Retention of stress susceptibility in the mdx mouse model of Duchenne muscular dystrophy after PGC-1α overexpression or ablation of IDO1 or CD38.

Duchenne muscular dystrophy (DMD) is a lethal degenerative muscle wasting disease caused by the loss of the structural protein dystrophin with secondary pathological manifestations including metabolic dysfunction, mood and behavioral disorders. In the mildly affected mdx mouse model of DMD, brief scruff stress causes inactivity, while more severe subordination stress results in lethality. Here, we investigated the kynurenine pathway of tryptophan degradation and the nicotinamide adenine dinucleotide (NAD+) metabolic pathway in mdx mice and their involvement as possible mediators of mdx stress-related pathology. We identified downregulation of the kynurenic acid shunt, a neuroprotective branch of the kynurenine pathway, in mdx skeletal muscle associated with attenuated peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) transcriptional regulatory activity. Restoring the kynurenic acid shunt by skeletal muscle-specific PGC-1α overexpression in mdx mice did not prevent scruff -induced inactivity, nor did abrogating extrahepatic kynurenine pathway activity by genetic deletion of the pathway rate-limiting enzyme, indoleamine oxygenase 1. We further show that reduced NAD+ production in mdx skeletal muscle after subordination stress exposure corresponded with elevated levels of NAD+ catabolites produced by ectoenzyme cluster of differentiation 38 (CD38) that have been implicated in lethal mdx response to pharmacological ß-adrenergic receptor agonism. However, genetic CD38 ablation did not prevent mdx scruff-induced inactivity. Our data do not support a direct contribution by the kynurenine pathway or CD38 metabolic dysfunction to the exaggerated stress response of mdx mice.

Mating-induced increase of kynurenine in Drosophila ovary enhances starvation resistance of progeny.

The maternal nutritional environment can impact progeny development, stress tolerance, and longevity. Such phenotypic variation of offspring resulting from the maternal environment is often referred to as the 'maternal effect' and is observed across taxa, including in humans. While some mechanisms behind maternal effects have been revealed, such as histone modification, many studies rely on drastic genetic or nutritional manipulation in describing these mechanisms. Here we aimed to reveal how the maternal environment is regulated under physiological conditions to affect the progeny. Specifically, we detailed metabolic regulation in oocytes in response to mating using Drosophila melanogaster fruit flies. Using liquid chromatography-mass spectrometry, we found that upon mating, the ovary metabolites shifted, predominantly toward increasing amino acids and the tryptophan/kynurenine (Kyn) pathway. This mating-induced increase in ovary Kyn was driven by increased Kyn production in the fat body, a functional counterpart of the mammalian liver and white adipose tissue and the source of Kyn storage for the ovary after mating. Furthermore, we show that maternal Kyn repression decreased the starvation resistance of progeny and that administering exogenous Kyn to the maternal generation enhanced the starvation resistance of female progeny. Taken together, these findings point to a previously unidentified role of fat body Kyn distribution during reproduction on progeny survival.

IDO1 promotes CSFV replication by mediating tryptophan metabolism to inhibit NF-κB signaling.

Tryptophan metabolism plays a crucial role in facilitating various cellular processes essential for maintaining normal cellular function. Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the conversion of tryptophan (Trp) into kynurenine (Kyn), thereby initiating the degradation of Trp. The resulting Kyn metabolites have been implicated in the modulation of immune responses. Currently, the role of IDO1-mediated tryptophan metabolism in the process of viral infection remains relatively unknown. In this study, we discovered that classical swine fever virus (CSFV) infection of PK-15 cells can induce the expression of IDO1, thereby promoting tryptophan metabolism. IDO1 can negatively regulate the NF-κB signaling by mediating tryptophan metabolism, thereby facilitating CSFV replication. We found that silencing the IDO1 gene enhances the expression of IFN-α, IFN-ß, and IL-6 by activating the NF-κB signaling pathway. Furthermore, our observations indicate that both silencing the IDO1 gene and administering exogenous tryptophan can inhibit CSFV replication by counteracting the cellular autophagy induced by Rapamycin. This study reveals a novel mechanism of IDO1-mediated tryptophan metabolism in CSFV infection, providing new insights and a theoretical basis for the treatment and control of CSFV.IMPORTANCEIt is well known that due to the widespread use of vaccines, the prevalence of classical swine fever (CSF) is shifting towards atypical and invisible infections. CSF can disrupt host metabolism, leading to persistent immune suppression in the host and causing significant harm when co-infected with other diseases. Changes in the host's metabolic profiles, such as increased catabolic metabolism of amino acids and the production of immunoregulatory metabolites and their derivatives, can also influence virus replication. Mammals utilize various pathways to modulate immune responses through amino acid utilization, including increased catabolic metabolism of amino acids and the production of immunoregulatory metabolites and their derivatives, thereby limiting viral replication. Therefore, this study proposes that targeting the modulation of tryptophan metabolism may represent an effective approach to control the progression of CSF.

