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

Stem Cell-Based Strategies: The Future Direction of Bioartificial Liver Development

Acute liver failure (ALF) results from severe liver damage or end-stage liver disease. It is extremely fatal and causes serious health and economic burdens worldwide. Once ALF occurs, liver transplantation (LT) is the only definitive and recommended treatment; however, LT is limited by the scarcity of liver grafts. Consequently, the clinical use of bioartificial liver (BAL) has been proposed as a treatment strategy for ALF. Human primary hepatocytes are an ideal cell source for these methods. However, their high demand and superior viability prevent their widespread use. Hence, finding alternatives that meet the seed cell quality and quantity requirements is imperative. Stem cells with self-renewing, immunogenic, and differentiative capacities are potential cell sources. MSCs and its secretomes encompass a spectrum of beneficial properties, such as anti-inflammatory, immunomodulatory, anti-ROS (reactive oxygen species), anti-apoptotic, pro-metabolomic, anti-fibrogenesis, and pro-regenerative attributes. This review focused on the recent status and future directions of stem cell-based strategies in BAL for ALF. Additionally, we discussed the opportunities and challenges associated with promoting such strategies for clinical applications.

Using Liver Organoids as Models to Study the Pathobiology of Rare Liver Diseases

Liver organoids take advantage of several important features of pluripotent stem cells that self-assemble in a three-dimensional culture matrix and reproduce many aspects of the complex organization found within their native tissue or organ counterparts. Compared to other 2D or 3D in vitro models, organoids are widely believed to be genetically stable or docile structures that can be programmed to virtually recapitulate certain biological, physiological, or pathophysiological features of original tissues or organs in vitro. Therefore, organoids can be exploited as effective substitutes or miniaturized models for the study of the developmental mechanisms of rare liver diseases, drug discovery, the accurate evaluation of personalized drug responses, and regenerative medicine applications. However, the bioengineering of organoids currently faces many groundbreaking challenges, including a need for a reasonable tissue size, structured organization, vascularization, functional maturity, and reproducibility. In this review, we outlined basic methodologies and supplements to establish organoids and summarized recent technological advances for experimental liver biology. Finally, we discussed the therapeutic applications and current limitations.

Liver organoids: a promising three-dimensional model for insights and innovations in tumor progression and precision medicine of liver cancer

Primary liver cancer (PLC) is one type of cancer with high incidence rate and high mortality rate in the worldwide. Systemic therapy is the major treatment for PLC, including surgical resection, immunotherapy and targeted therapy. However, mainly due to the heterogeneity of tumors, responses to the above drug therapy differ from person to person, indicating the urgent needs for personalized treatment for PLC. Organoids are 3D models derived from adult liver tissues or pluripotent stem cells. Based on the ability to recapitulate the genetic and functional features of in vivo tissues, organoids have assisted biomedical research to make tremendous progress in understanding disease origin, progression and treatment strategies since their invention and application. In liver cancer research, liver organoids contribute greatly to reflecting the heterogeneity of liver cancer and restoring tumor microenvironment (TME) by co-organizing tumor vasculature and stromal components in vitro. Therefore, they provide a promising platform for further investigation into the biology of liver cancer, drug screening and precision medicine for PLC. In this review, we discuss the recent advances of liver organoids in liver cancer, in terms of generation methods, application in precision medicine and TME modeling.

Multicellular Liver Organoids: Generation and Importance of Diverse Specialized Cellular Components

Over 40,000 patients in the United States are estimated to suffer from end-stage liver disease and acute hepatic failure, for which liver transplantation is the only available therapy. Human primary hepatocytes (HPH) have not been employed as a therapeutic tool due to the difficulty in growing and expanding them in vitro, their sensitivity to cold temperatures, and tendency to dedifferentiate following two-dimensional culture. The differentiation of human-induced pluripotent stem cells (hiPSCs) into liver organoids (LO) has emerged as a potential alternative to orthotropic liver transplantation (OLT). However, several factors limit the efficiency of liver differentiation from hiPSCs, including a low proportion of differentiated cells capable of reaching a mature phenotype, the poor reproducibility of existing differentiation protocols, and insufficient long-term viability in vitro and in vivo. This review will analyze various methodologies being developed to improve hepatic differentiation from hiPSCs into liver organoids, paying particular attention to the use of endothelial cells as supportive cells for their further maturation. Here, we demonstrate why differentiated liver organoids can be used as a research tool for drug testing and disease modeling, or employed as a bridge for liver transplantation following liver failure.

