The ratio and interaction between neurotrophin and immune signaling during electroconvulsive therapy in late-life depression
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Background: Electroconvulsive therapy (ECT) is the most effective treatment for severe late-life depression (LLD), and several hypotheses on the precise working mechanism have been proposed. Preclinical evidence suggests that ECT induces changes in neurotrophin and inflammatory signaling and that these neurotrophic and inflammatory systems affect each other. We examine the relation, interaction, and ratio between the neurotrophic brain-derived neurotrophic factor (BDNF) and the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α), and depression severity during ECT. Methods: In this naturalistic longitudinal study, linear mixed models were used to analyze the relation between BDNF, IL-6, TNF-α, and depression severity (determined by the Montgomery-Åsberg Depression Rating Scale; MADRS) in 99 patients with severe LLD before ECT (T0), three weeks after the first ECT (T1), and one week after the last ECT (T2). Results: No significant association was found between BDNF, IL-6 and TNF-α, and MADRS scores at any time point. However, a significant interaction between TNF-α and BDNF in relation to MADRS was established (p = .020) at all time points. With higher levels of TNF-α, the relation between BDNF and MADRS becomes more negative. Furthermore, a higher ratio of TNF-α/BDNF was associated with a higher score on the MADRS (p = .007). Conclusion: A possible explanation for the absence of a significant coevolution between the proinflammatory cytokines and BDNF could be that the study design was unable to determine parameters shortly after ECT sessions. However, the TNF-α/BDNF ratio was positively associated with depression severity, and the association of BDNF-level and depression severity depended on the level of TNF-α. This suggests that the interaction and balance between neurotrophin and immune signaling, specifically BDNF and TNF-α, could be relevant in LLD. This could be a focus in future research regarding treatment and the working mechanism of ECT.