Quinolinic Acid Responses during Interferon-α-Induced Depressive Symptomatology in Patients with Chronic Hepatitis C Infection - A Novel Aspect for Depression and Inflammatory Hypothesis

Therapeutic modulation of the kynurenine pathway in severe mental illness and comorbidities: A potential role for serotonergic psychedelics

Mounting evidence points towards a crucial role of the kynurenine pathway (KP) in the altered gut-brain axis (GBA) balance in severe mental illness (SMI, namely depression, bipolar disorder, and schizophrenia) and cardiometabolic comorbidities. Preliminary evidence shows that serotonergic psychedelics and their analogues may hold therapeutic potential in addressing the altered KP in the dysregulated GBA in SMI and comorbidities. In fact, aside from their effects on mood, psychedelics elicit therapeutic improvement in preclinical models of obesity, metabolic syndrome, and vascular inflammation, which are highly comorbid with SMI. Here, we review the literature on the therapeutic modulation of the KP in the dysregulated GBA in SMI and comorbidities, and the potential application of psychedelics to address the altered KP in the brain and systemic dysfunction underlying SMI and comorbidities. Psychedelics might therapeutically modulate the KP in the altered GBA in SMI and comorbidities either directly, via altering the metabolic pathway by influencing the rate-limiting enzymes of the KP and affecting the levels of available tryptophan, or indirectly, by affecting the gut microbiome, gut metabolome, metabolism, and the immune system. Despite promising preliminary evidence, the mechanisms and outcomes of the KP modulation with psychedelics in SMI and systemic comorbidities remain largely unknown and require further investigation. Several concerns are discussed surrounding the potential side effects of this approach in specific cohorts of individuals with SMI and systemic comorbidities.

Investigation of the Effect of Tai Chi Training on Depressive Symptoms in Perimenopausal Women on the Basis of Serum Kynurenine Metabolites

OBJECTIVE

To observe the effects of Tai Chi training on depression symptoms and serum kynurenine metabolites in perimenopausal women and explore the mechanism of Tai Chi training in anti-depression.

METHODS

A total of 72 perimenopausal women with depression were randomly selected from Lishi District and divided into a Tai Chi training group (36 cases) and a control group (36 cases). At the same time, 36 perimenopausal healthy women were randomly selected as the normal group. The Tai Chi training group was intervened with 24 simplified Tai Chi exercises, and the depression self-rating scale was used to evaluate the depression status. The levels of tryptophan (Trp) and kynurenine (KYN) metabolites in serum were determined by high-performance liquid chromatography-ultraviolet detection.

RESULTS

Before the experiment, compared with the normal healthy group, the depression self-rating scale scores, serum KYN and quinolinic acid (QUIN) levels, and KYN/Trp ratio of the control group and Tai Chi group were significantly increased (p < .01), and the serum kynurenic acid (KYNA) level was significantly decreased (p < .01). After the experiment, compared with the normal healthy group, the depression self-rating scale scores of the Tai Chi group were significantly decreased (p < .01), the serum KYNA content was increased (p < .01), the serum KYN and QUIN contents were significantly decreased (p < .01), and the KYN/Trp ratio was significantly decreased (p < .01).

CONCLUSION

Tai Chi training can significantly improve depression symptoms in perimenopausal women. The mechanism of Tai Chi training in improving depression symptoms in perimenopausal women may be achieved by regulating abnormal kynurenine metabolism.

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.

Optimizing human performance in extreme environments through precision medicine: From spaceflight to high-performance operations on Earth

Humans operating in extreme environments often conduct their operations at the edges of the limits of human performance. Sometimes, they are required to push these limits to previously unattained levels. As a result, their margins for error in execution are much smaller than that found in the general public. These same small margins for error that impact execution may also impact risk, safety, health, and even survival. Thus, humans operating in extreme environments have a need for greater refinement in their preparation, training, fitness, and medical care. Precision medicine (PM) is uniquely suited to address the needs of those engaged in these extreme operations because of its depth of molecular analysis, derived precision countermeasures, and ability to match each individual (and his or her specific molecular phenotype) with any given operating context (environment). Herein, we present an overview of a systems approach to PM in extreme environments, which affords clinicians one method to contextualize the inputs, processes, and outputs that can form the basis of a formal practice. For the sake of brevity, this overview is focused on molecular dynamics, while providing only a brief introduction to the also important physiologic and behavioral phenotypes in PM. Moreover, rather than a full review, it highlights important concepts, while using only selected citations to illustrate those concepts. It further explores, by demonstration, the basic principles of using functionally characterized molecular networks to guide the practical application of PM in extreme environments. At its core, PM in extreme environments is about attention to incremental gains and losses in molecular network efficiency that can scale to produce notable changes in health and performance. The aim of this overview is to provide a conceptual overview of one approach to PM in extreme environments, coupled with a selected suite of practical considerations for molecular profiling and countermeasures.

