Stem cell-derived hepatocytes and their use in toxicology

Evaluation of drug carrier hepatotoxicity using primary cell culture models

This study aims to establish a primary rat hepatocyte culture model to evaluate dose-dependent hepatotoxic effects of drug carriers (lipopolymer nanoparticles; LPNs) temporal. Primary rat hepatocyte cell cultures were used to determine half-maximal Inhibition Concentrations (IC50) of the drug-carrier library. Drug-carrier library, at concentrations <50 μg/mL, is benign to primary rat hepatocytes as determined using albumin and urea secretions. Albumin, as a hepatic biomarker, exhibited a more sensitive and faster outcome, compared to urea, for the determination of the IC50 value of LPNs. Temporal measurements of hepatic biomarkers including urea and albumin, and rigorous physicochemical (hydrodynamic diameter, surface charge, etc.) characterization, should be combined to evaluate the hepatotoxicity of drug carrier libraries in screens.

Current trends and research topics regarding liver 3D bioprinting: A bibliometric analysis research

Introduction: Over recent years, 3D bioprinting has changed dramatically. The articles related to liver 3D bioprinting have not been quantitatively analyzed. In this article, we screen all articles related to liver 3D bioprinting until January 2022 and analyzed them using bibliometric citation analysis to characterize the current trends in liver 3D bioprinting. Methods: The articles were identified and analyzed from the Clarivate Analytics Web of Science Core Collection database. Results: Until 1 January 2022, 71 articles focusing on liver 3D bioprinting were identified. There was an increase in the number of articles in 2015. Most articles came from the USA (n = 27), followed by South Korea (n = 22), China (n = 16), and Japan (n = 5). The printing technology of liver 3D printing was the most studied topic (n = 29). Biofabrication published the highest number of papers (n = 16) with 1,524 total citations. Conclusion: Based on bibliometric analysis of the articles until January 2022, a comprehensive analysis of the liver 3D bioprinting articles highlighted the current trends and research topics of this field. The data should provide clinicians and researchers insight into future directions relative to the liver 3D bioprinting.

The Efficacy of an N-Acetylcysteine-Antibiotic Combination Therapy on Achromobacter xylosoxidans in a Cystic Fibrosis Sputum/Lung Cell Model

Cystic fibrosis (CF) is a disorder causing dysfunctional ion transport resulting in the accumulation of viscous mucus. This environment fosters a chronic bacterial biofilm-associated infection in the airways. Achromobacter xylosoxidans, a gram-negative aerobic bacillus, has been increasingly associated with antibiotic resistance and chronic colonisation in CF. In this study, we aimed to create a reproducible model of CF infection using an artificial sputum medium (ASMDM-1) with bronchial (BEAS-2B) and macrophage (THP-1) cells to test A. xylosoxidans infection and treatment toxicity. This study was conducted in three distinct stages. First, the tolerance of BEAS-2B cell lines and two A. xylosoxidans strains against ASMDM-1 was optimised. Secondly, the cytotoxicity of combined therapy (CT) comprising N-acetylcysteine (NAC) and the antibiotics colistin or ciprofloxacin was tested on cells alone in the sputum model in both BEAS-2B and THP-1 cells. Third, the efficacy of CT was assessed in the context of a bacterial infection within the live cell/sputum model. We found that a model using 20% ASMDM-1 in both cell populations tolerated a colistin-NAC-based CT and could significantly reduce bacterial loads in vitro (~2 log10 CFU/mL compared to untreated controls). This pilot study provides the foundation to study other bacterial opportunists that infect the CF lung to observe infection and CT kinetics. This model also acts as a springboard for more complex co-culture models.

Organs-on-Chips Platforms Are Everywhere: A Zoom on Biomedical Investigation

Over the decades, conventional in vitro culture systems and animal models have been used to study physiology, nutrient or drug metabolisms including mechanical and physiopathological aspects. However, there is an urgent need for Integrated Testing Strategies (ITS) and more sophisticated platforms and devices to approach the real complexity of human physiology and provide reliable extrapolations for clinical investigations and personalized medicine. Organ-on-a-chip (OOC), also known as a microphysiological system, is a state-of-the-art microfluidic cell culture technology that sums up cells or tissue-to-tissue interfaces, fluid flows, mechanical cues, and organ-level physiology, and it has been developed to fill the gap between in vitro experimental models and human pathophysiology. The wide range of OOC platforms involves the miniaturization of cell culture systems and enables a variety of novel experimental techniques. These range from modeling the independent effects of biophysical forces on cells to screening novel drugs in multi-organ microphysiological systems, all within microscale devices. As in living biosystems, the development of vascular structure is the salient feature common to almost all organ-on-a-chip platforms. Herein, we provide a snapshot of this fast-evolving sophisticated technology. We will review cutting-edge developments and advances in the OOC realm, discussing current applications in the biomedical field with a detailed description of how this technology has enabled the reconstruction of complex multi-scale and multifunctional matrices and platforms (at the cellular and tissular levels) leading to an acute understanding of the physiopathological features of human ailments and infections in vitro.

Transcriptional and Epigenetic Consequences of DMSO Treatment on HepaRG Cells

Dimethyl sulfoxide (DMSO) is used to sustain or favor hepatocyte differentiation in vitro. Thus, DMSO is used in the differentiation protocol of the HepaRG cells that present the closest drug-metabolizing enzyme activities to primary human hepatocytes in culture. The aim of our study is to clarify its influence on liver-specific gene expression. For that purpose, we performed a large-scale analysis (gene expression and histone modification) to determine the global role of DMSO exposure during the differentiation process of the HepaRG cells. The addition of DMSO drives the upregulation of genes mainly regulated by PXR and PPARα whereas genes not affected by this addition are regulated by HNF1α, HNF4α, and PPARα. DMSO-differentiated-HepaRG cells show a differential expression for genes regulated by histone acetylation, while differentiated-HepaRG cells without DMSO show gene signatures associated with histone deacetylases. In addition, we observed an interplay between cytoskeleton organization and EMC remodeling with hepatocyte maturation.

