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Query: UMLS:C0030193 (pain)
 261,466 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Development of analgesic agents for the treatment of severe pain requires the identification of compounds that are devoid of opioid receptor liabilities. A potent (inhibition constant = 37 picomolar) neuronal nicotinic acetylcholine receptor (nAChR) ligand called ABT-594 was developed that has antinociceptive properties equal in efficacy to those of morphine across a series of diverse animal models of acute thermal, persistent chemical, and neuropathic pain states. These effects were blocked by the nAChR antagonist mecamylamine. In contrast to morphine, repeated treatment with ABT-594 did not appear to elicit opioid-like withdrawal or physical dependence. Thus, ABT-594 may be an analgesic that lacks the problems associated with opioid analgesia.
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PMID:Broad-spectrum, non-opioid analgesic activity by selective modulation of neuronal nicotinic acetylcholine receptors. 944 5

The discovery of (+/-)-epibatidine, a naturally occurring neuronal nicotinic acetylcholine receptor (nAChR) agonist with antinociceptive activity 200-fold more potent than that of morphine, has renewed interest in the potential role of nAChRs in pain processing. However, (+/-)-epibatidine has significant side-effect liabilities associated with potent activity at the ganglionic and neuromuscular junction nAChR subtypes which limit its potential as a clinical entity. ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine] is a novel, potent cholinergic nAChR ligand with analgesic properties (see accompanying paper by Bannon et al., 1998b) that shows preferential selectivity for neuronal nAChRs and a consequently improved in vivo side-effect profile compared with (+/-)-epibatidine. ABT-594 is a potent inhibitor of the binding of [3H](-)-cytisine to alpha 4 beta 2 neuronal nAChRs (Ki = 37 pM, rat brain; Ki = 55 pM, transfected human receptor). At the alpha 1 beta 1 delta gamma neuromuscular nAChR labeled by [125I] alpha-bungarotoxin (alpha-Btx), ABT-594 has a Ki value of 10,000 nM resulting in a greater than 180,000-fold selectivity of the compound for the neuronal alpha 4 beta 2 nAChR. In contrast, (+/-)-epibatidine has Ki values of 70 pM and 2.7 nM at the alpha 4 beta 2 and alpha 1 beta 1 delta gamma nAChRs, respectively, giving a selectivity of only 38-fold. The S-enantiomer of ABT-594, A-98593 has activity at the neuronal alpha 4 beta 2 nAChR identical with ABT-594 (Ki = 34-39 pM), which demonstrates a lack of stereospecific binding similar to that reported previously for (+/-)-epibatidine. A similar lack of stereoselectivity is seen at the human alpha 7 receptor. However, A-98593 is 3-fold more potent at the neuromuscular nAChR (Ki = 3420 nM) and the brain alpha-Btx-sensitive nAChR (Ki = 4620 nM) than ABT-594. ABT-594 has weak affinity in binding assays for adrenoreceptor subtypes alpha-1B (Ki = 890 nM), alpha-2B (Ki = 597 nM) and alpha-2C (Ki = 342 nM), and it has negligible affinity (Ki > 1000 nM) for approximately 70 other receptors, enzyme and transporter binding sites. Functionally, ABT-594 is an agonist. At the transfected human alpha 4 beta 2 neuronal nAChR (K177 cells), with increased 86Rb+ efflux as a measure of cation efflux, ABT-594 had an EC50 value of 140 nM with an intrinsic activity (IA) compared with (-)-nicotine of 130%; at the nAChR subtype expressed in IMR-32 cells (sympathetic ganglion-like), an EC50 of 340 nM (IA = 126%); at the F11 dorsal root ganglion cell line (sensory ganglion-like), an EC50 of 1220 nM (IA = 71%); and via direct measurement of ion currents, an EC50 value of 56,000 nM (IA = 83%) at the human alpha 7 homooligimeric nAChR produced in oocytes. A-98593 is 2- to 3-fold more potent and displays approximately 50% greater intrinsic activity than ABT-594 in all four functional assays. In terms of potency, ABT-594 is 8- to 64-fold less active than (+/-)-epibatidine and also has less IA in these functional assays. ABT-594 (30 microM) inhibits the release of calcitonin gene-related peptide from C-fibers terminating in the dorsal horn of the spinal cord, an effect mediated via nAChRs. Pharmacologically, ABT-594 has an in vitro profile distinct from that of the prototypic nicotinic analgesic (+/-)-epibatidine, with the potential for substantially reduced side-effect liability and, as such, represents a potentially novel therapeutic approach to pain management.
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PMID:ABT-594 [(R)-5-(2-azetidinylmethoxy)-2-chloropyridine]: a novel, orally effective analgesic acting via neuronal nicotinic acetylcholine receptors: I. In vitro characterization. 958 Jun 26

