The use of mass spectrometry to study amyloid-β peptides

Recent Advancements in Biosensors for the Detection and Characterization of Amyloids: A Review

Modern medicine has increased the human lifespan. However, with an increase in average lifespan risk of amyloidosis increases. Amyloidosis is a condition characterized by protein misfolding and aggregation. Early detection of amyloidosis is crucial, yet conventional diagnostic methods are costly and lack precision, necessitating innovative tools. This review explores recent advancements in diverse amyloid detection methodologies, highlighting the need for interdisciplinary research to develop a miniaturized electrochemical biosensor leveraging nanotechnology. However, the diagnostics industry faces obstacles such as skilled labor shortages, standardized selection processes, and concurrent multi-analyte identification challenges. Research efforts are focused on integrating electrochemical techniques into clinical applications and diagnostics, with the successful transition of miniaturized technologies from development to testing posing a significant hurdle. Label-free transduction techniques like voltammetry and electrochemical impedance spectroscopy (EIS) have gained traction due to their rapid, cost-effective, and user-friendly nature.

In Vivo Assays for Amyloid-Related Diseases

Amyloid-related diseases, such as Alzheimer's and Parkinson's disease, are devastating conditions caused by the accumulation of abnormal protein aggregates known as amyloid fibrils. While assays involving animal models are essential for understanding the pathogenesis and developing therapies, a wide array of standard analytical techniques exists to enhance our understanding of these disorders. These techniques provide valuable information on the formation and propagation of amyloid fibrils, as well as the pharmacokinetics and pharmacodynamics of candidate drugs. Despite ethical concerns surrounding animal use, animal models remain vital tools in the search for treatments. Regardless of the specific animal model chosen, the analytical methods used are usually standardized. Therefore, the main objective of this review is to categorize and outline the primary analytical methods used in in vivo assays for amyloid-related diseases, highlighting their critical role in furthering our understanding of these disorders and developing effective therapies.

Using mass spectrometry-based methods to understand amyloid formation and inhibition of alpha-synuclein and amyloid beta

Amyloid fibrils, insoluble β-sheets structures that arise from protein misfolding, are associated with several neurodegenerative disorders. Many small molecules have been investigated to prevent amyloid fibrils from forming; however, there are currently no therapeutics to combat these diseases. Mass spectrometry (MS) is proving to be effective for studying the high order structure (HOS) of aggregating proteins and for determining structural changes accompanying protein-inhibitor interactions. When combined with native MS (nMS), gas-phase ion mobility, protein footprinting, and chemical cross-linking, MS can afford regional and sometimes amino acid spatial resolution of the aggregating protein. The spatial resolution is greater than typical low-resolution spectroscopic, calorimetric, and the traditional ThT fluorescence methods used in amyloid research today. High-resolution approaches can struggle when investigating protein aggregation, as the proteins exist as complex oligomeric mixtures of many sizes and several conformations or polymorphs. Thus, MS is positioned to complement both high- and low-resolution approaches to studying amyloid fibril formation and protein-inhibitor interactions. This review covers basics in MS paired with ion mobility, continuous hydrogen-deuterium exchange (continuous HDX), pulsed hydrogen-deuterium exchange (pulsed HDX), fast photochemical oxidation of proteins (FPOP) and other irreversible labeling methods, and chemical cross-linking. We then review the applications of these approaches to studying amyloid-prone proteins with a focus on amyloid beta and alpha-synuclein. Another focus is the determination of protein-inhibitor interactions. The expectation is that MS will bring new insights to amyloid formation and thereby play an important role to prevent their formation.

The Insulin-Degrading Enzyme from Structure to Allosteric Modulation: New Perspectives for Drug Design

The insulin-degrading enzyme (IDE) is a Zn2+ peptidase originally discovered as the main enzyme involved in the degradation of insulin and other amyloidogenic peptides, such as the β-amyloid (Aβ) peptide. Therefore, a role for the IDE in the cure of diabetes and Alzheimer's disease (AD) has been long envisaged. Anyway, its role in degrading amyloidogenic proteins remains not clearly defined and, more recently, novel non-proteolytic functions of the IDE have been proposed. From a structural point of view, the IDE presents an atypical clamshell structure, underscoring unique enigmatic enzymological properties. A better understanding of the structure-function relationship may contribute to solving some existing paradoxes of IDE biology and, in light of its multifunctional activity, might lead to novel therapeutic approaches.

