Mechanisms of drug-induced liver disease

Endoplasmic reticulum stress in drug- and environmental toxicant-induced liver toxicity

Liver injury resulting from exposure to drugs and environmental chemicals is a major health problem. Endoplasmic reticulum stress (ER stress) is considered to be an important factor in a wide range of diseases, such as cancer, neurological and cardiovascular disease, diabetes, and inflammatory diseases. The role of ER stress in drug-induced and environmental toxicant-induced liver toxicity has been underestimated in the past; emerging evidence indicates that ER stress makes a substantial contribution to the pathogenesis of drug-induced liver toxicity. In this review, we summarize current knowledge on drugs and environmental toxicants that trigger ER stress in liver and on the underlying molecular mechanisms. We also discuss experimental approaches for ER stress studies.

High-content assays for hepatotoxicity using induced pluripotent stem cell-derived cells

Development of predictive in vitro assays for early toxicity evaluation is extremely important for improving the drug development process and reducing drug attrition rates during clinical development. High-content imaging-based in vitro toxicity assays are emerging as efficient tools for safety and efficacy testing to improve drug development efficiency. In this report we have used an induced pluripotent stem cell (iPSC)-derived hepatocyte cell model having a primary tissue-like phenotype, unlimited availability, and the potential to compare cells from different individuals. We examined a number of assays and phenotypic markers and developed automated screening methods for assessing multiparameter readouts of general and mechanism-specific hepatotoxicity. Endpoints assessed were cell viability, nuclear shape, average and integrated cell area, mitochondrial membrane potential, phospholipid accumulation, cytoskeleton integrity, and apoptosis. We assayed compounds with known mechanisms of toxicity and also evaluated a diverse hepatotoxicity library of 240 compounds. We conclude that high-content automated screening assays using iPSC-derived hepatocytes are feasible, provide information about mechanisms of toxicity, and can facilitate the safety assessment of drugs and chemicals.

Determination of intracellular unbound concentrations and subcellular localization of drugs in rat sandwich-cultured hepatocytes compared with liver tissue

Prediction of clinical efficacy, toxicity, and drug-drug interactions may be improved by accounting for the intracellular unbound drug concentration (C(unbound)) in vitro and in vivo. Furthermore, subcellular drug distribution may aid in predicting efficacy, toxicity, and risk assessment. The present study was designed to quantify the intracellular C(unbound) and subcellular localization of drugs in rat sandwich-cultured hepatocytes (SCH) compared with rat isolated perfused liver (IPL) tissue. Probe drugs with distinct mechanisms of hepatocellular uptake and accumulation were selected for investigation. Following drug treatment, SCH and IPL tissues were homogenized and fractionated by differential centrifugation to enrich for subcellular compartments. Binding in crude lysate and cytosol was determined by equilibrium dialysis; the C(unbound) and intracellular-to-extracellular C(unbound) ratio (K(pu,u)) were used to describe accumulation of unbound drug. Total accumulation (K(pobserved)) in whole tissue was well predicted by the SCH model (within 2- to 3-fold) for the selected drugs. Ritonavir (K(pu,u) ∼1) was evenly distributed among cellular compartments, but highly bound, which explained the observed accumulation within liver tissue. Rosuvastatin was recovered primarily in the cytosolic fraction, but did not exhibit extensive binding, resulting in a K(pu,u) >1 in liver tissue and SCH, consistent with efficient hepatic uptake. Despite extensive binding and sequestration of furamidine within liver tissue, a significant portion of cellular accumulation was attributed to unbound drug (K(pu,u) >16), as expected for a charged, hepatically derived metabolite. Data demonstrate the utility of SCH to predict quantitatively total tissue accumulation and elucidate mechanisms of hepatocellular drug accumulation such as active uptake versus binding/sequestration.

An indole derivative protects against acetaminophen-induced liver injury by directly binding to N-acetyl-p-benzoquinone imine in mice

AIMS

Acetaminophen (APAP)-induced liver injury is mainly due to the excessive formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) through the formation of a reactive intermediate, N-acetyl-p-benzoquinone imine (NAPQI), in both humans and rodents. Here, we show that the indole-derived synthetic compound has a protective effect against APAP-induced liver injury in C57Bl/6 mice model.

RESULTS

NecroX-7 decreased tert-butylhydroperoxide (t-BHP)- and APAP-induced cell death and ROS/RNS formation in HepG2 human hepatocarcinoma and primary mouse hepatocytes. In mice, NecroX-7 decreased APAP-induced phosphorylation of c-Jun N-terminal kinase (JNK) and 3-nitrotyrosine (3-NT) formation, and also protected mice from APAP-induced liver injury and lethality by binding directly to NAPQI. The binding of NecroX-7 to NAPQI did not require any of cofactors or proteins. NecroX-7 could only scavenge NAPQI when hepatocellular GSH levels were very low.

INNOVATION

NecroX-7 is an indole-derived potent antioxidant molecule, which can be bound to some types of radicals and especially NAPQI. It is well known that the NAPQI is a major intermediate of APAP, which causes necrosis of hepatocytes in rodents and humans. Thus, blocking NAPQI formation or eliminating NAPQI are novel strategies for the treatment or prevention of APAP-induced liver injury instead of GSH replenishment.

CONCLUSION

Our data suggest that the indole-derivative, NecroX-7, directly binds to NAPQI when hepatic GSH levels are very low and the NAPQI-NecroX-7 complex is secreted to the blood from the liver. NecroX-7 shows more preventive and similar therapeutic effects against APAP-induced liver injury when compared to the effect of N-acetylcysteine in C57Bl/6 mice.

