Assessment of Liver Function in Primary Cultures of Hepatocytes Using Diethoxy (5,6) Chloromethylfluorescein and Confocal Laser Scanning Microscopy

A method is presented which can be used to assess the function of hepatocytes in complex culture configurations without disrupting the integrity of the cell environment. It utilises a fluorescent probe for cytochrome P450 dependent mixed function oxidase (MFO) activity, diethoxy (5,6) chloromethylfluorescein, and confocal laser scanning microscopy. The MFO activity of individual cells in primary cultures of intact hepatocytes can be detected in situ, and quantified by image analysis. This may be a valuable means of monitoring the effect of culture conditions on the function of bioartificial liver devices, and could be used to assess the need for effective oxygenation of cells, the influence of shear stress and of exposure to patient serum during clinical use.

Extracorporeal Artificial Liver: The Influence of a Second Cell Layer on the Morphology and Function of Immobilized Human Hepatocytes

Hepatocytes in long-term cultures represent a promising approach to preserve liver function under standard culture conditions. Hepatocyte cultures as the key components in an extracorporeal artificial liver (EAL) in the treatment of hepatic insufficiency, would be a great advantage. However, one of the numerous unsolved problems is the limitation of the surface area of a future EAL. To decrease the dimensions of same, we modified the cell immobilization technique by placing a second layer of immobilized human hepatocytes onto a layer of pre-immobilized hepatocytes creating a “sandwich immobilization” (SI) system. Immobilization and sandwich immobilization were compared over an investigation period of 30 days: functional performance mirrored by cholinesterase (CHE) and albumin secretion showed remarkable differences only in the course of the first week, whereas we found almost no differences from day 8 on. The total DNA-values on days 0, 1, 7, 14, 21 and 30 varied strongly after the first week but were very similar up to day 30. Finally, it appears disadvantageous to enlarge number/cm2 of (human) hepatocytes in long-term cultures or for application in an EAL by means of sandwich immobilization.

Models and methods for in vitro testing of hepatic gap junctional communication

Inherent to their pivotal roles in controlling all aspects of the liver cell life cycle, hepatocellular gap junctions are frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity. Hepatic gap junctions, which are mainly built up by connexin32, are specifically targeted by tumor promoters and epigenetic carcinogens. This renders inhibition of gap junction functionality a suitable indicator for the in vitro detection of nongenotoxic hepatocarcinogenicity. The establishment of a reliable liver gap junction inhibition assay for routine in vitro testing purposes requires a cellular system in which gap junctions are expressed at an in vivo-like level as well as an appropriate technique to probe gap junction activity. Both these models and methods are discussed in the current paper, thereby focusing on connexin32-based gap junctions.

The Use of Long-term Hepatocyte Cultures for Detecting Induction of Drug Metabolising Enzymes: The Current Status

In this report, metabolically competent in vitro systems have been reviewed, in the context of drug metabolising enzyme induction. Based on the experience of the scientists involved, a thorough survey of the literature on metabolically competent long-term culture models was performed. Following this, a prevalidation proposal for the use of the collagen gel sandwich hepatocyte culture system for drug metabolising enzyme induction was designed, focusing on the induction of the cytochrome P450 enzymes as the principal enzymes of interest. The ultimate goal of this prevalidation proposal is to provide industry and academia with a metabolically competent in vitro alternative for long-term studies. In an initial phase, the prevalidation study will be limited to the investigation of induction. However, proposals for other long-term applications of these systems should be forwarded to the European Centre for the Validation of Alternative Methods for consideration. The prevalidation proposal deals with several issues, including: a) species; b) practical prevalidation methodology; c) enzyme inducers; and d) advantages of working with independent expert laboratories. Since it is preferable to include other alternative tests for drug metabolising enzyme induction, when such tests arise, it is recommended that they meet the same level of development as for the collagen gel sandwich long-term hepatocyte system. Those tests which do so should begin the prevalidation and validation process.

