Viability and primary culture of rat hepatocytes after hypothermic preservation: the superiority of the Leibovitz medium over the University of Wisconsin solution for cold storage

Short-Term Hypothermic Preservation of Porcine Hepatocyte Spheroids using uw Solution

The feasibility of University of Wisconsin (UW) solution in short-term hypothermic preservation of porcine hepatocyte spheroids was investigated, because they have great potential in bioartificial liver (BAL) systems. Porcine hepatocyte spheroids preserved for 3 days expressed almost comparable levels of albumin secretion as those without preservation, during 8 subsequent days of recultivation in continuous rotational culture, whereas isolated single cells did not reorganize into spheroids and completely lost their function in recultivation. Although for 3-day–preserved spheroids, the albumin secretion was lowered immediately after recultivation (Days 0–2), it was completely restored to that of nonpreserved ones. The function was completely lost in recultivation for 7-day–preserved ones. These results demonstrate that reorganization into spheroids is effective in preventing the functional loss of porcine hepatocytes occurring in hypothermic preservation, and that spheroid formation should precede the preservation as long as spheroid culture is finally used in BAL systems. Also, porcine hepatocyte spheroids are shown to be satisfactory stored in UW solution up to 3 days without significant cellular or functional loss.

Functional Recovery of Porcine Hepatocytes after Hypothermic or Cryogenic Preservation for Liver Support Systems

The provision of an immediate supply of isolated porcine hepatocytes for artificial liver support requires preservation techniques that will allow maintenance of cell viability and detoxification functions. By means of a simple and cost-effective cryopreservation system, porcine hepatocytes can be available for both local and distant medical treatment facilities. Additionally, cryopreservation provides an adequate period for quality control testing to be completed prior to use of any specific cell lot. We are reporting a dual approach, namely the preservation of porcine hepatocytes, at 4°C and at −196°C in liquid nitrogen (LN2). Using a combination of cryoprotectant agents with Chee's modified Eagle's culture media (CEM), collagenase isolated hepatocytes stored at 4°C for 24 h maintained 80% of the initial diazepam metabolism measured in freshly isolated cells and nearly 100% of initial function was preserved in hepatocytes stored up to 6 mo at -196°C. University of Wisconsin solution (UW) was also tested and while adequate for 4°C storage, it certainly did not match the performance of the CEM formulations for preservation of metabolic function of cells stored in liquid nitrogen. Based on our results of viability and detoxification function the combination of CEM with DMSO, polyethylene glycol and serum provided optimal protection for LN2 frozen cells. Other findings in these studies underlined the importance of the gradual introduction of DMSO in the prefreezing process, the period of osmotic equilibration, and the rapid postthaw withdrawal of this agent to minimize cytotoxic effects at these critical stages. Our freezing methodology provides the foundation for further technological developments in the cryopreservation of the large numbers of cells (billions) that are necessary for extracorporeal liver assist devices.

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.

The Optimization of Short-Term Hepatocyte Preservation Before Transplantation

Background

No optimal methods for short-term hepatocyte preservation have been established. We have recently developed a prominent oxygen-permeable bag (Tohoku Device [TD]) for pancreatic islet culture and transplantation. In this study, we investigated whether TD is also effective for hepatocyte preservation and tried to optimize other conditions.

Methods

Hepatocytes were preserved in the following conditions, and their outcomes were observed. First, the effectiveness of TD was investigated. Second, hepatocyte medium (HM) and organ preservation solutions with or without fetal bovine serum (FBS) were compared. Third, as supplementations, FBS and human serum albumin (HSA) were compared. Fourth, low, room and high temperature were compared. And finally, hepatocytes preserved in various conditions were transplanted into the subrenal capsule space of nonalbumin rats and engrafted areas were assessed.

Results

The survival rate of hepatocytes preserved in TD tended to be higher and their viability and function were maintained significantly greater than those of non-TD group. Irrespective of FBS supplementation, the survival rate of HM group was significantly higher than those of organ preservation solution group while viabilities and plating efficiency were similar among them. Although survival rates of groups without FBS were extremely low, results of HSA supplemented group were not inferior to FBS supplemented group. Hepatocytes preserved at high temperature had the worst results. The engrafted area of TD group tended to be higher than those of other groups.

Conclusions

TD is effective for short-term hepatocyte preservation. HSA is a useful substitute for FBS, and preserving in HM at low temperature is recommended.