Hybrid in silico models for drug-induced liver injury using chemical descriptors and in vitro cell-imaging information

Drug-induced liver injury (DILI) is a major adverse drug reaction that accounts for one-third of post-marketing drug withdrawals. Several classifiers for human hepatotoxicity using chemical descriptors with limited prediction accuracies have been published. In this study, we developed predictive in silico models based on a set of 156 DILI positive and 136 DILI negative compounds for DILI prediction. First, models based on a chemical descriptor (CDK, Dragon and MOE) and in vitro cell-imaging endpoints [human hepatocyte imaging assay technology (HIAT) descriptors] were built using random forest (RF) and five-fold cross-validation procedure. Then three hybrid models were built using HIAT and a single type of chemical descriptors. Generally, the models based only on chemical descriptors were poor, with a correct classification rate (CCR) around 0.60 when the default threshold value (i.e. threshold = 0.50) was used. The hybrid models afforded a CCR of 0.73 with a specificity of 0.74 and a better true positive rate (sensitivity of 0.71), which is crucial in drug toxicity screening for the purpose of patient safety. The benefit of hybrid models was even more drastic when stricter classification thresholds were employed (e.g. CCR would be 0.83 when double thresholds (non-toxic < 0.40 and toxic > 0.60) were used for the hybrid model). We have developed rigorously validated hybrid models which can be used in virtual screening of lead compounds with potential hepatotoxicity. Our study also showed a chemical structure and in vitro biological data can be complementary in enhancing the prediction accuracy of human hepatotoxicity and can afford rational mechanistic interpretation.

Characteristics of liver injury in drug-induced systemic hypersensitivity reactions

BACKGROUND

The liver is the most commonly involved internal organ in drug-induced systemic hypersensitivity. However, data obtained from these patients have yet to be analyzed in depth with respect to liver injury.

METHODS

The medical records of 136 patients who developed delayed-type drug hypersensitivity were reviewed at a tertiary referral hospital. Culprit drugs, the pattern and degree of liver injury, and the effect of systemic corticosteroids were evaluated in the group of patients with drug-induced systemic hypersensitivity and liver dysfunction (aspartate aminotransferase or alanine aminotransferase ≥80 IU/L). Clinical characteristics of patients with drug-induced systemic hypersensitivity and liver injury were analyzed.

RESULTS

Among the 61 patients with drug-induced systemic hypersensitivity and liver dysfunction, the clinical phenotypes were drug reaction with eosinophilia and systemic symptoms (n = 29, 48%), Stevens-Johnson syndrome/toxic epidermal necrolysis (n = 11, 18%), and maculopapular rash (n = 17, 28%). Antibiotics (n = 27, 44%) were the most common cause of drug-induced systemic hypersensitivity with liver dysfunction. Whereas patients with Stevens-Johnson syndrome/toxic epidermal necrolysis had mild hepatocellular-type liver injury of relatively brief duration, those with drug reaction with eosinophilia and systemic symptoms/drug-induced hypersensitivity syndrome had more severe and prolonged hepatocellular injury in addition to moderate to severe cholestatic-type liver injury. The use of systemic corticosteroids did not significantly affect either recovery from liver injury or mortality.

LIMITATIONS

This study was retrospective and the number of subjects was small.

CONCLUSION

The results suggest that the severity, pattern, and duration of liver injury differ according to the drug-hypersensitivity phenotype. Further studies are needed to evaluate the role of systemic corticosteroids in drug-induced systemic hypersensitivity and liver injury.

Acute hepatitis in a young woman with systemic lupus erythematosus: a diagnostic challenge

A 48-year-old woman with systemic lupus erythematosus diagnosis was on naproxen, hidroxichloroquine and acetylsalicylic acid. She had self-suspended all medication and resumed 1 year later. Five days after the medication was resumed, she developed acute hepatitis, with biochemical hepatic cytolysis, hypergamaglobulinaemia and a serum antinuclear antibody titre of 1/2560. Idiopathic autoimmune hepatitis was considered, but drug-induced liver injury could not definitely be ruled out. Patient declined liver biopsy. Oral prednisolone was started. Within 3 months with prednisolone being tapered to 10 mg/day, a new flare occurred. Liver biopsy was performed and it favoured autoimmune hepatitis diagnosis. We discuss the diagnostic options and treatment approach in a patient with autoimmune disease and possible drug-induced liver injury who initially declined liver biopsy.

Acetaminophen-induced acute liver injury in HCV transgenic mice

The exact etiology of clinical cases of acute liver failure is difficult to ascertain and it is likely that various co-morbidity factors play a role. For example, epidemiological evidence suggests that coexistent hepatitis C virus (HCV) infection increased the risk of acetaminophen-induced acute liver injury, and was associated with an increased risk of progression to acute liver failure. However, little is known about possible mechanisms of enhanced acetaminophen hepatotoxicity in HCV-infected subjects. In this study, we tested a hypothesis that HCV-Tg mice may be more susceptible to acetaminophen hepatotoxicity, and also evaluated the mechanisms of acetaminophen-induced liver damage in wild type and HCV-Tg mice expressing core, E1 and E2 proteins. Male mice were treated with a single dose of acetaminophen (300 or 500 mg/kg in fed animals; or 200 mg/kg in fasted animals; i.g.) and liver and serum endpoints were evaluated at 4 and 24h after dosing. Our results suggest that in fed mice, liver toxicity in HCV-Tg mice is not markedly exaggerated as compared to the wild-type mice. In fasted mice, greater liver injury was observed in HCV-Tg mice. In fed mice dosed with 300 mg/kg acetaminophen, we observed that liver mitochondria in HCV-Tg mice exhibited signs of dysfunction showing the potential mechanism for increased susceptibility.

