Decreased plasma levels of brain-derived neurotrophic factor (BDNF) during mixed episodes of bipolar disorder

Background: Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in neurogenesis and neuroplasticity. Decreased blood levels of BDNF have been found during acute manic and depressive states. BDNF has been proposed as a biomarker in illness phases of mood disorders. No information is available regarding BDNF levels during the mixed states of bipolar disorder (BD). The aim of this study was to evaluate BDNF levels during mixed episodes of BD patients and compare them with those of healthy subjects and depressed patients.

Methods: Plasma BDNF levels were measured by an ELISA assay in 18 patients with major depressive episode (MDE), 19 patients with mixed episode (ME) and 15 healthy subjects (HS).

Results: BDNF levels were significantly higher in HS, as compared with patients׳ samples (HS vs. MDE patients: p<001; HS vs. ME patients: p=.022). No significant differences were found between BDNF levels of ME and MDE patients. The severity of illness as assessed by CGI-S was significantly higher in ME than in MDE patients (p=.01).

Limitations: The small sample size may have weakened the power of statistical analyses. All patients received mood-stabilizing and antidepressant treatments which have been reported to influence peripheral BDNF levels.

Conclusions: Our results are consistent with previous studies showing reduced BDNF during both manic and depressive episodes. This finding supports the role of BDNF as a state-marker of mood episodes, and may represent a contribution to a unitary approach model between unipolar and BDs, as well as to the manic-depressive spectrum model.