[The numerous properties of the anticoagulant protein C]

The systemic inflammation associated to the simultaneous activation of blood coagulation and the alterated blood fibrinolysis, leads to microvascular endothelial injury, acute organ dysfunction and possibly death. Activated Protein C, a natural, multifunctional protein, has demonstrated antithrombotic, anti-inflammatory, and profibrinolitic properties and may be an important modulator of the vicious cycle whereby inflammation initiates coagulation and coagulation amplifies inflammation. Protein C couples with its receptor, EPCR (endothelial-cell protein-C receptor), and the ligand-receptor complex then interact with thrombin-thrombomodulin on endothelial surface to produce activated protein C (APC). Once activated, protein C then interact with its cofactor, protein S, to catalyze the inactivation of factors Va and VIIILa, two important accelerators of the clotting cascade, reducing thrombin generation and microvascular thrombosis. In addiction to its anticoagulant activity APC promotes profibrinolytic activity through the inhibition of plasminogen activator inhibitor-1, which is upregulated during inflammation. Inhibition of thrombin generation by APC decreases inflammation by inhibiting platelet activation, neutrophil recruitment, and mast-cell degranulation. APC also shows direct antiinflammatory properties, including blocking of cytokines production by monocytes and blocking cell adhesion. Moreover, APC has antiapoptotic properties that may contribute to its efficacy. In conclusion, APC, besides its physiologic role in the coagulation cascade, plays a key role in the pathophysiology of systemic inflammation justifying its potential therapeutic role in sepsis and systemic inflammatory responses.