Dialysis based-culture medium conditioning improved the generation of human induced pluripotent stem cell derived-liver organoid in a high cell density

Human pluripotent stem cell-derived liver organoids (HLOs) have recently become a promising alternative for liver regenerative therapy. To realize this application, a large amount of human-induced pluripotent stem cells (hiPSCs) derived-liver cells are required for partial liver replacement during transplantation. This method requires stepwise induction using costly growth factors to direct the hiPSCs into the hepatic lineage. Therefore, we developed a simple dialysis-based medium conditioning that fully utilized growth factors accumulation to improve hepatic differentiation of hiPSCs at a high cell density. The results demonstrated that the dialysis culture system could accumulate the four essential growth factors required in each differentiation stage: activin A, bone morphogenetic protein 4 (BMP4), hepatocyte growth factor (HGF), and oncostatin M (OSM). As a result, this low lactate culture environment allowed high-density bipotential hepatic differentiation of up to 4.5 × 10⁷ cells/mL of human liver organoids (HLOs), consisting of hiPSC derived-hepatocyte like cells (HLCs) and cholangiocyte like-cells (CLCs). The differentiated HLOs presented a better or comparable hepatic marker and hepatobiliary physiology to the one that differentiated in suspension culture with routine daily medium replacement at a lower cell density. This simple miniaturized dialysis culture system demonstrated the feasibility of cost-effective high-density hepatic differentiation with minimum growth factor usage.

Size-dependent hepatic differentiation of human induced pluripotent stem cells spheroid in suspension culture

Suspension culture of three-dimensional (3D) spheroid of human induced pluripotent stem cells (hiPSCs) has been known as a potential method to enhance the scalability of hepatic differentiation of hiPSCs. However, the impact of size-related factor of initial formed spheroid were not largely considered. To address this problem, we evaluate the impact of different specific spheroid size of hiPSCs by forming the individual spheroid from different number of hiPSCs and differentiated into hiPSCs-derived hepatocytes (iHeps). The results showed that larger spheroid exhibit enhanced capability to differentiated into hepatic lineage by increasing the expression marker albumin, CYP3A4 and lower expression of fetal hepatic marker AFP. Several factor such as the tendency of cystic like structure forming, the necrotic area of the large dense spheroid, and interference of WNT/β-catenin signaling was significantly affecting the resulted iHeps. In this study, we suggest that the optimal spheroid size for hepatic differentiation can be attained from 500 to 600 μm diameter spheroid formed from 12,500–25,000 hiPSCs. This size can be potentially applied for various practical use of hepatic differentiation in scalable suspension culture.

Physiological Microenvironmental Conditions in Different Scalable Culture Systems for Pluripotent Stem Cell Expansion and Differentiation

Human Pluripotent Stem Cells (PSCs) are a valuable cell type that has a wide range of biomedical applications because they can differentiate into many types of adult somatic cell. Numerous studies have examined the clinical applications of PSCs. However, several factors such as bioreactor design, mechanical stress, and the physiological environment have not been optimized. These factors can significantly alter the pluripotency and proliferation properties of the cells, which are important for the mass production of PSCs. Nutritional mass transfer and oxygen transfer must be effectively maintained to obtain a high yield. Various culture systems are currently available for optimum cell propagation by maintaining the physiological conditions necessary for cell cultivation. Each type of culture system using a different configuration with various advantages and disadvantages affecting the mechanical conditions in the bioreactor, such as shear stress. These factors make it difficult to preserve the cellular viability and pluripotency of PSCs. Additional limitations of the culture system for PSCs must also be identified and overcome to maintain the culture conditions and enable large-scale expansion and differentiation of PSCs. This review describes the different physiological conditions in the various culture systems and recent developments in culture technology for PSC expansion and differentiation.

Expression profiling of adhesion proteins during prenatal and postnatal liver development in rats

Culturing of primary hepatocytes and stem cell-derived hepatocytes faces a major issue of dedifferentiation due to absence of cell–cell adhesion and 3D structures. One of the possible ways to eliminate the problem of dedifferentiation is mimicking the expression pattern of adhesion proteins during the normal developmental process of liver cells. The purpose of this study was to evaluate the expression pattern of some key adhesion proteins, namely, E-cadherin, N-cadherin, epithelial CAM (EpCAM), intracellular CAM (ICAM), collagen 1α1, α-actinin, β-catenin and vimentin, in the liver tissue during prenatal and postnatal stages. Furthermore, differences in their expression between prenatal, early postnatal and adult stages were highlighted. Wistar rats were used to isolate livers at prenatal Day 14 and 17 as well as on postnatal Day 1, 3, 7 and 14. The liver from adult rats was used as control. Both conventional and real-time quantitative polymerase chain reactions (PCRs) were performed. For most of the adhesion proteins such as E-cadherin, N-cadherin, EpCAM, ICAM, collagen 1α1 and α-actinin, low expression was observed around prenatal Day 14 and an increasing expression was observed in the postnatal period. Moreover, β-catenin and vimentin showed higher expression in the early prenatal period, which decreased gradually in the postnatal period, but still this low expression was considerably higher than that in the adult control rats. This basic knowledge of the regulation of expression of adhesion proteins during different developmental stages indicates their vital role in liver development. This pattern can be further studied and imitated under in vitro conditions to achieve better cell–cell interactions.

