Characterization of a Hollow Fiber Bioartificial Liver Device

A three-compartment bioartificial liver (BAL) has been developed for potential treatment of fulminant hepatic failure. It has been shown previously that viability and liver-specific functions were maintained in laboratory-scale bioreactors of such design. In this study, the performance of hepatocytes in a clinical-scale bioartificial liver was verified by sustained specific production rates of albumin and urea, along with oxygen consumption rates for up to 56 h and liver-specific gene expression for up to 72 h. In addition, transmission of porcine endogenous retrovirus and other type C retroviral particles across the hollow fibers was not detected under both normal and extreme operating fluxes. These results demonstrate that the clinical-scale BAL performs at a level similar to the laboratory scale and that it offers a viral barrier against porcine retroviruses.

MARS--does it stand the test of time?

Artificial liver support systems have been tested for decades in the management of liver failure. Generally, after some promising results published as case series, the device either disappears or fails to show significant benefit in controlled trials. Recently, the molecular absorbent recycling systems (MARS) or extracorporeal albumin dialysis (ECAD) technique appears to have broken this trend. Responding to the title one could summarize by saying this technique so far has stood the test of time. Data in support of its use in acute liver failure (ALF) is still scant and difficult to assess. However, in a well known but not very well defined entity of acute on chronic liver failure (AOCLF) the ECAD technique has been shown to improve survival compared to a similar randomized control group receiving standard supportive therapy. This well tolerated liver support system has real potential for widespread application if further well designed multicenter clinical trials continue to support its effectiveness. Its future lies probably in the management of the moribund hospitalized patient on the transplant list awaiting a donor liver.

Blood coagulation in anhepatic pigs: effects of treatment with the AMC-bioartificial liver

The function of a newly devised bioartificial liver (AMC-BAL) based on viable, freshly isolated porcine hepatocytes has been evaluated in anhepatic pigs. The aim of this study was to assess the contribution of BAL treatment on blood coagulation parameters. Pigs were anesthetized and a total hepatectomy was performed (n = 15). The infrahepatic caval vein and the portal vein were connected to the subdiaphragmatic caval vein using a three-way prosthesis. Animals received standard intensive care (control, n= 5), treatment with an empty BAL (device control, n= 5) or with a cell-loaded BAL (BAL-treatment, n= 5) for a period of 24 h starting 24 h after hepatectomy. Coagulation parameters studied concerned prothrombin time (PT), platelet count, the procoagulant system (factors (F)II, FV, FVII, FVIII and fibrinogen), anticoagulant system (AT III), fibrinolytic system (t-PA, PAI-1) as well as markers of coagulation factor activation (TAT complexes, prothrombin fragment F1 + 2). FII, FV, FVII, AT III and fibrinogen rapidly decreased after total hepatectomy in pigs in accordance with the anhepatic state of the animals. FVIII levels were not influenced by the hepatectomy. A mild drop in platelet count was seen in all groups. Treatment of anhepatic pigs with the cell-loaded BAL did not restore PT or clotting factor levels. TAT and F1 + 2 complexes, however, were significantly increased in this group. Levels of t-PA and PAI-1 were not influenced by cell-loaded BAL treatment. Treatment of anhepatic pigs with the AMC-BAL based on freshly isolated porcine hepatocytes does not result in an improved coagulation state due to extensive consumption of clotting factors. However, increased levels of TAT complexes and prothrombin fragments F1 + 2 during treatment of anhepatic pigs indicate synthesis and direct activation of coagulation factors, leading to thrombin generation. This demonstrates that this bioartificial liver is capable of synthesizing coagulation factors.

Bridging a patient with acute liver failure to liver transplantation by the AMC-bioartificial liver

Recently a phase I clinical trial has been started in Italy to bridge patients with acute liver failure (ALF) to orthotopic liver transplantation (OLT) by the AMC-bioartificial liver (AMC-BAL). The AMC-BAL is charged with 10 x 10(9) viable primary porcine hepatocytes isolated from a specified pathogen-free (SPF) pig. Here we report a patient with ALF due to acute HBV infection. This patient was treated for 35 h by two AMC-BAL treatments and was bridged to OLT. There was improvement of biochemical and clinical parameters during the treatment. No severe adverse events were observed during treatment and follow-up of 15 months after hospital discharge. Possible porcine endogenous retrovirus (PERV) activity could not be detected in the patient's blood or blood cells up to 12 months after treatment.

