High content analysis assay for prediction of human hepatotoxicity in HepaRG and HepG2 cells

Emerging fluorescent probes for bioimaging of drug-induced liver injury biomarkers: Recent advances

Drug-induced liver injury (DILI) has emerged as a significant concern in clinical settings, being one of the leading causes of acute liver failure. However, the specific pathogenesis of DILI remains unclear, and there is currently a lack of effective targeted therapies. Numerous studies have demonstrated that the occurrence and progression of DILI involve complex pathological processes, closely linked with various cellular substrates and microenvironments. Thus, developing non-invasive, highly sensitive, specific, and reliable methods to detect changes in biomarkers and microenvironments in situ would greatly aid in the precise diagnosis of DILI and help guide therapeutic interventions. Fortunately, fluorescence imaging technology has shown great promise in detecting biological species, microenvironments, and diagnosing DILI due to its superior detection capabilities. In this context, this review described the design strategies, working principles, and practical applications of small molecule fluorescent probes for monitoring biological species and microenvironments in DILI. Importantly, this review highlighted current limitations and future development directions, which may help uncover the underlying relationships between biological species, microenvironments, and DILI. This understanding could lead to potential diagnostic protocols and establish a platform for evaluating treatments and drug efficacy in DILI.

Advances in liver organoids: replicating hepatic complexity for toxicity assessment and disease modeling

The lack of in vivo accurate human liver models hinders the investigation of liver-related diseases, injuries, and drug-related toxicity, posing challenges for both basic research and clinical applications. Traditional cellular and animal models, while widely used, have significant limitations in replicating the liver's complex responses to various stressors. Liver organoids derived from human pluripotent stem cells, adult stem cells primary cells, or tissues can mimic diverse liver cell types, major physiological functions, and architectural features. Recent advancements in the field have shown that some liver organoids have sufficient accuracy to replicate specific aspects of the human liver's complexity. This review highlights recent progress in liver organoid research, with a particular emphasis on their potential for toxicity assessment and disease modeling. The intrinsic advantages of liver organoids include higher sensitivity and suitability for long-term studies, which enhance the predictive value in drug and nanomaterial toxicity testing. The integration of liver organoids with microfluidic devices enables the simulation of the liver microenvironment and facilitates high-throughput drug screening. The liver organoids also serve as ideal platforms for studying liver diseases such as hepatitis, liver fibrosis, viral liver diseases, and monogenic diseases. Additionally, this review discusses the advantages and limitations of liver organoids along with potential avenues for future research.

Drug-induced cholestasis (DIC) predictions based on in vitro inhibition of major bile acid clearance mechanisms

Drug-induced cholestasis (DIC) is recognized as a major safety concern in drug development, as it represents one of the three types of drug-induced liver injury (DILI). Cholestasis is characterized by the disruption of bile flow, leading to intrahepatic accumulation of toxic bile acids. Bile acid regulation is a multifarious process, orchestrated by several hepatic mechanisms, namely sinusoidal uptake and efflux, canalicular secretion and intracellular metabolism. In the present study, we developed a prediction model of DIC using in vitro inhibition data for 47 marketed drugs on nine transporters and five enzymes known to regulate bile acid homeostasis. The resulting model was able to distinguish between drugs with or without DILI concern (p-value = 0.039) and demonstrated a satisfactory predictive performance, with the area under the precision-recall curve (PR AUC) measured at 0.91. Furthermore, we simplified the model considering only two processes, namely reversible inhibition of OATP1B1 and time-dependent inhibition of CYP3A4, which provided an enhanced performance (PR AUC = 0.95). Our study supports literature findings suggesting a contribution not only from a single process inhibition, but a rather synergistic effect of the key bile acid clearance processes in the development of cholestasis. The use of a quantitative model in the preclinical investigations of DIC is expected to reduce attrition rate in advanced development programs and guide the discovery and development of safe medicines.

Effect of supramolecular peptide hydrogel scaffold charge on HepG2 viability and spheroid formation

Supramolecular bioinspired self-assembling peptide hydrogel (SAPH) scaffolds represent a class of fully defined synthetic materials whose chemical and mechanical properties can be finely engineered. In this study, the relationship between SAPHs physicochemical properties and HepG2 cells viability, spheroid formation and function are discussed. We first report that negatively charged SAPHs promote hepatocyte proliferation and spheroids formation in vitro 3D culture while positively charged SAPHs lead to hepatocyte death irrespective of the hydrogel mechanical properties. More specifically HepG2 cultured in 3D in E(FKFE)2 negatively charged SAPH maintained a differentiated phenotype and assembled into well-defined spheroids with strong cell-cell interactions. Furthermore, HepG2 spheroids responded to acetaminophen exposure with upregulation of key CYP450 enzymes expression clearly showing their potential for drug toxicity testing. These findings demonstrate how fine-tuned functional SAPH scaffolds can be used to identify key scaffolds parameters affecting cells. In this case we demonstrated the potential of negatively charged SAPHs for the 3D culture of HepG2 with potential applications in drug screening.

RNA-Sequencing Identification of Genes Supporting HepG2 as a Model Cell Line for Hepatocellular Carcinoma or Hepatocytes

Background/Objectives: Cell lines do not faithfully replicate the authentic transcriptomic condition of the disease under study. The HepG2 cell line is widely used for studying hepatocellular carcinoma (HCC), but not all biological processes and genes exhibit congruent expression patterns between cell lines and the actual disease. The objective of this study is to perform a comparative transcriptomic analysis of the HepG2 cell line, HCC, and primary hepatocytes (PH) in order to identify genes suitable for research in HepG2 as a model for PH or HCC research. Methods: We conducted a differential expression analysis between publicly available data from HCC patients, PH, and HepG2. We examined specific overlaps of differentially expressed genes (DEGs) in a pairwise manner between groups in order to obtain a valuable gene list for studying HCC or PH using different parameter filtering. We looked into the function and druggability of these genes. Conclusions: In total, we identified 397 genes for HepG2 as a valuable HCC model and 421 genes for HepG2 as a valuable PH model, and with more stringent criteria, we derived a smaller list of 40 and 21 genes, respectively. The majority of genes identified as a valuable set for the HCC model are involved in DNA repair and protein degradation mechanisms. This research aims to provide detailed guidance on gene selection for studying diseases like hepatocellular carcinoma, primary hepatocytes, or others using cell lines.

