Sex differences in inflammatory markers in bipolar disorder

Chronic peripheral and brain inflammatory processes contribute to mood disorders. Elevated inflammation may serve as a biomarker for bipolar disorder (BD). Studies have noted sex differences in inflammatory marker levels in the general population, primarily focusing on the effects of surgeries or infections. We explored differences between men and women in serum levels of four inflammatory markers - IL-6, TNF-α, CCL-11, and CRP - among individuals with BD and healthy comparison (HC) participants and compared sex differences between groups.

Data from 156 participants (HC: 49 women, 45 men; BD: 38 women, 24 men) were averaged over three baseline visits of a longitudinal study on inflammation and cognitive aging in BD. Blood samples were collected every week during a two-week period and assessed for biomarker levels using electrochemiluminescence assays. General linear models were applied to examine the main effects of sex, diagnostic group, and sex x diagnostic group for IL-6, TNF-α, CCL-11, and CRP, with smoking, BMI, and age included as covariates.

Participants with BD showed higher levels of IL-6 than HC. Sex, diagnostic group, and their interaction showed effects in TNF-α, with higher levels in men with BD and lower levels in HC women. CCL-11 was higher in men than women. CRP levels were higher in BD men than HC men.

Men had higher TNF-α serum levels than women; this difference was more pronounced in BD than HC. CRP was elevated in BD compared to HC men. Future anti-inflammatory treatments should consider possible sex differences in BD.