Mitochondrial dysfunction and delayed hepatotoxicity: another lesson from troglitazone

Assessing immune hepatotoxicity of troglitazone with a versatile liver-immune-microphysiological-system

Drug-induced liver injury is a prevalent adverse event associated with pharmaceutical agents. More significantly, there are certain drugs that present severe hepatotoxicity only during the clinical phase, consequently leading to the termination of drug development during clinical trials or the withdrawal from the market after approval. The establishment of an evaluation model that can sensitively manifest such hepatotoxicity has always been a challenging aspect in drug development. In this study, we build a liver-immune-microphysiological-system (LIMPS) to fully demonstrate the liver injury triggered by troglitazone (TGZ), a drug that was withdrawn from the market due to hepatotoxicity. Leveraging the capabilities of organ-on-chip technology allows for the dynamic modulation of cellular immune milieu, as well as the synergistic effects between drugs, hepatocytes and multiple immune cells. Through the LIMPS, we discovered that 1) TGZ can promote neutrophils to adhered hepatocytes, 2) the presence of TGZ enhances the crosstalk between macrophages and neutrophils, 3) the induction of damage in hepatocytes by TGZ at clinically relevant blood concentrations not observed in other in vitro experiments, 4) no hepatotoxicity was observed in LIMPS when exposed to rosiglitazone and pioglitazone, structurally similar analogs of TGZ, even at the higher multiples of blood drug concentration levels. As an immune-mediated liver toxicity assessment method, LIMPS is simple to operate and can be used to test multiple drug candidates to detect whether they will cause severe liver toxicity in clinical settings as early as possible.

Mitochondrial Respiratory Complexes as Targets of Drugs: The PPAR Agonist Example

Mitochondrial bioenergetics are progressively acquiring significant pathophysiological roles. Specifically, mitochondria in general and Electron Respiratory Chain in particular are gaining importance as unintentional targets of different drugs. The so-called PPAR ligands are a class of drugs which not only link and activate Peroxisome Proliferator-Activated Receptors but also show a myriad of extrareceptorial activities as well. In particular, they were shown to inhibit NADH coenzyme Q reductase. However, the molecular picture of this intriguing bioenergetic derangement has not yet been well defined. Using high resolution respirometry, both in permeabilized and intact HepG2 cells, and a proteomic approach, the mitochondrial bioenergetic damage induced by various PPAR ligands was evaluated. Results show a derangement of mitochondrial oxidative metabolism more complex than one related to a simple perturbation of complex I. In fact, a partial inhibition of mitochondrial NADH oxidation seems to be associated not only with hampered ATP synthesis but also with a significant reduction in respiratory control ratio, spare respiratory capacity, coupling efficiency and, last but not least, serious oxidative stress and structural damage to mitochondria.

Liver-Heart on chip models for drug safety

Current pre-clinical models to evaluate drug safety during the drug development process (DDP) mainly rely on traditional two-dimensional cell cultures, considered too simplistic and often ineffective, or animal experimentations, which are costly, time-consuming, and not truly representative of human responses. Their clinical translation thus remains limited, eventually causing attrition and leading to high rates of failure during clinical trials. These drawbacks can be overcome by the recently developed Organs-on-Chip (OoC) technology. OoC are sophisticated in vitro systems capable of recapitulating pivotal architecture and functionalities of human organs. OoC are receiving increasing attention from the stakeholders of the DDP, particularly concerning drug screening and safety applications. When a drug is administered in the human body, it is metabolized by the liver and the resulting compound may cause unpredicted toxicity on off-target organs such as the heart. In this sense, several liver and heart models have been widely adopted to assess the toxicity of new or recalled drugs. Recent advances in OoC technology are making available platforms encompassing multiple organs fluidically connected to efficiently assess and predict the systemic effects of compounds. Such Multi-Organs-on-Chip (MOoC) platforms represent a disruptive solution to study drug-related effects, which results particularly useful to predict liver metabolism on off-target organs to ultimately improve drug safety testing in the pre-clinical phases of the DDP. In this review, we focus on recently developed liver and heart on chip systems for drug toxicity testing. In addition, MOoC platforms encompassing connected liver and heart tissues have been further reviewed and discussed.

