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

Engineered Microsystems for Spheroid and Organoid Studies

3D in vitro model systems such as spheroids and organoids provide an opportunity to extend the physiological understanding using recapitulated tissues that mimic physiological characteristics of in vivo microenvironments. Unlike 2D systems, 3D in vitro systems can bridge the gap between inadequate 2D cultures and the in vivo environments, providing novel insights on complex physiological mechanisms at various scales of organization, ranging from the cellular, tissue-, to organ-levels. To satisfy the ever-increasing need for highly complex and sophisticated systems, many 3D in vitro models with advanced microengineering techniques have been developed to answer diverse physiological questions. This review summarizes recent advances in engineered microsystems for the development of 3D in vitro model systems. The relationship between the underlying physics behind the microengineering techniques, and their ability to recapitulate distinct 3D cellular structures and functions of diverse types of tissues and organs are highlighted and discussed in detail. A number of 3D in vitro models and their engineering principles are also introduced. Finally, current limitations are summarized, and perspectives for future directions in guiding the development of 3D in vitro model systems using microengineering techniques are provided.

Organotypic Models in Drug Development "Tumor Models and Cancer Systems Biology for the Investigation of Anticancer Drugs and Resistance Development"

The landscape of cancer treatment has improved over the past decades, aiming to reduce systemic toxicity and enhance compatibility with the quality of life of the patient. However, at the therapeutic level, metastatic cancer remains hugely challenging, based on the almost inevitable emergence of therapy resistance. A small subpopulation of cells able to survive drug treatment termed the minimal residual disease may either harbor resistance-associated mutations or be phenotypically resistant, allowing them to regrow and become the dominant population in the therapy-resistant tumor. Characterization of the profile of minimal residual disease represents the key to the identification of resistance drivers that underpin cancer evolution. Therapeutic regimens must, therefore, be dynamic and tailored to take into account the emergence of resistance as tumors evolve within a complex microenvironment in vivo. This requires the adoption of new technologies based on the culture of cancer cells in ways that more accurately reflect the intratumor microenvironment, and their analysis using omics and system-based technologies to enable a new era in the diagnostics, classification, and treatment of many cancer types by applying the concept "from the cell plate to the patient." In this chapter, we will present and discuss 3D model building and use, and provide comprehensive information on new genomic techniques that are increasing our understanding of drug action and the emergence of resistance.

[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.

Large-Scale Preparation and Function of Porcine Hepatocyte Spheroids

To obtain a large number of porcine hepatocyte aggregates (spheroids) that have great potential in a bioartificial liver (BAL), we performed spheroid formation at a high cell density in a 1-L-scale spinner flask fitted with a silicon tubing apparatus for oxygen supply. We thereby obtained, within 24 hours, approximately fifty times more porcine hepatocyte spheroids as compared with the results of previous reports. The amount obtained corresponds to 2.5×109 cells and to roughly one-sixth of the cell number required for a BAL for a human patient. When we cultured spheroids continuously in suspension, they expressed three times more albumin secretion and twice the ammonium removal as compared with conventional monolayers during 10 days culture. Collagen gel entrapment of spheroids particularly lowered albumin secretion. We therefore conclude that the supension culture vessel of porcine hepatocyte spheroids is one of the most promising module types.

Single molecule microscopy in 3D cell cultures and tissues

From the onset of the first microscopic visualization of single fluorescent molecules in living cells at the beginning of this century, to the present, almost routine application of single molecule microscopy, the method has well-proven its ability to contribute unmatched detailed insight into the heterogeneous and dynamic molecular world life is composed of. Except for investigations on bacteria and yeast, almost the entire story of success is based on studies on adherent mammalian 2D cell cultures. However, despite this continuous progress, the technique was not able to keep pace with the move of the cell biology community to adapt 3D cell culture models for basic research, regenerative medicine, or drug development and screening. In this review, we will summarize the progress, which only recently allowed for the application of single molecule microscopy to 3D cell systems and give an overview of the technical advances that led to it. While initially posing a challenge, we finally conclude that relevant 3D cell models will become an integral part of the on-going success of single molecule microscopy.