Effects of Mixtures of Emerging Pollutants and Drugs on Modulation of Biomarkers Related to Toxicity, Oxidative Stress, and Cancer

Background/Objectives: Over time, the scientific community has developed a growing interest in the effects of mixtures of different compounds, for which there is currently no established evidence or knowledge, in relation to certain categories of xenobiotics. It is well known that exposure to pollutants causes oxidative stress, resulting in the overproduction of reactive oxygen species (ROS), which can affect signaling pathways that regulate the cell cycle, apoptosis, energy balance, and cellular metabolism. The aim of this study was to investigate the effects of sub-lethal concentrations of mixtures of emerging pollutants and pharmaceuticals on the modulation of biomarkers related to toxicity, oxidative stress, and cancer. Methods: In this study, the hepatoma cell line HepG2 was exposed to increasing concentrations of polybrominated diphenyl ether 47 (BDE-47), cadmium chloride (CdCl2), and carbamazepine (CBZ), both individually and in mixtures, for 72 h to assess cytotoxicity using the MTT assay. The subsequent step, following the identification of the sub-lethal concentration, was to investigate the effects of exposure at the gene expression level, through the evaluation of molecular markers related to cell cycle and apoptosis (p53), oxidative stress (NRF2), conjugation and detoxification of xenobiotics (CYP2C9 and GST), DNA damage (RAD51 and γH2AFX), and SUMOylation processes (SUMO1 and UBC9) in order to identify any potential alterations in pathways that are normally activated at the cellular level. Results: The results showed that contaminants tend to affect the enzymatic detoxification and antioxidant system, influencing DNA repair defense mechanisms involved in resistance to oxidative stress. The combined effect of the compounds at sub-lethal doses results in a greater activation of these pathways compared to exposure to each compound alone, thereby exacerbating their cytotoxicity. Conclusions: The biomarkers analyzed could contribute to the definition of early warning markers useful for environmental monitoring, while simultaneously providing insight into the toxicity and hazard levels of these substances in the environment and associated health risks.

Unveiling hepatotoxicity distinction of coumarin-related compounds from glycosides to aglycones in Fructus Psoraleae by integrating UPLC-Q-TOF-MS and high content analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Psoraleae (FP), the dried and ripe fruit of Cullen corylifolium (L.) Medik., is widely used due to its various clinical pharmacological effects, but its hepatotoxicity restricts its clinical application. So far, its hepatotoxic components and their underlying mechanism have not been systematically elucidated.

AIM OF THE STUDY

This study was undertaken to reveal the hepatotoxicity distinction of coumarin-related compounds from glycosides to aglycones in FP and elucidate their potential mechanism.

METHODS

Rats were administrated with the aqueous extract of Fructus Psoraleae (AEFP), in which eight coumarin-related compounds were focused. Subsequently, compounds exposed in rats' livers were detected by UPLC-Q-TOF-MS, and the identified hepatotoxic compounds were evaluated to elaborate their possible mechanism by the aid of high content analysis (HCA).

RESULTS

Eight coumarin-related compounds were identified, among which psoralenoside (PO), isopsoralenoside (IPO), psoralen (P), and isopsoralen (IP) were the principally exposed compounds in rats' livers. Furocoumarinic acid glucoside (FAG), (E)-3-(4-(((2S, 3R, 4S, 5S, 6R)-3,4,5-trihydroxy-6-(hydroxymethyl) tetrahydro-2H-pyran-2-yl) oxy) benzofuran-5-yl) acrylic acid (isofurocoumarinic acid glucoside, IFAG), furocoumarinic acid (FA), and (E)-3-(4-hydroxybenzofuran-5-yl) acrylic acid (isofurocoumarinic acid, IFA) were also detected in low abundance. P, IP, FA, and IFA were identified as the hepatotoxic compounds, while their glycosides were almost non-hepatotoxic. The HCA's results showed that hepatotoxic compounds disrupted the balance in reactive oxygen species (ROS), nuclear area, and mitochondrial membrane potential of HepG2 cells, leading to the occurrence of hepatotoxicity.

CONCLUSIONS

P, IP, FA, and IFA were identified as hepatotoxic compounds, from which P and IP were proposed as the important risk components for hepatotoxicity. The conversion from glycosides to aglycones played an essential role in FP-induced hepatotoxicity.

A multiscale, vertical-flow perfusion system with integrated porous microchambers for upgrading multicellular spheroid culture

Spheroid formation assisted by microengineered chambers is a versatile approach for morphology-controlled three-dimensional (3D) cell cultivation with physiological relevance to human tissues. However, the limitation in diffusion-based oxygen/nutrient transport has been a critical issue for the densely packed cells in spheroids, preventing maximization of cellular functions and thus limiting their biomedical applications. Here, we have developed a multiscale microfluidic system for the perfusion culture of spheroids, in which porous microchambers, connected with microfluidic channels, were engineered. A newly developed process of centrifugation-assisted replica molding and salt-leaching enabled the formation of single micrometer-sized pores on the chamber surface and in the substrate. The porous configuration generates a vertical flow to directly supply the medium to the spheroids, while avoiding the formation of stagnant flow regions. We created seamlessly integrated, all PDMS/silicone-based microfluidic devices with an array of microchambers. Spheroids of human liver cells (HepG2 cells) were formed and cultured under vertical-flow perfusion, and the proliferation ability and liver cell-specific functions were compared with those of cells cultured in non-porous chambers with a horizontal flow. The presented system realizes both size-controlled formation of spheroids and direct medium supply, making it suitable as a precision cell culture platform for drug development, disease modelling, and regenerative medicine.

