Elsevier

Neuropharmacology

Volume 65, February 2013, Pages 156-164
Neuropharmacology

Effects of alpha 7 positive allosteric modulators in murine inflammatory and chronic neuropathic pain models

https://doi.org/10.1016/j.neuropharm.2012.08.022Get rights and content

Abstract

Agonists and positive allosteric modulators (PAMs) of α7 nicotinic acetylcholine receptors (nAChRs) are currently being considered as novel therapeutic approaches for managing cognitive deficits in schizophrenia and Alzheimer's disease. Though α7 agonists were recently found to possess antinociceptive and anti-inflammatory properties in rodent models of chronic neuropathic pain and inflammation, the effects of α7 nAChRs PAMs on chronic pain and inflammation remain largely unknown. The present study investigated whether PAMs, by increasing endogenous cholinergic tone, potentiate α7 nAChRs function to attenuate inflammatory and chronic neuropathic pain in mice. We tested two types of PAMS, type I (NS1738) and type II (PNU-120596) in carrageenan-induced inflammatory pain and chronic constriction injury (CCI) neuropathic pain models. We found that both NS1738 and PNU-120596 significantly reduced thermal hyperalgesia, while only PNU-120596 significantly reduced edema caused by a hind paw infusion of carrageenan. Importantly, PNU-120596 reversed established thermal hyperalgesia and edema induced by carrageenan. In the CCI model, PNU-120596 had long-lasting (up to 6 h), dose-dependent anti-hyperalgesic and anti-allodynic effects after a single injection, while NS1738 was inactive. Systemic administration of the α7 nAChR antagonist MLA reversed PNU-120596's effects, suggesting the involvement of central and peripheral α7 nAChRs. Furthermore, PNU-120596 enhanced an ineffective dose of selective agonist PHA-543613 to produce anti-allodynic effects in the CCI model. Our results indicate that the type II α7 nAChRs PAM PNU-120596, but not the type I α7 nAChRs PAM NS1738, shows significant anti-edematous and anti-allodynic effects in inflammatory and CCI pain models in mice.

Highlights

► Alpha7 positive allosteric modulators are anti-inflammatory. ► PNU-120596 reversed carrageenan-induced thermal hyperalgesia and paw edema. ► PNU-120595 anti-inflammatory effects were α7 receptor-mediated. ► NS1738 did not attenuate hyperalgesia and allodynia in the CCI model. ► PNU-120596 reversed thermal hyperalgesia and allodynia in the CCI model.

Introduction

Chronic neuropathic pain arguably arises due to long-term plasticity changes in somatosensory pathways from the periphery to the cortex. These plasticity changes often occur after nerve injury and/or dysfunction in the central nervous system (CNS), resulting in significantly enhanced pain sensation (hyperalgesia) or in otherwise non-noxious stimuli to cause pain (allodynia) (Wang et al., 2011; Zhou, 2007; Harden, 2005). Increased pain sensitivity, one of the most common signs of an inflammatory disorder, is mediated by a host of different factors, including enzymes, neuropeptides, eicosanoids, chemokines and cytokines (Dray and Bevan, 1993; Sandkuhler, 2009; Wang et al., 2011). To date, several drugs, such as opioids and anti-inflammatory, anti-seizure and antidepressant agents, used to treat chronic neuropathic pain have major adverse effects and/or incomplete pain relief for patients. Thus, development of drugs possessing increased efficacy and safety is needed.

Previous studies suggest utility of nicotinic acetylcholine receptor (nAChR) agonists to treat chronic pain conditions (Bannon et al., 1998; Khan et al., 2003; Miao et al., 2004; Vincler, 2005; Pacini et al., 2010). Multiple subtypes of nAChRs are expressed in pain transmission pathways (Khan et al., 2003). For example, α4β2* and α7 subtypes are expressed in the spinal cord dorsal horn (Cordero-Erausquin et al., 2004; Cordero-Erausquin and Changeux, 2001; Marubio et al., 1999). Recent work has focused on the role of the α7 nAChRs in modulating inflammation and nociception (Westman et al., 2010; Marrero and Bencherif, 2009; Medhurst et al., 2008; de Jonge and Ulloa, 2007). In addition to their neuronal presence, α7 nAChRs are expressed on macrophages (Tracey, 2002; Wang and Wang, 2003; Ulloa, 2005), which are key immune cells involved in the initiation, maintenance, and resolution of inflammation (Fujiwara and Kobayashi, 2005). Previous studies have demonstrated the importance of acetylcholine (ACh) directly interacting with α7 nAChRs expressed on macrophages and other cytokine-producing cells in down-regulating proinflammatory cytokine synthesis and preventing tissue damage (Tracey, 2002; De Rosa et al., 2009; Wang et al., 2009). In addition, Xiao et al. (2002) showed an up-regulation of α7 nAChR subunit expression in the rat dorsal root ganglion fourteen days after sciatic nerve axotomy. Moreover, α7 nAChRs agonists elicited significant anti-inflammatory and antinociceptive effects in rodent models of chronic neuropathic pain and inflammation (Damaj et al., 2000; Wang et al., 2005; Hamurtekin and Gurun, 2006; Medhurst et al., 2008; Gurun et al., 2009; Rowley et al., 2010). Therefore, the α7 nAChR represents a promising target for the development of analgesic and anti-inflammatory agents. However, concerns regarding α7 nAChR agonists as clinical candidates persist. For example, α7 nAChRs desensitize rapidly in response to high agonist concentration in vitro followed by a long period of desensitization (Bertrand et al., 1992). Furthermore, an agonist-based therapeutic approach would disrupt endogenous cholinergic tone (Papke et al., 2009).

