The effects of cadmium and zinc ions on protein synthesis in mouse liver

Objective: The present investigation was undertaken to evaluate effects of cadmium and zinc ions on the total protein synthesis in mouse liver as well as on the activity of key components of liver translation machinery-tRNA and aminoacyl-tRNA synthetases. Methods: Experiments were done on outbred mice using intraperitoneal injections of CdCl2 solution (1.6 mg Cd2+ per 1 kg of body mass) and/orZnSO(4) (3.1 mg Zn2+ per I kg of body mass). Protein synthesis was evaluated by incorporation of [C-14]-labelled leucine into newly synthesized peptides and proteins. Total tRNAs were isolated from the mice liver using deproteinization of the tissue extract with phenol. Activities of tRNA(Leu) and leucyl-tRNA synthetase were measured by an aminoacylation reaction using [C-14]-labelled leucine. Results: Examination of kinetics of protein synthesis intensity in the mice liver within 24-hour-period after CdCl2 injection revealed its diminishing at the 2nd hour by 38% followed by the increase of 51% at the 8th hour and then by the decrease of 32% at the 24th hour. In the mice liver, zinc ions increased protein synthesis by 67% at the 8th hour after ZnSO4 injection. Examination of the common effect of cadmium and zinc ions in vivo showed that zinc ions favored towards resistance of protein synthesizing system against cadmium ions only at the 2nd hour of cadmium intoxication. Cadmium ions reduced both the acceptor activity of mouse liver tRNALeu by 44 - 74% and the activity of leucyl-tRNA synthetase by 20 - 30% within 24 hours of the liver exposure to Cd2+. In comparison with the control, the liver exposure to zinc ions caused activation of this enzyme by 27 and 41% after 8 and 24 hours, respectively, as well as inhibition of acceptor activity of tRNALeu by 31 - 58% within 24 hours. Pre-treatment with zinc ions mitigated cadmium-induced inhibition of tRNA(Leu) after 8 hours and leucyl-tRNA synthetase after 2 24 hours. In vitro, zinc ions had almost no effect on cadmium-induced inhibition of both tRNALeu and leucyl-tRNA synthetase. Conclusions: In vivo, zinc ions can counteract the inhibition of liver translation machinery induced by cadmium.