Predicting drug-induced cholestasis: preclinical models

Human liver cell-based assays for the prediction of hepatic bile acid efflux transporter inhibition by drugs

INTRODUCTION

Drug-mediated inhibition of bile salt efflux transporters may cause liver injury. In vitro prediction of drug effects toward canalicular and/or sinusoidal efflux of bile salts from human hepatocytes is therefore a major issue, which can be addressed using liver cell-based assays.

AREA COVERED

This review, based on a thorough literature search in the scientific databases PubMed and Web of Science, provides key information about hepatic transporters implicated in bile salt efflux, the human liver cell models available for investigating functional inhibition of bile salt efflux, the different methodologies used for this purpose, and the modes of expression of the results. Applications of the assays to drugs are summarized, with special emphasis to the performance values of some assays for predicting hepatotoxicity/cholestatic effects of drugs.

EXPERT OPINION

Human liver cell-based assays for evaluating drug-mediated inhibition of bile acid efflux transporters face various limitations, such as the lack of method standardization and validation, the present poor adaptability to high throughput approaches, and some pitfalls with respect to interpretation of bile acid biliary excretion indexes. Hepatotoxicity of drugs is additionally likely multifactorial, highlighting that inhibition of hepatic bile salt efflux by drugs provides important, but not full, information about potential drug hepatotoxicity.

Kuhuang injection exerts a protective effect by activating PPAR-γ in an in vitro model of chlorpromazine-induced cholestatic liver injury constructed by tissue engineering

CONTEXT

Kuhuang (KH) injection is a widely used anticholestatic drug in the clinic and the mechanisms are still unclear.

OBJECTIVE

This study uses a new 3D tissue-engineered (TE) liver platform to study the ability of kuhuang to ameliorate liver injury induced by chlorpromazine (CPZ) and the possible mechanisms involved.

MATERIALS AND METHODS

The TE livers (n = 25) were divided into 5 groups (n = 5 livers/group) as 3D, 3D + CPZ, 3D + CPZ + KH, 3D + CPZ + GW9662 (a PPARγ inhibitor) and 3D + CPZ + KH + GW9662. The treatments with kuhuang (1 mg/mL) and GW9662 (10 μmol/L) were given to the desired groups on the 7th day of the experimental process. 20 μmol/L CPZ was added on the 8th day.

RESULTS

According to the 2D experimental results, the minimum effective concentration of kuhuang is 10 μg/mL and the optimal effective concentration is 1 mg/mL. Kuhuang ameliorated tissue damage in the TE livers both in terms of tissue structure and culture supernatant. Kuhuang significantly reduced TBA accumulation (38%) and downregulated CYP7A1 (38%) and CYP8B1 (79%). It reduced hepatic levels of ROS (14%), MDA (27%) but increased the levels of GSH (41%), SOD (12%), BSEP (4.4-fold), and MRP2 (74%). Moreover, kuhuang downregulated DR5 (99%) but increased the mRNA expression of PPARγ (4-fold). Molecular docking analyses determined the bioactivity of the active compounds of kuhuang through their specific bindings to PPARγ.

CONCLUSIONS

Kuhuang could alleviate CPZ-induced cholestatic liver injury by activating PPARγ to reduce oxidative stress. Applying kuhuang for the treatment of CPZ-induced liver injury could be suggested.

Introducing CELLBLOKS®: a novel organ-on-a-chip platform allowing a plug-and-play approach towards building organotypic models

Human organs are structurally and functionally complex systems. Their function is driven by the interactions between many specialised cell types, which is difficult to unravel on a standard Petri dish format. Conventional "Petri dish" approaches to culturing cells are static and self-limiting. However, current organ-on-a-chip technologies are difficult to use, have a limited throughput and lack compatibility with standard workflow conditions. We developed CELLBLOKS® as a novel "plug-and-play" organ-on-a-chip platform that enables straightforward creation of multiple cell-type organ-specific microenvironments. Herein, we demonstrate its advantages by building a liver model representative of live tissue function. CELLBLOKS® allows one to systematically test and identify various cell combinations that replicate optimal hepatic relevance. The combined interactions of fibroblasts, endothelial cells and hepatocytes were analysed using hepatic biochemistry (CYP3A4 and urea), cellular proliferation indices and transporter activities (albumin). The results demonstrate that optimal liver function can be achieved by exploiting crosstalk in co-culture combinations compared to conventional mono-culture. The optimised CELLBLOKS® liver model was tested to analyse drug-induced liver toxicity using tamoxifen. The data suggests that our CELLBLOKS® liver model is highly sensitive to toxic insult compared to mono-culture liver models. In summary, CELLBLOKS® provides a novel cell culture technology for creating human-relevant organotypic models that are easy and straightforward to establish in laboratory settings.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44164-022-00027-8.

