Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/11/1995
Publication Date: N/A
Citation: Interpretive Summary: Current dietary guidelines recommend increased consumption of fruits, vegetables and grains and decreased consumption of meat and other animal products. In general, iron in meat is more available than that in plant foods. Thus, these recommendations could result in a shift from relatively available iron to poorly available iron. Since iron deficiency anemia is already a problem, it is essential to improve mineral availability from plant foods such as corn, wheat and rice. This will require assessment of iron availability from large numbers of plant varieties. Current methods of assessing iron availability involve costly animal and human feeding trials which are impracticable for screening a large number of samples. As a result, there is an urgent need for a fast, inexpensive, and accurate assay for measuring the availability of dietary non-heme iron. The present study reports on a rapid and inexpensive method of assessing iron availability which combines simulated digestion methods with measurement of iron uptake by Caco-2 cells, a human intestinal epithelial cell line. The objective was to determine if this method would produce results consistent with human studies which have shown that meat enhances iron uptake. We observed a 3-4 fold enhancement of Caco-2 cell iron uptake by meat (beef, chicken and fish) digests versus casein digests. These results are qualitatively similar to those of human feeding trials and support the usefulness of this model as a means of assessing iron availability.
Technical Abstract: We developed a model for assessing Fe bioavailability from foods which combines simulated peptic and intestinal digestion with measurement of Fe uptake by Caco-2 cell monolayers. Our objective was to further validate this model by determining if meat enhances Caco-2 cell Fe uptake relative to casein. Caco-2 cell monolayers were covered with Hank's Balanced Salt Solution (HBSS) buffered with HEPES, pH 7.4. An upper chamber was created over the cells by fitting the bottom of a Costar Transwell insert with a 12,000-14,000 molecular weight cut-off dialysis membrane. This membrane allowed low molecular weight Fe complexes to diffuse into the media bathing the cells and prevented damage to the cells from the digestive enzymes. Prior to digestion, each sample (homogenate of beef, chicken, fish or casein) was mixed with 59FeCl3 to achieve an Fe concentration of 10 umol/L. Following pepsin digestion (pH 2), pH was adjusted to 7.4, pancreatic enzymes and bile extract were added to each digest, and an aliquot was then introduced into the upper chamber of the culture dish. During this intestinal digestion period, 59Fe uptake occurred from Fe that dialyzed into the lower chamber. 59Fe uptake from beef, chicken and fish digests was 300-400% of the 59Fe uptake from a casein digest. Our results parallel human absorption studies indicating that meat enhances iron absorption. The results suggest that digestion products of the meat proteins were at least partially responsible for the enhancement of iron uptake. Overall, this study supports the usefulness of our model as a means of assessing iron bioavailability.