Spectroscopic studies of cutaneous photosensitizing agents--IX. A spin trapping study of the photolysis of amiodarone and desethylamiodarone

The Rationale for "Laser-Induced Thermal Therapy (LITT) and Intratumoral Cisplatin" Approach for Cancer Treatment

Cisplatin is one of the most widely used anticancer drugs in the treatment of various types of solid human cancers, as well as germ cell tumors, sarcomas, and lymphomas. Strong evidence from research has demonstrated higher efficacy of a combination of cisplatin and derivatives, together with hyperthermia and light, in overcoming drug resistance and improving tumoricidal efficacy. It is well known that the antioncogenic potential of CDDP is markedly enhanced by hyperthermia compared to drug treatment alone. However, more recently, accelerators of high energy particles, such as synchrotrons, have been used to produce powerful and monochromatizable radiation to induce an Auger electron cascade in cis-platinum molecules. This is the concept that makes photoactivation of cis-platinum theoretically possible. Both heat and light increase cisplatin anticancer activity via multiple mechanisms, generating DNA lesions by interacting with purine bases in DNA followed by activation of several signal transduction pathways which finally lead to apoptosis. For the past twenty-seven years, our group has developed infrared photo-thermal activation of cisplatin for cancer treatment from bench to bedside. The future development of photoactivatable prodrugs of platinum-based agents injected intratumorally will increase selectivity, lower toxicity and increase efficacy of this important class of antitumor drugs, particularly when treating tumors accessible to laser-based fiber-optic devices, as in head and neck cancer. In this article, the mechanistic rationale of combined intratumor injections of cisplatin and laser-induced thermal therapy (CDDP-LITT) and the clinical application of such minimally invasive treatment for cancer are reviewed.

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.

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

Amiodarone (AM), a drug used in the treatment of cardiac dysrrhythmias, can produce severe pulmonary adverse effects, including fibrosis. Although the pathogenesis of AM-induced pulmonary toxicity (AIPT) is not clearly understood, several hypotheses have been advanced, including increased inflammatory mediator release, mitochondrial dysfunction, and free-radical formation. The hypothesis that AM induces formation of reactive oxygen species (ROS) was tested in an in vitro model relevant for AIPT. Human peripheral lung epithelial HPL1A cells, as surrogates for target cells in AIPT, were susceptible to the toxicity of AM and N-desethylamiodarone (DEA), a major AM metabolite. Longer incubations (> or =6 h) of HPL1A cells with 100 microM AM significantly increased ROS formation. In contrast, shorter incubations (2 h) of HPL1A cells with AM resulted in mitochondrial dysfunction and cytoplasmic cytochrome c translocation. Preexposure of HPL1A cells to ubiquinone and alpha-tocopherol was more effective than that with Trolox C or 5,5-dimethylpyrolidine N-oxide (DMPO) at preventing AM cytotoxicity. These data suggest that mitochondrial dysfunction, rather than ROS overproduction, represents an early event in AM-induced toxicity in peripheral lung epithelial cells that may be relevant for triggering AIPT, and antioxidants that target mitochondria may potentially have beneficial effects in AIPT.

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.

Silymarin and vitamin E reduce amiodarone-induced lysosomal phospholipidosis in rats

