SSRI-induced modulation of cytokines, barrier permeability, and BDNF in adolescent depression

Background: Emerging evidence links immune activation to antidepressant response in adolescents with major depressive disorder (MDD). We examined how depressive symptoms, quality of life (QOL), and blood markers of inflammation, blood–brain barrier (BBB) integrity, and gut permeability change following antidepressant treatment in this population. Methods: Twenty-six adolescents with MDD were evaluated at baseline (pre-treatment), 12 weeks, and 24 weeks after starting therapy. Depression and anxiety were measured by the Hamilton Depression Rating Scale (HAMD) and Hamilton Anxiety Rating Scale (HAMA). QOL was assessed with the QOL Scale for Children and Adolescents (QLSCA) and an adolescent social support instrument. Serum levels of IL-1β, TNF-α, IL-6, IL-4, S100β, claudin-5, LBP, I-FABP, and brain-derived neurotrophic factor (BDNF) were quantified. Results: At baseline, pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) and IL-4 strongly correlated with BBB (S100β, claudin-5) and gut-permeability (I-FABP) markers. IL-4 levels rose significantly and were associated with reduced anxiety (HAMA: r = −0.48, p < 0.05) and better QOL (QLSCA: r = 0.57, p < 0.01). BBB integrity and gut-permeability markers remained stable. In responders only, BDNF increased at 12 weeks (p < 0.05) and IL-8 rose at 24 weeks (p < 0.05), suggesting their involvement in treatment efficacy. Conclusions: Antidepressant therapy in adolescents with MDD is accompanied by dynamic elevations in IL-4, IL-8, and BDNF that parallel clinical improvement and enhanced QOL. These biomarkers warrant further study to develop more targeted interventions for adolescent depression. Clinical trial number: Not applicable.