thromboplastin and bivalirudin

Clinical coagulation laboratory tests do not accurately reflect hemostasis and thrombosis in vivo. Thrombin generation in vivo occurs in 3 overlapping phases: initiation, priming, and propagation. During initiation, injury to the vessel wall exposes the cells to tissue factors, which lead to the production of small amounts of thrombin. During priming, the thrombin that is generated initially binds to platelets and activates them through protease-activated receptors. During the propagation phase, factor X is activated by the factor IXa/VIIIa complex that is assembled on the activated platelet surface. Subsequent formation of factor Xa/Va complexes on the platelet surface leads to a burst of thrombin and fibrin formation. Pharmacologic concentrations of a direct thrombin inhibitor, bivalirudin, inhibit thrombin-induced activation of platelets to a greater extent than pharmacologic concentrations of unfractionated heparin.

Topics: Anticoagulants; Blood Platelets; Fibrin; Heparin; Hirudins; Humans; Male; Peptide Fragments; Platelet Activation; Recombinant Proteins; Thrombin; Thromboplastin; Thrombosis

A major concern of stent implantation after percutaneous coronary intervention (PCI) is acute stent thrombosis. Effective inhibition of periprocedural platelet function in patients with coronary artery disease (CAD) leads to an improved outcome. In this study, we examined the periprocedural platelet reactivity after administrating bivalirudin during PCI compared to unfractionated heparin (UFH) administration. Further, the effect of bivalirudin on induced tissue factor (TF) expression in smooth muscle cells (SMC) was determined.. Patients with CAD (n = 58) and double antithrombotic medication were treated intraprocedural with UFH (n = 30) or bivalirudin (n = 28). Platelet activation markers were flow cytometrically measured before and after stenting. The expression of TF in SMC was determined by real-time PCR and Western blotting. The thrombogenicity of platelet-derived microparticles and SMC was assessed via a TF activity assay.. Bivalirudin significantly diminished the agonist-induced platelet reactivity post-PCI. Compared to UFH treatment, the adenosine diphosphate (ADP) and thrombin receptor-activating peptide (TRAP)-induced thrombospondin expression post-PCI was reduced when bivalirudin was administrated during intervention. In contrast to UFH, bivalirudin reduced the P-selectin expression of unstimulated and ADP-induced platelets post-PCI. Moreover, bivalirudin inhibited the thrombin-, but not FVIIa- or FVIIa/FX-induced TF expression and pro-coagulant TF activity of SMC. Moreover, bivalirudin reduced the TF activity of platelet-derived microparticles postinduction with TRAP or ADP.. Bivalirudin is better than UFH in reducing periprocedural platelet activation. Moreover, thrombin-induced TF expression is inhibited by bivalirudin. Thus, bivalirudin seems to be a better anticoagulant during PCI than UFH.

Topics: Aged; Anticoagulants; Antithrombins; Biomarkers; Blood Platelets; Blotting, Western; Cells, Cultured; Coronary Artery Disease; Factor VIIa; Factor X; Female; Flow Cytometry; Germany; Heparin; Hirudins; Humans; Male; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; P-Selectin; Peptide Fragments; Percutaneous Coronary Intervention; Platelet Activation; Platelet Function Tests; Real-Time Polymerase Chain Reaction; Recombinant Proteins; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Stents; Tetraspanin 30; Thromboplastin; Thrombospondins; Treatment Outcome

Our study sought to evaluate mechanisms of the current strategies for optimal anticoagulation during percutaneous coronary intervention (PCI).. Thirty-two high risk acute coronary syndrome patients were randomised to bivalirudin and provisional GPIIb/IIIa inhibition (GPIIb/IIIa) or unfractionated heparin (UFH) and mandatory GPIIb/IIIa. Flow cytometric measurements immediately after anticoagulation showed that, unlike UFH, bivalirudin did not activate platelets as indicated by P-selectin expression and fibrinogen binding while decreasing platelet-monocyte aggregates and monocyte expression of tissue factor. UFH released tissue factor pathway inhibitor (TFPI) during and immediately after PCI while bivalirudin (irrespective of GP IIb/IIIa) did not. Lower levels of TFPI with bivalirudin were seen during and immediately after PCI (P<0.01). Thrombin generation as indicated by prothrombin fragment F 1+2 levels was reduced during PCI in the UFH group (P<0.01) but not with bivalirudin. Soluble CD40 ligand is associated with thrombosis and levels were higher in the bivalirudin group irrespective of GPIIb/IIIa at the same stages (P<0.05).. Bivalirudin has some early advantages on platelet activation when compared to UFH. However, there are significant limitations in its mechanism of action, particularly a lack of release of tissue factor pathway inhibitor.

