Melatonin attenuates lung ischaemia-reperfusion injury via inhibition of oxidative stress and inflammation.

OBJECTIVES Lung ischaemia-reperfusion injury is a complex pathophysiological process due to the production of reactive oxygen species and the generation of inflammatory reaction. We investigated the protective effects and the corresponding mechanism of melatonin (MT), a potent free-radical scavenger, on lung injury induced by ischaemia-reperfusion in a mouse model. METHODS Adult male C57BL/6J mice (n = 30) were randomly and equally allocated into 5 groups: sham controls, IR, IR + 10 mg/kg MT, IR + 20 mg/kg MT and IR + 30 mg/kg MT. Lung ischaemia-reperfusion injury was induced by thoracotomy followed by clamping of the left hilum for 1 h and subsequent reperfusion for 2 h. RESULTS Histological scoring analysis showed that lung parenchymal damage was ameliorated in the melatonin pretreatment groups when compared with the IR group, with the IR + 20 mg/kg MT group showing the strongest effect among the melatonin pretreatment groups. Wet-to-dry weight ratio, detection of malondialdehyde, protein expressions of inflammatory factors (tumour necrosis factor-α, interleukin-1β, NF-κB and IKK-γ) and apoptotic factors (cleaved caspase-3 and Bax/Bcl-2), as well as TUNEL assay showed changes similar to those of the lung injury scores in all groups. In contrast, the examination of superoxide dismutase showed a pattern contrary to that of the lung injury score in all groups. In addition, immunohistochemistry staining showed that the expressions of the antioxidants glutathione peroxidase and glutathione reductase were increased in the melatonin pretreatment groups. CONCLUSIONS This study demonstrated that melatonin pretreatment attenuated lung ischaemia-reperfusion injury via inhibition of oxidative stress, inflammation and apoptosis.