M2 Muscarinic Receptor Research Articles

Lower levels of soluble β-amyloid precursor protein, but not β-amyloid, in the frontal cortex in schizophrenia

We identified a sub-group (25%) of people with schizophrenia (muscarinic receptor deficit schizophrenia (MRDS)) that are characterised because of markedly lower levels of cortical muscarinic M1 receptors (CHRM1) compared to most people with the disorder (non-MRDS). Notably, bioinformatic analyses of our cortical gene expression data shows a disturbance in the homeostasis of a biochemical pathway that regulates levels of CHRM1. A step in this pathway is the processing of β-amyloid precursor protein (APP) and therefore we postulated there would be altered levels of APP in the frontal cortex from people with MRDS. Here we measure levels of CHRM1 using [3H]pirenzepine binding, soluble APP (sAPP) using Western blotting and amyloid beta peptides (Aβ1–40 and Aβ1–42) using ELISA in the frontal cortex (Brodmann's area 6: BA 6; MRDS = 14, non-MRDS = 14, controls = 14). We confirmed the MRDS cohort in this study had the expected low levels of [3H]pirenzepine binding. In addition, we showed that people with schizophrenia, independent of their sub-group status, had lower levels of sAPP compared to controls but did not have altered levels of Aβ1–40 or Aβ1–42. In conclusion, whilst changes in sAPP are not restricted to MRDS our data could indicate a role of APP, which is important in axonal and synaptic pruning, in the molecular pathology of the syndrome of schizophrenia.

SUVN‐I6107: A True Positive Allosteric Modulator (PAM) at Muscarinic M1 Receptors for the Treatment of Cognitive Disorders

AbstractBackgroundMuscarinic acetylcholine receptors belong to the family of G‐protein coupled receptors and are expressed widely throughout the body. Muscarinic receptors have been implicated in the pathophysiology of various central nervous system disorders. M1 subtype of muscarinic receptors play a crucial role in cognition, attention, and sensory processing. The discovery and development of selective ligands targeting M1 subtype have been unsuccessful largely due to the highly conservative orthosteric binding site. Thus, ligands that selectively bind to a less conserved allosteric site of M1 receptors and positively modulate the orthosteric site may circumvent the selectivity issues as posed by orthosteric ligands.MethodSUVN‐I6107 is a clinical candidate identified from the M1 positive allosteric modulator (M1‐PAM) program. The effects of SUVN‐I6107 on the allosteric site of the M1 receptor were evaluated using the reporter gene assay. Binding liability towards orthosteric sites across all the muscarinic receptor subtypes was also evaluated. The pharmacokinetic properties of SUVN‐I6107 were studied both in rodent and non‐rodent species. The pro‐cognitive potential of SUVN‐I6107 was evaluated in diverse animal models of learning and memory. The safety of SUVN‐I6107 was assessed using various in vitro and in vivo systems.ResultSUVN‐I6107 was found to be a selective M1‐PAM with no agonistic activity at Muscarinic M1 and selective across other muscarinic receptor subtypes. SUVN‐I6107 showed good oral bioavailability in rat, dog and monkey. It also has excellent brain penetration with adequate protein free fraction. SUVN‐I6107 reversed the delay‐induced memory deficit in object recognition task. It also attenuated scopolamine‐induced memory deficit in the object recognition as well as contextual fear conditioning task. SUVN‐I6107 enhanced cerebral blood flow, potentiated the effects of donepezil and promoted non‐amyloidogenic amyloid precursor protein processing in rats. SUVN‐I6107 is devoid of side effects associated with the stimulation of the cholinergic system. SUVN‐I6107 was found to be safe in the safety pharmacology and phase‐1 enabling animal toxicity studies.ConclusionSUVN‐I6107, a novel, potent and selective M1‐PAM demonstrated efficacy in animal models and devoid of cholinergic side effects

Oral Vitamin C Intake Ameliorates Crude Oil-Polluted Water-Induced Jejunal Contractile Dysfunctions in Wistar rats

