Therapeutic potential of targeting kynurenine pathway in neurodegenerative diseases

An ultra-high-performance tandem mass spectrometry method to quantify tryptophan metabolites in aqueous humor of primary angle-closure glaucoma patients

This study presented the development and validation of a robust ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous quantification of tryptophan (TRP) and its nine metabolites in aqueous humor (AH) to explore the regulation of the TRP metabolic pathway in primary angle-closure glaucoma (PACG). The optimized UPLC-MS/MS method demonstrated good linearity (R² > 0.99), sensitivity (LLMI: 0.11 - 1.31 ng/mL), precision (CVs: 2.18 % and 12.88 %), recovery rates (85.06 % - 105.74 %), bench-top, long-term and on-instrument stabilities (CVs: 2.35 % - 6.88 %). The validated UPLC-MS/MS method was applied to AH samples from PACG patients with cataract and cataract-alone patients. The results showed that kynurenine and 3-hydroxykynurenine concentrations were significantly increased in the AH of the PACG group, indicating up-regulated indoleamine 2,3-dioxygenase activity and a metabolic shift towards the production of the neurotoxic metabolites within the kynurenine pathway. These findings underscore the potential involvement of TRP metabolism in PACG pathogenesis.

Computational screening of natural products as tryptophan 2,3-dioxygenase inhibitors: Insights from CNN-based QSAR, molecular docking, ADMET, and molecular dynamics simulations

Parkinson's disease (PD) is characterised by a complex array of motor, psychiatric, and gastrointestinal symptoms, many of which are linked to disruptions in neuroactive metabolites. Dysregulated activity of tryptophan 2,3-dioxygenase (TDO), a key enzyme in the kynurenine pathway (KP), has been implicated in these disturbances. TDO's regulation of tryptophan metabolism outside the central nervous system (CNS) plays a critical role in maintaining the balance between serotonin and kynurenine-derived metabolites, with its dysfunction contributing to the worsening of PD symptoms. Recent studies suggest that targeting TDO may help alleviate non-motor symptoms of PD, providing an alternative approach to conventional dopamine replacement therapies. In this study, a data-driven computational pipeline was employed to identify natural products as potential TDO inhibitors. Machine learning and convolutional neural network-based QSAR models were developed to predict TDO inhibitory activity. Molecular docking revealed strong binding affinities for several compounds, with docking scores ranging from -9.6 to -10.71 kcal/mol, surpassing that of tryptophan (-6.86 kcal/mol), and indicating favourable interactions. ADMET profiling assessed pharmacokinetic properties, confirming that the selected compounds could cross the blood-brain barrier (BBB), suggesting potential CNS activity. Molecular dynamics (MD) simulations provided further insight into the binding stability and dynamic behaviour of the top candidates within the TDO active site under physiological conditions. Notably, Peniciherquamide C maintained stronger and more stable interactions than the native substrate tryptophan throughout the simulation. MM/PBSA decomposition analysis highlighted the energetic contributions of van der Waals, electrostatic, and solvation forces, supporting the binding stability of key compounds. This integrated computational approach highlights the potential of natural products as TDO inhibitors, identifying promising leads that address PD symptoms beyond traditional dopamine-centric therapies. Nonetheless, experimental validation is necessary to confirm these findings.

Quinoline Quest: Kynurenic Acid Strategies for Next-Generation Therapeutics via Rational Drug Design

BACKGROUND

Quinoline-derived metabolites exhibit notable chemical complexity. What causes minor structural alterations to induce significant changes in disease outcomes? Historically, eclipsed by more straightforward scaffolds, these chemicals serve as a dynamic hub in tryptophan metabolism, linking immunomodulation, excitotoxicity, and cancer. However, many of these compounds struggle to cross the blood-brain barrier, and we still do not fully understand how certain structural changes affect their bioavailability or off-target effects. Thus, contemporary research highlights halogenation, esterification, and computational modeling to enhance structure-activity relationships.

SUMMARY

This narrative review emphasizes the integration of rational drug design, multi-target ligands, and prodrug methods in enhancing quinoline scaffolds. We explore each molecule's therapeutic promise, refine each scaffold's design, and develop each derivative to maximize clinical utility. Translating these laboratory findings into clinical practice, however, remains a formidable challenge.

CONCLUSIONS

Through the synthesis of findings regarding NMDA receptor antagonism, improved oral bioavailability, and reduced metabolic instability, we demonstrate how single-site changes might modulate excitotoxicity and immunological signaling. Advancing quinoline-based medicines will yield significant advancements in neurology, psychiatry, and oncology. This enlarged framework fosters collaborative discovery, engages various audiences, and advances the field towards next-generation disease-modifying therapies. Robust preclinical validation, patient classification, and comprehensive toxicity evaluations are crucial stages for achieving these extensive endeavors and fostering future therapeutic discoveries globally.

