Sterol-activated amyloid beta fibril formation.

The metabolic processes that link Alzheimer's disease (AD) to elevated cholesterol levels in the brain are not fully defined. Amyloid beta (Aß) plaque accumulation is believed to begin decades prior to symptoms and to contribute significantly to the disease. Cholesterol and its metabolites accelerate plaque formation through as-yet-undefined mechanisms. Here, the mechanism of cholesterol (CH) and cholesterol 3-sulfate (CS) induced acceleration of Aß42 fibril formation is examined in quantitative ligand binding, Aß42 fibril polymerization, and molecular dynamics studies. Equilibrium and pre-steady-state binding studies reveal that monomeric Aß42•ligand complexes form and dissociate rapidly relative to oligomerization, that the ligand/peptide stoichiometry is 1-to-1, and that the peptide is likely saturated in vivo. Analysis of Aß42 polymerization progress curves demonstrates that ligands accelerate polymer synthesis by catalyzing the conversion of peptide monomers into dimers that nucleate the polymerization reaction. Nucleation is accelerated ∼49-fold by CH, and ∼13,000-fold by CS - a minor CH metabolite. Polymerization kinetic models predict that at presumed disease-relevant CS and CH concentrations, approximately half of the polymerization nuclei will contain CS, small oligomers of neurotoxic dimensions (∼12-mers) will contain substantial CS, and fibril-formation lag times will decrease 13-fold relative to unliganded Aß42. Molecular dynamics models, which quantitatively predict all experimental findings, indicate that the acceleration mechanism is rooted in ligand-induced stabilization of the peptide in non-helical conformations that readily form polymerization nuclei.

Microglial P2X4 receptors promote ApoE degradation and contribute to memory deficits in Alzheimer's disease.

Numerous evidences support that microglia contributes to the progression of Alzheimer's disease. P2X4 receptors are ATP-gated channels with high calcium permeability, which are de novo expressed in a subset of reactive microglia associated with various pathological contexts, contributing to microglial functions. P2X4 receptors are mainly localized in lysosomes and trafficking to the plasma membrane is tightly regulated. Here, we investigated the role of P2X4 in the context of Alzheimer's disease (AD). Using proteomics, we identified Apolipoprotein E (ApoE) as a specific P2X4 interacting protein. We found that P2X4 regulates lysosomal cathepsin B (CatB) activity promoting ApoE degradation; P2rX4 deletion results in higher amounts of intracellular and secreted ApoE in both bone-marrow-derived macrophage (BMDM) and microglia from APPswe/PSEN1dE9 brain. In both human AD brain and APP/PS1 mice, P2X4 and ApoE are almost exclusively expressed in plaque-associated microglia. In 12-month-old APP/PS1 mice, genetic deletion of P2rX4 reverses topographical and spatial memory impairment and reduces amount of soluble small aggregates of Aß1-42 peptide, while no obvious alteration of plaque-associated microglia characteristics is observed. Our results support that microglial P2X4 promotes lysosomal ApoE degradation, indirectly altering Aß peptide clearance, which in turn might promotes synaptic dysfunctions and cognitive deficits. Our findings uncover a specific interplay between purinergic signaling, microglial ApoE, soluble Aß (sAß) species and cognitive deficits associated with AD.

Design of a multivalent bifunctional chelator for diagnostic 64Cu PET imaging in Alzheimer's disease.

Herein, we report a 64Cu positron emission tomography (PET) imaging agent that shows appreciable in vivo brain uptake and exhibits high specific affinity for beta-amyloid (Aß) aggregates, leading to the successful PET imaging of amyloid plaques in the brains of 5xFAD mice versus those of wild-type mice. The employed approach uses a bifunctional chelator with two Aß-interacting fragments that dramatically improves the Aß-binding affinity and lipophilicity for favorable blood-brain barrier penetration, while the use of optimized-length spacers between the Cu-chelating group and the Aß-interacting fragments further improves the in vivo Aß-binding specificity and brain uptake of the corresponding 64Cu PET imaging agent.

