Interaction between Copper and Iron Metabolism in the Human Intestinal Caco-2 Cells

It has long been known that copper deficiency impairs iron absorption, leading to an iron-resistant anemia. In recent years, links between iron uptake and cellular copper homeostasis have been established in yeast, by cloning iron transporters which require copper. However, in higher eucaryotes like mammals, such direct relationship has yet to be defined. We used the human intestinal in vitro model, the Caco-2 cell line, to investigate how modifications in cellular copper homeostasis could modulate intestinal iron absorption. The Caco-2 cell line is a human cultured cell line derived from a human colon adenocarcinoma, that undergoes in culture a process of spontaneous differentiation that leads to the formation of a monolayer of epithelial cells displaying several morphological and functional characteristics of the mature enterocytes. This cell model has extensively been utilized for the study of trans-epithelial passage and intracellular metabolism of several nutrients, including trace elements. Caco-2 cells were grown and allowed to differentiate on filters to reproduce in vitro the conditions of the intestinal mucosal cells in vivo. In copper loading experiments was added to complete basolateral medium for 18h. Under these conditions a ten fold increase of intracellular copper content was achieved, without modifications in the integrity of the monolayer, as monitored by measuring trans-epithelial electrical resistance (TEER) after copper loading. Apical ferrireductase activity, apical uptake of either as Fe(II) ascorbate or Fe(III)NTA and iron transport across the cells to the basolateral compartment were studied on Cu-loaded cells. Results showed that copper loading did not alter AP ferrireductase activity nor AP uptake of either Fe(II) or Fe(III). However, transport of iron,