Silver nanoparticle protein corona composition in cell culture media

The interaction of fluorescent nanodiamond probes with cellular media

Fluorescent nanodiamonds (FNDs) are promising tools to image cells, bioanalytes and physical quantities such as temperature, pressure, and electric or magnetic fields with nanometer resolution. To exploit their potential for intracellular applications, the FNDs have to be brought into contact with cell culture media. The interactions between the medium and the diamonds crucially influence sensitivity as well as the ability to enter cells. The authors demonstrate that certain proteins and salts spontaneously adhere to the FNDs and may cause aggregation. This is a first investigation on the fundamental questions on how (a) FNDs interact with the medium, and (b) which proteins and salts are being attracted. A differentiation between strongly binding and weakly binding proteins is made. Not all proteins participate in the formation of FND aggregates. Surprisingly, some main components in the medium seem to play no role in aggregation. Simple strategies to prevent aggregation are discussed. These include adding the proteins, which are naturally present in the cell culture to the diamonds first and then inserting them in the full medium. Graphical abstractSchematic of the interaction of nanodiamonds with cell culture medium. Certain proteins and salts adhere to the diamond surface and lead to aggregation or to formation of a protein corona.

Particle coatings but not silver ions mediate genotoxicity of ingested silver nanoparticles in a mouse model

Incorporation of silver nanoparticles (AgNPs) in toothpaste, food containers, dietary supplements and other consumer products can result in oral exposure to AgNPs and/or silver ions (Ag⁺) released from the surface of AgNPs. To examine whether ingestion of AgNPs or Ag⁺ results in genotoxic damage and whether AgNP coatings modulate the effect, we exposed mice orally to 20 nm citrate-coated AgNPs, polyvinylpyrrolidone (PVP)-coated AgNPs, silver acetate or respective vehicles at a 4 mg/kg dose (equivalent to 800x the EPA reference dose for Ag) for 7 days. Genotoxicity was examined in the systemic circulation and bone marrow at 1, 7, and 14 days post-exposure. We found that citrate-coated AgNPs induced chromosomal damage in bone marrow and oxidative DNA damage and double strand breaks in peripheral blood. These damages persisted for at least 14 days after exposure termination. Because oxidative DNA damage and strand breaks are repaired rapidly, their presence after exposure cessation indicates that citrate-coated AgNPs persist in the body. In contrast, PVP-coated AgNPs and silver acetate did not induce DNA or chromosomal damage at any time point measured. To determine whether coating-dependent genotoxicity is related to different AgNP changes in the gastrointestinal tract, we examined AgNP behavior and fate in an in vitro gastrointestinal digestion model using UV-visible spectroscopy and DLS. Citrate-coated AgNPs were more susceptible to agglomeration than PVP-coated AgNPs in digestive juices with or without proteins. In summary, AgNPs but not Ag⁺ are genotoxic following oral ingestion. Nanoparticle coatings modulate gastrointestinal transformation and genotoxicity of AgNPs, where higher agglomeration of AgNPs in gastrointestinal juices is associated with higher genotoxicity in tissues. Since genotoxicity is a strong indicator of cancer risk, further long-term studies focusing on cancer are warranted.

Silver nanoparticles: Significance of physicochemical properties and assay interference on the interpretation of in vitro cytotoxicity studies

Silver nanoparticles (AgNPs) have generated a great deal of interest in the research, consumer product, and medical product communities due to their antimicrobial and anti-biofouling properties. However, in addition to their antimicrobial action, concerns have been expressed about the potential adverse human health effects of AgNPs. In vitro cytotoxicity studies often are used to characterize the biological response to AgNPs and the results of these studies may be used to identify hazards associated with exposure to AgNPs. Various factors, such as nanomaterial size (diameter), surface area, surface charge, redox potential, surface functionalization, and composition play a role in the development of toxicity in in vitro test systems. In addition, the interference of AgNPs with in vitro cytotoxicity assays may result in false negative or false positive results in some in vitro biological tests. The goal of this review is to: 1) summarize the impact of physical-chemical parameters, including size, shape, surface chemistry and aggregate formation on the in vitro cytotoxic effects of AgNPs; and 2) explore the nature of AgNPs interference in in vitro cytotoxicity assays.