In vitro to in vivo extrapolation and high-content imaging for simultaneous characterization of chemically induced liver steatosis and markers of hepatotoxicity

Chemically induced steatosis is characterized by lipid accumulation associated with mitochondrial dysfunction, oxidative stress and nucleus distortion. New approach methods integrating in vitro and in silico models are needed to identify chemicals that may induce these cellular events as potential risk factors for steatosis and associated hepatotoxicity. In this study we used high-content imaging for the simultaneous quantification of four cellular markers as sentinels for hepatotoxicity and steatosis in chemically exposed human liver cells in vitro. Furthermore, we evaluated the results with a computational model for the extrapolation of human oral equivalent doses (OED). First, we tested 16 reference chemicals with known capacities to induce cellular alterations in nuclear morphology, lipid accumulation, mitochondrial membrane potential and oxidative stress. Then, using physiologically based pharmacokinetic modeling and reverse dosimetry, OEDs were extrapolated from data of any stimulated individual sentinel response. The extrapolated OEDs were confirmed to be within biologically relevant exposure ranges for the reference chemicals. Next, we tested 14 chemicals found in food, selected from thousands of putative chemicals on the basis of structure-based prediction for nuclear receptor activation. Amongst these, orotic acid had an extrapolated OED overlapping with realistic exposure ranges. Thus, we were able to characterize known steatosis-inducing chemicals as well as data-scarce food-related chemicals, amongst which we confirmed orotic acid to induce hepatotoxicity. This strategy addresses needs of next generation risk assessment and can be used as a first chemical prioritization hazard screening step in a tiered approach to identify chemical risk factors for steatosis and hepatotoxicity-associated events.

2-(4-Fluorophenyl)-1H-benzo[d]imidazole as a Promising Template for the Development of Metabolically Robust, α1β2γ2GABA-A Receptor-Positive Allosteric Modulators

Modulation of α1β2γ2GABA-A receptor subpopulation expressed in the basal ganglia region is a conceptually novel mode of pharmacological strategy that offers prospects to tackle a variety of neurological dysfunction. Although clinical findings provided compelling evidence for the validity of this strategy, the current chemical space of molecules able to modulate the α1/γ2 interface of the GABA-A receptor is limited to imidazo[1,2-a]pyridine derivatives that undergo rapid biotransformation. In response to a deficiency in the chemical repertoire of GABA-A receptors, we identified a series of 2-(4-fluorophenyl)-1H-benzo[d]imidazoles as positive allosteric modulators (PAMs) with improved metabolic stability and reduced potential for hepatotoxicity, where lead molecules 9 and 23 displayed interesting features in a preliminary investigation. We further disclose that the identified scaffold shows a preference for interaction with the α1/γ2 interface of the GABA-A receptor, delivering several PAMs of the GABA-A receptor. The present work provides useful chemical templates to further explore the therapeutic potential of GABA-A receptor ligands and enriches the chemical space of molecules suitable for the interaction with the α1/γ2 interface.

In vitro cell-based models of drug-induced hepatotoxicity screening: progress and limitation

Drug-induced liver injury (DILI) is one of the major causes of post-approval withdrawal of therapeutics. As a result, there is an increasing need for accurate predictive in vitro assays that reliably detect hepatotoxic drug candidates while reducing drug discovery time, costs, and the number of animal experiments. In vitro hepatocyte-based research has led to an improved comprehension of the underlying mechanisms of chemical toxicity and can assist the prioritization of therapeutic choices with low hepatotoxicity risk. Therefore, several in vitro systems have been generated over the last few decades. This review aims to comprehensively present the development and validation of 2D (two-dimensional) and 3D (three-dimensional) culture approaches on hepatotoxicity screening of compounds and highlight the main factors affecting predictive power of experiments. To this end, we first summarize some of the recognized hepatotoxicity mechanisms and related assays used to appraise DILI mechanisms and then discuss the challenges and limitations of in vitro models.

In vitro culture at 39 °C during hepatic maturation of human ES cells facilitates hepatocyte-like cell functions

Hepatocyte-like cells derived from human pluripotent stem cells (hPSC-HLCs) offer an alternative to primary hepatocytes commonly used for drug screenings and toxicological tests. However, these cells do not have hepatic functions comparable to those of hepatocytes in vivo due to insufficient hepatic differentiation. Here we showed that the hepatic functions of hPSC-HLCs were facilitated by applying physiological liver temperatures during hepatic differentiation. We identified the optimal temperature by treating HLCs derived from H9 human embryonic stem cells (hESC-HLCs) at 39 °C; the 42 °C treatment caused significantly greater cell death than the 39 °C treatment. We confirmed the improvement of hepatic functions, such as albumin secretion, cytochrome P450 3A activity, and collagen production, without severe cell damage. In combination with existing hepatic differentiation protocols, the method proposed here may further improve hepatic functions for hPSCs and lead to the realization of drug discovery efforts and drug toxicological tests.

