End-stage liver failure: filling the treatment gap at the intensive care unit

End-stage liver failure is a condition of collapsing liver function with mortality rates up to 80. Liver transplantation is the only lifesaving therapy. There is an unmet need for therapy to extend the waiting time for liver transplantation or regeneration of the native liver. Here we review the state-of-the-art of non-cell based and cell-based artificial liver support systems, cell transplantation and plasma exchange, with the first therapy relying on detoxification, while the others aim to correct also other failing liver functions and/or modulate the immune response. Meta-analyses on the effect of non-cell based systems show contradictory outcomes for different types of albumin purification devices. For bioartificial livers proof of concept has been shown in animals with liver failure. However, large clinical trials with two different systems did not show a survival benefit. Two clinical trials with plasma exchange and one with transplantation of mesenchymal stem cells showed positive outcomes on survival. Detoxification therapies lack adequacy for most patients. Correction of additional liver functions, and also modulation of the immune system hold promise for future therapy of liver failure.

Experimental Evaluation of a Cell Module for Hybrid Liver Support

Aim of the study was to evaluate a hybrid liver support system in a porcine model of acute liver failure, after hepatectomy. Pigs with a body weight of 70±18 kg underwent total hepatectomy and porto - cavo - caval shunting as well as ligation of the bile duct and the hepatic artery. Control animals were connected to the system (including capillary membrane plasma separation) containing a four compartment bioreactor with integral oxygenation and decentralized mass exchange but without liver cells. The treatment group received hybrid liver support with the same system including 370±42 g primary isolated porcine parenchymal liver cells in co-culture with hepatocyte nursing cells, tissue engineered to liver- like structures at high density. Treatment started after complete recovery from anesthesia and was performed continuously. A positive influence on peripheral vascular resistance and a reduced need of catecholamine dosage was observed in the treatment group. Hybrid liver support with a cell module upscaled for clinical application significantly prolonged survival time in animals after hepatectomy with the longest survival being 26 hours in the control group an 57 hours in the treatment group.

Mass Preparation of Primary Porcine Hepatocytes and the Design of a Hybrid Artificial Liver Module using Spheroid Culture for a Clinical Trial

To isolate a large number of porcine hepatocytes, we originally developed a mass preparation method that combined the usual collagenase perfusion method of a whole liver with a collagenase redigestion method of tissue fragments after liver perfusion. Using a pig of 10kg, collagenase perfusion only resulted in a yield of 63 ± 78 x 108 total cells with a viability of 69.2 ± 25.3 %, but our combined method had a yield of 167 ± 31 x 108 total cells with a viability of 87.9 ± 4.4 % (mean ± SD). Also, the combined method was applied to two pigs of 10kg body weight at the same time, and isolated 387 ± 89 x 108 hepatocytes with a viability of 87.1 ± 6.9 % and a purity of 93.6 ± 2.8 % in 11 experiments.

We designed a large multi-capillary polyurethane foam (MC-PUF) packed-bed module containing 1 x 1010 porcine hepatocytes on a clinical trial scale. The porcine hepatocytes in the module formed spherical multicellular aggregates (spheroids) of 200 – 500 μm diameter. Most hepatocytes forming spheroids were viable judged by fluorescein diacetate and ethidium bromide staining. The activities of ammonia removal, albumin secretion and oxygen consumption of the large MC-PUF module were the same as for a small MC-PUF module containing 2 x 108 porcine hepatocytes, and were maintained for at least 9 days of culture. These results show that a large MC-PUF module is successfully scaled up 50 times.

In conclusion, we succeeded in developing a mass preparation method of porcine hepatocytes and a large hybrid artificial liver module on a clinical trial scale.

A Novel Bioartificial Liver Containing Small Tissue Fragments: Efficiency in the Treatment of Acute Hepatic Failure Induced by Carbon Tetrachloride in Rats

The efficiency of a new bioartificial liver (BAL) containing small tissue fragments in the treatment of acute hepatic failure induced by carbon tetrachloride in rats was evaluated. A day after injection (i.p.) of CCl4 the animals were connected to a BAL containing liver fragments (fragment BAL) and a BAL containing no liver fragments (no-fragment BAL), and extracorporeal hemoperfusion was carried out for 4 h. The activities of alanine transaminase and lactate dehydrogenase as well as the concentrations of ammonia, glucose, urea, and amino acids in plasma were measured. A tendency to the stabilisation of ammonia, glucose, phenylalanine, tyrosine, and other amino acids was revealed at the end of hemoperfusion in poisoned rats connected to the fragment BAL. A statistically significant difference in survival between the animals connected to the fragment BAL and no-fragment BAL was found. The results obtained indicate that the bioreactor containing small liver fragments is effective in the treatment of acute hepatic failure in animals.

