Mechanisms of hepatocellular toxicity associated with dronedarone--a comparison to amiodarone

Amiodarone and Dronedarone Causes Liver Injury with Distinctly Different Clinical Presentations

OBJECTIVE

To describe hepatotoxicity due to amiodarone and dronedarone from the DILIN and the US FDA's surveillance database.

METHODS

Hepatotoxicity due to amiodarone and dronedarone enrolled in the U.S. Drug Induced Liver Injury Network (DILIN) from 2004 to 2020 are described. Dronedarone hepatotoxicity cases associated with liver biopsy results were obtained from the FDA Adverse Event Reporting System (FAERS) from 2009 to 2020.

RESULTS

Among DILIN's 10 amiodarone and 3 dronedarone DILIN cases, the latency for amiodarone was longer than with dronedarone (388 vs 119 days, p = 0.50) and the median ALT at DILI onset was significantly lower with amiodarone (118 vs 1191 U/L, p = 0.05). Liver biopsies in five amiodarone cases showed fibrosis, steatosis, and numerous Mallory-Denk bodies. Five patients died although only one from liver failure. One patient with dronedarone induced liver injury died of a non-liver related cause. Nine additional cases of DILI due to dronedarone requiring hospitalization were identified in the FAERS database. Three patients developed liver injury within a month of starting the medication. Two developed acute liver failure and underwent urgent liver transplant, one was evaluated for liver transplant but then recovered spontaneously, while one patient with cirrhosis died of liver related causes.

CONCLUSION

Amiodarone hepatotoxicity resembles that seen in alcohol related liver injury, with fatty infiltration and inflammation. Dronedarone is less predictable, typically without fat and with a shorter latency of use before presentation. These differences may be explained, in part, by the differing pharmacokinetics of the two drugs leading to different mechanisms of hepatotoxicity.

Mechanisms of hepatocellular toxicity associated with the components of St. John's Wort extract hypericin and hyperforin in HepG2 and HepaRG cells

St. John's Wort preparations are used for the treatment of mild to moderate depression. They are usually well tolerated but can cause adverse reactions including liver toxicity in rare cases. To date, the mechanism(s) underlying the hepatotoxicity of St. John's Wort extracts are poorly investigated. We studied the hepatocellular toxicity of hypericin and hyperforin as the two main ingredients of St. John's Wort extracts in HepG2 and HepaRG cells and compared the effects to citalopram (a synthetic serotonin uptake inhibitor) with a special focus on mitochondrial toxicity and oxidative stress. In HepG2 cells, hypericin was membrane-toxic at 100 µM and depleted ATP at 20 µM. In HepaRG cells, ATP depletion started at 5 µM. In comparison, hyperforin and citalopram were not toxic up to 100 µM. In HepG2 cells, hypericin decreased maximal respiration starting at 2 µM and mitochondrial ATP formation starting at 10 µM but did not affect glycolytic ATP production. Hypericin inhibited the activity of complex I, II and IV of the electron transfer system and caused mitochondrial superoxide accumulation in cells. The protein expression of mitochondrial superoxide dismutase 2 (SOD2) and thioredoxin 2 (TRX2) and total and reduced glutathione decreased in cells exposed to hypericin. Finally, hypericin diminished the mitochondrial DNA copy number and caused cell necrosis but not apoptosis. In conclusion, hypericin, but not hyperforin or citalopram, is a mitochondrial toxicant at low micromolar concentrations. This mechanism may contribute to the hepatotoxicity occasionally observed in susceptible patients treated with St. John's Wort preparations.

Quantitative chemometric phenotyping of three-dimensional liver organoids by Raman spectral imaging

Confocal Raman spectral imaging (RSI) enables high-content, label-free visualization of a wide range of molecules in biological specimens without sample preparation. However, reliable quantification of the deconvoluted spectra is needed. Here we develop an integrated bioanalytical methodology, qRamanomics, to qualify RSI as a tissue phantom calibrated tool for quantitative spatial chemotyping of major classes of biomolecules. Next, we apply qRamanomics to fixed 3D liver organoids generated from stem-cell-derived or primary hepatocytes to assess specimen variation and maturity. We then demonstrate the utility of qRamanomics for identifying biomolecular response signatures from a panel of liver-altering drugs, probing drug-induced compositional changes in 3D organoids followed by in situ monitoring of drug metabolism and accumulation. Quantitative chemometric phenotyping constitutes an important step in developing quantitative label-free interrogation of 3D biological specimens.

Administration of Secretome Derived from Human Mesenchymal Stem Cells Induces Hepatoprotective Effects in Models of Idiosyncratic Drug-Induced Liver Injury Caused by Amiodarone or Tamoxifen

Drug-induced liver injury (DILI) is one of the leading causes of acute liver injury. While many factors may contribute to the susceptibility to DILI, obese patients with hepatic steatosis are particularly prone to suffer DILI. The secretome derived from mesenchymal stem cell has been shown to have hepatoprotective effects in diverse in vitro and in vivo models. In this study, we evaluate whether MSC secretome could improve DILI mediated by amiodarone (AMI) or tamoxifen (TMX). Hepatic HepG2 and HepaRG cells were incubated with AMI or TMX, alone or with the secretome of MSCs obtained from human adipose tissue. These studies demonstrate that coincubation of AMI or TMX with MSC secretome increases cell viability, prevents the activation of apoptosis pathways, and stimulates the expression of priming phase genes, leading to higher proliferation rates. As proof of concept, in a C57BL/6 mouse model of hepatic steatosis and chronic exposure to AMI, the MSC secretome was administered endovenously. In this study, liver injury was significantly attenuated, with a decrease in cell infiltration and stimulation of the regenerative response. The present results indicate that MSC secretome administration has the potential to be an adjunctive cell-free therapy to prevent liver failure derived from DILI caused by TMX or AMI.

Nicorandil and Bone Marrow-derived Mesenchymal Stem Cells Therapeutic Effect after Ureteral Obstruction in Adult Male Albino Rats

BACKGROUND

Chronic kidney disease is a global health problem for which renal fibrogenesis is the final treatment target.

OBJECTIVE

In our work, we have highlighted two new strategies, nicorandil and Bone marrow-derived mesenchymal stem cells (BM-MSCs), as effective in reversing renal fibrosis induced by partial unilateral ureteral obstruction (PUUO).

METHODS

The current study included 96 male albino rats randomly divided into four groups, with 24 rats per group; Group I, the control group; Group II, PUUO, where two-thirds of the left ureter was entrenched in the psoas muscle; Group III, same surgical procedure as in Group II for 7 days, and then the rats received 15 mg/kg/day nicorandil once daily for 21 days; and Group IV, same surgical procedure as in Group II for 7 days, and then rats were given 3 × 106 of labeled MSCs injected intravenous, and left for 21 days. Blood and kidney tissues were collected for biochemical, histological, and molecular analyses.

RESULTS

Both the nicorandil and BM-MSCs treatment groups could ameliorate kidney damage evidenced by inhibition of MDA elevation and total antioxidant capacity reduction caused by PUUO. Also, there was a significant reduction observed in TNF, TGF, IL6, collagen I, and α-SMA in addition to improvement in histological examination. However, a significant difference was found between the BM-MSCs and nicorandil-treated groups.

CONCLUSION

Our results suggest that BM-MSCs and nicorandil improved renal fibrosis progression through their antiapoptotic, anti-inflammatory, and antifibrotic effects in male albino rats subjected to PUUO, with BM-MSCs being more effective compared to nicorandil.

Mitochondrial Effects of Common Cardiovascular Medications: The Good, the Bad and the Mixed

Mitochondria are central organelles in the homeostasis of the cardiovascular system via the integration of several physiological processes, such as ATP generation via oxidative phosphorylation, synthesis/exchange of metabolites, calcium sequestration, reactive oxygen species (ROS) production/buffering and control of cellular survival/death. Mitochondrial impairment has been widely recognized as a central pathomechanism of almost all cardiovascular diseases, rendering these organelles important therapeutic targets. Mitochondrial dysfunction has been reported to occur in the setting of drug-induced toxicity in several tissues and organs, including the heart. Members of the drug classes currently used in the therapeutics of cardiovascular pathologies have been reported to both support and undermine mitochondrial function. For the latter case, mitochondrial toxicity is the consequence of drug interference (direct or off-target effects) with mitochondrial respiration/energy conversion, DNA replication, ROS production and detoxification, cell death signaling and mitochondrial dynamics. The present narrative review aims to summarize the beneficial and deleterious mitochondrial effects of common cardiovascular medications as described in various experimental models and identify those for which evidence for both types of effects is available in the literature.

