Correction of the platelet abnormality in von Willebrand's disease by cryoprecipitate

Treatment of inherited coagulation disorders

Inherited coagulation protein deficiencies associated with bleeding diatheses may present with spontaneous bleeding early in life, or may not be recognized until the development of hemorrhage after trauma or surgery. Diagnostic evaluation with coagulation screening tests, followed by confirmation with coagulation factor assays, is essential for appropriate management. For moderate-to-severe hemophilia, treatment includes coagulation factor replacement with purified, plasma-derived coagulation factor, or in the case of hemophilia A, factor VIII concentrate produced with recombinant techniques. Increased use of pharmacologic agents such as desmopressin acetate for patients with mild hemophilia A or type 1 von Willebrand's disease has allowed physicians to treat patients without the risk of infectious complications from plasma-derived factor concentrates. In addition to the management of the inherited bleeding disorders, patients may also require management of human immunodeficiency virus infection, hepatitis, and coagulation factor inhibitors. Issues for the coming years will include continued work to ensure product safety, the role of prophylactic treatment to prevent longterm disabilities, and the application of gene therapy to the management of bleeding disorders.

Platelet function and immunologic parameters in von Willebrand's disease following cryoprecipitate and factor VIII concentrate infusion

Results of functional and immunologic tests of factor VIII and of platelet function were followed in two patients with severe von Willebrand's disease who were given cryoprecipitate during preparation for surgery. Initial correction of factor VIII coagulant activity was found to persist from 48 to 72 hours. Correction of immunologically measured factor VIII persisted for 48 hours and correlated with the patients' platelet response to ristocetin aggregation. Bleeding times were corrected for only 6 to 8 hours and showed fairly good correlation with the ristocetin aggregation factor, as suggested by Weiss. The administration of commercial factor VIII concentrate corrected all parameters except the bleeding time and the ristocetin aggregation factor measurement.

Infusion of human and canine factor VIII in dogs with von Willebrand's disease: studies of the von Willebrand and factor VIII synthesis stimulating factors

Dogs with von Willebrand's disease (VWD) were infused with a highly purified human and canine factor VIII preparation. Control infusions were performed using isotonic saline solution. Following all of the concentrate infusions, the bleeding times were shortened to within the normal range for up to 4 h. Factor VIII activity rose immediately after infusion, rapidly returned to preinfusion levels, and then increased again at 18 h. The levels of factor VIII-related antigen (F VIII-RA) as measured with anticanine factor VIII also increased after infusion and then gradually declined. There was no further increase in F VIII-RA at 18 h, when the factor VIII activity showed the secondary increase characteristic of VWD. With antihuman factor VIII, two identifiable antigens were present in the plasma of the dogs given human factor VIII. The reduced platelet retention of these animals was not significantly altered following infusion, whereas ristocetin-induced platelet aggregation was corrected in one of the dogs given human factor VIII. These studies indicate that factor VIII procoagulalant and von Willebrand factor activities reside on a single molecule or form part of a molecular complex. In addition, the factor VIII preparations appeared to contain the factor VIII synthesis-stimulating factor and/or a precursor of factor VIII procoagulant activity.

Synthesis of von Willebrand factor by cultured human endothelial cells

Cultured human endothelial cells synthesize and secrete a protein(s) which has Factor VIII antigen but which lacks Factor VIII clot-promoting activity (J. Clin. Invest. 52, 2757-2764, 1973). Von Willebrand factor activity has been identified in medium from cultured human endothelial cells. This activity was demonstrated by the ability to correct the defect in platelet adhesiveness of blood obtained from patients with von Willebrand's disease. This activity also supported ristocetin-induced aggregation of washed normal human platelets. The von Willebrand factor activity from cultured endothelial cells has physicochemical and immunologic properties like those of the von Willebrand factor activity and the Factor VIII antigen present in human plasma and the Factor VIII antigen synthesized by human endothelial cells in vitro. Rabbit antibody to chromatographic fractions containing endothelial cell von Willebrand factor inhibits the platelet retention of normal blood in glass bead columns.

Antihemophilic factor antigen. Localization in endothelial cells by immunofluorescent microscopy

The tissue localization of antihemophilic factor (AHF, Factor VIII) has been determined by immunofluorescent studies using monospecific rabbit antibody to human AHF. Specific staining demonstrating AHF antigens has been identified in endothelial cells of a wide range of human tissues. The staining pattern was observed in endothelial cells of arteries, capillaries, and veins as well as the cells lining hepatic and splenic sinusoids. Specific fluorescence was limited to these endothelial cells in sections of kidney, liver, spleen, lymph node, cardiac and smooth muscle, thyroid, umbilical cord, and skin. Absorption studies established that the staining was specific for cells in which there were proteins that had AHF antigens. The demonstration of fluorescence within the cytoplasm of endothelial cells suggests that these cells synthesize proteins that have AHF antigens.