Pharmacological treatments for pain have come largely from two classes of compounds--the opioids and the nonsteroidal anti-inflammatory drugs (NSAIDs). Because of deficiencies associated with these two classes of compounds, exploration of novel approaches to pain relief has intensified of late. Nicotine, a neuronal nicotinic acetylcholine receptor (nAChR) agonist, has long been known to have antinociceptive effects in both experimental animals and humans. The relatively modest antinociceptive effects and the toxicities associated with nicotine preclude its development as an analgesic agent. However, recent discoveries in the nAChR field have stimulated interest in nAChR-targeted compounds as potential analgesic agents. Epibatidine, a potent nAChR agonist, was found to have full efficacy relative to opioids in preclinical pain models. Although epibatidine is toxic, these observations demonstrated that modest efficacy is not a general limitation of nAChR agonists. Moreover, exploration of the molecular biology of nAChRs revealed evidence of receptor diversity, suggesting that nAChR subtype-selective agents less toxic than nicotine might be discovered; and early medicinal chemistry efforts already have resulted in compounds with improved safety profiles. For example, ABT-594 is a nAChR agonist with the antinociceptive efficacy of epibatidine, but with an improved safety profile. This commentary reviews recent findings with nAChR-targeted compounds, explores potential mechanisms responsible for nAChR-mediated antinociception, and raises issues that must be addressed in developing compounds of this class as analgesics.
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PMID:Therapeutic potential of neuronal nicotinic acetylcholine receptor agonists as novel analgesics. 1050 44

Due to the limitations of currently available analgesics, a number of novel alternatives are currently under investigation, including neuronal nicotinic acetylcholine receptor (nAChR) agonists. During the 1990s, the discovery of the antinociceptive properties of the potent nAChR agonist epibatidine in rodents sparked interest in the analgesic potential of this class of compounds. Although epibatidine also has several mechanism-related toxicities, the identification of considerable nAChR diversity suggested that the toxicities and therapeutic actions of the compound might be mediated by distinct receptor subtypes. Consistent with this view, a number of novel nAChR agonists with antinociceptive activity and improved safety profiles in preclinical models have now been identified, including A-85380, ABT-594, DBO-83, SIB-1663 and RJR-2403. Of these, ABT-594 is the most advanced and is currently in Phase II clinical evaluation. Nicotinically-mediated antinociception has been demonstrated in a variety of rodent pain models and is likely mediated by the activation of descending inhibitory pathways originating in the brainstem with the predominant high-affinity nicotine site in brain, the alpha4beta2 subtype, playing a critical role. Thus, preclinical findings suggest that nAChR agonists have the potential to be highly efficacious treatments in a variety of pain states. However, clinical proof-of-principle studies will be required to determine if nAChR agonists are active in pathological pain.
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PMID:The therapeutic potential of nicotinic acetylcholine receptor agonists for pain control. 1177 88

Idiopathic epilepsies, which account for up to 40% of all epilepsies, are mainly caused by genetic factors. Most idiopathic epilepsies are due to oligogenic or multifactorial rather than monogenetic inheritance. Nevertheless, most of what is known today about the molecular genetics of idiopathic epilepsies has been found by analysing large families with rare monogenetic forms of the disease. For the first time, gene defects can be linked to certain epilepsies. Mutations in the CHRNA4 or CHRNB subunits of the neuronal nicotinic acetylcholine receptor lead to familial nocturnal frontal lobe epilepsy, while defects in the voltage-gated potassium channels KCNQ2 and KCNQ3 have recently been found to cause benign familial neonatal convulsions. The voltage-gated sodium channel subunits SCN1B, SCN1A and SCN2A as well as the GABRG2 subunit of the GABA(A) receptor are involved in the pathology of the newly described syndrome generalized epilepsy with febrile seizures plus. These rare monogenetic epilepsies can serve as models for further genetic analysis of the common forms of idiopathic epilepsies.
Eur J Pain 2002
PMID:Channelopathies can cause epilepsy in man. 1188 38

Current analgesics, such as opioids and nonsteroidal anti-inflammatory drugs (NSAIDs), are largely refinements of approaches available for more than 100 years and have critical liabilities and limitations. A number of new molecular targets for analgesia have been proposed in recent years, including the neuronal nicotinic acetylcholine receptor (nAChR). Agonists at neuronal nAChRs have antinociceptive effects in a variety of preclinical pain models. Moreover, nicotine can decrease experimentally-induced pain in humans without disrupting normal tactile sensation. These data from both experimental animals and humans suggest that compounds targeting neuronal nAChRs may represent a new class of analgesic agents. In this paper, we provide brief overviews of the physiology of pain, the animal models used to assess potential analgesics preclinically, and the biology of nAChRs. We then provide a review of preclinical data on the antinociceptive effects of a variety of neuronal nAChR agonists and a discussion of potential mechanisms, including evidence that antinociception is mediated by activation of brainstem nuclei with descending inhibitory inputs to the spinal cord. An evaluation of the clinical potential of this approach must also consider potential side effects. Undesirable side effects of nicotine are well known, but as we will discuss in detail, these effects are not produced by all neuronal nAChR agonists and the existence of neuronal nAChR subtypes may provide a basis for separating therapeutic effects from toxicities.
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PMID:Nicotinic acetylcholine receptor agonists: a potential new class of analgesics. 1475 52

