M1-selective Antagonist Research Articles

Urothelial/Lamina Propria Spontaneous Activity and the Role of M3 Muscarinic Receptors in Mediating Rate Responses to Stretch and Carbachol

To investigate the effects of tissue stretch and muscarinic receptor stimulation on the spontaneous activity of the urothelium/lamina propria and identify the specific receptor subtype mediating these responses. Isolated strips of porcine urothelium with lamina propria were set up for in vitro recording of contractile activity. Muscarinic receptor subtype-selective antagonists were used to identify the receptors influencing the contractile rate responses to stretch and stimulation with carbachol. Isolated strips of urothelium with lamina propria developed spontaneous contractions (3.7 cycles/min) that were unaffected by tetrodotoxin, Nω-nitro-L-arginine, or indomethacin. Carbachol (1 μM) increased the spontaneous contractile rate of these tissue strips by 122% ± 27% (P < .001). These responses were significantly depressed in the presence of the M3-selective muscarinic antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (10-30 nM) but were not affected by the M1-selective antagonist pirenzepine (30-100 nM) or the M2-selective antagonist methoctramine (0.1-1 μM). Stretching of the tissue also caused an increase in the spontaneous contractile rate, and these responses were abolished by atropine (1 μM) and low concentrations of 4-diphenylacetoxy-N-methylpiperidine methiodide (10 nM). Darifenacin, oxybutynin, tolterodine, and solifenacin (1 μM) all significantly depressed the frequency responses to carbachol (1 μM). The urothelium with the lamina propria exhibits a spontaneous contractile activity that is increased during stretch. The mechanism appears to involve endogenous acetylcholine release acting on M3 muscarinic receptors. Anticholinergic drugs used clinically depress the responses of these tissues, and this mechanism might represent an additional site of action for these drugs in the treatment of bladder overactivity.

Systematic review of overactive bladder therapy in females

Although the prevalence of overactive bladder (OAB) is similar in both male and female populations, females have a greater tendency to seek medical advice regarding their symptoms. A review of the evidence of therapy among women shows that a variety of modalities has been shown to be effective for symptom improvement in women with OAB. Bladder retraining/re-education should be considered for all women with OAB. With respect to first-line pharmacotherapy with antimuscarinic agents, the development of extended release preparations, bladder selective M3 antagonists and alternative routes of delivery, have improved compliance and persistence. Other pharmacotherapeutic options with potential for providing benefit include antidepressants, vasopressin analogues, alpha-adrenoceptor antagonists and beta-adrenoceptor agonists. There are also a number of newer agents currently being investigated, including calcium channel blocking agents, potassium channel opening drugs, beta agonists and neurokinin receptor antagonists. Intravesical injections of botulinum toxin may be an alternative, while surgery can be considered for truly intractable cases.

Muscarinic receptor subtypes and signalling involved in the attenuation of isoprenaline-induced rat urinary bladder relaxation

β-Adrenoceptors are important mediators of smooth muscle relaxation in the urinary bladder, but the concomitant presence of a muscarinic agonist, e.g., carbachol, can attenuate relaxation responses by reducing potency and/or efficacy of β-adrenoceptor agonists such as isoprenaline. Therefore, the present study was designed to explore the subtypes and signalling pathways of muscarinic receptors involved in the attenuation of isoprenaline-induced isolated rat detrusor preparations using novel subtype-selective receptor ligands. In radioligand binding studies, we characterized BZI to be a M3-sparing muscarinic agonist, providing selective M2 stimulation in rat bladder, and THRX-182087 as a highly M2-selective antagonist. The use of BZI and of THRX-182087 in the presence of carbachol enabled experimental conditions with a selective stimulation of only M2 or M3 receptors, respectively. Confirming previous findings, carbachol attenuated isoprenaline-induced detrusor relaxation. M2-selective stimulation partly mimicked this attenuation, indicating that both M2 and M3 receptors are involved. During M3-selective stimulation, the attenuation of isoprenaline responses was reduced by the phospholipase C inhibitor U 73,122 but not by the protein kinase C inhibitor chelerythrine. We conclude that both M2 and M3 receptors contribute to attenuation of β-adrenoceptor-mediated relaxation of rat urinary bladder; the signal transduction pathway involved in the M3 component of this attenuation differs from that mediating direct contractile effects of M3 receptors.

