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Soliño M, Larrayoz IM, López EM, Rey-Funes M, Bareiro M, Loidl CF, Girardi E, Martínez A, López-Costa JJ. Adenosine A2A Receptor: A New Neuroprotective Target in Light-Induced Retinal Degeneration. Front Pharmacol 2022; 13:840134. [PMID: 35387355 PMCID: PMC8977837 DOI: 10.3389/fphar.2022.840134] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2021] [Accepted: 02/14/2022] [Indexed: 11/24/2022] Open
Abstract
Continuous illumination induces the degeneration of photoreceptors. This animal model of light-induced retinal degeneration resembles many characteristics of human degenerative diseases of the outer retina, such as age-related macular degeneration. This work aimed to evaluate the potential neuroprotective effect of the modulation of adenosine A2A receptor in the model of light-induced retinal degeneration. Sprague-Dawley rats were intravitreally injected in the right eye with either CGS 21680, an adenosine A2A receptor agonist, or SCH 58261, an adenosine A2A receptor antagonist. Contralateral eyes were injected with respective vehicles as control. Then, rats were subjected to continuous illumination (12,000 lux) for 24 h. Retinas were processed by glial fibrillary acidic protein (GFAP) immunohistochemistry, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) technique, Western blotting (WB), and quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Another group of rats was subjected to functional studies by electroretinography. Animals treated with CGS21680 showed a significant increase of apoptotic nuclei in the outer nuclear layer and a significant increase of GFAP immunoreactive area of the retinas but did not alter WB nor electroretinography results. qRT-PCR showed that CGS 21680 significantly increased the expression of interleukin-1β. On the opposite, SCH 58261 significantly decreased apoptotic nuclei in the outer nuclear layer and GFAP immunoreactive area of the retinas. It also significantly decreased GFAP and activated caspase-3 levels as measured by WB and preserved retinal function, as treated eyes showed significantly greater amplitudes of a- and b-waves and oscillatory potentials. qRT-PCR revealed that SCH 58261 significantly decreased the expression of tumor necrosis factor-α. These results show that the blockade of the A2A receptor before the start of the pathogenic process is neuroprotective, as it prevents light-induced retinal damage. The use of A2A receptor antagonists deserves to be evaluated in retinal degenerative diseases.
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Affiliation(s)
- Manuel Soliño
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Ignacio M Larrayoz
- Biomarkers and Molecular Signaling Group, Center for Biomedical Research of La Rioja (CIBIR), Logroño, Spain
| | - Ester María López
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Manuel Rey-Funes
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Mariana Bareiro
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Cesar Fabián Loidl
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Elena Girardi
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
| | - Alfredo Martínez
- Angiogenesis Study Group, Center for Biomedical Research of La Rioja (CIBIR), Logroño, Spain
| | - Juan José López-Costa
- Instituto de Biología Celular y Neurociencia "Prof. E. De Robertis" (IBCN), UBA-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Ciudad Autónoma de Buenos Aires, Argentina
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Brown EE, Scandura MJ, Mehrotra S, Wang Y, Du J, Pierce EA. Reduced nuclear NAD+ drives DNA damage and subsequent immune activation in the retina. Hum Mol Genet 2021; 31:1370-1388. [PMID: 34750622 DOI: 10.1093/hmg/ddab324] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 10/14/2021] [Accepted: 11/04/2021] [Indexed: 11/13/2022] Open
Abstract
Mutations in NMNAT1, a key enzyme involved in the synthesis of NAD+ in the nucleus, lead to an early onset severe inherited retinal degeneration (IRD). We aimed to understand the role of nuclear NAD+ in the retina and to identify the molecular mechanisms underlying NMNAT1-associated disease, using a mouse model that harbors the p.V9M mutation in Nmnat1 (Nmnat1V9M/V9M). We identified temporal transcriptional reprogramming in the retinas of Nmnat1V9M/V9M mice prior to retinal degeneration, which begins at 4 weeks of age, with no significant alterations in gene expression at 2 weeks of age and over 2600 differentially expressed genes by 3 weeks of age. Expression of the primary consumer of NAD+ in the nucleus, PARP1, an enzyme involved in DNA damage repair and transcriptional regulation, as well as 7 other PARP family enzymes, was elevated in the retinas of Nmnat1V9M/V9M. This was associated with elevated levels of DNA damage, PARP-mediated NAD+ consumption, and migration of Iba1+/CD45+ microglia/macrophages to the subretinal space in the retinas of Nmnat1V9M/V9M mice. These findings suggest that photoreceptor cells are especially sensitive to perturbation of genome homeostasis, and that PARP-mediated cell death may play a role in other genetic forms of IRDs, and potentially other forms of neurodegeneration.
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Affiliation(s)
- Emily E Brown
- Ocular Genomics Institute, Department of Ophthalmology, Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, 02114, USA
| | - Michael J Scandura
- Ocular Genomics Institute, Department of Ophthalmology, Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, 02114, USA
| | - Sudeep Mehrotra
- Ocular Genomics Institute, Department of Ophthalmology, Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, 02114, USA
| | - Yekai Wang
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV, 26506, USA.,Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA
| | - Jianhai Du
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV, 26506, USA.,Department of Biochemistry, West Virginia University, Morgantown, WV, 26506, USA
| | - Eric A Pierce
- Ocular Genomics Institute, Department of Ophthalmology, Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, 02114, USA
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Harsing LG, Szénási G, Zelles T, Köles L. Purinergic-Glycinergic Interaction in Neurodegenerative and Neuroinflammatory Disorders of the Retina. Int J Mol Sci 2021; 22:ijms22126209. [PMID: 34201404 PMCID: PMC8228622 DOI: 10.3390/ijms22126209] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Revised: 06/03/2021] [Accepted: 06/04/2021] [Indexed: 12/26/2022] Open
Abstract
Neurodegenerative–neuroinflammatory disorders of the retina seriously hamper human vision. In searching for key factors that contribute to the development of these pathologies, we considered potential interactions among purinergic neuromodulation, glycinergic neurotransmission, and microglia activity in the retina. Energy deprivation at cellular levels is mainly due to impaired blood circulation leading to increased release of ATP and adenosine as well as glutamate and glycine. Interactions between these modulators and neurotransmitters are manifold. First, P2Y purinoceptor agonists facilitate reuptake of glycine by glycine transporter 1, while its inhibitors reduce reverse-mode operation; these events may lower extracellular glycine levels. The consequential changes in extracellular glycine concentration can lead to parallel changes in the activity of NR1/NR2B type NMDA receptors of which glycine is a mandatory agonist, and thereby may reduce neurodegenerative events in the retina. Second, P2Y purinoceptor agonists and glycine transporter 1 inhibitors may indirectly inhibit microglia activity by decreasing neuronal or glial glycine release in energy-compromised retina. These inhibitions may have a role in microglia activation, which is present during development and progression of neurodegenerative disorders such as glaucomatous and diabetic retinopathies and age-related macular degeneration or loss of retinal neurons caused by thromboembolic events. We have hypothesized that glycine transporter 1 inhibitors and P2Y purinoceptor agonists may have therapeutic importance in neurodegenerative–neuroinflammatory disorders of the retina by decreasing NR1/NR2B NMDA receptor activity and production and release of a series of proinflammatory cytokines from microglial cells.
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Affiliation(s)
- Laszlo G. Harsing
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, H-1089 Budapest, Hungary; (T.Z.); (L.K.)
- Correspondence: ; Tel.: +36-1-210-4416
| | - Gábor Szénási
- Institute of Translational Medicine, Semmelweis University, H-1089 Budapest, Hungary;
| | - Tibor Zelles
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, H-1089 Budapest, Hungary; (T.Z.); (L.K.)
- Department of Oral Biology, Semmelweis University, H-1089 Budapest, Hungary
| | - László Köles
- Department of Pharmacology and Pharmacotherapy, Semmelweis University, H-1089 Budapest, Hungary; (T.Z.); (L.K.)
- Department of Oral Biology, Semmelweis University, H-1089 Budapest, Hungary
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Vestergaard N, Cehofski LJ, Honoré B, Aasbjerg K, Vorum H. Animal Models Used to Simulate Retinal Artery Occlusion: A Comprehensive Review. Transl Vis Sci Technol 2019; 8:23. [PMID: 31440422 PMCID: PMC6701503 DOI: 10.1167/tvst.8.4.23] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 06/10/2019] [Indexed: 12/18/2022] Open
Abstract
Purpose To present an overview of animal models of retinal artery occlusion (RAO). Methods Through a systematic literature search in PubMed and Embase, papers describing methods of inducing RAO in animal models were included. The identified methodologic approaches were presented in a narrative synthesis and compared with RAO in humans. Results In total, 83 papers reporting on 88 experiments were included. Six different species were used with rodents and monkeys being the most common, and a minority were performed using cats, dogs, rabbits, or pigs. The anatomy of pigs and monkeys resemble that of humans most closely. The two most frequently used methods were laser-induced occlusion or ligation of the arteries. Other methods included raised intraocular pressure, arterial clamping, administration of vasoconstricting agents, the use of an occluder, embolization, and endovascular approaches to induce occlusion. In general, occlusions lasted for only 30 to 90 minutes, often followed by reperfusion. Conclusions Although a broad range of methods have previously been used, they all have limitations. Preferably, the methods should imitate the human disease as closely as possible and avoid damaging other structures. Therefore, monkeys followed by pigs are to be preferred and ligation or clamping may be a suitable model in larger animals as there is a potential to isolate and occlude the retinal artery only. Being less invasive, laser-induced occlusion is another suitable approach. Translational Relevance This review aims at assisting researchers in deciding on the most ideal experimental setting, and thereby increase the translational value to human disease.
