Samul-tang suppresses RANKL-induced osteoclast differentiation in RAW264.7 cells

Samul-tang (SMT) is a traditional herbal medicine used for the treatment of ischemic brain and heart diseases. In this study, we investigated the molecular mechanism underlying the inhibitory effects of SMT on osteoclast differentiation induced by the receptor activator for nuclear factor κB ligand (RANKL) in RAW264.7 cells. SMT dose-dependently and significantly inhibited the RANKL-induced tartrate-resistant acid phosphatase (TRAP) activity and the formation of multi-nucleated osteoclasts. In addition, SMT significantly reduced the RANKL-induced mRNA expression of osteoclast differentiation-related genes that encode TRAP, c-src, matrix metalloproteinase (MMP)-9, cathepsin K, and the d2 isoform of vacuolar ATPase V(0) domain (ATPv0d2). SMT also inhibited the RANKL-induced activation of MAP kinases and NF-κB p65, and mRNA expression of transcription factors (Fra-2 and NFATc1). In conclusion, these results suggested that SMT suppresses the RANKL-induced activation of signaling molecules and transcription factors, which consequently inhibits osteoclast differentiation.