Astragaloside IV attenuates glucocorticoid-induced osteoclastogenesis and bone loss via the MAPK/NF-κB pathway

Astragaloside IV (AS-IV) is a bioactive saponin extracted from Radix Astragali, and it is reported to promote osteoblast differentiation while inhibiting osteoclastogenesis. However, the mechanism of AS-IV in glucocorticoid-induced osteoclastogenesis (GIO) remains undetermined. Herein, we examined the influence of AS-IV on GIO and bone loss. RAW264.7 cells were incubated with dexamethasone (Dex) alone or Dex and receptor activator of nuclear factor-B ligand (RANKL) (Dex and RANKL) for 2 days, and then treated with Dex or Dex and RANKL through AS-IV for the timeframes indicated. Following, mice were intraperitoneally administered with an intermediate-acting glucocorticoid, methylprednisolone (MP), or MP and AS-IV for 6 weeks. AS-IV significantly decreased Dex-induced osteoclast nucleus and area, however, it did not impact the number of Dex-induced osteoclasts in RAW264.7 cells. AS-IV also significantly decreased the osteoclastic marker protein expressions in Dex-induced RAW264.7 cells with concentration of dose dependent fashion. Additionally, AS-IV promoted p38 phosphorylation (p-) and p-p65 translocation to the nucleus, while inhibiting phosphorylation of extracellular signal-regulated kinase (ERK) (p-ERK) and inhibitor of Nuclear factor κB (NF-κB) (p-IκB) levels. However, the AS-IV-mediated action on p-MAPK, p-NF-κB, and osteoclastic marker expressions were reversed by MAPK or IκB inhibitor in Dex-induced RAW264.7 cells. Furthermore, our in vivo evaluation revealed that AS-IV also attenuated the MP-mediated bone loss, and suppressed osteoclastogenesis. This study demonstrates that AS-IV inhibits GIO and attenuates bone loss via the MAPK/NF-κB pathway. This also suggested that AS-IV could be a potential promising therapeutic agent for glucocorticoid-triggered bone loss.