Application of spheroid culture to human hepatocytes and maintenance of their differentiation

Two-Dimensional Cellular Patterning on a Polymer Film Based on Interfacial Stiffness

The mechanical properties in the outermost region of a polymer film strongly affect various material functions. We here propose a novel and promising strategy for the two-dimensional regulation of the mechanical properties of a polymer film at the water interface based on an inkjet drawing of silica nanoparticles (SNPs) underneath it. A film of poly(2-hydroxyethyl methacrylate) (PHEMA), which exhibits excellent bioinertness properties at the water interface, was well fabricated on a substrate with a pattern of SNPs. X-ray photoelectron spectroscopy and atomic force microscopy confirmed that the surface of the PHEMA film was flat and chemically homogeneous. However, the film surface was in-plane heterogeneous in stiffness due to the presence of the underlying SNP lines. It was also noted that NIH/3T3 fibroblast cells selectively adhered and formed aggregates on the areas under which an SNP line was drawn.

Characterization of Gastrospheres Using 3D Coculture System

To understand the molecular mechanisms involved in gastric disorders and regeneration, we need an in vitro tridimensional (3D) culture model, which can mimic the in vivo gastric microenvironment. A 3D coculture system named gastrosphere is proposed herein, composed of primary human gastric epithelial and stromal cells. The primary cultures were obtained from endoscopic gastric biopsies, and after mechanical and enzymatic dispersion, epithelial (HGE3) and stromal (HGS12) cells were expanded. After extensive immunocytochemical characterization, cells were seeded onto 96-well round bottom plates previously covered with 1% agarose. Cells were cultured in KM-F12 culture medium with 10% fetal bovine serum (FBS), antibiotics, and antimycotics, in humidified air at 37 °C and atmosphere containing 5% CO₂ for 72 h or until spheres formation. Then gastrospheres were carefully transferred to a rotary cell culture system (RCCS-4), and maintained for 07, 14, 21, and 28 days. Gastrospheres were morphologically characterized by immunocytochemistry [cytokeratins (CK), vimentin, α-smooth muscle actin (α-SMA), laminin (LN), fibronectin (FN), and type IV collagen (CIV), proliferating cell nuclear antigen (PCNA)], and electron microscopy. In gastrospheres, the cytokeratin-positive epithelial cells were found in the outer layer, while vimentin-positive stromal cells were localized in the center of the gastrospheres. PCNA+ cells were mainly seen at the peripheral and in the intermediary region while nestin+ cells were also depicted in the latter zone. Scanning electron microscopy revealed groups of cohesive gastric cells at the periphery, while transmission electron microscopy demonstrated some differentiated mucous-like or zymogenic-like cells in the periphery and stromal structures located at the center of the 3D structures. Extracellular matrix was deposed between cells. Our data suggest that in vitro gastrospheres recapitulate the in vivo gastric microenvironment.

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

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

Sarcoma Spheroids and Organoids-Promising Tools in the Era of Personalized Medicine

Cancer treatment is rapidly evolving toward personalized medicine, which takes into account the individual molecular and genetic variability of tumors. Sophisticated new in vitro disease models, such as three-dimensional cell cultures, may provide a tool for genetic, epigenetic, biomedical, and pharmacological research, and help determine the most promising individual treatment. Sarcomas, malignant neoplasms originating from mesenchymal cells, may have a multitude of genomic aberrations that give rise to more than 70 different histopathological subtypes. Their low incidence and high level of histopathological heterogeneity have greatly limited progress in their treatment, and trials of clinical sarcoma are less frequent than trials of other carcinomas. The main advantage of 3D cultures from tumor cells or biopsy is that they provide patient-specific models of solid tumors, and they overcome some limitations of traditional 2D monolayer cultures by reflecting cell heterogeneity, native histologic architectures, and cell-extracellular matrix interactions. Recent advances promise that these models can help bridge the gap between preclinical and clinical research by providing a relevant in vitro model of human cancer useful for drug testing and studying metastatic and dormancy mechanisms. However, additional improvements of 3D models are expected in the future, specifically the inclusion of tumor vasculature and the immune system, to enhance their full ability to capture the biological features of native tumors in high-throughput screening. Here, we summarize recent advances and future perspectives of spheroid and organoid in vitro models of rare sarcomas that can be used to investigate individual molecular biology and predict clinical responses. We also highlight how spheroid and organoid culture models could facilitate the personalization of sarcoma treatment, provide specific clinical scenarios, and discuss the relative strengths and limitations of these models.

Scaffold-Free, Size-Controlled Three-Dimensional Culture of Rabbit Adipose-Derived Stem Cells

Adipose-derived stem cells are capable of self-renewal and differentiation along multiple cell lineages, and have potential applications in a wide range of therapies. ASCs are commonly cultured as monolayers on tissue culture plastic, but there are indications that they may lose their cell-specific properties with time in vitro. There has been a growing interest in culturing adherent cells using three-dimensional techniques based on the understanding that growing cells on plastic surfaces cannot truly recapitulate 3D in vivo conditions. Here we describe a novel method for generating and culturing rabbit ASCs as scaffold-free 3D cell aggregates using micropatterned wells via a forced aggregation technique.

Enhanced hepatogenic differentiation of bone marrow derived mesenchymal stem cells on liver ECM hydrogel

Bone marrow derived mesenchymal stem cells (BM-MSC) is a promising alternative cell source to primary hepatocytes because of their ability to differentiate into hepatocyte-like cells. However, their inability to differentiate efficiently and potential to turn into myofibroblasts restrict their applications. This study developed a plate coating from the liver extracellular matrix (ECM) and investigated its ability in facilitating the BM-MSCs proliferation, hepatic differentiation, and hepatocyte-specific functions during in vitro culture. After 28-day culture, BM-MSCs on the ECM coating showed hepatocyte-like morphology, and certain cells took up low-density lipoprotein. Synthesis of albumin, urea, and anti-alpha-fetoprotein, as well as expression of certain hepatic markers, in cells cultured on ECM were higher than cells cultured on non-coated and Matrigel-coated plates. mRNA levels of CYP3A4, albumin, CK18, and CYP7A1 in cells on ECM coating were significantly higher than cells cultured on the non-coating environment. In conclusion, viability and hepatogenic differentiation of BM-MSCs cultured on both Matrigel and ECM coating were significantly enhanced compared with those cultured on non-coated plates. Moreover, the liver ECM coating induced additional metabolic functions relative to the Matrigel coating. The liver ECM hydrogel preserves the natural composition, promotes simple gelling, induces efficient stem cell hepatogenic differentiation, and may have uses as an injectable intermedium for hepatocytes. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 829-838, 2018.