Peptide-Modified Gemini Surfactants as Delivery System Building Blocks with Dual Functionalities for Glaucoma Treatment: Gene Carriers and Amyloid-Beta (Aß) Self-Aggregation Inhibitors.

Retinal ganglion cell (RGC) neurodegeneration in glaucoma has potential links with amyloid-ß (Aß) deposition. Targeting the Aß pathway was shown to reduce RGC apoptosis and protect RGCs from degeneration. We report exploratory studies on the amyloid Aß40 aggregation inhibition properties of four cell adhesion peptide (CAP)-gemini surfactants that are intended as building blocks for gene carrier nanoparticles for glaucoma treatment. The CAP-gemini surfactants (18-7N(p1-4)-18) were evaluated as potential Aß40 peptide aggregation inhibitors by a fluorescence kinetic assay and for their binding interactions with Aß40 dimers by molecular docking studies. In vitro Aß40 peptide aggregation inhibition studies showed that the 18-7N(p3)-18 and 18-7N(p1)-18 ligands inhibit Aß40 peptide aggregation and prevent the formation of higher order structures. CDOCKER energies and CDOCKER interaction energies demonstrated that the CAP-gemini surfactants formed more stable complexes in the Aß40 dimer assembly and underwent both polar and nonpolar interactions compared to CAP peptides alone. Also, 18-7N(p3)-18 showed a significantly lower CDOCKER energy compared to that of the unmodified gemini surfactant 18-7NH-18 (p < 0.0001) and 18-7N(p4)-18 (p < 0.001), 18-7N(p1)-18, and 18-7N(p2)-18. Similarly, 18-7N(p3)-18 showed a significantly lower CDOCKER interaction energy compared to that of 18-7NH-18, 18-7N(p4)-18 (p < 0.0001), and 18-7N(p2)-18 (p < 0.001), while 18-7N(p3)-18 and 18-7N(p1)-18 showed similar CDOCKER interaction energies. These studies suggest that a combination of both hydrophobic and electrostatic interactions contributes to the anti-Aß40 aggregation activity of CAP-gemini surfactants. CAP-gemini surfactants showed 10-fold better Aß40 peptide aggregation inhibition compared to previously reported values and could provide a new opportunity for glaucoma treatment as dual-functional gene carriers.

Guanidine-based ß amyloid precursor protein cleavage enzyme 1 (BACE-1) inhibitors for the Alzheimer's disease (AD): A review.

Alzheimer's disease (AD) is an irreversible, progressive neurological disorder characterized by amyloid plaques, hyperphosphorylated tau protein (hyper p-tau), neuronal damage, memory loss, etc. Various factors, such as age, lifestyle, family history, environmental factors, and gene mutation, cause AD. BACE-1 is an interesting target to prevent or reverse AD progression. BACE-1 cleaves amyloid precursor protein (APP) into soluble amyloid precursor protein ß (sAPPß) and membrane-bound C-terminal fragment called C99, a rate-limiting step, and C99 is further cleaved by gamma-secretase to generate neurotoxic amyloid ß (Aß). Discovery and development of selective ß amyloid precursor protein cleavage enzyme 1 (BACE-1) inhibitors have a great potential for the treatment and maintenance of Alzheimer's disease. In this review, we have compiled literature pertaining to guanidine-based novel BACE-1 inhibitors for the treatment and maintenance of AD. We have also discussed role of BACE-1 substrates, and its crystal structure, BACE-1 inhibitors in the clinical trial, and essential points to overcome challenges associated with selective development of BACE-1 inhibitors. This paper provides valuable information for the design and discovery of selective new BACE-1 inhibitors against other aspartyl protease enzymes to treat AD.

Amyloid ß structural polymorphism, associated toxicity and therapeutic strategies.

