301
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Gras G, Kaul M. Molecular mechanisms of neuroinvasion by monocytes-macrophages in HIV-1 infection. Retrovirology 2010; 7:30. [PMID: 20374632 PMCID: PMC2864195 DOI: 10.1186/1742-4690-7-30] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Accepted: 04/07/2010] [Indexed: 12/12/2022] Open
Abstract
HIV associated neurocognitive disorders and their histopathological correlates largely depend on the continuous seeding of the central nervous system with immune activated leukocytes, mainly monocytes/macrophages from the periphery. The blood-brain-barrier plays a critical role in this never stopping neuroinvasion, although it appears unaltered until the late stage of HIV encephalitis. HIV flux that moves toward the brain thus relies on hijacking and exacerbating the physiological mechanisms that govern blood brain barrier crossing rather than barrier disruption. This review will summarize the recent data describing neuroinvasion by HIV with a focus on the molecular mechanisms involved.
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Affiliation(s)
- Gabriel Gras
- Institute of Emerging Diseases and Innovative Therapies, Division of Immuno-Virology, CEA, 18 Route du Panorama, F92265 Fontenay-aux Roses, France.
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302
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Sathyasaikumar KV, Stachowski EK, Amori L, Guidetti P, Muchowski PJ, Schwarcz R. Dysfunctional kynurenine pathway metabolism in the R6/2 mouse model of Huntington's disease. J Neurochem 2010; 113:1416-25. [PMID: 20236387 DOI: 10.1111/j.1471-4159.2010.06675.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Elevated concentrations of neurotoxic metabolites of the kynurenine pathway (KP) of tryptophan degradation may play a causative role in Huntington's disease (HD). The brain levels of one of these compounds, 3-hydroxykynurenine (3-HK), are increased in both HD and several mouse models of the disease. In the present study, we examined this impairment in greater detail using the R6/2 mouse, a well-established animal model of HD. Initially, mutant and age-matched wild-type mice received an intrastriatal injection of (3)H-tryptophan to assess the acute, local de novo production of kynurenine, the immediate bioprecursor of 3-HK, in vivo. No effect of genotype was observed between 4 and 12 weeks of age. In contrast, intrastriatally applied (3)H-kynurenine resulted in significantly increased neosynthesis of (3)H-3-HK, but not other tritiated KP metabolites, in the R6/2 striatum. Subsequent ex vivo studies in striatal, cortical and cerebellar tissue revealed substantial increases in the activity of the biosynthetic enzyme of 3-HK, kynurenine 3-monooxygenase and significant reductions in the activity of its degradative enzyme, kynureninase, in HD mice starting at 4 weeks of age. Decreased kynureninase activity was most evident in the cortex and preceded the increase in kynurenine 3-monooxygenase activity. The activity of other KP enzymes showed no consistent brain abnormalities in the mutant mice. These findings suggest that impairments in its immediate metabolic enzymes jointly account for the abnormally high brain levels of 3-HK in the R6/2 model of HD.
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Affiliation(s)
- Korrapati V Sathyasaikumar
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD 21228, USA
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303
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Linderholm K, Powell S, Olsson E, Holtze M, Snodgrass R, Erhardt S. Role of the NMDA-receptor in Prepulse Inhibition in the Rat. Int J Tryptophan Res 2010; 3:1-12. [PMID: 22084584 PMCID: PMC3195246 DOI: 10.4137/ijtr.s4260] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Kynurenic acid (KYNA) is an endogenous metabolite of tryptophan. Studies have revealed increased brain KYNA levels in patients with schizophrenia. Prepulse inhibition (PPI) is a behavioral model for sensorimotor gating and found to be reduced in schizophrenia. Previous studies have shown that pharmacologically elevated brain KYNA levels disrupt PPI in the rat. The aim of the present study was to investigate the receptor(s) involved in this effect. Rats were treated with different drugs selectively blocking each of the sites that KYNA antagonizes, namely the glutamate recognition site of the N-methyl-D-aspartate receptor (NMDAR), the α7* nicotinic acetylcholine receptor (α7nAChR) and the glycine site of the NMDAR. Kynurenine (200 mg/kg) was given to replicate the effects of increased levels of KYNA on PPI. In order to block the glutamate recognition site of the NMDAR, CGS 19755 (10 mg/kg) or SDZ 220–581 (2.5 mg/kg) were administered and to antagonize the α7nAChR methyllycaconitine (MLA; 6 mg/kg) was given. L-701,324 (1 and 4 mg/kg) or 4-Chloro-kynurenine (4-Cl-KYN; 25, 50 and 100 mg/kg), a drug in situ converted to 7-Chloro-kynurenic acid, were used to block the glycine-site of the NMDAR. Administration of SDZ 220-581 or CGS 19755 was associated with a robust reduction in PPI, whereas L-701,324, 4-Cl-KYN or MLA failed to alter PPI. Kynurenine increased brain KYNA levels 5-fold and tended to decrease PPI. The present study suggests that neither antagonism of the glycine-site of the NMDA receptor nor antagonism of the α7nAChR disrupts PPI, rather with regard to the effects of KYNA, blockade of the glutamate recognition-site is necessary to reduce PPI.
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Affiliation(s)
- Klas Linderholm
- Dept. of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
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304
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Schwarcz R, Guidetti P, Sathyasaikumar KV, Muchowski PJ. Of mice, rats and men: Revisiting the quinolinic acid hypothesis of Huntington's disease. Prog Neurobiol 2010; 90:230-45. [PMID: 19394403 PMCID: PMC2829333 DOI: 10.1016/j.pneurobio.2009.04.005] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Accepted: 04/17/2009] [Indexed: 12/31/2022]
Abstract
The neurodegenerative disease Huntington's disease (HD) is caused by an expanded polyglutamine (polyQ) tract in the protein huntingtin (htt). Although the gene encoding htt was identified and cloned more than 15 years ago, and in spite of impressive efforts to unravel the mechanism(s) by which mutant htt induces nerve cell death, these studies have so far not led to a good understanding of pathophysiology or an effective therapy. Set against a historical background, we review data supporting the idea that metabolites of the kynurenine pathway (KP) of tryptophan degradation provide a critical link between mutant htt and the pathophysiology of HD. New studies in HD brain and genetic model organisms suggest that the disease may in fact be causally related to early abnormalities in KP metabolism, favoring the formation of two neurotoxic metabolites, 3-hydroxykynurenine and quinolinic acid, over the related neuroprotective agent kynurenic acid. These findings not only link the excitotoxic hypothesis of HD pathology to an impairment of the KP but also define new drug targets and therefore have direct therapeutic implications. Thus, pharmacological normalization of the imbalance in brain KP metabolism may provide clinical benefits, which could be especially effective in early stages of the disease.
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Affiliation(s)
- Robert Schwarcz
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD, USA.
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305
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Wang Y, Lawson MA, Dantzer R, Kelley KW. LPS-induced indoleamine 2,3-dioxygenase is regulated in an interferon-gamma-independent manner by a JNK signaling pathway in primary murine microglia. Brain Behav Immun 2010; 24:201-9. [PMID: 19577630 PMCID: PMC2818058 DOI: 10.1016/j.bbi.2009.06.152] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 06/25/2009] [Accepted: 06/29/2009] [Indexed: 01/03/2023] Open
Abstract
Inflammation-induced activation of the tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase (IDO) causes depressive-like behavior in mice following acute activation of the innate immune system by lipopolysaccharide (LPS). Here we investigated the mechanism of IDO expression induced by LPS in primary cultures of microglia derived from neonatal C57BL/6J mice. LPS (10 ng/ml) induced IDO transcripts that peaked at 8h and enzymatic activity at 24h, resulting in an increase in extracellular kynurenine, the catabolic product of IDO-induced tryptophan catabolism. This IDO induction by LPS was accompanied by synthesis and secretion of the proinflammatory cytokines TNFalpha and IL-6, but without detectable IFNgamma expression. To explore the mechanism of LPS-induced IDO expression, microglia were pretreated with the c-Jun-N-terminal kinase (JNK) inhibitor SP600125 for 30 min before LPS treatment. We found that SP600125 blocked JNK phosphorylation and significantly decreased IDO expression induced by LPS, which was accompanied by a reduction of LPS-induced expression of TNFalpha and IL-6. Collectively, these data extend to microglia the property that LPS induces IDO expression via an IFNgamma-independent mechanism that depends upon activation of JNK. Inhibition of the JNK pathway may provide a new therapy for inflammatory depression.
