Applicability and Limitations in the Characterization of Poly-Dispersed Engineered Nanomaterials in Cell Media by Dynamic Light Scattering (DLS)

Adapting the in vitro micronucleus assay (OECD Test Guideline No. 487) for testing of manufactured nanomaterials: recommendations for best practices

The current Organisation for Economic Co-Operation and Development test guideline number 487 (OECD TG No. 487) provides instruction on how to conduct the in vitro micronucleus assay. This assay is one of the gold standard approaches for measuring the mutagenicity of test items; however, it is directed at testing low molecular weight molecules and may not be appropriate for particulate materials (e.g. engineered nanoparticles [ENPs]). This study aimed to adapt the in vitro micronucleus assay for ENP testing and underpins the development of an OECD guidance document. A harmonized, nano-specific protocol was generated and evaluated by two independent laboratories. Cell lines utilized were human lymphoblastoid (TK6) cells, human liver hepatocytes (HepG2) cells, Chinese hamster lung fibroblast (V79) cells, whole blood, and buffy coat cells from healthy human volunteers. These cells were exposed to reference ENPs from the Joint Research Council (JRC): SiO2 (RLS-0102), Au5nm and Au30nm (RLS-03, RLS-010), CeO2 (NM212), and BaSO4 (NM220). Tungsten carbide-cobalt (WC/Co) was used as a trial particulate positive control. The chemical controls were positive in all cell cultures, but WC/Co was only positive in TK6 and buffy coat cells. In TK6 cells, mutagenicity was observed for SiO2- and both Au types. In HepG2 cells, Au5nm and SiO2 showed sub-two-fold increases in micronuclei. In V79 cells, whole blood, and buffy coat cells, no genotoxicity was detected with the test materials. The data confirmed that ENPs could be tested with the harmonized protocol, additionally, concordant data were observed across the two laboratories with V79 cells. WC/Co may be a suitable particulate positive control in the in vitro micronucleus assay when using TK6 and buffy coat cells. Detailed recommendations are therefore provided to adapt OECD TG No. 487 for testing ENP.

Interlaboratory comparison of centrifugal ultrafiltration with ICP-MS detection in a first-step towards methods to screen for nanomaterial release during certification of drinking water contact materials

A key requirement for evaluating the safety of nano-enabled water treatment devices is measuring concentrations of insoluble nanomaterials released from devices into water that may be ingested by consumers. Therefore, there is a need for simple technique that uses commonly available commercial laboratory techniques to discriminate between nanoparticles and dissolved by-products of the nanomaterial (e.g., ionic metals). Such capabilities would enable screening for particulate or dissolved metals released into water from nanomaterial-containing drinking water contact materials (e.g., paint coatings) or devices (e.g., filters). This multi-laboratory study sought to investigate the use of relatively inexpensive centrifugal ultrafilters to separate nanoparticulate from ionic metal in combination with inductively-coupled plasma mass spectrometry (ICP-MS) detection. The accuracy, precision, and reproducibility for the proposed method were assessed using mixtures of nanoparticulate and ionic gold (Au) in a standard and widely utilized model water matrix (NSF International Standard 53/61). Concentrations for both ionic and nanoparticulate gold based upon measurements of Au mass in the initial solutions and Au permeating the centrifugal ultrafilters. Results across different solution compositions and different participating labs showed that ionic and nanoparticulate Au could be consistently discriminated with ppb concentrations typically resulting in <10 % error. A mass balance was not achieved because nanoparticles were retained on membranes embedded in plastic holders inside the centrifuge tubes, and the entire apparatus could not be acid and/or microwave digested. This was a minor limitation considering the ultrafiltration method is a screening tool, and gold concentration in the permeate indicates the presence of ionic metal rather than nanoforms. With further development, this approach could prove to be an effective tool in screening for nanomaterial release from water-system or device materials as part of third-party certification processes of drinking water compatible products.

