Tocotrienol regulates osteoclastogenesis in rheumatoid arthritis

Background/Aims: The present study aimed to investigate whether tocotrienol regulates interleukin 17 (IL-17)-induced osteoclastogenesis in rheumatoid arthri tis (RA). Methods: We evaluated the effect of tocotrienol on IL-17-induced receptor activa tor of nuclear factor kappa B ligand (RANKL) production using RA fibroblast-like synoviocyte (FLS), together with real-time polymerase chain reaction and en zyme-linked immunosorbent assay. Osteoclast differentiation was confirmed after culturing IL-17-treated RA FLS and Th17 cells with tocotrienol and monocytes. We analyzed the suppressive effect of tocotrienol on Th17 cells percentage or Th17-cy tokine levels among peripheral blood mononuclear cells using flow cytometry. Results: We found that IL-17 stimulated FLS to produce RANKL and tocotrie nol decreased this IL-17-induced RANKL production. Tocotrienol decreased the IL-17-induced activation of mammalian target of rapamycin, extracellular signal-regulated kinase, and inhibitor of kappa B-alpha. When monocytes were incubated with IL-17, RANKL, IL-17-treated FLS or Th17 cells, osteoclasts were differentiated and tocotrienol decreased this osteoclast differentiation. Tocotrie nol reduced Th17 cell differentiation and the production of IL-17 and sRANKL; however, tocotrienol did not affect Treg cell differentiation. Conclusions: Tocotrienol inhibited IL-17- activated RANKL production in RA FLS and IL-17-activated osteoclast formation. In addition, tocotrienol reduced Th17 differentiation. Therefore, tocotrienol could be a new therapeutic choice to treat bone destructive processes in RA.