Kynurenine 3-monooxygenase limits de novo NAD+ synthesis through dietary tryptophan in renal proximal tubule epithelial cell models.

Nicotinamide adenine dinucleotide (NAD+) is a pivotal coenzyme, essential for cellular reactions, metabolism, and mitochondrial function. Depletion of kidney NAD+ levels and reduced de novo NAD+ synthesis through the tryptophan-kynurenine pathway are linked to acute kidney injury (AKI), whereas augmenting NAD+ shows promise in reducing AKI. We investigated de novo NAD+ biosynthesis using in vitro, ex vivo, and in vivo models to understand its role in AKI. Two-dimensional (2-D) cultures of human primary renal proximal tubule epithelial cells (RPTECs) and HK-2 cells showed limited de novo NAD+ synthesis, likely due to low pathway enzyme gene expression. Using three-dimensional (3-D) spheroid culture model improved the expression of tubular-specific markers and enzymes involved in de novo NAD+ synthesis. However, de novo NAD+ synthesis remained elusive in the 3-D spheroid culture, regardless of injury conditions. Further investigation revealed that 3-D cultured cells could not metabolize tryptophan (Trp) beyond kynurenine (KYN). Intriguingly, supplementation of 3-hydroxyanthranilic acid into RPTEC spheroids was readily incorporated into NAD+. In a human precision-cut kidney slice (PCKS) ex vivo model, de novo NAD+ synthesis was limited due to substantially downregulated kynurenine 3-monooxygenase (KMO), which is responsible for KYN to 3-hydroxykynurenine conversion. KMO overexpression in RPTEC 3-D spheroids successfully reinstated de novo NAD+ synthesis from Trp. In addition, in vivo study demonstrated that de novo NAD+ synthesis is intact in the kidney of the healthy adult mice. Our findings highlight disrupted tryptophan-kynurenine NAD+ synthesis in in vitro cellular models and an ex vivo kidney model, primarily attributed to KMO downregulation.NEW & NOTEWORTHY Nicotinamide adenine dinucleotide (NAD+) is essential in regulating mitochondrial function. Reduced NAD+ synthesis through the de novo pathway is associated with acute kidney injury (AKI). Our study reveals a disruption in de novo NAD+ synthesis in proximal tubular models, but not in vivo, attributed to downregulation of enzyme kynurenine 3-monooxygenase (KMO). These findings highlight a crucial role of KMO in governing de novo NAD+ biosynthesis within the kidney, shedding light on potential AKI interventions.

Exploring the kynurenine pathway in mild traumatic brain injury: A longitudinal study.

A potential source of novel biomarkers for mTBI is the kynurenine pathway (KP), a metabolic pathway of tryptophan (Trp), that is up-regulated by neuroinflammation and stress. Considering that metabolites of the KP (kynurenines) are implicated in various neuropsychiatric diseases, exploration of this pathway could potentially bridge the gap between physiological and psychological factors in the recovery process after mTBI. This study, therefore, set out to characterize the KP after mTBI and to examine associations with long-term outcome. Patients were prospectively recruited at the emergency department (ED), and blood samples were obtained in the acute phase (<24 h; N = 256) and at 1-month follow-up (N = 146). A comparison group of healthy controls (HC; N = 32) was studied at both timepoints. Trp, kynurenines, and interleukin (IL)-6 and IL-10 were quantified in plasma. Clinical outcome was measured at six months post-injury. Trp, xanthurenic acid (XA), and picolinic acid (PA) were significantly reduced in patients with mTBI relative to HC, corrected for age and sex. For Trp (d = -0.57 vs. d = -0.29) and XA (d = -0.98 vs. d = -0.32), larger effects sizes were observed during the acute phase compared to one-month follow-up, while for PA (d = -0.49 vs. d = -0.52) effect sizes remained consistent. Findings for other kynurenines (e.g., kynurenine, kynurenic acid, and quinolinic acid) were non-significant after correction for multiple testing. Within the mTBI group, lower acute Trp levels were significantly related to incomplete functional recovery and higher depression scores at 6 months post-injury. No significant relationships were found for Trp, XA, and PA with IL-6 or IL-10 concentrations. In conclusion, our findings indicate that perturbations of the plasma KP in the hyperacute phase of mTBI and 1 month later are limited to the precursor Trp, and glutamate system modulating kynurenines XA and PA. Correlations between acute reductions of Trp and unfavorable outcomes may suggest a potential substrate for pharmacological intervention.

