Pulmonary fibrosis induced in the hamster by amiodarone and desethylamiodarone

Involvement of Mitochondrial Mechanisms and Cyclooxygenase-2 Activation in the Effect of Desethylamiodarone on 4T1 Triple-Negative Breast Cancer Line

Novel compounds significantly interfering with the mitochondrial energy production may have therapeutic value in triple-negative breast cancer (TNBC). This criterion is clearly fulfilled by desethylamiodarone (DEA), which is a major metabolite of amiodarone, a widely used antiarrhythmic drug, since the DEA previously demonstrated anti-neoplastic, anti-metastasizing, and direct mitochondrial effects in B16F10 melanoma cells. Additionally, the more than fifty years of clinical experience with amiodarone should answer most of the safety concerns about DEA. Accordingly, in the present study, we investigated DEA’s potential in TNBC by using a TN and a hormone receptor positive (HR+) BC cell line. DEA reduced the viability, colony formation, and invasive growth of the 4T1 cell line and led to a higher extent of the MCF-7 cell line. It lowered mitochondrial transmembrane potential and induced mitochondrial fragmentation. On the other hand, DEA failed to significantly affect various parameters of the cellular energy metabolism as determined by a Seahorse live cell respirometer. Cyclooxygenase 2 (COX-2), which was upregulated by DEA in the TNBC cell line only, accounted for most of 4T1’s DEA resistance, which was counteracted by the selective COX-2 inhibitor celecoxib. All these data indicate that DEA may have potentiality in the therapy of TNBC.

Involvement of Mitochondrial Mechanisms in the Cytostatic Effect of Desethylamiodarone in B16F10 Melanoma Cells

Previously, we showed that desethylamiodarone (DEA), a major metabolite of the widely used antiarrhythmic drug amiodarone, has direct mitochondrial effects. We hypothesized that these effects account for its observed cytotoxic properties and ability to limit in vivo metastasis. Accordingly, we examined DEA’s rapid (3–12 h) cytotoxicity and its early (3–6 h) effects on various mitochondrial processes in B16F10 melanoma cells. DEA did not affect cellular oxygen radical formation, as determined using two fluorescent dyes. However, it did decrease the mitochondrial transmembrane potential, as assessed by JC-1 dye and fluorescence microscopy. It also induced mitochondrial fragmentation, as visualized by confocal fluorescence microscopy. DEA decreased maximal respiration, ATP production, coupling efficiency, glycolysis, and non-mitochondrial oxygen consumption measured by a Seahorse cellular energy metabolism analyzer. In addition, it induced a cyclosporine A–independent mitochondrial permeability transition, as determined by Co²⁺-mediated calcein fluorescence quenching measured using a high-content imaging system. DEA also caused outer mitochondrial membrane permeabilization, as assessed by the immunoblot analysis of cytochrome C, apoptosis inducing factor, Akt, phospho-Akt, Bad, and phospho-Bad. All of these data supported our initial hypothesis.

Amiodarone's major metabolite, desethylamiodarone inhibits proliferation of B16-F10 melanoma cells and limits lung metastasis formation in an in vivo experimental model

Previously, we demonstrated the in vitro anti-tumor effects of desethylamiodarone (DEA) in bladder and cervix cancer cell lines. In the present study, we intended to establish its potentiality in B16-F10 metastatic melanoma cells in vitro and in vivo. We assessed cell proliferation, apoptosis and cell cycle by using sulforhodamine B assay, Muse™ Annexin V & Dead Cell and Muse® Cell Cycle assays, respectively. We determined colony formation after crystal violet staining. For studying mechanistic aspects, immunoblotting analysis was performed. We used a C57BL/6 experimental lung metastasis model for demonstrating in vivo anti-metastatic potential of DEA. DEA inhibited in vitro proliferation and colony formation, and in vivo lung metastasizing properties of B16-F10 cells. It arrested the cells in G0/G1 phase of their cycle likely via p21 in a p53-dependent fashion, and induced caspase mediated apoptosis likely via inversely regulating Bcl-2 and Bax levels, and reducing Akt and ERK1/2 activation. In this study, we provided in vitro and in vivo experimental evidences for DEA’s potentiality in the therapy of metastatic melanomas. Since DEA is the major metabolite of amiodarone, a worldwide used antiarrhythmic drug, safety concerns could be resolved more easily for it than for a novel pharmacological agent.

Amiodarone's major metabolite, desethylamiodarone, induces apoptosis in human cervical cancer cells

Previously, we found that desethylamiodarone (DEA) may have therapeutic potentiality in bladder cancer. In this study, we determined its effects on human cervical cancer cells (HeLa). Cell viability was evaluated by Muse Cell Count & Viability Assay; cell apoptosis was detected by Muse Annexin V & Dead Cell Assay. Cell cycle was flow cytometrically determined by Muse Cell Cycle Kit and the morphological changes of the cells were observed under a fluorescence microscope after Hoechst 33342 staining. The changes in the expression levels of apoptosis-related proteins in the HeLa cells were assessed by immunoblot. Our results showed that DEA significantly inhibited the proliferation and viability of HeLa cells and induced apoptosis in vitro in dose-dependent and also in cell cycle-dependent manner because DEA induced G0/G1 phase arrest in the HeLa cell line. We found that DEA treatment downregulated the expression of phospho-Akt and phospho-Bad. In addition, DEA could downregulate expression of Bcl-2, upregulate Bax, and induce cytochrome c release. Our results indicate that DEA might have significance as an anti-tumor agent against human cervical cancer.

