Dietary casein phosphopeptides prevent bone loss in aged ovariectomized rats

Abstract

The effect of dietary Ca-bound casein phosphopeptides (CaCPP) on the bones of aged ovariectomized (OVX) rats was studied as a model for post-menopausal bone loss. Three groups of ovariectomized rats were fed a control diet or one of two experimental diets, and one group of sham-operated rats (SHAM) was fed the control diet. The experimental diets contained 0.5% Ca and 0.4% P. In one diet, CaCPP was the sole source of calcium and provided 62.5% of dietary phosphorus (CaCPP diet). In the other, Ca-free CPP provided 100% of dietary phosphorus (Ca-free CPP diet). In the control diet, CaCO3 and KH2PO4 were used. During a 17-wk feeding period, there was little change in femoral bone mineral densities (BMD) of ovariectomized rats fed CaCPP and Ca-free CPP, or in the SHAM rats fed the control diet, whereas the bone mineral densities in the control ovariectomized rats decreased with time. Some of the segmental bone mineral densities of the excised femurs from the rats fed CaCPP were significantly higher than those from the control ovariectomized rats, but the values of the Ca-free CPP group were similar to those of the control ovariectomized rats. In the Ca-free CPP group, the discrepancy in bone mineral densities obtained between in vivo results and excised specimens might have been the result of a loss in bone mass due to their significant loss in body weight. There were no significant differences in serum inorganic phosphorus, alkaline phosphatase activity, osteocalcin or 1 alpha-25-dihydroxycholecalciferol concentrations among the ovariectomized groups. In the CaCPP and Ca-free CPP groups, urinary phosphorus excretion decreased and urinary calcium excretion increased significantly with time. The inhibitory effect on bone loss in aged ovariectomized rats could be due to the effects of dietary CaCPP on phosphorus and calcium metabolism.