Cortical proteins may provide motor resilience in older adults

Motor resilience proteins may be a high value therapeutic target that offset the negative effects of pathologies on motor function. This study sought to identify cortical proteins associated with motor decline unexplained by brain pathologies that provide motor resilience. We studied 1226 older decedents with annual motor testing, postmortem brain pathologies and quantified 226 proteotypic peptides in prefrontal cortex. Twenty peptides remained associated with motor decline in models controlling for ten brain pathologies (FDR < 0.05). Higher levels of nine peptides and lower levels of eleven peptides were related to slower decline. A higher motor resilience protein score based on averaging the levels of all 20 peptides was related to slower motor decline, less severe parkinsonism and lower odds of mobility disability before death. Cortical proteins may provide motor resilience. Targeting these proteins in further drug discovery may yield novel interventions to maintain motor function in old age.

THE USE OF MASS SPECTROMETRY TO STUDY ZN-METALLOPROTEASE-SUBSTRATE INTERACTIONS

Zinc metalloproteases (ZnMPs) participate in diverse biological reactions, encompassing the synthesis and degradation of all the major metabolites in living organisms. In particular, ZnMPs have been recognized to play a very important role in controlling the concentration level of several peptides and/or proteins whose homeostasis has to be finely regulated for the correct physiology of cells. Dyshomeostasis of aggregation-prone proteins causes pathological conditions and the development of several different diseases. For this reason, in recent years, many analytical approaches have been applied for studying the interaction between ZnMPs and their substrates and how environmental factors can affect enzyme activities. In this scenario, mass spectrometric methods occupy a very important role in elucidating different aspects of ZnMPs-substrates interaction. These range from identification of cleavage sites to quantitation of kinetic parameters. In this work, an overview of all the main achievements regarding the application of mass spectrometric methods to investigating ZnMPs-substrates interactions is presented. A general experimental protocol is also described which may prove useful to the study of similar interactions. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Mass Spectrometry-Based Protein Footprinting for Higher-Order Structure Analysis: Fundamentals and Applications

Proteins adopt different higher-order structures (HOS) to enable their unique biological functions. Understanding the complexities of protein higher-order structures and dynamics requires integrated approaches, where mass spectrometry (MS) is now positioned to play a key role. One of those approaches is protein footprinting. Although the initial demonstration of footprinting was for the HOS determination of protein/nucleic acid binding, the concept was later adapted to MS-based protein HOS analysis, through which different covalent labeling approaches "mark" the solvent accessible surface area (SASA) of proteins to reflect protein HOS. Hydrogen-deuterium exchange (HDX), where deuterium in D2O replaces hydrogen of the backbone amides, is the most common example of footprinting. Its advantage is that the footprint reflects SASA and hydrogen bonding, whereas one drawback is the labeling is reversible. Another example of footprinting is slow irreversible labeling of functional groups on amino acid side chains by targeted reagents with high specificity, probing structural changes at selected sites. A third footprinting approach is by reactions with fast, irreversible labeling species that are highly reactive and footprint broadly several amino acid residue side chains on the time scale of submilliseconds. All of these covalent labeling approaches combine to constitute a problem-solving toolbox that enables mass spectrometry as a valuable tool for HOS elucidation. As there has been a growing need for MS-based protein footprinting in both academia and industry owing to its high throughput capability, prompt availability, and high spatial resolution, we present a summary of the history, descriptions, principles, mechanisms, and applications of these covalent labeling approaches. Moreover, their applications are highlighted according to the biological questions they can answer. This review is intended as a tutorial for MS-based protein HOS elucidation and as a reference for investigators seeking a MS-based tool to address structural questions in protein science.

