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

Two competitive inhibitors of TAFIa (activated thrombin-activable fibrinolysis inhibitor), 2-guanidinoethylmercaptosuccinic acid and potato tuber carboxypeptidase inhibitor, variably affect fibrinolysis of clotted human plasma. Depending on their concentration, the inhibitors shortened, prolonged, or had no effect on lysis in vitro. The inhibitor-induced effects were both tissue-type plasminogen activator (tPA) and TAFIa concentration-dependent. Inhibitor-dependent prolongation was favored at lower tPA concentrations. The magnitude of the prolongation increased with TAFIa concentration, and the maximal prolongation observed at each TAFIa concentration increased saturably with respect to TAFIa. A theoretical maximal prolongation of 20-fold was derived from a plot of the maximum prolongation versus TAFIa. This represents, for the first time, a measurement of the maximal antifibrinolytic potential of TAFIa in vitro. Because TAFIa spontaneously decays, the stabilization of TAFIa was investigated as a mechanism explaining the inhibitor-dependent prolongation of lysis. Both inhibitors stabilized TAFIa in a concentration-dependent, non-saturable manner. Although their KI values differed by three orders of magnitude, TAFIa was identically stabilized when the fraction of inhibitor-bound TAFIa was the same. The data fit a model whereby only free TAFIa decays. Therefore, the variable effects of competitive inhibitors of TAFIa on fibrinolysis can be rationalized in terms of free TAFIa and lysis time relative to the half-life of TAFIa.
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PMID:Stabilization versus inhibition of TAFIa by competitive inhibitors in vitro. 1264 76

We have previously confirmed, using a rat mesenteric arteriole thrombolysis model, that thrombin inhibition induces endogenous thrombolysis in vivo. In addition, we have shown that thrombin-activatable fibrinolysis inhibitor (TAFI) plays a role in the down regulation of endogenous thrombolysis. However, the mechanism of endogenous thrombolysis or spontaneous plasmin generation in vivo remains unclear. It has been shown in an in vitro system that plasma kallikrein activates pro-urokinase (pro uPA) and/or plasminogen, resulting in plasmin generation. These findings suggest that spontaneous fibrinolysis might be mediated by tPA and plasma kallikrein-dependent uPA. The aim of the present study was to examine whether these mechanisms play a dominant role in endogenous thrombolysis in vivo, using our rat mesenteric arterial thrombolysis model. Argatroban infusion enhanced endogenous thrombolysis. PKSI-527, anti uPA and anti tPA IgGs suppressed argatroban-induced thrombolysis. Also, the antibody IgG preparations suppressed endogenous thrombolysis in the absence of argatroban. In the presence of PKSI-527, anti tPA IgG was more effective than anti uPA IgG in suppressing argatroban-induced thrombolysis. The results suggested that both tPA and plasma kallikrein-mediated uPA activation and tPA release contribute to endogenous fibrinolytic or thrombolytic mechanisms.
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PMID:Suppression of argatroban-induced endogenous thrombolysis by PKSI-527, and antibodies to TPA and UPA, evaluated in a rat arterial thrombolysis model. 1271 78

Recently, a new inhibitor of fibrinolysis was described, which downregulated fibrinolysis after it was activated by thrombin, and was therefore named TAFI (thrombin-activatable fibrinolysis inhibitor; EC 3.4.17.20). TAFI turned out to be identical to the previously described proteins, procarboxypeptidase U, procarboxypeptidase R, and plasma procarboxypeptidase B. Activated TAFI (TAFIa) downregulates fibrinolysis by the removal of carboxy-terminal lysines from fibrin. These carboxy-terminal lysines are exposed upon limited proteolysis of fibrin by plasmin and act as ligands for the lysine-binding sites of plasminogen and tissue-type plasminogen activator (t-PA). Elimination of these lysines by TAFIa abrogates the fibrin cofactor function of t-PA-mediated plasminogen activation, resulting in a decreased rate of plasmin generation and thus downregulation of fibrinolysis. In this review, the characteristics of TAFI are summarized, with an emphasis on the pathways leading to activation of TAFI and the role of TAFIa in the inhibition of fibrinolysis. However, it cannot be ruled out that TAFI has other, as yet undefined, functions in biology.
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PMID:Thrombin-activatable fibrinolysis inhibitor (TAFI, plasma procarboxypeptidase B, procarboxypeptidase R, procarboxypeptidase U). 1287 Dec 92