Topics: Acute Coronary Syndrome; Aged; Angioplasty, Balloon, Coronary; Anticoagulants; Aspirin; Biomarkers; Blood Coagulation; CD40 Ligand; Clopidogrel; Drug Therapy, Combination; Female; Fibrinogen; Heparin; Hirudins; Humans; Lipoproteins; Male; Membrane Glycoproteins; Middle Aged; Monocytes; Peptide Fragments; Platelet Activation; Platelet Adhesiveness; Platelet Aggregation Inhibitors; Platelet Glycoprotein GPIIb-IIIa Complex; Prothrombin; Recombinant Proteins; Thromboplastin; Thrombosis; Ticlopidine; Treatment Outcome

Patients with diabetes who undergo percutaneous coronary intervention (PCI) are at high risk for thrombotic complications following the procedure. We sought to compare the anti-thrombotic effect of bivalirudin to that of eptifibatide plus unfractionated heparin in diabetic patients undergoing elective PCI. Thirty diabetic patients were randomized to receive during PCI either bivalirudin (bivalirudin group, n=15) or eptifibatide plus heparin (eptifibatide group, n=15) at standard dosing regimens. The drugs were continued for 20 minutes (bivalirudin) or 18 hours (eptifibatide) after PCI. Blood thrombogenicity was assessed using the Badimon ex vivo perfusion chamber. Each patient underwent two perfusion studies - at baseline (on aspirin and clopidogrel) and 15-20 minutes following PCI. Perfusion studies were performed at rheologic conditions of low and high shear rates (LSR, HSR). Porcine aortic tunica media served as the thrombogenic substrate. Aortic specimens were stained for total platelet-thrombus and fibrin deposition. Thrombus area was measured using computerized planimetry. There were no differences in clinical characteristics or baseline thrombus area between the two groups. Total platelet-thrombus area was reduced significantly in both groups, but the degree of reduction was lower in the bivalirudin group compared with the eptifibatide group (HSR: 69.5% vs. 89.3% reduction, respectively, P=0.04; LSR: 50.6% vs. 73.2%, P=0.03). Fibrin deposition was reduced in both groups by 47-49%. In conclusion, both bivalirudin and the combination of eptifibatide plus heparin, given to diabetic patients during PCI, achieved marked reductions in total thrombus formation and fibrin deposition. However, glycoprotein IIb/IIIa inhibition by eptifibatide caused a more pronounced reduction in thrombus formation.

Topics: Aged; Angioplasty, Balloon, Coronary; Anticoagulants; Diabetes Complications; Drug Therapy, Combination; Eptifibatide; Female; Fibrinolytic Agents; Heparin; Hirudins; Humans; Male; Middle Aged; P-Selectin; Peptide Fragments; Peptides; Platelet Aggregation Inhibitors; Recombinant Proteins; Thromboplastin; Thrombosis

The activated partial thromboplastin time (aPTT) test has been used for years to monitor parenteral direct thrombin inhibitors (DTIs) and unfractionated heparin. Because the aPTT correlates poorly with unfractionated heparin levels, we hypothesized that the aPTT may not be the best test for monitoring parenteral DTIs.. Using 235 excess plasma specimens from 82 adult patients receiving treatment with DTIs (argatroban, bivalirudin, or dabigatran), we compared the aPTT with the ecarin chromogenic assay (ECA), the dilute thrombin time (dTT) test, and the prothrombinase-induced clotting time (PiCT) test.. The aPTT correlated poorly with each of the other tests in both bivalirudin- and argatroban-containing samples (r(2) = 0.04-0.23). The ECA and dTT exhibited the best correlations (r(2) = 0.66-0.93). Intermediate correlations were seen when the results of the PiCT were plotted against the dTT or ECA (r(2) = 0.46-0.58). Nineteen specimens obtained from six patients receiving dabigatran showed a good correlation between the dTT and the ECA (r(2) = 0.92).. The aPTT does not correlate well with other tests that might be used to monitor parental DTI administration. Further studies are needed to evaluate the clinical usefulness of alternative tests and their correlation with clinical outcomes.

