Hemostasis II Flashcards
Thrombin activity is determined by __ and __
activation and inactivation
Name the Inhibitors of the coagulation cascade in each color
R: B, Serpins
G: A, non Serpins
B: C, TM- protein C system
What is the inhibitor type of A, non-serpins?
Kunitz-type inhibitor:
Describe structure of A, non-serpins inhibitor?
red: AAs which fit into the active site of the protease
Enzyme-Inhibitor Complex: reversible, Key-lock-model-
No conformational change
An example of non-serpins inhibitor?
TFPI is such an inhibitor
The role of Tissue Factor Pathway Inhibitor (TFPI)
1/ Inhibits the initiation of the cascade
2/ The only inhibitor which can also inhibit membrane-bound proteases
Kunitz-type Inhibitor, released from __ and ___
endothelial cells and platelets
Kunitz-type Inhibitor is reversible
-> There are ionic interactions between __ and __
the Kunitz-Domains (K) and the proteases
Kunitz-type Inhibitor
-> The role of Protein-S-binding
Protein S-binding enhances FXa-binding, which enhances FVIIa-binding, and both FXa and FVIIa will be inactivated in the TF/FVIIa/FXa-Complex
Does Kunitz-type Inhibitor have a high or low affinity?
HIGH
Kunitz-type Inhibitor is present in low or high concentration?
LOW CONCENTRATION
A, non-Serpins, No2: a2-Macroglobulin stericly hinders protease activity
-> Structural features?
-inhibits thrombin, plasmin, kallikrein
What are Serpins?
Serine-protease-Inhibitors
The role of Serpins
regulate many Ser-Proteases, and thereby many processes: Hemostasis, digestion, complement system- inflammation, ECM remodelling in embryonal development, cancer metastasis, tissue repair, apoptosis
Serpins cause reversible or irreversible inhibition.
-> Why?
Irreversible inhibition: enzyme cleaves the inhibitor, just like a substrate, but the hydrolysis of the acyl-enzyme intermediate is rather slow (weeks…)- irreversible
The role of Serpins in hemostasis:
Antithrombin – Thrombin, (FXa, (FIXa)) – target of heparin therapy Heparin cofactor II – Thrombin
a1-Protease Inhibitor – Trypsin, elastase, thrombin
3 steps of The TM-protein C-pathway
1, thrombomodulin (TM) on the surface of healthy endothelial cells
2, Thrombin binds to TM-via exosite I – specificity of thrombin changes: cleaves Protein C to activated Protein C (APC), instead of the other substrates
3, APC inactivates Va and VIIIa to Vi and VIIIi
What is the most important endogenous anticoagulant mechanism?
Membrane-bound enzyme complexes in hemostasis
-> The TM-protein C-pathway
Symtomps of Deep venous thrombosis/DVT
Most frequently in the legs,
-swelling, blocked venous blood flow
-lung emboli
– severe complication multifactorial
-Virchow-Triad
What is Virchow-Triad?
1, enhanced blood clottability,
2, disturbed blood flow,
3, endothelial cell damage
Anticoagulants applied in DVT
-> What are Anticoagulants for indirect inhibition?
Heparins: UFH, LMWH, fondaparinux
Vitamin K-antagonists (VKA):
Anticoagulants applied in DVT
-> What are Anticoagulants for Direct inhibition?
- Hirudin et al: block the active site of thrombin
- DOAC/(NOAC): direct/(novel) oral anticoagulants
Anticoagulants applied in DVT
-> What is the role of Heparins: UFH, LMWH, fondaparinux?
Work with Antithrombin together, accelerate the inactivation of thrombin by antithrombin
Anticoagulants applied in DVT
-> What is the role of Vitamin K-antagonists (VKA)?
Inhibit the formation of Gla-domains, and thereby the assembly of membrane- bound activation complexes – slower thrombin generation
What is Heparin?
a sulfated glucosaminoglycan
How does Heparin work?
Heparin binds both thrombin and antithrombin and accelerates the inactivation of thrombin by antithrombin (4000X!).
At the end of the reaction is heparin regenerated, so it is a catalysator
What is the minimal motif for heparin action?
Pentasaccharide
UFH (unfractionated heparin) isolated from ___
porcine intestinal mucosa
What are problems of UFH (unfractionated heparin)?
UFH is heterogenous, varying efficiency and elimination rate, and of animal origin - immunogenic
What are some derivatives of heparin
What is the Target of the vitamin K antagonists?
Vitamin K-oxidoreductase
What are Pitfals of the vit K-antagonists?
Drug interactions, diet-dependent (Vit-K-content). Individual elimination rate
Contraindicated in pregnancy, because it could interfere with fetal bone development
How can the vit K-antagonists act on gene expression?
- Slow turn-on (days)
- Slow turn-off (days) – factors must be re-synthesized
Molecular signs of “coumarin-necrosis”?
Protein C and S fall out first
(life-time: 8-24 h vs Prothrombin: 3-5 days)
- Transient prothrombotic state – heparin should be given first, followed by the VKAs
What is Hirudin?
Direct Thrombin-inhibitors
Characteristics of Direct Thrombin-inhibitors I. Hirudin
Binds like heparin+antithrombin
“too effective” – bleeding is frequent
Characteristics of Direct Thrombin-, and Xa - inhibitors II.
(DOAC: direct oral Anticoagulants:)
-per os (tablets), small reversible inhibitors blocking the active site -quick, short-lived, Antidotum exists,
- No need for regular monitoring
-bleeding frequency is ca 1/3 of the VKAs
-much more expensive, than VKA
Symptoms of Hemophilia
Unexplained and excessive bleeding from cuts or injuries, or after surgery or dental work.
Many large or deep bruises.
Hemophilia
-> Why do they bleed?
Amplification of thrombin generation falls out
