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 we re treated with amiodarone alone (500 mg/kg body weight per day) or to gether with antioxidants (silibinin or MTDQ-DA: 50 mg/kg body weight p er 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 wa s inhibited by the two dihydroquinolin-type antioxidants (MTDQ-DA, CH 402). Chemiluminometric results from liver homogenate demonstrated tha t simultaneous treatment with silibinin partially prevented the liver homogenate superoxide anion radical scavenger capacity decreasing effe ct of amiodarone. Amiodarone treatment caused a significant increase o f NADPH and Fe3+ induced lipid peroxidation in the liver microsomal fr action, which antioxidants (silibinin, MTDQ-DA) were unable to prevent . Light microscopy of the lung tissue in amiodarone-treated rats showe d accumulation of foamy macrophages with thickening of the interalveol ar septa, pneumonitis, and variable interstitial fibrosis. Antioxidant treatment did not prevent these changes. Electron micrographs of lung from amiodarone-treated rats showed lysosomal phospholipoidosis, intr alysosomal 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 rem ained the same. Simultaneous treatment with silibinin and amiodarone d ecreased 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 (Co-60-ga mma) radiolysis studies showed that the main free radical product in a reducing environment was a very reactive aryl radical formed after th e partial deiodination of the amiodarone molecule. The radiosensitizin g effect of amiodarone was also verified in rat liver microsomal prepa rations using in vivo amiodarone with or without MTDQ-DA pretreatment and Co-60-gamma irradiation with or without the in vitro addition of a ntioxidants (CH 402, MTDQ-DA). In vivo, the MTDQ-DA treatment also had a radiosensitizing effect; however, the in vitro addition of both ant ioxidants resulted in a radio-protective effect. The aryl radical also may emerge in vivo during the metabolism of amiodarone. Conclusion: T hese observations suggest that amiodarone in vitro and in vivo generat es free radicals that may play a role in the pathogenesis of amiodaron e toxicity beside other well-established mechanisms, and antioxidants may have a partial protective effect against amiodarone toxicity.