GRK5 Deficiency Accelerates β-Amyloid Accumulation in Tg2576 Mice via Impaired Cholinergic Activity

Membrane G protein-coupled receptor kinase 5 (GRK5) deficiency is linked to Alzheimer disease, yet its precise roles in the disease pathogenesis remain to be delineated. We have previously demonstrated that GRK5 deficiency selectively impairs desensitization of presynaptic M2 autoreceptors, which causes presynaptic M2 hyperactivity and inhibits acetylcholine release. Here we report that inactivation of one copy of Grk5 gene in transgenic mice overexpressing β-amyloid precursor protein (APP) carrying Swedish mutations (Tg2576 or APPsw) resulted in significantly increased β-amyloid (Aβ) accumulation, including increased Aβ(+) plaque burdens and soluble Aβ in brain lysates and interstitial fluid (ISF). In addition, secreted β-APP fragment (sAPPβ) also increased, whereas full-length APP level did not change, suggesting an alteration in favor of β-amyloidogenic APP processing in these animals. Reversely, perfusion of methoctramine, a selective M2 antagonist, fully corrected the difference between the control and GRK5-deficient APPsw mice for ISF Aβ. In contrast, a cholinesterase inhibitor, eserine, although significantly decreasing the ISF Aβ in both control and GRK5-deficient APPsw mice, failed to correct the difference between them. However, combining eserine with methoctramine additively reduced the ISF Aβ further in both animals. Altogether, these findings indicate that GRK5 deficiency accelerates β-amyloidogenic APP processing and Aβ accumulation in APPsw mice via impaired cholinergic activity and that presynaptic M2 hyperactivity is the specific target for eliminating the pathologic impact of GRK5 deficiency. Moreover, a combination of an M2 antagonist and a cholinesterase inhibitor may reach the maximal disease-modifying effect for both amyloid pathology and cholinergic dysfunction.

200 THE EFFECT OF KNOCK OUT OF UROTHELIAL M 3 RECEPTORS ON MOUSE BLADDER CONTRACTILITY

You have accessJournal of UrologyBladder and Urethra: Anatomy, Physiology and Pharmacology I1 Apr 2010200 THE EFFECT OF KNOCK OUT OF UROTHELIAL M3 RECEPTORS ON MOUSE BLADDER CONTRACTILITY Alan Braverman, Yael Kreitman, and Michael Ruggieri Alan BravermanAlan Braverman More articles by this author , Yael KreitmanYael Kreitman More articles by this author , and Michael RuggieriMichael Ruggieri More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.256AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Our previous studies demonstrate that outlet obstruction in the rat results in increased urothelial muscarinic receptors density. Urothelial muscarinic receptors activate calcium transients and modulate ATP and NO release which may act on afferent nerves to alter voiding frequency. The aim of the present study was to determine the effect of urothelial-specific M3 knock out on bladder contractility. METHODS Urothelial specific M3 KO mice were developed by breeding floxed M3 receptor mice with mice expressing cre-recombinase downstream from the uroplakin II promoter. Cumulative carbachol concentration effect curves were generated with and without darifenacin. In-vivo cystometry was performed with vehicle or antagonist infused at a rate of 1 ml/h through a suprapubic tube. RESULTS There is no difference between urothelium intact wild type (n=14) and uroM3 KO (n=6) bladder strips in the carbachol maximal or the KCl induced contraction. However, carbachol potency is significantly greater (p<0.05) in urothelium intact uroM3 KO than in wild type bladder strips (0.99 vs. 3.6 μM respectively at the 30% of KCl effect level). Carbachol potency is reduced following urothelium removal from uroM3 KO animals, but not wild type bladders. The M3 selective antagonist darifenacin is highly potent (pKb=9.2) in urothelium intact uroM3 KO mice bladder strips, consistent with M3 receptors mediating contraction (Figure 1). Darifenacin is not as potent in attenuating the maximal contraction with the urothelium removed. Micturition pressure is higher in uroM3 KO animals (33±10 cmH20) than in wild type animals (24±7 cmH20) but this difference is not statistically significant. 4-DAMP is significantly more potent (p<0.05) in reducing micturition pressure in wild type than uroM3 KO animals (Figure 2). CONCLUSIONS Urothelial muscarinic receptors modulate bladder contractility. Urothelial M3 receptors may mediate a negative feedback that reduces carbachol potency in-vitro and possibly micturition pressure in-vivo. Philadelphia, PA© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e79 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Alan Braverman More articles by this author Yael Kreitman More articles by this author Michael Ruggieri More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