Current Perspective: 3D Spheroid Models Utilizing Human-Based Cells for Investigating Metabolism-Dependent Drug-Induced Liver Injury

Drug-induced liver injury (DILI) remains a leading cause for the withdrawal of approved drugs. This has significant financial implications for pharmaceutical companies, places increasing strain on global health services, and causes harm to patients. For these reasons, it is essential that in-vitro liver models are capable of detecting DILI-positive compounds and their underlying mechanisms, prior to their approval and administration to patients or volunteers in clinical trials. Metabolism-dependent DILI is an important mechanism of drug-induced toxicity, which often involves the CYP450 family of enzymes, and is associated with the production of a chemically reactive metabolite and/or inefficient removal and accumulation of potentially toxic compounds. Unfortunately, many of the traditional in-vitro liver models fall short of their in-vivo counterparts, failing to recapitulate the mature hepatocyte phenotype, becoming metabolically incompetent, and lacking the longevity to investigate and detect metabolism-dependent DILI and those associated with chronic and repeat dosing regimens. Nevertheless, evidence is gathering to indicate that growing cells in 3D formats can increase the complexity of these models, promoting a more mature-hepatocyte phenotype and increasing their longevity, in vitro. This review will discuss the use of 3D in vitro models, namely spheroids, organoids, and perfusion-based systems to establish suitable liver models to investigate metabolism-dependent DILI.

Anti-Diabetic Effect of Telmisartan Through its Partial PPARγ-Agonistic Activity

Telmisartan is an angiotensin II receptor antagonist, which selectively inhibits the angiotensin II type 1 receptor. Thus, it is widely used for hypertension management. Nowadays, telmisartan's effect on peroxisome proliferator-activated receptors (PPARs) is gaining wider attention. PPARs are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. Telmisartan is reported to have a partial PPARγ-agonistic effect while avoiding the safety concerns found with full PPARγ agonists (thiazolidinediones). Telmisartan could be an alternative treatment option, with dual benefit for diabetes mellitus (DM) and hypertension. This review summarizes the anti-diabetic activity of telmisartan via its partial PPARγ-agonistic activity.

Integrating Biosensors in Organs-on-Chip Devices: A Perspective on Current Strategies to Monitor Microphysiological Systems

Organs-on-chip (OoC), often referred to as microphysiological systems (MPS), are advanced in vitro tools able to replicate essential functions of human organs. Owing to their unprecedented ability to recapitulate key features of the native cellular environments, they represent promising tools for tissue engineering and drug screening applications. The achievement of proper functionalities within OoC is crucial; to this purpose, several parameters (e.g., chemical, physical) need to be assessed. Currently, most approaches rely on off-chip analysis and imaging techniques. However, the urgent demand for continuous, noninvasive, and real-time monitoring of tissue constructs requires the direct integration of biosensors. In this review, we focus on recent strategies to miniaturize and embed biosensing systems into organs-on-chip platforms. Biosensors for monitoring biological models with metabolic activities, models with tissue barrier functions, as well as models with electromechanical properties will be described and critically evaluated. In addition, multisensor integration within multiorgan platforms will be further reviewed and discussed.

Mechanisms of Drug-Induced Hepatotoxicity

Drug-induced hepatotoxicity (DIH) is a significant cause of acute liver failure and liver transplantation. Diagnosis is challenging due to the idiosyncratic nature, its presentation in the form of other liver disease, and the lack of a definite diagnostic criteria. Generation of reactive metabolites, oxidative stress, and mitochondrial dysfunction are common mechanisms involved in DIH. Certain risk factors associated with a drug and within an individual further predispose patients to DIH.

Real-time monitoring of metabolic function in liver-on-chip microdevices tracks the dynamics of mitochondrial dysfunction

Microfluidic organ-on-a-chip technology aims to replace animal toxicity testing, but thus far has demonstrated few advantages over traditional methods. Mitochondrial dysfunction plays a critical role in the development of chemical and pharmaceutical toxicity, as well as pluripotency and disease processes. However, current methods to evaluate mitochondrial activity still rely on end-point assays, resulting in limited kinetic and prognostic information. Here, we present a liver-on-chip device capable of maintaining human tissue for over a month in vitro under physiological conditions. Mitochondrial respiration was monitored in real time using two-frequency phase modulation of tissue-embedded phosphorescent microprobes. A computer-controlled microfluidic switchboard allowed contiguous electrochemical measurements of glucose and lactate, providing real-time analysis of minute shifts from oxidative phosphorylation to anaerobic glycolysis, an early indication of mitochondrial stress. We quantify the dynamics of cellular adaptation to mitochondrial damage and the resulting redistribution of ATP production during rotenone-induced mitochondrial dysfunction and troglitazone (Rezulin)-induced mitochondrial stress. We show troglitazone shifts metabolic fluxes at concentrations previously regarded as safe, suggesting a mechanism for its observed idiosyncratic effect. Our microfluidic platform reveals the dynamics and strategies of cellular adaptation to mitochondrial damage, a unique advantage of organ-on-chip technology.

