Ecto-5 '-Nucleotidase (CD73) Inhibits Nociception by Hydrolyzing AMP to Adenosine in Nociceptive Circuits

Department of Cell and Molecular Physiology, UNC Neuroscience Center and Curriculum in Neurobiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 02/2010; 30(6):2235-44. DOI: 10.1523/JNEUROSCI.5324-09.2010
Source: PubMed


Ecto-5'-nucleotidase (NT5E, CD73) is a membrane-anchored protein that hydrolyzes extracellular adenosine 5'-monophosphate (AMP) to adenosine in diverse tissues but has not been directly studied in nociceptive neurons. We found that NT5E was located on peptidergic and nonpeptidergic nociceptive neurons in dorsal root ganglia (DRG) and on axon terminals in lamina II (the substantia gelatinosa) of spinal cord. NT5E was also located on epidermal keratinocytes, cells of the dermis, and on nociceptive axon terminals in the epidermis. Following nerve injury, NT5E protein and AMP histochemical staining were coordinately reduced in lamina II. In addition, AMP hydrolytic activity was reduced in DRG neurons and spinal cord of Nt5e(-/-) mice. The antinociceptive effects of AMP, when combined with the adenosine kinase inhibitor 5-iodotubericidin, were reduced by approximately 50% in Nt5e(-/-) mice and were eliminated in Adenosine A(1) receptor (A(1)R, Adora1) knock-out mice. Additionally, Nt5e(-/-) mice displayed enhanced sensitivity in the tail immersion assay, in the complete Freund's adjuvant model of inflammatory pain and in the spared nerve injury model of neuropathic pain. Collectively, our data indicate that the ectonucleotidase NT5E regulates nociception by hydrolyzing AMP to adenosine in nociceptive circuits and represents a new molecular target for the treatment of chronic pain. Moreover, our data suggest NT5E is well localized to regulate nucleotide signaling between skin cells and sensory axons.

