Synthesis and secretion of protein by hepatocytes entrapped within calcium alginate

[Transition of the Field from Biochemical Engineering to Pharmaceutical Sciences during 40 Years of the Research]

This review reflects back over almost 40 years of the author's basic research conducted at Graduate School of Pharmaceutical Sciences, Osaka University, Japan. After performing postdoctoral research in USA, the author became a research associate at Prof. Yoshiharu Miura's lab and started research on Biochemical Engineering in 1984. At that time, the main research purpose was to solve global environmental issues for maintaining human health. The author's achievements included novel useful material production system under inorganic conditions and genetically engineered whole-cell bacterial sensors detecting arsenite by naked eye without a detecting device. Another theme in the lab was to construct bioartificial liver support system. Various scaffolds for hepatocytes were newly prepared for constructing the compact reactor. Besides the bioreactor study, the author conducted cell transplantation research for the treatment of chronic liver diseases. It was shown that mesenchymal stem cells derived from third molars (wisdom teeth) could differentiate into hepatocytes and exhibit therapeutic effects in liver-damaged animals. After 2006, the lab started research on drug delivery systems, including noninvasive delivery of drugs such as peptides and nucleic acids by regulating epithelial tight junctions. Many substances enabling drug delivery through "paracellular" route were newly prepared. The author started basic research on Biochemical Engineering in the 1970s. Although these studies eventually shifted into the pharmaceutical field, the underlying concept was based on "engineering" throughout a 40-year research period. The author cordially thanks all colleagues for supporting engineering research in our lab.

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.

Sodium Alginate as a Scaffold Material for Hepatic Tissue Engineering

Sodium alginate, which has excellent biocompatibility, was evaluated as a scaffold material for hepatic tissue engineering. It is found that hepatocyte cells attached and proliferated well on films made from sodium alginate. Furthermore, the attached hepatocytes had normal functions, such as synthesizing albumin which was detected by immunohistochemical staining for albumin.

Collagen/Chitosan/Heparin Complex with Improved Biocompatibility for Hepatic Tissue Engineering

To make an implantable bioartificial liver (IBL), a new biocompatible collagen/chitosan/heparin complex was prepared using a crosslinking agent. The X-ray photoelectron spectroscopy (XPS), mechanical strength and biocompatibility with whole blood and hepatocytes were measured. The collagen/chitosan/heparin complex resulted in a superior blood compatibility compared to 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) crosslinked collagen matrix. The morphology and behavior of the cells on the collagen/chitosan/heparin membrane were found to be different from those on the collagen and collagen/chitosan membranes. Cells on the collagen membrane formed smaller three-dimensional aggregates than those on the collagen/chitosan membrane, while on the collagen/chitosan/heparin membrane, a round shape with no junctions were manifested. No adverse effects were found on the viability and function of the hepatocytes on the collagen/chitosan/heparin membrane compared to the collagen and collagen/chitosan membranes. These results suggest that this collagen/chitosan/heparin matrix is a potential candidate for hepatic tissue engineering.

Microgravity as a means to incorporate HepG2 aggregates in polysaccharide-protein hybrid scaffold

Tissue culture under microgravity provides a venue which promotes cell-cell association while avoiding the detrimental effects of high shear stress. Hepatocytes cultured on carriers or entrapped within matrices under simulated microgravity conditions showed improved cell function and proliferation. In the present study, a new approach was adopted where a non-cell adherent scaffold was incorporated with hepatospheroids (HepG2) under microgravity. Gum arabic (GA) was cross-linked with gelatin (GA-Gel) and collagen (GA-Col) to prepare non-cell adherent scaffolds. Microgravity experiments with GA-Gel and GA-Col indicated that GA-Col is a better substrate compared to GA-Gel. Microgravity experiments of GA-Col scaffolds with HepG2 cells confirmed that the non-adherent surface with porous architecture can incorporate hepatocyte spheroids and maintain liver specific functions. Albumin and urea synthesis of hepatocytes was sustained up to 6 days under microgravity conditions in the presence of GA-Col scaffold. This new approach of using non-cell adherent matrix and microgravity environment for developing biological substitutes will be beneficial in tissue engineering, bioartificial liver devices and in vitro safety assessment of drugs.

