Neopterin production, tryptophan degradation, and mental depression--what is the link?

Neopterin mediates sleep deprivation-induced microglial activation resulting in neuronal damage by affecting YY1/HDAC1/TOP1/IL-6 signaling

INTRODUCTION

Sleep deprivation (SD) is a common disorder in modern society. Hippocampus is an important region of the brain for learning, memory, and emotions. Dysfunction of hippocampus can lead to severe learning and memory disorder, significantly affecting quality of life. SD is accompanied by hippocampal microglia activation and a surge in inflammatory factors, but the precise mechanism remains unclear. Moreover, the ongoing unknown persists regarding how activated microglia in SD lead to neuronal damage. Topoisomerase 1 (TOP1) plays an essential role in the inflammatory process, including the tumor system and viral infection. In this study, we observed a significant elevation in TOP1 levels in the hippocampus of mice subjected to SD. Therefore, we hypothesize that TOP1 may be implicated in SD-induced microglia activation and neuronal damage.

OBJECTIVES

To investigate the role of TOP1 in SD-induced microglial activation, neuronal damage, and neurobehavioral impairments, and the molecular basis of SD-induced elevated TOP1 levels.

METHODS

TOP1-specific knockout mice in microglia were used to study the effects of TOP1 on microglial activation and neuronal damage. Transcription factor prediction, RNA interference, ChIP-qPCR, ChIP-seq database analysis, and luciferase reporter assays were performed to explore the molecular mechanisms of YY1 transcriptional activation. Untargeted metabolic profiling was employed to investigate the material basis of YY1 transcriptional activation.

RESULTS

Knockdown of TOP1 in hippocampal microglia ameliorates SD-induced microglial activation, inflammatory response, and neuronal damage. Mechanistically, TOP1 mediates the release of IL-6 from microglia, which consequently leads to neuronal dysfunction. Moreover, elevated TOP1 due to SD were associated with neopterin, which was attributed to its promotion of elevated levels of H3K27ac in the TOP1 promoter region by disrupting the binding of YY1 and HDAC1.

CONCLUSION

The present study reveals that TOP1-mediated microglial activation is critical for SD induced hippocampal neuronal damage and behavioral impairments.

Pentoxifylline as a Novel Add-on Therapy for Major Depressive Disorder in Adult Patients: A Randomized, Double-Blind, Placebo-Controlled Trial

BACKGROUND

Evidence indicates an association between immune dysregulation and major depressive disorder (MDD). Pentoxifylline (PTX), a phosphodiesterase inhibitor, has been shown to reduce pro-inflammatory activities. The aim of this study was to evaluate changes in depressive symptoms and pro-inflammatory markers after administration of PTX as an adjunctive agent to citalopram in patients with MDD.

METHODS

One hundred patients were randomly assigned to either citalopram (20 mg/day) plus placebo (twice daily) (n=50) or citalopram (20 mg/day) plus PTX (400 mg) (twice daily) (n=50). The Hamilton Depression Rating Scale-17 (HAM-D-17) scores at baseline, weeks 2, 4, 6, 8, 10, and 12 and serum levels of interleukin1-β (IL-1-β), tumor necrosis factor-α, C-reactive protein, IL-6, serotonin, IL-10, and brain-derived neurotrophic factor (BDNF) at baseline and week 12 were evaluated.

RESULTS

HAM-D-17 score in the PTX group significantly reduced in comparison to the control group after weeks 4, 6, 8,10, and 12 ((LSMD): - 2.193, p=0.021; - 2.597, p=0.036; - 2.916, p=0.019; - 4.336, p=0.005; and - 4.087, p=0.008, respectively). Patients who received PTX had a better response (83%) and remission rate (79%) compared to the placebo group (49% and 40%, p=0.006 and p=0.01, respectively). Moreover, the reduction in serum concentrations of pro-inflammatory factors and increase in serotonin and BDNF in the PTX group was significantly greater than in the placebo group (p<0.001).

CONCLUSION

These findings support the safety and efficacy of PTX as an adjunctive antidepressant agent with anti-inflammatory effects in patients with MDD.

Changes in tryptophan breakdown associated with response to multimodal treatment in depression

Background

Research on depression showed that dysregulations in tryptophan (TRP), kynurenine (KYN), and its KYN pathway metabolites are key aspects in the development and maintenance of depressive symptoms. In our previous reports, we described sex-specific changes in TRP breakdown as well as changes in KYN and KYN/TRP in association with treatment response and inflammatory and metabolic parameters. However, results of treatment effects on KYN pathway metabolites as well as how pathway changes are related to treatment response remain sparse.

Objective

We investigated potential changes of KYN and KYN pathway metabolites in association with therapeutic response of individuals with depression during a six-week multimodal psychiatric rehabilitation program.

Methods

87 participants were divided into treatment responders and non-responders (48 responders, 39 non-responders; 38 male, 49 female; M age = 51.09; SD age = 7.70) using scores of psychological questionnaires. KYN pathway metabolites serum concentrations as well as their ratios were collected using high performance liquid chromatography. Changes over time (time of admission (t1) vs. time of discharge (t2)) were calculated using repeated measure analyses of (co)variance.

Results

Non-responders exhibited higher levels of 3-Hydroxyanthralinic acid (3-HAA), nicotinic acid (NA), and 3-HAA/KYN, independently of measurement time. NA levels decreased, while 3-HAA levels increased over time in both groups, independently of treatment response. 3-HK/KYN levels decreased, while KYN levels increased in non-responders, but not in responders over time.

Discussion

The results indicate that some compounds of the KYN pathway metabolites can be altered through multimodal long-term interventions in association with treatment response. Especially the pathway degrading KYN further down to 3-HAA and 3-HK/KYN might be decisive for treatment response in depression.

The Influence of Kynurenine Metabolites on Neurodegenerative Pathologies

As the kynurenine pathway's links to inflammation, the immune system, and neurological disorders became more apparent, it attracted more and more attention. It is the main pathway through which the liver breaks down Tryptophan and the initial step in the creation of nicotinamide adenine dinucleotide (NAD+) in mammals. Immune system activation and the buildup of potentially neurotoxic substances can result from the dysregulation or overactivation of this pathway. Therefore, it is not shocking that kynurenines have been linked to neurological conditions (Depression, Parkinson's, Alzheimer's, Huntington's Disease, Schizophrenia, and cognitive deficits) in relation to inflammation. Nevertheless, preclinical research has demonstrated that kynurenines are essential components of the behavioral analogs of depression and schizophrenia-like cognitive deficits in addition to mediators associated with neurological pathologies due to their neuromodulatory qualities. Neurodegenerative diseases have been extensively associated with neuroactive metabolites of the kynurenine pathway (KP) of tryptophan breakdown. In addition to being a necessary amino acid for protein synthesis, Tryptophan is also transformed into the important neurotransmitters tryptamine and serotonin in higher eukaryotes. In this article, a summary of the KP, its function in neurodegeneration, and the approaches being used currently to target the route therapeutically are discussed.

Involvement of indoleamine 2, 3-dioxygenase (IDO) and brain-derived neurotrophic factor (BDNF) in the neuroprotective mechanisms of ferulic acid against depressive-like behaviour

OBJECTIVE

Ferulic acid (FA) is a common food ingredient that is abundantly present in various routinely consumed food and beverages. Like many cinnamic acid derivatives, FA produces wide-ranging effects in a dose-dependent manner and various studies link FA consumption with reduced risk of depressive disorders. The aim of this study was to exploit the neuroprotective mechanisms of FA including indoleamine 2,3-dioxygenase (IDO), brain-derived neurotrophic factor (BDNF), and other pro-inflammatory cytokines by employing lipopolysaccharide (LPS)-induced depressive-like behaviour model.

METHODS

C57BL/6J male mice were divided into 4 groups consisting of saline (SAL), LPS, FA and Imipramine (IMI). Animals were pretreated orally with FA (10 mg/kg) and IMI (10 mg/kg) for 21 days once daily and all groups except SAL were challenged with LPS (0.83 mg/kg) intraperitoneally on day 21.

RESULTS

LPS administration produced a biphasic change in the behaviour of the animals where the animals lost a significant weight and express high immobility time at 24 h. Proinflammatory cytokines including, TNF-α, IL-6, IL-1β, and IFN-γ were significantly increased along with increased lipid peroxidation and reduced BDNF. Furthermore, the increased kynurenine to tryptophan ratio was indicative of elevated IDO activity.

CONCLUSION

The results of this study emphasise that low dose of FA is effective in attenuating depressive-like behaviour by modulating IDO, BDNF and reducing neuroinflammation.

