Role of Nrf2/HO-1 signaling pathway in remote ischemic preconditioning-induced reduction of lipopolysaccharide-induced acute lung injury in mice

Abstract

Objective To evaluate the role of nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathway in remote ischemic preconditioning-induced reduction of lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. Methods Sixty-eight healthy male C57BL/6 mice, aged 6-8 weeks, weighing 22-26 g, were divided into 4 groups (n = 17 each) using a random number table: control group (group C), ALI group, remote ischemic preconditioning group (group RIPC) and brusatol plus remote ischemic preconditioning group (group B+ RIPC). Normal saline 100 μl was intratracheally instilled in group C. ALI was induced by intratracheal instillation of LPS 5 mg/kg in group ALI.Mice in group RIPC were subjected to 6 cycles of 5-min ischemia followed by 5-min reperfusion in the right hindlimbs using a tourniquet, and 1 h later the model of ALI was established.Nrf2 inhibitor brusatol 2 mg/kg (in 100 μl of 1% dimethyl sulfoxide) was intraperitoneally injected every other day for 10 days prior to establishment of the ALI model in group B. Brusatol 2 mg/kg was intraperitoneally injected every other day for 10 days prior to establishment of the ALI model, and remote ischemic preconditioning was performed at 1 h before establishment of the ALI model in group B+ RIPC.Seven mice in each group were selected at 24 h after establishment of the ALI model, and bronchoalveolar lavage fluid (BALF) was collected for determination of protein concentrations and neutrophil count.Mice were then sacrificed and lungs were removed for determination of lung water content, myeloperoxidase (MPO) activity, contents of interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α), and expression of Nrf2, HO-1 and high-mobility group box 1 protein (HMGB1) in lung tissues (by Western blot) and for examination of pathological changes (with a light microscope). Results Compared with group C, the lung water content, MPO activity, contents of IL-1β and TNF-α, and neutrophil count and protein concentrations in BALF were significantly increased, and the expression of Nrf2, HO-1 and HMGB1 was up-regulated in group ALI (P<0.05). Compared with group ALI, the lung water content, MPO activity, contents of IL-1β and TNF-α, and neutrophil count and protein concentrations in BALF were significantly decreased, the expression of Nrf2 and HO-1 was up-regulated, and the expression of HMGB1 was down-regulated (P<0.05), and the pathological changes were significantly attenuated in group RIPC.Compared with group RIPC, the lung water content, MPO activity, contents of IL-1β and TNF-α, and neutrophil count and protein concentrations in BALF were significantly increased, the expression of Nrf2 and HO-1 was down-regulated, and the expression of HMGB1 was up-regulated (P<0.05), and the pathological changes were aggravated in group B+ RIPC. Conclusion The activation of Nrf2/HO-1 signaling pathway is involved in remote ischemic preconditioning-induced reduction of LPS-induced ALI in mice. Key words: NF-E2-related factor 2; Heme oxygenase-1; Ischemic preconditioning; Respiratory distress syndrome, adult; Toxoids