MLAB 1227- Coagulation Keri Brophy-Martinez

1. MLAB 1227- CoagulationKeri Brophy-Martinez Fibrinolytic System

2. Fibrinolysis • Process of removing fibrin from the vasculature • Key Players • Plasminogen • Plasminogen activators (PA) • Active enzyme plasmin (PLN) • Fibrin • Fibrin/Fibrinogen degradation products • Inhibitors of plasminogen activators and PLN

3. Fibrinolytic System • Sensitive to imbalances • Restricts fibrin formation to area of injury • Initiated when coagulation cascade begins • Dissolves clot by digestion of fibrin

4. Overview • Under the influence of thrombin. • Fibrinogen cleaved into fibrin monomers • Fibrin monomers are cleaved into fibrin degradation products or fibrin split products

5. Process summary • Once clotting begins, the fibrinolytic system comes to life • Plasminogen (PLG) binds to fibrin in the developing thrombus • Tissue-type PLG activator (tPA) also binds to fibrin, increasing its enzymatic activity to convert plasminogen to plasmin (PLN) • Complex formation of tPA, PLG and fibrin results in the break-down of fibrin • PLN then further digest fibrin to soluble degradation products making fibrin fragments

6. Plasminogen • Produced in the liver • Found in normal plasma • Following injury, binds to fibrin during clot formation along with plasminogen activators

7. Activators of Fibrinolysis • Contact Phase/Intrinsic • Occurs by interactions of the contact factors (XIIa, HMWK, and PK) following intrinsic pathway activation(collagen exposure) • Physiologic • Activators released from tissues extrinsic to the blood • tPA: tissue- type PLG activator • Found in endothelial cells of small vessels • uPA: urokinase-type PLG activator • Made in renal tubular epithelium and vascular epithelium • Found in urine and plasma • Exogenous activation • Via medications given to lyse pathogenic clots (i.e. pulmonary emboli) • Example includes Streptokinase

8. Activators

9. Plasmin • Proteolytic enzyme • Dissolves fibrin/fibrinogen clots into protein fragments that are cleared from plasma by the liver • Provides a positive feedback loop for forming more plasminogen • Highly regulated • Temporarily active • Local

10. Fibrinogen and Fibrin • Fibrin degradation products are the protein fragments of fibrin or fibrinogen. • The protein fragments are designated X, Y, D, and E • Fragments are strong inhibitors of further coagulation by • interfering with the action of thrombin • interfering with platelet aggregation • In the lab, referred to as FDPs or FSPs • Fibrin degradation products are cleared by the liver • Fibrinogen and fibrin yield essentially the same fragments; however degradation of cross-linked fibrin is slower and leads to fragments that contain D-dimer.

11. Plasmin Degradation of Fibrinogen E Fibrinogen D D plasmin E D D Fragment X: small peptides from carboxyl end of α chain removed plasmin E Fragment Y + Fragment D D D plasmin E D Fragment D + Fragment E

12. Plasminogen Intrinsic/contact activation Physiologic activation Exogenous activation Plasmin Fibrin clot Fibrinogen Fibrin Degradation Fibrinogen Products Degradation Products X,Y,D=D,E X,Y,D,E,D

13. Inhibitors of Fibrinolysis • Used to regulate and limit plasmin activity and fibrinolysis • Also referred to as an antiplasmin • How? • Target PLG activation step • Target plasmin

14. Inhibitors of Fibrinolysis Inhibitors Inhibitors

15. Specific Inhibitors • Plasminogen Activator Inhibitor (PAI) • PAI-1: most significant • Inhibits tPA and uPA • Acute phase reactant protein • Thrombin Activatable Fibrinolysis Inhibitor (TAFI) • Eliminates fibrin binding sites for plasminogen

16. Specific Inhibitors • alpha-2-antiplasmin • Rapid inhibitor of plasmin • Functions to “catch” leaked PLN in the circulation, thus limiting activity to fibrin clot • Produced in liver and α granules in platelets • alpha-2-macroglobulin • Slower inhibitor of plasmin

17. References McKenzie, Shirlyn B., and J. Lynne. Williams. "Chapter 30." Clinical Laboratory Hematology. Boston: Pearson, 2010. Print.