Iron and copper alter tight junction permeability in human intestinal Caco-2 cells by distinct mechanisms

Human intestinal Caco-2 cells differentiated for 15-17 days on transparent filter inserts were treated for up to 3 h with 50 and 100 microM CuCl(2) or FeSO(4) in the AP compartment at pH 6.0. Trans-epithelial electrical resistance (TEER) showed a progressive decrease during the course of the experiment that was slower in cells treated with 50 microM CuCl(2) than in those treated with 100 microM CuCl(2). Both 50 and 100 microM FeSO(4) produced a similar decrease in TEER over time, tailing off after 120 min. F-actin localization by fluorescent phalloidin binding in control cells and in cells treated for 3 h with 50 microM CuCl(2) or FeSO(4) highlighted striking differences in the two treatments. Cu(II) led to an overall reduction in F-actin staining with extensive depolymerization in areas of the monolayer, in the absence of cellular loss. Conversely, Fe(II) treatment produced disorganization of F-actin and decreased staining of the perijunctional actin filaments. No changes in the localization and intensity of staining of the junctional proteins ZO1, occludin and E-cadherin were observed after treatment with 100 microM FeSO(4) in analogy with previous observations in Cu(II)-treated cells. The data presented suggest that different mechanisms are responsible for the changes to tight junction permeability produced by the two metals.