Activated protein C--an anticoagulant that does more than stop clots.

Activated protein C (APC) is a glycoprotein derived from its precursor, protein C and formed by the cleavage of an activation peptide by thrombin bound to thrombomodulin. Originally thought to be synthesized exclusively by the liver, recent reports have shown that protein C is synthesized by endothelial cells, keratinocytes and some hematopoietic cells. APC functions as a physiological anticoagulant with cytoprotective, anti-inflammatory and anti-apoptotic properties. In vitro and preclinical data have revealed that APC exerts its protective effects via an intriguing mechanism requiring endothelial protein C receptor and the thrombin receptor, protease-activated receptor-1. Remarkably, even though APC cleaves this receptor in an identical fashion to thrombin, it exerts opposing effects. Recently approved as a therapeutic agent for severe sepsis, APC is now emerging as a potential treatment for a number of autoimmune and inflammatory diseases including lung disorders, spinal cord injury and chronic wounds. The future pharmacologic use of APC holds remarkable promise.