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Affiliation(s)
- Nanna Vestergaard
- Department of Ophthalmology, Aalborg University Hospital, Aalborg, Denmark
| | - Lasse Jørgensen Cehofski
- Department of Ophthalmology, Odense University Hospital, Odense, Denmark.,Department of Ophthalmology, Vejle Hospital - part of Lillebaelt Hospital, Vejle, Denmark.,Department of Clinical Research, University of Southern Denmark, Odense, Denmark
| | - Bent Honoré
- Department of Biomedicine, Aarhus University, Aarhus, Denmark.,Department of Clinical Medicine, Aalborg University Hospital, Aalborg, Denmark
| | - Kristian Aasbjerg
- Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark.,Department of Epidemiology, Aalborg University Hospital, Aalborg, Denmark
| | - Henrik Vorum
- Department of Ophthalmology, Aalborg University Hospital, Aalborg, Denmark.,Department of Clinical Medicine, Aalborg University Hospital, Aalborg, Denmark
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Adenosine A1 receptor: A neuroprotective target in light induced retinal degeneration. PLoS One 2018; 13:e0198838. [PMID: 29912966 PMCID: PMC6005487 DOI: 10.1371/journal.pone.0198838] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Accepted: 05/25/2018] [Indexed: 02/04/2023] Open
Abstract
Light induced retinal degeneration (LIRD) is a useful model that resembles human retinal degenerative diseases. The modulation of adenosine A1 receptor is neuroprotective in different models of retinal injury. The aim of this work was to evaluate the potential neuroprotective effect of the modulation of A1 receptor in LIRD. The eyes of rats intravitreally injected with N6-cyclopentyladenosine (CPA), an A1 agonist, which were later subjected to continuous illumination (CI) for 24 h, showed retinas with a lower number of apoptotic nuclei and a decrease of Glial Fibrillary Acidic Protein (GFAP) immunoreactive area than controls. Lower levels of activated Caspase 3 and GFAP were demonstrated by Western Blot (WB) in treated animals. Also a decrease of iNOS, TNFα and GFAP mRNA was demonstrated by RT-PCR. A decrease of Iba 1+/MHC-II+ reactive microglial cells was shown by immunohistochemistry. Electroretinograms (ERG) showed higher amplitudes of a-wave, b-wave and oscillatory potentials after CI compared to controls. Conversely, the eyes of rats intravitreally injected with dipropylcyclopentylxanthine (DPCPX), an A1 antagonist, and subjected to CI for 24 h, showed retinas with a higher number of apoptotic nuclei and an increase of GFAP immunoreactive area compared to controls. Also, higher levels of activated Caspase 3 and GFAP were demonstrated by Western Blot. The mRNA levels of iNOS, nNOS and inflammatory cytokines (IL-1β and TNFα) were not modified by DPCPX treatment. An increase of Iba 1+/MHC-II+ reactive microglial cells was shown by immunohistochemistry. ERG showed that the amplitudes of a-wave, b-wave, and oscillatory potentials after CI were similar to control values. A single pharmacological intervention prior illumination stress was able to swing retinal fate in opposite directions: CPA was neuroprotective, while DPCPX worsened retinal damage. In summary, A1 receptor agonism is a plausible neuroprotective strategy in LIRD.
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Zhu S, Yam M, Wang Y, Linton JD, Grenell A, Hurley JB, Du J. Impact of euthanasia, dissection and postmortem delay on metabolic profile in mouse retina and RPE/choroid. Exp Eye Res 2018; 174:113-120. [PMID: 29864440 DOI: 10.1016/j.exer.2018.05.032] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Revised: 05/30/2018] [Accepted: 05/31/2018] [Indexed: 01/02/2023]
Abstract
Metabolomics studies in the retina and retinal pigment epithelium (RPE) in animal models or postmortem donors are essential to understanding the retinal metabolism and to revealing the underlying mechanisms of retinal degenerative diseases. We have studied how different methods of euthanasia (CO2 or cervical dislocation) different isolation procedures and postmortem delay affect metabolites in mouse retina and RPE/choroid using LC MS/MS and GC MS. Compared with cervical dislocation, CO2 exposure for 5 min dramatically degrades ATP and GTP into purine metabolites in the retina while raising intermediates in glucose metabolism and amino acids in the RPE/choroid. Isolation in cold buffer containing glucose has the least change in metabolites. Postmortem delay time-dependently and differentially impacts metabolites in the retina and RPE/choroid. In the postmortem retina, 18% of metabolites were changed at 0.5 h (h), 41% at 4 h and 51% at 8 h. However, only 6% of metabolites were changed in the postmortem RPE/choroid and it steadily increased to 20% at 8 h. Notably, both postmortem retina and RPE/choroid tissue showed increased purine metabolites. Storage of eyes in cold nutrient-rich medium substantially blocked the postmortem change in the retina and RPE/choroid. In conclusion, our study provides optimized methods to prepare fresh or postmortem retina and RPE/choroid tissue for metabolomics studies.
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Affiliation(s)
- Siyan Zhu
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506, USA; Department of Biochemistry, West Virginia University, Morgantown, WV 26506, USA
| | - Michelle Yam
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506, USA; Department of Biochemistry, West Virginia University, Morgantown, WV 26506, USA
| | - Yekai Wang
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506, USA; Department of Biochemistry, West Virginia University, Morgantown, WV 26506, USA
| | - Jonathan D Linton
- Department of Biochemistry, University of Washington, Seattle, WA 98109, USA
| | - Allison Grenell
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506, USA; Department of Biochemistry, West Virginia University, Morgantown, WV 26506, USA
| | - James B Hurley
- Department of Biochemistry, University of Washington, Seattle, WA 98109, USA; Department of Ophthalmology, University of Washington, Seattle, WA 98109, USA
| | - Jianhai Du
- Department of Ophthalmology, West Virginia University, Morgantown, WV 26506, USA; Department of Biochemistry, West Virginia University, Morgantown, WV 26506, USA.
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Andrés-Guerrero V, García-Feijoo J, Konstas AG. Targeting Schlemm's Canal in the Medical Therapy of Glaucoma: Current and Future Considerations. Adv Ther 2017; 34:1049-1069. [PMID: 28349508 PMCID: PMC5427152 DOI: 10.1007/s12325-017-0513-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2017] [Indexed: 11/23/2022]
Abstract
Schlemm’s canal (SC) is a unique, complex vascular structure responsible for maintaining fluid homeostasis within the anterior segment of the eye by draining the excess of aqueous humour. In glaucoma, a heterogeneous group of eye disorders afflicting approximately 60 million individuals worldwide, the normal outflow of aqueous humour into SC is progressively hindered, leading to a gradual increase in outflow resistance, which gradually results in elevated intraocular pressure (IOP). By and large available antiglaucoma therapies do not target the site of the pathology (SC), but rather aim to decrease IOP by other mechanisms, either reducing aqueous production or by diverting aqueous flow through the unconventional outflow system. The present review first outlines our current understanding on the functional anatomy of SC. It then summarizes existing research on SC cell properties; first in the context of their role in glaucoma development/progression and then as a target of novel and emerging antiglaucoma therapies. Evidence from ongoing research efforts to develop effective antiglaucoma therapies targeting SC suggests that this could become a promising site of future therapeutic interventions.
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Reichenbach A, Bringmann A. Purinergic signaling in retinal degeneration and regeneration. Neuropharmacology 2015; 104:194-211. [PMID: 25998275 DOI: 10.1016/j.neuropharm.2015.05.005] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2015] [Revised: 05/07/2015] [Accepted: 05/07/2015] [Indexed: 02/01/2023]
Abstract
Purinergic signaling is centrally involved in mediating the degeneration of the injured and diseased retina, the induction of retinal gliosis, and the protection of the retinal tissue from degeneration. Dysregulated calcium signaling triggered by overactivation of P2X7 receptors is a crucial step in the induction of neuronal and microvascular cell death under pathogenic conditions like ischemia-hypoxia, elevated intraocular pressure, and diabetes, respectively. Overactivation of P2X7 plays also a pathogenic role in inherited and age-related photoreceptor cell death and in the age-related dysfunction and degeneration of the retinal pigment epithelium. Gliosis of micro- and macroglial cells, which is induced and/or modulated by purinergic signaling and associated with an impaired homeostatic support to neurons, and the ATP-mediated propagation of retinal gliosis from a focal injury into the surrounding noninjured tissue are involved in inducing secondary cell death in the retina. On the other hand, alterations in the glial metabolism of extracellular nucleotides, resulting in a decreased level of ATP and an increased level of adenosine, may be neuroprotective in the diseased retina. Purinergic signals stimulate the proliferation of retinal glial cells which contributes to glial scarring which has protective effects on retinal degeneration and adverse effects on retinal regeneration. Pharmacological modulation of purinergic receptors, e.g., inhibition of P2X and activation of adenosine receptors, may have clinical importance for the prevention of photoreceptor, neuronal, and microvascular cell death in diabetic retinopathy, retinitis pigmentosa, age-related macular degeneration, and glaucoma, respectively, for the clearance of retinal edema, and the inhibition of dysregulated cell proliferation in proliferative retinopathies. This article is part of a Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.
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Affiliation(s)
- Andreas Reichenbach
- Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany.
| | - Andreas Bringmann
- Department of Ophthalmology and Eye Hospital, University of Leipzig, Leipzig, Germany
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10
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Dos Santos-Rodrigues A, Pereira MR, Brito R, de Oliveira NA, Paes-de-Carvalho R. Adenosine transporters and receptors: key elements for retinal function and neuroprotection. VITAMINS AND HORMONES 2015; 98:487-523. [PMID: 25817878 DOI: 10.1016/bs.vh.2014.12.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Adenosine is an important neuroactive substance in the central nervous system, including in the retina where subclasses of adenosine receptors and transporters are expressed since early stages of development. Here, we review some evidence showing that adenosine plays important functions in the mature as well as in the developing tissue. Adenosine transporters are divided into equilibrative and concentrative, and the major transporter subtype present in the retina is the ENT1. This transporter is responsible for a bidirectional transport of adenosine and the uptake or release of this nucleoside appears to be regulated by different signaling pathways that are also controlled by activation of adenosine receptors. Adenosine receptors are also key players in retina physiology regulating a variety of functions in the mature and developing tissue. Regulation of excitatory neurotransmitter release and neuroprotection are the main functions played be adenosine in the mature tissue, while regulation of cell survival and neurogenesis are some of the functions played by adenosine in developing retina. Since adenosine is neuroprotective against excitotoxic and metabolic dysfunctions observed in neurological and ocular diseases, the search for adenosine-related drugs regulating adenosine transporters and receptors can be important for advancement of therapeutic strategies against these diseases.
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Affiliation(s)
| | - Mariana R Pereira
- Program of Neurosciences, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil
| | - Rafael Brito
- Program of Neurosciences, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil
| | - Nádia A de Oliveira
- Program of Neurosciences, Fluminense Federal University, Niterói, Rio de Janeiro, Brazil
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D'Alessandro A, Cervia D, Catalani E, Gevi F, Zolla L, Casini G. Protective effects of the neuropeptides PACAP, substance P and the somatostatin analogue octreotide in retinal ischemia: a metabolomic analysis. MOLECULAR BIOSYSTEMS 2014; 10:1290-304. [PMID: 24514073 DOI: 10.1039/c3mb70362b] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Ischemia is a primary cause of neuronal death in retinal diseases and the somatostatin subtype receptor 2 agonist octreotide (OCT) is known to decrease ischemia-induced retinal cell death. Using a recently optimized ex vivo mouse model of retinal ischemia, we tested the anti-ischemic potential of two additional neuropeptides, pituitary adenylate cyclase activating peptide (PACAP) and substance P (SP), and monitored the major changes occurring at the metabolic level. Metabolomics analyses were performed via fast HPLC online using a microTOF-Q MS instrument, a workflow that is increasingly becoming the gold standard in the field of metabolomics. The metabolomic approach allowed detection of the most significant alterations induced in the retina by ischemia and of the significance of the protective effects exerted by OCT, PACAP or SP. All treatments were shown to reduce ischemia-induced cell death, vascular endothelial growth factor over-expression and glutamate release. The metabolomic analysis showed that OCT and, to a lesser extent, also PACAP or SP, were able to counteract the ischemia-induced oxidative stress and to promote, with various efficacies, (i) decreased accumulation of glutamate and normalization of glutathione homeostasis; (ii) reduced build-up of α-ketoglutarate, which might serve as a substrate for the enhanced biosynthesis of glutamate in response to ischemia; (iii) reduced accumulation of peroxidized lipids and inflammatory mediators; (iv) the normalization of glycolytic fluxes and thus preventing the over-accumulation of lactate or either promoting the down-regulation of the glyoxalate anti-oxidant system; (v) a reduced metabolic shift from glycolysis towards the PPP or either a blockade at the non-oxidative phase of the PPP; and (vi) tuning down of purine metabolism. In addition, OCT seemed to stimulate nitric oxide production. None of the treatments was able to restore ATP production, although ATP reservoirs were partly replenished by OCT, PACAP or SP. These data indicate that, in addition to that of somatostatin, peptidergic systems such as those of PACAP and SP deserve attention in view of peptide-based therapies to treat ischemic retinal disorders.
