Background: Recent reports have suggested a pathophysiological role for brain-derived neurotrophic factor (BDNF) in major depressive disorder (MDD). We evaluated plasma levels of BDNF in patients with MDD.
Methods: Plasma BDNF levels were measured in 77 MDD patients and 95 normal controls. The severity of psychiatric symptoms was measured with the Hamilton Depression Rating Scale and the Brief Psychiatric Rating Scale.
Results: Plasma BDNF levels were significantly lower in MDD patients than in normal control subjects (p<0.001). Plasma BDNF levels were significantly lower in MDD patients with recurrent episodes than in MDD patients with the first episode or normal controls (p<0.001). Plasma BDNF levels were significantly lower in non-psychotic MDD patients than in psychotic MDD patients or normal controls (p<0.001). Plasma BDNF in suicidal MDD patients were significantly lower than those in non-suicidal MDD patients (p<0.001).
Limitations: We measured only plasma levels of BDNF. However, the cellular sources of BDNF in human plasma are not yet clearly defined.
Conclusions: Our study suggests that there is a decrease in plasma BDNF levels in untreated MDD patients. However, relapsed or recurrent episodes, suicidal behavior, and psychotic features could also affect the plasma levels of BDNF. Further studies are required to understand the source and role of the circulating BDNF in depression.