Decrease of fibrinolytic potential is considered to be a risk factor for arterial thrombosis. The recently described thrombin-activatable fibrinolysis inhibitor (TAFI) attenuates fibrinolysis by cleaving of the C-terminal lysine residues from fibrin, thereby inhibiting tPA mediated plasminogen activation. The role of plasma TAFI antigen (Ag) levels and gene polymorphisms in arterial thrombosis is still not elucidated. In this prospective study, the association between plasma TAFI Ag levels and the TAFI gene polymorphisms, Ala147Thr, Thr325Ile and -438A/G, with refractory unstable angina pectoris (UAP) was determined. The study population consisted of 209 patients with UAP of whom 76 were refractory and 133 non-refractory to medical treatment. In the same study population the contribution of these polymorphisms to plasma TAFI Ag levels was determined. Plasma TAFI Ag levels were significantly higher in non-refractory patients compared to refractory patients (geometric mean 114.4 and 105.6 U/dl respectively, p=0.042). Plasma TAFI Ag levels in the lowest quartile resulted in a 2.6 fold (95% confidence interval 1.2-5.9) increased risk for refractory UAP compared to plasma TAFI Ag levels in the upper quartile. The three studied TAFI polymorphisms had an independent and additive effect on plasma TAFI Ag levels. However, no significant association between the individual TAFI polymorphisms and refractiveness was observed. In conclusion, in this study population plasma TAFI Ag levels are significantly correlated with refractiveness in patients with UAP. Furthermore, all three polymorphisms contribute independently to plasma TAFI Ag levels, but not to refractiveness.
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PMID:Association between thrombin-activatable fibrinolysis inhibitor (TAFI) and clinical outcome in patients with unstable angina pectoris. 1287 31

Arterial thrombosis is a complex disorder that involves multiple genetic and environmental factors interacting to produce the characteristic phenotype. In the past decades, investigators have focused on the molecular genetics of arterial vascular disorders and have identified numerous polymorphisms and mutations in genes related to the hemostatic system and to enzymes involved in the synthesis and bioavailability of nitric oxide (NO); however, the relation between most polymorphisms and the risk of coronary artery disease, ischemic stroke, and peripheral vascular disease remains highly controversial. In this review, we describe the most common genetic variations involved in the pathogenesis of arterial thrombosis, their functional implications, and their association with disease risk. Specifically, we consider polymorphisms in coagulation factors (fibrinogen, prothrombin, FV Leiden, FVII, and FXIII); fibrinolytic factors (tissue-type plasminogen activator, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor); platelet surface receptors; methylenetetrahydrofolate reductase; endothelial NO synthase; and the antioxidant enzymes paraoxonase and plasma glutathione peroxidase. Overall, there seems to be a modest contribution of individual genetic variants in the hemostatic and antioxidant systems to the risk of arterial thrombosis. Thus, future research ought to focus on identifying novel genetic determinants and on the interaction of these genetic risk factors with each other and the environment to understand better the pathobiology and susceptibility to arterial thrombotic disease.
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PMID:Genetic determinants of arterial thrombosis. 1461 95

