Direct mitochondrial dysfunction precedes reactive oxygen species production in amiodarone-induced toxicity in human peripheral lung epithelial HPL1A cells

Amiodarone but not propafenone impairs bioenergetics and autophagy of human myocardial cells

Cardiac and extra-cardiac side effects of common antiarrhythmic agents might be related to drug-induced mitochondrial dysfunction. Supratherapeutic doses of amiodarone have been shown to impair mitochondria in animal studies, whilst influence of propafenone on cellular bioenergetics is unknown. We aimed to assess effects of protracted exposure to pharmacologically relevant doses of amiodarone and propafenone on cellular bioenergetics and mitochondrial biology of human and mouse cardiomyocytes. In this study, HL-1 mouse atrial cardiomyocytes and primary human cardiomyocytes derived from the ventricles of the adult heart were exposed to 2 and 7 μg/mL of either amiodarone or propafenone. After 24 h, extracellular flux analysis and confocal laser scanning microscopy were used to measure mitochondrial functions. Autophagy was assessed by western blots and live-cell imaging of lysosomes. In human cardiomyocytes, amiodarone significantly reduced mitochondrial membrane potential and ATP production, in association with an inhibition of fatty acid oxidation and impaired complex I- and II-linked respiration in the electron transport chain. Expectedly, this led to increased anaerobic glycolysis. Amiodarone increased the production of reactive oxygen species and autophagy was also markedly affected. In contrast, propafenone-exposed cardiomyocytes did not exert any impairment of cellular bioenergetics. Similar changes after amiodarone treatment were observed during identical experiments performed on HL-1 mouse cardiomyocytes, suggesting a comparable pharmacodynamics of amiodarone among mammalian species. In conclusion, amiodarone but not propafenone in near-therapeutic concentrations causes a pattern of mitochondrial dysfunction with affected autophagy and metabolic switch from oxidative metabolism to anaerobic glycolysis in human cardiomyocytes.

Clinical and Mechanistic Review of Amiodarone-Associated Optic Neuropathy

Amiodarone-associated optic neuropathy (AAON) is a complex clinical diagnosis, requiring distinction from non-arteritic ischemic optic neuropathy (NAION) due to a shared at-risk patient population. Diagnosis of AAON is complicated by a varied clinical presentation and incomplete pathophysiologic mechanisms. This article reviews pertinent literature for describing and clinically delineating AAON from NAION, as well as newly reported protective mechanisms of insulin-like growth factor 1 (IGF-1) and PI3K/Akt against amiodarone-induced oxidative and apoptotic injury in retinal ganglion and pigment epithelial cells. These studies offer a basis for exploring mechanisms of amiodarone toxicity in the optic nerve.

Insulin-like growth factor-1 activates PI3K/Akt signalling to protect human retinal pigment epithelial cells from amiodarone-induced oxidative injury

BACKGROUND AND PURPOSE

Amiodarone is one of the most effective anti-arrhythmic drugs available, but its clinical applications are limited by toxic side effects including optic toxicity. The purpose of this study was to investigate the toxic effect of amiodarone on D407 cells (a human retinal pigmented epithelial (RPE) cell line) and the mechanisms of the protective effect of insulin-like growth factor-1 (IGF-1).

EXPERIMENTAL APPROACH

The involvement of the kinases, Akt and ERK, was analysed by Western blot. Intracellular accumulation of ROS was measured using fluorophotometric quantification. A pharmacological approach with inhibitors was used to investigate the pathways involved in the protective action of IGF-1.

KEY RESULTS

Amiodarone concentration-dependently augmented the production of ROS, lipid peroxidation and apoptosis in D407 cells. IGF-1 time- and concentration-dependently reversed these effects of amiodarone and protected D407 cells from amiodarone-mediated toxicity. Amiodarone inhibited the pAkt but not pErk, and IGF-1 reversed this inhibitory effect of amiodarone. However, IGF-1 failed to suppress amiodarone-induced cytotoxicity in the presence of PI3K/Akt inhibitor LY294002 suggesting the direct involvement of the PI3K/Akt pathway. Furthermore, in vivo rat flash electroretinogram (FERG) recordings showed that IGF-1 reverses the amiodarone-induced decrease in a- and b-waves. The immunocytochemistry findings confirmed that vitreous IGF-1 injections promote the survival of RPE cells in rat retina treated with amiodarone.

