A Scalable Approach for the Generation of Human Pluripotent Stem Cell-Derived Hepatic Organoids with Sensitive Hepatotoxicity Features

Scaffold-based 3D cell culture models in cancer research

Three-dimensional (3D) cell cultures have emerged as valuable tools in cancer research, offering significant advantages over traditional two-dimensional (2D) cell culture systems. In 3D cell cultures, cancer cells are grown in an environment that more closely mimics the 3D architecture and complexity of in vivo tumors. This approach has revolutionized cancer research by providing a more accurate representation of the tumor microenvironment (TME) and enabling the study of tumor behavior and response to therapies in a more physiologically relevant context. One of the key benefits of 3D cell culture in cancer research is the ability to recapitulate the complex interactions between cancer cells and their surrounding stroma. Tumors consist not only of cancer cells but also various other cell types, including stromal cells, immune cells, and blood vessels. These models bridge traditional 2D cell cultures and animal models, offering a cost-effective, scalable, and ethical alternative for preclinical research. As the field advances, 3D cell cultures are poised to play a pivotal role in understanding cancer biology and accelerating the development of effective anticancer therapies. This review article highlights the key advantages of 3D cell cultures, progress in the most common scaffold-based culturing techniques, pertinent literature on their applications in cancer research, and the ongoing challenges.

The Current Proceedings of PSC-Based Liver Fibrosis Therapy

Liver fibrosis was initially considered to be an irreversible process which will eventually lead to the occurrence of liver cancer. So far there has been no effective therapeutic approach to treat liver fibrosis although scientists have put tremendous efforts into the underlying mechanisms of this disease. Therefore, in-depth research on novel and safe treatments of liver fibrosis is of great significance to human health. Pluripotent stem cells (PSCs) play important roles in the study of liver fibrosis due to their unique features in self-renewal ability, pluripotency, and paracrine function. This article mainly reviews the applications of PSCs in the study of liver fibrosis in recent years. We discuss the role of PSC-derived liver organoids in the study of liver fibrosis, and the latest research advances on the differentiation of PSCs into hepatocytes or macrophages. We also highlight the importance of exosomes of PSCs for the treatment of liver fibrosis.

Progress and promise of alternative animal and non-animal methods in biomedical research

Cell culture and invertebrate animal models reflect a significant evolution in scientific research by providing reliable evidence on the physiopathology of diseases, screening for new drugs, and toxicological tests while reducing the need for mammals. In this review, we discuss the progress and promise of alternative animal and non-animal methods in biomedical research, with a special focus on drug toxicity.

Liver organoids: established tools for disease modeling and drug development

In the past decade, liver organoids have evolved rapidly as valuable research tools, providing novel insights into almost all types of liver diseases, including monogenic liver diseases, alcohol-associated liver disease, metabolic-associated fatty liver disease, various types of (viral) hepatitis, and liver cancers. Liver organoids in part mimic the microphysiology of the human liver and fill a gap in high-fidelity liver disease models to a certain extent. They hold great promise to elucidate the pathogenic mechanism of a diversity of liver diseases and play a crucial role in drug development. Moreover, it is challenging but opportunistic to apply liver organoids for tailored therapies of various liver diseases. The establishment, applications, and challenges of different types of liver organoids, for example, derived from embryonic, adult, or induced pluripotent stem cells, to model different liver diseases, are presented in this review.

Culture of organoids with vestibular cell-derived factors promotes differentiation of embryonic stem cells into inner ear vestibular hair cells

Vestibular hair cells (V-HCs) residing in the inner ear have important roles related to balance. Although differentiation of pluripotent stem cells into HCs has been shown, an effective method has yet to be established. We previously reported that use of vestibular cell-derived conditioned medium (V-CM) was helpful to induce embryonic stem (ES) cells to differentiate into V-HC-like cells in two-dimensional (2D) cultures of ES-derived embryoid bodies (EBs). In the present report, V-CM was used with three-dimensional (3D) cultures of EBs, which resulted in augmented expression of V-HC-related markers (Math1, Myosin6, Brn3c, Dnah5), but not of the cochlear HC-related marker Lmod3. Gene expression analyses of both 2D and 3D EBs cultured for two weeks revealed a greater level of augmented induction of HC-related markers in the 3D-cultured EBs. These results indicate that a 3D culture in combination with use of V-CM is an effective method for producing V-HCs.

