The Biosynthesis of Factor VIII

Elevated FVIII levels in hereditary hemorrhagic telangiectasia: Implications for clinical management

Objectives

The objective of this study was twofold: to determine the prevalence of arterial and venous thromboembolic events in the Norwegian Hereditary Hemorrhagic Telangiectasia (HHT) population, and to explore potential factors linked to such events, with particular emphasis on FVIII.

Methods

Patients with an HHT diagnosis attending the Otorhinolaryngology Department at Oslo University Hospital-Rikshospitalet were included consecutively between April 2021 and November 2022. We recorded the participants' medical history with an emphasis on thromboembolic events. Measurements of blood constituents, including FVIII, FIX, vWF, hemoglobin, iron, ferritin, and CRP were performed.

Results

One hundred and thirty-four patients were included in the study. The total prevalence of thromboembolic events among the participants was 23.1%. FVIII levels were high (>150 IU/dL) in the majority of HHT patients (n = 84) (68.3%) and were significantly associated with thromboembolic events (p < .001), as was age. Of the patients with high FVIII levels, 28 (33%) had experienced a thromboembolic event. Furthermore, FVIII levels were measured consecutively in 51 patients and were found to fluctuate above or below 150 IU/dL in 25% of these cases.

Conclusion

Thromboembolic events are highly prevalent in the Norwegian HHT population and are significantly associated with FVIII levels. FVIII levels can fluctuate, and measurements should be repeated in HHT patients to assess the risk of thromboembolic events.

Level of Evidence

4.

Vascular mechanisms of post-COVID-19 conditions: Rho-kinase is a novel target for therapy

BACKGROUND

In post-coronavirus disease-19 (post-COVID-19) conditions (long COVID), systemic vascular dysfunction is implicated, but the mechanisms are uncertain, and the treatment is imprecise.

METHODS AND RESULTS

Patients convalescing after hospitalization for COVID-19 and risk factor matched controls underwent multisystem phenotyping using blood biomarkers, cardiorenal and pulmonary imaging, and gluteal subcutaneous biopsy (NCT04403607). Small resistance arteries were isolated and examined using wire myography, histopathology, immunohistochemistry, and spatial transcriptomics. Endothelium-independent (sodium nitroprusside) and -dependent (acetylcholine) vasorelaxation and vasoconstriction to the thromboxane A2 receptor agonist, U46619, and endothelin-1 (ET-1) in the presence or absence of a RhoA/Rho-kinase inhibitor (fasudil), were investigated. Thirty-seven patients, including 27 (mean age 57 years, 48% women, 41% cardiovascular disease) 3 months post-COVID-19 and 10 controls (mean age 57 years, 20% women, 30% cardiovascular disease), were included. Compared with control responses, U46619-induced constriction was increased (P = 0.002) and endothelium-independent vasorelaxation was reduced in arteries from COVID-19 patients (P < 0.001). This difference was abolished by fasudil. Histopathology revealed greater collagen abundance in COVID-19 arteries {Masson's trichrome (MT) 69.7% [95% confidence interval (CI): 67.8-71.7]; picrosirius red 68.6% [95% CI: 64.4-72.8]} vs. controls [MT 64.9% (95% CI: 59.4-70.3) (P = 0.028); picrosirius red 60.1% (95% CI: 55.4-64.8), (P = 0.029)]. Greater phosphorylated myosin light chain antibody-positive staining in vascular smooth muscle cells was observed in COVID-19 arteries (40.1%; 95% CI: 30.9-49.3) vs. controls (10.0%; 95% CI: 4.4-15.6) (P < 0.001). In proof-of-concept studies, gene pathways associated with extracellular matrix alteration, proteoglycan synthesis, and viral mRNA replication appeared to be upregulated.

CONCLUSION

Patients with post-COVID-19 conditions have enhanced vascular fibrosis and myosin light change phosphorylation. Rho-kinase activation represents a novel therapeutic target for clinical trials.

Factor VIII can be synthesized in hemophilia A mice liver by bone marrow progenitor cell-derived hepatocytes and sinusoidal endothelial cells

Hemophilia A (HA) is caused by mutation in factor VIII (FVIII) gene in humans; it leads to inadequate synthesis of active protein. Liver is the primary site of FVIII synthesis; however, the specific cell types responsible for its synthesis remain controversial. We propose that the severity of the bleeding disorder could be ameliorated by partial replacement of mutated liver cells by healthy cells in HA mice. The aim of this investigation was to study the cellular origin of FVIII by examining bone marrow cell therapy for treatment of HA in mice. Recipient liver was perturbed with either acetaminophen or monocrotaline to facilitate the engraftment and differentiation of lineage-depleted (Lin(-)) enhanced green fluorescent protein-expressing bone marrow cells. Immunohistochemical analysis of liver tissue was conducted to identify the donor-derived cells that expressed FVIII. This identification was confirmed by transmission electron microscopy and quantitative gene expression analysis. The phenotypic correction in HA mice was determined by tail-clip challenge and FVIII level in plasma by Chromogenix and activated partial thromboplastin time assays. Immunohistochemical analysis showed that von Willebrand factor and cytokeratin-18-expressing endothelial cells and hepatocytes, respectively, were obtained from BM-derived cells. Both cell types expressed FVIII light chain mRNA and protein, which was further confirmed by transmission electron microscopy. The transplanted HA mice showed FVIII activity in plasma (P<0.01) and survived tail-clip challenge (P<0.001). Thus, we conclude that BM-derived hepatocytes and endothelial cells can synthesize FVIII in liver and correct bleeding phenotype in HA mice.

