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

Control compounds for preclinical drug-induced liver injury assessment: Consensus-driven systematic review by the ProEuroDILI network

BACKGROUND & AIMS

Idiosyncratic drug-induced liver injury (DILI) is a complex and unpredictable event caused by drugs, and herbal or dietary supplements. Early identification of human hepatotoxicity at preclinical stages remains a major challenge, in which the selection of validated in vitro systems and test drugs has a significant impact. In this systematic review, we analyzed the compounds used in hepatotoxicity assays and established a list of DILI-positive and -negative control drugs for validation of in vitro models of DILI, supported by literature and clinical evidence and endorsed by an expert committee from the COST Action ProEuroDILI Network (CA17112).

METHODS

Following 2020 PRISMA guidelines, original research articles focusing on DILI which used in vitro human models and performed at least one hepatotoxicity assay with positive and negative control compounds, were included. Bias of the studies was assessed by a modified 'Toxicological Data Reliability Assessment Tool'.

RESULTS

A total of 51 studies (out of 2,936) met the inclusion criteria, with 30 categorized as reliable without restrictions. Although there was a broad consensus on positive compounds, the selection of negative compounds lacked clarity. 2D monoculture, short exposure times and cytotoxicity endpoints were the most tested, although there was no consensus on drug concentrations.

CONCLUSIONS

Extensive analysis highlighted the lack of agreement on control compounds for in vitro DILI assessment. Following comprehensive in vitro and clinical data analysis together with input from the expert committee, an evidence-based consensus-driven list of 10 positive and negative control drugs for validation of in vitro models of DILI is proposed.

IMPACT AND IMPLICATIONS

Prediction of human toxicity early in the drug development process remains a major challenge, necessitating the development of more physiologically relevant liver models and careful selection of drug-induced liver injury (DILI)-positive and -negative control drugs to better predict the risk of DILI associated with new drug candidates. Thus, this systematic study has crucial implications for standardizing the validation of new in vitro models of DILI. By establishing a consensus-driven list of positive and negative control drugs, the study provides a scientifically justified framework for enhancing the consistency of preclinical testing, thereby addressing a significant challenge in early hepatotoxicity identification. Practically, these findings can guide researchers in evaluating safety profiles of new drugs, refining in vitro models, and informing regulatory agencies on potential improvements to regulatory guidelines, ensuring a more systematic and efficient approach to drug safety assessment.

Impact of the Physical Cellular Microenvironment on the Structure and Function of a Model Hepatocyte Cell Line for Drug Toxicity Applications

It is widely recognised that cells respond to their microenvironment, which has implications for cell culture practices. Growth cues provided by 2D cell culture substrates are far removed from native 3D tissue structure in vivo. Geometry is one of many factors that differs between in vitro culture and in vivo cellular environments. Cultured cells are far removed from their native counterparts and lose some of their predictive capability and reliability. In this study, we examine the cellular processes that occur when a cell is cultured on 2D or 3D surfaces for a short period of 8 days prior to its use in functional assays, which we term: "priming". We follow the process of mechanotransduction from cytoskeletal alterations, to changes to nuclear structure, leading to alterations in gene expression, protein expression and improved functional capabilities. In this study, we utilise HepG2 cells as a hepatocyte model cell line, due to their robustness for drug toxicity screening. Here, we demonstrate enhanced functionality and improved drug toxicity profiles that better reflect the in vivo clinical response. However, findings more broadly reflect in vitro cell culture practises across many areas of cell biology, demonstrating the fundamental impact of mechanotransduction in bioengineering and cell biology.

Liver function in transgender persons: Challenges in the COVID-19 era

Transgender persons constitute a non-negligible percentage of the general population. Physical gender-transitioning in trans persons is mainly achieved with hormonal cross-sex therapy and sex reassignment surgeries that aim to align bodily appearance with gender identity. Hormonal treatment acts via suppressing the secretion of the endogenous sex hormones and replacing them with the hormones of the desired sex. The administration of testosterone is the typical masculinizing treatment in trans men, whilst trans women are routinely treated with estradiol agents in combination with anti-androgens or gonadotrophin-releasing hormone agonists if testes are present. Exogenous androgenic steroids, estradiol agents, and anti-androgens have been implicated in a series of hepatotoxic effects. Thus, liver integrity is a major concern with the long-term administration of cross-sex therapy. Hepatic tissue is susceptible to coronavirus disease 19 (COVID-19) through various pathophysiological mechanisms. Special consideration should be paid to minimize the risk of hepatic damage from the potential cumulative effect of COVID-19 and gender-affirming treatment in transgender patients. Appropriate care is significant, with continuous laboratory monitoring, clinical observation and, if needed, specific treatment, especially in severe cases of infection and in persons with additional liver pathologies. The pandemic can be an opportunity to provide equal access to care for all and increase the resilience of the transgender population.

