High Selectivity and Sensitivity of Oligomeric p-Phenylene Ethynylenes for Detecting Fibrillar and Prefibrillar Amyloid Protein Aggregates

Detection and disaggregation of amyloid fibrils by luminescent amphiphilic platinum(II) complexes

Cyclometallated Pt(II) complexes possessing hydrophobic 2-phenylpyridine (ppy) ligands and hydrophilic acetonylacetone (acac) ligands have been investigated for their ability to detect amyloid fibrils via luminescence response. Using hen egg-white lysozyme (HEWL) as a model amyloid protein, Pt(II) complexes featuring benzanilide-substituted ppy ligands and ethylene glycol-functionalized acac ligands demonstrated enhanced luminescence in the presence of HEWL fibrils, whereas Pt(II) complexes lacking complementary hydrophobic/hydrophilic ligand sets displayed little to no emission enhancement. An amphiphilic Pt(II) complex incorporating a bis(ethylene glycol)-derivatized acac ligand was additionally found to trigger restructuring of HEWL fibrils into smaller spherical aggregates. Amphiphilic Pt(II) complexes were generally non-toxic to SH-SY5Y neuroblastoma cells, and several complexes also exhibited enhanced luminescence in the presence of Aβ42 fibrils associated with Alzheimer's disease. This study demonstrates that easily prepared and robust (ppy)PtII(acac) complexes show promising reactivity toward amyloid fibrils and represent attractive molecular scaffolds for design of small-molecule probes targeting amyloid assemblies.

Amyloidogenic Propensity of Metabolites in the Uric Acid Pathway and Urea Cycle Critically Impacts the Etiology of Metabolic Disorders

Novel insights into the etiology of metabolic disorders have recently been uncovered through the study of metabolite amyloids. In particular, inborn errors of metabolism (IEMs), including gout, Lesch-Nyhan syndrome (LNS), xanthinuria, citrullinemia, and hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, are attributed to the dysfunction of the urea cycle and uric acid pathway. In this study, we endeavored to understand and mechanistically characterize the aggregative property exhibited by the principal metabolites of the urea cycle and uric acid pathway, specifically hypoxanthine, xanthine, citrulline, and ornithine. Employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), we studied the aggregation profiles of the metabolites. Insights obtained through molecular dynamics (MD) simulation underscore the vital roles of π-π stacking and hydrogen bonding interactions in the self-assembly process, and thioflavin T (ThT) assays further corroborate the amyloid nature of these metabolites. The in vitro MTT assay revealed the cytotoxic trait of these assemblies, a finding that was substantiated by in vivo assays employing the Caenorhabditis elegans (C. elegans) model, which revealed that the toxic effects were more pronounced and dose-specific in the case of metabolites that had aged via longer preincubation. We hence report a compelling phenomenon wherein these metabolites not only aggregate but transform into a soft, ordered assembly over time, eventually crystallizing upon extended incubation, leading to pathological implications. Our study suggests that the amyloidogenic nature of the involved metabolites could be a common etiological link in IEMs, potentially providing a unified perspective to study their pathophysiology, thus offering exciting insights into the development of targeted interventions for these metabolic disorders.

Alpha-Synuclein Oligomers Driven T1-T2 Switchable Nanoprobes for Early and Accurate Diagnosis of Parkinson's Disease

The alpha-synuclein (α-syn) oligomers hold a central role in the pathology of Parkinson's disease (PD). Achieving accurate detection of α-syn oligomers in vivo presents a promising avenue for early and accurate diagnosis of PD. Magnetic resonance imaging (MRI), with non-invasion and exceptional tissue penetration, offers a potent tool for visualizing α-syn oligomers in vivo. Nonetheless, ensuring diagnostic specificity remains a formidable challenge. Herein, a novel MRI probe (ASOSN) is introduced, which encompasses highly sensitive antiferromagnetic nanoparticles functionalized with single-chain fragment variable antibodies, endowing it with the capacity for discerning recognition and binding to α-syn oligomers and triggering a switchable T1-T2 MRI signal. Significantly, ASOSN possesses the unique capability to accurately discriminate α-syn oligomers from neuroinflammation in vivo. Moreover, ASOSN facilitates the non-invasive and precise visualizing of endogenous α-syn oligomers in living systems. This innovative design heralds the development of a non-invasive visualization strategy for α-syn oligomers, marking a pivotal advancement for early and accurate diagnosis of PD.