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Affiliation(s)
- Yunxia Wang
- Department of Animal Sciences, Integrative Immunology and Behavior Program, University of Illinois at Urbana-Champaign, 227 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801-3873, USA.
| | - Marcus A. Lawson
- Department of Animal Sciences, Integrative Immunology and Behavior Program, University of Illinois at Urbana-Champaign, 227 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801-3873, USA
| | - Robert Dantzer
- Department of Animal Sciences, Integrative Immunology and Behavior Program, University of Illinois at Urbana-Champaign, 227 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801-3873, USA,Department of Pathology, College of ACES, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Keith W. Kelley
- Department of Animal Sciences, Integrative Immunology and Behavior Program, University of Illinois at Urbana-Champaign, 227 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801-3873, USA,Department of Pathology, College of ACES, University of Illinois at Urbana-Champaign, Urbana, IL, USA,Corresponding authors: Keith W. Kelley, 227 Edward R. Madigan Laboratory, 1201 W. Gregory Dr., University of Illinois at Urbana-Champaign, Urbana, IL 61801-3873. Tel: (217) 333-5141, Fax: (217) 244-5617, or Yunxia Wang, 800 Xiangyin Road, Department of Nautical Medicine, Second Military Medical University, Shanghai, China 200433,
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306
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Bonda DJ, Mailankot M, Stone JG, Garrett MR, Staniszewska M, Castellani RJ, Siedlak SL, Zhu X, Lee HG, Perry G, Nagaraj RH, Smith MA. Indoleamine 2,3-dioxygenase and 3-hydroxykynurenine modifications are found in the neuropathology of Alzheimer's disease. Redox Rep 2010; 15:161-8. [PMID: 20663292 PMCID: PMC2956440 DOI: 10.1179/174329210x12650506623645] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Tryptophan metabolism, through the kynurenine pathway, produces neurotoxic intermediates that are implicated in the pathogenesis of Alzheimer's disease. In particular, oxidative stress via 3-hydroxykynurenine (3-HK) and its cleaved product 3-hydroxyanthranilic acid (3-HAA) significantly damages neuronal tissue and may potentially contribute to a cycle of neurodegeneration through consequent amyloid-beta accumulation, glial activation, and up-regulation of the kynurenine pathway. To determine the role of the kynurenine pathway in eliciting and continuing oxidative stress within Alzheimer's diseased brains, we used immunocytochemical methods to show elevated levels of 3-HK modifications and the upstream, rate-limiting enzyme indoleamine 2,3-dioxygenase (IDO-1) in Alzheimer's diseased brains when compared to controls. Importantly, the association of IDO-1 with senile plaques was confirmed and, for the first time, IDO-1 was shown to be specifically localized in conjunction with neurofibrillary tangles. As senile plaques and neurofibrillary tangles are the pathological hallmarks of Alzheimer's disease, our study provides further evidence that the kynurenine pathway is involved with the destructive neurodegenerative pathway of Alzheimer's disease.
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Affiliation(s)
- David J. Bonda
- Department of PathologyCase Western Reserve University, Cleveland, Ohio, USA
| | - Maneesh Mailankot
- Department of Ophthalmology and Visual SciencesCase Western Reserve University, Cleveland, Ohio, USA
| | - Jeremy G. Stone
- Department of PathologyCase Western Reserve University, Cleveland, Ohio, USA
| | - Matthew R. Garrett
- Departments of PathologyCase Western Reserve University, Cleveland, Ohio, USA, Otolaryngology-Head and Neck Surgery, Ohio State University College of Medicine, Columbus, Ohio, USA
| | - Magdalena Staniszewska
- Department of Ophthalmology and Visual SciencesCase Western Reserve University, Cleveland, Ohio, USA, Schepens Eye Research Institute, Harvard Medical School, Boston, Massachusetts, USA
| | | | - Sandra L. Siedlak
- Department of PathologyCase Western Reserve University, Cleveland, Ohio, USA
| | - Xiongwei Zhu
- Department of PathologyCase Western Reserve University, Cleveland, Ohio, USA
| | - Hyoung-gon Lee
- Department of PathologyCase Western Reserve University, Cleveland, Ohio, USA
| | - George Perry
- Department of PathologyCase Western Reserve University, Cleveland, Ohio, USA, UTSA Neurosciences Institute and Department of Biology, University of Texas at San Antonio, San Antonio, Texas, USA
| | - Ram H. Nagaraj
- Department of Ophthalmology and Visual SciencesCase Western Reserve University, Cleveland, Ohio, USA
| | - Mark A. Smith
- Department of PathologyCase Western Reserve University, 2103 Cornell Road, Cleveland, Ohio 44106, USA;,
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307
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Modulation of the Kynurenine Pathway for the Potential Treatment of Neurodegenerative Diseases. TOPICS IN MEDICINAL CHEMISTRY 2010. [DOI: 10.1007/7355_2010_9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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308
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Ting KK, Brew BJ, Guillemin GJ. Effect of quinolinic acid on human astrocytes morphology and functions: implications in Alzheimer's disease. J Neuroinflammation 2009; 6:36. [PMID: 20003262 PMCID: PMC2797503 DOI: 10.1186/1742-2094-6-36] [Citation(s) in RCA: 113] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Accepted: 12/10/2009] [Indexed: 02/06/2023] Open
Abstract
The excitotoxin quinolinic acid (QUIN) is synthesized through the kynurenine pathway (KP) by activated monocyte lineage cells. QUIN is likely to play a role in the pathogenesis of several major neuroinflammatory diseases including Alzheimer's disease (AD). The presence of reactive astrocytes, astrogliosis, increased oxidative stress and inflammatory cytokines are important pathological hallmarks of AD. We assessed the stimulatory effects of QUIN at low physiological to high excitotoxic concentrations in comparison with the cytokines commonly associated with AD including IFN-γ and TNF-α on primary human astrocytes. We found that QUIN induces IL-1β expression, a key mediator in AD pathogenesis, in human astrocytes. We also explored the effect of QUIN on astrocyte morphology and functions. At low concentrations, QUIN treatment induced concomitantly a marked increase in glial fibrillary acid protein levels and reduction in vimentin levels compared to controls; features consistent with astrogliosis. At pathophysiological concentrations QUIN induced a switch between structural protein expressions in a dose dependent manner, increasing VIM and concomitantly decreasing GFAP expression. Glutamine synthetase (GS) activity was used as a functional metabolic test for astrocytes. We found a significant dose-dependent reduction in GS activity following QUIN treatment. All together, this study showed that QUIN is an important factor for astroglial activation, dysregulation and cell death with potential relevance to AD and other neuroinflammatory diseases.
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Affiliation(s)
- Ka Ka Ting
- St Vincent's Centre for Applied Medical Research, St Vincent's Hospital, Sydney, Australia.
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309
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Chen Y, Stankovic R, Cullen KM, Meininger V, Garner B, Coggan S, Grant R, Brew BJ, Guillemin GJ. The kynurenine pathway and inflammation in amyotrophic lateral sclerosis. Neurotox Res 2009; 18:132-42. [PMID: 19921535 DOI: 10.1007/s12640-009-9129-7] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2009] [Revised: 09/22/2009] [Accepted: 10/27/2009] [Indexed: 12/11/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is a progressive and fatal motor neuron disease of unknown pathogenesis. The kynurenine pathway (KP), activated during neuroinflammation, is emerging as a possible contributory factor in ALS. The KP is the major route for tryptophan (TRP) catabolism. The intermediates generated can be either neurotoxic, such as quinolinic acid (QUIN), or neuroprotective, such as picolinic acid (PIC), an important endogenous chelator. The first and inducible enzyme of the pathway is indoleamine 2,3-dioxygenase (IDO). The present study aimed to characterize the expression of the KP in cerebrospinal fluid (CSF), serum and central nervous system (CNS) tissue of ALS patients. Using high performance liquid chromatography, we analysed the levels of TRP and kynurenine (KYN), and, with gas chromatography/mass spectrometry, the levels of PIC and QUIN, in the CSF and serum of ALS patients and control subjects. Immunohistochemistry was employed to determine the expression of QUIN, IDO and human leukocyte antigen-DR (HLA-DR) in sections of brain and spinal cord from ALS patients. There were significantly increased levels of CSF and serum TRP (P < 0.0001), KYN (P < 0.0001) and QUIN (P < 0.05) and decreased levels of serum PIC (P < 0.05) in ALS samples. There was a significant increase in activated microglia expressing HLA-DR (P < 0.0001) and increased neuronal and microglial expression of IDO and QUIN in ALS motor cortex and spinal cord. We show the presence of neuroinflammation in ALS and provide the first strong evidence for the involvement of the KP in ALS. These data point to an inflammation-driven excitotoxic-chelation defective mechanism in ALS, which may be amenable to inhibitors of the KP.
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Affiliation(s)
- Yiquan Chen
- Department of Pharmacology, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia
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310
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Müller N, Myint AM, Schwarz MJ. The impact of neuroimmune dysregulation on neuroprotection and neurotoxicity in psychiatric disorders--relation to drug treatment. DIALOGUES IN CLINICAL NEUROSCIENCE 2009. [PMID: 19877499 PMCID: PMC3181925 DOI: 10.31887/dcns.2009.11.3/nmueller] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
An inflammatory pathogenesis has been postulated for schizophrenia and major depression (MD). In schizophrenia and depression, opposing patterns oftype-1 vs type-2 immune response seem to be associated with differences in the activation of the enzyme indoleamine 2,3-dioxygenase and in the tryptophan-kynurenine metabolism, resulting in increased production of kynurenic acid in schizophrenia and decreased production of kynurenic acid in depression. These differences are associated with an imbalance in the glutamatergic neurotransmission, which may contribute to an excessive agonist action of N-methyl-D-aspartate (NMDA) in depression and of NMDA antagonism in schizophrenia. Regarding the neuroprotective function of kynurenic acid and the neurotoxic effects of quinolinic acid (QUIN), different patterns of immune activation may also lead to an imbalance between the neuroprotective and the neurotoxic effects of the tryptophanlkynurenine metabolism. The differential activation of microglia cells and astrocytes may be an additional mechanism contributing to this imbalance. The immunological imbalance results in an inflammatory state combined with increased prostaglandin E2 production and increased cyclo-oxygenase-2 (COX-2) expression. The immunological effects of many existing antipsychotics and antidepressants, however, partly correct the immune imbalance and the excess production of the neurotoxic QUIN, COX-2 inhibitors have been tested in animal models of depression and in preliminary clinical trials, pointing to favorable effects in schizophrenia and in MD.
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Affiliation(s)
- Norbert Müller
- Department of Psychiatry and Psychotherapy, Ludwig-Maximilians-Universität München, Germany.