In Vitro Models for Studying Chronic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major clinical problem in terms of patient morbidity and mortality, cost to healthcare systems and failure of the development of new drugs. The need for consistent safety strategies capable of identifying a potential toxicity risk early in the drug discovery pipeline is key. Human DILI is poorly predicted in animals, probably due to the well-known interspecies differences in drug metabolism, pharmacokinetics, and toxicity targets. For this reason, distinct cellular models from primary human hepatocytes or hepatoma cell lines cultured as 2D monolayers to emerging 3D culture systems or the use of multi-cellular systems have been proposed for hepatotoxicity studies. In order to mimic long-term hepatotoxicity in vitro, cell models, which maintain hepatic phenotype for a suitably long period, should be used. On the other hand, repeated-dose administration is a more relevant scenario for therapeutics, providing information not only about toxicity, but also about cumulative effects and/or delayed responses. In this review, we evaluate the existing cell models for DILI prediction focusing on chronic hepatotoxicity, highlighting how better characterization and mechanistic studies could lead to advance DILI prediction.

Specificities of lipotoxicity of free fatty acids and cytokine profile in patients with chronic diffuse liver diseases

Non-alcoholic fatty liver disease is an important cause of global liver disease characterized by diffuse hepatocytes with hepatocellular ballooning, intrahepatic inflammation and progressive fibrosis. A relevant task is the study of the relationship between content of free fatty acids and serum cytokine profile in patients with chronic diffuse liver diseases. A total of 74 people with chronic diffuse liver diseases were examined, including 32 patients with non-alcoholic fatty liver disease, 22 patients with alcoholic liver disease, 20 patients with toxic hepatitis. Chromatographic examination of free fatty acids (FFA) in blood serum was carried out using a Chromatek-Crystal 5000 gas chromatography system. Patients with chronic diffuse liver diseases had a significant increase in the level of unsaturated free fatty acids (USFA) in cases of toxic hepatitis (by 2.92 times, P > 0.05) and a decrease in the level of saturated free fatty acids (SFA) in cases of non-alcoholic fatty liver disease (by 1.52 times, P > 0.05) compared with the control group; the balance between omega-6 and omega-3 PUFA significantly changed due to increase in linoleic acid in patients with alcoholic liver disease and toxic hepatitis (by 1.91 and 2.11 times, respectively) and arachidonic acid in patients with toxic hepatitis (by 1.78 times). The level of interleukin (IL)-6, IL-10, tumor necrosis factor alpha (TNF-α) were determined. In patients suffering chronic diffuse liver diseases there were multidirectional changes in the composition of free fatty acids of blood serum: a significant increase in the level of USFA, levels ІL-6 in toxic hepatitis; a decrease in the level of SFA, levels ІL-6 and TNF-α during non-alcoholic fatty liver disease; increased TNF-α production, ІL-6 during alcoholic liver disease compared with the control group. Significant change occurred in the balance between omega-6 and omega-3 PUFA due to increase in linoleic acid in cases of alcoholic liver disease and toxic hepatitis and arachidonic acid in cases of toxic hepatitis. The revealed correlations support the hypothesis that inflammation and lipotoxicity of FFA of blood serum contribute to the development and progression of structural changes in the liver. However, the pathomechanism of lipid metabolism and cytokine regulation with different etiological factors have their own characteristics, which should be taken into account when treating patients of these groups. Prospects for further research: these parameters may be used for serologic biomarkers of liver disease and development and implementation of the ratio between FFA and cytokines for the differential diagnosis of chronic diffuse liver disease in medical practice.