A review of the multidisciplinary scientific literature reveals a large variety of amyloid-ß (Aß) oligomeric species, differing in molecular weight, conformation and morphology. These species, which may assemble via either on- or off-aggregation pathways, exhibit differences in stability, function and neurotoxicity, according to different experimental settings. The conformations of the different Aß species are stabilized by intra- and inter-molecular hydrogen bonds and by electrostatic and hydrophobic interactions, all depending on the chemical and physical environment (e.g., solvent, ions, pH) and interactions with other molecules, such as lipids and proteins. This complexity and the lack of a complete understanding of the relationship between the different Aß species and their toxicity is currently dictating the nature of the inhibitor (or inducer)-based approaches that are under development for interfering with (or inducing) the formation of specific species and Aß oligomerization, and for interfering with the associated downstream neurotoxic effects. Here, we review the principles that underlie the involvement of different Aß oligomeric species in neurodegeneration, both in vitro and in preclinical studies. In addition, we provide an overview of the existing inhibitors (or inducers) of Aß oligomerization that serve as potential therapeutics for neurodegenerative diseases. The review, which covers the exciting studies that have been published in the past few years, comprises three main parts: 1) on- and off-fibrillar assembly mechanisms and Aß structural polymorphism; 2) interactions of Aß with other molecules and cell components that dictate the Aß aggregation pathway; and 3) targeting the on-fibrillar Aß assembly pathway as a therapeutic approach.

Influence of Cortisol on the Fibril Formation Kinetics of Aß42 Peptide: A Multi-Technical Approach.

Amyloid-ß peptide (Aß) aggregates are known to be correlated with pathological neurodegenerative diseases. The fibril formation process of such peptides in solution is influenced by several factors, such as the ionic strength of the buffer, concentration, pH, and presence of other molecules, just to mention a few. In this paper, we report a detailed analysis of in vitro Aß42 fibril formation in the presence of cortisol at different relative concentrations. The thioflavin T fluorescence assay allowed us to monitor the fibril formation kinetics, while a morphological characterization of the aggregates was obtained by atomic force microscopy. Moreover, infrared absorption spectroscopy was exploited to investigate the secondary structure changes along the fibril formation path. Molecular dynamics calculations allowed us to understand the intermolecular interactions with cortisol. The combined results demonstrated the influence of cortisol on the fibril formation process: indeed, at cortisol-Aß42 concentration ratio (ρ) close to 0.1 a faster organization of Aß42 fragments into fibrils is promoted, while for ρ = 1 the formation of fibrils is completely inhibited.

Type 2 Diabetes Mellitus and Alzheimer's Disease: Shared Molecular Mechanisms and Potential Common Therapeutic Targets.

The global prevalence of diabetes mellitus and Alzheimer's disease is increasing alarmingly with the aging of the population. Numerous epidemiological data suggest that there is a strong association between type 2 diabetes and an increased risk of dementia. These diseases are both degenerative and progressive and share common risk factors. The amyloid cascade plays a key role in the pathophysiology of Alzheimer's disease. The accumulation of amyloid beta peptides gradually leads to the hyperphosphorylation of tau proteins, which then form neurofibrillary tangles, resulting in neurodegeneration and cerebral atrophy. In Alzheimer's disease, apart from these processes, the alteration of glucose metabolism and insulin signaling in the brain seems to induce early neuronal loss and the impairment of synaptic plasticity, years before the clinical manifestation of the disease. The large amount of evidence on the existence of insulin resistance in the brain during Alzheimer's disease has led to the description of this disease as "type 3 diabetes". Available animal models have been valuable in the understanding of the relationships between type 2 diabetes and Alzheimer's disease, but to date, the mechanistical links are poorly understood. In this non-exhaustive review, we describe the main molecular mechanisms that may link these two diseases, with an emphasis on impaired insulin and IGF-1 signaling. We also focus on GSK3ß and DYRK1A, markers of Alzheimer's disease, which are also closely associated with pancreatic ß-cell dysfunction and type 2 diabetes, and thus may represent common therapeutic targets for both diseases.

Amyloidogenesis: What Do We Know So Far?

