Quinolinic acid: an endogenous neurotoxin with multiple targets

Regulation of and challenges in targeting NAD+ metabolism

Nicotinamide adenine dinucleotide, in its oxidized (NAD+) and reduced (NADH) forms, is a reduction-oxidation (redox) co-factor and substrate for signalling enzymes that have essential roles in metabolism. The recognition that NAD+ levels fall in response to stress and can be readily replenished through supplementation has fostered great interest in the potential benefits of increasing or restoring NAD+ levels in humans to prevent or delay diseases and degenerative processes. However, much about the biology of NAD+ and related molecules remains poorly understood. In this Review, we discuss the current knowledge of NAD+ metabolism, including limitations of, assumptions about and unappreciated factors that might influence the success or contribute to risks of NAD+ supplementation. We highlight several ongoing controversies in the field, and discuss the role of the microbiome in modulating the availability of NAD+ precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN), the presence of multiple cellular compartments that have distinct pools of NAD+ and NADH, and non-canonical NAD+ and NADH degradation pathways. We conclude that a substantial investment in understanding the fundamental biology of NAD+, its detection and its metabolites in specific cells and cellular compartments is needed to support current translational efforts to safely boost NAD+ levels in humans.

Hypocortisolemic ASIA: a vaccine- and chronic infection-induced syndrome behind the origin of long COVID and myalgic encephalomyelitis

Myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS), long COVID (LC) and post-COVID-19 vaccine syndrome show similarities in their pathophysiology and clinical manifestations. These disorders are related to viral or adjuvant persistence, immunological alterations, autoimmune diseases and hormonal imbalances. A developmental model is postulated that involves the interaction between immune hyperactivation, autoimmune hypophysitis or pituitary hypophysitis, and immune depletion. This process might begin with a deficient CD4 T-cell response to viral infections in genetically predisposed individuals (HLA-DRB1), followed by an uncontrolled immune response with CD8 T-cell hyperactivation and elevated antibody production, some of which may be directed against autoantigens, which can trigger autoimmune hypophysitis or direct damage to the pituitary, resulting in decreased production of pituitary hormones, such as ACTH. As the disease progresses, prolonged exposure to viral antigens can lead to exhaustion of the immune system, exacerbating symptoms and pathology. It is suggested that these disorders could be included in the autoimmune/adjuvant-induced inflammatory syndrome (ASIA) because of their similar clinical manifestations and possible relationship to genetic factors, such as polymorphisms in the HLA-DRB1 gene. In addition, it is proposed that treatment with antivirals, corticosteroids/ginseng, antioxidants, and metabolic precursors could improve symptoms by modulating the immune response, pituitary function, inflammation and oxidative stress. Therefore, the purpose of this review is to suggest a possible autoimmune origin against the adenohypophysis and a possible improvement of symptoms after treatment with corticosteroid replacement therapy.

Identification of metabolites associated with preserved muscle volume after aneurysmal subarachnoid hemorrhage due to high protein supplementation and neuromuscular electrical stimulation

The INSPIRE randomized clinical trial demonstrated that a high protein diet (HPRO) combined with neuromuscular electrical stimulation (NMES) attenuates muscle atrophy and may improve outcomes after aneurysmal subarachnoid hemorrhage We sought to identify specific metabolites mediating these effects. Blood samples were collected from subjects on admission prior to randomization to either standard of care (SOC; N = 12) or HPRO + NMES (N = 12) and at 7 days. Untargeted metabolomics were performed for each plasma sample. Sparse partial least squared discriminant analysis identified metabolites differentiating each group. Correlation coefficients were calculated between each metabolite and total protein per day and muscle volume. Multivariable models determined associations between metabolites and muscle volume. Unique metabolites (18) were identified differentiating SOC from HPRO + NMES. Of these, 9 had significant positive correlations with protein intake. In multivariable models, N-acetylleucine was significantly associated with preserved temporalis [OR 1.08 (95% CI 1.01, 1.16)] and quadricep [OR 1.08 (95% CI 1.02, 1.15)] muscle volume. Quinolinate was also significantly associated with preserved temporalis [OR 1.05 (95% CI 1.01, 1.09)] and quadricep [OR 1.04 (95% CI 1.00, 1.07)] muscle volume. N-acetylserine and β-hydroxyisovaleroylcarnitine were associated with preserved temporalis or quadricep volume. Metabolites defining HPRO + NMES had strong correlations with protein intake and were associated with preserved muscle volume.

The Mediating Role of Kynurenine Pathway Metabolites on the Relationship Between Inflammation and Muscle Mass in Oldest-Old Men

Tryptophan (TRP) metabolites along the kynurenine (KYN) pathway (KP) have been found to influence muscle. Proinflammatory cytokines are known to stimulate the degradation of TRP down the KP. Given that both inflammation and KP metabolites have been connected with loss of muscle, we assessed the potential mediating role of KP metabolites on inflammation and muscle mass in older men. Five hundred and five men (85.0 ± 4.2 years) from the Osteoporotic Fractures in Men cohort study with measured D3-creatine dilution (D3Cr) muscle mass, KP metabolites, and inflammation markers (C-reactive protein [CRP], alpha-1-acid glycoprotein [AGP] and a subsample [n = 305] with interleukin [IL-6, IL-1β, IL-17A] and tumor necrosis factor-α [TNF-α]) were included in the analysis. KP metabolites and inflammatory markers were measured using liquid chromatography-tandem mass spectrometry and immunoassays, respectively. 23%-92% of the inverse relationship between inflammatory markers and D3Cr muscle mass was mediated by KP metabolites (indirect effect p < .05). 3-hydroxyanthranilic acid (3-HAA), quinolinic acid (QA), TRP, xanthurenic acid (XA), KYN/TRP, 3-hydroxykynurenine (3-HK)/3-HAA, QA/3-HAA, and nicotinamide (NAM)/QA mediated the AGP relationship. 3-HAA, QA, KYN/TRP, 3-HK/XA, HKr ratio, 3-HK/3-HAA, QA/3-HAA, and NAM/QA mediated the CRP. KYN/TRP, 3-HK/XA, and NAM/QA explained the relationship for IL-6 and 3-HK/XA and QA/3-HAA for TNF-α. No mediation effect was observed for the other cytokines (indirect effect p > .05). KP metabolites, particularly higher ratios of KYN/TRP, 3-HK/XA, 3-HK/3-HAA, QA/3-HAA, and a lower ratio of NAM/QA, mediated the relationship between inflammation and low muscle mass. Our preliminary cross-sectional data suggest that interventions to alter D3Cr muscle mass may focus on KP metabolites rather than inflammation per se.

Gut Microbiota Metabolite Messengers in Brain Function and Pathology at a View of Cell Type-Based Receptor and Enzyme Reaction

The human gastrointestinal (GI) tract houses a diverse microbial community, known as the gut microbiome comprising bacteria, viruses, fungi, and protozoa. The gut microbiome plays a crucial role in maintaining the body's equilibrium and has recently been discovered to influence the functioning of the central nervous system (CNS). The communication between the nervous system and the GI tract occurs through a two-way network called the gut-brain axis. The nervous system and the GI tract can modulate each other through activated neuronal cells, the immune system, and metabolites produced by the gut microbiome. Extensive research both in preclinical and clinical realms, has highlighted the complex relationship between the gut and diseases associated with the CNS, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This review aims to delineate receptor and target enzymes linked with gut microbiota metabolites and explore their specific roles within the brain, particularly their impact on CNS-related diseases.

Understanding and treating postpartum depression: a narrative review

Postpartum depression (PPD) is an increasingly prevalent but still poorly characterized disorder. Causal and modulating factors include hormones fluctuations, such as estrogen, progesterone, and allopregnolone, pathways imbalances, such as oxytocin and kynurenine, chronobiological factors, and brain imaging alterations. Treatment may differ from the traditional major depression management, while selective serotonin reuptake inhibitors such as sertraline are commonly used and suggested by guidelines, neurosteroids such as brexanolone and the more convenient zuranolone have been recently approved. Newer neurosteroids such as ganaxolone, valaxanolone, and lysaxanolone are currently under development, but also esketamine and psychedelics are promising potential treatments. Other somatic treatments including brain stimulation techniques and light therapy also showed benefit. PPD is therefore increasingly understood as, at least partially, independent from major depressive disorder. Specific and individualized treatments including pharmacological and non-pharmacological therapies are progressively being introduced in the routine clinical practice.

Visualization of incrementally learned projection trajectories for longitudinal data

Longitudinal studies that continuously generate data enable the capture of temporal variations in experimentally observed parameters, facilitating the interpretation of results in a time-aware manner. We propose IL-VIS (incrementally learned visualizer), a new machine learning pipeline that incrementally learns and visualizes a progression trajectory representing the longitudinal changes in longitudinal studies. At each sampling time point in an experiment, IL-VIS generates a snapshot of the longitudinal process on the data observed thus far, a new feature that is beyond the reach of classical static models. We first verify the utility and correctness of IL-VIS using simulated data, for which the true progression trajectories are known. We find that it accurately captures and visualizes the trends and (dis)similarities between high-dimensional progression trajectories. We then apply IL-VIS to longitudinal multi-electrode array data from brain cortical organoids when exposed to different levels of quinolinic acid, a metabolite contributing to many neuroinflammatory diseases including Alzheimer's disease, and its blocking antibody. We uncover valuable insights into the organoids' electrophysiological maturation and response patterns over time under these conditions.

