Curculigoside regulates proliferation, differentiation, and pro-inflammatory cytokines levels in dexamethasone-induced rat calvarial osteoblasts.

BACKGROUND Curculigoside (CCG), one of the main bioactive phenolic compounds isolated from the rhizome of Curculigo orchioides Gaertn., is reported to prevent bone loss in ovariectomized rats. However, the underlying molecular mechanisms are largely unknown. Therefore, we investigated the effects of CCG on proliferation and differentiation of calvarial osteoblasts and discussed the related mechanisms. MATERIALS AND METHODS Osteoblasts were incubated with dexamethasone (DEX) in the absence or presence of CCG concentrations for 24-72 h. Cell proliferation was evaluated by Cell Counting Kit-8 assay. Mitochondria membrane potential (MMP) and reactive oxygen species (ROS) were assessed by flow cytometry. We assessed the anti-inflammatory responses of CCG on DEX-induced osteoblasts by an enzyme-linked immunosorbent assay (ELISA). Relative protein expression of BMP-2, b-catenin, RANKL, OPG and RANK was measured using Western blotting. RESULTS It was found that osteoblasts proliferation decreased significantly after treated with 1 μM of dexamethasone (DEX), compared with untreated osteoblasts and the cytotoxic effect of DEX was reversed remarkably when pretreatment with 25-100 μg/ml of CCG. Pretreatment with 25-100 μg/ml of CCG increased MMP level and decreased ROS production in osteoblasts induced by DEX. In addition, DEX-induced inhibition of differentiation markers such as alkaline phosphatase (ALP), OPG, BMP-2, β-catenin, IGF-1 and M-CSF level, and promotion of differentiation markers such as RANKL and RANK was significantly reversed in the presence of CCG. CCG also reversed DEX-induced production of pro-inflammatory cytokines. CONCLUSIONS These results provide new insights into the osteoblast-protective mechanisms of CCG through inducing proliferation and differentiation and reducing the inflammatory responses, indicating that CCG may be developed as an agent for the prevention and treatment of osteoporosis.