Rational deuteration of dronedarone attenuates its toxicity in human hepatic HepG2 cells

Deuteration is a chemical modification strategy that has recently gained traction in drug development. The replacement of one or more hydrogen atom(s) in a drug molecule with its heavier stable isotope deuterium can enhance its metabolic stability and pharmacokinetic properties. However, it remains uninterrogated if rational deuteration at bioactivation "hot-spots" could attenuate its associated toxicological consequences. Here, our preliminary screening with benzofuran antiarrhythmic agents first revealed that dronedarone and its major metabolite N-desbutyldronedarone elicited a greater loss of viability and cytotoxicity in human hepatoma G2 (HepG2) cells as compared with amiodarone and its corresponding metabolite N-desethylamiodarone. A comparison of dronedarone and its in-house synthesized deuterated analogue (termed poyendarone) demonstrated that deuteration could attenuate its in vitro toxicity in HepG2 cells by modulating the extent of mitochondrial dysfunction, reducing the dissipation of mitochondrial membrane potential, and evoking a distinct apoptotic kinetic signature. Furthermore, although pretreatment with the CYP3A inducer rifampicin or the substitution of glucose with galactose in the growth media significantly augmented the loss of cell viability elicited by dronedarone and poyendarone, a lower loss of cell viability was consistently observed in poyendarone across all concentrations. Taken together, our preliminary investigations suggested that the rational deuteration of dronedarone at its benzofuran ring reduces aberrant cytochrome P450 3A4/5-mediated bioactivation, which attenuated its mitochondrial toxicity in human hepatic HepG2 cells.

Mitochondrial Toxicity Associated with Imatinib and Sorafenib in Isolated Rat Heart Fibers and the Cardiomyoblast H9c2 Cell Line

Tyrosine kinase inhibitors (TKIs) are associated with cardiac toxicity, which may be caused by mitochondrial toxicity. The underlying mechanisms are currently unclear and require further investigation. In the present study, we aimed to investigate in more detail the role of the enzyme complexes of the electron transfer system (ETS), mitochondrial oxidative stress, and mechanisms of cell death in cardiac toxicity associated with imatinib and sorafenib. Cardiac myoblast H9c2 cells were exposed to imatinib and sorafenib (1 to 100 µM) for 24 h. Permeabilized rat cardiac fibers were treated with both drugs for 15 min. H9c2 cells exposed to sorafenib for 24 h showed a higher membrane toxicity and ATP depletion in the presence of galactose (favoring mitochondrial metabolism) compared to glucose (favoring glycolysis) but not when exposed to imatinib. Both TKIs resulted in a higher dissipation of the mitochondrial membrane potential in galactose compared to glucose media. Imatinib inhibited Complex I (CI)- and CIII- linked respiration under both conditions. Sorafenib impaired CI-, CII-, and CIII-linked respiration in H9c2 cells cultured with glucose, whereas it inhibited all ETS complexes with galactose. In permeabilized rat cardiac myofibers, acute exposure to imatinib and sorafenib decreased CI- and CIV-linked respiration in the presence of the drugs. Electron microscopy showed enlarged mitochondria with disorganized cristae. In addition, both TKIs caused mitochondrial superoxide accumulation and decreased the cellular GSH pool. Both TKIs induced caspase 3/7 activation, suggesting apoptosis as a mechanism of cell death. Imatinib and sorafenib impaired the function of cardiac mitochondria in isolated rat cardiac fibers and in H9c2 cells at plasma concentrations reached in humans. Both imatinib and sorafenib impaired the function of enzyme complexes of the ETS, which was associated with mitochondrial ROS accumulation and cell death by apoptosis.

Cell-Permeable Succinate Rescues Mitochondrial Respiration in Cellular Models of Amiodarone Toxicity

Amiodarone is a potent antiarrhythmic drug and displays substantial liver toxicity in humans. It has previously been demonstrated that amiodarone and its metabolite (desethylamiodarone, DEA) can inhibit mitochondrial function, particularly complexes I (CI) and II (CII) of the electron transport system in various animal tissues and cell types. The present study, performed in human peripheral blood cells, and one liver-derived human cell line, is primarily aimed at assessing the concentration-dependent effects of these drugs on mitochondrial function (respiration and cellular ATP levels). Furthermore, we explore the efficacy of a novel cell-permeable succinate prodrug in alleviating the drug-induced acute mitochondrial dysfunction. Amiodarone and DEA elicit a concentration-dependent impairment of mitochondrial respiration in both intact and permeabilized platelets via the inhibition of both CI- and CII-supported respiration. The inhibitory effect seen in human platelets is also confirmed in mononuclear cells (PBMCs) and HepG2 cells. Additionally, amiodarone elicits a severe concentration-dependent ATP depletion in PBMCs, which cannot be explained solely by mitochondrial inhibition. The succinate prodrug NV118 alleviates the respiratory deficit in platelets and HepG2 cells acutely exposed to amiodarone. In conclusion, amiodarone severely inhibits metabolism in primary human mitochondria, which can be counteracted by increasing mitochondrial function using intracellular delivery of succinate.

Dynamic Modeling of Mitochondrial Membrane Potential Upon Exposure to Mitochondrial Inhibitors

Mitochondria are the main bioenergetic organelles of cells. Exposure to chemicals targeting mitochondria therefore generally results in the development of toxicity. The cellular response to perturbations in cellular energy production is a balance between adaptation, by reorganisation and organelle biogenesis, and sacrifice, in the form of cell death. In homeostatic conditions, aerobic mitochondrial energy production requires the maintenance of a mitochondrial membrane potential (MMP). Chemicals can perturb this MMP, and the extent of this perturbation depends both on the pharmacokinetics of the chemicals and on downstream MMP dynamics. Here we obtain a quantitative understanding of mitochondrial adaptation upon exposure to various mitochondrial respiration inhibitors by applying mathematical modeling to partially published high-content imaging time-lapse confocal imaging data, focusing on MMP dynamics in HepG2 cells over a period of 24 h. The MMP was perturbed using a set of 24 compounds, either acting as uncoupler or as mitochondrial complex inhibitor targeting complex I, II, III or V. To characterize the effect of chemical exposure on MMP dynamics, we adapted an existing differential equation model and fitted this model to the observed MMP dynamics. Complex III inhibitor data were better described by the model than complex I data. Incorporation of pharmacokinetic decay into the model was required to obtain a proper fit for the uncoupler FCCP. Furthermore, oligomycin (complex V inhibitor) model fits were improved by either combining pharmacokinetic (PK) decay and ion leakage or a concentration-dependent decay. Subsequent mass spectrometry measurements showed that FCCP had a significant decay in its PK profile as predicted by the model. Moreover, the measured oligomycin PK profile exhibited only a limited decay at high concentration, whereas at low concentrations the compound remained below the detection limit within cells. This is consistent with the hypothesis that oligomycin exhibits a concentration-dependent decay, yet awaits further experimental verification with more sensitive detection methods. Overall, we show that there is a complex interplay between PK and MMP dynamics within mitochondria and that data-driven modeling is a powerful combination to unravel such complexity.

mTORC2 is an important target for simvastatin-associated toxicity in C2C12 cells and mouse skeletal muscle - Roles of Rap1 geranylgeranylation and mitochondrial dysfunction

Statins decrease the serum LDL-cholesterol concentration and reduce the risk for cardiovascular diseases but can cause myopathy, which may be related to mTORC inhibition. In the current study, we investigated which mTORC is inhibited by simvastatin and by which mechanisms. In C2C12 myoblasts and myotubes and mouse gastrocnemius, simvastatin was cytotoxic and inhibited S6rp and Akt Ser473 phosphorylation, indicating inhibition of mTORC1 and mTORC2, respectively. In contrast to simvastatin, the mTORC1 inhibitor rapamycin did not inhibit mTORC2 activity and was not cytotoxic. Like simvastatin, knock-down of Rictor, an essential component of mTORC2, impaired Akt Ser473 and S6rp phosphorylation and was cytotoxic for C2C12 myoblasts, suggesting that mTORC2 inhibition is an important myotoxic mechanism. The investigation of the mechanism of mTORC2 inhibition showed that simvastatin impaired Ras farnesylation, which was prevented by farnesol but without restoring mTORC2 activity. In comparison, Rap1 knock-down reduced mTORC2 activity and was cytotoxic for C2C12 myoblasts. Simvastatin impaired Rap1 geranylgeranylation and function, which was prevented by geranylgeraniol. In addition, simvastatin and the complex III inhibitor antimycin A caused mitochondrial superoxide accumulation and impaired the activity of mTORC2, which could partially be prevented by the antioxidant MitoTEMPO. In conclusion, mTORC2 inhibition is an important mechanism of simvastatin-induced myotoxicity. Simvastatin inhibits mTORC2 by impairing geranylgeranylation of Rap1 and by inducing mitochondrial dysfunction.

