Bone Abstracts

HLA-B27 transgenic rats, developed by inserting into rat genome the gene for HLA-B27, a human Class I major histocompatibility molecule involved in antigen presentation, spontaneously develop arthritis, ankylosing spondylitis, gastrointestinal inflammation, and severe alveolar bone loss, among other signs of a generalized inflammatory response. Clinical manifestations in these rats closely resemble features of HLA-B27–associated diseases in humans. More recently, investigators demonstrated that these animals have bones with lower biomechanical strength and reduced structural attributes (e.g., bone volume, trabecular thickness, bone mineral density). The bone-specific mechanisms implicated in the HLA-B27 rat osteopenia include increased bone resorption and dysregulation of the RANKL/OPG system.

In the present study, femora from transgenic rats (TG; n=6) and their sex- and age-matched controls (WT; n=6) were analyzed by means of Fourier transform infrared imaging and Raman microspectroscopy to establish their intrinsic material properties. The results indicated that, compared to WT, TG bones had significantly lower mineral to matrix ratio (a form of bone density that takes into account the amount of organic matrix present in the bone volume analyzed; shown to correlate with ash weight measurements), similar relative proteoglycan content (normalized to amount of organic matrix; modulators of mineralization), and significantly higher collagen cross-link ratio (pyridinoline/divalent). Moreover, the mineral to matrix ratio in the analyzed femora was significantly inversely correlated to alveolar bone loss in these animals.

The results of the present study indicate that intrinsic bone material properties are altered in the TG animals. These alterations may contribute to the poorer long bone mechanical properties and the severity of alveolar bone loss in these animals. The decrease in mineral to matrix ratio without a concomitant difference in relative proteoglycan content suggests the likelihood of lesser calcium and/or phosphate availability during mineralization in TG animals.