Inhabitants of rural Niger-Delta oil communities in Nigeria often, unintentionally, consume crude oil polluted water (COCW) due to crude oil spills in the region. The impact of vitamin C supplementation during COCW ingestion on the contractile mechanism of the jejunum is not fully known. Hence, this study investigates the outcomes of COCW water and vitamin C intake on the smooth muscle activity of the jejunum in Wistar rats using standard techniques. Data obtained showed that jejunal tissue SOD concentration was significantly reduced, while jejunal tissue MDA concentration was significantly increased in the COCW-only treated group. Contraction mediated by acetylcholine was significantly increased in the COCW-only treated rats. Calcium and potassium ion influx significantly increased jejunal contraction in the COCW-only rats. Incubation of the jejunal tissue in nifedipine, indomethacin, and L-NAME significantly increased acetylcholine-mediated contractions in the jejunal tissue of the COCW-only treated rats when compared to other groups. COCW causes free radical-induced jejunal damage that results in impaired jejunal contractile activity mediated by the M2 muscarinic receptor, nitric oxide synthase activity, voltage-gated large-conductance calcium channels, potassium channels, and prostaglandins. However, the oral intake of Vitamin C supplementation significantly ameliorated impairments by enhancing jejunal antioxidant activity.

Associations of genetic variations in the M3 receptor with salt sensitivity, longitudinal changes in blood pressure and the incidence of hypertension in Chinese adults.

Recent studies have reported the role of the M3 muscarinic acetylcholine receptor (M3R), a member of the G-protein coupled receptor superfamily, encoded by the CHRM3 gene, in cardiac function and the regulation of blood pressure (BP). The aim of this study was to investigate the associations of CHRM3 genetic variants with salt sensitivity, longitudinal BP changes, and the development of hypertension in a Chinese population. We conducted a chronic dietary salt intervention experiment in a previously established Chinese cohort to analyze salt sensitivity of BP. Additionally, a 14-year follow-up was conducted on all participants in the cohort to evaluate the associations of CHRM3 polymorphisms with longitudinal BP changes, as well as the incidence of hypertension. The single nucleotide polymorphism (SNP) rs10802811 within the CHRM3 gene displayed significant associations with low salt-induced changes in systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP), while rs373288072, rs114677844, and rs663148 exhibited significant associations with SBP and MAP responses to a high-salt diet. Furthermore, the SNP rs58359377 was associated with changes in SBP and pulse pressure (PP) over the course of 14 years. Additionally, the 14-year follow-up revealed a significant association between the rs619288 polymorphism and an increased risk of hypertension (OR=1.74, 95% CI: 1.06-2.87, p=.029). This study provides evidence that CHRM3 may have a role in salt sensitivity, BP progression, and the development of hypertension.

Cholinergic sensing of allergen exposure by airway epithelium promotes type 2 immunity in the lungs

Nonneuronal cells, including epithelial cells, can produce acetylcholine (ACh). Muscarinic ACh receptor antagonists are used clinically to treat asthma and other medical conditions; however, knowledge regarding the roles of ACh in type 2 immunity is limited. Our aim was to investigate the roles of epithelial ACh in allergic immune responses. Human bronchial epithelial (HBE) cells were cultured with allergen extracts, and their ACh production and IL-33 secretion were studied invitro. To investigate immune responses invivo, naive BALB/c mice were treated intranasally with different muscarinic ACh receptor antagonists and then exposed intranasally to allergens. At steady state, HBE cells expressed cellular components necessary for ACh production, including choline acetyltransferase and organic cation transporters. Exposure to allergens caused HBE cells to rapidly release ACh into the extracellular medium. Pharmacologic or small-interfering RNA-based blocking of ACh production or autocrine action through the M3 muscarinic ACh receptors in HBE cells suppressed allergen-induced ATP release, calcium mobilization, and extracellular secretion of IL-33. When naive mice were exposed to allergens, ACh was quickly released into the airway lumen. Aseries of clinical M3 muscarinic ACh receptor antagonists inhibited allergen-induced IL-33 secretion and innate type 2 immune response in the mouse airways. In a preclinical murine model of asthma, an ACh receptor antagonist suppressed allergen-induced airway inflammation and airway hyperreactivity. ACh is released quickly by airway epithelial cells on allergen exposure, and it plays an important role in type 2 immunity. The epithelial ACh system can be considered a therapeutic target in allergic airway diseases.