Characterisation of Drug-Induced Liver Injury in Patients with COVID-19 Detected by a Proactive Pharmacovigilance Program from Laboratory Signals

Coronavirus disease 2019 (COVID-19) has a wide spectrum of clinical manifestations. An elevation of liver damage markers has been observed in numerous cases, which could be related to the empirical use of potentially hepatotoxic drugs. The aim of this study was to describe the clinical and analytical characteristics and perform a causality analysis from laboratory signals available of drug-induced liver injury (DILI) detected by a proactive pharmacovigilance program in patients hospitalised for COVID-19 at La Paz University Hospital in Madrid (Spain) from 1 March 2020 to 31 December 2020. The updated Roussel Uclaf Causality Assessment Method (RUCAM) was employed to assess DILI causality. A lymphocyte transformation test (LTT) was performed on 10 patients. Ultimately, 160 patients were included. The incidence of DILI (alanine aminotransferase >5, upper limit of normal) was 4.9%; of these, 60% had previous COVID-19 hepatitis, the stay was 8.1 days longer and 98.1% were being treated with more than 5 drugs. The most frequent mechanism was hepatocellular (57.5%), with mild severity (87.5%) and subsequent recovery (88.1%). The most commonly associated drugs were hydroxychloroquine, azithromycin, tocilizumab and ceftriaxone. The highest incidence rate of DILI per 10,000 defined daily doses (DDD) was with remdesivir (992.7/10,000 DDD). Some 80% of the LTTs performed were positive, with a RUCAM score of ≥4. The presence of DILI after COVID-19 was associated with longer hospital stays. An immune mechanism has been demonstrated in a small subset of DILI cases.

Drug-induced organ injury in coronavirus disease 2019 pharmacotherapy: Mechanisms and challenges in differential diagnosis and potential protective strategies

The world is currently facing an unprecedented pandemic caused by a newly recognized and highly pathogenic coronavirus disease 2019 (COVID‐19; induced by SARS‐CoV‐2 virus), which is a severe and ongoing threat to global public health. Since COVID‐19 was officially declared a pandemic by the World Health Organization in March 2020, several drug regimens have rapidly undergone clinical trials for the management of COVID‐19. However, one of the major issues is drug‐induced organ injury, which is a prominent clinical challenge. Unfortunately, most drugs used against COVID‐19 are associated with adverse effects in different organs, such as the kidney, heart, and liver. These side effects are dangerous and, in some cases, they can be lethal. More importantly, organ injury is also a clinical manifestation of COVID‐19 infection. These adverse reactions are increasingly recognized as outcomes of COVID‐19 infection. Therefore, the differential diagnosis of drug‐induced adverse effects from COVID‐19‐induced organ injury is a clinical complication. This review highlights the importance of drug‐induced organ injury, its known mechanisms, and the potential therapeutic strategies in COVID‐19 pharmacotherapy. We review the potential strategies for the differential diagnosis of drug‐induced organ injury. This information can facilitate the development of therapeutic strategies, not only against COVID‐19 but also for future outbreaks of other emerging infectious diseases.

Adverse drug events are well‐known and common clinical problems in COVID‐19 patients.

The differential diagnosis of adverse drug effects and disease‐induced organ injury is a clinical challenge.

Obtaining a detailed history and biochemical analysis of blood‐based biomarkers from the patients as soon as they are admitted is critical for differential diagnosis of drug or disease‐induced organ injury.

Beyond Metabolism: Role of the Immune System in Hepatic Toxicity

The liver is primarily thought of as a metabolic organ; however, the liver is also an important mediator of immunological functions. Key perspectives on this emerging topic were presented in a symposium at the 2018 annual meeting of the American College of Toxicology entitled "Beyond metabolism: Role of the immune system in hepatic toxicity." Viral hepatitis is an important disease of the liver for which insufficient preventive vaccines exist. Host immune responses inadequately clear these viruses and often potentiate immunological inflammation that damages the liver. In addition, the liver is a key innate immune organ against bacterial infection. Hepatocytes and immune cells cooperatively control systemic and local bacterial infections. Conversely, bacterial infection can activate multiple types of immune cells and pathways to cause hepatocyte damage and liver injury. Finally, the immune system and specifically cytokines and drugs can interact in idiosyncratic drug-induced liver injury. This rare disease can result in a disease spectrum that ranges from mild to acute liver failure. The immune system plays a role in this disease spectrum.

Psoralidin, a major component of Psoraleae Fructus, induces inflammasome activation and idiosyncratic liver injury

