A genome-wide study identifies HLA alleles associated with lumiracoxib-related liver injury. Nat Genet. 2010;42:711-714. [PMID: 20639878 DOI: 10.1038/ng.632]

A comprehensive update on the human leukocyte antigen and idiosyncratic adverse drug reactions

INTRODUCTION

Idiosyncratic adverse drug reactions (IADRs) or drug hypersensitivity reactions (DHRs) represent a major health problem because they are unpredictable and can be severe with potential life-long or even lethal consequences. Their pathophysiology is not clear but thought to be immune mediated, supported by the significant statistical association of these reactions with specific alleles of the human leukocyte antigen (HLA) gene.

AREA COVERED

This comprehensive update review summarizes the currently available evidence on the role of HLA gene locus in IADRs and discusses the present understanding of the pathophysiology of IADRs. We searched the available literature in PubMed and Google Scholar with no date restriction for publications on HLA and adverse drug reactions. Findings are summarized and discussed in the context of the currently available evidence.

EXPERT OPINION

The role of the immune system in IADRs and the role of pharmacogenetic testing in this field is evident. HLA genetic testing is very promising in the management of these reactions. Many obstacles seem to prevent pharmacogenetic testing to meet its full potential including cost and health care providers' education. Further work in needed to provide more evidence and allow widespread use of pharmacogenetic testing in the clinical practice.

Disentangling effects of the DR and DQ isomers encoded by the HLA class II haplotype DRB1*15:01/DQB1*06:02 to help establish the true risk allele for FVIII inhibitor development in Hemophilia A

Introduction

Hemophilia A (HA) patients (HAPs) with the human leukocyte antigen (HLA)-class-II (HLAII) haplotype DRB1*15:01/DQB1*06:02, and thus antigen presenting cells which express HLAII β-polypeptide chains that form heterodimers of DR15- and DQ6-serotypes, respectively, have an increased risk of developing factor (F)VIII inhibitors (FEIs)-neutralizing antibodies against the therapeutic-FVIII-proteins (tFVIIIs) infused to prevent/arrest bleeding. As DRB1*15:01 and DQB1*06:02 exist in strong linkage disequilibrium, association analysis cannot determine which is the actual risk allele.

Methods

To establish the true risk allele of this haplotype, we analyzed the tFVIII-derived peptides (tFVIII-dPs) bound to either the DR or DQ molecules that comprise the individual HLAII repertoires expressed by monocyte-derived dendritic cells obtained from 25 normal blood donors and six HAPs, four without and two with FEIs. We performed log-linear mixed model analyses, where the dependent variable is the log of the measured peptide count. Under Model 1, we analyzed an HLAII allele predictor consisting of ten levels (four DRB1 and six DQB1 alleles) in the fixed effects and variables in the random effects to account for non-independence. Model 2-where the HLAII allele variable consisted of only DRB1*15:01 and DQB1*06:02-compares the HLAII alleles.

Results

Relative to the Model 1 reference, DRB1*15:01 and DQB1*06:02 significantly increased tFVIII-derived peptide counts, and DRB1*15:01 contributed significantly more than DQB1*06:02. Reported as risk ratios (RRs) and their 95% confidence interval (CI) lower- (LB) and upper-bound (UB), we found a RR (95% CI-LB, -UB) of 14.16 (10.38, 19.33) and 1.76 (1.24, 2.50) for DRB1*15:01 and DQB1*06:02, respectively. Under Model 2, we found an RR for DRB1*15:01 against DQB1*06:02 of 7.00 (5.80, 8.44).

Discussion/conclusion

Our results suggest that DRB1*15:01 is the offending HLAII allele and that DR15 allotypes underlie the increased FEI risk in HAPs.

Molecular docking to investigate HLA-associated idiosyncratic drug reactions

Idiosyncratic drug reactions (IDRs) pose severe threats to patient health. Unlike conventionally dose-dependent side effects, they are unpredictable and more frequently manifest as life-threatening conditions, such as severe cutaneous adverse reactions (SCARs) and drug-induced liver injury (DILI). Some HLA alleles, such as HLA-B*57:01, HLA-B*15:02, and HLA-B*58:01, are known risk factors for adverse reactions induced by multiple drugs. However, the structural basis underlying most HLA-associated adverse events remains poorly understood. This review summarizes the application of molecular docking to reveal the mechanisms of IDR-related HLA associations, covering studies using this technique to examine drug-HLA binding pockets and identify key binding residues. We provide a comprehensive overview of risk HLA alleles associated with IDRs, followed by a discussion of the utility and limitations of commonly used molecular docking tools in simulating complex molecular interactions within the HLA binding pocket. Through examples, including the binding of abacavir and flucloxacillin to HLA-B*57:01, carbamazepine to HLA-B*15:02, and allopurinol to HLA-B*58:01, we demonstrate how docking analyses can provide insights into the drug and HLA allele-specificity of adverse events. Furthermore, the use of molecular docking to screen drugs with unknown IDR liability is examined, targeting either multiple HLA variants or a single specific variant. Despite multiple challenges, molecular docking presents a promising toolkit for investigating drug-HLA interactions and understanding IDR mechanisms, with significant implications for preemptive HLA typing and safer drug development.

Genetic and Genomic Approaches to the Study of Drug-Induced Liver Injury

Idiosyncratic hepatotoxicity induced by prescribed drugs has been known since the early 20th century. Identifying risk factors, including genetic factors, that trigger this drug-induced liver injury (DILI) has been an important priority for many years, both to prevent drugs that cause liver injury being licensed and as a potential means of preventing at-risk patients being prescribed causative drugs. Improved methods for genomic analysis, particularly the development of genome-wide association studies, have facilitated the identification of genomic risk factors for DILI, but, to date, there are only two main examples, liver injury caused by amoxicillin-clavulanate (AC) and by flucloxacillin, where genetic risk factors causing the injury have been identified and replicated with understanding of the underlying mechanism. There has also been progress on identifying genetic risk factors for liver injury caused by other anti-infective agents, herbal remedies and nonsteroidal anti-inflammatory drugs. The majority of genetic risk factors identified to date are specific human leucocyte antigen (HLA) alleles and evidence that these alleles preferentially present self-peptides inappropriately to T cells in the liver has been obtained. Non-HLA genes also contribute to genetic susceptibility, both as co-factors in T-cell responses and, in the case of isoniazid-only, drug metabolism. Polygenic risk scores to predict DILI have been developed, both a simple score that predicts AC injury and complex scores that may be applied to DILI more generally and provide evidence that additional risk factors other than HLA genes exist.

Hepatic immune regulation and sex disparities

Chronic liver disease is a major cause of morbidity and mortality worldwide. Epidemiology, clinical phenotype and response to therapies for gastrointestinal and liver diseases are commonly different between women and men due to sex-specific hormonal, genetic and immune-related factors. The hepatic immune system has unique regulatory functions that promote the induction of intrahepatic tolerance, which is key for maintaining liver health and homeostasis. In liver diseases, hepatic immune alterations are increasingly recognized as a main cofactor responsible for the development and progression of chronic liver injury and fibrosis. In this Review, we discuss the basic mechanisms of sex disparity in hepatic immune regulation and how these mechanisms influence and modify the development of autoimmune liver diseases, genetic liver diseases, portal hypertension and inflammation in chronic liver disease. Alterations in gut microbiota and their crosstalk with the hepatic immune system might affect the progression of liver disease in a sex-specific manner, creating potential opportunities for novel diagnostic and therapeutic approaches to be evaluated in clinical trials. Finally, we identify and propose areas for future basic, translational and clinical research that will advance our understanding of sex disparities in hepatic immunity and liver disease.