A non-adhesive hybrid scaffold from gelatin and gum Arabic as packed bed matrix for hepatocyte perfusion culture

Development of liver support systems has become one of the most investigated areas for the last 50 years because of the shortage of donor organs for orthotopic liver transplantations. Bioartificial liver (BAL) device is one of the alternatives for liver failure which provides a curing method and support patients to recover from certain liver failure diseases. The biological compartment of BAL is called the bioreactor where functionally active hepatocytes are maintained to support the liver specific functions. We have developed a packed bed bioreactor with a cytocompatible, polysaccharide-protein hybrid scaffold. The scaffold prepared from gelatin and gum Arabic acts as a packed bed matrix for hepatocyte culture. Quantitative evaluation of the hepatocytes cultured using packed bed bioreactor demonstrated that cells maintained liver specific functions like albumin and urea synthesis for seven days. These results indicated that the system can be scaled up to form the biological component of a bioartificial liver.

Reduced liver cell death using an alginate scaffold bandage: a novel approach for liver reconstruction after extended partial hepatectomy

Extended partial hepatectomy may be needed in cases of large hepatic mass, and can lead to fulminant hepatic failure. Macroporous alginate scaffold is a biocompatible matrix which promotes the growth, differentiation and long-term hepatocellular function of primary hepatocytes in vitro. Our aim was to explore the ability of implanted macroporous alginate scaffolds to protect liver remnants from acute hepatic failure after extended partial hepatectomy. An 87% partial hepatectomy (PH) was performed on C57BL/6 mice to compare non-treated mice to mice in which alginate or collagen scaffolds were implanted after PH. Mice were scarified 3, 6, 24 and 48 h and 6 days following scaffold implantation and the extent of liver injury and repair was examined. Alginate scaffolds significantly increased animal survival to 60% vs. 10% in non-treated and collagen-treated mice (log rank=0.001). Mice with implanted alginate scaffolds manifested normal and prolonged aspartate aminotransferases and alanine aminotransferases serum levels as compared with the 2- to 20-fold increase in control groups (P<0.0001) accompanied with improved liver histology. Sustained normal serum albumin levels were observed in alginate-scaffold-treated mice 48 h after hepatectomy. Incorporation of BrdU-positive cells was 30% higher in the alginate-scaffold-treated group, compared with non-treated mice. Serum IL-6 levels were significantly decreased 3h post PH. Biotin-alginate scaffolds were quickly well integrated within the liver tissue. Collectively, implanted alginate scaffolds support liver remnants after extended partial hepatectomy, thus eliminating liver injury and leading to enhanced animal survival after extended partial hepatectomy.

Isolated hepatocytes in a bioartificial liver: A single group view and experience

Despite recent advances in medical supportive therapy, patients with severe fulminant hepatic failure (FHF) have mortality rate approaching 90%. Investigators have attempted to improve survival by using various extracorporeal liver support systems loaded with sorbents and liver tissue preparations. None of them succeeded in gaining clinical acceptance and orthotopic liver transplantation (OLT) remains a primary therapeutic option for patients with FHF. In this study, authors discuss the systems which utilize isolated hepatocytes. Most of these devices were tested in vitro and in animals with chemically and surgically induced liver failure. In some studies, signficant levels of detoxification and liver functions were achieved. The authors describe their own hepatocyte-based artificial liver (BAL). It is based on plasma perfusion through a hollow-fiber module seeded with matrix-anchored porcine hepatocytes. The BAL was used 14 times to treat 9 patients with acute liver failure. On 10 occasions, a charcoal column was included in the plasma circuit. Each treatment lasted 7 +/- 1 h. All procedures were tolerated well and 8 patients (including 6 patients with FHF) underwent OLT. Five patients with increased intracranial pressure (ICP) and evidence of decerebration had normalization of ICP and enjoyed full neurologic recovery after OLT. Laboratory data showed evidence for bilirubin conjugation, decrease in blood ammonia, maintenance of low lactic acid levels, and increase in the ration between the branched chain and aromatic amino acids. No allergic reactions to xenogeneic hepatocytes were observed. The authors conclude that BAL treatment with porcine hepatocytes appears to be safe and can help maintain patients alive and neurologically intact until a liver becomes available for transplantation. (c) 1994 John Wiley & Sons, Inc.