Several antioxidants have been shown to reduce lysosomal phospholipidosis, which is a potential mechanism of amiodarone toxicity, and prevent amiodarone toxicity by antioxidant and/or non-antioxidant mechanisms. The aim of this study was to test whether the co-administration of two structurally different antioxidants vitamin E and silymarin with amiodarone can reduce amiodarone-induced lysosomal phospholipidosis, and if yes, by reducing the tissue concentration of amiodarone and desethylamiodarone or by their antioxidant action. To this end, male Fischer 344 rats were treated by gavage once a day for 3 weeks and randomly assigned to the following four experimental groups: 1, control; 2, amiodarone (150 mg/(kg per day)); 3, amiodarone (150 mg/(kg per day)) plus vitamin E (100 mg/(kg per day)); 4, amiodarone (150 mg/(kg per day)) plus silymarin (60 mg/(kg per day)) treated groups. Total plasma phospholipid (PL), liver-conjugated diene, thiobarbituric acid reactive substances (TBARSs), amiodarone and desethylamiodarone concentrations were determined and the extent of lysosomal phospholipidosis in the liver was estimated by a semi-quantitative electron microscopic method. Amiodarone treatment increased significantly the liver-conjugated diene (P<0.001), TBARS (P=0.012), plasma total PL (P<0.001) concentrations compared with control. Antioxidants combined with amiodarone significantly decreased the liver-conjugated diene (P<0.001 for both), TBARS (P=0.016 for vitamin E, P=0.053 borderline for silymarin) and plasma total PL (P=0.058 borderline for vitamin E, P<0.01 for silymarin) concentrations compared with amiodarone treatment alone. Silymarin significantly (P=0.021) reduced liver amiodarone, but only tended to decrease desethylamiodarone concentration; however, vitamin E failed to do so. Amiodarone treatment increased lysosomal phospholipidosis (P<0.001) estimated by semi-quantitative electron microscopic method and both antioxidants combined with amiodarone reduced significantly (P<0.001 for both) the amiodarone-induced lysosomal phospholipidosis. In conclusion, silymarin presumably reduced lysosomal phospholipidosis by both antioxidant action and its liver amiodarone concentration decreasing effect, while vitamin E exerted similar effect by antioxidant action alone. Thus, both antioxidant action and inhibition of tissue uptake of amiodarone might have an important role in the preventative effect of antioxidants against amiodarone toxicity.

Combined amiodarone and silymarin treatment, but not amiodarone alone, prevents sustained atrial flutter in dogs

Amiodarone/Silymarin Treatment for Sustained Atrial Flutter.

INTRODUCTION

Because amiodarone generates free radicals that may mediate amiodarone's toxicity, simultaneous therapy with an antioxidant might be beneficial if the antioxidant did not impair amiodarone's antiarrhythmic action. We tested whether simultaneous administration of a flavonoid antioxidant, silymarin, altered the electrophysiologic (EP) actions of amiodarone in 62 open chest dogs with electrically induced atrial flutter created by a Y-shaped right atrial incision.

METHODS AND RESULTS

Fifteen dogs received oral amiodarone (600 mg/day); 15 dogs received amiodarone (600 mg/day) and silymarin (70 mg bid); and 8 dogs received silymarin (70 mg bid) alone. All dosing was for 8 weeks; 24 control dogs received no drugs prior to induction of atrial flutter. Atrial flutter was induced by rapid right atrial pacing, and EP measurements were made before (presurgical) and after (postsurgical) creation of a Y-shaped right atrial incision. There was no difference in the frequency of induction of atrial flutter lasting >30 minutes among amiodarone-treated (8/15 [53%]), silymarin-treated (4/6 [67%]), and control (15/21 [71%]) groups, whereas the frequency of induction in the amiodarone+silymarin dogs (2/15 [13%]) was significantly reduced (P = 0.008) compared with the other three groups. Both amiodarone and amiodarone+silymarin treatment prolonged the presurgical and postsurgical right atrial effective refractory period (P = 0.012) compared with control; however, there was no significant difference in either parameter between the amiodarone+silymarin-treated and amiodarone-treated groups. The increase in atrial flutter mean cycle length (postsurgical minus presurgical) was significantly (P = 0.005) less in the amiodarone+silymarin-treated and control dogs compared with the amiodarone-treated dogs (16 +/- 11 msec for amiodarone+silymarin; 24 +/- 8 msec for control; and 42 +/- 14 msec for amiodarone treatment). Amiodarone+silymarin treatment resulted in a longer postsurgical right atrial refractory period (155 +/- 13 msec) than atrial flutter mean cycle length (154 +/- 19 msec), consistent with reduction and/or elimination of the excitable gap. Silymarin alone did not exert significant EP or antiarrhythmic action.

