IRON-ABSORPTION BY CACO 2-CELLS CULTIVATED IN SERUM-FREE MEDIUM AS IN-VITRO MODEL OF THE HUMAN INTESTINAL EPITHELIAL BARRIER

A cell culture system consisting of confluent monolayer of human enter ocyte-like CaCo 2 cells, cultivated in a serum-free nutritive medium, on microporous synthetic membranes has been used as an in vitro model of the intestinal epithelial barrier. The uptake of 55ferric citrate, as well as the transepithelial passage from the apical to the basolate ral pole, have been studied. CaCo 2 cells accumulate iron in a time- a nd concentration-dependent process, largely specific from the apical p ole. When 55ferric citrate is added at the apical pole, radioiron appe ars at the basal pole and the clearance rate is approximately four tim es higher than in the opposite direction; the amounts of Fe-55 increas e with the concentration in iron citrate and the duration of incubatio n. At least two concurrent mechanisms could be involved in iron absorp tion across monolayers of CaCo 2 cells. A first route would correspond to a paracellular passage of the metal from the apical to the basal p ole. The second route would involve a selective intake of iron at the apical pole and could require a reduction of ferric iron, prior to the entry. Iron accumulated by the cells would, for a minor part, be stor ed within ferritin, whereas the major part would be excreted at the ba solateral pole, either as low molecular weight material of undetermine d chemical composition but from which iron is easily mobilized by apot ransferrin or associated with neosynthesized apotransferrin. Vesicular transport and protein synthesis seem to be required. (C) 1994 Wiley-L iss, Inc.