Oxidative-stress and long-term hepatotoxicity: comparative study in Upcyte human hepatocytes and hepaRG cells

Drug-induced liver injury (DILI) is one of the most common and serious adverse drug reactions and a major cause of drug development failure and withdrawal. Although different molecular mechanisms are implicated in DILI, enhanced ROS levels have been described as a major mechanism. Human-derived cell models are increasingly used in preclinical safety assessment because they provide quick and relatively inexpensive information in early stages of drug development. We have analyzed and compared the phenotype and functionality of two liver cell models (Upcyte human hepatocytes and HepaRG cells) to demonstrate their suitability for long-term hepatotoxicity assessments and mechanistic studies. The transcriptomic and functional analysis revealed the maintenance of phase I and phase II enzymes, and antioxidant enzymes along time in culture, although the differences found between both test systems underlie the differential sensitivity to hepatotoxins. The evaluation of several mechanisms of cell toxicity, including oxidative stress, by high-content screening, demonstrated that, by combining the stable phenotype of liver cells and repeated-dose exposure regimes to 12 test compounds at clinically relevant concentrations, both Upcyte hepatocytes and HepaRG offer suitable properties to be used in routine screening assays for toxicological assessments during drug preclinical testing.

Cell Models and Omics Techniques for the Study of Nonalcoholic Fatty Liver Disease: Focusing on Stem Cell-Derived Cell Models

Nonalcoholic fatty liver disease (NAFLD) is now the leading cause of chronic liver disease in western countries. The molecular mechanisms leading to NAFLD are only partially understood, and effective therapeutic interventions are clearly needed. Therefore, preclinical research is required to improve knowledge about NAFLD physiopathology and to identify new therapeutic targets. Primary human hepatocytes, human hepatic cell lines, and human stem cell-derived hepatocyte-like cells exhibit different hepatic phenotypes and have been widely used for studying NAFLD pathogenesis. In this paper, apart from employing the different in vitro cell models for the in vitro assessment of NAFLD, we also reviewed other approaches (metabolomics, transcriptomics, and high-content screening). We aimed to summarize the characteristics of different cell types and methods and to discuss their major advantages and disadvantages for NAFLD modeling.

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.

DMSO-free highly differentiated HepaRG spheroids for chronic toxicity, liver functions and genotoxicity studies

The liver is essential in the elimination of environmental and food contaminants. Given the interspecies differences between rodents and humans, the development of relevant in vitro human models is crucial to investigate liver functions and toxicity in cells that better reflect pathophysiological processes. Classically, the differentiation of the hepatic HepaRG cell line requires high concentration of dimethyl sulfoxide (DMSO), which restricts its usefulness for drug-metabolism studies. Herein, we describe undifferentiated HepaRG cells embedded in a collagen matrix in DMSO-free conditions that rapidly organize into polarized hollow spheroids of differentiated hepatocyte-like cells (Hepoid-HepaRG). Our conditions allow concomitant proliferation with high levels of liver-specific functions and xenobiotic metabolism enzymes expression and activities after a few days of culture and for at least 4 weeks. By studying the toxicity of well-known injury-inducing drugs by treating cells with 1- to 100-fold of their plasmatic concentrations, we showed appropriate responses and demonstrate the sensitivity to drugs known to induce various degrees of liver injury. Our results also demonstrated that the model is well suited to estimate cholestasis and steatosis effects of drugs following chronic treatment. Additionally, DNA alterations caused by four genotoxic compounds (Aflatoxin B₁ (AFB₁), Benzo[a]Pyrene (B[a]P), Cyclophosphamide (CPA) and Methyl methanesulfonate (MMS)) were quantified in a dose-dependent manner by the comet and micronucleus assays. Their genotoxic effects were significantly increased after either an acute 24 h treatment (AFB₁: 1.5-6 μM, CPA: 2.5-10 μM, B[a]P: 12.5-50 μM, MMS: 90-450 μM) or after a 14-day treatment at much lower concentrations (AFB₁: 0.05-0.2 μM, CPA: 0.125-0.5 μM, B[a]P: 0.125-0.5 μM) representative to human exposure. Altogether, the DMSO-free 3D culture of Hepoid-HepaRG provides highly differentiated and proliferating cells relevant for various toxicological in vitro assays, especially for drug-preclinical studies and environmental chemicals risk assessment.

Analytical and Omics-Based Advances in the Study of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a significant clinical issue, affecting 1-1.5 million patients annually, and remains a major challenge during drug development-toxicity and safety concerns are the second-highest reason for drug candidate failure. The future prevalence of DILI can be minimized by developing a greater understanding of the biological mechanisms behind DILI. Both qualitative and quantitative analytical techniques are vital to characterizing and investigating DILI. In vitro assays are capable of characterizing specific aspects of a drug's hepatotoxic nature and multiplexed assays are capable of characterizing and scoring a drug's association with DILI. However, an even deeper insight into the perturbations to biological pathways involved in the mechanisms of DILI can be gained through the use of omics-based analytical techniques: genomics, transcriptomics, proteomics, and metabolomics. These omics analytical techniques can offer qualitative and quantitative insight into genetic susceptibilities to DILI, the impact of drug treatment on gene expression, and the effect on protein and metabolite abundance. This review will discuss the analytical techniques that can be applied to characterize and investigate the biological mechanisms of DILI and potential predictive biomarkers.

UHPLC-QQQ-MS/MS assay for the quantification of dianthrones as potential toxic markers of Polygonum multiflorum Thunb: applications for the standardization of traditional Chinese medicines (TCMs) with endogenous toxicity

BACKGROUND

The raw and processed roots of Polygonum multiflorum Thunb (PM) are commonly used in clinical practice to treat diverse diseases; however, reports of hepatotoxicity induced by Polygoni Multiflori Radix (PMR) and Polygoni Multiflori Radix Praeparata (PMRP) have emerged worldwide. Thus, it is necessary for researchers to explore methods to improve quality standards to ensure their quality and treatment effects.

