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-ß (IFN-ß), 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.

Unravelling shared mechanisms: insights from recent ME/CFS research to illuminate long COVID pathologies.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic illness often triggered by an initiating acute event, mainly viral infections. The transition from acute to chronic disease remains unknown, but interest in this phenomenon has escalated since the COVID-19 pandemic and the post-COVID-19 illness, termed 'long COVID' (LC). Both ME/CFS and LC share many clinical similarities. Here, we present recent findings in ME/CFS research focussing on proposed disease pathologies shared with LC. Understanding these disease pathologies and how they influence each other is key to developing effective therapeutics and diagnostic tests. Given that ME/CFS typically has a longer disease duration compared with LC, with symptoms and pathologies evolving over time, ME/CFS may provide insights into the future progression of LC.

Stability Studies of Kynurenine Pathway Metabolites in Blood Components Define Optimal Blood Processing Conditions.

The kynurenine pathway (KP) is the main pathway of tryptophan (TRP) metabolism that generates energy for multiple cellular processes. The activity of this pathway has been shown to be dysregulated in multiple human diseases. The resultant modulation of metabolites has been suggested to comprise biomarkers to track disease progression or could identify new therapeutic targets. While metabolite changes can be measured readily in blood, there is limited knowledge on the effect of blood matrices and sample processing time may have on the stability of KP metabolites. Understanding the stability of KP metabolites in blood is integral to obtaining accurate KP data to correlate with clinical pathology. Hence, the aim of this study was to assess the concentration of KP metabolites in matched whole blood, plasma and serum. The impact of pre-analytical sample processing time in the various blood matrices was also analysed. Serum and plasma had the higher concentration of KP metabolites compared to whole blood. Furthermore, concentrations of KP metabolites declined when the collected blood was processed after 24 hours storage at 4°C. Our study shows that that type of blood matrix and the time to processing have an impact on the stability of the KP metabolites. Serum or plasma are the preferred choice of matrix and the isolation of these matrices from whole blood is best performed immediately after collection for optimal analytical KP data.

Dysregulation of the Kynurenine Pathway, Cytokine Expression Pattern, and Proteomics Profile Link to Symptomology in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS).

Dysregulation of the kynurenine pathway (KP) is believed to play a significant role in neurodegenerative and cognitive disorders. While some evidence links the KP to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), further studies are needed to clarify the overall picture of how inflammation-driven KP disturbances may contribute to symptomology in ME/CFS. Here, we report that plasma levels of most bioactive KP metabolites differed significantly between ME/CFS patients and healthy controls in a manner consistent with their known contribution to symptomology in other neurological disorders. Importantly, we found that enhanced production of the first KP metabolite, kynurenine (KYN), correlated with symptom severity, highlighting the relationship between inflammation, KP dysregulation, and ME/CFS symptomology. Other significant changes in the KP included lower levels of the downstream KP metabolites 3-HK, 3-HAA, QUIN, and PIC that could negatively impact cellular energetics. We also rationalized KP dysregulation to changes in the expression of inflammatory cytokines and, for the first time, assessed levels of the iron (Fe)-regulating hormone hepcidin that is also inflammation-responsive. Levels of hepcidin in ME/CFS decreased nearly by half, which might reflect systemic low Fe levels or possibly ongoing hypoxia. We next performed a proteomics screen to survey for other significant differences in protein expression in ME/CFS. Interestingly, out of the seven most significantly modulated proteins in ME/CFS patient plasma, 5 proteins have roles in maintaining gut health, which considering the new appreciation of how gut microbiome and health modulates systemic KP could highlight a new explanation of symptomology in ME/CFS patients and potential new prognostic biomarker/s and/or treatment avenues.

The kynurenine pathway relates to post-acute COVID-19 objective cognitive impairment and PASC.

