OBJECTIVETo investigate the molecular mechanisms of icariin (ICA) in regulating the bone formation of osteoblasts and the bone resorption of osteoclasts.

METHODSPrimary osteoblast cell cultures were obtained from newborn rat calvarial. Calcified nodules were stained by alizarin red. The mRNA levels of osterix (OSX), runt-related transcription factor 2 (Runx-2), alkaline phosphatase (ALP), Collagen1, osteoprotegerin (OPG), and receptor activator of nuclear factor-ΚB ligand (RANKL) were analyzed by quantitative real-time RT-PCR, the protein levels of OPG, RANKL, and Collagen1 were examined by Western blotting, and the intracellular Ca(2+) concentration of osteoblasts was measured on a flow cytometer using the Cellquest program.

RESULTSCompared with control group, ICA markedly promoted bone formation by significant up-regulating the gene expressions of OSX, Runx-2,ALP, and Collagen1, the protein expression of Collagen1(all P<0.01), and the Ca(2+) concentration. Furthermore, ICA remarkably inhibited bone resorption by significant up-regulating the mRNA and protein expressions of OPG as well as the OPG/RANKL ratio.

CONCLUSIONSICA could promote bone formation of osteoblasts through inducting the gene expressions of OSX,Runx-2, ALP and Collagen1, and the protein expressions of Collagen1, and by increasing the Ca (2+) concentration. Moreover, ICA could inhibit bone resorption of osteoclasts through regulating OPG/RANKL signal pathway.