Glutathione S-transferase m1 and t1 null genotypes increase susceptibility to idiosyncratic drug-induced liver injury

Genetic Factors Influencing Drug-Induced Liver Injury: Do They Have a Role in Prevention and Diagnosis?

Purpose of Review

The pathogenesis of DILI is currently unknown; however, research has shown strong genetic associations with some DILIs. This paper describes the variant alleles uncovered by GWAS and discusses their potential role as susceptibility biomarkers.

Recent Findings

An association with HLADRB1*15:01 and amoxicillin/clavulanate DILI has been shown by a number of research groups. The presence of the HLA-B*57:01 allele has been associated with an 81-fold increased risk of flucloxacillin DILI. The HLA-B*35:02 allele has significant association with minocycline DILI.

Summary

With the exception of abacavir for HIV therapy, no other prospective genetic screening tests have met the threshold for clinical application. This is largely because DILI incidence is too low to warrant the cost and effort associated with testing. Perhaps, with the development of personalised medicine, a panel of genes for disease susceptibility, drug efficacy and adverse reactions could be tested once off. This would change the cost-effectiveness paradigm, personalise healthcare and reduce DILI risk by avoiding medications in patients with specific HLA alleles.

Human glutathione S-transferases- and NAD(P)H:quinone oxidoreductase 1-catalyzed inactivation of reactive quinoneimines of amodiaquine and N-desethylamodiaquine: Possible implications for susceptibility to amodiaquine-induced liver toxicity

Amodiaquine (AQ), an antimalarial drug, widely prescribed in endemic areas of Africa and Asia, is used in combination with artesunate as recommended by the WHO. However, due to its idiosyncratic hepatotoxicity and agranulocytosis, the therapeutic use has been discontinued in most countries. Oxidative bioactivation to protein-reactive quinonimines (QIs) by hepatic cytochrome P450s and myeloperoxidase (MPO) have been suggested to be important mechanisms underlying AQ idiosyncratic toxicity. However, the inactivation of the reactive QIs by detoxifying enzymes such as human glutathione S-transferases (GSTs) and NAD(P)H:quinone oxidoreducatase 1 (NQO1) has not been characterized yet. In the present study, the activities of 15 recombinant human GSTs and NQO1 in the inactivation of reactive QIs of AQ and its pharmacological active metabolite, N-desethylamodiaquine (DEAQ) were investigated. The results showed that GSTP1-1, GSTA4-4, GSTM4-4, GSTM2-2 and GSTA2-2 (activity in decreasing order) were active isoforms in catalyzing GSH conjugation of reactive QIs of AQ and DEAQ. Additionally, NQO1 was shown to inactivate these QIs by reduction. Simulation of the variability of cytosolic GST-activity based on the hepatic GST contents from 22 liver donors, showed a large variation in cytosolic inactivation of QIs by GSH, especially at a reduced GSH-concentration. In conclusion, the present study demonstrates that a low hepatic expression of the active GSTs and NQO1 may increase the susceptibility of patients to AQ idiosyncratic hepatotoxicity.

Perturbation of microbiota in one-day old broiler chickens with antibiotic for 24 hours negatively affects intestinal immune development

Background

Gut microbial colonization and development of immune competence are intertwined and are influenced by early-life nutritional, environmental, and management factors. Perturbation of the gut microbiome at young age affects the crosstalk between intestinal bacteria and host cells of the intestinal mucosa.

Results

We investigated the effect of a perturbation of the normal early life microbial colonization of the jejunum in 1-day old chickens. Perturbation was induced by administering 0.8 mg amoxicillin per bird per day) via the drinking water for a period of 24 h. Effects of the perturbation were measured by 16S rRNA profiling of the microbiome and whole genome gene expression analysis. In parallel to what has been observed for other animal species, we hypothesized that such an intervention may have negative impact on immune development.

Trends were observed in changes of the composition and diversity of the microbiome when comparing antibiotic treated birds with their controls. in the jejunum, the expression of numerous genes changed, which potentially leads to changes in biological activities of the small intestinal mucosa. Validation of the predicted functional changes was performed by staining immune cells in the small intestinal mucosa and a reduction in the number of macrophage-like (KUL01⁺) cells was observed due to a direct or indirect effect of the antibiotic treatment. We provide evidence that a short, early life antibiotic treatment affects both the intestinal microbiota (temporarily) and mucosal gene expression over a period of 2 weeks.

Conclusion

These results underscore the importance of early life microbial colonization of the gut in relation to immune development and the necessity to explore the capabilities of a variety of early life dietary and/or environmental factors to modulate the programming for immune competence in broilers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3625-6) contains supplementary material, which is available to authorized users.

Genome-Wide Association Studies for Idiosyncratic Drug-Induced Hepatotoxicity: Looking Back-Looking Forward to Next-Generation Innovation

Idiosyncratic drug-induced hepatotoxicity is a formidable challenge for rational drug discovery and development, as well as the science of personalized medicine. There is evidence that hereditary factors, in part, contribute to drug toxicity. This expert analysis and review offer the insights gained, and the challenges ahead, for genome-wide association studies (GWASs) of idiosyncratic drug-induced hepatotoxicity. Published articles on genome-wide and subsequent replication studies were systematically searched in the PubMed electronic database. We found that the genetic risk variants that were identified genome-wide, and replication confirmed, are mainly related to polymorphisms in the human leukocyte antigen (HLA) region that include HLA-DQB1*06:02 for amoxicillin-clavulanate, HLA-B*57:01 for flucloxacillin, HLA-DRB1*15:01 for lumiracoxib, and HLA-DRB1*07:01 for lapatinib and ximelagatran-induced hepatotoxicity. Additionally, polymorphisms in ST6 β-galactosamide α-2, 6-sialyltranferase-1 (ST6GAL1), which plays a role in systemic inflammatory response, and variants in intron of family with sequence similarity-65 member-B (FAM65B) that play roles in liver inflammation displayed association with flucloxacillin and antituberculosis drug-induced hepatotoxicity, respectively. Taken together, these GWAS findings offer molecular leads on the central role that the immune system plays in idiosyncratic drug-induced hepatotoxicity. We conclude the expert review with a brief discussion of the salient challenges ahead. These include, for example, the need for discursive discovery paradigms that incorporate alternating GWASs and candidate gene studies, as well as the study of the environtome, the entire complement of environmental factors, including science and innovation policies that enact on global society and the human host, and by extension, on susceptibility for idiosyncratic drug-induced hepatotoxicity.

