Factor VIII antigen in the vessel walls in von Willebrand's disease and haemophilia A

von Willebrand factor is present in the vascular endothelium from normal dogs and from Doberman pinscher dogs with a plasma von Willebrand factor deficiency

An immunohistochemical study was undertaken to determine the presence and distribution of von Willebrand factor antigen (vWf:Ag) in blood vessels from normal dogs and from Doberman pinscher dogs with a marked plasma deficiency of vWf. vWf:Ag could not be detected in plasma from the Doberman pinscher dogs by ristocetin- and botrocetin-induced platelet agglutination or by EIA. An ELISA assay revealed vWf:Ag levels that were between 2-4% of that in normal canine plasma. Factor VIII:C activity was 30-46% of normal. The activated partial thromboplastin time (APTT) was increased but not the one-stage prothrombin time (OSPT). Four different antibody preparations were used in this study to detect vWf--a monoclonal and a polyclonal antibody prepared against human vWf and 2 polyclonal antibodies against canine vWf. vWf:Ag was detected with monospecific antibody in endothelial cells in veins, venules, and arterioles from normal dogs and vWf-deficient dogs. The histofluorescence observed in vessels of vWf-deficient dogs was indistinguishable from that observed in vessels from normal dogs.

von Willebrand disease

von Willebrand disease (vWD) is a bleeding disorder characterized by a complex hemostatic defect. Abnormal platelet function, usually reflected by a prolonged bleeding time, is the result of a quantitative or qualitative defect of von Willebrand factor (vWF). A secondary deficiency of factor VIII procoagulant protein (factor VIII) may occur leading to a coagulation defect as well. These two glycoprotein macromolecules circulate as a complex in plasma. This article will review current understanding of structures and functions of vWF factor and factor VIII as they relate to the pathogenesis, diagnosis, classification and therapy of vWD.

Formation and regulation of platelet and fibrin hemostatic plug

Formation of a hemostatic plug represents one of the earliest responses to vessel wall injury. Platelets react to any discontinuity in the vascular endothelium through initial contact, spreading, and formation of a thrombus (or aggregate). This development of a primary hemostatic plug requires platelet membrane receptors through which the adhesive macromolecules, von Willebrand factor (vWF) and fibrinogen, anchor platelets to the vessel wall and link them to each other. There are two receptor pathways--classic and alternative--for the binding of vWF to platelets; the latter induced by thrombin, and adenosine diphosphate (ADP) is shared with fibrinogen. Synthetic peptides, patterned after known binding domains of adhesive molecules, have been designed to inhibit their interactions with platelet receptors. A secondary hemostatic plug, composed of platelets enmeshed in fibrin, results from the action of thrombin, which is not only essential for formation of fibrin but also for exposure of platelet receptors for adhesive molecules and for "activation" of factors V and VIII. Thrombin generation is greatly enhanced through the activity of the prothrombinase complex formed on the surface of platelets, perturbed endothelial cells, and leukocytes. A pivotal event is activation of factor X through the intrinsic and extrinsic coagulation pathways. Binding of factors IXa and VIIa to the vascular endothelium represents a localized mechanism for factor Xa generation. Formation of a platelet and fibrin thrombus is controlled by regulatory mechanism: prostacyclin, endogenous heparin-antithrombin III complex, thrombomodulin-protein C-protein S system, and the fibrinolytic system. The balance of all components--vessel wall, platelets, adhesive and coagulation proteins, regulatory mechanisms--determines the effectiveness of the hemostatic plug in maintaining the structural and functional integrity of the circulatory system. An approach to detection of hemostatic derangements in patients at risk evolves from a full understanding of inherited and acquired deficiencies affecting each step of hemostatic plug formation and from selective use of laboratory tests.

Factor VIII-related activities after 1-deamino-8-D-arginine vasopressin in multicentric reticulohistiocytosis

A woman with multicentric reticulohistiocytosis, having symptoms including bleeding and a borderline level of factor VIII, was given an i.v. infusion of DDAVP as a pharmacological test to evaluate the release of factor VIII-related properties from storage sites. The results show a reduced response to DDAVP in the patient in comparison with a normal control subject. This could be due either to a defect in the release of the factor VIII complex after DDAVP or to a reduced synthesis and/or storage capacity by the storage cells.

