Interaction between synthetic amyloid-beta-peptide (1-40) and its aggregation inhibitors studied by electrospray ionization mass spectrometry

Melatonin facts: Lack of evidence that melatonin is a radical scavenger in living systems

Melatonin is a small natural compound, so called a neuro-hormone that is synthesized mainly in pineal gland in animals. Its main role is to master the clock of the body, under the surveillance of light. In other words, it transfers the information concerning night and day to the peripheral organs which, without it, could not "know" which part of the circadian rhythm the body is in. Besides its main circadian and circannual rhythms mastering, melatonin is reported to be a radical scavenger and/or an antioxidant. Because radical scavengers are chemical species able to neutralize highly reactive and toxic species such as reactive oxygen species, one would like to transfer this property to living system, despite impossibilities already largely reported in the literature. In the present commentary, we refresh the memory of the readers with this notion of radical scavenger, and review the possible evidence that melatonin could be an in vivo radical scavenger, while we only marginally discuss here the fact that melatonin is a molecular antioxidant, a feature that merits a review on its own. We conclude four things: (i) the evidence that melatonin is a scavenger in acellular systems is overwhelming and could not be doubted; (ii) the transposition of this property in living (animal) systems is (a) theoretically impossible and (b) not proven in any system reported in the literature where most of the time, the delay of the action of melatonin is over several hours, thus signing a probable induction of cellular enzymatic antioxidant defenses; (iii) this last fact needs a confirmation through the discovery of a nuclear factor-a key relay in induction processes-that binds melatonin and is activated by it and (iv) we also gather the very important description of the radical scavenging capacity of melatonin in acellular systems that is now proven and shared by many other double bond-bearing molecules. We finally discussed briefly on the reason-scientific or else-that led this description, and the consequences of this claim, in research, in physiology, in pathology, but most disturbingly in therapeutics where a vast amount of money, hope, and patient bien-être are at stake.

The structural and functional consequences of melatonin and serotonin on human αB-crystallin and their dual role in the eye lens transparency

Crystallins are the major soluble lens proteins, and α-crystallin, the most important protective protein of the eye lens, has two subunits (αA and αB) with chaperone activity. αB-crystallin (αB-Cry) with a relatively wide tissue distribution has an innate ability to interact effectively with the misfolded proteins, preventing their aggregation. Melatonin and serotonin have also been identified in relatively high concentrations in the lenticular tissues. This study investigated the effect of these naturally occurring compounds and medications on the structure, oligomerization, aggregation, and chaperone-like activity of human αB-Cry. Various spectroscopic methods, dynamic light scattering (DLS), differential scanning calorimetry (DSC), and molecular docking have been used for this purpose. Based on our results, melatonin indicates an inhibitory effect on the aggregation of human αB-Cry without altering its chaperone-like activity. However, serotonin decreases αB-Cry oligomeric size distribution by creating hydrogen bonds, decreases its chaperone-like activity, and at high concentrations increases protein aggregation.

Light, Water, and Melatonin: The Synergistic Regulation of Phase Separation in Dementia

The swift rise in acceptance of molecular principles defining phase separation by a broad array of scientific disciplines is shadowed by increasing discoveries linking phase separation to pathological aggregations associated with numerous neurodegenerative disorders, including Alzheimer’s disease, that contribute to dementia. Phase separation is powered by multivalent macromolecular interactions. Importantly, the release of water molecules from protein hydration shells into bulk creates entropic gains that promote phase separation and the subsequent generation of insoluble cytotoxic aggregates that drive healthy brain cells into diseased states. Higher viscosity in interfacial waters and limited hydration in interiors of biomolecular condensates facilitate phase separation. Light, water, and melatonin constitute an ancient synergy that ensures adequate protein hydration to prevent aberrant phase separation. The 670 nm visible red wavelength found in sunlight and employed in photobiomodulation reduces interfacial and mitochondrial matrix viscosity to enhance ATP production via increasing ATP synthase motor efficiency. Melatonin is a potent antioxidant that lowers viscosity to increase ATP by scavenging excess reactive oxygen species and free radicals. Reduced viscosity by light and melatonin elevates the availability of free water molecules that allow melatonin to adopt favorable conformations that enhance intrinsic features, including binding interactions with adenosine that reinforces the adenosine moiety effect of ATP responsible for preventing water removal that causes hydrophobic collapse and aggregation in phase separation. Precise recalibration of interspecies melatonin dosages that account for differences in metabolic rates and bioavailability will ensure the efficacious reinstatement of the once-powerful ancient synergy between light, water, and melatonin in a modern world.

Effects of Aluminum Oxide Nanoparticles in the Cerebrum, Hippocampus, and Cerebellum of Male Wistar Rats and Potential Ameliorative Role of Melatonin

Aluminum oxide nanoparticles (Al₂O₃ NPs) have been widely used in vaccine manufacture, food additives, human care products, and cosmetics. However, they also have adverse effects on different organs, including the liver, kidneys, and testes. Melatonin is a potent antioxidant, particularly against metals by forming melatonin-metal complexes. The present study aimed to investigate the protective effects of melatonin against Al₂O₃ NP-induced toxicity in the rat brain. Forty adult male Wistar rats were allocated to four groups: the untreated control (received standard diet and distilled water), Al₂O₃ NP-treated (received 30 mg/kg body weight Al₂O₃ NPs), melatonin and Al₂O₃ NP-treated (received 30 mg/kg body weight Al₂O₃ NPs + 10 mg/kg body weight melatonin), and melatonin-treated (received 10 mg/kg body weight melatonin) groups. All treatments were by oral gavages and administered daily for 28 days. Afterward, the rats were sacrificed, and samples from various brain regions (cerebrum, cerebellum, and hippocampus) were subjected to biochemical, histopathological, and immunohistochemical analyses. Al₂O₃ NPs substantially increased malondialdehyde, β-amyloid 1-42 peptide, acetylcholinesterase, and β-secretase-1 expression, whereas they markedly decreased glutathione levels. Furthermore, Al₂O₃ NPs induced severe histopathological alterations, including vacuolation of the neuropil, enlarged pericellular and perivascular spaces, vascular congestion, neuronal degeneration, and pyknosis. Al₂O₃ NP treatment also resulted in an intense positive caspase-3 immunostaining. Conversely, the administration of melatonin alleviated the adverse effects induced by Al₂O₃ NPs. Therefore, melatonin can diminish the neurotoxic effects induced by Al₂O₃ NPs.

