Alzheimer’s disease (AD) is a progressive neurodegenerative disorder. Amyloid precursor protein (APP) processing and the subsequent generation of amyloid β (Aβ) are central to the pathogenesis of AD, as soluble, oligomeric Aβ peptides are thought to be the toxic species driving disease progression. Flavonoids, a group of dietary polyphenols, have been shown to possess cognitive health benefits. Epidemiological evidence suggests they could play a role in risk reduction in dementia. In vitro and in vivo reports suggest flavonoids can modulate APP metabolism and Aβ production, although the most effective compounds and the underlying mechanism of action remain unclear. This study identified select flavonoids that were able to reduce amyloidogenic processing in primary cortical neurons at physiologically relevant concentrations. An APP-Gal4 gene reporter assay was characterised for identification of modulators of APP processing in primary neurons. It was tested under physiological conditions, in a pro-oxidant environment or against pathological levels of Aβ production through introduction of a known familial AD (FAD) causing mutation of APP (K595N/M596L). Using this system, five flavonoids were identified that inhibited amyloidogenic APP processing at 100 nM, these were: fisetin, pelargonidin, sinensetin, (-) epicatechin and epigallocatechin. Due to known bioavailability, the catechin family were investigated further and epigallocatechin and (-) epicatechin were confirmed as potent (low nanomolar) inhibitors of amyloidogenic processing. Investigation into the mechanism of action by (-) epicatechin suggested it was likely through indirect BACE1 activity inhibition, independent of BACE1 expression. In addition to activity at APP processing (-) epicatechin also induced extracellular signal-regulated kinase (ERK) activation and transcriptional activity. Investigation of other lead flavonoids also identified fisetin as an inhibitor of ERK-dependent transcriptional activity. This study supports the hypothesis that flavonoids are modulators of APP processing and that they could offer a potential therapy for the prophylaxis of AD.
|Date of Award
|14 May 2014
|Robert Williams (Supervisor) & Sue Wonnacott (Supervisor)