Protective effects of nicotinamide against acetaminophen-induced acute liver injury

Nicotinamide (NAM), the amide form of vitamin B3, is involved in a wide range of biological processes. Recent evidence revealed the anti-inflammatory and anti-oxidant properties of NAM and suggests it may be used as a novel strategy in the prevention of acute liver injury. In the present study, we investigated the potential protective effects of NAM on acetaminophen (APAP)-induced acute liver injury in mice. Mice were treated with NAM at 400mg/kg 30 min before or after administration of APAP at a hepatotoxic dose of 400mg/kg body weight via intraperitoneal injection. Liver injury and the expression of inflammation-related molecules were determined by histological examination and biochemical analysis, respectively. In addition, the survival rate of mice was assessed after APAP administration. Pretreatment with NAM for 30 min significantly decreased plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and malondialdehyde (MDA), and diminished histopathologic evidence of hepatic toxicity in mice following APAP administration. Similarly, posttreatment with NAM also decreased plasma ALT and AST levels in APAP-administrated mice. Furthermore, both pretreatment and posttreatment with NAM prolonged the survival rate of acute liver injury mice, accompanied by a significant reduction in the plasma levels of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interferon-γ (INF-γ), and interleukin-6 (IL-6). Together, these findings suggest that NAM possesses protective effects on APAP-induced liver injury, which may involve the anti-inflammatory action.

Toxicity monitoring with primary cultured hepatocytes underestimates the acetaminophen-induced inflammatory responses of the mouse liver

In vitro gene expression profiling with isolated hepatocytes has been used to assess the hepatotoxicity of certain chemicals because of animal welfare issues. However, whether an in vitro system can completely replace the in vivo system has yet to be elucidated in detail. Using a focused microarray established in our laboratory, we examined gene expression profiles in the mouse liver and primary cultured hepatocytes after treatment with different doses of acetaminophen, a widely used analgesic that frequently causes liver injury. The acute hepatotoxicity of acetaminophen was confirmed by showing the induction of an oxidative stress marker, heme oxygenase-1, elevated levels of serum transaminase, and histopathological findings. In vivo microarray and network analysis showed that acetaminophen treatment provoked alterations in relation to the inflammatory response, and that tumor necrosis factor-α plays a central role in related pathway alterations. By contrast, pathway analyses in in vitro isolated hepatocytes did not find such prominent changes in the inflammation-related networks compared with the in vivo situation. Thus, although in vitro gene expression profiles are useful for evaluating the direct toxicity of chemicals, indirect toxicities including inflammatory responses mediated by cell-cell interactions or secondary toxicity due to pathophysiological changes in the whole body may be overlooked. Our results indicate that the in vitro hepatotoxicity prediction system using isolated hepatocytes does not fully reflect the in vivo cellular response. An in vitro system may be appropriate, therefore, for high throughput screening to detect the direct hepatotoxicity of a test compound.

Imitation of drug metabolism in human liver and cytotoxicity assay using a microfluidic device coupled to mass spectrometric detection

In this work, we developed a microfluidic device for the imitation of drug metabolism in human liver and its cytotoxicity on cells. The integrated microfluidic device consists of three sections: (1) bioreactors containing poly(ethylene) glycol (PEG) hydrogel encapsulated human liver microsomes (HLMs); (2) cell culture chambers for cytotoxicity assay; and (3) integrated micro solid-phase extraction (SPE) columns to desalt and concentrate the products of enzymatic reaction. To verify the feasibility of the integrated microchip, we studied uridine 5'-diphosphate-glucuronosyltransferase (UGT) metabolism of acetaminophen (AP) and the cytotoxicity of products on HepG2 cells. The products of the reaction in one region of the device were injected into the cell culture chamber for cytotoxicity assay, while those in another region were directly detected online with an electrospray ionization quadrupole time-of-flight mass spectrometer (ESI-Q-TOF MS) after micro-SPE pre-treatment. Semiquantitative analysis achieved in the experiments could be related to the drug-induced HepG2 cell cytotoxicity. Total analysis time for one product was about 30 min and only less than 4 μg HLM protein was required for one reaction region. The results demonstrated that the established platform could be used to imitate drug metabolism occurring in the human liver, thereby replacing animal experiments in the near future. In addition, the integrated microchip will be a useful tool for drug metabolism studies and cytotoxicity assays, which are pivotal in drug development.

Itraconazole-induced cholestasis: involvement of the inhibition of bile canalicular phospholipid translocator MDR3/ABCB4

Biliary secretion of bile acids and phospholipids, both of which are essential components of biliary micelles, are mediated by the bile salt export pump (BSEP/ABCB11) and multidrug resistance 3 P-glycoprotein (MDR3/ABCB4), respectively, and their genetic dysfunction leads to the acquisition of severe cholestatic diseases. In the present study, we found two patients with itraconazole (ITZ)-induced cholestatic liver injury with markedly high serum ITZ concentrations. To characterize the effect of ITZ on bile formation in vivo, biliary bile acids and phospholipids were analyzed in ITZ-treated rats, and it was revealed that biliary phospholipids, rather than bile acids, were drastically reduced in the presence of clinically relevant concentrations of ITZ. Moreover, by using MDR3-expressing LLC-PK1 cells, we found that MDR3-mediated efflux of [¹⁴C]phosphatidylcholine was significantly reduced by ITZ. In contrast, BSEP-mediated transport of [³H]taurocholate was not significantly affected by ITZ, which is consistent with our in vivo observations. In conclusion, this study suggests the involvement of the inhibition of MDR3-mediated biliary phospholipids secretion in ITZ-induced cholestasis. Our approach may be useful for analyzing mechanisms of drug-induced cholestasis and evaluating the cholestatic potential of clinically used drugs and drug candidates.