Biological and methodological complexities of beta-amyloid peptide: Implications for Alzheimer's disease research

Although controversial, the amyloid cascade hypothesis remains central to the Alzheimer's disease (AD) field and posits amyloid-beta (Aβ) as the central factor initiating disease onset. In recent years, there has been an increase in emphasis on studying the role of low molecular weight aggregates, such as oligomers, which are suggested to be more neurotoxic than fibrillary Aβ. Other Aβ isoforms, such as truncated Aβ, have also been implicated in disease. However, developing a clear understanding of AD pathogenesis has been hampered by the complexity of Aβ biochemistry in vitro and in vivo. This review explores factors contributing to the lack of consistency in experimental approaches taken to model Aβ aggregation and toxicity and provides an overview of the different techniques available to analyse Aβ, such as electron and atomic force microscopy, nuclear magnetic resonance spectroscopy, dye-based assays, size exclusion chromatography, mass spectrometry and SDS-PAGE. The review also explores how different types of Aβ can influence Aβ aggregation and toxicity, leading to variation in experimental outcomes, further highlighting the need for standardisation in Aβ preparations and methods used in current research.

Melatonin: Regulation of Biomolecular Condensates in Neurodegenerative Disorders

Biomolecular condensates are membraneless organelles (MLOs) that form dynamic, chemically distinct subcellular compartments organizing macromolecules such as proteins, RNA, and DNA in unicellular prokaryotic bacteria and complex eukaryotic cells. Separated from surrounding environments, MLOs in the nucleoplasm, cytoplasm, and mitochondria assemble by liquid-liquid phase separation (LLPS) into transient, non-static, liquid-like droplets that regulate essential molecular functions. LLPS is primarily controlled by post-translational modifications (PTMs) that fine-tune the balance between attractive and repulsive charge states and/or binding motifs of proteins. Aberrant phase separation due to dysregulated membrane lipid rafts and/or PTMs, as well as the absence of adequate hydrotropic small molecules such as ATP, or the presence of specific RNA proteins can cause pathological protein aggregation in neurodegenerative disorders. Melatonin may exert a dominant influence over phase separation in biomolecular condensates by optimizing membrane and MLO interdependent reactions through stabilizing lipid raft domains, reducing line tension, and maintaining negative membrane curvature and fluidity. As a potent antioxidant, melatonin protects cardiolipin and other membrane lipids from peroxidation cascades, supporting protein trafficking, signaling, ion channel activities, and ATPase functionality during condensate coacervation or dissolution. Melatonin may even control condensate LLPS through PTM and balance mRNA- and RNA-binding protein composition by regulating N6-methyladenosine (m6A) modifications. There is currently a lack of pharmaceuticals targeting neurodegenerative disorders via the regulation of phase separation. The potential of melatonin in the modulation of biomolecular condensate in the attenuation of aberrant condensate aggregation in neurodegenerative disorders is discussed in this review.

Melatonin regulates Aβ production/clearance balance and Aβ neurotoxicity: A potential therapeutic molecule for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease with multiple predisposing factors and complicated pathogenesis. Aβ peptide is one of the most important pathogenic factors in the etiology of AD. Accumulating evidence indicates that the imbalance of Aβ production and Aβ clearance in the brain of AD patients leads to Aβ deposition and neurotoxic Aβ oligomer formation. Melatonin shows a potent neuroprotective effect and can prevent or slow down the progression of AD, supporting the view that melatonin is a potential therapeutic molecule for AD. Melatonin modulates the regulatory network of secretase expression and affects the function of secretase, thereby inhibiting amyloidogenic APP processing and Aβ production. Additionally, melatonin ameliorates Aβ-induced neurotoxicity and probably promotes Aβ clearance through glymphatic-lymphatic drainage, BBB transportation and degradation pathways. In this review, we summarize and discuss the role of melatonin against Aβ-dependent AD pathogenesis. We explore the potential cellular and molecular mechanisms of melatonin on Aβ production and assembly, Aβ clearance, Aβ neurotoxicity and circadian cycle disruption. We summarize multiple clinical trials of melatonin treatment in AD patients, showing that melatonin has a promising effect on improving sleep quality and cognitive function. This review aims to stimulate further research on melatonin as a potential therapeutic agent for AD.

Effect of Melatonin on Tau aggregation and Tau-mediated cell surface morphology

Aggregation of Microtubule-associated protein Tau and its deposition in the form of neurofibrillary tangles (NFTs) is one of the pathological hallmarks of Alzheimer's disease (AD). Tau aggregation inhibition has been targeted in various studies including natural compounds and synthetic small molecules. Here, we have studied neurohormone- Melatonin against in vitro Tau aggregation and observed its effect on membrane topology, tubulin network and Tau phosphorylation in Neuro2A and N9 cell lines. The aggregation and conformation of Tau was determined by ThT fluorescence and CD spectroscopy respectively. The morphology of Tau aggregates in presence and absence of Melatonin was studied by transmission electron microscopy. Melatonin was found to reduce the formation of higher order oligomeric structures without affecting the overall aggregation kinetics of Tau. Melatonin also modulates and helps to maintain membrane morphology, independent on tubulin network as evidenced by FE-SEM and immunofluorescence analysis. Overall, Melatonin administration shows mild anti-aggregation and cytoprotective effects.

Study of the noncovalent interactions of ginsenosides and amyloid-β-peptide by CSI-MS and molecular docking

Noncovalent interactions between drugs and proteins play significant roles for drug metabolisms and drug discoveries. Mass spectrometry has been a commonly used method for studying noncovalent interactions. However, the harsh ionization process in electrospray ionization mass spectrometry (ESI-MS) is not conducive to the preservation of noncovalent and unstable biomolecular complexes compared with the cold spray ionization mass spectrometry (CSI-MS). A cold spray ionization providing a stable solvation-ionization at low temperature is milder than ESI, which was more suitable for studying noncovalent drug-protein complexes with exact stoichiometries. In this paper, we apply CSI-MS to explore the interactions of ginsenosides toward amyloid-β-peptide (Aβ) and clarify the therapeutic effect of ginsenosides on Alzheimer's disease (AD) at the molecular level for the first time. The interactions of ginsenosides with Aβ were performed by CSI-MS and ESI-MS, respectively. The ginsenosides Rg1 bounded to Aβ at the stoichiometries of 1:1 to 5:1 could be characterized by CSI-MS, while dehydration products are more readily available by ESI-MS. The binding force depends on the number of glycosyls and the type of ginsenosides. The relative binding affinities were sorted in order as follows: Rg1 ≈ Re > Rd ≈ Rg2 > Rh2, protopanaxatriol by competition experiments, which were supported by molecular docking experiment. CSI-MS is expected to be a more appropriate approach to determine the weak but specific interactions of proteins with other natural products especially polyhydroxy compounds.

