Mechanisms of Cholinesterase Inhibitors on Beta-amyloid

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Alzheimer's disease (AD) is characterized by the severe loss of cholinergic neurons and depositions of amyloid beta peptide (Abeta). Three FDA- approved drugs (tacrine, donepezil and rivastigmine) for treating AD subjects belong to the category of cholinesterase (ChE) inhibitor (ChEI), which works by increasing the brain's supply of acetylcholine, a nerve communication chemical that is deficient in AD. These drugs are approved for treatment of mild to moderate AD and may not be as useful in more advanced stages. Our goal is to study the mechanism of ChEI drugs on amyloidogenic pathways that process beta-amyloid precursor protein (APP) to potentially neurotoxic Abeta. Such study is significant as there is increasing evidence that Abeta plays an important role in AD pathogenesis. This proposal is based on our discovery that treating cultured cells with certain ChEIs, such as tacrine and phenserine, significantly reduced levels of secreted APP (sAPP) and Abeta and may serve to slow the progression of AD as well as improve cognition. Notably, the mechanism of reduction of Abeta did not increase known alternative processing pathways and may therefore be less damaging. We are interested in identification of the mechanisms by which ChEIs block Abeta secretion to take advantage of the Abeta lowering property in developing novel therapeutic agents. SPEC. AIMS: The specific aims are: 1. To study the effects of acetyl- ChEI (AChEI) and butyrl-ChEI (BchEI) on sAPP and Abeta levels. To examine the specificity of their actions, effects of i) AchEI (e.g., pheneserine) ii)BChEI (e.g. cymserine), and iii) compounds that are tacrine-derivatives (e.g. velnacrine) will be tested to identify structural aspects that lower Abeta. 2. To investigate the role of ChEIs on APP metabolism. Effects of ChEIs on i)APP processing in FAD-APP mutant cell lines and ii) the fate of APP carboxyl-truncated fragments will be tested. 3. To determine the possible targets of the drugs. Effects of ChEIs on the i) APP-cleaving enzyme (BACE), ii) 5' -untranslated region and iii) inhibition of Abeta levels in transgenic mice model of AD. We will mechanically select ChEIs that interact with the peripheral allosteric binding domain of ChEenzyme, or with the esteractic and anionic binding domains (phenserine and cymserine) and test it in APP/PS1 double transgenic mice. These results will indicate a unique effect of ChEIs on APP processing, which is independent of their selectivity for the enzyme. This property will be further investigated to maximize their potential effects in decreasing amyloid depositions, and which can be utilized to design better drugs for the treatment of AD.