The roles of the kynurenine pathway in COVID-19 neuropathogenesis

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the highly contagious respiratory disease Corona Virus Disease 2019 (COVID-19) that may lead to various neurological and psychological disorders that can be acute, lasting days to weeks or months and possibly longer. The latter is known as long-COVID or more recently post-acute sequelae of COVID (PASC). During acute COVID-19 infection, a strong inflammatory response, known as the cytokine storm, occurs in some patients. The levels of interferon-γ (IFN-γ), interferon-β (IFN-β), interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-α) are particularly increased. These cytokines are known to activate the enzyme indoleamine 2,3-dioxygenase 1 (IDO-1), catalysing the first step of tryptophan (Trp) catabolism through the kynurenine pathway (KP) leading to the production of several neurotoxic and immunosuppressive metabolites. There is already data showing elevation in KP metabolites both acutely and in PASC, especially regarding cognitive impairment. Thus, it is likely that KP involvement is significant in SARS-CoV-2 pathogenesis especially neurologically.

A Review of the Evidence for Tryptophan and the Kynurenine Pathway as a Regulator of Stem Cell Niches in Health and Disease

Stem cells are ubiquitously found in various tissues and organs in the body, and underpin the body's ability to repair itself following injury or disease initiation, though repair can sometimes be compromised. Understanding how stem cells are produced, and functional signaling systems between different niches is critical to understanding the potential use of stem cells in regenerative medicine. In this context, this review considers kynurenine pathway (KP) metabolism in multipotent adult progenitor cells, embryonic, haematopoietic, neural, cancer, cardiac and induced pluripotent stem cells, endothelial progenitor cells, and mesenchymal stromal cells. The KP is the major enzymatic pathway for sequentially catabolising the essential amino acid tryptophan (TRP), resulting in key metabolites including kynurenine, kynurenic acid, and quinolinic acid (QUIN). QUIN metabolism transitions into the adjoining de novo pathway for nicotinamide adenine dinucleotide (NAD) production, a critical cofactor in many fundamental cellular biochemical pathways. How stem cells uptake and utilise TRP varies between different species and stem cell types, because of their expression of transporters and responses to inflammatory cytokines. Several KP metabolites are physiologically active, with either beneficial or detrimental outcomes, and evidence of this is presented relating to several stem cell types, which is important as they may exert a significant impact on surrounding differentiated cells, particularly if they metabolise or secrete metabolites differently. Interferon-gamma (IFN-γ) in mesenchymal stromal cells, for instance, highly upregulates rate-limiting enzyme indoleamine-2,3-dioxygenase (IDO-1), initiating TRP depletion and production of metabolites including kynurenine/kynurenic acid, known agonists of the Aryl hydrocarbon receptor (AhR) transcription factor. AhR transcriptionally regulates an immunosuppressive phenotype, making them attractive for regenerative therapy. We also draw attention to important gaps in knowledge for future studies, which will underpin future application for stem cell-based cellular therapies or optimising drugs which can modulate the KP in innate stem cell populations, for disease treatment.

Quinolinic acid links kidney injury to brain toxicity

Kidney dysfunction often leads to neurological impairment, yet the complex kidney-brain relationship remains elusive. We employed spatial and bulk metabolomics to investigate a mouse model of rapid kidney failure induced by mouse double minute 2 ( Mdm2) conditional deletion in the kidney tubules to interrogate kidney and brain metabolism. Pathway enrichment analysis of focused plasma metabolomics panel pinpointed tryptophan metabolism as the most altered pathway with kidney failure. Spatial metabolomics showed toxic tryptophan metabolites in the kidneys and brains, revealing a novel connection between advanced kidney disease and accelerated kynurenine degradation. In particular, the excitotoxic metabolite quinolinic acid was localized in ependymal cells adjacent to the ventricle in the setting of kidney failure. These findings were associated with brain inflammation and cell death. A separate mouse model of acute kidney injury also had an increase in circulating toxic tryptophan metabolites along with altered brain inflammation. Patients with advanced CKD similarly demonstrated elevated plasma kynurenine metabolites and quinolinic acid was uniquely correlated with fatigue and reduced quality of life in humans. Overall, our study identifies the kynurenine pathway as a bridge between kidney decline, systemic inflammation, and brain toxicity, offering potential avenues for diagnosis and treatment of neurological issues in kidney disease.

Graphene oxide quantum dots (GOQDs) induce behavioral disorders via the disturbance of kynurenine pathway in zebrafish larvae

The emergence of graphene quantum dots (GQDs) expands the use of graphene derivatives in nanomedicine for its direct therapeutic applications in treating neurodegeneration, inflammation, metabolic dysfunction, and among others. Nevertheless, the biosafety assessment of GQDs remains deficient mostly because of the diverse surface characteristics of the nanoparticles. Our prior work demonstrated that GQDs can induce strong thigmotactic effects in zebrafish larvae over a wide range of concentrations, yet the underlying metabolic mechanisms remain largely unknown. In this study, we conducted a further exploration about graphene oxide quantum dots (GOQDs) for its potential neurotoxic effect on the behaviors of zebrafish larvae by combining neurotransmitter-targeted metabolomics with locomotion analysis. After continuous exposure to a concentration gradient of GOQDs (12.5 - 25 - 50 - 100 - 200 μg/mL) for 7 days, the thigmotactic activities of zebrafish larvae were observed across all exposure concentrations relative to the control group, while the basal locomotor activities, including distance moved and average velocity, were significantly changed by low concentrations of GOQDs. Targeted metabolomics was performed using zebrafish larvae at 7 days post-fertilization (dpf) that were exposed to 12.5 and 200 μg/mL, both of which were found to perturb the kynurenine pathway by regulating the levels of kynurenine, 3-hydroxyanthranilic acid (3-HAA), and quinolinic acid (QA). Furthermore, the thigmotaxis of larval fish induced by GOQDs during exposure could be counteracted by supplementing Ro-61-8048, an agonist acting on kynurenine 3-monooxygenase (KMO). In conclusion, our study establishes the involvement of the kynurenine pathway in GOQDs-induced thigmotaxis, which is independent of the transcriptional modulation of glutamate receptor families.

Neopterin, kynurenine metabolites, and indexes related to vitamin B6 are associated with post-stroke cognitive impairment: The Nor-COAST study

BACKGROUND AND AIMS

We have previously shown that systemic inflammation was associated with post-stroke cognitive impairment (PSCI). Because neopterin, kynurenine pathway (KP) metabolites, and B6 vitamers are linked to inflammation, in our study we investigated whether those biomarkers were associated with PSCI.

MATERIAL AND METHODS

The Norwegian Cognitive Impairment After Stroke study is a prospective multicenter cohort study of patients with acute stroke recruited from May 2015 through March 2017. Plasma samples of 422 participants (59 % male) with ischemic stroke from the index hospital stay and 3 months post-stroke were available for analyses of neopterin, KP metabolites, and B6 vitamers using liquid chromatography-tandem mass spectrometry. Mixed linear regression analyses adjusted for age, sex, and creatinine, were used to assess whether there were associations between those biomarkers and cognitive outcomes, measured by the Montreal Cognitive Assessment scale (MoCA) at 3-, 18-, and 36-month follow-up.

RESULTS

Participants had a mean (SD) age of 72 (12) years, with a mean (SD) National Institutes of HealthStroke Scale score of 2.7 (3.6) at Day 1. Higher baseline values of quinolinic acid, PAr (i.e., an inflammatory marker based on vitamin B6 metabolites), and HKr (i.e., a marker of functional vitamin B6 status based on selected KP metabolites) were associated with lower MoCA score at 3, 18, and 36 months post-stroke (p < 0.01). Higher baseline concentrations of neopterin and 3-hydroxykynurenine were associated with lower MoCA scores at 18 and 36 months, and higher concentrations of xanthurenic acid were associated with higher MoCA score at 36 months (p < 0.01). At 3 months post-stroke, higher concentrations of neopterin and lower values of pyridoxal 5́-phosphate were associated with lower MoCA scores at 18- and 36-month follow-up, while lower concentrations of picolinic acid were associated with a lower MoCA score at 36 months (p < 0.01).

CONCLUSION

Biomarkers and metabolites of systemic inflammation, including biomarkers of cellular immune activation, indexes of vitamin B6 homeostasis, and several neuroactive metabolites of the KP pathway, were associated with PSCI.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02650531.

L-kynurenine and quinolinic acid inhibited markers of cell survival in B16 F10 melanoma cells in vitro

Melanoma is an aggressive malignancy and remains a major cause of skin cancer mortality, highlighting the need for new treatment strategies. Recent findings revealed that L-kynurenine and quinolinic acid induce cytotoxicity and morphological changes in B16 F10 melanoma cells in vitro. This paper highlights the effects of L-kynurenine and quinolinic acid at previously determined half-maximal inhibitory concentrations on cell cycle progression, cell death and extracellular signal-regulated protein kinase inhibition. Melanoma, B16 F10 and murine macrophages, RAW 264.7 cells were used in this study, as both cell lines express all the enzymes associated with the kynurenine pathway. Post exposure to the compounds at half-maximal inhibitory concentrations, transmission electron microscopy was used to assess intracellular morphological changes. Flow cytometry was used to analyse cell cycle progression and quantify apoptosis via the dual staining of Annexin V and propidium iodide and cell survival via extracellular signal-regulated protein kinase. L-kynurenine and quinolinic acid at half-maximal inhibitory concentrations induced intracellular morphological changes representative of cell death. Flow cytometry revealed alterations in cell cycle distribution, increased apoptosis and significantly inhibition of cell survival. L-kynurenine and quinolinic acid are exogenous kynurenine compounds which inhibited cell survival through extracellular signal-regulated protein kinase inhibition, induced cell cycle alterations and induced apoptosis in B16 F10 melanoma cells.

