A spectroscopic study on the Amyloid-ß interaction with clicked peptide-porphyrin conjugates: a vision toward the detection of Aß peptides in aqueous solution.

Alzheimer's disease (AD) is a multifactorial form of dementia mainly affecting people in the elderly, but no effective cure is available. According to the amyloid hypothesis the aggregation of Amyloid-ß (Aß) into oligomeric toxic species is believed to concur with the onset and progression of the disease heavily. By using a click chemistry approach, we conjugated a suitable designed peptide sequence to a metalloporphyrin moiety to obtain three hybrid peptide systems to be studied for their interact ion with Amyloid-ß peptides. The aim is to get new tools for the diagnosis and therapy in AD. The results described in this study, which were obtained through spectroscopic techniques (UV-Vis, CD, Bis-Ans and intrinsic porphyrin Fluorescence), Microfluidics (GCI) and cell biology (MTT, Live cell imaging and flow cytometry), reveal interesting features about the structure-activity relationships connecting these conjugates with the interaction with Aß, as well as on their potential use as sensing systems. In our opinion the data reported in this paper make the porphyrin-peptide conjugates highly compelling for further exploration as spectroscopic probes to detect Aß biomarkers in biological fluids.

Aß and Tau Interact with Metal Ions, Lipid Membranes and Peptide-Based Amyloid Inhibitors: Are These Common Features Relevant in Alzheimer's Disease?

In the last two decades, the amyloid hypothesis, i.e., the abnormal accumulation of toxic Aß assemblies in the brain, has been considered the mainstream concept sustaining research in Alzheimer's Disease (AD). However, the course of cognitive decline and AD development better correlates with tau accumulation rather than amyloid peptide deposition. Moreover, all clinical trials of amyloid-targeting drug candidates have been unsuccessful, implicitly suggesting that the amyloid hypothesis needs significant amendments. Accumulating evidence supports the existence of a series of potentially dangerous relationships between Aß oligomeric species and tau protein in AD. However, the molecular determinants underlying pathogenic Aß/tau cross interactions are not fully understood. Here, we discuss the common features of Aß and tau molecules, with special emphasis on: (i) the critical role played by metal dyshomeostasis in promoting both Aß and tau aggregation and oxidative stress, in AD; (ii) the effects of lipid membranes on Aß and tau (co)-aggregation at the membrane interface; (iii) the potential of small peptide-based inhibitors of Aß and tau misfolding as therapeutic tools in AD. Although the molecular mechanism underlying the direct Aß/tau interaction remains largely unknown, the arguments discussed in this review may help reinforcing the current view of a synergistic Aß/tau molecular crosstalk in AD and stimulate further research to mechanism elucidation and next-generation AD therapeutics.

Cyclodextrin Polymers as Delivery Systems for Targeted Anti-Cancer Chemotherapy.

In the few last years, nanosystems have emerged as a potential therapeutic approach to improve the efficacy and selectivity of many drugs. Cyclodextrins (CyDs) and their nanoparticles have been widely investigated as drug delivery systems. The covalent functionalization of CyD polymer nanoparticles with targeting molecules can improve the therapeutic potential of this family of nanosystems. In this study, we investigated cross-linked γ- and ß-cyclodextrin polymers as carriers for doxorubicin (ox) and oxaliplatin (Oxa). We also functionalized γ-CyD polymer bearing COOH functionalities with arginine-glycine-aspartic or arginine moieties for targeting the integrin receptors of cancer cells. We tested the Dox and Oxa anti-proliferative activity in the presence of the precursor polymer with COOH functionalities and its derivatives in A549 (lung, carcinoma) and HepG2 (liver, carcinoma) cell lines. We found that CyD polymers can significantly improve the antiproliferative activity of Dox in HepG2 cell lines only, whereas the cytotoxic activity of Oxa resulted as enhanced in both cell lines. The peptide or amino acid functionalized CyD polymers, loaded with Dox, did not show any additional effect compared to the precursor polymer. Finally, studies of Dox uptake showed that the higher antiproliferative activity of complexes correlates with the higher accumulation of Dox inside the cells. The results show that CyD polymers could be used as carriers for repositioning classical anticancer drugs such as Dox or Oxa to increase their antitumor activity.

Cyclodextrin polymers decorated with RGD peptide as delivery systems for targeted anti-cancer chemotherapy.