CONCLUSION AND IMPLICATIONS

IGF-1 can protect RPE cells from amiodarone-mediated injury via the PI3K/Akt pathway in vivo and in vitro. IGF-1 has potential as a protective drug for the prevention and treatment of amiodarone-induced optic toxicity.

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Role of endoplasmic reticulum stress in drug-induced toxicity

Drug‐induced toxicity is a key issue for public health because some side effects can be severe and life‐threatening. These adverse effects can also be a major concern for the pharmaceutical companies since significant toxicity can lead to the interruption of clinical trials, or the withdrawal of the incriminated drugs from the market. Recent studies suggested that endoplasmic reticulum (ER) stress could be an important event involved in drug liability, in addition to other key mechanisms such as mitochondrial dysfunction and oxidative stress. Indeed, drug‐induced ER stress could lead to several deleterious effects within cells and tissues including accumulation of lipids, cell death, cytolysis, and inflammation. After recalling important information regarding drug‐induced adverse reactions and ER stress in diverse pathophysiological situations, this review summarizes the main data pertaining to drug‐induced ER stress and its potential involvement in different adverse effects. Drugs presented in this review are for instance acetaminophen (APAP), arsenic trioxide and other anticancer drugs, diclofenac, and different antiretroviral compounds. We also included data on tunicamycin (an antibiotic not used in human medicine because of its toxicity) and thapsigargin (a toxic compound of the Mediterranean plant Thapsia garganica) since both molecules are commonly used as prototypical toxins to induce ER stress in cellular and animal models.

Metabolic Reprogramming Is Required for Myofibroblast Contractility and Differentiation

Contraction is crucial in maintaining the differentiated phenotype of myofibroblasts. Contraction is an energy-dependent mechanism that relies on the production of ATP by mitochondria and/or glycolysis. Although the role of mitochondrial biogenesis in the adaptive responses of skeletal muscle to exercise is well appreciated, mechanisms governing energetic adaptation of myofibroblasts are not well understood. Our study demonstrates induction of mitochondrial biogenesis and aerobic glycolysis in response to the differentiation-inducing factor transforming growth factor β1 (TGF-β1). This metabolic reprogramming is linked to the activation of the p38 mitogen-activated protein kinase (MAPK) pathway. Inhibition of p38 MAPK decreased accumulation of active peroxisome proliferator-activated receptor γ coactivator 1α in the nucleus and altered the translocation of mitochondrial transcription factor A to the mitochondria. Genetic or pharmacologic approaches that block mitochondrial biogenesis or glycolysis resulted in decreased contraction and reduced expression of TGF-β1-induced α-smooth muscle actin and collagen α-2(I) but not of fibronectin or collagen α-1(I). These data indicate a critical role for TGF-β1-induced metabolic reprogramming in regulating myofibroblast-specific contractile signaling and support the concept of integrating bioenergetics with cellular differentiation.

Effect of Aronia melanocarpa fruit juice on amiodarone-induced pneumotoxicity in rats

Background:

The fruits of Aronia melanocarpa (Michx.) Elliot is extremely rich in biologically active polyphenols.

Objective:

We studied the protective effect of A. melanocarpa fruit juice (AMFJ) in a model of amiodarone (AD)-induced pneumotoxicity in rats.

Materials and Methods:

AD was instilled intratracheally on days 0 and 2 (6.25 mg/kg). AMFJ (5 mL/kg and 10 mL/kg) was given orally from day 1 to days 2, 4, 9, and 10 to rats, which were sacrificed respectively on days 3, 5, 10, and 28 when biochemical, cytological, and immunological assays were performed.

