Hepatocyte polarity and the peroxisomal compartment: a comparative study

Development of a tunable method to generate various three-dimensional microstructures by replenishing macromolecules such as extracellular matrix components and polysaccharides

Multicellular spheroids (spheroids) are expected to be a promising approach to mimic in vivo organ functions and cell microenvironments. However, conventional spheroids do not fully consider the existence of extracellular matrices (ECMs). In this study, we developed a tunable method for replenishing macromolecules, including ECM components and polysaccharides, into spheroids without compromising cell viability by injecting a microvolume cell suspension into a high density of methylcellulose dissolved in the culture medium. Adjusting the ECM concentration in the cell suspension enabled the generation of different three-dimensional microstructures, such as "ECM gel capsules", which contained individually separated cells, and "ECM-loaded spheroids", which had thin ECM layers between cells. ECM-loaded spheroids with a 30-fold dilution of Matrigel (0.3 mg/ml) showed significantly higher albumin secretion than control spheroids composed of Hep G2 or HuH-7 cells. Additionally, the expression levels of major CYP genes were decreased in ECM gel capsules with undiluted Matrigel (9 mg/ml) compared to those in control spheroids. However, 0.3 mg/ml Matrigel did not disrupt gene expression. Furthermore, cell polarity associated with tight junction proteins (ZO-1 and Claudin-1) and the transporter protein MRP2 was markedly induced by using 0.3 mg/ml Matrigel. Thus, high-performance three-dimensional tissues fabricated by this method are applicable to increasing the efficiency of drug screening and to regenerative medicine.

A cell lines derived microfluidic liver model for investigation of hepatotoxicity induced by drug-drug interaction

The poor metabolic ability of cell lines fails to meet the requirements of an in vitro model for drug interaction testing which is crucial for the development or clinical application of drugs. Herein, we describe a liver sinusoid-on-a-chip device composed of four kinds of transformed cell lines (HepG2 cells, LX-2 cells, EAhy926 cells, and U937 cells) that were ordered in a physiological distribution with artificial liver blood flow and biliary efflux flowing in the opposite direction. This microfluidic device applied three-dimensional culturing of HepG2 cells with high density (107 ml-1), forming a tightly connected monolayer of EAhy926 cells and achieving the active transport of drugs in HepG2 cells. Results showed that the device maintained synthetic and secretory functions, preserved cytochrome P450 1A1/2 and uridine diphosphate glucuronyltransferase enzymatic activities, as well as sensitivity of drug metabolism. The cell lines derived device enables the investigation of a drug-drug interaction study. We used it to test the hepatotoxicity of acetaminophen and the following combinations: "acetaminophen + rifampicin," "acetaminophen + omeprazole," and "acetaminophen + ciprofloxacin." The variations in hepatotoxicity of the combinations compared to acetaminophen alone, which is not found in a 96-well plate model, in the device were -17.15%, 14.88%, and -19.74%. In addition, this result was similar to the one tested by the classical primary hepatocyte plate model (-13.22%, 13.51%, and -15.81%). Thus, this cell lines derived liver model provides an alternative to investigate drug hepatotoxicity, drug-drug interaction.

In vivo-like 3-D model for sodium nitrite- and acrylamide-induced hepatotoxicity tests utilizing HepG2 cells entrapped in micro-hollow fibers

To address the need for a high throughput toxicity test in the modern food industry, an in vivo-like 3-D cell model was constructed in this study to provide an alternative to controversial long-term animal models and to improve the sensitivity and accuracy of the traditional monolayer model. The model formed cell cylindroids within polyvinylidene fluoride (PVDF) hollow fibers and therefore mimicked the microenvironment of liver tissue. Microscopy methods were used, and liver-specific functions were measured to demonstrate the superiority of the model compared to the monolayer model, as well as to optimize the model for best cell performances. Later, toxicity tests of sodium nitrite and acrylamide were conducted in both the 3-D model and the monolayer model to study the sensitivity of the 3-D model in toxicity responses. As expected, HepG2 cells within the 3-D model responded at lower concentrations and shorter exposure times compared to cells within the monolayer model. Furthermore, western blot analysis of apoptosis pathways also supported the argument.