The study of protein aggregation, and amyloidosis in particular, has gained considerable interest in recent times. Several neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) show a characteristic buildup of proteinaceous aggregates in several organs, especially the brain. Despite the enormous upsurge in research articles in this arena, it would not be incorrect to say that we still lack a crystal-clear idea surrounding these notorious aggregates. In this review, we attempt to present a holistic picture on protein aggregation and amyloids in particular. Using a chronological order of discoveries, we present the case of amyloids right from the onset of their discovery, various biophysical techniques, including analysis of the structure, the mechanisms and kinetics of the formation of amyloids. We have discussed important questions on whether aggregation and amyloidosis are restricted to a subset of specific proteins or more broadly influenced by the biophysiochemical and cellular environment. The therapeutic strategies and the significant failure rate of drugs in clinical trials pertaining to these neurodegenerative diseases have been also discussed at length. At a time when the COVID-19 pandemic has hit the globe hard, the review also discusses the plausibility of the far-reaching consequences posed by the virus, such as triggering early onset of amyloidosis. Finally, the application(s) of amyloids as useful biomaterials has also been discussed briefly in this review.

Novel hydroxybenzylamine-deoxyvasicinone hybrids as anticholinesterase therapeutics for Alzheimer's disease.

A series of novel 2-hydroxybenzylamine-deoxyvasicinone hybrid analogs (8a-8n) have been synthesized and evaluated as inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), and as inhibitors of amyloid peptide (Aß1-42) aggregation, for treatment of Alzheimer's disease (AD). These dual acting compounds exhibited good AChE inhibitory activities ranging from 0.34 to 6.35 µM. Analogs8g and 8n were found to be the most potent AChE inhibitors in the series with IC50values of 0.38 µM and 0.34 µM, respectively. All the analogs (8a-8n) exhibited weak BuChE inhibitory activities ranging from 14.60 to 21.65 µM. Analogs8g and 8n exhibited BuChE with IC50values of 15.38 µM and 14.60 µM, respectively, demonstrating that these analogs were greater than 40-fold more selective for inhibition of AChE over BuChE. Additionally, compounds8g and 8n were also found to be the best inhibitors of self-induced Aß1-42 peptide aggregation with IC50values of 3.91 µM and 3.22 µM, respectively; 8g and 8n also inhibited AChE-induced Aß1-42 peptide aggregation by 68.7% and 72.6%, respectively. Kinetic analysis and molecular docking studies indicate that analogs 8g and 8n bind to a new allosteric pocket (site B) on AChE. In addition, the observed inhibition of AChE-induced Aß1-42 peptide aggregation by 8n is likely due to allosteric inhibition of the binding of this peptide at the CAS site on AChE. Overall, these results indicate that 8g and 8n are examples of dual-acting lead compounds for the development of highly effective anti-AD drugs.

Oligomeric and Fibrillar Species of Aß42 Diversely Affect Human Neural Stem Cells.

Amyloid-ß 42 peptide (Aß1-42 (Aß42)) is well-known for its involvement in the development of Alzheimer's disease (AD). Aß42 accumulates and aggregates in fibers that precipitate in the form of plaques in the brain causing toxicity; however, like other forms of Aß peptide, the role of these peptides remains unclear. Here we analyze and compare the effects of oligomeric and fibrillary Aß42 peptide on the biology (cell death, proliferative rate, and cell fate specification) of differentiating human neural stem cells (hNS1 cell line). By using the hNS1 cells we found that, at high concentrations, oligomeric and fibrillary Aß42 peptides provoke apoptotic cellular death and damage of DNA in these cells, but Aß42 fibrils have the strongest effect. The data also show that both oligomeric and fibrillar Aß42 peptides decrease cellular proliferation but Aß42 oligomers have the greatest effect. Finally, both, oligomers and fibrils favor gliogenesis and neurogenesis in hNS1 cells, although, in this case, the effect is more prominent in oligomers. All together the findings of this study may contribute to a better understanding of the molecular mechanisms involved in the pathology of AD and to the development of human neural stem cell-based therapies for AD treatment.

Modulation of γ-Secretase Activity by a Carborane-Based Flurbiprofen Analogue.

