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The hexapeptide hIAPP22–27 (NFGAIL) is known as a crucial amyloid core sequence of the human islet amyloid polypeptide (hIAPP) whose aggregates can be used to better understand the wild‐type hIAPP′s toxicity to β‐cell death. In amyloid research, the role of hydrophobic and aromatic‐aromatic interactions as potential driving forces during the aggregation process is controversially discussed not only in case of NFGAIL, but also for amyloidogenic peptides in general. We have used halogenation of the aromatic residue as a strategy to modulate hydrophobic and aromatic‐aromatic interactions and prepared a library of NFGAIL variants containing fluorinated and iodinated phenylalanine analogues. We used thioflavin T staining, transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS) to study the impact of side‐chain halogenation on NFGAIL amyloid formation kinetics. Our data revealed a synergy between aggregation behavior and hydrophobicity of the phenylalanine residue. This study introduces systematic fluorination as a toolbox to further investigate the nature of the amyloid self‐assembly process.
Aluminum (Al) can be taken up from food, packaging, or the environment and thus reaches the human gastrointestinal tract. Its toxic potential after oral uptake is still discussed. The fate of different solid and ionic Al species during the passage through the digestive tract is the focus of this research, as well as the cellular effects caused by these different Al species. The present study combines the physicochemical processing of three recently studied Al species (metallic Al0, mineral Al2O3, and soluble AlCl3) in artificial digestion fluids with in vitro cell systems for the human intestinal barrier. Inductively coupled plasma mass spectrometry (ICP-MS) and small-angle X-ray scattering (SAXS) methods were used to characterize the Al species in the artificial digestion fluids and in cell culture medium for proliferating and differentiated intestinal Caco-2 cells. Cytotoxicity testing and cellular impedance measurements were applied to address the effects of digested Al species on cell viability and cell proliferation. Microarray-based transcriptome analyses and quantitative real-time PCR were conducted to obtain a deeper insight into cellular mechanisms of action and generated indications for cellular oxidative stress and an influence on xenobiotic metabolism, connected with alterations in associated signaling pathways. These cellular responses, which were predominantly caused by formerly ionic Al species and only at very high concentrations, were not impacted by artificial digestion. A two-directional conversion of Al between ionic species and solid particles occurred throughout all segments of the gastrointestinal tract, as evidenced by the presence of nanoscaled particles. Nevertheless, this presence did not increase the toxicity of the respective Al species.
We report on etching of polyacrylic acid-stabilised silver nanoparticles in the presence of glutathione (GSH). The initial particles with a radius of 3.2 nm and consisting of ∼8100 silver atoms dissolve in a two-step reaction mechanism while in parallel smaller silver particles with a radius of 0.65 nm and consisting of 60 to 70 silver atoms were formed. The kinetics of the etching of the initial particles, accompanied by formation of smaller silver particles was interpreted based on in situ, time-resolved small-angle X-ray scattering (SAXS) experiments.
Fate of fluorescence labels - Their adsorption and desorption kinetics to silver nanoparticles
(2018)
Silver nanoparticles are among the most widely used and produced nanoparticles. Because of their frequent application in consumer products, the assessment of their toxicological potential has seen a renewed importance. A Major difficulty is the traceability of nanoparticles in in vitro and in vivo experiments. Even if the particles are labeled, for example, by a fluorescent marker, the dynamic exchange of ligands often prohibits their spatial localization. Our study provides an insight into the adsorption and desorption kinetics of two different fluorescent labels on silver nanoparticles with a core radius of 3 nm by dynamic light scattering, small-angle X-ray scattering, and fluorescence spectroscopy. We used BSA-FITC and tyrosine as examples for common fluorescent ligands. It is shown that the adsorption of BSA-FITC takes at least 3 days, whereas tyrosine adsorbs immediately. The quantitative amount of stabilizer on the particle surface was determined by fluorescence spectroscopy and revealed that the particles are stabilized by a monolayer of BSA-FITC (corresponding to 20 ± 9 molecules), whereas tyrosine forms a multilayered structure consisting of 15900 ± 200 molecules. Desorption experiments show that the BSA-FITC-stabilized particles are ideally suited for application in in vitro and in vivo experiments because the ligand desorption takes several days. Depending on the BSA concentration in the particles surroundings, the rate constant is k = 0.2 per day or lower when applying first order kinetics, that is, 50% of the BSAFITC molecules are released from the particle’s surface within 3.4 days. For illustration, we provide a first application of the fluorescence-labeled particles in an uptake study with two different commonly used cell lines, the human liver cell model HepG2 and the human intestinal cell model of differentiated Caco-2 cells.
The application of appropriate analytical techniques is essential for nanomaterial (NM) characterization. In this study, we compared different analytical techniques for NM analysis. Regarding possible adverse health effects, ionic and particulate NM effects have to be taken into account. As NMs behave quite differently in physiological media, special attention was paid to techniques which are able to determine the biosolubility and complexation behavior of NMs. Representative NMs of similar size were selected: aluminum (Al0) and aluminum oxide (Al2O3), to compare the behavior of metal and metal oxides. In addition, titanium dioxide (TiO2) was investigated. Characterization techniques such as dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) were evaluated with respect to their suitability for fast characterization of nanoparticle dispersions regarding a particle's hydrodynamic diameter and size distribution. By application of inductively coupled plasma mass spectrometry in the single particle mode (SP-ICP-MS), individual nanoparticles were quantified and characterized regarding their size. SP-ICP-MS measurements were correlated with the information gained using other characterization techniques, i.e. transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The particle surface as an important descriptor of NMs was analyzed by X-ray diffraction (XRD). NM impurities and their co-localization with biomolecules were determined by ion beam microscopy (IBM) and confocal Raman microscopy (CRM). We conclude advantages and disadvantages of the different techniques applied and suggest options for their complementation. Thus, this paper may serve as a practical guide to particle characterization techniques.
