Phosphorylation of hepatocyte growth factor receptor and epidermal growth factor receptor of human hepatocytes can be maintained in a (3D) collagen sandwich culture system

Effects of Pro-Inflammatory Cytokines on Hepatic Metabolism in Primary Human Hepatocytes

Three decades of hepatocyte transplantation have confirmed such a cell-based approach as an adjunct or alternative treatment to solid organ transplantation. Donor cell survival and engraftment were indirectly measured by hepatospecific secretive or released metabolites, such as ammonia metabolism in urea cycle defects. In cases of sepsis or viral infection, ammonia levels can significantly and abruptly increase in these recipients, erroneously implying rejection. Pro-inflammatory cytokines associated with viral or bacterial infections are known to affect many liver functions, including drug-metabolizing enzymes and hepatic transport activities. We examined the influence of pro-inflammatory cytokines in primary human hepatocytes, isolated from both normal donors or patients with metabolic liver diseases. Different measures of hepatocyte functions, including ammonia metabolism and phase 1-3 metabolism, were performed. All the hepatic functions were profoundly and significantly suppressed after exposure to concentrations of from 0.1 to 10 ng/mL of different inflammatory cytokines, alone and in combination. Our data indicate that, like phase I metabolism, suppression of phase II/III and ammonia metabolism occurs in hepatocytes exposed to pro-inflammatory cytokines in the absence of cell death. Such inflammatory events do not necessarily indicate a rejection response or loss of the cell graft, and these systemic inflammatory signals should be carefully considered when the immunosuppressant regiment is reduced or relieved in a hepatocyte transplantation recipient in response to such alleged rejection.

In vitro models for non-alcoholic fatty liver disease: Emerging platforms and their applications

Non-alcoholic fatty liver disease (NAFLD) represents a global healthcare challenge, affecting 1 in 4 adults, and death rates are predicted to rise inexorably. The progressive form of NAFLD, non-alcoholic steatohepatitis (NASH), can lead to fibrosis, cirrhosis, and hepatocellular carcinoma. However, no medical treatments are licensed for NAFLD-NASH. Identifying efficacious therapies has been hindered by the complexity of disease pathogenesis, a paucity of predictive preclinical models and inadequate validation of pharmacological targets in humans. The development of clinically relevant in vitro models of the disease will pave the way to overcome these challenges. Currently, the combined application of emerging technologies (e.g., organ-on-a-chip/microphysiological systems) and control engineering approaches promises to unravel NAFLD biology and deliver tractable treatment candidates. In this review, we will describe advances in preclinical models for NAFLD-NASH, the recent introduction of novel technologies in this space, and their importance for drug discovery endeavors in the future.

In vitro models for non-alcoholic fatty liver disease: Emerging platforms and their applications

Non-alcoholic fatty liver disease (NAFLD) represents a global healthcare challenge, affecting 1 in 4 adults, and death rates are predicted to rise inexorably. The progressive form of NAFLD, non-alcoholic steatohepatitis (NASH), can lead to fibrosis, cirrhosis, and hepatocellular carcinoma. However, no medical treatments are licensed for NAFLD-NASH. Identifying efficacious therapies has been hindered by the complexity of disease pathogenesis, a paucity of predictive preclinical models and inadequate validation of pharmacological targets in humans. The development of clinically relevant in vitro models of the disease will pave the way to overcome these challenges. Currently, the combined application of emerging technologies (e.g., organ-on-a-chip/microphysiological systems) and control engineering approaches promises to unravel NAFLD biology and deliver tractable treatment candidates. In this review, we will describe advances in preclinical models for NAFLD-NASH, the recent introduction of novel technologies in this space, and their importance for drug discovery endeavors in the future.

The Influence of Different Cultivation Conditions on the Metabolic Functionality of Encapsulated Primary Hepatocytes

The clinical application of bioartificial liver support systems (BALS) is still limited because of technical problems associated with the storage, transport and scale-up of common systems. The encapsulation of primary hepatocytes could solve these problems since the scale-up depends only on the number of the beads and encapsulation leads to protection of the cells during the process of freezing and thawing. Many efforts have been made to find an appropriate material for the encapsulation of primary hepatocytes in terms of mechanical resistance as well as appropriate bio- and hemo-compatibility This study focuses on the improvement of the metabolic functionality of encapsulated primary hepatocytes. A comparison between two different cultivation models showed that dynamic cultivation conditions lead to a 20.4-fold increase in the albumin production and a 5.21-fold increase in the urea synthesis of encapsulated hepatocytes. Furthermore, the influence of different ratios of the number of the cells to the volume of the media was analyzed. Encapsulated hepatocytes cultured with a high amount of medium were characterized by a significantly higher metabolic activity compared to encapsulated hepatocytes cultured with a low level of medium. Interestingly, the cell concentration per mL alginate has no significant influence on the metabolic activity of encapsulated hepatocytes. In conclusion, different optimization strategies are discussed and, finally, the functionality of encapsulated hepatocytes is compared to the standard model of hepatocyte culture, the collagen sandwich.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