Modification of histone acetylation facilitates hepatic differentiation of human bone marrow mesenchymal stem cells

The multi-potentiality of mesenchymal stem cells makes them excellent options for future tissue engineering and clinical therapy, including liver injury. In this study, we investigated the effects of valproic acid (VPA), a direct inhibitor of histone deacetylase (HDAC), on the hepatic differentiation of human bone marrow mesenchymal stem cells (BMMSCs). The cells were found to differentiate into a more homogeneous hepatocyte-like population when pretreated with 5 mM VPA for 72 h. The expression of liver-specific markers was significantly upregulated in the VPA-treated group at the mRNA and protein levels. VPA treatment also significantly enhanced the hepatic functions of the differentiated cells, including glycogen storage, cytochrome P450 activity, AFP and ALB synthesis, and urea production. Further analysis showed that treatment with 5 mM of VPA for 72 h greatly improved the histones H3 and H4 acetylation. These results demonstrated that VPA could considerably improve the hepatic differentiation of human BMMSCs, probably because the chromatin-acetylated state changes upon VPA treatment through its HDAC inhibitory effect. Thus, this study provides a direct research model for producing human hepatocytes for clinical purposes.

Insulin-like growth factor 1 (IGF-I) improves hepatic differentiation of human bone marrow-derived mesenchymal stem cells

The ability of MSCs (mesenchymal stem cells) to differentiate between other cell types makes these cells an attractive therapeutic tool for cell transplantation. This project was designed to improve transdifferentiation of human MSCs into liver cells using IGF-I (insulin-like growth factor 1) which, despite its important role in liver development, has not been used for in vitro hepatic differentiation. In the present study, the MSCs derived from healthy human bone marrow samples were cultured and characterized by immunophenotyping and differentiation potential into osteoblast and adipocytes. Transdifferentiation into hepatocyte-like cells was performed in the presence/absence of IGF-I in combination with predefined hepatic differentiation cocktail. To evaluate transdifferentiation, morphological features, immuno-cytochemical staining of specific biological markers and hepatic functions were assessed. Morphological assessment and evaluation of glycogen content, albumin and AFP (α-feto protein) expression as well as albumin and urea secretion revealed statistically significant difference between experimental groups compared with the control. Morphology and function (albumin secretion) of IGF-I-treated cells were significantly better than IGF-I-free experimental group. To the best of our knowledge, our study is the first to demonstrate that the combination of IGF-I with the predefined hepatic differentiation cocktail will significantly improve the morphological features of the differentiated cells and albumin secretion.

Hepatogenic differentiation of mesenchymal stem cells induced by insulin like growth factor-I

AIM

To improve hepatic differentiation of human mesenchymal stem cell (MSC) using insulin growth factor 1 (IGF-I), which has important role in liver development, hepatocyte differentiation and function.

METHODS

Bone marrow of healthy donors was aspirated from the iliac crest. The adherent cells expanded rapidly and were maintained with periodic passages until a relatively homogeneous population was established. The identification of these cells was carried out by immunophenotype analysis and differentiation potential into osteocytes and adipocytes. To effectively induce hepatic differentiation, we designed a protocol based on a combination of IGF-I and liver specific factors (hepatocyte growth factor, oncostatin M and dexamethasone). Morphological features, hepatic functions and cytological staining were assessed to evaluate transdifferentiation of human marrow-derived MSCs.

RESULTS

Flow cytometric analysis and the differentiation potential into osteoblasts and adipocytes showed that more than 90% of human MSCs which were isolated and expanded were positive by specific markers and functional tests. Morphological assessment and evaluation of glycogen storage, albumin and α-feto protein expression, as well as albumin and urea secretion revealed a statistically significant difference between the experimental groups and control.

CONCLUSION

In vitro differentiated MSCs using IGF-I were able to display advanced liver metabolic functions, supporting the possibility of developing them as potential alternatives to primary hepatocytes.

