The effect of dietary xylitol on recalcifying and newly formed cortical long bone in rats

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Abstract
Thirty-six 3-week-old male Wistar rats were labeled with a single intraperitoneal tetracycline injection. Twenty-four of them were then fed a Ca-deficient basal diet for 3 weeks, while the control group received the basal diet supplemented with CaCO3 (12 g/kg). The tetracycline labeling was then repeated and six animals in each group were decapitated. The diet of the remaining formerly Ca-deficient animals was returned to normal, and half the test rats also received xylitol supplementation (50 g/kg). After 4 weeks of rehabilitation the labeling was repeated and the animals were decapitated and their tibias were prepared. The tibias were measured in terms of weight and density and cross sections were prepared for the examination of mineral content. Bone element analysis was performed by scanning electron microscopy with electron-probe microanalysis, examining separately the bone areas formed during the various dietary periods. Areas of the former Ca-deficient and newly formed cortical bone were identified by tetracycline fluorescence under ultraviolet light, and the amount of cortical bone in each group was measured. The mineralization-promoting effect of dietary xylitol as compared with CaCO3 supplementation alone was seen more clearly in the newly formed periosteal bone than in remineralization of the formerly Ca-deficient bone, the concentrations of Ca and P being significantly elevated (P < 0.05), as also was the total mineral content (P < 0.01). The cortical bone volume was similar following the CaCO3 and CaCO3 + xylitol supplementations, suggesting unaltered formation of the organic matrix. The results show that the effect of xylitol on bone during dietary Ca rehabilitation particularly concerns newly formed bone mineral. This may be due to the slow process of remodeling in the former mineralized bone or to xylitol induced effects on osteoblast and/or osteoclast metabolism.