Thrombolytic Therapies

Question 1

Define heaemostasis

Answer 1

Normal process in which our bodies control bleeding

Question 2

Define thrombosis

Answer 2

The clotting of blood that may become pathological if haemostasis is disregukated

Question 3

What four main factors does haemostasis and thrombosis depend on

Answer 3

Vascular wall integrity
Platlet response
Blood coagulation cascade
Fibrinolysis

Question 4

Main stages of maintenance of vascular wall

Answer 4

1. Injury or damage to the tissue
   Yhis may be due to a physical injury or through oxidative stress which could lead to chronic inflammation of the tissue.

2.blood vessels contract
When a tissue becomes damaged or injured , the blood vessels contract ti restrict and contain circulating blood to the injured site. Thus is known as vasoconstriction or vascular spasm

3. Formation of the platelet plug.
   Platelets become activated and aggregate at the site of injury. Here they bind to th endothelium to form a temporary platelet plug.
4. Formation of the fibrin clot.
   Platelet contain hugh levels of clotting factors that cleave fibrinogen into fibrin in order to strengthen the platelet plug. As a result blood coagulation occurs.

Question 5

What role does platelets play in the clotting of blood

Answer 5

Platelets secrete pro clotting factors which result in the blood coagulation cascade.
Furthermore platekts cause the aggregation of further platelets Leading to the formation of a temporary platelet plug.

Playwkts are derived from pro megakaryocytes that mature into megakaryocytes upon their activation.
Megakaryocytes adhere ti damaged blood vessels penetrating the wall with finger like projections call proplatelts which subsequently release platelets into the circulating blood

Too little - excessive bleeding

Too many - excessive clotting

Question 6

How is the platelet plug strengthened

Answer 6

A network of insoluble fibrin. Fibrin is formed by the cleavage of soluble fibrinogen into insoluble fibrin by the serine protease thrombin.

Question 7

Intrinsic pathway

Answer 7

Longer pathway.
Damaged surface of the endothelial becomes exposed revealing a collagen complex formed from kininogen and kallikrein.

Kininogen is a precursor of mining which are bio active peptides eg bradykinin an inflammatory mediator causing vasodilation.
Kallikriems are a family of Serine proteases
Both kallikrein and kininogen ctakyse the conversion of
Factor 12-12a
11-11a
9-91 and 10-10a
Known as a cascade of events

Question 8

Extrinsic pathway

Answer 8

Shorter in comparison.
When external damage occurs
Tissue factors are release which convert
7-7a
10-10a
Where the 2 pathways merge.

Question 9

Final common pathway

Answer 9

Meeges at factOr 10a leads to subsequent conversion
Prothrombin - thrombin
Fibriongen - fibrin
Leading to formation of cross link clot.

Question 10

Distinguish embolus v embolism

Answer 10

Embolus is a travelling clot
Whenever it becomes lodged it is known as an embolism

Question 11

Example of coagulation co factors

Answer 11

Tissue factor 8a and 5a

Question 12

How is coagulation cascade regulated

Answer 12

Through deactivators

Protein c Deactuvates tissue factor 8a and 5a
Antithrombin 3 Deactivates 12a 11a 10a 9a 7a and thrombin 2a
Tissue factor pathway inhibitor inactivates 7a and 10a
Plasmin deactivates fibrin

Question 13

Define Fibrinolysis

Answer 13

A normal bodily procedure that initiates the breakdown of clots. This occurs via activation of plasminogen into plasmin which is able to dissolve the fibrin clot.