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

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

The effects of human umbilical cord perivascular cells on rat hepatocyte structure and functional polarity

Hepatocyte culture is a useful tool for the study of their biology and the development of bioartificial livers. However, many challenges have to be overcome since hepatocytes rapidly lose their normal phenotype in vitro. We have recently demonstrated that human umbilical cord perivascular cells (HUCPVCs) are able to provide support to hepatocytes. In the present study we go further into exploring the effects that HUCPVCs have in the functional polarization, and both the internal and external organization, of hepatocytes. Also, we investigate HUCPVC–hepatocyte crosstalk by tracking both the effects of HUCPVCs on hepatocyte transcription factors and those of hepatocytes on the expression of hepatotrophic factors in HUCPVCs. Our results show that HUCPVCs maintain the functional polarity of hepatocytes ex vivo, as judged by the secretion of fluorescein into bile canaliculi, for at least 40 days. Transmission electron microscopy revealed that hepatocytes in coculture organize in an organoid-like structure embedded in extracellular matrix surrounded by HUCPVCs. In coculture, hepatocytes displayed a higher expression of C/EBPα, implicated in maintenance of the mature hepatocyte phenotype, and HUCPVCs upregulated hepatocyte growth factor and Jagged1 indicating that these genes may play important roles in HUCPVC–hepatocyte interactions.

Expression of albumin and cytochrome P450 enzymes in HepG2 cells cultured with a nanotechnology-based culture plate with microfabricated scaffold

The Nanoculture plate (NCP) is a recently developed plate which essentially consists of a textured surface with specific characteristics that induce spheroid formation: microfabrications with a micro-square pattern on the culture surface. The NCP can be used to generate uniform adhesive spheroids of cancer cell lines using conventional techniques without the need of any animal compounds. In this study, we assessed the performance of human hepatoma cell line HepG2 cells cultured with an NCP to evaluate the effects of the NCP on their hepatocyte-specific functions. The NCP facilitated the formation of three-dimensional (3D) HepG2 cell architecture. HepG2 cells cultured with an NCP exhibited enhanced mRNA expression levels of albumin and cytochrome P450 (CYP) enzymes compared to those cultured with a two-dimensional (2D) conventional plate. The expression levels of two specific liver-enriched transcription factors, hepatocyte nuclear factor 4α (HNF4α) and CCAAT/enhancer binding protein α (C/EBPα), were higher in HepG2 cells grown with the NCP than those in HepG2 cells grown with conventional plates before albumin and CYP enzymes expression levels were increased. The inducibility of CYP1A2 and CYP3A4 mRNA following exposure to inducers in HepG2 cells cultured with an NCP was comparable to that in HepG2 cells cultured with conventional plates, while the expression levels of CYP1A2 and CYP3A4 mRNA following exposure to inducers were higher when using an NCP than when using conventional plates. These results suggest that the use of an NCP enhances the hepatocyte-specific functions of HepG2 cells, such as drug-metabolizing enzyme expression, making the NCP/HepG2 system a useful tool for evaluating drug metabolism in vitro.

The gallbladder of Uranoscopus scaber L. (teleost perciform fish) is lined by specialized cholecystocytes

The gallbladder of Uranoscopus exhibits a mucosal surface layer of simple columnar epithelium composed of specialized cholecystocytes. The apices show storage and mucous secretions, typical microvilli, and very apical projections extending deep into the luminal contents. Many organelles and heterogeneous vesicles of diverse size fill the cytoplasm, including neutral mucins, mitochondria, peroxisomes, lysosomal bodies, and lipid-rich deposits with cholesterol inclusions. The fibromuscular layer shows little blood supply and contains scattered lymph-like walls with minute cholesterol inclusions. The remaining muscular, subserosal, and serosal or adventitial layers of this species do not show any histologic differences to those of other vertebrates. It was unexpected to find cholesterol inclusions in the fatty deposits of the cholecystocytes, similar to those noted in human cholesterolosis and in some forms of hypercholesterolemia, in this teleostean. In addition, aggregations of mitochondria and anomalous mitochondrial morphologies were found that resemble oncocytoma-like changes.