METHODS

In the present study, an ultra-high performance liquid chromatography triple quadrupole mass spectrometry (UHPLC-QQQ-MS/MS) method was optimized and validated for the determination of dianthrones in PMR and PMRP using bianthronyl as the internal standard. Chromatographic separation with a gradient mobile phase [A: acetonitrile and B: water containing 0.1% formic acid (v/v)] at a flow rate of 0.25 mL/min was achieved on an Agilent ZORBAX SB-C₁₈ column (2.1 mm × 50 mm, 1.8 μm). The triple quadrupole mass spectrometer (TQMS) was operated in negative ionization mode with multiple reaction monitoring for the quantitative analysis of six dianthrones. Moreover, compounds 5 and 6 were further evaluated for their cytotoxicity in HepaRG cells by CCK-8 assay.

RESULTS

The UHPLC-QQQ-MS/MS method was first developed to simultaneously determine six dianthrones in PMR and PMRP, namely, polygonumnolides C1-C4 (1-4), trans-emodin dianthrones (5), and cis-emodin dianthrones (6). The contents of 1-6 in 90 batches of PMR were in the ranges of 0.027-19.04, 0.022-13.86, 0.073-15.53, 0.034-23.35, 0.38-83.67 and 0.29-67.00 µg/g, respectively. The contents of 1-6 in 86 batches of commercial PMRP were in the ranges of 0.020-13.03, 0.051-8.94, 0.022-7.23, 0.030-12.75, 0.098-28.54 and 0.14-27.79 µg/g, respectively. Compounds 1-4 were almost completely eliminated after reasonable processing for 24 h and the contents of compounds 5 and 6 significantly decreased. Additionally, compounds 5 and 6 showed inhibitory activity in HepaRG cells with IC₅₀ values of 10.98 and 15.45 μM, respectively. Furthermore, a systematic five-step strategy to standardize TCMs with endogenous toxicity was proposed for the first time, which involved the establishment of determination methods, the identification of potentially toxic markers, the standardization of processing methods, the development of limit standards and a risk-benefit assessment.

CONCLUSION

The results of the cytotoxicity evaluation of the dianthrones indicated that trans-emodin dianthrones (5) and cis-emodin dianthrones (6) could be selected as toxic markers of PMRP. Taking PMR and PMRP as examples, we hope this study provides insight into the standardization and internationalization of endogenous toxic TCMs, with the main purpose of improving public health by scientifically using TCMs to treat diverse complex diseases in the future.

Bioluminescence Measurement of Time-Dependent Dynamic Changes of CYP-Mediated Cytotoxicity in CYP-Expressing Luminescent HepG2 Cells

We sought to develop a cell-based cytotoxicity assay using human hepatocytes, which reflect the effects of drug-metabolizing enzymes on cytotoxicity. In this study, we generated luminescent human hepatoblastoma HepG2 cells using the mouse artificial chromosome vector, in which click beetle luciferase alone or luciferase and major drug-metabolizing enzymes (CYP2C9, CYP2C19, CYP2D6, and CYP3A4) are expressed, and monitored the time-dependent changes of CYP-mediated cytotoxicity expression by bioluminescence measurement. Real-time bioluminescence measurement revealed that compared with CYP-non-expressing cells, the luminescence intensity of CYP-expressing cells rapidly decreased when the cells were treated with low concentrations of aflatoxin B1 or primaquine, which exhibits cytotoxicity in the presence of CYP3A4 or CYP2D6, respectively. Using kinetics data obtained by the real-time bioluminescence measurement, we estimated the time-dependent changes of 50% inhibitory concentration (IC₅₀) values in the aflatoxin B1- and primaquine-treated cell lines. The first IC₅₀ value was detected much earlier and at a lower concentration in primaquine-treated CYP-expressing HepG2 cells than in primaquine-treated CYP-non-expressing cells, and the decrease of IC₅₀ values was much faster in the former than the latter. Thus, we successfully monitored time- and concentration-dependent dynamic changes of CYP-mediated cytotoxicity expression in CYP-expressing luminescent HepG2 cells by means of real-time bioluminescence measurement.

High-Content Screening for the Detection of Drug-Induced Oxidative Stress in Liver Cells

Drug-induced liver injury (DILI) remains a major cause of drug development failure, post-marketing warnings and restriction of use. An improved understanding of the mechanisms underlying DILI is required for better drug design and development. Enhanced reactive oxygen species (ROS) levels may cause a wide spectrum of oxidative damage, which has been described as a major mechanism implicated in DILI. Several cell-based assays have been developed as in vitro tools for early safety risk assessments. Among them, high-content screening technology has been used for the identification of modes of action, the determination of the level of injury and the discovery of predictive biomarkers for the safety assessment of compounds. In this paper, we review the value of in vitro high-content screening studies and evaluate how to assess oxidative stress induced by drugs in hepatic cells, demonstrating the detection of pre-lethal mechanisms of DILI as a powerful tool in human toxicology.

Effect of Microbial Short-Chain Fatty Acids on CYP3A4-Mediated Metabolic Activation of Human Pluripotent Stem Cell-Derived Liver Organoids

The early and accurate prediction of the hepatotoxicity of new drug targets during nonclinical drug development is important to avoid postmarketing drug withdrawals and late-stage failures. We previously established long-term expandable and functional human-induced pluripotent stem cell (iPSC)-derived liver organoids as an alternative source for primary human hepatocytes. However, PSC-derived organoids are known to present immature fetal characteristics. Here, we treated these liver organoids with microbial short-chain fatty acids (SCFAs) to improve metabolic maturation based on microenvironmental changes in the liver during postnatal development. The effects of the three main SCFA components (acetate, propionate, and butyrate) and their mixture on liver organoids were determined. Propionate (1 µM) significantly promoted the CYP3A4/CYP3A7 expression ratio, and acetate (1 µM), propionate (1 µM), and butyrate (1 µM) combination treatment, compared to no treatment (control), substantially increased CYP3A4 activity and albumin secretion, as well as gene expression. More importantly, mixed SCFA treatment accurately revealed troglitazone-induced hepatotoxicity, which was redeemed on a potent CYP3A4 inhibitor ketoconazole treatment. Overall, we determined, for the first time, that SCFA mixture treatment might contribute to the accurate evaluation of the CYP3A4-dependent drug toxicity by improving metabolic activation, including CYP3A4 expression, of liver organoids.

