Dried Plum Polyphenols Inhibit Osteoclastogenesis by Downregulating NFATc1 and Inflammatory Mediators
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Dried plums and their polyphenols have been shown to suppress bone resorption by downregulating receptor activator NF-κB ligand (RANKL). Due to the anti-inflammatory and antioxidant properties of these compounds, this study was designed to investigate whether dried plum polyphenols exert additional, more direct effects on osteoclasts and their precursors. RAW 264.7 macrophages were used as a model to study osteoclast precursors and osteoclast differentiation and activity. Under inflammatory conditions induced by lipopolysaccharide (LPS), polyphenols extracted from dried plum (10, 20, and 30 μg/mL) downregulated osteoclast precursor cyclooxygenase expression and nitric oxide (NO) by inhibiting inducible NO synthase. NO and tumor necrosis factor (TNF)-α were also suppressed in the presence of RANKL during osteoclastogenesis by the polyphenols. Increased TNF-α production in response to oxidative stress, but not LPS, was decreased over time. As expected, LPS and H2O2 significantly increased the number of tartrate-resistant acid phosphatase-positive cells by 127% and 30%, respectively. Dried plum polyphenols decreased osteoclast differentiation under normal as well as inflammatory and oxidative stress conditions, coincident with the suppression of the transcription factor, nuclear factor for activated T cells (NFATc1). These inhibitory effects on osteoclastogenesis were confirmed in primary bone marrow cultures. Resorption pit formation was decreased to a similar extent as osteoclast differentiation, suggesting that dried plum polyphenols primarily affect osteoclast differentiation as opposed to activity. Our data demonstrate that dried plum polyphenols directly inhibit osteoclastogenesis, leading to a decrease in osteoclast activity, by downregulating NFATc1 and inflammatory mediators.
KeywordsBone Osteoclast Antioxidant Osteoporosis Macrophage
This material is based upon work supported by Cooperative State Research, Education and Extension Service, U.S. Department of Agriculture, under award 2006-35200-17383. Additionally, this study was supported by the California Dried Plum Board and the Oklahoma Center for the Advancement of Science and Technology (HR06-109).
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