Conformational Stability of A?-(25?35) in the Presence of Thiazolidine Derivatives

β-Amyloid-acetylcholine molecular interaction: new role of cholinergic mediators in anti-Alzheimer therapy?

BACKGROUND

For long time Alzheimer's disease has been attributed to a cholinergic deficit. More recently, it has been considered dependent on the accumulation of the amyloid beta peptide (Aβ), which promotes neuronal loss and impairs neuronal function. Results/methodology: In the present study, using biophysical and biochemical experiments we tested the hypothesis that in addition to its role as a neurotransmitter, acetylcholine may exert its action as an anti-Alzheimer agent through a direct interaction with Aβ.

CONCLUSION

Our data provide evidence that acetylcholine favors the soluble peptide conformation and exerts a neuroprotective effect against the neuroinflammatory and toxic effects of Aβ. The present paper paves the way toward the development of new polyfunctional anti-Alzheimer therapeutics capable of intervening on both the cholinergic transmission and the Aβ aggregation.

Bioactivity-guided Separation of the Active Compounds in Acacia Pennata Responsible for the Prevention of Alzheimer's Disease

The objective of this study was to evaluate the health benefits of plants used in Thai food, specifically Acacia pennata Willd., in Alzheimer's prevention. A. pennata twigs strongly inhibited β-amyloid aggregation. Bioactivity-guided separation of the active fractions yielded six known compounds, tetracosane (1), 1-(heptyloxy)-octadecane (2), methyl tridecanoate (3), arborinone (4), confertamide A (5) and 4-hydroxy-1-methyl-pyrrolidin-2-carboxylic acid (6). The structures were determined by spectroscopic analysis. Biological testing revealed that tetracosane (1) was the most potent inhibitor of β-amyloid aggregation, followed by 1-(heptyloxy)-octadecane (2) with IC50 values of 0.4 and 12.3 μM. Methyl tridecanoate (3), arborinone (4) and 4-hydroxy-1-methyl-pyrrolidin-2-carboxylic acid (6) moderately inhibited β-amyloid aggregation. In addition, tetracosane (1) and methyl tridecanoate (3) weakly inhibited acetylcholinesterase (AChE). These results suggested that the effect of A pennata on Alzheimer's disease was likely due to the inhibition of β-amyloid aggregation. Thus A. pennata may be beneficial for Alzheimer's prevention.

Aggregation of Aß(25-35) on DOPC and DOPC/DHA bilayers: an atomic force microscopy study

β amyloid peptide plays an important role in both the manifestation and progression of Alzheimer disease. It has a tendency to aggregate, forming low-molecular weight soluble oligomers, higher-molecular weight protofibrillar oligomers and insoluble fibrils. The relative importance of these single oligomeric-polymeric species, in relation to the morbidity of the disease, is currently being debated. Here we present an Atomic Force Microscopy (AFM) study of Aβ(25–35) aggregation on hydrophobic dioleoylphosphatidylcholine (DOPC) and DOPC/docosahexaenoic 22∶6 acid (DHA) lipid bilayers. Aβ(25–35) is the smallest fragment retaining the biological activity of the full-length peptide, whereas DOPC and DOPC/DHA lipid bilayers were selected as models of cell-membrane environments characterized by different fluidity. Our results provide evidence that in hydrophobic DOPC and DOPC/DHA lipid bilayers, Aβ(25-35) forms layered aggregates composed of mainly annular structures. The mutual interaction between annular structures and lipid surfaces end-results into a membrane solubilization. The presence of DHA as a membrane-fluidizing agent is essential to protect the membrane from damage caused by interactions with peptide aggregates; to reduces the bilayer defects where the delipidation process starts.

Acidic elements in histamine H(3) receptor antagonists

Antagonists of the human histamine H(3) receptor (hH(3)R) often contain a second basic moiety, which is well known to boost affinity on this histamine receptor subtype. Here, we prepared compounds with acidic moieties of different pK(a) values to figure out that the hH(3)R tolerates these functionalities when added to a common pharmacophore blueprint. Depending on the acidic, electronic and steric features the designed ligands showed hH(3)R affinities in the nanomolar concentration range. Additionally, selected ligands were tested but failed as dual acting hH(3)R/hPPAR (human peroxisome proliferator-activated receptor) ligands.

