Metformin attenuates traumatic osteoarthritis in obese mice induced by high-fat diet partly by reducing leptin

Abstract

Purpose: Obesity is one of the main risk factors for osteoarthritis (OA), and evidence is accumulating that proinflammatory adipokines such as leptin play an important role in OA. Metformin (Met) has been shown to reduce weight and relieve inflammation. Here, we combine surgical joint damage with high-fat diet (HFD) in mice to investigate the effect of metformin on OA and its potential mechanism. Methods: Mice were fed with HFD or normal diet (ND) from 3 weeks old and destabilization of the medial meniscus (DMM) surgery was performed at 12 weeks old. Metformin was administrated in drinking water immediately after DMM and the joint structural changes were observed at 5 and 10 weeks after the surgery. OA was evaluated by Osteoarthritis Research Society International (OARSI) score, synovitis score, and osteophyte volume reconstructed by micro-computed tomography. Macrophage infiltration in synovium and leptin expression in adipose tissue were detected by immunofluorescence. In vitro, the apoptosis of primary human chondrocytes and the subtypes of macrophages were detected by flow cytometry. Murine chondrogenic cell line ATDC5 and macrophage cell line RAW264.7 were incubated in fat conditioned medium (FCM) from mouse abdominal fat, and the metabolic changes were detected by western blot and ELISA. Results: The OARSI score, synovitis score and osteophyte volume of ND + DMM + Met mice and HFD + DMM + Met mice were significantly lower than that of ND + DMM mice and HFD + DMM mice, respectively. Importantly, the interaction between diet and Met on OARSI score was statistically significant at 5 weeks (F = 6.364, P = 0.020) and 10 weeks (F = 4.949, P = 0.038) after DMM. The mean difference of OARSI score in HFD mice (2.08 at 5 weeks and 3.17 at 10 weeks) was greater than that in ND mice (0.8 at 5 weeks and 2 at 10 weeks). Metformin reduced the expression of ADAMTS-5 and MMP13 in articular chondrocytes, and increased the expression of autophagy marker LC3. The M1 macrophage marker iNOS was decreased and the M2 macrophage marker CD206 was increased in synovium of metformin- treated mice. Interestingly, metformin reduced the leptin levels in abdominal fat and articular chondrocytes in HFD mice but not ND mice. The expression of MMP-13, ADAMTS-5 and p-S6 of ATDC5 cells in HFD + DMM + Met FCM was significantly lower than that in HFD + DMM FCM. The content of TNF-α and IL-1β of RAW264.7 cells in HFD + DMM + Met FCM was significantly lower than that in HFD + DMM FCM. Furthermore, the expression of ADAMTS-5 and p-S6 in ATDC5 and the secretion of TNF-α and IL-1β in RAW264.7 was significantly reduced after neutralization of leptin in HFD + DMM FCM. Conclusions: Metformin showed a therapeutic effect on OA both in ND mice and in HFD mice. The therapeutic effect of metformin on OA in HFD mice is better than that in ND mice, which may be related to decreasing leptin levels.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)