(Q)SAR: A Tool for the Toxicologist

A continuing education (CE) course at the 2014 American College of Toxicology annual meeting covered the topic of (Quantitative) Structure-Activity Relationships [(Q)SAR]. The (Q)SAR methodologies use predictive computer modeling based on predefined rules to describe the relationship between chemical structure and a chemical's associated biological activity or statistical tools to find correlations between biologic activity and the molecular structure or properties of a compound. The (Q)SAR has applications in risk assessment, drug discovery, and regulatory decision making. Pressure within industry to reduce the cost of drug development and societal pressure for government regulatory agencies to produce more accurate and timely risk assessment of drugs and chemicals have necessitated the use of (Q)SAR. Producing a high-quality (Q)SAR model depends on many factors including the choice of statistical methods and descriptors, but first and foremost the quality of the data input into the model. Understanding how a (Q)SAR model is developed and applied is critical to the successful use of such a tool. The CE session covered the basic principles of (Q)SAR, practical applications of these computational models in toxicology, how regulatory agencies use and interpret (Q)SAR models, and potential pitfalls of using them.

Hyperammonia induces specific liver injury through an intrinsic Ca2+-independent apoptosis pathway

Background

Numerous pathological processes that affect liver function in patients with liver failure have been identified. Among them, hyperammonia is one of the most common phenomena.The purpose of this study was to determine whether hyperammonia could induced specific liver injury.

Methods

Hyperammonemic cells were established using NH₄Cl. The cells were assessed by MTT, ELISA, and flow cytometric analyses. The expression levels of selected genes and proteins were confirmed by quantitative RT-PCR and western blot analyses.

Results

The effects of 20 mM NH₄Cl pretreatment on the cell proliferation and apoptosis of primary hepatocytes and other cells were performed by MTT assays and flow cytometric analyses. Significant increasing in cytotoxicity and apoptosis were only observed in hepatocytes. The cell damage was reduced after adding BAPTA-AM but unchanged after adding EGTA. The expression levels of caspase-3, cytochrome C, calmodulin, and inducible nitric oxide synthase were increased and that of bcl-2 was reduced. The Na⁺-K⁺-ATPase activities in hyperammonia liver cells was no signiaficant difference compaired with the control group, but was decreased in astrocytes. NH₄Cl pretreatment of primary hepatocytes promoted the activation of mitochondrial permeability transition pores and the mitochondria swelled irregularly.

Conclusions

Hyperammonia induces specific liver injury through an intrinsic Ca²⁺-independent apoptosis pathway.

Hepatobiliary transporters in drug-induced cholestasis: a perspective on the current identifying tools

INTRODUCTION

Impaired bile formation leads to the accumulation of cytotoxic bile salts in hepatocytes and, consequently, cholestasis and severe liver disease. Knowledge of the role of hepatobiliary transporters, especially the bile salt export pump (BSEP), in the pathogenesis of cholestasis is continuously increasing.

AREAS COVERED

This review provides an introduction into the role of these transport proteins in bile formation. It addresses the clinical relevance and pathophysiologic consequences of altered functions of these transporters by genetic mutations and drugs. In particular, the current practical aspects of identification and mitigation of drug candidates with liver liabilities employed during drug development, with an emphasis on preclinical screening for BSEP interaction, are discussed.

EXPERT OPINION

Within the potential pathogenetic mechanisms of acquired cholestasis, the inhibition of BSEP by drugs is well established. Interference of a new compound with BSEP transport activity should raise a warning sign to conduct follow-up experiments and to monitor liver function during clinical development. A combination of in vitro screening for transport interaction, in silico predicting models, and consideration of physicochemical and metabolic properties should lead to a more efficient screening of potential liver liability.

