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Haddad M, Cherchi F, Alsalem M, Al-saraireh YM, Madae’en S. Adenosine Receptors as Potential Therapeutic Analgesic Targets. Int J Mol Sci 2023; 24:13160. [PMID: 37685963 PMCID: PMC10487796 DOI: 10.3390/ijms241713160] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Revised: 08/18/2023] [Accepted: 08/23/2023] [Indexed: 09/10/2023] Open
Abstract
Pain represents an international burden and a major socio-economic public health problem. New findings, detailed in this review, suggest that adenosine plays a significant role in neuropathic and inflammatory pain, by acting on its metabotropic adenosine receptors (A1AR, A2AAR, A2BAR, A3AR). Adenosine receptor ligands have a practical translational potential based on the favorable efficacy and safety profiles that emerged from clinical research on various agonists and antagonists for different pathologies. The present review collects the latest studies on selected adenosine receptor ligands in different pain models. Here, we also covered the many hypothesized pathways and the role of newly synthesized allosteric adenosine receptor modulators. This review aims to present a summary of recent research on adenosine receptors as prospective therapeutic targets for a range of pain-related disorders.
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Affiliation(s)
- Mansour Haddad
- Faculty of Pharmacy, Yarmouk University, Irbid 21163, Jordan
| | - Federica Cherchi
- Department of Neuroscience, Psychology, Drug Research and Child Health (NEUROFARBA), Section of Pharmacology and Toxicology, University of Florence, 50139 Florence, Italy;
| | - Mohammad Alsalem
- School of Medicine, The University of Jordan, Amman 11942, Jordan;
| | - Yousef M. Al-saraireh
- Department of Pharmacology, Faculty of Medicine, Mutah University, P.O. Box 7, Al-Karak 61710, Jordan;
| | - Saba Madae’en
- Department of Clinical Pharmacy and Pharmacy Practice, Faculty of Pharmaceutical Sciences, The Hashemite University, Zarqa 13133, Jordan;
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2
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Liu J, Jia S, Huang F, He H, Fan W. Peripheral role of glutamate in orofacial pain. Front Neurosci 2022; 16:929136. [PMID: 36440288 PMCID: PMC9682037 DOI: 10.3389/fnins.2022.929136] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Accepted: 10/10/2022] [Indexed: 09/10/2023] Open
Abstract
Glutamate is the principal excitatory neurotransmitter in the central nervous system. In the periphery, glutamate acts as a transmitter and involves in the signaling and processing of sensory input. Glutamate acts at several types of receptors and also interacts with other transmitters/mediators under various physiological and pathophysiological conditions including chronic pain. The increasing amount of evidence suggests that glutamate may play a role through multiple mechanisms in orofacial pain processing. In this study, we reviewed the current understanding of how peripheral glutamate mediates orofacial pain, how glutamate is regulated in the periphery, and how these findings are translated into therapies for pain conditions.
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Affiliation(s)
- Jinyue Liu
- Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Shilin Jia
- Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Fang Huang
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Hongwen He
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Wenguo Fan
- Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
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Yudin Y, Rohacs T. Inhibitory G i/O-coupled receptors in somatosensory neurons: Potential therapeutic targets for novel analgesics. Mol Pain 2018; 14:1744806918763646. [PMID: 29580154 PMCID: PMC5882016 DOI: 10.1177/1744806918763646] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Primary sensory neurons in the dorsal root ganglia and trigeminal ganglia are responsible for sensing mechanical and thermal stimuli, as well as detecting tissue damage. These neurons express ion channels that respond to thermal, mechanical, or chemical cues, conduct action potentials, and mediate transmitter release. These neurons also express a large number of G-protein coupled receptors, which are major transducers for extracellular signaling molecules, and their activation usually modulates the primary transduction pathways. Receptors that couple to phospholipase C via heterotrimeric Gq/11 proteins and those that activate adenylate cyclase via Gs are considered excitatory; they positively regulate somatosensory transduction and they play roles in inflammatory sensitization and pain, and in some cases also in inducing itch. On the other hand, receptors that couple to Gi/o proteins, such as opioid or GABAB receptors, are generally inhibitory. Their activation counteracts the effect of Gs-stimulation by inhibiting adenylate cyclase, as well as exerts effects on ion channels, usually resulting in decreased excitability. This review will summarize knowledge on Gi-coupled receptors in sensory neurons, focusing on their roles in ion channel regulation and discuss their potential as targets for analgesic and antipruritic medications.
