Studying the intracellular bile acid concentration and toxicity in drug-induced cholestasis: Comprehensive LC-MS/MS analysis with human liver slices

Drug-induced cholestasis (DIC) is a leading cause of drug-induced liver injury post-drug marketing, characterized by bile flow obstruction and toxic bile constituent accumulation within hepatocytes. This study investigates the toxicity associated with intracellular bile acid (BA) accumulation during DIC development. Using liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis, we examined intracellular BA concentrations in human precision-cut liver slices (PCLS) following the administration of cyclosporin A and chlorpromazine, both with and without an established BA mixture. Our findings indicate toxicity of cyclosporin A upon BA addition, while chlorpromazine's toxicity remained unaffected. Although neither drug led to the accumulation of all BAs intracellularly, BA mixture addition resulted in the accumulation of unconjugated BAs associated with DIC, such as deoxycholic acid (DCA) and cholic acid (CA). Additionally, cyclosporin A increased taurolithocholic acid (TLCA) concentrations. In the absence of the BA mixture, a decrease in conjugated BAs was observed, suggesting inhibition of BA metabolism by cholestatic drugs and warranting further investigation. The evident increase in CA and DCA for both drugs (and TLCA for cyclosporin A), despite not exacerbating toxicity with chlorpromazine, suggests these increases may be related to DIC development and possible toxicity. In conclusion, the current human PCLS model is appropriate for investigating and detecting essential contributors to DIC and can be used in future studies elucidating DIC ex vivo.

In vitro screening of understudied PFAS with a focus on lipid metabolism disruption

Per- and polyfluoroalkyl substances (PFAS) are man-made chemicals used in many industrial applications. Exposure to PFAS is associated with several health risks, including a decrease in infant birth weight, hepatoxicity, disruption of lipid metabolism, and decreased immune response. We used the in vitro cell models to screen six less studied PFAS [perfluorooctane sulfonamide (PFOSA), perfluoropentanoic acid (PFPeA), perfluoropropionic acid (PFPrA), 6:2 fluorotelomer alcohol (6:2 FTOH), 6:2 fluorotelomer sulfonic acid (6:2 FTSA), and 8:2 fluorotelomer sulfonic acid (8:2 FTSA)] for their capacity to activate nuclear receptors and to cause differential expression of genes involved in lipid metabolism. Cytotoxicity assays were run in parallel to exclude that observed differential gene expression was due to cytotoxicity. Based on the cytotoxicity assays and gene expression studies, PFOSA was shown to be more potent than other tested PFAS. PFOSA decreased the gene expression of crucial genes involved in bile acid synthesis and detoxification, cholesterol synthesis, bile acid and cholesterol transport, and lipid metabolism regulation. Except for 6:2 FTOH and 8:2 FTSA, all tested PFAS downregulated PPARA gene expression. The reporter gene assay also showed that 8:2 FTSA transactivated the farnesoid X receptor (FXR). Based on this study, PFOSA, 6:2 FTSA, and 8:2 FTSA were prioritized for further studies to confirm and understand their possible effects on hepatic lipid metabolism.

Role of Hepatocyte Transporters in Drug-Induced Liver Injury (DILI)-In Vitro Testing

Bile acids and bile salts (BA/BS) are substrates of both influx and efflux transporters on hepatocytes. Canalicular efflux transporters, such as BSEP and MRP2, are crucial for the removal of BA/BS to the bile. Basolateral influx transporters, such as NTCP, OATP1B1/1B3, and OSTα/β, cooperate with canalicular transporters in the transcellular vectorial flux of BA/BS from the sinusoids to the bile. The blockage of canalicular transporters not only impairs the bile flow but also causes the intracellular accumulation of BA/BS in hepatocytes that contributes to, or even triggers, liver injury. In the case of BA/BS overload, the efflux of these toxic substances back to the blood via MRP3, MRP4, and OST α/β is considered a relief function. FXR, a key regulator of defense against BA/BS toxicity suppresses de novo bile acid synthesis and bile acid uptake, and promotes bile acid removal via increased efflux. In drug development, the early testing of the inhibition of these transporters, BSEP in particular, is important to flag compounds that could potentially inflict drug-induced liver injury (DILI). In vitro test systems for efflux transporters employ membrane vesicles, whereas those for influx transporters employ whole cells. Additional in vitro pharmaceutical testing panels usually include cellular toxicity tests using hepatocytes, as well as assessments of the mitochondrial toxicity and accumulation of reactive oxygen species (ROS). Primary hepatocytes are the cells of choice for toxicity testing, with HepaRG cells emerging as an alternative. Inhibition of the FXR function is also included in some testing panels. The molecular weight and hydrophobicity of the drug, as well as the steady-state total plasma levels, may positively correlate with the DILI potential. Depending on the phase of drug development, the physicochemical properties, dosing, and cut-off values of BSEP IC₅₀ ≤ 25-50 µM or total C_ss,plasma/BSEP IC₅₀ ≥ 0.1 may be an indication for further testing to minimize the risk of DILI liability.

Construction of a culture protocol for functional bile canaliculi formation to apply human iPS cell-derived hepatocytes for cholestasis evaluation

Cholestatic toxicity causes the failure of pharmaceutical agents during drug development and, thus, should be identified at an early stage of drug discovery and development. The formation of functional bile canaliculi in human hepatocytes is required for in vitro cholestasis toxicity tests conducted during the early stage of drug development. In this study, we investigated the culture conditions required for the formation of bile canaliculi using human-induced pluripotent stem cell-derived hepatocytes (hiPSC-Heps). When hiPSC-Heps were sandwich-cultured under the condition we established, extended bile canaliculi were formed on the whole well surfaces. Biliary efflux transporters were localized in the formed bile canaliculi structures which had junctional complexes. After the model substrates of the biliary efflux transporters were taken up into cells, their subsequent excretion into the bile canaliculi was observed and was found to be impeded by each inhibitor of the biliary efflux transporter. These findings suggest that bile canaliculi have transporter-specific bile excretion abilities. We will continue to study the application of this culture protocol to cell-based cholestasis assay system. As a result, the culture protocol could lead to a highly predictable, robust cell-based cholestasis assay system because it forms functional bile canaliculi reproducibly and efficiently.

