3',4',7,8-Tetrahydroxyflavone inhibits RANKL-induced osteoclast formation and bone resorption.

Osteoclasts, which are specialized bone multinuclear cells, are responsible for bone lytic diseases such as osteoporosis. 3',4',7,8-tetrahydroxyflavone is a flavonoid from Acacia confusa. In the present study, we found that 3',4',7,8-tetrahydroxyflavone markedly inhibited receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastic differentiation from mouse bone marrow-derived macrophages (BMMs). 3',4',7,8-tetrahydroxyflavone also reduced the mRNA expression levels of osteoclastic marker genes including the calcitonin receptor (CTR) and cathepsin K. In addition, 3',4',7,8-tetrahydroxyflavone decreased the bone resorption activity of osteoclasts on dentin slices. We found that 3',4',7,8-tetrahydroxyflavone inhibited RANKL-induced expression of c-Fos and nuclear factor of activated T cells c1 (NFATc1), a key transcription factor of osteoclast differentiation. Furthermore, ectopic overexpression of a constitutively active form of NFATc1 completely rescued the anti-osteoclastogenic effect of 3',4',7,8-tetrahydroxyflavone, suggesting that the anti-osteoclastogenic effect was mainly attributed to the reduction in NFATc1 expression. Taken together, our data suggest that 3',4',7,8-tetrahydroxyflavone inhibits osteoclast differentiation and bone loss and may therefore be considered a promising drug candidate for treating or preventing bone-lytic diseases.