Exploring the Multi-Target Performance of Mitochondriotropic Antioxidants against the Pivotal Alzheimer's Disease Pathophysiological Hallmarks

Abstract

Alzheimer disease (AD) is the most common neurodegenerative disease featuring progressive and degenerative neurological impairments resulting in memory loss and cognitive decline. The specific mechanisms underlying AD are still poorly understood, but it is suggested that a deficiency in the brain neurotransmitter acetylcholine, the deposition of insoluble aggregates of fibrillar β-amyloid 1-42 (Aβ₄₂), and iron and glutamate accumulation play an important role in the disease progress. Despite the existence of approved cholinergic drugs, none of them demonstrated effectiveness in modifying disease progression. Accordingly, the development of new chemical entities acting on more than one target is attracting progressively more attention as they can tackle intricate network targets and modulate their effects. Within this endeavor, a series of mitochondriotropic antioxidants inspired on hydroxycinnamic (HCA's) scaffold were synthesized, screened toward cholinesterases and evaluated as neuroprotectors in a differentiated human SH-SY5Y cell line. From the series, compounds 7 and 11 with a 10-carbon chain can be viewed as multi-target leads for the treatment of AD, as they act as dual and bifunctional cholinesterase inhibitors and prevent the neuronal damage caused by diverse aggressors related to protein misfolding and aggregation, iron accumulation and excitotoxicity.

Keywords: Alzheimer disease; cholinesterase inhibitors; excitotoxicity; iron accumulation; mitochondriotropic antioxidants; oxidative stress; β-amyloid.

Figure 1

Acetylcholinesterase inhibitors used for the treatment of Alzheimer’s disease.

Figure 2

Chemical structures of mitochondriotropic antioxidants used in this work.

Figure 3

(a) General view of compound 1 (CPK representation) inside the BChE (ribbons) extracted from docking simulations; (b) Pose generated by docking for compound 1 (green carbons) in the BChE; (c) Binding mode extracted for compound 2 (pink carbons) in the BChE; (d) Binding mode calculated by docking for compound 3 (color code: hydrogen bonds represented in yellow dashes, green dashes for π–cation interactions, blue dashes for π–π stacking interactions).

Figure 4

Coulomb and van der Waals interactions between the hydroxyphenyl framework of Compounds 3 and 6 and the BChE residues.

Figure 5

(a) Binding mode yielded by molecular docking for Compound 7 inside the BChE (hydrogen bonds: yellow dashes, π–cation interactions: green dashes, π–π stacking interactions: blue dashes); (b) Residue contributions (sum of Coulomb and van der Waals energies) to the binding between the BChE and Compounds 7 (magenta color) and 1 (green color).

Figure 6

Evaluation of the protective effects of Compounds 7 (10 and 50 µM) and 11 (10 µM) in SH-SY5Y cells against glutamate (16 mM, A), iron(III) (1 mM, B) and Aβ₄₂ (25 µM, C) as oxidative stress inducers. The cells were pre-treated with antioxidants for 30 min and exposed to the aggressors for 24 h. The data are expressed as the means of three independent experiments together with the standard deviation (Mean ± SD). Statistical comparisons were estimated using the nonparametric method of Kruskal–Wallis [one-way ANOVA on ranks] followed by Dunn’s post hoc test (A,B) and using the parametric method of one-way analysis of variance (ANOVA) followed by Dunnett’s multiple comparison test (C, F = 364.2) (Supplementary Table S2). In all cases, p values lower than 0.05 were considered significant (^## p < 0.05, ^#### p < 0.0001 vs. control data; ** p < 0.01, *** p < 0.001, **** p < 0.0001 vs. aggressor values).