Polymeric cyclodextrin-based nanoparticles are currently undergoing clinical trials as nanotherapeutics. Using a non-covalent approach, we decorated two cross-linked cyclodextrin polymers of different molecular weights with an RGD peptide derivative to construct a novel carrier for the targeted delivery of doxorubicin. RGD is the binding sequence for the integrin receptor family that is highly expressed in tumour tissues. The assembled host-guest systems were investigated using NMR and DLS techniques. We found that, in comparison with free doxorubicin or the binary complex doxorubicin/cyclodextrin polymer, the RGD units decorating the cyclodextrin-based nanosystems improved the selectivity and cytotoxicity of the complexed doxorubicin towards cultured human tumour cell lines. Our results suggest that the nanocarriers under study may contribute to the development of new platforms for cancer therapy.

Ion mobility spectrometry combined with multivariate statistical analysis: revealing the effects of a drug candidate for Alzheimer's disease on Aß1-40 peptide early assembly.

Inhibition of the initial stages of amyloid-ß peptide self-assembly is a key approach in drug development for Alzheimer's disease, in which soluble and highly neurotoxic low molecular weight oligomers are produced and aggregate in the brain over time. Here we report a high-throughput method based on ion mobility mass spectrometry and multivariate statistical analysis to rapidly select statistically significant early-stage species of amyloid-ß1-40 whose formation is inhibited by a candidate theranostic agent. Using this method, we have confirmed the inhibition of a Zn-porphyrin-peptide conjugate in the early self-assembly of Aß40 peptide. The MS/MS fragmentation patterns of the species detected in the samples containing the Zn-porphyrin-peptide conjugate suggested a porphyrin-catalyzed oxidation at Met-35(O) of Aß40. We introduce ion mobility MS combined with multivariate statistics as a systematic approach to perform data analytics in drug discovery/amyloid research that aims at the evaluation of the inhibitory effect on the Aß early assembly in vitro models at very low concentration levels of Aß peptides.

Ac-LPFFD-Th: A Trehalose-Conjugated Peptidomimetic as a Strong Suppressor of Amyloid-ß Oligomer Formation and Cytotoxicity.

The inhibition of amyloid formation is a promising therapeutic approach for the treatment of neurodegenerative diseases. Peptide-based inhibitors, which have been widely investigated, are generally derived from original amyloid sequences. Most interestingly, trehalose, a nonreducing disaccharide of α-glucose, is effective in preventing the aggregation of numerous proteins. We have determined that the development of hybrid compounds could provide new molecules with improved properties that might synergically increase the potency of their single moieties. In this work, the ability of Ac-LPFFD-Th, a C-terminally trehalose-conjugated derivative, to slow down the Aß aggregation process was investigated by means of different biophysical techniques, including thioflavin T fluorescence, dynamic light scattering, ESI-MS, and NMR spectroscopy. Moreover, we demonstrate that Ac-LPFFD-Th modifies the aggregation features of Aß and protects neurons from Aß oligomers' toxic insult.

New Insight in Copper-Ion Binding to Human Islet Amyloid: The Contribution of Metal-Complex Speciation To Reveal the Polypeptide Toxicity.