Stimulation of liver functions in hierarchical co-culture of bone marrow cells and hepatocytes

A hierarchial co-culture, in which rat hepatocytes and non-parenchymal liver cells (NPLCs) were separated by a collagen layer and which was designed to mimic the in vivo microenvironment, was carried out with the aim of developing a module for bio-artificial liver support. Compared with a monolayer co-culture and hepatocytes cultured alone in a monolayer, higher urea synthesis activity was maintained for 6 d in the hierarchical co-culture. When a rat hepatoma cell line H4-II-E-C3, which retains the induction of tyrosine aminotransferase (TAT), was co-cultured in a monolayer with NPLCs, dose-dependent stimulation of TAT induction was observed. In a hierarchical co-culture, NPLCs further stimulated TAT induction in H4-II-E-C3 cells. Since peritoneal macrophages could stimulate TAT induction in hepatocytes in both monolayer and hierarchical co-cultures, bone marrow cells, which can proliferate and differentiate into macrophages in vitro, were investigated as a possible substitute for NPLCs. Bone marrow cells isolated from rat femurs were cultivated in the presence of IL-3 and macrophage colony-stimulating factor (M-CSF), and co-cultured with hepatocytes. Urea synthesis and TAT induction of hepatocytes were stimulated in the co-culture. The co-culture of bone marrow and H4-II-E-C3 cells, both of which have proliferation ability in vitro, was also shown to be effective in stimulating liver functions. The hierarchical configuration, in which two cell types can communicate with the soluble factor(s) through a collagen layer, was found to be more effective than a monolayer in long-term co-culture.

Liver tissue engineering: promises and prospects of new technology

Today, many patients suffer from acute liver failure and hepatoma. This is an area of high unmet clinical need as these conditions are associated with very high mortality. There is an urgent need to develop techniques that will enable liver tissue engineering or generate a bioartificial liver, which will maintain or improve liver function or offer the possibility of liver replacement. Liver tissue engineering is an innovative way of constructing an implantable liver and has the potential to alleviate the shortage of organ donors for orthotopic liver transplantation. In this review we describe, from an engineering perspective, progress in the field of liver tissue engineering, including three main aspects involving cell sources, scaffolds and vascularization.

Preparation and HL-7702 cell functionality of titania/chitosan composite scaffolds

Titania/chitosan composite scaffolds were prepared through a freeze-drying technique. The composite scaffolds were highly porous with the average pore size of 120-300 microm, and the titania (TiO(2)) powders were uniformly dispersed on the surface of the pore walls. The compressive strength of the composite scaffolds was significantly improved compared to that of pure chitosan scaffolds. Composite scaffold with 0.3 of TiO(2)/chitosan weight ratio showed the maximum compressive strength of 159.7 +/- 21 kPa. Hepatic immortal cell line HL-7702 was used as seeding cells on the scaffolds, and after different culture periods, cell attachment and function was analyzed. HL-7702 cells attached on the pore walls of the scaffolds with the spheroid shape after 1 day of culture, but more cell aggregations formed within the TiO(2)/chitosan composite scaffolds as compared to pure chitosan scaffolds. Liver-specific functions, albumin secretion and urea synthesis were detected using a spectrometric method. The results showed that albumin secretion and urea synthesis rate of HL-7702 cells slightly decreased with the culture time, and there was no significant difference between composite scaffolds and pure chitosan scaffolds. In conclusion, the TiO(2)/chitosan composite scaffolds possessed an improved mechanical strength compared to pure chitosan scaffolds and supported the attachment and functional expression of hepatocyte, implying their potential application in liver tissue engineering.

Bioartificial liver systems: why, what, whither?

