Boldine isolated from Litsea cubeba inhibits bone resorption by suppressing the osteoclast differentiation in collagen-induced arthritis

Objective: To investigate the effect of boldine isolated from Litsea cubeba on collagen-induced arthritis (CIA) rats and explore the molecular mechanism predicted by network pharmacology.

Material and methods: CIA rats were orally administered with boldine. The bone destruction of paws was analyzed by histologic examination, tartrate-resistant Acid Phosphatase (TRACP) staining and micro-computed tomography. Prediction of signal pathway associated with boldine network molecules and CIA genes was applied by the network pharmacology analysis. The expressions of Osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) in the ankle were detected by immunohistochemistry. In vitro osteoclasts were cultured in the presence of variable doses of boldine and the RANK expressions were evaluated using Real-time polymerase chain reaction and western blot.

Results: Boldine reduced ankle swelling, alleviated pathological damage and significantly prevented bone destruction in CIA rats. Consistent with this, Enzyme linked immunosorbent assay revealed boldine decreased serum TRACP5b levels and osteoclast number in the ankle region by TRACP staining from CIA rats. The network pharmacology analysis indicated that RANK signaling in osteoclasts was the most significant canonical pathway associated with boldine network molecules and CIA genes, which was verified by the increased expression of OPG, reduced expression of RANK, RANKL and RANKL/OPG in boldine-treated CIA rats. The in vitro study further confirmed that boldine inhibited osteoclastogenesis by inhibiting the RANKL/RANK signaling pathway.

Conclusion: Taken together, our study first indicates that boldine from Litsea cubeba suppresses osteoclastogenesis, improves bone destruction by down-regulating the OPG/RANKL/RANK signal pathway and may be a potential therapeutic agent for rheumatoid arthritis.