The comorbidity of depression and neurocognitive disorder in persons with HIV infection: call for investigation and treatment

Depression and neurocognitive disorder continue to be the major neuropsychiatric disorders affecting persons with HIV (PWH). The prevalence of major depressive disorder is two to fourfold higher among PWH than the general population (∼6.7%). Prevalence estimates of neurocognitive disorder among PWH range from 25 to over 47% - depending upon the definition used (which is currently evolving), the size of the test battery employed, and the demographic and HIV disease characteristics of the participants included, such as age range and sex distribution. Both major depressive disorder and neurocognitive disorder also result in substantial morbidity and premature mortality. However, though anticipated to be relatively common, the comorbidity of these two disorders in PWH has not been formally studied. This is partly due to the clinical overlap of the neurocognitive symptoms of these two disorders. Both also share neurobehavioral aspects - particularly apathy - as well as an increased risk for non-adherence to antiretroviral therapy. Shared pathophysiological mechanisms potentially explain these intersecting phenotypes, including neuroinflammatory, vascular, and microbiomic, as well as neuroendocrine/neurotransmitter dynamic mechanisms. Treatment of either disorder affects the other with respect to symptom reduction as well as medication toxicity. We present a unified model for the comorbidity based upon deficits in dopaminergic transmission that occur in both major depressive disorder and HIV-associated neurocognitive disorder. Specific treatments for the comorbidity that decrease neuroinflammation and/or restore associated deficits in dopaminergic transmission may be indicated and merit study.

Interferon therapy and its association with depressive disorders - A review

Interferons (IFNs) are important in controlling the innate immune response to viral infections. Besides that, studies have found that IFNs also have antimicrobial, antiproliferative/antitumor and immunomodulatory effects. IFNs are divided into Type I, II and III. Type I IFNs, in particular IFN-α, is an approved treatment for hepatitis C. However, patients developed neuropsychological disorders during treatment. IFN-α induces proinflammatory cytokines, indoleamine 2,3-dioxygenase (IDO), oxidative and nitrative stress that intensifies the body's inflammatory response in the treatment of chronic inflammatory disease. The severity of the immune response is related to behavioral changes in both animal models and humans. Reactive oxygen species (ROS) is important for synaptic plasticity and long-term potentiation (LTP) in the hippocampus. However, excess ROS will generate highly reactive free radicals which may lead to neuronal damage and neurodegeneration. The limbic system regulates memory and emotional response, damage of neurons in this region is correlated with mood disorders. Due to the drawbacks of the treatment, often patients will not complete the treatment sessions, and this affects their recovery process. However, with proper management, this could be avoided. This review briefly describes the different types of IFNs and its pharmacological and clinical usages and a focus on IFN-α and its implications on depression.

Myeloperoxidase as a Potential Biomarker of Acute-Myocardial-Infarction-Induced Depression and Suppression of the Innate Immune System

While myeloperoxidase (MPO) serves as an indicator of both neutrophil and innate-immune-system function, the potential suppression of the innate immune system in patients with acute myocardial infarction (AMI)-induced depression might be evidenced by a decrease in MPO serum levels. The aim of this prospective study was to (1) determine whether serum concentrations of MPO vary immediately and 6 months after AMI and (2) to investigate whether MPO concentrations at the time of the AMI are significant predictors of AMI-induced depression and the depression-associated suppression of the innate immune system. A total of 109 AMI patients were assessed with the Hamilton Depression Scale (HAMD-17) immediately after admission to the hospital and 6 months later. The MPO status was assessed with serum samples, which were also collected immediately and 6 months after AMI. The depressive patients showed significantly lower MPO blood levels immediately and 6 months after the AMI compared to the patients without depression (ANCOVA: MPO (depression) F = 4.764, df = 1, p = 0.031). The baseline MPO was observed as a significant predictor (p = 0.027) of AMI-induced depression 6 months after AMI. MPO is a potential biomarker for AMI-induced depression, indicating a depression-associated suppression of the innate immune system.

The role and mechanism of tryptophan - kynurenine metabolic pathway in depression

Major depressive disorder (MDD) is a common mental illness characterized by persistent low mood and anhedonia, normally accompanied with cognitive impairment. Due to its rising incidence and high rate of recurrence and disability, MDD poses a substantial threat to patients' physical and mental health, as well as a significant economic cost to society. However, the etiology and pathogenesis of MDD are still unclear. Chronic inflammation may cause indoleamine-2,3-dioxygenase (IDO) to become overactive throughout the body and brain, resulting in excess quinolinic acid (QUIN) and less kynuric acid (KYNA) in the brain. QUIN's neurotoxicity damages glial cells and neurons, accelerates neuronal apoptosis, hinders neuroplasticity, and causes depression due to inflammation. Therefore, abnormal TRP-KYN metabolic pathway and its metabolites have been closely related to MDD, suggesting changes in the TRP-KYN metabolic pathway might contribute to MDD. In addition, targeting TRP-KYN with traditional Chinese medicine showed promising treatment effects for MDD. This review summarizes the recent studies on the TRP-KYN metabolic pathway and its metabolites in depression, which would provide a theoretical basis for exploring the etiology and pathogenesis of depression.

