Structural characterization of a novel oligosaccharide from Achyranthes bidentata and its anti-osteoporosis activities

Achyranthes bidentata Blume is one of the most frequently used medicinal herbs prescribed for treatment of osteoporosis in China. This study describes the crude saccharide (AB90) from A. bidentata and reports the osteoprotective effects of AB90 in ovariectomized (OVX) rats. The results indicated that AB90 significantly increased the bone mineral content (BMC) and bone mineral density (BMD) and improved the biomechanical properties in OVX rats. To further explore the fraction(s) responsible for above activity, a novel oligosaccharide (ABW90-1) was isolated continuously by DEAE-Cellulose 52 and Sephacryl S-100 filtration columns and characterized by infrared spectroscopy, monosaccharide analysis, methylation and NMR analysis. It was composed of (2 → 6)-linked-β-d-fructofuranosyl (Fruf), (2 → 1)-linked-β-d-Fruf residues and was terminated with Glc and Fru residues. The advanced structure and conformation of novel polysaccharide ABW90-1 were investigated by circular dichroism (CD) and scanning electron microscopy (SEM) data, and the results indicated that ABW90-1 was composed of randomly distributed sheet-like appearances instead of a triple-helix structure. In addition, in vitro activity of ABW90-1 was evaluated by using primary osteoblasts, and the data suggested that ABW90-1 exhibited favorable effects on the proliferation and differentiation of primary osteoblasts.