PPAR Could Contribute to the Pathogenesis of Hepatocellular Carcinoma

Viral hepatitis with hepatitis C virus or hepatitis B virus and chronic liver disease such as alcoholic or nonalcoholic steatohepatitis are critical factors in the development of hepatocellular carcinoma (HCC). Furthermore, diabetes is known as an independent risk factor for HCC. Peroxisome proliferator-activated receptor (PPAR) is known to have an important role in fatty liver, and the mechanism of carcinogenesis has been clarified. PPAR controls ligand-dependent transcription, and three subtypes (α, δ, and γ) in humans are known. PPARs could contribute to the mechanisms of cell cycling, anti-inflammatory responses, and apoptosis. Therefore, to clarify the pathogenesis of HCC, we should examine PPAR signaling. In this paper, we have summarized the relevance of PPARs to the pathogenesis of HCC and cancer stem cells and possible therapeutic options through modifying PPAR signaling.

Effect of 2,4-thiazolidinedione on limousin cattle growth and on muscle and adipose tissue metabolism

The main adipogenic transcription factor PPARγ possesses high affinity to 2,4-TZD, a member of the Thiazolidinedione family of insulin-sensitizing compounds used as adipogenic agents. We evaluated 2,4-TZD's effect on bovine growth and PPAR tissue expression. Seventeen Limousin bulls (18 month-old; 350 kg body weight (BW)) were assigned into 2 treatments: control and 2,4-TZD (8 mg/70 kg BW) and were fed until bulls reached 500 kg BW. They were weighed and their blood was sampled. DNA, RNA, and protein were determined in liver; skeletal muscle; subcutaneous (SC), omental, perirenal adipose tissues (AT) to determine protein synthesis rate and cellular size. Expression of PPAR mRNA was measured in liver and muscle (PPARα, -δ, and -γ) and SC adipose tissue (γ) by real-time PCR. No significant differences were found (P > 0.1) in weight gain, days on feed, and carcass quality. Muscle synthesis was greater in controls (P < 0.05); cell size was larger with 2,4-TZD (P < 0.05). PPARα, -δ, and -γ expressions with 2,4-TZD in liver were lower (P < 0.01) than in muscle. No differences were found for PPARγ mRNA expression in SCAT. The results suggest the potential use of 2,4-TZD in beef cattle diets, because it improves AT differentiation, liver, and muscle fatty acid oxidation that, therefore, might improve energy efficiency.

Examining the safety of PPAR agonists - current trends and future prospects

INTRODUCTION

The peroxisome proliferator-activated receptor (PPAR)-α and -γ agonists, fibrates and glitazones, are effective treatments for dyslipidemia and type 2 diabetes mellitus, respectively, but exhibit class-related, as well as compound-specific safety characteristics.

AREAS COVERED

This article reviews the profiles of PPAR-α, PPAR-γ, and dual PPAR-α/γ agonists with regard to class-related and compound-specific efficacy and adverse effects. We explore how learnings from first-generation drugs are being applied to develop safer PPAR-targeted therapies.

EXPERT OPINION

The finding that rosiglitazone may increase risk for cardiovascular events has led to regulatory guidelines requiring demonstration of cardiovascular safety in appropriate outcome trials for new type 2 diabetes mellitus drugs. The emerging data on the possibly increased risk of bladder cancer with pioglitazone may prompt the need for post-approval safety studies for new drugs. Since PPAR-α and -γ affect key cardiometabolic risk factors (diabetic dyslipidemia, insulin resistance, hyperglycemia, and inflammation) in a complementary fashion, combining their benefits has emerged as a particularly attractive option. New PPAR-targeted therapies that balance the relative potency and/or activity toward PPAR-α and -γ have shown promise in retaining efficacy while reducing potential side effects.