Amiodarone, Unlike Dronedarone, Activates Inflammasomes via Its Reactive Metabolites: Implications for Amiodarone Adverse Reactions

Amiodarone is a benzofuran derivative used to treat arrhythmias, but its use is limited by adverse reactions. There is evidence that some of the severe adverse reactions such as liver injury and interstitial lung disease are immune-mediated; however, details of the mechanism have not been elucidated. We tested the ability of amiodarone to induce the release of danger-associated molecular patterns (DAMPs) that activate inflammasomes. Human hepatocarcinoma functional liver cell-4 (FLC-4) cells were used for drug bioactivation, and the detection of inflammasome activation was performed with the human macrophage cell line, THP-1 cells. Amiodarone is known to be oxidized to reactive quinone metabolites. The supernatant from the incubation of amiodarone with FLC-4 cells for 7 days increased caspase-1 activity and production of IL-1ß by THP-1 cells. In the supernatant of FLC-4 cells with amiodarone, the heat shock protein (HSP) 40 was significantly increased. Addition of a cytochrome P450 inhibitor to the FLC-4 cells prevented the release of HSP40 from the FLC-4 cells and activation of THP-1 inflammasomes by the FLC-4 supernatant. These results suggested that the reactive quinone metabolites of amiodarone can cause the release of DAMPs from hepatocytes which can activate inflammasomes. Dronedarone, a safer analog of amiodarone, did not activate inflammasomes. Inflammasome activation may be an important step in the activation of the immune system by amiodarone, which in some patients, can cause immune-related adverse events. In addition, our data suggest that drugs that block the effects or the formation of IL-1β would provide better treatment of amiodarone-induced immune-related adverse reactions.

C2C12 myoblasts are more sensitive to the toxic effects of simvastatin than myotubes and show impaired proliferation and myotube formation

Statins reduce cardiovascular complications in patients with high LDL-cholesterol but are associated with myopathy. We compared the toxicity of simvastatin of C2C12 myoblasts and myotubes. Since myoblasts can proliferate and fuse to myotubes, myoblasts can be considered as satellite cells and myotubes as mature muscle fibers. Simvastatin increased plasma membrane permeability and decreased the cellular ATP content in both myoblasts and myotubes, but with a stronger effect on myoblasts. While insulin prevented cytotoxicity up to 8 h after addition of simvastatin to myotubes, prevention in myoblasts required simultaneous addition. Mevalonate and geranylgeraniol prevented simvastatin-associated cytotoxicity in both myoblasts and myotubes. Simvastatin impaired the phosphorylation of the insulin receptor (IR β), Akt ser473 and S6rp, and increased phosphorylation of AMPK thr172 in both myotubes and myoblasts, which was prevented by insulin and mevalonate. Simvastatin impaired oxygen consumption and increased superoxide production by myoblasts and myotubes and induced apoptosis via cytochrome c release. In addition, simvastatin impaired proliferation and fusion of myoblasts to myotubes by inhibiting the expression of the nuclear transcription factor MyoD and of the metalloprotease ADAM-12. Decreased expression of the proliferation factor Ki-67 and of ADAM-12 were also observed in gastrocnemius of mice treated with simvastatin. In conclusion, myoblasts were more susceptible to the toxic effects of simvastatin and simvastatin impaired myoblast proliferation and myotube formation. Impaired muscle regeneration may represent a new mechanism of statin myotoxicity.

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

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

Characterization of cytochrome P450s (CYP)-overexpressing HepG2 cells for assessing drug and chemical-induced liver toxicity

Hepatic metabolism catalyzed by the cytochrome P450 (CYP) superfamily affects liver toxicity associated with exposures to natural compounds and xenobiotic agents. Previously we generated a battery of HepG2-derived stable cell lines that individually express 14 CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). In this study, we comprehensively characterized each cell line for its CYP expression and enzyme activity. Specifically, we measured the mRNA expression, protein expression, and metabolite formation. Using CYP3A4, 2D6, and 2C9-overexpressing cells as representatives, we examined the stability of these cells in long-term cultures for up to 10 passages. The results showed that CYPs can be stably overexpressed for up to 10 cell culture passages without losing their activities. The robustness of responses to stimuli among the cells at different passages was also investigated in CYP3A4-overexpressing cells and the response to amiodarone and dronedarone showed no difference between the cells at the passage 2 and 10. Moreover, the mRNA expression level of most CYPs was higher in CYP-overexpressing HepG2 cells than that in HepaRG cells and primary human hepatocytes. This study confirmed the stability of CYP-overexpressing HepG2 cell lines and provided useful information for a broader use of these cells in pharmacologic and toxicologic research.

Safety and efficacy of dronedarone from clinical trials to real-world evidence: implications for its use in atrial fibrillation

Efficacy and safety of dronedarone was shown in the ATHENA trial for paroxysmal or persistent atrial fibrillation (AF) patients. Further trials revealed safety concerns in patients with heart failure and permanent AF. This review summarizes insights from recent real-world studies and meta-analyses, including reports on efficacy, with focus on liver safety, mortality risk in patients with paroxysmal/persistent AF, and interactions of dronedarone with direct oral anticoagulants. Reports of rapidly progressing liver failure in dronedarone-prescribed patients in 2011 led to regulatory cautions about potential liver toxicity. Recent real-world evidence suggests dronedarone liver safety profile is similar to other antiarrhythmics and liver toxicity could be equally common with many Class III antiarrhythmics. Dronedarone safety concerns (increased mortality in patients with permanent AF) were raised based on randomized controlled trials (RCT) (ANDROMEDA and PALLAS), but comedication with digoxin may have increased the mortality rates in PALLAS, considering the dronedarone-digoxin pharmacokinetic (PK) interaction. Real-world data on apixaban-dronedarone interactions and edoxaban RCT observations suggest no significant safety risks for these drug combinations. Median trough plasma concentrations of dabigatran 110 mg during concomitant use with dronedarone are at acceptable levels, while PK data on the rivaroxaban-dronedarone interaction are unavailable. In RCTs and real-world studies, dronedarone significantly reduces AF burden and cardiovascular hospitalizations, and demonstrates a low risk for proarrhythmia in patients with paroxysmal or persistent AF. The concerns on liver safety must be balanced against the significant reduction in hospitalizations in patients with non-permanent AF and low risk for proarrhythmias following dronedarone treatment.

Novel advances in biotransformation and bioactivation research-2019 year in review

Biotransformation is one of the main mechanisms used by the body to eliminate drugs. As drug molecules become more complicated, the involvement of drug metabolizing enzymes increases beyond those that are typically studied, such as the cytochrome P450 enzymes. In this review, we try to capture the many outstanding articles that were published in the past year in the field of biotransformation (see Table 1). We have divided the articles into two categories of (1) metabolites and drug metabolizing enzymes, and (2) bioactivation and safety.  This annual review is the fifth of its kind since 2016 (Baillie et al. 2016; Khojasteh et al. 2017, 2018, 2019). This effort in itself also continues to evolve. We have followed the same format we used in previous years in terms of the selection of articles and the authoring of each section. I am pleased of the continued support of Rietjens, Miller, Zhang, Driscoll and Mitra to this review. We would like to welcome Klarissa D. Jackson as a new author for this year's issue. We strive to maintain a balance of authors from academic and industry settings.  We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. Cyrus Khojasteh, on behalf of the authors.

Lapatinib Activates the Kelch-Like ECH-Associated Protein 1-Nuclear Factor Erythroid 2-Related Factor 2 Pathway in HepG2 Cells

The receptor tyrosine kinase inhibitor lapatinib, indicated to treat patients with HER2-positive breast cancer in combination with capecitabine, can cause severe hepatotoxicity. Lapatinib is further associated with mitochondrial toxicity and accumulation of reactive oxygen species. The effect of lapatinib on the Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, the major cellular defense pathway against oxidative stress, has so far not been studied in detail. In the present study, we show that lapatinib (2–20 µM) activates the Keap1-Nrf2 pathway in HepG2 cells, a hepatocellular carcinoma-derived cell line, in a concentration-dependent manner upon 24 h of treatment. Lapatinib stabilized the transcription factor Nrf2 at concentrations ≥5 µM and caused its nuclear translocation. Well-established Nrf2 regulated genes (Nqo1, Gsta1, Gclc, and Gclm) were upregulated at lapatinib concentrations ≥10 µM. Furthermore, cellular and mitochondrial glutathione (GSH) levels increased starting at 10 µM lapatinib. As a marker of oxidative stress, cellular GSSG significantly increased at 10 and 20 µM lapatinib. Furthermore, the gene expression of mitochondrial Glrx2 and SOD2 were increased upon lapatinib treatment, which was also observed for the mitochondrial SOD2 protein content. In conclusion, lapatinib treatment for 24 h activated the Keap1-Nrf2 pathway in HepG2 cells starting at 10 μM, which is a clinically relevant concentration. As a consequence, treatment with lapatinib increased the mRNA and protein expression of antioxidative and other cytoprotective genes and induced GSH synthesis, but these measures could not completely block the oxidative stress associated with lapatinib.

