[Effects of sulfur dioxide on alveolar macrophage apoptosis in acute lung injury induced by limb ischemia/reperfusion in rats].

OBJECTIVE: To investigate the effect of sulfur dioxide (SO2) on the apoptosis of alveolar macrophage (AM) in lung protection of limb ischemia/reperfusion (I/R) induced acute lung injury (ALI), and to find a new target for the control of inflammatory response. METHODS: Twenty pathogen-free, adult male Sprague-Dawley (SD) rats (180-230 g) were used in this study. Five rats were to be used for limb ischemia/reperfusion, then plasma was extracted as ischemia/reperfusion serum stimulation. Fifteen rats were to be used for extracting AM by bronchoalveolar lavage. The AM was isolated and cultured, then the cell count was adjusted to 1×106/mL, and randomly divided into the following 4 groups (n=6): control group, I/R group, SO2 group, and I/R+SO2 group. The I/R group was given ischemia/reperfusion serum (500 µg/L) to stimulate 6 h; the SO2 group was given an SO2 donor, Na2SO3/NaHSO3 [(0.54 mmol/kg) / (0.18 mmol/kg)]; and the I/R+SO2 group was given the same ischemia/reperfusion serum and Na2SO3/NaHSO3 at the same time. The level of mitochondrial membrane potential, the state of mitochondrial permeability transition pore (mPTP), the rate of AM apoptosis, the expression of Bcl-2 and Caspase-3 proteins were detected by flow cytometry, microplate reader and Western blotting. RESULTS: Compared with the control group, in the I/R group, the ratio of red to green fluorescence and the absorbance decreased significantly, the percentage of apoptotic cells increased obviously, the apoptotic rate was 43.81%±2.40%, Caspase-3 protein expression increased, Bcl-2 protein expression decreased. While compared with the I/R group, in the I/R+SO2 group, the ratio of red to green fluorescence and the absorbance increased significantly; the apoptotic rate decreased to 37.01%±1.93%, Caspase-3 protein expression decreased, Bcl-2 protein expression increased. CONCLUSION: Exogenous SO2 has the effect of accelerating AM apoptosis by stimulating mPTP to open and mitochondrial membrane potential to decrease; besides, exogenous SO2 could stimulate AM to secrete more anti-inflammatory cytokines and less inflammatory cytokines. In conclusion, exogenous SO2 can reduce macrophage apoptosis by inhibiting mitochondrial pathways.