OBJECTIVE: To determine the prevalence and natural history of post-acute COVID-19 objective cognitive impairment and function, and their relationship to demographic, clinical factors, post-acute sequelae of COVID-19 (PASC), and biomarkers. METHODS: A total of 128 post-acute COVID-19 patients (age = 46 ± 15; 42% women, acute disease severity: not hospitalized: 38.6% mild: 0-1 symptoms, 52% 2+ symptoms; 9.4% hospitalized) completed standard cognition, olfaction, and mental health examinations 2-, 4-, and 12-month post diagnosis. Over the same time frame, WHO-defined PASC was determined. Blood cytokines, peripheral neurobiomarkers, and kynurenine pathway (KP) metabolites were measured. Objective cognitive function was demographically/practice corrected, and impairment prevalence was determined using the evidence-based Global Deficit Score method to detect at least mild cognitive impairment (GDS > 0.5). Linear mixed effect regression models with time effect (month post diagnosis) evaluated the relationships to cognition. RESULTS: Across the 12-month study period, mild to moderate cognitive impairment ranged from 16% to 26%, and 46.5% were impaired at least once. Impairment associated with poorer work capacity (p < 0.05), and 2-month objectively tested anosmia (p < 0.05). PASC with (p = 0.01) and without disability (p < 0.03) associated with acute COVID-19 severity. KP measures showed prolonged activation (2 to 8 months) (p < 0.0001) linked to IFN-beta in those with PASC. Of the blood analytes, only the KP metabolites (elevated quinolinic acid, 3-hydroxyanthranilic acid, kynurenine, the kynurenine/tryptophan ratio) associated (p < 0.001) with poorer cognitive performance and greater likelihood of impairment. PASC, independent of disability associated with abnormal kynurenine/tryptophan (p < 0.03). INTERPRETATION: The kynurenine pathway relates to post-acute COVID-19 objective cognitive impairment and PASC, thereby enabling biomarker and therapeutic possibilities.

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.

Involvement of the kynurenine pathway in breast cancer: updates on clinical research and trials.

Breast cancer (BrCa) is the leading cause of cancer incidence and mortality in women worldwide. While BrCa treatment has been shown to be highly successful if detected at an early stage, there are few effective strategies to treat metastatic tumours. Hence, metastasis remains the main cause in most of BrCa deaths, highlighting the need for new approaches in this group of patients. Immunotherapy has been gaining attention as a new treatment for BrCa metastasis and the kynurenine pathway (KP) has been suggested as one of the potential targets. The KP is the major biochemical pathway in tryptophan (TRP) metabolism, catabolising TRP to nicotinamide adenine dinucleotide (NAD+). The KP has been reported to be elevated under inflammatory conditions such as cancers and that its activity suppresses immune surveillance. Dysregulation of the KP has previously been reported implicated in BrCa. This review aims to discuss and provide an update on the current mechanisms involved in KP-mediated immune suppression and cancer growth. Furthermore, we also provide a summary on 58 studies about the involvement of the KP and BrCa and five clinical trials targeting KP enzymes and their outcome.

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.

Temporal Profile of Kynurenine Pathway Metabolites in a Rodent Model of Autosomal Recessive Polycystic Kidney Disease.

Autosomal recessive polycystic kidney disease (ARPKD) is an early onset genetic disorder characterized by numerous renal cysts resulting in end stage renal disease. Our study aimed to determine if metabolic reprogramming and tryptophan (Trp) metabolism via the kynurenine pathway (KP) is a critical dysregulated pathway in PKD. Using the Lewis polycystic kidney (LPK) rat model of PKD and Lewis controls, we profiled temporal trends for KP metabolites in plasma, urine, and kidney tissues from 6- and 12-week-old mixed sex animals using liquid and gas chromatography, minimum n = 5 per cohort. A greater kynurenine (KYN) concentration was observed in LPK kidney and plasma of 12-week rats compared to age matched Lewis controls (P ⩽ .05). LPK kidneys also showed an age effect (P ⩽ .05) with KYN being greater in 12-week versus 6-week LPK. The metabolites xanthurenic acid (XA), 3-hydroxykynurenine (3-HK), and 3-hydroxyanthranilic acid (3-HAA) were significantly greater in the plasma of 12-week LPK rats compared to age matched Lewis controls (P ⩽ .05). Plasma XA and 3-HK also showed an age effect (P ⩽ .05) being greater in 12-week versus 6-week LPK. We further describe a decrease in Trp levels in LPK plasma and kidney (strain effect P ⩽ .05). There were no differences in KP metabolites in urine between cohorts. Using the ratio of product and substrates in the KP, a significant age-strain effect (P ⩽ .05) was observed in the activity of the KYN/Trp ratio (tryptophan-2,3-dioxygenase [TDO] or indoleamine-2,3-dioxygenase [IDO] activity), kynurenine 3-monooxygenase (KMO), KAT A (kynurenine aminotransferase A), KAT B, total KAT, total KYNU (kynureninase), KYNU A, KYNU B, and total KYNU within LPK kidneys, supporting an activated KP. Confirmation of the activation of these enzymes will require verification through orthogonal techniques. In conclusion, we have demonstrated an up-regulation of the KP in alignment with progression of renal impairment in the LPK rat model, suggesting that KP activation may be a critical contributor to the pathobiology of PKD.

