Improving Outcomes in Cardiovascular Diseases: A Review on Vorapaxar.

Antiplatelet agents are the standard of practice in the management of atherosclerosis and acute coronary syndrome. In contrast to the available antiplatelet agents, vorapaxar represents a novel mechanism of action. It is an antagonist of the platelet protease-activated receptor-1 and inhibits thrombin-induced and thrombin receptor agonist peptide-induced platelet aggregation. The Thrombin Receptor Antagonist in Secondary Prevention of Atherothrombotic Ischemic Events-Thrombolysis in Myocardial Infarction 50 (TRA 2°P-TIMI 50) trial led to the approval of vorapaxar by the Food and Drug Administration and European Medicines Agency for the reduction of thrombotic cardiovascular events in patients with a history of myocardial infarction (MI) or peripheral arterial disease. TRA 2°P-TIMI 50 trial showed that the use of vorapaxar (2.5 mg once/daily) in addition to standard dual antiplatelet therapy with aspirin and a P2Y12 receptor inhibitor was effective in the secondary prevention of recurrent thrombotic events among patients with previous atherothrombosis, particularly in patients with prior MI; at the expense of an increase in major bleeding. Another recently published Vorapaxar Therapy in Patients With Prior Myocardial Infarction Treated With Newer Generation P2Y12 Receptor Inhibitors Prasugrel and Ticagrelor (VORA-PRATIC) study showed that among post-MI patients treated with potent P2Y12 inhibitors (prasugrel or ticagrelor), vorapaxar reduced platelet-driven global thrombogenicity, an effect that persisted, albeit attenuated, in the absence of aspirin. The current review summarizes an up-to-date literature on pharmacokinetics, pharmacodynamics, and clinical efficacy of vorapaxar and proposes future directions of research.

In Vivo and protease-activated receptor-1-mediated platelet activation in patients presenting for cardiac catheterization.

Pathways of platelet activation that are not targeted by current antithrombotic therapy may be crucial for the development of ischemic events in patients undergoing coronary angiography. We therefore investigated whether in vivo and thrombin receptor activating peptide (TRAP)-stimulated platelet activation and monocyte-platelet aggregate (MPA) levels can serve as independent risk markers for adverse outcomes in aspirin-treated patients presenting for cardiac catheterization. In vivo and TRAP-stimulated platelet surface P-selectin, activated glycoprotein IIb/IIIa (GPIIb/IIIa) and MPA levels were determined in 682 consecutive patients undergoing cardiac catheterization and in 47 healthy controls. Two-year follow-up data were obtained from 562 patients. In vivo platelet surface P-selectin, activated GPIIb/IIIa and MPA levels were significantly higher in patients with angiographically-proven coronary artery disease than in healthy controls (all p≤0.02). Patients with an acute coronary syndrome (ACS; n=125) had significantly higher levels of in vivo MPA than patients without ACS (n=437; p=0.01). In the overall study population (n=562) the surface expression of P-selectin and activated GPIIb/IIIa, and the levels of MPA in vivo and in response to TRAP were similar in patients without and with subsequent ischemic events (all p>0.05). Similar results were obtained when only patients with angiographically-proven coronary artery disease (n=459), stent implantation (n=205) or ACS (n=125) were analyzed. Receiver-operating characteristic curve analyses did not reveal cut-off values for P-selectin, activated GPIIb/IIIa, and MPA levels for the prediction of ischemic events. In conclusion, in vivo and TRAP-stimulated platelet activation and MPA levels did not predict adverse ischemic outcomes in aspirin-treated patients presenting for cardiac catheterization.

Dabigatrán: experiencia en la práctica clínica habitual / Dabigatran: experience in standard clinical practice

Introducción y objetivos. Dabigatrán es un fármaco anticoagulante, inhibidor directo de la trombina, aprobado para la prevención de ictus isquémico secundario a fibrilación auricular no valvular. El objetivo de este estudio fue determinar la eficacia de dabigatrán en la práctica clínica para la prevención de eventos isquémicos cerebrales asociados a fibrilación auricular no valvular, así como su perfil de tolerancia y seguridad. Material y métodos. Estudio descriptivo y retrospectivo en el que se incluyó a todos los pacientes que iniciaron tratamiento anticoagulante con dabigatrán entre los meses de noviembre de 2011 y septiembre de 2012. Se realizó seguimiento desde el comienzo del tratamiento hasta junio de 2013. Se determinó la incidencia de eventos isquémicos de origen cerebral, cardíaco y periférico, así como la aparición de efectos adversos y complicaciones hemorrágicas, determinando su localización y gravedad. Resultados. Se analizó a 316 pacientes con una edad media de 76,46±8,37 años, de los que el 53,5% eran varones. Dos pacientes (0,55/100 pacientes-año) presentaron ictus isquémico (incluyendo una amaurosis fugax). Ocho (2,18/100 pacientes-año) tuvieron un evento adverso isquémico, que fue de origen cardíaco en 5 (1,36/100 pacientes-año) casos y periférico en 3 (0,81/100 pacientes-año). Cuarenta (10,91/100 pacientes-año) tuvieron una complicación hemorrágica: 32 hemorragias menores (8,73/100 pacientes-año) y 8 mayores (2,18/100 pacientes-año). Conclusiones. Dabigatrán en la práctica clínica habitual es eficaz en la prevención de ictus y presenta un perfil de seguridad similar al reportado en los ensayos clínicos (AU)