Advances in MS Based Strategies for Probing Ligand-Target Interactions: Focus on Soft Ionization Mass Spectrometric Techniques

The non-covalent interactions between small drug molecules and disease-related proteins (ligand-target interactions) mediate various pharmacological processes in the treatment of different diseases. The development of the analytical methods to assess those interactions, including binding sites, binding energies, stoichiometry and association-dissociation constants, could assist in clarifying the mechanisms of action, precise treatment of targeted diseases as well as the targeted drug discovery. For the last decades, mass spectrometry (MS) has been recognized as a powerful tool to study the non-covalent interactions of the ligand-target complexes with the characteristics of high sensitivity, high-resolution, and high-throughput. Soft ionization mass spectrometry, especially the electrospray mass spectrometry (ESI-MS) and matrix assisted laser desorption ionization mass spectrometry (MALDI-MS), could achieve the complete transformation of the target analytes into the gas phase, and subsequent detection of the small drug molecules and disease-related protein complexes, and has exerted great advantages for studying the drug ligands-protein targets interactions, even in case of identifying active components as drug ligands from crude extracts of medicinal plants. Despite of other analytical techniques for this purpose, such as the NMR and X-ray crystallography, this review highlights the principles, research hotspots and recent applications of the soft ionization mass spectrometry and its hyphenated techniques, including hydrogen-deuterium exchange mass spectrometry (HDX-MS), chemical cross-linking mass spectrometry (CX-MS), and ion mobility spectrometry mass spectrometry (IMS-MS), in the study of the non-covalent interactions between small drug molecules and disease-related proteins.

Multi-Faceted Role of Melatonin in Neuroprotection and Amelioration of Tau Aggregates in Alzheimer's Disease

Alzheimer's disease (AD) is one of the major age related neurodegenerative diseases whose pathology arises due to the presence of two distinct protein aggregates, viz., amyloid-β plaques in extracellular matrix and tau neurofibrillary tangles in neurons. Multiple factors play a role in AD pathology, which includes familial mutations, oxidative stress, and post-translational modifications. Melatonin is an endocrine hormone, secreted during darkness, derived from tryptophan, and produced mainly by the pineal gland. It is an amphipathic molecule, which makes it suitable to cross not only blood-brain barrier, but also to enter several other subcellular compartments like mitochondria and endoplasmic reticulum. In this context, the neuroprotective effect of melatonin may be attributed to its role as an antioxidant. Melatonin's pleiotropic function as an antioxidant and neuroprotective agent has been widely studied. However, its direct effect on the aggregation of tau and amyloid-β needs to be explored. Furthermore, an important aspect of its function is its ability to regulate the process of phosphorylation of tau by affecting the function of kinases and phosphatases. In this review, we are focusing on the pleiotropic function of melatonin on the aspect of its neuroprotective function in tau pathology, which includes antioxidant function, regulation of enzymes, including kinases and enzymes involved in free radical scavenging and mitochondrial protection.

Monoamines and their Derivatives on GPCRs: Potential Therapy for Alzheimer's Disease

Albeit cholinergic depletion remains the key event in Alzheimer's Disease (AD), recent information describes stronger links between monoamines (trace amines, catecholamines, histamine, serotonin, and melatonin) and AD than those known in the past century. Therefore, new drug design strategies focus efforts to translate the scope on these topics and to offer new drugs which can be applied as therapeutic tools in AD. In the present work, we reviewed the state-of-art regarding genetic, neuropathology and neurochemistry of AD involving monoamine systems. Then, we compiled the effects of monoamines found in the brain of mammals as well as the reported effects of their derivatives and some structure-activity relationships. Recent derivatives have triggered exciting effects and pharmacokinetic properties in both murine models and humans. In some cases, the mechanism of action is clear, essentially through the interaction on G-protein-coupled receptors as revised in this manuscript. Additional mechanisms are inhibition of enzymes for their biotransformation, regulation of free-radicals in the central nervous system and others for the effects on Tau phosphorylation or amyloid-beta accumulation. All these data make the monoamines and their derivatives attractive potential elements for AD therapy.

Interaction of the N-AcAβ(13–23)NH2 segment of the beta amyloid peptide with beta-sheet-blocking peptides: site and edge specificity

The region encompassing residues 13–23 of the amyloid beta peptide (Aβ(13–23)) of Alzheimer’s disease is the self-recognition site that initiates toxic oligomerization and fibrillization and also is the site of interaction of Aβ with many other proteins. We describe herein a study by molecular dynamics of the complexes formed by R (= N-AcAβ(13–23)NH2(N-CH3C(O)HHQKLVFFAEDNH2)) with several pseudopeptides designed to form β-sheets with Aβ(1-40,42) and prevent oligomer and fibril formation. Adhesion to both edges of the R β-strand is examined by structure analysis. Umbrella sampling along a dissociation pathway reveals approximate free energies of binding in the submicromolar range. One of the three pseudopeptides binds strongly to one edge of the R β-strand and another to the opposite edge, while the third displays strong binding to both edges. It is desirable to block both edges of the self-recognition site of Aβ to prevent oligomer formation. The study reveals that this may be accomplished by a single pseudopeptide or two in combination. Thus the pseudopeptides, used singly or in pairs, may be competitive inhibitors of Aβ oligomerization at stoichiometric concentrations.