Potential cardioprotective effects of acetylcholinesterase inhibitors in patients with Alzheimer's disease

Abstract Background In patients with mild to moderate Alzheimer's disease (AD), acetylcholinesterase inhibitors (AChE-I) are commonly employed to improve cognitive function. They increase the amount of acetylcholine (ACh) in the neuronal synapses, but bradycardia, cardiac electrical conduction blocks and hypotension due to muscarinic M2 receptor stimulation are potential side effects. However, whether these "side effects" could play a potential protective effect on cardiovascular (CV) events is not yet well defined. Purpuses To evaluate potential beneficial cardiac effects of AChE-Is in patients with AD, in terms of reduction of major adverse cardiovascular events (MACEs). Methods We conducted a retrospective, monocentric, observational cohort study in patients referred to our hospital. Two groups were considered: the interventional group included AD patients treated with AChE-I. The control group enrolled a cohort of subjects matched for age and comorbidities, recruited between caregivers of intervention group subjects that were cognitively unimpaired and not taking AchE-I. The primary endpoint was a composite of hospitalization for heart failure (HF), non-fatal acute myocardial infarction (AMI), myocardial revascularization, hospitalization for cardiovascular (CV) causes, cardiovascular mortality and occurrence of stroke and/or TIA during total 5 year follow-up period (MACEs). Secondary endpoints were each individual component of the primary end point, total deaths, non-cardiovascular death and incidence of pacemaker implant. Results 221 AD patients treated with AChE-I (91 with Donepezil, 130 with Rivastigmine) were included in intervention group and 221 non-AD patients in control group. Groups were homogeneous in terms of age, gender and main cardiovascular risk factors, except for family history of cardiovascular diseases (CVD), which was more frequent in control group. During a median follow-up of 3.1 years the primary endpoint occurred in 24 patients in intervention group (2.1 per 100 patient-years) compared to 56 patients in the control group (5.0 per 100 patient-years). Therefore, AChE-I therapy resulted a protective factor from primary endpoint (HR 0.48, 95% CI 0.24-0.95; p= 0.036). Even not significant, the difference was mainly driven by myocardial revascularization (3.2% in intervention group vs 6.8% in controls) and hospitalization for heart failure (4.5% in intervention group vs 14.5% in controls). Non-CVD mortality was significantly higher in treatment group (13,6% in intervention group vs 2,7% in controls). No significant difference was observed between groups in terms of other secondary outcomes. Conclusions Among patients with AD, use of AChE-I may be protective for CV outcomes, especially reducing HF hospitalisation and myocardial revascularization.Kaplan-Meier of cumulative MACEsNumber of Event/Years

Abstract 16323: Functional Autoantibody Analysis in Post-Acute Sequela of COVID-19 Patients With and Without Pots: A Case Control Study

Introduction: Post-Acute Sequela of COVID-19 (PASC) occurs after recovery from the initial illness. Autonomic dysfunction (AD) may explain these findings. We have previously shown orthostatic intolerance (OI) on standard Italian protocol head-up tilt table in 23 of 24 prospectively studied subjects with PASC and no prior OI. Postural orthostatic tachycardia syndrome (POTS) was noted in 4 of the 23. POTS is associated with elevated levels of autoantibodies. There is a paucity of data evaluating autoantibody presence in subjects with PASC related POTS. Hypothesis: We hypothesized that individuals with PASC related POTS would demonstrate higher levels of certain autoantibodies than controls. Methods: We recruited healthy, COVID-19 PCR negative controls, all previously vaccinated for COVID, who were age and gender matched with the 4 previously identified PASC related POTS patients. Serum was tested for autoantibodies in both groups. Results: Mean ages for the PASC related POTS and control groups were 29 and 31 years, respectively. The PASC related POTS patients had higher levels of functional autoantibodies to several G-protein coupled receptors than controls. The median values for adrenergic A1, adrenergic B2, muscarinic M4, angiotensin 2 and endothelin receptors, comparing controls to PASC related POTS patients, were 10.4 vs 27.5, 14.9 vs 38.5, 7.8 vs 29.0, 12.2 vs 29.5 and 12.6 vs 31.7 Units/ml, respectively. The small size of the 2 groups precludes meaningful statistical testing, but the box plots in Figure 1 show consistent differences in the concentration of antibody receptors seen between the 2 groups. Conclusions: Functional autoantibodies to several G-protein coupled receptors were seen in higher amount in subjects with PASC related POTS compared to healthy controls. While this is a small, case-control study, it suggests a potential autoantibody mediated mechanism that may explain some of the AD seen in PASC patients with POTS.