Hepatic differentiation of porcine embryonic stem cells for translational research of hepatocyte transplantation

Porcine embryonic stem cells (ES) are considered attractive preclinical research tools for human liver diseases. Although several studies previously reported generation of porcine ES, none of these studies has described hepatic differentiation from porcine ES. The aim of this study was to generate hepatocytes from porcine ES and analyze their characteristics. We optimized conditions for definitive endoderm induction and developed a 4-step hepatic differentiation protocol. A brief serum-free condition with activin A efficiently induced definitive endoderm differentiation from porcine ES. The porcine ES-derived hepatocyte-like cells highly expressed hepatic markers including albumin and α-fetoprotein, and displayed liver characteristics such as glycogen storage, lipid production, and low-density lipoprotein uptake. For the first time, we describe a highly efficient protocol for hepatic differentiation from porcine ES. Our findings provide valuable information for translational liver research using porcine models, including hepatic regeneration and transplant studies, drug screening, and toxicology.

In vitro culture of isolated primary hepatocytes and stem cell-derived hepatocyte-like cells for liver regeneration

Various liver diseases result in terminal hepatic failure, and liver transplantation, cell transplantation and artificial liver support systems are emerging as effective therapies for severe hepatic disease. However, all of these treatments are limited by organ or cell resources, so developing a sufficient number of functional hepatocytes for liver regeneration is a priority. Liver regeneration is a complex process regulated by growth factors (GFs), cytokines, transcription factors (TFs), hormones, oxidative stress products, metabolic networks, and microRNA. It is well-known that the function of isolated primary hepatocytes is hard to maintain; when cultured in vitro, these cells readily undergo dedifferentiation, causing them to lose hepatocyte function. For this reason, most studies focus on inducing stem cells, such as embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), hepatic progenitor cells (HPCs), and mesenchymal stem cells (MSCs), to differentiate into hepatocyte-like cells (HLCs) in vitro. In this review, we mainly focus on the nature of the liver regeneration process and discuss how to maintain and enhance in vitro hepatic function of isolated primary hepatocytes or stem cell-derived HLCs for liver regeneration. In this way, hepatocytes or HLCs may be applied for clinical use for the treatment of terminal liver diseases and may prolong the survival time of patients in the near future.

Trichostatin A combined with cytokines induces differentiation of embryonic stem cells into hepatocytes

AIM: To present a novel 3-step procedure to efficiently direct the differentiation of mouse embryonic stem cells (ESCs) into hepatocytes.

METHODS: Mouse ESCs were first induced to differentiate into definitive endoderm cells by three days of activin A treatment. Next, definitive endoderm cells were induced to efficiently differentiate to hepatocytes in the presence of acid fibroblast growth factor (aFGF) and trichostatin A (TSA) in the culture medium for 5 d.

RESULTS: After 10 d of further in vitro maturation, the morphological and phenotypic markers of hepatocytes were characterized using light microscopy, immunofluorescence and RT-PCR. Furthermore, these cells were tested for the functions associated with mature hepatocytes including glycogen storage, indocyanine green uptake and release, and the rate of hepatic differentiation was determined by counting the albumin-positive cells, which showed that the rate of hepatic differentiation was 57.38%.

CONCLUSION: The method presented in this study provides a new resource for hepatocyte transplantation.

An efficient method for differentiation of human induced pluripotent stem cells into hepatocyte-like cells retaining drug metabolizing activity

The use of human induced pluripotent stem (iPS) cells would be of great value for a variety of applications involving drug development studies. Several reports have been published on the differentiation of human iPS cells into hepatocyte-like cells; however, the cells were insufficient for application in drug metabolism studies. In this study, we aimed to establish effective methods for differentiation of human iPS cells into hepatocytes. Two human iPS cell lines were differentiated by addition of activin A, dimethyl sulfoxide, hepatocyte growth factor, oncostatin M, and dexamethasone. The differentiated cells expressed hepatocyte markers and drug-metabolizing enzymes, revealing that the human iPS cells were differentiated into hepatocyte-like cells. Expression of CYP3A4 and UGT1A1 mRNAs increased with treatment with typical inducers of the enzymes, and the response of the cells against the inducers was similar to that of human hepatocytes. Furthermore, the drug-metabolizing activity of CYP3A4, as monitored by testosterone 6β-hydroxylase activity, was elevated by these inducers. In conclusion, we established methods for differentiation of hepatocyte-like cells expressing drug metabolizing activity from human iPS cells. The hepatocyte-like cells derived from human iPS cells will be useful for drug metabolism studies.