Harnessing conserved signaling and metabolic pathways to enhance the maturation of functional engineered tissues

The development of induced-pluripotent stem cell (iPSC)-derived cell types offers promise for basic science, drug testing, disease modeling, personalized medicine, and translatable cell therapies across many tissue types. However, in practice many iPSC-derived cells have presented as immature in physiological function, and despite efforts to recapitulate adult maturity, most have yet to meet the necessary benchmarks for the intended tissues. Here, we summarize the available state of knowledge surrounding the physiological mechanisms underlying cell maturation in several key tissues. Common signaling consolidators, as well as potential synergies between critical signaling pathways are explored. Finally, current practices in physiologically relevant tissue engineering and experimental design are critically examined, with the goal of integrating greater decision paradigms and frameworks towards achieving efficient maturation strategies, which in turn may produce higher-valued iPSC-derived tissues.

Porcine Intestinal Organoids: Overview of the State of the Art

The intestinal tract is a crucial part of the body for growth and development, and its dysregulation can cause several diseases. The lack of appropriate in vitro models hampers the development of effective preventions and treatments against these intestinal tract diseases. Intestinal organoids are three-dimensional (3D) polarized structures composed of different types of cells capable of self-organization and self-renewal, resembling their organ of origin in architecture and function. Porcine intestinal organoids (PIOs) have been cultured and are used widely in agricultural, veterinary, and biomedical research. Based on the similarity of the genomic sequence, anatomic morphology, and drug metabolism with humans and the difficulty in obtaining healthy human tissue, PIOs are also considered ideal models relative to rodents. In this review, we summarize the current knowledge on PIOs, emphasizing their culturing, establishment and development, and applications in the study of host–microbe interactions, nutritional development, drug discovery, and gene editing potential.

Comparison of Microglial Morphology and Function in Primary Cerebellar Cell Cultures on Collagen and Collagen-Mimetic Hydrogels

Neuronal-glial cell cultures are usually grown attached to or encapsulated in an adhesive environment as evenly distributed networks lacking tissue-like cell density, organization and morphology. In such cultures, microglia have activated amoeboid morphology and do not display extended and intensively branched processes characteristic of the ramified tissue microglia. We have recently described self-assembling functional cerebellar organoids promoted by hydrogels containing collagen-like peptides (CLPs) conjugated to a polyethylene glycol (PEG) core. Spontaneous neuronal activity was accompanied by changes in the microglial morphology and behavior, suggesting the cells might play an essential role in forming the functional neuronal networks in response to the peptide signalling. The present study examines microglial cell morphology and function in cerebellar cell organoid cultures on CLP-PEG hydrogels and compares them to the cultures on crosslinked collagen hydrogels of similar elastomechanical properties. Material characterization suggested more expressed fibril orientation and denser packaging in crosslinked collagen than CLP-PEG. However, CLP-PEG promoted a significantly higher microglial motility (determined by time-lapse imaging) accompanied by highly diverse morphology including the ramified (brightfield and confocal microscopy), more active Ca2+ signalling (intracellular Ca2+ fluorescence recordings), and moderate inflammatory cytokine level (ELISA). On the contrary, on the collagen hydrogels, microglial cells were significantly less active and mostly round-shaped. In addition, the latter hydrogels did not support the neuron synaptic activity. Our findings indicate that the synthetic CLP-PEG hydrogels ensure more tissue-like microglial morphology, motility, and function than the crosslinked collagen substrates.

