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The Journal of Pharmacology and... Nov 2022A series of dipicolyl amine pyrimidines (DPPs) were previously identified as potential 7 agonists by means of a calcium influx assay in the presence of the positive...
A series of dipicolyl amine pyrimidines (DPPs) were previously identified as potential 7 agonists by means of a calcium influx assay in the presence of the positive allosteric modulator (PAM) 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxazol-3-yl)-urea (PNU-120596). The compounds lack the quaternary or strongly basic nitrogens of typical nicotinic agonists. Although differing in structure from typical nicotinic agonists, based on crystallographic data with the acetylcholine binding protein, they appeared to engage the site shared by such typical orthosteric agonists. Using oocytes expressing human 7 receptors, we found that the DPPs were efficacious activators of the receptor, with currents showing rapid desensitization characteristic of 7 receptors. However, we note that the rate of recovery from this desensitization depends strongly on structural features within the DPP family. Although the activation of receptors by DPP was blocked by the competitive antagonist methyllycaconitine (MLA), MLA had no effect on the DPP-induced desensitization, suggesting multiple modes of DPP binding. As expected, the desensitized conformational states could be reactivated by PAMs. Mutants made insensitive to acetylcholine by the C190A mutation in the agonist binding site were weakly activated by DPPs. The observation that activation of C190A mutants by the DPP compounds was resistant to the allosteric antagonist (-)-4-(2,3,5,6-tetramethylphenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide supports the hypothesis that the activity of these noncanonical agonists in the orthosteric binding sites was not entirely dependent on the classic epitopes controlling activation by typical agonists and that perhaps they may access alternative modes for promoting the conformational changes associated with activation and desensitization. SIGNIFICANCE STATEMENT: This study reports a family of nicotinic acetylcholine receptor agonists that break the rules about what the structure of a nicotinic acetylcholine receptor agonist should be. It shows that the activity of these noncanonical agonists in the orthosteric binding sites is not dependent on the classical epitopes controlling activation by typical agonists and that through different binding poses, they promote unique conformational changes associated with receptor activation and desensitization.
Topics: Animals; Humans; Nicotinic Agonists; alpha7 Nicotinic Acetylcholine Receptor; Acetylcholine; Allosteric Regulation; Calcium; Xenopus laevis; Quinolines; Sulfonamides; Pyrimidines; Epitopes; Receptors, Nicotinic
PubMed: 36279397
DOI: 10.1124/jpet.122.001354 -
The Journal of Neuroscience : the... Nov 2023The recent increase in the use of nicotine products by teenagers has revealed an urgent need to better understand the impact of nicotine on the adolescent brain. Here,...
The recent increase in the use of nicotine products by teenagers has revealed an urgent need to better understand the impact of nicotine on the adolescent brain. Here, we sought to examine the actions of extracellular ATP as a neurotransmitter and to investigate whether ATP and nicotinic signaling interact during adolescence. With the GRAB (G-protein-coupled receptor activation-based ATP sensor), we first demonstrated that nicotine induces extracellular ATP release in the medial habenula, a brain region involved in nicotine aversion and withdrawal. Using patch-clamp electrophysiology, we then demonstrated that activation of the ATP receptors P2X or P2Y increases the neuronal firing of cholinergic neurons. Surprisingly, contrasting interactive effects were observed with nicotine exposure. For the P2X receptor, activation had no observable effect on acute nicotine-mediated activity, but during abstinence after 10 d of nicotine exposure, coexposure to nicotine and the P2X agonist potentiated neuronal activity in female, but not male, neurons. For P2Y signaling, a potentiated effect of the agonist and nicotine was observed with acute exposure, but not following extended nicotine exposure. These data reveal a complex interactive effect between nicotinic and ATP signaling in the adolescent brain and provide mechanistic insights into extracellular ATP signaling with sex-specific alterations of neuronal responses based on prior drug exposure. In these studies, it was discovered that nicotine induces extracellular ATP release in the medial habenula and subsequent activation of the ATP purinergic receptors increases habenular cholinergic neuronal firing in the adolescent brain. Interestingly, following extended nicotine exposure, nicotine was found to alter the interplay between purinergic and nicotinic signaling in a sex-specific manner. Together, these studies provide a novel understanding for the role of extracellular ATP in mediating habenular activity and reveal how nicotine exposure during adolescence alters these signaling mechanisms, which has important implications given the high incidence of e-cigarette/vape use by youth.
