Gallic acid disruption of Aβ_1-42 aggregation rescues cognitive decline of APP/PS1 double transgenic mouse

Alzheimer's disease (AD) treatment represents one of the largest unmet medical needs. Developing small molecules targeting Aβ aggregation is an effective approach to prevent and treat AD. Here, we show that gallic acid (GA), a naturally occurring polyphenolic small molecule rich in grape seeds and fruits, has the capacity to alleviate cognitive decline of APP/PS1 transgenic mouse through reduction of Aβ_1-42 aggregation and neurotoxicity. Oral administration of GA not only improved the spatial reference memory and spatial working memory of 4-month-old APP/PS1 mice, but also significantly reduced the more severe deficits developed in the 9-month-old APP/PS1 mice in terms of spatial learning, reference memory, short-term recognition and spatial working memory. The hippocampal long-term-potentiation (LTP) was also significantly elevated in the GA-treated 9-month-old APP/PS1 mice with increased expression of synaptic marker proteins. Evidence from atomic force microscopy (AFM), dynamic light scattering (DLS) and thioflavin T (ThT) fluorescence densitometry analyses showed that GA significantly reduces Aβ_1-42 aggregation both in vitro and in vivo. Further, pre-incubating GA with oligomeric Aβ_1-42 reduced Aβ_1-42-mediated intracellular calcium influx and neurotoxicity. Molecular docking studies identified that the 3,4,5-hydroxyle groups of GA were essential in noncovalently stabilizing GA binding to the Lys28-Ala42 salt bridge and the -COOH group is critical for disrupting the salt bridge of Aβ_1-42. The predicated covalent interaction through Schiff-base formation between the carbonyl group of the oxidized product and ε-amino group of Lys16 is also critical for the disruption of Aβ_1-42 S-shaped triple-β-motif and toxicity. Together, these studies demonstrated that GA can be further developed as a drug to treat AD through disrupting the formation of Aβ_1-42 aggregation.