Energy metabolism and re-establishment of intercellularadhesion complexes of gel entrapped hepatocytes

We studied the effect of continuous medium flow on the viabilityand structural organization of hepatocytes high density entrapped inalginate gel beads in the first few hours after isolation.The metabolic energy status of the entrapped cells, monitored invivo by (31)P NMR spectroscopy, was stable during theexperimental time and a physiological redox ratio was reachedafter the first three hours of culture. The morphologicalanalysis revealed that the entrapped hepatocytes placed in a fixed-bed bioreactor under continuous flow showed a polyhedricalshape with numerous microvilli on cell surface and reconstitutedtight junctions as well as bile canalicular structures, closelyresembling those present in the liver.These results suggest that continuous flow allows the culture ofhepatocytes at very high cell density within a matrix withoutloss of viability and accelerates cellular tissue reconstructionat very short times after isolation. This type of culture couldrepresent a very useful model for physiological andtoxicological studies as well as a promising approach toward thedevelopment of a bioartificial hybrid support device in acuteliver failure.

Cytotoxicity evaluation of reactive metabolites using rat liver homogenate microsome-encapsulated alginate gel microbeads

We present an improved cytotoxicity test for reactive metabolites, in which the S9 microsomal fraction of rat liver homogenate is encapsulated in alginate gel microbeads to avoid cytotoxic effects of S9-self-generated toxicants, microsomal lipid peroxides. The S9-encapsulated gel microbeads were prepared by a coaxial two-fluid nozzle and surfaces of the microbeads were coated with poly-L-lysine (PLL). Although the initial metabolic rate of the S9-encapsulated gel microbeads was about 20% slower than that of bare S9, the microbeads prevented the leakage of microsomal lipid peroxides thanks to the dense alginate and PLL polymer networks. In fact, the half maximal effective concentration of the indirect mutagen cyclophosphamide on NIH3T3 cells in the presence of the S9-encapsulated gel microbeads was about 5 times higher than that in the presence of bare S9. Use of the S9-encapsulated gel microbeads enabled the more accurate evaluation of the cytotoxicity of the reactive metabolites without the S9-based cytotoxicity.

In vitro large-scale cultivation and evaluation of microencapsulated immortalized human hepatocytes (HepLL) in roller bottles

BACKGROUND/AIMS

Microencapsulated hepatocytes have been proposed as promising bioactive agents for packed-bed or fluidized-bed bioartificial liver assist devices (BLaDs) and for hepatocyte transplantation because of the potential advantages they offer of high mass transport rate and an optimal microenvironment for hepatocyte culture. We developed a large-scale and high-production alginate-chitosan (AC) microcapsule roller bottle culture system for the encapsulation of hepLL immortalized human hepatocytes. In this study, the efficacy of upscaling encapsulated hepLL cells production with roller bottle cultivation was evaluated in vitro.

METHODS

Microencapsulated hepLL cells were grown at high yield in large-scale roller bottles, with free cells cultured in roller bottle spinners serving as controls. The mechanical stability and the permeability of the AC microcapsules were investigated, and the growth, metabolism and functions of the encapsulated hepLL cells were evaluated as compared to free cells.

RESULTS

The microcapsules withstood well the shear stress induced by high agitation rates. The microcapsules were permeable to albumin, but prevented the release of immunoglobulins. Culture in roller bottles of immortalized human hepatocytes immobilized in the AC microcapsules improved cell growth, albumin synthesis, ammonia elimination and lidocaine clearance as compared with free cells cultured in roller bottles.

CONCLUSIONS

Encapsulated hepLL cells may be cultured on a large scale in roller bottles. This makes them possible candidates for use in cell-based liver assist therapies.

Preparation of calcium alginate microgel beads in an electrodispersion reactor using an internal source of calcium carbonate nanoparticles

An electrodispersion reactor has been used to prepare calcium alginate (Ca-alginate) microgel beads in this study. In the electrodispersion reactor, pulsed electric fields are utilized to atomize aqueous mixtures of sodium alginate and CaCO3 nanoparticles (dispersed phase) from a nozzle into an immiscible, insulating second liquid (continuous phase) containing a soluble organic acid. This technique combines the features of the electrohydrodynamic force driven emulsion processes and externally triggered gelations in microreactors (the droplets) ultimately to yield soft gel beads. The average particle size of the Ca-alginate gels generated by this method changed from 412 +/- 90 to 10 +/- 3 microm as the applied peak voltage was increased. A diagram depicting structural information for the Ca-alginate was constructed as a function of the concentrations of sodium alginate and CaCO3 nanoparticles. From this diagram, a critical concentration of sodium alginate required for sol-gel transformation was observed. The characteristic highly porous structure of Ca-alginate particles made by this technique appears suitable for microencapsulation applications. Finally, time scale analysis was performed for the electrodispersion processes that include reactions in the microreactor droplets to provide guidelines for the future employment of this technique. This electrodispersion reactor can be used potentially in the formation of many reaction-based microencapsulation systems.

