Bifunctional carbon dots for cell imaging and inhibition of human insulin fibrillation in the whole aggregation process

The influence of near-infrared carbon dots on the conformational variation and enzymatic activity of glucose oxidase: A multi-spectroscopic and biochemical study with molecular docking

In recent years, the exceptional biocatalytic properties of glucose oxidase (GOx) have spurred the development of various GOx-functionalized nanocatalysts for cancer diagnosis and treatment. Carbon dots, renowned for their excellent biocompatibility and distinctive fluorescence properties, effectively incorporate GOx. Given the paramount importance of GOx's enzymatic activity in therapeutic efficacy, this study conducts a thorough exploration of the molecular-level binding dynamics between GOx and near-infrared carbon dots (NIR-CDs). Utilizing various spectrometric and molecular simulation techniques, we reveal that NIR-CDs form a ground-state complex with GOx primarily via hydrogen bonds and van der Waals forces, interacting directly with amino acid residues in GOx's active site. This binding leads to conformational change and reduces thermal stability of GOx, slightly inhibiting its enzymatic activity and demonstrating a competitive inhibition effect. In vitro experiments demonstrate that NIR-CDs attenuate the GOx's capacity to produce H2O2 in HeLa cells, mitigating enzyme-induced cytotoxicity and cellular damage. This comprehensive elucidation of the intricate binding mechanisms between NIR-CDs and GOx provides critical insights for the design of NIR-CD-based nanotherapeutic platforms to augment cancer therapy. Such advancements lay the groundwork for innovative and efficacious cancer treatment strategies.

Low temperature synthesis of chiral carbon dots for reducing H2O2 damage

Recently, researches focused towards the chiral nanostructures have attracted vast attention. However, the synthesis of chiral carbon dots (CDs) through one-step method is still rather scarce. Herein, a universal approach to green synthesis of chiral CDs at low temperature was proposed. In brief, L-FruCDs and D-FruCDs were obtained by only heating the fructose and chiral cysteine molecules in the sodium hydroxide aqueous solution under atmospheric pressure. Circular dichroism spectra show that these prepared CDs exhibit opposite chirality ranging from 210 to 260 nm. Specially, the prepared L-FruCDs could reduce the intracellular oxidative damage induced by hydrogen peroxide and display a superior performance than that of D-FruCDs. Mechanism studies indicate that the probably protect mechanism is ascribed to the directly consumption the intracellular ROS. And the clearance efficiency of intracellular reactive oxygen species of L-FruCDs is 3-times than that of D-FruCDs. Furthermore, this newly synthesized method is scalable by replacing fructose precursor with ascorbic acid, sucrose or lactose. In sum, our work provides a new method for the preparation of chiral CDs and achieve a great success in exploring the chiral biological effects at nanoscale.

Carboxylic Group Functionalized Carbon Quantum Dots inhibit Hen Egg White Lysozyme Amyloidogenesis, leading to the Formation of Spherical Aggregates with Reduced Toxicity and ROS Generation

INTRODUCTION

Proteinopathies are a group of diseases where the protein structure has been altered. These alterations are linked to the production of amyloids, which are persistent, organized clumps of protein molecules through inter-molecular interactions. Several disorders, including Alzheimer's and Parkinson's, have been related to the presence of amyloids. Highly ordered beta sheets or beta folds are characteristic of amyloids; these structures can further self- assemble into stable fibrils.

METHODS

Protein aggregation is caused by a wide variety of environmental and experimental factors, including mutations, high pH, high temperature, and chemical modification. Despite several efforts, a cure for amyloidosis has yet to be found. Due to its advantageous semi-conducting characteristics, unique optical features, high surface area-to-volume ratio, biocompatibility, etc., carbon quantum dots (CQDs) have lately emerged as key instruments for a wide range of biomedical applications. To this end, we have investigated the effect of CQDs with a carboxyl group on their surface (CQD-CA) on the in vitro amyloidogenesis of hen egg white lysozyme (HEWL).