Functional role of peroxisome-proliferator-activated receptor γ in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide. Major risk factors of HCC include infection with hepatitis B or C viruses, alcohol and non-alcoholic fatty liver disease. HCC is difficult to diagnose at early stage, and has a very poor survival rate when diagnosed at a late stage. The majority of HCC-related deaths result from local invasion (to cause liver failure) or distant metastases. There is an urgent need to identify effective molecular targets for the treatment of the disease. As the target of an established class of therapeutic agent thiazolidinediones (TZDs), peroxisome-proliferator-activated receptor γ (PPARγ) has been widely studied for its role in the development of HCC. A substantial body of evidence based on in vitro and in vivo models indicates that the activation of PPARγ is able to inhibit HCC cell proliferation and tumor growth through inducing cell cycle arrest and apoptosis via the regulation of a panel of downstream effector molecules. PPARγ activation also induces an inhibitory effect on HCC metastasis. Meanwhile, there is new evidence suggesting that PPARγ inhibition could also be anti-tumorigenic. In the present review, we summarize the available information on the role of PPARγ in HCC development and spread, and discuss whether PPARγ activation by TZDs could play a role in the treatment of HCC, summarizing both in vitro and in vivo. Considering the available data, PPARγ seems to exert beneficial effects against HCC and may therefore represent as a therapeutic target.

Synergistic effect of cyanidin and PPAR agonist against nonalcoholic steatohepatitis-mediated oxidative stress-induced cytotoxicity through MAPK and Nrf2 transduction pathways

Nonalcoholic steatohepatitis (NASH) is caused by an elevation in oxidative stress, which might further lead to hepatic fibrogenesis. Importantly, both peroxisome proliferator-activated receptor (PPAR) and nuclear factor erythroid 2-related factor 2 (Nrf2) play roles in modulating oxidative stress-mediated hepatic dysfunction. The objective of this study was to investigate the mechanisms of the multifunctional effects of cyanidin on regulating antioxidant enzymes and oxidative stress-induced hepatotoxicity. The data indicated that cyanidin-mediated antioxidant enzyme expression involved the extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) pathways and Nrf2 activation. Furthermore, the synergistic effect of cyanidin and the PPAR agonist, troglitazone, on Nrf2-PPAR activation, was also observed. Besides, treatment of cyanidin and troglitazone abolished H₂O₂-induced downregulation of genes involved in lipid metabolism. In addition, H₂O₂-mediated cytotoxicity, which was caused by inducing ROS formation and apoptotic cell death, was also ameliorated upon cyanidin and troglitazone stimulation. In conclusion, mitogen-activated protein kinases (MAPKs) and the transcription factor Nrf2 played regulatory roles in cyanidin-mediated antioxidant enzyme activation. Furthermore, the combination of cyanidin and troglitazone activated PPARγ-Nrf2 and improved H₂O₂-mediated perturbation of genes involved in lipid metabolism. These data suggested that cyanidin and PPAR agonists might have synergistic benefits against metabolic dysfunction-related oxidative damage.

Pioglitazone and bladder cancer in human studies: is it diabetes itself, diabetes drugs, flawed analyses or different ethnicities?

This article reviews human observations on pioglitazone and bladder cancer risk. The PROspective pioglitAzone Clinical Trial In macroVascular Events trial showed an imbalance in bladder cancer between users of pioglitazone and placebo (14 versus six cases, p = 0.069). However, after excluding bladder cancer probably ascribed to other etiology, a blind assessment concluded that the imbalance might not be related to pioglitazone. Epidemiologic studies conducted in the United States and France using insurance databases independently suggested that pioglitazone use for >2 years might confer a 20%-40% higher risk. Another study evaluating bladder cancer risk in diabetic patients using the National Health Insurance in Taiwan did not find any incident bladder cancer case among 422 pioglitazone users for a follow-up of up to 3 years. Because observational studies may suffer from selection and information bias, and inadequate adjustment for confounders may inflate the estimated risk, causal inference from these studies should be interpreted with caution. While investigating cancer risk associated with a medication, indication bias should also be attended, especially when the medication is used at a late stage of the disease. Because pioglitazone is usually a second or third line antidiabetic agent, the users are always characterized by older age, longer diabetes duration, poorer glycemic control, and higher rates of complications and comorbidities. Biased estimates will also result if these differences are not appropriately addressed in the analyses. Current evidence neither concludes nor excludes a causal role of pioglitazone on bladder cancer. Clinical trials aiming at evaluating the risk of cancer associated with a medication is not ethical and may not be expected to provide an answer on the issue of pioglitazone-related bladder cancer. However, a meta-analysis using all available clinical trials to compare the bladder cancer risk between pioglitazone and comparators will be helpful. Well-conducted epidemiologic observational studies are probably other options. Because bladder cancer incidence and their risk factors may differ significantly among different ethnicities, a clarification of such a link in different ethnicities is needed, better by using long-term databases with large and representative sample size and appropriate adjustment for confounders. Furthermore, the interactions with other comorbidities and concomitant medications should be addressed.

