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)

Three commercial prothrombin complex concentrates (PCC) were compared in vitro. Differences in the activities or contents, respectively, of the PCC factors FII, FVII, FIX, FX and the proteins C, S, and Z (antigen) in particular were found. Global tests of activated factors did not reveal marked differences between the products. Neither free thrombin nor elevated levels of activated FX were detected. In contrast, analyses of FVIIa, of residual amidolytic activities, and of concentrations of unwanted ingredients demonstrated considerable differences between the products. While antithrombin III was detected only in two of three concentrates, heparin was found in all PCCs but in markedly different concentrations. Although the homogeneity of the products has been clearly improved in comparison with former comparative investigations, the products can be distinguished by their compound profile and by a couple of in vitro assays.
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PMID:Comparative in vitro investigation of prothrombin complex concentrates. 957 40

The intensity of warfarin therapy for prevention of primary and secondary thromboembolic complications in paediatric patients, is extrapolated from guidelines for adults, which may not be optimal. Therefore, we assessed thrombin regulation ex vivo and in vitro in plasmas from 40 children (1 to 18 years old with a median age of 13 years) and 27 adults receiving warfarin with an international normalized ratio of 2 to 3 (child: 2.5 +/- 0.15; adult: 2.4 +/- 0.14). Ex vivo concentrations of prothrombin fragment 1.2 were significantly lower in children (0.30 +/- 0.03 nM) compared to adults (0.45 +/- 0.04 nM; p <0.01). Thrombin generation in defibrinated plasmas (Arvin) was decreased and delayed for children compared to adults when activated by either activated partial thromboplastin time (child = 32 +/- 1.7, adult = 45 +/- 1.9 microM x s) or prothrombin time (child = 35 +/- 0.7, adult = 46 +/- 1.0 microM x s) reagents (p <0.01 for both). Although plasma concentrations of factors (F) II, FVII, FIX, F X, protein C and protein S were similar, more of the thrombin generated was complexed to alpha2 macroglobulin (alpha2M) at times close to peak thrombin activity (60 s) in plasma from children (general linear analysis of variance; p <0.03). Thus, increased alpha2M levels may enhance thrombin regulation in paediatric compared to adult patients receiving warfarin, suggesting that clinical trials in children, using less intense warfarin treatment, may be required to determine optimum therapy.
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PMID:Enhanced thrombin regulation during warfarin therapy in children compared to adults. 979 71

High levels of recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) have been found to be effective in providing haemostasis in haemophiliacs and in normal individuals with acquired inhibitors to factor VIII (FVIII) or FIX. However, the mechanism of this therapeutic effect of FVIIa is unclear. Opinion is divided over whether high-dose FVIIa therapy works primarily by a tissue factor (TF)-dependent or -independent mechanism. Our group originally favoured a TF-dependent mechanism; however, we have recently found that, at levels comparable with those attained therapeutically, FVIIa activates enough FX on activated platelets to restore platelet surface thrombin generation. These data now lead us to favour a primarily (although not necessarily exclusively) TF-independent mechanism for the haemostatic effect of high-dose FVIIa. We believe that a platelet surface localization of FVIIa activity explains both its safety and efficacy, as well as its haemostatic effect in patients with thrombocytopenia and platelet function defects. Localization on activated platelets would tend to restrict the activity of FVIIa to sites of injury. Activation of FX on the platelet surface in haemophiliacs would provide FXa in a favourable location to escape inhibition by plasma protease inhibitors and be incorporated into platelet prothrombinase complexes. Activation of FIX and FX on platelet surfaces in thrombocytopenia would result in more thrombin generation per platelet, possibly leading to formation of a stable fibrin network even in the absence of an optimal initial platelet plug.
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PMID:Activated factor VII activates factors IX and X on the surface of activated platelets: thoughts on the mechanism of action of high-dose activated factor VII. 981 30