Small molecule-based fluorescent probes for the detection of α-Synuclein aggregation states

The formation of aggregates due to protein misfolding is encountered in various neurodegenerative diseases. α-Synuclein (α-Syn) aggregation is linked to Parkinson's disease (PD). It is one of the most prevalent neurodegenerative disorders after Alzheimer's disease. Aggregation of α-Syn is associated with Lewy body formation and degeneration of the dopaminergic neurons in the brain. These are the pathological hallmarks of PD progression. α-Syn aggregates in a multi-step process. The native unstructured α-Syn monomers combine to form oligomers, followed by amyloid fibrils, and finally Lewy bodies. Recent evidence suggests that α-Syn oligomerization and fibrils formation play major roles in PD development. α-Syn oligomeric species is the main contributor to neurotoxicity. Therefore, the detection of α-Syn oligomers and fibrils has drawn significant attention for potential diagnostic and therapeutic development. In this regard, the fluorescence strategy has become the most popular approach for following the protein aggregation process. Thioflavin T (ThT) is the most frequently used probe for monitoring amyloid kinetics. Unfortunately, it suffers from several significant drawbacks including the inability to detect neurotoxic oligomers. Researchers developed several small molecule-based advanced fluorescent probes compared to ThT for the detection/monitoring of α-Syn aggregates states. These are summarized here.

Selective In Vitro and Ex Vivo Staining of Brain Neurofibrillary Tangles and Amyloid Plaques by Novel Ethylene Ethynylene-Based Optical Sensors

The identification of protein aggregates as biomarkers for neurodegeneration is an area of interest for disease diagnosis and treatment development. In this work, we present novel super luminescent conjugated polyelectrolyte molecules as ex vivo sensors for tau-paired helical filaments (PHFs) and amyloid-β (Aβ) plaques. We evaluated the use of two oligo-p-phenylene ethynylenes (OPEs), anionic OPE12- and cationic OPE24+, as stains for fibrillar protein pathology in brain sections of transgenic mouse (rTg4510) and rat (TgF344-AD) models of Alzheimer's disease (AD) tauopathy, and post-mortem brain sections from human frontotemporal dementia (FTD). OPE12- displayed selectivity for PHFs in fluorimetry assays and strong staining of neurofibrillary tangles (NFTs) in mouse and human brain tissue sections, while OPE24+ stained both NFTs and Aβ plaques. Both OPEs stained the brain sections with limited background or non-specific staining. This novel family of sensors outperformed the gold-standard dye Thioflavin T in sensing capacities and co-stained with conventional phosphorylated tau (AT180) and Aβ (4G8) antibodies. As the OPEs readily bind protein amyloids in vitro and ex vivo, they are selective and rapid tools for identifying proteopathic inclusions relevant to AD. Such OPEs can be useful in understanding pathogenesis and in creating in vivo diagnostically relevant detection tools for neurodegenerative diseases.

Controlled Growth and Self-Assembly of Multiscale Organic Semiconductor

Currently, organic semiconductors (OSs) are widely used as active components in practical devices related to energy storage and conversion, optoelectronics, catalysis, and biological sensors, etc. To satisfy the actual requirements of different types of devices, chemical structure design and self-assembly process control have been synergistically performed. The morphology and other basic properties of multiscale OS components are governed on a broad scale from nanometers to macroscopic micrometers. Herein, the up-to-date design strategies for fabricating multiscale OSs are comprehensively reviewed. Related representative works are introduced, applications in practical devices are discussed, and future research directions are presented. Design strategies combining the advances in organic synthetic chemistry and supramolecular assembly technology perform an integral role in the development of a new generation of multiscale OSs.

Controlled and Selective Photo-oxidation of Amyloid-β Fibrils by Oligomeric p-Phenylene Ethynylenes

Photodynamic therapy (PDT) has been explored as a therapeutic strategy to clear toxic amyloid aggregates involved in neurodegenerative disorders such as Alzheimer's disease. A major limitation of PDT is off-target oxidation, which can be lethal for the surrounding cells. We have shown that a novel class of oligo-p-phenylene ethynylenes (OPEs) exhibit selective binding and fluorescence turn-on in the presence of prefibrillar and fibrillar aggregates of disease-relevant proteins such as amyloid-β (Aβ) and α-synuclein. Concomitant with fluorescence turn-on, OPE also photosensitizes singlet oxygen under illumination through the generation of a triplet state, pointing to the potential application of OPEs as photosensitizers in PDT. Herein, we investigated the photosensitizing activity of an anionic OPE for the photo-oxidation of Aβ fibrils and compared its efficacy to the well-known but nonselective photosensitizer methylene blue (MB). Our results show that, while MB photo-oxidized both monomeric and fibrillar conformers of Aβ40, OPE oxidized only Aβ40 fibrils, targeting two histidine residues on the fibril surface and a methionine residue located in the fibril core. Oxidized fibrils were shorter and more dispersed but retained the characteristic β-sheet rich fibrillar structure and the ability to seed further fibril growth. Importantly, the oxidized fibrils displayed low toxicity. We have thus discovered a class of novel theranostics for the simultaneous detection and oxidization of amyloid aggregates. Importantly, the selectivity of OPE's photosensitizing activity overcomes the limitation of off-target oxidation of traditional photosensitizers and represents an advancement of PDT as a viable strategy to treat neurodegenerative disorders.