Central role of mitochondria in drug-induced liver injury

A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.

Safety during the monitoring of diabetic patients: trial teaching course on health professionals and diabetics - SEGUDIAB study

Background

Safety for diabetic patients means providing the most suitable treatment for each type of diabetic in order to improve monitoring and to prevent the adverse effects of drugs and complications arising from the disease. The aim of this study is to analyze the effect of imparting educational interventions to health professionals regarding the safety of patients with Diabetes Mellitus (DM).

Methods

Design: A cluster randomized trial with a control group.

Setting and sample: The study analyzed ten primary healthcare centres (PHC) covering approximately 150,000 inhabitants. Two groups of 5 PHC were selected on the basis of their geographic location (urban, semi-urban and rural), their socio-economic status and the size of their PHC, The interventions and control groups were assigned at random. The study uses computerized patient records to individually assess subjects aged 45 to 75 diagnosed with type 1 and type 2 DM, who met the inclusion conditions and who had the variables of particular interest to the study.

Trial: The educational interventions consisted of a standardized teaching course aimed at doctors and nurses. The course lasted 6 hours and was split into three 2-hour blocks with subsequent monthly refresher courses.

Measurement: For the health professionals, the study used the Diabetes Attitude Scale (DAS-3) to assess their attitudes and motivation when monitoring diabetes. For the patients, the study assessed factors related to their degree of control over the disease at onset, 6, 12 and 24 months.

Main variables: levels of HbA1c.

Analysis: The study analyzed the effect of the educational interventions both on the attitudes and motivations of health professionals and on the degree of control over the diabetes in both groups.

Discussion

Imparting educational interventions to health professionals would improve the monitoring of diabetic patients. The most effective model involves imparting the course to both doctors and nurses. However, these models have not been tested on our Spanish population within the framework of primary healthcare.

Trial registration

ClinicalTrials.gov: NCT01087541

Lipophilicity as a determinant of thiazolidinedione action in vitro: findings from BLX-1002, a novel compound without affinity to PPARs

The pharmacology of thiazolidinediones (TZDs) seems to be driven not only by activation of peroxisome proliferator-activated receptor-γ (PPARγ), but also by PPARγ-independent effects on mitochondrial function and cellular fuel handling. This study portrayed such actions of the novel hydrophilic TZD compound BLX-1002 and compared them to those of conventional TZDs. Mitochondrial function and fuel handling were examined in disrupted rat muscle mitochondria, intact rat liver mitochondria, and specimens of rat skeletal muscle. BLX-1002 was superior to most other TZDs as an inhibitor of respiratory complex 1 in disrupted mitochondria, but had less effect than any other TZD on oxygen consumption by intact mitochondria and on fuel metabolism by intact tissue. The latter finding was obviously related to the hydrophilic properties of BLX-1002, because high potentials of individual TZDs to shift muscle fuel metabolism from the aerobic into the anaerobic pathway were associated with high ClogP values indicative of high lipophilicity and low hydrophilicity (e.g., % increase in lactate release induced by 10 μmol/l of respective compound: BLX-1002, ClogP 0.39, +10 ± 8%, not significant; pioglitazone, ClogP 3.53, +68 ± 12%, P < 0.001; troglitazone, ClogP 5.58, +157 ± 14%, P < 0.001). The observed specific properties of BLX-1002 could result from relatively strong direct affinity to an unknown mitochondrial target, but limited access to this target. Results suggest 1) that impairment of mitochondrial function and increased anaerobic fuel metabolism are unlikely to account for PPARγ-independent glucose lowering by BLX-1002, and 2) that higher lipophilicity of an individual TZD is associated with stronger acceleration of anaerobic glycolysis.

Genetic variations of bile salt transporters as predisposing factors for drug-induced cholestasis, intrahepatic cholestasis of pregnancy and therapeutic response of viral hepatitis

INTRODUCTION

Drug-induced cholestasis, intrahepatic cholestasis of pregnancy and viral hepatitis are acquired forms of liver disease. Cholestasis is a pathophysiologic state with impaired bile formation and subsequent accumulation of bile salts in hepatocytes. The bile salt export pump (BSEP) (ABCB11) is the key export system for bile salts from hepatocytes.