Topics: Male; Adolescent; Female; Humans; Nicotine; Nicotinic Agonists; Habenula; Electronic Nicotine Delivery Systems; Synaptic Transmission; Cholinergic Neurons; Receptors, Purinergic P2; Adenosine Triphosphate
PubMed: 37821229
DOI: 10.1523/JNEUROSCI.1290-23.2023 -
Anesthesia and Analgesia Jan 2021Burn injury (BI) pain consists of inflammatory and neuropathic components and activates microglia. Nicotinic alpha 7 acetylcholine receptors (α7AChRs) expressed in...
BACKGROUND
Burn injury (BI) pain consists of inflammatory and neuropathic components and activates microglia. Nicotinic alpha 7 acetylcholine receptors (α7AChRs) expressed in microglia exhibit immunomodulatory activity during agonist stimulation. Efficacy of selective α7AChR agonist GTS-21 to mitigate BI pain and spinal pain-mediators was tested.
METHODS
Anesthetized rats after hind-paw BI received intraperitoneal GTS-21 or saline daily. Allodynia and hyperalgesia were tested on BI and contralateral paw for 21 days. Another group after BI receiving GTS-21 or saline had lumbar spinal cord segments harvested (day 7 or 14) to quantify spinal inflammatory-pain transducers or microglia activation using fluorescent marker, ionized calcium-binding adaptor protein (Iba1).
RESULTS
BI significantly decreased allodynia withdrawal threshold from baseline of ~9-10 to ~0.5-1 g, and hyperalgesia latency from ~16-17 to ~5-6 seconds by day 1. Both doses of GTS-21 (4 or 8 mg/kg) mitigated burn-induced allodynia from ~0.5-1 to ~2-3 g threshold (P = .089 and P = .010), and hyperalgesia from ~5-6 to 8-9 seconds (P < .001 and P < .001) by day 1. The GTS-21 group recovered to baseline pain threshold by day 15-17 compared to saline-treated, where the exaggerated nociception persisted beyond 15-17 days. BI significantly (P < .01) increased spinal cord microgliosis (identified by fluorescent Iba1 staining), microglia activation (evidenced by the increased inflammatory cytokine), and pain-transducer (protein and/or messenger RNA [mRNA]) expression (tumor necrosis factor-α [TNF-α], interleukin-1β [IL-1β], nuclear factor-kappa B [NF-κB], interleukin-6 [IL-6], Janus-associated kinase signal transducer and activator of transcription 3 [JAK-STAT3], and/or N-methyl-D-aspartate receptor [NMDAR]). GTS-21 mitigated pain-transducer changes. The α7AChR antagonist methyllycaconitine nullified the beneficial effects of GTS-21 on both increased nociception and pain-biomarker expression.
CONCLUSIONS
Nonopioid, α7AChR agonist GTS-21 elicits antinociceptive effects at least in part by decreased activation spinal-cord pain-inducers. The α7AChR agonist GTS-21 holds promise as potential therapeutic adjunct to decrease BI pain by attenuating both microglia changes and expression of exaggerated pain transducers.
Topics: Animals; Benzylidene Compounds; Burns; Inflammation Mediators; Male; Nicotinic Agonists; Pain; Pain Measurement; Pyridines; Rats; Rats, Sprague-Dawley; Spinal Cord
PubMed: 33264122
DOI: 10.1213/ANE.0000000000005274 -
Journal of Natural Products Mar 2010In 1992, John Daly et al. reported the isolation and structure determination of epibatidine. Epibatidine's unique structure and its potent nicotinic agonist activity...
