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

Murine coagulation factor VIII is synthesized in endothelial cells

The primary cellular source of factor VIII (FVIII) biosynthesis is controversial, with contradictory evidence supporting an endothelial or hepatocyte origin. LMAN1 is a cargo receptor in the early secretory pathway that is responsible for the efficient secretion of factor V (FV) and FVIII to the plasma. Lman1 mutations result in combined deficiency of FV and FVIII, with levels of both factors reduced to ~10% to 15% of normal in human patients. We generated Lman1 conditional knockout mice to characterize the FVIII secretion profiles of endothelial cells and hepatocytes. We demonstrate that endothelial cells are the primary biosynthetic source of murine FVIII and that hepatocytes make no significant contribution to the plasma FVIII pool. Utilizing RiboTag mice and polyribosome immunoprecipitation, we performed endothelial cell-specific messenger RNA isolation and quantitative polymerase chain reaction analyses to confirm that endothelial cells highly express F8 and to explore the heterogeneity of F8 expression in different vascular beds. We demonstrate that endothelial cells from multiple, but not all, tissues contribute to the plasma FVIII pool in the mouse.

Human liver sinusoidal endothelial cells but not hepatocytes contain factor VIII

BACKGROUND

Although the liver is the major site of coagulation factor VIII (FVIII) synthesis, the type of cells producing FVIII within the liver is still unclear.

OBJECTIVES

To measure FVIII in extracts of primary liver sinusoidal endothelial cells (LSECs) and hepatocytes, thereby preventing potential bias resulting from the modifications of the cell phenotype that can take place during in vitro culture.

METHODS

LSECs were purified by flow cytometry cell sorting on the basis of their coexpression of Tie2 and CD32b. The purity of the cells was controlled by RNA sequencing. FVIII activity (FVIII:C) in extracts of purified cells was measured with a sensitive FVIII chromogenic assay, in which the specificity of the reaction is controlled by neutralization of FVIII activity with specific inhibitor antibodies.

RESULTS

The FVIII:C concentration in purified LSECs ranged from 0.3 to 2.8 nU per cell. In contrast, FVIII:C was undetectable in hepatocytes. The intracellular FVIII:C concentrations are therefore at least 10-100-fold higher in LSECs than in hepatocytes.

CONCLUSIONS

Our data demonstrate that LSECs, but not hepatocytes, contain measurable amounts of FVIII:C, and suggest that the former are the main cells producing FVIII in the human liver.

Mesenchymal stem cells contribute to endogenous FVIII:c production

Besides the liver, it has been difficult to identify which organ(s) and/or cellular component(s) contribute significantly to the production of human FVIII:c (FVIII). Thus far, only endothelial cells have been shown to constitute a robust extrahepatic source of FVIII, possibly explaining both the diverse presence of FVIII mRNA in the body, and the observed increase in FVIII levels during liver failure. Here, we investigate whether human mesenchymal stem cells (MSC), ubiquitously present in different organs, could also contribute to FVIII production. MSC isolated from human lung, liver, brain, and bone marrow expressed FVIII message as determined by quantitative-RT-PCR. Using an antibody specific for FVIII, confocal microscopy, and umbilical cord-derived endothelial cells (HUVEC) as a negative control, we demonstrated that, in MSC, FVIII protein was not stored in granules; rather, it localized to the perinuclear region. Furthermore, functional FVIII was detected in MSC supernatants and cell lysates by aPTT and chromogenic assays. These results demonstrate that MSC can contribute at low levels to the functional FVIII pool, and advance the understanding of the physiology of FVIII production and secretion.

Activation of human endothelial cells from specific vascular beds induces the release of a FVIII storage pool

Although the liver is known to be the main site of factor VIII (FVIII) production, other organs are probably also important for the regulation of FVIII secretion. However, the study of the regulation of extrahepatic FVIII production has been hampered by the lack of definitive identification of human tissues able to secrete FVIII. Recent studies have shown that lung endothelial cells can synthesize FVIII. We therefore studied the production of FVIII by endothelial cells purified from other vascular beds. Because physiologic stress results in a rapid elevation of FVIII, we also investigated whether endothelial cells can store FVIII and secrete it after treatment with agonists. Microvascular endothelial cells from lung, heart, intestine, and skin as well as endothelial cells from pulmonary artery constitutively secreted FVIII and released it after treatment with phorbol-myristate acetate and epinephrine. By contrast, endothelial cells from the aorta, umbilical artery and umbilical vein did not constitutively secrete FVIII or release it after treatment with agonists, probably because of a lack of FVIII synthesis. Extrahepatic endothelial cells from certain vascular beds therefore appear to be an important FVIII production and storage site with the potential to regulate FVIII secretion in chronic and acute conditions.

