In vitro evaluation of a novel bioreactor based on an integral oxygenator and a spirally wound nonwoven polyester matrix for hepatocyte culture as small aggregates

Evidence for Galalpha(1-3)Gal expression on primary porcine hepatocytes: implications for bioartificial liver systems

BACKGROUND/AIMS

To bridge acute liver failure (ALF) patients to orthotopic liver transplantation, several bioartificial liver (BAL) systems have been developed. The bio-component of most BAL systems consists mainly of porcine hepatocytes. Plasma or blood of ALF patients is perfused through the BAL thereby contacting porcine hepatocytes. Xenogeneic BAL systems may suffer from hyperacute rejection similar to whole-organ xenotransplants. Hyperacute rejection is mediated by antibodies directed against Galalpha(1-3)Gal, a carbohydrate structure present on most mammalian cells. Galalpha(1-3)Gal is produced by the enzyme alpha1,3-galactosyltansferase (alphaGal-T). Conflicting data have been published concerning Galalpha(1-3)Gal expression on hepatocytes in intact porcine liver. We investigated whether isolated porcine hepatocytes express Galalpha(1-3)Gal.

METHODS

Immunofluorescence, flow cytometry, RT-PCR and enzyme activity assays were performed on freshly isolated and cultured porcine hepatocytes and liver biopsies. Anti-Galalpha(1-3)Gal antibodies were measured in plasma from patients treated with BAL by ELISA.

RESULTS

Isolated porcine hepatocytes express (alphaGal-T) at low levels and Galalpha(1-3)Gal is present in low quantities on these cells, in contrast to hepatocytes in situ. Furthermore, IgG and IgM anti-Galalpha(1-3)Gal are depleted from the plasma of ALF patients during BAL treatment.

CONCLUSIONS

Isolation and culture of porcine hepatocytes induce Galalpha(1-3)Gal expression, which may elicit immunological responses potentially compromising BAL functionality.

The SlideReactor-A Simple Hollow Fiber Based Bioreactor Suitable for Light Microscopy

Most bioartificial liver support systems are based on hollow fiber capillaries within modified dialysis cartridges or more sophisticated bioreactor constructions. Due to their design microscopic follow-up of reorganization and growth of tissue between the hollow fibers is not possible. The SlideReactor is a simple hollow fiber based bioreactor construction suitable for light microscopy and time-lapse video observation. The SlideReactor offers a cell compartment separated from a medium inflow and outflow compartment. Cell compartment access ports enable easy filling of the cell compartment with cell suspension, as well as fixation of the tissue. For more complex procedures or full access to all the cells, the bioreactor can be opened easily by cutting the silicone seal with a scalpel. Due to its simple design and the utilization of standard materials, it could serve as a suitable, cost-efficient tool to evaluate the behavior of cells cultured between hollow fiber capillaries. The paper describes the production process: similar to open source projects in software engineering, we would like to propose the concept as an open platform to anyone interested in hollow fiber based cell culture.

Cellular therapies for liver replacement

Insufficient donor organs for orthotopic liver transplantation worldwide have urgently increased the requirement for new therapies for acute and chronic liver disease. Whilst none are yet clinically proven there are at least two different approaches for which there is extensive experimental data, some human anecdotal evidence and some data emerging from Phase 1 clinical trials. Both approaches involve bio-engineering. In vivo tissue engineering involves isolated liver cell transplantation into the liver and/or other ectopic sites and in vitro tissue engineering, using an extracorporeal hepatic support system or bioartificial liver. Some questions are common to both these approaches, such as the best cell source and the therapeutic mass required, and are discussed. Others are specific to each approach. For cell transplantation in vivo the initial engraftment and repopulation will make a critical difference to the outcome, and development of markers for transplanted cells has enabled significant advances in understanding, and therefore manipulating, the process. Moreover, the role of immunosuppression is also important and novel approaches to natural immunosuppression are discussed. For use in a bioartificial liver, the ability for hepatocytes to perform ex vivo at in vivo levels is critical. Three dimensional culture improves cell performance over monolayer cultures. Alginate encapsulated cells offer a suitable 3-D environment for a bioartificial liver since they are both easily manipulatable and cryopreservable. The use of cells derived from stem cells or foetal rather than adult liver cells is also emerging as a potential human cell source which may overcome problems associated with xenogeneic cells.

Hepatic tissue engineering

Fulminant hepatic failure (FHF) attributes to rising medical cost and accounts for many deaths each year in the United States. Currently, the only solution is organ transplantation. Due to increasing donor organ shortage, many in need of transplantation continue to remain on the waiting list. Liver Assist Devices (LADs) are being used to temporarily sustain liver function and bridge the period between FHF and transplantation. Hepatic Tissue Engineering is a step toward alleviating the need for donor organs; yet many challenges must be overcome including scaffold choice, cell source and immunological barriers. Bioreactors have aided in hepatocyte survival and have proven to sustain viable cells for several weeks. Achieving the necessary functions required for hepatic replacement is aided by the incorporation of growth factors and mitogens many that now can be bound to the polymer scaffold and released in a timely manner. Utilizing concepts such as MicroElectroMechanical systems (MEMs) technology, our laboratory is able to mimic the natural vasculature of the liver and sustain functional and viable hepatocytes. Expanding and improving upon this platform technology, advancements made will continue toward the development of a fully functioning and implantable liver.

Development of a scaled up liver device incorporating cryo-preserved pig liver micro-organs

BACKGROUND/AIMS

Currently there is no effective therapy for most patients with fulminant or end stage liver disease.

METHODS

Pig liver micro-organs (LMOs), which preserve liver micro-architecture and ensure a maximal 150-200mum distance from a source of nutrients and gases have been prepared and a method to cryo-preserve them has been developed. A new scaled-up extra-corporeal liver device termed aLIVE-H in which LMOs are exposed to liver-like hemodynamic conditions has also been developed. The purpose of this work is to test the safety and function of cryo-preserved LMOs and how the hemodynamic properties of the scaled up aLIVE device affect their function.

RESULTS

Pig LMOs in aLIVE-H, transcribe albumin and Factor V at similar levels, irrespective of their position within the bioreactor, indicating that the hemodynamic features of the aLIVE-H device allow for homogeneous plasma distribution and proper function at different locations. Cryo-preserved LMOs transcribe albumin and Factor V at levels comparable to those transcribed by a normal pig liver. Connecting the aLIVE-H bioreactor to normal pigs did not affect key blood components and biochemical parameters.

