Coagulation factor Xa and thrombin via antithrombin (FXa/FIIa via AT)

Coagulation factors Xa and IIa (thrombin) are key serine proteases in the blood coagulation cascade, where factor Xa catalyzes the conversion of prothrombin to thrombin, and thrombin subsequently converts fibrinogen to fibrin [PubMed: PMC3035135]. Antithrombin III (ATIII), a member of the serpin family, serves as the primary endogenous inhibitor of these enzymes by forming stable 1:1 complexes with them [StatPearls: Antithrombin III Deficiency]. The therapeutic targeting of factors Xa and IIa via ATIII is the primary mechanism of action for heparin-based anticoagulants. Heparin binds to ATIII through a specific pentasaccharide sequence, inducing a conformational change that increases the rate of factor Xa inhibition by approximately 1,000-fold [StatPearls: Heparin]. For the inhibition of thrombin (IIa), heparin must also act as a template, binding both ATIII and the enzyme simultaneously, a feat requiring longer polysaccharide chains found in unfractionated heparin [PubMed: PMC3035135]. This pathway is essential for managing conditions like deep vein thrombosis and acute coronary syndromes, though it carries risks of hemorrhage and immune-mediated complications like heparin-induced thrombocytopenia [StatPearls: Heparin].

Other names

Factor Xa and Factor IIa inhibition via Antithrombin IIIHeparin-mediated inhibition of FXa and FIIaAntithrombin-dependent inhibition of thrombin and factor XaATIII-mediated inhibition of coagulation factors

The mechanism involves the indirect inhibition of the serine proteases Factor Xa and Factor IIa (thrombin) by potentiating the activity of the endogenous inhibitor Antithrombin III (ATIII). Heparinoids bind to ATIII via a specific pentasaccharide sequence, causing a conformational change in its reactive center loop that significantly accelerates its ability to neutralize these target coagulation factors [StatPearls: Heparin, PubMed: PMC3035135].