Acute liver disease is a life-threatening condition for which liver transplantation is the only recognized effective therapy. While etiology varies considerably, the clinical course of acute liver failure is common among the etiologies: encephalopathy progressing toward coma and multiple organ failure. Detoxification processes, such as molecular adsorbent recirculating system (MARS®) and Prometheus, have had limited success in altering blood chemistries positively in clinical evaluations, but have not been shown to be clinically effective with regard to patient survival or other clinical outcomes in any Phase III prospective, randomized trial. Bioartificial liver systems, which use liver cells (hepatocytes) to provide metabolic support as well as detoxification, have shown promising results in early clinical evaluations, but again have not demonstrated clinical significance in any Phase III prospective, randomized trial. Cell transplantation therapy has had limited success but is not practicable for wide use owing to a lack of cells (whole-organ transplantation has priority). New approaches in regenerative medicine for treatment of liver disease need to be directed toward providing a functional cell source, expandable in large quantities, for use in various applications. To this end, a novel bioreactor design is described that closely mimics the native liver cell environment and is easily scaled from microscopic (<1 ml cells) to clinical (∼600 ml cells) size, while maintaining the same local cell environment throughout the bioreactor. The bioreactor is used for study of primary liver cell isolates, liver-derived cell lines and stem/progenitor cells.

Functional analysis of encapsulated hepatic progenitor cells

A major challenge in developing therapies based on progenitor or stem cell populations (from sources other than bone marrow) involves developing a mode to deliver these cells in a manner that optimizes their viability, engraftment, proliferation, and differentiation. We have previously isolated a hepatic progenitor cell (HPC) population from adult liver tissue that differentiates into hepatic and biliary cell subtypes. We postulated that, using electrostatic encapsulation, we could reproducibly generate an ex vivo environment for the HPCs. We also theorized that this approach would foster cellular viability and function of the progenitor cell population. Using this encapsulation process, we consistently produced beads with uniform diameters between 200 and 700 microm. In vitro analysis of the encapsulated beads demonstrated extended periods of viability and function based on albumin production, urea metabolism, and glycogen storage. In conclusion, HPC encapsulation fosters the subsequent differentiation of HPCs into functional cells while maintaining their viability in long-term culture. These results demonstrate the efficacy of this method using somatic-derived progenitor cell populations and pave the way for clinical therapies.

Morphology and albumin secretion of adult rat hepatocytes cultured on a hydrophobic porous expanded polytetrafluoroethylene membrane

Primary culture of rat hepatocytes was performed on a hydrophobic porous expanded polytetrafluoroethylene (ePTFE) membrane incorporated into the base of a culture dish. Two types of ePTFE membranes, a uniaxially expanded type (ePTFE-1) and a biaxially expanded type (ePTFE-2), could be used as the culture surfaces for hepatocytes. The formation of multicellular aggregates was observed in the culture dish when each membrane type was used. A pore size of 1 mum or higher was adequate for cell adhesion and albumin secretion for both membrane types. The activity of albumin secretion in the dish with the ePTFE membrane was markedly higher than that in the polystyrene dish. Spheroidal multicellular aggregates (spheroids) were observed when hepatocytes were cultured on the ePTFE-1 membrane. The ePTFE-1 membrane maintained the albumin secretion activity for a longer period than the non-expanded PTFE film. It was assumed that the cooperative action of membrane structure and oxygen permeability promoted the formation of cell aggregates and increased the albumin secretion activity.

A novel bioartificial liver with culture of porcine hepatocyte aggregates under simulated microgravity

An extracorporeal bioartificial liver device could provide vital support to patients suffering from acute liver failure. We designed a novel, customized bioreactor for use as a bioartificial liver (patent pending). The Innsbruck Bioartificial Liver (IBAL) contains aggregates of porcine hepatocytes grown under simulated microgravity. The culture vessel rotates around its longitudinal axis and is perfused by two independent circuits. The circuit responsible for exchange of plasma components with the patient consists of a dialysis tube winding spirally around the internal wall of the culture vessel. IBAL was evaluated in vitro. Viability tests showed sufficient viability of hepatocytes for up to 10 days. Cytologic examination of samples from the bioreactor showed liver cell aggregates. These were also examined by electron microscopy. A number of biochemical parameters were analyzed. In conclusion, cell culture is possible for at least 10 days in the IBAL system, organoid hepatocyte aggregates are formed and synthetic activity of the hepatocytes was demonstrated.

