92 research outputs found
CYTISINE AND CYTISINE DERIVATIVES. MORE THAN SMOKING CESSATION AIDS
Cytisine, a natural bioactive compound that is mainly isolated from plants of the Leguminosae family (especially the seeds of Laburnum anagyroides), has been marketed in central and eastern Europe as an aid in the clinical management of smoking cessation for more than 50 years. Its main targets are neuronal nicotinic acetylcholine receptors (nAChRs), and pre-clinical studies have shown that its interactions with various nAChR subtypes located in different areas of the central and peripheral nervous systems are neuroprotective, have a wide range of biological effects on nicotine and alcohol addiction, regulate mood, food intake and motor activity, and influence the autonomic and cardiovascular systems. Its relatively rigid conformation makes it an attractive template for research of new derivatives. Recent studies of structurally modified cytisine have led to the development of new compounds and for some of them the biological activities are mediated by still unidentified targets other than nAChRs, whose mechanisms of action are still being investigated. The aim of this review is to describe and discuss: 1) the most recent pre-clinical results obtained with cytisine in the fields of neurological and non-neurological diseases; 2) the effects and possible mechanisms of action of the most recent cytisine derivatives; and 3) the main areas warranting further research
Nicotine inside neurons
The crucial effects of chronic nicotine exposure are intracellular and include a cell-specific influence on the assembly and stoichiometry of the nAChRs exported to the
plasma membrane, that affects the function of surface nAChRs and cholinergic transmission. In this context, it is worthwhile to consider extraneuronal tissues, especially where nicotine may reach much higher concentrations such as the lung epithelia. Many peripheral cell types and tissues express nAChR subunit transcripts, that may play crucial roles in signal transduction underlying tumor initiation or growt
Nicotinic acetylcholine receptors (nACh) in GtoPdb v.2021.3
Nicotinic acetylcholine (ACh) receptors are members of the Cys-loop family of transmitter-gated ion channels that includes the GABAA, strychnine-sensitive glycine and 5-HT3 receptors [215, 3, 159, 225, 259]. All nicotinic receptors are pentamers in which each of the five subunits contains 4 TM domains. Genes encoding a total of 17 subunits (α1-10, β1-4, γ, δ and ε) have been identified [120]. All subunits with the exception of α8 (present in avian species) have been identified in mammals. All α subunits possess two tandem cysteine residues near to the site involved in acetylcholine binding, and subunits not named α lack these residues [159]. The orthosteric ligand binding site is formed by residues within at least three peptide domains on the α subunit (principal component), and three on the adjacent subunit (complementary component). Nicotinic ACh receptors contain several allosteric modulatory sites. One such site, for positive allosteric modulators (PAMs) and allosteric agonists, has been proposed to reside within an intrasubunit cavity between the 4 TM domains [264, 87]; see also [106]). The high resolution crystal structure of the molluscan ACh binding protein, a structural homologue of the extracellular binding domain of a nicotinic receptor pentamer, in complex with several nicotinic receptor ligands (e.g.[35]) and the crystal structure of the extracellular domain of the α1 subunit bound to α-bungarotoxin at 1.94Â resolution [55], has revealed the orthosteric binding site in detail (reviewed in [215, 120, 39, 198]). Nicotinic receptors at the somatic neuromuscular junction of adult animals have the stoichiometry (α1)2β1δε, whereas an extrajunctional (α1)2β1γδ receptor predominates in embryonic and denervated skeletal muscle and other pathological states. Other nicotinic receptors are assembled as combinations of α(2-6) and β(2-4) subunits. For α2, α3, α4 and β2 and β4 subunits, pairwise combinations of α and β (e.g. α3β4 and α4β2) are sufficient to form a functional receptor in vitro, but far more complex isoforms may exist in vivo (reviewed in [96, 93, 159]). There is strong evidence that the pairwise assembly of some α and β subunits can occur with variable stoichiometry [e.g. (α4)2(β2)2 or (α4)3(β2)2] which influences the biophysical and pharmacological properties of the receptor [159]. α5 and β3 subunits lack function when expressed alone, or pairwise, but participate in the formation of functional hetero-oligomeric