Increased serum interleukin-6 levels in early stages of psychosis: Associations with at-risk mental states and the severity of psychotic symptoms

Abstract

Schizophrenia patients experience activated inflammatory responses, but little is known about the presence of such inflammatory processes at or prior to disease onset. We measured interleukin-6 (IL-6) and C-reactive protein (CRP) serum levels and plasma fibrinogen in 17 at-risk mental state (ARMS) subjects, 77 patients with psychotic disorder (PD) and 25 healthy control subjects (HC). ARMS subjects were followed-up, and transition to psychosis was registered. IL6 rs1800795 SNP was genotyped, as IL-6 levels may be influenced by this genetic variant. We did not observe significant differences in the IL6 rs1800795 SNP genotype frequencies between the groups. ARMS subjects exhibited significantly higher IL-6 levels than did controls (p=0.019). In subjects not taking cannabis, we found that patients diagnosed with ARMS or PD exhibited increased IL-6 levels when compared with HC (p=0.004). In both ARMS and PD subjects, IL-6 levels were positively associated with negative symptoms. However, with respect to positive psychotic symptoms, a different relationship was observed in the ARMS and PD groups (positive relationship in ARMS; negative relationship in PD). These findings could not be attributed to confounding variables, including gender, body mass index (BMI), tobacco consumption or the rs1800795 genotype. Six of 17 ARMS subjects (35%) exhibited a transition to psychosis during the follow-up period of 26 months. ARMS subjects who developed psychosis exhibited increased median IL-6 levels compared with those who did not transition (0.61 vs. 0.35pg/mL). However, this difference was not statistically significant, which could be explained by a lack of statistical power due to the small sample size. Our results suggest that IL-6 may be a biomarker for early psychotic symptoms; however, further studies in larger samples are needed to confirm this result.