RESUMO
The current study evaluated a new series of N,N'-alkane-diyl-bis-3-picolinium (bAPi) analogs with C6-C12 methylene linkers as nicotinic acetylcholine receptor (nAChR) antagonists, for nicotine-evoked [3H]dopamine (DA) overflow, for blood-brain barrier choline transporter affinity, and for attenuation of discriminative stimulus and locomotor stimulant effects of nicotine. bAPi analogs exhibited little affinity for alpha4beta2* (* indicates putative nAChR subtype assignment) and alpha7* high-affinity ligand binding sites and exhibited no inhibition of DA transporter function. With the exception of C6, all analogs inhibited nicotine-evoked [3H]DA overflow (IC50 = 2 nM-6 microM; Imax = 54-64%), with N,N'-dodecane-1,12-diyl-bis-3-picolinium dibromide (bPiDDB; C12) being most potent. bPiDDB did not inhibit electrically evoked [3H]DA overflow, suggesting specific nAChR inhibitory effects and a lack of toxicity to DA neurons. Schild analysis suggested that bPiDDB interacts in an orthosteric manner at nAChRs mediating nicotine-evoked [3H]DA overflow. To determine whether bPiDDB interacts with alpha-conotoxin MII-sensitive alpha6beta2-containing nAChRs, slices were exposed concomitantly to maximally effective concentrations of bPiDDB (10 nM) and alpha-conotoxin MII (1 nM). Inhibition of nicotine-evoked [3H]DA overflow was not different with the combination compared with either antagonist alone, suggesting that bPiDDB interacts with alpha6beta2-containing nAChRs. C7, C8, C10, and C12 analogs exhibited high affinity for the blood-brain barrier choline transporter in vivo, suggesting brain bioavailability. Although none of the analogs altered the discriminative stimulus effect of nicotine, C8, C9, C10, and C12 analogs decreased nicotine-induced hyperactivity in nicotine-sensitized rats, without reducing spontaneous activity. Further development of nAChR antagonists that inhibit nicotine-evoked DA release and penetrate brain to antagonize DA-mediated locomotor stimulant effects of nicotine as novel treatments for nicotine addiction is warranted.
Assuntos
Comportamento Animal/efeitos dos fármacos , Dopamina , Nicotina/farmacologia , Antagonistas Nicotínicos/farmacologia , Picolinas/farmacologia , Receptores Nicotínicos/metabolismo , Animais , Transporte Biológico Ativo , Barreira Hematoencefálica/metabolismo , Corpo Estriado/efeitos dos fármacos , Corpo Estriado/metabolismo , Aprendizagem por Discriminação/efeitos dos fármacos , Dopamina/metabolismo , Masculino , Estrutura Molecular , Atividade Motora/efeitos dos fármacos , Proteínas do Tecido Nervoso/metabolismo , Antagonistas Nicotínicos/química , Antagonistas Nicotínicos/farmacocinética , Picolinas/química , Picolinas/farmacocinética , Proteínas da Membrana Plasmática de Transporte de Neurotransmissores/metabolismo , Ligação Proteica , Ratos , Ratos Endogâmicos F344 , Ratos Sprague-Dawley , Relação Estrutura-AtividadeRESUMO
Pyridine N-n-alkylation of S(-)-nicotine (NIC) affords N-n-alkylnicotinium analogs, previously shown to competitively inhibit [(3)H]NIC binding and interact with alpha4beta2* nicotinic receptors (nAChRs). The present study determined the ability of the analogs to inhibit NIC-evoked (86)Rb(+) efflux from rat thalamic synaptosomes to assess functional interaction with alpha4beta2* nAChRs. In a concentration-dependent manner, NIC evoked (86)Rb(+) efflux (EC(50) = 170 nmol/L). Analog-induced inhibition of NIC-evoked (86)Rb(+) efflux varied over a approximately 450-fold range. Analogs with long n-alkyl chain lengths (C(9)-C(12)) inhibited efflux in the low nmol/L range (IC(50) = 9-20 nmol/L), similar to dihydro-beta-erythroidine (IC(50) = 19 nmol/L). Compounds with shorter n-alkyl chain lengths (C(1)-C(8)) produced inhibition in the low micromol/L range (IC(50) = 3-12 micromol/L). C(10) and C(12) analogs completely inhibited NIC-evoked efflux, whereas C(1-9) analogs produced maximal inhibition of only 10% to 60%. While the C(10) analog N-n-decylnicotinium iodide (NDNI) did not produce significant inhibition of NIC-evoked dopamine release in previously reported studies, NDNI possesses high affinity for [(3)H]NIC binding sites (K(i) = 90 nmol/L) and is a potent and efficacious inhibitor of NIC-evoked (86)Rb(+) efflux as demonstrated in the current studies. Thus, NDNI is a competitive, selective antagonist at alpha4beta2* nAChRs.