CONCLUSIONS

An extra-corporeal liver device aLIVE-H which imitates the hemodynamic and functional properties of the normal liver and incorporates cryo-preserved LMOs has been developed and characterized. aLIVE-H was found to perform key synthetic liver functions.

Hepatic tissue engineering for adjunct and temporary liver support: critical technologies

The severe donor liver shortage, high cost, and complexity of orthotopic liver transplantation have prompted the search for alternative treatment strategies for end-stage liver disease, which would require less donor material, be cheaper, and less invasive. Hepatic tissue engineering encompasses several approaches to develop adjunct internal liver support methods, such as hepatocyte transplantation and implantable hepatocyte-based devices, as well as temporary extracorporeal liver support techniques, such as bioartificial liver assist devices. Many tissue engineered liver support systems have passed the "proof of principle" test in preclinical and clinical studies; however, they have not yet been found sufficiently reliably effective for routine clinical use. In this review we describe, from an engineering perspective, the progress and remaining challenges that must be resolved in order to develop the next generation of implantable and extracorporeal devices for adjunct or temporary liver assist.

The immobilization of hepatocytes on 24 nm-sized gold colloid for enhanced hepatocytes proliferation

Bioartificial liver and hepatocyte transplantation is anticipated to supply a temporary metabolic support for candidates of liver transplantation or for patients with fulminant liver failure. An essential restriction of this form is the inability to acquire an enough amount of hepatocytes. Enhancement of the proliferation and differentiated function of hepatocytes is becoming a pursued target. Here, porcine hepatocytes were successfully immobilized on nano-sized gold colloid particles to construct a "hepatocyte/gold colloid" interface at which hepatocytes can be quickly proliferated. The properties of this resulting interface were characterized and confirmed by scanning electron microscopy and atomic force microscopy. The proliferative mechanism of hepatocytes was also discussed. The proliferated hepatocytes could be applied to the clinic based on their excellent functions for the synthesis of protein, glucose and urea as well as lower lactate dehydrogenase release.

Clinical application of bioartificial liver support systems

OBJECTIVE

To review the present status of bioartificial liver (BAL) devices and their obtained clinical results.

BACKGROUND

Acute liver failure (ALF) is a disease with a high mortality. Standard therapy at present is liver transplantation. Liver transplantation is hampered by the increasing shortage of organ donors, resulting in high incidence of patients with ALF dying on the transplantation waiting list. Among a variety of liver assist therapies, BAL therapy is marked as the most promising solution to bridge ALF patients to liver transplantation or to liver regeneration, because several BAL systems showed significant survival improvement in animal ALF studies. Until today, clinical application of 11 different BAL systems has been reported.

METHODS

A literature review was performed using MEDLINE and additional library searches. Only BAL systems that have been used in a clinical trial were included in this review.

RESULTS

Eleven BAL systems found clinical application. Three systems were studied in a controlled trial, showing no significant survival benefits, in part due to the insufficient number of patients included. The other systems were studied in a phase I trial or during treatment of a single patient and all showed to be safe. Most BAL therapies resulted in improvement of clinical and biochemical parameters.

CONCLUSIONS

Bioartificial liver therapy for bridging patients with ALF to liver transplantation or liver regeneration is promising. Its clinical value awaits further improvement of BAL devices, replacement of hepatocytes of animal origin by human hepatocytes, and assessment in controlled clinical trials.

Rapid formation of hepatic organoid in collagen sponge by rat small hepatocytes and hepatic nonparenchymal cells

BACKGROUND/AIMS

Hybrid bioartificial liver devices supporting a large mass of metabolically active hepatocytes are thought to be necessary for the successful treatment of patients with severe acute liver failure. However, it is very difficult to obtain cells with both growth activity and differentiated functions. Rat small hepatocytes (SHs), which are hepatic progenitor cells, can differentiate into mature hepatocytes and reconstruct a hepatic organoid by interacting with hepatic nonparenchymal cells (NPCs).

METHODS

Colonies of SHs were collected and replated on a collagen sponge. Hepatic functions were examined by ELISA, immunoblotting, and Northern blotting. Cells in the sponge were characterized by immunocytochemistry and transmission electron microscopy. Urea synthesis was measured and metabolization of fluorescein diacetate was examined.

RESULTS

SHs could proliferate and expand to form a hepatic organoid in the sponge. Albumin secretion and other hepatic protein production of the cells in the sponge increased with time in culture and the amounts were much larger than for those obtained from cells grown on dishes. Morphologically and functionally differentiated hepatocytes were observed and some CK19-positive cells formed duct-like structures within the sponge. Excretion of fluorescein was observed in bile canaliculi.

CONCLUSIONS

Hepatic organoids can be rapidly reconstructed in a collagen sponge by rat SHs and NPCs.

Liver micro-organs transcribe albumin and clotting factors and increase survival of 92% hepatectomized rats

BACKGROUND/AIMS

Currently there is no effective non-surgical therapy for most patients with fulminant or end stage chronic liver disease.

METHODS

We have prepared rat liver micro-organs (LMOs), which preserve the liver micro-architecture and ensure that no cell is more than 150 microm away from a source of nutrients and gases. The function of LMOs has been evaluated in vitro and in a new extra-corporeal liver device termed aLIVE in which LMOs are exposed to liver-like hemodynamic conditions.

RESULTS

In vitro LMOs maintain normal physiological and biochemical functions including oxygen consumption, glucose metabolism, conversion of ammonia to urea, secretion of albumin and de novo transcription of genes coding for albumin and clotting factors. Inside the aLIVE bioreactor, LMOs also display sustained oxygen consumption, glucose metabolism and transcription of albumin and clotting factors IX and X, when connected both to normal and to 92% hepatectomized rats. Survival of 92% hepatectomized rats was 40% longer following a single 4-h treatment with aLIVE, compared to untreated animals.

CONCLUSIONS

An extra-corporeal liver device, aLIVE, which provides key liver functions, has been developed. When tested in 92% hepatectomized rats, aLIVE improved the clinical condition and significantly increased survival time of the treated rats.

