A latent green fluorescent styrylcoumarin probe for the selective growth and detection of Gram negative bacteria.

A novel, green fluorescent ß-alanylstyrylcoumarin derivative was synthesized and evaluated for its performance as a fluorogenic enzyme substrate on a range of clinically relevant microorganisms. The substrate was selectively hydrolysed by ß-alanyl aminopeptidase producing P. aeruginosa resulting in an on-to-off fluorescent signal. Growth inhibitory effect of the substrate was observed on Gram positive bacteria and yeasts. Meanwhile, Gram negative species, despite their extremely protective cell envelope, showed ready uptake and accumulation of the substrate within their healthy growing colonies displaying intense green fluorescence.

Plasma Proteome Association and Catalytic Activity of Stealth Polymer-Grafted Iron Oxide Nanoparticles.

Polyethylene glycol (PEG) is widely used as an antifouling and stealth polymer in surface engineering and nanomedicine. However, recent research has revealed adverse effects of bioaccumulation and immunogenicity following the administration of PEG, prompting this proteomic examination of the plasma protein coronae association with superparamagnetic iron oxide nanoparticles (IONPs) grafted with brushed PEG (bPEG) and an alternative, brushed phosphorylcholine (bPC). Using label-free quantitation by liquid chromatography tandem-mass spectrometry, this study determines protein abundances for the in vitro hard coronae of bare, bPC-, and bPEG-grafted IONPs in human plasma. This study also shows unique protein compositions in the plasma coronae of each IONP, including enrichment of coagulation factors and immunogenic complement proteins with bPEG, and enhanced binding of apolipoproteins with bPC. Functional analysis reveals that plasma protein coronae elevate the horseradish peroxidase-like activities of the bPC- and bPEG-IONPs by approximately twofold, an effect likely mediated by the diverse composition and physicochemical properties of the polymers as well as their associated plasma proteins. Taken together, these observations support the rational design of stealth polymers based on a quantitative understanding of the interplay between IONPs and the plasma proteome, and should prove beneficial for the development of materials for nanomedicine, biosensing, and catalysis.

Star Polymers Reduce Islet Amyloid Polypeptide Toxicity via Accelerated Amyloid Aggregation.

Protein aggregation into amyloid fibrils is a ubiquitous phenomenon across the spectrum of neurodegenerative disorders and type 2 diabetes. A common strategy against amyloidogenesis is to minimize the populations of toxic oligomers and protofibrils by inhibiting protein aggregation with small molecules or nanoparticles. However, melanin synthesis in nature is realized by accelerated protein fibrillation to circumvent accumulation of toxic intermediates. Accordingly, we designed and demonstrated the use of star-shaped poly(2-hydroxyethyl acrylate) (PHEA) nanostructures for promoting aggregation while ameliorating the toxicity of human islet amyloid polypeptide (IAPP), the peptide involved in glycemic control and the pathology of type 2 diabetes. The binding of PHEA elevated the ß-sheet content in IAPP aggregates while rendering a new morphology of "stelliform" amyloids originating from the polymers. Atomistic molecular dynamics simulations revealed that the PHEA arms served as rodlike scaffolds for IAPP binding and subsequently accelerated IAPP aggregation by increased local peptide concentration. The tertiary structure of the star nanoparticles was found to be essential for driving the specific interactions required to impel the accelerated IAPP aggregation. This study sheds new light on the structure-toxicity relationship of IAPP and points to the potential of exploiting star polymers as a new class of therapeutic agents against amyloidogenesis.

Lysophosphatidylcholine modulates the aggregation of human islet amyloid polypeptide.

Amyloid aggregation of human islet amyloid polypeptide (IAPP) is a hallmark of type 2 diabetes (T2D), a metabolic disease and a global epidemic. Although IAPP is synthesized in pancreatic ß-cells, its fibrils and plaques are found in the extracellular space indicating a causative transmembrane process. Numerous biophysical studies have revealed that cell membranes as well as model lipid vesicles promote the aggregation of amyloid-ß (associated with Alzheimer's), α-synuclein (associated with Parkinson's) and IAPP, through electrostatic and hydrophobic interactions between the proteins/peptides and lipid membranes. Using a thioflavin T kinetic assay, transmission electron microscopy, circular dichroism spectroscopy, discrete molecular dynamics simulations as well as free energy calculations here we show that micellar lysophosphatidylcholine (LPC), the most abundant lysophospholipid in the blood, inhibited the amyloid aggregation of IAPP through nonspecific interactions while elevating the α-helical peptide secondary structure. This surprising finding suggests a native protective mechanism against IAPP aggregation in vivo.

Nanoparticle-proteome in vitro and in vivo.

The protein corona is a concept central to a range of disciplines exploiting the bio-nano interface. As the literature continues to expand in this field, it is essential to condense and contextualize the in vitro and in vivo proteome databases accumulated over the past decade: a goal which this review intends to achieve for the benefit of nanomedicine and nanobiotechnology. The parameters used for our review are the physicochemical characteristics of the nanoparticles, their surface ligands, the biological matrix from which a corona was formed, methods employed, plus the top-ten enriched corona proteins. In addition, the protein coronal networks and their implications in vivo are highlighted for selected studies.