Provenance information as a tool for addressing engineered nanoparticle reproducibility challenges

Nanoparticles of various types are of increasing research and technological importance in biological and other applications. Difficulties in the production and delivery of nanoparticles with consistent and well defined properties appear in many forms and have a variety of causes. Among several issues are those associated with incomplete information about the history of particles involved in research studies, including the synthesis method, sample history after synthesis, including time and nature of storage, and the detailed nature of any sample processing or modification. In addition, the tendency of particles to change with time or environmental condition suggests that the time between analysis and application is important and some type of consistency or verification process can be important. The essential history of a set of particles can be identified as provenance information and tells the origin or source of a batch of nano-objects along with information related to handling and any changes that may have taken place since it was originated. A record of sample provenance information for a set of particles can play a useful role in identifying some of the sources and decreasing the extent of particle variability and the lack of reproducibility observed by many researchers.

Biocorona Bound Gold Nanoparticles Augment Their Hematocompatibility Irrespective of Size or Surface Charge

Despite colloidal gold nanoparticles (AuNP) being proposed for a multitude of biomedical applications, there is a lack of understanding on how the protein corona (PC) formation over AuNP influences its interaction with blood components. Herein, 40 and 80 nm AuNP with branched polyethylenimine, lipoic acid, and polyethylene glycol surface coatings were exposed to human plasma, and time-dependent evolution of the PC was evaluated using differential centrifugation sedimentation. Further, the impact of PC-AuNP interaction with human blood components was studied by evaluating red blood cell (RBC) aggregation, hemolysis, platelet activation and aggregation, prothrombin time, activated partial thromboplastin time, complement activation and cytokine release. In contrast to bare AuNP, PC-coated AuNP exhibited enhanced compatibility with RBC, platelets, and lymphocytes. More importantly, PC-AuNP did not activate the platelet coagulation cascade or complement system or elicit an immune response up to a relatively higher dose of 100 μg/mL. This study suggests that, irrespective of the physicochemical properties, the adsorption of the PC over AuNP significantly influences its biological impact by alleviating adverse hematotoxicity of bare NP.

Nanomaterial and toxicity: what can proteomics tell us about the nanotoxicology?

1. In the last few years, a substantial scientific work is focused to identify the potential toxicity of nanomaterials by studying the cellular pathways under in vitro and in vivo conditions. Owing to high surface area to volume ratio nanoparticles (NPs) can pass through cell membranes which might be responsible for creating adverse interactions in biological systems. Simultaneously, researchers are also interested to assess the fate of NP inside the living system, which may lead to altered protein expression as well as protein corona formation. 2. According to published reports, NP-mediated toxicity involves altered cellular system including cell morphology, cell differentiation, cell metabolism, cell mobility, cellular immunity, which is derived from the side effects of nanoformulation and leading to apoptosis and necrosis. These results indicate the existence of potential toxic effect of these particles to human health. 3. The advent of proteomics with sophisticated technical improvement coupled with advanced bioinformatics has led to identify altered proteins due to nanomaterial exposure that could provide a new avenue to biomarker discovery. 4. This review aims to provide the current status of safe production and use of nanomaterials.

Potent antimicrobial and antibiofilm activities of bacteriogenically synthesized gold–silver nanoparticles against pathogenic bacteria and their physiochemical characterizations