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.

Hepatocyte hollow-fibre bioreactors: design, set-up, validation and applications

Hepatocytes carry out many vital biological functions, such as synthetic and catabolic reactions, detoxification and excretion. Due to their ability to restore a tissue-like environment, hollow-fibre bioreactors (HFBs) show great potential among the different systems used to culture hepatocytes. Several designs of HFBs have been proposed in which hepatocytes or hepatocyte-derived cell lines can be cultured in suspensions or on a solid support. Currently the major use of hepatocyte HFBs is as bioartificial livers to sustain patients suffering from acute liver failure, but they can also be used to synthesize cell products and as cellular models for drug metabolism and transport studies. Here, we present an overview of the set-up of hepatocyte HFBs and aim to provide potential users with the basic knowledge necessary to develop their own system. First, general information on HFBs is given, including basic principles, transport phenomena, designs and cell culture conditions. The importance of the tests necessary to assess the performance of the HFBs, i.e. the viability and functionality of hepatocytes, is underlined. Special attention is paid to drug metabolism studies and to adequate analytical methods. Finally, the potential uses of hepatocyte HFBs are described.

Superior Cell Delivery Features of Poly(ethylene glycol) Incorporated Alginate, Chitosan, and Poly-l-lysine Microcapsules

Microencapsulation is an emerging technology in the development of bioartificial organs for drug, protein, and delivery systems. One of the advancements in establishing an appropriate membrane material for live cell and tissue encapsulation is the incorporation of poly(ethylene glycol) (PEG) to the widely studied alginate microcapsules. The current study investigates the properties of integrating PEG to microcapsules coated with poly-L-lysine (PLL) and chitosan as well as a novel microcapsule membrane which combines both PLL and chitosan. Results show that microcapsules containing PEG can support cell viability and protein secretion. The addition of PEG to PLL and chitosan-coated microcapsules improves the stability of microcapsules when exposed to a hypotonic solution. We also compared the novel microcapsule with two other previously used microcapsules including alginate-chitosan-PEG and alginate-PLL-PEG-alginate. Results show that all three membranes are capable of providing immunoprotection to the cells and have the potential for long-term storage at -80 degrees C. The novel membrane containing PEG, chitosan, and PLL, however, revealed the highest cell viability and mechanical strength when exposed to external rotational force, but it was unable to sustain osmotic pressure. The study revealed the potential of using PEG-incorporated alginate, chitosan, and PLL microcapsules for encapsulating live cells producing proteins and hormones for therapy.

Engineering liver therapies for the future

Treatment of liver disease has been greatly improved by the advent and evolution of liver transplantation. However, as demand for donor organs continues to increase beyond their availability, the need for alternative liver therapies is clear. Several approaches including extracorporeal devices, cell transplantation, and tissue-engineered constructs have been proposed as potential adjuncts or even replacements for transplantation. Simultaneously, experience from the liver biology community have provided valuable insight into tissue morphogenesis and in vitro stabilization of the hepatocyte phenotype. The next generation of cellular therapies must therefore consider incorporating cell sources and cellular microenvironments that provide both a large population of cells and strategies to maintain liver-specific functions over extended time frames. As cell-based therapies evolve, their success will require contribution from many diverse disciplines including regenerative medicine, developmental biology, and transplant medicine.