Polystyrene microplastics induce hepatotoxicity and disrupt lipid metabolism in the liver organoids

Microplastic particles (MP) has been detected in the environment widespread. Human beings are inevitably exposed to MP via multiple routines. However, the hazard identifications, as direct evidence of exposure and health risk, have not been fully characterized in human beings. Many studies suggest the liver is a potential target organ, but currently no study regarding the MP on human liver has been reported. In this study, we used a novel in vitro 3D model, the liver organoids (LOs) generated from human pluripotent stem cells, as an alternative model to the human liver, to explore the adverse biological effect of 1 μm polystyrene-MP (PS-MP) microbeads applying a non-static exposure approach. When the LOs were exposed to 0.25, 2.5 and 25 μg/mL PS-MP (the lowest one was relevant to the environmental concentrations, calculated to be 102 ± 7 items/mL). The potential mechanisms of PS-MP induced hepatotoxicity and lipotoxicity, in aspects of cytotoxicity, levels of key molecular markers, ATP production, alteration in lipid metabolism, ROS generation, oxidative stress and inflammation response, were determined. Specifically, it has been firstly observed that PS-MP could increase the expression of hepatic HNF4A and CYP2E1. Based on these findings, the potential adverse outcome pathways (AOPs) relevant to PS-MP were proposed, and the potential risks of PS-MP on liver steatosis, fibrosis and cancer were implicated. The combined application of novel LOs model and AOPs framework provides a new insight into the risk assessment of MP. Further studies are anticipated to validate the hepatotoxic molecular mechanism of PS-MP based on HNF4A or CYP2E1, and to investigate the MP-induced physical damage and its relationship to hepatic adverse effect for human beings. CAPSULE: Microplastics cause hepatotoxicity and disrupt lipid metabolism in the human pluripotent stem cells-derived liver organoids, providing evidence for human implication.

Human Organoids for Predictive Toxicology Research and Drug Development

Organoids are three-dimensional structures fabricated in vitro from pluripotent stem cells or adult tissue stem cells via a process of self-organization that results in the formation of organ-specific cell types. Human organoids are expected to mimic complex microenvironments and many of the in vivo physiological functions of relevant tissues, thus filling the translational gap between animals and humans and increasing our understanding of the mechanisms underlying disease and developmental processes. In the last decade, organoid research has attracted increasing attention in areas such as disease modeling, drug development, regenerative medicine, toxicology research, and personalized medicine. In particular, in the field of toxicology, where there are various traditional models, human organoids are expected to blaze a new path in future research by overcoming the current limitations, such as those related to differences in drug responses among species. Here, we discuss the potential usefulness, limitations, and future prospects of human liver, heart, kidney, gut, and brain organoids from the viewpoints of predictive toxicology research and drug development, providing cutting edge information on their fabrication methods and functional characteristics.

Challenges for the Applications of Human Pluripotent Stem Cell-Derived Liver Organoids

The current organoid culture systems allow pluripotent and adult stem cells to self-organize to form three-dimensional (3D) structures that provide a faithful recapitulation of the architecture and function of in vivo organs. In particular, human pluripotent stem cell-derived liver organoids (PSC-LOs) can be used in regenerative medicine and preclinical applications, such as disease modeling and drug discovery. New bioengineering tools, such as microfluidics, biomaterial scaffolds, and 3D bioprinting, are combined with organoid technologies to increase the efficiency of hepatic differentiation and enhance the functional maturity of human PSC-LOs by precise control of cellular microenvironment. Long-term stabilization of hepatocellular functions of in vitro liver organoids requires the combination of hepatic endodermal, endothelial, and mesenchymal cells. To improve the biological function and scalability of human PSC-LOs, bioengineering methods have been used to identify diverse and zonal hepatocyte populations in liver organoids for capturing heterogeneous pathologies. Therefore, constructing engineered liver organoids generated from human PSCs will be an extremely versatile tool in in vitro disease models and regenerative medicine in future. In this review, we aim to discuss the recent advances in bioengineering technologies in liver organoid culture systems that provide a timely and necessary study to model disease pathology and support drug discovery in vitro and to generate cell therapy products for transplantation.

Liver organoid as a 3D in vitro model for drug validation and toxicity assessment

The past decade has seen many advancements in the development of three-dimensional (3D) in vitro models in pharmaceutical sciences and industry. Specifically, organoids present a self-organising, self-renewing and more physiologically relevant model than conventional two-dimensional (2D) cell cultures. Liver organoids have been developed from a variety of cell sources, including stem cells, cell lines and primary cells. They have potential for modelling patient-specific disease and establishing personalised therapeutic approaches. Additionally, liver organoids have been used to test drug efficacy and toxicity. Herein we summarise cell sources for generating liver organoids, the advantages and limitations of each cell type, as well as the application of the organoids in modelling liver diseases. We focus on the use of liver organoids as tools for drug validation and toxicity assessment.

