A metabolomics cell-based approach for anticipating and investigating drug-induced liver injury

In preclinical stages of drug development, anticipating potential adverse drug effects such as toxicity is an important issue for both saving resources and preventing public health risks. Current in vitro cytotoxicity tests are restricted by their predictive potential and their ability to provide mechanistic information. This study aimed to develop a metabolomic mass spectrometry-based approach for the detection and classification of drug-induced hepatotoxicity. To this end, the metabolite profiles of human derived hepatic cells (i.e., HepG2) exposed to different well-known hepatotoxic compounds acting through different mechanisms (i.e., oxidative stress, steatosis, phospholipidosis, and controls) were compared by multivariate data analysis, thus allowing us to decipher both common and mechanism-specific altered biochemical pathways. Briefly, oxidative stress damage markers were found in the three mechanisms, mainly showing altered levels of metabolites associated with glutathione and γ-glutamyl cycle. Phospholipidosis was characterized by a decreased lysophospholipids to phospholipids ratio, suggestive of phospholipid degradation inhibition. Whereas, steatosis led to impaired fatty acids β-oxidation and a subsequent increase in triacylglycerides synthesis. The characteristic metabolomic profiles were used to develop a predictive model aimed not only to discriminate between non-toxic and hepatotoxic drugs, but also to propose potential drug toxicity mechanism(s).

Inhibition of bile canalicular network formation in rat sandwich cultured hepatocytes by drugs associated with risk of severe liver injury

Idiosyncratic drug-induced liver injury is a clinical concern with serious consequences. Although many preclinical screening methods have been proposed, it remains difficult to identify compounds associated with this rare but potentially fatal liver condition. Here, we propose a novel assay system to assess the risk of liver injury. Rat primary hepatocytes were cultured in a sandwich configuration, which enables the formation of a typical bile canalicular network. From day 2 to 3, test drugs, mostly selected from a list of cholestatic drugs, were administered, and the length of the network was semi-quantitatively measured by immunofluorescence. Liver injury risk information was collected from drug labels and was compared with in vitro measurements. Of 23 test drugs examined, 15 exhibited potent inhibition of bile canalicular network formation (<60% of control). Effects on cell viability were negligible or minimal as confirmed by lactate dehydrogenase leakage and cellular ATP content assays. For the potent 15 drugs, IC50 values were determined. Finally, maximum daily dose divided by the inhibition constant gave good separation of the highest risk of severe liver toxicity drugs such as troglitazone, benzbromarone, flutamide, and amiodarone from lower risk drugs. In conclusion, inhibitory effect on the bile canalicular network formation observed in in vitro sandwich cultured hepatocytes evaluates a new aspect of drug toxicity, particularly associated with aggravation of liver injury.

Human Upcyte Hepatocytes: Characterization of the Hepatic Phenotype and Evaluation for Acute and Long-Term Hepatotoxicity Routine Testing

The capacity of human hepatic cell-based models to predict hepatotoxicity depends on the functional performance of cells. The major limitations of human hepatocytes include the scarce availability and rapid loss of the hepatic phenotype. Hepatoma cells are readily available and easy to handle, but are metabolically poor compared with hepatocytes. Recently developed human upcyte hepatocytes offer the advantage of combining many features of primary hepatocytes with the unlimited availability of hepatoma cells. We analyzed the phenotype of upcyte hepatocytes comparatively with HepG2 cells and adult primary human hepatocytes to characterize their functional features as a differentiated hepatic cell model. The transcriptomic analysis of liver characteristic genes confirmed that the upcyte hepatocytes expression profile comes closer to human hepatocytes than HepG2 cells. CYP activities were measurable and showed a similar response to prototypical CYP inducers than primary human hepatocytes. Upcyte hepatocytes also retained conjugating activities and key hepatic functions, e.g. albumin, urea, lipid and glycogen synthesis, at levels close to hepatocytes. We also investigated the suitability of this cell model for preclinical hepatotoxicity risk assessments using multiparametric high-content screening, as well as transcriptomics and targeted metabolomic analysis. Compounds with well-documented in vivo hepatotoxicity were screened after acute and repeated doses up to 1 week. The evaluation of complex mechanisms of cell toxicity, drug-induced steatosis and oxidative stress biomarkers demonstrated that, by combining the phenotype of primary human hepatocytes and the ease of handling of HepG2 cells, upcyte hepatocytes offer suitable properties to be potentially used for toxicological assessments during drug development.