Desethylamiodarone-A metabolite of amiodarone-Induces apoptosis on T24 human bladder cancer cells via multiple pathways

Bladder cancer (BC) is a common malignancy of the urinary tract that has a higher frequency in men than in women. Cytostatic resistance and metastasis formation are significant risk factors in BC therapy; therefore, there is great interest in overcoming drug resistance and in initiating research for novel chemotherapeutic approaches. Here, we suggest that desethylamiodarone (DEA)–a metabolite of amiodarone—may have cytostatic potential. DEA activates the collapse of mitochondrial membrane potential (detected by JC-1 fluorescence), and induces cell death in T24 human transitional-cell bladder carcinoma cell line at physiologically achievable concentrations. DEA induces cell cycle arrest in the G0/G1 phase, which may contribute to the inhibition of cell proliferation, and shifts the Bax/Bcl-2 ratio to initiate apoptosis, induce AIF nuclear translocation, and activate PARP-1 cleavage and caspase-3 activation. The major cytoprotective kinases—ERK and Akt—are inhibited by DEA, which may contribute to its cell death-inducing effects. DEA also inhibits the expression of B-cell-specific Moloney murine leukemia virus integration site 1 (BMI1) and reduces colony formation of T24 bladder carcinoma cells, indicating its possible inhibitory effect on metastatic potential. These data show that DEA is a novel anti-cancer candidate of multiple cell death-inducing effects and metastatic potential. Our findings recommend further evaluation of its effects in clinical studies.

Attenuation of amiodarone induced lung fibrosis and phospholipidosis in hamsters, by treatment with the platelet activating factor receptor antagonist, WEB 2086

Therapeutic use of amiodarone (AMD), a Class III antiarrhythmic drug is complicated by the development of lung fibrosis (LF) and phospholipidosis (PL). In the present study, the effectiveness of a PAF antagonist, WEB 2086, against AMD induced LF and PL has been tested in hamsters. The animals were randomly divided into four groups: (1) saline + H₂O; (2) WEB + H₂O; (3) saline + AMD; and (4) WEB + AMD. Saline or WEB (10 mg/kg i.p.) was given 2 days prior to intratracheal instillation of water or AMD (1.5 μmol/0.25 ml/100 g BW) and thereafter daily throughout the study. Twenty-eight days after intratracheal instillation, the animals were killed and the lungs processed for various assays. The amount of lung hydroxyproline, an index of LF, in saline + H₂O, WEB + H₂O, saline + AMD, and WEB + AMD groups were 959 ± 46, 1035 ± 51, 1605 ± 85 and 1374 ± 69 μg/lung, respectively. Total lung PL, an index of phospholipidosis, in the corresponding groups were 8.4 ± 0.4, 8.3 ± 0.3, 11.7 ± 0.3 and 9.9 μg/lung. Lung malondialdehyde, an index of lipid peroxidation and superoxide dismutase activity in saline + H₂O WEB + H₂O, saline + AMD, and WEB + AMD were 93.0 ± 4.3, 93.0 ± 2.7, 138.9 ± 6.0 and 109.0 ± 3.8 nmol/lung and 359.7 ± 13.9, 394.0 ± 22.8, 497.5 ± 19.7 and 425.5 ± 4.9 units/lung, respectively. Administration of AMD alone caused significant increases in all the above indexes of lung toxicity, and treatment with WEB 2086 minimized the AMD induced toxicity as reflected by significant decreases in these indexes. Histopathological studies revealed a marked reduction in the extent and severity of lung lesions in the WEB + AMD group compared with the saline + AMD group. Treatment with WEB 2086 also reduced the acute mortality from 35% in saline + AMD group to 22% in WEB + AMD group. It was concluded that PAF is involved in the AMD induced lung fibrosis and phospholipidosis and that the PAF receptor antagonist may, therefore, be potentially useful in reducing AMD induced lung toxicity.

Amiodarone inhibits arterial thrombus formation and tissue factor translation

BACKGROUND

In patients with coronary artery disease and reduced ejection fraction, amiodarone reduces mortality by decreasing sudden death. Because the latter may be triggered by coronary artery thrombosis as much as ventricular arrhythmias, amiodarone might interfere with tissue factor (TF) expression and thrombus formation.

METHODS AND RESULTS

Clinically relevant plasma concentrations of amiodarone reduced TF activity and impaired carotid artery thrombus formation in a mouse photochemical injury model in vivo. PTT, aPTT, and tail bleeding time were not affected; platelet number was slightly decreased. In human endothelial and vascular smooth muscle cells, amiodarone inhibited tumor necrosis factor (TNF)-alpha and thrombin-induced TF expression as well as surface activity. Amiodarone lacking iodine and the main metabolite of amiodarone, N-monodesethylamiodarone, inhibited TF expression. Amiodarone did not affect mitogen-activated protein kinase activation, TF mRNA expression, and TF protein degradation. Metabolic labeling confirmed that amiodarone inhibited TF protein translation.

CONCLUSIONS

Amiodarone impairs thrombus formation in vivo; in line with this, it inhibits TF protein expression and surface activity in human vascular cells. These pleiotropic actions occur within the range of amiodarone concentrations measured in patients, and thus may account at least in part for its beneficial effects in patients with coronary artery disease.

