Predicting Treatment Outcome in Major Depressive Disorder Using Serotonin 4 Receptor PET Brain Imaging, Functional MRI, Cognitive-, EEG-Based, and Peripheral Biomarkers: A NeuroPharm Open Label Clinical Trial Protocol

Many studies have explored the association between soluble interleukin-2 receptor (sIL-2R), cytokines and major depressive disorder (MDD). However, the results of these studies were not consistent. The aim of our study is to compare the levels of sIL-2R and cytokines in the blood between MDD patients and controls by a meta-analysis and to identify moderators accounting for potential heterogeneity in the levels of sIL-2R and cytokines in MDD patients versus controls by meta-regression analyses. A comprehensive literature search was performed to identify studies comparing the levels of sIL-2R and cytokines between MDD patients and controls. We pooled the effect sizes for standardized mean differences (SMD) of the levels of sIL-2R and cytokines. We also performed meta-regression and sensitivity analyses to investigate the roles of age, gender, sample type, ethnic origin and selected studies' quality in explaining potential heterogeneity and differences in results respectively. Twenty-nine studies were selected for this analysis. The levels of sIL-2R, TNF-α and IL-6 in MDD patients were significantly higher than those of healthy controls (SMD=0.555, p<0.001, SMD=0.567, p=0.010; SMD=0.680, p<0.001). Mean age of all subjects was a significant moderator to explain the high heterogeneity of IL-6. Sensitivity analysis found that European but not non-European subjects have higher levels difference of sIL-2R, TNF-α and IL-1β between MDD patients and controls. The severity of MDD was not considered. The blood levels of sIL-2R, TNF-α and IL-6 were significantly higher in MDD patients than controls. Age, samples source and ethnic origins may play a potential role in heterogeneity. Copyright © 2011 Elsevier B.V. All rights reserved.

In the field of depression, inflammation-associated depression stands up as an exception since its causal factors are obvious and it is easy to mimic in an animal model. In addition, quasi-experimental studies can be carried out in patients who are treated chronically with recombinant cytokines for a medical condition since these patients can be studied longitudinally before, during and after stimulation of the immune system. These clinical studies have revealed that depression is a late phenomenon that develops over a background of early appearing sickness. Incorporation of this feature in animal models of inflammation-associated depression has allowed the demonstration that alterations of brain serotoninergic neurotransmission do not play a major role in the pathogenesis. This is in contrast to the activation of the tryptophan degrading enzyme indoleamine 2,3-dioxygenase that generates potentially neurotoxic kynurenine metabolites such as 3-hydroxy kynurenine and quinolinic acid. Although the relative importance of peripherally versus centrally produced kynurenine and the cellular source of production of this compound remain to be determined, these findings provide new targets for the treatment of inflammation-associated depression that could be extended to other psychiatric conditions mediated by activation of neuroimmune mechanisms. Copyright © 2010 Elsevier Ltd. All rights reserved.

In a controlled study, such immunological parameters as whole blood production of the cytokines interleukin-6 (IL-6) and tumor-necrosis factor-alpha (TNF-alpha) were assessed in 24 inpatients with a major depressive disorder (MDD) both before and again under treatment. After a 6-week treatment period with amitriptyline, patients were classified as responders or nonresponders according to their psychopathological outcome as evaluated by the Hamilton and the Montgomery-Asberg Depression Rating Scales. Pre-treatment levels of c-reactive protein (CRP) were significantly higher in both patient subgroups than in the control subjects. In comparison to the controls, unstimulated pretreatment production of IL-6 was significantly decreased in the responders; whereas it was significantly increased in the nonresponder subgroup. Post-treatment values did not differ significantly among the patient and control groups. Pretreatment levels of TNF-alpha were increased in both patient subgroups, with a significant decrease during treatment only in the responder subgroup. Pretreatment levels of IL-6/10(5) mononuclear cells and the ratio between lymphocytes and monocytes acted as independent variables with regard to the clinical response. Our data indicate that unstimulated secretion of TNF-alpha is related to the psychopathological improvement; whereas, IL-6 levels might dichotomize the patients into subsequent responders and nonresponders already at admission.