Tissue factor Vila complex

A number of 1-substituted 2(l//)-pyrazinone derivatives show antithrombotic activity as selective inhibitors of the tissue Factor Vila complex <2003BML23I9> and were examined as mast cell tryptase inhibitors <2004BML48I9>. As a curious effect, dihydropyrazines proved to show DNA strand-breakage activity <2005CPB1359>. 

Initiation of Clotting The Tissue Factor-Vila Complex... 

The coagulation pathway can be activated by one of two pathways the extrinsic (tissue factor) pathway or the intrinsic (contact activation) pathway (Figure 13-1). The main coagulation pathway in vivo is the tissue factor pathway. Tissue factor is exposed by damaged endothelium. This exposed tissue factor binds and activates factor VII, which, in turn, activates factor X. Factor Xa results in the generation of a thrombin (factor lla) burst. Thrombin, in turn activates factors XI, VIII, and V, leading to the further generation of thrombin and clottable fibrin. Additionally, the tissue factor Vila complex activates factor IX, which further contributes to the activation of factor X. 

Tissue factor pathway inhibitor (TFPI), a 42-kDa protein with three Kunitz domains, is a potent inhibitor of coagulation. It inhibits tissue factor-factor Vila complex upon binding to the active site of Kunitz domain one. Factor Xa is inhibited upon binding to the active site of the second Kunitz domain of TFPI (27). 

Hemostasis begins with the formation of the platelet plug, followed by activation of the clotting cascade, and propagation of the clot. One of the major multicomponent complexes in the coagulation cascade consists of activated factor IX (factor IXa) as the protease, activated factor VIII (factor Villa), calcium, and phospholipids as the cofactors, and factor X as the substrate. Factor IXa can be generated by either factor Xa activation of the intrinsic pathway or by the tissue factor/factor Vila complex. 

Human recombinant Factor Vila Complex tissue factor/factor Vila ligands designed to bind to the Gla-domain in Factor Vila. Solid-phase combinatorial chemistry solution-phase synthesis of a sub-library Affinity chromatography SPR 7,15 ... 

Roussel P, Bradley M, Kane P, Bailey C, Arnold R, Cross A. Inhibition of the tissue factor/factor Vila complex-lead optimization using combinatorial chemistry. Tetrahedron 1999 55 6129-6230. 

Also see color figure.) Tissue factor-factor Vila complex. The three-dimensional structure of the complex of factor Vila and tissue factor (minus the transmembrane polypeptide domain of the tissue factor) in the absence of membrane surface. It is approximately 115 A in length and has a diameter of 40-50 A. Factor Vila shows its four distinct domains the Gla domain, two EGF-like domains, and the proteinase domain. Tissue factor contacts factor VHa via the interface between the two fibronectin type Ill-like domains. All four domains of factor Vila appear to be involved in the interaction between tissue factor and factor Vila. The Gla domain of factor Vila is folded very similarly to the Gla domain of prothrombin (Gla domain of prothrombin fragment 1). Activation of factor VII can be catalyzed by thrombin, factor Xa, factor Vila, and factor Xlla—all by cleavage at Arg -Ile . Secondary structures are shown in the center diagram two views of the close interactions between TF and factor Vila are shown in the two diagrams at each side. 

Moons AH, Peters RJ, Bijsterveld NR, Piek JJ, Prins MH, Vlasuk GP, Rote WE, BuUer HR. Recombinant nematode anticoagulant protein c2, an inhibitor of the tissue factor/factor Vila complex, in patients undergoing elective coronary angioplasty. J Am Coll Cardiol. 2003 41 2147-2153. 

J. H. Morrissey, E. Tajkhorshid, S. G. Sligar and C. M. Rienstra, Tissue Factor/Factor Vila Complex Role of the Membrane Surface, Thromb. Res.,... 

Figure 51-1. The pathways of blood coagulation. The intrinsic and extrinsic pathways are indicated. The events depicted below factor Xa are designated the final common pathway, culminating in the formation of cross-linked fibrin. New observations (dotted arrow) include the finding that complexes of tissue factor and factor Vila activate not only factor X (in the classic extrinsic pathway) but also factor IX in the intrinsic pathway, in addition, thrombin and factor Xa feedback-activate at the two sites indicated (dashed arrows). (PK, prekallikrein HK, HMW kininogen PL, phospholipids.) (Reproduced, with permission, from Roberts HR, Lozier JN New perspectives on the coagulation cascade. Hosp Pract [Off Ed] 1992Jan 27 97.)...

Activated on surface of activated platelets by tenase complex (Ca, factors Villa and IXa) and by factor Vila in presence of tissue factor and Ca. ... 

Four naturally occurring thrombin inhibitors exist in normal plasma. The most important is antithrombin III (often called simply antithrombin), which contributes approximately 75% of the antithrombin activity. Antithrombin III can also inhibit the activities of factors IXa, Xa, XIa, Xlla, and Vila complexed with tissue factor. a2-Macroglobulin contributes most of the remainder of the antithrombin activity, with heparin cofactor II and aj-antitrypsin acting as minor inhibitors under physiologic conditions. 

The activity of factor Vila is enhanced astronomically (10 millionfold) upon binding to tissue factor. The VII or VHa-tissue factor complex activates factors IX and X and autoactivates factor VII. Although the activity of the tissue factor-factor VII complex is expressed without the presence of the negatively charged phosphatidylserine, the activity can be enhanced by its presence (9). 

Some 5-25 per cent of individuals suffering from haemophilia A develop anti-factor VIII antibodies, and 3-6 per cent of haemophilia B sufferers develop anti-factor IX antibodies. This complicates treatment of these conditions and, as mentioned previously, one approach to their treatment is direct administration of factor Vila. The therapeutic rationale is that factor Vila could directly activate the final common steps of the coagulation cascade, independently of either factor VIII or IX (Figure 12.1). Factor Vila forms a complex with tissue factor that, in the presence of phospholipids and Ca2+, activates factor X. 

Figure 9.4. Schematic representation of the mechanism of action of the coaguligand approach. Cross linking of truncated Tissue Factor to tumour endothelial cells leads to local blood coagulation via the tTF/fVIIa complex. tTF, truncated Tissue Factor fVIIa, factor Vila fX (A), factor X (A).

Factor VII exhibits a weak procoagulant activity on its own, typically accounting for about I -2% of the total factor Vll/Vlla activity (17), Upon binding to tissue factor, a 10,000,000-fold increase in factor Vila enzymatic activity is observed (18). Both factor VII and factor Vila bind to tissue factor with equal affinity (19), How factor VII is initially activated is not known, though it is hypothesized that factor Xa can activate factor VII in a back-activation reaction. The factor VIla—tissue factor complex can then activate factor X leading to the generation of thrombin and ultimately to the formation of fibrin strands. 

Banner, D. W., D Arcy, A. D., Chene, C., Winkler, F. K., Guha, A., Konigsberg, W. H., Nermerson, Y, and Kirchhofer, D. (1996). The crystal structure of the complex of blood coagulation factor Vila with soluble tissue factor. Nature 380, 41-46. 

Two pathways initiate a fibrin clot. Extrinsic path is mediated by tissue factor, also called thromboplastin. This membrane protein is exposed when pericytes are damaged. It binds to factor Vila in blood. Factor Vila is a protease and the phospholipid-VIIa-TF complex activates (converts) factor X by cleaving it to Xa. Intrinsic path is initiated by factor XII (Hageman factor), whose conformation is changed to a protease (XHa) by contact with a negatively charged surface such as RNA from damaged or necrotic cells. 

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