To understand the significance of the plasma derived coagulation factors in treatment of bleeding orders it is important to first understand the normal coagulation cascade. There are 10 coagulation factors that are produced by the liver cells (hepatocytes) and released into the blood to regulate hemostasis or blood clotting. In some patients with hemophilia genetic mutations prevent the release of the coagulation factors by the hepatocytes into blood, making them unavailable for the clotting cascade . Under some instances the coagulation factors are not synthesized at all by the body. In some patients factors with structural defects rendering them physiologically non-functional are also produced.
The physiological function of the coagulation cascade is to allow the conversion of soluble fibrinogen to insoluble fibrin plug. The figure below explains the details of the platelet plug formation and the coagulation cascade.
In the absence of any coagulation factor in the cascade the normal physiological functions are inhibited. By supplementing deficiencies in these coagulation factors from plasma derived products the disease symptoms can be successfully alleviated. Following are some examples of purified coagulation factors that are used as part of the replacement therapy for patients with hereditary and acquired coagulopathies. Recombinant alternatives to human plasma derived coagulation factors are currently being used as the primary treatment modality for factor VIII and factor IX related deficiencies.
- Hemophilia A
- Hemophilia B
- Von Willebrand Disease
Factor VIII and VWF
Coagulation factor VIII, also known as Anti-Hemophilic factor (AHF) is normally present is very low amounts in human plasma (300 to 450 IU per litre of source plasma ). Therefore it takes upto 1200 donations per year to meet medical requirements for a patient with Hemophilia A.
During the fractionation process AHF is the first plasma protein product to be purified as part of the cryoprecipitate. Another protein that precipitates with the AHF is Von willebrand factor (VWF). In healthy individuals Factor VIII once released by the hepatocytes into circulation forms a complex with Von Willebrand Factor (VWF) . VWF is a natural stabilizer of factor VIII and prevents its degradation. Following the precipitation, viral inactivation and filtration steps are performed to generate a pure final product of factor VIII and VWF complex.
FVIII/VWF concentrates are currently used in type 3 VWD (Von willebrand factor deficiency) and in type 1 or 2 VWD patients who are unresponsive to desmopressin (DDAVP, stimulates release of VWF from endothelial cells) . Von Willebrand binds to sub endothelial collagen exposed on the site of injury, triggering the plateles to adhere which then form a plug with the fibrinogen produced by the coagulating cascade.
Purified and stable fractions of factor VIII without VWF are used in the treatment of Hemophilia A patients. When infused the plasma derived factor VIII forms a complex with the VWF in the patient’s blood. Upon activation, factor VIII with other factors allows the conversion of fibrinogen into insoluble fibrin plug to stop the bleeding in Hemophilia A patients.
Coagulation factor IX like other coagulation factors is produced by the liver cells and released into circulation in an inactive form. One litre of source plasma contains 180 to 200 IU of factor IX . Individuals with hemophilia B either express low or no factor IX or have genetic mutations that prevent its release into blood. They may even produce structurally deformed factor IX. Under all these instances factor IX fails to function normally and therefore activation of factor X and fibrin clot formation does not take place. In normal physiology, factor IX is activated through the intrinsic pathway and together with factor VIII initiates activation of factor X (see coagulation cascade).
During the fractionation process, factor IX is collected from the further processing of the cyro-poor plasma. The purified factor IX is infused into Hemophilia B deficient patients as part of the replacement therapy.
Prothrombin Complex Concentrate (PCC)
Other coagulation factors that precipitate together with factor IX are factor II, factor VII and factor X, together known as the prothrombin complex concentrate. The PCC also contain anticoagulation factors Protein C and S. Factor IX, II, VII and X are Vitamin-K dependent factors, vitamin-K activates these factors by adding a gamma carboxyl group. In the absence of vitamin-K these factors cannot participate in the coagulation cascade.
PCC is used for the treatment of acquired deficiencies of clotting factors. This most commonly occurs in individuals treated with anticoagulants (Warfarin, Coumadin) to prevent clot formation in the veins leading to organ damage. Warfarin inhibits activation of vitamin-K, which inturn results in inactivation of all vitamin-K dependent factors. Infusion with the PCC provides the patient with the necessary coagulation factors to regulate bleeding and to begin clot formation. Supplementation with vitamin K is also sufficient in some instances to overcome Warfarin induced coagulation factor deficiency.
- Lenting, P.J., van Mourik, J.A., Mertens, K.The life cycle of coagulation factor VIII in view of its structure and function.Blood. 1998 Dec 1;92(11):3983-96.
- Plasma Protein Therapeutics Association. Plasma Protein Therapy Manufacturing Fact Sheet
- Federici, A.B.The factor VIII/von Willebrand factor complex: basic and clinical issues.Haematologica. 2003 Jun;88(6):EREP02.
1.Endothelial cells lining the blood vessel
2.Site of Injury
3.The sub-endothelial collagen is exposed causing the VWF to bind to the collagen
4.VWF trigger the platelets to adhere to them, also known as platelet adhesion
5.Platelets expresses certain glycoprotein on the surface to aggregate other platelets to the site of injury (Platelet aggregation)
6.Platelets form a temporary plug with fibrinogen also known as the primary hemostatic plug
7. Platelets then trigger the coagulation cascade to convert fibrinogen into the insoluble and stable fibrin plug
1.Exposure of blood to collagen at the site of injury triggers activation of the intrinsic pathway, the first step is conversion of factor XII to its active form XIIa
2. Factor XIIa activates XI
3. Factor XIa activates Factor IX (also known as, Christmas Factor, Hemophilia B patients are deficient in factor IX)
4.Factor IXa together with activated Factor VIII (Hemophilia A patients are deficient in this factor) trigger the activation of Factor X
5.Factor Xa converts prothrombin (Factor II) to thrombin (Factor IIa)
6.Thrombin (Factor IIa) converts fibrin (Factor I) to fibrinogen (Factor Ia)
Thrombin also activates Factor XIII which when activated helps convert fibrin to fibrinogen (not shown)
7. Activation of the cascade can be triggered by extrinsic factors (not initiated by blood) such as release of Tissue Factor (TF) by damaged cells. TF triggers the activation of Factor VII.
8. Activated FactorVIIa triggers factor X which leads to conversion of fibrinogen to fibrin plug