Tissues and Tumor Microenvironment (TME) in 3D: Models to Shed Light on Immunosuppression in Cancer

Immunosuppression in cancer has emerged as a major hurdle to immunotherapy efforts. Immunosuppression can arise from oncogene-induced signaling within the tumor as well as from tumor-associated immune cells. Understanding various mechanisms by which the tumor can undermine and evade therapy is critical in improving current cancer immunotherapies. While mouse models have allowed for the characterization of key immune cell types and their role in tumor development, extrapolating these mechanisms to patients has been challenging. There is need for better models to unravel the effects of genetic alterations inherent in tumor cells and immune cells isolated from tumors on tumor growth and to investigate the feasibility of immunotherapy. Three-dimensional (3D) organoid model systems have developed rapidly over the past few years and allow for incorporation of components of the tumor microenvironment such as immune cells and the stroma. This bears great promise for derivation of patient-specific models in a dish for understanding and determining the impact on personalized immunotherapy. In this review, we will highlight the significance of current experimental models employed in the study of tumor immunosuppression and evaluate current tumor organoid-immune cell co-culture systems and their potential impact in shedding light on cancer immunosuppression.

Production and cryopreservation of definitive endoderm from human pluripotent stem cells under defined and scalable culture conditions

The endodermal germ layer gives rise to respiratory epithelium, hepatocytes, pancreatic cells and intestinal lineages, among other cell types. These lineages can be differentiated from human pluripotent stem cells (hPSCs) via a common definitive endoderm (DE) intermediate that is characterized by the co-expression of the cell surface markers CXCR4, c-KIT and EPCAM and the transcription factors SOX17 and FOXA2. Here we provide a detailed protocol for mass production of DE from hPSCs in scalable and easy-to-handle suspension culture using a rotating Erlenmeyer flask or a sophisticated, fully controllable, 150-ml stirred tank bioreactor. This protocol uses two different media formulations that are chemically defined and xeno free and therefore good manufacturing practice ready. Our protocol allows for efficient hPSC-derived DE specification in multicellular aggregates within 3 days and generates up to 1 × 10⁸ DE cells with >92% purity in one differentiation batch when using the bioreactor. The hPSC-derived DE cells that are generated can be cryopreserved for later downstream differentiation into various endodermal lineages. This protocol should facilitate the flexible production of mature DE derivatives for physiologically relevant disease models, high-throughput drug screening, toxicology testing and cellular therapies.

Human liver model systems in a dish

The human adult liver has a multi-cellular structure consisting of large lobes subdivided into lobules containing portal triads and hepatic cords lined by specialized blood vessels. Vital hepatic functions include filtering blood, metabolizing drugs, and production of bile and blood plasma proteins like albumin, among many other functions, which are generally dependent on the location or zone in which the hepatocyte resides in the liver. Due to the liver's intricate structure, there are many challenges to design differentiation protocols to generate more mature functional hepatocytes from human stem cells and maintain the long-term viability and functionality of primary hepatocytes. To this end, recent advancements in three-dimensional (3D) stem cell culture have accelerated the generation of a human miniature liver system, also known as liver organoids, with polarized epithelial cells, supportive cell types and extra-cellular matrix deposition by translating knowledge gained in studies of animal organogenesis and regeneration. To facilitate the efforts to study human development and disease using in vitro hepatic models, a thorough understanding of state-of-art protocols and underlying rationales is essential. Here, we review rapidly evolving 3D liver models, mainly focusing on organoid models differentiated from human cells.

Historical evolution of spheroids and organoids, and possibilities of use in life sciences and medicine

BACKGROUND

An impressive percentage of biomedical advances were achieved through animal research and cell culture investigations. For drug testing and disease researches, both animal models and preclinical trials with cell cultures are extremely important, but present some limitations, such as ethical concern and inability of representing complex tissues and organs. 3D cell cultures arise providing a more realistic in vitro representation of tissues and organs. Environment and cell type in 3D cultures can represent in vivo conditions and thus provide accurate data on cell-to-cell interactions, and cultivation techniques are based on a scaffold, usually hydrogel or another polymeric material, or without scaffold, such as suspended microplates, magnetic levitation, and microplates for spheroids with ultra-low fixation coating.