Historical Perspectives and Advances in Mesenchymal Stem Cell Research for the Treatment of Liver Diseases

Liver transplantation is the only effective therapy for patients with decompensated cirrhosis and fulminant liver failure. However, due to a shortage of donor livers and complications associated with immune suppression, there is an urgent need for new therapeutic strategies for patients with end-stage liver diseases. Given their unique function in self-renewal and differentiation potential, stem cells might be used to regenerate damaged liver tissue. Recent studies have shown that stem cell-based therapies can improve liver function in a mouse model of hepatic failure. Moreover, acellular liver scaffolds seeded with hepatocytes produced functional bioengineered livers for organ transplantation in preclinical studies. The therapeutic potential of stem cells or their differentiated progenies will depend on their capacity to differentiate into mature and functional cell types after transplantation. It will also be important to devise methods to overcome their genomic instability, immune reactivity, and tumorigenic potential. We review directions and advances in the use of mesenchymal stem cells and their derived hepatocytes for liver regeneration. We also discuss the potential applications of hepatocytes derived from human pluripotent stem cells and challenges to using these cells in treating end-stage liver disease.

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 × 109 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.

Subnormothermic Preservation Maintains Viability and Function in a Porcine Hepatocyte Culture Model Simulating Bioreactor Transport

Bioartificial liver (BAL) systems have been developed to bridge patients with acute liver failure (ALF) to liver transplantation or liver regeneration. Clinical application of BAL systems is dependent on the supportive quality of cells used and direct availability of the whole system. Reliable transport of BAL systems from the laboratory to remote treatment centers is therefore inevitable. Subsequently, preservation conditions play a crucial role during transport of a BAL, with temperature being one of the most determining factors. In this study, we assessed the effect of subnormothermic preservation on freshly isolated porcine hepatocytes cultured in monolayer under oxygenation. Additionally, the effect of the University of Wisconsin (UW) preservation solution was compared with Williams' E (WE) culture medium at 4°C. The control group was cultured for 3 days at 37°C, whereas the transport groups were cultured at 4°C, 15°C, 21°C, or 28°C for 24 h at day 2. All groups were tested each day for cell damage and hepatic functions. Subnormothermic culture (i.e., 15°C to 28°C) for a period of 24 h did not reduce any hepatic function and did not increase cellular damage. In contrast, culture of hepatocytes in WE medium and preservation in UW solution at 4°C significantly reduced hepatic function. In conclusion, freshly isolated porcine hepatocytes can be preserved for 24 h at subnormothermic temperatures as low as 15°C. Future research will focus on the implementation of the AMC-BAL in an oxygenated culture medium perfusion system for transport between the laboratory and the hospital.

Neurologic manifestations of acute liver failure

Fulminant hepatic failure presents with a hepatic encephalopathy and may progress to coma and often brain death from cerebral edema. This natural progression in severe cases contributes to early mortality, but outcome can be good if liver transplantation is appropriately timed and increased intracranial pressure (ICP) is managed. Neurologists and neurosurgeons have become more involved in these very challenging patients and are often asked to rapidly identify patients who are at risk of cerebral edema, to carefully select the patient population who will benefit from invasive ICP monitoring, to judge the correct time to start monitoring, to participate in treatment of cerebral edema, and to manage complications such as intracranial hemorrhage or seizures. This chapter summarizes the current multidisciplinary approach to fulminant hepatic failure and how to best bridge patients to emergency liver transplantation.

Evaluation of the Hepa Wash® treatment in pigs with acute liver failure

Background

Mortality of patients with acute liver failure (ALF) is still unacceptably high. Available liver support systems are still of limited success at improving survival. A new type of albumin dialysis, the Hepa Wash^® system, was newly introduced. We evaluated the new liver support system as well as the Molecular Adsorbent Recycling System (MARS) in an ischemic porcine model of ALF.

Methods

In the first study animals were randomly allocated to control (n=5) and Hepa Wash (n=6) groups. In a further pilot study, two animals were treated with the MARS-system. All animals received the same medical and surgical procedures. An intraparenchymal intracranial pressure was inserted. Hemodynamic monitoring and goal-directed fluid therapy using the PiCCO system was done. Animals underwent functional end-to-side portacaval shunt and ligation of hepatic arteries. Treatment with albumin dialysis was started after fall of cerebral perfusion pressure to 45 mmHg and continued for 8 h.

Results

All animals in the Hepa Wash group survived the 13-hour observation period, except for one that died after stopping treatment. Four of the control animals died within this period (p=0.03). Hepa Wash significantly reduced impairment of cerebral perfusion pressure (23±2 vs. 10±3 mmHg, p=0.006) and mean arterial pressure (37±1 vs. 24±2 mmHg, p=0.006) but had no effect on intracranial pressure (14±1 vs. 15±1 mmHg, p=0.72). Hepa Wash also enhanced cardiac index (4.94±0.32 vs. 3.36±0.25 l/min/m2, p=0.006) and renal function (urine production, 1850 ± 570 vs. 420 ± 180 ml, p=0.045) and eliminated water soluble (creatinine, 1.3±0.2 vs. 3.2±0.3 mg/dl, p=0.01; ammonia 562±124 vs. 1382±92 μg/dl, p=0.006) and protein-bound toxins (nitrate/nitrite 5.54±1.57 vs. 49.82±13.27 μmol/l, p=0.01). No adverse events that could be attributed to the Hepa Wash treatment were observed.

