Dried plum's unique capacity to reverse bone loss and alter bone metabolism in postmenopausal osteoporosis model

Abstract

Interest in dried plum has increased over the past decade due to its promise in restoring bone and preventing bone loss in animal models of osteoporosis. This study compared the effects of dried plum on bone to other dried fruits and further explored the potential mechanisms of action through which dried plum may exert its osteoprotective effects. Adult osteopenic ovariectomized (OVX) C57BL/6 mice were fed either a control diet or a diet supplemented with 25% (w/w) dried plum, apple, apricot, grape or mango for 8 weeks. Whole body and spine bone mineral density improved in mice consuming the dried plum, apricot and grape diets compared to the OVX control mice, but dried plum was the only fruit to have an anabolic effect on trabecular bone in the vertebra and prevent bone loss in the tibia. Restoration of biomechanical properties occurred in conjunction with the changes in trabecular bone in the spine. Compared to other dried fruits in this study, dried plum was unique in its ability to down-regulate osteoclast differentiation coincident with up-regulating osteoblast and glutathione (GPx) activity. These alterations in bone metabolism and antioxidant status compared to other dried fruits provide insight into dried plum's unique effects on bone.

Figure 1. Histological Images of the Tibia and µCT Analyses of Trabecular Bone Volume in the Vertebra and Tibia.

Representative images of the proximal tibia are shown with H&E stain following the 8 week treatment period (A). Comparisons of trabecular bone morphometric parameters in sham-operated (Sham) and osteopenic ovariectomized (OVX) mice fed control diet, or control diet supplemented with either 25% (w/w) dried plum, apple, apricot, grape, or mango. Trabecular bone microarchitectural of (B) bone volume/total volume (BV/TV) in the vertebral body (□) and proximal tibia (▪). Bars represent the mean ± SE, n  =  6 mice in each group. Bars that share the same superscript letter are not significantly different from each other (p<0.05).

Figure 2. Percent Change in Vertebral Trabecular Bone Normalized to OVX-Control at Baseline.

Percent change in vertebral BV/TV in ovariectomized (OVX) mice fed control diet, or control diet supplemented with either 25% (w/w) dried plum, apple, apricot, grape, or mango relative to baseline OVX controls. The percent change was calculated by determining the difference between the OVX group mean BV/TV at baseline and BV/TV of individual animals at the final time point, and then expressing that value relative to baseline. Bars represent the mean ± SE, n  =  6 mice in each group. Bars that share the same superscript letter are not significantly different from each other (p<0.05).

Figure 3. Alterations in Plasma Glutathione Peroxidase Activity (GPx) with Dried Fruit Treatments.

Comparisons of plasma GPx in sham-operated (Sham) and ovariectomized (OVX) mice fed control diet, or control diet supplemented with either 25% (w/w) dried plum, apple, apricot, grape, or mango for 8 weeks. Bars represent the mean ± SE, n  =  8 mice in each group. Bars that share the same superscript letter are not significantly different from each other (p<0.05).

Figure 4. qRT-PCR Analyses of Genes Involved in Osteoclastogenesis and Osteoblast Activity.

Bone marrow (A) was analyzed for relative mRNA abundance of the osteoclastgensis gene nuclear factor of activated T-cells (Nfatc1), while the flushed femur (B-D) was used to assess genes involved in osteoblast activity and function: alkaline phosphatase (Alp), type 1 collagen (Col1a1), and osteocalcin (Ocn) in sham-operated (Sham) and ovariectomized (OVX) mice fed control diet, or control diet supplemented with either 25% (w/w) dried plum, apple, apricot, grape, or mango. Bars represent the mean ± SE, n  =  6 mice in each group. Bars that share the same superscript letter are not significantly different from each other (p<0.05).

Figure 5. Relative mRNA Abundance of Apoptotic Genes.

The relative mRNA abundance of apoptotic genes was assessed in the bone marrow (A) and flushed femur (B–D). Genes of interest including, B-cell lymphoma homologous antagonist/killer (Bak1), caspase -3 (Casp3) and -9 (Casp9) from sham-operated (Sham) and ovariectomized (OVX) mice fed control diet, or control diet supplemented with either 25% (w/w) dried plum, apple, apricot, grape, or mango. Bars represent the mean ± SE, n  =  6 mice in each group. Bars that share the same superscript letter are not significantly different from each other (p<0.05).