Interleukin-8 is a potential inflammation biomarker in major depressive disorder

•Interleukin-8 (IL-8) is an inflammatory cytokine and potential biomarker for depression.•Two groups of MDD patients were treated with escitalopram or quetiapine.•IL-8 levels were significantly higher at baseline compared to healthy controls.•IL-8 levels trended lower at the end of treatment with either agent.•There was no significant correlation between IL-8 and depression or anxiety scores.•The relationship between IL-8 and MDD suggests possible role in the pathophysiology of MDD. The neuroinflammatory hypothesis of Major Depressive Disorder (MDD) postulates that dysregulated cytokine production is implicated in the etiopathology of the disorder. This study aimed to determine baseline levels of Interleukin-8 (IL-8), an inflammatory cytokine, in MDD and identify possible changes in response to antidepressant drug therapy. Two independent groups of MDD patients who met study criteria were enrolled; one group was treated with Escitalopram and the other with Quetiapine for twelve weeks. There was a healthy control (HC) group. In the Escitalopram group 30 patients completed the baseline visit and in the Quetiapine group 43 patients. Plasma concentrations of IL-8 were measured at baseline, week eight, and week 12 of treatment. IL-8 levels were correlated with depression severity at baseline and week 12. The sample size for IL-8 analysis was 17 study completers in the Escitalopram study, 21 study completers in the Quetiapine study, and 19 HCs. We used the Student's t-test and the Pearson Correlation Coefficient for statistical analyses. MDD patients exhibited elevated IL-8 levels at baseline compared to healthy controls (p = 0.007). However, IL-8 levels did not show a significant reduction after 12 weeks of treatment and were not significantly correlated with depression severity at either baseline or week 12 of treatment. However, there was a notable downtrend in IL-8 levels after treatment in both groups though not statistically significant. Study limitations include sample size variations and power, and study length. No formal assessment was conducted to rule out Axis II diagnoses. These findings underscore the relationship between IL-8 and MDD, suggesting that IL-8 may play a role in the pathophysiology of MDD, but its relationship with antidepressant treatment requires a prolonged period of treatment. This study suggests a role for IL-8 in MDD as a pro-inflammatory biomarker, while the lack of immediate normalization post-treatment indicates the need for fu