Implications of metabolism on multi-systems healthy aging across the lifespan

Aging is increasingly thought to involve dysregulation of metabolism in multiple organ systems that culminate in decreased functional capacity and morbidity. Here, we seek to understand complex interactions among metabolism, aging, and systems-wide phenotypes across the lifespan. Among 2469 adults (mean age 74.7 years; 38% Black) in the Health, Aging and Body Composition study we identified metabolic cross-sectionally correlates across 20 multi-dimensional aging-related phenotypes spanning seven domains. We used LASSO-PCA and bioinformatic techniques to summarize metabolome-phenome relationships and derive metabolic scores, which were subsequently linked to healthy aging, mortality, and incident outcomes (cardiovascular disease, disability, dementia, and cancer) over 9 years. To clarify the relationship of metabolism in early adulthood to aging, we tested association of these metabolic scores with aging phenotypes/outcomes in 2320 participants (mean age 32.1, 44% Black) of the Coronary Artery Risk Development in Young Adults (CARDIA) study. We observed significant overlap in metabolic correlates across the seven aging domains, specifying pathways of mitochondrial/cellular energetics, host-commensal metabolism, inflammation, and oxidative stress. Across four metabolic scores (body composition, mental-physical performance, muscle strength, and physical activity), we found strong associations with healthy aging and incident outcomes, robust to adjustment for risk factors. Metabolic scores for participants four decades younger in CARDIA were related to incident cardiovascular, metabolic, and neurocognitive performance, as well as long-term cardiovascular disease and mortality over three decades. Conserved metabolic states are strongly related to domain-specific aging and outcomes over the life-course relevant to energetics, host-commensal interactions, and mechanisms of innate immunity.

Role of the immune-kynurenine pathway in treatment-resistant schizophrenia

BACKGROUND

The immune-inflammatory response system (IRS) and kynurenine pathway (KP) have been implicated in the pathophysiology of schizophrenia. Studies have shown inflammation-related effects on KP metabolism in patients with schizophrenia. This study investigated the relationship between KP metabolites, IRS, and the compensatory immune-regulatory reflex system (CIRS) in patients with treatment-resistant schizophrenia (TRS).

METHODS

Patients with (n = 53) and without TRS (n = 47), and healthy controls (HCs, n = 49) were enrolled. We quantified plasma levels of pro-inflammatory cytokines (interleukin [IL]-1β, IL-2, IL-6, soluble(s)IL-6 receptor, IL-8, IL-12, IL-17, IL-18, interferon-γ, and tumor necrosis factor[TNF]-α) and anti-inflammatory cytokines (IL-1 receptor antagonist, IL-4, IL-10, tumor growth factor [TGF]-β1, TGF-β2, soluble (s) IL-2 receptor subunit α, sIL-2 receptor subunit β, and sTNF-α receptor 1) and calculated the IRS/CIRS ratio. We also tested serum metabolites of the KP, including kynurenine (KYN), kynurenic acid (KYNA), and quinolinic acid (QUIN), along with the QUIN/KYNA ratio.

RESULTS

Patients with TRS had significantly higher IRS/CIRS ratio than non-TRS patients (p = 0.002) and HCs (p = 0.007), and significantly lower KYN (p = 0.001) and KYNA (p = 0.01) levels than HCs. Binary logistic regression analysis revealed that a younger age at illness onset (odds ratio [OR] = 0.91, p = 0.02) and a higher IRS/CIRS ratio (OR = 1.22; p = 0.007) were risk factors for patients with TRS. After further adjusted for age of onset, the QUIN/KYNA ratio (β = 0.97; p = 0.02) significantly moderated the relationship between IRS/CIRS and TRS, showing that in the higher QUIN/KYNA condition, higher IRS/CIRS ratio were significantly and more likely to be associated with patients with TRS (β = 0.12, z = 3.19, p = 0.001), whereas in the low QUIN/KYNA condition, the association between IRS/CIRS ratio and TRS was weak and insignificant.

CONCLUSIONS

The peripheral immune response was imbalanced in TRS and was preferentially directed towards the IRS compared to patients without TRS and healthy controls, which is likely to play a role in neurotoxicity. Additionally, peripheral KP activation was also imbalanced, as evidenced by significantly reduced KYN and KYNA levels in patients with TRS compared to healthy controls, but none of KP metabolisms were significantly difference in non-TRS patients compared to healthy controls. QUIN/KYNA ratio involving to the degree of activation of NMDA receptors, indicated the neurotoxic level of the KP activation. The interaction between IRS/CIRS and QUIN/KYNA ratio was significant in predicting TRS, and our findings suggest a potential role for the immune-kynurenine pathway in TRS pathogenesis.

The dangerous "West Coast Swing" by hyperglycaemia and chronic stress in the mouse hippocampus: Role of kynurenine catabolism

Growing epidemiological studies highlight a bi-directional relationship between depressive symptoms and diabetes mellitus. However, the detrimental impact of their co-existence on mental health suggests the need to treat this comorbidity as a separate entity rather than the two different pathologies. Herein, we characterized the peculiar mechanisms activated in mouse hippocampus from the concurrent development of hyperglycaemia, characterizing the different diabetes subtypes, and chronic stress, recognized as a possible factor predisposing to major depression. Our work demonstrates that kynurenine overproduction, leading to apoptosis in the hippocampus, is triggered in a different way depending on hyperglycaemia or chronic stress. Indeed, in the former, kynurenine appears produced by infiltered macrophages whereas, in the latter, peripheral kynurenine preferentially promotes resident microglia activation. In this scenario, QA, derived from kynurenine catabolism, appears a key mediator causing glutamatergic synapse dysfunction and apoptosis, thus contributing to brain atrophy. We demonstrated that the coexistence of hyperglycaemia and chronic stress worsened hippocampal damage through alternative mechanisms, such as GLUT-4 and BDNF down-expression, denoting mitochondrial dysfunction and apoptosis on one hand and evoking the compromission of neurogenesis on the other. Overall, in the degeneration of neurovascular unit, hyperglycaemia and chronic stress interacted each other as the partners of a "West Coast Swing" in which the leading role can be assumed alternatively by each partner of the dance. The comprehension of these mechanisms can open novel perspectives in the management of diabetic/depressed patients, but also in the understanding the pathogenesis of other neurodegenerative disease characterized by the compromission of hippocampal function.

Omega-3 fatty acid supplementation affects tryptophan metabolism during a 12-week endurance training in amateur runners: a randomized controlled trial

The effects of long-term omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation during endurance training on tryptophan (Trp) metabolism and mental state of healthy individuals have not been evaluated so far. Concentrations of plasma Trp, its metabolites and IL-6 were assessed in 26 male runners before and after a 12-week training program combined with supplementation of n-3 PUFAs (O-3 + TRAIN group) or medium chain triglycerides (MCTs; TRAIN group). After the 12-week program participants' mood before and after stress induction was also assessed. The effects of the same supplementation protocol were evaluated also in 14 inactive subjects (O-3 + SEDEN group). Concentrations of 3-hydroxykynurenine (3-HK) and picolinic acid (PA) significantly increased only in the O-3 + TRAIN group (p = 0.01; [Formula: see text] = 0.22 and p = 0.01; [Formula: see text]= 0.26). Favorable, but not statistically significant changes in the concentrations of kynurenic acid (KYNA) (p = 0.06; [Formula: see text]= 0.14), xanthurenic acid (XA) (p = 0.07; [Formula: see text]= 0.13) and 3-hydroxyanthranilic acid (3-HAA) (p = 0.06; [Formula: see text]= 0.15) and in the ratio of neurotoxic to neuroprotective metabolites were seen also only in the O-3 + TRAIN group. No changes in mood and IL-6 concentrations were observed in either group. Supplementation with n-3 PUFAs during endurance training has beneficial effects on Trp's neuroprotective metabolites.Trial registry: This study was registered at ClinicalTrials.gov with identifier NCT05520437 (14/07/2021 first trial registration and 2018/31/N/NZ7/02962 second trial registration).

An exploratory metabolomic comparison of participants with fast or absent functional progression from 2CARE, a randomized, double-blind clinical trial in Huntington's disease

Huntington's disease (HD) is increasingly recognized for diverse pathology outside of the nervous system. To describe the biology of HD in relation to functional progression, we previously analyzed the plasma and CSF metabolome in a cross-sectional study of participants who had various degrees of functional impairment. Here, we carried out an exploratory study in plasma from HD individuals over a 3-year time frame to assess whether differences exist between those with fast or absent clinical progression. There were more differences in circulating metabolite levels for fast progressors compared to absent progressors (111 vs 20, nominal p < 0.05). All metabolite changes in faster progressors were decreases, whereas some metabolite concentrations increased in absent progressors. Many of the metabolite levels that decreased in the fast progressors were higher at Screening compared to absent progressors but ended up lower by Year 3. Changes in faster progression suggest greater oxidative stress and inflammation (kynurenine, diacylglycerides, cysteine), disturbances in nitric oxide and urea metabolism (arginine, citrulline, ornithine, GABR), lower polyamines (putrescine and spermine), elevated glucose, and deficient AMPK signaling. Metabolomic differences between fast and absent progressors suggest the possibility of predicting functional decline in HD, and possibly delaying it with interventions to augment arginine, polyamines, and glucose regulation.