Resveratrol-mediated cleavage of amyloid β1-42 peptide: potential relevance to Alzheimer's disease

Aggregation of amyloid β_1-42 (Aβ_1-42) peptide within the brain is considered one of the main causes of the neuropathological changes associated with Alzheimer's disease. Resveratrol is a well-known antioxidant but has also been reported to bind to Aβ_1-42 peptide, thereby reducing aggregation. However, little is known of the precise mechanism by which resveratrol reduces Aβ_1-42 peptide aggregation. Using the thioflavin-T assay, the ability of resveratrol to reduce the extent of Aβ_1-42 peptide aggregation was investigated. The findings of the present study demonstrate that interaction of resveratrol with Aβ_1-42 peptide resulted in the cleavage of Aβ_1-42 peptide into smaller fragments, as detected by matrix assisted laser desorption ionization-time of flight mass spectrometry. Atomic force microscopy analyses revealed Aβ_1-42 peptide, under control conditions, aggregated into oligomers, protofibrils, and fibrils, whereas there was a distinct lack of these structures when Aβ_1-42 peptide was incubated with resveratrol. Following 10 days incubation of Aβ_1-42 peptide with resveratrol, particles with a mean z-height of 1.940 nm (range 0.675-3.275 nm) were observed, which are characteristic of shorter peptide species. In cell-based studies, resveratrol significantly reduced the cytotoxicity of Aβ_1-42 peptide toward SH-SY5Y human neuroblastoma cells, suggesting a protective effect of the polyphenol. We therefore propose a novel mechanism by which resveratrol disrupts Aβ_1-42 aggregation by mediating fragmentation of Aβ_1-42 into smaller peptides, which have no propensity to aggregate further.

Trans-cinnamaldehyde improves neuroinflammation-mediated NMDA receptor dysfunction and memory deficits through blocking NF-κB pathway in presenilin1/2 conditional double knockout mice

A chronic neuroinflammatory response has been considered as a critical pathogenesis promoting neurodegenerative progression in Alzheimer's disease (AD). During neuroinflammatory process, microglia are excessively activated and simultaneously release numerous pro-inflammatory mediators that cause synaptic dysfunction in the forebrain prior to neuronal degeneration and memory deficits in AD. Thus, prevention of neuroinflammation-mediated synaptic dysfunction may be a potential therapeutic approach against neurodegenerative disorders. Trans-cinnamaldehyde (TCA) is a primary bioactive component derived from the stem bark of Cinnamomum cassia, and it possesses potent anti-inflammatory and neuroprotective activities in in vivo and in vitro experiments. However, the in-depth molecular mechanisms of TCA underlying anti-neuroinflammatory and neuroprotective effects on memory deficits in AD are still unclear. The presenilin 1 and 2 conditional double knockout (PS cDKO) mice exhibit AD-like phenotypes including obvious neuroinflammatory responses and synaptic dysfunction and memory deficits. Here, PS cDKO were used to evaluate the potential neuroprotective effects of TCA against neuroinflammation-mediated dementia by performing behavioral tests, electrophysiological recordings and molecular biology analyses. We observed that TCA treatment reversed abnormal expression of synaptic proteins and tau hyperphosphorylation in the hippocampus and prefrontal cortex of PS cDKO mice. TCA treatment also ameliorated NMDA receptor (NMDAR) dysfunction including impaired NMDAR-mediated responses and long-term potentiation (LTP) induction in the hippocampus of PS cDKO mice. Moreover, TCA possesses an ability to suppress neuroinflammatory responses by diminishing microglial activation and levels of pro-inflammatory mediators in the hippocampus and prefrontal cortex of PS cDKO mice. Importantly, improving NMDAR dysfunction and memory deficits of PS cDKO mice was due to the inhibition of neuroinflammatory responses through TCA's interruptive effect on the nuclear factor kappa B (NF-κB) signaling pathway. Therefore, TCA may be a potential anti-neuroinflammatory agent for deterring neurodegenerative progression of AD.