Hepatic bile acid synthesis and secretion: Comparison of in vitro methods

Reliable hepatic in vitro systems are crucial for the safety assessment of xenobiotics. Certain xenobiotics decrease the hepatic bile efflux, which can ultimately result in cholestasis. Preclinical animal models and the currently available in vitro systems poorly predict a xenobiotic's cholestatic potential. Here, we compared the phenotype and capacity of three liver derived in vitro systems to emulate human functionality to synthesize and secrete bile acids (BAs). To this end, basal BA production of sandwich cultured human hepatocytes (SCHHs), HepaRG cells (HepaRGs) and hepatocyte-like intrahepatic cholangiocyte organoids (ICO-heps) were analysed, and the effect of the known BSEP (Bile Salt Export Pump)-inhibitors bosentan and lopinavir on BA disposition in SCHHs and HepaRGs was quantified. RT-qPCR of selected target genes involved in maturation status, synthesis, transport and conjugation of BAs was performed to mechanistically underpin the observed differences in BA homeostasis. ICO-heps produced a (very) low amount of BAs. SCHHs are a powerful tool in cholestasis-testing due to their high basal BA production and high transporter expression compared to the other models tested. HepaRGs were responsive to both selected BSEP-inhibitors and produced a BA profile that is most similar to the human in vivo situation, making them a suitable and practical candidate for cholestasis-testing.

Mouse precision-cut liver slices as an ex vivo model to study drug-induced cholestasis

Drugs are often withdrawn from the market due to the manifestation of drug-induced liver injury (DILI) in patients. Drug-induced cholestasis (DIC), defined as obstruction of hepatic bile flow due to medication, is one form of DILI. Because DILI is idiosyncratic, and the resulting cholestasis complex, there is no suitable in vitro model for early DIC detection during drug development. Our goal was to develop a mouse precision-cut liver slice (mPCLS) model to study DIC and to assess cholestasis development using conventional molecular biology and analytical chemistry methods. Cholestasis was induced in mPCLS through a 48-h-incubation with three drugs known to induce cholestasis in humans, namely chlorpromazine (15, 20, and 30 µM), cyclosporin A (1, 3, and 6 µM) or glibenclamide (25, 50, and 65 µM). A bile-acid mixture (16 µM) that is physiologically representative of the human bile-acid pool was added to the incubation medium with drug, and results were compared to incubations with no added bile acids. Treatment of PCLS with cholestatic drugs increased the intracellular bile-acid concentration of deoxycholic acid and modulated bile-transporter genes. Chlorpromazine led to the most pronounced cholestasis in 48 h, observed as increased toxicity; decreased protein and gene expression of the bile salt export pump; increased gene expression of multidrug resistance-associated protein 4; and accumulation of intracellular bile acids. Moreover, chlorpromazine-induced cholestasis exhibited some transition into fibrosis, evidenced by increased gene expression of collagen 1A1 and heatshock protein 47. In conclusion, we demonstrate that mPCLS can be used to study human DIC onset and progression in a 48 h period. We thus propose this model is suited for other similar studies of human DIC.

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.

Effects of Diminished NADPH:cytochrome P450 Reductase in Human Hepatocytes on Lipid and Bile Acid Homeostasis

NADPH:cytochrome P450 oxidoreductase (POR) is the obligate electron donor for microsomal cytochrome P450 (CYP) enzymes involved in the biosynthesis of endogenous substances like bile acids and other steroids as well as in the oxidative metabolism of xenobiotics. P450 oxidoreductase also supports other redox enzymes in fatty acid and cholesterol pathways. Recently, we have established CRISPR/Cas9-mediated POR knockdown in a human hepatic cell model, HepaRG, and demonstrated the differential effects of limited POR expression on CYP activity. The aim of the present work was to systematically investigate the impact of POR knockdown with a focus on the expression of ADME (absorption, distribution, metabolism, and excretion) genes and related regulators. Functional consequences have been assessed using quantitative mass spectrometry for targeted metabolomics covering bile acids, and cholesterol and its precursors, and for untargeted proteomics. In addition to the previously described alteration of RNA expression of CYP genes, we showed significant downregulation of transcriptional regulators of drug metabolism and transport, including NR1I3 (CAR), NR1I2 (PXR), NR1H4 (FXR), and NR1H3 (LXRα) in cells with POR gene disruption. Furthermore, POR knockdown resulted in deregulated bile acid and cholesterol biosynthesis demonstrated by low levels of cholic acid derivates and increased concentrations of chenodeoxycholic acid derivates, respectively. Systemic effects of POR knockdown on global protein expression were indicated by downregulation of several metabolic pathways including lipid metabolism and biological oxidation reactions. The deduced protein network map corroborates CYP enzymes as direct interaction partners, whereas changes in lipid metabolism and homeostasis are the result of indirect effects. In summary, our results emphasize a widespread role of POR in various metabolic pathways and provide the first human data on the effects of diminished POR expression on drug and endogenous metabolism in a genomeedited HepaRG cell model.

