Dried plum polyphenols attenuate the detrimental effects of TNF-α on osteoblast function coincident with up-regulation of Runx2, Osterix and IGF-I

Previous studies have demonstrated that dried plums which contain high amounts of polyphenols can restore bone mass and structure, and significantly increase indices of bone formation. The purpose of this study was to determine how dried plum polyphenols influence osteoblast activity and mineralized nodule formation under normal and inflammatory conditions. MC3T3-E1 cells were plated and pretreated with dried plum polyphenols (0, 2.5, 5, 10 and 20 μg/ml) and 24 h later stimulated with TNF-α (0 or 1.0 ng/ml). The 5, 10 and 20 μg/ml doses of polyphenols significantly increased intracellular ALP activity under normal conditions at 7 and 14 days, and restored the TNF-α-induced suppression of intracellular ALP activity by 14 days (P<.001). Polyphenols also increased mineralized nodule formation under normal and inflammatory conditions. In the absence of TNF-α, 5 μg/ml of polyphenols significantly up-regulated the growth factor, IGF-I, compared to controls, and the 5 and 10 μg/ml doses increased the expression of lysyl oxidase involved in collagen crosslinking. TNF-α decreased the expression of Runx2, Osterix and IGF-I, and polyphenols restored their mRNA levels to that of the controls. Although TNF-α failed to alter lysyl oxidase at 18 h, the polyphenols up-regulated its expression (P<.05) in the presence of TNF-α. As expected, TNF-α up-regulated RANKL mRNA and polyphenols suppressed RANKL expression without altering OPG. Based on these findings, we conclude that dried plum polyphenols enhance osteoblast activity and function by up-regulating Runx2, Osterix and IGF-I and increasing lysyl oxidase expression, and at the same time attenuate osteoclastogenesis signaling.