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 (phi 25x150cm); 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.