Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mesothelium contains both procoagulant and fibrinolytic activities. An imbalance between these activities could account for the abnormal fibrin turnover and pleural fibrin deposition that is characteristic of pleural inflammation. Procoagulant activity of human pleural mesothelial cells (HPMC) is in part due to tissue factor, and the prothrombinase complex can also assemble at the HPMC surface. HPMC express tissue plasminogen activator (tPA) but no detectable fibrinolytic activity in a fibrin plate assay. Inhibition of HPMC fibrinolytic activity is due, in part, to elaboration of plasminogen activator inhibitors-1 and -2 (PAI-1 and PAI-2) as well as antiplasmins. Synthesis of PAI-1 and PAI-2 is inhibited by actinomycin D and cyclohexamide. HPMC PAI-1 is increased by transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha), as is tPA release, while PAI-1 mRNA is unchanged and tPA mRNA is increased. PAI-2 release is induced by TNF-alpha and TGF-beta. Because they are a rich source of PAI-1 and PAI-2, HPMC may contribute to the high levels of these inhibitors in pleural exudates. Stimulation of HPMC by TNF-alpha or TGF-beta in vitro did not alter HPMC procoagulant activity nor the balance of elevated PAI and antiplasmins relative to PA, changes that collectively favor formation and persistence of pericellular fibrin.
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PMID:Pathways of fibrin turnover of human pleural mesothelial cells in vitro. 138 10

Increases in thrombin activity in patients given fibrinolytic agents for acute myocardial infarction have been shown to be important in limiting the ultimate success of coronary thrombolysis. The present study was designed to determine whether increases in thrombin activity reflect, in part, activation of prothrombin accompanying thrombolysis. Plasma concentrations of prothrombin fragment 1.2, a polypeptide released when prothrombin is activated by factor Xa, were measured in 22 patients with acute myocardial infarction before and after treatment with 100 mg of recombinant tissue-type plasminogen activator (rt-PA). Concentrations of prothrombin fragment 1.2 increased from 0.83 +/- 1.1 nM (mean +/- SD) before rt-PA infusion to 1.5 +/- 1.5 nM 2 h after initiation of the infusion (p less than 0.05). After a 5,000-U intravenous dose of heparin given at the end of the infusion of rt-PA, concentrations of prothrombin fragment 1.2 decreased from 1.8 +/- 1.5 to 1.1 +/- 0.9 nM (n = 20, p less than 0.05), although values were still increased compared with concentrations before rt-PA. These results indicate that thrombin activity increases in patients given rt-PA at least in part because of activation of the coagulation system leading to activation of prothrombin. Thus, inhibition of the reactions involving coagulant proteins that lead to activation of prothrombin may be of value as conjunctive treatment to potentiate the efficacy of pharmacologic thrombolysis.
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PMID:Activation of prothrombin accompanying thrombolysis with recombinant tissue-type plasminogen activator. 155 97

Fluid cadaveric blood is generally known as a characteristic of sudden death. However, it has been reported that soft blood clots have been observed in a number of cases of sudden death after alcohol drinking. Such a tendency was also recognized on autopsy cases in our laboratory. This study was carried out to reveal the effects on clotting and fibrinolytic system in golden hamsters under acute alcohol intoxication. Furthermore, the influences of ether anaesthesia were also observed. Activities of clotting and fibrinolytic factors were measured with fluorogenic peptide substrate. Prothrombin and factor X activities began to decrease 1 hr after administration of alcohol. But thrombin-like and factor Xa-like activities significantly increased after 1 hr and then returned to the initial value 4 hr after administration. Plasminogen activity began to decrease 1 hr after administration, whereas plasmin-like and t-PA-like activities increased after 1 hr and returned to the initial values or decreased after 4 hr. These results show that under acute alcohol intoxication clotting and fibrinolytic factors (prothrombin, factor X and plasminogen) in golden hamsters were converted temporarily to their active forms (thrombin, factor Xa and plasmin). No influence of only ether anaesthesia on clotting and fibrinolytic activities was observed. At 1 hr after administration of alcohol some effects of ether anaesthesia on prothrombin, prekallikrein and kallikrein were observed and then were not observed after 4 hr. But it seems that the influence of ether anaesthesia on clotting and fibrinolytic activities was negligible in the process after alcohol consumption.
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PMID:[Clotting and fibrinolytic activities in acute alcoholic golden hamsters with or without ether anaesthesia]. 192 Sep 21