Cross-Reactive Fluorescent Sensor Array for Discrimination of Amyloid Beta Aggregates

It has been hypothesized that misfolding and misassembly of proteins into various aggregation states contribute to several neurodegenerative diseases. For instance, amyloid beta (Aβ) aggregation is considered a major factor in Alzheimer's disease pathogenesis. Herein, a fluorescent sensor array for detecting Aβ aggregates was fabricated using two probe pairs of conjugated polyelectrolytes and organic dye molecules, PPE1-Thioflavin T (ThT) and PPESO3-Nile Red (NR). Pattern recognition was achieved by linear discriminant analysis and hierarchical clustering analysis algorithms. As a result of distinguishing among monomers and three pure aggregate species, namely oligomers, protofibrils, and fibrils, the cross-reactive sensor array was also able to monitor aggregation kinetics in various aggregate forms and distinguish between on- and off- aggregate pathways. Our study provides a convenient approach for simultaneous detection of Aβ aggregates in mixtures, which may also be applied to the analysis of other disease-related proteins that are prone to aggregates.

Two-photon excited lasing for detection of amyloids in brain tissue

Two-photon excitation of emissive markers with near-infrared (NIR) light is of a particular interest for imaging in biology and medicine because NIR light is relatively weakly absorbed and scattered by tissues. At the same time the mechanism of two-photon absorption allows excitation of molecules located deep inside a scattering medium. In this work we demonstrate that the two-photon excitation combined with the effect of light amplification in the stimulated emission process provides a sensitive method for detecting amyloids of different forms. We investigate the two-photon excited amplified spontaneous emission (ASE) of a fluorescent dye, coumarin 307, in the brain tissue infiltrated with various amyloid phantoms i.e. oligomers, protofibrils and mature fibrils. All these forms of amyloids can be detected by observation of ASE and determination of thresholds for light amplification. On this basis we suggest that a relatively simple extension of currently used emission-based optical spectroscopy techniques can provide key information on pathogenic amyloid structures in tissue.

Engineering of a protein probe with multiple inputs and multiple outputs for evaluation of alpha synuclein aggregation states

The aggregation of α-synuclein (αS) into oligomers and fibrils is implicated in the pathology of Parkinson's Disease (PD). While a molecular probe for rapid and comprehensive evaluation of αS aggregation states is critical for a better understanding of PD pathology, identification of therapeutic candidates, and the development of early diagnostic strategies, no such probe has yet to be developed. A structurally flexible αS variant, PG65, was previously developed as a target binding-driven, conformation-switching molecular probe for rapid αS oligomer detection. Though informative, detection using PG65 provides no comprehensive assessment of the αS aggregation states. In the present study, we report engineering of a molecular probe, PG65-MIMO (a PG65 variant with Multiple-Inputs and Multiple-Outputs), that rapidly (within 2 hr) produces comprehensive information on αS aggregation states. PG65-MIMO generates distinct fluorescence responses to the three major αS conformers (monomers, oligomers, and fibrils). PG65-MIMO also displays unique fluorescent signals for αS oligomers, depending on the tris(2-carboxyethyl)phosphine (TCEP) concentration. Our results suggest that the TCEP dependent signaling of PG65-MIMO may be associated with its conformational states. Overall, our study illustrates engineering of an αS variant to create a molecular probe for handling multiple inputs and multiple outputs, addressing the technological gap in αS detection.

A Portrait of the OPE as a Biological Agent

Oligophenylene ethynylenes, known as OPEs, are a sequence of aromatic rings linked by triple bonds, the properties of which can be modulated by varying the length of the rigid main chain or/and the nature and position of the substituents on the aromatic units. They are luminescent molecules with high quantum yields and can be designed to enter a cell and act as antimicrobial and antiviral compounds, as biocompatible fluorescent probes directed towards target organelles in living cells, as labelling agents, as selective sensors for the detection of fibrillar and prefibrillar amyloid in the proteic field and in a fluorescence turn-on system for the detection of saccharides, as photosensitizers in photodynamic therapy (due to their capacity to highly induce toxicity after light activation), and as drug delivery systems. The antibacterial properties of OPEs have been the most studied against very popular and resistant pathogens, and in this paper the achievements of these studies are reviewed, together with almost all the other roles held by such oligomers. In the recent decade, their antifungal and antiviral effects have attracted the attention of researchers who believe OPEs to be possible biocides of the future. The review describes, for instance, the preliminary results obtained with OPEs against severe acute respiratory syndrome coronavirus 2, the virus responsible for the COVID-19 pandemic.

