M3 muscarinic receptors as targets for drug development in neurodegenerative disorders

Polyethylenimine-Poly(lactic-co-glycolic acid)2 Nanoparticles Show an Innate Targeting Ability to the Submandibular Salivary Gland via the Muscarinic 3 Receptor

Polymeric nanoparticles have been extensively explored for biomedical applications, especially as framework materials for the construction of functional nanostructures. However, less attention has been paid to the inherent biological activities of those polymers. In this work, one of the commonly used polymers in gene and protein delivery, polyethylenimine-poly(lactic-co-glycolic acid)₂ (PEI-PLGA), was discovered by accident to be able to mediate the nanoparticles to target the submandibular salivary glands of mice after intravenous injection. PEI-PLGA nanoparticles with an unmodified PEI surface selectively accumulated in submandibular salivary glands with ex vivo and in vitro study, suggesting that a ligand-receptor interaction between PEI and muscarinic acetylcholine receptor subtype 3 (M3 receptor) contributed to this affinity. Docking computation for the molecular binding mode between PEI segments and M3 receptor indicated the way they interacted was similar to that of the FDA-approved specific M3 receptor antagonist, tiotropium. The key amino acids mediated this specific interaction between PEI-PLGA nanoparticles and M3 receptor were identified via a simulated alanine mutation study. This work demonstrates the unique characteristic of PEI-PLGA nanoparticles, which may be useful for the development of muscarinic receptor targeted nanomedicines and should be taken into consideration when PEI-based nanoparticles are applied in gene delivery.

M1 muscarinic receptor activation mediates cell death in M1-HEK293 cells

HEK293 cells have been used extensively to generate stable cell lines to study G protein-coupled receptors, such as muscarinic acetylcholine receptors (mAChRs). The activation of M1 mAChRs in various cell types in vitro has been shown to be protective. To further investigate M1 mAChR-mediated cell survival, we generated stable HEK293 cell-lines expressing the human M1 mAChR. M1 mAChRs were efficiently expressed at the cell surface and efficiently internalised within 1 h by carbachol. Carbachol also induced early signalling cascades similar to previous reports. Thus, ectopically expressed M1 receptors behaved in a similar fashion to the native receptor over short time periods of analysis. However, substantial cell death was observed in HEK293-M1 cells within 24 h after carbachol application. Death was only observed in HEK cells expressing M1 receptors and fully blocked by M1 antagonists. M1 mAChR-stimulation mediated prolonged activation of the MEK-ERK pathway and resulted in prolonged induction of the transcription factor EGR-1 (>24 h). Blockade of ERK signalling with U0126 did not reduce M1 mAChR-mediated cell-death significantly but inhibited the acute induction of EGR-1. We investigated the time-course of cell death using time-lapse microscopy and xCELLigence technology. Both revealed the M1 mAChR cytotoxicity occurs within several hours of M1 activation. The xCELLigence assay also confirmed that the ERK pathway was not involved in cell-death. Interestingly, the MEK blocker did reduce carbachol-mediated cleaved caspase 3 expression in HEK293-M1 cells. The HEK293 cell line is a widely used pharmacological tool for studying G-protein coupled receptors, including mAChRs. Our results highlight the importance of investigating the longer term fate of these cells in short term signalling studies. Identifying how and why activation of the M1 mAChR signals apoptosis in these cells may lead to a better understanding of how mAChRs regulate cell-fate decisions.

Receptor screening technologies in the evaluation of Amazonian ethnomedicines with potential applications to cognitive deficits

ETHNOPHARMACOLOGICAL RELEVANCE

Amazonian peoples utilize a variety of psychoactive plants that may contain novel biologically active compounds. Efforts to investigate such remedies in terms of neuropharmacology have been limited.

AIM OF THIS STUDY

This study identified Amazonian ethnomedicines with potential for the treatment of cognitive deficits in schizophrenia and dementias, and characterized their interactions with CNS neurotransmitter receptors in vitro.

MATERIALS AND METHODS

Approximately 300 Amazonian species with folk uses or constituents indicative of central nervous system activity were incorporated into a database constructed from literature searches, herbarium surveys, and interviews with traditional practitioners. Approximately 130 of these targeted species were collected in Loreto province, Peru, and 228 fractions derived from them were screened in 31 radioreceptor assays via the resources of the NIMH Psychoactive Drug Screening Program. A subset was also screened in functional assays at selected serotonin, muscarinic, and adrenergic receptors.

RESULTS

Ninety-one samples displayed ≥60% inhibition of radioligand binding activity in receptor assays; 135 samples displayed agonist or antagonist activity (or both) in functional assays.

CONCLUSIONS

Potential CNS activity was detected in about 40% of the samples screened, with some correlations to both folk uses and phytochemical constituents. These results may point to novel and potentially therapeutic CNS active compounds.