Beta-secretase cleavage represents the first step in the generation of Abeta polypeptides and initiates the amyloid cascade that leads to neurodegeneration in Alzheimer's disease. By comparative Western blot analysis, we show a 2.7-fold increase in protein expression of the beta-secretase enzyme BACE in the brain cortex of Alzheimer's disease patients as compared to age-matched controls. Similarly, we found the levels of the amyloid precursor protein C-terminal fragment produced by beta-secretase to be increased by nearly twofold in Alzheimer's disease cortex.

Biometals play an important role in Alzheimer disease, and recent reports have described the development of potential therapeutic agents based on modulation of metal bioavailability. The metal ligand clioquinol (CQ) has shown promising results in animal models and small phase clinical trials; however, the actual mode of action in vivo has not been determined. We now report a novel effect of CQ on amyloid ␤-peptide (A␤) metabolism in cell culture. Treatment of Chinese hamster ovary cells overexpressing amyloid precursor protein with CQ and Cu 2؉ or Zn 2؉ resulted in an ϳ85-90% reduction of secreted A␤-(1-40) and A␤-(1-42) compared with untreated controls. Analogous effects were seen in amyloid precursor protein-overexpressing neuroblastoma cells. The secreted A␤ was rapidly degraded through up-regulation of matrix metalloprotease (MMP)-2 and MMP-3 after addition of CQ and Cu 2؉ . MMP activity was increased through activation of phosphoinositol 3-kinase and JNK. CQ and Cu 2؉ also promoted phosphorylation of glycogen synthase kinase-3, and this potentiated activation of JNK and loss of A␤-(1-40). Our findings identify an alternative mechanism of action for CQ in the reduction of A␤ deposition in the brains of CQ-treated animals and potentially in Alzheimer disease patients. Alzheimer disease (AD)4 is characterized by progressive neuronal dysfunction, reactive gliosis, and the formation of amyloid plaques in the brain. The major constituent of AD plaques is the amyloid ␤-peptide (A␤), which is cleaved from the membrane-bound amyloid precursor protein (APP) (1). Aggregated or oligomeric A␤ can induce neurotoxicity through pathways involving free radical production and increased neuronal oxidative stress (2). Among the factors capable of promoting A␤ aggregation in vivo, recent evidence supports a central role for biometals such as Cu 2ϩ and Zn 2ϩ in this process (3). An important factor in controlling A␤ accumulation in AD patients is the activity of A␤-degrading enzymes. Recent studies have identified several candidate proteases that may contribute to catabolism of A␤ in the brain. Neprilysin, insulin-degrading enzyme, angiotensin-converting enzyme, and matrix metalloproteases (MMPs) have all demonstrated A␤-degrading activity in vitro and/or in vivo (4 -6). Reduced activity of these or other A␤-degrading proteases with age may play a role in promoting accumulation and deposition of A␤ in AD patients. Development of strategies to enhance clearance of A␤ may lead to novel therapeutic treatments for AD patients.Promoting A␤ clearance may be achieved through modulating metal sequestration or metal-protein interactions. 5-Chloro-7-iodo-8-hydroxyquinoline or clioquinol (CQ), a disused antibiotic, has received considerable attention as a potential metal ligand in AD and Parkinson disease patients (7-9). Preliminary studies revealed that CQ rapidly and potently dissolved aggregates of synthetic or AD brain-derived A␤ in vitro (10). In subsequent animal studies, a 9-week oral treatment with CQ resulted in a 49% reduction of...

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Proteolytic processing of the amyloid precursor protein by beta -and gamma-secretases results in the production of Alzheimer's disease (AD) Abeta amyloid peptides. Modulation of secretase activity is being investigated as a potential therapeutic approach. Recent studies with human brain have revealed that the beta-secretase protein, BACE, is increased in cortex of AD patients. Analysis of betaCTF (or C99), the amyloid precursor protein (APP) product of BACE cleavage that is the direct precursor to Abeta, shows it is also elevated in AD, underlying the importance of beta-secretase cleavage in AD pathogenesis. The C-terminal product of gamma-secretase cleavage of APP, epsilonCTF (or AICD), is enriched in human brain cortical nuclear fractions, a subcellular distribution appropriate for a putative involvement of APP cytosolic domain in signal transduction. Analysis of AD cortex samples, particularly that of a carrier of a familial APP mutation, suggests that processing of APP transmembrane domain generates an alternative CTF product. All these particularities observed in the AD brain demonstrate that APP processing is altered in AD. The transgenic mouse model Tg2576 seems to be a promising laboratory tool to test potential modulators of Abeta formation. Indeed, C-terminal products of alpha-, beta-, and gamma-secretase cleavage are readily detectable in the brain of these transgenic mice. Finally, the finding of the same secretase products in platelets and neurons make platelets a potentially useful and easily accessible clinical tool to monitor effects of novel therapies based on inhibition of beta- or gamma-secretase.