1
|
Newton A, McCann L, Huo L, Liu A. Kynurenine Pathway Regulation at Its Critical Junctions with Fluctuation of Tryptophan. Metabolites 2023; 13:metabo13040500. [PMID: 37110158 PMCID: PMC10143591 DOI: 10.3390/metabo13040500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2023] [Revised: 03/14/2023] [Accepted: 03/28/2023] [Indexed: 04/29/2023] Open
Abstract
The kynurenine pathway (KP) is the primary route for the catabolism of the essential amino acid tryptophan. The central KP metabolites are neurologically active molecules or biosynthetic precursors to critical molecules, such as NAD+. Within this pathway are three enzymes of interest, HAO, ACMSD, and AMSDH, whose substrates and/or products can spontaneously cyclize to form side products such as quinolinic acid (QA or QUIN) and picolinic acid. Due to their unstable nature for spontaneous autocyclization, it might be expected that the levels of these side products would be dependent on tryptophan intake; however, this is not the case in healthy individuals. On top of that, the regulatory mechanisms of the KP remain unknown, even after a deeper understanding of the structure and mechanism of the enzymes that handle these unstable KP metabolic intermediates. Thus, the question arises, how do these enzymes compete with the autocyclization of their substrates, especially amidst increased tryptophan levels? Here, we propose the formation of a transient enzyme complex as a regulatory mechanism for metabolite distribution between enzymatic and non-enzymatic routes during periods of increased metabolic intake. Amid high levels of tryptophan, HAO, ACMSD, and AMSDH may bind together, forming a tunnel to shuttle the metabolites through each enzyme, consequently regulating the autocyclization of their products. Though further research is required to establish the formation of transient complexation as a solution to the regulatory mysteries of the KP, our docking model studies support this new hypothesis.
Collapse
Affiliation(s)
- Ashley Newton
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Luree McCann
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Lu Huo
- Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
| | - Aimin Liu
- Department of Chemistry, University of Texas at San Antonio, San Antonio, TX 78249, USA
- Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
| |
Collapse
|
2
|
Badawy AAB. Hypothesis kynurenic and quinolinic acids: The main players of the kynurenine pathway and opponents in inflammatory disease. Med Hypotheses 2018; 118:129-138. [PMID: 30037600 DOI: 10.1016/j.mehy.2018.06.021] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 05/19/2018] [Accepted: 06/19/2018] [Indexed: 12/22/2022]
Abstract
I hypothesize that the intermediates of the kynurenine (Kyn) pathway (KP) of tryptophan (Trp) degradation kynurenic acid (KA) and quinolinic acid (QA) play opposite roles in inflammatory diseases, with KA being antiinflammatory and QA being immunosuppressant. Darlington et al. have demonstrated a decrease in the ratio of plasma 3-hydroxyanthranilic acid to anthranilic acid ([3-HAA]/[AA]) in many inflammatory conditions and proposed that this decrease either reflects inflammatory disease or is an antiinflammatory response. I argue in favour of the latter possibility and provide evidence that KA is responsible for the decrease in this ratio by increasing AA formation from Kyn through activation of the kynureninase reaction. Immunosuppression has been attributed to some Kyn metabolites tested at concentrations far greater than could occur in microenvironments. So far, only QA has been shown using immunohistochemistry to reach immunosuppressive levels. Future immune studies of the KP should focus on QA as the potentially main microenvironmentally measurable immunosuppressant and should include KA as an antiinflammatory metabolite.
Collapse
Affiliation(s)
- Abdulla A-B Badawy
- School of Health Sciences, Cardiff Metropolitan University, Western Avenue, Cardiff CF5 2YB, Wales, UK.