Topics: Antithrombins; Arginine; Benzimidazoles; beta-Alanine; Blood Coagulation; Blood Coagulation Tests; Dabigatran; Drug Monitoring; Heparin; Hirudins; Humans; Partial Thromboplastin Time; Peptide Fragments; Pipecolic Acids; Recombinant Proteins; Sulfonamides; Thrombin; Thrombin Time; Thromboplastin

Islet and hepatocyte transplantation are associated with tissue factor-dependent activation of coagulation which elicits instant blood mediated inflammatory reaction, thereby contributing to a low rate of engraftment. The aim of this study was i) to evaluate the procoagulant activity of human adult liver-derived mesenchymal progenitor cells (hALPCs), ii) to compare it to other mesenchymal cells of extra-hepatic (bone marrow mesenchymal stem cells and skin fibroblasts) or liver origin (liver myofibroblasts), and iii) to determine the ways this activity could be modulated. Using a whole blood coagulation test (thromboelastometry), we demonstrated that all analyzed cell types exhibit procoagulant activity. The hALPCs pronounced procoagulant activity was associated with an increased tissue factor and a decreased tissue factor pathway inhibitor expression as compared with hepatocytes. At therapeutic doses, the procoagulant effect of hALPCs was inhibited by neither antithrombin activators nor direct factor Xa inhibitor or direct thrombin inhibitors individually. However, concomitant administration of an antithrombin activator or direct factor Xa inhibitor and direct thrombin inhibitor proved to be a particularly effective combination for controlling the procoagulant effects of hALPCs both in vitro and in vivo. The results suggest that this dual antithrombotic therapy should also improve the efficacy of cell transplantation in humans.

Topics: Adolescent; Adult; Aged; Anticoagulants; Blood Coagulation; Child; Female; Heparin; Hirudins; Humans; Lipoproteins; Liver Transplantation; Male; Mesenchymal Stem Cells; Middle Aged; Peptide Fragments; Recombinant Proteins; Thromboplastin; Young Adult

Bivalirudin, a synthetic analog of the carboxy-terminus of hirudin, is a reversible thrombin inhibitor used during coronary balloon angioplasty. The objective of this study was to evaluate the influence of bivalirudin on thrombin generation. Three in-vitro models (numerical simulations, synthetic coagulation proteome and whole blood) of contact pathway-independent blood coagulation triggered with tissue factor were used in this study. Increasing concentrations of bivalirudin prolong the initiation phase of thrombin generation in a concentration-dependent manner. At subpharmacologic bivalirudin concentrations (0.5-2 micromol/l), total thrombin generation was significantly increased. At a pharmacologic concentration (5 micromol/l), bivalirudin suppressed thrombin generation in the synthetic coagulation proteome; in numerical simulations and contact pathway-inhibited whole blood, no thrombin generation was detected over 1200-2000 s and platelet activation was inhibited by 80%. The addition of a pharmacologic concentration (9 micromol/l) of a naturally occurring protease inhibitor aprotinin in the presence of at least 0.5 micromol/l bivalirudin provided limited enhancement of the bivalirudin inhibitory effect. In conclusion, bivalirudin at pharmacologic concentrations is an efficient inhibitor of thrombin generation, platelet activation and clot formation, which acts not as a modulator but as an 'on-off' switch of blood coagulation.