CONCLUSION

Amiodarone exerted no preventative antiarrhythmic action in this atrial flutter model, probably because it could not reduce the excitable gap of atrial flutter. However, an antioxidant, silymarin, without a direct antiarrhythmic action, when administered together with amiodarone, potentiated amiodarone's antiarrhythmic actions and prevented sustained atrial flutter by reduction and/or elimination of the excitable gap.

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.

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.

The effect of amiodarone and/or antioxidant treatment on splenocyte blast transformation

Previous studies have shown that free radical reactions may play an important role in the pathogenesis of the adverse effects of the antiarrhythmic agent amiodarone. The aim of this study was to investigate the role of free radical reactions in amiodarone-induced changes in the cell-mediated immune response. Therefore, we investigated the effects of amiodarone alone and in combination with either vitamin E or silymarin on (a) spontaneous blast transformation of splenocytes, (b) concanavalin A (con A)-induced proliferation of splenocytes at three different lectin concentrations, and (c) the content of conjugated dienes in liver homogenate. Forty-eight male Fischer 344 rats were randomized to one of the following groups: 1, control; 2, amiodarone; 3, vitamin E; 4, amiodarone+vitamin E; 5, silymarin; 6, amiodarone+silymarin. The con A-induced splenocyte proliferation was significantly decreased in amiodarone-treated rats at all three lectin concentrations. In the amiodarone-treated group, the change of spontaneous blast transformation was not significantly different from the control. In groups treated with amiodarone plus either antioxidant, both the spontaneous and con A-induced splenocyte proliferation were significantly increased compared with the amiodarone-treated group, and were similar to those in the control group. Amiodarone treatment significantly increased, and both silymarin and vitamin E combined with amiodarone significantly decreased, the conjugated diene content of liver homogenate compared with amiodarone treatment alone. In conclusion, free radicals generated by amiodarone may be implicated in the adverse effects of amiodarone on cell-mediated immune response, and antioxidants applied together with amiodarone may protect against or reduce both the unfavorable immunological effects of amiodarone and amiodarone toxicity.

Cell damage induced by Angiovist-370 and 308nm excimer laser radiation

BACKGROUND AND OBJECTIVE

Radiographic contrast media containing iodine-labeled organic compounds can be present in the irradiated field during laser angioplasty using 308 nm excimer laser radiation. These compounds absorb light at 308 nm and may undergo photochemical reactions that produce products that damage cells.

STUDY DESIGN/MATERIALS AND METHODS

This study was undertaken to determine whether photoproducts that damage human lymphocytes in vitro are formed when Angiovist 370 (AV), a contrast medium containing triiodinated aromatic compounds, is exposed to 308 nm radiation.

RESULTS

The absorption spectrum of AV developed a new peak at 360 nm that extended to wavelengths greater than 500 nm when dilute AV solutions were exposed to 308 nm radiation indicating that photoproducts were formed. Irradiating dilute AV solutions above a layer of human lymphocytes caused a dose-dependent decrease in thymidine incorporation using fluence rates between 5.2 x 10(6) and 1.0 x 10(8) W/cm2. Decreased DNA synthesis was independent of the pulse length (10 ns vs. 230 ns) but was lower, at a given dose, when the highest fluence rate was used. Incubation of lymphocytes with preirradiated AV solutions also decreased incorporation of thymidine in a radiation dose-dependent manner. The cell damaging photoproducts in preirradiated AV solutions were unstable; within 15 min, the effectiveness had decreased by approximately 85%.

CONCLUSIONS

These results indicate that exposure of AV to 308 nm excimer laser radiation produces photochemical products that damage human cells in vitro.