Overexpression of the constitutive androstane receptor and shaken 3D-culturing increase biotransformation and oxidative phosphorylation and sensitivity to mitochondrial amiodarone toxicity of HepaRG cells

The liver cell line HepaRG is one of the preferred sources of human hepatocytes for in vitro applications. However, mitochondrial energy metabolism is relatively low, which affects hepatic functionality and sensitivity to hepatotoxins. Culturing in a bioartificial liver (BAL) system with high oxygen, medium perfusion, low substrate stiffness, and 3D conformation increases HepaRG functionality and mitochondrial activity compared to conventional monolayer culturing. In addition, drug metabolism has been improved by overexpression of the constitutive androstane receptor (CAR), a regulator of drug and energy metabolism in the new HepaRG-CAR line. Here, we investigated the effect of BAL culturing on the HepaRG-CAR line by applying a simple and downscaled BAL culture procedure based on shaking 3D cultures, named Bal-in-a-dish (BALIAD). We compared monolayer and BALIAD cultures of HepaRG and HepaRG-CAR cells. CAR overexpression and BALIAD culturing synergistically or additively increased transcript levels of CAR and three of the seven tested CAR target genes in biotransformation. Additionally, Cytochrome P450 3A4 activity was 35-fold increased. The mitochondrial energy metabolism was enhanced; lactate production and glucose consumption switched into lactate elimination and glucose production. BALIAD culturing alone reduced glycogen content and increased oxygen consumption and mitochondrial content. Both CAR overexpression and BALIAD culturing decreased mitochondrial superoxide levels. HepaRG-CAR BALIADs were most sensitive to mitochondrial toxicity induced by the hepatotoxin amiodarone, as indicated by oxygen consumption and mitochondrial superoxide accumulation. These data show that BALIAD culturing of HepaRG-CAR cells induces high mitochondrial energy metabolism and xenobiotic metabolism, increasing its potential for drug toxicity studies.

Reactive Metamizole Metabolites Enhance the Toxicity of Hemin on the ATP Pool in HL60 Cells by Inhibition of Glycolysis

Metamizole is an analgesic, whose pharmacological and toxicological properties are attributed to N-methyl-aminoantipyrine (MAA), its major metabolite. In the presence of heme iron, MAA forms reactive metabolites, which are toxic for granulocyte precursors. Since decreased cellular ATP is characteristic for MAA-associated toxicity, we studied the effect of MAA with and without hemin on energy metabolism of HL60 cells, a granulocyte precursor cell line. The combination MAA/hemin depleted the cellular ATP stronger than hemin alone, whereas MAA alone was not toxic. This decrease in cellular ATP was observed before plasma membrane integrity impairment. MAA/hemin and hemin did not affect the proton leak but increased the maximal oxygen consumption by HL60 cells. This effect was reversed by addition of the radical scavenger N-acetylcysteine. The mitochondrial copy number was not affected by MAA/hemin or hemin. Hemin increased mitochondrial superoxide generation, which was not accentuated by MAA. MAA decreased cellular ROS accumulation in the presence of hemin. In cells cultured in galactose (favoring mitochondrial ATP generation), MAA/hemin had less effect on the cellular ATP and plasma membrane integrity than in glucose. MAA/hemin impaired glycolysis more than hemin or MAA alone, and N-acetylcysteine blunted this effect of MAA/hemin. MAA/hemin decreased protein expression of pyruvate kinase more than hemin or MAA alone. In conclusion, cellular ATP depletion appears to be an important mechanism of MAA/hemin toxicity on HL60 cells. MAA itself is not toxic on HL60 cells up to 100 µM but boosts the inhibitory effect of hemin on glycolysis through the formation of reactive metabolites.

Identification of a novel toxicophore in anti-cancer chemotherapeutics that targets mitochondrial respiratory complex I

Disruption of mitochondrial function selectively targets tumour cells that are dependent on oxidative phosphorylation. However, due to their high energy demands, cardiac cells are disproportionately targeted by mitochondrial toxins resulting in a loss of cardiac function. An analysis of the effects of mubritinib on cardiac cells showed that this drug did not inhibit HER2 as reported, but directly inhibits mitochondrial respiratory complex I, reducing cardiac-cell beat rate, with prolonged exposure resulting in cell death. We used a library of chemical variants of mubritinib and showed that modifying the 1H-1,2,3-triazole altered complex I inhibition, identifying the heterocyclic 1,3-nitrogen motif as the toxicophore. The same toxicophore is present in a second anti-cancer therapeutic carboxyamidotriazole (CAI) and we demonstrate that CAI also functions through complex I inhibition, mediated by the toxicophore. Complex I inhibition is directly linked to anti-cancer cell activity, with toxicophore modification ablating the desired effects of these compounds on cancer cell proliferation and apoptosis.

The pharmaceutical industry needs to make safe and effective drugs. At the same time this industry is under pressure to keep the costs of developing these drugs at an acceptable level. Drugs work by interacting with and typically blocking a specific target, such as a protein in a particular type of cell. Sometimes, however, drugs also bind other unexpected targets. These “off-target” effects can be the reason for a drug’s toxicity, and it is important – both for the benefit of patients and the money that can be saved when developing drugs – to identify how drugs cause toxic side effects. The earlier researchers detect off-target effects, the better.

Recent data has suggested that an anti-cancer drug called mubritinib has off-target effects on the compartments within cells that provide the cell with most of their energy, the mitochondria. This drug’s intended target is a protein called HER2, which is found in large amounts on the surfaces of some breast cancer cells. Yet if mubritinib has this off-target effect on mitochondria, it may be harmful to other cells including heart cells because the heart is an organ that needs a large amount of energy from its mitochondria.

Stephenson et al. have now performed experiments to show that mubritinib does not actually interact with HER2 at all, but only targets mitochondria. The effect of mubritinib as an anti-cancer drug is therefore only due to its activity against mitochondria. Digging deeper into the chemistry revealed the small parts of its chemical structure that was responsible for mubritinib’s toxicity against heart cells, the so-called toxic substructure. Another anti-cancer drug called carboxyamidotriazole also has the same toxic substructure. Carboxyamidotriazole is supposed to stop cells from taking up calcium ions, but a final set of experiments demonstrated that this drug also only acts by inhibiting mitochondria.

Often there is not enough information about many drugs’ substructures, meaning off-target effects and toxicities cannot be predicted. The pharmaceutical industry will now be able to benefit from this new knowledge about the toxic substructures within some drugs. This research may also help patients who take mubritinib or carboxyamidotriazole, because their doctors will have to check for side effects on the heart more carefully.

Para-Halogenation of Amphetamine and Methcathinone Increases the Mitochondrial Toxicity in Undifferentiated and Differentiated SH-SY5Y Cells

Halogenation of amphetamines and methcathinones has become a common method to obtain novel psychoactive substances (NPS) also called “legal highs”. The para-halogenated derivatives of amphetamine and methcathinone are available over the internet and have entered the illicit drug market but studies on their potential neurotoxic effects are rare. The primary aim of this study was to explore the neurotoxicity of amphetamine, methcathinone and their para-halogenated derivatives 4-fluoroamphetamine (4-FA), 4-chloroamphetamine (PCA), 4-fluoromethcathinone (4-FMC), and 4-chloromethcathinone (4-CMC) in undifferentiated and differentiated SH-SY5Y cells. We found that 4-FA, PCA, and 4-CMC were cytotoxic (decrease in cellular ATP and plasma membrane damage) for both cell types, whereby differentiated cells were less sensitive. IC₅₀ values for cellular ATP depletion were in the range of 1.4 mM for 4-FA, 0.4 mM for PCA and 1.4 mM for 4-CMC. The rank of cytotoxicity observed for the para-substituents was chloride > fluoride > hydrogen for both amphetamines and cathinones. Each of 4-FA, PCA and 4-CMC decreased the mitochondrial membrane potential in both cell types, and PCA and 4-CMC impaired the function of the electron transport chain of mitochondria in SH-SY5Y cells. 4-FA, PCA, and 4-CMC increased the ROS level and PCA and 4-CMC induced apoptosis by the endogenous pathway. In conclusion, para-halogenation of amphetamine and methcathinone increases their neurotoxic properties due to the impairment of mitochondrial function and induction of apoptosis. Although the cytotoxic concentrations were higher than those needed for pharmacological activity, the current findings may be important regarding the uncontrolled recreational use of these compounds.