Extraction and fractionation of the seaweed Sargassum plagyophylum and evauation of fractions on depression induced by interferon alpha in mice

Background:

Marine organisms such as seaweeds, produce potent chemicals with characteristic biological features. Sargassum species have great potential to be used for neuronal protection as part of nutraceuticals. The aim was to investigate the effects of hexane and methanol extracts of Sargassum plagyophylum from the Persian Gulf on depression induced by interferon-α (IFNa) in mice.

Materials and Methods:

S. plagyophylum was extracted by maceration with methanol-ethyl acetate solvent (1:1). The extract was evaporated and partitioned by hexane and methanol solvents. Male mice were used, depression was induced by SC injecting IFNα (16 × 10 ^5IU/kg) for 6 days. Animals were subject to the forced swimming test (FST) after the locomotor test, on day 7. The extracts were administered IP either one single dose (acute) before the test, or simultaneously with IFNα (sub-acute).

Results:

The locomotor activity was not different from control values. IFNa increased the immobility time during FST (140 ± 14 s vs. control group 95 ± 9 s, P < 0.05). Hexane extract acute (40 mg/kg) injection was not effective while its sub-acute (20 mg/kg) injection reduced immobility time (46 ± 8 s, P < 0.001 vs. IFNa alone). Methanol extract acute (20 mg/kg) and sub-acute (20 mg/kg) administration significantly reduced immobility during the FST (78 ± 20 s, and 72 ± 8 s respectively, P < 0.05 vs. IFNa alone).

Conclusion:

S. plagyophylum has antidepressant effects, the hexane extract could prevent depression while the methanol extract not only prevented but also treated depression induced by IFNa in mice. Since this species is abundant in the Persian Gulf further clinical studies on its psychological effects are warranted.

The role of the kynurenine pathway and quinolinic acid in adolescent major depressive disorder

BACKGROUND

The biological mechanisms underlying major depressive disorder (MDD) are not yet sufficiently understood. The kynurenine pathway has been proposed to play a key role between peripheral inflammation and alterations in the central nervous system. This is because of reduced usability of tryptophan (TRP) and production of oxygen radicals and highly potent neurotoxic agents in this pathway.

OBJECTIVE

In this study, we aimed to compare the metabolites of the serum kynurenine pathway (tryptophan, kynurenine, quinolinic acid and kynurenic acid) and IFN-γ, IL-6, IL-1β and high-sensitivity C-reactive protein (hsCRP) levels in patients with major depressive disorder and in healthy controls and to evaluate the relationship between cytokine levels and the functioning of the kynurenine pathway.

METHODS

Clinical and biochemical data from the patients were obtained and assessed in a cross-sectional design. Serum samples were analysed for IL-6, IL-1β, interferon (IFN)-γ, tryptophan (TRP), quinolinic acid (QUIN), kynurenic acid (KYNA) and kynurenine (Kyn) levels by the enzyme-linked immunosorbent assay. hsCRP test was analysed by the immunoturbidimetric method.

RESULTS

In total, 48 adolescent patients with major depressive disorder (no drug use) and 31 healthy controls were included in the study. TRP levels were observed to be significantly lower in patients with MDD than in healthy controls (P = .046); the Kyn/TRP ratio was significantly higher in patients with MDD than in healthy controls (P = .032); the levels of QUIN were significantly higher in patients with MDD than in healthy controls (P = .003). No significant difference was found between the groups in terms of other kynurenine metabolites and cytokines levels.

CONCLUSION

These results suggest that the Kyn and related molecular pathways may play a role in the pathophysiology of MDD. The most important finding was the increased level of QUIN, which has a neurotoxic effect, in the kynurenine pathway.

Kynurenine Pathway of Tryptophan Metabolism in Neuropsychiatric Disorders: Pathophysiologic and Therapeutic Considerations

