ASSESSMENT OF IRON AVAILABILITY USING COMBINED IN-VITRO DIGESTION ANDCACO-2 CELL-CULTURE

A model for the rapid assessment of iron availability was developed th at combines in vitro digestion with iron uptake by Caco-2 cell monolay ers. In this method, samples (beef, ascorbic acid, or citric acid) wer e adjusted to pH 2, labeled with Fe-59, and subjected to pepsin digest ion (pH 2, 37 degrees C) for 1 h to simulate gastric digestion. Next, a dialysis bag (12,000-14,000 molecular weight cutoff) containing 150 mM PIPES buffer (pH 6.7) was placed in the digest and incubation conti nued for 30 min. Then, a pancreatin-bile mixture was added, and incuba tion was continued for an additional 2 h. The contents of the dialysis bag were removed and an aliquot applied to Caco-2 cell monolayers. Af ter a 60 min incubation, iron that was non-specifically bound to the s urface of the monolayer was removed by rinsing with a solution contain ing bathophenanthrolinedisulfonic acid and sodium dithionite. Cells we re then counted for Fe-59 activity to measure uptake. Beef and ascorbi c acid enhanced Caco-2 cell iron uptake, whereas citric acid had no ef fect. These results compare favorably with literature reports of human studies and suggest that a dialyzable factor(s) less than 14,000 dalt ons, released during beef digestion, was responsible for the iron abso rption-enhancing properties of beef. We believe that this system will be useful for studying basic mechanisms of iron absorption and for in vitro estimation of iron bioavailability.