Quiz #3 Material

Question 1

Hemostasis: four major events occur following a wound

Answer 1

• VPCF
• Vascular Constriction:
  
  • Limits the flow of blood to the injury
• Platelet aggregation:
  
  • Blood platelets clump when binding to collagen that becomes exposed following rupture. Blood platelets become activated and aggregate at the site of injury
• Clot formation:
  
  • To inure stability of the initially loose platelet plug, a fibrin mesh (aka clot) forms and entraps the plug
• Fibrinolysis:
  
  • The clot must be dissolved in order for normal blood flow to resume following tissue repair. The dissolution of the clot occurs through the action of plasmin

Question 2

Platelets

Answer 2

• Platelets are NOT cells but really just a type of vesicle that pinches off of the megakaryocyte.
• No nucleus
• Hemopoetic stem cell→Promegakaryocyte→Megakaryocyte→Platelet

Question 3

Major Drugs Acting on Platelets:

• ADP antagonists
• PDE Inhibitor
• Platelet surface bind
• COX inhibitor
• (Multiple Mechanisms)

Answer 3

• ADP antagonists
  
  • Clopidogrel (Plavix)
  • Ticlopidine (Ticlid)
  • Prasugrel (Ticagrelor)
• PDE Inhibitor
  
  • Dipyridamole (Aggrenox)
• Platelet surface bind
  
  • Abciximab (ReoPro)
  • Tirofiban (Aggrastat)
  • Eptifibatide (Integrelin)
• COX inhibitor
  
  • Aspirin
• (Multiple Mechanisms)
  
  • Thrombin

Question 4

Three Steps of Clot Formation

Answer 4

• Activation
  
  • Activation/Adhesion of platelets
• Release
  
  • Release of factors to drive the activation and adhesion of platelets (ADP, thromboxane A2)
• Recruitment
  
  • Recruitment of more platelets, aggregation and formation of a clot

Question 5

Important Concept of Platelet Aggregation Mechanism

Answer 5

• Works on a feed-forward mechanism
• Is turned off by excretions from the endothelium
  
  • EDRF, PGI₂, tPA, and heparin

Question 6

Thrombin

Answer 6

• Factor IIa
• Cleaves N-terminus of PAR-1
  
  • Leaves behind a ‘tethered ligand’ that can provide continuous activity of the receptor until receptor recycling
  • Irreversible (actually slowly reversible)

Question 7

Molecular Basis of Platelet Aggregation and Activation

Answer 7

• Collagen/damaged endothelium bind Von Willebrand Factor which in turn has high affinity for GP1b/Gp IIb
• Gp Ia: platelet receptor for collagen
• Gp Ib: platelet receptor for VWF
• Gp IIb-IIIa: integrin that binds fibrin
• Antagonists to GpIIb/IIIa prevent binding to fibrin
  
  • Abciximab (Reopro): coronoary artery procedures to prevent platelet sticking
  • Tirofiban (RGD)
  • Eptifibatide (Integrilin, C-term of fibrinogen)

Question 8

Synthesis and Effects of Arachadonic Acid Metabolites

Answer 8

• COX Enzymes metabolize arachadonic acid, leading to the production of thromboxanes and prostacyclin
  
  • Thromboxanes: made in platelets and lead to increased platelet aggregration
  • Prostacylin: made in endothelial tissue and lead to decreased platelet aggregation
    
    • opposing factors

Question 9

Action of Aspirin

Answer 9

• Irreversibly inhibits COX to inhibit both:
  
  • Inhibits thrombaxane synthesis: decrease in platelet aggregation
    
    • Can’t be produced by COX enzmes until platelets are fully recycled
  • Inhibits prostacyclin synthesis
    
    • Can be recovered because endothelial cells have nuclei
• Aspirin + PGHS2→Salicylic acid + acetylated PGHS2
• Use low dose:
  
  • Platelet COX1 has highest affinity for aspirin
  • Aspirin doesn’t inhibit endothelium COX1

