Prediction of the Clinical Risk of Drug-Induced Cholestatic Liver Injury Using an In Vitro Sandwich Cultured Hepatocyte Assay

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.

Contribution of Japanese scientists to drug metabolism and disposition

Japanese researchers have played a pivotal role in advancing the field of drug metabolism and disposition, as demonstrated by their substantial contributions to the journal Drug Metabolism and Disposition (DMD) over the past 5 decades. This review highlights the historical and ongoing impact of Japanese scientists on DMD, celebrating their achievements in elucidating drug metabolism, membrane transport, pharmacokinetics, and toxicology. From the discovery of cytochrome P450 by Tsuneo Omura and Ryo Sato in 1962 to subsequent advances in drug transport research, Japan has maintained a leading position in the field. A geographical analysis of DMD publications reveals a notable increase in contributions from Japan during the 1980s, ranking second globally and maintaining this position through the 2000s. However, recent years have seen a slight decline in output, likely influenced by the COVID-19 pandemic and increased online journals as well as structural changes within academia and industry. Importantly, this trend is not unique to Japan. To sustain excellence and innovation in this field, it is crucial to strengthen funding for absorption, distribution, metabolism, excretion, and toxicity research and promote collaborations between academia, industry, and regulatory agencies. By prioritizing the translation of fundamental discoveries into drug development and clinical applications, scientists in this area can further advance global efforts toward achieving optimal drug efficacy and safety. This review underscores the enduring contributions of Japanese researchers to DMD and calls for renewed efforts to drive innovation and progress in this vital area of science. SIGNIFICANCE STATEMENT: Over the past 5 decades, Japanese scientists have made significant contributions to Drug Metabolism and Disposition through groundbreaking discoveries and advancements in the study of drug-metabolizing enzymes, transporters, pharmacokinetics analysis, and related areas. These contributions continue to shape the field, offering a foundation for future innovation in this area. We hope that the next generation of Japanese scientists will further solidify their global leadership in this area to advance drug development and proper pharmacotherapy.

Physiologically based pharmacokinetic modeling for confirming the role of CYP3A1/2 and P-glycoprotein in detoxification mechanism between glycyrrhizic acid and aconitine in rats

Fuzi, an effective common herb, is often combined with Gancao to treat disease in clinical practice with enhancing its efficacy and alleviating its toxicity. The major toxic and bioactive compounds in Fuzi and Gancao are aconitine (AC) and glycyrrhizic acid (GL), respectively. This study aims to elucidate detoxification mechanism between AC and GL from pharmacokinetic perspective using physiologically based pharmacokinetic (PBPK) model. In vitro experiments exhibited that AC was mainly metabolized by CYP3A1/2 in rat liver microsomes and transported by P-glycoprotein (P-gp) in Caco-2 cells. Kinetics assays showed that the Km and Vmax of AC towards CYP3A1/2 were 2.38 μM and 57.3 pmol/min/mg, respectively, whereas that of AC towards P-gp was 11.26 μM and 147.1 pmol/min/mg, respectively. GL markedly induced the mRNA expressions of CYP3A1/2 and MDR1a/b in rat primary hepatocytes. In vivo studies suggested that the intragastric and intravenous administration of GL significantly reduced systemic exposure of AC by 27% and 33%, respectively. Drug-drug interaction (DDI) model of PBPK predicted that co-administration of GL would decrease the exposure of AC by 39% and 45% in intragastric and intravenous dosing group, respectively. The consistency between predicted data and observed data confirmed that the upregulation of CYP3A1/2 and P-gp was the crucial detoxification mechanism between AC and GL. Thus, this study provides a demonstration for elucidating the compatibility mechanisms of herbal formula using PBPK modeling and gives support for the clinical co-medication of Fuzi and Gancao.