Hepatocyte Transplantation in the Long Evans Cinnamon Rat Model of Wilson's Disease

Wilson's disease (WD), caused by a mutation in the P-type copper transporting ATPase (Atp7b) gene, results in excessive accumulation of copper in the liver. Long Evans Cinnamon rats (LEC) bear a mutation in the atp7b gene and share clinical characteristics of human WD. To explore hepatocyte transplantation (HT) as therapy for metabolic liver diseases, 8-week-old LEC rats (n = 12) were transplanted by intrasplenic injection of hepatocytes from donor Long Evans (LE) rats. Immunosuppression was maintained with intraperitoneal tacrolimus. The success of HT was monitored at 24 weeks of life. Serum aminotransferases and bilirubin peaked at 14–21 weeks in both HT rats and nontransplanted controls, but at 24 weeks, survival was 97% in LEC-HT versus 63% in controls. All transplanted rats showed restored biliary copper excretion and reduced liver iron concentration associated with increased ceruloplasmin oxidase activity. Liver tissue expressed atp7b mRNA (11.9 ± 13.6%) indicative of engraftment of normal cells in 7 of 12 HT rats, associated with a reduced liver copper concentration compared to untreated LEC rats. Periportal islets of normal appearing hepatocytes, recognized by atp7b antibody, were observed in transplanted livers while lobular host cells showed persistent pleomorphic changes and inflammatory infiltrates. In conclusion, transplantation of normal hepatocytes prevented fulminant hepatitis, reduces chronic inflammation, and improved 6-month survival in LEC rats. Engraftment of transplanted cells, which express atp7b mRNA, repopulated the recipient liver with normal functional capacity.

Generation of non-viral, transgene-free hepatocyte like cells with piggyBac transposon

Somatic cells can be reprogrammed to induced hepatocyte-like cells (iHeps) by overexpressing certain defined factors in direct reprogramming techniques. Of the various methods to deliver genes into cells, typically used genome-integrating viral vectors are associated with integration-related adverse events such as mutagenesis, whereas non-integrating viral vectors have low efficiency, making viral vectors unsuitable for clinical application. Therefore, we focused on developing a transposon system to establish a non-viral reprogramming method. Transposons are unique DNA elements that can be integrated into and removed from chromosomes. PiggyBac, a type of transposon, has high transduction efficiency and cargo capacity, and the integrated transgene can be precisely excised in the presence of transposase. This feature enables the piggyBac vector to achieve efficient transgene expression and a transgene-free state, thus making it a promising method for cell reprogramming. Here, we attempted to utilize the piggyBac transposon system to generate iHeps by integrating a transgene consisting of Hnf4a and Foxa3, and successfully obtained functional iHeps. We then demonstrated removal of the transgene to obtain transgene-free iHeps, which still maintained hepatocyte functions. This non-viral, transgene-free reprogramming method using the piggyBac vector may facilitate clinical applications of iHeps in upcoming cell therapy.

Enhanced hepatic differentiation of rat bone marrow-derived mesenchymal stem cells in spheroidal aggregate culture on a decellularized liver scaffold

In the present study, we aimed to determine whether the combination of aggregate culture and decellularized liver scaffolds (DLSs) promoted the hepatic differentiation of murine bone marrow-derived mesenchymal stem cells (BM-MSCs) into high yields of mature hepatocytes in vitro. Four culturing methods for differentiation [single cell (2D), spheroids (3D), 2D + DLS and 3D + DLS] were studied. To determine the differentiation stages of the MSCs, RT-qPCR of the hepatocyte genes, immunostaining of hepatocyte markers, and functional analyses were all performed. Compared with the other groups, hepatocyte-like cells which differentiated from BM-MSC spheroids on extracellular matrix (ECM) exhibited more intensive staining of stored glycogen, an elevated level of urea biosynthesis and albumin secretion as well as the higher expression of hepatocyte-specific genes. Our results indicated that DLSs combined with spheroidal aggregate culture may be used as an effective method to facilitate the hepatic maturation of BM-MSCs and may have future applications in stem cell-based liver regenerative medicine.

Emerging In Vitro Liver Technologies for Drug Metabolism and Inter-Organ Interactions

In vitro liver models provide essential information for evaluating drug metabolism, metabolite formation, and hepatotoxicity. Interfacing liver models with other organ models could provide insights into the desirable as well as unintended systemic side effects of therapeutic agents and their metabolites. Such information is invaluable for drug screening processes particularly in the context of secondary organ toxicity. While interfacing of liver models with other organ models has been achieved, platforms that effectively provide human-relevant precise information are needed. In this concise review, we discuss the current state-of-the-art of liver-based multiorgan cell culture platforms primarily from a drug and metabolite perspective, and highlight the importance of media-to-cell ratio in interfacing liver models with other organ models. In addition, we briefly discuss issues related to development of optimal liver models that include recent advances in hepatic cell lines, stem cells, and challenges associated with primary hepatocyte-based liver models. Liver-based multiorgan models that achieve physiologically relevant coupling of different organ models can have a broad impact in evaluating drug efficacy and toxicity, as well as mechanistic investigation of human-relevant disease conditions.

Deterministically patterned biomimetic human iPSC-derived hepatic model via rapid 3D bioprinting

The functional maturation and preservation of hepatic cells derived from human induced pluripotent stem cells (hiPSCs) are essential to personalized in vitro drug screening and disease study. Major liver functions are tightly linked to the 3D assembly of hepatocytes, with the supporting cell types from both endodermal and mesodermal origins in a hexagonal lobule unit. Although there are many reports on functional 2D cell differentiation, few studies have demonstrated the in vitro maturation of hiPSC-derived hepatic progenitor cells (hiPSC-HPCs) in a 3D environment that depicts the physiologically relevant cell combination and microarchitecture. The application of rapid, digital 3D bioprinting to tissue engineering has allowed 3D patterning of multiple cell types in a predefined biomimetic manner. Here we present a 3D hydrogel-based triculture model that embeds hiPSC-HPCs with human umbilical vein endothelial cells and adipose-derived stem cells in a microscale hexagonal architecture. In comparison with 2D monolayer culture and a 3D HPC-only model, our 3D triculture model shows both phenotypic and functional enhancements in the hiPSC-HPCs over weeks of in vitro culture. Specifically, we find improved morphological organization, higher liver-specific gene expression levels, increased metabolic product secretion, and enhanced cytochrome P450 induction. The application of bioprinting technology in tissue engineering enables the development of a 3D biomimetic liver model that recapitulates the native liver module architecture and could be used for various applications such as early drug screening and disease modeling.