Preclinical models of idiosyncratic drug-induced liver injury (iDILI): Moving towards prediction

Idiosyncratic drug-induced liver injury (iDILI) encompasses the unexpected harms that prescription and non-prescription drugs, herbal and dietary supplements can cause to the liver. iDILI remains a major public health problem and a major cause of drug attrition. Given the lack of biomarkers for iDILI prediction, diagnosis and prognosis, searching new models to predict and study mechanisms of iDILI is necessary. One of the major limitations of iDILI preclinical assessment has been the lack of correlation between the markers of hepatotoxicity in animal toxicological studies and clinically significant iDILI. Thus, major advances in the understanding of iDILI susceptibility and pathogenesis have come from the study of well-phenotyped iDILI patients. However, there are many gaps for explaining all the complexity of iDILI susceptibility and mechanisms. Therefore, there is a need to optimize preclinical human in vitro models to reduce the risk of iDILI during drug development. Here, the current experimental models and the future directions in iDILI modelling are thoroughly discussed, focusing on the human cellular models available to study the pathophysiological mechanisms of the disease and the most used in vivo animal iDILI models. We also comment about in silico approaches and the increasing relevance of patient-derived cellular models.

Current Models for Predicting Drug-induced Cholestasis: The Role of Hepatobiliary Transport System

Drug-induced cholestasis is the main type of liver disorder accompanied by high morbidity and mortality. Evidence for the role of hepatobiliary pumps in the cholestasis patho-mechanism is constantly increasing. Recognition of the interactions of chemical agents with these transporters at the initial phases of drug discovery can help develop new drug candidates with low cholestasis potential. This review delivers an outline of the role of these transport proteins in bile creation. It addresses the pathophysiological mechanism for drug-induced cholestasis. In-vitro models, including cell-based and membrane-based approaches and In-vivo models such as genetic knockout animals, are considered. The benefits and restrictions of each model are discussed in this review. Current understandings into the cellular and molecular process that control the activity of hepatobiliary pumps have directed to a better understanding of the pathophysiology of drug-induced cholestasis. A combination of in-vitro monitoring for transport interaction, in-silico predicting systems, and consideration of and metabolic and physicochemical properties must cause more effective monitoring of possible liver problems.

A Model-Based Workflow to Benchmark the Clinical Cholestasis Risk of Drugs

We present a generic workflow combining physiology-based computational modeling and in vitro data to assess the clinical cholestatic risk of different drugs systematically. Changes in expression levels of genes involved in the enterohepatic circulation of bile acids were obtained from an in vitro assay mimicking 14 days of repeated drug administration for 10 marketed drugs. These changes in gene expression over time were contextualized in a physiology-based bile acid model of glycochenodeoxycholic acid. The simulated drug-induced response in bile acid concentrations was then scaled with the applied drug doses to calculate the cholestatic potential for each compound. A ranking of the cholestatic potential correlated very well with the clinical cholestasis risk obtained from medical literature. The proposed workflow allows benchmarking the cholestatic risk of novel drug candidates. We expect the application of our workflow to significantly contribute to the stratification of the cholestatic potential of new drugs and to support animal-free testing in future drug development.

Functional Proliferating Human Hepatocytes: In Vitro Hepatocyte Model for Drug Metabolism, Excretion, and Toxicity

To develop a functional alternative hepatocyte model for primary human hepatocytes (PHHs) with proliferative property, essential drug metabolic, and transporter functions, proliferating human hepatocytes (ProliHHs) expanded from PHHs were fully characterized in vitro. Herein, ProliHHs generated from multiple PHHs donors could be expanded more than 200-fold within four passages and maintained their metabolic or transporter capacities partially. Furthermore, ProliHHs were able to regain the mature hepatic property after three-dimensional (3D) culture. Particularly, the downregulated mRNA expression and function of three major cytochrome P450 (P450) enzymes (CYP1A2, CYP2B6, and CYP3A4) in the proliferating process (ProliHHs-P) could be recovered by 3D culture. The metabolic variabilities across different PHHs donors could be inherited to their matured ProliHHs (ProliHHs-M). The intrinsic clearances of seven major P450 enzymes in ProliHHs-M correlated well (r = 0.87) with those in PHHs. Also, bile canaliculi structures could be observed in sandwich-cultured ProliHHs (SC-ProliHHs), and the biliary excretion index of four probe compounds [cholyl-lys-fluorescein, 5-(and-6)-carboxy-2', 7'-dichlorofluorescein diacetate (CDF), deuterium-labeled sodium taurocholate acid, and rosuvastatin] in SC-ProliHHs (>10%) were close to sandwich-cultured PHHs. More importantly, both ProliHHs-P and ProliHHs-M could be used to evaluate hepatotoxicity. Therefore, these findings demonstrated that the 3D and sandwich culture system could be used to recover the metabolic and transporter functions in ProliHHs for clearance prediction and cholestasis risk assessment, respectively. Together, ProliHHs could be a promising substitute for PHHs in drug metabolism, transport, and hepatotoxicity screening. SIGNIFICANCE STATEMENT: This report describes the study of drug metabolic capacities, efflux transporter functions, and toxicity assessments of proliferating human hepatocytes (ProliHHs). The metabolic variability in different primary human hepatocyte donors could be inherited by their matured ProliHHs derivatives. Also, ProliHHs could form canalicular networks in sandwich culture and display biliary excretion capacities. More importantly, both the proliferative and maturation statuses of ProliHHs could be used to evaluate hepatotoxicity. Together, ProliHHs were feasible to support drug candidate screening in hepatic metabolism, disposition, and toxicity.

