Protective Effects of Moderate Ca Supplementation against Cd-Induced Bone Damage under Different Population-Relevant Doses in Young Female Rats

Abstract

Estimation of the skeleton-protective effects of Ca in Cd-induced bone damage is helpful in the assessment of Cd health risk. The aim of this study was to identify whether Ca supplementation during exposure to different population-relevant doses of Cd can prevent Cd-induced bone damage under the tolerable upper intake level of Ca supplementation. Young female Sprague-Dawley rats were given different population-relevant doses of Cd (1, 5, and 50 mg Cd/kg diet) and Ca supplementation (0.4% Ca supplementation) intervention. Ca supplementation significantly decreased Cd-induced bone microstructure damage, increased bone biomechanics (p < 0.05), serum bone formation marker level (p < 0.05) and expression of osteogenic gene markers exposure to the 5 and 50 mg Cd/kg diets. However, it had no impact on these indicators under the 1 mg Cd/kg diets, with the exception of expression of osteogenic marker genes. Ca supplementation significantly decreased serum Klotho level (p < 0.05), and fibroblast growth factor 23/Klotho-associated gene expression in the kidney and bone showed significant changes. In conclusion, Ca supplementation has a positive effect on bone formation and bone quality against the damaging impact of Cd, especially with exposure to the 5 mg and 50 mg Cd/kg diet, which may be related to its impact on the fibroblast growth factor 23/Klotho axis.

Keywords: bone; cadmium; calcium; fibroblast growth factor 23; klotho.

Figure 1

Representative HE images of kidney in female rats fed the AIN93G diet without Cd (control) (a), with 1 mg Cd/kg diet (b), and with 1 mg Cd/kg diet plus 0.15% Ca supplementation (c), with 1 mg Cd/kg diet plus 0.4% Ca supplementation (d), with 1 mg Cd/kg diet plus 0.6% Ca supplementation Ca (e). Tubular epithelial cell calcification and tubular vacuolation are shown in (d,e).

Figure 2

Representative HE staining of distal left tibia sections without Cd (a); with 1 mg Cd/kg diet Cd (b), with 1 mg Cd/kg diet plus Ca (c), 5 mg Cd/kg diet (d), 5 mg Cd/kg diet plus Ca (e), 50 mg Cd/kg diet (f), and 50 mg Cd/kg diet plus Ca (g). The trabecular number and cortical thickness decreased and that the trabecular separation increased in d, f groups. Ca supplementation led to a significantly increased in trabecular number and cortical thickness (e,g). But there were no significant differences in exposure to the 1 mg Cd/kg diet with (c) or without Ca supplementation (b).