Clues of HLAs, metabolic SNPs, and epigenetic factors in T cell-mediated drug hypersensitivity reactions

Drug hypersensitivities are common reactions due to immunologic responses. They are of utmost importance because they may generate severe and fatal outcomes. Some drugs may cause Adverse Drug Reactions (ADRs), such as drug hypersensitivity reactions (DHRs), which can occur due to the interaction of intact drugs or their metabolites with Human Leukocyte Antigens (HLAs) and T cell receptors (TCRs). This type develops over a period of 24-72 h after exposure and is classified as type IV of DHRs. Acute generalized exanthematic pustulosis (AGEP), Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS) are types of Severe Cutaneous Adverse Reactions (SCARs). In this review, we aim to discuss the types of ADRs, the mechanisms involved in their development, and the role of immunogenetic factors, such as HLAs in type IV DHRs, single-nucleotide polymorphisms (SNPs), and some epigenetic modifications, e.g., DNA/histone methylation in a variety of genes and their promoters which may predispose subjects to DHRs. In conclusion, development of promising novel in vitro or in vivo diagnostic and prognostic markers is essential for identifying susceptible subjects or providing treatment protocols to work up patients with drug allergies as personalized medicine.

Human Leucocyte Antigen Genetics in Idiosyncratic Drug-Induced Liver Injury with Evidence Based on the Roussel Uclaf Causality Assessment Method

The human leucocyte antigen (HLA) allele variability was studied in cohorts of patients with idiosyncratic drug-induced liver injury (iDILI). Some reports showed an association between HLA genetics and iDILI, proposing HLA alleles as a potential risk factor for the liver injury. However, the strength of such assumptions heavily depends on the quality of the iDILI diagnosis, calling for a thorough analysis. Using the PubMed database and Google Science, a total of 25 reports of case series or single cases were retrieved using the terms HLA genes and iDILI. It turned out that in 10/25 reports (40%), HLA genetics were determined in iDILI cases, for which no causality assessment method (CAM) was used or a non-validated tool was applied, meaning the findings were based on subjective opinion, providing disputable results and hence not scoring individual key elements. By contrast, in most iDILI reports (60%), the Roussel Uclaf Causality Assessment Method (RUCAM) was applied, which is the diagnostic algorithm preferred worldwide to assess causality in iDILI cases and represents a quantitative, objective tool that has been well validated by both internal and external DILI experts. The RUCAM provided evidence-based results concerning liver injury by 1 drug class (antituberculotics + antiretrovirals) and 19 different drugs, comprising 900 iDILI cases. Among the top-ranking drugs were amoxicillin-clavulanate (290 cases, HLA A*02:01 or HLA A*30:02), followed by flucloxacillin (255 cases, HLA B*57:01), trimethoprim-sulfamethoxazole (86 cases, HLA B*14:01 or HLA B*14:02), methimazole (40 cases, HLA C*03:02), carbamazepine (29 cases, HLA A*31:01), and nitrofurantoin (26 cases, HLA A*33:01). In conclusion, the HLA genetics in 900 idiosyncratic drug-induced liver injury cases with evidence based on the RUCAM are available for studying the mechanistic steps leading to the injury, including metabolic factors through cytochrome P450 isoforms and processes that activate the innate immune system to the adaptive immune system.

The expanding role of HLA gene tests for predicting drug side effects

Adverse drug reactions can be either dose-dependent (Type A) or idiosyncratic (Type B). Type B adverse drug reactions tend to be extremely rare and difficult to predict. They are usually immune-mediated. Examples include severe skin reactions and drug-induced liver injury. For many commonly prescribed drugs (such as antibiotics), the risk of developing an idiosyncratic adverse drug reaction is influenced by variability in the human leukocyte antigen (HLA) genes. Because these HLA-mediated adverse drug reactions can be lethal, there is growing interest in defining which specific drug-gene relationships might benefit from pre-emptive HLA genotyping and automated clinical decision support. This review summarizes the literature for HLA-mediated adverse reactions linked to common drugs.

Patients with naproxen-induced liver injury display T-cell memory responses toward an oxidative (S)-O-desmethyl naproxen metabolite but not the acyl glucuronide

BACKGROUND

Exposure to nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (IBU) and naproxen (NAP) is associated with idiosyncratic drug-induced liver injury (DILI). Carboxylate bioactivation into reactive metabolites (e.g., acyl glucuronides, AG) and resulting T-cell activation is hypothesized as causal for this adverse event. However, conclusive evidence supporting this is lacking.

METHODS

In this work, we identify CD4+ and CD8+ T-cell hepatic infiltration in a biopsy from an IBU DILI patient. Lymphocyte transformation test and IFN-γ ELIspot, conducted on peripheral blood mononuclear cells (PBMCs) of patients with NAP-DILI, were used to explore drug-specific T-cell activation. T-cell clones (TCC) were generated and tested for drug specificity, phenotype/function, and pathways of T-cell activation. Cells were exposed to NAP, its oxidative metabolite 6-O-desmethyl NAP (DM-NAP), its AG or synthesized NAP-AG human-serum albumin adducts (NAP-AG adduct).

RESULTS

CD4+ and CD8+ T-cells from patients expressing a range of different Vβ receptors were stimulated to proliferate and secrete IFN-γ and IL-22 when exposed to DM-NAP, but not NAP, NAP-AG or the NAP-AG adduct. Activation of the CD4+ TCC was HLA-DQ-restricted and dependent on antigen presenting cells (APC); most TCC were activated with DM-NAP-pulsed APC, while fixation of APC blocked the T-cell response. Cross-reactivity was not observed with structurally-related drugs.

CONCLUSION

Our results confirm hepatic T-cell infiltrations in NSAID-induced DILI, and show a T-cell memory response toward DM-NAP indicating an immune-mediated basis for the adverse event. Whilst bioactivation at the carboxylate group is widely hypothesized to be pathogenic for NSAID associated DILI, we found no evidence of this with NAP.

Genome-wide association study of abnormal elevation of ALT in patients exposed to atabecestat

BACKGROUND

Atabecestat, a potent brain penetrable BACE1 inhibitor that reduces CSF amyloid beta (Aβ), was developed as an oral treatment for Alzheimer's disease (AD). Elevated liver enzyme adverse events were reported in three studies although only one case met Hy's law criteria to predict serious hepatotoxicity.

METHOD

We performed a case-control genome-wide association study (GWAS) to identify genetic risk variants associated with liver enzyme elevation using 42 cases with alanine transaminase (ALT) above three times the upper limit of normal (ULN) and 141 controls below ULN. Additionally, we performed a GWAS using continuous maximal ALT/ULN (expressed as times the ULN) upon exposure to atabecestat as the outcome measure (n = 285).

RESULTS

No variant passed the genome-wide significance threshold (p = 5 × 10- 8) in the case-control GWAS. We identified suggestive association signals in genes (NLRP1, SCIMP, and C1QBP) implicated in the inflammatory processes. Among the genes implicated by position mapping using variants suggestively associated (p < 1 × 10- 5) with ALT elevation case-control status, gene sets involved in innate immune response (adjusted p-value = 0.05) and regulation of cytokine production (adjusted p-value = 0.04) were enriched. One genomic region in the intronic region of GABRG3 passed the genome-wide significance threshold in the continuous max(ALT/ULN) GWAS, and this variant was nominally associated with ALT elevation case status (p = 0.009).

CONCLUSION

The suggestive GWAS signals in the case-control GWAS analysis suggest the potential role of inflammation in atabecestat-induced liver enzyme elevation.