Copper, dityrosine cross-links and amyloid-β aggregation

Copper is involved in Alzheimer's disease (AD) where it appears to affect the aggregation of amyloid-β (Aβ) and to catalyze the production of reactive oxygen species (ROS). Oxidative stress apparently produces Aβ dimers that are covalently linked through two tyrosine residues. Such dityrosine cross-links are considered as potential markers of the disease and seem to be implicated in the pathological disorder. In the present study, pure o,o'-dityrosine (diY) was prepared enzymatically (with horseradish peroxidase; HRP), which was subsequently used to construct calibration lines aimed at quantifying nanomolar amounts of diY in reaction mixtures by fluorescence spectroscopy. Hence, diY concentrations down to 67 nM could be determined, which allowed to find that ca. 3% of dityrosine-bridged dimers of Aβ(1-40) were produced after 3 days at 37 °C in the presence of copper and dihydrogen peroxide. These cross-linked dimers in the presence of copper(II) ions completely inhibit the typical aggregation of Aβ, since β sheets could not be detected applying the usual Thioflavin T (ThT) method. Furthermore, the use of a potent Cu(II) chelator, such as the ATCUN tripeptide, L-histidyl-L-alanyl-L-histidine (HAH), efficiently prevented the copper-mediated generation of ROS and the associated dityrosine-bridged Aβ dimers, suggesting that such metal chelators may find future applications in the field of anti-AD drug design.

Detection of amyloid beta peptides in body fluids for the diagnosis of alzheimer's disease: Where do we stand?

Alzheimer's disease (AD) is an incurable neurodegenerative disease characterized by progressive decline of cognitive abilities. Amyloid beta peptides (Aβ), Tau proteins and the phosphorylated form of the Tau protein, p-Tau, are the core pathological biomarkers of the disease, and their detection for the diagnosis of patients is progressively being implemented. However, to date, their quantification is mostly performed on cerebrospinal fluid (CSF), the collection of which requires an invasive lumbar puncture. Early diagnosis has been shown to be important for disease-modifying treatment, which is currently in development, to limit the progression of the disease. Nevertheless, the diagnosis is often delayed to the point where the disease has already progressed, and the tools currently available do not allow for a systematic follow-up of patients. Thus, the search for a molecular signature of AD in a body fluid such as blood or saliva that can be collected in a minimally invasive way offers hope. A number of methods have been developed for the quantification of core biomarkers, especially in easily accessible fluids such as the blood, that improve their accuracy, specificity and sensitivity. This review summarizes and compares these approaches, focusing in particular on their use for Aβ detection, the earliest biomarker to be modified in the course of AD. The review also discusses biomarker quantification in CSF, blood and saliva and their clinical applications.

Modulation of Amyloid-β42 Conformation by Small Molecules Through Nonspecific Binding

Aggregation of amyloid-β (Aβ) peptides is a crucial step in the progression of Alzheimer's disease (AD). Identifying aggregation inhibitors against AD has been a great challenge. We report an atomistic simulation study of the inhibition mechanism of two small molecules, homotaurine and scyllo-inositol, which are AD drug candidates currently under investigation. We show that both small molecules promote a conformational change of the Aβ42 monomer toward a more collapsed phase through a nonspecific binding mechanism. This finding provides atomistic-level insights into designing potential drug candidates for future AD treatments.

Mass spectrometry is a multifaceted weapon to be used in the battle against Alzheimer's disease: Amyloid beta peptides and beyond

Amyloid-β peptide (Aβ) accumulation and aggregation have been considered for many years the main cause of Alzheimer's disease (AD), and therefore have been the principal target of investigation as well as of the proposed therapeutic approaches (Grasso [2011] Mass Spectrom Rev. 30: 347-365). However, the amyloid cascade hypothesis, which considers Aβ accumulation the only causative agent of the disease, has proven to be incomplete if not wrong. In recent years, actors such as metal ions, oxidative stress, and other cofactors have been proposed as possible co-agents or, in some cases, main causative factors of AD. In this scenario, MS investigation has proven to be fundamental to design possible diagnostic strategies of this elusive disease, as well as to understand the biomolecular mechanisms involved, in the attempt to find a possible therapeutic solution. We review the current applications of MS in the search for possible Aβ biomarkers of AD to help the diagnosis of the disease. Recent examples of the important contributions that MS has given to prove or build theories on the molecular pathways involved with such terrible disease are also reviewed.