Oxygen Plasma Substrate and Specific Nanopattern Promote Early Differentiation of HepaRG Progenitors

Fully differentiated HepaRG™ cells are the hepatic cell line of choice for in vitro study in toxicology and drug trials. They are derived from a hepatoblast-like progenitor (HepaRG-P) that differentiates into a coculture of hepatocyte-like and cholangiocyte-like cells. This process that requires 2 weeks of proliferation followed by 2 weeks of differentiation using dimethyl sulfoxide (DMSO) can be time consuming and costly. Identifying a method to accelerate HepaRG-Ps toward a mature lineage would save both time and money. The ability to do this in the absence of DMSO would remove the possibility of confounding toxicology results caused by DMSO induction of CYP pathways. It has been shown that tissue culture substrates play an important role in the development and maturity of a cell line, and this is particularly important for progenitor cells, which retain some form of plasticity. Oxygen plasma treatment is used extensively to modify cell culture substrates. There is also evidence that patterned rather than planar surfaces have a positive effect on proliferation and differentiation. In this study, we compared the effect of standard tissue culture plastic (TCP), oxygen plasma coated (OPC), and nanopatterned substrates (NPS) on early differentiation and function of HepaRG-P cells. Since NPS were OPC we initially compared the effect of TCP and OPC to enable comparison between all three culture surfaces using OPC as control to asses if patterning further enhanced early differentiation and functionality. The results show that HepaRG-P's grown on OPC substrate exhibited earlier differentiation, proliferation, and function compared with TCP. Culturing HepaRG-P's on OPC with the addition of NPS did not confer any additional advantage. In conclusion, OPC surface appeared to enhance hepatic differentiation and functionality and could replace traditional methods of differentiating HepaRG-P cells into fully differentiated and functional HepaRGs earlier than standard methods. Impact statement We show significantly earlier differentiation and function of HepaRG progenitor cells when grown in dimethyl sulfoxide-free medium on oxygen plasma substrates versus standard tissue culture plastic. Further investigation showed that nanopatterning of oxygen plasma substrates did not confer any additional advantage over smooth oxygen plasma, although one pattern (DSQ120) showed comparable early differentiation and function.

Modeling the Human Body on Microfluidic Chips

Animals often fail to faithfully mimic human diseases and drug toxicities, and most in vitro models are not complex enough to recapitulate human body function and pathophysiology. Organ-on-chip culture technology, however, offers a promising tool for the study of tissue development and homeostasis, which has brought us one step closer to performing human experimentation in vitro. To recapitulate the complex functionality of multiple organs at once, their respective on-chip models can be linked to create a functional human body-on-chip platform. Here, we highlight the advantages and translational potentials of body-on-chip platforms in disease modeling, therapeutic development, and personalized medicine. We provide the reader with current limitations of the body-on-chip approach and new ideas to address the pending issues moving forwards.

Analysis of reproducibility and robustness of a human microfluidic four-cell liver acinus microphysiology system (LAMPS)

A human microfluidic four-cell liver acinus microphysiology system (LAMPS), was evaluated for reproducibility and robustness as a model for drug pharmacokinetics and toxicology. The model was constructed using primary human hepatocytes or human induced pluripotent stem cell (iPSC)-derived hepatocytes and 3 human cell lines for the endothelial, Kupffer and stellate cells. The model was tested in two laboratories and demonstrated to be reproducible in terms of basal function of hepatocytes, Terfenadine metabolism, and effects of Tolcapone (88 μM), Troglitazone (150 μM), and caffeine (600 μM) over 9 days in culture. Additional experiments compared basal outputs of albumin, urea, lactate dehydrogenase (LDH) and tumor necrosis factor (TNF)α, as well as drug metabolism and toxicity in the LAMPS model, and in 2D cultures seeded with either primary hepatocytes or iPSC-hepatocytes. Further experiments to study the effects of Terfenadine (10 μM), Tolcapone (88 μM), Trovafloxacin (150 μM with or without 1 μg/mL lipopolysaccharide), Troglitazone (28 μM), Rosiglitazone (0.8 μM), Pioglitazone (3 μM), and caffeine (600 μM) were carried out over 10 days. We found that both primary human hepatocytes and iPSC-derived hepatocytes in 3D culture maintained excellent basal liver function and Terfenadine metabolism over 10 days compared the same cells in 2D cultures. In 2D, non-overlay monolayer cultures, both cell types lost hepatocyte phenotypes after 48 h. With respect to drug effects, both cell types demonstrated comparable and more human-relevant effects in LAMPS, as compared to 2D cultures. Overall, these studies show that LAMPS is a robust and reproducible in vitro liver model, comparable in performance when seeded with either primary human hepatocytes or iPSC-derived hepatocytes, and more physiologically and clinically relevant than 2D monolayer cultures.

Flow-Based Three-Dimensional Co-Culture Model for Long-Term Hepatotoxicity Prediction

We developed concave microwell arrays to establish a size-controllable 3-D co-culture liver model for in vitro drug toxicity testing, to predict hepatotoxicity. The interaction of hepatocytes with hepatic stellate cells (HSCs) was investigated by co-culturing primary 3-D hepatocyte spheroids and HSCs (heterosphere), using 3-D liver-on-a-chip. The effect of HSCs was investigated during spheroid formation; they were involved in controlling the organization of spheroidal aggregates and the formation of tight cell–cell contacts. Scanning electron microscopy (SEM) images showed that co-cultured spheroids with smoother surfaces in the flow chip aggregated more tightly and rapidly, compared to mono-cultured spheroids, until 13 days. Metabolic function analysis revealed that heterospheres secreted 40% more albumin and urea than hepatospheres on day 13. Additionally, an acetaminophen (AAP) and isoniazid (INH) concentration-dependent increase in CYP3A4 expression was detected in the 3-D cultures, and an increase in Lactate dehydrogenase (LDH) release after AAP and INH treatment was observed. CYP1A2, Mrp1 and UGT1A5 mRNA expression levels in the heterospheres and hepatospheres were evaluated from days 3 to 13. To examine the potential for toxicity testing in the flow-conditioned culture of the heterospheres, we evaluated cytotoxicity using the endpoint LDH release in the heterospheres and hepatospheres. IC₅₀ values for AAP and INH after 24 h of exposure were calculated from the dose–response curves of the compounds. Flow-conditioned heterosphere culture results suggest that it may be suitable for long-term culture and cytotoxicity testing. Thus, our co-culture system closely resembles the in vivo environment and allows long-term in vitro hepatotoxicity prediction.

