Decreased factor VIII levels during acetaminophen-induced murine fulminant hepatic failure

During human fulminant hepatic failure (FHF) circulating levels of most hemostatic proteins fall dramatically. Concurrently, factor VIII (fVIII) procoagulant activity rises despite destruction of the hepatocytes considered responsible for fVIII synthesis. This observation suggests a role for cells other than hepatocytes in fVIII biosynthesis during FHF. We have attempted to identify nonhepatocytic sites of fVIII biosynthesis by inducing FHF in mice using acetaminophen overdose, a common cause of human FHF. Acetaminophen-treated mice consistently displayed signs characteristic of FHF, including elevated plasma aminotransferase activity. However, acetaminophen-treated mice demonstrated markedly reduced fVIII activity, contrary to the observation in human FHF. von Willebrand factor antigen levels were only mildly reduced, suggesting that the decrease in fVIII is not secondary to loss of von Willebrand factor. These results imply that there are fundamental differences in the regulation of plasma fVIII levels between humans and mice.     

Antihaemophilic factor A activity, F VIII-related antigen and von Wilebrand factor in hepatic cirrhosis.

F VIII activity, F VIII-related antigen and von Willebrand factor were measured in 46 patients with hepatic cirrhosis and in 30 normal individuals. These parameters were significantly higher in hepatic cirrhosis than in the controls. Linear relationships between F VIII activity and F VIII-related antigen and between F VIII-related antigen and von Willebrand factor were found in patients with hepatic cirrhosis as well as in normal individuals. However, in both groups no relationship between F VIII activity and von Willebrand factor was present. The existence of a low-grade intravascular coagulation in hepatic cirrhosis may be postulated but more information about the metabolism of F VIII protein is needed before such a statement can be proven.     

Treatment of von Willebrand disease

Summary. von Willebrand disease is the most frequent of inherited bleeding disorders (1:100 affected individuals in the general population). The aim of treatment is to correct the dual defects of haemostasis, i.e., abnormal coagulation expressed by low levels of factor VIII and abnormal platelet adhesion expressed by a prolonged bleeding time. There are two main options available for the management of von Willebrand disease: desmopressin and transfusion therapy with blood products. Desmopressin is the treatment of choice in patients with type 1 von Willebrand disease, who account for approximately 80% of cases. This pharmacological compound raises endogenous factor VIII and von Willebrand factors and thereby corrects the intrinsic coagulation defect and the prolonged bleeding time in most type 1 patients. In type 3 and in the majority of type 2 patients desmopressin is not effective, and it is necessary to resort to plasma concentrates containing factor VIII and von Willebrand factor. Treated with virucidal methods, these concentrates are effective and currently safe, but the bleeding time defect is not always corrected by them. Platelet concentrates or desmopressin can be used as adjunctive treatments when poor correction of the bleeding time after concentrates is associated with continued bleeding.     

Production of factor VIII deficient plasma by immunodepletion using three monoclonal antibodies

Factor VIII deficient plasma was made from pooled, HIV antibody and hepatitis B antigen screened, normal human plasma by cryoprecipitation and immuno-depletion, using three different monoclonal antibodies bound to Sepharose columns, in series. These monoclonal antibodies are specific respectively for von Willebrand factor, factor VIII heavy chain and factor VIII light chain. The immunodepleted plasma contained less than 0.002 u/ml factor VIII coagulation activity (VIII:C) less than 0.0001 u/ml von Willebrand factor antigen and 1-2 g/l fibrinogen, while the levels of other clotting factors were unchanged. This immunodepleted plasma was compared with commercial factor VIII deficient plasma obtained from a severe haemophilia A patient as substrate in the one-stage factor VIII assay. Plasmas obtained from 20 normal subjects and 28 patients with von Willebrand's disease or haemophilia A were assayed for VIII:C using the two substrates. The results were very highly correlated (r = 0.96). The columns have high capacity and can be regenerated at least 10 times. Large-scale production of a substrate for factor VIII assays free of virus contamination is now feasible.     

