Extended liver-specific functions of porcine hepatocyte spheroids entrapped in collagen gel

Current strategies with implementation of three-dimensional cell culture: the challenge of quantification

From growing cells in spheroids to arranging them on complex engineered scaffolds, three-dimensional cell culture protocols are rapidly expanding and diversifying. While these systems may often improve the physiological relevance of cell culture models, they come with technical challenges, as many of the analytical methods used to characterize traditional two-dimensional (2D) cells must be modified or replaced to be effective. Here we review the advantages and limitations of quantification methods based either on biochemical measurements or microscopy imaging. We focus on the most basic of parameters that one may want to measure, the number of cells. Precise determination of this number is essential for many analytical techniques where measured quantities are only meaningful when normalized to the number of cells (e.g. cytochrome p450 enzyme activity). Thus, accurate measurement of cell number is often a prerequisite to allowing comparisons across different conditions (culturing conditions or drug and treatment screening) or between cells in different spatial states. We note that this issue is often neglected in the literature with little or no information given regarding how normalization was performed, we highlight the pitfalls and complications of quantification and call for more accurate reporting to improve reproducibility.

Kinetic Analysis of Lidocaine Elimination by Pig Liver Cells Cultured in 3D Multi-Compartment Hollow Fiber Membrane Network Perfusion Bioreactors

Liver cells cultured in 3D bioreactors is an interesting option for temporary extracorporeal liver support in the treatment of acute liver failure and for animal models for preclinical drug screening. Bioreactor capacity to eliminate drugs is generally used for assessing cell metabolic competence in different bioreactors or to scale-up bioreactor design and performance for clinical or preclinical applications. However, drug adsorption and physical transport often disguise the intrinsic drug biotransformation kinetics and cell metabolic state. In this study, we characterized the intrinsic kinetics of lidocaine elimination and adsorption by porcine liver cells cultured in 3D four-compartment hollow fiber membrane network perfusion bioreactors. Models of lidocaine transport and biotransformation were used to extract intrinsic kinetic information from response to lidocaine bolus of bioreactor versus adhesion cultures. Different from 2D adhesion cultures, cells in the bioreactors are organized in liver-like aggregates. Adsorption on bioreactor constituents significantly affected lidocaine elimination and was effectively accounted for in kinetic analysis. Lidocaine elimination and cellular monoethylglicinexylidide biotransformation featured first-order kinetics with near-to-in vivo cell-specific capacity that was retained for times suitable for clinical assist and drug screening. Different from 2D cultures, cells in the 3D bioreactors challenged with lidocaine were exposed to close-to-physiological lidocaine and monoethylglicinexylidide concentration profiles. Kinetic analysis suggests bioreactor technology feasibility for preclinical drug screening and patient assist and that drug adsorption should be accounted for to assess cell state in different cultures and when laboratory bioreactor design and performance is scaled-up to clinical use or toxicological drug screening.

3D hepatic mimics - the need for a multicentric approach

The liver is a center of metabolic activity, including the metabolism of drugs, and consequently is prone to drug-induced liver injury. Failure to detect hepatotoxicity of drugs during their development will lead to the withdrawal of the drugs during clinical trials. To avoid such clinical and economic consequences, in vitro liver models that can precisely predict the toxicity of a drug during the pre-clinical phase is necessary. This review describes the different technologies that are used to develop in vitro liver models and the different approaches aimed at mimicking different functional aspects of the liver at the fundamental level. This involves mimicking of the functional and structural units like the sinusoid, the bile canalicular system, and the acinus.

Microfluidic technologies to engineer mesenchymal stem cell aggregates-applications and benefits

Three-dimensional cell culture and the forming multicellular aggregates are superior over traditional monolayer approaches due to better mimicking of in vivo conditions and hence functions of a tissue. A considerable amount of attention has been devoted to devising efficient methods for the rapid formation of uniform-sized multicellular aggregates. Microfluidic technology describes a platform of techniques comprising microchannels to manipulate the small number of reagents with unique properties and capabilities suitable for biological studies. The focus of this review is to highlight recent studies of using microfluidics, especially droplet-based types for the formation, culture, and harvesting of mesenchymal stem cell aggregates and their subsequent application in stem cell biology, tissue engineering, and drug screening. Droplet-based microfluidics can be used to form microgels as carriers for delivering cells and to provide biological cues to the target tissue so as to be minimally invasive. Stem cell-laden microgels with a shape-forming property can be used as smart building blocks by injecting them into the injured tissue thereby constituting the cornerstone of tissue regeneration.

Co-cultured spheroids of human periodontal ligament mesenchymal stem cells and vascular endothelial cells enhance periodontal tissue regeneration

Introduction

Human periodontal ligament mesenchymal stem cells (hPDLMSCs) have been known that they play important roles in homeostasis and regeneration of periodontal tissues. Additionally, spheroids are superior to monolayer-cultured cells. We investigated the characteristics and potential of periodontal tissue regeneration in co-cultured spheroids of hPDLMSCs and human umbilical vein endothelial cells (HUVECs) in vitro and in vivo.

Methods

Co-cultured spheroids were prepared with cell ratios of hPDLMSCs: HUVECs = 1:1, 1:2, and 2:1, using microwell chips. Real-time polymerase chain reaction (PCR) analysis, Enzyme-Linked Immuno Sorbent Assay (ELISA), and nodule formation assay were performed to examine the properties of co-cultured spheroids. Periodontal tissue defects were prepared in the maxillary first molars of rats and subjected to transplantation assay.

Results

The expression levels of stemness markers, vascular endothelial growth factor (VEGF), osteogenesis-related genes were up-regulated in co-cultured spheroids, compared with monolayer and spheroid-cultured hPDLMSCs. The nodule formation was also increased in co-cultured spheroids, compared with monolayer and spheroid cultures of hPDLMSCs. Treatment with co-cultured spheroids enhanced new cementum formation after 4 or 8 weeks of transplantation, although there was no significant difference in the new bone formation between co-cultured spheroids and hPDLMSC spheroids.

Conclusions

We found that co-cultured spheroids enhance the periodontal tissue regeneration. Co-cultured spheroids of hPDLMSCs and HUVECs may be a useful therapy that can induce periodontal tissue regeneration.