Ketamine - A New Antidepressant Drug with Anti-Inflammatory Properties

Ketamine is a new, potent and rapid-acting antidepressant approved for therapy of treatment-resistant depression, which has a different mechanism of action than currently-available antidepressant therapies. It owes its uniquely potent antidepressant properties to a complex mechanism of action, which currently remains unclear. However, it is thought that it acts by modulating the functioning of the glutamatergic system, which plays an important role in the process of neuroplasticity associated with depression. However, preclinical and clinical studies have also found ketamine to reduce inflammation, either directly or indirectly (by activating neuroprotective branches of the kynurenine pathway), among patients exhibiting higher levels of inflammation. Inflammation and immune system activation are believed to play key roles in the development and course of depression. Therefore, the present work examines the role of the antidepressant effect of ketamine and its anti-inflammatory properties in the treatment of depression. SIGNIFICANCE STATEMENT: The present work examines the relationship between the antidepressant effect of ketamine and its anti-inflammatory properties, and the resulting benefits in treatment-resistant depression (TRD). The antidepressant mechanism of ketamine remains unclear, and there is an urgent need to develop new therapeutic strategies for treatment of depression, particularly TRD.

The Neurochemistry of Depression: The Good, The Bad and The Ugly

A large constellation of experimental evidence suggests that neuroinflammation is involved in the onset of depression and neurodegenerative disorders. Many studies have shown impairments in tryptophan metabolism, the major pathway for the synthesis of serotonin, the mood regulating neurotransmitter. This article reviews the various metabolites generated in the competing pathways of tryptophan metabolism including the kynurenine pathway. Increased synthesis of the neurotoxic compound quinolinic acid occurs at the expense of the synthesis of the neuroprotective metabolite kynurenic acid. This shift in equilibrium plays a critical role in the induction of oxidative stress, neuroinflammation, and neurotoxicity. Sufficient protein intake with adequate amounts of tryptophan along with dietary antioxidants and flavonoids may offer protection against major depressive and neurodegenerative disorders.

Triphenyl phosphate disrupts placental tryptophan metabolism by activating MAOA/ROS/NFκB

Triphenyl phosphate (TPhP) is an organophosphate flame retardant widely distributed in the environment. The neurodevelopmental toxicity of TPhP has been observed in animals and humans. Previously, we found that prenatal TPhP exposure disturbed placental tryptophan metabolism, impaired neurodevelopment in male offspring, and induced abnormal neurobehavior; however, the underlying mechanisms are unknown. In this study, using the trophoblast cell line JEG-3, we found that TPhP altered gene and protein expression in the tryptophan metabolism pathway, inhibited the tryptophan-serotonin pathway, and activated the tryptophan-kynurenine pathway. Meanwhile, TPhP induced oxidative stress by activating monoamine oxidase A (MAOA), promoting inflammatory factors including nuclear factor kappa-B (NFκB), interleukin-6, and tumor necrosis factor α. The NFκB inhibitor sulfasalazine could alleviate the effects of TPhP on tryptophan metabolism disturbance. The MAOA inhibitor clorgyline or the antioxidant N-acetylcysteine can mitigate oxidative stress and eliminate TPhP-induced inflammatory factors and tryptophan metabolism disturbances. The data above suggest that TPhP disturbed tryptophan metabolism by activating NFκB through MAOA-mediated oxidative stress. Finally, using the mouse intrauterine exposure model, the results confirmed that TPhP induced oxidative stress, activated inflammatory factors, disturbed tryptophan metabolism, and increased the levels of the tryptophan metabolites serotonin, kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid in the placenta during the second trimester of pregnancy. Overall, TPhP can disturb placental tryptophan metabolism by activating the inflammatory factor NFκB, which was induced by MAOA-induced oxidative stress. The results of this study confirm that indirect exposure to xenobiotic compounds at an early life stage can impair offspring development and provide a novel perspective on the neurodevelopmental toxicity of TPhP.

Systems biology and machine learning approaches identify metabolites that influence dietary lifespan and healthspan responses across flies and humans

Dietary restriction (DR) is a potent method to enhance lifespan and healthspan, but individual responses are influenced by genetic variations. Understanding how metabolism-related genetic differences impact longevity and healthspan are unclear. To investigate this, we used metabolites as markers to reveal how different genotypes respond to diet to influence longevity and healthspan traits. We analyzed data from Drosophila Genetic Reference Panel strains raised under AL and DR conditions, combining metabolomic, phenotypic, and genome-wide information. Employing two computational methods across species-random forest modeling within the DGRP and Mendelian randomization in the UK Biobank-we pinpointed key traits with cross-species relevance that influence lifespan and healthspan. Notably, orotate was linked to parental age at death in humans and counteracted DR effects in flies, while threonine extended lifespan, in a strain- and sex-specific manner. Thus, utilizing natural genetic variation data from flies and humans, we employed a systems biology approach to elucidate potential therapeutic pathways and metabolomic targets for diet-dependent changes in lifespan and healthspan.

Effect of Quinolinic Acid on Behavior, Morphology, and Expression of Inflammatory/oxidative Status in Rats' Striatum: Is Coenzyme Q10 a Good Protector?

Quinolinic acid (QUIN) is a toxic compound with pro-oxidant, pro-inflammatory, and pro-apoptotic actions found at high levels in the central nervous system (CNS) in several pathological conditions. Due to the toxicity of QUIN, it is important to evaluate strategies to protect against the damage caused by this metabolite in the brain. In this context, coenzyme Q10 (CoQ10) is a provitamin present in the mitochondria with a protective role in cells through several mechanisms of action. Based on these, the present study was aimed at evaluating the possible neuroprotective role of CoQ10 against damage caused by QUIN in the striatum of young Wistar rats. Twenty-one-day-old rats underwent a 10-day pretreatment with CoQ10 or saline (control) intraperitoneal injections and on the 30th day of life received QUIN intrastriatal or saline (control) administration. The animals were submitted to behavior tests or euthanized, and the striatum was dissected to neurochemical studies. Results showed that CoQ10 was able to prevent behavioral changes (the open field, object recognition, and pole test tasks) and neurochemical parameters (alteration in the gene expression of IL-1β, IL-6, SOD, and GPx, as well as in the immunocontent of cytoplasmic Nrf2 and nuclear p-Nf-κβ) caused by QUIN. These findings demonstrate the promising therapeutic effects of CoQ10 against QUIN toxicity.

Higher concentrations of kynurenic acid in CSF are associated with the slower clinical progression of Alzheimer's disease

INTRODUCTION

The kynurenine pathway's (KP) malfunction is closely related to Alzheimer's disease (AD), for antagonistic kynurenic acid (KA) and agonistic quinolinic acid act on the N-methyl-D-aspartate receptor, a possible therapeutic target in treating AD.

METHODS

In our longitudinal case-control study, KP metabolites in the cerebrospinal fluid were analyzed in 311 patients with AD and 105 cognitively unimpaired controls.

RESULTS

Patients with AD exhibited higher concentrations of KA (β = 0.18, P < 0.01) and picolinic acid (β = 0.20, P < 0.01) than the controls. KA was positively associated with tau pathology (β = 0.29, P < 0.01), and a higher concentration of KA was associated with the slower progression of dementia.

DISCUSSION

The higher concentrations of neuroprotective metabolites KA and picolinic acid suggest that the activation of the KP's neuroprotective branch is an adaptive response in AD and may be a promising target for intervention and treatment. Highlights Patients with Alzheimer's disease (AD) exhibited higher concentrations of kynurenic acid and picolinic acid than controls. Higher concentrations of kynurenic acid were associated with slower progression of AD. Potential neurotoxic kynurenines were not increased among patients with AD. Activation of the kynurenine pathway's neuroprotective branch may be an adaptive response in AD.

Hepatocyte nuclear factor 4α mediated quinolinate phosphoribosylltransferase (QPRT) expression in the kidney facilitates resilience against acute kidney injury

Nicotinamide adenine dinucleotide (NAD+) levels decline in experimental models of acute kidney injury (AKI). Attenuated enzymatic conversion of tryptophan to NAD+ in tubular epithelium may contribute to adverse cellular and physiological outcomes. Mechanisms underlying defense of tryptophan-dependent NAD+ production are incompletely understood. Here we show that regulation of a bottleneck enzyme in this pathway, quinolinate phosphoribosyltransferase (QPRT) may contribute to kidney resilience. Expression of QPRT declined in two unrelated models of AKI. Haploinsufficient mice developed worse outcomes compared to littermate controls whereas novel, conditional gain-of-function mice were protected from injury. Applying these findings, we then identified hepatocyte nuclear factor 4 alpha (HNF4α) as a candidate transcription factor regulating QPRT expression downstream of the mitochondrial biogenesis regulator and NAD+ biosynthesis inducer PPARgamma coactivator-1-alpha (PGC1α). This was verified by chromatin immunoprecipitation. A PGC1α - HNF4α -QPRT axis controlled NAD+ levels across cellular compartments and modulated cellular ATP. These results propose that tryptophan-dependent NAD+ biosynthesis via QPRT and induced by HNF4α may be a critical determinant of kidney resilience to noxious stressors.

