Plasminogen Activator Inhibitor with Very Long Half-life (VLHL PAI-1) can Reduce Bleeding in PAI-1-deficient Patients

Abstract

This review summarizes our current knowledge of plasminogen activator inhibitor (PAI-1) deficiency and proposes some novel treatments for this condition. PAI-1 is a fast acting inhibitor of tissue and urokinase plasminogen activators (tPA and uPA). PAI-1 controls/slows clot lysis triggered by tPA activated plasminogen. PAI-1 deficiency was once considered to be an extremely rare disorder characterized by frequent and prolonged bleeding episodes. PAI-1 deficiency is now thought to be more frequent than initially reported and is known to be caused by mutations in the PAI-1 gene that produce a dysfunctional PAI-1 protein or slow the secretion of PAI-1 into the circulation. PAI-1 deficiency is characterized by hyperfibrinolysis that results in frequent bleeding episodes. Patients with this condition form normal blood clots that are quickly lysed by unopposed tPA-activated plasmin. Spontaneous bleeding is rare in PAI-1 deficient patients, but moderate hemorrhaging of the knees, elbows, nose, and gums can be triggered by mild trauma. Additionally, prolonged bleeding after surgery is common and menstrual bleeding may be severe. Moderate PAI-1 deficiency is associated with a lifelong bleeding tendency, but severe deficiencies can be life-threatening. The diagnosis of this disorder remains challenging due to the lack of a clear definition of PAI-1 deficiency as well as a lack of standardized tests. Patients with mild PAI-1 deficiency may be treated with antifibrinolytic agents (ε-aminocaproic acid or tranexamic acid); however, not all patients respond well to these treatments. These patients may be treated with wild-type PAI-1; however, this molecule quickly converts into its inactive form. We propose to use PAI-1 with an extended half-life to treat these patients.