Mechanical evaluation of debilitated tibia diaphysis in rats during the growth period -Combination therapy with high-calcium diet and grape seed proanthocyanidin extract-

The main ingredient of grape seed proanthocyanidin extract (GSPE), is proanthocyanidin, a kind of flavonoid. Proanthocyanidins are known to have a variety of biological regulatory activities, such as antioxidant effects; however, little is known the effects on bone. In the present study, we performed mechanical analysis using three-dimensional peripheral quantitative computed tomography (pQCT), bone strength tests and quantitative analysis of a combination therapy composed of high-calcium diet and GSPE fed to rats during their growth. Forty male Wistar rats, 5 weeks old, were divided randomly into control (A), low-calcium diet (B), low-calcium/high-calcium diet (C) and low-calcium/high-calcium diet with supplementary GSPE (D) groups. After 6 weeks, the tibias were removed and cortical bone density, cross-sectional area, mineral content, cortical bone thickness, periosteal perimeters, endosteal perimeters, and stress strain index (SSI) were measured. Invasive three-point bending tests, and quantitative analysis of Ca, P, Mg and Zn using inductively coupled plasma (ICP) spectral analysis were performed. Body weights were not significantly different in the 4 groups. Cortical bone density and mineral content in group D were significantly higher than those in group C (P < 0.01) as was the periosteal perimeter (P < 0.05). SSI and three-point bending test results for group D were not significantly different than those for group C, but recovery in group D was similar to that in the control group. As for the quantitative analysis, Ca, P, and Zn levels in group D were significantly higher than those in group C (P < 0.01). Our findings suggest that a combined therapy with a high-calcium diet and GSPE can improve the quality and strength of rat tibias during their growth.