The amyloid-beta peptide and its role in Alzheimer's disease

Danshensu inhibits Aβ aggregation and neurotoxicity as one of the main prominent features of Alzheimer's disease

It has been found that the main cause of neurodegenerative proteinopathies, especially Alzheimer's disease (AD) is the formation of Aβ amyloid plaques, which can be regulated by application of potential small molecules. In the present study, we aimed to investigate the inhibitory effect of danshensu on Aβ(1-42) aggregation and relevant apoptotic pathway in neurons. A broad range of spectroscopic, theoretical, and cellular assays were done to investigate the anti-amyloidogenic characteristics of danshensu. It was found that danshensu triggers its inhibitory effect against Aβ(1-42) aggregation through modulation of hydrophobic patches as well as structural and morphological changes through a stacking interaction. Furthermore, it was observed that incubation of Aβ(1-42) samples with danshensu during aggregation process recovered the cell viability and mitigated the expression of caspase-3 mRNA and protein as well caspase-3 activity deregulated by Aβ(1-42) amyloid fibrils alone. In general, obtained data showed that danshensu potentially inhibits Aβ(1-42) aggregation and associated proteinopathies through regulation of apoptotic pathway in a concentration-dependent manner. Therefore, danshensu may be used as a promising biomolecule against the Aβ aggregation and associated proteinopathies, which can be further analyzed in the future studies for the treatment of AD.

Effectiveness of coenzyme Q10 on learning and memory and synaptic plasticity impairment in an aged Aβ-induced rat model of Alzheimer's disease: a behavioral, biochemical, and electrophysiological study

RATIONALE

Aging is the major risk factor for Alzheimer's disease (AD), and cognitive and memory impairments are common among the elderly. Interestingly, coenzyme Q10 (Q10) levels decline in the brain of aging animals. Q10 is a substantial antioxidant substance, which has an important role in the mitochondria.

OBJECTIVE

We assessed the possible effects of Q10 on learning and memory and synaptic plasticity in aged β-amyloid (Aβ)-induced AD rats.

METHODS

In this study, 40 Wistar rats (24-36 months old; 360-450 g) were randomly assigned to four groups (n = 10 rats/group)-group I: control, group II: Aβ, group III: Q10; 50 mg/kg, and group IV: Q10+Aβ. Q10 was administered orally by gavage daily for 4 weeks before the Aβ injection. The cognitive function and learning and memory of the rats were measured by the novel object recognition (NOR), Morris water maze (MWM), and passive avoidance learning (PAL) tests. Finally, malondialdehyde (MDA), total antioxidant capacity (TAC), total thiol group (TTG), and total oxidant status (TOS) were measured.

RESULTS

Q10 improved the Aβ-related decrease in the discrimination index in the NOR test, spatial learning and memory in the MWM test, passive avoidance learning and memory in the PAL test, and long-term potentiation (LTP) impairment in the hippocampal PP-DG pathway in aged rats. In addition, Aβ injection significantly increased serum MDA and TOS levels. Q10, however, significantly reversed these parameters and also increased TAC and TTG levels in the Aβ+Q10 group.

CONCLUSIONS

Our experimental findings suggest that Q10 supplementation can suppress the progression of neurodegeneration that otherwise impairs learning and memory and reduces synaptic plasticity in our experimental animals. Therefore, similar supplemental Q10 treatment given to humans with AD could possibly provide them a better quality of life.

Emerging Applications of Nanotechnology in Healthcare Systems: Grand Challenges and Perspectives

Healthcare, as a basic human right, has often become the focus of the development of innovative technologies. Technological progress has significantly contributed to the provision of high-quality, on-time, acceptable, and affordable healthcare. Advancements in nanoscience have led to the emergence of a new generation of nanostructures. Each of them has a unique set of properties that account for their astonishing applications. Since its inception, nanotechnology has continuously affected healthcare and has exerted a tremendous influence on its transformation, contributing to better outcomes. In the last two decades, the world has seen nanotechnology taking steps towards its omnipresence and the process has been accelerated by extensive research in various healthcare sectors. The inclusion of nanotechnology and its allied nanocarriers/nanosystems in medicine is known as nanomedicine, a field that has brought about numerous benefits in disease prevention, diagnosis, and treatment. Various nanosystems have been found to be better candidates for theranostic purposes, in contrast to conventional ones. This review paper will shed light on medically significant nanosystems, as well as their applications and limitations in areas such as gene therapy, targeted drug delivery, and in the treatment of cancer and various genetic diseases. Although nanotechnology holds immense potential, it is yet to be exploited. More efforts need to be directed to overcome these limitations and make full use of its potential in order to revolutionize the healthcare sector in near future.