Assuntos
Nicotina/antagonistas & inibidores , Antagonistas Nicotínicos/farmacologia , Receptores Nicotínicos/metabolismo , Radioisótopos de Rubídio/metabolismo , Tálamo/metabolismo , Animais , Relação Dose-Resposta a Droga , Masculino , Nicotina/metabolismo , Antagonistas Nicotínicos/química , Ratos , Ratos Sprague-Dawley , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismo , Tálamo/efeitos dos fármacosRESUMO
The minor tobacco alkaloids nornicotine, anabasine, and anatabine from Nicotiana tobacum are known to possess nicotinic receptor agonist activity, although they are relatively less potent than S-(-)-nicotine, the principal tobacco alkaloid. Previous pharmacological investigations and structure-activity studies have been limited owing to the lack of availability of the optically pure forms of these minor alkaloids. We now report a 2-step synthetic procedure for the enantioselective synthesis of the optical isomers of nornicotine and anabasine, and a modified procedure for the synthesis of anatabine enantiomers. These procedures involve initial formation of the chiral ketimine resulting from the condensation of either 1R, 2R, 5R-(+)- or 1S, 2S, 5S-(-)-2-hydroxy-3-pinanone with 3-(aminomethyl)pyridine followed by enantioselective C-alkylation with an appropriate halogenoalkane or halogenoalkene species, N-deprotection, and base-catalyzed intramolecular ring closure, to form the appropriate, chirally pure minor tobacco alkaloid. Using this approach, the R-(+)- and S-(-)-enantiomers of the above minor tobacco alkaloids were obtained in good overall chemical yield and excellent enantomeric excess.
Assuntos
Alcaloides/síntese química , Anabasina/síntese química , Nicotiana , Nicotina/análogos & derivados , Piridinas/síntese química , Nicotina/síntese química , EstereoisomerismoRESUMO
N-n-Alkylpicolinium and N,N'-alkyl-bis-picolinium analogues were assessed in nicotinic receptor (nAChR) assays. The most potent and subtype-selective analogue, N,N'-dodecyl-bis-picolinium bromide (bPiDDB), inhibited nAChRs mediating nicotine-evoked [(3)H]dopamine release (IC(50)=5 nM; I(max) of 60%), and did not interact with alpha4beta2* or alpha7* nAChRs. bPiDDB represents the current lead compound for development as a tobacco use cessation agent.
Assuntos
Antagonistas Nicotínicos/farmacologia , Picolinas/farmacologia , Receptores Nicotínicos/efeitos dos fármacos , Abandono do Hábito de Fumar , Animais , Bioensaio , Masculino , Estrutura Molecular , Nicotina/farmacologia , Antagonistas Nicotínicos/química , Picolinas/química , Ratos , Ratos Sprague-Dawley , Receptores Nicotínicos/metabolismo , Relação Estrutura-AtividadeRESUMO
N-n-Alkylation of nicotine converts it from an agonist into an antagonist at neuronal nicotinic acetylcholine receptor subtypes mediating nicotine-evoked dopamine release. Conformationally restricted analogues exhibit both high affinity and selectivity at this site, and are able to access the brain due to their ability to act as substrates for the blood-brain barrier choline transporter.
