Guaiacol Suppresses Osteoclastogenesis by Blocking Interactions of RANK with TRAF6 and C-Src and Inhibiting NF-κB, MAPK and AKT Pathways

Angelica sinensis (AS; Dang Gui), a traditional Chinese herb, has for centuries been used for the treatment of bone diseases, including osteoporosis and osteonecrosis. However, the effective ingredient and underlying mechanisms remain elusive. Here, we identified guaiacol as the active component of AS by two-dimensional cell membrane chromatography/C18 column/time-of-flight mass spectrometry (2D CMC/C18 column/TOFMS). Guaiacol suppressed osteoclastogenesis and osteoclast function in bone marrow monocytes (BMMCs) and RAW264.7 cells in vitro in a dose-dependent manner. Co-immunoprecipitation indicated that guaiacol blocked RANK-TRAF6 association and RANK-C-Src association. Moreover, guaiacol prevented phosphorylation of p65, p50, IκB (NF-κB pathway), ERK, JNK, c-fos, p38 (MAPK pathway) and Akt (AKT pathway), and reduced the expression levels of Cathepsin K, CTR, MMP-9 and TRAP. Guaiacol also suppressed the expression of nuclear factor of activated T-cells cytoplasmic 1(NFATc1) and the RANKL-induced Ca oscillation. In vivo, it ameliorated ovariectomy-induced bone loss by suppressing excessive osteoclastogenesis. Taken together, our findings suggest that guaiacol inhibits RANKL-induced osteoclastogenesis by blocking the interactions of RANK with TRAF6 and C-Src, and by suppressing the NF-κB, MAPK and AKT signalling pathways. Therefore, this compound shows therapeutic potential for osteoclastogenesis-related bone diseases, including postmenopausal osteoporosis.