Amiodarone is a pharmacologically safe drug for porphyrias

Amiodarone (AD) is an effective antidysrythmic drug, however, there can be serious side effects, such as hepatic and neurological alterations, as well as skin photosensitization, as seen in porphyrias. Clinical signs in porphyrias might be triggered by the so-called porphyrinogenic drugs. Without sound basis, Amiodarone has been classified as an unsafe drug for porphyric patients. The aim of this work has been to study the effect of AD, both in vivo and in vitro, on heme metabolism. In the in vivo assays, the activities of 5-aminolevulinate synthetase (ALA-S), ALA dehydratase (ALA-D), porphobilinogenase (PBGase) and PBG-deaminase (PBG-D) in blood, liver, and kidney; hepatic and fecal porphyrins, urinary ALA, PBG and porphyrins in male mice strain CF1 treated with AD (100 mg i.p. daily) for 1 week and 1 month, were measured. No significanat differences were found for any of these parameters in the AD treated animals as compared to controls. In the in vitro experiments human blood, and mice blood, liver, and kidney, were used to measure the activities of ALA-S, ALA-D, PBGase, PBG-D and uroporphyrinogen decarboxylase, in the presence of varying concentrations of AD (0.0172-4.304 mM). AD did not modify any of the enzyme activities. All of the above biochemical parameters were studied in 17 cardiac patients under AD treatment for 3 to 20 years. Neither the activities of the heme enzymes, nor the levels of precursors and porphyrins in urine and plasma were altered. These findings clearly demonstrate that AD is a pharmacologically safe drug and can be used for the treatment of associated pathologies in porphyrias.

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.

Photosensitizing drugs containing the benzophenone chromophore

The nonsteroidal anti-inflammatory agents ketoprofen, tiaprofenic acid, suprofen and tolmetin, together with the anti-hyperlipoproteinemic drug fenofibrate and the anti-arrhythmic amiodarone can be included in the group of benzophenone-derived photosensitizing drugs. They contain a diaryl ketone chromophore and mediate the development of phototoxic reactions. In some cases, photoallergic responses have been reported. These properties have been substantiated in clinical reports, as well as by means of in vivo and in vitro assays. Tolmetin is phototoxic in vitro, however there are no reports on photosensitization by this drug in humans. In general, photochemical and photobiological studies strongly suggest that photosensitization involves formal hydrogen abstraction (either in a single step or via electron transfer followed by proton transfer) by the benzophenone-like chromophore from the excited triplet state. In the case of amiodarone, the radicals generated by photodehalogenation from the triplet are responsible for the photosensitivity side-effects.

Effect of amiodarone (AMD) on the antioxidant enzymes, lipid peroxidation and mitochondrial metabolism

The effects of amiodarone (AMD) on lipid peroxidation of rat liver mitochondria, the formation of superoxide anions at the respiratory chain level, and the cytosolic and mitochondrial enzymatic protective mechanisms of oxidative stress were studied. An attempt of classify AMD according to its toxic ability to interfere with the integrated function of electron transport enzymes was also investigated. The results confirm the effects of AMD on complex I and permit the placing of this drug in class A of the classification of Knobeloch, together with rotenone, amytal and chaotropic agents. AMD has no effect on the activity of the enzymes superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase, nor on glucose 6-phosphate dehydrogenase. AMD did not promote an increase in the formation of anion superoxide at the respiratory chain level. Pre-incubation with AMD (16.6 microM) inhibited about 70 per cent of lipid peroxidation. The results suggest a protective effect of AMD against lipid peroxidation in mitochondrial membranes by iron-dependent systems.

Photodegradation products of sulphonamide-derived oral antidiabetics and diuretics are not phototoxic in vitro

The oral antidiabetics glibenclamide and glipizide, and the diuretics bendroflumethiazide and furosemide, all sulphonamide derived drugs, were investigated in vitro for phototoxic properties. Irradiation with broad-band UV induced phototoxic inhibition of colony forming ability in cell cultures. During irradiation, the substances lost one absorption maximum in the UVA region, demonstrated by UV spectroscopy. These findings correlate well with the UV applied, the action spectrum being in the UVA region. Photoproducts detected during and after irradiation showed a decomposition of the substances due to ionization and fragmentation. Incubation of these preirradiated drugs with the cell cultures revealed no phototoxic effects.

The role of free radicals in the pathogenesis of amiodarone toxicity

INTRODUCTION

In vitro and in vivo studies were performed to elucidate the pathogenesis of amiodarone toxicity.