Alginate-encapsulated producer cells: a potential new approach for the treatment of malignant brain tumors

In recent years gene therapy has evolved as a new treatment for brain tumors, where genetically engineered cells can be used to deliver specific substances to target cells. However, clinical success has been limited due to insufficient gene transfer, lack of prolonged gene expression, and immunorejection of producer cells. These obstacles may be overcome by encapsulating producer cells into immunoisolating substances such as alginate. This may provide a stable in situ delivery system of specific proteins, which can interfere with tumor growth and differentiation. This article represents a fundamental study describing the in vitro and the in vivo behavior of alginate-encapsulated producer cells. The viability and cell cycle distribution of encapsulated NIH 3T3 cells was studied by confocal laser scanning microscopy (CLSM) and by flow cytometry. The CLSM study showed a high viability of the encapsulated NIH 3T3 cells during 9 weeks in culture. The flow cytometric analysis revealed a change in cellular ploidy after 1 week in culture, with normalization in ploidy after 3 and 9 weeks. The production of the bacterial E. coli beta-galactosidase in alginate-encapsulated BT4CnVlacZ cells was studied by x-gal staining, and the cells expressed prolonged beta-galactosidase activity. H528 hybridoma cells producing monoclonal antibodies (mAbs) against the human epidermal growth factor receptor (EGFR) were encapsulated in alginate, and the mAb release was determined. The release of mAbs stabilized around 400 ng/ml/h after 12 days in vitro. To actually demonstrate that alginate-encapsulated H528 cells potentially inhibit a heterogeneous glioma cell population, cell migration from human GaMg glioma spheroids was studied during stimulation with EGF in the presence of encapsulated H528 cells. The migration in vitro was totally inhibited in the presence of H528 encapsulated cells. Alginate beads with H528 cells were also implanted into rat brains, and after 9 weeks the distribution of mAbs within the brain was studied by immunohistochemistry. It is shown that the alginate entrapped H528 cells produce mAbs inside the brain for prolonged periods and that the mAbs are distributed within all CSF compartments. Encapsulated producer cells represent a potential delivery system for specific proteins to brain tumors. Different producer cells may be encapsulated in alginate to target phenotypic features and microenvironmental factors, which may influence the progressive growth of brain tumors.

Cells encapsulated in alginate: a potential system for delivery of recombinant proteins to malignant brain tumours

Growth and progression of malignant brain tumours occurs in a micromilieu consisting of both tumour and normal cells. Several proteins have been identified with the potential of interfering directly with tumour cells or with the neovascularisation process, thereby inhibiting tumour growth. A continuous delivery of such inhibitory proteins to the tumour microenvironment by genetically engineered cells could theoretically be of considerable therapeutic importance. In this study we have investigated the growth characteristics of cells encapsulated in alginate, which represents a potential delivery system for recombinant proteins that may have antitumour effects. Three different cell lines, NHI 3T3, 293 and BT4C were encapsulated in alginate, which is an immuno-isolating substance extracted from brown seaweed. The encapsulated cells were observed at specific intervals during a 4-month period after in vitro propagation and as transplants into the cortex of BD-IX rats. Morphological studies showed that encapsulated cells proliferated and formed spheroids within the alginate in the in vitro cultures and after implantation into the brain. Even after 4 months in vivo a substantial amount of living cells were observed within the alginate beads. A vigorous infiltration of mononuclear cells was observed in the brain bordering the alginate beads, one week after implantation. However, there was a gradual decrease of mononuclear cells at the border zone beyond the first week of implantation. The majority of inflammatory cells were reactive microglia and invading monocytes, as verified by immunohistochemistry. The data further shows that alginate encapsulated cells can be frozen in liquid N2 and will retain their viability and proliferative capacity.

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.

Transplantation of microencapsulated hepatocytes for liver function replacement

Recent advances in cell biology and biotechnology have lead the way for a greater understanding of cell function and the potential therapeutic use of transplanted cells for treating a wide array of illnesses. Treatment of disease by transplantation of normal healthy cells, for the replacement of specific biological deficiencies or as a form of auxiliary support for a failing organ, offers important therapeutic applications and also serves as a model for assessing cellular physiology. In the long-term, cell transplantation may also have potential in the development of artificial organ support systems for sustaining patients with severe and chronic diseases such as diabetes, liver failure, endocrine and exocrine disorders, neurological abnormalities, and congenital metabolic defects. Several groups have demonstrated the feasibility and efficacy of cell transplantation in providing specific function in various experimental animal models of human disease. However, without adequate immunosuppression, complications due to tissue rejection remain a significant problem. Microencapsulation of cells within a synthetic semipermeable membrane, prior to transplantation, has been proposed for circumventing immunological complications following transplantation. The microcapsule's semipermeable membrane allows permeant molecules to freely diffuse across while preventing the microencapsulated cells from escaping. This membrane also keeps unwanted substances, such as cells and antibodies, from entering the microcapsule. Thus, microencapsulation provides an innovative and unique technique for the transplantation of foreign tissue and cells without the need for immunosuppression.

