Amiodarone and multilamellar inclusion bodies

Life cell imaging of amiodarone sequestration into lamellar bodies of alveolar type II cells

Amiodarone is widely used to treat cardiac arrhythmias and is very effective in preventing these disorders. However, its use is limited by a wide range of adverse effects, mainly affecting the lungs, and ranging from mild shortness of breath to pulmonary fibrosis. Amiodarone has been shown to accumulate strongly in lung tissue, exceeding its plasma concentration by a hundredfold. However, the site of accumulation and the mechanisms of transport are not fully understood. In this study, we used live cell imaging of primary rat alveolar type II cells to show that amiodarone specifically accumulates in large amounts in lamellar bodies, the surfactant storage organelles. Fluorescence imaging and correlation, and colocalization studies combined with confocal Raman microscopy identified these organelles as a major target for sequestration. Accumulation was rapid, on the order of a few hours, while storage was much more persistent. Partial uptake was observed in chemically fixed, dead cells, or cells treated with bafilomycin A1. Not only was uptake pH dependent, but intraluminal pH, measured with lysosomotropic pH sensitive dyes, was also affected. From these observations and from the physicochemical properties of amiodarone, we propose that passive diffusion, ion-trapping and lipophilic interactions are the main mechanisms for intracellular bioaccumulation. Furthermore, we demonstrate that measurement of amiodarone autofluorescence is highly useful for tracking cellular uptake and sequestration.

Regulation of macroautophagy in amiodarone-induced pulmonary fibrosis

Amiodarone (AD) is an iodinated benzofuran derivative, especially known for its antiarrhythmic properties. It exerts serious side‐effects even in patients receiving low doses. AD is well‐known to induce apoptosis of type II alveolar epithelial cells (AECII), a mechanism that has been suggested to play an important role in AD‐induced lung fibrosis. The precise molecular mechanisms underlying this disease are, however, still unclear. Because of its amphiphilic nature, AD becomes enriched in the lysosomal compartments, affecting the general functions of these organelles. Hence, in this study, we aimed to assess the role of autophagy, a lysosome‐dependent homeostasis mechanism, in driving AECII apoptosis in response to AD. In vitro, AD‐treated MLE12 and primary AECII cells showed increased proSP‐C and LC3B positive vacuolar structures and underwent LC3B‐dependent apoptosis. In addition, AD‐induced autophagosome‐lysosome fusion and increased autophagy flux were observed. In vivo, in C57BL/6 mice, LC3B was localised at the limiting membrane of lamellar bodies, which were closely connected to the autophagosomal structures in AECIIs. Our data suggest that AD causes activation of macroautophagy in AECIIs and extensive autophagy‐dependent apoptosis of alveolar epithelial cells. Targeting the autophagy pathway may therefore represent an attractive treatment modality in AD‐induced lung fibrosis.

Altered surfactant homeostasis and alveolar epithelial cell stress in amiodarone-induced lung fibrosis

Amiodarone (AD) is a highly efficient antiarrhythmic drug with potentially serious side effects. Severe pulmonary toxicity is reported in patients receiving AD even at low doses and may cause interstitial pneumonia as well as lung fibrosis. Apoptosis of alveolar epithelial type II cells (AECII) has been suggested to play an important role in this disease. In the current study, we aimed to establish a murine model of AD-induced lung fibrosis and analyze surfactant homeostasis, lysosomal, and endoplasmic reticulum (ER) stress in this model. AD/vehicle was instilled intratracheally into C57BL/6 mice, which were sacrificed on days 7, 14, 21, and 28. Extent of lung fibrosis development was assessed by trichrome staining and hydroxyproline measurement. Cytotoxicity was assessed by lactate dehydrogenase assay. Phospholipids (PLs) were analyzed by mass spectrometry. Surfactant proteins (SP) and markers for apoptosis, lysosomal, and ER stress were studied by Western blotting and immunohistochemistry. AECII morphology was evaluated by electron microscopy. Extensive lung fibrosis and AECII hyperplasia were observed in AD-treated mice already at day 7. Surfactant PL and SP accumulated in AECII over time. In parallel, induction of apoptosis, lysosomal, and ER stress was encountered in AECII of mice lungs and in MLE12 cells treated with AD. In vitro, siRNA-mediated knockdown of cathepsin D did not alter the AD-induced apoptotic response. Our data suggest that mice exposed to intratracheal AD develop severe pulmonary fibrosis, exhibit extensive surfactant alterations and cellular stress, but AD-induced AECII apoptosis is not mediated primarily via cathepsin D.