Type-2 diabetes (T2D) is considered to be a potential threat on a global level. Recently, T2D has been listed as a misfolding disease, such as Alzheimer's and Parkinson's diseases. Human islet amyloid polypeptide (hIAPP) is a molecule cosecreted in pancreatic ß cells and represents the main constituent of an aggregated amyloid found in individuals affected by T2D. The trace-element serum level is significantly influenced during the development of diabetes. In particular, the dys-homeostasis of Cu(2+) ions may adversely affect the course of the disease. Conflicting results have been reported on the protective role played by complex species formed by Cu(2+) ions with hIAPP or its peptide fragments in vitro. The histidine (His) residue at position 18 represents the main binding site for the metal ion, but contrasting results have been reported on other residues involved in metal-ion coordination, in particular those toward the N or C terminus. Sequences that encompass regions 17-29 and 14-22 were used to discriminate between the two models of the hIAPP coordination mode. Due to poor solubility in water, poly(ethylene glycol) (PEG) derivatives were synthesized. A peptide fragment that encompasses the 17-29 region of rat amylin (rIAPP) in which the arginine residue at position 18 was substituted by a histidine residue was also obtained to assess that the PEG moiety does not alter the peptide secondary structure. The complex species formed by Cu(2+) ions with Ac-PEG-hIAPP(17-29)-NH2 , Ac-rIAPP(17-29)R18H-NH2 , and Ac-PEG-hIAPP(14-22)-NH2 were studied by using potentiometric titrations coupled with spectroscopic methods (UV/Vis, circular dichroism, and EPR). The combined thermodynamic and spectroscopic approach allowed us to demonstrate that hIAPP is able to bind Cu(2+) ions starting from the His18 imidazole nitrogen atom toward the N-terminus domain. The stability constants of copper(II) complexes with Ac-PEG-hIAPP(14-22)-NH2 were used to simulate the different experimental conditions under which aggregate formation and oxidative stress of hIAPP has been reported. Speciation unveils: 1) the protective role played by increased amounts of Cu(2+) ions on the hIAPP fibrillary aggregation, 2) the effect of adventitious trace amounts of Cu(2+) ions present in phosphate-buffered saline (PBS), and 3) a reducing fluorogenic probe on H2 O2 production attributed to the polypeptide alone.

The N-Terminal Peptides of the Three Human Isoforms of the Mitochondrial Voltage-Dependent Anion Channel Have Different Helical Propensities.

The voltage-dependent anion channel (VDAC) is the main mitochondrial porin allowing the exchange of ions and metabolites between the cytosol and the mitochondrion. In addition, VDAC was found to actively interact with proteins playing a fundamental role in the regulation of apoptosis and being of central interest in cancer research. VDAC is a large transmembrane ß-barrel channel, whose N-terminal helical fragment adheres to the channel interior, partially closing the pore. This fragment is considered to play a key role in protein stability and function as well as in the interaction with apoptosis-related proteins. Three VDAC isoforms are differently expressed in higher eukaryotes, for which distinct and complementary roles are proposed. In this work, the folding propensity of their N-terminal fragments has been compared. By using multiple spectroscopic techniques, and complementing the experimental results with theoretical computer-assisted approaches, we have characterized their conformational equilibrium. Significant differences were found in the intrinsic helical propensity of the three peptides, decreasing in the following order: hVDAC2 > hVDAC3 > hVDAC1. In light of the models proposed in the literature to explain voltage gating, selectivity, and permeability, as well as interactions with functionally related proteins, our results suggest that the different chemicophysical properties of the N-terminal domain are possibly correlated to different functions for the three isoforms. The overall emerging picture is that a similar transmembrane water accessible conduit has been equipped with not identical domains, whose differences can modulate the functional roles of the three VDAC isoforms.

Cross-talk between the octarepeat domain and the fifth binding site of prion protein driven by the interaction of copper(II) with the N-terminus.

Prion diseases are a group of neurodegenerative diseases based on the conformational conversion of the normal form of the prion protein (PrP(C)) to the disease-related scrapie isoform (PrP(Sc)). Copper(II) coordination to PrP(C) has attracted considerable interest for almost 20 years, mainly due to the possibility that such an interaction would be an important event for the physiological function of PrP(C). In this work, we report the copper(II) coordination features of the peptide fragment Ac(PEG11)3PrP(60-114) [Ac = acetyl] as a model for the whole N-terminus of the PrP(C) metal-binding domain. We studied the complexation properties of the peptide by means of potentiometric, UV/Vis, circular dichroism and electrospray ionisation mass spectrometry techniques. The results revealed that the preferred histidyl binding sites largely depend on the pH and copper(II)/peptide ratio. Formation of macrochelate species occurs up to a 2:1 metal/peptide ratio in the physiological pH range and simultaneously involves the histidyl residues present both inside and outside the octarepeat domain. However, at increased copper(II)/peptide ratios amide-bound species form, especially within the octarepeat domain. On the contrary, at basic pH the amide-bound species predominate at any copper/peptide ratio and are formed preferably with the binding sites of His96 and His111, which is similar to the metal-binding-affinity order observed in our previous studies.

New Conjugates of Hyaluronic Acid with γ-Cyclodextrin as Sorafenib Carrier in Cancer Cells.

