The amyloid-beta (Abeta) peptides and specifically the highly amyloidogenic isoform Abeta42 appear to be key agents in the pathogenesis of familial and sporadic forms of Alzheimer's disease (AD). The final step in the generation of Abeta from the amyloid precursor protein is catalyzed by the multiprotein complex gamma-secretase, which constitutes a prime drug target for prevention and therapy of the disease. However, highly potent gamma-secretase inhibitors that block formation of all Abeta peptides have provoked troubling side effects in preclinical animal models of AD. This toxicity can be readily explained by the promiscuous substrate specificity of gamma-secretase and its essential role in the NOTCH signaling pathway. For that reason and because of the crucial role of Abeta42 in the pathogenesis of the disease, selective inhibition of Abeta42 production would seem to be a more promising alternative to complete inhibition of gamma-secretase activity. This theoretical concept has edged much closer to clinical reality with the surprising finding that certain nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen, and derived compounds display preferential Abeta42-lowering activity. In contrast to gamma-secretase inhibitors, these gamma-secretase modulators effectively suppress Abeta42 production while sparing processing of NOTCH and other gamma-secretase substrates. Although not fully resolved on the molecular level, the mechanism of action of Abeta42-lowering NSAIDs is independent of cyclooxygenase inhibition and most likely involves direct interaction with components of the gamma-secretase complex or its substrates. Current efforts to improve the pharmacological shortcomings of available gamma-secretase modulators will hopefully lead to the development of clinically useful Abeta42-lowering compounds in the near future.
Copyright 2006 S. Karger AG, Basel.