High-Protein Supplementation and Neuromuscular Electric Stimulation after Aneurysmal Subarachnoid Hemorrhage Increases Systemic Amino Acid and Oxidative Metabolism: A Plasma Metabolomics Approach

Background The INSPIRE randomized clinical trial demonstrated that a high protein diet (HPRO) combined with neuromuscular electrical stimulation (NMES) attenuates muscle atrophy and may improve functional outcomes after aSAH. Using an untargeted metabolomics approach, we sought to identify specific metabolites mediating these effects. Methods Blood samples were collected from subjects on admission prior to randomization to either standard of care (SOC; N=12) or HPRO+NMES (N=12) and at 7 days as part of the INSPIRE protocol. Untargeted metabolomics were performed for each plasma sample. Paired fold changes were calculated for each metabolite among subjects in the HPRO+NMES group at baseline and 7 days after intervention. Changes in metabolites from baseline to 7 days were compared for the HPRO+NMES and SOC groups. Sparse partial least squared discriminant analysis (sPLS-DA) identified metabolites discriminating each group. Pearson's correlation coefficients were calculated between each metabolite and total protein per day, nitrogen balance, and muscle volume Multivariable models were developed to determine associations between each metabolite and muscle volume. Results A total of 18 unique metabolites were identified including pre and post treatment and differentiating SOC vs HPRO+NMES. Of these, 9 had significant positive correlations with protein intake: N-acetylserine (ρ=0.61, P =1.56x10 -3 ), N-acetylleucine (ρ=0.58, P =2.97x10 -3 ), β-hydroxyisovaleroylcarnitine (ρ=0.53, P =8.35x10 -3 ), tiglyl carnitine (ρ=0.48, P =0.0168), N-acetylisoleucine (ρ=0.48, P =0.0183), N-acetylthreonine (ρ=0.47, P =0.0218), N-acetylkynurenine (ρ=0.45, P =0.0263), N-acetylvaline (ρ=0.44, P =0.0306), and urea (ρ=0.43, P =0.0381). In multivariable regression models, N-acetylleucine was significantly associated with preserved temporalis [OR 1.08 (95%CI 1.01, 1.16)] and quadricep [OR 1.08 (95%CI 1.02, 1.15)] muscle volume. Quinolinate was also significantly associated with preserved temporalis [OR 1.05 (95%CI 1.01, 1.09)] and quadricep [OR 1.04 (95%CI 1.00, 1.07)] muscle volume. N-acetylserine, N-acetylcitrulline, and b-hydroxyisovaleroylcarnitine were also associated with preserved temporalis or quadricep volume. Conclusions Metabolites defining the HPRO+NMES intervention mainly consisted of amino acid derivatives. These metabolites had strong correlations with protein intake and were associated with preserved muscle volume.

Nutritional considerations in major depressive disorder: current evidence and functional testing for clinical practice

Depression is a multifaceted condition with diverse underlying causes. Several contributing and inter-related factors such as genetic, nutritional, neurological, physiological, gut-brain-axis, metabolic and psychological stress factors play a role in the pathophysiology of depression. This review aims to highlight the role that nutritional factors play in the aetiology of depression. Secondly, we discuss the biomedical and functional pathology tests which measure these factors, and the current evidence supporting their use. Lastly, we make recommendations on how practitioners can incorporate the latest evidence-based research findings into clinical practice. This review highlights that diet and nutrition greatly affect the pathophysiology of depression. Nutrients influence gene expression, with folate and vitamin B12 playing vital roles in methylation reactions and homocysteine regulation. Nutrients are also involved in the tryptophan/kynurenine pathway and the expression of brain-derived neurotrophic factor (BDNF). Additionally, diet influences the hypothalamic-pituitary-adrenal (HPA) response and the composition and diversity of the gut microbiome, both of which have been implicated in depression. A comprehensive dietary assessment, combined with appropriate evaluation of biochemistry and blood pathology, may help uncover contributing factors to depressive symptoms. By employing such an approach, a more targeted and personalised treatment strategy can be devised, ultimately leading to improved patient outcomes.

Complete spectrum of adverse events associated with chimeric antigen receptor (CAR)-T cell therapies

Chimeric antigen receptor (CAR)-T cell therapies have been approved by FDA to treat relapsed or refractory hematological malignancies. However, the adverse effects of CAR-T cell therapies are complex and can be challenging to diagnose and treat. In this review, we summarize the major adverse events, including cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), and CAR T-cell associated HLH (carHLH), and discuss their pathophysiology, symptoms, grading, and diagnosis systems, as well as management. In a future outlook, we also provide an overview of measures and modifications to CAR-T cells that are currently being explored to limit toxicity.

The complexity of nicotinamide adenine dinucleotide (NAD), hypoxic, and aryl hydrocarbon receptor cell signaling in chronic kidney disease

Early-stage detection of chronic kidney diseases (CKD) is important to treatment that may slow and occasionally halt CKD progression. CKD of diverse etiologies share similar histologic patterns of glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Macro-vascular disease and micro-vascular disease promote tissue ischemia, contributing to injury. Tissue ischemia promotes hypoxia, and this in turn activates the hypoxia-inducible transcription factors (HIFs). HIF-1α and HIF-2α, share a dimer partner, HIF-1β, with the aryl hydrocarbon receptor (AHR) and are each activated in CKD and associated with kidney cellular nicotinamide adenine dinucleotide (NAD) depletion. The Preiss-Handler, salvage, and de novo pathways regulate NAD biosynthesis and gap-junctions regulate NAD cellular retention. In the Preiss-Handler pathway, niacin forms NAD. Niacin also exhibits crosstalk with HIF and AHR cell signals in the regulation of insulin sensitivity, which is a complication in CKD. Dysregulated enzyme activity in the NAD de novo pathway increases the levels of circulating tryptophan metabolites that activate AHR, resulting in poly-ADP ribose polymerase activation, thrombosis, endothelial dysfunction, and immunosuppression. Therapeutically, metabolites from the NAD salvage pathway increase NAD production and subsequent sirtuin deacetylase activity, resulting in reduced activation of retinoic acid-inducible gene I, p53, NF-κB and SMAD2 but increased activation of FOXO1, PGC-1α, and DNA methyltransferase-1. These post-translational responses may also be initiated through non-coding RNAs (ncRNAs), which are additionally altered in CKD. Nanoparticles traverse biological systems and can penetrate almost all tissues as disease biomarkers and drug delivery carriers. Targeted delivery of non-coding RNAs or NAD metabolites with nanoparticles may enable the development of more effective diagnostics and therapies to treat CKD.

The possible role of quinolinic acid as a predictive marker in patients with SARS-CoV-2

BACKGROUND AND AIMS

Quinolinic acid (QA) is a metabolite of the kynurenine pathway, which is activated by inflammatory stimuli during viral infection. We investigated the role of QA in patients infected with SARS-CoV-2, particularly its prognostic value for survival.

METHODS

Overall, 104 unvaccinated inpatients were included, divided into a survival (N = 80) and a deceased group (N = 24). Plasma levels of tryptophan, kynurenine, QA, C-reactive protein (CRP) and procalcitonin (PCT) were measured on admission and after seven days. The QA/TRP ratio and the relative differences between the measurements for QA (QA-Diff) and QA/TRP (Diff-QA/TRP) were calculated.

RESULTS

Among the kynurenine pathway markers, QA-Diff showed the highest discriminatory power for the survival prognosis (Youden index 0.467, cut-off -1.3 %, AUC 0.733, p < 0.001, sensitivity 0.79, specificity 0.675). Among the inflammatory markers, CRP showed the highest discriminatory power (Youden index 0.533, cut-off 25.0 mg/L, AUC 0.794, p < 0.001, sensitivity 0.958, specificity 0.575). A significant correlation between QA and PCT was found on admission and after one week (Spearman's rho 0.455 and 0.539, all p-values < 0.001).

CONCLUSIONS

QA may serve as prognostic marker for survival in patients with SARS-CoV-2. The repeated measurements during the first week of the disease may enhance the prognostic power.

COVID-19. Biology, pathophysiology, and immunology: a pathologist view

Even if the SARS-CoV-2 pandemic has been declared over, several risks and clinical problems remain to be faced, including long-COVID sequelae and possible outbreaks of pathogenic variants. Intense research on COVID-19 has provided in these few years a striking amount of data covering different fields and disciplines, which can help to provide a knowledge shield against new potential infective spreads, and may also potentially be applied to other fields of medicine, including oncology and neurology. Nevertheless, areas of uncertainty still remain regarding the pathogenic mechanisms that subtend the multifaceted manifestations of the disease. To better clarify the pathogenesis of the disease, a systematic multidisciplinary evaluation of the many mechanisms involved in COVID-19 is mandatory, including clinical, physiological, radiological, immunological and pathological studies. In COVID-19 syndrome the pathological studies have been mainly performed on autopsy cases, and only a few studies are available on biopsies. Nevertheless, these studies have provided relevant information that can substantially contribute to decipher the complex scenario characterizing the different forms of COVID-19 and long-COVID-19. In this review the data provided by pathological investigations are recapitulated and discussed, in the light of different hypothesis and data provided by clinical, physiological and immunological data.

Oligofructose alone and in combination with 2'fucosyllactose induces physiologically relevant changes in γ-aminobutyric acid and organic acid production compared to sole 2'fucosyllactose supplementation: an in vitro study

We explored the potential for the prebiotic oligofructose and prebiotic candidate 2'fucosyllactose, alone and in combination (50:50 blend) to induce physiologically relevant increases in neurotransmitter (γ-aminobutyric acid, serotonin, tryptophan, and dopamine) and organic acid (acetate, propionate, butyrate, lactate, and succinate) production as well as microbiome changes using anaerobic pH-controlled in vitro batch culture fermentations over 48 h. Changes in organic acid and neurotransmitter production were assessed by gas chromatography and liquid chromatography and, bacterial enumeration using fluorescence in situ hybridization, respectively. Both oligofructose and oligofructose/2'fucosyllactose combination fermentations induced physiologically relevant concentrations of γ-aminobutyric acid, acetate, propionate, butyrate, and succinate at completion (all P ≤ .05). A high degree of heterogeneity was seen amongst donors in both neurotransmitter and organic acid production in sole 2'FL fermentations suggesting a large responder/nonresponder status exists. Large increases in Bifidobacterium, Lactobacillus, and Bacteroides numbers were detected in oligofructose fermentation, smallest increases being detected in 2'fucosyllactose fermentation. Bacterial numbers in the combined oligofructose/2'fucosyllactose fermentation were closer to that of sole oligofructose. Our results indicate that oligofructose and oligofructose/2'fucosyllactose in combination have the potential to induce physiologically relevant increases in γ-aminobutyric and organic acid production along with offsetting the heterogenicity seen in response to sole 2'fucosyllactose supplementation.