Developing a partially perfused liver model using caprine liver explant conditioned to the chicken extra-embryonic perfusion system

The Liver is constantly subjected to mechanical, chemical and pathological insults throughout life, as a result of which there is a common occurrence of various liver diseases. Due to the complex nature of liver architecture, it is not possible to mimic the in-vivo conditions beyond a certain limit. Hence, the development of in-vitro and ex-vivo models to study various liver diseases has gained more importance over the last few decades. The present study aims to develop a semi-perfused liver explant model to give an extended lifetime for studying liver pathology and treatment options. Caprine liver tissue explants were sliced, weighed (25 mg) and placed on the area vasculosa of fertilized chicken eggs. Unfertilized eggs were used as controls. After varying time intervals of incubation on area vasculosa of fertilized chicken eggs, the liver slices were subjected to cell viability assay, lactate dehydrogenase assay and Serum glutamic pyruvic transaminase assays. The results indicate that the viability and functional properties of such semi-perfused liver tissue explants holds good up to 6 h. Finally, the liver tissue explants were pre-treated with FBS, with and without anti-fibrotic drugs, and placed on chick embryo area vasculosa up to 6 h. The anti-fibrotic drug-treated semi perfused liver tissue explant showed a decrease in collagen formation as confirmed by histology and western blot. We deem that the use of extra-embryonic vasculature of chicken bed for extending the life of tissue explants will serve as a cost-effective alternative to animal models to understand disease mechanisms under drug treatments.

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.

Mechanisms and in vitro models of drug-induced cholestasis

Cholestasis underlies one of the major manifestations of drug-induced liver injury. Drug-induced cholestatic liver toxicity is a complex process, as it can be triggered by a variety of factors that induce 2 types of biological responses, namely a deteriorative response, caused by bile acid accumulation, and an adaptive response, aimed at removing the accumulated bile acids. Several key events in both types of responses have been characterized in the past few years. In parallel, many efforts have focused on the development and further optimization of experimental cell culture models to predict the occurrence of drug-induced cholestatic liver toxicity in vivo. In this paper, a state-of-the-art overview of mechanisms and in vitro models of drug-induced cholestatic liver injury is provided.

Innovation for hepatotoxicity in vitro research models: A review

Many categories of drugs can induce hepatotoxicity, so improving the prediction of toxic drugs is important. In vitro models using human hepatocytes are more accurate than in vivo animal models. Good in vitro models require an abundance of metabolic enzyme activities and normal cellular polarity. However, none of the in vitro models can completely simulate hepatocytes in the human body. There are two ways to overcome this limitation: enhancing the metabolic function of hepatocytes and changing the cultural environment. In this review, we summarize the current state of research, including the main characteristics of in vitro models and their limitations, as well as improved technology and developmental prospects. We hope that this review provides some new ideas for hepatotoxicity research.

In vitro Models and On-Chip Systems: Biomaterial Interaction Studies With Tissues Generated Using Lung Epithelial and Liver Metabolic Cell Lines

In vitro models are very important in medicine and biology, because they provide an insight into cells' and microorganisms' behavior. Since these cells and microorganisms are isolated from their natural environment, these models may not completely or precisely predict the effects on the entire organism. Improvement in this area is secured by organ-on-a-chip development. The organ-on-a-chip assumes cells cultured in a microfluidic chip. The chip simulates bioactivities, mechanics and physiological behavior of organs or organ systems, generating artificial organs in that way. There are several cell lines used so far for each tested artificial organ. For lungs, mostly used cell lines are 16HBE, A549, Calu-3, NHBE, while mostly used cell lines for liver are HepG2, Hep 3B, TPH1, etc. In this paper, state of the art for lung and liver organ-on-a-chip is presented, together with the established in vitro testing on lung and liver cell lines, with the emphasis on Calu-3 (for lung cell lines) and Hep-G2 (for liver cell lines). Primary focus in this review is to discuss different researches on the topics of lung and liver cell line models, approaches in determining fate and transport, cell partitioning, cell growth and division, as well as cell dynamics, meaning toxicity and effects. The review is finalized with current research gaps and problems, stating potential future developments in the field.

Studying non-alcoholic fatty liver disease: the ins and outs of in vivo, ex vivo and in vitro human models

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing. Determining the pathogenesis and pathophysiology of human NAFLD will allow for evidence-based prevention strategies, and more targeted mechanistic investigations. Various in vivo, ex situ and in vitro models may be utilised to study NAFLD; but all come with their own specific caveats. Here, we review the human-based models and discuss their advantages and limitations in regards to studying the development and progression of NAFLD. Overall, in vivo whole-body human studies are advantageous in that they allow for investigation within the physiological setting, however, limited accessibility to the liver makes direct investigations challenging. Non-invasive imaging techniques are able to somewhat overcome this challenge, whilst the use of stable-isotope tracers enables mechanistic insight to be obtained. Recent technological advances (i.e. normothermic machine perfusion) have opened new opportunities to investigate whole-organ metabolism, thus ex situ livers can be investigated directly. Therefore, investigations that cannot be performed in vivo in humans have the potential to be undertaken. In vitro models offer the ability to perform investigations at a cellular level, aiding in elucidating the molecular mechanisms of NAFLD. However, a number of current models do not closely resemble the human condition and work is ongoing to optimise culturing parameters in order to recapitulate this. In summary, no single model currently provides insight into the development, pathophysiology and progression across the NAFLD spectrum, each experimental model has limitations, which need to be taken into consideration to ensure appropriate conclusions and extrapolation of findings are made.

