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Associations among peripheral and central kynurenine pathway metabolites and inflammation in depression.

ABSTRACT: Kynurenine pathway (KP) metabolites are believed to be a link between inflammation and depression through effects on brain glutamate receptors. However, neither the relationship between plasma and cerebrospinal fluid (CSF) KP metabolites nor their association with inflammatory mediators is well-established in depression. Moreover, the clinical profile associated with combined activation of plasma inflammatory and kynurenine pathways is unknown. Accordingly, plasma and CSF-KP metabolites and inflammatory markers along with depressive symptoms and antidepressant treatment response were measured in 72 unmedicated depressed patients. Following bivariate analyses, component factors representing immune and kynurenine variables in the plasma and CSF were extracted and were used to examine directionality of associations in a path model. In addition, patients were clustered using individual markers that most accounted for the association between plasma immune and KP systems. Path analysis revealed a directional association extending from plasma inflammatory markers to plasma kynurenines, to CSF kynurenines. Among immune markers, plasma tumor necrosis factor (TNF) was robustly associated with plasma kynurenine (KYN) and KYN/tryptophan (TRP), which was in turn significantly associated with CSF KYN, kynurenic acid, and quinolinic acid. Clustering of patients based on plasma TNF and KYN/TRP yielded subgroups of high (N = 17) and low (N = 55) TNF-KYN/TRP groups. High TNF-KYN/TRP subjects exhibited greater depression severity, anhedonia, and treatment nonresponse. In conclusion, plasma-KP metabolites may mediate an inflammation-associated depressive symptom profile via CNS KP metabolites that can serve as a target for intervention at the level of inflammation, peripheral KYN metabolism, KYN transport to the brain, or effects of KP metabolites on glutamate receptors.

SUBMITTER: Haroon E

PROVIDER: S-EPMC7162907 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The importance of the kynurenine pathway in normal immune system function has led to an appreciation of its possible contribution to autoimmune disorders such as rheumatoid arthritis. Indoleamine-2,3-dioxygenase (IDO) activity exerts a protective function, limiting the severity of experimental arthritis, whereas deletion or inhibition exacerbates the symptoms. Other chronic disorder with an inflammatory component, such as atherosclerosis, are also suppressed by IDO activity. It is suggested that this overall anti-inflammatory activity is mediated by a change in the relative production or activity of Th17 and regulatory T cell populations. Kynurenines may play an anti-inflammatory role also in CNS disorders such as Huntington's disease, Alzheimer's disease and multiple sclerosis, in which signs of inflammation and neurodegeneration are involved. The possibility is discussed that in Huntington's disease kynurenines interact with other anti-inflammatory molecules such as Human Lymphocyte Antigen-G which may be relevant in other disorders. Kynurenine involvement may account for the protection afforded to animals with cerebral malaria and trypanosomiasis when they are treated with an inhibitor of kynurenine-3-monoxygenase (KMO). There is some evidence that changes in IL-10 may contribute to this protection and the relationship between kynurenines and IL-10 in arthritis and other inflammatory conditions should be explored. In addition, metabolites of kynurenine downstream of KMO, such as anthranilic acid and 3-hydroxy-anthranilic acid can influence inflammation, and the ratio of these compounds is a valuable biomarker of inflammatory status although the underlying molecular mechanisms of the changes require clarification. Hence it is essential that more effort be expended to identify their sites of action as potential targets for drug development. Finally, we discuss increasing awareness of the epigenetic regulation of IDO, for example by DNA methylation, a phenomenon which may explain differences between individuals in their susceptibility to arthritis and other inflammatory disorders.

Project description:Inflammation-related changes in the concentrations of inflammatory mediators such as c-reactive protein (CRP), interleukin 1β (IL-1), and IL-6 as well as kynurenine metabolites are associated with major depressive disorder (MDD) and affect depressive behavior, cognition, and hippocampal plasticity in animal models. We previously reported that the ratios of kynurenic acid (KynA) to the neurotoxic metabolites, 3-hydroxykynurenine (3HK) and quinolinic acid (QA), were positively correlated with hippocampal volume in depression. The hippocampus is critical for autobiographical memory (AM) recall which is impaired in MDD. Here we tested whether the ratios, KynA/3HK and KynA/QA were associated with AM recall performance as well as hippocampal activity during AM recall. Thirty-five unmedicated depressed participants and 25 healthy controls (HCs) underwent fMRI scanning while recalling emotionally-valenced AMs and provided serum samples for the quantification of kynurenine metabolites, CRP, and cytokines (IL-1 receptor antagonist - IL-1RA; IL-6, tumor necrosis factor alpha - TNF, interferon gamma -IFN-γ, IL-10). KynA/3HK and KynA/QA were lower in the MDD group relative to the HCs. The concentrations of the CRP and the cytokines did not differ significantly between the HCs and the MDD group. Depressed individuals recalled fewer specific AMs and displayed increased left hippocampal activity during the recall of positive and negative memories. KynA/3HK was inversely associated with left hippocampal activity during specific AM recall in the MDD group. Further, KynA/QA was positively correlated with percent negative specific memories recalled in the MDD group and showed a non-significant trend toward a positive correlation with percent positive specific memories recalled in HCs. In contrast, neither CRP nor the cytokines were significantly associated with AM recall or activity of the hippocampus during AM recall. Conceivably, an imbalance in levels of KynA versus QA-pathway metabolites may adversely impact the function of the hippocampus and AM recall, raising the possibility that kynurenine pathway may affect emotion-dependent memory within the context of depression.

Project description:BackgroundNeuroinflammation plays a significant role in the progression of frontotemporal dementia (FTD). However, the association between peripheral inflammatory factors and brain neurodegeneration is poorly understood. We aimed to examine changes in peripheral inflammatory markers in patients with behavioural variant FTD (bvFTD) and explore the potential association between peripheral inflammation and brain structure, metabolism, and clinical parameters.MethodsThirty-nine bvFTD patients and 40 healthy controls were enrolled and underwent assessment of plasma inflammatory factors, positron emission tomography/magnetic resonance imaging, and neuropsychological assessments. Group differences were tested using Student's t test, Mann‒Whitney U test, or ANOVA. Partial correlation analysis and multivariable regression analysis were implemented using age and sex as covariates to explore the association between peripheral inflammatory markers, neuroimaging, and clinical measures. The false discovery rate was used to correct for the multiple correlation test.ResultsPlasma levels of six factors, including interleukin (IL)-2, IL-12p70, IL-17A, tumour necrosis superfamily member 13B (TNFSF/BAFF), TNFSF12 (TWEAK), and TNFRSF8 (sCD30), were increased in the bvFTD group. Five factors were significantly associated with central degeneration, including IL-2, IL-12p70, IL-17A, sCD30/TNFRSF8, and tumour necrosis factor (TNF)-α; the association between inflammation and brain atrophy was mainly distributed in frontal-limbic-striatal brain regions, whereas the association with brain metabolism was mainly in the frontal-temporal-limbic-striatal regions. BAFF/TNFSF13B, IL-4, IL-6, IL-17A and TNF-α were found to correlate with clinical measures.ConclusionPeripheral inflammation disturbance in patients with bvFTD participates in disease-specific pathophysiological mechanisms, which could be a promising target for diagnosis, treatment, and monitoring therapeutic efficacy.

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Associations among peripheral and central kynurenine pathway metabolites and inflammation in depression.

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