Multiendpoint mechanistic profiling of hepatotoxicants in HepG2/C3A human hepatoma cells and novel statistical approaches for development of a prediction model for acute hepatotoxicity

In Vitro Hepatotoxicity of Routinely Used Opioids and Sedative Drugs

A hepatocyte cell line was used to determine the hepatotoxicity of sedatives and opioids, as the hepatotoxicity of these drugs has not yet been well characterized. This might pose a threat, especially to critically ill patients, as they often receive high cumulative doses for daily analgosedation and often already have impaired liver function due to an underlying disease or complications during treatment. A well-established biosensor based on HepG2/C3A cells was used for the determination of the hepatotoxicity of commonly used sedatives and opioids in the intensive care setting (midazolam, propofol, s-ketamin, thiopental, fentanyl, remifentanil, and sufentanil). The incubation time was 2 × 3 days with clinically relevant (Cmax) and higher concentrations (C5× and C10×) of each drug in cell culture medium or human plasma. Afterward, we measured the cell count, vitality, lactate dehydrogenase (LDH), mitochondrial dehydrogenase activity, cytochrome P 450 1A2 (CYP1A2), and albumin synthesis. All tested substances reduced the viability of hepatocyte cells, but sufentanil and remifentanil showed more pronounced effects. The cell count was diminished by sufentanil in both the medium and plasma and by remifentanil only in plasma. Sufentanil and remifentanil also led to higher values of LDH in the cell culture supernatant. A reduction of mitochondrial dehydrogenase activity was seen with the use of midazolam and s-ketamine. Microalbumin synthesis was reduced in plasma after its incubation with higher concentrations of sufentanil and remifentanil. Remifentanil and s-ketamine reduced CYP1A2 activity, while propofol and thiopental increased it. Our findings suggest that none of the tested sedatives and opioids have pronounced hepatotoxicity. Sufentanil, remifentanil, and s-ketamine showed moderate hepatotoxic effects in vitro. These drugs should be given with caution to patients vulnerable to hepatotoxic drugs, e.g., patients with pre-existing liver disease or liver impairment as part of their underlying disease (e.g., hypoxic hepatitis or cholestatic liver dysfunction in sepsis). Further studies are indicated for this topic, which may use more complex cell culture models and global pharmacovigilance reports, addressing the limitation of the used cell model: HepG2/C3A cells have a lower metabolic capacity due to their low levels of CYP enzymes compared to primary hepatocytes. However, while the test model is suitable for parental substances, it is not for toxicity testing of metabolites.

Influence of Antibiotics on Functionality and Viability of Liver Cells In Vitro

(1) Antibiotics are an important weapon in the fight against serious bacterial infections and are considered a common cause of drug-induced liver injury (DILI). The hepatotoxicity of many drugs, including antibiotics, is poorly analyzed in human in vitro models. (2) A standardized assay with a human hepatoma cell line was used to test the hepatotoxicity of various concentrations (Cmax, 5× Cmax, and 10× Cmax) of antibiotics. In an ICU, the most frequently prescribed antibiotics, ampicillin, cefepime, cefuroxime, levofloxacin, linezolid, meropenem, rifampicin, tigecycline, and vancomycin, were incubated with HepG2/C3A cells for 6 days. Cell viability (XTT assay, LDH release, and vitality), albumin synthesis, and cytochrome 1A2 activity were determined in cells. (3) In vitro, vancomycin, rifampicin, and tigecycline showed moderate hepatotoxic potential. The antibiotics ampicillin, cefepime, cefuroxime, levofloxacin, linezolid, and meropenem were associated with mild hepatotoxic reactions in test cells incubated with the testes Cmax concentration. Rifampicin and cefuroxime showed significantly negative effects on the viability of test cells. (4) Further in vitro studies and global pharmacovigilance reports should be conducted to reveal underlying mechanism of the hepatotoxic action of vancomycin, rifampicin, tigecycline, and cefuroxime, as well as the clinical relevance of these findings.

