Effects of selenite on O2 consumption, glutathione oxidation and NADPH levels in isolated hepatocytes and the role of redox changes in selenite toxicity.

Isolated hepatocytes incubated with selenite (30-100 microM) exhibited changes in the glutathione redox system as shown by an increase in O2 consumption, oxidation of glutathione and loss of NADPH. Selenite (50 microM) raised O2 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 microM selenite more pronounced effects were obtained such as a total depletion of thiols. This concentration of selenite also lysed cells within 3 h. Arsenite, HgCl2 and KCN prevented the increase in O2 uptake, counteracted loss of thiols and delayed selenite induced lysis. p-Tert-butylbenzoic acid, an inhibitor of gluconeogenesis, decreased selenite dependent O2 consumption and potentiated the effect on NADPH levels as well as the toxic effect. Finally, methionine further enhanced O2 consumption by selenite and also delayed loss of thiols and potentiated selenite toxicity. These results indicated that selenite catalyzed a reduction of O2 in glutathione dependent redox cycles with NADPH as an electron donor. With subtoxic concentrations of selenite (50 microM) there were indications that O2 reduction was terminated by selenite biotransformation to methylated metabolites. With toxic concentrations of selenite (100 microM) it appeared that O2 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.