The Food Contaminants Pyrrolizidine Alkaloids Disturb Bile Acid Homeostasis Structure-Dependently in the Human Hepatoma Cell Line HepaRG

Pyrrolizidine alkaloids (PAs) are a group of secondary plant metabolites being contained in various plant species. The consumption of contaminated food can lead to acute intoxications in humans and exert severe hepatotoxicity. The development of jaundice and elevated bile acid concentrations in blood have been reported in acute human PA intoxication, indicating a connection between PA exposure and the induction of cholestasis. Additionally, it is considered that differences in toxicity of individual PAs is based on their individual chemical structures. Therefore, we aimed to elucidate the structure-dependent disturbance of bile acid homeostasis by PAs in the human hepatoma cell line HepaRG. A set of 14 different PAs, including representatives of all major structural characteristics, namely, the four different necine bases retronecine, heliotridine, otonecine and platynecine and different grades of esterification, was analyzed in regard to the expression of genes involved in bile acid synthesis, metabolism and transport. Additionally, intra- and extracellular bile acid levels were analyzed after PA treatment. In summary, our data show significant structure-dependent effects of PAs on bile acid homeostasis. Especially PAs of diester type caused the strongest dysregulation of expression of genes associated with cholestasis and led to a strong decrease of intra- and extracellular bile acid concentrations.

Active Transport of Hepatotoxic Pyrrolizidine Alkaloids in HepaRG Cells

1,2-unsaturated pyrrolizidine alkaloids (PAs) are secondary plant metabolites occurring as food contaminants that can cause severe liver damage upon metabolic activation in hepatocytes. However, it is yet unknown how these contaminants enter the cells. The role of hepatic transporters is only at the beginning of being recognized as a key determinant of PA toxicity. Therefore, this study concentrated on assessing the general mode of action of PA transport in the human hepatoma cell line HepaRG using seven structurally different PAs. Furthermore, several hepatic uptake and efflux transporters were targeted with pharmacological inhibitors to identify their role in the uptake of the PAs retrorsine and senecionine and in the disposition of their N-oxides (PANO). For this purpose, PA and PANO content was measured in the supernatant using LC-MS/MS. Also, PA-mediated cytotoxicity was analyzed after transport inhibition. It was found that PAs are taken up into HepaRG cells in a predominantly active and structure-dependent manner. This pattern correlates with other experimental endpoints such as cytotoxicity. Pharmacological inhibition of the influx transporters Na⁺/taurocholate co-transporting polypeptide (SLC10A1) and organic cation transporter 1 (SLC22A1) led to a reduced uptake of retrorsine and senecionine into HepaRG cells, emphasizing the relevance of these transporters for PA toxicokinetics.

Pyrrolizidine Alkaloids Disturb Bile Acid Homeostasis in the Human Hepatoma Cell Line HepaRG

1,2-unsaturated pyrrolizidine alkaloids (PAs) belong to a group of secondary plant metabolites. Exposure to PA-contaminated feed and food may cause severe hepatotoxicity. A pathway possibly involved in PA toxicity is the disturbance of bile acid homeostasis. Therefore, in this study, the influence of four structurally different PAs on bile acid homeostasis was investigated after single (24 h) and repeated (14 days) exposure using the human hepatoma cell line HepaRG. PAs induce a downregulation of gene expression of various hepatobiliary transporters, enzymes involved in bile acid synthesis, and conjugation, as well as several transcription regulators in HepaRG cells. This repression may lead to a progressive impairment of bile acid homeostasis, having the potential to accumulate toxic bile acids. However, a significant intracellular and extracellular decrease in bile acids was determined, pointing to an overall inhibition of bile acid synthesis and transport. In summary, our data clearly show that PAs structure-dependently impair bile acid homeostasis and secretion by inhibiting the expression of relevant genes involved in bile acid homeostasis. Furthermore, important biliary efflux mechanisms seem to be disturbed due to PA exposure. These mole-cular mechanisms may play an important role in the development of severe liver damage in PA-intoxicated humans.

Impairment of bile acid metabolism by perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) in human HepaRG hepatoma cells

Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are man-made chemicals that are used for the fabrication of many products with water- and dirt-repellent properties. The toxicological potential of both substances is currently under debate. In a recent Scientific Opinion, the European Food Safety Authority (EFSA) has identified increased serum total cholesterol levels in humans as one major critical effect being associated with exposure to PFOA or PFOS. In animal studies, both substances induced a decrease of serum cholesterol levels, and the underlying molecular mechanism(s) for these opposed effects are unclear so far. In the present study, we examined the impact of PFOA and PFOS on cholesterol homoeostasis in the human HepaRG cell line as a model for human hepatocytes. Cholesterol levels in HepaRG cells were not affected by PFOA or PFOS, but both substances strongly decreased synthesis of a number of bile acids. The expression of numerous genes whose products are involved in synthesis, metabolism and transport of cholesterol and bile acids was strongly affected by PFOA and PFOS at concentrations above 10 µM. Notably, both substances led to a strong decrease of CYP7A1, the key enzyme catalyzing the rate-limiting step in the synthesis of bile acids from cholesterol, both at the protein level and at the level of gene expression. Moreover, both substances led to a dilatation of bile canaliculi that are formed by differentiated HepaRG cells in vitro. Similar morphological changes are known to be induced by cholestatic agents in vivo. Thus, the strong impact of PFOA and PFOS on bile acid synthesis and bile canalicular morphology in our in vitro experiments may allow the notion that both substances have a cholestatic potential that is connected to the observed increased serum cholesterol levels in humans in epidemiological studies.

