Boron Supplementation Influences Bone Mineralization by Modulating Expression of Genes Regulating Calcium Utilization

The influence of dietary boron (B) supplementation on bone mineralization in rats with or without dietary calcium (Ca) restriction was studied in a feeding trial of 90d. Wister strain male rats (n=84; ∼34 wks of age) were divided into seven dietary groups (4 replicates of 3 each) namely, Normal-Ca (100%) basal diet alone (NC, control; 1.69 ppm B) or supplemented with B at 5 (NCB-5), 10 (NCB-10), 20 (NCB20) and 40 ppm (NCB-40) levels; low-Ca (50%) basal diet alone (LC) or supplemented with 40 ppm B (LCB-40). After 90d of experimental feeding, a 5d digestibility trial was conducted to estimate gut absorption of minerals. Eight rats from each group were sacrificed to collect blood for estimation of minerals, femur bone for assessment of minerals, bone breaking strength and radiography, and liver for appraisal of relative mRNA abundance of calmodulin (CAL), vitamin D binding protein (VDBP) and thyroid receptor binding protein (TRBP). Boron supplementation to Ca adequate diets improved (P<0.05) the gut absorption efficiency of Ca (at 5 and 10 ppm B) and Ca content in serum (at 20 at 40 ppm B). The Ca content in femur bone, its (bone) breaking strength and cortical index were observed to be lowest (P<0.05) in the LC group, and were improved (P<0.05) with B-supplementation (40 ppm). Supplementation of B improved (P<0.01) the relative mRNA expression levels for VDBP (at 10 ppm B) and CAL (at 10, 20 and 40 ppm B) in liver tissue as compared to control. The present study indicates a positive and supportive role of B in Ca utilization with both normal and restricted level of dietary Ca and bone mineralization which was mediated through modulation of Ca regulating genes.