|BRISKE ANDERSON, MARY|
|Newman Jr, Samuel|
Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 29, 1996
Publication Date: N/A
Interpretive Summary: It is important to know how one nutrient in the diet affects the absorption and utilization of another. For example, diets containing large amounts of zinc will reduce the absorption of copper into the body. From results of previous studies, we had suggested that the theory used to explain this effect might not be true. This theory states that the presence of high zinc in the diet will cause the intestine to produce a small sticky protein (metallothionein, MT) that will bind up the copper and prevent its passage into the body. For this to be true, the copper must stick to the protein. We found that this did not occur in animals. In the whole animal there are too many factors to control at one time. Therefore, in the present study we used a single cell type that acts like the intestinal cell and grew it in culture dishes with and without zinc. We then watched to see if the zinc content reduced the amount of copper taken up by the cell or the amount transported across to the other side. We found that copper uptake and transport were reduced when zinc concentration was increased in the culture medium. When zinc concentration was too high, transport of copper increased. However, it turns out that this reduction in copper uptake was opposite to the amount of MT in the cell. Even though there was 200 times more MT in the cell of zinc fed cells than those not fed zinc, the copper uptake rate in the cell was reduced. The results of this experiment suggest again that MT probably does not play a role in regulation of the metabolism of copper in cells of intestinal origin.
Technical Abstract: Previous studies suggest that high dietary zinc reduces the copper status of animals by reducing copper transport across the intestinal mucosa. The present study was designed to use an enterocyte mimic, the Caco-2 cell, grown on porus membranes as a model to assess the effects of varying concentrations of zinc (6 to 200 umol/L) in the culture and assay media on copper uptake and transport. Results showed that differentiated cells held for 7 d in culture media containing 50 umol of zinc/L, took up significantly less copper into the cell and transported significantly less copper across the monolayer than similar cells exposed to 6 umol of zinc/L of culture media. However, when cells were exposed to 200 umol of zinc/L for the same amount of time, copper transport was significantly increased over those with 6 umol of zinc/L. Further investigation suggested that 200 umol of zinc/L may have affected the integrity of the cell monolayer with time. Cells exposed for 1 h to 200 umol of zinc/L in the uptake/transport media alone did not show reduced copper uptake or transport. Exposure of Caco-2 cells to 50 to 200 umol of zinc/L caused a proportional increase in cellular metallothionein (MT) concentration. However, there was a negative correlation between the amount of MT in the cell and the rate of copper uptake and/or transport only in those cells exposed to 50 umol of zinc/L of media. The results further showed that the Caco-2 cell can be used as a model for copper uptake/transport studies, but the conditions must be rigorously defined and controlled.