Improvement of short-term hypothermic preservation of microencapsulated hepatocytes

OBJECTIVES

To determine the optimal storage solution containing suitable protective agents for the preservation of microencapsulated hepatocytes at 4 °C as well as the optimum incubation time after hypothermic preservation.

RESULTS

L15 was the optimum solution for both maintaining microcapsule integrity and cell viability. Furthermore, 5 %(v/v) PEG (20 or 35 kDa) added to Leibovitz-15 medium was optimal for microencapsulated C3A cells, enhancing cell viability and liver-specific functions, including albumin and urea synthesis as well as CYP1A2 and CYP3A4 activities. The transcription levels of several CYP450-related genes were also dramatically increased in cells incubated in the optimal solution. Pre-incubation for 2 h was the optimal time for restoring favorable levels of CYP1A2 and CYP3A4 activities in microencapsulated C3A cells for short term, 2 day storage.

CONCLUSIONS

Leibovitz-15 medium supplemented with 5 % (v/v) PEG is a promising cold solution for microencapsulated hepatocytes at 4 °C, with an incubation of 2 h at 37 °C after hypothermic preservation being the best incubation duration for further cell application.

Hypothermic storage of human hepatocytes for transplantation

Transplantation of human hepatocytes is gaining recognition as a bridge or an alternative to orthotopic liver transplantation for patients with acute liver failure and genetic defects. Since most patients require multiple cell infusions over an extended period of time, we investigated hepatic functions in cells maintained in University of Wisconsin solution at 4°C up to 72 h. Eleven different assessments of hepatic viability and function were investigated both pre- and posthypothermic storage, including plating efficiency, caspase-3/7 activity, ammonia metabolism, and drug-metabolizing capacity of isolated hepatocytes. Long-term function, basal, and induced cytochrome P450 activities were measured after exposure to prototypical inducing agents. Cells from 47 different human liver specimens were analyzed. Viability significantly decreased in cells cold stored in UW solution, while apoptosis level and plating efficiency were not significantly different from fresh cells. Luminescent and fluorescent methods assessed phases I and II activities both pre- and post-24-72 h of cold preservation. A robust induction (up to 200-fold) of phase I enzymes was observed in cultured cells. Phase II and ammonia metabolism remained stable during hypothermic storage, although the inductive effect of culture on each metabolic activity was eventually lost. Using techniques that characterize 11 measurements of hepatic viability and function from plating efficiency, to ammonia metabolism, to phases I and II drug metabolism, it was determined that while viability decreased, the remaining viable cells in cold-stored suspensions retained critical hepatic functions for up to 48 h at levels not significantly different from those observed in freshly isolated cells.

Cold Preservation of Human Adult Hepatocytes for Liver Cell Therapy

Hepatocyte transplantation is a promising alternative therapy for the treatment of hepatic failure, hepatocellular deficiency, and genetic metabolic disorders. Hypothermic preservation of isolated human hepatocytes is potentially a simple and convenient strategy to provide on-demand hepatocytes in sufficient quantity and of the quality required for biotherapy. In this study, first we assessed how cold storage in three clinically safe preservative solutions (UW, HTS-FRS, and IGL-1) affects the viability and in vitro functionality of human hepatocytes. Then we evaluated whether such cold-preserved human hepatocytes could engraft and repopulate damaged livers in a mouse model of liver failure. Human hepatocytes showed comparable viabilities after cold preservation in the three solutions. The ability of fresh and cold-stored hepatocytes to attach to a collagen substratum and to synthesize and secrete albumin, coagulation factor VII, and urea in the medium after 3 days in culture was also equally preserved. Cold-stored hepatocytes were then transplanted in the spleen of immunodeficient mice previously infected with adenoviruses containing a thymidine kinase construct and treated with a single dose of ganciclovir to induce liver injury. Engraftment and liver repopulation were monitored over time by measuring the blood level of human albumin and by assessing the expression of specific human hepatic mRNAs and proteins in the recipient livers by RT-PCR and immunohistochemistry, respectively. Our findings show that cold-stored human hepatocytes in IGL-1 and HTS-FRS preservative solutions can survive, engraft, and proliferate in a damaged mouse liver. These results demonstrate the usefulness of human hepatocyte hypothermic preservation for cell transplantation.