PURPOSE AND SCOPE

This review aims at presenting an updated summary of the most common 3D cell culture models available, as well as a historical background of their establishment and possible applications.

SUMMARY

Even though 3D culturing is incapable of replacing other current research types, they will continue to substitute some unnecessary animal experimentation, as well as complement monolayer cultures.

CONCLUSION

In this aspect, 3D culture emerges as a valuable alternative to the investigation of functional, biochemical, and molecular aspects of human pathologies.

A stem cell based in vitro model of NAFLD enables the analysis of patient specific individual metabolic adaptations in response to a high fat diet and AdipoRon interference

Non-alcoholic fatty liver disease (NAFLD) is a multifactorial disease. Its development and progression depend on genetically predisposed susceptibility of the patient towards several ‘hits’ that induce fat storage first and later inflammation and fibrosis. Here, we differentiated induced pluripotent stem cells (iPSCs) derived from four distinct donors with varying disease stages into hepatocyte like cells (HLCs) and determined fat storage as well as metabolic adaptations after stimulations with oleic acid. We could recapitulate the complex networks that control lipid and glucose metabolism and we identified distinct gene expression profiles related to the steatosis phenotype of the donor. In an attempt to reverse the steatotic phenotype, cells were treated with the small molecule AdipoRon, a synthetic analogue of adiponectin. Although the responses varied between cells lines, they suggest a general influence of AdipoRon on metabolism, transport, immune system, cell stress and signalling.

Summary: A stem cell based in vitro model of NAFLD recapitulates regulatory networks and suggests a steatosis associated phenotype. AdipoRon treatment influences metabolism, immune system, cell stress and signalling.

Advancements in stem cell-derived hepatocyte-like cell models for hepatotoxicity testing

Drug-induced liver injury (DILI) is one of the leading causes of clinical trial failures and high drug attrition rates. Currently, the commonly used hepatocyte models include primary human hepatocytes (PHHs), animal models, and hepatic cell lines. However, these models have disadvantages that include species-specific differences or inconvenient cell extraction methods. Therefore, a novel, inexpensive, efficient, and accurate model that can be applied to drug screening is urgently needed. Owing to their self-renewable ability, source abundance, and multipotent competence, stem cells are stable sources of drug hepatotoxicity screening models. Because 3D culture can mimic the in vivo microenvironment more accurately than can 2D culture, the former is commonly used for hepatocyte culture and drug screening. In this review, we introduce the different sources of stem cells used to generate hepatocyte-like cells and the models for hepatotoxicity testing that use stem cell-derived hepatocyte-like cells.

Human-Induced Pluripotent Stem Cell-Derived Hepatocytes and their Culturing Methods to Maintain Liver Functions for Pharmacokinetics and Safety Evaluation of Pharmaceuticals

Human hepatocytes are essential cell types for pharmacokinetics and the safety evaluation of pharmaceuticals. However, widely used primary hepatocytes with individual variations in liver function lose those functions rapidly in culture. Hepatic cell lines are convenient to use but have low liver functions. Human-Induced Pluripotent Stem (hiPS) cells can be expanded and potentially differentiated into any cell or tissue, including the liver. HiPS cell-derived Hepatocyte-Like Cells (hiPSHeps) are expected to be extensively used as consistent functional human hepatocytes. Many laboratories are investigating methods of using hiPS cells to differentiate hepatocytes, but the derived cells still have immature liver functions. In this paper, we describe the current uses and limitations of conventional hepatic cells, evaluating the suitability of hiPS-Heps to pharmacokinetics and the safety evaluation of pharmaceuticals, and discuss the potential future use of non-conventional non-monolayer culture methods to derive fully functional hiPS-Heps.

