Biodistribution of strontium and barium in the developing and mature skeleton of rats

Bone acts as a reservoir for many trace elements. Understanding the extent and pattern of elemental accumulation in the skeleton is important from diagnostic, therapeutic, and toxicological perspectives. Some elements are simply adsorbed to bone surfaces by electric force and are buried under bone mineral, while others can replace calcium atoms in the hydroxyapatite structure. In this article, we investigated the extent and pattern of skeletal uptake of barium and strontium in two different age groups, growing, and skeletally mature, in healthy rats. Animals were dosed orally for 4 weeks with either strontium chloride or barium chloride or combined. The distribution of trace elements was imaged in 3D using synchrotron K-edge subtraction micro-CT at 13.5 µm resolution and 2D electron probe microanalysis (EPMA). Bulk concentration of the elements in serum and bone (tibiae) was also measured by mass spectrometry to study the extent of uptake. Toxicological evaluation did not show any cardiotoxicity or nephrotoxicity. Both elements were primarily deposited in the areas of active bone turnover such as growth plates and trabecular bone. Barium and strontium concentration in the bones of juvenile rats was 2.3 times higher, while serum levels were 1.4 and 1.5 times lower than adults. In all treatment and age groups, strontium was preferred to barium even though equal molar concentrations were dosed. This study displayed spatial co-localization of barium and strontium in bone for the first time. Barium and strontium can be used as surrogates for calcium to study the pathological changes in animal models of bone disease and to study the effects of pharmaceutical compounds on bone micro-architecture and bone remodeling in high spatial sensitivity and precision.