receptors when expressed as a third subunit with another α and β pair [e.g. α4α5αβ2, α4αβ2β3, α5α6β2, see [159] for further examples]. The α6 subunit can form a functional receptor when co-expressed with β4 in vitro, but more efficient expression ensues from incorporation of a third partner, such as β3 [263]. The α7, α8, and α9 subunits form functional homo-oligomers, but can also combine with a second subunit to constitute a hetero-oligomeric assembly (e.g. α7β2 and α9α10). For functional expression of the α10 subunit, co-assembly with α9 is necessary. The latter, along with the α10 subunit, appears to be largely confined to cochlear and vestibular hair cells. Comprehensive listings of nicotinic receptor subunit combinations identified from recombinant expression systems, or in vivo, are given in [159]. In addition, numerous proteins interact with nicotinic ACh receptors modifying their assembly, trafficking to and from the cell surface, and activation by ACh (reviewed by [158, 9, 118]).The nicotinic receptor Subcommittee of NC-IUPHAR has recommended a nomenclature and classification scheme for nicotinic acetylcholine (nACh) receptors based on the subunit composition of known, naturally- and/or heterologously-expressed nACh receptor subtypes [143]. Headings for this table reflect abbreviations designating nACh receptor subtypes based on the predominant α subunit contained in that receptor subtype. An asterisk following the indicated α subunit denotes that other subunits are known to, or may, assemble with the indicated α subunit to form the designated nACh receptor subtype(s). Where subunit stoichiometries within a specific nACh receptor subtype are known, numbers of a particular subunit larger than 1 are indicated by a subscript following the subunit (enclosed in parentheses- see also [46])
Visual acuity is reduced in alpha 7 nicotinic receptor knockout mice.
PURPOSE Nicotinic receptors (nAChRs) are part of a heterogeneous family of pentameric ligand-gated ion channels that are widely expressed in the visual system. The impact of α7 homomeric nAChRs on visual function was investigated using mutant mice lacking the α7 nicotinic receptor subunit. METHODS The spatial resolution limit was measured in α7 knockout (α7 KO) and age-matched control mice using three independent methods: an operant behavioral visual task (Prusky maze), cortical visual evoked potentials (VEPs), and the pattern electroretinogram (PERG) evoked by alternating gratings of different spatial frequencies and contrasts. RESULTS Visual acuity measured by means of the visual water maze task was significantly decreased in the α7 KO mice and, concordantly, there was a reduction of the cortical spatial resolution limit measured by VEPs. However, the PERG was normal in α7 KO mice, compared with control mice. The use of fluorescently tagged cholera toxin showed that projections from the retina segregate normally in α7 KO mice and, in line with this, the visual cortical responses elicited by stimulating either eye were normally balanced in both visual cortices and showed no retinotopic anomalies. CONCLUSIONS These findings indicate that the absence of the α7 nicotinic subunit reduces visual acuity. Because the cortical output has an abnormal spatial resolution but retinal output is preserved, it can be concluded that the low visual acuity was due to a deficit specifically present in the visual cortex
Antagonism of the prokineticin system prevents and reverses allodynia and inflammation in a mouse model of diabetes
Neuropathic pain is a severe diabetes complication and its treatment is not satisfactory. It is associated with neuroinflammation-related events that participate in pain generation and chronicization. Prokineticins are a new family of chemokines that has emerged as critical players in immune system, inflammation and pain. We investigated the role of prokineticins and their receptors as modulators of neuropathic pain and inflammatory responses in experimental diabetes. In streptozotocin-induced-diabetes in mice, the time course expression of prokineticin and its receptors was evaluated in spinal cord and sciatic nerves, and correlated with mechanical allodynia. Spinal cord and sciatic nerve pro- and anti-inflammatory cytokines were measured as protein and mRNA, and spinal cord GluR subunits expression studied. The effect of preventive and therapeutic treatment with the prokineticin receptor antagonist PC1 on behavioural and biochemical parameters was evaluated. Peripheral immune activation was assessed measuring macrophage and T-helper cytokine production. An