Effects of dried plum supplementation on bone metabolism in adult C57BL/6 male mice

Abstract

Dietary supplementation of dried plum (DP) prevents bone loss and restores bone mass in osteopenic animal models. This study was designed to determine the effects of DP supplementation on bone metabolic activity over time using adult (6-month-old) male C57BL/6 mice (n = 40) receiving control (CON = AIN93 M) or CON+DP 25 % (w/w) diets for 4 or 12 weeks. After 4 weeks of treatment, animals consuming the DP diet had a higher whole-body bone mineral density, vertebral trabecular bone volume (BV/TV), and femoral cortical thickness compared to the CON animals. In the distal metaphysis of the femur, BV/TV was increased in the DP-treated animals, but only after 12 weeks. Bone histomorphometric analyses revealed that DP decreased osteoblast surface (67 %) and osteoclast surface (62 %) at 4 weeks, but these surfaces normalized to the CON animals by 12 weeks. Coincident with these changes, the mineralizing surface (MS/BS) and cancellous bone formation rate (BFR/BS) were reduced at 4 weeks in the DP group compared to the CON, but by 12 weeks of DP supplementation, BFR/BS (~twofold) and MS/BS (~1.7-fold) tended to be increased (p < 0.10). The relative abundance of RNA for key regulators of osteoblast and osteoclast differentiation and indicators of osteoblast activity were reduced in the DP group at 4 weeks with no difference between groups at 12 weeks. These results indicate that supplementing the diet with DP initially suppressed cancellous bone turnover, but a biphasic response occurs over time, resulting in a positive effect on bone mass and structure.

Fig. 1

DP supplementation alters serum markers of bone metabolism at 4 and 12 weeks: a procollagen type 1 amino terminal propeptide (P1NP) and b pyridinoline crosslinks. Bars represent the mean ± SE. t tests were performed at each time point to compare DP treatment groups to their respective controls. *p < 0.05; n = 9–10 mice/group

Fig. 2

Alterations in serum glutathione peroxidase activity in response to 4 and 12 weeks of DP treatment. Bars represent the mean ± SE; t tests were performed at each time point to compare DP treatment groups to their respective controls. *p < 0.05; n = 9–10 mice/group

Fig. 3

Effects of DP treatment at 4 and 12 weeks on trabecular bone histomorphometric indices of the distal femoral metaphysis: a osteoclast surface, b osteoblast surface, c mineralizing surface, d bone formation rate, and e mineral apposition rate. Values presented are mean ± SE, and statistical analyses consisted of t tests to compare treatment groups at each time point. *DP treatment group is different from control at given time point, p < 0.05; n = 5–10 mice/group

Fig. 4

Alterations in gene expression related to osteoblast differentiation and activity. The relative mRNA abundance of a peroxisome proliferator-activated receptor gamma (Pparγ), b runt-related transcription factor 2 (Runx2), c osterix (Osx), d bone morphogenetic protein 2 (Bmp2), e bone morphogenetic protein 4 (Bmp4), f alkaline phosphatase (Alp), g collagen type 1, alpha 1 (Col1a1), and h osteocalcin (Bglap2) are shown after 4 and 12 weeks of DP supplementation. *DP treatment group is different from control at given time point, p < 0.05; n = 5–6 mice/group

Fig. 5

Alterations in gene expression related to osteoclast differentiation and activity. The relative mRNA abundance of a receptor activator of NF-κB ligand (Rankl) and b osteoprotegerin (Opg) in the flushed femur, and c nuclear factor of activated T cells (Nfatc1), and d cathepsin K (Ctsk) in the bone marrow are shown after 4 and 12 weeks of DP supplementation. *DP treatment group is different from control at given time point, p < 0.05; n = 9–10 mice/group