Assuntos
Aconitina/análogos & derivados , Dopamina/metabolismo , Antagonistas Nicotínicos/química , Antagonistas Nicotínicos/farmacologia , Receptores Nicotínicos/efeitos dos fármacos , Aconitina/antagonistas & inibidores , Aconitina/metabolismo , Animais , Sítios de Ligação , Ligação Competitiva/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Colina/antagonistas & inibidores , Colina/metabolismo , Ligantes , Masculino , Estrutura Molecular , Nicotina/antagonistas & inibidores , Nicotina/metabolismo , Nicotina/farmacologia , Ratos , Ratos Sprague-Dawley , Receptores Nicotínicos/metabolismo , Relação Estrutura-AtividadeRESUMO
Structural simplification of N-n-alkylnicotinium analogs, antagonists at neuronal nicotinic acetylcholine receptors (nAChRs), was achieved by removal of the N-methylpyrrolidino moiety affording N-n-alkylpyridinium analogs with carbon chain lengths of C1 to C20. N-n-Alkylpyridinium analog inhibition of [3H]nicotine and [3H]methyllycaconitine binding to rat brain membranes assessed interaction with alpha4beta2* and alpha7* nAChRs, respectively, whereas inhibition of nicotine-evoked 3H overflow from [3H]dopamine ([3H]DA)-preloaded rat striatal slices assessed antagonist action at nAChR subtypes mediating nicotine-evoked DA release. No inhibition of [3H]methyllycaconitine binding was observed, although N-n-alkylpyridinium analogs had low affinity for [3H]nicotine binding sites, i.e., 1 to 3 orders of magnitude lower than that of the respective N-n-alkylnicotinium analogs. These results indicate that the N-methylpyrrolidino moiety in the N-n-alkylnicotinium analogs is a structural requirement for potent inhibition of alpha4beta2* nAChRs. Importantly, N-n-alkylpyridinium analogs with n-alkyl chains < C10 did not inhibit nicotine-evoked [3H]DA overflow, whereas analogs with n-alkyl chains ranging from C10 to C20 potently and completely inhibited nicotine-evoked [3H]DA overflow (IC50 = 0.12-0.49 microM), with the exceptions of N-n-pentadecylpyridinium bromide (C15) and N-n-eicosylpyridinium bromide (C20), which exhibited maximal inhibition of approximately 50%. The mechanism of inhibition of a representative analog of this structural series, N-n-dodecylpyridinium iodide, was determined by Schild analysis. Linear Schild regression with slope not different from unity indicated competitive antagonism at nAChRs mediating nicotine-evoked [3H]DA overflow and a KB value of 0.17 microM. Thus, the simplified N-n-alkylpyridinium analogs are potent, selective, and competitive antagonists of nAChRs mediating nicotine-evoked [3H]DA overflow, indicating that the N-methylpyrrolidino moiety is not a structural requirement for interaction with nAChR subtypes mediating nicotine-evoked DA release.
Assuntos
Aconitina/análogos & derivados , Aconitina/farmacologia , Corpo Estriado/efeitos dos fármacos , Dopamina/metabolismo , Antagonistas Nicotínicos/farmacologia , Compostos de Piridínio/farmacologia , Receptores Nicotínicos/metabolismo , Animais , Encéfalo/citologia , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Corpo Estriado/metabolismo , Técnicas In Vitro , Nicotina/farmacologia , Ratos , Ratos Sprague-Dawley , TrítioRESUMO
The current study demonstrates that N-n-alkylnicotinium analogs with increasing n-alkyl chain lengths from 1 to 12 carbons have varying affinity (Ki = 90 nM-20 microM) for S-(-)-[3H]nicotine binding sites in rat striatal membranes. A linear relationship was observed such that increasing n-alkyl chain length provided increased affinity for the alpha4beta2* nicotinic acetylcholine receptor (nAChR) subtype, with the exception of N-n-octylnicotinium iodide (NONI). The most potent analog was N-n-decylnicotinium iodide (NDNI; Ki = 90 nM). In contrast, none of the analogs in this series exhibited high affinity for the [3H]methyllycaconitine binding site, thus indicating low affinity for the alpha7* nAChR. The C8 analog, NONI, had low affinity for S-(-)-[3H]nicotine binding sites but was a potent inhibitor of S-(-)-nicotine-evoked [3H]dopamine (DA) overflow from superfused striatal slices (IC50 = 0.62 microM), thereby demonstrating selectivity for the nAChR subtype mediating S-(-)-nicotine-evoked [3H]DA overflow (alpha3alpha6beta2* nAChRs). Importantly, the N-n-alkylnicotinium analog with highest affinity for the alpha4beta2* subtype, NDNI, lacked the ability to inhibit S-(-)-nicotine-evoked [3H]DA overflow and, thus, appears to be selective for alpha4beta2* nAChRs. Furthermore, the present study demonstrates that the interaction of these analogs with the alpha4beta2* subtype is via a competitive mechanism. Thus, selectivity for the alpha4beta2* subtype combined with competitive interaction with the S-(-)-nicotine binding site indicates that NDNI is an excellent candidate for studying the structural topography of alpha4beta2* agonist recognition binding sites, for identifying the antagonist pharmacophore on the alpha4beta2* nAChR, and for defining the role of this subtype in physiological function and pathological disease states.