Hyperthermia Increases Neurotoxicity Associated with Novel Methcathinones

Hyperthermia is one of the severe acute adverse effects that can be caused by the ingestion of recreational drugs, such as methcathinones. The effect of hyperthermia on neurotoxicity is currently not known. The primary aim of our study was therefore to investigate the effects of hyperthermia (40.5 °C) on the neurotoxicity of methcathinone (MC), 4-chloromethcathinone (4-CMC), and 4-methylmethcathinone (4-MMC) in SH-SY5Y cells. We found that 4-CMC and 4-MMC were cytotoxic (decrease in cellular ATP and plasma membrane damage) under both hyper- (40.5 °C) and normothermic conditions (37 °C), whereby cells were more sensitive to the toxicants at 40.5 °C. 4-CMC and 4-MMC impaired the function of the mitochondrial electron transport chain and increased mitochondrial formation of reactive oxygen species (ROS) in SH-SY5Y cells, which were accentuated under hyperthermic conditions. Hyperthermia was associated with a rapid expression of the 70 kilodalton heat shock protein (Hsp70), which partially prevented cell death after 6 h of exposure to the toxicants. After 24 h of exposure, autophagy was stimulated by the toxicants and by hyperthermia but could only partially prevent cell death. In conclusion, hyperthermic conditions increased the neurotoxic properties of methcathinones despite the stimulation of protective mechanisms. These findings may be important for the understanding of the mechanisms and clinical consequences of the neurotoxicity associated with these compounds.

PGC-1α plays a pivotal role in simvastatin-induced exercise impairment in mice

AIM

Statins decrease cardiovascular complications, but can induce myopathy. Here, we explored the implication of PGC-1α in statin-associated myotoxicity.

METHODS

We treated PGC-1α knockout (KO), PGC-1α overexpression (OE) and wild-type (WT) mice orally with 5 mg simvastatin kg^-1  day^-1 for 3 weeks and assessed muscle function and metabolism.

RESULTS

In WT and KO mice, but not in OE mice, simvastatin decreased grip strength, maximal running distance and vertical power assessed by ergometry. Post-exercise plasma lactate concentrations were higher in WT and KO compared to OE mice. In glycolytic gastrocnemius, simvastatin decreased mitochondrial respiration, increased mitochondrial ROS production and free radical leak in WT and KO, but not in OE mice. Simvastatin increased mRNA expression of Sod1 and Sod2 in glycolytic and oxidative gastrocnemius of WT, but decreased it in KO mice. OE mice had a higher mitochondrial DNA content in both gastrocnemius than WT or KO mice and simvastatin exhibited a trend to decrease the citrate synthase activity in white and red gastrocnemius in all treatment groups. Simvastatin showed a trend to decrease the mitochondrial volume fraction in both muscle types of all treatment groups. Mitochondria were smaller in WT and KO compared to OE mice and simvastatin further reduced the mitochondrial size in WT and KO mice, but not in OE mice.

CONCLUSIONS

Simvastatin impairs skeletal muscle function, muscle oxidative metabolism and mitochondrial morphology preferentially in WT and KO mice, whereas OE mice appear to be protected, suggesting a role of PGC-1α in preventing simvastatin-associated myotoxicity.

Valproic acid affects fatty acid and triglyceride metabolism in HepaRG cells exposed to fatty acids by different mechanisms

Treatment with valproate is associated with hepatic steatosis, but the mechanisms are not fully elucidated in human cell systems. We therefore investigated the effects of valproate on fatty acid and triglyceride metabolism in HepaRG cells, a human hepatoma cell line. In previously fatty acid loaded HepaRG cells, valproate impaired lipid droplet disposal starting at 1 mM after incubation for 3 or 7 days. Valproate increased the expression of genes associated with fatty acid import and triglyceride synthesis, but did not relevantly affect expression of genes engaged in fatty acid activation. Valproate impaired mitochondrial fatty acid metabolism by inhibiting β-ketothiolase and the function of the electron transport chain, which was associated with increased mitochondrial reactive oxygen species production. Valproate increased the mitochondrial DNA copy number per HepaRG cell, possibly as a consequence of impaired mitochondrial function. Valproate decreased the hepatocellular mRNA and protein expression of the fatty acid binding protein 1 (FABP1) and of the microsomal triglyceride transfer protein (MTTP) at 1 mM and increased the hepatocellular concentration of free fatty acids. Furthermore, valproate decreased protein expression and excretion of ApoB100 in HepaRG cells at 1 mM, reflecting impaired formation and excretion of very low-density lipoprotein (VLDL). In conclusion, valproate increased the hepatocellular triglyceride content by multiple mechanisms, whereby impaired expression of FABP1 and MTTP as well as impaired VLDL formation and excretion appeared to be dominant. Valproate caused cell death mainly by apoptosis, which may be a consequence of mitochondrial oxidative stress and increased hepatocellular concentration of free fatty acids.

Increased hepatic acylcarnitines after oral administration of amiodarone in rats

Amiodarone is known to induce hepatic injury in some recipients. We applied an untargeted metabolomics approach to identify endogenous metabolites with potential as biomarkers for amiodarone-induced liver injury. Oral amiodarone administration for 1 week in rats resulted in significant elevation of acylcarnitines and phospholipids in the liver. Hepatic short- and medium-chain acylcarnitines were dramatically increased in a dose-dependent manner, while the serum levels of these acylcarnitines did not change substantially. In addition, glucose levels were significantly increased in both the serum and liver. Gene expression profiling showed that the hepatic mRNA levels of Cpt1, Cpt2, and Acat1 were significantly suppressed, whereas those of Acot1, Acly, Acss2, and Acsl3 were increased. These results suggest that hepatic acylcarnitines and glucose levels might be increased due to disruption of mitochondrial function and suppression of glucose metabolism. Perturbation of energy metabolism might be associated with amiodarone-induced hepatotoxicity.

Immunohistochemical expression of autophagosome markers LC3 and p62 in preneoplastic liver foci in high fat diet-fed rats

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive deposition of droplets in hepatocytes. Patients with NAFLD can be at risk for nonalcoholic steatohepatitis, which can lead to hepatocellular carcinoma. Autophagy is a cellular pathway that is crucial for survival and homeostasis, and which protects against pathophysiological changes like obesity and cancer. We determined the expression of autophagy markers in preneoplastic hepatic lesions and the effects of an autophagy repressor chloroquine (CQ) or inducer amiodarone (AM) in a steatosis-related hepatocarcinogenesis model. Male F344 rats were fed a control diet or high fat diet (HFD), and subjected to initiation and promotion steps with N-nitrosodiethylamine injection at week 0 and a partial hepatectomy at week 3. Several HFD-fed rats were administered 0.1% CQ and 0.5% AM in their drinking water during week 2 and 8. CQ and AM did not improve HFD-induced obesity. AM, but not CQ, significantly decreased the number of glutathione S-transferase placental form-positive preneoplastic liver foci in the liver. Autophagosome markers LC3 and the LC3-binding protein p62 were heterogeneously expressed in the preneoplastic foci. CQ might inhibit autophagy by significantly increased p62/LC3 ratio, while AM might have a potential of inducing autophagy by showing an increased gene expression of the autophagy regulator, Atg5. These results suggest that preneoplastic lesions express autophagosome markers and that AM might decrease steatosis-related early hepatocarcinogenesis by potentially inducing autophagy in HFD-fed rats, while inhibition of autophagy by CQ did not alter the hepatocarcinogenesis. However, an immunohistochemical trial revealed a technical limitation in detecting autophagosome markers because there were variations in each preneoplastic lesion.

A Novel Lipidomics-Based Approach to Evaluating the Risk of Clinical Hepatotoxicity Potential of Drugs in 3D Human Microtissues

The importance of adsorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis is expected to grow substantially due to recent failures in detecting severe toxicity issues of new chemical entities during preclinical/clinical development. Traditionally, safety risk assessment studies for humans have been conducted in animals during advanced preclinical or clinical phase of drug development. However, potential drug toxicity in humans now needs to be detected in the drug discovery process as soon as possible without reliance on animal studies. The "omics", such as genomics, proteomics, and metabolomics, have recently entered pharmaceutical research in both drug discovery and drug development, but to the best of our knowledge, no applications in high-throughput safety risk assessment have been attempted so far. This paper reports an innovative method to anticipate adverse drug effects in an early discovery phase based on lipid fingerprints using human three-dimensional microtissues. The risk of clinical hepatotoxicity potential was evaluated for a data set of 22 drugs belonging to five different therapeutic chemical classes and with various drug-induced liver injury effect. The treatment of microtissues with repeated doses of each drug allowed collecting lipid fingerprints for five time points (2, 4, 7, 9, and 11 days), and multivariate statistical analysis was applied to search for correlations with the hepatotoxic effect. The method allowed clustering of the drugs based on their hepatotoxic effect, and the observed lipid impairments for a number of drugs was confirmed by literature sources. Compared to traditional screening methods, here multiple interconnected variables (lipids) are measured simultaneously, providing a snapshot of the cellular status from the lipid perspective at a molecular level. Applied here to hepatotoxicity, the proposed workflow can be applied to several tissues, being tridimensional microtissues from various origins.

Hyperammonemic Encephalopathy and Lipid Dysmetabolism in a Critically Ill Patient After a Short Course of Amiodarone

The case is reported of a 39-year-old severely obese woman who developed acute metabolic disorders after the administration of a short course of intravenous amiodarone. The main biological features were hypertriglyceridemia, hypoglycaemia, hyperlactatemia and hyperammonemia; all were reversible after amiodarone discontinuation. There was an associated rise in liver enzymes. However, the influence of co-factors on these metabolic disorders, such as acquired carnitine deficiency, severe obesity, a long-term course of pancreatitis, and abdominal infections, could not be excluded.