CSF neopterin and quinolinic acid are biomarkers of neuroinflammation and neurotoxicity in FIRES and other infection-triggered encephalopathy syndromes

OBJECTIVE

Infection-triggered encephalopathy syndromes (ITES) are potentially devastating neuroinflammatory conditions. Although some ITES syndromes have recognisable MRI neuroimaging phenotypes, there are otherwise few biomarkers of disease. Early detection to enable immune modulatory treatments could improve outcomes.

METHODS

We measured CSF neopterin, quinolinic acid, kynurenine and kynurenine/tryptophan ratio using a liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) system. The CSF of 18 children with ITES were compared with acute encephalitis (n = 20), and three control groups, namely epilepsy (n = 20), status epilepticus (n = 18) and neurogenetic controls (n = 20).

RESULTS

The main ITES phenotypes in 18 patients were acute encephalopathy with biphasic seizures and late restricted diffusion (AESD, n = 4), febrile infection-related epilepsy syndrome (FIRES n = 4) and other ITES phenotypes. Influenza A was the most common infectious trigger (n = 5), and 50% of patients had a preceding notable neurodevelopmental or family history. CSF neopterin, quinolinic acid and kynurenine were elevated in ITES group compared to the three control groups (all p < 0.0002). The ROC (area under curve) for CSF neopterin (99.3%, CI 98.1-100) was significantly better than CSF pleocytosis (87.3% CI 76.4-98.2) (p = 0.028). Elevated CSF neopterin could discriminate ITES from other causes of seizures, status epilepticus and febrile status epilepticus (all p < 0.0002). The elevated CSF metabolites normalised during longitudinal testing in two patients with FIRES.

INTERPRETATION

CSF neopterin and quinolinic acid are neuroinflammatory and excitotoxic metabolites. This CSF metabolomic inflammatory panel can discriminate ITES from other causes of new onset seizures or status epilepticus, and rapid results (4 h) may facilitate early immune modulatory therapy.

Molecular signalling during cross talk between gut brain axis regulation and progression of irritable bowel syndrome: A comprehensive review

Irritable bowel syndrome (IBS) is a chronic functional disorder which alters gastrointestinal (GI) functions, thus leading to compromised health status. Pathophysiology of IBS is not fully understood, whereas abnormal gut brain axis (GBA) has been identified as a major etiological factor. Recent studies are suggestive for visceral hyper-sensitivity, altered gut motility and dysfunctional autonomous nervous system as the main clinical abnormalities in IBS patients. Bidirectional signalling interactions among these abnormalities are derived through various exogenous and endogenous factors, such as microbiota population and diversity, microbial metabolites, dietary uptake, and psychological abnormalities. Strategic efforts focused to study these interactions including probiotics, antibiotics and fecal transplantations in normal and germ-free animals are clearly suggestive for the pivotal role of gut microbiota in IBS etiology. Additionally, neurotransmitters act as communication tools between enteric microbiota and brain functions, where serotonin (5-hydroxytryptamine) plays a key role in pathophysiology of IBS. It regulates GI motility, pain sense and inflammatory responses particular to mucosal and brain activity. In the absence of a better understanding of various interconnected crosstalks in GBA, more scientific efforts are required in the search of novel and targeted therapies for the management of IBS. In this review, we have summarized the gut microbial composition, interconnected signalling pathways and their regulators, available therapeutics, and the gaps needed to fill for a better management of IBS.

The kynurenine pathway in traumatic brain injuries and concussion

Up to 10 million people per annum experience traumatic brain injury (TBI), 80-90% of which are categorized as mild. A hit to the brain can cause TBI, which can lead to secondary brain injuries within minutes to weeks after the initial injury through unknown mechanisms. However, it is assumed that neurochemical changes due to inflammation, excitotoxicity, reactive oxygen species, etc., that are triggered by TBI are associated with the emergence of secondary brain injuries. The kynurenine pathway (KP) is an important pathway that gets significantly overactivated during inflammation. Some KP metabolites such as QUIN have neurotoxic effects suggesting a possible mechanism through which TBI can cause secondary brain injury. That said, this review scrutinizes the potential association between KP and TBI. A more detailed understanding of the changes in KP metabolites during TBI is essential to prevent the onset or at least attenuate the severity of secondary brain injuries. Moreover, this information is crucial for the development of biomarker/s to probe the severity of TBI and predict the risk of secondary brain injuries. Overall, this review tries to fill the knowledge gap about the role of the KP in TBI and highlights the areas that need to be studied.

Kynurenine promotes Calcitonin secretion and reduces cortisol in the Japanese flounder Paralichthys olivaceus

Deep ocean water (DOW) exerts positive effects on the growth of marine organisms, suggesting the presence of unknown component(s) that facilitate their aquaculture. We observed that DOW suppressed plasma cortisol (i.e., a stress marker) concentration in Japanese flounder (Paralichthys olivaceus) reared under high-density condition. RNA-sequencing analysis of flounder brains showed that when compared to surface seawater (SSW)-reared fish, DOW-reared fish had lower expression of hypothalamic (i.e., corticotropin-releasing hormone) and pituitary (i.e., proopiomelanocortin, including adrenocorticotropic hormone) hormone-encoding genes. Moreover, DOW-mediated regulation of gene expression was linked to decreased blood cortisol concentration in DOW-reared fish. Our results indicate that DOW activated osteoblasts in fish scales and facilitated the production of Calcitonin, a hypocalcemic hormone that acts as an analgesic. We then provide evidence that the Calcitonin produced is involved in the regulatory network of genes controlling cortisol secretion. In addition, the indole component kynurenine was identified as the component responsible for osteoblast activation in DOW. Furthermore, kynurenine increased plasma Calcitonin concentrations in flounders reared under high-density condition, while it decreased plasma cortisol concentration. Taken together, we propose that kynurenine in DOW exerts a cortisol-reducing effect in flounders by facilitating Calcitonin production by osteoblasts in the scales.

Chronic stress, neuroinflammation, and depression: an overview of pathophysiological mechanisms and emerging anti-inflammatories

In a subset of patients, chronic exposure to stress is an etiological risk factor for neuroinflammation and depression. Neuroinflammation affects up to 27% of patients with MDD and is associated with a more severe, chronic, and treatment-resistant trajectory. Inflammation is not unique to depression and has transdiagnostic effects suggesting a shared etiological risk factor underlying psychopathologies and metabolic disorders. Research supports an association but not necessarily a causation with depression. Putative mechanisms link chronic stress to dysregulation of the HPA axis and immune cell glucocorticoid resistance resulting in hyperactivation of the peripheral immune system. The chronic extracellular release of DAMPs and immune cell DAMP-PRR signaling creates a feed forward loop that accelerates peripheral and central inflammation. Higher plasma levels of inflammatory cytokines, most consistently interleukin IL-1β, IL-6, and TNF-α, are correlated with greater depressive symptomatology. Cytokines sensitize the HPA axis, disrupt the negative feedback loop, and further propagate inflammatory reactions. Peripheral inflammation exacerbates central inflammation (neuroinflammation) through several mechanisms including disruption of the blood-brain barrier, immune cellular trafficking, and activation of glial cells. Activated glial cells release cytokines, chemokines, and reactive oxygen and nitrogen species into the extra-synaptic space dysregulating neurotransmitter systems, imbalancing the excitatory to inhibitory ratio, and disrupting neural circuitry plasticity and adaptation. In particular, microglial activation and toxicity plays a central role in the pathophysiology of neuroinflammation. Magnetic resonance imaging (MRI) studies most consistently show reduced hippocampal volumes. Neural circuitry dysfunction such as hypoactivation between the ventral striatum and the ventromedial prefrontal cortex underlies the melancholic phenotype of depression. Chronic administration of monoamine-based antidepressants counters the inflammatory response, but with a delayed therapeutic onset. Therapeutics targeting cell mediated immunity, generalized and specific inflammatory signaling pathways, and nitro-oxidative stress have enormous potential to advance the treatment landscape. Future clinical trials will need to include immune system perturbations as biomarker outcome measures to facilitate novel antidepressant development. In this overview, we explore the inflammatory correlates of depression and elucidate pathomechanisms to facilitate the development of novel biomarkers and therapeutics.

A unified model of the biology of peripartum depression

Peripartum depression (PPD) is a prevalent and debilitating disorder that adversely affects the development of mothers and infants. Recently, there has been a plea for increased mental health screening during the peripartum period; however, currently, there is no accurate screening tool to identify women at risk of PPD. In addition, some women do not respond to current treatment schemes and develop treatment-resistant depression. The current perspective aims to propose a unified understanding of the biological underpinnings of PPD (UmPPD) that considers the heterogeneity in the onset, symptoms cluster, and severity of PPD. Such a model could promote basic and applied research on PPD and suggest new treatment avenues. The central hub of the model is the kynurenine pathway (KP) and the KP-serotonin ratio. The forces and specific processes at play that cause an imbalance within the KP and between KP and serotonin are inflammation, stress, reproductive hormones (especially estradiol and progesterone), and oxytocin. UmPPD predicts that the most severe PPD would comprise prolonged inflammation, ongoing or multiple stressors, excessive estrogen, progesterone resistance, and avoidance of breastfeeding, skin-to-skin contact, and social proximity. These factors would be associated with a higher likelihood of developing PPD, early onset, and more significant symptom severity. In addition, subtypes of PPD would consist of different compositions and expressions of these components, with one central common factor. UmPPD could aid in directing future research and possibly detecting critical processes that could help discover, develop, and utilize novel treatments for PPD.