The objective of this study was to develop a bimetallic nanoparticle with enhanced antibacterial activity that would improve the therapeutic efficacy against bacterial biofilms. Bimetallic gold–silver nanoparticles were bacteriogenically synthesized using γ-proteobacterium, Shewanella oneidensis MR-1. The antibacterial activities of gold–silver nanoparticles were assessed on the planktonic and biofilm phases of individual and mixed multi-cultures of pathogenic Gram negative ( Escherichia coli and Pseudomonas aeruginosa) and Gram positive bacteria ( Enterococcus faecalis and Staphylococcus aureus), respectively. The minimum inhibitory concentration of gold–silver nanoparticles was 30–50 µM than that of other nanoparticles (>100 µM) for the tested bacteria. Interestingly, gold–silver nanoparticles were more effective in inhibiting bacterial biofilm formation at 10 µM concentration. Both scanning and transmission electron microscopy results further accounted the impact of gold–silver nanoparticles on biocompatibility and bactericidal effect that the small size and bio-organic materials covering on gold–silver nanoparticles improves the internalization and thus caused bacterial inactivation. Thus, bacteriogenically synthesized gold–silver nanoparticles appear to be a promising nanoantibiotic for overcoming the bacterial resistance in the established bacterial biofilms.

Biomolecular Interactions and Biological Responses of Emerging Two-Dimensional Materials and Aromatic Amino Acid Complexes

The present work experimentally investigates the interaction of aromatic amino acids viz., tyrosine, tryptophan, and phenylalnine with novel two-dimensional (2D) materials including graphene, graphene oxide (GO), and boron nitride (BN). Photoluminescence, micro-Raman spectroscopy, and cyclic voltammetry were employed to investigate the nature of interactions and possible charge transfer between 2D materials and amino acids. Graphene and GO were found to interact strongly with aromatic amino acids through π-π stacking, charge transfer, and H-bonding. Particularly, it was observed that both physi and chemisorption are prominent in the interactions of GO/graphene with phenylalanine and tryptophan while tyrosine exhibited strong chemisorption on graphene and GO. In contrast, BN exhibited little or no interactions, which could be attributed to localized π-electron clouds around N atoms in BN lattice. Lastly, the adsorption of amino acids on 2D materials was observed to considerably change their biological response in terms of reactive oxygen species generation. More importantly, these changes in the biological response followed the same trends observed in the physi and chemisorption measurements.

From the Cover: Disease-Induced Disparities in Formation of the Nanoparticle-Biocorona and the Toxicological Consequences

Nanoparticle (NP) association with macromolecules in a physiological environment forms a biocorona (BC), which alters NP distribution, activity, and toxicity. While BC formation is dependent on NP physicochemical properties, little information exists on the influence of the physiological environment. Obese individuals and those with cardiovascular disease exist with altered serum chemistry, which is expected to influence BC formation and NP toxicity. We hypothesize that a BC formed on NPs following incubation in hyperlipidemic serum will result in altered NP-BC protein content, cellular association, and toxicity compared to normal serum conditions. We utilized Fe3O4 NPs, which are being developed as MRI contrast and tumor targeting agents to test our hypothesis. We used rat aortic endothelial cells (RAECs) within a dynamic flow in vitro exposure system to more accurately depict the in vivo environment. A BC was formed on 20nm PVP-suspended Fe3O4 NPs following incubation in water, 10% normal or hyperlipidemic rat serum. Addition of BCs resulted in increased hydrodynamic size and decreased surface charge. More cholesterol associated with Fe3O4 NPs after incubation in hyperlipidemic as compared with normal serum. Using quantitative proteomics, we identified unique differences in BC protein components between the 2 serum types. Under flow conditions, formation of a BC from both serum types reduced RAECs association of Fe3O4 NPs. Addition of BCs was found to exacerbate RAECs inflammatory gene responses to Fe3O4 NPs (Fe3O4-hyperlipidemic > Fe3O4-normal > Fe3O4) including increased expression of IL-6, TNF-α, Cxcl-2, VCAM-1, and ICAM-1. Overall, these findings demonstrate that disease-induced variations in physiological environments have a significant impact NP-BC formation, cellular association, and cell response.