Influence of small doses of various drug vehicles on acetaminophen-induced liver injury

The biological effects of drug vehicles are often overlooked, often leading to artifacts in acetaminophen-induced liver injury assessment. Therefore, we decided to investigate the effect of dimethylsulfoxide, dimethylformamide, propylene glycol, ethanol, and Tween 20 on acetaminophen-induced liver injury. C57BL/6 male mice received a particular drug vehicle (0.6 or 0.2 mL/kg, i.p.) 30 min before acetaminophen administration (300 mg/kg, i.p.). Control mice received vehicle alone. Liver injury was assessed by measuring the concentration of alanine aminotransferase in plasma and observing histopathological changes. The level of reduced glutathione (GSH) was assessed by measuring total nonprotein hepatic sulfhydrils. Dimethylsulfoxide and dimethylformamide (at both doses) almost completely abolished acetaminophen toxicity. The higher dose of propylene glycol (0.6 mL/kg) was markedly protective, but the lower dose (0.2 mL/kg) was only slightly protective. These solvents also reduced acetaminophen-induced GSH depletion. Dimethylformamide was protective when given 2 h before or 1 h after acetaminophen administration, but was ineffective if given 2.5 h after acetaminophen. Ethanol at the higher dose (0.6 mL/kg) was partially protective, whereas ethanol at the lower dose (0.2 mL/kg) as well as Tween 20 at any dose had no influence. None of the vehicles (0.6 mL/kg) was hepatotoxic per se, and none of them was protective in a model of liver injury caused by d-galactosamine and lipopolysaccharide.

Drug bioactivation and protein adduct formation in the pathogenesis of drug-induced toxicity

Adverse drug reactions (ADRs) remain a major complication of drug therapy and can be classified as 'on-target' or 'off-target' (idiosyncratic) reactions. On-target reactions can be predicted from the known primary or secondary pharmacology of the drug and often represent an exaggeration of the pharmacological effect of the drug. In contrast, off-target adverse reactions cannot be predicted from knowledge of the basic pharmacology of the drug. The exact mechanisms of idiosyncratic drug reactions are still unclear; however it is believed that they can be initiated by chemically reactive drug metabolites. It is well known that xenobiotics can undergo metabolic bioactivation reactions which have the potential to cause cellular stress and damage. Bioactivation of drugs is thought to have the potential of initiating covalent linkages between cellular protein and drugs which can be recognised by the adaptive immune system in the absence of detectable cellular stress. This process cannot yet be predicted in pre-clinical models or discovered in clinical trials. Because of this hazard perception, the formation of chemically reactive metabolites in early drug discovery remains a serious impediment to the development of new medicines and can lead to withdrawal of an otherwise effective therapeutic agent. The fear of such reactions occurring at the post-licensing stage - when such problems first become evident - is a major contribution to drug attrition. The first step towards such methodology has been the development of chemically reactive metabolite screens. The chemical basis of drug bioactivation can usually be rationalised and synthetic strategies put in place to prevent such bioactivation. However, there is no simple correlation between drug bioactivation in vitro and adverse drug reactions in the clinic. Such a chemical approach is clearly limited by the facts that (a) not all drugs that can undergo bioactivation by human drug-metabolising enzymes are associated with hypersensitivity in the clinic and (b) drug bioactivation may not always be a mandatory step in drug hypersensitivity. To predict such reactions in early drug development, it will require an integrated understanding of the chemical, immunological and genetic basis of adverse drug reactions in patients, which in turn will depend on the development of novel in vitro experimental systems.

Clinical syndromes and consequences of antiretroviral-related hepatotoxicity

Highly active antiretroviral therapy (HAART)-related hepatotoxicity complicates the management of patients infected with human immunodeficiency virus (HIV), increases medical costs, alters the prescription patterns, and affects the guideline recommendations. Among the clinical consequences derived from HAART-related liver toxicity, hypersensitivity reactions and lactic acidosis are recognized as acute events with potential to evolve into fatal cases, whereas there seems to be other syndromes not as well characterized but of equal concern as possible long-term liver complications. Belonging to the latter category of syndrome, HAART-related nonalcoholic steatohepatitis, liver fibrosis, portal hypertension, and nodular regenerative hyperplasia are discussed in this review. Updated information on liver toxicity of current antiretroviral drugs, including the most recently licensed, is provided. Management and prevention of liver toxicity among HIV-infected patients treated with HAART are reviewed as well.

