Strontium ranelate changes the composition and crystal structure of the biological bone-like apatite produced in osteoblast cell cultures

We evaluate the effects of strontium ranelate on the composition and crystal structure of the biological bone-like apatite produced in osteoblast cell cultures, a system that gave us the advantage of obtaining mineral samples produced exclusively during treatment. Cells were treated with strontium ranelate at concentrations of 0.05 and 0.5 mM Sr²⁺. Mineral substances were isolated and analyzed by using a combination of methods: Fourier transform infrared spectroscopy, solid-state ¹H nuclear magnetic resonance, X-ray diffraction, micro-Raman spectroscopy and energy dispersive X-ray spectroscopy. The minerals produced in all cell cultures were typical bone-like apatites. No changes occurred in the local structural order or crystal size of the minerals. However, we noticed several relevant changes in the mineral produced under 0.5 mM Sr²⁺: (1) increase in type-B CO ₃ ^2- substitutions, which often lead to the creation of vacancies in Ca²⁺ and OH^- sites; (2) incorporation of Sr²⁺ by substituting slightly less than 10 % of Ca²⁺ in the apatite crystal lattice, resulting in an increase in both lattice parameters a and c; (3) change in the PO₄ ^3- environments, possibly because of the expansion of the lattice; (4) the Ca/P ratio of this mineral was reduced, but its (Ca+Sr)/P ratio was the same as that of the control, indicating that its overall cation/P ratio was preserved. Thus, strontium ranelate changes the composition and crystal structure of the biological bone-like apatite produced in osteoblast cell cultures.