Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.21.5 (thrombin)
33,306 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombus formation at an artificial surface in contact with blood is a complex process that encompasses accretion of platelets from flowing blood and fibrin deposition. Platelet adhesion and fibrin formation are intimately intertwined reactions that are triggered by different sets of surface adsorbed plasma proteins. To dissect the contribution of protein adsorption and platelet adhesion to thrombin formation, a coherent study was performed with non-coated (NC) and heparin-coated (HC) surfaces. Thrombin production in whole blood, platelet adhesion and protein adsorption were studied using an amidolytic thrombin assay, a dynamic platelet adhesion assay and ellipsometry, respectively. Thrombin generation in flowing whole blood exposed to HC surfaces was greatly diminished when compared with NC surfaces. However, separate platelet adhesion and protein adsorption studies with anticoagulated whole blood revealed that platelets do not adhere because fibrinogen is not available in the protein layer that was deposited during the perfusion. These findings indicate that the in vitro thrombogenicity of a material cannot be predicted from platelet adhesion and protein adsorption data when these measurements are performed with anti-coagulated blood or platelet rich plasma. Preincubation of NC and HC surfaces with fibrinogen or 2000-fold diluted plasma resulted in similar amounts of surface-bound fibrinogen and mediated massive platelet adhesion from flowing whole blood. These results indicate that a) platelet adhesion correlates with the availability of surface-bound fibrinogen and b) NC and HC surfaces are indistinguishable with respect to protein (fibrinogen) adsorption and platelet adhesion. It is apparent that the heparinized surface used in our studies exerts its anti-thrombogenic properties by neutralizing locally formed thrombin and not by reducing fibrinogen-dependent platelet adhesion.
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PMID:Fibrinogen adsorption, platelet adhesion and thrombin generation at heparinized surfaces exposed to flowing blood. 1200 60

Thrombotic events contribute significantly to the morbidity, mortality, and health care costs of patients undergoing major orthopedic surgery. Despite therapy with unfractionated heparin, low-molecular-weight heparin, or warfarin, thrombotic events continue to occur at an unacceptably high rate in populations at risk. The need for improved prophylaxis against venous thromboembolism has resulted in the development of several new antithrombotics, both recently approved and investigational, that target specific steps in the hemostatic pathway. These include direct thrombin inhibitors, agents that inhibit the factor VIIa-tissue factor complex, and selective factor Xa inhibitors. Fondaparinux is the first of the selective factor Xa inhibitors. It was evaluated in the most comprehensive drug development program ever in major orthopedic surgery, culminating in four phase III trials involving more than 7000 enrollees, and is the first agent in its class to be approved by the U.S. Food and Drug Administration and the European Agency for the Evaluation of Medicinal Products. It has been suggested that fondaparinux's superior efficacy may be related to its ability to initiate selective inhibition of factor Xa and its predictable linear pharmacokinetics.
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PMID:Optimizing prophylaxis of venous thromboembolism. 1207 77

Titanium alloy (Ti) commonly is used for long-term blood pumps as a conventional blood contacting material. Thrombus formation in the pump, however, is still a critical problem. Once thrombin is generated on the Ti surface, it activates platelets and the coagulation cascade, leading to thrombus formation. It would be expected that an inhibition of thrombin generation on a blood-contacting surface would prevent thrombus formation. In this study, the titania gel (Ti-gel) on the surface of Ti was formed with chemical modification. The surface structure and its effects on the coagulation cascade were evaluated. Scanning electron microscopic study revealed numerous cracks on the dried surface of Ti-gel, indicating a water-enriched layer. Blood coagulation on the Ti-gel was less than that on the Ti. Generated thrombin on the Ti-gel was less than that on the Ti in both the extrinsic and intrinsic pathways. There was no statistical difference of thrombin degradation. These results suggest that coagulation cascade on the Ti surface was inhibited by the Ti-gel formation. The Ti-gel may have better antithrombogenic characteristics for blood pumps because of its antiblood-coagulation effects.
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PMID:Titania gel reduces thrombin generation. 1240 51

