Dietary silicon affects bone turnover differently in ovariectomized and sham-operated growing rats†‡§¶

Abstract

An experiment was performed to test the hypothesis that low dietary silicon affects blood, bone, and urine indices associated with bone formation and breakdown, bone strength and physical characteristics, and the circulating amount of an extracellular matrix protein (osteopontin) involved in bone cell adhesion and activation. A second objective was to ascertain whether ovariectomy (estrogen deficiency) alters the effects of low dietary silicon on bone formation. Female rats weighing about 56 g were assigned to groups of 10 in a factorially arranged experiment. The variables were supplemental dietary silicon at 0 or 35 mg/kg and ovariectomy (estrogen-deficient) or sham operation at the start of the experiment. The basal silicon-low diet contained about 2 mg Si/kg. Low dietary silicon compared with adequate silicon decreased plasma osteopontin concentration, increased plasma sialic acid concentration, and increased urinary helical peptide excretion. Low dietary silicon also affected the response to estrogen deficiency. Ovariectomy increased plasma alkaline phosphatase in the silicon-supplemented, but not in the silicon-low rats. In contrast, ovariectomy decreased liver ornithine aminotransferase in silicon-low but not in silicon-supplemented rats. Ovariectomy increased the urinary excretion of deoxypyridinoline and decreased the femur concentration of sialic acid more markedly in silicon-supplemented than silicon-low rats. Silicon and an interaction between silicon and ovariectomy only mildly changed bone strength and physical measurements and did not affect femur calcium concentration. The findings suggest that silicon has a biochemical function that affects bone growth processes before bone crystal formation by affecting bone collagen turnover and sialic acid-containing extracellular matrix proteins such as osteopontin. J. Trace Elem. Exp. Med. 17:137–149, 2004. Published 2004 Wiley-Liss, Inc.