Inflammation and neurodegeneration in patients with early-stage and chronic bipolar disorder

Objective: The increase in the circulatory cytokine levels observed in patients with bipolar disorder (BD) may imply involvement of inflammation in the pathogenesis of mood disorders. However, the association between the inflammatory process and the stage and severity of illness is not well understood. In this study, our aim was to investigate the association between neuroinflammation and disease progression in the clinical course of BD. Method: IL-6, TNF-α, IL-1 receptor antagonist (IL-1RA), neuron- specific enolase (NSE) and S100B were measured by ELISA in plasma samples of patients at early-stage BD (n=30), chronic BD (n=77) and healthy controls (n=30). Results: Chronic BD patients showed significantly increased levels of all measured inflammatory markers as compared to early-stage BD patients and the healthy controls. IL-6 and IL-1RA levels correlated with NSE and/or S100B levels and TNF-α levels correlated with Montgomery-Asberg Depression Rating Scale scores and Clinical Global Impression Scale scores. Conclusion: Our results indicate that inflammation appears to be particularly associated with IL-1RA and IL-6 activity, progressing at later stages of BD and possibly associated with gliosis and neuronal loss.