Idiosyncratic drug-induced liver injury (IDILI) is a rare but potentially fatal disease that is unpredictable and independent of the dose of the drug. Increasing evidence suggests that the majority of IDILI cases are immune-mediated, and the aberrant activation of inflammasome plays a vital role in progression. Psoraleae Fructus (PF), a tonic Chinese medicine, has been able to cause IDILI, but the precise mechanism of hepatotoxicity remains unclear. In this study, eight bioactive compounds involved in PF-induced inflammasome activation were investigated. The results demonstrated that psoralidin activated the inflammasomes followed by secreting caspase-1 and interleukin 1β (IL-1β) in a dose-dependent manner. Interestingly, MCC950, a potent inhibitor of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, could not entirely suppress the psoralidin-induced inflammasome activation. Moreover, psoralidin significantly induced IL-1β maturation and caspase-1 activation in NLRP3-knockout bone marrow-derived macrophages (BMDMs), suggesting that psoralidin not only activates the NLRP3 inflammasome but also activates other types of inflammasomes. The results also demonstrated that psoralidin activated the inflammasomes by promoting the C-terminal caspase recruitment domain (ASC) oligomerization, and the production of mitochondrial reactive oxygen species (mtROS) is a decisive factor in psoralidin-induced inflammasome activation. Importantly, in vivo data revealed that psoralidin induced hepatic inflammation, increased aminotransferase activity and increased the production of IL-1β and tumor necrosis factor(TNF-α) in a susceptible mouse model of lipopolysaccharide (LPS)-mediated IDILI. In summary, these results confirmed that psoralidin causes IDILI by inducing inflammasome activation. The study suggests that psoralidin is a possible risk factor and is responsible for PF-induced IDILI.

Betulinic Acid Exerts Cytoprotective Activity on Zika Virus-Infected Neural Progenitor Cells

Zika virus (ZIKV), a member of the Flaviviridae family, was brought into the spotlight due to its widespread and increased pathogenicity, including Guillain-Barré syndrome and microcephaly. Neural progenitor cells (NPCs), which are multipotent cells capable of differentiating into the major neural phenotypes, are very susceptible to ZIKV infection. Given the complications of ZIKV infection and potential harm to public health, effective treatment options are urgently needed. Betulinic acid (BA), an abundant terpenoid of the lupane group, displays several biological activities, including neuroprotective effects. Here we demonstrate that Sox2⁺ NPCs, which are highly susceptible to ZIKV when compared to their neuronal counterparts, are protected against ZIKV-induced cell death when treated with BA. Similarly, the population of Sox2⁺ and Casp3⁺ NPCs found in ZIKV-infected cerebral organoids was significantly higher in the presence of BA than in untreated controls. Moreover, well-preserved structures were found in BA-treated organoids in contrast to ZIKV-infected controls. Bioinformatics analysis indicated Akt pathway activation by BA treatment. This was confirmed by phosphorylated Akt analysis, both in BA-treated NPCs and brain organoids, as shown by immunoblotting and immunofluorescence analyses, respectively. Taken together, these data suggest a neuroprotective role of BA in ZIKV-infected NPCs.

What have we learned from animal models of idiosyncratic, drug-induced liver injury?

INTRODUCTION

Idiosyncratic, drug-induced liver injury (IDILI) continues to plague patients and restrict the use of drugs that are pharmacologically effective. Mechanisms of IDILI are incompletely understood, and a better understanding would reduce speculation and could help to identify safer drug candidates preclinically. Animal models have the potential to enhance knowledge of mechanisms of IDILI.

AREAS COVERED

Numerous hypotheses have emerged to explain IDILI pathogenesis, many of which center on the roles of the innate and/or adaptive immune systems. Animal models based on these hypotheses are reviewed in the context of their contributions to understanding of IDILI and their limitations.

EXPERT OPINION

Animal models of IDILI based on an activated adaptive immune system have to date failed to reproduce major liver injury that is of most concern clinically. The only models that have so far resulted in pronounced liver injury are based on the multiple determinant hypothesis or the inflammatory stress hypothesis. The liver pathogenesis in IDILI animal models involves various leukocytes and immune mediators such as cytokines. Insights from animal models are changing the way we view IDILI pathogenesis and are leading to better approaches to preclinical prediction of IDILI potential of new drug candidates.

Hepatic Injury Caused by the Environmental Toxicant Vinyl Chloride is Sex-Dependent in Mice