Melatonin and Other Tryptophan Metabolites Produced by Yeasts: Implications in Cardiovascular and Neurodegenerative Diseases

Yeast metabolism produces compounds derived from tryptophan, which are found in fermented beverages, such as wine and beer. In particular, melatonin and serotonin, may be relevant due to their bioactivity in humans. Indeed, the former is a neurohormone related to circadian rhythms, which also has a putative protective effect against degenerative diseases. Moreover, serotonin is a neurotransmitter itself, in addition to being a precursor of melatonin synthesis. This paper summarizes data reported on fermented beverages, to evaluate dietary intake. Additionally, the article reviews observed effects of yeast amino acid metabolites on the prevention of neurodegenerative diseases (Alzheimer’s and Parkinson’s) and angiogenesis, focusing on evidence of the molecular mechanism involved and identification of molecular targets.

Melatonin attenuates impairments of structural hippocampal neuroplasticity in OXYS rats during active progression of Alzheimer's disease-like pathology

Translational research on Alzheimer's disease (AD) has often focused on reducing the high cerebral levels of amyloid-β (Aβ) as a key characteristic of AD pathogenesis. There is, however, a growing body of evidence that synaptic dysfunction may be crucial for the development of the most common (sporadic) form of AD. The applicability of melatonin (mainly produced by the pineal gland) to the treatment of AD is actively evaluated, but usually, such studies are based on animal models of early-onset AD, which is responsible for only ~5% of AD cases. We have shown previously that in OXYS rats (an established model of sporadic AD), accumulation of toxic forms of Aβ in the brain occurs later than does the development of signs of neurodegenerative changes and synaptic failure. In this regard, recently, we uncovered beneficial neuroprotective effects of melatonin (prophylactic dietary supplementation) in OXYS rats. Our aim here was to evaluate, starting at the age of active progression of AD-like pathology in OXYS rats, the effects of long-term oral administration of melatonin on the structure of synapses and on neuronal and glial cells of the hippocampus. Melatonin significantly increased hippocampal synaptic density and the number of excitatory synapses, decreased the number of inhibitory synapses, and upregulated pre- and postsynaptic proteins (synapsin I and PSD-95, respectively). Furthermore, melatonin improved the ultrastructure of neuronal and glial cells and reduced glial density. Based on our past and present results, the repair of neuroplasticity by melatonin is a promising strategy against AD.

Prophylactic melatonin significantly reduces Alzheimer's neuropathology and associated cognitive deficits independent of antioxidant pathways in AβPP(swe)/PS1 mice

Background

Alzheimer’s disease (AD) underlies dementia for millions of people worldwide, and its occurrence is set to double in the next 20 years. Currently, approved drugs for treating AD only marginally ameliorate cognitive deficits, and provide limited symptomatic relief, while newer substances under therapeutic development are potentially years away from benefiting patients. Melatonin (MEL) for insomnia has been proven safe with >15 years of over-the-counter access in the US. MEL exerts multiple complementary mechanisms of action against AD in animal models; thus it may be an excellent disease-modifying therapeutic. While presumed to provide neuroprotection via activation of known G-protein-coupled melatonin receptors (MTNRs), some data indicate MEL acts intracellularly to protect mitochondria and neurons by scavenging reactive oxygen species and reducing free radical formation. We examined whether genetic deletion of MTNRs abolishes MEL’s neuroprotective actions in the AβPP^swe/PSEN1dE9 mouse model of AD (2xAD). Beginning at 4 months of age, both AD and control mice either with or without both MTNRs were administered either MEL or vehicle in drinking water for 12 months.

Results

Behavioral and cognitive assessments of 15-month-old AD mice revealed receptor-dependent effects of MEL on spatial learning and memory (Barnes maze, Morris Water Maze), but receptor-independent neuroprotective actions of MEL on non-spatial cognitive performance (Novel Object Recognition Test). Similarly, amyloid plaque loads in hippocampus and frontal cortex, as well as plasma Aβ_1–42 levels, were significantly reduced by MEL in a receptor-independent manner, in contrast to MEL’s efficacy in reducing cortical antioxidant gene expression (Catalase, SOD1, Glutathione Peroxidase-1, Nrf2) only when receptors were present. Increased cytochrome c oxidase activity was seen in 16mo AD mice as compared to non-AD control mice. This increase was completely prevented by MEL treatment of 2xAD/MTNR+ mice, but only partially prevented in 2xAD/MTNR- mice, consistent with mixed receptor-dependent and independent effects of MEL on this measure of mitochondrial function.

Conclusions

These findings demonstrate that prophylactic MEL significantly reduces AD neuropathology and associated cognitive deficits in a manner that is independent of antioxidant pathways. Future identification of direct molecular targets for MEL action in the brain should open new vistas for development of better AD therapeutics.

Applications of mass spectrometry to the study of protein aggregation

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles. Nowadays mass spectrometry-based approaches play a pivotal role in both detection and characterization of proteins. Here we describe two applications to study insoluble proteins: (a) hydrogen/deuterium exchange combined with mass spectrometry to analyze structural properties of amyloid fibrils and (b) the screening for inhibitors of the aggregation process by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Melatonin in Alzheimer's disease

Alzheimer’s disease (AD), an age-related neurodegenerative disorder with progressive cognition deficit, is characterized by extracellular senile plaques (SP) of aggregated β-amyloid (Aβ) and intracellular neurofibrillary tangles, mainly containing the hyperphosphorylated microtubule-associated protein tau. Multiple factors contribute to the etiology of AD in terms of initiation and progression. Melatonin is an endogenously produced hormone in the brain and decreases during aging and in patients with AD. Data from clinical trials indicate that melatonin supplementation improves sleep, ameliorates sundowning and slows down the progression of cognitive impairment in AD patients. Melatonin efficiently protects neuronal cells from Aβ-mediated toxicity via antioxidant and anti-amyloid properties. It not only inhibits Aβ generation, but also arrests the formation of amyloid fibrils by a structure-dependent interaction with Aβ. Our studies have demonstrated that melatonin efficiently attenuates Alzheimer-like tau hyperphosphorylation. Although the exact mechanism is still not fully understood, a direct regulatory influence of melatonin on the activities of protein kinases and protein phosphatases is proposed. Additionally, melatonin also plays a role in protecting the cholinergic system and in anti-inflammation. The aim of this review is to stimulate interest in melatonin as a potentially useful agent in the prevention and treatment of AD.

