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Alzheimer's disease is characterized by deposition of the amyloid β-peptide (Aβ) in brain tissue of affected individuals. In recent years, many potential lead structures have been suggested that can potentially be used for diagnosis and therapy. However, the mode of action of these compounds is so far not understood. Among these small molecules, the Non-Steroidal Anti-Inflammatory Drug (NSAID) sulindac sulfide received a lot of attention. In this manuscript, we characterize the interaction between the monomeric Aβ peptide and the NSAID sulindac sulfide. We find that sulindac sulfide efficiently depletes the pool of toxic oligomers by enhancing the rate of fibril formation In vitro, sulindac sulfide forms colloidal particles which catalyze the formation of fibrils. Aggregation is immediate, presumably by perturbing the supersaturated Aβ solution. We find that sulindac sulfide induced aggregates are structurally homogeneous. The C-terminal part of the peptide adopts β-sheet structure, whereas the N-terminus is disordered. The salt bridge between D23 and K28 is present, similar as in the wild type fibril structure. 13C-19F TEDOR experiments suggest that sulindac sulfide co-localizes with the Aβ peptide in the aggregate.

Alzheimer's disease is the most severe neurodegenerative disease worldwide. In the past years, a plethora of small molecules interfering with amyloid-β (Aβ) aggregation have been suggested. However, their mode of interaction with amyloid fibers is not understood. Non-steroidal anti-inflammatory drugs (NSAIDs) are known γ-secretase modulators (GSMs). It has been suggested that NSAIDs are pleiotrophic and can interact with more than one pathomechanism. We present here a magic angle spinning (MAS) solid-state NMR study that shows that the NSAID sulindac sulfide interacts specifically with Alzheimer's disease Aβ fibrils. We find that sulindac sulfide does not induce drastic architectural changes in the fibrillar structure, but intercalates between the two β-strands of the amyloid fibril and binds to hydrophobic cavities, which are found consistently in all analyzed structures. The characteristic D23-K28 salt bridge is not affected upon interacting with sulindac sulfide. The primary binding site is located in the vicinity of residue G33, a residue involved in M35 oxidation. The results presented here could be useful in the search for pharmacologically active molecules which can potentially be employed as lead structures to guide the design of small molecules for the treatment of Alzheimer's disease.

The aggregation of the amyloid-{beta} (Abeta) peptide plays a pivotal role in the pathogenesis of Alzheimer's disease, as soluble oligomers are intimately linked to neuronal toxicity and inhibition of hippocampal long-term potentiation (LTP). In the C-terminal region of Abeta there are three consecutive GxxxG dimerization motifs, which we could previously demonstrate to play a critical role in the generation of Abeta. Here, we show that glycine 33 (G33) of the central GxxxG interaction motif within the hydrophobic Abeta sequence is important for the aggregation dynamics of the peptide. Abeta peptides with alanine or isoleucine substitutions of G33 displayed an increased propensity to form higher oligomers, which we could attribute to conformational changes. Importantly, the oligomers of G33 variants were much less toxic than Abeta(42) wild type (WT), in vitro and in vivo. Also, whereas Abeta(42) WT is known to inhibit LTP, Abeta(42) G33 variants had lost the potential to inhibit LTP. Our findings reveal that conformational changes induced by G33 substitutions unlink toxicity and oligomerization of Abeta on the molecular level and suggest that G33 is the key amino acid in the toxic activity of Abeta. Thus, a specific toxic conformation of Abeta exists, which represents a promising target for therapeutic interventions.

Recent evidence indicates that both intraneuronal Abeta and Cu are involved in the pathological processes in Alzheimer's disease (AD). This perspective shows a possible interrelation of these factors. AbetaPP, the precursor of Abeta which represents the main constituent of amyloid plaques, is involved in Cu homeostasis in mammals. In vitro observations and in vivo data obtained from AbetaPP mouse models provide strong evidence that AbetaPP and the resulting Abeta overproduction facilitate intracellular Cu to leave the cell. An increased Cu efflux seems to lead to Cu deficiency and, subsequently, reduced SOD-1 activity. The Cu-dependent SOD-1 activity is the main enzyme involved in detoxifying free radicals. Several reports have shown that oxidative stress is an invariable age-dependent feature in the brain of AD patients. Increased oxidative stress leads to an increase in intraneuronal Abeta accumulation, which has been shown to be the main trigger for neuronal loss in transgenic mouse models. Thus, we conclude that bioavailability of Cu is a crucial point for the pathogenesis of AD.

The presenilin (PS)-dependent site 3 (S3) cleavage of Notch liberates its intracellular domain (NICD), which is required for Notch signaling. The similar γ-secretase cleavage of the β-amyloid precursor protein (βAPP) results in the secretion of amyloid β-peptide (Aβ). However, little is known about the corresponding C-terminal cleavage product (CTFγ). We have now identified CTFγ in brain tissue, in living cells, as well as in an in vitro system. Generation of CTFγ is facilitated by PSs, since a dominant-negative mutation of PS as well as a PS gene knock out prevents its production. Moreover, γ-secretase inhibitors, including one that is known to bind to PS, also block CTFγ generation. Sequence analysis revealed that CTFγ is produced by a novel γ-secretase cut, which occurs at a site corresponding to the S3 cleavage of Notch.