Abstract
The main objective of the present study was to establish whether the mixed σ&sub1;/muscarinic ligand ANAVEX2-73, shown to be neuroprotective in Alzheimer's disease (AD) models in vivo and currently in clinical phase I/IIa, could have the ability to reduce the appearance of hyperphosphorylated Tau and amyloid-β&sub1;₋&sub4;&sub2; (Aβ&sub1;₋&sub4;&sub2; in the Aβ&sub2;₅₋&sub3;₅ mouse model of AD. We therefore first confirmed that Aβ&sub2;₅₋&sub3;₅ injection induced hyperphosphorylation of Tau protein, by showing that it rapidly decreased Akt activity and activated glycogen synthase kinase-3β (GSK-3β) in the mouse hippocampus. Second, we showed that the kinase activation, and resulting Tau alteration, directly contributed to the amyloid toxicity, as co-administration of the selective GSK-3β inhibitor 2-thio(3-iodobenzyl)-5-(1-pyridyl)-[1,3,4]-oxidiazole blocked both Tau phosphorylation and Aβ&sub2;₅₋&sub3;₅-induced memory impairments. Third, we analyzed the ANAVEX2-73 effect on Tau phosphorylation and activation of the related kinase pathways (Akt and GSK-3β). And fourth, we also addressed the impact of the drug on Aβ&sub2;₅₋&sub3;₅-induced Aβ&sub1;₋&sub4;&sub2; seeding and observed that the compound significantly blocked the increase in Aβ&sub1;₋&sub4;&sub2; and C99 levels in the hippocampus, suggesting that it may alleviate amyloid load in AD models. The comparison with PRE-084, a selective and reference σ&sub1; receptor agonist, and xanomeline, a muscarinic ligand presenting similar profile as ANAVEX2-73 on M1 and M2 subtypes, confirmed that both muscarinic and σ&sub1; targets are involved in the ANAVEX2-73 effects. The drug, acting synergistically on both targets, but with moderate affinity, presents a promising pharmacological profile.