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

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

Fabrication of macroporous cryogels as potential hepatocyte carriers for bioartificial liver support

Two different cryogels composed of copolymer of acrylonitrile (AN) and N-vinyl-2-pyrrolidone (NVP) (poly(AN-co-NVP)) and interpenetrated polymer networks (IPN) of chitosan and poly(N-isopropylacrylamide) (poly(NiPAAm)-chitosan) were fabricated by gelation at sub-zero temperatures. The two cryogels possess an interconnected network of macropores of size 20-100 μm and efficient transport properties as determined by physiochemical analysis. Both cryogels support in vitro growth and function of fibroblasts (COS-7) and human liver hepatocarcinoma cells (HepG2). The cryogels are hemocompatible as demonstrated by low albumin adsorption and platelet adherence. Furthermore, in vivo implantation of poly(NiPAAm)-chitosan cryogel in mice shows its biocompatibility with the surrounding tissue. Primary rat hepatocytes grown on poly(NiPAAm)-chitosan cryogel for 96 h formed cellular aggregates and maintained their functions in terms of, ammonia removal, ureagenesis and drug detoxification. Cryogel-based closed continuous bioreactor systems could maintain HepG2 cells at high density for 7 days. Off-line clinical evaluation of these cryogel-based bioreactors showed the ability of immobilized cells to detoxify circulating plasma obtained from patients with acute on chronic liver failure (ACLF). Altogether, the presented data suggests cryogels as a potential bioreactor matrix for bio-artificial liver support system.

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

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

In vitro characterization of scaffold-free three-dimensional mesenchymal stem cell aggregates

Mesenchymal stem cells (MSCs) are capable of self-renewal and differentiation along multiple cell lineages and have potential applications in a wide range of therapies. These cells are commonly cultured as monolayers on tissue culture plastic but possibly lose their cell-specific properties with time in vitro. There is growing interest in culturing adherent cells via three-dimensional (3D) techniques in order to recapitulate 3D in vivo conditions. We describe a novel method for generating and culturing rabbit MSCs as scaffold-free 3D cell aggregates by using micropatterned wells via a forced aggregation technique. The viability and proliferative capability of MSC aggregates were assessed via Live/Dead staining and 5-ethynyl-2'-deoxyuridine (EdU) incorporation. Enzyme-linked immunosorbent assay and antibody-based multiplex protein assays were used to quantify released growth factors and chemokines. The gene expression profile of MSCs as 3D aggregates relative to MSCs grown as monolayers was evaluated via quantitative real-time polymerase chain reaction. The rabbit MSCs were able to form compact cell aggregates and remained viable in 3D culture for up to 7 days. We also demonstrated enhanced gene and protein expression related to angiogenesis and wound healing in MSCs cultured under 3D conditions. In vitro tube formation and scratch assay revealed superior neovessel formation and greater cell recovery and migration in response to 3D conditioned media after wounding. Our data further suggest that adipose-derived stem cell aggregates have greater potential than dermal fibroblasts or bone-marrow-derived MSCs in accelerating wound healing and reducing scarring.

Dynamic interplay of flow and collagen stabilizes primary hepatocytes culture in a microfluidic platform

The creation of stable flow cultures of hepatocytes is highly desirable for the development of platforms for drug toxicity screening, bio-artificial liver support devices, and models for investigating liver physiology and pathophysiology. Given that hepatocytes cultured using the collagen overlay or in 'sandwich' configuration maintain a wide range of differentiated functions, we describe a simple method for adapting this culture configuration within a microfluidic device. The device design consists of a porous membrane sandwiched between two layers of PDMS resulting in a two-chambered device. In the bottom chamber, hepatocytes are cultured in the collagen sandwich configuration, while the top chamber is accessible for flow. We demonstrate that hepatocytes cultured under flow exhibit higher albumin and urea secretions and induce cytochrome P450 1A1 activity in comparison to static cultures. Furthermore, over two weeks, hepatocytes cultured under flow show a well-connected cellular network with bile canaliculi formation, whereas static cultures show formation of gaps in the cellular network that progressively increase over time. Although enhanced functional response of hepatocytes cultured under flow has been observed in multiple prior studies, the exact mechanism for this flow induced effect remains unknown. In our work, we identified that hepatocytes secrete a higher level of collagen in the flow cultures; inhibiting collagen secretion within the flow cultures reduced albumin secretion and restored the appearance of gaps in the cellular network similar to the static cultures. These results demonstrate the importance of the increased collagen secretion by hepatocytes cultured under flow as a mechanism to maintain a well-connected cellular network and a differentiated function.

Biomaterial strategies for stem cell maintenance during in vitro expansion

Stem cells, having the potential for self-renewal and multilineage differentiation, are the building blocks for tissue/organ regeneration. Stem cells can be isolated from various sources but are, in general, available in too small numbers to be used directly for clinical purpose without intermediate expansion procedures in vitro. Although this in vitro expansion of undifferentiated stem cells is necessary, stem cells typically diminish their ability to self-renew and proliferate during passaging. Consequently, maintaining the stemness of stem cells has been recognized as a major challenge in stem cell-based research. This review focuses on the latest developments in maintaining the self-renewal ability of stem cells during in vitro expansion by biomaterial strategies. Further, this review highlights what should be the focus for future studies using stem cells for regenerative applications.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Generation of functional hepatocyte-like cells from human pluripotent stem cells in a scalable suspension culture

