Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.68 (tissue plasminogen activator)
 11,311 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Potential approaches to improve thrombolytic agents comprise the construction of mutants and variants of tissue-type plasminogen activator (tPA) or of single chain urokinase-type plasminogen activator (scuPA, pro-urokinase), of chimeric plasminogen activators and of conjugates of plasminogen activators with monoclonal antibodies. tPA mutants have been constructed with altered pharmacokinetic properties or altered functional properties, including binding to and stimulation by fibrin, resistance to plasmin and to protease inhibitors. Mutants of tPA described to date, obtained by deletion/substitution of functional domains or of single amino acids, have markedly reduced clearances, but usually also reduced specific thrombolytic potencies. Mutants of scuPA with improved thrombolytic potencies have thus far not been reported. Chimeric molecules containing functional domains of both tPA and scuPA have intact enzymatic properties of uPA and some fibrin affinity of tPA. Surprisingly, chimeras endowed with fibrin affinity usually have unaltered or reduced thrombolytic potencies. However, a chimera consisting of amino acids 87-274 of tPA and amino acids 138-411 of scuPA, with negligible fibrin affinity, has a 10-fold higher thrombolytic potency than scuPA in animal models of venous thrombosis, as a result of a delayed in vivo clearance and a relatively maintained specific thrombolytic activity. Plasminogen activators conjugated with antifibrin or antiplatelet monoclonal antibodies, either chemically or by recombinant DNA technology, are targeted to blood clots, resulting in a 5- to 10-fold increased thrombolytic potency. Thus, it is possible to develop plasminogen activators with improved thrombolytic potency. Whether such agents will be clinically useful remains to be established.
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PMID:Remaining perspectives of mutant and chimeric plasminogen activators. 130 56

Procoagulant, anticoagulant, and fibrinolytic activities are associated with endothelial cells and involve the production, secretion, and receptor mediated binding of proteins involved in these processes. The procoagulant aspect of endothelial cells function involves the production and release of von Willebrand Factor(vWF), the production of tissue factor, and the presence of Factor IX/IXa receptors on the cell surface. Secretion of vWf will promote the initial steps in thrombus formation by supporting platelet-platelet interaction and platelet-subendothelial matrix adhesion. Tissue factor which is undetectable in resting cells appears after exposure to various cytokines and initiates factor VIIa activation of factors IX and X. Receptors of Factor IX/IXa are also present and mediate the assembly of the prothrombinase complex on the endothelial cell surface. The anticoagulant pathway involves the cell surface protein thrombomodulin, protein C and its cofactor protein S. Thrombomodulin binds thrombin which activates protein C which in the presence of protein S cleaves and inactivates Factors V and VIII. Inactivation of these two coagulation cofactors halts the coagulation. Finally, endothelial cells also play a pivotal role in the fibrinolytic system. Production and regulated secretion of tissue plasminogen activator creates a profibrinolytic state in the endothelial cell environment. In addition, receptors for plasminogen and urokinase are also present, constituting a cell surface mediated fibrinolytic pathway. Plasminogen activator inhibitor type I, the primary inhibitor of tPA, is also produced by endothelial cells. Thus endothelial cells can promote and inhibit fibrinolysis, depending on the prevailing environmental conditions.
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PMID:[Endothelial cells and vascular hemostasis]. 131 12