A novel derivative of xanomeline improves fear cognition in aged mice

The M1/M4 muscarinic acetylcholine receptor agonist xanomeline can significantly improve the cognitive function, but the intolerable side effects limit its clinical usefulness. Our recent study has reported a novel derivative of xanomeline, 3-[3-(3-(3-florophenyl)-2-propyn-1-ylthio)-1,2,5-thiadiazol-4-yl]-1,2,5,6-tetrahydro-1-methylpyridine oxalate (EUK1001), exhibited higher affinity of mAChRs and less side effects relative to xanomeline. In the present study, we further utilized behavioral and electrophysiological techniques to investigate the effects of EUK1001 on fear cognition and hippocampal long-term potentiation (LTP) in aged mice. Behavioral testing showed that 0.1, 0.5 or 1.0 mg/kg EUK1001 group, like 1.0 mg/kg xanomeline group, exhibited better performance in contextual fear conditioning and passive avoidance test than vehicle-controls. In the cued fear conditioning test, just 0.5 or 1.0, but not 0.1 mg/kg EUK1001, significantly enhanced the levels of freezing response. In addition, theta-burst stimulation (TBS) induced the significant larger hippocampal LTP in brain slices perfused with artificial cerebrospinal fluid (ACSF) containing 0.01 μM EUK1001 or in brain slices from aged mice injected intraperitoneally (i.p.) with EUK1001. This enhancing effect was blocked by 0.25 μM pirenzepine, a selective M1 antagonist. Together, these results show that EUK1001 can enhance fear cognition and synaptic plasticity via the activation of M1 muscarinic acetylcholine receptors. Thus, EUK1001 may possibly represent a promising lead compound for the treatment of Alzheimer's disease and age-related cognitive deficits.

Inhibition of field stimulation-induced contractions of rabbit vas deferens by muscarinic receptor agonists: selectivity of McN-A-343 for M1 receptors.