A novel melatonin agonist Neu-P11 facilitates memory performance and improves cognitive impairment in a rat model of Alzheimer' disease

Previous studies have shown that melatonin is implicated in modulating learning and memory processing. Melatonin also exerts neuroprotective activities against Aβ-induced injury in vitro and in vivo. Neu-P11 (piromelatine, N-(2-(5-methoxy-1H-indol-3-yl)ethyl)-4-oxo-4H-pyran-2-carboxamide) is a novel melatonin (MT1/MT2) receptor agonist and a serotonin 5-HT1A/1D receptor agonist recently developed for the treatment of insomnia. In the present study we firstly investigated whether Neu-P11 and melatonin enhance memory performance in the novel object recognition (NOR) task in rats, and then assessed whether Neu-P11 and melatonin improve neuronal and cognitive impairment in a rat model of Alzheimer' disease (AD) induced by intrahippocampal Aβ(1-42) injection. The results showed that a single morning or afternoon administration of Neu-P11 enhanced object recognition memory measured at 4 or 24h after training. Melatonin was effective in the memory facilitating effects only when administered in the afternoon. Further results showed that intrahippocampal Aβ(1-42) injection resulted in hippocampal cellular loss, as well as decreased learning ability and memory in the Y maze and NOR tasks in rats. Neu-P11 but not melatonin attenuated cellular loss and cognitive impairment in the rat AD model. The current data suggest that Neu-P11 may serve as a novel agent for the treatment of AD.

Advances in ion mobility spectrometry-mass spectrometry reveal key insights into amyloid assembly

Interfacing ion mobility spectrometry to mass spectrometry (IMS-MS) has enabled mass spectrometric analyses to extend into an extra dimension, providing unrivalled separation and structural characterization of lowly populated species in heterogeneous mixtures. One biological system that has benefitted significantly from such advances is that of amyloid formation. Using IMS-MS, progress has been made into identifying transiently populated monomeric and oligomeric species for a number of different amyloid systems and has led to an enhanced understanding of the mechanism by which small molecules modulate amyloid formation. This review highlights recent advances in this field, which have been accelerated by the commercial availability of IMS-MS instruments. This article is part of a Special Issue entitled: Mass spectrometry in structural biology.

Alzheimer's disease: pathological mechanisms and the beneficial role of melatonin

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder of the aged that has multiple factors which contribute to its etiology in terms of initiation and progression. This review summarizes these diverse aspects of this form of dementia. Several hypotheses, often with overlapping features, have been formulated to explain this debilitating condition. Perhaps the best-known hypothesis to explain AD is that which involves the role of the accumulation of amyloid-β peptide in the brain. Other theories that have been invoked to explain AD and summarized in this review include the cholinergic hypothesis, the role of neuroinflammation, the calcium hypothesis, the insulin resistance hypothesis, and the association of AD with peroxidation of brain lipids. In addition to summarizing each of the theories that have been used to explain the structural neural changes and the pathophysiology of AD, the potential role of melatonin in influencing each of the theoretical processes involved is discussed. Melatonin is an endogenously produced and multifunctioning molecule that could theoretically intervene at any of a number of sites to abate the changes associated with the development of AD. Production of this indoleamine diminishes with increasing age, coincident with the onset of AD. In addition to its potent antioxidant and anti-inflammatory activities, melatonin has a multitude of other functions that could assist in explaining each of the hypotheses summarized above. The intent of this review is to stimulate interest in melatonin as a potentially useful agent in attenuating and/or delaying AD.

Anti-amyloidogenic and anti-apoptotic role of melatonin in Alzheimer disease

Alzheimer disease (AD) is an age-related neurodegenerative disorder characterized by the presence of senile plaques, neurofibrillary tangles and neuronal loss. Amyloid-β protein (Aβ) deposition plays a critical role in the development of AD. It is now generally accepted that massive neuronal death due to apoptosis is a common characteristic in the brains of patients suffering from neurodegenerative diseases, and apoptotic cell death has been found in neurons and glial cells in AD. Melatonin is a secretory product of the pineal gland; melatonin is a potent antioxidant and free radical scavenger and may play an important role in aging and AD. Melatonin decreases during aging and patients with AD have a more profound reduction of this indoleamine. Additionally, the antioxidant properties, the anti-amyloidogenic properties and anti-apoptotic properties of melatonin in AD models have been studied. In this article, we review the anti-amyloidogenic and anti-apoptotic role of melatonin in AD

The use of mass spectrometry to study amyloid-β peptides

Amyloid-β peptide (Aβ) varies in size from 39 to 43 amino acids and arises from sequential β- and γ-secretase processing of the amyloid precursor protein. Whereas the non-pathological role for Aβ is yet to be established, there is no disputing that Aβ is now widely regarded as central to the development of Alzheimer's disease (AD). The so named "amyloid cascade hypothesis" states that disease progression is the result of an increased Aβ burden in affected areas of the brain. To elucidate the Aβ role in AD, many analytical approaches have been proposed as suitable tools to investigate not only the total Aβ load but also many other issues that are considered crucial for AD, such as: (i) the aggregation state in which Aβ is present; (ii) its interaction with other species or metals; (iii) its ability to induce oxidative stress; and (iv) its degradative pathways. This review provides an insight into the use of mass spectrometry (MS) in the field of Aβ investigation aimed to assess its role in AD. In particular, the different MS-based approaches applied in vitro and in vivo that can provide detailed information on the above-mentioned issues are reviewed. Moreover, the advantages offered by the MS methods over all the other techniques are highlighted, together with the recent developments and uses of combined analytical approaches to detect and characterize Aβ.

Differential interactions of isomeric amino sugars with insulin studied under electrospray ionisation mass spectrometry

Protein-ligand interactions were studied for bovine insulin-amino sugar systems under electrospray ionisation mass spectrometry conditions. The isomeric amino sugars showed differences in the relative abundance of 1:1 protein-ligand complex formation. The electrospray ionisation and tandem mass spectrometry results of the complex clearly demonstrated that the differences in the interaction of isomeric sugars with insulin are mainly due to the differences in their gas-phase basicity. The same phenomenon is replicated in the formation of complexes between insulin and other ligands, such as amino acids, as well as in the binding of the amino sugars with amyloid β 1-40 peptide.

