Exploring the Association between Depression, Suicidality, and Serum Brain-Derived Neurotrophic Factor, FAM19A5, Total Antioxidant Status, Total Oxidant Status, Oxidative Stress Index, and Cytokine Levels: A Case-Control Study of Drug-Naive Adolescents with First-Episode Major Depressive Disorder

<b><i>Introduction:</i></b> Considering the importance of neuroinflammation and neurodegeneration in the pathophysiology of major depressive disorder (MDD), peripheral blood biomarkers are promising for the prediction of diagnosis and treatment outcomes. We aimed to elucidate the neuroinflammatory pathophysiology of depression by evaluating serum levels of FAM19A5 as a new biomarker of inflammatory activation, proinflammatory cytokines, brain-derived neurotrophic factor (BDNF), and oxidative stress parameters. <b><i>Methods:</i></b> Adolescents diagnosed with first-episode drug-naive MDD (<i>n</i> = 35) were compared neurobiologically healthy control group (<i>n</i> = 33). Serum FAM19A5 levels, cytokine levels, BDNF and oxidative stress parameters were evaluated using the enzyme-linked immunoassay method. All participants were assessed with the Level-2 Depression Severity Scale, Sleep Disturbance Scale, Somatic Symptom Scale. <b><i>Results:</i></b> BDNF levels were significantly higher in the patient group compared to the control group. While BDNF showed a positive correlation with all scale scores; BDNF was significantly higher in the suicide risk groups than the control group. IL-1β levels displayed a negative correlation with the severity of sleep disturbances. <b><i>Conclusions:</i></b> In adolescents with MDD, inflammatory and oxidative stress markers were not raised in peripheral blood, unlike in adults. However, BDNF levels, which typically decrease in neurodegenerative conditions, were higher in those with MDD.