Cryopreservation of Hepatocytes

The use of cryopreserved hepatocytes has increased in the last decade due to the improvement of the freezing and thawing methods, and has even achieved acceptance by the US Food and Drug Administration for use in drug metabolizing enzyme induction studies. This chapter provides an overview of the theories behind the process of cryopreservation as well as practical advice on methods to cryopreserve hepatocytes, which retain functions similar to fresh cells after thawing. Parameters, such as cell density, cryoprotectants, freezing media, storage conditions, and thawing techniques, should be critically considered. Special emphasis is put on human hepatocytes, but information for the cryopreservation of animal hepatocytes is also described.

Liver slices in in vitro pharmacotoxicology with special reference to the use of human liver tissue

In the early years of research in in vitro pharmacotoxicology liver slices have been used. After a decline in the application of slices in favour of the use of isolated hepatocytes and the isolated perfused liver preparation, the development of the Krumdieck slicer in the 1980s led to a ;comeback' of the technique. This review will focus on the use of human liver, with special reference to the comparison of slices with isolated hepatocytes in in vitro pharmacotoxicology. In addition, an overview on the predictive value of these in vitro systems for drug disposition and toxicity in vivo will be given. Preservation techniques for liver slices and hepatocytes will also be discussed. These techniques ensure an efficient utilization of the scarce human material. For long-term storage of liver slices and hepatocytes, cryopreservation seems most promising. However, cryopreservation is still in its infancy, and reports mainly deal with drug metabolism studies after cryopreservation. Drug toxicity, metabolism and transport data determined in slices and isolated hepatocytes, from both human and animal liver showed good correlation with the corresponding parameters measured in vivo. Therefore, the results obtained in such studies may give rise to more in-depth research on the mechanisms of pharmactoxicology in the human liver.

General review on in vitro hepatocyte models and their applications

In vitro hepatocyte models represent very useful systems in both fundamental research and various application areas. Primary hepatocytes appear as the closest model for the liver in vivo. However, they are phenotypically unstable, have a limited life span and in addition, exhibit large interdonor variability when of human origin. Hepatoma cell lines appear as an alternative but only the HepaRG cell line exhibits various functions, including major cytochrome P450 activities, at levels close to those found in primary hepatocytes. In vitro hepatocyte models have brought a substantial contribution to the understanding of the biochemistry, physiology, and cell biology of the normal and diseased liver and in various application domains such as xenobiotic metabolism and toxicity, virology, parasitology, and more generally cell therapies. In the future, new well-differentiated hepatocyte cell lines derived from tumors or from either embryonic or adult stem cells might be expected and although hepatocytes will continue to be used in various fields, these in vitro liver models should allow marked advances, especially in cell-based therapies and predictive and mechanistic hepatotoxicity of new drugs and other chemicals. All models will benefit from new developments in throughput screening based on cell chips coupled with high-content imaging and in toxicogenomics technologies.

Optimisation of the cryopreservation of primary hepatocytes

The use of cryopreserved hepatocytes has increased in the last decade due to the improvement of the freezing and thawing methods and has even achieved acceptance by the U.S. Food and Drug Administration for use in drug-metabolising enzyme induction studies. This chapter provides an overview of the theories behind the process of cryopreservation and some of the most important advances which have led to the ability to cryopreserve hepatocytes, which when thawed retain functions similar to fresh cells. Parameters such as cell density, cryoprotectants and freezing media should be considered as well as storage conditions and thawing techniques. Special emphasis is placed on human hepatocytes but information for the cryopreservation of animal hepatocytes is also described. Finally, a suggested method for optimising cryopreservation method is outlined.

Evaluation of drug-metabolizing and functional competence of human hepatocytes incubated under hypothermia in different media for clinical infusion

