In vitro study of intestinal transport of fluoride using the Caco-2 cell line

Water and food are the main sources of fluoride exposure and therefore it is necessary to study intestinal absorption in order to make a correct evaluation of the risk/benefit associated with exposure to fluoride. The present study characterizes intestinal transport of fluoride, using the Caco-2 cell line as a model of the intestinal epithelium, and evaluates the coefficients of apparent permeability and intracellular accumulation in various conditions (pH, temperature, opening of cell junctions, presence of anions). The results indicate that fluoride is an element with moderate absorption (<70%) in both directions (absorptive and secretory). Both in absorption (apical–basolateral) and in secretion (basolateral–apical) there is transport by the paracellular pathway, which may be considered predominant. Absorption and secretion of fluoride increase at acid pH levels, possibly because of its non-ionized state at these pHs and/or because of participation of a F−/H+ cotransporter or a F−/OH− antiporter. The results also suggest transcellular participation of mechanisms involved in transport of Cl− and of an active transport in the secretory direction. The present study extend the knowledge on the cellular transport of fluoride and provide the basis for future studies aimed at identifying potential transporters involved in human fluoride absorption.