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311
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312
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Erhardt S, Olsson SK, Engberg G. Pharmacological manipulation of kynurenic acid: potential in the treatment of psychiatric disorders. CNS Drugs 2009; 23:91-101. [PMID: 19173370 DOI: 10.2165/00023210-200923020-00001] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The kynurenine pathway constitutes the main route of tryptophan degradation and generates the production of several neuroactive compounds; quinolinic acid is an excitotoxic NMDA receptor agonist, 3-hydroxykynurenine is a free-radical generator and kynurenic acid (KYNA) is an antagonist at glutamate and nicotinic receptors. In low micromolar concentrations, KYNA blocks the glycine site of the NMDA receptor and the nicotinic alpha(7) acetylcholine receptor. Knowledge regarding kynurenine metabolites and their involvement in neurophysiological processes has increased dramatically in recent years. In particular, endogenous KYNA appears to tightly control firing of midbrain dopamine neurons and to be involved in cognitive functions. Thus, decreased endogenous levels of rat brain KYNA have been found to reduce firing of these neurons, and mice with a targeted deletion of kynurenine aminotransferase II display low endogenous brain KYNA levels concomitant with an increased performance in cognitive tests. It is also suggested that kynurenines participate in the pathophysiology of psychiatric disorders. Thus, elevated levels of KYNA have been found in the CSF as well as in the post-mortem brain of patients with schizophrenia. Advantages in understanding how kynurenines can be pharmacologically manipulated may provide new possibilities in the treatment of psychiatric disorders, such as schizophrenia.
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Affiliation(s)
- Sophie Erhardt
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
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313
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Grant RS, Coggan SE, Smythe GA. The physiological action of picolinic Acid in the human brain. Int J Tryptophan Res 2009; 2:71-9. [PMID: 22084583 PMCID: PMC3195224 DOI: 10.4137/ijtr.s2469] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Picolinic Acid is an endogenous metabolite of L-tryptophan (TRP) that has been reported to possess a wide range of neuroprotective, immunological, and anti-proliferative affects within the body. However the salient physiological function of this molecule is yet to be established. The synthesis of picolinic acid as a product of the kynurenine pathway (KP) suggests that, similar to other KP metabolites, picolinic acid may play a role in the pathogenesis of inflammatory disorders within the CNS and possibly other organs. In this paper we review the limited body of literature dealing with the physiological actions of picolinic acid in the CNS and its associated synthesis via the kynurenine pathway in health and disease. Discrepancies and gaps in our current knowledge of picolinic acid are identified highlighting areas of research to promote a more complete understanding of its endogenous function in the brain.
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Affiliation(s)
- R S Grant
- School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney NSW, 2052
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314
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Braidy N, Grant R, Adams S, Brew BJ, Guillemin GJ. Mechanism for Quinolinic Acid Cytotoxicity in Human Astrocytes and Neurons. Neurotox Res 2009; 16:77-86. [DOI: 10.1007/s12640-009-9051-z] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Revised: 03/31/2009] [Accepted: 04/02/2009] [Indexed: 12/28/2022]
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315
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Braidy N, Grant R, Brew BJ, Adams S, Jayasena T, Guillemin GJ. Effects of Kynurenine Pathway Metabolites on Intracellular NAD Synthesis and Cell Death in Human Primary Astrocytes and Neurons. Int J Tryptophan Res 2009; 2:61-9. [PMID: 22084582 PMCID: PMC3195228 DOI: 10.4137/ijtr.s2318] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The kynurenine pathway (KP) is a major route of L-tryptophan catabolism resulting in the production of the essential pyridine nucleotide nicotinamide adenine dinucleotide, (NAD+). Up-regulation of the KP during inflammation leads to the release of a number of biologically active metabolites into the brain. We hypothesised that while some of the extracellular KP metabolites may be beneficial for intracellular NAD+ synthesis and cell survival at physiological concentrations, they may contribute to neuronal and astroglial dysfunction and cell death at pathophysiological concentrations. In this study, we found that treatment of human primary neurons and astrocytes with 3-hydroxyanthranilic acid (3-HAA), 3-hydroxykynurenine (3-HK), quinolinic acid (QUIN), and picolinic acid (PIC) at concentrations below 100 nM significantly increased intracellular NAD+ levels compared to non-treated cells. However, a dose dependent decrease in intracellular NAD+ levels and increased extracellular LDH activity was observed in human astrocytes and neurons treated with 3-HAA, 3-HK, QUIN and PIC at concentrations >100 nM and kynurenine (KYN), at concentrations above 1 μM. Intracellular NAD+ levels were unchanged in the presence of the neuroprotectant, kynurenic acid (KYNA), and a dose dependent increase in intracellular NAD+ levels was observed for TRP up to 1 mM. While anthranilic acid (AA) increased intracellular NAD+ levels at concentration below 10 μM in astrocytes. NAD+ depletion and cell death was observed in AA treated neurons at concentrations above 500 nM. Therefore, the differing responses of astrocytes and neurons to an increase in KP metabolites should be considered when assessing KP toxicity during neuroinflammation.
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Affiliation(s)
- Nady Braidy
- University of New South Wales, Faculty of Medicine, Sydney, Australia
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316
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Abstract
Chronic stress, by initiating changes in the hypothalamic-pituitary-adrenal (HPA) axis and the immune system, acts as a trigger for anxiety and depression. There is experimental and clinical evidence that the rise in the concentration of pro-inflammatory cytokines and glucocorticoids, which occurs in a chronically stressful situation and also in depression, contribute to the behavioural changes associated with depression. A defect in serotonergic function is associated with these hormonal and immune changes. Neurodegenerative changes in the hippocampus, prefrontal cortex and amygdalae are the frequent outcome of the changes in the HPA axis and the immune system. Such changes may provide evidence for the link between chronic depression and dementia in later life.
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Affiliation(s)
- Brian E Leonard
- Pharmacology Department, National University of Ireland, Galway, Ireland.
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317
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Metallothionein Treatment Attenuates Microglial Activation and Expression of Neurotoxic Quinolinic Acid Following Traumatic Brain Injury. Neurotox Res 2009; 15:381-9. [DOI: 10.1007/s12640-009-9044-y] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Revised: 02/19/2009] [Accepted: 03/10/2009] [Indexed: 10/20/2022]
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318
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Vamos E, Pardutz A, Klivenyi P, Toldi J, Vecsei L. The role of kynurenines in disorders of the central nervous system: possibilities for neuroprotection. J Neurol Sci 2009; 283:21-7. [PMID: 19268309 DOI: 10.1016/j.jns.2009.02.326] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The metabolism of tryptophan mostly proceeds through the kynurenine pathway. The biochemical reaction includes both an agonist (quinolinic acid) at the N-methyl-d-aspartate receptor and an antagonist (kynurenic acid). Besides the N-methyl-d-aspartate antagonism, an important feature of kynurenic acid is the blockade of the alpha7-nicotinic acetylcholine receptor and its influence on the alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptor. Kynurenic acid has proven to be neuroprotective in several experimental settings. On the other hand, quinolinic acid is a potent neurotoxin with an additional and marked free radical-producing property. In consequence of these various receptor activities, the possible roles of these substances in various neurological disorders have been proposed. Moreover, the possibility of influencing the kynurenine pathway to reduce quinolinic acid and increase the level of kynurenic acid in the brain offers a new target for drug action designed to change the balance, decreasing excitotoxins and enhancing neuroprotectants. This review surveys both the early and the current research in this field, focusing on the possible therapeutic effects of kynurenines.
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Affiliation(s)
- Eniko Vamos
- Department of Neurology, Albert Szent-Györgyi Clinical Centre, University of Szeged, Hungary
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Baran H, Kepplinger B. Cerebrolysin lowers kynurenic acid formation--an in vitro study. Eur Neuropsychopharmacol 2009; 19:161-8. [PMID: 19008081 DOI: 10.1016/j.euroneuro.2008.09.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2008] [Revised: 09/10/2008] [Accepted: 09/30/2008] [Indexed: 11/24/2022]
Abstract
The therapeutic effect of Cerebrolysin in the treatment of dementia and brain injury has been proposed because of neurotrophic properties of this compound. Since an increased kynurenine metabolism has been documented in several brain pathologies including dementia the aim of the present study was to investigate the biochemical properties of Cerebrolysin with respect to kynurenic acid (KYNA) formation in an in vitro study. KYNA is an endogenous metabolite of the kynurenine pathway of tryptophan degradation and is an antagonist of the glutamate ionotropic excitatory amino acid and of the nicotine cholinergic receptors. The activities of the KYNA synthesizing enzymes kynurenine aminotransferases I, II and III (KAT I, KAT II and KAT III) in rat liver, and rat and human brain homogenates were analysed in the presence of Cerebrolysin. KAT I, II and III activities were measured using a radio-enzymatic method in the presence of 1 mM pyruvate and 100 microM [H(3)]L-kynurenine. Cerebrolysin, dose-dependently and significantly reduced KAT I, KAT II and KAT III activities of rat liver homogenate. Furthermore, Cerebrolysin exerted a dose-dependent inhibition of rat and human brain KAT I, KAT II and KAT III activities, too. The inhibitory effect of Cerebrolysin was more pronounced for KAT I than for KAT II and KAT III. The present study for the first time demonstrates the ability of Cerebrolysin to lower KYNA formation in rat liver as well as in rat and human brain homogenates. We propose Cerebrolysin as a compound susceptible of therapeutic exploitation in some disorders associated with elevated KYNA metabolism in the brain and/or other tissues. We suggest that the anti-dementia effect of Cerebrolysin observed in Alzheimer patients could be in part due to Cerebrolysin induced reduction of KYNA levels, thus modulating the cholinergic and glutamatergic neurotransmissions.