Exploring the Impact of Nanoparticle Stealth Coatings in Cancer Models: From PEGylation to Cell Membrane-Coating Nanotechnology

Nanotechnological platforms offer advantages over conventional therapeutic and diagnostic modalities. However, the efficient biointerfacing of nanomaterials for biomedical applications remains challenging. In recent years, nanoparticles (NPs) with different coatings have been developed to reduce nonspecific interactions, prolong circulation time, and improve therapeutic outcomes. This study aims to compare various NP coatings to enhance surface engineering for more effective nanomedicines. We prepared and characterized polystyrene NPs with different coatings of poly(ethylene glycol), bovine serum albumin, chitosan, and cell membranes from a human breast cancer cell line. The coating was found to affect the colloidal stability, adhesion, and elastic modulus of NPs. Protein corona formation and cellular uptake of NPs were also investigated, and a 3D tumor model was employed to provide a more realistic representation of the tumor microenvironment. The prepared NPs were found to reduce protein adsorption, and cell-membrane-coated NPs showed significantly higher cellular uptake. The secretion of proinflammatory cytokines in human monocytes after incubation with the prepared NPs was evaluated. Overall, the study demonstrates the importance of coatings in affecting the behavior and interaction of nanosystems with biological entities. The findings provide insight into bionano interactions and are important for the effective implementation of stealth surface engineering designs.

Interactions Between Silver Nanoparticles and Culture Medium Biomolecules with Dose and Time Dependencies

The interaction between silver nanoparticles (AgNPs) and molecules producing coronas plays a key role in cytotoxicity mechanisms. Once adsorbed coronas determine the destiny of nanomaterials in vivo, their effective deployment in the biomedical field requires a comprehensive understanding of the dynamic interactions of biomolecules with nanoparticles. In this work, we characterized 40 nm AgNPs in three different nutritional cell media at different molar concentrations and incubation times to study the binding mechanism of molecules on surface nanoparticles. In addition, their cytotoxic effects have been studied in three cell lineages used as tissue regeneration models: FN1, HUV-EC-C, RAW 264.7. According to the data, when biomolecules from DMEM medium were in contact with AgNPs, agglomeration and precipitation occurred. However, FBS medium proteins indicated the formation of coronas over the nanoparticles. Nonetheless, little adsorption of molecules around the nanoparticles was observed when compared to DMEM supplemented with 10% FBS. These findings indicate that when nanoparticles and bioproteins from supplemented media interact, inorganic salts from DMEM contribute to produce large bio-coronas, the size of which varies with the concentration and time. The static quenching mechanism was shown to be responsible for the fluorescence quenching of the bioprotein aggregates on the AgNPs surface. The calculated bioprotein-nanoparticle surface binding constants were on the order of 105 M-1 at 37 °C, with hydrophobic interactions driven by enthalpy and entropy playing a role, as confirmed by thermodynamic analysis. Cytotoxicity data showed a systematic degrowth in the viable cell population as the number of nanoparticles increased and the diameter of coronas decreased. Cytotoxic intervals associated with half decrease of cell population were established for AgNPs molar concentration of 75 µM for 24 h and 50 µM for 48 h. In summary, through the cytotoxicity mechanism of bio-coronas we are able to manipulate cells' expansion rates to promote specific processes, such inflammatory mechanisms, at different time instants.

Caveat Emptor: Commercialized Manganese Oxide Nanoparticles Exhibit Unintended Properties

Nano-encapsulated manganese oxide (NEMO) particles are noteworthy contrast agents for magnetic resonance imaging (MRI) due to their bright, pH-switchable signal ("OFF" to "ON" at low pH), high metal loading, and targeting capability for increased specificity. For the first time, we performed a head-to-head comparison of NEMO particles from In-house and commercialized sources (US Nano vs Nanoshel) to assess their potential as bright T₁ MRI contrast agents. Manganese oxide nanocrystals (MnO, Mn₂O₃, and Mn₃O₄) were systematically evaluated for size, chemistry, release of manganese ions, and MRI signal pre- and post-encapsulation within poly(lactic-co-glycolic acid) (PLGA). Suprisingly, a majority of the commercialized formulations were not as advertised by displaying unintended sizes, morphologies, chemistry, dissolution profiles, and/or MRI signal that precludes in vivo use. US Nano's Mn₃O₄ and Mn₂O₃ nanocrystals contained impurities that impacted Mn ion release as well as micron-sized rodlike structures. Nanoshel's MnO and Mn₂O₃ nanoparticles had very large hydrodynamic sizes (>600 nm). In-house MnO and Nanoshel's Mn₃O₄ nanoparticles demonstrated the best characteristics with brighter T₁ MRI signals, small hydrodynamic sizes, and high encapsulation efficiencies. Our findings highlight that researchers must confirm the properties of purchased nanomaterials before utilizing them in desired applications, as their experimental success may be impacted.