Hepatocyte transplantation has been proposed as a method to support patients with liver insufficiency. Key factors for clinical cell transplantation to progress is to prevent hepatocyte damage, loss of viability and cell functionality, factors that depend on the nature of the tissue used for isolation to a large extent. The main sources of tissue for hepatocyte isolation are marginal livers that are unsuitable for transplantation, and segments from reduced cadaveric grafts. Hepatocellular transplantation requires infusing human hepatocytes in suspension over a period of minutes to hours. The beneficial effect of hypothermic preservation of hepatocytes in infusion medium has been reported, but how critical issues towards the success of cell transplantation, such as the composition of infusion medium and duration of hepatocyte storage will affect hepatocyte quality for clinical cell infusion has not been systematically investigated. Infusion media composition is phosphate-buffered saline containing anticoagulants and human serum albumin. The supplementation of infusion media with glucose or N-acetyl-cystein, or with both components at the same time, has been investigated. After isolation, hepatocytes were suspended in each infusion medium and a sample at the 0 time point was harvested for cell viability and functional assessment. Thereafter, cells were incubated in different infusion media agitated on a rocker platform to simulate the clinical infusion technique. The time course of hepatocyte viability, funtionality (drug-metabolizing enzymes, ureogenic capability, ATP, glycogen, and GSH levels), apoptosis (caspase-3 activation), and attachment and monolayer formation were analyzed. The optimal preservation of cell viability, attaching capacity, and functionality, particularly GSH and glycogen levels, as well as drug-metabolizing cytochrome P450 enzymes, was found in infusion media supplemented with 2 mM N-acetyl-cystein and 15 mM glucose.

Evolving concepts in liver tissue modeling and implications for in vitro toxicology

The development of human cell models stably expressing functional properties of the in vivo cells they are derived from for predicting toxicity of chemicals is a major challenge. For mimicking the liver, a major target of toxic chemicals, primary hepatocytes represent the most pertinent model. Their use is limited by interdonor functional variability and early phenotypic changes although their lifespan can be extended not only by culturing in a 2D dimension under sophisticated conditions but also by the use of synthetic and natural scaffolds as 3D supporting templates that allow cells to have a more stable microenvironment. Hepatocytes derived from stem cells could be the most appropriate alternative but up to now only liver progenitors/hepatoblasts are obtained in vitro. A few hepatocyte cell lines have retained a variable set of liver-specific functions. Among them are the human hepatoma HepaRG cells that express drug metabolism capacity at levels close to those found in primary hepatocytes making them a suitable model for both acute and chronic toxicity studies. New screening strategies are now proposed based on miniaturized and automated systems; they include the use of microfluidic chips and cell chips coupled with high content imaging analysis. Toxicogenomics technologies (particularly toxicotranscriptomics) have emerged as promising in vitro approaches for better identification and discrimination of cellular responses to chemicals. They should allow to discriminate compounds on the basis of the identification of a set of markers and/specific signaling pathways.

Hypothermic storage and cryopreservation of hepatocytes: the protective effect of alginate gel against cell damages

Hepatocyte-based therapy has been proposed as an alternative to organ transplantation in the treatment of liver disorders. In the clinical context, a major issue is the constant supply of quality assurance-controlled hepatocytes, thereby requiring their cold storage in good conditions. We have analyzed the protective effects of alginate entrapment of rat hepatocytes after either 24 or 48 h of hypothermic storage or cryopreservation on the cell viability, cell yield, both mitochondrial and other cytoplasmic functional activities, and apoptosis. Decrease in viability, as evaluated by the MTT inclusion test, was 4% and 13% (24 h at 4 degrees C), 15% and 33% (48 h at 4 degrees C), and 9% and 19% (liquid nitrogen) for entrapped and free suspended hepatocytes, respectively. Viable cell yields were 86 +/- 8% and 51 +/- 6% for cryopreserved entrapped and free suspended hepatocytes, respectively. The mitochondrial (MTS assay), 7-ethoxyresorufin O-deethylase (EROD), and glutathione-S-transferase (GST) activities were better preserved in entrapped than in free suspended hepatocytes. Both hypothermic storage and cryopreservation were found to induce early caspase-3-like activities, being always much lower in entrapped hepatocytes, particularly after cryopreservation (98.4 +/- 42.4 vs. 6.4 +/- 4.0 fluorescence arbitrary units/hours/microg protein). Thus, cold-induced apoptosis in hepatocytes can be significantly reduced following their entrapment within alginate gel beads and this is associated with an improvement of both their viability and function.

Hypothermic preservation of hepatocytes

This paper presents a review of recent research on the hypothermic storage of hepatocytes. The first focus is on the diversity of methodologies currently employed in this area. The cell damage caused by hypothermic preservation and its possible mechanism are then investigated on both morphological and molecular biology. Later, the gene expressions on a mRNA level or enzyme level after hypothermic preservation are further discussed. Finally, the improvement of hypothermic storage by preconditioning, such as by increasing temperature, is explored.