Pharmacokinetics and fibrin specificity of alteplase (recombinant tissue-type plasminogen activator) were determined in 10 patients with acute myocardial infarction undergoing an accelerated infusion regimen during the alteplase/anistreplase patency study (TAPS). Fifteen milligrams of alteplase was administered as an intravenous bolus injection, followed by infusions of 50 mg over 30 min and 35 mg over a further 60 min. Mean steady state plasma concentrations of alteplase during the initial 30 min were 3.2 +/- 0.84 micrograms/ml, measured immunochemically, and 2.1 +/- 0.23 micrograms/ml, measured using a functional activity assay. These values were 45% and 51% higher, respectively, than those during the standard infusion schedule (p less than 0.01). However, the predominant plasma half-life determined by model fitting based on either assay (3.3 to 3.5 min) was unaltered compared with the standard regimen. Maximal concentrations of fibrin and fibrinogen degradation products were 5.1 +/- 2.2 and 1.9 +/- 1.1 micrograms/ml, respectively. Plasminogen decreased to 70% and alpha 2-antiplasmin to 35% of values before infusion. The results indicate that 1) improved coronary patency rates during "front-loaded" infusions can be rationalized in terms of higher plasma concentrations of both free and immunoreactive alteplase, 2) kinetic variables are comparable with those of other dosing strategies, and 3) fibrin specificity is not diminished relative to that of the standard infusion regimen.
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PMID:Pharmacokinetics and fibrin specificity of alteplase during accelerated infusions in acute myocardial infarction. 155 98

Plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of tissue plasminogen activator (tPA), plays a crucial role in the regulation of fibrinolysis. Both hepatocytes and endothelial cells have been implicated as major sources of plasma PAI-1. To study the relative contribution of these cell types to hepatic PAI-1 production, we have separated hepatocytes and hepatic sinusoidal endothelial cells by fractionation of freshly isolated rat livers using metrizamide density gradients and centrifugal elutriation. In untreated animals, PAI-1 messenger RNA (mRNA) was detected only in the purified endothelial cell fraction, and not in the hepatocyte fraction or in unfractionated liver. However, when the animals were treated with dexamethasone, PAI-1 mRNA expression was transiently induced in the liver. This induction paralleled the appearance of PAI-1 mRNA in purified hepatocytes, while PAI-1 expression in sinusoidal endothelial cells was unchanged. Four hours after dexamethasone treatment, plasma PAI-1 levels were increased approximately twofold over levels measured in animals treated with the diluent alone. These data suggest that PAI-1 production by hepatocytes may contribute to elevated plasma PAI-1 levels in the setting of acute injury and stress.
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PMID:Plasminogen activator inhibitor-1 messenger RNA expression is induced in rat hepatocytes in vivo by dexamethasone. 137 8

Plasmin inhibition by alpha 2-antiplasmin (alpha 2AP) is regulated by the vascular components fibrin(ogen) fragments, plasminogen and lipoprotein (a). Kinetic analysis demonstrates that CNBr-derived fibrinogen fragments completely protect plasmin from alpha 2AP. Plasminogen and 6-aminohexanoic acid decrease the rate of inhibition by 5- and 10-fold respectively. These studies show that CNBr-derived fibrinogen fragments and 6-aminohexanoic acid bind plasmin kringle(s) with binding constants of 2 micrograms/ml and 120 microM respectively, and that plasminogen binds to alpha 2AP with an affinity of 0.5 nM. The unmodulated inhibition is not effected by the presence of lipoprotein (a), but in the presence of protective CNBr-derived fibrinogen fragments the rate of inhibition is increased by the presence of the lipoprotein. The kinetics demonstrate that lipoprotein (a) binds to CNBr-derived fibrinogen fragments with an affinity of 4 nM, displacing plasmin from the protective surface. In addition, tissue-type plasminogen activator and trypsin inhibition by alpha 2AP is not slowed by the presence of CNBr-derived fibrinogen fragments or plasminogen (Pg), respectively. These kinetics suggest that the initial reversible interaction between plasmin and alpha 2AP is mediated by binding of the inhibitor to the kringle 1 domain of plasmin, with a reversible inhibition constant (Ki) of 5.0 x 10(-10) M. Under conditions where this kringle-inhibitor interaction is blocked, the reversible inhibition still occurs between the plasmin and alpha 2AP, but the initial Ki is increased to 5.0 x 10(-9) M. These data suggest that, in the circulation, plasmin inhibition by alpha 2AP may be down-regulated by fibrin, fibrin(ogen) fragments and Pg, but up-regulated by lipoprotein (a) in the presence of fibrin or fibrin(ogen) fragments. The lipoprotein (a)-mediated promotion of plasmin inhibition may provide an additional mechanism by which the lipoprotein impairs fibrinolysis and promotes atherosclerosis.
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PMID:Lipoprotein (a) promotes plasmin inhibition by alpha 2-antiplasmin. 138 85