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Affiliation(s)
- Halina Baran
- Neurophysiology, Institute of Physiology, Department for Biomedical Sciences, Veterinary Medical University Vienna, Vienna, Austria.
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320
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Myint AM, Schwarz MJ, Steinbusch HWM, Leonard BE. Neuropsychiatric disorders related to interferon and interleukins treatment. Metab Brain Dis 2009; 24:55-68. [PMID: 19067144 DOI: 10.1007/s11011-008-9114-5] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Accepted: 10/28/2008] [Indexed: 01/18/2023]
Abstract
Certain cytokines such as interferon-alpha and interleukin-2 are often used in the treatment certain cancers and chronic diseases such as melanoma, hepatitis C infection and multiple sclerosis. Several neuropsychiatric side effects such as depression, anxiety, psychosis, suicidal ideation, hypomanic mood and cognitive impairment were reported in those patients who received those medications. In certain patients with those neuropsychiatric side effects, the symptoms ceased when the medication was stopped. However, in some cases, the cognitive impairment persisted even for years after cessation of the medication. In animal studies, those cytokines could induce sickness behaviour, anxiety behaviour and social anhedonia. The increased in pro-inflammatory cytokines in certain neuropsychiatric disorders was widely reported. In addition, in animal studies, the treatment with interferon-alpha or interleukin-1 could induce depressive like behaviour. Recently, the role of certain pro-inflammatory cytokines that could enhance the activity of the enzyme, indoleamine 2-3, dioxygenase (IDO) which in turn would increase tryptophan degradation into kynurenine and decrease tryptophan availability of tryptophan in the brain to synthesize serotonin, a neurotransmitter which is necessary for the normal mood state became of interest in pathophysiology of psychiatric disorders. Furthermore, the imbalance in the further downward catabolic kynurenine pathway and their interactions with other neurotransmitters has been proposed to play an important role. The presence of such an imbalance in patients being treated with cytokines and in patients with psychiatric disorders and the possible consequence of those changes on the neuroprotective function in the brain are discussed in this review.
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Affiliation(s)
- Aye Mu Myint
- Laboratory Section for Psychoneuroimmunology and Therapeutic Drug Monitoring, Ludwig-Maximilians University, Nussbaumstrasse 7, 80336 Munich, Germany.
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321
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Amori L, Guidetti P, Pellicciari R, Kajii Y, Schwarcz R. On the relationship between the two branches of the kynurenine pathway in the rat brain in vivo. J Neurochem 2009; 109:316-25. [PMID: 19226371 DOI: 10.1111/j.1471-4159.2009.05893.x] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the mammalian brain, kynurenine aminotransferase II (KAT II) and kynurenine 3-monooxygenase (KMO), key enzymes of the kynurenine pathway (KP) of tryptophan degradation, form the neuroactive metabolites kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK), respectively. Although physically segregated, both enzymes use the pivotal KP metabolite l-kynurenine as a substrate. We studied the functional consequences of this cellular compartmentalization in vivo using two specific tools, the KAT II inhibitor BFF 122 and the KMO inhibitor UPF 648. The acute effects of selective KAT II or KMO inhibition were studied using a radiotracing method in which the de novo synthesis of KYNA, and of 3-HK and its downstream metabolite quinolinic acid (QUIN), is monitored following an intrastriatal injection of (3)H-kynurenine. In naïve rats, intrastriatal BFF 122 decreased newly formed KYNA by 66%, without influencing 3-HK or QUIN production. Conversely, UPF 648 reduced 3-HK synthesis (by 64%) without affecting KYNA formation. Similar, selective effects of KAT II and KMO inhibition were observed when the inhibitors were applied acutely together with the excitotoxin QUIN, which impairs local KP metabolism. Somewhat different effects of KMO (but not KAT II) inhibition were obtained in rats that had received an intrastriatal QUIN injection 7 days earlier. In these neuron-depleted striata, UPF 648 not only decreased both 3-HK and QUIN production (by 77% and 66%, respectively) but also moderately raised KYNA synthesis (by 27%). These results indicate a remarkable functional segregation of the two pathway branches in the brain, boding well for the development of selective KAT II or KMO inhibitors for cognitive enhancement and neuroprotection, respectively.
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Affiliation(s)
- Laura Amori
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, Maryland, USA
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322
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Chen Y, Guillemin GJ. Kynurenine pathway metabolites in humans: disease and healthy States. Int J Tryptophan Res 2009; 2:1-19. [PMID: 22084578 PMCID: PMC3195227 DOI: 10.4137/ijtr.s2097] [Citation(s) in RCA: 428] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Tryptophan is an essential amino acid that can be metabolised through different pathways, a major route being the kynurenine pathway. The first enzyme of the pathway, indoleamine-2,3-dioxygenase, is strongly stimulated by inflammatory molecules, particularly interferon gamma. Thus, the kynurenine pathway is often systematically up-regulated when the immune response is activated. The biological significance is that 1) the depletion of tryptophan and generation of kynurenines play a key modulatory role in the immune response; and 2) some of the kynurenines, such as quinolinic acid, 3-hydroxykynurenine and kynurenic acid, are neuroactive. The kynurenine pathway has been demonstrated to be involved in many diseases and disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, AIDS dementia complex, malaria, cancer, depression and schizophrenia, where imbalances in tryptophan and kynurenines have been found. This review compiles most of these studies and provides an overview of how the kynurenine pathway might be contributing to disease development, and the concentrations of tryptophan and kynurenines in the serum, cerebrospinal fluid and brain tissues in control and patient subjects.
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Affiliation(s)
- Yiquan Chen
- School of Medical Sciences, University of New South Wales, Sydney 2052, Australia
| | - Gilles J. Guillemin
- School of Medical Sciences, University of New South Wales, Sydney 2052, Australia
- St. Vincent’s Centre for Applied Medical Research, Darlinghurst 2010, Australia
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323
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Induction of the kynurenine pathway by neurotropic influenza a virus infection. J Neurosci Res 2008; 86:3674-83. [DOI: 10.1002/jnr.21799] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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324
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Müller N. Inflammation and the glutamate system in schizophrenia: implications for therapeutic targets and drug development. Expert Opin Ther Targets 2008; 12:1497-507. [DOI: 10.1517/14728220802507852] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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325
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Induction of indolamine 2,3-dioxygenase and kynurenine 3-monooxygenase in rat brain following a systemic inflammatory challenge: a role for IFN-gamma? Neurosci Lett 2008; 441:29-34. [PMID: 18584961 DOI: 10.1016/j.neulet.2008.06.007] [Citation(s) in RCA: 156] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2008] [Revised: 05/10/2008] [Accepted: 06/04/2008] [Indexed: 12/31/2022]
Abstract
Inflammation-mediated dysregulation of the kynurenine pathway has been implicated as a contributor to a number of major brain disorders. Consequently, we examined the impact of a systemic inflammatory challenge on kynurenine pathway enzyme expression in rat brain. Indoleamine 2,3-dioxygenase (IDO) expression was induced in cortex and hippocampus following systemic lipopolysaccharide (LPS) administration. Whilst IDO expression was paralleled by increased circulating interferon (IFN)-gamma concentrations, IFN-gamma expression in the brain was only modestly altered following LPS administration. In contrast, induction of IDO was associated with increased central tumour necrosis factor (TNF)-alpha and interleukin (IL)-6 expression. Similarly, in cultured glial cells LPS-induced IDO expression was accompanied by increased TNF-alpha and IL-6 expression, whereas IFN-gamma was not detectable. These findings indicate that IFN-gamma is not required for LPS-induced IDO expression in brain. A robust increase in kynurenine-3-monooxygenase (KMO) expression was observed in rat brain 24h post LPS, without any change in kynurenine aminotransferase II (KAT II) expression. In addition, we report that constitutive expression of KAT II is approximately 8-fold higher than KMO in cortex and 20-fold higher in hippocampus. Similarly, in glial cells constitutive expression of KAT II was approximately 16-fold higher than KMO, and expression of KMO but not KAT II was induced by LPS. These data are the first to demonstrate that a systemic inflammatory challenge stimulates KMO expression in brain; a situation that is likely to favour kynurenine metabolism in a neurotoxic direction. However, our observation that expression of KAT II is much higher than KMO in rat brain is likely to counteract potential neurotoxicity that could arise from KMO induction following an acute inflammation.
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326
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Ting KK, Brew B, Guillemin G. The involvement of astrocytes and kynurenine pathway in Alzheimer's disease. Neurotox Res 2008; 12:247-62. [PMID: 18201952 DOI: 10.1007/bf03033908] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The kynurenine pathway (KP) and several of its neuroactive products, especially quinolinic acid (QUIN), are considered to be involved in the neuropathogenesis of Alzheimer's disease (AD). There is growing evidence suggesting that astrocytes play a critical role in the regulation of the excitotoxicity and inflammatory processes that occur during the evolution of AD. This review focuses on the role of astrocytes through their relation with the KP to the different features associated with AD including cytokine, chemokine and adhesion molecule production, cytoskeletal changes, astrogliosis, excitotoxicity, apoptosis and neurodegeneration.
