Longan fruit increase bone mineral density in zebrafish and ovariectomized rat by suppressing RANKL-induced osteoclast differentiation

Background: The receptor activator of nuclear factor-kappa B ligand (RANKL)-induced nuclear factor-kappa B (NF-kappa B) signaling pathway plays essential roles in osteoclast differentiation and may serve as an attractive target for the development of therapeutics for osteoporosis. Purpose: This study aimed to identify plant extracts that attenuated RANKL-induced NF-kappa B signaling pathway and examine their anti-osteoporotic effects in animal model systems. Methods: Osteoclast differentiation was determined by western blot analysis, RT-PCR, and tartrate-resistant acid phosphatase (TRAP) assay. The effect of Longan (Dimocarpus longan Lour.) fruit extract (LFE) on bone mineral density was evaluated by calcein staining in zebrafish and micro-CT analysis in ovariectomized (OVX) rat. Results: LFE nullified RANKL-induced down-regulation of inhibitor of NF-kappa B, which keeps NF-kappa B sequestered in the cytosol, thereby inhibiting translocation of NF-kappa B to the nucleus, in RAW264.7 cells. In addition, LFE decreased the nuclear levels of c-Fos and nuclear factor of activated T-cells c1, which play crucial roles in RANKL-induced osteoclast differentiation, in RAW264.7 cells. LFE repressed RANKL-activated cathepsin K and TRAP expression in RAW264.7 cells, resulting in a reduction of the number of TRAP-positive multinucleated cells, without cytotoxicity. Furthermore, LFE increased bone mineralization in zebrafish and prevented bone loss in OVX rat. Conclusion: Collectively, our findings suggest that LFE exerts its anti-osteoporotic activity through inhibition of osteoclast differentiation and may have potential as a herbal therapeutic or preventive agent for the treatment of osteoporosis.