The effect of dietary zinc on intestinal copper absorption

Abstract

Everted duodenal segments, tied into sacs, taken from animals fed different amounts of zinc were used to investigate the antagonistic effect of dietary zinc on copper absorption. The intestinal segments taken from animals fed low amounts of zinc transferred more copper from a nutrient medium across the mucosal cells than did intestines from rats fed high levels of zinc. The mucosal cells from animals fed low amounts of zinc retained less copper than the cells from animals fed high amounts of the element. This retained copper was bound to a protein fraction having a molecular weight similar to that of metallothionein. The data suggest that zinc exerts its antagonistic effect by inducing the synthesis of a copper-binding ligand, probably a thionein, in the mucosal cells which sequesters copper from the nutrient medium, making it unavailable for serosal transfer. This may be a possible mechanism by which dietary zinc decreases copper absorption and leads to a decreased copper status.

Influence of environmental zinc on the association between environmental and biological measures of lead in children

“…Intestinal segments taken from rats fed low amounts of zinc transferred more copper from a nutrient medium across the mucosal cells than did intestines from rats fed high levels of zinc (Fischer et al, 1981). Further, the copper was sequestered in the mucosal cells by a protein with a molecular weight similar to that of metallothionein (Fischer et al, 1981). A similar mechanism of increased binding of lead to zinc-induced intestinal metallothionein could explain the influence of zinc on blood lead levels.…”

“…The induction of intestinal metallothionein due to high zinc levels could account for reduced absorption of other divalent cations that bind more strongly to metallothionein. Intestinal segments taken from rats fed low amounts of zinc transferred more copper from a nutrient medium across the mucosal cells than did intestines from rats fed high levels of zinc (Fischer et al, 1981). Further, the copper was sequestered in the mucosal cells by a protein with a molecular weight similar to that of metallothionein (Fischer et al, 1981).…”

“…At extremely high doses, persistent exposure to zinc can cause adverse health effects such as anemia and pancreatic damage (ATSDR, 1994b). Animal studies suggest that zinc at moderate exposure levels can influence the absorption and toxicity of other metals (Fischer et al, 1981;Hempe and Cousins, 1992). The interaction between environmental exposures of lead and zinc on blood lead levels has not been studied in humans.…”

Toxicological Profile for Zinc

“…Inhibition of intestinal copper absorption by zinc may demonstrate competition between the two metals at the brush border of the lumen (Wapnir and Balkman 1991). Dietary intake of copper (1, 6, and 36 mg/kg) or zinc (5, 30, and 180 mg/kg) do not significantly alter the absorption of the other (Oestreicher and Cousins 1985), but when zinc levels are much higher than copper levels, copper absorption is depressed (Fischer et al 1981). This fact has been used therapeutically in the treatment of…”

“…Both copper and zinc appear to bind to the same metallothionein protein; however, copper has a higher affinity for metallothionein than zinc and displaces the zinc that is attached to the metallothionein (Ogiso et al 1979). Copper complexed with metallothionein is retained in the mucosal cell, relatively unavailable for transfer to plasma, and is excreted in the feces when the mucosal cells are sloughed off (Fischer et al 1981; L'Abbe and Fischer…”