Conclusions

Hepa Wash was a safe procedure and improved multiorgan system failure in pigs with ALF. The survival benefit could be the result of ameliorating different organ functions in association with the detoxification capacity of water soluble and protein-bound toxins.

Artificial liver support system reduces intracranial pressure more effectively than bioartificial system: an experimental study

OBJECTIVES

Extracorporeal liver support (ELS) may play a role in bridging therapy in patients with acute liver failure (ALF). The aim of this study was to compare the influence of nonbiological and biological methods on intracranial pressure (ICP) in an animal model of ALF.

METHODS

A surgical devascularization model of ALF in pigs (35-40 kg) was used. Elimination therapy started after the onset of hypoglycemia. Biochemical parameters (bilirubin, ammonia, lactate, etc.) as well as ICP and cerebral perfusion pressure (CPP) were monitored for 12 hours. Of the total 31 pigs with ALF, 14 animals were treated by fractionated plasma separation and absorption (FPSA), 10 were treated with a bioartificial liver (BAL), and 7 animals were used as a control group.

RESULTS

FPSA and BAL treatment started on average 3 hours 17 minutes and 2 hours 21 minutes, after devascularization and lasted for 5 hours 54 minutes and 5 hours 43 minutes, respectively. Ammonia levels were lower in the FPSA group, and bilirubin levels differed significantly in both the FPSA and BAL groups compared with controls. However, ICP values were reduced more effectively in pigs treated by FPSA: 19.1 vs. 27.0 mm Hg at 9 hours, 22.5 vs. 28.7 mm Hg at 11 hours, and 24.0 vs. 33.0 mm Hg at 12 hours (p<0.05).

CONCLUSIONS

The artificial liver support system FPSA reduced ICP values more effectively than the Performer O. Liver RanD BAL system. Compared with this BAL system, the nonbiological elimination method of FPSA is a simpler application with the advantage that it can be applied in a more continuous way.

Artificial and bioartificial liver support

The fact that liver failure constitutes a life-threatening condition and can, in most cases, only be overcome by orthotopic liver transplantation, lead to the development of various artificial and bioartificial liver support devices. While artificial systems are based on the principles of adsorption and filtration, the more complex concept of bioartificial devices includes the provision of liver cells. Instead of solely focussing on detoxification, these concepts also support the failing organ concerning synthetic and regulative functions.The systems were evaluated in a variety of clinical studies, demonstrating their safety and investigating the impact on the patient's clinical condition. This review gives an overview over the most common artificial and bioartificial liver support devices and summarizes the results of the clinical studies.

Current development of bioreactors for extracorporeal bioartificial liver (Review)

The research and development of extracorporeal bioartificial liver is gaining pace in recent years with the introduction of a myriad of optimally designed bioreactors with the ability to maintain long-term viability and liver-specific functions of hepatocytes. The design considerations for bioartificial liver are not trivial; it needs to consider factors such as the types of cell to be cultured in the bioreactor, the bioreactor configuration, the magnitude of fluid-induced shear stress, nutrients' supply, and wastes' removal, and other relevant issues before the bioreactor is ready for testing. This review discusses the exciting development of bioartificial liver devices, particularly the various types of cell used in current reactor designs, the state-of-the-art culturing and cryopreservation techniques, and the comparison among many today's bioreactor configurations. This review will also discuss in depth the importance of maintaining optimal mass transfer of nutrients and oxygen partial pressure in the bioreactor system. Finally, this review will discuss the commercially available bioreactors that are currently undergoing preclinical and clinical trials.

Stable overexpression of pregnane X receptor in HepG2 cells increases its potential for bioartificial liver application

To bridge patients with acute liver failure to transplantation or liver regeneration, a bioartificial liver (BAL) is urgently needed. A BAL consists of an extracorporeal bioreactor loaded with a bioactive mass that would preferably be of human origin and display high hepatic functionality, including detoxification. The human hepatoma cell line HepG2 exhibits many hepatic functions, but its detoxification function is low. In this study, we investigated whether stable overexpression of pregnane X receptor (PXR), a master regulator of diverse detoxification functions in the liver [eg, cytochrome P450 3A (CYP3A) activity], would increase the potential of HepG2 for BAL application. Stable overexpression was achieved by lentiviral expression of the human PXR gene, which yielded cell line cBAL119. In monolayer cultures of cBAL119 cells, PXR transcript levels increased 29-fold versus HepG2 cells. Upon activation of PXR by rifampicin, the messenger RNA levels of CYP3A4, CYP3A5, and CYP3A7 increased 49- to 213-fold versus HepG2 cells. According to reporter gene assays with different inducers, the highest increase in CYP3A4 promoter activity (131-fold) was observed upon induction with rifampicin. Inside BALs, the proliferation rates, as measured by the DNA content, were comparable between the 2 cell lines. The rate of testosterone 6beta-hydroxylation, a measure of CYP3A function inside BALs, increased 4-fold in cBAL119 BALs versus HepG2 BALs. Other functions, such as apolipoprotein A1 synthesis, urea synthesis, glucose consumption, and lactate production, remained unchanged or increased. Thus, stable PXR overexpression markedly increases the potential of HepG2 for BAL application.