Question 10

Ibuprofen and other NSAIDS

Answer 10

• Other NSAIDs don’t work for clotting because they are reversible

Question 11

Ticlid and Plavix

Answer 11

• Thienopyridines
• ADP receptor antagonists
• Prevent recuring DVT, strokes and intermittent claudication
• Plavix (clopidogrel)
  
  • Requires activation by CYP2C19
  • Low dose ASA + Plavix not more effective than ASA alone
  • Thrombocytic thrombocytopenia
• Ticlid (ticlopidine)
  
  • Safety? bleeds and hemorraging
• THM: Covalent/Irreversible

Question 12

newer ADP receptor antagonists

Answer 12

• Prasugrel (Effient)
  
  • Requires enzymatic activation
  • Noncompetitive antagonist at the P2Y12 purinergic receptor
• Ticagrelor (Brilinta)
  
  • Reversible allosteric agonist
• Better safety and efficacy when used in combo with ASA?

Question 13

Dipyridamole

Answer 13

• Dipyridamole (Persantin)
• Cilostazol, PDE3 inihibitor, approved for intermittent claudication
• Aggrenox
  
  • Dipyridamole with tartaric acid to solubilize
  • Sustained release pellets with ASA

Question 14

Factors on platelet surface involed in clot formation

Answer 14

• GpIa: receptor for collagen
• GpIb: receptor of VWF
• GpIIb-GpIIIa: integrin that binds fibrin

Question 15

ADP Receptor Antagonists: MOA and Example

Answer 15

• Block the ADP receptor from being activated by ADP→block platelet adhesion
  
  • Plavix (clopidegrel) falls into this category

Question 16

Clotting Cascade: Key Players

Answer 16

• Xa: converts prothrombin→thrombin
• IIa: thrombin; converts fibrinogen→fibrin
• XIIIa: transglutaminase enzyme that converts soluble fibrin to insoluable fibrin, the final step of the clotting cascade

Question 17

Direct vs. Indirect clotting cascade effectors: General MOA and examples

Answer 17

• Indirect Effectors:
  
  • Doesn’t directly effect coagulation cascade factors
  • Warfarin
• Direct Effectors:
  
  • Directly effects coagulation cascade factors
  • Antibodies
  • Heparin

Question 18

Warfarin Mechanism

Answer 18

• Indirect effector
• Vitamin K analog→binds and inhibits the recycling of factors that drive the ‘active’ prothrombin
• Very NTI
• Easily reversible with vitamin K

Question 19

Antibody Anticoagulants Mechanism

Answer 19

• Direct effectors
• Inhibit the enzymes in the cascade by preventing their action
• Ex: dabigatran blocks IIa in converting fibrin→fibrinogen
• Do not require a cofactor

Question 20

Heparin Mechansim

Answer 20

• Direct Effector
• Endogenous
• Form a complex with antithrombin III
• Act quickly
• Inhibts the actions of factor Xa and IIa (thrombin)
• LMW heparins can be more specific
• Reversal with protamine sulfate

Question 21

What is coagulation controlled physiologically by?

Answer 21

• Plasma Protease Inhibitors
  
  • inhibit many of the coagulation factors
• Protein C
  
  • active protease which drives fibrinolytic action
  • This is often a cause of bleeding following warfarin withdrawal

Question 22

How to dissolve a clot

Answer 22

• Thrombolytics/fibrinolytics
• Tissue plasminogen activator (tPA)
• Streptokinase
• Urokinase

Question 23

tPA Mechansim

Answer 23

• Is made by healthy endothelial tissues and converts plasminogen to plasmin (an active protease which drives the breakdown of insoluable fibrin clots)
  
  • Acts by having an increased affinity for fibrin-bound plasminogen (to activate it to fibrin)
• protease

Question 24

Streptokinase MOA

Answer 24

• Binds to plasminogen and the complex activates a second plasminogen molecule to active plasmin
• Direct binding activator