A novel 3D mammalian cell perfusion-culture system in microfluidic channels

Mammalian cells cultured on 2D surfaces in microfluidic channels are increasingly used in drug development and biological research applications. These systems would have more biological or clinical relevance if the cells exhibit 3D phenotypes similar to the cells in vivo. We have developed a microfluidic channel based system that allows cells to be perfusion-cultured in 3D by supporting them with adequate 3D cell-cell and cell-matrix interactions. The maximal cell-cell interaction was achieved by perfusion-seeding cells through an array of micropillars; and 3D cell-matrix interactions were achieved by a polyelectrolyte complex coacervation process to form a thin layer of matrix conforming to the 3D cell shapes. Carcinoma cell lines (HepG2, MCF7), primary differentiated (hepatocytes) and primary progenitor cells (bone marrow mesenchymal stem cells) were perfusion-cultured for 72 hours to 1 week in the microfluidic channel, which preserved their 3D cyto-architecture and cell-specific functions or differentiation competence. This transparent 3D microfluidic channel-based cell culture system also allows direct optical monitoring of cellular events for a wide range of applications.

The effect of three-dimensional co-culture of hepatocytes and hepatic stellate cells on key hepatocyte functions in vitro

In this study, we demonstrate the ability of a three-dimensional co-culture model to preserve some key aspects of differentiated hepatocyte function in vitro. Freshly isolated rat hepatocytes in co-culture with activated stellate cells rapidly aggregate to form well-defined viable spheroids. After 5 days in culture, the spheroids have a complex extracellular matrix support and hepatic ultrastructure including bile canaliculi, tight junctions, desmosomes and lipid storage. Co-culture spheroids have superior cytochrome P450 (CYP450) 3A and 2B function, and increased inducibility of 2B function, relative to a range of hepatocyte monoculture techniques (high-performance liquid chromatography of testosterone metabolites). Increased function in co-culture is supported by greater expression of CYP450 3A23, 1A2, and 2E1 mRNA relative to monoculture (reverse transcriptase quantitative polymerase chain reaction). Also, high hepatocyte growth factor mRNA expression in co-culture suggests a post-traumatic, or possibly regenerative, environment. A preliminary study of human hepatocytes co-cultured with rat stellate cells demonstrated prolonged function of CYP450 3A4, 2C19 and 2C9. This study shows that stellate cells facilitate spheroid formation, influence spheroid architecture, and are an effective method of preserving some aspects of hepatocyte function in the early stage of culture.

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.

Preservation of the synthetic and metabolic capacity of isolated human hepatocytes by coculture with human biliary epithelial cells

Bioartificial liver support systems have demonstrated limited efficacy in compensation of liver detoxification and substitution of liver-derived factors. However, in these devices, the biological substitution of the complex liver function has been restricted to xenogeneic or transformed hepatocytes. Therefore, we have examined the long-term effect of coculturing normal human hepatocytes (HCs) with allogeneic biliary epithelial cells (BECs). We applied functional in vitro assays to examine their metabolic potential by ammonia detoxification to urea, cytochrome P450-dependent lignocaine conversion to mono-ethyl-glycine-xylidide (MEGX), and protein expression and secretion. As the liver has a pivotal role in the synthesis of coagulation factors, we measured antithrombin III (AT III), factor VII, and albumin, comparing HCs plated on collagen or inside 3-dimensional collagen gels. Over 30 days, expression and secretion of albumin and clotting factors by human HCs were augmented by culture inside collagen gel, but were also enhanced and better maintained by coculture with BECs. Higher proportions of BECs cocultured with HCs substantially increased the protein synthesis and urea production. Remarkably, the almost absent cytochrome P450 activity of HC alone after 1 week could be reversed and maintained over 3 weeks by coculture with BECs. The pattern of these effects differed from the extent of interleukin-6 (IL-6) production and HC viability under the compared conditions. In conclusion, coculture of human HCs with BECs impressively restores the synthetic and metabolic liver function in vitro. These results suggest mechanisms of improved liver epithelial differentiation supported by coculture conditions. This technique offers new perspectives in bioartificial liver support, hepatocyte transplantation, and stem cell differentiation.