Robustness testing and optimization of an adverse outcome pathway on cholestatic liver injury

Adverse outcome pathways (AOPs) have been recently introduced as tools to map the mechanisms underlying toxic events relevant for chemical risk assessment. AOPs particularly depict the linkage between a molecular initiating event and an adverse outcome through a number of intermediate key events. An AOP has been previously introduced for cholestatic liver injury. The objective of this study was to test the robustness of this AOP for different types of cholestatic insult and the in vitro to in vivo extrapolation. For this purpose, in vitro samples from human hepatoma HepaRG cell cultures were exposed to cholestatic drugs (i.e. intrahepatic cholestasis), while in vivo samples were obtained from livers of cholestatic mice (i.e. extrahepatic cholestasis). The occurrence of cholestasis in vitro was confirmed through analysis of bile transporter functionality and bile acid analysis. Transcriptomic analysis revealed inflammation and oxidative stress as key events in both types of cholestatic liver injury. Major transcriptional differences between intrahepatic and extrahepatic cholestatic liver insults were observed at the level of cell death and metabolism. Novel key events identified by pathway analysis included endoplasmic reticulum stress in intrahepatic cholestasis, and autophagy and necroptosis in both intrahepatic as extrahepatic cholestasis. This study demonstrates that AOPs constitute dynamic tools that should be frequently updated with new input information.

Increased serum bile acid level is associated with high-risk coronary artery plaques in an asymptomatic population detected by coronary computed tomography angiography

Background

There are limited data on the association between serum total bile acid level and coronary plaque characteristics. This study investigated the relationship between serum total bile acid level and the severity of coronary stenosis and coronary plaque features in an asymptomatic population using coronary computed tomography angiography (CTA).

Methods

A total of 1,137 consecutive participants with no known coronary artery disease (CAD) undergoing CTA as part of a general routine health evaluation were recruited. Serum total bile acid level and clinical parameters were assayed. Coronary stenosis and high-risk plaques features (napkin-ring sign, low-attenuation plaque, spotty calcification, positive remodelling) were evaluated. Associations between serum total bile acid concentration and high-risk coronary plaques was tested through univariate and multivariate analyses.

Results

A total of 101 high-risk coronary plaques subjects and 93 controls were eligible for study inclusion. The severity of coronary artery stenosis and high-risk coronary plaques increased with serum total bile acid level quartiles (all P<0.001). The independent predictor of high-risk coronary plaques in multivariate analysis was serum total bile acid level (P<0.001). Receiver operating characteristic (ROC) confirmed that serum total bile acid concentration significantly differentiated high-risk coronary plaques [the area under the curve (AUC) =0.876; P<0.001, with a sensitivity of 87.13% and a specificity of 86.02%].

Conclusions

Higher serum total bile acid level was associated with the severity of coronary artery stenosis and high-risk coronary artery plaques detected by CTA in asymptomatic populations.

Current insights in the complexities underlying drug-induced cholestasis

Drug-induced cholestasis (DIC) poses a major challenge to the pharmaceutical industry and regulatory agencies. It causes both drug attrition and post-approval withdrawal of drugs. DIC represents itself as an impaired secretion and flow of bile, leading to the pathological hepatic and/or systemic accumulation of bile acids (BAs) and their conjugate bile salts. Due to the high number of mechanisms underlying DIC, predicting a compound's cholestatic potential during early stages of drug development remains elusive. A profound understanding of the different molecular mechanisms of DIC is, therefore, of utmost importance. Although many knowledge gaps and caveats still exist, it is generally accepted that alterations of certain hepatobiliary membrane transporters and changes in hepatocellular morphology may cause DIC. Consequently, liver models, which represent most of these mechanisms, are valuable tools to predict human DIC. Some of these models, such as membrane-based in vitro models, are exceptionally well-suited to investigate specific mechanisms (i.e. transporter inhibition) of DIC, while others, such as liver slices, encompass all relevant biological processes and, therefore, offer a better representation of the in vivo situation. In the current review, we highlight the principal molecular mechanisms associated with DIC and offer an overview and critical appraisal of the different liver models that are currently being used to predict the cholestatic potential of drugs.

Untargeted liquid chromatography-mass spectrometry metabolomics to assess drug-induced cholestatic features in HepaRG® cells

Cholestasis is a liver disease associated with retention of bile in the liver, which leads to local hepatic inflammation and severe liver damage. In order to investigate the mode of action of drug-induced cholestasis, in vitro models have shown to be able to recapitulate important elements of this disease. In this study, we applied untargeted metabolomics to investigate the metabolic perturbances in HepaRG® cells exposed for 24 h and 72 h to bosentan, a cholestatic reference toxicant. Intracellular profiles were extracted and analysed with liquid chromatography and accurate-mass spectrometry. Metabolites of interest were selected using partial least-squares discriminant analysis and random forest classifier models. The observed metabolic patterns associated with cholestasis in vitro were complex. Acute (24 h) exposure revealed metabolites related to apoptosis, such as ceramide and triglyceride accumulation, in combination with phosphatidylethanolamine, choline and carnitine depletion. Metabolomic alterations during exposure to lower dosages and a prolonged exposure (72 h) included carnitine upregulation and changes in the polyamine metabolism. These metabolites were linked to changes in phospholipid metabolism, mitochondrial pathways and energy homeostasis. The metabolic changes confirmed the mitotoxic effects of bosentan and revealed the potential involvement of phospholipid metabolism as part of the mode of action of drug-induced cholestasis.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Pro-inflammatory cytokines enhance dilatation of bile canaliculi caused by cholestatic antibiotics

Many drugs can induce liver injury, characterized by hepatocellular, cholestatic or mixed hepatocellular-cholestatic lesions. While an inflammatory stress is known to aggravate hepatocellular injury caused by some drugs much less evidence exists for cholestatic features. In this study, the influence of pro-inflammatory cytokines (IL-6, IL-1β and TNF-α), either individually or combined, on cytotoxic and cholestatic properties of antibiotics was evaluated using differentiated HepaRG cells. Six antibiotics of various chemical structures and known to cause cholestasis and/or hepatocellular injury in clinic were investigated. Caspase-3 activity was increased with all these tested hepatotoxic drugs and except with erythromycin, was further augmented in presence of cytokines mainly when these were co-added as a mixture. TNF-α and IL-1β aggravated cytotoxicity of TVX more than IL-6. Bile canaliculi (BC) dilatation induced by cholestatic drugs was increased by co-treatment with IL-6 and IL-1β but not with TNF-α. Reduced accumulation of carboxy-dichlorofluorescein, a substrate of the multi-drug resistance-associated protein 2, in antibiotic-induced dilatated BC, was further extended in presence of individual or mixed cytokines. In conclusion, our data demonstrate that pro-inflammatory cytokines either individually or in mixture, can modulate cholestatic and/or cytotoxic responses to antibiotics and that the extent of these effects is dependent on the cytokine and the cholestatic antibiotic.