up-regulation of the Prokineticin system was present in spinal cord and nerves of diabetic mice, and correlated with allodynia. Therapeutic PC1 reversed allodynia while preventive treatment blocked its development. PC1 normalized prokineticin levels and prevented the up-regulation of GluN2B subunits in the spinal cord. The antagonist restored the pro-/anti-inflammatory cytokine balance altered in spinal cord and nerves and also reduced peripheral immune system activation in diabetic mice, decreasing macrophage proinflammatory cytokines and the T-helper 1 phenotype. The prokineticin system contributes to altered sensitivity in diabetic neuropathy and its inhibition blocked both allodynia and inflammatory events underlying disease
nicotinic acetylcholine receptors version 2019 4 in the iuphar bps guide to pharmacology database
Nicotinic acetylcholine receptors are members of the Cys-loop family of transmitter-gated ion channels that includes the GABAA, strychnine-sensitive glycine and 5-HT3 receptors [210, 3, 155, 220, 252]. All nicotinic receptors are pentamers in which each of the five subunits contains four α-helical transmembrane domains. Genes encoding a total of 17 subunits (α1-10, β1-4, γ, δ and ε) have been identified [117]. All subunits with the exception of α8 (present in avian species) have been identified in mammals. All α subunits possess two tandem cysteine residues near to the site involved in acetylcholine binding, and subunits not named α lack these residues [155]. The orthosteric ligand binding site is formed by residues within at least three peptide domains on the α subunit (principal component), and three on the adjacent subunit (complementary component). nAChRs contain several allosteric modulatory sites. One such site, for positive allosteric modulators (PAMs) and allosteric agonists, has been proposed to reside within an intrasubunit cavity between the four transmembrane domains [257, 85]; see also [103]). The high resolution crystal structure of the molluscan acetylcholine binding protein, a structural homologue of the extracellular binding domain of a nicotinic receptor pentamer, in complex with several nicotinic receptor ligands (e.g.[33]) and the crystal structure of the extracellular domain of the α1 subunit bound to α-bungarotoxin at 1.94 Å resolution [53], has revealed the orthosteric binding site in detail (reviewed in [210, 117, 37, 193]). Nicotinic receptors at the somatic neuromuscular junction of adult animals have the stoichiometry (α1)2β1δε, whereas an extrajunctional (α1)2β1γδ receptor predominates in embryonic and denervated skeletal muscle and other pathological states. Other nicotinic receptors are assembled as combinations of α(2-6) and &beta(2-4) subunits. For α2, α3, α4 and β2 and β4 subunits, pairwise combinations of α and β (e.g. α3β4 and α4β2) are sufficient to form a functional receptor in vitro, but far more complex isoforms may exist in vivo (reviewed in [94, 91, 155]). There is strong evidence that the pairwise assembly of some α and β subunits can occur with variable stoichiometry [e.g. (α4)2(β2)2 or (α4)3(β2)2] which influences the biophysical and pharmacological properties of the receptor [155]. α5 and β3 subunits lack function when expressed alone, or pairwise, but participate in the formation of functional hetero-oligomeric receptors when expressed as a third subunit with another α and β pair [e.g. α4α5αβ2, α4αβ2β3, α5α6β2, see [155] for further examples]. The α6 subunit can form a functional receptor when co-expressed with β4 in vitro, but more efficient expression ensues from incorporation of a third partner, such as β3 [256]. The α7, α8, and α9 subunits form functional homo-oligomers, but can also combine with a second subunit to constitute a hetero-oligomeric assembly (e.g. α7β2 and α9α10). For functional expression of the α10 subunit, co-assembly with α9 is necessary. The latter, along with the α10 subunit, appears to be largely confined to cochlear and vestibular hair cells. Comprehensive listings of nicotinic receptor subunit combinations identified from recombinant expression systems, or in vivo, are given in [155]. In addition, numerous proteins interact with nicotinic ACh receptors modifying their assembly, trafficking to and from the cell surface, and activation by ACh (reviewed by [154, 9, 115]).The nicotinic receptor Subcommittee of NC-IUPHAR has recommended a nomenclature and classification scheme for nicotinic acetylcholine (nACh) receptors based on the subunit composition of known, naturally- and/or heterologously-expressed nACh receptor subtypes [139]. Headings for this table reflect abbreviations designating nACh receptor subtypes based on the predominant α subunit contained in that receptor subtype. An asterisk following the indicated α subunit denotes that other subunits are known to, or may, assemble with the indicated α subunit to form the designated nACh receptor subtype(s). Where subunit stoichiometries within a specific nACh receptor subtype are known, numbers of a particular subunit larger than 1 are indicated by a subscript following the subunit (enclosed in parentheses – see also [44])
