ORIGINAL ARTICLESOn the mechanism of inhibition of tissue factor pathway by the synthetic pentasaccharide during coagulation of human plasmaGerotziafas, Grigoris Ta; Elalamy, Ismaila; Depasse, Françoisb; Chakroun, Tahara; Bara, Luciennea; Arzoglou, Pantelisc; Samama, Meyer Ma,bAuthor Information aService d'Hématologie Biologique, Hôpital Hôtel-Dieu de Paris, bLaboratoire LCL, Ivry sur Seine, France and cFaculty of Chemistry, Laboratory of Biochemistry, Aristotle University of Thessaloniki, Greece. Correspondence and requests for reprints to Grigoris T. Gerotziafas, MD, PhD, Service d'Hématologie Biologique, Hôpital Hôtel Dieu, 1 Place du Parvis, Notre-Dame 75181, Paris Cedex 04, France. Tel: +33 1 4234 8266; fax: +33 1 4234 8254; e-mail: firstname.lastname@example.org Received 5 November 2002 Revised 10 March 2003 Accepted 17 March 2003 Blood Coagulation & Fibrinolysis: October 2003 - Volume 14 - Issue 7 - p 633-638 Buy Abstract The tissue factor (TF) pathway is preponderant in the initiation of blood coagulation in normal haemostasis and in thrombotic states. In the present study we investigated the mechanisms by which the synthetic pentasaccharide may influence the regulation of the TF pathway during clotting of human platelet poor plasma (PPP). Clotting of normal PPP or plasmas immuno-depleted of a single clotting factor (factor VII, factor XII, factor XI, factor IX, factor VIII, factor X, factor V, factor II) was initiated by triggering the TF pathway in the presence of fondaparinux (0.5 μg/ml). Activated factor VII (FVIIa) levels were measured in serum obtained at several time intervals after re-calcification of PPP. A clotting assay highly specific for FVIIa was used. The synthetic pentasaccharide inhibited the generation of FVIIa by 66%. The inhibitory effect of fondaparinux on FVIIa was completely abolished when antithrombin activity of plasma was inhibited by a specific antibody. Following the activation of TF pathway in plasmas depleted of factor X or factor IX, the inhibitory effect of fondaparinux on FVIIa generation was completely abolished, whereas it was not significantly modified when the other clotting factor-depleted plasmas were clotted. When fondaparinux was added in the serum, after the maximal generation of FVIIa, it inhibited by 20–30% the activity of the FVIIa–TF complex. These data suggest that fondaparinux enhances the antithrombin-dependent downregulation of the TF pathway by decreasing the generation of FVIIa via the inhibition of the generation and the activity of activated factor IX and activated factor X, and by inhibiting the activity of the FVIIa–TF complex. © 2003 Lippincott Williams & Wilkins, Inc.