Here, we assessed the differences in serum levels of interleukin 6 (IL-6) and interleukin 8 (IL-8) as well as C-reactive protein (CRP) in patients with MDD and BD.
Single studies suggest the role of CRP, interleukin(IL)-1 receptor antagonist, IL-6 and TNF-α with its receptors in the development of cognitive impairment in BD.
Compared with healthy controls, significantly elevated levels of IL-6 and sICAM-1 and significantly lower levels of TNF-α and sVCAM-1 were identified in acute and remission phases of BD.
We investigated the relationship between high-sensitive CRP (hsCRP) and Interleukin 6 (IL-6), two inflammatory markers and characteristics of course of illness (e.g. number of affective episodes, depressive and manic symptoms) amongst a group of 190 individuals with BD.
Here, we have focused on the cytokine interleukin-6 (IL-6), since increased circulating levels of IL-6 are associated with neural pathologies such as autism and bipolar disorder.
The risk of BD without psychotic features was decreased among subjects with higher maternal levels of first trimester log-transformed IL-4 (OR (95% CI)=0.76 (0.58, 0.98); p=0.04) and third trimester log-transformed IL-6 (OR (95% CI)=0.64 (0.42, 0.98); p=0.04).
Higher serum levels of soluble interleukin-6 receptor (sIL-6R), which forms a ligand-receptor complex with the potent proinflammatory cytokine IL-6, have been consistently observed in patients with BD.
In addition, IL-6 and IL-10 levels were positively correlated with functional impairment in subjects with BD (IL-6: r=0.349, p=0.016; and IL-10: r=0.351, p=0.016).
Adolescents with BD had significantly greater waist circumference (BD: 81.72 cm [11.67 cm], HC: 75.64 cm [8.63 cm]; U = 547.5, P = .021), body mass index (BMI) (BD: 25.50 kg/m²undefined[5.29 kg/m²], HC: 21.76 kg/m² [3.43 kg/m²]; U = 608.5, P < .0001), pulse pressure (BD: 42.31 mm Hg [10.57 mm Hg], HC: 33.84 mm Hg [6.69 mm Hg]; U = 561.5, P < .001), and IL-6 (BD: 8.93 pg/mL [7.71 pg/mL], HC: 4.96 pg/mL [6.38 pg/mL]; U = 516.0, P < .0001) than HC adolescents.
The kynurenine pathway is also critically regulated by cytokines, and, indeed, the pro-inflammatory cytokines interleukin (IL)-1β and IL-6 are elevated in schizophrenia and bipolar disorder and stimulate the production of kynurenic acid.
We propose that the changes observed in the sleep of patients with bipolar disorder are related to the elevation of IL-6 and that this correlates with an elevated expression of mRNA coding for IL-6 expression in peripheral monocytes.