One of the hallmarks of AD is the presence of senile plaques
in the hippocampus, which are primarily formed
from the extracellular deposition of Aβ, a 40-42(3)
amino acid polypeptide. The Aβ is deprived from a large
transmembrane protein, the amyloid precursor protein
(APP) by sequential proteolysis of two proteases, the β-
and γ-secretase, at the N- and C-terminus of the Aβ sequence
respectively. Alternatively, APP can also be processed
by α-secretase within the Aβ sequence and thus
not only preclude the formation of Aβ peptide but also
generate a soluble neurotrophic sAPPα. Many experiments
indicated that Aβ is a neurotoxin; it aggregates
and forms deposits that finally lead to neuronal dysfunction.
The pathological accumulation of Aβ in the brain
leads to oxidative stress, neuronal destruction and finally
the clinical symptoms of AD. Following this hypothesis,
secondary prevention of AD can be made by: decreasing
the production of Aβ, stimulation of clearance of Aβ
formed or prevention of aggregation of Aβ into amyloid
plaques (Figure 1). The corresponding targets are also
indicated in the figure.