Metallothionein mRNA levels are influenced by dietary cyclodextrins in rats

The relationship between metallothionein mRNA levels and the amounts of copper and zinc in liver, kidney and small intestine by feeding dietary cyclodextrin was examined in growing Wistar rats. α-, β- or γ-cyclodextrin was fed at 50 g/kg of diet for a 7-days period (ad libitum). After feeding, the liver zinc of rats fed β-cyclodextrin was greater than those of rats fed the other three diets. Copper accumulated in kidney of rats fed α- or β-cyclodextrin. Copper content in the small intestine did not show any alterations among rats fed all kinds of diets. The cyclodextrin-supplemented diets were ineffective in zinc content in every organ. There was the greatest level of copper in serum of rats fed β-cyclodextrin, whereas the highest level of serum zinc was observed in rats fed γ-cyclodextrin diet. Northern blot analysis demonstrated that dietary β- and γ-cyclodextrins, but not α-cyclodextrin markedly increased the metallothionein mRNA in the liver, whereas small intestinal metallothionein mRNA levels were markedly decreased. Kidney metallothionien mRNA levels were raised appreciably by all dietary cyclodextrin intakes. Metallothionein gene expressions in liver, kidney and small intestine were not proportional to liver and serum copper or zinc levels in those tissues. These results suggest that regulation of the metallothionein mRNA levels may at least partly involved with the accumulation of metals as copper in liver and kidney of rats fed cyclodextrins.