Morphological and Functional Characterization and Assessment of iPSC-Derived Hepatocytes for In Vitro Toxicity Testing

Combination of tea catechins and ornithine effectively activates the urea cycle: an in vitro and human pilot study

PURPOSE

Accumulation of ammonia causes central and peripheral fatigue. This study aimed to investigate the synergistic effect of tea catechins and low-dose ornithine in activating the urea cycle to reduce blood ammonia levels during exercise.

METHODS

We used hepatocyte-like cells derived from human-induced pluripotent stem (iPS) cells to assess the effect of tea catechins combined with ornithine on urea cycle activity. The urea production and expression of key genes involved in the metabolism of urea were investigated. We then examined the synergistic improvement in ammonia metabolism by tea catechins in combination with ornithine in a human pilot study.

RESULTS

Tea catechins combined with ornithine increased urea cycle activity in hepatocyte-like cells derived from human iPS cells. Intake of 538.6 mg of tea catechins with 1592 mg of ornithine for 2 consecutive days during exercise loading suppressed the exercise-induced increase in the blood ammonia concentration as well as stabilized blood glucose levels.

CONCLUSION

Controlling the levels of ammonia, a toxic waste produced in the body, is important in a variety of situations, including exercise. The present study suggests that a heterogeneous combination of polyphenols and amino acids efficiently suppresses elevated ammonia during exercise in humans by a mechanism that includes urea cycle activation.

TRIAL REGISTRATION

This study was registered in the University Hospital Medical Information Network Clinical Trial Registry (No. UMIN000035484, dated January 8, 2019).

Sex difference in liver diseases: How preclinical models help to dissect the sex-related mechanisms sustaining NAFLD and hepatocellular carcinoma

Only a few preclinical findings are confirmed in the clinic, posing a critical issue for clinical development. Therefore, identifying the best preclinical models can help to dissect molecular and mechanistic insights into liver disease pathogenesis while being clinically relevant. In this context, the sex relevance of most preclinical models has been only partially considered. This is particularly significant in NAFLD and HCC, which have a higher prevalence in men when compared to pre-menopause women but not to those in post-menopausal status, suggesting a role for sex hormones in the pathogenesis of the diseases. This review gathers the sex-relevant findings and the available preclinical models focusing on both in vitro and in vivo studies and discusses the potential implications and perspectives of introducing the sex effect in the selection of the best preclinical model. This is a critical aspect that would help to tailor personalized therapies based on sex.

Analysis of reproducibility and robustness of OrganoPlate® 2-lane 96, a liver microphysiological system for studies of pharmacokinetics and toxicological assessment of drugs

Establishing the functionality, reproducibility, robustness, and reliability of microphysiological systems is a critical need for adoption of these technologies. A high throughput microphysiological system for liver studies was recently proposed in which induced pluripotent stem cell-derived hepatocytes (iHeps) and non-parenchymal cells (endothelial cells and THP-1 cells differentiated with phorbol 12-myristate 13-acetate into macrophage-like cells) were co-cultured in OrganoPlate® 2-lane 96 devices. The goal of this study was to evaluate this platform using additional cell types and conditions and characterize its utility and reproducibility. Primary human hepatocytes or iHeps, with and without non-parenchymal cells, were cultured for up to 17 days. Image-based cell viability, albumin and urea secretion into culture media, CYP3A4 activity and drug metabolism were assessed. The iHeps co-cultured with non-parenchymal cells demonstrated stable cell viability and function up to 17 days; however, variability was appreciable both within and among studies. The iHeps in monoculture did not form clusters and lost viability and function over time. The primary human hepatocytes in monoculture also exhibited low cell viability and hepatic function. Metabolism of various drugs was most efficient when iHeps were co-cultured with non-parenchymal cells. Overall, we found that the OrganoPlate® 2-lane 96 device, when used with iHeps and non-parenchymal cells, is a functional liver microphysiological model; however, the high-throughput nature of this model is somewhat dampened by the need for replicates to compensate for high variability.

Shedding light on non-alcoholic fatty liver disease: Pathogenesis, molecular mechanisms, models, and emerging therapeutics

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder globally impacting an estimated 25% of the population associated with severe consequences such as cirrhosis, hepatocellular carcinoma (HCC), and overall mortality. Fatty liver disease is triggered through multiple pathways, but the most prominent cause is either diabetes or obesity, or a combination of both. Therefore, hepatic glucose, insulin and fatty acid signaling becomes a dire need to understand which is well elaborated in this review. This review summarizes the popular two-hit pathogenesis of NAFLD, the molecular mechanisms underlying hepatic insulin resistance. As fatty liver disease gets advanced, it requires in-vitro as well as in-vivo models closer to disease progression in humans for better understanding the pathological state and identifying a novel therapeutic target. This review summarizes in-vitro (2D cell-culture/co-culture, 3D spheroid/organoid/liver-on-a-chip) models as well as in-vivo (genetically/dietary/chemically induced fatty liver disease) research models. Fatty liver disease research has gathered lots of attention recently since there is no FDA approved therapy available so far. However, there have been numerous promising targets to treat fatty liver disease including potential therapeutic targets under clinical trials are listed in this review.

Using liver models generated from human-induced pluripotent stem cells (iPSCs) for evaluating chemical-induced modifications and disease across liver developmental stages

The liver is a pivotal organ regulating critical developmental stages of fetal metabolism and detoxification. Though numerous studies have evaluated links between prenatal/perinatal exposures and adverse health outcomes in the developing fetus, the central role of liver to health disruptions resulting from these exposures remains understudied, especially concerning early development and later-in-life health outcomes. While numerous in vitro methods for evaluating liver toxicity have been established, the use of iPSC-derived hepatocytes appears to be particularly well suited to contribute to this critical research gap due to their potential to model a diverse range of disease phenotypes and different stages of liver development. The following key aspects are reviewed: (1) an introduction to developmental liver toxicity; (2) an introduction to embryonic and induced pluripotent stem cell models; (3) methods and challenges for deriving liver cells from stem cells; and (4) applications for iPSC-derived hepatocytes to evaluate liver developmental stages and their associated responses to insults. We conclude that iPSC-derived hepatocytes have great potential for informing liver toxicity and underlying disease mechanisms via the generation of patient-specific iPSCs; implementing large-scale drug and chemical screening; evaluating general biological responses as a potential surrogate target cell; and evaluating inter-individual disease susceptibility and response variability.

Induced pluripotent stem cell-based organ-on-a-chip as personalized drug screening tools: A focus on neurodegenerative disorders

The Organ-on-a-Chip (OoC) technology shows great potential to revolutionize the drugs development pipeline by mimicking the physiological environment and functions of human organs. The translational value of OoC is further enhanced when combined with patient-specific induced pluripotent stem cells (iPSCs) to develop more realistic disease models, paving the way for the development of a new generation of patient-on-a-chip devices. iPSCs differentiation capacity leads to invaluable improvements in personalized medicine. Moreover, the connection of single-OoC into multi-OoC or body-on-a-chip allows to investigate drug pharmacodynamic and pharmacokinetics through the study of multi-organs cross-talks. The need of a breakthrough thanks to this technology is particularly relevant within the field of neurodegenerative diseases, where the number of patients is increasing and the successful rate in drug discovery is worryingly low. In this review we discuss current iPSC-based OoC as drug screening models and their implication in development of new therapies for neurodegenerative disorders.