Inhibition of the field stimulation-induced twitch responses of the rabbit vas deferens by the muscarinic receptor agonist, McN-A-343, has been attributed to presynaptic muscarinic receptors of the M1 subtype located on noradrenergic nerve terminals. Stimulation of these receptors causes inhibition of transmitter release and inhibition of the contractile response. However, the selectivity of McN-A-343 for M1 receptors has been questioned and this throws doubt on whether the prejunctional receptors of the rabbit vas deferens are of the M1 subtype. In this study we have undertaken a comprehensive re-evaluation of the inhibition of prostatic and epididymal portions of the rabbit isolated field-stimulated vas deferens by several agonists, including McN-A-343, and quantified the antagonism by M1-selective antagonists, pirenzepine and telenzepine. Prostatic and epididymal portions of vasa deferentia from New Zealand White rabbits were immersed in a low Ca2+ Krebs solution at 32+/-0.5 degrees C gassed with 5% CO2 in oxygen. Yohimbine (1.0mM) was present throughout to block prejunctional alpha2-adrenoceptors. Field stimulation was applied by repeated application of single pulses (30 V, 0.05 Hz, 0.5 ms) and isometric contractions recorded. Carbachol and oxotremorine initially potentiated the epididymal contractions but at higher concentrations there was inhibition. In the prostatic portion, oxotremorine only inhibited. McN-A-343 produced inhibitory responses only in both epididymal and prostatic portions. Pirenzepine shifted the concentration-response curves forthe inhibitory responses to oxotremorine to the right. However, the potentiation of the twitches also became more apparent with the lower concentrations of oxotremorine. Schild plots for the antagonism by pirenzepine yielded pA2 values of 7.96+/-0.004 and 7.7+/-0.02 for the epididymal and prostatic portions, respectively. The concentration-response curves for the inhibition of twitches by McN-A-343 were displaced to the right in a parallel manner by pirenzepine in both prostatic and epididymal portions with no potentiation of the twitches. The Schild plot for this antagonism generated pA2 values of 7.68+/-0.01 and 8.07+/-0.01, respectively. Telenzepine caused parallel shifts of the McN-A-343 concentration-response curves to the right in prostatic portions, the pA2 value being 8.70+/-0.13. Telenzepine (10(-7) M) abolished the inhibitory effect of carbachol to reveal only concentration-dependent potentiation of the contractions. The Schild plot for antagonism of this contractile effect yielded a pA2 value (7.07+/-0.09) that was significantly less by almost two orders of magnitude (1.70) than the value for the antagonism by telenzepine of the McN-A-343-induced inhibitory response. The pA2 values of pirenzepine and telenzepine against the inhibitory responses of the rabbit vas deferens are consistent with the involvement of M1 receptors. This leads to the conclusion that McN-A-343 causes inhibition through this receptor type. The doubts concerning the selectivity of McN-A-343 for M1 receptors are therefore unfounded. The fact that McN-A-343 does not display a selective binding profile suggests that its selectivity does not arise from affinity differences but probably resides in its intrinsic efficacy.

Differential Roles of M2 and M3 Muscarinic Receptor Subtypes in Modulation of Bladder Afferent Activity in Rats

To investigate the effects of various muscarinic acetylcholine receptor (mAChR) antagonists, including selective M2 and M3 mAChR antagonists, on bladder overactivity. It has been proposed that the urothelium modulates the activity of bladder afferent pathways. However, the differential roles of mAChR subtypes in local bladder afferent activation remain unclear. Cystometry was performed in urethane-anesthetized female rats. We examined the effects of intravesical administration of antimuscarinic agents (nonselective mAChR antagonists: atropine sulfate, tolterodine tartrate, and propiverine hydrochloride; M2-selective antagonists: dimethindene maleate and methoctramine hemihydrate; M3-selective antagonists: darifenacin hydrobromide and 4-DAMP) on bladder overactivity induced by oxotremorine-M (oxo-M; nonselective mAChR agonist). Intravesical administration of oxo-M (200 microM) elicited bladder overactivity as evidenced by decreased intercontraction interval, bladder capacity, and pressure threshold. These effects were blocked by intravesical administration of nonselective or M2-selective antagonists (30-60 microM), whereas M3-selective antagonists (150 microM) did not suppress the overactivity. When instilled intravesically by itself, none of the antimuscarinic agents (nonselective, M2-selective or M3-selective antagonists) affected any cystometric parameters. The M2 mAChR subtype plays an important role in the local cholinergic modulation of bladder afferent activity that contributes to bladder overactivity in normal rats. Therefore, it is expected that antimuscarinic agents that have antagonistic activity against M2 mAChR can be more beneficial for the treatment of patients with overactive bladder if enhanced acetylcholine mechanisms are involved in pathogenesis of overactive bladder.