Structure and function of the factor VIII/von Willebrand factor complex

In the blood plasma factor VIII is bound to the von Willebrand factor. The primary structure of the two proteins were clarified by gene clonation. Factor VIII descends from a precursor protein with 2,351 amino acids by splitting of 19 amino acid residues and is activated by partial proteolysis. In the blood coagulation factor VIII acts as co-factor for the activation of factor X by factor IX in the presence of phospholipids and Ca++ within the intrinsic coagulation system. The formation of the von Willebrand factor takes place by splitting of 22 and 741 amino acid residues, respectively, from pre-pro-von Willebrand factor via pro-von Willebrand factor. The subunits of the von Willebrand factor consist od 2,050 amino acid residues. In the blood plasma the von Willebrand factor is existing as a mixture of multimeres. Receptors of the von Willebrand factor on the thrombocytic membrane are the glycoproteins GPIb and GPIIb/GPIIIa, by means of which the adhesion of thrombocytes at the subendoethelium of the vascular wall and the aggregation of thrombocytes are mediated.     

Persistent factor VIII-dependent factor X activation on endothelial cells is independent of von Willebrand factor.

Endothelial cells are able to support the activation of coagulation factor X by activated factor IX in the presence of its cofactor, factor VIII. We have previously reported that this reaction is persistent on endothelial cells, but transient on activated platelets and phospholipid vesicles when activated factor X (Xa) is used as activator of factor VIII. Aim of the present study was to explore the influence of von Willebrand factor and that of the factor VIII activator, either factor Xa or thrombin, on the decay of factor X activation on the endothelial cell surface. Kinetics of factor X activation on human umbilical vein endothelial cells was compared with that on phospholipid vesicles employing purified coagulation factors from plasma as well as recombinant factor VIII variants. Employing factor Xa as factor VIII activator, rate constants for decay of membrane-bound factor X activation were consistently low on endothelial cells (0.02 min) as compared with phospholipid vesicles (0.2 min). Activation of factor VIII by thrombin resulted in two-fold increased decay rates. In the presence of excess of von Willebrand factor over factor VIII, decay rates were not significantly changed. Factor VIII variants with and without a Tyr to Phe substitution, which abolishes high-affinity binding to von Willebrand factor, displayed the same factor X activation decay kinetics. Although previous studies have shown that von Willebrand factor modulates factor VIII activation and stabilisation, this apparently does not affect the progression of factor X activation at the endothelium.     

Combined factor V/VIII deficiency: a case report including levels of factor V and factor VIII coagulant and antigen as well as protein C inhibitor

Comprehensive coagulation studies were performed on members of a family with combined factor V/VIII deficiency. The purpose of these studies was to investigate the hypothesis that combined factor V/VIII deficiency is due to a lack of the inhibitor to activated protein C. The analyses performed included routine APTT and PT, factor V and VIII coagulant activity and antigen levels, von Willebrand factor levels, protein C antigen assay, and both protein C inhibitor activity and antigen levels. Three of the 19 family members studied were found to have a deficiency of both factors V and VIII. These three individuals showed prolonged APTTs and PTs and decreased levels of factor V and factor VIII coagulant activity and antigen. Factor VIII related antigen and ristocetin cofactor (von Willebrand factor) levels were normal. Protein C and both protein C inhibitor activity and antigen levels were also found to be normal. These findings confirm the results of other recent investigators and indicate that the autosomal, inherited combined factor V/VIII deficiency is not due to a protein C inhibitor deficiency. The real defect in this combined deficiency remains to be determined.     

von Willebrand factor binds to the surface of dendritic cells and modulates peptide presentation of factor VIII

It has been proposed that von Willebrand factor might affect factor VIII immunogenicity by reducing factor VIII uptake by antigen presenting cells. Here we investigate the interaction of recombinant von Willebrand factor with immature monocyte-derived dendritic cells using flow cytometry and confocal microscopy. Surprisingly, von Willebrand factor was not internalized by immature dendritic cells, but remained bound to the cell surface. As von Willebrand factor reduces the uptake of factor VIII, we investigated the repertoire of factor VIII presented peptides when in complex with von Willebrand factor. Interestingly, factor VIII-derived peptides were still abundantly presented on major histocompatibility complex class II molecules, even though a reduction of factor VIII uptake by immature dendritic cells was observed. Inspection of peptide profiles from 5 different donors showed that different core factor VIII peptide sequences were presented upon incubation with factor VIII/von Willebrand factor complex when compared to factor VIII alone. No von Willebrand factor peptides were detected when immature dendritic cells were pulsed with different concentrations of von Willebrand factor, confirming lack of von Willebrand factor endocytosis. Several von Willebrand factor derived peptides were recovered when cells were pulsed with von Willebrand factor/factor VIII complex, suggesting that factor VIII promotes endocytosis of small amounts of von Willebrand factor by immature dendritic cells. Taken together, our results establish that von Willebrand factor is poorly internalized by immature dendritic cells. We also show that von Willebrand factor modulates the internalization and presentation of factor VIII-derived peptides on major histocompatibility complex class II.     