METHODS AND RESULTS

Rats were treated with amiodarone alone (500 mg/kg body weight per day) or together with antioxidants (silibinin or MTDQ-DA: 50 mg/kg body weight per day) or with either antioxidant alone. They received amiodarone for 30 days and antioxidant for 33 days (3 days pretreatment). In vitro, amiodarone induced a dose-dependent chemiluminescence signal, which was inhibited by the two dihydroquinolin-type antioxidants (MTDQ-DA, CH 402). Chemiluminometric results from liver homogenate demonstrated that simultaneous treatment with silibinin partially prevented the liver homogenate superoxide anion radical scavenger capacity decreasing effect of amiodarone. Amiodarone treatment caused a significant increase of NADPH and Fe3+ induced lipid peroxidation in the liver microsomal fraction, which antioxidants (silibinin, MTDQ-DA) were unable to prevent. Light microscopy of the lung tissue in amiodarone-treated rats showed accumulation of foamy macrophages with thickening of the interalveolar septa, pneumonitis, and variable interstitial fibrosis. Antioxidant treatment did not prevent these changes. Electron micrographs of lung from amiodarone-treated rats showed lysosomal phospholipoidosis, intralysosomal electron dense deposits, and increased lysosome number and size. In contrast to rats treated with amiodarone alone, those treated with both amiodarone and silibinin had significantly fewer lysosomes (P < 0.01); the lysosome size, shape, and internal characteristics remained the same. Simultaneous treatment with silibinin and amiodarone decreased lysosomal phospholipoidosis compared to amiodarone treatment alone. Simultaneous treatment with MTDQ-DA and amiodarone did not show any beneficial effect. Pulse radiolysis and cobalt 60-gamma (60Co-gamma) radiolysis studies showed that the main free radical product in a reducing environment was a very reactive aryl radical formed after the partial deiodination of the amiodarone molecule. The radiosensitizing effect of amiodarone was also verified in rat liver microsomal preparations using in vivo amiodarone with or without MTDQ-DA pretreatment and 60Co-gamma irradiation with or without the in vitro addition of antioxidants (CH 402, MTDQ-DA). In vivo, the MTDQ-DA treatment also had a radiosensitizing effect; however, the in vitro addition of both antioxidants resulted in a radioprotective effect. The aryl radical also may emerge in vivo during the metabolism of amiodarone.

CONCLUSION

These observations suggest that amiodarone in vitro and in vivo generates free radicals that may play a role in the pathogenesis of amiodarone toxicity beside other well-established mechanisms, and antioxidants may have a partial protective effect against amiodarone toxicity.

High-performance liquid chromatographic assay for amiodarone N-deethylation in microsomes of rat liver

A reversed-phase high-performance liquid chromatographic assay using ultraviolet detection is described for determining the production of the major N-dealkylated metabolite of amiodarone in rat liver microsomes. The principal advantages of this method are its simple sample preparation (protein precipitation by acetonitrile), low detection limit for N-desethylamiodarone (0.05 mumol/l) and relatively short analysis time (16 min). Its analytical applicability is demonstrated by the comparison of the kinetic parameters (maximum velocity and Michaelis-Menten constant) between Sprague-Dawley and Dark-Agouti rats.

Interactions of amiodarone with model membranes and amiodarone-photoinduced peroxidation of lipids