Neopterin Levels in Bonobos Vary Seasonally and Reflect Symptomatic Respiratory Infections

As environmental changes exacerbate the threat coming from infectious diseases in wild mammal species, monitoring their health and gaining a better understanding of the immune functioning at the species level have become critically important. Neopterin is a biomarker of cell-mediated immune responses to intracellular infections. We investigated the variation of urinary neopterin (uNeo) levels of wild, habituated bonobos (Pan paniscus) in relation to individual and environmental factors. We used 309 urine samples collected between 2010 and 2018 at the LuiKotale field site, DRC. Based on current knowledge on zoo-housed conspecifics and closely related species, we predicted uNeo levels to increase (1) during infections, (2) with increasing age, (3) over the gestation period and in estrous females; and (4) to vary seasonally. Our results showed uNeo levels varied over a one-year period and increased in individuals showing respiratory symptoms. Contrary to chimpanzees, uNeo levels did not vary with age or female reproductive status, possibly due to our small sample size. Our study provides a baseline for a better understanding of bonobo's immunocompetence in the context of socio-ecological pressures and for monitoring the health of wild populations.

Connexin 43: An Interface Connecting Neuroinflammation to Depression

Major depressive disorder (MDD) is a leading chronic mental illness worldwide, characterized by anhedonia, pessimism and even suicidal thoughts. Connexin 43 (Cx43), mainly distributed in astrocytes of the brain, is by far the most widely and ubiquitously expressed connexin in almost all vital organs. Cx43 forms gap junction channels in the brain, which mediate energy exchange and effectively maintain physiological homeostasis. Increasing evidence suggests the crucial role of Cx43 in the pathogenesis of MDD. Neuroinflammation is one of the most common pathological features of the central nervous system dysfunctions. Inflammatory factors are abnormally elevated in patients with depression and are closely related to nearly all links of depression. After activating the inflammatory pathway in the brain, the release and uptake of glutamate and adenosine triphosphate, through Cx43 in the synaptic cleft, would be affected. In this review, we have summarized the association between Cx43 and neuroinflammation, the cornerstones linking inflammation and depression, and Cx43 abnormalities in depression. We also discuss the significant association of Cx43 in inflammation and depression, which will help to explore new antidepressant drug targets.

Indoleamine 2, 3-dioxygenase is responsible for low stress tolerance after intracerebral hemorrhage

In the chronic phase after intracerebral hemorrhage (ICH), the aftereffect-associated lowering of motivation burdens many patients; however, the pathogenic mechanism is unclear. Here, we revealed for the first time that indoleamine 2, 3-dioxygenase (IDO) expression and enzyme activity are increased in the collagenase-induced murine ICH model. IDO is a rate-limiting enzyme situated at the beginning of the kynurenine pathway and converts tryptophan, a source of serotonin (5-hydroxytryptamine; 5-HT), to kynurenine. In this study, we showed that IDO is localized in 5-HTergic neurons. After ICH, the synaptosomal 5-HT level decreased, but this effect was neutralized by subcutaneous injections of 1-methyl tryptophan (MT), a specific IDO inhibitor. These results suggest that ICH-induced IDO weakens the activity of 5-HTergic neurons. Accordingly, we next investigated whether the IDO increase contributes to the depression-like behaviors of ICH mice. The immobility times of tail suspension and forced swimming tests were significantly prolonged after ICH but shortened by the administration of 1-MT. In conclusion, the increased IDO after ICH was found to decrease 5-HT levels and subsequently reduce stress tolerance. These findings indicate that IDO is a novel therapeutic target for the ICH aftereffect-associated lowering of motivation.

Potential shared gene signatures and molecular mechanisms between atherosclerosis and depression: Evidence from transcriptome data

BACKGROUND

Atherosclerosis and depression contribute to each other; however, mechanisms linking them at the genetic level remain unexplored. This study aimed to identify shared gene signatures and related pathways between these comorbidities.

METHODS

Atherosclerosis-related datasets were downloaded from the Gene Expression Omnibus database. Differential and weighted gene co-expression network analyses were employed to identify atherosclerosis-related genes. Depression-related genes were downloaded from the DisGeNET database, and the overlaps between atherosclerosis-related genes and depression-related genes were characterized as crosstalk genes. The functional enrichment analysis and protein-protein interaction network were performed in these gene sets. Subsequently, the Boruta algorithm and Recursive Feature Elimination algorithm were performed to identify feature-selection genes. A support vector machine was constructed to measure the accuracy of calculations, and two external validation sets were included to verify the results.

RESULTS

Based on two atherosclerosis-related datasets (GSE28829 and GSE43292), 165 genes were determined as atherosclerosis-related genes. Meanwhile, 1478 depression-related genes were obtained. After intersecting, 24 crosstalk genes were identified, and two pathways, "lipid and atherosclerosis" and "tryptophan metabolism," were revealed as mutual pathways according to the enrichment analysis results. Through the protein-protein interaction network, Molecular Complex Detection plugin, and cytoHubba plugin, PTPRC and MMP9 were identified as the hub gene. Moreover, SLC22A3, CASP1, AMPD3, and PIK3CG were recognized as feature-selection genes. Based on two external validation sets, CASP1 and MMP9 were finally determined as the critical crosstalk genes.

CONCLUSIONS

"Lipid and atherosclerosis" and "tryptophan metabolism" were possibly the pathways of atherosclerosis secondary to depression and depression due to atherosclerosis, respectively. CASP1 and MMP9 were revealed as the most pivotal candidates linking atherosclerosis and depression by mediating these two pathways. Further experimentation is needed to confirm these conclusions.

Acute administration of ibuprofen increases serum concentration of the neuroprotective kynurenine pathway metabolite, kynurenic acid: a pilot randomized, placebo-controlled, crossover study

RATIONALE

At least six different types of antidepressant treatments have been shown to either increase the neuroprotective kynurenine pathway (KP) metabolite, kynurenic acid (KynA), or decrease the neurotoxic KP metabolite, quinolinic acid (QA). Nonsteroidal anti-inflammatory drugs (NSAIDs) including ibuprofen have shown some efficacy in the treatment of depression but their effects on the KP have not been studied in humans.

OBJECTIVES

To evaluate the effect of ibuprofen on circulating KP metabolites.

METHODS

In a randomized, placebo-controlled, crossover study, 20 healthy adults (10 women) received a single oral dose of 200-mg ibuprofen, 600-mg ibuprofen, or placebo in a counterbalanced order (NCT02507219). Serum samples were drawn in the mid-afternoon, 5 h after ibuprofen/placebo administration. KP metabolites were measured blind to visit by tandem mass spectrometry. Data were analyzed with linear mixed effect models. The primary outcome was KynA/QA and the secondary outcome was KynA.

RESULTS

After Bonferroni correction, there was a significant effect of treatment on KynA/QA. The effect was driven by an increase in KynA concentration after the 600-mg dose but not the 200-mg dose relative to placebo (Cohen's d = 1.71). In contrast, both the 200-mg (d = 1.03) and 600-mg (d = 2.05) doses of ibuprofen decreased tryptophan concentrations relative to placebo.

CONCLUSIONS

Given its KynA-elevating effects, ibuprofen could have neuroprotective effects in the context of depression as well as other neuroinflammatory disorders that are characterized by a reduction in KynA.

High frequency repetitive transcranial magnetic stimulation improves cognitive performance parameters in patients with Alzheimer's disease - an exploratory pilot study

BACKGROUND

Currently available medication for Alzheimer's disease (AD) may slows cognitive decline only transitory, but has failed to bring about long term positive effects. For this slowly progressive neurodegenerative disease so far no disease modifying therapy exists.

OBJECTIVE

To find out if non-pharmacologic non-ivasive neuromodulatory repetitive transcranial magnetic stimulation (rTMS) may offer a new alternative or an add on therapeutic strategy against loss of cognitive functions.

METHODS

In this exploratory intervention study safety and symptom development before and after frontopolar cortex stimulation (FPC) using intermittent theta burst stimulation (iTBS) at 10 subsequent working days was monitored as add-on treatment in 28 consecutive patients with AD. Out of these, 10 randomly selected patients received sham stimulation as a control. In addition, ​serum concentrations of neurotransmitter precursor amino acids, of immune activation and inflammation markers, of brain derived neurotrophic factor (BDNF) as well as of nitrite were measured.

RESULTS

Treatment was well tolerated, no serious adverse effects were observed. Improvement of cognition was detected by an increase of Mini Mental State Examination score (MMSE; p<0.01, paired rank test) and also by an increase in a modified repeat address phrase test, part of the 6-item cognitive ​impairment test (p < 0.01). A trend to an increase in the clock drawing test (CDT; p = 0.08) was also found in the verum treated group. Furtheron, in 10 of the AD patients with additional symptoms of depression treated with iTBS, a significant decrease in the HAMD-7 scale (p <0.01) and a trend to lower serum phenylalanine concentrations (p = 0.08) was seen. No changes of the parameters tested were found in the sham treated patients.