Investigation of a coagulation accelerating factor (CAF) in glomerulonephritis

A coagulation accelerating factor was purified from the plasma of two patients with glomerulonephritis (GN) who suffered from thrombotic complications. The factor co-purified with factor VIII/von Willebrand factor complex (FVIII/vWf) and under dissociating conditions remained associated with the factor VIII coagulant activity (FVIII). Control purified FVIII/vWf showed no coagulation accelerating activity under the experimental conditions used. The levels of coagulation accelerating factor, FVIII and von Willebrand factor (vWf) were reduced by incubation with rabbit anti-human FVIII/vWf or human anti-FVIII serum indicating a close association of these three activities. Multimeric analysis of the plasma FVIII/vWf complex from the two patients demonstrated a reduction in the high molecular weight multimers and the presence of an additional band not present on analysis of normal FVIII/vWf. It is suggested that the coagulation accelerating factor represents an active form of FVIII which has different in vitro properties to thrombin activated FVIII.     

Management of inherited von Willebrand disease.

von Willebrand disease is a bleeding disorder caused by quantitative or qualitative defects of von Willebrand factor. The diagnosis is based on measurements of plasma and platelet von Willebrand factor, the ability of von Willebrand factor to interact with its platelet receptor and the analysis of the multimeric composition of von Willebrand factor. Owing to the heterogeneity of von Willebrand factor defects, a correct diagnosis of types and subtypes may be sometimes difficult but is very important for an appropriate therapy. The aim of treatment is to correct the dual defects of haemostasis, i.e. abnormal coagulation, expressed by a low level of factor VIII, and abnormal platelet adhesion, expressed by a prolonged bleeding time. Desmopressin is the treatment of choice in patients with type I von Willebrand disease, who account for approximately 70% of cases, because it corrects the factor VIII/von Willebrand factor level and the prolonged bleeding time in most of these patients. In type 3 and in the majority of type 2 von Willebrand disease patients, desmopressin is not effective and it is necessary to resort to plasma concentrates containing factor VIII and von Willebrand factor. Treated with virucidal methods, these concentrates are effective and currently safe, but they do not always correct the bleeding time defect. Platelet concentrates or desmopressin can be used as adjunctive treatments when a poor correction of the bleeding time after concentrates is associated with continued bleeding. Studies are in progress, first to better characterize patients with type I von Willebrand disease and to determine their response to desmopressin, and second, to evaluate the pharmacokinetics of factor VIII following factor VIII/von Willebrand factor concentrates and to establish the indication for concentrates.     

La maladie de Willebrand

Von Willebrand factor is involved in primary hemostasis (adhesion of platelets to subendothelium and platelet aggregation) and acts as the carrier of coagulation factor VIII. Von Willebrand disease, resulting from a quantitative or qualitative defect of this factor, is the most frequent inherited bleeding disorder. It is mainly responsible for symptoms such as mucocutaneous bleeding and excessive bleeding after trauma or invasive procedures, but can also cause gastro-intestinal bleeding or hemarthrosis in the most severe forms of the disease. There are numerous causes of physiological variation of von Willebrand factor plasma levels which can be responsible for diagnostic difficulty or changes in symptoms over time. Diagnosis relies primarily on clinical symptoms but requires the use of several laboratory analyses: von Willebrand factor activity and antigen testing and factor VIII activity. More specialized assays allow classification of the disease in various types and subtypes which imply different management strategies (types 1, 2A, 2B, 2M, 2N, and 3). Treatment is based on desmopressin, responsible for an increase in plasma concentration of von Willebrand factor, and plasma-derived von Willebrand factor concentrates which can be combined with factor VIII.     