Assessing the metabolic competence of sandwich-cultured mouse primary hepatocytes

Primary human and rat hepatocyte cultures are well established in vitro systems used in toxicological studies. However, whereas transgenic mouse models provide an opportunity for studying mechanisms of toxicity, mouse primary hepatocyte cultures are less well described. The potential usefulness of a mouse hepatocyte-based in vitro model was assessed in this study by investigating time-dependent competence for xenobiotic metabolism and gene expression profiles. Primary mouse hepatocytes, isolated using two-step collagenase perfusion, were cultured in a collagen sandwich configuration. Gene expression profiles and the activities of various cytochrome P450 (P450) enzymes were determined after 0, 42, and 90 h in culture. Principal component analysis of gene expression profiles shows that replicates per time point are similar. Gene expression levels of most phase I biotransformation enzymes decrease to approximately 69 and 57% of the original levels at 42 and 90 h, respectively, whereas enzyme activities for most of the studied P450s decrease to 59 and 34%. The decrease for phase II gene expression is only to 96 and 92% of the original levels at 42 and 90 h, respectively. Pathway analysis reveals initial effects at the level of proteins, external signaling pathways, and energy production. Later effects are observed for transcription, translation, membranes, and cell cycle-related gene sets. These results indicate that the sandwich-cultured primary mouse hepatocyte system is robust and seems to maintain its metabolic competence better than that of the rat hepatocyte system.

Perfusion culture improves the maintenance of cultured liver tissue slices

Cultured precision-cut liver tissue slices are useful for studying the metabolism and toxicity of xenobiotics in liver. They may also be used to investigate the behavior of and interaction between different cell types in an intact histo-architecture. Because cultured liver tissues undergo a loss of function and morphology because of their separation from the blood supply, we investigated changes in key protein marker expressions in parenchymal and non-parenchymal cells, as well as in the extracellular matrix (ECM) at different time points. We also compared conventional culture methods such as static and dynamic cultures with perfusion culture, which allows a continuous exchange of the culture medium. In conventional culture methods, the expression of vimentin and collagen type IV decreased after 5 h in the non-parenchymal cells and the ECM, respectively, whereas the hepatocyte nuclear factor 4 alpha (HNF4alpha) staining in the hepatocytes remained constant. In perfusion culture, on the other hand, vimentin, collagen type IV, and HNF4alpha staining were clearly detectable after 5 h. The histo-architecture obtained from perfusion culture was also more compact than those obtained from conventional culture methods. After 24 h, only the perfusion cultured sample retained protein marker expression in all components of the liver tissue. Our results suggest that, to develop improved culture techniques for liver slices, changes at the early time-points should be taken into consideration. Our results also show that culture techniques that enable a continuous exchange of the culture medium seem to be superior to static or dynamic cultures in terms of maintaining the protein expression and the histo-architecture.

Involvement of cell junctions in hepatocyte culture functionality

In liver, like in other multicellular systems, the establishment of cellular contacts is a prerequisite for normal functioning. In particular, well-defined cell junctions between hepatocytes, including adherens junctions, desmosomes, tight junctions, and gap junctions, are known to play key roles in the performance of liver-specific functionality. In a first part of this review article, we summarize the current knowledge concerning cell junctions and their roles in hepatic (patho)physiology. In a second part, we discuss their relevance in liver-based in vitro modeling, thereby highlighting the use of primary hepatocyte cultures as suitable in vitro models for preclinical pharmaco-toxicological testing. We further describe the actual strategies to regain and maintain cell junctions in these in vitro systems over the long-term.

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.

Sequential exposure to cytokines reflecting embryogenesis: the key for in vitro differentiation of adult bone marrow stem cells into functional hepatocyte-like cells