3D bioprinting of functional tissue models for personalized drug screening and in vitro disease modeling

3D bioprinting is emerging as a promising technology for fabricating complex tissue constructs with tailored biological components and mechanical properties. Recent advances have enabled scientists to precisely position materials and cells to build functional tissue models for in vitro drug screening and disease modeling. This review presents state-of-the-art 3D bioprinting techniques and discusses the choice of cell source and biomaterials for building functional tissue models that can be used for personalized drug screening and disease modeling. In particular, we focus on 3D-bioprinted liver models, cardiac tissues, vascularized constructs, and cancer models for their promising applications in medical research, drug discovery, toxicology, and other pre-clinical studies.

Towards Multi-Organoid Systems for Drug Screening Applications

A low percentage of novel drug candidates succeed and reach the end of the drug discovery pipeline, mainly due to poor initial screening and assessment of the effects of the drug and its metabolites over various tissues in the human body. For that, emerging technologies involving the production of organoids from human pluripotent stem cells (hPSCs) and the use of organ-on-a-chip devices are showing great promise for developing a more reliable, rapid and cost-effective drug discovery process when compared with the current use of animal models. In particular, the possibility of virtually obtaining any type of cell within the human body, in combination with the ability to create patient-specific tissues using human induced pluripotent stem cells (hiPSCs), broadens the horizons in the fields of drug discovery and personalized medicine. In this review, we address the current progress and challenges related to the process of obtaining organoids from different cell lineages emerging from hPSCs, as well as how to create devices that will allow a precise examination of the in vitro effects generated by potential drugs in different organ systems.

Transcriptomic characterization of bovine primary cultured hepatocytes; a cross-comparison with a bovine liver and the Madin-Darby bovine kidney cells

Bovine primary cultured hepatocytes (CHs) are widely used in vitro models for liver toxicity testing. However, little is known about their whole-transcriptome profile and its resemblance to the normal liver tissue. In the present study, we profiled - by microarray - the whole-transcriptome of bovine CHs (n=4) and compared it with the transcriptomic landscape of control liver samples (n=8), as well the Madin-Darby bovine kidney (MDBK) cells (n=4). Compared with liver tissue, the bovine CHs relatively expressed (fold change >2, P<0.05) about 2155 and 2073 transcripts at a lower and higher abundance, respectively. Of those expressed at a lower abundance, many were drug biotransformation enzyme-coding genes, such as the cytochrome P450 family (CYPs), sulfotransferases, methyltransferases, and glutathione S-transferases. Also, several drug transporters and solute carriers were expressed at a lower abundance in bovine CHs. 'Drug metabolism', 'PPAR signaling', and 'metabolism of xenobiotics by CYPs' were among the most negatively-enriched pathways in bovine CHs compared with liver. A qPCR cross-validation using 8 selected genes evidenced a high correlation (r=0.95, P=0.001) with the corresponding microarray results. Although from a kidney origin, and albeit to a lower extent compared to bovine CHs, the MDBK cells showed a basal expression of many CYP-coding genes. Our study provides a whole-transcriptome-based evidence for the bovine CHs and hepatic tissue resemblance. Overall, the bovine CHs' transcriptomic profile might render it unreliable as an in vitro model to study drug metabolism.

Self-assembled 3D spheroids and hollow-fibre bioreactors improve MSC-derived hepatocyte-like cell maturation in vitro

3D cultures of human stem cell-derived hepatocyte-like cells (HLCs) have emerged as promising models for short- and long-term maintenance of hepatocyte phenotype in vitro cultures by better resembling the in vivo environment of the liver and consequently increase the translational value of the resulting data. In this study, the first stage of hepatic differentiation of human neonatal mesenchymal stem cells (hnMSCs) was performed in 2D monolayer cultures for 17 days. The second stage was performed by either maintaining cells in 2D cultures for an extra 10 days, as control, or alternatively cultured in 3D as self-assembled spheroids or in multicompartment membrane bioreactor system. All systems enabled hnMSC differentiation into HLCs as shown by positive immune staining of hepatic markers CK-18, HNF-4α, albumin, the hepatic transporters OATP-C and MRP-2 as well as drug-metabolizing enzymes like CYP1A2 and CYP3A4. Similarly, all models also displayed relevant glucose, phase I and phase II metabolism, the ability to produce albumin and to convert ammonia into urea. However, EROD activity and urea production were increased in both 3D systems. Moreover, the spheroids revealed higher bupropion conversion, whereas bioreactor showed increased albumin production and capacity to biotransform diclofenac. Additionally, diclofenac resulted in an IC₅₀ value of 1.51 ± 0.05 and 0.98 ± 0.03 in 2D and spheroid cultures, respectively. These data suggest that the 3D models tested improved HLC maturation showing a relevant biotransformation capacity and thus provide more appropriate reliable models for mechanistic studies and more predictive systems for in vitro toxicology applications.

Deterministically patterned biomimetic human iPSC-derived hepatic model via rapid 3D bioprinting

The functional maturation and preservation of hepatic cells derived from human induced pluripotent stem cells (hiPSCs) are essential to personalized in vitro drug screening and disease study. Major liver functions are tightly linked to the 3D assembly of hepatocytes, with the supporting cell types from both endodermal and mesodermal origins in a hexagonal lobule unit. Although there are many reports on functional 2D cell differentiation, few studies have demonstrated the in vitro maturation of hiPSC-derived hepatic progenitor cells (hiPSC-HPCs) in a 3D environment that depicts the physiologically relevant cell combination and microarchitecture. The application of rapid, digital 3D bioprinting to tissue engineering has allowed 3D patterning of multiple cell types in a predefined biomimetic manner. Here we present a 3D hydrogel-based triculture model that embeds hiPSC-HPCs with human umbilical vein endothelial cells and adipose-derived stem cells in a microscale hexagonal architecture. In comparison with 2D monolayer culture and a 3D HPC-only model, our 3D triculture model shows both phenotypic and functional enhancements in the hiPSC-HPCs over weeks of in vitro culture. Specifically, we find improved morphological organization, higher liver-specific gene expression levels, increased metabolic product secretion, and enhanced cytochrome P450 induction. The application of bioprinting technology in tissue engineering enables the development of a 3D biomimetic liver model that recapitulates the native liver module architecture and could be used for various applications such as early drug screening and disease modeling.