In vitro models for non-alcoholic fatty liver disease: Emerging platforms and their applications

Non-alcoholic fatty liver disease (NAFLD) represents a global healthcare challenge, affecting 1 in 4 adults, and death rates are predicted to rise inexorably. The progressive form of NAFLD, non-alcoholic steatohepatitis (NASH), can lead to fibrosis, cirrhosis, and hepatocellular carcinoma. However, no medical treatments are licensed for NAFLD-NASH. Identifying efficacious therapies has been hindered by the complexity of disease pathogenesis, a paucity of predictive preclinical models and inadequate validation of pharmacological targets in humans. The development of clinically relevant in vitro models of the disease will pave the way to overcome these challenges. Currently, the combined application of emerging technologies (e.g., organ-on-a-chip/microphysiological systems) and control engineering approaches promises to unravel NAFLD biology and deliver tractable treatment candidates. In this review, we will describe advances in preclinical models for NAFLD-NASH, the recent introduction of novel technologies in this space, and their importance for drug discovery endeavors in the future.

In vitro models for non-alcoholic fatty liver disease: Emerging platforms and their applications

Non-alcoholic fatty liver disease (NAFLD) represents a global healthcare challenge, affecting 1 in 4 adults, and death rates are predicted to rise inexorably. The progressive form of NAFLD, non-alcoholic steatohepatitis (NASH), can lead to fibrosis, cirrhosis, and hepatocellular carcinoma. However, no medical treatments are licensed for NAFLD-NASH. Identifying efficacious therapies has been hindered by the complexity of disease pathogenesis, a paucity of predictive preclinical models and inadequate validation of pharmacological targets in humans. The development of clinically relevant in vitro models of the disease will pave the way to overcome these challenges. Currently, the combined application of emerging technologies (e.g., organ-on-a-chip/microphysiological systems) and control engineering approaches promises to unravel NAFLD biology and deliver tractable treatment candidates. In this review, we will describe advances in preclinical models for NAFLD-NASH, the recent introduction of novel technologies in this space, and their importance for drug discovery endeavors in the future.

Ensemble Models Based on QuBiLS-MAS Features and Shallow Learning for the Prediction of Drug-Induced Liver Toxicity: Improving Deep Learning and Traditional Approaches

Drug-induced liver injury (DILI) is a key safety issue in the drug discovery pipeline and a regulatory concern. Thus, many in silico tools have been proposed to improve the hepatotoxicity prediction of organic-type chemicals. Here, classifiers for the prediction of DILI were developed by using QuBiLS-MAS 0-2.5D molecular descriptors and shallow machine learning techniques, on a training set composed of 1075 molecules. The best ensemble model build, E13, was obtained with good statistical parameters for the learning series, namely, the following: accuracy = 0.840, sensibility = 0.890, specificity = 0.761, Matthew's correlation coefficient = 0.660, and area under the ROC curve = 0.904. The model was also satisfactorily evaluated with Y-scrambling test, and repeated k-fold cross-validation and repeated k-holdout validation. In addition, an exhaustive external validation was also carried out by using two test sets and five external test sets, with an average accuracy value equal to 0.854 (±0.062) and a coverage equal to 98.4% according to its applicability domain. A statistical comparison of the performance of the E13 model, with regard to results and tools (e.g., Padel DDPredictor Software, Deep Learning DILIserver, and Vslead) reported in the literature, was also performed. In general, E13 presented the best global performance in all experiments. The sum of the ranking differences procedure provided a very similar grouping pattern to that of the M-ANOVA statistical analysis, where E13 was identified as the best model for DILI predictions. A noncommercial and fully cross-platform software for the DILI prediction was also developed, which is freely available at http://tomocomd.com/apps/ptoxra. This software was used for the screening of seven data sets, containing natural products, leads, toxic materials, and FDA approved drugs, to assess the usefulness of the QSAR models in the DILI labeling of organic substances; it was found that 50-92% of the evaluated molecules are positive-DILI compounds. All in all, it can be stated that the E13 model is a relevant method for the prediction of DILI risk in humans, as it shows the best results among all of the methods analyzed.