Under physiological conditions 95% of the ingested essential amino acid tryptophan is metabolized by the kynurenine pathway (KP) to yield the ubiquitous co-enzyme nicotinamide adenine dinucleotide, fulfilling cellular energy require-ments. Importantly, the intermediaries of KP exert crucial effects throughout the body, including the central nervous system. Besides, KP metabolites are implicated in diverse disease processes such as inflammation/immune disorders, endocrine/metabolic conditions, cancers and neuropsychiatric diseases. A burgeoning body of research indicates that the KP plays a pathogenic role in major psychiatric diseases like mood disorders and schizophrenia. Triggered by inflammatory processes, the balance between neurotoxic and neuroprotective branches of the KP is disturbed. In preclinical models these discrepancies result in behaviors reminiscent of depression and psychosis. In clinical samples, recent studies are discovering key kynurenine pathway abnormalities which incriminate it in the pathogenesis of the main psychiatric disorders. Harnessing this knowledge has the potential to find disease biomarkers helpful in identifying and prognosticating neuropsychiatric disorders. Concurrently, earnest research efforts directed towards manipulating the KP hold the promise of discovering novel pharmacological agents that have therapeutic value. In this manuscript, an in-depth appraisal of the extant literature is done to understand the working of KP as this applies to neuropsychiatric disorders. It is concluded that this pathway plays an overarching role in the development of major psychiatric disorders, the KP metabolites have the potential to serve as disease markers and new medications based on KP modulation can bring lasting cures for patients suffering from these intractable conditions.

Effect of immune activation on the kynurenine pathway and depression symptoms - A systematic review and meta-analysis

Dysregulated kynurenine (KYN) pathway has been implicated in the pathophysiology of depression. In this systematic review, we examined the relationship between kynurenine pathway metabolites (KYN, kynurenic acid KYNA, tryptophan TRP, quinolinic acid QUIN, KYN/TRP ratio) and depression symptoms in the context of pro-inflammatory activation and immune response. Out of 5,082 articles, fifteen studies were suitable; ten studies (N = 315 medically ill patients treated with interferon-alpha IFN-α) reported baseline and post-intervention plasma KYN, TRP and KYN/TRP ratios which were included in quantitative meta-analysis. Data from five studies were summarized (IFN-α, interferon-beta IFN-β, and lipopolysaccharide LPS). We found that IFN-α treatment in patients with chronic illnesses was associated with decreased TRP, increased levels of KYN and KYN/TRP ratio and depression scores from baseline to follow-up at both 4 and 24 weeks. Our findings suggest that increased risk of depression observed after immune-activating agents in patients with chronic medical illnesses is likely mediated by the kynurenine pathway. Further prospective studies are required to investigate the exact pathophysiology of the KYN pathway in depression.

The kynurenine pathway: a finger in every pie

The kynurenine pathway (KP) plays a critical role in generating cellular energy in the form of nicotinamide adenine dinucleotide (NAD+). Because energy requirements are substantially increased during an immune response, the KP is a key regulator of the immune system. Perhaps more importantly in the context of psychiatry, many kynurenines are neuroactive, modulating neuroplasticity and/or exerting neurotoxic effects in part through their effects on NMDA receptor signaling and glutamatergic neurotransmission. As such, it is not surprising that the kynurenines have been implicated in psychiatric illness in the context of inflammation. However, because of their neuromodulatory properties, the kynurenines are not just additional members of a list of inflammatory mediators linked with psychiatric illness, but in preclinical studies have been shown to be necessary components of the behavioral analogs of depression and schizophrenia-like cognitive deficits. Further, as the title suggests, the KP is regulated by, and in turn regulates multiple other physiological systems that are commonly disrupted in psychiatric disorders, including endocrine, metabolic, and hormonal systems. This review provides a broad overview of the mechanistic pathways through which the kynurenines interact with these systems, thus impacting emotion, cognition, pain, metabolic function, and aging, and in so doing potentially increasing the risk of developing psychiatric disorders. Novel therapeutic approaches targeting the KP are discussed. Moreover, electroconvulsive therapy, ketamine, physical exercise, and certain non-steroidal anti-inflammatories have been shown to alter kynurenine metabolism, raising the possibility that kynurenine metabolites may have utility as treatment response or therapeutic monitoring biomarkers.

Association of Serum Kynurenine Levels and Neural Networks in Patients with First-Episode, Drug-Naïve Major Depression: A Source-Based Morphometry Study

PURPOSE

The kynurenine (KYN) pathway can directly or indirectly influence cerebral volume and neural integrity in patients with major depression (MD). The aim of the present study was to investigate neural network systems and the KYN pathway in patients with first-episode, drug-naïve MD.

PATIENTS AND METHODS

Twenty right-handed drug-naïve patients, with MD diagnosed using the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition, Text Revision, Research Version, were included in this study. Magnetic resonance imaging scans and scores on the Hamilton Rating Scale for Depression were assessed, and serum sampling was performed prior to the start of pharmacological treatment. Image processing and data analysis were performed according to our recently published procedure. Serum metabolomes were measured in the cation and anion modes of CE-FTMS-based metabolome analysis.

RESULTS

We found that serum KYN levels were positively correlated with the Z-scores of the salience network but not with those of the central executive network or default mode network. No associations were observed between serum glutamate levels and the Z-score of any of the three networks.

CONCLUSION

Our results indicate that serum KYN levels might affect the activity of the salience network in first-episode, drug-naïve patients with MD.

Metabolomics approach in the investigation of depression biomarkers in pharmacologically induced immune-related depression

Background

The aim of this study was to identify previously unrecognised biological pathways and biomarkers that might expand the inflammatory hypothesis of depression.