Stable immobilization of rat hepatocyte spheroids on galactosylated nanofiber scaffold

Primary rat hepatocytes self-assemble into multi-cellular spheroids and maintain differentiated functions when cultured on a two-dimensional (2-D) substrate conjugated with galactose ligand. The aim of this study is to investigate how a functional nanofiber scaffold with surface-galactose ligand influences the attachment, spheroid formation and functional maintenance of rat hepatocytes in culture, as compared with the functional 2-D substrate. Highly porous nanofiber scaffolds comprising of fibers with an average diameter of 760 nm were prepared by electrospinning of poly(epsilon-caprolactone-co-ethyl ethylene phosphate) (PCLEEP), a novel biodegradable copolymer. Galactose ligand with a density of 66 nmol/cm(2) was achieved on the nanofiber scaffold via covalent conjugation to a poly(acrylic acid) spacer UV-grafted onto the fiber surface. Hepatocytes cultured on the galactosylated PCLEEP nanofiber scaffold exhibited similar functional profiles in terms of cell attachment, ammonia metabolism, albumin secretion and cytochrome P450 enzymatic activity as those on the functional 2-D substrate, although their morphologies are different. Hepatocytes cultured on galactosylated PCLEEP film formed 50-300 microm spheroids that easily detached from surface upon agitation, whereas hepatocytes cultured on galactosylated nanofiber scaffold formed smaller aggregates of 20-100 microm that engulfed the functional nanofibers, resulting in an integrated spheroid-nanofiber construct.

Hybrid artificial liver support system for treatment of severe liver failure

AIM: To construct a novel hybrid artificial liver support system (HALSS) and to evaluate its efficacy in patients with severe liver failure.

METHODS: Hepatocytes were isolated from suckling pig by the modified Seglen’s method. Isolated hepatocytes were cultured in a spinner flask for 24 h to form spheroids before use and the functions of spheroids were detected. HALSS consisted of a plasma separator, a hemo-adsorba and a bioreactor with hepatocytes spheroids in its extra-fiber space. HALSS was applied to 10 patients with severe liver failure. The general condition and the biochemical indexes of the patients were studied just before and after the treatment.

RESULTS: The number of cells per liver was about 2-4×10¹⁰ (mean, 3.1±1.5×10¹⁰). The cell viabilities were more than 95%. After 24 h of spheroid culture, most hepatocytes formed spheroids. The levels of albumin and urea in the medium of spheroid culture were higher than those in supernatant of petri dish culture (P = 0.0015 and 0.0001, respectively). The capacity of albumin production and urea synthesis remained stable for more than one wk and declined rapidly after two weeks in vitro. In HALSS group, the duration of HALSS treatment was 6-10 h each time. All patients tolerated the treatment well without any fatal adverse reaction. After HALSS treatment, the general condition, psychic state, encephalopathy and hepatic function of the patients were improved. The survival rate of the HALSS group, Plasmapheresis group and control group was 30% (3/10), 20% (2/10) and 0% (0/10), respectively (P = 0.024). Two weeks after treatment, Tbil and ALT decreased and the PTA level elevated in HALSS group and pasmapheresis group (P value: 0.015 vs 0.020, 0.009 vs 0.012 and 0.032 vs 0.041, respectively). But there was no significant change of blood albumin concentration before and after treatment in HALSS group and Plasmapheresis group.

CONCLUSION: The HALSS established by us is effective in supporting liver function of patients with severe liver failure.

Biochemical and functional changes of rat liver spheroids during spheroid formation and maintenance in culture: I. morphological maturation and kinetic changes of energy metabolism, albumin synthesis, and activities of some enzymes