Effects on coagulation factor production following primary hepatomitogen-induced direct hyperplasia

AIM: To investigate the molecular mechanisms involved in coagulation factor expression and/or function during direct hyperplasia (DH)-mediated liver regeneration.METHODS: Direct hyperplasia-mediated liver regeneration was induced in female C57BL/6 mice by administering 1,4-bis[2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP), a representative hepatomitogen. Mice were weighed and sacrificed at various time points [Day 0 (D0: prior to injection), 3 h, D1, D2, D3, and D10] after TCPOBOP administration to obtain liver and blood samples. Using the RNA samples extracted from the liver, a comprehensive analysis was performed on the hepatic gene expression profiling of coagulation-related factors by real-time RT-PCR (fibrinogen, prothrombin, factors V, VII, VIII, IX, X, XI, XII, XIIIβ, plasminogen, antithrombin, protein C, protein S, ADAMTS13, and VWF). The corresponding plasma levels of coagulation factors (fibrinogen, prothrombin, factors V, VII, VIII, IX, X, XI, XII, XIII, and VWF) were also analyzed and compared with their mRNA levels.RESULTS: Gavage administration of TCPOBOP (3 mg/kg body weight) resulted in a marked and gradual increase in the weight of the mouse livers relative to the total body weight to 220% by D10 relative to the D0 (control) ratios. At the peak of liver regeneration (D1 and D2), the gene expression levels for most of the coagulation-related factors (fibrinogen, prothrombin, factors V, VII, VIII, IX, XI, XII, XIIIβ, plasminogen, antithrombin, protein C, ADAMTS13, VWF) were found to be down-regulated in a time-dependent manner, and gradually recovered by D10 to the basal levels. Only mRNA levels of factor X and protein S failed to show any decrease during the regenerative phase. As for the plasma levels, 5 clotting factors (prothrombin, factors VIII, IX, XI, and XII) demonstrated a significant decrease (P < 0.05) during the regeneration phase compared with D0. Among these 5 factors, factor IX and factor XI showed the most dramatic decline in their activities by about 50% at D2 compared to the basal levels, and these reductions in plasma activity for both factors were consistent with our RT-PCR findings. In contrast, the plasma activities of the other coagulation factors (fibrinogen, factors V, VII, XIII, and VWF) were not significantly reduced, despite the reduction in the liver mRNA levels. Unlike the other factors, FX showed a temporal increase in its plasma activity, with significant increases (P < 0.05) detected at D1.CONCLUSION: Investigating the coagulation cascade protein profiles during liver regeneration by DH may help to better understand the basic biology of the liver under normal and pathological conditions.     

Abnormal proteolysis (DIC)--successful treatment with antithrombin III concentrate and a concentrate containing F XIII and native von Willebrand factor

Two patients with life-threatening disseminated intravascular coagulation (DIC) syndrome, one caused by Gram-negative bacteria and one by premature separation of the placenta, are described. Specific substitution was given by antithrombin III concentrate and AHF-Kabi, a low purity factor VIII concentrate containing native von Willebrand factor and factor XIII. The treatment quickly returned the extremely low levels of antithrombin III, factor VIII:C, fibrinogen and factor XIII, initially found, to normal, and also returned the multimeric pattern of von Willebrand factor to normal. This resulted in diminished bleeding, enabling surgical treatment of the underlying disease.     

Carrier detection in haemophilia A families: comparison of conventional coagulation parameters with DNA polymorphism analysis – first report from India

Linear discriminants that include data on factor VIII:C and von Willebrand factor antigen levels are well-established tools in estimating the probability of carriership in haemophilia A families. A comparison between the conventional coagulation data, i.e. the ratio of factor VIII:C and von Willebrand factor antigen, and the DNA analysis techniques was made in 98 confirmed carriers (39 obligatory, 69 detected by gene tracking analysis) and 71 normal age matched females who did not have any history of bleeding and were not taking any drug. The lowest misclassification rate, i.e. 7% among the carriers, was seen when a cut-off value of 0.7 was chosen. In the case of normals, all were outside this cut-off value. Thus, it was considered as a workable reference value for classifying the carriers in haemophilia A families in our laboratory. We conclude that the optimal service for haemophilia A carrier diagnosis must include above coagulation test probabilities as well as DNA marker studies. However, it is recommended that the smaller laboratories in developing countries can benefit immensely by only establishing factor VIII:C and von Willebrand factor antigen estimation.     