Methods

Broad metabolomics analyses in plasma samples from 31 chronic hepatitis C-infected patients with and without immune-related depression were carried out using the Absolute IDQ p180 kit—a targeted metabolomics approach of combined direct flow injection and liquid chromatography that measures acylcarnitines, amino acids, biogenic amines, glycerophospholipids, sphingolipids, and sugars.

Results

The measurements showed that the average concentration of the branched-chain amino acid isoleucine was significantly lower in depressive HCV patients in comparison to non-depressive HCV patients [depression group: Median 51.35 (43.4–60.2 μmol/L) vs. Median 62.10 (38.4–81.7 μmol/L); U = -2.958; p = 0.002]. All other amino acids, acylcarnitines, biogenic amines, glycerophospholipids, sphingolipids, sugars, liver enzymes and thyroid levels showed no statistically significant differences.

Conclusions

The results of the present study suggest that the branched-chain amino acid isoleucine might play a role in the pathophysiology of immune-related major depression, which expands existing knowledge about inflammatory hypothesis of depression.

The role of IDO, IL-10, and TGF-β in the HCV-associated chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma

Indoleamine-2,3-dioxygenase (IDO) is an enzyme that catalyzes tryptophan to kynurenine and studies have revealed that IDO play a vital role in regulation of liver immunity and inflammation activities. This study investigated the association between plasma IDO and disease severity and the possible marker role of IDO in the inflammatory process of hepatitis C. In this study, 80 individuals with HCV infection were retrospectively selected. Plasma levels of IDO, IL-10, and TGF-β were assayed by ELISA. Clinical characteristics of patients, including the levels of ALT, AST, and total bilirubin (TBil) were collected from clinical databases. HCV-related liver cirrhosis (HC-Cirr) and HCV-related Hepatocellular carcinoma (HCV-HCC) had significantly high plasma levels of IDO compared to other patient groups and healthy controls. Plasma IL-10 level were significantly greater in all chronic liver disease groups and with respect to TGF-β, the level was high in all the selected patients with HCV infection compare with controls. Moreover, HCV-HCC patients showed highest values for both IL-10 and TGF-β, with significant difference compared with other groups. In addition, plasma IDO was positively correlated with TGF-β among all patients with HCV infection (r = 0.4509, P < 0.0001), with IL-10 in CHC patients (r = 0.4787, P = 0.0047), with TBil in HCV-Cirr patients (r = 0.4671; P = 0.0093). High level of IDO and TGF-β is associated with hepatocyte necrosis and intrahepatic inflammation, and may be used as an index of disease progression for patients with chronic HCV infection.

Role of Kynurenine pathway and its metabolites in mood disorders: A systematic review and meta-analysis of clinical studies

Activation of the kynurenine pathway is one of the described mechanisms by which inflammation can induce depression. It involves multiple pathways including interference with the bioavailability of tryptophan central to the synthesis of the neurotransmitter serotonin. In this systematic review, we examine the relationship between kynurenine metabolites (kynurenine, kynurenic acid, tryptophan, quinolinic acid, the ratio of kynurenine and tryptophan) and mood disorders by conducting a meta-analysis. Fifty-six studies were identified, 21 met inclusion criteria and 14 were deemed suitable (9 investigating unipolar depression and 5 bipolar disorder). We found decreased levels of kynurenine in unipolar major depression vs. healthy controls but studies were significantly heterogeneous in nature. No significant differences were found in tryptophan levels or kynurenine/tryptophan ratios. Kynurenine metabolites are likely to play a role in major depression but an exact etiological role in mood disorder seem complex and requires further research.

A longitudinal study assessing depression in hepatitis C: Does gender play a role in the new-onset depression during interferon-alpha treatment?

In this prospective study conducted from October 2013 to June 2015 in Brighton, England, we examined differences between men and women in new-onset major depressive disorder (MDD) during interferon-alpha-based (IFN-α) therapy for hepatitis C virus (HCV). We included 155 HCV-infected patients (47 women), eligible to receive HCV therapy, including direct-acting antivirals. The Semi-Structured Clinical Interview was used to assess MDD. Severity of depressive symptoms was assessed using the Hamilton Depression Rating Scale. Patients were assessed at baseline, during treatment and 6 months after treatment completion. A significant increase in depressive symptoms was observed in the total sample from baseline to week 4, and a significant decrease was observed from end of treatment (week 24) to the sustained virological response (SVR) end point at 6 months posttreatment. Women were more likely to have a MDD at week 24. In both men and women, neurovegetative and mood-cognitive syndromes increased significantly at the early stage of treatment but remitted by the end of HCV therapy. Proportions with SVR were similar among females and males (91.5 percent vs. 87 percent). Under an inflammatory condition, boosted by interferon-based treatments, these results suggest that female gender is not associated with increased vulnerability for developing depression during IFN-α therapy.