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Affiliation(s)
- Angelo D'Alessandro
- Dipartimento di Scienze Ecologiche e Biologiche, Università della Tuscia, L.go dell'Università snc, I-01100 Viterbo, Italy.
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Cinalli AR, Guarracino JF, Fernandez V, Roquel LI, Losavio AS. Inosine induces presynaptic inhibition of acetylcholine release by activation of A3 adenosine receptors at the mouse neuromuscular junction. Br J Pharmacol 2014; 169:1810-23. [PMID: 23731236 DOI: 10.1111/bph.12262] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Revised: 04/19/2013] [Accepted: 05/02/2013] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE The role of inosine at the mammalian neuromuscular junction (NMJ) has not been clearly defined. Moreover, inosine was classically considered to be the inactive metabolite of adenosine. Hence, we investigated the effect of inosine on spontaneous and evoked ACh release, the mechanism underlying its modulatory action and the receptor type and signal transduction pathway involved. EXPERIMENTAL APPROACH End-plate potentials (EPPs) and miniature end-plate potentials (MEPPs) were recorded from the mouse phrenic-nerve diaphragm preparations using conventional intracellular electrophysiological techniques. KEY RESULTS Inosine (100 μM) reduced MEPP frequency and the amplitude and quantal content of EPPs; effects inhibited by the selective A3 receptor antagonist MRS-1191. Immunohistochemical assays confirmed the presence of A3 receptors at mammalian NMJ. The voltage-gated calcium channel (VGCC) blocker Cd(2+) , the removal of extracellular Ca(2+) and the L-type and P/Q-type VGCC antagonists, nitrendipine and ω-agatoxin IVA, respectively, all prevented inosine-induced inhibition. In the absence of endogenous adenosine, inosine decreased the hypertonic response. The effects of inosine on ACh release were prevented by the Gi/o protein inhibitor N-ethylmaleimide, PKC antagonist chelerytrine and calmodulin antagonist W-7, but not by PKA antagonists, H-89 and KT-5720, or the inhibitor of CaMKII KN-62. CONCLUSION AND IMPLICATIONS Our results suggest that, at motor nerve terminals, inosine induces presynaptic inhibition of spontaneous and evoked ACh release by activating A3 receptors through a mechanism that involves L-type and P/Q-type VGCCs and the secretory machinery downstream of calcium influx. A3 receptors appear to be coupled to Gi/o protein. PKC and calmodulin may be involved in these effects of inosine.
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Affiliation(s)
- A R Cinalli
- Laboratorio de Neurofisiología, Instituto de Investigaciones Médicas Alfredo Lanari, Universidad de Buenos Aires - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
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Narayanan SP, Rojas M, Suwanpradid J, Toque HA, Caldwell RW, Caldwell RB. Arginase in retinopathy. Prog Retin Eye Res 2013; 36:260-80. [PMID: 23830845 PMCID: PMC3759622 DOI: 10.1016/j.preteyeres.2013.06.002] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 06/14/2013] [Accepted: 06/25/2013] [Indexed: 12/12/2022]
Abstract
Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.
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Affiliation(s)
- S. Priya Narayanan
- Vision Discovery Institute, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
- Vascular Biology Center, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
| | - Modesto Rojas
- Vision Discovery Institute, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
- Vascular Biology Center, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
| | - Jutamas Suwanpradid
- Vision Discovery Institute, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
- Vascular Biology Center, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
| | - Haroldo A. Toque
- Department of Pharmacology & Toxicology, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
| | - R. William Caldwell
- Vision Discovery Institute, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
- Department of Pharmacology & Toxicology, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
| | - Ruth B. Caldwell
- Vision Discovery Institute, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
- Vascular Biology Center, Georgia Regents University, 1459 Laney Walker Boulevard, Augusta, 30912, USA
- VA Medical Center, One Freedom Way, Augusta, GA, USA
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14
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Zhong YS, Wang J, Liu WM, Zhu YH. Potassium ion channels in retinal ganglion cells (review). Mol Med Rep 2013; 8:311-9. [PMID: 23732984 DOI: 10.3892/mmr.2013.1508] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 05/22/2013] [Indexed: 11/06/2022] Open
Abstract
Retinal ganglion cells (RGCs) consolidate visual processing and constitute the last step prior to the transmission of signals to higher brain centers. RGC death is a major cause of visual impairment in optic neuropathies, including glaucoma, age‑related macular degeneration, diabetic retinopathy, uveoretinitis and vitreoretinopathy. Discharge patterns of RGCs are primarily determined by the presence of ion channels. As the most diverse group of ion channels, potassium (K+) channels play key roles in modulating the electrical properties of RGCs. Biochemical, molecular and pharmacological studies have identified a number of K+ channels in RGCs, including inwardly rectifying K+ (Kir), ATP‑sensitive K+ (KATP), tandem‑pore domain K+ (TASK), voltage‑gated K+ (Kv), ether‑à‑go‑go (Eag) and Ca2+‑activated K+ (KCa) channels. Kir channels are important in the maintenance of the resting membrane potential and controlling RGC excitability. KATP channels are involved in RGC survival and neuroprotection. TASK channels are hypothesized to contribute to the regulation of resting membrane potentials and firing patterns of RGCs. Kv channels are important regulators of cellular excitability, functioning to modulate the amplitude, duration and frequency of action potentials and subthreshold depolarizations, and are also important in RGC development and protection. Eag channels may contribute to dendritic repolarization during excitatory postsynaptic potentials and to the attenuation of the back propagation of action potentials. KCa channels have been observed to contribute to repetitive firing in RGCs. Considering these important roles of K+ channels in RGCs, the study of K+ channels may be beneficial in elucidating the pathophysiology of RGCs and exploring novel RGC protection strategies.
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Affiliation(s)
- Yi-Sheng Zhong
- Department of Ophthalmology, Ruijin Hospital Affiliated Medical School, Shanghai Jiaotong University, Shanghai 200025, P.R. China
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15
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Zhong Y, Yang Z, Huang WC, Luo X. Adenosine, adenosine receptors and glaucoma: An updated overview. Biochim Biophys Acta Gen Subj 2013; 1830:2882-90. [DOI: 10.1016/j.bbagen.2013.01.005] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Revised: 12/21/2012] [Accepted: 01/07/2013] [Indexed: 01/30/2023]
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16
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Reichenbach A, Bringmann A. New functions of Müller cells. Glia 2013; 61:651-78. [PMID: 23440929 DOI: 10.1002/glia.22477] [Citation(s) in RCA: 450] [Impact Index Per Article: 40.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 01/10/2012] [Indexed: 12/12/2022]
Abstract
Müller cells, the major type of glial cells in the retina, are responsible for the homeostatic and metabolic support of retinal neurons. By mediating transcellular ion, water, and bicarbonate transport, Müller cells control the composition of the extracellular space fluid. Müller cells provide trophic and anti-oxidative support of photoreceptors and neurons and regulate the tightness of the blood-retinal barrier. By the uptake of glutamate, Müller cells are more directly involved in the regulation of the synaptic activity in the inner retina. This review gives a survey of recently discoved new functions of Müller cells. Müller cells are living optical fibers that guide light through the inner retinal tissue. Thereby they enhance the signal/noise ratio by minimizing intraretinal light scattering and conserve the spatial distribution of light patterns in the propagating image. Müller cells act as soft, compliant embedding for neurons, protecting them in case of mechanical trauma, and also as soft substrate required for neurite growth and neuronal plasticity. Müller cells release neuroactive signaling molecules which modulate neuronal activity, are implicated in the mediation of neurovascular coupling, and mediate the homeostasis of the extracellular space volume under hypoosmotic conditions which are a characteristic of intense neuronal activity. Under pathological conditions, a subset of Müller cells may differentiate to neural progenitor/stem cells which regenerate lost photoreceptors and neurons. Increasing knowledge of Müller cell function and responses in the normal and diseased retina will have great impact for the development of new therapeutic approaches for retinal diseases.
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Affiliation(s)
- Andreas Reichenbach
- Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany.
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17
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Yu J, Huang X, Wu Q, Wang J, Yu X, Zhao P. Effect of A(2A) receptor antagonist (SCH 442416) on the mRNA expression of glutamate aspartate transporter and glutamine synthetase in rat retinal Müller cells under hypoxic conditions in vitro. Exp Ther Med 2012; 3:803-806. [PMID: 22969972 DOI: 10.3892/etm.2012.486] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2011] [Accepted: 01/30/2012] [Indexed: 11/06/2022] Open
Abstract
The purpose of the present study was to investigate the effect of the A(2A) receptor antagonist (SCH 442416) on the mRNA expression of glutamate aspartate transporter (GLAST) and glutamine synthetase (GS) in rat retinal Müller cells under hypoxic conditions in vitro. Immunofluorescent staining of GS and GFAP was used for the identification of Müller cells. The GLAST and GS mRNA expression of Müller cells treated with 0.1, 1 and 10 μM SCH 442416 under hypoxic conditions was examined by real-time PCR. Müller cells increased the mRNA expression of GLAST under hypoxic conditions; those treated with 0.1 μM SCH 442416 showed a further significant increase in the mRNA expression of GLAST in vitro. Although the mRNA expression of GS was decreased under hypoxic conditions, the mRNA expression was increased when Müller cells were treated with 0.1 μM SCH 442416. A(2A) receptor antagonist increased the GLAST and GS expression of Müller cells and accelerated the clearance of extracellular glutamate under hypoxic conditions in vitro.