Microphysiological Models for Mechanistic-Based Prediction of Idiosyncratic DILI

Drug-induced liver injury (DILI) is a major contributor to high attrition rates among candidate and market drugs and a key regulatory, industry, and global health concern. While acute and dose-dependent DILI, namely, intrinsic DILI, is predictable and often reproducible in preclinical models, the nature of idiosyncratic DILI (iDILI) limits its mechanistic understanding due to the complex disease pathogenesis, and recapitulation using in vitro and in vivo models is extremely challenging. However, hepatic inflammation is a key feature of iDILI primarily orchestrated by the innate and adaptive immune system. This review summarizes the in vitro co-culture models that exploit the role of the immune system to investigate iDILI. Particularly, this review focuses on advancements in human-based 3D multicellular models attempting to supplement in vivo models that often lack predictability and display interspecies variations. Exploiting the immune-mediated mechanisms of iDILI, the inclusion of non-parenchymal cells in these hepatoxicity models, namely, Kupffer cells, stellate cells, dendritic cells, and liver sinusoidal endothelial cells, introduces heterotypic cell-cell interactions and mimics the hepatic microenvironment. Additionally, drugs recalled from the market in the US between 1996-2010 that were studies in these various models highlight the necessity for further harmonization and comparison of model characteristics. Challenges regarding disease-related endpoints, mimicking 3D architecture with different cell-cell contact, cell source, and the underlying multi-cellular and multi-stage mechanisms are described. It is our belief that progressing our understanding of the underlying pathogenesis of iDILI will provide mechanistic clues and a method for drug safety screening to better predict liver injury in clinical trials and post-marketing.

Genetic and Epigenetic Basis of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a rare but severe adverse drug reaction seen in pharmacotherapy and a major cause of postmarketing drug withdrawals. Advances in genome-wide studies indicate that genetic and epigenetic diversity can lead to inter-individual differences in drug response and toxicity. It is necessary to identify how the genetic variations, in the presence of environmental factors, can contribute to development and progression of DILI. Studies on microRNA, histone modification, DNA methylation, and single nucleotide polymorphisms related to DILI were retrieved from databases and were analyzed for the current research and updated to develop this narrative review. We have compiled some of the major genetic, epigenetic, and pharmacogenetic factors leading to DILI. Many validated genetic risk factors of DILI, such as variants of drug-metabolizing enzymes, HLA alleles, and some transporters were identified. In conclusion, these studies provide useful information in risk alleles identification and on implementation of personalized medicine.

Per- and polyfluoroalkyl substances activate UPR pathway, induce steatosis and fibrosis in liver cells

Per- and polyfluoroalkyl substances (PFAS), which include perfluorooctanoic acid (PFOA), heptafluorobutyric acid (HFBA), and perfluorotetradecanoic acid (PFTA), are commonly occurring organic pollutants. Exposure to PFAS affects the immune system, thyroid and kidney function, lipid metabolism, and insulin signaling and is also involved in the development of fatty liver disease and cancer. The molecular mechanisms by which PFAS cause fatty liver disease are not understood in detail. In the current study, we investigated the effect of low physiologically relevant concentrations of PFOA, HFBA, and PFTA on cell survival, steatosis, and fibrogenic signaling in liver cell models. Exposure of PFOA and HFBA (10 to 1000 nM) specifically promoted cell survival in HepaRG and HepG2 cells. PFAS increased the expression of TNFα and IL6 inflammatory markers, increased endogenous reactive oxygen species (ROS) production, and activated unfolded protein response (UPR). Furthermore, PFAS enhanced cell steatosis and fibrosis in HepaRG and HepG2 cells which were accompanied by upregulation of steatosis (SCD1, ACC, SRBP1, and FASN), and fibrosis (TIMP2, p21, TGFβ) biomarkers expression, respectively. RNA-seq data suggested that chronic exposures to PFOA modulated the expression of fatty acid/lipid metabolic genes that are involved in the development of NFALD and fatty liver disease. Collectively our data suggest that acute/chronic physiologically relevant concentrations of PFAS enhance liver cell steatosis and fibrosis by the activation of the UPR pathway and by modulation of NFALD-related gene expression.

The Potential Role of Metabolomics in Drug-Induced Liver Injury (DILI) Assessment

Drug-induced liver injury (DILI) is one of the most frequent adverse clinical reactions and a relevant cause of morbidity and mortality. Hepatotoxicity is among the major reasons for drug withdrawal during post-market and late development stages, representing a major concern to the pharmaceutical industry. The current biochemical parameters for the detection of DILI are based on enzymes (alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP)) and bilirubin serum levels that are not specific of DILI and therefore there is an increasing interest on novel, specific, DILI biomarkers discovery. Metabolomics has emerged as a tool with a great potential for biomarker discovery, especially in disease diagnosis, and assessment of drug toxicity or efficacy. This review summarizes the multistep approaches in DILI biomarker research and discovery based on metabolomics and the principal outcomes from the research performed in this field. For that purpose, we have reviewed the recent scientific literature from PubMed, Web of Science, EMBASE, and PubTator using the terms “metabolomics”, “DILI”, and “humans”. Despite the undoubted contribution of metabolomics to our understanding of the underlying mechanisms of DILI and the identification of promising novel metabolite biomarkers, there are still some inconsistencies and limitations that hinder the translation of these research findings into general clinical practice, probably due to the variability of the methods used as well to the different mechanisms elicited by the DILI causing agent.

An Updated Review of Genetic Associations With Severe Adverse Drug Reactions: Translation and Implementation of Pharmacogenomic Testing in Clinical Practice

Adverse drug reactions (ADR) remain the major problems in healthcare. Most severe ADR are unpredictable, dose-independent and termed as type B idiosyncratic reactions. Recent pharmacogenomic studies have demonstrated the strong associations between severe ADR and genetic markers, including specific HLA alleles (e.g., HLA-B*15:02/HLA-B*57:01/HLA-A*31:01 for carbamazepine-induced severe cutaneous adverse drug reactions [SCAR], HLA-B*58:01 for allopurinol-SCAR, HLA-B*57:01 for abacavir-hypersensitivity, HLA-B*13:01 for dapsone/co-trimoxazole-induced SCAR, and HLA-A*33:01 for terbinafine-induced liver injury), drug metabolism enzymes (such as CYP2C9*3 for phenytoin-induced SCAR and missense variant of TPMT/NUDT15 for thiopurine-induced leukopenia), drug transporters (e.g., SLCO1B1 polymorphism for statin-induced myopathy), and T cell receptors (Sulfanilamide binding into the CDR3/Vα of the TCR 1.3). This mini review article aims to summarize the current knowledge of pharmacogenomics of severe ADR, and the potentially clinical use of these genetic markers for avoidance of ADR.

Roles of Cofactors in Drug-Induced Liver Injury: Drug Metabolism and Beyond

Drug-induced liver injury (DILI) remains one of the major concerns for healthcare providers and patients. Unfortunately, it is difficult to predict and prevent DILI in the clinic because detailed mechanisms of DILI are largely unknown. Many risk factors have been identified for both "intrinsic" and "idiosyncratic" DILI, suggesting that cofactors are an important aspect in understanding DILI. This review outlines the cofactors that potentiate DILI and categorizes them into two types: (1) the specific cofactors that target metabolic enzymes, transporters, antioxidation defense, immune response, and liver regeneration; and (2) the general cofactors that include inflammation, age, gender, comorbidity, gut microbiota, and lifestyle. The underlying mechanisms by which cofactors potentiate DILI are also discussed. SIGNIFICANCE STATEMENT: This review summarizes the risk factors for DILI, which can be used to predict and prevent DILI in the clinic. This work also highlights the gaps in the DILI field and provides future perspectives on the roles of cofactors in DILI.