Effects of Icariin and Its Metabolites on GPCR Regulation and MK-801-Induced Schizophrenia-Like Behaviors in Mice.

Icariin, a major bioactive compound found in the Epimedium genus, has been reported to exert protective effects against neurodegenerative disorders. In the current study, we aimed to investigate the regulatory effect of icariin and its active metabolites (icariside II and icaritin) against prime G-protein-coupled receptor targets, considering their association with neuronal disorders. Icariside II exhibited selective agonist activity towards the dopamine D3 receptor (D3R), with half-maximal effective concentrations of 13.29 μM. Additionally, they effectively inhibited the specific binding of radioligands to D3R. Molecular docking analysis revealed that icariside II potentially exerts its agonistic effect through hydrogen-bonding interaction with Asp110 of the D3R, accompanied by negative binding energy. Conversely, icaritin demonstrated selective antagonist effects on the muscarinic acetylcholine M2 receptor (M2R). Radioligand binding assay and molecular docking analysis identified icaritin as an orthosteric ligand for M2R. Furthermore, all three compounds, icariin and its two metabolites, successfully mitigated MK-801-induced schizophrenia-like symptoms, including deficits in prepulse inhibition and social interaction, in mice. In summary, these findings highlight the potential of icariin and its metabolites as promising lead structures for the discovery of new drugs targeting cognitive and neurodegenerative disorders.

Mechanisms of Organophosphate Toxicity and the Role of Acetylcholinesterase Inhibition.

Organophosphorus compounds (OPs) have applications in agriculture (e.g., pesticides), industry (e.g., flame retardants), and chemical warfare (nerve agents). In high doses or chronic exposure, they can be toxic or lethal. The primary mechanism, common among all OPs, that initiates their toxic effects is the inhibition of acetylcholinesterase. In acute OP exposure, the subsequent surge of acetylcholine in cholinergic synapses causes a peripheral cholinergic crisis and status epilepticus (SE), either of which can lead to death. If death is averted without effective seizure control, long-term brain damage ensues. This review describes the mechanisms by which elevated acetylcholine can cause respiratory failure and trigger SE; the role of the amygdala in seizure initiation; the role of M1 muscarinic receptors in the early stages of SE; the neurotoxic pathways activated by SE (excitotoxicity/Ca++ overload/oxidative stress, neuroinflammation); and neurotoxic mechanisms linked to low-dose, chronic exposure (Ca++ dyshomeostasis/oxidative stress, inflammation), which do not depend on SE and do not necessarily involve acetylcholinesterase inhibition. The evidence so far indicates that brain damage from acute OP exposure is a direct result of SE, while the neurotoxic mechanisms activated by low-dose chronic exposure are independent of SE and may not be associated with acetylcholinesterase inhibition.

The Muscarinic Acetylcholine M2 Receptor-Induced Nitration of p190A by eNOS Increases RhoA Activity in Cardiac Myocytes.

p190RhoGAP, which exists in two paralogs, p190RhoGAP-A (p190A) and p190RhoGAP-B (p190B), is a GTPase activating protein (GAP) contributing to the regulation of the cellular activity of RhoGTPases. Recent data showed that M2 muscarinic acetylcholine receptor (M2R) stimulation in neonatal rat cardiac myocytes (NRCM) induces the binding of p190RhoGAP to the long isoform of the regulator of G protein signaling 3 (RGS3L). This complex formation alters the substrate preference of p190RhoGAP from RhoA to Rac1. By analyzing carbachol-stimulated GAP activity, we show herein that p190A, but not p190B, alters its substrate preference in NRCM. Based on data that the RhoGAP activity of p190A in endothelial cells is diminished upon nitration by endothelial nitric oxide synthase (eNOS)-derived peroxynitrite, we studied whether carbachol-induced NO/peroxynitrite formation contributes to the carbachol-induced RhoA activation in NRCM. Interestingly, the carbachol-induced RhoA activation in NRCM was suppressed by the eNOS-preferring inhibitor L-NIO as well as the non-selective NOS inhibitor L-NAME. Using L-NIO, we firstly verified the carbachol-induced NO production concurrent with eNOS activation and, secondly, the carbachol-induced nitration of p190A in NRCM. By co-immunoprecipitation, the carbachol-induced complex formation of eNOS, p190A, RGS3L and caveolin-3 was detected. We thus conclude that the NO production by M2R-induced eNOS activation in caveolae in NRCM is required for the nitration of p190A, leading to the binding to RGS3L and the change in substrate preference from RhoA to Rac1. In line with this interpretation, the disruption of caveolae in NRCM by methyl-β-cyclodextrin suppressed carbachol-induced RhoA activation in NRCM to a similar extent as the inhibition of NO production.

