Synthesis and Degradation of Metallothionein and Its Relation to the Toxicity of Cadmium

Abstract

Recent studies on the in vivo synthesis and degradation of matallothionein (MT) were reviewed mainly on the viewpoint of correlations between chemical forms of cadmium in the liver and kidneys and the toxicity of cadmium as follows. i) Analytical methods of MT and general cautions for the procedures which may affect the results of chemical forms. ii) Basal amounts of MT in the liver and kidneys, and their relations to the induction mechanisms. iii) Metal compositions which affect the degradation rate of MT. iv) Synthesis and degradation of MT in the liver after single injection of cadmium, zinc, copper, and endotoxin. v) Chemical forms of cadmium in the liver after repeated injections of cadmium. vi) Degradation and resynthesis of MT in the kidneys after single injection of MT and kidney injury. vii) Changes of chemical forms of cadmium in the kidneys during repeated injections of cadmium and its relation to transitory kidney injury. Transitory kidney injury after single injection of MT and during repeated injections of cadmium were explained as follows : Excess cadmium (than the capacity of basal MT biosynthesis) from the degraded MT for injection of MT or by the accumulation for repeated injections of cadmium cannot be sequestered as MT and causes kidney injury. However, the cadmium induces biosynthesis of MT (transcription of MT mRNA) and, therefore, the restoration occurs despite the constant amount of cadmium or consequtive loadings of cadmium. Persistent kidney injury was supposed to occur when the amount of accumulated cadmium exceeds the capacity of induced MT biosynthesis.