Maintenance of integrity and function of isolated hepatocytes during extended suspension culture at 25 degrees C

Isolated hepatocytes in suspension provide a number of advantages for use in bioartificial liver device, however, poor stability of this cell preparation at physiological temperatures is an apparent barrier preventing their use. We therefore investigated the integrity and differentiated function of isolated rat hepatocytes under conditions of mild hypothermia. Isolated hepatocytes were suspended in a bicarbonate buffered saline medium, supplemented with glucose and bovine serum albumin (BSA), and maintained for 48 h at 25 degrees C on a rotary shaker under an atmosphere of 95% O2 and 5% CO2. Under these conditions there was no significant decline in cell viability and good preservation of cellular morphology on transmission electron microscopy for at least 24 h. Isolated hepatocytes in suspension at 25 degrees C were also able to maintain normal Na+ and K+ ion gradients. The cellular energy status ([ATP], ATP/ADP ratio, cytoplasmic and mitochondrial redox potentials), metabolic function (urea synthesis and ammonia removal), albumin synthesis and phase I and phase II drug detoxification activity of these cells were also maintained for at least 24 h post isolation. These observations demonstrate the robust nature of mildly hypothermic isolated hepatocytes in suspension and encourage further studies re-examining the feasibility of using this cell preparation in bioartificial livers.

The effect of hypothermia on primary porcine hepatocyte metabolism monitored by (1H) nuclear magnetic resonance spectroscopy

OBJECTIVE

The aim of our study was to use (1H) nuclear magnetic resonance (NMR) spectroscopy as a tool to assess metabolic functions of hepatocytes and to monitor major metabolic pathways of these cells during culture following hypothermic preservation.

METHODS

After isolation, 2 x 10(7) primary porcine hepatocytes were preserved at 4 degrees C in supplemented Leibovitz L-15 medium for 48 h. Viability was assessed at isolation, 24 and 48 h. At isolation and at 48 h cells were plated and cultured with serum free supplemented Williams E medium. 1H NMR spectroscopy was used to assess indices of glucose metabolism, ammonia clearance indices and ketone bodies precursors at 48 h post-plating. Peak integration was applied with sodium 3-(trimethylsilyl-2,2,3,3-2H4)-1-propionate as an internal standard to obtain quantitative results.

RESULTS

Results were obtained from six isolations. Viability was 78.1 +/- 1.2% at isolation, 69 +/- 3.4% at 24 h and 58.9 +/- 3.8% at 48 h of hypothermia. Plating efficiency was 87 +/- 4% for freshly isolated cells and 33.6 +/- 7.6% for hypothermically preserved cells. Glucose consumption was comparable in both groups. Hypothermically preserved cells consumed more threonine, produced more pyruvate and alanine but less lactate. They also produced less acetate and consumed less tyrosine. Glutamate and glutamine concentrations were similar under both conditions.

CONCLUSION

1H NMR spectroscopy is a valid method for assessing metabolic pathways of cultured primary porcine hepatocytes. Although hypothermically preserved cells had a reduced plating efficiency, they were still metabolically active. Thus, hypothermia can be used as a temporary preservation technique for primary porcine hepatocytes.

In vitro models to study hepatotoxicity

Drug discovery and development consists of a series of processes starting with the demonstration of pharmacological effects in experimental cell and animal models and ending with drug safety and efficacy studies in patients. A main limitation is often the unacceptable level of toxicity with the liver as the primary target organ. Therefore, approaches to study hepatic toxicity in the early phase of drug discovery represent an important step towards rational drug development. A variety of in vitro liver models have been developed in the past years. Next to their use in drug development, they can also be applied to study environmental toxins and their hepatotoxicity. The 3 main approaches are ex vivo isolated and perfused organ models, precision-cut liver slices and cell culture models. Although the advantage of whole organ perfusions is based on the assessment of physiologic parameters such as bile production and morphologic parameters such as tissue histology, cell culture models can be efficiently used to assess cellular metabolism, cytotoxicity and genotoxicity. The advantage of precision-cut liver slices is based on the juxtaposition of cellular assays and tissue morphology. None of these models can be compared as they all focus on different fields of hepatoxicology. For the future, the ideal setup for testing the hepatic toxicity of a new compound could of primary studies in cell or slice cultures to assess cellular effects and secondary studies using ex vivo perfused organs to examine gross organ function parameters and histology.

Prevention of proteolysis in cold-stored rat liver by addition of amino acids to the preservation solution

BACKGROUND

One process identified as detrimental in liver preservation is proteolysis.