Advantageous use of HepaRG cells for the screening and mechanistic study of drug-induced steatosis

Only a few in vitro assays have been proposed to evaluate the steatotic potential of new drugs. The present study examines the utility of HepaRG cells as a cell-based assay system for screening drug-induced liver steatosis. A high-content screening assay was run to evaluate multiple toxicity-related cell parameters in HepaRG cells exposed to 28 compounds, including drugs reported to cause steatosis through different mechanisms and non-steatotic compounds. Lipid content was the most sensitive parameter for all the steatotic drugs, whereas no effects on lipid levels were produced by non-steatotic compounds. Apart from fat accumulation, increased ROS production and altered mitochondrial membrane potential were also found in the cells exposed to steatotic drugs, which indicates that all these cellular events contributed to drug-induced hepatotoxicity. These findings are of clinical relevance as most effects were observed at drug concentrations under 100-fold of the therapeutic peak plasmatic concentration. HepaRG cells showed increased lipid overaccumulation vs. HepG2 cells, which suggests greater sensitivity to drug-induced steatosis. An altered expression profile of transcription factors and the genes that code key proteins in lipid metabolism was also found in the cells exposed to drugs capable of inducing liver steatosis. Our results generally indicate the value of HepaRG cells for assessing the risk of liver damage associated with steatogenic compounds and for investigating the molecular mechanisms involved in drug-induced steatosis.

The HepaRG cell line, a superior in vitro model to L-02, HepG2 and hiHeps cell lines for assessing drug-induced liver injury

Drug-induced liver injury (DILI) is a leading cause of discontinuation of new drug approval or withdrawal of marketed medicine based on safety due to organ vulnerability. The aim of this research is to investigate the potential abilities of four different in vitro cell models (L-02, HepG2, HepaRG, and hiHeps cell lines) in assessing marketed drugs labeled with apparently different types of liver injury. A total of 17 drugs with versatile pharmacological profiles were chosen, of which, 14 drugs are recognized as DILI agents and 3 drugs are DILI irrelevant. Preliminary cellular screening assays indicated that the HepaRG cell line had an advantage over other cell lines in predicting drugs associated with DILI in vitro as it had the highest Youden's index (71.4%). A multi-parametric screening assay showed that oxidative stress, mitochondrial damage, and disorders of neutral lipid metabolism were changed notably in the HepaRG cell line after DILI-related drugs exposure, accounting for its high sensitivity in comparison with other three cell lines. In addition, aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and malate dehydrogenase (MDH) all correlated with the cytotoxic effects of diclofenac sodium (p < 0.05), buspirone hydrochloride (p < 0.01), and danazol (p < 0.01) in the HepaRG cell line. We conclude that the HepaRG cell line is a superior in vitro cell model to other three cell lines for evaluating drugs with DILI potential.

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

Drug-induced liver injury (DILI) results in the termination of drug development or withdrawal of a drug from the market. The establishment of a predictive, high-throughput preclinical test system to evaluate potential clinical DILI is therefore required. Here, we established a high content analysis (HCA) assay in human hepatocyte cell lines such as the HepaRG with normal expression levels of CYP enzymes and HepG2 with extremely low expression levels of CYP enzymes. Clinical DILI or non-DILI compounds were evaluated for reactive oxygen species (ROS) production, glutathione (GSH) consumption, and mitochondrial membrane potential (MMP) attenuation. A proportion of DILI compounds induced ROS generation, GSH depletion, and MMP dysfunction, which was consistent with reported mechanisms of DILI of these compounds. In particular, DILI compounds that deplete GSH via reactive metabolites exhibited a more marked decrease in intracellular GSH or increase in ROS production in HepaRG cells than in HepG2 cells. Comparison of the two cell lines with different levels of CYP expression might help clarify the contribution of metabolism to hepatocyte toxicity. These results suggest that the HCA assay in HepaRG and HepG2 cells might help improve the accuracy of evaluating clinical DILI potential during drug screening.

High Content Analysis of Human Pluripotent Stem Cell Derived Hepatocytes Reveals Drug Induced Steatosis and Phospholipidosis

Hepatotoxicity is one of the most cited reasons for withdrawal of approved drugs from the market. The use of nonclinically relevant in vitro and in vivo testing systems contributes to the high attrition rates. Recent advances in differentiating human induced pluripotent stem cells (hiPSCs) into pure cultures of hepatocyte-like cells expressing functional drug metabolizing enzymes open up possibilities for novel, more relevant human cell based toxicity models. The present study aimed to investigate the use of hiPSC derived hepatocytes for conducting mechanistic toxicity testing by image based high content analysis (HCA). The hiPSC derived hepatocytes were exposed to drugs known to cause hepatotoxicity through steatosis and phospholipidosis, measuring several endpoints representing different mechanisms involved in drug induced hepatotoxicity. The hiPSC derived hepatocytes were benchmarked to the HepG2 cell line and generated robust HCA data with low imprecision between plates and batches. The different parameters measured were detected at subcytotoxic concentrations and the order of which the compounds were categorized (as severe, moderate, mild, or nontoxic) based on the degree of injury at isomolar concentration corresponded to previously published data. Taken together, the present study shows how hiPSC derived hepatocytes can be used as a platform for screening drug induced hepatotoxicity by HCA.