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Affiliation(s)
- Ka Ka Ting
- Centre for Immunology, St. Vincent's Hospital, Darlinghurst 2010, Sydney, NSW, Australia
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327
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Abstract
L-kynurenine is an intermediate in the pathway of the metabolism of L-tryptophan to nicotinic acid. L-kynurenine is formed in the mammalian brain (40%) and is taken up from the periphery (60%), indicating that it can be transported across the BBB. It was discovered some 30 years ago that compounds in the kynurenine family have neuroactive properties. L-kynurenine, the central agent of this pathway, can be converted into two other important compounds: the neuroprotective kynurenic acid and the neurotoxic quinolinic acid. Kynurenines have been shown to be involved in many diverse physiological and pathological processes. There are a number of neurodegenerative disorders whose pathogenesis has been demonstrated to involve multiple imbalances of the kynurenine pathway metabolism. This review summarizes the main steps of the kynurenine pathway under normal conditions, discusses the metabolic disturbances and changes in this pathway in certain neurodegenerative disorders, and finally introduces the therapeutic possibilities with kynurenines.
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Affiliation(s)
- Hermina Robotka
- University of Szeged, Department of Physiology, Anatomy & Neuroscience, POB 533, and,Department of Neurology, POB 427, H-6701 Szeged, Hungary
| | - József Toldi
- University of Szeged, Department of Physiology, Anatomy & Neuroscience, POB 533, H-6701 Szeged, Hungary
| | - László Vécsei
- University of Szeged, Department of Neurology, POB 427, H-6701 Szeged, Hungary
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328
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Owe-Young R, Webster NL, Mukhtar M, Pomerantz RJ, Smythe G, Walker D, Armati PJ, Crowe SM, Brew BJ. Kynurenine pathway metabolism in human blood-brain-barrier cells: implications for immune tolerance and neurotoxicity. J Neurochem 2008; 105:1346-57. [PMID: 18221377 DOI: 10.1111/j.1471-4159.2008.05241.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The catabolic pathway of l-tryptophan (l-trp), known as the kynurenine pathway (KP), has been implicated in the pathogenesis of a wide range of brain diseases through its ability to lead to immune tolerance and neurotoxicity. As endothelial cells (ECs) and pericytes of the blood-brain-barrier (BBB) are among the first brain-associated cells that a blood-borne pathogen would encounter, we sought to determine their expression of the KP. Using RT-PCR and HPLC/GC-MS, we show that BBB ECs and pericytes constitutively express components of the KP. BBB ECs constitutively synthesized kynurenic acid, and after immune activation, kynurenine (KYN), which is secreted basolaterally. BBB pericytes produced small amounts of picolinic acid and after immune activation, KYN. These results have significant implications for the pathogenesis of inflammatory brain diseases in general, particularly human immunodeficiency virus (HIV)-related brain disease. Kynurenine pathway activation at the BBB results in local immune tolerance and neurotoxicity: the basolateral secretion of excess KYN can be further metabolized by perivascular macrophages and microglia with synthesis of quinolinic acid. The results point to a mechanism whereby a systemic inflammatory signal can be transduced across an intact BBB to cause local neurotoxicity.
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Affiliation(s)
- Robert Owe-Young
- University of New South Wales Centre for Immunology, St. Vincent's Hospital, Darlinghurst, New South Wales, Australia.
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329
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Abstract
The kynurenine pathway is a major route of L-tryptophan catabolism producing neuroactive metabolites implicated in neurodegeneration and immune tolerance. We characterized the kynurenine pathway in human neurons and the human SK-N-SH neuroblastoma cell line and found that the kynurenine pathway enzymes were variably expressed. Picolinic carboxylase was expressed only in primary and some adult neurons but not in SK-N-SH cells. Because of this difference, SK-N-SH cells were able to produce the excitotoxin quinolinic acid, whereas human neurons produced the neuroprotectant picolinic acid. The net result of kynurenine pathway induction in human neurons is therefore predicted to result in neuroprotection, immune regulation, and tumor inhibition, whereas in SK-N-SH cells, it may result in neurotoxicity, immune tolerance, and tumor promotion. This study represents the first comprehensive characterization of the kynurenine pathway in neurons and the first description of the involvement of the kynurenine pathway as a mechanism for controlling both tumor cell neurotoxicity and persistence.
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330
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Giorgini F, Möller T, Kwan W, Zwilling D, Wacker JL, Hong S, Tsai LCL, Cheah CS, Schwarcz R, Guidetti P, Muchowski PJ. Histone deacetylase inhibition modulates kynurenine pathway activation in yeast, microglia, and mice expressing a mutant huntingtin fragment. J Biol Chem 2007; 283:7390-400. [PMID: 18079112 DOI: 10.1074/jbc.m708192200] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The kynurenine pathway of tryptophan degradation is hypothesized to play an important role in Huntington disease, a neurodegenerative disorder caused by a polyglutamine expansion in the protein huntingtin. Neurotoxic metabolites of the kynurenine pathway, generated in microglia and macrophages, are present at increased levels in the brains of patients and mouse models during early stages of disease, but the mechanism by which kynurenine pathway up-regulation occurs in Huntington disease is unknown. Here we report that expression of a mutant huntingtin fragment was sufficient to induce transcription of the kynurenine pathway in yeast and that this induction was abrogated by impairing the activity of the histone deacetylase Rpd3. Moreover, numerous genetic suppressors of mutant huntingtin toxicity that are functionally unrelated converged unexpectedly on the kynurenine pathway, supporting a critical role for the kynurenine pathway in mediating mutant huntingtin toxicity in yeast. Histone deacetylase-dependent regulation of the kynurenine pathway was also observed in a mouse model of Huntington disease, in which treatment with a neuroprotective histone deacetylase inhibitor blocked activation of the kynurenine pathway in microglia expressing a mutant huntingtin fragment in vitro and in vivo. These findings suggest that a mutant huntingtin fragment can perturb transcriptional programs in microglia, and thus implicate these cells as potential modulators of neurodegeneration in Huntington disease that are worthy of further investigation.
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Affiliation(s)
- Flaviano Giorgini
- Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
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331
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OXENKRUG GREGORYF. Genetic and Hormonal Regulation of Tryptophan-Kynurenine Metabolism. Ann N Y Acad Sci 2007; 1122:35-49. [DOI: 10.1196/annals.1403.003] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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332
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The immunological basis of glutamatergic disturbance in schizophrenia: towards an integrated view. JOURNAL OF NEURAL TRANSMISSION. SUPPLEMENTUM 2007:269-80. [PMID: 17982903 DOI: 10.1007/978-3-211-73574-9_33] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This overview presents a hypothesis to bridge the gap between psychoneuroimmunological findings and recent results from pharmacological, neurochemical and genetic studies in schizophrenia. In schizophrenia, a glutamatergic hypofunction is discussed to be crucially involved in dopaminergic dysfunction. This view is supported by findings of the neuregulin- and dysbindin genes, which have functional impact on the glutamatergic system. Glutamatergic hypofunction is mediated by NMDA (N-methyl-D-aspartate) receptor antagonism. The only endogenous NMDA receptor antagonist identified up to now is kynurenic acid (KYN-A). KYN-A also blocks the nicotinergic acetycholine receptor, i.e. increased KYN-A levels can explain psychotic symptoms and cognitive deterioration. KYN-A levels are described to be higher in the CSF and in critical CNS regions of schizophrenics. Another line of evidence suggests that of the immune system in schizophrenic patients is characterized by an imbalance between the type-1 and the type-2 immune responses with a partial inhibition of the type-1 response, while the type-2 response is relatively over-activated. This immune constellation is associated with the inhibition of the enzyme indoleamine 2,3-dioxygenase (IDO), because type-2 cytokines are potent inhibitors of IDO. Due to the inhibition of IDO, tryptophan is predominantly metabolized by tryptophan 2,3-dioxygenase (TDO), which is located in astrocytes, but not in microglia cells. As indicated by increased levels of S100B, astrocytes are activated in schizophrenia. On the other hand, the kynurenine metabolism in astrocytes is restricted to the dead-end arm of KYN-A production. Accordingly, an increased TDO activity and an accumulation of KYN-A in the CNS of schizophrenics have been described. Thus, the immune-mediated glutamatergic-dopaminergic dysregulation may lead to the clinical symptoms of schizophrenia. Therapeutic consequences, e.g. the use of antiinflammatory cyclooxygenase-2 inhibitors, which also are able to directly decrease KYN-A, are discussed.
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333
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Lim CK, Smythe GA, Stocker R, Brew BJ, Guillemin GJ. Characterization of the kynurenine pathway in human oligodendrocytes. ACTA ACUST UNITED AC 2007. [DOI: 10.1016/j.ics.2007.07.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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334
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Guillemin GJ, Brew BJ. Chronic HIV infection leads to an Alzheimer's disease like illness. Involvement of the kynurenine pathway. ACTA ACUST UNITED AC 2007. [DOI: 10.1016/j.ics.2007.07.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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335
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Abstract
The metabolism of tryptophan by the kynurenine pathway leads to the production of several neurotoxic compounds, some of which have been associated with neurological disorders. Recent investigation of some relevant compounds in this pathway has provided further evidence of their neurotoxicity.
