Anticholinesterase induces nicotinic receptor modulation

Differential effects of TAK-802, a selective acetylcholinesterase inhibitor, and carbamate acetylcholinesterase inhibitors on contraction of the detrusor smooth muscle of the guinea pig

The aim of this study was to compare the effects of TAK-802, a novel acetylcholinesterase (AChE) inhibitor, and carbamate AChE inhibitors on the detrusor smooth muscle contractility in vitro using isometric tension measurements. The effects of drugs on the nicotine-induced contractions and basal tone of the isolated detrusor muscle of the guinea pig were examined. All of the drugs, namely, TAK-802, distigmine, neostigmine and pyridostigmine, enhanced the nicotine-induced contractions of the muscle strips in a concentration-dependent manner. On the other hand, while neostigmine and pyridostigmine markedly increased the basal tone, and distigmine slightly but significantly increased the basal tone, TAK-802 had no influence on the basal tone of the muscle strips at all. However, following co-treatment with tetraisopropyl pyrophosphoramide, a selective butyrylcholinesterase (BuChE) inhibitor, TAK-802 also did increase the basal tone. The increase of the basal tone by all of the above treatments was completely abolished by atropine. These results reveal that while all the four AChE inhibitors enhanced endogenous acetylcholine-induced contractions, their effects on the basal tone were clearly different. The effect of carbamate AChE inhibitors of increasing the basal tone could be partly attributed to their dual inhibition of both AChE and BuChE, because both cholinesterases may play a critical role in maintaining the resting tension of the urinary bladder. TAK-802, however, did not increase the basal tone of the detrusor muscle strips, probably because of its selective inhibitory effect against AChE. The effect of carbamate AChE inhibitors on the basal tone of the detrusor muscle may explain the decrease of bladder compliance observed in our previous study on guinea pigs as well as the deterioration of the bladder-storage function reported with their clinical use.

The acetylcholinesterase inhibitor BW284c51 is a potent blocker of Torpedo nicotinic AchRs incorporated into the Xenopus oocyte membrane

This work was aimed to determine if 1,5-bis(4-allyldimethylammoniumphenyl)pentan-3-one dibromide (BW284c51), the most selective acetylcholinesterase inhibitor (AchEI), affects the nicotinic acetylcholine (Ach) receptor (AchR) function. Purified Torpedo nicotinic AchRs were injected into Xenopus laevis oocytes and BW284c51 effects on Ach- and carbamylcholine (Cch)-elicited currents were assessed using the voltage-clamp technique.BW284c51 (up to 1 mM) did not evoke any change in the oocyte membrane conductance. When BW284c51 (10 pM-100 microM) and Ach were co-applied, Ach-evoked currents (I(Ach)) were reversibly inhibited in a concentration-dependent manner (Hill coefficient, 1; IC(50), 0.2-0.5 muM for 0.1-1000 microM Ach). Cch-elicited currents showed a similar inhibition by BW284c51.I(Ach) blockade by BW284c51 showed a strong voltage dependence, being only apparent at hyperpolarising potentials. BW284c51 also enhanced I(Ach) desensitisation.BW284c51 changed the Ach concentration-dependence curve of Torpedo AchR response from two-site to single-site kinetics, without noticeably affecting the EC(50) value. The BW284c51 blocking effect was highly selective for nicotinic over muscarinic receptors. BW284c51 inhibition potency was stronger than that of tacrine, and similar to that of d-tubocurarine (d-TC). Coapplication of BW284c51 with either tacrine or d-TC revealed synergistic inhibitory effects. Our results indicate that BW284c51 antagonises nicotinic AchRs in a noncompetitive way by blocking the receptor channel, and possibly by other, yet unknown, mechanisms. Therefore, besides acting as a selective AchEI, BW284c51 constitutes a powerful and reversible blocker of nicotinic AchRs that might be used as a valuable tool for understanding their function.