Setup and Use of HepaRG Cells in Cholestasis Research

Since HepaRG cells can differentiate into well-polarized mature hepatocyte-like cells that synthesize, conjugate, and secrete bile acids, they represent an appropriate surrogate to primary human hepatocytes for investigations on drug-induced cholestasis mechanisms. In this chapter, culture conditions for obtaining HepaRG hepatocytes and the main methods used to detect cholestatic potential of drugs are described. Assays for evaluation of bile canaliculi dynamics and morphology are mainly based on time-lapse and phase-contrast microscopy analysis. Bile acid uptake, trafficking, and efflux are investigated using fluorescent probes. Individual bile acids are quantified in both culture media and cell layers by high-pressure liquid chromatography/tandem mass spectrometry. Preferential cellular accumulation of toxic hydrophobic bile acids is easily evidenced when exogenous primary and secondary bile acids are added to the culture medium.

Regulation of Cytosolic Sulfotransferases in Models of Human Hepatocyte Development

Cytosolic sulfotransferases (SULTs) are expressed during early life and therefore metabolize endogenous and xenobiotic chemicals during development. Little is currently known about the regulation of individual SULTs in the developing human liver. We characterized SULT expression in primary cultures of human fetal hepatocytes and the HepaRG model of liver cell differentiation. SULT1A1 (transcript variants 1-4), SULT1C2, SULT1C4, SULT1E1, and SULT2A1 were the most abundant transcripts in human fetal hepatocytes. In HepaRG cells, SULT1B1, SULT1C2/3/4, and SULT1E1 mRNA levels increased during the transition from proliferation to confluency and then decreased as the cells underwent further differentiation. By contrast, SULT2A1 mRNA levels increased during differentiation, whereas SULT1A1 and SULT2B1 mRNA levels remained relatively constant. The temporal patterns of SULT1C2, SULT1E1, and SULT2A1 protein content were consistent with those observed at the mRNA level. To identify regulators of SULT expression, cultured fetal hepatocytes and HepaRG cells were treated with a panel of lipid- and xenobiotic-sensing receptor activators. The following effects were observed in both fetal hepatocytes and HepaRG cells: 1) liver X receptor activator treatment increased SULT1A1 transcript variant 5 levels; 2) vitamin D receptor activator treatment increased SULT1C2 and SULT2B1 mRNA levels; and 3) farnesoid X receptor activator treatment decreased SULT2A1 expression. Activators of aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, and peroxisome proliferator-activated receptors produced additional gene-dependent effects on SULT expression in HepaRG cells. These findings suggest that SULT-regulating chemicals have the potential to modulate physiologic processes and susceptibility to xenobiotic stressors in the developing human liver.

Predicting drug-induced cholestasis: preclinical models

INTRODUCTION

In almost 50% of patients with drug-induced liver injury (DILI), the bile flow from the liver to the duodenum is impaired, a condition known as cholestasis. However, this toxic response only appears in a small percentage of the treated patients (idiosyncrasy). Prediction of drug-induced cholestasis (DIC) is challenging and emerges as a safety issue that requires attention by professionals in clinical practice, regulatory authorities, pharmaceutical companies, and research institutions. Area covered: The current synopsis focuses on the state-of-the-art in preclinical models for cholestatic DILI prediction. These models differ in their goal, complexity, availability, and applicability, and can widely be classified in experimental animals and in vitro models. Expert opinion: Drugs are a growing cause of cholestasis, but the progress made in explaining mechanisms and differences in susceptibility is not growing at the same rate. We need reliable models able to recapitulate the features of DIC, particularly its idiosyncrasy. The homogeneity and the species-specific differences move animal models away from a fair predictability. However, in vitro human models are improving and getting closer to the real hepatocyte phenotype, and they will likely be the choice in the near future. Progress in this area will not only need reliable predictive models but also mechanistic insights.

Omics-based responses induced by bosentan in human hepatoma HepaRG cell cultures

Bosentan is well known to induce cholestatic liver toxicity in humans. The present study was set up to characterize the hepatotoxic effects of this drug at the transcriptomic, proteomic, and metabolomic levels. For this purpose, human hepatoma-derived HepaRG cells were exposed to a number of concentrations of bosentan during different periods of time. Bosentan was found to functionally and transcriptionally suppress the bile salt export pump as well as to alter bile acid levels. Pathway analysis of both transcriptomics and proteomics data identified cholestasis as a major toxicological event. Transcriptomics results further showed several gene changes related to the activation of the nuclear farnesoid X receptor. Induction of oxidative stress and inflammation were also observed. Metabolomics analysis indicated changes in the abundance of specific endogenous metabolites related to mitochondrial impairment. The outcome of this study may assist in the further optimization of adverse outcome pathway constructs that mechanistically describe the processes involved in cholestatic liver injury.