Epidemiology and Genetic Risk Factors of Drug Hepatotoxicity

Idiosyncratic drug-induced liver injury (DILI) from prescription medications and herbal and dietary supplements has an annual incidence rate of approximately 20 cases per 100,000 per year. However, the risk of DILI varies greatly according to the drug. In the United States and Europe, antimicrobials are the commonest implicated agents, with amoxicillin/clavulanate the most common, whereas in Asian countries, herbal and dietary supplements predominate. Genetic analysis of DILI is currently limited, but multiple polymorphisms of human leukocyte antigen genes and genes involved in drug metabolism and transport have been identified as risk factors for DILI.

Drug metabolism and liver disease: a drug-gene-environment interaction

Despite the central role of the liver in drug metabolism, surprisingly there is lack of certainty in anticipating the extent of modification of the clearance of a given drug in a given patient. The intent of this review is to provide a conceptual framework in considering the impact of liver disease on drug disposition and reciprocally the impact of drug disposition on liver disease. It is proposed that improved understanding of the situation is gained by considering the issue as a special example of a drug-gene-environment interaction. This requires an integration of knowledge of the drug's properties, knowledge of the gene products involved in its metabolism, and knowledge of the pathophysiology of its disposition. This will enhance the level of predictability of drug disposition and toxicity for a drug of interest in an individual patient. It is our contention that advances in pharmacology, pharmacogenomics, and hepatology, together with concerted interests in the academic, regulatory, and pharmaceutical industry communities provide an ideal immediate environment to move from a qualitative reactive approach to quantitative proactive approach in individualizing patient therapy in liver disease.

Clearance Prediction of Targeted Covalent Inhibitors by In Vitro-In Vivo Extrapolation of Hepatic and Extrahepatic Clearance Mechanisms

The concept of target-specific covalent enzyme inhibitors appears attractive from both an efficacy and a selectivity viewpoint considering the potential for enhanced biochemical efficiency associated with an irreversible mechanism. Aside from potential safety concerns, clearance prediction of covalent inhibitors represents a unique challenge due to the inclusion of nontraditional metabolic pathways of direct conjugation with glutathione (GSH) or via GSH S-transferase-mediated processes. In this article, a novel pharmacokinetic algorithm was developed using a series of Pfizer kinase selective acrylamide covalent inhibitors based on their in vitro-in vivo extrapolation of systemic clearance in rats. The algorithm encompasses the use of hepatocytes as an in vitro model for hepatic clearance due to oxidative metabolism and GSH conjugation, and the use of whole blood as an in vitro surrogate for GSH conjugation in extrahepatic tissues. Initial evaluations with clinical covalent inhibitors suggested that the scaling algorithm developed from rats may also be useful for human clearance prediction when species-specific parameters, such as hepatocyte and blood stability and blood binding, were considered. With careful consideration of clearance mechanisms, the described in vitro-in vivo extrapolation approach may be useful to facilitate candidate optimization, selection, and prediction of human pharmacokinetic clearance during the discovery and development of targeted covalent inhibitors.

Are Polymorphisms in Genes Relevant to Drug Disposition Predictors of Susceptibility to Drug-Induced Liver Injury?

Despite considerable progress in identifying specific HLA alleles as genetic risk factors for some forms of drug-induced liver injury, progress in understanding whether genetic polymorphisms relevant to drug disposition also contribute to risk for developing this serious toxicity has been more limited. Evidence from both candidate-gene case control studies and genome-wide association studies is now discussed. In the case of genes relevant to drug metabolism, polymorphisms in cytochromes P450, UDP-glucuronosyltransferases, N-acetyltransferases and glutathione S-transferases as risk factors for DILI are assessed. The relevance of ABC transporters to drug-induced liver injury is also considered, together with data showing associations of particular ABCB11, ABCB1 and ABCC2 polymorphisms with some forms of drug-induced liver injury. Very few of the associations with genes relevant to drug disposition that have been reported have been well replicated. Even apparently well-studied associations such as that between isoniazid liver injury and N-acetyltransferase 2 slow acetylators remain problematic, though it seems likely that polymorphisms in drug metabolism genes do contribute to risk for some specific drugs. A better understanding of genetic risk factors for drug-induced liver injury will require further genome-wide association studies with larger numbers of cases, especially for forms of drug-induced liver injury where HLA genotype does not appear to be a risk factor.

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.

FCERI and Histamine Metabolism Gene Variability in Selective Responders to NSAIDS

The high-affinity IgE receptor (Fcε RI) is a heterotetramer of three subunits: Fcε RIα, Fcε RIβ, and Fcε RIγ (αβγ2) encoded by three genes designated as FCER1A, FCER1B (MS4A2), and FCER1G, respectively. Recent evidence points to FCERI gene variability as a relevant factor in the risk of developing allergic diseases. Because Fcε RI plays a key role in the events downstream of the triggering factors in immunological response, we hypothesized that FCERI gene variants might be related with the risk of, or with the clinical response to, selective (IgE mediated) non-steroidal anti-inflammatory (NSAID) hypersensitivity. From a cohort of 314 patients suffering from selective hypersensitivity to metamizole, ibuprofen, diclofenac, paracetamol, acetylsalicylic acid (ASA), propifenazone, naproxen, ketoprofen, dexketoprofen, etofenamate, aceclofenac, etoricoxib, dexibuprofen, indomethacin, oxyphenylbutazone, or piroxicam, and 585 unrelated healthy controls that tolerated these NSAIDs, we analyzed the putative effects of the FCERI SNPs FCER1A rs2494262, rs2427837, and rs2251746; FCER1B rs1441586, rs569108, and rs512555; FCER1G rs11587213, rs2070901, and rs11421. Furthermore, in order to identify additional genetic markers which might be associated with the risk of developing selective NSAID hypersensitivity, or which may modify the putative association of FCERI gene variations with risk, we analyzed polymorphisms known to affect histamine synthesis or metabolism, such as rs17740607, rs2073440, rs1801105, rs2052129, rs10156191, rs1049742, and rs1049793 in the HDC, HNMT, and DAO genes. No major genetic associations with risk or with clinical presentation, and no gene-gene interactions, or gene-phenotype interactions (including age, gender, IgE concentration, antecedents of atopy, culprit drug, or clinical presentation) were identified in patients. However, logistic regression analyses indicated that the presence of antecedents of atopy and the DAO SNP rs2052129 (GG) were strongly related (P < 0.001 and P = 0.005, respectively) with selective hypersensitivity to ibuprofen. With regard to patients with selective hypersensitivity to ASA, men were more prone to develop such a reaction than women (P = 0.011), and the detrimental DAO SNP rs10156191 in homozygosity increased the risk of developing such hypersensitivity (P = 0.039).