CONCLUSION

Our preliminary results may indicate that iTBS is effective in the treatment of AD. Also a slight influence of iTBS on the metabolism of phenylalanine was found after 10 iTBS sessions. An impact of iTBS to influence the enzyme phenylalanine hydroxylase (PAH), as found in previous series of treatment resistant depression, could not be seen in this our first observational trial in 10 AD patients with comorbidity of depression. Longer treatment periods for several weeks in a higher number of AD patients with depression could cause more intense and disease modifying effects visible in different neurotransmitter concentrations important in the pathogenesis of AD.

The Role of Tryptophan Metabolites in Neuropsychiatric Disorders

In recent decades, neuropsychiatric disorders such as major depressive disorder, schizophrenia, bipolar, etc., have become a global health concern, causing various detrimental influences on patients. Tryptophan is an important amino acid that plays an indisputable role in several physiological processes, including neuronal function and immunity. Tryptophan’s metabolism process in the human body occurs using different pathways, including the kynurenine and serotonin pathways. Furthermore, other biologically active components, such as serotonin, melatonin, and niacin, are by-products of Tryptophan pathways. Current evidence suggests that a functional imbalance in the synthesis of Tryptophan metabolites causes the appearance of pathophysiologic mechanisms that leads to various neuropsychiatric diseases. This review summarizes the pharmacological influences of tryptophan and its metabolites on the development of neuropsychiatric disorders. In addition, tryptophan and its metabolites quantification following the neurotransmitters precursor are highlighted. Eventually, the efficiency of various biomarkers such as inflammatory, protein, electrophysiological, genetic, and proteomic biomarkers in the diagnosis/treatment of neuropsychiatric disorders was discussed to understand the biomarker application in the detection/treatment of various diseases.

Tryptophan: Its Metabolism along the Kynurenine, Serotonin, and Indole Pathway in Malignant Melanoma

(1) Background: Tryptophan metabolism is known to be one of the important mechanisms used by cancer to evade immune surveillance. Altered tryptophan metabolism was studied in patients with pigmented malignant melanoma confirmed histologically by the anatomic stage grouping for cutaneous melanoma using clinical staging on the basis of the Breslow thickness of the melanoma, the degree of spread to regional lymph nodes, and by the presence of distant metastasis. (2) Methods: Urinary tryptophan metabolites were detected by RP-HPLC method. (3) Results: In the present work, we provided evidence of altered metabolism of all tryptophan pathways in melanoma patients. (4) Conclusions: Knowledge of the shifted serotonin pathway toward DHICA formation and kynurenine pathway shifted toward NAD+ production could serve in the early detection of the disease and the initiation of early treatment of malignant melanoma.

Elevated neopterin in tuberculosis and co-infection with HIV and the effect of treatment: A systematic review, meta-analysis, and meta-regression

BACKGROUND

Neopterin (NEO) is a marker of immune stimulation. Increased NEO levels have been associated with autoimmune diseases, infections, and malignancies. Studies of NEO alterations in tuberculosis (TB) with or without HIV co-infection show inconsistent results. Moreover, challenges exist regarding TB diagnosis in people with HIV.

METHODS

We did a systematic review and meta-analysis of studies comparing urinary, pleural, and blood NEO levels between patients with TB or HIV-TB co-infection as the case group and subjects without TB and HIV or subjects with HIV without TB as the control group, respectively.

RESULTS

Blood NEO levels in patients with active TB were higher than healthy controls, with a large effect size of 1.99. Patients with TB had higher blood NEO levels before anti-tuberculosis therapy (ATT) than after ATT for months or when treatment ended with moderate effect sizes (1.13-1.46). meta-analysis of studies of patients with HIV-TB co-infection yielded similar results, with higher blood NEO levels in patients than controls that remained significant in subgroups of studies on pulmonary TB (PTB) patients and serum NEO and higher blood NEO levels in patients before than after ATT.

CONCLUSION

Meta-analyses reveal alteration in NEO levels in different specimens, e.g., blood, urine, and pleural fluid, in patients with TB with or HIV-TB co-infection compared to the control groups. Future studies need to investigate the utility of NEO as a diagnostic/prognostic biomarker for TB. Also, cellular and molecular mechanisms linking NEO and TB remain to be addressed.

Comparative study of brain damage and oxidative stress using two animal models of the shaken baby syndrome

The objective was compare the morphological damages in brain and to evaluate the participation of oxidative stress, using two animal models of shaken baby syndrome (SBS). Five-day-old Wistar rats were used to develop two models of SBS as follows: Gyrotwister (GT) group was subjected to low intensity, high duration rotating movements and Ratshaker (RS) group made to undergo high intensity, low duration anteroposterior movements. Both groups presented respiratory distress, weight loss and shorter stature compared with the control group. In addition, involuntary movements occurred in both experimental models. Hemorrhage was observed in 10 % of the GT group and in 40 % of the RS group. This last group experienced lesser weight gain at 30 days. Glutathione decreased by 25.7 % (GT) and 59.96 (RT). Cell data analysis revealed the presence of crenate and pyknotic cells, characterized by apparent absence of nucleus and nucleolus as well as vacuolation in the GT group. In the RS group, there were a high number of angular, pyknotic and shrunken cells, and a lot of vacuolization. The severity of the brain damage can be related to the magnitude of biochemical modifications, specifically, those related to the production of reactive oxygen or nitrogen species, oxidative stress, oxidative damage.

Sodium Benzoate—Harmfulness and Potential Use in Therapies for Disorders Related to the Nervous System: A Review

Currently, due to the large number of reports regarding the harmfulness of food additives, more and more consumers follow the so-called “clean label” trend, i.e., prefer and choose the least-processed food products. One of the compounds known as a preservative with a high safety profile is sodium benzoate. While some studies show that it can be used to treat conditions such as depression, pain, schizophrenia, autism spectrum disorders, and neurodegenerative diseases, others report its harmfulness. For example, it was found to cause mutagenic effects, generate oxidative stress, disrupt hormones, and reduce fertility. Due to such disparate results, the purpose of this study is to comprehensively discuss the safety profile of sodium benzoate and its potential use in neurodegenerative diseases, especially in autism spectrum disorder (ASD), schizophrenia, major depressive disorder (MDD), and pain relief.

The importance of neopterin in COVID-19: The prognostic value and relation with the disease severity

Coronavirus Disease 2019 [COVID-19], caused by severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2], has rapidly evolved into a global health emergency. Neopterin [NPT], produced by macrophages when stimulated with interferon [IFN-]gamma, is an essential cytokine in the antiviral immune response. NPT has been used as a marker for the early assessment of disease severity in different diseases. The leading cause of NPT production is the pro-inflammatory cytokine IFN-. Macrophage activation has also been revealed to be linked with disease severity in SARS-CoV-2 patients. We demonstrate the importance of NPT in the pathogenesis of SARS-CoV-2 and suggest that targeting NPT in SARS-CoV-2 infection may be critical in the early prediction of disease progression and provision of timely management of infected individuals.

The association between depression and chronic lower back pain from disc degeneration and herniation of the lumbar spine

Chronic lower back pain induced by lumbar disc degeneration or herniation exerts a great impact on patients' daily lives. Depression and anxiety often exist among patients with lower back pain. Some studies mentioned about mechanisms, such as inflammatory biomarkers, which are commonly seen in herniated intervertebral disc (HIVD) and major depressive disorder (MDD). Method: Our study used a large database from the National Health Insurance to explore the incidence rate of MDD in patients with HIVD and correlated risk factors. A total of 41,874 patients with HIVD were included in this work. The control group was matched by using propensity scores. Results: The results showed a temporal association between prior HIVD and subsequent MDD after adjusting for potential confounding factors. Patients with HIVD were at high risk of developing MDD (hazard ratio, HR: 9.00, 95% confidence interval, CI: 7.196-11.257) even after adjusting for demographic characteristics and comorbidities (HR: 8.47, 95% CI: 6.84-10.49, p < 0.0001). Conclusions: The combination of HIVD and MDD represents an important health problem that is associated with higher disability rates, socioeconomic disadvantage, and greater utilization of health care resources. Early detection and combined treatment of depressive symptoms may benefit patients with HIVD.

Tryptophan Metabolism in Bipolar Disorder in a Longitudinal Setting

Immune-mediated inflammatory processes and oxidative stress are involved in the aetiopathogenesis of bipolar disorder (BD) and weight-associated comorbidities. Tryptophan breakdown via indoleamine 2,3-dioxygenase-1 (IDO-1) along the kynurenine axis concomitant with a pro-inflammatory state was found to be more active in BD, and associated with overweight/obesity. This study aimed to investigate tryptophan metabolism in BD compared to controls (C), stratified by weight classes, in a longitudinal setting, dependent on the incidence of BD episodes. Peripheral tryptophan, kynurenine, and neopterin were assessed in the serum of 226 BD individuals and 142 C. Three samples in a longitudinal assessment were used for 75 BD individuals. Results showed a higher kynurenine/tryptophan in both BD compared to C and overweight compared to normal weight persons. Levels remained stable over time. In the longitudinal course, no differences were found between individuals who were constantly euthymic or not, or who had an illness episode or had none. Findings indicate that tryptophan, kynurenine, and IDO-1 activity may play a role in pathophysiology in BD but are not necessarily associated with clinical manifestations. Accelerated tryptophan breakdown along the kynurenine axis may be facilitated by being overweight. This may increase the risk of accumulation of neurotoxic metabolites, impacting BD symptomatology, cognition, and somatic comorbidities.