From the Cover: MechanisticInsights in Cytotoxic and Cholestatic Potential of the Endothelial Receptor Antagonists Using HepaRG Cells

Several endothelin receptor antagonists (ERAs) have been developed for the treatment of pulmonary arterial hypertension (PAH). Some of them have been related to clinical cases of hepatocellular injury (sitaxentan [SIT]) and/or cholestasis (bosentan [BOS]). We aimed to determine if ambrisentan (AMB) and macitentan (MAC), in addition to BOS and SIT, could potentially cause liver damage in man by use of human HepaRG cells. Our results showed that like BOS, MAC-induced cytotoxicity and cholestatic disorders characterized by bile canaliculi dilatation and impairment of myosin light chain kinase signaling. Macitentan also strongly inhibited taurocholic acid and carboxy-2',7'-dichlorofluorescein efflux while it had a much lower inhibitory effect on influx activity compared to BOS and SIT. Moreover, these three drugs caused decreased intracellular accumulation and parallel increased levels of total bile acids (BAs) in serum-free culture media. In addition, all drugs except AMB variably deregulated gene expression of BA transporters. In contrast, SIT was hepatotoxic without causing cholestatic damage, likely via the formation of reactive metabolites and AMB was not hepatotoxic. Together, our results show that some ERAs can be hepatotoxic and that the recently marketed MAC, structurally similar to BOS, can also cause cholestatic alterations in HepaRG cells. The absence of currently known or suspected cases of cholestasis in patients suffering from PAH treated with MAC is rationalized by the lower therapeutic doses and Cmax, and longer receptor residence time compared to BOS.

Progressive and Preferential Cellular Accumulation of Hydrophobic Bile Acids Induced by Cholestatic Drugs Is Associated with Inhibition of Their Amidation and Sulfation

Drug-induced intrahepatic cholestasis is characterized by cellular accumulation of bile acids (BAs), whose mechanisms remain poorly understood. The present study aimed to analyze early and progressive alterations of BA profiles induced by cyclosporine A, chlorpromazine, troglitazone, tolcapone, trovafloxacin, and tacrolimus after 4-hour, 24-hour, and 6-day treatments of differentiated HepaRG cells. In BA-free medium, the potent cholestatic drugs cyclosporine A, chlorpromazine, and troglitazone reduced endogenous BA synthesis after 24 hours, whereas the rarely cholestatic drugs tolcapone, trovafloxacin, and tacrolimus reduced BA synthesis only after 6 days. In the presence of physiologic serum BA concentrations, cyclosporine A, chlorpromazine, and troglitazone induced early and preferential cellular accumulation of unconjugated lithocholic, deoxycholic, and chenodeoxycholic acids that increased 8- to 12-fold and 47- to 50-fold after 24 hours and 6 days, respectively. Accumulation of these hydrophobic BAs resulted from strong inhibition of amidation, and in addition, for lithocholic acid reduction of its sulfoconjugation, and was associated with variable alterations of uptake and efflux transporters. Trovafloxacin also caused BA accumulation, especially after 6 days, whereas tolcapone and tacrolimus were still without effect. However, when exogenous BAs were added to the medium at cholestatic serum concentrations, a 6-day treatment with all drugs resulted in cellular BA accumulation with higher folds of chenodeoxycholic and lithocholic acids. At the tested concentration, tolcapone had the lowest effect. These results bring the first demonstration that major cholestatic drugs can cause preferential and progressive in vitro cellular accumulation of unconjugated toxic hydrophobic BAs and bring new insights into mechanisms involved in drug-induced cellular accumulation of toxic BAs.

Penicillinase-resistant antibiotics induce non-immune-mediated cholestasis through HSP27 activation associated with PKC/P38 and PI3K/AKT signaling pathways

The penicillinase-resistant antibiotics (PRAs), especially the highly prescribed flucloxacillin, caused frequent liver injury via mechanisms that remain largely non-elucidated. We first showed that flucloxacillin, independently of cytotoxicity, could exhibit cholestatic effects in human hepatocytes in the absence of an immune reaction, that were typified by dilatation of bile canaliculi associated with impairment of the Rho-kinase signaling pathway and reduced bile acid efflux. Then, we analyzed the sequential molecular events involved in flucloxacillin-induced cholestasis. A crucial role of HSP27 by inhibiting Rho-kinase activity was demonstrated using siRNA and the specific inhibitor KRIBB3. HSP27 activation was dependent on the PKC/P38 pathway, and led downstream to activation of the PI3K/AKT pathway. Other PRAs induced similar cholestatic effects while non PRAs were ineffective. Our results demonstrate that PRAs can induce cholestatic features in human hepatocytes through HSP27 activation associated with PKC/P38 and PI3K/AKT signaling pathways and consequently support the conclusion that in clinic they can cause a non-immune-mediated cholestasis that is not restricted to patients possessing certain genetic determinants.

Polygoni Multiflori Radix derived anthraquinones alter bile acid disposition in sandwich-cultured rat hepatocytes

Hepatic adverse reaction associated with Polygoni Multiflori Radix (PMR) has been frequently reported in recent years. Highly-enriched anthraquinones (AQs) in PMR, such as emodin, chrysophanol and physcion, have been found to be hepatotoxic. In the present study, sandwich-cultured rat hepatocytes (SCRHs) were employed to investigate the effect of individual and combined AQs on the disposition of endogenous bile acids (BAs) and exogenous probe substrates including deuterium-labeled taurocholate (d5-TCA), glycochenodeoxycholic acid (d4-GCDCA) and 5 (and 6)-carboxy-2',7'-dichlorofluorescein (CDF). Emodin and chrysophanol significantly inhibited bile salt export pump and multidrug resistance-associated protein 2 (Mrp2), respectively, as evidenced by decreased biliary excretion index (BEI) of d5-TCA and CDF. Moreover, basolateral efflux transporters were inhibited by all individual and combined AQs. As a result, cellular accumulation of total and specific endogenous BAs were significantly elevated by individual AQs, alone or combined. In addition, down-regulation of Mrps in both gene and protein levels by AQs served as another critical contributing factor for BA accumulation in SCRHs. To be noted, subsequent adaptive gene regulation, including reduced Ntcp expression, upregulated Bsep levels, and downregulated Cyp8b1, alleviated, to a certain extent, but not prevented from toxic BA accumulation. In summary, all three AQs of interest are likely to alter BA disposition through direct inhibition of BA transporters as well as regulated expression of BA transporters and enzymes.