One alternative approach to selectively enhance activity of the α7 nAChRs is via positive allosteric modulation. As reported previously (Faghih et al., 2007), positive allosteric modulators (PAMs) facilitate endogenous neurotransmission and/or enhance the efficacy and potency of an agonist without directly stimulating the agonist-binding sites. In principle, PAMs do not exhibit intrinsic activity at the receptor, however they can reinforce endogenous cholinergic neurotransmission without directly activating α7 nAChRs (Albuquerque et al., 2001; Faghih et al., 2007, 2008). PAMs have been classified as either type I, such as NS1738, or type II, such as PNU-120596, on the basis of their distinct effects on desensitization (Bertrand and Gopalakrisshnan, 2007; Bertrand et al., 2008; Timmermann et al., 2007). PNU-120596, but not NS1738, modifies the equilibrium among active and desensitized states resulting in significantly prolonged responses, even promoting the activation of previously desensitized receptors (Grønlien et al., 2007; Hurst et al., 2005; Roncarati et al., 2008). Initially, allosteric modulators of the α7 nAChRs were developed for the treatment of cognitive disorders such as Alzheimer's disease and schizophrenia, however their effects in pain models have not been reported (Ahring et al., 2007; Faghih et al., 2007; Conejero-Goldberg et al., 2008; McLean et al., 2012).

Therefore, in the present study, we evaluated whether potentiating the endogenous α7 cholinergic system through the allosteric modulation of α7 nAChRs produces anti-inflammatory, anti-hyperalgesic and anti-allodynic effects in mouse models of inflammation and chronic neuropathic pain. Accordingly, NS1738 (a type I α7 nAChR PAM) and PNU-120596 (a type II α7 nAChR PAM) were evaluated in the carrageenan short-term inflammatory pain and the chronic constriction injury (CCI) neuropathic pain models. In addition, we evaluated whether PNU-120596 enhances the antinociceptive effects of a selective α7 nAChRs agonist, PHA-543611, in these models.

Section snippets

Subjects

Naïve male adult ICR (Harlan Laboratories; Indianapolis, IN) mice weighing between 20 and 30 g served as subjects. Mice were housed 4–5 per cage in a temperature-controlled (20–22 °C) environment with a 12-h light–dark cycle and were given unlimited access to food and water in their home cages. All animals were maintained in a facility approved by the American Association for Accreditation of Laboratory Animal Care and the study was approved by the Institutional Animal Care and Use Committee of

Effect of NS1738 and PNU-120596 in the carrageenan test

Mice were given an intraplantar injection of carrageenan and then tested for hyperalgesia and edema 6 h later. Anti-hyperalgesic and anti-edematous effects of the α7 nAChRs PAMs were determined after i.p. administration of the drugs. The administration of 10 and 30 mg/kg of NS1738 15 min before intraplantar carrageenan blocked the development of hyperalgesic responses [F(2,27) = 9.07, p < 0.01] (Fig. 1A). The anti-hyperalgesic effect of NS1738 at 30 mg/kg was blocked by pretreating the animals

Discussion

The objective of the present study was to examine the effects of type I (NS1738) and II (PNU-120596) α7 nAChR PAMs in murine inflammatory and chronic neuropathic pain models after acute administration. Overall, our results showed that while both NS1738 and PNU-120596 attenuated hyperalgesia associated with inflammation, only PNU-120596 decreased the hyperalgesia and allodynia in the chronic neuropathic pain model. Whereas PNU-120596 produced consistent effects in carrageenan and CCI models,

References (76)

  • B. Gao et al.

    Pharmacological effects of nonselective and subtype-selective nicotinic acetylcholine receptor agonists in animal models of persistent pain

    Pain

    (2010)
  • E. Hamurtekin et al.

    The antinociceptive effects of centrally administered CDP-choline on acute pain models in rats: the involvement of cholinergic system

    Brain Res.