Growth hormone and endothelial function during exercise in diabetics with and without retinopathy

Changes in plasma growth hormone (GH), factor VIII related antigen (VIIIR:Ag), and plasminogen activator activity (PAA) during exercise were evaluated in 50 insulin-dependent diabetics. In patients with a short to moderately long duration of diabetes (5-19 years, mean 11), GH increased only in those with retinopathy. VIIIR:Ag and PAA increased most pronouncedly in retinopathy patients as well. In diabetics with long duration of the disease (21-49 years, mean 35), GH, VIIIR:Ag and PAA increased almost equally in those with and without retinopathy.

Extra-hepatic factor VIII expression in porcine fulminant hepatic failure

In humans, fulminant hepatic failure (FHF) is frequently associated with increased factor VIII (FVIII) levels, despite widespread liver cell death. The mechanisms leading to increased FVIII levels and cellular sites of this enhanced FVIII production are poorly understood. We studied the effect of total hepatectomy in pigs, a large-animal model of FHF, on the expression of plasma and tissue FVIII during 24-hour follow-up. Tissue FVIII expression was determined before and 24 h after hepatectomy, both at the mRNA level and immunohistochemically. The expression of plasma and tissue von Willebrand factor (VWF), the natural stabilizing carrier protein of FVIII, was also measured. Total hepatectomy elicited a gradual and sustained twofold elevation of circulating FVIII, whereas FVIII mRNA levels in various organs did not increase after hepatectomy. The half-life of FVIII increased from 7.7 to 10.3 h and VWF levels were also elevated in anhepatic pigs. The increase in the half-life of FVIII and increased levels of VWF were not sufficient to explain the rise in plasma FVIII levels. At the protein level, prominent changes in the cellular distribution of FVIII were seen in spleen and kidney. These observations suggest that in this model of FHF the lack of hepatic FVIII synthesis is adequately compensated by other organs, notably spleen and kidneys.

Bleeding manifestations in males with von Willebrand disease

von Willebrand disease (vWD) is the most common congenital bleeding disorder in the USA, affecting 1-3% of the population. Previously characterizing the bleeding symptoms in females with type 1 vWD, we evaluated 42 males with type 1 vWD, mean age 16 years (1-64), of whom 24 (57%) presented with bleeding symptoms. The most common initial symptom was postoperative bleeding (26%). The most common bleeding symptoms ever were epistaxis (53%), bruising (50%), postoperative bleeding (47%), haematomas (29%) and oral bleeding (29%). Of postoperative bleeding, ear/nose/throat (44%), dental (17%) and circumcision bleeding (22%) occurred at a median 10 years of age, despite a previous bleeding or family history in 89%. Complications included anaemia in five (12%), neurological sequelae after subdural haematoma and tonsillectomy in two (5%), transfusion-associated hepatitis C in two (5%) and degenerative joint disease after traumatic haemarthroses in one (2%). The bleeding time (BT) was prolonged in 83%, and the ristocetin cofactor (vW:RCoF) and factor VIII (FVIII:C) decreased in 64% and 43%, respectively. Haemarthroses and haematoma formation were associated with a longer activated partial thromboplastin time (APTT) (P < 0.05), and anaemia with a lower FVIII:C (P < 0.05). In 81%, a haemostatic response occurred with 1-8 deamino-d-arginine vasopressin (DDAVP), although, in 13%, surgical intervention was also required to achieve haemostasis. Postoperative bleeding could have been avoided in 89%, if a preoperative past bleeding history or family history had been obtained, and, in at least 94%, if a preoperative BT and APTT had also been performed. The failure to avoid postoperative bleeding and related complications in patients with vWD by taking a personal and family bleeding history constitutes a major public health problem.

