Effects of a novel M4 muscarinic positive allosteric modulator on behavior and cognitive deficits relevant to Alzheimer's disease and schizophrenia in rhesus monkey

Targeting muscarinic receptors for the treatment of alcohol use disorders: Opportunities and hurdles for clinical development

Emerging evidence suggests muscarinic acetylcholine receptors represent novel targets to treat alcohol use disorder. In this review, we draw from literature across medicinal chemistry, molecular biology, addiction and learning/cognition fields to interrogate the proposition for muscarinic receptor ligands in treating various aspects of alcohol use disorder, including cognitive dysfunction, motivation to consume alcohol and relapse. In support of this proposition, we describe cholinergic dysfunction in the pathophysiology of alcohol use disorder at a network level, including alcohol-induced adaptations present in both human post-mortem brains and reverse-translated rodent models. Preclinical behavioural pharmacology implicates specific muscarinic receptors, in particular, M4 and M5 receptors, as potential therapeutic targets worthy of further interrogation. We detail how these receptors can be selectively targeted in vivo by the use of subtype-selective allosteric modulators, a strategy that overcomes the issue of targeting a highly conserved orthosteric site bound by acetylcholine. Finally, we highlight the intense pharma interest in allosteric modulators of muscarinic receptors for other indications that provide an opportunity for repurposing into the alcohol use disorder space and provide some currently unanswered questions as a roadmap for future investigation.

New Drug Treatments for Schizophrenia: A Review of Approaches to Target Circuit Dysfunction

Schizophrenia is a leading cause of global disease burden. Current drug treatments are associated with significant side effects and have limited efficacy for many patients, highlighting the need to develop new approaches that target other aspects of the neurobiology of schizophrenia. Preclinical, in vivo imaging, postmortem, genetic, and pharmacological studies have highlighted the key role of cortical GABAergic (gamma-aminobutyric acidergic)-glutamatergic microcircuits and their projections to subcortical dopaminergic circuits in the pathoetiology of negative, cognitive, and psychotic symptoms. Antipsychotics primarily act downstream of the dopaminergic component of this circuit. However, multiple drugs are currently in development that could target other elements of this circuit to treat schizophrenia. These include drugs for GABAergic or glutamatergic targets, including glycine transporters, D-amino acid oxidase, sodium channels, or potassium channels. Other drugs in development are likely to primarily act on pathways that regulate the dopaminergic system, such as muscarinic or trace amine receptors or 5-HT2A receptors, while PDE10A inhibitors are being developed to modulate the downstream consequences of dopaminergic dysfunction. Our review considers where new drugs may act on this circuit and their latest clinical trial evidence in terms of indication, efficacy, and side effects. Limitations of the circuit model, including whether there are neurobiologically distinct subgroups of patients, and future directions are also considered. Several drugs based on the mechanisms reviewed have promising clinical data, with the muscarinic agonist KarXT most advanced. If these drugs are approved for clinical use, they have the potential to revolutionize understanding of the pathophysiology and treatment of schizophrenia.

The potential of muscarinic M1 and M4 receptor activators for the treatment of cognitive impairment associated with schizophrenia

Cognitive impairment is a core symptom of schizophrenia and a major determinant of poor long-term functional outcomes. Despite considerable efforts, we do not yet have any approved pharmacological treatments for cognitive impairment associated with schizophrenia (CIAS). A combination of advances in pre-clinical research and recent clinical trial findings have led to a resurgence of interest in the cognition-enhancing potential of novel muscarinic acetylcholine receptor (mAChR) agonists in schizophrenia. This article provides an overview of the scientific rationale for targeting M1 and M4 mAChRs. We describe the evolution of neuroscience research on these receptors since early drug discovery efforts focused on the mAChR agonist xanomeline. This work has revealed that M1 and M4 mAChRs are highly expressed in brain regions that are implicated in cognition. The functional significance of M1 and M4 mAChRs has been extensively characterized in animal models via use of selective receptor subtype compounds through neuronal and non-neuronal mechanisms. Recent clinical trials of a dual M1/M4 mAChR agonist show promising, replicable evidence of potential pro-cognitive effects in schizophrenia, with several other mAChR agonists in clinical development.

A golden age of muscarinic acetylcholine receptor modulation in neurological diseases

Over the past 40 years, the muscarinic acetylcholine receptor family, particularly the M1-receptor and M4-receptor subtypes, have emerged as validated targets for the symptomatic treatment of neurological diseases such as schizophrenia and Alzheimer disease. However, despite considerable effort and investment, no drugs have yet gained clinical approval. This is largely attributable to cholinergic adverse effects that have halted the majority of programmes and resulted in a waning of interest in these G-protein-coupled receptor targets. Recently, this trend has been reversed. Driven by advances in structure-based drug design and an appreciation of the optimal pharmacological properties necessary to deliver clinical efficacy while minimizing adverse effects, a new generation of M1-receptor and M4-receptor orthosteric agonists and positive allosteric modulators are now entering the clinic. These agents offer the prospect of novel therapeutic solutions for 'hard to treat' neurological diseases, heralding a new era of muscarinic drug discovery.

