Association between increased serum interleukin-6 levels and sustained attention deficits in patients with major depressive disorder

Background. The pathophysiology of cognitive impairment in patients with the major depressive disorder (MDD) may involve neuroinflammation mediated by cytokines. Objective. The aim of this study was to examine the serum interleukin-6 (IL-6) levels, sustained attention, and their association in patients with MDD. Methods. Thirty patients with MDD and 30 healthy controls were enrolled in this case-control study. Sustained attention was measured using the Rapid Visual Information Processing (RVP) task in the Cambridge Neuropsychological Tests Automated Battery. The serum IL-6 levels of all subjects were assessed by sandwich enzyme-linked immunosorbent assays. Results. There were significant differences in the log(10)RVP total hits, log(10)RVP total misses, and log(10)RVP mean latency between patients with MDD and healthy controls (F = 6.04, p = 0.017; F = 19.77, p < 0.0001; F = 14.42, p < 0.0001, respectively). The serum levels of Log(10)IL-6 were significantly higher in patients with MDD than in healthy controls (F = 192.27, p < 0.0001). The log(10)IL-6 levels were also positively correlated with the log(10)RVP mean latency in patients with MDD (r = 0.45, p = 0.013). A further stepwise multivariate regression analysis indicated that the log(10)IL-6 levels were significantly associated with the log(10)RVP mean latency in patients with MDD (beta = 0.31, t = 2.41, p = 0.025). Conclusions. Our data suggested that increased IL-6 levels were associated with the psychopathology of MDD, and that abnormal IL-6 levels were implicated in the impairment of sustained attention in patients with MDD.