BDNF and major depressive disorder: In this study, 95 patients had depression, with a probability of 43.2%, the BDNF level of depressed patients was lower than that of nondepressed patients, and this indicator showed a negative correlation with BDI scores (r = −0.3277, P = 0.001), owing to the fact that BDNF can control the nuclear translocation of the redox-sensitive transcription nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of redox homeostasis.