FVIII production by human lung microvascular endothelial cells

While extrahepatic factor VIII (FVIII) synthesis suffices for hemostasis, the extrahepatic production sites are not well defined. We therefore investigated the ability of the human lungs to produce FVIII. Lungs from heart-beating donors who were declined for transplantation were perfused and ventilated in an isolated reperfusion model for 2 hours. A progressive accumulation of FVIII and von Willebrand factor (VWF) was recorded in the perfusion medium in 3 of 4 experiments. By contrast, factor V, fibrinogen, and immunoglobulin G (IgG) levels remained constant during the perfusion period, indicating that the accumulation of FVIII and VWF was not due to diffusion from the intercellular medium into the vascular system. Purified human lung microvascular endothelial cells produced FVIII during at least 2 passages in vitro. Altogether, these data identify the lung endothelial cells as a FVIII production site in humans.

Familial multiple coagulation factor deficiencies: new biologic insight from rare genetic bleeding disorders

Combined deficiency of factor (F)V and FVIII (F5F8D) and combined deficiency of vitamin K-dependent clotting factors (VKCFD) comprise the vast majority of reported cases of familial multiple coagulation factor deficiencies. Recently, significant progress has been made in understanding the molecular mechanisms underlying these disorders. F5F8D is caused by mutations in two different genes (LMAN1 and MCFD2) that encode components of a stable protein complex. This complex is localized to the secretory pathway of the cell and likely functions in transporting newly synthesized FV and FVIII, and perhaps other proteins, from the ER to the Golgi. VKCFD is either caused by mutations in the gamma-carboxylase gene or in a recently identified gene encoding the vitamin K epoxide reductase. These two proteins are essential components of the vitamin K dependent carboxylation reaction. Deficiency in either protein leads to under-carboxylation and reduced activities of all the vitamin K-dependent coagulation factors, as well as several other proteins. The multiple coagulation factor deficiencies provide a notable example of important basic biological insight gained through the study of rare human diseases.

Expression of factor VIII in recombinant and transgenic systems

Deficiency in a coagulation factor VIII (FVIII) causes a genetic disorder hemophilia A, which is treated by repeated infusions of expensive FVIII products. Recombinant FVIII (rFVIII), the culmination of years of extensive international research, is an important alternative to plasma-derived FVIII (pdFVIII) and is considered to have a higher margin of safety. Advances in biotechnology allowed production of rFVIII at industrial scale, which significantly improved treatment of hemophilia A patients. We review the contemporary methods used for FVIII expression in mammalian cell culture systems and discuss the factors responsible for insufficient recoveries of rFVIII, such as inefficient accumulation of FVIII mRNA in the cell, complexity of the mechanisms of FVIII secretion, and instability of secreted FVIII. The approaches to improve the yield of rFVIII in cell culture systems include genetic engineering of B-domain-deleted FVIII, introduction of introns into FVIII cDNA constructs for more efficient processing and accumulation of FVIII mRNA, and introduction of mutations into chaperone-binding sites of FVIII to improve its secretion. Design of FVIII with prolonged half-life in vivo is considered as another promising direction in improving rFVIII protein and efficiency of hemophilia A therapy. As an alternative to expression of rFVIII in cell culture systems, we discuss production of rFVIII in transgenic animals, where high levels of rFVIII have been successfully secreted into milk. We also pay attention to the major limitations of this approach, such as safety issues associated with potential transmission of animal pathogens. Finally, we present a brief characterization of commercial recombinant FVIII products currently available on the market for hemophilia A treatment.

Roles of phytanoyl-CoA alpha-hydroxylase in mediating the expression of human coagulation factor VIII

The coagulation factor VIII (FVIII) is the coagulation factor deficient in the X-chromosome-linked bleeding disorder hemophilia A. Previous transfection studies demonstrated that factor VIII was 10-100-fold less efficiently expressed than the homologous coagulation factor, factor V. To investigate the regulatory mechanisms of FVIII synthesis and secretion, we used the yeast two-hybrid system as an approach to search for proteins that associated with FVIII. The A2 domain (337-740 amino acids) of factor VIII (FVIII-A2) was used as a bait and phytanoyl-CoA alpha-hydroxylase (PAHX) was identified as a binding protein of FVIII-A2. PAHX had potential to interact with the residues 373-508 within the A2 domain, but not with A1 and A3 (the homologous domains of A2). The interaction between the A2 domain and PAHX was independent of the type 2 peroxisomal targeting signal (PTS2) of PAHX. Overexpression of PAHX in FVIII-produced cells decreased the expression of FVIII by about 70%. The elevated expression of von Willebrand factor had no effect on the suppression of FVIII secretion by PAHX. Expression of the green fluorescent PAHX fusion protein in SMMC-7721 cells affected the intracellular trafficking of FVIII-A2. These results suggested that the interaction between PAHX and FVIII-A2 was in part responsible for the low-level expression of factor VIII.

