Abietic acid attenuates RANKL induced osteoclastogenesis and inflammation associated osteolysis by inhibiting the NF-KB and MAPK signaling.

Osteoporosis is a major debilitating cause of fractures and decreases the quality of life in elderly patients. Bone homeostasis is maintained by bone forming osteoblasts and bone resorpting osteoclasts. Substantial evidences have shown that targeting osteoclasts using natural products is a promising strategy for the treatment of osteoporosis. In the current study, we investigated the osteoprotective effect of Abietic acid (AA) in in vitro and in vivo models of osteolysis. In vitro experiments demonstrated that, AA suppressed receptor activator of nuclear factor-kappa B ligand (RANKL)-induced osteoclastogenesis and F-actin ring formation in a concentration dependent manner. Mechanistically, AA abrogated RANKL-induced phosphorylation of IKK alpha/beta (ser 176/180), IkB alpha (ser 32), and inhibited the nuclear translocation of NF-kappa B. We also found that, AA attenuated the RANKL-induced phosphorylation of MAPKs and decreased the expression of osteoclast specific genes such as TRAP, DC-STAMP, c-Fos, and NFATc1. Consistent with in vitro results, in vivo Lipoploysaccharide (LPS)-induced osteolysis model showed that AA inhibited the LPS-induced serum surge in cytokines TNF-alpha and IL-6. mu-CT analysis showed that AA prevented the LPS-induced osteolysis. Furthermore, histopathology and TRAP staining results suggested that AA decreased the number of osteoclasts in LPS-injected mice. Taken together, we demonstrated that the osteoprotective action of AA is coupled with the inhibition of NF-kappa B and MAPK signaling and subsequent inhibition of NFATc1 and c-Fos activities. Hence, AA may be considered as a promising drug candidate for the treatment of osteoporosis.