The Investigation on Resorcinarenes towards either Inhibiting or Promoting Insulin Fibrillation

Inhibition of insulin fibrillation by carboxyphenylboronic acid-modified chitosan oligosaccharide based on electrostatic interactions and hydrophobic interactions

A novel inhibitor, carboxyphenylboronic acid-modified chitosan oligosaccharide (COS-CPBA), was developed by coupling carboxyphenylboronic acid (CPBA) with chitosan oligosaccharide (COS) to inhibit insulin fibrillation. Extensive biophysical assays indicated that COS-CPBA could decelerate insulin aggregation, hinder the conformational transition from α-helix to β-sheet structure, change the morphology of insulin aggregates and alter fibrillation pathway. A mechanism for the inhibition of insulin fibrillation by COS-CPBA was proposed. It considers that insulin molecules bind to COS-CPBA via hydrophobic interactions, while the positively charged groups in COS-CPBA exert electrostatic repulsion on the bound insulin molecules. These two opposite forces cause the insulin molecules to display extended conformations and hinder the conformational transition of insulin from α-helix to β-sheet structure necessary for fibrillation, thus decelerating aggregation and altering the fibrillation pathway of insulin. The studies provide novel ideas for the development of more effective inhibitors of amyloid fibrillation.

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.

Amyloid Fibrillation of Insulin: Amelioration Strategies and Implications for Translation

Insulin is a therapeutically relevant molecule with use in treating diabetes patients. Unfortunately, it undergoes a range of untoward and often unpredictable physical transformations due to alterations in its biochemical environment, including pH, ionic strength, temperature, agitation, and exposure to hydrophobic surfaces. The transformations are prevalent in its physiologically active monomeric form, while the zinc cation-coordinated hexamer, although physiologically inactive, is stable and less susceptible to fibrillation. The resultant molecular reconfiguration, including unfolding, misfolding, and hydrophobic interactions, often results in agglomeration, amyloid fibrillogenesis, and precipitation. As a result, a part of the dose is lost, causing a compromised therapeutic efficacy. Besides, the amyloid fibrils form insoluble deposits, trigger immunologic reactions, and harbor cytotoxic potential. The physical transformations also hold back a successful translation of non-parenteral insulin formulations, in addition to challenges related to encapsulation, chemical modification, purification, storage, and dosing. This review revisits the mechanisms and challenges that drive such physical transformations in insulin, with an emphasis on the observed amyloid fibrillation, and presents a critique of the current amelioration strategies before prioritizing some future research objectives.

A Review of the Application of Resorcinarenes and SBA-15 in Drug Delivery

Due to the diseases that people face today, scientists dedicate a part of their research to the synthesis, characterization, and study of functional compounds for controlled drug delivery. On the one hand, resorcinarenes are macrocycles obtained by condensation reactions of resorcinol and aldehyde. They include an upper and a lower rim functioning with different groups that confer solubility to the macrocycle and favor interactions with other compounds, therefore the hydroxyl groups on the upper rim improve the formation of hydrogen bonds. Additionally, resorcinarenes feature a cavity studied for forming host-guest complexes. SBA-15, on the other hand, is a mesoporous silica characterized by ordered pores in its structure and a large surface area. As a result of its properties, it has been used for several purposes, including absorbents, drug delivery, catalysis, and environmental processes. This review shows the recent advances in synthesis methods, characterization, micelle formation, interaction with other compounds, and host-guest procedures, as well as techniques for evaluating toxicity, drug retention, and their preliminary uses in pharmacology for macrocycles, such as resorcin[4]arenes and SBA-15.

Strategies for interference of insulin fibrillogenesis: challenges and advances

The discovery of insulin came up with very high hopes for diabetic patients. In the year 2021, the world celebrated the 100 th anniversary of the discovery of this vital hormone. However, external use of insulin is highly affected by its aggregating tendency that occurs during its manufacturing, transportation, and improper handling which ultimately leads its pharmaceutically and biologically ineffective form. In this review, we aim to discuss the various approaches used for decelerating insulin aggregation which results in the enhancement of its overall structural stability and usage. The approaches that are discussed are broadly classified as either a measure through excipient additions or by intrinsic modifications in the insulin native structure.