Understanding the kynurenine pathway: A narrative review on its impact across chronic pain conditions.

Chronic pain is a debilitating symptom with a significant negative impact on the quality of life and socioeconomic status, particularly among adults and the elderly. Major Depressive Disorder (MDD) stands out as one of the most important comorbid disorders accompanying chronic pain. The kynurenine pathway serves as the primary route for tryptophan degradation and holds critical significance in various biological processes, including the regulation of neurotransmitters, immune responses, cancer development, metabolism, and inflammation. This review encompasses key research studies related to the kynurenine pathway in the context of headache, neuropathic pain, gastrointestinal disorders, fibromyalgia, chronic fatigue syndrome, and MDD. Various metabolites produced in the kynurenine pathway, such as kynurenic acid and quinolinic acid, exhibit neuroprotective and neurotoxic effects, respectively. Recent studies have highlighted the significant involvement of kynurenine and its metabolites in the pathophysiology of pain. Moreover, pharmacological interventions targeting the regulation of the kynurenine pathway have shown therapeutic promise in pain management. Understanding the underlying mechanisms of this pathway presents an opportunity for developing personalized, innovative, and non-opioid approaches to pain treatment. Therefore, this narrative review explores the role of the kynurenine pathway in various chronic pain disorders and its association with depression and chronic pain.

Immmunometabolism of systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a potentially fatal chronic autoimmune disease which is underlain by complex dysfunction of the innate and adaptive immune systems. Although a series of well-defined genetic and environmental factors have been implicated in disease etiology, neither the development nor the persistence of SLE is well understood. Given that several disease susceptibility genes and environmental factors interact and influence inflammatory lineage specification through metabolism, the field of immunometabolism has become a forefront of cutting edge research. Along these lines, metabolic checkpoints of pathogenesis have been identified as targets of effective therapeutic interventions in mouse models and validated in clinical trials. Ongoing studies focus on mitochondrial oxidative stress, activation of the mechanistic target of rapamycin, calcium signaling, glucose utilization, tryptophan degradation, and metabolic cross-talk between gut microbiota and the host immune system.

Oral tryptophan activates duodenal aryl hydrocarbon receptor in healthy subjects: a crossover randomized controlled trial.

Tryptophan is an essential amino acid transformed by host and gut microbial enzymes into metabolites that regulate mucosal homeostasis through aryl hydrocarbon receptor (AhR) activation. Alteration of tryptophan metabolism has been associated with chronic inflammation; however, whether tryptophan supplementation affects the metabolite repertoire and AhR activation under physiological conditions in humans is unknown. We performed a randomized, double blind, placebo-controlled, crossover study in 20 healthy volunteers. Subjects on a low tryptophan background diet were randomly assigned to a 3-wk l-tryptophan supplementation (3 g/day) or placebo, and after a 2-wk washout switched to opposite interventions. We assessed gastrointestinal and psychological symptoms by validated questionnaires, AhR activation by cell reporter assay, tryptophan metabolites by liquid chromatography and high-resolution mass spectrometry, cytokine production in isolated monocytes by ELISA, and microbiota profile by 16S rRNA Illumina technique. Oral tryptophan supplementation was well tolerated, with no changes in gastrointestinal or psychological scores. Compared with placebo, tryptophan increased AhR activation capacity by duodenal contents, but not by feces. This was paralleled by higher urinary and plasma kynurenine metabolites and indoles. Tryptophan had a modest impact on fecal microbiome profiles and no significant effect on cytokine production. At the doses used in this study, oral tryptophan supplementation in humans induces microbial indole and host kynurenine metabolic pathways in the small intestine, known to be immunomodulatory. The results should prompt tryptophan intervention strategies in inflammatory conditions of the small intestine where the AhR pathway is impaired.NEW & NOTEWORTHY We demonstrate that in healthy subjects, orally administered tryptophan activates microbial indole and host kynurenine pathways in the small intestine, the primary metabolic site for dietary components, and the richest source of immune cells along the gut. This study provides novel insights in how to optimally activate immunomodulatory AhR pathways and indole metabolism in the small intestine, serving as basis for future therapeutic trials using l-tryptophan supplementation in chronic inflammatory conditions affecting the small intestine.

Dysfunction in endocannabinoids, palmitoylethanolamide, and degradation of tryptophan into kynurenine in individuals with depressive symptoms.

