Full Length ArticleParathyroid hormone attenuates radiation-induced increases in collagen crosslink ratio at periosteal surfaces of mouse tibia

- Limited field irradiation induces an increase in bone collagen crosslink ratio, as measured by Raman spectroscopy.
- PTH administration partially attenuates the radiation-induced increase in collagen crosslink ratio.
- Molecular alignment of bone mineral and collagen are increased post-irradiation, and this is not attenuated by PTH supplementation.
- These data suggest that initial radiation damage to bone has extensive, persistent effects on the quality of tissue formed post-irradiation.
- Preventing initial radiation damage to bone matrix may be critical to preventing later bone fragility resulting from material embrittlement.

As part of our ongoing efforts to understand underlying mechanisms contributing to radiation-associated bone fragility and to identify possible treatments, we evaluated the longitudinal effects of parathyroid hormone (PTH) treatment on bone quality in a murine model of limited field irradiation. We hypothesized PTH would mitigate radiation-induced changes in the chemical composition and structure of bone, as measured by microscope-based Raman spectroscopy. We further hypothesized that collagen crosslinking would be especially responsive to PTH treatment. Raman spectroscopy was performed on retrieved tibiae (6-7/group/time point) to quantify metrics associated with bone quality, including: mineral-to-matrix ratio, carbonate-to-phosphate ratio, mineral crystallinity, collagen crosslink (trivalent:divalent) ratio, and the mineral and matrix depolarization ratios. Irradiation disrupted the molecular structure and orientation of bone collagen, as evidenced by a higher collagen crosslink ratio and lower matrix depolarization ratio (vs. non-irradiated control bones), persisting until 12 weeks post-irradiation. Radiation transiently affected the mineral phase, as evidenced by increased mineral crystallinity and mineral-to-matrix ratio at 4 weeks compared to controls. Radiation decreased bone mineral depolarization ratios through 12 weeks, indicating increased mineral alignment. PTH treatment partially attenuated radiation-induced increases in collagen crosslink ratio, but did not restore collagen or mineral alignment. These post-radiation matrix changes are consistent with our previous studies of radiation damage to bone, and suggest that the initial radiation damage to bone matrix has extensive effects on the quality of tissue deposited thereafter. In addition to maintaining bone quality, preventing initial radiation damage to the bone matrix (i.e. crosslink ratio, matrix orientation) may be critical to preventing late-onset fragility fractures.

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