Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “THROMBIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources
PubMedDate not supplied

Effects of the oral direct thrombin inhibitor ximelagatran on p-selectin expression and thrombin generation in atrial fibrillation.

This study investigated the pharmacodynamic effects of the oral direct thrombin inhibitor ximelagatran on platelet activation and thrombin generation in patients with nonvalvular atrial fibrillation. Using an open, group-matched study design, the effects of ximelagatran (36 mg twice daily for 5 days) were studied in 12 patients with permanent nonvalvular atrial fibrillation and in 12 healthy controls. After ximelagatran for 5 days, elevated platelet P-selectin expression in atrial fibrillation patients was lowered to that during coumarin treatment or in controls but had no effect in control subjects. Using the endogenous thrombin potential as a marker, ximelagatran decreased and delayed thrombin generation in both groups. In conclusion, direct thrombin inhibition with ximelagatran reduced elevated platelet P-selectin expression and inhibited thrombin generation.

Adult↗
PubMed2003

Thrombin generation in severe haemophilia A and B: the endogenous thrombin potential in platelet-rich plasma.

Thrombin generation was investigated in platelet-rich plasma (PRP) from 11 healthy controls, 17 patients with severe haemophilia A and 7 patients with severe haemophilia B. Mean endogenous thrombin potential (ETP) in arbitrary fluorescence units (FU) was 226.9 +/- 44.6, 186.4 +/- 22.5, 154.2 +/- 41.3 in controls, haemophilia A and B, respectively, all at a platelet count of 200 x 10(9)/l (p = 0.004 for controls vs. haemophilia A, p = 0.003 for controls vs. haemophilia B, no significant difference between haemophilia A and B). The contribution of FVIII to thrombin generation in haemophilia A was 1.31 +/- 0.16 FU/% of FVIII:C activity, while for FIX in haemophilia B this was 0.80 +/- 0.21 FU/% of FIX activity. There was an almost linear relationship between increasing platelet count and thrombin generation up to a mean platelet count of 100 x 10(9)/l. Further increase in platelet count has only a marginal influence on thrombin generation. Platelets increase ETP in haemophilia A by 0.184 +/- 0.022 FU/10(9) platelets/l and in haemophilia B by 0.319 +/- 0.085 FU/10(9) platelets/l, and this was significantly different between the two groups (p = 0.0002). This influence of plate-lets diminishes with increasing concentration of either FVIII or FIX. In conclusion, there is a difference in thrombin generation between haemophilia A and B, and this may be attributed to the role of platelets in the assembly of the tenase complex on their surface.

Adult↗
PubMed2004

Platelets in patients with acute ischemic stroke are exhausted and refractory to thrombin, due to cleavage of the seven-transmembrane thrombin receptor (PAR-1).

Platelet activation is involved in the pathogenesis of cerebrovascular ischemia, but the major agonist involved has yet to be identified. To investigate the role of thrombin in platelet activation in patients with acute ischemic stroke, and while thrombin is the most likely candidate for activation of the thrombin receptor PAR-1 in vivo, we assessed its cleavage and internalization using the antibodies SPAN12, binding to uncleaved PAR-1, and WEDE15, recognizing cleaved and uncleaved, but not internalized PAR-1. In contrast to healthy age-matched controls, platelets from stroke patients exhibited significant cleavage and internalization of PAR-1 (P<0.001) and failed to respond to thrombin in vitro. Enhanced surface expression of CD62P, CD63, TSP-1 and less mepacrine uptake showed platelet degranulation during stroke. Platelets from patients with acute cerebral ischemia are exhausted and desensitized to thrombin through cleavage of PAR-1, indicating that high concentrations of thrombin occur with acute cerebrovascular ischemic events in vivo.

Acute Disease↗
PubMed2003

Effects of thrombin inhibitor on thrombin-related signal transduction and cerebral vasospasm in the rabbit subarachnoid hemorrhage model.