Culture methods focusing on bile canalicular formation using primary human hepatocytes in a short time

The development of models for predicting hepatotoxicity is warranted, as the hepatotoxicity risk of 38-51% of compounds is undetectable in nonclinical studies. Cholestatic drug-induced liver injury (DILI) is a condition in which bile acids are abnormally excreted into the capillary bile canaliculi and are accumulated in hepatocytes, caused by the inhibition of bile salt export pump (BSEP), a transporter that is mainly associated with excretion of bile acids. Although laboratory animals are used as models, the use of human-derived cells is required owing to species differences. Unfortunately, primary human hepatocytes (PHHs) show rapid loss of function in culture and difficulties in forming bile canaliculi. Therefore, we aimed to develop an in vitro culture method for the efficient formation of bile canaliculi and for assessing the function of BSEP in PHHs. Here, PHHs were cultured from 1 h after thawing to day 2 with Z-VAD-FMK, a total caspase inhibitor, and RevitaCell™ supplement, an irreversible Rho-associated coiled-coil forming kinase (ROCK) inhibitor, in combination with RM-101. The PHHs formed bile canaliculi and showed BSEP function on day 6 of culture. Our findings suggest that cultured PHHs may improve the prediction accuracy of the risks of cholestatic DILI-contained toxicity on bile canaliculi.

Yinchen decoction protects against cholic acid diet-induced cholestatic liver injury in mice through liver and ileal FXR signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Cholestasis is a pathophysiological syndrome characterized by the accumulation of bile acids (BAs) that leads to severe liver disease. Artemisia capillaris is documented in Chinese Pharmacopoeia as the authentic resources for Yinchen. Although Yinchen (Artemisia capillaris Thunb.) decoction (YCD) has been used in China for thousands of years to treat jaundice, the underlying mechanisms to ameliorate cholestatic liver injury have not been elucidated.

AIM OF THE STUDY

To investigate the molecular mechanism of how YCD protects against 1% cholic acid (CA) diet-induced intrahepatic cholestasis through FXR signaling.

MATERIALS AND METHODS

Wild-type and Fxr-deficient mice were fed a diet containing 1% CA to establish the intrahepatic cholestasis model. The mice received low-, medium-, or high-dose YCD for 10 days. Plasma biochemical markers were analyzed, liver injury was identified by histopathology, and hepatic and plasma BA content was analyzed. Western blot was used to determine the expression levels of transporters and enzymes involved in BA homeostasis in the liver and intestine.

RESULTS

In wild-type mice, YCD significantly improved plasma transaminase levels, multifocal hepatocellular necrosis, and hepatic and plasma BA contents, upregulated the expression of hepatic FXR and downstream target enzymes and transporters. Meanwhile, YCD significantly induced the expressions of intestinal FXR and FGF15 and hepatic FGFR4. In contrast, the hepatic protective effect of YCD on cholestasis was abolished in Fxr-deficient mice.

CONCLUSION

YCD protects against cholestatic liver injury induced by a CA diet by restoring the homeostasis of BAs via activation of the liver FXR/SHP and ileal FXR/FGF15 signaling pathways. Furthermore, chlorogenic acid and caffeic acid may be the pharmacological agents in YCD responsible for protecting against cholestatic liver injury.

An integrated strategy combining network toxicology and feature-based molecular networking for exploring hepatotoxic constituents and mechanism of Epimedii Folium-induced hepatotoxicity in vitro

Epimedii Folium (EF), a commonly used herbal medicine to treat osteoporosis, has caused serious concern due to potential hepatotoxicity. Until now, its intrinsic hepatotoxic mechanism and hepatotoxic ingredients remain unclear. Here, a novel high-throughput approach was designed to investigate the intrinsic hepatotoxic of EF. High-content screen imaging (HCS) and biochemical tests were first performed to obtain the cytotoxicity parameter matrix of 17 batch EF samples. EF-treated alpha mouse liver 12 (AML12) cells showed increased reactive oxygen species (ROS), reduced glutathione (GSH) and mitochondrial membrane potential (MMP), and apoptosis and cholestasis were further observed. Network toxicology predicted that EF-triggered hepatotoxiciy was involved in transcription factor (TF) activity. The FXR expression, screened by a TF PCR array, exhibited down-regulation following EF extract administration. Moreover, EF inhibited bile acid (BA) metabolism pathway in an FXR-dependent manner. Pearson correlation between the cytotoxicity parameter matrix and quantification feature table obtained from UHPLC-QTOF data of EF suggested 7 prenylated flavonoids possessed potent hepatotoxicities and their cytotoxicity order was further summarized. The transcriptional repression effects of them on FXR were also verified. Collectively, our findings indicate that FXR is probably responsible for EF-induced hepatotoxicity and prenylated flavonoids may be a major class of hepatotoxic constituents in EF.

