Evaluation of reactive oxygen species involvement in amiodarone pulmonary toxicity in vivo and in vitro.

Amiodarone (AM) is an effective antidysrhythmic agent, restricted in use by the development of adverse effects, including potentially fatal AM-induced pulmonary toxicity (AIPT). Although the pathogenesis of AIPT is unknown, an oxidant mechanism has been proposed. The present study evaluated the role of reactive oxygen species (ROS) in AM-induced toxicity. The effect of inhibiting lung antioxidant defense on in vivo development of AIPT was evaluated in hamsters. Lung glutathione reductase activity was inhibited by 66%, 6 hours following administration of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) (20 mg/kg i.p.). When AM (1.83 mumol) was administered intratracheally 6 hours after BCNU, toxicity was enhanced, as indicated by lung hydroxyproline content and histological evaluation 21 days later. However, BCNU treatment did not affect AM-induced alterations in lung glutathione, suggesting that the increased toxicity was not due to decreased antioxidant capacity following BCNU. The effect of BCNU on AM cytotoxicity in vitro was evaluated using rabbit lung alveolar macrophages. Incubation with 5 microM BCNU for 2 hours caused greater than 95% inhibition of glutathione reductase activity. However, BCNU treatment had no effect on 146 microM AM-induced cytotoxicity, as assessed by lactate dehydrogenase latency following 12 hours of incubation. Rabbit macrophages loaded with 2',7'-dichlorofluorescein, which is oxidized by ROS to fluorescent 2',7'-dichlorofluorescein (DCF), were used to evaluate ROS generation by AM. Incubation of macrophages with AM (73 or 146 microM) for 1 hour, with or without the catalase inhibitor sodium azide (1 mM), did not result in DCF formation. Overall, these results do not support the hypothesis that AIPT is due to ROS action.