BACKGROUND AND PURPOSE: Thrombin is activated in the cerebrospinal fluid (CSF) after a subarachnoid hemorrhage (SAH). However, the relationship between thrombin and cerebral vasospasm has not yet been fully established. The aim of this study was to investigate the possibility of thrombin as a causative factor for cerebral vasospasm and to delineate the signal transduction mechanism that results in thrombin-inducing sustained vasoconstriction in cerebral vasospasm. METHODS: In the SAH group, SAH was simulated by the 2-hemorrhage rabbit model. In the treatment group, antithrombin III (AT-III) was injected into the cisterna magna just before production of the SAH. CSF samples were obtained serially to measure d-dimer with latex photometric immunoassay. On day 4, the basilar artery was excised after perfusion-fixation. The degree of cerebral vasospasm was evaluated by measuring the cross-sectional area of each basilar arterial lumen, and the expression of mitogen-activated protein kinase (MAPK) in the vascular wall was examined with an immunohistochemical technique. RESULTS: In the treatment group, the value of d-dimer on day 4 was 0.83+/-0.07 microg/mL, which was statistically significantly lower than that in the nontreated SAH group (2.49+/-0.09 microg/mL, P<0.01). The cross-sectional area of the arterial lumen in the treatment group was 3.67x10(5)+/-1.58x10(4) square pixels, which was statistically significantly larger than that in the nontreated SAH group (2.60x10(5)+/-2.29x10(4) square pixels; P<0.01). MAPK was detected diffusely in the vascular smooth muscle cell layer in the nontreated SAH group, but it was absent in the treatment group. CONCLUSIONS: Inhibition of thrombin activity leads to amelioration of cerebral vasospasm and suppression of MAPK diphosphorylation. This suggests that thrombin and its related signal transduction, including the MAPK cascade, appear to play an important role in the pathogenesis of cerebral vasospasm after SAH.

Animals↗
PubMed1997

Thrombin-mediated activation of factor XI results in a thrombin-activatable fibrinolysis inhibitor-dependent inhibition of fibrinolysis.

Recently, it has been shown that Factor XI can be activated by thrombin, and that Factor XIa significantly contributes to the generation of thrombin via the intrinsic pathway after the clot has been formed. This additional thrombin, generated inside the clot, was found to protect the clot from fibrinolysis. A plausible mechanism for this inhibitory effect of thrombin involves TAFI (thrombin-activatable fibrinolysis inhibitor, procarboxypeptidase B) which, upon activation, may inhibit fibrinolysis by removing carboxy-terminal lysines from fibrin. We studied the role of Factor XI and TAFI in fibrinolysis using a clot lysis assay. The lysis time was decreased twofold when TAFI was absent, when TAFI activation was inhibited by anti-TAFI antibodies, or when activated TAFI was inhibited by the competitive inhibitor (2-guanidinoethylmercapto)succinic acid. Inhibition of either TAFI activation or Factor XIa exhibited equivalent profibrinolytic effects. In the absence of TAFI, no additional effect of anti-Factor XI was observed on the rate of clot lysis. We conclude that the mechanism of Factor XI-dependent inhibition of fibrinolysis is through the generation of thrombin via the intrinsic pathway, and is dependent upon TAFI. This pathway may play a role in determining the fate of in vivo formed clots.

Antibodies, Monoclonal↗
PubMed2003

Effect of non-heparin thrombin antagonists on thrombin generation, platelet function, and clot structure in whole blood.

Platelet contractile force (PCF), which is absent in blood obtained during cardiopulmonary bypass, significantly recovers after protamine sulfate administration. In vitro studies reveal this effect to be primarily caused by heparin. Because many of heparin's effects are mediated by suppression of thrombin generation and activity, this study assessed the influence of thrombin inhibition on PCF. The effects of natural and synthetic antithrombins were measured. Clots were formed by the addition of batroxobin (0.21 microg/mL) to whole blood (platelet count 200,000/microL). Force development was measured from the moment of batroxobin addition. After 1200 s of clotting, purified antithrombin III (22 microM) reduced PCF by 74%. Thrombomodulin (0.014 microM) reduced PCF by 60%. At 0.040 microM, PCF was reduced by 82% (6.5-1.2 Kdynes). Hirudin decreased PCF in a dose-dependent fashion, with complete suppression at concentrations > or = 0.30 microM. At concentrations between 0.04 and 0.29 microM, Lepirudin (Refludan, a recombinant therapeutic hirudin) produced dose-dependent delay and suppression of PCF. Above 0.29 microM Lepirudin, PCF was totally suppressed. At 1.60 microM, bivalirudin (a synthetic, 20 amino acid peptide) delayed and reduced PCF by 50%. At 6.40 micro;M, PCF was completely suppressed. Although 20 microM of P-PACK II (d-Phenylalanyl-L-Phenylalanylarginine- chloro-methyl ketone 2 HCl) had little effect, 40 microM delayed onset of force development from 300 to 600 s and reduced PCF at 1200 s from 5.2 to 3.3 Kdynes. At 120 microM, force development was totally suppressed. Four micromol Thromstop (BNas-Gly-(pAM)Phe-Pip) delayed force development by greater than 800 s and PCF at 1200 s was reduced by 70%. At 0.20 microM, Argatroban (a synthetic polypeptide direct thrombin antagonist) delayed onset of PCF from 300 to 540 s and decreased PCF by 40%. At a concentration of 0.40 microM and above, Argatroban totally suppressed PCF. These results indicate that some of the antiplatelet effects of heparin are the result of thrombin inhibition and that low-level thrombin generation is essential for clot retraction. The sensitivity of PCF to the presence of thrombin may permit monitoring of antithrombin agents via this assay.