Recent advances in human embryonic and induced pluripotent stem cell-based therapies in animal models of hepatic failure have led to an increased appreciation of the need to translate the proof-of-principle concepts into more practical and feasible protocols for scale up and manufacturing of functional hepatocytes. In this study, we describe a scalable stirred-suspension bioreactor culture of functional hepatocyte-like cells (HLCs) from the human pluripotent stem cells (hPSCs). To promote the initial differentiation of hPSCs in a carrier-free suspension stirred bioreactor into definitive endoderm, we used rapamycin for "priming" phase and activin A for induction. The cells were further differentiated into HLCs in the same system. HLCs were characterized and then purified based on their physiological function, the uptake of DiI-acetylated low-density lipoprotein (LDL) by flow cytometry without genetic manipulation or antibody labeling. The sorted cells were transplanted into the spleens of mice with acute liver injury from carbon tetrachloride. The differentiated HLCs had multiple features of primary hepatocytes, for example, the expression patterns of liver-specific marker genes, albumin secretion, urea production, collagen synthesis, indocyanin green and LDL uptake, glycogen storage, and inducible cytochrome P450 activity. They increased the survival rate, engrafted successfully into the liver, and continued to present hepatic function (i.e., albumin secretion after implantation). This amenable scaling up and outlined enrichment strategy provides a new platform for generating functional HLCs. This integrated approach may facilitate biomedical applications of the hPSC-derived hepatocytes.

Engraftment potential of spheroid-forming hepatic endoderm derived from human embryonic stem cells

Transplantation and drug discovery programs for liver diseases are hampered by the shortage of donor tissue. While recent studies have shown that hepatic cells can be derived from human embryonic stem cells (hESCs), few cases have shown selective enrichment of hESC-derived hepatocytes and their integration into host liver tissues. Here we demonstrate that the dissociation and reaggregation procedure after an endodermal differentiation of hESC produces spheroids mainly consisted of cells showing hepatic phenotypes in vitro and in vivo. A combined treatment with Wnt3a and bone morphogenic protein 4 efficiently differentiated hESCs into definitive endoderm in an adherent culture. Dissociation followed by reaggregation of these cells in a nonadherent condition lead to the isolation of spheroid-forming cells that preferentially expressed early hepatic markers from the adherent cell population. Further differentiation of these spheroid cells in the presence of the hepatocyte growth factor, oncostatin M, and dexamethasone produced a highly enriched population of cells exhibiting characteristics of early hepatocytes, including glycogen storage, indocyanine green uptake, and synthesis of urea and albumin. Furthermore, we show that grafted spheroid cells express hepatic features and attenuate the serum aspartate aminotransferase level in a model of acute liver injury. These data suggest that hepatic progenitor cells can be enriched by the spheroid formation of differentiating hESCs and that these cells have engraftment potential to replace damaged liver tissues.

3D spheroid culture of hESC/hiPSC-derived hepatocyte-like cells for drug toxicity testing. Biomaterials. 2013;34:1781-1789. [PMID: 23228427 DOI: 10.1016/j.biomaterials.2012.11.029]

Although it is expected that hepatocyte-like cells differentiated from human embryonic stem (ES) cells or induced pluripotent stem (iPS) cells will be utilized in drug toxicity testing, the actual applicability of hepatocyte-like cells in this context has not been well examined so far. To generate mature hepatocyte-like cells that would be applicable for drug toxicity testing, we established a hepatocyte differentiation method that employs not only stage-specific transient overexpression of hepatocyte-related transcription factors but also a three-dimensional spheroid culture system using a Nanopillar Plate. We succeeded in establishing protocol that could generate more matured hepatocyte-like cells than our previous protocol. In addition, our hepatocyte-like cells could sensitively predict drug-induced hepatotoxicity, including reactive metabolite-mediated toxicity. In conclusion, our hepatocyte-like cells differentiated from human ES cells or iPS cells have potential to be applied in drug toxicity testing.

Functional 3D human primary hepatocyte spheroids made by co-culturing hepatocytes from partial hepatectomy specimens and human adipose-derived stem cells

We have generated human hepatocyte spheroids with uniform size and shape by co-culturing 1∶1 mixtures of primary human hepatocytes (hHeps) from partial hepatectomy specimens and human adipose-derived stem cells (hADSCs) in concave microwells. The hADSCs in spheroids could compensate for the low viability and improve the functional maintenance of hHeps. Co-cultured spheroids aggregated and formed compact spheroidal shapes more rapidly, and with a significantly higher viability than mono-cultured spheroids. The liver-specific functions of co-cultured spheroids were greater, although they contained half the number of hepatocytes as mono-cultured spheroids. Albumin secretion by co-cultured spheroids was 10% higher on day 7, whereas urea secretion was similar, compared with mono-cultured spheroids. A quantitative cytochrome P450 assay showed that the enzymatic activity of co-cultured spheroids cultured for 9 days was 28% higher than that of mono-cultured spheroids. These effects may be due to the transdifferentiation potential and paracrine healing effects of hADSCs on hHeps. These co-cultured spheroids may be useful for creating artificial three-dimensional hepatic tissue constructs and for cell therapy with limited numbers of human hepatocytes.

Multilayer rat hepatocyte aggregates formed on expanded polytetrafluoroethylene surface

Feasibility of using a macroporous membrane material, expanded polytetrafluoroethylene (ePTFE), for culturing hepatocytes on its surface was examined. Adult rat hepatocytes were attached to an ePTFE surface and cultured in a hormonally defined medium supplemented with or without fetal calf serum (FCS, 10%) or bovine serum albumin (BSA, 0.03-3%). When cultured in a FCS-suplemented medium, hepatocytes reorganized themselves into multilayer cell aggregates on an ePTFE surface. The morphological characteristics of hepatocytes were influenced by the modification of the ePTFE surface as well as the culture medium. Hepatocytes cultured on a polyvinylalcohol (PVA)-coated ePTFE surface formed many more multilayer cell aggregates than those cultured on an uncoated ePTFE surface. Such highly multilayered hepatocyte aggregates were also noted when the cells were cultivated in a BSA-supplemented medium. On the other hand, when cultured in a FCS- or BSA-free medium, hepatocytes formed cell monolayers on both PVA-coated and uncoated ePTFE surfaces as did the cells on a collagen-coated polystyrene surface. The hepatocytes in the aggregates exhibited high albumin expression capability and low DNA synthesis rate as compared with those in monolayer cultures. The multilayer hepatocyte aggregates, as immobilized on a PVA-coated ePTFE surface in a serum-supplemented medium, are shown to be not only morphologically, but functionally differentiated, and will provide us a model system for the development of a bioreactor using hepatocytes, particularly for a hybrid-type artificial liver.

