Bispyridinium Compounds Inhibit Both Muscle and Neuronal Nicotinic Acetylcholine Receptors in Human Cell Lines

Abstract

Standard treatment of poisoning by organophosphorus anticholinesterases uses atropine to reduce the muscarinic effects of acetylcholine accumulation and oximes to reactivate acetylcholinesterase (the effectiveness of which depends on the specific anticholinesterase), but does not directly address the nicotinic effects of poisoning. Bispyridinium molecules which act as noncompetitive antagonists at nicotinic acetylcholine receptors have been identified as promising compounds and one has been shown to improve survival following organophosphorus poisoning in guinea-pigs. Here, we have investigated the structural requirements for antagonism and compared inhibitory potency of these compounds at muscle and neuronal nicotinic receptors and acetylcholinesterase. A series of compounds was synthesised, in which the length of the polymethylene linker between the two pyridinium moieties was increased sequentially from one to ten carbon atoms. Their effects on nicotinic receptor-mediated calcium responses were tested in muscle-derived (CN21) and neuronal (SH-SY5Y) cells. Their ability to inhibit acetylcholinesterase activity was tested using human erythrocyte ghosts. In both cell lines, the nicotinic response was inhibited in a dose-dependent manner and the inhibitory potency of the compounds increased with greater linker length between the two pyridinium moieties, as did their inhibitory potency for human acetylcholinesterase activity in vitro. These results demonstrate that bispyridinium compounds inhibit both neuronal and muscle nicotinic receptors and that their potency depends on the length of the hydrocarbon chain linking the two pyridinium moieties. Knowledge of structure-activity relationships will aid the optimisation of molecular structures for therapeutic use against the nicotinic effects of organophosphorus poisoning.

Synthesis of a Series of Structurally Diverse MB327 Derivatives and Their Affinity Characterization at the Nicotinic Acetylcholine Receptor

“…The following compounds were prepared according to published methods:p ropane-1,3-diyl bis(trifluoromethanesulfonate) (21), [44,45] 2-tert-butylpyridine (17), [27] 2-(pyridin-3-yl)propan-2-ol (9), [33] rac-nicotine (rac-26), [28] 1-(tert-butyl)-1H-imidazole (41) [29] and the 4-tertbutyl-substituted pyridine derivatives 4-(tert-butyl)-3-methylpyridine (33), 4-(tert-butyl)-3-methoxypyridine (31), 4-(tert-butyl)-3chloropyridine (28), 3-bromo-4-(tert-butyl)pyridine (29), 4-(tert-butyl)pyridine-3-carbonitrile (30), ethyl 4-(tert-butyl)pyridine-3-carboxylate (36), 4-(tert-butyl)-3-fluoropyridin-1-ium chloride (27), 4-(tertbutyl)-3-phenylpyridine (34), 4-(tert-butyl)-N,N-dimethylpyridine-3carboxamide (32), and 4-(tert-butyl)-3-ethynylpyridine (35). [30] Generalprocedures Synthesis of symmetric bispyridinium compounds by N-alkylation with 21 (GP1): 21 (1.0 equiv) was carefully added to asolution of the corresponding pyridine derivative (2.5 equiv) in CH 2 Cl 2 (0.8 mL mmol À1 )o rt ot he neat pyridine derivative (2.5 equiv) at room temperature.…”

“…This problem could, however,b eovercome using the far more reactivep ropane-1,3-diyl bis(trifluormethanesulfonate) (21). This problem could, however,b eovercome using the far more reactivep ropane-1,3-diyl bis(trifluormethanesulfonate) (21).…”

Evaluation of the Influence of Three Newly Developed Bispyridinium Anti‐nicotinic Compounds (MB408, MB442, MB444) on the Efficacy of Antidotal Treatment of Nerve Agent Poisoning in Mice

“…Among them, the direct block exerted by certain bispyridinium oximes on nAChR ion channels, which correlates with recovery of neuromuscular function in soman‐poisoned nerve–muscle preparations, was demonstrated . Based on this finding, bispyridinium non‐oximes were developed to optimize this aspect of bispyridinium action to improve recovery of neuromuscular function by a presumed non‐competitive mechanism of action . It has also been suggested that these bispyridinium non‐oximes possibly interact with nAChR subtypes as positive allosteric modulators .…”

Aplicação do conceito do par iônico e seus efeitos sobre a lipofilicidade de brometos de amônio quaternários estruturalmente análogos a procaína, com atividade de bloqueio da transmissão neuromuscular, para estudos de <i>(Q)SAR</i>

“…A atividade do receptor pode ser inibida por mecanismos não-competitivo e alostéricos (o ligante não compete com agonistas e se liga a outro sítio, que não o ativo) bem como por mecanismo competitivo (em que há competição no sítio ativo com agonistas). A inibição não competitiva e alostérica do RAChn foi observada para anestésicos locais, como a procaína e a lidocaína (Pagan et al, 2007;Rhee et al, 2015), assim como para agentes bloqueadores neuromusculares (incluindo sais de amônio quaternários, como o QX-222) (Gentry & Lukas, 2001;Heiny et al, 2010;Ring et al, 2015), que serão apresentados a seguir.…”

“…A interação entre agentes bloqueadores neuromusculares e os receptores nicotínicos, localizados na junção neuromuscular esquelética, pode ser denominada bloqueio da transmissão neuromuscular. O bloqueio da transmissão neuromuscular pode ocorrer por interrupção dos impulsos nervosos na junção neuromuscular, causando paralisia ou relaxamento dos músculos esqueléticos (Bowman, 2006;Ring et al, 2015). Estudos envolvendo a relação entre a estrutura e a atividade de agentes bloqueadores neuromusculares sugerem que tanto a presença de grupos com carga positiva bem como a lipofilicidade são características importantes que contribuem para a(s) interação (ões) com o RAChn (Siqueira, 2001;Bowman, 2006;Pagan et al, 2007;Ring et al, 2015).…”