Decreased cerebrospinal fluid kynurenic acid in epileptic spasms: A biomarker of response to corticosteroids.

BACKGROUND: Epileptic (previously infantile) spasms is the most common epileptic encephalopathy occurring during infancy and is frequently associated with abnormal neurodevelopmental outcomes. Epileptic spasms have a diverse range of known (genetic, structural) and unknown aetiologies. High dose corticosteroid treatment for 4 weeks often induces remission of spasms, although the mechanism of action of corticosteroid is unclear. Animal models of epileptic spasms have shown decreased brain kynurenic acid, which is increased after treatment with the ketogenic diet. We quantified kynurenine pathway metabolites in the cerebrospinal fluid (CSF) of infants with epileptic spasms and explored clinical correlations. METHODS: A panel of nine metabolites in the kynurenine pathway (tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, anthranilic acid, 3-hydroxyanthranilic acid, quinolinic acid, and picolinic acid) were measured using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). CSF collected from paediatric patients less than 3 years of age with epileptic spasms (n=34, 19 males, mean age 0.85, median 0.6, range 0.3-3 yrs) were compared with other epilepsy syndromes (n=26, 9 males, mean age 1.44, median 1.45, range 0.3-3 yrs), other non-inflammatory neurological diseases (OND) (n=29, 18 males, mean age 1.47, median 1.6, range 0.1-2.9 yrs) and inflammatory neurological controls (n=12, 4 males, mean age 1.80, median 1.80, range 0.8-2.5 yrs). FINDINGS: There was a statistically significant decrease of CSF kynurenic acid in patients with epileptic spasms compared to OND (p<0.0001). In addition, the kynurenic acid/kynurenine (KYNA/KYN) ratio was lower in the epileptic spasms subgroup compared to OND (p<0.0001). Epileptic spasms patients who were steroid responders or partial steroid responders had lower KYNA/KYN ratio compared to patients who were refractory to steroids (p<0.005, p<0.05 respectively). INTERPRETATION: This study demonstrates decreased CSF kynurenic acid and KYNA/KYN in epileptic spasms, which may also represent a biomarker for steroid responsiveness. Given the anti-inflammatory and neuroprotective properties of kynurenic acid, further therapeutics able to increase kynurenic acid should be explored. FUNDING: Financial support for the study was granted by Dale NHMRC Investigator grant APP1193648, Petre Foundation, Cerebral Palsy Alliance and Department of Biochemistry at the Children's Hospital at Westmead. Prof Guillemin is funded by NHMRC Investigator grant APP1176660 and Macquarie University.

Could the kynurenine pathway be the key missing piece of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) complex puzzle?

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex and debilitating disease with a substantial social and economic impact on individuals and their community. Despite its importance and deteriorating impact, progresses in diagnosis and treatment of ME/CFS is limited. This is due to the unclear pathophysiology of the disease and consequently lack of prognostic biomarkers. To investigate pathophysiology of ME/CFS, several potential pathologic hallmarks have been investigated; however, these studies have failed to report a consistent result. These failures in introducing the underlying reason for ME/CFS have stimulated considering other possible contributing mechanisms such as tryptophan (TRP) metabolism and in particular kynurenine pathway (KP). KP plays a central role in cellular energy production through the production of nicotinamide adenine dinucleotide (NADH). In addition, this pathway has been shown to mediate immune response and neuroinflammation through its metabolites. This review, we will discuss the pathology and management of ME/CFS and provide evidence pertaining KP abnormalities and symptoms that are classic characteristics of ME/CFS. Targeting the KP regulation may provide innovative approaches to the management of ME/CFS.