Excitotoxicity in the pathogenesis of neurological and psychiatric disorders: Therapeutic implications

Neurological and psychiatric disorders are leading contributors to the global disease burden, having a serious impact on the quality of life of both patients and their relatives. Although the molecular events underlying these heterogeneous diseases remain poorly understood, some studies have raised the idea of common mechanisms involved. In excitotoxicity, there is an excessive activation of glutamate receptors by excitatory amino acids, leading to neuronal damage. Thus, the excessive release of glutamate can lead to a dysregulation of Ca²⁺ homeostasis, triggering the production of free radicals and oxidative stress, mitochondrial dysfunction and eventually cell death. Although there is a consensus in considering excitotoxicity as a hallmark in most neurodegenerative diseases, increasing evidence points to the relevant role of this pathological mechanism in other illnesses affecting the central nervous system. Consequently, antagonists of glutamate receptors are used in current treatments or in clinical trials in both neurological and psychiatric disorders. However, drugs modulating other aspects of the excitotoxic mechanism could be more beneficial. This review discusses how excitotoxicity is involved in the pathogenesis of different neurological and psychiatric disorders and the promising strategies targeting the excitotoxic insult.

Revisiting the tryptophan-serotonin deficiency and the inflammatory hypotheses of major depression in a biopsychosocial approach

Background

The aim of this cross-sectional study was to identify important biopsychosocial correlates of major depression. Biological mechanisms, including the inflammatory and the tryptophan-serotonin deficiency hypotheses of major depression, were investigated alongside health-related quality of life, life satisfaction, and social support.

Methods

The concentrations of plasma tryptophan, plasma kynurenine, plasma kynurenic acid, serum quinolinic acid, and the tryptophan breakdown to kynurenine were determined alongside health-related quality of life (Medical Outcome Study Form, SF-36), life satisfaction (Life Satisfaction Questionnaire, FLZ), and social support (Social Support Survey, SSS) in 71 depressive patients at the time of their in-patient admittance and 48 healthy controls.

Results

Corresponding with the inflammatory hypothesis of major depression, our study results suggest a tryptophan breakdown to kynurenine in patients with major depression, and depressive patients had a lower concentration of neuroprotective kynurenic acid in comparison to the healthy controls (Mann-Whitney-U: 1315.0; p = 0.046). Contradicting the inflammatory theory, the concentrations of kynurenine (t: -0.945; df = 116; p = 0.347) and quinolinic acid (Mann-Whitney-U: 1376.5; p = 0.076) in depressive patients were not significantly different between depressed and healthy controls. Our findings tend to support the tryptophan-serotonin deficiency hypothesis of major depression, as the deficiency of the serotonin precursor tryptophan in depressive patients (t: -3.931; df = 116; p < 0.001) suggests dysfunction of serotonin neurotransmission. A two-step hierarchical linear regression model showed that low tryptophan concentrations, low social support (SSS), occupational requirements (FLZ), personality traits (FLZ), impaired physical role (SF-36), and impaired vitality (SF-36) predict higher Beck Depression Inventory (BDI-II) scores.

Discussion

Our study results argue for the validity of a biopsychosocial model of major depression with multiple pathophysiological mechanisms involved.

Upregulation of neuronal kynurenine 3-monooxygenase mediates depression-like behavior in a mouse model of neuropathic pain

Pain and depression often co-occur, but the underlying mechanisms have not been elucidated. Here, we used the spared nerve injury (SNI) model in mice to induce both neuropathic pain and depression-like behavior. We investigated whether brain interleukin (IL)-1 signaling and activity of kynurenine 3-monoxygenase (KMO), a key enzyme for metabolism of kynurenine into the neurotoxic NMDA receptor agonist quinolinic acid, are necessary for comorbid neuropathic pain and depression-like behavior. SNI mice showed increased expression levels of Il1b and Kmo mRNA in the contralateral side of the brain. The SNI-induced increase of Kmo mRNA was associated with increased KMO protein and elevated quinolinic acid and reduced kynurenic acid in the contralateral hippocampus. The increase in KMO-protein in response to SNI mostly took place in hippocampal NeuN-positive neurons rather than microglia. Inhibition of brain IL-1 signaling by intracerebroventricular administration of IL-1 receptor antagonist after SNI prevented the increase in Kmo mRNA and depression-like behavior measured by forced swim test. However, inhibition of brain IL-1 signaling has no effect on mechanical allodynia. In addition, intracerebroventricular administration of the KMO inhibitor Ro 61-8048 abrogated depression-like behavior without affecting mechanical allodynia after SNI. We show for the first time that the development of depression-like behavior in the SNI model requires brain IL-1 signaling and activation of neuronal KMO, while pain is independent of this pathway. Inhibition of KMO may represent a promising target for treating depression.

