The relationship of interleukin-18 and interleukin-6 levels with cognitive functions in Bipolar Disorder

Abstract

Objective: Immune function impairment has been proposed to play a key role in the cognitive decline of those with bipolar disorder (BD); however, there is little research regarding the impact of inflammation on cognitive function. This study aimed to compare levels of IL-18 and IL-6 in BD patients vs controls and to determine the relationship between these levels and cognitive impairment. Method: Thirty-six euthymic BD-I patients and 38 age, sex, and educational level matched healthy controls were enrolled in this study. All participants were evaluated with neurocognitive tests. The plasma IL-6 and IL-18 levels of both groups were measured by ELISA. Results: The levels of IL-6 and IL-18 in the patients and healthy controls were not significantly different. In the patients, IL-18 had a positive correlation with the completed categories score and a negative correlation with perseverative response and perseverative errors. Further in the patients, IL-18 was positively correlated with immediate recall, delayed recall, and learning scores, and negatively correlated with Stroop interference scores. There were no correlations between IL-6 levels and neuropsychological test scores in the patient group. Conclusion: This is the first study to investigate the relationship between IL-18 and cognitive function. While the possible detrimental or protective effects of IL-18 in BD are not yet clear, the positive association between IL-18 and neuropsychological test scores might indicate a neuroprotective role of IL-18 in the euthymic period of BD, which is the state that is closest to physiological conditions.