Muscarinic receptor agonist-induced βPix binding to β-catenin promotes colon neoplasia

M3 muscarinic receptors (M3R) modulate β-catenin signaling and colon neoplasia. CDC42/RAC guanine nucleotide exchange factor, βPix, binds to β-catenin in colon cancer cells, augmenting β-catenin transcriptional activity. Using in silico, in vitro, and in vivo approaches, we explored whether these actions are regulated by M3R. At the invasive fronts of murine and human colon cancers, we detected co-localized nuclear expression of βPix and β-catenin in stem cells overexpressing M3R. Using immunohistochemistry, immunoprecipitation, proximity ligand, and fluorescent cell sorting assays in human tissues and established and primary human colon cancer cell cultures, we detected time-dependent M3R agonist-induced cytoplasmic and nuclear association of βPix with β-catenin. βPix knockdown attenuated M3R agonist-induced human colon cancer cell proliferation, migration, invasion, and expression of PTGS2, the gene encoding cyclooxygenase-2, a key player in colon neoplasia. Overexpressing βPix dose-dependently augmented β-catenin binding to the transcription factor TCF4. In a murine model of sporadic colon cancer, advanced neoplasia was attenuated in conditional knockout mice with intestinal epithelial cell deficiency of βPix. Expression levels of β-catenin target genes and proteins relevant to colon neoplasia, including c-Myc and Ptgs2, were reduced in colon tumors from βPix-deficient conditional knockout mice. Targeting the M3R/βPix/β-catenin axis may have therapeutic potential.

Selective Activation of M1 Muscarinic Receptors Attenuates Human Colon Cancer Cell Proliferation.

M3 muscarinic receptor (M3R) activation stimulates colon cancer cell proliferation, migration, and invasion; M3R expression is augmented in colon cancer and ablating M3R expression in mice attenuates colon neoplasia. Several lines of investigation suggest that in contrast to these pro-neoplastic effects of M3R, M1R plays an opposite role, protecting colon epithelial cells against neoplastic transformation. To pursue these intriguing findings, we examined the relative expression of M1R versus M3R in progressive stages of colon neoplasia and the effect of treating colon cancer cells with selective M1R agonists. We detected divergent expression of M1R and M3R in progressive colon neoplasia, from aberrant crypt foci to adenomas, primary colon cancers, and colon cancer metastases. Treating three human colon cancer cell lines with two selective M1R agonists, we found that in contrast to the effects of M3R activation, selective activation of M1R reversibly inhibited cell proliferation. Moreover, these effects were diminished by pre-incubating cells with a selective M1R inhibitor. Mechanistic insights were gained using selective chemical inhibitors of post-muscarinic receptor signaling molecules and immunoblotting to demonstrate M1R-dependent changes in the activation (phosphorylation) of key downstream kinases, EGFR, ERK1/2, and p38 MAPK. We did not detect a role for drug toxicity, cellular senescence, or apoptosis in mediating M1R agonist-induced attenuated cell proliferation. Lastly, adding M1R-selective agonists to colon cancer cells augmented the anti-proliferative effects of conventional chemotherapeutic agents. Collectively, these results suggest that selective M1R agonism for advanced colon cancer, alone or in combination with conventional chemotherapy, is a therapeutic strategy worth exploring.

Animals Experimentally Infected with SARS-CoV-2 Generate Functional Autoantibodies against G-Protein-Coupled Receptors.