Application of In Vitro Metabolism Activation in High-Throughput Screening

In vitro methods which incorporate metabolic capability into the assays allow us to assess the activity of metabolites from their parent compounds. These methods can be applied into high-throughput screening (HTS) platforms, thereby increasing the speed to identify compounds that become active via the metabolism process. HTS was originally used in the pharmaceutical industry and now is also used in academic settings to evaluate biological activity and/or toxicity of chemicals. Although most chemicals are metabolized in our body, many HTS assays lack the capability to determine compound activity via metabolism. To overcome this problem, several in vitro metabolic methods have been applied to an HTS format. In this review, we describe in vitro metabolism methods and their application in HTS assays, as well as discuss the future perspectives of HTS with metabolic activity. Each in vitro metabolism method has advantages and disadvantages. For instance, the S9 mix has a full set of liver metabolic enzymes, but it displays high cytotoxicity in cell-based assays. In vitro metabolism requires liver fractions or the use of other metabolically capable systems, including primary hepatocytes or recombinant enzymes. Several newly developed in vitro metabolic methods, including HepaRG cells, three-dimensional (3D) cell models, and organ-on-a-chip technology, will also be discussed. These newly developed in vitro metabolism approaches offer significant progress in dissecting biological processes, developing drugs, and making toxicology studies quicker and more efficient.

Suaeda vermiculata Aqueous-Ethanolic Extract-Based Mitigation of CCl4-Induced Hepatotoxicity in Rats, and HepG-2 and HepG-2/ADR Cell-Lines-Based Cytotoxicity Evaluations

Suaeda vermiculata, an edible halophytic plant, used by desert nomads to treat jaundice, was investigated for its hepatoprotective bioactivity and safety profile on its mother liquor aqueous-ethanolic extract. Upon LC-MS (Liquid Chromatography-Mass Spectrometry) analysis, the presence of several constituents including three major flavonoids, namely quercetin, quercetin-3-O-rutinoside, and kaempferol-O-(acetyl)-hexoside-pentoside were confirmed. The aqueous-ethanolic extract, rich in antioxidants, quenched the DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals, and also showed noticeable levels of radical scavenging capacity in ABTS (2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid) assay. For the hepatoprotective activity confirmation, the male rat groups were fed daily, for 7 days (n = 8/group, p.o.), either carboxyl methylcellulose (CMC) 0.5%, silymarin 200 mg/kg, the aqueous-ethanolic extract of the plant Suaeda vermiculata (100, 250, and 500 mg/kg extract), or quercetin (100 mg/kg) alone, and on day 7 of the administrations, all the animal groups, excluding a naïve (250 mg/kg aqueous-ethanolic extract-fed), and an intact animal group were induced hepatotoxicity by intraperitoneally administering carbon tetrachloride (CCl₄). All the animals were sacrificed after 24 h, and aspartate transaminase and alanine transaminase serum levels were observed, which were noted to be significantly decreased for the aqueous-ethanolic extract, silymarin, and quercetin-fed groups in comparison to the CMC-fed group (p < 0.0001). No noticeable adverse effects were observed on the liver, kidney, or heart's functions of the naïve (250 mg/kg) group. The aqueous-ethanolic extract was found to be safe in the acute toxicity (5 g/kg) test and showed hepatoprotection and safety at higher doses. Further upon, the cytotoxicity testings in HepG-2 and HepG-2/ADR (Adriamycin resistant) cell-lines were also investigated, and the IC₅₀ values were recorded at 56.19±2.55 µg/mL, and 78.40±0.32 µg/mL (p < 0.001, Relative Resistance RR 1.39), respectively, while the doxorubicin (Adriamycin) IC₅₀ values were found to be 1.3±0.064, and 4.77±1.05 µg/mL (p < 0.001, RR 3.67), respectively. The HepG-2/ADR cell-lines when tested in a combination of the aqueous-ethanolic extract with doxorubicin, a significant reversal in the doxorubicin's IC₅₀ value by 2.77 folds (p < 0.001, CI = 0.56) was noted as compared to the cytotoxicity test where the extract was absent. The mode of action for the reversal was determined to be synergistic in nature indicating the role of the aqueous-ethanolic extract.

Molecular Profiling of Human Induced Pluripotent Stem Cell-Derived Cells and their Application for Drug Safety Study

Drug-induced toxicity remains one of the leading causes of discontinuation of the drug candidate and post-marketing withdrawal. Thus, early identification of the drug candidates with the potential for toxicity is crucial in the drug development process. With the recent discovery of human- Induced Pluripotent Stem Cells (iPSC) and the establishment of the differentiation protocol of human iPSC into the cell types of interest, the differentiated cells from human iPSC have garnered much attention because of their potential applicability in toxicity evaluation as well as drug screening, disease modeling and cell therapy. In this review, we expanded on current information regarding the feasibility of human iPSC-derived cells for the evaluation of drug-induced toxicity with a focus on human iPSCderived hepatocyte (iPSC-Hep), cardiomyocyte (iPSC-CMs) and neurons (iPSC-Neurons). Further, we CSAHi, Consortium for Safety Assessment using Human iPS Cells, reported our gene expression profiling data with DNA microarray using commercially available human iPSC-derived cells (iPSC-Hep, iPSC-CMs, iPSC-Neurons), their relevant human tissues and primary cultured human cells to discuss the future direction of the three types of human iPSC-derived cells.