Diet restriction inhibits apoptosis and HMGB1 oxidation and promotes inflammatory cell recruitment during acetaminophen hepatotoxicity

Acetaminophen (APAP) overdose is a major cause of acute liver failure and serves as a paradigm to elucidate mechanisms, predisposing factors and therapeutic interventions. The roles of apoptosis and inflammation during APAP hepatotoxicity remain controversial. We investigated whether fasting of mice for 24 h can inhibit APAP-induced caspase activation and apoptosis through the depletion of basal ATP. We also investigated in fasted mice the critical role played by inhibition of caspase-dependent cysteine 106 oxidation within high mobility group box-1 protein (HMGB1) released by ATP depletion in dying cells as a mechanism of immune activation. In fed mice treated with APAP, necrosis was the dominant form of hepatocyte death. However, apoptosis was also observed, indicated by K18 cleavage, DNA laddering and procaspase-3 processing. In fasted mice treated with APAP, only necrosis was observed. Inflammatory cell recruitment as a consequence of hepatocyte death was observed only in fasted mice treated with APAP or fed mice cotreated with a caspase inhibitor. Hepatic inflammation was also associated with loss in detection of serum oxidized-HMGB1. A significant role of HMGB1 in the induction of inflammation was confirmed with an HMGB1-neutralizing antibody. The differential response between fasted and fed mice was a consequence of a significant reduction in basal hepatic ATP, which prevented caspase processing, rather than glutathione depletion or altered APAP metabolism. Thus, the inhibition of caspase-driven apoptosis and HMGB1 oxidation by ATP depletion from fasting promotes an inflammatory response during drug-induced hepatotoxicity/liver pathology.

Acute ANIT toxicity in male IL-10 knockout and wild-type mice

The innate immune response is known to modify hepatocellular injury induced by toxicants. To assess the role of IL-10, a component of the innate immune response, in toxicant-induced injury of biliary epithelium, wild-type (WT) and IL-10 knockout mice (KO) were given a single toxic dose (50 mg/kg) of alpha-napthylisothiocyanate (ANIT) and assessed at twenty-four-hour intervals for four days following treatment. Clinical signs of toxicity were greater in WT mice. Unexpectedly, over the course of the study, there was a consistent tendency for ANIT-treated IL-10 KO mice to have less hepatocellular injury than WT mice. However, changes in the biliary epithelium differed in that there was more histologic evidence of inflammation and necrosis on days 2 and 3, respectively, in ANIT-treated IL-10 KO mice compared with WT mice. Proliferation of biliary epithelium and hepatocytes was greater and/or occurred earlier in the ANIT-treated IL-10 KO mice compared with the ANIT-treated WT mice, suggesting a greater reparative response was needed for recovery after toxicant injury in the IL-10 KO mice. Overall, our data suggest that IL-10 KO mice have less hepatocellular injury than WT mice following a toxic dose of ANIT and that biliary epithelial injury is accentuated in the KO mice.

The characteristics and clinical outcome of drug-induced liver injury: a single-center experience

BACKGROUND AND GOALS

The aim of this cohort study was to determine the characteristics and clinical outcome of 170 patients with drug-induced liver injury (DILI) in a single center.

STUDY

Between January 2001 and June 2007, a total of 170 individuals who were diagnosed with DILI were retrospectively analyzed. The median follow-up period was 110.0 days.

RESULTS

During the study period, a total of 5471 new patients were assessed for liver test abnormalities. Of those, 170 patients (3.1%) fulfilled the criteria of DILI. A total of 83 different drugs were considered to be related to the hepatotoxicity; a single drug was suspected in 57.6% of individuals. The median interval between the suspicious drug intake and DILI recognition was 15.0 days. Hepatocellular pattern was observed in 50.0% of patients with a mean alanine aminotransferase level of 952.2+/-907.0 U/L. The main causative group of drugs was antibiotics. Sixty-two patients required hospitalization; acute liver failure developed in 14 (8.2%), chronicity was observed in 19 (11.2%), and 7 died (4.1%). Overall, complete recovery occurred in 82% of patients. The presence of jaundice on admission and shorter interval period between drug intake and DILI recognition were identified as risk factors for the development of acute liver failure.

CONCLUSIONS

DILI is an important cause of liver test abnormalities in outpatient clinics, and antibiotics represent the most common drug group. Overall, complete recovery after the withdrawal of the suspicious drug occurred in the majority of patients, but DILI may progress to acute liver failure, chronicity, and death.

Pegvisomant-induced liver injury is related to the UGT1A1*28 polymorphism of Gilbert's syndrome

CONTEXT

Pegvisomant (PEG) therapy has been associated with drug-induced liver dysfunction in acromegalic patients. The mechanism of its toxicity remains unknown.

OBJECTIVE

The primary objective was to determine whether or not the UGT1A1*28 polymorphism associated with Gilbert's syndrome influences the development of liver dysfunction during PEG treatment.

DESIGN AND SETTING

A cross-sectional study was conducted in four Spanish university hospitals.

PATIENTS

Thirty-six acromegalic patients with active disease, resistant to somatostatin analogs, participated.

RESULTS

The prevalence of the UGT1A1*28 homozygous and heterozygous genotypes in acromegalic patients was 14 and 44%, respectively. Ten patients (28%) developed liver function test (LFT) abnormalities. There was a tendency for more frequent liver function abnormalities in males (70% males vs. 30% females, P = 0.058). Carriers of the UGT1A1*28 polymorphism had a higher incidence of LFT abnormalities than the UGT1A1 wild type (43% carriers vs. 7% wild type, P = 0.024). This difference persisted when adjusted in an all-factors multiple regression analysis [coefficient of determination (R(2)) = 0.463; P = 0.008] for age, gender, alcohol consumption, and UGT1A1*28 polymorphism. A stepwise multivariate likelihood binary logistic regression analysis (R(2) = 0.40; P = 0.003) identified male gender (beta = 7.21; P = 0.033) and UGT1A1*28 polymorphism (beta = 14.1; P = 0.028) as the only significant predictors for the development of LFT abnormalities.

CONCLUSIONS

The UGT1A1*28 genotype and male gender predict an increased incidence of LFT abnormalities during PEG therapy in acromegaly.