The Role of Kynurenine Pathway and NAD+ Metabolism in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a serious, complex, and highly debilitating long-term illness. People with ME/CFS are typically unable to carry out their routine activities. Key hallmarks of the disease are neurological and gastrointestinal impairments accompanied by pervasive malaise that is exacerbated after physical and/or mental activity. Currently, there is no validated cure of biomarker signature for this illness. Impaired tryptophan (TRYP) metabolism is thought to play significant role in the pathobiology of ME/CFS. TRYP is an important precursor for serotonin and the essential pyridine nucleotide nicotinamide adenine dinucleotide (NAD+). TRYP has been associated with the development of some parts of the brain responsible for behavioural functions. The main catabolic route for TRYP is the kynurenine pathway (KP). The KP produces NAD+ and several neuroactive metabolites with neuroprotective (i.e., kynurenic acid (KYNA)) and neurotoxic (i.e., quinolinic acid (QUIN)) activities. Hyperactivation of the KP, whether compensatory or a driving mechanism of degeneration can limit the availability of NAD+ and exacerbate the symptoms of ME/CFS. This review discusses the potential association of altered KP metabolism in ME/CFS. The review also evaluates the role of the patient's gut microbiota on TRYP availability and KP activation. We propose that strategies aimed at raising the levels of NAD+ (e.g., using nicotinamide mononucleotide and nicotinamide riboside) may be a promising intervention to overcome symptoms of fatigue and to improve the quality of life in patients with ME/CFS. Future clinical trials should further assess the potential benefits of NAD+ supplements for reducing some of the clinical features of ME/CFS.

Development of a translational inflammation panel for the quantification of cerebrospinal fluid Pterin, Tryptophan-Kynurenine and Nitric oxide pathway metabolites.

BACKGROUND: Neuroinflammatory diseases such as encephalitis, meningitis, multiple sclerosis and other neurological diseases with inflammatory components, have demonstrated a need for diagnostic biomarkers to define treatable and reversible neuroinflammation. The development and clinical validation of a targeted translational inflammation panel using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) could provide early diagnosis, rapid treatment and insights into neuroinflammatory mechanisms. METHODS: An inflammation panel of 13 metabolites (neopterin, tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, xanthurenic acid, anthranilic acid, 3-hydroxyanthranilic acid, quinolinic acid, picolinic acid, arginine, citrulline and methylhistamine) was measured based on a simple precipitation and filtration method using minimal CSF volume. The chromatographic separation was achieved using the Acquity UPLC BEH C18 column in combination with a gradient elution within a 12-min time frame. Acute encephalitis (n=10; myelin oligodendrocyte glycoprotein encephalitis n=3, anti-N-methyl-D-aspartate encephalitis n=2, acute disseminated encephalomyelitis n=2, herpes simplex encephalitis n=1, enteroviral encephalitis n=1) and frequency-matched non-inflammatory neurological disease controls (n=10) were examined. FINDINGS: The method exhibited good sensitivity as the limits of quantification ranged between 0.75 and 3.00 ng mL-1, good linearity (r2 > 0.99), acceptable matrix effects (<± 19.4%) and high recoveries (89.8-109.1 %). There were no interferences observed from common endogenous CSF metabolites, no carryover and concordance with well-established clinical methods. The accuracy and precision for all analytes were within tolerances, at <± 15 mean relative error and < 15 % coefficient of variation respectively. All analytes in matrix-matched pooled human CSF calibrators and human CSF extracts were stable for 24 h after extraction and two freeze-thaw cycles. INTERPRETATION: The method was successfully applied to a pilot study investigating acute brain inflammation case-control groups. Statistical discrimination between encephalitis (n=10) and control groups (n=10) was achieved using orthogonal partial least squares discriminant analysis and heatmap cluster analysis. Statistical analysis of the measured metabolites identified significant alterations of seven metabolites in the tryptophan-kynurenine pathway (tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, anthranilic acid, 3-hydroxyanthranilic acid, quinolinic acid), arginine and neopterin in presence of acute neuroinflammation. Furthermore, elevated ratios of CSF kynurenine/tryptophan ratio, quinolinic acid/kynurenic acid and anthranilic acid/3-hydroxyanthranilic acid provided strong discriminative power for neuroinflammatory conditions. Studies of large groups of neurological diseases are required to explore the sensitivity and specificity of the inflammation panel. FUNDING: Financial support for the study was granted by Dale NHMRC Investigator grant APP1193648, Petre Foundation, Cerebral Palsy Alliance and Department of Biochemistry at the Children's Hospital at Westmead.

