Dichloromethane extracts of Sophora japonica L. stimulate osteoblast differentiation in mesenchymal stem cells

Sophora japonica L. fruit prevents bone loss by inhibiting osteoclast activity. We hypothesized that S japonica L. extracts could promote osteoblast differentiation. To test this hypothesis, we investigated the effect of S japonica L. on osteoblast differentiation and identified the bioactive compound(s) from S japonica L. The mature fruit of S japonica L. was partitioned with ethanol, hexane, dichloromethane (DCM), ethyl acetate, and butanol, and their effects were tested on osteoblast differentiation of C3H10T1/2 cells. DCM fractionated extracts were identified as the most osteogenic fractions. DCM fractionated extracts dose-dependently stimulated alkaline phosphatase activity and matrix mineralization. The DCM fractions also induced expression of osteoblast markers such as alkaline phosphatase, osterix, and osteocalcin in C3H10T1/2 and primary bone marrow cells. Genistein was found abundantly in the DCM fractions. Furthermore, the genistein and DCM fractions similarly modulated the expression of estrogen target genes and were both active in transfection assays that measured estrogen agonistic activity. Finally, pharmacological inhibition by treatment with an estrogen receptor antagonist or specific inhibition of gene expression by small interference RNAs targeted to estrogen receptor-β abolished the effects of the DCM extracts, further supporting the idea that the genistein in the DCM extracts mediated the pro-osteogenic effects. Taken together, we identified genistein as the key phytoestrogen responsible for the effects of S japonica L. on osteoblast differentiation.