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Affiliation(s)
- Jun Yu
- Department of Ophthalmology, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine
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18
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Puro DG. Retinovascular physiology and pathophysiology: new experimental approach/new insights. Prog Retin Eye Res 2012; 31:258-70. [PMID: 22333041 DOI: 10.1016/j.preteyeres.2012.01.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 01/28/2012] [Accepted: 01/31/2012] [Indexed: 01/09/2023]
Abstract
An important challenge in visual neuroscience is to understand the physiology and pathophysiology of the intra-retinal vasculature, whose function is required for ophthalmoception by humans and most other mammals. In the quest to learn more about this highly specialized portion of the circulatory system, a newly developed method for isolating vast microvascular complexes from the rodent retina has opened the way for using techniques such as patch-clamping, fluorescence imaging and time-lapse photography to elucidate the functional organization of a capillary network and its pre-capillary arteriole. For example, the ability to obtain dual perforated-patch recordings from well-defined sites within an isolated microvascular complex permitted the first characterization of the electrotonic architecture of a capillary/arteriole unit. This analysis revealed that this operational unit is not simply a homogenous synctium, but has a complex functional organization that is dynamically modulated by extracellular signals such as angiotensin II. Another recent discovery is that a capillary and its pre-capillary arteriole have distinct physiological differences; capillaries have an abundance of ATP-sensitive potassium (K(ATP)) channels and a dearth of voltage-dependent calcium channels (VDCCs) while the converse is true for arterioles. In addition, voltage transmission between abluminal cells and the endothelium is more efficient in the capillaries. Thus, the capillary network is well-equipped to generate and transmit voltages, and the pre-capillary arteriole is well-adapted to transduce a capillary-generated voltage into a change in abluminal cell calcium and thereby, a vasomotor response. Use of microvessels isolated from the diabetic retina has led to new insights concerning retinal vascular pathophysiology. For example, soon after the onset of diabetes, the efficacy of voltage transmission through the endothelium is diminished; arteriolar VDCCs are inhibited, and there is increased vulnerability to purinergic vasotoxicity, which is a newly identified pathobiological mechanism. Other recent studies reveal that K(ATP) channels not only have an essential physiological role in generating vasomotor responses, but their activation substantially boosts the lethality of hypoxia. Thus, the pathophysiology of the retinal microvasculature is closely linked with its physiology.
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Affiliation(s)
- Donald G Puro
- Department of Ophthalmology & Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
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Caprara C, Grimm C. From oxygen to erythropoietin: relevance of hypoxia for retinal development, health and disease. Prog Retin Eye Res 2011; 31:89-119. [PMID: 22108059 DOI: 10.1016/j.preteyeres.2011.11.003] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Revised: 11/01/2011] [Accepted: 11/07/2011] [Indexed: 12/20/2022]
Abstract
Photoreceptors and other cells of the retina consume large quantities of energy to efficiently convert light information into a neuronal signal understandable by the brain. The necessary energy is mainly provided by the oxygen-dependent generation of ATP in the numerous mitochondria of retinal cells. To secure the availability of sufficient oxygen for this process, the retina requires constant blood flow through the vasculature of the retina and the choroid. Inefficient supply of oxygen and nutrients, as it may occur in conditions of disturbed hemodynamics or vascular defects, results in tissue ischemia or hypoxia. This has profound consequences on retinal function and cell survival, requiring an adaptational response by cells to cope with the reduced oxygen tension. Central to this response are hypoxia inducible factors, transcription factors that accumulate under hypoxic conditions and drive the expression of a large variety of target genes involved in angiogenesis, cell survival and metabolism. Prominent among these factors are vascular endothelial growth factor and erythropoietin, which may contribute to normal angiogenesis during development, but may also cause neovascularization and vascular leakage under pathologically reduced oxygen levels. Since ischemia and hypoxia may have a role in various retinal diseases such as diabetic retinopathy and retinopathy of prematurity, studying the cellular and molecular response to reduced tissue oxygenation is of high relevance. In addition, the concept of preconditioning with ischemia or hypoxia demonstrates the capacity of the retina to activate endogenous survival mechanisms, which may protect cells against a following noxious insult. Part of these mechanisms is the local production of protective factors such as erythropoietin. Due to its plethora of effects in the retina including neuro- and vaso-protective activities, erythropoietin has gained strong interest as potential therapeutic factor for retinal degenerative diseases.
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Affiliation(s)
- Christian Caprara
- Lab for Retinal Cell Biology, Department of Ophthalmology, University of Zurich, Zurich, Switzerland
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20
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Bringmann A, Wiedemann P. Müller glial cells in retinal disease. ACTA ACUST UNITED AC 2011; 227:1-19. [PMID: 21921569 DOI: 10.1159/000328979] [Citation(s) in RCA: 276] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Accepted: 04/27/2011] [Indexed: 11/19/2022]
Abstract
Virtually all pathogenic stimuli activate Müller cells. Reactive Müller cells exert protective and toxic effects on photoreceptors and neurons. They contribute to oxidative stress and glutamate toxicity due to malfunctions of glutamate uptake and glutathione synthesis. Downregulation of potassium conductance disrupts transcellular potassium and water transport, resulting in neuronal hyperexcitability and edema. Protective effects of reactive Müller cells include upregulation of adenosine 5'-triphosphate (ATP)-degrading ectoenzymes, which enhances the extracellular availability of the neuroprotectant adenosine, abrogation of the osmotic release of ATP, which might protect retinal ganglion cells from apoptosis, and the release of antioxidants and neurotrophic factors. The dedifferentiation of reactive Müller cells to progenitor-like cells might have an impact on future therapeutic approaches. A better understanding of the gliotic mechanisms will be helpful in developing efficient therapeutic strategies aiming at increased protective and regenerative properties and decreased toxicity of reactive Müller cells.
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Affiliation(s)
- Andreas Bringmann
- Department of Ophthalmology and Eye Hospital, University of Leipzig, Leipzig, Germany
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21
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Wurm A, Pannicke T, Iandiev I, Francke M, Hollborn M, Wiedemann P, Reichenbach A, Osborne NN, Bringmann A. Purinergic signaling involved in Müller cell function in the mammalian retina. Prog Retin Eye Res 2011; 30:324-42. [DOI: 10.1016/j.preteyeres.2011.06.001] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 06/06/2011] [Accepted: 06/06/2011] [Indexed: 10/18/2022]
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22
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Lipophilicity and Transporter Influence on Blood-Retinal Barrier Permeability: A Comparison with Blood-Brain Barrier Permeability. Pharm Res 2010; 27:2715-24. [DOI: 10.1007/s11095-010-0272-x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2010] [Accepted: 09/02/2010] [Indexed: 11/25/2022]
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23
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Choi JY, Yoon YJ, Choi HJ, Park SH, Kim CD, Kim IS, Kwon TH, Do JY, Kim SH, Ryu DH, Hwang GS, Kim YL. Dialysis modality-dependent changes in serum metabolites: accumulation of inosine and hypoxanthine in patients on haemodialysis. Nephrol Dial Transplant 2010; 26:1304-13. [PMID: 20844182 DOI: 10.1093/ndt/gfq554] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND The body metabolism of patients with end-stage renal disease may be altered in response to long-term dialysis treatment. Moreover, the pattern of serum metabolites could change depending on the type of dialysis modality used. However, dialysis modality-dependent changes in serum metabolites are poorly understood. Our aim was to profile comprehensively serum metabolites by exploiting a novel method of (1)H-NMR-based metabonomics and identify the differences in metabolite patterns in subjects receiving haemodialysis (HD) and peritoneal dialysis (PD). METHODS Anuric and non-diabetic HD patients were matched to PD patients for age, sex and dialysis duration. Accurate concentrations of serum metabolites were determined using the target-profiling procedure, and differences in the levels of metabolites were compared using multivariate analysis. RESULTS Principal Components Analysis score plots showed that the metabolic patterns could be discriminated by dialysis modalities. Hypoxanthine and inosine were present only with HD, whereas serum xanthine oxidase activity and uric acid levels were not different. In contrast, PD was associated with higher levels of lactate, glucose, maltose, pyruvate, succinate, alanine, and glutamate linked to glucose metabolism and the tri-carboxylic acid cycle. Maltose appeared only in patients using icodextrin solution for PD. Known uraemic retention solutes such as urea, creatinine, myo-inositol and trimethylamine-N-oxide were increased in both dialysis groups. CONCLUSIONS Metabonomics shows apparent differences in the profiles of serum metabolites between HD and PD, which were influenced by dialysis-related processes. Inosine and hypoxanthine are present only in HD patients, which is likely to represent more hypoxic and oxidative stress.
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Affiliation(s)
- Ji-Young Choi
- Division of Nephrology, Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea
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Cortés D, Guinzberg R, Villalobos-Molina R, Piña E. Evidence that endogenous inosine and adenosine-mediated hyperglycaemia during ischaemia-reperfusion through A3 adenosine receptors. ACTA ACUST UNITED AC 2009; 29:157-64. [PMID: 19740086 DOI: 10.1111/j.1474-8665.2009.00443.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
1 The molecular mechanism underlying stress-induced hyperglycemia has not been comprehensively clarified. Recently, we demonstrated in ischaemia-reperfusion (I-R) stress-subjected liver that inosine and adenosine are mainly responsible for the hyperglycemia observed. 2 We aimed to advance in the knowledge of the role of inosine plus adenosine as mediators of hepatic-induced hyperglycemia detected after I-R in lower limbs. 3 Acute ischaemia was conducted in anesthetized rats by occluding downstream abdominal aorta and cava vein; then, reperfusion was allowed. Blood samples from hepatic or abdominal cava veins were taken throughout the experiments to measure glucose, inosine and adenosine. Antagonists to adenosine (AdoR) and adrenergic receptors (AdrR) were administered during ischaemia to analyze their effect on hepatic glucose release. 4 Ischaemia up to 60 min produced minor increase of glucose and nucleosides blood values, but 5 min of ischaemia followed by 2- (or 10-) min reperfusion increased glucose 23%, and those of inosine or adenosine by 100%. After 60 min of ischaemia and 10 min of reperfusion, glycemia rose 2-fold and blood inosine and adenosine, 3.3- and 2.7-fold, respectively. A linear positive correlation, r(2), as high as 0.839 between glucose and either nucleoside blood values was calculated. The hyperglycemia response to I-R decreased by 0, 25, 33, 45 and 100% after selective inhibition of A(2B) AdoR, A(2A) AdoR, a(1B) AdrR, A(1) AdoR, and A(3) AdoR, respectively. 5 Inosine-adenosine couple through activation of hepatic A(3) AdoR is the main signal for releasing glucose from liver glycogen and for promoting hyperglycemia following experimental injury of I-R from lower limbs.
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Affiliation(s)
- D Cortés
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico
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Adenosine-evoked hyperpolarization of retinal ganglion cells is mediated by G-protein-coupled inwardly rectifying K+ and small conductance Ca2+-activated K+ channel activation. J Neurosci 2009; 29:11237-45. [PMID: 19741130 DOI: 10.1523/jneurosci.2836-09.2009] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Adenosine is a neuromodulator that activates presynaptic receptors to regulate synaptic transmission and postsynaptic receptors to hyperpolarize neurons. Here, we report that adenosine-induced hyperpolarization of retinal ganglion cells is produced by the activation of A(1) receptors, which initiates a signaling cascade that activates G-protein-coupled inwardly rectifying K(+) (GIRK) channels and small conductance Ca(2+)-activated K(+) (SK) channels. Rat retinal ganglion cells were stimulated by focal ejection of the adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) while cell activity was monitored with whole-cell patch recordings and Ca(2+) imaging. Focal ejections of NECA evoked outward currents in all cells tested and reduced light- and depolarization-induced spiking. The NECA-evoked current was abolished by the A(1) antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) but was unaffected by A(2a), A(2b), and A(3) antagonists, indicating that the response was mediated entirely by A(1) receptors. The GIRK channel blocker rTertiapin-Q diminished the NECA-evoked inhibitory current by 56 +/- 12%, whereas the SK channel blocker apamin decreased the NECA-induced current by 42 +/- 7%. The SK component of the NECA-evoked current coincided with an increase in intracellular Ca(2+) and was blocked by IP(3) receptor antagonists and depletion of internal Ca(2+) stores, suggesting that A(1) receptor activation leads to an increase in IP(3), which then elevates intracellular Ca(2+) and activates SK channels. This A(1)-mediated, prolonged SK channel activation has not been described previously. The coactivation of GIRK and SK channels represents a novel mechanism of adenosine-mediated neuromodulation that could contribute to the regulation of retinal ganglion cell activity.