Neurotransmitter Precursor Amino Acid Ratios Show Differential, Inverse Correlations with Depression Severity in the Low and High Depression Score Range

The immunomodulatory capacity of mental stress is one of the basic concepts of psychoneuroimmunology. The current prospective longitudinal study was designed to evaluate the effect of acute mental stress on neurotransmitter precursor amino acid levels in individuals with depression at 2 time points. Ten physically healthy patients with a diagnosis of major depressive episode and Montgomery–Åsberg Depression Rating Scale scores (MADRAS) ⩾20 points at inclusion were assessed on 2 study days (once with higher MADRAS scores, once with lower MADRAS scores; median 34.5 days apart) and subjected to a standardized acute mental stress test on each study day. Blood was collected at 4 time points: once prior to and at 3 time points (0, 30 minutes, 60 minutes) following mental stress. Neurotransmitter precursor amino acid levels, that is kynurenine/tryptophan (KYN/TRP) and phenylalanine/tyrosine (PHE/TYR), as well as neopterin and nitrite were analyzed in a total of 80 individual blood samples. Regression and correlation analyses were performed. Regression analyses of PHE/TYR (R² = .547) and KYN/TRP (R² = .440) in relation to MADRAS depression severity showed a quadratic curve fit. This was reflected by a negative linear correlation between MADRAS scores and PHE/TYR as well as KYN/TRP in the lower score range (r = −.805, P < .001 and r = −.586, P < .001 respectively) and a positive correlation in the higher MADRAS score range (r = .713, P < .001 and r = .379, P = .016 respectively). No effect of acute mental stress was found. This analysis exemplifies the implications of sampling as well as data distributions on results. The crosstalk of biological mechanisms that orchestrate metabolic and immunological signaling may vary depending on depression severity resulting in non-linear associations that may explain the heterogeneity of results found in the literature.

Ingestion of Lactobacillus rhamnosus modulates chronic stress-induced feather pecking in chickens

Feather pecking (FP) is a stress-induced neuropsychological disorder of birds. Intestinal dysbiosis and inflammation are common traits of these disorders. FP is, therefore, proposed to be a behavioral consequence of dysregulated communication between the gut and the brain. Probiotic bacteria are known to favorably modulate the gut microbiome and hence the neurochemical and immune components of the gut-brain axis. Consequently, probiotic supplementation represents a promising new therapeutic to mitigate widespread FP in domestic chickens. We monitored FP, gut microbiota composition, immune markers, and amino acids related to the production of neurochemicals in chickens supplemented with Lactobacillus rhamnosus or a placebo. Data demonstrate that, when stressed, the incidence of FP increased significantly; however, L. rhamnosus prevented this increase. L. rhamnosus supplementation showed a strong immunological effect by increasing the regulatory T cell population of the spleen and the cecal tonsils, in addition to limiting cecal microbiota dysbiosis. Despite minimal changes in aromatic amino acid levels, data suggest that catecholaminergic circuits may be an interesting target for further studies. Overall, our findings provide the first data supporting the use of a single-strain probiotic to reduce stress-induced FP in chickens and promise to improve domestic birds' welfare.

Repetitive transcranial magnetic stimulation in the treatment of resistant depression: changes of specific neurotransmitter precursor amino acids

Repetitive transcranial magnetic stimulation (rTMS) for treatment-resistant major depression offers an alternative therapy, since more than every third patient is not responding to adequate antidepressive treatment. In this interventional study safety, symptom development and changes of serum concentrations of neurotransmitter precursor amino acids, of immune activation and inflammation markers, of brain-derived neurotrophic factor (BDNF), nitrite as well as of salivary amylase were measured before and after a frontal polar cortex stimulation using rTMS as add-on treatment in 38 patients with treatment-resistant depression. Out of these, 17 patients received sham stimulation as a control. Treatment was well tolerated: with the exception of one patient of the verum group, who described discomfort during the second treatment, no serious adverse effects were observed. Improvement of depression with a significant decrease in the HAMD-7 scale (p = 0.001) was found in patients treated with rTMS, but not in sham-treated patients. Furthermore, serum phenylalanine and tyrosine dropped significantly (p = 0.03 and p = 0.027, respectively) in rTMS-treated patients. The kynurenine to tryptophan ratio (Kyn/Trp) tended to decrease under rTMS (p = 0.07). In addition, associations between concentrations of BDNF and neopterin as well as serum nitrite levels were found in patients after rTMS treatment, which indicates an influence of immune regulatory circuits on BDNF levels. In the sham-treated patients, no changes of biomarker concentrations were observed. Results show that rTMS is effective in the treatment of resistant depression. rTMS appears to influence the enzyme phenylalanine hydroxylase, which plays a central role in the biosynthesis of neurotransmitter precursors tyrosine and dihydroxyphenylalanine (DOPA).

The Footprint of Kynurenine Pathway in Neurodegeneration: Janus-Faced Role in Parkinson's Disorder and Therapeutic Implications

Progressive degeneration of neurons and aggravation of dopaminergic neurons in the substantia nigra pars compacta results in the loss of dopamine in the brain of Parkinson's disease (PD) patients. Numerous therapies, exhibiting transient efficacy have been developed; however, they are mostly accompanied by side effects and limited reliability, therefore instigating the need to develop novel optimistic treatment targets. Significant therapeutic targets have been identified, namely: chaperones, protein Abelson, glucocerebrosidase-1, calcium, neuromelanin, ubiquitin-proteasome system, neuroinflammation, mitochondrial dysfunction, and the kynurenine pathway (KP). The role of KP and its metabolites and enzymes in PD, namely quinolinic acid (QUIN), kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), 3-hydroxyanthranillic acid (3-HAA), kunurenine-3-monooxygenase (KMO), etc. has been reported. The neurotoxic QUIN, N-methyl-D-aspartate (NMDA) receptor agonist, and neuroprotective KYNA-which antagonizes QUIN actions-primarily justify the Janus-faced role of KP in PD. Moreover, KP has been reported to play a biomarker role in PD detection. Therefore, the authors detail the neurotoxic, neuroprotective, and immunomodulatory neuroactive components, alongside the upstream and downstream metabolic pathways of KP, forming a basis for a therapeutic paradigm of the disease while recognizing KP as a potential biomarker in PD, thus facilitating the development of a suitable target in PD management.

Tryptophan Catabolites in Bipolar Disorder: A Meta-Analysis

Objective

Tryptophan catabolites (TRYCATs) are implicated in the pathophysiology of mood disorders by mediating immune-inflammation and neurodegenerative processes. We performed a meta-analysis of TRYCAT levels in bipolar disorder (BD) patients compared to healthy controls.

Methods

A systematic literature search in seven electronic databases (PubMed, Embase, Web of Science, Cochrane, Emcare, PsycINFO, Academic Search Premier) was conducted on TRYCAT levels in cerebrospinal fluid or peripheral blood according to the PRISMA statement. A minimum of three studies per TRYCAT was required for inclusion. Standardized mean differences (SMD) were computed using random effect models. Subgroup analyses were performed for BD patients in a different mood state (depressed, manic). The methodological quality of the studies was rated using the modified Newcastle-Ottawa Quality assessment Scale.

Results

Twenty-one eligible studies were identified. Peripheral levels of tryptophan (SMD = -0.44; p < 0.001), kynurenine (SMD = - 0.3; p = 0.001) and kynurenic acid (SMD = -.45; p = < 0.001) were lower in BD patients versus healthy controls. In the only three eligible studies investigating TRP in cerebrospinal fluid, tryptophan was not significantly different between BD and healthy controls. The methodological quality of the studies was moderate. Subgroup analyses revealed no significant difference in TRP and KYN values between manic and depressed BD patients, but these results were based on a limited number of studies.

Conclusion

The TRYCAT pathway appears to be downregulated in BD patients. There is a need for more and high-quality studies of peripheral and central TRYCAT levels, preferably using longitudinal designs.

Plasma levels of interleukin-6 and antidepressant response to Paroxetine in Chinese depressive patients

This study aimed to investigate the correlation between interleukin-6 (IL-6) plasma levels and treatment outcomes of selective serotonin reuptake inhibitors in patients with major depressive disorder (MDD). A total of 104 patients (33 males and 71 females), aged 18 to 72 years, were enrolled. Peripheral blood samples were collected before treatment initiation (baseline) and eight weeks after oral paroxetine treatment. The Hamilton Depression Rating Scale (HAMD)-17 was used to evaluate the efficacy of paroxetine. Baseline plasma IL-6 levels were found to be significantly lower in patients who responded to treatment than in non-responders. A negative correlation was found between the HAMD-17 reduction rate and baseline IL-6 levels. Furthermore, associations were examined between HAMD-17 reduction rate in patients and other factors, such as IL-6 levels, sex, age, and body mass index. Baseline IL-6 was the only factor showing a significant impact on the reduction rate of HAMD-17 at week 8. These results suggest that plasma IL-6 level may be a promising biological marker for predicting the likely treatment response to paroxetine in individual patients with MDD.