Forty-two strains of Neisseria meningitidis and 17 of Neisseria gonorrhoeae were tested for their ability to interact with 125I-labeled Glu-plasminogen. All strains tested reacted substantially with plasminogen, resulting in uptake values of 20%-48%. Scatchard analysis with selected N. meningitidis strains demonstrated a dual-phase receptor interaction, one more avid receptor with a Kd of 50 nM and 3000-6000 receptors per bacterium and a second receptor with a Kd of 200 nM and 10,000-20,000 receptors per bacterium. Plasminogen uptake could be completely eliminated by low concentrations of epsilon-aminocaproic acid, suggesting that the lysine binding sites on the plasminogen molecule are involved in the receptor-ligand interaction. The binding of plasminogen to the bacterial receptor facilitates the tissue-type plasminogen activator-mediated conversion to Glu-plasmin, which also modifies itself to the Lys form. Receptor-associated plasmin is enzymatically active, monitored as a breakdown of the chromogenic substrate S-2251, and retains its activity in the presence of naturally occurring inhibitors in plasma.
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PMID:Binding of plasminogen to Neisseria meningitidis and Neisseria gonorrhoeae and formation of surface-associated plasmin. 138 49

Several reports have evaluated the in vitro effect of lipoprotein(a) [Lp(a)] levels on the fibrinolytic system, suggesting that high Lp(a) levels may inhibit fibrinolysis by competing for plasminogen binding in different systems. We have studied plasminogen activation induced by tissue-type plasminogen activator (t-PA), as well as other fibrinolytic parameters, in 25 subjects with Lp(a) levels greater than 30 mg/dl and the results were compared with those found in 23 subjects with Lp(a) less than 30 mg/dl. Both groups were similar in age, sex distribution, living habits and lipid pattern. Plasminogen activation, when measured by t-PA-induced euglobulin clot lysis, was significantly decreased in the group with elevated Lp(a) levels (lysis time, 16.7 +/- 3.3 min) compared with the group with low Lp(a) levels (11.8 +/- 2.0 min), although 8 of the 25 subjects with high Lp(a) levels showed plasminogen activation within the range of the control group. A positive significant correlation between Lp(a) levels and t-PA-induced euglobulin clot lysis time was found. No statistical differences were demonstrated between groups for the other fibrinolytic parameters studied. Addition of purified Lp(a) to the euglobulin fraction or to plasma resulted in a decrease in euglobulin clot lysis. The present study shows that t-PA induced plasminogen activation is decreased in individuals with high circulating levels of Lp(a) supporting the hypothesis that Lp(a) may interfere with the physiological functions of plasminogen.
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PMID:Euglobulin clot lysis induced by tissue-type plasminogen activator is reduced in subjects with increased levels of lipoprotein (a). 138 93

Aspirin at high but not at low doses reduces the fibrinolytic response to venous occlusion. Inhibition of vascular prostacyclin synthesis could be involved in this effect. Fish oil supplementation may redirect prostanoid metabolism toward an overall "antithrombotic" condition but with controversial effects on prostacyclin formation. In this study we investigated the effect of low-dose aspirin together with n-3 polyunsaturated fatty acid (PUFA) supplementation on the fibrinolytic response to venous occlusion. Following a double-blind, randomized, crossover design, six healthy volunteers (three men and three women, 24-37 years old) were given for 29 days 5.3 g eicosapentaenoic and docosahexaenoic acids or a corresponding dose of n-6 PUFAs as control; aspirin (40 mg/day) was then added for an additional 14 days. A 2-month washout period was allowed before the crossover. Blood was collected before and after venous stasis on days 0, 29, and 43 of each test period. A combination of aspirin with n-3 PUFAs reduced the fibrinolytic response to venous occlusion in all subjects, the mean value of fibrinolytic activity after stasis being 240 +/- 40 mm2, a value significantly lower than at baseline (366 +/- 51 mm2, mean +/- SEM, p < 0.05). Similarly, the tissue-type plasminogen activator (t-PA) antigen level was lower in the aspirin + PUFA-treated group. Plasminogen activator inhibitor activity before stasis was enhanced by n-3 PUFA supplementation (from 7.5 +/- 2 to 14.8 +/- 3 IU/ml, p < 0.05), an effect not affected by aspirin.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Modulation of fibrinolytic response to venous occlusion in humans by a combination of low-dose aspirin and n-3 polyunsaturated fatty acids. 139 May 91

