Muscarinic acetylcholine receptors are membrane receptors involved in many physiological processes. Malfunction of muscarinic signaling is a cause of various internal diseases, as well as psychiatric and neurologic conditions. Cholesterol, neurosteroids, neuroactive steroids, and steroid hormones are molecules of steroid origin that, besides having well-known genomic effects, also modulate membrane proteins including muscarinic acetylcholine receptors. Here, we review current knowledge on the allosteric modulation of muscarinic receptors by these steroids. We give a perspective on the research on the non-genomic effects of steroidal compounds on muscarinic receptors and drug development, with an aim to ultimately exploit such knowledge.

• Keywords
• allosteric modulation, cholesterol, muscarinic receptors, neuroactive steroids, neurosteroids,
• MeSH
• Cholesterol MeSH
• Hormones metabolism   MeSH
• Neurosteroids * pharmacology   MeSH
• Receptors, Muscarinic MeSH
• Steroids pharmacology   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Cholesterol MeSH
• Hormones MeSH
• Neurosteroids * MeSH
• Receptors, Muscarinic MeSH
• Steroids MeSH

G-protein coupled receptors (GPCRs) are membrane proteins that convey extracellular signals to the cellular milieu. They represent a target for more than 30% of currently marketed drugs. Here we review the effects of membrane cholesterol on the function of GPCRs of Class A. We review both the specific effects of cholesterol mediated via its direct high-affinity binding to the receptor and non-specific effects mediated by cholesterol-induced changes in the properties of the membrane. Cholesterol binds to many GPCRs at both canonical and non-canonical binding sites. It allosterically affects ligand binding to and activation of GPCRs. Additionally, it changes the oligomerization state of GPCRs. In this review, we consider a perspective of the potential for the development of new therapies that are targeted at manipulating the level of membrane cholesterol or modulating cholesterol binding sites on to GPCRs.

• Keywords
• GPCRs, allosteric modulation, cholesterol,
• MeSH
• Allosteric Regulation MeSH
• Anticholesteremic Agents pharmacology   therapeutic use   MeSH
• Cell Membrane metabolism   MeSH
• Cholesterol chemistry   metabolism   MeSH
• Molecular Targeted Therapy methods   MeSH
• Humans MeSH
• Ligands MeSH
• Receptors, G-Protein-Coupled chemistry   classification   metabolism   MeSH
• Protein Binding MeSH
• Binding Sites drug effects   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Anticholesteremic Agents MeSH
• Cholesterol MeSH
• Ligands MeSH
• Receptors, G-Protein-Coupled MeSH

BACKGROUND AND PURPOSE: More than 30% of currently marketed medications act via GPCRs. Thus, GPCRs represent one of the most important pharmacotherapeutic targets. In contrast to traditional agonists activating multiple signalling pathways, agonists activating a single signalling pathway represent a new generation of drugs with increased specificity and fewer adverse effects. EXPERIMENTAL APPROACH: We have synthesized novel agonists of muscarinic ACh receptors and tested their binding and function (on levels of cAMP and inositol phosphates) in CHO cells expressing individual subtypes of muscarinic receptors, primary cultures of rat aortic smooth muscle cells and suspensions of digested native tissues from rats. Binding of the novel compounds to M2 receptors was modelled in silico. KEY RESULTS: Two of the tested new compounds (1-(thiophen-2-ylmethyl)-3,6-dihydro-2H-pyridinium and 1-methyl-1-(thiophen-2-ylmethyl)-3,6-dihydro-2H-pyridinium) only inhibited cAMP synthesis in CHO cells, primary cultures, and native tissues, with selectivity for M2 muscarinic receptors and displaying bias towards the Gi signalling pathway at all subtypes of muscarinic receptors. Molecular modelling revealed interactions with the orthosteric binding site in a way specific for a given agonist followed by agonist-specific changes in the conformation of the receptor. CONCLUSIONS AND IMPLICATIONS: The identified compounds may serve as lead structures in the search for novel non-steroidal and non-opioid analgesics acting via M2 and M4 muscarinic receptors with reduced side effects associated with activation of the phospholipase C signalling pathway.

• MeSH
• Muscarinic Agonists * pharmacology   MeSH
• Muscarinic Antagonists pharmacology   MeSH
• CHO Cells MeSH
• Cricetulus MeSH
• Cricetinae MeSH
• Rats MeSH
• Receptor, Muscarinic M2 MeSH
• Receptors, Muscarinic * MeSH
• Signal Transduction MeSH
• Animals MeSH
• Check Tag
• Cricetinae MeSH
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Muscarinic Agonists * MeSH
• Muscarinic Antagonists MeSH
• Receptor, Muscarinic M2 MeSH
• Receptors, Muscarinic * MeSH

Allosteric modulators are ligands that bind to a site on the receptor that is spatially separated from the orthosteric binding site for the endogenous neurotransmitter. Allosteric modulators modulate the binding affinity, potency, and efficacy of orthosteric ligands. Muscarinic acetylcholine receptors are prototypical allosterically-modulated G-protein-coupled receptors. They are a potential therapeutic target for the treatment of psychiatric, neurologic, and internal diseases like schizophrenia, Alzheimer's disease, Huntington disease, type 2 diabetes, or chronic pulmonary obstruction. Here, we reviewed the progress made during the last decade in our understanding of their mechanisms of binding, allosteric modulation, and in vivo actions in order to understand the translational impact of studying this important class of pharmacological agents. We overviewed newly developed allosteric modulators of muscarinic receptors as well as new spin-off ideas like bitopic ligands combining allosteric and orthosteric moieties and photo-switchable ligands based on bitopic agents.

• Keywords
• acetylcholine, allosteric modulation, muscarinic receptors,
• MeSH
• Muscarinic Agonists metabolism   MeSH
• Allosteric Regulation physiology   MeSH
• Muscarinic Antagonists metabolism   MeSH
• Humans MeSH
• Ligands MeSH
• Receptors, Muscarinic metabolism   physiology   MeSH
• Receptors, G-Protein-Coupled MeSH
• Binding Sites MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Muscarinic Agonists MeSH
• Muscarinic Antagonists MeSH
• Ligands MeSH
• Receptors, Muscarinic MeSH
• Receptors, G-Protein-Coupled MeSH