In 1992, John Daly et al. reported the isolation and structure determination of epibatidine. Epibatidine's unique structure and its potent nicotinic agonist activity have had a tremendous impact on nicotine receptor research. This research has led to a better understanding of the nicotinic acetylcholine receptor (nAChR) pharmacophore and to epibatidine analogues with potential as pharmacotherapies for treating various CNS disorders. In this study, we report the synthesis, receptor binding ([(3)H]epibatidine and [(125)I]iodoMLA), and in vivo pharmacological properties (mouse tail flick, hot plate, hypothermia, and spontaneous activity) of a series of 3'-(substituted phenyl)epibatidine analogues (5a-m). Results from these studies have added to the understanding of the nAChR pharmacophore and led to nicotinic partial agonists that may have potential for smoking cessation. All the analogues had affinities for the alpha4beta2 nAChR similar to epibatidine (1). 3'-(3-Dimethylaminophenyl)epibatidine (5m) has a nicotinic partial agonist pharmacological profile similar to the smoking cessation drug varenicline. Other analogues are partial agonists with varying degrees of nicotinic functional agonist and antagonist activity. 3'-(3-Aminophenyl)epibatidine (5j) is a more potent functional agonist and antagonist in all tests than varenicline. 3'-(3-Fluorophenyl)epibatidine and 3'-(3-chlorophenyl)epibatidine (5c and 5e) are more potent than varenicline when tested as agonists in four pharmacological tests and antagonists when evaluated against nicotine in the analgesia hot-plate test.
Topics: Analgesics; Animals; Bridged Bicyclo Compounds, Heterocyclic; Male; Mice; Molecular Structure; Nicotinic Agonists; Pyridines; Rats; Receptors, Nicotinic
PubMed: 20038125
DOI: 10.1021/np9006124 -
Anesthesiology Jun 2019Opioid analgesics are widely used for treatment of acute, postoperative, and chronic pain. However, activation of opioid receptors can result in severe respiratory...
BACKGROUND
Opioid analgesics are widely used for treatment of acute, postoperative, and chronic pain. However, activation of opioid receptors can result in severe respiratory depression. There is an unmet clinical need to develop a pharmacologic therapy to counter opioid-induced respiratory depression without interfering with analgesia. Further, additional advances to confront accidental lethal overdose with the use of fentanyl and other opioids are needed. Here, the authors test the hypothesis that activation of nicotinic receptors expressed within respiratory rhythm-generating networks would counter opioid-induced respiratory depression without compromising analgesia.
METHODS
Respiratory neural discharge was measured using in vitro brainstem-spinal cord and medullary slice rat preparations. In vivo, plethysmographic recording, nociception testing, and righting reflexes were used to examine respiratory ventilation, analgesia, and sedation, respectively.
RESULTS
The administration of nicotine, selective α4β2 nicotinic receptor agonist A85380, but not α7 nicotinic receptor agonist PNU282987, reversed opioid-induced respiratory depression in neonatal pups in vitro and in vivo. In adult rats in vivo, administration of A85380 (0.03 mg/kg), but not PNU282987, provides a rapid and robust reversal of fentanyl-induced decrease in respiratory rate (93.4 ± 33.7% of control 3 min after A85380 vs. 31 ± 20.5% of control after vehicle, n = 8 each, P < 0.001), without marked side effects. The coadministration of A85380 (0.06 mg/kg) with fentanyl or remifentanil markedly reduced respiratory depression and apneas, and enhanced the fentanyl-induced analgesia, as evidenced by increased paw withdrawal latency in Hargreaves plantar test (14.4 ± 2.8 s vs. vehicle: 11.3 ± 2.4 s, n = 8 each, P = 0.013) and decreased formalin-induced nocifensive duration (2.5 ± 2.4 min vs. vehicle: 5.4 ± 2.7 min, n = 8 each, P = 0.029).