Results:

AMFJ antagonized AD-induced increase of the lung weight coefficient. In bronchoalveolar lavage fluid, AD increased significantly the protein content, total cell count, polymorphonuclear cells, lymphocytes and the activity of lactate dehydrogenase, acid phosphatase and alkaline phosphatase on days 3 and 5. In AMFJ-treated rats these indices of direct toxic damage did not differ significantly from the control values. In lung tissue, AD induced oxidative stress measured by malondialdehyde content and fibrosis assessed by the hydroxyproline level. AMFJ prevented these effects of AD. In rat serum, AD caused a significant elevation of interleukin IL-6 on days 3 and 5, and a decrease of IL-10 on day 3. In AMFJ-treated rats, these indices of inflammation had values that did not differ significantly from the control ones.

Conclusion:

AMFJ could have a protective effect against AD-induced pulmonary toxicity as evidenced by the reduced signs of AD-induced direct toxic damage, oxidative stress, inflammation, and fibrosis.

Activation of autophagy rescues amiodarone-induced apoptosis of lung epithelial cells and pulmonary toxicity in rats

Amiodarone, bi-iodinated benzofuran derivative, is one of the most frequently prescribed and efficacious antiarrhythmic drugs. Despite its low incidence, amiodarone-induced pulmonary toxicity is of great concern and the leading cause of discontinuation. Autophagy is an essential homeostatic process that mediates continuous recycling of intracellular materials when nutrients are scarce. It either leads to a survival advantage or initiates death processes in cells under stress. In the present study, we investigated the role of autophagy in amiodarone-induced pulmonary toxicity. Amiodarone treatment-induced autophagy in H460 human lung epithelial cells and BEAS-2B normal human bronchial epithelial cells was demonstrated by increased LC3-II conversion, Atg7 upregulation, and autophagosome formation. Autophagic flux, as determined by the lysosomal inhibitor bafilomycin A1, was also increased following amiodarone treatment. To determine the role of autophagy in amiodarone toxicity, amiodarone-induced cell death was evaluated in the presence of 3-methyladenine or by knocking down the autophagy-related genes Atg7. Inhibition of autophagy decreased cellular viability and significantly increased apoptosis. Intratracheal instillation of amiodarone in rats increased the number of inflammatory cells recovered from bronchoalveolar lavage fluid, and periodic acid-Schiff-positive staining in bronchiolar epithelial cells. However, induction of autophagy by rapamycin treatment inhibited amiodarone-induced pulmonary toxicity. In conclusion, amiodarone treatment induced autophagy, which is involved in protection against cell death and pulmonary toxicity.

In vitro study on the pulmonary cytotoxicity of amiodarone

CONTEXT

Amiodarone (an iodinated benzofuran) is a Class III antiarrhythmic drug that produces significant pulmonary disease. Proposed mechanisms of this cytotoxicity include necrosis, apoptosis, mitochondrial dysfunction and glutathione depletion.

OBJECTIVE

This study was designed primarily to explore whether amiodarone impairs lung tissue cellular bioenergetics in BALB/c and Taylor Outbred mice.

MATERIALS AND METHODS

Cellular respiration (mitochondrial O2 consumption), ATP, caspase activity and glutathione were measured in lung fragments incubated in vitro with 22 µM amiodarone for several hours.

RESULTS

Without amiodarone, lung tissue cellular mitochondrial O2 consumption decayed exponentially with time, showing two distinct phases sharply separated at t ≥ 150 min. The rate of cellular respiration was 6-10-fold higher in the late phase compared to the early phase (p<0.0001). Lung tissue ATP also decayed exponentially with time, suggesting "uncoupling oxidative phosphorylation" was the responsible mechanism (low cellular ATP with high mitochondrial O2 consumption, resulting in rapid depletion of cellular metabolic fuels). Although intracellular caspase activity increased exponentially with time, the uncoupling was not prevented by the pancaspase inhibitor zVAD-fmk (N-benzyloxycarbonyl-val-ala-asp (O-methyl)-fluoromethylketone). The same profiles were noted in the presence of amiodarone; but cellular ATP decayed 50% faster. Cellular glutathione for untreated tissue was 560 ± 287 pmol mg(-1) (n=12) and for treated tissue was 490 ± 226 pmol mg(-1) (n=12, p=0.5106).

