Elucidating the effect of specific surface area on the gastrointestinal absorption of nanostructured calcium through Calcium-45 in vivo radiotracing

Abstract

Low dietary calcium intake and absorption may increase the risk of hypocalcaemia disease states. Reducing the particle size of calcium-containing powders and increasing the specific surface area (SSA), may have high oral calcium bioavailability. The absorption of a single dose of different sized calcium carbonate nanoparticles was traced in Sprague-Dawley rats with radioactive calcium-45 (half-life = 162.6 days, β^- endpoint = 258 keV; 100%). Four calcium carbonate formulations (calcium-45) were administered to Sprague-Dawley rodents (6 per treatment; n = 24). The groups were [⁴⁵Ca]CaCO₃ SSA 3 m²/g, [⁴⁵Ca]CaCO₃ 36 m²/g, [⁴⁵Ca]CaCO₃ 64 m²/g and a separate [⁴⁵Ca]CaCO₃ 36 m²/g formulation produced by flame assisted pyrolysis. Blood and urine were sampled periodically, and organs collected and analysed after euthanasia. No changes in SSA or crystallinity were observed when powders before or after irradiation were compared. The [⁴⁵Ca]CaCO₃ 64 m²/g formulation presented with higher levels in blood 2 h after administration and a higher liver and femur concentration. These findings suggest [⁴⁵Ca]CaCO₃ 64 m²/g could lead to increased oral bioavailability.

Keywords: Calcium carbonate; Flame-assisted pyrolysis (FASP); Hypocalcemia; Nanoparticles.