Liver toxicity of anthraquinones: A combined in vitro cytotoxicity and in silico reverse dosimetry evaluation

Anthraquinones are found in a variety of consumer products such as dietary supplements, traditional Chinese medicines, and drugs. Along with their widespread use, potential safety concerns have emerged, especially liver toxicity. Therefore, there is a need to conduct rapid and inexpensive safety assessment for anthraquinones due to a lack of animal and human toxicological data. Here, a combined in vitro cytotoxicity and in silico reverse dosimetry approach was adopted to consider the potential human liver toxicity of 16 anthraquinones and derivatives. First, cytotoxicity (EC₅₀) in two human liver cell lines (HepG2/C3A and HuH-7) was measured under two conditions (single and repeated dosing, 72 h). Second, toxic doses (D_tox) required to yield plasma steady-state concentrations (C_ss) equal to in vitro EC₅₀ values were predicted by reverse dosimetry simulation using a PBPK model. Finally, D_tox was compared to literature-derived estimated daily intake (EDI) of anthraquinones to assess safety. Among the 16 anthraquinones, rhein was identified as a potential hepatotoxicant due to a combination of cytotoxicity, plasma concentration, and daily intake level. These in vitro and in silico findings provide preliminary data and guidance for further animal and clinical studies to confirm liver toxicity of anthraquinones.

Hepatotoxicity of Antimycotics Used for Invasive Fungal Infections: In Vitro Results

Purpose. Drug-induced liver injury (DILI) is the most common cause of liver injury and a serious clinical problem; antimycotics are involved in approximately 3% of all DILI cases. The hepatotoxicity of many drugs, including the antimycotics, is poorly screened in human models. Methods. In a standardized assay the cytotoxicity on hepatocytes of different concentrations (Cmax, 5x Cmax, and 10x Cmax) of the antimycotics used for systemic infections was tested. Anidulafungin (ANI), liposomal amphotericerin B (L-AmB), caspofungin (CASPO), fluconazole (FLUCO), and voriconazole (VORI) were incubated with HepG2/C3A cells. After incubation, the viability of cells (XTT test, LDH release, trypan blue staining), the synthesis of albumin, the cytochrome 1A2 activity, and the cell death (DNA fragmentation) were determined. Kruskal-Wallis and Mann-Whitney tests were used for statistical analyses. Results. L-AmB, ANI, and CASPO showed a mild hepatotoxicity in the Cmax concentrations. Higher concentrations of anidulafungin led to a severe impairment of hepatocyte viability and function. The azoles FLUCO and VORI had a higher hepatotoxic potential in all concentrations. Conclusion. Antimycotics, especially azoles, used for systemic infections should be given with caution in patient with liver insufficiency or liver failure or high risk for this; therefore, therapeutic drug monitoring should be used. Further studies with this approach are encouraged.

A transcriptomic study suggesting human iPSC-derived hepatocytes potentially offer a better in vitro model of hepatotoxicity than most hepatoma cell lines

Hepatocytes derived from human induced pluripotent stem cells (iPSCs) hold great promise as an in vitro liver model by virtue of their unlimited long-term supply, stability and consistency in functionality, and affordability of donor diversity. However, the suitability of iPSC-derived hepatocytes (iPSC-Heps) for toxicology studies has not been fully validated. In the current study, we characterized global gene expression profiles of iPSC-Heps in comparison to those of primary human hepatocytes (PHHs) and several human hepatoma cell lines (HepaRG, HuH-7, HepG2, and HepG2/C3A). Furthermore, genes associated with hepatotoxicity, drug-metabolizing enzymes, transporters, and nuclear receptors were extracted for more detailed comparisons. Our results showed that iPSC-Heps correlate more closely to PHHs than hepatoma cell lines, suggesting that iPSC-Heps had a relatively mature hepatic phenotype that more closely resembles that of adult hepatocytes. HepaRG was the sole exception but nonetheless suffers from lack of donor diversity and poor prediction of hepatotoxicity. The effects of sex differences and DMSO treatment on gene expression of the cellular models were also investigated. Overall, the results presented in the current study suggest that iPSC-Heps represent a reproducible source of human hepatocytes and a promising in vitro model for hepatotoxicity evaluation. Further studies are needed to develop a robust protocol for hepatocyte differentiation towards a more mature adult phenotype.

