E ffects of Selenium on Apoptosis Induced by Methyl Merc u ry Chloride in RAW 264.7 Cells

Objective: This study was performed to evaluate the protective effects of selenium against the methyl mercury chloride (MeHgCl) induced cell apoptosis. M e t h o d s: The effect of selenium on the MeHgCl induced cell apoptosis was observed in mouse macrophage-derived RAW 264.7 cells, in vitro. The cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM). Results: MeHgCl exerted a dose dependent cytotoxicity, as demonstrated by the MTT assay, an assay dependent, in part, on mitochondrial function. Concurrent exposure to selenium pro vided complete protective effects against the cytotoxicity induced by MeHgCl. Pretreatment with selenium increased the protective effects of subsquent administrations of selenium in con junction with MeHgCl, but pretreatment of selenium alone did not provide protection against MeHgCl when given alone. Selenium administered after exposure to MeHgCl did not repair the existing MeHgCl induced cytotoxicity. Furthermore, the apoptosis induced by MeHgCl was revealed by the DNA fragmentation, using the terminal deoxynucleotidyl transferase Biotin-dUTP nick end labeling (TUNEL) assay, alterations to the nuclear morphology, by nuclei staining, and the plasma membrane lipid orga nization, as shown by cell flow cytometry. The apoptosis induced by MeHgCl was prevented by the concurrent exposure to selenium, or pretreatment with selenium, prior to the administration of selenium in conjunction with MeHgCl. However, no inhibittion of the MeHgCl induced apoptosis was observed with selenium pretreatment prior to exposure to MeHgCl alone, or with the administration of selenium after exposure to MeHgCl. Conclusions: These results suggest that the coexistence of selenium and MeHgCl are essen tial for the protective effects of selenium against the MeHgCl-induced apoptosis, and the cytotoxicity, in RAW 264.7 cells, and may involve selenium-MeHgCl binding.