Metformin ameliorates HMGB1-mediated oxidative stress through mTOR pathway in experimental periodontitis

Periodontitis is an oral chronic inflammatory disease. Inhibiting tissue destruction and promoting tissue regeneration are important means for the treatment of periodontitis. Metformin not only has hypoglycemic effect but also has anti-inflammatory effect. Metformin has been shown to inhibit oxidative stress and activate autophagy through AMPK/mTOR pathway. High mobility group box 1 (HMGB1) has been implicated in the pathogenesis of many inflammatory diseases including periodontitis, it can participate in the induction of oxidative stress. HMGB1 is an autophagy regulator under oxidative stress, which can activate mTOR pathway. However, it is not clear whether metformin is related to HMGB1 and its mechanism in the process of periodontitis. Cell viability and expression of inflammatory cytokines were clarified by Cell Counting Kit-8, real-time PCR and enzyme-linked immunosorbent assay. Western blot and immunofluorescence were conducted to determine HMGB1 intracellular localization and expression of autophagy-associated proteins in vitro. Experimental periodontitis mice model was induced by administering a ligature. Immunohistochemistry was performed to detect the expression and localization of HMGB1 in vivo. The results of CCK-8, real-time PCR, enzyme-linked immunosorbent assay, Western blot and immunofluorescence showed lipopolysaccharide (LPS) treatment inhibited cell viability, and increased HMGB1 expression at a dose-independent manner. Metformin can reduce the effect of LPS. It also improves autophagy pathway inhibited by LPS and down-regulates mTOR expression. In addition, metformin attenuated alveolar bone resorption induced by ligation. This study provides new evidence for that metformin is a potential drug for the treatment of periodontitis and HMGB1 may be a potential target for periodontal intervention.