Amiodarone increases the accumulation of DEA in a human alveolar epithelium-derived cell line

Amiodarone (AMD)-induced pulmonary toxicity (AIPT) is the most life-threatening side-effect of AMD treatment. N-Monodesethylamiodarone (DEA), an active metabolite of AMD, also exhibits cytotoxicity and tends to accumulate in the lung more intensively than AMD. In this study, we characterized the mechanism of DEA accumulation using A549 cells as a model of the alveolar epithelium. Typical ATP-depletion compounds caused an approximately 30% increase in the accumulation of DEA in A549 cells, although these effects were less than those in Caco-2 cells. Triiodothyronine (T(3)), which exhibited an inhibitory effect on DEA efflux in Caco-2 cells, did not affect the accumulation of DEA in A549 cells. On the other hand, 100 microM AMD caused an approximately 200% increase in DEA content in A549 cells, although AMD accumulation was not affected by 100 microM DEA. Since the reducing effect of AMD on cellular ATP levels and that of FCCP were similar, the mechanism by which DEA accumulation is increased by AMD might be different from the ATP-dependent DEA efflux mechanism. The decrease in cell viability by DEA in the presence of AMD (IC(50) value of DEA for A549 cell viability: 25.4+/-2.4 microM) was more pronounced than that by DEA alone (IC(50) value: 11.5+/-3.0 microM). This further DEA accumulation by AMD might be a factor responsible for the greater accumulation of DEA than that of AMD in the lung in long-term AMD-treated patients.

Efflux transport of N-monodesethylamiodarone by the human intestinal cell-line Caco-2 cells

Amiodarone (AMD) is a benzofurane derivative with class III antiarrhythmic activity that is effective in controlling intractable cardiac arrhythmias. One of the most common and serious drug interactions in clinical practice is the interaction between digoxin and an antiarrhythmic agent. It has been reported that AMD and N-monodesethylamiodarone (DEA), the active metabolite of AMD, inhibit the P-glycoprotein (P-gp/MDR1)-mediated digoxin transport. However, the intestinal transport processes of AMD and DEA have not been fully revealed. In this study, we focused on the intestinal transport mechanism of DEA and characterized the intestinal transport of DEA using Caco-2 cells. Basal-to-apical transport of DEA by Caco-2 cells was greater than apical-to-basal transport. The relationship between concentration and basal-to-apical flux rate appeared to approach saturation. The uptake of DEA by Caco-2 cells was increased in the presence of typical ATP-depletion compounds and thyroid hormones. On the other hand, substrates for P-gp, multidrug resistance-associated proteins (MRPs/ABCCs) and breast cancer resistance protein (BCRP/ABCG2) had no effect on the efflux of DEA. These results suggest that an ATP-binding cassette (ABC) transporter, which is different from P-gp, MRPs and BCRP, mediates the efflux of DEA across the apical membrane in Caco-2 cells and that thyroid hormone inhibits this transporter.

Aryl radical involvement in amiodarone-induced pulmonary toxicity: Investigation of protection by spin-trapping nitrones

Amiodarone (AM), an antidysrrhythmic drug, can produce serious adverse effects, including potentially fatal AM-induced pulmonary toxicity (AIPT). AM-induced cytotoxicity and pulmonary fibrosis are well recognized, but poorly understood mechanistically. The hypothesis of aryl radical involvement in AM toxicity was tested in non-biological and biological systems. Photolysis of anaerobic aqueous solutions of AM, or N-desethylamiodarone (DEA) resulted in the formation of an aryl radical, as determined by spin-trapping and electron paramagnetic resonance (EPR) spectroscopy experiments. The non-iodinated AM analogue, didesiodoamiodarone (DDIA), did not form aryl radicals under identical conditions. The toxic susceptibility of human lung epithelioid HPL1A cells to AM, DEA, and DDIA showed time- and concentration-dependence. DEA had a more rapid and potent toxic effect (LC(50)=8 microM) than AM (LC(50)=146 microM), whereas DDIA cytotoxicity was intermediate (LC(50)=26 microM) suggesting a minor contribution of the iodine atoms. Incubation of human lung epithelial cells with the spin-trapping nitrones alpha-phenyl-N-t-butylnitrone (PBN, 10 mM) or alpha-(4-pyridyl N-oxide)-N-t-butylnitrone (POBN, 5.0 mM) did not significantly protect against AM, DEA, or DDIA cytotoxicity. Intratracheal administration of AM to hamsters produced pulmonary fibrosis at day 21, which was not prevented by 4 days of treatment with 150 mg/kg/day PBN or 164 mg/kg/day POBN. However, the body weight loss in AM-treated animals was counteracted by PBN. These results suggest that, although AM can generate an aryl radical photochemically, its in vivo formation may not be a major contributor to AM toxicity, and that spin-trapping reagents do not halt the onset of AM toxicity.