BACKGROUND: The endocannabinoid (eCB) system and the serotonin (5-HT) are both implicated in the severity of the depression. 5-HT is synthesized from the amino acid tryptophan (Trp), which is also a precursor for kynurenine (Kyn) whose production is increased at the expense of 5-HT in depressed patients. No clinical studies have investigated the crosstalk between the eCB system and the Trp/5-HT/Kyn pathways. Here, we hypothesized that the eCB system is associated with an enhanced Kyn production in relation to the severity of depressive symptoms. METHODS: Eighty-two subjects (51 patients with a diagnosis of depressive disorder (DSM-5) and 31 healthy volunteers), were assessed with the Montgomery-Åsberg Depression Rating Scale (MADRS), Beck Depression Scale, and Global Clinical Impression. Serum concentrations of eCBs (N-arachidonoylethanolamine (AEA) and 2-arachidonoylglycerol (2-AG)); structurally related fatty acyl compounds 2-oleoylglycerol (2-OG), oleoylethanolamide (OEA), and palmitoylethanolamide (PEA); Trp, Kyn, Kyn/Trp ratio (an index of Trp degradation into Kyn) and 5-HT were also determined. RESULTS: Following a principal component analysis including the severity of depression, Kyn and the Kyn/Trp ratio appear to be directly associated with 2-AG, AEA, and PEA. Interestingly, these biomarkers also permitted to distinguish the population into two main clusters: one of individuals having mild/severe depressive symptoms and the other with an absence of depressive symptoms. Using parametric analysis, higher serum levels of 2-AG, Kyn, and the ratio Kyn/Trp and lower levels of Trp and 5-HT were found in individuals with mild/severe depressive symptoms than in those without depressive symptoms. While in asymptomatic people, PEA was directly associated to Trp, and OEA indirectly linked to 5-HT, in individuals with depressive symptoms, these correlations were lost, and instead, positive correlations between AEA and 2-AG, PEA and AEA, and PEA vs 2-AG and OEA concentrations were found. CONCLUSIONS: Parametric and non-parametric analyses suggest a possible association between eCBs, tryptophan/kynurenine biomarkers, and severity of depression, confirming a likely interplay among inflammation, stress, and depression. The enhanced relationships among the biomarkers of the 2-AG and AEA pathways and related lipids seen in individuals with depressive symptoms, but not in asymptomatics, suggest an altered metabolism of the eCB system in depression.

IDO-1 inhibition improves outcome after fluid percussion injury in adult male rats.

The enzyme indoleamine 2,3 dioxygenase 1 (IDO1) catalyzes the rate-limiting step in the kynurenine pathway (KP) which produces both neuroprotective and neurotoxic metabolites. Neuroinflammatory signals produced as a result of pathological conditions can increase production of IDO1 and boost its enzymatic capacity. IDO1 and the KP have been implicated in behavioral recovery after human traumatic brain injury (TBI), but their roles in experimental models of TBI are for the most part unknown. We hypothesized there is an increase in KP activity in the fluid percussion injury (FPI) model of TBI, and that administration of an IDO1 inhibitor will improve neurological recovery. In this study, adult male Sprague Dawley rats were subjected to FPI or sham injury and received twice-daily oral administration of the IDO1 inhibitor PF-06840003 (100 mg/kg) or vehicle control. FPI resulted in a significant increase in KP activity, as demonstrated by an increased ratio of kynurenine: tryptophan, in the perilesional neocortex and ipsilateral hippocampus 3 days postinjury (DPI), which normalized by 7 DPI. The increase in KP activity was prevented by PF-06840003. IDO1 inhibition also improved memory performance as assessed in the Barnes maze and anxiety behaviors as assessed in open field testing in the first 28 DPI. These results suggest increased KP activity after FPI may mediate neurological dysfunction, and IDO1 inhibition should be further investigated as a potential therapeutic target to improve recovery.

Identification and experimental validation of KMO as a critical immune-associated mitochondrial gene in unstable atherosclerotic plaque.

