1PHTX 441Drugs that affect Coagulation and Clot IntegritySteve SawyerSept 28, 2004Anticoagulants and Thrombolytic AgentsLearning Objectives:1. Coagulation cascade- learn in vivo pathway and key steps in blood coagulation and platelet reaction in both hemostasis and thrombosis. 2. Injectable anticoagulants- mechanism of heparin and hirudin action3. Oral anticoagulants- warfarin and related compounds-action in Vitamin K-dependent reactions4. Vitamin K mechanism of action5. Agents that accelerate and suppress Fibrinolysis-TPA, streptokinase, transexamic acid6. Agents that promote clotting- Vitamin K, Clotting factors for replacement, Desmopressin..2Hemostasis•Hemostasis is the arrest of blood loss from damaged vessels and is essential for survival. •The main phenomena are:1) platelet activation, 2) blood coagulation and 3) vascular contraction. •The lecture is primarily focused on blood coagulation.THROMBUSFIBRINFIBRINOGENThrombinFibrin forms framework of clot: fibrin acts to traps blood cells that form bulk of clotBlood Clot formed by FibrinBlood Vessel(Soluble)RBCplateletswbcVASCULAR DAMAGE or ATHEROSCLEROTIC PLAQUEPLATELET REACTIONSBLOOD COAGULATION ADHESION, ACTIVATIONAND AGGREGATION OFPLATELETS EXPOSUREOF ACIDIC /negativePHOSPHOLIPIDSRELEASE OF FACTORS, ADP, TXA2, PAF, ETC. FURTHER AGGREGATIONOF PLATELETSIN VIVO CONTACT PATHWAY(tissue factor & VIIa)(factors XII,XI,& IX ) X Xaprothrombin, IITHROMBINFIBRINOGEN FIBRINTHROMBUS (CLOT) + + + FIGURE 1. Simplified version of coagulation that results in clot formation or thrombus from either vascular damage oratherosclerotic plaqueHEMOSTASIS AND THROMBOSIS 1. Hemostasis is the arrest of blood loss from damaged vessels and is essential for survival. The main phenomena are i) platelet adhesion and activation and ii) blood coagulation (fibrin formation), and iii) vascular contraction.2. Thrombosis is a pathological condition. Venous thrombosis usually results from slow blood flow and coagulation without significant initial platelet activation. Arterial thrombosis usually is associated with arteriosclerosis and platelet activation. Thrombus may break away from vessel wall becoming an embolus. Embolus is a major cause of death. PLASMAThrombosisThrombosis is the pathological condition of (unnecessary) clotting1. Venous thrombosis due to slow circulation without significant platelet activation. Thrombus may break away from vessel wall forming an embolus. Emboli clogging vessels in the heart, lungs and brain results in tissues deprived of circulation (oxygen) and are a major cause of death.2. Arterial thrombosis usually associated with arteriosclerosis and inappropriate platelet activation. Heart Attack and Stroke result primarily from arterial thrombosis in either heart or brain.3Much of knowledge of the molecular / biochemical basis of Blood Coagulation comes from the study of genetic diseases that affect coagulation. An example is as classic hemophilia which results from a mutation of Factor VIII on the X chromosome.In Vivo Pathway of Blood Coagulationi. Tissue factor exposed by vessel damage-the binding site of VIIa located at the wound site, additional binding sites (acidic phospholipids) provided by activated platelets.ii. Common pathway after factor X.Factor Xa cleaves factor II (prothrombin) to IIa (thrombin) in the presence of factor Va bound to membranes.iii. Thrombin, IIa, is central in control of coagulation-acts to cleave factor I, fibrinogen, to insoluble fibrin. Fibrin meshwork traps blood cells to form the clot. Also converts XIII to XIIIa to stabilize the fibrin meshwork, activates factors V, VII, VIII, & XI, activates platelets, and acts on endothelial cells.THE IN VIVO OR EXTRINSIC PATHWAY TISSUE DAMAGE Tissue factor VIIaCaNegative PLTHE CONTACT SYSTEM OR INTRINSIC PATHWAY XIIaXII XIXIXIa IXIXa X XaVIIIa CaNeg PLII, prothrombin IIa, thrombinVaNegative PLPLATELETS XIIIXIIIa CaI, Fibrinogen FIBRIN Stabilized Fibrin + + + BLOOD COAGULATIN- fibrin formation1. Clotting system is a cascade of enzymes and cofactors- factors I through XIII.2. Inactive precursors are activated in series, each giving rise to the next.3. The last enzyme, thrombin, derived from prothrombin, converts soluble fibrinogen (factor I) into insoluble meshwork of Fibrin in which blood cells are trapped, forming the clot.4. There are two pathways in the cascade: the extrinsic is apparently the in vivo pathway while the intrinsic apparently is triggered in the test tube. 5. Both pathway activate Factor X, which converts prothrombin to thrombin. 6. Calcium and negatively charged phospholipids are required in three enzymatic cleavage steps: IX on X, VII on X, and X on II.7. Negative phospholipids are provided by activated platelets that have adhered to the site of injury. This localizes the site of clot formation. 8. Binding proteins as well as enzymes are used, i.e. factor V in X cleaving II. CaA. Hemostasis-physiological arrest of blood loss1. Platelet Reactionsa. Adhesion, activation, and aggregation of plateletsb. Exposure of acidic (negatively charged) phospholipids that are binding sites for coagulation factorsc. Release of factors: [ADP, TXA2, PAF]d. Further Aggregation of Platelets4Vitamin KDiscovered in Denmark and named the “Koagulation” Vitamin Necessary for efficient blood coagulationVitamin K Function& Inhibition of Vitamin K re-use by WarfarinThe activation of prothrombin (Factor II) by factor XaII. Agents that increase coagulation.A.Vitamin K- Phytonadione (Aqua Mephyton, Konakion), Menadiol Sodium (Synkavite)1. Action- required for post-translational modifications of glutamic acid residues on clotting factors that allow these proteins to bind to the membranes (negatively charged phospholipids) of damaged cells in the vessel wall.2. Clinical use of Vitamin Ki. bleeding due to excess oral anticoagulantsii. hemorrhagic disease of newbornsiii. vitamin k deficiencies-i.e. adsorption problems5Agents that increase coagulation.Replacement of missing of defective Plasma Clotting Factors- treatment of genetic diseases of coagulationa. Factor VIII, lacking in classic hemophilia or Hemophilia A (Hemofil M, Monoclate P, Koate HP, Profilate OSD, b. Factor IX lacking in Hemophilia B(Konyne 80, Proplex T, Humate-P, Profilnine)c. Desmopressin (DDAVP, STIMATE, RHINYLE): posterior pituitary hormone used to maintain hemostasis in hemophilia and Von Willebrand’s disease by promoting release of Factor VIII from stores in platelets