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Affiliation(s)
- Yevgen Yudin
- 1 Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, USA
| | - Tibor Rohacs
- 1 Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, NJ, USA
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4
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Adenosine receptor targets for pain. Neuroscience 2016; 338:1-18. [DOI: 10.1016/j.neuroscience.2015.10.031] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Revised: 09/29/2015] [Accepted: 10/15/2015] [Indexed: 12/21/2022]
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5
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Wang Y, Yu C, Pan Y, Yang X, Huang Y, Feng Z, Li X, Yang S, Liang G. A novel synthetic mono-carbonyl analogue of curcumin, A13, exhibits anti-inflammatory effects in vivo by inhibition of inflammatory mediators. Inflammation 2012; 35:594-604. [PMID: 21614553 DOI: 10.1007/s10753-011-9350-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Curcumin is a pleiotropic molecule against inflammatory related diseases. However, poor bioavailability greatly limits its application in clinic. Our previous study synthesized and evaluated a hydrosoluble mono-carbonyl analogue of curcumin, (2E,5E)-2,5-bis(4-(3-(dimethylamino)-propoxy)benzylidene)cyclopentanone (A13). In the present study, we further evaluated the anti-inflammatory effect of A13 in vivo. In lipopolysaccharide-challenged mice, pretreatment of A13 (15 mg/kg, i.v.) attenuated the increase of plasma level of NO, TNF-α, and IL-6, significantly inhibited the increase of hepatic inflammatory gene transcription, and improved pulmonary damages. In addition, A13 (10 or 30 mg/kg, i.p.) reduced vascular permeability in Institute of Cancer Research mice and inhibited pain reaction in chemically induced inflammatory models. Together, A13 exhibits anti-inflammatory activities both in vitro and in vivo by the inhibition of various inflammatory mediators.
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Affiliation(s)
- Yi Wang
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, 325035, China
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6
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Wang Y, Yu C, Pan Y, Li J, Zhang Y, Ye F, Yang S, Zhang H, Li X, Liang G. A novel compound C12 inhibits inflammatory cytokine production and protects from inflammatory injury in vivo. PLoS One 2011; 6:e24377. [PMID: 21931698 PMCID: PMC3169595 DOI: 10.1371/journal.pone.0024377] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 08/05/2011] [Indexed: 01/21/2023] Open
Abstract
Inflammation is a hallmark of many diseases. Although steroids and cyclooxygenase inhibitors are main anti-inflammatory therapeutical agents, they may cause serious side effects. Therefore, developing non-steroid anti-inflammatory agents is urgently needed. A novel hydrosoluble compound, C12 (2,6-bis(4-(3-(dimethylamino)-propoxy)benzylidene)cyclohexanone), has been designed and synthesized as an anti-inflammatory agent in our previous study. In the present study, we investigated whether C12 can affect inflammatory processes in vitro and in vivo. In mouse primary peritoneal macrophages, C12 potently inhibited the production of the proinflammatory gene expression including TNF-α, IL-1β, IL-6, iNOS, COX-2 and PGE synthase. The activity of C12 was partly dependent on inhibition of ERK/JNK (but p38) phosphorylation and NF-κB activation. In vivo, C12 suppressed proinflammatory cytokine production in plasma and liver, attenuated lung histopathology, and significantly reduced mortality in endotoxemic mice. In addition, the pre-treatment with C12 reduced the inflammatory pain in the acetic acid and formalin models and reduced the carrageenan-induced paw oedema and acetic acid-increased vascular permeability. Taken together, C12 has multiple anti-inflammatory effects. These findings, coupled with the low toxicity and hydrosolubility of C12, suggests that this agent may be useful in the treatment of inflammatory diseases.
