Effect of Calcium, Tannic Acid, Phytic Acid and Pectin over Iron Uptake in an In Vitro Caco-2 Cell Model

Calcium, phytic acid, polyphenols and fiber are major inhibitors of iron absorption and they could be found in excess in some diets, thereby altering or modifying the iron nutrition status. The purpose of this study is to evaluate the effect of calcium, tannic acid, phytic acid, and pectin over iron uptake, using an in vitro model of epithelial cells (Caco-2 cell line). Caco-2 cells were incubated with iron (10-30 mu M) with or without CaCl2 (500 and 1,000 mu M) for 24 h. Then, cells were challenged with phytic acid (50-150 mu M); pectin (50-150 nM) or tannic acid (100-500 mu M) for another 24 h. Finally, Fe-55 (10 mu M) uptake was determined. Iron dialyzability was studied using an in vitro digestion method. Iron uptake in cells pre-incubated with 20 and 30 mu M Fe was inhibited by CaCl2 (500 mu M). Iron uptake decreased in cells cultured with tannic acid (300 mu M) and CaCl2 (500-1,000 mu M) (two-way ANOVA, p = 0.002). Phytic acid also decreased iron uptake mainly when cells were treated with CaCl2 (1,000 mu M) (two-way ANOVA; p < 0.05). Pectin slightly decreased iron uptake (p = NS). Iron dialyzability decreased when iron was mixed with CaCl2 and phytic or tannic acid (T test p < 0.0001, for both) but not when mixed with pectin. Phytic acid combined with calcium is a strong iron uptake inhibitor. Pectin slightly decreased iron uptake with or without calcium. Tannic acid showed an unexpected behavior, inducing an increase on iron uptake, despite its low Fe dialyzability.