Silicon deprivation and arginine and cystine supplementation affect bone collagen and bone and plassma trace mineral concentrations in rats

Because arginine has been established as an essential amino acid for collagen formation, and several bone-remodeling proteins are rich in cysteine, we performed a study to ascertain whether supplemental arginine (Arg) and cystine (Cys) would affect bone collagen and mineral composition changes in animals deprived of silicon (Si). Male weanling Sprague-Dawley rats were randomly assigned to treatment groups of 12 in a 2 x 2 factorially arranged experiment. The rats were fed for 9 weeks a basal casein-ground corn-corn oil diet containing per g 2 micrograms Si, 1.7 mg Cys, 4.7 mg methionine, and 7.8 mg Arg. The independent treatment variables, per g fresh diet, were supplemental Si (as sodium metasilicate) at 0 and 35 μg and Cys or Arg at 0 and 12 mg. Silicon deprivation decreased the concentration of hydroxyproline in femur and potassium in vertebra. An interaction between Si and amino acid supplementation affected hematocrit, liver iron concentration, and bone copper and manganese concentrations. In animals deprived of Si, Cys supplementation compared to Arg supplementation depressed hematocrit, liver iron concentration, and tibia and vertebral copper concentrations and increased tibia and vertebral manganese concentrations. On the other hand, in animals fed adequate Si, supplemental Cys compared to supplemental Arg increased hematocrit, liver iron concentration, and tibia and vertebral copper concentrations and decreased tibia and vertebral manganese concentrations. Dietary Si also influenced the effect of Cys on mineral composition of the vertebra. The calcium and phosphorus concentrations in the vertebra were markedly increased by supplemental Cys compared to supplemental Arg when dietary Si was inadequate but had no effect on these concentrations when dietary Si was adequate. These findings indicate that silicon is needed for collagen formation, that high dietary Cys enhances changes induced by Si deprivation in trabecular-rich bone, and that Si nutriture has more impact on trabecular-rich bone than in cortical-rich bone.