High Content Imaging (HCI) on Miniaturized Three-Dimensional (3D) Cell Cultures

High content imaging (HCI) is a multiplexed cell staining assay developed for better understanding of complex biological functions and mechanisms of drug action, and it has become an important tool for toxicity and efficacy screening of drug candidates. Conventional HCI assays have been carried out on two-dimensional (2D) cell monolayer cultures, which in turn limit predictability of drug toxicity/efficacy in vivo; thus, there has been an urgent need to perform HCI assays on three-dimensional (3D) cell cultures. Although 3D cell cultures better mimic in vivo microenvironments of human tissues and provide an in-depth understanding of the morphological and functional features of tissues, they are also limited by having relatively low throughput and thus are not amenable to high-throughput screening (HTS). One attempt of making 3D cell culture amenable for HTS is to utilize miniaturized cell culture platforms. This review aims to highlight miniaturized 3D cell culture platforms compatible with current HCI technology.

Mechanism underlying protective effect of Inonotus obliquus polysaccharide on anti-tuberculosis drug induced liver injury

AIM: To explore the mechanism underlying the protective effect of Inonotus obliquus polysaccharide (IOP) on liver injury induced by isoniazid and rifampicin.

METHODS: One hundred mice were randomly divided into a normal control group, a model group, and high-, medium- and low-dose IOP groups, with 20 mice in each group. Except the control group, the other groups were intragastrically administered with isoniazid and rifampicin. Two hours later, the mice of the IOP groups were given different doses of IOP, and the mice in the control group were given normal saline. The intervention lasted 4 wk. After that, the mice were killed. Serum levels of transaminase and bilirubin, hepatic contents of malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPX), expression levels of multidrug resistance associated protein 2 (MRP2), bile salt export pump (BSEP), P-glycoprotein (P-GP), sodium taurocholate cotransporting polypeptide (NTCP), nuclear factor related factor 2 (NRF-2), glutathione-s-transferase A1 (GSTA1), as well as reactive oxygen species (ROS) and 8-hydroxy-2deoxyguanosine (8-OHDG) levels were detected. Hepatic pathological changes were evaluated by HE staining.

RESULTS: Serum levels of transaminase and bilirubin as well as hepatic levels of MDA, MRP2, BSEP, P-GP, NRF-2 and GSTA1were significantly higher, and the levels of NTCP, SOD, and GPX were significantly lower in the normal control group than in the model group (P < 0.05). Serum levels of transaminase and bilirubin, hepatic levels of MDA, MRP2, BSEP, P-GP, NRF-2 and GSTA1, as well as ROS and 8-OHDG were significantly lower, and the levels of NTCP, SOD, and GPX were significantly higher in mice treated with IOP than in model mice (P < 0.05). The above parameters were significantly different among mice treated with different doses of IOP (P < 0.05). Hepatic pathological changes were obviously more serious in the model group than in the normal control group and IOP treated groups.

CONCLUSION: IOP can reduce the levels of MRP2, BSEP, P-GP, NRF-2, GSTA1, ROS, and 8-OHDG, and increase NTCP, SOD and GPX to protect against liver injury caused by antituberculosis drugs.

Effects of Nano-CeO₂ with Different Nanocrystal Morphologies on Cytotoxicity in HepG2 Cells

Cerium oxide nanoparticles (nano-CeO₂) have been reported to cause damage and apoptosis in human primary hepatocytes. Here, we compared the toxicity of three types of nano-CeO₂ with different nanocrystal morphologies (cube-, octahedron-, and rod-like crystals) in human hepatocellular carcinoma cells (HepG2). The cells were treated with the nano-CeO₂ at various concentrations (6.25, 12.5, 25, 50, 100 μg/mL). The crystal structure, size and morphology of nano-CeO₂ were investigated by X-ray diffractometry and transmission electron microscopy. The specific surface area was detected using the Brunauer, Emmet and Teller method. The cellular morphological and internal structure were observed by microscopy; apoptotic alterations were measured using flow cytometry; nuclear DNA, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) and glutathione (GSH) in HepG2 cells were measured using high content screening technology. The scavenging ability of hydroxyl free radicals and the redox properties of the nano-CeO₂ were measured by square-wave voltammetry and temperature-programmed-reduction methods. All three types of nano-CeO₂ entered the HepG2 cells, localized in the lysosome and cytoplasm, altered cellular shape, and caused cytotoxicity. The nano-CeO₂ with smaller specific surface areas induced more apoptosis, caused an increase in MMP, ROS and GSH, and lowered the cell’s ability to scavenge hydroxyl free radicals and antioxidants. In this work, our data demonstrated that compared with cube-like and octahedron-like nano-CeO₂, the rod-like nano-CeO₂ has lowest toxicity to HepG2 cells owing to its larger specific surface areas.