BACKGROUND: The heightened risk of cardiovascular and cerebrovascular events is associated with the increased instability of atherosclerotic plaques. However, the lack of effective diagnostic biomarkers has impeded the assessment of plaque instability currently. This study was aimed to investigate and identify hub genes associated with unstable plaques through the integration of various bioinformatics tools, providing novel insights into the detection and treatment of this condition. METHODS: Weighted Gene Co-expression Network Analysis (WGCNA) combined with two machine learning methods were used to identify hub genes strongly associated with plaque instability. The cell-type identification by estimating relative subsets of RNA transcripts (CIBERSORT) method was utilized to assess immune cell infiltration patterns in atherosclerosis patients. Additionally, Gene Set Variation Analysis (GSVA) was conducted to investigate the potential biological functions, pathways, and mechanisms of hub genes associated with unstable plaques. To further validate the diagnostic efficiency and expression of the hub genes, immunohistochemistry (IHC), quantitative real-time polymerase chain reaction (RT-qPCR), and enzyme-linked immunosorbent assay (ELISA) were performed on collected human carotid plaque and blood samples. Immunofluorescence co-staining was also utilized to confirm the association between hub genes and immune cells, as well as their colocalization with mitochondria. RESULTS: The CIBERSORT analysis demonstrated a significant decrease in the infiltration of CD8 T cells and an obvious increase in the infiltration of M0 macrophages in patients with atherosclerosis. Subsequently, two highly relevant modules (blue and green) strongly associated with atherosclerotic plaque instability were identified. Through intersection with mitochondria-related genes, 50 crucial genes were identified. Further analysis employing least absolute shrinkage and selection operator (LASSO) logistic regression and support vector machine recursive feature elimination (SVM-RFE) algorithms revealed six hub genes significantly associated with plaque instability. Among them, NT5DC3, ACADL, SLC25A4, ALDH1B1, and MAOB exhibited positive correlations with CD8 T cells and negative correlations with M0 macrophages, while kynurenine 3-monooxygenas (KMO) demonstrated a positive correlation with M0 macrophages and a negative correlation with CD8 T cells. IHC and RT-qPCR analyses of human carotid plaque samples, as well as ELISA analyses of blood samples, revealed significant upregulation of KMO and MAOB expression, along with decreased ALDH1B1 expression, in both stable and unstable samples compared to the control samples. However, among the three key genes mentioned above, only KMO showed a significant increase in expression in unstable plaque samples compared to stable plaque samples. Furthermore, the expression patterns of KMO in human carotid unstable plaque tissues and cultured mouse macrophage cell lines were assessed using immunofluorescence co-staining techniques. Finally, lentivirus-mediated KMO silencing was successfully transduced into the aortas of high-fat-fed ApoE-/- mice, with results indicating that KMO silencing attenuated plaque formation and promoted plaque stability in ApoE-/- mice. CONCLUSIONS: The results suggest that KMO, a mitochondria-targeted gene associated with macrophage cells, holds promise as a valuable diagnostic biomarker for assessing the instability of atherosclerotic plaques.

Tryptophan-kynurenine metabolic pathway and daytime dysfunction in women with HIV.

Sleep disturbances are prevalent in women with HIV (WWH). Tryptophan-kynurenine (T-K) pathway metabolites are associated with alterations in actigraphy derived sleep measures in WWH, although may not always correlate with functional impairment. We investigated the relationship between T-K pathway metabolites and self-reported daytime dysfunction in WWH and women without HIV (WWoH). 141 WWH on stable antiretroviral therapy and 140 demographically similar WWoH enrolled in the IDOze Study had targeted plasma T-K metabolites measured using liquid chromatography-tandem mass spectrometry. We utilized the daytime dysfunction component of the Pittsburgh Sleep Quality Index (PSQI) to assess functional impairment across HIV-serostatus. Lower levels of 5-hydroxytryptophan and serotonin were associated with greater daytime dysfunction in all women. In WWH, daytime dysfunction was associated with increased kynurenic acid (R = 0.26, p < 0.05), and kynurenic acid-tryptophan (KA-T) ratio (R = 0.28, p < 0.01). WWH with daytime dysfunction had a 0.7 log fold increase in kynurenic acid compared to WWH without daytime dysfunction. Kynurenic acid levels and the KA-T ratio were associated with daytime dysfunction in WWH but not in WWoH. Longitudinal studies are needed to establish a causal relationship and directionality between T-K metabolic changes and sleep impairment in WWH.

First trimester maternal tryptophan metabolism and embryonic and fetal growth: the Rotterdam Periconceptional Cohort (Predict Study).