A 3D Printed Hanging Drop Dripper for Tumor Spheroids Analysis Without Recovery

Compared with traditional monolayer cell culture, the three-dimensional tumor spheroid has emerged as an essential in vitro model for cancer research due to the recapitulation of the architecture and physiology of solid human tumors. Herein, by implementing the rapid prototyping of a benchtop 3D printer, we developed a new strategy to generate and analyze tumor spheroids on a commonly used multi-well plate. In this method, the printed artifact can be directly mounted on a 96/384-well plate, enables hanging drop-based spheroid formation, avoiding the tedious fabrication process from micromechanical systems. Besides long-term spheroid culture (20 days), this method supports subsequent analysis of tumor spheroid by seamlessly dripping from the printed array, thereby eliminating the need for spheroids retrieval for downstream characterization. We demonstrated several tumor spheroid-based assays, including tumoroid drug testing, metastasis on or inside extracellular matrix gel, and tumor transendothelial (TEM) assay. Based on quantitative phenotypical and molecular analysis without any precarious retrieval and transfer, we found that the malignant breast cancer (MDA-MB-231) cell aggregate presents a more metastatic morphological phenotype than the non-malignant breast cancer (MCF-7) and colonial cancer (HCT-116) cell spheroid, and shows an up-regulation of epithelial-mesenchymal transition (EMT) relevant genes (fold change > 2). Finally, we validated this tumor malignancy by the TEM assay, which could be easily performed using our approach. This methodology could provide a useful workflow for expediting tumoroid modeled in vitro assay, allowing the “Lab-on-a-Cloud” scenario for routine study.

Fabrication of size-controllable human mesenchymal stromal cell spheroids from micro-scaled cell sheets

Recently, stromal cell spheroids have been actively studied for use in tissue regeneration. In this study, we report a method for the fabrication of size-controllable stromal cell spheroids in different sizes from micro-scaled cell sheets (μCS) using thermosensitive hydrogels and investigated their effects on stromal cell function. Mesenchymal stromal cells isolated from different tissues such as human turbinate tissue, bone marrow, and adipose tissue were adhered selectively to each micro-pattern (squares with widths of 100 and 400 μm) on the surface of the hydrogel and formed μCS. The diameters of the spheroids were modulated by the size of the patterns (45 ± 5 and 129 ± 4 μm in diameter for the 100 and 400 μm micro-patterns, respectively) and the seeding density (129 ± 4, 149 ± 6, and 163 ± 6 μm for 5.0, 10.0, and 15.0 × 10⁴ cells cm^-2, respectively, on 400 μm micro-pattern). In addition, the spheroids were successfully fabricated regardless of stromal cell origin, and the diameter of the spheroids was also affected by cell spreading area on a cell culture dish. Stemness markers were highly expressed in the spheroids regardless of the spheroid size. Furthermore, an increase in E-cadherin and decrease in N-cadherin gene expression showed the stable formation of spheroids of different sizes. Gene expression levels of hypoxia inducible factors and secretion of vascular endothelial growth factor were increased (13.2 ± 1.4, 325 ± 83.4 and 534.3 ± 121.5 pg ng^-1 DNA in a monolayer, and 100 and 400 μm micro-patterned spheroids, respectively) proportional to the diameters of the spheroids. The size of spheroids were maintained even after injection, cryopreservation and 7 d of suspension culture with high viability (∼90%). In conclusion, this novel technique to fabricate spheroids with controlled size could be widely applied in various applications that require a controlled size in regenerative medicine.

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.

Development of a Hybrid Artificial Liver using a Polyurethane Foam/Hepatocyte-Spheroid Packed-Bed Module

Primary dog hepatocytes spontaneously formed spheroids in the pores of polyurethane foam (PUF) within 1–2 days of stationary culture. The spheroids, about 100–150 μm in diameter, partly attached to the surface and immobilized inside these pores.

The lidocaine disappearance rate decreased to about 4 μg/105 viable cells/day for 10 days, while in the PUF/spheroid culture the rate was maintained at almost the initial level of 8 μg/105 viable cells/day for 10 days. Then, two scales of PUF packed-bed modules were designed. A small module (PUF volume; 14.5 cm3) was used for in vitro culture to investigate optimum culture conditions, and a large module (PUF volume; 300 cm3) was designed for dog experiments. Hepatocytes inoculated in these modules also formed spheroids and maintained almost the same activity of albumin secretion rate (111 μg/cm3 PUF/day in the small module and 87.7 μg/cm3 PUF/day in the large module). These results indicate that the PUF packed-bed module containing hepatocyte-spheroids is promising as a hybrid artificial liver

A Paired Bead and Magnet Array for Molding Microwells with Variable Concave Geometries

A spheroid culture is a useful tool for understanding cellular behavior in that it provides an in vivo-like three-dimensional environment. Various spheroid production methods such as non-adhesive surfaces, spinner flasks, hanging drops, and microwells have been used in studies of cell-to-cell interaction, immune-activation, drug screening, stem cell differentiation, and organoid generation. Among these methods, microwells with a three-dimensional concave geometry have gained the attention of scientists and engineers, given their advantages of uniform-sized spheroid generation and the ease with which the responses of individual spheroids can be monitored. Even though cost-effective methods such as the use of flexible membranes and ice lithography have been proposed, these techniques incur serious drawbacks such as difficulty in controlling the pattern sizes, achievement of high aspect ratios, and production of larger areas of microwells. To overcome these problems, we propose a robust method for fabricating concave microwells without the need for complex high-cost facilities. This method utilizes a 30 x 30 through-hole array, several hundred micrometer-order steel beads, and magnetic force to fabricate 900 microwells in a 3 cm x 3 cm polydimethylsiloxane (PDMS) substrate. To demonstrate the applicability of our method to cell biological applications, we cultured adipose stem cells for 3 days and successfully produced spheroids using our microwell platform. In addition, we performed a magnetostatic simulation to investigate the mechanism, whereby magnetic force was used to trap the steel beads in the through-holes. We believe that the proposed microwell fabrication method could be applied to many spheroid-based cellular studies such as drug screening, tissue regeneration, stem cell differentiation, and cancer metastasis.