Mechanisms of pathogenesis in drug hepatotoxicity putting the stress on mitochondria

Mitochondria play key roles in aerobic life and in cell death. Thus, interference of normal mitochondrial function impairs cellular energy and lipid metabolism and leads to the unleashing of mediators of cell death. The role of mitochondria in cell death due to drug hepatotoxicity has been receiving renewed attention and it is therefore timely to assess the current status of this area.

The role of cytokines in the mechanism of adverse drug reactions

Cytokines are thought to play a role in acute and/or immune-mediated adverse drug reactions (ADRs) due to their ability to regulate the innate and adaptive immune systems. This role is highly complex owing to the pluripotent nature of cytokines, which enables the same cytokine to play multiple roles depending on target organ(s) involved. As a result, the discussion of cytokine involvement in ADRs is organized according to target organ(s); specifically, ADRs targeting skin and liver, as well as ADRs targeting multiple organs, such as drug-induced autoimmunity and infusion-related reactions. In addition to discussing the mechanism(s) by which cytokines contribute to the initiation, propagation, and resolution of ADRs, we also discuss the usefulness and limitations of current methodologies available to conduct such mechanistic studies. While animal models appear to hold the most promise for uncovering additional mechanisms, this field is plagued by a lack of good animal models and, as a result, the mechanism of cytokine involvement in ADRs is often studied using less informative in vitro studies. The recent formation of the Drug-Induced Liver Injury Network, whose goal is collect thousands of samples from drug-induced liver injury patients, has enormous potential to advance knowledge in this field, by enabling large-scale cytokine polymorphism studies. In conclusion, we discuss how further advances in this field could be of significant benefit to patients in terms of preventing, predicting, and treating ADRs.

Lactoferrin protects against acetaminophen-induced liver injury in mice

Acetaminophen-induced liver injury (AILI) is a significant health problem and represents the most frequent cause of drug-induced liver failure in the United States. The development and implementation of successful therapeutic intervention strategies have been demanding, due to significant limitations associated with the current treatment for AILI. Lactoferrin (Lac), a glycoprotein present in milk, has been demonstrated to possess a multitude of biological functions. Our study demonstrated a profound protective effect of Lac in a murine model of AILI, which was not dependent on its iron-binding ability, inhibition of acetaminophen (APAP) metabolism, or a direct cytoprotective effect on hepatocytes. Instead, Lac treatment significantly attenuated APAP-induced liver sinusoidal endothelial cell dysfunction and ameliorated hepatic microcirculation disorder. This protective effect of Lac appeared to be dependent on hepatic resident macrophages (Kupffer cells [KCs]).

CONCLUSION

Collectively, our data indicate that Lac, through activation of KCs, inhibited APAP-induced liver sinusoidal endothelial cell damage and improved hepatic congestion, thereby protecting against AILI. These findings reveal the significant therapeutic potential of Lac during AILI and other types of liver diseases.

Bacterial- and viral-induced inflammation increases sensitivity to acetaminophen hepatotoxicity

Acetaminophen (APAP)-induced hepatotoxicity accounts for nearly half of acute liver failure cases in the United States. The doses that produce hepatotoxicity vary considerably and many risk factors have been proposed, including liver inflammation from viral hepatitis. Interestingly, inflammatory stress from another stimulus, bacterial endotoxin (lipopolysaccharide, LPS), renders the liver more sensitive to hepatotoxicity from numerous xenobiotic agents. The purpose of these studies was to test the hypothesis that inflammation induced by LPS or infection with reovirus increases sensitivity to APAP-induced liver injury. For LPS-induced inflammation, C57BL/6J mice were treated with either saline or LPS (44 x 10(6) EU/kg, ip) 2 h before treatment with APAP (100-400 mg/kg, ip) or saline. No elevation in serum alanine aminotransferase (ALT) activity was observed in mice that received vehicle or LPS alone. LPS co-treatment produced a leftward shift of the dose-response curve for APAP-induced hepatotoxicity and led to significantly greater tumor necrosis factor-alpha (TNF) production than APAP alone. Reovirus serotype 1 (10(8) PFU, iv) induced inflammation in Balb/c mice as evidenced by increases in hepatic mRNAs for macrophage inhibitory protein-2, interleukin-6, and TNF. Co-administration of reovirus and APAP at doses of 450 and 700 mg/kg (2 h after reovirus) led to increases in serum ALT activity, whereas neither reovirus nor APAP alone produced liver injury. Consistent with the increases in serum ALT activity, histopathologic examination revealed centrilobular necrosis with marked neutrophilic accumulation only in livers of mice treated with LPS/APAP or with reovirus/APAP. The results suggest that normally noninjurious doses of APAP are rendered hepatotoxic by modest inflammation, whether bacterial or viral in origin.

The use of hepatocytes to investigate drug toxicity

The liver is very active in metabolizing foreign compounds and the major target for toxicity caused by drugs. Hepatotoxicity may be the result of the drug itself or, more frequently, a result of the bioactivation process and the production of reactive metabolites. Prioritization of compounds based on human hepatotoxicity potential is currently a key unmet need in drug discovery, as it can become a major problem for several lead compounds in later stages of the drug discovery pipeline. Therefore, evaluation of potential hepatotoxicity represents a critical step in the development of new drugs. Cultured hepatocytes are increasingly used by the pharmaceutical industry for the screening of hepatotoxic potential of new molecules. Hepatocytes in culture retain hepatic key functions and constitute a valuable tool to identify chemically induced cellular damage. Their use has notably contributed to the understanding of mechanisms responsible for hepatotoxicity (disruption of cellular energy status, alteration of Ca(2+) homeostasis, inhibition of transport systems, metabolic activation, oxidative stress, covalent binding, etc.). Assessment of current cytotoxicity and hepatic-specific biochemical effects is limited by the inability to measure a wide spectrum of potential mechanistic changes involved in the drug-induced toxic injury. A convenient selection of endpoints allows a multiparametric evaluation of drug toxicity. In this regard, cytomic, proteomic, toxicogenomic and metabonomic approaches help to define patterns of hepatotoxicity for early identification of potential adverse effects of the drug to the liver.

