Positive Allosteric Modulation of mGlu and Muscarinic Receptors Differentially Regulate Nitric Oxide-Dependent Signaling in a Scopolamine-Induced Model of Cognitive Impairment
TL;DR
None of the tested compounds fully restored neurochemical balance, suggesting that combination strategies (e.g., with (NO֗) donors or modulators of the (NO֗)-cGMP pathway) may represent a promising direction for future Alzheimer's disease treatments.
Abstract
Background/Objectives: The aim of the study was to evaluate the effects of positive allosteric modulators (PAMs) of metabotropic glutamate (mGlu2, mGlu5) and muscarinic (M1, M4) receptors on nitric oxide (NO֗)-dependent pathways. Scopolamine-induced cognitive impairment model reflecting cholinergic dysfunction characteristic of Alzheimer’s disease was used. Methods: The experiments were performed in vivo in Albino Swiss mice and in vitro in astrocytic cell lines (C8D1A, 1321N1). Chronic (14 days) scopolamine and mGlu2 (LY487379), mGlu5 (CDPPB), M1 (VU0357017), and M4 (VU0152100) PAMs were administered in vivo. In brain tissue samples (frontal cortex or hippocampus) cGMP levels (ELISA), total and protein-specific S-nitrosylation (biotin switch assay), and neuronal (nNOS) or endothelial (eNOS) synthase-dependent (NO֗) release (nanoelectrochemical detection) were measured. In vitro oxidative stress (NBT assay) was performed. Results: Significantly reduced cGMP levels, decreased both nNOS- and eNOS-dependent (NO֗) release, and lowered total protein S-nitrosylation in brain tissue were observed. mGlu2 and mGlu5 PAMs prevented the reduction in nNOS-related (NO֗) release and restored total S-nitrosylation. CDPPB did not protect against eNOS-related impairment. Muscarinic receptors modulators effectively counteracted eNOS dysfunction. All investigated compounds attenuated oxidative stress, with particularly pronounced effects in human astrocytes. Conclusions: mGlu and muscarinic receptor PAMs differentially modulate (NO֗)-related signaling pathways, demonstrating both therapeutic potential and potential safety limitations. None of the tested compounds fully restored neurochemical balance, suggesting that combination strategies (e.g., with (NO֗) donors or modulators of the (NO֗)-cGMP pathway) may represent a promising direction for future Alzheimer’s disease treatments.