Platelet-vessel-wall interactions: experiences with von Willebrand platelets

Adhesion of platelets from 15 patients with von Willebrand's disease was tested in an ex vivo human umbilical vein model. Experiments employed umbilical veins still in their umbilical cords taken from patients undergoing cesarean section and platelets (fetal, adult and vW) either apyrase-washed or used as platelet-rich plasma or whole blood. F VIII R:Ag, F VIII:Rcof, and F VIII:C were measured in initial fresh plasma and in effluents from the umbilical vein segments. F VIII:Rcof increased in most perfusates. Binding of latex-linked specific antihuman F VIII R:Ag demonstrated that F VIII R:Ag existed on subendothelium and on injured endothelial cells. Scanning electron microscopy three-dimensionally displayed vW platelet--vessel-wall interactions. Although vW platelets adhered to injured vein, both qualitative and quantitative differences existed in comparison with adhesion of normal platelets. The differences correlated best with the plasma F VIII:Rcof level. The best adhesion shown by vW platelets was only 51 percent of the adhesion of control fetal or adult platelets. vW platelets had less surface activity, fewer pseudopods, and little ability to spread and pave the exposed subendothelium. Pretreatment of the vein with F VIII R:Ag antibody partly blocked adhesion. Coperfusion of cryoprecipitate with vW platelets improved their adhesivity, state of activation on subendothelium, and ability to form aggregates. ABO differences in blood cell types of fetal material and platelet donors seemed without effect, which further establishes this model's validity for studies of platelet dysfunction and platelet or endothelial reactive agents.

Factor VIII complex in normal pregnancy, pre-eclampsia and fetal growth retardation

The levels of the three components of factor VIII complex (VIII R:AG, VIII R:WF, VIII:C) were measured during normal late pregnancy, in pre-eclampsia and in pregnancies complicated by fetal growth retardation. In late normal pregnancy, there was a steady increase in factor VIII complex and the highest level was reached at delivery; in primary fetal growth retardation, the values were similar. In pregnancies complicated by pre-eclampsia, with or without fetal growth retardation, there was a significant increase of VIII R:AG VIII R:WF; the more severe the course of the disease, the greater the increase. The level of VIII R:AG-VIII R:WF appears to be an indicator of vascular pathology and it is suggested that this assessment may be of value in monitoring high risk pregnancies.

Binding and release of factor VIII/von Willebrand's factor by human endothelial cells

The uptake and release of factor VIII/von Willebrand's protein by cultured human umbilical vein endothelial cells have been examined using highly purified 125I-factor VIII possessing von Willebrand's factor activity. 125I-factor VIII/vWF was taken up by the cells, reaching maximum binding within 4 h with a t1-2 of binding of 15 min. Endothelial cell binding of 125I-factor VIII/vWF reached saturation at a concentration of 1.5 mg/l. Binding was inhibited by coincubation of excess unlabelled factor VIII/vWF. Most of the cell-associated radioactivity was released by treatment of the cells with trypsin. Internalization of bound protein was evidenced by the incorporation into the cells of radioactivity which could not be released by trypsin. Human vascular smooth muscle cells did not bind 125I-factor VIII/vWF. Addition of 0.1 microM epinephrine to the 125I-factor VIII/vWF labelled endothelial cultures induced the release of cell bound, protein-associated radioactivity into the medium. Propranolol inhibited completely epinephrine-induced release, whereas phenylephrine had no effect. Endothelial cells maintained in medium partially depleted of factor VIII/vWF by tricalcium citrate cellulose treatment of plasma did not release factor VIII antigen into the culture medium during subsequent incubation. Although [3H]proline was incorporated into proteins released by endothelial cells under these experimental conditions, specific incorporation of label into factor VIII/vWF antigen was not detectable by a sensitive solid-phase immunoradiometric assay. We conclude that factor VIII/vWF binds to endothelial cells and that this cell-bound protein is mobilized by epinephrine through beta-adrenergic stimulation.

Fanconi's anaemia associated with haemophilia A

Fanconi's anaemia and haemophilia A are born inherited diseases creating haemostatic defects. The association of these two rare diseases in one patient is described. The patient's haemophilia was studied with a newly developed immunological technique determining the plasma antigen associated with Factor VIII activity, and was found to be a genetic variant of moderately severe haemophilia A. It was not possible to demonstrate a common bone marrow defect or a common immunological or genetical background of the two diseases. The double haemostatic defect created, i.e. Factor VIII deficiency and thrombocytopenia, resulted in only a slight increase in bleeding tendency. A favourable result was obtained with corticosteroid and androgenic treatment.