Factor VIII expression in azoxymethane-induced murine fulminant hepatic failure

Fulminant hepatic failure (FHF) in humans produces a bleeding diathesis due in large part to a reduction in the biosynthesis of liver-derived coagulation factors. Remarkably, factor VIII procoagulant activity is elevated in most of these patients despite widespread liver cell death. FHF can be modeled in mice by administration of azoxymethane, the active ingredient found in cycad palm nuts. We compared the expression of factor VIII to other hepatic hemostatic factors in azoxymethane-induced murine FHF. Mice displayed dose-dependent decreases in all coagulation factor activities measured, including factors V, VII, VIII, and IX. At the highest dose of azoxymethane (50 microg/g body weight), factor VIII activity in plasma decreased by 98% within 36 hours after treatment, which was associated with an 80% reduction in hepatic factor VIII messenger RNA (mRNA). In contrast, factor VIII mRNA levels in spleen, kidney, and lung tissue of azoxymethane-treated mice were unchanged. Cellular damage in these mice appeared to be limited to hepatocytes as evident by histologic examination. This finding is supported by 2 observations. First, hepatic mRNA levels of von Willebrand factor, which is synthesized by liver sinusoidal endothelial cells but not hepatocytes, were unchanged. Second, von Willebrand factor was detected antigenically in liver sections of azoxymethane-treated mice by immunofluorescence. These results indicate that the contribution of the liver to factor VIII biosynthesis is not replaced or significantly supplemented by other tissues in this model of FHF.

Expression of factor VIII by murine liver sinusoidal endothelial cells

Factor VIII (fVIII) is the procoagulant plasma glycoprotein that is missing or decreased in hemophilia A. The cellular origin of fVIII synthesis is controversial. Liver transplantation cures hemophilia A, demonstrating that the liver is a major site of fVIII synthesis. We detected fVIII mRNA in purified populations of murine liver sinusoidal endothelial cells (LSECs) and hepatocytes, but not Kupffer cells. LSECs and hepatocytes contained comparable numbers of fVIII mRNA (40 and 70 transcripts per cell, respectively) by quantitative competitive reverse transcriptase-polymerase chain reaction analysis. There was not detectable mRNA for factor IX, a hepatocyte marker, in the LSEC preparation, nor was there detectable mRNA for von Willebrand factor, an endothelial cell marker, in the hepatocyte preparation. This excludes the possibility that detectable fVIII mRNA is due to cross-contamination in the hepatocyte or LSEC preparations. Primary cultures of LSECs were established in which fVIII mRNA levels were indistinguishable from purified LSECs. LSECs secreted active fVIII into the culture medium. This finding represents the first demonstration of homologous expression of fVIII mRNA and protein in cell culture and should facilitate studies of fVIII gene regulation. Additionally, LSECs potentially are targets for a fVIII transgene during gene therapy of hemophilia A.

Plasma levels of von Willebrand factor in non-insulin-dependent diabetes mellitus are influenced by dietary monounsaturated fatty acids

We have previously demonstrated a lowering effect on von Willebrand Factor (vWF) of a diet rich in monounsaturated fatty acids (MUFA) as compared with a high-carbohydrate diet. In the present study 16 non-insulin dependent diabetic (NIDDM) subjects participated in a cross-over experiment on an out-patient basis comparing the effects on vWF of three weeks treatments with two diets similar in carbohydrate and protein content, one rich in MUFA (30 energy %) and one rich in polyunsaturated fatty acids (PUFA) (30 energy %). Before and on the last day of the two diets, the levels of vWF, fibrinogen, fibronectin and alpha 2-macroglobulin were measured. After 3 weeks diet intervention vWF levels were lower after the MUFA regimen compared with the PUFA diet (mean +/- SD) (1.15 +/- 0.36 vs 1.32 +/- 0.42 U/ml, p = 0.003). Similar and unchanged levels of fibrinogen, fibronectin and alpha 2-macroglobulin were seen. In conclusion, three weeks on a diet rich in MUFA lowers vWF as compared with a PUFA rich diet, suggesting a beneficial effect of MUFA on the endothelium in NIDDM patients.

Microalbuminuria, insulin sensitivity and haemostatic factors in non-diabetic treated hypertensive men. Risk Factor Intervention Study Group

OBJECTIVE

To examine whether microalbuminuria in non-diabetic, treated hypertensive men is associated with insulin resistance and measures of endothelial function, thrombogenesis and fibrinolysis.

DESIGN

Cross-sectional study.

SETTING

Outpatient clinic in city hospital.

PATIENTS

Ninety-two treated hypertensive men, aged 57-77 years, either with a serum cholesterol of > or = 6.5 mmol L-1 or smokers, or both. Patients with diabetes mellitus or overnight urinary albumin excretion of > 100 mg 12 h-1 were excluded.

MAIN OUTCOME MEASURES

Overnight urinary albumin excretion, insulin-mediated glucose disposal (hyperinsulinaemic euglycaemic clamp), blood glucose and plasma insulin during oral glucose tolerance test, fibrinogen, von Willebrand factor and plasminogen activator inhibitor activity.

