MB acts as Nrf2 activator. (A) mRNA levels of HO1, NQO1 and Gclc in Nrf2 WT and Nrf2 KO MEFs. Nrf2 WT MEFs treated with 0.1, 1 or 10 μm MB showed significantly increased levels of HO1 mRNA compared with Nrf2 WT MEFs treated with vehicle; however, HO1 mRNA levels remained unchanged in Nrf2 KO MEFs treated with 0.1, 1 or 10 μm MB (paired Student’s t-test, *P < 0.05). Nrf2 WT MEFs treated with 10 μm MB showed significantly increased levels of NQO1 mRNA compared with Nrf2 WT MEFs treated with vehicle and Nrf2 WT MEFs treated with 0.1 or 1 μm MB showed a trend for increased levels of NQO1 (paired Student’s t-test, *P < 0.05). NQO1 mRNA levels remained unchanged in Nrf2 KO MEFs treated with 0.1, 1 or 10 μm MB. Nrf2 WT MEFs treated with 0.1, 1 or 10 μm MB showed significantly increased levels of Gclc mRNA compared with Nrf2 WT MEFs treated with vehicle; however, Gclc mRNA levels remained unchanged in Nrf2 KO MEFs treated with 0.1, 1 or 10 μm MB (paired Student’s t-test, *P < 0.05).