Formation of a Sheet-Shaped Organoid Using Rat Primary Hepatocytes for Long-Term Maintenance of Liver-Specific Functions

In recent years, use of hepatocyte aggregates has led to development of a hybrid artificial liver support system (HALSS) that has high performance. However, in general, their thickness is 100 μm or more, and generation of a dead cell layer due to oxygen exhaustion inside the aggregates has been a universal problem. The present study proposes a novel organoid culture method with better performance than previous organoid culture methods by forming a sheet-shaped organoid (organoid-sheet) with a thickness of approximately 100 μm. The cell number of the organoid-sheet was maintained at approximately 75% of the initial number at 4 days of culture. On the other hand, that of a cylindrical organoid (cylindroid), which formed inside of a plasma separation hollow fiber with 285 μm inner diameter in our previous study, decreased to approximately 50% within 2 days. The ammonia removal rate of the cells in the organoid-sheet was higher than that of the cells in the cylindroid on the first day, but it decreased during the culture time. At day 15, the rate was reduced by almost 50% with respect to the value on the first day. The cells in the cylindroid displayed a lower ammonia removal rate. A significant difference was not observed between the albumin synthesis rates of the two cultures on the first day. However, over a period of time the cells in the organoid-sheet showed a higher albumin synthesis rate than cells in the cylindroid. As this novel organoid maintains these functions for at least 1 month, it is expected to be applied for the development of a HALSS with higher performance.

Hypothermic Maintenance of Hepatocyte Spheroids

Primary hepatocytes form spheroids under some culture conditions. These spheroids exhibit many tissuelike ultrastructures and retain many liver-specific functions over a long period of time. They are attractive for many applications employing liver cells. The ability to maintain their viability and functions at a reduced temperature to allow for transportation to the site of their application will facilitate their use. Furthermore, with their structural and functional similarity, they could possibly be used as a model system for studying various liver ischemias. The effect of hypothermic treatment was assessed by oxygen consumption rate, ATP, H2O2, and caspase 8 content, as well as albumin and urea synthesis, during and posttreatment. No single outcome variable gives a superlative quantification of hypothermic damage. Taken together, the hypothermic treatment can be seen as increasingly damaging as the temperature decreases from 21°C to 15°C and 4°C. The addition of the chemical protectants glutathione, N-acetyl-L-cystein (NAC), and tauroursodeoxycholic acid (TUDCA) decreased the damaging effect of hypothermic treatment. This protection effect was even more profound when spheroids were preincubated with the protectant for 24 h, and was most prominent at 4°C. The viability of the hypothermically treated hepatocyte spheroids was confirmed by laser scanning confocal microscopy. The method reported provides a means of maintaining spheroids' viability and may allow for their distribution to application sites at a distance.

Comparison of Bioenergetic Activity of Primary Porcine Hepatocytes Cultured in Four Different Media

Primary hepatocytes have extensively been used in biochemical, pharmacological, and physiological research. Recently, primary porcine hepatocytes have been regarded as the cells of choice for bioartificial liver support systems. The optimum culture medium for hepatocytes to be used in such devices has yet to be defined. In this study we investigated the effectiveness of four culture media in driving energy metabolism of primary porcine hepatocytes. The media selected were William's E medium, medium 1640, medium 199, and hepatocyte medium. Cells (3 × 1010; viability 87 ± 6%) were isolated from weanling piglets and seeded on 90-mm plates in the above media supplemented with antibiotics and hormones at a density of 8 × 106 viable cells per plate. Using 1H NMR spectroscopy we looked at indices of glycolysis, gluconeogenesis, ketogenesis, and ureagenesis on days 2, 4, and 6 of the experiments (n = 9). We also studied urea and albumin synthesis and total P450 content. The examined metabolic pathways of the hepatocytes were maintained by all media, although there were statistically significant differences between them. All media performed well in glycolysis, ureagenesis, and albumin synthesis. William's E medium and medium 199 outperformed the rest in gluconeogenesis. Medium 199 was best in ketogenesis. Overall, medium 199 was the best at driving energy metabolism from its constituent substrates and we think that it preferentially should be used in the culture of primary porcine hepatocytes.

Microfluidic Technology for the Generation of Cell Spheroids and Their Applications

A three-dimensional (3D) tissue model has significant advantages over the conventional two-dimensional (2D) model. A 3D model mimics the relevant in-vivo physiological conditions, allowing a cell culture to serve as an effective tool for drug discovery, tissue engineering, and the investigation of disease pathology. The present reviews highlight the recent advances and the development of microfluidics based methods for the generation of cell spheroids. The paper emphasizes on the application of microfluidic technology for tissue engineering including the formation of multicellular spheroids (MCS). Further, the paper discusses the recent technical advances in the integration of microfluidic devices for MCS-based high-throughput drug screening. The review compares the various microfluidic techniques and finally provides a perspective for the future opportunities in this research area.

Cancer cell spheroids for screening of chemotherapeutics and drug-delivery systems

Over the last few decades, the most popular platform to perform high-throughput screening for viable anti-neoplastic compounds has been monolayer cell culture. However, cells in monolayer culture lose many of their in vivo characteristics. As a result, this platform provides a limited predictive value in determining the clinical outcome of the compounds of interest. Using a technique known as 3D spheroid culture, may be the answer to this conundrum. Spheroids have been shown to mimic the tissue-like properties of tumors necessary for the proper evaluation of compounds. In this review, production of cancer cell spheroids, utilization of these spheroids in understanding various therapeutic mechanisms and the potential for their use in high-throughput screening of drugs and drug-delivery systems are discussed in detail.

Pluripotent Stem Cell-Derived Hepatocyte-like Cells: A Tool to Study Infectious Disease

Purpose of Review

Liver disease is an important clinical and global problem and is the 16th leading cause of death worldwide and responsible for 1 million deaths worldwide each year. Infectious disease is a major cause of liver disease specifically and overall is even a greater cause of patient morbidity and mortality. Tools to study human liver disease and infectious disease have been lacking which has significantly hampered the study of liver disease generally and hepatotropic pathogens more specifically. Historically, hepatoma cell lines have been used for in vitro cell culture models to study infectious disease. Significant differences between human hepatoma cell lines and the human hepatocyte has hampered our understanding of hepatocyte pathogen infection and hepatocyte--pathogen interactions.