[Strategic assessment for nonclinical safety in drug discovery]

Given that safety (toxicity) liabilities in drug development still account for a large proportion of development discontinuations and market withdrawals, establishing an appropriate safety prediction and evaluation strategy is an important topic. In particular, discontinuation in the late stage of development following large investment has a significant impact. Accurate safety assessment in the early preclinical stage is therefore highly desirable. However, pre-GLP (exploratory) safety evaluation is not subject to regulatory guidelines, and structure and practices accordingly vary widely among companies. Against this background, it can be difficult for non-safety researchers to understand why a particular evaluation/assay system and study design have been selected and tested, and why these differ from those in other companies. This article introduces the background to and concept of a revised strategy for exploratory safety assessment at Astellas, and explains that exploratory safety assessment is not uniform but varies with strategy.

The evolution of strategies to minimise the risk of human drug-induced liver injury (DILI) in drug discovery and development

Early identification of toxicity associated with new chemical entities (NCEs) is critical in preventing late-stage drug development attrition. Liver injury remains a leading cause of drug failures in clinical trials and post-approval withdrawals reflecting the poor translation between traditional preclinical animal models and human clinical outcomes. For this reason, preclinical strategies have evolved over recent years to incorporate more sophisticated human in vitro cell-based models with multi-parametric endpoints. This review aims to highlight the evolution of the strategies adopted to improve human hepatotoxicity prediction in drug discovery and compares/contrasts these with recent activities in our lab. The key role of human exposure and hepatic drug uptake transporters (e.g. OATPs, OAT2) is also elaborated.

A head-to-head Caco-2 assay comparison of the mechanisms of action of the intestinal permeation enhancers: SNAC and sodium caprate (C10)

Salcaprozate sodium (SNAC) and sodium caprate (C₁₀) are the two leading intestinal permeation enhancers (PEs) in oral peptide formulations in clinical trials. There is debate over their mechanism of action on intestinal epithelia. The aims were: (i) to compare their effects on the barrier function by measuring transepithelial electrical resistance (TEER), permeability of FITC-4000 (FD4) across Caco-2 monolayers, and on immunohistochemistry of tight junction (TJ)-associated proteins; and (ii) to compare cellular parameters using conventional end-point cytotoxicity assays and quantitative high content analysis (HCA) of multiple sub-lethal parameters in Caco-2 cells. C₁₀ (8.5 mM) reversibly reduced TEER and increased FD4 permeability across monolayers, whereas SNAC had no effects on either parameter except at cytotoxic concentrations. C₁₀ exposure induced reorganization of three TJ proteins, whereas SNAC only affected claudin-5 localization. High concentrations of C₁₀ and SNAC were required to cause end-point toxicology changes in vitro. SNAC was less potent than C₁₀ at inducing lysosomal and nuclear changes and plasma membrane perturbation. In parallel, HCA revealed that both agents displayed detergent-like features that reflect initial membrane fluidization followed by changes in intracellular parameters. In conclusion, FD4 permeability increases in monolayers in response to C₁₀ were in the range of concentrations that altered end-point cytotoxicity and HCA parameters. For SNAC, while HCA parameters were also altered in a similar overall pattern as C₁₀, they did not lead to increased paracellular flux. These assays show that both agents are primarily surfactants, but C₁₀ has additional TJ-opening effects. While these in vitro assays illucidate their epithelial mechanism of action, clinical experience suggests that they over-estimate their toxicology in the dynamic intestinal environment.

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.

Mechanism-based integrated assay systems for the prediction of drug-induced liver injury

Drug-induced liver injury (DILI) can cause hepatic failure and result in drug withdrawal from the market. It has host-related and compound-dependent mechanisms. Preclinical prediction of DILI risk is very challenging and safety assessments based on animals inadequately forecast human DILI risk. In contrast, human-derived in vitro cell culture-based models could improve DILI risk prediction accuracy. Here, we developed and validated an innovative method to assess DILI risk associated with various compounds. Fifty-four marketed and withdrawn drugs classified as DILI risks of "most concern", "less concern", and "no concern" were tested using a combination of four assays addressing mitochondrial injury, intrahepatic lipid accumulation, inhibition of bile canalicular network formation, and bile acid accumulation. Using the inhibitory potencies of the drugs evaluated in these in vitro tests, an algorithm with the highest available DILI risk prediction power was built by artificial neural network (ANN) analysis. It had an overall forecasting accuracy of 73%. We excluded the intrahepatic lipid accumulation assay to avoid overfitting. The accuracy of the algorithm in terms of predicting DILI risks was 62% when it was constructed by ANN but only 49% when it was built by the point-added scoring method. The final algorithm based on three assays made no DILI risk prediction errors such as "most concern " instead of "no concern" and vice-versa. Our mechanistic approach may accurately predict DILI risks associated with numerous candidate drugs.