Liver Cell Culture Devices

In the last 15 years many different liver cell culture devices, consisting of functional liver cells and artificial materials, have been developed. They have been devised for numerous different applications, such as temporary organ replacement (a bridge to liver transplantation or native liver regeneration) and as in vitro screening systems in the early stages of the drug development process, like assessing hepatotoxicity, hepatic drug metabolism, and induction/inhibition studies. Relevant literature is summarized about artificial human liver cell culture systems by scrutinizing PubMed from 2003 to 2009. Existing devices are divided in 2D configurations (e.g., static monolayer, sandwich, perfused cells, and flat plate) and 3D configurations (e.g., liver slices, spheroids, and different types of bioreactors). The essential features of an ideal liver cell culture system are discussed: different types of scaffolds, oxygenation systems, extracellular matrixes (natural and artificial), cocultures with nonparenchymal cells, and the role of shear stress problems. Finally, miniaturization and high-throughput systems are discussed. All these factors contribute in their own way to the viability and functionality of liver cells in culture. Depending on the aim for which they are designed, several good systems are available for predicting hepatotoxicity and hepatic metabolism within the general population. To predict hepatotoxicity in individual cases genomic analysis might be essential as well.

Use of a rotary bioartificial liver in the differentiation of human liver stem cells

The use of bioartificial livers (BALs) for the expansion of human adult liver stem cells and the production of growth factors could be a potential strategy for cell-based extracorporeal liver support. The present study aimed to assessing the differentiation of human adult liver stem cells in a rotary BAL. Liver stem cells were seeded into a polysulphone membrane filter at a density of 3 x 10(8) cells, and the filter was connected to a rotary bioreactor perfusion system (37 degrees C, 50 mL/min, 48 h). Viability, cell differentiation, and metabolic performances were evaluated at 24 and 48 h. Hepatocyte growth factor production from human adult liver stem cells, mature hepatocytes, and mesenchymal stem cells in adhesion and in the rotary BAL conditions was compared. Liver stem cells cultured in the rotary BAL produced the highest amounts of albumin (p = 0.002) and ammonia-induced urea (p = 0.0001), and had an increased cytochrome P450 expression in respect to liver stem cells in adhesion. Remarkably, liver stem cells in the rotary BAL produced very high amounts of hepatocyte growth factor (p = 0.005) in respect to hepatocytes and mesenchymal stem cells. Moreover, the cells lost their stem cell markers and acquired several markers of mature hepatocytes. In conclusion, the rotary BAL favored liver stem cell differentiation into mature hepatocyte-like cells.

Future of bioartificial liver support

Many different artificial liver support systems (biological and non-biological) have been developed, tested pre-clinically and some have been applied in clinical trials. Based on theoretical considerations a biological artificial liver (BAL) should be preferred above the non-biological ones. However, clinical application of the BAL is still experimental. Here we try to analyze which hurdles have to be taken before the BAL will become standard equipment in the intensive care unit for patients with acute liver failure or acute deterioration of chronic liver disease.

A surgical model of fulminant hepatic failure in rabbits

AIM

Animal models of fulminant hepatic failure (FHF) have been developed for characterization of disease progression and to evaluate the effectiveness of liver-assist devices, some by treatment with hepatotoxic drugs, viral hepatitis or surgical procedures. We have developed a model in the rabbit by combining resection of the three anterior lobes with ligation of the pedicle of the right lateral lobes, resulting in liver necrosis; the remnant quadrate lobes are left intact.

MATERIALS AND METHODS

Adult male New Zealand white rabbits (n=16) were used. Six animals were killed to measure the weight of the separate liver lobes. The others (n=10) underwent left neck central line placement to monitor continuous blood pressure and collect blood for laboratory analysis, and a burr hole on the right parietal bone to monitor the intracranial pressure (ICP). Blood laboratory analysis, clinical hepatic encephalopathy and ICP levels were measured in FHF animals (n=6). Animals (n=4) undergoing a sham operation served as controls.

RESULTS

All FHF animals died between 12 and 26 h after liver surgery from FHF characterized by a progressive increase in liver enzymes, ammonia, total bilirubin, coagulopathy, hepatic encephalopathy and intracranial hypertension. Histological features of the ischaemic lobes showed coagulative necrosis of hepatocytes with absence of nuclei and collapse of cell plates. Brain histology revealed hypoxic cell damage.

CONCLUSION

We have developed a simple, reproducible model of FHF in rabbits that has a number of features comparable with clinical FHF patients and is well suited for testing experimental bioartificial liver systems and investigating the pathogenesis of FHF.

A new surgical model for hepatectomy in pigs

BACKGROUND

Anhepatic animal models are suitable for simulating acute liver failure. Hepatectomy in pigs includes en bloc resection of the vena cava, and therefore, a temporary extracorporeal bypass and total clamping of the inferior vena cava are needed. These steps cause severe depression of circulation with impaired survival.