Exogenous Iron Increases Fasciocidal Activity and Hepatocellular Toxicity of the Synthetic Endoperoxides OZ78 and MT04

The synthetic peroxides OZ78 and MT04 recently emerged as fasciocidal drug candidates. However, the effect of iron on fasciocidal activity and hepatocellular toxicity of these compounds is unknown. We investigated the in vitro fasciocidal activity and hepatocellular toxicity of OZ78 and MT04 in absence and presence of Fe(II)chloride and hemin, and conducted a toxicological study in mice. Studies were performed in comparison with the antimalarial artesunate (AS), a semisynthetic peroxide. Fasciocidal effects of OZ78 and MT04 were confirmed and enhanced by Fe²⁺ or hemin. In HepG2 cells, AS reduced cellular ATP and impaired membrane integrity concentration-dependently. In comparison, OZ78 or MT04 were not toxic at 100 µM and reduced the cellular ATP by 13% and 19%, respectively, but were not membrane-toxic at 500 µM. The addition of Fe²⁺ or hemin increased the toxicity of OZ78 and MT04 significantly. AS inhibited complex I, II, and IV of the mitochondrial electron transport chain, and MT04 impaired complex I and II, whereas OZ78 was not toxic. All three compounds increased cellular reactive oxygen species (ROS) concentration-dependently, with a further increase by Fe²⁺ or hemin. Mice treated orally with up to 800 mg OZ78, or MT04 showed no relevant hepatotoxicity. In conclusion, we confirmed fasciocidal activity of OZ78 and MT04, which was increased by Fe²⁺ or hemin. OZ78 and MT04 were toxic to HepG2 cells, which was explained by mitochondrial damage associated with ROS generation in the presence of iron. No relevant hepatotoxicity was observed in mice in vivo, possibly due to limited exposure and/or high antioxidative hepatic capacity.

Mitochondrial oxidative stress plays a critical role in the cardiotoxicity of sunitinib: Running title: Sunitinib and oxidative stress in hearts

Sunitinib is cardiotoxic, but the mechanisms are not entirely clear. We aimed to enlarge our knowledge about the role of mitochondria in cardiac toxicity of sunitinib in vitro and in vivo. For this reason, we studied the toxicity of sunitinib on cardiac H9c2 cells exposed for 24 h, permeabilized rat cardiac fibers exposed for 15 min and in mice treated orally with sunitinib for 2 weeks (7.5 mg/kg/day). In H9c2 cells exposed for 24 h, sunitinib was more cytotoxic under galactose (favoring mitochondrial metabolism) compared to glucose conditions (favoring glycolysis). Sunitinib dissipated the mitochondrial membrane potential starting at 10 μM under glucose and at 5 μM under galactose conditions. Sunitinib reduced activities of mitochondrial enzyme complexes of the electron transport chain (ETC), increased mitochondrial ROS accumulation and decreased the cellular GSH pool. Electron microscopy revealed swollen mitochondria with loss of cristae. Accordingly, sunitinib caused caspase 3 activation and DNA fragmentation in H9c2 cells. Co-exposure with mito-TEMPO (mitochondrial-specific ROS scavenger) for 24 h prevented ATP and GSH depletion, as well as the increases in H₂O₂ and caspase 3/7 activity observed with sunitinib. In mice, treatment with sunitinib for two weeks increased plasma concentrations of troponin I and creatine kinase MB, indicating cardiomyocyte damage. The activity of enzyme complexes of the ETCwas decreased, mitochondrial ROS were increased and cleavage of caspase 3 was increased, suggesting cardiomyocyte apoptosis. In conclusion, mitochondrial damage with ROS accumulation appears to be an important mechanism of cardiotoxicity associated with sunitinib, eventually leading to apoptotic cell death.

Comparative evaluation of the hepatotoxicity, phototoxicity and photosensitizing potential of dronedarone hydrochloride and its cyclodextrin-based inclusion complexes

In this study, the hepatotoxicity, phototoxicity and photosensitizing potential of free dronedarone (DRO) and its inclusion complexes with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), prepared by different methods, were investigated by using in vitro cell-based approaches. The results of the 3T3 NRU phototoxicity assay showed that free DRO and the CD-based inclusion complexes did not present any substantial phototoxic potential. The photosensitizing potential was assessed by using THP-1 cells and IL-8 as a biomarker, and the experimental data confirmed that both the free drug and the inclusion complexes are likely to cause skin photosensitization, as they were able to induce IL-8 release after irradiation. Nevertheless, the inclusion complexes obtained by kneading followed by spray-drying induced a lower IL-8 release and also presented a smaller stimulation index in comparison with free DRO, suggesting a reduction in the photosensitizing potential. Finally, the free drug and inclusion complexes were also tested for hepatotoxicity using HepG2 cells. Even though lower IC50 values were found for the inclusion complexes prepared by kneading followed by spray-drying, there was no significant difference, indicating that the complexation of dronedarone did not induce hepatotoxicity. Overall, the obtained data confirmed that the inclusion complexes prepared by kneading followed by spray-drying, especially those based on HP-β-CD, appeared to be the most promising formulations and, therefore, could be encouragingly explored in the development of novel pharmaceutical dosage forms containing DRO, presumably with reduced side effects and improved safety profile.

Dronedarone-Induced Cardiac Mitochondrial Dysfunction and Its Mitigation by Epoxyeicosatrienoic Acids

Dronedarone and amiodarone are structurally similar antiarrhythmic drugs. Dronedarone worsens cardiac adverse effects with unknown causes while amiodarone has no cardiac adversity. Dronedarone induces preclinical mitochondrial toxicity in rat liver and exhibits clinical hepatotoxicity. Here, we further investigated the relative potential of the antiarrhythmic drugs in causing mitochondrial injury in cardiomyocytes. Differentiated rat H9c2 cardiomyocytes were treated with dronedarone, amiodarone, and their respective metabolites namely N-desbutyldronedarone (NDBD) and N-desethylamiodarone (NDEA). Intracellular ATP content, mitochondrial membrane potential (Δψm), and inhibition of carnitine palmitoyltransferase I (CPT1) activity and arachidonic acid (AA) metabolism were measured in H9c2 cells. Inhibition of electron transport chain (ETC) activities and uncoupling of ETC were further studied in isolated rat heart mitochondria. Dronedarone, amiodarone, NDBD and NDEA decreased intracellular ATP content significantly (IC50 = 0.49, 1.84, 1.07, and 0.63 µM, respectively) and dissipated Δψm potently (IC50 = 0.5, 2.94, 12.8, and 7.38 µM, respectively). Dronedarone, NDBD, and NDEA weakly inhibited CPT1 activity while amiodarone (IC50 > 100 µM) yielded negligible inhibition. Only dronedarone inhibited AA metabolism to its regioisomeric epoxyeicosatrienoic acids (EETs) consistently and potently. NADH-supplemented ETC activity was inhibited by dronedarone, amiodarone, NDBD and NDEA (IC50 = 3.07, 5.24, 11.94, and 16.16 µM, respectively). Cytotoxicity, ATP decrease and Δψm disruption were ameliorated via exogenous pre-treatment of H9c2 cells with 11, 12-EET and 14, 15-EET. Our study confirmed that dronedarone causes mitochondrial injury in cardiomyocytes by perturbing Δψm, inhibiting mitochondrial complex I, uncoupling ETC and dysregulating AA-EET metabolism. We postulate that cardiac mitochondrial injury is one potential contributing factor to dronedarone-induced cardiac failure exacerbation.

Abnormal Liver Enzymes

Abnormal liver enzymes are frequently encountered in primary care offices and hospitals and may be caused by a wide variety of conditions, from mild and nonspecific to well-defined and life-threatening. Terms such as "abnormal liver chemistries" or "abnormal liver enzymes," also referred to as transaminitis, should be reserved to describe inflammatory processes characterized by elevated alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. Although interchangeably used with abnormal liver enzymes, abnormal liver function tests specifically denote a loss of synthetic functions usually evaluated by serum albumin and prothrombin time. We discuss the entities that most commonly cause abnormal liver enzymes, specific patterns of enzyme abnormalities, diagnostic modalities, and the clinical scenarios that warrant referral to a hepatologist.

