Marie Shinohara

Combination of microwell structures and direct oxygenation enables efficient and size-regulated aggregate formation of an insulin-secreting pancreatic β-cell line.

Spherical three‐dimensional (3D) cellular aggregates are valuable for various applications such as regenerative medicine or cell‐based assays due to their stable and high functionality. However, previous methods to form aggregates have shown drawbacks, being labor‐intensive, showing low productivity per unit area or volume and difficulty to form homogeneous aggregates. We proposed a novel strategy based on oxygen‐permeable polydimethylsiloxane (PDMS) honeycomb microwell sheets, which can theoretically supply about 80 times as much oxygen as conventional polystyrene culture dishes, to produce recoverable aggregates in controllable sizes using mouse insulinoma cells (MIN6‐m9). In 48 hours of culture, the PDMS sheets produced aggregates whose diameters were strictly controlled (⋍32, 60, 90, 150 and 280 mm) even at an inoculum density eight times higher (8.0×105 cells/cm2) than that of normal confluent monolayers (1.0×105 cells/cm2). Measurement of the oxygen tension near the cell layer and glucose/lactate analysis clearly showed that cells exhibit aerobic respiration on the PDMS‐based culture system. Glucose‐responsive insulin secretion of the recovered aggregates showed that the aggregates around 90 mm in diameter secreted the largest amounts of insulin. This confirmed the advantages of 3D cellular organization and the existence of a suitable aggregate size, above which excess organization leads to a decreased metabolic response. These results demonstrated that this microwell‐based PDMS culture system provides a promising method to form size‐regulated and better functioning 3D cellular aggregates of various kinds of cells with a high yield per surface area.

Production of Cisplatin-Incorporating Hyaluronan Nanogels via Chelating Ligand-Metal Coordination.

Hyaluronan (HA) is a promising drug carrier for cancer therapy because of its CD44 targeting ability, good biocompatibility, and biodegradability. In this study, cisplatin (CDDP)-incorporating HA nanogels were fabricated through a chelating ligand-metal coordination cross-linking reaction. We conjugated chelating ligands, iminodiacetic acid or malonic acid, to HA and used them as a precursor polymer. By mixing the ligand-conjugated HA with CDDP, cross-linking occurred via coordination of the ligands with the platinum in CDDP, resulting in the spontaneous formation of CDDP-loaded HA nanogels. The nanogels showed pH-responsive release of CDDP, because the stability of the ligand-platinum complex decreases in an acidic environment. Cell viability assays for MKN45P human gastric cancer cells and Met-5A human mesothelial cells revealed that the HA nanogels selectively inhibited the growth of gastric cancer cells. In vivo experiments using a mouse model of peritoneal dissemination of gastric cancer demonstrated that HA nanogels specifically localized in peritoneal nodules after the intraperitoneal administration. Moreover, penetration assays using multicellular tumor spheroids indicated that HA nanogels had a significantly higher ability to penetrate tumors than conventional, linear HA. These results suggest that chelating-ligand conjugated HA nanogels will be useful for targeted cancer therapy.

Liver tissue engineering based on aggregate assembly: efficient formation of endothelialized rat hepatocyte aggregates and their immobilization with biodegradable fibres*

To realize long-term in vitro culture of hepatocytes at a high density while maintaining a high hepatic function for aggregate-based liver tissue engineering, we report here a novel culture method whereby endothelialized rat hepatocyte aggregates were formed using a PDMS microwell device and cultured in a perfusion bioreactor by introducing spacers between aggregates to improve oxygen and nutrient supply. Primary rat hepatocyte aggregates around 100 µm in diameter coated with human umbilical vein endothelial cells were spontaneously and quickly formed after 12 h of incubation, thanks to the continuous supply of oxygen by diffusion through the PDMS honeycomb microwell device. Then, the recovered endothelialized rat hepatocyte aggregates were mixed with biodegradable poly-l-lactic acid fibres in suspension and packed into a PDMS-based bioreactor. Perfusion culture of 7 days was successfully achieved with more than 73.8% cells retained in the bioreactor. As expected, the fibres acted as spacers between aggregates, which was evidenced from the enhanced albumin production and more spherical morphology compared with fibre-free packing. In summary, this study shows the advantages of using PDMS-based microwells to form heterotypic aggregates and also demonstrates the feasibility of spacing tissue elements for improving oxygen and nutrient supply to tissue engineering based on modular assembly.