AREAS COVERED

This article provides an introduction into the physiology of bile formation followed by a summary of the current knowledge on the key bile salt transporters, namely, the sodium-taurocholate co-transporting polypeptide NTCP, the organic anion transporting polypeptides (OATPs), BSEP and the multi-drug resistance protein 3. The pathophysiologic consequences of altered functions of these transporters, with an emphasis on molecular and genetic aspects, are then discussed.

EXPERT OPINION

Knowledge of the role of hepatocellullar transporters, especially BSEP, in acquired cholestasis is continuously increasing. A common variant of BSEP (p.V444A) is now a well-established susceptibility factor for acquired cholestasis and recent evidence suggests that the same variant also influences the therapeutic response and disease progression of viral hepatitis C. Studies in large independent cohorts are now needed to confirm the relevance of p.V444A. Genome-wide association studies should lead to the identification of additional genetic factors underlying cholestatic liver disease.

Role of the bile salt export pump, BSEP, in acquired forms of cholestasis

Generation of bile is a key function of the liver. Its impairment leads to accumulation of cytotoxic bile salts in hepatocytes and, consequently, to liver disease. The bile salt export pump, BSEP, is critically involved in the secretion of bile salts into bile. Its function can be disturbed or abolished by inherited mutations. This will lead to progressive intrahepatic cholestais and severe liver disease. In addition to mutations, BSEP can be inhibited by acquired factors, such as xenobiotics or drugs, aberrant bile salt metabolites, or pregnancy. This inhibition will lead to acquired cholestasis. Some drugs are now known to be competitive inhibitors of Bsep. In addition, a polymorphism in the gene coding for BSEP has been identified as a potential susceptibility factor for acquired cholestasis.

Interference with bile salt export pump function is a susceptibility factor for human liver injury in drug development

The bile salt export pump (BSEP) is an efflux transporter, driving the elimination of endobiotic and xenobiotic substrates from hepatocytes into the bile. More specifically, it is responsible for the elimination of monovalent, conjugated bile salts, with little or no assistance from other apical transporters. Disruption of BSEP activity through genetic disorders is known to manifest in clinical liver injury such as progressive familial intrahepatic cholestasis type 2. Drug-induced disruption of BSEP is hypothesized to play a role in the development of liver injury for several marketed or withdrawn therapeutics. Unfortunately, preclinical animal models have been poor predictors of the liver injury associated with BSEP interference observed for humans, possibly because of interspecies differences in bile acid composition, differences in hepatobiliary transporter modulation or constitutive expression, as well as other mechanisms. Thus, a BSEP-mediated liver liability may go undetected until the later stages of drug development, such as during clinical trials or even postlicensing. In the absence of a relevant preclinical test system for BSEP-mediated liver injury, the toxicological relevance of available in vitro models to human health rely on the use of benchmark compounds with known clinical outcomes, such as marketed or withdrawn drugs. In this study, membrane vesicles harvested from BSEP-transfected insect cells were used to assess the activity of more than 200 benchmark compounds to thoroughly investigate the relationship between interference with BSEP function and liver injury. The data suggest a relatively strong association between the pharmacological interference with BSEP function and human hepatotoxicity. Although the most accurate translation of risk would incorporate pharmacological potency, pharmacokinetics, clearance mechanisms, tissue distribution, physicochemical properties, indication, and other drug attributes, the additional understanding of a compound's potency for BSEP interference should help to limit or avoid BSEP-related liver liabilities in humans that are not often detected by standard preclinical animal models.

Important elements for the diagnosis of drug-induced liver injury

BACKGROUND & AIMS

Drug-induced liver disease is the leading cause of acute liver failure in the United States. Accurate reporting of drug-induced liver injury is essential for early detection of hepatotoxicity and for developing reliable, interpretable literature. We assessed the extent to which published case reports of drug-induced liver disease include sufficient clinical data for interpreting the cause of toxicity.

METHODS

We developed a list of 42 predetermined, specific minimal elements necessary in evaluating causality of drug-induced liver injury. We then analyzed 97 published case reports or series studies of hepatotoxicity from 6 drugs (from 3 classes): amoxicillin/clavulanic acid (n = 35), troglitazone (n = 32), rosiglitazone (n = 10), pioglitazone (n = 8), zafirlukast (n = 8), and montelukast (n = 4).

