LACK OF CORRELATION BETWEEN THE INDUCIBILITY OF METALLOTHIONEIN MESSENGER-RNA AND METALLOTHIONEIN PROTEIN IN CADMIUM-EXPOSED RODENTS

Cadmium (Cd) is carcinogenic in humans and laboratory animals. Dependi ng on the duration and route of exposure, Cd can also induce damage in the liver, kidneys and lungs. In certain tissues, metallothionein (MT ) proteins are induced by Cd exposure and associated with native and a cquired tolerance to the metal. Rats are generally more sensitive than mice to Cd carcinogenicity; however, sensitivity can vary markedly be tween different strains of the same rodent species. To further define the role of MT in Cd toxicity and carcinogenesis, adult male Wistar ra ts and adult male C57 and DBA mice were treated with CdCl2, and liver, kidney, and lung were analyzed for Cd, MT mRNA, and MT protein 24 h l ater. Dose-related increases in Cd were detected in the livers and kid neys of all animals tested; however, increases in pulmonary Cd were ob served only in C57 mice, and only at the highest CdCl2 dose. While hep atic Cd concentrations were similar in the rats and mice, renal Cd con centrations were similar in the rats and DBA mice but were nearly 2-fo ld higher in C57 mice at the highest CdCl2 dose. Dose-related increase s in MT mRNA occurred in the livers and lungs of all animals tested. H epatic MT mRNA concentrations were highest in the rats, and C57 mice e xhibited the greatest magnitude of hepatic MT mRNA induction. Dose-rel ated increases in renal MT mRNA were also detected in both strains of mice, but between the two strains, C57 mice exhibited substantially hi gher levels of renal MT mRNA induction. Basal levels of renal MT mRNA were higher in the rats than in the mice, and transcription of the MT gene was not inducible in the rat kidney at any of the CdCl2 doses use d. In comparison, basal levels of pulmonary MT mRNA were similar in th e rats and DBA mice, were substantially lower in C57 mice, and increas es in pulmonary MT mRNA were most pronounced in the rats. Analysis of MT protein revealed dose-related increases in the livers and kidneys o f all animals tested. C57 mice had the lowest basal and induced levels of hepatic MT, and basal levels of renal MT were much higher in the r ats than in mice of either strain. Although dose-related increases in pulmonary MT were similar in both strains of mice, pulmonary MT levels were much lower and not inducible in the rats. Overall our experiment s revealed complex profiles of Cd distribution and MT expression that varied between tissues, species and strains, and often did not directl y correlate with sensitivity to damage. The results suggest that Cd di stribution, inducibility of the MT gene, and levels of MT protein, mus t all be considered when predicting susceptibility to Cd toxicity and carcinogenicity at particular target sites. (C) 1997 Elsevier Science Ireland Ltd.