Cannabidiol antidepressant-like effect in the lipopolysaccharide model in mice: Modulation of inflammatory pathways

Major Depression is a severe psychiatric condition with a still poorly understood etiology. In the last years, evidence supporting the neuroinflammatory hypothesis of depression has increased. In the current clinical scenario, in which the available treatments for depression is far from optimal, there is an urgent need to develop fast-acting drugs with fewer side effects. In this regard, recent pieces of evidence suggest that cannabidiol (CBD), the major non-psychotropic component of Cannabis sativa with anti-inflammatory properties, appears as a drug with antidepressant properties. In this work, CBD 30 mg/kg was administered systemically to mice 30 min before lipopolysaccharide (LPS; 0.83 mg/kg) administration as a neuroinflammatory model, and behavioral tests for depressive-, anhedonic- and anxious-like behavior were performed. NF-ĸB, IκBα and PPARγ levels were analyzed by western blot in nuclear and cytosolic fractions of cortical samples. IL-6 and TNFα levels were determined in plasma and prefrontal cortex using ELISA and qPCR techniques, respectively. The precursor tryptophan (TRP), and its metabolites kynurenine (KYN) and serotonin (5-HT) were measured in hippocampus and cortex by HPLC. The ratios KYN/TRP and KYN/5-HT were used to estimate indoleamine 2,3-dioxygenase (IDO) activity and the balance of both metabolic pathways, respectively. CBD reduced the immobility time in the tail suspension test and increased sucrose preference in the LPS model, without affecting locomotion and central activity in the open-field test. CBD diminished cortical NF-ĸB activation, IL-6 levels in plasma and brain, and the increased KYN/TRP and KYN/5-HT ratios in hippocampus and cortex in the LPS model. Our results demonstrate that CBD produced antidepressant-like effects in the LPS neuroinflammatory model, associated to a reduction in the kynurenine pathway activation, IL-6 levels and NF-ĸB activation. As CBD stands out as a promising antidepressant drug, more research is needed to completely understand its mechanisms of action in depression linked to inflammation.

Tryptophan Metabolism and Related Pathways in Psychoneuroimmunology: The Impact of Nutrition and Lifestyle

In the past, accelerated tryptophan breakdown was considered to be a feature of clinical conditions, such as infection, inflammation, and malignant disease. More recently, however, the focus has changed to include the additional modulation of tryptophan metabolism by changes in nutrition and microbiota composition. The regulation of tryptophan concentration is critical for the maintenance of systemic homeostasis because it integrates essential pathways involved in nutrient sensing, metabolic stress response, and immunity. In addition to tryptophan being important as a precursor for the synthesis of the neurotransmitter serotonin, several catabolites along the kynurenine axis are neuroactive. This emphasizes the importance of the immunometabolic fate of this amino acid for processes relevant to neuropsychiatric symptoms. In humans, besides hepatic catabolism, there is usually a strong relationship between immune activation-associated tryptophan breakdown and increased levels of biomarkers, such as neopterin, which has particular relevance for both acute and chronic diseases. A shift towards neopterin synthesis during oxidative stress may indicate a corresponding decrease in tetrahydrobiopterin, a cofactor of several mono-oxygenases, providing a further link between tryptophan metabolism and serotonergic and catecholaminergic neurotransmission. The psychoneuroimmunological consequences of tryptophan metabolism and the susceptibility of this pathway to modulation by a variety of nutritional and lifestyle-related factors have important implications for the development of both diagnostic and treatment options.

Immune Activation and Anemia Are Associated with Decreased Quality of Life in Patients with Solid Tumors

Anemia often coincides with depression and impaired quality of life (QoL) in cancer patients. Sustained immune activation can lead to the development of anemia. Furthermore, it also may go along with changes in tryptophan and phenylalanine metabolism. The aim of our pilot study was to study the relationship between anemia, immune-mediated changes in amino acid metabolism, and the QoL and mood of cancer patients. Questionnaires to measure QoL and depression were completed by 152 patients with solid tumors. Hemoglobin, parameters of immune activation as well as tryptophan and phenylalanine metabolism were determined in the patients’ sera. Anemic patients (51.7%) presented with higher inflammatory markers, and a higher tryptophan breakdown with lower tryptophan concentrations. They reported an impaired QoL and had higher depression scores. Patients with an impaired QoL (65.8%) also suffered from more fatigue and impaired physical, emotional, and social functioning. They, furthermore, presented with higher concentrations of inflammatory markers (C-reactive protein (CRP) and neopterin) as well as higher tryptophan degradation (in men) and higher phenylalanine concentrations (in women). Sixty-one patients (40.1%) had (mostly mild) depression. In these patients, a higher degree of Th1 immune activation was found. The results of our study suggest that cancer-related anemia goes along with an impaired QoL, which is also associated with immune-mediated disturbances of tryptophan and phenylalanine metabolism.

Kynurenine Pathway in Chronic Kidney Disease: What’s Old, What’s New, and What’s Next?

Impaired kidney function and increased inflammatory process occurring in the course of Chronic Kidney Disease (CKD) contribute to the development of complex amino-acid alterations. The essential amino-acid tryptophan (TRP) undergoes extensive metabolism along several pathways, resulting in the production of many biologically active compounds. The results of many studies have shown that its metabolism via the kynurenine pathway is potently increased in the course of CKD. Metabolites of this pathway exhibit differential, sometimes opposite, roles in several biological processes. Their accumulation in the course of CKD may induce oxidative cell damage which stimulates inflammatory processes. They can also modulate the activity of numerous cellular signaling pathways through activation of the aryl hydrocarbon receptor, leading to the disruption of homeostasis of various organs. As a result, they can contribute to the development of the systemic disorders accompanying the course of chronic renal failure. This review gathers and systematizes reports concerning the knowledge connecting the kynurenine pathway metabolites to systemic disorders accompanying the development of CKD.

Acute and Chronic Mental Stress Both Influence Levels of Neurotransmitter Precursor Amino Acids and Derived Biogenic Amines

Acute and chronic mental stress are both linked to somatic and psychiatric morbidity, however, the neurobiological pathways of these associations are still not fully elucidated. Mental stress is known to be immunomodulatory, which is one of the basic concepts of psychoneuroimmunology. In the present study, neurotransmitter precursor amino acid levels and derived biogenic amines were analyzed prior to and at 0, 30 and 60 min following an acute mental stress test (with/without chronic mental stress) in 53 healthy subjects. Psychometric measurements of mental stress, depression and anxiety were collected. Kynurenine/tryptophan was influenced by the factor acute mental stress (KYN/TRP increase), no influence of the factor chronic mental stress or any interaction was found. Phenylalanine/tyrosine was influenced by the factor acute mental stress (PHE/TYR increase) as well as by chronic mental stress (PHE/TYR decrease). Interactions were not significant. KYN/TRP correlated with state anxiety values, while PHE/TYR correlated negatively with chronic stress parameters. Kynurenic acid was significantly reduced in the acute and quinolinic acid in the chronic mental stress condition. In conclusion, neurotransmitter precursor amino acid levels and derived biogenic amines are influenced by acute and chronic mental stress. Mechanisms beyond direct immunological responses may be relevant for the modulation of neurotransmitter metabolism such as effects on enzyme function through cofactor availability or stress hormones.

Acetylation of Phenylalanine Hydroxylase and Tryptophan 2,3-Dioxygenase Alters Hepatic Aromatic Amino Acid Metabolism in Weaned Piglets

Weaning significantly alters hepatic aromatic amino acid (AAA) metabolism and physiological functions. However, less is known about the regulating mechanism of hepatic AAA metabolism after weaning. A total of 200 21-day-old piglets (Duroc × Landrace) were assigned randomly to the control group and the weaning group. In this study, weaning significantly decreased the concentration of phenylalanine, tryptophan, and tyrosine in piglet livers (p < 0.05). Additionally, through the detection of liver AAA metabolites and metabolic enzyme activity, it was observed that hepatic tryptophan catabolism was enhanced, while that of phenylalanine was weakened (p < 0.05). Intriguingly, acetyl-proteome profiling of liver from weaned piglets showed that weaning exacerbated the acetylation of phenylalanine hydroxylase (PAH) and the deacetylation of tryptophan 2,3-dioxygenase (TDO). Analysis of PAH and TDO acetylation in Chang liver cells showed that acetylation decreased the PAH activity, while deacetylation increased the TDO activity (p < 0.05). Furthermore, metabolites of AAAs and the acetylation statuses of PAH and TDO in primary hepatocytes from weaned piglets were consistent with the results in vivo. These findings indicated that weaning altered the PAH and TDO activity by affecting the acetylation state of the enzyme in piglets’’ livers. Lysine acetylation may be a potential regulatory mechanism for AAA metabolism in response to weaning.

