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)

The fibrinolytic system plays a pivotal role in the regulation of hemostasis and the prevention of thrombosis. There are no drugs that will increase the plasma fibrinolytic activity for a lasting duration to prevent thrombotic events effectively. Despite the ability of vasoactive agents such as nicotinic acid and metformin to release PA from the vessel wall, this therapeutic effect has not been evaluated adequately. The PAs are short-acting and indicated only for thrombolysis and not for prophylaxis. Future directions are directed at finding, agents that can enhance plasminogen activator release or inhibit PAW-1 activity. As there are multiple factors involved in the pathogenesis of thrombosis, there are a number of conditions in which abnormal fibrinolysis is only a contributory factor. Examples are seen in pregnancy, especially during puerperium, when the thromboembolic risk is at its highest. The levels of inhibitors of fibrinolysis. both PAI-1 and PAI-2, are also at their highest. Another example was seen recently in the antiphospholipid syndrome, where antibodies against Annexin II, a receptor for tPA, were found to be higher than in healthy controls. Thus, a thorough investigation into other hereditary and acquired risk factors for thrombosis is recommended.
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PMID:Hereditary and acquired defects in the fibrinolytic system associated with thrombosis. 1262 65

The causes of thrombosis and pregnancy loss in antiphospholipid syndrome (APS) are still unknown, although several hypotheses have been proposed and hypofibrinolysis has been implicated. Anti-tissue-type plasminogen activator (tPA) antibodies may induce fibrinolytic defects and preliminary data indicate an association with thrombosis in APS. We measured plasma anti-tPA antibody levels in 91 consecutive patients with APS, 91 healthy controls, 40 patients with antiphospholipid antibodies without APS symptoms, and 23 patients with systemic lupus erythematosus (SLE) without antiphospholipid antibodies and APS symptoms. Patients with APS had anti-tPA antibody levels higher than controls (P = .0001), patients with SLE (P = .0001), and asymptomatic antiphospholipid patients (P = .05). A subgroup of 53 patients had plasma levels of tPA antigen higher (P = .0001) and tPA activity lower (P = .05) than controls, with an inverse correlation (r = -0.454; P = .003) between anti-tPA antibody levels and tPA activity and no correlation with tPA antigen. The 2 patients with the highest antibody levels had tPA activity below the normal range. Their antibodies were, respectively, IgG1 and IgG3; both recognized human tPA, recombinant tPA, and the catalytic domain of tPA, but not beta 2-glycoprotein I, prothrombin, or plasminogen. Our data indicate that anti-tPA antibodies specifically interacting with the catalytic domain of tPA can be found in patients with APS, representing a possible cause of hypofibrinolysis.
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PMID:Antibodies to tissue-type plasminogen activator (tPA) in patients with antiphospholipid syndrome: evidence of interaction between the antibodies and the catalytic domain of tPA in 2 patients. 1463 Jul 88

Beta2-glycoprotein-I (beta2GPI) is a phospholipid-binding plasma protein that consists of five homologous domains. Domain V is distinguished from others by bearing a positively charged lysine cluster and hydrophobic extra C-terminal loop. Beta2GPI has been known as a natural anticoagulant regulator. Beta2GPI exerts anticoagulant activity by inhibition of phospholipid-dependent coagulation reactions such as prothrombinase, tenase, and factor XII activation. It also binds factor XI and inhibits its activation. On the other hand, beta2GPI inhibits anticoagulant activity of activated protein C. According to the data from knockout mice, beta2GPI may contribute to thrombin generation in vivo. Phospholipid-bound beta2GPI is one of the major target antigens for antiphospholipid antibodies present in patients with antiphospholipid syndrome (APS). Binding of pathogenic anti-beta2GPI antibodies increases the affinity of beta2GPI to the cell surface and disrupts the coagulation/fibrinolysis balance on the cell surface. These pathogenic antibodies activate endothelial cells via signal transduction events in the presence of beta2GPI. Impaired fibrinolysis has been reported in patients with APS. Using a newly developed chromogenic assay, we demonstrated lower activity of intrinsic fibrinolysis in euglobulin fractions from APS patients. Addition of monoclonal anti-beta2GPI antibodies with beta2GPI also decreased fibrinolytic activity in this assay system. beta2GPI is proteolytically cleaved by plasmin in domain V (nicked beta2GPI) and becomes unable to bind to phospholipids, reducing antigenicity against antiphospholipid antibodies. This cleavage occurs in patients with increased fibrinolysis turnover. Nicked beta2GPI binds to plasminogen and suppresses plasmin generation in the presence of fibrin, plasminogen, and tissue plasminogen activator (tPA). Thus, nicked beta2GPI plays a role in the extrinsic fibrinolysis via a negative feedback pathway loop.
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PMID:Beta2-glycoprotein I, anti-beta2-glycoprotein I, and fibrinolysis. 1550 79