    (2006)
  • A.H. Lichtman et al.

    Mice lacking fatty acid amide hydrolase exhibit a cannabinoid receptor-mediated phenotypic hypoalgesia

    Pain

    (2004)
  • M.B. Marrero et al.

    Convergence of alpha 7 nictonic acetylcholine receptor-activated pathways for anti-apoptosis and anti-inflammation: central role for JAK2 activation of STAT 3 and NF-kappaB

    Brain Res.

    (2009)
  • S.J. Medhurst et al.

    Activation of the alpha7-nicotinic acetylcholine receptor reverses complete freund adjuvant-induced mechanical hyperalgesia in the rat via a central site of action

    J. Pain

    (2008)
  • M. Menegazzi et al.

    Glycyrrhizin attenuates the development of carrageenan-induced lung injury in mice

    Pharmacol. Res.

    (2008)
  • F.J. Miao et al.

    Central terminals of nociceptors are targets for nicotine suppression of inflammation

    Neuroscience

    (2004)
  • M.J. Millan

    Descending control of pain

    Prog. Neurobiol.

    (2002)
  • S.W. Min et al.

    Inhibitory effect of eupatilin and jaceosidin isolated from Artemisia princeps on carrageenan-induced inflammation in mice

    J. Ethnopharmacol.

    (2009)
  • A. Pacini et al.

    Protective effect of alpha7 nAChR: behavioural and morphological features on neuropathy

    Pain

    (2010)
  • M.H. Rashid et al.

    Tonic inhibitory role of alpha4beta2 subtype of nicotinic acetylcholine receptors on nociceptive transmission in the spinal cord in mice

    Pain

    (2006)
  • T.J. Rowley et al.

    Antinociceptive and anti-inflammatory effects of choline in a mouse model of posperative pain

    Br. J. Anaesth.

    (2010)
  • K. Walker et al.

    Animal models for pain research

    Mol. Med. Today

    (1999)
  • D.W. Wang et al.

    Role of cholinergic anti-inflammatory pathway in regulating host response and its interventional strategy for inflammatory diseases

    Chin. J. Traumatol.

    (2009)
  • L.X. Wang et al.

    Animal and cellular models of chronic pain

    Adv. Drug Deliv. Rev.

    (2003)
  • Y. Wang et al.

    Antinociceptive effects of choline against acute and inflammatory pain

    Neuroscience

    (2005)
  • I. Yalcin et al.

    Nociceptive thresholds are controlled through spinal β2-subunit-containing nicotinic acetylcholine receptors

    Pain

    (2011)
  • P.K. Ahring et al.

    An allosteric modulator of the α 7 nicotinic acetylcholine receptor possessing cognition-enhancing properties in vivo

    J. Pharmacol. Exp. Ther.

    (2007)
  • E.X. Albuquerque et al.

    Modulation of nicotinic receptor activity in the central nervous system: a novel approach to the treatment of Alzheimer disease

    Alzheimer Dis. Assoc. Disord.

    (2001)
  • P.A. Baeuerle et al.

    Function and activation of NF-kappa B in the immune system

    Annu. Rev. Immunol.

    (1994)
  • A.W. Bannon et al.

    Broad-spectrum, non-opioid analgesic activity by selective modulation of neuronal nicotinic acetylcholine receptors

    Science

    (1998)
  • T.R. Bernik et al.

    Pharmacological stimulation of the cholinergic antiinflammatory pathway

    J. Exp. Med.

    (2002)
  • D. Bertrand et al.

    Positive allosteric modulation of the α7 nicotinic acetylcholine receptor: ligand interactions with distinct sites and evidence for a prominent role of the M2-M3 segment

    Mol. Pharmacol.

    (2008)
  • A. Borthakur et al.

    Carrageenan induces interleukin-8 production through distinct Bcl10 pathway in normal human colonic epithelial cells

    Am. J. Physiol. Gastrointest. Liver Physiol.

    (2007)
  • D. Carnevale et al.

    Microglia-neuron interaction in inflammatory and degenerative diseases: role of cholinergic and noradrenergic systems

    CNS Neurol. Disord. Drug Targets

    (2007)
  • D.Z. Christensen et al.

    Repeated administration of alpha7 nicotinic acetylcholine receptor (nAChR) agonists, but not positive allosteric modulators, increases alpha7 nAChR levels in the brain

    J. Neurochem.

    (2010)
  • M. Cordero-Erausquin et al.

    Tonic nicotinic modulation of serotoninergic transmission in the spinal cord

    Proc. Nati Acad. Sci. U.S.A.

    (2001)
  • W.J. de Jonge et al.

    The alpha7 nicotinic acetylcholine receptor as a pharmacological target for inflammation

    Br. J. Pharmacol.

    (2007)
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