Associations of cardiovascular disease and depression with memory related disease: A Chinese national prospective cohort study

BACKGROUND

Association of cardiovascular disease (CVD) or depression and memory has been studied. But hardly any studies on the association of coexistence of CVD and depression and memory.

METHODS

This is a prospective cohort study of a nationally representative sample of 12,272 adults aged 45 years and more who participated in the China health and retirement longitudinal study 2011 to 2015. All variables were acquired by self-reporting questions. The associations between coexistence of CVD and depression with memory related disease (MRD) were investigated by using Cox proportional hazards regression models.

RESULTS

Among the 12,272 participants (mean age 65.69 years; 46.8% male) in this study, 56.9% no CVD or depression and 6.7% coexistence of CVD and depression. After adjustment for age, sex, marriage, living place, registered permanent residence, education level, smoking status, alcoholic intake, sleep status, nap status, social communication, health before 15 years, life satisfaction, cognitive function, and 11 chronic diseases risk factors, depression alone was significantly high risk for MRD (HR:1.64; 95% CI: 1.09-2.49); coexistence of CVD and depression increased the risk for MRD significantly higher (HR: 4.72; 95%CI: 2.91-7.64).

LIMITATIONS

Diseases were all self-reported and we couldn't adjust for all the potential confounders, which might be prone to information error and residual confounding.

CONCLUSIONS

In a nationally representative cohort with median 4 years of follow-up, depression alone and co-existence of depression and CVD could significantly increase the risk of MRD. Our study supports the idea of prevention of memory disease from a psycho-cardiology aspect.

Effects of prebiotics on affect and cognition in human intervention studies

Studies conducted in rodents have highlighted that neurobiological processes underlying cognition and affect are modulated by the gut microbiota. Certain dietary fibers are able to modulate the composition of gut microbiota and are thus considered prebiotics. A review of the impact of the available prebiotic intervention studies in humans on cognition and affect, addressing the potential mediating role of the microbiota, was conducted. PubMed, Scopus, and PsycINFO were selected as sources. Fourteen articles were eligible for narrative synthesis. Data extraction and quality assessment were performed with characteristics established a priori. Some chronic prebiotic interventions (>28 d) improved affect and verbal episodic memory compared with a placebo. Acute prebiotic interventions (<24 h) were more efficient in improving cognitive variables (eg, verbal episodic memory). Future research should measure microbiota using adequate methodologies and recruit patients with dysbiosis, inflammation, or psychopathology. More research is needed to unravel the conditions required to obtain effects on affect and cognition.

Do We Build Similar Molecules for Comorbid Diseases? Tevarud in Drug Design, an Analysis for Depression and Inflammation

Tevarud designates two poets coincidently writing a same verse in the Ottoman Divan literature. This study aims to analyze the structural similarity of molecules independently designed for inflammation and depression to determine if coincidentally we are building similar molecules for comorbid diseases. For this purpose, a molecule library was first constituted with structures that were developed as anti-inflammatory (AI) and antidepressant (AD) agents these last decades. Then, the similarity of the structures was determined by calculating the Tanimoto and Cosine similarity coefficients for each AD/AI pair. The highest scores were obtained for two theophylline derivatives: AD17 (for which some AI activity was found to be mentioned) and AI42. The study also pointed out the similarity of some AD coumarins with some AI flavonoids interestingly found to be highly similar to some AI coumarins and AD flavonoids, respectively. Thus, our investigation demonstrated that structures independently developed as AD and AI derivatives can present extremely high structural similarity, a finding that can suggest mechanistic interconnection for these comorbid diseases and also guide for the design of novel bioactive compounds.

IDO activation, inflammation and musculoskeletal disease

The IDO/kynurenine pathway is now established as a major regulator of immune system function. The initial enzyme, indoleamine 2,3-dioxygenase (IDO1) is induced by IFNγ, while tryptophan-2,3-dioxygenase (TDO) is induced by corticosteroids. The pathway is therefore positioned to mediate the effects of systemic inflammation or stress-induced steroids on tissue function and its expression increases with age. Disorders of the musculoskeletal system are a common feature of ageing and many of these conditions are characterized by an inflammatory state. In inflammatory arthritis and related disorders, kynurenine protects against the development of disease, while inhibition or deletion of IDO1 increases its severity. The long-term regulation of autoimmune disorders may be influenced by the epigenetic modulation of kynurenine pathway genes, with recent data suggesting that methylation of IDO may be involved. Osteoporosis is also associated with abnormalities of the kynurenine pathway, reflected in an inversion of the ratio between blood levels of the metabolites anthranilic acid and 3-hydroxy-anthranilic acid. This review discusses evidence to date on the role of the IDO/kynurenine pathway and the highly prevalent age-related disorders of osteoporosis and rheumatoid arthritis and identifies key areas that require further research.

Neopterin levels and Kyn/Trp ratios were significantly increased in dengue virus patients and subsequently decreased after recovery

OBJECTIVES

During dengue fever, a pronounced gamma-interferon immune response produces neopterin and promotes tryptophan degradation by the enzyme indoleamine-2,3-dioxygenase 1 (IDO-1). Activated IDO-1 is indicated by an increased kynurenine to tryptophan ratio (Kyn/Trp) in patients.

METHODS

Plasma levels of neopterin, kynurenine, and tryptophan were measured in 72 hospitalized dengue virus (DENV) patients and 100 healthy individuals. Plasma levels of neopterin, kynurenine, and tryptophan were also measured prospectively in a second cohort of 13 DENV patients; on the day of hospitalization, on day 2-3 at discharge, and 7-10 days after discharge. DENV RNA positivity was determined by qualitative and quantitative methodologies.

RESULTS

DENV RNA-positive patients presented significantly higher levels of neopterin (mean 36.5nmol/l) and Kyn/Trp ratios (mean 102μmol/mmol) compared to DENV RNA-negative individuals. A significant correlation between neopterin levels and Kyn/Trp ratios was observed in both DENV RNA-positive (Spearman's rho=0.37, p< 0.01) and DENV RNA-negative (Spearman's rho=0.89, p<0.001) patients. Kyn/Trp ratios were negatively correlated with platelet counts (Spearman's rho=-0.43, p<0.01) and positively correlated with liver enzymes: AST (Spearman's rho=0.68, p<0.01) and ALT (Spearman's rho=0.51, p<0.05). In addition, the follow-up data presented a significant decrease in neopterin levels and Kyn/Trp ratios within 10 days after hospital entry.

CONCLUSIONS

Neopterin levels and Kyn/Trp ratios were significantly increased in DENV patients and subsequently decreased after recovery.

Grey and white matter structure associates with the activation of the tryptophan to kynurenine pathway in bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a severe mental illness characterised by reduced grey matter (GM) volumes and cortical thickness, and disrupted white matter (WM) microstructure. Activation of indoleamine 2,3-dioxygenase following a pro-inflammatory state could increase the amount of tryptophan (Trp) converted to kynurenine (Kyn) possibly leading to the production of detrimental catabolites of the Kyn pathway with neurotoxic effects. We investigated if peripheral levels of Trp-and Kyn and the breakdown of Trp-into Kyn (Kyn/Trp-ratio) are related to WM and GM integrity in BD.

METHODS

Peripheral levels of Trp-and Kyn were analysed in 72 patients with BD and 33 controls. Patients also underwent MRI in a Philips 3T scanner.

RESULTS

Patients showed higher Kyn levels and Kyn/Trp-ratio compared to controls. MRI analyses performed in patients with BD showed a negative association between the Kyn/Trp-ratio and the integrity of corpus callosum microstructure, the volume of the amygdala and cortical thickness in fronto-parietal regions.

LIMITATION

The lack of information on the levels of downstream metabolites of Kyn prevent us to confirm the possible unbalance between quinolinic and kynurenic acids as well as their possible relationship with changes in GM and WM markers. The activation of the Kyn pathway as suggested by the increased Kyn/Trp-ratio may lead to an imbalance of the neurotoxic vs the neuroprotective arm of the biochemical pathway, resulting in significant changes in GM and WM regions of brain areas strongly implicated in the pathophysiology of BD, such as amygdala and corpus callosum.