Topics: Angioplasty, Balloon; Anticoagulants; Blood Coagulation; Dose-Response Relationship, Drug; Hirudins; Humans; Models, Biological; Peptide Fragments; Platelet Activation; Recombinant Proteins; Thrombin; Thromboplastin

Four direct thrombin inhibitors (DTIs), lepirudin, bivalirudin, argatroban, and melagatran, differ in their ability to prolong the prothrombin time (PT). Paradoxically, the DTI in clinical use with the lowest affinity for thrombin (argatroban) causes the greatest PT prolongation. We compared the effects of these DTIs on various clotting assays and on inhibition of human and bovine factor Xa (FXa). On a mole-for-mole basis, lepirudin was most able to prolong the PT, activated partial thromboplastin time (APTT), and thrombin clotting time (TCT), whereas argatroban had the least effect. At concentrations that doubled the APTT (argatroban, 1 micromol/l; melagatran, 0.5 micromol/l; bivalirudin, 0.25 micromol/l; lepirudin, 0.06 micromol/l), the rank order for PT prolongation was: argatroban > melagatran > bivalirudin > lepirudin. Although the Ki's associated with inhibition of human FXa by melagatran (1.4 micromol/l) and argatroban (3.2 micromol/l) approach their therapeutic concentrations, inhibition of FXa did not appear to be a major contributor to PT prolongation, since argatroban also prolonged the PT of bovine plasma (despite a Ki for bovine FXa of 2,600 micromol/l). Only melagatran inhibited prothrombinase-bound FXa. We conclude that the differing effects of the DTIs on PT prolongation are primarily driven by their respective molar plasma concentrations required for clinical effect. DTIs with a relatively low affinity for thrombin require high plasma concentrations to double the APTT; these higher plasma concentrations, in turn, quench more of the thrombin generated in the PT, thereby more greatly prolonging the PT.

Topics: Animals; Anticoagulants; Arginine; Azetidines; Benzylamines; Blood Coagulation; Cattle; Dose-Response Relationship, Drug; Factor Xa; Factor Xa Inhibitors; Glycine; Hirudins; Humans; In Vitro Techniques; Partial Thromboplastin Time; Peptide Fragments; Pipecolic Acids; Prothrombin Time; Recombinant Proteins; Species Specificity; Sulfonamides; Thrombin; Thrombin Time; Thromboplastin

Restenosis is responsible to approximately 30% of long-term failure following therapeutic vascular procedures. Thrombosis plays a key role in the development of restenosis. Thrombin-specific inhibitors have been considered as one type of candidates for the prevention of restenosis. Previous studies by our group demonstrated that a novel thrombin-specific inhibitor, hirulog-like peptide (HLP), reduced balloon catheter-induced neointima formation in rat carotid arteries. The present study examined the effect of HLP on angioplasty-induced restenosis in carotid arteries of atherosclerotic rabbits. New Zealand white rabbits were subject to air desiccation of the lumen of the right carotid arteries, then received high cholesterol/fat diet for 3 weeks. The rabbits were intravenously infused with HLP (1.6 mg/(kg/h)) or saline (n=7 per group) for 4 h started before angioplasty which dilated atherosclerotic lesions in right common carotid artery. Four weeks after the angioplasty, neointimal area, stenosis and neointima/media ratio in injured carotid arteries were reduced in atherosclerotic rabbits treated with HLP compared to saline controls by 62, 39 and 59% (P<0.05). The expression of tissue factor (TF) and transforming growth factor (TGF)-beta in the neointima of carotid arteries of rabbits treated with HLP was significantly weaker than saline controls (P<0.05 or <0.01). Activated partial thromboplastin time and bleeding time in HLP-treated rabbits were not significantly prolonged compared to controls. The results of the present study suggest that HLP may substantially reduce angioplasty-induced restenosis in atherosclerotic rabbits without increasing bleeding tendency. The inhibition on the expression of TF and TGF-beta in the neointima of the arterial wall may contribute to the preventive effect of HLP on restenosis in atherosclerotic rabbits.

Topics: Animals; Arteriosclerosis; Bleeding Time; Carotid Artery, Common; Carotid Stenosis; Collagen; Hirudins; Humans; Immunohistochemistry; Male; Partial Thromboplastin Time; Peptide Fragments; Rabbits; Rats; Recombinant Proteins; Recurrence; Thromboplastin; Transforming Growth Factor beta; Tunica Intima