Water extract of Uncaria sinensis suppresses RANKL-induced bone loss by attenuating osteoclast differentiation and bone resorption

Background The hooks and stems of Uncaria sinensis have been used to mitigate cardiovascular and central nervous system disorders in Asia traditional medicine. Regulation of osteoclast differentiation and activity is a major target for preventing and treating pathological bone diseases. Methods Tartrate-resistant acid phosphatase (TRAP) activity and the number of TRAP-stained multinucleated cells were used to examine receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation. The activation of RANKL-induced signaling pathways and the expression of transcription factors were investigated by western blot analysis and quantitative real-time polymerase chain reaction. The bone resorption activity of osteoclast was studied using a plate coated with hydroxyl-apatite. Trabecular bone destruction was investigated using a RANKL-induced trabecular bone loss mouse model. Results We found that water extract of the hooks and stems of U. sinensis (WEUS) inhibits RANKL-induced differentiation of murine bone marrow macrophages and RAW264.7 cells into osteoclasts. WEUS inhibited the activation of NF-κB and the expression of nuclear factor of activated T-cells, cytoplasmic 1. In addition, WEUS suppressed the bone resorbing activity of mature osteoclasts without affecting their survival. Furthermore, oral administration of WEUS suppressed RANKL-induced bone loss with a significant amelioration of trabecular bone micro-structures. WEUS also reduced RANKL-induced increase in serum TRAP5b activity and C-terminal cross-linked telopeptide of type I collagen levels. Conclusion The present study demonstrates that WEUS has a pharmacological activity that inhibits osteoclast-mediated bone destruction by suppressing osteoclast differentiation and function. These results suggest that U. sinensis could be a promising herbal candidate for preventing and treating bone diseases such as osteoporosis.