Promising Gastric Cancer Biomarkers-Focus on Tryptophan Metabolism via the Kynurenine Pathway

Currently, gastric cancer treatment remains an enormous challenge and requires a multidisciplinary approach. Globally, the incidence and prevalence of gastric cancer vary, with the highest rates found in East Asia, Central Europe, and Eastern Europe. Early diagnosis is critical for successful surgical removal of gastric cancer, but the disease often develops asymptomatically. Therefore, many cases are diagnosed at an advanced stage, resulting in poor survival. Metastatic gastric cancer also has a poor prognosis. Therefore, it is urgent to identify reliable molecular disease markers and develop an effective medical treatment for advanced stages of the disease. This review summarizes potential prognostic or predictive markers of gastric cancer. Furthermore, the role of tryptophan metabolites from the kynurenine pathway as prognostic, predictive, and diagnostic factors of gastric cancer is discussed, as this metabolic pathway is associated with tumor immune resistance.

Neuroinflammatory Proteins in Huntington's Disease: Insights into Mechanisms, Diagnosis, and Therapeutic Implications

Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by a CAG tract expansion in the huntingtin gene (HTT). HD is characterized by involuntary movements, cognitive decline, and behavioral changes. Pathologically, patients with HD show selective striatal neuronal vulnerability at the early disease stage, although the mutant protein is ubiquitously expressed. Activation of the immune system and glial cell-mediated neuroinflammatory responses are early pathological features and have been found in all neurodegenerative diseases (NDDs), including HD. However, the role of inflammation in HD, as well as its therapeutic significance, has been less extensively studied compared to other NDDs. This review highlights the significantly elevated levels of inflammatory proteins and cellular markers observed in various HD animal models and HD patient tissues, emphasizing the critical roles of microglia, astrocytes, and oligodendrocytes in mediating neuroinflammation in HD. Moreover, it expands on recent discoveries related to the peripheral immune system's involvement in HD. Although current immunomodulatory treatments and inflammatory biomarkers for adjunctive diagnosis in HD are limited, targeting inflammation in combination with other therapies, along with comprehensive personalized treatment approaches, shows promising therapeutic potential.

Xanthurenic acid: A role in brain intercellular signaling

Xanthurenic acid (XA) raises a growing multidisciplinary interest based upon its oxidizing properties, its ability to complex certain metal ions, and its detoxifier capacity of 3-hydroxykynurenine (3-HK), its brain precursor. However, little is still known about the role and mechanisms of action of XA in the central nervous system (CNS). Therefore, many research groups have recently investigated XA and its central functions extensively. The present paper critically reviews and discusses all major data related to XA properties and neuronal activities to contribute to the improvement of the current knowledge on XA's central roles and mechanisms of action. In particular, our data showed the existence of a specific G-protein-coupled receptor (GPCR) for XA localized exclusively in brain neurons exhibiting Ca2+-dependent dendritic release and specific electrophysiological responses. XA properties and central activities suggest a role for this compound in brain intercellular signaling. Indeed, XA stimulates cerebral dopamine (DA) release contrary to its structural analog, kynurenic acid (KYNA). Thus, KYNA/XA ratio could be fundamental in the regulation of brain glutamate and DA release. Cerebral XA may also represent an homeostatic signal between the periphery and several brain regions where XA accumulates easily after peripheral administration. Therefore, XA status in certain psychoses or neurodegenerative diseases seems to be reinforced by its brain-specific properties in balance with its formation and peripheral inputs.

The Biology and Biochemistry of Kynurenic Acid, a Potential Nutraceutical with Multiple Biological Effects

Kynurenic acid (KYNA) is an antioxidant degradation product of tryptophan that has been shown to have a variety of cytoprotective, neuroprotective and neuronal signalling properties. However, mammalian transporters and receptors display micromolar binding constants; these are consistent with its typically micromolar tissue concentrations but far above its serum/plasma concentration (normally tens of nanomolar), suggesting large gaps in our knowledge of its transport and mechanisms of action, in that the main influx transporters characterized to date are equilibrative, not concentrative. In addition, it is a substrate of a known anion efflux pump (ABCC4), whose in vivo activity is largely unknown. Exogeneous addition of L-tryptophan or L-kynurenine leads to the production of KYNA but also to that of many other co-metabolites (including some such as 3-hydroxy-L-kynurenine and quinolinic acid that may be toxic). With the exception of chestnut honey, KYNA exists at relatively low levels in natural foodstuffs. However, its bioavailability is reasonable, and as the terminal element of an irreversible reaction of most tryptophan degradation pathways, it might be added exogenously without disturbing upstream metabolism significantly. Many examples, which we review, show that it has valuable bioactivity. Given the above, we review its potential utility as a nutraceutical, finding it significantly worthy of further study and development.

