Fraxetin inhibits the induction of anti-Fas IgM, tumor necrosis factor-α and interleukin-1β-mediated apoptosis by Fas pathway inhibition in human osteoblastic cell line MG-63

The survival of osteoblast cells is one of the determinants of the development of osteoporosis in patients with inflamed synovium, such as in rheumatoid arthritis (RA). By means of alkaline phosphatase (ALP) activity and osteocalcin ELISA assay, we have shown that fraxetin exhibits a significant induction of differentiation in the human osteoblast-like cell line MG-63. In addition, we also assessed whether fraxetin affects inflammatory cytokine-mediated apoptosis in osteoblast cells. TNF-α or IL-1β enhance apoptotic DNA fragmentation in anti-Fas IgM-treated MG-63 cells by increasing Fas receptor expression. However, TNF-α or IL-1β treatment alone does not induce apoptosis. Treatment of MG-63 cells with fraxetin not only inhibited anti-Fas IgM-induced apoptosis, but also blocked the synergetic effect of anti-Fas IgM with TNF-α or IL-1β on cell death. The apoptotic inhibition of fraxetin is associated with inhibition of TNF-α and IL-1β-mediated Fas expression and enhancement of FLIP expression, resulting in a decrease of caspase-8 and caspase-3 activation. These results indicate a potential use of fraxetin in preventing osteoporosis by inhibiting inflammatory cytokine-mediated apoptosis in osteoblast cells.