Effects of selenite on O 2 consumption, glutathione oxidation and NADPH levels in isolated hepatocytes and the role of redox changes in selenite toxicity

Abstract

Isolated hepatocytes incubated with selenite (30–100 μM) exhibited changes in the glutathione redox system as shown by an increase in O 2 consumption, oxidation of glutathione and loss of NADPH. Selenite (50 μM) raised O 2 consumption within the 1 h and induced an partial depletion of thiols with a concomitant increase in oxidized glutathione, as well as a decrease in NADPH levels within 2 h. With 100 μM selenite more pronounced effects were obtained such as a total depletion of thiols. This concentration of selenite also lysed cells within 3 h. Arsenite, HgCl 2 and KCN prevented the increase in O 2 uptake, counteracted loss of thiols and delayed selenite induced lysis. p-Tert-butylbenzoic acid, an inhibitor of gluconeogenesis, decreased selenite dependent O 2 consumption and potentiated the effect on NADPH levels as well as the toxic effect. Finally, methionine further enhanced O 2 consumption by selenite and also delayed loss of thiols and potentiated selenite toxicity. These results indicated that selenite catalyzed a reduction of O 2 in glutathione dependent redox cycles with NADPH as an electron donor. With subtoxic concentrations of selenite (50 μM) there were indications that O 2 reduction was terminated by selenite biotransformation to methylated metabolites. With toxic concentrations of selenite (100 μM) it appeared that O 2 reduction was eventually limited by the capacity of the cell to regenerate NADPH. It is suggested that a depletion of NADPH mediated the observed cytotoxicity of selenite.