Evaluation of the photo-degradation of Alzheimer's amyloid fibrils with a label-free approach

Degradation of amyloid-β (Aβ) aggregates has been considered as an attractive therapeutic and preventive strategy against Alzheimer's disease (AD). However, an in situ, real-time, and label-free technique is still lacking to understand the degradation process of Aβ aggregates. In this work, we developed a novel method to quantitatively evaluate the degradation of Aβ fibrils by photoactive meso-tetra(4-sulfonatophenyl)porphyrin under UV irradiation with quartz crystal microbalance (QCM).

Resveratrol Brain Delivery for Neurological Disorders Prevention and Treatment

Resveratrol (RES) is a natural polyphenolic non-flavonoid compound present in grapes, mulberries, peanuts, rhubarb and in several other plants. Numerous health effects have been related with its intake, such as anti-carcinogenic, anti-inflammatory and brain protective effects. The neuroprotective effects of RES in neurological diseases, such as Alzheimer's (AD) and Parkinson's (PD) diseases, are related to the protection of neurons against oxidative damage and toxicity, and to the prevention of apoptotic neuronal death. In brain cancer, RES induces cell apoptotic death and inhibits angiogenesis and tumor invasion. Despite its great potential as therapeutic agent for the treatment of several diseases, RES exhibits some limitations. It has poor water solubility and it is chemically instable, being degraded by isomerization once exposed to high temperatures, pH changes, UV light, or certain types of enzymes. Thus, RES has low bioavailability, limiting its biological and pharmacological benefits. To overcome these limitations, RES can be delivered by nanocarriers. This field of nanomedicine studies how the drug administration, pharmacokinetics, and pharmacodynamics are affected by the use of nanosized materials. The role of nanotechnology, in the prevention and treatment of neurological diseases, arises from the necessity to mask the physicochemical properties of therapeutic drugs to prolong the half-life and to be able to cross the blood-brain barrier (BBB). This can be achieved by encapsulating the drug in a nanoparticle (NP), which can be made of different kinds of materials. An increasing trend to encapsulate and direct RES to the brain has been observed. RES has been encapsulated in many different types of nanosystems, as liposomes, lipid and polymeric NPs. Furthermore, some of these nanocarriers have been modified with targeting molecules able to recognize the brain areas. Then, this article aims to overview the RES benefits and limitations in the treatment of neurological diseases, as the different nanotechnology strategies to overcome these limitations.

Resveratrol and Grape Extract-loaded Solid Lipid Nanoparticles for the Treatment of Alzheimer's Disease

The aggregation of amyloid-β peptide (Aβ) has been linked to the formation of neuritic plaques, which are pathological hallmarks of Alzheimer's disease (AD). Various natural compounds have been suggested as therapeutics for AD. Among these compounds, resveratrol has aroused great interest due to its neuroprotective characteristics. Here, we provide evidence that grape skin and grape seed extracts increase the inhibition effect on Aβ aggregation. However, after intravenous injection, resveratrol is rapidly metabolized into both glucuronic acid and sulfate conjugations of the phenolic groups in the liver and intestinal epithelial cells (within less than 2 h), which are then eliminated. In the present study, we show that solid lipid nanoparticles (SLNs) functionalized with an antibody, the anti-transferrin receptor monoclonal antibody (OX26 mAb), can work as a possible carrier to transport the extract to target the brain. Experiments on human brain-like endothelial cells show that the cellular uptake of the OX26 SLNs is substantially more efficient than that of normal SLNs and SLNs functionalized with an unspecific antibody. As a consequence, the transcytosis ability of these different SLNs is higher when functionalized with OX-26.

Constant-pH Hybrid Nonequilibrium Molecular Dynamics-Monte Carlo Simulation Method

A computational method is developed to carry out explicit solvent simulations of complex molecular systems under conditions of constant pH. In constant-pH simulations, preidentified ionizable sites are allowed to spontaneously protonate and deprotonate as a function of time in response to the environment and the imposed pH. The method, based on a hybrid scheme originally proposed by H. A. Stern (J. Chem. Phys. 2007, 126, 164112), consists of carrying out short nonequilibrium molecular dynamics (neMD) switching trajectories to generate physically plausible configurations with changed protonation states that are subsequently accepted or rejected according to a Metropolis Monte Carlo (MC) criterion. To ensure microscopic detailed balance arising from such nonequilibrium switches, the atomic momenta are altered according to the symmetric two-ends momentum reversal prescription. To achieve higher efficiency, the original neMD-MC scheme is separated into two steps, reducing the need for generating a large number of unproductive and costly nonequilibrium trajectories. In the first step, the protonation state of a site is randomly attributed via a Metropolis MC process on the basis of an intrinsic pKa; an attempted nonequilibrium switch is generated only if this change in protonation state is accepted. This hybrid two-step inherent pKa neMD-MC simulation method is tested with single amino acids in solution (Asp, Glu, and His) and then applied to turkey ovomucoid third domain and hen egg-white lysozyme. Because of the simple linear increase in the computational cost relative to the number of titratable sites, the present method is naturally able to treat extremely large systems.