Bioartificial liver support devices: historical perspectives

Fulminant hepatic failure (FHF) is an important cause of death worldwide. Despite significant improvements in critical care therapy there has been little impact on survival with mortality rates approaching 80%. In many patients the cause of the liver failure is reversible and if short-term hepatic support is provided, the liver may regenerate. Survivors recover full liver function and a normal life expectancy. For many years the only curative treatment for this condition has been liver transplantation, subjecting many patients to replacement of a potentially self-regenerating organ, with the lifetime danger of immunosuppression and its attendant complications, such as malignancy. Because of the shortage of livers available for transplantation, many patients die before a transplant can be performed, or are too ill for operation by the time a liver becomes available. Many patients with hepatic failure do not qualify for liver transplantation because of concomitant infection, metastatic cancer, active alcoholism or concurrent medical problems. The survival of patients excluded from liver transplantation or those with potentially reversible acute hepatitis might be improved with temporary artificial liver support. With a view to this, bioartificial liver support devices have been developed which replace the synthetic, metabolic and detoxification functions of the liver. Some such devices have been evaluated in clinical trials. During the last decade, improvements in bioengineering techniques have been used to refine the membranes and hepatocyte attachment systems used in these devices, in the hope of improving function. The present article reviews the history of liver support systems, the attendant problems encountered, and summarizes the main systems that are currently under evaluation.

Effect of flow baffles on the dialysate flow distribution of hollow-fiber hemodialyzers: a nonintrusive experimental study using MRI

We used an innovative, nonintrusive MRI technique called the two-dimensional (2D) Phase-Contrast (2DPC) velocity-imaging technique to investigate the effect of flow baffles on the dialysate-side flow distribution in two different hollow-fiber hemodialyzers (A and B); each with flow rates between 200 and 1000 mL/min (3.33 x 10(-6) and 1.67 x 10(-5) m3/s). Our experimental results show that (1) the dialysate-side flow distribution was nonuniform with channeling flow occurred at the peripheral cross section of these hollow-fiber hemodialyzers, and (2) the existing designs of flow baffles failed to promote uniform dialysate-side flow distribution for all flow rates studies.

Bioartificial liver inoculated with porcine hepatocyte spheroids for treatment of canine acute liver failure model

The aim of this study was to evaluate a novel bioartificial system in a canine model of acute liver failure. An acute liver failure model in canines was induced by an end-side portocaval shunt combined with common bile duct ligation and transection. The bioartificial liver system, which utilized blood perfusion through a hollow fiber bioreactor from BIOLIV A3A inoculated with 1.0 - 3.1 x 1010 porcine hepatocyte spheroids, was developed for the treatment of acute liver failure. Sixteen acute liver failure model canines were divided between a group treated with bioartificial liver (n=8) and a control group (n=8) for 5 h. Blood alanine aminotransferase (ALT), alkaline phosphatase (AKP), total bilirubin (TBi), direct bilirubin (DBi), prothrombin time (PT), ammonia levels, and the ratio of branched chain to aromatic amino acids (Fischer's ratio) were determined. ALT, AKP, TBi, DBi, and ammonia levels were significantly elevated, PT was significantly prolonged, and Fischer's ratio decreased significantly in the canine model of the two groups on day 14 after operation compared to baseline. There were no significant differences between the two groups in laboratory data before treatment. In canines treated with the bioartificial liver system, ALT, AKP, TBi, DBi, and ammonia levels decreased significantly, PT was significantly shortened, Fischer's ratio was significantly elevated after treatment, and the survival rate by day 7 after treatment was 100%. In canines in the control group, on the other hand, there were no significant differences in ALT, AKP, TBi, DBi, PT, and ammonia levels between pretreatment and posttreatment, though these indices decreased to a slight degree after treatment. The survival rate by day 7 after treatment was 62.5% in the control group. Fischer's ratio decreased after treatment. ALT, AKP, TBi, DBi, PT, and ammonia levels in the bioartificial liver system group were lower, and Fischer's ratio and survival rate were higher than those in the control group after treatment. These results indicate that the novel bioartificial liver system we developed has a significant impact on the course of canine acute liver failure model and has potential advantages for clinical use in patients with acute liver failure.

Artificial liver support in the third millennium

Analogous to the artificial kidney there is a need for an effective and safe liver support system to bridge patients with hepatic failure to liver transplantation or own liver regeneration. An overview is given of the biological and non-biological systems used in clinical practice in the past and at present. The conclusion is drawn that only the biological systems might have the potential to prolong life significantly in patients with acute liver failure. The systems with this potential are summarised. Both in Europe and the USA good bioreactors are available. Most of them are based on porcine hepatocytes, which have immunological and zoonotic drawbacks. What is missing is the well differentiated human hepatocyte in sufficient amounts. Successful development of this cell will be the crown on bioartificial liver research in the third millenium.

Efficacy of an extracorporeal flat-plate bioartificial liver in treating fulminant hepatic failure

BACKGROUND

Fulminant hepatic failure is associated with a high mortality rate. Orthotopic liver transplantation is the only established treatment for patients who do not respond to medical management. A major limitation of this treatment is a shortage of donor organs, resulting in many patients dying while waiting for a transplant. An extracorporeal bioartificial liver (BAL) has the potential to provide temporary support for patients with fulminant hepatic failure (FHF) and for patients awaiting orthotopic liver transplantation. We developed a flat-plate BAL with an internal membrane oxygenator in which porcine hepatocytes were cultured as a monolayer.

MATERIALS AND METHODS

Twenty-four hours after cannulation of the left carotid artery and right jugular vein, FHF was induced in rats by administering 2 intraperitoneal injections of D-galactosamine (GalN) (1.2 g/kg) at a 12-h interval. The rats were connected to a BAL device 24 h after the first GalN injection and underwent extracorporeal perfusion for a duration of 10 h. Liver histology, liver-specific markers, and animal survival up to 168 h (7 days) were examined.

RESULTS

Histologically, liver damage was reduced in the animal group treated with the hepatocyte-based BAL device. Significant reductions occurred in the plasma ammonia levels and prothrombin times in the group treated with the seeded BAL device. Animal survival in the group treated with the seeded BAL device was significantly higher (50.0%) than in the control animal group treated with an unseeded BAL device (11.1%).

CONCLUSIONS

This flat-plate BAL with an internal membrane oxygenator and cultured porcine hepatocytes has yielded encouraging results in the treatment of rats with GalN-induced FHF.

The development of a new bioartificial liver and its application in 12 acute liver failure patients

AIM: Bioartificial liver is a hope of supporting liver functions in acute liver failure patients. Using polysulfon fibers, a new bioartificial liver was developed. The aim of this study was to show whether this bioartificial liver could support liver functions or not.

