RESUMO
As tri-n-butyltin (TBT), one of the environmental pollutants, is accumulated in wild animals, concern regarding the toxicity of TBT in both wildlife and human is increasing. TBT has been reported to increase intracellular Ca(2+) concentration in several types of cells. In order to examine how Ca(2+) is involved in TBT-induced cell death, the effect of TBT on rat thymocytes has been compared with that of A23187, a calcium ionophore, under various concentrations of external Ca(2+) using a flow cytometer and fluorescent probes. Although both TBT and A23187 were toxic to cells under normal Ca(2+) condition, under external Ca(2+)-free condition the cytotoxic action of TBT was potentiated without changing the threshold concentration while that of A23187 was completely abolished. A23187 attenuated the TBT-induced descent in cell viability under normal Ca(2+) concentration despite intracellular Ca(2+) concentration was increased. As external Ca(2+) concentration increased, the TBT-induced increase in number of dead cells gradually decreased whereas the number of cells in an early stage of apoptosis increased. Results suggest that Ca(2+) has contradictory actions on the process of TBT-induced cell death in rat thymocytes.
RESUMO
The biomedical and industrial uses of organobismuth compounds have become widespread, although there is limited information concerning their cytotoxicity. Therefore, the actions of triphenylbismuth on rat thymocytes were examined using a flow cytometer with ethidium bromide, annexin V-FITC, fluo-3-AM, and 5-chloromethylfluorescein (5CMF) diacetate. Triphenylbismuth at 3-30 microM increased the population of cells stained with ethidium, indicating a decrease in cell viability. Organobismuth at 30 microM increased the population of cells positive to annexin V, suggesting an increase in the population of apoptotic cells. Triphenylbismuth at 3 microM or more decreased cellular glutathione content (5CMF fluorescence intensity) and increased intracellular Ca(2+) concentration ([Ca(2+)](i), fluo-3 fluorescence intensity) in a dose-dependent manner. Because an increase in [Ca(2+)](i) is linked to cell death or cell injury and a decrease in cellular glutathione content increases cell vulnerability to oxidative stress, the triphenylbismuth-induced changes in cellular parameters may be responsible for triphenylbismuth-induced cytotoxicity. Bismuth chloride at 10-30 microM did not significantly affect cell viability. These results suggest that triphenylbismuth at micromolar concentrations exerts cytotoxic action on rat thymocytes, possibly related to a health hazard. Although the cytotoxicity of triphenylbismuth was less than that of triphenyltin, one of the environmental pollutants, it is necessary to direct our attention to the use and disposal of organobismuth compounds.
