A new culture technique for hepatocyte organoid formation and long-term maintenance of liver-specific functions

A bioartificial liver device based on three-dimensional culture of genetically engineered hepatoma cells using hollow fibers

The bioartificial liver (BAL) device is an extracorporeal liver support system incorporating living hepatocytes. A major problem in BAL device development is to obtain a high number of functional cells. In this study, we focused on a genetically engineered mouse hepatoma cell line, Hepa/8F5, in which elevated liver functions are induced via overexpression of liver-enriched transcription factors activated by doxycycline (Dox) addition. We applied a three-dimensional culture technique using hollow fibers (HFs) to Hepa/8F5 cells. Hepa/8F5 cells responded to Dox addition by reducing their proliferative activity and performing liver-specific functions of ammonia removal and albumin secretion. The functional activities of cells depended on the timing of Dox addition. We also found that Hepa/8F5 cells in the HF culture were highly functional in a low rather than high cell density environment. We further fabricated an HF-type bioreactor with immobilized Hepa/8F5 cells as a BAL device. Although ammonia removal activity of this BAL device was lower than that of the small-scale HF bundle, albumin secretion activity was slightly higher. These results indicated that the BAL device with immobilized Hepa/8F5 cells was highly functional with potential to show curative effects in liver failure treatment.

Toxicity testing of four silver nanoparticle-coated dental castings in 3-D LO2 cell cultures

To address the controversial issue of the toxicity of dental alloys and silver nanoparticles in medical applications, an in vivo-like LO2 3-D model was constructed within polyvinylidene fluoride hollow fiber materials to mimic the microenvironment of liver tissue. The use of microscopy methods and the measurement of liver-specific functions optimized the model for best cell performances and also proved the superiority of the 3-D LO2 model when compared with the traditional monolayer model. Toxicity tests were conducted using the newly constructed model, finding that four dental castings coated with silver nanoparticles were toxic to human hepatocytes after cell viability assays. In general, the toxicity of both the castings and the coated silver nanoparticles aggravated as time increased, yet the nanoparticles attenuated the general toxicity by preventing metal ion release, especially at high concentrations.

Evaluation of hollow fiber culture for large-scale production of mouse embryonic stem cell-derived hematopoietic stem cells

Hematopoietic stem cells (HSCs) have the ability to differentiate into all types of blood cells and can be transplanted to treat blood disorders. However, it is difficult to obtain HSCs in large quantities because of the shortage of donors. Recent efforts have focused on acquiring HSCs by differentiation of pluripotent stem cells. As a conventional differentiation method of pluripotent stem cells, the formation of embryoid bodies (EBs) is often employed. However, the size of EBs is limited by depletion of oxygen and nutrients, which prevents them from being efficient for the production of HSCs. In this study, we developed a large-scale hematopoietic differentiation approach for mouse embryonic stem (ES) cells by applying a hollow fiber (HF)/organoid culture method. Cylindrical organoids, which had the potential for further spontaneous differentiation, were established inside of hollow fibers. Using this method, we improved the proliferation rate of mouse ES cells to produce an increased HSC population and achieved around a 40-fold higher production volume of HSCs in HF culture than in conventional EB culture. Therefore, the HF/organoid culture method may be a new mass culture method to acquire pluripotent stem cell-derived HSCs.

Engineered Livers for Infectious Diseases

Engineered liver systems come in a variety of platform models, from 2-dimensional cocultures of primary human hepatocytes and stem cell-derived progeny, to 3-dimensional organoids and humanized mice. Because of the species-specificity of many human hepatropic pathogens, these engineered systems have been essential tools for biologic discovery and therapeutic agent development in the context of liver-dependent infectious diseases. Although improvement of existing models is always beneficial, and the addition of a robust immune component is a particular need, at present, considerable progress has been made using this combination of research platforms. We highlight advances in the study of hepatitis B and C viruses and malaria-causing Plasmodium falciparum and Plasmodium vivax parasites, and underscore the importance of pairing the most appropriate model system and readout modality with the particular experimental question at hand, without always requiring a platform that recapitulates human physiology in its entirety.

