Metformin Activates the Protective Effects of the AMPK Pathway in Acute Lung Injury Caused by Paraquat Poisoning

OBJECTIVE: To observe whether metformin (MET) plays a protective role in acute lung injury (ALI) induced by paraquat (PQ) poisoning in rats by activating the AMPK/NF-κB signaling pathway. METHODS: PQ exposure was used to construct a rat model of ALI and a model of acute type II alveolar epithelial cell (RLE-6TN) injury, and MET intervention was performed. Rat lung tissue samples were collected to evaluate pathological changes in rat lung tissue, the oxidation index, and inflammatory factors; cell viability was detected by CCK-8 assays, and the protein expression levels of phospho-AMPK and phospho-NF-κBp65 in rat lung tissue and RLE-6TN cells were observed by Western blotting. RESULTS: Compared with the PQ group, the MET treatment group showed significantly (1) reduced lung wet/dry ratio (W/D: 4.67 ± 0.31 vs. 5.45 ± 0.40, P < 0.001), (2) reduced pathological changes in lung tissue, (3) decreased MDA levels (nmol/mg prot: 2.70 ± 0.19 vs. 3.08 ± 0.15, P < 0.001) and increased SOD and GSH-Px activities (U/mg prot: 76.17 ± 5.22 vs. 45.23 ± 6.58, 30.40 ± 2.84 vs. 21.00 ± 3.20; all P < 0.001) in lung tissue homogenate, (4) reduced levels of IL-1β, IL-6, and TNF-α in lung tissue homogenates (pg/mL: 47.87 ± 5.06 vs. 66.77 ± 6.55; 93.03 ± 7.41 vs. 107.39 ± 9.81; 75.73 ± 6.08 vs. 89.12 ± 8.94; all P < 0.001), (5) increased activity of RLE-6TN cells (%: 0.69 ± 0.09, 0.76 ± 0.06, and 0.58 ± 0.03 vs. 0.50 ± 0.05; all P < 0.05), (6) decreased protein levels of phospho-NF-κBp65 in lung homogenates and RLE-6TN cells (p-NF-κB/NF-κB: 0.47 ± 0.09 vs. 0.81 ± 0.13; 0.26 ± 0.07 vs. 0.79 ± 0.13; all P < 0.01), and (7) upregulated protein expression of phospho-AMPK in lung homogenates and RLE-6TN cells (p-AMPK/AMPK: 0.88 ± 0.05 vs. 0.36 ± 0.12; 0.93 ± 0.03 vs. 0.56 ± 0.15; all P < 0.01). After the addition of the AMPK inhibitor Compound C (Com C), the protein expression levels of phospho-AMPK and phospho-NF-κBp65 returned to baseline. CONCLUSION: MET can effectively alleviate ALI induced by paraquat poisoning and increase the viability of cells exposed to paraquat. The mechanism may be related to the activation of the AMPK/NF-κB pathway, downregulation of inflammatory mediators such as IL-6 and TNF-α, and upregulation of the SOD and GSH-Px oxidation index, and these effects can be inhibited by the AMPK inhibitor Com C.