P4–289: Mechanistic insights into the in vitro and in vivo modulation of Aβ42 levels and amyloid pathology by NSAIDS and related compounds

Increased production of the amyloid beta peptide 1–42 (Aβ42) has been linked to the development of Alzheimer's disease (AD). While epidemiological studies have associated the use of non–steroidal anti–inflammatory drugs (NSAIDs) with a decreased risk of developing AD. Previous studies identified prototypical NSAIDs that selectively lower the production of Aβ42 and are being tested as potential therapeutic agents for AD. Subsequent studies demonstrated that this was independent of their primary target, the cyclooxygenases, or other known targets. Long–term studies in Tg2576 mice decreased Aβ levels and plaque burden. Recently, we identified compounds, including NSAIDs, natural products and COX–2 inhibitors that mimic AD–causing mutations by augmenting the production of Aβ42. A great deal of data suggests that these molecules influence the production of Aβ peptides by directly modifying the cleavage specificity of γ–secretase. However, the precise mechanism by which they shift cleavage remains enigmatic. Investigating the mechanism of NSAID and other small molecule mediated modulation of Aβ42 levels will provide important insight into the biology of Aβ production and may aid in the development of more potent and selective lowering agents that may be efficacious in treating Alzheimer's disease (AD). Using cell–based assays we identified fenofibrate as a potent Aβ42 elevating agent that was amenable to modification with a biotin tag to develop a ligand for photoaffinity labeling (PAL). This technique was previously used to show that γ–secretase inhibitors bind presenilin. PAL experiments with fenofibrate–biotin (FB) demonstrate selectively labeling of APP COOH terminal fragments (APP–CTF) the substrate cleaved by γ–secretase to produce Aβ. Preliminary experiments suggest that the Aβ sequence may represent the binding site for these compounds on APP–CTFs. Experiments are being conducted to investigate the specificity of FB labeling for other γ–secretase substrates, such as Notch. NSAIDs and related compounds appear to influence the production of Aβ peptides by interacting with APP–CTFs within the γ–secretase complex. We hypothesize that both raising and lowering agents have opposing actions on the same molecular target. The interaction of these compounds with Aβ is likely to produce complex effects on the production, clearance and aggregation of Aβ.