Synthesis and radiosynthesis of N5‐[18F]fluoroethyl‐Pirenzepine and its metabolite N5‐[18F]fluoroethyl‐LS 75

AbstractThe well established M1 selective muscarinergic antagonist Pirenzepine 11‐[2‐(4‐methyl‐piperazin‐1‐yl)‐acetyl]‐5,11‐dihydro‐benzo[e]pyrido[3,2‐b][1,4]diazepin‐6‐one (1) exhibits an unusual behaviour in vivo, which cannot be explained with M1 antagonism exclusively. One of the aspects discussed is a specific interaction with poly ADP‐ribose polymerase (PARP‐1). 1 undergoes metabolism to form LS 75 5,11‐dihydro‐benzo[e]pyrido[3,2‐b][1,4]diazepin‐6‐one (2). In order to study deviations in Pirenzepine efficacy from pure M1 binding in vivo using PET, appropriate positron emitter labelled analogues of 1 and 2 were synthesised. Non‐radioactive reference compounds 3 and 4 were tested for PARP‐1 inhibition. The n‐octanol–water partition coefficients of compounds 1, 2, 3 and 4 at pH 7.4 (logD7.4) were determined. Both, 3 and 4 were labelled with 18F via 2‐[18F]fluoroalkylation in position 5 of the benzodiazepinone moiety to obtain N5‐[18F]fluoroethyl Pirenzepine [18F]‐3 and N5‐[18F]fluoroethyl LS 75 [18F]‐4. Radiotracers [18F]‐3 and [18F]‐4 were obtained in radiochemical yields of 15±4 % and 30±5% after 120 and 110 min, respectively. Metabolism of both compounds was investigated in vitro in human and rat plasma, respectively. Compound 3 did not show activity as an inhibitor of PARP‐1. Contrary, 4 displays moderate PARP‐1 inhibition potency. The new radiotracer [18F]‐4 can be applied for molecular imaging using autoradiography and PET. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Discovery and Development of a Potent and Highly Selective Small Molecule Muscarinic Acetylcholine Receptor Subtype I (mAChR 1 or M1) Antagonist In Vitro and In Vivo Probe

This article describes the discovery and development of the first highly selective, small molecule antagonist of the muscarinic acetylcholine receptor subtype I (mAChR1 or M(1)). An M(1) functional, cell-based calcium-mobilization assay identified three distinct chemical series with initial selectivity for M(1) versus M(4). An iterative parallel synthesis approach was employed to optimize all three series in parallel, which led to the development of novel microwave-assisted chemistry and provided important take home lessons for probe development projects. Ultimately, this effort produced VU0255035, a potent (IC(50) = 130 nM) and selective (>75-fold vs. M(2)-M(5) and > 10 microM vs. a panel of 75 GPCRs, ion channels and transporters) small molecule M(1) antagonist. Further profiling demonstrated that VU0255035 was centrally penetrant (Brain(AUC)/Plasma(AUC) of 0.48) and active in vivo, rendering it acceptable as both an in vitro and in vivo MLSCN/ MLPCN probe molecule for studying and dissecting M(1) function.

Medicinal chemistry and therapeutic potential of muscarinic M3 antagonists

Muscarinic acetylcholine receptors belong to the G-protein-coupled receptors family. Currently five different receptor subtypes have been identified and cloned. M3 receptor subtypes are coupled to G(q) family proteins and increase phosphatidyl inositol hydrolysis and calcium release from internal stores. They are widely distributed both in the central nervous system and in the periphery. At the central level, M3 receptor subtypes are involved in modulation of neurotransmitter release, temperature homeostasis, and food intake, while in the periphery they induce smooth muscle contraction, gland secretion, indirect relaxation of vascular smooth muscle, and miosis. The main therapeutic applications of M3 antagonists include overactive bladder (OAB), chronic obstructive pulmonary disease (COPD), and pain-predominant irritable bowel syndrome (IBS). The introduction of selective M3 antagonists has not improved clinical efficacy compared with the old non-selective antimuscarinics but has reduced the rate of adverse events mediated by the blockade of cardiac M2 receptors (tachycardia) and central M1 receptors (cognitive impairment). Improved tolerability has been obtained also with controlled release or with inhaled formulations. However, there is still a need for safer M3 antagonists for the treatment of COPD and better-tolerated and more effective compounds for the therapy of OAB. New selective muscarinic M3 antagonists currently in early discovery and under development have been designed to address these issues. However, as M3 receptors are widely located in various tissues including salivary glands, gut smooth muscles, iris, and ciliary muscles, further clinical improvements may derive from the discovery and the development of new compounds with tissue rather than muscarinic receptor subtype selectivity.