Advances toward gene therapy for hemophilia at the millennium

Hemophilia A and hemophilia B are both X chromosome-linked recessive bleeding disorders that affect about 1 in 5000 males and result from a deficiency in the coagulation factors VIII and IX, respectively. Severely affected individuals require frequent administration of factor VIII or factor IX preparations derived from human plasma, and more recently, from recombinant DNA technology. Although these preparations have greatly reduced the contamination with blood-borne pathogens, there still exist significant limitations with protein replacement therapy. As we elucidate more about the expression, structure, and function of these coagulation factors new avenues will open for the development of novel genetically improved coagulation factors. Several aspects of the hemophilias A and B make these diseases attractive candidates for gene therapy. These advantages include the following: (1) these proteins are readily delivered into the circulation from a variety of different cell types; (2) low levels of expression would significantly improve the management of bleeding episodes in these patients; (3) it is unlikely that regulated expression of these proteins will be required; and (4) there are excellent animal models for these diseases. Although progress with gene transfer of factor IX has proceeded at a greater rate than factor VIII, success with both molecules has demonstrated partial persistent correction in mouse and canine models of hemophilia A and B. The information gained from these animal studies has provided new insights into gene therapeutic approaches for genetic diseases. In addition, several gene therapy clinical studies for the treatment of hemophilia A and B were initiated in 1999.

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.

von Willebrand Factor Elevates Plasma Factor VIII Without Induction of Factor VIII Messenger RNA in the Liver

Factor VIII and von Willebrand factor (vWF) circulate in the plasma as a noncovalent protein complex. Circulating levels of factor VIII are coordinately regulated with circulating levels of vWF in which the ratio is maintained at 1 molecule of factor VIII for 50 to 100 vWF subunits. Infusion of vWF into vWF-deficient animal models and human patients yields a secondary increase in circulating levels of factor VIII. We have studied the mechanism of the secondary rise in factor VIII in a porcine model of vWF deficiency. On infusion of vWF into a vWF-deficient pig there was an approximately fivefold increase in circulating factor VIII activity. Liver biopsies were taken pre- and post-vWF infusion for isolation of total messenger RNA (mRNA). Factor VIII–specific mRNA was measured by an RNAse protection assay. The results showed no difference in the liver-specific factor VIII mRNA on vWF infusion. These results indicate that the secondary rise in factor VIII levels in response to exogenous vWF infusion is not dependent on increased steady-state levels of factor VIII mRNA in the liver.

von Willebrand Factor Elevates Plasma Factor VIII Without Induction of Factor VIII Messenger RNA in the Liver

Factor VIII and von Willebrand factor (vWF) circulate in the plasma as a noncovalent protein complex. Circulating levels of factor VIII are coordinately regulated with circulating levels of vWF in which the ratio is maintained at 1 molecule of factor VIII for 50 to 100 vWF subunits. Infusion of vWF into vWF-deficient animal models and human patients yields a secondary increase in circulating levels of factor VIII. We have studied the mechanism of the secondary rise in factor VIII in a porcine model of vWF deficiency. On infusion of vWF into a vWF-deficient pig there was an approximately fivefold increase in circulating factor VIII activity. Liver biopsies were taken pre- and post-vWF infusion for isolation of total messenger RNA (mRNA). Factor VIII–specific mRNA was measured by an RNAse protection assay. The results showed no difference in the liver-specific factor VIII mRNA on vWF infusion. These results indicate that the secondary rise in factor VIII levels in response to exogenous vWF infusion is not dependent on increased steady-state levels of factor VIII mRNA in the liver.

Can we improve on nature? "Super molecules" of factor VIII

Treatment of haemophilia A requires frequent infusion of plasma- or recombinant-derived factor VIII. This regimen is limited due to the high cost and inconvenient access to peripheral veins. In addition, patients frequently develop inhibitory antibodies that limit available therapeutic regimens. Two major advances in factor VIII research over the past 15 years were the ability to isolate homogeneous preparations of factor VIII and the isolation of the factor VIII gene that provided for a detailed biochemical and structural characterization of the factor VIII molecule. With an increased understanding of the requirements for factor VIII function, studies have attempted to produce improved factor VIII molecules for replacement therapy. These findings have produced forms of factor VIII that are more efficiently produced, that are less immunogenic, and that have higher specific activity. The future will see the engineering of novel factor VIII molecules with increased therapeutic efficiency while minimizing inhibitor antibody development. In addition, there are now structural models of factor VIII available that should in the future direct development of novel peptidomimetics that may eventually overcome the requirement for replacement therapy with factor VIII protein.