CSF neopterin, quinolinic acid and kynurenine/tryptophan ratio are biomarkers of active neuroinflammation

BACKGROUND

Defining the presence of acute and chronic brain inflammation remains a challenge to clinicians due to the heterogeneity of clinical presentations and aetiologies. However, defining the presence of neuroinflammation, and monitoring the effects of therapy is important given its reversible and potentially damaging nature. We investigated the utility of CSF metabolites in the diagnosis of primary neuroinflammatory disorders such as encephalitis and explored the potential pathogenic role of inflammation in epilepsy.

METHODS

Cerebrospinal fluid (CSF) collected from 341 paediatric patients (169 males, median age 5.8 years, range 0.1-17.1) were examined. The patients were separated into a primary inflammatory disorder group (n = 90) and epilepsy group (n = 80), who were compared with three control groups including neurogenetic and structural (n = 76), neurodevelopmental disorders, psychiatric and functional neurological disorders (n = 63), and headache (n = 32).

FINDINGS

There were statistically significant increases of CSF neopterin, kynurenine, quinolinic acid and kynurenine/tryptophan ratio (KYN/TRP) in the inflammation group compared to all control groups (all p < 0.0003). As biomarkers, at thresholds with 95% specificity, CSF neopterin had the best sensitivity for defining neuroinflammation (82%, CI 73-89), then quinolinic acid (57%, CI 47-67), KYN/TRP ratio (47%, CI 36-56) and kynurenine (37%, CI 28-48). CSF pleocytosis had sensitivity of 53%, CI 42-64). The area under the receiver operating characteristic curve (ROC AUC) of CSF neopterin (94.4% CI 91.0-97.7%) was superior to that of CSF pleocytosis (84.9% CI 79.5-90.4%) (p = 0.005). CSF kynurenic acid/kynurenine ratio (KYNA/KYN) was statistically decreased in the epilepsy group compared to all control groups (all p ≤ 0.0003), which was evident in most epilepsy subgroups.

INTERPRETATION

Here we show that CSF neopterin, kynurenine, quinolinic acid and KYN/TRP are useful diagnostic and monitoring biomarkers of neuroinflammation. These findings provide biological insights into the role of inflammatory metabolism in neurological disorders and provide diagnostic and therapeutic opportunities for improved management of neurological diseases.

FUNDING

Financial support for the study was granted by Dale NHMRC Investigator grant APP1193648, University of Sydney, Petre Foundation, Cerebral Palsy Alliance and Department of Biochemistry at the Children's Hospital at Westmead. Prof Guillemin is funded by NHMRC Investigator grant APP 1176660 and Macquarie University.

Inflammation, stress and depression: An exploration of ketamine's therapeutic profile

Well-established animal models of depression have described a proximal relationship between stress and central nervous system (CNS) inflammation - a relationship mirrored in the peripheral inflammatory biomarkers of individuals with depression. Evidence also suggests that stress-induced proinflammatory states can contribute to the neurobiology of treatment-resistant depression. Interestingly, ketamine, a rapid-acting antidepressant, can partially exert its therapeutic effects via anti-inflammatory actions on the hypothalamic-pituitary adrenal (HPA) axis, the kynurenine pathway or by cytokine suppression. Further investigations into the relationship between ketamine, inflammation and stress could provide insight into ketamine's unique therapeutic mechanisms and stimulate efforts to develop rapid-acting, anti-inflammatory-based antidepressants.

Pharmacological Characterization of [18F]-FNM and Evaluation of NMDA Receptors Activation in a Rat Brain Injury Model

PURPOSE

NMDA receptors (NMDARs) dysfunction plays a central role in the physiopathology of psychiatric and neurodegenerative disorders whose mechanisms are still poorly understood. The development of a PET (positron emission tomography) tracer able to selectively bind to the NMDARs intra-channel PCP site may make it possible to visualize NMDARs in an open and active state. We describe the in vitro pharmacological characterization of [¹⁸F]-fluoroethylnormemantine ([¹⁸F]-FNM) and evaluate its ability to localize activated NMDA receptors in a rat preclinical model of excitotoxicity.

PROCEDURES

The affinity of the non-radioactive analog for the intra-channel PCP site was determined in a radioligand competition assay using [³H]TCP ([³H]N-(1-[thienyl]cyclohexyl)piperidine) on rat brain homogenates. Selectivity was also investigated by the displacement of specific radioligands targeting various cerebral receptors. In vivo brain lesions were performed using stereotaxic quinolinic acid (QA) injections in the left motor area (M1) of seven Sprague Dawley rats. Each rat was imaged with a microPET/CT camera, 40 min after receiving a dose of 30 MBq + / - 20 of [¹⁸F]-FNM, 24 and 72 h after injury. Nine non-injured rats were also imaged using the same protocol.

RESULTS

FNM displayed IC₅₀ value of 13.0 ± 8.9 µM in rat forebrain homogenates but also showed significant bindings on opioid receptors. In the frontal and left somatosensory areas, [¹⁸F]FNM PET detected a mean of 37% and 41% increase in [¹⁸F]FNM uptake (p < 0,0001) 24 and 72 h after QA stereotaxic injection, respectively, compared to the control group.

CONCLUSIONS

In spite of FNM's poor affinity for NMDAR PCP site, this study supports the ability of this tracer to track massive activation of NMDARs in neurological diseases.

Ketamine and serotonergic psychedelics: An update on the mechanisms and biosignatures underlying rapid-acting antidepressant treatment

The discovery of ketamine as a rapid-acting antidepressant spurred significant research to understand its underlying mechanisms of action and to identify other novel compounds that may act similarly. Serotonergic psychedelics (SPs) have shown initial promise in treating depression, though the challenge of conducting randomized controlled trials with SPs and the necessity of long-term clinical observation are important limitations. This review summarizes the similarities and differences between the psychoactive effects associated with both ketamine and SPs and the mechanisms of action of these compounds, with a focus on the monoaminergic, glutamatergic, gamma-aminobutyric acid (GABA)-ergic, opioid, and inflammatory systems. Both molecular and neuroimaging aspects are considered. While their main mechanisms of action differ-SPs increase serotonergic signaling while ketamine is a glutamatergic modulator-evidence suggests that the downstream mechanisms of action of both ketamine and SPs include mechanistic target of rapamycin complex 1 (mTORC1) signaling and downstream GABAA receptor activity. The similarities in downstream mechanisms may explain why ketamine, and potentially SPs, exert rapid-acting antidepressant effects. However, research on SPs is still in its infancy compared to the ongoing research that has been conducted with ketamine. For both therapeutics, issues with regulation and proper controls should be addressed before more widespread implementation. This article is part of the Special Issue on "Ketamine and its Metabolites".

Effect of pharmacological modulation of the kynurenine pathway on pain-related behavior and opioid analgesia in a mouse model of neuropathic pain

Dysfunction of the central nervous system are accompanied by changes in tryptophan metabolism, with the kynurenine pathway (KP) being the main route of its catabolism. Recently, KP metabolites, which are collectively called kynurenines, have become an area of intense research due to their ability to directly and indirectly affect a variety of classic neurotransmitter systems. However, the significance of KP in neuropathic pain is still poorly understood. Therefore, we designed several experiments to verify changes in the mRNA levels of KP enzymes in parallel with other factors related to this metabolic route after chronic constriction injury of the sciatic nerve (CCI model) in mice. The analysis revealed an increase in, Kmo, Kynu and Haoo mRNA levels in the spinal cord on the 7th day after CCI, while Kat1, Kat2, Tdo2, Ido2 and Qprt mRNA levels remain unchanged. Subsequent pharmacological studies provided evidence that modulation of KP by single intrathecal administration of 1-D-MT, UPF468 or L-kynurenine attenuates mechanical and thermal hypersensitivity and increases the effectiveness of selected opioids in mice as measured on day 7 after CCI. Moreover, our results provide the first evidence that the injection of L-kynurenine preceded by UPF468 (KMO inhibitor) is more effective at reducing hypersensitivity in animals with neuropathic pain. Importantly, L-kynurenine also exerts an analgesic effect after intravenous injections, which is enhanced by the administration of minocycline, an inhibitor of microglial activation. Additionally, L-kynurenine administered intrathecally and intravenously enhances analgesia evoked by all tested opioids (morphine, buprenorphine and oxycodone). Overall, our results indicate that the modulation of KP at different levels might be a new pharmacological tool in neuropathy management.

Butyrate ameliorates quinolinic acid-induced cognitive decline in obesity models

Obesity is a risk factor for neurodegenerative disease associated with cognitive dysfunction, including Alzheimer's disease. Low-grade inflammation is common in obesity, but the mechanism between inflammation and cognitive impairment in obesity is unclear. Accumulative evidence shows that quinolinic acid (QA), a neuroinflammatory neurotoxin, is involved in the pathogenesis of neurodegenerative processes. We investigated the role of QA in obesity-induced cognitive impairment and the beneficial effect of butyrate in counteracting impairments of cognition, neural morphology, and signaling. We show that in human obesity, there was a negative relationship between serum QA levels and cognitive function and decreased cortical gray matter. Diet-induced obese mice had increased QA levels in the cortex associated with cognitive impairment. At single-cell resolution, we confirmed that QA impaired neurons, altered the dendritic spine's intracellular signal, and reduced brain-derived neurotrophic factor (BDNF) levels. Using Caenorhabditis elegans models, QA induced dopaminergic and glutamatergic neuron lesions. Importantly, the gut microbiota metabolite butyrate was able to counteract those alterations, including cognitive impairment, neuronal spine loss, and BDNF reduction in both in vivo and in vitro studies. Finally, we show that butyrate prevented QA-induced BDNF reductions by epigenetic enhancement of H3K18ac at BDNF promoters. These findings suggest that increased QA is associated with cognitive decline in obesity and that butyrate alleviates neurodegeneration.