Intrinsic versus idiosyncratic drug-induced hepatotoxicity--two villains or one?

"Intrinsic" and "idiosyncratic" drug-induced liver injury reactions are commonly thought to arise by different modes of action. Intrinsic toxicity is reproducible in animals and occurs dose-dependently at sublethal doses. Environmental and genetic sensitivity factors can influence the toxicity of intrinsic hepatotoxicants. Among these is inflammatory stress. For example, exposure of mice to inflammatory bacterial lipopolysaccharide (LPS) causes a leftward shift in the dose-response relationship for acetaminophen hepatotoxicity; that is, acetaminophen toxicity is enhanced by LPS-induced inflammatory stress. Idiosyncratic reactions present themselves very differently than intrinsic ones; they happen in a minority of patients, with variable time of onset and no obvious relationship to drug dose, and they are not reproducible in usual animal tests. Although these characteristics seem to distinguish them from intrinsic reactions, consideration of fundamental principles of dose response can explain the differences. For a drug that causes idiosyncratic hepatotoxicity, the liver may not be a typical target for toxicity because the dose-response curve for hepatotoxicity lies to the right of the lethal dose. However, a sporadically occurring sensitivity factor, such as an inflammatory episode, could shift the dose-response curve for hepatotoxicity to the left, thereby bringing hepatotoxic doses into the therapeutic range. This hypothesis can account for the bizarre characteristics of idiosyncratic reactions and is supported by recent results showing that several drugs associated with human idiosyncratic reactions can be rendered hepatotoxic to rodents upon interaction with an inflammatory stimulus. In light of this view, intrinsic and idiosyncratic reactions may not be that different after all.

The role of damage associated molecular pattern molecules in acetaminophen-induced liver injury in mice

The idiosyncratic nature, severity and poor diagnosis of drug-induced liver injury (DILI) make these reactions a major safety issue during drug development, as well as the most common cause for the withdrawal of drugs from the pharmaceutical market. Elucidation of the underlying mechanism(s) is necessary for identifying predisposing factors and developing strategies in the treatment and prevention of DILI. Acetaminophen (APAP) is a widely used over the counter therapeutic that is known to be effective and safe at therapeutic doses. However, in overdose situations fatal and non-fatal hepatic necrosis can result. Evidence suggests that the chemically reactive metabolite of the drug initiates hepatocyte damage and that inflammatory innate immune responses also occur within the liver, leading to the exacerbation and progression of tissue injury. Here we investigate whether following APAP-induced liver injury (AILI) damaged hepatocytes release "danger" signals or damage associated molecular pattern (DAMP) molecules, which induce pro-inflammatory activation of hepatic macrophages, further contributing to the progression of liver injury. Our study demonstrated a clear activation of Kupffer cells following early exposure to APAP (1h). Activation of a murine macrophage cell line, RAW cells, was also observed following treatment with liver perfusate from APAP-treated mice, or with culture supernatant of APAP-challenged hepatocytes. Moreover, in these media, the DAMP molecules, heat-shock protein-70 (HSP-70) and high mobility group box-1 (HMGB1) were detected. Overall, these findings reveal that DAMP molecules released from damaged and necrotic hepatocytes may serve as a crucial link between the initial hepatocyte damage and the activation of innate immune cells following APAP-exposure, and that DAMPs may represent a potential therapeutic target for AILI.

Drug-induced hepatotoxicity or drug-induced liver injury

Drug-induced hepatotoxicity is underreported and underestimated in the United States. It is an important cause of acute liver failure. Common classes of drugs causing drug-induced hepatotoxicity include antibiotics, lipid lowering agents, oral hypoglycemics, psychotropics, antiretrovirals, acetaminophen, and complementary and alternative medications. Hepatotoxic drugs often have a signature or pattern of liver injury including patterns of liver test abnormalities, latency of symptom onset, presence or absence of immune hypersensitivity, and the course of the reaction after drug withdrawal.

Characterization of hepatic mitochondrial injury induced by fatty acid oxidation inhibitors

Impairment of liver mitochondrial beta-oxidation is an important mechanism of drug-induced liver injury. Four inhibitors of fatty acid oxidation were compared in short-term rat in vivo studies in which the rats were administered one or four doses. The hepatocellular vacuolation represented ultra-structural mitochondrial changes. Urine nuclear magnetic resonance (NMR) spectroscopy revealed that both FOX988 and SDZ51-641 induced a persistent dicarboxylic aciduria, suggesting an inhibition of mitochondrial beta-oxidation and incomplete fatty acid metabolism. Etomoxir caused minimal mitochondrial ultrastructural changes and induced only transient dicarboxylic aciduria. CPI975 served as a negative control, in that there were no significant perturbations to the mitochondrial ultrastructural morphology or in the urine NMR composition; however, compound exposure was confirmed by the up-regulation of liver gene expression compared to vehicle control. The liver gene expression changes that were altered by the compounds were indicative of mitochondria, general and oxidative stress, and peroxisomal enzymes involved in beta-oxidation, suggestive of a compensatory response to the inhibition in the mitochondria. In addition, both FOX988 and SDZ51-641 up-regulated ribosomal genes associated with apoptosis, as well as p53 pathways linked with apoptosis. In summary, metabonomics and liver gene expression provided mechanistic information on mitochondrial dysfunction and impaired fatty acid oxidation to further define the clinical pathology and histopathology findings of hepatotoxicity.