A Comparison of Mesenchymal Stem Cell-derived Hepatocyte-like Cells and HepG2 Cells for Use in Drug-Induced Liver Injury Studies

Liver cell lines obtained from hepatomas, for example, HepG2 cells, are commonly used in drug toxicity studies. However, functional hepatocyte-like cells derived from mesenchymal stem cells (MSCs) could be a better option for use in the study of drug metabolism and toxicity. Overdose of acetaminophen (APAP) and excess alcohol consumption are common causes of liver damage. The objective of the present study was to investigate the use of MSC-derived hepatocyte-like cells (MSCdH) in the assessment of drug-induced liver injury (by using APAP and ethanol), and to compare the toxic effects observed in the MSCdH with those exhibited by HepG2 cells. MSCs were isolated from umbilical cord and their functionality confirmed by their ability to differentiate into adipocytes, osteocytes and hepatocyte-like cells. It was shown that the MSCs successfully differentiated into hepatocyte-like cells, and these cells were further characterised by using various enzyme assays and by assessing albumin secretion and urea synthesis. Cytotoxicity was evaluated in the HepG2 and MSCdH after exposure to ethanol and APAP, with cell viability being determined by using the MTT assay. After exposure to ethanol and to APAP, cell viability decreased in a concentration-dependent manner for both types of hepatocytes. The respective EC50 values of ethanol-induced toxicity for HepG2 and MSCdH cells were 2.5% and 1.3% v/v ( p < 0.001); for APAP-induced toxicity they were 19.1 mM and 12.6 mM ( p < 0.001). These findings show that there is a distinct difference between the two types of hepatocytes in terms of APAP-induced and ethanol-induced liver injury.

Common Polymorphism That Protects From Cardiovascular Disease Increases Fibronectin Processing and Secretion

BACKGROUND

Fibronectin (FN1) is an essential regulator of homodynamic processes and tissue remodeling that have been proposed to contribute to atherosclerosis. Moreover, recent large-scale genome-wide association studies (GWAS) have linked common genetic variants within the FN1 gene to coronary artery disease risk.

METHODS

Public databases were analyzed by 2-Sample Mendelian Randomization. Expression constructs encoding short FN1 reporter constructs and full-length plasma FN1 variants were introduced in various cell models. Secreted and cellular levels were then analyzed and quantified by SDS-PAGE and fluorescence microscopy. Mass spectrometry and glycosylation analyses were performed to probe possible posttranscriptional differences.

RESULTS

Bioinformatic analyses revealed that common coronary artery disease risk single nucleotide polymorphisms in the FN1 locus associate with circulating levels of FN1 and that higher FN1 (fibronectin 1) protein levels in plasma are linked to lower coronary artery disease risk. The coronary artery disease-associated FN1 locus encompasses a common polymorphism that translates a L15Q variant situated within the FN1 signal peptide. Introduction of FN1 reporter constructs, differing at position 15, revealed differences in secretion, with the FN1 Q15 variant being less well secreted. Moreover, the L15Q polymorphism was found to alter glycosylation in some cell models but not in human plasma.

CONCLUSIONS

In addition to providing novel functional evidence implicating FN1 in cardioprotection, these findings demonstrate that a common variant within a secretion signal peptide regulates protein function.

Current Status and Challenges of Human Induced Pluripotent Stem Cell-Derived Liver Models in Drug Discovery

The pharmaceutical industry is in high need of efficient and relevant in vitro liver models, which can be incorporated in their drug discovery pipelines to identify potential drugs and their toxicity profiles. Current liver models often rely on cancer cell lines or primary cells, which both have major limitations. However, the development of human induced pluripotent stem cells (hiPSCs) has created a new opportunity for liver disease modeling, drug discovery and liver toxicity research. hiPSCs can be differentiated to any cell of interest, which makes them good candidates for disease modeling and drug discovery. Moreover, hiPSCs, unlike primary cells, can be easily genome-edited, allowing the creation of reporter lines or isogenic controls for patient-derived hiPSCs. Unfortunately, even though liver progeny from hiPSCs has characteristics similar to their in vivo counterparts, the differentiation of iPSCs to fully mature progeny remains highly challenging and is a major obstacle for the full exploitation of these models by pharmaceutical industries. In this review, we discuss current liver-cell differentiation protocols and in vitro iPSC-based liver models that could be used for disease modeling and drug discovery. Furthermore, we will discuss the challenges that still need to be overcome to allow for the successful implementation of these models into pharmaceutical drug discovery platforms.

Evaluation of the utility of the Beta Human Liver Emulation System (BHLES) for CFSAN's regulatory toxicology program

Microphysiological systems (MPS), such as organ-on-a-chip platforms, are an emerging alternative model that may be useful for predicting human physiology and/or toxicity. Due to the interest in these platforms, the Center for Food Safety and Applied Nutrition partnered with Emulate to evaluate the utility of the Beta Human Liver Emulation System (BHLES) for its regulatory science program. Using known hepatotoxic compounds (usnic acid, benzbromarone, tamoxifen, and acetaminophen) and compounds that have no reported human cases of liver toxicity (dimethyl sulfoxide, theophylline, and aminohippurate) the platforms' performance was evaluated. Chemical toxicity was assessed by albumin secretion, urea and LDH release, nuclei number, mitochondrial membrane potential, and apoptosis. System/platform performance was evaluated in terms of sensitivity and specificity, power, and variability and repeatability. Chemical interactions with the Chip material were also assessed. Preliminary findings suggested that for the model test compounds selected, the BHLES was able to accurately predict toxicity, demonstrated high sensitivity and specificity, high power, and low variability. However, some compounds interacted with the Chip material indicating variable exposure levels that should be accounted for when planning experimentation. The details of the evaluation are presented herein.

Puromycin-based purification of cells with high expression of the cytochrome P450 CYP3A4 gene from a patient with drug-induced liver injury (DILI)

BACKGROUND

Many drugs have the potential to induce the expression of drug-metabolizing enzymes, particularly cytochrome P450 3A4 (CYP3A4), in hepatocytes. Hepatocytes can be accurately evaluated for drug-mediated CYP3A4 induction; this is the gold standard for in vitro hepatic toxicology testing. However, the variation from lot to lot is an issue that needs to be addressed. Only a limited number of immortalized hepatocyte cell lines have been reported. In this study, immortalized cells expressing CYP3A4 were generated from a patient with drug-induced liver injury (DILI).

METHODS

To generate DILI-derived cells with high expression of CYP3A4, a three-step approach was employed: (1) Differentiation of DILI-induced pluripotent stem cells (DILI-iPSCs); (2) Immortalization of the differentiated cells; (3) Selection of the cells by puromycin. It was hypothesized that cells with high cytochrome P450 gene expression would be able to survive exposure to cytotoxic antibiotics because of their increased drug-metabolizing activity. Puromycin, a cytotoxic antibiotic, was used in this study because of its rapid cytocidal effect at low concentrations.

RESULTS

The hepatocyte-like cells differentiated from DILI-iPSCs were purified by exposure to puromycin. The puromycin-selected cells (HepaSM or SI cells) constitutively expressed the CYP3A4 gene at extremely high levels and exhibited hepatocytic features over time. However, unlike primary hepatocytes, the established cells did not produce bile or accumulate glycogen.

CONCLUSIONS

iPSC-derived hepatocyte-like cells with intrinsic drug-metabolizing enzymes can be purified from non-hepatocytes and undifferentiated iPSCs using the cytocidal antibiotic puromycin. The puromycin-selected hepatocyte-like cells exhibited characteristics of hepatocytes after immortalization and may serve as another useful source for in vitro hepatotoxicity testing of low molecular weight drugs.

