Cytotoxicity induced by thallium(I) acetate, thallium(I) sulfate, and thallium(III) chloride was studied using human peripheral lymphocytes and four different in vitro assays. In all cases, the cells were treated with 0.5, 1, 5, 10, 50, and 100 µg/mL of the three thallium compounds and were evaluated 2, 4, 8, and 24 h later. The three thallium compounds reduced cell viability and increased cell death via apoptosis and necrosis in a concentration- and time-dependent manner. Methyl tetrazolium reduction assay showed the highest sensitivity for recording thallium-induced cytotoxicity. When cells in the G0 phase were treated with thallium compounds, the mitotic index decreased in a concentration-dependent manner. These results suggest that the cell membrane is the target of thallium. Both oxidation states induced cell death at the lowest concentrations tested (0.5 and 1 µg/mL) and with short-term exposure (4 and 8 h), which decreased the cellular proliferative capacity. These results indicate that mitochondria are the most sensitive to the effects of thallium.
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