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.

Research and Development of Microphysiological Systems in Japan Supported by the AMED-MPS Project

Microphysiological systems (MPS) have been actively developed as a new technology for in vitro toxicity testing platforms in recent years. MPS are culture techniques for the reconstruction of the specific functions of human organs or tissues in a limited space to create miniaturized human test systems. MPS have great promise as next-generation in vitro toxicity assessment systems. Here, I will review the current status of MPS and discuss the requirements that must be met in order for MPS to be implemented in the field of drug discovery, presenting the example of an in vitro cell assay system for drug-induced liver injury, which is the research subject in our laboratory. Projects aimed at the development of MPS were implemented early in Europe and the United States, and the AMED-MPS project was launched in Japan in 2017. The AMED-MPS project involves industry, government, and academia. Researchers in the field of drug discovery in the pharmaceutical industry also participate in the project. Based on the discussions made in the project, I will introduce the requirements that need to be met by liver-MPS as in vitro toxicity test platforms.

In Vitro Assay System to Detect Drug-Induced Bile Acid-Dependent Cytotoxicity Using Hepatocytes

Inhibition of bile acid excretion by drugs is a significant factor in the development of drug-induced cholestatic liver injury. We constructed a new in vitro assay system to detect bile acid-dependent cytotoxicity in hepatocytes. This cell-based system can assess the toxicity of the parent compound, as well as the contribution of metabolite(s). In addition, this system can utilize several types of hepatocytes (primary hepatocytes, hepatoma cell line, and induced pluripotent stem cell-induced hepatocytes). In this chapter, a method to detect drug-induced bile acid-dependent toxicity in hepatocytes is described.

[The trends in predicting drug-induced liver injury]

Drug-induced liver injury (DILI) is the major reason for the discontinuation of new drug development and the withdrawal of drugs from the market. Hence, the evaluation systems which predict the onset of DILI in the pre-clinical stage are needed. To date, many researchers have conducted the mechanism of DILI, but the DILI prediction is poor because of the complexity of DILI. In this regard, based on the information obtained from basic research and clinical case, several pharmaceutical companies have been developed DILI prediction methods with high sensitivity and specificity by combining multiple targets. Another reason for low predictability is derived from the conventional culture method which causes a rapid decrease in hepatocyte function. To overcome these problems, the construction of a high-level in vitro evaluation system has been developed and applied to DILI evaluation. On the other hand, these in vitro evaluation methods require a lot of labor and cost so, in silico prediction methods have also been constructed in recent years. Based on this point, this article reviews the trends in DILI prediction systems in the non-clinical stage.

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

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

Understanding Idiosyncratic Toxicity: Lessons Learned from Drug-Induced Liver Injury

Idiosyncratic adverse drug reactions (IADRs) encompass a diverse group of toxicities that can vary by drug and patient. The complex and unpredictable nature of IADRs combined with the fact that they are rare makes them particularly difficult to predict, diagnose, and treat. Common clinical characteristics, the identification of human leukocyte antigen risk alleles, and drug-induced proliferation of lymphocytes isolated from patients support a role for the adaptive immune system in the pathogenesis of IADRs. Significant evidence also suggests a requirement for direct, drug-induced stress, neoantigen formation, and stimulation of an innate response, which can be influenced by properties intrinsic to both the drug and the patient. This Perspective will provide an overview of the clinical profile, mechanisms, and risk factors underlying IADRs as well as new approaches to study these reactions, focusing on idiosyncratic drug-induced liver injury.