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Affiliation(s)
- Yi Wang
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
| | - Congcong Yu
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
| | - Yong Pan
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
| | - Jianling Li
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
| | - Yali Zhang
- Institute of Bioengineering, Nanjing University of Science and Technology, Nanjing, People's Republic of China
| | - Faqing Ye
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
| | - Shulin Yang
- Institute of Bioengineering, Nanjing University of Science and Technology, Nanjing, People's Republic of China
| | - Hui Zhang
- Department of Pharmacy, The First Affiliated Hospital, Wenzhou Medical College, Wenzhou, People's Republic of China
| | - Xiaokun Li
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
- Norman Bethune College of Medical Science, Jilin University, Changchun, People's Republic of China
| | - Guang Liang
- Bioorganic and Medicinal Chemistry Research Center, School of Pharmaceutical Science, Wenzhou Medical College, Wenzhou, People's Republic of China
- Institute of Bioengineering, Nanjing University of Science and Technology, Nanjing, People's Republic of China
- * E-mail:
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Ferré S, Diamond I, Goldberg SR, Yao L, Hourani SMO, Huang ZL, Urade Y, Kitchen I. Adenosine A2A receptors in ventral striatum, hypothalamus and nociceptive circuitry implications for drug addiction, sleep and pain. Prog Neurobiol 2007; 83:332-47. [PMID: 17532111 PMCID: PMC2141681 DOI: 10.1016/j.pneurobio.2007.04.002] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 03/15/2007] [Accepted: 04/05/2007] [Indexed: 11/22/2022]
Abstract
Adenosine A2A receptors localized in the dorsal striatum are considered as a new target for the development of antiparkinsonian drugs. Co-administration of A2A receptor antagonists has shown a significant improvement of the effects of l-DOPA. The present review emphasizes the possible application of A2A receptor antagonists in pathological conditions other than parkinsonism, including drug addiction, sleep disorders and pain. In addition to the dorsal striatum, the ventral striatum (nucleus accumbens) contains a high density of A2A receptors, which presynaptically and postsynaptically regulate glutamatergic transmission in the cortical glutamatergic projections to the nucleus accumbens. It is currently believed that molecular adaptations of the cortico-accumbens glutamatergic synapses are involved in compulsive drug seeking and relapse. Here we review recent experimental evidence suggesting that A2A antagonists could become new therapeutic agents for drug addiction. Morphological and functional studies have identified lower levels of A2A receptors in brain areas other than the striatum, such as the ventrolateral preoptic area of the hypothalamus, where adenosine plays an important role in sleep regulation. Although initially believed to be mostly dependent on A1 receptors, here we review recent studies that demonstrate that the somnogenic effects of adenosine are largely mediated by hypothalamic A2A receptors. A2A)receptor antagonists could therefore be considered as a possible treatment for narcolepsy and other sleep-related disorders. Finally, nociception is another adenosine-regulated neural function previously thought to mostly involve A1 receptors. Although there is some conflicting literature on the effects of agonists and antagonists, which may partly be due to the lack of selectivity of available drugs, the studies in A2A receptor knockout mice suggest that A2A receptor antagonists might have some therapeutic potential in pain states, in particular where high intensity stimuli are prevalent.
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Affiliation(s)
- S Ferré
- Preclinical Pharmacology Section, National Institute on Drug Abuse, Intramural Research Program, Department of Health and Human Services, Baltimore, MD 21224, USA.
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Abstract
Adenosine and ATP, via P1 and P2 receptors respectively, can modulate pain transmission under physiological, inflammatory, and neuropathic pain conditions. Such influences reflect peripheral and central actions and effects on neurons as well as other cell types. In general, adenosine A1 receptors produce inhibitory effects on pain in a number of preclinical models and are a focus of attention. In humans, i.v. infusions of adenosine reduce some aspects of neuropathic pain and can reduce postoperative pain. For P2X receptors, there is a significant body of information indicating that inhibition of P2X3 receptors may be useful for relieving inflammatory and neuropathic pain. More recently, data have begun to emerge implicating P2X4, P2X7 and P2Y receptors in aspects of pain transmission. Both P1 and P2 receptors may represent novel targets for pain relief.
