Saikosaponin a inhibits RANKL-induced osteoclastogenesis by suppressing NF-κB and MAPK pathways

Inflammatory cytokines play an important role in osteoclastogenesis. Saikosaponin a (SSa) possesses anti-inflammatory activity. However, the role of SSa in osteoporosis is still unclear. Therefore, the objective of this study was to investigate the effects of SSa on receptor activator of the nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis and signaling pathway by in vitro assay. In mouse bone marrow monocytes (BMMs), SSa suppressed RANKL plus macrophage colony-stimulating factor (M-CSF)-induced osteoclast differentiation in a dose-dependent manner. Moreover, SSa decreased osteoclastogenesis-related marker proteins expression, including NFATc1, c-fos and cathepsin K. At molecular levels, SSa inhibited RANKL-induced IκBα phosphorylation, p65 phosphorylation and NF-κB luciferase activity in RAW264.7 cells. And SSa also suppressed RANKL-induced p-38, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) phosphorylation. Taken together, these findings suggest that SSa suppresses osteoclastogenesis through inhibiting RANKL-induced p-38, ERK, JNK and NF-κB activation. SSa is a novel agent in the treatment of osteoclast-related diseases, such as osteoporosis.