| |
Collapse
|
3
|
Expression and regulation of immune-modulatory enzyme indoleamine 2,3-dioxygenase (IDO) by human airway epithelial cells and its effect on T cell activation. Oncotarget 2018; 7:57606-57617. [PMID: 27613847 PMCID: PMC5295376 DOI: 10.18632/oncotarget.11586] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 08/20/2016] [Indexed: 12/16/2022] Open
Abstract
Indoleamine 2,3-dioxygenase (IDO) catalyzes the degradation of tryptophan, which plays a critical role in immune suppression through regulating the production of a series of metabolites that are generally referred to as kynurenines. It has become increasingly clear that epithelial cells (ECs) play an active role in maintaining lung homeostasis by modulating the function of immune cells via producing cytokines, chemokines, and anti-microbial mediators. In this study we assessed the regulation of IDO activity and expression in human primary ECs and EC lines under steady state conditions and in response to bacterial and allergenic stimuli. We also investigated the potential immune modulatory functions of IDO expression in human airway ECs. Our data clearly show that airway ECs produce IDO, which is down-regulated in response to allergens and TLR ligands while up-regulated in response to IFN-γ. Using gene silencing, we further demonstrate that IDO plays a key role in the EC-mediated suppression of antigen-specific and polyclonal proliferation of T cells. Interestingly, our data also show that ECs lose their inhibitory effect on T cell activation in response to different TLR agonists mimicking bacterial or viral infections. In conclusion, our work provides an understanding of how IDO is regulated in ECs as well as demonstrates that “resting” ECs can suppress T cell activation in an IDO dependent manner. These data provide new insight into how ECs, through the production of IDO, can influence downstream innate and adaptive responses as part of their function in maintaining immune homeostasis in the airways.
Collapse
|
4
|
Jacobs KR, Guillemin GJ, Lovejoy DB. Development of a Rapid Fluorescence-Based High-Throughput Screening Assay to Identify Novel Kynurenine 3-Monooxygenase Inhibitor Scaffolds. SLAS DISCOVERY 2018; 23:554-560. [PMID: 29420107 DOI: 10.1177/2472555218757180] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Kynurenine 3-monooxygenase (KMO) is a well-validated therapeutic target for the treatment of neurodegenerative diseases, including Alzheimer's disease (AD) and Huntington's disease (HD). This work reports a facile fluorescence-based KMO assay optimized for high-throughput screening (HTS) that achieves a throughput approximately 20-fold higher than the fastest KMO assay currently reported. The screen was run with excellent performance (average Z' value of 0.80) from 110,000 compounds across 341 plates and exceeded all statistical parameters used to describe a robust HTS assay. A subset of molecules was selected for validation by ultra-high-performance liquid chromatography, resulting in the confirmation of a novel hit with an IC50 comparable to that of the well-described KMO inhibitor Ro-61-8048. A medicinal chemistry program is currently underway to further develop our novel KMO inhibitor scaffolds.
Collapse
Affiliation(s)
- K R Jacobs
- 1 Neuroinflammation Group, Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - G J Guillemin
- 1 Neuroinflammation Group, Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - D B Lovejoy
- 1 Neuroinflammation Group, Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| |
Collapse
|
5
|
Jacobs KR, Castellano-Gonzalez G, Guillemin GJ, Lovejoy DB. Major Developments in the Design of Inhibitors along the Kynurenine Pathway. Curr Med Chem 2017; 24:2471-2495. [PMID: 28464785 PMCID: PMC5748880 DOI: 10.2174/0929867324666170502123114] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/13/2017] [Accepted: 04/18/2017] [Indexed: 12/20/2022]
Abstract
Disrupted kynurenine pathway (KP) metabolism has been implicated in the progression of neurodegenerative disease, psychiatric disorders and cancer. Modulation of enzyme activity along this pathway may therefore offer potential new therapeutic strategies for these conditions. Considering their prominent positions in the KP, the enzymes indoleamine 2,3-dioxygenase, kynurenine 3-monooxygenase and kynurenine aminotransferase, appear the most attractive targets. Already, increasing interest in this pathway has led to the identification of a number of potent and selective enzyme inhibitors with promising pre-clinical data and the elucidation of several enzyme crystal structures provides scope to rationalize the molecular mechanisms of inhibitor activity. The field seems poised to yield one or more inhibitors that should find clinical utility.
Collapse
Affiliation(s)
- Kelly R Jacobs
- Neuroinflammation Group, Department of Biomedical Research, Faculty of Medicine and Health Sciences, Macquarie University, Sydney. Australia
| | - Gloria Castellano-Gonzalez
- Neuroinflammation Group, Department of Biomedical Research, Faculty of Medicine and Health Sciences, Macquarie University, Sydney. Australia
| | - Gilles J Guillemin
- Department of Biomedical Research, Faculty of Medicine and Health Science, Macquarie University, 2 Technology Place, Sydney. Australia
| | - David B Lovejoy
- Department of Biomedical Research, Faculty of Medicine and Health Science, Macquarie University, 2 Technology Place, Sydney. Australia
| |
Collapse
|
6
|
Abstract
Over the last two decades, evidence for the involvement of quinolinic acid (QUIN) in neuroinflammatory diseases has been exponentially increasing. Within the brain, QUIN is produced and released by infiltrating macrophages and activated microglia, the very cells that are prominent during neuroinflammation. QUIN acts as an agonist of the N-methyl-D-aspartate receptor and as such is considered to be a brain endogenous excitotoxin. Since the discovery of the excitotoxic activity of QUIN in the early 1980s, several other cytotoxic mechanisms have been identified. We know today that QUIN acts as a neurotoxin, gliotoxin, proinflammatory mediator, pro-oxidant molecule and can alter the integrity and cohesion of the blood-brain barrier. This paper aims to review some of the most recent findings about the effects of QUIN and its mode of action.