Size-selected silver nanoparticles for MALDI-TOF mass spectrometry of amyloid-beta peptides

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is one of the most efficient mass spectrometric techniques for the analysis of high-molecular-weight compounds with superior selectivity and sensitivity. Common MALDI matrices are low molecular weight (LMW) organics and will therefore produce a large amount of matrix-related ion peaks, which limits the use of MALDI-MS for the detection of LMW molecules. A major breakthrough of this limitation was made by the introduction of surface assisted desorption/ionization techniques, with graphite particles firstly as the matrix, followed by expansion into other types of nanoparticles or nanostructures. However, previous studies failed to address well the optimum size and concentration of Ag NPs to be used as the MALDI matrix. In this study, to explore and compare the efficiency of different sized silver nanoparticles (Ag NPs) as the MALDI matrix for the detection of LMW molecules, three different sized Ag NPs (2.8 ± 1.0, 12.8 ± 3.2 and 44.2 ± 5.0 nm) have been successfully developed as the MALDI time-of-flight MS (MALDI-TOF MS) matrix and amyloid-beta (Aβ) peptides, crucially involved in Alzheimer's disease and a variety of cancers, were chosen as an example of LMW molecules in our MALDI-TOF MS analysis with Ag NPs as matrices. The results showed size-selected MS signals with the smallest (2.8 ± 1.0 nm) Ag NP matrix producing the highest spectral intensities, when compared with other larger sized Ag NP matrices and conventional matrices such as SA and DHB. Furthermore, the optimal concentrations for different sized Ag NPs as matrices were determined as follows: 0.125 nM (2.8 ± 1.0 nm Ag NPs), 0.0625 nM (12.8 ± 3.2 nm Ag NPs), and 0.03125 nM (44.2 ± 5.0 nm Ag NPs), respectively. These results not only corroborated that Ag NPs could act as a very suitable matrix to assist in the desorption/ionization of LMW molecules but also revealed size-selected mass spectrometry signals with smaller Ag NPs as the MALDI matrix bearing more advantages than their larger counterparts. These novel findings paved the way for wider applications of MALDI-MS using Ag NPs as matrices for the analysis of LMW molecules.

Outstanding Phenotypic Differences in the Profile of Amyloid-β between Tg2576 and APPswe/PS1dE9 Transgenic Mouse Models of Alzheimer's Disease

APPswe/PS1dE9 and Tg2576 are very common transgenic mouse models of Alzheimer’s disease (AD), used in many laboratories as tools to research the mechanistic process leading to the disease. In order to augment our knowledge about the amyloid-β (Aβ) isoforms present in both transgenic mouse models, we have developed two chromatographic methods, one acidic and the other basic, for the characterization of the Aβ species produced in the brains of the two transgenic mouse models. After immunoprecipitation and micro-liquid chromatography-electrospray ionization mass spectrometry/mass spectrometry, 10 species of Aβ, surprisingly all of human origin, were detected in the brain of Tg2576 mouse, whereas 39 species, of both murine and human origin, were detected in the brain of the APP/PS1 mouse. To the best of our knowledge, this is the first study showing the identification of such a high number of Aβ species in the brain of the APP/PS1 transgenic mouse, whereas, in contrast, a much lower number of Aβ species were identified in the Tg2576 mouse. Therefore, this study brings to light a relevant phenotypic difference between these two popular mice models of AD.

Understanding the metal mediated assembly and hydrogel formation of a β-hairpin peptide

We report the Zn²⁺-mediated hydrogel formation of a β-hairpin peptide that proceeded via an intermolecular metal- coordination mechanism.

