BDNF and major depressive disorder: Major depressive disorder (MDD), a psychiatric disorder marked by a persistent low mood and loss of interest, has become a leading cause of mental and physical disability worldwide and is widely recognized as one of the most urgent mental health issues.627 Traditionally, MDD was attributed to neurotransmitter alterations or brain-derived neurotrophic factor disorders; however, recent research has revealed a significant connection between oxidative stress, ferroptosis in the brain, and depression.628