Synthetic Notch-Receptor-Mediated Transmission of a Transient Signal into Permanent Information via CRISPR/Cas9-Based Genome Editing

Synthetic receptor biology and genome editing are emerging techniques, both of which are currently beginning to be used in preclinical and clinical applications. We were interested in whether a combination of these techniques approaches would allow for the generation of a novel type of reporter cell that would recognize transient cellular events through specifically designed synthetic receptors and would permanently store information about these events via associated gene editing. Reporting cells could be used in the future to detect alterations in the cellular microenvironment, including degenerative processes or malignant transformation into cancer cells. Here, we explored synthetic Notch (synNotch) receptors expressed in human embryonic kidney cells to investigate the efficacy of antigen recognition events in a time- and dose-dependent manner. First, we evaluated the most suitable conditions for synNotch expression based on dsRed-Express fluorophore expression. Then, we used a synNotch receptor coupled to transcriptional activators to induce the expression of a Cas9 nuclease targeted to a specific genomic DNA site. Our data demonstrate that recognition of various specific antigens via synNotch receptors robustly induced Cas9 expression and resulted in an indel formation frequency of 34.5%–45.5% at the targeted CXCR4 locus. These results provide proof of concept that reporter cells can be designed to recognize a given event and to store transient information permanently in their genomes.

FGF2 Inhibits Early Pancreatic Lineage Specification during Differentiation of Human Embryonic Stem Cells

Growth factors are important regulators during organ development. For many vertebrates (but not humans) it is known how they contribute to the formation and expansion of PDX1-positive cells during pancreas organogenesis. Here, the effects of the fibroblast growth factors FGF2, FGF7, FGF10, and epidermal growth factor (EGF) on pancreas development in humans were assessed by using human pluripotent stem cells (hPSCs). During this, FGF2 was identified as a potent anti-pancreatic factor whereas FGF7, FGF10, and EGF increased the cell mass while retaining PDX1-positivity. FGF2 increased the expression of the anti-pancreatic factor sonic hedgehog (SHH) while suppressing PDX1 in a dose-dependent manner. Differentiating cells secreted SHH to the medium and we interrogated the cells’ secretome during differentiation to globally examine the composition of secreted signaling factors. Members of the TGF-beta-, Wnt-, and FGF-pathways were detected. FGF17 showed a suppressive anti-pancreatic effect comparable to FGF2. By inhibition of specific branches of FGF-receptor signaling, we allocated the SHH-induction by FGF2 to MEK/ERK-signaling and the anti-pancreatic effect of FGF2 to the receptor variant FGFR1c or 3c. Altogether, we report findings on the paracrine activity of differentiating hPSCs during generation of pancreatic progenitors. These observations suggest a different role for FGF2 in humans compared to animal models of pancreas organogenesis.

Dissolved oxygen concentration regulates human hepatic organoid formation from pluripotent stem cells in a fully controlled bioreactor

Developing technologies for scalable production of human organoids has gained increased attention for "organoid medicine" and drug discovery. We developed a scalable and integrated differentiation process for generation of hepatic organoid from human pluripotent stem cells (hPSCs) in a fully controlled stirred tank bioreactor with 150 ml working volume by application of physiological oxygen concentrations in different liver tissue zones. We found that the 20-40% dissolved oxygen concentration [DO] (corresponded to 30-60 mmHg pO₂ within the liver tissue) significantly influences the process outcome via regulating the differentiation fate of hPSC aggregates by enhancing mesoderm induction. Regulation of the [DO] at 30% DO resulted in efficient generation of human fetal-like hepatic organoids that had a uniform size distribution and were comprised of red blood cells and functional hepatocytes, which exhibited improved liver-specific marker gene expressions, key liver metabolic functions, and, more important, higher inducible cytochrome P450 activity compared to the other trials. These hepatic organoids were successfully engrafted in an acute liver injury mouse model and produced albumin after implantation. These results demonstrated the significant impact of the dissolved oxygen concentration on hPSC hepatic differentiation fate and differentiation efficacy that should be considered ascritical translational aspect of established scalable liver organoid generation protocols for potential clinical and drug discovery applications.