Protective effect of amiodarone but not N-desethylamiodarone on postischemic hearts through the inhibition of mitochondrial permeability transition

Amiodarone is a widely used and potent antiarrhythmic agent that is metabolized to desethylamiodarone. Both amiodarone and its metabolite possess antiarrhythmic effect, and both compounds can contribute to toxic side effects. Here, we compare the effect of amiodarone and desethylamiodarone on mitochondrial energy metabolism, membrane potential, and permeability transition and on mitochondria-related apoptotic events. Amiodarone but not desethylamiodarone protects the mitochondrial energy metabolism of the perfused heart during ischemia in perfused hearts. At low concentrations, amiodarone stimulated state 4 respiration due to an uncoupling effect, inhibited the Ca2+-induced mitochondrial swelling, whereas it dissipated the mitochondrial membrane potential (Deltapsi), and prevented the ischemia-reperfusion-induced release of apoptosis-inducing factor (AIF). At higher concentrations, amiodarone inhibited the mitochondrial respiration and simulated a cyclosporin A (CsA)-independent mitochondrial swelling. In contrast to these, desethylamiodarone did not stimulate state 4 respiration, did not inhibit the Ca2+-induced mitochondrial permeability transition, did not induce the collapse of Deltapsi in low concentrations, and did not prevent the nuclear translocation of AIF in perfused rat hearts, but it induced a CsA-independent mitochondrial swelling at higher concentration, like amiodarone. That is, desethylamiodarone lacks the protective effect of amiodarone seen at low concentrations, such as the inhibition of calcium-induced mitochondrial permeability transition and inhibition of the nuclear translocation of the proapoptotic AIF. On the other hand, both amiodarone and desethylamiodarone at higher concentration induced a CsA-independent mitochondrial swelling, resulting in apoptotic death that explains their extracardiac toxic effect.

Intratracheal amiodarone administration to F344 rats directly damages lung airway and parenchymal cells

Amiodarone (AD) is gaining support as a first-line antiarrhythmic drug despite its potentially fatal pulmonary toxicity involving inflammation and fibrosis. We previously reported a model for this amiodarone-induced pulmonary toxicity (AIPT) in which F344 rats were intratracheally (i.t.) instilled with AD (6.25 mg/kg) in sterile water on days 0 and 2, which led to transient pulmonary inflammation and lung damage and subsequent fibrosis. The goals of this study were to determine the direct effect of the drug in the lung damage occurring after i.t. AD administration, to identify its location, and to examine its potential mechanisms. Using bronchoalveolar lavage and laser-scanning confocal microscopy, it was discovered that AD instillation produces rapid and massive damage to the alveolar-capillary barrier and damage or death to lung airway and parenchymal cells. While AD in solution was found to be capable of generating hydroxyl radicals, protection from AD-induced damage could not be obtained by incorporating water-soluble antioxidants in the drug solution. However, damage induced by free-radicals could still occur after AD partitions into lipid membranes. AD could also be directly disrupting cellular membranes via its amphiphilic structure. It is not known if the mechanism(s) of damage following i.t. AD treatment are similar to the mechanisms that underlie human AIPT. Therefore these data suggest that investigators should use caution in extrapolating results from animal studies that utilize i.t. administration of AD to human AIPT.

Attenuation of amiodarone-induced pulmonary fibrosis by vitamin E is associated with suppression of transforming growth factor-beta1 gene expression but not prevention of mitochondrial dysfunction

Amiodarone (AM) is an efficacious antidysrhythmic agent that can cause numerous adverse effects, including potentially life-threatening pulmonary fibrosis. The current study was undertaken to investigate potential protective mechanisms of vitamin E against AM-induced pulmonary toxicity (AIPT) in the hamster. Three weeks after intratracheal administration of AM (1.83 micromol), increased pulmonary hydroxyproline content and histological damage were observed, indicative of fibrosis. These effects were preceded by increased pulmonary levels of transforming growth factor (TGF)-beta1 mRNA at 1 week post-AM, which remained elevated 3 weeks post-AM. Dietary supplementation with vitamin E resulted in rapid pulmonary accumulation of the vitamin, and prevention of AM-induced increases in TGF-beta1, hydroxyproline, and histological damage. Although dietary supplementation also markedly elevated lung mitochondrial vitamin E content, it did not attenuate AM-induced inhibition of mitochondrial respiration or disruption of mitochondrial membrane potential in vitro, or lung mitochondrial respiratory inhibition resulting from in vivo AM administration. These results suggest that vitamin E reduces the extent of pulmonary damage after AM administration via down-regulating TGF-beta1 overexpression but that it does not modify AM-induced mitochondrial dysfunction, a potential initiating event in AIPT.

Induction of c-jun and TGF-beta 1 in Fischer 344 rats during amiodarone-induced pulmonary fibrosis

Amiodarone (AM) is an antidysrhythmic agent with a propensity to cause pulmonary toxicity, including potentially fatal fibrosis. In the present study, the potential roles of c-Jun and transforming growth factor (TGF)-beta 1 in AM-induced inflammation and fibrogenesis were examined after intratracheal administration of AM (1.83 micromol/day on days 0 and 2) or an equivalent volume (0.4 ml) of distilled water to male Fischer 344 rats. Northern and immunoblot analyses demonstrated that lung TGF-beta 1 (mRNA and protein) expression was increased 1.5- to 1.8-fold relative to control during the early inflammation period and 1 day, 1 wk, and 2 wk post-AM treatment. Lung c-Jun protein expression was increased concomitantly with evidence of AM-induced fibrosis; at 5 wk post-AM treatment, c-Jun protein was increased 3.3-fold relative to control. The results indicate a role for induction of c-jun and TGF-beta 1 expression in the development of AM-induced pulmonary fibrosis in the Fischer 344 rat and provide potential targets for therapeutic intervention.