Fluorescent probes for bioimaging of potential biomarkers in Parkinson's disease

This review comprehensively summarizes various types of fluorescent probes for PD and their applications for detection of various PD biomarkers.

Protein aggregation detection with fluorescent macromolecular and nanostructured probes: challenges and opportunities

Nanoprobes based on various nanomaterials, polymers or AIEgens are overcoming previous limitations for diagnosis and therapy of early-stage protein aggregation.

Highly Effective Inactivation of SARS-CoV-2 by Conjugated Polymers and Oligomers

In the present study, we examined the inactivation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by synthetic conjugated polymers and oligomers developed in our laboratories as antimicrobials for bacteria, fungi, and nonenveloped viruses. The results show highly effective light-induced inactivation with several of these oligomers and polymers including irradiation with near-UV and visible light. In the best case, one oligomer induced a 5-log reduction in pfu/mL within 10 min. In general, the oligomers are more active than the polymers; however, the polymers are active with longer wavelength visible irradiation. Although not studied quantitatively, the results show that in the presence of the agents at concentrations similar to those used in the light studies, there is essentially no dark inactivation of the virus. Because three of the five materials/compounds examined are quaternary ammonium derivatives, this study indicates that conventional quaternary ammonium antimicrobials may not be active against SARS-CoV-2. Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks, and clothing and other personal protection equipment that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses.

Computational Investigation of the Binding Dynamics of Oligo p-Phenylene Ethynylene Fluorescence Sensors and Aβ Oligomers

Amyloid protein aggregates are pathological hallmarks of neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's (PD) diseases and are believed to be formed well before the onset of neurodegeneration and cognitive impairment. Monitoring the course of protein aggregation is thus vital to understanding and combating these diseases. We have recently demonstrated that a novel class of fluorescence sensors, oligomeric p-phenylene ethynylene (PE)-based electrolytes (OPEs) selectively bind to and detect prefibrillar and fibrillar aggregates of AD-related amyloid-β (Aβ) peptides over monomeric Aβ. In this study, we investigated the binding between two OPEs, anionic OPE12- and cationic OPE24+, and to two different β-sheet rich Aβ oligomers using classical all-atom molecular dynamics simulations. Our simulations have revealed a number of OPE binding sites on Aβ oligomer surfaces, and these sites feature hydrophobic amino acids as well as oppositely charged amino acids. Binding energy calculations show energetically favorable interactions between both anionic and cationic OPEs with Aβ oligomers. Moreover, OPEs bind as complexes as well as single molecules. Compared to free OPEs, Aβ protofibril bound OPEs show backbone planarization with restricted rotations and reduced hydration of the ethyl ester end groups. These characteristics, along with OPE complexation, align with known mechanisms of binding induced OPE fluorescence turn-on and spectral shifts from a quenched, unbound state in aqueous solutions. This study thus sheds light on the molecular-level details of OPE-Aβ protofibril interactions and provides a structural basis for fluorescence turn-on sensing modes of OPEs.

Advances in nanomedicines for diagnosis of central nervous system disorders

In spite of a great improvement in medical health services and an increase in lifespan, we have witnessed a skyrocket increase in the incidence of central nervous system (CNS) disorders including brain tumors, neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease), ischemic stroke, and epilepsy, which have seriously undermined the quality of life and substantially increased economic and societal burdens. Development of diagnostic methods for CNS disorders is still in the early stage, and the clinical outcomes suggest these methods are not ready for the challenges associated with diagnosis of CNS disorders, such as early detection, specific binding, sharp contrast, and continuous monitoring of therapeutic interventions. Another challenge is to overcome various barrier structures during delivery of diagnostic agents, especially the blood-brain barrier (BBB). Fortunately, utilization of nanomaterials has been pursued as a potential and promising strategy to address these challenges. This review will discuss anatomical and functional structures of BBB and transport mechanisms of nanomaterials across the BBB, and special emphases will be placed on the state-of-the-art advances in the development of nanomedicines from a variety of nanomaterials for diagnosis of CNS disorders. Meanwhile, current challenges and future perspectives in this field are also highlighted.

