The prebiotic arabinogalactan of Anoectochilus formosanus prevents ovariectomy-induced osteoporosis in mice

Anoectochilus formosanus (Orchidaceae) has previously been shown to exhibit anti-osteoporosis and prebiotic properties. In this study, these bioactivities were verified and associated with an isolated type II arabinogalactan (AGAF) in ovariectomized (OVX) mice model. Female ICR mice were OVX and administrated AGAF (5 and 15 mg/kg) or inulin (400 mg/kg) orally for 3 weeks. Streptomycin was used for blocking the bioactivities of AGAF. In results, AGAF increased the level of fecal bifidobacteria, cecal soluble Ca and short chain fatty acids. Comparing to OVX control group, AGAF improved bone mineral content, trabecular bone volume, and the number of trabecular significantly. In RT-PCR analysis, AGAF reduced the expression of tartrate-resistant acid phosphatase, cathepsin K, and osteocalcin. Streptomycin inhibited both anti-osteoporosis and prebiotic effects of AGAF. In vitro experiments revealed butyrate, not AGAF could activate osteoblasts and inhibit osteoclasts differentiation. Thus, this study demonstrated that AGAF prevents bone loss in OVX mice through prebiotic effects in vivo and in vitro.