Graphene quantum dots against human IAPP aggregation and toxicity in vivo.

The development of biocompatible nanomaterials has become a new frontier in the detection, treatment and prevention of human amyloid diseases. Here we demonstrated the use of graphene quantum dots (GQDs) as a potent inhibitor against the in vivo aggregation and toxicity of human islet amyloid polypeptide (IAPP), a hallmark of type 2 diabetes. GQDs initiated contact with IAPP through electrostatic and hydrophobic interactions as well as hydrogen bonding, which subsequently drove the peptide fibrillization off-pathway to eliminate the toxic intermediates. Such interactions, probed in vitro by a thioflavin T kinetic assay, fluorescence quenching, circular dichroism spectroscopy, a cell viability assay and in silico by discrete molecular dynamics simulations, translated to a significant recovery of embryonic zebrafish from the damage elicited by IAPP in vivo, as indicated by improved hatching as well as alleviated reactive oxygen species production, abnormality and mortality of the organism. This study points to the potential of using zero-dimensional nanomaterials for in vivo mitigation of a range of amyloidosis.

Human plasma proteome association and cytotoxicity of nano-graphene oxide grafted with stealth polyethylene glycol and poly(2-ethyl-2-oxazoline).

Polyethylene glycol (PEG) is a gold standard against protein fouling. However, recent studies have revealed surprising adverse effects of PEG, namely its immunogenicity and shortened bio-circulation upon repeated dosing. This highlights a crucial need to further examine 'stealth' polymers for controlling the protein 'corona', a new challenge in nanomedicine and bionanotechnology. Poly(2-ethyl-2-oxazoline) (PEtOx) is another primary form of stealth polymer that, despite its excellent hydrophilicity and biocompatibility, has found considerably less applications compared with PEG. Herein, we performed label-free proteomics to compare the associations of linear PEG- and PEtOx-grafted nano-graphene oxide (nGO) sheets with human plasma proteins, complemented by cytotoxicity and haemolysis assays to compare the cellular interactions of these polymers. Our data revealed that nGO-PEG enriched apolipoproteins, while nGO-PEtOx displayed a preferred binding with pro-angiogenic and structural proteins, despite high similarities in their respective top-10 enriched proteins. In addition, nGO-PEG and nGO-PEtOx exhibited similar levels of enrichment of complement proteins. Both PEG and PEtOx markedly reduced nGO toxicity to HEK 293 cells while mitigating nGO haemolysis. This study provides the first detailed profile of the human plasma protein corona associated with PEtOx-grafted nanomaterials and, in light of the distinctions of PEtOx in chemical adaptability, in vivo clearance and immunogenicity, validates the use of PEtOx as a viable stealth alternative to PEG for nanomedicines and bionanotechnologies.

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.

Effects of Protein Corona on IAPP Amyloid Aggregation, Fibril Remodelling, and Cytotoxicity.

Aggregation of islet amyloid polypeptide (IAPP), a peptide hormone co-synthesized and co-stored with insulin in pancreatic cells and also co-secreted to the circulation, is associated with beta-cell death in type-2 diabetes (T2D). In T2D patients IAPP is found aggregating in the extracellular space of the islets of Langerhans. Although the physiological environments of these intra- and extra-cellular compartments and vascular systems significantly differ, the presence of proteins is ubiquitous but the effects of protein binding on IAPP aggregation are largely unknown. Here we examined the binding of freshly-dissolved IAPP as well as pre-formed fibrils with two homologous proteins, namely cationic lysozyme (Lys) and anionic alpha-lactalbumin (aLac), both of which can be found in the circulation. Biophysical characterizations and a cell viability assay revealed distinct effects of Lys and aLac on IAPP amyloid aggregation, fibril remodelling and cytotoxicity, pointing to the role of protein "corona" in conferring the biological impact of amyloidogenic peptides. Systematic molecular dynamics simulations further provided molecular and structural details for the observed differential effects of proteins on IAPP amyloidosis. This study facilitates our understanding of the fate and transformation of IAPP in vivo, which are expected to have consequential bearings on IAPP glycemic control and T2D pathology.

Towards Photo Watercolorization with Artistic Verisimilitude.

We present a novel artistic-verisimilitude driven system for watercolor rendering of images and photos. Our system achieves realistic simulation of a set of important characteristics of watercolor paintings that have not been well implemented before. Specifically, we designed several image filters to achieve: 1) watercolor-specified color transferring; 2) saliency-based level-of-detail drawing; 3) hand tremor effect due to human neural noise; and 4) an artistically controlled wet-in-wet effect in the border regions of different wet pigments. A user study indicates that our method can produce watercolor results of artistic verisimilitude better than previous filter-based or physical-based methods. Furthermore, our algorithm is efficient and can easily be parallelized, making it suitable for interactive image watercolorization.