All over the world, societies are facing rapidly aging populations combined with a growing number of patients suffering from Alzheimer's disease (AD). One focus in pharmaceutical research to address this issue is on the reduction of the longer amyloid-ß (Aß) fragments in the brain by modulation of γ-secretase, a membrane-bound protease. R-Flurbiprofen (tarenflurbil) was studied in this regard but failed to show significant improvement in AD patients in a phase 3 clinical trial. This was mainly attributed to its low ability to cross the blood-brain barrier (BBB). Here, we present the synthesis and in vitro evaluation of a racemic meta-carborane analogue of flurbiprofen. By introducing the carborane moiety, the hydrophobicity could be shifted into a more favourable range for the penetration of the blood-brain barrier, evident by a logD7.4 value of 2.0. Furthermore, our analogue retained γ-secretase modulator activity in comparison to racemic flurbiprofen in a cell-based assay. These findings demonstrate the potential of carboranes as phenyl mimetics also in AD research.

Memory-related process in physiological status and alzheimer's disease.

Rejecting central dogma around static status of adult mammalian brain, CNS has the nascent neurons generated in subgranular zone of dentate gyrus in hippocampus which develop to novel glutamatergic granule cells, with the innate feature of transmuting to memory disks. Structural plasticity proceeds with synaptic plasticity to process all the developing stages required to successful maturation and functional integration, whereby the memory context is ready to leave the hippocampus toward cortex network through consolidation process, for being installed and run the memory disk forever. However, in Alzheimer's disease, brain deal with subtle deadly progressive loss of synapsis, neuronal dysfunction and ultimately network failure, resulting in memory decay and cognitive decline-concluding that AD destroys memory formation related-pathways.

Nanocomposites Inhibit the Formation, Mitigate the Neurotoxicity, and Facilitate the Removal of ß-Amyloid Aggregates in Alzheimer's Disease Mice.

Alzheimer's disease (AD) is a progressive and irreversible brain disorder. Recent studies revealed the pivotal role of ß-amyloid (Aß) in AD. However, there is no conclusive indication that the existing therapeutic strategies exerted any effect on the mitigation of Aß-induced neurotoxicity and the elimination of Aß aggregates simultaneously in vivo. Herein, we developed a novel nanocomposite that can eliminate toxic Aß aggregates and mitigate Aß-induced neurotoxicity in AD mice. This nanocomposite was designed to be a small-sized particle (14 ± 4 nm) with Aß-binding peptides (KLVFF) integrated on the surface. The nanocomposite was prepared by wrapping a protein molecule with a cross-linked KLVFF-containing polymer layer synthesized by in situ polymerization. The presence of the nanocomposite remarkably changed the morphology of Aß aggregates, which led to the formation of Aß/nanocomposite coassembled nanoclusters instead of Aß oligomers. With the reduction of the pathological Aß oligomers, the nanocomposites attenuated the Aß-induced neuron damages, regained endocranial microglia's capability to phagocytose Aß, and eventually protected hippocampal neurons against apoptosis. Thus, we anticipate that the small-sized nanocomposite will potentially offer a feasible strategy in the development of novel AD treatments.

The Palladium(II) Complex of Aß4-16 as Suitable Model for Structural Studies of Biorelevant Copper(II) Complexes of N-Truncated Beta-Amyloids.

The Aß4-42 peptide is a major beta-amyloid species in the human brain, forming toxic aggregates related to Alzheimer's Disease. It also strongly chelates Cu(II) at the N-terminal Phe-Arg-His ATCUN motif, as demonstrated in Aß4-16 and Aß4-9 model peptides. The resulting complex resists ROS generation and exchange processes and may help protect synapses from copper-related oxidative damage. Structural characterization of Cu(II)Aß4-x complexes by NMR would help elucidate their biological function, but is precluded by Cu(II) paramagneticism. Instead we used an isostructural diamagnetic Pd(II)-Aß4-16 complex as a model. To avoid a kinetic trapping of Pd(II) in an inappropriate transient structure, we designed an appropriate pH-dependent synthetic procedure for ATCUN Pd(II)Aß4-16, controlled by CD, fluorescence and ESI-MS. Its assignments and structure at pH 6.5 were obtained by TOCSY, NOESY, ROESY, 1H-13C HSQC and 1H-15N HSQC NMR experiments, for natural abundance 13C and 15N isotopes, aided by corresponding experiments for Pd(II)-Phe-Arg-His. The square-planar Pd(II)-ATCUN coordination was confirmed, with the rest of the peptide mostly unstructured. The diffusion rates of Aß4-16, Pd(II)-Aß4-16 and their mixture determined using PGSE-NMR experiment suggested that the Pd(II) complex forms a supramolecular assembly with the apopeptide. These results confirm that Pd(II) substitution enables NMR studies of structural aspects of Cu(II)-Aß complexes.