MAOS protocols for the general synthesis and lead optimization of 3,6-disubstituted-[1,2,4]triazolo[4,3- b]pyridazines

General, high-yielding MAOS protocols for the expedient synthesis of functionalized 3,6-disubstituted-[1,2,4]triazolo[4,3- b]pyridazines are described amenable to an iterative analog library synthesis strategy for the lead optimization of an M1 antagonist screening hit. Optimized compounds proved to be highly selective M1 antagonists.

Antagonist of M1 Muscarinic Acetylcholine Receptor Prevents Neurotoxicity Induced by Amphetamine via Nitric Oxide Pathway

The psychostimulant amphetamine (AMPH) has been found to induce striatal acetylcholine release and neurotoxic processes via nitric oxide (NO) and lipid peroxidation (LPO). Our purpose was to determine whether blocking striatal muscarinic (M1) receptors by the selective M1 antagonist toxin 7 (MT 7; bilaterally, 2 microg per side) might attenuate the effects of AMPH (4 x 5 mg/kg, i.p.). Systemic AMPH administration increased NO and LPO in the striatal tissue. Stimulation of M1 receptors by i.c.v. injection of M1 agonist McN-A-343 (200 microg) caused a similar enhancement of NO and LPO. Pretreatment with the MT7 prevented the AMPH-induced NO generation and greatly reduced the LPO caused by the psychostimulant. These results show that M1 acetylcholine receptors are critically involved in neurotoxic processes induced by AMPH via NO and LPO.

Activated Cholinergic Signaling Provides a Target in Squamous Cell Lung Carcinoma

The binding of exogenous nicotine to nicotinic acetylcholine (ACh) receptors (nAChR) and the binding of endogenous ACh to both nAChR and muscarinic ACh receptors (mAChR) stimulate growth of both small cell and non-small cell lung carcinomas. Understanding how cholinergic signaling is up-regulated in lung cancer may suggest new therapeutic approaches. Analysis of 28 squamous cell lung carcinomas (SCC) showed increased levels of alpha5 and beta3 nAChR mRNA and increased levels of ACh associated with increased levels of choline acetyltransferase mRNA and decreased cholinesterase mRNAs. Lynx1, an allosteric inhibitor of nAChR activity, was also decreased in SCC. Thus, cholinergic signaling is broadly increased in SCC caused by increased levels of receptors, increased levels of ligands, and decreased levels of receptor inhibitors. Partially explaining the cholinergic up-regulation seen in SCC, incubation of the H520 SCC cell line with nicotine increased levels of ACh secretion, increased expression of nAChR, and, as measured by electrophysiologic recording, increased activity of the expressed nAChR. Consistent with these effects, nicotine stimulated proliferation of H520 cells. One approach to blocking proliferative effects of nicotine and ACh on growth of lung cancers may be through M3 mAChR antagonists, which can limit the activation of mitogen-activated protein kinase that is caused by both nicotinic and muscarinic signaling. This was tested with the M3-selective muscarinic antagonist darifenacin. Darifenacin blocked nicotine-stimulated H520 growth in vitro and also blocked H520 growth in nude mice in vivo. Thus, cholinergic signaling is broadly up-regulated in SCC and blocking cholinergic signaling can limit basal and nicotine-stimulated growth of SCC.

Two-year multicenter, randomized, double-masked, placebo-controlled, parallel safety and efficacy study of 2% pirenzepine ophthalmic gel in children with myopia