METHODS

We tested the effects of adding antiproteolytic amino acids (L-alanine, L-glutamine, L-histidine, L-leucine, L-methionine, L-phenylalanine, L-proline, L-tryptophan) to the preservation medium, in a model of reperfusion of 24 h cold-stored rat livers.

RESULTS

During the preservation period, antiproteolytic amino acids inhibited the proteolysis observed in stored livers as shown by branched-chain amino acid fluxes, which switched from release to uptake. During reperfusion, cold storage of lives without the addition of antiproteolytic amino acids resulted in a decrease in the total amino acid and branched-chain amino acid uptake and a lower perfusion flow rate. The addition of antiproteolytic amino acids during liver storage resulted in the maintenance of total amino acid and branched-chain amino acid uptake and a significant improvement in the perfusion flow rate during reperfusion.

CONCLUSIONS

The presence of antiproteolytic amino acids in the preservation medium might be of interest in improving hepatic graft viability in transplantation.

Hepatocellular defence against acidosis is preserved after cold storage

BACKGROUND

Primary non-function of liver allografts is related to preservation time, during which hypoxia leads to intracellular accumulation of acid. Preservation-induced failure of hepatocellular pH regulation may play a role in the pathogenesis of primary graft non-function.

METHODS

Using cultured/suspended rat hepatocytes and fluorimetric determination of intracellular pH, we determined whether preservation in University of Wisconsin solution (4 degrees C) impairs hepatocellular defence mechanisms against acidosis.

RESULTS

In non-preserved, 24-h-preserved and 48-h-preserved hepatocytes acidified to pH 6.7-6.8, initial Na+/H+ antiport-mediated H+ fluxes averaged 12 +/- 5, 9 +/- 5 and 12 +/- 5 nmol microL-1 min-1 and initial Na+/HCO3- symport-mediated HCO3- fluxes 7 +/- 2, 7 +/- 3 and 6 +/- 2 nmol microL-1 min respectively (P = NS). Preservation did not affect the inverse relationship between Na+/H+ antiport activity and intracellular pH. Thus, hepatocellular defence against intracellular acidosis is maintained during up to 48 h in University of Wisconsin solution.

CONCLUSION

Altered pHi homeostasis is unlikely to play a role in the pathogenesis of primary non-function of liver allografts.

[Hepatocytes in cell therapy]

Cell-based therapy could represent an alternative treatment to orthotopic liver transplantation in acute liver failures and for the correction of genetic defects of various enzymatic functions. Several recent studies indicate that hepatocytes injected either in the spleen or in portal vein can restore liver-specific function(s) in animal model systems. Alternatively, an extracorporal hybrid bioartificial liver might provide liver-specific functions, maintain the patient alive and allow spontaneous recovery of the patient's own liver, or act as a bridge toward liver transplantation in acute liver failures. Various drawbacks of devices such as flat culture substrates, hollow-fiber bioreactors or microcarriers led us to develop a reliable extracorporeal bioartificial liver based on alginate-entrapped hepatocytes. This system was used successfully for the correction of the Gunn rat genetic defect which results in the lack of bilirubin conjugation. The development of this system for clinical purposes requires large yields of functional hepatocytes. We isolated porcine hepatocytes by collagenase perfusion of the liver and cells were immobilized within alginate beads which were subsequently inoculated in a bioreactor. Porcine hepatocytes expressed liver-functions at high levels, particularly those involved in detoxification and biotransformation processes; they were immunoisolated from immunoglobins and could be cryopreserved. This system represents a promising tool for the design of an extracorporeal bioartificial liver in human beings.

Long-term maintenance of drug-metabolizing enzyme activities in rat hepatocytes after cryopreservation

Recent studies have demonstrated that freshly isolated adult hepatocytes from various species can be hypothermically preserved for a short period or cryopreserved for a prolonged period before seeding in primary culture. This study was designed to determine whether rat hepatocytes could be maintained functional for a prolonged period after either hypothermic preservation or cryopreservation. Cold storage was carried out in University of Wisconsin solution (UW) and freezing in Leibovitz medium added with 10% fetal calf serum and 16% dimethyl sulfoxide. Rat hepatocytes were then set up either in pure conventional culture or in coculture with rat liver epithelial cells. Various functions were measured over 4- and 15-day periods, i.e., albumin secretion rate, deethylation of ethoxyresorufin and phenacetin, dealkylation of pentoxyresorufin, glucuronidation and sulfoconjugation of paracetamol, and N-acetylation of procainamide. No major differences were observed between unfrozen, frozen, and UW-preserved cells. While in pure culture all the functions tested were markedly decreased after 3 or 4 days, they remained high over the 15-day period in coculture, being either maintained or increased after 7-12 days compared to initial values. These results clearly demonstrate that when maintained under suitable culture conditions, rat hepatocytes can fully recover after hypothermic preservation or cryopreservation and therefore represent a suitable in vitro model system for pharmacotoxicological studies.

