2.14  Immunohistochemistry and TUNEL assay
Immunohistochemical stains against Nrf2, NQO1, HO-1, GCLC, ABCC5 and Ki-67 were performed using immunohistochemistry kit (KeyGen, Nanjing, China) according to the manufacturer's instructions. In situ cell apoptosis were detected by using TUNEL apoptosis detection kit (Beyotime Institute of Biotechnology, Shanghai, China) according to the manufacturer's instructions. Inverted fluorescence microscope (Nikon, Japan) was used to photograph all sections.