The potential importance of pleural fibrin deposition in the pathogenesis of pleural injury is supported by both clinical and experimental observations. We hypothesized that the local equilibrium between procoagulant and fibrinolytic activities is disrupted to favor fibrin deposition in exudative pleuritis. To test this hypothesis, we characterized procoagulant and fibrinolytic activities in pleural exudates from patients with pneumonia, lung cancer, or empyema and transudates from patients with congestive heart failure. Procoagulant activity was generally increased in exudative processes and was due mainly to tissue factor. All effusions contained antithrombin III and inhibited factor Xa and thrombin, but endogenous prothrombinase or thrombin activities were variably detected. Pleural fluid fibrinolytic activity was increased in congestive heart failure and was due to both tissue plasminogen activator and urokinase. Depressed fibrinolytic activity was found in pleural exudates despite increased concentrations of plasminogen, mainly glu-1-plasminogen, and was due to inhibition of plasminogen activation by plasminogen activator inhibitors 1 and 2 and of plasmin, in part by alpha 2-antiplasmin. Concentrations of PAI-1 in exudative pleural fluids were increased up to 913-fold, compared with normal pooled plasma. Exudative pleural effusions are characterized by increased procoagulant and depressed fibrinolytic activity, favoring fibrin deposition in the pleural space. The balance of these activities is reversed and favors fibrin clearance in congestive heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Abnormalities of pathways of fibrin turnover in the human pleural space. 206 28

Parameters of the fibrinolytic system were studied in a primate model where the generation of thrombin was promoted in vivo. The procoagulant stimulus used was a combination of human factor Xa in combination with phosphatidylcholine/phosphatidylserine lipid vesicles (PCPS) as the source of coagulant active phospholipid. The dosage of each component was formulated to provide a gradation of thrombin generating potential assessed prior to in vivo study in an in vitro clotting assay. These ranged from 25.25-36.60 pMole/kg (factor Xa) and 18.85-56.30 nMole/kg (PCPS). In each case, the ratio of the dose of factor Xa/PCPS was maintained at 0.65 (pMole factor Xa/nMole PCPS). Individual dosage combinations producing recalcification clotting times in vitro of 15, 20, 25 and 30 s were used in detailed in vivo studies. Previous studies in dogs had confirmed the thrombin generating potential of factor Xa/PCPS infusions and demonstrated an associated activation of protein C and increased fibrinolytic activity. This has now been extensively characterized in the chimpanzee as follows: 10 min after the infusion of the highest dose (36.6 pMole factor Xa/56.3 nMole PCPS kg bodyweight), the level of circulating t-PA had risen to 900 ng/ml (antigen), 885 IU/ml (functional). Dosage was observed with the lowest dose of 12.25 pMole factor Xa and 18.85 nMole PCPS being associated with relatively minor increases in circulating t-PA activity. There were no changes in u-PA at any dosage during the full time course of the experimental period (90 min). Plasminogen activation was also apparent with alpha-2 antiplasmin levels falling to 30-40% of pre-infusion levels at the highest dosages.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The fibrinolytic potential of the normal primate following the generation of thrombin in vivo. 240 50

Incubation of HTC rat hepatoma cells with the synthetic glucocorticoid dexamethasone rapidly inhibits plasminogen activator (PA) activity secondary to the induction of a specific acid-stable inhibitor of plasminogen activation (Cwikel, B. J., Barouski-Miller, P.A., Coleman, P.L., and Gelehrter, T.D. (1984) J. Biol. Chem. 259, 6847-6851). We have further characterized this inhibitor with respect to its interaction with both urokinase and tissue plasminogen activator, and its protease specificity. The HTC PA inhibitor rapidly inhibits urokinase and tissue plasminogen activator with an apparent second-order rate constant of 3-5 x 10(7) M-1 X s-1. The inhibitor forms stable covalent complexes with both urokinase and tissue plasminogen activator, with which plasmin, trypsin, and factor Xa apparently do not compete. Complex formation is saturable and requires the active site of the PA. The mass of the inhibitor-PA complex is 50,000 daltons greater than that of PA alone, consistent with an Mr for the PA inhibitor of 50,000 as demonstrated directly by reverse fibrin autography. The HTC PA inhibitor does not inhibit thrombin and differs in its kinetic and biochemical properties from protease nexin.
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PMID:Characterization of the dexamethasone-induced inhibitor of plasminogen activator in HTC hepatoma cells. 293 42

As the cells forming the luminal vascular surface, endothelial cells are strategically positioned to play an important role in the regulation of coagulation. They cannot be regarded as an inert surface lining the vessel wall since they possess multiple activities. Anticoagulant properties include provision of a cell surface with heparin-like molecules (which can serve as binding sites for antithrombin III), synthesis of thrombomodulin (which alters the substrate specificity of thrombin), maintenance of a low level of tissue factor and generation of prostacyclin. In addition to these anticoagulant properties, endothelial cells can play a role in procoagulant reactions. Studies which have examined mechanisms underlying the localization of thrombotic processes have suggested the possible involvement of endothelial cells in procoagulant events. Endothelial cells have been found to propagate factor X and prothrombin activation once factor IXa and factor Xa have been formed. Factors regulating the balance of plasminogen activator and inhibitor synthesis are also under study. Perturbation of endothelial cells with induction of tissue factor and production of platelet-activating factor and thromboxane provides a model of the thrombotic state in which endothelium can promote coagulation. The multiple properties of endothelial cells indicate that a continuous blood flow in an unperturbed region of the vessel wall results from a complex interplay of anticoagulant and procoagulant activities. In a perturbed region, endothelial cells might initiate coagulation and the thrombin formed on the surface of endothelial cells might then lead to recruitment of platelets.
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PMID:The role of endothelium in the homeostatic balance of haemostasis. 299 30

