Effect of tart cherry polyphenols on osteoclast differentiation and activity
Bone is maintained by an intricate balance between bone formation and bone resorption. The presence of inflammation can contribute to an imbalance in bone homeostasis by enhancing differentiation and activity of osteoclasts, the cells that participate in the breakdown of bone. Polyphenols such as flavonoids found in plant-derived foods have been shown to have anti-inflammatory effects in various tissues. Tart cherries are a rich source of such polyphenolic compounds. Using mouse macrophage cells (RAW 264.7), we examined whether tart cherry polyphenols (TCP) could dose-dependently inhibit the proliferation and activity of RANKL-differentiated osteoclasts under inflammatory conditions. Tartrate resistant acid phosphatase (TRAP) activity and staining of TRAP positive multinucleated cells, used as indicators of osteoclast differentiation and activity, decreased in a dose-dependent manner with TCP treatment. Osteoprotegerin (OPG) expression by osteoclasts was decreased in a dose-dependent manner as well. A significant increase in nitrite concentration was observed with the lower doses of TCP of 50 and 100 μg/mL (p<0.05). However, higher doses of TCP (200 and 300 μg/mL) reduced nitrite concentrations below that of the control that received no TCP treatment (p<0.05). Western blot analyses showed that protein expression of COX-2 followed a similar trend, although results were not statistically significant. Conversely, TCP treatments dose-dependently increased iNOS protein expression with statistical significance noted at doses of 200 and 300 μg/mL. Overall, our findings suggest that the polyphenols associated with tart cherries inhibit the negative effects of osteoclasts on bone health.