Toxicity of methylmercury conjugated with L-cysteine on rat thymocytes and human leukemia K562 cells in comparison with that of methylmercury chloride.

Abstract In order to reveal the implication of use of methylmercury chloride (MeHgCl) in in vitro study, the effects of 10 μM MeHgCl on rat thymocytes and human leukemia K562 cells were compared with those of methylmercury conjugated with l -cysteine (10 μM MeHg–Cys) using a flow cytometer and fluorescent probes to monitor cellular physiological and pathological parameters. MeHgCl hyperpolarized membranes of thymocytes, followed by depolarization within a few minutes after the application, while MeHg–Cys persistently hyperpolarized them. MeHgCl increased intracellular concentration of Ca 2+ , decreased cellular content of glutathione and increased generation of superoxide anion in the cells. The effects of MeHg–Cys were much less than those of MeHgCl. MeHgCl greatly increased both numbers of the cells undergoing apoptosis and dead cells in cell suspension containing thymocytes, while this was not the case for MeHg–Cys. MeHgCl reduced the cell viability of human leukemia K562 cells and completely inhibited the cell growth. The effects of MeHg–Cys on K562 cells were less than those of MeHgCl. It can be concluded that the effects of MeHgCl on rat thymocytes and K562 cells are different from those of MeHg–Cys. The results obtained from the in vitro studies using MeHgCl may be less implicit to elucidate the mechanism of MeHg intoxication in humans and experimental animals because MeHg are present in forms of MeHg–Cys and/or MeHg–S conjugate under the in vivo conditions.