Investigation of the noncovalent interactions between anti-amyloid agents and amyloid beta peptides by ESI-MS

This paper describes an efficient and reproducible screening method for identifying low molecular weight compounds that bind to amyloid beta peptides (Abeta) peptides using electrospray ionization mass spectrometry (ESI-MS). Low molecular weight compounds capable of interacting with soluble Abeta may be able to modulate/inhibit the Abeta aggregation process and serve as potential disease-modifying agents for AD. The present approach was used to rank the binding affinity of a library of compounds to Abeta1-40 peptide. The results obtained show that low molecular weight compounds bind similarly to Abeta1-42, Abeta1-40, as well as Abeta1-28 peptides and they underline the critical role of Abeta peptide charge motif in binding at physiological pH. Finally, some elements of structure-activity relationship (SAR) involved in the binding affinity of homotaurine to soluble Abeta peptides are discussed.

Amyloid-beta neurotoxicity in organotypic culture is attenuated by melatonin: involvement of GSK-3beta, tau and neuroinflammation

Alzheimer's disease (AD) is a progressive neurodegenerative disorder marked by accumulation of extracellular deposits of amyloid-beta (Abeta) peptide in brain regions that are important for memory and cognition. The buildup of Abeta aggregates in the AD is followed by the formation of intracellular neurofibrillary tangles and activation of neuroinflammatory reactions. The present study investigated whether melatonin possesses a neuroprotective effect against Abeta-induced toxicity. For this purpose, organotypic hippocampal slices were cultured and exposed to 25 microm of Abeta(25-35) in the absence or in the presence of melatonin (25, 50, or 100 microm). In addition, the authors have investigated the involvement of GSK-3beta, tau protein, astroglial, and microglial activation, and cytokine levels in the melatonin protection against Abeta-induced neurotoxicity. Melatonin prevented the cell damage in hippocampus induced by the exposure to Abeta(25-35). In addition, melatonin significantly reduced the activation of GSK-3beta, the phosphorylation of tau protein, the glial activation and the Abeta-induced increase of TNF-alpha and IL-6 levels. On the basis of these findings, we speculate that melatonin may provide an effective therapeutic strategy for AD, by attenuating Abeta-induced phosphorylation of tau protein, and preventing GSK-3beta activation and neuroinflammation.

Protection against cognitive deficits and markers of neurodegeneration by long-term oral administration of melatonin in a transgenic model of Alzheimer disease

The neurohormone melatonin has been reported to exert anti-beta-amyloid aggregation, antioxidant, and anti-inflammatory actions in various in vitro and animal models. To comprehensively determine the potential for long-term melatonin treatment to protect Alzheimer's transgenic mice against cognitive impairment and development of beta-amyloid (Abeta) neuropathology, we administered melatonin (100 mg/L drinking water) to APP + PS1 double transgenic (Tg) mice from 2-2.5 months of age to their killing at age 7.5 months. A comprehensive behavioral battery administered during the final 6 weeks of treatment revealed that Tg mice given melatonin were protected from cognitive impairment in a variety of tasks of working memory, spatial reference learning/memory, and basic mnemonic function; Tg control mice remained impaired in all of these cognitive tasks/domains. Immunoreactive Abeta deposition was significantly reduced in hippocampus (43%) and entorhinal cortex (37%) of melatonin-treated Tg mice. Although soluble and oligomeric forms of Abeta1-40 and 1-42 were unchanged in the hippocampus and cortex of the same melatonin-treated Tg mice, their plasma Abeta levels were elevated. These Abeta results, together with our concurrent demonstration that melatonin suppresses Abeta aggregation in brain homogenates, are consistent with a melatonin-facilitated removal of Abeta from the brain. Inflammatory cytokines such as tumor necrosis factor (TNF)-alpha were decreased in hippocampus (but not plasma) of Tg+ melatonin mice. Finally, the cortical mRNA expression of three antioxidant enzymes (SOD-1, glutathione peroxidase, and catalase) was significantly reduced to non-Tg levels by long-term melatonin treatment in Tg mice. Thus, melatonin's cognitive benefits could involve its anti-Abeta aggregation, anti-inflammatory, and/or antioxidant properties. Our findings provide support for long-term melatonin therapy as a primary or complementary strategy for abating the progression of Alzheimer disease.

Conformation and topology of amyloid beta-protein adsorbed on a tethered artificial membrane probed by surface plasmon field-enhanced fluorescence spectroscopy

Progressive depositions of cerebral amyloid are primary neuropathologic features of Alzheimer's disease (AD). The amyloid is composed of a 39-42 amino acid peptide called the amyloid beta-protein (Abeta). Repeated investigation suggests that the conformational transition of Abeta from alpha-helix or random coil to beta-sheet structure plays a key role in the inappropriate accumulation of cerebral amyloid plaques. In this manuscript, we describe a fluorescence-based immunoassay technology to investigate the conformation and topology of Abeta peptides interacting with peptide-tethered planar lipid bilayers. Dual monoclonal antibodies (mAbs) labelled with fluorophores were employed to recognise a linear N- and a beta-sheet C-terminus of Abeta peptides on the model membrane, respectively. Kinetics of antibody-Abeta binding were determined by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The conformational transition of Abeta by melatonin, a defined beta-sheet breaker, was probed using paired monoclonal antibodies. The Abeta interaction with the membrane was evaluated by carefully analyzing the change in kinetic/affinity parameters in the presence or absence of melatonin. These results show that SPFS can be used to examine conformational transition of Abeta on an artificial membrane, providing a novel and versatile platform for conveniently monitoring protein-membrane interaction and screening for new beta-sheet breakers.

