Metformin relieves acute respiratory distress syndrome by reducing miR-138 expression.

Abstract

To investigate whether metformin can relieve acute respiratory distress syndrome (ARDS). Its potential mechanism was also explored. The ARDS model was established by injecting LPS into mice that received metformin in advance and the mice in the control group. Pulmonary edema was detected by W/D ratios (wet-to-dry weight ratios), and the vascular exudation was reflected by the protein content and cell number of alveolar lavage fluid. Meanwhile, MPO (myeloperoxidase) activity assay was performed to analyze the neutrophil aggregation. The expression of inflammatory cytokines, including TNF-α, IL-1β, IL-6, and IL-17, were detected by enzyme-linked immunosorbent assay (ELISA). This series of experiments reflected the alleviation effect of metformin on ARDS. To further study the mechanism, we cultured alveolar macrophages (NR8383) in vitro and treated them with LPS and metformin. Western blot was used to detect the phosphorylation levels of p38, ERK, NF-kB, and SIRT1 expression level. Bioinformatics method was then used to predict the binding of miR-138 to SIRT1. The mRNA and protein expression of SIRT1 was detected in NR8383 cells transfected with miR-138 inhibitor. The dual luciferase gene reporter assay was used to detect the relative luciferase activities of miR-138 and SIRT1. Pulmonary edema, vascular exudation, and neutrophil accumulation were observed in the ARDS model mice, and the levels of inflammatory cytokines including TNF-α, IL-1b, IL-6, and IL-17 were significantly increased. After metformin treatment, these pulmonic damage indicators were found to be partially reversed. At the same time, metformin could significantly reduce LPS-induced death. After NR8383 was treated with metformin and LPS, the expression of SIRT1 was higher than that of LPS treatment alone, but the expression of p-p38, p-ERK, and p-NF-κB was significantly decreased. After the addition of metformin in NR8383 after LPS treatment, the expression level of miR-138-5p was significantly decreased, and miR-138-5p was confirmed to target SIRT1 and regulate its expression. Metformin could reduce LPS-induced pulmonic injury and increase expression of inflammatory factors. A possible mechanism might be that metformin-induced low expression of mir-138-5p could target SIRT1 to increase its expression and suppress the MAPK pathway, thus alleviating ARDS.