Effects of comorbid alcohol use disorder on bipolar disorder: Focusing on neurocognitive function and inflammatory markers

Background: Alcohol use disorder (AUD) is a highly prevalent comorbid disorder in patients with bipolar disorder (BD). Both BD and AUD were found to be associated with inflammation and cognitive deficits, but few study has been done on BD comorbid with AUD (BD+AUD). We aimed to investigate the impacts of comorbid AUD and BD on cognitive function, inflammatory and neurotrophic markers. Method: We recruited 641 BD patients, 150 patients with BD+AUD, and 185 healthy controls (HC). Neuropsychological tests [Wisconsin card sorting test (WCST), continuous performance test (CPT), and Wechsler memory scale - third edition (WMS-III)] and cytokine plasma levels [tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), interleukin-8 (IL-8), transforming growth factor-β1 (TGF-β1), and brain-derived neurotrophic factor (BDNF)] were assessed. Results: BD+AUD patients had worse cognitive performance than those without AUD. There was a significant difference in the plasma levels of TNF-α, IL-8, and BDNF (P < 0.001, <0.001, and 0.01, respectively) between the patients and the HC groups. Post hoc analysis showed that BD+AUD patients had higher levels of TNF-α and IL-8 than BD-only patients (P < 0.001). Additionally, plasma IL-8 levels were negatively associated with number of completed categories in WCST (P = 0.02), and TNF-α levels were negatively associated with visual immediate index in WMS-III (P = 0.05). Conclusion: Our results suggest that comorbid AUD and BD might worsen cognitive impairments and inflammatory processes. Further longitudinal studies on BD+AUD may be needed.