OBJECTIVE To investigate the effect of osthole,a natural coumarin isolated from traditional Chinese medicine Fructus Cnidii,on osteogenesis in vitro and bone fracture healing in vivo.METHODS Primary bone marrow mesenchymal stem cells(MSCs)were isolated from 6-week C57/B6 mice,and osteogenic differentiation was assessed by alkaline phosphate(ALP)activity and calcium nodule formation.Adult(12-week)C57mice were subjected to mid-shaft osteotomy on femur.The mice were oral administrated with osthole(5,20 or 50mg·kg-1)or vehicle solvent daily from post-operational week 1.Radiographic imaging,real time molecular imaging,micro computed tomography(μCT)and histology analysis were performed to evaluate the healing progress.RESULTS Results showed that osthole promoted osteogenesis of bone marrow MSCs by enhancing ALP activity and mineralization dose dependently in the range of 1-100μmol·L-1.Plain radiographs showed that administration of osthole at 20 and 50 mg·kg-1 significantly accelerated fracture healing by reducing the period of reparative phase.Further investigation withμCT and histology showed that osthole-treated group had high proportion of newly-formed woven bone and smaller cartilage island compare to control group at week 2;and treatment group had completed endochondral ossification and started remodeling phase at week 3.Molecular imaging of near-infrared(NIR)fluorescent labeled palmidronate depositing on newly formed bone suggested that osthole treatment(20 mg·kg-1)augmented callus mineralization process at both postoperative week 2 and week 3 by 80.72% and 25.95% respectively.CONCLUSION Osthole demonstrates significant osteopromotive effect in vitro and anabolic effect on bone formation in fracture repair,which makes it a potential agent for bone regeneration and against osteoporosis. OBJECTIVE To investigate the effect of osthole, a natural coumarin isolated from traditional Chinese medicine Fructus Cnidii, on osteogenesis in vitro and bone fracture healing in vivo. METHODS Primary bone marrow mesenchymal stem cells (MSCs) were isolated from 6-week C57 / B6 mice , and osteogenic differentiation was assessed by alkaline phosphate (ALP) activity and calcium nodule formation. Adult (12-week) C57mice were subjected to mid-shaft osteotomy on femur. The mice were oral administered with osthole (5, 20 or 50 mg · kg -1) or vehicle solvent daily from post-operational week 1. Radiographic imaging, real time molecular imaging, micro computed tomography (μCT) and histology analysis were performed to evaluate the healing progress .RESULTS Results showed that that osthole promoted osteogenesis of bone marrow MSCs by enhancing ALP activity and mineralization dose dependently in the range of 1-100 μmol·L-1.Plain radiographs showed that administration of osthole at 20 and 50 mg · kg-1 significantly accelerated fracture healing by reducing the period of reparative phase. Fluorrther investigation withμCT and histology showed that osthole-treated group had high proportion of newly-formed woven bone and smaller cartilage island compare to control group at week 2; and treatment group had completed endochondral ossification and started remodeling phase at week 3. Molecular imaging of near-infrared (NIR) fluorescent labeled palmidronate depositing on newly formed bone suggested that osthole treatment (20 mg · kg -1) augmented callus mineralization process at both postoperative week 2 and week 3 by 80.72 % and 25.95% respectively. CONCLUSION Osthole demonstrates significant osteopromotive effect in vitro and anabolic effect on bone formation in fracture repair, which makes it a potential agent for bone regeneration and against osteoporosis.