Antithrombin III↗
PubMed2005

Human thrombin for treatment of pseudoaneurysms: comparison of bovine and human thrombin sonogram-guided injection.

OBJECTIVE: The purpose of this research was to review our experience and determine the success rate of percutaneous sonogram-guided human thrombin injection to treat iatrogenic femoral pseudoaneurysms and compare this with the results obtained with bovine thrombin injection. CONCLUSION: In our experience, the use of human thrombin for the treatment of iatrogenic femoral pseudoaneurysms is highly efficient (100%), the administered dose is significantly less than with bovine thrombin, and the risk for allergy is potentially lower. At our hospital, human thrombin has replaced bovine thrombin and is the first line of treatment for an iatrogenic pseudoaneurysm.

Aged↗
PubMed1976

Comparison of the actions of thrombin and the thrombin-like venom enzymes ancrod and batroxobin.

Thrombin acts on several coagulant proteins to produce products with physiologic, pharmacologic and pathologic potential. The most sensitive thrombin substrate seems to be factor VIII. Some thrombin dependent reactions studied in vitro and proposed as control reactions seem too insensitive to the action of thrombin to be of in vivo significance. The only enzymic reaction the thrombin-like venom enzymes, Ancrod and Batroxobin, have in common with thrombin is the removal of fibrinopeptide A.

Ancrod↗
PubMed2002

Inhibition of thrombin generation by the oral direct thrombin inhibitor ximelagatran in shed blood from healthy male subjects.

Ximelagatran, an oral direct thrombin inhibitor, whose active form is melagatran, was studied using a model of thrombin generation in humans. Healthy male volunteers (18 per group) received ximelagatran (60 mg p.o.), dalteparin (120 IU/kg s.c.) or a control (water p.o.). Shed blood, collected after incision of the forearm with standardised bleeding time devices at pre-dose, and at 2, 4 and 10 h post-dosing, was analysed for markers of thrombin generation. Statistically significant reductions (p < 0.05) in levels of prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin complex (TAT) in shed blood were detected at 2 and 4 h post-dosing in both the ximelagatran and dalteparin groups. Shed blood F1+2 and TAT levels had returned to pre-dose levels at 10 h post-dosing. Using a shed blood model, we demonstrate that the reversible thrombin inhibitor melagatran and, therefore, oral administration of ximelagatran, inhibits thrombin generation in humans after acute activation of coagulation.

Administration, Oral↗
PubMed1976

[The state of anticoagulant system of animals following injections of purified thrombin and N-acetyl-thrombin].

I. v. administration of N-acetyl-thrombin, similar to thrombin, increases the fermentative fibrinolytic potency of the plasma, although to a lesser extent. This is also expressed in the increased esterase activity of the plasma and euglobulin fraction. When blocking the forming plasmin, esterase activity is observed in kallekreine. (The inhibitory effect of plasma after N-acetyl-thrombin administration tells also on the nonfermentative fibrinolytic activity of the Fibrinogen-Heparin complex, activity of the latter dropping practically to the zero level. Warming up at 60 degrees C decreases the nonfermentative fibrinolytic activity of the complex N-acetyl-thrombin (thrombin-esterase) does not provoke the activation of the second anticoagulang system, while the native thrombin does it.

Animals↗
PubMed1991

Thrombin structure and function: why thrombin is the primary target for antithrombotics.

Thrombin has both beneficial and harmful effects. In order of importance, at very low concentrations, alpha-thrombin firstly amplifies its own generation through the activation of factors V and VIII, which are the primary targets of antithrombotic agents. It secondly functions at the cellular level where, at low concentrations it activates platelets, and at higher concentrations, induces endothelial cell changes (e.g., shape changes, albumin transport release of plasminogen activators and other substances). It thirdly converts fibrinogen into clottable fibrin and becomes actively incorporated into the forming thrombus. In addition, it activates protein C, which in turn degrades factors V and VIII (and/or their activated forms) and causes the shutdown of thrombin generation. When compared to other serine proteinases of the blood coagulation and fibrinolytic systems, alpha-thrombin is unique in that it loses most of its proenzyme activation fragment and has developed multisite short-ranged bridge-binding interactions, which appear to explain thrombin specificity. To understand thrombin is to understand haemostasis.