Effect of oxygen concentration on viability and metabolism in a fluidized-bed bioartificial liver using ³¹P and ¹³C NMR spectroscopy

Many oxygen mass-transfer modeling studies have been performed for various bioartificial liver (BAL) encapsulation types; yet, to our knowledge, there is no experimental study that directly and noninvasively measures viability and metabolism as a function of time and oxygen concentration. We report the effect of oxygen concentration on viability and metabolism in a fluidized-bed NMR-compatible BAL using in vivo ³¹P and ¹³C NMR spectroscopy, respectively, by monitoring nucleotide triphosphate (NTP) and ¹³C-labeled nutrient metabolites, respectively. Fluidized-bed bioreactors eliminate the potential channeling that occurs with packed-bed bioreactors and serve as an ideal experimental model for homogeneous oxygen distribution. Hepatocytes were electrostatically encapsulated in alginate (avg. diameter, 500 μm; 3.5×10⁷ cells/mL) and perfused at 3 mL/min in a 9-cm (inner diameter) cylindrical glass NMR tube. Four oxygen treatments were tested and validated by an in-line oxygen electrode: (1) 95:5 oxygen:carbon dioxide (carbogen), (2) 75:20:5 nitrogen:oxygen:carbon dioxide, (3) 60:35:5 nitrogen:oxygen:carbon dioxide, and (4) 45:50:5 nitrogen:oxygen:carbon dioxide. With 20% oxygen, β-NTP steadily decreased until it was no longer detected at 11 h. The 35%, 50%, and 95% oxygen treatments resulted in steady β-NTP levels throughout the 28-h experimental period. For the 50% and 95% oxygen treatment, a ¹³C NMR time course (∼5 h) revealed 2-¹³C-glycine and 2-¹³C-glucose to be incorporated into [2-¹³C-glycyl]glutathione (GSH) and 2-¹³C-lactate, respectively, with 95% having a lower rate of lactate formation. ³¹P and ¹³C NMR spectroscopy is a noninvasive method for determining viability and metabolic rates. Modifying tissue-engineered devices to be NMR compatible is a relatively easy and inexpensive process depending on the bioreactor shape.

Stem cells in liver failure

Orthotopic liver transplantation (OLT) represents the only reliable therapeutic approach for acute liver failure (ALF), liver failure associated to end-stage chronic liver diseases (CLD) and non-metastatic liver cancer. The clinical impact of liver failure is relevant because of the still high ALF mortality and the increasing worldwide prevalence of cirrhosis that, in turn, is the main predisposing cause for hepatocellular carcinoma (HCC). Moreover, in the next decade because an increased number of patients reaching end-stage disease and requiring OLT may face a shortage of donor livers. This clinical scenario led several laboratories to explore the feasibility and efficiency of alternative approaches, involving cellular therapy, to counteract liver failure. The present chapter overviews results and concepts emerged from recent experimental and clinical studies in which adult or embryonic hepatocytes, hepatic stem/progenitor cells, induced pluripotent stem (iPS) cells as well as extrahepatic stem cells have been used as putative transplantable cell sources.

Generation of functional hepatic cells from pluripotent stem cells

Liver diseases affect millions of people worldwide, especially in developing country. According to the American Liver Foundation, nearly 1 in every 10 Americans suffers from some form of liver disease. Even though, the liver has great ability to self-repair, in end-stage liver diseases including fibrosis, cirrhosis, and liver cancer induced by viral hepatitis and drugs, the liver regenerative capacity is exhausted. The only successful treatment for chronic liver failure is the whole liver transplantation. More recently, some clinical trials using hepatocyte transplantation have shown some clinical improvement for metabolic liver diseases and acute liver failure. However, the shortage of donor livers remains a life-threatening challenge in liver disease patients. To overcome the scarcity of donor livers, hepatocytes generated from embryonic stem cell or induced pluripotent stem cell differentiation cultures could provide an unlimited supply of such cells for transplantation. This review provides an updated summary of hepatic differentiation protocols published so far, with a characterization of the hepatic cells generated in vitro and their ability to regenerate damaged livers in vivo following transplantation in pre-clinical liver deficient mouse models.