Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 1996
Publication Date: N/A
Interpretive Summary: Iron deficiency anemia is generally considered the most widespread nutritional deficiency in both the USA and the world. In part, this is the result of poor bioavailability of dietary iron, i.e., generally, less than 5% of the iron in the diet is absorbed. Efforts to improve bioavailability of food iron, particularly from plant foods, have been hampered by the lack kof a rapid and inexpensive means of estimating bioavailability. There is considerable interest amongst the nutrition community in using Caco-2 cells, a human derived intestinal cell line, to estimate bioavailability of iron and other nutrients. In this study, we investigated the effects of various amino acids and small peptides (products of protein digestion) on iron uptake by Caco-2 cells. We found that cysteine, a sulfur-containing, amino acid, and cysteinyl-glycine, a sulfur-containing peptide, enhanced iron uptake by Caco-2 cells. These results are similar to those observed in human trials and reinforce the potential of Caco-2 cells as a useful model for estimating iron bioavailability. Development of a rapid, inexpensive procedure for estimating bioavailability would be an important contribution to the efforts of plant breeders and nutritionists to develop varieties of plant foods that are better sources of iron.
Technical Abstract: Human and animal studies have shown that amino acids and peptides influence iron absorption from the intestinal lumen. The objectives of the present study were to determine if similar effects occur using Caco-2 cell monolayers as the experimental model. The present study demonstrates the enhancing effect of cysteine on ferric iron uptake by Caco-2 cells. Addition of glutathione to the transport media had no effect on ferrous or ferric iron uptake by Caco-2 cells, nor did it affect iron solubility. Cysteine and reduced cysteinyl-glycine increased iron solubility when added to a solution containing insoluble iron. This effect is different from that of ascorbate, which must be combined with soluble ferric iron at low pH to have a reducing effect. Taken together, these observations are evidence that cysteine and reduced N-terminal cysteine peptides are capable of enhancing iron uptake from soluble and insoluble ferric iron. These results qualitatively reflect those observed in human studies. The similarity between the present study and the above human studies further reinforce the Caco-2 cell model as a useful tool in studies of iron absorption and bioavailability.