Protective role of renal metallothionein against Cd nephropathy in rats

Rats were treated with four types of Cd compound: CdCl2, Cd bound (Cd-peptide), and Cd bound to metallothionein (Cd-MT). This treatment caused no nephropathy. Subsequently, toxic doses of Cd compounds were administered to these pretreated rats and their effects on renal function were examined. When 1.4 mg Cd/kg as Cd-Cys was administered, marked increases in urinary protein, glucose, and amino acid were observed. However, when the animals were pretreated with 1 mg Cd/kg/day as CdCl2 for 3 days, and 1.4 mg Cd/kg as Cd-Cys was administered 24 hr later, no renal damage was observed. Such a protective effect against the nephrotoxic action of Cd-Cys was also shown by pretreatment with Cd-Cys, Cd-peptide, or Cd-MT. Furthermore such a phenomenon was also observed when the nephropathy was caused by Cd-peptide or Cd-MT. The efficacy of pretreatment depended on the time before subsequent administration of Cd and the dose used for pretreatment. Incorporation of Cd into the liver and the kidney was not altered by the pretreatment. No matter in which form the nephrotoxic dose of Cd was administered, the incorporated Cd was distributed between particulates and cytosol; 3 hr after administration, cytosolic Cd was present in almost equal amounts in the high-molecular-weight and the MT fractions in the nonpretreated rats. However, after pretreatment, more of the Cd subsequently administered was found in the MT fraction. These results suggest that MT participates in the detoxication mechanism against Cd in the kidney, as it does in the liver.