Evaluation of metallothionein formation as a proxy for zinc absorption in an in vitro digestion/Caco-2 ceEvaluation of metallothionein formation as a proxy for zinc absorption in an in vitro digestion/Caco-2 cell culture model.

摘要

Caco-2 cell metallothionein (MT) formation was studied to determine if MT could be used as a proxy for Zn absorption in a cell culture model. MT intracellular concn. was determined using a Cd/haemoglobin affinity assay. Cellular Zn uptake was determined by acid digests (5% HNO₃) using inductively-coupled argon-plasma emission spectroscopy. Effect of phytic acid (PA) on cellular Zn and MT concn. was also studied. Cells were treated with a media containing 0, 2, 5, 10, 25, 50, 75 mumol/l Zn (ZnCl₂). Effects of varying Zn:PA molar ratios (1:0, 1:1, 1:5, 1:10, 1:20) on Zn uptake and MT formation were determined. Results showed a positive linear correlation between Zn-media concn. and cellular Zn uptake, and MT formation was observed. Zn and MT concn. in cells treated with increasing levels of Zn (>25 mumol/l Zn) were elevated. Zn and MT concn. in cells incubated with Zn (when <10 mumol/l) were similar to untreated cells. PA markedly lowered cellular Zn and MT concn. When Zn:PA molar ratios were >1:5, cellular MT concn. were no different to untreated cells. When a combined in vitro digestion/cell model was used, cellular MT concn. in white or red beans and fish samples were no different to the cell baseline. Results suggest that measurements of cellular Zn and MT concn. have some limitations (<10 mumol/l Zn). PA was observed to be a potent inhibitor of Zn uptake. Under the conditions of this in vitro model, Caco-2 cell monolayers are not useful for evaluating the Zn availability from foods.