Aluminium Binding to Modified Amyloid-ß Peptides: Implications for Alzheimer's Disease.

Aluminium (Al) is clearly neurotoxic and considerable evidence exists that Al may play a role in the aetiology or pathogenesis of Alzheimer's disease (AD). Nevertheless, the link between AD pathology and Al is still open to debate. Therefore, we investigated here the interaction of aluminium ions with two Aß peptide fragments and their analogues. First, we synthesised by the Fmoc/tBu solid-phase peptide synthesis (SPPS) strategy using an automated peptide synthesiser two new peptides starting from the Aß(1-16) native peptide fragment. For this purpose, the three histidine residues (H6, H13, and H14) of the Aß(1-16) peptide were replaced by three alanine and three serine residues to form the modified peptides Aß(1-16)A36,13,14 and Aß(1-16)S36,13,14 (primary structures: H-1DAEFRADSGYEVAAQK16-NH2 and H-1DAEFRSDSGYEVSSQK16-NH2). In addition, the Aß(9-16) peptide fragment (H-9GYEVHHQK16-NH2) and its glycine analogues, namely Aß(9-16)G110, (H-9GGEVHHQK16-NH2), Aß(9-16)G213,14 (H-9GYEVGGQK16-NH2), and Aß(9-16)G310,13,14 (H-9GGEVGGQK16-NH2), were manually synthesised in order to study Al binding to more specific amino acid residues. Both the peptides and the corresponding complexes with aluminium were comparatively investigated by mass spectrometry (MS), circular dichroism spectroscopy (CD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR). Al-peptide molecular ions and Al-fragment ions were unambiguously identified in the MS and MS/MS spectra. AFM images showed dramatic changes in the film morphology of peptides upon Al binding. Our findings from the investigation of N-terminal 1-16 and even 9-16 normal and modified sequences of Aß peptides suggest that they have the capability to be involved in aluminium ion binding associated with AD.

Computational design and evaluation of ß-sheet breaker peptides for destabilizing Alzheimer's amyloid-ß42 protofibrils.

The ß-sheet breaker (BSB) peptides interfere with amyloid fibril assembly and used as therapeutic agents in the treatment of Alzheimer's disease (AD). In this regard, a simple yet effective in silico screening methodology was applied in the present study to evaluate a potential 867 pentapeptide library based on known BSB peptide, LPFFD, for destabilizing Aß42 protofibrils. The molecular docking based virtual screening was used to filter out pentapeptides having binding affinities stronger than LPFFD. In the next step, binding free energies of the top 10 pentapeptides were evaluated using the MM-PBSA method. The residue-wise binding free energy analysis reveals that two pentapeptides, PVFFE, and PPFYE, bind to the surface of Aß42 protofibril and another pentapeptide, PPFFE, bind in the core region of Aß42 protofibril. By employing molecular dynamics simulation as a post filter for the top-hit peptides from MM-PBSA, the pentapeptides, PPFFE, PVFFE, and PPFYE, have been identified as potential BSB peptides for destabilizing Aß42 protofibril structure. The conformational microstate analysis, a significant decrease in the ß-sheet content of Aß42 protofibril, a loss in the total number of hydrogen bonds in Aß42 protofibril, Asp23-Lys28 salt bridge destabilization and analysis of the free energy surfaces highlight Aß42 protofibril structure destabilization in presence of pentapeptides. Among three top-hit pentapeptides, PPFFE displayed the most potent Aß42 protofibril destabilization effect that shifted the energy minima toward lowest value of ß-sheet content as well as lowest number of hydrogen bonds in Aß42 protofibril. The in silico screening workflow presented in the study highlight an alternative tool for designing novel peptides with enhanced BSB ability as potential therapeutic agents for AD.