(1) Background: SARS-CoV-2 infection has been linked to diverse clinical manifestations in humans, including cardiovascular complications. Functional autoantibodies targeting G-protein-coupled receptors have emerged as potential contributors to these effects. This study sought to investigate the production and activity of functional autoantibodies targeting G-protein-coupled receptors after SARS-CoV-2 infection of selected animal species. (2) Methods: The presence of functional autoantibodies such as 2-adrenoceptor, angiotensin II AT1 receptor, muscarinic M2 receptor, and angiotensin 1-7 MAS receptor was assessed in cattle and ferrets experimentally infected with SARS-CoV-2. Bioassays were conducted to evaluate the positive or negative chronotropic responses induced by these autoantibodies. Further experiments identified the extracellular domains to which the functional autoantibodies bind, and receptor antagonists were employed to block the induced responses. (3) Results: Only two out of six cattle that were inoculated with SARS-CoV-2 displayed viral replication and tested positive for functional autoantibodies against G-protein-coupled receptors. These functional autoantibodies specifically recognized β2-adrenoceptor, angiotensin II AT1 receptor, muscarinic M2 receptor, and angiotensin 1-7 MAS receptor and induced distinct positive and negative chronotropic effects in the bioassay. Infected ferrets generated functional autoantibodies against β2-adrenoceptor and muscarinic M2 receptor and presented bioactivity similar to that in cattle. (4) Conclusions: This study uncovers functional autoantibodies targeting G-protein-coupled receptors in cattle and ferrets post-SARS-CoV-2 infection, with implications for cardiovascular function.

Opioid ligands may act by blocking the muscarinic anti-inflammatory effect through allostericity in M1 receptors

Muscarinic receptors are also involved in the cholinergic anti-inflammatory function through a central mechanism, as well as a peripheral one, which was recently evidenced. The selective M1 agonist, McN-A-343, showed high anti-inflammatory potential in experimental acetic acid colitis. The opioid pathway also shows an attenuating effect on inflammation in the colitis models through the activation of µ and к receptors, what may show the interconnection of these pathways in the anti-inflammatory effect. The allosteric sites of the M1 and M4 muscarinic receptors have been the target of several pharmacological investigations. Dynorphin, an endogenous opioid kappa receptor agonist, is a negative allosteric agent of M1 muscarinic receptors. The hypothesis pointed out here is that the kappa antagonist, norbinaltomiphine (nor-BNI), also acts as a negative allosteric modulator in M1 receptors, since previous studies show that the simultaneous administration of nor-BNI and McN-A-343 during experimental colitis in mice causes reversal of the anti-inflammatory effect of the M1 agonist. Other kappa antagonists appear to act as negative allosteric modulators at M1. Furthermore, nor-BNI combines many of the common structural features of allosteric modulators of muscarinic receptors. Added to this is the fact that McN-A-343 needs bitopic binding, both in the orthosteric and allosteric sites of the M1 receptor, for its effective action.

Early treatment with an M1 and sigma-1 receptor agonist prevents cognitive decline in a transgenic rat model displaying Alzheimer-like amyloid pathology

The application of the selective allosteric M1 muscarinic and sigma-1 receptor agonist, AF710B (aka ANAVEX3-71), has shown to attenuate Alzheimer’s disease-like hallmarks in McGill-R-Thy1-APP transgenic rats when administered at advanced pathological stages. It remains unknown whether preventive treatment strategies applying this compound may be equally effective. We tested whether daily oral administration of AF710B (10 µg/kg) in 7-month-old, preplaque, McGill-R-Thy1-APP rats for 7 months, followed by a 4-week washout period, could prevent Alzheimer’s disease-like pathological hallmarks. Long-term AF710B treatment prevented the cognitive impairment of McGill-R-Thy1-APP rats. The effect was accompanied by a reduction in the number of amyloid plaques in the hippocampus and the levels of Aβ42 and Aβ40 peptides in the cerebral cortex. AF710B treatment also reduced microglia and astrocyte recruitment toward CA1 hippocampal Aβ-burdened neurons compared to vehicle-treated McGill-R-Thy1-APP rats, also altering the inflammatory cytokines profile. Lastly, AF710B treatment rescued the conversion of brain-derived neurotrophic factor precursor to its mature and biologically active form. Overall, these results suggest preventive and disease-modifying properties of the compound.

Xanomeline displays concomitant orthosteric and allosteric binding modes at the M4 mAChR

The M4 muscarinic acetylcholine receptor (M4 mAChR) has emerged as a drug target of high therapeutic interest due to its expression in regions of the brain involved in the regulation of psychosis, cognition, and addiction. The mAChR agonist, xanomeline, has provided significant improvement in the Positive and Negative Symptom Scale (PANSS) scores in a Phase II clinical trial for the treatment of patients suffering from schizophrenia. Here we report the active state cryo-EM structure of xanomeline bound to the human M4 mAChR in complex with the heterotrimeric Gi1 transducer protein. Unexpectedly, two molecules of xanomeline were found to concomitantly bind to the monomeric M4 mAChR, with one molecule bound in the orthosteric (acetylcholine-binding) site and a second molecule in an extracellular vestibular allosteric site. Molecular dynamic simulations supports the structural findings, and pharmacological validation confirmed that xanomeline acts as a dual orthosteric and allosteric ligand at the human M4 mAChR. These findings provide a basis for further understanding xanomeline’s complex pharmacology and highlight the myriad of ways through which clinically relevant ligands can bind to and regulate GPCRs.