Differential interaction of coagulation factor VIII and factor V with protein chaperones calnexin and calreticulin

Factor VIII (FVIII) and factor V (FV) are homologous coagulation cofactors sharing a similar domain organization (A1-A2-B-A3-C1-C2) and are both extensively glycosylated within their B-domains. In mammalian cell expression systems, compared with FV, the FVIII primary translation product is inefficiently transported out of the endoplasmic reticulum. Here we show that FVIII is degraded within the cell by a lactacystin-inhibitable pathway, implicating the cytosolic 20 S proteasome machinery. Protein chaperones calnexin (CNX) and calreticulin (CRT) preferentially interact with glycoproteins containing monoglucosylated N-linked oligosaccharides and are proposed to traffic proteins through degradative and/or secretory pathways. Utilizing co-immunoprecipitation assays, intracellular FVIII was detected in association with CNX maximally within 30 min to 1 h following synthesis, whereas FV could not be detected in association with CNX. In contrast, both FVIII and FV displayed interaction with CRT during transit through the secretory pathway. B-domain deleted FVIII significantly reduced the CNX and CRT interaction, indicating the B-domain may represent a primary CNX and CRT interaction site. In the presence of inhibitors of glucose trimming, the interactions of FVIII with CNX, and of FVIII and FV with CRT, were significantly reduced whereas the secretion of FVIII, and not FV, was inhibited. In addition, transfection in a glucosidase I-deficient Chinese hamster ovary cell line (Lec23) demonstrated that both degradation and secretion of FVIII were inhibited, with little effect on the secretion of FV. These results support that CNX and CRT binding, mediated at least in part by the B-domain of FVIII, is required for efficient FVIII degradation and secretion. In contrast, FV does not require CNX interaction for efficient secretion. The results suggest a unique requirement for carbohydrate processing and molecular chaperone interactions that may limit the productive secretion of FVIII.

A 110-amino acid region within the A1-domain of coagulation factor VIII inhibits secretion from mammalian cells

Factor VIII is the coagulation factor deficient in the X-chromosome-linked bleeding disorder hemophilia A. Factor VIII is homologous to blood coagulation factor V, both having a domain structure of A1-A2-B-A3-C1-C2. Previous transfection studies demonstrated that factor VIII is 10-fold less efficiently expressed than the homologous coagulation factor, factor V. The inefficient expression correlated with interaction of the factor VIII primary translation product with the protein chaperonin BiP in the lumen of the endoplasmic reticulum. In contrast, factor V was not detected in association with BiP and was secreted efficiently. To determine whether specific amino acid sequences within factor VIII inhibit secretion, we have studied the secretion of factor VIII deletion and factor VIII/factor V chimeric proteins upon transient transfection of COS-1 monkey cells. A chimeric factor VIII protein that contained the A1- and A2-domains of factor V was secreted with a similar efficiency as wild-type factor V, whereas the complementary chimera having the A1- and A2-domains of factor VIII was secreted with low efficiency, similar to wild-type factor VIII. These results suggested that sequences within the A1- and A2-domains were responsible for the low secretion efficiency of factor VIII. Secretion of A1-domain-deleted factor VIII was increased approximately 10-fold compared to wild-type factor VIII or A2-domain-deleted factor VIII. Expression of the factor VIII A1-domain alone did not yield secreted protein, whereas expression of the factor VIII A2-domain alone or the factor V A1-domain or A2-domain alone directed synthesis of secreted protein. Secretion of a hybrid in which the carboxyl-terminal 110 amino acids of the A1-domain were replaced by homologous sequences from the factor V A1-domain was also increased 10-fold compared to wild-type factor VIII, however, the secreted protein was not functional and the heavy and light chains were not associated. These results localize a 110-amino acid region within the A1-domain that inhibits factor VIII secretion. This region is clustered with multiple short peptide sequences that have potential to bind BiP.

Blood coagulation factors changes during liver regeneration in rats

Effects of partial hepatectomy on blood coagulation factors were investigated in rats. Analysis were performed 24, 48 and 72 hours after surgery. Howell's time was significantly higher after 24 and 48 h compared to the control value. Prothrombin time was significantly prolonged after 24 h. Partial thromboplastin time did not differ significantly in any time. FII values were significantly reduced after 24 and 48 h, but FV values only after 24 h. FVII showed significant decrease after 24 h, but significant increase at 48 h. FVIII and ATIII average values were significantly lower after 24, 48 and 72 h. Plasma fibrinogen increased. Significant differences were observed 48 and 72 h after surgery. Differences in normalization time of these coagulation factors are most probably the consequence of their synthesis in various cell types, regenerated at different periods after partial hepatectomy.

