Targeting Amyloids with Coated Nanoparticles: A Review on Potential Combinations of Nanoparticles and Bio-Compatible Coatings

Amyloidosis is the major cause of many neurodegenerative diseases, such as, Alzheimer's and Parkinson's where the misfolding and deposition of a previously functional protein make it inept for carrying out its function. The genesis of amyloid fibril formation and the strategies to inhibit it have been studied extensively, although some parts of this puzzle still remain unfathomable to date. Many classes of molecules have been explored as potential drugs in vitro, but their inability to work in vivo by crossing the blood-brain-barrier has made them an inadequate treatment option. In this regard, nanoparticles (NPs) have turned out to be an exciting alternative because they could overcome many drawbacks of previously studied molecules and provide advantages, such as, greater bioavailability of molecules and target-specific delivery of drugs. In this paper, we present an overview on several coated NPs which have shown promising efficiency in inhibiting fibril formation. A hundred and thirty papers published in the past two decades have been comprehensively reviewed, which majorly encompass NPs comprising different materials like gold, silver, iron-oxide, poly(lactic-co-glycolic acid), polymeric NP, etc., which are coated with various molecules of predominantly natural origin, such as different types of amino acids, peptides, curcumin, drugs, catechin, etc. We hope that this review will shed light on the advancement of symbiotic amalgamation of NPs with molecules from natural sources and will inspire further research on the tremendous therapeutic potential of these combinations for many amyloid-related diseases.

Differential effects of silver and iron oxide nanoparticles on IAPP amyloid aggregation

Recent studies have shown promise on the use of small molecules and nanoparticles (NPs) for the inhibition of protein aggregation, a hallmark of neurodegenerative diseases and type 2 diabetes (T2D). Towards this end here we show the differential effects of silver and iron oxide nanoparticles (AgNPs and IONPs) on the mesoscopic properties of human islet amyloid polypeptide (IAPP) aggregation associated with T2D. Both citrate- and branched polyethyleneimine-coated AgNPs (c-AgNPs, bPEI-AgNPs) inhibited IAPP aggregation at 500 μg mL^-1, likely through electrostatic attraction and sequestering of IAPP monomers from fibrillation. In comparison, bare, brushed polyethylene glycol- and phosphorylcholine-grafted IONPs (bPEG-IONPs, bPC-IONPs) at 500 μg mL^-1 elicited no major effect on IAPP fibril contour length, while bPC-IONPs induced significant fibril softening and looping likely mediated by dipolar interactions. While monovalent Ag⁺ up to 50 μg mL^-1 showed no effect on the contour length or stiffness of IAPP fibrils, multivalent Fe³⁺ at 5 μg mL^-1 halted IAPP fibrillation likely through ion-peptide crosslinking. Except bPEI-AgNPs, all three types of IONPs and c-AgNPs at 100 μg mL^-1 alleviated IAPP toxicity in HEK293 cells indicating no clear correlation between protein aggregation and their induced cytotoxicity. This study demonstrates the complexity of protein aggregation intervened by NPs of different physicochemical properties and - together with existing literature - facilitates nanotechnological applications for mitigating amyloid-mediated pathologies.

Recent advances in nanomaterials for water protection and monitoring

Nanomaterials (NMs) for adsorption, catalysis, separation, and disinfection are scrutinized. NMs-based sensor technologies and environmental transformations of NMs are highlighted.

Biological and environmental surface interactions of nanomaterials: characterization, modeling, and prediction

The understanding of nano-bio interactions is deemed essential in the design, application, and safe handling of nanomaterials. Proper characterization of the intrinsic physicochemical properties, including their size, surface charge, shape, and functionalization, is needed to consider the fate or impact of nanomaterials in biological and environmental systems. The characterizations of their interactions with surrounding chemical species are often hindered by the complexity of biological or environmental systems, and the drastically different surface physicochemical properties among a large population of nanomaterials. The complexity of these interactions is also due to the diverse ligands of different chemical properties present in most biomacromolecules, and multiple conformations they can assume at different conditions to minimize their conformational free energy. Often these interactions are collectively determined by multiple physical or chemical forces, including electrostatic forces, hydrogen bonding, and hydrophobic forces, and calls for multidimensional characterization strategies, both experimentally and computationally. Through these characterizations, the understanding of the roles surface physicochemical properties of nanomaterials and their surface interactions with biomacromolecules can play in their applications in biomedical and environmental fields can be obtained. To quantitatively decipher these physicochemical surface interactions, computational methods, including physical, statistical, and pharmacokinetic models, can be used for either analyses of large amounts of experimental characterization data, or theoretical prediction of the interactions, and consequent biological behavior in the body after administration. These computational methods include molecular dynamics simulation, structure-activity relationship models such as biological surface adsorption index, and physiologically-based pharmacokinetic models. WIREs Nanomed Nanobiotechnol 2017, 9:e1440. doi: 10.1002/wnan.1440 For further resources related to this article, please visit the WIREs website.

Effect of dendrimeric composition on the removal of pyrene from water

Several closely related branched structures related to the well-established benzyl ether dendrimers were tested as hosts for the removal of pyrene from water. Fluorescence spectroscopy based complexation studies showed that the first generation benzyl ether dendrimers removed on average 94 % of pyrene from a saturated aqueous solution after 30 min. By contrast, branched systems containing modified benzyl ether or cyclohexane functional groups removed between 0 and 75 % of pyrene at the same time point while systems with benzyl amine resulted in a 77 % decrease in pyrene. This selectivity eroded over two days after which time all dendrimeric types removed pyrene to approximately the same extent. Inclusion constants of 10⁹–10¹¹ M⁻¹ were calculated for the branched systems studied.

PAMAM dendrimers and graphene: materials for removing aromatic contaminants from water

We present results from experiments and atomistic molecular dynamics simulations on the remediation of naphthalene by polyamidoamine (PAMAM) dendrimers and graphene oxide (GrO). Specifically, we investigate 3rd-6th generation (G3-G6) PAMAM dendrimers and GrO with different levels of oxidation. The work is motivated by the potential applications of these emerging nanomaterials in removing polycyclic aromatic hydrocarbon contaminants from water. Our experimental results indicate that GrO outperforms dendrimers in removing naphthalene from water. Molecular dynamics simulations suggest that the prominent factors driving naphthalene association to these seemingly disparate materials are similar. Interestingly, we find that cooperative interactions between the naphthalene molecules play a significant role in enhancing their association to the dendrimers and GrO. Our findings highlight that while selection of appropriate materials is important, the interactions between the contaminants themselves can also be important in governing the effectiveness of a given material. The combined use of experiments and molecular dynamics simulations allows us to comment on the possible factors resulting in better performance of GrO in removing polyaromatic contaminants from water.

Structure-function relationship of PAMAM dendrimers as robust oil dispersants

PAMAM dendrimers have recently been investigated as efficient and biocompatible oil dispersants utilizing their encapsulation capacity; however, their high cationic charge density has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity and understand the effects of such changes. Presented here is a synergistic experimental and computational approach to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. Uncharged dendrimers collapse by forming intramolecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pKa of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, ∼30%. This unexpected change in the interior protonation state causes electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. The present work highlights the robust nature of dendrimer oil dispersion and also illuminates potentially unintended or unanticipated effects of varying dendrimer surface chemistry on their encapsulation or hosting efficacy, which is important for their environmental, industrial, and biomedical applications.