METHODS

Previous to en bloc hepatectomy including retrohepatic vena cava in 20 female pigs, a Y-shaped bypass was implanted starting with end-to-side anastomosis between the vena cava and the portal vein, followed by anastomosis to the intrathoracic vena cava.

RESULTS

Blood flow was constant during and after hepatectomy because vessels were only partially clamped. No venous stasis of intestinal organs was observed. Hemodynamic parameters like heart rate, mean arterial pressure, central venous pressure, pulse oximetry and intracranial pressure remained extremely stabile during and after hepatectomy. Postoperative survival time was 100% after 12 h. Maximum survival time was 84.9 h and mean survival time 51.2 +/- 18.7 h. All animals died from multiple organ failure. Intracranial pressure remained stable during the surgical procedure and rose continuously until death. The autopsy showed massive brain edema.

CONCLUSIONS

This new surgical technique is safe and easy to perform and permits total hepatectomy with minimal blood loss under stable circulation without requiring an extracorporeal bypass.

Time-related analysis of metabolic liver functions, cellular morphology, and gene expression of hepatocytes cultured in the bioartificial liver of the Academic Medical Center in Amsterdam (AMC-BAL)

A comprehensive understanding of the mechanisms that underlie hepatic differentiation inside a bioartificial liver (BAL) device is obtained when functional, histological, and gene expression analyses can be combined. We therefore developed a novel cell-sampling technique that enabled us to analyze adherent hepatocytes inside a BAL device during a 5-day culture period, without the necessity of terminating the culture. Biochemical data showed that hepatocyte-specific functions were relatively stable, despite an increase in glycolytic activity. Quantitative reverse transcriptase polymerase chain reaction analysis of hepatic genes cytochrome p450 3A29, albumin, glutamine synthetase, alpha-1 antitrypsin, and carbamoyl-phosphate synthetase, but also de-differentiation marker pi-class glutathione S transferase showed stable messenger ribonucleic acid (mRNA) levels from day 1 to 5. In contrast, mRNA levels of alpha-fetoprotein, pro- and anti-apoptotic genes Bax-alpha and Bcl-X(L), metabolic genes lactate dehydrogenase and uncoupling protein 2, and cytoskeleton genes alpha- and beta-tubulin and beta-actin increased in 5 days. Histological analysis revealed viable tissue-like structures with adaptation to the in vitro environment. We conclude that hepatocytes show a tendency for de-differentiation shortly after seeding but thereafter remain acceptably differentiated during 5 days of culture. Furthermore, partly impaired mitochondrial function is suggestive for local hypoxic regions and may trigger the observed metabolic changes. Anti-apoptotic activity seems to balance pro-apoptotic activity. This new cell-sampling technique facilitates the analysis of dynamic processes of hepatocyte culture inside a BAL.

In vitro comparison of two bioartificial liver support systems: MELS CellModule and AMC-BAL

Clinically applied bioartificial liver (BAL) support systems are difficult to compare with regard to overall hepatocyte-specific function and clinical outcome. We compared two clinically applied BAL systems, the Modular Extracorporeal Liver Support (MELS) CellModule and the AMC-bioartificial liver (AMC-BAL) in an in vitro set-up. Both BAL systems were loaded with 10 billion freshly isolated porcine hepatocytes, cultured for 7 days and tested on days 1, 2, 4 and 7. Average decrease in hepatocyte-specific functions over 7 days was 9.7%. Three parameters differed between both bioreactors: lidocaine elimination at days 1 and 2 was significantly higher in the AMCBAL, ammonia elimination showed a significantly higher trend for the AMC-BAL over 7 days and LDH release was significantly lower at day 7 for the MELS CellModule. In conclusion, this first in vitro comparison of two clinically applied BAL systems shows comparable functional capacity over a period of 7 days.

Significant survival prolongation in pigs with fulminant hepatic failure treated with a novel microgravity-based bioartificial liver

The aim of this study was to evaluate the efficacy and safety of our novel Innsbruck Bioartificial Liver (IBAL; US patent no. 10/641275), which contains aggregates of porcine hepatocytes grown under simulated microgravity, in a porcine model of fulminant hepatic failure (FHF). FHF was induced by a combination of 75-80% liver resection and ischemia of the remnant segments for 60 min in 12 pigs. Two experimental groups were studied: the control group (n = 5) received standard intensive care and the study group (n = 5) received IBAL treatment. The survival of pigs with FHF was significantly prolonged by about 150% with IBAL treatment as compared to controls (controls: 20.4 +/- 2.8 h, IBAL: 51.0 +/- 2.2 h; P = 0.00184). In addition, intracranial pressure, blood ammonia, lactate, aspartate aminotransferase, and alkaline phosphatase levels were lower in the IBAL group than in controls, indicating metabolic activity of porcine hepatocytes in the bioreactor. No adverse effects were observed.