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336
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Abstract
This manuscript deals with whether immune-mediated mechanisms of inflammation contribute to the pathogenesis of schizophrenia. A model is presented which integrates psychoneuroimmunologic findings and actual results from pharmacological, neurochemical, and genetic studies in schizophrenia. A pivotal role in the neurobiology of schizophrenia is played by dopaminergic neurotransmission, which is modulated by influences of the glutamatergic system. The decreased function of the glutamate system described in schizophrenia seems primarily mediated by N-methyl-D-aspartate (NMDA) receptor antagonism. Kynurenine acid is the only known endogenous NMDA receptor antagonist. In higher concentrations it blocks the NMDA receptor, but in lower concentrations it blocks the nicotinergic acetylcholin receptor, which has a prominent role in cognitive functions. Therefore, higher levels of kynurenine acid may explain psychotic symptoms and cognitive dysfunction. Several findings point out that prenatal infection, associated with an early sensitisation of the immune system, may result in an imbalance of the immune response (type 1 vs type 2) in schizophrenia. This immune constellation leads to inhibition of the enzyme indoleamin dioxigenase (IDO). It and tryptophane 2,3-dioxygenase (TDO) both catalyse the degradation from tryptophan to kynurenine. Due to the inhibition of IDO, tryptophan is metabolised to kynurenine primarily by TDO. In the CNS, TDO is located only in astrocytes, which are in particular activated in schizophrenia and in which kynurenine acid is the final product and can not be further metabolised. Therefore kynurenine acid accumulates in the CNS of schizophrenics and - due to its NMDA-antagonistic properties - leads to cognitive dysfunction and psychotic symptoms. This model describes the pathway of immune-mediated glutamatergic-dopaminergic dysregulation, which may lead to the clinical symptoms of schizophrenia. Therapeutic consequences (e.g. cyclo-oxygenase-2 inhibitors) are discussed.
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Affiliation(s)
- N Müller
- Klinik für Psychiatrie und Psychotherapie, Ludwig-Maximilians-Universität, Nussbaumstrasse 7, 80336 München.
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337
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Linderholm KR, Andersson A, Olsson S, Olsson E, Snodgrass R, Engberg G, Erhardt S. Activation of rat ventral tegmental area dopamine neurons by endogenous kynurenic acid: a pharmacological analysis. Neuropharmacology 2007; 53:918-24. [PMID: 17959203 DOI: 10.1016/j.neuropharm.2007.09.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Revised: 08/24/2007] [Accepted: 09/03/2007] [Indexed: 10/22/2022]
Abstract
Kynurenic acid (KYNA) is an endogenous NMDA receptor antagonist as well as a blocker of the alpha7* nicotinic receptor and mounting evidence suggests that the compound participates in the pathophysiology of schizophrenia. Previous studies have shown that elevated levels of endogenous KYNA are associated with an increased firing of midbrain dopamine (DA) neurons. In the present study, utilizing extracellular single unit cell recording techniques, the mechanism involved in this excitatory action of the compound was analyzed in male Sprague-Dawley rats. Administration of 4-chlorokynurenine (4-Cl-KYN; 25mg/kg, i.p.), which is converted to the selective NMDA glycine-site antagonist 7-chloro-kynurenic acid (7-Cl-KYNA), was found to increase firing rate and per cent burst firing activity of ventral tegmental area (VTA) DA neurons to the same magnitude as pretreatment of kynurenine (causing a 25-fold elevation in extracellular brain KYNA). Intravenous administration of the selective antagonist at the alpha7* nicotinic receptor methyllycaconitine (MLA; 1-4mg/kg) did not affect firing of VTA DA neurons, whereas intraperitoneal administration of this drug in a high dose (6mg/kg) was associated with a decreased firing rate and per cent burst firing activity. Administration of SDZ 220-581 (10mg/kg, i.v.), a competitive antagonist at the glutamate recognition-site of the NMDA receptor, was found to increase firing rate and per cent burst firing. Present results have potential implications for the treatment of schizophrenia, and indicate that the increased activity of VTA DA neurons following elevation of brain KYNA is mediated through glutamatergic rather than by nicotinergic mechanisms.
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Affiliation(s)
- Klas R Linderholm
- Department of Physiology and Pharmacology, Karolinska Institutet, 171 77 Stockholm, Sweden
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338
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Leonard BE. Inflammation, Depression and Dementia: Are they Connected? Neurochem Res 2007; 32:1749-56. [PMID: 17705097 DOI: 10.1007/s11064-007-9385-y] [Citation(s) in RCA: 246] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2007] [Accepted: 05/10/2007] [Indexed: 01/18/2023]
Abstract
Chronic inflammation is now considered to be central to the pathogenesis not only of such medical disorders as cardiovascular disease, multiple sclerosis, diabetes and cancer but also of major depression. If chronic inflammatory changes are a common feature of depression, this could predispose depressed patients to neurodegenerative changes in later life. Indeed there is now clinical evidence that depression is a common antecedent of Alzheimer's disease and may be an early manifestation of dementia before the cognitive declines becomes apparent. This review summarises the evidence that links chronic low grade inflammation with changes in brain structure that could precipitate neurodegenerative changes associated with Alzheimer's disease and other dementias. For example, neuronal loss is a common feature of major depression and dementia. It is hypothesised that the progress from depression to dementia could result from the activation of macrophages in the blood, and microglia in the brain, that release pro-inflammatory cytokines. Such cytokines stimulate a cascade of inflammatory changes (such as an increase in prostaglandin E2, nitric oxide in addition to more pro-inflammatory cytokines) and a hypersecretion of cortisol. The latter steroid inhibits protein synthesis thereby reducing the synthesis of neurotrophic factors and preventing reairto damages neuronal networks. In addition, neurotoxic end products of the tryptophan-kynurenine pathway, such as quinolinic acid, accumulate in astrocytes and neurons in both depression and dementia. Thus increased neurodegeneration, reduced neuroprotection and neuronal repair are common pathological features of major depression and dementia. Such changes may help to explain why major depression is a frequent prelude to dementia in later life.
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Affiliation(s)
- Brian E Leonard
- Department of Psychiatry and Neuropsychology, Brain and Behaviour Research Institute, University of Maastricht, Maastricht, The Netherlands.
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339
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Suh HS, Zhao ML, Rivieccio M, Choi S, Connolly E, Zhao Y, Takikawa O, Brosnan CF, Lee SC. Astrocyte indoleamine 2,3-dioxygenase is induced by the TLR3 ligand poly(I:C): mechanism of induction and role in antiviral response. J Virol 2007; 81:9838-50. [PMID: 17626075 PMCID: PMC2045380 DOI: 10.1128/jvi.00792-07] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme in the kynurenine pathway of tryptophan catabolism and has been implicated in neurotoxicity and suppression of the antiviral T-cell response in HIV encephalitis (HIVE). Here we show that the Toll-like receptor 3 (TLR3) ligand poly(I:C) (PIC) induces the expression of IDO in human astrocytes. PIC was less potent than gamma interferon (IFN-gamma) but more potent than IFN-beta in inducing IDO. PIC induction of IDO was mediated in part by IFN-beta but not IFN-gamma, and both NF-kappaB and interferon regulatory factor 3 (IRF3) were required. PIC also upregulated TLR3, thereby augmenting the primary (IFN-beta) and secondary (IDO and viperin) response genes upon subsequent stimulation with PIC. In HIVE, the transcripts for TLR3, IFN-beta, IDO, and viperin were increased and IDO immunoreactivity was detected in reactive astrocytes as well as macrophages and microglia. PIC caused suppression of intracellular replication of human immunodeficiency virus pseudotyped with vesicular stomatitis virus G protein and human cytomegalovirus in a manner dependent on IRF3 and IDO. The involvement of IDO was demonstrated by partial but significant reversal of the PIC-mediated antiviral effect by IDO RNA interference and/or tryptophan supplementation. Importantly, the cytokine interleukin-1 abolished IFN-gamma-induced IDO enzyme activity in a nitric oxide-dependent manner without suppressing protein expression. Our results demonstrate that IDO is an innate antiviral protein induced by double-stranded RNA and suggest a therapeutic utility for PIC in human viral infections. They also show that IDO activity can be dissociated from protein expression, indicating that the local central nervous system cytokine and nitric oxide environment determines IDO function.