Functional human induced hepatocytes (hiHeps) with bile acid synthesis and transport capacities: A novel in vitro cholestatic model

Drug-induced cholestasis is a leading cause of drug withdrawal. However, the use of primary human hepatocytes (PHHs), the gold standard for predicting cholestasis in vitro, is limited by their high cost and batch-to-batch variability. Mature hepatocyte characteristics have been observed in human induced hepatocytes (hiHeps) derived from human fibroblast transdifferentiation. Here, we evaluated whether hiHeps could biosynthesize and excrete bile acids (BAs) and their potential as PHH alternatives for cholestasis investigations. Quantitative real-time PCR (qRT-PCR) and western blotting indicated that hiHeps highly expressed BA synthases and functional transporters. Liquid chromatography tandem mass spectrometry (LC-MS/MS) showed that hiHeps produced normal intercellular unconjugated BAs but fewer conjugated BAs than human hepatocytes. When incubated with representative cholestatic agents, hiHeps exhibited sensitive drug-induced bile salt export pump (BSEP) dysfunction, and their response to cholestatic agent-mediated cytotoxicity correlated well with that of PHHs (r² = 0.8032). Deoxycholic acid (DCA)-induced hepatotoxicity in hiHeps was verified by elevated aspartate aminotransferase (AST) and γ-glutamyl-transferase (γ-GT) levels. Mitochondrial damage and cell death suggested DCA-induced toxicity in hiHeps, which were attenuated by hepatoprotective drugs, as in PHHs. For the first time, hiHeps were reported to biosynthesize and excrete BAs, which could facilitate predicting cholestatic hepatotoxicity and screening potential therapeutic drugs against cholestasis.

Early Alterations of Bile Canaliculi Dynamics and the Rho Kinase/Myosin Light Chain Kinase Pathway Are Characteristics of Drug-Induced Intrahepatic Cholestasis

Intrahepatic cholestasis represents 20%-40% of drug-induced injuries from which a large proportion remains unpredictable. We aimed to investigate mechanisms underlying drug-induced cholestasis and improve its early detection using human HepaRG cells and a set of 12 cholestatic drugs and six noncholestatic drugs. In this study, we analyzed bile canaliculi dynamics, Rho kinase (ROCK)/myosin light chain kinase (MLCK) pathway implication, efflux inhibition of taurocholate [a predominant bile salt export pump (BSEP) substrate], and expression of the major canalicular and basolateral bile acid transporters. We demonstrated that 12 cholestatic drugs classified on the basis of reported clinical findings caused disturbances of both bile canaliculi dynamics, characterized by either dilatation or constriction, and alteration of the ROCK/MLCK signaling pathway, whereas noncholestatic compounds, by contrast, had no effect. Cotreatment with ROCK inhibitor Y-27632 [4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride] and MLCK activator calmodulin reduced bile canaliculi constriction and dilatation, respectively, confirming the role of these pathways in drug-induced intrahepatic cholestasis. By contrast, inhibition of taurocholate efflux and/or human BSEP overexpressed in membrane vesicles was not observed with all cholestatic drugs; moreover, examples of noncholestatic compounds were reportedly found to inhibit BSEP. Transcripts levels of major bile acid transporters were determined after 24-hour treatment. BSEP, Na+-taurocholate cotransporting polypeptide, and organic anion transporting polypeptide B were downregulated with most cholestatic and some noncholestatic drugs, whereas deregulation of multidrug resistance-associated proteins was more variable, probably mainly reflecting secondary effects. Together, our results show that cholestatic drugs consistently cause an early alteration of bile canaliculi dynamics associated with modulation of ROCK/MLCK and these changes are more specific than efflux inhibition measurements alone as predictive nonclinical markers of drug-induced cholestasis.

Towards a 21st-century roadmap for biomedical research and drug discovery: consensus report and recommendations

Decades of costly failures in translating drug candidates from preclinical disease models to human therapeutic use warrant reconsideration of the priority placed on animal models in biomedical research. Following an international workshop attended by experts from academia, government institutions, research funding bodies, and the corporate and non-governmental organisation (NGO) sectors, in this consensus report, we analyse, as case studies, five disease areas with major unmet needs for new treatments. In view of the scientifically driven transition towards a human pathways-based paradigm in toxicology, a similar paradigm shift appears to be justified in biomedical research. There is a pressing need for an approach that strategically implements advanced, human biology-based models and tools to understand disease pathways at multiple biological scales. We present recommendations to help achieve this.

Key Challenges and Opportunities Associated with the Use of In Vitro Models to Detect Human DILI: Integrated Risk Assessment and Mitigation Plans

Drug-induced liver injury (DILI) is a major cause of late-stage clinical drug attrition, market withdrawal, black-box warnings, and acute liver failure. Consequently, it has been an area of focus for toxicologists and clinicians for several decades. In spite of considerable efforts, limited improvements in DILI prediction have been made and efforts to improve existing preclinical models or develop new test systems remain a high priority. While prediction of intrinsic DILI has improved, identifying compounds with a risk for idiosyncratic DILI (iDILI) remains extremely challenging because of the lack of a clear mechanistic understanding and the multifactorial pathogenesis of idiosyncratic drug reactions. Well-defined clinical diagnostic criteria and risk factors are also missing. This paper summarizes key data interpretation challenges, practical considerations, model limitations, and the need for an integrated risk assessment. As demonstrated through selected initiatives to address other types of toxicities, opportunities exist however for improvement, especially through better concerted efforts at harmonization of current, emerging and novel in vitro systems or through the establishment of strategies for implementation of preclinical DILI models across the pharmaceutical industry. Perspectives on the incorporation of newer technologies and the value of precompetitive consortia to identify useful practices are also discussed.