Efficient implementation of constant pH molecular dynamics on modern graphics processors

The treatment of pH sensitive ionization states for titratable residues in proteins is often omitted from molecular dynamics (MD) simulations. While static charge models can answer many questions regarding protein conformational equilibrium and protein-ligand interactions, pH-sensitive phenomena such as acid-activated chaperones and amyloidogenic protein aggregation are inaccessible to such models. Constant pH molecular dynamics (CPHMD) coupled with the Generalized Born with a Simple sWitching function (GBSW) implicit solvent model provide an accurate framework for simulating pH sensitive processes in biological systems. Although this combination has demonstrated success in predicting pKa values of protein structures, and in exploring dynamics of ionizable side-chains, its speed has been an impediment to routine application. The recent availability of low-cost graphics processing unit (GPU) chipsets with thousands of processing cores, together with the implementation of the accurate GBSW implicit solvent model on those chipsets (Arthur and Brooks, J. Comput. Chem. 2016, 37, 927), provide an opportunity to improve the speed of CPHMD and ionization modeling greatly. Here, we present a first implementation of GPU-enabled CPHMD within the CHARMM-OpenMM simulation package interface. Depending on the system size and nonbonded force cutoff parameters, we find speed increases of between one and three orders of magnitude. Additionally, the algorithm scales better with system size than the CPU-based algorithm, thus allowing for larger systems to be modeled in a cost effective manner. We anticipate that the improved performance of this methodology will open the door for broad-spread application of CPHMD in its modeling pH-mediated biological processes. © 2016 Wiley Periodicals, Inc.

Cellular uptake of PLGA nanoparticles targeted with anti-amyloid and anti-transferrin receptor antibodies for Alzheimer's disease treatment

During the last few decades, relevant efforts have been reported to design nanocarriers for drug transport through the blood brain barrier (BBB). New drugs, such as peptide iAβ5, capable to inhibit the aggregates associated with Alzheimeŕs disease (AD) are being tested but the most frequent drawback is to reach the brain in the desired concentrations due to the low BBB permeability-surface area. Our approach, as a proof of concept to improve drug transport through the BBB, is based on poly(lactic-co-glycolic acid) (PLGA) nanoparticles with surface functionalized with anti-transferrin receptor monoclonal antibody (OX26) and anti-Aβ (DE2B4) to deliver encapsulated iAβ5 into the brain. Porcine brain capillary endothelial cells (PBCECs) were used as a BBB model to evaluate the system efficacy and toxicity. The uptake of immune nanoparticles with a controlled delivery of the peptide iAβ5 was substantially increased compared to the nanoparticles (NPs) without monoclonal antibody functionalization.

The road to the synthesis of "difficult peptides"

The last decade has witnessed a renaissance of peptides as drugs. This progress, together with advances in the structural behavior of peptides, has attracted the interest of the pharmaceutical industry in these molecules as potential APIs. In the past, major peptide-based drugs were inspired by sequences extracted from natural structures of low molecular weight. In contrast, nowadays, the peptides being studied by academic and industrial groups comprise more sophisticated sequences. For instance, they consist of long amino acid chains and show a high tendency to form aggregates. Some researchers have claimed that preparing medium-sized proteins is now feasible with chemical ligation techniques, in contrast to medium-sized peptide syntheses. The complexity associated with the synthesis of certain peptides is exemplified by the so-called "difficult peptides", a concept introduced in the 80's. This refers to sequences that show inter- or intra-molecular β-sheet interactions significant enough to form aggregates during peptide synthesis. These structural associations are stabilized and mediated by non-covalent hydrogen bonds that arise on the backbone of the peptide and-depending on the sequence-are favored. The tendency of peptide chains to aggregate is translated into a list of common behavioral features attributed to "difficult peptides" which hinder their synthesis. In this regard, this manuscript summarizes the strategies used to overcome the inherent difficulties associated with the synthesis of known "difficult peptides". Here we evaluate several external factors, as well as methods to incorporate chemical modifications into sequences, in order to describe the strategies that are effective for the synthesis of "difficult peptides". These approaches have been classified and ordered to provide an extensive guide for achieving the synthesis of peptides with the aforementioned features.

Structure-activity relationships for a series of compounds that inhibit aggregation of the Alzheimer's peptide, Aβ42

Inhibiting aggregation of the amyloid-beta (Aβ) peptide may be an effective strategy for combating Alzheimer's disease. As the high-resolution structure of the toxic Aβ aggregate is unknown, rational design of small molecule inhibitors is not possible, and inhibitors are best isolated by high-throughput screening. We applied high-throughput screening to a collection of 65,000 compounds to identify compound D737 as an inhibitor of Aβ aggregation. D737 diminished the formation of oligomers and fibrils, and reduced Aβ42-induced cytotoxicity. Most importantly, D737 increased the life span and locomotive ability of transgenic flies in a Drosophila melanogaster model of Alzheimer's disease (J Biol Chem, 287, 2012, 38992). To explore the chemical features that make D737 an effective inhibitor of Aβ42 aggregation and toxicity, we tested a small collection of eleven analogues of D737. Overall, the ability of a compound to inhibit Aβ aggregation was a good predictor of its efficacy in prolonging the life span and locomotive ability of transgenic flies expressing human Aβ42 in the central nervous system. Two compounds (D744 and D830) with fluorine substitutions on an aromatic ring were effective inhibitors of Aβ42 aggregation and increased the longevity of transgenic flies beyond that observed for the parent compound, D737.