Von Willebrand Factor: Gene Dosage Relationships and Transfusion Response in Bleeder Swine—a New Bioassay

Aggregation of human platelets by bovine plasma was recently recognized as a marker for the study of the antihemophilic and von Willebrand factors. A similar marker in porcine plasma is shown to be specific for the platelet-active von Willebrand factor of plasma, but not for the antihemophilic factor (factor VIII). A new quantitative assay for the von Willebrand factor is based on the dose-response relationship observed between the concentration of von Willebrand factor and platelet aggregation times determined macroscopically. Bleeder swine, homozygous for von Willebrand disease, had no detectable platelet aggregating activity, while heterozygotes, carriers of the disease, had reduced levels of approximately 50% of normal. Exact detection of non-obligate carriers, hitherto impossible, becomes readily feasible because of the gene dosage relationship to the von Willebrand factor plasma levels. Transfusion of bleeder swine with normal plasma results in an immediate post-transfusion rise of the von Willebrand factor, followed by a rapid falloff. At 24 hr post-transfusion, no von Willebrand factor is detectable at a time when the factor VIII response is at its maximum. The discordance in plasma levels of this platelet-active von Willebrand factor and factor VIII in carrier animals and in the bleeder animals after transfusion suggests a different molecular and genetic basis for these two biological activities.     

How I treat patients with von Willebrand disease

Von Willebrand disease (vWD) is a frequent inherited disorder of hemostasis that affects both sexes. Two abnormalities are characteristic of the disease, which is caused by a deficiency or a defect in the multimeric glycoprotein called von Willebrand factor: low platelet adhesion to injured blood vessels and defective intrinsic coagulation owing to low plasma levels of factor VIII. There are 2 main options available for the treatment of spontaneous bleeding episodes and for bleeding prophylaxis: desmopressin and transfusional therapy with plasma products. Desmopressin is the treatment of choice for most patients with type 1 vWD, who account for approximately 70% to 80% of cases. This nontransfusional hemostatic agent raises endogenous factor VIII and von Willebrand factor 3 to 5 times and thereby corrects both the intrinsic coagulation and the primary hemostasis defects. In patients with the more severe type 3 and in most patients with type 2 disease, desmopressin is ineffective or is contraindicated and it is usually necessary to resort to plasma concentrates containing both factor VIII and von Willebrand factor. Concentrates treated with virucidal methods should be preferred to cryoprecipitate because they are equally effective and are perceived as safer. (Blood. 2001;97:1915-1919)     

Molecular and cellular biology of von Willebrand factor

Von Willebrand factor (vWF), a central protein in the regulation of blood coagulation, serves as a major adhesive link between platelets and the blood vessel wall and also functions as a carrier in plasma for factor VIII. Abnormalities of vWF result in von Willebrand disease (vWD), a common inherited human bleeding disorder. Deficient von Willebrand factor function has been proposed as potentially protective against the development of coronary vascular disease and several recent investigational therapies are directed at the vWF-platelet interaction. This review summarizes the current state of knowledge regarding the biosynthesis and processing of vWF and the relationship of vWF structure to function. Finally, recent progress in identifying specific genetic mutations responsible for the many variants of vWD is discussed.     

Coagulation factors,inflammation markers,and venous thromboembolism: the longitudinal investigation of thromboembolism etiology (LITE)

PURPOSE: We sought to assess prospectively whether higher levels of blood coagulation factors and inflammation markers are risk factors for venous thromboembolism. SUBJECTS AND METHODS: In two pooled population-based cohort studies, we measured levels of factor VII, factor VIII, von Willebrand factor, fibrinogen, and C-reactive protein, and white blood cell count, in samples obtained from 19,237 adults with no baseline history of venous thromboembolism, cancer, or warfarin use. The endpoint was validated venous thromboembolism during follow-up (median, 7.8 years). RESULTS: A total of 159 venous thromboembolism events occurred. Factor VIII and von Willebrand factor were linearly associated with increased risk of venous thromboembolism (P for trend <0.0001). As compared with those in the lowest quartile, the multivariate-adjusted hazard ratio (HR) of venous thromboembolism was 2.6 (95% confidence interval [CI]: 1.6 to 4.3) for factor VIII levels in the highest quartile and 3.8 (95% CI: 2.0 to 7.2) for the highest fifth percentile. For von Willebrand factor, the hazard ratios in middle-aged subjects were 4.6 (95% CI: 2.2 to 9.2) for the highest quartile and 7.6 (95% CI: 3.1 to 18) for the highest fifth percentile. Factor VII levels above the 95th percentile, as compared with the lowest quartile, also conveyed a higher risk of venous thromboembolism (HR = 2.4; 95% CI: 1.2 to 4.8). In contrast, there was no association of venous thromboembolism with fibrinogen or C-reactive protein levels, or white cell count. CONCLUSIONS: In this prospective study, elevated factor VIII and von Willebrand factor levels were common, independent, and dose-dependent risk factors for venous thromboembolism, and an elevated factor VII level was a possible risk factor. Venous thromboembolism, unlike arterial disease, was not related to inflammatory markers.     

