Effects of cadmium ions on the initial stage of translation and the cell death in mouse liver

Leonid Ivanov^{1, 2}, Vaiva Lesauskaitė³, Laima Ivanovienė², Ilona Sadauskienė^{1, 2}, Rasa Gailevičiūtė¹, Dovilė Karčiauskaitė³, Hiliaras Rodovičius²

¹Institute for Biomedical Research, ²Department of Biochemistry, ³Institute of Cardiology, Kaunas University of Medicine, Lithuania

Key words: cadmium, tRNA, leucyl-tRNA synthetase, apoptosis, necrosis.

Summary. Objective. To evaluate in vivo and in vitro effects of cadmium ions on the activities of mice liver tRNA^Leu and leucyl-tRNA synthetase and on the type of liver cells death.

Material and methods. White laboratory mice were intoxicated by intraperitoneal injection of cadmium chloride solution (1.6 mg cadmium ions/1 kg of body weigh). Total tRNAs were isolated by adding ethanol and isopropanol into the phenol-deproteinized supernatant of mouse liver homogenate. Post-mitochondrial fraction of the liver cells was used as a source of leucyl-tRNA synthetase. Acceptor activity of tRNA^Leu and activity of leucyl-tRNA synthetase were measured in tRNA aminoacylation reaction with [¹⁴C]-labeled leucine as a substrate. An apoptotic cell death was assessed by the TUNEL assay using in situ cell death detection kit. DNA degradation was verified by electrophoresis. Results. It was determined that 2–24 hours after intoxication with sublethal dose of cadmium ions the acceptor activity of mice liver tRNA^Leu was decreased by 43–73% as compared to control. At the same time intervals, the activity of leucyl-tRNA synthetase was reduced about 20–30%. Experiments in vitro revealed that 10–20 µM concentrations of cadmium ions suppressed the activities of mice liver tRNA^Leu and leucyl-tRNA synthetase by 40–98%. No significant difference was observed between the number of TUNEL positive apoptotic liver cells in the control mice and 24 hours after intoxication with cadmium chloride. Electrophoresis revealed extensive degradation of nuclear DNA.

Conclusions. Cadmium ions significantly reduce activities of tRNA^Leu and leucyl-tRNA synthetase in vivo and in vitro. There is no significant difference between the number of apoptotic cells in the control liver specimens and in those after 24 hours of intoxication with cadmium chloride. In latter specimens DNA electrophoresis revealed as extensive degradation of DNA, which is characteristic to the cell necrosis.

Correspondence to I. Sadauskienė, Institute for Biomedical Research, Kaunas University of Medicine, Eivenių 4, 50009 Kaunas, Lithuania. E-mail: ilona_sad@omni.lt

Received 10 February 2004, accepted 5 December 2004