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Affiliation(s)
- J Sawynok
- Department of Pharmacology, Dalhousie University, Halifax NS, B3H 1X5, Canada.
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Chen HS, He X, Wang Y, Wen WW, You HJ, Arendt-Nielsen L. Roles of capsaicin-sensitive primary afferents in differential rat models of inflammatory pain: a systematic comparative study in conscious rats. Exp Neurol 2006; 204:244-51. [PMID: 17188267 DOI: 10.1016/j.expneurol.2006.10.011] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Revised: 10/26/2006] [Accepted: 10/31/2006] [Indexed: 11/20/2022]
Abstract
To characterize the role of capsaicin-sensitive primary afferents in inflammatory pain, the effects of subcutaneous (s.c.) injection of 0.15% capsaicin on different chemical irritants-induced pathological nociception including persistent spontaneous nociception, primary thermal and mechanical hyperalgesia, and inflammatory response were systematically investigated in unanesthetized conscious rats. Four different animal models of inflammatory pain: the bee venom (BV) test, the formalin test, the carrageenan model, and the complete Freund's adjuvant (CFA) model, were employed and compared. Local pre-treatment with capsaicin produced a significant inhibition on the s.c. BV and formalin induced long-lasting persistent spontaneous nociception. However, this capsaicin-induced inhibitory effect on spontaneous nociception in the BV test was only found within the late phase (tonic nociception; 11-60 min), but not the early phase (acute nociception; 0-10 min). A complete preventing effect of capsaicin on the decreased thermal paw withdrawal latency was found in the BV, carrageenan, and CFA models. Nevertheless, pre-treatment with capsaicin only produced complete blocking effects on the decreased mechanical paw withdrawal threshold in the BV and carrageenan models, but not in the CFA model. For inflammatory response, a significant inhibition of the BV-elicited paw swelling was found following capsaicin treatment. In marked contrast, capsaicin did not produce any effects on the paw inflammation during exposure to carrageenan, CFA, and formalin. These data suggest that capsaicin-sensitive primary afferents may play differential roles in the induction and development of pathological nociception in differential inflammatory pain models. In contrast to other chemical irritants, BV-induced long-term spontaneous nociception, facilitated nociceptive behavior, and inflammation are modulated by peripheral capsaicin-sensitive afferents.
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Affiliation(s)
- Hui-Sheng Chen
- Department of Neurology, General Hospital of Shen-Yang Military Region, Shen Yang 110016, PR China.
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Sawynok J, Reid AR, Liu XJ, Parkinson FE. Amitriptyline enhances extracellular tissue levels of adenosine in the rat hindpaw and inhibits adenosine uptake. Eur J Pharmacol 2005; 518:116-22. [PMID: 16156010 DOI: 10.1016/j.ejphar.2005.06.030] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Local administration of amitriptyline into the rat hindpaw produces peripheral antinociception; this is reduced by adenosine receptor antagonists and appears to involve endogenous adenosine. The present study used peripheral microdialysis: (a) to determine whether amitriptyline could enhance extracellular tissue levels of endogenous adenosine in the rat hindpaw and (b) to examine mechanisms by which such an increase could occur. Local injection of amitriptyline into the plantar hindpaw, at doses that produce peripheral antinociception (100-300 nmol), produced an increase in local extracellular levels of adenosine. When injected in combination with formalin, which also enhances such levels of adenosine, an additive increase was observed. This adenosine originated partly as nucleotide, as inhibition of ecto-5'-nucleotidase reduced the amount of adenosine detected in the probe following administration of amitriptyline. When administered in combination with exogenous adenosine, amitriptyline augmented recovery of adenosine in the probe. Pretreatment of rats with capsaicin augmented the ability of amitriptyline to increase adenosine levels detected in the dialysis probe; it also enhanced tissue recovery of exogenously administered adenosine. In uptake studies using cultured rat C6 glioma cells, amitriptyline inhibited adenosine uptake by an adenosine transporter (IC50 0.37 +/- 0.12 mM). In enzyme assays, amitriptyline had no effect on adenosine kinase or adenosine deaminase activity. These results demonstrate that amitriptyline: (a) enhances extracellular tissue levels of adenosine in the rat hindpaw following local administration in vivo and (b) inhibits adenosine uptake but has no effect on metabolism in vitro. Therefore, increased extracellular adenosine levels in vivo appear to result partially from extracellular conversion of nucleotide and partially from inhibition of uptake.