Insight into the kinetic of amyloid beta (1-42) peptide self-aggregation: elucidation of inhibitors' mechanism of action

The initial transition of amyloid beta (1-42) (Abeta42) soluble monomers/small oligomers from unordered/alpha-helix to a beta-sheet-rich conformation represents a suitable target to design new potent inhibitors and to obtain effective therapeutics for Alzheimer's disease. Under optimized conditions, this reliable and reproducible CD kinetic study showed a three-step sigmoid profile that was characterized by a lag phase (prevailing unordered/alpha-helix conformation), an exponential growth phase (increasing beta-sheet secondary structure) and a plateau phase (prevailing beta-sheet secondary structure). This kinetic analysis brought insight into the inhibitors' mechanism of action. In fact, an increase in the duration of the lag phase can be related to the formation of an inhibitor-Abeta complex, in which the non-amyloidogenic conformation is stabilized. When the exponential rate is affected exclusively, such as in the case of Congo red and tetracycline, then the inhibitor affinity might be higher for the pleated beta-sheet structure. Finally, by adding the inhibitor at the end of the exponential phase, the soluble protofibrils can be disrupted and the Abeta amyloidogenic structure can revert into monomers/small oligomers. Congo red and tetracycline preferentially bind to amyloid in the beta-sheet conformation because both decreased the slope of the exponential growth, even if to a different extent, whereas no effect was observed for tacrine and galantamine. Some very preliminary indications can be derived about the structural requirements for binding to nonamyloidogenic or beta-sheet amyloid secondary structure for the development of potent antiaggregating agents. On these premises, memoquin, a multifunctional molecule that was designed to become a drug candidate for the treatment of Alzheimer's disease, was investigated under the reported circular dichroism assay and its anti-amyloidogenic mechanism of action was elucidated.

Role of melatonin in Alzheimer-like neurodegeneration

Alzheimer disease (AD), an age-related neurodegenerative disorder with progressive loss of memory and deterioration of comprehensive cognition, is characterized by extracellular senile plaques of aggregated beta-amyloid (Abeta), and intracellular neurofibrillary tangles that contain hyperphosphorylated tau protein. Recent studies showed that melatonin, an indoleamine secreted by the pineal gland, may play an important role in aging and AD as an antioxidant and neuroprotector. Melatonin decreases during aging and patients with AD have a more profound reduction in this hormone. Data from clinical trials indicate that melatonin supplementation improves sleep, ameliorates sundowning, and slows down the progression of cognitive impairment in Alzheimer patients. Melatonin efficiently protects neuronal cells from Abeta-mediated toxicity via antioxidant and anti-amyloid properties: it not only inhibits Abeta generation, but also arrests the formation of amyloid fibrils by a structure-dependent interaction with Abeta. Our recent studies have demonstrated that melatonin efficiently attenuates Alzheimer-like tau hyperphosphorylation. Although the exact mechanism is still not fully understood, a direct regulatory influence of melatonin on the activities of protein kinases and protein phosphatases is proposed. Additionally, melatonin also plays a role in protecting cholinergic neurons and in anti-inflammation. Here, the neuroprotective effects of melatonin and the underlying mechanisms by which it exerts its effects are reviewed. The capacity of melatonin to prevent or ameliorate tau and Abeta pathology further enhances its potential in the prevention or treatment of AD.

Molecular recognition by mass spectrometry

A recent major advance in the field of mass spectrometry in the biomolecular sciences is represented by the study of the supramolecular interactions among two or more partners in the gas phase. A great deal of chemistry and most of biochemistry concerns molecular interactions taking place in solution. The electrospray technique, which allows direct sampling from solution, and soft ionization of the solute without deposition into the analyte of large amounts of energy, guarantees in many cases the survival of noncovalent bondings and, hence, the direct analysis of the supramolecular complexes present in the condensed phase. The proper preparation of the solution to be studied and also the expert and accurate setting and use of the instrumental parameters are the prerequisites for gaining results as to the specific interactions between, for instance, a protein conformationally modified by its specific metal ion, eventually, and a ligand molecule. The analysis of the charge state of the protein itself and of the modifications of the complex integrity by activating collisions are also methods for studying the biomolecule-molecule interactions. Accordingly, this new mass spectrometric approach to the supramolecular chemistry, which could be also defined as 'supramolecular mass spectrometry', allows the study of ion-protein, protein-protein, protein-ligand and DNA-drug interactions. Chiral recognition can also be performed in the gas phase, studying by electrospray mass spectrometry the fragmentation of diastereomeric complex ions. Not the least, a deep insight can also be obtained into the formation and nature of inclusion complexes like those formed with crown ethers, cyclodextrins and calixarenes as host molecules. All these topics are treated to a certain extent in this special feature article.

The study on the interaction between seryl-histidine dipeptide and proteins by circular dichroism and molecular modeling

The selective cleavage of proteins is very important in key biological processes. Chemical (nonenzymatic) reagents such as cyanogen bromide and transition metal complexes are used extensively with great defects. In this paper, the binding of seryl-histidine dipeptide (abbreviated as SH) with bovine serum albumin (BSA) and lysozyme were investigated by the circular dichroism spectroscopy (CD) at 298K, molecular docking studies and quantum chemical calculations based on the previous results of polyacrylamide gel electrophoresis (PAGE). From the studies of CD, it showed that SH interacted strongly with BSA and lysozyme. The change percentages of the secondary structures of BSA and lysozyme were calculated. The contents of the beta-sheets decreased remarkably. It indicated that the interactions between SH and proteins could break the hydrogen bonds of beta-sheets selectively. The docking studies between SH and BSA showed that the position of the oxygen atom of the hydroxyl group of SH (O(12)) was in favor of a nucleophilic attack on carbon atom of the amide bond of a beta-sheet (C(34)) because the distance between O(12) and C(34) was 3.37A. Natural charges, natural atomic hybrid percentages and square sums of HOMO coefficients calculated by the NBO and population analysis at HF/6-31G* supported the suggested mechanism. And so SH may be an interesting agent for the therapeutic use.

Study of the non-covalent interaction between amyloid-beta-peptide and melatonin using electrospray ionization mass spectrometry

Oxidative stress and unregulated immune response are believed to play a key role in the processes inherent to Alzheimer's disease (AD). The fact that free radicals can result in neurodegeneration suggests that actions against reactive oxygen species may be beneficial in treating and preventing AD. In the light of the suggested link between oxidative stress and AD, it is proposed that antioxidants and, even more, endogenous antioxidants may offer a therapeutic regime for protection against the risk of this disease. For this reason, the formation of non-covalent complexes between amyloid-beta-peptide (A beta) or its oxidized forms and melatonin was studied by quadrupole and Fourier transform ion cyclotron resonance electrospray ionization mass spectrometry. The stability of the non-covalent complex was examined under several experimental conditions, such as orifice voltage, pH, presence of organic modifier, concentration and time. Two different digestion protocols combined with mass spectrometric analysis of the resulting peptide fragments were employed in order to locate the binding site of melatonin in A beta.

