Basic Science of Platelets and Coagulation Factors Flashcards
Von Willibrand Factor
• Tertiary Structure
• Alterations needed for a functional protein
• Binding sites
vWF
Tertiary Structure:
• Very Long Linear Multimer of Homodimers
Alterations
• These MUST be trimmed to the optimal length
• BINDING TO COLLAGEN ALTERS THE TERTIARY STRUCTURE TO EXPOSE MORE PLATELET BINDING SITES
Binding Sites
• Collagen
• Platelet Gp1b
• Factor VIII
What is the relationship between vWF and factor VIII?
Von Willibrand Factor Stabilizes it
What proteins are involved in platelet BINDING?
- Gp1b binds vWF
* GPIa/IIa binds collagen
What is secreted by platelets on ACTIVATION?
• TXA2
• ADP
• Including Ca2+
**Factor 5, fibrinOGEN
What proteins allow for platelet aggregation?
• ACTIVATION of GpIIb/IIIa which binds fibrinOGEN
In general how does a protease act on a pro-enzyme and co-factor to AMPLIFY each step of the cascade?
Pro-enzyme and cofactor are EACH acted on by the Protease and combine to form an ACTIVE Protease:Cofactor product
• Many of this Protease:Cofactor product will be made and Each of these will initiate another step by acting on Pro-enzyme2 and cofactor2 (so forth and so on)
how does calcium act to activate factor VII and other proteases?
- Ca2+ binds Negative residues and and puts more charge around hydrophobic residues on the inside of the protein
- Hydrophobic residues move to the exterior to avoid the charge and hang down allowing them to interact with hydrophobic residues in the membrane
***Ca2+ putting + charge where the negative charge once was also allows for favorable electrostatic interactions with the exterior of the cells
T or F: the conformational change created by Ca2+ binding is important for enzyme ACTIVATION only.
False, it IS needed for ACTIVATION but it is also needed to flip out hydrophobic residues so that it can anchor into the membrane
What is the importance of Vit. K in blood coagulation?
• SPECIFICALLY, what factors is this important to?
- Vit. K is needed in gamma-carboxylation of AA residues so that they become bi-dentate and can bind divalent Ca2+
- NEEDED FOR: Factors II, VII, IX, X
What is the INITIAL job of thrombin (factor II) in the coagulation cascade?
• What does it do later?
• activated thrombin (IIa) catalyzes 2 rxns
- VIII to VIIIa
- IX to IXa
at this point Thrombin is localized to the endothelial cell surface so it does NOT yet cleave fibrinogen to fibrin
What activates the intrisic pathway?
• how is this done?
Activated Thrombin (IIa) Kicks of the intrinsic cascade through catalysis of 2 rxns that lead to the formation of TENASE (VIIIa/IXa)
What is the importance of Factor IXa being able to “swim?”
it can diffuse from the damaged endothelial surface to the site where there is more substrate (aka Factor 10)
T or F: Activated thrombin (IIa) ACCELERATES and FINALIZES the process of fibrin generation
True
What 5 rxns are catalyzed by thrombin?
Factor VIII activation Factor IX activation Factor V activation (Propagation phase only) Fibrinogen ----> Fibrin Factor XIII activation
What does Antithrombin inactivate?
• Where is it produced?
• Where does it typically exist?
Antithrombin inactivates Thrombin (IIa) as well as factor Xa
- Produced by the Liver
- Typically exists in Plasma
How does thrombomodulin work?
• Where is typically found?
Co-Factor for thrombin FOUND ON NORMAL EPITHELIAL cells that MODULATES thrombin activity to Activate Protein C
How does protein C work?
• what pathways does it work on?
• How so?
Protein C is activated by Thombin:Thombomodulin and combines with protein S to make APC:S which INACTIVATES Factor VIIIa and Factor Va
What protein works to break down Cross-Linked Fibrin and Limit the extent of the clot to damage area only?
• Where is the protein made?
• How is it activated?
• How does the clot stay local?
- Plasmin breaks down the clot, its precursor PLASMINOGEN circulates normally in the blood.
- Plasminogen is activated to Plasmin by t-PA (tissue plasminogen activator)
- t-PA is found on NORMAL-UNDAMAGED epithelial cells, thus fibrin is broken down only in that region
What does the PT measure?
