Reduced TRL is unable to activate Nrf2. (A) TRL was reduced to remove the electrophilic functional group in it. The box indicates the elctrophilic fuctional group. (B) HCT116 cells were treated with 200 μM of either TRL or rTRL. Nuclear Nrf2 and HO-1 protein levels were assessed after 2 and 8 h, respectively, by western blotting. (C) HCT116 cells were cotransfected with an ARE-responsive luciferase reporter plasmid and a CMV Renilla luciferase plasmid for 24 h. The cells were treated with 200 μM of either TRL or rTRL for 8 h. Luciferase activity was measured and normalized to CMV Renilla luciferase activity. For western blotting in (B), equivalent loading of proteins was verified using TATA box protein (TBP) for nuclear Nrf2 protein and β-actin for HO-1 protein. NM, not measurable. Data in (C) are presented as mean ± standard deviation (n = 3). *: p < 0.05 vs. control, #: p < 0.05.