Self-Organizing Human Induced Pluripotent Stem Cell Hepatocyte 3D Organoids Inform the Biology of the Pleiotropic TRIB1 Gene

Establishment of a physiologically relevant human hepatocyte‐like cell system for in vitro translational research has been hampered by the limited availability of cell models that accurately reflect human biology and the pathophysiology of human disease. Here we report a robust, reproducible, and scalable protocol for the generation of hepatic organoids from human induced pluripotent stem cells (hiPSCs) using short exposure to nonengineered matrices. These hepatic organoids follow defined stages of hepatic development and express higher levels of early (hepatocyte nuclear factor 4A [HNF4A], prospero‐related homeobox 1 [PROX1]) and mature hepatic and metabolic markers (albumin, asialoglycoprotein receptor 1 [ASGR1], CCAAT/enhancer binding protein α [C/EBPα]) than two‐dimensional (2D) hepatocyte‐like cells (HLCs) at day 20 of differentiation. We used this model to explore the biology of the pleiotropic TRIB1 (Tribbles‐1) gene associated with a number of metabolic traits, including nonalcoholic fatty liver disease and plasma lipids. We used genome editing to delete the TRIB1 gene in hiPSCs and compared TRIB1‐deleted iPSC‐HLCs to isogenic iPSC‐HLCs under both 2D culture and three‐dimensional (3D) organoid conditions. Under conventional 2D culture conditions, TRIB1‐deficient HLCs showed maturation defects, with decreased expression of late‐stage hepatic and lipogenesis markers. In contrast, when cultured as 3D hepatic organoids, the differentiation defects were rescued, and a clear lipid‐related phenotype was noted in the TRIB1‐deficient induced pluripotent stem cell HLCs. Conclusion: This work supports the potential of genome‐edited hiPSC‐derived hepatic 3D organoids in exploring human hepatocyte biology, including the functional interrogation of genes identified through human genetic investigation.

Organoid models of gastrointestinal cancers in basic and translational research

Cancer is a major public health problem worldwide. Gastrointestinal cancers account for approximately one-third of the total global cancer incidence and mortality. Historically, the mechanisms of tumour initiation and progression in the gastrointestinal tract have been studied using cancer cell lines in vitro and animal models. Traditional cell culture methods are associated with a strong selection of aberrant genomic variants that no longer reflect the original tumours in terms of their (metastatic) behaviour or response to therapy. Organoid technology has emerged as a powerful alternative method for culturing gastrointestinal tumours and the corresponding normal tissues in a manner that preserves their genetic, phenotypic and behavioural traits. Importantly, accumulating evidence suggests that organoid cultures have great value in predicting the outcome of therapy in individual patients. Herein, we review the current literature on organoid models of the most common gastrointestinal cancers, including colorectal cancer, gastric cancer, oesophageal cancer, liver cancer and pancreatic cancer, and their value in modelling tumour initiation, metastatic progression and therapy response. We also explore the limitations of current organoid models and discuss how they could be improved to maximally benefit basic and translational research in the future, especially in the fields of drug discovery and personalized medicine.

Advances in generating liver cells from pluripotent stem cells as a tool for modeling liver diseases

Developing robust in vitro models of the liver is essential for studying the pathogenesis of liver diseases, hepatotoxicity testing, and regenerative medicine. Earlier studies were conducted using cell lines derived from hepatomas. Due to the inherent limitations of cell lines, researchers used primary human hepatocytes (PHHs), which are considered a gold standard for in vitro modeling of the liver. However, due to the high cost of PHHs and lack of donors, researchers have sought an alternative source for functional liver cells. Pluripotent stem cells (PSCs) emerged as a viable alternative due to their plasticity and high proliferative capacity. This review gives an overview of the major advances that have been achieved to develop protocols to generate liver cells such as hepatocytes, cholangiocytes, and Küpffer cells from PSCs. We also discuss their application in modeling the pathogenesis of liver diseases such as drug‐induced liver injury, acute liver failure, and hepatic steatosis.

Organoids are promising tools for species-specific in vitro toxicological studies

Organoids are three-dimensional self-aggregating structures generated from stem cells (SCs) or progenitor cells in a process that recapitulates molecular and cellular stages of early organ development. The differentiation process leads to the appearance of specialized mature cells and is connected with changes in the organoid internal structure rearrangement and self-organization. The formation of organ-specific structures in vitro with highly ordered architecture is also strongly influenced by the extracellular matrix. These features make organoids as a powerful model for in vitro toxicology. Nowadays this technology is developing very quickly. In this review we present, from a toxicological and species-specific point of view, the state of the art of organoid generation from adult SCs and pluripotent SCs: embryonic SCs or induced pluripotent SCs. The current culture organoid techniques are discussed for their main advantages, disadvantages and limitations. In the second part of the review, we concentrated on the characterization of species-specific organoids generated from tissue-specific SCs of different sources: mammary (bovine), epidermis (canine), intestinal (porcine, bovine, canine, chicken) and liver (feline, canine).