Molecular Toxicological Mechanisms of Synthetic Cathinones on C2C12 Myoblasts

Synthetic cathinones are popular psychoactive substances that may cause skeletal muscle damage. In addition to indirect sympathomimetic myotoxicity, these substances could be directly myotoxic. Since studies in myocytes are currently lacking, the aim of the present study was to investigate potential toxicological effects by synthetic cathinones on C2C12 myoblasts (mouse skeletal muscle cell line). We exposed C2C12 myoblasts to 3-methylmethcathinone, 4-methylmethcathinone (mephedrone), 3,4-methylenedioxymethcathinone (methylone), 3,4-methylenedioxypyrovalerone (MDPV), alpha-pyrrolidinovalerophenone (α-PVP), and naphthylpyrovalerone (naphyrone) for 1 or 24 h before cell membrane integrity, ATP content, mitochondrial oxygen consumption, and mitochondrial superoxide production was measured. 3,4-Methylenedioxymethamphetamine (MDMA) was included as a reference compound. All investigated synthetic cathinones, as well as MDMA, impaired cell membrane integrity, depleted ATP levels, and increased mitochondrial superoxide concentrations in a concentration-dependent manner in the range of 50–2000 μM. The two pyrovalerone derivatives α-PVP and naphyrone, and MDMA, additionally impaired basal and maximal cellular respiration, suggesting mitochondrial dysfunction. Alpha-PVP inhibited complex I, naphyrone complex II, and MDMA complex I and III, whereas complex IV was not affected. We conclude that, in addition to sympathetic nervous system effects and strenuous muscle exercise, direct effects of some cathinones on skeletal muscle mitochondria may contribute to myotoxicity in susceptible synthetic cathinone drugs users.

Mechanisms of insulin resistance by simvastatin in C2C12 myotubes and in mouse skeletal muscle

Statins inhibit cholesterol biosynthesis and lower serum LDL-cholesterol levels. They are generally well tolerated, but can cause insulin resistance in patients. Therefore, we investigated the mechanisms underlying the statin-induced insulin resistance. We used mice and C2C12 myotubes (murine cell line): mice (n = 10) were treated with oral simvastatin (5 mg/kg/day) or water (control) for 21 days and C2C12 cells were exposed to 10 μM simvastatin for 24 h. After intraperitoneal glucose application (2 g/kg), simvastatin-treated mice had higher glucose but equal insulin plasma concentrations than controls and lower glucose transport into skeletal muscle. Similarly, glucose uptake by C2C12 myotubes exposed to 10 μM simvastatin for 24 h was impaired compared to control cells. In simvastatin-treated C2C12 myotubes, mRNA and protein expression of the insulin receptor (IR) β-chain was increased, but the phosphorylation (Tyr1361) was impaired. Simvastatin decreased numerically Akt/PKB Thr308 phosphorylation (via insulin signaling pathway) and significantly Akt/PKB Ser473 phosphorylation (via mTORC2), which was explained by impaired phosphorylation of mTOR Ser2448. Reduced phosphorylation of Akt/PKB impaired downstream phosphorylation of GSK3β, leading to impaired translocation of GLUT4 into plasma membranes of C2C12 myotubes. In contrast, reduced phosphorylation of AS160 could be excluded as a reason for impaired GLUT4 translocation. In conclusion, simvastatin caused insulin resistance in mice and impaired glucose uptake in C2C12 myotubes. The findings in myotubes can be explained by diminished activation of Akt/PKB by mTORC2 and downstream effects on GSK3β, impairing the translocation of GLUT4 and the uptake of glucose.

Review article: drug-induced liver injury in the context of nonalcoholic fatty liver disease - a physiopathological and clinical integrated view

BACKGROUND

Nonalcoholic fatty disease (NAFLD) is the most common liver disease, since it is strongly associated with obesity and metabolic syndrome pandemics. NAFLD may affect drug disposal and has common pathophysiological mechanisms with drug-induced liver injury (DILI); this may predispose to hepatoxicity induced by certain drugs that share these pathophysiological mechanisms. In addition, drugs may trigger fatty liver and inflammation per se by mimicking NAFLD pathophysiological mechanisms.

AIMS

To provide a comprehensive update on (a) potential mechanisms whereby certain drugs can be more hepatotoxic in NAFLD patients, (b) the steatogenic effects of drugs, and (c) the mechanism involved in drug-induced steatohepatitis (DISH).

METHODS

A language- and date-unrestricted Medline literature search was conducted to identify pertinent basic and clinical studies on the topic.

RESULTS

Drugs can induce macrovesicular steatosis by mimicking NAFLD pathogenic factors, including insulin resistance and imbalance between fat gain and loss. Other forms of hepatic fat accumulation exist, such as microvesicular steatosis and phospholipidosis, and are mostly associated with acute mitochondrial dysfunction and defective lipophagy, respectively. Drug-induced mitochondrial dysfunction is also commonly involved in DISH. Patients with pre-existing NAFLD may be at higher risk of DILI induced by certain drugs, and polypharmacy in obese individuals to treat their comorbidities may be a contributing factor.

CONCLUSIONS

The relationship between DILI and NAFLD may be reciprocal: drugs can cause NAFLD by acting as steatogenic factors, and pre-existing NAFLD could be a predisposing condition for certain drugs to cause DILI. Polypharmacy associated with obesity might potentiate the association between this condition and DILI.

Effects of dronedarone on all-cause mortality and on cardiovascular events in patients treated for atrial fibrillation: a meta-analysis of RCTs

INTRODUCTION

The efficacy and safety profiles of the dronedarone were rather praised when the molecule was placed on the market (2009). However, there are today some safety concerns (in particular, risk of liver toxicity) that have led to limit the use of this drug to paroxysmal or persistent atrial fibrillation, and to exclude it from therapy protocols for ventricular tachyarrhythmias. The aim of the present study was to explore some efficacy and safety endpoints concerning dronedarone, by analyzing the evidence derived from quantitative evaluation (meta-analysis) of literature data.

EVIDENCE ACQUISITION

We comprised in the meta-analysis exclusively randomized controlled trials (RCTs) that reported relevant clinical outcomes with dronedarone. In addition, eligible RCTs had to have randomized 100 patients at least in order to have adequate statistical power, and they had to have clearly reported the outcomes of interest. Primary efficacy outcomes were a) all-cause mortality,b) major acute cardiovascular events and c) worsening heart failure. Secondary outcomes of interest were ventricular tachyarrhythmias, stroke and systemic embolism. We performed a number of sensitivity analyses to better ascertain the sources of heterogeneity. We also performed a number of subgroup analyses.

EVIDENCE SYNTHESIS

At the end of the selection process, the studies regarded suitable for meta-analysis were seven. Dronedarone use was not associated with any significant advantage as regards all-cause mortality(pooled odds ratio =1.31; 95% CI: 0.78 to 2.18; P= 0.31) and major cardiovascular events (pooled odds ratio=1.45; 95% CI: 0.7 to 3.01; P=0.28), as well as regarding the endpoint" worsening heart failure" (pooled odds ratio =1.32; 95% CI: 0.87 to 2.01; P= 0.20). Moreover, using subgroup analyses, in patients with permanent AF, dronedarone use was associated with increased all-cause mortality compared to placebo(P=0.03),as well as with higher risk of major acute cardiovascular events (P=0.04) and episodes of worsening heart failure(P=0.02). In addition, when data from ATHENA study were excluded, dronedarone use was associated with increased all-cause mortality (post exclusion pooled odds ratio=1.77; 95% CI: 1.15 to 2.72; P=0.0089), increased risk of major cardiovascular events (post exclusion pooled odds ratio=2.16; 95% CI: 1.34 to 3.47; P= 0.0014) and increased risk of worsening heart failure(post exclusion pooled odds ratio= 1.618; 95% CI: 1.14 to 2.3; P=0.006).

CONCLUSIONS

In our meta-analysis, dronedarone did not provide any significant benefit with regard to all-cause mortality and major cardiovascular events, as well as regarding the risk of worsening heart failure. Sensitivity analyses then showed that the exclusion of a study, namely ATHENA study, caused a shift in the overall odds ratio, so as to convert the dronedarone use to the ominous role of predictor of higher mortality, worse cardiovascular morbidity and increased risk of worsening heart failure. Thus, dronedarone should be used with caution as second-line medication and exclusively for the secondary prevention of paroxysmal or persistent atrial fibrillation, in patients without signs or symptoms of cardiac decompensation, preferably for limited periods of time and under assiduous clinical and laboratory surveillance.

Sunitinib induces hepatocyte mitochondrial damage and apoptosis in mice

Reports concerning hepatic mitochondrial toxicity of sunitinib are conflicting. We therefore decided to conduct a toxicological study in mice. After having determined the highest dose that did not affect nutrient ingestion and body weight, we treated mice orally with sunitinib (7.5 mg/kg/day) for 2 weeks. At the end of treatment, peak sunitinib plasma concentrations were comparable to those achieved in humans and liver concentrations were approximately 25-fold higher than in plasma. Sunitinib did not affect body weight, but increased plasma ALT activity 6-fold. The activity of enzyme complexes of the electron transport chain (ETC) was decreased numerically in freshly isolated and complex III activity significantly in previously frozen liver mitochondria. In previously frozen mitochondria, sunitinib decreased NADH oxidase activity concentration-dependently in both treatment groups. The hepatic mitochondrial reactive oxygen species (ROS) content and superoxide dismutase 2 expression were increased in sunitinib-treated mice. Protein and mRNA expression of several subunits of mitochondrial enzyme complexes were decreased in mitochondria from sunitinib-treated mice. Protein expression of PGC-1α, citrate synthase activity and mtDNA copy number were all decreased in livers of sunitinib-treated mice, indicating impaired mitochondrial proliferation. Caspase 3 activation and TUNEL-positive hepatocytes were increased in livers of sunitinib-treated mice, indicating hepatocyte apoptosis. In conclusion, sunitinib caused concentration-dependent toxicity in isolated mitochondria at concentrations reached in livers in vivo and inhibited hepatic mitochondrial proliferation. Daily mitochondrial insults and impaired mitochondrial proliferation most likely explain hepatocellular injury observed in mice treated with sunitinib.