RESULTS

By generating a stable compound that is resistant to fibrillation, our findings show that CQD-CA can suppress amyloid and disaggregate HEWL. In addition, CQD-CA caused the creation of non-toxic spherical aggregates, which generated much less reactive oxygen species (ROS).

CONCLUSION

Overall, our results show that more research into amyloidosis treatments, including surface functionalized CQDs, is warranted.

Amine Group Surface-Functionalized Carbon Quantum Dots Exhibit Anti-amyloidogenic Effects Towards Hen Egg White Lysozyme by Inducing Formation of Nontoxic Spherical Aggregates

The tendency of polypeptide chains to deviate from their conventional protein folding pathway and instead get trapped as off-pathway intermediates, has been a matter of great concern. These off-pathway intermediates eventually lead to the formation of insoluble, ordered fibrillar aggregates called amyloids, which are responsible for a host of neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Type II diabetes. In spite of extensive research, development of an effective therapeutic strategy against amyloidosis still remains elusive. In recent times, carbon quantum dots (CQD) have grabbed the attention of researchers against amyloidogenesis due to their ease of preparation, aqueous soluble nature, unique optical properties, high surface to volume ratio, physio-chemical properties, semi-conducting nature and mainly biocompatible. In the current study, we have reported an easy-to-prepare procedure for synthesis of amine group surface functionalized CQDs from commonly available kitchen spices with anti-oxidant properties. The as-synthesized CQDs were evaluated for their anti-amyloidogenic properties towards Hen Egg White Lysozyme (HEWL). Our results clearly show that the surfaced functionalized CQDs were able to interact with HEWL, thereby forming a stable complex, which was resistant towards amyloid formation and instead lead to the formation of non-toxic globular aggregates.

Inhibition mechanism of human insulin fibrillation by Bodipy carbon polymer dots and photothermal defibrillation effect of Bodipy carbon polymer dots modified by ThT

Fibrillation process of human insulin (HI) is closely related to type 2 diabetes (T2D). In the present work, Carbon Polymer Dots (CPDs) was synthesized by Bodipy to control the process of insulin fibrillation. The inhibition process of insulin fibrillation with the existence of CPDs was completed investigated. The hydrophobic interaction of CPDs and insulin was used to inhibit the change of insulin's secondary structure in the lag phase and growth period. ThT fluorescence analysis and transmission electron microscopy (TEM) characterization of the CPDs were used to explore the kinetics of insulin fibrillation and regulation process by CPDs. Isothermal titration calorimetry (ITC) was applied to explore the regulatory mechanism by CPDs at all stages of the insulin fibrillation process. ThT was used to complete the chemical modification of CPDs by Friedel-Crafts alkylation, which made the CPDs maintain the characteristics of photothermal effect and also obtain the ability to bind specifically to the fibers. Finally, the process of defibrillation of human insulin fibers under the Near-infrared light's irradiation was realized. In this work, we clarified the mechanism of the regulation process by Bodipy CPDs and made CPDs able to defibrillate the insulin fibers by chemical modification.

Peptide Inhibitors of Insulin Fibrillation: Current and Future Challenges

Amyloidoses include a large variety of local and systemic diseases that share the common feature of protein unfolding or refolding into amyloid fibrils. The most studied amyloids are those directly involved in neurodegenerative diseases, while others, such as those formed by insulin, are surprisingly far less studied. Insulin is a very important polypeptide that plays a variety of biological roles and, first and foremost, is at the basis of the therapy of diabetic patients. It is well-known that it can form fibrils at the site of injection, leading to inflammation and immune response, in addition to other side effects. In this concise review, we analyze the current knowledge on insulin fibrillation, with a focus on the development of peptide-based inhibitors, which are promising candidates for their biocompatibility but still pose challenges to their effective use in therapy.