In the process of isolated single liver cells coming together to form three-dimensional spheroids, cells undergo dramatic environmental changes. How liver cells respond to these changes has not been well studied before. This study characterized the functional and biochemical changes during liver spheroid formation and maintenance. Spheroids were prepared in 6-well plates from freshly isolated liver cells from male Sprague rats by a gyrotatory-mediated method. Morphological formation, and functional and biochemical parameters of liver spheroids were evaluated over a period of 21 days in culture. Liver spheroid formation was divided into two stages, immature (1-5 days) and mature (>5 days), according to their size and shape, and changes in their functionality. Galactose and pyruvate consumption was maintained at a relatively stable level throughout the period of observation. However, glucose secretion and cellular GPT and GOT activities were higher in immature spheroids, decreased upto day 5 and remained stable thereafter. Cellular gamma-glutamyltransferase (gamma-GT) and lactate dehydrogenase (LDH) activities were initially undetectable or low and increased as spheroids matured. Albumin secretion decreased rapidly within the first 2 days and increased as spheroids matured. It is concluded that cells undergo functional and biochemical changes during spheroid formation following isolation of liver cells from intact tissue. Functionality and biochemical properties recovered and were maintained in mature spheroids. A relatively stable period (6-15 days) of functionality in mature spheroids was identified and is recommended for applications of the model.

Alginate as a new biomaterial for the growth of porcine retinal pigment epithelium

OBJECTIVE

Determine the effect of a 3-dimensional alginate matrix on the growth and differentiation of cells isolated from porcine retinal pigment epithelium (RPE).

PROCEDURES

Porcine RPE cells were harvested from enucleated eyecups, isolated by differential gravity sedimentation and cultured in either alginate alone (Group 1) or on plastic tissue culture plates followed by alginate (Group 2). Group 1 cells were cultured in alginate to evaluate the efficacy of the matrix as a culture medium. Group 2 cells were initially cultured on plastic to induce dedifferentiation. The cells were then harvested, suspended in alginate beads, and incubated for a second culture period to determine if the induced dedifferentiation was reversible.

RESULTS

The number of Group 1 cells was significantly greater (P < or = 0.01) at the end of the culture period. The amount of pigment and cell morphology of Group 1 cells at the end of the culture period was similar to that seen at initial cell isolation. The initial culture of Group 2 cells on plastic showed characteristic features of dedifferentiation marked by the loss of pigment and alterations in microscopic appearance. Secondary culture of dedifferentiated Group 2 cells in alginate beads resulted in a return to pigmentation and characteristic morphology for a majority of the cultured cells.

CONCLUSIONS

Porcine RPE cells can be propagated in alginate culture with a significant increase in cell numbers while maintaining normal morphology. Under the conditions described in the present study, the dedifferentiation of porcine RPE induced by standard in vitro culture methods is reversible.

Preparation and culture of hepatocyte on gelatin microcarriers

Porous gelatin microcarriers having a diameter of 80-100 microm were prepared by the suspension method using toluene as the oil phase. Rat hepatocytes were cultured on gelatin and cytodexIII microcarriers. The cells retained its spherical shape, which is similar in vivo, and showed no morphological changes to the flat state. Hepatocyte aggregates on microcarriers maintained higher metabolic functions than monolayer cells. Pore size of microcarrier plays an important role in the attachment and metabolic function of cells in culture. Phase-contrast micrograph and cell activity showed that hepatocytes cultures on gelatin microcarrier of <1 microm pore size is better than that of 5-10 microm.

Preparation of alginate/galactosylated chitosan scaffold for hepatocyte attachment

Galactose-carrying lactobionic acid was covalently coupled with chitosan for determining hepatocyte specificity. Galactosylated chitosan (GC) was reacted with Ca-alginate (ALG) gel through the electrostatic interaction of carboxylic groups of alginate with amine groups of GC. Highly porous, three-dimensional sponge composed of ALG and GC was prepared to provide specific hepatocyte recognition signals and enhance the mechanical property of the ALG sponge. Observation of the sponge through scanning electron microscopy revealed that sponge was a highly porous microstructure with interconnected pores. Porosity and pore size of the sponge were greatly dependent on the content and molecular weight of GC, and freezing temperature. The mechanical property of the ALG/GC sponge was enhanced with an increase of the GC content. Spheroid formation and viability of hepatocytes of the ALG/GC sponge were higher than those of the ALG one.