In vitro screening of cell bioenergetics to assess mitochondrial dysfunction in drug development

Drug-induced mitochondrial toxicity is considered as a common cellular mechanism that can induce a variety of organ toxicities. In the present manuscript, 17 in vitro mitochondrial toxic drugs, reported to induce Drug-Induced Liver Injury (DILI) and 6 non-mitochondrial toxic drugs (3 with DILI and 3 without DILI concern), were tested in HepG2 cells using a bioenergetics system. The 17 mitochondrial toxic drugs represent a wide variety of mitochondrial dysfunctions as well as DILI and include 4 pairs of drugs which are structurally related but associated with different DILI concerns in human. Cell bioenergetics were measured using the XF96e analyzer which simultaneous monitor oxygen consumption rate (OCR) and extracellular acidification rate (ECAR), indirect measurements of oxidative phosphorylation and glycolysis, respectively. OCR associated with ATP production, maximal respiration, proton leak and spare respiratory capacity, were also assessed. Duplicate experiments resulted in a sensitivity of 82% (14/17) and specificity of 83% (5/6). The addition of stressors improved specificity considerably. Cut-offs, statistics and rules are clearly discussed to facilitate the use of this assay for screening purposes. Overall, the authors consider that this assay should be part of the battery of safety screening assays at early stages of drug development.

Hepatocellular Toxicity of Imidazole and Triazole Antimycotic Agents

Hepatotoxicity has been described for all antimycotic azoles currently marketed. A possible mechanism involving mitochondrial dysfunction has been postulated for ketoconazole, but not for the other azoles. The aim of the current investigations was to study the toxicity of different azoles in human cell models and to find out mechanisms of their toxicity. In HepG2 cells, posaconazole and ketoconazole were cytotoxic starting at 20 and 50 µM and decreased the cellular ATP content starting at 5 and 10 µM, respectively. In HepaRG cells, cytotoxicity started at 20 and 100 µM for posaconazole and ketoconazole, respectively, and was slightly accentuated by cytochrome P450 3A4 induction with rifampicin and 1A2 with 3-methylcholantrene. Voriconazole and fluconazole were not cytotoxic. In isolated mouse liver mitochondria, ketoconazole impaired membrane potential and complex I activity, whereas the other azoles were not toxic. In HepG2 cells exposed for 24 h, both posaconazole and ketoconazole (but not fluconazole or voriconazole) decreased the mitochondrial membrane potential, impaired the function of enzyme complexes of the electron transport chain, were associated with mitochondrial superoxide accumulation, decreased mitochondrial DNA and induced apoptosis. In HepG2 cells with mitochondrial dysfunction induced by the vitamin B12 antagonist hydroxy-cobalamin[c-lactam], cytotoxicity and/or ATP depletion was more accentuated than in untreated cells. We conclude that ketoconazole and posaconazole are mitochondrial toxicants starting at concentrations, which can be reached in vivo. Cytotoxicity and ATP depletion are more accentuated in cells with mitochondrial damage, suggesting that preexisting mitochondrial dysfunction is a susceptibility factor for hepatotoxicity associated with these drugs.

DNA damage-induced apoptosis and mitogen-activated protein kinase pathway contribute to the toxicity of dronedarone in hepatic cells

Dronedarone, an antiarrhythmic drug, has been marketed as an alternative to amiodarone. The use of dronedarone has been associated with severe liver injury; however, the mechanisms remain unclear. In this study, the possible mechanisms of dronedarone induced liver toxicity were characterized in HepG2 cells. Dronedarone decreased cells viability and induced apoptosis and DNA damage in a concentration- and time-dependent manner. Pretreatment of the HepG2 cells with apoptosis inhibitors (caspase-3, -8, and -9) or the necrosis inhibitor (Necrox-5), partially, but significantly, reduced the release of lactate dehydrogenase. Dronedarone caused the release of cytochrome c from mitochondria to cytosol, a prominent feature of apoptosis. In addition, the activation of caspase-2 was involved in dronedarone induced DNA damage and the activation of JNK and p38 signaling pathways. Inhibition of JNK and p38 by specific inhibitors attenuated dronedarone-induced cell death, apoptosis, and DNA damage. Additionally, suppression of caspase-2 decreased the activities of JNK and p38. Dronedarone triggered DNA damage was regulated by downregulation of topoisomerase IIα at both transcriptional and post-transcriptional levels. Taken together, our data show that DNA damage, apoptosis, and the activation of JNK and p38 contribute to dronedarone-induced cytotoxicity. Environ. Mol. Mutagen. 59:278-289, 2018. © 2018 Wiley Periodicals, Inc.

Effect of Toxicants on Fatty Acid Metabolism in HepG2 Cells

Impairment of hepatic fatty acid metabolism can lead to liver steatosis and injury. Testing drugs for interference with hepatic fatty acid metabolism is therefore important. To find out whether HepG2 cells are suitable for this purpose, we investigated the effect of three established fatty acid metabolism inhibitors and of three test compounds on triglyceride accumulation, palmitate metabolism, the acylcarnitine pool and dicarboxylic acid accumulation in the cell supernatant and on ApoB-100 excretion in HepG2 cells. The three established inhibitors [etomoxir, methylenecyclopropylacetic acid (MCPA), and 4-bromocrotonic acid (4-BCA)] depleted mitochondrial ATP at lower concentrations than cytotoxicity occurred, suggesting mitochondrial toxicity. They inhibited palmitate metabolism at similar or lower concentrations than ATP depletion, and 4-BCA was associated with cellular fat accumulation. They caused specific changes in the acylcarnitine pattern and etomoxir an increase of thapsic (C18 dicarboxylic) acid in the cell supernatant, and did not interfere with ApoB-100 excretion (marker of VLDL export). The three test compounds (amiodarone, tamoxifen, and the cannabinoid WIN 55,212-2) depleted the cellular ATP content at lower concentrations than cytotoxicity occurred. They all caused cellular fat accumulation and inhibited palmitate metabolism at similar or higher concentrations than ATP depletion. They suppressed medium-chain acylcarnitines in the cell supernatant and amiodarone and tamoxifen impaired thapsic acid production. Tamoxifen and WIN 55,212-2 decreased cellular ApoB-100 excretion. In conclusion, the established inhibitors of fatty acid metabolism caused the expected effects in HepG2 cells. HepG cells proved to be useful for the detection of drug-associated toxicities on hepatocellular fatty acid metabolism.

The role of hepatic cytochrome P450s in the cytotoxicity of dronedarone

Dronedarone is used to treat patients with cardiac arrhythmias and has been reported to be associated with liver injury. Our previous mechanistic work demonstrated that DNA damage-induced apoptosis contributes to the cytotoxicity of dronedarone. In this study, we examined further the underlying mechanisms and found that after a 24-h treatment of HepG2 cells, dronedarone caused cytotoxicity, G1-phase cell cycle arrest, suppression of topoisomerase II, and DNA damage in a concentration-dependent manner. We also investigated the role of cytochrome P450s (CYPs)-mediated metabolism in the dronedarone-induced toxicity using our previously established HepG2 cell lines expressing individually 14 human CYPs (1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5, and 3A7). We demonstrated that CYP3A4, 3A5, and 2D6 were the major enzymes that metabolize dronedarone, and that CYP3A7, 2E1, 2C19, 2C18, 1A1, and 2B6 also metabolize dronedarone, but to a lesser extent. Our data showed that the cytotoxicity of dronedarone was decreased in CYP3A4-, 3A5-, or 2D6-overexpressing cells compared to the control HepG2 cells, indicating that the parent dronedarone has higher potency than the metabolites to induce cytotoxicity in these cells. In contrast, cytotoxicity was increased in CYP1A1-overexpressing cells, demonstrating that CYP1A1 exerts an opposite effect in dronedarone's toxicity, comparing to CYP3A4, 3A5, or 2D6. We also studied the involvement of topoisomerase II in dronedarone-induced toxicity, and demonstrated that the overexpression of topoisomerase II caused an increase in cell viability and a decrease in γ-H2A.X induction, suggesting that suppression of topoisomerase II may be one of the mechanisms involved in dronedarone-induced liver toxicity.