Highly Effective Inactivation of SARS-CoV-2 by Conjugated Polymers and Oligomers

The current Covid-19 Pandemic caused by the highly contagious SARS-CoV-2 virus has proven extremely difficult to prevent or control. Currently there are few treatment options and very few long-lasting disinfectants available to prevent the spread. While masks and protective clothing and social distancing may offer some protection, their use has not always halted or slowed the spread. Several vaccines are currently undergoing testing; however there is still a critical need to provide new methods for inactivating the virus before it can spread and infect humans. In the present study we examined the inactivation of SARS-CoV-2 by synthetic conjugated polymers and oligomers developed in our laboratories as antimicrobials for bacteria, fungi and non-enveloped viruses. Our results show that we can obtain highly effective light induced inactivation with several of these oligomers and polymers including irradiation with near-UV and visible light. With both the oligomers and polymers, we can reach several logs of inactivation with relatively short irradiation times. Our results suggest several applications involving the incorporation of these materials in wipes, sprays, masks and clothing and other Personal Protection Equipment (PPE) that can be useful in preventing infections and the spreading of this deadly virus and future outbreaks from similar viruses.

Protective Effects of a Neurohypophyseal Hormone Analogue on Prion Aggregation, Cellular Internalization, and Toxicity

Herein, we report novel neuroprotective activity of the neurohypophyseal hormone analogue desmopressin (DDAVP) against toxic conformations of human prion protein. Systematic analysis using biophysical techniques in conjunction with surface plasmon resonance, high-end microscopy, conformational antibodies, and cell-based assays demonstrated DDAVP's specific binding and potent antiaggregating effects on prion protein (rPrP^res). In addition to subjugating conformational conversion of rPrP^res into oligomeric forms, DDAVP also exhibits potent fibril modulatory effects. It eventually ameliorated neuronal toxicity of rPrP^res oligomers by significantly reducing their cellular internalization. Molecular dynamics simulations showed that DDAVP prevents β-sheet transitions in the N-terminal amyloidogenic region of prion and induces antagonistic mobilities in its α2-α3 and β2-α2 loop regions. Collectively, our data proposes DDAVP as a new structural motif for rational drug discovery against prion diseases.

Well-Defined Conjugated Macromolecules Based on Oligo(Arylene Ethynylene)s in Sensing

Macromolecules with well-defined structures in terms of molar mass and monomer sequence became interesting building blocks for modern materials. The precision of the macromolecular structure makes fine-tuning of the properties of resulting materials possible. Conjugated macromolecules exhibit excellent optoelectronic properties that make them exceptional candidates for sensor construction. The importance of chain length and monomer sequence is particularly important in conjugated systems. The oligomer length, monomer sequence, and structural modification often influence the energy bang gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the molecules that reflect in their properties. Moreover, the supramolecular aggregation that is often observed in oligo-conjugated systems is usually strongly affected by even minor structural changes that are used for sensor designs. This review discusses the examples of well-defined conjugated macromolecules based on oligo(arylene ethynylene) skeleton used for sensor applications. Here, exclusively examples of uniform macromolecules are summarized. The sensing mechanisms and importance of uniformity of structure are deliberated.

M. Brito R. Structure and Aggregation Mechanisms in Amyloids

The aggregation of a polypeptide chain into amyloid fibrils and their accumulation and deposition into insoluble plaques and intracellular inclusions is the hallmark of several misfolding diseases known as amyloidoses. Alzheimer′s, Parkinson′s and Huntington’s diseases are some of the approximately 50 amyloid diseases described to date. The identification and characterization of the molecular species critical for amyloid formation and disease development have been the focus of intense scrutiny. Methods such as X-ray and electron diffraction, solid-state nuclear magnetic resonance spectroscopy (ssNMR) and cryo-electron microscopy (cryo-EM) have been extensively used and they have contributed to shed a new light onto the structure of amyloid, revealing a multiplicity of polymorphic structures that generally fit the cross-β amyloid motif. The development of rational therapeutic approaches against these debilitating and increasingly frequent misfolding diseases requires a thorough understanding of the molecular mechanisms underlying the amyloid cascade. Here, we review the current knowledge on amyloid fibril formation for several proteins and peptides from a kinetic and thermodynamic point of view, the structure of the molecular species involved in the amyloidogenic process, and the origin of their cytotoxicity.

Design principles and fundamental understanding of biosensors for amyloid-β detection

Aβ as biomarker in Alzheimer’s disease (AD) drives the significant research efforts for developing different biosensors with different sensing strategies, materials, and mechanisms for Aβ detection.