Nanomaterial Characterization in Complex Media-Guidance and Application

A broad range of inorganic nanoparticles (NPs) and their dissolved ions possess a possible toxicological risk for human health and the environment. Reliable and robust measurements of dissolution effects may be influenced by the sample matrix, which challenges the analytical method of choice. In this study, CuO NPs were investigated in several dissolution experiments. Two analytical techniques (dynamic light scattering (DLS) and inductively-coupled plasma mass spectrometry (ICP-MS)) were used to characterize NPs (size distribution curves) time-dependently in different complex matrices (e.g., artificial lung lining fluids and cell culture media). The advantages and challenges of each analytical approach are evaluated and discussed. Additionally, a direct-injection single particle (DI sp)ICP-MS technique for assessing the size distribution curve of the dissolved particles was developed and evaluated. The DI technique provides a sensitive response even at low concentrations without any dilution of the complex sample matrix. These experiments were further enhanced with an automated data evaluation procedure to objectively distinguish between ionic and NP events. With this approach, a fast and reproducible determination of inorganic NPs and ionic backgrounds can be achieved. This study can serve as guidance when choosing the optimal analytical method for NP characterization and for the determination of the origin of an adverse effect in NP toxicity.

Smartphone-based holographic measurement of polydisperse suspended particulate matter with various mass concentration ratios

Real-time monitoring of suspended particulate matter (PM) has become essential in daily life due to the adverse effects of long-term exposure to PMs on human health and ecosystems. However, conventional techniques for measuring micro-scale particulates commonly require expensive instruments. In this study, a smartphone-based device is developed for real-time monitoring of suspended PMs by integrating a smartphone-based digital holographic microscopy (S-DHM) and deep learning algorithms. The proposed S-DHM-based PM monitoring device is composed of affordable commercial optical components and a smartphone. Overall procedures including digital image processing, deep learning training, and correction process are optimized to minimize the prediction error and computational cost. The proposed device can rapidly measure the mass concentrations of coarse and fine PMs from holographic speckle patterns of suspended polydisperse PMs in water with measurement errors of 22.8 ± 18.1% and 13.5 ± 9.8%, respectively. With further advances in data acquisition and deep learning training, this study would contribute to the development of hand-held devices for monitoring polydisperse non-spherical pollutants suspended in various media.

Changes of physico-chemical properties of nano-biomaterials by digestion fluids affect the physiological properties of epithelial intestinal cells and barrier models

Background

The widespread use of nano-biomaterials (NBMs) has increased the chance of human exposure. Although ingestion is one of the major routes of exposure to NBMs, it is not thoroughly studied to date. NBMs are expected to be dramatically modified following the transit into the oral-gastric-intestinal (OGI) tract. How these transformations affect their interaction with intestinal cells is still poorly understood. NBMs of different chemical nature—lipid-surfactant nanoparticles (LSNPs), carbon nanoparticles (CNPs), surface modified Fe₃O₄ nanoparticles (FNPs) and hydroxyapatite nanoparticles (HNPs)—were treated in a simulated human digestive system (SHDS) and then characterised. The biological effects of SHDS-treated and untreated NBMs were evaluated on primary (HCoEpiC) and immortalised (Caco-2, HCT116) epithelial intestinal cells and on an intestinal barrier model.

Results

The application of the in vitro SDHS modified the biocompatibility of NBMs on gastrointestinal cells. The differences between SHDS-treated and untreated NBMs could be attributed to the irreversible modification of the NBMs in the SHDS. Aggregation was detected for all NBMs regardless of their chemical nature, while pH- or enzyme-mediated partial degradation was detected for hydroxyapatite or polymer-coated iron oxide nanoparticles and lipid nanoparticles, respectively. The formation of a bio-corona, which contains proteases, was also demonstrated on all the analysed NBMs. In viability assays, undifferentiated primary cells were more sensitive than immortalised cells to digested NBMs, but neither pristine nor treated NBMs affected the intestinal barrier viability and permeability. SHDS-treated NBMs up-regulated the tight junction genes (claudin 3 and 5, occludin, zonula occludens 1) in intestinal barrier, with different patterns between each NBM, and increase the expression of both pro- and anti-inflammatory cytokines (IL-1β, TNF-α, IL-22, IL-10). Notably, none of these NBMs showed any significant genotoxic effect.

Conclusions

Overall, the results add a piece of evidence on the importance of applying validated in vitro SHDS models for the assessment of NBM intestinal toxicity/biocompatibility. We propose the association of chemical and microscopic characterization, SHDS and in vitro tests on both immortalised and primary cells as a robust screening pipeline useful to monitor the changes in the physico-chemical properties of ingested NBMs and their effects on intestinal cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00491-w.