Recent Findings

Despite these limitations, great progress was made in the understanding of specific aspects of the life cycle of the canonical hepatocyte viral pathogen, Hepatitis C Virus. Over time various specific drugs targeting various proteins of the HCV virion or aspects of the HCV viral life cycle have been created that enable almost complete elimination of the virus in vitro and clinically. These drugs, direct-acting antivirals have enabled achieving sustained virologic response in over 90-95 percent of patients.

Summary

Despite the development of direct-acting antivirals and the extreme success in achieving sustained virologic response, there has only been limited success elucidating host-pathogen interactions largely due to the poor nature of the hepatoma platform. Alternative approaches are needed. Pluripotent stem cells are renewable, can be derived from a single donor and can be efficiently and reproducibly differentiated towards many cell types including ectodermal-, endodermal-, and mesodermal-derived lineages. The development of pluripotent stem cell-derived hepatocyte-like cells (iHLCS) changes the paradigm as robust cells with the phenotype and function of hepatocytes can be readily created on demand with a variety of genetic background or alterations. iHLCs are readily used as models to study human drug metabolism, human liver disease, and human hepatotropic infectious disease. In this review, we discuss the biology of the HCV virus, the use of iHLCs as models to study human liver disease, and review the current work on using iHLCs to study HCV infection.

Engineering a perfusable 3D human liver platform from iPS cells

In vitro models of human tissue are crucial to our ability to study human disease as well as develop safe and effective drug therapies. Models of single organs in static and microfluidic culture have been established and shown utility for modeling some aspects of health and disease; however, these systems lack multi-organ interactions that are critical to some aspects of drug metabolism and toxicity. Thus, as part of a consortium of researchers, we have developed a liver chip that meets the following criteria: (1) employs human iPS cells from a patient of interest, (2) cultures cells in perfusable 3D organoids, and (3) is robust to variations in perfusion rate so as to be compatible in series with other specialized tissue chips (e.g. heart, lung). In order to achieve this, we describe methods to form hepatocyte aggregates from primary and iPS-derived cells, alone and in co-culture with support cells. This necessitated a novel culture protocol for the interrupted differentiation of iPS cells that permits their removal from a plated surface and aggregation while maintaining phenotypic hepatic functions. In order to incorporate these 3D aggregates in a perfusable platform, we next encapsulated the cells in a PEG hydrogel to prevent aggregation and overgrowth once on chip. We adapted a C-trap chip architecture from the literature that enabled robust loading with encapsulated organoids and culture over a range of flow rates. Finally, we characterize the liver functions of this iHep organoid chip under perfusion and demonstrate a lifetime of at least 28 days. We envision that such this strategy can be generalized to other microfluidic tissue models and provides an opportunity to query patient-specific liver responses in vitro.

A mechanistic study on tumour spheroid formation in thermosensitive hydrogels: experiments and mathematical modelling

Thermo-reversible microgels to culture and harvest uniform-sized tumour spheroids with a narrow size-distribution.

Biofunctionalized Hydrogel Microscaffolds Promote 3D Hepatic Sheet Morphology

Development of artificial tissues providing the proper geometrical, mechanical, and environmental cues for cells is highly coveted in the field of tissue engineering. Recently, microfabrication strategies in combination with other chemistries have been utilized to capture the architectural complexity of intricate organs, such as the liver, in in vitro platforms. Here it is shown that a biofunctionalized poly (ethylene glycol) (PEG) hydrogel scaffold, fabricated using a sphere-template, facilitates hepatic sheet formation that follows the microscale patterns of the scaffold surface. The design takes advantage of the excellent diffusion properties of porous, uniform 3D hydrogel platforms, and the enhanced-cell-extracellular matrix interaction with the display of conjugated collagen type I, which in turn elicits favorable Huh-7.5 response. Collectively, the experimental findings and corresponding simulations demonstrate the importance of biofunctionalized porous scaffolds and indicate that the microscaffold shows promise in liver tissue engineering applications and provides distinct advantages over current cell sheet and hepatocyte spheroid technologies.

Spheroid culture for enhanced differentiation of human embryonic stem cells to hepatocyte-like cells

Stem cell-derived hepatocyte-like cells hold great potential for the treatment of liver disease and for drug toxicity screening. The success of these applications hinges on the generation of differentiated cells with high liver specific activities. Many protocols have been developed to guide human embryonic stem cells (hESCs) to differentiate to the hepatic lineage. Here we report cultivation of hESCs as three-dimensional aggregates that enhances their differentiation to hepatocyte-like cells. Differentiation was first carried out in monolayer culture for 20 days. Subsequently cells were allowed to self-aggregate into spheroids. Significantly higher expression of liver-specific transcripts and proteins, including Albumin, phosphoenolpyruvate carboxykinase, and asialoglycoprotein receptor 1 was observed. The differentiated phenotype was sustained for more than 2 weeks in the three-dimensional spheroid culture system, significantly longer than in monolayer culture. Cells in spheroids exhibit morphological and ultrastructural characteristics of primary hepatocytes by scanning and transmission electron microscopy in addition to mature functions, such as biliary excretion of metabolic products and cytochrome P450 activities. This three-dimensional spheroid culture system may be appropriate for generating high quality, functional hepatocyte-like cells from ESCs.

Hollow fiber bioartificial liver utilizing collagen-entrapped porcine hepatocyte spheroids

A xenogeneic hollow fiber bioreactor utilizing collagen-entrapped dispersed hepatocytes has been developed as an extracorporeal bioartificial liver (BAL) for potential treatment of acute human fulminant hepatitis. Prolonged viability, enhanced liver-specific functions, and differentiated state have been observed in primary porcine hepatocytes cultivated as spheroids compared to dispersed hepatocytes plated on a monolayer. Entrapment of spheroids into the BAL can potentially improve performance over the existing device. Therefore, studies were conducted to evaluate the feasibility of utilizing spheroids as the functionally active component of our hybrid device. Confocal microscopy indicated high viability of spheroids entrapped into cylindrical collagen gel. Entrapment of spheroids alone into collagen gel showed reduced ability to contract collagen gel. By mixing spheroids with dispersed cells, the extent of collagen gel contraction was increased. Hepatocyte spheroids collagen-entrapped into BAL devices were maintained for over 9 days. Assessment of albumin synthesis and ureagenesis within a spheroid-entrapment BAL indicated higher or at least as high activity on a per-cell basis compared to a dispersed hepatocyte-entrapment BAL device. Clearance of 4-methylumbelliferone to its glucuronide was detected throughout the culture period as a marker of phase II conjugation activity. A spheroid-entrapment bioartificial liver warrants further studies for potential human therapy. (c) 1996 John Wiley & Sons, Inc.