DAMPs ramp up drug toxicity

The clinical syndrome of acetaminophen-induced liver injury represents the combined result of drug toxicity and a potent innate immune response that follows drug-induced cell death. In this issue of the JCI, Imaeda and colleagues report that DNA released from dying hepatocytes is a key stimulus of innate immune activation in the acetaminophen-treated mouse liver (see the related article beginning on page 305). They present evidence indicating that hepatocyte DNA promotes immune activation by acting as a danger-associated molecular pattern (DAMP) that stimulates cytokine production in neighboring sinusoidal endothelial cells via Tlr9 and the Nalp3 inflammasome.

Using controlled clinical trials to learn more about acute drug-induced liver injury

Drug-induced liver injury (DILI) is of major interest to hepatologists and clinicians in general, patients, government regulators, and the pharmaceutical industry. Understanding why this form of injury occurs only in certain individuals has major implications for the development and availability of drug therapies and in the prevention of these events. A single controlled clinical trial may be unlikely to show cases of such rare events, but in the aggregate, clinical trials offer a unique resource for learning more about individual susceptibility and developing truly predictive new biomarkers for DILI. We pose the question as to whether clinical trials could be modified or improved to provide data that would better answer some of the outstanding issues. At a recent (March 2008) public meeting, experts from academia, industry, and regulatory bodies discussed several major issues regarding liver safety in clinical trials including: what signals of liver injury should justify stopping administration of study drug or allowing it to continue; if deliberate rechallenge should be done and under what circumstances; whether patients with liver disease should be included in clinical trials; and what kinds of new biomarkers will be needed to answer these questions more clearly. Past clinical trials have not provided data to settle those issues, and reliance has defaulted to consensus of expert opinions. Modified and better clinical trials with standardized collection of data and biospecimens are probably the best source of new and potentially valuable information to supplant current rules based on consensus of expert opinions and to understand by what mechanisms and how to distinguish those individuals who are susceptible to severe DILI.

Pathogenic role of natural killer T and natural killer cells in acetaminophen-induced liver injury in mice is dependent on the presence of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is commonly used in biological studies to dissolve drugs and enzyme inhibitors with low solubility. Although DMSO is generally thought of as being relatively inert, it can induce biological effects that are often overlooked. An example that highlights this potential problem is found in a recent report demonstrating a pathogenic role for natural killer T (NKT) and natural killer (NK) cells in acetaminophen-induced liver injury (AILI) in C57Bl/6 mice in which DMSO was used to facilitate acetaminophen (APAP) dissolution. We report that NKT and NK cells do not play a pathologic role in AILI in C57Bl/6 mice in the absence of DMSO. Although AILI was significantly attenuated in mice depleted of NKT and NK cells prior to APAP treatment in the presence of DMSO, no such effect was observed when APAP was dissolved in saline. Because of this unexpected finding, the effects of DMSO on hepatic NKT and NK cells were subsequently investigated. When given alone, DMSO activated hepatic NKT and NK cells in vivo as evidenced by increased NKT cell numbers and higher intracellular levels of the cytotoxic effector molecules interferon-gamma (IFN-gamma) and granzyme B in both cell types. Similarly, when used as a solvent for APAP, DMSO again increased NKT cell numbers and induced IFN-gamma and granzyme B expression in both cell types.

CONCLUSION

These data demonstrate a previously unappreciated effect of DMSO on hepatic NKT and NK cells, suggesting that DMSO should be used cautiously in experiments involving these cells.

Relationship between daily dose of oral medications and idiosyncratic drug-induced liver injury: search for signals

Idiosyncratic drug-induced liver injury (DILI) is traditionally thought not to be dose-related. However, it has been pointed out that most medicines that were withdrawn from marketing or received a black-box warning because of hepatotoxicity were prescribed at daily doses greater than 50 mg/day. To examine the relationship between daily dose of medications and idiosyncratic DILI, we conducted a study with two aims. First, using two pharmaceutical databases, we examined the relationship between daily dose of commonly prescribed medicines in the United States and reported frequency of their selected hepatic adverse events. Second, we examined serious DILI cases reported to the Swedish Adverse Drug Reactions Advisory Committee (1970-2004) for any signals supporting the relationship between daily dose and idiosyncratic DILI. Medications were categorized into < or =10 mg/day, 11-49 mg/day, and > or =50 mg/day groups. Among US prescription medicines, a statistically significant relationship was observed between daily dose of oral medicines and reports of liver failure (P = 0.009), liver transplantation (P < 0.001), and death caused by DILI (P = 0.004) but not alanine aminotransferase (ALT) > 3 x upper limit of normal (P = 0.10) or jaundice (P = 0.16). Of 598 eligible Swedish DILI cases, 9% belonged to the < or =10 mg/day group, 14.2% to the 11-49 mg/day group, and 77% of cases were caused by medications given at dose > or =50 mg/day. A statistically significant relationship was noted between daily dose and poor outcome (death or liver transplantation) of Swedish DILI cases (2%, 9.4%, and 13.2% in < or =10, 11-49, and > or =50 mg/day groups, respectively, P = 0.03).

CONCLUSION

These data suggest a relationship between daily doses of oral prescription medications and idiosyncratic DILI. More studies are needed to validate these observations and to explore their implications.