Increased plasma levels of brain-derived neurotrophic factor in patients with long-term bipolar disorder

Recent data indicate that neurotrophins may play a role in the physiopathology of bipolar disorder (BD) and may be useful as biomarkers of the disease. The aim of this study was to evaluate the plasma concentrations of brain-derived neurotrophic factor (BDNF) in BD patients, and to correlate their levels with clinical parameters. BDNF was measured in plasma from 53 BD type I subjects (34 during mania and 19 during euthymia) and 38 healthy controls by enzyme-linked immuno-sorbent assay (ELISA). Patients were assessed by a structured clinical interview (Mini-plus), Young mania and Hamilton depression rating scales. Plasma BDNF levels were significantly increased in patients with mania (P ≤ 0.001) and euthymia (P ≤ 0.001) when compared with controls, but did not correlate with any clinical parameters. BDNF concentration was higher in BD patients with 10 or more years of disease. BDNF plasma levels were increased in BD patients, mainly in those with a longer course of disease. In line with previous studies, it is conceivable that BDNF may play a role in the pathophysiology of BD.