Antiphospholipid syndrome (APS) is characterized by recurrent thrombosis or pregnancy morbidity associated with antiphospholipid antibodies (aPL). Impaired fibrinolysis is a contributing factor for the development of thrombosis, and the effect of aPL in the fibrinolytic system has been investigated. Impaired release of tPA and enhanced release of PAI-1 after endothelial activation is reported in patients with APS. Elevated Lipoprotein (a) levels have been found in APS, which results in inhibition of fibrinolytic activity. Phospholipid-bound beta(2)-glycoprotein I (beta(2)GPI) is a major autoantigen for aPLs. beta(2)GPI exerts both anti-coagulant and pro-coagulant properties mainly by interacting with other phospholipid-binding proteins such as coagulation factors and protein C. Dramatic increase in the affinity of beta(2)GPI to the cell surface is induced by binding of pathogenic anti-beta(2)GPI antibodies, which may modify the physiological function of beta(2)GPI and may affect the coagulation/fibrinolysis balance on the cell surface. Using chromogenic assays for measuring fibrinolytic activity, we demonstrated that addition of monoclonal anticardiolipin antibody (aCL) decreases the activity of extrinsic/intrinsic fibrinolysis. Significantly lower activity of intrinsic fibrinolysis was also demonstrated in the euglobulin fractions from APS patients. Endothelial cells and monocytes are activated by aPLs in vitro, resulting in production of tissue factor (TF), a major initiator of the coagulation system. Recently, aPLs are reported to induce thrombocytes to produce thromboxane. The importance of apoE receptor 2 on platelets for the binding of artificially dimerized beta(2)GPI was suggested. By investigating aPL-inducible genes in peripheral blood mononuclear cells, we found that the mitogen-activated protein kinase (MAPK) pathway was up-regulated. Using a monocyte cell line, phosphorylation of p38 MAPK, NF-kappaB translocation to the nuclear fraction, and up-regulated TF mRNA expression were demonstrated after treatment with monoclonal aCL. These phenomena were observed only in the presence of beta(2)GPI. Moreover, a specific p38 MAPK inihibitor SB203580 decreased aCL/beta(2)GPI-induced TF mRNA expression. Thus, aCL/beta(2)GPI plays dual roles in the pathogenesis of APS, firstly by deranging the fibrinolytic system and secondly by activating monocytes, endothelial cells and thrombocytes to produce TF or thromboxane.
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PMID:Pathogenesis of antiphospholipid antibodies: impairment of fibrinolysis and monocyte activation via the p38 mitogen-activated protein kinase pathway. 1632 97