Factor VIII: Structure, function and analysis

Factor VIII is an important blood coagulation protein whose genetic deficiency leads to the serious bleeding disorder, classic haemophilia (haemophilia A). Here we review the structure, function and analysis of this protein for diagnostic and therapeutic applications. Because factor VIII is tightly associated with von Willebrand factor some recent work on the latter is also considered so as to clarify the relationship between them.

Expression of blood clotting factor VIII:C gene in capillary endothelial cells

The essential role of Factor VIII:C (FVIII:C, anti-hemophilia factor A) as a cofactor for Factor IXa-dependent activation of Factor X has been established. In this paper, we describe that capillary endothelial cells from bovine adrenal medulla express active FVIII:C gene. Accumulation of FVIII:C in conditioned media from an 8-day-old culture is approximately twice as high as that stored in the cell when immunoprecipitated FVIII:C was analyzed for its ability to convert Factor X to Factor Xa. Analysis of [35S]methionine-labeled and immunoprecipitated FVIII:C from cells or conditioned media on SDS-PAGE under fully denatured conditions indicated that the newly synthesized FVIII:C consists of heavy chain of M(r) 200,000 and light chain of M(r) 46,000. The secreted FVIII:C in the non-reduced condition however, has a molecular weight of 270,000 which suggests that in native protein, the heavy and light chains are held together by S-S bonds. Furthermore, susceptibility of the immunoprecipitated FVIII:C to N-glycanase digestion establishes that the endothelial cells derived FVIII:C contains asparagine-linked carbohydrate side chains.

Secretion of coagulant factor VIII activity and antigen by in vitro cultivated rat liver sinusoidal endothelial cells

Different types of liver cells and a few extrahepatic cell types were analysed for the presence and production of factor VIII activity (VIII:C). Only freshly prepared suspensions of rat liver sinusoidal cells and pure monolayer cultures of rat liver endothelial cells (LEC) were found to contain and secrete detectable amounts of the coagulation factor. Secretion of VIII:C by cultured LEC was inhibited by cycloheximide and by monensin. Constant levels of VIII:C were produced for at least 48 h suggesting continuous synthesis rather than a burst release of stored material. VIII:C, as measured spectro-photometrically by conversion of X to Xa, was inhibited by anti-human VIII:C antiserum. Indirect immunocytochemistry using this antiserum gave positive staining only with LEC. Immunoprecipitation of metabolically labelled proteins in conditioned rat LEC medium with the anti human VIII:C antiserum revealed the presence of proteins of similar sizes to those reported for human VIII:C. These results indicate that rat LEC are an important site for production and secretion of procoagulant factor VIII and are not only a site for storage and release of the factor. The established conditions for synthesis of VIII:C in in vitro cultivated rat LEC should provide the means to study the regulation of VIII:C synthesis.

Human hepatic sinusoidal endothelial cells in culture produce von Willebrand factor and contain Weibel-Palade bodies

Human hepatic sinusoidal endothelial cells were derived from cadaveric human livers. Cells were grown in culture for several weeks to produce small patches of confluent endothelial cells. The ultrastructure of sinusoidal endothelial cells was examined, cell monolayers were stained immunocytochemically for von Willebrand factor antigen, and antigen in cell culture media was measured by enzyme-linked immunosorbent assay. Human hepatic sinusoidal endothelial cells contained von Willebrand factor antigen and Weibel-Palade bodies, were fenestrated, and released von Willebrand factor antigen into media in a time-dependent manner. Although in some respects human hepatic endothelial cells were different from vascular cells, there was no evidence that there were qualitative differences in their capacity to produce von Willebrand factor.

Effect of von Willebrand factor coexpression on the synthesis and secretion of factor VIII in Chinese hamster ovary cells

In plasma, antihemophilic factor (factor VIII) exists as a 200-kilodalton heavy-chain polypeptide in a metal ion association with an 80-kilodalton light-chain polypeptide. This complex is bound by hydrophobic and hydrophilic interactions to a large multimeric glycoprotein, von Willebrand factor (vWF). Accumulation of secreted human factor VIII activity expressed in Chinese hamster ovary cells requires the addition of serum in the growth medium, which provides vWF. Here we report that coexpression of vWF with factor VIII in Chinese hamster ovary cells resulted in increased stable accumulation of factor VIII activity in the absence of serum in the growth medium. In the coexpressing cells, the vWF cDNA transcription unit was transcribed to yield mRNA which was efficiently translated. vWF was properly processed and secreted to yield disulfide-bonded high-molecular-weight multimers similar to those observed in vWF secreted from human endothelial cells. Nuclear run-on assays showed that the factor VIII gene was transcribed at a level similar to that of the vWF gene, but the mRNA did not accumulate to high levels in the cytoplasm. In addition, although the translation efficiency of the factor VIII mRNA was similar to that of vWF, the processing and secretion of the factor VIII primary translation product was dramatically reduced compared with vWF. These results demonstrate that in Chinese hamster ovary cells both factor VIII mRNA accumulation and the processing and secretion of the primary factor VIII translation product are inefficient processes.

