Cross-linking and new bone collagen synthesis in immobilized and recovering primate osteoporosis

Quantification of collagen cross-links of monkey bone (tibia), from various time periods of immobilization (up to 7 months) and their subsequent reambulation (up to 40 months) was determined. Results indicated reducible cross-link concentrations markedly increased and peaked at the seven-month period of immobilization and returned to control values after 40 months of recovery. Chromatographic profiles of the major cross-linked peptides indicated that the increased cross-linking after seven months immobilization occurred between residue Hylald-16c as well as Lysald-16c of the alpha 1 chains and residue 87 Hyl of alpha chains of type I collagen. Mature, stable cross-link concentrations as well as their molecular loci remained constant throughout immobilization and reambulation. These results strongly suggest that rapid new bone collagen synthesis occurred during the osteoporotic state due to immobilization. With long-term recovery, the rate of collagen synthesis apparently returned to match the control bone.