Strategies for inhibiting the effects of thrombin.

Thrombin's catalytic site and flanking clusters of accessory binding domains regulate its interactions with substrates and inhibitors. Inactivation of soluble thrombin by heparin involves the complexing of thrombin with plasma antithrombin, and heparin with heparin, plasma antithrombin and thrombin via binding domains shared by fibrin, thereby explaining the heparin resistance for thrombin bound to thrombus. By contrast, because antithrombin-independent peptide inhibitors, such as hirudin or synthetic antithrombin peptides, inactivate both thrombus-bound and soluble thrombin, they interrupt the formation of both platelet-rich arterial thrombi and fibrin-rich venous thrombi. Recent studies in experimental animals indicate that platelet-dependent thrombus formation will also be prevented without compromising haemostasis by inhibiting its receptors on platelets or by inactivating serine proteases comprising the coagulation pathways producing thrombin.