Metabolomics of silver nanoparticles toxicity in HaCaT cells: structure-activity relationships and role of ionic silver and oxidative stress

The widespread use of silver nanoparticles (AgNPs) is accompanied by a growing concern regarding their potential risks to human health, thus calling for an increased understanding of their biological effects. The aim of this work was to systematically study the extent to which changes in cellular metabolism were dependent on the properties of AgNPs, using NMR metabolomics. Human skin keratinocytes (HaCaT cells) were exposed to citrate-coated AgNPs of 10, 30 or 60 nm diameter and to 30 nm AgNPs coated either with citrate (CIT), polyethylene glycol (PEG) or bovine serum albumin (BSA), to assess the influence of NP size and surface chemistry. Overall, CIT-coated 60 nm and PEG-coated 30 nm AgNPs had the least impact on cell viability and metabolism. The role of ionic silver and reactive oxygen species (ROS)-mediated effects was also studied, in comparison to CIT-coated 30 nm particles. At concentrations causing an equivalent decrease in cell viability, Ag(+ )ions produced a change in the metabolic profile that was remarkably similar to that seen for AgNPs, the main difference being the lesser impact on the Krebs cycle and energy metabolism. Finally, this study newly reported that while down-regulated glycolysis and disruption of energy production were common to AgNPs and H2O2, the impact on some metabolic pathways (GSH synthesis, glutaminolysis and the Krebs cycle) was independent of ROS-mediated mechanisms. In conclusion, this study shows the ability of NMR metabolomics to define subtle biochemical changes induced by AgNPs and demonstrates the potential of this approach for rapid, untargeted screening of pre-clinical toxicity of nanomaterials in general.

Quantifying the Impact of Nanoparticle Coatings and Nonuniformities on XPS Analysis: Gold/Silver Core-Shell Nanoparticles

Spectral modeling of photoelectrons can serve as a valuable tool when combined with X-ray photoelectron spectroscopy (XPS) analysis. Herein, a new version of the NIST Simulation of Electron Spectra for Surface Analysis (SESSA 2.0) software, capable of directly simulating spherical multilayer NPs, was applied to model citrate stabilized Au/Ag-core/shell nanoparticles (NPs). The NPs were characterized using XPS and scanning transmission electron microscopy (STEM) to determine the composition and morphology of the NPs. The Au/Ag-core/shell NPs were observed to be polydispersed in size, nonspherical, and contain off-centered Au-cores. Using the average NP dimensions determined from STEM analysis, SESSA spectral modeling indicated that washed Au/Ag-core-shell NPs were stabilized with a 0.8 nm layer of sodium citrate and a 0.05 nm (one wash) or 0.025 nm (two wash) layer of adventitious hydrocarbon, but did not fully account for the observed XPS signal from the Au-core. This was addressed by a series of simulations and normalizations to account for contributions of NP nonsphericity and off-centered Au-cores. Both of these nonuniformities reduce the effective Ag-shell thickness, which effect the Au-core photoelectron intensity. The off-centered cores had the greatest impact for the particles in this study. When the contributions from the geometrical nonuniformities are included in the simulations, the SESSA generated elemental compositions that matched the XPS elemental compositions. This work demonstrates how spectral modeling software such as SESSA, when combined with experimental XPS and STEM measurements, advances the ability to quantitatively assess overlayer thicknesses for multilayer core-shell NPs and deal with complex, nonideal geometrical properties.

Silver nanoparticles inhibit fish gill cell proliferation in protein-free culture medium

While short-term exposures of vertebrate cells, such as from fish, can be performed in defined, serum-free media, long-term cultures generally require addition of growth factors and proteins, normally supplied with a serum supplement. However, proteins are known to alter nanoparticle properties by binding to nanoparticles. Therefore, in order to be able to study nanoparticle-cell interactions for extended periods, the rainbow trout (Oncorhynchus mykiss) gill cell line, RTgill-W1, was adapted to proliferate in a commercial, serum-free medium, InVitrus VP-6. The newly adapted cell strain was named RTgill-W1-pf (protein free). These cells proliferate at a speed similar to the RTgill-W1 cells cultured in a fully supplemented medium containing 5% fetal bovine serum. As well, they were successfully cryopreserved in liquid nitrogen and fully recovered after thawing. Yet, senescence set in after about 10 passages in InVitrus VP-6 medium, revealing that this medium cannot fully support long-term culture of the RTgill-W1 strain. The RTgill-W1-pf cell line was subsequently applied to investigate the effect of silver nanoparticles (AgNP) on cell proliferation over a period of 12 days. Indeed, cell proliferation was inhibited by 10 μM AgNP. This effect correlated with high levels of silver being associated with the cells. The new cell line, RTgill-W1-pf, can serve as a unique representation of the gill cell-environment interface, offering novel opportunities to study nanoparticle-cell interactions without serum protein interference.