Hepatic sinusoidal cell destruction in the development of intravascular coagulation in acute liver failure of rats

Rats received a dose of dimethylnitrosamine (DMN) or carbon tetrachloride (CCl4). In the liver of rats given DMN, apoptosis of fat-storing cells occurred at 7.5 h, and sinusoidal endothelial cell degeneration followed, with parenchymal cell necrosis after 9 h. Fibrin thrombi appeared in the sinusoids as well as in these necrotic areas after 12 h. In contrast, in the liver of rats given CCl4, parenchymal cell degeneration was seen after 6 h and necrosis with fibrin thrombi developed after 9 h. Fat-storing cells and endothelial cells were almost intact, and fibrin thrombi were not present in the sinusoids. SGPT values increased with decreased plasma levels of fibrinogen and antithrombin III and prolonged prothrombin time after 3 and 6 h, in the CCl4 and DMN models, respectively. An extensive reduction in plasma factor VIIIC levels and peripheral platelets was seen after 18 and 24 h, respectively, only in the DMN model. These results suggest that endothelial cells destruction can cause fibrin formation in the hepatic sinusoids in acute liver injury. Fat-storing cell injury may contribute to the destruction.

Effect of von Willebrand factor coexpression on the synthesis and secretion of factor VIII in Chinese hamster ovary cells

In plasma, antihemophilic factor (factor VIII) exists as a 200-kilodalton heavy-chain polypeptide in a metal ion association with an 80-kilodalton light-chain polypeptide. This complex is bound by hydrophobic and hydrophilic interactions to a large multimeric glycoprotein, von Willebrand factor (vWF). Accumulation of secreted human factor VIII activity expressed in Chinese hamster ovary cells requires the addition of serum in the growth medium, which provides vWF. Here we report that coexpression of vWF with factor VIII in Chinese hamster ovary cells resulted in increased stable accumulation of factor VIII activity in the absence of serum in the growth medium. In the coexpressing cells, the vWF cDNA transcription unit was transcribed to yield mRNA which was efficiently translated. vWF was properly processed and secreted to yield disulfide-bonded high-molecular-weight multimers similar to those observed in vWF secreted from human endothelial cells. Nuclear run-on assays showed that the factor VIII gene was transcribed at a level similar to that of the vWF gene, but the mRNA did not accumulate to high levels in the cytoplasm. In addition, although the translation efficiency of the factor VIII mRNA was similar to that of vWF, the processing and secretion of the factor VIII primary translation product was dramatically reduced compared with vWF. These results demonstrate that in Chinese hamster ovary cells both factor VIII mRNA accumulation and the processing and secretion of the primary factor VIII translation product are inefficient processes.

Cure of hemophilia A by orthotopic liver transplantation

A patient with hemophilia A and transfusion-associated end-stage chronic liver disease underwent orthotopic liver transplantation. He had no requirement for exogenous factor VIII replacement during the 27 mo he survived. Although his hemophilia was cured, he had antibodies to the human immunodeficiency virus; ultimately he died of complications arising from acquired immunodeficiency syndrome. Liver transplantation for cirrhotic hemophiliacs can free them of the need for antihemophilic-factor therapy; however, application of this approach may be limited by the high prevalence of human immunodeficiency virus infection in multitransfused hemophiliacs.

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.

Coagulation defects of aflatoxin intoxicated rabbits

Twelve New Zealand white rabbits were intoxicated with aflatoxin B1. Most rabbits developed a coagulation defect near the time of death. Immediately prior to death there were significant decreases in factors V, VII, and VIII coagulant activities and fibrinogen concentration without a change in plasma fibrin(ogen) degradation product concentration, platelet number, and detectable plasma fibrin monomers. Microscopic evidence of disseminated intravascular coagulation was present in one rabbit with marked, diffuse hepatic necrosis. Terminal serum albumin concentration was significantly correlated to plasma factors V and VII activities and fibrinogen concentration. The coagulation defect of aflatoxicosis is primarily due to diminished hepatic synthesis of coagulation factors except when hepatic necrosis is severe enough to initiate intravascular coagulation and consumption of coagulation factors.

