Flavonoids compounds from Tridax procumbens inhibit osteoclast differentiation by down-regulating c-Fos activation

The total flavonoids from Tridax procumbens (TPFs) have been reported significantly to suppress on RANKL-induced osteoclast differentiation and bone resorption in mouse primary cultured osteoclasts. However, the effects of ethyl ether fraction of Tridax procumbens flavonoids (TPF) on osteoclastogenesis remain unknown. In this study, we investigated the effects of TPF on lipopolysaccharides (LPS)-induced osteoclast differentiation, actin ring formation, and explored its molecular mechanism in vitro. Matured osteoclast was counted as the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, and activity of osteoclast was assessed by performing the pit formation assays. Real-time polymerase chain reaction (RT-PCR) was performed for evaluation of the expression of osteoclast differentiation-related genes. TPF reduced the TRAP-positive multinucleated osteoclasts, inhibited TRAP and acid phosphatase (ACP) activities and decreased the expression of osteoclast differentiating genes, including cathepsin K, metalloproteinase-2 (MMP-2), MMP-9, MMP-13 and osteoclast-associated receptor (OSCAR). Furthermore, osteoclast-dependent actin rings formation and resorption pits were dramatically inhibited by the treatment with TPF. TPF markedly decreased the expression levels of transcription factors such as c-Fos, nuclear factor of activated T cells cytoplasmic 1 (NFATc1) and activator protein-1 (AP-1). Taken together, our findings indicated that TPF suppressed both osteoclast differentiation and activities. Therefore, TPF might be a promising and emerging drug candidate for the treatment of bone diseases such as osteoporosis.