Hyperprothrombinemia associated with prothrombin G20210A mutation inhibits plasma fibrinolysis through a TAFI-mediated mechanism

Abstract

The prothrombin gene mutation G20210A is a common risk factor for thrombosis and is associated with increased prothrombin levels. However, the mechanism whereby hyperprothrombinemia predisposes to thrombosis remains unclear. Because thrombin is the physiologic activator of TAFI (thrombin activatable fibrinolysis inhibitor), the precursor of an antifibrinolytic carboxypeptidase (TAFIa), we evaluated the influence of hyperprothrombinemia on fibrinolysis. Thirty-two heterozygous carriers of the G20210A mutation and 30 noncarriers were studied.Plasma fibrinolytic factors and TAFI levels were similar in the 2 groups. Mean lysis time of tissue factor-induced plasma clots exposed to 25 ng/mL exogenous tissue-type plasminogen activator (t-PA) was significantly longer in 20210A carriers than in control donors. This difference disappeared on addition of a specific inhibitor of TAFIa. Determination of thrombin and TAFIa activity, generated during clot lysis, revealed that G20210A mutation was associated with a significant enhancement of late thrombin formation and an increase in TAFI activation.Plasma prothrombin level was highly significantly correlated with both clot lysis time and TAFI activation. The addition of purified prothrombin, but not of factors X or VIIa, to normal plasma caused a concentration-dependent, TAFI-mediated inhibition of fibrinolysis. These findings provide a new mechanism that might contribute to the thrombotic risk in prothrombin 20210A carriers. IntroductionThe prothrombin gene mutation G20210A is the second most common genetic disorder associated with venous thrombosis. It is found in 4.6% to 8% of unselected patients with a first episode of deep vein thrombosis, as contrasted to 0.7% to 2.6% in healthy controls, and heterozygote carriers have a 2-to 7-fold increased risk of thrombosis (reviewed in Vicente et al 1 ). The presence of the 20210A allele is associated with elevated prothrombin levels, and hyperprothrombinemia has been shown to be an independent risk factor for thrombosis. 2 However, the underlying mechanism by which elevated prothrombin promotes thrombosis is still unclear. On the basis of in vitro 3 and in vivo 4 data, it is surmised that hyperprothrombinemia enhances thrombin generation whenever blood clotting is activated in vivo, thereby promoting excessive fibrin formation. Thrombin plays also an important role in the down-regulation of fibrinolysis by catalyzing the activation of TAFI (thrombin activatable fibrinolysis inhibitor), a plasma precursor of a carboxypeptidase B that inhibits plasmin formation by removing the plasminogen binding sites from partially degraded fibrin. 5 This study was designed to evaluate the influence of the G20210A mutation and of hyperprothrombinemia on TAFI-mediated inhibition of fibrinolysis. Patients, materials, and methods PatientsThirty-two carriers of the prothrombin G20210A mutation (all heterozygous) and 30 noncarriers were studied. Blood was collected by vacuum collection tubes (Vacutainer; Becton Dickinson, Meylan, France) containing 1/1...

Tissue factor-expressing monocytes inhibit fibrinolysis through a TAFI-mediated mechanism, and make clots resistant to heparins

“…6,7 Thirdly, prothrombin G20210A mutation and APC resistance have been reported to inhibit the fibrinolytic process by enhancing thrombin-mediated TAFI activation. [8][9][10] However, other findings suggest that changes in thrombin generation need not necessarily be accompanied by modifications in fibrinolysis. As a matter of fact, some anticoagulants, e.g.…”

“…However, this assumption is challenged by the results obtained with purified TF, showing that variations in TF concentrations, even over a very broad range, are not accompanied by changes in fibrinolysis time. 8,14 In this scenario, it is difficult to foresee whether and to what extent cell-associated TF will be able to inhibit fibrinolysis. Our study was undertaken to evaluate and characterize the effect of TF-expressing monocytes on plasma fibrinolysis.…”

“…11,12 Moreover, the enhanced thrombin generation induced by factor VIIa or by tissue factor (TF) has virtually no effect on the fibrinolysis rate, at least under certain conditions. 8,13,14 This highlights the complexity of the interplay between coagulation and fibrinolysis and suggests that the up-and down-regulation of coagulation will be translated into fibrinolytic changes on condition that specific requirements are fulfilled, among which the intensity and timing (in relation to fibrin formation) of thrombin generation play a major role. 2 Monocytes/macrophages play a central role in fibrin deposition associated with numerous pathological conditions, including atherothrombosis and immuneinflammatory processes, mainly through the synthesis and surface expression of TF in response to a variety of agents and conditions that have a pathophysiological relevance.…”

Venous thrombosis risk associated with plasma hypofibrinolysis is explained by elevated plasma levels of TAFI and PAI-1

“…For example, persons with the prothrombin G20210A mutation have longer CLTs as a result of increased thrombin generation, resulting in increased TAFI activation. 6 On the basis of the experiments with purified proteins, we surmised CLT will be explained by a combination of plasma levels of plasminogen, ␣2-antiplasmin, TAFI, and PAI-1. Because a high concentration of t-PA is added to test plasma to induce fibrinolysis, the role of plasma t-PA levels in CLT is probably minor.…”

Aging of Acute Deep Vein Thrombosis Measured by Radiolabeled 99mTc-rt-PA

“…Elevated plasma TAFI is associated with a prolonged in vitro clot lysis time for human plasma (18). In a model of tissue-factor-induced human plasma clotting, increased TAFI activation and prolonged clot lysis time were observed in FII G20210A heterozygotes compared with plasma controls (19). A similar pathogenesis has been proposed for the association between vein thrombosis and elevated factor XI (20) and factor V Leiden (21).…”