Kema I, Vogels S, M. Geleijnse J, Westerhuis R, J. R. Ipema K, J. L. Bakker S, F. M. Franssen C. Tryptophan Intake and Tryptophan Losses in Hemodialysis Patients: A Balance Study

Tryptophan depletion is common in hemodialysis patients. The cause of this depletion remains largely unknown, but reduced nutritional tryptophan intake, losses during dialysis or an increased catabolism due to an inflammatory state are likely contributors. Currently, little is known about tryptophan homeostasis in hemodialysis patients. We assessed dietary tryptophan intake, measured plasma tryptophan during dialysis, and measured the combined urinary and dialysate excretion of tryptophan in 40 hemodialysis patients (66 ± 15 years and 68% male). Patients had low tryptophan concentrations (27 ± 9 µmol/L) before dialysis. Mean dietary tryptophan intake was 4454 ± 1149 µmol/24 h. Mean urinary tryptophan excretion was 15.0 ± 12.3 μmol/24 h, dialysate excretion was 209 ± 67 μmol/24 h and combined excretion was 219 ± 66 µmol/24 h, indicating only 5% of dietary tryptophan intake was excreted. No associations were found between plasma tryptophan concentration and tryptophan intake, plasma kynurenine/tryptophan ratio or inflammatory markers. During dialysis, mean plasma tryptophan concentration increased 16% to 31 ± 8 µmol/L. Intradialytic increase in plasma tryptophan was associated with a lower risk of mortality, independent of age, sex and dialysis vintage (HR: 0.87 [0.76–0.99]; P = 0.04). Tryptophan intake was well above the dietary recommendations and, although tryptophan was removed during dialysis, mean plasma tryptophan increased during dialysis. The cause of this phenomenon is unknown, but it appears to be protective.

An exploratory study of neopterin and kynurenine pathway in pterygium

Pterygium is an inflammatory, vascular and degenerative disorder with unknown aetiology. The aim of this study was to evaluate the changes in neopterin levels, reflecting T-cell immunity, and the kynurenine pathway, the main degradation process of tryptophan, in pterygium. For this purpose, neopterin concentrations were measured in serum and tear samples by enzyme-linked immunosorbent assay (ELISA) in pterygium patients (n=31) and control group (n=32). Kynurenine (KYN) and tryptophan (TRP) serum levels were simultaneously determined by high-performance liquid chromatography (HPLC) for evaluation of the kynurenine pathway. Serum neopterin concentrations and kynurenine to tryptophan ratio (KYN/TRP) as an index of tryptophan breakdown were found increased in pterygium compared to controls (p<0.05). Although there was a 3-fold difference observed between serum and tear neopterin levels, no significant relationship was found. It can be concluded that neopterin may be used as a nonspecific biomarker that reflects immunological activity in pterygium and has clinical potential for evaluation of pterygium pathogenesis. These immune- or inflammatory-mediated changes were also supported by an increased KYN/TRP ratio in pterygium patients.

How acute and chronic physical disease may influence mental health - An Analysis of neurotransmitter precursor amino acid levels

Patients with somatic diseases are more likely to develop depression than physically healthy individuals, and comorbid depression has been shown to incrementally worsen patients´ health. Physical conditions are known to influence neurotransmitter precursor amino acids, changes in which are associated with depressive symptoms. In this prospective study we investigated neurotransmitter precursor amino acids levels in patients with acute and chronic physical disease and evaluated their association with depressive symptoms. 177 subjects with and without chronic medical comorbidity (factor: chronic physical disease) admitted to the trauma and orthopaedic surgery ward for a surgical intervention (factor: acute physical disease) were included in the analysis. Chronic medical comorbidity was scored using Charlson Index and depressive and anxiety symptoms using the Hospital Anxiety and Depression Scale (HADS, factor: mental health). The effect of covariates was also evaluated. C-reactive protein (CRP), neopterin, kynurenine/tryptophan (KYN/TRP) and phenylalanine/tyrosine (PHE/TYR) were analysed by HPLC or ELISA prior to surgery and at discharge. Mixed Model as well as correlation analyses were performed. CRP and neopterin levels were influenced by the factors "acute physical disease" (both p < 0.001) and "chronic physical disease" (p = 0.024, p = 0.001 respectively). PHE/TYR, an index of the catecholamine pathway) was related to the factors "acute physical disease" (p < 0.001) and "mental health-depression" (p = 0.012), while KYN/TRP (an index of the kynurenine pathway affecting also serotonin) was associated with "chronic physical disease" (p = 0.005). No significant effect of "mental health-anxiety" was found. The effect of "mental health-depression" on PHE/TYR was more pronounced in females (gender p = 0.003). Differences in HADS depression values correlated with changes in PHE/TYR and both correlated with CRP values. In conclusion, inflammatory reactions related to acute or chronic physical conditions can influence the availability of neurotransmitter precursor amino acids l and these changes are associated with mental health.

Treatment of patients with geriatric depression with repetitive transcranial magnetic stimulation

Repetitive transcranial magnetic stimulation (rTMS) has become a useful tool to treat different neuropsychiatric conditions such as depression, dementia and extrapyramidal syndromes insufficiently responding to conventional treatment. In this SHAM-controlled exploratory study safety, symptom improvement as well as changes in inflammation markers and neurotransmitter precursor amino acids availability were studied after a prefrontal cortex (PFC) stimulation using rTMS as add-on treatment in 29 patients with geriatric depression. Out of these, ten patients received SHAM treatment. Treatment was well tolerated, no serious adverse effects were observed. A clear improvement in symptoms of depression with a significant decrease in the HAMD-7 (U = 3.306, p = 0.001) was found by rTMS treatment. In parallel, serum phenylalanine dropped significantly (U = 2.340, p < 0.02), and there was a decline of tryptophan and of Phe/Tyr concentrations, both the effects, however, failed to reach the levels of statistical significance. In the patients who underwent SHAM treatment, no significant changes of HAMD-7 or the concentrations of any biomarker in the study could be found. In addition to the significant effect of rTMS on depression scores, these results point to a possible influence of rTMS on the enzyme phenylalanine hydroxylase (PAH), which plays a crucial role in the biosynthesis of neurotransmitter precursors related to geriatric depression.

The Role of Tryptophan-Kynurenine in Feather Pecking in Domestic Chicken Lines

Research into the role of tryptophan (TRP) breakdown away from the serotonergic to the kynurenine (KYN) pathway by stimulating the brain-endocrine-immune axis system interaction has brought new insight into potential etiologies of certain human behavioral and mental disorders. TRP is involved in inappropriate social interactions, such as feather-destructive pecking behavior (FP) in birds selected for egg laying. Therefore, our goal was to determine the effect of social disruption stress on FP and the metabolism of the amino acids TRP, phenylalanine (PHE), tyrosine (TYR), their relevant ratios, and on large neutral amino acids which are competitors with regard to their transport across the blood-brain barriers, at least in the human system, in adolescent birds selected for and against FP behavior. We used 160 laying hens selected for high (HFP) or low (LFP) FP activity and an unselected control line (UC). Ten pens with 16 individuals each (4 HFP birds; 3 LFP birds; 9 UC birds) were used. At 16 weeks of age, we disrupted the groups twice in 5 pens by mixing individuals with unfamiliar birds to induce social stress. Blood plasma was collected before and after social disruption treatments, to measure amino acid concentrations. Birds FP behavior was recorded before and after social disruption treatments. HFP birds performed significantly more FP and had lower KYN/TRP ratios. We detected significantly higher FP activity and significantly lower plasma PHE/TYR ratios and a trend to lower KYN/TRP ratios in socially disrupted compared to control pens. This might indicate that activating insults for TRP catabolism along the KYN axis in laying hens differs compared to humans and points toward the need for a more detailed analysis of regulatory mechanisms to understand the role of TRP metabolism for laying hen immune system and brain function.

Yield and kernel nutritional quality in normal maize and quality protein maize cultivars exposed to ozone

BACKGROUND

Tropospheric ozone (O₃ ) is phytotoxic and therefore impacts global food security. In the present study yield responses and kernel quality traits of two maize cultivars [DHM117: normal maize (NM)] and [HQPM1: quality protein maize (QPM)] are investigated. Cultivars were exposed to two doses of elevated O₃ , namely NFC + 15 and NFC + 30 ppb O₃ above ambient level (NFC, non-filtered chambers) while filtered chambers served as control.

RESULTS

Test weight (thousand kernel weight), weight of kernels per square meter and kernel starch content reduced more in NM than QPM due to elevated O₃ exposure. Total soluble and reducing sugars increased in both the cultivars being more in NM. Though, endosperm protein showed comparatively more increase in QPM than NM, decline in essential amino acids tryptophan and lysine was higher in QPM. Majority of nutrient elements increased after O₃ treatment, while reductions in oil content as well as saturated fatty acids were observed in both test cultivars. Of the two essential fatty acids, omega 3 fatty acid reduced while omega 6 fatty acid contents increased in QPM. Oil became more unsaturated (increase in polyunsaturated fatty acids) upon O₃ exposure, thus increasing its reactivity and hence became more prone to auto-oxidation.

CONCLUSIONS

Elevated O₃ caused losses in yield of maize cultivars and NM showed higher sensitivity than QPM. Kernel quality analysis revealed significant changes in nutritional parameters. Carbohydrate content reduced more in NM, while essential amino acids and saturated fatty acids showed more decline in QPM. © 2018 Society of Chemical Industry.