Bioartificial liver: its pros and cons

Both the large variety of liver functions for maintaining body homeostasis and the proven effectivity of whole liver transplantation in the therapy of acute liver failure (ALF), are important reasons to presume that cell-free liver support systems will not be able to adequately support the failing liver. Accordingly, bioartificial liver (BAL) systems have shown their efficacy in experimental ALF models in small and large animals, and have shown to be suitable and safe in phase 1 studies in humans with ALF. However, the optimal BAL system is still under development. Important issues are the source of the cellular component and the configuration of the BAL system with regard to cell attachment, mass transfer characteristics and oxygenation at site. The deficiency of all BAL systems to excrete bile effectively is another important topic for improvement. The great challenge for the future is to develop a well-functioning and safe human hepatic cell line which can replace the widely used porcine (xenogeneic) hepatocytes. Theoretically, a combination of a cell-free liver support system and a BAL system might be optimal for the treatment of ALF patients in the near future.

Three-dimensional numerical modeling and computational fluid dynamics simulations to analyze and improve oxygen availability in the AMC bioartificial liver

A numerical model to investigate fluid flow and oxygen (O(2)) transport and consumption in the AMC-Bioartificial Liver (AMC-BAL) was developed and applied to two representative micro models of the AMC-BAL with two different gas capillary patterns, each combined with two proposed hepatocyte distributions. Parameter studies were performed on each configuration to gain insight in fluid flow, shear stress distribution and oxygen availability in the AMC-BAL. We assessed the function of the internal oxygenator, the effect of changes in hepatocyte oxygen consumption parameters in time and the effect of the change from an experimental to a clinical setting. In addition, different methodologies were studied to improve cellular oxygen availability, i.e. external oxygenation of culture medium, culture medium flow rate, culture gas oxygen content (pO(2)) and the number of oxygenation capillaries. Standard operating conditions did not adequately provide all hepatocytes in the AMC-BAL with sufficient oxygen to maintain O(2) consumption at minimally 90% of maximal uptake rate. Cellular oxygen availability was optimized by increasing the number of gas capillaries and pO(2) of the oxygenation gas by a factor two. Pressure drop over the AMC-BAL and maximal shear stresses were low and not considered to be harmful. This information can be used to increase cellular efficiency and may ultimately lead to a more productive AMC-BAL.

Bioreactors for extracorporeal liver support

Hybrid extracorporeal liver support is an option to assist liver transplantation therapy. An overview on liver cell bioreactors is given and our own development is described. Furthermore, the prospects of the utilization of human liver cells from discarded transplantation organs due to steatosis, cirrhosis, or traumatic injury, and liver progenitor cells are discussed. Our Modular Extracorporeal Liver Support (MELS) concept proposes an integrative approach for the treatment of hepatic failure with appropriate extracorporeal therapy units, tailored to suit the actual clinical needs of each patient. The CellModule is a specific bioreactor (charged actually with primary human liver cells, harvested from human donor livers found to be unsuitable for transplantation). The DetoxModule enables albumin dialysis for the removal of albumin-bound toxins, reducing the biochemical burden of the liver cells and replacing the bile excretion of hepatocytes in the bioreactor. A Dialysis Module for continuous veno-venous hemofiltration can be added to the system if required in hepato-renal syndrome.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

Evaluation of a bioartificial liver based on a nonwoven fabric bioreactor with porcine hepatocytes in pigs

BACKGROUND/AIMS

We developed a bioartificial liver (BAL) based on a direct hemoperfusion typed nonwoven fabric bioreactor containing porcine hepatocytes. In this study, the efficacy of our BAL was evaluated with a pig fulminant hepatic failure (FHF) model.

METHODS

FHF was induced with intravenous administration of D-galactosamine (1.3 g/kg) in each pig. Twelve hours post D-galactosamine injection, fifteen pigs were divided into: a BAL group (n = 5), in which pigs received the BAL treatment with 1.0 to 1.3 x 10(9) hepatocytes for 6 h, a sham BAL group (n = 5), in which pigs received the BAL treatment without hepatocytes, and a FHF group (n = 5), in which pigs only received intensive care. Parameters related to liver function and animal survival up to 168 h were determined.

RESULTS

In the BAL group, blood ammonia and plasma lactate levels were lower, and serum glucose levels and Fischer index were higher than those in the other two groups. Survival time of pigs in the BAL group was significantly prolonged as compared with the sham BAL and the FHF group.

CONCLUSIONS

The BAL based on a nonwoven fabric bioreactor containing porcine hepatocytes appears to be effective in the treatment of FHF in pigs.

Development and perspectives of perfusion treatment for liver failure

To treat patients with severe liver failure, liver transplantation and blood purification therapy, including plasmapheresis, hemodiafiltration, and bioartificial liver support, are available. The two mainstream systems developed for bioartificial liver support are extracorporeal whole liver perfusion (ECLP) and the bioreactor system (BIS). We developed a method of cross-plasma perfusion, in which plasma is exchanged between the blood circuit of the patient and that of a hepatic functioning unit, through which immunologically free whole human blood is perfused. From the aspects of efficacy and epidemic safety, the best system of bioartificial liver support for clinical use is considered to be ECLP in cross-plasma perfusion. In opposition, a social antagonist for zoonosis has consistently been raised, with controversy surrounding the use of xenogeneic organs for human treatment, which might be final obstacle. It is possible that the combination therapy of hemodiafiltration and the administration of human serum albumin and anticoagulant factors, which minimizes the economic and medical resource costs through the development of transgenic livestock that secrete human pharmaceuticals systemically, will become a more desirable and practical treatment for patients with severe liver failure.