Urokinase-type (uPA) and tissue-type (tPA) plasminogen activators were identified by fibrinolytic autography in the sulcus epithelium of human gingival mucosa but not in the orthokeratinized gingival epithelium. Fibrinolytic activity was present only over blood vessels in frozen sections of oral squamous cell carcinomas, the malignant epithelial cells showing no plasminogen activator activity. Plasminogen activators could not be demonstrated in either the sulcus or gingival epithelium by immunofluorescence, but both uPA and tPA were found in occasional squamous carcinoma cells. Fibrinolytic activity of culture fluids from epithelial explants grown in vitro from human gingival mucosa showed marked variation, but activity was much higher in the culture supernatants than in the cell lysates. Fibrinolytic activity of culture fluids from epithelial explants of squamous cell carcinomas was low both in supernatants and lysates. Zymogram overlays of sodium dodecyl sulphate-polyacrylamide electrophoretic gels from culture supernatants showed that the low fibrinolytic activity of culture supernatants of oral squamous cell carcinomas was due to the associated presence of plasminogen activator inhibitors. The fibrinolytic activity in the zymogram was due predominantly to uPA but some lysis was due also to tPA.
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PMID:Plasminogen activators in normal and malignant oral epithelium in vivo and in vitro. 141 24

Plasminogen, the zymogen form of the fibrinolytic enzyme plasmin, is known to undergo plasmin-mediated modification in vitro. The modified form, Lys-plasminogen, is superior to the native Glu-plasminogen in fibrin binding and as a substrate for activation by tissue-type plasminogen activator (t-PA). The present study was undertaken to determine the existence and significance of the Glu- to Lys-plasminogen conversion during t-PA-mediated lysis of plasma clots in vitro. When human plasma was supplemented with exogenous Lys-plasminogen and clotted, a dose-dependent shortening of lysis time was observed. Formation of Lys-plasminogen in situ during fibrinolysis was determined using 131I-Glu-plasminogen-supplemented plasma. By the time of lysis, Lys-plasminogen had accumulated to about 20% of the initial concentration of Glu-plasminogen. Quantitation of activation of both Glu- and Lys-plasminogen as well as the conversion of Glu- to Lys-plasminogen in plasma supplemented with both 131I-Glu-plasminogen and 125I-Lys-plasminogen was accomplished by determining the flux of the isotopically labeled species along three pathways: Glu-plasminogen-->Glu-plasmin, Glu-plasminogen-->Lys-plasminogen, and Lys-plasminogen-->Lys-plasmin. After a brief lag, the Glu-plasminogen activation rate was constant until lysis was achieved, at which point activation ceased. The Lys-plasminogen activation rate also was essentially constant until lysis but was not characterized by a lag phase. The rate of conversion of Glu- to Lys-plasminogen was nonlinear and correlated directly with the rate of fibrinolysis. By the time lysis had occurred, Glu-plasminogen consumption had been distributed equally between direct activation to plasmin and conversion to Lys-plasminogen, and 45% of the plasmin which had been formed was derived from Lys-plasminogen. These results demonstrate both the formation and the subsequent activation of Lys-plasminogen during fibrinolysis. As a result of improved fibrin binding and activation of Lys-plasminogen compared to Glu-plasminogen, the formation of Lys-plasminogen within a clot constitutes a positive feedback mechanism that can further stimulate the activation of plasminogen by t-PA as fibrinolysis progresses.
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PMID:Lys-plasminogen is a significant intermediate in the activation of Glu-plasminogen during fibrinolysis in vitro. 146 25


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