Toxicity testing and drug screening using iPSC-derived hepatocytes, cardiomyocytes, and neural cells

Unexpected toxicity in areas such as cardiotoxicity, hepatotoxicity, and neurotoxicity is a serious complication of clinical therapy and one of the key causes for failure of promising drug candidates in development. Animal studies have been widely used for toxicology research to provide preclinical security evaluation of various therapeutic agents under development. Species differences in drug penetration of the blood-brain barrier, drug metabolism, and related toxicity contribute to failure of drug trials from animal models to human. The existing system for drug discovery has relied on immortalized cell lines, animal models of human disease, and clinical trials in humans. Moreover, drug candidates that are passed as being safe in the preclinical stage often show toxic effects during the clinical stage. Only around 16% drugs are approved for human use. Research on induced pluripotent stem cells (iPSCs) promises to enhance drug discovery and development by providing simple, reproducible, and economically effective tools for drug toxicity screening under development and, on the other hand, for studying the disease mechanism and pathways. In this review, we provide an overview of basic information about iPSCs, and discuss efforts aimed at the use of iPSC-derived hepatocytes, cardiomyocytes, and neural cells in drug discovery and toxicity testing.

High-Content Assay Multiplexing for Toxicity Screening in Induced Pluripotent Stem Cell-Derived Cardiomyocytes and Hepatocytes

Cell-based high-content screening (HCS) assays have become an increasingly attractive alternative to traditional in vitro and in vivo testing in pharmaceutical drug development and toxicological safety assessment. The time- and cost-effectiveness of HCS assays, combined with the organotypic nature of human induced pluripotent stem cell (iPSC)-derived cells, open new opportunities to employ physiologically relevant in vitro model systems to improve screening for potential chemical hazards. In this study, we used two human iPSC types, cardiomyocytes and hepatocytes, to test various high-content and molecular assay combinations for their applicability in a multiparametric screening format. Effects on cardiomyocyte beat frequency were characterized by calcium flux measurements for up to 90 min. Subsequent correlation with intracellular cAMP levels was used to determine if the effects on cardiac physiology were G-protein-coupled receptor dependent. In addition, we utilized high-content cell imaging to simultaneously determine cell viability, mitochondrial integrity, and reactive oxygen species (ROS) formation in both cell types. Kinetic analysis indicated that ROS formation is best detectable 30 min following initial treatment, whereas cytotoxic effects were most stable after 24 h. For hepatocytes, high-content imaging was also used to evaluate cytotoxicity and cytoskeletal integrity, as well as mitochondrial integrity and the potential for lipid accumulation. Lipid accumulation, a marker for hepatic steatosis, was most reliably detected 48 h following treatment with test compounds. Overall, our results demonstrate how a compendium of assays can be utilized for quantitative screening of chemical effects in iPSC cardiomyocytes and hepatocytes and enable rapid and cost-efficient multidimensional biological profiling of toxicity.

Toxicogenomics-based prediction of acetaminophen-induced liver injury using human hepatic cell systems

Primary human hepatocytes (hHEP), human HepaRG and HepG2 cell lines are the most used human liver-based in vitro models for hepatotoxicity testing, including screening of drug-induced liver injury (DILI)-inducing compounds. hHEP are the reference hepatic in vitro system, but their availability is limited and the cells available for toxicology studies are often of poor quality. Hepatic cell lines on the other hand are highly proliferative and represent an inexhaustible hepatic cell source. However, these hepatoma-derived cells do not represent the population diversity and display reduced hepatic metabolism. Alternatively, stem cell-derived hepatic cells, which can be produced in high numbers and can differentiate into multiple cell lineages, are also being evaluated as a cell source for in vitro hepatotoxicity studies. Human skin-derived precursors (hSKP) are post-natal stem cells that, after conversion towards hepatic cells (hSKP-HPC), respond to hepatotoxic compounds in a comparable way as hHEP. In the current study, four different human hepatic cell systems (hSKP-HPC, hHEP, HepaRG and HepG2) are evaluated for their capacity to predict hepatic toxicity. Their hepatotoxic response to acetaminophen (APAP) exposure is compared to data obtained from patients suffering from APAP-induced acute liver failure (ALF). The results indicate that hHEP, HepaRG and hSKP-HPC identify comparable APAP-induced hepatotoxic functions and that HepG2 cells show the slightest hepatotoxic response. Pathway analyses further points out that HepaRG cells show the highest predicted activation of the functional genes related to 'damage of liver', followed by hSKP-HPC and hHEP cells that generated similar results. HepG2 did not show any activation of this function.

Differences in the Epigenetic Regulation of Cytochrome P450 Genes between Human Embryonic Stem Cell-Derived Hepatocytes and Primary Hepatocytes

Human pluripotent stem cell-derived hepatocytes have the potential to provide in vitro model systems for drug discovery and hepatotoxicity testing. However, these cells are currently unsuitable for drug toxicity and efficacy testing because of their limited expression of genes encoding drug-metabolizing enzymes, especially cytochrome P450 (CYP) enzymes. Transcript levels of major CYP genes were much lower in human embryonic stem cell-derived hepatocytes (hESC-Hep) than in human primary hepatocytes (hPH). To verify the mechanism underlying this reduced expression of CYP genes, including CYP1A1, CYP1A2, CYP1B1, CYP2D6, and CYP2E1, we investigated their epigenetic regulation in terms of DNA methylation and histone modifications in hESC-Hep and hPH. CpG islands of CYP genes were hypermethylated in hESC-Hep, whereas they had an open chromatin structure, as represented by hypomethylation of CpG sites and permissive histone modifications, in hPH. Inhibition of DNA methyltransferases (DNMTs) during hepatic maturation induced demethylation of the CpG sites of CYP1A1 and CYP1A2, leading to the up-regulation of their transcription. Combinatorial inhibition of DNMTs and histone deacetylases (HDACs) increased the transcript levels of CYP1A1, CYP1A2, CYP1B1, and CYP2D6. Our findings suggest that limited expression of CYP genes in hESC-Hep is modulated by epigenetic regulatory factors such as DNMTs and HDACs.

