Ultrastructural changes in the intestine of rats fed high-zinc diets

Abstract

The feeding of high-zinc diets to humans is often used as therapy for patients with Wilson’s disease, an autosomal recessive disorder of copper accumulation. There seem to be no outward adverse effects of this treatment; however, preliminary studies in our laboratory have shown apparent weaknesses in the intestinal wall of rats fed high-zinc diets. As a consequence, this study was carried out to determine if feeding high-zinc diets to rats would affect the ultrastructural morphology of the small intestine. The effects of treatment on copper status of the rats also were determined. Weanling male rats were fed diets containing either 35 or 350 mg of zinc/kg. After 7 weeks, blood and various tissues were collected to measure copper status indicators, and portions of the upper duodenum were excised and prepared for light and electron microscopy. Results showed that rats fed high-zinc diets had significantly lower copper status as indicated by low serum copper, serum ceruloplasmin activity, and liver copper, than rats fed normal-zinc diets. Liver superoxide dismutase or cytochrome c oxidase activities were not affected by high zinc. Observations of sections of the duodenum by electron microscopy showed that non-assembled collagen molecules of the lamina propria were more often disorganized and formed tangled masses in rats fed the high-zinc diet than in those fed normal-zinc diets. This suggests that low copper status caused by high-zinc feeding might be affecting the activity of lysyl oxidase, a copper-dependent enzyme, and thus crosslinking of the collagen molecules. However, these observations did not always correlate with low copper status. Other possible explanations include a direct competition between zinc and copper for sites on lysyl oxidase, zinc blocking of aldehyde residues on the collagen molecule, or some unrecognized process involving other enzymes or other aspects of collagen assembly. Whether such processes or affinities actually exist is still under investigation. J. Trace Elem. Exp. Med. 10: 37–46, 1997. Published 1997 Wiley-Liss, Inc.1 This article is a US Government work and, as such, is in the public domain in the United States of America.