Thrombin-activable fibrinolysis inhibitor (TAFI) is a recently described inhibitor of fibrinolysis. The aim of this study was to estimate the risk of deep venous thrombosis (DVT) caused by the polymorphisms in the TAFI gene in relation to polymorphisms of the other fibrinolytic variables such as PAI-844A>G and t-PA-7,351C>T. This study includes 130 patients with DVT and 130 age- and sex-matched healthy controls. Our results showed no association of the investigated "TAFI-increasing" alleles TAFI 505A (Thr147) and TAFI+1542C with the risk of venous thrombosis. However the adjustment for age, sex, factor V Leiden, PAI-844A allele and t-PA-7,351T allele indicates a tendency to a moderately increased thrombotic risk of TAFI+1542GG carriers (low TAFI level).
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PMID:Polymorphisms in the TAFI gene and the risk of venous thrombosis. 1465 35

The majority of deaths among patients after renal transplantation is attributed to cardiovascular disease (CVD). Intima media thickness (IMT) of the common carotid artery is related to coronary and cerebrovascular arterial disease. One of the major causes of death due to CVD is acute coronary syndrome, which is precipitated by coronary plaque rupture and subsequent thrombosis. The aim of the study was to evaluate associations between some fibrinolytic factors: antigens of tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor (PAI-1), and thrombin-activatable fibrinolysis inhibitor (TAFI), and IMT in a population of renal transplant recipients. The study was performed on 33 Caucasian, clinically stable kidney transplant recipients (11 women, mean age 43 years, range 26 to 62 years). All the patients were on triple immunosuppressive regimen (cyclosporine, prednisone, and azathioprine) and had stable graft function (serum creatinine 1.7 +/- 0.7 mg/dL). The mean time since transplantation was 49.9 months (range 4.1 to 131.8 months). In univariate analysis IMT correlated significantly with age (r =.5; P =.001), pulse pressure (PP) (r =.4; P =.05), time on dialysis prior to transplantation (r =.6; P =.001), fibrinogen (r =.4; P =.02), and t-PA (r =.6; P =.001). Multiple regression analysis showed that t-PA antigen concentration (P =.001), fibrinogen (P <.05), and time on dialysis prior to transplantation (P <.05) were positive independent predictors of IMT. These data support the concept of the coincidence of disturbances in fibrinolysis and arterial remodelling in patients after kidney transplantation. On the other hand the study shows that the duration of dialysis therapy before transplantation is detrimental to the arterial vasculature.
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PMID:Plasma tissue-type plasminogen activator, fibrinogen, and time on dialysis prior to transplantation are related to carotid intima media thickness in renal transplant recipients. 1469 41

Activated thrombin-activable fibrinolysis inhibitor (TAFIa) is a carboxypeptidase B-like plasma enzyme that can slow clot lysis by removing lysine residues exposed on fibrin as it is cleaved by plasmin. Previously, it was shown that fibrin treated with TAFIa is less able to promote plasminogen activation by tissue-type plasminogen activator. In this study, the effect of TAFIa modification of a fibrin surface on the rate of plasmin inhibition by antiplasmin was studied using high molecular weight fibrin degradation products (HMw-FDPs) as a soluble model for intact plasmin-modified fibrin. To quantify the inhibition, a novel end point assay was employed where plasmin, antiplasmin, and cofactors were mixed in the presence of a chromogenic substrate and the end point in the substrate hydrolysis reaction was used to measure the second order rate constant of inhibition. When HMw-FDPs were titrated in the presence of plasmin and antiplasmin, the rate constant for inhibition decreased by 16-fold at saturation (9.6 x 10(6) m(-1) s(-1) to 0.59 x 10(6) m(-1) s(-1)). When HMw-FDPs were pretreated with TAFIa, nearly two-thirds of the protective effect was lost. When 730 nm HMw-FDPs were treated for 20 min with TAFIa, the rate constant for plasmin inhibition was increased 3-fold from 1.9 x 10(6) m(-1) s(-1) to 6.2 x 10(6) m(-1) s(-1). Therefore, a novel mechanism was identified whereby TAFIa can modulate plasmin levels by increasing the susceptibility of plasmin to inhibition by antiplasmin.
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PMID:Activated thrombin-activatable fibrinolysis inhibitor reduces the ability of high molecular weight fibrin degradation products to protect plasmin from antiplasmin. 1471 54

