Factor VIII function

Von Willebrand factor (VWF) is a large multimeric glycoprotein with two main functions in hemostasis to aid the platelet adhesion to injured blood vessel walls and to carry and stabilize factor VIII in plasma. Table 64—4 represents three main vWD phenotypes, their frequency, and genetic transmission.17... 

A 2B 2M 2N Type 3 vWD Decreased platelet-dependent vWF function owing to lack of larger multime rs Increased platelet-dependent vWF function owing to lack of larger multime rs Defective platelet-dependent vWF functions not associated with multimer defects Defective vWF binding to factor VIII Severe quantitative deficiency of vWF 1 %-5% Autosomal recessive... 

Most patients with type 1 vWD (functionally normal vWF) and a minor bleeding episode can be treated successfully with desmopressin, which induces secretion of autologous factor VIII and vWF into plasma. The recommended dose is the same as that used to treat mild factor VIII deficiency (0.3 mcg/kg intravenously in 50 mL of normal saline infused over 15 to 30 minutes). This therapy generally is ineffective in type 2A patients who secrete qualitatively abnormal vWF and is controversial in type 2B patients because it may increase the risk of postinfusion thrombocytopenia. Type 3 vWD patients who lack releasable stores of vWF do not respond to DDAVP therapy.18... 

Many small proteins, in particular those that function extracellularly (e.g. insulin, GH and various cytokines) are quite stable and may be fractionated on a variety of HPLC columns without significant denaturation or decrease in bioactivity. Preparative HPLC is used in industrial-scale purification of insulin and of IL2. In contrast, many larger proteins (e.g. blood factor VIII) are relatively labile, and loss of activity due to protein denaturation may be observed upon high-pressure fractionation. 

Fig. 3.3.1. Electrical resistance as a function of temperature. Upper excipient solution lower solution with factor VIII. Cooling rate 15 °C/min. Measurements for [3.23], not published.

Therapy is determined by the level of factor VIII deficiency. Severely affected patients have concentrations less than 1 %, in moderate disease this is present between 1 and 5 % whereas plasma levels between 5 and 30 % may be associated with bleeding only after trauma such as dental extraction. Additionally, the choice of replacement is modified by the site of bleeding and the presence or absence of inhibitors that interfere with the function of the factor. Cryoprecipitate or lyophilised concentrate is becom-... 

Fig. 3.2. Schematic of recombinant AAV dual-vector strategies for gene therapy for hemophilia A. (A) depicts the individual expression of the 5 and 3 ends of the factor VIII protein followed by heterodimerization to generate a function protein. (B) shows concatamerized 5 and 3 vectors in the correct head-to-tail orientation. Splicing of vectors to remove the intron and inverted terminal repeats leads to expression of the entire factor VIII protein from a single mature mRNA transcript. ITR, AAV inverted terminal repeat SD, splice donor SA, splice acceptor An, poly A.

Gnatenko, D. V., Saenko, E. L., Jesty, J., Cao, L. X., Hearing, P. and Bahou, W. F. (1999). Human factor VIII can be packaged and functionally expressed in an adeno-associated virus background Applicability to haemophilia A gene therapy. Br. J. Haematol. 104, 27-36. 

Finally, the common pathway involves thrombin in a number of functions. Its primary role is the conversion of fibrinogen to fibrin, the building block of a haemostatic plug. In addition, it activates factors VIII and V and their inhibitor protein C (in the presence of thrombomoduhn), and it activates factor XIII, which cross-links the fibrin polymers. 

The functions of the above three classes of proteins are directly related to the protein-bound copper ions. In those cases where functions have been unequivocally established, they are either electron storage and transfer or redox catalysis. Representative proteins from each of the above-mentioned classes have been purified directly from their natural sources and extensively characterized both structurally and biophysically. In addition, there are well-established protocols for their expression and purification from different heterologous systems. [Factor VIII is a special case for which blue copper binding has not been experimentally demonstrated, although at least two such sites can be identified in its amino acid sequence (Section VIII).]... 

Quick s value A drop in the coagulation factors II, V, Vn, IX and X is a reliable indicator of the still remaining liver function. Factor VIII increases. With massive liver cell destruction, a dangerous decrease in factors V and VII is witnessed within 1 or 2 days (corresponding to the half-life of the factors) together with a reduction in Quick s value and Colombi s index (<60 - 80%). (45, 47, 71) (s. p. 105)... 

The question of the required number of hepatocytes has stiU not been resolved the collapse of a certain liver function (e. g. normalization of factor VIII values in serum) can be compensated by a far lower number of hepatocytes than is the case with total liver failure (e. g. acute liver failure). Calculations made up to now have claimed that there are at least 10 —10 liver cells in partially resected liver parenchyma. 

Tagliavaoca, L., Moon, N-, Dunham, W and Kaufman, R. (1997). Identication and functional ret uirement of Cu(l) and its ligands within coagulation factor VIII. /. Bioi. Chem. 272, 27428-27434. 

There has been some concern about the possible effects of factor VIII formulations on the immune system. In vitro experiments with coagulation factor concentrates have shown immunosuppressive effects (16,17), such as the impairment of Fc receptor-mediated phagocytosis and intracellular bacterial killing (18). Inhibition of IL-2 production, an impaired MLR, and impairment of PHA transformation have been demonstrated (19). A fall in the number of T4 lymphocytes has also been found. Whether these findings reflect functional impairment of the immune system is still unclear. 

If the modulation of certain immune functions is in fact due to contaminating components in the preparations, one would expect the new generation of factor VIII preparations of very high purity to behave differently. Highly purified factor VIII with a specific activity of 100-150 U/mg protein is now available, as is factor VIII purified by immunoaffinity chromatography using mouse monoclonal antibodies. 

Mannhalter JW, Ahmad R, Leibl H, Gottlicher J, Wolf HM, Eibl MM. Comparable modulation of human monocyte functions by commercial factor VIII concentrates of varying purity. Blood 1988 71(6) 1662-8. 

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