If the production of a toxic β-amyloid species could be considered as a “toxic gain of function” in the majority view, the minority view would regard familial Alzheimer’s disease mutations as “loss of γ secretase function.” While this view would appear consistent with the apparent reductions in the rate of cleavage of the APP (and some other substrates) noted with Inhibitors,research,lifescience,medical mutant APP or presenilin 1, a major problem is to provide an explanation
for the abundant deposition of β-amyloid in the Alzheimer brain. If less amyloid is made, why is there so much deposition? Regardless of the position taken on the molecular details of APP processing in Alzheimer’s disease, it remains Inhibitors,research,lifescience,medical true that the vast majority of attempts at therapy for Alzheimer’s disease to date are directed at reducing the amount of γ-amyloid in brain. These attempts fall into four
different groups, depending on the approach. Use of inhibitors of amyloid aggregation The first interventional amyloid approach, based on the unmodified amyloid cascade hypothesis, was an attempt to prevent amyloid aggregation and/or to Inhibitors,research,lifescience,medical disrupt preformed amyloid aggregates. Enthusiasm for this mechanism of intervention has waned somewhat, in tandem with the original version of the amyloid cascade hypothesis. Although a major clinical trial of an aggregation inhibitor, called Alzhemed16,17 was carried out recently, results appear to have been negative, although some debate Inhibitors,research,lifescience,medical about variability between clinical trial sites has prevented a clear
statement on this issue. Given the possibility that deposition of β-amyloid in tissues sequesters toxic species, and that disruption of deposition may increase toxic effects, further attempts along these lines appear unlikely. Use of inhibitors of β-secretase The proteolytic enzyme that Inhibitors,research,lifescience,medical cuts APP to liberate the Nterminus of the β-amyloid peptide, β secretase or BACE1, was identified and cloned by several groups, and it appears to be a single protein that cleaves APP and only a few other protein substrates.18,19 Mice in which the BACE1 gene is knocked out appear relatively normal, surviving into adulthood with subtle, if any, neuronal defects.20 BACE1 appears to from be essential for generation of β-amyloid, such that mice overexpressing mutant human APP do not generate any measurable β-amyloid in the absence of the mouse BAC El gene.21 Clearly, the generation of specific inhibitors of BACE1 is an obvious and attractive prospect for prevention of production of β-amyloid. X-ray crystallography has been used to determine the INNO-406 cost precise structure of BACE1, and this should facilitate the development of inhibitors.