Preclinical models of idiosyncratic drug-induced liver injury (iDILI): Moving towards prediction

Idiosyncratic drug-induced liver injury (iDILI) encompasses the unexpected harms that prescription and non-prescription drugs, herbal and dietary supplements can cause to the liver. iDILI remains a major public health problem and a major cause of drug attrition. Given the lack of biomarkers for iDILI prediction, diagnosis and prognosis, searching new models to predict and study mechanisms of iDILI is necessary. One of the major limitations of iDILI preclinical assessment has been the lack of correlation between the markers of hepatotoxicity in animal toxicological studies and clinically significant iDILI. Thus, major advances in the understanding of iDILI susceptibility and pathogenesis have come from the study of well-phenotyped iDILI patients. However, there are many gaps for explaining all the complexity of iDILI susceptibility and mechanisms. Therefore, there is a need to optimize preclinical human in vitro models to reduce the risk of iDILI during drug development. Here, the current experimental models and the future directions in iDILI modelling are thoroughly discussed, focusing on the human cellular models available to study the pathophysiological mechanisms of the disease and the most used in vivo animal iDILI models. We also comment about in silico approaches and the increasing relevance of patient-derived cellular models.

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.

Variability in Human In Vitro Enzyme Kinetics

There are many factors which are known to cause variability in human in vitro enzyme kinetic data. Factors such as the source of enzyme and how it was prepared, the genetics and background of the donor, how the in vitro studies are designed, and how the data are analyzed contribute to variability in the resulting kinetic parameters. It is important to consider not only the factors which cause variability within an experiment, such as selection of a probe substrate, but also those that cause variability when comparing kinetic data across studies and laboratories. For example, the artificial nature of the microsomal lipid membrane and microenvironment in some recombinantly expressed enzymes, relative to those found in native tissue microsomes, has been shown to influence enzyme activity and thus can be a source of variability when comparing across the two different systems. All of these factors, and several others, are discussed in detail in the chapter below. In addition, approaches which can be used to visualize the uncertainty arising from the use of enzyme kinetic data within the context of predicting human pharmacokinetics are discussed.

Experimental liver models: From cell culture techniques to microfluidic organs-on-chip

The liver is one of the most studied organs of the human body owing to its central role in xenobiotic and drug metabolism. In recent decades, extensive research has aimed at developing in vitro liver models able to mimic liver functions to study pathophysiological clues in high-throughput and reproducible environments. Two-dimensional (2D) models have been widely used in screening potential toxic compounds but have failed to accurately reproduce the three-dimensionality (3D) of the liver milieu. To overcome these limitations, improved 3D culture techniques have been developed to recapitulate the hepatic native microenvironment. These models focus on reproducing the liver architecture, representing both parenchymal and nonparenchymal cells, as well as cell interactions. More recently, Liver-on-Chip (LoC) models have been developed with the aim of providing physiological fluid flow and thus achieving essential hepatic functions. Given their unprecedented ability to recapitulate critical features of the liver cellular environments, LoC have been extensively adopted in pathophysiological modelling and currently represent a promising tool for tissue engineering and drug screening applications. In this review, we discuss the evolution of experimental liver models, from the ancient 2D hepatocyte models, widely used for liver toxicity screening, to 3D and LoC culture strategies adopted for mirroring a more physiological microenvironment for the study of liver diseases.

Generation of Hepatobiliary Cell Lineages from Human Induced Pluripotent Stem Cells: Applications in Disease Modeling and Drug Screening

The possibility to reproduce key tissue functions in vitro from induced pluripotent stem cells (iPSCs) is offering an incredible opportunity to gain better insight into biological mechanisms underlying development and disease, and a tool for the rapid screening of drug candidates. This review attempts to summarize recent strategies for specification of iPSCs towards hepatobiliary lineages -hepatocytes and cholangiocytes-and their use as platforms for disease modeling and drug testing. The application of different tissue-engineering methods to promote accurate and reliable readouts is discussed. Space is given to open questions, including to what extent these novel systems can be informative. Potential pathways for improvement are finally suggested.

Hydrogels: A potential platform for induced pluripotent stem cell culture and differentiation

Induced pluripotent stem cells (iPSCs) can be used to generate desired types of cells that belong to the three germ layers (i.e., ectoderm, endoderm and mesoderm). These cells possess great potential in regenerative medicine. Before iPSCs are used in various biomedical applications, the existing xenogeneic culture methods must be improved to meet the technical standards of safety, cost effectiveness, and ease of handling. In addition to commonly used 2D substrates, a culture system that mimics the native cellular environment in tissues will be a good choice when culturing iPS cells and differentiating them into different lineages. Hydrogels are potential candidates that recapitulate the native complex three-dimensional microenvironment. They possess mechanical properties similar to those of many soft tissues. Moreover, hydrogels support iPSC adhesion, proliferation and differentiation to various cell types. They are xeno-free and cost-effective. In addition to other substrates, such as mouse embryonic fibroblast (MEF), Matrigel, and vitronectin, the use of hydrogel-based substrates for iPSC culture and differentiation may help generate large numbers of clinical-grade cells that can be used in potential clinical applications. This review mainly focuses on the use of hydrogels for the culture and differentiation of iPSCs into various cell types and their potential applications in regenerative medicine.

The Application of Induced Pluripotent Stem Cells Against Liver Diseases: An Update and a Review

Liver diseases are a major health concern globally, and are associated with poor survival and prognosis of patients. This creates the need for patients to accept the main alternative treatment of liver transplantation to prevent progression to end-stage liver disease. Investigation of the molecular mechanisms underpinning complex liver diseases and their pathology is an emerging goal of stem cell scope. Human induced pluripotent stem cells (hiPSCs) derived from somatic cells are a promising alternative approach to the treatment of liver disease, and a prospective model for studying complex liver diseases. Here, we review hiPSC technology of cell reprogramming and differentiation, and discuss the potential application of hiPSC-derived liver cells, such as hepatocytes and cholangiocytes, in refractory liver-disease modeling and treatment, and drug screening and toxicity testing. We also consider hiPSC safety in clinical applications, based on genomic and epigenetic alterations, tumorigenicity, and immunogenicity.

Human induced pluripotent stem cell derived hepatocytes provide insights on parenteral nutrition associated cholestasis in the immature liver

Parenteral nutrition-associated cholestasis (PNAC) significantly limits the safety of intravenous parenteral nutrition (PN). Critically ill infants are highly vulnerable to PNAC-related morbidity and mortality, however the impact of hepatic immaturity on PNAC is poorly understood. We examined developmental differences between fetal/infant and adult livers, and used human induced pluripotent stem cell-derived hepatocyte-like cells (iHLC) to gain insights into the contribution of development to altered sterol metabolism and PNAC. We used RNA-sequencing and computational techniques to compare gene expression patterns in human fetal/infant livers, adult liver, and iHLC. We identified distinct gene expression profiles between the human feta/infant livers compared to adult liver, and close resemblance of iHLC to human developing livers. Compared to adult, both developing livers and iHLC had significant downregulation of xenobiotic, bile acid, and fatty acid metabolism; and lower expression of the sterol metabolizing gene ABCG8. When challenged with stigmasterol, a plant sterol found in intravenous soy lipids, lipid accumulation was significantly higher in iHLC compared to adult-derived HepG2 cells. Our findings provide insights into altered bile acid and lipid metabolizing processes in the immature human liver, and support the use of iHLC as a relevant model system of developing liver to study lipid metabolism and PNAC.

