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

Synthesis and identification of azocoumarin derivatives toward imaging of α-synuclein aggregates in the brain

To identify α-synuclein aggregation in synucleinopathies is still challenging, due to the lack of specific probes for α-synuclein aggregates with efficient brain uptake. In this work, compact molecules based on coumarin scaffold were synthesized and evaluated for detection and bioimaging of α-synuclein aggregates in the brain. Among the developed compounds, azocoumarin 5 containing push-pull electronic architecture featured selective fluorescence enhancement towards α-synuclein aggregates in comparison to other β-sheet protein species (β-amyloid, tau). In addition, azocoumarin [18F]Cou-NNF was succesfully developed, and demonstrated its potential as radiotracer for imaging brain α-synuclein aggregates, owing to its favorable affinity for α-synuclein aggregates accompanied with efficient brain uptake and little defluorination in vivo. Overall, compact azocoumarin provides an effective lead structure for developing α-synuclein probes, and N=N bond shows promise in enhancing selective affinity for α-synuclein aggregates.

Exploring the Application Potential of α-Synuclein Molecular Probes in Early Diagnosis of Parkinson's Disease: Focus on Imaging Methods

This review aims to explore the potential application of α-synuclein (α-syn) molecular probes in the early diagnosis of Parkinson's disease (PD), particularly through systematic evaluation using medical imaging methods. In recent years, The abnormal aggregation of α-syn within the central nervous system is now recognized as a central driver of PD pathophysiology, solidifying its role as a critical diagnostic and prognostic biomarker. Early diagnosis of PD is critical for enabling precision therapeutic interventions and mitigating neurodegenerative progression, thereby enhancing long-term functional outcomes and the quality of life. However, challenges remain in clinical practice, particularly concerning the late timing of diagnosis and the lack of specific biomarkers. By analyzing the existing literature, we will assess the effectiveness of different imaging techniques combined with α-syn probes and discuss their advantages and limitations in clinical applications. These imaging methods can provide visualization of early pathological changes, helping to improve the recognition rate of PD. Finally, we emphasize the importance of future research to explore new molecular probes and imaging technologies that can improve early diagnosis rates and treatment outcomes for PD.

Regulating aggregation of an intrinsically disordered chaperone-like casein

Protein aggregation involving the conversion of soluble protein monomers into insoluble aggregates is prevalent in human diseases, food processing, food formulations, biotechnology-based therapeutics, etc. Molecular chaperones are typically globular proteins that regulate protein folding and aggregation. However, a unique chaperone-like milk protein namely, β-casein, is intrinsically disordered and prone to aggregation under physiological conditions. To regulate protein aggregation, there is a pressing need to devise strategic interventions that require a detailed understanding of the protein conformational changes during self-association. Here, we show that sodium chloride (NaCl) can modulate calcium ions (Ca2+)-induced spontaneous aggregation of β-casein under physiological conditions. Using fluorescence and Raman spectroscopy coupled with light scattering and transmission electron microscopy, we delineate the structural attributes of β-casein during Ca2+-mediated self-association. Our findings reveal that the binding of divalent Ca2+ to five phosphorylated serine residues (calcium phosphate binding-short linear sequence motif; CaP-SLiM), located within the N-terminal-domain of β-casein, is an obligatory prerequisite. This binding event subsequently triggers the formation of inter-casein bridges that facilitate multivalent interactions between the hydrophilic, disordered β-caseins, driving the self-assembly wherein hydrophobic interactions are insignificant compared to β-casein-CaCl2 interactions. Further, the Ca2+-induced β-casein aggregation is accompanied by a disorder-to-order transition resulting in non-amyloid, spherical aggregates. We also demonstrate that NaCl influences the aggregation propensity of β-casein by electrostatically screening the polypeptide and leads to the formation of aggregation-incompetent oligomers by abolishing the binding of Ca2+ to β-casein and the subsequent formation of inter-casein linkages, thus, affirming the pivotal role of CaP-SLiMs and multivalency during β-casein aggregation.

Is Cocaine Protonated When it Binds to the Dopamine Transporter?

