Apoptosis mediated by selenium in HL-60 cells

Abstract

Cytotoxicity and apoptosis mediated by selenium were investigated in human promyelocytic leukemia (HL-60) cells. Treatment of selenite or selenodiglutathione (SDG), an initial metabolite of selenite, resulted in concentration-dependent cytotoxicity, measured by lactate dehydrogenase (LDH) leakage assay for detection of membrane damage, and by tetrazolium salt reduction assay reflecting mitochondrial function within the cell. Treatment with selenite or SDG also induced apoptosis in a dose-dependent manner, as detected by enzyme-linked immunosorbent assay (ELISA) specific for histone-associated DNA fragments, DNA fragmentation assay, and gel electrophoresis. SDG exerted more potent effect on the induction of apoptosis and cytotoxicity. Time-course study of cellular selenium uptake suggests that the stronger effect of SDG is largely due to faster and greater selenium uptake rate. The activity of poly(ADP-ribose)polymerase (PARP) was increased preceding DNA fragmentation, suggesting an involvement of PARP in selenium-mediated apoptosis. The dose-response data of apoptosis induced by selenite or SDG were similar to those of cytotoxicity, implicating a relationship between the induction of apoptosis and cytotoxicity. Zn, an inhibitor of apoptosis, dose-dependently blocked not only the induction of apoptosis, but also the membrane damage induced by selenium, corroborating this hypothesis. It was noted that the inhibition of apoptosis by Zn exerted little protective effect on cytotoxicity at higher concentrations of selenium, compared with a perfect protective effect at low concentration of selenium. These results suggest that cytotoxicity induced by selenium may be partially correlated with apoptosis. Treatment with cyanide, a specific trapper of SDG, was effective to reduce cytotoxicity and apoptosis induced by selenite or SDG in a dose dependent manner. The similar trends of reduced cytotoxicity and apoptosis were shown by co-treatment with $Hg^{2+}$, which has been...