Amyloid Precursor Protein in Platelets of Patients With Alzheimer Disease

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Abstract
Amyloid precursor protein (APP) forms with apparent molecular weights of 130, 110, and 106 kd are present in human platelets. It has been demonstrated that Alzheimer disease (AD) is specifically associated with a decreased APP forms ratio in platelets.To investigate whether acetylcholinesterase (AChE) inhibitor treatment modifies the ratio of platelet APP forms in patients with AD.From a large sample of patients with probable AD, 30 with mild to moderate AD were selected. Each patient underwent a clinical evaluation including the Mini-Mental State Examination (MMSE) and platelet APP forms analysis at baseline and after 30 days. During this interval, 20 of 30 patients with AD were treated with donepezil hydrochloride (5 mg/d), a piperidine phosphate-based cholinesterase inhibitor. Platelets were subjected to Western blot analysis using monoclonal antibody (22C11). The ratio between the immunoreactivity of the higher-molecular-weight APP form (130 kd) and the lower forms (106 and 110 kd) was measured.All patients taking donepezil completed the 30 days of treatment without adverse effects. The platelet APP forms ratio at baseline did not differ between the 2 AD groups (mean +/- SD optical density ratio: untreated AD, 0.47 +/- 0.12; treated AD, 0.38 +/- 0.18), whereas a significant difference was found at follow-up (mean +/- SD optical density ratio: untreated AD, 0.45 +/- 0.17; treated AD, 0.77 +/- 0.29; P<.001). A significant improvement in MMSE scores in treated AD patients was observed from baseline (16.9 +/- 3.8) to 30 days (18.9 +/- 4.42) (P<.009, 30 days vs baseline), but no significant correlation was found in treated AD patients between MMSE score improvement and APP forms/ratio increase (P =.09).Administration of AChE inhibitors increases the ratio of APP forms in platelets of patients with AD, suggesting a potential effect of AChE inhibitors on APP trafficking or processing in a peripheral cell.