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Affiliation(s)
- Jana Sawynok
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 1X5.
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Puntambekar P, Van Buren J, Raisinghani M, Premkumar LS, Ramkumar V. Direct interaction of adenosine with the TRPV1 channel protein. J Neurosci 2004; 24:3663-71. [PMID: 15071115 PMCID: PMC6729738 DOI: 10.1523/jneurosci.4773-03.2004] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Vanilloid receptor 1 (TRPV1), a nonspecific cation channel expressed primarily in small sensory neurons, mediates inflammatory thermal pain sensation. The function and expression of TRPV1 are enhanced during inflammation and certain neuropathies, leading to sustained hyperalgesia. Activation of TRPV1 in the spinal cord and periphery promotes release of adenosine, which produces analgesia by activating A(1) and A(2A) adenosine receptor (AR) on central and peripheral neurons. This study provides evidence of a direct interaction of AR analogs with TRPV1. Adenosine analogs inhibit TRPV1-mediated Ca(2+) entry in human embryonic kidney (HEK293) cells stably expressing TRPV1 (HEK/TRPV1) and DRG neurons. This inhibition was independent of A(2A)AR activation. Specific binding of [(3)H]resiniferatoxin (RTX) in plasma membrane preparations was inhibited by CGS21680, an A(2A)AR agonist. Similar degrees of inhibition were observed with both agonists and antagonists of ARs. Adenosine analogs inhibited [(3)H]RTX binding to affinity-purified TRPV1, indicative of a direct interaction of these ligands with the receptor. Furthermore, specific capsaicin-sensitive binding of [(3)H]CGS21680 was observed in Xenopus oocyte membranes expressing TRPV1. Capsaicin-induced inward currents in DRG neurons were inhibited by adenosine and agonist and antagonist of A(2A)AR at nanomolar concentrations. Increasing the concentrations of capsaicin reversed the inhibitory response to capsaicin, suggesting a competitive inhibition at TRPV1. Finally, exposure of HEK/TRPV1 cells to capsaicin induced an approximately 2.4-fold increase in proapoptotic cells that was abolished by adenosine analogs. Together, these data suggest that adenosine could serve as an endogenous inhibitor of TRPV1 activity by directly interacting with the receptor protein.
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Affiliation(s)
- Preeti Puntambekar
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois 62794-9629, USA
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Abstract
In the central nervous system (CNS), adenosine is an important neuromodulator and regulates neuronal and non-neuronal cellular function (e.g. microglia) by actions on extracellular adenosine A(1), A(2A), A(2B) and A(3) receptors. Extracellular levels of adenosine are regulated by synthesis, metabolism, release and uptake of adenosine. Adenosine also regulates pain transmission in the spinal cord and in the periphery, and a number of agents can alter the extracellular availability of adenosine and subsequently modulate pain transmission, particularly by activation of adenosine A(1) receptors. The use of capsaicin (which activates receptors selectively expressed on C-fibre afferent neurons and produces neurotoxic actions in certain paradigms) allows for an interpretation of C-fibre involvement in such processes. In the spinal cord, adenosine availability/release is enhanced by depolarization (K(+), capsaicin, substance P, N-methyl-D-aspartate (NMDA)), by inhibition of metabolism or uptake (inhibitors of adenosine kinase (AK), adenosine deaminase (AD), equilibrative transporters), and by receptor-operated mechanisms (opioids, 5-hydroxytryptamine (5-HT), noradrenaline (NA)). Some of these agents release adenosine via an equilibrative transporter indicating production of adenosine inside the cell (K(+), morphine), while others release nucleotide which is converted extracellularly to adenosine by ecto-5'-nucleotidase (capsaicin, 5-HT). Release can be capsaicin-sensitive, Ca(2+)-dependent and involve G-proteins, and this suggests that within C-fibres, Ca(2+)-dependent intracellular processes regulate production and release of adenosine. In the periphery, adenosine is released from both neuronal and non-neuronal