RESULTS

Microalbuminuric patients had increased blood glucose concentrations during the oral glucose tolerance test and higher plasma fibrinogen levels compared with the normoalbuminuric patients. In a randomly selected subgroup (n = 36), insulin-mediated glucose disposal was lower in microalbuminuric than in normoalbuminuric patients, and an inverse relationship between insulin sensitivity and albuminuria (r = -0.37; P = 0.028) was found. This relationship was not significant after adjustment for body-mass index (P = 0.098). In the univariate analyses including all patients, albuminuria was associated with blood glucose, serum creatinine, body-mass index, systolic blood pressure, fibrinogen, von Willebrand factor and cholesterol (negatively). In a multiple regression analysis, only the body-mass index was independently related to urinary albumin excretion.

CONCLUSIONS

Microalbuminuria was associated with insulin resistance but obesity was a confounding factor. Relationships between microalbuminuria and fibrinogen as well as von Willebrand factor were found, but only in univariate analysis.

Increased cardiovascular risk factors and features of endothelial activation and dysfunction in dialyzed uremic patients

Due to the incidence of symptomatic atherosclerosis in uremic patients, hemostasis-derived cardiovascular risk factors, basal plasma concentrations of some endothelial-derived glycoproteins and desmopressin-induced variations of endothelial-derived proteins were studied in 22 uremic patients on prolonged maintenance hemodialysis with no cardiovascular antecedent. Compared to control subjects, patients had increased predialysis hemostasis-related cardiovascular risk factors: high fibrinogen, proconvertin, and type 1 plasminogen activator inhibitor plasma concentrations; low albumin values; generally low antithrombin III values but sometimes high. They had high predialysis plasma concentrations of endothelium-derived glycoproteins: von Willebrand factor, tissue-type plasminogen activator and urokinase-type plasminogen activator, which are secreted by endothelial cells, but also soluble thrombomodulin, a marker of endothelial cell injury. The desmopressin-induced release of tissue-type plasminogen activator and of von Willebrand factor were lower than in controls. High fibrinogen, type 1 plasminogen activator inhibitor and low albumin plasma concentrations may be linked to repeated acute phase reactions associated with hemodialysis. Data concerning endothelium-related proteins are concordant with the co-existence of a chronic in vivo endothelial activation and endothelial injury in uremia. This could be linked to the initiation and progression of atherosclerosis.

Patients with severe von Willebrand disease are insensitive to the releasing effect of DDAVP: evidence that the DDAVP-induced increase in plasma factor VIII is not secondary to the increase in plasma von Willebrand factor

It is generally held that factor VIII (FVIII) does not increase in the plasma of severe von Willebrand disease (vWD) patients treated with DDAVP because they lack von Willebrand factor (vWF), which is the plasma carrier for FVIII. To test this hypothesis, FVIII plasma levels were monitored in severe vWD patients treated with DDAVP after normalization of vWF plasma levels with infusions of cryoprecipitate. Each of four severe vWD patients underwent four different treatments at intervals of at least 15 d: (1) cryoprecipitate plus DDAVP; (2) cryoprecipitate plus saline; (3) cryoprecipitate plus recombinant FVIII (rFVIII); (4) saline plus rFVIII. Cryoprecipitate increased the plasma levels of FVIII and vWF. The infusions of saline or DDAVP after cryoprecipitate did not further increase FVIII and vWF plasma levels and had no effect on the plasma levels of tissue plasminogen activator (tPA), which are raised by DDAVP in normal subjects and in patients with vWD of other types. The infusion of rFVIII further increased by 182 +/- 32 U/dl (mean +/- SEM) the plasma levels attained after cryoprecipitate, which disappeared from the circulation with a half-life of 11.95 +/- 0.86 h. In contrast, the infusion of rFVIII after saline increased by only 107 +/- 18 U/dl the plasma levels of FVIII, which disappeared from the circulation with a half-life of 2.68 +/- 0.14 h, indicating that the vWF infused with cryoprecipitate is able to bind additional FVIII. These studies indicate that DDAVP does not increase the plasma levels of FVIII in patients with severe vWD even after normalization of plasma vWF. The possibility is discussed that severe vWD patients may be insensitive to the releasing effect of DDAVP.

von Willebrand factor and early diabetic retinopathy: no evidence for a relationship in patients with type 1 (insulin-dependent) diabetes mellitus and normal urinary albumin excretion