Effects of vitamin E on cytotoxicity of amiodarone and N-desethylamiodarone in isolated hamster lung cells

Amiodarone (AM) is a potent and efficacious antidysrhythmic agent that can cause potentially life-threatening pulmonary fibrosis. Vitamin E has been demonstrated to decrease AM-induced pulmonary fibrosis in vivo in hamsters. In the present in vitro study, we investigated the effects of vitamin E on cell death induced by AM and its primary metabolite, N-desethylamiodarone (DEA), in freshly isolated hamster lung cells. Following incubation for 24 or 36 h, 300 microM vitamin E decreased (P<0.05) 100 microM AM-induced cytotoxicity (0.5% trypan blue uptake) in alveolar macrophages by 11.7+/-3% or 21.4+/-12%, respectively, but did not decrease cytotoxicity in fractions enriched with alveolar type II cells or non-ciliated bronchiolar epithelial (Clara cells) or in isolated unseparated cells (cell digest). Vitamin E had no effect on 50 microM DEA-induced cytotoxicity. Vitamin E did not alter cellular levels of AM or DEA in any cell fraction. Lipid peroxidation (assessed by isoprostane formation) was increased (P<0.05) in cell digest, alveolar type II cell and Clara cell enriched fractions incubated with 500 microM carbon tetrachloride (CCl(4)) for 4 h but not in enriched fractions of cells exposed to 100 microM AM or 50 microM DEA. No AM-induced loss of viability was observed at this time point, but DEA decreased (P<0.05) Clara cell viability by approximately 25%. These results demonstrate cell type selective protection against AM-induced cytotoxicity by vitamin E, and suggest that lipid peroxidation does not initiate AM- or DEA-induced cytotoxicity in isolated hamster lung cells.

A characterization of amiodarone-induced pulmonary toxicity in F344 rats and identification of surfactant protein-D as a potential biomarker for the development of the toxicity

Amiodarone (AD) is gaining support as a first-line antiarrhythmic drug despite its potentially fatal pulmonary toxicity involving inflammation and fibrosis. The goals of this study were to characterize a rat model of AD-induced pulmonary toxicity (AIPT) and identify a serum biomarker to aid in the diagnosis of the onset of pulmonary toxicity. Male F344 rats were instilled intratracheally with AD (6.25 mg/kg with a 3.125 mg/ml solution) in sterile water or the sterile water vehicle on days 0 and 2, a protocol that led to the development of pulmonary fibrosis on day 28 in the AD-treated animals. Animals were killed on days 3, 5, 6, 7, or 10 and bronchoalveolar lavage (BAL) was performed. Recovery of alveolar macrophages and eosinophils was increased on days 3 and 5, while neutrophil recovery and albumin levels in the first BAL fraction were significantly elevated only on day 3. BAL cells recovered from AD-treated rats at day 3 produced more phorbol myristate acetate-stimulated luminol-dependent chemiluminescence (LDCL) over 20 min than BAL cells from control rats. Experiments using specific inhibitors implicated superoxide and nitric oxide in at least part of the LDCL response. Serum levels of surfactant protein-D (SP-D), a surfactant-associated protein, were increased concurrently with the inflammatory response in the lungs. These findings indicate that this model exhibits transient pulmonary inflammation and damage, with the potential for elevated oxidant production in the lungs and subsequent pulmonary fibrosis. Also, SP-D is proposed as a specific biomarker to monitor the onset of AIPT in this model.

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-induced disruption of hamster lung and liver mitochondrial function: lack of association with thiobarbituric acid-reactive substance production

Amiodarone (AM) is an efficacious antidysrhythmic agent that is limited clinically by numerous adverse effects. Of greatest concern is AM-induced pulmonary toxicity (AIPT) due to the potential for mortality. Mitochondrial alterations and free radicals have been implicated in the etiology of AM-induced toxicities, including AIPT. Isolated hamster lung and liver mitochondria were assessed for AM-induced effects on respiration, membrane potential, and lipid peroxidation. AM (50-400 microM) stimulated state 4 (resting) respiration at complexes I and II of tightly coupled lung mitochondria, with higher concentrations (200 and 400 microM) resulting in a subsequent inhibition. This biphasic effect of AM (200 microM) was also observed with isolated liver mitochondria. Only inhibition of respiration was observed with AM (50-400 microM) in less tightly coupled lung mitochondria. Based on safranine fluorescence, 200 microM AM decreased lung mitochondrial membrane potential (p < 0.05), while a concentration-dependent (50-200 microM) decrease of membrane potential was observed with liver mitochondria exposed to AM (p < 0.05). Formation of thiobarbituric acid-reactive substances (TBARS) was not altered by AM (50-400 microM) in incubations lasting up to 1 h. These results indicate that lipid peroxidation, as indicated by levels of TBARS, does not play a role in AM-induced alterations in mitochondrial respiration and membrane potential.

