OF NORTH AMERICA Coagulation 2006 : A Modern View of Hemostasis (original) (raw)
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Research and practice in thrombosis and haemostasis, 2018
This 9th Symposium on Hemostasis is an international scientific meeting held biannually in Chapel Hill, North Carolina. The meeting is in large measure the result of the close friendship between the late Dr. Harold R. Roberts of UNC Chapel Hill and Dr. Ulla Hedner of Novo Nordisk. When Novo Nordisk was developing the hemophilia therapy that would become NovoSeven, they sponsored a series of meetings to understand the basic biology and clinical applications of factor VIIa. The first meeting in Chapel Hill was held April 4-6, 2002 with Dr. Roberts as the organizer. Over the years, the conference emphasis has expanded from discussions of factor VIIa and tissue factor to additional topics in hemostasis and thrombosis. This year's meeting includes presentations by internationally renowned speakers that discuss the state-of-the-art on an array of important topics, including von Willebrand factor, engineering advances, coagulation and disease, tissue factor biology, therapeutic advance...
Remodeling the Blood Coagulation Cascade
Journal of Thrombosis and Thrombolysis, 2000
The concept of a coagulation cascade describes the biochemical interactions of the coagulation factors, but has flaws as a model of the hemostatic process in vivo. For example, the model cannot explain why hemophiliacs bleed when they have an intact factor VIIa/tissue factor ("extrinsic") pathway. Hemostasis requires the formation of an impermeable platelet and fibrin plug at the site of vessel injury, but it also requires that the powerful procoagulant substances activated in this process remain localized to the site of injury.
Rethinking the coagulation cascade
Current hematology reports, 2005
The concept of coagulation as a "cascade" of proteolytic reactions was a conceptual breakthrough in understanding how the coagulation process acts as a biologic amplifier. The model that it evolved into, with "extrinsic" and "intrinsic" pathways meeting in a common pathway, delineates the interactions between the coagulation proteins and provides a framework for interpreting the common screening coagulation tests. The coagulation "cascade" has significant limitations as a model of how hemostasis occurs in vivo, however. This article describes how the modern view of hemostasis has evolved to emphasize the role of cells in controlling and directing the coagulation reactions. It also highlights how host factors that are not part of the coagulation process per se can influence the effectiveness of coagulation.
Biochemistry-moscow, 2002
The process of tissue factor initiated blood coagulation is discussed. Reactions of the blood coagulation cascade are propagated by complex enzymes containing a vitamin K-dependent serine protease and an accessory cofactor protein that are assembled on a membrane surface in a calcium-dependent manner.These complexes are 105 109-fold more efficient in proteolyses of their natural substrates than enzymes alone. Based upon
The Tissue Factor Requirement in Blood Coagulation
Journal of Biological Chemistry, 2005
Formation of thrombin is triggered when membrane-localized tissue factor (TF) is exposed to blood. In closed models of this process, thrombin formation displays an initiation phase (low rates of thrombin production cause platelet activation and fibrinogen clotting), a propagation phase (>95% of thrombin production occurs) and a termination phase (prothrombin activation ceases and free thrombin is inactivated). A current controversy centers on whether the TF stimulus requires supplementation from a circulating pool of blood TF in order to sustain an adequate procoagulant response. We have evaluated the requirement for TF during the progress of the blood coagulation reaction and have extended these analyses to assess the requirement for TF during resupply ("flow replacement"). Elimination of TF activity at various times during the initiation phase indicated: a period of absolute dependence (<10s); a transitional period in which the dependence on TF is partial and decreases as the reaction proceeds (10-240s); and a period in which the progress of the reaction is TF independent (>240s). Resupply of reactions late during the termination phase with fresh reactants, but no TF, yielded immediate bursts of thrombin formation similar in magnitude to the original propagation phases. Our data show that independence from the initial TF stimulus is achieved by the onset of the propagation phase and that the ensemble of coagulation products and intermediates which yield this TF independence maintain their prothrombin-activating potential for considerable time. These observations support the hypothesis that the transient, localized expression of TF is sufficient to sustain a TF-independent procoagulant response as long as flow persists.
Blood coagulation dynamics in haemostasis
Hämostaseologie, 2009
Our studies involve computational simulations, a reconstructed plasma/platelet proteome, whole blood in vitro and blood exuding from microvascular wounds. All studies indicate that in normal haemostasis, the binding of tissue factor (TF) with plasma factor (F) VIIa (extrinsic FXase complex) results in the initiation phase of the procoagulant response. This phase is negatively regulated by tissue factor pathway inhibitor (TFPI) in combination with antithrombin (AT) and the protein C (PC) pathway. The synergy between these inhibitors provides a threshold-limited reaction in which a stimulus of sufficient magnitude must be provided for continuation of the reaction. With sufficient stimulus, the FXa produced activates some prothrombin. This initial thrombin activates the procofactors and platelets required for presentation of the intrinsic FXase (FVIIIa-FIXa) and prothrombinase (FVa-FXa) complexes which drive the subsequent propagation phase; continuous downregulation of which is provid...
Factors IXa and Xa play distinct roles in tissue factor-dependent initiation of coagulation
Blood, 1995
Tissue factor is the major initiator of coagulation. Both factor IX and factor X are activated by the complex of factor Vlla and tissue factor (Vlla/TF). The goal of this study was t o determine the specific roles of factors IXa and Xa in initiating coagulation. We used a model system of in vitro coagulation initiated by Vlla/TF and that included unactivated platelets and plasma concentrations of factors II, V, VIII, IX, and X, tissue factor pathway inhibitor, and antithrombin 111. In some cases, factor IX and/or factor X were activated by tissue factor-bearing monocytes, but in some experiments, picomolar concentrations of preactivated factor IX or factor X were used t o initiate the reactions. Timed samples were assayed for both platelet activation and thrombin activity. Factor Xa was 10 times more potent than factor IXa in initiating platelet activation, but factor IXa was much more effective in promoting thrombin generation than was factor Xa. In the presence of Vlla/TF, factor X was required for both platelet activation and thrombin generation, while factor IX