In recent years, nanoparticles based on cyclodextrins have been widely investigated, mainly for drug delivery. In this work, we synthesized nanoparticles with a hyaluronic acid backbone (11 kDa and 45 kDa) functionalized with γ-cyclodextrins. We tested sorafenib in the presence of the new hyaluronan-cyclodextrin conjugates in A2780 (ovarian cancer), SK-HeP-1 (adenocarcinoma) and MDA-MB-453 (breast cancer) cell lines. We found that hyaluronan-cyclodextrin conjugates improve the antiproliferative activity of sorafenib. Remarkably, the system based on the 11 kDa hyaluronan conjugate was the most effective and, in the MDA-MB-453 cell line, significantly reduced the IC50 value of sorafenib cells by about 75 %.

Affinity, speciation, and molecular features of copper(II) complexes with a prion tetraoctarepeat domain in aqueous solution: insights into old and new results.

Characterization of the copper(II) complexes formed with the tetraoctarepeat peptide at low and high metal-to-ligand ratios and in a large pH range, would provide a breakthrough in the interpretation of biological relevance of the different metal complexes of copper(II)-tetraoctarepeat system. In the present work, the potentiometric, UV/Vis, circular dichroism (CD), and electron paramagnetic resonance (EPR) studies were carried out on copper(II) complexes with a PEG-ylated derivative of the tetraoctarepeats peptide sequence (Ac-PEG27 -(PHGGGWGQ)4 -NH2 ) and the peptide Ac-(PHGGGWGQ)2 -NH2 . Conjugation of tetraoctarepeat peptide sequence with polyethyleneglycol improved the solubility of the copper(II) complexes. The results enable a straightforward explanation of the conflicting results originated from the underestimation of all metal-ligand equilibria and the ensuing speciation. A complete and reliable speciation is therefore obtained with the released affinity and binding details of the main complexes species formed in aqueous solution. The results contribute to clarify the discrepancies of several studies in which the authors ascribe the redox activity of copper(II)-tetraoctarepeat system considering only the average effects of several coexisting species with very different stoichiometries and binding modes.

Impact of magnetic resonance in the preoperative staging and the surgical planning for treating small bowel neoplasms.

PURPOSE: The role of MR enteroclysis/enterography (MRE) in the diagnosis of small bowel (SB) tumor has not been fully evaluated. The aims of this study were to assess the capability of MRE correctly identifying the site, stage and histology of such neoplasms. METHODS: MR enteroclysis/enterography was employed in consecutive patients suspected of having an SB tumor following negative upper and lower endoscopies. The SB was subdivided into proximal jejunum, middle SB and distal ileum. The histological examination (HE) of the surgical specimen was the reference standard. RESULTS: One hundred and fifty-eight patients were examined. Thirty-one out of 32 (96.9 %) SB detected by HE were correctly identified by MRE. The concordance rate between MRE and HE was 100 % for localization, and 87.1, 80.6 and 96.8 % for T, N and M stages, respectively. The concordance rate was 62.2 % for histological diagnosis. CONCLUSIONS: The high concordance rates between MRE and HE for the localization of SB tumors and for their staging have a significant impact upon surgical planning, particularly if laparoscopy is being considered. A preoperative histological diagnosis is not sufficiently reliable.

Probing the residual structure in avian prion hexarepeats by CD, NMR and MD techniques.

Many proteins perform essential biological functions by means of regions that lacking specific organized structure exist as an ensemble of interconverting transient conformers. The characterization of such regions, including the description of their structural propensities, number of conformations and relative populations can provide useful insights. Prion diseases result from the conversion of a normal glycoprotein into a misfolded pathogenic isoform. The structures of mammal and chicken prion proteins show a similar fold with a globular domain and a flexible N-terminal portion that contains different repeated regions: octarepeats (PHGGGWGQ) in mammals and hexarepeats (PHNPGY) in chickens. The higher number of prolines in the hexarepeat region suggests that this region may retain a significant amount of residual secondary structure. Here, we report the CD, NMR and MD characterization of a peptide (2-HexaPY) composed of two hexarepeats. We combine experimental NMR data and MD to investigate at atomic level its ensemble-averaged structural properties, demonstrating how each residue of both repeats has a different quantified PPII propensity that shows a periodicity along the sequence. This feature explains the absence of cooperativity to stabilize a PPII conformation. Nonetheless, such residual structure can play a role in nucleating local structural transitions as well as modulating intra-molecular or inter-molecular interactions.