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MESH Headings
- Astrocytes/enzymology
- Astrocytes/immunology
- Astrocytes/virology
- Cells, Cultured
- Cytokines/immunology
- Cytokines/pharmacology
- Cytomegalovirus/genetics
- Cytomegalovirus/immunology
- Cytomegalovirus Infections/enzymology
- Cytomegalovirus Infections/genetics
- Cytomegalovirus Infections/immunology
- Encephalitis, Viral/enzymology
- Encephalitis, Viral/genetics
- Encephalitis, Viral/immunology
- Gene Expression Regulation, Enzymologic/drug effects
- Gene Expression Regulation, Enzymologic/genetics
- Gene Expression Regulation, Enzymologic/immunology
- HIV Infections/enzymology
- HIV Infections/genetics
- HIV Infections/immunology
- HIV-1/genetics
- HIV-1/immunology
- Humans
- Indoleamine-Pyrrole 2,3,-Dioxygenase/biosynthesis
- Indoleamine-Pyrrole 2,3,-Dioxygenase/genetics
- Indoleamine-Pyrrole 2,3,-Dioxygenase/immunology
- Interferon Inducers/pharmacology
- Interferon Regulatory Factor-3/immunology
- Interferon Regulatory Factor-3/metabolism
- Kynurenine/genetics
- Kynurenine/immunology
- Kynurenine/metabolism
- Ligands
- Macrophages/enzymology
- Macrophages/immunology
- Macrophages/virology
- Membrane Glycoproteins/genetics
- Membrane Glycoproteins/immunology
- Membrane Glycoproteins/metabolism
- Microglia/enzymology
- Microglia/immunology
- Microglia/virology
- NF-kappa B/immunology
- NF-kappa B/metabolism
- Nitric Oxide/immunology
- Nitric Oxide/metabolism
- Oxidoreductases Acting on CH-CH Group Donors
- Poly I-C/pharmacology
- Proteins/immunology
- Proteins/metabolism
- Toll-Like Receptor 3/agonists
- Toll-Like Receptor 3/immunology
- Toll-Like Receptor 3/metabolism
- Tryptophan/immunology
- Tryptophan/metabolism
- Viral Envelope Proteins/genetics
- Viral Envelope Proteins/immunology
- Viral Envelope Proteins/metabolism
- Virus Replication/drug effects
- Virus Replication/genetics
- Virus Replication/immunology
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Affiliation(s)
- Hyeon-Sook Suh
- Department of Pathology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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340
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Sas K, Robotka H, Toldi J, Vécsei L. Mitochondria, metabolic disturbances, oxidative stress and the kynurenine system, with focus on neurodegenerative disorders. J Neurol Sci 2007; 257:221-39. [PMID: 17462670 DOI: 10.1016/j.jns.2007.01.033] [Citation(s) in RCA: 313] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The mitochondria have several important functions in the cell. A mitochondrial dysfunction causes an abatement in ATP production, oxidative damage and the induction of apoptosis, all of which are involved in the pathogenesis of numerous disorders. This review focuses on mitochondrial dysfunctions and discusses their consequences and potential roles in the pathomechanism of neurodegenerative disorders. Other pathogenetic factors are also briefly surveyed. The second part of the review deals with the kynurenine metabolic pathway, its alterations and their potential association with cellular energy impairment in certain neurodegenerative diseases. During energy production, most of the O(2) consumed by the mitochondria is reduced fully to water, but 1-2% of the O(2) is reduced incompletely to give the superoxide anion (O(2)(-)). If the function of one or more respiratory chain complexes is impaired for any reason, the enhanced production of free radicals further worsens the mitochondrial function by causing oxidative damage to macromolecules, and by opening the mitochondrial permeability transition pores thereby inducing apoptosis. These high-conductance pores offer a pathway which can open in response to certain stimuli, leading to the induction of the cells' own suicide program. This program plays an essential role in regulating growth and development, in the differentiation of immune cells, and in the elimination of abnormal cells from the organism. Both failure and exaggeration of apoptosis in a human body can lead to disease. The increasing amount of superoxide anions can react with nitric oxide to yield the highly toxic peroxynitrite anion, which can destroy cellular macromolecules. The roles of oxidative, nitrative and nitrosative damage are discussed. Senescence is accompanied by a higher degree of reactive oxygen species production, and by diminished functions of the endoplasmic reticulum and the proteasome system, which are responsible for maintenance of the normal protein homeostasis of the cell. In the event of a dysfunction of the endoplasmic reticulum, unfolded proteins aggregate in it, forming potentially toxic deposits which tend to be resistant to degradation. Cells possess adaptive mechanisms with which to avoid the accumulation of incorrectly folded proteins. These involve molecular chaperones that fold proteins correctly, and the ubiquitin proteasome system which degrades misfolded, unwanted proteins. Both the endoplasmic reticulum and the ubiquitin proteasome system fulfill cellular protein quality control functions. The kynurenine system: Tryptophan is metabolized via several pathways, the main one being the kynurenine pathway. A central compound of the pathway is kynurenine (KYN), which can be metabolized in two separate ways: one branch furnishing kynurenic acid, and the other 3-hydroxykynurenine and quinolinic acid, the precursors of NAD. An important feature of kynurenic acid is the fact that it is one of the few known endogenous excitatory amino acid receptor blockers with a broad spectrum of antagonistic properties in supraphysiological concentrations. One of its recently confirmed sites of action is the alpha7-nicotinic acetylcholine receptor and interestingly, a more recently identified one is a higher affinity positive modulatory binding site at the AMPA receptor. Kynurenic acid has proven to be neuroprotective in several experimental settings. On the other hand, quinolinic acid is a specific agonist at the N-methyl-d-aspartate receptors, and a potent neurotoxin with an additional and marked free radical-producing property. There are a number of neurodegenerative disorders whose pathogenesis has been demonstrated to involve multiple imbalances of the kynurenine pathway metabolism. These changes may disturb normal brain function and can add to the pathomechanisms of the diseases. In certain disorders, there is a quinolinic acid overproduction, while in others the alterations in brain kynurenic acid levels are more pronounced. A more precise knowledge of these alterations yields a basis for getting better therapeutic possibilities. The last part of the review discusses metabolic disturbances and changes in the kynurenine metabolic pathway in Parkinson's, Alzheimer's and Huntington's diseases.
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Affiliation(s)
- Katalin Sas
- Department of Neurology, University of Szeged, POB 427, H-6701 Szeged, Hungary
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341
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Myint AM, Kim YK, Verkerk R, Scharpé S, Steinbusch H, Leonard B. Kynurenine pathway in major depression: evidence of impaired neuroprotection. J Affect Disord 2007; 98:143-51. [PMID: 16952400 DOI: 10.1016/j.jad.2006.07.013] [Citation(s) in RCA: 395] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 07/18/2006] [Accepted: 07/18/2006] [Indexed: 12/16/2022]
Abstract
The neurodegeneration hypothesis proposed major depression as a consequence of the imbalance between neuroprotective and neurodegenerative metabolites in the kynurenine pathway. To test the hypothesis, plasma tryptophan and kynurenine pathway metabolites were studied in 58 patients with major depression and 189 normal controls. The mean tryptophan breakdown index was higher (p=0.036), and mean kynurenic acid concentration and mean neuroprotective ratios were lower, in depressed patients (p=0.003 and 0.003, respectively). In receiver operating characteristic analysis, the kynurenic acid concentrations and the neuroprotective ratio showed clear discrimination between depressed patients and controls with area under the curve 79% and 76.3% respectively. The neuroprotective ratio did not change after treatment in those with repeated episodes of depression but it increased significantly (p=0.044) in those with first episodes. The results suggested that the reduction in neuroprotective markers, which indicated an impaired neuroprotection, might play an important role in pathophysiology of major depression.
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Affiliation(s)
- Aye-Mu Myint
- University of Maastricht, Department of Psychiatry and Neuropsychology, UNS 50, Maastricht, 6200MD, The Netherlands.
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342
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Guidetti P, Hoffman GE, Melendez-Ferro M, Albuquerque EX, Schwarcz R. Astrocytic localization of kynurenine aminotransferase II in the rat brain visualized by immunocytochemistry. Glia 2007; 55:78-92. [PMID: 17024659 DOI: 10.1002/glia.20432] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Kynurenic acid (KYNA), a metabolite of the kynurenine pathway of tryptophan degradation, is a neuroinhibitory agent present in the mammalian brain. Endogenous KYNA preferentially affects the alpha7 nicotinic acetylcholine (alpha7nACh) receptor and, possibly, the glycine co-agonist (glycineB) site of the NMDA receptor. Functionally relevant fluctuations in brain KYNA occur under both physiological and pathological conditions, affecting cholinergic and glutamatergic neurotransmission. Kynurenine aminotransferase II (KAT II), the major biosynthetic enzyme of KYNA in the rat brain, catalyzes the irreversible formation of KYNA from its immediate bioprecursor, kynurenine. We now purified rat kidney KAT II to homogeneity, generated a polyclonal rabbit anti-rat KAT II antibody, and purified the antibody using routine biochemical methods. The antibody selectively recognized KAT II by Western blot analysis and in immunotitration experiments. Used for immunocytochemistry, the antibody revealed discrete, specific staining of KAT II-positive astrocyte-like cells throughout the adult rat brain. The presence of KAT II in astrocytes was confirmed by double fluorescence immunostaining with an antibody against the astrocyte-specific marker glial fibrillary acidic protein (GFAP). No specific labeling was detected in neurons or microglia. However, KAT II-positive astrocytes were intimately associated with select neuron populations, supporting a neuromodulatory role of KYNA. Intense staining was frequently seen around brain capillaries, with astrocytic end feet contacting the capillary wall. This may explain the rapid access of blood-derived kynurenine to KAT II-containing astrocytes. The new anti-KAT II antibody should be useful in the further elucidation of the presumed role of KYNA in brain physiology and pathology.
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Affiliation(s)
- Paolo Guidetti
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, Maryland 21228, USA
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343
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Leonard BE, Myint A. Inflammation and depression: is there a causal connection with dementia? Neurotox Res 2007; 10:149-60. [PMID: 17062376 DOI: 10.1007/bf03033243] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Epidemiological studies show that there is a correlation between chronic depression and the likelihood of dementia in later life. There is evidence that inflammatory changes in the brain are pathological features of both depression and dementia. This suggests that an increase in inflammation-induced apoptosis, together with a reduction in the synthesis of neurotrophic factors caused by a rise in brain glucocorticoids, may play a role in the pathology of these disorders. A reduction in the neuroprotective components of the kynurenine pathway, such as kynurenic acid, and an increase in the neurodegenerative components, 3- hydroxykynurenine and quinolinic acid, contribute to the pathological changes. Such changes are postulated to cause neuronal damage and thereby predispose chronically depressed patients to dementia.
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Affiliation(s)
- B E Leonard
- Brain and Behaviour Research Institute, Department of Psychiatry and Neuropsychology, University of Maastricht, The Netherlands.