A real-time working memory evaluation system for macaques in microwave fields

With the development and widespread application of electromagnetic technology, the health hazards of electromagnetic radiation have attracted much attention and concern. The effect of electromagnetic radiation on the nervous system, especially on learning, memory, and cognitive functions, is an important research topic in the field of electromagnetic biological effects. Most previous studies were conducted with rodents, which are relatively mature. As research has progressed, studies using non-human primates as experimental subjects have been carried out. Compared to rodents, non-human primates such as macaques not only have brain structures more similar to those of humans but also exhibit learning and memory processes that are similar. In this paper, we present a behavioral test system for the real-time evaluation of the working memory (WM) of macaques in a microwave environment. The system consists of two parts: hardware and software. The hardware consists of four modules: the operation terminal, the control terminal, the optical signal transmission, and detection module and the reward feedback module. The software program can implement the feeding learning task, the button-pressing learning task, and the delayed match-to-sample task. The device is useful for the real-time evaluation of the WM of macaques in microwave environments, showing good electromagnetic compatibility, a simple and reliable structure, and easy operation.

Beyond dopamine: Novel strategies for schizophrenia treatment

Despite extensive research efforts aimed at discovering novel antipsychotic compounds, a satisfactory pharmacological strategy for schizophrenia treatment remains elusive. All the currently available drugs act by modulating dopaminergic neurotransmission, leading to insufficient management of the negative and cognitive symptoms of the disorder. Due to these challenges, several attempts have been made to design agents with innovative, non-dopaminergic mechanisms of action. Consequently, a number of promising compounds are currently progressing through phases 2 and 3 of clinical trials. This review aims to examine the rationale behind the most promising of these strategies while simultaneously providing a comprehensive survey of study results. We describe the versatility behind the cholinergic neurotransmission modulation through the activation of M1 and M4 receptors, exemplified by the prospective drug candidate KarXT. Our discussion extends to the innovative approach of activating TAAR1 receptors via ulotaront, along with the promising outcomes of iclepertin, a GlyT-1 inhibitor with the potential to become the first treatment option for cognitive impairment associated with schizophrenia. Finally, we evaluate the 5-HT2A antagonist paradigm, assessing two recently developed serotonergic agents, pimavanserin and roluperidone. We present the latest advancements in developing novel solutions to the complex challenges posed by schizophrenia, offering an additional perspective on the diverse investigated drug candidates.

Muscarinic Receptors and Alzheimer's Disease: New Perspectives and Mechanisms

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases on a global scale. Historically, this pathology has been linked to cholinergic transmission, and despite the scarcity of effective therapies, numerous alternative processes and targets have been proposed as potential avenues for comprehending this complex illness. Nevertheless, the fundamental pathophysiological mechanisms underpinning AD remain largely enigmatic, with a growing body of evidence advocating for the significance of muscarinic receptors in modulating the brain's capacity to adapt and generate new memories. This review summarizes the current state of the art in the field of muscarinic receptors' involvement in AD. A specific key factor was the relationship between comorbidity and the emergence of new mechanisms.

Muscarinic M1 and M4 receptor agonists for schizophrenia: promising candidates for the therapeutic arsenal

INTRODUCTION

Successful phase 3 trials of KarXT in people with schizophrenia herald a new era of treating the disorder with drugs that do not target the dopamine D2 receptor. The active component of KarXT is xanomeline, a muscarinic (CHRM) M1 and M4 agonist, making muscarinic receptors a viable target for treating schizophrenia.

AREAS COVERED

This review covers the process of taking drugs that activate the muscarinic M1 and M4 receptors from conceptualization to the clinic and details the mechanisms by which activating the CHRM1 and 4 can affect the broad spectrum of symptoms experienced by people with schizophrenia.

EXPERT OPINION

Schizophrenia is a syndrome which means drugs that activate muscarinic M1 and M4 receptors, as was the case for antipsychotic drugs acting on the dopamine D2 receptor, will not give optimal outcomes in everyone within the syndrome. Thus, it would be ideal to identify people who are responsive to drugs activating the CHRM1 and 4. Given knowledge of the actions of these receptors, it is possible treatment non-response could be restricted to sub-groups within the syndrome who have deficits in cortical CHRM1 or those with one of the cognitive endophenotypes that may be identifiable by changes in the blood transcriptome.

The muscarinic M4 acetylcholine receptor exacerbates symptoms of movement disorders

Barbeau's seesaw hypothesis of dopamine-acetylcholine balance has predominated movement disorders literature for years. Both the simplicity of the explanation and the matching efficacy of anticholinergic treatment in movement disorders seem to support this hypothesis. However, evidence from translational and clinical studies in movement disorders indicates that many features of this simple balance are lost, broken, or absent from movement disorders models or in imaging studies of patients with these disorders. This review reappraises the dopamine-acetylcholine balance hypothesis in light of recent evidence and describes how the Gαi/o coupled muscarinic M4 receptor acts in opposition to dopamine signaling in the basal ganglia. We highlight how M4 signaling can ameliorate or exacerbate movement disorders symptoms and physiological correlates of these symptoms in specific disease states. Furthermore, we propose future directions for investigation of this mechanisms to fully understand the potential efficacy of M4 targeting therapeutics in movement disorders. Overall, initial evidence suggest that M4 is a promising pharmaceutical target to ameliorate motor symptoms of hypo- and hyper-dopaminergic disorders.