The Complex World of Kynurenic Acid: Reflections on Biological Issues and Therapeutic Strategy

It has been unequivocally established that kynurenic acid has a number of actions in a variety of cells and tissues, raising, in principle, the possibility of targeting its generation, metabolism or sites of action to manipulate those effects to a beneficial therapeutic end. However, many basic aspects of the biology of kynurenic acid remain unclear, potentially leading to some confusion and misinterpretations of data. They include questions of the source, generation, targets, enzyme expression, endogenous concentrations and sites of action. This essay is intended to raise and discuss many of these aspects as a source of reference for more balanced discussion. Those issues are followed by examples of situations in which modulating and correcting kynurenic acid production or activity could bring significant therapeutic benefit, including neurological and psychiatric conditions, inflammatory diseases and cell protection. More information is required to obtain a clear overall view of the pharmacological environment relevant to kynurenic acid, especially with respect to the active concentrations of kynurenine metabolites in vivo and changed levels in disease. The data and ideas presented here should permit a greater confidence in appreciating the sites of action and interaction of kynurenic acid under different local conditions and pathologies, enhancing our understanding of kynurenic acid itself and the many clinical conditions in which manipulating its pharmacology could be of clinical value.

Nitroquinolone Fused Salicyl and Naphthyl Hydrazone Fluorescent Probes for the Detection of Fe3+and Pb2+ Ions

The application of quinolones stretches over a large umbrella of medicinal field as well as chemosensor due to the presence of privileged heterocyclic aromatic rig system. Salicyl and Naphthyl Hydrazide motifs are also established fluorophore groups. Therefore in this work, we have designed and synthesized Salicyl hydrazide (3a-c) and naphthyl hydrazide fused nitroquinolones (5a-c) investigated for their fluorescent behaviour. Preliminary UV- absorption studies were carried out and the metal selectivity were examined with various metal ion. Among them, it was found that compound 3a was selective towards Fe3+ ions (λex = 330 nm, 1:1 DMF:H2O at pH = 7.4 in HEPES Buffer medium). 3a shows decrease emission intensity in presence of Fe3+ ions. Compound 5a shows enhancement in fluorescence intensity upon addition of Pb2+ ion (λex = 280 nm, 1:1 DMF:H2O at pH = 7.4 in HEPES Buffer medium). Further, the concentration dependence, competitive binding and EDTA reversibility were studied for selected compounds towards the respective cations selectivity. Jobs plot analysis indicate that 1:1 binding of 3a with Fe3+ ion (Ka = 3.17 x104M-1 and Limit Of Detection (LOD) = 5.1 × 10-7 M) whereas 5a showed 1:2 binding mode with Pb2+ ions (Ka = 2.14 × 106 M-1 and Limit Of Detection (LOD) = 2.613 × 10-9 M). Density Function Theoretical studies were performed as support for the experimental results.

Laquinimod Inhibits Microglial Activation, Astrogliosis, BBB Damage, and Infarction and Improves Neurological Damage after Ischemic Stroke

Glial activation is involved in neuroinflammation and blood-brain barrier (BBB) damage, which plays a key role in ischemic stroke-induced neuronal damage; therefore, regulating glial activation is an important way to inhibit ischemic brain injury. Effects of laquinimod (LAQ) include inhibiting axonal damage and neuroinflammation in multiple neuronal injury diseases. However, whether laquinimod can exert neuroprotective effects after ischemic stroke remains unknown. In this study, we investigated the effect of LAQ on glial activation, BBB damage, and neuronal damage in an ischemic stroke model. Adult ICR mice were used to create a photothrombotic stroke (PT) model. LAQ was administered orally at 30 min after ischemic injury. Neurobehavioral tests, Evans Blue, immunofluorescence, TUNEL, Nissl staining, and western blot were performed to evaluate the neurofunctional outcome. Quantification of immunofluorescence was evaluated by unbiased stereology. LAQ post-treatment significantly reduced infarction and improved forepaw function at 5 days after PT. Interestingly, LAQ treatment significantly promoted anti-inflammatory microglial activation. Moreover, LAQ treatment reduced astrocyte activation, glial scar formation, and BBB breakdown in ischemic brains. Therefore, this study demonstrated that LAQ post-treatment restricted microglial polarization, astrogliosis, and glial scar and improved BBB damage and behavioral function. LAQ may serve as a novel target to develop new therapeutic agents for ischemic stroke.