Surface Treatment With Hydrophobic Coating Reagents (Organosilanes) Strongly Reduces the Bioactivity of Synthetic Amorphous Silica in vitro

Synthetic amorphous silica (SAS) is industrially relevant material whose bioactivity in vitro is strongly diminished, for example, by protein binding to the particle surface. Here, we investigated the in vitro bioactivity of fourteen SAS (pyrogenic, precipitated, or colloidal), nine of which were surface-treated with organosilanes, using alveolar macrophages as a highly sensitive test system. Dispersion of the hydrophobic SAS required pre-wetting with ethanol and extensive ultrasonic treatment in the presence of 0.05% BSA (Protocol 1). Hydrophilic SAS was suspended by moderate ultrasonic treatment (Protocol 2) and also by Protocol 1. The suspensions were administered to NR8383 alveolar macrophages under serum-free conditions for 16 h, and the release of LDH, GLU, H2O2, and TNFα was measured in cell culture supernatants. While seven surface-treated hydrophobic SAS exhibited virtually no bioactivity, two materials (AEROSIL® R 504 and AEROSIL® R 816) had minimal effects on NR8383 cells. In contrast, non-treated SAS elicited considerable increases in LDH, GLU, and TNFα, while the release of H2O2 was low except for CAB-O-SIL® S17D Fumed Silica. Dispersing hydrophilic SAS with Protocol 1 gradually reduced the bioactivity but did not abolish it. The results show that hydrophobic coating reagents, which bind covalently to the SAS surface, abrogate the bioactivity of SAS even under serum-free in vitro conditions. The results may have implications for the hazard assessment of hydrophobic surface-treated SAS in the lung.

Serum Lowers Bioactivity and Uptake of Synthetic Amorphous Silica by Alveolar Macrophages in a Particle Specific Manner

Various cell types are compromised by synthetic amorphous silica (SAS) if they are exposed to SAS under protein-free conditions in vitro. Addition of serum protein can mitigate most SAS effects, but it is not clear whether this is solely caused by protein corona formation and/or altered particle uptake. Because sensitive and reliable mass spectrometric measurements of SiO₂ NP are cumbersome, quantitative uptake studies of SAS at the cellular level are largely missing. In this study, we combined the comparison of SAS effects on alveolar macrophages in the presence and absence of foetal calf serum with mass spectrometric measurement of ²⁸Si in alkaline cell lysates. Effects on the release of lactate dehydrogenase, glucuronidase, TNFα and H₂O₂ of precipitated (SIPERNAT^® 50, SIPERNAT^® 160) and fumed SAS (AEROSIL^® OX50, AEROSIL^® 380 F) were lowered close to control level by foetal calf serum (FCS) added to the medium. Using a quantitative high resolution ICP-MS measurement combined with electron microscopy, we found that FCS reduced the uptake of particle mass by 9.9% (SIPERNAT^® 50) up to 83.8% (AEROSIL^® OX50). Additionally, larger particle agglomerates were less frequent in cells in the presence of FCS. Plotting values for lactate dehydrogenase (LDH), glucuronidase (GLU) or tumour necrosis factor alpha (TNFα) against the mean cellular dose showed the reduction of bioactivity with a particle sedimentation bias. As a whole, the mitigating effects of FCS on precipitated and fumed SAS on alveolar macrophages are caused by a reduction of bioactivity and by a lowered internalization, and both effects occur in a particle specific manner. The method to quantify nanosized SiO₂ in cells is a valuable tool for future in vitro studies.

Mechanistic Insights into the Role of Iron, Copper, and Carbonaceous Component on the Oxidative Potential of Ultrafine Particulate Matter

Transition metals play a key role in the pathogenic potential of urban particulate matter (PM). However, air quality regulations include exposure limits only for metals having a known toxic potential like Pb, As, Cd, and Ni, neglecting other transition metals like Fe and Cu. Fe and Cu are mainly found in the water-soluble fraction of PM. However, a fraction of the ions may persist strongly bound to the particles, thus potentially acting as surface reactive sites. The contribution of surface ions to the oxidative potential (OP) of PM is likely different from that of free ions since the redox activity of metals is modulated by their local chemical environment. The aim of this study was to investigate how Fe and Cu bound to carbonaceous particles affect the OP and associated toxicity of PM toward epithelial cells and macrophages. Carbonaceous nanoparticles (CNPs) having well-defined size were loaded with controlled amounts of Cu and Fe. The effect of Cu and Fe on the OP of CNPs was evaluated by electronic paramagnetic resonance (EPR) spectroscopy associated with the spin-trapping technique and correlated with the ability to induce cytotoxicity (LDH, WST-1), oxidative stress (Nrf2 translocation), and DNA damage (comet assay) on lung macrophages (NR8383) and/or epithelial cells (RLE-6TN). The release of pro-inflammatory cytokines (TNF-α, MCP-1, and CXCL2) by macrophages and epithelial cells was also investigated. The results indicate a major contribution of surface Cu to the surface reactivity of CNPs, while Fe has a minor role. At the same time, Cu increases the cytotoxicity of CNPs and their ability to induce oxidative stress and DNA damage. In contrast, surface Fe increases the release of pro-inflammatory cytokines by macrophages. Overall, these results confirm the role of Cu and Fe in PM toxicity and suggest that the total metals content in PM might be a better indicator of pathogenicity than water-soluble metals.

