Induction of metallothionein as an adaptive mechanism affecting the magnitude and progression of toxicological injury.
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.
Klaassen
C D
CD
Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City 66160-7417, USA. cklaasse@kumc.edu
Liu
J
J
D000222:Adaptation, Physiological; D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D002251:Carbon Tetrachloride / Q000633:toxicity*; D008099:Liver / Q000187:drug effects*; D008668:Metallothionein / Q000096:biosynthesis*; D051379:Mice; D051381:Rats
D002104:Cadmium; D008668:Metallothionein; D002251:Carbon Tetrachloride