Neuropathological Mechanisms of ß-N-Methylamino-L-Alanine (BMAA) with a Focus on Iron Overload and Ferroptosis.

The incidence of neurodegenerative diseases and cyanobacterial blooms is concomitantly increasing worldwide. The cyanotoxin ß-N-methylamino-L-alanine (BMAA) is produced by most of the Cyanobacteria spp. This cyanotoxin is described as a potential environmental etiology factor for some sporadic neurodegenerative diseases. Climate change and eutrophication significantly increase the frequency and intensity of cyanobacterial bloom in water bodies. This review evaluates different neuropathological mechanisms of BMAA at molecular and cellular levels and compares the related studies to provide some useful recommendations. Additionally, the structure and properties of BMAA as well as its microbial origin, especially by gut bacteria, are also briefly covered. Unlike previous reviews, we hypothesize the possible neurotoxic mechanism of BMAA through iron overload. We also discuss the involvement of BMAA in excitotoxicity, TAR DNA-binding protein 43 (TDP-43) translocation and accumulation, tauopathy, and other protein misincorporation and misfolding.

Recent advances in clinical trials targeting the kynurenine pathway.

The kynurenine pathway (KP) is the major catabolic pathway for the essential amino acid tryptophan leading to he production of nicotinamide adenine dinucleotide. In inflammatory conditions, the activation of the KP leads to the production of several bioactive metabolites including kynurenine, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, kynurenic acid and quinolinic acid. These metabolites can have redox and immune suppressive activity, be neurotoxic or neuroprotective. While the activity of the pathway is tightly regulated under normal physiological condition, it can be upregulated by immunological activation and inflammation. The dysregulation of the KP has been implicated in wide range of neurological diseases and psychiatric disorders. In this review, we discuss the mechanisms involved in KP-mediated neurotoxicity and immune suppression, and its role in diseases of our expertise including cancer, chronic pain and multiple sclerosis. We also provide updates on the clinical trials evaluating the efficacy of KP inhibitors and/or analogues in each respective disease.

Involvement of Kynurenine Pathway in Hepatocellular Carcinoma.

As the second and third leading cancer-related death in men and the world, respectively, primary liver cancer remains a major concern to human health. Despite advances in diagnostic technology, patients with primary liver cancer are often diagnosed at an advanced stage. Treatment options for patients with advanced hepatocarcinoma (HCC) are limited to systemic treatment with multikinase inhibitors and immunotherapy. Furthermore, the 5-year survival rate for these late-stage HCC patients is approximately 12% worldwide. There is an unmet need to identify novel treatment options and/or sensitive blood-based biomarker(s) to detect this cancer at an early stage. Given that the liver harbours the largest proportion of immune cells in the human body, understanding the tumour-immune microenvironment has gained increasing attention as a potential target to treat cancer. The kynurenine pathway (KP) has been proposed to be one of the key mechanisms used by the tumour cells to escape immune surveillance for proliferation and metastasis. In an inflammatory environment such as cancer, the KP is elevated, suppressing local immune cell populations and enhancing tumour growth. In this review, we collectively describe the roles of the KP in cancer and provide information on the latest research into the KP in primary liver cancer.