Characterization of a commercially available line of iPSC hepatocytes as models of hepatocyte function and toxicity for regulatory purposes

It has recently become possible to produce hepatocytes from human induced pluripotent stem cells (iPSC-heps), which may offer some advantages over primary human hepatocytes (Prim-heps) in the regulatory environment. The aim of this research was to assess similarities and differences between commercially available iPSC-heps and Prim-heps in preliminary assays of drug metabolism, hepatotoxicity, and drug transport. Hepatocytes were either cultured in collagen-coated 96-well plates (Prim-heps and 2d-iPSC-heps) or in ultra-low adhesion plates as spheroids (3d-iPSC-heps). 3d-iPSC-heps were used to enhance physiological cell-cell contacts, which is essential to maintain the phenotype of mature hepatocytes. Cytochrome P450 (CYP) 3A4, CYP1A2, and CYP2B6 activity levels were evaluated using fluorescent assays. Phase II metabolism was assessed by HPLC measurement of formation of glucuronides and sulfates of 4-methylumbelliferone, 1-naphthol, and estradiol. The toxicity of acetaminophen, amiodarone, aspirin, clozapine, tacrine, tamoxifen, and troglitazone was monitored using a luminescent cell viability assay. Canaliculi formation was monitored by following the fluorescence of 5,6-carboxy-2',7'-dichlorofluorescein diacetate. All culture models showed similar levels of basal CYP3A4, CYP1A2 and CYP2B6 activity. However, while Prim-heps showed a vigorous response to CYP inducing agents, 2d-iPSC-heps showed no response and 3d-iPSC-heps displayed an inconclusive response. 2d-iPSC-heps showed reduced, yet appreciable, glucuronide and sulfate formation compared to Prim-heps. All culture models showed similar activity in tests of hepatotoxicity, with Prim-heps generally being more sensitive. All models formed canaliculi capable of transporting carboxy-2',7'-dichlorofluorescein. The iPSC-heps appear to be useful for toxicity and transport studies, but metabolic activity is not optimum, and metabolism studies would benefit from a more mature model.

Exploration of xenobiotic metabolism within cell lines used for Tox21 chemical screening

The Tox21 Program has investigated thousands of chemicals with high-throughput screening assays using cell-based assays to link thousands of chemicals to individual molecular targets/pathways. However, these systems have been widely criticized for their suspected lack of 'metabolic competence' to bioactivate or detoxify chemical exposures. In this study, 9 cell line backgrounds used in Tox21 assays (i.e., HepG2, HEK293, Hela, HCT116, ME180, CHO-K1, GH3.TRE-Luc, C3H10T1/2 and MCF7) were evaluated via metabolite formation rates, along with metabolic clearance and metabolite profiling for HepG2, HEK293, and MCF-7aroERE, in comparison to pooled donor (50) suspensions of primary human hepatocytes (PHHs). Using prototype clinical drug substrates for CYP1A2, CYP2B6, and CYP3A4/5, extremely low-to-undetectable CYP450 metabolism was observed (24 h), and consistent with their purported 'lack' of metabolic competence. However, for Phase II metabolizing enzymes and metabolic clearance, surprisingly proficient metabolism was observed for bisphenol AF, bisphenol S, and 7-hydroxycoumarin. Here, comparatively low glucuronidation relative to sulfation was observed in contrast to equivalent levels in PHHs. Overall, while a lack of CYP450 metabolism was confirmed in this benchmarking effort, Tox21 cell lines were not 'incompetent' for xenobiotic metabolism, and displayed surprisingly high proficiency for sulfation that rivaled PHHs. These findings have implications for the interpretation of Tox21 assay data, and establish a framework for evaluating of 'metabolic competence' with in vitro models.

Ammonia-based enrichment and long-term propagation of zone I hepatocyte-like cells

Ammonia has a cytotoxic effect and can therefore be used as a selection agent for enrichment of zone I hepatocytes. However, it has not yet been determined whether ammonia-treated hepatocyte-like cells are able to proliferate in vitro. In this study, we employed an ammonia selection strategy to purify hepatocyte-like cells that were differentiated from human embryonic stem cells (ESCs) and from induced pluripotent stem cells (iPSCs). The resistance to cytotoxicity or cell death by ammonia is likely attributable to the metabolism of ammonia in the cells. In addition to ammonia metabolism-related genes, ammonia-selected hepatocytes showed increased expression of the cytochrome P450 genes. Additionally, the ammonia-selected cells achieved immortality or at least an equivalent life span to human pluripotent stem cells without affecting expression of the liver-associated genes. Ammonia treatment in combination with in vitro propagation is useful for obtaining large quantities of hepatocytes.

Stem cells based in vitro models: trends and prospects in biomaterials cytotoxicity studies

Advanced biomaterials are increasingly used for numerous medical applications from the delivery of cancer-targeted therapeutics to the treatment of cardiovascular diseases. The issues of foreign body reactions induced by biomaterials must be controlled for preventing treatment failure. Therefore, it is important to assess the biocompatibility and cytotoxicity of biomaterials on cell culture systems before proceeding to in vivo studies in animal models and subsequent clinical trials. Direct use of biomaterials on animals create technical challenges and ethical issues and therefore, the use of non-animal models such as stem cell cultures could be useful for determination of their safety. However, failure to recapitulate the complex in vivo microenvironment have largely restricted stem cell cultures for testing the cytotoxicity of biomaterials. Nevertheless, properties of stem cells such as their self-renewal and ability to differentiate into various cell lineages make them an ideal candidate for in vitro screening studies. Furthermore, the application of stem cells in biomaterials screening studies may overcome the challenges associated with the inability to develop a complex heterogeneous tissue using primary cells. Currently, embryonic stem cells, adult stem cells, and induced pluripotent stem cells are being used as in vitro preliminary biomaterials testing models with demonstrated advantages over mature primary cell or cell line based in vitro models. This review discusses the status and future directions of in vitro stem cell-based cultures and their derivatives such as spheroids and organoids for the screening of their safety before their application to animal models and human in translational research.

Systematic transcriptome-based comparison of cellular adaptive stress response activation networks in hepatic stem cell-derived progeny and primary human hepatocytes

Various adaptive cellular stress response pathways are critical in the pathophysiology of liver disease and drug-induced liver injury. Human-induced pluripotent stem cell (hiPSC)-derived hepatocyte-like cells (HLCs) provide a promising tool to study cellular stress response pathways, but in this context there is limited insight on how HLCs compare to other in vitro liver models. Here, we systematically compared the transcriptomic profiles upon chemical activation in HLCs, hiPSC, primary human hepatocytes (PHH) and HepG2 liver cancer cells. We used targeted RNA-sequencing to map concentration transcriptional response using benchmark concentration modeling for the various stress responses in the different test systems. We found that HLCs are very sensitive towards oxidative stress and inflammation conditions as corresponding genes were activated at over 3 fold lower concentrations of the corresponding pathway inducing compounds as compared to PHH. PHH were the most sensitive model when studying UPR related effects. Due to the non-proliferative nature of PHH and HLCs, these do not pose a good/sensitive model to pick up DNA damage responses, while hiPSC and HepG2 were more sensitive in these conditions. We envision that this study contributes to a better understanding on how HLCs can contribute to the assessment of cell physiological stress response activation to predict hepatotoxic events.

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.

In Vitro and In Vivo Models of Non-Alcoholic Fatty Liver Disease: A Critical Appraisal

Non-alcoholic fatty liver disease (NAFLD), including non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH), represents the hepatic manifestation of obesity and metabolic syndrome. Due to the spread of the obesity epidemic, NAFLD is becoming the most common chronic liver disease and one of the principal indications for liver transplantation. However, no pharmacological treatment is currently approved to prevent the outbreak of NASH, which leads to fibrosis and cirrhosis. Preclinical research is required to improve our knowledge of NAFLD physiopathology and to identify new therapeutic targets. In the present review, we summarize advances in NAFLD preclinical models from cellular models, including new bioengineered platforms, to in vivo models, with a particular focus on genetic and dietary mouse models. We aim to discuss the advantages and limits of these different models.

