Intracellular GSH/GSSG ratios in A549, HepaRG, and CHO cells after treatment with 50 μM t-BHP and 500 μg/ml SFE. GSH/GSSG ratios were determined after 24 h of treatment for control, SFE, t-BHP, and t-BHP + SFE groups. Exposure to t-BHP (50 μM) significantly decreased intracellular GSH/GSSG ratio. Pretreatment with SFE (500 μg/ml) 2 h before the addition of t-BHP, prevented such a dramatic decrease. *p ≤ 0.05 compared to t-BHP group.