1. Interleukin-6 as a biomarker in major depressive disorder

Abstract

Interleukin-6 is a pro-inflammatory cytokine that stimulates the HPA-axis, sympathetic nervous system, and production of acute-phase reactants. Elevations of IL-6 have been reported in patients with major depressive disorder (MDD). Further studies have suggested that IL-6 is an indicator of the severity of symptoms, especially suicidality. Forty-eight MDD patients and 23 healthy subjects were analyzed from two consecutive studies of identical design. Subjects met DSM-IV criteria for primary MDD. Severity of depression was assessed using the HAMD-17 scale. Anxiety was assessed with the HAMA scale. Patients in the first study were treated for 12 weeks with escitalopram. In the second study, patients received quetiapine XR for 12 weeks with flexible dosing. The data for IL-6 were not normally distributed, so non-parametric tests were used for statistical analyses. Patients with MDD (n = 48) had significantly higher baseline serum IL-6 than healthy controls (n = 20) (p = 0.05). Serum IL-6 failed to normalize with either escitalopram or quetiapine after treatment. Treatment response (⩽50% reduction or ⩽7 in HAM-D17 score) did not correlate with baseline level of IL-6. There was a significant correlation between baseline IL-6 and depression severity as measured by HAMD-7 (p = 0.05). This significance was lost with the HAMD-17 scale. There were no correlations between baseline IL-6 and severity of anxiety. Age was the only confound as younger MDD patients (<39 yrs) had higher IL-6 than healthy controls (p = 0.01).