Differentiation of induced pluripotent stem cells to hepatocyte-like cells on cellulose nanofibril substrate

Differentiation of hepatocyte-like cells (HLCs) from human induced pluripotent stem cells (iPSCs) in vitro has great potential in regenerative medicine. Current protocol uses matrigel of animal origin as a substrate for the differentiation of iPSCs to HLCs. Use of an appropriate non-xenogenic substrate is very important for potential future clinical applications. Towards this goal, we used Cellulose Nanofibril (CNF) gel, a natural, non-toxic, biocompatible and biodegradable polymer in humans as a thin film substrate for the differentiation of iPSCs to HLCs. Here we demonstrated that CNF as a substrate film can efficiently differentiate human iPSCs to HLCs. We investigated the expression profile of the endoderm markers (SOX17 and CXCR4), hepatoblast markers (EpCAM and AFP) and mature hepatocyte marker (ASGPR1) by flow cytometry during the differentiation of iPSCs to HLCs on both CNF and matrigel substrates. We also tested the HLCs generated from both the substrates for the expression of hepatic markers such as A1AT, HNF4A, CYP450 isotypes by Real Time-PCR and its mature hepatocyte functions (lipid accumulation and albumin expression). Our results showed that the differentiated HLCs from both the substrates are comparable and expressed stage specific hepatocyte markers as well as functional maturity. We have demonstrated that CNF, a natural biomaterial, may be used in tissue engineering applications as a potential substrate for the differentiation of iPSCs to HLCs.

Microengineered systems with iPSC-derived cardiac and hepatic cells to evaluate drug adverse effects

Hepatic and cardiac drug adverse effects are among the leading causes of attrition in drug development programs, in part due to predictive failures of current animal or in vitro models. Hepatocytes and cardiomyocytes differentiated from human induced pluripotent stem cells (iPSCs) hold promise for predicting clinical drug effects, given their human-specific properties and their ability to harbor genetically determined characteristics that underlie inter-individual variations in drug response. Currently, the fetal-like properties and heterogeneity of hepatocytes and cardiomyocytes differentiated from iPSCs make them physiologically different from their counterparts isolated from primary tissues and limit their use for predicting clinical drug effects. To address this hurdle, there have been ongoing advances in differentiation and maturation protocols to improve the quality and use of iPSC-differentiated lineages. Among these are in vitro hepatic and cardiac cellular microsystems that can further enhance the physiology of cultured cells, can be used to better predict drug adverse effects, and investigate drug metabolism, pharmacokinetics, and pharmacodynamics to facilitate successful drug development. In this article, we discuss how cellular microsystems can establish microenvironments for these applications and propose how they could be used for potentially controlling the differentiation of hepatocytes or cardiomyocytes. The physiological relevance of cells is enhanced in cellular microsystems by simulating properties of tissue microenvironments, such as structural dimensionality, media flow, microfluidic control of media composition, and co-cultures with interacting cell types. Recent studies demonstrated that these properties also affect iPSC differentiations and we further elaborate on how they could control differentiation efficiency in microengineered devices. In summary, we describe recent advances in the field of cellular microsystems that can control the differentiation and maturation of hepatocytes and cardiomyocytes for drug evaluation. We also propose how future research with iPSCs within engineered microenvironments could enable their differentiation for scalable evaluations of drug effects.

Hepatocyte-like cells derived from human induced pluripotent stem cells using small molecules: implications of a transcriptomic study

Background

Hepatocyte-like cells (HLCs) derived from human induced pluripotent stem cells (iPSCs) hold great promise in toxicological applications as well as in regenerative medicine. Previous efforts on hepatocyte differentiation have mostly relied on the use of growth factors (GFs) to recapitulate developmental signals under in vitro conditions. Recently, the use of small molecules (SMs) has emerged as an attractive tool to induce cell fate transition due to its superiority in terms of both quality and cost. However, HLCs derived using SMs have not been well characterized, especially on the transcriptome level.

Methods

HLCs were differentiated from human iPSCs using a protocol that only involves SMs and characterized by transcriptomic analysis using whole genome microarrays.

Results

HLCs derived using the SM protocol (HLC_SM) displayed specific hepatic marker expression and demonstrated key hepatic functions. Transcriptomic analysis of the SM-driven differentiation defined a hepatocyte differentiation track and characterized the expression of some key marker genes in major stages of hepatocyte differentiation. In addition, HLC_SM were scored with CellNet, a bioinformatics tool quantifying how closely engineered cell populations resemble their target cell type, and compared to primary human hepatocytes (PHHs), adult liver tissue, fetal liver tissue, HLCs differentiated using GFs (HLC_GF), and commercially available HLCs. Similar to HLC_GF, HLC_SM displayed a mixed phenotype of fetal and adult hepatocytes and had relatively low expression of metabolic enzymes, transporters, and nuclear receptors compared to PHHs. Finally, the differentially expressed genes in HLC_SM compared to HLC_GF and to PHHs were analyzed to identify pathways and upstream transcription regulators which could potentially be manipulated to improve the differentiation of HLCs.

Conclusions

Overall, the present study demonstrated the usefulness of the SM-based hepatocyte differentiation method, offered new insights into the molecular basis of hepatogenesis and associated gene regulation, and suggested ways for further improvements in hepatocyte differentiation in order to obtain more mature HLCs that could be used in toxicological studies.

iPSC-Derived Liver Organoids: A Journey from Drug Screening, to Disease Modeling, Arriving to Regenerative Medicine

Liver transplantation is the most common treatment for patients suffering from liver failure that is caused by congenital diseases, infectious agents, and environmental factors. Despite a high rate of patient survival following transplantation, organ availability remains the key limiting factor. As such, research has focused on the transplantation of different cell types that are capable of repopulating and restoring liver function. The best cellular mix capable of engrafting and proliferating over the long-term, as well as the optimal immunosuppression regimens, remain to be clearly well-defined. Hence, alternative strategies in the field of regenerative medicine have been explored. Since the discovery of induced pluripotent stem cells (iPSC) that have the potential of differentiating into a broad spectrum of cell types, many studies have reported the achievement of iPSCs differentiation into liver cells, such as hepatocytes, cholangiocytes, endothelial cells, and Kupffer cells. In parallel, an increasing interest in the study of self-assemble or matrix-guided three-dimensional (3D) organoids have paved the way for functional bioartificial livers. In this review, we will focus on the recent breakthroughs in the development of iPSCs-based liver organoids and the major drawbacks and challenges that need to be overcome for the development of future applications.

Quantifying drug-induced structural toxicity in hepatocytes and cardiomyocytes derived from hiPSCs using a deep learning method

Cardiac and hepatic toxicity result from induced disruption of the functioning of cardiomyocytes and hepatocytes, respectively, which is tightly related to the organization of their subcellular structures. Cellular structure can be analyzed from microscopy imaging data. However, subtle or complex structural changes that are not easily perceived may be missed by conventional image-analysis techniques. Here we report the evaluation of PhenoTox, an image-based deep-learning method of quantifying drug-induced structural changes using human hepatocytes and cardiomyocytes derived from human induced pluripotent stem cells. We assessed the ability of the deep learning method to detect variations in the organization of cellular structures from images of fixed or live cells. We also evaluated the power and sensitivity of the method for detecting toxic effects of drugs by conducting a set of experiments using known toxicants and other methods of screening for cytotoxic effects. Moreover, we used PhenoTox to characterize the effects of tamoxifen and doxorubicin-which cause liver toxicity-on hepatocytes. PhenoTox revealed differences related to loss of cytochrome P450 3A4 activity, for which it showed greater sensitivity than a caspase 3/7 assay. Finally, PhenoTox detected structural toxicity in cardiomyocytes, which was correlated with contractility defects induced by doxorubicin, erlotinib, and sorafenib. Taken together, the results demonstrated that PhenoTox can capture the subtle morphological changes that are early signs of toxicity in both hepatocytes and cardiomyocytes.