Alkoxyresorufin O-dealkylase assay using a rat hepatocyte spheroid microarray

Hepatocyte multicellular aggregates (spheroids), which maintain high expression of liver functions, have been advocated as a useful culture technique for various cell-based assays. In this study, we investigated the drug metabolic function of a hepatocyte spheroid microarray (HSM) chip, which contained an array of 672 spheroids of primary rat hepatocytes within a 100-mm(2) region in the center of a poly(methylmethacrylate) plate (24 x 24 mm) and used an alkoxyresorufin (ethoxy-, methoxy-, pentoxy- and benzyloxyresorufin) O-dealkylase assay system. Ethoxyresorufin O-dealkylase (EROD) activity of the HSM chip initiated by 3-methylcholanthrene (3-MC), an inducer of cytochrome P450 enzymes, was 5- to 10-fold higher than that of monolayer hepatocytes, with activity being maintained for at least 2 weeks. We also demonstrated that 3-MC induced EROD, methoxyresorufin O-dealkylase (MROD) and benzyloxyresorufin O-dealkylase (BROD) activities in the HSM chip, while sodium phenobarbital (P450 inducer) induced pentoxyresorufin O-dealkylase (PROD), BROD, EROD and MROD activities. Induction of these activities was confirmed by increased gene expression of the related P450 enzymes. These results showed that the HSM chip had a good response to P450 inducers and that function was maintained for long periods of time. The HSM chip therefore may be a promising cellular platform for drug metabolic assays using hepatocytes.

Oxidative stress enzymes in Ficus religiosa L.: biochemical, histochemical and anatomical evidences

In order to unveil the reasons behind the successful survival of Ficus religiosa L. grown under normal and adverse habitats (AH), i.e., on concrete roof tops were subjected to biochemical, histochemical and physiological studies with a focus on reactive oxygen species (ROS) and oxidative stress enzymes (OSE). The specific objectives were: to localize the OSE, peroxidase (POX) and catalase (CAT); to localize and quantify the main ROS, hydrogen peroxide (H(2)O(2)); to estimate the activities of POX, CAT and glycolate oxidase (GO); and to study the diurnal variations in stomatal activity by scanning electron microscopy (SEM). From the results, plants grown in AH showed 55% higher H(2)O(2) production with about 30% increase in POX activity. Of the three substrates tested for POX activity (guaiacol, ascorbate and o-dianisidine), o-dianisidine was found as the preferred substrate of F. religiosa POX with about 7-fold more activity over its counterparts. Cytosolic POX activity showed 11-fold increase over cell wall bound POX. Similarly, CAT activity in specimens from AH showed about 2-fold increase during day time. The physiological interaction between CAT and its substrate H(2)O(2) in the plant was determined by quantifying H(2)O(2) and assaying the CAT, in which CAT showed 4-fold increases in activity, especially during night. F. religiosa has higher amount of H(2)O(2) deposition during night than day time, which was in correlation high CAT activity during night, coupled with scotoactive opening of stomata as shown by the SEM images. Moreover, GO did not show much habitat-dependent variation. In toto, F. religiosa grown in AH showed elevated production of ROS and their scavenging OSE, which is the direct evidence for drought stress and also giving an insight into its evolution and ecological niche.

