Inhibitors of Aβ peptide aggregation as potential anti-Alzheimer agents

Alzheimer's disease (AD), the most common form of dementia in elderly people, is characterized, from the pathological standpoint, by the extracellular deposition of a 39-43 amino acid peptide, referred to as the amyloid β-peptide (Aβ), in the form of insoluble, protease resistant amyloid plaques. Aβ peptides are known to aggregate spontaneously in vitro with the formation of amyloid fibrils. A great body of evidence has accumulated on the dependence of Aβ toxicity on its aggregation state: on this basis, the hypothesis has been put forward that the deposition of amyloid plaques is a causative factor in AD. Therefore, the intervention on the Aβ peptide aggregation process can be envisaged as an approach to stop or, at least, to slow down the progression of AD. In the last few years, a number of small molecules have been reported to interfere with the in vitro aggregation of Aβ peptides. β-cyclodextrin and rifampicin are the first compounds that were shown to inhibit fibril formation by Aβ peptides; Congo Red, chrysamine G and other sulfonated dyes were found to display the same activity and, recently, nicotine and iododoxorubicin were reported to act as aggregation inhibitors as well. Although most of these molecules can only be considered as tools, they should be regarded as structural hits in the search for more active and pharmacologically useful compounds. The available data on these compounds are reported in this review.