Characterization of insulin-degrading enzyme-mediated cleavage of Aβ in distinct aggregation states

To enhance our understanding of the potential therapeutic utility of insulin-degrading enzyme (IDE) in Alzheimer's disease (AD), we studied in vitro IDE-mediated degradation of different amyloid-beta (Aβ) peptide aggregation states. Our findings show that IDE activity is driven by the dynamic equilibrium between Aβ monomers and higher ordered aggregates. We identify Met(35)-Val(36) as a novel IDE cleavage site in the Aβ sequence and show that Aβ fragments resulting from IDE cleavage form non-toxic amorphous aggregates. These findings need to be taken into account in therapeutic strategies designed to increase Aβ clearance in AD patients by modulating IDE activity.

Supermetallization of peptides and proteins during electrospray ionization

The formation of metal-peptide complexes during electrospray ionization (ESI) is a widely known phenomenon and is often considered to be undesirable. Such effect considerably limits the use of ESI mass spectrometry for the investigation of biologically relevant metal-peptide compounds that are present in the solution and play critical roles in many bioprocesses such as progression of neurodegenerative diseases. In the article, it is demonstrated that under specific conditions such as high temperature of the desolvating capillary, an interesting effect, which can be called as 'supermetallization', occurs. Using a model peptide Αβ amyloid domain 1-16, it was observed that an increase in the temperature of the desolvating capillary results in multiple substitutions of hydrogen atoms by Zn atoms in this peptide. At high temperatures (T ~ 400 °C), up to 11 zinc atoms can be covalently bound to (1-16) Αβ. It was observed that supermetallization of (1-16) Αβ depends on the solvent composition and pH. Supermetallization was also demonstrated for proteins, such as ubiquitin and cytochrome C. That proves that the supermetallization is a general phenomenon for peptides and proteins. For the structural investigation of supermetallized complexes, electron-capture dissociation (ECD) fragmentation was applied. The effect of hydrogen rearranging during ECD was observed. In addition, quantum chemical calculations were used to estimate the possible structures of different supermetallized complexes. These results allow a more deep understanding of the limitations of the use of ESI mass spectrometry for the investigation of biologically relevant metal-peptide complexes. Copyright © 2015 John Wiley & Sons, Ltd.

Magneto-immunocapture with on-bead fluorescent labeling of amyloid-β peptides: towards a microfluidized-bed-based operation

Novel combination of Magneto-immunocapture and on-beads fluorescent labeling of Aβ peptides for their sensitive determination in cerebro spinal fluid samples.

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.

Sulforaphane interaction with amyloid beta 1-40 peptide studied by electrospray ionization mass spectrometry

RATIONALE

Aggregation of amyloid beta 1-40 (Aβ) in the brain causes Alzheimer's disease (AD) and several small molecules are known to inhibit the aggregation process. Sulforaphane (SFN) is a natural isothiocyanate which is known to prevent various neurodegenerative processes. However, its interaction with Aβ is yet to be explored. Such studies could provide new mechanistic insights for its neuroprotective properties.

METHODS

Liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) and in-source fragmentation experiments were performed on an Orbitrap mass spectrometer. The solution of Aβ and SFN was incubated and analyzed by mass spectrometry. Isotopic distribution patterns, accurate mass values and theoretical product ions were used to analyze the mass spectrometry data. The nature of binding of SFN and its binding sites with Aβ were evaluated by LC/MS and trypsin digestion experiments.

RESULTS

ESI-MS analysis of the incubated solution of Aβ and SFN showed a 1:1 complex of [Aβ+SFN]. LC/MS analysis revealed that the solution contains three different [Aβ+SFN] complexes due to covalent binding of SFN to Aβ at three different sites. The in-source fragmentation experiments revealed that SFN is binding to free NH(2) groups (N-terminal amino acid and lysines) in Aβ. Trypsin digestion experiments further confirmed the SFN binding sites in Aβ.