Introduction and objectives. Dabigatran is an anticoagulant drug and a direct thrombin inhibitor and has been approved for the prevention of ischaemic stroke secondary to nonvalvularauricular auricular fibrillation. The aim of this study was to determine the efficacy of dabigatran in clinical practice for preventing cerebral ischaemic events associated with nonvalvularauricular auricular fibrillation, as well as its tolerance and safety profile. Material and methods. A descriptive and retrospective study was conducted, which included all patients who started anticoagulant treatment with dabigatran between November 2011 and September 2012. Follow-up was performed from the start of treatment until June 2013. The incidence of ischaemic events of cerebral, cardiac and peripheral origin was recorded, as was the onset of adverse effects and haemorrhagic complications, whose location and severity were determined. Results. We analysed 316 patients, with a mean age of 76.46±8.37 years, of whom 53.5% were men. Two patients (0.55/100 patient-years) presented ischaemic stroke (including one amaurosis fugax). Eight (2.18/100 patient-years) patients had an adverse ischaemic event, whose origin was cardiac in 5 (1.36/100 patient-years) cases and peripheral in 3 (0.81/100 patient-years). Forty (10.91/100 patient-years) patients had a haemorrhagic complication: 32 minor (8.73/100 patient-years) and 8 major (2.18/100 patient-years) haemorrhages. Conclusions. Dabigatran is effective in standard clinical practice in preventing stroke and has a safety profile similar to that reported in the clinical trials (AU)

Dabigatrán en la vida real / Dabigatran in real life

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Solulin increases clot stability in whole blood from humans and dogs with hemophilia.

Solulin is a soluble form of thrombomodulin that is resistant to proteolysis and oxidation. It has been shown to increase the clot lysis time in factor VIII (fVIII)-deficient plasma by an activated thrombin-activatable fibrinolysis inhibitor (TAFIa)-dependent mechanism. In the present study, blood was drawn from humans and dogs with hemophilia, and thromboelastography was used to measure tissue factor-initiated fibrin formation and tissue-plasminogen activator-induced fibrinolysis. The kinetics of TAFI and protein C activation by the thrombin-Solulin complex were determined to describe the relative extent of anticoagulation and antifibrinolysis. In severe hemophilia A, clot stability increased by > 4-fold in the presence of Solulin while minimally affecting clot lysis time. Patients receiving fVIII/fIX prophylaxis showed a similar trend of increased clot stability in the presence of Solulin. The catalytic efficiencies of TAFI and protein C activation by the thrombin-Solulin complex were determined to be 1.53 and 0.02/µM/s, respectively, explaining its preference for antifibrinolysis over anticoagulation at low concentrations. Finally, hemophilic dogs given Solulin had improved clot strength in thromboelastography assays. In conclusion, the antifibrinolytic properties of Solulin are exhibited in hemophilic human (in vitro) and dog (in vivo/ex vivo) blood at low concentrations. Our findings suggest the therapeutic utility of Solulin at a range of very low doses.

Antiplatelet therapy: thrombin receptor antagonists.

Activated platelets stimulate thrombus formation in response to rupture of an atherosclerotic plaque or endothelial cell erosion, promoting atherothrombotic disease. Multiple pathways contribute to platelet activation. Aspirin, an irreversible inhibitor of thromboxane A2 synthesis, in combination with clopidogrel, an inhibitor of P2Y(12) adenosine diphosphate platelet receptors, represent the current standard-of-care of antiplatelet therapy for patients with acute coronary syndrome and for those undergoing percutaneous coronary intervention. Although these agents have demonstrated significant clinical benefit, the increased risk of bleeding and the recurrence of thrombotic events represent substantial limitations. Thrombin is one of the most important platelet activators. The inhibition of protease-activated receptor 1 showed a good safety profile in preclinical studies. In fact, phase II studies with vorapaxar (SCH530348) and atopaxar (E5555) showed no increase of bleeding events in addition to the current standard-of-care of antiplatelet therapy. Although the results of phase III trials for both drugs are awaited, this family is a promising new addition to the current clinical practice for patients with atherothrombotic disease, not only as an alternative, but also as additional therapy.