Targeting nanoparticles across the blood-brain barrier with monoclonal antibodies

Development of therapeutics for brain disorders is one of the more difficult challenges to be overcome by the scientific community due to the inability of most molecules to cross the blood-brain barrier (BBB). Antibody-conjugated nanoparticles are drug carriers that can be used to target encapsulated drugs to the brain endothelial cells and have proven to be very promising. They significantly improve the accumulation of the drug in pathological sites and decrease the undesirable side effect of drugs in healthy tissues. We review the systems that have demonstrated promising results in crossing the BBB through receptor-mediated endocytic mechanisms for the treatment of neurodegenerative disorders such as Alzheimer's and Parkinson's disease.

Does aluminium bind to histidine? An NMR investigation of amyloid β12 and amyloid β16 fragments

Aluminium and zinc are known to be the major triggering agents for aggregation of amyloid peptides leading to plaque formation in Alzheimer's disease. While zinc binding to histidine in Aβ (amyloid β) fragments has been implicated as responsible for aggregation, not much information is available on the interaction of aluminium with histidine. In the NMR study of the N-terminal Aβ fragments, DAEFRHDSGYEV (Aβ12) and DAEFRHDSGYEVHHQK (Aβ16) presented here, the interactions of the fragments with aluminium have been investigated. Significant chemical shifts were observed for few residues near the C-terminus when aluminium chloride was titrated with Aβ12 and Aβ16 peptides. Surprisingly, it is nonhistidine residues which seem to be involved in aluminium binding. Based on NMR constrained structure obtained by molecular modelling, aluminium-binding pockets in Aβ12 were around charged residues such as Asp, Glu. The results are discussed in terms of native structure propagation, and the relevance of histidine residues in the sequences for metal-binding interactions. We expect that the study of such short amyloid peptide fragments will not only provide clues for plaque formation in aggregated conditions but also facilitate design of potential drugs for these targets.

The protective role of carnosic acid against beta-amyloid toxicity in rats

Oxidative stress is one of the pathological mechanisms responsible for the beta- amyloid cascade associated with Alzheimer's disease (AD). Previous studies have demonstrated the role of carnosic acid (CA), an effective antioxidant, in combating oxidative stress. A progressive cognitive decline is one of the hallmarks of AD. Thus, we attempted to determine whether the administration of CA protects against memory deficit caused by beta-amyloid toxicity in rats. Beta-amyloid (1-40) was injected by stereotaxic surgery into the Ca1 region of the hippocampus of rats in the Amyloid beta (Aβ) groups. CA was delivered intraperitoneally, before and after surgery in animals in the CA groups. Passive avoidance learning and spontaneous alternation behavior were evaluated using the shuttle box and the Y-maze, respectively. The degenerating hippocampal neurons were detected by fluoro-jade b staining. We observed that beta-amyloid (1-40) can induce neurodegeneration in the Ca1 region of the hippocampus by using fluoro-jade b staining. Also, the behavioral tests revealed that CA may recover the passive avoidance learning and spontaneous alternation behavior scores in the Aβ + CA group, in comparison with the Aβ group. We found that CA may ameliorate the spatial and learning memory deficits induced by the toxicity of beta-amyloid in the rat hippocampus.

Capturing molten globule state of α-lactalbumin through constant pH molecular dynamics simulations

The recently developed methods of constant pH molecular dynamics directly captures the correlation between protonation and conformation to probe protein structure, function, and dynamics. In this work, we investigate the effect of pH on the conformational properties of the protein human α-lactalbumin. Constant pH simulations at both acidic and alkaline medium indicate the formation of the molten globule state, which is in accordance with the previous experimental observations (especially, in acidic medium). The size of the protein measured by its radius of gyration (RG) exhibits a marked increase in both acidic and alkaline medium, which matches with the corresponding experimentally observed value of RG found in the molten globule. The probability of native contacts is also considerably reduced at acidic and basic pH as compared to that of native structure crystallized at neutral pH. The mean fractal dimension D2 of the protein records a sharp increase in basic medium as compared to those in neutral and acidic solutions implying a significant pH induced conformational change. The mean square fluctuations of all residues of the entire protein are found to increase by several folds in both acidic and basic medium, which may be correlated with the normalized solvent accessibility of the residues indicating role of solvent accessible surface area on protein internal dynamics. The helices comprising the α-domain of the protein are moderately preserved in the acidic and alkaline pH. However, the β-sheet structures present in the β-domain are completely disrupted in both acidic as well as basic pH.