Concentration-dependent toxicogenomic changes of silver nanoparticles in hepatocyte-like cells derived from human induced pluripotent stem cells

The application of silver nanoparticles (AgNPs) in consumer products has been increasing rapidly over the past decades. Therefore, in vitro models capable of accurately predicting the toxicity of AgNPs are much needed. Hepatocyte-like cells (HLCs) derived from human induced pluripotent stem cells (iPSCs) represent an attractive alternative in vitro hepatotoxicity model. Yet, the use of iPSC-derived HLCs (iPSC-HLCs) for the study of nanoparticle toxicity has not been reported so far. In the present study, transcriptomic changes induced by varying concentrations (5-25 μg/ml) of AgNPs were characterized in iPSC-HLCs after 24-h exposure. AgNPs caused concentration-dependent gene expression changes in iPSC-HLCs. At all the concentrations, members of the metallothionein (MT) and the heat shock protein (HSP) families were the dominating upregulated genes, suggesting that exposure to AgNPs induced oxidative stresses in iPSC-HLCs and as a result elicited cellular protective responses in the cells. Functional analysis showed that the differentially expressed genes (DEGs) were majorly involved in the biological processes of metabolism, response to stress, and cell organization and biogenesis. Ingenuity Pathway Analysis revealed that cancer was at the top of diseases and disorders associated with the DEGs at all concentrations. These results were in accordance with those reported previously on hepatoma cell lines and primary hepatocytes. Considering the advantages iPSC-HLCs have over other liver cell models in terms of unlimited supply, consistency in quality, sustainability of function in long-term culture, and, more importantly, affordability of donor specificity, the results of the current study suggest that iPSC-HLCs may serve as a better in vitro model for liver nanotoxicology.

Comparative study between lactose-silk fibroin conjugates and extracellular matrices as a substrate for the culture of human induced pluripotent stem cell-derived hepatocytes

BACKGROUND

Human induced pluripotent stem cell (hiPSC)-derived hepatocytes are an attractive alternative cell source to primary human hepatocytes for tissue regeneration.

OBJECTIVES

This study presents an application of lactose-silk fibroin conjugates (Lac-CY-SF) bearing 𝛽-galactose residues as a substrate for culture of hiPSC-derived hepatocytes. A comparison of hiPSC-derived hepatocytes cultured on three different substrates; Lac-CY-SF conjugates, Matrigel and type I collagen was performed.

METHODS

Cell morphology, viability, maturation and albumin secretory function were assessed by phase-contrast microscopy, tetrazolium-based colorimetric assay, immunofluorescence staining and enzyme-linked immunosorbent assay.

RESULTS

Morphological characteristics of the cells cultured on the conjugates resembled those on Matrigel throughout the 6-day culture period. The number of viable cells cultured on the conjugates was comparable to that on Matrigel at day 2 and 6. The protein expression of mature hepatocyte markers, asialoglycoprotein receptor 1 and albumin, by the cells cultured on the conjugates resembled that by the cells cultured on collagen at day 2 and 6. Albumin secretory function per cell cultured on the conjugates was higher than that on collagen and comparable to that on Matrigel.

CONCLUSIONS

These limited results suggest that Lac-CY-SF conjugates may be as useful as Matrigel and collagen for cultivation of hiPSC-derived hepatocytes.

Transplantation of mesenchymal stem cells and their derivatives effectively promotes liver regeneration to attenuate acetaminophen-induced liver injury

Acetaminophen (APAP)-induced injury is a common clinical phenomenon that not only occurs in a dose-dependent manner but also occurs in some idiosyncratic individuals in a dose-independent manner. APAP overdose generally results in acute liver injury via the initiation of oxidative stress, endoplasmic reticulum (ER) stress, autophagy, liver inflammation, and microcirculatory dysfunction. Liver transplantation is the only effective strategy for treating APAP-induced liver failure, but liver transplantation is inhibited by scarce availability of donor liver grafts, acute graft rejection, lifelong immunosuppression, and unbearable costs. Currently, N-acetylcysteine (NAC) effectively restores liver functions early after APAP intake, but it does not protect against APAP-induced injury at the late stage. An increasing number of animal studies have demonstrated that mesenchymal stem cells (MSCs) significantly attenuate acute liver injury through their migratory capacity, hepatogenic differentiation, immunoregulatory capacity, and paracrine effects in acute liver failure (ALF). In this review, we comprehensively discuss the mechanisms of APAP overdose-induced liver injury and current therapies for treating APAP-induced liver injury. We then comprehensively summarize recent studies about transplantation of MSC and MSC derivatives for treating APAP-induced liver injury. We firmly believe that MSCs and their derivatives will effectively promote liver regeneration and liver injury repair in APAP overdose-treated animals and patients. To this end, MSC-based therapies may serve as an effective strategy for patients who are waiting for liver transplantation during the early and late stages of APAP-induced ALF in the near future.

The importance of transporters and cell polarization for the evaluation of human stem cell-derived hepatic cells

One of the most promising applications of human pluripotent stem cells is their utilization for human-based pharmacological models. Despite the fact that membrane transporters expressed in the liver play pivotal role in various hepatic functions, thus far only little attention was devoted to the membrane transporter composition of the stem cell-derived liver models. In the present work, we have differentiated HUES9, a human embryonic stem cell line, toward the hepatic lineage, and monitored the expression levels of numerous differentiation marker and liver transporter genes with special focus on ABC transporters. In addition, the effect of bile acid treatment and polarizing culturing conditions on hepatic maturation has been assessed. We found that most transporter genes crucial for hepatic functions are markedly induced during hepatic differentiation; however, as regards the transporter composition the end-stage cells still exhibited dual, hepatocyte and cholangiocyte character. Although the bile acid treatment and sandwich culturing only slightly influenced the gene expressions, the stimulated cell polarization resulted in formation of bile canaliculi and proper localization of transporters. Our results point to the importance of membrane transporters in human stem cell-derived hepatic models and demonstrate the relevance of cell polarization in generation of applicable cellular models with correctly localized transporters. On the basis of our observations we suggest that conventional criteria for the evaluation of the quality of stem cell-derived hepatocyte-like cells ought to be augmented with additional elements, such as polarized and functional expression of hepatic transporters.

iPSC-Derived Hepatocytes as a Platform for Disease Modeling and Drug Discovery

The liver is one of the largest organs in the body and is responsible for a diverse repertoire of metabolic processes. Such processes include the secretion of serum proteins, carbohydrate and lipid metabolism, bile acid and urea synthesis, detoxification of drugs and metabolic waste products, and vitamin and carbohydrate storage. Currently, liver disease is one of the most prevalent causes of mortality in the USA with congenital liver defects contributing to a significant proportion of these deaths. Historically the study of liver disease has been hampered by a shortage of organ donors, the subsequent scarcity of healthy tissue, and the failure of animal models to fully recapitulate human liver function. In vitro culture of hepatocytes has also proven difficult because primary hepatocytes rapidly de-differentiate in culture. Recent advances in stem cell technology have facilitated the generation of induced pluripotent stem cells (iPSCs) from various somatic cell types from patients. Such cells can be differentiated to a liver cell fate, essentially providing a limitless supply of cells with hepatocyte characteristics that can mimic the pathophysiology of liver disease. Furthermore, development of the CRISPR-Cas9 system, as well as advancement of miniaturized differentiation platforms has facilitated the development of high throughput models for the investigation of hepatocyte differentiation and drug discovery. In this review, we will explore the latest advances in iPSC-based disease modeling and drug screening platforms and examine how this technology is being used to identify new pharmacological interventions, and to advance our understanding of liver development and mechanisms of disease. We will cover how iPSC technology is being used to develop predictive models for rare diseases and how information gained from large in vitro screening experiments can be used to directly inform clinical investigation.