RESULTS

Patient age, sex, primary disease, and drug name were reported in most, if not all, published case reports. However, many elements were underreported; some publications did not mention initial bilirubin levels (12%), many did not provide initial alkaline phosphatase levels (58%), and others provided vague descriptions of how certain diagnoses were excluded, that is, tests for hepatitis A, B, and C were negative. Data on abnormal results from serial liver tests frequently were absent. Exclusions of competing viral etiologies were reported in less than 50% of the studies.

CONCLUSIONS

Reports of drug-induced liver diseases often do not provide the data needed to determine the causes of the adverse effects. Efforts to promote and include a list of essential diagnostic elements in research articles could increase the quality and clinical utility of published case reports of drug toxicity.

Anticancer Role of PPARgamma Agonists in Hematological Malignancies Found in the Vasculature, Marrow, and Eyes

The use of targeted cancer therapies in combination with conventional chemotherapeutic agents and/or radiation treatment has increased overall survival of cancer patients. However, longer survival is accompanied by increased incidence of comorbidities due, in part, to drug side effects and toxicities. It is well accepted that inflammation and tumorigenesis are linked. Because peroxisome proliferator-activated receptor (PPAR)-gamma agonists are potent mediators of anti-inflammatory responses, it was a logical extension to examine the role of PPARgamma agonists in the treatment and prevention of cancer. This paper has two objectives: first to highlight the potential uses for PPARgamma agonists in anticancer therapy with special emphasis on their role when used as adjuvant or combined therapy in the treatment of hematological malignancies found in the vasculature, marrow, and eyes, and second, to review the potential role PPARgamma and/or its ligands may have in modulating cancer-associated angiogenesis and tumor-stromal microenvironment crosstalk in bone marrow.

Liver tissue engineering in the evaluation of drug safety

Assessment of drug-liver interactions is an integral part of predicting the safety profile of new drugs. Existing model systems range from in vitro cell culture models to FDA-mandated animal tests. Data from these models often fail, however, to predict human liver toxicity, resulting in costly failures of clinical trials. In vitro screens based on cultured hepatocytes are now commonly used in early stages of development, but many toxic responses in vivo seem to be mediated by a complex interplay among several different cell types. We discuss some of the evolving trends in liver cell culture systems applied to drug safety assessment and describe an experimental model that captures complex liver physiology through incorporation of heterotypic cell-cell interactions, 3D architecture and perfused flow. We demonstrate how heterotypic interactions in this system can be manipulated to recreate an inflammatory environment and apply the model to test compounds that potentially exhibit idiosyncratic drug toxicity. Finally, we provide a perspective on how the range of existing and emerging in vitro liver culture approaches, from simple to complex, might serve needs across the range of stages in drug discovery and development, including applications in molecular therapeutics.

Drug-induced liver injury: what was new in 2008?

BACKGROUND

Given the number of publications appearing annually regarding drug-induced liver injury (DILI), there remains a need to concisely summarize each year's new crop of case series and reports as well as the advances in mechanisms of liver injury and in the field of pharmacogenomics relating to DILI.

OBJECTIVE

To present an up-to-date review of the past year's most important clinical studies and reports of DILI, placing them into context of previous publications.

METHODS

A Medline search was conducted of all manuscripts appearing in the fields "hepatotoxicity" and "drug-induced liver injury" during the calendar year 2008. The most clinically relevant English language case reports and studies exploring mechanisms and risk factors for DILI were then chosen for review, and supplemented with older literature where appropriate.

CONCLUSIONS

As in past years, 2008 was replete with publications dealing with virtually all facets of DILI, including updated incidence and prevalence data, as well as the latest information regarding mechanisms of liver injury. Data from the first 300 patients in the National Institute of Health-sponsored DILI Network registry of > 100 non-acetaminophen causes were presented. Antimicrobials and CNS drugs were responsible for > 60% of cases, with herbals and dietary supplements being increasingly reported. Identification of genetic predispositions to DILI is coming of age with the FDA calling for the testing of human leukocyte antigen B(*)5701 before the use of abacavir to reduce the risk of hypersensitivity reactions. Several groups emphasized the pitfalls in utilizing Roussel Uclaf Causality Assessment Method and other causality assessment methodologies, and an updated review appeared on the use of potentially hepatotoxic medications in patients with underlying liver disease.