Comparison of pro-inflammatory cytokines among patients with bipolar disorder and unipolar depression and normal controls.

OBJECTIVE: Research evidence has shown that bipolar disorder (BD) and unipolar depression (UD) are both related to inflammatory dysregulation, but few studies have compared the levels of cytokines between these two disorders.

METHODS: Study subjects were age- and gender-matched outpatients with BD or UD and normal controls (NC). Severities of depression and mania symptoms were assessed with the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Young Mania Rating Scale (YMRS). Pro-inflammatory cytokines, including soluble interleukin-6 receptor (sIL-6R), soluble interleukin-2 receptor (sIL-2R), C-reactive protein (CRP), soluble tumor necrosis factor receptor type 1 (sTNF-R1), soluble p-selectin receptor (sP-selectin), and monocyte chemotactic protein-1 (MCP-1), were assessed in all subjects by enzyme-linked immunosorbent assays.

RESULTS: In all, 130 patients with BD, 149 patients with UD, and 130 NC were enrolled in the study; 67.6% were female and the average age was mean ± standard deviation (SD) 43.5 ± 11.8 years. The BD group had a significantly higher smoking rate, more medical comorbidity, higher body mass index (BMI), and higher levels of sIL-2R, sIL-6R, CRP, sTNF-R1, and MCP-1 (all p < 0.01) than the UD and NC groups. When the remitted patients with BD (YMRS scores ≤ 12) were compared with the patients with UD, controlling for age, MADRS score, smoking, medical comorbidity, and BMI in the regression model, the results showed that the BD group had significantly higher levels of sIL-6R (p < 0.001), CRP (p = 0.045), sTNF-R1 (p = 0.036), and MCP-1 (p = 0.001) than the UD group.

CONCLUSIONS: Higher levels of sIL-6R, CRP, sTNF-R1, and MCP-1 were noted in BD than in UD. These results may suggest a more severe inflammatory dysregulation in BD. Further studies are required to investigate whether these cytokines could be biomarkers for affective disorders.