Does escitalopram reduce neurotoxicity in major depression?

Serum levels of inflammatory cytokines, for example, tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6), and IL-1 beta (IL-1β), are elevated in subjects with major depressive disorder (MDD). The reason why this occurs is unclear. Elevated levels of inflammatory cytokines could be a result of brain dysfunction in MDD. It is also possible that inflammatory cytokines contribute to depressive symptoms in MDD. If the first assumption is correct, one would expect levels to normalize with resolution of the depressive episode after treatment. Several studies have measured changes in cytokine levels during antidepressant treatment; however, the results vary. The purpose of this study was to pool all available data on changes in serum levels of TNFα, IL-6, and IL-1β during antidepressant treatment to determine whether these levels change. Studies were included if they used an approved pharmacological treatment for depression, patients had a diagnosis of MDD, and serum levels of TNFα, IL-6, and/or IL-1β were measured before and after treatment. Twenty-two studies fulfilled these criteria. Meta-analysis of these studies showed that, overall, while pharmacological antidepressant treatment reduced depressive symptoms, it did not reduce serum levels of TNFα. On the other hand, antidepressant treatment did reduce levels of IL-1β and possibly those of IL-6. Stratified subgroup analysis by class of antidepressant indicated that serotonin reuptake inhibitors may reduce levels of IL-6 and TNFα. Other antidepressants, while efficacious for depressive symptoms, did not appear to reduce cytokine levels. These results argue against the notion that resolution of a depressive episode is associated with normalization of levels of circulating inflammatory cytokines; however, the results are consistent with the possibility that inflammatory cytokines contribute to depressive symptoms and that antidepressants block the effects of inflammatory cytokines on the brain.

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.

Increased inflammation and reduced neurogenesis have been associated with the pathophysiology of major depression. Here, we show for the first time how IL-1β, a pro-inflammatory cytokine shown to be increased in depressed patients, decreases neurogenesis in human hippocampal progenitor cells. IL-1β was detrimental to neurogenesis, as shown by a decrease in the number of doublecortin-positive neuroblasts (-28%), and mature, microtubule-associated protein-2-positive neurons (-36%). Analysis of the enzymes that regulate the kynurenine pathway showed that IL-1β induced an upregulation of transcripts for indolamine-2,3-dioxygenase (IDO), kynurenine 3-monooxygenase (KMO), and kynureninase (42-, 12- and 30-fold increase, respectively, under differentiating conditions), the enzymes involved in the neurotoxic arm of the kynurenine pathway. Moreover, treatment with IL-1β resulted in an increase in kynurenine, the catabolic product of IDO-induced tryptophan metabolism. Interestingly, co-treatment with the KMO inhibitor Ro 61-8048 reversed the detrimental effects of IL-1β on neurogenesis. These observations indicate that IL-1β has a critical role in regulating neurogenesis whereas affecting the availability of tryptophan and the production of enzymes conducive to toxic metabolites. Our results suggest that inhibition of the kynurenine pathway may provide a new therapy to revert inflammatory-induced reduction in neurogenesis.