CONCLUSION

Uncoupling oxidative phosphorylation was demonstrated in untreated mouse lung tissues. Amiodarone lowered cellular ATP. Further studies are needed to explore the susceptibility of the lung to these deleterious insults and their relevance to human diseases.

Tumor necrosis factor-alpha potentiates the cytotoxicity of amiodarone in Hepa1c1c7 cells: roles of caspase activation and oxidative stress

Amiodarone (AMD), a class III antiarrhythmic drug, causes idiosyncratic hepatotoxicity in human patients. We demonstrated previously that tumor necrosis factor-alpha (TNF-α) plays an important role in a rat model of AMD-induced hepatotoxicity under inflammatory stress. In this study, we developed a model in vitro to study the roles of caspase activation and oxidative stress in TNF potentiation of AMD cytotoxicity. AMD caused cell death in Hepa1c1c7 cells, and TNF cotreatment potentiated its toxicity. Activation of caspases 9 and 3/7 was observed in AMD/TNF-cotreated cells, and caspase inhibitors provided minor protection from cytotoxicity. Intracellular reactive oxygen species (ROS) generation and lipid peroxidation were observed after treatment with AMD and were further elevated by TNF cotreatment. Adding water-soluble antioxidants (trolox, N-acetylcysteine, glutathione, or ascorbate) produced only minor attenuation of AMD/TNF-induced cytotoxicity and did not influence the effect of AMD alone. On the other hand, α-tocopherol (TOCO), which reduced lipid peroxidation and ROS generation, prevented AMD toxicity and caused pronounced reduction in cytotoxicity from AMD/TNF cotreatment. α-TOCO plus a pancaspase inhibitor completely abolished AMD/TNF-induced cytotoxicity. In summary, activation of caspases and oxidative stress were observed after AMD/TNF cotreatment, and caspase inhibitors and a lipid-soluble free-radical scavenger attenuated AMD/TNF-induced cytotoxicity.

Amiodarone pretreatment of organ donors exerts anti-oxidative protection but induces excretory dysfunction in liver preservation and reperfusion

The continuous shortage of organs necessitates the use of marginal organs from donors with various diseases, including arrhythmia-associated cardiac failure. One of the most frequently used anti-arrhythmic drugs is amiodarone (AM), which is given in particular in emergency situations. Apart from its anti-arrhythmic actions, AM provides anti-oxidative properties in cardiomyocytes. Thus, we were interested in whether AM donor pretreatment affects the organ quality and function of livers procured for preservation and transplantation. Donor rats were pretreated with AM (5 mg/kg of body weight) 10 minutes before flush-out of the liver with a cold (4 degrees C) histidine-tryptophan-ketoglutarate solution (n = 8). Livers were then stored for 24 hours at 4 degrees C before ex situ reperfusion with a 37 degrees C Krebs-Henseleit solution for 60 minutes in a nonrecirculating system. At the end of reperfusion, tissue samples were taken for histology and Western blot analysis. Animals with vehicle only (0.9% NaCl) served as ischemia/reperfusion controls (n = 8). Additionally, livers of untreated animals (n = 8) not subjected to 24 hours of cold ischemia served as sham controls. AM pretreatment effectively attenuated lipid peroxidation, stress protein expression, and apoptotic cell death. This was indicated by an AM-mediated reduction of malondialdehyde, heme oxygenase-1, and caspase-3 activation. However, AM treatment also induced mitochondrial damage and hepatocellular excretory dysfunction, as indicated by a significantly increased glutamate dehydrogenase concentration in the effluate and decreased bile production. In conclusion, AM donor pretreatment exerts anti-oxidative actions in liver preservation and reperfusion. However, these protective AM actions are counteracted by an induction of mitochondrial damage and hepatocellular dysfunction. Accordingly, AM pretreatment of donors for anti-arrhythmic therapy should be performed with caution.