The Cumulative Risk Assessment of Hepatotoxic Chemicals: A Hepatic Histopathology Perspective

The increased concern on the consequence of exposure to multiple chemical combinations has led national regulatory authorities to develop different concepts to conduct risk assessments on chemical mixtures. Pesticide residues were identified as "problem formulation" in the respective European regulations and in this context, the European Food and Safety Authority has suggested to group pesticidal active ingredients (AIs) into cumulative assessment groups (CAGs) based on the toxicological properties of each AI. One proposed CAG, on the liver, currently consists of 15 subgroups, each representing a specific hepatotoxic effect observed in toxicity studies. Dietary cumulative risk assessments would then have to be conducted assuming dose additivity of all members of each CAG subgroup. The purpose of this publication is to group AIs based upon the knowledge of the pathogenesis of liver effects to discriminate between primary end points (direct consequence of chemical interaction with a biological target) and secondary end points (which are a consequence of, or that arise out of, a previous pathological change). Focusing on the relevant primary end points strengthens and simplifies the selection of compounds for cumulative risk assessment regarding the liver and better rationalizes the basis for chemical grouping. Relevant dose additivity is to be expected at the level of the primary/leading pathological end points and not at the level of the secondary end points. We recognize, however, that special consideration is needed for substances provoking neoplasia, and this category is included in the group of primary end points for which chemicals inducing them are grouped for risk assessment. Using the pathological basis for defining the respective CAGs, 6 liver subgroups and 2 gallbladder/bile duct groups are proposed. This approach simplifies the cumulative assessment calculation without obviously affecting consumer safety.

Epistane, an anabolic steroid used for recreational purposes, causes cholestasis with elevated levels of cholic acid conjugates, by upregulating bile acid synthesis (CYP8B1) and cross-talking with nuclear receptors in human hepatocytes

Anabolic-androgenic steroids are testosterone derivatives, used by body-builders to increase muscle mass. Epistane (EPI) is an orally administered 17α-alkylated testosterone derivative with 2a-3a epithio ring. We identified four individuals who, after EPI consumption, developed long-lasting cholestasis. The bile acid (BA) profile of three patients was characterized, as well the molecular mechanisms involved in this pathology. The serum BA pool was increased from 14 to 61-fold, basically on account of primary conjugated BA (cholic acid (CA) conjugates), whereas secondary BA were very low. In in vitro experiments with cultured human hepatocytes, EPI caused the accumulation of glycoCA in the medium. Moreover, as low as 0.01 μM EPI upregulated the expression of key BA synthesis genes (CYP7A1, by 65% and CYP8B1, by 67%) and BA transporters (NTCP, OSTA and BSEP), and downregulated FGF19. EPI increased the uptake/accumulation of a fluorescent BA analogue in hepatocytes by 50-70%. Results also evidenced, that 40 μM EPI trans-activated the nuclear receptors LXR and PXR. More importantly, 0.01 μM EPI activated AR in hepatocytes, leading to an increase in the expression of CYP8B1. In samples from a human liver bank, we proved that the expression of AR was positively correlated with that of CYP8B1 in men. Taken together, we conclude that EPI could cause cholestasis by inducing BA synthesis and favouring BA accumulation in hepatocytes, at least in part by AR activation. We anticipate that the large phenotypic variability of BA synthesis enzymes and transport genes in man provide a putative explanation for the idiosyncratic nature of EPI-induced cholestasis.

Strategies for Early Prediction and Timely Recognition of Drug-Induced Liver Injury: The Case of Cyclin-Dependent Kinase 4/6 Inhibitors

The idiosyncratic nature of drug-induced liver injury (DILI) represents a current challenge for drug developers, regulators and clinicians. The myriad of agents (including medications, herbals, and dietary supplements) with recognized DILI potential not only strengthens the importance of the post-marketing phase, when urgent withdrawal sometimes occurs for rare unanticipated liver toxicity, but also shows the imperfect predictivity of pre-clinical models and the lack of validated biomarkers beyond traditional, non-specific liver function tests. After briefly reviewing proposed key mechanisms of DILI, we will focus on drug-related risk factors (physiochemical and pharmacokinetic properties) recently proposed as predictors of DILI and use cyclin-dependent kinase 4/6 inhibitors, relatively novel oral anticancer medications approved for breast cancer, as a case study to discuss the feasibility of early detection of DILI signals during drug development: published data from pivotal clinical trials, unpublished post-marketing reports of liver adverse events, and pharmacokinetic properties will be used to provide a comparative evaluation of their liver safety and gain insight into drug-related risk factors likely to explain the observed differences.

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.