There has been much controversy about whether the well-known alkaloid and tertiary amine base cocaine (pK a = 8.5) binds to the human dopamine transporter (DAT) in its protonated form. Most potent DAT inhibitors are also strong amines-yet there are some noteworthy examples where neutral cocaine analogues have high affinity, while the quaternary ammonium analog of cocaine, cocaine methiodide, is a comparatively poor inhibitor. In this paper, we show that a fluorescent cocaine analog, with a lower pK a than cocaine, becomes protonated in the DAT binding site and conclude that similar behavior must be expected from cocaine. By determining the pK a of the aspartate residue in DAT believed to interact with the amine of cocaine, we are able to explain the apparently contradictory structure-activity data of cocaine analogues.

Navigating α-Synuclein Aggregation Inhibition: Methods, Mechanisms, and Molecular Targets

Parkinson's disease is a yet incurable, age-related neurodegenerative disorder characterized by the aggregation of small neuronal protein α-synuclein into amyloid fibrils. Inhibition of this process is a prospective strategy for developing a disease-modifying treatment. We overview here small molecule, peptide, and protein inhibitors of α-synuclein fibrillization reported to date. Special attention was paid to the specificity of inhibitors and critical analysis of their action mechanisms. Namely, the importance of oxidation of polyphenols and cross-linking of α-synuclein into inhibitory dimers was highlighted. We also compared strategies of targeting monomeric, oligomeric, and fibrillar α-synuclein species, thoroughly discussed the strong and weak sides of different approaches to testing the inhibitors.

Development of fluorophores for the detection of oligomeric aggregates of amyloidogenic proteins found in neurodegenerative diseases

Alzheimer's disease and Parkinson's disease are the two most common neurodegenerative diseases globally. These neurodegenerative diseases have characteristic late-stage symptoms allowing for differential diagnosis; however, they both share the presence of misfolded protein aggregates which appear years before clinical manifestation. Historically, research has focused on the detection of higher-ordered aggregates (or amyloids); however, recent evidence has shown that the oligomeric state of these protein aggregates plays a greater role in disease pathology, resulting in increased efforts to detect oligomers to aid in disease diagnosis. In this review, we summarize some of the exciting new developments towards the development of fluorescent probes that can detect oligomeric aggregates of amyloidogenic proteins present in Alzheimer's and Parkinson's disease patients.

Development of a hydroxyflavone-labelled 4554W peptide probe for monitoring αS aggregation

Parkinson's is the second most common neurodegenerative disease, with the number of individuals susceptible due to increase as a result of increasing life expectancy and a growing worldwide population. However, despite the number of individuals affected, all current treatments for PD are symptomatic-they alleviate symptoms, but do not slow disease progression. A major reason for the lack of disease-modifying treatments is that there are currently no methods to diagnose individuals during the earliest stages of the disease, nor are there any methods to monitor disease progression at a biochemical level. Herein, we have designed and evaluated a peptide-based probe to monitor αS aggregation, with a particular focus on the earliest stages of the aggregation process and the formation of oligomers. We have identified the peptide-probe K1 as being suitable for further development to be applied to number of applications including: inhibition of αS aggregation; as a probe to monitor αS aggregation, particularly at the earliest stages before Thioflavin-T is active; and a method to detect early-oligomers. With further development and in vivo validation, we anticipate this probe could be used for the early diagnosis of PD, a method to evaluate the effectiveness of potential therapeutics, and as a tool to help in the understanding of the onset and development of PD.

Recent advances in the modulation of amyloid protein aggregation using the supramolecular host-guest approaches

Misfolding of proteins is associated with many incurable diseases in human beings. Understanding the process of aggregation from monomers to fibrils, the characterization of all intermediate species, and the origin of toxicity is very challenging. Extensive research including computational and experimental shed some light on these tricky phenomena. Non-covalent interactions between amyloidogenic domains of proteins play a major role in their self-assembly which can be disrupted by designed chemical tools. This will lead to the development of inhibitors of detrimental amyloid formations. In supramolecular host-guest chemistry approaches, different macrocycles function as hosts for encapsulating hydrophobic guests, i.e. phenylalanine residues of proteins, in their hydrophobic cavities via non-covalent interactions. In this way, they can disrupt the interactions between adjacent amyloidogenic proteins and prevent their self-aggregation. This supramolecular approach has also emerged as a prospective tool to modify the aggregation of several amyloidogenic proteins. In this review, we discussed recent supramolecular host-guest chemistry-based strategies for the inhibition of amyloid protein aggregation.