Microfluidic platforms for hepatocyte cell culture: new technologies and applications

In this article, we summarize the key elements of microfluidic platforms for mimicking in vivo hepatocyte cell culture and the major recent advances in this area. Specifically, we will give brief background and rationale for key design requirements for mimicking in vivo hepatocyte cell culture, and then summarize findings, applications, and limitations from microfluidic platforms that addressed these design requirements. Although no ideal microfluidic platform has so far been developed for fully mimicking in vivo hepatocyte cell culture, some approaches and designs have demonstrated great potential in this area.

Perfusion-based microfluidic device for three-dimensional dynamic primary human hepatocyte cell culture in the absence of biological or synthetic matrices or coagulants

We describe a perfusion-based microfluidic device for three-dimensional (3D) dynamic primary human hepatocyte cell culture. The microfluidic device was used to promote and maintain 3D tissue-like cellular morphology and cell-specific functionality of primary human hepatocytes by restoring membrane polarity and hepatocyte transport function in vitro without the addition of biological or synthetic matrices or coagulants. A unique feature of our dynamic cell culture device is the creation of a microenvironment, without the addition of biological or synthetic matrices or coagulants, that promotes the 3D organization of hepatocytes into cord-like structures that exhibit functional membrane polarity as evidenced by the expression of gap junctions and the formation of an extended, functionally active, bile canalicular network.

Dynamic three-dimensional culture methods enhance mesenchymal stem cell properties and increase therapeutic potential

Mesenchymal stem cells (MSCs) are capable of self-renewal and differentiation along the osteogenic, chondrogenic, and adipogenic lineages and have potential applications in a range of therapies. MSCs can be cultured as monolayers on tissue culture plastic, but there are indications that they lose cell-specific properties with time in vitro and so poorly reflect in vivo MSC behavior. We developed dynamic three-dimensional (3D) techniques for in vitro MSC culture using spinner flasks and a rotating wall vessel bioreactor. We characterized the two methods for dynamic 3D MSC culture and compared the properties of these cultures with monolayer MSCs. Our results showed that under optimal conditions, MSCs form compact cellular spheroids and remain viable in dynamic 3D culture. We demonstrated altered cell size and surface antigen expression together with enhanced osteogenic and adipogenic differentiation potential in MSCs from dynamic 3D conditions. By microarray analysis of monolayer and spinner flask MSCs, we identified many differences in gene expression, including those confirming widespread changes to the cellular architecture and extracellular matrix. The upregulation of interleukin 24 in dynamic 3D cultures was shown to selectively impair the viability of prostate cancer cells cultured in medium conditioned by dynamic 3D MSCs. Overall, this work suggests a novel therapeutic application for dynamic 3D MSCs and demonstrates that these methods are a viable alternative to monolayer techniques and may prove beneficial for retaining MSC properties in vitro.

High throughput assembly of spatially controlled 3D cell clusters on a micro/nanoplatform

Guided assembly of microscale tissue subunits (i.e. 3D cell clusters/aggregates) has found applications in cell therapy/tissue engineering, cell and developmental biology, and drug discovery. As cluster size and geometry are known to influence cellular responses, the ability to spatially control cluster formation in a high throughput manner could be advantageous for many biomedical applications. In this work, a micro- and nanofabricated platform was developed for this purpose, consisting of a soft-lithographically fabricated array of through-thickness microwells structurally bonded to a sheet of electrospun fibers. The microwells and fibers were manufactured from several polymers of biomedical interest. Human hepatocytes were used as model cells to demonstrate the ability of the platform to allow controlled cluster formation. In addition, the ability of the device to support studies on semi-controlled heterotypic interactions was demonstrated by co-culturing hepatocytes and fibroblasts. Preliminary experiments with other cells of interest (pancreatic cells, embryonic stem cells, and cardiomyocytes) were also conducted. Our platform possesses several advantages over previously developed microwell arrays: a more in vivo-like topographical stimulation of cells; better nutrient/waste exchange through the underlying nanofiber mat; and easy integration into standard two-chamber cell culture well systems.

Liver cell culture techniques

Different sources of hepatic tissue, including whole or split livers from organ donors or from cadavers, waste liver from therapeutic hepatectomies or small-sized surgical biopsies, can be successfully used to prepare human hepatocytes cultures. The two-step collagenase perfusion remains the most effective way to isolate high yields of viable hepatocytes from human liver samples that express many typical hepatic functions, among them drug-metabolising (detoxification) enzymes, when placed in primary culture. Once isolated, human hepatocytes cultured in monolayer in chemically defined conditions (serum-free) survive for limited periods of time gradually losing their differentiated phenotype, in particular the drug-metabolising enzymes. Supplementation of chemically defined media with growth factors, hormones and other specific additives has been used with variable success to extend hepatocyte survival and functionality in culture. Other culture improvements include the use of extracellular components to coat plates or to entrap cells. Conditions for short-term monolayer cultures, allowing the maintenance of liver-specific functions for approximately 1 week, are now well established. Cultures on plastic dishes coated with extracellular matrix components (i.e. Matrigel(TM), collagen, fibronectin or mixture of collagen and fibronectin) do meet many of the requirements for short-term incubation experiments, without adding too much complexity to the system. Practical details on how to carry out these cultures and to assess their functionality (CYP activity and ureogenesis) are discussed in this chapter.

Cloning and Characterization of Liver Progenitor Cells from the Scattered Cell Clusters in Primary Culture of Porcine Livers

The scattered cell clusters that can differentiate into hepatocytes or biliary epithelial cells have been isolated from primary cultures of adult porcine livers. We have generated 11 clonal cell lines from this system and identified liver progenitor cells (LPCs) among the clonal lines. These clonal lines expressed c-kit, HNF-1, HNF-6, and/or CK19 mRNA. An immunocytochemical study of the clonal lines indicated that clonal line CL-11 expressed liver epithelial cell markers CK14, vimentin, CK18, and BD-1. The expression of albumin and α1-antitrypsin (α1-AT) mRNA was only upregulated in CL-11 among the clonal lines when they were grown as aggregates. Under these conditions, CL-11 also exhibited ammonia metabolic activity and several indicators that suggest hepatocytic differentiation, including the upregulation of liver-specific genes such as dipeptidyl peptidase IV, CYP1A1, and CYP3A4 mRNA, and the downregulation of biliary cell markers such as γ-glutamyltrans-peptidase (GGT), CK19, and HNF6 mRNA. After culturing CL-11 in Matrigel, the expression of GGT and HNF6 mRNA was upregulated. These results indicate that CL-11 has dual potential: the ability to differentiate as hepatocytes or as bile duct cells. The isolation of scattered cells could provide a simple method to generate LPC lines from adult livers.