The antithrombotic effects of direct (ximelagatran and hirudin) and indirect (dalteparin) anticoagulants were compared using a deep venous thrombosis (DVT) treatment model in conscious rats. Thrombus formation was induced in the inferior caval vein by total stasis plus topically applied ferric chloride. After 1-h thrombus maturation, one group of 10 rats were sacrificed and the mean thrombus weight in this group was 27.3 +/- 2.7 mg. This thrombus weight was handled as a reference to which all other results were compared. In all other groups, the total occlusion was removed after 1 h but a partial stasis was retained, permitting some blood flow around the thrombus. Groups of animals received subcutaneous (s.c.) dalteparin (200 IU/kg), s.c. hirudin (0.75 micromol/kg), one of four oral doses of ximelagatran (2.5, 5, 10 or 20 micromol/kg) or s.c. saline (control). After the 3-h treatment, mean thrombus weight in the saline group (26.5 +/- 3.3 mg) did not differ significantly from that of the reference group (27.3 +/- 2.7 mg, see above). Ximelagatran decreased thrombus weight in a dose-dependent manner, with an estimated ID(50) of 15 micromol/kg. Mean thrombus weight with the highest ximelagatran dose (11.1 +/- 1.3 mg) was similar to that with hirudin (13.0 +/- 1.5 mg). The effect of dalteparin on thrombus regression was much less pronounced (20.2 +/- 1.2 mg), compared with ximelagatran and hirudin, even though it was administered at a dose that yielded a similar activated partial thromboplastin time (APTT) prolongation. In conclusion, the results from this DVT treatment model showed that direct thrombin inhibitors ximelagatran and hirudin exhibited superior antithrombotic properties to low molecular weight heparin (LMWH).
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PMID:Effects of ximelagatran, the oral form of melagatran, in the treatment of caval vein thrombosis in conscious rats. 1243 84

Unfractionated heparin is the current antithrombotic of choice in peripheral vascular interventions. The rate of in-hospital major complications during peripheral angioplasty procedures (PTA) using heparin as the primary anticoagulant has not been well defined. In this single-center study, the charts of 213 consecutive PTA procedures in a 1-year period were reviewed. Of unstaged procedures, a total of 131 patients (57.3% males; mean age, 66.4 12.1 years) met inclusion criteria. Forty-five patients (34.4%) had recent onset of claudication and 15 (11.5%) had ulceration. Thrombus was angiographically visualized in 16.7% of patients. Unfractionated heparin was administered at a mean of 4,672 1,238 U (59.1 20.0 U/kg) during the procedure. The highest activated clotting time (ACT) during the procedure was recorded in 114 patients. ACTs were < 300, 300 400 and > 400 seconds in 29.0%, 29.0% and 42.1%, respectively. In-hospital clinical events occurred in 12 patients (9.2%) who met any one of the following endpoints: death (0.8%), limb loss (1.5%), major bleeding (4.6%), emergent need for repeat revascularization of the same vessel (7.6%), embolic stroke (0.0%) and vascular complications (1.5%). The best model associated with salvage revascularization included cigarette smoking within the past year, recent onset of claudication and PTA treatment below the knee. Increased dosages of heparin (U/kg) were associated with a trend toward higher rates of complications. A significant number of patients have in-hospital major complications following PTA procedures using unfractionated heparin as the primary anticoagulant. Current ongoing registries are evaluating the feasibility of direct thrombin inhibitors bivalirudin instead of heparin as a primary anticoagulant during PTA.
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PMID:In-hospital complications of peripheral vascular interventions using unfractionated heparin as the primary anticoagulant. 1273 Jun 31

Unfractionated heparin is a widely utilized anticoagulant during peripheral angioplasty procedures (PTA). In contrast to heparin, bivalirudin is a direct thrombin inhibitor with predictable anticoagulation, does not activate platelets, and inhibits both soluble and bound thrombin. The experience with bivalirudin during PTA remains limited. In this single-center prospective study, 48 consecutive patients (60.4% males, mean age 70.0 12.1) received bivalirudin as the primary anticoagulant during PTA (0.75 mg/kg bolus, 1.75 mg/kg/h during the procedure). Thirty-four (70.8%) had claudication and 6 (12.5%) had ulceration. Thrombus was angiographically seen in 3 (6.3%) patients. In-hospital serious procedural complications were limited to 2 (4.2%) (exact 95% confidence interval: (0.5%,14.3%]) patients with major bleeding; none (0.0%) of the other following endpoints occurred: death, limb loss, emergent need for revascularization of the same vessel, embolic strokes, and vascular complications (exact 95% confidence intervals: [0.0%,6.1%]). This compared favorably to previously reported data using unfractionated heparin and the same serious procedural complications endpoints from our group at the same institution (9.2%). We conclude that the use of bivalirudin during PTA appears feasible and safe. Large prospective registries are needed to confirm these findings.
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PMID:Bivalirudin in peripheral vascular interventions: a single center experience. 1284 Feb 39