Sleep disturbance and kynurenine metabolism in depression

OBJECTIVE

Although the interrelationships between sleep disturbance, inflammation, and depression have been found, molecular mechanisms that link these conditions are largely unknown. Kynurenine metabolism is hypothesized to be a key mechanism that links inflammation and depression. Inflammation activates the kynurenine pathway, leading to increases in 3-hydroxykynurenine (3HK) and quinolinic acid (QA), potentially neurotoxic metabolites, and decreases in kynurenic acid (KynA), a potentially neuroprotective compound. This relative neurotoxic shift in the balance of kynurenine metabolites has been associated with depression, but never been examined regarding sleep disturbance. We tested the association between sleep disturbance and this relative neurotoxic shift in 68 currently depressed, 26 previously depressed, and 66 never depressed subjects.

METHODS

Sleep disturbance was assessed using the Pittsburgh Sleep Quality Index. Serum concentrations of kynurenine metabolites were measured using high performance liquid chromatography. Putative neuroprotective indices reflecting the relative activity of neuroprotective and neurotoxic kynurenine metabolites were calculated as KynA/QA and KynA/3HK (primary outcomes).

RESULTS

Sleep disturbance was associated with reduced KynA/QA in the currently depressed group only (unadjusted beta -0.43, p<0.001). This association remained significant even after controlling for age, sex, analysis batch, body-mass index, and depressive symptoms in currently depressed subjects (adjusted beta -0.30, p=0.02). There was no significant association between sleep disturbance and KynA/3HK in any of the groups. Sleep disturbance was associated with increased C-reactive protein in currently depressed subjects only (unadjusted beta 0.38, p=0.007; adjusted beta 0.33, p=0.02).

CONCLUSION

These data support the hypothesis that altered kynurenine metabolism may molecularly link sleep disturbance and depression.

Desipramine decreases expression of human and murine indoleamine-2,3-dioxygenases

Abundant evidence connects depression symptomology with immune system activation, stress and subsequently elevated levels of kynurenine. Anti-depressants, such as the tricyclic norepinephrine/serotonin reuptake inhibitor desipramine (Desip), were developed under the premise that increasing extracellular neurotransmitter level was the sole mechanism by which they alleviate depressive symptomologies. However, evidence suggests that anti-depressants have additional actions that contribute to their therapeutic potential. The Kynurenine Pathway produces tryptophan metabolites that modulate neurotransmitter activity. This recognition identified another putative pathway for anti-depressant targeting. Considering a recognized role of the Kynurenine Pathway in depression, we investigated the potential for Desip to alter expression of rate-limiting enzymes of this pathway: indoleamine-2,3-dioxygenases (Ido1 and Ido2). Mice were administered lipopolysaccharide (LPS) or synthetic glucocorticoid dexamethasone (Dex) with Desip to determine if Desip alters indoleamine-dioxygenase (DO) expression in vivo following a modeled immune and stress response. This work was followed by treating murine and human peripheral blood mononuclear cells (PBMCs) with interferon-gamma (IFNγ) and Desip. In vivo: Desip blocked LPS-induced Ido1 expression in hippocampi, astrocytes, microglia and PBMCs and Ido2 expression by PBMCs. Ex vivo: Desip decreased IFNγ-induced Ido1 and Ido2 expression in murine PBMCs. This effect was directly translatable to the human system as Desip decreased IDO1 and IDO2 expression by human PBMCs. These data demonstrate for the first time that an anti-depressant alters expression of Ido1 and Ido2, identifying a possible new mechanism behind anti-depressant activity. Furthermore, we propose the assessment of PBMCs for anti-depressant responsiveness using IDO expression as a biomarker.

Beta-trace Protein as a new non-invasive immunological Marker for Quinolinic Acid-induced impaired Blood-Brain Barrier Integrity

Quinolinic acid, a macrophage/microglia-derived excitotoxin fulfills a plethora of functions such as neurotoxin, gliotoxin, and proinflammatory mediator, and it alters the integrity and cohesion of the blood-brain barrier in several pathophysiological states. Beta-trace protein (BTP), a monomeric glycoprotein, is known to indicate cerebrospinal fluid leakage. Thus, the prior aim of this study was to investigate whether BTP might non-invasively indicate quinolinic acid-induced impaired blood-brain barrier integrity. The research hypotheses were tested in three subsamples with different states of immune activation (patients with HCV-infection and interferon-α, patients with major depression, and healthy controls). BTP has also been described as a sensitive marker in detecting impaired renal function. Thus, the renal function has been considered. Our study results revealed highest quinolinic acid and highest BTP- levels in the subsample of patients with HCV in comparison with the other subsamples with lower or no immune activation (quinolinic acid: F = 21.027, p < 0.001 [ANOVA]; BTP: F = 6.792, p < 0.01 [ANOVA]). In addition, a two-step hierarchical linear regression model showed that significant predictors of BTP levels are quinolinic acid, glomerular filtration rate and age. The neurotoxin quinolinic acid may impair blood-brain barrier integrity. BTP might be a new non-invasive biomarker to indicate quinolinic acid-induced impaired blood-brain barrier integrity.