Effects of Tryptophan Supplementation and Exercise on the Fate of Kynurenine Metabolites in Mice and Humans.

The kynurenine pathway of tryptophan (TRP) degradation (KP) generates metabolites with effects on metabolism, immunity, and mental health. Endurance exercise training can change KP metabolites by changing the levels of KP enzymes in skeletal muscle. This leads to a metabolite pattern that favors energy expenditure and an anti-inflammatory immune cell profile and reduces neurotoxic metabolites. Here, we aimed to understand if TRP supplementation in untrained vs. trained subjects affects KP metabolite levels and biological effects. Our data show that chronic TRP supplementation in mice increases all KP metabolites in circulation, and that exercise reduces the neurotoxic branch of the pathway. However, in addition to increasing wheel running, we did not observe other effects of TRP supplementation on training adaptations, energy metabolism or behavior in mice. A similar increase in KP metabolites was seen in trained vs. untrained human volunteers that took a TRP drink while performing a bout of aerobic exercise. With this acute TRP administration, TRP and KYN were higher in the trained vs. the untrained group. Considering the many biological effects of the KP, which can lead to beneficial or deleterious effects to health, our data encourage future studies of the crosstalk between TRP supplementation and physical exercise.

Splicing factor proline and glutamine rich intron retention, reduced expression and aggregate formation are pathological features of amyotrophic lateral sclerosis.

AIM: Splicing factor proline and glutamine rich (SFPQ) is an RNA-DNA binding protein that is dysregulated in Alzheimer's disease and frontotemporal dementia. Dysregulation of SFPQ, specifically increased intron retention and nuclear depletion, has been linked to several genetic subtypes of amyotrophic lateral sclerosis (ALS), suggesting that SFPQ pathology may be a common feature of this heterogeneous disease. Our study aimed to investigate this hypothesis by providing the first comprehensive assessment of SFPQ pathology in large ALS case-control cohorts. METHODS: We examined SFPQ at the RNA, protein and DNA levels. SFPQ RNA expression and intron retention were examined using RNA-sequencing and quantitative PCR. SFPQ protein expression was assessed by immunoblotting and immunofluorescent staining. At the DNA level, SFPQ was examined for genetic variation novel to ALS patients. RESULTS: At the RNA level, retention of SFPQ intron nine was significantly increased in ALS patients' motor cortex. In addition, SFPQ RNA expression was significantly reduced in the central nervous system, but not blood, of patients. At the protein level, neither nuclear depletion nor reduced expression of SFPQ was found to be a consistent feature of spinal motor neurons. However, SFPQ-positive ubiquitinated protein aggregates were observed in patients' spinal motor neurons. At the DNA level, our genetic screen identified two novel and two rare SFPQ sequence variants not previously reported in the literature. CONCLUSIONS: Our findings confirm dysregulation of SFPQ as a pathological feature of the central nervous system of ALS patients and indicate that investigation of the functional consequences of this pathology will provide insight into ALS biology.

Machine learning workflows identify a microRNA signature of insulin transcription in human tissues.

Dicer knockout mouse models demonstrated a key role for microRNAs in pancreatic ß-cell function. Studies to identify specific microRNA(s) associated with human (pro-)endocrine gene expression are needed. We profiled microRNAs and key pancreatic genes in 353 human tissue samples. Machine learning workflows identified microRNAs associated with (pro-)insulin transcripts in a discovery set of islets (n = 30) and insulin-negative tissues (n = 62). This microRNA signature was validated in remaining 261 tissues that include nine islet samples from individuals with type 2 diabetes. Top eight microRNAs (miR-183-5p, -375-3p, 216b-5p, 183-3p, -7-5p, -217-5p, -7-2-3p, and -429-3p) were confirmed to be associated with and predictive of (pro-)insulin transcript levels. Use of doxycycline-inducible microRNA-overexpressing human pancreatic duct cell lines confirmed the regulatory roles of these microRNAs in (pro-)endocrine gene expression. Knockdown of these microRNAs in human islet cells reduced (pro-)insulin transcript abundance. Our data provide specific microRNAs to further study microRNA-mRNA interactions in regulating insulin transcription.