METHODS: Hepatocytes were procured from swine using Seglen’s methods. The bioartificial liver was constructed by polysulfon bioreactor and more than 10¹⁰ hepatocytes. It was applied 14 times in 12 patients, who were divided into 7 cases of simultaneous HBAL and 5 cases of non-simultaneous HBAL. Each BAL treatment lasted 6 hours. The general condition of the patients and the biochemical indexes were studied.

RESULTS: After treatment with bioartificial liver, blood ammonia, prothrombin time and total bilirubin showed significant decrease. 2 d later, blood ammonia still showed improvment. within one month period, 1 case (1/7) in simultaneous group died while in non-simultaneous group 2 cases (2/5) died. The difference was significant. Mortality rate was 25%.

CONCLUSION: The constructed bioartificial liver can support liver functions in acute liver failure. The simultaneous HBAL is better than non-simultaneous HBAL.

The development of a new bioartificial liver and its application in 12 acute liver failure patients

AIM

Bioartificial liver is a hope of supporting liver functions in acute liver failure patients. Using polysulfon fibers, a new bioartificial liver was developed. The aim of this study was to show whether this bioartificial liver could support liver functions or not.

METHODS

Hepatocytes were procured from swine using Seglen's methods. The bioartificial liver was constructed by polysulfon bioreactor and more than 10(10) hepatocytes. It was applied 14 times in 12 patients, who were divided into 7 cases of simultaneous HBAL and 5 cases of non-simultaneous HBAL. Each BAL treatment lasted 6 hours. The general condition of the patients and the biochemical indexes were studied.

RESULTS

After treatment with bioartificial liver, blood ammonia, prothrombin time and total bilirubin showed significant decrease. 2 days later, blood ammonia still showed improvment. within one month period, 1 case (1/7) in simultaneous group died while in non-simultaneous group 2 cases (2/5) died. The difference was significant. Mortality rate was 25 %.

CONCLUSION

The constructed bioartificial liver can support liver functions in acute liver failure. The simultaneous HBAL is better than non-simultaneous HBAL.

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.

Bioartificial liver support anno 2001

Despite maximal intensive care, mortality of acute fulminant hepatic failure is high: 60%-75% in several studies. In addition patients with chronic liver insufficiency suffer from a bad quality of life: all patients suffer from fatigue; symptoms of hepatic encephalopathy, jaundice, and itching are often present. Analogous to artificial kidney treatment in patients with renal failure, an artificial liver assist device is needed not only to bridge patients with fulminant hepatic failure to liver transplantation or own liver regeneration, but also to improve the quality of life of patients with chronic liver insufficiency. Several modalities of artificial liver support are under investigation, like plasma exchange, haemodialysis, haemadsorption, albumin dialysis, liver cell transplantation, and the bioartificial liver. Artificial livers based on only supportive detoxification function do not show significant improvement of survival in controlled studies. Bioartificial liver support systems have also the potential to support hepatic synthetic functions. Bioreactors can be charged with freshly isolated or cryopreserved porcine hepatocytes, but also by human hepatoma cell lines. Several uncontrolled studies in humans show safety of such a treatment, even by using porcine cells. Transmission of porcine endogenous retrovirus to recipients has not been found. Furthermore, beneficial effects have been reported on symptoms of hepatic encephalopathy, on the height of intracranial pressure and on hemodynamic parameters. By using porcine cells immunological problems (e.g., serum sickness) can be expected during treatments longer than one week. However, "proof of the pudding" in the sense of improvement of survival is not yet available. The creation of a "liver dialysis unit" in the near future depends mainly on the development of well-differentiated immortalized human hepatocytes. Some progress in this field has already been obtained.

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.

Morphology, viability and functions of suckling pig hepatocytes cultured in serum-free medium at high density

BACKGROUND

In bioartificial liver preparation, serum-contained medium is ordinarily replaced by serum-free medium and hepatocytes are generally cultured at high density. This study was to undertaken to evaluated the dynamic changes in morphology, viability and functions of porcine hepatocytes in serum-free medium at high density.

METHODS

Hepatocytes were isolated from suckling pigs by modified two-step in situ collagenase perfusion method and cultured in serum-free medium at high density. Morphology, viability, protein and glucose syntheses, G-6-Pase activity, diazepam transformation of hepatocytes and release of LDH in supernatant during 7 days of culture were evaluated. These measurements were also determined on both groups of hepatocytes cultured at low-density in serum-free medium and serum-contained medium, which served as control groups.

RESULTS

Morphology and protein synthesis of hepatocytes cultured in serum-free medium at high density were stable over the course of 7 days. High viability (>90%) was obtained though it declined with time. Diazepam transformation of cells was higher on days 2 and 3. Glucose synthesis of cells declined from day 3 to day 7. G-6-Pase activity of the hepatocytes declined apparently after 1 day of culture and it was maintained at a low level from day 1 to day 7. Release of LDH in supernatant was higher on days 1, 2 and 3. There were no significant differences in viability and functions of hepatocytes except for G-6-Pase activity at low-density culture between the serum-free medium group and the serum-contained medium group. The functions of hepatocytes cultured at high density were lower than at low-density culture.

CONCLUSIONS

The results showed that the morphology, viability, protein synthesis and diazepam transformation of hepatocytes cultured in serum-free medium at high density were maintained during 7 days of culture. The serum-free medium provided indices of cell viability and functions that were comparable to serum-contained medium. The functions of hepatocyte cultured at high density (1 x 10(7) cells/ml) were lower than at low density (5 x 10(5) cells/ml).

Phase I clinical trial with the AMC-bioartificial liver

Recently a bio-artificial liver (BAL) system has been developed at the Academic Medical Center (AMC) of Amsterdam to bridge patients with acute liver failure (ALF) to orthotopic liver transplantation (OLT). After successful testing of the AMC-BAL in rodents and pigs with ALF, a phase I study in ALF patients waiting for (OLT) was started in Italy. We present the safety outcome of the first 7 patients aged 21-56 years with coma grade III or IV The total AMC-BAL treatment time ranged from 8 to 35 hours. Three patients received 2 treatments with two different BAL's within three days. Six of the 7 patients were successfully bridged to OLT. One patient showed improved liver function after two treatments and did not need OLT. No severe adverse events of the BAL treatment were noted.

