Radix Astragalus has been shown to exert beneficial effects regarding the prevention postmenopausal osteoporosis. However, its mechanism of action remains to be investigated. Calycosin, formononetin, and calycosin-7-O-β-d-glucoside are the main isoflavone constituents of Astragalus. In this study, the abilities of these 3 compounds to promote osteogenic function of osteoblasts were compared, and the structure-activity relationships of these osteotrophic isoflavones were determined. Calycosin exhibited a greater effect than formononetin and calycosin-7-O-β-d-glucoside regarding improvements in osteogenic function of osteoblasts, as demonstrated by cell proliferation, alkaline phosphatase activity, collagen I and osteocalcin secretion, and the number and area of mineralized bone nodules. This suggests that calycosin may be better than formononetin and calycosin-7-O-β-d-glucoside at preserving bone mass. In addition, calycosin, formononetin, and calycosin-7-O-β-d-glucoside stimulate the expression of bone morphogenetic protein 2 and runt-related transcription factor 2 proteins, which indicates that all 3 agents may promote the osteogenesis of osteoblasts via regulation of bone morphogenetic protein 2 expression. In conclusion, calycosin may be the best candidate, with higher osteogenic activity than formononetin and calycosin-7-O-β-d-glucoside. The higher osteogenic activity of calycosin could be attributable to the superiority of its chemical structure (a hydroxyl group at position C3 of Ring B and no glucosyl group).
Keywords: calycosin; calycosin-7-O-β-d-glucoside; formononetin; osteoblasts; osteogenic activities; osteoporosis.
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