Diagnosis and recommended management of esophageal perforation and rupture

Over the past 47 years (1937 to 1984), a total of 127 patients with esophageal perforation or rupture were evaluated at Duke Medical Center or the Durham Veterans Administration Medical Center. In 13 patients, the diagnosis was established at the time of autopsy and in the remaining 114, the diagnosis was established clinically. The etiology, radiological findings, underlying esophageal disease, time interval between onset of symptoms and therapy, and eventual outcome were evaluated. Patients with anastomotic leaks and those in whom carcinoma resulted in perforation or fistula were excluded. Iatrogenic causes were responsible for 55% of perforations, followed by spontaneous rupture in 15%, foreign body perforation in 14%, and traumatic perforation in 10%. Of the 127 patients, 114 underwent treatment involving primary closure (43%), drainage alone (28%), resection (9%), or nonoperative therapy (20%). The overall mortality among these 114 patients was 21%. Fourteen patients sustained a major complication requiring additional operative intervention. The overall mortality among patients requiring reoperation was 57%. Survival was significantly influenced by a delay in treatment of greater than 24 hours. With the exception of nonoperative therapy, survival was improved for all forms of treatment instituted within 24 hours. Primary closure within 24 hours resulted in the most favorable outcome (92% survival). In addition to early treatment, other factors associated with a favorable outcome included traumatic perforation (100% survival), foreign-body perforations (94% survival), and iatrogenic causes (80% survival). Spontaneous rupture resulted in the lowest survival (37%). The incidence of esophageal perforation has increased dramatically since 1967.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The effect of an acute phase reaction and BCG innoculation on factor VIII in the guinea-pig

Factor VIII antigen (VIII:Ag) and vWF:Antigen (vWF:Ag) were measured in guinea-pigs treated with intraperitoneal turpentine to induce an acute phase reaction, and with BCG to stimulate the reticulo-endothelial system. In the turpentine treated animals there was a significant rise of fibrinogen at 24 and 48 hours after injection (1.43 +/- 0.01 g/l) when compared with controls (1.15 +/- 0.1 g/l), mean +/- SEM n = 3 p 0.01). There was no change in plasma VIII:Ag but a significant rise of vWF:Ag at (2.0 +/- .3 units/ml) when compared with controls (1.1 +/- 0.05 units/ml, mean +/- SEM n = 3 p less than 0.001). Examination of perfused guinea-pig organs showed a reduction in hepatic VIII:Ag (82%) and vWF:Ag (90%) and a 76% increase in splenic vWF:Ag only in the turpentine treated animals. Distribution of 125I Albumin to detect trapped blood in tissues demonstrated efficient clearance of blood by perfusion. There was no change in the plasma concentration of either VIII:Ag or vWF:Ag following BCG inoculation but there was a 45% increase in the splenic concentration of vWF:Ag. It is concluded that only the factor vWF:Ag and not the factor VIII:Ag component of the factor VIII complex is an acute phase reactant in guinea-pig and that this may be due to increased synthesis of vWF:Ag by vascular endothelium in the spleen. Although BCG inoculation may have stimulated synthesis or storage of vWF:Ag in the spleen it did not have an appreciable effect on the plasma concentration of either VIII:Ag or vWF:Ag.

The effect of liver disease on factors V, VIII and protein C

The components of the factor VIII complex were estimated by immuno- and bioassays in 85 patients with liver disease. The plasma concentrations of the antigens were elevated in 65% (VIII:CAg) and in 76% (VIIIR:Ag) of patients while the biological activities were elevated in only 14% (VIII:C) and 15% (VIII:RiCof). There was no correlation with C-reactive protein, used as a measure of an acute phase reaction (X2 = 0.7; P = 0.1); or with severity of liver disease as judged by prothrombin ratio (P = 1.0) but highest values were observed in patients with cholestatic liver disease. Following parenteral vitamin K there was a significant fall in both the biological activity of VIIIC (36%) and of VIII:CAg (38%) in 13 vitamin K deficient patients (P less than 0.001) but no change in 23 vitamin K replete patients or in the VIIIR:Ag levels in either group. Factor V levels were lower in patients with parenchymal liver disease (0.54 +/- 0.1 units/ml, mean +/- SEM, n = 12; normal range 0.5-1.5 units/ml) than in patients with extrahepatic cholestasis who were vitamin K deficient (1.2 +/- 0.1 units/ml, P less than 0.0001). The levels of protein C antigen, the vitamin K dependent protease which inactivates factors VIII:C and V, was at the lower end of the range in both groups (0.7 +/- 0.1, mean +/- SEM, n = 18, normal range 0.74-1.4 units/ml). There was no significant change in either protein C antigen or factor V following vitamin K. The discrepancy between the biological activity of factor VIII and the antigen levels could represent accumulation of partially degraded factor VIII or production of a hypoactive form. There is no evidence that the reduction in VIIIC and VIII:CAg following vitamin K was mediated by protein C.

