Metformin inhibits LPS-stimulated microglial proliferation and reduces the release of inflammatory cytokines

This study was designed to determine the effect of metformin on the release of inflammatory factors by lipopolysaccharide (LPS)-stimulated microglia and investigate the mechanisms potentially underlying these effects. The cytotoxicity of metformin was evaluated in microglia by trypan blue staining. Microglial cells were randomly divided into a control group, an LPS-stimulated group (LPS group: cells were cultured with 50 ng/mL LPS for 24 h) and a metformin plus LPS group (observation group: cells were first cultured with 0.02, 2, 8, or 16 mmol/L metformin for 24 h and then cultured with 50 ng/mL LPS for 24 h). TNF-alpha levels were measured by ELISA. Cell proliferation was evaluated by cell counting. Cell viability was evaluated by MTT assays. The cell cycle was examined by propidium iodide staining + flow cytometry. The apoptotic rate was analyzed by an improved propidium iodide staining + flow cytometry method. There were no differences in trypan blue staining among microglia treated with different concentrations of metformin. TNF-alpha levels were lower, proliferation was slower, and the apoptotic rate was higher in the metformin pretreatment group than in the group treated with only LPS, and these effects were dose-dependent. As the metformin concentration increased, the percentage of microglia in the G1 phase increased. There were significant differences in the percentage of microglia in the G1 phase between the LPS group and the observation groups pretreated with 8 and 16 mmol/L metformin. Metformin decreased the release of inflammatory factors from LPS-stimulated microglia, and this effect may be related to the reduced proliferation and increased apoptosis observed in the microglia.