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Ishizaki E, Fukumoto M, Puro DG. Functional K(ATP) channels in the rat retinal microvasculature: topographical distribution, redox regulation, spermine modulation and diabetic alteration. J Physiol 2009; 587:2233-53. [PMID: 19289546 DOI: 10.1113/jphysiol.2009.169003] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The essential task of the circulatory system is to match blood flow to local metabolic demand. However, much remains to be learned about this process. To better understand how local perfusion is regulated, we focused on the functional organization of the retinal microvasculature, which is particularly well adapted for the local control of perfusion. Here, we assessed the distribution and regulation of functional K(ATP) channels whose activation mediates the hyperpolarization induced by adenosine. Using microvascular complexes freshly isolated from the rat retina, we found a topographical heterogeneity in the distribution of functional K(ATP) channels; capillaries generate most of the K(ATP) current. The initiation of K(ATP)-induced responses in the capillaries supports the concept that the regulation of retinal perfusion is highly decentralized. Additional study revealed that microvascular K(ATP) channels are redox sensitive, with oxidants increasing their activity. Furthermore, the oxidant-mediated activation of these channels is driven by the polyamine spermine, whose catabolism produces oxidants. In addition, our observation that spermine-dependent oxidation occurs predominately in the capillaries accounts for why they generate most of the K(ATP) current detected in retinal microvascular complexes. Here, we also analysed retinal microvessels of streptozotocin-injected rats. We found that soon after the onset of diabetes, an increase in spermine-dependent oxidation at proximal microvascular sites boosts their K(ATP) current and thereby virtually eliminates the topographical heterogeneity of functional K(ATP) channels. We conclude that spermine-dependent oxidation is a previously unrecognized mechanism by which this polyamine modulates ion channels; in addition to a physiological role, spermine-dependent oxidation may also contribute to microvascular dysfunction in the diabetic retina.
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Affiliation(s)
- Eisuke Ishizaki
- Department of Ophthalmology and Visual Sciences, University of Michigan, 1000 Wall Street, Ann Arbor, MI 48105, USA
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27
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Housley GD, Bringmann A, Reichenbach A. Purinergic signaling in special senses. Trends Neurosci 2009; 32:128-41. [DOI: 10.1016/j.tins.2009.01.001] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Revised: 12/22/2008] [Accepted: 01/05/2009] [Indexed: 02/06/2023]
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Crooke A, Guzmán-Aranguez A, Peral A, Abdurrahman MKA, Pintor J. Nucleotides in ocular secretions: their role in ocular physiology. Pharmacol Ther 2008; 119:55-73. [PMID: 18562011 DOI: 10.1016/j.pharmthera.2008.04.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2008] [Accepted: 04/28/2008] [Indexed: 12/15/2022]
Abstract
The eye is the sense organ that permits the detection of light owing to the existence of a sophisticated neuronal array, called the retina, which is responsive to photons. The correct functioning of this complex system requires the coordination of several intraocular structures that ultimately permit the perfect focusing of images on the neural retina. Light has to pass through different media: the tear, the cornea, aqueous humour, lens, and vitreous humour before it reaches the retina. Moreover, the composition and structure of some of these media can change due to several physiological mechanisms. Nucleotides are active components of the humours bathing relevant ocular structures. The tear contains nucleotides and dinucleotides that control the process of tearing, wound healing and protects of superficial infections. In the inner eye, the aqueous humour also presents a collection of mono and dinucleotides that affect pupil contraction, aqueous humour production and accommodation. Behind the lens and between this structure and the retina the vitreous humour can modify the physiology of the retinal cells, mostly the ganglion cells. By investigating the actions of nucleotides and dinucleotide present in the ocular humours we will be able not only to understand the functioning of the ocular structures but also to develop new pharmacological therapies for pathologies such as dry eye, glaucoma or retinal detachment.
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Affiliation(s)
- Almudena Crooke
- Departamento de Bioquímica, E.U. Optica, Universidad Complutense de Madrid, 28037 Madrid, Spain
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Mitchell CH, Lu W. Chapter 10 Retinal Ganglion Cells and Glaucoma. CURRENT TOPICS IN MEMBRANES 2008. [DOI: 10.1016/s1063-5823(08)00410-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Stella SL, Hu WD, Vila A, Brecha NC. Adenosine inhibits voltage-dependent Ca2+ influx in cone photoreceptor terminals of the tiger salamander retina. J Neurosci Res 2007; 85:1126-37. [PMID: 17304584 PMCID: PMC3737423 DOI: 10.1002/jnr.21210] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Endogenous adenosine has already been shown to inhibit transmitter release from the rod synapse by suppressing Ca(2+) influx through voltage-gated Ca(2+) channels. However, it is not clear how adenosine modulates the cone synapse. Cone photoreceptors, like rod photoreceptors, also possess L-type Ca(2+) channels that regulate the release of L-glutamate. To assess the impact of adenosine on Ca(2+) influx though voltage-gated Ca(2+) channels in cone terminals, whole-cell perforated-patch clamp recording and Ca(2+) imaging with fluo-4 were used on isolated cones and salamander retinal slices. Synaptic markers (VAMP and piccolo) and activity-dependent dye labeling revealed that tiger salamander cone terminals contain a broad, vesicle-filled cytoplasmic extension at the base of the somatic compartment, which is unlike rod terminals that contain one or more thin axons, each terminating in a large bulbous synaptic terminal. The spatiotemporal Ca(2+) responses of the cone terminals do not differ significantly from the Ca(2+) responses of the soma or inner segment like that observed in rods. Whole-cell recording of cone I(Ca) and Ca(2+) imaging of synaptic terminals in cones demonstrate that adenosine inhibited both I(Ca) and the depolarization-evoked Ca(2+) increase in cone terminals in a dose-dependent manner from 1 to 50 muM. These results indicate that, as in rods, adenosine's ability to suppress voltage-dependent Ca(2+) channels at the cone synapse will limit the amount of L-glutamate released. Therefore, adenosine has an inhibitory effect on L-glutamate release at the first synapse, which likely favors elevated adenosine levels in the dark or during dark-adapted conditions.
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Affiliation(s)
- Salvatore L Stella
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, USA.
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Husain S, Shearer TW, Crosson CE. Mechanisms Linking Adenosine A1 Receptors and Extracellular Signal-Regulated Kinase 1/2 Activation in Human Trabecular Meshwork Cells. J Pharmacol Exp Ther 2006; 320:258-65. [PMID: 17015637 DOI: 10.1124/jpet.106.110981] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study was designed to evaluate the signaling pathways coupling adenosine A1 receptors and extracellular signal-regulated kinase (ERK) 1 and 2 in human trabecular meshwork (HTM) cells. Studies were conducted using cultures of primary HTM cells and the HTM-3 cell line. Activation of ERK1/2, location of protein kinase C (PKC) isoforms, and matrix metalloproteinase (MMP) secretion were determined by Western blotting. In primary HTM cells and the HTM-3 cell line, administration of the A1 agonist N6-cyclohexyladenosine (CHA) produced a concentration-dependent increase in ERK1/2 activation. This CHA-induced ERK activation was blocked by pretreatment with the A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine or pertussis toxin. Transfection with dominant negative N17 Ras produced only a small (31%) decline in CHA-induced ERK activation, and the response was not altered by pretreatment with the Src tyrosine kinase inhibitor, PP2 [3-(4-chlorophenyl)1-(1,1-dimethylethyl)-1H-pyrazolo[3,4-D] pyrimidin-4-amine], the phosphoinositide kinase-3 inhibitor, LY-294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one], or the A3 receptor antagonist, MRS-1191 [3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate]. Administration of CHA also induced the translocation of PKCalpha from the cytosol to the membrane, and pretreatment with the phospholipase C (PLC) inhibitor, U73122 [1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]-hexyl]-1H-pyrrole-2,5-dione], blocked ERK1/2 activation induced by CHA. Transfection of short interfering RNA targeting PKCalpha blocked the CHA-induced ERK1/2 activation and the secretion of MMP-2. These results confirm the existence of functional adenosine A1 receptors in the trabecular meshwork cells. These receptors are coupled to the activation of ERK1/2 through G(i/o) proteins and dependent upon the upstream activation of PLC and PKCalpha. These studies provide evidence that adenosine A1 receptor agonists increase outflow facility through sequential activation of G(i/o) > PLC > PKCalpha > c-Raf > mitogen-activated protein kinase kinase > ERK1/2, leading to secretion of MMP-2.
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Affiliation(s)
- S Husain
- Hewitt Laboratory of the Ola B. Williams Glaucoma Center, Department of Ophthalmology, Storm Eye Institute, Medical University of South Carolina, 167 Ashley Avenue, Charleston, SC 29425, USA
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Zhang X, Zhang M, Laties AM, Mitchell CH. Balance of purines may determine life or death of retinal ganglion cells as A3 adenosine receptors prevent loss following P2X7 receptor stimulation. J Neurochem 2006; 98:566-75. [PMID: 16805847 DOI: 10.1111/j.1471-4159.2006.03900.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The purines ATP and adenosine can act as a coordinated team of transmitters. As extracellular adenosine is frequently derived from the enzymatic dephosphorylation of released ATP, the distinct actions of the two purines can be synchronized. In retinal ganglion cells (RGCs), stimulation of the P2X7 receptor for ATP leads to increased intracellular Ca2+ and death. Here we define the contrasting effects of adenosine and identify protective actions mediated by the A3 receptor. Adenosine attenuated the rise in Ca2+ produced by the P2X7 agonist 3'-O-(4-benzoylbenzoyl)ATP (BzATP). Adenosine was also neuroprotective, increasing the survival of ganglion cells exposed to BzATP. The A3 adenosine receptor agonist 2-chloro-N6-(3-iodobenzyl)-adenosine-5'-N-methyluronimide (Cl-IB-MECA) mimicked the inhibition of the Ca2+ rise, whereas the A3 antagonist 3-Ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS-1191) reduced the protective effects of adenosine. Both Cl-IB-MECA and a second A3 receptor agonist IB-MECA reduced the cell loss triggered by BzATP. The actions of BzATP were mimicked by ATPgammaS, but not by ATP. In summary, adenosine can stop the rise in Ca2+ and cell death resulting from stimulation of the P2X7 receptor on RGCs, with the A3 adenosine receptor contributing to this protection. Hydrolysis of ATP into adenosine and perhaps inosine shifts the balance of purinergic action from that of death to the preservation of life.
