Fourier transform infrared imaging spectroscopy (FT-IRIS) of mineralization in bisphosphonate-treated oim/oim mice

Abstract

Fourier transform infrared microscopy (FT-IRM) and imaging spectroscopy (FT-IRIS) are increasingly used to analyze the molecular components of mineralized tissues. A primary advantage of these techniques is the capability to simultaneously image the quantity and quality of multiple components in histological sections at 7 microm spatial resolution. In the current study, FT-IRM and FT-IRIS were used to characterize bone mineralization in a mouse model of osteogenesis imperfecta (OI) after treatment with the bisphosphonate alendronate (ALN). This application is currently relevant since recent studies have demonstrated great promise for the treatment of children with OI with bisphosphonates, but have not identified bisphosphonate-associated bone quality changes. Growing oim/oim mice, a model of moderate-to-severe OI, were treated with ALN (73 microg ALN/kg/day for 4 weeks followed by 26 mg/kg/day for 4 weeks) or saline from 6 to 14 weeks of age, and mineralization was evaluated in femoral cortical and metaphyseal bone. Infrared vibrations of the mineral (a carbonated apatite) and the matrix phases were monitored. The relative amounts of mineral and matrix present (min:matrix), the relative amount of carbonate present in the mineral (carb:min), and the crystallinity of the mineral phase were calculated. In untreated oim/oim bone, the min:matrix was greater and the crystallinity was reduced (indicative of less mature mineral) in the primary versus the secondary spongiosa, most likely due to the presence of calcified cartilage. With ALN treatment, the oim/oim mm:matrix increased in the secondary spongiosa, but the mineral crystallinity was not changed. In the cortical bone, no changes were evident with ALN treatment. These data demonstrate that in this mouse model, ALN treatment results in increased metaphyseal bone mineralization, but does not improve mineral maturity.