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  • br Introduction Alzheimer s disease


    Introduction Alzheimer's disease (AD) affects ca. 46 million people worldwide [1] and it is expected that the number will double or triple by 2030 or 2050, respectively, while no significant progress has been made in research for early diagnosis and new efficient therapies. Currently available medications are symptomatic and their efficacy is questioned. One of the characteristic histopathological markers of AD is the presence of extracellular plaques consisting predominantly of amyloid-β peptides (Aβ) with 40 or 42 PFTα mg (Aβ40 and Aβ42). Recent research suggests that monomers and/or soluble oligomers of Aβ are responsible for AD symptoms [2], when at the same time another protein, tau, which is found in neuronal tangles, may play an important role [[3], [4], [5]]. Amyloidogenic Aβ peptides originate from the cleavage of the type I amyloid precursor protein (APP) by two aspartyl proteases, β- and γ-secretase, both large transmembrane enzyme complexes [6,7]. Aβ peptides are continuously produced throughout life in the healthy brain [8] and an increase in either total levels of Aβ or of relative concentrations of Aβ40 and Aβ42 has been implicated in the late-onset of AD pathogenesis [[9], [10], [11]], e.g. they acquire the capacity to aggregate and form plaques. One of the promising strategies for AD therapy is the modulation of the γ-secretase activity to control the ratio of Aβ peptides without affecting other activities of this enzyme complex, e.g. the cleavage of Notch [12,13]. As for most drugs, γ-secretase modulators must be sufficiently selective to avoid interactions with other enzymes. Interestingly, non-steroidal anti-inflammatory drugs (NSAIDs) were shown to modulate γ-secretase activity [14,15]. NSAIDs are capable to inhibit the generation of Aβ peptides, but most of them require toxic concentrations to be effective [15]. Carprofens, which belong to an NSAID family used in veterinary medicine, have been evaluated as an alternative. They have appeared particularly efficient as selective and non-toxic modulators of γ-secretase [16]. They are capable of modulating production of Aβ40 and Aβ42 to shorter non-amyloidogenic peptides, such as Aβ38. Carprofens that were N-substituted with a lipophilic moiety have shown to be 10 times more active when compared to non-substituted ones [16]. Benzylcarprofen and sulfonylcarprofen (Table 1), which are introduced in this study, are chemically close to other active N-substituted carprofens [16,17]. The mechanism of γ-secretase activity modulation by carprofens has not been elucidated so far, even though three-dimensional structures have been described recently [18,19]. As suggested from their amphiphilic character [16] benzyl- and sulfonylcarprofens most PFTα mg likely partition into membranes, i.e., localized close to APP cleavage sites, that generate Aβ40 and Aβ42 peptides. Here we present a joint experimental and theoretical investigation describing the positioning of two newly synthesized carprofens in lipid bilayers, which required using a set of highly complementary techniques. We report the results obtained by neutron diffraction experiments, oriented solid-state nuclear magnetic resonance spectroscopy (solid-state NMR), both with specifically deuterated compounds, and molecular dynamics (MD) simulations. The aim of this work was to use this ensemble of techniques to provide an atomic view of carprofen-membrane interactions (ca. 0.1 nm resolution). These data pave the way towards understanding how ‘membrane catalysis’ helps these compounds to target their γ-secretase interaction sites [20] and to interfere with the cleavage reactions of APP [21]. The cleavage product Aβ itself changes membrane dynamics and effects the diffusion of membrane components [22].
    Materials and methods
    Results and discussion
    Conclusions This study, based on neutron diffraction, 2H solid-state NMR spectroscopy and MD simulations, determines the position and orientation of two carprofen derivatives, modulators of AD APP γ-secretase, in different membrane phases and at two temperatures and can serve as a promising tool box to rationalize drug/target interactions in membranes. Membrane composition and temperature influence phase properties of lipid bilayers, and subsequently positioning and orientation of these carprofen derivatives. Their membrane partitioning is characterized by two energetic minima, corresponding to locations just above and below the bilayer surface. In the inner position, the compounds are intercalated between the lipid fatty acyl chains thereby losing rotational flexibility. Positioning and orientation are mainly controlled by the carboxylate that acts as an anchor to the polar head group region. In the event of re-protonation in this region, a greater population of the inner position is expected [58,59]. The combination of techniques used in this work can be deployed in drug design to adjust the amphiphilic and hydrophobic character of the drugs for a more accurate positioning of the molecules relative to the target sites.