Recombinant TFPI and variants: potential implications in the treatment of cardiovascular disorders.
The Kunitz-type proteinase inhibitor, tissue factor pathway inhibitor (TFPI), is the only endogenous inhibitor of the tissue factor (TF)-mediated coagulation pathway that plays a dominant role in normal haemostasis. TFPI exerts its action by binding to factor Xa (FXa) forming a TFPI-FXa complex that then, in a second step, binds and effectively inhibits the TF-factor VIIa (FVIIa) complex. Both full-length TFPI and chemically modified forms (e.g., truncated, glycosylated or phosphorylated TFPI variants) exert various pharmacological effects. The anticoagulant and antiplatelet actions of TFPI, its potency in inhibiting thrombin and FXa generation, as well as its favourable antithrombotic effectiveness seen in different animal models of venous and arterial thrombosis make this inhibitor a promising agent that could be potentially useful in several clinical indications. The inhibitory action of TFPI is accelerated by heparin. Heparin, as well as low molecular weight heparin (LMWH) derivatives, release TFPI from the vascular endothelium, an effect which seems to contribute mainly to the antithrombotic effectiveness of these drugs. The clinical relevance of TFPI is still undefined. Based on the beneficial actions in animal studies, as well as on the results obtained in first clinical investigations, TFPI is expected to be effective in the treatment of various diseases, such as disseminated intravascular coagulation, sepsis, coronary syndromes, stroke and acute respiratory distress syndrome (ARD). Further clinical trials should clarify the role of TFPI and more importantly define its potential usefulness as a prophylactic and/or therapeutic agent.
Center for Vascular Biology and Medicine, Friedrich Schiller University Jena, Erfurt, Germany. kaiser@zmkh.ef.uni-jena.de
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