Development of a bioartificial liver employing xenogeneic hepatocytes

Liver failure is a major cause of mortality. A bioartificial liver (BAL) employing isolated hepatocytes can potentially provide temporary support for liver failure patients. We have developed a bioartificial liver by entrapping hepatocytes in collagen loaded in the luminal side of a hollow fiber bioreactor. In the first phase of development, liver-specific metabolic activities of biosynthesis, biotransformation and conjugation were demonstrated. Subsequently anhepatic rabbits were used to show that rat hepatocytes continued to function after the BAL was linked to the test animal. For scale-up studies, a canine liver failure model was developed using D-galactosamine overdose. In order to secure a sufficient number of hepatocytes for large animal treatment, a collagenase perfusion protocol was established for harvesting porcine hepatocytes at high yield and viability. An instrumented bioreactor system, which included dissolved oxygen measurement, pH control, flow rate control, an oxygenator and two hollow fiber bioreactors in series, was used for these studies. An improved survival of dogs treated with the BAL was shown over the controls. In anticipated clinical applications, it is desirable to have the liver-specific activities in the BAL as high as possible. To that end, the possibility of employing hepatocyte spheroids was explored. These self-assembled spheroids formed from monolayer culture exhibited higher liver-specific functions and remained viable longer than hepatocytes in a monolayer. To ease the surface requirement for large-scale preparation of hepatocyte spheroids, we succeeded in inducing spheroid formation in stirred tank bioreactors for both rat and porcine hepatocytes. These spheroids formed in stirred tanks were shown to be morphologically and functionally indistinguishable from those formed from a monolayer. Collagen entrapment of these spheroids resulted in sustaining their liver-specific functions at higher levels even longer than those of spheroids maintained in suspension. For use in the BAL, a mixture of spheroids and dispersed hepatocytes was used to ensure a proper degree of collagen gel contraction. This mixture of spheroids and dispersed cells entrapped in the BAL was shown to sustain the high level of liver-specific functions. The possibility of employing such a BAL for improved clinical performance warrants further investigations.

Formation of porcine hepatocyte spherical multicellular aggregates (spheroids) and analysis of drug metabolic functions

Porcine hepatocytes are used in the hybrid artificial liver support system that we are developing because of their high level of liver functions in vitro and because human hepatocytes can not be used in Japan for ethical reasons. Spherical multicellular aggregates or spheroids have been found to be effective in vitro for long-term maintenance of liver functions. Therefore, we formed spherical multicellular aggregates (spheroids) of primary porcine hepatocytes using a polyurethane foam (PUF) as a culture substratum and analyzed their drug metabolic functions in vitro. Primary porcine hepatocytes inoculated into the pores of a flat PUF plate (25 x 25 x 1 mm), spontaneously formed spheroids within the range of 100 to 150 mum in diameter 24 to 36 h after inoculation. The formed spheroids were attached to the bottom surface of the PUF pores, and their morphology and viability were maintained for more than 12 days. The P-450 activity in the spheroids of porcine hepatocytes was demonstrated by detecting production of monoethylglycinexylidide from lidocaine. In addition, the conjugation enzyme activity was demonstrated by detecting glucuronidation and sulfation of acetaminophen. These activities were maintained for 12 days at a level twice as high as in the monolayer culture. This result shows that the porcine hepatocyte spheroids formed by using PUF can maintain the drug metabolic functions important in a hybrid artificial liver device. Consequently, culturing porcine hepatocyte spheroids using PUF seems to be promising for development of a hybrid artificial liver.

Three-dimensional co-culture of hepatocytes and stellate cells

Hepatocytes self-assemble in culture to form compacted spherical aggregates, or spheroids, that mimic the structure of the liver by forming tight junctions and bile canalicular channels. Hepatocyte spheroids thus resemble the liver to a great extent. However, liver tissue contains other cell types and has bile ducts and sinusoids formed by endothelial cells. Reproducing 3-D co-culture in vitro could provide a means to develop a more complex tissue-like structure. Stellate cells participate in revascularization after liver injury by excreting between hepatocytes a laminin trail that endothelial cells follow to form sinusoids. In this study we investigated co-culture of rat hepatocytes and a rat hepatic stellate cell line, HSC-T6. HSC-T6, which does not grow in serum-free spheroid medium, was able to grow under co-culture conditions. Using a three-dimensional cell tracking technique, the interactions of HSC-T6 and hepatocyte spheroids were visualized. The two cell types formed heterospheroids in culture, and HSC-T6 cell invasion into hepatocyte spheroids and subsequent retraction was observed. RT-PCR revealed that albumin and cytochrome P450 2B1/2 expression were better maintained in co-culture conditions. These three-dimensional heterospheroids provide an attractive system for in vitro studies of hepatocyte-stellate cell interactions.

Scalable robotic biofabrication of tissue spheroids

Development of methods for scalable biofabrication of uniformly sized tissue spheroids is essential for tissue spheroid-based bioprinting of large size tissue and organ constructs. The most recent scalable technique for tissue spheroid fabrication employs a micromolded recessed template prepared in a non-adhesive hydrogel, wherein the cells loaded into the template self-assemble into tissue spheroids due to gravitational force. In this study, we present an improved version of this technique. A new mold was designed to enable generation of 61 microrecessions in each well of a 96-well plate. The microrecessions were seeded with cells using an EpMotion 5070 automated pipetting machine. After 48 h of incubation, tissue spheroids formed at the bottom of each microrecession. To assess the quality of constructs generated using this technology, 600 tissue spheroids made by this method were compared with 600 spheroids generated by the conventional hanging drop method. These analyses showed that tissue spheroids fabricated by the micromolded method are more uniform in diameter. Thus, use of micromolded recessions in a non-adhesive hydrogel, combined with automated cell seeding, is a reliable method for scalable robotic fabrication of uniform-sized tissue spheroids.