Assuntos
Neurônios/efeitos dos fármacos , Nicotina/análogos & derivados , Antagonistas Nicotínicos/farmacologia , Receptores Nicotínicos/efeitos dos fármacos , Animais , Sítios de Ligação/efeitos dos fármacos , Ligação Competitiva/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Di-Hidro-beta-Eritroidina/farmacologia , Dopamina/metabolismo , Técnicas In Vitro , Cinética , Masculino , Membranas/efeitos dos fármacos , Membranas/metabolismo , Neostriado/efeitos dos fármacos , Neostriado/metabolismo , Nicotina/metabolismo , Nicotina/farmacologia , Ratos , Ratos Sprague-Dawley , Relação Estrutura-Atividade , Receptor Nicotínico de Acetilcolina alfa7RESUMO
The structure of the S(-)-nicotine molecule was modified via N-n-alkylation of the pyridine-N atom to afford a series of N-n-alkylnicotinium iodide salts with carbon chain lengths varying between C(1) and C(12). The ability of these analogs to evoke [(3)H] overflow and inhibit S(-)-nicotine-evoked [(3)H] overflow from [(3)H]dopamine ([(3)H]DA)-preloaded rat striatal slices was determined. At high concentrations, analogs with chain lengths > or =C(6) evoked [(3)H] overflow. Specifically, N-n-decylnicotinium iodide (NDNI; C(10)) evoked significant [(3)H] overflow at 1 microM, and N-n-dodecylnicotinium iodide (NDDNI; C(12)) at 10 microM, whereas N-n-octylnicotinium iodide (NONI; C(8)), N-n-heptylnicotinium iodide (NHpNI; C(7)), and N-n-hexylnicotinium iodide (C(6)) evoked [(3)H] overflow at 100 microM. Thus, intrinsic activity at these concentrations prohibited assessment of inhibitory activity. The most potent N-n-alkylnicotinium analog to inhibit S(-)-nicotine-evoked [(3)H] overflow was NDDNI, with an IC(50) value of 9 nM. NHpNI, NONI, and N-n-nonylnicotinium iodide (C(9)) also inhibited S(-)-nicotine-evoked [(3)H] overflow with IC(50) values of 0.80, 0.62, and 0.21 microM, respectively. In comparison, the competitive neuronal nicotinic acetylcholine receptor (nAChR) antagonist, dihydro-beta-erythroidine, had an IC(50) of 1.6 microM. A significant correlation of N-n-alkyl chain length with analog-induced inhibition was observed, with the exception of NDNI, which was devoid of inhibitory activity. The mechanism of N-n-alkylnicotinium-induced inhibition of the high-affinity, low-capacity component of S(-)-nicotine-evoked [(3)H] overflow was determined via Schild analysis, using the representative analog, NONI. Linear Schild regression and slope not different from unity suggested that NONI competitively interacts with a single nAChR subtype to inhibit S(-)-nicotine-evoked [(3)H]DA release (K(i) value = 80.2 nM). Thus, modification of the S(-)-nicotine molecule converts this agonist into an antagonist at nAChRs, mediating S(-)-nicotine-evoked DA release in striatum.