Acute liver failure: a critical appraisal of available animal models

The availability of adequate experimental models of acute liver failure (ALF) is of prime importance to provide a better understanding of this condition and allow the development and testing of new therapeutic approaches for patients with ALF. However, the numerous etiologies and complications of ALF contribute to the complexity of this condition and render the development of an ideal experimental model of ALF more difficult than expected. Instead, a number of different models that may be used for the study of specific aspects of ALF have been developed. The most common approaches used to induce ALFin experimental animals are surgical procedures, toxic liver injury,or a combination of both. Despite the high prevalence of viral hepatitis worldwide, very few satisfactory viral models of ALF are available. Established and newly developed models of ALF are reviewed.

Mild Hypothermic Preservation for Transport Purposes of the AMC Bioartificial Liver Charged with Porcine Hepatocytes

BACKGROUND

Preservation conditions play a crucial role during transport of a bioartificial liver (BAL) from the laboratory to the hospital. We assessed the possibility to preserve the AMC-BAL loaded with freshly isolated porcine hepatocytes at mild hypothermic temperatures.

METHODS

Two laboratory-scale AMC-bioreactors were loaded with 1 billion freshly isolated porcine hepatocytes per experiment (n=6). Bioreactors in the control group were kept for three days at 37 degrees C. Bioreactors in the transport group were kept at 37 degrees C during day 1, at 15 degrees C during day 2, and again at 37 degrees C during day 3. In addition, long-term mild hypothermic preservation periods of 45 and 110 hr at 15 degrees C and 26 degrees C, respectively, were assessed. The effect of mild hypothermic preservation on hepatocytes inside the bioreactors was tested by determination of cell damage parameters, as well as metabolic and hepatocyte-specific functions.

RESULTS

A 24-hour period of mild hypothermic preservation did not reduce any hepatocyte-specific function. LDH release was significantly higher only at day 2. Albumin production at day 2 and lidocaine elimination at day 3 were significantly higher with glucose consumption and lactate production being significantly lower at both test days. Long-term mild hypothermic preservation had a drastic negative effect on cellular viability and hepatocyte-specific function.

CONCLUSIONS

Mild hypothermic preservation at temperatures as low as 15 degrees C and for a duration of 24 hr is a feasible method to preserve BAL systems loaded with freshly isolated porcine liver cells and will simplify the logistics of BAL transport from the laboratory to the hospital.

Assessment and improvement of liver specific function of the AMC-bioartificial liver

The variety of methods for measuring bioactive mass and functionality of bioartificial livers (BAL) is confusing and prevents accurate comparison of reported data. Here we present a comparison of different hepatocyte quantification methods and propose that estimation of cell pellet volume after centrifugation generates a reliable, useful and fast method. In addition a correlation is made between several function tests performed in 26 bioreactors to assess their predictive value. The ammonia eliminating capacity was found to be most predictive for other liver functions, except for lidocaine elimination as a measure of mixed function oxidase activity, which should therefore be determined separately. The oxygen consumption test proved to be an easy and predictive parameter as well. The first generation of our BAL system needed further development to assure optimal treatment of acute liver failure (ALF) patients. Changes in the porcine hepatocyte isolation method and bioreactor loading as well as changes in bioreactor configuration, including use of different materials, resulted in a significantly improved level and maintenance of in vitro BAL function. A fourfold increase in ammonia eliminating capacity, which is only reduced to 75% after seven days of culturing, offers promising prospects for further clinical application.

CONCLUSION

The current second generation of our BAL and improvement of hepatocyte isolation and testing protocols have led to a significant increase in the level as well as the maintenance of hepatocyte specific function in our BAL. Finally, consensus on definition of the bioactive mass to be loaded in the bioreactor and insight in the variation and reliability of the functional and metabolic parameters enhances comparison of the different types of bioartificial livers presented in literature.

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 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.

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.

Large animal models of fulminant hepatic failure in artificial and bioartificial liver support research

Among the large range of organs involved in the field of tissue engineering (skin, blood vessels, cartilage, etc.) the liver has been given broad attention in the last decade. Liver support systems encompassing artificial and bioartificial systems are applied to treat patients with fulminant hepatic failure (FHF) as a bridge to orthotopic liver transplantation or to liver regeneration. To test safety, technical applicability and therapeutic effect of liver support systems, reliable animal models are needed. Due to the complexity of FHF many diverse attempts have been made to develop an adequate animal model to study liver failure, liver regeneration and liver support systems. In this paper an overview is given of the different models and their advantages and disadvantages are discussed. Suggestions are made for the most suitable large animal model to test liver support systems.

