The mechanisms for regulating absorption of Fe bis-glycine chelate and Fe-ascorbate in Caco-2 cells are similar

Abstract

Inorganic iron (Fe) absorption from the diet is controlled mainly in the intestinal tract where apical Fe uptake is inversely related to the Fe content in the enterocyte. Iron bis-glycine chelate is an iron compound that may be absorbed by a mechanism different from the regulated nonheme Fe pathway. Because Fe bis-glycine chelate is used increasingly as an Fe fortificant in foods, the critical question is whether this compound is a safe Fe supplement. We compared apical Fe uptake and transepithelial transport offered either as Fe-59 bis-glycine chelate or a Fe-59-ascorbate (Fe-AA) complex in Caco-2 cells, as a model of human intestinal epithelia, grown in different Fe concentrations in the media (0.5, 5 and 20 mumol/L Fe). Apical Fe uptake from Fe-59-AA and Fe-59 bis-glycine chelate did not differ nor did transepithelial transport rates. The rate of 59Fe uptake decreased with increasing intracellular Fe concentration (P < 0.001), an indication of a common absorption regulatory mechanism. We also evaluated the effect of an excess of Fe (100 &mu;mol/L) provided as Fe bis-glycine chelate or Fe-AA on the incorporation of 1 &mu;mol/L Fe-55-AA into Fe-replete Caco-2 cells. The inhibition of Fe bis-glycine chelate on the absorption of the extrinsic tag of Fe-55-AA (87.5%) did not differ from that of Fe added as Fe-AA (86.8%). These results suggest that Fe derived from Fe bis-glycine chelate and Fe-AA have similar regulatory absorption mechanisms.