Fructus Ligustri Lucidi ethanol extract inhibits osteoclastogenesis in RAW264.7 cells via the RANKL signaling pathway

Fructus ligustri Lucidi (FLL) is the fruit of Ligustrum lucidum Ait and a traditional Chinese medicine, primarily known for its role in osteoporosis prevention and treatment. The present study aimed to elucidate the effect and underlying mechanism of action of ethanol extract of FLL on osteoclast differentiation and bone resorption, and to identify the active compounds within it. RAW264.7 murine monocyte/macrophage cells were stimulated with the receptor activator of nuclear factor kappa B ligand (RANKL) to induce osteoclast differentiation in vitro. The present study demosntrated that FLL extract and its two primary components, oleanolic acid (OA) and ursolic acid (UA), significantly suppressed RANKL-induced tartrate resistant acid phosphatase (TRAP) activity and multinucleate osteoclast formation without inducing cytotoxicity; however, no effect was observed on the apoptosis of mature osteoclasts. Additionally, RANKL-induced mRNA expression levels of the key transcription factors, tumor necrosis factor receptor associated factor-6, nuclear factor of activated T cell-c1 and c-Fos, and the osteoclast markers, TRAP, cathepsin K and matrix metalloproteinase-9 were suppressed by FLL, OA and UA. However, no effect was observed on RANKL-induced mRNA expression levels of Src. These results demonstrated that FLL may inhibit osteoclastogenesis in RAW264.7 cells via RANKL signaling pathways. OA and UA are active compounds in inducing this effect; however, their specific roles remain to be elucidated.