Technological advancements for the development of stem cell-based models for hepatotoxicity testing

Stem cells are characterized by their self-renewal capacity and their ability to differentiate into multiple cell types of the human body. Using directed differentiation strategies, stem cells can now be converted into hepatocyte-like cells (HLCs) and therefore, represent a unique cell source for toxicological applications in vitro. However, the acquired hepatic functionality of stem cell-derived HLCs is still significantly inferior to primary human hepatocytes. One of the main reasons for this is that most in vitro models use traditional two-dimensional (2D) setups where the flat substrata cannot properly mimic the physiology of the human liver. Therefore, 2D-setups are progressively being replaced by more advanced culture systems, which attempt to replicate the natural liver microenvironment, in which stem cells can better differentiate towards HLCs. This review highlights the most recent cell culture systems, including scaffold-free and scaffold-based three-dimensional (3D) technologies and microfluidics that can be employed for culture and hepatic differentiation of stem cells intended for hepatotoxicity testing. These methodologies have shown to improve in vitro liver cell functionality according to the in vivo liver physiology and allow to establish stem cell-based hepatic in vitro platforms for the accurate evaluation of xenobiotics.

Human iPS Cell-Derived Patient Tissues and 3D Cell Culture Part 2: Spheroids, Organoids, and Disease Modeling

Human induced pluripotent stem cells (HiPSCs) provide several advantages for drug discovery, but principally they provide a source of clinically relevant tissue. Furthermore, the use of HiPSCs cultured in three-dimensional (3D) systems, as opposed to traditional two-dimensional (2D) culture approaches, better represents the complex tissue architecture in vivo. The use of HiPSCs in 3D spheroid and organoid culture is now growing, but particularly when using myocardial, intestinal enteric nervous system, and retinal cell lines. However, organoid cell culture is perhaps making the most notable impact in research and drug discovery, in which 3D neuronal cell cultures allow direct modeling of cortical cell layering and neuronal circuit activity. Given the specific degeneration seen in discrete neuronal circuitry in Alzheimer’s disease (AD) and Parkinson’s disease (PD), HiPSC culture systems are proving to be a major advance. In the present review, the second part of a two-part review, we discuss novel methods in which 3D cell culture systems (principally organoids) are now being used to provide insights into disease mechanisms. (The use of HiPSCs in target identification was reviewed in detail in Part 1.)

In situ differentiation and generation of functional liver organoids from human iPSCs in a 3D perfusable chip system

Liver organoids derived from human pluripotent stem cells (PSCs) represent a new type of in vitro liver model for understanding organ development, disease mechanism and drug testing. However, engineering liver organoids with favorable functions in a controlled cellular microenvironment remains challenging. In this work, we present a new strategy for engineering liver organoids derived from human induced PSCs (hiPSCs) in a 3D perfusable chip system by combining stem cell biology with microengineering technology. This approach enabled formation of hiPSC-based embryoid bodies (EBs), in situ hepatic differentiation, long-term 3D culture and generation of liver organoids in a perfusable micropillar chip. The generated liver organoids exhibited favorable growth and differentiation of hepatocytes and cholangiocytes, recapitulating the key features of human liver formation with cellular heterogeneity. The liver organoids in perfused cultures displayed improved cell viability and higher expression of endodermal genes (SOX17 and FOXA2) and mature hepatic genes (ALB and CYP3A4) under perfused culture conditions. In addition, the liver organoids showed a marked enhancement of hepatic-specific functions, including albumin and urea production and metabolic capabilities, indicating the role of mechanical fluid flow in promoting the functions of the liver organoids. Moreover, the liver organoids exhibited hepatotoxic response after exposure to acetaminophen (APAP) in a dose- and time-dependent manner. The established liver organoid-on-a-chip system may provide a promising platform for engineering stem cell-based organoids with applications in regenerative medicine, disease modeling and drug testing.