Beta2-glycoprotein I (beta2GPI) is a glycoprotein of unknown physiological function. It is the main target antigen for antiphospholipid antibodies in patients with antiphospholipid syndrome (APS). beta2GPI binds with high affinity to the atherogenic lipoprotein Lp(a) which shares structural homology with plasminogen, a key molecule in the fibrinolytic system. Impaired fibrinolysis has been described in APS. The present work reports the interaction between beta2GPI and Glu-Plasminogen which may explain the recently described proteolytic effect of plasmin on beta2GPI. In the process of Glu-Plasminogen activation, we found an increase in plasmin generation both at fibrin and cellular surface level as a function of the concentration of beta2GPI added, suggesting an important role as a cofactor in the trimolecular complex beta2GPI-Plasminogen-tPA. This phenomenon represents a novel regulatory step both in the positive feedback mechanism for extrinsic fibrinolysis and in antithrombotic regulation. IgG anti-beta2GPI antibodies recognized the beta2GPI at the endothelial surface inducing its activation with an increase of ICAM-I and a decrease in the expression of thrombomodulin favoring a pro-thrombotic state in the vascular endothelium. The interference in the plasmin conversion by anti-beta2GPI antibodies could generate thrombosis as observed in APS.
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PMID:The role of beta2-glycoprotein I (beta2GPI) in the activation of plasminogen. 1648 Sep 36

Acute cerebral ischemia resulting from the occlusion of a large or medium size intracranial artery is a known complication of antiphospholipid antibody syndrome (AAS). Usually these patients are treated by low dose aspirin and anticoagulants to prevent a stroke. We are reporting a case of acute stroke in a patient with AAS in whom combined intravenous and intraarterial thrombolytics were used emergently with an excellent outcome. A 32-year-old woman presented with a left hemispheric stroke of 2.5 hours duration. A computed tomography (CT) study of the brain was normal. The patient was treated with intravenous tissue plasminogen activator but remained aphasic and hemiplegic. Subsequently, the patient had a stable xenon CT cerebral blood flow study demonstrating low flow in the left middle cerebral artery (MCA) territory and an angiogram, which demonstrated occlusion of the left MCA. The patient was then treated with intraarterial urokinase with a rapid and marked improvement in her neurological deficit. The case suggests that stroke patients can be treated safely and effectively with combined thrombolytics.
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PMID:Combined intravenous and intraarterial thrombolytic therapy for treatment of an acute ischemic stroke: a case report. 1789 75

Because both immunoglobulin G (IgG) and phospholipids interfere with fibrinolysis, their combined modulating effects were investigated in experimental models of three consecutive steps of the fibrinolytic process [diffusion of tissue-type plasminogen activator (tPA) into the clot, plasminogen activation on fibrin surface and fibrin dissolution by plasmin] using IgGs isolated from healthy subjects and from patients with antiphospholipid syndrome in combination with mixtures of synthetic dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine. In fibrin clots containing phospholipids the normal IgG enhanced the barrier function of the phospholipids with respect to the diffusion of tPA and plasminogen activation, but did not modify the lysis by plasmin. One of the examined antiphospholipid syndrome-IgGs also restricted the diffusion of tPA, but it accelerated the plasminogen activation on the fibrin surface and slowed down the lysis of fibrin by plasmin. Another antiphospholipid syndrome IgG, which did not affect significantly the tPA penetration into the fibrin gel, did not modify the plasminogen activation on its own, but it partially opposed the inhibiting effect of phospholipids on plasmin formation and accelerated the end-stage lysis of fibrin containing phospholipids. The IgGs from the two examined antiphospholipid syndrome patients did not show consistent deviation from the pattern of normal IgG effects on fibrinolysis in phospholipid environment. Thus, a high degree of heterogeneity with respect to the profibrinolytic or antifibrinolytic effects of the pathological IgGs can be expected in the antiphospholipid syndrome patient population, which may contribute to the variable thrombotic symptoms in this clinical syndrome.
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PMID:Modulation of fibrinolysis by the combined action of phospholipids and immunoglobulins. 1818 Jun 21

