Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/1998
Publication Date: N/A
Interpretive Summary: We have developed an experimental model that simulates the digestion of the stomach and intestine combined with culture of a human intestinal epithelial cell line (Caco-2). In this manuscript, we describe how this model has been adapted to measure Fe uptake from non-radiolabeled foods. This methodology is significant as food Fe radiolabeling can be inconvenient, expensive and controversial. To assess Fe availability, we measure Caco-2 cell ferritin formation following exposure to food digests. Formation of ferritin, an intracellular Fe storage protein, occurs in response to Fe uptake by the Caco-2 cells. In this study we have documented known differences in Fe availability observed in human and animal trials, thereby accomplishing our objective of validating this method. For example: Fe ingested with ascorbic acid (vitamin C) is a better source of dietary iron (ie. more available) than Fe ingested with citric acid. In our model system, greater ferritin formation occurred in the cultured cells exposed to the Fe plus ascorbic acid versus the Fe plus citric acid. In addition, Fe availability from meat (beef and fish) is greater than that of plant foods such as corn and green beans. Overall, the results document the promotional effects of ascorbic acid and animal tissue on Fe uptake as measured indirectly by ferritin formation. The results of this study indicate that ferritin formation by Caco-2 cell monolayers is highly sensitive and accurately measures food Fe availability in this model system.
Technical Abstract: We have adapted an in vitro digestion/Caco-2 cell model to assess Fe availability from foods, using ferritin formation by Caco-2 cells as an indicator of Fe uptake. Ferritin formation by Caco-2 cells occurs in response to Fe uptake at concentrations of available Fe greater than that of the culture media to which the cells have been adapted. This methodology circumvents the need for using radioactive Fe and thus eliminates costs and controversies associated with food radiolabeling. In order to validate this method, we measured ferritin formation in Caco-2 cells exposed to digests containing Fe of relatively high and low availability. Our objective was to determine if ferritin formation would be proportional to Fe uptake and sufficiently sensitive to be an indicator of Fe availability from food digests. Our model uses established in vitro digestion techniques coupled with uptake of Fe by Caco-2 cell monolayers. Measurement of cell ferritin was done by a commercially available radioimmunoassay. Higher ferritin formation was observed in cells exposed to digests containing FeSO4 plus ascorbic acid versus digests containing FeSO4 plus citric acid. Additional comparisons of Fe availability from digests of beef, fish, corn and green beans yielded results which demonstrate higher Fe availability (ie. greater ferritin formation) from beef and fish digests than from digests of corn and green beans. Overall, the results document the promotional effects of ascorbic acid and animal tissue on Fe uptake as measured indirectly by ferritin formation. The results of this study indicate that ferritin formation by Caco-2 cell monolayers is highly sensitive and accurately measures food Fe availability in this in vitro system.