Olive polyphenols attenuate TNF-α-stimulated M-CSF and IL-6 synthesis in osteoblasts: Suppression of Akt and p44/p42 MAP kinase signaling pathways

Background: Olive oil polyphenols, which possess cytoprotective activities like anti-oxidant and antiinflammatory effects, could modulate osteoblast functions. The aim of this study is to elucidate the effects and the underlying mechanisms of hydroxytyrosol and oleuropein on the tumor necrosis factor-alpha (TNF-alpha)-induced macrophage colony-stimulating factor (M-CSF) and interleukin-6 (IL-6) synthesis in osteoblasts. Methods: Osteoblast-like MC3T3-E1 cells were pretreated with hydroxytyrosol, oleuropein, deguelin, PD98059 or wedelolactone, and then stimulated by TNF-alpha. The levels of M-CSF and IL-6 in the conditioned medium were determined with ELISA. The mRNA expression levels of M-CSF or IL-6 were determined with real-time RT-PCR. The phosphorylation levels of Akt, p44/p42 mitogen-activated protein (MAP) kinase or NF-Kappa B in the cell lysates were determined with Western blot analysis. Results: Hydroxytyrosol and oleuropein attenuated the TNF-alpha-stimulated M-CSF release. Deguelin, an inhibitor of Akt, significantly suppressed the TNF-alpha-stimulated M-CSF release, which failed to be affected by the MEK1/2 inhibitor PD98059 or the I Kappa B inhibitor wedelolactone. Hydroxytyrosol and oleuropein suppressed the TNF alpha-induced phosphorylation of Akt and p44/p42 MAP kinase. Hydroxytyrosol and oleuropein attenuated the TNF alpha-stimulated IL-6 release. Hydroxytyrosol suppressed the TNF-alpha-induced mRNA expressions of M-CSF and IL-6. Hydroxytyrosol or oleuropein failed to affect the cell viability. Conclusion: Our present findings strongly suggest that olive oil polyphenols hydroxytyrosol and oleuropein down regulates TNF-alpha signaling at the points upstream of Akt and p44/p42 MAP kinase in osteoblasts, leading to the attenuation of M-CSF and IL-6 synthesis.

Automated summary

The study revealed that olive oil polyphenols, hydroxytyrosol and oleuropein, attenuated the synthesis of M-CSF and IL-6 in osteoblasts by inhibiting TNF-α signaling through Akt and p44/p42 MAP kinase pathways. These polyphenols did not significantly affect cell viability.