Thrombotic disorders can lead to uncontrolled thrombin generation and clot formation within the circulatory system leading to vascular thrombosis. Direct inhibitors of thrombin have been developed and tested in clinical trials for the treatment of a variety of these thrombotic disorders. The bleeding complications observed during these trials have raised questions about their clinical use. The development of a computer-based model of coagulation using the kinetic rates of individual reactions and concentrations of the constituents involved in each reaction within blood has made it possible to study coagulation pathologies in silico. We present an extension of our initial model of coagulation to include several specific thrombin inhibitors. Using this model we have studied the effect of a variety of inhibitors on thrombin generation and compared these results with the clinically observed data. The data suggest that numerical models will be useful in predicting the effectiveness of inhibitors of coagulation.
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PMID:Predicting the pharmacology of thrombin inhibitors. 1287 72

Antithrombin (AT) inhibits thrombin and some other coagulation factors in a reaction that is dramatically accelerated by binding of a pentasaccharide sequence present in heparin/heparan-sulfate to a heparin-binding site on AT. Based on the involvement of R47 in the heparin/AT interaction and the frequent occurrence of R47 mutations in AT deficiency patients, targeted knock-in of the corresponding R48C substitution in AT in mice was performed to generate a murine model of spontaneous thrombosis. The mutation efficiently abolished the effect of heparin-like molecules on coagulation inhibition in vitro and in vivo. Mice homozygous for the mutation (AT(m/m) mice) developed spontaneous, life-threatening thrombosis, occurring as early as the day of birth. Only 60% of the AT(m/m) offspring reached weaning age, with further loss at different ages. Thrombotic events in adult homozygotes were most prominent in the heart, liver, and in ocular, placental, and penile vessels. In the neonate, spontaneous death invariably was associated with major thrombosis in the heart. This severe thrombotic phenotype underlines a critical function of the heparin-binding site of antithrombin and its interaction with heparin/heparan-sulfate moieties in health, reproduction, and survival, and represents an in vivo model for comparative analysis of heparin-derived and other antithrombotic molecules.
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PMID:Life-threatening thrombosis in mice with targeted Arg48-to-Cys mutation of the heparin-binding domain of antithrombin. 1459 98

Thrombotic complications account for a large proportion of in-hospital deaths from acute myocardial infarction (MI). Although thrombolytic therapy has greatly improved clinical outcomes following MI, thrombin released during clot lysis has a prothrombotic effect, and the thrombolytic agents themselves may directly activate platelets. Antithrombotic therapy as an adjunct to thrombolysis improves the speed and extent of artery recanalization and reduces the incidence of secondary ischemic complications. The current treatment standard is unfractionated heparin (UFH) administered intravenously for 24-48 h. However, UFH has not been unequivocally shown to improve outcomes in large-scale, randomized clinical trials, and shows no evidence of benefit when used as an adjunct to streptokinase-based thrombolysis. Unfractionated heparin also has several clinical and practical disadvantages, such as the need for coagulation monitoring, difficulties attaining a stable and reliable anticoagulant effect, and the risk of hemorrhagic side effects. Low-molecular-weight heparin (LMWH) represents a safe and effective alternative antithrombotic therapy, with a stable and predictable anticoagulant effect, potential for use in combination with either fibrin-specific or streptokinase-based thrombolysis, no need for anticoagulation monitoring, and a low risk of hemorrhagic and other heparin-related complications. Several randomized clinical trials have shown that adjunctive LMWH is at least as effective as UFH in the acute phase of MI, is associated with fewer in-hospital recurrent ischemic events, and has an acceptable safety profile.
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PMID:Optimizing adjunctive antithrombotic therapy in the treatment of acute myocardial infarction: a role for low-molecular-weight heparin. 1474 48

There have been major advances in our understanding of thrombosis and antithrombotic drugs. This review focuses on the molecular aspects of thrombus formation and antithrombotic therapy. Molecules involved in arterial thrombosis are derived from inflammatory cells in the atherosclerotic plaque and blood platelets. These molecules work in concert to promote plaque instability and thrombogenicity. Thrombus formation on the ruptured plaque is mediated by platelet and coagulation activation. By contrast, molecules involved in venous thrombosis are derived from the activated coagulation cascade. Platelets appear to play a secondary role. The antithrombotic drugs are classified according to their targeted constituents: antiplatelet agents and anticoagulants; the latter are further divided into non-specific anticoagulants, such as vitamin K antagonists and heparin, and direct thrombin inhibitors, including hirudin and argatroban. Currently available antiplatelet agents target glycoprotein IIbIIIa (abciximab, tirofiban, eptifibatide), cyclooxygenase-1 (aspirin) or adenosine diphosphate receptor, P2Y12 (clopidogrel).
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PMID:Molecular aspects of thrombosis and antithrombotic drugs. 1604 40


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