Can Galactose Be Converted to Glucose in HepG2 Cells? Improving the in Vitro Mitochondrial Toxicity Assay for the Assessment of Drug Induced Liver Injury

Human hepatocellular carcinoma cells, HepG2, are often used for drug mediated mitochondrial toxicity assessments. Glucose in HepG2 culture media is replaced by galactose to reveal drug-induced mitochondrial toxicity as a marked shift of drug IC50 values for the reduction of cellular ATP. It has been postulated that galactose sensitizes HepG2 mitochondria by the additional ATP consumption demand in the Leloir pathway. However, our NMR metabolomics analysis of HepG2 cells and culture media showed very limited galactose metabolism. To clarify the role of galactose in HepG2 cellular metabolism, U-¹³C₆-galactose or U-¹³C₆-glucose was added to HepG2 culture media to help specifically track the metabolism of those two sugars. Conversion to U-¹³C₃-lactate was hardly detected when HepG2 cells were incubated with U-¹³C₆-galactose, while an abundance of U-¹³C₃-lactate was produced when HepG2 cells were incubated with U-¹³C₆-glucose. In the absence of glucose, HepG2 cells increased glutamine consumption as a bioenergetics source. The requirement of additional glutamine almost matched the amount of glucose needed to maintain a similar level of cellular ATP in HepG2 cells. This improved understanding of galactose and glutamine metabolism in HepG2 cells helped optimize the ATP-based mitochondrial toxicity assay. The modified assay showed 96% sensitivity and 97% specificity in correctly discriminating compounds known to cause mitochondrial toxicity from those with prior evidence of not being mitochondrial toxicants. The greatest significance of the modified assay was its improved sensitivity in detecting the inhibition of mitochondrial fatty acid β-oxidation (FAO) when glutamine was withheld. Use of this improved assay for an empirical prediction of the likely contribution of mitochondrial toxicity to human DILI (drug induced liver injury) was attempted. According to testing of 65 DILI positive compounds representing numerous mechanisms of DILI together with 55 DILI negative compounds, the overall prediction of mitochondrial mechanism-related DILI showed 25% sensitivity and 95% specificity.

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.

Establishment of a novel hepatocyte model that expresses four cytochrome P450 genes stably via mammalian-derived artificial chromosome for pharmacokinetics and toxicity studies

The utility of HepG2 cells to assess drug metabolism and toxicity induced by chemical compounds is hampered by their low cytochrome P450 (CYP) activities. To overcome this limitation, we established HepG2 cell lines expressing major CYP enzymes involved in drug metabolism (CYP2C9, CYP2C19, CYP2D6, and CYP3A4) and CYP oxidoreductase (POR) using the mammalian-derived artificial chromosome vector. Transchromosomic HepG2 (TC-HepG2) cells expressing four CYPs and POR were used to determine time- and concentration-dependent inhibition and toxicity of several compounds by luminescence detection of CYP-specific substrates and cell viability assays. Gene expression levels of all four CYPs and POR, as well as the CYP activities, were higher in TC-HepG2 clones than in parental HepG2 cells. Additionally, the activity levels of all CYPs were reduced in a concentration-dependent manner by specific CYP inhibitors. Furthermore, preincubation of TC-HepG2 cells with CYP inhibitors known as time-dependent inhibitors (TDI) prior to the addition of CYP-specific substrates determined that CYP inhibition was enhanced in the TDI group than in the non-TDI group. Finally, the IC50 of bioactivable compound aflatoxin B1 was lower in TC-HepG2 cells than in HepG2 cells. In conclusion, the TC-HepG2 cells characterized in the current study are a highly versatile model to evaluate drug-drug interactions and hepatotoxicity in initial screening of candidate drug compounds, which require a high degree of processing capacity and reliability.

Long-Term Stability of Cryopreserved Human Hepatocytes: Evaluation of Phase I and II Drug-Metabolizing Enzyme Activities and CYP3A4/5 Induction for More than a Decade

We evaluated the long-term stability of hepatocytes stored in the vapor phase of liquid nitrogen for their viability, cytochrome P450 (CYP) 1A2 activity, CYP3A4/5 activity, uridine diphosphate-glucuronosyl transferase (UGT) activity, sulfotransferase (SULT) activity, and CYP3A4/5 induction during 14 years of preservation. No substantial degradation of viability, CYP1A2 activity, UGT activity, or CYP3A4/5 induction was observed. CYP3A4/5 activity showed a slight decrease after 7 years of storage, and SULT activity gradually decreased during storage, although substantial activities remained even after 14 years. These results indicate that cryopreserved human hepatocytes can be stored stably for more than a decade with little or no change in viability, activity of drug-metabolizing enzymes, or CYP3A4/5 induction, and can be widely applicable to qualitative research in drug metabolism.

In vitro toxicological evaluation of NCS-382, a high-affinity antagonist of γ-hydroxybutyrate (GHB) binding

γ-Hydroxybutyric acid (GHB), a minor metabolite of the inhibitory neurotransmitter GABA, can accumulate to significant concentrations in the heritable disorder of GABA degradation, succinic semialdehyde dehydrogenase (SSADH) deficiency (SSADHD). Moreover, GHB may be employed in therapeutic settings (treatment of narcolepsy), as well as instances of illicit activity, including acquaintance sexual assault and the induction of euphoria. High-affinity binding sites for GHB in the brain have been identified, although the absolute identity of these receptors remains unclear. Pharmacological antagonism of GHB binding may have multiple instances of therapeutic relevance. The high affinity GHB receptor antagonist, NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5H-benzo-cyclohept-6-ylideneacetic acid) has not been piloted in humans. To address the potential clinical utility of NCS-382, we have piloted initial studies of its toxicology in HepG2 and primary hepatocyte cells. At high dose (0.5mM), NCS-382 showed no capacity for inhibition of microsomal CYPs (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4) and minimal potential for activation of xenobiotic nuclear receptors. Additional cellular integrity and functional assays (viability, oxidative stress, apoptosis, ATP production) revealed little evidence for cytotoxicity, and a low degree of dysregulation of >370 genes actively engaged in the mediation of cellular toxicity. In vitro testing indicates a low probability of cellular toxicity associated with NCS-382.