High plasma levels of von Willebrand factor, an indicator of endothelial cell dysfunction, have been reported in both diabetic retinopathy and nephropathy. It is unclear, however, whether von Willebrand factor is related to diabetic retinopathy in the absence of diabetic nephropathy. The relationship between retinal status and plasma von Willebrand factor concentration was investigated in a cohort of 17 patients with Type 1 (insulin-dependent) diabetes mellitus who were followed-up for a median of 42 months. The patients were examined three times. They were selected for having had normal urinary albumin excretion and no evidence of retinopathy (on fundoscopy) at the first and second examination. They were then divided into two groups, according to absence (Group A; n = 9) or presence (Group B; n = 8) of retinopathy on fundoscopy or fluorescein angiography at the third examination. Urinary albumin excretion remained normal in all patients. Plasma von Willebrand factor levels were similar in both groups: (median) 128 vs 123%, 164 vs 132% and 159 vs 130% (first, second and third examination, respectively). Median changes in plasma von Willebrand factor were also similar: +7 vs +9% and +5 vs +1% (first-second and second-third examination). Patients in whom the plasma von Willebrand factor concentration increased had higher systolic blood pressure at the third examination (150 +/- 30 vs 130 +/- 12 mmHg, p = 0.02) when compared to those in whom plasma von Willebrand factor did not increase, but were of similar age and had similar diabetes duration, retinal status, diastolic blood pressure, glycated haemoglobin and serum cholesterol concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Observation of the activity of factor VIII in the endometrium of women pre- and post-insertion of three types of IUDs

The endometrial materials were obtained from 90 women who had been randomly inserted with three types of IUDs (Stainless steel ring, SS; copper T 220, TCu 220, and levonorgestrel-releasing device, LNG). An immunoperoxidase reaction, PAP method, with the antiserum of Factor VIII as the primary antibody, was carried out to detect the Factor VIII activity in the endometrial endothelium pre- (control) and post-insertion of the IUDs. The results revealed that: 1. There was a generalized lower Factor VIII activity in the endometrium of women post-insertion of IUDs (except LNG). 2. Comparison of the Factor VIII activity in the endometrium of women using different types of IUDs showed that the TCu type and the SS type decreased the activity significantly whereas the activity remained unchanged after 3-6 months' use of the LNG-IUD. The different types of IUDs seemed to influence the coagulation regulatory system in different ways; the lower Factor VIII activity, the more tendency to bleeding. 3. The Factor VIII activity in the endometrium of women using IUDs was lower in all phases of the menstrual cycle including the proliferative phase when the Factor VIII activity is normally high. It cannot be excluded that this could be a contributing factor to IUD-induced bleedings.

Effects of exercise and ethanol ingestion on platelet thromboxane release in healthy men

We studied the effects of repeated bicycle exercises and ethanol ingestion (1.5 g/kg) on platelet aggregation and thromboxane (TxB2) release in 10 healthy male volunteers. After a bicycle exercise performed in the morning, the adenosine diphosphate (ADP)-induced platelet aggregation and the aggregation-associated thromboxane release were found to be decreased in fasting men. In contrast, after ingestion of fruit juice and a second exercise at noon, platelet aggregation and thromboxane release were increased. These latter changes were negligible when ethanol was ingested together with fruit juice. A third exercise, performed in the evening, again caused a decrease in the aggregation and associated thromboxane release during the control session, but provoked an increase during the ethanol session. Exercise increased the urinary excretion of 2,3-dinor-6-keto-PGF1 alpha. Changes in the plasma arachidonic acid (AA) concentration probably influenced the platelet thromboxane release. The results suggest that both physical exercise and ingestion of ethanol in fruit juice influence the ADP-stimulated platelet thromboxane release.

von Willebrand factor: clinical features of inherited and acquired disorders

The physiologic mechanisms that influence plasma levels of von Willebrand factor (vWF) are poorly understood but include race, blood group, age, pregnancy, exercise, and adrenergic and neurohumoral stimuli. Inherited abnormalities in von Willebrand's disease (vWD) are associated with a defect of the vWF gene on chromosome 12, but in some cases, coexistence of impaired response of plasminogen activator and telangiectasia suggests the presence of a regulatory defect or more extensive endothelial perturbation. Three broad types of vWD are recognized; in addition, a platelet-type vWD (pseudo-vWD) is due to an abnormal platelet receptor for vWF. The prevalence of vWD, which is difficult to determine because of variations in severity even within a kindred, is reportedly as high as 1%. In a survey of European patients, the prevalence of treated vWD varied from 4.5 to 24 per million. Preliminary results of an international survey of vWD indicate that about 3% of treated patients have seroconversion to human immunodeficiency virus, 50% of whom have symptoms. Inhibitor of vWF occurs in type III vWD after treatment and is associated with the presence of gene deletions. Acquired vWD may complicate lymphoproliferative and autoimmune disorders, and proteolytic degradation of vWF complicates myeloproliferative disorders. The level of vWF is increased during pregnancy and in vascular and other disorders; it may be involved in the pathogenesis of atherosclerosis. High-molecular-weight multimers of vWF and a cofactor are thought to promote the formation of microthrombi in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome. Thus, study of vWD has shed light on pathogenetic mechanisms in a wide range of disorders.