The importance of physiological oxygen concentrations in the sandwich cultures of rat hepatocytes on gas-permeable membranes

Oxygen supply is a critical issue in the optimization of in vitro hepatocyte microenvironments. Although several strategies have been developed to balance complex oxygen requirements, these techniques are not able to accurately meet the cellular oxygen demand. Indeed, neither the actual oxygen concentration encountered by cells nor the cellular oxygen consumption rates (OCR) was assessed. The aim of this study is to define appropriate oxygen conditions at the cell level that could accurately match the OCR and allow hepatocytes to maintain liver specific functions in a normoxic environment. Matrigel overlaid rat hepatocytes were cultured on the polydimethylsiloxane (PDMS) membranes under either atmospheric oxygen concentration [20%‐O2 (+)] or physiological oxygen concentrations [10%‐O2 (+), 5%‐O2 (+)], respectively, to investigate the effects of various oxygen concentrations on the efficient functioning of hepatocytes. In parallel, the gas‐impermeable cultures (polystyrene) with PDMS membrane inserts were used as the control groups [PS‐O2 (−)]. The results indicated that the hepatocytes under 10%‐O2 (+) exhibited improved survival and maintenance of metabolic activities and functional polarization. The dramatic elevation of cellular OCR up to the in vivo liver rate proposed a normoxic environment for hepatocytes, especially when comparing with PS‐O2 (−) cultures, in which the cells generally tolerated hypoxia. Additionally, the expression levels of 84 drug‐metabolism genes were the closest to physiological levels. In conclusion, this study clearly shows the benefit of long‐term culture of hepatocytes at physiological oxygen concentration, and indicates on an oxygen‐permeable membrane system to provide a simple method for in vitro studies.

Comparison of the transcriptomic profile of hepatic human induced pluripotent stem like cells cultured in plates and in a 3D microscale dynamic environment

We have compared the transcriptomic profiles of human induced pluripotent stem cells after their differentiation in hepatocytes like cells in plates and microfluidic biochips. The biochips provided a 3D and dynamic support during the cell differentiation when compared to the 2D static cultures in plates. The microarray have demonstrated the up regulation of important pathway related to liver development and maturation during the culture in biochips. Furthermore, the results of the transcriptomic profile, coupled with immunostaining, and RTqPCR analysis have shown typical biomarkers illustrating the presence of responders of biliary like cells, hepatocytes like cells, and endothelial like cells. However, the overall tissue still presented characteristic of immature and foetal patterns. Nevertheless, the biochip culture provided a specific micro-environment in which a complex multicellular differentiation toward liver could be oriented.

Formation and harvesting of thick pancreatic β-cell sheets on a highly O2-permeable plate modified with poly(N-isopropylacrylamide)

Producing sheet-like tissues is a promising strategy for implantable engineered tissues, because in vitro pre-vascularization is dispensable in this configuration. We developed a simple methodology for the formation and non-destructive harvesting of a thick pancreatic β-cell sheet consisting of mouse insulinoma MIN6-m9 cells and mouse NIH3T3 fibroblasts using an O2-permeable polydimethylsiloxane plate modified with poly(N-isopropylacrylamide) (O2+/PNIPA-PDMS plate). Owing to the direct oxygenation of the cells through the PNIPA-modified PDMS plate, a viable, metabolically active sheet 5-6 cell layers thick (ca. 60 μm thick) was formed spontaneously; in the absence of direct oxygenation, only a thin cell sheet could be formed consisting of at most 2 layers (ca. 20 μm thick) with mainly anaerobic metabolism. Consequently, the net density of MIN6-m9 cells under direct oxygenation was about twice as high as in the absence of direct oxygenation. Accordingly, the insulin secretion for 10 to 60 min after glucose stimulation was also about 1.5 times higher with oxygenation. Furthermore, the thick cell sheet was successfully harvested from the O2+/PNIPA-PDMS plate surface in a non-destructive manner by inducing a phase transition of PNIPA by lowering the temperature below the lower critical solution temperature. Thus, the present report shows a promising and simple method to produce thick sheet-like engineered tissues for transplantation that could be used as a treatment for type 1 diabetes.