Effect of spirocyclopiperazinium salt compound LXM-15 on spinal nerve injury in rats.

Currently available therapies for neuropathic pain show limited efficacy. This study aimed to investigate the anti-nociceptive effect of the spirocyclopiperazinium salt compound LXM-15 in spinal nerve ligation (SNL) rats and to explore the potential mechanisms. Mechanical allodynia and thermal hyperalgesia tests were used to evaluate the effects of LXM-15 in SNL rats. The expression of CaMKIIα, CREB, JAK2, STAT3, c-fos and TNF-α was detected by western blotting, ELISA or qRT-PCR analysis. Receptor blocking test was performed to explore possible target. Administration of LXM-15 (1, 0.5, 0.25 mg/kg, i.g.) dose-dependently attenuated mechanical allodynia and thermal hyperalgesia in rats subjected to SNL (p < 0.01, p < 0.05), and the effects were completely blocked by peripheral α7 nicotinic or M4 muscarinic receptor antagonist (p > 0.05). LXM-15 significantly decreased the overexpression of phosphorylated CaMKIIα, CREB, JAK2 and STAT3 proteins and the mRNA levels of TNF-α and c-fos (p < 0.01, p < 05). All of the effects could be blocked by α7 or M4 receptor antagonist. Furthermore, LXM-15 reduced the protein expression of TNF-α and c-fos (p < 0.01, p < 0.05). No significant acute toxicity or abnormal hepatorenal function was observed. This is the first study to report that LXM-15 exerts significant anti-nociceptive effect on SNL rats. This effect may occur by activating peripheral α7 nicotinic and M4 muscarinic receptors, further inhibiting the CaMKIIα/CREB and JAK2/STAT3 signalling pathways, and finally inhibiting the expression of TNF-α and c-fos. Existing treatments for neuropathic pain show limited efficacy with severe adverse reactions. This paper is the first to report that LXM-15, a new spirocyclopiperazinium salt compound, exerts a significant anti-nociception in SNL rats without obvious toxicity. The underlying mechanisms include activating peripheral α7 nicotinic and M4 muscarinic receptors, then inhibiting the signalling pathways of CaMKIIα/CREB and JAK2/STAT3 and the expressions of TNF-α and c-fos. This study sheds new light on the development of novel analgesic drugs with fewer side effects.

The biased M3 mAChR ligand PD 102807 mediates qualitatively distinct signaling to regulate airway smooth muscle phenotype

Airway smooth muscle (ASM) cells attain a hypercontractile phenotype during obstructive airway diseases. We recently identified a biased M3 muscarinic acetylcholine receptor (mAChR) ligand, PD 102807, that induces GRK-/arrestin-dependent AMP-activated protein kinase (AMPK) activation to inhibit transforming growth factor-β-induced hypercontractile ASM phenotype. Conversely, the balanced mAChR agonist, methacholine (MCh), activates AMPK yet does not regulate ASM phenotype. In the current study, we demonstrate that PD 102807- and MCh-induced AMPK activation both depend on Ca2+/calmodulin-dependent kinase kinases (CaMKKs). However, MCh-induced AMPK activation is calcium-dependent and mediated by CaMKK1 and CaMKK2 isoforms. In contrast, PD 102807-induced signaling is calcium-independent and mediated by the atypical subtype protein kinase C-iota and the CaMKK1 (but not CaMKK2) isoform. Both MCh- and PD 102807-induced AMPK activation involve the AMPK α1 isoform. PD 102807-induced AMPK α1 (but not AMPK α2) isoform activation mediates inhibition of the mammalian target of rapamycin complex 1 (mTORC1) in ASM cells, as demonstrated by increased Raptor (regulatory-associated protein of mTOR) phosphorylation as well as inhibition of phospho-S6 protein and serum response element-luciferase activity. The mTORC1 inhibitor rapamycin and the AMPK activator metformin both mimic the ability of PD 102807 to attenuate transforming growth factor-β-induced α-smooth muscle actin expression (a marker of hypercontractile ASM). These data indicate that PD 102807 transduces a signaling pathway (AMPK-mediated mTORC1 inhibition) qualitatively distinct from canonical M3 mAChR signaling to prevent pathogenic remodeling of ASM, thus demonstrating PD 102807 is a biased M3 mAChR ligand with therapeutic potential for the management of obstructive airway disease.