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    • "Interestingly, a single i.t. injection of PAP or ecto-5 0 -nucleotidase produced sustained antinociception lasting for 2–3 days in models of inflammatory and neuropathic pain (Zylka et al., 2008; Sowa et al., 2009, 2010b). This effect results from A 1 R activation as it was blocked by a selective A 1 R antagonist and was no longer seen in A 1 R knockout mice (Zylka et al., 2008; Sowa et al., 2009, 2010c). "
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    ABSTRACT: The main focus for development of adenosine targets as analgesics to date has been A1Rs due to its antinociceptive profile in various preclinical pain models. The usefulness of systemic A1R agonists may be limited by other effects (cardiovascular, motor), but enhanced selectivity for pain might occur with partial agonists, potent and highly selective agonists, or allosteric modulators. A2AR agonists exhibit some peripheral pronociceptive effects, but also act on immune cells to suppress inflammation and on spinal glia to suppress pain signalling and may be useful for inflammatory and neuropathic pain. A2BR agonists exhibit peripheral proinflammatory effects on immune cells, but also spinal antinociceptive effects similar to A2AR agonists. A3Rs are now demonstrated to produce antinociception in several preclinical neuropathic pain models, with mechanistic actions on glial cells, and may be useful for neuropathic pain. Endogenous adenosine levels can be augmented by inhibition of metabolism (via adenosine kinase) or increased generation (via nucleotidases), and these approaches have implications for pain. Endogenous adenosine contributes to antinociception by several pharmacological agents, herbal remedies, acupuncture, transcutaneous electrical nerve stimulation, exercise, joint mobilization, and water immersion via spinal and/or peripheral effects, such that this system appears to constitute a major pain regulatory system. Finally, caffeine inhibits A1-, A2A- and A3Rs with similar potency, and dietary caffeine intake will need attention in trials of: (a) agonists and/or modulators acting at these receptors, (b) some pharmacological and herbal analgesics, and (c) manipulations that enhance endogenous adenosine levels, all of which are inhibited by caffeine and/or A1R antagonists in preclinical studies. All adenosine receptors have effects on spinal glial cells in regulating nociception, and gender differences in the involvement of such cells in chronic neuropathic pain indicate gender may also need attention in preclinical and human trials evaluating efficacy of adenosine-based analgesics.
    Full-text · Article · Oct 2015 · Neuroscience
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    • "yed by Wachstein and Meisel for histochemical characterization of hepatic phosphatases ( Wachstein & Meisel , 1957 ) . Using this approach , tissue and cellular localization as well as substrate specificity of different purinergic enzymes has been char - acterized in the murine brain ( Langer et al . , 2008 ) , dorsal root ganglion , spinal cord ( Sowa et al . , 2010 ; Street et al . , 2013 ; Zylka et al . , 2008 ) and other neurogenic zones ( Langer et al . , 2007 ) , rat liver ( Fausther et al . , 2012 ) , murine pancreas , salivary glands , gastrointestinal tract ( Kittel et al . , 2004a ; Lavoie et al . , 2011 ) and thoracic aortas ( Kauffenstein et al . , 2010 ; Mercier et al . , 2012 ) , mouse"
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    ABSTRACT: Abstract Extracellular nucleotides and nucleosides mediate diverse signaling effects in virtually all organs and tissues. Most models of purinergic signaling depend on functional interactions between distinct processes, including (i) the release of endogenous ATP and other nucleotides, (ii) triggering of signaling events via a series of nucleotide-selective ligand-gated P2X and metabotropic P2Y receptors as well as adenosine receptors and (iii) ectoenzymatic interconversion of purinergic agonists. The duration and magnitude of purinergic signaling is governed by a network of ectoenzymes, including the enzymes of the nucleoside triphosphate diphosphohydrolase (NTPDase) family, the nucleotide pyrophosphatase/phosphodiesterase (NPP) family, ecto-5'-nucleotidase/CD73, tissue-nonspecific alkaline phosphatase (TNAP), prostatic acid phosphatase (PAP) and other alkaline and acid phosphatases, adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP). Along with "classical" inactivating ectoenzymes, recent data provide evidence for the co-existence of a counteracting ATP-regenerating pathway comprising the enzymes of the adenylate kinase (AK) and nucleoside diphosphate kinase (NDPK/NME/NM23) families and ATP synthase. This review describes recent advances in this field, with special emphasis on purine-converting ectoenzymes as a complex and integrated network regulating purinergic signaling in such (patho)physiological states as immunomodulation, inflammation, tumorigenesis, arterial calcification and other diseases. The second part of this review provides a comprehensive overview and basic principles of major approaches employed for studying purinergic activities, including spectrophotometric Pi-liberating assays, high-performance liquid chromatographic (HPLC) and thin-layer chromatographic (TLC) analyses of purine substrates and metabolites, capillary electrophoresis, bioluminescent, fluorometric and electrochemical enzyme-coupled assays, histochemical staining, and further emphasizes their advantages, drawbacks and suitability for assaying a particular catalytic reaction.
    Full-text · Article · Nov 2014 · Critical Reviews in Biochemistry and Molecular Biology
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    • "The role of peripheral adenosine systems, and specifically activation of A1Rs on peripheral sensory nerves in inhibiting pain, is now receiving renewed attention. This reflects several developments including: (1) identification of nucleotidases (CD73, PAP) that generate endogenous adenosine from nucleotides in nociceptive circuits (Zylka et al., 2008; Sowa et al., 2010b); (2) implication of peripheral adenosine (and nucleotides) in acupuncture analgesia in mice (Goldman et al., 2010) and in humans (Takano et al., 2012); (3) peripheral administration of PAP into acupoints leads to long-lasting antinociception (several days) that is dependent on A1Rs (Hurt and Zylka, 2012); (4) exercise regimens that produce analgesia in a model of neuropathic pain involve A1Rs (peripheral adenosine levels increase due to increased ATP utilization in muscle) (Martins et al., 2013). Several strategies may potentially recruit this peripheral system: (1) topical administration of small molecule drugs that directly or indirectly activate peripheral A1Rs; (2) optimizing acupuncture by augmenting adenosine production or inhibiting adenosine metabolism; (3) novel delivery techniques such as localized delivery of nucleotidases to acupuncture sites (Zylka, 2011; Hurt and Zylka, 2012; Sawynok, 2013). "
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    ABSTRACT: Topical analgesics applied locally to skin or to specialized compartments modify pain by actions on sensory nerve endings and/or adjacent cellular elements. With this approach, there are low systemic drug levels, good tolerability and few drug interactions, and combination with oral formulations is feasible. The goal of this review is to provide an overview of the potential for topical analgesics to contribute to improved management of neuropathic pain. Mechanistic and preclinical studies indicate much potential for development of novel topical analgesics for neuropathic pain. In humans, two topical analgesics are approved for use in post-herpetic neuralgia (lidocaine 5% medicated plaster, capsaicin 8% patch), and there is evidence for efficacy in other neuropathic pain conditions. Comparative trials indicate similar efficacy between topical and oral analgesics. Not all individuals respond to topical analgesics, and there is interest in determining factors (patient factors, sensory characteristics) which might predict responsiveness to topical analgesics. There is a growing number of controlled trials and case reports of investigational agents (vasodilators, glutamate receptor antagonists, α2-adrenoreceptor agonists, antidepressants, centrally acting drugs), including combinations of several agents, indicating these produce pain relief in neuropathic pain. There is interest in compounding topical analgesics for neuropathic pain, but several challenges remain for this approach. Topical analgesics have the potential to be a valuable additional approach for the management of neuropathic pain.
    Full-text · Article · Apr 2014 · European journal of pain (London, England)
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