LC-MS untargeted metabolomic analysis of drug-induced hepatotoxicity in HepG2 cells

Hepatotoxicity is the number one cause for agencies not approving and withdrawing drugs for the market. Drug-induced human hepatotoxicity frequently goes undetected in preclinical safety evaluations using animal models. Human-derived in vitro models represent a common alternative to in vivo tests to detect toxic effects during preclinical testing. Most current in vitro toxicity assays rely on the measurement of nonspecific or low sensitive endpoints, which result in poor concordance with human liver toxicity. Therefore, making more accurate predictions of the potential hepatotoxicity of new drugs remains a challenge. Metabolomics, whose aim is to globally assess all the metabolites present in a biological sample, may represent an alternative in the search for sensitive sublethal markers of drug-induced hepatotoxicity. To this end, a comprehensive LC-MS-based untargeted metabolite profiling analysis of HepG2 cells, exposed to a set of well-described model hepatotoxins and innocuous compounds, was performed. It allowed to determine meaningful metabolic changes triggered by a toxic insult and gave a first estimation of the main toxicity-related pathways. Based on these metabolic patterns, a partial least squares-discriminant analysis model, able to discriminate between nontoxic and hepatotoxic compounds, was constructed. The approach described herein may provide an alternative for animal testing in preclinical stages of drug development and a controlled experimental approach to gain a better understanding of the underlying causes of hepatotoxicity.

Multiparametric assay using HepaRG cells for predicting drug-induced liver injury

The utility of HepaRG cells as an in vitro cell-based assay system for assessing drug-induced liver injury (DILI) risk was investigated. Seventeen DILI-positive and 15 DILI-negative drugs were selected for the assay. HepaRG cells were treated with each drug for 24h at concentrations that were 1.6-, 6.3-, 25-, and 100-fold the therapeutic maximum plasma concentration (Cmax). After treatment, the cell viability, glutathione content, caspase 3/7 activity, lipid accumulation, leakage of lactate dehydrogenase, and albumin secretion were measured. The sensitivity and specificity were calculated to assess the ability of the assay to predict DILI. Our multiparametric assay using HepaRG cells exhibited a 67% sensitivity and 73% specificity at a 100-fold concentration of Cmax and a 41% sensitivity and 87% specificity at a 25-fold concentration of Cmax. When a 25-fold Cmax cut-off was applied, approximately 70% of drugs exhibiting positive responses were classified into the high DILI risk category. HepaRG cells distinguished relatively safe drugs from their high-risk analogs. Our study indicates that HepaRG cells may be of use to (1) prioritize drug analogs, (2) analyze the mechanism of DILI, and (3) assess the risk for DILI in the early drug discovery stage.

High-content analysis for drug delivery and nanoparticle applications

High-content analysis (HCA) provides quantitative multiparametric cellular fluorescence data. From its origins in discovery toxicology, it is now addressing fundamental questions in drug delivery. Nanoparticles (NPs), polymers, and intestinal permeation enhancers are being harnessed in drug delivery systems to modulate plasma membrane properties and the intracellular environment. Identifying comparative mechanistic cytotoxicity on sublethal events is crucial to expedite the development of such systems. NP uptake and intracellular routing pathways are also being dissected using chemical and genetic perturbations, with the potential to assess the intracellular fate of targeted and untargeted particles in vitro. As we discuss here, HCA is set to make a major impact in preclinical delivery research by elucidating the intracellular pathways of NPs and the in vitro mechanistic-based toxicology of formulation constituents.

High-content screening technology for studying drug-induced hepatotoxicity in cell models

High-content screening is the application of automated microscopy and image analysis to both cell biology and drug discovery. Over the last decade, this technique has emerged as a useful technology that allows the simultaneous measurement of different parameters at a single-cell level. Hepatotoxicity is a compelling reason for drug nonapprovals and withdrawals. It is recognized that the safety of a compound cannot be based on a single in vitro assay, and existing methods are not predictive of drug-induced toxicity. However, different HCS assays have been recently demonstrated as being powerful for identifying different mechanisms implicated in drug-induced toxicity with high sensitivity and specificity. These assays integrate the data obtained from different cell function indicators and can be easily incorporated into basic screening processes for the safety evaluation and selection of drug candidates; thus, they contribute greatly to lessen the likelihood of drug failure. Exploring the use of cellular imaging technology in drug-induced liver injury by reviewing the different tests proposed provides evidence that this technology has a strong impact on drug discovery.

Prediction of Drug-Induced Liver Injury in Micropatterned Co-cultures Containing iPSC-Derived Human Hepatocytes