sources. Neuronal release from capsaicin-sensitive afferents is induced by glutamate and by neurogenic inflammation (capsaicin, low concentration of formalin), while that from sympathetic postganglionic neurons (probably as adenosine 5'-triphosphate (ATP) with NA) occurs following more generalized inflammation. Such release is modified differentially by inhibitors of AK and AD. Following nerve injury, there is an alteration in capsaicin-sensitive adenosine release, as spinal release now is less responsive to opioids, while peripheral release is less responsive to inhibitors of metabolism. Following inflammation, adenosine is released from a variety of cell types in addition to neurons (e.g. endothelial cells, neutrophils, mast cells, fibroblasts). ATP is released both spinally and peripherally following inflammation or injury, and may be converted to adenosine by ecto-5'-nucleotidase contributing an additional source of adenosine. Release of adenosine from both spinal and peripheral compartments has inhibitory effects on pain transmission, as methylxanthine adenosine receptor antagonists reduce analgesia produced by agents which augment extracellular levels of adenosine spinally (morphine, 5-HT, substance P, AK inhibitors) and peripherally (AK inhibitors, AD inhibitors). Increases in extracellular adenosine availability also may contribute to antiinflammatory effects of certain agents (methotrexate, sulfasalazine, salicylates, AK inhibitors), and this could have secondary effects on pain signalling in chronic inflammation. The purpose of the present review is to consider: (a). the factors that regulate the extracellular availability of adenosine in the spinal cord and at peripheral sites; and (b). the extent to which this adenosine affects pain signalling in these two distinct compartments.
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Affiliation(s)
- Jana Sawynok
- Department of Pharmacology, Dalhousie University, Halifax, NS Canada B3H 1X5.
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Liu XJ, White TD, Sawynok J. Enhanced release of adenosine in rat hind paw following spinal nerve ligation: involvement of capsaicin-sensitive sensory afferents. Neuroscience 2002; 114:379-87. [PMID: 12204207 DOI: 10.1016/s0306-4522(02)00295-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Modulation of endogenous adenosine levels by inhibition of adenosine metabolism produces a peripheral antinociceptive effect in a neuropathic pain model. The present study used microdialysis to investigate the neuronal mechanisms modulating extracellular adenosine levels in the rat hind paw following tight ligation of the L5 and L6 spinal nerves. Subcutaneous injection of 50 microl saline into the nerve-injured paw induced a rapid and short-lasting increase in extracellular adenosine levels in the subcutaneous tissues of the rat hind paw ipsilateral to the nerve injury. Saline injection did not increase adenosine levels in sham-operated rats or non-treated rats. The adenosine kinase inhibitor 5'-amino-5'-deoxyadenosine and the adenosine deaminase inhibitor 2'-deoxycoformycin, at doses producing a peripheral antinociceptive effect, did not further enhance subcutaneous adenosine levels in the nerve-injured paw. Systemic pretreatment with capsaicin, a neurotoxin selective for small-diameter sensory afferents, markedly reduced the saline-evoked release of adenosine in rat hind paw following spinal nerve ligation. Systemic pretreatment with 6-hydroxydopamine, a neurotoxin selective for sympathetic afferent nerves, did not affect release. These results suggest that following nerve injury, peripheral capsaicin-sensitive primary sensory afferent nerve terminals are hypersensitive, and are able to release adenosine following a stimulus that does not normally evoke release in sham-operated or intact rats. Sympathetic postganglionic afferents do not appear to be involved in such release. The lack of effect on such release by the inhibitors of adenosine metabolism suggests an altered peripheral adenosine system following spinal nerve ligation.
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Affiliation(s)
- X J Liu
- Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7.
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