Effects of UFP-512 on Nrf2 and KEAP1 mRNA expression after H/R. In HEK293t cells treated with DOR activation and/or inhibition, Nrf2 and KEAP1 mRNAs were measured by relative quantitative real-time PCR in both normoxia and after H/R. C, normoxic control. —, H/R alone. U, DOR activation with UFP-512 during H/R condition. N, DOR inhibition with naltrindole during H/R condition. U + N, UFP-512 and naltrindole co-administration during H/R condition. *P < 0.05, **P < 0.01, ***P < 0.005, significantly different from control cells in normoxia. ##P < 0.01, significantly different from H/R alone. At least three independent experiments were carried out for each group. Note that UFP-512 had no direct effect on Nrf2 expression.