Mollugin from Rubea cordifolia suppresses receptor activator of nuclear factor-κB ligand-induced osteoclastogenesis and bone resorbing activity in vitro and prevents lipopolysaccharide-induced bone loss in vivo.

Osteopenic diseases, such as osteoporosis, are characterized by progressive and excessive bone resorption mediated by enhanced receptor activator of nuclear factor-κB ligand (RANKL) signaling. Therefore, downregulation of RANKL downstream signals may be a valuable approach for the treatment of bone loss-associated disorders. In this study, we investigated the effects of the naphthohydroquinone mollugin on osteoclastogenesis and its function in vitro and in vivo. Mollugin efficiently suppressed RANKL-induced osteoclast differentiation of bone marrow macrophages (BMMs) and bone resorbing activity of mature osteoclasts by inhibiting RANKL-induced c-Fos and NFATc1 expression. Mollugin reduced the phosphorylation of signaling pathways activated in the early stages of osteoclast differentiation, including the MAP kinase, Akt, and GSK3β and inhibited the expression of different genes associated with osteoclastogenesis, such as OSCAR, TRAP, DC-STAMP, OC-STAMP, integrin αν, integrin β3, cathepsin K, and ICAM-1. Furthermore, mice treated with mollugin showed significant restoration of lipopolysaccharide (LPS)-induced bone loss as indicated by micro-CT and histological analysis of femurs. Consequently, these results suggested that mollugin could be a novel therapeutic candidate for bone loss-associated disorders including osteoporosis, rheumatoid arthritis, and periodontitis.