Limonoid 7-Deacetoxy-7-oxogedunin (CG-1) Attenuates RANKL-Induced Osteoclastogenesis via Inhibiting PI3K/Akt-NFATc1 Axis.

Excessive bone resorption by osteoclasts causes pathological bone loss in diseases such as osteoporosis. 7-Deacetoxy-7-oxogedunin (CG-1), a limonoid isolated from Carapa guianensis (Meliaceae), exhibits various biological activities. Here, we examined the anti-osteoclastogenic effect of CG-1 and its underlying mechanism in receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation of RAW264.7 cells. CG-1 inhibited the formation of tartrate-resistant acid phosphatase-positive multinucleated cells and decreased the expression of osteoclastogenesis-related genes. When CG-1 was added to the culture during the first 3 days of the 5-day-osteoclastogenesis period, the expression levels of the osteoclastogenesis-related genes (Nfatc1, Acp5, Src, Ctsk, and Mmp9) were decreased, as was observed when CG-1 was added continuously for 5 days. Furthermore, CG-1 lowered RANKL-induced Akt phosphorylation, which is similar to the results seen with the PI3K inhibitor, LY294002. Moreover, CG-1 and LY294002 suppressed the RANKL-induced expression of NFATc1, the master transcription factor for regulating terminal differentiation into osteoclasts. These results suggest that CG-1 attenuated RANKL-induced osteoclastogenesis by inhibiting the PI3K/Akt-NFATc1 axis during the early stage of osteoclast differentiation. Thus, CG-1 has the potential to suppress osteoclast-mediated bone resorption.