The histopathological evaluation of the effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy in a rat model.

ABSTRACT

PURPOSE: This study presents the histopathological evaluation of the effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy. MATERIALS AND METHODS: Thirty-two Wistar rats were divided into four groups. The rats in Group 1 received melatonin and underwent radiation therapy. The rats in Group 2 received no melatonin and underwent radiation therapy. The rats in Group 3 received melatonin and underwent sham radiation therapy. The rats in Group 4 received no melatonin and underwent sham radiation therapy. Melatonin was administered at a dose of 100 mg/kg using an intraperitoneal injection. Radiation therapy was delivered on a Cobalt-60 unit using a single fraction of 18 Gy through an anterior portal covering the right lung in entirety. The rats underwent euthanasia at 6 weeks following radiation therapy. The lungs were dissected and blinded histopathological evaluation was performed. RESULTS: Concerning the right lung, a decrease in intra-alveolar edema and intra-alveolar erythrocytes was observed despite an increase in activated macrophages, intra-alveolar fibrosis, hyaline arteriosclerosis and alveolar wall thickness for the rats in Group 1 as compared to the rats in Group 2. Concerning the left lung, a decrease in alveolar neutrophils and intra-alveolar erythrocytes was evident despite an increase in activated macrophages, hyaline arteriosclerosis and alveolar wall thickness for the rats in Group 1 as compared to the rats in Group 2. CONCLUSIONS: This study puts forward the histopathological evidence regarding the effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy through restrained inflammation, regrettably at the expense of promoted fibrosis. The effectiveness of melatonin as a protectant against acute lung injury induced by radiation therapy needs to be evaluated further for the unresolved concerns regarding the safety.