Facile Synthesis of Green Fluorescent Carbon Dots and Their Application to Fe3+ Detection in Aqueous Solutions

Carbon dots (CDs), a class of fluorescent nanomaterials, have attracted widespread attention from researchers. Because of their unique chemical properties, these high-quality fluorescent probes are widely used for ion and molecule detection. Excess intake of many ions or molecules can cause harm to the human body. Although iron (in the form of Fe3+ ions) is essential for the human body, excess iron in the human body can cause many diseases, such as iron poisoning. In this study, we have synthesized fluorine and nitrogen co-doped carbon dots (FNCDs) by a hydrothermal method. These FNCDs exhibited good stability, selectivity, and anti-interference ability for Fe3+. Fe3+ could be detected in the range of 0.2-300 μM, and their detection limit is up to 0.08 μM. In addition, the recovery and relative standard deviation measured by the standard addition recovery method were not higher than 107.5% and 1.1%, respectively, indicating that FNCDs have good recovery and accuracy for Fe3+ detection.

Inhibiting protein aggregation with nanomaterials: The underlying mechanisms and impact factors

Protein aggregation is correlated with the onset and progression of protein misfolding diseases (PMDs). Inhibiting the generation of toxic aggregates of misfolded proteins has been proposed as a therapeutic approach for PMDs. Due to their unique properties, nanomaterials have been extensively investigated for their ability to inhibit protein aggregation and have shown great potential in the diagnosis and treatment of PMDs. However, the precise mechanisms by which nanomaterials interact with amyloidogenic proteins and the factors influencing these interactions remain poorly understood. Consequently, developing a rational design strategy for nanomaterials that target specific proteins in PMDs has been challenging. In this review, we elucidate the effects of nanomaterials on protein aggregation and describe the mechanisms through which nanomaterials interfere with protein aggregation. The major factors impacting protein-nanomaterial interaction such as size, charge, concentration, surface modification and morphology that can be rationally addressed to achieve the desired effects of nanomaterials on protein aggregation are summarized. The prospects and challenges to the clinical application of nanomaterials for the treatment of PMDs are also discussed.

Nitrogen and sulfur co-doped carbon dots with bright fluorescence for intracellular detection of iron ion and thiol

Carbon dots (CDs) have been widely used in recent years because of their excellent water solubility and abundant surface functional groups. However, compared with quantum dots or biological probes, the quantum yield of CDs is lower, and the fluorescence mainly concentrated in the blue-green range, which significantly limits the biological applications of CDs. Heteroatoms doping is the most common method to improve the luminescence of CDs. In this work, nitrogen and sulfur co-doped luminescent CDs were successfully synthesized by microwave assisted method using glutathione (GSH) and p-phenylenediamine (PPD) as raw materials. It can emit bright green fluorescence in ethanol solution, and the maximum emission wavelength is 535 nm when excited at 374 nm, and the absolute quantum yield is as high as 63%. Iron ion (Fe³⁺) can interact with the functional groups on the surface of the CDs to form CDs/Fe³⁺, which is a non-fluorescence complex, and Fe³⁺ can be reduced to ferrous ion (Fe²⁺). In other words, the reaction mechanism of CDs and Fe³⁺ is a combination of dynamic quenching and static quenching. The fluorescence of CDs quenched by Fe³⁺ can be restored by thiol, because there is a stronger binding force between sulfhydryl (-SH) on the surface of thiol and Fe³⁺, which enables CDs to be released. In addition, the CDs has good biocompatibility and stability, indicating that it has excellent potential in bioimaging. This discovery will expand the application of CDs in the fields of biosensing and imaging.