To evaluate if the safety and efficacy of the relatively selective M1-antagonist, pirenzepine, in slowing the progression of myopia in children is sustained over a 2-year period. This was a multicenter, parallel-group, placebo-controlled, double-masked, randomized clinical trial. Enrolled were children aged 8 to 12 years, with entry spherical equivalent refractive error of -0.75 to -4.00 D and astigmatism </=1.00 D. Patients were randomized in a 2:1 ratio to receive 2% pirenzepine ophthalmic gel or a placebo control (vehicle), twice daily to each eye. The main outcome measure was spherical equivalent refractive error via cycloplegic autorefraction. At study entry, spherical equivalent was -2.10 +/- 0.90 D (mean +/- SD) for the pirenzepine group (n = 117) and -1.93 +/- 0.83 D for the placebo group (n = 57; p = 0.22). At 1 year, there was a mean increase in myopia of 0.26 D in the pirenzepine group versus 0.53 D in the placebo group (p < 0.001). Eighty-four patients elected to continue for a second year (pirenzepine = 53, placebo = 31). At 2 years, the mean increase in myopia was 0.58 D for the pirenzepine group and 0.99 D for the placebo group (p = 0.008). Thirteen (11%) pirenzepine patients dropped out due to adverse effects in the first year, and 1 did so in the second year. Pirenzepine ophthalmic gel 2% was effective compared with placebo in slowing the progression of myopia over a 2-year treatment period and demonstrated a clinically acceptable safety profile.

Neuroprotection of muscarinic receptor agonist pilocarpine against glutamate-induced apoptosis in retinal neurons.

Neuroprotection offers potential as an alternative therapy for glaucoma. Pilocarpine, as a typical muscarinic receptor agonist, remains among the major intraocular pressure lowering drugs for the conventional treatment of glaucoma. However, whether pilocarpine also possesses neuroprotection against glutamate cytotoxicity in retinal neurons is still unknown. In rat primary retinal cultures, identification of neuron, cell viability, apoptosis, intracellular Ca(2+) concentration, mitochondrial membrane potential, gene expression were studied by immunofluorescence, MTT, High Content Scanning, confocal microscopy, reverse-transcription PCR, and western blot analysis, respectively. Pretreatment of pilocarpine could prevent glutamate-induced neuron death, which was blocked by the non-selective antagonist atropine and the M1-selective muscarinic receptor antagonist pirenzepine. The antiapoptotic effect of pilocarpine was associated with maintaining calcium homeostasis, recovering mitochondrial membrane potential, and regulating the expression of Bcl-2 and Caspase-3. These studies demonstrated that pilocarpine had effective protection against glutamate-induced neuronal apoptosis through M1 muscarinic receptor. The results may provide an insight into the new mechanism of glaucoma therapy that pilocarpine may potentially act as a retinal neuroprotectant.

The Spinal Muscarinic M1 Receptors and GABAA Receptors Contribute to the McN-A-343–Induced Antinociceptive Effects During Thermal Stimulation of Mice

The present study was undertaken to clarify how spinal muscarinic receptors are involved in the antinociceptive effects in thermal stimulation. Intrathecal (i.t.) injection of the muscarinic agonist McN-A-343 inhibited the tail-flick response to noxious thermal stimulation in a dose-dependent manner (31.5 – 63.0 nmol). This McN-A-343–induced antinociceptive effect was dose-dependently inhibited by intrathecal (i.t.) injection of a nonselective muscarinic receptor antagonist atropine, the selective muscarinic M1 antagonist pirenzepine, or the M4 antagonist himbacine. The inhibition of pirenzepine was greater than that of himbacine. In contrast, the selective muscarinic M2 antagonist methoctramine did not inhibit the antinociceptive effects of McN-A-343. In addition, the McN-A-343–induced antinociceptive effect was attenuated by i.t. injection of the GABAA antagonist bicuculline, but not by injection of the GABAB antagonist CGP35348. These results suggest that McN-A-343 produces its antinociceptive effect on the response to thermal stimulation via spinal muscarinic M1 receptors and, at least in part, through neuronal pathways involving spinal GABAA receptors in mice.