Vinyl chloride (VC), a common industrial chemical, has been associated with hemangiosarcoma and toxicant-associated steatohepatitis (TASH) in men working at rubber-production plants. Our group previously demonstrated that chronic VC inhalation at environmentally relevant levels (< 1 ppm) in male mice exacerbated hepatic injury caused by high-fat diet (HFD) feeding. Because VC studies on TASH have only been performed in male models, the objective of this study is to examine VC inhalation in female mice in the context of TASH mechanisms. Male and female C57Bl/6 mice were fed either a low-fat diet or HFD and exposed to VC or room air using an inhalation chamber, for 12 weeks (6 h, 5 days/week); and plasma and liver samples were collected after euthanasia. Compared with males, females were less susceptible to HFD+VC-induced obesogenic effects demonstrated by lower body weight and fat composition. Histological analysis revealed that whereas VC exacerbated HFD-induced steatosis in males, this effect was absent in females. In addition, females were more resistant to VC-induced hepatic inflammation whereas males had increased liver weights and higher hepatic Tnfα mRNA levels. Systemic markers of hepatic injury, namely alanine aminotransaminase and thrombin/antithrombin levels were increased by HFD+VC co-exposures only in males. In addition, females did not show significant cell death as previously reported in males. Taken together, the results suggested that VC inhalation led to sex-dependent liver and metabolic toxicity. This study implicated the importance of assessing sex differences in environmental basic science and epidemiologic studies to better identify at-risk populations in both men and women.

Predictivity/Translatability of Toxicities Observed in Nonclinical Toxicology Studies to Clinical Safety Outcomes in Drug Development: Case Examples

Nonclinical toxicology studies are conducted to characterize the potential toxicities and establish a safe starting dose for new drugs in clinical studies, but the question remains as to how predictable/translatable the nonclinical safety findings are to humans. In many cases, there is good concordance between nonclinical species and patients. However, there are cases for which there is a lack of predictivity or translatability that led to early termination of clinical studies due to unanticipated toxicities or early termination of programs before making it to the clinic due to unacceptable nonclinical toxicities assumed to be translatable. A few case examples of safety findings that are translatable versus safety findings that are not translatable and why they are not translateable were presented as a symposium at the 38th Annual Meeting of the American College of Toxicology in Palm Springs, California, and are discussed in this article.

Latest advances in diagnosing and predicting DILI: what was new in 2017?

Drug-induced liver injury (DILI) remains an increasingly recognized cause of hepatotoxicity and liver failure worldwide. In 2017, we continued to learn about predicting, diagnosing, and prognosticating drug hepatotoxicity. Areas covered: In this review, we selected from over 1200 articles from 2017 to synopsize updates in DILI. There were new HLA haplotypes associated with medications including HLA-C0401 and HLA-B*14. There has been continued work with quantitative systems pharmacology, particularly with the DILIsym® initiative, which employs mathematical representations of DILI mechanisms to predict hepatotoxicity in simulated populations. Additionally, knowledge regarding microRNAs (miRNAs) continues to expand. Some new miRNAs this past year include miRNA-223 and miRNA-605. Aside from miRNAs, other biomarkers for diagnosis, prognosis, and even prediction of DILI were explored. Studies on K18, OPN, and MCSFR have correlated DILI and liver-associated death within 6 months. Conversely, a new prognostic panel using apolipoportein-A1 and haptoglobin has been proposed to predict recovery. Further study of CDH5 has also provided researchers a possible new biomarker for prediction and susceptibility to DILI. Expert commentary: Although research on DILI remains quite promising, there is yet to be a reliable, simple method to predict, diagnose, and risk assess this form of hepatotoxicity.

Do In Vitro Assays Predict Drug Candidate Idiosyncratic Drug-Induced Liver Injury Risk?

In vitro assays are commonly used during drug discovery to try to decrease the risk of idiosyncratic drug-induced liver injury (iDILI). But how effective are they at predicting risk? One of the most widely used methods evaluates cell cytotoxicity. Cytotoxicity assays that used cell lines that are very different from normal hepatocytes, and high concentrations of drug, were not very accurate at predicting idiosyncratic drug reaction risk. Even cytotoxicity assays that use more biologically normal cells resulted in many false-positive and false-negative results. Assays that quantify reactive metabolite formation, mitochondrial injury, and bile salt export pump (BSEP) inhibition have also been described. Although evidence suggests that reactive metabolite formation and BSEP inhibition can play a role in the mechanism of iDILI, these assays are not very accurate at predicting risk. In contrast, inhibition of the mitochondrial electron transport chain appears not to play an important role in the mechanism of iDILI, although other types of mitochondrial injury may do so. It is likely that there are many additional mechanisms by which drugs can cause iDILI. However, simply measuring more parameters is unlikely to provide better predictive assays unless those parameters are actually involved in the mechanism of iDILI. Hence, a better mechanistic understanding of iDILI is required; however, mechanistic studies of iDILI are very difficult. There is substantive evidence that most iDILI is immune mediated; therefore, the most accurate assays may involve those that determine immune responses to drugs. New methods to manipulate immune tolerance may greatly facilitate development of more suitable methods.