The potent antiarrhythmic drug, amiodarone (AMIO) exhibits phototoxicity, which is thought to be related to its interaction with biological membranes. We report here a spectroscopic study of the interactions of this drug with phosphatidylglycerol (PG) and phosphatidylcholine (PC) liposomes used as membrane model systems. A linear increase in absorbance at 300 nm was observed with increasing addition of AMIO to dimyristoyl-DL-PC (DMPC) liposomes over all the drugs-lipid molar ratio (Ri)s tested. In contrast, in the dimyristoyl-DL-PG (DMPG) liposomes, there was a dramatic increase in absorbance at values of Ri above unity. Light scattering by DMPG liposomes at 350 nm increased with increasing AMIO concentration up to a Ri = 1, and then decreased with increasing drug concentration. Such changes were not observed with the DMPC liposomes. Moreover, addition of AMIO changed the fluorescence polarization rate of 1,6-diphenyl 1,3,5-hexatriene embedded in these liposomes. It reduced the rate below the phase transition temperature (Tt) of the lipid, but increased it above this temperature. These effects on the lipidic phases observed at low Ri were more pronounced on the DMPG than on the DMPC liposomes. The strong interactions of AMIO with phospholipids, especially the acidic ones, were confirmed by liposome size determinations. All these data strongly suggest that the drug was incorporated in the core of the lipid bilayers. Such a penetration would favor a drug-photoinduced peroxidation of lipids. Indeed, UV irradiation of AMIO-DOPG mixtures led to the disappearance of the unsaturated fatty acids of phospholipids, checked by gas chromatography measurements, which was correlated with the amount of oxygen consumed. This showed that AMIO did photosensitize phospholipid peroxidation.

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.

Radical adducts of nitrosobenzene and 2-methyl-2-nitrosopropane with 12,13-epoxylinoleic acid radical, 12,13-epoxylinolenic acid radical and 14,15-epoxyarachidonic acid radical. Identification by h.p.l.c.-e.p.r. and liquid chromatography-thermospray-m.s

Linoleic acid-derived radicals, which are formed in the reaction of linoleic acid with soybean lipoxygenase, were trapped with nitrosobenzene and the resulting radical adducts were analysed by h.p.l.c.-e.p.r. and liquid chromatography-thermospray-m.s. Three nitrosobenzene radical adducts (peaks I, II and III) were detected; these gave the following parent ion masses: 402 for peak I, 402 for peak II, and 386 for peak III. The masses of peaks I and II correspond to the linoleic acid radicals with one more oxygen atom [L(O).]. The radicals are probably carbon-centred, because the use of 17O2 did not result in an additional hyperfine splitting. Computer simulation of the peak I radical adduct e.p.r. spectrum also suggested that the radical is carbon-centred. The peak I radical was also detected in the reaction of 13-hydroperoxylinoleic acid with FeSO4. From the above results, peak I is probably the 12,13-epoxylinoleic acid radical. An h.p.l.c.-e.p.r. experiment using [9,10,12,13-2H4]linoleic acid suggested that the 12,13-epoxylinoleic acid radical is a C-9-centred radical. Peak II is possibly an isomer of peak I. Peak III, which was observed in the reaction mixture without soybean lipoxygenase, corresponds to a linoleic acid radical (L.). The 12,13-epoxylinoleic acid radical, 12,13-epoxylinolenic acid radical and 14,15-epoxyarachidonic acid radical were also detected in the reactions of linoleic acid, linolenic acid and arachidonic acid respectively, with soybean lipoxygenase using nitrosobenzene and 2-methyl-2-nitrosopropane as spin-trapping agents.

Evaluation of amiodarone free radical toxicity in rat hepatocytes

The possible roles of free radicals and lipid peroxidation in the mechanism of toxicity of amiodarone (AD) [2-butyl-3-(3',5'-diiodo-4' alpha-diethylaminoethoxybenzoyl)benzofuran] and its principle metabolite, desethylamiodarone (DE), were examined in primary cultured Sprague-Dawley male rat hepatocytes. AD (20 and 40 micrograms/ml) and DE (10 and 25 micrograms/ml) killed hepatocytes in concentration- and time-dependent fashions. Several antioxidants [Cu,Zn-superoxide dismutase (200 U/ml), catalase (200 U/ml), N,N'-diphenylphenylenediamine (DPPD; 25 microM), butylated hydroxytoluene (0.1 mM), and N-acetylcysteine (5 mM)] were incapable of preventing AD and DE hepatocyte toxicity. Only vitamin E (VE, d,l-alpha-tocopherol acetate; 20-200 microM) prevented AD and DE toxicity. No correlation between the onset of hepatocyte death by AD and DE and hepatocyte lipid peroxidation was seen. Both drugs inhibited NADPH-dependent rat liver microsomal superoxide production. These results, excluding the preventive effects of VE, do not support a free radical/lipid peroxidation mechanism of hepatocyte toxicity by AD and DE. VE may have prevented hepatocyte toxicity through non-antioxidant effects.