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

[Recent findings regarding the mechanism of idiosyncratic drug toxicity]

Animal experiments cannot predict the probability of idiosyncratic drug toxicity; consequently, an important goal of the pharmaceutical industry is to develop a new methodology for preventing this form of drug reaction. Although the mechanism remains unclear, immune reactions are likely involved in the toxic processes underlying idiosyncratic drug toxicity: the drug is first activated into a chemically reactive metabolite that binds covalently to proteins and then acts as an immunogen. Therefore, screening tests to detect chemically reactive metabolites are conducted early during drug development and typically involve trapping with glutathione. More quantitative methods are then used in a later stage of drug development and frequently employ (14)Cor (3)H-labeled compounds. It has recently been demonstrated that a zone classification system can be used to separate risky drugs from likely safe drugs: by plotting the amount of each protein-bound reactive metabolite in vitro against the dose levels in vivo, the risk associated with each drug candidate can be assessed. A mechanism for idiosyncratic drug-induced hepatotoxicity was proposed by analogy to virus-induced hepatitis, in which cytotoxic T lymphocytes play an important role. This mechanism suggests that polymorphism in human leukocyte antigens is involved in idiosyncrasy, and a strong correlation with a specific genotype of human leukocyte antigens has been found in many cases of idiosyncratic drug toxicity. Therefore, gene biomarkers hold promise for reducing the clinical risk and prolonging the life cycle of otherwise useful drugs.

Glutathione Transferase Gene Variants Influence Busulfan Pharmacokinetics and Outcome After Myeloablative Conditioning

Supplemental Digital Content is Available in the Text.

Background:

Busulfan (Bu) and cyclophosphamide (Cy) are frequently included in conditioning regimens before hematopoietic stem cell transplantation (HSCT). Both drugs are detoxified by glutathione transferases (GST), and GST gene variants may explain some of the interindividual variability in pharmacokinetics and drug toxicity.

Methods:

The study investigated adult patients (n = 114) receiving oral Bu pre-HSCT. Bu doses were adjusted to obtain an average steady-state concentration (C_ss) of 900 mcg/L.

Results:

Median first dose Bu C_ss was 1000 mcg/L (600–1780 mcg/L). Patients carrying 1 and 2 GSTA1*B (rs3957357) alleles demonstrated median 12% and 16% higher Bu C_ss (P ≤ 0.05). Bu exposure (average C_ss; odds ratio = 1.009, 95% confidence interval = 1.002–1.017, P = 0.013) and GSTM1 gene copy number (odds ratio = 17.1, 95% confidence interval = 1.46–201, P = 0.024) were significant predictors of mortality ≤30 days. The mortality was 25% versus 2% among carriers of 2 versus no GSTM1 copies (P = 0.021). Mortality ≤3 months was associated with higher first dose Bu exposure (1090 versus 980 mcg/L, P = 0.021). GSTM1 expression and high Bu exposure may increase Cy toxicity by reducing intracellular glutathione.

Conclusions:

GST genotyping before HSCT may allow better prediction of Bu pharmacokinetics and drug toxicity, and thereby improve outcome after BuCy conditioning.

Genetic risk factors for clozapine-induced neutropenia and agranulocytosis in a Dutch psychiatric population

Prescription of clozapine is complicated by the occurrence of clozapine-induced reduction of neutrophils. The aim of this study was to identify genetic risk factors in a population of 310 Dutch patients treated with clozapine, including 38 patients developing neutropenia and 31 patients developing agranulocytosis. NQO2 1541AA (NRH quinone oxidoreductase 2; protects cells against oxidative metabolites) was present at a higher frequency in agranulocytosis patients compared with control (23% versus 7%, P=0.03), as was ABCB1 (ABC-transporter-B1; drug efflux transporter) 3435TT (32% versus 20%, P=0.05). In patients developing neutropenia, ABCB1 3435TT and homozygosity for GSTT1^null (glutathione-S-transferase; conjugates reactive clozapine metabolites into glutathione) were more frequent compared with control (34% versus 20%, P=0.05 and 31% versus 14%, P=0.03), whereas GSTM1^null was less frequent in these patients (31% versus 52%, P=0.03). To investigate whether combinations of the identified genetic risk factors have a higher predictive value, should be confirmed in a larger case-control study.

Drug-Induced Liver Injury Network Causality Assessment: Criteria and Experience in the United States

Hepatotoxicity due to drugs, herbal or dietary supplements remains largely a clinical diagnosis based on meticulous history taking and exclusion of other causes of liver injury. In 2004, the U.S. Drug-Induced Liver Injury Network (DILIN) was created under the auspices of the U.S. National Institute of Diabetes and Digestive and Kidney Diseases with the aims of establishing a large registry of cases for clinical, epidemiological and mechanistic study. From inception, the DILIN has used an expert opinion process that incorporates consensus amongst three different DILIN hepatologists assigned to each case. It is the most well-established, well-described and vigorous expert opinion process for DILI to date, and yet it is an imperfect standard. This review will discuss the DILIN expert opinion process, its strengths and weaknesses, psychometric performance and future.

