Abstract
Summary Statement
Obovatol inhibits receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis and prevents inflammatory bone loss in mice
Introduction
Adult skeletal mass and integrity are maintained by balancing osteoclast-mediated bone resorption and osteoblast-induced bone formation during bone remodeling. Abnormal increases in osteoclastic bone resorption can lead to excessive bone destruction as observed in osteoporosis, rheumatoid arthritis, and metastatic cancers Therefore, Modulation of osteoclast formation and function is a promising strategy for the treatment of bone-destructive diseases. To search for compounds that inhibit osteoclast formation, we tested the effect of obovatol, a natural product isolated from the medicinal plant Magnolia obovata, on osteoclastogenesis and inflammatory bone loss.
Methods
Osteoclastogenesis was assessed using bone marrow-derived macrophages. RANKL signaling was assessed by immunoblotting and apoptosis by cell death ELISA assay. Actin ring staining and resorption pit assay was performed. Bone morphometric parameters were determined using a microcomputed tomography system.
Results
We found that obovatol strongly inhibited osteoclast formation from bone marrow-derived macrophages in a dose-dependent manner without cytotoxicity. Obovatol significantly suppressed RANKL-induced activation of NF-κB, JNK, and ERK signaling pathways. Obovatol also inhibited RANKL-induced expression of the genes c-Fos and nuclear factor of activated T cells c1, which are transcription factors important for osteoclastogenesis. In addition to osteoclast differentiation, obovatol blocked cytoskeletal organization and abrogated the bone resorbing activity of mature osteoclast. Obovatol also accelerated osteoclast apoptosis through the induction of caspase-3 activation. Consistent with its in vitro anti-resorptive effect, obovatol prevented bone loss induced by lipopolysaccharide (LPS) in vivo.
Conclusion
Our findings demonstrate that obovatol, a natural compound isolated from Magnolia obovata, suppresses the differentiation, function, and survival of osteoclasts. Furthermore, obovatol protected against LPS-induced bone loss in vivo. Therefore, we suggest that obovatol may have therapeutic potential for the treatment of bone-destructive diseases characterised by increased osteoclast number and/or activity.