The thrombomodulin analog Solulin promotes reperfusion and reduces infarct volume in a thrombotic stroke model.

BACKGROUND: Currently there is no approved anticoagulant for treating acute stroke. This is largely because of concern for hemorrhagic complications, and suggests a critical need for safer anticoagulants. Solulin is a soluble analog of the endothelial cell receptor thrombomodulin, able to bind free thrombin and convert it to an activator of the anticoagulant, protein C. OBJECTIVE: Solulin was tested for its ability to inhibit middle cerebral artery occlusion (MCAO) induced by photothrombosis, and to restore MCA patency after establishment of stable occlusion. METHODS: Cerebral blood flow (CBF) was monitored by laser Doppler for 1.5 h after occlusion and again 72 h later. RESULTS: Solulin treatment 30 min before thrombosis resulted in an approximately 50% increase in time to form a stable occlusion. When administered 30 or 60 min after MCAO, Solulin significantly improved CBF within 90 min of treatment. In contrast, none of the vehicle-treated mice showed restoration of CBF in the first 90 min and only 17% did so by 72 h. Solulin treatment was associated with a significant reduction in infarct volume, and was well tolerated with no overt hemorrhage observed in any treatment group. Mechanistic studies in mice homozygous for the factor (F)V Leiden mutation, suggest that Solulin's efficacy derives primarily from the anticoagulant activity of the thrombin-Solulin complex and not from direct anti-inflammatory or neuroprotective effects of Solulin or activated protein C. CONCLUSIONS: Our data indicate that Solulin is a safe and effective anticoagulant that is able to antagonize active thrombosis in acute ischemic stroke, and to reduce infarct volume.

Coagulation and fibrosis in chronic liver disease.

In the hepatic tissue repair mechanism, hepatic stellate cells (HSCs) are recruited at the site of injury and their changes reflect paracrine stimulation by all neighbouring cell types, including sinusoidal endothelial cells, Kupffer cells, hepatocytes, platelets and leucocytes. Thrombin converts circulating fibrinogen to fibrin, promotes platelet aggregation, is a potent activator of endothelial cells, acts as a chemoattractant for inflammatory cells and is a mitogen and chemoattractant for fibroblasts and vascular smooth muscle cells. Most of the cellular effects elicited by thrombin are mediated via a family of widely expressed G-protein-coupled receptors termed protease activated receptors (PARs). All known members of the PAR family stimulate cell proliferation/activation in a rat HSC line. Thrombin receptors are constitutively expressed in the liver, and their expression increases in parallel with the severity and/or the duration of liver disease. In human studies, thrombotic risk factors were found to be independently associated with the extent of fibrosis; severity of hepatitis C virus (HCV)-associated liver disease appears to be less in patients with haemophilia when compared with those with HCV alone. Several studies, based mostly on rat models, demonstrate that anticoagulants or antiplatelet agents prevent hepatic necrosis and fibrosis by acting on HSCs. These drugs could be therapeutic agents in patients with chronic liver disease and specific studies should be initiated.

Factors controlling smooth muscle proliferation and airway remodelling.

It is clear that airway smooth muscle plays an important role in the hyperresponsiveness and remodelling that occur in the asthmatic airway. This is by virtue of its roles as a contractile cell, a cell that undergoes proliferation as part of the inflammatory response, a cell that actively participates in the inflammatory response via the production of cytokines and chemokines, and perhaps as a cell that undergoes migration. Now that airway smooth muscle cells cultured from asthmatic patients have been studied in vitro, it is apparent that there is an abnormality in the growth of these cells such that they grow more rapidly than cells derived from nonasthmatic patients. This raises the possibility of identifying the exact point(s) in the signal transduction pathways at which this abnormality occurs. To do this it is necessary to define precisely the mitogenic pathways that lead to proliferation in the airway smooth muscle cell, and this information is accumulating rapidly. The possibility is raised for new therapeutic targets that are aimed specifically at the airway smooth muscle, leading to an effective method for reversing or preventing the airway remodelling that accompanies chronic severe asthma.

Protease-activated receptors in inflammation, neuronal signaling and pain.

The ability of proteases to regulate cell function via protease-activated receptors (PARs) has led to new insights about the potential physiological functions of these enzymes. Several studies suggest that PARs play roles in both inflammation and tissue repair, depending on the cellular environment in which they act. The recent detection of PARs on peripheral and central neurons suggests that neuronal PARs might be involved not only in neurogenic inflammation and neurodegenerative processes, but also in nociception. Thus, the list of potential roles for PARs has lengthened considerably and their physiological course of action might be much broader than initially anticipated.