Primary human hepatocytes (PHHs) are a limited resource for drug screening, their quality for in vitro use can vary considerably across different lots, and a lack of available donor diversity restricts our understanding of how human genetics affect drug-induced liver injury (DILI). Induced pluripotent stem cell-derived human hepatocyte-like cells (iPSC-HHs) could provide a complementary tool to PHHs for high-throughput drug screening, and ultimately enable personalized medicine. Here, we hypothesized that previously developed iPSC-HH-based micropatterned co-cultures (iMPCCs) with murine embryonic fibroblasts could be amenable to long-term drug toxicity assessment. iMPCCs, created in industry-standard 96-well plates, were treated for 6 days with a set of 47 drugs, and multiple functional endpoints (albumin, urea, ATP) were evaluated in dosed cultures against vehicle-only controls to enable binary toxicity decisions. We found that iMPCCs correctly classified 24 of 37 hepatotoxic drugs (65% sensitivity), while all 10 non-toxic drugs tested were classified as such in iMPCCs (100% specificity). On the other hand, conventional confluent cultures of iPSC-HHs failed to detect several liver toxins that were picked up in iMPCCs. Results for DILI detection in iMPCCs were remarkably similar to published data in PHH-MPCCs (65% versus 70% sensitivity) that were dosed with the same drugs. Furthermore, iMPCCs detected the relative hepatotoxicity of structural drug analogs and recapitulated known mechanisms of acetaminophen toxicity in vitro. In conclusion, iMPCCs could provide a robust tool to screen for DILI potential of large compound libraries in early stages of drug development using an abundant supply of commercially available iPSC-HHs.

Transcriptomics of Hepatocytes Treated with Toxicants for Investigating Molecular Mechanisms Underlying Hepatotoxicity

Transcriptomics is a powerful tool for high-throughput gene expression profiling. Transcriptome microarray experiments conducted with RNA isolated from hepatocytes after exposure to toxicants enable a deep insight into the molecular mechanisms of hepatotoxicity. This understanding, along with structure-activity relationships underlying hepatotoxicity, will provide a novel strategy to design cost-effective and safer therapeutics. Transcriptomics studies conducted with established hepatotoxic drugs in various in vitro and in vivo hepatotoxicity test systems have contributed to the elucidation of the mechanistic basis of liver insults, which were later on substantiated at the proteomics and metabolomics levels. The present chapter is focused on comprehensive transcriptomics of cultured primary hepatocytes treated with chemicals by applying Affymetrix microarray technology. It also describes the detailed protocol for culturing of hepatocytes, their exposure to toxicants as well as sample collection, including RNA isolation, RNA target preparation and finally the hybridization to gene chips for microarray expression analysis.

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.

Toward predictive models for drug-induced liver injury in humans: are we there yet?

Drug-induced liver injury (DILI) is a frequent cause for the termination of drug development programs and a leading reason of drug withdrawal from the marketplace. Unfortunately, the current preclinical testing strategies, including the regulatory-required animal toxicity studies or simple in vitro tests, are insufficiently powered to predict DILI in patients reliably. Notably, the limited predictive power of such testing strategies is mostly attributed to the complex nature of DILI, a poor understanding of its mechanism, a scarcity of human hepatotoxicity data and inadequate bioinformatics capabilities. With the advent of high-content screening assays, toxicogenomics and bioinformatics, multiple end points can be studied simultaneously to improve prediction of clinically relevant DILIs. This review focuses on the current state of efforts in developing predictive models from diverse data sources for potential use in detecting human hepatotoxicity, and also aims to provide perspectives on how to further improve DILI prediction.

WITHDRAWN: Systems Biology and Immune Aging

The Publisher regrets that this article is an accidental duplication of anarticle that has already been published, http://dx.doi.org/10.1016/j.imlet.2014.09.009. The duplicate article has therefore been withdrawn.

The plant decapeptide OSIP108 can alleviate mitochondrial dysfunction induced by cisplatin in human cells

We investigated the effect of the Arabidopsis thaliana-derived decapeptide OSIP108 on human cell tolerance to the chemotherapeutic agent cisplatin (Cp), which induces apoptosis and mitochondrial dysfunction. We found that OSIP108 increases the tolerance of HepG2 cells to Cp and prevents Cp-induced changes in basic cellular metabolism. More specifically, we demonstrate that OSIP108 reduces Cp-induced inhibition of respiration, decreases glycolysis and prevents Cp-uptake in HepG2 cells. Apart from its protective action against Cp in human cells, OSIP108 also increases the yeast Saccharomyces cerevisiae tolerance to Cp. A limited yeast-based study of OSIP108 analogs showed that cyclization does not severely affect its activity, which was further confirmed in HepG2 cells. Furthermore, the similarity in the activity of the d-stereoisomer (mirror image) form of OSIP108 with the l-stereoisomer suggests that its mode of action does not involve binding to a stereospecific receptor. In addition, as OSIP108 decreases Cp uptake in HepG2 cells and the anti-Cp activity of OSIP108 analogs without free cysteine is reduced, OSIP108 seems to protect against Cp-induced toxicity only partly via complexation. Taken together, our data indicate that OSIP108 and its cyclic derivatives can protect against Cp-induced toxicity and, thus, show potential as treatment options for mitochondrial dysfunction- and apoptosis-related conditions.