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Affiliation(s)
- Xiulan Zhang
- Department of Ophthalmology, University of Pensylvania, School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA
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Weuste M, Wurm A, Iandiev I, Wiedemann P, Reichenbach A, Bringmann A. HB-EGF: Increase in the ischemic rat retina and inhibition of osmotic glial cell swelling. Biochem Biophys Res Commun 2006; 347:310-8. [PMID: 16806064 DOI: 10.1016/j.bbrc.2006.06.077] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Accepted: 06/15/2006] [Indexed: 10/24/2022]
Abstract
We determined whether the expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF) in the sensory rat retina alters during ischemia-reperfusion, and whether HB-EGF affects the osmotic swelling which is a characteristic feature of Müller glial cells after ischemia. Transient retinal ischemia was induced by elevation of the intraocular pressure for 1 h. Western blots revealed an upregulation of HB-EGF in the retina at 1, 3, and 7 days after reperfusion. HB-EGF inhibited the swelling of glial cells in retinal slices, via stimulation of the synaptic release of glutamate and subsequent activation of glial metabotropic glutamate receptors which resulted in an autocrine release of purinergic receptor agonists. Finally, activation of A1 receptors resulted in opening of glial K(+) and Cl(-) channels. It is suggested that the increased expression of HB-EGF and the inhibition of glial cell swelling may be parts of a protective role of HB-EGF in the ischemic retina.
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Affiliation(s)
- Malte Weuste
- Paul Flechsig Institute of Brain Research, University of Leipzig Medical Faculty, Germany
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Uckermann O, Wolf A, Kutzera F, Kalisch F, Beck-Sickinger AG, Wiedemann P, Reichenbach A, Bringmann A. Glutamate release by neurons evokes a purinergic inhibitory mechanism of osmotic glial cell swelling in the rat retina: activation by neuropeptide Y. J Neurosci Res 2006; 83:538-50. [PMID: 16435394 DOI: 10.1002/jnr.20760] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Glial cell swelling is a central cause of ischemic edema in the brain and retina; however, the regulation of glial cell volume by endogenous factors in situ is largely unknown. In slices of the postischemic retina of the rat, the somata of glial (Müller) cells swell upon hypotonic stress that is not observed in slices of control retinas. We describe an endogenous signaling pathway that leads to inhibition of the osmotic glial cell swelling, and that is evoked by the release of glutamate from retinal neurons upon application of neuropeptide Y. Glutamate activates metabotropic glutamate receptors on swollen glial cells, which evokes a Ca2+ -independent purinergic signaling cascade that involves release of ATP, P2Y1 receptor activation, and transporter-mediated release of adenosine. Activation of A1 receptors causes the inhibition of osmotic glial cell swelling, by a protein kinase A-dependent activation of K+ and Cl- channels. It is proposed that the glutamate-evoked purinergic receptor signaling of glial cells is crucially involved in the cell volume homeostasis of the retina, and that this mechanism may contribute to the protective effect of adenosine in the ischemic tissue.
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Affiliation(s)
- Ortrud Uckermann
- Paul Flechsig Institute of Brain Research, Medical Faculty of the University of Leipzig, Leipzig, Germany
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Guinzberg R, Cortés D, Díaz-Cruz A, Riveros-Rosas H, Villalobos-Molina R, Piña E. Inosine released after hypoxia activates hepatic glucose liberation through A3 adenosine receptors. Am J Physiol Endocrinol Metab 2006; 290:E940-51. [PMID: 16352677 DOI: 10.1152/ajpendo.00173.2005] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Inosine, an endogenous nucleoside, has recently been shown to exert potent effects on the immune, neural, and cardiovascular systems. This work addresses modulation of intermediary metabolism by inosine through adenosine receptors (ARs) in isolated rat hepatocytes. We conducted an in silico search in the GenBank and complete genomic sequence databases for additional adenosine/inosine receptors and for a feasible physiological role of inosine in homeostasis. Inosine stimulated glycogenolysis (approximately 40%, EC50 4.2 x 10(-9) M), gluconeogenesis (approximately 40%, EC50 7.8 x 10(-9) M), and ureagenesis (approximately 130%, EC50 7.0 x 10(-8) M) compared with basal values; these effects were blunted by the selective A3 AR antagonist 9-chloro-2-(2-furanyl)-5-[(phenylacetyl)amino][1,2,4]-triazolo[1,5-c]quinazoline (MRS 1220) but not by selective A1, A2A, and A2B AR antagonists. In addition, MRS 1220 antagonized inosine-induced transient increase (40%) in cytosolic Ca2+ and enhanced (90%) glycogen phosphorylase activity. Inosine-induced Ca2+ mobilization was desensitized by adenosine; in a reciprocal manner, inosine desensitized adenosine action. Inosine decreased the cAMP pool in hepatocytes when A1, A2A, and A2B AR were blocked by a mixture of selective antagonists. Inosine-promoted metabolic changes were unrelated to cAMP decrease but were Ca2+ dependent because they were absent in hepatocytes incubated in EGTA- or BAPTA-AM-supplemented Ca2+-free medium. After in silico analysis, no additional cognate adenosine/inosine receptors were found in human, mouse, and rat. In both perfused rat liver and isolated hepatocytes, hypoxia/reoxygenation produced an increase in inosine, adenosine, and glucose release; these actions were quantitatively greater in perfused rat liver than in isolated cells. Moreover, all of these effects were impaired by the antagonist MRS 1220. On the basis of results obtained, known higher extracellular inosine levels under ischemic conditions, and inosine's higher sensitivity for stimulating hepatic gluconeogenesis, it is suggested that, after tissular ischemia, inosine contributes to the maintenance of homeostasis by releasing glucose from the liver through stimulation of A3 ARs.
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Affiliation(s)
- Raquel Guinzberg
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apdo. Postal 70159, Mexico City, 04510, Mexico
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Konno T, Sato A, Uchibori T, Nagai A, Kogi K, Nakahata N. Adenosine A2A receptor mediated protective effect of 2-(6-cyano-1-hexyn-1-yl)adenosine on retinal ischaemia/reperfusion damage in rats. Br J Ophthalmol 2006; 90:900-5. [PMID: 16613921 PMCID: PMC1857139 DOI: 10.1136/bjo.2006.091496] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
AIMS To determine the effect of 2-(6-cyano-1-hexyn-1-yl)adenosine (2-CN-Ado), an adenosine A2A receptor agonist, on retinal ischaemia/reperfusion damage in rats. METHODS Retinal ischaemia/reperfusion damage was induced by elevating the intraocular pressure of one eye to 130 mm Hg for 60 minutes and returning it to normal. 7 days later, retinal ischaemia/reperfusion damage was histologically quantified by measuring the thickness of retinal layers. Intraocular pressure was measured by pressure transducer. RESULTS Retinal ischaemia/reperfusion caused cell loss in the ganglion cell layer and thinning of the inner plexiform and nuclear layer. Both ocular topical and intravenous administration of 2-CN-Ado caused a reduction of retinal ischaemia/reperfusion damage. A selective A2A receptor antagonist, 1,3,7-trimethyl-8-(3-chlorostyryl) xanthine (CSC), but not a selective A1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), or a selective A2B receptor antagonist, alloxazine, reduced the protective effect of 2-CN-Ado. While ocular topical administration of 2-CN-Ado caused a sustained reduction of intraocular pressure, intravenous administration of 2-CN-Ado showed a transient ocular hypotensive effect. CONCLUSIONS These results suggest that 2-CN-Ado attenuates retinal ischaemia/reperfusion damage, and at least some of this protective effect of 2-CN-Ado might be mediated via activation of the adenosine A2A receptor.
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Affiliation(s)
- T Konno
- Drug Research Section II, Fukushima Research Laboratories, Toa Eiyo Ltd, Yuno, Iizaka, Fukushima 960-0280, Japan.
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Schlötzer-Schrehardt U, Zenkel M, Hofmann-Rummelt C, Kruse FE, Naumann GO. [Functional significance of adenosine receptors in the eye and their dysregulation in pseudoexfoliation syndrome]. Ophthalmologe 2006; 102:1074-80, 1082. [PMID: 15830199 DOI: 10.1007/s00347-005-1216-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
BACKGROUND Adenosine regulates many physiologic processes, such as aqueous humor secretion and intraocular pressure, via activation of its receptors. We investigated the expression of the receptor isoforms in eyes with PEX syndrome, which is associated with anterior chamber hypoxia and elevated intraocular pressure. MATERIALS AND METHODS The mRNA and protein expression of the adenosine receptor subtypes in anterior segment tissues of patients with PEX syndrome, glaucomas, and normal control eyes were analyzed comparatively. RESULTS Whereas the receptor subtypes A1, A2a, and A2b displayed no differential expression between PEX and control tissues, expression of the A3 adenosine receptor was consistently enhanced in the nonpigmented ciliary epithelium of all PEX eyes, independent of the presence of glaucoma, compared to normal and glaucomatous control eyes. CONCLUSION Considering the known role of the A3 adenosine receptor in modulating aqueous humor secretion, its selective upregulation in the ciliary epithelium may confer cytoprotection and be accessible to therapeutic intervention in PEX patients.
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Nagase K, Tomi M, Tachikawa M, Hosoya KI. Functional and molecular characterization of adenosine transport at the rat inner blood–retinal barrier. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1758:13-9. [PMID: 16487924 DOI: 10.1016/j.bbamem.2006.01.011] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2005] [Revised: 12/06/2005] [Accepted: 01/11/2006] [Indexed: 10/25/2022]
Abstract
The purpose of the present study was to characterize the adenosine transport system(s) at the inner blood-retinal barrier (inner BRB). A conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2), used as an in vitro model of the inner BRB, expresses equilibrative nucleoside transporter 1 (ENT1), ENT2, concentrative nucleoside transporter 2 (CNT2), and CNT3 mRNAs. TR-iBRB2 cells exhibited an Na+-independent and concentration-dependent [3H]adenosine uptake with a Michaelis-Menten constant of 28.5 microM and a maximum uptake rate of 814 pmol/(min mg protein). [3H]Adenosine uptake by TR-iBRB2 cells was strongly inhibited by 2 mM adenosine, inosine, uridine, and thymidine. On the other hand, this process was not inhibited by 100 nM nitrobenzylmercaptopurine riboside and dipyridamole. These uptake studies suggest that ENT2 is involved in [3H]adenosine uptake by TR-iBRB2 cells. Quantitative real-time PCR revealed that the expression of ENT2 mRNA is 5.5-fold greater than that of ENT1 mRNA. An in vivo study suggested that [3H]adenosine is transported from the blood to the retina and significantly inhibited by adenosine and thymidine. The results of this study show that ENT2 most likely mediates adenosine transport at the inner BRB and is expected to play an important role in regulating the adenosine concentration in the retina.
