Mechanism of Bone Collagen Degradation due to KOH Treatment

BACKGROUND: The mechanisms underlying the effect of alterations in type I collagen on bone mechanical properties are not well defined. In a previous study, male and female emu tibiae were endocortically treated with 1M potassium hydroxide (KOH) solution for 1-14days. This treatment resulted in negligible mass loss (0.5%), collagen loss (0.05%), no differences in geometrical parameters but significant changes in mechanical properties. The objective of this study was to determine the mechanism of collagen degradation due to KOH treatment in order to explain the previously observed mechanical property changes. METHODS: Bone mineral was assessed using x-ray diffraction (XRD), microhardness and backscattered electron imaging (BSE). Bone collagen was assessed using α-chymotrypsin digestion, differential scanning calorimetry (DSC), gel electrophoresis (SDS-PAGE) and polarized light microscopy (PLM). RESULTS: BSE, microhardness and XRD revealed no changes in bone mineral due to KOH treatment. DSC showed an altered curve shape (lower and broader), indicating a change in collagen organization due to KOH treatment. Decreased α-chain band intensity in 14-day KOH treated groups detected using SDS-PAGE indicated α-chain fragmentation due to KOH treatment. PLM images revealed differences in collagen structure in terms of pattern distribution of preferentially oriented collagen between the periosteal and endocortical regions. CONCLUSION: These results suggest that endocortical KOH treatment causes in situ collagen degradation, which explains the previously reported altered mechanical properties. GENERAL SIGNIFICANCE: Compromising the organic component of bone contributes to an increase in bone fragility