Amelioration of superoxide dismutase on ventilator-induced lung injury by suppressing leukocyte in the lungs and systemic circulation

Superoxide dismutase (SOD) is a free radical scavenger and a broad-spectrum antioxidant. Its anti-inflammatory and immunomodulatory effects have recently been noted. We studied the effects of this antioxidant on lung damage, oxidative stress, and inflammation in a model of ventilator-induced lung injury (VILI), using 8- to 12-wk-old Sprange-Dawley rats (n = 40). Animals were randomized and evenly divided into two experimental groups, low tidal volume (VT) ventilation (VT = 9 ml/kg) and high VT ventilation (VT = 28 ml/kg). Each group was evenly divided into two subgroups: ten animals were treated with superoxide dismutase (SOD; 10,000 U/kg iv, 2 h prior to the ventilation) and the rests were treated with vehicle. Lung injury was evaluated by histological examination, and cells counts of red blood cells (RBC) and white blood cells (WBC) in the alveoli and the septal wall thickness in lung tissues and serum lactate dehydrogenase (LDH). The lung permeability was assessed by the wet-to-dry weight ratio (W/D), lung weight to body weight ratio (LW/BW) and protein concentration in broncholavage fluid (BALF). Levels of oxidative stress and lipid peroxidation in the lungs were evaluated by tissue malondialdehyde (MDA) and methylguanidine (MG) in BALF, respectively. SOD pretreatment significantly decreased WBC counts in systemic circulation and in alveoli, and effectively attenuated high VT ventilation induced lung injury by reducing hyaline membrane development, septal wall thickness, lung W/D and LW/BW and serum LDH in relation to those of the control. In addition, lung tissue MDA and MG in BALF were also notably reduced.