Plasma levels of IL-6 in patients with untreated major depressive disorder: Comparison with catecholamine metabolites

Objective: IL-6 and catecholamines play roles in the pathophysiology of major depressive disorder (MDD). Aim: The present study investigated associations between plasma IL-6 and plasma catecholamine metabolites in patients with MDD. Participants and methods: A total of 148 patients (male/female 65/83, age 49.5±12.1 years) who met the criteria for MDD based on the Diagnostic and Statistical Manual of Mental Disorders IV and 40 participants as healthy controls (HC; male/female 23/17, age 44.0±10.5 years) were enrolled in the present study. Plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were analyzed using high-performance liquid chromatography, and plasma IL-6 levels were measured using ELISA. Results: No correlations were observed among plasma IL-6 levels, MHPG levels, and HVA levels in patients with MDD. Plasma IL-6 levels in patients with MDD were significantly higher than in the HC. A positive correlation was found between plasma IL-6 levels and Hamilton Rating Scale for Depression-17 scores. Conclusion: No correlations existed between plasma IL-6 levels and plasma catecholamine metabolite levels in patients with MDD, and the severity of depressive state was related to plasma IL-6 levels in MDD.