Technique for the control of spheroid diameter using microfabricated chips

This paper describes a new technique for the control of spheroid diameter in liver-derived cell lines using microfabricated chips that were prepared by combining microfabrication with chemical surface modification. The chip possesses multicavities in a triangular arrangement in the central region (10 mm x 10 mm) of a polymethylmethacrylate (PMMA) plate (24 mm x 24 mm), and the surface of the chip was modified with polyethylene glycol, thereby producing a surface that is non-adhesive to cells. HepG2 cells, a model liver-derived cell line, inoculated onto the chip were trapped within each cavity and proliferated to gradually form spheroids with smooth surfaces and high circularity. Although the spheroid diameters increased with cell proliferation during the initial 10 days of culture, they remained constant thereafter. The spheroid diameters were dependent on the scales of the multicavities on the chip, and the spheroid configuration with uniform diameter was maintained for at least 1 month. In particular, it was demonstrated using chips of various designs that the cavity diameter and the pitch between cavities were effective factors in controlling the spheroid diameter. Furthermore, the protein secretion activities of the spheroid formed on the chip were higher than those of the monolayers for at least 1 month of culture. These results indicate that this chip is a useful technique for the control of spheroid diameter and for the mass preparation of uniform spheroids.

Improved hepatocyte excretory function by immediate presentation of polarity cues

Liver tissue constructs with excretory function are crucial to developing realistic hepatocyte models for engineering effective bioartificial liver-assisted devices and for modeling the in vivo tissue. Current hepatocyte in vitro models suffer from limited or inefficient hepatocyte repolarization, which results in poor removal of xenobiotics and other waste products from the cells. We hypothesized that the temporal and spatial presentation of the cell matrix and cell-cell contacts as polarity cues would be important to define the axis of polarization to improve the excretory function of hepatocytes. The spatial presentation of polarity cues can be best achieved with sandwich configuration. We improve the temporal presentation of polarity cues by introducing the collagen overlay immediately in synchrony with cell-cell contacts instead of after 24 h in conventional sandwich culture. We demonstrate that the immediate presentation of the collagen matrix overlay enhances the formation of apicobasolateral domains, tight junctions, and the recovery of the functional activity of 2 canalicular transporters, the multidrug resistance-associated protein (Mrp2) and P-glycoprotein (P-gp) at 48 h of culture, and enhances the albumin secretion, urea production, and 7-ethoxyresorufin-O-deethylation cytochrome P450 activities of hepatocytes over 14 days of culture as compared to the 24-h overlay controls. The improvement in the excretory function of hepatocytes for the removal of waste products deleterious to cells may improve the functional maintenance and the in vivo fidelity of tissue-engineered liver constructs.

Involvement of cell junctions in hepatocyte culture functionality

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

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.

Human peroxisomal disorders

Peroxisomes are single membrane-bound cell organelles performing numerous metabolic functions. The present article aims to give an overview of our current knowledge about inherited peroxisomal disorders in which these organelles are lacking or one or more of their functions are impaired. They are multiorgan disorders and the nervous system is implicated in most. After a summary of the historical names and categories, each having distinct symptoms and prognosis, microscopic pathology is reviewed in detail. Data from the literature are added to experience in the authors' laboratory with 167 liver biopsy and autopsy samples from peroxisomal patients, and with a smaller number of chorion samples for prenatal diagnosis, adrenal-, kidney-, and brain samples. Various light and electron microscopic methods are used including enzyme- and immunocytochemistry, polarizing microscopy, and morphometry. Together with other laboratory investigations and clinical data, this approach continues to contribute to the diagnosis and further characterization of peroxisomal disorders, and the discovery of novel variants. When liver specimens are examined, three main groups including 9 novel variants (33 patients) are distinguished: (1) absence or (2) presence of peroxisomes, and (3) mosaic distribution of cells with and without peroxisomes (10 patients). Renal microcysts, polarizing trilamellar inclusions, and insoluble lipid in macrophages in liver, adrenal cortex, brain, and in interstitial cells of kidney are also valuable for classification. On a genetic basis, complementation of fibroblasts has classified peroxisome biogenesis disorders into 12 complementation groups. Peroxisome biogenesis genes (PEX), knock-out-mice, and induction of redundant genes are briefly reviewed, including some recent results with 4-phenylbutyrate. Finally, regulation of peroxisome expression during development and in cell cultures, and by physiological factors is discussed.