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.

Transitioning from Idiopathic to Explainable Autoimmune Hepatitis

Autoimmune hepatitis lacks an identifiable cause, and its diagnosis requires the exclusion of etiologically defined diseases that resemble it. Insights into its pathogenesis are moving autoimmune hepatitis from an idiopathic to explainable disease, and the goal of this review is to describe the insights that are hastening this transition. Two types of autoimmune hepatitis are justified by serological markers, but they also have distinctive genetic associations (DRB1 and DQB1 genes) and autoantigens. DRB1 alleles are the principal susceptibility factors in white adults, and a six amino acid sequence encoded in the antigen-binding groove of class II molecules of the major histocompatibility complex can influence the selection of autoantigens. Polymorphisms, including variants of SH2B3 and CARD10 genes, may affect immune reactivity and disease severity. The cytochrome mono-oxygenase, CYP2D6, is the autoantigen associated with type 2 autoimmune hepatitis, and it shares homologies with multiple viruses that might promote self-intolerance by molecular mimicry. Chemokines, especially CXCL9 and CXCL10, orchestrate the migration of effector cells to sites of injury and are associated with disease severity. Cells of the innate and adaptive immune responses promote tissue damage, and possible deficiencies in the number and function of regulatory T cells may facilitate the injurious process. Receptor-mediated apoptosis is the principal mechanism of hepatocyte loss, and cell-mediated and antibody-dependent mechanisms of cytotoxicity also contribute. Insights that explain autoimmune hepatitis will allow triggering exogenous antigens to be characterized, risk management to be improved, prognostic indices to be refined, and site-specific therapeutic interventions to emerge.

Drug-Induced Liver Injury

CONTEXT

Drug-induced liver injury (DILI) represents a diverse set of responses following exposure to any manufactured or naturally occurring chemical compound. Drug-induced liver injury is of major concern owing to the ever increasing number of compounds introduced into the market for treatment of various diseases as well as the increasing popularity of herbals, which lend themselves to self-medication but are not rigorously regulated.

OBJECTIVE

To provide an overview of the prevalence, classification, and diagnosis of DILI with emphasis on pathogenesis and the role of a liver biopsy. To focus on the most common, emerging, and herbal agents that cause DILI with emphasis on the histologic pattern of injury observed.

DATA SOURCES

A review of the literature was drawn from the PubMed (US National Library of Medicine) repository, textbooks, and online databases. All figures were taken from cases seen at our tertiary referral center, which is 1 of 12 participating sites in the National Institutes of Health-funded Drug-Induced Liver Injury Network.

CONCLUSIONS

Drug-induced liver injury due to prescription, over-the-counter, and herbal products is a major cause of liver disease in the United States and around the world. Diagnosis of DILI is challenging because there is no single clinical, laboratory, or histologic feature specific to DILI. Accurate diagnosis requires establishing a causal relationship with the suspected agent and excluding competing causes of liver injury. The liver biopsy is an essential component in the management of DILI by offering clues to the underlying pathogenesis, providing prognostic information, and guiding therapy.

Characterization of a highly sensitive and selective novel trapping reagent, stable isotope labeled glutathione ethyl ester, for the detection of reactive metabolites

INTRODUCTION

Glutathione (GSH) trapping assays are widely used to predict the post-marketing risk for idiosyncratic drug reactions (IDRs) in the pharmaceutical industry. Although several GSH derivatives have been introduced as trapping reagents for reactive intermediates, more sensitive and selective reagents are desired to prevent the generation of erroneous results. In this study, stable isotope labeled GSH ethyl ester (GSHEE-d5) was designed and its detection capability was evaluated.

METHODS

GSHEE-d5 was synthesized and its detection potential was compared with stable isotope labeled GSH ([(13)C2,(15)N]GSH) as a reference trapping reagent. The trapping reagents were added to human liver microsomes as a 1:1 mixture with GSHEE or GSH, respectively, and incubated with seven IDR positive drugs and three IDR negative drugs. The adducts formed between the reagents and reactive metabolites were analyzed by unit resolution mass spectrometer (MS) using isotope pattern-dependent scan with neutral loss filtering.

RESULTS

A single-step reaction of GSH and ethanol-d6 produced GSHEE-d5 with a yield of 85%. The GSHEE-d5 assay detected adducts with all seven IDR positive drugs, and no adducts were detected with the three IDR negative drugs. In contrast, the [(13)C2,(15)N]GSH assay failed to detect adducts with three of the IDR positive drugs. In the case of diclofenac, the GSHEE-d5 assay showed a 4-times greater signal intensity than the [(13)C2,(15)N]GSH assay.

DISCUSSION

GSHEE-d5 enabled the detection of reactive metabolites with greater sensitivity and selectivity than [(13)C2,(15)N]GSH. These results demonstrate that GSHEE-d5 would be a useful trapping reagent for evaluating the risk of IDRs with unit resolution MS.

Drug-induced liver injury: Interactions between drug properties and host factors

Idiosyncratic drug-induced liver injury (DILI) is a common cause for drug withdrawal from the market and although infrequent, DILI can result in serious clinical outcomes including acute liver failure and the need for liver transplantation. Eliminating the iatrogenic "harm" caused by a therapeutic intent is a priority in patient care. However, identifying culprit drugs and individuals at risk for DILI remains challenging. Apart from genetic factors predisposing individuals at risk, the role of the drugs' physicochemical and toxicological properties and their interactions with host and environmental factors need to be considered. The influence of these factors on mechanisms involved in DILI is multi-layered. In this review, we summarize current knowledge on 1) drug properties associated with hepatotoxicity, 2) host factors considered to modify an individuals' risk for DILI and clinical phenotypes, and 3) drug-host interactions. We aim at clarifying knowledge gaps needed to be filled in as to improve risk stratification in patient care. We therefore broadly discuss relevant areas of future research. Emerging insight will stimulate new investigational approaches to facilitate the discovery of clinical DILI risk modifiers in the context of disease complexity and associated interactions with drug properties, and hence will be able to move towards safety personalized medicine.