Question 14

Outline the activation of plasminogen into plasmin

Answer 14

Plasminogen is deposited on fibrin strands. Plasminogen is cleaved by plasminogen activators
These activator cleave plasma gems activation loop at Arg 561- val 562. Val 562 now forms a salt bridge with asp 740 and results in a conformational change and hence activation of plasmin.
Fibrin is now cleaved into fibrin degradation products by plasmin.
Clot lysis occurs

Question 15

What therapeutic therapies can be taken to prevent blood clotting

Answer 15

Anti platelet therapies
Anti coagulant therapies
Fibrolytics and thrombolytic therapies

Question 16

Anti platelet therapies overview

Answer 16

Platekts are derived and hence aggregate upon factors such as Thromboxane , ADP, thrombin , serotonin and collagen. These factors activate GP IIb/IIa receptors leading to a conformational change in the structure of these receptors. As a result , fibrinogen is able to bind to the receptor and results in the binding or aggregation of many platekts.
There for anti platelet therapies have been aimed at preventing the synthesis of GP IIb/IIa antagonists

Question 17

Types of anti platelet therapies

Answer 17

Thromboxane synthesis inhibitors
ADP inhibitors
GP IIb/ IIa antagonists

Question 18

Thromboxane synthesis inhibitors

Answer 18

TXA2 is formed as a result of the arachidonic acid metabolism during inflammation. The enzyme COX1 is responsible for the formation of TXA2.
THEREFORE , COX1 inhibitors would result in the inhibition of TXA2 synthesis . Aspirin is and examoke of a cox 1 enzyme inhibitors.

Question 19

ADP inhibitors

Answer 19

Eg clopidogrel

Question 20

GP IIb/IIa antagonists

Answer 20

Blocking GP IIb/IIa receptors from accepting fibrinogen will prevent the aggregation of platekts. This group of antagonist are usually delivered iv with heparin and aspirin eg abcixmab

Question 21

Anti coagulant therapies overview

Answer 21

Target coagulation cascade of events

Question 22

Types of anti coagulant therapies

Answer 22

Direct thrombin inhibitors
Indirect thrombin inhibitors
Vit k reductase inhibitors

Question 23

Indirect thrombin inhibitors

Answer 23

Target 10a and the subsequent cascade of the final pathway. Eg apixaban

Question 24

Direct thrombin inhibitors

Answer 24

Directly bind to thrombin either univalentky or bivalently at the active site or active site and exosite
Bivalent thrombin inhibitors have a higher affinity and specificity for thrombin over univalent inhibitors
Eg hirudin

Question 25

Vit k reductase inhibitors

Answer 25

Vit k is required for the activation of cofactors along the coagulation cascade. These factors are inactive until carboxylated by Vit k As a result Vit k is oxidised and requires reduction by Vit k reductase to continue the CC Abscence of Vit k reductase prevents the CC from occurring Eg warfarin

Question 26

Types of thrombolytic therapies

Answer 26

Streptokinase Urokinase plasminogen activator uPA Prourokinase APSAC

Question 27

Streptokinase

Answer 27

It was found that streptococcus aggregated to from clumps of plasma and that it could subsequently dissolve clots. The protein streptokinase was isolated and purified and eventually used for treatment for MI, DVT etc Cheap to produce and good patient response however risk of allergy so rarely used. It was initially thought that SK causes direct degration of fibrin by dissolving the blood clot. In contrast , it has an indirect role Plasminogen upon binding to SK becomes activated into plasmin due to a conformational change , Plasmin can bid dissolve the fibrin clot. No cleavage in the activation loop of plasminigen occurs.

Question 28

Urokinase plasminogen activator

Answer 28

Follow discovery of SK, uPA was found to be synthesised in the kidneys and so was found preodominatejt in the urine but also in the blood. The Serine protease uPA , Cleaves the arg-val bond.

Question 29

Prourokinase

Answer 29

2nd gen drug formed from uPA acts as a prodrug. Inactivate protein that becomes activated into uPA upon the presence of plasmin or kallikrein

Question 30

APSAC

Answer 30

formed from human plasminogen and SK complexed together. SK in this form is acelyated to protect the active site from degradation However upon administration SK is deaceylated and frees the plasminogen SK complex for activation of plasmin It is used for rapid IV treatment and offers great clot selectivity on plasminogen associated clots and more thrombolytic activity