STUDY QUESTION: What is the association between first trimester maternal tryptophan (TRP) metabolites and embryonic and fetal growth? SUMMARY ANSWER: Higher 5-hydroxytryptophan (5-HTP) concentrations are associated with reduced embryonic growth and fetal growth and with an increased risk of small-for-gestational age (SGA), while higher kynurenine (KYN) concentrations are associated with a reduced risk of SGA. WHAT IS KNOWN ALREADY: The maternal TRP metabolism is involved in many critical processes for embryonic and fetal growth, including immune modulation and regulation of vascular tone. Disturbances in TRP metabolism are associated with adverse maternal and fetal outcomes. STUDY DESIGN, SIZE, DURATION: This study was embedded within the Rotterdam Periconceptional Cohort (Predict Study), an ongoing prospective observational cohort conducted at a tertiary hospital from November 2010 onwards. PARTICIPANTS/MATERIALS, SETTING, METHODS: A total of 1115 women were included before 11 weeks of gestation between November 2010 and December 2020. Maternal serum samples were collected between 7 and 11 weeks of gestation, and TRP metabolites (TRP, KYN, 5-HTP, 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid) were determined using a validated liquid chromatography (tandem) mass spectrometry method. Serial 3D ultrasound scans were performed at 7, 9, and 11 weeks of gestation to accurately assess features of embryonic growth, including crown-rump length (CRL) and embryonic volume (EV) offline using virtual reality systems. Fetal growth parameters were retrieved from medical records and standardized according to Dutch reference curves. Mixed models were used to assess associations between maternal TRP metabolites and CRL and EV trajectories. Linear and logistic regression models were utilized to investigate associations with estimated fetal weight (EFW) and birthweight, and with SGA, respectively. All analyses were adjusted for potential confounders. MAIN RESULTS AND THE ROLE OF CHANCE: Maternal 5-HTP concentrations and the maternal 5-HTP/TRP ratio were inversely associated with embryonic growth (5-HTP, √CRL: ß = -0.015, 95% CI = -0.028 to -0.001; 5-HTP 3√EV: ß = -0.009, 95% CI = -0.016 to -0.003). An increased maternal 5-HTP/TRP ratio was also associated with lower EFW and birthweight, and with an increased risk of SGA (odds ratio (OR) = 1.006, 95% CI = 1.00-1.013). In contrast, higher maternal KYN concentrations were associated with a reduced risk of SGA in the unadjusted models (OR = 0.548, 95% CI = 0.320-0.921). LIMITATIONS, REASONS FOR CAUTION: Residual confounding cannot be ruled out because of the observational design of this study. Moreover, this study was conducted in a single tertiary hospital, which assures high internal validity but may limit external validity. WIDER IMPLICATIONS OF THE FINDINGS: The novel finding that maternal 5-HTP concentrations are associated with a smaller embryo and fetus implies that disturbances of the maternal serotonin pathway in the first trimester of pregnancy are potentially involved in the pathophysiology of fetal growth restriction. The association between higher maternal KYN concentrations and a reduced risk of SGA substantiate the evidence that the KYN pathway has an important role in fetal growth. More research is needed to delve deeper into the potential role of the maternal TRP metabolism during the periconception period and pregnancy outcome for mother and offspring. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the Department of Obstetrics and Gynecology and the Department of Clinical Chemistry of the Erasmus MC, University Medical Center, Rotterdam, the Netherlands. The authors have no competing interests to disclose. TRIAL REGISTRATION NUMBER: N/A.

Circulating N-lactoyl-amino acids and N-formyl-methionine reflect mitochondrial dysfunction and predict mortality in septic shock.

INTRODUCTION: Sepsis is a highly morbid condition characterized by multi-organ dysfunction resulting from dysregulated inflammation in response to acute infection. Mitochondrial dysfunction may contribute to sepsis pathogenesis, but quantifying mitochondrial dysfunction remains challenging. OBJECTIVE: To assess the extent to which circulating markers of mitochondrial dysfunction are increased in septic shock, and their relationship to severity and mortality. METHODS: We performed both full-scan and targeted (known markers of genetic mitochondrial disease) metabolomics on plasma to determine markers of mitochondrial dysfunction which distinguish subjects with septic shock (n = 42) from cardiogenic shock without infection (n = 19), bacteremia without sepsis (n = 18), and ambulatory controls (n = 19) - the latter three being conditions in which mitochondrial function, proxied by peripheral oxygen consumption, is presumed intact. RESULTS: Nine metabolites were significantly increased in septic shock compared to all three comparator groups. This list includes N-formyl-L-methionine (f-Met), a marker of dysregulated mitochondrial protein translation, and N-lactoyl-phenylalanine (lac-Phe), representative of the N-lactoyl-amino acids (lac-AAs), which are elevated in plasma of patients with monogenic mitochondrial disease. Compared to lactate, the clinical biomarker used to define septic shock, there was greater separation between survivors and non-survivors of septic shock for both f-Met and the lac-AAs measured within 24 h of ICU admission. Additionally, tryptophan was the one metabolite significantly decreased in septic shock compared to all other groups, while its breakdown product kynurenate was one of the 9 significantly increased. CONCLUSION: Future studies which validate the measurement of lac-AAs and f-Met in conjunction with lactate could define a sepsis subtype characterized by mitochondrial dysfunction.

Metabolic profiling of tryptophan pathways: Implications for obesity and metabolic dysfunction-associated steatotic liver disease.