Functional recovery of porcine hepatocytes after hypothermic or cryogenic preservation for liver support systems

The provision of an immediate supply of isolated porcine hepatocytes for artificial liver support requires preservation techniques that will allow maintenance of cell viability and detoxification functions. By means of a simple and cost-effective cryopreservation system, porcine hepatocytes can be available for both local and distant medical treatment facilities. Additionally, cryopreservation provides an adequate period for quality control testing to be completed prior to use of any specific cell lot. We are reporting a dual approach, namely the preservation of porcine hepatocytes, at 4 degrees C and at -196 degrees C in liquid nitrogen (LN2). Using a combination of cryoprotectant agents with Chee's modified Eagle's culture media (CEM), collagenase isolated hepatocytes stored at 4 degrees C for 24 h maintained 80% of the initial diazepam metabolism measured in freshly isolated cells and nearly 100% of initial function was preserved in hepatocytes stored up to 6 mo at -196 degrees C. University of Wisconsin solution (UW) was also tested and while adequate for 4 degrees C storage, it certainly did not match the performance of the CEM formulations for preservation of metabolic function of cells stored in liquid nitrogen. Based on our results of viability and detoxification function the combination of CEM with DMSO, polyethylene glycol and serum provided optimal protection for LN2 frozen cells. Other findings in these studies underlined the importance of the gradual introduction of DMSO in the prefreezing process, the period of osmotic equilibration, and the rapid postthaw withdrawal of this agent to minimize cytotoxic effects at these critical stages. Our freezing methodology provides the foundation for further technological developments in the cryopreservation of the large numbers of cells (billions) that are necessary for extracorporeal liver assist devices.

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

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

Use of hepatocyte cultures for the study of hepatotoxic compounds

Human and animal hepatocytes in primary culture are widely used in pharmacotoxicological research. They represent a unique in vitro model since they retain both phase I and phase II enzyme activities as well as their inducibility by xenobiotics. Hepatocyte cultures are used for drug screening, identification of the lesions induced by toxic compounds and determination of mechanisms by which xenobiotics exert liver injury.

Cultured hepatocytes as investigational models for hepatic toxicity: practical applications in drug discovery and development

Drugs can fail at any phase during discovery, preclinical or clinical development due to unacceptable levels of toxicity, and liver is commonly the principle target organ. Investigational toxicology methods, using appropriate models and hypotheses, can often resolve problems, identify toxic chemical substituents and salvage therapeutic discovery programs. While in vivo models are used to investigate hepatic drug effects in the context of toxicokinetics and systemic influences, cell culture models provide in vitro systems for investigating specific mechanisms in a precisely controlled environment. Using primary hepatocytes isolated from laboratory animals, we have explored several drug-induced hepatic disorders that surfaced during different phases of drug discovery and development. Additionally, the use of human hepatocytes has allowed us to address concerns for human exposure, examine human relevance of animal data, and provide perspective on problems encountered in clinical trials.

In vitro evaluation of donor liver preservation fluids on human hepatocyte function

Successful liver transplantation depends on adequate preservation of cellular function. We therefore tested the effects of two currently used liver preservation fluids, Euro-Collins (EC) solution and University of Wisconsin (UW) solution, on the viability and some functional activities of hepatocytes isolated from human livers. Cells in primary culture were maintained under hypoxic (95% N2/5% CO2) and hypothermic (4 degrees C) conditions for 24 h, either in EC or UW solution. This treatment did not result in significant hepatocyte damage, as judged by phase contrast microscopy, intracellular LDH release, and the MTT mitochondrial test. However, neutral red uptake indicated that lysosomal functions were slightly affected (35% decrease) when compared to control conditions. At the end of the hypoxia/hypothermia period, hepatocyte monolayers were incubated at 37 degrees C under normoxic conditions for 24 h, in order to simulate the reperfusion of a transplanted liver. Three drugs--midazolam, diazepam, zidovudine--were used as diagnostic substrates to check the metabolic abilities of human hepatocytes replaced in normal conditions. Both phase I (hydroxylation, demethylation) and phase II (glucuronidation) metabolic reactions were affected by the hypoxia/hypothermia shock. Indeed, a 30%-50% decrease in these activities was observed as compared to values obtained in control hepatocytes. No difference could, however, be found at the cellular level regarding the solution used for cold storage. These results suggest that the superiority of UW over EC solution, already reported in clinical practice after transplantation of preserved human livers, was not due to a better preservation of the hepatocytes.

