Protective effect of N-acetylcysteine against pneumocyte apoptosis during ischemia/reperfusion injury of lung in rats

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To investigate the effect of N-acetylcysteine (NAC) on apoptosis of pneumocytes and expression of caspase-3 during lung ischemia/reperfusion injury (LIRI) in rats, and to explore the possible role of NAC in pneumocyte apoptosis. Forty-two male Sprague-Dawley rats were randomly divided into three groups: sham operation group, LIRI group (LIRI was produced by 45 minutes of clamping of the pulmonary hilum followed by 3 hours or 6 hours of reperfusion), and NAC group (NAC 150 mg/kg was injected intraperitoneally before LIRI). Lung specimens were harvested 3 hours or 6 hours after LIRI. Apoptosis rate in lung tissue was determined with flow cytometer after Annexin V-fluorescein isothiocyanate (FITC) and propidium iodide (PI) staining. Malondialdehyde (MDA, thiobarbituric acid) and superoxide dismutase (SOD, xanthine oxidase) of lung tissue were measured. Expression of caspase-3 in lung was determined by reverse transcription-polymerase chain reaction (RT-PCR), and the changes in ultrastructure of lung tissue were observed by electron microscope. Compared with that of the sham operation group, apoptosis rate of pulmonary cells was significantly increased at 3 hours and 6 hours in LIRI group [(25.60 ± 3.22)% vs. (2.19 ± 0.48)% , (26.01 ± 4.50)% vs. (2.55 ± 0.36)%], the content of MDA (nmol/mg) was significantly increased (3.26 ± 0.32 vs. 0.73 ± 0.23, 3.53 ± 0.46 vs. 1.08 ± 0.42), and the activity of SOD (U/mg) was significantly lowered (32.80 ± 3.82 vs. 60.51 ± 6.81, 33.44 ± 3.24 vs. 64.19 ± 6.60), and the expression of caspase-3 mRNA in lung tissue was significantly up-regulated (0.717 ± 0.037 vs. 0.216 ± 0.046, 0.744 ± 0.046 vs. 0.227 ± 0.037, all P < 0.01). Compared with that of the LIRI group, apoptosis rate of pulmonary cell was significantly decreased [(14.42 ± 1.61)% vs. (25.60 ± 3.22)%, (10.02 ± 1.64)% vs. (26.01 ± 4.50)%], content of MDA (nmol/mg) was lowered significantly (1.75 ± 0.33 vs. 3.26 ± 0.32, 2.15 ± 0.25 vs. 3.53 ± 0.46), and activity of SOD (U/mg) was significantly elevated (42.76 ± 2.06 vs. 32.80 ± 3.82, 44.94 ± 3.11 vs. 33.44 ± 3.24, all P < 0.01) in NAC group. The expression of caspase-3 in lung tissue was remarkably down-regulated compared with that of LIRI group (0.441 ± 0.038 vs. 0.717 ± 0.037, 0.410 ± 0.037 vs. 0.744 ± 0.046, both P < 0.01). The ultrastructure changes in lung tissue were milder in NAC group than in LIRI group. Positive correlation was found between the expression of caspase-3 and apoptosis rate and the content of MDA (3 hours: r = 0.9036, 0.9216; 6 hours: r = 0.9655, 0.9650, all P < 0.01), but negative correlation was found between apoptosis rate and activity of SOD (3 hours: r = -0.9511, 6 hours: r = - 0.9574, both P < 0.01) after LIRI 3 hours and 6 hours. During early period of LIRI, caspase-3 was significantly deregulated by NAC, therefore the cellular apoptosis was inhibited, thus protecting lung tissue from LIRI.