Role of α7nAChR in reduction of endotoxin-induced acute lung injury by limb ischemic preconditioning in mice

Abstract

Objective To evaluate the role of α7 nicotinic acetylcholine receptor (α7nAChR) in reduction of endotoxin-induced acute lung injury (ALI) by limb ischemic preconditioning in mice. Methods Eighty healthy male C57BL/6 mice, aged 8-10 weeks, weighing 22-26 g, were randomly divided into 5 groups (n=16 each) using a random number table: control group (group C), ALI group, limb ischemic preconditioning group (group P), α-bungarotoxin (α-BGT) group, and limb ischemic preconditioning + α-BGT group (group P+ α-BGT). Normal saline 100 μl was intratracheally instilled in group C. In group ALI, lipopolysaccharide 5 mg/kg was intratracheally instilled (in normal saline) to establish the model of endotoxin-induced ALI.In group P, the mice were subjected to 6 cycles of 5-min ischemia of the right hindlimb followed by 5-min reperfusion, and then the model of ALI was established.In group α-BGT, α-BGT 1 μg/kg was injected intraperitoneally before establishment of the model.In group P+ α-BGT, limb ischemic preconditioning was performed, α-BGT 1 μg/kg was then injected intraperitoneally, and the model of ALI was established.At 24 h after LPS instillation, 6 mice were selected from each group and sacrificed, and lungs were removed for microscopic examination and for determination of wet and dry lung weight, myeloperoxidase (MPO) activities, contents of interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α) and IL-6, and expression of α7nAChR and high mobility group box-1 (HMGB1) in lung tissues.The lung water content was calculated.The survival of the left 10 mice in each group was observed at 7 days after establishment of the model, and the survival rate was calculated. Results Compared with group C, the lung water content, MPO activities, contents of IL-1β, TNF-α and IL-6, and HMGB1 expression were significantly increased, α7nAChR expression was significantly down-regulated, and the 7-day survival rate was significantly decreased in group ALI (P<0.05). Compared with group ALI, the lung water content, MPO activities, contents of IL-1β, TNF-α and IL-6, and HMGB1 expression were significantly decreased, α7nAChR expression was significantly up-regulated, and the 7-day survival rate was significantly increased in group P (P<0.05). Compared with group P, the lung water content, MPO activities, contents of IL-1β, TNF-α and IL-6, and HMGB1 expression were significantly increased, α7nAChR expression was significantly down-regulated, and the 7-day survival rate was significantly decreased in group P+ α-BGT (P<0.05). Conclusion The mechanism by which limb ischemic preconditioning inhibits inflammatory responses and reduces endotoxin-induced ALI is related to activation of α7nAChR in mice. Key words: Receptors, nicotinic; Ischemic preconditioning; Respiratory distress syndrome, adult; Inflammation