Aß8-20 Fragment as an Anti-Fibrillogenic and Neuroprotective Agent: Advancing toward Efficient Alzheimer's Disease Treatment.

Alzheimer's disease (AD) is the most common cause of dementia, characterized by a spectrum of symptoms associated with memory loss and cognitive decline with deleterious consequences in everyday life. The lack of specific drugs for the treatment and/or prevention of this pathology makes AD an ever-increasing economic and social emergency. Oligomeric species of amyloid-beta (Aß) are recognized as the primary cause responsible for synaptic dysfunction and neuronal degeneration, playing a crucial role in the onset of the pathology. Several studies have been focusing on the use of small molecules and peptides targeting oligomeric species to prevent Aß aggregation and toxicity. Among them, peptide fragments derived from the primary sequence of Aß have also been used to exploit any eventual recognition abilities toward the full-length Aß parent peptide. Here, we test the Aß8-20 fragment which contains the self-recognizing Lys-Leu-Val-Phe-Phe sequence and lacks Arg 5 and Asp 7 and the main part of the C-terminus, key points involved in the aggregation pathway and stabilization of the fibrillary structure of Aß. In particular, by combining chemical and biological techniques, we show that Aß8-20 does not undergo random coil to ß sheet conformational transition, does not form amyloid fibrils by itself, and is not toxic for neuronal cells. Moreover, we demonstrate that Aß8-20 mainly interacts with the 4-11 region of Aß1-42 and inhibits the formation of toxic oligomeric species and Aß fibrils. Finally, our data show that Aß8-20 protects neuron-like cells from Aß1-42 oligomer toxicity. We propose Aß8-20 as a promising drug candidate for the treatment of AD.

Quantifying the relationship between specialisation and reputation in an online platform.

Online platforms implement digital reputation systems in order to steer individual user behaviour towards outcomes that are deemed desirable on a collective level. At the same time, most online platforms are highly decentralised environments, leaving their users plenty of room to pursue different strategies and diversify behaviour. We provide a statistical characterisation of the user behaviour emerging from the interplay of such competing forces in Stack Overflow, a long-standing knowledge sharing platform. Over the 11 years covered by our analysis, we represent the interactions between users and topics as bipartite networks. We find such networks to display nested structures akin to those observed in ecological systems, demonstrating that the platform's user base consistently self-organises into specialists and generalists, i.e., users who focus on narrow and broad sets of topics, respectively. We relate the emergence of these behaviours to the platform's reputation system with a series of data-driven models, and find specialisation to be statistically associated with a higher ability to post the best answers to a question. We contrast our findings with observations made in top-down environments-such as firms and corporations-where generalist skills are consistently found to be more successful.

Pairwise and high-order dependencies in the cryptocurrency trading network.

In this paper we analyse the effects of information flows in cryptocurrency markets. We first define a cryptocurrency trading network, i.e. the network made using cryptocurrencies as nodes and the Granger causality among their weekly log returns as links, later we analyse its evolution over time. In particular, with reference to years 2020 and 2021, we study the logarithmic US dollar price returns of the cryptocurrency trading network using both pairwise and high-order statistical dependencies, quantified by Granger causality and O-information, respectively. With reference to the former, we find that it shows peaks in correspondence of important events, like e.g., Covid-19 pandemic turbulence or occasional sudden prices rise. The corresponding network structure is rather stable, across weekly time windows in the period considered and the coins are the most influential nodes in the network. In the pairwise description of the network, stable coins seem to play a marginal role whereas, turning high-order dependencies, they appear in the highest number of synergistic information circuits, thus proving that they play a major role for high order effects. With reference to redundancy and synergy with the time evolution of the total transactions in US dollars, we find that their large volume in the first semester of 2021 seems to have triggered a transition in the cryptocurrency network toward a more complex dynamical landscape. Our results show that pairwise and high-order descriptions of complex financial systems provide complementary information for cryptocurrency analysis.

KLVFF oligopeptide-decorated amphiphilic cyclodextrin nanomagnets for selective amyloid beta recognition and fishing.

