The Relationship of Interleukin-18 and Interleukin-6 Levels with Cognitive Functions in Bipolar Disorder

Abstract

Impairment in immune functions is proposed as a key factor in the cognitive decline in bipolar disorder (BD) however there is scarcity of research on the impact of inflammation on cognitive functions. Our aim is to compare IL-18 and IL-6 levels in BD patients and controls and to study the relationship between IL-18 and IL-6 levels and cognitive impairment METHOD: Thirty-six euthymic BD-I patients and 38 age, sex and educational level matched healthy controls were enrolled in the study. All participants were evaluated with neurocognitive tests. The plasma IL-6 and IL-18 levels of both groups were measured with ELISA kits. There was no statistically significant difference between IL-6 and IL-18 levels of patient and healthy control groups. In the patient group, IL-18 level was positively correlated with completed categories score wheras there was a negative correlation with perseverative response and perseverative errors. Moreover IL-18 level was positively correlated with immediate recall, delayed recall and learning scores while there was a negative correlation with stroop interference scores. No correlation was found between IL-6 level and neuropsychological test scores in the patient group. This is the first study that investigates the relation of IL-18 with cognitive functions. Possible detrimental or protective effects of IL-18 in BD is not yet clear, however the positive association of IL-18 level and neuropsychological test scores might indicate a neuroprotective role of IL-18 in the euthymic period of BD which is the closest state to physiological condition.