Metabolic activation of hepatotoxic drug (benzbromarone) induced mitochondrial membrane permeability transition

The risk of drug-induced liver injury (DILI) is of great concern to the pharmaceutical industry. It is well-known that metabolic activation of drugs to form toxic metabolites (TMs) is strongly associated with DILI onset. Drug-induced mitochondrial dysfunction is also strongly associated with increased risk of DILI. However, it is difficult to determine the target of TMs associated with exacerbation of DILI because of difficulties in identifying and purifying TMs. In this study, we propose a sequential in vitro assay system to assess TM formation and their ability to induce mitochondrial permeability transition (MPT) in a one-pot process. In this assay system, freshly-isolated rat liver mitochondria were incubated with reaction solutions of 44 test drugs preincubated with liver microsomes in the presence or absence of NADPH; then, NADPH-dependent MPT pore opening was assessed as mitochondrial swelling. In this assay system, several hepatotoxic drugs, including benzbromarone (BBR), significantly induced MPT in a NADPH-dependent manner. We investigated the rationality of using BBR as a model drug, since it showed the most prominent MPT in our assay system. Both the production of a candidate toxic metabolite of BBR (1',6-(OH)2 BBR) and NADPH-dependent MPT were inhibited by several cytochrome P450 (CYP) inhibitors (clotrimazole and SKF-525A, 100μM). In summary, this assay system can be used to evaluate comprehensive metabolite-dependent MPT without identification or purification of metabolites.

Mechanisms of drug-induced liver injury

PURPOSE OF REVIEW

Idiosyncratic drug-induced liver injury (iDILI) is a relatively rare condition, but can have serious consequences for the individual patient, public health, regulatory agencies and the pharmaceutical industry. Despite increased awareness of iDILI, its underlying mechanism is still not fully understood. This review summarizes the current understanding of the molecular mechanism behind iDILI.

RECENT FINDINGS

Genetic variations in drug metabolizing genes are in line with proposed mechanisms based on acetaminophen hepatotoxicity, whereby reactive metabolites covalently bind to cellular proteins and disturb the redox balance. In addition, immune-mediated effects have been reported for flucloxacillin hepatotoxicity, demonstrating both haptenization and direct binding between the drug and immune receptors.

SUMMARY

Idiosyncratic DILI development is believed to be orchestrated by multiple events, such as reactive metabolite formations, oxidative stress and signalling pathway inductions, with the mitochondria taking centre stage. Evidence also points towards the immune system (innate and adaptive responses) as important components in iDILI. Interindividual differences in one or more of these events, due to genetic variations and environmental factors, are likely to contribute to the idiosyncratic nature of this condition and subsequently distinguish between patient susceptibility and tolerance.

Stem Cell Strategies to Evaluate Idiosyncratic Drug-induced Liver Injury

The host-dependent nature of idiosyncratic drug-induced liver injury (iDILI) suggests that rare genetic polymorphisms may contribute to the disease. Indeed, a few mutations in key genes have already been identified using conventional human genetics approaches. Over 50 commonly used drugs can precipitate iDILI, making this a substantial medical problem. Only recently have human induced pluripotent stem cells been used as a research tool to discover novel iDILI genes and to study the mechanisms of iDILI in vitro. Here we review the current state of stem cell use in the investigation of iDILI, with a special focus on genetics. In addition, the concerns and difficulties associated with genetics and animal model research are discussed. We then present the features of patient-specific pluripotent stem cells (which may be derived from iDILI patients themselves), and explain why these cells may be of great utility. A variety of recent approaches to produce hepatocyte-like cells from pluripotent cells and the associated advantages and limitations of such cells are discussed. Future directions for the use of stem cell science to investigate iDILI include novel ways to identify new iDILI genes, a consideration of epigenetic impacts on iDILI, and the development of new and improved strategies for the production of hepatocytes from human pluripotent cells.

MicroRNAs in Drug-induced Liver Injury

Drug-induced liver injury (DILI) is a leading cause of acute liver failure, and a major reason for the recall of marketed drugs. Detection of potential liver injury is a challenge for clinical management and preclinical drug safety studies, as well as a great obstacle to the development of new, effective and safe drugs. Currently, serum levels of alanine and aspartate aminotransferases are the gold standard for evaluating liver injury. However, these levels are assessed by nonspecific, insensitive, and non-predictive tests, and often result in false-positive results. Therefore, there is an urgent need for better DILI biomarkers to guide risk assessment and patient management. The discovery of microRNAs (miRNAs) as a new class of gene expression regulators has triggered an explosion of research, particularly on the measurement of miRNAs in various body fluids as biomarkers for many human diseases. The properties of miRNA-based biomarkers, such as tissue specificity and high stability and sensitivity, suggest they could be used as novel, minimally invasive and stable DILI biomarkers. In the current review, we summarize recent progress concerning the role of miRNAs in diagnosing and monitoring both clinical and preclinical DILI, and discuss the main advantages and challenges of miRNAs as novel DILI biomarkers.

Polymorphisms in CYP2E1, GSTM1 and GSTT1 and anti-tuberculosis drug-induced hepatotoxicity

Anti-tuberculosis drug-induced hepatitis (ATD- induced hepatitis) has been linked to polymorphisms in genes encoding drug metabolizing enzymes. N-acetyltransferase 2 (NAT2), cytochrome P450 2E1 (CYP2E1) and glutathione S-transferase (loci GSTM1 and GSTT1) are involved in the metabolism of isoniazid, the most toxic drug for the treatment of tuberculosis (TB). This study was designed to determine the frequency and to evaluate whether polymorphisms at CYP2E1, GSTM1 and GSTT1 genes are associated with drug response, as well as to identify clinical risk factors for ATD-induced hepatitis. A total of 245 Brazilian patients undergoing treatment for TB were genotyped using polymerase chain reaction and restriction fragment length polymorphism and sequencing methods. The frequencies of the CYP2E1 polymorphic alleles RsaI, PstI and DraI are 8%, 8.5% and 12%, respectively. GSTM1 and GSTT1 genes are deleted in 42.9% and 12.4% of the population, respectively. Fifteen patients (6.1%) developed hepatotoxicity. Clinical (HIV, female sex and extrapulmonary TB) and genetic characteristics (CYP2E1 without any mutations, having NAT2 slow acetylator profile) are at higher risk of developing ATD-induced hepatitis in this population. Genotyping for GSTM1 and GSTT1 showed no influence on drug response.