• How is the assay performed?
• What specifically is being measured?
• Factors involved?
• How long it takes the Plasma to form Fibrin
How its performed:
• “Prothrombin” - a mixture of Ca2+, Phospholipids, and Tissue Factor (TF) are mixed with Pts. blood and time to clot is measured
Pathways measured:
• Extrinsic and Common Pathways
What drugs is the PT test particularly sensitive to? why?
• Factors measured?
• Why include calcium?
Sensitive to:
Warfarin —> because warfarin is a gamma carboxylation antagonist that works by acting on Vit. K
Factors measured (all the Vit. K factors except IX):
• Factor VII (MAINLY) - b/c it has fastest turnover rate of all Vit. K dep. factors
• Factor II
• Factor V
• Factor X
What does the PTT assay measure?
• Pathway, Factors?
Measures time it takes the EXTRINSIC pathway to create a clot
• Factor IIa
• Factor VIIIa
• Factor IXa
**These are the primary factors that are measured
What reagent is added to perform the PTT assay?
Activated Partial Thromboplastin:
• Ground Glass
• Phospholipids
• Ca2+
T or F: Factors XII and VII play huge roles in the coagulation cascade in vivo and thats why we measure them using PTT and PT respectively.
False, in vivo these proteins just kick of the cascades
What happens when there are defects in the actual structure of the vWF homo dimers?
• what disorder occurs as a result?
• Inherited?
Von Willibrand’s Disease
• Bleeding Disorder
• Autosomal Dominant
What drugs upregulates circulating vWF AND Factor VIII?
DDAVP
What disorders occur as a result of failure to cleave vWF?
• what type of disorders are these?
Thrombophilia disorders
TTP (thrombotic thrombocytopenia purpura)
HUS (hemolytic uremic syndrome)
What causes the subtypes of Von Willibrand’s disease?
Defects in:
• Gp1b - Bernard-Soulier Syndrome (RARE)
• Factor VIII
What causes Bernard-Soullier?
• compare frequency of cases compared to von Willibrand’s disease.
• Inherited?
Defects in Gp1b
- Much more rare than von Willibrand’s Disease
- Yes, inherited (mode not stated)
What drug blocks the receptor for ADP?
• Irreversible or Reversible?
Clopidogrel
• IRREVERSIBLE
What disease results from inability to activate GpIIb/IIIa?
• Drugs are used to induce a similar state?
Glanzmann’s Thrombasthenia (rare bleeding disorder)
Used at Drug Target for:
• abciximab
• eptifibatide
• tirofiban
What disease result from defects in factors VIII and IX?
Hemophilia A (VIII) Hemophilia B (IX)
What drugs act as direct factor Xa inhibitors?
- Apixaban
* Rivaroxaban
What drugs act as direct thrombin (II) inhibitors?
- Dabigatran
* Hirudin
Which test would you want to use to see if the coumadin you gave is working? why?
• How does this drug work?
PT
• It measures the EXTRINSIC pathway that is kicked off by Factor VII
• Factor VII is vit. K dependent (as are II, IX, X), BUT it is the fastest protein to be turned over so it is the 1st factor to show affect
Coumadin = Warfarin
• Both inhibit Vit. K dependent gamma carboxylation
How does heparin work?
Heparin (high or low MW) activates Antithrombin just like Heparin-Like Molecules do in nature
**antithrombin will just go on to block IIa (thrombin) from converting fibrinogen to fibrin
What are some defects involving Protein C that you should be aware of?
• state whether each of these conditions are inherited or not?
ALL are inherited PROTHROMBOTIC conditions
• Protein C deficiency
• Protein S deficiency
• Factor V leiden (APC resistant)
What test would you use to test for Hemophilia A?
• would this work for hemophilia B?
PTT because it measures the extrinsic pathway
- The intrinsic pathways involves factors XII, XI, IX, and VIII
- Factors 8 and 9 are involved in hemophilia A and B so PTT is a useful test here
In addition to being used to test for Hemophilia A and B. What drug is the PTT useful for measuring the effectiveness of?
PTT good at measuring Heparin effectivness because Heparin activates thrombomodulin which inactivates thrombin (IIa)
**Note: PTT is good for measure COMMON and INTRINSIC pathways