Cerebrospinal fluid quinolinic acid is strongly associated with delirium and mortality in hip-fracture patients

BACKGROUNDThe kynurenine pathway (KP) has been identified as a potential mediator linking acute illness to cognitive dysfunction by generating neuroactive metabolites in response to inflammation. Delirium (acute confusion) is a common complication of acute illness and is associated with increased risk of dementia and mortality. However, the molecular mechanisms underlying delirium, particularly in relation to the KP, remain elusive.METHODSWe undertook a multicenter observational study with 586 hospitalized patients (248 with delirium) and investigated associations between delirium and KP metabolites measured in cerebrospinal fluid (CSF) and serum by targeted metabolomics. We also explored associations between KP metabolites and markers of neuronal damage and 1-year mortality.RESULTSIn delirium, we found concentrations of the neurotoxic metabolite quinolinic acid in CSF (CSF-QA) (OR 2.26 [1.78, 2.87], P < 0.001) to be increased and also found increases in several other KP metabolites in serum and CSF. In addition, CSF-QA was associated with the neuronal damage marker neurofilament light chain (NfL) (β 0.43, P < 0.001) and was a strong predictor of 1-year mortality (HR 4.35 [2.93, 6.45] for CSF-QA ≥ 100 nmol/L, P < 0.001). The associations between CSF-QA and delirium, neuronal damage, and mortality remained highly significant following adjustment for confounders and multiple comparisons.CONCLUSIONOur data identified how systemic inflammation, neurotoxicity, and delirium are strongly linked via the KP and should inform future delirium prevention and treatment clinical trials that target enzymes of the KP.FUNDINGNorwegian Health Association and South-Eastern Norway Regional Health Authorities.

The kynurenine pathway implicated in patient delirium: possible indications for indoleamine 2,3 dioxygenase inhibitors

Tryptophan (Trp) metabolism plays a central role in sleep, mood, and immune system regulation. The kynurenine pathway (KP), which is regulated by the enzymes tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3 dioxygenase (IDO), which catalyze the conversion of Trp to kynurenine (Kyn), facilitates immune regulation and influences neurocognition. Notably, Kyn metabolites bind the N-methyl-d-aspartate receptor (NMDAR), essential for memory encoding, and in turn, cognition. Aberrant NMDAR activity through agonist binding influences excitability and cell death. In this issue of the JCI, Watne and authors demonstrate that KP pathway end products were elevated in the serum and the cerebrospinal fluid (CSF) of subjects with delirium. This observation provides insight regarding the basis of a variety of commonly observed clinical conditions including sundowning, abnormal sleep-wake cycles in hospitalized patients, neurodegenerative cognitive impairment, radiation-induced cognitive impairment, neurocognitive symptomatology related to COVID-19, and clinical outcomes observed in patients with CNS tumors, such as gliomas.

Systemic Activation of the Kynurenine Pathway in Graves` Disease with and without Ophthalmopathy

PURPOSE

To characterize the kynurenine pathway, activated during interferon-γ mediated inflammation and cellular (Th1-type) immunity, in Graves` disease (GD) patients with and without thyroid eye disease (TED).

METHODS

We analyzed 34 biomarkers by mass spectrometry in serum samples from 100 patients with GD (36 with TED) and 100 matched healthy controls. The analytes included 10 metabolites and three indices from the kynurenine pathway, six microbiota-derived metabolites, 10 B-vitamers and five serum proteins reflecting inflammation and kidney function.

RESULTS

GD patients showed significantly elevated levels of seven biomarkers compared with healthy controls (omega squared (ω2) > 0.06, P < 0.01). Out of these seven, the six biomarkers with the strongest effect size were all components of the kynurenine pathway. Factor analysis showed that biomarkers related to cellular immunity and the Th1 responses (3-hydroxykynurenine, kynurenine and quinolinic acid with the highest loading) were most strongly associated with GD. Further, a factor mainly reflecting acute phase response (CRP and serum amyloid A) showed weaker association with GD by factor analysis. There were no differences in biomarker levels between GD patients with and without TED.

CONCLUSION

This study supports activation of interferon-γ inflammation and Th1 cellular immunity in GD, but also a contribution of acute phase reactants. Our finding of no difference in systemic activation of the kynurenine pathway in GD patients with and without TED implies that the local Th1 immune response in the orbit is not reflected systemically.

Quinolinic acid catabolism is initiated by a novel four-component hydroxylase QuiA in Alcaligenes faecalis JQ191

Quinolinic acid (QA) is an essential nitrogen-containing aromatic heterocyclic compounds in organisms and it also acts as an important intermediate in chemical industry, which has strong neurotoxicity and cytotoxicity. The wide range of sources and applications caused the release and accumulation of QA in the environment which might poses a hazard to ecosystems and human health. However, few research on the degradation of QA by microorganisms and toxicity of QA and its metabolites were reported. Alcaligenes faecalis JQ191 could degrade QA but the genetic foundation of QA degradation has not been studied. In this study, the gene cluster quiA1A2A3A4 was identified from A. faecalis JQ191, which was responsible for the initial catabolism step of QA. The quiA1A2A3A4 gene cluster encodes a novel cytoplasmic four-component hydroxylase QuiA. The ¹H nuclear magnetic resonance indicated that QuiA catalyzed QA to 6-hydroxyquinolinic acid (6HQA) and the H₂¹⁸O-labeling analysis confirmed that the hydroxyl group incorporating into 6HQA was derived from water. Toxicity tests showed that the QA could approximately inhibit 20%-80% growth of Chlorella ellipsoidea, and 6HQA could relieve at least 50% QA growth inhibition of Chlorella ellipsoidea, indicating that the 6-hydroxylation of QA by QuiA is a detoxification process. This research provides new insights into the metabolism of QA by microorganism and potential application in the bioremediation of toxic pyridine derivatives-contaminated environments.

States of quinolinic acid excess in urine: A systematic review of human studies

Introduction

Quinolinic acid is an intermediate compound derived from the metabolism of dietary tryptophan. Its accumulation has been reported in patients suffering a broad spectrum of diseases and conditions. In this manuscript, we present the results of a systematic review of research studies assessing urinary quinolinic acid in health and disease.

Methods

We performed a literature review using PubMed, Cochrane, and Scopus databases of all studies reporting data on urinary quinolinic acid in human subjects from December 1949 to January 2022.

Results

Fifty-seven articles met the inclusion criteria. In most of the reported studies, compared to the control group, quinolinic acid was shown to be at increased concentration in urine of patients suffering from different diseases and conditions. This metabolite was also demonstrated to correlate with the severity of certain diseases including juvenile idiopathic inflammatory myopathies, graft vs. host disease, autism spectrum disorder, and prostate cancer. In critically ill patients, elevated quinolinic acid in urine predicted a spectrum of adverse outcomes including hospital mortality.

Conclusion

Quinolinic acid has been implicated in the pathophysiology of multiple conditions. Its urinary accumulation appears to be a feature of acute physiological stress and several chronic diseases. The exact significance of these findings is still under investigation, and further studies are needed to reveal the subsequent implications of this accumulation.

Moxibustion alleviates depression-like behavior in rats with Crohn's disease by inhibiting the kynurenine pathway metabolism in the gut-brain axis

Background

Moxibustion is a potential therapy for inflammatory bowel disease-related depression, but its specific mechanism of action is unclear. This study aimed to investigate the molecular mechanism by which moxibustion alleviates depressive behavior in rats with Crohn's disease (CD).

Methods

The CD rat model was established with 2,4,6-trinitrobenzenesulfonic acid. Treatment with moxibustion was applied to Tianshu (ST25, bilateral), Qihai (CV6), and Baihui (GV20) acupoints, and the effect of moxibustion was compared with that of the combination of moxibustion plus indoleamine-2,3-dioxygenase 1 (IDO1) inhibitor, 1-methyltryptophan (1-MT). The effects of moxibustion and moxibustion plus 1-MT combination on colonic inflammation and depressive behavior (assessed by forced swimming test, sucrose preference test, and open field test) were investigated. The changes in IDO1, TNF-α, and IL-1β in rat colon and hippocampus were assessed by Western blot (WB). Gas chromatography-mass spectrometry, immunofluorescence staining, and WB were applied to detect kynurenine pathway (KP) metabolites, hippocampal neuronal activity, and microglia activation, respectively.

Results

Both moxibustion and moxibustion plus 1-MT combination significantly alleviated intestinal inflammation and depressive behavior, downregulated the levels of IDO1 in the colon and hippocampus, and inhibited inflammation-inducing factors IL-1β and TNF-α, as well as the kynurenine/tryptophan (KYN/TRP) ratio of KP metabolites, and upregulated the kynurenic acid (KYNA)/KYN ratio and the KYNA/quinolinic acid (QUIN) ratio in the hippocampus in rats with CD; Hippocampal ionized calcium-binding adaptor molecule-1 (Iba-1), c-fos protein expression, activated microglia, and neuronal activation was also significantly reduced by moxibustion and moxibustion plus 1-MT. The addition of 1-MT did not significantly increase the therapeutic effect of moxibustion.

Conclusion

Moxibustion can improve depressive behavior in rats with CD, which may be related to its regulation of KP metabolism in the gut-brain axis and inhibition of hippocampal microglia activation and neuronal activation.