Modulation of GSH level and its relationship with apoptosis. (A-B) Relative GSH levels, as determined by monochlorobimane derivatization, in U-937 cell cultures treated for 24 hours with LY294002 and the indicated concentrations of As₂O₃, alone and in combination (A); and in U-937 and NB4 cell cultures treated for the indicated time periods with 4 μM (U-937) and 2 μM (NB4) As₂O₃ alone, with LY294002 alone, and with As₂O₃ plus either LY294002, wortmannin, or Akt_i5 (B). All results are expressed in relation to untreated U-937 cell cultures (approximate GSH content, 9 nmol/10⁶ cells), which received the arbitrary value of one. (C) Frequency of apoptotic cells in U-937 cell cultures treated for 24 hours with BSO alone, and with As₂O₃, camptothecin, cisplatin, and lonidamine, either alone (-) or in combination with BSO. (D) Relative GSH levels in U-937 cells treated for 24 hours with LY294002, with BSO, and with the combination of As₂O₃ plus either LY294002, TPA, or ascorbic acid (AA), in the absence (-) or the presence of NAC (+NAC). (E) Frequency of apoptotic cells in U-937 cell cultures treated for 24 hours with As₂O₃ alone, TPA alone, AA alone, and NAC alone, and with the combinations of As₂O₃ plus either LY294002, TPA, or AA, in the absence (-) or the presence of NAC. BSO, TPA, AA, and NAC were used at 1 mM, 20 nM, 150 μM, and 10 mM, respectively. All drugs were applied simultaneously. The data represent the means ± standard deviation of at least 3 determinations. All other conditions were as in Figure 1.