Charged surfactants induce a non-fibrillar aggregation pathway of amyloid-beta peptide

The amyloid β-peptide with a sequence of 42 amino acids is the major constituent of extracellular amyloid deposits in Alzheimer's disease plaques. The control of the peptide self-assembly is difficult to achieve because the process is fast and is affected by many variables. In this paper, we describe the effect of different charged and non-charged surfactants on Aβ(₁₋₄₂) fibrillation to define common alternate aggregation pathways. The characterization of the peptide-surfactant interactions by ultra-structural analysis, thioflavin T assay and secondary structure analysis, suggested that charged surfactants interact with Aβ(₁₋₄₂) through electrostatic interactions. Charged micelles slow down the aggregation process and stabilize the peptide in the oligomeric state, whereas non-charged surfactants promote the Aβ(₁₋₄₂) fibril formation.

In silico investigation and targeting of amyloid β oligomers of different size

Aggregation of amyloid β (Aβ) peptides into fibrils has been implicated in the pathogenesis of Alzheimer's disease (AD). As a result, in recent years, substantial efforts have been expended in the study of the mechanism of aggregation of the Aβ peptide as well as of its inhibition by potential drug molecules. In this context, we have built a model of the Aβ(17-42) deca-oligomer using the solid-state NMR (ssNMR) structure of the Aβ(17-42) penta-oligomer as a reference. Both the penta- and deca-oligomer systems have been studied by all-atom molecular dynamics (MD) simulations and used as target systems for the investigation of the mechanism of action of a trehalose-derived Aβ aggregation inhibitor. In the deca-oligomer all the main structural features of the putative fibrillar state are retained. Moreover, the simulations reveal a remarkable gain in stability as the oligomer grows. MD studies of the inhibitor in complex with the penta- and deca-oligomers indicate a significant destabilization of the structure beyond the hampering of the addition of successive Aβ peptides at the ends of the fibril due to the presence of the inhibitor molecule. Our work provides an easy and effective approach which could be useful for the in silico development of potential drug molecules acting at different stages of the progression of Aβ-related diseases.

Interaction between amyloid-β peptide and heme probed by electrochemistry and atomic force microscopy

Heme binds to amyloid β-peptide (Aβ) in the brain of Alzheimer's disease (AD) patients, thus forming Aβ-heme complexes and leading the characteristic pathological features of AD. The interaction between heme and Aβ might have important biological relevance to AD etiology. In this work, the electrochemical performances of heme after incubation with Aβ1-42, Aβ fragments, and mutated Aβ were systematically investigated using cyclic voltammetry and differential pulse voltammetry. Our results indicated that His13 and His14 were possible binding sites, and Aβ bound two molecules of heme with a binding constant of K(a1) = 7.27 × 10(6) M(-1) (n(1) = 1.5) and K(a2) = 2.89 × 10(6) M(-1) (n(1) = 1.8). Detailed analysis with atomic force microscopy (AFM) of Aβ1-42 in the absence or presence of heme under the same incubation conditions showed that heme inhibited the formation of Aβ fibrils. According to results of the spectroscopic characterization, Arg5 was the key residue in making the heme-Aβ1-42 complex as a peroxidase.

Glutamate system, amyloid ß peptides and tau protein: functional interrelationships and relevance to Alzheimer disease pathology

Alzheimer disease is the most prevalent form of dementia globally and is characterized premortem by a gradual memory loss and deterioration of higher cognitive functions and postmortem by neuritic plaques containing amyloid ß peptide and neurofibrillary tangles containing phospho-tau protein. Glutamate is the most abundant neurotransmitter in the brain and is essential to memory formation through processes such as long-term potentiation and so might be pivotal to Alzheimer disease progression. This review discusses how the glutamatergic system is impaired in Alzheimer disease and how interactions of amyloid ß and glutamate influence synaptic function, tau phosphorylation and neurodegeneration. Interestingly, glutamate not only influences amyloid ß production, but also amyloid ß can alter the levels of glutamate at the synapse, indicating that small changes in the concentrations of both molecules could influence Alzheimer disease progression. Finally, we describe how the glutamate receptor antagonist, memantine, has been used in the treatment of individuals with Alzheimer disease and discuss its effectiveness.

