Characterization of amoxicillin- and clavulanic acid-specific T cells in patients with amoxicillin-clavulanate-induced liver injury

Test systems in drug discovery for hazard identification and risk assessment of human drug-induced liver injury

INTRODUCTION

The liver is an important target for drug-induced toxicities. Early detection of hepatotoxic drugs requires use of well-characterized test systems, yet current knowledge, gaps and limitations of tests employed remains an important issue for drug development. Areas Covered: The current state of the science, understanding and application of test systems in use for the detection of drug-induced cytotoxicity, mitochondrial toxicity, cholestasis and inflammation is summarized. The test systems highlighted herein cover mostly in vitro and some in vivo models and endpoint measurements used in the assessment of small molecule toxic liabilities. Opportunities for research efforts in areas necessitating the development of specific tests and improved mechanistic understanding are highlighted. Expert Opinion: Use of in vitro test systems for safety optimization will remain a core activity in drug discovery. Substantial inroads have been made with a number of assays established for human Drug-induced Liver Injury. There nevertheless remain significant gaps with a need for improved in vitro tools and novel tests to address specific mechanisms of human Drug-Induced Liver Injury. Progress in these areas will necessitate not only models fit for application, but also mechanistic understanding of how chemical insult on the liver occurs in order to identify translational and quantifiable readouts for decision-making.

Definition of the Nature and Hapten Threshold of the β-Lactam Antigen Required for T Cell Activation In Vitro and in Patients

Covalent modification of protein by drugs may disrupt self-tolerance, leading to lymphocyte activation. Until now, determination of the threshold required for this process has not been possible. Therefore, we performed quantitative mass spectrometric analyses to define the epitopes formed in tolerant and hypersensitive patients taking the β-lactam antibiotic piperacillin and the threshold required for T cell activation. A hydrolyzed piperacillin hapten was detected on four lysine residues of human serum albumin (HSA) isolated from tolerant patients. The level of modified Lys541 ranged from 2.6 to 4.8%. Analysis of plasma from hypersensitive patients revealed the same pattern and levels of modification 1-10 d after the commencement of therapy. Piperacillin-responsive skin-homing CD4+ clones expressing an array of Vβ receptors were activated in a dose-, time-, and processing-dependent manner; analysis of incubation medium revealed that 2.6% of Lys541 in HSA was modified when T cells were activated. Piperacillin-HSA conjugates that had levels and epitopes identical to those detected in patients were shown to selectively stimulate additional CD4+ clones, which expressed a more restricted Vβ repertoire. To conclude, the levels of piperacillin-HSA modification that activated T cells are equivalent to the ones formed in hypersensitive and tolerant patients, which indicates that threshold levels of drug Ag are formed in all patients. Thus, the propensity to develop hypersensitivity is dependent on other factors, such as the presence of T cells within an individual's repertoire that can be activated with the β-lactam hapten and/or an imbalance in immune regulation.

Association of Liver Injury From Specific Drugs, or Groups of Drugs, With Polymorphisms in HLA and Other Genes in a Genome-Wide Association Study

BACKGROUND & AIMS

We performed a genome-wide association study (GWAS) to identify genetic risk factors for drug-induced liver injury (DILI) from licensed drugs without previously reported genetic risk factors.

METHODS

We performed a GWAS of 862 persons with DILI and 10,588 population-matched controls. The first set of cases was recruited before May 2009 in Europe (n = 137) and the United States (n = 274). The second set of cases were identified from May 2009 through May 2013 from international collaborative studies performed in Europe, the United States, and South America. For the GWAS, we included only cases with patients of European ancestry associated with a particular drug (but not flucloxacillin or amoxicillin-clavulanate). We used DNA samples from all subjects to analyze HLA genes and single nucleotide polymorphisms. After the discovery analysis was concluded, we validated our findings using data from 283 European patients with diagnosis of DILI associated with various drugs.

RESULTS

We associated DILI with rs114577328 (a proxy for A*33:01 a HLA class I allele; odds ratio [OR], 2.7; 95% confidence interval [CI], 1.9-3.8; P = 2.4 × 10^-8) and with rs72631567 on chromosome 2 (OR, 2.0; 95% CI, 1.6-2.5; P = 9.7 × 10^-9). The association with A*33:01 was mediated by large effects for terbinafine-, fenofibrate-, and ticlopidine-related DILI. The variant on chromosome 2 was associated with DILI from a variety of drugs. Further phenotypic analysis indicated that the association between DILI and A*33:01 was significant genome wide for cholestatic and mixed DILI, but not for hepatocellular DILI; the polymorphism on chromosome 2 was associated with cholestatic and mixed DILI as well as hepatocellular DILI. We identified an association between rs28521457 (within the lipopolysaccharide-responsive vesicle trafficking, beach and anchor containing gene) and only hepatocellular DILI (OR, 2.1; 95% CI, 1.6-2.7; P = 4.8 × 10^-9). We did not associate any specific drug classes with genetic polymorphisms, except for statin-associated DILI, which was associated with rs116561224 on chromosome 18 (OR, 5.4; 95% CI, 3.0-9.5; P = 7.1 × 10^-9). We validated the association between A*33:01 terbinafine- and sertraline-induced DILI. We could not validate the association between DILI and rs72631567, rs28521457, or rs116561224.