The role of natural processes and surface energy of inhaled engineered nanoparticles on aggregation and corona formation

The surface chemistry of engineered nanoparticles (ENPs) becomes more important as their size decreases and enters the nanometer-range. This review explains the fundamental properties of the surface chemistry of nanoparticles, and argues that their agglomeration and the formation of corona around them are natural processes that reduce surface energy. ENP agglomeration and surface corona formation are further discussed in the context of inhaled ENPs, as the lung is a major port of ENP entry to the body. The pulmonary surfactant layer, which the inhaled ENPs first encounter as they land on the lung surface, represents a unique environment with a variety of well-defined biomolecules. Many factors, such as hydrophobicity, surface charge of ENPs, protein/phospholipid concentrations of the alveolar lining fluid, etc. influence the complex processes of ENP agglomeration and corona formation in the alveolar lining fluid, and these events occur even before the ENPs reach the cells. We suggest that molecular dynamic simulations can represent a promising future direction for research of the behavior of inhaled ENPs, complementing the experimental approaches. Moreover, we want to remind biologists working on ENPs of the importance relationship between ENP surface energy and size.

Surface coating affects behavior of metallic nanoparticles in a biological environment

Silver (AgNPs) and maghemite, i.e., superparamagnetic iron oxide nanoparticles (SPIONs) are promising candidates for new medical applications, which implies the need for strict information regarding their physicochemical characteristics and behavior in a biological environment. The currently developed AgNPs and SPIONs encompass a myriad of sizes and surface coatings, which affect NPs properties and may improve their biocompatibility. This study is aimed to evaluate the effects of surface coating on colloidal stability and behavior of AgNPs and SPIONs in modelled biological environments using dynamic and electrophoretic light scattering techniques, as well as transmission electron microscopy to visualize the behavior of the NP. Three dispersion media were investigated: ultrapure water (UW), biological cell culture medium without addition of protein (BM), and BM supplemented with common serum protein (BMP). The obtained results showed that different coating agents on AgNPs and SPIONs produced different stabilities in the same biological media. The combination of negative charge and high adsorption strength of coating agents proved to be important for achieving good stability of metallic NPs in electrolyte-rich fluids. Most importantly, the presence of proteins provided colloidal stabilization to metallic NPs in biological fluids regardless of their chemical composition, surface structure and surface charge. In addition, an assessment of AgNP and SPION behavior in real biological fluids, rat whole blood (WhBl) and blood plasma (BlPl), revealed that the composition of a biological medium is crucial for the colloidal stability and type of metallic NP transformation. Our results highlight the importance of physicochemical characterization and stability evaluation of metallic NPs in a variety of biological systems including as many NP properties as possible.

Lipid-Mediated Targeting with Membrane-Wrapped Nanoparticles in the Presence of Corona Formation

Membrane-wrapped nanoparticles represent a versatile platform for utilizing specific lipid-receptor interactions, such as siallyllactose-mediated binding of the ganglioside GM3 to Siglec1 (CD169), for targeting purposes. The membrane wrap around the nanoparticles not only serves as a matrix to incorporate GM3 as targeting moiety for antigen-presenting cells but also offers unique opportunities for constructing a biomimetic surface from lipids with potentially protein-repellent properties. We characterize nonspecific protein adsorption (corona formation) to membrane-wrapped nanoparticles with core diameters of approximately 35 and 80 nm and its effect on the GM3-mediated targeting efficacy as a function of surface charge through combined in vitro and in vivo studies. The stability and fate of the membrane wrap around the nanoparticles in a simulated biological fluid and after uptake in CD169-expressing antigen-presenting cells is experimentally tested. Finally, we demonstrate in hock immunization studies in mice that GM3-decorated membrane-wrapped nanoparticles achieve a selective enrichment in the peripheral regions of popliteal lymph nodes that contain high concentrations of CD169-expressing antigen-presenting cells.