Viability, attachment efficiency, and xenobiotic metabolizing enzyme activities are well maintained in EDTA isolated rat liver parenchymal cells after hypothermic preservation for up to 3 days in University of Wisconsin solution

Rat liver parenchymal cells were isolated by EDTA perfusion and were subsequently purified by Percoll centrifugation. The freshly isolated liver cells had a mean viability of 95% as judged by trypan blue exclusion. Isolated liver parenchymal cells were then stored at 0 degrees C for up to 1 wk in University of Wisconsin solution (UW). During this hypothermic preservation, the viability was only slightly reduced to 92% after 1 d and to 85% after 3 d at 0 degrees C. Thereafter, the viability decreased rapidly. After cold storage for up to 3 d, it was possible to use the parenchymal liver cells either in short-term suspension or in cell culture. The attachment efficiency in cell culture was the same for freshly isolated liver cells (84%) and after 2 d cold preservation (81%). The cytochrome P450 content and the enzyme activities of soluble epoxide hydrolase, UDP-glucuronosyl transferase, phenol sulfotransferase, and glutathione S-transferase were not significantly different between freshly isolated cells and cells after 3 d of hypothermic preservation. Furthermore, freshly isolated and intact liver cells stored for 3 d were used in the cell-mediated Salmonella mutagenicity test as a metabolizing system. Both fresh and stored liver parenchymal cells metabolized benzo(a)pyrene,2-aminoanthracene, and cyclophosphamide to their ultimate mutagens.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 beta antagonizes phenobarbital induction of several major cytochromes P450 in adult rat hepatocytes in primary culture

We have investigated the effects of interleukin (IL)-1 beta and IL6 on expression and phenobarbital (PB) induction of ethoxyresorufin O-deethylase (EROD) and pentoxyresorufin O-deethylase (PROD) activities, as well as on mRNA levels of cytochromes P450 (CYP) 1A, 2B, 2C, 2E and 3A, in rat hepatocytes in primary culture. IL6 slightly antagonized PB-induced PROD activity. Strikingly, IL1 beta strongly inhibited basal EROD and PROD activities, and fully blocked their induction by PB in a dose-dependent fashion. Furthermore IL1 beta completely suppressed PB induction of all CYP mRNAs analyzed. Our results demonstrate that IL1 beta can suppress basal CYP activities, as well as PB-inducible expression of five CYP mRNAs in rat hepatocytes in primary culture.

Maintenance of viability and transport function after preservation of isolated rat hepatocytes in various simplified University of Wisconsin solutions

Rat hepatocytes were preserved for 24 hr with high recovery and good maintenance of viability and transport function both in University of Wisconsin (UW) solution and in various simplified UW solutions. Cell quality is somewhat affected after 48 hr of preservation in both the original UW solution and the simplified solutions. ATP content and uptake rate of taurocholic acid are more sensitive markers of cell viability than Trypan blue exclusion or the MTT test. A much less expensive solution than UW, containing only K(+)-lactobionate, KH2PO4, MgSO4 and raffinose, can be used successfully for preservation of rat hepatocytes for 24 hr for drug transport studies.

Use of human hepatocyte cultures for drug metabolism studies

Among the in vitro models developed to investigate drug metabolism isolated hepatocytes have become the most powerful model. Human hepatocytes can be prepared from whole livers and surgical wedge biopsies. When placed in culture they retain their specific drug metabolizing activities including inducible cytochrome P450 enzymes for several days. Primary human hepatocyte cultures are now increasingly used for studying drug behavior during preclinical development, e.g. drug interactions, stereoselective drug metabolism and drug metabolic profiles. As a rule there is a good in vivo/in vitro correlation in drug biotransformation activity. The main metabolites found in vivo are recovered in vitro. However, quantitative differences are frequently observed.