Increased GDNF but not BDNF Plasma Levels in Type II Compared to Type I Bipolar Disorder

Abstract

Background: The brain-derived neurotrophic factor (BDNF) is a neurotrophin important for synaptic plasticity and neurogenesis, whereas the glial cell-line derived neurotrophic factor (GDNF) modulates the activity of monoaminergic neurons and glial cells. Previous works have suggested that abnormal peripheral levels of these proteins might relate to different mood states in bipolar disorder (BD), but none study so far have evaluated it with regard to potential differences between the types I (BD-I) and II (BD-II) subtypes of the disorder. Methods: Eighteen BD-I and 19 BD-II patients presenting with an acute mood episode (depressive, manic or mixed), and 23 healthy controls were studied. Plasma levels of BDNF and GDNF were measured using enzyme-linked immunosorbent assay (ELISA). Results: BD-II individuals showed significantly increased levels of GDNF compared to both BD-I patients and controls (ANOVA, df=2, F= 5.74, p=0.005; Tukey for post hoc comparisons). When we focused our analysis on the treatment-naïve patients only (14 BD-I and 13 BD-II), this result became even more significant (ANOVA, df=2, F= 7.33, p=0.002). No significant between-groups differences were observed on BDNF levels. Also, no significant correlation was observed between BDNF or GDNF levels and depressive and manic symptoms. Conclusions: BD-II at an acute phase of the illness is associated with increased plasma levels of GDNF. Previous use of mood stabilizer and antipsychotic agents might produce a chronic effect on GDNF production.