Improving the next generation of bioartificial liver devices

Several extracorporeal bioartificial liver (BAL) devices are currently being evaluated as an alternative or adjunct therapy for liver disease. While these hybrid systems show promise, in order to become a clinical reality, BAL devices must clearly demonstrate efficacy in improving patient outcomes. Here, we present aspects of BAL devices that could benefit from fundamental advances in cell and developmental biology. In particular, we examine the development of human hepatocyte cell lines, strategies to stabilize the hepatocyte phenotype in vitro, and emphasize the importance of the cellular microenvironment in bioreactor design. Consideration of these key components of BAL systems will greatly improve next generation devices.

The effect of serum from liver cancer patients on the growth and function of primary and immortalised hepatocytes

A limiting factor in the efficacy of bioartificial liver (BAL) for the treatment of liver failure is the toxicity of the patients' serum to the hepatocytes in the device. This study investigates the interaction of liver cancer patient serum with primary and immortalised rat hepatocytes. Liver cancer serum increased the growth rate of immortalised hepatocytes, without affecting reduced glutathione levels. The activities of DT-diaphorase and pi glutathione-S-transferase (GST), enzymes associated with de-differentiation, were also increased. Exposure of primary hepatocytes to liver cancer serum resulted in a decrease in cytochrome P450 (CYP) content, and in P450 dependent metabolism of testosterone. Formation of 2-alpha- and 6-beta- hydroxy testosterone was decreased. These reactions are predominantly associated with CYP 2C11 and 3A1 respectively in normal rat liver. The activity of total GST was also decreased, although that of the pi isoenzyme of GST was not affected. Our results suggest that exposure of hepatocytes in a bioreactor to liver cancer patient serum will result in overgrowth of cells, if proliferating cells are being used, and in de-differentiation. The serum may have to be pretreated with adsorbants to remove toxins prior to BAL treatment.

Bioartificial liver support

Bioartificial liver support has been increasingly the focus of both basic and clinical research in an attempt to replicate the multiplicity of normal liver function. The concept is attractive because, if it is effective, patients with acute liver failure may be supported until native liver regeneration occurs or, by optimizing their condition, until liver transplantation is possible. Current bioartificial liver support systems utilize primary porcine hepatocytes or transformed human hepatocytes, which are housed within a bioreactor, through which the patient's blood or plasma is pumped in an extracorporeal circuit. The optimal source for the hepatocytes is an area of debate; however, a genetically engineered cell line may provide optimal function. Novel three-dimensional matrices that anchor the hepatocytes are being designed to mimic architectural features of the normal liver. Large multicentre, randomized, controlled trials are ongoing following several pilot studies. Serious side effects such as hemodynamic instability and immune reactions have been infrequent. Much controversy, however, surrounds the issue of possible transmission of pig endogenous retrovirus to humans, and current trials are being carefully monitored. Bioartificial liver support is a promising technology, and the results of current and planned studies are awaited with great interest.

Artificial organs and vanishing boundaries

With the first clinical use of the artificial kidney over 5 decades ago, we entered into a new era of medicine-that of substitutive and replacement therapy. Yet it took nearly another 15 years until chronic treatment was possible and nearly another 15 years until widespread treatment was possible due to government support. The history of development and clinical use of other artificial organ technologies such as the artificial heart and heart valves, the artificial lung, artificial blood, joint replacements, the artificial liver, the artificial pancreas, immunologic, metabolic, and neurologic support, neurocontrol, and tissue substitutes have followed similar long development paths. Despite their relatively long time to be put into clinical use, the contributions of artificial organ technologies to the betterment of mankind have been unquestionably a major success. For example, modern day surgery would not be possible without heart-lung support, and the technologies for heart support have led to the development of various minimally invasive technologies. The powerful impact that artificial organ technologies presently has on our lives is seen through the statistic that in the U.S.A. nearly 1 in 10 persons is living with an implanted medical device. With the aging of our population and the improvements in technologies, these numbers will only increase.

Evaluation of a novel bioartificial liver in rats with complete liver ischemia: treatment efficacy and species-specific alpha-GST detection to monitor hepatocyte viability

BACKGROUND/AIMS

There is an urgent need for an effective bioartificial liver system to bridge patients with fulminant hepatic failure to liver transplantation or to regeneration of their own liver. Recently, we proposed a bioreactor with a novel design for use as a bioartificial liver (BAL). The reactor comprises a spirally wound nonwoven polyester fabric in which hepatocytes are cultured (40 x 10(6) cells/ml) as small aggregates and homogeneously distributed oxygenation tubing for decentralized oxygen supply and CO2 removal. The aims of this study were to evaluate the treatment efficacy of our original porcine hepatocyte-based BAL in rats with fulminant hepatic failure due to liver ischemia (LIS) and to monitor the viability of the porcine hepatocytes in the bioreactor during treatment. The latter aim is novel and was accomplished by applying a new species-specific enzyme immunoassay (EIA) for the determination of porcine alpha-glutathione S-transferase (alpha-GST), a marker for hepatocellular damage.

