Strontium is incorporated into mineral crystals only in newly formed bone during strontium ranelate treatment

Abstract

Strontium ranelate has been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk. The aim of this study was to investigate the potential influence of strontium ranelate (Protelos) treatment on human bone tissue characteristics and quality at the micro- and nanostructural levels. We investigated transiliac biopsies from patients treated for 36 months with strontium ranelate or placebo (n = 5 per group) using synchrotron radiation with a microbeam combining scanning small-angle scattering, X-ray diffraction, and fluorescence spectroscopy (SAXS/XRD/XRF) for a detailed characterization of the mineral crystals within the collagenous bone matrix. A scanning procedure allowed the simultaneous determination of maps of the chemical composition together with thickness, length, and lattice spacing of these mineral crystals within each of the 15- or 25-microm-wide pixels in a thin bone section. The fluorescence results show that only bone packets or osteons formed during the strontium ranelate treatment contain significant amounts of strontium and that up to 0.5 of 10 calcium atoms in the mineral crystals are replaced by strontium, as revealed by a corresponding shift in apatite lattice spacing. The thickness and length of the plate-shaped bone mineral crystals were not affected by the strontium ranelate treatment. As a consequence, there was no indication for a change in human bone tissue quality at the nanoscale after a 36-month treatment of postmenopausal osteoporotic women with strontium ranelate, except for a partial replacement of calcium by strontium ions in the hydroxyapatite crystals, only in newly formed bone.