Objective: To investigate the effect of heme oxygenase-1 (HO-1) on the apoptosis of type II alveolar epithelial cells (AEC-II) in rats with hyperoxia-induced acute lung injury (HALI).
Methods: Twenty-four healthy male Sprague-Dawley (SD) rats were randomly divided into 4 groups (n = 6): control group, HALI group, HO-1 group, and HO-1 inhibition group. The control group was fed in the room air; the HALI group was fed in the hyperoxia box (the oxygen concentration was more than 90%, the temperature was kept at 25-27 centigrade, the humidity was maintained at 50%-70%, and the CO2 concentration was less than 0.5%); the HO-1 group was fed in the hyperoxia box after HO-1 (0.2 μmol/L) treatment; and the HO-1 inhibition group was fed in the hyperoxia box after treatment with zinc protoporphyrin IX (20 μmol/L). After 48 hours of hyperoxia treatment, rats were sacrificed, left upper lung tissue was stained with hematoxylin-eosin (HE) and the pathological changes of lung tissue were observed under light microscope. The ratio of wet/dry weight (W/D) was measured in the lower left lung. AEC II was extracted from the right lung tissue, the apoptosis rate was detected by flow cytometry, and the expressions of apoptosis-related proteins Bcl-2 and caspase-3 were detected by Western Blot.
Results: (1) It was shown by light microscopy that the lung tissue structure of the control group was clear. In HALI group and HO-1 inhibitor group, the lung tissue structure was disordered, alveolar wall was broken and fused into pulmonary alveoli, alveolar septum was obviously swollen and widened, a large number of inflammatory cells infiltrated, and edema fluid and inflammatory cells appeared in alveolar cavity. The pathological changes of lung tissue in HO-1 group were significantly less than those in HALI group. (2) Compared with the control group, the lung W/D ratio, the apoptosis rate of AEC II and the expression of Bcl-2 protein in the HALI group and the HO-1 inhibitor group were significantly increased, and the expression of caspase-3 was significantly decreased [lung W/D ratio: 4.61±0.41 vs. 3.68±0.45, apoptosis rate of AEC II: (42.44±0.93)% vs. (24.74±0.64)%, Bcl-2 (integral absorbance): 0.72±0.18 vs. 0.41±0.12, caspase-3 (integral absorbance): 1.32±0.32 vs. 1.81±0.69, all P < 0.05]. Compared with the HALI group, the lung W/D ratio, the apoptosis rate of AEC II, the expression of Bcl-2 protein in HO-1 group were significantly decreased, and the expression of caspase-3 was significantly increased [lung W/D ratio: 3.82±0.28 vs. 4.61±0.41, apoptosis rate of AEC II: (26.67±1.58)% vs. (42.44±0.93)%, Bcl-2 (integral absorbance): 0.39±0.08 vs. 0.72±0.18, caspase-3 (integral absorbance): 1.78±0.46 vs. 1.32±0.32, all P < 0.05]. There was no significant difference between HO-1 inhibitor group and HALI group.
Conclusions: HO-1 can reduce the apoptosis rate of AEC II in rats with HALI, which may be related to the expressions of apoptosis related proteins Bcl-2 and caspase-3.