BACKGROUND AND AIMS: The rise in obesity highlights the need for improved therapeutic strategies, particularly in addressing metabolic dysfunction-associated steatotic liver disease (MASLD). We aim to assess the role of tryptophan metabolic pathways in the pathogenesis of obesity and in the different histological stages of MASLD. MATERIALS AND METHODS: We used ultra-high performance liquid chromatography to quantify circulating levels of 15 tryptophan-related metabolites from the kynurenine, indole and serotonin pathways. A cohort of 76 subjects was analysed, comprising 18 subjects with normal weight and 58 with morbid obesity, these last being subclassified into normal liver (NL), simple steatosis (SS) and metabolic dysfunction-associated steatohepatitis (MASH). Then, we conducted gene expression analysis of hepatic IDO-1 and kynyrenine-3-monooxygenase (KMO). RESULTS: Key findings in obesity revealed a distinct metabolic signature characterized by a higher concentration of different kynurenine-related metabolites, a decrease in indole-3-acetic acid and indole-3-propionic acid, and an alteration in the serotonin pathway. Elevated tryptophan levels were associated with MASLD presence (37.659 (32.577-39.823) µM of tryptophan in NL subjects; 41.522 (38.803-45.276) µM in patients with MASLD). Overall, pathway fluxes demonstrated an induction of tryptophan catabolism via the serotonin pathway in SS subjects and into the kynurenine pathway in MASH. We found decreased IDO-1 and KMO hepatic expression in NL compared to SS. CONCLUSIONS: We identified a distinctive metabolic signature in obesity marked by changes in tryptophan catabolic pathways, discernible through altered metabolite profiles. We observed stage-specific alterations in tryptophan catabolism fluxes in MASLD, highlighting the potential utility of targeting these pathways in therapeutic interventions.

Identification of kynurenine and quinolinic acid as promising serum biomarkers for drug-induced interstitial lung diseases.

BACKGROUND: Drug-induced interstitial lung disease (DILD) is a lung injury caused by various types of drugs and is a serious problem in both clinical practice and drug development. Clinical management of the condition would be improved if there were DILD-specific biomarkers available; this study aimed to meet that need. METHODS: Biomarker candidates were identified by non-targeted metabolomics focusing on hydrophilic molecules, and further validated by targeted approaches using the serum of acute DILD patients, DILD recovery patients, DILD-tolerant patients, patients with other related lung diseases, and healthy controls. RESULTS: Serum levels of kynurenine and quinolinic acid (and kynurenine/tryptophan ratio) were elevated significantly and specifically in acute DILD patients. The diagnostic potentials of these biomarkers were superior to those of conventional lung injury biomarkers, Krebs von den Lungen-6 and surfactant protein-D, in discriminating between acute DILD patients and patients with other lung diseases, including idiopathic interstitial pneumonia and lung diseases associated with connective tissue diseases. In addition to identifying and evaluating the biomarkers, our data showed that kynurenine/tryptophan ratios (an indicator of kynurenine pathway activation) were positively correlated with serum C-reactive protein concentrations in patients with DILD, suggesting the potential association between the generation of these biomarkers and inflammation. Our in vitro experiments demonstrated that macrophage differentiation and inflammatory stimulations typified by interferon gamma could activate the kynurenine pathway, resulting in enhanced kynurenine levels in the extracellular space in macrophage-like cell lines or lung endothelial cells. Extracellular quinolinic acid levels were elevated only in macrophage-like cells but not endothelial cells owing to the lower expression levels of metabolic enzymes converting kynurenine to quinolinic acid. These findings provide clues about the molecular mechanisms behind their specific elevation in the serum of acute DILD patients. CONCLUSIONS: The serum concentrations of kynurenine and quinolinic acid as well as kynurenine/tryptophan ratios are promising and specific biomarkers for detecting and monitoring DILD and its recovery, which could facilitate accurate decisions for appropriate clinical management of patients with DILD.

AT-0174, a novel dual IDO1/TDO2 enzyme inhibitor, synergises with temozolomide to improve survival in an orthotopic mouse model of glioblastoma.

