Thallium toxicity and potassium protective effect in vitro

Thallium is a naturally occurring, highly toxic trace element. Human exposure to thallium is mainly connected to occupational exposure, environmental contamination and food accumulation. The exact mechanism of thallium toxicity is still poorly understood, however its toxic effect is often connected to disruption of potassium-dependent processes and development of oxidative stress. The aim of this study was to access the cytotoxic effect of thallium on several cell culture lines and relate the obtained results with its specific toxicity to a particular organ. In addition, possible protective effect of potassium on toxicity of thallium was also examined. Human keratinocytes (HaCaT), human hepatocellular carcinoma (HepG2), porcine kidney epithelial cells (PK15), human neuroblastoma (SH-SY5Y) and Chinese hamster lung fibroblast cells (V79) were treated with thallium (I) acetate in a wide concentration range (3.9-500 µg/ml) for 24h, 48h and 72h. Based on cytotoxicity results, four concentrations (15.6, 31.25, 62.5, 125 µg/ml) were chosen to be tested in combination with potassium acetate (500 μg/ml) to assess their competitive interaction during 24h treatment. Cell morphological changes were monitored on inverted microscope, and cytotoxic effect was assessed by 3-(4, 5-dimethylthiazole-2-yl)-2, 5-diphenyltetrazolium bromide (MTT-test). Thallium toxicity for each cell line tested was both, time- and dose-dependent. For each measurement point SH-SY5Y cells had the lowest IC50 values and appeared to be most sensitive, while HepG2 were most resistant to thallium exposure. Simultaneous treatment of cells with thallium and potassium (I) acetate resulted with higher viability compared to treatment with thallium (I) acetate alone. Results of our study indicate that tissue origin contributes to cell’s susceptibility to thallium toxicity. Different toxic effect of thallium could be attributed to cell’s antioxidant capacity as well as transport systems through which thallium and potassium compete for entering the cell. The obtained results point to importance of monitoring thallium concentrations in the environment and call for further research into the mechanism of its toxicity.