Novel acetylcholinesterase inhibitor as increasing agent on rhythmic bladder contractions: SAR of 8-{3-[1-(3-fluorobenzyl)piperidin-4-yl]propanoyl}-1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one (TAK-802) and related compounds

As part of an on-going investigation to develop an increasing agent on rhythmic bladder contractions, 1-aryl-3-(1-benzylpiperidin-4-yl)propanones were synthesized and examined as noncarbamate acetylcholinesterase (AChE) inhibitors. Among compounds with various aryl groups, 1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one derivative 9c was found to possess a potent AChE inhibition activity with an IC(50) value of 1.3nM. The compound 9c increased rhythmic bladder contractions in Guinea pigs and rats without affecting the basal intravesical pressure, which suggests that 9c may be useful for the treatment of voiding dysfunction caused by detrusor underactivity.

Effects of TAK-802, a novel acetylcholinesterase inhibitor, and various cholinomimetics on the urodynamic characteristics in anesthetized guinea pigs

In the present study, we investigated the effects of cholinomimetic drugs on the urodynamic characteristics in anesthetized guinea pigs. 8-[3-[1-[(3-fluorophenyl)methyl]-4-piperidinyl]-1-oxopropyl]-1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one (TAK-802), a novel acetylcholinesterase inhibitor, (0.003-0.03 mg/kg, i.v.) increased the voided volume and the maximum flow rate without affecting either the intravesical pressure or the bladder compliance. Distigmine (0.03-0.3 mg/kg, i.v.) and neostigmine (0.01-0.1 mg/kg, i.v.), both carbamate acetylcholinesterase inhibitors, while not increasing the maximum flow rate, increased the intravesical pressure at the maximum flow rate. They also decreased the bladder compliance. Bethanechol (0.1-1 mg/kg, i.v.), a muscarinic receptor agonist, decreased the voided volume and the bladder compliance but did not affect the maximum flow rate. TAK-802 did not affect the intraurethral pressure at doses of up to 0.03 mg/kg in anesthetized guinea pigs. Distigmine increased the intraurethral pressure when administered at the dose of 0.3 mg/kg, and the effect was completely abolished by pretreatment with d-tubocurarine. These results suggest that TAK-802 reinforces the bladder-voiding functions by increasing the bladder contractility without decreasing the storage function. On the other hand, carbamate acetylcholinesterase inhibitors not only deteriorate the voiding function by inducing contraction of the external urethral sphincter muscle, resulting in increasing the urethral resistance, but also cause deterioration of the storage function. Bethanechol obviously decreased the bladder capacity, possibly due to a direct contractile effect on the detrusor smooth muscle. TAK-802 may therefore be a more useful drug than either carbamate acetylcholinesterase inhibitors or muscarinic receptor agonists in the treatment of voiding dysfunction associated with impaired detrusor contractility.

Effects of TAK-802, a novel acetylcholinesterase inhibitor, on distension-induced rhythmic bladder contractions in rats and guinea pigs

In the present study, we investigated the effects of 8-[3-[1-[(3-fluorophenyl)methyl]-4-piperidinyl]-1-oxopropyl]-1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one (TAK-802), a novel acetylcholinesterase inhibitor, on distension-induced rhythmic bladder contractions in urethane-anesthetized rats and guinea pigs. TAK-802 potently inhibited human-erythrocyte-derived acetylcholinesterase activity with an IC(50) value of 1.5 nM, which represented a potency 30 and 250 times greater than that of the two carbamate acetylcholinesterase inhibitors, neostigimine and distigmine, respectively. Unlike the carbamate acetylcholinesterase inhibitors, TAK-802 exhibits high selectivity for acetylcholinesterase inhibition over butyrylcholinesterase inhibition. In an assay conducted to measure the muscarinic and nicotinic actions, TAK-802 was found to exhibit higher selectivity for muscarinic actions over nicotinic actions in comparison to distigmine. Both TAK-802 and distigmine increased isovolumetric bladder contractions in rats and guinea pigs in a dose-dependent manner, with a minimum effective dose (MED) of 0.01 and 0.03 mg/kg i.v., respectively, in rats, and 0.01 and 0.1 mg/kg i.v., respectively, in guinea pigs. The effects of both the drugs were completely abolished by atropine. These results suggest that TAK-802 and other acetylcholinesterase inhibitors can effectively increase reflex bladder contractions by increasing the efficacy of acetylcholine released by nerve impulses. On the other hand, bethanechol, a muscarinic agonist, markedly changed the pattern of distension-induced bladder contractions when administered at the dose of 1 mg/kg i.v., and it did not necessarily augment well-coordinated bladder contractions. Thus, considering that it has some selectivity for muscarinic action, TAK-802 might be expected to be useful in the treatment of voiding dysfunction caused by impaired detrusor contractility.