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Affiliation(s)
- Katsuhiko Nagase
- Faculty of Pharmaceutical Sciences, University of Toyama, 2630, Sugitani, Toyama 930-0194, Japan
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Uckermann O, Kutzera F, Wolf A, Pannicke T, Reichenbach A, Wiedemann P, Wolf S, Bringmann A. The Glucocorticoid Triamcinolone Acetonide Inhibits Osmotic Swelling of Retinal Glial Cells via Stimulation of Endogenous Adenosine Signaling. J Pharmacol Exp Ther 2005; 315:1036-45. [PMID: 16144977 DOI: 10.1124/jpet.105.092353] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The glucocorticoid triamcinolone acetonide is clinically used for the treatment of macular edema. However, the edema-resolving mechanisms of triamcinolone are incompletely understood. Since cell swelling is a central cause of cytotoxic edema in the brain and retina, we determined the effects of triamcinolone acetonide on the swelling of retinal ganglion and Müller glial cells in acutely isolated retinas from rats and guinea pigs in situ. Triamcinolone acetonide (100 microM) had no effect on the swelling of ganglion cells that was evoked in isolated whole mounts of the guinea pig retina by acute application of glutamate (1 mM) or high K+ (50 mM). However, triamcinolone reversed the osmotic swelling of Müller glial cells in retinas of the rat that was observed under various experimental conditions: in retinas isolated at 3 days after transient retinal ischemia, in retinas of eyes with lipopolysaccharide-induced ocular inflammation, and in control retinas in the presence of Ba2+ (1 mM), H2O2 (200 microM), arachidonic acid (10 microM), or prostaglandin E2 (30 nM). The inhibiting effect of triamcinolone on osmotic glial cell swelling was mediated by stimulation of transporter-mediated release of endogenous adenosine and subsequent A1 receptor activation, resulting in an elevation of the intracellular cAMP level and activation of the protein kinase A, and, finally, in an opening of extrusion pathways for K+ and Cl- ions. The inhibitory effect on the cytotoxic swelling of glial cells may contribute to the fast edema-resolving effect of vitreal triamcinolone observed in human patients.
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Affiliation(s)
- Ortrud Uckermann
- Paul Flechsig Institute of Brain Research, University of Leipzig, Liebigstrasse 10-14, D-04103 Leipzig, Germany
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Oku H, Goto W, Kobayashi T, Okuno T, Hirao M, Sugiyama T, Yoneda S, Hara H, Ikeda T. Adenosine protects cultured retinal neurons against NMDA-induced cell death through A1 receptors. Curr Eye Res 2005; 29:449-55. [PMID: 15764089 DOI: 10.1080/02713680490522443] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE To determine whether adenosine can protect cultured retinal neurons, consisting mainly of amacrine cells, from N-methyl-D-aspartate (NMDA)-induced neurotoxicity, and to determine whether agonists and antagonists of adenosine receptors also have a protective effect. METHODS Cultured retinal neurons obtained from fetal Wistar rats (gestational age 18-19 days) were maintained for 10-11 days. Neurons were exposed to NMDA (1.0 mM) for 10 min with or without adenosine or to NMDA with adenosine receptor agonists or antagonists. Neuronal death was assessed by the trypan-blue exclusion method 24 hr after the exposure. RESULTS Adenosine at doses of 0.01 microM and higher significantly protected (p < 0.05, Dunnett) primary cultured fetal rat retinal neurons from apoptotic and/or necrotic death induced by NMDA (1.0 mM). The protective effect of adenosine (10 microM) against NMDA-induced neuronal death was lost by simultaneous exposure to selective A1 receptor antagonist but not to A2a receptor antagonist. Selective A1 receptor agonists had similar effects as adenosine, but A2a receptor agonists and 8-Br-cyclic AMP had no effect on cell viability. CONCLUSIONS Adenosine can protect cultured retinal neurons against NMDA-induced cell death via the A1 receptor.
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Affiliation(s)
- Hidehiro Oku
- Department of Ophthalmology, Osaka Medical, Osaka, Japan.
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Hirao M, Oku H, Goto W, Sugiyama T, Kobayashi T, Ikeda T. Effects of adenosine on optic nerve head circulation in rabbits. Exp Eye Res 2004; 79:729-35. [PMID: 15500831 DOI: 10.1016/j.exer.2004.08.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2004] [Accepted: 08/09/2004] [Indexed: 10/26/2022]
Abstract
This study was performed to determine whether intravitreal or intravenous adenosine can alter the microcirculation in the optic nerve head (ONH) of rabbits. Capillary blood flow in the ONH was measured serially with a laser speckle tissue analyser for 2 hr after the intravitreal (0.1, 1.0 and 10 nmol) or intravenous (0.2 and 0.6 mg kg(-1)min) injections of adenosine. In addition, the effect of specific adenosine A(1) and A(2a) antagonists and an adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel blockers on the adenosine-induced changes on the ONH blood flow was analysed. Intravitreal adenosine increased the capillary blood flow in the ONH in a dose-dependent manner, while intravenous adenosine had no effect. Co-administration of the specific adenosine A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 nmol) significantly suppressed (P=0.006, ANOVA) the increase in the ONH blood flow induced by adenosine (10 nmol). The specific A(2a) receptor antagonist, 8-(3-chlorostyryl) caffeine (CSC, 10 nmol), had a weak effect in inhibiting the increase but the change was not significant (P=0.08, ANOVA). Both specific A(1) and A(2a) receptor agonists, N(6)-cyclopentyladenosine (CPA, 10 nmol) and 2-p-(2-carboxyethyl) phenethyl-amino-5'-N-ethylcarboxamidoadenosine (CGS-21680, 10 nmol), increased the ONH tissue blood flow (P<0.01, ANOVA). Glibenclamide (10 nmol), a selective K(ATP) channels antagonist, suppressed the increase of ONH blood flow induced by 10 nmol adenosine significantly (P<0.001, ANOVA). On the other hand, 10 nmol of 8-Br-cAMP, a cAMP analog, failed to enhance the capillary blood flow in the ONH. These results indicate that adenosine increases the capillary blood flow in the ONH of rabbits, and it acts through A(1) and A(2a) receptors from the ablumenal side where pericytes are located. Activation of K(ATP) channels is strongly related to the mechanism of adenosine-induced increase in ONH blood flow, while the participation of adenylate cyclase is less likely.
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Affiliation(s)
- Mami Hirao
- Department of Ophthalmology, Osaka Medical College, 2-7 Daigaku-cho, Takatsuki, Osaka 569-8686, Japan
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Protective effect of ischemic preconditioning on retinal ischemia-reperfusion injury in rats. Can J Ophthalmol 2004. [DOI: 10.1016/s0008-4182(04)80066-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Stella SL, Bryson EJ, Cadetti L, Thoreson WB. Endogenous adenosine reduces glutamatergic output from rods through activation of A2-like adenosine receptors. J Neurophysiol 2003; 90:165-74. [PMID: 12843308 DOI: 10.1152/jn.00671.2002] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Adenosine is released from retina in darkness; photoreceptors possess A2 adenosine receptors, and A2 agonists inhibit L-type Ca2+ currents (ICa) in rods. We therefore investigated whether A2 agonists inhibit rod inputs into second-order neurons and whether selective antagonists to A1, A2A, or A3 receptors prevent Ca2+ influx through rod ICa. [Ca2+]i changes in rods were assessed with fura-2. ICa in rods and light responses of rods and second-order neurons were recorded using perforated patch-clamp techniques in the aquatic tiger salamander retinal slice preparation. Consistent with earlier results using the A2 agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)-ethyl]adenosine (DPMA), the A2A agonist CGS-21680 significantly inhibited ICa and depolarization-evoked [Ca2+]i increases in rods. The A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), and A2A antagonist, ZM-241385, but not the A3 antagonist, VUF-5574, inhibited effects of adenosine on Ca2+ influx in rods. DPCPX and ZM-241385 also inhibited effects of CGS-21680, suggesting they both act at A2A receptors. Both A2 agonists, CGS-21680 and DPMA, reduced light-evoked currents in second-order neurons but not light-evoked voltage responses of rods, suggesting that activation of A2 receptors inhibits transmitter release from rods. The inhibitory effects of CGS-21680 on both depolarization-evoked Ca2+ influx and light-evoked currents in second-order neurons were antagonized by ZM-241385. By itself, ZM-241385 enhanced the light-evoked currents in second-order neurons, suggesting that endogenous levels of adenosine inhibit transmitter release from rods. The effects of these drugs suggest that endogenous adenosine activates an A2-like adenosine receptor on rods leading to inhibition of ICa, which in turn inhibits l-glutamate release from rod photoreceptors.
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Affiliation(s)
- Salvatore L Stella
- Department of Pharmacology and Department of Ophthalmology, University of Nebraska Medical Center, Omaha, Nebraska 68198-5540, USA.
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Daines BS, Kent AR, McAleer MS, Crosson CE. Intraocular adenosine levels in normal and ocular-hypertensive patients. J Ocul Pharmacol Ther 2003; 19:113-9. [PMID: 12804056 DOI: 10.1089/108076803321637645] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
PURPOSE Adenosine receptors modulate several ocular responses; however, our understanding of factors that influence ocular extracellular adenosine levels is limited. The objective of this study was to evaluate how changes in intraocular pressure (IOP) influence endogenous levels of the purines adenosine and inosine, in the aqueous humor of normal and ocular-hypertensive patients. PATIENTS AND METHODS Informed consent was obtained from 51 individuals undergoing cataract extraction or glaucoma surgical procedures. IOP was measured immediately prior to surgery. At the start of the surgical procedure, an aqueous sample of 75-100 microL was obtained. Purine levels were determined by reverse-phase HPLC. RESULTS In normotensive individuals, mean aqueous adenosine and inosine levels were 5.2 +/- 1.1 and 19.4 +/- 2.2 ng/100 microL, respectively. No significant correlation between IOP and purine concentration was measured in this group. In ocular hypertensive individuals, the mean aqueous adenosine and inosine concentration was significantly elevated when compared to normotensive individuals. In the ocular hypertensive individual, this elevation in adenosine level was significantly correlated with IOP (r(2) = 0.42). CONCLUSIONS These results demonstrate that in ocular hypertensive individuals, aqueous adenosine concentration is correlated with IOP. As the activation of adenosine receptors can modulate IOP and retinal blood flow, adenosine release during periods of ocular hypertension may play an important role in the physiological responses to elevated IOP.
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Affiliation(s)
- Bradley S Daines
- Hewitt Laboratory of the Ola B. Williams Glaucoma Center, Department of Ophthalmology, Medical University of South Carolina, Charleston, SC, USA
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Jeppesen P, Aalkjaer C, Bek T. Adenosine relaxation in small retinal arterioles requires functional Na-K pumps and K(ATP) channels. Curr Eye Res 2002; 25:23-8. [PMID: 12518240 DOI: 10.1076/ceyr.25.1.23.9966] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
PURPOSE To study the effect of Na-K pump and K(ATP) channel inhibition on the diameter and the adenosine-induced vasodilation of small retinal arterioles. METHODS Thirty isolated porcine arterioles with a diameter of approximately 70 microm were mounted in a double-barrelled pipette system placed in an organ bath, and diameter changes were studied under isobaric no-flow conditions. After an equilibration period, the arterioles were incubated with the Na-K pump inhibitors ouabain and low K(+) medium or the K(ATP) channel inhibitor glibenclamide, and spontaneous diameter changes were studied. Subsequently, the arterioles were precontracted and the adenosine concentration response curve was measured with and without the presence of inhibitors. RESULTS Inhibition of the Na-K pump elicited a significant decrease in the spontaneous diameter of the vessels (P = 0.047), whereas no change in the spontaneous diameter was induced by inhibition of the K(ATP) channels (P = 0.754). Inhibition of the Na-K pump with ouabain or with low K(+) medium, as well as inhibition of the K(ATP) channels with glibenclamide, both diminished the adenosine induced vasodilation (P = 0.003, P = 0.01, and P = 0.003, respectively). CONCLUSION The adenosine-induced vasodilation of small retinal arterioles involves the K(ATP) channels and the Na-K pump. Changes in the metabolism of adenosine as well as the activity of the K(ATP) channels or the Na-K pump can be expected to influence the retinal blood flow.
