BDNF and major depressive disorder: Injections of β-hydroxybutyrate were found to increase both β-hydroxybutyrate and H3K9bhb levels, as well as enhance the expression of brain-derived neurotrophic factor (BDNF).290 This deduction posits that H3K9bhb could serve as a pivotal regulatory factor for the expression of BDNF, hinting at the role of histone bhb as a significant avenue for unraveling the underpinning mechanisms of MDD.