The impact of nanoparticle protein corona on cytotoxicity, immunotoxicity and target drug delivery

In a perfect sequence of events, nanoparticles (NPs) are injected into the bloodstream where they circulate until they reach the target tissue. The ligand on the NP surface recognizes its specific receptor expressed on the target tissue and the drug is released in a controlled manner. However, once injected in a physiological environment, NPs interact with biological components and are surrounded by a protein corona (PC). This can trigger an immune response and affect NP toxicity and targeting capabilities. In this review, we provide a survey of recent findings on the NP-PC interactions and discuss how the PC can be used to modulate both cytotoxicity and the immune response as well as to improve the efficacy of targeted delivery of nanocarriers.

Antibacterial Low Molecular Weight Cationic Polymers: Dissecting the Contribution of Hydrophobicity, Chain Length and Charge to Activity

The balance of cationicity and hydrophobicity can profoundly affect the performance of antimicrobial polymers. To this end a library of 24 cationic polymers with uniquely low degrees of polymerization was synthesized via Cu(0)-mediated polymerization, using three different cationic monomers and two initiators: providing two different hydrocarbon chain tail lengths (C2 and C12). The polymers exhibited structure-dependent antibacterial activity when tested against a selection of bacteria, viz, Staphylococcus aureus ATCC 29213, Klebsiella pneumoniae ATCC 13883, Acinetobacter baumannii ATCC 19606, and Pseudomonas aeruginosa ATCC 27853 as a representative palette of Gram-positive and Gram-negative ESKAPE pathogens. The five best-performing polymers were identified for additional testing against the polymyxin-resistant A. baumannii ATCC 19606R strain. Polymers having the lowest DP and a C12 hydrophobic tail were shown to provide the broadest antimicrobial activity against the bacteria panel studied as evidenced by lower minimum inhibitory concentrations (MICs). An optimal polymer composition was identified, and its mechanism of action investigated via membrane permeability testing against Escherichia coli. Membrane disruption was identified as the most probable mechanism for bacteria cell killing.

Cytotoxic and sublethal effects of silver nanoparticles on tendon-derived stem cells - implications for tendon engineering

Tendon injuries occur commonly in sports and workplace. Tendon-derived stem cells (TDSCs) have great potential for tendon healing because they can differentiate into functional tenocytes. To grow TDSCs properly in vivo, a scaffold is needed. Silver nanoparticles (AgNPs) have been used in a range of biomedical applications for their anti-bacterial and -inflammatory effects. AgNPs are therefore expected to be a good scaffolding coating material for tendon engineering. Yet, their cytotoxicity in TDSCs remains unknown. Moreover, their sublethal effects were mysterious in TDSCs. In our study, decahedral AgNPs (43.5 nm in diameter) coated with polyvinylpyrrolidone (PVP) caused a decrease in TDSCs' viability beginning at 37.5 μg ml-1 but showed non-cytotoxic effects at concentrations below 18.8 μg ml-1. Apoptosis was observed in the TDSCs when higher doses of AgNPs (75-150 μg ml-1) were used. Mechanistically, AgNPs induced reactive oxygen species (ROS) formation and mitochondrial membrane potential (MMP) depolarization, resulting in apoptosis. Interestingly, treating TDSCs with N-acetyl-l-cysteine (NAC) antioxidant significantly antagonized the ROS formation, MMP depolarization and apoptosis indicating that ROS accumulation was a prominent mediator in the AgNP-induced cytotoxicity. On the other hand, AgNPs inhibited the tendon markers' mRNA expression (0-15 μg ml-1), proliferation and clonogenicity (0-15 μg ml-1) in TDSCs under non-cytotoxic concentrations. Taken together, we have reported here for the first time that the decahedral AgNPs are cytotoxic to rat TDSCs and their sublethal effects are also detrimental to stem cells' proliferation and tenogenic differentiation. Therefore, AgNPs are not a good scaffolding coating material for tendon engineering.