Haemostatic measures in type 2 diabetic patients with microalbuminuria

The major cause of disability and early mortality in Type 2 diabetes is cardiovascular disease. An enhanced urinary albumin excretion is strongly predictive of increased mortality, but the causal relationship behind this association is unclear. Abnormalities in the haemostatic system may be involved in the vascular pathology. We therefore studied the level of von Willebrand factor (vWf:Ag), factor VIII (VIII:Ag), fibrinogen, and fibronectin in male diabetic patients 50-70 years of age, with normal albumin excretion (n = 14), microalbuminuria (n = 14), and frank albuminuria (n = 7). Fourteen healthy age-matched males served as a reference group. There were no significant differences between normo- and micro-albuminuric patients but vWf:Ag (p less than 0.01), VIII:Ag (p less than 0.01), and fibrinogen (p less than 0.05) were increased in those with frank albuminuria. Urinary albumin excretion rate was significantly correlated to vWf:Ag (r = 0.46, p = 0.005), VIII:Ag (r = 0.45, p = 0.007), and fibrinogen (r = 0.49, p = 0.003). The known duration of diabetes was correlated to vWf and F VIII. The increased level of vWf:Ag in Type 2 diabetes and the significant association to the urinary albumin excretion rate may suggest a linkage between albuminuria and cardiovascular disease. However, the present study demonstrated no increase in haemostatic variables in patients with microalbuminuria as compared with those with normal albumin excretion.

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.

Correlation between plasma levels of growth factors and von Willebrand factor

Intimal proliferation of smooth muscle cells is an important characteristic of developing atherosclerotic lesions and late occlusion of venous bypass grafts. Platelet-derived growth factor, released from aggregating platelets at sites of endothelial injury, has been suggested as a main factor responsible for intimal hyperplasia. The von Willebrand factor is a platelet binding protein secreted by endothelial cells and increased plasma levels of this factor has been identified as a marker of endothelial injury. In the present study we have analysed plasma levels of von Willebrand factor and growth factors in healthy controls, young post-infarction patients and patients with recent coronary bypass surgery. The results demonstrate a significant correlation between plasma growth factor activity and the level of von Willebrand factor (R = 0.52, p less than 0.01) and support the notion of a coupling between endothelial injury and release of platelets mitogens.

Molecular pathology and immunology of factor VIII (hemophilia A and factor VIII inhibitors)

Factor VIII is a large procoagulant glycoprotein that circulates in plasma in a noncovalent complex with von Willebrand factor. It is essential for the efficient cleavage of coagulation factor X by factor IXa, and its absence causes a severe bleeding disorder. Plasma factor VIII is reduced from the normal range of approximately 100 to 200 ng/ml in patients with the hereditary coagulation defect, hemophilia A, as well as in patients who develop autoantibodies that inactivate factor VIII. The understanding of factor VIII structure has been enhanced by recent studies that have characterized the X chromosome gene responsible for its synthesis, and preliminary information is now available about specific genetic defects. The basis for antibody formation in approximately 15 per cent of repeatedly transfused hemophilic patients is less clear at this time, however, for these individuals appear to have a variety of genetic defects that are not characteristically different from the patients who do not develop inhibitors. Although the antibodies cause a serious problem for affected individuals, they have been very useful in characterizing normal factor VIII and nonfunctional factor VIII-like protein that is found in the plasmas of 10 per cent of patients with mild hemophilia. Moreover, they are very useful reagents that can be used for immunoassay of factor VIII that has been modified in ways that have destroyed its procoagulant function.

Factor VIII R:Ag as a prognostic parameter in intracranial haemorrhage

Factor VIII R:Ag was measured serially in 42 patients who had intracranial haemorrhage. It was found that the factor decreased or remained static in the 24 patients who improved (p less than 0.025), while it increased in the 18 who died (p less than 0.0005). It is suggested that this factor can be used as a prognostic parameter to predict the outcome after intracranial haemorrhage.

Hemostasis and fibrinolysis in severe liver failure and their relation to hemorrhage

In a study of severe, decompensated liver failure, we tried to find a correlation between hemorrhage and parameters of hemostasis and fibrinolysis. Three groups of patients were studied: alcoholic cirrhosis; nonalcoholic cirrhosis, and acute liver failure without known prior liver disease. The two cirrhotic groups did not differ significantly from each other in coagulation or in fibrinolytic parameters, although liver function was more impaired in nonalcoholic cirrhosis. The levels of clotting factors, antithrombin III, prekallikrein, plasminogen and alpha 2-antiplasmin were significantly lower in the third group. Mean values of fibrinolytic activity (fibrin plate method) were slightly reduced as compared to normal in all three groups. Tissue plasminogen activator-related antigen tended to be elevated especially in alcoholic cirrhosis. The free fast-acting plasminogen activator inhibitor showed extremely high and extremely low levels in some patients among all three groups. Nonvariceal, capillary-type bleeding, including mucosal bleeding, hematomas and bleeding from puncture sites correlated with low thrombotest and normotest levels (p less than 0.01), low fibrinogen concentration (p less than 0.05) and with a high quotient of fibrinolytic activity (square root of lysis area) and normotest (p less than 0.001). The ratio between fibrin formation and dissolution appears to be an important parameter of hemorrhagic tendency in liver disease. Variceal bleeding appeared not to be related to impairment of hemostasis or fibrinolysis.