CONCLUSION

Treatment of ALF patients with the AMC-BAL is a safe and feasible technique to bridge the waiting time for an adequate liver-graft.

Biologic liver support: optimal cell source and mass

Hepatic support is indicated in acute liver failure (ALF) patients to foster liver regeneration, or until a liver becomes available for orthotopic liver transplantation (OLT), in primary non function of the transplanted liver, and hopefully in chronic liver disease patients affected by ALF episodes, in whom OLT is not a therapeutic option. The concept of bioartificial liver (BAL) is based on the assumption that only the hepatocytes can perform the whole spectrum of biotransformation functions, which are needed to prevent hepatic encephalopathy, coma and cerebral edema. Among others, two important issues are related to BAL development: 1) the choice of the cellular component; 2) the cell mass needed to perform an adequate BAL treatment. Primary hepatocytes, of human or animal origin, should be considered the first choice because they express highly differentiated functions. Accordingly, a minimal cell mass corresponding to 10% of a human adult liver, i.e. 150 grams of freshly isolated, > or = 90% viable hepatocytes should be used. When 4 degrees C cold-stored or cryopreserved hepatocytes are used, the cellular mass should be increased because of a drop in cell viability and function. In case of hepatoma-derived cells, cultured cell lines or engineered cells, an adequate functional cell mass should be used, expressing metabolic and biotransformation activities comparable to those of primary hepatocytes. Finally, the use of porcine hepatocytes or other animal cells in BAL devices should be presently directed only to ALF patients as a bridge treatment to OLT, because of potential transmission of animal retrovirus and prions which may potentially cause major pandemics.

A new bioassay including a small scale hepatocyte bioreactor for hepato-mediated toxicity testing in a target cell line

New approaches for in vitro testing of hepato-mediated toxicity are undertaken to offer alternatives to in vivo animal testing. The described bioassay for hepato-mediated toxicity testing is based on a small scale hepatocyte-bioreactor with pig hepatocytes connected to a silicon sensor based microphysiometer system for monitoring of the extracellular acidification rate (EAR) of cells and the microphysiometer alone. EAR represents the metabolic activity of tested cells (hepatocytes and ZR 751 cells) under the influence of perfused media, compared to controls, which were set to 100%. Cyclophosphamide (CYCL), whose cytostatic effect is dependent on CYP 450 biotransformation was used as a model substrate. CYCL showed decrease of EAR in hepatocytes, but not in ZR 751 cells. Bioreactor supernatant including CYCL was pumped into the microphysiometer and EARs of the target ZR 751 cell line were recorded. After 7 h of bioreactor supernatant perfusion the ZR 751 cell line showed an EAR decrease of 18.68% +/- 10.18, as compared to controls (bioreactor supernatant from the identical set-up without CYCL). Thus the presented model of hepato-activated toxicity showed an EAR decrease in the ZR 751 cell line that reflected the toxic activation of CYCL by the bioreactor. This new bioassay serves as an example of future applications for hepatocyte bioreactors in automated toxicity testing devices, e.g. in preclinical drug studies or evaluation of hepato-mediated toxicity, not depending on cell destruction or further assays.

Cultivation of porcine hepatocytes in polyurethane nonwovens as part of a biohybrid liver support system

Many patients suffering from end-stage liver disease cannot be transplanted within reasonable time due to the shortage of donor organs. Bioartificial liver support systems may contribute to the liver regeneration or bridging the time until a liver graft for transplantation becomes available. Nonwovens with integrated oxygenation capacity have been developed and manufactured by melt blow technology using thermoplastic polyurethane. Capillary membranes for oxygenation were integrated into the nonwoven during the processing. The polyurethane nonwoven structures with adapted pore size and high pore volume allow high cell densities in the hepatocyte culture. The three-dimensional cell culture was housed by a flow bioreactor system and was integrated in a closed loop circulation with monitoring possibilities for pressure, pH, temperature, ammonia, and oxygen. Hepatocytes were isolated from rats or pigs by collagenase perfusion and infused into the medium-perfused circulation. Cells showed high viability and hepatocyte specific cytochrome P450-dependent metabolic function in culture (MEGX test).

Treatment of acute liver failure in pigs reduces hepatocyte function in a bioartificial liver support system

Several different types of bioartificial liver (BAL) support systems have been developed to bridge patients suffering from acute liver failure (ALF) to transplantation or liver regeneration. In this study we assessed the effects of ALF plasma on hepatocyte function in the BAL system that has been developed in our center. Pigs (40-60 kg) were anaesthetised and a total hepatectomy was performed. Cells were isolated from the resected livers and were transferred to the bioreactor of the BAL system. Twenty hours after cell isolation, hepatocytes in the BAL were tested for cell viability and functional activity by using a recirculating test medium in which assessment of LDH leakage, ammonia clearance, urea synthesis, 7-ethoxycoumarin O-deethylase (ECOD) activity and pseudocholine esterase production was performed. Subsequently, two groups were studied. In one group (I, n=5), the cell-loaded bioreactor was used to treat the donor pig, rendered anhepatic, for 24 hours. In the second group (II, n=5) the bioreactor was cultured for 24 h and served as a control. After 24 hours treatment or culturing, the cell viability count and functional activity tests were repeated. The results show that hepatocytes in the BAL remained viable after 24 h treatment of anhepatic pigs, as shown by the LDH release and pseudocholine esterase production. However, metabolic functions such as ammonia clearance, ECOD and urea synthesis were reduced after 24 h exposure of hepatocytes to autologous ALF plasma, whereas these functions were unaltered after 24 h culturing of the cells in the bioreactor.