Amyloid-ß induced neuropathological actions are suppressed by Padina gymnospora (Phaeophyceae) and its active constituent α-bisabolol in Neuro2a cells and transgenic Caenorhabditis elegans Alzheimer's model.

The inhibition of Aß peptide development and aggregation is a hopeful curative approach for the discovery of disease modifying drugs for Alzheimer's disease (AD) treatment. Recent research mainly focuses on the discovery of drugs from marine setting due to their immense therapeutic potential. The present study aims to evaluate the brown macroalga Padina gymnospora and its active constituent α-bisabolol against Aß25-35 induced neurotoxicity in Neuro2a cells and transgenic Caenorhabditis elegans (CL2006 and CL4176). The results of the in vitro study revealed that the acetone extract of P. gymnospora (ACTPG) and its active constituent α-bisabolol restores the Aß25-35 induced alteration in the oxidation of intracellular protein and lipids. In addition, ACTPG and α-bisabolol inhibited cholinesterase and ß-secretase activity in Neuro2a cells. Moreover, the intracellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) production was reduced by ACTPG and α-bisabolol in Neuro2a cells. The decrease in the expression level of apoptotic proteins such as Bax and caspase-3 in ACTPG and α-bisabolol treated group indicates that the seaweed and its bioactive compound have anti-apoptotic property. Further, the in vivo study revealed that the ACTPG and α-bisabolol exerts neuroprotective effect against Aß induced proteotoxicity in transgenic C. elegans strains of AD. Moreover it altered the Aß mediated pathways, lifespan, macromolecular damage and down regulated the AD related gene expression of ace-1, hsp-4 and Aß, thereby preventing Aß synthesis. Overall, the outcome of the study signifies the neuroprotective effect of ACTPG and α-bisabolol against Aß mediated AD pathology.

Human glutaminyl cyclase: Structure, function, inhibitors and involvement in Alzheimer's disease.

Human glutaminyl cyclase (hQC) is an important enzyme for post-translational modification by converting the N-terminal glutaminyl and glutamyl into pyroglutamate (pGlu) through cyclization. The two isoforms of hQC, secretory glutaminyl cyclase (sQC) and golgi resident glutaminyl cyclase (gQC), are involved in various pathological conditions especially in Alzheimer's disease (AD). The sQC is known to mediate the formation of pyroglutamate containing amyloid beta (pGlu-Aß) peptides while gQC mediates the maturation of C-C motif chemokine ligand 2 (CCL2). Therefore, hQC (both sQC and gQC) inhibition is considered to be an attractive strategy to prevent the formation of pGlu-Aß and to reduce neuroinflammation and hence provides a new opportunity for the treatment of AD. In this review, we summarize our current understanding on the structure, function and inhibitors of hQC and its involvement in Alzheimer's disease.

Alzheimer's disease: Key developments support promising perspectives for therapy.

Alzheimer's is the neurodegenerative disease affecting the largest number of patients in the world. In spite of the intense research of the last decades, progress about its knowledge and therapy was limited. In particular, various cytotoxic processes remained debated, while the few drugs approved for therapy were of only marginal relevance. Recent studies have identified key aspects of the disease, such as the mechanisms governing the development of pathology. In order to operate the Aß peptide, known as the key factor, requires a complex assembled by its high affinity binding to PrPc, a cell surface prion protein, and mGluR5, a metabotropic glutamate receptor. Aß and its associates bind also phosphorylated tau transferred to the extracellular space, with final activation of intracellular cytotoxic signals. Pathology is further affected by factors (including genes, receptors and their agonists) and by glial cells governing (via vesicles, cytokines and enzymes) cell immunology, inflammation and oxidative stress. Concomitant to pathology studies, strong attempts have been made for the development of new, effective therapies. Critical for this are biomarkers, by which Alzheimer's patients are recognized even before appearance of their symptoms. The question was whether patients take advantage from drugs not yet approved. The latter, first identified in mice, were found effective also in men, however only before appearance or at early stage of the disease. In other words, the drugs not yet approved induce effective protection of patients still healthy or in a preliminary stage of the disease. In contrast, developed Alzheimer's disease is practically irreversible.