Antidepressant effects of direct-acting antivirals against hepatitis C virus-Results from a pilot study

BACKGROUND AND AIMS

The new direct-acting antiviral agents (DAA) have revolutionized the treatment of patients with chronic hepatitis C virus (HCV) infection. This study investigates to which extent DAA affect fatigue and mood and, if so, whether this results from changes to tryptophan (TRP) metabolism, as reflected by two critical biosynthetic pathways, serotonin (SRT) generation from TRP and TRP degradation through kynurenines (KYN) via indoleamine 2,3-dioxygenase (IDO).

METHODS

This study assessed 24 patients with chronic HCV infection, before (T1), during (T2: at 4 weeks) and 12 weeks post-treatment with DAA (T3) with respect to viral load, fatigue and depressive symptoms (BDI-II questionnaire), physical activity (actigraph) and plasma serotonin-tryptophan metabolites (LC/MS). The KYN:TRP ratio reflected IDO activity.

RESULTS

All participants achieved sustained virological response (SVR12) with DAA treatment (79% sofosbuvir-based). Fatigue (scores at T1:0.83 ± 0.70, T2:0.48 ± 0.70, T3:0.30 ± 0.50; P = 0.023) and depressive symptoms (scores at T1:9.8 ± 10.2, T2:6.0 ± 7.3, T3:5.0 ± 7.6; P = 0.005) improved significantly on therapy, whereas no changes were noted in five untreated controls. TRP plasma concentrations markedly decreased (T1:306 ± 179 mg/L, T2:283 ± 84 mg/L), whereas 5-HTP levels increased (T1:0.08 ± 0.01 mg/L, T2:0.10 ± 0.06 mg/L). KYN concentrations (T1:2.4 ± 2.0 mg/L, T2:3.7 ± 1.4 mg/L, P = 0.003) increased significantly during treatment, as did IDO activity (T1:0.008 ± 0.006 mg/L, T2:0.014 ± 0.004 mg/L; P < 0.001).

CONCLUSIONS

In this study, DAA exert positive and persistent effects on both fatigue and mood in patients with chronic HCV infection. These extrahepatic benefits are, at least in part, related to the modulation of TRP metabolism. The robust elevation of KYN concentrations challenges the current paradigm of low KYN levels as prerequisite for mental health.

Changes in the tryptophan-kynurenine axis in association to therapeutic response in clinically depressed patients undergoing psychiatric rehabilitation

INTRODUCTION

In recent decades a number of studies have shown an association between the Tryptophan (Trp)-Kynurenine (Kyn) axis and neuropsychiatric disorders. However, the role of the Trp-Kyn pathway on the affective status in a general psychiatric cohort requires clarification. This study aimed to measure peripheral changes in Trp, Kyn and the Kyn/Trp-ratio as well as in the inflammatory markers high sensitive C-reactive protein (hsCRP) and interleukine-6 (IL-6) in individuals undergoing a six-week course of intensive treatment program comparing subgroups of treatment responders and non-responders.

METHODS

In this investigation 87 currently depressed individuals with a life-time history of depressive disorders were divided into treatment responders (n = 48) and non-responders (n = 39). The individuals were selected for an extreme group comparison out of 598 patients undergoing a 6-week psychiatric rehabilitation program in Austria. Responders were defined according to great changes in Becks Depression Inventory (BDI-II) between time of admission and discharge (BDI-II > 29 to BDI-II <14), while non-responders had no or minimal changes (BDI >20, max. 4 points change over time). Differences in the levels of Trp, Kyn, and the Kyn/Trp ratio as well as levels of hsCRP and IL-6, were compared between groups. Differences were analyzed at the time of admission as well as at discharge.

RESULTS

A significant group x time interaction was found for Kyn [F(1.82) = 5.79; p = 0.018] and the Kyn/Trp ratio [F(1.85) = 4.01, p = 0.048]. Importantly, Kyn increased significantly in the non-responder group, while the Kyn/Trp ratio decreased significantly in the responder group over time. Furthermore, changes in Kyn as well as hsCRP levels correlated significantly with changes in the body mass index over time (Kyn: r=0.24, p = 0.030; hsCRP: r=0.25, p = 0.021). No significant interactions were found for Trp and hsCRP, although they increased significantly over time.

DISCUSSION

Given the limitations of the study, we could show that the therapeutic response to a multimodal treatment in clinically depressed patients not receiving cytokine treatment is associated with changes in Kyn levels and the Kyn/Trp ratio as well as with hsCRP. However, it is too early to draw any causal conclusion. Future research should clarify relevant clinical and neurobiological parameters associated with changes in Kyn levels and Kyn/Trp ratio, especially in regard to clinical response.

An Expanded Neuroimmunomodulation Axis: sCD83-Indoleamine 2,3-Dioxygenase-Kynurenine Pathway and Updates of Kynurenine Pathway in Neurologic Diseases

Many neurologic diseases are related to autoimmune dysfunction and a variety of molecules or reaction pathways are involved in the regulation of immune function of the nervous system. Soluble CD83 (sCD83) is the soluble form of CD83, a specific marker of mature dendritic cell, which has recently been shown to have an immunomodulatory effect. Indoleamine 2,3-dioxygenase (IDO; corresponding enzyme intrahepatic, tryptophan 2,3-dioxygenase, TDO), a rate-limiting enzyme of extrahepatic tryptophan kynurenine pathway (KP) participates in the immunoregulation through a variety of mechanisms solely or with the synergy of sCD83, and the imbalances of metabolites of KP were associated with immune dysfunction. With the complement of sCD83 to IDO-KP, a previously known immunomodulatory axis, this review focused on an expanded neuroimmunomodulation axis: sCD83-IDO-KP and its involvement in nervous system diseases.

Total sleep time and kynurenine metabolism associated with mood symptom severity in bipolar disorder

OBJECTIVE

Chronic, low-level inflammation is associated with symptomatic bipolar disorder (BD) and with chronic insomnia. Disrupted sleep is a feature of episodes of both mania and depression. We examined the effect of neopterin, a marker of cellular immune activation, and kynurenine (KYN), an inflammatory byproduct of the serotonin pathway, on the association between total sleep time and depression severity in BD.

METHOD

Twenty-one symptomatic BD participants and 28 healthy controls (HC) were recruited and followed during usual clinical care. At baseline and after symptomatic recovery, total sleep time was objectively measured with actigraphy for 1 week and blood plasma was collected to measure the serotonin precursor tryptophan (TRP), KYN, the KYN/TRP ratio, and neopterin levels. Statistical analyses were conducted using chi-square, independent t tests and hierarchical linear multiple regression models.

RESULTS

Total sleep time was correlated positively with depressive severity and negatively with manic severity. TRP was significantly reduced in BD participants compared to HC. KYN, TRP, and the KYN/TRP ratio were associated with depressive severity when total sleep time and body mass index (BMI) were included in the model. The KYN/TRP ratio trended towards a negative association with mania symptoms, controlling for BMI and total sleep time, in acutely symptomatic BD participants. Neopterin was not associated with sleep or mood severity. After usual clinical care, BD participants showed significantly decreased clinical symptoms but no significant differences in sleep phenotype or biomarkers.

CONCLUSION

Inflammation, sleep, and mood are closely intertwined. Future research into the effect of inflammation on sleep in BD may lead to clinical markers of outcome.

IDO chronic immune activation and tryptophan metabolic pathway: A potential pathophysiological link between depression and obesity

Obesity and depression are among the most pressing health problems in the contemporary world. Obesity and depression share a bidirectional relationship, whereby each condition increases the risk of the other. By inference, shared pathways may underpin the comorbidity between obesity and depression. Activation of cell-mediated immunity (CMI) is a key factor in the pathophysiology of depression. CMI cytokines, including IFN-γ, TNFα and IL-1β, induce the catabolism of tryptophan (TRY) by stimulating indoleamine 2,3-dioxygenase (IDO) resulting in the synthesis of kynurenine (KYN) and other tryptophan catabolites (TRYCATs). In the CNS, TRYCATs have been related to oxidative damage, inflammation, mitochondrial dysfunction, cytotoxicity, excitotoxicity, neurotoxicity and lowered neuroplasticity. The pathophysiology of obesity is also associated with a state of aberrant inflammation that activates aryl hydrocarbon receptor (AHR), a pathway involved in the detection of intracellular or environmental changes as well as with increases in the production of TRYCATs, being KYN an agonists of AHR. Both AHR and TRYCATS are involved in obesity and related metabolic disorders. These changes in the TRYCAT pathway may contribute to the onset of neuropsychiatric symptoms in obesity. This paper reviews the role of immune activation, IDO stimulation and increased TRYCAT production in the pathophysiology of depression and obesity. Here we suggest that increased synthesis of detrimental TRYCATs is implicated in comorbid obesity and depression and is a new drug target to treat both diseases.