Dr. Daniel Acosta and In Vitro toxicology at the U.S. Food and Drug Administration's National Center for Toxicological Research

For the past five years, Dr. Daniel Acosta has served as the Deputy Director of Research at the National Center for Toxicological Research (NCTR), a principle research laboratory of the U.S. Food and Drug Administration (FDA). Over his career at NCTR, Dr. Acosta has had a major impact on developing and promoting the use of in vitro assays in regulatory toxicity and product safety assessments. As Dr. Acosta nears his retirement we have dedicated this paper to his many accomplishments at the NCTR. Described within this paper are some of the in vitro studies that have been conducted under Dr. Acosta's leadership. These studies include toxicological assessments involving developmental effects, and the development and application of in vitro reproductive, heart, liver, neurological and airway cell and tissue models.

The application of omics-based human liver platforms for investigating the mechanism of drug-induced hepatotoxicity in vitro

Drug-induced liver injury (DILI) complicates safety assessment for new drugs and poses major threats to both patient health and drug development in the pharmaceutical industry. A number of human liver cell-based in vitro models combined with toxicogenomics methods have been developed as an alternative to animal testing for studying human DILI mechanisms. In this review, we discuss the in vitro human liver systems and their applications in omics-based drug-induced hepatotoxicity studies. We furthermore present bioinformatic approaches that are useful for analyzing toxicogenomic data generated from these models and discuss their current and potential contributions to the understanding of mechanisms of DILI. Human pluripotent stem cells, carrying donor-specific genetic information, hold great potential for advancing the study of individual-specific toxicological responses. When co-cultured with other liver-derived non-parenchymal cells in a microfluidic device, the resulting dynamic platform enables us to study immune-mediated drug hypersensitivity and accelerates personalized drug toxicology studies. A flexible microfluidic platform would also support the assembly of a more advanced organs-on-a-chip device, further bridging gap between in vitro and in vivo conditions. The standard transcriptomic analysis of these cell systems can be complemented with causality-inferring approaches to improve the understanding of DILI mechanisms. These approaches involve statistical techniques capable of elucidating regulatory interactions in parts of these mechanisms. The use of more elaborated human liver models, in harmony with causality-inferring bioinformatic approaches will pave the way for establishing a powerful methodology to systematically assess DILI mechanisms across a wide range of conditions.

Simultaneous UHPLC-MS/MS method of estradiol metabolites to support the evaluation of Phase-2 metabolic activity of induced pluripotent stem cell derived hepatocytes

The goal of this study was to develop and validate a high-throughput UHPLC-MS/MS method for simultaneous quantitation of three estradiol metabolites namely estradiol 3-β-D-glucuronide (E3G), estradiol 17-β-D-glucuronide (E17G) and estradiol 3-sulfate (E3S) in cell culture medium to support the characterization of metabolic function of induced pluripotent stem cell (iPSC) derived hepatocytes. To achieve this goal, a simple protein precipitation method was used for sample cleanup. All the metabolites were separated chromatographically using a C-18 column where 10 mM ammonium acetate and acetonitrile was used in gradient flow for 4 min. The analytes were quantitated by triple quadrupole mass spectrometer with the use of isotopically labeled internal standard (IS). This method was validated as per the U.S Food and Drug Administration's Bioanalytical Method Validation, Guidance for Industry. Linearity for E3G and E17G was in the range of 2-1500 ng/mL whereas for E3S it was 0.3-500 ng/mL. Inter-day and intra-day accuracy and precision of this method were in the acceptable limits. In addition, multiple stability tests (freeze thaw, autosampler, water bath (37 °C), bench top and long term) were performed for all the metabolites in cell culture medium. All the metabolites were stable up to 3 freeze thaw cycles at -20 °C and - 80 °C, 48 h in autosampler, 24 h at 37 °C, 48 h at room temperature and 173 days at -20 °C. Extraction recoveries for the metabolites were reproducible and were in the range of 94-108%. This method was used to quantitate estradiol metabolites generated by iPSC hepatocytes in-vitro studies.

Advances in Human Induced Pluripotent Stem Cell-Derived Hepatocytes for Use in Toxicity Testing

Induced pluripotent stem cells (iPSCs) can be differentiated into multiple cell types in the body while maintaining proliferative capabilities. The generation of hepatocyte-like cells (HLCs) from iPSCs has resulted in a new source for liver cells. Since healthy primary human hepatocytes and hepatic cells are difficult to obtain, HLCs are gaining attention. HLCs can be obtained from a continuous, stable source while maintaining their original donor genotype, which opens new avenues into patient-specific testing and therapeutics. Studies have utilized HLCs for toxicity testing to further understand their drug metabolizing capabilities. This review focuses on advances being made to achieve hepatic functions from HLCs, their current use in hepatotoxicity testing, and their potential for future liver-related toxicity evaluations.

Collagen vitrigel promotes hepatocytic differentiation of induced pluripotent stem cells into functional hepatocyte-like cells

Differentiation of stem cells to hepatocytes provides an unlimited supply of human hepatocytes and therefore has been vigorously studied. However, to date, the stem cell-derived hepatocytes were suggested to be of immature features. To obtain matured hepatocytes from stem cells, we tested the effect of culturing human-induced pluripotent stem (hiPS) cell-derived endoderm cells on collagen vitrigel membrane and compared with our previous reported nanofiber matrix. We cultured hiPS cell-derived endoderm cells on a collagen vitrigel membrane and examined the expression profiles, and tested the activity of metabolic enzymes. Gene expression profile analysis of hepatocytic differentiation markers revealed that upon culture on collagen vitrigel membrane, immature markers of AFP decreased, with a concomitant increase in the expression of mature hepatocyte transcription factors and mature hepatocyte markers such as ALB, ASGR1. Mature markers involved in liver functions, such as transporters, cytochrome P450 enzymes and phase II metabolic enzymes were also upregulated. We observed the upregulation of the liver markers for at least 2 weeks. Gene array profiling analysis revealed that hiPS cell-derived hepatocyte-like cells (hiPS-hep) resemble those of the primary hepatocytes. Functions of the CYP enzyme activities were tested in multi-institution and all revealed high CYP1A, CYP2C19, CYP2D6, CYP3A activity, which could be maintained for at least 2 weeks in culture. Taken together, the present approach identified that collagen vitrigel membrane provides a suitable environment for the generation of hepatocytes from hiPS cells that resemble many characteristics of primary human hepatocytes.

Summary: We found that collagen vitrigel membrane used as scaffold potentiates differentiation of human induced pluripotent stem cells to differentiate into mature hepatocyte-like cells that exhibit mature functions of the hepatocytes.