Identification of functional farnesoid X receptors in brain neurons

Farnesoid X receptor (FXR) has been confirmed to sense bile acids in various tissues. However, its expression in brain neurons remains obscure. In this study, we identified FXR mRNA and protein expression in mouse brain neurons and in mouse/human brain tissues. FXR was predominantly localized in the nucleus in cultured neurons, but in neurons in vivo, it mainly appeared in the cytoplasm. In nuclear compartments, the neuronal FXR exhibited a punctate distribution. Activation of FXR increased the small heterodimer partner (SHP) mRNA and protein expression levels in cultured neurons and in brain tissues. These findings will help explore new functions of FXR in the brain.

Rho-kinase/myosin light chain kinase pathway plays a key role in the impairment of bile canaliculi dynamics induced by cholestatic drugs

Intrahepatic cholestasis represents a frequent manifestation of drug-induced liver injury; however, the mechanisms underlying such injuries are poorly understood. In this study of human HepaRG and primary hepatocytes, we found that bile canaliculi (BC) underwent spontaneous contractions, which are essential for bile acid (BA) efflux and require alternations in myosin light chain (MLC2) phosphorylation/dephosphorylation. Short exposure to 6 cholestatic compounds revealed that BC constriction and dilation were associated with disruptions in the ROCK/MLCK/myosin pathway. At the studied concentrations, cyclosporine A and chlorpromazine induced early ROCK activity, resulting in permanent MLC2 phosphorylation and BC constriction. However, fasudil reduced ROCK activity and caused rapid, substantial and permanent MLC2 dephosphorylation, leading to BC dilation. The remaining compounds (1-naphthyl isothiocyanate, deoxycholic acid and bosentan) caused BC dilation without modulating ROCK activity, although they were associated with a steady decrease in MLC2 phosphorylation via MLCK. These changes were associated with a common loss of BC contractions and failure of BA clearance. These results provide the first demonstration that cholestatic drugs alter BC dynamics by targeting the ROCK/MLCK pathway; in addition, they highlight new insights into the mechanisms underlying bile flow failure and can be used to identify new predictive biomarkers of drug-induced cholestasis.

Chenodeoxycholic acid significantly impacts the expression of miRNAs and genes involved in lipid, bile acid and drug metabolism in human hepatocytes

AIMS

Bile acids (BAs) are important gut signaling hormones, influencing lipid, glucose, and energy homeostasis. The exact mechanisms behind these effects are not yet fully understood. Lately, they have come to the fore as putative therapeutics in metabolic diseases, such as e.g. nonalcoholic fatty liver disease (NAFLD). We elucidate to what extent BAs impacts on the mRNAome and microRNAome in hepatocytes to gather novel insights into the mechanisms behind metabolic and toxicologic effects of bile acids.

MAIN METHODS

Five batches of primary human hepatocytes were treated with 50μmol/l chenodeoxycholic acid (CDCA) for 24 or 48h. Total RNA was extracted, size fractionated and subjected to Next Generation Sequencing to generate mRNA and miRNA profiles.

KEY FINDINGS

Expression of 738 genes and 52 miRNAs were CDCA dependently decreased, whereas 1566 genes and 29 miRNAs were significantly increased in hepatocytes. Distinct gene clusters controlling BA and lipid homeostasis (FGF(R), APO and FABP family members, HMGCS2) and drug metabolism (CYP, UGT and SULT family members) were significantly modulated by CDCA. Importantly, CDCA affected distinct microRNAs, including miR-34a, -505, -885, -1260 and -552 that systematically correlated in expression with gene clusters responsible for bile acid, lipid and drug homeostasis incorporating genes, such as e.g. SLCO1B1, SLC22A7, FGF19, CYP2E1, CYP1A2, APO family members and FOXO3.

SIGNIFICANCE

Bile acids significantly modulate metabolic and drug associated gene networks that are connected to distinct shifts in the microRNAome These findings give novel insights on how BA enfold metabolic and system toxic effects.

Ursodeoxycholic and deoxycholic acids: Differential effects on intestinal Ca(2+) uptake, apoptosis and autophagy of rat intestine

The aim of this work was to study the effect of sodium deoxycholate (NaDOC) and ursodeoxycholic acid (UDCA) on Ca(2+) uptake by enterocytes and the underlying mechanisms. Rats were divided into four groups: a) controls, b) treated with NaDOC, c) treated with UDCA d) treated with NaDOC and UDCA. Ca(2+) uptake was studied in enterocytes with different degrees of maturation. Apoptosis, autophagy and NO content and iNOS protein expression were evaluated. NaDOC decreased and UDCA increased Ca(2+) uptake only in mature enterocytes. The enhancement of protein expression of Fas, FasL, caspase-8 and caspase-3 activity by NaDOC indicates triggering of the apoptotic extrinsic pathway, which was blocked by UDCA. NO content and iNOS protein expression were enhanced by NaDOC, and avoided by UDCA. The increment of acidic vesicular organelles and LC3 II produced by NaDOC was also prevented by UDCA. In conclusion, the inhibitory effects of NaDOC on intestinal Ca(2+) absorption occur by decreasing the Ca(2+) uptake by mature enterocytes. NaDOC triggers apoptosis and autophagy, in part as a result of nitrosative stress. In contrast, UDCA increases the Ca(2+) uptake by mature enterocytes, and in combination with NaDOC acts as an antiapoptotic and antiautophagic agent normalizing the transcellular Ca(2+) pathway.