Citrate-Coated Platinum Nanoparticles Exhibit a Primary Particle-Size Dependent Effect on Stimulating Melanogenesis in Human Melanocytes

Hypopigmentation disorders due to an underproduction of the pigment melanin by melanocytes cause uneven skin coloration, while in hair follicles they cause grey hair. There is a need for novel materials which can stimulate melanogenesis in the skin and hair for personal care use. While titanium dioxide, gold and silver nanoparticles have been extensively used for applications in cosmetic and personal-care products (PCP), the use of relatively inert platinum nanoparticles (PtNPs) has remained underappreciated. PtNPs have been reported to be a mimetic of the enzyme catechol oxidase with small size PtNPs reported to exhibit a higher catechol oxidase activity in a cell-free system, but no testing has been conducted in melanocytes to date. Herein, we have investigated if PtNPs of two sizes (SPtNP: 5 nm; LPtNP: 50 nm) might have an effect on melanogenesis. To this end, we have used MNT-1 human melanoma cells and primary human melanocytes from moderately-pigmented skin (HEMn-MP). Both SPtNP and LPtNP were nontoxic over a concentration range 6.25–25 μg/mL, hence these concentrations were used in further experiments. Both PtNPs stimulated higher extracellular melanin levels than control; SPtNP at concentrations 12.5 and 25 μg/mL significantly stimulated higher levels of extracellular melanin as compared to similar concentrations of LPtNP in MNT-1 cells, in the absence of ROS generation. The effects of PtNPs on melanin secretion were reversible upon removal of PtNPs from the culture medium. The results of primary particle size-specific augmentation of extracellular melanin by SPtNPs were also validated in HEMn-MP cells. Our results thus provide a proof-of-principle that SPtNP might hold potential as a candidate for the treatment of white skin patches, for sunless skin-tanning and for use in anti-greying hair products in cosmetics.

Biotransformation of Food-Grade and Nanometric TiO2 in the Oral-Gastro-Intestinal Tract: Driving Forces and Effect on the Toxicity toward Intestinal Epithelial Cells

Background: Oral exposure to titanium dioxide (TiO₂) is common since it is widely used in food and pharmaceutical products. Concern on the safety of this substance has been recently raised, due to the presence of an ultrafine fraction in food-grade TiO₂. Discrepancy exists among data reported in in vitro and in vivo studies on intestinal acute/chronic toxicity of TiO₂. This might be due to the different biological identity of TiO₂ in traditional in vitro test by respect in vivo conditions. Methods: One food-grade TiO₂ and two nanometric TiO₂ samples were treated with a simulated human digestive dystem (SHDS) in order to investigate the bio-transformation occurring to the particles once ingested in term of size distribution (Dynamic Light Scattering—DLS-, Flow Particle Imaging, Asymmetric Flow Field Flow Fractionation-AF4-) and surface modification (Electrophoretic Light Scattering—ELS-, Electron Paramagnetic Resonance Spectroscopy—EPR-). The effect of SHDS on the cyto-, genotoxicity and potential to induce oxidative stress towards human colorectal carcinoma HCT116 cells was also assessed. Results: Aggregation as a consequence of the high ionic strength of the gastric and intestinal simulated fluids was observed, together with the formation of a partially irreversible bio-corona containing phosphate ions and proteins. Such bio-corona led to a partial masking of the TiO₂ particles surface and reactivity. Pristine and treated TiO₂ nanoparticles showed comparable acute toxicity and genotoxicity toward HCT116 cells, whereas a small decrease of the induction of oxidative stress after treatment was observed. Conclusions: Overall the results underline the importance of SHDS as a tool to improve the predictive power of in vitro tests towards intestinal nanomaterial toxicity.