Lurasidone for the Treatment of Schizophrenia: Design, Development, and Place in Therapy.

Thisreviewaims to provide a comprehensive overview of the current literature on the drug design, development, and therapy of lurasidone for the treatment of schizophrenia. Lurasidone has antagonistic effects on the dopamine D2, 5-hydroxytryptamine (5-HT)2A, and 5-HT7 receptors and a partial agonistic effect on the 5-HT1A receptor with low affinities for muscarinic M1, histamine H1, and a1 adrenergic receptors. The receptor-binding profile of lurasidone is thought to be associated with fewer side effects such as anticholinergic effects, lipid abnormalities, hyperglycemia, and weight gain. Behavioral pharmacological studies have demonstrated that lurasidone exerts anxiolytic and antidepressive effects and improves cognitive function, which are associated with the modulation of 5-HT7 and 5-HT1A receptors. Literature search using PubMed was performed to find published studies of randomized controlled trials and recent meta-analyses regarding efficacy and safety, particularly metabolic side effects of lurasidone in schizophrenia. In short-term studies, the results of randomized placebo-controlled trials and meta-analyses have suggested that lurasidone was superior to placebo in improving total psychopathology, positive symptoms, negative symptoms, and general psychopathology in patients with acute schizophrenia. Regarding safety, lurasidone had minimal metabolic side effects, and was identified as one of the drugs with the most benign profiles for metabolic side effects. Long-term trials revealed that lurasidone had the preventive effects on relapse, with minimal effects on weight gain and other metabolic side effects. Furthermore, lurasidone improves cognitive and functional performance of patients with schizophrenia, especially in long-term treatment. Patients with schizophrenia require long-term treatment with antipsychotics for relapse prevention; thus, minimizing weight gain and other side effects is crucial. Lurasidone is suitable as one of the first-line antipsychotic drugs in the acute phase, and a switching strategy should be considered during the maintenance phase, to balance efficacy and adverse effects and achieve favorable outcomes in the long-term course of schizophrenia.

Enhancement of muscarinic receptor-mediated excitation in spontaneously hypertensive rat adrenal medullary chromaffin cells.

One of the mechanisms for hypertension is an increase in blood catecholamines due to increased secretion from sympathetic nerve terminals and adrenal medullary chromaffin (AMC) cells. Spontaneously hypertensive rats (SHRs) are used as an animal model of hypertension. Catecholamine secretion in AMC cells occurs in response to humoral factors and neuronal inputs from the sympathetic nerve fibres. Acetylcholine (ACh) released from the nerve terminals activates nicotinic as well as muscarinic ACh receptors. The present experiment aimed to elucidate whether muscarinic receptor-mediated excitation is altered in SHR AMC cells and, if it is, how. Compared with normotensive rat AMC cells, muscarinic stimulation induced greater catecholamine secretion and larger depolarising inward currents in SHR AMC cells. In contrast to normotensive rat AMC cells, the muscarine-induced current consisted of quinine-sensitive and quinine-insensitive components. The former and the latter are possibly ascribed to nonselective cation channel activation and TWIK-related acid-sensitive K+ (TASK) channel inhibition, as noted in guinea pig AMC cells. In fact, immunoreactive material for TASK1 and several isoforms of transient receptor potential canonical (TRPC) channels was detected in SHR AMC cells. Stromal interaction molecule 1 (STIM1), which plays an essential role for heteromeric TRPC1-TRPC4 channel formation and is not expressed in normotensive rat AMC cells, was detected in the cytoplasm and co-localised with TRPC1. The expression of muscarinic M1 receptors was enhanced in SHR AMC cells compared with normotensive rats. The results indicate that muscarinic excitation is enhanced in SHR AMC cells, probably through facilitation of TRPC channel signalling.