Amiodarone-induced pulmonary toxicity in Fischer rats: release of tumor necrosis factor alpha and transforming growth factor beta by pulmonary alveolar macrophages

Amiodarone is an antiarrhythmic drug with numerous side effects, the most serious being the development of pulmonary toxicity. We have previously reported that a single intratracheal instillation of amiodarone to Fischer 344 rats results in pulmonary fibrosis within 6 wk of treatment. Presently, the mechanism of amiodarone-induced pulmonary toxicity is unknown. Cytokines that stimulate fibroblast proliferation and/or collagen production may play a role in amiodarone-induced pulmonary toxicity. To investigate this possibility, female rats were given a single intratracheal instillation of amiodarone (6.25 mg/kg), its metabolite desethylamiodarone (5 mg/kg), or vehicle (sterile water). At 1, 2, 3, or 6 wk after treatment the lungs were lavaged and the recovered cells were counted and identified. The alveolar macrophages were isolated by attachment to plastic petri dishes, cultured overnight, and the spent media collected for tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta) analyses. Desethylamiodarone treatment resulted in a neutrophilic alveolitis, but the levels of TNF-alpha and TGF-beta were not significantly different from control animals. In contrast, amiodarone treatment resulted in a lymphocytic alveolitis and significantly higher amounts of TNF-alpha were observed at 3 and 6 wk after treatment. A trend toward higher levels of TGF-beta was also noted in the amiodarone-treated group at wk 1-3 but the values were not significantly different from those of controls. In conclusion, the release of TNF-alpha may play a role in the development of amiodarone-induced pulmonary toxicity.

Amiodarone-induced lymphocyte toxicity and mitochondrial function

Amiodarone is one of the most effective antiarrhythmic drugs available. However, its use is often limited by potentially life-threatening toxicities, including hepatotoxicity and pulmonary toxicity. We have used human lymphocytes as a system in which to study amiodarone-induced cytotoxicity. Using a tetrazolium dye reduction assay, we observed amiodarone-induced cytotoxicity with a lethal dose (LD)50 of 10.0 +/- 31.1 microM (mean +/- SD, n = 5) with a cellular concentration of 2.2 +/- 0.2 million/ml and of 55.5 and 39.2 microM with cellular concentrations of 8.9 and 7.2 million/ml, respectively, after only 2.75 h of drug exposure. Damage to mitochondria, but not other organelles, was observed with electron microscopy at an amiodarone concentration of 7.3 microM. Alterations in ATP synthesis and lactate dehydrogenase (LDH) release from cells had concentration-response curves similar to those for cytotoxicity. However, we did not observe extracellular accumulation of adenine nucleotides. These results suggest that amiodarone may have a direct toxic effect on mitochondria, beginning at < 10 microM, with membrane-damaging effects at higher drug concentrations.

Amiodarone-induced pulmonary fibrosis in Fischer 344 rats

Amiodarone is a potent antiarrhythmic agent with a number of side-effects, the most serious being the development of pulmonary toxicity. The purpose of the study was to determine if a single intratracheal instillation of amiodarone would induce pulmonary fibrosis and associated functional changes in rats. Female Fischer 344 rats were given a single intratracheal instillation of 200 microliters containing 1.25 mg amiodarone (n = 9) while the control group received an equivalent volume of sterile water (n = 8). After 6 weeks, pulmonary function tests, lung hydroxyproline measurements and lung histology were performed. The amiodarone-treated animals showed a significant reduction in the coefficient of diffusion (kCO) and a significant increase in lung hydroxyproline levels as compared to the control group. The treated group had abnormal histology including areas of septal thickening with cellular infiltration of the interstitial and alveolar spaces, whereas the control group had normal histology. These observations suggest that the intratracheal instillation route of amiodarone treatment produces a fibrotic response in rats that can be measured physiologically, biochemically and histologically. This model may aid in the elucidation of the mechanism of amiodarone-induced pulmonary toxicity (AIPT)./ABS.

Metabolism of amiodarone following intratracheal instillation in hamsters

Intratracheal instillation of the antiarrhythmic drug amiodarone (AD) in hamsters is an established animal model of AD-induced pulmonary fibrosis. A metabolite of AD, desethylamiodarone (dAD), has also been shown to produce pulmonary fibrosis in this model. It was previously reported that following intratracheal instillation of AD in hamsters, metabolite could not be detected in lung tissue. However, in studies in our laboratory dAD was detected following instillation of AD. The goal of the present study was to monitor the distribution of AD and dAD to lung and liver within 1 h of AD instillation and to investigate the site of AD metabolism. Both AD and dAD were detected in the lung and liver within 5 min of AD instillation; lung and liver concentrations of AD and dAD were also quantified at 30 and 60 min following AD instillation. Incubation of lung and liver microsomes with AD showed that the liver is a probable site of AD metabolism following the intratracheal administration of AD to hamsters.

Acute pulmonary inflammation in hamsters following intratracheal administration of amiodarone

The use of the antiarrythmic drug amiodarone (AD) has been limited by the propensity of the drug to cause severe lung damage. AD has been shown to produce a transient pulmonary fibrosis in hamsters after intratracheal instillation. The goal of this study was to characterize the early inflammatory events associated with the administration of AD. Male Syrian hamsters that were instilled intratracheally with AD or saline vehicle underwent bronchoalveolar lavage (BAL). Total cells, macrophages, and eosinophils obtained by BAL were elevated by AD treatment at day 3. At both days 1 and 3 after instillation, AD-treated animals had significant elevations in neutrophil number. BAL fluid albumin was significantly elevated at day 1 in treated animals. Chemiluminescence (CL) performed on cells obtained by BAL showed an increase in CL of AD-treated samples compared to controls in phorbol myristate acetate (PMA) stimulated CL. PMA-induced increases in responsiveness were diminished by superoxide dismutase and catalase. These results indicate that oxidants such as superoxide and hydrogen peroxide may be involved in this inflammatory process. The results of this study show that intratracheal instillation of AD results in an inflammatory response that can be assessed by cellular, biochemical, and functional means.