Hypoxic preconditioning potentiates the trophic effects of mesenchymal stem cells on co-cultured human primary hepatocytes

Introduction

Mesenchymal stem/stromal cells (MSCs) improve the metabolic function of co-cultured hepatocytes. The present study aimed to further enhance the trophic effects of co-culture with hepatocytes using hypoxic preconditioning (HPc) of the MSCs and also to investigate the underlying molecular mechanisms involved.

Methods

Human adipose tissue-derived MSCs were subjected to hypoxia (2 % O₂; HPc) or normoxia (20 % O₂) for 24 h and then co-cultured with isolated human hepatocytes. Assays of metabolic function and apoptosis were performed to investigate the hepatotrophic and anti-apoptotic effects of co-culture. Indirect co-cultures and co-culture with MSC-conditioned medium investigated the role of paracrine factors in the hepatotrophic effects of co-culture. Reactive oxygen species (ROS) activity was antagonised with N-acetylcysteine to investigate whether HPc potentiated the effects of MSCs by intracellular ROS-dependent mechanisms. Tumour necrosis factor (TNF)-α, transforming growth factor (TGF)-β1, and extracellular collagen production was determined and CASP9 and BAX/BCL-2 signalling pathways analysed to investigate the role of soluble factors, extracellular matrix deposition, and apoptosis-associated gene signalling in the effects of co-culture.

Results

HPc potentiated the hepatotrophic and anti-apoptotic effects of co-culture by ROS-dependent mechanisms. There was increased MSC TGF-β1 production, and enhanced MSC deposition of extracellular collagen, with reduced synthesis of TNF-α, as well as a downregulation of the expression of pro-apoptotic CASP9, BAX, BID and BLK genes and upregulated expression of anti-apoptotic BCL-2 in hepatocytes.

Conclusions

HPc potentiated the trophic and anti-apoptotic effects of MSCs on hepatocytes via mechanisms including intracellular ROS, autocrine TGF-β, extracellular collagen and caspase and BAX/BCL-2 signalling pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0218-7) contains supplementary material, which is available to authorized users.

New Methods in Tissue Engineering: Improved Models for Viral Infection

New insights in the study of virus and host biology in the context of viral infection are made possible by the development of model systems that faithfully recapitulate the in vivo viral life cycle. Standard tissue culture models lack critical emergent properties driven by cellular organization and in vivo-like function, whereas animal models suffer from limited susceptibility to relevant human viruses and make it difficult to perform detailed molecular manipulation and analysis. Tissue engineering techniques may enable virologists to create infection models that combine the facile manipulation and readouts of tissue culture with the virus-relevant complexity of animal models. Here, we review the state of the art in tissue engineering and describe how tissue engineering techniques may alleviate some common shortcomings of existing models of viral infection, with a particular emphasis on hepatotropic viruses. We then discuss possible future applications of tissue engineering to virology, including current challenges and potential solutions.

Effects of coencapsulation of hepatocytes with adipose-derived stem cells in the treatment of rats with acute-on-chronic liver failure

Introduction

Cell transplantation is an alternative to liver transplantation, which is hampered by short survival time and immunorejection. The goal of this study was to evaluate the therapeutic potential of hepatocytes coencapsulated with adipose-derived stem cells (ADSCs) in treating acute-on-chronic liver failure (ACLF).

Methods

Rat hepatocytes and ADSCs were isolated, and coencapsulated by alginate-poly-L-lysinealginate microencapsulation. The morphological and functional changes of heterotypic interactions were characterized. ACLF in rats was induced by D-galactosamine administration following CCl4-induced cirrhosis. These rats were subjected to intraperitoneal transplantation of 5 × 10⁷ coencapsulated hepatocytes with ADSCs, 5 × 10⁷ encapsulated hepatocytes alone, or empty vehicles after 24 h, respectively. The survival rate and liver functions were assessed.

Results

Hepatocyte performance levels such as albumin secretion and urea synthesis induction were all significantly enhanced in the coencapsulation group compared with the homo-encapsulated hepatocytes group (p<0.05). The results of cell cycle analysis showed that larger populations of hepatocytes with ADSC treatment were accumulated in the G2-S phase, and there were fewer in the G0-G1 phase compared to encapsulation of hepatocytes alone. Intraperitoneal transplantation of coencapsulated hepatocytes with ADSCs not only increased the survival rate, but also improved liver functions in a rat model of ACLF.