An artificial digestion of silver nitrate is reported. It is shown that AgSCN nanoparticles emerge from ionic silver in saliva and remain present during the entire digestion process. The particles were characterized by infrared spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) regarding their composition and size distribution.
Reaction procedures have been improved to achieve higher yields and shorter reaction times: one possibility is the usage of microwave reactors. In the literature, this is under discussion, for example, nonthermal effects resulting from the microwave radiation are claimed. Especially for the synthesis of nanomaterials, it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare the syntheses of ultra-small silver nanoparticles via conventional and microwave heating. We employed a versatile one-pot polyol synthesis of poly(acrylic acid)-stabilized silver nanoparticles, which display superior catalytic properties. No microwave-specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering and dynamic light scattering, are revealed. Because of the characteristics of a closed system, microwave reactors give access to elevated temperatures and pressures. Therefore, the speed of particle formation can be increased by a factor of 30 when the reaction temperature is increased from 200 to 250 °C. The particle growth process follows a cluster coalescence mechanism. A postsynthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particle size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A compromise between short reaction times and high yields can be found at a temperature of 250 °C and a corresponding reaction time of 30 s.
Aluminum has gathered toxicological Attention based on relevant human exposure and its suspected hazardous potential. Nanoparticles from food supplements or Food contact materials may reach the human gastrointestinal tract.
Here, we monitored the physicochemical fate of aluminum containing nanoparticles and aluminum ions when passaging an in vitro model of the human gastrointestinal tract. Smallangle X-ray scattering (SAXS), transmission electron microscopy (TEM), ion beam microscopy (IBM), secondary ion beam mass spectrometry (TOF-SIMS), and inductively coupled plasma mass spectrometry (ICP-MS) in the singleparticle mode were employed to characterize two aluminumcontaining nanomaterials with different particle core materials (Al0, γAl2O3) and soluble AlCl3. Particle size and shape remained unchanged in saliva, whereas strong Agglomeration of both aluminum nanoparticle species was observed at low pH in gastric fluid together with an increased ion release. The levels of free aluminum ions decreased in intestinal fluid and the particles deagglomerated, thus liberating primary particles again. Dissolution of nanoparticles was limited and substantial changes of their shape and size were not detected. The amounts of particle-associated phosphorus, chlorine, potassium, and calcium increased in intestinal fluid, as compared to nanoparticles in standard dispersion.
Interestingly, nanoparticles were found in the intestinal fluid after addition of ionic aluminum. We provide a comprehensive characterization of the fate of aluminum nanoparticles in simulated gastrointestinal fluids, demonstrating that orally ingested nanoparticles probably reach the intestinal epithelium. The balance between dissolution and de novo complex formation should be considered when evaluating nanotoxicological experiments.
This paper presents the first worldwide inter-laboratory comparison of small-angle X-ray scattering (SAXS) for nanoparticle sizing. The measurands in this comparison are the mean particle radius, the width of the size distribution and the particle concentration. The investigated sample consists of dispersed silver nanoparticles, surrounded by a stabilizing polymeric shell of poly(acrylic acid). The silver cores dominate the X-ray scattering pattern, leading to the determination of their radius size distribution using (i) the generalized indirect Fourier transformation method, (ii) classical model fitting using SASfit and (iii) a Monte Carlo fitting approach using McSAS. The application of these three methods to the collected data sets from the various laboratories produces consistent mean number- and volume-weighted core radii of Rn = 2.76 (6) nm and Rv = 3.20 (4) nm, respectively. The corresponding widths of the lognormal radius distribution of the particles were σn = 0.65 (1) nm and σv = 0.71 (1) nm. The particle concentration determined using this method was 3.0 (4) g l−1 or 4.2 (7) × 10−6 mol l−1. These results are affected slightly by the choice of data evaluation procedure, but not by the instruments: the participating laboratories at synchrotron SAXS beamlines, commercial and in-house-designed instruments were all able to provide highly consistent data. This demonstrates that SAXS is a suitable method for revealing particle size distributions in the sub-20 nm region (at minimum), out of reach for most other analytical methods.
Size and shape are crucial parameters which have impact on the potential of nanoparticles to penetrate cell membranes and epithelial barriers. Current research in nanotoxicology additionally focuses on particle coating. To distinguish between core- and coating-related effects in nanoparticle uptake and translocation, two nanoparticles equal in size, coating and charge but different in core material were investigated.
Silver and iron oxide nanoparticles coated with poly(acrylic acid) were chosen and extensively characterized by small-angle x-ray scattering, nanoparticle tracing analysis and transmission electron microscopy (TEM). Uptake and transport were studied in the intestinal Caco-2 model in a Transwell System with subsequent elemental analysis. TEM and ion beam microscopy were conducted for particle visualization.
Although equal in size, charge and coating, the behavior of the two particles in Caco-2 cells was different: while the internalized amount was comparable, only iron oxide nanoparticles additionally passed the epithelium. Our findings suggest that the coating material influenced only the uptake of the nanoparticles whereas the translocation was determined by the core material.
Knowledge about the different roles of the particle coating and core materials in crossing biological barriers will facilitate toxicological risk assessment of nanoparticles and contribute to the optimization of pharmacokinetic properties of nano-scaled pharmaceuticals.