Artificial liver support: state of the art

Severe liver disease is very often life-threatening and dramatically diminishes quality of life. Liver support systems based on detoxification alone have proven ineffective because they cannot correct biochemical disorders. An effective artificial liver support system should be capable of carrying out the liver's essential processes such as synthetic and metabolic functions, detoxification, and excretion. It should be capable of sustaining patients with fulminant hepatic failure, preparing patients for liver transplantation when a donor liver is not readily available (i.e., bridge to transplantation), and improving the survival and quality of life for patients for whom transplantation is not a therapeutic option. Recent advances in cell biology, tissue culture techniques, and biotechnology have led the way for the potential use of isolated hepatocytes in treating an array of liver disorders. Isolated hepatocytes may be transplanted to replace liver-specific deficiencies or as an important element of an auxiliary hybrid, bioartificial extracorporeal liver support device, which are important therapeutic applications for treating severe liver disease. Although several hepatocyte-based liver support systems have been proposed, there is no current consensus on its eventual design configuration. Furthermore, application of tissue engineering technology, based on cell-surface interaction studies proposed by our group and others, has enhanced interest in the development of highly efficient hybrid, bioartificial, liver support devices.

Transplantation of isolated hepatocytes and their role in extrahepatic life support systems

Transplantation of isolated hepatocytes for the replacement of liver function and the use of isolated hepatocytes as a bridge-to-transplantation in extrahepatic bioartificial liver support devices offer important therapeutic advances for treating severe liver disease. Progress in cell biology, tissue culture techniques and biotechnology have led the way for the potential therapeutic use of isolated hepatocytes in a wide array of liver disorders. Transplanted hepatocytes show considerable promise of performing the full range of liver functions in several animal models of liver disease, ranging from fulminant hepatic failure to congenital metabolic liver disease. Recently, several interesting designs for extrahepatic liver support systems have been proposed. Although there is no current consensus on its eventual design configuration, the hollow fiber hepatocyte bioreactor design has the greatest potential for therapeutic benefit.

Assessment of artificial liver support technology

Despite more than 30 yr of research and development, an artificial liver has still not yet become clinical reality. Although previous attempts using a multiplicity of techniques including hemodialysis, hemoperfusion, plasma exchange, extracorporeal perfusion, and crosshemodialysis have shown minor improvement in patients with acute hepatic failure, limited clinical trials have failed to demonstrate any survival benefit. Encouraged by the progress on techniques that maintain long-term cultures of hepatocytes, more recent efforts have been directed at the use of hepatocytes as the basis of liver support. This review takes a critical look at past and present concepts in the development of artificial liver supports and both qualitatively and quantitatively evaluates the advantages and disadvantages of the available methodology.

Development of a bioartificial liver using isolated hepatocytes

Severe liver disease is very often life-threatening and dramatically diminishes quality of life. Liver support systems based on detoxification alone have been proved ineffective because they cannot correct biochemical disorders. An effective artificial liver support system should be capable of carrying out the liver's essential processes, such as synthetic and metabolic functions, detoxification, and excretion. It should be capable of sustaining patients with fulminant hepatic failure, preparing patients for liver transplantation when a donor liver is not readily available (i.e., bridge to transplantation), and improving the survival and quality of life for patients for whom transplantation is not a therapeutic option. Recent advances in cell biology, tissue culture techniques, and biotechnology have led the way for the potential use of isolated hepatocytes in treating an array of liver disorders. Isolated hepatocytes may be transplanted to replace liver-specific deficiencies or as an important element of an auxiliary hybrid, bioartificial extracorporeal liver support device, which are important therapeutic applications for treating severe liver disease. Recently, several hepatocyte-based liver support systems have been proposed. Although there is no current consensus on its eventual design configuration, the hollow fiber hepatocyte bioreactor shows the greatest promise. Furthermore, application of tissue engineering technology, based on cell-surface interaction studies proposed by our group and others, has enhanced interest in the development of highly efficient hybrid, bioartificial, liver support devices.