1H NMR spectroscopy as a tool to evaluate key metabolic functions of primary porcine hepatocytes after cryopreservation

Proton NMR spectroscopy of biological fluids has produced interesting results lately. We used the technique to investigate the effects of cryopreservation on primary porcine hepatocytes as successful cryopreservation of primary porcine hepatocytes is of importance to the development of bioartificial liver support systems. After isolation 10(8) hepatocytes were cryopreserved for 1 week in Williams E/10% DMSO, either by quick freezing (-5 to -30 degrees C/min), slow freezing (-0.3 to -3 degrees C/min) or stepwise freezing protocols on cell suspensions and confluent cell plates. Plating efficiency was assessed by percentage LDH release. Metabolic functions of cryopreserved hepatocytes at 24 h post-thawing were compared with those of fresh hepatocyte cultures at 48 h. 1H nuclear magnetic resonance spectroscopy of the culture medium post-incubation, using the presaturation technique, assessed the following: glucose metabolism, transamination and glutamine synthesis and succinate synthesis. Freshly isolated cells had a viability of 82 +/- 4.3% and a plating efficiency of 87 +/- 3.8%. All cryopreservation protocols resulted in significantly reduced viability and plating efficiency. No significant differences were observed between different cryopreservation media or protocols. When comparing cryopreserved with freshly isolated cells, we observed that metabolism of acetyl-CoA precursors was significantly impaired in cryopreserved cells. Lactate and pyruvate production was also significantly less, although glucose consumption was similar. No differences were observed in gluconeogenic amino acid metabolism, transamination and urea synthesis. 1H NMR spectroscopy can be used to provide information about metabolic activity and functions of cultured primary cells.

Extracorporeal support of the failing liver

Successes in machine-based extracorporeal support for different organ functions stimulated research in the field of liver support approximately 50 years ago. Initial failure to improve outcome using detoxification methods like dialysis, blood and plasma exchange, or plasmapheresis over sorbents fueled interest in biologic liver support concepts using bioreactors or combined methods. New device configurations, technical improvement of existing detoxification methods, and the refinement in cell culture techniques led to a boost in research on biologic and nonbiologic approaches. Currently, many systems are in the preclinical phase or have entered clinical studies. A number of completed clinical trials have reported a favorable therapeutic impact of the most advanced solutions on the course and outcome of liver failure. Often, findings must be reconfirmed. However, current knowledge suggests that extracorporeal liver support can successfully stabilize liver function, improve the clinical condition of patients, and considerably improve survival in certain subgroups of patients with fulminant hepatic failure and acute decompensation of chronic hepatic failure. Although the initial focus of liver support methods was bridging to liver transplantation, bridging to recovery of organ function and treatment of intractable pruritus are now valuable indications.

A bioartificial liver--state of the art

End-stage liver disease is treated by liver transplantation, but donor organ shortages remain a serious problem. This has prompted the design of bioartificial liver devices to "bridge" patients until they either recover or receive a liver transplant. In these devices, patient plasma is circulated extracorporeally through a bioreactor that houses liver cells (hepatocytes) sandwiched between artificial plates or capillaries.

Assessment of the AMC-bioartificial liver in the anhepatic pig

BACKGROUND

The anhepatic pig model was used to evaluate a bioartificial liver developed in our institution (AMC-BAL). The bioartificial liver is based on oxygenated plasma perfusion of porcine hepatocytes attached to a polyester matrix.

METHODS

Pigs (n=15) underwent total hepatectomy with restoration of caval continuity using a polyethylene, three-way prosthesis. In group I, pigs received limited intensive care under continuation of general anesthesia (n=5). Group II pigs (n=5) underwent, in addition, extracorporeal plasma perfusion of an AMC-BAL without hepatocytes (device control group). In group III (n=5), plasma perfusion occurred with an AMC-BAL loaded with autologous hepatocytes. Groups II and III were connected to the extracorporeal system 24 hr after hepatectomy, for a period of 24 hr. The main outcome parameters were as follows: survival time, liver enzymes (aspartate aminotransferase, alanine aminotransferase), blood ammonia, and total/direct bilirubin.

RESULTS

Survival (mean +/- SD) of the anhepatic pigs was significantly increased in the BAL-treated group (group III: 65+/-15 hr), as compared with the control groups (group I: 46+/-6 hr and group II: 43+/-14 hr). Mean blood ammonia levels during BAL treatment were significantly lower in the BAL-treated group in comparison with both control groups (P=0.02). Total and direct bilirubin levels gradually increased after hepatectomy and reached maximum values of 1.98 mg/dl and 1.50 mg/dl, respectively, showing no differences between the three groups.

CONCLUSIONS

(1) Treatment of anhepatic pigs with the AMC-BAL containing autologous hepatocytes significantly increases survival time, which is associated with a significant decrease in blood ammonia. 2) Anhepatic pigs demonstrate increasing direct bilirubin levels as a result of extrahepatic bilirubin conjugation.

Extracorporeal tissue engineered liver-assist devices

The treatment of acute liver failure has evolved to the current concept of hybrid bioartificial liver (BAL) support, because wholly artificial systems have not proved efficacious. BAL devices are still in their infancy. The properties that these devices must possess are unclear because of our lack of understanding of the pathophysiology of liver failure. The considerations that attend the development of BAL devices are herein reviewed. These considerations include choice of cellular component, choice of membrane component, and choice of BAL system configuration. Mass transfer efficiency plays a role in the design of BAL devices, but the complexity of the systems renders detailed mass transfer analysis difficult. BAL devices based on hollow-fiber bioreactors currently show the most promise, and available results are reviewed herein. BAL treatment is designed to support patients with acute liver failure until an organ becomes available for transplantation. The results obtained to date, in this relatively young field, point to a bright future. The risks of using xenogeneic treatments have yet to be defined. Finally, the experience gained from the past and current BAL systems can be used as a basis for improvement of future BAL technology.

A novel multi-coaxial hollow fiber bioreactor for adherent cell types. Part 1: hydrodynamic studies

A novel multi-coaxial bioreactor for three-dimensional cultures of adherent cell types, such as liver, is described. It is composed of four tubes of increasing diameter placed one inside the other, creating four spatially isolated compartments. Liver acinar structure and physiological parameters are mimicked by sandwiching cells in the space between the two innermost semi-permeable tubes, or hollows fibers, and creating a radial flow of media from an outer compartment (ECC), through the cell mass compartment, and to an inner compartment (ICC). The outermost compartment is created by gas-permeable tubing, and the housing is used to oxygenate the perfusion media to periportal levels in the ECC. Experiments were performed using distilled water to correlate the radial flow rate (Q(r)) with (1) the pressure drop (DeltaP) between the media compartments that sandwich the cell compartment and (2) the pressure in the cell compartment (P(c)). These results were compared with the theoretical profile calculated based on the hydraulic permeability of the two innermost fibers. Phase-contrast velocity-encoded magnetic resonance imaging was used to visualize directly the axial velocities inside the bioreactor and confirm the assumptions of laminar flow and zero axial velocity at the boundaries of each compartment in the bioreactor. Axial flow rates were calculated from the magnetic resonance imaging results and were similar to the measured axial flow rates for the previously described experiments.