CONCLUSIONS
The novel strategy of targeting α4β2 nicotinic acetylcholine receptors has the potential for advancing pain control and reducing opioid-induced respiratory depression and overdose.
Topics: Analgesics, Opioid; Animals; Animals, Newborn; Azetidines; Female; Fentanyl; Male; Nicotinic Agonists; Pregnancy; Rats; Rats, Sprague-Dawley; Receptors, Nicotinic; Respiratory Insufficiency
PubMed: 31008764
DOI: 10.1097/ALN.0000000000002676 -
Biochemical Pharmacology Oct 2013Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation-conducting transmembrane channels from the cys-loop receptor superfamily. The neuronal subtypes of... (Review)
Review
Nicotinic acetylcholine receptors (nAChRs) are ligand-gated cation-conducting transmembrane channels from the cys-loop receptor superfamily. The neuronal subtypes of these receptors (e.g. the α7 and α4β2 subtypes) are involved in neurobehavioral processes such as anxiety, the central processing of pain, food intake, nicotine seeking behavior, and a number of cognitive functions like learning and memory. Neuronal nAChR dysfunction is involved in the pathophysiology of many neurological disorders, and behavioral studies in animals are useful models to assess the effects of compounds that act on these receptors. Allosteric modulators are ligands that bind to the receptors at sites other than the orthosteric site where acetylcholine, the endogenous agonist for the nAChRs, binds. While conventional ligands for the neuronal nAChRs have been studied for their behavioral effects in animals, allosteric modulators for these receptors have only recently gained attention, and research on their behavioral effects is growing rapidly. Here we will discuss the behavioral effects of allosteric modulators of the neuronal nAChRs.
Topics: Animals; Behavior, Animal; Molecular Structure; Neurons; Nicotinic Agonists; Nicotinic Antagonists; Receptors, Nicotinic
PubMed: 23732296
DOI: 10.1016/j.bcp.2013.05.018 -
Nature Neuroscience Sep 2011The α(7) acetylcholine receptor (AChR) mediates pre- and postsynaptic neurotransmission in the central nervous system and is a potential therapeutic target in...
The α(7) acetylcholine receptor (AChR) mediates pre- and postsynaptic neurotransmission in the central nervous system and is a potential therapeutic target in neurodegenerative, neuropsychiatric and inflammatory disorders. We determined the crystal structure of the extracellular domain of a receptor chimera constructed from the human α(7) AChR and Lymnaea stagnalis acetylcholine binding protein (AChBP), which shares 64% sequence identity and 71% similarity with native α(7). We also determined the structure with bound epibatidine, a potent AChR agonist. Comparison of the structures revealed molecular rearrangements and interactions that mediate agonist recognition and early steps in signal transduction in α(7) AChRs. The structures further revealed a ring of negative charge within the central vestibule, poised to contribute to cation selectivity. Structure-guided mutational studies disclosed distinctive contributions to agonist recognition and signal transduction in α(7) AChRs. The structures provide a realistic template for structure-aided drug design and for defining structure-function relationships of α(7) AChRs.