Efficient functional cyst formation of biliary epithelial cells using microwells for potential bile duct organisation in vitro

Establishing a bile duct in vitro is valuable to obtain relevant hepatic tissue culture systems for cell-based assays in chemical and drug metabolism analyses. The cyst constitutes the initial morphogenesis for bile duct formation from biliary epithelial cells (BECs) and serves the main building block of bile duct network morphogenesis from the ductal plate during embryogenesis in rodents. Cysts have been commonly cultured via Matrigel-embedded culture, which does not allow structural organisation and restricts the productivity and homogeneity of cysts. In this study, we propose a new method utilising oxygen permeable honeycomb microwells for efficient cyst establishment. Primary mouse BECs were seeded on four sizes of honeycomb microwell (46, 76, 126, and 326 µm-size in diameter). Matrigel in various concentrations was added to assist in cyst formation. The dimension accommodated by microwells was shown to play an important role in effective cyst formation. Cytological morphology, bile acid transportation, and gene expression of the cysts confirmed the favourable basic bile duct function compared to that obtained using Matrigel-embedded culture. Our method is expected to contribute to engineered in vitro liver tissue formation for cell-based assays.

Tissue engineering-based approaches to enhance physiological relevancy of cell-based assays

Animal-free and mechanism-based understanding of human body responses is the ultimate goal of alternative to animal experiments. To achieve this goal, integration of advanced cell-based assays using iPS/ES cell technologies with various numerical methods are required. In this review, from the standpoint of tissue engineering, we focused first on the enhancement of physiological relevance of tissue culture models by overcoming the problem between 3D cellular organization and oxygen/nutrient supply. Second, we summarized the concept and actual systems of microfluidic-based body/organ on-a-chip systems, also called as microphysiological system, MPS, particularly for liver on-a-chip systems. Finally, remaining issues were discussed to realize better physiological relevance in vitro.

Adhesion of Pancreatic Cancer Cells in a Liver-Microvasculature Mimicking Coculture Correlates with Their Propensity to Form Liver-Specific Metastasis In Vivo

Organ-specific characteristic of endothelial cells (ECs) is crucial for specific adhesion of cancer cells to ECs, which is a key factor in the formation of organ-specific metastasis. In this study, we developed a coculture of TMNK-1 (immortalized liver sinusoidal ECs) with 10T1/2 (resembling hepatic stellate cells) to augment organ-specific characteristic of TMNK-1 and investigated adhesion of two pancreatic cancer cells (MIA-PaCa-2 and BxPC-3) in the culture. MIA-PaCa-2 and BxPC-3 adhesion in TMNK-1+10T1/ 2|coating culture (TMNK-1 monolayer over 10T1/2 layer on collagen coated surface) were similar. However, in TMNK-1+10T1/ 2|gel (coculture on collagen gel surface), MIA-PaCa-2 adhesion was significantly higher than BxPC-3, which was congruent with the reported higher propensity of MIA-PaCa-2 than BxPC-3 to form liver metastasis in vivo. Notably, as compared to BxPC-3, MIA-PaCa-2 adhesion was lower and similar in TMNK-1 only culture on the collagen coated and gel surfaces, respectively. Investigation of the adhesion in the representative human umbilical vein ECs (HUVECs) cultures and upon blocking of surface molecules of ECs revealed that MIA-PaCa-2 adhesion was strongly dependent on the organ-specific upregulated characteristics of TMNK-1 in TMNK-1+10T1/ 2|gel culture. Therefore, the developed coculture would be a potential assay for screening novel drugs to inhibit the liver-microvasculature specific adhesion of cancer cells.