Bone protective effects of dried plum and its polyphenols under inflammatory and oxidative stress conditions

Abstract

Scope and Method of Study: The purpose of this study was to utilize the combination of in vivo and in vitro studies to investigate the effects of dried plum (DP) on bone and bone cell activity under conditions of elevated pro-inflammatory mediators. In Study 1, 9-month-old male osteopenic orchidectomized rats were randomly assigned to control (AIN-93M) or DP diet (25%, w/w) for 90 days. The positive control group consumed the control diet and received PTH (80 ug/kg). In Study 2, macrophages (RAW 264.7) were pretreated with the polyphenols extracted from DP (0, 10, 20, or 30 ug/ml) cultured with or without RANKL and then stimulated with either LPS or hydrogen peroxide (H2O2). TRAP-positive osteoclasts and resorption pit formation were evaluated and inflammatory mediators such as NO and TNF-a by macrophages and during their differentiation into osteoclasts were assessed. In Study 3, MC3T3-E1 cells, murine pre-osteoblasts, were utilized to determine how DP polyphenols influence osteoblast activity, function and signaling under normal and inflammatory conditions. Cells were pretreated with polyphenols (0, 2.5, 5, 10 and 20 ug/ml) prior to stimulation with TNF- (0 or 1.0 ng/ml). ALP activity and mineralized nodule formation were measured and alterations in gene expression of RANKL, OPG, Runx2, Osterix and IGF-I were analyzed.

Findings and Conclusions: Study 1 showed that dietary supplementation with DP restored the ORX-induced loss of bone mass and deterioration of bone structure. The restoration of bone microarchitecture by dried plum was comparable to PTH. Study 2 revealed that DP polyphenols inhibit osteoclastogenesis and osteoclast activity which may be mediated by the down-regulation of cytokines such as TNF- and NO. Study 3 showed that DP polyphenols enhance osteoblast activity and mineralized nodule formation under normal and inflammatory conditions. Results in vitro studies suggest that dried plum which has ability to down-regulate inflammatory mediators, has potent effects on osteoclast and osteoblast activity and provide possible mechanisms by which dried plum preserves bone mass and microarchitecture as reported in current and previous in vivo studies.