High zinc concentrations in culture media affect copper uptake and transport in differentiated human colon adenocarcinoma cells.

Previous studies suggest that high dietary zinc reduces the copper status of animals by reducing copper transport across the intestinal mucosa. The present study used an enterocyte mimic, the Caco-2 cell, grown on porus membranes as a model to assess the effects of various concentrations of zinc (6 to 200 micromol/L) in the culture and assay media on 67Cu uptake and transport. Differentiated cells incubated for 7 d in a culture medium containing 50 micromol zinc + 0.7 micromol copper/L transported significantly less 67Cu across the monolayer than similar cells exposed to 6 micromol zinc/L. However, cells exposed to 200 micromol zinc/L for the same period transported significantly more 67Cu than those exposed to 6 micromol zinc/L. Cells exposed for only 1 h to 200 micromol zinc/L in the uptake-transport medium alone did not show lower 67Cu uptake or transport, suggesting that time of exposure of the cells to high zinc was a contributing factor. Caco-2 cells exposed to 50 through 200 micromol zinc/L had higher cellular metallothionein (MT) than those exposed to 6 micromol zinc/L. As the amount of MT in cells increased upon exposure to 50 and 100 micromol zinc/L, the rate of 67Cu transport decreased. At higher zinc concentrations in the medium, there was even more MT in the cells, but a greater rate Of 67Cu transport. These studies demonstrate the use of the Caco-2 cell as a model for copper uptake-transport studies, but the conditions must be rigorously defined and controlled.