Equivalent uptake of organic and inorganic zinc by monkey kidney fibroblasts, human intestinal epithelial cells, or perfused mouse intestine.

Zinc (Zn) is recognized as an essential nutrient, and is added as a supplement to animal and human diets. There are claims that zinc methionine (ZnMet) forms a stable complex that is preferentially transported into tissues, and this has contributed to uncertainty about conflicting reports on the bioavailability of various Zn compounds. This study evaluated the cellular and intestinal uptake of inorganic and organic forms of Zn. Steady-state uptake of 65Zn by human intestine epithelial cells, and monkey kidney fibroblasts was not significantly different with zinc chloride (ZnCl2), ZnMet, or zinc propionate (ZnProp) (P > 0.05). Uptake of 65Zn from zinc chelated with EDTA was significantly lower (P < 0.01). In live mice, 65Zn uptake by perfused intestine and deposition in intestine and liver showed no significant difference between ZnCl2 and ZnMet. Equimolar [65Zn]methionine and zinc[35S]methionine were prepared according to a patented method that yields "complexed" Zn. Cellular uptake of the radiolabeled methionine was <0.1% of the radiolabeled Zn from these complexes, indicating separate uptake of the Zn and methionine. Gel filtration did not distinguish between 65Zn in ZnCl2, ZnProp, or reagent ZnMet, though feed-grade ZnMet containing >10% protein did give a higher-mol-wt form of 65Zn. Results of this study show equivalent uptake of Zn from inorganic and organic compounds, and support recent feed trials on Zn bioavailability.