A double blind randomized cross-over multi-center study has been conducted to compare the pharmacokinetic and coagulation activation markers of high-purity factor IX concentrate subjected to both solvent/ detergent (SD) treatment and 15 nm-filtration (FIX-SD-15) with the licensed product subjected only to solvent-detergent (FIX-SD). This filtration process allows the elimination of small particles, such as non-enveloped viruses (i.e., hepatitis A and parvovirus B19). Eleven severe hemophilia B patients (FIX coagulant activity <2 IU/dl) received one infusion of 60 IU/kg of FIX-SD and one infusion of 60 IU/kg of FIX-SD-15 at least at 10 days interval. Blood samples were obtained before and at various time up to 72 h after infusion. The decay curves of factor IX (FIX:C and FIX:Ag) were evaluated by a model independent method. Bioequivalence was found between the two concentrates using the Schuirmann test. The mean FIX:C and FIX:Ag recovery of FIX-SD-15 was 1.08 and 0.89 IU/dl/IU/kg respectively with a mean half-life of 33.3 h for FIX:C and 25.6 h for FIX:Ag. Six months after initial enrollment, pharmacokinetic parameters were similar in the 7 patients tested. There was no significant variation of prothrombin fragment 1+2 and thrombin-antithrombin complexes measured up to 6 h after infusion, indicating that there was no activation process after administration of FIX. In conclusion, these data demonstrate that the introduction of a 15 nm filtration does not alter the pharmacokinetic profile of a well characterized SD FIX concentrate while providing additional viral safety.
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PMID:A cross-over pharmacokinetic study of a double viral inactivated factor IX concentrate (15 nm filtration and SD) compared to a SD factor IX concentrate. 986 61

By virtue of a severely prolonged aPTT with a normal thromboplastin time (prothrombin time) and a normal thrombin time, severe FXII deficiency has been diagnosed in a woman without a bleeding diathesis or a history of thromboembolic complications. A deficiency of a factor of the contact activation system (FXII, prekallikrein, high molecular weight kininogen) is usually diagnosed during routine coagulation tests demonstrating a prolonged aPTT. The severe and partial deficiency of FXII, of prekallikrein or high molecular weight kininogen is not associated with a bleeding tendency. In contrast, severely factor XI deficient subjects may suffer from a mild hemorrhagic diathesis, whereas FVIII deficiency (hemophilia A, autoimmune "hemophilia", von Willebrand disease) and FIX deficiency (hemophilia B) are associated with a bleeding tendency of varying severity, depending on the clotting activity of FVIII or FIX, respectively. An isolated prolongation of the aPTT due to a lupus anticoagulant, however, is frequently associated with arterial and/or venous thrombosis. Therefore, in case of a prolongation of the aPTT, its cause has to be determined.
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PMID:[A patient with isolated prolongation of aPTT without hemorrhagic diathesis anamnesis: severe, hereditary factor XII deficiency]. 1051 21

Initiation of haemostasis involves the formation of a complex between tissue factor (TF) and activated factor VII (FVIIa) following injury. TF is found in the deeper layers of the vessel wall, in atherosclerotic plaques and in some types of tumour cell and is only exposed to circulating blood after tissue damage. Likewise, FVII is only enzymatically active when complexed with TF (TF/FVIIa). It has recently been shown that the administration of recombinant activated FVII (rFVIIa) in high doses (approximately 100 microg/kg) can induce haemostasis in the absence of FVIII and FIX. In addition, from in-vitro studies it appears that rFVIIa can bind with low affinity to the activated platelet surface and, independently of TF, induce the thrombin burst needed for haemostasis. The ability of rFVIIa to compensate for FVIII/FIX deficiency has been proven clinically in haemophilia patients with life- and limb-threatening bleeds. In addition, patients with congenital FVII deficiency have been successfully treated for bleeds with rFVIIa. Recombinant FVIIa has been used in patients with platelet disorders; five patients with Glanzmann's thrombasthenia and one with Bernard-Soulier's thrombasthenia have had bleeding episodes managed effectively. Recombinant FVIIa has also been shown to normalize prothrombin time in patients with liver disease and in warfarin-treated individuals.
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PMID:NovoSeven as a universal haemostatic agent. 1085 May 74

Blood coagulation is initiated in response to vessel damage in order to preserve the integrity of the mammalian vascular system. The coagulation cascade can also be initiated by mediators of the inflammatory response, and fibrin deposition has been noted in a variety of pathological states. The cascade of coagulation zymogen activations which leads to clot formation is initiated by exposure of flowing blood to Tissue Factor (TF), the cellular receptor and cofactor for Factor VII (FVII). FVII binds to the receptor in a I:I stoichiometric complex and is rapidly activated. FVIIa undergoes an active site transition upon binding TF in the presence of calcium which enhances the fundamental properties of the enzyme. This results in rapid autocatalytic activation of FVII to FVIIa, thereby amplifying the response by generating more TF-FVIIa complexes. The TF-FVIIa activates both FIX and FX. Further FXa generation by the FIXa-FVIIIa-Ca2+-phospholipid complex is required to sustain the coagulation mechanism, since the TF-FVIIa complex is rapidly inactivated by Tissue Factor pathway inhibitor (TFPI). TFPI circulates in plasma, is associated with vascular cell surface and is released from platelets following stimulation by thrombin. TFPI requires the formation of an active TF-FVIIa complex and FXa generation before inhibition can occur. TFPI prevents further participation of TF in the coagulation process by forming a stable quaternary complex, TF-FVIIa-FXa-TFPI.
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PMID:Tissue factor pathway. 1085 75