Development of an in vitro cholestatic drug-induced liver injury evaluation system using HepG2-hNTCP-C4 cells in sandwich configuration

Toxicological approaches in screening drugs that cause drug-induced liver injury (DILI) are urgently needed to reduce the risk of developing DILI and avoid immense costs resulting from late-stage drug withdrawal from clinical trials. Cholestatic DILI is characterized by bile acid (BA) accumulation in hepatocytes, typically caused by drug-induced inhibition of important bile transporters, such as bile salt export pump (BSEP) and multidrug resistance-associated protein 2/3/4 (MRP2/3/4). Therefore, NTCP expression is essential for construction of an in vitro hepatocellular toxicity evaluation system. Here, we investigated whether sandwich-cultured HepG2-hNTCP-C4 (SCHepG2-hNTCP-C4) cells were applicable for evaluation of cholestatic DILI. In SCHepG2-hNTCP-C4 cells, NTCP and MRP2/4 expression levels were comparable to those in human primary hepatocytes; however, BSEP expression was low. In addition, the substrates tauro-nor-THCA-24 DBD and CDF confirmed the functionality of NTCP and MRP2, respectively. When 22 known hepatotoxins were exposed to BAs to evaluate cholestatic DILI, cytotoxicity in SCHepG2-hNTCP-C4 cells was more frequent than that in SCHepG2 cells. Thus, SCHepG2-hNTCP-C4 cells may be useful preclinical screening tools to predict the risk of cholestatic DILI induced by drug candidates. However, further studies are needed to determine why the cholestatic cytotoxicity of some compounds would be still insufficient in SCHepG2-hNTCP-C4 cells.

Evaluation of Drug Biliary Excretion Using Sandwich-Cultured Human Hepatocytes

Evaluation of hepatobiliary transport of drugs is an important challenge, notably during the development of new molecular identities. In this context, sandwich-cultured human hepatocytes (SCHH) have been proposed as an interesting and integrated tool for predicting in vitro biliary excretion of drugs. The present review was therefore designed to summarize key findings about SCHH, including their establishment, their main functional features and their use for the determination of canalicular transport and the prediction of in vivo biliary clearance and hepatobiliary excretion-related drug-drug interactions. Reviewed data highlight the fact that SCHH represent an original and probably unique holistic in vitro approach to predict biliary clearance in humans, through taking into account sinusoidal drug uptake, passive drug diffusion, drug metabolism and sinusoidal and canalicular drug efflux. Limits and proposed refinements for SCHH-based analysis of drug biliary excretion, as well as putative human alternative in vitro models to SCHH are also discussed.

In vitro bile acid-dependent hepatocyte toxicity assay system using human induced pluripotent stem cell-derived hepatocytes: Current status and disadvantages to overcome

Cholestatic drug-induced liver injury (DILI) is a type of hepatotoxicity. Its underlying mechanisms are dysfunction of bile salt export pump (BSEP) and multidrug resistance-associated protein 2/3/4 (MRP2/3/4), which play major roles in bile acid (BA) excretion into the bile canaliculi and blood, resulting in accumulation of BAs in hepatocytes. The sandwich-cultured hepatocyte (SCH) model can simultaneously analyze hepatic uptake and biliary excretion. Therefore, we investigated whether sandwich-cultured human induced pluripotent stem cell (iPS cell)-derived hepatocytes (SCHiHs) are suitable for evaluating cholestatic DILI. Fluorescent N-(24-[7-(4-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole)]amino-3α,7α,12α-trihydroxy-27-nor-5β-cholestan-26-oyl)-2'-aminoethanesulfonate (tauro-nor-THCA-24-DBD, a BSEP substrate) was accumulated in bile canaliculi, which supports the presence of a functional bile canaliculi lumen. MRP2 was highly expressed in the Western blot analysis, whereas the mRNA expression of BSEP was hardly detectable. MRP3/4 mRNA levels were maintained. Of the 22 compounds known to cause DILI with BAs, 7 showed significant cytotoxicity. Most high-risk drugs were detected using the developed SCHiH system. However, a shortcoming was the considerably low expression level of BSEP, which prevented the detection of some relevant drugs whose risks should be detected in primary human hepatocytes.