Cholinergic Regulation of Orexin/Hypocretin Neurons Through M3Muscarinic Receptor in Mice

The cholinergic system plays an important role in regulation of arousal and REM sleep. In the present study, we showed that a muscarinic receptor agonist, carbachol (CCh), activates almost 20% of orexin-producing neurons (orexin neurons), which play a critical role in maintenance of arousal. We also found that a very small population of orexin neurons (1%) was inhibited by CCh. Muscarinic receptor antagonists inhibited the CCh-induced activation of orexin neurons in a dose-dependent manner. The M3-selective muscarinic receptor antagonist 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP) affected the response at a significantly lower concentration compared with the M1-selective muscarinic antagonist pirenzepine. IC50of 4-DAMP and pirenzepine was 0.30 ± 0.15 and 59.9 ± 18.6 nM, respectively. The CCh-induced inward current was attenuated by the nonselective cation channel blocker SKF96365. These results indicate that CCh activates 20% of orexin neurons through the M3muscarinic receptor and subsequent activation of nonselective cation channels.

Long-term darifenacin treatment for overactive bladder in patients aged 65 years and older: analysis of results from a 2-year, open-label extension study

ABSTRACTObjectives: This analysis evaluated the long-term safety, tolerability and efficacy of darifenacin, a muscarinic M3 selective receptor antagonist, in the treatment of overactive bladder (OAB) in patients ≥ 65 years of age.Methods: Patients who completed one of two 12-week, placebo-controlled, double-blind, feeder studies received once-daily (o.d.) treatment with darifenacin 7.5 mg for the first 2 weeks of the 2-year, open-label extension study. The dose could be subsequently adjusted (7.5 or 15 mg o.d.) according to need. Safety and tolerability were assessed, and efficacy variables/endpoints were evaluated from patient diary data.Results: 214 patients (65–89 years) entered and 137 (64.0%) completed the 2-year extension study, amounting to 308 patient-years’ drug exposure. Darifenacin was well tolerated with no new safety concerns. The most common adverse events (AEs) were dry mouth and constipation, which infrequently resulted in discontinuation (2.3% and 4.2%, respectively). Darifenacin produced significant improvements in OAB symptoms that were maintained over the 2-year period (median reduction from feeder-study baseline to 2 years: –11.0 [–83.7%] for incontinence episodes/week and –1.2 [–12.4%] for micturitions/day, both p < 0.05), with 44.4% patients achieving ≥ 90% reduction in incontinence episodes at 2 years.Conclusions: Darifenacin demonstrated good tolerability and safety in older patients with OAB. The improvement in OAB symptoms was sustained throughout the 2-year extension, resulting in high treatment persistence rates. Results were comparable with those in the overall OAB population from this study, indicating that darifenacin treatment is effective and well tolerated irrespective of age.

Effect of acute and chronic acid suppression on plasma gastrin release in the rat.

The mechanisms by which administration of the H+,K(+)-ATPase inhibitor B 831-78 or intragastric perfusion with NaHCO3 induces plasma gastrin release were studied in the rat. Experiments were performed after a washout of residual intragastric contents in fasted animals provided with chronic gastric fistulae. Acute and chronic administration of B 831-78 elevated plasma gastrin dose-dependently up to 5-6 times above control levels, while the increase was only twofold with intragastric NaHCO3 infusion despite similar neutralization of gastric acidity. The profound hypergastrinaemia induced by the H+,K(+)-ATPase inhibitor, after both acute and chronic treatment, was completely prevented or reversed by intragastric perfusion with physiological amounts of acid (0.15 N HCl, 2.5 ml/h). The hypergastrinaemia was, however, largely resistant to high doses of atropine (4.3 mumol/kg) and of the M1 selective muscarinic antagonist telenzepine (10 mumol/kg). In contrast, the modest increase in plasma gastrin induced by gastric perfusion with NaHCO3 was completely suppressed by the high atropine dose and was attenuated by small doses of atropine or telenzepine (0.01 mumol/kg and 1 mumol/kg). These results demonstrate that, in the rat, blockade of the H+,K(+)-ATPase can potently induce gastrin release in the absence of a meal. Moreover, they suggest that interruption of the negative feedback between acid and gastrin release is the main mechanism through which this class of drugs releases gastrin in the rat. Since a similar degree of gastrin release cannot be achieved by alkalinization of gastric contents, additional hormonal or neural regulatory factors may contribute to the drug-induced hypergastrinaemia.