Long-term maintenance of cytochrome P450 activities by rat hepatocyte/3T3 cell co-cultures in heparinized human plasma

Little information on the effect of plasma on hepatocyte cytochrome P450 (CYP) activities is currently available. We characterized the effect of plasma on CYPs of hepatocyte-mesenchymal cell co-cultures, which exhibit stable liver specific functions and may be potentially useful for bioartificial liver design. Rat hepatocyte-mouse 3T3-J2 cell co-cultures were maintained for 6 days in medium, and then switched to heparinized human plasma containing 3-methylcholanthrene (3MC; 2 microM), phenobarbital (PB; 1 mM), or no inducer for up to 7 days. CYP activities were measured in situ based on the o-dealkylation of ethoxy- (EROD), methoxy- (MROD), pentoxy- (PROD), or benzyloxy- (BROD) resorufin. Plasma alone increased PROD/BROD but not EROD/MROD. The endogenous inducer was in the high molecular weight fraction (>5 kD) of plasma and inhibited by >5 nM okadaic acid and >10 microM dibutyryl cyclic AMP, two inhibitors of PB-inducible CYPs. Furthermore, plasma increased CYP1A1 and CYP2B1/2 mRNA levels. In plasma, 3MC induced EROD/MROD to about 60% of the level induced in culture medium while PB induced PROD/BROD that were three- to 10-fold above levels induced in medium. CYP activities decreased between days 2 and 7 of plasma exposure, but were enhanced by plasma supplementation with amino acids, insulin, glucagon, and hydrocortisone.

Derivation of pharmacokinetics equations for quantitative evaluation of bioartificial liver functions

A bioartificial liver (BAL) is an extracorporeal medical device incorporating living hepatocytes in a cartridge. A variety of BALs have been developed and new devices are being introduced. Some of them have been clinically applied and from the results obtained they are claimed to be useful devices for assisting the liver functions of patients. However, there is still uncertainty as to their efficacy and their limitations are not clear. It is important to establish methods to quantitatively evaluate the metabolic and synthetic functions of BAL. In this paper, we derive simple equations for the quantitative evaluation of BAL functions on the basis of pharmacokinetics. Pharmacokinetics was originally developed to understand the processes of absorption, distribution, and elimination of administered drugs. Metabolic functions of the natural liver have been analyzed using pharmacokinetics and values of the useful parameters, clearance (CL) and intrinsic clearance (CLint), have been reported. The metabolic functions of the BAL expressed using values of CL and CLint are easily compared with those of the normal human liver. We believe that our method provides a useful basis for estimating the clinical effectiveness of BAL.

Long-term expression of highly differentiated functions by isolated porcine hepatocytes perfused in a radial-flow bioreactor

To overcome the limitations of standard hollow-fiber module in ensuring efficient cell perfusion and long-term expression of highly differentiated hepatocyte functions, we developed a novel bioreactor in which a three-dimensional hepatocyte culture system was perfused in radial-flow geometry. Isolated porcine hepatocytes were cultured for 2 weeks in recirculating serum-free tissue culture medium, in which NH4Cl and lidocaine were repeatedly added, and ammonia removal, urea synthesis, monoethylglycinexylide (MEGX) production, albumin secretion, Po2, Pco2, O2 consumption, and pH were measured thereafter. During the whole duration of the study, ammonia removal was paralleled by urea production, while MEGX concentration was constantly increased. Our results indicated that hepatocytes remained differentiated and metabolically active throughout the duration of the study. The radial-flow bioreactor allowed physiological contact between recirculating fluid and cells by equalizing the concentration of the perfusing components, including O2, throughout the module, suggesting a potential use of this configuration for extracorporeal liver support.

Effects of oxygenation and flow on the viability and function of rat hepatocytes cocultured in a microchannel flat-plate bioreactor

The goal of this study was to investigate the viability and synthetic function of rat hepatocytes cocultured with 3T3-J2 fibroblasts in a small-scale microchannel flat-plate bioreactor with and without an internal membrane oxygenator under flow. Bioreactor channel heights ranged between 85 and 500 microm and medium flow rates ranged between 0.06 and 4.18 mL/min. The results showed that the bioreactor without the oxygenator resulted in significantly decreased viability and function of hepatocytes, whereas hepatocytes in the bioreactor with internal membrane oxygenator were able to maintain their viability and function. The shear stress calculations showed that, at lower wall shear stresses (0.01 to 0.33 dyn/cm(2)), hepatocyte functions, measured as albumin and urea synthesis rates, were as much as 2.6- and 1.9-fold greater, respectively, than those at higher wall shear stresses (5 to 21 dyn/cm(2)). Stable albumin and urea synthesis rates for 10 days of perfusion were also demonstrated in the bioreactor with internal membrane oxygenator. These results are relevant in the design of hepatocyte bioreactors and the eventual scaling-up to clinical devices.

High density culturing of porcine hepatocytes immobilized on nonwoven polyurethane-based biomatrices

OBJECTIVE

Hepatocytes are increasingly used as functional units in bioartificial liver devices. The objective of the present study was to investigate the feasibility of culturing porcine hepatocytes in high density on a novel polyurethane-based nonwoven three-dimensional matrix. We investigated (1) the optimal cell density within this culture configuration, (2) the maintenance of liver-specific morphology and cell functions over long-term periods and (3) the necessity to apply an additional extracellular matrix component (collagen gel).

METHODS

Nonwoven polyurethane matrices were manufactured by a specially developed fiber extrusion technology. Pig hepatocytes were cultured at various cell densities of 0.1, 0.25, 0.5, 0.75, 1 and 2 x 10(6) cells/cm(2) on three-dimensional networks of nonwoven polyurethane matrices and cell adhesion as well as functional parameters (DNA of nonattached/attached cells, lactate dehydrogenase release and cytochrome P450 activity) were determined. To assess the performance of cells within this configuration albumin and urea excretion was measured over 8 days. The potentially beneficial effect of an additional extracellular matrix configuration was evaluated by comparing the average albumin synthesis in groups of identical cell numbers.

