Ebselen induces apoptosis in HepG₂ cells through rapid depletion of intracellular thiols

Ebselen, 2-phenyl-1, 2-benzisoselenazol-3(2H)-one, is a synthetic seleno- organic compound with antioxidant capability. In the present study, we systematically examined the ability of ebselen to induce apoptosis in a human hepatoma cell line, HepG₂. Ebselen-induced apoptosis was evaluated by (i) TdT-mediated dUTP nick end labeling assay', (ii) analysis of sub-G1 cells; (iii) cell morphology, including cell size and granularity examination; and (iv) DNA gel electrophoresis. The results showed that ebselen was able to induce typical apoptosis in HepG₂ cells in a dose- and time-dependent manner. In order to explore the possible mechanisms involved in ebselen- induced apoptosis, the effect of ebselen on intracellular thiol concentrations including reduced glutathione (GSH) and protein thiols and the effect of N-acetylcysteine (NAC) and buthionine sulfoximine (BSO) pretreatment on ebselen-induced apoptosis were investigated. It was found that (i) ebselen rapidly depleted intracellular GSH and protein thiols, moreover, the depletion preceded the occurrence of apoptosis; (ii) NAC, a precursor of intracellular GSH synthesis, significantly alleviated ebselen- induced apoptosis; and (iii) BSO, a specific inhibitor of intracellular GSH synthesis, augmented ebselen-induced apoptosis significantly. Taken together, the present study demonstrates that ebselen is able to induce apoptosis in HepG₂ cells, most probably through rapid depletion of intracellular thiols. (C) 2000 Academic Press.