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Affiliation(s)
- Peter Jeppesen
- Dept of Ophthalmology, Arhus University Hospital, Arhus, Denmark.
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Li Q, Puro DG. Adenosine activates ATP-sensitive K(+) currents in pericytes of rat retinal microvessels: role of A1 and A2a receptors. Brain Res 2001; 907:93-9. [PMID: 11430889 DOI: 10.1016/s0006-8993(01)02607-5] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In the CNS, contractile pericytes are positioned on the endothelial walls of microvessels where they are thought to play a role in adjusting blood flow to meet local metabolic needs. This function may be particularly important in the retina where pericytes are more numerous than at any other site. Despite the putative importance of pericytes, knowledge of the mechanisms by which vasoactive molecules, such as adenosine, regulate their function is limited. Using the perforated-patch configuration of the patch-clamp technique to monitor the whole-cell currents of pericytes located on microvessels freshly isolated from the adult rat retina, we found that adenosine reversibly activated a hyperpolarizing current in 98% of the sampled pericytes. This adenosine-induced current is likely to be due to the opening of ATP-sensitive potassium (K(ATP)) channels since it had a reversal potential near the equilibrium potential for K(+), was inhibited by the K(ATP) channel blocker, glibenclamide, and was mimicked by pinacidil, which is a K(ATP) channel opener. Experiments with specific agonists and antagonists indicated that both the high affinity A1 and the lower affinity A2a adenosine receptors provided effective pathways for activating K(ATP) currents in pericytes recorded under normal metabolic conditions. However, during chemical ischemia, the A1 receptor pathway rapidly became ineffective. In contrast, activation of A2a adenosine receptors continued to open K(ATP) channels in ischemic pericytes. These results suggest that the regulation of K(ATP) channels via A1 and A2a receptors allows adenosine to serve over a broad range of metabolic conditions as a vasoactive signal in the retinal microvasculature.
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Affiliation(s)
- Q Li
- Department of Ophthalmology and Visual Sciences, The University of Michigan, 1000 Wall Street, Ann Arbor, MI 48105, USA
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Rosenbaum DM, Rosenbaum PS, Singh M, Gupta G, Gupta H, Li B, Roth S. Functional and morphologic comparison of two methods to produce transient retinal ischemia in the rat. J Neuroophthalmol 2001; 21:62-8. [PMID: 11315985 DOI: 10.1097/00041327-200103000-00015] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES Much of our knowledge of the pathophysiology of retinal ischemic injury is from a multitude of studies that use in vitro or in vivo animal models of retinal ischemia followed by reperfusion. The objective of this study was to compare histopathologic and electrophysiologic (electroretinography) parameters using two different models of transient retinal ischemia: high intraocular pressure (HIOP) and suture ligation of the optic nerve (SL). METHODS Transient retinal ischemia was induced using the HIOP model or the SL model in the Sprague-Dawley rat for either 30 or 60 minutes. Histopathologic outcome was determined at 1 and 7 days after ischemia. In addition, electroretinography (ERG) was performed at 2 hours, I day, 3 days, and 7 days after ischemia. RESULTS At 1 and 7 days after 30 minutes of ischemia, there were no significant histopathologic abnormalities in the retina with either model, except for a slight decrease of the cell count in the ganglion cell layer (GCL) with the SL method. After 60 minutes of ischemia, there was significant thinning of the inner retina. There was a significant early dropout of cells at 1 day in the inner nuclear layer (INL) in the HIOP method compared to the SL method where the dropout was delayed and gradually progressive. Dropout of cells in the GCL was early (I day) and gradually progressive in both models but more severe in HIOP than SL. There was a significant decrease in the ERG b-wave amplitudes as early as 2 hours after both 30 and 60 minutes of ischemia compared to preischemic baselines. CONCLUSIONS The degree of retinal injury after transient retinal ischemia was more severe at 1 day after reperfusion in the HIOP method compared to the SL method but was similar at 7 days in both models. Furthermore, our data suggests that functional assessment of ischemic damage by electroretinography may be a more sensitive parameter than conventional histopathologic quantification. The timing of either measurement relative to the ischemic stimulus is critical because histologic measurements performed too early after ischemia may underestimate the degree of injury.
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Affiliation(s)
- D M Rosenbaum
- Department of Neurology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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Ettaiche M, Heurteaux C, Blondeau N, Borsotto M, Tinel N, Lazdunski M. ATP-sensitive potassium channels (K(ATP)) in retina: a key role for delayed ischemic tolerance. Brain Res 2001; 890:118-29. [PMID: 11164774 DOI: 10.1016/s0006-8993(00)03152-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The objectives of the present study were to determine the localization of K(ATP) channels in normal retina and to evaluate their potential roles in ischemic preconditioning (IPC) in a rat model of ischemia induced by increased intraocular pressure (IOP). Brown Norway rats were subjected to sublethal 3-, lethal 20- and 40-min ischemia and the functional recovery was evaluated using electroretinography. The time interval between ischemic insults ranged from 1 to 72 h. The effects of K(ATP) channel blockade on IPC protection were studied by treatment with 0.01% glipizide. IPC was mimicked by injection of K(ATP) channel openers of 0.01% (-)cromakalim or 0.01% P1060 72 h before 20-min ischemia. Co-expression of K(ATP) channel subunits Kir6.2/SUR1 was observed in the retinal pigment epithelium, inner segments of photoreceptors, outer plexiform and ganglion cell layers and at the border of the inner nuclear layer. In contrast to a 20- or 40-min ischemia, a 3-min ischemia induced no alteration of the electroretinogram (ERG) and constituted the preconditioning stimulus. An ischemic challenge of 40 min in preconditioned rats induced impairment of retinal function. However, animals preconditioned 24, 48 and 72 h before 20-min ischemia had a significant improvement of the ERG. (-)Cromakalim and P1060 mimicked the effect of IPC. Glipizide significantly suppressed the protective effects of preconditioning. In conclusion, activation of K(ATP) channels plays an important role in the mechanism of preconditioning by enhancing the resistance of the retina against a severe ischemic insult.
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Affiliation(s)
- M Ettaiche
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, UPR 411, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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Li B, Yang C, Rosenbaum DM, Roth S. Signal transduction mechanisms involved in ischemic preconditioning in the rat retina in vivo. Exp Eye Res 2000; 70:755-65. [PMID: 10843780 DOI: 10.1006/exer.2000.0843] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ischemic preconditioning (IPC) protects the rat retina against the injury that ordinarily follows severe ischemia. We showed previously that release of adenosine and de novo protein synthesis were required for IPC protection. The mechanisms of IPC were studied in the rat retina by examining the signal transduction mediators responsible, in particular, those theorized to be downstream of adenosine receptors. In addition, we examined the hypothesis that nitric oxide and hydroxyl radicals were involved in the IPC protective phenomenon. Retinal ischemia was produced for 60 min in ketamine/xylazine-anesthetized Sprague-Dawley rats, and recovery was measured using electroretinography. We tested the effects on the protective effect of IPC resulting from antagonism of protein kinase C, potassium ATP channels, nitric oxide synthase, or hydroxyl radicals. The effects of the inhibition of de novo protein synthesis or of protein kinase C, and blockade of potassium ATP channels on the mimicking of IPC by adenosine receptor agonists was examined.IPC protection was strongly attenuated by inhibition of protein kinase C and by blockade of potassium ATP channels, but unaffected by the inhibition of hydroxyl radicals. Blockade of nitric oxide synthase produced a trend toward enhancement of IPC protection. Mimicking of IPC protection by adenosine receptor agonists was inhibited by blockade of protein synthesis or of protein kinase C, as well as by potassium ATP channel antagonism. These results demonstrate that protein kinase C and potassium ATP channels are mediators of the protective effect produced by IPC. In addition, the results show that stimulation of adenosine receptor subtypes A1 and A2a is responsible for IPC protection via downstream stimulation of protein kinase C, the opening of potassium ATP channels, and de novo protein synthesis.
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Affiliation(s)
- B Li
- Department of Anaesthesia and Critical Care, The University of Chicago, Chicago, IL 60637, USA
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Rego AC, Agostinho P, Melo J, Cunha RA, Oliveira CR. Adenosine A2A receptors regulate the extracellular accumulation of excitatory amino acids upon metabolic dysfunction in chick cultured retinal cells. Exp Eye Res 2000; 70:577-87. [PMID: 10870516 DOI: 10.1006/exer.1999.0815] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of endogenous extracellular adenosine as a tonic modulator of the extracellular accumulation of excitatory amino acids (glutamate and aspartate) caused by metabolic inhibition was investigated in cultured retinal cells. The selective adenosine A2A receptor antagonist, 4-[2-[7-amino-2-(2-furyl)(1,2,4)-triazin-5-ylamino]-ethyl]ph enol (ZM241385) (50 nM), increased the release of glutamate (three- to four-fold) and of aspartate (nearly two-fold) upon iodoacetic acid-induced glycolysis inhibition, in the presence or in the absence of Ca2+. Blockade of tonic activation of A2A receptors by ZM241385 also increased (nearly two-fold) the ischemia-induced release of glutamate and aspartate. Furthermore, another selective A2A receptor antagonist, 5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5- c] pyrimidine (SCH58261), also increased the release of aspartate and glutamate by about two-fold in cells submitted to glycolysis inhibition. In contrast, the selective adenosine A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (100 nM), did not significantly modify the extracellular accumulation of either glutamate or aspartate caused by inducers of chemical ischemia or glycolytic inhibitors. Inhibition of glycolysis also increased (about three-fold) the extracellular accumulation of GABA, which was virtually unchanged by ZM241385. Furthermore, the GABAA receptor antagonist, bicuculline (10 microM), only increased (nearly two-fold) the iodoacetic acid-induced Ca(2+)-dependent release of glutamate, whereas the GABAB receptor antagonist, 3-aminopropyl(diethoxymethyl) phosphinic acid, CGP35348 (100 microM), was devoid of effects on the extracellular accumulation of glutamate and aspartate. These results show that endogenous extracellular adenosine, which rises under conditions of inhibited glycolysis, tonically inhibits the extracellular accumulation of excitatory amino acid through the activation of A2A, but not A1, adenosine receptors, and this effect is independent of GABAA and GABAB functions in the cultured retinal cells.
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Affiliation(s)
- A C Rego
- Center for Neurosciences of Coimbra, University of Coimbra, Portugal
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