Total flavonoid fraction of rhizoma drynaria improves bone properties in ovariectomized mice and exerts estrogen-like activities in rat osteoblast-like (UMR-106) cells

Rhizoma Drynaria (RD) has been widely used for healing bone fractures or related diseases in traditional Chinese medicine. The present study was designed to determine if RD total flavonoids (RDTF) could exert estrogen-like protective actions on bone. Young C57/BL6J mice were ovariectomized (OVX) and treated orally with RDTF (0.087, 0.173 or 0.346 mg/g/day), 17β-estradiol (2μg/g/day) or its vehicle for 6 weeks. Bone mineral densities (BMD) was measured by peripheral quantitative computed tomography (pQCT). Rat osteoblast-like UMR-106 cells were co-incubated with ER antagonist ICI 182, 780 to determine if the effects of RDTF on osteoblastic functions were ER-dependent. The functional transactivation of ER-α and ER-β as well as ER-αphosphorylation by RDTF were also studied. RDTF increased trabecular-rich BMD at distal femur and lumbar spine in OVX mice. 0.173 mg/g/day was most effective in improving bone properties in OVX mice. The stimulatory effects of RDTF on osteoblastic functions could be abolished by co-incubation with ICI 182, 780 in UMR-106 cells. Transient transfection study indicated that RDTF dose-dependently stimulated ERE-dependent luciferase activity in UMR-106 cells via ER-α and ER-β. Moreover, 0.2 μg/mL of RDTF significantly induced ER-α phosphorylation at serine 118 in UMR-106 cells.