Recognition and capture of amyloid beta (Aß) is a challenging task for the early diagnosis of neurodegenerative disorders, such as Alzheimer's disease. Here, we report a novel KLVFF-modified nanomagnet based on magnetic nanoparticles (MNP) covered with a non-ionic amphiphilic ß-cyclodextrin (SC16OH) and decorated with KLVFF oligopeptide for the self-recognition of the homologous amino-acids sequence of Aß to collect Aß (1-42) peptide from aqueous samples. MNP@SC16OH and MNP@SC16OH/Ada-Pep nanoassemblies were fully characterized by complementary techniques both as solid powders and in aqueous dispersions. Single domain MNP@SC16OH/Ada-Pep nanomagnets of 20-40 nm were observed by TEM analysis. DLS and ζ-potential measurements revealed that MNP@SC16OH nanoassemblies owned in aqueous dispersion a hydrodynamic radius of about 150 nm, which was unaffected by Ada-Pep decoration, while the negative ζ-potential of MNP@SC16OH (-40 mV) became less negative (-30 mV) in MNP@SC16OH/Ada-Pep, confirming the exposition of positively charged KLVFF on nanomagnets surface. The ability of MNP@SC16OH/Ada-Pep to recruit Aß (1-42) in aqueous solution was evaluated by MALDI-TOF and compared with the ineffectiveness of undecorated MNP@SC16OH and VFLKF scrambled peptide-decorated nanoassemblies (MNP@SC16OH/Ada-scPep), pointing out the selectivity of KLVFF-decorated nanohybrid towards Aß (1-42). Finally, the property of nanomagnets to extract Aß in conditioned medium of cells over-producing Aß peptides was investigated as proof of concept of effectiveness of these nanomaterials as potential diagnostic tools.

Copper(I) and copper(II) inhibit Aß peptides proteolysis by insulin-degrading enzyme differently: implications for metallostasis alteration in Alzheimer's disease.

Accumulation of neurotoxic amyloid-ß peptide (Aß) and alteration of metal homeostasis (metallostasis) in the brain are two main factors that have been very often associated with neurodegenerative diseases, such as Alzheimer's disease (AD). Aß is constantly produced from the amyloidprecursor-protein APP precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Aß and/or metal ions seems to lead to a pathological deposition. Although insulin-degrading enzyme (IDE) is the main metalloprotease involved in Aß degradation in the brain being up-regulated in some areas of AD brains, the role of IDE for the onset and development of AD is far from being understood. Moreover, the biomolecular mechanisms involved in the recognition and interaction between IDE and its substrates are still obscure. In spite of the important role of metals (such as copper, aluminum, and zinc), which has brought us to propose a "metal hypothesis of AD", a targeted study of the effect of metallostasis on IDE activity has never been carried out. In this work, we have investigated the role that various metal ions (i.e., Cu(2+), Cu(+), Zn(2+), Ag(+), and Al(3+)) play in modulating the interaction between IDE and two Aß peptide fragments, namely Aß(1-16) and Aß(16-28). It was therefore possible to identify the direct effect that such metal ions have on IDE structure and enzymatic activity without interferences caused by metal-induced substrate modifications. Mass spectrometry and kinetic studies revealed that, among all the metal ions tested, only Cu(2+), Cu(+), and Ag(+) have an inhibitory effect on IDE activity. Moreover, the inhibition of copper(II) is reversed by adding zinc(II), whereas the monovalent cations affect the enzyme activity irreversibly. The molecular basis of their action on the enzyme is also discussed on the basis of computational investigations.

Zn2+'s ability to alter the distribution of Cu2+ among the available binding sites of Aß(1-16)-polyethylenglycol-ylated peptide: implications in Alzheimer's disease.

The formation of mixed copper(II) and zinc(II) complexes with Aß(1-16)-PEG has been investigated. The peptide fragment forms stable mixed metal complexes at physiological pH in which the His13/His14 dyad is the zinc(II)'s preferred binding site, while copper(II) coordination occurs at the N-terminus also involving the His6 imidazole. Copper(II) is prevented by zinc(II) excess from the binding to the two His residues, His13 and His14. As the latter binding mode has been recently invoked to explain the redox activity of the copper-Aß complex, the formation of ternary metal complexes may justify the recently proposed protective role of zinc(II) in Alzheimer's disease. Therefore, the reported results suggest that zinc(II) competes with copper for Aß binding and inhibits copper-mediated Aß redox chemistry.