Inflammatory monocyte gene expression: trait or state marker in bipolar disorder?

Background: This study aimed to examine whether inflammatory gene expression was a trait or a state marker in patients with bipolar disorder (BD). Methods: 69 healthy controls (HC), 82 euthymic BD patients and 8 BD patients with a mood episode (7 depressed, 1 manic) were included from the MOODINFLAME study. Six of the eight patients who had a mood episode were also investigated when they were euthymic (6 of the 82 euthymic patients). Of these participants the expression of 35 inflammatory genes was determined in monocytes using quantitative-polymerase chain reaction, of which a total gene expression score was calculated as well as a gene expression score per sub-cluster. Results: There were no significant differences in inflammatory monocyte gene expression between healthy controls and euthymic patients. Patients experiencing a mood episode, however, had a significantly higher total gene expression score (10.63 +/- 2.58) compared to healthy controls (p = .004) and euthymic patients (p = .009), as well as when compared to their own scores when they were euthymic (p = .02). This applied in particular for the sub-cluster 1 gene expression score, but not for the sub-cluster 2 gene expression score. Conclusions: Our study indicates that in BD inflammatory monocyte, gene expression is especially elevated while in a mood episode compared to being euthymic.