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344
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Atlas A, Gisslén M, Nordin C, Lindström L, Schwieler L. Acute psychotic symptoms in HIV-1 infected patients are associated with increased levels of kynurenic acid in cerebrospinal fluid. Brain Behav Immun 2007; 21:86-91. [PMID: 16603336 DOI: 10.1016/j.bbi.2006.02.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 01/27/2006] [Accepted: 02/26/2006] [Indexed: 11/21/2022] Open
Abstract
Human immunodeficiency virus type 1 (HIV-1) infection is associated with psychiatric complications including cognitive impairment, affective disorders, and psychosis. Previous studies have revealed a disturbed kynurenine metabolism in these patients leading to increased levels of neuroactive compounds acting at glutamatergic neurotransmission. Kynurenic acid (KYNA), one of these metabolites is a glutamate-receptor antagonist, preferentially blocking the glycine site of the N-methyl-d-aspartate (NMDA) receptor. Increased levels of brain KYNA have been suggested to induce a NMDA receptor hypofunction that is associated with psychotic symptoms. In the present study, we analyze the concentration of KYNA in the cerebrospinal fluid (CSF) from HIV-1 infected patients (n=22), including HIV-1 infected patients with psychotic symptoms (n=8) and HIV-1 infected patients without psychiatric symptoms (n=14). We found that HIV-1 infected patients had significantly higher median concentration of CSF KYNA (3.02nM) compared to healthy controls (1.17nM). Furthermore, CSF KYNA levels were significantly elevated in HIV-1 infected patients with psychotic symptoms (4.54nM) compared to patients with HIV-1 without psychiatric symptoms (2.28nM). Present results indicate that increased levels of CSF KYNA may be associated with development of psychotic symptoms in HIV-1 infected patients.
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Affiliation(s)
- Ann Atlas
- Infectious Diseases Unit, Department of Medicine, Karolinska Institutet, Karolinska University Hospital, Solna, SE-171 76 Stockholm, Sweden.
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345
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Finkbeiner S, Maria Cuervo A, Morimoto RI, Muchowski PJ. Disease-modifying pathways in neurodegeneration. J Neurosci 2006; 26:10349-57. [PMID: 17035516 PMCID: PMC6674695 DOI: 10.1523/jneurosci.3829-06.2006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Steven Finkbeiner
- Gladstone Institute of Neurological Disease and
- Departments of Physiology
- Neurology, and
| | - Ana Maria Cuervo
- Department of Anatomy and Structural Biology, Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, and
| | - Richard I. Morimoto
- Department of Biochemistry, Molecular Biology, and Cell Biology, Rice Institute for Biomedical Research, Northwestern University, Evanston, Illinois 60208
| | - Paul J. Muchowski
- Gladstone Institute of Neurological Disease and
- Neurology, and
- Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California 94158
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346
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Guillemin GJ, Meininger V, Brew BJ. Implications for the kynurenine pathway and quinolinic acid in amyotrophic lateral sclerosis. NEURODEGENER DIS 2006; 2:166-76. [PMID: 16909022 DOI: 10.1159/000089622] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
The kynurenine pathway (KP) is a major route of L-tryptophan catabolism leading to production of several neurobiologically active molecules. Among them is the excitotoxin quinolinic acid (QUIN) that is known to be involved in the pathogenesis of several major inflammatory neurological diseases. In amyotrophic lateral sclerosis (ALS) degeneration of motor neurons is associated with a chronic and local inflammation (presence of activated microglia and astrocytes). There is emerging evidence that the KP is important in ALS. Recently, we demonstrated that QUIN is significantly increased in serum and CSF of ALS patients. Moreover, most of the factors associated with QUIN toxicity are found in ALS, implying that QUIN may play a substantial role in the neuropathogenesis of ALS. This review details the potential role the KP has in ALS and advances a testable hypothetical model.
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Affiliation(s)
- Gilles J Guillemin
- Centre for Immunology and University of New South Wales, School of Medicine and School of Medical Sciences, Sydney, Australia.
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347
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Leonard BE, Myint A. Changes in the immune system in depression and dementia: causal or coincidental effects? DIALOGUES IN CLINICAL NEUROSCIENCE 2006. [PMID: 16889103 PMCID: PMC3181774 DOI: 10.31887/dcns.2006.8.2/bleonard] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Epidemiological studies show that there is a correlation between chronic depression and the likelihood of demential in later life. There is evidence that inflammatory changes in the brain are pathological features of both depression and dementia. This suggests that an increase in inflammation-induced apoptosis, together with a reductin in the synthesis of neurotrophic factors caused by a rise in brain glucocorticoids, may play a role in the pathology of these disorders. A reduction in the neuroprotective components of the kynurenine pathway, such as kynurenic acid, and an increase in the neurodegenerative components, 3-hydroxykynurenine and quinolinic acid, contribute to the pathological changes. Such changes are postulated t cause neuronal damage, and thereby predispose chronically depressed patients to demential.
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Affiliation(s)
- Brian E Leonard
- Department of Pharmacology, National University of Ireland, Galway.
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348
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Wu HQ, Rassoulpour A, Schwarcz R. Kynurenic acid leads, dopamine follows: A new case of volume transmission in the brain? J Neural Transm (Vienna) 2006; 114:33-41. [PMID: 16932989 DOI: 10.1007/s00702-006-0562-y] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2006] [Accepted: 07/11/2006] [Indexed: 12/01/2022]
Abstract
Intrastriatal infusion of nanomolar concentrations of kynurenic acid (KYNA), an astrocyte-derived neuroinhibitory tryptophan metabolite, reduces basal extracellular dopamine (DA) levels in the rat striatum. This effect is initiated by the inhibition of alpha7 nicotinic acetylcholine receptors (alpha7nAChRs) on glutamatergic afferents. The present study was designed to further investigate this functional link between KYNA and DA using striatal microdialysis in awake animals. In rats, increases in KYNA, caused by intrastriatal infusions of KYNA itself (100 nM) or of KYNA's bioprecursor L-kynurenine (2 microM), were associated with substantial reductions in DA. Co-infusion of KYNA with the alpha7nAChR agonist galantamine (5 microM), but not with the NMDA receptor agonist D-serine (100 nM), prevented this effect. Moreover, KYNA also reduced DA levels in the NMDA-lesioned striatum. Conversely, extracellular DA levels were enhanced when KYNA formation was compromised, either by astrocyte poisoning with fluorocitrate or by perfusion with aminooxyacetic acid (AOAA; 5 mM), a non-specific inhibitor of KYNA synthesis. Notably, this effect of AOAA was prevented by co-perfusion with 100 nM KYNA. In the striatum of 21 day-old mice with a targeted deletion of kynurenine aminotransferase II, extracellular KYNA levels were reduced by 67 +/- 6%, while extracellular DA levels were simultaneously increased by 170 +/- 14%. Taken together, a picture emerges where fluctuations in the astrocytic production of KYNA, possibly through volume transmission, inversely regulate dopaminergic tone. This newly uncovered mechanism may profoundly influence DA function under physiological and pathological conditions.
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Affiliation(s)
- H-Q Wu
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, Maryland 21228, USA
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349
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Kapoor R, Lim KS, Cheng A, Garrick T, Kapoor V. Preliminary evidence for a link between schizophrenia and NMDA-glycine site receptor ligand metabolic enzymes, d-amino acid oxidase (DAAO) and kynurenine aminotransferase-1 (KAT-1). Brain Res 2006; 1106:205-210. [PMID: 16828464 DOI: 10.1016/j.brainres.2006.05.082] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Revised: 05/19/2006] [Accepted: 05/23/2006] [Indexed: 12/18/2022]
Abstract
Preliminary investigations, studying gene expression and biochemical activities of enzymes d-amino acid oxidase (DAAO) and kynurenine aminotransferase-1 (KAT-1), revealed elevated cerebellar KAT-1 and DAAO activities in post-mortem brain samples from schizophrenic versus normal individuals. In addition, we have identified a transcript of DAAO, which was expressed in significantly higher quantities in the diseased cerebellum but not detected in the parietal cortex where DAAO activity is absent.
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Affiliation(s)
- Ranjna Kapoor
- Department of Physiology and Pharmacology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney 2052, Australia.
| | - Kelly Sy Lim
- Department of Physiology and Pharmacology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney 2052, Australia
| | - Alice Cheng
- Department of Physiology and Pharmacology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney 2052, Australia
| | - Therese Garrick
- The Australian Brain Donor Programs NSW Tissue Resource Centre, Department of Pathology, DO6, University of Sydney, Sydney 2006, Australia
| | - Vimal Kapoor
- Department of Physiology and Pharmacology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney 2052, Australia
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350
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Guidetti P, Bates GP, Graham RK, Hayden MR, Leavitt BR, MacDonald ME, Slow EJ, Wheeler VC, Woodman B, Schwarcz R. Elevated brain 3-hydroxykynurenine and quinolinate levels in Huntington disease mice. Neurobiol Dis 2006; 23:190-7. [PMID: 16697652 DOI: 10.1016/j.nbd.2006.02.011] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 02/08/2006] [Accepted: 02/27/2006] [Indexed: 11/29/2022] Open
Abstract
The brain levels of the endogenous excitotoxin quinolinic acid (QUIN) and its bioprecursor, the free radical generator 3-hydroxykynurenine (3-HK), are elevated in early stage Huntington disease (HD). We now examined the status of these metabolites in three mouse models of HD. In R6/2 mice, 3-HK levels were significantly and selectively elevated in the striatum, cortex and cerebellum starting at 4 weeks of age. In contrast, both 3-HK and QUIN levels were increased in the striatum and cortex of the full-length HD models, beginning at 8 months (YAC128) and 15 months (Hdh(Q92) and Hdh(Q111)), respectively. No changes were seen in 13-month-old shortstop mice, which show no signs of motor or cognitive dysfunction or selective neuropathology. These results demonstrate both important parallels and intriguing differences in the progressive neurochemical changes in these HD mouse models and support the hypothesis that QUIN may play a role in the striatal and cortical neurodegeneration of HD.
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Affiliation(s)
- Paolo Guidetti
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD 21228, USA
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