Idiosyncratic drug-induced liver injury: an update on the 2007 overview

INTRODUCTION

Idiosyncratic drug induced liver injury (DILI) is rare, with an incidence of approximately 19 per 100,000 treated individuals.

AREAS COVERED

An update on the epidemiology, pathogenic mechanisms, diagnosis, outcome, risk factors for idiosyncratic drug-induced hepatotoxicity, specific classes of drug hepatotoxicity and biomarkers to predict DILI are covered. Cumulative drug exposure and HLA phenotypes play an important role in the pathogenesis of DILI. Patients who present with suspected DILI and jaundice should have biliary obstruction and acute viral hepatitis, including hepatitis E excluded. Immune-mediated DILI will respond to steroid therapy. Patients with an elevated bilirubin and a hepatocellular pattern of liver function tests have severe liver injury with a mortality of greater than 10% and a risk of acute liver failure. Women have an increased risk of hepatocellular DILI. Antibiotics, anticonvulsants, and antidepressant therapy remain the commonest causes of DILI in the Western Hemisphere. Statin therapy rarely causes severe liver injury.

EXPERT OPINION

The establishment of prospective registries for DILI has provided valuable data on the pathogenesis and outcome of DILI. Drug-specific computerised causality assessment tools should improve the diagnosis of DILI. The clinical utility of genetic polymorphisms associated with drug-specific DILI is limited.

Systematic identification and characterization of glutathione S-transferases in cynomolgus macaque

Glutathione S-transferases (GSTs) are essential drug-metabolizing enzymes, involved in conjugation of various endogenous and exogenous substrates. Cynomolgus macaque is an important primate species in drug metabolism studies; however, cynomolgus GSTs have not been fully characterized. In this study the cDNAs of 12 GSTs (GSTA3-A5, GSTK1, GSTM2-M4, GSTO2, GSTP1, GSTS1, and GSTT1/2) were isolated from cynomolgus macaque and rhesus macaque liver. Cynomolgus GSTM1 cDNA was not amplified and only an aberrantly spliced GSTM1 transcript was isolated from rhesus macaque. Amino acid sequences of these 12 GSTs shared high sequence identities (93-98%) and were clustered into the same clades as the human orthologs in the phylogenetic tree. The 12 GSTs had exon-intron structures similar to the human orthologs, and exhibited distinct tissue expression patterns. GSTA3, GSTA5, and GSTM3/O2 were expressed predominantly in adrenal gland, jejunum, and testis, respectively, whereas the other GSTs showed universal expression patterns in the 10 tissues analyzed. Comparison of expression levels showed that GSTA1, GSTK1, GSTA3, and GSTM3 were most abundantly expressed in liver/jejunum, kidney, adrenal gland, and testis, respectively. Metabolic assays of proteins expressed heterologously in Escherichia coli, showed that all 12 GSTs and 5 previously identified GSTs, GSTA1/2, GSTM5, GSTO1, and GSTZ1, catalyzed the conjugation of GST substrate(s) 1-chloro-2,4-dinitrobenzene and/or 1,2-epoxy-3-(p-nitrophenoxy)propane, indicating that these 17 GSTs are functional drug-metabolizing enzymes. These results suggest that the 12 GST genes examined in this study are expressed and encoded functional enzymes in cynomolgus macaque.

Pharmacogenomics of severe cutaneous adverse reactions and drug-induced liver injury

Rare but severe adverse drug reactions (ADRs) are an important issue in drug development and in the proper usage of drugs during the post-approval phase. The ability to predict patient susceptibility to severe ADRs would prevent drug administration to high-risk patients. This would save lives and ensure the quality of life for these patients, but occurrence of idiosyncratic severe ADRs had been very difficult to predict for a long time. However, in this decade, genetic markers have been found for several ADRs, especially for severe cutaneous adverse reactions (SCARs) and drug-induced liver injury (DILI). In this review, we summarize recent progress in identifying genetic markers for SCARS and DILI, and discuss issues that remain unresolved. As for SCARs, associations of HLA-B*15:02 or HLA-A*31:01 and HLA-B*58:01 have been revealed for carbamazepine- and allopurinol-related Stevens-Johnson syndrome and toxic epidermal neclolysis, respectively. HLA-B*57:01 is strongly associated with abacavir-induced hypersensitivity syndrome. Several HLA alleles also demonstrate drug-specific associations with DILI, such as HLA-A*33:03 for ticlopidine, HLA-B*57:01 for flucloxacillin and HLA-DQA1*02:01 for lapatinib. Efforts should be continued to find other genetic markers to achieve high predictability for ADRs, with the goal being development of genetic tests for use in clinical settings.

Metabolism and disposition of acetaminophen: recent advances in relation to hepatotoxicity and diagnosis

Acetaminophen (APAP) is one of the most widely used drugs. Though safe at therapeutic doses, overdose causes mitochondrial dysfunction and centrilobular necrosis in the liver. The first studies of APAP metabolism and activation were published more than 40 years ago. Most of the drug is eliminated by glucuronidation and sulfation. These reactions are catalyzed by UDP-glucuronosyltransferases (UGT1A1 and 1A6) and sulfotransferases (SULT1A1, 1A3/4, and 1E1), respectively. However, some is converted by CYP2E1 and other cytochrome P450 enzymes to a reactive intermediate that can bind to sulfhydryl groups. The metabolite can deplete liver glutathione (GSH) and modify cellular proteins. GSH binding occurs spontaneously, but may also involve GSH-S-transferases. Protein binding leads to oxidative stress and mitochondrial damage. The glucuronide, sulfate, and GSH conjugates are excreted by transporters in the canalicular (Mrp2 and Bcrp) and basolateral (Mrp3 and Mrp4) hepatocyte membranes. Conditions that interfere with metabolism and metabolic activation can alter the hepatotoxicity of the drug. Recent data providing novel insights into these processes, particularly in humans, are reviewed in the context of earlier work, and the effects of altered metabolism and reactive metabolite formation are discussed. Recent advances in the diagnostic use of serum adducts are covered.