A novel method for faster formation of rat liver cell spheroids

Hepatocyte spheroids are expected to be the main component of the artificial liver bioreactor for their higher function. The preparation of hepatocyte spheroids, however, can require as many as 24 to 96 h. To reduce this time, we investigated a method employing a new technique of rat hepatocyte preparation and a dynamic culture. The modified Seglen's method for standard hepatocyte isolation was altered by elimination of ethyleneglycol bis(aminoethylether) tetraacetate from the first perfusate and calcium from the second perfusate. Isolated hepatocytes were cultured in a spinner flask by spinning at 120 rpm. The modified Seglen's method was used as a control. Cells obtained by the new method were more cohesive and formed a higher proportion of cell aggregates than control cells. In the spinning culture, hepatocytes had a tendency to aggregate and 80% of cells formed spheroids within 6 h of culturing. The mean size of spheroids was 68.5 +/- 18.5 microm. Confocal laser scanning microscopy revealed that individual spheroids contained approximately 30% of nonparenchymal cells over their surface. Using the new hepatocyte preparation method followed by a spinning culture, we were able to produce hepatocyte spheroids in as few as 6 h.

Galactosylated alginate as a scaffold for hepatocytes entrapment

Galactose moieties were covalently coupled with alginate through ethylenediamine as the spacer for enhancing the interaction of hepatocytes with alginate. Adhesion of hepatocytes onto the galactosylated alginate (GA)-coated polystyrene (PS) surface showed an 18-fold increase as compared with that of the alginate-coated surface and it increased with an increase in the concentration of GA. The morphologies of attached hepatocytes were observed to spread out at the 0.15 wt% GA-coated PS surface while round cells were observed at the 0.5 wt% GA-coated PS surface. Inhibition of hepatocytes attachment onto the galactose-carrying PS-coated surface occurred with the addition of the GA into the hepatocyte suspension, indicating the binding of GA with hepatocytes via the patch of asialoglycoprotein receptors. Primary hepatocytes were entrapped in the GA/Ca2+ capsules (GAC). Higher cell viability and more spheroid formation of hepatocytes were obtained in the GAC than in the alginate/Ca2+ capsules (AC). Moreover, liver functions of the hepatocytes such as albumin secretion and urea synthesis in the GAC were improved in comparison with those in the AC.

The role of actin filaments and microtubules in hepatocyte spheroid self-assembly

Cultured rat hepatocytes self-assemble into three-dimensional structures or spheroids that exhibit ultrastructural characteristics of native hepatic tissue and enhanced liver-specific functions. The spheroid formation process involves cell translocation and changes in cell shape, indicative of the reorganization of the cytoskeletal elements. To elucidate the function of the cytoskeleton, hepatocytes undergoing spheroid formation were treated with drugs that disrupt the different cytoskeletal components. Cytochalasin D, which targets the actin filaments, caused inhibition of spheroid formation. The role of microtubules in this process was assessed by incubating the cells with taxol or nocodazole. Perturbation of microtubules had minimal effects on spheroid assembly. Scanning electron micrographs showed no morphological differences between spheroids formed in control cultures and those formed in the presence of taxol or nocodazole. In addition, the effects of those agents on hepatocyte functions were investigated. Albumin secretion and cytochrome P450 2B1/2 activities of hepatocytes were comparable in spheroids formed in the presence of taxol or nocodazole to those formed in control cultures. The levels of these liver-specific activities were lower in cytochalasin D--treated cultures where only dispersed cells or cell clumps were found but spheroids had not found. Thus, hepatocytes require an intact actin network to self-assemble efficiently into functional tissue-like structures. Perturbation of the microtubule lattice does not impair the formation process. Events that transpire during hepatocyte spheroid self-assembly exhibit striking similarities to processes commonly observed in tissue morphogenesis. The results provide insight into the mechanisms that cells employ to organize into tissues and can contribute to our understanding of how to control the cellular assembly in tissue engineering and clinical applications.

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.