Determination of liver specific toxicities in rat hepatocytes by high content imaging during 2-week multiple treatment

DILI is a major safety issue during drug development and one of the leading causes for market withdrawal. Despite many efforts made in the past, the prediction of DILI using in vitro models remains very unreliable. In the present study, the well-established hepatocyte Collagen I-Matrigel™ sandwich culture was used, mimicking chronic drug treatment after multiple incubations for 14 days. Ten drugs associated with different types of specific preclinical and clinical liver injury were evaluated at non-cytotoxic concentrations. Mrp2-mediated transport, intracellular accumulation of neutral lipids and phospholipids were selected as functional endpoints by using Cellomics™ Arrayscan® technology and assessed at five timepoints (day 1, 3, 7, 10, 14). Liver specific functional impairments after drug treatment were enhanced over time and could be monitored by HCI already after few days and before cytotoxicity. Phospholipidosis-inducing drugs Chlorpromazine and Amiodarone displayed the same response as in vivo. Cyclosporin A, Chlorpromazine, and Troglitazone inhibited Mrp2-mediated biliary transport, correlating with in vivo findings. Steatosis remained difficult to be reproduced under the current in vitro testing conditions, resulting into false negative and positive responses. The present results suggest that the repeated long-term treatment of rat hepatocytes in the Collagen I-Matrigel™ sandwich configuration might be a suitable tool for safety profiling of the potential to induce phospholipidosis and impair Mrp2-mediated transport processes, but not to predict steatosis.

A testing strategy to predict risk for drug-induced liver injury in humans using high-content screen assays and the 'rule-of-two' model

Drug-induced liver injury (DILI) is a major cause of drug failures in both the preclinical and clinical phase. Consequently, improving prediction of DILI at an early stage of drug discovery will reduce the potential failures in the subsequent drug development program. In this regard, high-content screening (HCS) assays are considered as a promising strategy for the study of DILI; however, the predictive performance of HCS assays is frequently insufficient. In the present study, a new testing strategy was developed to improve DILI prediction by employing in vitro assays that was combined with the RO2 model (i.e., 'rule-of-two' defined by daily dose ≥100 mg/day & logP ≥3). The RO2 model was derived from the observation that high daily doses and lipophilicity of an oral medication were associated with significant DILI risk in humans. In the developed testing strategy, the RO2 model was used for the rational selection of candidates for HCS assays, and only the negatives predicted by the RO2 model were further investigated by HCS. Subsequently, the effects of drug treatment on cell loss, nuclear size, DNA damage/fragmentation, apoptosis, lysosomal mass, mitochondrial membrane potential, and steatosis were studied in cultures of primary rat hepatocytes. Using a set of 70 drugs with clear evidence of clinically relevant DILI, the testing strategy improved the accuracies by 10 % and reduced the number of drugs requiring experimental assessment by approximately 20 %, as compared to the HCS assay alone. Moreover, the testing strategy was further validated by including published data (Cosgrove et al. in Toxicol Appl Pharmacol 237:317-330, 2009) on drug-cytokine-induced hepatotoxicity, which improved the accuracies by 7 %. Taken collectively, the proposed testing strategy can significantly improve the prediction of in vitro assays for detecting DILI liability in an early drug discovery phase.

Detection of radicals in single droplets of oil-in-water emulsions with the lipophilic fluorescent probe BODIPY(665/676) and confocal laser scanning microscopy

Lipid oxidation is a widespread phenomenon in foods and other systems of biological origin. Detection methods for early stages of lipid oxidation are in demand to understand the progress of oxidation in space and time. The fluorescence spectrum of the nonpolar fluorescent probe BODIPY(665/676) changes upon reacting with peroxyl radicals originating from 2,2'-azobis(2,4-dimethyl)valeronitrile and tert-butoxyl radicals generated from di-tert-butylperoxide. The excitation wavelength of the main peak of BODIPY(665/676) was 675 nm in the fluorometer, and 670 nm under the microscope, and the optimum excitation wavelength for the secondary peak of BODIPY(665/676) was 580 nm. Advantages of using BODIPY(665/676) are fewer problems with autofluorescence and the possibility of combining several fluorescent probes that are excited and emitted at lower wavelengths. However, because of the spectrum of the probe, specific lasers and detectors are needed for optimal imaging under the microscope. Furthermore, BODIPY(665/676) is resistant to photobleaching at both excitation wavelengths, 670 and 580 nm. In diffusion studies, BODIPY(665/676) is highly lipophilic, remaining in the lipid phase and not diffusing into the aqueous phase or between lipid droplets.