Generation of factor VIII coagulant activity by isolated, perfused neonatal pig livers and adult rat livers

Isolated, normal, neonatal pig livers released VIII:C into perfusates of porcine von Willebrand blood lacking VIIIR:AG and VIII:RWF. Neonatal von Willebrand livers released VIII:C only when partially purified VIIIR:AG was added to the von Willbrand blood. Adult rat livers, perfused with frozen-thawed erythrocytes suspended in Tyrode's solution containing 6% bovine serum albumin and hence no VIIIR:AG released VIII:C only when serum, adsorbed serum or cryoprecipitate from rat plasma was added to the perfusate. Cycloheximide blocked the release of VIII:C from rat liver.

Fatal iron intoxication with multiple coagulation defects and degradation of factor VIII and factor XIII

A severe iron intoxication in a 15-year-old girl resulted in profound damage to vital organs and multiple clotting defects, but no haemorrhagic diathesis. Investigation revealed not only impaired synthesis of coagulation factors but also abnormal proteolysis by plasmin as well as by other proteolytic enzymes liberated from leucocytes and damaged tissue cells affecting especially factor VIII and factor XIII.

Platelet responses in health and disease

This article summarizes recent ultrastructure findings from our laboratory and documents some of the information accumulated primarily since 1975 from many laboratories. Special attention is given to documentation by scanning electron microscopy which affords insight into platelet activation (adhesion, aggregation, release/secretion) and especially platelet-vessel wall interactions. Structural physiology of platelets is considered in some detail as a basis for understanding platelet disorders contributing to clinical problems of thrombosis and hemorrhage. The impaired ability of von Willebrand platelets to adhere to injured vessel wall is reported using the human umbilical vein perfusion model. Relationships between platelets and blood coagulation factors focus on the exquisite sensitivity of platelets to minute amounts of thrombin. Unmasking of platelet factor 3 sites is identified on activated platelets, after glutaraldehyde fixation, by their reaction ot latex bearing anti-platelet factor 3 markers. The basis for platelet-collagen interactions is reviewed. Conditions for and possible mechanisms behind platelet interaction with vessel wall are discussed. Ex vivo flowing blood-vessel wall models offer opportunities for improved understanding of the platelets role(s) in vascular diseases.

Factor VIII coagulant activity and factor VIII-related antigen released from isolated perfused human spleens

Eight human spleens were perfused for up to 65 h at normothermia and the coagulant Factor VIII activity measured in the perfusate. In addition, in three experiments Factor VIII-related antigen was determined in the perfusate. Although the spleens were pathologically enlarged and the normal structure involved by different diseases, all spleens released Factor VIII coagulant activity and Factor VIII-related antigen. On average the total amount of Factor VIII coagulant activity released was equivalent to that of 3.5 l of human plasma.

Factor-VIII activity and antigen, platelet count and biochemical changes after adrenoceptor stimulation

Adrenaline, isoprenaline and salbutamol were administered by intravenous infusion to human subjects. Isoprenaline was covered with practolol in an attempt to reduce the unpleasantness of the circulatory effects. Changes were recorded in pulse rate and blood pressure, and in blood levels of factors V, VIII, X, XI, and XII, platelet count, lactate, pyruvate, potassium and free fatty acids. Factor VIII was studied by clotting assays, by reactions with two rabbit antisera and two human antibodies, and by desulphated agarose chromatography. At the rate at which they were adiminstered, all three drugs increased the pulse rate by 20-40 beats/min. Factor VIII rose c. 2.5 X with adrenaline but only c. 1.5 X with isoprenaline and salbutamol; but other clotting factors did not alter. Chromatography provided no evidence of a change in the size of the molecule carrying factor-VIII clotting activity. The rate of clearance of the heightened plasma activity could not be shown to differ from that of "ordinary" factor VIII infused into haemophiliacs. The platelet count rose after adrenaline, fell after salbutamol and did not change significantly after isoprenaline. Among the biochemical responses, the only significant difference between the drugs was that lactate rose after adrenaline and salbutamol but did not change after isoprenaline. The rise in factor-VIII clotting activity after adrenaline is considered to represent a real increase in blood concentration, presumably by release of additional factor VIII from stores. The evidence suggests that this could be classified as a beta2 effect; and that the quantity which can be released is unrelated to the current plasma level. The rise in platelet count produced by adrenaline may be the resultant of an alpha-mediated rise due to contraction of the exchangeable splenic pool and a beta2-mediated fall, the alpha effect predominating.

