Intracellular Retention of Three Quinuclidine Derivatives in Caco-2 Permeation Experiments: Mechanisms and Impact on Estimating Permeability and Active Efflux Ratio

In vitro evaluation of different organic matrices used to modulate silicon bioavailability

Silicon (Si) has numerous health properties. It is an element of the extracellular matrix; it is involved in collagen synthesis, bone mineralization, and immune system modulation; and it reduces metal accumulation in Alzheimer's disease and the risk of atherosclerosis. Given its poor intestinal absorption, Si is ingested in the form of orthosilicic acid (OSA) to promote its bioavailability. The aim of this work was to compare different commercial dietary supplements containing stabilized OSA to ascertain their bioaccessibility, bioavailability, and safety in a model of human intestinal epithelium. Biocompatibility with the glycocalyx was also investigated. Supplements containing collagen, maltodextrins, and choline as OSA stabilizers were analyzed. Bioaccessibility was explored by means of an in vitro digestive process. Bioavailability was investigated using a Caco2 cell line alone, or co-culturing with a HT29-MTX cell line. The safety of the compounds tested (in terms of intestinal epithelium integrity) was judged on the grounds of MTS assay, transepithelial electrical resistance, and apparent permeability. The three formulations were also tested in a Caco2 cell model of intestinal glycocalyx Si retention. The choline-formulated OSA formulation outperformed the maltodextrin-stabilized supplement, with a Si bioavailability about 14 times higher (P < .05). The choline-formulated OSA formulation increased cell permeability, with consequent intestinal epithelium disruption. The supplements' absorption and bioavailability (and harmfulness) differed considerably, depending on the OSA stabilizer involved. Of the three formulations tested, the collagen-formulated OSA represents the best Si dietary supplement.