A novel inhibitor of amyloid β (Aβ) peptide aggregation: from high throughput screening to efficacy in an animal model of Alzheimer disease

Compelling evidence indicates that aggregation of the amyloid β (Aβ) peptide is a major underlying molecular culprit in Alzheimer disease. Specifically, soluble oligomers of the 42-residue peptide (Aβ42) lead to a series of events that cause cellular dysfunction and neuronal death. Therefore, inhibiting Aβ42 aggregation may be an effective strategy for the prevention and/or treatment of disease. We describe the implementation of a high throughput screen for inhibitors of Aβ42 aggregation on a collection of 65,000 small molecules. Among several novel inhibitors isolated by the screen, compound D737 was most effective in inhibiting Aβ42 aggregation and reducing Aβ42-induced toxicity in cell culture. The protective activity of D737 was most significant in reducing the toxicity of high molecular weight oligomers of Aβ42. The ability of D737 to prevent Aβ42 aggregation protects against cellular dysfunction and reduces the production/accumulation of reactive oxygen species. Most importantly, treatment with D737 increases the life span and locomotive ability of flies in a Drosophila melanogaster model of Alzheimer disease.

Role of cholesterol in APP metabolism and its significance in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disorder believed to be initiated by accumulation of amyloid β (Aβ)-related peptides derived from proteolytic processing of amyloid precursor protein (APP). Research over the past two decades provided a mechanistic link between cholesterol and AD pathogenesis. Genetic polymorphisms in genes regulating the pivotal points in cholesterol metabolism have been suggested to enhance the risk of developing AD. Altered neuronal membrane cholesterol level and/or subcellular distribution have been implicated in aberrant formation, aggregation, toxicity, and degradation of Aβ-related peptides. However, the results are somewhat contradictory and we still do not have a complete understanding on how cholesterol can influence AD pathogenesis. In this review, we summarize our current understanding on the role of cholesterol in regulating the production/function of Aβ-related peptides and also examine the therapeutic potential of regulating cholesterol homeostasis in the treatment of AD pathology.

Altered levels and distribution of amyloid precursor protein and its processing enzymes in Niemann-Pick type C1-deficient mouse brains

Niemann-Pick type C (NPC) disease is an autosomal recessive neurodegenerative disorder characterized by intracellular accumulation of cholesterol and glycosphingolipids in many tissues including the brain. The disease is caused by mutations of either NPC1 or NPC2 gene and is accompanied by a severe loss of neurons in the cerebellum, but not in the hippocampus. NPC pathology exhibits some similarities with Alzheimer's disease, including increased levels of amyloid beta (Abeta)-related peptides in vulnerable brain regions, but very little is known about the expression of amyloid precursor protein (APP) or APP secretases in NPC disease. In this article, we evaluated age-related alterations in the level/distribution of APP and its processing enzymes, beta- and gamma-secretases, in the hippocampus and cerebellum of Npc1(-/-) mice, a well-established model of NPC pathology. Our results show that levels and expression of APP and beta-secretase are elevated in the cerebellum prior to changes in the hippocampus, whereas gamma-secretase components are enhanced in both brain regions at the same time in Npc1(-/-) mice. Interestingly, a subset of reactive astrocytes in Npc1(-/-) mouse brains expresses high levels of APP as well as beta- and gamma-secretase components. Additionally, the activity of beta-secretase is enhanced in both the hippocampus and cerebellum of Npc1(-/-) mice at all ages, while the level of C-terminal APP fragments is increased in the cerebellum of 10-week-old Npc1(-/-) mice. These results, taken together, suggest that increased level and processing of APP may be associated with the development of pathology and/or degenerative events observed in Npc1(-/-) mouse brains.

Direct solid-phase synthesis of the beta-amyloid (1-42) peptide using controlled microwave heating

Standard linear Fmoc/t-Bu solid-phase synthesis of the 42-mer beta-amyloid (1-42) peptide was achieved under controlled microwave conditions at 86 degrees C using inexpensive DIC/HOBt as coupling reagent on ChemMatrix resin. In order to avoid racemization of the sensitive amino acids, the coupling of the three His residues in the difficult peptide sequence was performed at room temperature. The desired peptide was obtained within 15 h overall processing time in high yield and purity (78% crude yield).

CHARMM-GUI: a web-based graphical user interface for CHARMM

CHARMM is an academic research program used widely for macromolecular mechanics and dynamics with versatile analysis and manipulation tools of atomic coordinates and dynamics trajectories. CHARMM-GUI, http://www.charmm-gui.org, has been developed to provide a web-based graphical user interface to generate various input files and molecular systems to facilitate and standardize the usage of common and advanced simulation techniques in CHARMM. The web environment provides an ideal platform to build and validate a molecular model system in an interactive fashion such that, if a problem is found through visual inspection, one can go back to the previous setup and regenerate the whole system again. In this article, we describe the currently available functional modules of CHARMM-GUI Input Generator that form a basis for the advanced simulation techniques. Future directions of the CHARMM-GUI development project are also discussed briefly together with other features in the CHARMM-GUI website, such as Archive and Movie Gallery.