Development and characterization of a small-scale bioreactor based on a bioartificial hepatic culture model for predictive pharmacological in vitro screenings

A vast majority of pharmacons are beset by possible interactions and side effects which have usually been tested in laboratory animals. However, better methods are needed to reduce the number of animal experiments and interspecies differences with respect to drug metabolism, as well as to provide a faster and more cost-effective way of analysis. These facts have led to the development of in vitro models based on isolated primary hepatocytes to better assess drug metabolism, interactions, and toxicity. A new small-scale bioreactor with the hepatic sandwich model and a gas-permeable membrane at the bottom allowing a definable oxygen exchange, has been constructed and compared with the conventional well plates. Compared to hepatocytes cultured in conventional systems, the cells exhibited a stronger liver-specific capacity and remained in a differentiated state in the small-scale bioreactor over a cultivation period of 17 days. This in vitro model could serve as a tool to predict the liver response to newly developed drugs.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

How to induce non-polarized cells of hepatic origin to express typical hepatocyte polarity: generation of new highly polarized cell models with developed and functional bile canaliculi

Few in vitro models expressing complex hepatocyte polarity are available. We used the unpolarized rat Fao cell line to isolate the polarized WIF-B line. These complex rat-human hybrid cells form functional simple bile canaliculi. To obtain Fao-derived polarized models with a simpler chromosome content and developed bile canaliculi, we employed two approaches. Partial success was achieved with monochromosomal hybrids. As shown by the immunolocalization of apical, basolateral, and tight-junctional proteins, monochromosomal hybrid 11-3 cells were polarized. They formed simple functional bile canaliculi and transiently expressed the typical polarity of simple epithelial cells. One subclone blocked in this polarity state was isolated. A more robust approach was provided by spheroid culture, a three-dimensional system that strengthens cell-cell contacts. Transient spheroid culture induced irreversible polarization of Fao cells. This induction occurred in most spheroids (approximately 1% of the cells). From populations enriched in stably polarized cells, we generated new polarized cell models, designated Can. Can 3-1 cells formed simple functional bile canaliculi when plated at high density. Regardless of plating density, Can 9 and Can 10 cells formed long tubular branched canaliculi competent for vectorial transport of organic anions and bile acids, and involving several dozen adjacent cells. Thus, we have generated new cell models stably expressing typical hepatocyte polarity. Among these models, Can 9 and Can 10 are the first capable of forming functional, highly developed bile canaliculi similar to those formed in vivo.

Cell-based models to study hepatic drug metabolism and enzyme induction in humans

Cell-based in vitro models are invaluable tools in elucidating the pharmacokinetic profile of a drug candidate during its drug discovery and development process. As biotransformation is one of the key determinants of a drug's disposition in the body, many in vitro models to study drug metabolism have been established, and others are still being developed and validated. This review is aimed at providing the reader with a concise overview of the characteristics and optimal application of established and emerging in vitro cell-based models to study human drug metabolism and induction of drug metabolising enzymes in the liver. The strengths and weaknesses of liver-derived models, such as primary hepatocytes, either freshly isolated or cryopreserved, and from adult or fetal donors, precision-cut liver slices, and cell lines, including immortalised cells, reporter cell lines, hepatocarcinoma-derived cell lines and recombinant cell lines, are discussed. Relevant cell culture configuration aspects as well as other models such as stem cell-derived hepatocyte-like cells and humanised animal models are also reviewed. The status of model development, their acceptance by health authorities and recommendations for the most appropriate use of the models are presented.

Long-term extensive expansion of mouse hepatic stem/progenitor cells in a novel serum-free culture system

BACKGROUND & AIMS

The liver has high regenerative potential. We attempted to establish a novel culture system for extensive expansion of fetal mouse hepatic stem/progenitor cells and to characterize cultured cells.

METHODS

Hepatic spheroids collected from 6-day floating cultures were cultured on collagen-coated dishes in serum-free conditions in medium containing growth factors. Cultured cells were mainly characterized by immunocytochemistry and flow cytometry or transplanted into adult mice.

RESULTS

Approximately 400 expanding hepatic spheroids were generated from every 1 x 10(6) fetal liver cells. Subsequently, highly replicative colonies were subcultured with maintaining colony formation on collagen-coated dishes. These colonies consisted of small immature alpha-fetoprotein-positive cells and hepatocytic and cholangiocytic lineage-committed cells. The immature alpha-fetoprotein-positive cells could be expanded in a reproducible manner at least 5 x 10(5)-fold (which involved at least 30 passages over >6 months) without losing differentiation potential. Flow cytometric analysis showed that all cultured cells expressed CD49f, but not CD34, Thy-1, c-kit, or CD45. Nearly 15% of the cells expressed Sca-1, and approximately 5%-20% of the cells were side population cells. Both sorted side population cells and Sca-1-positive cells (especially side population cells) produced a large number of alpha-fetoprotein-positive cells and lineage-committed cells. Expanded cells had bidirectional differentiation potential and improved serum albumin levels in mice with severe liver damage.

CONCLUSIONS

Long-term extensive expansion of transplantable hepatic stem/progenitor cells was reproducibly achieved in a novel serum-free culture system. Moreover, this culture system yielded side population and Sca-1-positive cell populations that included hepatic stem/progenitor cells with differentiation and proliferation properties.

The use of 3-D cultures for high-throughput screening: the multicellular spheroid model

Over the past few years, establishment and adaptation of cell-based assays for drug development and testing has become an important topic in high-throughput screening (HTS). Most new assays are designed to rapidly detect specific cellular effects reflecting action at various targets. However, although more complex than cell-free biochemical test systems, HTS assays using monolayer or suspension cultures still reflect a highly artificial cellular environment and may thus have limited predictive value for the clinical efficacy of a compound. Today's strategies for drug discovery and development, be they hypothesis free or mechanism based, require facile, HTS-amenable test systems that mimic the human tissue environment with increasing accuracy in order to optimize preclinical and preanimal selection of the most active molecules from a large pool of potential effectors, for example, against solid tumors. Indeed, it is recognized that 3-dimensional cell culture systems better reflect the in vivo behavior of most cell types. However, these 3-D test systems have not yet been incorporated into mainstream drug development operations. This article addresses the relevance and potential of 3-D in vitro systems for drug development, with a focus on screening for novel antitumor drugs. Examples of 3-D cell models used in cancer research are given, and the advantages and limitations of these systems of intermediate complexity are discussed in comparison with both 2-D culture and in vivo models. The most commonly used 3-D cell culture systems, multicellular spheroids, are emphasized due to their advantages and potential for rapid development as HTS systems. Thus, multicellular tumor spheroids are an ideal basis for the next step in creating HTS assays, which are predictive of in vivo antitumor efficacy.