Plasma procarboxypeptidase B, also known as thrombin-activatable fibrinolysis inhibitor (TAFI), is converted by thrombin into the active enzyme, carboxypeptidase B (CPB)/activated TAFI. Plasma CPB down-regulates fibrinolysis by removing carboxy-terminal lysines, the ligands for plasminogen and tissue-type plasminogen activator (tPA), from partially degraded fibrin. To target thrombosis in a new way, we have identified and optimized a phosphinic acid-containing inhibitor of CPB, EF6265 [(S)-7-amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino) propyl]hydroxyphosphinoyl]methyl]heptanoic acid] and determined both the pharmacological profile and pathophysiological role of CPB in rat thrombolysis. EF6265 specifically inhibited plasma CPB activity with an IC(50) (50% inhibitory concentration) of 8.3 nM and enhanced tPA-mediated clot lysis in a concentration-dependent manner. EF6265 decreased detectable thrombi (percentage of glomerular fibrin deposition; control, 98 +/- 1.1; EF6265, 0.1 mg/kg, 27 +/- 9.1) that had been generated by tissue factor in a rat microthrombosis model with concomitant increases in plasma D-dimer concentration (control, <0.5 microg/ml; EF6265, 0.1 mg/kg, 15 +/- 3.5 microg/ml). EF6265 reduced plasma alpha2-antiplasmin activity to a lesser extent than tPA. In an arteriovenous shunt model, EF6265 (1 mg/kg) enhanced exogenous tPA-mediated thrombolysis under the same conditions that neither EF6265 nor tPA (600 kIU/kg) alone reduced thrombi. EF6265 (1 and 30 mg/kg) did not affect the bleeding time in rats. Moreover, it did not prolong the bleeding time evoked by tPA (600 kIU/kg). These results confirm that circulating procarboxypeptidase B functions as a fibrinolysis inhibitor's zymogen and validates the use of CPB inhibitors as both an enhancer of physiological fibrinolysis in microcirculation and as a novel adjunctive agent to tPA for thromboembolic diseases while maintaining a small effect on primary hemostasis.
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PMID:Enhancement of fibrinolysis by EF6265 [(S)-7-amino-2-[[[(R)-2-methyl-1-(3-phenylpropanoylamino)propyl]hydroxyphosphinoyl] methyl]heptanoic acid], a specific inhibitor of plasma carboxypeptidase B. 1476 98

In an in vitro clot lysis model in human plasma, carboxypeptidase U (CPU) is generated by thrombin following the coagulation and by plasmin at the later stage of clot lysis. CPU is able to slow down clot lysis by suppressing the cofactor activity of partially degraded fibrin in the plasminogen activation by tissue-type plasminogen activator (t-PA). Making use of thrombomodulin and a thrombin inhibitor, the generation of CPU during the in vitro clot lysis can be manipulated both in terms of magnitude and time course. The data obtained demonstrate that CPU affects the clot dissolution through a threshold-dependent mechanism: as long as the CPU activity remains above the threshold value, lysis is prevented from proceeding into the propagation phase. From the moment the CPU activity drops below this threshold value, the rate of lysis accelerates. This threshold value for CPU activity is dictated by the t-PA concentration: increasing the t-PA concentration increases the CPU threshold and vice versa. This implies that the effect of the CPU pathway will become more apparent at a lower fibrinolytic capacity. Our threshold-based hypothesis indicates that the time course of proCPU activation, the stability of CPU and the t-PA concentration all play a crucial role in determining the result of the in vitro clot lysis experiment. Furthermore, this hypothesis provides us with new insights into previously published data on the effects of CPU on in vitro clot lysis by high and low t-PA concentrations.
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PMID:Carboxypeptidase U (TAFIa) prevents lysis from proceeding into the propagation phase through a threshold-dependent mechanism. 1740 10


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