Recognition of conformational changes in beta-lactoglobulin by molecularly imprinted thin films

Pathogenesis in protein conformational diseases is initiated by changes in protein secondary structure. This molecular restructuring presents an opportunity for novel shape-based detection approaches, as protein molecular weight and chemistry are otherwise unaltered. Here we apply molecular imprinting to discriminate between distinct conformations of the model protein beta-lactoglobulin (BLG). Thermal- and fluoro-alcohol-induced BLG isoforms were imprinted in thin films of 3-aminophenylboronic acid on quartz crystal microbalance chips. Enhanced rebinding of the template isoform was observed in all cases when compared to the binding of nontemplate isoforms over the concentration range of 1-100 microg mL(-1). Furthermore, it was observed that the greater the changes in the secondary structure of the template protein the lower the binding of native BLG challenges to the imprint, suggesting a strong steric influence in the recognition system. This feasibility study is a first demonstration of molecular imprints for recognition of distinct conformations of the same protein.

Amyloid-beta aggregation

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in the growing population of elderly people. A hallmark of AD is the accumulation of plaques in the brain of AD patients. The plaques predominantly consist of aggregates of amyloid-beta (Abeta), a peptide of 39-42 amino acids generated in vivo by specific, proteolytic cleavage of the amyloid precursor protein. There is a growing body of evidence that Abeta aggregates are ordered oligomers and the cause rather than a product of AD. The analysis of the assembly pathway of Abeta in vitro and biochemical characterization of Abeta deposits isolated from AD brains indicate that Abeta oligomerization occurs via distinct intermediates, including oligomers of 3-50 Abeta monomers, annular oligomers, protofibrils, fibrils and plaques. Of these, the most toxic species appear to be small Abeta oligomers. This article reviews the current knowledge of the mechanism of Abeta assembly in vivo and in vitro, as well as the influence of inherited amino acid replacements in Abeta and experimental conditions on Abeta aggregation. Challenges regarding the reproducible handling of the Abeta peptide for in vitro assembly studies are discussed.

Pellagra: A clue as to why energy failure causes diseases?

Pellagra is a curable dietary illness that unchecked leads to dementia, diarrhoea, dermatitis and death due to lack of the precursors for NAD(H). In addition it caused a wide range of monosyndromic degenerative and functional neurological disorders as well as profound developmental, premature aging and metabolic syndromes. Pellagrins harbour many chronic infections including tuberculosis, yeasts and malaria, that may be symbionts supplying nicotinamide adenine dinucleotide {NAD(H)} when the diet is poor. Many common diseases and aging may be caused by electrogenic energy mismatches from lack of a timely supply of NAD(H) creating disturbed metabolic fields and "protonopathies". Initially these may present in compartments fronted by homeostatic corrections from chronic symbiotic infections to inflammatory disease, cancer and degenerative/autophagic diseases that can all release NAD(H).

Amyloid β-peptide Aβ1–42 but not Aβ1–40 attenuates synaptic AMPA receptor function

The brains of Alzheimer's disease (AD) patients have large numbers of plaques that contain amyloid beta (Abeta) peptides which are believed to play a pivotal role in AD pathology. Several lines of evidence have established the inhibitory role of Abeta peptides on hippocampal memory encoding, a process that relies heavily on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function. In this study the modulatory effects of the two major Abeta peptides, Abeta(1-40) and Abeta(1-42), on synaptic AMPA receptor function was investigated utilizing the whole cell patch clamp technique and analyses of single channel properties of synaptic AMPA receptors. Bath application of Abeta(1-42) but not Abeta(1-40) reduced both the amplitude and frequency of AMPA receptor mediated excitatory postsynaptic currents in hippocampal CA1 pyramidal neurons by approximately 60% and approximately 45%, respectively, in hippocampal CA1 pyramidal neurons. Furthermore, experiments with single synaptic AMPA receptors reconstituted in artificial lipid bilayers showed that Abeta(1-42) reduced the channel open probability by approximately 42% and channel open time by approximately 65% and increased the close times by several fold. Abeta(1-40), however, did not show such inhibitory effects on single channel properties. Application of the reverse sequence peptide Abeta(42-1) also did not alter the mEPSC or single channel properties. These results suggest that Abeta(1-42) but not Abeta(1-40) closely interacts with and exhibits inhibitory effects on synaptic AMPA receptors and may contribute to the memory impairment observed in AD.

Mitoenergetic failure in Alzheimer disease

Brain cells are highly energy dependent for maintaining ion homeostasis during high metabolic activity. During active periods, full mitochondrial function is essential to generate ATP from electrons that originate with the oxidation of NADH. Decreasing brain metabolism is a significant cause of cognitive abnormalities of Alzheimer disease (AD), but it remains uncertain whether this is the cause of further pathology or whether synaptic loss results in a lower energy demand. Synapses are the first to show pathological symptoms in AD before the onset of clinical symptoms. Because synaptic function has high energy demands, interruption in mitochondrial energy supply could be the major factor in synaptic failure in AD. A newly discovered age-related decline in neuronal NADH and redox ratio may jeopardize this function. Mitochondrial dehydrogenases and several mutations affecting energy transfer are frequently altered in aging and AD. Thus, with the accumulation of genetic defects in mitochondria at the level of energy transfer, the issue of neuronal susceptibility to damage as a function of age and age-related disease becomes important. In an aging rat neuron model, mitochondria are both chronically depolarized and produce more reactive oxygen species with age. These concepts suggest that multiple treatment targets may be needed to reverse this multifactorial disease. This review summarizes new insights based on the interaction of mitoenergetic failure, glutamate excitotoxicity, and amyloid toxicity in the exacerbation of AD.