RESULTS

The optimal cell density in this three-dimensional culture configuration was 1 x 10(6) cells/cm(2). The functional capacity of hepatocytes was stable for 8 days at an average level of 53.7 +/- 5.6 ng/h/microg DNA and of 1.8 +/- 0.14 microg/h/microg DNA for albumin and urea excretion, respectively. The supplementation of an extracellular matrix configuration did not improve functional activity of cells. Average albumin synthesis was 35.6 ng/h/microg DNA (28.7, 42.8) and 32.7 ng/h/microg DNA (23.4, 49.2) for collagen-immobilized and control cultures, respectively.

CONCLUSION

The results of the study indicate that nonwoven polyurethane sheets supply a biocompatible support structure for functionally active high density cultures. Thus, nonwoven polyurethane matrices should be further investigated on with respect to their role in the development, optimization and design of bioartificial liver systems.

The simulated microgravity environment maintains key metabolic functions and promotes aggregation of primary porcine hepatocytes

The high aspect ratio vessel allows the culture of primary porcine hepatocytes in an environment of low shear stress and simulated microgravity. Primary porcine hepatocytes have been difficult to maintain in culture long term while preserving their metabolic functions. This study was carried out in order to characterise key metabolic functions of cell aggregates formed by primary porcine hepatocytes cultured in a high aspect ratio vessel for a predetermined period of 21 days. 10(8) porcine hepatocytes were loaded into the high aspect ratio vessel and continuously rotated during the experiments. 0.7 ml of the culture medium was sampled on days 1, 2, 4, 7, 10, 14 and 21. 1H nuclear magnetic resonance spectroscopy of the culture medium, using the presaturation technique, assessed the following: glucose metabolism, glutamine synthesis and ketogenesis. There was glucose breakdown anaerobically during the first 10 days as manifested by lactate production and pyruvate and threonine consumption. After day 10 there was significantly smaller lactate production (day 1 vs day 10 P < 0.01), and significantly smaller pyruvate (day 1 vs day 14 P < 0.03) and threonine consumption (day 1 vs day 10 P < 0.002), indicative of an aerobic metabolic pattern. Significantly more glutamate was produced after day 10 (day 1 vs day 10 P < 0.031), and more glutamine was consumed after day 14. There was a steadily diminishing production of acetate which reached a minimum on day 14 (day 2 vs day 14 P < 0.00014). After an initial 10 day period of acclimatisation cell aggregates formed in the high aspect ratio vessel switched from the anaerobic pattern of metabolism to the more efficient aerobic pattern, which was exhibited until the experiments were terminated. The high aspect ratio vessel is suitable for long-term culture of porcine hepatocytes and it is worthwhile carrying out scale-up feasibility studies.

Human hepatocyte cell lines proliferating as cohesive spheroid colonies in alginate markedly upregulate both synthetic and detoxificatory liver function

BACKGROUND/AIMS

Bio-artificial liver support systems for treatment of hepatic failure require maintained expression of hepatocyte function in vitro. We studied cultures of human hepatocyte cell-lines proliferating within alginate beads, investigating the hypothesis that 3-dimensional cohesive colonies of hepatocyte cell-lines would achieve polarity and cell-to-cell contact resulting in upregulation of function.

METHODS

HepG2 and HHY41 human cell lines in alginate beads were cultured for >20 days.

RESULTS

Proliferation was maintained for 20 days. Production of albumin, prothrombin, fibrinogen, alpha-1-acid glycoprotein and alpha-1-antitrypsin was maintained throughout, maximal at days 8-10, when upregulation was 300-1100% compared with monolayer cultures at similar cell number per unit volume. Detoxificatory functions: ethoxyresorufin deethylase activity, androstenedione metabolism, and urea synthesis from arginine was also increased several-fold. Function returned to pre-freezing levels within 18 h of thawing after cryopreservation of cells in alginate. Electron microscopy revealed spherical colonies of cells of cuboidal shape, with cell-to-cell contact via desmosomes and junctional complexes, abundant microvilli, and cytoplasmic appearances suggesting transcriptionally active hepatocytes.

CONCLUSION

Hepatocyte cell-lines, proliferating in alginate express a range of liver-specific functions at levels approaching those found in vivo, relevant to their use in liver support systems.

Which hepatocyte will it be? Hepatocyte choice for bioartificial liver support systems

Liver failure, notwithstanding advances in medical management, remains a cause of considerable morbidity and mortality in the developed world. Although bioartificial liver (BAL) support systems offer the potential of significant therapeutic benefit for such patients, many issues relating to their use are still to be resolved. In this review, these issues are examined in terms of the functions required, the cells of choice in such a system, and the most appropriate environment to optimize the function of such cells. The major functions identified to date for a BAL are ammonia detoxification and biotransformation of toxic compounds, although this somewhat belies the complexity of the functions required. Two practical choices for cell type within such a system are xenogenic hepatocytes and immortalized human hepatocyte lines. Both these choices have drawbacks, such as the transmission of zoonoses and malignant infiltration, respectively. Finally, improvements in culture conditions, such as supplemented media, biodegradable scaffolds, and coculture, offer the possibility of prolonging the differentiated function of hepatocytes in a BAL.

Acute liver failure: targeted artificial and hepatocyte-based support of liver regeneration and reversal of multiorgan failure

Acute liver failure (ALF) still represents a major therapeutic challenge for hepatologists due to its high mortality rate as a result of multiorgan failure. Although emergency orthotopic liver transplantation represents a major advance in the management of selected patients, it is not applicable to all candidates due to limited organ availability. Therefore, new therapeutic options should be developed to bridge selected patients to transplantation or to treat patients not candidates for liver transplantation. Although new techniques for cell culture and perfusion have resulted in a number of promising devices for the provision of temporary liver support in acute liver failure, their clinical efficacy is as yet uncertain. Controlled trials on a multi-centre basis in well-defined patient groups and with standardised outcome measures, including the extent to which treatment influences cell damage and regeneration and prevents or reverses multiorgan failure, will be essential to properly evaluate the clinical value of current and evolving artificial and bioartificial devices. The same considerations must also apply to the assessment of therapeutic efficacy of hepatocyte transplantation. A better understanding of mechanisms responsible for the development of liver cell death, along with cellular and molecular mechanisms allowing surviving cells to proliferate in a hostile environment, will be required if a more targeted therapeutic approach to decreasing hepatocellular injury and enhancing liver regeneration is to be achieved. Whether extracorporeal devices or the transplantation of primary hepatocytes, stem cells or cells genetically engineered to over-express key metabolic functions, a proliferative phenotype and/or cytoprotective pathways will be best suited to meeting these demanding challenges remains to be determined.