The binding of RANKL to its receptor RANK leads to the recruitment of TNF receptor-associated factor 6 (TRAF6) to the cytoplasmic domain of RANK [6, 7]. The downstream targets of TRAF6 are predominantly mediated by a trimeric complex containing the NF-κB essential modulator (NEMO), an inhibitor of NF-κB kinase (IKK) α and IKKβ. IKK regulates the degradation of the inhibitor of NF-κB, selleck chemical IκBα, by promoting its phosphorylation and further degradation via the proteasome–selleck ubiquitin pathway. Liberated NF-κB subsequently translocates into the nucleus, where it binds to DNA and promotes the transcription of various genes [8]. NF-κB is important for the initial induction

of the nuclear factor of activated T cell c1 (NFATc1) expression. NFATc1 binds to its own promoter, thus switching on a robust induction of NFATc1 [8]. NFATc1 is likely a key regulator of RANKL-induced osteoclast differentiation, fusion, and activation [9, 10]. Alendronate is a synthetic agent that is currently the most widely used drug for postmenopausal osteoporosis. Alendronate is a bone resorption inhibitor that maintains bone mass by inhibiting the function of osteoclasts [11]. Some people taking alendronate have experienced severe effects, such as osteonecrosis and insufficiency fractures [12, 13]. Growing evidence shows

that the benefits of natural products, which are thought to be healthier and safer for the treatment of osteoporosis, can overcome the side effects of this synthetic drug. Kinsenoside [3-(R)-3-β-d-glucopyranosyloxybutanolide] is a significant and active compound STA-9090 of the Anoectochilus formosanus (Orchidaceae), an important ethnomedicinal plant in Taiwan [14]. This compound has hepatoprotective, hypoglycemic, and antiinflammatory effects [15–17]. Kinsenoside inhibits NF-κB activation by lipopolysaccharide (LPS) in mouse peritoneal lavage macrophages (MPLMs) [17]. Several reports have shown that crude extracts of A. formosanus can ameliorate the osteoporosis induced by ovariectomy in rats [18, 19]. However, the antiosteoporotic activity of kinsenoside remains unclear. This study investigates the effects of kinsenoside on osteopenia in OVX mice, using

alendronate Farnesyltransferase as a positive control drug. In vivo study indicates that the antiosteoporotic activity of kinsenoside might be related to its inhibitory effect on osteoclastogenesis. This study also investigates the effects of kinsenoside on RANKL-induced NF-κB activation and on osteoclastogenesis in osteoclast precursor cells. Materials and methods Preparation of kinsenoside Kinsenoside was prepared by Professor Wu. The identity and purity of kinsenoside (>85 %) were analyzed by HPLC according to a previous report [15]. For the in vivo study, kinsenoside was dissolved in distilled water and concentrations of 10 and 30 mg/ml were prepared. Animals Female Wistar rats and imprinting control region (ICR) mice were purchased from BioLASCO Co., Ltd. (Taipei, Taiwan).