A complex series of reactions are involved in the assembly, function, and regulation of the prothrombinase complex. Since the enzyme is multicomponent in nature and each component is required for catalytic function, modulation of enzymatic activity can be achieved in a variety of ways. In addition, since complex assembly so profoundly affects reaction rates, mechanisms that perturb complex formation either positively or negatively have a profound effect on thrombin generation and its local physiologic effects. All of the cells that support prothrombinase assembly and hence thrombin generation respond to thrombin in a variety of ways. Thrombin selectively binds to thrombomodulin and heparin-like molecules expressed on the endothelial cell surface. Thrombin induces the release (and possible synthesis of) prostacyclin, plasminogen activator inhibitor, platelet-derived growth factor, and interleukin-1 and inhibits the release of plasminogen activator from vascular endothelium. Interleukin-1 is a potent mediator of inflammatory phenomena as well as an inducer of tissue factor synthesis in vascular endothelium. With respect to platelets, thrombin selectively binds and stimulates the platelet release reaction and subsequent aggregation. The thrombin-induced release of platelet-derived growth factor from both platelets and vascular endothelium may play a role in inflammation, wound healing, and atherogenesis. Thrombin itself is a potent mitogen of mesenchymal cells, and more recently has been shown to be not only a chemoattractant, but also a mitogen for monocytes. Thrombin also appears to bind selectively to monocytes and in so doing induces release of interleukin-1. Thrombin affects a myriad of cellular responses related to hemostasis, thrombosis, inflammation, would repair, and atherogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Regulation of thrombin generation at cell surfaces. 305 86

It has been demonstrated that the surface of large VLDL Sf 100-400 can bind both prothrombin and Factor X(Xa) and that on VLDL Factor Xa can convert prothrombin to thrombin, which degrades apo B and apo E. It has been reported also that the VLDL kinetically supports the conversion of prothrombin to thrombin. The binding of vitamin K-dependent proteins to phospholipid is partially Ca2+-dependent and probably involves their Gla residues. The complex of VLDL, prothrombin, Factor Xa, and Ca2+ lacks only Factor Va, a lipid associating, non-Gla residue containing 330 kd protein, to complete the "prothrombinase complex." Factor V (Va) is found at very low concentrations in the circulation, but is localized on platelets, monocytes, and the endothelium. VLDL can bind both to monocytes and to the endothelium, for example, through both receptor and non-receptor pathways. When carrying this complement of the prothrombinase complex, this subpopulation of VLDL, in the presence of Factor Va on cell surfaces, could conceivably upset the local balance of pro- and anticoagulant activities. Thus, directly or indirectly the increased triglyceride levels, reflected in increased VLDL in patients, may alter this balance, and thereby produce a "hypercoagulable state." This is a simplistic view of the potential role of VLDL in the interplay of cells, coagulation proteins, and the regulatory systems involved in vivo. To realize the degree of complexity that we may need to address, we need only look at the work of Booyse et al in this issue of Seminars, in which they demonstrate that hypertriglyceridemic VLDL, in contrast to normal VLDL, do not support the early release of t-PA from endothelial cells, an antifibrinolytic event.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Vitamin K-dependent proteins bind to very low-density lipoproteins. 305 90

Lysis of clots prepared from native or citrated whole blood as measured by release of 125I fibrinogen degradation products was 10% or less at 20 hours. Lysis of these clots was accelerated by activated protein C in a dose-dependent manner (0.1 to 20 micrograms/ml) from less than 10% to 60-80% at 20 hours. Lysis of clots prepared from native or citrated platelet poor plasma across the same concentration range of activated protein C was less than 15%. Gla-domain-less activated protein C was equally effective in accelerating clot lysis whereas DIP-activated protein C or factor Xa did not accelerate clot lysis. This suggested that this action of activated protein C was enzymatic and this this action was limited to protein C among the vitamin K dependent proteins. The unresponsiveness of platelet poor plasma to activated protein C was completely restored to that of whole blood by addition of mononuclear leukocytes. Addition of red corpuscles or platelets alone had no effect on this response, while addition of polymorphonuclear leukocytes partially restored this response. Addition of metabolic inhibitors 2-deoxyglucose and oligomycin inhibited the response of whole blood and of plasma-mononuclear leukocytes to activated protein C. Reconstitution studies of platelet poor plasma made deficient in plasminogen activator and plasminogen showed that accelerated clot lysis produced by mononuclear leukocytes and activated protein C required the presence of plasminogen. We concluded, therefore, that activated protein C accelerates whole blood or plasma-leukocyte clot lysis by modulating activation of the plasminogen system by metabolically active leukocytes.
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PMID:Whole blood clot lysis: in vitro modulation by activated protein C. 383 29


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