METHODS

Three experimental groups were studied: the first control group (LIS Control, n = 13) received a glucose infusion only; a second control group (LIS No-Cell-BAL, n = 8) received BAL treatment without cells; and the treated group (LIS Cell-BAL, n = 8) was connected to our BAL which had been seeded with 4.4 x 10(8) viable primary porcine hepatocytes.

RESULTS/CONCLUSIONS

In contrast to previous comparable studies, BAL treatment significantly improved survival time in recipients with LIS. In addition, the onset of hepatic encephalopathy was significantly delayed and the mean arterial blood pressure significantly improved. Significantly lower levels of ammonia and lactate in the LIS Cell-BAL group indicated that the porcine hepatocytes in the bioreactor were metabolically activity. Low pig alpha-GST levels suggested that our bioreactor was capable of maintaining hepatocyte viability during treatment. These results provide a rationale for a comparable study in LIS-pigs as a next step towards potential clinical application.

Simple and reliable methods to assess hepatocyte viability in bioartificial liver support system matrices

New assays were compared with tritiated thymidine (3HTdR) and trypan blue dye exclusion for evaluating hepatocyte viability on cytodex 3 beads and in microcapsules, the matrices used in bioartificial liver support systems. They were the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) 5 min qualitative assay and the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4 -sulfophenyl)-2H -tetrazolium, inner salt (MTS) 1 h quantitative assay. Both tetrazolium salts are cleaved in active mitochondria, the reaction occurring, therefore, in living cells only. After bathing at 39 degrees C with MTT for 5 min, porcine or rat hepatocytes on cytodex 3 beads were detached by collagenase while those in microcapsules were released by citrate treatment or passage through a fine needle. Cell viability was determined directly by microscope. The MTT 5 min metabolic inclusion test and MTS 1 h quantitative assay results correlated closely with those obtained by the 3HTdR, trypan blue dye exclusion, and fluorescein diacetate (FDA) methods. Both the new assays are sensitive, accurate, simple, and time-saving.

Hepatocytes entrapped in collagen gel following 14 days of storage at 4 degrees C: preservation of hybrid artificial liver

Preservation of hepatocytes is a key technical factor toward the successful clinical application of hybrid artificial livers. It was possible to culture hepatocytes that had been preserved with collagen gel for 8 and 14 days in 4 degrees C University of Wisconsin solution. Phase-difference and scanning electron microscopy showed that most of the stored hepatocytes maintained a round-shaped morphology. In the 14 day preservation group, on Days 2 and 8, respectively, ureogenesis was 98.3% and 69.6%, gluconeogenesis was 65.2% and 80.7%, lidocaine clearance was 81.7% and 72.5%, urea synthesis after ammonia load was 47.6% and 57.5% of those in the comparable control group. This implies that preserved hepatocytes maintained adequate functional capability even after 14 days of preservation. We suggest that our preservation method will be valuable for the future application and development of a practical hybrid artificial liver.

Comparative evaluation of different membranes for the construction of an artificial liver support system

During the past decades, many technological improvements have been made in the construction of extracorporeal liver support systems. Among these achievements, membranes of artificial capillary system, used as substrates of hepatocyte growth, aroused our interest in their application for the construction of bioreactors. The present paper studied the comparison of hepatocyte growth and function on six different membranes. Four of them are cellulose based membranes, Cuprophan, Hemophan, Cellulose acetate, and Bioflux; two are synthetic polymer SPAN and Polysulphone. Human hepatoma cell line SMMC-7721, with moderately differentiated hepatocyte-specific functions, was inoculated into the hollow fiber cartridges. These cells were allowed to attach and to grow over these membranes. It was found that there existed differences in hepatocyte immobilization and growth among these membranes. They influenced the growth and functions of hepatoma cells in vitro to some extent. These results show that membrane is an important factor in the construction of capillary membrane bioreactors for artificial liver support.

