Treatment with LMWHs inhibits factor VIIa generation during in vitro coagulation of whole blood

The role of factor VII and activated factor VII (VIIa) is considered to be crucial in the coagulation process. The efficacy of low molecular weight heparins (LMWHs) in the prevention and treatment of thromboembolic episodes has been established in numerous controlled therapeutic trials. However, the mechanisms of their antithrombotic action are still disputed. Heparins exert their anticoagulant effect by enhancing ATIII inhibitory action on factor Xa and thrombin, which results in decreased factor X activation, prothrombinase formation, prothrombin activation and thrombin generation. Moreover, it is clearly established that both kinds of heparins (unfractionated heparin and LMWHs) induce the release of tissue factor pathway inhibitor (TFPI). Therefore, they are involved indirectly in tissue factor (TF)/factor VIIa complex inhibition by the TFPI/factor Xa complex. Factor VII activation is an essential step in the process of blood coagulation and it plays an important role in thrombogenesis. A method for the measurement of factor VIIa has been recently developed. A study on the effects of antithrombotic drugs, as heparins, on factor VIIa generation might allow to better understand the mechanisms that regulate its activation. We investigated ex vivo the effect of treatment with LMWHs on factor VIIa generation during in vitro coagulation of whole blood in order to clarify if LMWHs interfere with factor VIIa generation.