Advances in drug-induced cholestasis: Clinical perspectives, potential mechanisms and in vitro systems

Despite growing research, drug-induced liver injury (DILI) remains a serious issue of increasing importance to the medical community that challenges health systems, pharmaceutical industries and drug regulatory agencies. Drug-induced cholestasis (DIC) represents a frequent manifestation of DILI in humans, which is characterised by an impaired canalicular bile flow resulting in a detrimental accumulation of bile constituents in blood and tissues. From a clinical point of view, cholestatic DILI generates a wide spectrum of presentations and can be a diagnostic challenge. The drug classes mostly associated with DIC are anti-infectious, anti-diabetic, anti-inflammatory, psychotropic and cardiovascular agents, steroids, and other miscellaneous drugs. The molecular mechanisms of DIC have been investigated since the 1980s but they remain debatable. It is recognised that altered expression and/or function of hepatobiliary membrane transporters underlies some forms of cholestasis, and this and other concomitant mechanisms are very likely in DIC. Deciphering these processes may pave the ways for diagnosis, prognosis and prevention, for which currently major gaps and caveats exist. In this review, we summarise recent advances in the field of DIC, including clinical aspects, the potential mechanisms postulated so far and the in vitro systems that can be useful to investigate and identify new cholestatic drugs.

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.

BMSCs protect against liver injury via suppressing hepatocyte apoptosis and activating TGF-β1/Bax singling pathway

Many factors cause liver injury, including chronic consumption of alcohol, irregular use of drugs, excessive levels of arsenic in water. This study aims to investigate role of bone marrow-derived mesenchymal stem cells (BMSCs) in liver injury recovery and to explore mechanism. BMSCs and primary hepatocytes were isolated, cultured and identified. Hepatocyte model and hepatic fibrosis (HF) model were established using carbon tetrachloride (CCL-4). The role of BMSCs were investigated in both in vitro and in vivo levels. Cell proliferation was examined using MTT assay. Transforming growth factor-β1 (TGF-β1), Bcl-2 and Bax expression were detected using western blot and real-time PCR, respectively. Results indicated that BMSCs and primary hepatocytes were successfully isolated and identified, and hepatocyte model was successfully established. BMSCs and HGF treatment enhance viability of normal hepatocytes and hepatocyte injury model. Cell viability in BMSCs treatment and Bax-1 inhibitor treatment group was higher significantly compared to normal hepatocyte control and injury hepatocyte model, respectively (P<0.05). Bax-1 expression was significantly lower and Bcl-2 was significantly higher in Bax-1 inhibitor treatment and BMSCs treatment group compared to normal hepatocyte control (normal rats) and injury hepatocyte model (HF model), respectively (P<0.05). BMSCs significantly decreased ALT and AST levels compared to Saline group (P<0.05). In conclusion, function of BMSCs in liver injury was triggered by inhibiting hepatocyte apoptosis and leading cell proliferation through TGF-β1/Bax singling pathway. Our study proved protective role of BMSCs against liver injury via TGF-β1/Bax pathway, which would enrich application of BMSC in clinical.

Synergistic Cytotoxicity from Drugs and Cytokines In Vitro as an Approach to Classify Drugs According to Their Potential to Cause Idiosyncratic Hepatotoxicity: A Proof-of-Concept Study

Idiosyncratic drug-induced liver injury (IDILI) typically occurs in a small fraction of patients and has resulted in removal of otherwise efficacious drugs from the market. Current preclinical testing methods are ineffective in predicting which drug candidates have IDILI liability. Recent results suggest that immune mediators such as tumor necrosis factor-α (TNF) and interferon-γ (IFN) interact with drugs that cause IDILI to kill hepatocytes. This proof-of-concept study was designed to test the hypothesis that drugs can be classified according to their ability to cause IDILI in humans using classification modeling with covariates derived from concentration-response relationships that describe cytotoxic interaction with cytokines. Human hepatoma (HepG2) cells were treated with drugs associated with IDILI or with drugs lacking IDILI liability and cotreated with TNF and/or IFN. Detailed concentration-response relationships were determined for calculation of parameters such as the maximal cytotoxic effect, slope, and EC50 for use as covariates for classification modeling using logistic regression. These parameters were incorporated into multiple classification models to identify combinations of covariates that most accurately classified the drugs according to their association with human IDILI. Of 14 drugs associated with IDILI, almost all synergized with TNF to kill HepG2 cells and were successfully classified by statistical modeling. IFN enhanced the toxicity mediated by some IDILI-associated drugs in the presence of TNF. In contrast, of 10 drugs with little or no IDILI liability, none synergized with inflammatory cytokines to kill HepG2 cells and were classified accordingly. The resulting optimal model classified the drugs with extraordinary selectivity and specificity.

