Basic Aspects of Fibrinolysis and Thrombolysis

Abstract

The hypothesis underlying thrombolytic therapy of thromboembolic disease is that early and sustained recanalization prevents cell death, reduces infarct size, preserves organ function, and reduces early and late mortality. Thrombolysis consists of the pharmacological dissolution of the blood clot, by intravenous infusion of plasminogen activators that activate the fibrinolytic system (Fig. 1). The fibrinolytic system includes a proenzyme, plasminogen, which is converted by plasminogen activators to the active enzyme plasmin, which in turn digests fibrin to soluble degradation products. Inhibition of the fibrinolytic system occurs by plasminogen activator inhibitors (mainly plasminogen activator inhibitor-1, PAI-1) and by plasmin inhibitors (mainly α2-antiplasmin) [1]. Thrombolytic agents that are either approved or under clinical investigation in patients with acute myocardial infarction include streptokinase, recombinant tissue-type plasminogen activator (rt-PA or alteplase), rt-PA derivatives such as reteplase and TNK-rtPA, anisoylated plasminogen-streptokinase activator complex (APSAC or anistreplase), two-chain urokinase-type plasminogen activator (tcu-PA or urokinase), recombinant single-chain u-PA (scu-PA, pro-u-PA or prourokinase), and recombinant staphylokinase and derivatives [2]. Open image in new window Fig. 1. Schematic representation of the fibrinolytic system. The proenzyme plasminogen is activated to the active enzyme plasmin by tissue-type or urokinase-type plasminogen activator. Plasmin degrades fibrin into soluble fibrin degradation products. Inhibition of the fibrinolytic system may occur at the level of the plasminogen activators, by plasminogen activator inhibitors, or at the level of plasmin, mainly by α2-antiplasmin