Axillaridine A suppresses osteoclastogenesis and alleviates ovariectomy-induced bone loss via inhibition of RANKL-mediated RANK signaling pathways

Steroidal alkaloids are the main active components in many medicinal plants and exhibit diverse biological activities. Axillaridine A (AA) is a newly discovered steroidal alkaloid. However, whether AA could suppress osteoclastogenesis and alleviate ovariectomy-induced bone loss in mice remains unknown. In vitro, AA significantly suppressed the receptor activator of nuclear factor-‍κB (NF-‍κB) ligand (RANKL)‍-induced osteoclast differentiation via downregulating the expression of osteoclastogenesis-related marker genes, proteins, and transcriptional regulators, including tartrate-resistant acid phosphatase (TRAP), c-Src, matrix metallopeptidase-9 (MMP-9), cathepsin K, nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), and c-Fos. This was achieved by blocking RANKL-RANK interaction and inhibiting RANKL-mediated RANK signaling pathways, including NF‍-‍κB, AKT, and mitogen-activated protein kinases (MAPKs) in osteoclast precursors. In vivo, AA significantly inhibited the ovariectomized (OVX)‍-induced body weight gain and blood glucose increase in mice. AA did not adversely affect the histomorphologies, weights, and indices of the kidney and liver in OVX mice. AA effectively ameliorated bone loss in OVX mice by inhibiting osteoclastogenesis. AA significantly inhibited the serum levels of tartrate-resistant acid phosphatase 5b (TRACP-5b) and C-telopeptide of type I collagen (CTX-‍I). AA significantly inhibited the OVX-induced expression of osteoclastogenesis-related marker genes and proteins in the femur. In summary, AA alleviates ovariectomy-induced bone loss in mice by suppressing osteoclastogenesis via inhibition of RANKL-mediated RANK signaling pathways and could be potentially used for the prevention and treatment of osteoclast-related diseases such as osteoporosis.