The interactions of cis-diamminedichloroplatinum with metallothionein and glutathione in rat liver and kidney

Abstract

The involvement of metallothionein (MT) in the nephrotoxicity of cis-diamminedichloroplatinum (c-DDP) was investigated in rats using enzyme excretion and histology as indicators of renal damage. In addition, the effects of renal glutathione (GSH) depletion on the nephrotoxicity of c-DDP was assessed by organic anion transport in renal cortical slices. A dose of 6.0 mg c-DDP/kg body wt, i.p. was administered to rats either as a single injection of 6.0 mg/kg or as six daily injections of 1.0 mg/kg. Concentrations of platinum (Pt) after c-DDP injection in both dosing regimens were approximately 12 micrograms/g in kidney and 2 micrograms/g in liver. However, there were no increases in either hepatic or renal concentrations of MT after both series of c-DDP injections. Fractionation of kidney cytosols from c-DDP injected rats on Sephadex G-75 columns revealed that 60-70% of cytosolic Pt was associated with proteins of high molecular weight and 15-20% of the Pt associated with the low molecular weight ligands. No discernable Pt peak was detected in the elution volume of MT. Pretreatment of rats with ZnSO4 increased both hepatic and renal concentrations of MT, but there was no Pt associated with the MT fraction after a subsequent injection of c-DDP. Small increases in the urinary excretion of the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase and two brush border enzymes, alkaline phosphatase and gamma-glutamyltranspeptidase were observed 2 and 3 days after a single injection of c-DDP (6.0 mg/kg body wt, i.p.). Urinary creatinine excretion decreased by 50% 1 day after c-DDP injection and continued to decrease for the next 2 days. On the third day after c-DDP treatment, a small but significant decrease in body weight was also observed in the c-DDP injected animals. Pretreatment with Zn did not alter the c-DDP-induced enzymuria or renal tubular damage but slightly attenuated both the decrease in creatinine excretion and the loss in body weight. Uptake of the organic anion, p-aminohippuric acid (PAH) was reduced at 12 and 24 h after c-DDP injection. Reduction of tissue GSH concentrations by pretreatment with buthionine sulfoxime (BSO), resulted in only a slight increase in the c-DDP-induced inhibition of PAH uptake at 24 h after c-DDP injection. These results suggest that, in rats, neither MT nor GSH appear to play major roles in the binding or nephrotoxicity of c-DDP.