Ionic effects on supramolecular hosts: solvation and counter-ion binding in polar media

For the progress of synthetic supramolecular chemistry in aqueous solution the design of host molecules soluble in this medium is essential. A possible route is the introduction of ionic residues, with the additional advantage that also electrostatic interactions can be used to form supramolecular architectures. In this work we study the effect of different ionic substituents on a resorcin[4]arene host on solvation and counterion binding in water and dimethyl sulfoxide (DMSO). To do so, we combine dielectric relaxation spectroscopy (DRS) at 298.15 K and dilute-solution conductivity measurements covering 278.15-308.15 K. The results indicate that studied substituents lead to a comparable increase in solubility in both water and the dipolar-aprotic DMSO. However, solvation and counterion binding not only depend on the nature of the ionic substituent but also on the solvent. Although intrinsically hydrophobic in nature, resorcin[4]arenes with ionic substituents also show strong hydrophilic hydration in water, with the extent depending on the nature of the ionic group. In contrast to that, solvophobicity apparently dominates the interactions of DMSO with the solute. Counterion binding was found for both solvents and is essentially determined by solvent polarity. It appears that, compared to neat DMSO, the solubility of the cationic resorcin[4]arene with dimethylamine substituents is strongly increased in water-DMSO mixtures due to the formation of hydrogen bonds between two DMSO molecules and one water molecule.

Recognition and Removal of Amyloid-β by a Heteromultivalent Macrocyclic Coassembly: A Potential Strategy for the Treatment of Alzheimer's Disease

The imbalance of amyloid-β (Aβ) production and clearance causes aggregation of Aβ1-42 monomers to form fibrils and amyloid plaques, which is an indispensable process in the pathogenesis of Alzheimer's disease (AD), and eventually leads to pathological changes and cognitive impairment. Consequently, Aβ1-42 is the most important target for the treatment of AD. However, developing a single treatment method that can recognize Aβ1-42 , inhibit Aβ1-42 fibrillation, eliminate amyloid plaques, improve cognitive impairments, and alleviate AD-like pathology is challenging. Here, a coassembly composed of cyclodextrin (CD) and calixarene (CA) is designed, and it is used as an anti-Aβ therapy agent. The CD-CA coassembly is based on the previously reported heteromultivalent recognition strategy and is able to successfully eliminate amyloid plaques and degrade Aβ1-42 monomers in 5xFAD mice. More importantly, the coassembly improves recognition and spatial cognition deficits, and synaptic plasticity impairment in the 5xFAD mice. In addition, the coassembly ameliorates AD-like pathology including prevention of neuronal apoptosis and oxidant stress, and alteration of M1/M2 microglial polarization states. This supramolecular approach makes full use of both molecular recognition and self-assembly of macrocyclic amphiphiles, and is a promising novel strategy for AD treatment.

Insulin fibrillation: toward strategies for attenuating the process

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

Enthalpies of Solution of C-Alkylresorcin[4]arenes in Water and Acetonitrile: Hydrophilic and Hydrophobic Effects

Enthalpies of solution, Δ_sln H, of six C-alkylresorcin[4]arene ( C-ARA) solids, with alkyl substituents varying systematically from methyl (Me) to hexyl (Hx), have been measured in water, using solubility data, and in acetonitrile, by direct calorimetry. For all of the C-ARAs studied, the values of Δ_sln H were highly favorable (exothermic) for dissolution into water but were strongly unfavorable (endothermic) for dissolution into acetonitrile (ACN). The differences between the two solvents varied systematically with increasing carbon chain length, from about 100 kJ·mol^-1 (for Me) to 140 kJ·mol^-1 (for Hx). These extraordinary variances can be attributed to the loss of hydrophilic hydration of the eight -OH groups on the rim of the C-ARAs and also by the loss of (enthalpically favorable) hydrophobic hydration of the alkyl chains upon transfer from the highly structured, strongly H-bonding water to the aprotic, relatively weak donor/acceptor ACN. Although Δ_sln H values for the present C-ARAs in H₂O are strongly favorable, they are more than counteracted by even larger negative changes in the entropy of dissolution, Δ_sln S. This enthalpy/entropy compensation effect is consistent with the low aqueous solubilities (<10^-3 mol·kg^-1) of the C-ARAs and their slight increase with increasing carbon chain length, which is opposite to typical behavior of the homologous series of organic molecules.

Toward a Rational Design to Regulate β-Amyloid Fibrillation for Alzheimer's Disease Treatment

The last decades have witnessed a growing global burden of Alzheimer's disease (AD). Evidence indicates that the onset and progression of AD is associated with β-amyloid (Aβ) peptide fibrillation. As such, there is a strong passion with discovering potent Aβ fibrillation inhibitors that can be developed into anti-amyloiddogenic agents for AD treatment. Current challenges that have arisen with this development involve with Aβ oligomer toxicity suppression and Blood Brain Barrier penetration capability. Considering most natural or biological events, one would observe that there is usually a "seed" to direct natural materials to assemble in response to a certain stimulation. Inspired by this, several materials or compounds, including nanoparticle, peptide or peptide mimics, and organic molecules, have been designed for the purpose of redirecting or impeding Aβ aggregation. Achieving these tasks requires comprehensive understanding on (1) initial Aβ assembly into insoluble deposits, (2) main concerns with fibrillation inhibition, and (3) current major methodologies to disrupt the aggregation. Herein, the objective of this review is to address these three areas, and enable the pathway for a promising therapeutic agent design for AD treatment.