CONCLUSIONS

In a GWAS of persons of European descent with DILI, we associated HLA-A*33:01 with DILI due to terbinafine and possibly fenofibrate and ticlopidine. We identified polymorphisms that appear to be associated with DILI from statins, as well as 2 non-drug-specific risk factors.

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

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

Drug-specific CD4+ T-cell immune responses are responsible for antituberculosis drug-induced maculopapular exanthema and drug reaction with eosinophilia and systemic symptoms syndrome

BACKGROUND

A multidrug regimen including isoniazid, rifampicin, pyrazinamide and ethambutol is commonly used as first-line treatment for tuberculosis. However, this regimen can occasionally result in severe adverse drug reactions, such as drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome and drug-induced liver injury. The culprit drug and mechanistic basis for the hypersensitive reaction are unknown.

OBJECTIVES

To investigate drug-specific T-cell responses in patients with antituberculosis drug (ATD)-induced cutaneous hypersensitivity and its underlying mechanism.

METHODS

We enrolled eight patients with ATD-induced maculopapular exanthema and DRESS and performed a lymphocyte transformation test. Subsequently, drug-specific T-cell clones were generated from four of the patients who showed proliferation in response to ATDs. We measured the drug-specific proliferative responses and counted the drug-specific interferon (IFN)-γ/granzyme B-producing cells after drug stimulation. Antihuman leukocyte antigen (HLA) class I and class II blocking antibodies were used to analyse human leukocyte antigen-restricted T-cell responses.

RESULTS

Positive proliferative responses to ATDs were mostly found in patients with cutaneous hypersensitivity. Furthermore, we isolated isoniazid/rifampicin-specific T cells from patients, which consisted primarily of CD4+ T cells. Drug-specific CD4+ T cells proliferated and secreted IFN-γ/granzyme B when stimulated with isoniazid or rifampicin, respectively. Isoniazid-responsive T-cell clones did not proliferate in the presence of rifampicin and vice versa. Drug-specific T-cell responses were blocked in the presence of anti-HLA class II antibodies.

CONCLUSIONS

This study identifies the presence of isoniazid/rifampicin-specific T cells in patients with ATD-induced maculopapular exanthema and DRESS. Furthermore, it highlights the important role of drug-specific T-cell immune responses in the pathogenesis of these reactions.

HLA-DRB1*16: 01-DQB1*05: 02 is a novel genetic risk factor for flupirtine-induced liver injury

OBJECTIVE

Flupirtine is a nonopioid analgesic with regulatory approval in a number of European countries. Because of the risk of serious liver injury, its use is now limited to short-term pain management. We aimed to identify genetic risk factors for flupirtine-related drug-induced liver injury (DILI) as these are unknown.

MATERIALS AND METHODS

Six flupirtine-related DILI patients from Germany were included in a genome-wide association study (GWAS) involving a further 614 European cases of DILI because of other drugs and 10,588 population controls. DILI was diagnosed by causality assessment and expert review. Human leucocyte antigen (HLA) and single nucleotide polymorphism genotypes were imputed from the GWAS data, with direct HLA typing performed on selected cases to validate HLA predictions. Four replication cases that were unavailable for the GWAS were genotyped by direct HLA typing, yielding an overall total of 10 flupirtine DILI cases.

RESULTS

In the six flupirtine DILI cases included in the GWAS, we found a significant enrichment of the DRB1*16:01-DQB1*05:02 haplotype compared with the controls (minor allele frequency cases 0.25 and minor allele frequency controls 0.013; P=1.4 × 10(-5)). We estimated an odds ratio for haplotype carriers of 18.7 (95% confidence interval 2.5-140.5, P=0.002) using population-specific HLA control data. The result was replicated in four additional cases, also with a haplotype frequency of 0.25. In the combined cohort (six GWAS plus four replication cases), the haplotype was also significant (odds ratio 18.7, 95% confidence interval 4.31-81.42, P=6.7 × 10(-5)).

CONCLUSION

We identified a novel HLA class II association for DILI, confirming the important contribution of HLA genotype towards the risk of DILI generally.