Distribution of factor VIII mRNA and antigen in human liver and other tissues

The cellular site of synthesis of factor VIII (FVIII:C; anti-haemophilic factor) has long been sought. Previous studies suggested the liver as a major site of synthesis, but extrahepatic sources such as spleen and lung have been implicated. Using an immunoradiometric assay (IRMA), we recently localized factor VIII antigen (FVIII:Ag, formerly FVIII:CAg), to whole perfused guinea pig liver and spleen, and to isolated hepatocytes, with lesser or trace amounts in other tissues. Using an immunohistological technique, Stel et al. detected FVIII:Ag in normal human liver sinusoidal endothelial cells, while Exner et al. detected FVIII:Ag by IRMA in extracts of human lymph nodes, lung, liver and spleen. The localization of antigen in tissues does not, however, distinguish sites of factor VIII synthesis from those of storage, and such experiments are subject to misinterpretation due to entrapment of plasma factor VIII in tissues. The recent cloning of the human factor VIII gene provides hybridization probes for the detection of factor VIII messenger RNA in cells, thus directly determining sites of synthesis. During complementary DNA cloning, we detected factor VIII mRNA in liver, and it has been localized by others in liver and placenta and in liver and kidney. In the present study, we detected factor VIII mRNA in isolated human hepatocytes, in spleen and in numerous tissues including lymph nodes and kidney, but not in white blood cells or cultured endothelial cells. We also found that the factor VIII, factor VII, factor IX and protein C antigens in liver are predominantly localized in hepatocytes, while very little von Willebrand factor antigen (vWF:Ag, formerly FVIIIR Ag) is detectable in this organ.

Ultrastructural localization of factor VIII procoagulant antigen in human liver hepatocytes

Factor VIII is generally believed to circulate in blood as a multimeric complex of two glycoproteins which are physiologically and immunologically distinct. One component of the factor VIII complex is factor VIII procoagulant activity (FVIII:C) which is associated with factor VIII/procoagulant antigen (FVIII:Ag, formerly FVIII/CAg). The second, larger unit of the complex is factor VIII/von Willebrand factor (vWF:Ag, formerly factor VIII-related antigen or FVIIIRAg). FVIII:C has anti-haemophilic activity and is defective or deficient in patients with classical haemophilia, and vWF:Ag is absent in patients with von Willebrand disease. FVIII:Ag was demonstrated recently in endothelial cells lining hepatic sinusoids, by using immunoperoxidase staining and light microscopy, whereas biochemical data had indicated its presence predominantly in the hepatocyte fractions and in lesser amounts in endothelial cells. Moreover, recent hybridization experiments detected FVIII:C messenger RNA in liver and kidney tissues. Despite several efforts, the cells responsible for FVIII:C synthesis have not been unequivocally identified. Here we use protein A-gold complex labelling to demonstrate the ultrastructural localization of FVIII:C in human liver cells; the results indicate that hepatocytes may synthesize FVIII:Ag.

Monoclonal antibodies to human FVIIIR:Ag and FVIIIC

A series of monoclonal antibodies have been produced which recognize different epitopes of the factor VIII molecule. The antibodies were raised in mice against high purity factor VIII (FVIII) and the mouse spleens used in cell fusion experiments. Following cell fusion the hybridoma supernatants were used for screening with a solid phase radioimmunoassay (RIA) technique. The antibodies detected were differentiated by their degree of attachment to 2 components of the FVIII molecule, FVIII related antigen (FVIIIR:Ag) (also called von Willebrand's Factor) and FVIII coagulant (FVIIIC). Immunofluorescence and immunoperoxidase studies both showed the FVIIIR:Ag antibodies to be localized to the endothelial cells of the blood vessel walls. They can, therefore, be used for histological identification of these cells on cryostat and paraffin sections. The anti-FVIIIR:Ag antibodies have no anticoagulant properties, whereas the anti-FVIIIC antibody reacts as an instant inhibitor with a strength of 35,000 new Oxford U/ml. These antibodies are stable reagents and suitable for radioimmunoassay for both FVIIIR:Ag and FVIIIC.

Expression of active human factor VIII from recombinant DNA clones

DNA clones encoding the complete 2,351 amino acid sequence for human factor VIII have been isolated and used to produce biologically active factor VIII in cultured mammalian cells. The recombinant protein corrects the clotting time of plasma from haemophiliacs and has many of the biochemical and immunological characteristics of serum-derived factor VIII.

Characterization of the human factor VIII gene

The complete 186,000 base-pair (bp) human factor VIII gene has been isolated and consists of 26 exons ranging in size from 69 to 3,106 bp and introns as large as 32.4 kilobases (kb). Nine kb of mRNA and protein-coding DNA has been sequenced and the mRNA termini have been mapped. The relationship between internal duplications in factor VIII and evolution of the gene is discussed.