β-carotene and inhibitors of iron absorption modify iron uptake by Caco-2 cells

A National fortification program instated in Venezuela in 1993 reduced iron deficiency and anemia by half in only 1 y. The fortification mixture contained ferrous fumarate, vitamin A and other vitamins. We conducted experiments to characterize ferrous fumarate uptake by Caco-2 cells. Increasing amounts of ferrous fumarate, vitamin A, phytate, tannic acid and beta-carotene were added to incubation mixtures using a range of concentrations that included the molar ratios used in the Venezuelan fortification program. Cells were incubated for 1 h at 37 degrees C with 37 kBq Fe-59 and the compound to be evaluated. They were then rinsed, trypsinized and counted to measure uptake. Effects of ascorbic acid, days in culture and use of flasks or inserts were also evaluated. Optimal conditions for uptake experiments were pH 5.5, in the presence of ascorbic acid and at 16 d in culture. Use of flasks or inserts did not affect uptake. Vitamin A did not significantly increase iron uptake under the experimental conditions employed. However, beta-carotene (6 mu mol/L) significantly increased iron uptake compared to no beta-carotene addition (114.9 +/- 6.3 and 47.2 +/- 5.9 pmol/mg cell protein, respectively). Moreover, in the presence of phytates or tannic acid, beta-carotene generally overcame the inhibitory effects of both compounds depending on their concentrations. We conclude that beta-carotene improves iron uptake and overcomes the inhibition by potent inhibitors of iron absorption. These experiments also validated the usefulness of Caco-2 cell model system to evaluate iron metabolism.