Drug-Induced Hypersensitivity Syndrome (DIHS)/Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS): Clinical Features and Pathogenesis

Drug-induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DIHS/DRESS) is one example of a severe delayed T-cell-mediated adverse drug reaction. DIHS/DRESS presents with fever, widespread rash and facial edema, organ involvement, and hematological abnormalities, including eosinophilia and atypical lymphocytosis. DIHS/DRESS is associated with relapse 2 to 4 weeks after acute symptoms, often coinciding with reactivation of prevalent chronic persistent human herpesviruses such as human herpesvirus 6, EBV, and cytomegalovirus. The mortality of DIHS/DRESS is up to 10% and often related to unrecognized myocarditis and cytomegalovirus complications, with longer-term consequences that contribute to morbidity including autoimmune diseases such as thyroiditis. It is essential that all potential drug causes, including all new drugs introduced within the 8 weeks preceding onset of DIHS/DRESS symptoms, are identified. All potential drug culprits, as well as drugs that are closely related structurally to the culprit drug, should be avoided in the future. Systemic corticosteroids have remained the mainstay for the treatment of DIHS/DRESS with internal organ involvement. Steroid-sparing agents, such as cyclosporine, mycophenolate mofetil, and monthly intravenous immune globulin, have been successfully used for treatment, and careful follow-up for cytomegalovirus reactivation is recommended. Strong associations between HLA class I alleles and DIHS/DRESS predisposition include HLA-B∗13:01 and dapsone, HLA-B∗58:01 and allopurinol, and HLA-B∗32:01 and vancomycin. These have opened a pathway for prevention, risk stratification, and earlier diagnosis. Single-cell sequencing and other studies of immunopathogenesis promise to identify targeted treatment approaches.

In vitro cell-based models of drug-induced hepatotoxicity screening: progress and limitation

Drug-induced liver injury (DILI) is one of the major causes of post-approval withdrawal of therapeutics. As a result, there is an increasing need for accurate predictive in vitro assays that reliably detect hepatotoxic drug candidates while reducing drug discovery time, costs, and the number of animal experiments. In vitro hepatocyte-based research has led to an improved comprehension of the underlying mechanisms of chemical toxicity and can assist the prioritization of therapeutic choices with low hepatotoxicity risk. Therefore, several in vitro systems have been generated over the last few decades. This review aims to comprehensively present the development and validation of 2D (two-dimensional) and 3D (three-dimensional) culture approaches on hepatotoxicity screening of compounds and highlight the main factors affecting predictive power of experiments. To this end, we first summarize some of the recognized hepatotoxicity mechanisms and related assays used to appraise DILI mechanisms and then discuss the challenges and limitations of in vitro models.

Human Leukocyte Antigen (HLA) Testing in Pharmacogenomics

The genetic region on the short arm of chromosome 6 where the human leukocyte antigen (HLA) genes are located is the major histocompatibility complex. The genes in this region are highly polymorphic, and some loci have a high degree of homology with other genes and pseudogenes. Histocompatibility testing has traditionally been performed in the setting of transplantation and involves determining which specific alleles are present. Several HLA alleles have been associated with disease risk or increased risk of adverse drug reaction (ADR) when treated with certain medications. Testing for these applications differs from traditional histocompatibility in that the desired result is simply presence or absence of the allele of interest, rather than determining which allele is present. At present, the majority of HLA typing is done by molecular methods using commercially available kits. A subset of pharmacogenomics laboratories has developed their own methods, and in some cases, query single nucleotide variants associated with certain HLA alleles rather than directly testing for the allele. In this chapter, a brief introduction to the HLA system is provided, followed by an overview of a variety of testing technologies including those specifically used in pharmacogenomics, and the chapter concludes with details regarding specific HLA alleles associated with ADR.

The Immunological Mechanisms and Immune-Based Biomarkers of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) has become one of the major challenges of drug safety all over the word. So far, about 1,100 commonly used drugs including the medications used regularly, herbal and/or dietary supplements, have been reported to induce liver injury. Moreover, DILI is the main cause of the interruption of new drugs development and drugs withdrawn from the pharmaceutical market. Acute DILI may evolve into chronic DILI or even worse, commonly lead to life-threatening acute liver failure in Western countries. It is generally considered to have a close relationship to genetic factors, environmental risk factors, and host immunity, through the drug itself or its metabolites, leading to a series of cellular events, such as haptenization and immune response activation. Despite many researches on DILI, the specific biomarkers about it are not applicable to clinical diagnosis, which still relies on the exclusion of other causes of liver disease in clinical practice as before. Additionally, circumstantial evidence has suggested that DILI is mediated by the immune system. Here, we review the underlying mechanisms of the immune response to DILI and provide guidance for the future development of biomarkers for the early detection, prediction, and diagnosis of DILI.

Cannabinoids: Revealing their complexity and role in central networks of fear and anxiety

The first aim of the present review is to provide an in-depth description of the cannabinoids and their known effects at various neuronal receptors. It reveals that cannabinoids are highly diverse, and recent work has highlighted that their effects on the central nervous system (CNS) are surprisingly more complex than previously recognized. Cannabinoid-sensitive receptors are widely distributed throughout the CNS where they act as primary modulators of neurotransmission. Secondly, we examine the role of cannabinoid receptors at key brain sites in the control of fear and anxiety. While our understanding of how cannabinoids specifically modulate these networks is mired by their complex interactions and diversity, a plausible framework(s) for their effects is proposed. Finally, we highlight some important knowledge gaps in our understanding of the mechanism(s) responsible for their effects on fear and anxiety in animal models and their use as therapeutic targets in humans. This is particularly important for our understanding of the phytocannabinoids used as novel clinical interventions.

Analytical and Omics-Based Advances in the Study of Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a significant clinical issue, affecting 1-1.5 million patients annually, and remains a major challenge during drug development-toxicity and safety concerns are the second-highest reason for drug candidate failure. The future prevalence of DILI can be minimized by developing a greater understanding of the biological mechanisms behind DILI. Both qualitative and quantitative analytical techniques are vital to characterizing and investigating DILI. In vitro assays are capable of characterizing specific aspects of a drug's hepatotoxic nature and multiplexed assays are capable of characterizing and scoring a drug's association with DILI. However, an even deeper insight into the perturbations to biological pathways involved in the mechanisms of DILI can be gained through the use of omics-based analytical techniques: genomics, transcriptomics, proteomics, and metabolomics. These omics analytical techniques can offer qualitative and quantitative insight into genetic susceptibilities to DILI, the impact of drug treatment on gene expression, and the effect on protein and metabolite abundance. This review will discuss the analytical techniques that can be applied to characterize and investigate the biological mechanisms of DILI and potential predictive biomarkers.

Drug-Induced Vanishing Bile Duct Syndrome: From Pathogenesis to Diagnosis and Therapeutics

The most concerned issue in the context of drug/herb-induced chronic cholestasis is vanishing bile duct syndrome. The progressive destruction of intrahepatic bile ducts leading to ductopenia is usually not dose dependent, and has a delayed onset that should be suspected when abnormal serum cholestasis enzyme levels persist despite drug withdrawal. Immune-mediated cholangiocyte injury, direct cholangiocyte damage by drugs or their metabolites once in bile, and sustained exposure to toxic bile salts when biliary epithelium protective defenses are impaired are the main mechanisms of cholangiolar damage. Current therapeutic alternatives are scarce and have not shown consistent beneficial effects so far. This review will summarize the current literature on the main diagnostic tools of ductopenia and its histological features, and the differential diagnostic with other ductopenic diseases. In addition, pathomechanisms will be addressed, as well as the connection between them and the supportive and curative strategies for ductopenia management.

HLA class II peptide-binding-region analysis reveals funneling of polymorphism in action

BACKGROUND

HLA-class II proteins hold important roles in key physiological processes. The purpose of this study was to compile all class II alleles reported in human population and investigate patterns in pocket variants and their combinations, focusing on the peptide-binding region (PBR).