High-content analysis in toxicology: screening substances for human toxicity potential, elucidating subcellular mechanisms and in vivo use as translational safety biomarkers

High-content analysis (HCA) of in vitro biochemical and morphological effects of classic (small molecule) drugs and chemicals is concordant with potential for human toxicity. For hepatotoxicity, concordance is greater for cytotoxic effects assessed by HCA than for conventional cytotoxicity tests and for regulatory animal toxicity studies. Additionally, HCA identifies chronic toxicity potential, and drugs producing idiosyncratic adverse reactions and/or toxic metabolites are also identified by HCA. Mechanistic information on the subcellular basis for the toxicity is frequently identified, including various mitochondrial effects, oxidative stress, calcium dyshomeostasis, phospholipidosis, apoptosis and antiproliferative effects, and a fingerprinting of the sequence and pattern of subcellular events. As these effects are frequently non-specific and affect many cell types, some toxicities may be detected and monitored by HCA of peripheral blood cells, such as for anticancer and anti-infective drugs. Critical methodological and interpretive features are identified that are critical to the effectiveness of the HCA cytotoxicity assessment, including the need for multiple days of exposure of cells to drug, use of a human hepatocyte cell line with metabolic competence, assessment of multiple pre-lethal effects in individual live cells, consideration of hormesis, the need for interpretation of relevance of cytotoxicity concentration compared to efficacy concentration and quality management. Limitations of the HCA include assessment of drugs that act on receptors, transporters or processes not found in hepatocytes. HCA may be used in a) screening lead candidates for potential human toxicity in drug discovery alongside of in vitro assessment of efficacy and pharmacokinetics, b) elucidating mechanisms of toxicity and c) monitoring in vivo toxicity of drugs with known toxicity of known mechanism.

Quantitative high content imaging of cellular adaptive stress response pathways in toxicity for chemical safety assessment

Over the past decade, major leaps forward have been made on the mechanistic understanding and identification of adaptive stress response landscapes underlying toxic insult using transcriptomics approaches. However, for predictive purposes of adverse outcome several major limitations in these approaches exist. First, the limited number of samples that can be analyzed reduces the in depth analysis of concentration-time course relationships for toxic stress responses. Second these transcriptomics analysis have been based on the whole cell population, thereby inevitably preventing single cell analysis. Third, transcriptomics is based on the transcript level, totally ignoring (post)translational regulation. We believe these limitations are circumvented with the application of high content analysis of relevant toxicant-induced adaptive stress signaling pathways using bacterial artificial chromosome (BAC) green fluorescent protein (GFP) reporter cell-based assays. The goal is to establish a platform that incorporates all adaptive stress pathways that are relevant for toxicity, with a focus on drug-induced liver injury. In addition, cellular stress responses typically follow cell perturbations at the subcellular organelle level. Therefore, we complement our reporter line panel with reporters for specific organelle morphometry and function. Here, we review the approaches of high content imaging of cellular adaptive stress responses to chemicals and the application in the mechanistic understanding and prediction of chemical toxicity at a systems toxicology level.

A simple transcriptomic signature able to predict drug-induced hepatic steatosis

It is estimated that only a few marketed drugs are able to directly induce liver steatosis. However, many other drugs may exacerbate or precipitate fatty liver in the presence of other risk factors or in patients prone to non-alcoholic fatty liver disease. On the other hand, current in vitro tests for drug-induced steatosis in preclinical research are scarce and not very sensitive or reproducible. In the present study, we have investigated the effect of well-characterized steatotic drugs on the expression profile of 47 transcription factors (TFs) in human hepatoma HepG2 cells and found that these drugs are able to up- and down-regulate a substantial number of these factors. Multivariate data analysis revealed a common TF signature for steatotic drugs, which consistently and significantly repressed FOXA1, HEX and SREBP1C in cultured cells. This signature was also observed in the livers of rats and in cultured human hepatocytes. Therefore, we selected these three TFs as predictive biomarkers for iatrogenic steatosis. With these biomarkers, a logistic regression analysis yielded a predictive model, which was able to correctly classify 92 % of drugs. The developed algorithm also predicted that ibuprofen, nifedipine and irinotecan are potential steatotic drugs, whereas troglitazone is not. In summary, this is a sensitive, specific and simple RT-PCR test that can be easily implemented in preclinical drug development to predict drug-induced steatosis. Our results also indicate that steatotic drugs affect expression of both common and specific subsets of TF and lipid metabolism genes, thus generating complex transcriptomic responses that cause or contribute to steatosis in hepatocytes.

Circulating extracellular vesicles as a potential source of new biomarkers of drug-induced liver injury

Like most cell types, hepatocytes constantly produce extracellular vesicles (EVs) such as exosomes and microvesicles that are released into the circulation to transport signaling molecules and cellular waste. Circulating EVs are being vigorously explored as biomarkers of diseases and toxicities, including drug-induced liver injury (DILI). Emerging data suggest that (a) blood-borne EVs contain liver-specific mRNAs and microRNAs (miRNAs), (b) the levels can be remarkably elevated in response to DILI, and (c) the increases correlate well with classical measures of liver damage. The expression profile of mRNAs in EVs and the compartmentalization of miRNAs within EVs or other blood fractions were found to be indicative of the offending drug involved in DILI, thus providing more informative assessment of liver injury than using alanine aminotransferase alone. EVs in the urine and cell culture medium were also found to contain proteins or mRNAs that were indicative of DILI. However, major improvements in EV isolation methods are needed for the discovery, evaluation, and quantification of possible DILI biomarkers in circulating EVs.