Conclusions

Transplantation of coencapsulated hepatocytes and ADSCs might be a promising strategy for cell-based therapy of acute liver diseases.

Application of open porous poly(D,L-lactide-co-glycolide) microspheres and the strategy of hydrophobic seeding in hepatic tissue cultivation

In this article, porous poly(D,L-lactide-co-glycolide) (PLGA) microsphere scaffolds with a size of ∼ 400 μm and pores of ∼ 20 μm were prepared for constructing injectable three-dimensional hepatocyte spheroids. The porous sites of PLGA microspheres provided a spatial space for hepatocyte distribution. Hepatocytes spheroids were cocultured with human umbilical vein endothelial cell, bone marrow mesenchymal stem cell, or NIH/3T3 cells by combining the porous PLGA microspheres with the relatively hydrophobic culture strategy. The combination of open porous microspheres, hepatocytes, and nonparenchymal cells was demonstrated for application in functional hepatic tissue reconstruction. Hepatocellular-specific functions can sustained up to 2 weeks in the support of coculturing with nonparenchymal cells. The spheroidal hepatocyte coculture system had the advantages of an injectable delivery, higher cell seeding density, protection from exerted shear stress, better exchange of nutrients, oxygen and metabolites, and heterotypic cell-cell contact within and between microspheres.

Controlled formation of heterotypic hepatic micro-organoids in anisotropic hydrogel microfibers for long-term preservation of liver-specific functions

We have developed a hydrogel-based cell cultivation platform for forming 3D restiform hepatic micro-organoids consisting of primary rat hepatocytes and feeder cells (Swiss 3T3 cells). Sodium alginate solutions containing hepatocytes/3T3 cells were continuously introduced into a microfluidic channel to produce cell-incorporating anisotropic Ba-alginate hydrogel microfibers, where hepatocytes at the center were closely sandwiched by 3T3 cells. Hydrogel fiber-based cultivation under high oxygen tension enabled the formation of heterotypic micro-organoids with a length of up to 1 mm and a diameter of ∼50 μm, mimicking the hepatic cord structures found in the liver, while maintaining a high hepatocyte viability (∼80%) over 30 days. Long-term observation of up to 90 days revealed a significant enhancement of hepatic functions because of heterotypic and homotypic cell-cell interactions, including albumin secretion and urea synthesis as well as expression of hepatocyte-specific genes, compared with conventional monolayer culture and single cultivation in the hydrogel fibers. The encapsulated hepatic constructs were recovered as scaffold-free micro-organoids by enzymatically digesting the hydrogel matrices using alginate lyase. This technique for creating heterotypic micro-organoids with precisely ordered multiple cell types will be useful for the development of a new liver tissue engineering approach and may be applicable to the fabrication of extracorporeal bioartificial liver (BAL) devices and assessment tools for drug development and testing.

Biotransformation of diclofenac and effects on the metabolome of primary human hepatocytes upon repeated dose exposure

In vitro repeated dose testing for the assessment of chronic drug-induced effects is a huge challenge in preclinical pharmaceutical drug development. Chronic toxicity results in discontinuation of therapy or post-marketing withdrawal of drugs despite in vivo preclinical screening. In case of hepatotoxicity, due to limited long term viability and functionality of primary hepatocytes, chronic hepatic effects are difficult to detect. In this study, we maintained primary human hepatocytes in a serum-free cultivation medium for more than 3 weeks and analyzed physiology, viability and drug metabolizing capacities of the hepatocytes. Moreover, we assessed acute (24 h) diclofenac toxicity in a range of (10-1000 μM) concentrations. The chronic (9 repeated doses) toxicity at one clinically relevant and another higher concentration (6.4 and 100 μM) was also tested. We investigated phase I and II metabolism of diclofenac upon repeated dose exposure and analyzed effects on the cellular exometabolome. Acute 24 h assessment revealed toxicity only for the highest tested concentration (1 mM). Upon repeated dose exposure, toxic effects were observed even at a low, clinically relevant concentration (6.4 μM). Biotransformation pathways were active for 3 weeks and diclofenac-acylglucuronide was detected as the predominant metabolite. Dose dependent diclofenac-induced effects on exometabolome, such as on the production of lactate and 3-hydroxybutyric acid as well as glucose and galactose metabolism, were observed upon nine repeated doses. Summarizing, we show that repeated dose testing on long-term functional cultures of primary human hepatocytes may be included for the assessment of long term toxic effects in preclinical screening and can potentially help replace/reduce in vivo animal testing.

