Iron regulates the uptake of ascorbic acid and the expression of sodium-dependent vitamin C transporter 1 (SVCT1) in human intestinal Caco-2 cells

Ascorbic acid (vitamin C) has major effects on the intestinal uptake and utilisation of Fe in humans. The objective of the present study was to investigate the impact of Fe on the acquisition of ascorbic acid. The strategy was to study the cellular uptake and transport of ascorbic acid in the presence of Fe and also to observe the expression of the Na-dependent vitamin C transporter 1 (SVCT1) protein in human intestinal Caco-2 cells. SVCT1 is involved in the cellular uptake of ascorbic acid and is therefore a candidate for playing a role in the regulation of Fe utilisation. Caco-2 cells were cultured on transmembrane inserts in a three-compartment system followed by treatment with various combinations of FeCl(2 center dot)4H(2)O (10-20 mu mol/l) and sodium ascorbate (150 mu mol/l). ELISA and Western blot analyses revealed that both SVCT1 and ferritin expressions were up-regulated in the presence of ascorbic acid in the basal compartment underneath the cells (10 and 22%, respectively). Furthermore, when cells deficient in ascorbic acid were exposed to Fe, SVCT1 expression increased significantly (23.7%). The increase in SVCT1 expression correlated with an increase in ascorbic acid uptake (285%) in Fe-treated cells, as indicated by the SVCT1 inhibitor quercetin. We conclude that Fe plays an important role in regulating the uptake of ascorbic acid in human intestinal Caco-2 cells. This new angle could change the conceptual thinking of Fe and ascorbic acid utilisation and assist in the treatment and prevention of ascorbic acid-deficiency syndromes such as scurvy.