Muscarinic acetylcholine receptors for psychotic disorders: bench-side to clinic

Modern interest in muscarinic acetylcholine receptor (mAChR) activators for schizophrenia began in the 1990s when xanomeline, an M₁/M₄-preferring mAChR agonist developed for cognitive symptoms of Alzheimer's disease (AD), had unexpected antipsychotic activity. However, strategies to address tolerability concerns associated with activation of peripheral mAChRs were not available at that time. The discovery of specific targeted ligands and combination treatments to reduce peripheral mAChR engagement have advanced the potential of mAChR activators as effective treatments for psychotic disorders. This review provides perspectives on the background of the identification of mAChRs as potential antipsychotics, advances in the preclinical understanding of mAChRs as targets, and the current state of mAChR activators under active clinical development for schizophrenia.

Meta-Analysis of the Efficacy and Safety of Olanzapine versus Clozapine when Treating Senile Dementia

Objective

To systematically assess the safety and efficacy of olanzapine versus clozapine when treating senile dementia and to provide evidence-based medicine basis for its promotion and use.

Methods

PubMed, Embase, ScienceDirect, Cochrane Library, China Knowledge Network Database (CNKI), China VIP Database, Wanfang Database, and China Biomedical Literature Database (CBM) online database were searched for randomized controlled trials (RCT) of olanzapine and clozapine when treating senile dementia. The retrieval time limit is from the establishment of the database to the present. The data were extracted independently by two researchers, and the bias risk of each contained literature was analyzed in accordance with the standard of Cochrane Handbook 5.3. RevMan 5.4 statistical software was used to analyze the collected data by meta-analysis.

Results

Finally, 6 randomized controlled trial articles were included, with a total of 490 samples. Meta-analysis of clinical efficacy showed that the clinical efficacy was similar and there was no significant difference (P > 0.05). Two articles used Alzheimer's disease pathological behavior rating scale (BEHAVE-AD) to compare the pathological behavior of different stages after treatment. Statistical analysis showed that there was no significant difference between the total score of BEHAVE-AD and the scores of each factor in each week after treatment. The non-treatment adverse reaction scale (TESS) of the study group and the control group was analyzed by meta-analysis. The TESS score of the study group after treatment was significantly lower than that of the control group. The BPRS scores of different stages after treatment were analyzed by meta-analysis, and there was no significant difference in the total score and factor scores of BPRS in each week after treatment. Two clinical trials reported the incidence of neurological symptoms after treatment. Olanzapine and clozapine treatment can effectively reduce the risk of aging. There was no significant difference in the incidence of neurological symptoms in patients with dementia (P > 0.05). According to the analysis of meat products, the incidence of adverse reactions in the study group was significantly lower than that in the control group (P < 0.05).

Conclusion

Olanzapine and clozapine have similar efficacy when treating mental and behavioral disorders in patients with senile dementia, in which olanzapine is more effective in improving the symptoms of patients with Alzheimer's disease (AD), with less adverse reactions and high safety, which is worth popularizing in clinical practice. However, more studies and follow-up with higher methodological quality and longer intervention time are needed to further verify.

The Basal Forebrain Cholinergic Nuclei and Their Relevance to Schizophrenia and Other Psychotic Disorders

The basal forebrain cholinergic nuclei (BFCN) provide the main cholinergic input to prefrontal cortices, the hippocampi, and amygdala. These structures are highly relevant for the regulation and maintenance of many cognitive functions, such as attention and memory. In vivo neuroimaging studies reported alterations of the cholinergic system in psychotic disorders. Particularly, a downregulation of nicotinic and muscarinic acetylcholine receptors has been found. Crucially, such alterations in neurotransmission have been associated with cognitive impairments and positive and negative symptoms. Recent pharmacological studies support these findings, as they demonstrated an association between the manipulation of cholinergic transmission and an attenuation in symptom severity. Targeting acetylcholine receptors has therefore become a focus for the development of novel psychopharmacological drugs. However, many open questions remain. For instance, it remains elusive what causes such alterations in neurotransmission. While evidence supports the idea that BFCN structural integrity is altered in schizophrenia, it remains to be determined whether this is also present in other psychotic disorders. Furthermore, it is unclear when throughout the course of the disorder these alterations make their appearance and whether they reflect changes in the BFCN alone or rather aberrant interactions between the BFCN and other brain areas. In this review, the specific role of the BFCN and their projections are discussed from a neuroimaging perspective and with a focus on psychotic disorders alongside future directions. These directions set the stage for the development of new treatment targets for psychotic disorders.