Porous and single-skinned polyethersulfone membranes support the growth of HepG2 cells: A potential biomaterial for bioartificial liver systems

In this study, we evaluated a porous and single-layer skin polyethersulfone (PES) membrane as a material for use in hybrid bioartificial liver support systems. The PES membrane has been characterized as a single-layer skin structure, with a rough porous surface. Specifically, we studied the ability of the human hepatoblastoma cell lines (HepG2) to adhere, grow, and spread on the PES membrane. Furthermore, we examined albumin secretion, low-density lipoprotein uptake, and CYP450 activity of HepG2 cells that grew on the membrane. HepG2 cells readily adhered onto the outer surfaces of PES membranes. Over time, HepG2 cells proliferated actively, and confluent monolayer of cells covered the available surface area of the membrane, eventually forming cell clusters and three-dimensional aggregates. Furthermore, HepG2 cells grown on PES membranes maintained highly specific functions, including uptake capability, biosynthesis and biotransformation. These results indicate that PES membranes are potential substrates for the growth of human liver cells and may be useful in the construction of hollow fiber bioreactors. Porous and single-layer skin PES membranes and HepG2 cells may be potential biomaterials for the development of biohybrid liver devices.

Hepatic differentiation of mouse embryonic stem cells and induced pluripotent stem cells during organoid formation in hollow fibers

We have focused on pluripotent stem cells as a potential source of a hybrid-type artificial liver (HAL) and tried to develop a method for differentiating the pluripotent stem cells into cells of a hepatic lineage. In this study, we investigated the hepatic differentiation of mouse embryonic stem (ES) cells and induced pluripotent stem (iPS) cells by applying hollow fiber (HF)/organoid culture method, in which cultured cells form a cellular aggregate called an "organoid" in the lumen of the HF. ES and iPS cells were injected into HFs to induce organoid formation, and cells were cultured. To induce hepatic differentiation, we added differentiation-promoting agents to the culture medium. The expression levels of differentiation-related genes were up-regulated, with cell proliferation and organoid formation inside HFs. Since we were able to achieve a high cell density in culture, the maximum levels of liver-specific functions per unit volume in the differentiating ES and iPS cells reached a level comparable to or better than that of primary mouse hepatocytes. In conclusion, ES and iPS cells have the potential to be a cell source for a HAL, and the HF/organoid culture method, therefore, has promise as a basic technology for the development of a HAL.

An approach for formation of vascularized liver tissue by endothelial cell-covered hepatocyte spheroid integration

Tissue vascularization in vitro is necessary for cell transplantation and is a major challenge in tissue engineering. To construct large and regularly vascularized tissue, we focused on the integration of endothelial cell-covered spheroids. Primary rat hepatocytes were cultured on a rotary shaker, and 100-150 mum spheroids were obtained by filtration. The hepatocyte spheroids were coated with collagen by conjugation with a type 1 collagen solution. Collagen-coated hepatocyte spheroids were cocultured with human umbilical vein endothelial cells (HUVECs), and monolayered HUVEC-covered hepatocyte spheroids were constructed. Without a collagen coat, many HUVECs invaded hepatocyte spheroids but did not cover the spheroid surface. To construct regularly vascularized tissue, we packed HUVEC-covered hepatocyte spheroids in hollow fibers used for plasma separation. Packed spheroids attached to each other forming a large cellular tissue with regular distribution of HUVECs. At day 9 after packing, HUVECs invaded the hepatocyte spheroids and a dense vascular network was constructed. Collagen coating of spheroids is useful for the formation of endothelial cell-covered spheroids and subsequent regular vascularized tissue construction.

