Objectives: We aimed to investigate levels of brain-derived neurotrophic factor (BDNF), adiponectin, and proinflammatory cytokines in various subtypes of depression in a cohort of young men.
Methods: Sixty-two men 18-30 years of age were recruited for the study. Forty-two were newly diagnosed with depression according to DSM-IV criteria and were divided into three subtypes: reactive depression (N = 13), major depression (N = 18), and bipolar depression (N = 10). Controls included 21 young men without significant clinical morbidity. Serum levels of BDNF, adiponectin, high sensitivity C-reactive protein (hsCRP), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) were measured.
Results: Serum BDNF was significantly lower and TNF-alpha significantly higher than controls for all subtypes of depression. No statistically significant differences between subtypes were found for BDNF, adiponectin, hsCRP, TNF-alpha, or IL-6. Although established diagnosis of depression and level of TNF-alpha were found to independently affect BDNF level in depressed subjects, they executed inverse effects. No associations were found between BDNF and adiponectin, hsCRP, TNF-alpha, or IL-6 in any depressed subject, showing that decreased BDNF in depression is influenced by multiple factors and complex mechanisms, including environmental and genetic concerns. No influence of age on BDNF level was found in any depressive subtype.
Conclusions: Our results lend support to the cytokine and neurotrophic hypotheses of depression by demonstrating significantly lower levels of BDNF in all subtypes of depression. The mechanism underlying this phenomenon is uncertain and assumed to be multifactorial. Development of novel antidepressant treatments will require a multidisciplinary approach.