Internally self-assembled thermoreversible gelling emulsions: ISAsomes in methylcellulose, kappa-carrageenan, and mixed hydrogels

Self-assembled thermo-gelling emulsions were developed by blending internally self-assembled particles (ISAsomes) with thermoreversible polysaccharide hydrogels of methylcellulose (MC), kappa-carrageenan (KC), and their 1:1 mixture. In this way, the hierarchical structure of ISAsome samples was successfully promoted. The gelified polymer network corresponds to the highest level of the hierarchical structure and as such represents the capturing matrix for the medium structural level, i.e., dispersed emulsion particles, which are further internally structured as the lowest level of structure. Utilizing small-angle X-ray scattering, differential scanning calorimetry, dynamic light scattering, and oscillatory rheological experiments in the temperature regime from 20 to 70 degrees C, we were able to show that the ISAsomes stay practically intact during such embedment into a hydrogel matrix retaining its internal self-assembled structure and its functionality. The characteristic sol-gel and gel-sol transition temperatures of the ISAsome-loaded hydrogel samples showed a slight shift in comparison to the unloaded hydrogel samples. Furthermore, we found that MC is actually able to stabilize the ISAsomes at higher temperatures (tests were conducted up to 90 degrees C). Gels made from MC and KC show quite different features in terms of rheology and differential scanning calorimetry. However, the most interesting results were obtained for the ISAsome-loaded MC-KC (1:1) gelifying system, which behaves as a low- and high-temperature gel with a narrow intermediate temperature window where it is a sol. This specific thermal behavior allows for easy temperature tuning of the system's aggregate state as well as the internal self-assembled structure. As such, this system is suggested to be further tested as the potential media for a temperature-controlled burst/sustained release media of various hydrophilic, hydrophobic, or amphiphilic guest functional molecules.

Recent advances in three-dimensional multicellular spheroid culture for biomedical research

Many types of mammalian cells can aggregate and differentiate into 3-D multicellular spheroids when cultured in suspension or a nonadhesive environment. Compared to conventional monolayer cultures, multicellular spheroids resemble real tissues better in terms of structural and functional properties. Multicellular spheroids formed by transformed cells are widely used as avascular tumor models for metastasis and invasion research and for therapeutic screening. Many primary or progenitor cells on the other hand, show significantly enhanced viability and functional performance when grown as spheroids. Multicellular spheroids in this aspect are ideal building units for tissue reconstruction. Here we review the current understanding of multicellular spheroid formation mechanisms, their biomedical applications, and recent advances in spheroid culture, manipulation, and analysis techniques.

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.

Cell encapsulation in sub-mm sized gel modules using replica molding

For many types of cells, behavior in two-dimensional (2D) culture differs from that in three-dimensional (3D) culture. Among biologists, 2D culture on treated plastic surfaces is currently the most popular method for cell culture. In 3D, no analogous standard method—one that is similarly convenient, flexible, and reproducible—exists. This paper describes a soft-lithographic method to encapsulate cells in 3D gel objects (modules) in a variety of simple shapes (cylinders, crosses, rectangular prisms) with lateral dimensions between 40 and 1000 μm, cell densities of 10⁵ – 10⁸ cells/cm³, and total volumes between 1×10⁻⁷ and 8×10⁻⁴ cm³. By varying (i) the initial density of cells at seeding, and (ii) the dimensions of the modules, the number of cells per module ranged from 1 to 2500 cells. Modules were formed from a range of standard biopolymers, including collagen, Matrigel™, and agarose, without the complex equipment often used in encapsulation. The small dimensions of the modules allowed rapid transport of nutrients by diffusion to cells at any location in the module, and therefore allowed generation of modules with cell densities near to those of dense tissues (10⁸ – 10⁹ cells/cm³). This modular method is based on soft lithography and requires little special equipment; the method is therefore accessible, flexible, and well suited to (i) understanding the behavior of cells in 3D environments at high densities of cells, as in dense tissues, and (ii) developing applications in tissue engineering.

Fabrication of a modular tissue construct in a microfluidic chip

By combining microfluidics and soft-lithographic molding of gels containing mammalian cells, a device for three-dimensional (3D) culture of mammalian cells in microchannels was developed. Native components of the extracellular matrix, including collagen or Matrigel, made up the matrix of each molded piece (module) of cell-containing gel. Each module had at least one dimension below approximately 300 microm; in modules of these sizes, the flux of oxygen, nutrients, and metabolic products into and out of the modules was sufficient to allow cells in the modules to proliferate to densities comparable to those of native tissue (10(8)-10(9) cells cm(-3)). Packing modules loosely into microfluidic channels and chambers yielded structures permeated with a network of pores through which cell culture medium could flow to feed the encapsulated cells. The order in the packed assemblies increased as the width of the microchannels approached the width of the modules. Multiple cell types could be spatially organized in the small microfluidic channels. Recovery and analysis of modules after 24 h under constant flow of medium (200 microL h(-1)) showed that over 99% of encapsulated cells survived this interval in the microfluidic chamber.

Modular tissue engineering: fabrication of a gelatin-based construct

Modular tissue-engineered constructs are assembled from sub-millimetre-sized cylindrical modules which are seeded with a surface layer of endothelial cells. The resulting construct is permeated by a network of interconnected, endothelial cell-lined channels to facilitate blood perfusion and nutrient delivery. To provide adequate stiffness, yet consist of a substrate suitable for endothelial cells, modular constructs were fabricated from gelatin, the denatured form of collagen. Gelatin modules containing HepG2 cells or spheroids were fabricated using a sieving process. A surface layer of bovine aortic endothelial cells completely covering the modules was generated within 1 week of seeding. Modules were assembled into constructs within a flow circuit and flow rate-pressure difference profiles measured. Fluid perfusion resulted in negligible construct compaction, even at high flow rates. It was necessary, however, to crosslink the gelatin modules with glutaraldehyde to prevent dissolution at 37 degrees C. This resulted in a significant loss of cell viability within the modules. A strategy to enable non-toxic crosslinking of the gelatin modules is required to fabricate constructs containing viable cells.