Differentiation of adult bone marrow stem cells (BMSC) into hepatocyte-like cells is commonly performed by continuous exposure to a cytokines-cocktail. Here, it is shown that the differentiation efficacy in vitro can be considerably enhanced by sequential addition of liver-specific factors (fibroblast growth factor-4, hepatocyte growth factor, insulin-transferrin-sodium selenite, and dexamethasone) in a time-dependent order that closely resembles the secretion pattern during in vivo liver embryogenesis. Quantitative RT-PCR analysis and immunocytochemistry showed that, upon sequential exposure to liver-specific factors, different stages of hepatocyte differentiation, as seen during liver embryogenesis, can be mimicked. Indeed, expression of the early hepatocyte markers alpha-fetoprotein and hepatocyte nuclear factor (HNF)3beta decreased as differentiation progressed, whereas levels of the late liver-specific markers albumin (ALB), cytokeratin (CK)18, and HNF1alpha were gradually upregulated. In contrast, cocktail treatment did not significantly alter the expression pattern of the hepatic markers. Moreover, sequentially exposed cells featured highly differentiated hepatic functions, including ALB secretion, glycogen storage, urea production, and inducible cytochrome P450-dependent activity, far more efficiently compared to the cocktail condition. In conclusion, sequential induction of the differentiation process, analogous to in vivo liver development, is crucial for in vitro differentiation of adult rat BMSC into functional hepatocyte-like cells. This model may not only be applicable for in vitro studies of endoderm differentiation but it also provides a "virtually unlimited" source of functional hepatocytes, suitable for preclinical pharmacological research and testing, and cell and organ development.

Perfusion of medium with supplemented growth factors changes metabolic activities and cell morphology of hepatocyte-nonparenchymal cell coculture

To develop a feasible perfusion-type bioartificial liver device, perfusion of hepatocyte-nonparenchymal cell (NPC) cocultures with medium supplemented with hepatocyte growth factor (HGF) and heparin-binding epidermal growth factor-like growth factor (HB-EGF) was carried out. On day 1 of culture, perfusion at a constant shear stress of 1.3 dyn/cm2 enhanced ammonia metabolic and urea synthetic activities of hepatocytes. These enhanced activities were sustained up to day 7 only when growth factors were present. In contrast, no beneficial effects of growth factors on these activities were observed in static cultures. In perfusion cultures, three-dimensional cell aggregates were formed. On the surface of these aggregates, flattened cell layers composed mainly of NPCs were found, and the central cluster of cell aggregates was composed of round-shaped hepatocytes and reticulin fibrils. These observations strongly suggested that the reconstruction of different types of liver cells and connective tissues formed tissue-mimicking cell aggregates in the perfusion culture that was able to modulate the liver-specific functions of hepatocytes. Thus, perfusion culture conditions of the hepatocyte--NPC coculture system should be appropriately designed to induce suitable reconstruction of the cultured cells for use as a bioartificial liver device.

Advances in bioartificial liver assist devices

Rapid advances in development of bioartificial liver assist devices (BLADs) are exciting clinical interest in the application of BLAD technology for support of patients with acute liver failure. Four devices (Circe Biomedical HepatAssist, Vitagen ELAD, Gerlach BELS, and Excorp Medical BLSS) that rely on hepatocytes cultured in hollow-fiber membrane technology are currently in various stages of clinical evaluation. Several alternative approaches for culture and perfusion of hepatocytes have been evaluated in preclinical, large animal models of liver failure, or at a laboratory scale. Engineering design issues with respect to xenotransplantation, BLAD perfusion, hepatocyte functionality and culture maintenance, and ultimate distribution of a BLAD to a clinical site are delineated.

Adsorption of xenobiotics to plastic tubing incorporated into dynamic in vitro systems used in pharmacological research--limits and progress

Commonly used materials incorporated into dynamic culture systems typically show the feature of adsorption of lipophilic xenobiotics. Yet, this phenomenon is strongly limiting the use of dynamic culture models and ex vivo organ perfusions in pharmacological and toxicological research. The aim of the study was to characterize different materials with respect to their capacity for drug adsorption and to find methods or materials to reduce the loss of substrate by adsorption in order to improve the use of dynamic in vitro systems. The adsorption of different xenobiotics (lidocaine, midazolam, lormetazepam, phenobarbital, testosterone, ethoxyresoroufine) to tubes used in dynamic in vitro systems (polyvinyl-chloride, silicone) were investigated and compared to a new material (silicone-caoutchouc-mixture). In addition, the role of protein deposition onto the tubing was studied and it was investigated whether it was possible to reach saturation of the inner tube surface by pre-loading it with the test compound. We found that silicone tubes provided the highest comfort with respect to handling and reusability, but they also demonstrated the highest capacity for substrate adsorption. Polyvinyl-chloride was the second best in handling but also demonstrated a high complexity in its adsorption behavior. The silicone-caoutchouc-mixture reached acceptable experimental results with respect to its handling and demonstrated a very low capacity for substrate adsorption.