STAT3 Inhibition Suppresses Hepatic Stellate Cell Fibrogenesis: HJC0123, a Potential Therapeutic Agent for Liver Fibrosis

Hepatic Stellate Cells (HSCs) are the major source of the excessive extracellular matrix (ECM) production that replaces liver parenchyma with fibrous tissue during liver fibrosis. The signal transducer and activator of transcription 3 (STAT3) promotes HCSs survival, proliferation, and activation contributing to fibrogenesis. We have previously used a fragment-based drug design approach and have discovered a novel STAT3 inhibitor, HJC0123. Here, we explored the biological effects of HJC0123 on the fibrogenic properties of HSCs. HJC0123 treatment resulted in the inhibition of HSCs proliferation at submicromolar concentrations. HJC0123 reduced the phosphorylation, nuclear translocation, and transcriptional activity of STAT3. It decreased the expression of STAT3-regulated proteins, induced cell cycle arrest, promoted apoptosis and downregulated SOCS3. HJC0123 treatment inhibited HSCs activation and downregulated ECM protein fibronectin and type I collagen expression. In addition, HJC0123 increased IL-6 production and decreased TGF-β induced Smad2/3 phosphorylation. These results demonstrate that HJC0123 represents a novel STAT3 inhibitor that suppresses the fibrogenic properties of HSCs, suggesting its therapeutic potential in liver fibrosis.

Combined cytotoxic effects of pesticide mixtures present in the Chinese diet on human hepatocarcinoma cell line

Consumers might be simultaneously exposed to several pesticide residues contained in their food. Based on the results of previous studies, 20 pesticides were selected due to their high exposure levels to which the Chinese population is likely exposed through the diet. The purpose of this study was to measure the cytotoxicity of these pesticides in HepG2 cells in vitro, as an alternative approach to assess the toxicity of chemicals. Then, the pesticides and some of the mixtures with comparatively high cell-proliferating inhibitory activities were selected to test the cellular ROS level and apoptosis-related protein Caspase-3/7 content in HepG2 cells. The combined effects of these pesticide mixtures with the prediction was based on a combination index (CI)-isobologram equation and the pesticide combinations exhibited various types of interactions (synergism, antagonism, and additivity). Two individuals, one binary combinations, and three uniform design (UD) mixtures of the pesticides were found to have significant cytotoxic effects, along with significant time- and dose-dependent induction of caspase-3/7 activity in vitro, indicating that cytotoxicity caused by these pesticides might be attributed to the pro-oxidative and apoptosis induced potential.

Human Hepatic HepaRG Cells Maintain an Organotypic Phenotype with High Intrinsic CYP450 Activity/Metabolism and Significantly Outperform Standard HepG2/C3A Cells for Pharmaceutical and Therapeutic Applications

Conventional in vitro human hepatic models for drug testing are based on the use of standard cell lines derived from hepatomas or primary human hepatocytes (PHHs). Limited availability, interdonor functional variability and early phenotypic alterations in PHHs restrict their use, whilst standard cell lines such as HepG2 lack a substantial and variable set of liver‐specific functions such as CYP450 activity. Alternatives include the HepG2‐derivative C3A cells selected as a more differentiated and metabolically active hepatic phenotype. Human HepaRG cells are an alternative organotypic co‐culture model of hepatocytes and cholangiocytes reported to maintain in vivo‐like liver‐specific functions, including intact Phase I–III drug metabolism. In this study, we compared C3A and human HepaRG cells using phenotypic profiling, CYP450 activity and drug metabolism parameters to assess their value as hepatic models for pre‐clinical drug testing or therapeutics. Compared with C3As, HepaRG co‐cultures exhibit a more organotypic phenotype, including evidence of hepatic polarity with the strong expression of CYP3A4, the major isoform involved in the metabolism of over 60% of marketed drugs. Significantly greater CYP450 activity and expression of CYP1A2, CYP2E1 and CYP3A4 genes in HepaRG cells (comparable with that of human liver tissue) was demonstrated. Moreover, HepaRG cells also preferentially expressed the hepatic integrin α₅β₁ – an important modulator of cell behaviour including growth and survival, differentiation and polarity. Drug metabolite profiling of phenacetin (CYP1A2) and testosterone (CYP3A4) using LC‐MS/MS and HPLC, respectively, revealed that HepaRGs had more intact (Phase I–II) metabolism profile. Thus, HepaRG cells significantly outperform C3A cells for the potential pharmaceutical and therapeutic applications.