Amino Acid Sequence↗
PubMed1986

The glycocalicin portion of platelet glycoprotein Ib expresses both high and moderate affinity receptor sites for thrombin. A soluble radioreceptor assay for the interaction of thrombin with platelets.

A soluble radioreceptor assay has been developed to characterize thrombin receptor activities of the human platelet membrane. 125I-Thrombin was added to platelet membranes solubilized in 1% Triton X-100, and thrombin bound to platelet receptors was separated from free thrombin by precipitation with wheat germ agglutinin (WGA) in the presence of alpha 1-acid glycoprotein as carrier. Both high affinity binding (Ki, 0.09 nM; R1, 0.30 pmol/mg protein) and moderate affinity binding (K2, 38 nM; R2, 72 pmol/mg protein) were detected in the detergent-solubilized membrane preparations and these binding parameters were in excellent agreement with values previously determined using intact platelets (Harmon, J. T., and Jamieson, G. A. (1985) Biochemistry 24, 58-64). Using the soluble radioreceptor assay, both high and moderate affinity binding was detected in highly purified preparations of glycoprotein Ib (GPIb) and glycocalicin, and the binding isotherms were identical with those of the crude detergent-solubilized membrane preparation. Treatment of detergent-solubilized membranes with increasing concentrations of a monospecific polyclonal antibody to glycocalicin resulted in the stepwise depletion of GPIb and concomitant reductions of thrombin binding activity. These results demonstrate that both high and moderate affinity binding of thrombin to platelets is completely expressed in the glycocalicin portion of GPIb.

Animals↗
PubMed1993

Effects of thrombin and thrombin receptor activating peptides on rat aortic vascular smooth muscle.

The role of thrombin receptor activation in isolated rat aortic rings was examined. The human thrombin receptor activating peptides (TRAPs) SFLLRNPNDKYEPF (TRAP1-14), SFLLRNP (TRAP1-7) and rat TRAP1-7 (SFFLRNP) all caused concentration-related (0.1-100 microM) contractions of endothelium-rubbed rat aortic rings. Reversal of the first two amino acids in TRAP1-14 ("reverse TRAP1-14") resulted in total loss of activity. The contractions caused by the TRAPs were reduced substantially in endothelium-intact rings due to endothelium-derived relaxing factor release because the reduced contractions were reversed by N omega-nitro-L-arginine or methylene blue. Contractions were significantly but only slightly enhanced by alpha receptor blockade and were not affected by thromboxane- or endothelin-receptor blockade or by cyclooxygenase inhibition. TRAP1-7 had no effect on contractile responses to norepinephrine, serotonin, angiotensin II or endothelin-1; however, pretreatment with nifedipine or removal of extracellular Ca++ markedly inhibited the contraction. Neither human nor rat alpha-thrombin had any contractile effect on rat aortic rings. In cultured rat aortic smooth muscle cells, alpha-thrombin (EC50 = 1.9 +/- 0.7 nM), TRAP1-14 (EC50 = 30 +/- 4 microM) and TRAP1-7 (EC50 = 20 +/- 9 microM) caused concentration-dependent increases in intracellular calcium [Ca++]i, whereas reverse TRAP1-14 was ineffective. The effect of thrombin on [Ca++]i was abolished by the thrombin inhibitor MD-805, whereas the responses to TRAP were unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Effects of thrombin receptor activating peptide on phosphoinositide hydrolysis and protein kinase C activation in cultured rat aortic smooth muscle cells: evidence for "tethered-ligand" activation of smooth muscle cell thrombin receptors.

Phosphoinositide hydrolysis and protein kinase C (PKC) activation were examined in response to treatment of rat aortic smooth muscle cells with alpha-thrombin and a seven amino acid thrombin receptor activating peptide (TRAP-7; SFLLRNP). alpha-Thrombin and TRAP-7 stimulated total inositol phosphate (IP) accumulation and phosphorylation of a specific endogenous substrate for activated PKC. Acetylated TRAP-7 and "reverse" TRAP (FSLLRNPNDKYEPF) were ineffective in stimulating signal transduction. The active site inhibitor, MD805 (argatroban), and the anion-binding exosite inhibitor, BMS 180,742, reduced the IP response to alpha-thrombin in a concentration-dependent manner. In contrast, the TRAP-7-induced IP response was not affected by either inhibitor. These data are consistent with the tethered-ligand hypothesis for thrombin receptor activation in rat aortic smooth muscle cells.