Maintenance of liver functions in rat hepatocytes cultured as spheroids in a rotating wall vessel

Rat hepatocytes were cultured initially as spheroids on culture plates and then transferred into a rotating wall vessel (high-aspect ratio vessel [HARV]) for further culturing. Morphological evaluation based on electron microscopy showed that hepatocyte spheroids cultured for 30 d in the HARV had a compact structure with tight cell-cell junctions, numerous smooth and rough endoplasmic reticulum, intact mitochondria, and bile canaliculi lined with microvilli. The viability and differentiated properties of the hepatocytes cultured in the HARV were further substantiated by the presence of both phase I oxidation and phase II conjugation drug-metabolizing enzyme activities, as well as albumin synthesis. Homogenates prepared from freshly isolated hepatocytes and hepatocytes cultured in the HARV showed similar cytochrome P450 2B activities measured as pentoxyresorufin-O-dealkylase and testosterone 16beta-hydroxylase. Further, intact hepatocytes cultured in the HARV were found to metabolize chlorzoxazone to 6-hydroxychlorzoxazone; dextromethorphan to dextrorphan, 3-methoxymorphinan, and 3-hydroxymorphinan; midazolam to 1-hydroxymidazolam and 4-hydroxymidazolam; and 7-hydroxycoumarin to its glucuronide and sulfate conjugates. In conclusion, we found that hepatocyte spheroids could be cultured in a HARV to retain cellular and physiological properties of the intact liver, including drug-metabolizing enzyme activities, plasma protein production, and long-term (1 mo) maintenance of viability and cellular function.

Three-dimensional co-culture of primary human liver cells in bioreactors for in vitro drug studies: effects of the initial cell quality on the long-term maintenance of hepatocyte-specific functions

In vitro culture models that employ human liver cells could be potent tools for predictive studies on drug toxicity and metabolism in the pharmaceutical industry. A bioreactor culture model was developed that permits the three-dimensional co-culture of liver cells under continuous medium perfusion with decentralised mass exchange and integral oxygenation. We tested the ability of the system to support the long-term maintenance and differentiation of primary human liver cells. The effects of the initial cell quality were investigated by comparing cultures from resected, non-preserved liver with cultures from liver graft tissue damaged by long-term preservation. In cultures originating from non-preserved liver, protein and urea synthesis, glucose metabolism, and cytochrome (CYP450) activities were stable over the 2-week culture period, with maximal activities at the end of the first week in culture. Enzyme induction led to increased 7-ethoxyresorufin O-deethylase activities of up to 20 times the basal value. In cultures from preservation-damaged liver, recovery of metabolic activities was detected during bioreactor culture. After two weeks, most biochemical parameters approached those of cultures from non-preserved human liver. Light microscopy demonstrated the three-dimensional reorganisation of hepatocytes and non-parenchymal cells in co-culture. Long-term maintenance, and even the regeneration of specific functional activities of human liver cells, can be achieved in the bioreactor. This could facilitate the introduction into the pharmaceutical industry of in vitro drug testing with primary human liver cells.

Chylomicron-bound endotoxin selectively inhibits NF-kappaB activation in rat hepatocytes

Triglyceride-rich lipoproteins (chylomicrons and very low-density lipoproteins) bind endotoxin (lipopolysaccharide [LPS]), forming lipoprotein-LPS complexes, and protect against endotoxic shock and death in rodent models of gram-negative sepsis. Hepatocytes play a central role in the protective process, as demonstrated by the increased uptake of chylomicron (CM)-bound LPS by these cells. We have previously reported that CM-LPS complexes inhibit nitric oxide (NO) production by hepatocytes as compared with LPS or CM alone. Herein, we report that CM-LPS selectively inhibits NF-kappaB in hepatocytes. Pretreating cultured primary hepatocyte spheroids with CM-bound LPS inhibited cytokine-induced NF-kappaB activation by approximately 60% vs. untreated control cells (P < 0.03). The lipoprotein-mediated inhibition of NF-kappaB was non-toxic, selective, and associated with inhibition of IkappaB degredation. These data indicate that the mechanism by which CM protect against LPS involves inhibition of the hepatocellular response to proinflammatory stimulation and also support a role for triglyceride-rich lipoproteins as components of the innate host immune response to infection.

Advances in bioartificial liver assist devices

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

Multicellular gastric cancer spheroids recapitulate growth pattern and differentiation phenotype of human gastric carcinomas

BACKGROUND & AIMS

Advanced gastric cancer has a poor prognosis and is largely unresponsive to currently available chemotherapeutic drugs. The development of more effective therapies would be aided by better preclinical models.

METHODS

An in vitro multicellular gastric cancer spheroid model was established using the liquid overlay technique and compared with the corresponding xenografts in immunodeficient mice.

RESULTS

Twelve of 17 (71%) gastric cancer cell lines reflected growth characteristics of their parental gastric carcinomas in three-dimensional culture. Thus, cell lines derived from peritoneal and pleural carcinomatosis grew as single cells (HSC-39, KATO-II, KATO-III) and cell aggregates (SNU-5, SNU-16). Cell lines representing adenosquamous (MKN-1) and tubular differentiation (MKN-28, MKN-74, N87) formed partly compact multicellular spheroids recapitulating the tumor architecture of the respective original tumor. The differentiated phenotype was lost after subcutaneous implantation of the in vitro spheroids in mice. The degree of morphologic differentiation was reflected by the levels of mucin and constitutive E-cadherin expression. Heterogeneous changes of other adhesion molecules (EpCAM, alpha2beta1, CD44s, Le(x), sLe(x)) were observed. In contrast, cell lines derived from poorly differentiated gastric carcinomas (Hs-746T, RF-1, RF-48) formed fully compact spheroids mimicking the poorly differentiated phenotype, were E-cadherin negative, and showed only CD44s up-regulation.

