Executive dysfunction in euthymic bipolar disorder patients and its association with plasma biomarkers

Background: Despite the old Kraepelinean concept that bipolar disorder (BD) does not evolve with cognitive decline, the presence of cognitive impairment, especially executive dysfunction has been recognized in BD patients. Brain-derived neurotrophic factor (BDNF) and pro-inflammatory molecules are important contributors to the pathophysiology of BD, and imbalance in peripheral levels of these molecules may be implicated in the cognitive decline observed in BD patients. We aimed to investigate the executive performance of BD type I euthymic patients and its relation with the plasma levels of BDNF, TNF-α and its related soluble receptors (sTNFR1 and sTNFR2). Methods: We evaluated executive functioning through the Frontal Assessment Battery (FAB). Plasma levels of BDNF, TNF-α, sTNFR1 and sTNFR2 were measured using enzyme-linked immunosorbent assay (ELISA) in 25 euthymic type I BD patients and 25 age and gender matched healthy controls. Results: BD patients had an impairment in executive functioning (p < 0.006), particularly sensitivity of interference (p = 0.02), inhibitory control (p = 0.02), and increased BDNF plasma levels (p = 0.001) in comparison with controls. Plasma levels of TNF-α were correlated with inhibitory control in BD patients (ρ = 0.50, p = 0.02) while motor programming was negatively correlated with sTNFR2 plasma levels (ρ = - 0.47, p = 0.02) in controls. Executive function correlated with age and MMSE, but not with BDNF, neither was influenced by psychiatric and clinical comorbidities nor medications in use. Conclusion: BDNF is altered in BD but do not correlate with executive functioning.