Use of the Combination Index to determine interactions between plant-derived phenolic acids on hepatotoxicity endpoints in human and rat hepatoma cells

The beneficial or adverse effects of isolated phytochemicals are not always concordant with effects of the botanical dietary supplements from which they were derived. This disparity could be due to interactions between the various phytochemicals present in the whole plant. The phenolic acids, rosmarinic acid (RA), caffeic acid (CA) and ferulic acid (FA) are widely present in foods and dietary supplements, and they are assumed to exert various beneficial biological effects. However, there is little data on the potential biological interactions of these three phenolic acids which commonly occur together and are linked metabolically. In the present study, liver toxicity of the three phenolic acids was assessed on the three compounds singly and in various binary and one ternary combinations. A series of in vitro endpoints relevant to liver toxicity were evaluated in both a human (HepG2/C3A) and rat (MH1C1) hepatocyte cell line. The Combination Index (CI) was calculated for each endpoint from both the concentration responses of the single compounds and the responses of the various binary and ternary mixtures. Both synergistic and antagonistic interactions were observed for some endpoints and some combinations of test agents. Interactions were most prevalent in measures of oxidative stress and cytochrome P450 activities in both cell types. There was only a 53% concordance between the rat and human cells which may be suggestive of species differences. The data suggest an approach for better characterizing the beneficial or adverse effects of complex botanical products through evaluation of interactions between individual phytochemical components.

Determination of drug toxicity using 3D spheroids constructed from an immortal human hepatocyte cell line

Numerous publications have documented that the immortal cells grown in three-dimensional (3D) cultures possess physiological behavior, which is more reminiscent of their parental organ than when the same cells are cultivated using classical two-dimensional (2D) culture techniques. The goal of this study was to investigate whether this observation could be extended to the determination of LD₅₀ values and whether 3D data could be correlated to in vivo observations. We developed a noninvasive means to estimate the amount of protein present in a 3D spheroid from it is planar area (± 21%) so that a precise dose can be provided in a manner similar to in vivo studies. This avoided correction of the actual dose given based on a protein determination after treatment (when some cells may have lysed). Conversion of published in vitro LC₅₀ data (mM) for six common drugs (acetaminophen, amiodarone, diclofenac, metformin, phenformin, and valproic acid) to LD₅₀ data (mg compound/mg cellular protein) showed that the variation in LD₅₀ values was generally less than that suggested by the original LC₅₀ data. Toxicological analysis of these six compounds in 3D spheroid culture (either published or presented here) demonstrated similar LD₅₀ values. Although in vitro 2D HepG2 data showed a poor correlation, the primary hepatocyte and 3D spheroid data resulted in a much higher degree of correlation with in vivo lethal blood plasma levels. These results corroborate that 3D hepatocyte cultures are significantly different from 2D cultures and are more representative of the liver in vivo.

