Fig 3. UFH, enoxaparin and dalteparin block TFPIα inhibition of prothrombinase, but fondaparinux does not.

Prothrombinase activity assays were performed by incubating FV810^QQ (0.5 nM) with phospholipid vesicles (20 μM), prothrombin (1.4 μM), the thrombin inhibitor dansylarginine N-(3-ethyl-1,5-pentanediyl)amine (DAPA; 3 μM) and tissue factor pathway inhibitor alpha (TFPIα), in the absence (▲) or presence of unfractionated heparin (UFH; (u/ml, ■), enoxaparin (0.8 u/ml, ●), dalteparin (1 u/ml, ○) or fondaparinux (0.8 u/ml, △), followed by the addition of FXa (5 nM) to initiate the reaction. The heparin concentrations were chosen to mimic the average recommended therapeutic concentrations of each. Shown are the initial rates of thrombin generation, expressed as the percentage of a control experiment performed in the absence of TFPIα (mean±standard error of the mean, n≥3). Note that the dalteparin and enoxaparin curves are very similar.