Several plant-derived compounds have demonstrated efficacy in pre-clinical Alzheimer's disease (AD) rodent models. Each of these compounds share a gallic acid (GA) moiety, and initial assays on this isolated molecule indicated that it might be responsible for the therapeutic benefits observed. To test this hypothesis in a more physiologically relevant setting, we investigated the effect of GA in the mutant human amyloid β-protein precursor/presenilin 1 (APP/PS1) transgenic AD mouse model. Beginning at 12 months, we orally administered GA (20 mg/kg) or vehicle once daily for 6 months to APP/PS1 mice that have accelerated Alzheimer-like pathology. At 18 months of age, GA therapy reversed impaired learning and memory as compared with vehicle, and did not alter behavior in nontransgenic littermates. GA-treated APP/PS1 mice had mitigated cerebral amyloidosis, including brain parenchymal and cerebral vascular β-amyloid deposits, and decreased cerebral amyloid β-proteins. Beneficial effects co-occurred with reduced amyloidogenic and elevated nonamyloidogenic APP processing. Furthermore, brain inflammation, gliosis, and oxidative stress were alleviated. We show that GA simultaneously elevates α- and reduces β-secretase activity, inhibits neuroinflammation, and stabilizes brain oxidative stress in a pre-clinical mouse model of AD. We further demonstrate that GA increases abundance of a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10, Adam10) proprotein convertase furin and activates ADAM10, directly inhibits β-site APP cleaving enzyme 1 (BACE1, Bace1) activity but does not alter Adam10 or Bace1 transcription. Thus, our data reveal novel post-translational mechanisms for GA. We suggest further examination of GA supplementation in humans will shed light on the exciting therapeutic potential of this molecule.
Keywords: Alzheimer's disease; amyloid β-protein (Aβ); amyloid β-protein precursor (APP); gallic acid; nonamyloidogenic; phenolic compound; plant; secretase.
© 2020 Mori et al.