Animals↗
PubMed2003

Differential Ca(2+)responses induced by thrombin and thrombin-receptor agonist peptides in HSY-EA1 cells.

We examined the mechanism by which protease-activated receptor (PAR)-1 is desensitized by comparing the effect of thrombin and the soluble agonist peptide SFLLRN on Ca(2+)responses in HSY-EA1 cells. Thrombin-induced increases in cytosolic Ca(2+)concentrations ([Ca(2+)](i)) returned to basal levels within 60 s, but SFLLRN generated a sustained [Ca(2+)](i)elevation. Interestingly, thrombin-desensitized cells partially retained their ability to respond to SFLLRN. We desensitized PAR-2 by pretreating cells with SLIGKV to confirm that this response was not due to PAR-2, which can recognize SFLLRN. The highly specific PAR-1 agonist peptide TFLLR also increased [Ca(2+)](i)in PAR-2-desensitized cells pretreated with thrombin. These observations indicate that thrombin disarms PAR-1 from further proteolytic activation, but leaves the receptor responsive for non-tethered ligands.

Calcium↗
PubMed1992

Action of thrombin receptor polypeptide in gastric smooth muscle: identification of a core pentapeptide retaining full thrombin-mimetic intrinsic activity.

We have used a guinea pig gastric longitudinal (LM) smooth muscle bioassay system to evaluate the contractile activities of a previously described thrombin receptor-derived polypeptide, S42FLLRNPNDKYEPF55 (one-letter amino acid code) (TRP42-55) and of a series of peptides derived from this sequence. The contractile activities of the polypeptides were compared with the actions of thrombin. Shortened peptides of the sequences S42FLLRNPND50, S42FLLRN47, and S42FLLR46 (TRP42-46) all exhibited contractile activities that were equivalent to or greater than those of the parent polypeptide, TRP42-55. Both TRP42-55 and TRP42-46 mimicked the action of thrombin, in terms of two different signal transduction pathways that were activated either in the LM preparation or in the related but distinct gastric circular muscle assay. In the LM preparation, the peptide FSLLR also exhibited appreciable, but much reduced, activity. Minimal activity was exhibited in the LM by the sequence SFLLA, but the lysine-containing analogue S42FLLK46 was about one fifth as potent as TRP42-46. In contrast, the receptor-derived sequences S42FLL45, S42FL44-NH2, F43LLR46, and S42ALLR46, as well as arginine-containing polypeptides beginning with the SF motif, SFRG and SFRGHITR, were inactive in the LM bioassay system, at concentrations of greater than or equal to 200 microM, as either agonists or antagonists against TRP42-55. In addition to its actions in the LM and circular muscle preparations, the active pentapeptide, TRP42-46, also exhibited thrombin-mimetic intrinsic activity in a rat aortic arterial ring relaxation bioassay, whereas the pentapeptide S42FLLA46 and the tetrapeptide S42FLL45 were inactive. We conclude that the intrinsic biological activity of the thrombin receptor-derived peptide resides in the pentapeptide TRP42-46 and that the phenylalanine and arginine residues at positions 43 and 46 play key roles in the activity of this pentapeptide in smooth muscle systems.

Amino Acid Sequence↗
PubMed1996

Restenosis following percutaneous revascularization--the potential role of thrombin and the thrombin receptor.

Thrombin is present at sites of vascular injury and elicits many effects which may contribute to neointimal growth. Further studies are needed to order to determine steps involved in thrombin-induced effects and to identify potential sites to regulate these effects. The failure of the Helvetica trial to demonstrate an effect of treatment with hirudin on restenosis may relate more to our inability to safely inhibit thrombin than to a lack of a role for thrombin in restenosis. A therapy which enables safe and effective control of thrombin-induced responses following vascular injury may yet prove effective at reducing restenosis following percutaneous coronary revascularization.

Angioplasty, Balloon, Coronary↗
PubMed1989

Gamma-thrombin-induced phospholipase A2 activation in rabbit platelets: comparison with alpha-thrombin.

gamma-Thrombin stimulated release of [3H]arachidonic acid ([3H]AA) accompanied by a significant production of PAF and lyso-PAF by rabbit platelets. These responses, which reflect PLA2 activation, were observed after a prolonged lag and to a lower extent when compared to those induced by alpha-thrombin which evoked a much higher elevation in intracellular calcium. This elevation together with [3H]AA release were markedly reduced by EDTA. However, addition of ionophore A23187 enhanced the release of [3H]AA by gamma-thrombin to the levels similar to those of alpha-thrombin. We conclude that gamma-thrombin is able to activate PLA2 and suggest that calcium influx may be a limiting factor for this activation.

Animals↗