From whole body to cellular models of hepatic triglyceride metabolism: man has got to know his limitations

The liver is a main metabolic organ in the human body and carries out a vital role in lipid metabolism. Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, encompassing a spectrum of conditions from simple fatty liver (hepatic steatosis) through to cirrhosis. Although obesity is a known risk factor for hepatic steatosis, it remains unclear what factor(s) is/are responsible for the primary event leading to retention of intrahepatocellular fat. Studying hepatic processes and the etiology and progression of disease in vivo in humans is challenging, not least as NAFLD may take years to develop. We present here a review of experimental models and approaches that have been used to assess liver triglyceride metabolism and discuss their usefulness in helping to understand the aetiology and development of NAFLD.

Competency of different cell models to predict human hepatotoxic drugs

INTRODUCTION

The liver is the most important target for drug-induced toxicity. This vulnerability results from functional liver features and its role in the metabolic elimination of most drugs. Drug-induced liver injury is a significant leading cause of acute, chronic liver disease and an important safety issue when developing new drugs.

AREAS COVERED

This review describes the advantages and limitations of hepatic cell-based models for early safety risk assessment during drug development. These models include hepatocytes cultured as monolayer, collagen-sandwich; emerging complex 3D configuration; liver-derived cell lines; stem cell-derived hepatocytes.

EXPERT OPINION

In vitro toxicity assays performed in hepatocytes or hepatoma cell lines can potentially provide rapid and cost-effective early feedback to identify toxic candidates for compound prioritization. However, their capacity to predict hepatotoxicity depends critically on cells' functional performance. In an attempt to improve and prolong functional properties of cultured cells, different strategies to recreate the in vivo hepatocyte environment have been explored. 3D cultures, co-cultures of hepatocytes with other cell types and microfluidic devices seem highly promising for toxicological studies. Moreover, hepatocytes derived from human pluripotent stem cells are emerging cell-based systems that may provide a stable source of hepatocytes to reliably screen metabolism and toxicity of candidate compounds.

High Content Imaging and Analysis Enable Quantitative In Situ Assessment of CYP3A4 Using Cryopreserved Differentiated HepaRG Cells

High-throughput imaging-based hepatotoxicity studies capable of analyzing individual cells in situ hold enormous promise for drug safety testing but are frequently limited by a lack of sufficient metabolically competent human cells. This study examined cryopreserved HepaRG cells, a human liver cell line which differentiates into both hepatocytes and biliary epithelial cells, to determine if these cells may represent a suitable metabolically competent cellular model for novel High Content Analysis (HCA) applications. Characterization studies showed that these cells retain many features characteristic of primary human hepatocytes and display significant CYP3A4 and CYP1A2 induction, unlike the HepG2 cell line commonly utilized for HCA studies. Furthermore, this study demonstrates that CYP3A4 induction can be quantified via a simple image analysis-based method, using HepaRG cells as a model system. Additionally, data demonstrate that the hepatocyte and biliary epithelial subpopulations characteristic of HepaRG cultures can be separated during analysis simply on the basis of nuclear size measurements. Proof of concept studies with fluorescent cell function reagents indicated that further multiparametric image-based assessment is achievable with HepaRG. In summary, image-based screening of metabolically competent human hepatocyte models cells such as HepaRG offers novel approaches for hepatotoxicity assessment and improved drug screening tools.

Pathogenesis of idiosyncratic drug-induced liver injury and clinical perspectives

Idiosyncratic drug-induced liver injury (DILI) is a rare disease that develops independently of drug dose, route, or duration of administration. Furthermore, idiosyncratic DILI is not a single disease entity but rather a spectrum of rare diseases with varying clinical, histological, and laboratory features. The pathogenesis of DILI is not fully understood. Standardization of the DILI nomenclature and methods to assess causality, along with the information provided by the LiverTox Web site, will harmonize and accelerate research on DILI. Studies of new serum biomarkers such as glutamate dehydrogenase, high mobility group box protein 1, and microRNA-122 could provide information for use in diagnosis and prognosis and provide important insights into the mechanisms of the pathogenesis of DILI. Single nucleotide polymorphisms in the HLA region have been associated with idiosyncratic hepatotoxicity attributed to flucloxacillin, ximelagatran, lapatinib, and amoxicillin-clavulanate. However, genome-wide association studies of pooled cases have not associated any genetic factors with idiosyncratic DILI. Whole genome and whole exome sequencing analyses are under way to study cases of DILI attributed to a single medication. Serum proteomic, transcriptome, and metabolome as well as intestinal microbiome analyses will increase our understanding of the mechanisms of this disorder. Further improvements to in vitro and in vivo test systems should advance our understanding of the causes, risk factors, and mechanisms of idiosyncratic DILI.

Drug safety testing paradigm, current progress and future challenges: an overview

Early assessment of the toxicity potential of new molecules in pharmaceutical industry is a multi-dimensional task involving predictive systems and screening approaches to aid in the optimization of lead compounds prior to their entry into development phase. Due to the high attrition rate in the pharma industry in last few years, it has become imperative for the nonclinical toxicologist to focus on novel approaches which could be helpful for early screening of drug candidates. The need is that the toxicologists should change their classical approach to a more investigative approach. This review discusses the developments that allow toxicologists to anticipate safety problems and plan ways to address them earlier than ever before. This includes progress in the field of in vitro models, surrogate models, molecular toxicology, 'omics' technologies, translational safety biomarkers, stem-cell based assays and preclinical imaging. The traditional boundaries between teams focusing on efficacy/ safety and preclinical/ clinical aspects in the pharma industry are disappearing, and translational research-centric organizations with a focused vision of bringing drugs forward safely and rapidly are emerging. Today's toxicologist should collaborate with medicinal chemists, pharmacologists, and clinicians and these value-adding contributions will change traditional toxicologists from side-effect identifiers to drug development enablers.