Predictivity of dog co-culture model, primary human hepatocytes and HepG2 cells for the detection of hepatotoxic drugs in humans

Drug induced liver injury (DILI) is a major cause of attrition during early and late stage drug development. Consequently, there is a need to develop better in vitro primary hepatocyte models from different species for predicting hepatotoxicity in both animals and humans early in drug development. Dog is often chosen as the non-rodent species for toxicology studies. Unfortunately, dog in vitro models allowing long term cultures are not available. The objective of the present manuscript is to describe the development of a co-culture dog model for predicting hepatotoxic drugs in humans and to compare the predictivity of the canine model along with primary human hepatocytes and HepG2 cells. After rigorous optimization, the dog co-culture model displayed metabolic capacities that were maintained up to 2 weeks which indicates that such model could be also used for long term metabolism studies. Most of the human hepatotoxic drugs were detected with a sensitivity of approximately 80% (n=40) for the three cellular models. Nevertheless, the specificity was low approximately 40% for the HepG2 cells and hepatocytes compared to 72.7% for the canine model (n=11). Furthermore, the dog co-culture model showed a higher superiority for the classification of 5 pairs of close structural analogs with different DILI concerns in comparison to both human cellular models. Finally, the reproducibility of the canine system was also satisfactory with a coefficient of correlation of 75.2% (n=14). Overall, the present manuscript indicates that the dog co-culture model may represent a relevant tool to perform chronic hepatotoxicity and metabolism studies.

Screen for small molecules increasing the mitochondrial membrane potential

The identification of small molecules that positively modulate the mitochondrial respiratory function has broad applications in fundamental research, therapeutic target validation, and drug discovery. We present an approach in which primary screens for mitochondrial function in yeast are used to efficiently identify a subset of high-value compounds that can in turn be rapidly tested against a broad range of mammalian cell lines. The ability of the yeast assay to successfully identify in a high-throughput format hit compounds that increase the mitochondrial membrane potential and adenosine triphosphate (ATP) levels by as little as 15% was demonstrated. In this study, 14 hits were identified from a collection of 13,680 compounds. Secondary testing with myotubes, fibroblasts, and PC-12 and HepG2 cells identified two compounds increasing ATP levels in hepatocytes and two other compounds increasing ATP in fibroblasts. The effect on hepatocytes was further studied using genomic and mitochondrial proteomic tools to characterize the changes induced by the two compounds. Changes in the accumulation of a series of factors involved in early gene response or apoptosis or linked to metabolic functions (i.e., β-Klotho, RORα, PGC-1α, G6PC, IGFBP1, FTL) were discovered.

Multiparametric evaluation of the cytoprotective effect of the Mangifera indica L. stem bark extract and mangiferin in HepG2 cells

OBJECTIVE

Mango (Mangifera indica L.) stem bark extract (MSBE) is a natural product with biological properties and mangiferin is the major component. This paper reported the evaluation of the protective effects of MSBE and mangiferin against the toxicity induced in HepG2 cells by tert-butyl hydroperoxide or amiodarone.

METHOD

Nuclear morphology, cell viability, intracellular calcium concentration and reactive oxygen species (ROS) production were measured by using a high-content screening multiparametric assay.

KEY FINDINGS

MSBE and mangiferin produced no toxicity below 500 mg/ml doses. A marked recovery in cell viability, which was reduced by the toxicants, was observed in cells pre-exposed to MSBE or mangiferin at 5-100 mg/ml doses. We also explored the possible interaction of both products over P-glycoprotein (P-gp). MSBE and mangiferin above 100 mg/ml inhibited the activity of P-gp in HepG2 cells.

CONCLUSIONS

MSBE and mangiferin showed cytoprotective effects of against oxidative damage and mitochondrial toxicity induced by xenobiotics to human hepatic cells but it seemed that other constituents of the extract could contribute to MSBE protective properties. In addition, the drug efflux should be taken into account because of the inhibition of the P-gp function observed in those cells exposed to both natural products.

"Drugs on oxygen": an update and perspective on the role of cytochrome P450 testing in pharmacology

Low hit rates for lead compounds and high attrition remain a major problem for drug development. The reasons for compound failure range from poor pharmacokinetics to toxic metabolites and adverse drug interactions; all of which are frequently mediated by cytochrome P450-dependent monooxygenases (CYPs). However, despite some 30 years of assay development and refinement, CYP metabolism remains a critical issue during drug development. While current testing strategies succeed in characterizing single substance toxicity, they are challenged by practical issues such as assay standardization or complex scenarios such as multidrug usage. This editorial summarizes where we stand and highlights the major challenges we face with CYPs in drug development today. The article also tries to spell out the future direction of CYP testing. The latter will depend on the extended inclusion of polypharmacy into testing strategies, as well as on our capability to make use of upcoming complex in vitro test systems and their inclusion into tiered testing strategies.