Notoginsenoside R1 stimulates osteogenic function in primary osteoblasts via estrogen receptor signaling

Notoginsenoside R1 (NGR1), a novel phytoestrogen isolated from Panax notoginseng, has been widely used in the treatment of microcirculatory diseases in Asian countries. Here we investigated the effect of NGR1 on osteoblast differentiation and mineralization process. Furthermore, we also evaluated NGR1's estrogenic properties, especially its effects on estrogen receptors (ERs). NGR1 activated the transcriptional activity of phosphorylated estrogen response element (pERE)-luciferase (Luc) and induced ERα phosphorylation in hBMSC. In addition, ER activation correlated with induction and was associated with osteoblast differentiation biomarkers including alkaline phosphatase activity and transcription of osteoblastic genes, e.g., type I collagen (COL1), osteonectin, osteocalcin (OC), runt related protein 2 (Runx2), and osterix. NGR1 also promoted the mineralization process of osteoblasts. The NGR1-induced effects were confirmed to be mediated by the ER by the observation that pretreatment of the osteoblasts with the ER antagonist, ICI 182,780 fully blocked the effects. Our results showed that NGR1 stimulates osteogenic differentiation of cultured osteoblasts by activating ER signaling and in turn might be a potential therapeutic alternative for the prevention and treatment of osteoporosis.