Defective ristocetin-induced platelet aggregation in von Willebrand's disease and its correction by factor VIII

The antibiotic ristocetin, in concentrations of 1.0-1.5 mg/ml, aggregated normal platelets in citrated platelet-rich plasma by a mechanism in which the release reaction played only a minor role. Platelet aggregation by ristocetin in a concentration of 1.2 mg/ml was absent or markedly decreased in 10 patients with von Willebrand's disease. Lesser degrees of abnormality were obtained with a concentration of 1.5 mg/ml. The magnitude of the defect in ristocetin-induced platelet aggregation correlated well with the degree of abnormality of the bleeding time and the levels of antihemophilic factor (AHF, VIII(AHF)) procoagulant activity. In all patients, the defect in ristocetin-induced platelet aggregation was corrected in vitro by normal plasma. Correction was also obtained with a fraction of normal cryoprecipitate that eluted in the void volume with VIII(AHF) after chromatography on a gel that excludes molecules larger than 5 x 10(6). A similar fraction, devoid of VIII(AHF) activity, obtained from patients with von Willebrand's disease had no corrective effect, but fractions obtained from patients with hemophilia were just as effective as those obtained from normal subjects. The correction activity of plasma and partially purified factor VIII was inhibited by a rabbit antibody to human factor VIII but not by a human antibody against VIII(AHF) procoagulant activity. The studies provide further evidence that patients with von Willebrand's disease are deficient in a plasma factor that is necessary for normal platelet function. The activity of this factor appears to be associated with factor VIII but is unrelated to VIII(AHF) procoagulant activity.

Quantitative assay of a plasma factor deficient in von Willebrand's disease that is necessary for platelet aggregation. Relationship to factor VIII procoagulant activity and antigen content

In a previous paper, we showed that the abnormality of ristocetin-induced platelet aggregation in platelet-rich plasma in 10 patients with von Willebrand's disease could be corrected by a factor in normal plasma that was present in the same fractions as factor VIII procoagulant activity (antihemophilic factor, AHF, VIII(AHF)) when prepared by chromatography on Bio-Gel 5 M (Bio-Rad Laboratories, Richmond, Calif.). This observation suggests that patients with this disorder are deficient in a plasma factor, associated with the factor VIII molecule, that is necessary for normal platelet function. In the present paper, we describe, an assay for this factor, the von Willebrand factor (VIII(VWF)), based on the observation that a log-log relationship exists between the amount of ristocetin-induced aggregation of washed, normal platelets and the concentration of normal plasma present in the test system. We assayed the activity of VIII(VWF) as well as antihemophilic factor procoagulant activity (VIII(AHF)) and factor VIII antigen (VIII(AGN)) in 15 patients with von Willebrand's disease and 20 normal subjects. A highly significant correlation (r approximately 0.80) between VIII(VWF) and both VIII(AHF) was found in normal subjects and in patients with von Willebrand's disease. This finding, in addition to the observation that agarose gel chromatography fractions that have VIII(AHF) procoagulant activity also have VIII(VWF) activity, strongly suggests that the von Willebrand factor is associated with the factor VIII molecule. VIII(VWF) in normal plasma was not inhibited by human anti-VIII, and VIII(VWF) levels were normal in hemophilic plasma. Thus, the VIII(VWF) site on the factor VIII molecule appears to be different from that determining VIII(AHF). Finally, the activity of VIII(VWF) appeared to correlate better with the bleeding time than either VIII(AHF) or VIII(AGN). This suggests that VIII(VWF) assayed in this study may be the "anti-bleeding factor" that is deficient in von Willebrand's disease. These findings are consistent with a decreased synthesis of the factor VIII molecule in von Willebrand's disease and suggest the possibility of additional abnormalities of the site on the molecule that determines the activity of VIII(VWF).

Factor VIII coagulant activity and factor VIII-like antigen: independent molecular entities

Factor VIII coagulant activity (VIII(C)) and the von Willebrand's disease antigen (Factor VIII-like antigen, vW-Ag) are biologically linked, and it has been suggested that they reside on the same molecule. However, insolubilized human isoantibody to VIII(C) and rabbit antiserum containing antibodies to VIII(C) and vW-Ag differentially bind and remove these entities from plasma, thus physically segregating one from the other. These findings indicate that Factor VIII coagulant activity resides on a molecule distinct from that expressing the von Willebrand's antigen.