title: Ascorbic acid offsets the inhibitory effect of bioactive dietary polyphenolic compounds on transepithelial iron transport in Caco-2 intestinal cells.
abstract: We previously reported that (-)-epigallocatechin-3-gallate (EGCG) and grape seed extract (GSE) at high concentration nearly blocked intestinal iron transport across the enterocyte. In this study, we aimed to determine whether small amounts of EGCG, GSE, and green tea extract (GT) are capable of inhibiting iron absorption, to examine if ascorbic acid counteracts the inhibitory action of polyphenols on iron absorption, and to explore the mechanisms of polyphenol-mediated apical iron uptake and basolateral iron release. An(55)Fe absorption study was conducted by adding various concentrations of EGCG, GSE, and GT using Caco-2 intestinal cells. Polyphenols were found to inhibit the transepithelial (55)Fe transport in a dose-dependent manner. The addition of ascorbic acid offset the inhibitory effects of polyphenols on iron transport. Ascorbic acid modulated the transepithelial iron transport without changing the apical iron uptake and the expression of ferroportin-1 protein in the presence of EGCG. The polyphenol-mediated apical iron uptake was inhibited by membrane impermeable Fe(2+) chelators (P < 0.001), but at a low temperature (4°C), the apical iron uptake was still higher than the control values at 37°C (P < 0.001). These results suggest that polyphenols enhance the apical iron uptake partially by reducing the conversion of ferric to ferrous ions and possibly by increasing the uptake of polyphenol-iron complexes via the energy-independent pathway. The present results indicate that the inhibitory effects of dietary polyphenols on iron absorption can be offset by ascorbic acid. Further studies are needed to confirm the current findings in vivo.
authors: Department of Nutritional Sciences, Pennsylvania State University, University Park, PA 16802, USA.
authors: Eun-Young
authors: EY
authors: Kim
authors: Soo-Kyung
authors: SK
authors: Ham
authors: Daniel
authors: D
authors: Bradke
authors: Qianyi
authors: Q
authors: Ma
authors: Okhee
authors: O
authors: Han
mesh_terms: D001205:Ascorbic Acid; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D002392:Catechin / Q000009:adverse effects / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism; D027682:Cation Transport Proteins / Q000378:metabolism; D016764:Cell Polarity; D003080:Cold Temperature; D004032:Diet / Q000009:adverse effects*; D019587:Dietary Supplements / Q000009:adverse effects; D020895:Enterocytes / Q000187:drug effects / Q000378:metabolism*; D005419:Flavonoids / Q000009:adverse effects* / Q000037:antagonists & inhibitors / Q000378:metabolism; D056604:Grape Seed Extract / Q000009:adverse effects / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D007408:Intestinal Absorption; D007502:Iron Chelating Agents / Q000494:pharmacology; D007504:Iron Radioisotopes; D019266:Iron, Dietary / Q000378:metabolism*; D010084:Oxidation-Reduction; D010636:Phenols / Q000009:adverse effects* / Q000037:antagonists & inhibitors / Q000378:metabolism; D010936:Plant Extracts / Q000009:adverse effects / Q000037:antagonists & inhibitors / Q000378:metabolism; D059808:Polyphenols; D013662:Tea / Q000737:chemistry; D000098742:Ferroportin
chemical_list: D027682:Cation Transport Proteins; D005419:Flavonoids; D056604:Grape Seed Extract; D007502:Iron Chelating Agents; D007504:Iron Radioisotopes; D019266:Iron, Dietary; D010636:Phenols; D010936:Plant Extracts; D059808:Polyphenols; D013662:Tea; D000098742:Ferroportin; D002392:Catechin; C045651:epigallocatechin gallate; D001205:Ascorbic Acid