Donor-Dependent and Other Nondefined Factors Have Greater Influence on the Hepatic Phenotype Than the Starting Cell Type in Induced Pluripotent Stem Cell Derived Hepatocyte-Like Cells

Drug‐induced liver injury is the greatest cause of post‐marketing drug withdrawal; therefore, substantial resources are directed toward triaging potentially dangerous new compounds at all stages of drug development. One of the major factors preventing effective screening of new compounds is the lack of a predictive in vitro model of hepatotoxicity. Primary human hepatocytes offer a metabolically relevant model for which the molecular initiating events of hepatotoxicity can be examined; however, these cells vary greatly between donors and dedifferentiate rapidly in culture. Induced pluripotent stem cell (iPSC)‐derived hepatocyte‐like cells (HLCs) offer a reproducible, physiologically relevant and genotypically normal model cell; however, current differentiation protocols produce HLCs with a relatively immature phenotype. During the reprogramming of somatic cells, the epigenome undergoes dramatic changes; however, this “resetting” is a gradual process, resulting in an altered differentiation propensity, skewed toward the lineage of origin, particularly in early passage cultures. We, therefore, performed a comparison of human hepatocyte‐ and dermal fibroblast‐derived iPSCs, assessing the impact of epigenetic memory at all stages of HLC differentiation. These results provide the first isogenic assessment of the starting cell type in human iPSC‐derived HLCs. Despite a trend toward improvement in hepatic phenotype in albumin secretion and gene expression, few significant differences in hepatic differentiation capacity were found between hepatocyte and fibroblast‐derived iPSCs. We conclude that the donor and inter‐clonal differences have a greater influence on the hepatocyte phenotypic maturity than the starting cell type. Therefore, it is not necessary to use human hepatocytes for generating iPSC‐derived HLCs. Stem Cells Translational Medicine2017;6:1321–1331

A nonalcoholic fatty liver disease model in human induced pluripotent stem cell-derived hepatocytes, created by endoplasmic reticulum stress-induced steatosis

Hepatic steatosis, a reversible state of metabolic dysregulation, can promote the onset of nonalcoholic steatohepatitis (NASH), and its transition is thought to be critical in disease evolution. The association between endoplasmic reticulum (ER) stress response and hepatocyte metabolism disorders prompted us to characterize ER stress-induced hepatic metabolic dysfunction in human induced pluripotent stem cell-derived hepatocytes (hiPSC-Hep), to explore regulatory pathways and validate a phenotypic in vitro model for progression of liver steatosis. We treated hiPSC-Hep with a ratio of unsaturated and saturated fatty acids in the presence of an inducer of ER stress to synergistically promote triglyceride accumulation and dysregulate lipid metabolism. We monitored lipid accumulation by high-content imaging and measured gene regulation by RNA sequencing and reverse transcription quantitative PCR analyses. Our results show that ER stress potentiated intracellular lipid accumulation by 5-fold in hiPSC-Hep in the absence of apoptosis. Transcriptome pathway analysis identified ER stress pathways as the most significantly dysregulated of all pathways affected. Obeticholic acid dose dependently inhibited lipid accumulation and modulated gene expression downstream of the farnesoid X receptor. We were able to identify modulation of hepatic markers and gene pathways known to be involved in steatosis and nonalcoholic fatty liver disease (NAFLD), in support of a hiPSC-Hep disease model that is relevant to clinical data for human NASH. Our results show that the model can serve as a translational discovery platform for the understanding of molecular pathways involved in NAFLD, and can facilitate the identification of novel therapeutic molecules based on high-throughput screening strategies.

Summary: Our study demonstrates expanded use of human induced pluripotent stem cell-derived hepatocytes for molecular studies and drug screening, to evaluate new therapeutics with an antisteatotic mechanism of action for nonalcoholic fatty liver disease.

Pathological Features of Mitochondrial Ultrastructure Predict Susceptibility to Post-TIPS Hepatic Encephalopathy

BACKGROUND

Post-TIPS hepatic encephalopathy (PSE) is a complex process involving numerous risk factors; the root cause is unclear, but an elevation of blood ammonia due to portosystemic shunt and metabolic disorders in hepatocytes has been proposed as an important risk factor.

AIMS

The aim of this study was to investigate the impact of pathological features of mitochondrial ultrastructure on PSE via transjugular liver biopsy at TIPS implantation.

METHODS

We evaluated the pathological damage of mitochondrial ultrastructure on recruited patients by the Flameng classification system. A score ≤2 (no or low damage) was defined as group A, and a score >2 (high damage level) was defined as group B; routine follow-up was required at 1 and 2 years; the incidence of PSE and multiple clinical data were recorded.

RESULTS

A total of 78 cases in group A and 42 in group B completed the study. The incidence of PSE after 1 and 2 years in group B (35.7% and 45.2%, respectively) was significantly higher than that in group A (16.7% and 24.4%, respectively); the 1- and 2-year OR (95% CI) were 2.778 (1.166-6.615) and 2.565 (1.155-5.696), respectively, for groups A and B. Importantly, group B had worse incidence of PSE than group A [P=0.014, hazard ratio (95%CI): 2.172 (1.190-4.678)].

CONCLUSION

Aggressive damage to mitochondrial ultrastructure in liver shunt predicts susceptibility to PSE. The registration number is NCT02540382.

Critical differences in drug metabolic properties of human hepatic cellular models, including primary human hepatocytes, stem cell derived hepatocytes, and hepatoma cell lines

Primary human hepatocytes (PHH), HepaRG™, HepG2, and two sources of induced pluripotent stem cell (iPSC) derived hepatocytes were characterized regarding gene expression and function of key hepatic proteins, important for the metabolic fate of drugs. The gene expression PCA analysis showed a distance between the two iPSC derived hepatocytes as well as the HepG2 and HepaRG™ cells to the three PHH donors and PHH pool, which were clustered more closely together. Correlation-based hierarchical analysis clustered HepG2 close to the stem cell derived hepatocytes both when the expression of 91 genes related to liver function or only cytochrome P450 (P450) genes were analyzed indicating the non-liver feature and a similar low P450 profile in these cell models. The specific P450 activities and the metabolic pattern of well-characterized drug substances in the cell models demonstrated that iPSC derived hepatocytes had modest levels of CYP3A and CYP2C9, while CYP1A2, 2B6, 2C8, 2C9, 2C19, and 2D6 were barely detectable. High expression of several extrahepatic P450s such as CYP1A1 and 1B1 detected in the stem cell derived hepatocytes may have significant effects on metabolite profiles. However, one of the iPSC derived hepatocytes demonstrated significant combined P450 and conjugating enzyme activity of certain drugs. HepaRG™ cells showed many metabolic properties similar to PHHs and will in many respects be a good model in studies of metabolic pathways and induction of drug metabolism whereas there is still ground to cover before iPSC derived hepatocytes will be seen as a substitute to PHH in drug metabolism studies.

High-throughput toxicity testing of chemicals and mixtures in organotypic multi-cellular cultures of primary human hepatic cells

High-throughput screening (HTS) of liver toxicants can bridge the gap in understanding adverse effects of chemicals on humans. Toxicity testing of mixtures is time consuming and expensive, since the number of possible combinations increases exponentially with the number of chemicals. The combination of organotypic culture models (OCMs) and HTS assays can lead to the rapidly evaluation of chemical toxicity in a cost and time-effective manner while prioritizing chemicals that warrant additional investigation. We describe the design, assembly and toxicant response of multi-cellular hepatic organotypic culture models comprised of primary human or rat cells assembled in 96-well plates (denoted as μOCMs). These models were assembled using automated procedures that did not affect hepatocyte function or viability, rendering them ideal for large-scale toxicity evaluations. Rat μOCMs were assembled to obtain insights into deviations from human toxicity. Four test chemicals (acetaminophen, ethanol, isoniazid, and perfluorooctanoic acid) were added to the μOCMs individually or in mixtures. HTS assays were utilized to measure cell death, apoptosis, glutathione depletion, mitochondrial membrane damage, and cytochrome P450 2E1 activity. The μOCMs exhibited increased toxicant sensitivity compared to hepatocyte sandwich cultures. Synergistic and non-synergistic interactions were observed when the toxicants were added as mixtures. Specifically, chemical interactions in the μOCMs were manifested by changes in apoptosis and decreased glutathione. The μOCMs accurately predicted hepatotoxicity for individual and mixtures of toxicants, demonstrating their potential for large-scale toxicity evaluations in the future.