The alpha-to-beta conformational transition of Alzheimer's Abeta-(1-42) peptide in aqueous media is reversible: a step by step conformational analysis suggests the location of beta conformation seeding

Current views of the role of beta-amyloid (Abeta) peptide fibrils range from regarding them as the cause of Alzheimer's pathology to having a protective function. In the last few years, it has also been suggested that soluble oligomers might be the most important toxic species. In all cases, the study of the conformational properties of Abeta peptides in soluble form constitutes a basic approach to the design of molecules with "antiamyloid" activity. We have experimentally investigated the conformational path that can lead the Abeta-(1-42) peptide from the native state, which is represented by an alpha helix embedded in the membrane, to the final state in the amyloid fibrils, which is characterized by beta-sheet structures. The conformational steps were monitored by using CD and NMR spectroscopy in media of varying polarities. This was achieved by changing the composition of water and hexafluoroisopropanol (HFIP). In the presence of HFIP, beta conformations can be observed in solutions that have very high water content (up to 99 % water; v/v). These can be turned back to alpha helices simply by adding the appropriate amount of HFIP. The transition of Abeta-(1-42) from alpha to beta conformations occurs when the amount of water is higher than 80 % (v/v). The NMR structure solved in HFIP/H2O with high water content showed that, on going from very apolar to polar environments, the long N-terminal helix is essentially retained, whereas the shorter C-terminal helix is lost. The complete conformational path was investigated in detail with the aid of molecular-dynamics simulations in explicit solvent, which led to the localization of residues that might seed beta conformations. The structures obtained might help to find regions that are more affected by environmental conditions in vivo. This could in turn aid the design of molecules able to inhibit fibril deposition or revert oligomerization processes.

Noncovalent interaction between amyloid-beta-peptide (1-40) and oleuropein studied by electrospray ionization mass spectrometry

Beta amyloid peptide (Abeta) is the major proteinaceous component of senile plaques formed in Alzheimer's disease (AD) brain. The aggregation of Abeta is associated with neurodegeneration, loss of cognitive ability, and premature death. It has been suggested that oxidative stress and generation of free radical species have implications in the fibrillation of Abeta and its subsequent neurotoxicity. For this reason, it is proposed that antioxidants may offer a protective or therapeutic alternative against amyloidosis. This study is the first report of the formation of the noncovalent complex between Abeta or its oxidized form and the natural derived antioxidant oleuropein (OE) by electrospray ionization mass spectrometry (ESI MS). ESI MS allowed the real time monitoring of the complex formation between Abeta, OE, and variants thereof. Several experimental conditions, such as elevated orifice potential, low pH values, presence of organic modifier, and ligand concentration were examined, to assess the specificity and the stability of the formed noncovalent complexes.

Structure and Orientation of Peptide Inhibitors Bound to Beta-amyloid Fibrils

Polymerization of the soluble beta-amyloid peptide into highly ordered fibrils is hypothesized to be a causative event in the development of Alzheimer's disease. Understanding the interactions of Abeta with inhibitors on an atomic level is fundamental for the development of diagnostics and therapeutic approaches, and can provide, in addition, important indirect information of the amyloid fibril structure. We have shown recently that trRDCs can be measured in solution state NMR for peptide ligands binding weakly to amyloid fibrils. We present here the structures for two inhibitor peptides, LPFFD and DPFFL, and their structural models bound to fibrillar Abeta(14-23) and Abeta(1-40) based on transferred nuclear Overhauser effect (trNOE) and transferred residual dipolar coupling (trRDC) data. In a first step, the inhibitor peptide structure is calculated on the basis of trNOE data; the trRDC data are then validated on the basis of the trNOE-derived structure using the program PALES. The orientation of the peptide inhibitors with respect to Abeta fibrils is obtained from trRDC data, assuming that Abeta fibrils orient such that the fibril axis is aligned in parallel with the magnetic field. The trRDC-derived alignment tensor of the peptide ligand is then used as a restraint for molecular dynamics docking studies. We find that the structure with the lowest rmsd value is in agreement with a model in which the inhibitor peptide binds to the long side of an amyloid fibril. Especially, we detect interactions involving the hydrophobic core, residues K16 and E22/D23 of the Abeta sequence. Structural differences are observed for binding of the inhibitor peptide to Abeta14-23 and Abeta1-40 fibrils, respectively, indicating different fibril structure. We expect this approach to be useful in the rational design of amyloid ligands with improved binding characteristics.