METHODS

For this purpose, all protein sequences of DPA1, DQA1, DPB1, DQB1 and DRB1 were selected and filtered, in order to have full PBR sequences. Proportional representation was used for pocket variants while population data were also used.

RESULTS

All pocket variants and PBR sequences were retrieved and analyzed based on the preference of amino acids and their properties in all pocket positions. The observed number of pocket variants combinations was much lower than the possible inferred, suggesting that PBR formation is under strict funneling. Also, although class II proteins are very polymorphic, in the majority of the reported alleles in all populations, a significantly less polymorphic pocket core was found.

CONCLUSIONS

Pocket variability of five HLA class II proteins was studied revealing favorable properties of each protein. The actual PBR sequences of HLA class II proteins appear to be governed by restrictions that lead to the establishment of only a fraction of the possible combinations and the polymorphism recorded is the result of intense funneling based on function.

Drug-specific T-cell responses in patients with liver injury following treatment with the BACE inhibitor atabecestat

BACKGROUND

Atabecestat is an orally administered BACE inhibitor developed to treat Alzheimer's disease. Elevations in hepatic enzymes were detected in a number of in trial patients, which resulted in termination of the drug development programme. Immunohistochemical characterization of liver tissue from an index case of atabecestat-mediated liver injury revealed an infiltration of T-lymphocytes in areas of hepatocellular damage. This coupled with the fact that liver injury had a delayed onset suggests that the adaptive immune system may be involved in the pathogenesis. The aim of this study was to generate and characterize atabecestat(metabolite)-responsive T-cell clones from patients with liver injury.

METHODS

Peripheral blood mononuclear cells were cultured with atabecestat and its metabolites (diaminothiazine [DIAT], N-acetyl DIAT & epoxide) and cloning was attempted in a number of patients. Atabecestat(metabolite)-responsive clones were analysed in terms of T-cell phenotype, function, pathways of T-cell activation and cross-reactivity with structurally related compounds.

RESULTS

CD4⁺ T-cell clones activated with the DIAT metabolite were detected in 5 out of 8 patients (up to 4.5% cloning efficiency). Lower numbers of CD4⁺ and CD8⁺ clones displayed reactivity against atabecestat. Clones proliferated and secreted IFN-γ, IL-13 and cytolytic molecules following atabecestat or DIAT stimulation. Certain atabecestat and DIAT-responsive clones cross-reacted with N-acetyl DIAT; however, no cross-reactivity was observed between atabecestat and DIAT. CD4⁺ clones were activated through a direct, reversible compound-HLA class II interaction with no requirement for protein processing.

CONCLUSION

The detection of atabecestat metabolite-responsive T-cell clones activated via a pharmacological interactions pathway in patients with liver injury is indicative of an immune-based mechanism for the observed hepatic enzyme elevations.

Artificial intelligence methods for a Bayesian epistemology-powered evidence evaluation

RATIONALE, AIMS AND OBJECTIVES

The diversity of types of evidence (eg, case reports, animal studies and observational studies) makes the assessment of a drug's safety profile into a formidable challenge. While frequentist uncertain inference struggles in aggregating these signals, the more flexible Bayesian approaches seem better suited for this quest. Artificial Intelligence (AI) offers great promise to these approaches for information retrieval, decision support, and learning probabilities from data.

METHODS

E-Synthesis is a Bayesian framework for drug safety assessments built on philosophical principles and considerations. It aims to aggregate all the available information, in order to provide a Bayesian probability of a drug causing an adverse reaction. AI systems are being developed for evidence aggregation in medicine, which increasingly are automated.

RESULTS

We find that AI can help E-Synthesis with information retrieval, usability (graphical decision-making aids), learning Bayes factors from historical data, assessing quality of information and determining conditional probabilities for the so-called 'indicators' of causation for E-Synthesis. Vice versa, E-Synthesis offers a solid methodological basis for (semi-)automated evidence aggregation with AI systems.

CONCLUSIONS

Properly applied, AI can help the transition of philosophical principles and considerations concerning evidence aggregation for drug safety to a tool that can be used in practice.

Advances in Genomic Discovery and Implications for Personalized Prevention and Medicine: Estonia as Example

The current paradigm of personalized medicine envisages the use of genomic data to provide predictive information on the health course of an individual with the aim of prevention and individualized care. However, substantial efforts are required to realize the concept: enhanced genetic discoveries, translation into intervention strategies, and a systematic implementation in healthcare. Here we review how further genetic discoveries are improving personalized prediction and advance functional insights into the link between genetics and disease. In the second part we give our perspective on the way these advances in genomic research will transform the future of personalized prevention and medicine using Estonia as a primer.

Oxidative Stress in Drug-Induced Liver Injury (DILI): From Mechanisms to Biomarkers for Use in Clinical Practice

Idiosyncratic drug-induced liver injury (DILI) is a type of hepatic injury caused by an uncommon drug adverse reaction that can develop to conditions spanning from asymptomatic liver laboratory abnormalities to acute liver failure (ALF) and death. The cellular and molecular mechanisms involved in DILI are poorly understood. Hepatocyte damage can be caused by the metabolic activation of chemically active intermediate metabolites that covalently bind to macromolecules (e.g., proteins, DNA), forming protein adducts-neoantigens-that lead to the generation of oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress, which can eventually lead to cell death. In parallel, damage-associated molecular patterns (DAMPs) stimulate the immune response, whereby inflammasomes play a pivotal role, and neoantigen presentation on specific human leukocyte antigen (HLA) molecules trigger the adaptive immune response. A wide array of antioxidant mechanisms exists to counterbalance the effect of oxidants, including glutathione (GSH), superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX), which are pivotal in detoxification. These get compromised during DILI, triggering an imbalance between oxidants and antioxidants defense systems, generating oxidative stress. As a result of exacerbated oxidative stress, several danger signals, including mitochondrial damage, cell death, and inflammatory markers, and microRNAs (miRNAs) related to extracellular vesicles (EVs) have already been reported as mechanistic biomarkers. Here, the status quo and the future directions in DILI are thoroughly discussed, with a special focus on the role of oxidative stress and the development of new biomarkers.

Human Leukocyte Antigen B*14:01 and B*35:01 Are Associated With Trimethoprim-Sulfamethoxazole Induced Liver Injury

BACKGROUND AND AIMS

Trimethoprim (TMP)-sulfamethoxazole (SMX) is an important cause of idiosyncratic drug-induced liver injury (DILI), but its genetic risk factors are not well understood. This study investigated the relationship between variants in the human leukocyte antigen (HLA) class 1 and 2 genes and well-characterized cases of TMP-SMX DILI.

APPROACH AND RESULTS

European American and African American persons with TMP-SMX DILI were compared with respective population controls. HLA sequencing was performed by Illumina MiSeq (Illumina, San Diego, CA) for cases. The HLA genotype imputation with attribute bagging program was used to impute HLA alleles for controls. The allele frequency difference between case patients and controls was tested by Fisher's exact tests for each ethnic group. For European Americans, multivariable logistic regression with Firth penalization was used to test the HLA allelic effect after adjusting for age and the top two principal components. Molecular docking was performed to assess HLA binding with TMP and SMX. The European American subset had 51 case patients and 12,156 controls, whereas the African American subset had 10 case patients and 5,439 controls. Four HLA alleles were significantly associated in the European American subset, with HLA-B*14:01 ranking at the top (odds ratio, 9.20; 95% confidence interval, 3.16, 22.35; P = 0.0003) after covariate adjustment. All carriers of HLA-B*14:01 with TMP-SMX DILI possessed HLA-C*08:02, another significant allele (P = 0.0026). This pattern was supported by HLA-B*14:01-HLA-C*08:02 haplotype association (P = 1.33 × 10^-5 ). For the African American patients, HLA-B*35:01 had 2.8-fold higher frequency in case patients than in controls, with 5 of 10 patients carrying this allele. Molecular docking showed cysteine at position 67 in HLA-B*14:01 and phenylalanine at position 67 in HLA-B*35:01 to be the predictive binding sites for SMX metabolites.