Localization of agonist and competitive antagonist binding sites on nicotinic acetylcholine receptors

Identification of all residues involved in the recognition and binding of cholinergic ligands (e.g. agonists, competitive antagonists, and noncompetitive agonists) is a primary objective to understand which structural components are related to the physiological function of the nicotinic acetylcholine receptor (AChR). The picture for the localization of the agonist/competitive antagonist binding sites is now clearer in the light of newer and better experimental evidence. These sites are located mainly on both alpha subunits in a pocket approximately 30-35 A above the surface membrane. Since both alpha subunits are identical, the observed high and low affinity for different ligands on the receptor is conditioned by the interaction of the alpha subunit with other non-alpha subunits. This molecular interaction takes place at the interface formed by the different subunits. For example, the high-affinity acetylcholine (ACh) binding site of the muscle-type AChR is located on the alphadelta subunit interface, whereas the low-affinity ACh binding site is located on the alphagamma subunit interface. Regarding homomeric AChRs (e.g. alpha7, alpha8, and alpha9), up to five binding sites may be located on the alphaalpha subunit interfaces. From the point of view of subunit arrangement, the gamma subunit is in between both alpha subunits and the delta subunit follows the alpha aligned in a clockwise manner from the gamma. Although some competitive antagonists such as lophotoxin and alpha-bungarotoxin bind to the same high- and low-affinity sites as ACh, other cholinergic drugs may bind with opposite specificity. For instance, the location of the high- and the low-affinity binding site for curare-related drugs as well as for agonists such as the alkaloid nicotine and the potent analgesic epibatidine (only when the AChR is in the desensitized state) is determined by the alphagamma and the alphadelta subunit interface, respectively. The case of alpha-conotoxins (alpha-CoTxs) is unique since each alpha-CoTx from different species is recognized by a specific AChR type. In addition, the specificity of alpha-CoTxs for each subunit interface is species-dependent. In general terms we may state that both alpha subunits carry the principal component for the agonist/competitive antagonist binding sites, whereas the non-alpha subunits bear the complementary component. Concerning homomeric AChRs, both the principal and the complementary component exist on the alpha subunit. The principal component on the muscle-type AChR involves three loops-forming binding domains (loops A-C). Loop A (from mouse sequence) is mainly formed by residue Y(93), loop B is molded by amino acids W(149), Y(152), and probably G(153), while loop C is shaped by residues Y(190), C(192), C(193), and Y(198). The complementary component corresponding to each non-alpha subunit probably contributes with at least four loops. More specifically, the loops at the gamma subunit are: loop D which is formed by residue K(34), loop E that is designed by W(55) and E(57), loop F which is built by a stretch of amino acids comprising L(109), S(111), C(115), I(116), and Y(117), and finally loop G that is shaped by F(172) and by the negatively-charged amino acids D(174) and E(183). The complementary component on the delta subunit, which corresponds to the high-affinity ACh binding site, is formed by homologous loops. Regarding alpha-neurotoxins, several snake and alpha-CoTxs bear specific residues that are energetically coupled with their corresponding pairs on the AChR binding site. The principal component for snake alpha-neurotoxins is located on the residue sequence alpha1W(184)-D(200), which includes loop C. In addition, amino acid sequence 55-74 from the alpha1 subunit (which includes loop E), and residues gammaL(119) (close to loop F) and gammaE(176) (close to loop G) at the low-affinity binding site, or deltaL(121) (close to the homologous region of loop G) at the high-affinity binding site, are i