Collapse
Affiliation(s)
- Gilles J Guillemin
- Department of Pharmacology, School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia.
| |
Collapse
|
7
|
von Bubnoff D, Wilms H, Scheler M, Brenk M, Koch S, Bieber T. Human myeloid dendritic cells are refractory to tryptophan metabolites. Hum Immunol 2011; 72:791-7. [DOI: 10.1016/j.humimm.2011.05.026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 05/24/2011] [Accepted: 05/25/2011] [Indexed: 12/18/2022]
|
8
|
Flint MS, Hood BL, Sun M, Stewart NA, Jones-Laughner J, Conrads TP. Proteomic Analysis of the Murine Liver in Response to a Combined Exposure to Psychological Stress and 7,12-Dimethylbenz(a)anthracene. J Proteome Res 2009; 9:509-20. [DOI: 10.1021/pr900861j] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Melanie S. Flint
- Department of Pharmacology & Chemical Biology, Cancer Biomarkers Facility - Mass Spectrometry Platform, University of Pittsburgh Cancer Institute, and Center for Clinical Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Brian L. Hood
- Department of Pharmacology & Chemical Biology, Cancer Biomarkers Facility - Mass Spectrometry Platform, University of Pittsburgh Cancer Institute, and Center for Clinical Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Mai Sun
- Department of Pharmacology & Chemical Biology, Cancer Biomarkers Facility - Mass Spectrometry Platform, University of Pittsburgh Cancer Institute, and Center for Clinical Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Nicolas A. Stewart
- Department of Pharmacology & Chemical Biology, Cancer Biomarkers Facility - Mass Spectrometry Platform, University of Pittsburgh Cancer Institute, and Center for Clinical Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Jacqueline Jones-Laughner
- Department of Pharmacology & Chemical Biology, Cancer Biomarkers Facility - Mass Spectrometry Platform, University of Pittsburgh Cancer Institute, and Center for Clinical Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Thomas P. Conrads
- Department of Pharmacology & Chemical Biology, Cancer Biomarkers Facility - Mass Spectrometry Platform, University of Pittsburgh Cancer Institute, and Center for Clinical Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| |
Collapse
|
9
|
Terness P, Chuang JJ, Opelz G. The immunoregulatory role of IDO-producing human dendritic cells revisited. Trends Immunol 2006; 27:68-73. [PMID: 16406698 DOI: 10.1016/j.it.2005.12.006] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 11/17/2005] [Accepted: 12/15/2005] [Indexed: 11/29/2022]
Abstract
Following the finding that indoleamine 2,3-dioxygenase (IDO), an enzyme expressed in the placenta, prevents rejection of allogeneic fetuses in mice, many studies have focused on the role of IDO in the regulation of the immune response. Most arguments for an immunoregulatory role of IDO in vivo are based on observations in mice. Here, we critically examine the arguments for and against a function of IDO-expressing human dendritic cells (DCs) and conclude that proof for an immunoregulatory role in vivo is still lacking.
Collapse
Affiliation(s)
- Peter Terness
- Institute of Immunology, Department of Transplantation Immunology, INF 305, University of Heidelberg, 69120 Heidelberg, Germany.
| | | | | |
Collapse
|
10
|
Abstract
Human immunodeficiency virus (HIV) infection is often complicated by the development of acquired immunodeficiency syndrome (AIDS) dementia complex (ADC). Quinolinic acid (QUIN) is an end product of tryptophan, metabolized through the kynurenine pathway (KP) that can act as an endogenous brain excitotoxin when produced and released by activated macrophages/microglia, the very cells that are prominent in the pathogenesis of ADC. This review examines QUIN's involvement in the features of ADC and its role in pathogenesis. We then synthesize these findings into a hypothetical model for the role played by QUIN in ADC, and discuss the implications of this model for ADC and other inflammatory brain diseases.
Collapse
Affiliation(s)
- Gilles J Guillemin
- Centre for Immunology, Department of Neurology, St Vincent's Hospital, Sydney, Australia
| | | | | |
Collapse
|