Clinical organ toxicity of antiarrhythmic compounds: ocular and pulmonary manifestations

The history of antiarrhythmic therapy reveals these agents to be associated with a high incidence of toxicity. Although several agents have ocular effects, amiodarone is the most widely recognized for producing adverse effects in the eyes. Corneal microdeposits are almost ubiquitous in patients being treated with amiodarone. However, they are, for the most part, benign and produce no changes in visual acuity. Lack of microdeposits should prompt the physician to investigate whether there is a problem with drug absorption or adherence to therapy. Other effects on the eye have been reported including optic neuropathy, but no causal link has been proved with amiodarone. The population of patients treated with amiodarone often have ischemic disease and/or diabetes, which affect retinal and optic nerve health. Many antiarrhythmic agents also affect lung function. The frequent association of procainamide with a lupus-like syndrome, where half the cases develop pleural-pericardial involvement, may require discontinuation of that drug. Although beta blockers and to a lesser degree, calcium antagonists, may cause bronchospasm in some patients, this is not usually a major clinical problem. Again, it is amiodarone that has the most widespread reputation for causing pulmonary toxicity. Although infrequent (< 1% incidence), it generates the most fear as it is sometimes fatal. Because of the lack of a diagnostic "gold standard," it is often overdiagnosed, placing patients at risk from overlooked congestive heart failure and infections and from recurrent arrhythmias after drug withdrawal. Patients with pre-existing pulmonary disease appear to be more at risk. Common features include indolent onset of cough, malaise and fever associated with patchy peripheral infiltrates, and severely decreased diffusion capacity. Several cases of pulmonary toxicity have had inordinately high serum desethylamiodarone to amiodarone ratios. Most cases recover with cessation of amiodarone therapy. Steroids are commonly used, but are of unproved efficacy. In terms of its toxicity, amiodarone remains the most feared of the antiarrhythmic agents. In the future, a better understanding of its pharmacokinetics, mechanisms of toxicity, and optimal dosing regimens should provide a possibility of better strategies for avoidance, early diagnosis, and more directed therapy of toxicities associated with amiodarone.

Amiodarone- and desethylamiodarone-induced myelinoid inclusion bodies and toxicity in cultured rat hepatocytes

Hepatocytes isolated from Sprague-Dawley rats were incubated with various concentrations of either amiodarone or desethylamiodarone for 0 to 96 hr. Both drugs produced a concentration-dependent increase of lactate dehydrogenase release in the culture medium, which correlated well with cell death as measured by trypan blue exclusion test. Desethylamiodarone was more toxic than amiodarone in the cultured hepatocytes. Incubation with subtoxic concentrations of either amiodarone (7.6 microM) or desethylamiodarone (8 microM) for 24 hr resulted in the development of myelinoid inclusion bodies in the hepatocytes without any excess release of lactate dehydrogenase. In experimental protocols where the hepatocytes were exposed to either amiodarone or desethylamiodarone for up to 96 hr, there was an increase in lactate dehydrogenase and the percent volume-density of multilamellar inclusion bodies with cumulative drug exposure with time. A linear correlation between hepatocyte drug concentration and multilamellar inclusion bodies was found for both amiodarone and desethylamiodarone. These results demonstrate that both amiodarone and its major metabolite, desethylamiodarone, induce lysosomal inclusions, which, under appropriate conditions, can be dissociated from cell death. Withdrawal of the drug after 24 hr exposure did not result in disappearance of the inclusion bodies from the hepatocytes for up to 96 hr of tissue culture. The concentrations at which amiodarone- or desethylamiodarone-induced electron microscopic changes and hepatotoxicity were only two to five times as high as the usual serum drug levels in patients given antiarrhythmic therapy with amiodarone.

Basic and clinical pharmacology of amiodarone: relationship of antiarrhythmic effects, dose and drug concentrations to intracellular inclusion bodies

Amiodarone is a unique class III antiarrhythmic drug with several unusual pharmacokinetic, pharmacodynamic, and toxicological actions which are quite distinct from those of the standard antiarrhythmic drugs. Extensive animal and clinical studies have demonstrated that amiodarone and its major metabolite, desethylamiodarone, both produce a marked increase in the duration of transmembrane action potential, which may be related to their antiarrhythmic as well as clinical electrophysiological activity. Unlike most other cardiovascular drugs, it has been recognized for more than 20 years that optimal antiarrhythmic effects may take several days to weeks after onset of oral therapy. Amiodarone is highly lipid soluble and exhibits at least three separate compartments of drug distribution, with a long elimination half-life of 14-120 days after chronic therapy. The pharmacokinetic profile of desethylamiodarone is qualitatively similar to that of amiodarone, but its elimination half-life is even longer and its tissue distribution may be slightly different. Although there may not be any correlation between serum drug levels and clinical toxicity of amiodarone during long-term therapy, recent animal as well as clinical data suggest that multilamellar intracellular inclusions can be dissociated from cell death or clinical toxicity. Thus, it is possible that amiodarone toxicity can be minimized with low doses or low serum drug concentrations. The metabolite(s) of amiodarone may play a major role in its pharmacological and toxicological actions.