4th Annual Predictive Toxicology Summit 2012

INTRODUCTION

This meeting report presents a brief summary on the 4th Annual Predictive Toxicology Summit 2012, which was held on 15 - 16 February 2012 in London.

AREAS COVERED

The majority of presentations came from global pharmaceutical companies, although small and medium enterprise (SME) and academic researchers were represented too. Major regulatory bodies were also present. The article highlights the summit, which was considered a good learning opportunity to catch up on the recent advances in predictive toxicology.

EXPERT OPINION

Predictive toxicology has become more and more important due to social and economic pressure and scientific reasons. Technological developments are rapid, but there is a gulf between the technology developers and the pharmaceutical end users; hence, early engagement is desirable. Stem cell-derived cell-based assays as well as three-dimensional in vitro tissue/organ model development are within the reach now, but a lot needs to be done to optimise and validate the developed protocols and products. The field of predictive toxicology needs fundamental research of interdisciplinary nature, which requires much needed trained personnel and funding.

Therapeutic effect of transplanting magnetically labeled bone marrow stromal stem cells in a liver injury rat model with 70%-hepatectomy

Background

There are only few reports about the use of bone marrow stromal stem cells (BMSCs) for the treatment of traumatic liver injury. This study aimed to study the therapeutic effect of fluorescence-labeled BMSCs administered to rats subject to traumatic liver injury.

Material/Methods

Male SD rats with a 70% resection of the liver were injected with feridex-labeled BMSCs which could be induced to functional hepatocytes in vitro. Liver function was assayed and the liver scanned by 1.5-T MRI at 12 hrs and on days 1, 3, 5, 7, and 14 post-operation. The pathological changes of liver sections were monitored.

Results

The serum levels of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, direct bilirubin, and total bilirubin in the transplantation group were significantly lower than the control group. The MRI showed rats of the transplantation group had an oval low signal area at 12 hr after operation; the low signal range gradually expanded and the signal intensity gradually decreased over 14 days after operation. The low signal range in the control group disappeared 12 hr after the operation. After Prussian blue staining, rats of the transplantation group contained blue granules with no significant hypertrophy or edema in hepatocytes, while the control group showed no blue granules with significant hypertrophy and edema.

Conclusions

The BMSCs transplanted into the injured rat liver gradually migrate to the surrounding liver tissue and partially repair the liver surgical injury in rats. BMSCs may represent an effective therapeutic approach for acute liver injury.

The HepaRG cell line: a valuable in vitro tool for hepatitis virus infection studies

Hepatitis virus infections, mainly hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, constitute a major problem for public health since they have a worldwide distribution and because they are associated with hepatocellular carcinoma and death. Current anti-HBV vaccines seem to be effective in the majority of people. However, an important issue waiting to be tackled nowadays is how to cure patients with chronic hepatitis B. Moreover, no vaccine is available today for the prevention of HCV infection. Therefore, the use of adequate in vitro infection systems is a prerequisite for the molecular understanding of the infection events of these viruses, which could result in the development of novel powerful therapeutics. In this respect, the HepaRG cell line exhibits a hepatocyte-like morphology and displays drug metabolism capacity similar to that of primary hepatocytes. HepaRG cells have yet been proven to be a useful tool in the study of viral infections, particularly for deciphering the mechanism of HBV entry into hepatocytes.

In vitro models for liver toxicity testing

Over the years, various liver-derived in vitro model systems have been developed to enable investigation of the potential adverse effects of chemicals and drugs. Liver tissue slices, isolated microsomes, perfused liver, immortalized cell lines, and primary hepatocytes have been used extensively. Immortalized cell lines and primary isolated liver cells are currently most widely used in vitro models for liver toxicity testing. Limited throughput, loss of viability, and decreases in liver-specific functionality and gene expression are common shortcomings of these models. Recent developments in the field of in vitro hepatotoxicity include three-dimensional tissue constructs and bioartificial livers, co-cultures of various cell types with hepatocytes, and differentiation of stem cells into hepatic lineage-like cells. In an attempt to provide a more physiological environment for cultured liver cells, some of the novel cell culture systems incorporate fluid flow, micro-circulation, and other forms of organotypic microenvironments. Co-cultures aim to preserve liver-specific morphology and functionality beyond those provided by cultures of pure parenchymal cells. Stem cells, both embryonic- and adult tissue-derived, may provide a limitless supply of hepatocytes from multiple individuals to improve reproducibility and enable testing of the individual-specific toxicity. This review describes various traditional and novel in vitro liver models and provides a perspective on the challenges and opportunities afforded by each individual test system.

Application of three-dimensional culture conditions to human embryonic stem cell-derived definitive endoderm cells enhances hepatocyte differentiation and functionality

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) provide an unlimited source for the generation of human hepatocytes, owing to their indefinite self-renewal and pluripotent properties. Both hESC-/iPSC-derived hepatocytes hold great promise in treating liver diseases as potential candidates for cell replacement therapies or as an in vitro platform to conduct new drug trials. It has been previously demonstrated that the initiation of hESC differentiation in monolayer cultures increases the generation of definitive endoderm (DE) and subsequently of hepatocyte differentiation. However, monolayer culture may hinder the maturation of hESC-derived hepatocytes, since such two-dimensional (2D) conditions do not accurately reflect the complex nature of three-dimensional (3D) hepatocyte specification in vivo. Here, we report the sequential application of 2D and 3D culture systems to differentiate hESCs to hepatocytes. Human ESCs were initially differentiated in a monolayer culture to DE cells, which were then inoculated into Algimatrix scaffolds. Treatments of hESC-DE cells with a ROCK inhibitor before and after inoculation dramatically enhanced their survival and the formation of spheroids, which are distinct from HepG2 carcinoma cells. In comparison with monolayer culture alone, sequential 2D and 3D cultures significantly improved hepatocyte differentiation and function. Our results demonstrate that hESC-DE cells can be incorporated into Algimatrix 3D culture systems to enhance hepatocyte differentiation and function.

