Abstract: BACKGROUND: The diabetic microenvironment can cause excessive M1 polarization of macrophages, and this hyperglycemic inflammatory state can inhibit osteogenic differentiation of bone marrow mesenchymal stem cells, thus affecting the healing of diabetic bone defects. Studies have indicated that mogroside V possesses anti-inflammatory, antioxidant, and hypoglycemic properties. However, its potential to modulate M1 polarization of macrophages and osteogenic differentiation of bone marrow mesenchymal stem cells under high glucose and inflammatory condition remains unclear.
OBJECTIVE: To explore the effect of mogroside V on regulating M1 macrophage polarization and its effect on osteogenic differentiation of bone marrow mesenchymal stem cells under high glucose and inflammatory condition. 
METHODS: Murine diabetic models were established using C57BL/6 mice. Bone marrow-derived macrophages were isolated from tibia and fibula of normal and diabetic mice, and cultured in low-glucose and high-glucose media. Then M1 polarization of bone marrow-derived macrophages was induced using lipopolysaccharide and interferon-γ. Bone marrow-derived macrophages were treated with 160, 320, and 640 μmol/L mogroside V. Flow cytometry was employed to determine the proportion of F4/80+CD86+ cells. qRT-PCR was utilized to assess mRNA expression levels of inducible nitric oxide synthase, interleukin 1β, and interleukin 6. ELISA was employed to evaluate tumor necrosis factor-α secretion in bone marrow-derived macrophage supernatants. Bone marrow mesenchymal stem cells were isolated from tibia and fibula of C57BL/6 suckling mice, and induced osteogenic differentiation using low- or high-glucose osteogenic induction medium. Bone marrow mesenchymal stem cells were treated with M1 macrophage-conditioned mediums with or without 320 μmol/L mogroside V in osteogenic differentiation process. qRT-PCR was employed to assess the mRNA expression of alkaline phosphatase, Runt-related factor 2, osteocalcin, and osteopontin on day 14 after osteogenic induction. Alizarin red staining and quantitative analysis were conducted to evaluate calcium deposition on day 21 after osteogenic induction. 
RESULTS AND CONCLUSION: (1) Flow cytometry results showed that with the treatment of 320 and 640 μmol/L mogroside V, the proportion of F4/80+CD86+ bone marrow-derived macrophages was significantly lower than that in the high-glucose control group (P < 0.05). (2) qRT-PCR results showed that with the treatment of 160, 320, and 640 μmol/L mogroside V, the mRNA expression levels of inducible nitric oxide synthase and interleukin 6 were significantly lower than that in the high-glucose control group (P < 0.05). With the treatment of 320 and 640 μmol/L mogroside V, the mRNA expression level of interleukin 1β was significantly lower than that in the high-glucose control group (P < 0.05). (3) ELISA results exhibited that with the treatment of 160, 320, and 640 μmol/L mogroside V, the tumor necrosis factor-α secretion level was significantly lower than that in the high-glucose control group (P < 0.05). (4) With the treatment of 320 μmol/L mogroside V, calcium salt deposition was increased in bone marrow mesenchymal stem cells under high glucose and inflammatory conditions (P < 0.05), and the mRNA relative expression levels of alkaline phosphatase, Runt-related factor 2, and osteopontin were increased (P < 0.05). These findings indicate that mogroside V can promote osteogenic differentiation of bone marrow mesenchymal stem cells by inhibiting the M1 polarization of bone marrow-derived macrophages under high glucose and inflammatory conditions and reducing the generation of inflammatory factors. 

Key words: mogroside V, macrophage, M1 polarization, bone marrow mesenchymal stem cell, inflammatory reaction, osteogenic differentiation, high glucose