Thrombocytopenia prevalance and its association with antiphospholipid syndrome, disorders of the hemostasis system, the course and activity of the disease have been studied in SLE patients. 10.5% of 457 SLE patients in central and western part of Ukraine had thrombocytopenia which non-significantly depended on sex, age and disease duration but was tightly associated with cardiovascular disorders. Thrombocytopenia appears as an independent risk factor for vascular disorders which does not depend on lipid metabolic disorders and system inflammatory reaction but is firmly associated with the presence of antiphospholipid syndrome, beta-2-glycoprotein I levels, thrombocyte hyperactivity, antithrombin III and tissue plasminogen activator deficiency.
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PMID:[Thrombocytopenia in patients with systemic lupus erythematosis as a risk factor for thrombotic complications and its connection with severity and the course of the disease, systemic lupus erythematosis]. 1871 94

Antiphospholipid (aPL) antibodies recognize receptor-bound beta(2) glycoprotein I (beta(2)GPI) on target cells, and induce an intracellular signaling and a procoagulant/proinflammatory phenotype that leads to thrombosis. Evidence indicates that annexin A2 (A2), a receptor for tissue plasminogen activator and plasminogen, binds beta(2)GPI on target cells. However, whether A2 mediates pathogenic effects of aPL antibodies in vivo is unknown. In this work, we studied the effects of human aPL antibodies in A2-deficient (A2(-/-)) mice. A2(-/-) and A2(+/+) mice were injected with immunoglobulin G (IgG) isolated from either a patient with antiphospholipid syndrome (IgG-APS), a healthy control subject (IgG-normal human serum), a monoclonal anti-beta(2)GPI antibody (4C5), an anti-A2 monoclonal antibody, or monoclonal antibody of irrelevant specificity as control. We found that, after IgG-APS or 4C5 injections and vascular injury, mean thrombus size was significantly smaller and tissue factor activity was significantly less in A2(-/-) mice compared with A2(+/+) mice. The expression of vascular cell adhesion molecule-1 induced by IgG-APS or 4C5 in explanted A2(-/-) aorta was also significantly reduced compared with A2(+/+) mice. Interestingly, anti-A2 monoclonal antibody significantly decreased aPL-induced expression of intercellular cell adhesion molecule-1, E-selectin, and tissue factor activity on cultured endothelial cells. Together, these data indicate for the first time that A2 mediates the pathogenic effects of aPL antibodies in vivo and in vitro APS.
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PMID:Annexin A2 is involved in antiphospholipid antibody-mediated pathogenic effects in vitro and in vivo. 1962 8

The antiphospholipid syndrome (APS) is characterized by venous and/or arterial thrombosis, or recurrent fetal loss, in the presence of antiphospholipid antibodies (APL). The pathogenesis of APS is multifaceted and involves numerous mechanisms including activation of endothelial cells, monocytes, and/or platelets; inhibition of natural anticoagulant pathways such as protein C, tissue factor inhibitor, and annexin A5; activation of the complement system; and impairment of the fibrinolytic system. Fibrinolysis--the process by which fibrin thrombi are remodeled and degraded--involves the conversion of plasminogen to plasmin by tissue plasminogen activator (tPA) or urokinase-type plasminogen activator, and is tightly regulated. Although the role of altered fibrinolysis in patients with APS is relatively understudied, several reports suggest that deficient fibrinolytic activity may contribute to the pathogenesis of disease in these patients. This article discusses the function of the fibrinolytic system and reviews studies that have reported alterations in fibrinolytic pathways that may contribute to thrombosis in patients with APL. Some of these mechanisms include elevations in plasminogen activator inhibitor-1 levels, inhibitory antibodies against tPA or other components of the fibrinolytic system, antibodies against annexin A2, and finally, antibodies to beta(2)-glycoprotein-I (beta(2)GPI) that block the ability of beta(2)GPI to stimulate tPA-mediated plasminogen activation.
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PMID:Impaired fibrinolysis in the antiphospholipid syndrome. 2042 34


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