We determined the numbers, cellular origin and thrombin-generating properties of microparticles in healthy individuals (n = 15). Microparticles, isolated from fresh blood samples and identified by flow cytometry, originated from platelets [237 x 10(6)/L (median; range 116-565)], erythrocytes (28 x 10(6)/L; 13-46), granulocytes (46 x 10(6)/L; 16-94) and endothelial cells (64 x 10(6)/L; 16-136). They bound annexin V, indicating surface exposure of phosphatidylserine, and supported coagulation in vitro. Interestingly, coagulation occurred via tissue factor (TF)-independent pathways, because antibodies against TF or factor (F)VII were ineffective. In contrast, in our in vitro experiments coagulation was partially inhibited by antibodies against FXII (12%, p = 0.006), FXI (36%, p <0.001), FIX (28%, p <0.001) or FVIII (32%, p <0.001). Both the number of annexin V-positive microparticles present in plasma and the thrombin-generating capacity inversely correlated to the plasma concentrations of thrombin-antithrombin complex (r = -0.49, p = 0.072 and r = -0.77, p = 0.001, respectively), but did not correlate to prothrombin fragment F1+2 (r = -0.002, p = 0.99). The inverse correlations between the number of microparticles and their thrombin-forming capacity and the levels of thrombin-antithrombin complex in plasma may indicate that microparticles present in the circulation of healthy individuals have an anticoagulant function by promoting the generation of low amounts of thrombin that activate protein C. We conclude that microparticles in blood from healthy individuals support thrombin generation via TF- and FVII-independent pathways, and which may have an anticoagulant function.
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PMID:Cell-derived microparticles circulate in healthy humans and support low grade thrombin generation. 1134 98

Blood coagulation has been thought to be composed of both intrinsic and extrinsic pathways. Recent evidence strongly supports the critical role of the extrinsic pathway in the initiation of blood coagulation. This investigation established an assay that examines the role of FXI in the thromboplastin-initiated (extrinsic) coagulation based on this new concept. Plasma clotting times were measured at different concentrations of thromboplastin with activated FXII inhibited (FXIIa-inhibited Diluted Thromboplastin Time, FXIIaiDTT). Only at low concentrations of thromboplastin was FXIIaiDTT of FXI-deficient plasma significantly prolonged than that of normal plasma. Depletion of FXI from normal plasma prolonged its FXIIaiDTT and replenishment of FXI shortened it. FXIIaiDTTs of both FVIII-deficient and FIX-deficient plasma were remarkably prolonged, and addition of normal plasma dose-dependently shortened it. Furthermore, earlier alpha-thrombin inhibition was directly correlated with decreasing FXa generation. The amount of FXa production was: platelet-rich plasma > platelet-poor plasma > FXI-deficient plasma. Therefore, our findings from the FXIIaiDTT assays not only support the critical role of extrinsic pathway in blood coagulation initiation, but also demonstrate the importance of FXI as an amplifier of thrombin generation in thromboplastin-initiated coagulation.
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PMID:The role of factor XI in a dilute thromboplastin assay of extrinsic coagulation pathway. 1143 84

To account for the variable hemostatic defect in patients with factor XI (FXI) deficiency, with normal hemostasis in contact factor deficiencies, a coagulation paradigm is presented whereby trace quantities of thrombin, generated transiently by exposure of tissue factor at sites of vascular injury, activates FXI bound to the platelet surface in the presence of prothrombin or high Mr kininogen (HK). Tissue factor pathway inhibitor (TFPI) limits the flux of thrombin generated by the tissue factor pathway, and protease nexin II (PNII), released from activated platelets, inhibits solution phase FXIa and localizes FIX activation to the platelet surface where FXIa is protected from inactivation by PNII. Either prothrombin or HK binds to the Apple 1 (A1) domain of FXI, thereby exposing a platelet-binding site in the FXI A3 domain. Dimeric FXI binds to activated platelets directly through the A3 domain of one monomer. After proteolytic activation of platelet-bound FXI by thrombin (or FXIIa), a substrate binding site for FIX is exposed in the opposite monomer that promotes FIX activation on the platelet surface resulting in the local explosive generation of thrombin and the formation of hemostatic thrombi at sites of vascular injury.
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PMID:Roles of platelets and factor XI in the initiation of blood coagulation by thrombin. 1148 44


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