A new series of 1,3-dihidro-imidazo[1,5-c]thiazole-5,7-dione derivatives: synthesis and interaction with Abeta(25-35) amyloid peptide

Deposition of senile plaques composed of fibrillar aggregates of Abeta-amyloid peptide is a characteristic hallmark of Alzheimer's disease. A widely employed approach in the study of anti-Alzheimer agents involves the identification of substances able to prevent amyloid aggregation, or to disaggregate the amyloid fibrils through a direct structural interaction with the soluble or aggregated forms of the peptide. Here, we report the synthesis of a set of 1,3-dihydro-3,6-disubstituted-imidazo[1,5-c]thiazole-5,7-dione derivatives supporting different alkyl, aryl and alkylamine side chains. The ability of these compounds to interact with the Abeta(25-35) peptide was evaluated using circular dichroism, nuclear magnetic resonance and thioflavin fluorescence spectroscopy. A molecular model for Abeta(25-35)-ligand interactions was calculated by molecular docking procedures. Our data show that the ability of the synthesized compounds to modify the structural behaviour of Abeta(25-35) varies as a function of the overall structural features of the ligands rather contributions from specific individual substituents.

Calpastatin overexpression attenuates amyloid-beta-peptide toxicity in differentiated PC12 cells

Amyloid beta peptide (Abeta) plays a major role in the pathogenesis of Alzheimer's disease (AD). Abeta is toxic to neurons, possibly through causing initial synaptic dysfunction and neuronal membrane dystrophy, promoted by increased cellular Ca(2+). Calpain (Ca(2+)-dependent protease) and caspase have been implicated in AD. Previously, we used calpain and caspase pharmacological inhibitors to study effects of Abeta25-35 (sAbeta) on neuronal-like differentiated PC12 cells. We reported that sAbeta-treated cells exhibited calpain activation and protein degradation (due to both calpain and caspase-8). We have now found that overexpression of the calpain specific inhibitor calpastatin in differentiated PC12 cells significantly inhibited the sAbeta-induced calpain activation and decreased the protease activity. Calpastatin overexpression inhibited the sAbeta-promoted degradation of fodrin, protein kinase Cepsilon, beta-catenin (membrane structural proteins and proteins involved in signal transduction pathways), and prevented the sAbeta-induced alteration of neurite structure (manifested by varicosities). Overexpression of calpastatin also inhibited Ca(2+)-promoted calpain activation and protein degradation; this is consistent with the notion that the Abeta-induced increase in calpain activity results from a rise in cellular Ca(2+), provided the calpastatin level is not so high as to strongly inhibit calpain. Carrying out transfection without selection allowed the comparison in the same culture of calpastatin-overexpressing with non-overexpressing cells. In cultures transfected with green fluorescent protein (GFP)-calpastatin plasmid, calpastatin overexpression (indicated by GFP-labeling) led to inhibition in sAbeta-induced membrane propidium iodide (PI) permeability, whereas non-transfected, GFP-unlabeled cells exhibited PI permeability. Overall, the results demonstrate that the effects of Abeta-toxicity studied here were attenuated to a large extent by calpastatin overexpression, indicating that the protease calpain is involved in Abeta-toxicity (obviating a primary, direct role for caspases). Increased expression of calpastatin and/or decrease in calpain may serve as one of the means for ameliorating some of the early symptoms of AD.

Structure?activity Relationships of Amyloid Beta-aggregation Inhibitors Based on Curcumin: Influence of Linker Length and Flexibility

Self-assembly of amyloid beta into fibrillar plaques is characteristic of Alzheimer's disease and oligomers of this peptide are believed to be involved in neurodegeneration. Natural organic dyes, such as congo red and curcumin, bind tightly to amyloid beta and, at higher concentrations, block its self-assembly. The ability of these molecules to prevent amyloid accumulation has generated interest in understanding which of their structural features contribute to inhibitory potency. In general, amyloid beta ligands tend to be flat, planar molecules with substituted aromatic end groups; however, a comprehensive structure-activity study has not been reported. To better understand these ligands, we surveyed the effect of three prominent features on inhibition of amyloid aggregation: the presence of two aromatic end groups, the substitution pattern of these aromatics, and the length and flexibility of the linker region. We found that modification of any one of the modules has profound effects on activity. Further, we report that the optimal length of the linker lies within a surprisingly narrow regime (6-19 A). These results offer insight into the key chemical features required for inhibiting amyloid beta aggregation. In turn, these findings help define the nature of the docking site for small molecules on the amyloid beta surface.