HaCaT cells were treated with 10 μM compound (6a, 6b, 17, 23; positive control CDDO-Im) or vehicle (DMSO) for 6 h (A) or 24 h (D) as shown in the immunoblots. Cell lysates were prepared, equal amount of protein was probed with antibodies specific for NRF2, NQO1 or GCLM. GAPDH was used as a reference. Quantification of band intensities of NRF2 (B, E), NQO1 (C, F) and GCLM levels (G) are shown. DMSO-treated sample values were used as one arbitrary unit.*:p<0.05; **:p<0.01; ***:p<0.001; if no * is indicated, p>0.05.