CONCLUSIONS

HLA-B*14:01 is associated with TMP-SMX DILI in European Americans, and HLA-B*35:01 may be a potential genetic risk factor for African Americans.

Drug response in association with pharmacogenomics and pharmacomicrobiomics: towards a better personalized medicine

Researchers have long been presented with the challenge imposed by the role of genetic heterogeneity in drug response. For many years, Pharmacogenomics and pharmacomicrobiomics has been investigating the influence of an individual's genetic background to drug response and disposition. More recently, the human gut microbiome has proven to play a crucial role in the way patients respond to different therapeutic drugs and it has been shown that by understanding the composition of the human microbiome, we can improve the drug efficacy and effectively identify drug targets. However, our knowledge on the effect of host genetics on specific gut microbes related to variation in drug metabolizing enzymes, the drug remains limited and therefore limits the application of joint host-microbiome genome-wide association studies. In this paper, we provide a historical overview of the complex interactions between the host, human microbiome and drugs. While discussing applications, challenges and opportunities of these studies, we draw attention to the critical need for inclusion of diverse populations and the development of an innovative and combined pharmacogenomics and pharmacomicrobiomics approach, that may provide an important basis in personalized medicine.

Models of Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of attrition during the early and late stages of drug development and after a drug is marketed. DILI is generally classified as either intrinsic or idiosyncratic. Intrinsic DILI is dose dependent and predictable (e.g., acetaminophen toxicity). However, predicting the occurrence of idiosyncratic DILI, which has a very low incidence and is associated with severe liver damage, is difficult because of its complex nature and the poor understanding of its mechanism. Considering drug metabolism and pharmacokinetics, we established experimental animal models of DILI for 14 clinical drugs that cause idiosyncratic DILI in humans, which is characterized by the formation of reactive metabolites and the involvement of both innate and adaptive immunity. On the basis of the biomarker data obtained from the animal models, we developed a cell-based assay system that predicts the potential risks of drugs for inducing DILI. These findings increase our understanding of the mechanisms of DILI and may help predict and prevent idiosyncratic DILI due to certain drugs.

The American lifestyle-induced obesity syndrome diet in male and female rodents recapitulates the clinical and transcriptomic features of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis

The pathogenesis of nonalcoholic fatty liver disease (NAFLD) and the progression to nonalcoholic steatohepatitis (NASH) and increased risk of hepatocellular carcinoma remain poorly understood. Additionally, there is increasing recognition of the extrahepatic manifestations associated with NAFLD and NASH. We demonstrate that intervention with the American lifestyle-induced obesity syndrome (ALIOS) diet in male and female mice recapitulates many of the clinical and transcriptomic features of human NAFLD and NASH. Male and female C57BL/6N mice were fed either normal chow (NC) or ALIOS from 11 to 52 wk and underwent comprehensive metabolic analysis throughout the duration of the study. From 26 wk, ALIOS-fed mice developed features of hepatic steatosis, inflammation, and fibrosis. ALIOS-fed mice also had an increased incidence of hepatic tumors at 52 wk compared with those fed NC. Hepatic transcriptomic analysis revealed alterations in multiple genes associated with inflammation and tissue repair in ALIOS-fed mice. Ingenuity Pathway Analysis confirmed dysregulation of metabolic pathways as well as those associated with liver disease and cancer. In parallel the development of a robust hepatic phenotype, ALIOS-fed mice displayed many of the extrahepatic manifestations of NAFLD, including hyperlipidemia, increased fat mass, sarcopenia, and insulin resistance. The ALIOS diet in mice recapitulates many of the clinical features of NAFLD and, therefore, represents a robust and reproducible model for investigating the pathogenesis of NAFLD and its progression.NEW & NOTEWORTHY Nonalcoholic fatty liver disease (NAFLD) affects 30% of the general population and can progress to nonalcoholic steatohepatitis (NASH) and potentially hepatocellular carcinoma. Preclinical models rely on mouse models that often display hepatic characteristics of NAFLD but rarely progress to NASH and seldom depict the multisystem effects of the disease. We have conducted comprehensive metabolic analysis of both male and female mice consuming a Western diet of trans fats and sugar, focusing on both their hepatic phenotype and extrahepatic manifestations.

Hepatocyte-Derived Exosomes Promote Liver Immune Tolerance: Possible Implications for Idiosyncratic Drug-Induced Liver Injury

Most idiosyncratic drug-induced liver injury appears to result from an adaptive immune attack on the liver. Recent evidence suggests that the T-cell response may be facilitated by the loss of immune tolerance. In this study, we explored the hypothesis that constitutively released hepatocyte-derived exosomes (HDE) are important for maintaining normal liver immune tolerance. Exosomes were isolated from the conditioned medium of primary human hepatocytes via polymer precipitation. Mock controls were prepared by processing fresh medium that was not hepatocyte exposed with precipitation reagent. THP-1 monocytes were then treated with HDE or an equivalent volume of mock control for 24 h, followed by a 6-h stimulation with LPS. HDE exposure resulted in a significant decrease in the LPS-induced media levels of interleukin-1β and interleukin-8. Gene expression profiling performed in THP-1 cells just prior to LPS-induced stimulation identified a significant decrease among genes associated with innate immune response. MicroRNA (miRNA) profiling was performed on the HDE to identify exosome contents that may drive immune suppression. Many of the predicted mRNA target genes for the most abundant microRNAs in HDE were among the differentially expressed genes in THP-1 cells. Taken together, our data suggest that HDE play a role in maintaining normal liver immune tolerance. Future experiments will explore the possibility that drugs causing idiosyncratic liver injury promote the loss of homeostatic HDE signaling.

Drug-Induced liver Injury Associated with Severe Cutaneous Hypersensitivity Reactions: A Complex Entity in Need of a Multidisciplinary Approach

Idiosyncratic drug-induced liver injury (DILI) occasionally occurs in the setting of severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS). This strengthens the proposed immunologic mechanism associated with this adverse reaction. DRESS exhibits the most common association with DILI. SCARs have a wide spectrum of heterogeneous clinical presentations and severity, and genetic predisposition has been identified. In the context of SCARs, DILI present a different clinical picture, ranging from mild injury to acute liver failure. Elucidating the role of DILI in the clinical presentation and outcome of SCARs represents a challenge due to limited information from published studies and the lack of consensus on definitions. The cholestatic and mixed pattern of liver damage typically predominates in the case of DILI associated with SCARs, which is different from DILI without SCARs where hepatocellular is the most common injury pattern. Only a few drugs have been associated with both DILI and SCARs. Is this article, the criteria used for DILI recognition among SCARS have been revised and discussed, along with the drugs most commonly involved in these syndromes as well as the outcome, prognostic factors and the need for a multidisciplinary approach to improve the management of DILI in the context of SCARs.

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.

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.

