[Dysfunction of fibrinolysis as a risk factor of thrombosis]

Fibrinolytic system constitutes a part of the haemostasis responsible for the degradation of fibrin deposits. Plasminogen proenzyme, the main component of the fibrinolytic system is activated into its active enzyme form--plasmin by activators, mainly by tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). t-PA is the main plasminogen activator in the intravascular fibrinolysis, whereas u-PA is rather involved in the extracellular proteolysis. Fibrinolytic activity can be regulated as well by plasminogen activation inhibition (inhibitors: PAl-1 and PAl-2) as by plasmin activity inhibition (alpha2-antiplasmin). Under physiological conditions a balance between coagulation and fibrinolysis exists, that may be altered under pathophysiological conditions. It has been reported that in the pathogenesis of many diseases, the inflammatory processes, expression of proinflammatory mediators, enhanced tissue factor level and/or impaired fibrinolysis are involved. Inflammation disturbs haemostasis and shifts the haemostatic mechanisms in favor of thrombosis. Moreover, the endothelial dysfunction may contribute to the decrease of antithrombotic properties of vessel wall endothelium. Under pathophysiological conditions where a hypofibrinolytic state occurs, impaired fibrinolysis is considered to be an additional risk factor of thrombosis.