Drug-induced liver injury: the role of drug metabolism and transport

Many studies have pinpointed the significant contribution of liver-mediated drug metabolism and transport to the complexity of drug-induced liver injury (DILI). Phase I cytochrome P450 (CYP450) enzymes can lead to altered drug metabolism and formation of toxic metabolites, whilst Phase II enzymes are also associated with DILI. The emerging role of hepatic transporters in regulating the movement of endogenous and exogenous chemicals (e.g., bile acids and drugs) across cellular and tissue membranes is critical in determining the pathophysiology of liver disease as well as drug toxicity and efficacy. Genetic and environmental factors can have a significant impact on drug metabolism and transporter proteins, consequently increasing the risk of DILI in susceptible individuals. The assessment of these factors therefore represents an important approach for predicting and preventing DILI, by better understanding the pharmacological profile of a specific drug. This review focuses on the mechanisms of DILI associated with drug metabolism and hepatic transport, and how they can be influenced by underlying factors.

Role of pharmacogenetics in busulfan/cyclophosphamide conditioning therapy prior to hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a curative treatment for several malignant and nonmalignant disorders. Busulfan (Bu) and cyclophosphamide (Cy) are the most commonly used alkylators in high-dose pretransplant conditioning for HSCT; a treatment that is correlated with drug-related toxicity and relapse. Pharmacogenetic investigations have shown that CYP450, as well as aldehyde dehydrogenase, are clearly involved with Cy metabolism and are associated with altered treatment response, Cy metabolism and the unique stem-cell sparing capacity. Moreover, glutathione-S-transferase isoenzymes have been associated with cellular outward transport of various alkylating agents, including Cy metabolites, melphalan, Bu and chlorambucil. A shift from genetic-based studies to whole-genome-based investigations of Cy- and Bu-associated markers may contribute to personalizing the conditioning therapy and enhancing the clinical outcome of HSCT.

Genetic interaction between NAT2, GSTM1, GSTT1, CYP2E1, and environmental factors is associated with adverse reactions to anti-tuberculosis drugs

BACKGROUND

Adverse drug reactions (ADRs) associated with anti-tuberculosis (anti-TB) drug regimens have considerable impact on anti-TB treatment, potentially leading to unsuccessful outcomes. Nevertheless, the risk factors that play a role in anti-TB drug-induced ADRs are not well established. It is well documented that genetic polymorphisms in drug-metabolizing enzymes (DMEs) result in considerably complex variability in anti-TB drug disposition. In addition, the impact of pharmacogenetic variation on the metabolism of anti-TB drugs may be modifiable by environmental exposure. Thus, an assessment of pharmacogenetic variability combined with biomarkers of environmental exposure may be helpful for demonstrating the effect of the gene-environment interaction on susceptibility to ADRs induced by anti-TB drug therapy.

OBJECTIVE

The aim of the study was to investigate the impact of the interaction between environmental risk factors and pharmacogenetic polymorphisms in four common DMEs--N-acetyltransferase 2 (arylamine N-acetyltransferase) [NAT2], glutathione S-transferase theta 1 [GSTT1], glutathione S-transferase mu 1 [GSTM1], and cytochrome P450 2E1 [CYP2E1]--on commonly reported ADRs to first-line anti-TB drugs in 129 patients receiving homogeneous TB treatment.

METHODS

TB patients monitored during drug treatment were divided into subgroups according to the presence or absence of ADRs. Additionally, the patients' clinical and demographic characteristics were collected in order to identify the environmental factors that are potential triggers for ADRs induced by anti-TB drug treatment. Pharmacogenetic variability was determined by gene sequencing, TaqMan® assays, or polymerase chain reaction.

RESULTS

The findings of this study suggest that the NAT2 slow acetylator haplotype, female sex, and smoking are important determinants of susceptibility to ADRs induced by anti-TB drugs. Patients carrying multiple, but not single, polymorphisms in the NAT2, GSTM1, GSTT1, and CYP2E1 genes were found to have an increased risk of ADRs, as revealed by gene-gene interaction analysis. Moreover, we also identified meaningful gene-environment interaction models that resulted in the highest levels of ADR risk.

CONCLUSION

The study findings provide evidence of the clinical impact of the interaction between pharmacogenetic variability and environmental factors on ADRs induced by anti-TB drug therapy. Predictive pharmacogenetic testing and a comprehensive clinical history would therefore be helpful for identification and careful monitoring of patients at high risk of this complication.

Inhibition and induction of glutathione S-transferases by flavonoids: possible pharmacological and toxicological consequences

Many studies reviewed herein demonstrated the potency of some flavonoids to modulate the activity and/or expression of glutathione S-transferases (GSTs). Because GSTs play a crucial role in the detoxification of xenobiotics, their inhibition or induction may significantly affect metabolism and biological effects of many drugs, industrials, and environmental contaminants. The effect of flavonoids on GSTs strongly depends on flavonoid structure, concentration, period of administration, as well as on GST isoform and origin. Moreover, the results obtained in vitro are often contrary to the vivo results. Based on these facts, the revelation of important flavonoid-drug or flavonoid-pollutant interaction has been complicated. However, it should be borne in mind that ingestion of certain flavonoids in combination with drugs or pollutants (e.g., acetaminophen, simvastatin, cyclophosphamide, cisplatine, polycyclic aromatic hydrocarbons, chlorpyrifos, acrylamide, and isocyanates), which are GST substrates, could have significant pharmacological and toxicological consequences. Although reasonable consumptions of a flavonoids-rich diet (that may lead to GST induction) are mostly beneficial, the uncontrolled intake of high concentrations of certain flavonoids (e.g., quercetin and catechins) in dietary supplements (that may cause GST inhibition) may threaten human health.