Rapid formation of multicellular spheroids of adult rat hepatocytes by rotation culture and their immobilization within calcium alginate

Tyrosine aminotransferase (TAT) induction and albumin secretion abilities were examined in rat hepatocytes immobilized within calcium alginate; the immobilized hepatocytes lost these abilities within a week. An attempt was then made to immobilize multicellular spheroids of hepatocytes for the purpose of stabilizing the liver functions. Although it takes at least 4 days to form spheroids in the conventional method using monolayer-cultured cells, in this study we developed a new method for rapid spheroid formation. Isolated hepatocytes were seeded into a polystyrene dish and incubated on a rotary shaker. Hepatocytes started to aggregate after 6 h of the rotation culture, and spheroids approximately 100 microns in diameter formed within 24 h. The immobilized spheroids had higher TAT induction and albumin secretion abilities, which were maintained for a longer time, than the immobilized nonaggregated cells. Further stabilization was observed in immobilized heterospheroids formed in the presence of nonparenchymal liver cells. This method for the rapid formation of spheroids consisting of hepatocytes and nonparenchymal liver cells could be utilized in the construction of a bioartificial liver support system.

Prolonged biochemical and morphological stability of encapsulated liver cells--a new method

In this work a new type of polyelectrolyte complex capsules is introduced as an artificial housing for liver cells. Male Wistar rat hepatocytes were encapsulated using cellulose sulphate and polydimethyldialyllammonium chloride as polyelectrolytes. Amino acid metabolism rate and urea synthesis of the cells increased over the investigation period in contrast to the decrease observed in control monolayer cultures. The encapsulated cells were morphologically characterized. The described procedure represents a sufficient method for the cultivation of living cells in mechanically stable semipermeable microcapsules.

Cloning hybridomas in a reversible three-dimensional alginate matrix

Alginate is a transparent polymer of guluronic and mannuronic acids that provide a favorable microenvironment for cell growth. Alginate gelation is calcium dependent and temperature independent. To facilitate the isolation of stable and productive antibody-producing hybridomas, we have developed a technique of cloning hybridomas in the three-dimensional alginate matrix. To provide cavities for hybridoma growth, we encorporated 10-15% (v/v) gelatin into the alginate prior to gelation. We have cloned more than 90 monoclonal antibody-producing hybridomas using the alginate matrix. The alginate matrix is readily reversible with the addition of a calcium chelator. The alginate matrix permits efficient cloning in limited incubator space, without the use of a feeder layer, and with minimal amount of medium. The transparent matrix also permits easy screening for clonality and growth.

Primary culture of rat hepatocytes entrapped in cylindrical collagen gels: An in vitro system with application to the bioartificial liver

A static culture model employing cylindrical collagen-hepatocyte gels is reported for large scale testing of conditions relevant to the three compartment hollow fiber bioartificial liver. High density hepatocyte cultivation was achieved by cell entrapment within the collagen-hepatocyte gel. Hepatocyte viability was assessed by vital staining, gel contraction, and insulin utilization. Measures of hepatocyte-specific function included albumin synthesis, ureagenesis, lidocaine biotransformation, and cholate conjugation. Although hepatocyte viability remained stable through the seven day incubation period, hepatocyte functions were not uniformly preserved. Albumin synthesis remained stable, while representative P-450 and conjugation activities decreased with time. This static culture system will facilitate the development of a hollow fiber bioartificial liver which utilizes cylindrical collagen-hepatocyte gels.

Stimulative effect of non-parenchymal liver cells on ability of tyrosine aminotransferase induction in hepatocytes

Hepatocytes and non-parenchymal liver cells were isolated from adult rat liver and co-cultured for 48 hours as a monolayer on polystyrene culture dishes. The ability of tyrosine aminotransferase (TAT) induction in hepatocytes was examined in the presence of dexamethasone and dibutyryl cAMP. Non-parenchymal cells greatly enhance the ability of TAT induction of hepatocytes. A soluble factor with molecular weight of more than 10,000 is responsible for this enhancement, because conditioned medium prepared from non-parenchymal cells is also stimulatory. Non-parenchymal cells restored the ability in hepatocytes damaged with the addition of D-galactosamine. Conditioned medium prepared from non-parenchymal cells treated with D-galactosamine had higher activity of enhancement than the medium from normal cells. The soluble factor might be released in response to some signal of injury. Hepatocytes and non-parenchymal cells were immobilized within Ca-alginate, and although immobilized hepatocytes rapidly lost the ability to induce TAT, hepatocytes co-immobilized with non-parenchymal cells maintained the ability during 4 days of culture. These results indicated that non-parenchymal liver cells, as well as hepatocytes, could be used to construct a bioartificial liver support system.

