Cadmium retention increase: a probable key mechanism of the protective effect of zinc on cadmium-induced toxicity in the kidney.

Zinc (Zn) reverses cadmium (Cd)-induced toxicity in kidneys although it increases Cd tissue burden, hence, the present study is designed to study the relationships between Cd, Zn and antioxidants in the kidneys of rats exposed to Cd orally. Male rats received either tap water, Cd or Cd+Zn in their drinking water during five weeks. Cd-induced increase in Cd and Zn accumulation was accompanied by a decrease in important variables (GSH, GSH/GSSG, CuZn SOD and GPx activities) and by an increase in others (Cd/Zn, GSSG and CuZn SOD/GPx). Zn supply intensified Cd retention and Cd/Zn; it amplified CuZn SOD activity, CuZn SOD/GPx and GSH/GSSG compared to normal values, but had no effect on Zn content increase. Besides, it ameliorated GPx activity and corrected GSSG level. High positive correlations were found between Cd concentrations and the majority of the studied variables suggesting a direct influence of Cd on them. Zn concentration had positive correlation with CuZn SOD/GPx, and negative one with GPx activity, which reflects an indirect protective effect of Zn. In conclusion, our results suggest that Zn increases Cd tissue retention in the kidney and that is probably the key mechanism of the protective effect of Zn.