Recent Progress in Hepatocyte Culture Models and Their Application to the Assessment of Drug Metabolism, Transport, and Toxicity in Drug Discovery: The Value of Tissue Engineering for the Successful Development of a Microphysiological System

Tissue engineering technology has provided many useful culture models. This article reviews the merits of this technology in a hepatocyte culture system and describes the applications of the sandwich-cultured hepatocyte model in drug discovery. In addition, we also review recent investigations of the utility of the 3-dimensional bioprinted human liver tissue model and spheroid model. Finally, we present the future direction and developmental challenges of a hepatocyte culture model for the successful establishment of a microphysiological system, represented as an organ-on-a-chip and even as a human-on-a-chip. A merit of advanced culture models is their potential use for detecting hepatotoxicity through repeated exposure to chemicals as they allow long-term culture while maintaining hepatocyte functionality. As a future direction, such advanced hepatocyte culture systems can be connected to other tissue models for evaluating tissue-to-tissue interaction beyond cell-to-cell interaction. This combination of culture models could represent parts of the human body in a microphysiological system.

Drug-induced liver injury: Advances in mechanistic understanding that will inform risk management

Drug-induced liver injury (DILI) is a major public health problem. Intrinsic (dose-dependent) DILI associated with acetaminophen overdose is the number one cause of acute liver failure in the US. However, the most problematic type of DILI impacting drug development is idiosyncratic, occurring only very rarely among treated patients and often only after several weeks or months of treatment with the offending drug. Recent advances in our understanding of the pathogenesis of DILI suggest that three mechanisms may underlie most hepatocyte effects in response to both intrinsic and idiosyncratic DILI drugs: mitochondrial dysfunction, oxidative stress, and alterations in bile acid homeostasis. However, in some cases hepatocyte stress promotes an immune response that results in clinically important idiosyncratic DILI. This review discusses recent advances in our understanding of the pathogenesis of both intrinsic and idiosyncratic DILI as well as emerging tools and techniques that will likely improve DILI risk identification and management.

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.

Assessment of mitochondrial dysfunction-related, drug-induced hepatotoxicity in primary rat hepatocytes

Evidence that mitochondrial dysfunction plays a central role in drug-induced liver injury is rapidly accumulating. In contrast to physiological conditions, in which almost all adenosine triphosphate (ATP) in hepatocytes is generated in mitochondria via aerobic respiration, the high glucose content and limited oxygen supply of conventional culture systems force primary hepatocytes to generate most ATP via cytosolic glycolysis. Thus, such anaerobically poised cells are resistant to xenobiotics that impair mitochondrial function, and are not suitable to identify drugs with mitochondrial liabilities. In this study, primary rat hepatocytes were cultured in galactose-based medium, instead of the conventional glucose-based medium, and in hyperoxia to improve the reliance of energy generation on aerobic respiration. Activation of mitochondria was verified by diminished cellular lactate release and increased oxygen consumption. These conditions improved sensitivity to the mitochondrial complex I inhibitor rotenone. Since oxidative stress is also a general cause of mitochondrial impairment, cells were exposed to test compounds in the presence of transferrin to increase the generation of reactive oxygen species via increased uptake of iron. Finally, 14 compounds with reported mitochondrial liabilities were tested to validate this new drug-induced mitochondrial toxicity assay. Overall, the culture of primary rat hepatocytes in galactose, hyperoxia and transferrin is a useful model for the identification of mitochondrial dysfunction-related drug-induced hepatotoxicity.