Dopamine-Conjugated Carbon Dots Inhibit Human Calcitonin Fibrillation

The development of biocompatible nanomaterials has become a new trend in the treatment and prevention of human amyloidosis. Human calcitonin (hCT), a hormone peptide secreted from parafollicular cells, plays a major role in calcium–phosphorus metabolism. Moreover, it can be used in the treatment of osteoporosis and Paget’s disease. Unfortunately, it tends to form amyloid fibrils irreversibly in an aqueous solution, resulting in a reduction of its bioavailability and therapeutic activity. Salmon calcitonin is the replacement of hCT as a widely therapeutic agent due to its lower propensity in aggregation and better bioactivity. Herein, we used citric acid to synthesize carbon dots (CDs) and modified their surface properties by a variety of chemical conjugations to provide different functionalized CDs. It was found that dopamine-conjugated CDs can effectively inhibit hCT aggregation especially in the fibril growth phase and dissociate preformed hCT amyloids. Although the decomposition mechanism of dopamine-conjugated CDs is not clear, it seems to be specific to hCT amyloids. In addition, we also tested dopamine-conjugated mesoporous silica nanoparticles in preventing hCT fibrillization. They also can work as inhibitors but are much less effective than CDs. Our studies emphasized the importance of the size and surface functionalization of core materials in the development of nanomaterials as emerging treatments for amyloidosis. On the other hand, proper functionalized CDs would be useful in hCT formulation.

Inhibition of Insulin Amyloid Fibrillation by Salvianolic Acids and Calix[n]arenes: Molecular Docking Insight

In this study, the ability of salvianolic acids A, B, C, F, G and calix[[Formula: see text]]arenes ([Formula: see text], 5, 6 and 8) with different upper rims in the inhibition of insulin amyloid fibril formation was studied using molecular docking. The results were analyzed from a molecular point of view. All of the considering ligands interacted with significant residues of insulin, which had a crucial role in the process of insulin fibrillation. The interactions among the ligands and insulin residues could be done through hydrogen bonding and hydrophobic interactions with good binding affinity. So, these ligands could prevent the formation of the insulin fibril. The good consistency of the docking results of [Formula: see text]-sulfonatocalix[4]arene and [Formula: see text]-sulfonatocalix[6]arene with the experimental results in the previous literature represented the capacity of the current theoretical method to supplement and interpret experimental findings. Also, in this study, salvianolic acids A, C, F and G were suggested as new inhibitors of the insulin amyloid fibril.

Zn-doped Cu2S quantum dots as new high-efficiency inhibitors against human insulin fibrillation based on specific electrostatic interaction with oligomers

Inhibition of protein fibrillation process with nanomaterials is a promising strategy to combat neurodegenerative diseases. Copper-based nanomaterials have been seldom utilized in fibrillation inhibiting research due to Copper ions are generally considered as accelerators of fibrosis. Here, we proposed ultra-small Zn doped Cu₂S (Zn:Cu₂S) QDs as inhibitors of human insulin (HI) fibrosis. ThT, DLS, CD and TEM confirm that Zn:Cu₂S QDs effectively inhibited insulin fibrosis in a dose-dependent manner with lag phase time extended (beyond 13-time by Zn:Cu₂S QDs of 1 mg·mL^-1), final fibril formation and the conversion from α-helix to β-sheet reduced. Additionally, thermodynamics analyzed results reveal that the HI fluorescence quenching process is static quenching dominated, and the Zn:Cu₂S QDs inhibit HI fibrosis mainly through specific electrostatic interaction with oligomers. The positively charged amino acid residues of oligomers bind to the negatively charged Zn:Cu₂S QDs, which prevents the self-assembly of the oligomers from growing into mature fibers to enhance the stability of the protein. Unlike free Copper ions, the as-prepared QDs show an excellent inhibition in HI fibrillation, breaking through the bottleneck of copper-based materials in inhibiting protein fibrosis and providing a potential strategy to inhibit protein fibrosis in-situ by biosynthesizing copper-based fibrosis inhibitors.

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.

Insulin fibrillation: toward strategies for attenuating the process

The environmental factors affecting the rate of insulin fibrillation. The factors are representative.