5.3. The effects of xylitol on bone composition and structure
5.3.1. The effects on bone inorganic fraction
The weight of the tibia in the rats that were fed xylitol supplemented diets was similar to that of the controls (study I). When comparing the rats fed diets of different polyol supplementations (study II), the weight of scapula was significantly smaller in the sorbitol administration group than in the control (p<0.05) and D-mannitol (p<0.05) groups. In experimental osteoporosis studies, tibial weights of the ovariectomized rats with and without dietary xylitol supplementation were similar, but both exceeded those of the sham-operated controls in study V (p<0.05).
Tibial density and humeral ash weight of the ovariectomized rats were significantly smaller than those of the sham-operated rats (p<0.05) (Study V). However, in the ovariectomized rats fed the diet supplemented with 10% xylitol, the decrease of tibial density was eliminated, and the decrease of humeral ash weight significantly reduced. Furthermore, dietary xylitol supplementation inhibited the decrease of humeral calcium and phosphorus concentrations observed after ovariectomy (Table 5-1).
Table 5-1. Tibial density and biochemical data of the inorganic fraction of humerus in ovariectomized rats (ovx), in ovariectomized rats fed a diet supplemented with 10% xylitol (ovx+xyl), and in sham-operated rats (sham)*
| Sham | Ovx | Ovx + Xyl | |
|---|---|---|---|
| Tibia | |||
| Density, g/cm3 | 1.661±0.031b | 1.637±0.024a | 1.655±0.020b |
| Humerus | |||
| Ash weight, g/100g | 62.2±1.0b | 58.8±1.4a | 60.6±1.4b |
| Calcium, mg/g | 204.9±10.9b | 188.5±15.4a | 203.2±17.3b |
| Phosphorus, mg/g | 113.3±5.0b | 105.9±3.1 | 112.4±5.8b |
| *All values are expressed as mean±SD, n = 14. Group means in a row with different superscript letters differ significantly (p<0.05). Statistical test used was one-way ANOVA, further comparisons made by Fisher"s PLSD. | |||
5.3.2. The effects on bone collagen
No quantitative changes of bone collagenous structures were detected among the rats that were fed the basal diet or the diets with 5, 10 or 20% xylitol supplementation. The measured variables were the amount of collagen per dry weight of organic matrix, the concentrations of pyridinoline and deoxypyridinoline in collagen, and the ratio of these crosslinks in the humerus (study IV).
Ovariectomy, as compared to the sham-operated controls, caused a significant decrease in the amount of hydroxyproline in the organic fraction of tibia (p<0.0001) (Study III). The concentrations of pyridinoline (p=0.0007) and deoxypyridinoline (p=0.0028) were decreased in proportion. The 10% dietary xylitol supplementation normalized the above mentioned decreases, so that no significant difference was seen between the xylitol-fed ovariectomized rats and the sham-operated controls. The ratio between the crosslink analogs remained unchanged in all groups.
5.3.3. The effects on bone trabeculation
The histomorphometrical data for the secondary spongiosa of the proximal tibia (Figure 5-4) revealed that trabecular bone volume (BV/TV) was significantly increased after the 5% (p=0.025), 10% (p=0.004) and 20% (p<0.001) dietary xylitol supplementation as compared to the controls (study IV).
Figure 5-4. Proximal tibia (representing average) of a control rat (A), and of a rat fed a diet supplemented with 5% (B), 10% (C), or 20% xylitol (D). Trabecular bone volumes (%, mean±SD) of different groups were 15.3±2,5, 18.4±4.1, 19.3±2.6 and 25.9±2.3, respectively (n=10 in each group) (Study IV, Fig. 2.).
In the experimental osteoporosis study, the trabecular bone volume of the ovariectomized rats was only about one half of that of the sham-operated controls (p<0.0001) (Studies III and V). However, in the ovariectomized rats fed the 10% xylitol-supplemented diet, the trabecular bone volume was significantly higher than that of the ovariectomized rats without xylitol (p<0.0001). In study III (Figure 5-5), the trabecular bone volume (%, mean ± SD) was 27.5 ± 6.0 in controls, 13.5 ± 3.2 in ovariectomized rats, and 20.2 ± 1.9 in xylitol-fed ovariectomized rats.