Strain-dependent viral dynamics and virus-cell interactions in a novel in vitro system supporting the life cycle of blood-borne hepatitis C virus

We developed an in vitro system that can be used for the study of the life cycle of a wide variety of blood-borne hepatitis C viruses (HCV) from various patients using a three-dimensional hollow fiber culture system and an immortalized primary human hepatocyte (HuS-E/2) cell line. Unlike the conventional two-dimensional culture, this system not only enhanced the infectivity of blood-borne HCV but also supported its long-term proliferation and the production of infectious virus particles. Both sucrose gradient fractionation and electron microscopy examination showed that the produced virus-like particles are within a similar fraction and size range to those previously reported. Infection with different HCV strains showed strain-dependent different patterns of HCV proliferation and particle production. Fluctuation of virus proliferation and particle production was found during prolonged culture and was found to be associated with change in the major replicating virus strain. Induction of cellular apoptosis was only found when strains of HCV-2a genotype were used for infection. Interferon-alpha stimulation also varied among different strains of HCV-1b genotypes tested in this study.

CONCLUSION

These results suggest that this in vitro infection system can reproduce strain-dependent events reflecting viral dynamics and virus-cell interactions at the early phase of blood-borne HCV infection, and that this system can allow the development of new anti-HCV strategies specific to various HCV strains.

Evaluation of a bioreactor with stacked sheet shaped organoids of primary hepatocytes

Hepatocyte organoids have an in vivo-like cell morphology and maintain cell viability and function in vitro. On the other hand, the oxygen supply to hepatocytes is sometimes limited in the core of organoids that are more than 100 mum in thickness. In this study, we designed and examined a new bioreactor using sheet-shaped organoids (organoid-sheets) in which the thickness was controlled to prevent hepatocyte death in the core of organoid due to limitation of oxygen supply. The cell culture space consisted of stacked organoid formation spaces and medium flow channels. Each space was separated by flat porous polycarbonate membranes, and the organoid thickness was controlled at 100 microm with a stainless steel spacer. Freshly isolated hepatocytes (7.0 x 10(7)) were immobilized in the bioreactor, yielding a cell density of 4.5 x 10(7) cells/cm(3)-bioreactor. Of the five flow rates tested (1.0, 5.0, 10, 20, and 50 mL/min), the bioreactor with the 10 mL/min had the highest ammonia removal and albumin secretion activities for at least 14 days. In conclusion, a new bioreactor controlling organoid thickness is useful for achieving high cell density culture and the maintenance of hepatocyte function to avoid cell death in the core of the organoids due to limitation of oxygen supply. The bioreactor may be useful for the development of various applications using cultured hepatocytes.

Establishment of a three-dimensional co-culture system by porcine hepatocytes and bone marrow mesenchymal stem cells in vitro

AIM

The application of porcine hepatocytes in liver support systems has been hampered by the short-term survival. Co-cultivation of hepatocytes with non-parenchymal cells may be beneficial for optimizing cell functions via heterotypic interactions. In this study, we present a new cultivation system of porcine hepatocytes and mesenchymal stem cells (MSCs) in a randomly distributed co-culture manner.

METHODS

Mononuclear cells were isolated from bone marrow aspirate of swines (n = 3) by density gradient centrifugation. MSCs were characterized by flow cytometry with CD29, CD44, CD45 and CD90, respectively. Then freshly isolated hepatocytes were simultaneously inoculated with MSCs in a hepatocyte dominant manner. The morphological and functional changes of heterotypic interactions were characterized.

RESULTS

Ninety percent MSCs of passage 3 were positive for CD29, CD44 and CD90, but negative for CD45. A rapid attachment and self-organization of three-dimensional hepatocyte aggregates were encouraged. The cell ultrastructure indicating heterotypic junctions remained similar to that of hepatocytes in vivo. Fluorescence microscopy further verified that MSCs served as a feeder layer for hepatocyte aggregates. Hepatocyte performance levels such as albumin secretion, urea synthesis and CYP3A1 induction were all significantly enhanced in co-culture group compared with hepatocyte homo-culture (P < 0.05). The best hepatic function levels were achieved on day 2 and moderately decreased in the following co-culture days. Moreover, the cell cycle of hepatocytes manifested the same trend in parallel to the enhancement of hepatocyte functionality.

CONCLUSIONS

A three-dimensional co-culture system by porcine hepatocytes and bone marrow MSCs was for the first time established in vitro. Enhanced liver-specific functions make such a co-culture system a promising tool for tissue engineering, cell biology, and bioartificial liver devices.