Retinoic acid maintains differentiated cell morphology and functions in long-term cultured porcine hepatocytes: obtaining functional cells for prolonged treatments with bioartificial liver

Porcine hepatocytes show several immunological characteristics and enzymatic activities of human liver, representing an ideal xenogenic source of cells as biological component of bioartificial liver (BAL). Isolated hepatocytes rapidly lose their specific metabolic activities and their typical morphology when cultured in the presence of serum. Since in BAL porcine hepatocytes are perfused by the patient's plasma, procedures able to minimize de-differentiation of cells could be useful for long-term treatment of acute liver failure (ALF). In this work we found that, in the presence of micromolar concentration of All trans-retinoic acid (ATRA), porcine parenchymal liver cells undergo to a lower extent the de-differentiating effects of long-term culture in the presence of serum. The evaluation of lidocaine metabolism showed that ATRA-treated cells retain specific hepatocyte function for a significantly longer time when compared to control hepatocytes. A tyrosine phosphorylation of PLC-gamma1 was observed in concomitance with the ATRA-induced maximal functional activity. An increased expression of PLC-beta3 and PKC-alpha and -beta2 was also evidentiated at the longer time points explored, when the effects of ATRA in preservation of the differentiated morphology were maximal. These results provide the first evidence that ATRA plays a differentiating role in adult porcine hepatocytes cultured under de-differentiating conditions. The administration of ATRA to isolated parenchymal cells from pig liver may provide functional hepatocytes for prolonged treatment with BAL.

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.

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.

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.

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.

Plasma versus whole blood perfusion in a bioartificial liver assist device

The ramifications of using whole blood or plasma for perfusion off an hepatocyte containing bioartificial liver bioreactor in which the hepatocytes are separated by a membrane or other physical barrier from the perfusate stream on the rate of change of patient blood concentrations are explored through dynamic modeling of whole blood perfusion as a two compartment system (patient tissue and blood compartments), and plasma perfusion as a three compartment system (patient tissue and blood compartments, and a plasma reservoir). The whole blood perfusion model is described by three dimensionless parameters: the Damkohler number, Da, which represents the ratio of the rate of conversion by the bioreactor to the rate of perfusion; kappa, which represents the ratio of the rate of internal reequilibration between the tissue and blood compartments and the rate of perfusion; and Vtb, the tissue/blood volume ratio. The plasma perfusion model has three additional dimensionless parameters: f, the fraction of plasma withdrawn from the blood in a plasma separator; alpha, the ratio of the plasma perfusion rate in the bioreactor to the blood draw rate; and Vbr, the blood/plasma reservoir volume ratio. Within the physiologic range of parameters, the rate of reduction in blood concentration in both the whole blood-perfused and plasma-perfused systems are sensitive to Damkohler number up to Da approximately 2. Neither system is sensitive to variations in kappa, and the plasma perfusion system has little sensitivity to alpha. Given bioreactors of equivalent activity, a greater rate of blood concentration reduction and lower endpoint blood concentration at equivalent perfusion times will be achieved with whole blood perfusion. There are two physical reasons for this. The first is that the plasma perfused system is only processing a fraction, f, of the blood compared with the whole blood perfusion system. The second reason is that, although the blood-perfused system is limited by overall bioreactor performance, the plasma-perfused system is mass transfer limited to the rate of blood concentration dilution into the plasma reservoir rather than limited by the overall bioreactor performance.

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.

Modulation of hepatocyte function in an immortalized human hepatocyte cell line following exposure to liver-failure plasma

For hepatocytes to function effectively in a bioartificial liver device, maintained function in the milieu of plasma from patients with liver failure will be required. We have investigated the effect of plasma obtained at plasmapheresis from patients with acute liver failure on the performance of the human hepatocyte cell line HHY41 in liver-failure plasma, normal plasma, and culture medium. Cytotoxicity of plasma, DNA synthesis by thymidine incorporation, oxidative status, and cytochrome P450 functions were assayed after a 16 h culture with normal plasma, liver-failure plasma, or culture medium. Some, but not all, samples of liver-failure plasma were deleterious to the performance of the cell line, inducing cytotoxicity and oxidative stress, with diminished DNA synthesis, protein synthesis, and cytochrome P4501A activity. Strategies to minimize the toxic effects of liver-failure plasma may improve the performance of liver cells in extracorporeal liver-support devices.

Recent developments on human cell lines for the bioartificial liver

Most bioartificial liver (BAL) devices contain porcine primary hepatocytes as their biological component. However, alternatives are needed due to xenotransplantation associated risks. Human liver cell lines have excellent growth characteristics and are therefore candidates for application in BAL devices. Tumour-derived cell lines HepG2 and C3A express a variety of liver functions, but some specific liver functions, like ammonia detoxification and ureagenesis are insufficient. Immortalised human hepatocytes might offer better prospects. The balance between immortalisation and transformation with dedifferentiation of cells seems controllable by conditional immortalisation and/or the use of telomerase as immortalising agent. Another promising approach will be the use of embryonic or adult human stem cells. Rodent stem cells have been directed to hepatic differentiation in vitro, which might be applicable to human stem cells. However, both functionality and safety of immortalised human liver cell lines and differentiated stem cells should be improved before successful use in BAL devices becomes reality.

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.