Bioartificial liver using hepatocytes on biosilon microcarriers: treatment of chemically induced acute hepatic failure in rats

An artificial liver support procedure based on hemoperfusion via hepatocytes cultured on microcarriers is described. The efficiency of the system was assessed by the survival rate of rats treated with either lethal dosage of 7% CCl4 [30 ml/kg body weight (b.w.)] or D-galactosamine (2.5 g/kg b.w.). In CCl4-treated rats, hemoperfusion via empty microcarriers (n = 16) revealed no surviving animals, whereas the use of the bioartificial liver (n = 11) resulted in 80% (p less than 0.01) and 60% (p less than 0.05) survival 48 and 168 h after hepatotoxin, respectively. For the same time periods, the survival rate in D-galactosamine-intoxicated rats after hemoperfusion with hepatocytes (n = 20) was approximately 60% (p less than 0.05) and was only 5% in those of rats treated with empty microcarriers (n = 20). Sublethal dosage of 7% CCl4 (15 ml/kg b.w.) caused 25% mortality and prolonged (48 h) increase of activity of the liver enzymes and bilirubin levels in the serum of surviving animals. In these rats (n = 8) at the end of 3 h of hemoperfusion via hepatocytes, the bilirubin concentration decreased by 45% as compared with the control group (n = 6) treated with empty microcarriers. Moreover, by 48 h after intoxication, the use of the bioartificial liver resulted in more than a three-fold decrease in glutamate-oxaloacetate transaminase and a 10-fold decrease in glutamate-pyruvate transaminase serum activity as well as a fivefold decline in total and a ninefold decline in conjugated bilirubin levels as compared with the control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

A new approach to the cryopreservation of hepatocytes in a sandwich culture configuration

Current methods of cryopreservation of hepatocytes in single cell suspensions result in low overall yields of hepatocytes, demonstrating long-term preservation of hepatocellular functions. A novel culture method has recently been developed to culture liver cells in a sandwich configuration of collagen layers in order to stabilize the phenotypic expression of these cells in vitro (J. C. Y. Dunn, M. L. Yarmush, H. G. Koebe, and R. G. Tompkins, FASEB J. 3, 174, 1989). Using this culture system, rat hepatocytes were frozen with 15% (v/v) Me2SO to -70 degrees C, and stored at approximately -100 degrees C. Following rapid thawing, long-term function was assessed by measuring albumin secretion in culture for 7-14 days postfreezing. Comparison was made with cryopreservation of liver cells in single cell suspensions. Cryopreservation of liver cells in suspension resulted in only a 2% yield of cells which could be successfully cultured; albumin secretion rates in these cultured cells over 48 hr were 26-30% of secretion rates for nonfrozen hepatocytes. Freezing cultured liver cells in the sandwich configuration after 3, 7, and 11 days in culture maintained 0, 26, and 19% of the secretion rates of nonfrozen hepatocytes, respectively. Morphology of the cryopreserved cells appeared grossly similar to cells without freezing; however, this morphological result was patchy and represented approximately 30% of the cells in culture. These results represent the first demonstration of any quantitative long-term preservation of hepatocellular function by cryopreservation, suggesting that cultured hepatocytes can survive freezing and maintain function.

In vitro maintenance of terminal-differentiated state in hepatocytes entrapped within calcium alginate

In cultured hepatocytes entrapped within Ca-alginate, liver-specific functions such as induction of tyrosine aminotransferase and serine dehydratase were stimulated by increasing the cell density. In contrast, a growth-related function such as induction of glucose-6-phosphate dehydrogenase was strongly stimulated by decreasing the cell density. This reciprocal regulation was mimicked by the addition of plasma membranes purified from adult rat liver to entrapment cultures at low cell density. Also, gluconeogenesis from lactate was stimulated by the addition of epinephrine (alpha,beta-agonist) with propranolol (beta-blocker). These results suggest that entrapped hepatocytes maintain not only terminal-differentiated state but also alpha-adrenergic response as shown in vivo.