Mineralization Altered by Collagen Cross-links Inhibition in Bone and Enamel

Objectives: Compromised collagen and mineral can lead to decreases in bone and enamel quality in a variety of genetic conditions and systemic diseases. It is unknown if perturbed collagen cross-links dictate the mineralization of the collagen similarly in long bones and dental tissues. Most collagen cross-links occur enzymatically by the activity of the lysyl oxidase (LOX) enzyme family, yet much less is known about the small, yet important, proportions of collagens found during enamel formation. Our hypothesis is that mineralization in both bone and dental tissues will be negatively affected by perturbations to collagen cross-linking.
Methods: To study the effects of cross-link inhibition on mineralization, mice are injected with b-aminoproprionitrile (BAPN) to inhibit LOX activity. Long bones (n=7-8) and mandibles (n=3) from mice treated with BAPN or phosphate buffered saline (PBS) were analyzed by Raman spectroscopy for mineral composition and crystallinity.
Results: Femora of mice treated with BAPN showed a significantly higher mineral:phenylalanine (p=0.02) ratio and a trend towards a lower carbonate:phosphate ratio (p=0.06), with no difference in crystallinity. Enamel showed a significant increase in hydroxyproline and proline bands (p=0.012) with BAPN treatment as well as a decrease in the phosphate:hydroxyproline+proline (p=0.026) and mineral crystallinity (p=0.051).
Conclusions: These results suggest that collagen cross-links may influence both the relative amount and composition of mineral in bone and enamel in vivo. When the collagen matrix is perturbed via LOX inhibition, long bones are hypermineralized, as seen by the increase in mineral:matrix ratio. In enamel, perturbed collagen cross-links are associated with an increased mineral:protein ratio. These results suggest that proper mineral formation is impacted by collagen cross-linking in both long bones and enamel.