Mesoderm-derived stem cells: the link between the transcriptome and their differentiation potential

Human adult stem cells (hASCs) have become an attractive source for autologous cell transplantation, tissue engineering, developmental biology, and the generation of human-based alternative in vitro models. Among the 3 germ cell layers, the mesoderm is the origin of today's most widely used and characterized hASC populations. A variety of isolated nonhematopoietic mesoderm-derived stem cell populations exist, and all of them show important differences in terms of function, efficacy, and differentiation potential both in vivo and in vitro. To better understand whether the intrinsic properties of these cells contribute to the overall differentiation potential of hASCs, we compared the global gene expression profiles of 4 mesoderm-derived stem cell populations: human adipose tissue-derived stromal cells, human bone marrow-derived stromal cells (hBMSCs), human (fore)skin-derived precursor cells (hSKPs), and human Wharton's jelly-derived mesenchymal stem cells (hWJs). Significant differences in gene expression profiles were detected between distinct stem cell types. hSKPs predominantly expressed genes involved in neurogenesis, skin, and bone development, whereas hWJs and, to some extent, hBMSCs showed an increased expression of genes involved in cardiovascular and liver development. Interestingly, the observed differential gene expression of distinct hASCs could be linked to existing differentiation data in which hASCs were differentiated toward specific cell types. As such, our data suggest that the intrinsic gene expression of the undifferentiated stem cells has an important impact on their overall differentiation potential as well as their application in stem cell-based research. Yet, the factors that define these intrinsic properties remain to be determined.

Organotypic liver culture models: meeting current challenges in toxicity testing

Prediction of chemical-induced hepatotoxicity in humans from in vitro data continues to be a significant challenge for the pharmaceutical and chemical industries. Generally, conventional in vitro hepatic model systems (i.e. 2-D static monocultures of primary or immortalized hepatocytes) are limited by their inability to maintain histotypic and phenotypic characteristics over time in culture, including stable expression of clearance and bioactivation pathways, as well as complex adaptive responses to chemical exposure. These systems are less than ideal for longer-term toxicity evaluations and elucidation of key cellular and molecular events involved in primary and secondary adaptation to chemical exposure, or for identification of important mediators of inflammation, proliferation and apoptosis. Progress in implementing a more effective strategy for in vitro-in vivo extrapolation and human risk assessment depends on significant advances in tissue culture technology and increasing their level of biological complexity. This article describes the current and ongoing need for more relevant, organotypic in vitro surrogate systems of human liver and recent efforts to recreate the multicellular architecture and hemodynamic properties of the liver using novel culture platforms. As these systems become more widely used for chemical and drug toxicity testing, there will be a corresponding need to establish standardized testing conditions, endpoint analyses and acceptance criteria. In the future, a balanced approach between sample throughput and biological relevance should provide better in vitro tools that are complementary with animal testing and assist in conducting more predictive human risk assessment.

Optimization of the HepaRG cell model for drug metabolism and toxicity studies

The HepaRG cell line is the first human cell line able to differentiate in vitro into mature hepatocyte-like cells. Our main objective within the framework of the EEC-LIINTOP project was to optimize the use of this cell line for drug metabolism and toxicity studies, especially after repeat treatments. The main results showed that differentiated HepaRG cells: (i) retained their drug metabolism capacity (major CYPs, phase 2 enzymes, transporters and nuclear receptors) and responsiveness to prototypical inducers at relatively stable levels for several weeks at confluence. The levels of several functions, including some CYPs such as CYP3A4, were dependent on the addition of dimethyl sulfoxide in the culture medium; (ii) sustained the different types of chemical-induced hepatotoxicity, including steatosis, phospholipidosis and cholestasis, after acute and/or repeat treatment with reference drugs. In particular, drug-induced vesicular steatosis was demonstrated in vitro for the first time. In conclusion, our results from the LIINTOP project, together with other studies reported concomitantly or more recently in the literature, support the conclusion that the metabolically competent human HepaRG cells represent a surrogate to primary human hepatocytes for investigating drug metabolism parameters and both acute and chronic effects of xenobiotics in human liver.

Oxidative stress-induced biomarkers for stem cell-based chemical screening

Stem cells have been considered for their potential in pharmaceutical research, as well as for stem cell-based therapy for many diseases. Despite the potential for their use, the challenge remains to examine the safety and efficacy of stem cells for their use in therapies. Recently, oxidative stress has been strongly implicated in the functional regulation of cell behavior of stem cells. Therefore, development of rapid and sensitive biomarkers, related to oxidative stress is of growing importance in stem cell-based therapies for treating various diseases. Since stem cells have been implicated as targets for carcinogenesis and might be the origin of "cancer stem cells", understanding of how oxidative stress-induced signaling, known to be involved in the carcinogenic process could lead to potential screening of cancer chemopreventive and chemotherapeutic agents. An evaluation of antioxidant states reducing equivalents like GSH and superoxide dismutase (SOD), as well as reactive oxygen species (ROS) and nitric oxide (NO) generation, can be effective markers in stem cell-based therapies. In addition, oxidative adducts, such as 4-hydroxynonenal, can be reliable markers to detect cellular changes during self-renewal and differentiation of stem cells. This review highlights the biomarker development to monitor oxidative stress response for stem cell-based chemical screening.

Primary hepatocyte cultures as in vitro tools for toxicity testing: quo vadis?

Cultures of primary hepatocytes are versatile tools that can serve many in vitro toxicity testing purposes. However, they cope with dedifferentiation, a process that is already initiated during the hepatocyte isolation procedure and that is manifested as the progressive loss of functionality upon subsequent cultivation. A number of strategies to prevent dedifferentiation have been introduced over the last decades, all which aim at re-establishing the in vivo hepatocyte micro-environment in vitro, but that are of merely limited success. Recent mechanistic insight into the mechanisms that underlie hepatocyte dedifferentiation has opened new avenues for the development of novel approaches that target the actual causes of this deteriorative process and thus for the generation of a long-term hepatic in vitro tool. Such experimental system is urgently needed, especially in the light of the stringent European legislative modifications that are currently encountered by the pharmaceutical, chemical and, particularly, the cosmetic industry.