Role of the lung in accumulation and metabolism of xenobiotic compounds--implications for chemically induced toxicity

The mammalian lung is exposed to and affected by many airborne and bloodborne foreign compounds. This review summarizes the role of lung in accumulation and metabolism of xenobiotics, some of which are spontaneously reactive or are metabolically activated to toxic intermediates. The specific architectural arrangement of mammalian lung favors that so-called pneumophilic drugs are filtered out of the blood and are retained within the tissue as shown in particular for amphetamine, chlorphentermine, amiodarone, imipramine, chlorpromazine, propranolol, local anaesthetics, and some miscellaneous therapeutics. There is strong evidence that intrapulmonary distribution activity and regulation of drug-metabolizing enzymes in lung is distinct from liver. This review focuses on the metabolic rate of selected compounds in lung such as 5-fluoro-2'-deoxyuridine, local anesthetics, nicotine, benzo(alpha)pyrene, ipomeanol, 4-methylnitrosamino-1-(3-pyridyl)-1-butanone. It is widely accepted that the formation of radical species is a key event in the pneumotoxic mechanisms induced by bleomycin, paraquat, 3-methylindole, butylhydroxytoluene, or nitrofurantoin. Finally, methodological approaches to assess the capacity of lung to eliminate foreign compounds as well as biochemical features of the pulmonary tissue are evaluated briefly.

Resistance of the hamster to amiodarone-induced pulmonary toxicity following repeated intraperitoneal administration

Amiodarone is an effective antidysrhythmic agent, restricted in use by the development of pulmonary toxicity. Several in vivo animal models have been used to study amiodarone-induced pulmonary toxicity. Intratracheal administration of amiodarone to the hamster has been used as a model for the critical amiodarone-induced pulmonary fibrosis (AIPF). In order to investigate the cellular mechanism of human AIPF, which occurs following oral or intravenous administration, an animal model of AIPF resulting from systemic administration of the drug would appear to be preferable. We have evaluated pulmonary toxicity following repeated intraperitoneal amiodarone administration to the hamster. Intraperitoneal treatment of hamsters for 1, 4, or 7 weeks with amiodarone (100 mg/kg/day) did not lead to pulmonary toxicity based on wet lung weight, hydroxyproline content, or histological examination. Furthermore, when comparing 1- and 7-week treatment groups, there was no pulmonary accumulation of either amiodarone or desethylamiodarone beyond levels found at 1 week. Therefore, failure to develop pulmonary toxicity may be due to an inability to accumulate sufficient amiodarone and/or desethylamiodarone. Intratracheal administration of amiodarone to rodents remains the only in vivo animal model for studying the mechanism(s) of AIPF.

Cellular accumulation of amiodarone and desethylamiodarone in cultured human cells. Consequences of drug accumulation on cellular lipid metabolism and plasma membrane properties of chronically exposed cells

Amiodarone (AMIO), a potent antiarrhythmic drug, is clinically widely used despite its frequent side effects after chronic administration. These side effects coincide with an intralysosomal accumulation of AMIO and its main metabolite desethylamiodarone (DEA) and may be causally related to the drug-induced intracellular storage of phospholipids (PL). Kinetics of cellular uptake and release of radiolabelled AMIO and DEA were studied following single and multiple exposures of cultured human skin fibroblasts to 5 and 10 microM drug concentrations. AMIO and DEA were efficiently taken up into cultured cells. The rate of uptake was slower than that of other cationic amphiphilic drugs. The intracellular steady state concentrations were in the millimolar range suggesting a lysosomal trapping. Repetitive exposures of cultures resulted in a cumulative and partly saturable drug uptake. The accumulation of DEA was higher than that of AMIO throughout. AMIO and DEA previously taken up into the cells during a 2 hr exposure were completely released into the washing media, suggesting an exchangeable form of the accumulated drugs. Following repetitive exposures only part of the drugs was released. Under chasing conditions using washing media containing non-labelled AMIO and DEA respectively or ammonium chloride the release of the chronically accumulated 14C-labelled drugs was increased. This suggested a drug storage in the form of complexes in acidic compartments. Phospholipid (PL) content as well as individual PL fractions were changed in whole cells and in isolated plasma membranes. PL accumulation is assumed to occur by inhibition of PL degradation due to formation of non-degradable drug-PL complexes or by inhibition of phospholipase activities. Cellular PL accumulation seemed to interfere with PL recycling. Changes in PL composition of purified plasma membranes were in part complementary to the ones in whole cells. The alterations in membrane PL composition may explain the changes in membrane fluidity and the decrease in beta-adrenoceptor density and in isoproterenol-stimulated cAMP formation. The results obtained provide an explanation for the pharmacokinetic, and possibly for the pharmacodynamic and also toxicological behaviour of AMIO and DEA in vivo.

