The effect of vitamin D on the structural crosslinks and maturation of chick bone collagen

The quantitative relationships were determined between the structural crosslinks, dihydroxylysinonorleucine (Lys(OH)2-Nle) and hydroxylysinonorleucine (Lys (OH) -Nle) in NaB 3H4-reduced diaphyseal bone collagen from 1-, 2-, 3- and 4-week-old chicks fed either a vitamin D-deficient diet, a normal-vitamin D diet or a high-, but non toxic, vitamin D diet from time of hatching. Chicks fed the normal diet showed a progressive decrease in the ratio of Lys(OH)2-Nle/Lys(OH)-Nle with age. This decrease was accelerated in chicks receiving the High-vitamin D diet. In the vitamin D-deficient group, the ratio was higher than controls at 1 and 2 weeks and increased further at 3 and 4 weeks. Similar changes in Lys(OH)2-Nle/Lys(OH)-Nle ratio did not occur in skin collagen. Compared to Control-vitamin D animals, the increased crosslink ratios in the vitamin D-deficient bone collagen occurred prior to changes in growth rate and could not be correlated with lysine hydroxylation or the hypocalcemia seen in this group. These results suggest that the type of crosslink analysis used in this study provides one of the earliest and most sensitive indications of a bone disturbance due to vitamin D deficiency and that vitamin D specifically acts to increase the rate of maturation of bone collagen.