A carrier-mediated transport of toxins in a hybrid membrane. Safety barrier between a patients blood and a bioartificial liver

Combination of detoxifying liver support systems with liver cell bioreactors may have additional benefits for the treatment of liver failure due to the replacement of known and unknown metabolic activities of the liver. However, the problem of side effects and possible risks caused by the use of animal hepatocytes or hepatoma cells remains unsolved which underlines the need of a safety barrier between the patients blood and the extracorporeal bioreactor. Passive filters do not meet the requirements of such membranes, because in liver failure desired and undesired molecules in the patients blood share similar physicochemical properties. That challenges the development of biologically designed separation membranes. A hybrid membrane is formed by implementation of transport proteins into a highly permeable hollow fiber. The transport of free solutes and albumin bound toxins is tested in vitro in comparison with conventional high flux membranes. The transport characteristics for tightly albumin bound toxins are significantly improved for the hybrid membrane. The transport of albumin bound toxins across the membrane is not associated with albumin. The selectivity of the transport is evaluated in vivo. No significant loss of middle molecular weight hormones attached to other carrier proteins was observed. Neither transport of immunologically relevant proteins across the membrane nor loss of valuable proteins was measured. Also in vivo, a significant reduction of protein bound toxins and a transport of metabolically relevant solutes, like amino acids, was shown. The presented hybrid membrane may be used like an "intelligent membrane" as a safety barrier between the patients blood and cell devices.

Development of a hybrid liver support system: a review

Hybrid liver support systems (LSS) for the use of the detoxifying, metabolic synthetic and regulatory capabilities of liver cells are under development for extracorporeal therapy of acute liver failure and for bridging to liver transplantation. A summary of our development is discussed. A five-step technique for primary liver cell isolation has been introduced in order to address larger scale procurement of hepatocytes. Immobilisation of the cells after isolation appears to be one of the main factors in maintaining hepatocyte function in vitro. Different techniques have been investigated. Using the cell-cell adhesion technique, a culture model was developed for the immobilisation of hepatocytes between capillary membranes. Four separate capillary membrane systems, each forming independent compartments are woven in order to create a three dimensional network. A bioreactor design has been developed. The construction provides different functions, including decentralised cell perfusion. The bioreactor enables 3 dimensional reorganisation of cells, integral oxygenation and decentralised metabolite exchange. The bioreactor has been scaled-up to allow hepatocytes and sinusoidal endothelial cells to be cultured in quantities sufficient for therapeutic application. In a healthy pig model, possible limiting side effects of therapy with this device were excluded. The efficacy of the system has been demonstrated in a hepatectomised pig model. Subsequently, a complete hybrid liver support system for human studies was introduced and applied clinically.

Long-term performance of albumin secretion of hepatocytes cultured in a packed-bed reactor utilizing porous resin

A packed-bed reactor utilizing the porous polymer, polyvinyl formal (PVF) resin, as a supporting material was applied for the long-term culture of rat hepatocytes. Perfusion cultures using this reactor, as well as monolayer cultures, were performed for up to 1 week under 3 different media conditions. When serum-free or epidermal growth factor-containing medium was used, albumin secretion rates showed constant decreases in both the perfusion and the monolayer cultures, and approximately 10% of the activity exhibited on Day 1 was preserved at the end of the cultures. In contrast, the hepatocytes supplemented with serum-containing medium exhibited stable ability of albumin secretion throughout the culture period under the perfusion culture condition using PVF resin. From the microscopic observation, the immobilized hepatocytes in this medium revealed round shapes, and a cluster of cell aggregates was scarcely seen.

Evaluation of extracorporeal bioartificial liver devices

The initial clinical studies on artificial liver support were performed at King's College Hospital, London during the late 1970s. Initially using charcoal haemoperfusion, and subsequently resin haemoperfusion, and these studies culminated in a controlled clinical trial of charcoal haemoperfusion in which overall survival was high, but no statistically significant benefit was found. From this study, much information was also obtained about the clinical importance of the various complications of acute liver failure, and the experience of King's over the last 2 decades exceeds 1,000 patients. The aim of this article is to review the potential of the exciting new developments in this field of bioartificial liver support incorporating hepatocytes. It focuses on the published findings of early clinical use of these systems and attempts to identify what is needed in further studies. It is of paramount importance that future trials are designed to give the greatest information on the effects of bioartificial liver support. For these, the biocompatibility of the systems should to be confirmed with detailed assessment and sensitive tests need to be developed to determine the metabolic functional efficacy of these devices. The possible relationship of treatment to liver regeneration has been considered, because without this these systems will in many cases be limited to use as a bridge to liver transplantation. Finally, some of the possible future modifications of the cell-based liver support systems are discussed.