BACKGROUND: Glioblastoma is an aggressive brain cancer, usually of unknown etiology, and with a very poor prognosis. Survival from diagnosis averages only 3 months if left untreated and this only increases to 12-15 months upon treatment. Treatment options are currently limited and typically comprise radiotherapy plus a course of the DNA-alkylating chemotherapeutic temozolomide. Unfortunately, the disease invariably relapses after several months of treatment with temozolomide, due to the development of resistance to the drug. Increased local tryptophan metabolism is a feature of many solid malignant tumours through increased expression of tryptophan metabolising enzymes. Glioblastomas are notable for featuring increased expression of the tryptophan catabolizing enzymes indole-2,3-dioxygenase-1 (IDO1), and especially tryptophan-2,3-dioxygenase-2 (TDO2). Increased IDO1 and TDO2 activity is known to suppress the cytotoxic T cell response to tumour cells, and this has led to the proposal that the IDO1 and TDO2 enzymes represent promising immuno-oncology targets. In addition to immune modulation, however, recent studies have also identified the activity of these enzymes is important in the development of resistance to chemotherapeutic agents. METHODS: In the current study, the efficacy of a novel dual inhibitor of IDO1 and TDO2, AT-0174, was assessed in an orthotopic mouse model of glioblastoma. C57BL/6J mice were stereotaxically implanted with GL261(luc2) cells into the striatum and then administered either vehicle control, temozolomide (8 mg/kg IP; five 8-day cycles of treatment every 2 days), AT-0174 (120 mg/kg/day PO) or both temozolomide + AT-0174, all given from day 7 after implantation. RESULTS: Temozolomide decreased tumour growth and improved median survival but increased the infiltration of CD4+ Tregs. AT-0174 had no significant effect on tumour growth or survival when given alone, but provided clear synergy in combination with temozolomide, further decreasing tumour growth and significantly improving survival, as well as elevating CD8+ T cell expression and decreasing CD4+ Treg infiltration. CONCLUSION: AT-0174 exhibited an ideal profile for adjunct treatment of glioblastomas with the first-line chemotherapeutic drug temozolomide to prevent development of CD4+ Treg-mediated chemoresistance.

Dysregulated placental expression of kynurenine pathway enzymes is associated with inflammation and depression in pregnancy.

BACKGROUND: Perinatal depression (including antenatal-, postnatal-, and depression that spans both timepoints) is a prevalent disorder with high morbidity that affects both mother and child. Even though the full biological blueprints of perinatal depression remain incomplete, multiple studies indicate that, at least for antenatal depression, the disorder has an inflammatory component likely linked to a dysregulation of the enzymatic kynurenine pathway. The production of neuroactive metabolites in this pathway, including quinolinic acid (QUIN), is upregulated in the placenta due to the multiple immunological roles of the metabolites during pregnancy. Since neuroactive metabolites produced by the pathway also may affect mood by directly affecting glutamate neurotransmission, we sought to investigate whether the placental expression of kynurenine pathway enzymes controlling QUIN production was associated with both peripheral inflammation and depressive symptoms during pregnancy. METHODS: 68 placentas obtained at birth were analyzed using qPCR to determine the expression of kynurenine pathway enzymes. Cytokines and metabolites were quantified in plasma using high-sensitivity electroluminescence and ultra-performance liquid chromatography, respectively. Maternal depressive symptoms were assessed using the Edinburgh Postnatal Depression Scale (EPDS) throughout pregnancy and the post-partum. Associations between these factors were assessed using robust linear regression with ranked enzymes. RESULTS: Low placental quinolinate phosphoribosyl transferase (QPRT), the enzyme responsible for degrading QUIN, was associated with higher IL-6 and higher QUIN/kynurenic acid ratios at the 3rd trimester. Moreover, women with severe depressive symptoms in the 3rd trimester had significantly lower placental expression of both QPRT and 2-amino-3-carboxymuconate-6-semialdehyde decarboxylase (ACMSD); impaired activity of these two enzymes leads to QUIN accumulation. CONCLUSION: Overall, our data support that a compromised placental environment, featuring low expression of critical kynurenine pathway enzymes is associated with increased levels of plasma cytokines and the dysregulated kynurenine metabolite pattern observed in depressed women during pregnancy.

Exploring the parity paradox: Differential effects on neuroplasticity and inflammation by APOEe4 genotype at middle age.

Female sex and Apolipoprotein E (APOE) ε4 genotype are top non-modifiable risk factors for Alzheimer's disease (AD). Although female-unique experiences like parity (pregnancy and motherhood) have positive effects on neuroplasticity at middle age, previous pregnancy may also contribute to AD risk. To explore these seemingly paradoxical long-term effects of parity, we investigated the impact of parity with APOEε4 genotype by examining behavioural and neural biomarkers of brain health in middle-aged female rats. Our findings show that primiparous (parous one time) hAPOEε4 rats display increased use of a non-spatial cognitive strategy and exhibit decreased number and recruitment of new-born neurons in the ventral dentate gyrus of the hippocampus in response to spatial working memory retrieval. Furthermore, primiparity and hAPOEε4 genotype synergistically modulate inflammatory markers in the ventral hippocampus. Collectively, these findings demonstrate that previous parity in hAPOEε4 rats confers an added risk to present with reduced activity and engagement of the hippocampus as well as elevated pro-inflammatory signaling, and underscore the importance of considering female-specific factors and genotype in health research.

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.