CONCLUSIONS

Recapitulating some complexity of their in vivo counterparts, multicellular gastric cancer spheroids may represent a physiologically valid model for studying the biology of this cancer, and testing new therapeutic strategies.

Induction of CYP1A by Benzo[k]fluoranthene in Human Hepatocytes: CYP1A1 or CYP1A2?

While fresh human hepatocyte cultures are widely used to model hepatic cytochrome P450 (CYP) regulation and activity, their CYP1A subfamily composition induced by, e.g., polycyclic aromatic hydrocarbons is ambiguous. CYP1A1, CYP1A2, or both have been reported to be expressed, and their varied roles in chemical carcinogenesis makes resolution of which CYPs are expressed essential. We have used an immunoblot system with Bis-Tris-HCl-buffered polyacrylamide gel, which clearly resolves human CYP1A1 and CYP1A2, and polyclonal goat anti-human CYP1A1/CYP1A2 and rabbit anti-human CYP1A2 antibodies to probe the expressed CYP1A1 and CYP1A2 composition of seven individual human hepatocyte cultures induced with 5 microM benzo[k]fluoranthene (BKF) for 24 h. In six of the cultures only CYP1A1 was detected, and in the seventh both CYPs were detected. In most vehicle-treated hepatocyte cultures, neither CYP1A1 nor CYP1A2 was detected. In three additional hepatocyte cultures treated individually with BKF and 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD), the resultant induced CYP1A1/1A2 profiles were essentially not influenced by the nature of the inducing agents. To develop an activity-based assay to differentiate between CYP1A1 and CYP1A2 expression in human hepatocytes, our previously published R warfarin assay (Drug Metab. Disp. (1995) 23, 1339-1345) was applied to TCDD (10 nM)-treated hepatocyte culture. The low concentration of TCDD did not produce inhibition of the warfarin metabolism-such inhibition could confound the results. Based on the ratios of 6- to 8-hydroxywarfarin formed in two cultures, the ratios of CYP1A1/CYP1A2 expressed in these cultures were determined and they agreed with the ratios determined by immunoblot analysis. Thus each individual human hepatocyte culture must be characterized for induced CYP1A1 and CYP1A2 expression in studies of CYP1A activity. The warfarin assay provides a means of characterizing the cultures.

Evaluation of the effect of culture matrices on induction of CYP3A isoforms in cultured porcine hepatocytes

Several bioartificial liver devices have been developed as temporary therapy for patients suffering from fulminant hepatic failure. Some of these devices contain porcine hepatocytes entrapped in collagen matrices. In order to improve the function of these BAL devices, there exists a need to optimize metabolic function of cultured hepatocytes. The goal of these investigations was to evaluate the effect of altering culture conditions on rifampin-mediated induction of CYP3A isoforms in cultured porcine hepatocytes. Midazolam metabolism was compared in porcine hepatocytes cultured in a monolayer configuration on collagen gels, in a sandwich configuration between collagen gels and a Matrigel overlay, and in spheroidal cultures. The effect of culture conditions was evaluated, by measuring CYP3A-mediated metabolism of midazolam and by immunoblotting to detect CYP3A proteins, in control cultures and in rifampin-treated cultures. Results obtained by normalizing the metabolism rate data to cell numbers (based on DNA content) present at the end of the culture experiment, showed that there was no difference between the different culture conditions tested. Our results suggest that culturing porcine hepatocytes as spheroids or in a sandwich configuration between collagen and Matrigel, offers no advantage in terms of CYP3A-mediated metabolic function on a per cell basis compared to culturing on collagen gels.

Morphologic studies of hepatocytes entrapped in hollow fibers of a bioartificial liver

A bioartificial liver cartridge was prepared by inoculating porcine hepatocytes into the inner space of hollow fibers of a hemodialyzer. The hepatocytes formed rod shaped cell aggregates during in vitro perfusion culture within 1 day. Morphologic examination was carried out on the aggregates by optical and electron microscopy. Each hepatocyte was in direct contact with adjacent cells and a bile canaliculus-like structure was occasionally seen between hepatocytes. High magnification observation showed that the canaliculus was separated from the remainder of the intercellular space by a tight junction. These facts suggest that the hepatocytes formed functionally associated cell aggregates with a compact morphology not unlike hepatocyte spheroids. These structures were well maintained for 7 days in culture, and then the amorphous area in the aggregates and the nonviable cell number increased with lengthening culture period. The bioartificial liver maintained the ability to metabolize lidocaine, ammonia, and galactose for 7 days and then deteriorated with time.

Polymer substrate topography actively regulates the multicellular organization and liver-specific functions of cultured hepatocytes

This study examines the role of topography of porous synthetic polymer substrates in regulating the tissue-specific morphogenesis of cultured hepatocytes. Porous foams of amorphous 50/50 poly(D,L glycolic-co-lactic acid) (PGLA) with a wide range of controlled pore-size distributions ( approximately 1 to 100 microm) were used as culture model surfaces. We found that the induction of microporosity in PGLA substrates significantly improved cell attachment and viability in comparison to those observed on non-porous PGLA films. A detailed evaluation of cellular morphogenesis on the microporous matrices showed that hepatocellular organization was sensitively dependent on the topographical feature size of the foam surfaces. Foams with subcellular size voids ( approximately 3 microm) induced kinetics of two-dimensional hepatocyte reorganization, yet limited the extent of three-dimensional aggregation. In contrast, foams with supercellular size voids ( approximately 67-microm) restricted hepatocyte motility, thereby promoting the kinetics of 3D aggregation. At intermediate void sizes ( approximately 17 microm), both 2D and 3D reorganization kinetics were promoted. Albumin secretory kinetics progressively increased on all void size configurations, the most rapid and sustained kinetics observed in supercellular sized voids, which may serve to minimize cell-polymer contacts and maximize cell-cell contacts in 3D. Overall, these studies demonstrate that void topography of porous polymer substrates is a critical textural feature to induce short-term cell adhesion and viability, and to also selectively regulate the kinetics and extent of multicellular spreading versus 3D aggregation. By virtue of its effects on cell adhesion and morphogenesis, the void topography of nonphysiological polymer scaffolds also is a powerful variable to microengineer hepatospecific activity of tissue analogs.