Role of Kynurenine Metabolism Pathway Activation in Major Depressive Disorders

A proportion of depressed individuals show evidence of inflammation. Both animal, quasi-experimental, and longitudinal studies indicate that inflammatory processes may play a causal role in the developmental of depressive illness. While there may be multiple causal pathways through which inflammatory processes affect mood, activation of the kynurenine pathway is essential for the development of depression-like behavior in rodents. Studies of hepatitis C or cancer patients receiving treatment with inflammation-inducing medications show increased activation of the kynurenine pathway and decreased levels of tryptophan that correlate with inflammation-induced depression. Further, this treatment has been shown to lead to increased production of neurotoxic kynurenine pathway metabolites such as quinolinic acid (QA). Similarly, in non-medically ill patients with major depression, multiple studies have found activation of the kynurenine pathway and/or preferential activation of the neurotoxic (QA) pathway at the expense of the production of the NMDA antagonist, kynurenic acid. Initially, activation of the kynurenine pathway was believed to precipitate depressive symptoms by depleting brain serotonin, however, the weight of the evidence now suggests that an imbalance between neurotoxic and neuroprotective metabolites may be the principal driver of depression; conceivably via its effects on glutamatergic neurotransmission.

Evaluation of the effect of soybean diet on interferon-α-induced depression in male mice

OBJECTIVE

Interferon-α (IFN) therapy can cause depressive symptom which may lead to drug discontinuation. By interfering with tryptophan pathway, the available level of tryptophan required for serotonin synthesis decreases which could be related to depression. The aim of this study was to evaluate whether soybean diet could improve IFN-induced depression.

MATERIALS AND METHODS

Male mice weighing 28±3 g were used in the forced swimming test (FST) as an animal model of depression; also, locomotor activity was recorded. IFN 16×10⁵ IU/kg was injected subcutaneously for 6 days. Animals were fed with regular diet or soybean diet at 3 concentrations throughout the experiment. Fluoxetine was the reference drug. To check whether the tryptophan content in the soy bean diet was effective, a group of animals was injected with a single dose of tryptophan on the test day.

RESULTS

IFN-α increased the immobility time in the FST (192 sec ± 5.4), that denotes depression in mice. Soybean diets caused less immobility that was more profound with 50% soybean (26.4 sec ± 6). This diet overcame the depression caused by IFN in the FST (54 sec±18). This result was parallel with that of tryptophan injected to animals (38 sec±17). All the animals showed normal locomotor activity.

CONCLUSION

For the first time, we showed that soybean diet could counteract with depression caused by IFN-α. Since tryptophan therapy had similar effects, possibly the tryptophan content of soybean had induced the serotonin synthesis. Thus, not only less harmful kynurenine was produced but also more serotonin was available in the brain to overcome depression. However, this interpretation needs further evaluations.

Role of glutamate receptors and glial cells in the pathophysiology of treatment-resistant depression

Treatment-resistant depression (TRD) causes substantial socioeconomic burden. Although a consensus on the definition of TRD has not yet been reached, it is certain that classic monoaminergic antidepressants are ineffective for TRD. One decade ago, many researchers found ketamine, an N-methyl-d-aspartate receptor (NMDAR) antagonist, to be an alternative to classic monoaminergic antidepressants. The major mechanisms of action of ketamine rapidly induce synaptogenesis in the brain-derived neurotrophic factor (BDNF) pathway. Although excessive glutamatergic neurotransmission and consequent excitotoxicity were considered a major cause of TRD, recent evidence suggests that the extrasynaptic glutamatergic receptor signal pathway mainly contributes to the detrimental effects of TRD. Glial cells such as microglia and astrocytes, early life adversity, and glucocorticoid receptor dysfunction participate in complex cross-talk. An appropriate reuptake of glutamate at the astrocyte is crucial for preventing 'spill-over' of synaptic glutamate and binding to the extrasynaptic NMDA receptor. Excessive microglial activation and the inflammatory process cause astrocyte glutamatergic dysfunction, which in turn activates microglial function. Early life adversity and glucocorticoid receptor dysfunction result in vulnerability to stress in adulthood. A maladaptive response to stress leads to increased glutamatergic release and pro-inflammatory cytokines, which then activate microglia. However, since the role of inflammatory mediators such as pro-inflammatory cytokines is not specific for depression, more disease-specific mechanisms should be identified. Last, although much research has focused on ketamine as an alternative antidepressant for TRD, its long-lasting effectiveness and adverse events have not been rigorously demonstrated. Additionally, evidence suggests that substantial brain abnormalities develop in ketamine abusers. Thus, more investigations for ketamine and other novel glutamatergic agents are needed.