N-n-alkylnicotinium analogs, a novel class of antagonists at α4β2* Nicotinic acetylcholine receptors: Inhibition of S(-)-nicotine-evoked 86Rb+Efflux from rat thalamic synaptosomes

Abstract

A BSTRACTPyridine N-n-alkylation of S(-)-nicotine (NIC) affords N-nalkylnicotinium analogs, previously shown to competitively inhibit [ 3 H]NIC binding and interact with a 4 b 2* nicotinic receptors (nAChRs). The present study determined the ability of the analogs to inhibit NIC-evoked 86 Rb + effl ux from rat thalamic synaptosomes to assess functional interaction with a 4 b 2* nAChRs. In a concentration-dependent manner, NIC evoked 86 Rb + effl ux (EC 50 = 170 nmol/L). Analoginduced inhibition of NIC-evoked 86 Rb + effl ux varied over a ~450-fold range. Analogs with long n -alkyl chain lengths (C 9 -C 12 ) inhibited effl ux in the low nmol/L range (IC 50 = 9-20 nmol/L), similar to dihydro-b -erythroidine (IC 50 = 19 nmol/L). Compounds with shorter n -alkyl chain lengths (C 1 -C 8 ) produced inhibition in the low m mol/L range (IC 50 = 3-12 m mol/L). C 10 and C 12 analogs completely inhibited NIC-evoked effl ux, whereas C 1-9 analogs produced maximal inhibition of only 10% to 60%. While the C 10 analog Nn -decylnicotinium iodide (NDNI) did not produce signifi cant inhibition of NIC-evoked dopamine release in previously reported studies, NDNI possesses high affi nity for [ 3 H]NIC binding sites (K i = 90 nmol/L) and is a potent and effi cacious inhibitor of NIC-evoked 86 Rb + effl ux as demonstrated in the current studies. Thus, NDNI is a competitive, selective antagonist at a 4 b 2* nAChRs.

Central Nicotinic Receptors: Structure, Function, Ligands, and Therapeutic Potential

“…[112] As a matter of fact, 54 a is a potent inhibitor of nicotine-evoked 86 Rb + efflux from rat synaptosomes. [113] Both affinity and functional activity are sensitive to structural modifications on the conformational flexibility of the alkyl chain. [114] Indeed, introduction of double or triple bonds into the octyl chain of 54 b increases the affinity for [ 3 H]nicotine binding sites and the potency in inhibiting nicotine-evoked [ 3 H]DA overflow with respect to the parent compound.…”

Lobeline esters as novel ligands for neuronal nicotinic acetylcholine receptors and neurotransmitter transporters

“…32 Lobeline ( 1 ) and lobeline tosylate ( 11 ) have been previously shown to act as potent nAChRs antagonists in the 86 Rb + efflux assay. 10 A representative aromatic carboxylic acid ester, the O -benzoyl ester of lobeline ( 2 ) and a representative aromatic sulfonic acid ester, the O -benzoyl sulfonic acid ester of lobeline ( 10 ) were both assessed in this assay for inhibition of nicotine-evoked 86 Rb + efflux from rat thalamic synaptosomes.…”

“…32 Thalamus preparations were homogenized and centrifuged at 1000×g for 10 min at 4°C. Supernatants were centrifuged at 12,000×g for 20 min at 4°C.…”

“…TTX and CsCl were included in the buffer to block voltage-gated Na + and K + channels, respectively, and to reduce the rate of basal 86 Rb + efflux. 32 Experiments determined the ability of analog (1 nM–10 μM) to inhibit 86 Rb + efflux evoked by 1 μM nicotine. The concentration of nicotine was chosen based on the results of the previous experiment.…”

Targeting Reward-Relevant Nicotinic Receptors in the Discovery of Novel Pharmacotherapeutic Agents to Treat Tobacco Dependence

“…Unfortunately, with chain lengths of C 9 -C 12 , a loss of selectivity was observed, since these compounds also exhibited significant affinity (Ki = 0.23 – 2.1 μM) for α4β2* (Wilkins, Grinevich, Ayers, Crooks, & Dwoskin, 2003). Interestingly, further increases in affinity for the α4β2* nAChR subtype were observed with N - n -alkyl chain lengths of C 13 -C 20 (unpublished data); however, none of the analogs had high affinity for the α7* subtype (Dwoskin et al, 2004; Crooks et al, 2004; Sumithran et al, 2005; Wilkins et al, 2003; Wilkins, Miller, Ayers, Crooks, & Dwoskin, 2006 and unpublished data). Importantly, these N - n -alkylnicotinium analogs exhibited high affinity for the blood-brain barrier choline transporter (Allen, Lockman, Roder, Dwoskin, & Crooks, 2003; Crooks et al, 2004).…”