Exploration of Biomarkers for Amoxicillin/Clavulanate-Induced Liver Injury: Multi-Omics Approaches

To explore potential biomarkers for amoxicillin/clavulanate‐induced liver injury (AC‐DILI), we conducted a clinical trial in 32 healthy subjects based on multi‐omics approaches. Every subject was administered amoxicillin/clavulanate for 14 days. The liver‐specific microRNA‐122 (miR‐122) level increased prior to and correlated well with the observed alanine aminotransferase (ALT) level increase. This result indicates its potential as a sensitive early marker for AC‐DILI. We also identified urinary metabolites, such as azelaic acid and 7‐methylxanthine, with levels that significantly differed among the groups classified by ALT elevation level on day 8 after drug administration (P < 0.05). Lymphocyte proliferation in response to the drug was also observed. These findings demonstrate sequential changes in the process of AC‐DILI, including metabolic changes, increased miR‐122 level, increased liver enzyme activity, and enhanced lymphocyte proliferation after drug administration. In conclusion, this study provides potential biomarkers for AC‐DILI based on currently known mechanisms using comprehensive multi‐omics approaches.

The Importance of Patient-Specific Factors for Hepatic Drug Response and Toxicity

Responses to drugs and pharmacological treatments differ considerably between individuals. Importantly, only 50%-75% of patients have been shown to react adequately to pharmacological interventions, whereas the others experience either a lack of efficacy or suffer from adverse events. The liver is of central importance in the metabolism of most drugs. Because of this exposed status, hepatotoxicity is amongst the most common adverse drug reactions and hepatic liabilities are the most prevalent reason for the termination of development programs of novel drug candidates. In recent years, more and more factors were unveiled that shape hepatic drug responses and thus underlie the observed inter-individual variability. In this review, we provide a comprehensive overview of different principle mechanisms of drug hepatotoxicity and illustrate how patient-specific factors, such as genetic, physiological and environmental factors, can shape drug responses. Furthermore, we highlight other parameters, such as concomitantly prescribed medications or liver diseases and how they modulate drug toxicity, pharmacokinetics and dynamics. Finally, we discuss recent progress in the field of in vitro toxicity models and evaluate their utility in reflecting patient-specific factors to study inter-individual differences in drug response and toxicity, as this understanding is necessary to pave the way for a patient-adjusted medicine.

The chemical, genetic and immunological basis of idiosyncratic drug–induced liver injury

Idiosyncratic drug reactions can be extremely severe and are not accounted for by the regular pharmacology of a drug. Thus, the mechanism of idiosyncratic drug–induced liver injury (iDILI), a phenomenon that occurs with many drugs including β-lactams, anti-tuberculosis drugs and non-steroidal anti-inflammatories, has been difficult to determine and remains a pressing issue for patients and drug companies. Evidence has shown that iDILI is multifactorial and multifaceted, which suggests that multiple cellular mechanisms may be involved. However, a common initiating event has been proposed to be the formation of reactive drug metabolites and covalently bound adducts. Although the fate of these metabolites are unclear, recent evidence has shown a possible link between iDILI and the adaptive immune system. This review highlights the role of reactive metabolites, the recent genetic innovations which have provided molecular targets for iDILI, and the current literature which suggests an immunological basis for iDILI.

Update on Advances in Research on Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major concern for public health, as well as for drug development in the pharmaceutical industry, since it can cause liver failure and lead to drug withdrawal from the market and black box warnings. Thus, it is important to identify biomarkers for early prediction to increase our understanding of mechanisms underlying DILI that will ultimately aid in the exploration of novel therapeutic strategies to prevent or manage DILI. DILI can be subdivided into 'intrinsic' and 'idiosyncratic' categories, although the validity of this classification remains controversial. Idiosyncratic DILI occurs in a minority of susceptible individuals with a prolonged latency, while intrinsic DILI results from drug-induced direct hepatotoxicity over the course of a few days. The rare occurrence of idiosyncratic DILI requires multicenter collaborative investigations and phenotype standardization. Recent progress in research on idiosyncratic DILI is based on key developments in 3 areas: (1) newly developed high-throughput genotyping across the whole genome allowing for the identification of genetic susceptibility markers, (2) new mechanistic concepts on the pathogenesis of DILI revealing a key role of drug-responsive T lymphocytes in the immunological response, and (3) broad multidisciplinary approaches using different platform "-omics" technologies that have identified novel biomarkers for the prediction of DILI. An association of a specific human leukocyte antigen (HLA) allele with DILI has been reported for several drugs. HLA-restricted T-cell immune responses have also been investigated using lymphocytes and T-cell clones isolated from patients. A microRNA, miR-122, has been discovered as a promising biomarker for the early prediction of DILI. In this review, we summarize recent advances in research on idiosyncratic DILI with an understanding of the key role of adaptive immune systems.