Effect of levothyroxine replacement therapy on coagulation and fibrinolysis in severe hypothyroidism

OBJECTIVE: We previously demonstrated that patients suffering from moderate hypothyroidism were at increased risk of thrombosis contrasting with the bleeding tendency of those presenting severe hypothyroidism. The latter state is associated with hemostatic anomalies including von Willebrand type 1 disease and increased fibrinolytic capacity. With the exception of von Willebrand type 1 disease, reversibility of hemostatic changes is not established after levothyroxine replacement therapy. Therefore our objective was to analyze the reversibility of these anomalies. MATERIALS AND METHODS: We analyzed the impact of levothyroxine treatment on lipid parameters, fibrinogen, platelet count, D-dimers, alpha2 antiplasmin activity, plasminogen activity, tissue plasminogen activator antigen (t-PA Ag), plasminogen activator inhibitor type 1 antigen (PAI-1 Ag) and coagulation factors (factor VIII coagulant, von Willebrand factor antigen, von Willebrand factor and factor IX) in 23 patients with severe hypothyroidism (TSH level > 50 mU/ I). RESULTS: Mean fibrinogen levels increased by 14.2% while t-PA Ag and PAI-1 Ag increased by 42.6 and 69%, respectively, after correction of hypothyroidism. Interestingly, post-treatment PAI-1 Ag levels tended to be higher in patients with normal-high final TSH levels than in patients with normal-low final TSH levels. Our results suggest that normalization of fibrinolysis is obtained after a transient decrease of fibrinolytic activity. We also confirmed the correction of coagulation factor abnormalities upon levothyroxine replacement therapy. CONCLUSIONS: We demonstrated that the coagulation disorders and the hyperfibrinolytic status of severe hypothyroid patients were corrected upon levothyroxine therapy. However, the clinical consequences of the transient decrease of the fibrinolytic activity during the course of TSH normalization need further studies.     

Tumor necrosis factor alpha in the pathogenesis of human and murine fulminant hepatic failure

BACKGROUND & AIMS: The tumor necrosis factor (TNF)-alpha/TNF receptor system is critical for liver development because hepatocytes undergo apoptosis if the antiapoptotic cascades resulting in RelA NF-kappaB activation are not effective. Therefore, we studied the role of TNF-alpha in fulminant hepatic failure (FHF) and developed a new therapeutic strategy. METHODS: Serum levels and hepatic expression of TNF-alpha and both TNF receptors were determined by enzyme-linked immunosorbent assay and immunohistochemistry. Adenoviral vectors were constructed expressing dominant-negative proteins interfering with intracellular TNF-alpha-dependent pathways. The relevance of these constructs was studied in primary mouse hepatocytes and in a murine model of FHF. RESULTS: Serum levels of TNF-alpha and TNF receptors are significantly increased in FHF; this increase correlates with patient prognosis. In livers of patients with FHF, infiltrating mononuclear cells express high amounts of TNF-alpha and hepatocytes overexpress TNF receptor 1 (TNF-R1). Apoptotic hepatocytes are significantly increased in FHF, and there is a strong correlation with TNF-alpha expression, which is even more pronounced in areas of mononuclear infiltrates. In an in vivo FHF model, the Fas-associated death domain (FADD), adenovirus selectively blocked the intracellular pathway, leading to mitochondrial cytochrome c release, caspase-3 activation, and, thus, apoptosis of hepatocytes. CONCLUSIONS: The results show that the TNF-alpha/TNF-R1 system is involved in the pathogenesis of FHF in humans. Studies in this animal model indicate that FADD may serve as a molecular target to prevent liver cell death in vivo.