Prevention of Alzheimer's Disease-associated Aβ Aggregation by Rationally Designed Nonpeptidic β-Sheet Ligands

A new concept is introduced for the rational design of beta-sheet ligands, which prevent protein aggregation. Oligomeric acylated aminopyrazoles with a donor-acceptor-donor (DAD) hydrogen bond pattern complementary to that of a beta-sheet efficiently block the solvent-exposed beta-sheet portions in Abeta-(1-40) and thereby prevent formation of insoluble protein aggregates. Density gradient centrifugation revealed that in the initial phase, the size of Abeta aggregates was efficiently kept between the trimeric and 15-meric state, whereas after 5 days an additional high molecular weight fraction appeared. With fluorescence correlation spectroscopy (FCS) exactly those two, i.e. a dimeric aminopyrazole with an oxalyl spacer and a trimeric head-to-tail connected aminopyrazole, of nine similar aminopyrazole ligands were identified as efficient aggregation retardants whose minimum energy conformations showed a perfect complementarity to a beta-sheet. The concentration dependence of the inhibitory effect of a trimeric aminopyrazole derivative allowed an estimation of the dissociation constant in the range of 10(-5) m. Finally, electrospray ionization mass spectrometry (ESI-MS) was used to determine the aggregation kinetics of Abeta-(1-40) in the absence and in the presence of the ligands. From the comparable decrease in Abeta monomer concentration, we conclude that these beta-sheet ligands do not prevent the initial oligomerization of monomeric Abeta but rather block further aggregation of spontaneously formed small oligomers. Together with the results from density gradient centrifugation and fluorescence correlation spectroscopy it is now possible to restrict the approximate size of soluble Abeta aggregates formed in the presence of both inhibitors from 3- to 15-mers.

Characterization of noncovalent complexes of antimalarial agents of the artemisinin-type and FE(III)-heme by electrospray mass spectrometry and collisional activation tandem mass spectrometry

In this study, we demonstrate, using electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation tandem mass spectrometry (ESI-MS/CID/MS), that stable noncovalent complexes can be formed between Fe(III)-heme and antimalarial agents, i.e., quinine, artemisinin, and the artemisinin derivatives, dihydroartemisinin, alpha- and beta-artemether, and beta-arteether. Differences in the binding behavior of the examined drugs with Fe(III)-heme and the stability of the drug-heme complexes are demonstrated. The results show that all tested antimalarial agents form a drug-heme complex with a 1:1 stoichiometry but that quinine also results in a second complex with the heme dimer. ESI-MS performed on mixtures of pairs of various antimalarial agents with heme indicate that quinine binds preferentially to Fe(III)-heme, while ESI-MS/CID/MS shows that the quinine-heme complex is nearly two times more stable than the complexes formed between heme and artemisinin or its derivatives. Moreover, it is found that dihydroartemisinin, the active metabolite of the artemisinin-type drugs in vivo, results in a Na(+)-containing heme-drug complex, which is as stable as the heme-quinine complex. The efficiency of drug-heme binding of artemisinin derivatives is generally lower and the decomposition under CID higher compared with quinine, but these parameters are within the same order of magnitude. These results suggest that the efficiency of antimalarial agents of the artemisinin-type to form noncovalent complexes with Fe(III)-heme is comparable with that of the traditional antimalarial agent, quinine. Our study illustrates that electrospray ionization mass spectrometry and collision-induced dissociation tandem mass spectrometry are suitable tools to probe noncovalent interactions between heme and antimalarial agents. The results obtained provide insights into the underlying molecular modes of action of the traditional antimalarial agent quinine and of the antimalarials of the artemisinin-type which are currently used to treat severe or multidrug-resistant malaria.

Two-Site Binding of β-Cyclodextrin to the Alzheimer Aβ(1−40) Peptide Measured with Combined PFG-NMR Diffusion and Induced Chemical Shifts

The interactions of Alzheimer's amyloid beta-peptide with cyclodextrins were studied by (1)H NMR: the translational diffusion coefficient of the peptide and chemical shift changes were studied by the presence of variable concentrations of cyclodextrins. For the full-length peptide, Abeta(1-40), the combined results of translational diffusion and chemical shift changes are consistent with a model where aromatic side chains interact with beta-cyclodextrin with dissociation constants in the millimolar range. The diffusion data were consistent with two beta-cyclodextrin molecules bound per peptide. The binding occurs at two sites, at F(19) and/or F(20) and at Y(10), with dissociation constants K(d)(F) = 4.7 mM and K(d)(Y) = 6.6 mM, respectively, in 10 mM sodium phosphate, pH 7.4 and 298 K. Shorter Alzheimer peptide fragments were studied to measure specific affinities for different binding sites. The N-terminal fragment Abeta(1-9) with a putative binding site at F(4) does not show measurable affinity for beta-cyclodextrin. The fragment Abeta(12-28) has similar apparent affinity (K(d) = 3.8 mM) to beta-cyclodextrin as the full-length peptide Abeta(1-40). Here, the diffusion data suggests a one-to-one stoichiometry, and the binding site is F(19) and/or F(20). Both diffusion results and chemical shift changes give the same affinity. A variant Abeta(12-28)G(19)G(20) without phenylalanines does not bind to beta-cyclodextrin. Other potential ligands, alpha-cyclodextrin, gamma-cyclodextrin, nicotine, and nornicotine do not bind to the Abeta(12-28) fragment. This study shows that combined (1)H NMR diffusion and chemical shift changes may be used to quantitatively determine affinities and stoichiometries of weak interactions, using unlabeled ligands and hosts of comparable sizes.

Fullerene inhibits beta-amyloid peptide aggregation

We report that fullerene inhibits strongly the amyloid peptide aggregation at the early stage. It specifically binds to the central hydrophobic motif, KLVFF, of A beta peptides. The IC(50) value has been measured as 9 microM for both A beta(11-25) and A beta(1-40). On the other hand, a control experiment shows melatonin rather specifically binds to the C-terminus region. The IC(50) value of fullerene appears to be at least four times larger for A beta(1-40), compared with melatonin, and 15 times larger for A beta(11-25). This work shows that fullerene can be a promising candidate in search of AD therapeutics because it has the very high IC(50) value for A beta aggregation.