Question 25

Urokinase MOA

Answer 25

* Proteolytically activates plasminogen directly * A protease

Question 26

Apixaban and Rivaroxaban

Answer 26

Factor Xa

Question 27

Lepirudin

Answer 27

* Recombinant form of hirudin * From leach * Direct thrombin inhibitor

Question 28

Heparin and Fondaparinux

Answer 28

* Heparin pentasaccharide binds to anti-thrombin III * Accelerates interaction with Xa * When thrombin binds complex, needs tail to loop around to inhibit * Need to be at least 18 saccharide units (5400 Da) * Fondapurinux (1500 Da): LMWH heparin less likely to bind to ATIII:IIa and inhibit it * If only have the pentasaccharide, only acceleratie ATIII:Xa inhibition

Question 29

How are coagulation reaction limited?

Answer 29

* Endothelial health * PGI₂, EDRF * Plasma protease inhibitors: * Excess (anti-thrombin III) * Remember endothelium makes heparin * Thrombomodulin/Protein C: * Another endothelial/thrombin dependent pathway

Question 30

Thrombin/Thrombomodulin Model of Protein C Action

Answer 30

* Thrombin bound to thrombomodulin * endothelial surface * cleaves protein C to activated protein C * Cleaves factors Va and VIIIa to give inactive products→Anticoagulant activity * process is accelerated in the presence of protein S and platelets * Both protein C and protein S are GLA-containing proteins, are vitamin K-dependent, and are affected by warfarin. * Inactivates tPA inhibitor→increases tPA activity→fibrinolytic action * Protein C has most rapid turn over of any Ca²⁺ dependent proteases

Question 31

Clinical Significance of Thrombolytic Therapy

Answer 31

* 80% of MI never get thrombolytic treatment * Delivery is a big problem * Time to treatment is cruical for stroke * is it a hemorrhagic stroke? * needs to be within 3+ hours

Question 32

Lipoproteins: Why do we need to be concerned?

Answer 32

* High LDL cholestrol is poitvely associated with increased risk of coronary artery disease and death * Clog, break off, exposed phospholipid surface that starts coagulation rxn

Question 33

The order of cholesterol transport

Answer 33

* Gut: chylomicron→VLDL→LDL→IDL→HDL: Liver * Needed to transport and store chlesterol around the body * Very hydrophobic and wouldn't be able to move freely in body's water-based environment

Question 34

Chylomicrons

Answer 34

* Deliver triglycerides derived from dietary fat to non-hepatic tissues * Apolipoproteins: B48, CII and CIII * Act as cofactors for lipoprotein lipase and allow interaction with downstream molecules for dilevery to fat cells

Question 35

VLDL

Answer 35

* Deliver triglycerides derived from liver synthesis to non-hepatic tissues * Apolipoproteins: C, E, B100 * B100 is same gene as B48, but longer→allows for binding to LDL receptor

Question 36

LDL

Answer 36

* Derived from VLDL and deliver cholesterol derived from liver synthesis to various tissues * Apoliprotein B: * Has same B100 protein to bind LDL receptor

Question 37

HDL

Answer 37

* Collect (scavenge) cholesterol from non-hepatic tissues and deliver to the liver * ApoA-I and ApoA-II * Remove excess cholesterol from foam cells and transport to where they may be less toxic * Role is to remove 'free cholesterol' and convert to cholesterol esters and deliver to liver or steroidogenic tissue (uses SR-B1) * Cholesterol can be transferred to other lipoproteins by CETP * ApoC: cofactor with lipase to break down triglycerides

Question 38

What must be true about B100 for it to bind LDL receptor

Answer 38

* Must be oxidized

Question 39

Lp(A)

Answer 39

* Very artherogenic form of lipoprotein * More/longer coiled "pringles" make them more artherogenic * Form disulfide bond with B100 * Plaque promoting * Things that lower LDL also lower Lp(A) because half of Lp(A) is LDL

Question 40

Framingham Study

Answer 40

* High ration of HDL to total cholesterol is often protective * We now know not ALL forms of HDL are 'good' * We particularly want HDL3