The Caco-2 cell culture system can be used as a model to study food iron availability

To assess the usefulness of the Caco-2 cell culture system as a model to study the availability of dietary iron, preliminary experiments were performed to determine the optimal conditions for iron uptake and transport. Iron uptake of radioactive ferrous sulfate was optimal at pH 5.5 using a 2:1 molar ratio of ascorbic acid to iron and a 1-h incubation time. Under these experimental conditions, we studied the effect on iron uptake of adding supernatants from homogenates of different meat sources, soybean protein isolates, egg albumen and bovine serum albumin. Iron uptake was 6.3 +/- 1.7% from meat, which was significantly greater (P < 0.001) than the values of 1.2 +/- 0.3% from soybean protein, 1.3 +/- 0.3% from egg albumen and 0.8 +/- 0.1% from bovine serum albumin. Iron uptake was also significantly higher from digested meat samples than from undigested meat when the protein concentration was equalized. Measurements of iron uptake and protein concentration from fractions obtained after preparative isoelectric focusing of meat and soybean protein extracts showed two peaks of higher protein concentration and iron uptake in meat, apparently not found in soybean protein, that contained the factor(s) responsible for the higher iron uptake by the cells. In view of these observed similarities with iron absorption studies in humans, we conclude that the Caco-2 cell culture system is a useful in vitro model to study food iron availability.