Thrombomodulin: protectorate God of the vasculature in thrombosis and inflammation

Thrombomodulin (TM) is an endothelial anticoagulant cofactor that promotes thrombin-mediated activation of protein C. Recently, we conducted a multicentre, double-blind, randomized trial to evaluate the efficacy and safety of recombinant human soluble thrombomodulin (rhsTM, also known as ART-123) for the treatment of disseminated intravascular coagulation (DIC), and found that rhsTM therapy is more effective and safer than low-dose heparin therapy. Thus, in 2008, rhsTM (Recomodulin) was approved for the treatment of DIC in Japan. Here we re-evaluate the therapeutic basis of this drug from the view of its anticoagulant, anti-inflammatory, and cytoprotective properties. Structurally, the extracellular portion of TM is composed of three domains: an N-terminal lectin-like domain (TM-D1), followed by an epidermal growth factor (EGF)-like domain (TM-D2), and an O-glycosylation-rich domain (TM-D3). TM-D2 and TM-D3 are important for the protein's anticoagulant cofactor activities, i.e. inhibition of thrombin and activation of protein C. TM-D1 plays an important role in attenuation of inflammatory responses, through inhibition of leukocyte adhesion to endothelial cells, inhibition of complement pathways, neutralization of lipopolysaccharide (LPS), and sequestration and degradation of pro-inflammatory high-mobility group box 1 protein (HMGB1). Thus, TM on the surface of endothelial cells prevents dissemination of pro-coagulant and pro-inflammatory molecules, and by doing so, allows these molecules to act locally at the site of injury. In patients with sepsis and DIC, TM expression is down-regulated, which may result in dissemination of pro-coagulant and pro-inflammatory molecules throughout the systemic circulation. Replacement with rhsTM may offer therapeutic value in such conditions.