Morphological and functional analysis of rat hepatocyte spheroids generated on poly(L-lactic acid) polymer in a pulsatile flow bioreactor

Liver neo-tissue suitable for transplantation has not been established. Primary rat hepatocytes were cultured on three-dimensional biodegradable polymer matrices in a pulsatile flow bioreactor with the intention of inducing tissue formation and improving cell survival. Functional and structural analysis of the hepatocytes forming liver neo-tissue was performed. Biodegradable poly(L-lactic acid) (PLLA) polymer discs were seeded with 4 x 10(6) primary rat hepatocytes each, were exposed to a pulsatile medium flow of 24 mL/min for 1, 2, 4, or 6 days and were investigated for monoethylglycinexylidine (MEGX) formation, ammonia detoxification, Cytokeratin 18 (CK18) expression, and preserved glycogen storage. Fine structural details were obtained using scanning and transmission electron microscopy. Spheroids of viable hepatocytes were formed. MEGX-specific production was maintained and ammonia removal capacity remained high during the entire flow-culture period of 6 days. CK18 distribution was normal. Periodic-acid- Schiff reaction demonstrated homogenous glycogen storage. The hepatocytes reassembled to form intercellular junctions and bile canaliculi. Functional and morphological analysis of rat hepatocytes forming spheroids in a pulsatile flow bioreactor indicated preserved and intact hepatocyte morphology and specific function. Pulsatile flow culture on PLLA scaffolds is a promising new method of hepatic tissue engineering leading to liver neo-tissue formation.

Regulation of hepatocyte cell cycle progression and differentiation by type I collagen structure

Cell behavior is strongly influenced by the extracellular matrix (ECM) to which cells adhere. Both chemical determinants within ECM molecules and mechanical properties of the ECM network regulate cellular response, including proliferation, differentiation, and apoptosis. Type I collagen is the most abundant ECM protein in the body with a complex structure that can be altered in vivo by proteolysis, cross-linking, and other processes. Because of collagen's complex and dynamic nature, it is important to define the changes in cell response to different collagen structures and its underlying mechanisms. This chapter reviews current knowledge of potential mechanisms by which type I collagen affects cell behavior, and it presents data that elucidate specific intracellular signaling pathways by which changes in type I collagen structure differentially regulate hepatocyte cell cycle progression and differentiation. A network of polymerized fibrillar type I collagen (collagen gel) induces a highly differentiated but growth-arrested phenotype in primary hepatocytes, whereas a film of monomeric collagen adsorbed to a rigid dish promotes cell cycle progression and dedifferentiation. Studies presented here demonstrate that protein kinase A (PKA) activity is significantly elevated in hepatocytes on type I collagen gel relative to collagen film, and inhibition of this elevated PKA activity can promote hepatocyte cell cycle progression on collagen gel. Additional studies are presented that examine changes in hepatocyte cell cycle progression and differentiation in response to increased rigidity of polymerized collagen gel by fiber cross-linking. Potential mechanisms underlying these cellular responses and their implications are discussed.

Improvement of C3A cell metabolism for usage in bioartificial liver support systems

BACKGROUND/AIMS

The use of cell lines in bioartificial liver support systems (BALSS) to treat fulminant hepatic failure (FHF) is hindered by their reduced metabolic functions, which could be further decreased by the patient's serum/plasma. Hence, the aim of this study was to (i) test the effect of the FHF serum on C3A cell metabolism; (ii) precondition the cells to improve their metabolic capacity.

METHODS

C3A cells were preconditioned in a medium developed at the University of Edinburgh (UoE) or a 10% FHF serum medium. Metabolism capacity was assessed on days 3, 7 and 10 and compared with primary porcine hepatocytes. Preconditioned-cell metabolism was reassessed after (i) passage and (ii) incubation with 10% FHF serum.

RESULTS

UoE-preconditioned cells showed time-dependent increase in gluconeogenesis (500%), ureogenesis (200%), galactose elimination (240%) albumin synthesis (250%). These results were in the same order of magnitude as the ones obtained with primary porcine hepatocytes and were further enhanced by cell passage. UoE-preconditioning prevented the decrease of metabolism induced by acute incubation with FHF serum on control C3A cells. Preconditioning with FHF serum did not improve cell metabolism.

CONCLUSIONS

Cell preconditioning with UoE-medium increases metabolic capacity and would greatly improve BALSS efficacy.

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.

Efficacy of a larger version of the hybrid artificial liver support system using a polyurethane foam/spheroid packed-bed module in a warm ischemic liver failure pig model for preclinical experiments

We have reported the usefulness of a polyurethane foam packed-bed culture system of hepatocyte spheroids as a hybrid artificial liver support system (PUF-HALSS). The aim of this study was to evaluate in detail the efficacy in serum parameters regarding the liver function of a larger version of the PUF-HALSS containing 2 x 10(10) porcine hepatocytes for clinical use in warm ischemic liver failure pigs. Warm ischemic liver failure pigs weighing 25 kg were divided into two groups: (1) a control group (n = 3), in which each pig was attached to a PUF-HALSS without hepatocytes, and (2) a HALSS group (n = 3), in which each pig was attached to a PUF-HALSS. In the HALSS group, the increase of blood ammonia was completely suppressed and blood lactate levels were significantly suppressed. The Fisher's ratio was better maintained, and the increase of total bile acid, glycochenodeoxycholic acid, and taurochenodeoxycholic acid was significantly suppressed in the HALSS group. Serum creatinine levels were significantly lower, and blood glucose levels were significantly higher in the HALSS group. Serum levels of tumor necrosis factor- a were not elevated in either group. In conclusion, the larger version of the PUF-HALSS demonstrated many advantages as a liver support system in warm ischemic liver failure pigs.

Manipulation of in vitro toxicant sensors in an ultrasonic standing wave

Multi-cellular spheroids are increasingly employed as in vitro sensors of toxicants and a single spheroid can be used as a test object. An ultrasonic standing wave trap (USWT) can hold small particles in a medium-flowing system. This study investigated the conditions for holding HepG2 spheroids in an USWT and its relevance to use in toxicity testing. It can take many hours to reach a detectable end point of cell damage in a standard cellular in vitro toxicant assay and the process might be accelerated through increased sample flow past the spheroid. A USWT was employed here to levitate and hold HepG2 spheroids stationary against a flow of 3 mm s(-1) when the acoustic pressure amplitude is 1.9 MPa. The ultrasonic drive frequency was 1.64 MHz. Acoustic microstreaming in the standing wave chamber generated 1 mm s(-1) flow past a levitated spheroid-scale (80 microm diameter) latex particle in the absence of sample through-flow. The conditions required to form aggregates of cells of a HepG2 cell line in a single half wavelength ultrasonic standing wave mini-chambers are also described here. It is argued that the manipulation capabilities demonstrated may have potential in increasing the efficiency of in vitro toxicant detection by spheroids. Preliminary, visual (unquantified) fluorescence microscopy observations of spheroids levitated in the standing wave in the presence of the toxicant DL-propranolol do suggest accelerated loss of viability compared with controls.