Hepatocyte behavior within three-dimensional porous alginate scaffolds

A potential approach to facilitate the performance of implanted hepatocytes is to enable their aggregation and re-expression of their differentiated function prior to implantation. Here we examined the behavior of freshly isolated rat adult hepatocytes seeded within a novel three-dimensional (3-D) scaffold based on alginate. The attractive features of this scaffold include a highly porous structure (sponge-like) with interconnecting pores, and pore sizes with diameters of 100-150 microm. Due to their hydrophilic nature, seeding hepatocytes onto the alginate sponges was efficient. DNA measurements showed that the total cell number within the sponges did not change over 2 weeks, indicating that hepatocytes do not proliferate under these culture conditions. Nearly all seeded cells maintained viability, according to the MTT assay. Within 24 h post-seeding, small clusters of viable cells, were seen scattered within the sponge. More than 90% of the seeded cells participated in the aggregation; the high efficiency is attributed to the non-adherent nature of alginate. The spheroids had smooth boundaries and by day 4 in culture reached an average diameter of 100 microm, which is at the same magnitude of the sponge pore size. The cells appeared to synthesize fibronectin which was deposited on the spheroids. No laminin or collagen type IV were detected in the deposit. The 3-D arrangement of hepatocytes within the alginate sponges promoted their functional expression; within a week the cells secreted the maximal albumin secretion rate of 60 microg albumin/10(6) cells/day. Urea secretion rate did not depend on cell aggregation and was similar to that obtained when hepatocytes were cultured on collagen type I coated dishes (100 microg/10(6) cells/day). Our studies show that alginate sponges can provide a conducive environment to facilitate the performance of cultured hepatocytes by enhancing their aggregation.

Multicellular spheroids: a three-dimensional in vitro culture system to study tumour biology

The growth of tumour cells as three-dimensional multicellular spheroids in vitro has led to important insights in tumour biology, since properties of the in vivo-tumour such as proliferation or nutrient gradients, can be studied under controlled conditions. While this review starts with an update of recent data on spheroid monocultures, especially concerning tumour microenvironment and therapeutic modalities, the main emphasis is put on the spectrum of heterologous cultures which have evolved in previous years. This type of culture includes tumour cell interaction with endothelial, fibroblast or immunocompetent cells. The relation of the spheroid culture model to other types of three-dimensional culture and our critical evaluation and presentation of the technical aspects of growing and analysing spheroids are included in the text. These topics are chosen to help the experimental pathologist design experiments with tumour spheroids and to stimulate discussion.

CHO transfectants produce large amounts of recombinant protein in suspension culture

Chinese hamster ovary (CHO) cells transfected with various genes are widely used as adherent cell monolayers to produce recombinant proteins. In this report we present a new culture technique for CHO cells transfected with the vector pPOL-DHFR-CD14 using a minifermenter (miniPERM, Heraeus) for the production of recombinant human endotoxin receptor CD14 (rCD14). The transfectants were cultured for 12-17 days under serum-free conditions and formed spheroids. From this system we harvested supernatants containing up to 3.1 mg/ml recombinant CD14 (rCD14). This represents a 200-fold increase of rCD14 yield compared to conventional adherent CHO cell culture.

Reciprocal regulation of prothrombin secretion and tyrosine aminotransferase induction in hepatocytes

Multicellular spheroids of hepatocytes are known to maintain liver functions for a long period. Rat hepatocytes were isolated to form spheroids by rotation culture and immobilized within calcium alginate. Immobilized spheroids had a much higher extent of tyrosine aminotransferase induction, which is one of the liver-specific differentiated functions, than immobilized non-aggregated cells, while the spheroids secreted significantly less prothrombin than non-aggregated cells. Co-culture of hepatocytes and non-parenchymal liver cells in a monolayer enhanced tyrosine aminotransferase induction and suppressed prothrombin secretion, while conditioned medium prepared from non-parenchymal cells greatly stimulated tyrosine aminotransferase induction and suppressed the prothrombin secretion and DNA synthesis in monolayer-cultured hepatocytes. Prothrombin secretion in hepatocytes was subjected to cell-density-dependent regulation. In a similar manner to other growth-related functions, prothrombin secretion was stimulated at low cell density. It has been reported that thrombin activates the zymogen of hepatocyte growth factor activator [Shimomura, T., Kondo, J., Ochiai, M., Naka, D., Miyazawa, K., Morimoto, Y. & Kitamura, N. (1993) J. Biol. Chem. 268, 22,927-22,932]. Therefore, prothrombin secretion could be one of the growth-related functions and involved in wound healing and liver regeneration.