The physiology and pathophysiology of the factor VIII complex

The factor VIII complex consists of two noncovalently linked proteins: von Willebrand factor (VWF) and factor VIII (FVIII). VWF plays an important role in primary hemostasis by mediating the adherence of blood platelets to the damaged vessel wall. A review of the literature on VWF is given with regard to its physicochemical properties and mode of action. FVIII acts as a cofactor in the factor Xa-generating enzyme complex of the intrinsic coagulation cascade. Starting with the recently published primary structure of FVIII, the literature is reviewed for structural information on FVIII. Also, an effort is made to characterize the interaction of FVIII with VWF and to discuss the possible physiological significance of FVIII-VWF complex formation. Interaction of FVIII with the clotting factors of the intrinsic pathway of coagulation is described in detail. Hemophilia and von Willebrand's disease (VWD) are both congenital bleeding disorders affecting a great many people. The different variants of these diseases are described with some reference to therapy and detection.

Factor VIII related antigen in gestational trophoblastic disease

Serum factor VIII related antigen (factor VIII R:Ag) levels were determined in 34 patients with hydatidiform mole at diagnosis and at 2, 4 and 6 weeks after evacuation of uterus and in 272 normal pregnant women. Serum factor VIII R:Ag levels in molar pregnancies before evacuation of the uterus were significantly higher than those in normal pregnancies of the same gestation age. Serum factor VIII R:Ag levels in the group of patients with residual trophoblastic disease were significantly higher than those in the group without residual trophoblastic disease before evacuation and at 6 weeks after evacuation of uterus, but there is considerable overlap in the levels of factor VIII R:Ag between the two groups of patients especially before evacuation of uterus. Factor VIII R:Ag level does not appear to be an useful marker in predicting the outcome of hydatidiform mole.

Factor VIII-related antigen levels in normal pregnancy and puerperium

The changes in serum Factor VIII-related antigen (Factor VIII RAg) levels in normal pregnancy and puerperium in Chinese women were studied by the Laurell 'rocket' immunoelectrophoresis. At 6 wk of gestation, the serum Factor VIII RAg levels were already higher than those of non-pregnant women and gradually increased through term pregnancy. Parturition did not have immediate effects on the circulating levels of Factor VIII RAg. The levels of Factor VIII RAg observed during labour and days 1-5 postpartum were similar to those of term pregnancy. By the 6th wk postpartum, the serum Factor VIII RAg declined to basal levels, similar to those of non-pregnant control samples.

Localization of factor VIIIC: antigen in guinea-pig tissues and isolated liver cell fractions

Factor VIIIC:antigen (VIII:CAg) was estimated in guinea-pig tissues by an immunoradiometric assay using a human inhibitor antibody. In homogenized guinea-pig tissues, VIII:CAg was shown to be stable and to be predominantly located in the liver (9 +/- 1.2 units; mean +/- SEM, n = 8). Lesser amounts were detected in spleen (1.3 +/- 0.02 units), lung (0.6 +/- 0.07) and kidney (0.4 +/- 0.06). In isolated liver cell fractions separated by centrifugal elutriation VIII:CAg was mainly detected in the hepatocyte fraction (0.3 +/- 0.07 units/10(8) cells;mean +/- SEM, n = 5) and in lesser amounts in the endothelial (0.02 +/- 0.01 units/10(8) cells) and the Kupffer cell fractions (0.05 +/- 0.02 units/10(8) cells). The liver concentration of VIII:CAg was (0.17 +/- 0.02 units/g) which was 20% of the plasma concentration (0.96 +/- 0.01 units/ml, n = 8) suggesting that VIII:CAg may not be stored in the liver but is rapidly exported following synthesis.

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.

Measurement of factor VIII CAg by immunoradiometric assay in human tissue extracts

Samples of normal tissues taken from three patients within 24 hours of death were physically disrupted, washed and extracted. Centrifuged supernatants were tested for factor VIII coagulant antigen (VIII CAg) and factor VIII related antigen (VIII RAg) by radioimmunoassays using homologous and heterologous antisera respectively. VIII RAg was readily washed out by isotonic saline whereas VIII CAg required 1.5 M sodium chloride for optimal extraction from tissue homogenates. Highest levels of VIII CAg were detected in some lymph nodes followed by lung, liver and spleen. There was rapid loss of VIII CAg from most tissues in the absence of proteolytic inhibitors.