CONCLUSIONS

The interaction of SFN, an anticancer agent, with Aβ was studied using ESI-MS. SFN is found to bind covalently and specifically with the free NH(2) group of N-terminal aspartic acid and the ε-amino group of lysine at positions 16 and 28. Aggregation assay studies showed a lesser inclination of Aβ to aggregate when SFN is present. Hence the present study helps in understanding the mechanism of the action of SFN on the Aβ peptide.

The role of copper(II) and zinc(II) in the degradation of human and murine IAPP by insulin-degrading enzyme

Amylin or islet amyloid polypeptide (IAPP) is a 37-residue peptide hormone secreted from the pancreatic islets into the blood circulation and is cleared by peptidases in the kidney. IAPP aggregates are strongly associated with β-cell degeneration in type 2 diabetes, as demonstrated by the fact that more than 95% of patients exhibit IAPP amyloid upon autopsy. Recently, it has been reported that metal ions such as copper(II) and zinc(II) are implicated in the aggregation of IAPP as well as able to modulate the proteolytic activity of IAPP degrading enzymes. For this reason, in this work, the role of the latter metal ions in the degradation of IAPP by insulin-degrading enzyme (IDE) has been investigated by a chromatographic and mass spectrometric combined method. The latter experimental approach allowed not only to assess the overall metal ion inhibition of the human and murine IAPP degradation by IDE but also to have information on copper- and zinc-induced changes in IAPP aggregation. In addition, IDE cleavage site preferences in the presence of metal ions are rationalized as metal ion-induced changes in substrate accessibility.

New pharmacological strategies for treatment of Alzheimer's disease: focus on disease modifying drugs

Current approved drug treatments for Alzheimer disease (AD) include cholinesterase inhibitors (donepezil, rivastigmine, galantamine) and the NMDA receptor antagonist memantine. These drugs provide symptomatic relief but poorly affect the progression of the disease. Drug discovery has been directed, in the last 10 years, to develop 'disease modifying drugs' hopefully able to counteract the progression of AD. Because in a chronic, slow progressing pathological process, such as AD, an early start of treatment enhances the chance of success, it is crucial to have biomarkers for early detection of AD-related brain dysfunction, usable before clinical onset. Reliable early biomarkers need therefore to be prospectively tested for predictive accuracy, with specific cut off values validated in clinical practice. Disease modifying drugs developed so far include drugs to reduce β amyloid (Aβ) production, drugs to prevent Aβ aggregation, drugs to promote Aβ clearance, drugs targeting tau phosphorylation and assembly and other approaches. Unfortunately none of these drugs has demonstrated efficacy in phase 3 studies. The failure of clinical trials with disease modifying drugs raises a number of questions, spanning from methodological flaws to fundamental understanding of AD pathophysiology and biology. Recently, new diagnostic criteria applicable to presymptomatic stages of AD have been published. These new criteria may impact on drug development, such that future trials on disease modifying drugs will include populations susceptible to AD, before clinical onset. Specific problems with completed trials and hopes with ongoing trials are discussed in this review.

Metal ions affect insulin-degrading enzyme activity

Insulin degradation is a finely tuned process that plays a major role in controlling insulin action and most evidence supports IDE (insulin-degrading enzyme) as the primary degradative agent. However, the biomolecular mechanisms involved in the interaction between IDE and its substrates are often obscure, rendering the specific enzyme activity quite difficult to target. On the other hand, biometals, such as copper, aluminum and zinc, have an important role in pathological conditions such as Alzheimer's disease or diabetes mellitus. The metabolic disorders connected with the latter lead to some metallostasis alterations in the human body and many studies point at a high level of interdependence between diabetes and several cations. We have previously reported (Grasso et al., Chem. Eur. J. 17 (2011) 2752-2762) that IDE activity toward Aβ peptides can be modulated by metal ions. Here, we have investigated the effects of different metal ions on the IDE proteolytic activity toward insulin as well as a designed peptide comprising a portion of the insulin B chain (B20-30), which has a very low affinity for metal ions. The results obtained by different experimental techniques clearly show that IDE is irreversibly inhibited by copper(I) but is still able to process its substrates when it is bound to copper(II).