Abstract
Dietary components have been known for many years to have a variable effect on non-haem iron uptake in humans. Since it is impractical and expensive to employ in vivo methods for iron uptake, in this study, a human intestinal Caco-2 cell line was utilised for investigation of the effect of dietary components on non-haem iron uptake.Using a radioactive iron isotope 55Fe, it is possible to observe iron uptake activity in Caco-2 cell whether or not the dietary components are present in the media. Several dietary components including ascorbate, B-carotene, amino acids, organic acids and two types of polyphenols (rutin dihydrate and catechin dihydrate) increased iron uptake in Caco-2 TC7 cells. In contrast, phytate and zinc reduced iron uptake, and vitamin E showed no effect on iron uptake. Interestingly, effects of ascorbate, zinc and phytate on iron uptake were found to follow Michaelis-Menten equation.Fe(III) reduction was measured by analysing the formation of Fe(II) via the spectrophotometric measurement of Fe(II)-bathophenanthrolinedisulfonic acid. Ascorbate and β-carotene had a significant effect on the reduction of Fe(III) to Fe(II), thereby increasing the aqueous solubility of iron. This study model also sheds some light on the potential capability of β-carotene to reduce Fe(III) before Fe(II) is taken up by the cells.Western blotting was used to study the effect of dietary components on the transporter proteins (DMT1 and Iregl) levels. Western blotting demonstrated that most of the amino acids and organic acids tested were able to reduce the expression of membrane DMT1 levels. On the contrary, zinc and phytate caused a significant increase effect in membrane DMT1 levels (p<0. 05) but ascorbate had no effect in membrane DMT1 levels. Iregl was significantly increased in the presence of phytate in the medium but there was no effect of ascorbate, β-carotene and zinc on Iregl. These findings provide evidence that although membrane DMT1 levels responded to the addition of selected dietary components in the medium, most if not all had no effect on Iregl expression. The results suggest that the effect of dietary components on iron transporters is merely a mucosal block phenomenon, where the first step of iron uptake is regulated by DMT1. In addition, the effects of ascorbate are not simply on the reduction and chelation of iron, but also on the transporter protein DMT1 itself.