Drynaria fortunei-derived total flavonoid fraction and isolated compounds exert oestrogen-like protective effects in bone.

Drynaria fortunei (Kunze) J. Sm. (DF), a Chinese herb commonly used for the treatment of bone fracture, was previously shown to exert anabolic effects on bone. However, its active ingredients as well as the mechanisms of action are far from clear. The present study aimed to characterise the bone anabolic effects of DF flavonoid fraction (DFTF) in ovariectomised (OVX) mice and to determine if DFTF and its isolated compounds exert oestrogen-like effects in rat osteoblast-like UMR-106 cells. Young OVX C57/BL6J mice were treated orally with DFTF (0·087, 0·173 or 0·346 mg/g per d), 17b-oestradiol (2 mg/g per d) or its vehicle for 6 weeks. Serum and urine samples were collected for biochemical marker analysis. Bones were collected for computed tomography analysis. UMR-106 cells were treated with DFTF and isolated compounds naringin, (2S)-5,7,30,50-tetrahydroxy-flavonone 7-O-neohesperidoside (compound 1) and 5,7-dihydroxychromone 7-O-neohesperidoside (compound 2). DFTF exerted dose-dependent effects in improving bone mineral densities as well as bone strength at the femur, tibia and lumbar spine L1 in OVX mice. DFTF and the three isolated compounds stimulated osteoblastic cell proliferation and alkaline phosphatase activities in a dose-dependent manner. In addition, they stimulated the ratio of osteoprotegrin and receptor-activator NF-kB ligand mRNA expression, suggesting their involvement in inhibiting osteoclastogenesis. These stimulatory effects on osteoblastic functions were abolished in the presence of oestrogen receptor (ER) antagonist, ICI 182780. The present results suggested that DFTF is effective in protecting against OVX-induced bone loss in mice, and its actions in regulating osteoblastic activities appear to be mediated by ER.

Naringin improves bone properties in ovariectomized mice and exerts oestrogen-like activities in rat osteoblast-like (UMR-106) cells.

BACKGROUND AND PURPOSE: Naringin, a flavanone glycoside in citrus fruits, has been recently reported to stimulate bone formation in vitro and in vivo. The present study was designed to determine if naringin could exert oestrogen-like protective actions in bone. EXPERIMENTAL APPROACH: Young C57/BL6J mice were ovariectomized (OVX) and treated orally with naringin (0.2 or 0.4 mg*g(-1)*day(-1)), 17beta-oestradiol (2 microg*g(-1)*day(-1)) or its vehicle for 6 weeks. Bone mineral densities (BMD) and polar stresss-train index (SSI) were measured by peripheral quantitative computed tomography. Rat osteoblast-like UMR-106 cells were co-incubated with the oestrogen receptor (ER) antagonist ICI 182780 to determine if the effects of naringin on osteoblastic functions were ER dependent. Functional transactivation of ERalpha and ERbeta as well as ERalpha phosphorylation by naringin were also studied. KEY RESULTS: Naringin at 0.4 mg*g(-1)*day(-1) increased BMD at trabecular-rich bone in OVX mice. Naringin (at both doses) significantly increased SSI at distal femur and lumbar spine and increased biomechanical strength (ultimate load and energy for breaking) at tibia diaphysis in OVX mice. The stimulatory effects of naringin on osteoblastic functions could be abolished by co-incubation with ICI 182780 in UMR-106 cells. Naringin failed to stimulate ERalpha- or ERbeta-mediated oestrogen response element-dependent luciferase activity but could significantly induce ERalpha phosphorylation at serine 118, in UMR-106 cells. CONCLUSIONS AND IMPLICATIONS: Naringin was effective in protecting against OVX-induced bone loss in mice and its actions might be mediated through ligand-independent activation of ER in osteoblastic cells.

Effects of eleven flavonoids from the osteoprotective fraction of Drynaria fortunei (KUNZE) J. SM. on osteoblastic proliferation using an osteoblast-like cell line.

Drynaria fortunei (KUNZE) J. SM. (DFE) is one of the most frequently used traditional Chinese medicines prescribed for the treatment of osteoporosis in China. The present study was designed to investigate the osteoprotective constituents from Drynaria fortunei. The 60% ethanol extract of the rhizome of D. fortunei (DFE) was chromatographed on a D-101 macroporous resin column (psi 25x150 cm); three fractions (DFA eluted with water, DFB eluted with 30% and 50% ethanol, and DFC eluted with 95% ethanol) were obtained and their osteoprotective activity as examined both in vivo and in vitro. DFB showed significant activity on both the proliferation of UMR106 cells and promoting bone mineral density (BMD) in ovariectomized (OVX) mice. A bioactivity-guided method led to the isolation of 11 flavonoids from this fraction (DFB) with antiosteoporotic activity, including two new compounds, kaempferol 3-O-beta-D-glucopyranoside-7-O-alpha-L-arabinofuranoside (1) and (R)-5,7,3',5'-tetrahydroxy-flavanone 7-O-neohesperidoside (2), along with nine known ones: three flavanones (3-5), one flavone (7), one flavonol (6), two chromones (8, 10), maltol glucoside (9), and (-)-epicatechin (11). Compounds 4-11 are reported for the first time from this genus. We investigated the proliferative effects of the 11 compounds in the UMR106 osteoblastic cell line in vitro. All compounds exhibited the proliferative activity in the UMR106 cells at most of the concentrations tested. Most compounds are reported for the first time from the Drynaria genus and this was the first study of their proliferative activity in osteoblast-like cells. The main peaks in the HPLC fingerprint of the active fraction (DFB) were also identified.