This paper demonstrates the capacity of the neuronal nicotinic acetylcholine receptor (nAChR) antagonist alpha-conotoxin Vc1.1 to inhibit pain responses in vivo. Vc1.1 suppressed pain behaviors when tested in two models of peripheral neuropathy of the rat sciatic nerve, the chronic constriction injury (CCI) and partial nerve ligation (PNL) models. Mechanical hyperalgesia was assessed using an Ugo Basile Analgesymeter. Vc1.1 was administered by intramuscular bolus injection near the site of injury at doses of 0.036 microg, 0.36 microg and 3.6 microg in CCI rats and at a dose of 0.36 microg in PNL rats. Vc1.1 was also administered contralaterally in CCI rats at doses of 0.36 microg and 3.6 microg. Treatment started after the development of hyperalgesia and continued for 7 days. Vc1.1 significantly attenuated mechanical hyperalgesia in both CCI and PNL rats for up to a week following cessation of treatment. Vc1.1 also accelerated functional recovery of injured neurones. A blister was raised over the footpad innervated by the peripheral terminals of the injured nerve. The ability of these terminals to mount an inflammatory vascular response upon perfusion of the blister base with substance P provided a measure of functional recovery. This study shows that alpha-conotoxin Vc1.1, a neuronal nAChR antagonist, suppressed mechanical pain responses associated with peripheral neuropathy in rats in vivo and accelerated functional recovery of the injured neurones. A role for neuronal nAChRs in the analgesic activity of Vc1.1 is proposed.
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PMID:Alpha-conotoxin Vc1.1 alleviates neuropathic pain and accelerates functional recovery of injured neurones. 1618 58

A-85380 [3-(2(s)-azetidinylmethoxy) pyridine] is a neuronal nicotinic acetylcholine receptor (nAChR) agonist that has been a useful tool in the investigation of the function of nAChRs in both preclinical and clinical studies. Amongst nAChR subtypes, A-85380 shows selectivity for the alpha(4)beta(2) vs. the alpha(7) or alpha(1)beta(1)deltagamma nAChRs. In functional in vitro cation flux assays, A-85380 is a potent and full agonist. A-85380 has a broad-spectrum analgesic profile with efficacy in acute, persistent, and neuropathic pain models. As demonstrated using selective nAChR antagonists or alpha(4) antisense, the alpha(4)beta(2) nAChR mediates the analgesic effects of A-85380. Interestingly, the site of action depends upon the type of pain as antinociception is mediated by descending inhibition into the spinal cord whereas anti-allodynia in neuropathic pain is mediated at both central and peripheral sites. Radiolabelled forms of A-85380 have been developed and shown to be safe for use in vivo in humans. In clinical studies using positron and photon emission tomography, marked decreases in alpha(4)beta(2) nAChRs have been seen in patients with Parkinson's and Alzheimer's disease. Although not developed as a therapeutic agent, A-85380 has proven to be an important component in the development of novel nAChR ligands for the treatment of pain and other disorders.
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PMID:A-85380: a pharmacological probe for the preclinical and clinical investigation of the alphabeta neuronal nicotinic acetylcholine receptor. 1695 84

A series of potent neuronal nicotinic acetylcholine receptor (nAChR) ligands based on a 3,8-diazabicyclo[4.2.0]octane core have been synthesized and evaluated for affinity and agonist efficacy at the human high affinity nicotine recognition site (halpha4beta2) and in a rat model of persistent nociceptive pain (formalin model). Numerous analogs in this series exhibit picomolar affinity in radioligand binding assays and nanomolar agonist potency in functional assays, placing them among the most potent nAChR ligands known for the halpha4beta2 receptor. Several of the compounds reported in this study (i.e., 24, 25, 28, 30, 32, and 47) exhibit equivalent or greater affinity for the halpha4beta2 receptor relative to epibatidine, and like epibatidine, many exhibit robust analgesic efficacy in the rat formalin model of persistent pain.
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PMID:Synthesis and structure-activity relationships of 3,8-diazabicyclo[4.2.0]octane ligands, potent nicotinic acetylcholine receptor agonists. 1718 Nov 67

The present study was designed to investigate the role of spinal neuronal nicotinic acetylcholine receptors in the analgesic effects of isoflurane. After having established the mice model of analgesia by intraperitoneally injecting (i.p.) appropriate doses of isoflurane, nicotine, a neuronal nicotinic acetylcholine receptor agonist was intrathecally injected. The effects of isoflurane and nicotine on paw licking times and formalin-induced c-fos expression in the spinal cord dorsal horn were examined. Our correlative studies have shown that isoflurane can decrease the paw licking times and simultaneously suppress c-fos expression after injection of formalin in the mice. Nicotine can partially antagonize the effects induced by isoflurane above. Spinal neuronal nicotinic acetylcholine receptors may be important targets for the analgesic effects of isoflurane in formalin pain.
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PMID:Effects of intrathecal injection of nicotine on the analgesic effects of isoflurane in a model of inflammatory pain. 1938 46


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