Induction of metallothionein as an adaptive mechanism affecting the magnitude and progression of toxicological injury.

Open Access
Publisher Website
Google Scholar
Abstract
Pretreatment of rats with low doses of Cd produces adaptive tolerance to a subsequent high dose of Cd-induced lethality, thus shifting the dose-response curve to the right. Cd pretreatment of animals also protects against the hepatotoxicity produced by high doses of Cd. This protection is attributable to the 10- to 50-fold induction of hepatic metallothionein (MT) by Cd pretreatment. As a result hepatic subcellular distribution of Cd is significantly altered, with more Cd bound to MT in the cytosol and a concomitant reduction of Cd in other critical organelles. In addition MT-transgenic animals are more resistant, whereas MT-null mice are more sensitive than controls to Cd-induced lethality and hepatotoxicity. This further demonstrates that MT is important in Cd detoxication. Induction of hepatic MT by zinc also protects mice from carbon tetrachloride (CCl4)-induced liver injury, with more 14C-CCl4 bound to MT in the cytosol. MT-null mice are more sensitive to CCl4-induced hepatotoxicity, which supports the hypothesis that induction of MT also plays a protective role for nonmetallic chemicals. These results indicate that MT is a part of cellular adaptive mechanisms affecting the magnitude and progression of toxic insults from metals such as Cd as well as from organic chemicals such as CCl4.