Gas6, una proteína dependiente de la vitamina k implicada en la respuesta a la infección por sars-cov-2

Trabajo presentado en el LXIII Congreso Nacional SEHH/ XXXVII Congreso Nacional SETH, celebrado en Pamplona (Navarra) del 14 al 16 de octubre de 2021

Altered inactivation pathway of factor Va by activated protein C in the presence of heparin

Inactivation of factor Va (FVa) by activated protein C (APC) is a predominant mechanism in the down-regulation of thrombin generation. In normal FVa, APC-mediated inactivation occurs after cleavage at Arg306 (with corresponding rate constant k'(306)) or after cleavage at Arg506 (k(506)) and subsequent cleavage at Arg306 (k(306)). We have studied the influence of heparin on APC-catalyzed FVa inactivation by kinetic analysis of the time courses of inactivation. Peptide bond cleavage was identified by Western blotting using FV-specific antibodies. In normal FVa, unfractionated heparin (UFH) was found to inhibit cleavage at Arg506 in a dose-dependent manner. Maximal inhibition of k(506) by UFH was 12-fold, with the secondary cleavage at Arg306 (k(306)) being virtually unaffected. In contrast, UFH stimulated the initial cleavage at Arg306 (k'(306)) two- to threefold. Low molecular weight heparin (Fragmin(R)) had the same effects on the rate constants of FVa inactivation as UFH, but pentasaccharide did not inhibit FVa inactivation. Analysis of these data in the context of the 3D structures of APC and FVa and of simulated APC-heparin and FVa-APC complexes suggests that the heparin-binding loops 37 and 70 in APC complement electronegative areas surrounding the Arg506 site, with additional contributions from APC loop 148. Fewer contacts are observed between APC and the region around the Arg306 site in FVa. The modeling and experimental data suggest that heparin, when bound to APC, prevents optimal docking of APC at Arg506 and promotes association between FVa and APC at position Arg306

Identification of the MMRN1 binding region within the C2 domain of human factor V

In platelets, coagulation cofactor V is stored in complex with multimerin 1 in alpha-granules for activation- induced release during clot formation. The molecular nature of multimerin 1 factor V binding has not been determined, although multimerin 1 is known to interact with the factor V light chain. We investigated the region in factor V important for multimerin 1 binding using modified enzyme-linked immunoassays and recombinant factor V constructs. Factor V constructs lacking the C2 region or entire light chain had impaired and absent multimerin 1 binding, respectively, whereas the B domain deleted construct had modestly reduced binding. Analyses of point mutated constructs indicated that the multimerin 1 binding site in the C2 domain of factor V partially overlaps the phosphatidylserine binding site and that the factor V B domain enhances multimerin 1 binding. Multimerin 1 did not inhibit factor V phosphatidylserine binding, and it bound to phosphatidylserine independently of factor V. There was a reduction in factor V in complex with multimerin 1 after activation, and thrombin cleavage significantly reduced factor V binding to multimerin 1. In molar excess, multimerin 1 minimally reduced factor V procoagulant activity in prothrombinase assays and only if it was added before factor V activation. The dissociation of factor V-multimerin 1 complexes following factor V activation suggests a role for multimerin 1 in delivering and localizing factor V onto platelets prior to prothrombinase assembly

Lessons from the aprotinin saga : current perspective on antifibrinolytic therapy in cardiac surgery

Antifibrinolytic agents have been prophylactically administered to patients undergoing cardiopulmonary bypass (CPB) to reduce postoperative bleeding due to plasmin-mediated coagulation disturbances. After the recent market withdrawal of aprotinin, a potent bovine-derived plasmin inhibitor, two lysine analogs, epsilon-aminocaproic acid and tranexamic acid are currently available for clinical use. Although the use of aprotinin recently raised major concerns about postoperative thrombosis and organ dysfunctions, there is a paucity of information on the potential complications related to lysine analogs. Using the available preclinical and clinical data, we present current perspectives on the hemostatic mechanism and potential harms of antifbirnolytic therapy related to cardiac surgery. Fibrin formation is the critical step for hemostasis at the site of vascular injury, and localized fibrinolytic activity counterbalances excess fibrin formation which might result in vascular occlusion. Inhibition of the endogenous fibrinolytic system may be associated with thrombotic complications in susceptible organs. It is thus important to understand CPB-related changes in endogenous fibrinolytic proteins (e.g., tissue plasminogen activator (tPA), plasminogen) and antifibrinolytic proteins (e.g., alpha(2)-antiplasmin)