HLA associations with infliximab-induced liver injury

Biomarkers that are able to identify patients at risk of drug-induced liver injury (DILI) after treatment with infliximab could be important in increasing the safety of infliximab use. We performed a genetic analysis to identify possible human leukocyte antigen (HLA) associations with DILI in European Caucasian users of infliximab in a retrospective study of 16 infliximab-DILI patients and 60 matched controls. In infliximab-associated liver injury, multiple potentially causal individual HLA associations were observed, as well as possible haplotypes. The strongest associated HLA allele was HLA-B*39:01 (P = 0.001; odds ratio [OR] 43.6; 95% confidence interval [CI] 2.8-infinity), which always appeared with another associated allele C*12:03 (P = 0.032; OR 6.1; 95% CI 0.9-47.4). Other associations were observed with HLAs DQB1*02:01 (P = 0.007; OR 5.7; 95% CI 1.4-24.8), DRB1*03:01 (P = 0.012; OR 4.9; 95% CI 1.2-20.5), and B*08:01 (P = 0.048; OR 3.4; 95% CI 0.9-13.2), which also appeared together whenever present in cases. Additional associations were found with HLA-DPB1*10:01 (P = 0.042; OR 20.9; 95% CI 0.7-infinity) and HLA-DRB1*04:04 (P = 0.042; OR 20.9; 95% CI 0.7-infinity). A strong association with HLA-B*39:01 was identified as a potentially causal risk factor for infliximab-induced DILI. Future work should aim to validate this finding and explore possible mechanisms through which the biologic interacts with this particular allele.

Liver safety assessment in clinical trials of new agents for chronic hepatitis B

Investigational agents that reduce or eliminate covalently closed circular DNA (cccDNA) or enhance host immunity against hepatitis B virus (HBV)-infected hepatocytes are intended to induce a durable off-treatment clearance of hepatitis B surface antigen (HBsAg) (referred to as functional cure). The aim of this paper was to highlight challenges in interpreting liver safety data in clinical trials of these agents when given alone or in combination regimens. The incidence, grading and management of spontaneous serum ALT flares in untreated chronic HBV patients are reviewed along with a summary of serum ALT flares observed during the registration trials for peginterferon and nucleos(t)ide reverse transcriptase inhibitors. Recommendations regarding the detection, management and interpretation of liver safety biomarker data in future clinical trials as well as suggested inclusion and exclusion criteria for phase 1/2 vs phase 3 studies are provided. Criteria to help classify liver safety signals as being due to the intended therapeutic response, emergence of drug-resistant HBV virions, or idiosyncratic drug-induced liver injury are provided along with a review of the role of an expert hepatic adjudication panel in assessing a compound's hepatotoxicity profile. Finally, an algorithmic approach to the differential diagnosis and recommended medical evaluation and management of individual clinical trial patients that develop a liver safety signal is provided along with the rationale to collect and test research blood samples for future mechanistic studies.

Next-Generation DILI Biomarkers: Prioritization of Biomarkers for Qualification and Best Practices for Biospecimen Collection in Drug Development

The diagnosis and management of drug-induced liver injury (DILI) remains a challenge in clinical trials in drug development. The qualification of emerging biomarkers capable of predicting DILI soon after the initiation of treatment, differentiating DILI from underlying liver disease, identifying the causal entity, and assigning appropriate treatment options after DILI is diagnosed are needed. Qualification efforts have been hindered by lack of properly stored and consented biospecimens that are linked to clinical data relevant to a specific context of use. Recommendations are made for biospecimen collection procedures, with the focus on clinical trials, and for specific emerging biomarkers to focus qualification efforts.

Genetic Predisposition to Drug-Induced Liver Injury

Identification of genetic predisposition to drug-induced liver injury (DILI) is of paramount importance. Early candidate gene studies have identified various polymorphisms in drug-metabolizing genes that infer increased DILI susceptibility. Few of these have been confirmed in more recent genome-wide association studies, which have identified several specific human leukocyte antigen (HLA) alleles. The low incidence rate of DILI, however, leads to a low positive predictive value for currently identified genetic variations, making them unsuitable for pre-prescription screening. HLA screening incorporated into clinical practice can aid the diagnostic process resulting in enhanced diagnostic accuracy and confidence.

Quantitative HLA-class-II/factor VIII (FVIII) peptidomic variation in dendritic cells correlates with the immunogenic potential of therapeutic FVIII proteins in hemophilia A

BACKGROUND

Plasma-derived (pd) or recombinant (r) therapeutic factor VIII proteins (FVIIIs) are infused to arrest/prevent bleeding in patients with hemophilia A (PWHA). However, FVIIIs are neutralized if anti-FVIII-antibodies (inhibitors) develop. Accumulating evidence suggests that pdFVIIIs with von Willebrand factor (VWF) are less immunogenic than rFVIIIs and that distinct rFVIIIs are differentially immunogenic. Since inhibitor development is T-helper-cell-dependent, human leukocyte antigen (HLA)-class-II (HLAcII) molecules constitute an important early determinant.

OBJECTIVES

Use dendritic cell (DC)-protein processing/presentation assays with mass-spectrometric and peptide-proteomic analyses to quantify the DP-bound, DQ-bound, and DR-bound FVIII-derived peptides in individual HLAcII repertoires and compare the immunogenic potential of six distinct FVIIIs based on their measured peptide counts.

PATIENTS/METHODS

Monocyte-derived DCs from normal donors and/or PWHA were cultured with either: Mix-rFVIII, a VWF-free equimolar mixture of a full-length (FL)-rFVIII [Advate® (Takeda)] and four distinct B-domain-deleted (BDD)-rFVIIIs [Xyntha® (Pfizer), NovoEight® (Novo-Nordisk), Nuwiq® (Octapharma), and Afstyla® (CSL Behring GmBH)]; a pdFVIII + pdVWF [Beriate® (CSL Behring GmBH)]; Advate ± pdVWF; Afstyla ± pdVWF; and Xyntha + pdVWF.

RESULTS

We showed that (i) Beriate had a significantly lower immunogenic potential than Advate ± pdVWF, Afstyla - pdVWF, and Mix-rFVIII; (ii) distinct FVIIIs differed significantly in their immunogenic potential in that, in addition to (i), Afstyla + pdVWF had a significantly lower immunogenic potential than Beriate, while the immunogenic potential of Beriate was not significantly different from that of Xyntha + pdVWF; and (iii) rFVIIIs with pdVWF had significantly lower immunogenic potentials than the same rFVIIIs without pdVWF.

CONCLUSIONS

Our results provide HLAcII peptidomic level explanations for several important clinical observations/issues including the differential immunogenicity of distinct FVIIIs and the role of HLAcII genetics in inhibitor development.

Definition of the Chemical and Immunological Signals Involved in Drug-Induced Liver Injury

Idiosyncratic drug-induced liver injury (iDILI), which is rare and often recognized only late in drug development, poses a major public health concern and impediment to drug development due to its high rate of morbidity and mortality. The mechanisms of DILI are not completely understood; both non-immune- and immune-mediated mechanisms have been proposed. Non-immune-mediated mechanisms including direct damage to hepatocytes, mitochondrial toxicity, interference with transporters, and alteration of bile ducts are well-known to be associated with drugs such as acetaminophen and diclofenac; whereas immune-mediated mechanisms involving activation of both adaptive and innate immune cells and the interactions of these cells with parenchymal cells have been proposed. The chemical signals involved in activation of both innate and adaptive immune responses are discussed with respect to recent scientific advances. In addition, the immunological signals including cytokine and chemokines that are involved in promoting liver injury are also reviewed. Finally, we discuss how liver tolerance and regeneration can have profound impact on the pathogenesis of iDILI. Continuous research in developing in vitro systems incorporating immune cells with liver cells and animal models with impaired liver tolerance will provide an opportunity for improved prediction and prevention of immune-mediated iDILI.