Increased factor VIII related antigen in cerebral thrombosis

Changes of Factor VIII related antigen (FVIIIR:Ag) were measured in patients with cerebral thrombosis on day 1-15 (125 cases), 16-45 (acute reaction phase, 70 cases), and during 1.5-5 months (recovery phase, 29 cases) after onset of the disease. FVIIIR:Ag was significantly (P less than 0.001) increased in both acute and recovery phase as compared to 108 healthy controls, although slightly decreased in recovery than in acute phase. The persistently high FVIIIR:Ag levels in acute phase are unlikely to be caused by the so-called acute phase reaction but are probably due to increased synthesis and endothelial changes in atherosclerotic lesions releasing FVIIIR:Ag from its endothelial pool. It suggested that increased FVIIIR:Ag mainly reflects the degree of vascular involvement and it may be used as a marker (or indicator) of arterial endothelial injury in patients with cerebral thrombosis.

Differential localisation and synthesis of porcine factor VIII related antigen (VIIIR:AG) in vascular endothelium and in endothelial cells in culture

Porcine and human umbilical vein and adult blood vessels were studied for the presence and synthesis of factor VIII related antigen (VIIIR:Ag) and fibronectin (Fn) by immunofluorescence histology and immunoautoradiography. Investigation of human tissue confirmed the widespread distribution of VIIIR:Ag on the endothelium of all blood vessels examined but observations on porcine tissue gave different results. Porcine umbilical vein and porcine adult veins were positively stained for VIIIR:Ag whilst porcine aorta and other pig arteries appeared to be negative or only weakly positive. Some blood vessels (?venous) in the adventitia of porcine aorta were positively stained whilst adjacent ones (?arterial) were negative. Radiolabelled methionine was added to culture medium and proteins synthesised by cultured EC were examined by two dimensional crossed immunoelectrophoresis and autoradiography. Identification of radiolabelled precipitin arcs provided a highly sensitive method for confirming the specificity of antisera and for detecting VIIIR:Ag and Fn. Examination of cultured human umbilical vein EC confirmed the synthesis of VIIIR:Ag and distinguished between VIIIR:Ag and Fn. Studies of porcine umbilical vein EC in culture gave similar results to those observed with corresponding human EC. However, cultures derived from porcine aorta did not demonstrate synthesis of VIIIR:Ag and microscopy failed to locate VIIIR:Ag in these cells with certainty. The results confirmed the synthesis of VIIIR:Ag by human and porcine umbilical vein EC but differences in staining reactions and the apparent inability to synthesise VIIIR:Ag by cells derived from porcine aorta suggested that porcine EC at different anatomical sites may subserve different functions.

Twenty-four hour variations of von Willebrand factor and factor VIII-related antigen in diabetic retinopathy

Factor VIII/von Willebrand factor (vWF) could play a role in the pathogenesis of diabetic microangiopathy. It has been suggested that its biologic activity is controlled by hormonal and metabolic mechanisms. To verify this hypothesis, vWF was monitored over a 24 hr period in 9 insulin treated patients with diabetic retinopathy, together with factor VIII-related antigen (VIII-RAG), plasma glucose, growth hormone (GH) and prolactin. vWF levels oscillated during the 24 hr, the mean values being higher during the day than at night-time, p less than 0.01. Compared to a group of normal controls in whom blood samples were taken randomly between 9.00 and 13.00, the levels of vWF were significantly increased at 11.00, p less than 0.02, and at 13.00, p less than 0.02, but at no other time. VIII-RAG values were also higher during the day than at night-time, p less than 0.01. The mean 24 hr levels of vWF correlated with those of VIII-RAG, p less than 0.01, with the age of the patients, p less than 0.01, and with the duration of disease, p less than 0.01. The levels of plasma glucose were higher during the day, while GH and prolactin rose at night-time. No correlations were found between vWF or VIII-RAG and plasma glucose, GH or prolactin, nor between the mean 24 hr levels of all these parameters and ponderal index, daily insulin dose, degree of metabolic control, severity of retinopathy. Insulin treated diabetics with microangiopathy show circadian variations in their plasma concentrations of vWF and VIII-RAG which should be taken into account when measuring these factors for clinical or research purposes.

Factor VII related antigen as an endothelial cell marker in benign and malignant diseases

The presence and distribution of Factor VIII related antigen (FVIIR:Ag) in formation fixed, paraffin embedded tissue were studied in benign and malignant vascular tumors, inflammatory vascular diseases, normal tissue from various organs and a number of malignant tumors. The unlabeled peroxidase-anti-peroxidase method was utilized. Immunostaining was observed only in endothelial cells, in tumor cells of endothelial cell origin and in megakaryocytes and platelets. The staining method gave a distinct picture of the vascular pattern in all types of tissue examined. The demonstration of FVIIIR:Ag by means of the immunoperoxidase technique is considered a valuable method in diagnosing tumors of vascular origin. The method also facilitates detection of vascular invasion of malignant tumors in small caliber vessels.

Hemophilia

The clinical manifestations of hemophilia depend upon both age and the severity of the factor VIII or IX deficiency. Hemophilia A and B cannot be differentiated on clinical grounds. Laboratory tests include platelet count, prothrombin time, partial thromboplastin time, and bleeding time.