Immunological tolerance to hapten prevents subsequent induction of hapten-immune pulmonary interstitial fibrosis (HIPIF)

Pulmonary interstitial fibrosis (PIF) is a morphological term which in part can be defined as accumulation of collagen in the extracellular matrix. Previously we showed that hamsters sensitized with 2,4,6-trinitro-1-chlorobenzene (TNCB) developed PIF 14 days after an intratracheal challenge with 2,4,6-trinitrobenzene sulfonic acid (TNBS). The participation of delayed-type hypersensitivity (DTH) in lung collagen deposition was clearly demonstrated. In this paper, we use an adaptation of this model to mice and show that the lung collagen deposition observed was related to the genetic ability of the strain to maintain a DTH response to the immunizing hapten (TNP). Specifically, the lung collagen deposition on Day 14 in hapten-sensitized, challenged animals in high responder to TNP (BALB/c, H-2d) was higher than that in low responder mouse (C57BL/6, H-2b). Furthermore, aged C57BL/6 strain (retired breeders) possessed a DTH response to TNP and produced significantly higher accumulation of hydroxyproline than that of TNBS-challenged-only animals. A DTH mechanism for the induction of the fibrosis is consistent with the observation that responder mice that were made tolerant to the antigen were unable to respond to the lung challenge with a specific increase in lung index or collagen deposition. These results suggest that effector T lymphocytes that are important in DTH play a key role in the regulation of lung collagen deposition in hapten-immune pulmonary interstitial fibrosis (HIPIF) in mice.

Amiodarone pulmonary toxicity

Amiodarone is an effective antiarrhythmic agent whose utility is limited by many side-effects, the most problematic being pneumonitis. The pulmonary toxicity of amiodarone is thought to result from direct injury related to the intracellular accumulation of phospholipid and T cell-mediated hypersensitivity pneumonitis. The clinical and radiographic features of amiodarone-induced pulmonary toxicity are characteristic but nonspecific. The diagnosis depends on exclusion of other entities, such as heart failure, infection, and malignancy. While withdrawal of amiodarone leads to clinical improvement in majority of cases, this is not always possible or advisable. Dose reduction or concomitant steroid therapy may have a role in selected patients.

Accumulation of amiodarone and desethylamiodarone by rat alveolar macrophages in cell culture

Amiodarone is a clinically effective antiarrhythmic drug shown to cause lung damage in humans and animals. While the mechanism of this pulmonary toxicity is unknown, it may be associated with the accumulation of amiodarone and its principal metabolite, desethylamiodarone, by alveolar macrophages. In the present study, characteristics of the uptake of these drugs by rat alveolar macrophages in vitro were examined. The alveolar macrophages were collected by pulmonary lavage from male Fischer 344 rats. Amiodarone and desethylamiodarone were incubated separately (2.5 microM) with the cells in culture for 1, 2, 4 and 18 hr. High performance liquid chromatography was used to measure drug uptake. At 1 and 2 hr, the uptake of desethylamiodarone by alveolar macrophages was significantly greater (P less than 0.05) than that of amiodarone, but over time, the accumulation of amiodarone began to approach that of desethylamiodarone and was not significantly different by 4 hr. To simulate a more physiological situation, plasma levels achieved in the adult male rat after 1 week of amiodarone treatment (150 mg/kg) were used. Amiodarone (1.95 micrograms/mL) and desethylamiodarone (0.80 microgram/mL) were added together into the cell culture. At 1 and 18 hr, the ratio of desethylamiodarone/amiodarone uptake was significantly greater (P less than 0.05) than in incubation medium containing no cells, indicating an enhanced uptake of desethylamiodarone. Metabolic inhibitors (KCN, 2,4-dinitrophenol, and ouabain) and other cationic, amphiphilic drugs (chlorcyclizine, chlorphentermine, and imipramine) were added individually to the cell cultures containing amiodarone or desethylamiodarone. During 1 hr of incubation, these agents had no effect in blocking the accumulation of amiodarone and desethylamiodarone in the cells. The efflux of amiodarone or desethylamiodarone was measured from cells following incubation for 4 hr with each drug. After this time, the medium was replaced with drug-free medium, and the cells were incubated for another 24 hr. Sixty-three percent of amiodarone was lost as compared to only 31% of desethylamiodarone over the 24-hr period (P less than 0.05). The results of this study are suggestive of a preferential uptake and retention of desethylamiodarone as compared to amiodarone. The accumulation of the drugs appears not to be due to active transport or associated with any carrier protein involved in the transport of other structurally-related compounds.

Response of alveolar macrophages to amiodarone and desethylamiodarone, in vitro

Administration of the antiarrhythmic drug amiodarone to humans or animals may result in lung damage. Amiodarone is metabolized to desethylamiodarone and other minor metabolites. Because amiodarone and the metabolites accumulate in the lungs, it is not possible to ascertain the role of each of these compounds in the induction of toxicity. In the present study, we utilized primary cell cultures of rat alveolar macrophages to study the actions of amiodarone and desethylamiodarone individually and in combination. Neither drug species was metabolized by the cells over 42 h in culture thereby permitting assessment of the actions of each. Both drugs induced the formation of lamellar inclusions, indicative of the development of cellular phospholipidosis. Desethylamiodarone appeared to induce formation of the structures in a shorter period of time than did amiodarone, although given adequate exposure, the two drugs produced similar responses. At shorter times of exposure and lower concentrations, desethylamiodarone was more cytotoxic than amiodarone as assessed by the release of lactate dehydrogenase. The two in combination resulted in cytotoxicity that was more than additive. The results of this study indicate that in vitro cultures of alveolar macrophages may be quite useful in studying the role these cells play in the pulmonary toxicity associated with amiodarone therapy. Additionally, this study supports the idea that a significant portion of the toxicity may result from the actions of desethylamiodarone.