Topics: Amino Acid Sequence; Animals; Binding Sites; Bridged Bicyclo Compounds, Heterocyclic; Chimera; Conserved Sequence; Crystallography, X-Ray; Humans; Ligands; Lymnaea; Models, Molecular; Molecular Sequence Data; Nicotinic Agonists; Protein Binding; Protein Conformation; Pyridines; Receptors, Nicotinic
PubMed: 21909087
DOI: 10.1038/nn.2908 -
British Journal of Pharmacology Mar 2007Selective receptor antagonists are one of the most powerful resources in a pharmacologist's toolkit and are essential for the identification and classification of... (Review)
Review
Selective receptor antagonists are one of the most powerful resources in a pharmacologist's toolkit and are essential for the identification and classification of receptor subtypes and dissecting their roles in normal and abnormal body function. However, when the actions of antagonists are measured inappropriately and misleading results are reported, confusion and wrong interpretations ensue. This article gives a general overview of Schild analysis and the method of determining antagonist equilibrium constants. We demonstrate why this technique is preferable in the study of competitive receptor antagonism than the calculation of antagonist concentration that inhibit agonist-evoked responses by 50%. In addition we show how the use of Schild analysis can provide information on the outcome of single amino acid mutations in structure-function studies of receptors. Finally, we illustrate the need for caution when studying the effects of potent antagonists on synaptic transmission where the timescale of events under investigation is such that ligands and receptors never reach steady-state occupancy.
Topics: Animals; Binding, Competitive; Computer Simulation; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Humans; Ion Channel Gating; Ion Channels; Kinetics; Ligands; Models, Biological; Nicotinic Agonists; Nicotinic Antagonists; Point Mutation; Protein Binding; Receptors, Cell Surface; Receptors, N-Methyl-D-Aspartate; Receptors, Nicotinic; Reproducibility of Results; Synaptic Transmission
PubMed: 17245371
DOI: 10.1038/sj.bjp.0706997 -
Missouri Medicine 2014Tobacco smoking remains the highest cause of preventable deaths worldwide. Electronic cigarettes have recently become popular as nicotine alternatives. With public use... (Review)
Review
Tobacco smoking remains the highest cause of preventable deaths worldwide. Electronic cigarettes have recently become popular as nicotine alternatives. With public use on the rise and recent tobacco industry interest, field experts and regulatory agencies voiced concerns about their safety and unregulated production. Electronic cigarettes are safer than conventional cigarettes and at least as safe as other approved nicotine replacement therapies. Further evidence is needed as their popularity increases amidst controversy over safety and efficacy.
Topics: Equipment and Supplies; Humans; Nicotine; Nicotinic Agonists; Perception; Smoking; Smoking Cessation
PubMed: 25011347
DOI: No ID Found -
Biochemical Pharmacology Oct 2009The identification and characterization of drugs for the treatment of cognitive disorders has been hampered by the absence of comprehensive hypotheses. Such hypotheses... (Review)
Review
The identification and characterization of drugs for the treatment of cognitive disorders has been hampered by the absence of comprehensive hypotheses. Such hypotheses consist of (a) a precisely defined cognitive operation that fundamentally underlies a range of cognitive abilities and capacities and, if impaired, contributes to the manifestation of diverse cognitive symptoms; (b) defined neuronal mechanisms proposed to mediate the cognitive operation of interest; (c) evidence indicating that the putative cognition enhancer facilitates these neuronal mechanisms; (d) and evidence indicating that the cognition enhancer facilitates cognitive performance by modulating these underlying neuronal mechanisms. The evidence on the neuronal and attentional effects of nAChR agonists, specifically agonists selective for alpha4beta2* nAChRs, has begun to support such a hypothesis. nAChR agonists facilitate the detection of signals by augmenting the transient increases in prefrontal cholinergic activity that are necessary for a signal to gain control over behavior in attentional contexts. The prefrontal microcircuitry mediating these effects include alpha4beta2* nAChRs situated on the terminals of thalamic inputs and the glutamatergic stimulation of cholinergic terminals via ionotropic glutamate receptors. Collectively, this evidence forms the basis for hypothesis-guided development and characterization of cognition enhancers.
Topics: Acetylcholine; Animals; Attention; Cognition; Cognition Disorders; Glutamic Acid; Humans; Nerve Net; Neurons; Nicotinic Agonists; Prefrontal Cortex; Receptors, Glutamate; Receptors, Nicotinic; Thalamus
PubMed: 19406107
DOI: 10.1016/j.bcp.2009.04.019