Drug-induced liver injury: present and future

Liver injury due to prescription and nonprescription medications is a growing medical, scientific, and public health problem. Worldwide, the estimated annual incidence rate of drug-induced liver injury (DILI) is 13.9-24.0 per 100,000 inhabitants. DILI is one of the leading causes of acute liver failure in the US. In Korea, the annual extrapolated incidence of cases hospitalized at university hospital is 12/100,000 persons/year. Most cases of DILI are the result of idiosyncratic metabolic responses or unexpected reactions to medication. There is marked geographic variation in relevant agents; antibiotics, anticonvulsants, and psychotropic drugs are the most common offending agents in the West, whereas in Asia, 'herbs' and 'health foods or dietary supplements' are more common. Different medical circumstances also cause discrepancy in definition and classification of DILI between West and Asia. In the concern of causality assessment, the application of the Roussel Uclaf Causality Assessment Method (RUCAM) scale frequently undercounts the cases caused by 'herbs' due to a lack of previous information and incompatible time criteria. Therefore, a more objective and reproducible tool that could be used for the diagnosis of DILI caused by 'herbs' is needed in Asia. In addition, a reporting system similar to the Drug-Induced Liver Injury Network (DILIN) in the US should be established as soon as possible in Asia.

The roles of GSTM1 and GSTT1 null genotypes and other predictors in anti-tuberculosis drug-induced liver injury

WHAT IS KNOWN AND OBJECTIVE

Anti-tuberculosis drugs (ATD), although highly effective, often cause liver injury. Glutathione S-transferases (GST) play a crucial protective role in the detoxifying mechanisms of drugs. Several studies have investigated the genetic null variants of GSTM1 and GSTT1 as possible risk factors for ATD-induced liver injury; however, those findings are inconsistent. We investigated GSTM1 and GSTT1 null genotypes in Brazilian patients with tuberculosis (TB), adjusting for other possible predictors of ATD-induced liver injury.

METHODS

This was a prospective cohort study with patients who were treated for TB from 2006 to 2011. GSTM1 and GSTT1 gene deletions were analysed from genomic DNA by polymerase chain reaction (PCR). Demographic, clinical and laboratory data were extracted from medical records and possible predictors of liver injury were evaluated.

RESULTS AND DISCUSSION

This study enrolled 177 patients. Anti-tuberculosis drugs-induced liver injury incidence was 33.3%. Hepatitis B infection (HBV) and increased alanine aminotransferase (ALT) baseline were significant predictors. Neither GSTM1 nor GSTT1 null genotypes were associated with ATD-induced liver injury; nevertheless, the comparison among four different liver toxicity grades showed that GSTM1 non-null genotype was significant more frequent among the higher grades of liver toxicity.

WHAT IS NEW AND CONCLUSION

GSTM1 and GSTT1 null genotypes do not seem to play important roles in ATD-induced liver injury in Brazilians. However, there was evidence that GSTM1 polymorphisms were possibly related to the intensity of toxicity. Active HBV and initial high ALT could predict ATD-induced liver injury.

Evaluation of hepatic glutathione transferase Mu 1 and Theta 1 activities in humans and mice using genotype information

We investigated the impact of glutathione transferases Mu 1 (GSTM1)- and glutathione transferase Theta 1 (GSTT1)-null genotypes on hepatic GST activities in humans and compared the results with those of Gstm1- and Gstt1-null mice. In liver with GSTM1/Gstm1-null genotype, GST activity toward p-nitrobenzyl chloride (NBC) was significantly decreased in both humans and mice. In addition, in liver with GSTT1/Gstt1-null genotype, GST activity toward dichloromethane (DCM) was significantly decreased in both humans and mice. Therefore, null genotypes of GSTM1/Gstm1 and GSTT1/Gstt1 are considered to decrease hepatic GST activities toward NBC and DCM, respectively, in both humans and mice. This observation shows the functional similarity between humans and mice for GSTM1 and GSTT1 toward some substrates. In the case of NBC and DCM, Gst-null mice would be relevant models for humans with GST-null genotype. In addition, decreases in GST activities toward 1,2-dichloro-4-nitrobenzene, trans-4-phenyl-3-buten-2-one, and 1-chloro-2,4,-dinitrobenzene were observed in Gstm1-null mice, and a decrease in GST activity toward 1,2-epoxy-3-(p-nitrophenoxy)propane was observed in Gstt1-null mice. However, an impact of GST-null genotypes on GST activities toward these substrates was not observed in humans. In the case of these mouse-specific substrates, Gst-null mice may be relevant models for humans regardless of GST genotype, because GST activities, which are higher in wild-type mice than in humans, were eliminated in Gst-null mice. This study shows that comparison of hepatic GST activities between humans and mice using genotype information would be valuable in using Gst-null mice as human models.

Trends in qualifying biomarkers in drug safety. Consensus of the 2011 meeting of the spanish society of clinical pharmacology

In this paper we discuss the consensus view on the use of qualifying biomarkers in drug safety, raised within the frame of the XXIV meeting of the Spanish Society of Clinical Pharmacology held in Málaga (Spain) in October, 2011. The widespread use of biomarkers as surrogate endpoints is a goal that scientists have long been pursuing. Thirty years ago, when molecular pharmacogenomics evolved, we anticipated that these genetic biomarkers would soon obviate the routine use of drug therapies in a way that patients should adapt to the therapy rather than the opposite. This expected revolution in routine clinical practice never took place as quickly nor with the intensity as initially expected. The concerted action of operating multicenter networks holds great promise for future studies to identify biomarkers related to drug toxicity and to provide better insight into the underlying pathogenesis. Today some pharmacogenomic advances are already widely accepted, but pharmacogenomics still needs further development to elaborate more precise algorithms and many barriers to implementing individualized medicine exist. We briefly discuss our view about these barriers and we provide suggestions and areas of focus to advance in the field.