Relation of amiodarone hepatic and pulmonary toxicity to serum drug concentrations and superoxide dismutase activity

Hepatic enzymes, pulmonary function, serum amiodarone and desethylamiodarone (DEA) concentrations and erythrocyte superoxide dismutase (SOD) activity were monitored at regular intervals for 1 year in 30 patients receiving amiodarone. Subclinical hepatotoxicity developed in 5 patients. These patients had higher baseline alanine transaminase values (42.6 +/- 6.8 vs 22.9 +/- 1.8 U/liter) and had an increase in serum aspartate transaminase from 27 +/- 4.1 at baseline to 147 +/- 77.3 U/liter at 12 months. The other patients had little variation in aspartate transaminase. Six patients with normal baseline carbon monoxide diffusing capacity had subclinical pulmonary toxicity develop with a mean decrease in diffusing capacity to 0.7 +/- 0.05 of the baseline value, which correlated with decreasing erythrocyte SOD activity. Mean carbon monoxide diffusing capacity and SOD activity remained unchanged in the other patients. The mechanisms of hepatic and pulmonary injury remain unknown, but appear to be associated with exposure to higher total serum concentrations of amiodarone plus DEA. Patients who had hepatic and/or pulmonary abnormalities develop received higher doses of amiodarone (440 +/- 27 vs 340 +/- 18 mg/day), but also had a higher amiodarone:DEA ratio suggesting that dose-dependent kinetics contributed to the higher concentrations. Elevated baseline alanine transaminase may indicate increased risk for hepatotoxicity while a progressive decrease in erythrocyte SOD may be an early indication of pulmonary toxicity. The latter finding indicates a need to investigate the role of free radicals in the pathogenesis of amiodarone pulmonary toxicity.

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.

Near UV-induced free radicals in ocular lens, studied by ESR and spin trapping

An electron spin resonance (ESR) study on UV-photolysis of human and canine lens nuclei was carried out at room temperature. (1) At least two kinds of free radical signals, a narrow signal and a broad one, were detected at around g = 2.004. The latter is similar to that observed upon irradiation of a model solution containing both tryptophan and cysteine. (2) Two spin adducts were detected upon irradiation of canine lens in the presence of a spin trapping reagent (DMPO, 5,5-dimethyl-1-pyrroline N-oxide), i.e. a spin adduct of sulphur-centered radical (most likely glutathione thiyl radical) and the protonated adduct of solvated electron (presumably due to photo-ionization of tryptophan). (3) A tentative and simplified reaction mechanism of UV-induced damage is discussed on the basis of these observations.

O2- photogenerated from aqueous solutions of tetracycline antibiotics (pH 7.3) as evidenced by DMPO spin trapping and cytochrome c reduction

UV-irradiation of several tetracycline antibiotics in aqueous buffer (pH 7.3) resulted in the generation of the superoxide anion radical (O2-) which was detected by cytochrome c reduction and by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide and was inhibited by superoxide dismutase. A comparison of the O2- yields from the tetracyclines examined showed the trend chlortetracycline (CTC) greater than oxytetracycline (OXY) greater than demeclocycline (DEM) much greater than (doxycycline (DOXY) = tetracycline (TC) = minocycline (MINO) = 0). This trend is in reasonable agreement with clinical reports that CTC, OXY and DEM are potent photosensitizers, TC is only weakly phototoxic whereas MINO is not. These findings suggest that the O2- production may be involved in tetracycline-induced phototoxicity. While the two methods for O2- detection gave comparable results for most of the tetracyclines, the spin trapping technique was clearly superior for DOXY which reduced cytochrome c in the dark.