The role of free radicals in the pathogenesis of amiodarone toxicity.
BACKGROUND
In vitro and in vivo studies were performed to elucidate the pathogenesis of amiodarone toxicity.


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.


CONCLUSIONS
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.
Vereckei
A
A
Second Department of Medicine, Semmelweis Medical School, Budapest, Hungary.
Blazovics
A
A
Gyorgy
I
I
Feher
E
E
Toth
M
M
Szenasi
G
G
Zsinka
A
A
Foldiak
G
G
Feher
J
J
D000638:Amiodarone / Q000633:toxicity*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D005609:Free Radicals; D066298:In Vitro Techniques; D015227:Lipid Peroxidation; D008099:Liver / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D008163:Luminescent Measurements; D008168:Lung / Q000187:drug effects / Q000473:pathology / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D017208:Rats, Wistar
D000975:Antioxidants; D005609:Free Radicals; D000638:Amiodarone