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

BACKGROUND/AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

A novel configuration of bioartificial liver support system based on circulating microcarrier culture

The purpose of this investigation is to initiate a new bioartificial liver support system that utilizes circulating microcarrier cultures in the extracapillary space of a hollow fiber cartridge. The material exchange occurs on the membranes of the hollow fiber. Toxins are metabolized by the circulating cells on the microcarriers driven by a centrifugal pump. We inoculated 2-3 x 10E8 Hep G2 cells on 2.5 grams of Cytodex 3 microcarriers, and allowed them flowing in the extracapillary space of a modified plasma filter. 10% FCS Medium was pumped through the capillaries at different rates. Cells keep morphological integrity and functionality during the circulation. These preliminary results suggest that this configuration of a bioartificial liver support system offers a future investigation.

Bioreactors for hybrid liver support: historical aspects and novel designs

A novel bioreactor construction has been designed for the utilization of hepatocytes and sinusoidal endothelial cells. The reactor is based on capillaries for hepatocyte aggregate immobilization. Three separate capillary membrane systems, each permitting a different function are woven in order to create a three dimensional network. Cells are perfused via independent capillary membrane compartments. Decentralized oxygen supply and carbon dioxide removal with low gradients are possible. The use of identical parallel units to supply hepatocytes facilitates scale up. In vitro studies demonstrate long-term external metabolic function in primary isolated hepatocytes within bioreactors. These systems are capable of supporting essential liver functions. Animal experiments have verified the possibility of scaling-up the bioreactors for clinical treatment. However, since there is no reliable animal model for investigation of the treatment of acute liver failure, the promising results obtained from these studies have limited relevance. The small number of clinical studies performed so far is not sufficient to reach conclusions about improvements in the therapy of acute liver failure. Although important progress has been made in the development of these systems, various hepatocyte culture models and bioreactor constructions are being discussed in the literature, which indicates competition in this field of medical research. An overview, which emphasizes the development of hepatocyte culture models for bioreactors, subsequent in vitro studies, animal studies, and clinical application, is also provided.

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

BACKGROUND/AIMS

The development of custom-made bioreactors for use as a bioartificial liver (BAL) is considered to be one of the last challenges on the road to successful temporary extracorporeal liver support therapy. We devised a novel bioreactor (patent pending) which allows individual perfusion of high density cultured hepatocytes with low diffusional gradients, thereby more closely resembling the conditions in the intact liver lobuli.

METHODS

The bioreactor consists of a spirally wound nonwoven polyester matrix, i.e. a sheet-shaped, three-dimensional framework for hepatocyte immobilization and aggregation, and of integrated hydrophobic hollow-fiber membranes for decentralized oxygen supply and CO2 removal. Medium (plasma in vivo) was perfused through the extrafiber space and therefore in direct hepatocyte contact. Various parameters were assessed over a period of 4 days including galactose elimination, urea synthesis, lidocaine elimination, lactate/pyruvate ratios, amino acid metabolism, pH, the last day being reserved exclusively for determination of protein secretion.

RESULTS

Microscopic examination of the hepatocytes revealed cytoarchitectural characteristics as found in vivo. The biochemical performance of the bioreactor remained stable over the investigated period. The urea synthesizing capacity of hepatocytes in the bioreactor was twice that of hepatocytes in monolayer cultures. Flow sensitive magnetic resonance imaging (MRI) revealed that the bioreactor construction ensured medium flow through all parts of the device irrespective of its size.

CONCLUSIONS

The novel bioreactor showed encouraging efficiency. The device is easy to manufacture with scale-up to the liver mass required for possible short-term support of patients in hepatic failure.