Metformin inhibits LPS-induced inflammatory response in VSMCs by regulating TLR4 and PPAR-γ.

OBJECTIVE: This study aims to explore whether the inhibitory role of metformin could inhibit LPS-induced inflammatory response in vascular smooth muscle cells (VSMCs) and its underlying mechanism. MATERIALS AND METHODS: VSMCs were extracted from aorta of Sprague Dawley rats. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay was performed to detect VSMCs viability after treatment with different concentrations of metformin. Levels of monocyte chemoattractant protein-1 (MCP-1), interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) in VSMCs were detected by ELISA (enzyme-linked immunosorbent assay) and qRT-PCR (quantitative Real time-polymerase chain reaction). Protein and mRNA levels of toll like receptor 4 (TLR4) and peroxisome proliferators activated receptor γ (PPAR-γ) in VSMCs were detected by Western blot and qRT-PCR, respectively. Finally, VSMCs were treated with the PPAR-γ antagonist GW9662 and inflammatory indicators in cells were detected. RESULTS: No significant difference in VSMCs viability was found after 0-2 mM metformin treatment or 500 µg/L LPS induction for 24 h. After 500 µg/L LPS induction in VSMCs for 24 h, levels of MCP-1, TNF-α and IL-6 were remarkably elevated. Both mRNA and protein levels of TLR4 in VSMCs were upregulated after 500 µg/L LPS induction for 24 h, which were remarkably reversed by the treatment of different concentrations of metformin. Knockdown of TLR4 remarkably inhibited LPS-induced inflammatory response in VSMCs, manifesting as decreased levels of MCP1, TNF-α and IL-6, which were further downregulated after combination treatment of TLR4 knockdown and 20 mM metformin. Furthermore, both mRNA and protein levels of PPAR-γ in VSMCs were downregulated after 500 µg/L LPS induction for 24 h, which were remarkably reversed by the treatment of different concentrations of metformin. GW9662 treatment resulted in elevated expressions of MCP-1, TNF-α and IL-6, which were reversed by metformin treatment. CONCLUSIONS: Metformin can effectively inhibit the mRNA and protein expressions of IL-6, MCP-1, and TNF-α in LPS-induced VSMCs. The anti-inflammatory effects of metformin inhibit the inflammatory response through downregulating rely on the downregulation of TLR4 expression and upregulation ofng PPAR-γ activity.