The effects of epinephrine infusion in patients with von Willebrand's disease

Epinephrine infusion causes variable increases in the components of the Factor VIII (antihemophilic factor) complex in patients with von Willebrand's disease. The increase in antihemophilic factor procoagulant activity was greater than that of Factor VIII-related antigen and von Willebrand factor activity in two patients with von Willebrand's disease. Similar increases in the three individual factors were demonstrated in two other patients. A 4-10-fold increase in Factor VIII-related properties was identified in each of these individuals after infusion. One patient has been studied with very severe von Willebrand's disease; none of the Factor VIII-related properties increased despite two infusions of epinephrine. Bleeding times were normalized or remained normal in the two patients whose von Willebrand factor activity was greater than 25 U/100 ml. It remained prolonged in those three patients whose von Willebrand factor activity levels remained below that concentration. The increase in procoagulant activity was transient in all patients and t 1/2 values were estimated to be between 0.8 and 3.4 h.

Absence of ristocetin aggregation factor from the skin of a patient with von Willebrand's disease

Samples of apparently normal skin from one patient with von Willebrand's disease (vWD) and five patients without vWD were examined with fluorescein-tagged antiserum to the component of factor VIII required for aggregation of platelets by ristocetin (VIII-R.A.F.). No evidence of VIII-R.A.F. was found in the vWD skin, while bright granules were seen on and/or in the endothelial cells of dermal capillaries in all patients without vWD. VIII-R.A.F. granules were also found in the interstitial vasculature of all of twelve renal-biopsy specimens from patients without vWD. These observations support the concept that an abnormality of the vascular endothelium is involved in the pathogenesis of vWD.

Subunit structure of factor VIII antigen synthesized by cultured human endothelial cells

Cultured human endothelial cells were labeled with (3H)leucine, and the radioactive Factor VIII antigen present in the postculture medium was isolated by double anitbody immunoprecipitation and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after reduction with dithiothreitol. The Factor VIII antigen synthesized by cultured endothelial cells was found to contain the same single polypeptide subunit (mol wt 225,000) present in plasma Factor VIII antigen. These results suggest that in vivo, the endothelial cell is a major site of synthesis of circulating Factor VIII antigen.

Coagulation and platelet adhesion-inducing factor in the endothelium of the retinal vessels

By means of an immunofluorescent technique, we found factors promoting blood coagulation and platelet adhesion in the intima of retinal vessels. These factors coexisted with other agents causing the opposite process, fibrin dissolution. The components of this vascular hemostatic balance are possibly involved in the thrombotic occlusion of the retinal vessels, their canalization, and in the pathogenesis of diabetic retinopathy.

Subcellular platelet factor VIII antigen and von Willebrand factor

Subcellular membrane and granule fractions derived from human platelets contain factor VIIII antigen and von Willebrand factor activity but not factor VII procoagulant activity. Circulating platelets constitute a significant reservoir of plasma factor VIII antigen, containing approximately 15% of the amount of factor VIII antigen present in platelet-poor plasma. The antibiotic ristocetin, which aggregates human platelets in the presence of von Willebrand factor, nonspecifically precipitates platelet membrane factor VIII antigen. Thus normal platelets contain surface-bound as well as internally stored von Willebrand factor, a protein synthesized by endothelial cells which is necessary for normal platelet function in vivo.

Mechanism of plasminogen activator and factor VIII increase after vasoactive drugs

Adrenaline, nicotinic acid (NA), vasopressin (LVP) and other drugs affecting vascular motility are known to increase plasminogen activator (PA) and factor-VIII plasma levels in man. To evaluate the hypothesis that NA, LVP and adrenaline release PA from the endothelial cells of the vessel wall through their common effect on vascular motility, PA has been characterized by means of a histochemical technique on vein biopsies obtained from human volunteers after infusion of the compounds. Furthermore, the effect of single and repeated administration has been compared in order to investigate whether the pattern of PA and factor-VIII variations in plasma is similar with the three drugs. There was no major difference in the PA content of the veins following the marked and sustained increase of the corresponding plasma activities. A simple explanation is that the intensity and duration of the stimulus may not be sufficient to deplete the large stores of the vessel walls. The magnitude, time course and duration of the plasmatic response after single and repeated infusions was on the whole different and peculiar for each drug. A derivative of LVP which is free of vasoactive actions was more effective than LVP in inducing the responses, which could also be elicited in two anephric subjects. These findings suggest that vasoactivity is unlikely to provide the clue to a common pathway for the fibrinolysis and coagulation response after the compounds, and support the existence of different specific receptors.