Exosomal Transport of Hepatocyte-Derived Drug-Modified Proteins to the Immune System

Idiosyncratic drug-induced liver injury (DILI) is a rare, often difficult-to-predict adverse reaction with complex pathomechanisms. However, it is now evident that certain forms of DILI are immune-mediated and may involve the activation of drug-specific T cells. Exosomes are cell-derived vesicles that carry RNA, lipids, and protein cargo from their cell of origin to distant cells, and they may play a role in immune activation. Herein, primary human hepatocytes were treated with drugs associated with a high incidence of DILI (flucloxacillin, amoxicillin, isoniazid, and nitroso-sulfamethoxazole) to characterize the proteins packaged within exosomes that are subsequently transported to dendritic cells for processing. Exosomes measured between 50 and 100 nm and expressed enriched CD63. Liquid chromatography-tandem mass spectrometry (LC/MS-MS) identified 2,109 proteins, with 608 proteins being quantified across all exosome samples. Data are available through ProteomeXchange with identifier PXD010760. Analysis of gene ontologies revealed that exosomes mirrored whole human liver tissue in terms of the families of proteins present, regardless of drug treatment. However, exosomes from nitroso-sulfamethoxazole-treated hepatocytes selectively packaged a specific subset of proteins. LC/MS-MS also revealed the presence of hepatocyte-derived exosomal proteins covalently modified with amoxicillin, flucloxacillin, and nitroso-sulfamethoxazole. Uptake of exosomes by monocyte-derived dendritic cells occurred silently, mainly through phagocytosis, and was inhibited by latrunculin A. An amoxicillin-modified 9-mer peptide derived from the exosomal transcription factor protein SRY (sex determining region Y)-box 30 activated naïve T cells from human leukocyte antigen A*02:01-positive human donors. Conclusion: This study shows that exosomes have the potential to transmit drug-specific hepatocyte-derived signals to the immune system and provide a pathway for the induction of drug hapten-specific T-cell responses.

Translating new knowledge on drug-induced liver injury into clinical practice

Drug-induced liver injury (DILI) is one of the main reasons for drug withdrawal from the market, and a cause of worldwide morbidity. Although several issues on DILI are still unsolved, there have been significant advances in new definitions and diagnosis tools. DILI is the result of a complex interaction between genetic and environmental factors, and constitutes an expanding area of investigation. DILI can mimic virtually all known hepatopathies, including vascular disorders and liver tumours. As part of this broad spectrum of clinical presentations, DILI severity ranges from asymptomatic elevations of aminotransferases to acute liver failure. Although biomarkers are emerging as valuable diagnostic tools, they are not available in clinical practice. Accurate DILI diagnosis is a challenging issue, particularly the establishing of causal relationships with the culprit agent and the exclusion of competing causes of liver injury. Given that the understanding of the mechanisms inducing DILI is growing, and both DILI causality assessment scales and the performance of international DILI networks have been improved, hepatotoxicity may be recognised earlier in clinical practice. In this review, advances and results obtained by DILI registries around the world, case characterisations, particularly those relevant to newer definitions in DILI, and the behaviour of chronic liver disease induced by drugs will be updated. In addition, recently published data on herbal and dietary supplements and new predictive scores for acute liver failure assessment will also be discussed.

Shared Genetic Risk Factors Across Carbamazepine-Induced Hypersensitivity Reactions

Carbamazepine (CBZ) causes life‐threating T‐cell‐mediated hypersensitivity reactions, including serious cutaneous adverse reactions (SCARs) and drug‐induced liver injury (CBZ‐DILI). In order to evaluate shared or phenotype‐specific genetic predisposing factors for CBZ hypersensitivity reactions, we performed a meta‐analysis of two genomewide association studies (GWAS) on a total of 43 well‐phenotyped Northern and Southern European CBZ‐SCAR cases and 10,701 population controls and a GWAS on 12 CBZ‐DILI cases and 8,438 ethnically matched population controls. HLA‐A*31:01 was identified as the strongest genetic predisposing factor for both CBZ‐SCAR (odds ratio (OR) = 8.0; 95% CI 4.10–15.80; P = 1.2 × 10⁻⁹) and CBZ‐DILI (OR = 7.3; 95% CI 2.47–23.67; P = 0.0004) in European populations. The association with HLA‐A*31:01 in patients with SCAR was mainly driven by hypersensitivity syndrome (OR = 12.9; P = 2.1 × 10⁻⁹) rather than by Stevens‐Johnson syndrome/toxic epidermal necrolysis cases, which showed an association with HLA‐B*57:01. We also identified a novel risk locus mapping to ALK only for CBZ‐SCAR cases, which needs replication in additional cohorts and functional evaluation.

HLA-B*35:01 Allele Is a Potential Biomarker for Predicting Polygonum multiflorum-Induced Liver Injury in Humans

Polygonum multiflorum (PM) is a well-known Chinese herbal medicine that has been reported to induce inflammation-associated idiosyncratic liver injury. This study aimed to identify the genetic basis of susceptibility to PM-drug-induced liver injury (PM-DILI) and to develop biological markers for predicting the risk of PM-DILI in humans. The major histocompatibility complex (MHC) regions of 11 patients with PM-DILI were sequenced, and all human leukocyte antigen (HLA)-type frequencies were compared to the Han-MHC database. An independent replication study that included 15 patients with PM-DILI, 33 patients with other DILI, and 99 population controls was performed to validate the candidate allele by HLA-B PCR sequence-based typing. A prospective cohort study that included 72 outpatients receiving PM for 4 weeks was designed to determine the influence of the risk allele on PM-DILI. In the pilot study, the frequency of HLA-B*35:01 was 45.4% in PM-DILI patients compared with 2.7% in the Han Chinese population (odds ratio [OR], 30.4; 95% confidence interval [CI], 11.7-77.8; P = 1.9 × 10^-10 ). In the independent replication study and combined analyses, a logistic regression model confirmed that HLA-B*35:01 is a high-risk allele of PM-DILI (PM-DILI versus other DILI, OR, 86.5; 95% CI, 14.2-527.8, P = 1.0 × 10^-6 ; and PM-DILI versus population controls, OR, 143.9; 95% CI, 30.1-687.5, P = 4.8 × 10^-10 ). In the prospective cohort study, an asymptomatic increase in transaminase levels was diagnosed in 6 patients, representing a significantly higher incidence (relative risk, 8.0; 95% CI, 1.9-33.2; P < 0.02) in the HLA-B*35:01 carriers (37.5%) than in the noncarriers (4.7%). Conclusion: The HLA-B*35:01 allele is a genetic risk factor for PM-DILI and a potential biomarker for predicting PM-DILI in humans.

Association of HLA-C*03:02 with methimazole-induced liver injury in Graves' disease patients

Methimazole (MMI) has been used for the treatment of Graves' Disease (GD) for more than half a century. The MMI treatment has been reported to be associated with hepatotoxicity. Previous studies have demonstrated that human leukocyte antigen (HLA) genetic polymorphisms were associated with many drugs-induced liver injuries. To investigate HLA genetic susceptibility to MMI-induced liver injury (MMI-DILI), we characterized both HLA class I and class Ⅱ in a well-characterized phenotypic cohort with 40 MMI-DILI cases and 118 MMI-tolerant controls. Among the 40 MMI-DILI cases, 57.5% were women and 50% were cholestatic liver damage with occurring time from days to months after MMI dosing. The frequency of HLA-C*03:02 was 6.7% (5/75) in the MMI-DILI case patients and 6.4% (4/62) in MMI-induced cholestatic/mixed liver damage, which were significantly different from the percentage of 0.4% (1/231) in the MMI-tolerant patients (odds ratio (OR) = 15.4, 95% confidence interval (CI) = 1.77-133.9, adjusted P = 0.0292; OR=14.9, 95% CI=2.38-182.9, adjusted P = 0.0323; respectively). HLA-A*02:01 was also found to be associated with MMI-induced cholestatic/mixed liver injury (OR = 3.13, 95%CI=1.45-6.91, adjusted P = 0.0464). The present study demonstrated that individuals carrying HLA-C*03:02 allele are at increased risk of developing MMI-induced DILI. These results may assist doctors to prevent the occurrence of hepatotoxicity in GD patients receiving MMI.