6,7,4'-Trihydroxyflavone inhibits osteoclast formation and bone resorption in vitro and in vivo.

The balance between the osteoblasts and the osteoclasts is important for the maintenance of the skeleton of the human body. The osteoclasts absorb bone after differentiated into polymorphonuclear cells by the fusion of monocytes/macrophages. We have found that 6,7,4'-Trihydroxyflavone (THF), a compound from the heartwood of Dalbergia Odorifera inhibits receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation, actin ring formation, and bone resorption in RAW 264.7 cells and bone marrow macrophage. THF significantly inhibited the c-Jun-N-terminal kinase signaling pathway without affecting extracellular signal-regulated kinase, p38, and AKT signaling. Moreover, THF inhibited the expression of c-Fos, nuclear factor-activated T cells cytoplasm 1, cathepsin K, and c-src by RANKL. We used a lipopolysaccharide (LPS)-induced bone loss model in mice. Consequently, bone volume per tissue volume, trabecular number's reduction was recovered in THF-treated mice, and trabecular separation's augmentation was also attenuated by THF administration. In summary, THF inhibits RANKL-induced osteoclast differentiation by MAPK signaling pathway and inhibits bone resorption by destroying the actin ring in mature osteoclasts. THF also prevented LPS-induced bone loss in a mice model. Thus, THF may be useful in the treatment of bone diseases associated with excessive osteoclast differentiation and bone resorption.