Cellular glutathione in fatty liver in vitro models

The range of non-alcoholic fatty liver disease (NAFLD) includes simple hepatic steatosis, the inflammatory non-alcoholic steatohepatitis (NASH), fibrosis and cirrhosis. The accumulation of specific lipids in hepatocytes has been associated with oxidative stress and progression of the disease. Elevated serum free fatty acids and hepatocyte lipotoxicity can be studied in an in vitro cellular model. For this purpose, we cultured the human liver cell line, HepG2/C3A, in medium supplemented with increasing amounts of oleic acid (C18:1) and evaluated oxidative stress by measuring the content of the cellular antioxidant, glutathione (GSH). We observed a dose-dependent steatosis, as determined by Nile Red staining, with concurrent increases of GSH; similar findings were also observed in cultured human hepatocytes. Cells cultured with palmitic acid (C16:0) or the combination oleic/palmitic acids (2:1 ratio) also exhibited a dose-dependent increase of GSH; however palmitic-supplemented cultures did not sustain the GSH increase after 24h. We also detected an increase in the formation of lipid peroxides (LPO) indicating that the increase of GSH was a cellular mechanism that may be related to the high exposure of fatty acids. The results of this in vitro study suggest an antioxidant response against fat overloading and indicate potential differences in response to specific fatty acid-induced hepatic steatosis and associated lipotoxicity.

Effects of dietary phenolics and botanical extracts on hepatotoxicity-related endpoints in human and rat hepatoma cells and statistical models for prediction of hepatotoxicity

Toxicity assessment of botanical materials is difficult because they are typically complex mixtures of phytochemicals. In the present study, 16 phenolics were tested in both human (HepG2/C3A) and rat (MH1C1) hepatoma cells using a battery of eight toxicity endpoints. Cluster analysis was used to group the phenolics into four clusters for each cell type. Comparison of overall and individual liver activity of phenolics on both human and rat hepatoma cell lines showed significant differences for some endpoints. However, the cluster membership was similar across both cell types with the majority of phenolics clustering with the solvent control group (cluster 1). Each cell type produced a cluster of compounds with reported in vivo liver toxicity (cluster 2). Five herbal extracts were prepared and then tested as above. Using the cluster model developed with the phenolics, in the HepG2/C3A cells green tea was assigned to cluster 2 and the remaining four extracts to cluster 1. In the MH1C1 cells, green tea and thyme were assigned to cluster 2, cinnamon to cluster 4, and juniper berry and peppermint to cluster 1. The data suggest that this in vitro model may be useful for identifying hepatotoxic phenolics and botanical preparations rich in phenolics.

General review on in vitro hepatocyte models and their applications

In vitro hepatocyte models represent very useful systems in both fundamental research and various application areas. Primary hepatocytes appear as the closest model for the liver in vivo. However, they are phenotypically unstable, have a limited life span and in addition, exhibit large interdonor variability when of human origin. Hepatoma cell lines appear as an alternative but only the HepaRG cell line exhibits various functions, including major cytochrome P450 activities, at levels close to those found in primary hepatocytes. In vitro hepatocyte models have brought a substantial contribution to the understanding of the biochemistry, physiology, and cell biology of the normal and diseased liver and in various application domains such as xenobiotic metabolism and toxicity, virology, parasitology, and more generally cell therapies. In the future, new well-differentiated hepatocyte cell lines derived from tumors or from either embryonic or adult stem cells might be expected and although hepatocytes will continue to be used in various fields, these in vitro liver models should allow marked advances, especially in cell-based therapies and predictive and mechanistic hepatotoxicity of new drugs and other chemicals. All models will benefit from new developments in throughput screening based on cell chips coupled with high-content imaging and in toxicogenomics technologies.

Non-Animal Approaches for Consumer Safety Risk Assessments: Unilever's Scientific Research Programme

Non-animal based approaches to risk assessment are now routinely used for assuring consumer safety for some endpoints (such as skin irritation) following considerable investment in developing and applying new methods over the past 20 years. Unilever's research programme into non-animal approaches for safety assessment is currently focused on the application of new technologies to risk assessments in the areas of skin allergy, cancer and general toxicity (including inhalation toxicity). In all of these areas, a long-term investment is essential to increase the scientific understanding of the underlying biological and chemical processes that we believe will ultimately form a sound basis for novel risk assessment approaches. Our research programme in these priority areas consists of in-house research as well as Unilever-sponsored academic research, involvement with EU-funded projects (e.g. Sens-it-iv, carcino-GENOMICS), participation in cross-industry collaborative research (e.g. COLIPA, EPAA) and ongoing involvement with other scientific initiatives on non-animal approaches to risk assessment (e.g. UK NC3Rs, US ‘Human Toxicology Project’ consortium).