Biochemical and functional changes of rat liver spheroids during spheroid formation and maintenance in culture: II. nitric oxide synthesis and related changes

Liver cells isolated from intact tissue can reaggregate to form three-dimensional, multicellular spheroids in vitro. During this process, cells undergo a histological and environmental change. How cells respond biochemically to this change has not been studied in detail previously. We have investigated some biochemical changes in rat liver cells during the formation and maintenance of spheroids. Liver cells were isolated from male Sprague rats and spheroids cultured by a gyrotatory-mediated method. Liver cells were shown to respond to the isolation procedure and the formation of spheroids triggered histological environmental changes that increased arginine uptake, nitric oxide (NO) and urea syntheses, as well as raised levels of GSH, GSSG, glutamic acid and aspartic acid secretion within the first couple of days after cell isolation. Levels were maintained at a relatively stable level in the mature spheroids (>5 days) over the 3 week period of observation. P450 1A1 activity was lost in the first 2 days and gradually recovered thereafter. This study, for the first time, shows that liver cells after isolation and during spheroid formation actively uptake arginine and increase NO and urea syntheses. A high level of NO is likely to play an important role in modulating a series of biochemical changes in liver cells. It is considered that liver cells actively respond to the 'challenge' induced by the isolation procedure and subsequent histological environmental changes, and biochemical modulation and instability result. The stable cell-cell contacts and histological environment in mature spheroids permit and support functional recovery and maintenance in vitro. This period of stability permits the use of spheroids in toxicity studies to establish acute and chronic paradigms.

Ammonium detoxification performed by porcine hepatocyte spheroids in a bioartificial liver for pediatric use: preliminary report

Bioartificial liver devices are alternative therapies for patients suffering from acute hepatic failure or metabolic defects. Here, we show a bioartificial device, developed with a cartridge used for pediatric hemofiltration and spheroids of porcine hepatocytes housed in the extracapillary space of the cartridge. The cartridge was attached to a robotic arm that supplied a continuous, oscillatory movement. It was connected through the capillary circulation to a neonatal membrane oxygenator contain-ing human blood supplemented with ammonium and diazepam. A decrease in ammonium concentration was observed, reaching an almost 70% decrease upon 9 h of operation. In addition, urea was detected and diazepam metabolism proved from the fourth hour of operation. It is worth mentioning that the system described was assembled with commercially available components for current clinical use. The setup may be done in a short period, thus eliminating long-term culture times and the need for cell anchoring to matrices.

Characterisation of some cytotoxic endpoints using rat liver and HepG2 spheroids as in vitro models and their application in hepatotoxicity studies. I. Glucose metabolism and enzyme release as cytotoxic markers

Cytotoxicity endpoints, spontaneous glucose secretion/consumption and LDH and gamma-GT release, were characterised in rat liver and HepG2 spheroids as in vitro models for toxicology studies. Preprepared rat liver spheroids and HepG2 spheroids cultured in a six-well plate format were exposed to varying concentrations of galactosamine, propranolol, diclofenac, and paracetamol. All four model toxins significantly affected glucose secretion, which agreed well with LDH and/or gamma-GT release in rat liver spheroids. These toxins also significantly increased LDH and/or gamma-GT release in HepG2 spheroids. Whereas glucose consumption in HepG2 spheroids did not show conclusive results, LDH activities in both types of spheroids were similar and their levels were relatively high. Accordingly, the level of LDH leakage in both types of spheroids was much higher than gamma-GT after exposure to the toxins. In contrast, gamma-GT activity in HepG2 spheroids was sixfold higher than that in rat liver spheroids. This study revealed that galactosamine interfered with the gamma-GT assay and paracetamol interfered with the LDH assay. It demonstrated, for the first time, that glucose secretion by liver spheroids can be used as a functional indicator of cytotoxicity. Test compounds may interfere with enzymatic assays as indicated by LDH and gamma-GT release in this study. Combining functional parameters together with two or more indicators of enzyme releases can provide a reliable cytotoxicity evaluation. Liver and HepG2 spheroids as in vitro models showed good predictions in chemical-induced hepatic cytotoxicity.

Characterisation of some cytotoxic endpoints using rat liver and HepG2 spheroids as in vitro models and their application in hepatotoxicity studies. II. Spheroid cell spreading inhibition as a new cytotoxic marker

Cells in liver spheroids and Hep G2 spheroids transferred from gyrotatory culture conditions and maintained in normal static culture conditions will spread out at the edges. Based on this observation, we developed a new test called the Spheroid Cell Spreading Inhibition Test (SCSIT) to screen hepatic cytotoxicity of xenobiotics and determine the spheroid cell spreading inhibition concentration (SCSIC) of test chemicals. Four model hepatoxicants, D-galactosamine, propranolol, diclofenac, and paracetamol, were studied with SCSIT in both rat liver and HepG2 spheroids. Both liver and HepG2 spheroids were prepared under gyrotatory culture conditions and used at 6 days in vitro. The results showed that all four hepatotoxicants tested inhibited cell spreading in liver spheroids (D-galactosamine at 20 mM, propranolol at 125 microM, diclofenac at 500 microM, and paracetamol at 25 mM) and HepG2 spheroids (D-galactosamine at 16 mM, propranolol at 125 microM, diclofenac at 500 microM, and paracetamol at 25 mM). The SCSIT results agreed with the conventional cytotoxic indicators, release of LDH and/or gamma-GT and the inhibition of glucose secretion from rat liver spheroids. In conclusion, this study, for the first time, described the biological characteristics of liver and HepG2 spheroid cell spreading and demonstrates its application in hepatic cytotoxicity studies. This method may be used in testing in vitro "acute" toxicity, comparing relative cytotoxicity and generating reference concentrations for subsequent studies. Therefore, SCSIT could be a useful tool for screening hepatotoxicity relevant to preclinical lead optimization and compound library screening.