosis over six months following coronary stenting.

Abstract: Clopidogrel low-responsiveness assessed with multiple electrode platelet aggregometry (MEA) has been shown to be a strong and independent predictor of early stent thrombosis (ST) after coronary stenting. The relation of clopidogrel response status, as assessed with MEA, with incidence and timing of ST during an extended follow-up period has never been reported. Here, we report the six-month follow-up results of a prospective trial assessing clopidogrel responsiveness with MEA in patients undergoing percutaneous coronary intervention (PCI). A total of 1,608 consecutive patients with planned drug-eluting stent placement were enrolled in this study. Before PCI patients uniformly received 600 mg clopidogrel and blood was taken directly before PCI to measure ADP-induced platelet aggregation with MEA. The upper quintile (20%) of patients according to MEA measurements (n=323) was defined as clopidogrel low responders. Compared with normal responders (n=1,285), the cumulative incidence of definite ST within six months was significantly higher in low responders [2.5% vs. 0.4%; OR 6.5; 95% CI, 2.4-17.0; P<0.001]. The combined incidence of definite or probable ST was higher as well in low vs. normal responders [4.1% vs. 0.7%; OR 5.8; 95% CI, 2.8-12.3; P<0.0001]. A significant inverse correlation of MEA values and the timing of definite or probable ST (in days) was observed (Spearman coefficient = -0.45; P=0.04) with events occurring earlier in the low-responder group. MEA measurements are highly predictive for the occurrence of ST during the first six months following coronary stenting. In the majority of clopidogrel low responders suffering ST, the ischaemic event occurs early in the course after the procedure.