A conserved arginine with non-conserved function is a key determinant of agonist selectivity in α7 nicotinic ACh receptors
Background and Purpose: The α7 and α4β2* (“*” denotes possibly assembly with another subunit) nicotinic acetylcholine receptors (nAChRs) are the most abundant nAChRs in the mammalian brain. These receptors are the most targeted nAChRs in drug discovery programmes for brain disorders. However, the development of subtype-specific agonists remains challenging due to the high degree of sequence homology and conservation of function in nAChRs. We have developed C(10) variants of cytisine, a partial agonist of α4β2 nAChR that has been used for smoking cessation. The C(10) methyl analogue used in this study displays negligible affinity for α7 nAChR, while retaining high affinity for α4β2 nAChR. Experimental Approach: The structural underpinning of the selectivity of 10-methylcytisine for α7 and α4β2 nAChRs was investigated using molecular dynamic simulations, mutagenesis and whole-cell and single-channel current recordings. Key Results: We identified a conserved arginine in the β3 strand that exhibits a non-conserved function in nAChRs. In α4β2 nAChR, the arginine forms a salt bridge with an aspartate residue in loop B that is necessary for receptor expression, whereas in α7 nAChR, this residue is not stabilised by electrostatic interactions, making its side chain highly mobile. This lack of constrain produces steric clashes with agonists and affects the dynamics of residues involved in agonist binding and the coupling network. Conclusion and Implications: We conclude that the high mobility of the β3-strand arginine in the α7 nAChR influences agonist binding and possibly gating network and desensitisation. The findings have implications for rational design of subtype-selective nAChR agents.</p
A conserved arginine with non-conserved function is a key determinant of agonist selectivity in α7 nicotinic ACh receptors
The α7 and α4β2* (“*” denotes possibly assembly with another subunit) nicotinic acetylcholine receptors (nAChRs) are the most abundant nAChRs in the mammalian brain. These receptors are the most targeted nAChRs in drug discovery programmes for brain disorders. However, the development of subtype-specific agonists remains challenging due to the high degree of sequence homology and conservation of function in nAChRs. We have developed C(10) variants of cytisine, a partial agonist of α4β2 nAChR that has been used for smoking cessation. The C(10) methyl analogue used in this study displays negligible affinity for α7 nAChR, while retaining high affinity for α4β2 nAChR.Fil: Minguez Viñas, Teresa. Oxford Brookes University; Reino UnidoFil: Nielsen, Beatriz Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Shoemark, Deborah K.. University Of Bristol; Reino UnidoFil: Gotti, Cecilia. Università degli Studi di Milano; ItaliaFil: Sessions, Richard B.. University Of Bristol; Reino UnidoFil: Mulholland, Adrian J.. University Of Bristol; Reino UnidoFil: Bouzat, Cecilia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Wonnacott, Susan. University of Bath; Reino UnidoFil: Gallagher, Timothy. University Of Bristol; Reino UnidoFil: Bermudez, Isabel. University of Oxford; Reino UnidoFil: Oliveira, Ana Sofia. University Of Bristol; Reino Unid
Iridium-Catalysed C-H Borylation of 2-Pyridones; Bisfunctionalisation of CC4
The high regioselectivity associated with the iridium-catalysed borylation of pyridones has been exploited to provide a very direct and efficient entry to C(10) doubly substituted CC4 variants of cytisine. Two approaches have been evaluated based on (i) C-H activation of cytisine (or an N-substituted derivative) followed by N-alkylation (to enable dimer formation) and (ii) direct C-H activation and borylation of CC4 itself. Both approaches provide access to C(10)-functionalized CC4 derivatives, but direct borylation of CC4 allows for a wider range of functional group interconversions to be tolerated.</p
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