Copper oxide nanoparticles inhibit the metabolic activity of Saccharomyces cerevisiae

Copper oxide nanoparticles (CuO NPs) are used increasingly in industrial applications and consumer products and thus may pose risk to human and environmental health. The interaction of CuO NPs with complex media and the impact on cell metabolism when exposed to sublethal concentrations are largely unknown. In the present study, the short-term effects of 2 different sized manufactured CuO NPs on metabolic activity of Saccharomyces cerevisiae were studied. The role of released Cu(2+) during dissolution of NPs in the growth media and the CuO nanostructure were considered. Characterization showed that the 28 nm and 64 nm CuO NPs used in the present study have different primary diameter, similar hydrodynamic diameter, and significantly different concentrations of dissolved Cu(2+) ions in the growth media released from the same initial NP mass. Exposures to CuO NPs or the released Cu(2+) fraction, at doses that do not have impact on cell viability, showed significant inhibition on S. cerevisiae cellular metabolic activity. A greater CuO NP effect on the metabolic activity of S. cerevisiae growth under respiring conditions was observed. Under the tested conditions the observed metabolic inhibition from the NPs was not explained fully by the released Cu ions from the dissolving NPs.

Dispersion Behaviour of Silica Nanoparticles in Biological Media and Its Influence on Cellular Uptake

Given the increasing variety of manufactured nanomaterials, suitable, robust, standardized in vitro screening methods are needed to study the mechanisms by which they can interact with biological systems. The in vitro evaluation of interactions of nanoparticles (NPs) with living cells is challenging due to the complex behaviour of NPs, which may involve dissolution, aggregation, sedimentation and formation of a protein corona. These variable parameters have an influence on the surface properties and the stability of NPs in the biological environment and therefore also on the interaction of NPs with cells. We present here a study using 30 nm and 80 nm fluorescently-labelled silicon dioxide NPs (Rubipy-SiO₂ NPs) to evaluate the NPs dispersion behaviour up to 48 hours in two different cellular media either supplemented with 10% of serum or in serum-free conditions. Size-dependent differences in dispersion behaviour were observed and the influence of the living cells on NPs stability and deposition was determined. Using flow cytometry and fluorescence microscopy techniques we studied the kinetics of the cellular uptake of Rubipy-SiO₂ NPs by A549 and CaCo-2 cells and we found a correlation between the NPs characteristics in cell media and the amount of cellular uptake. Our results emphasize how relevant and important it is to evaluate and to monitor the size and agglomeration state of nanoparticles in the biological medium, in order to interpret correctly the results of the in vitro toxicological assays.

A hyperspectral and toxicological analysis of protein corona impact on silver nanoparticle properties, intracellular modifications, and macrophage activation

The inevitable adsorption of biomolecules on nanomaterials results in the formation of a protein corona (PC), which modifies the nanoparticle (NP)–cell interface resulting in modified uptake, activity, clearance, and toxicity. While the physicochemical properties of the NP govern the composition of PC, the formation of PC in turn alters the characteristics of the NP by imparting a new unique “biological” identity. To assess how the PC influences AgNP properties, intracellular modifications, and cellular responses, we utilized a combination of hyperspectral and toxicological analyses. AgNPs were coated with a complex PC (multiple proteins, eg, 10% fetal bovine serum) or a simple PC (single protein, eg, bovine serum albumin [BSA]) and evaluated by hyperspectral and dynamic light scattering for modifications in AgNP properties. Mouse macrophages were exposed to AgNPs with PCs and examined for differences in uptake, cytotoxicity, and cell activation. Hyperspectral imaging revealed intracellular modifications to AgNPs that were found to spectrally match alterations in AgNPs following incubation in lysosomal fluid. Addition of the PC influenced AgNP uptake and cytotoxicity; however, hydrodynamic size and surface charge did not contribute to these responses. Assessments of all endpoints demonstrated differences between complex and BSA PC, suggesting that these responses are not purely driven by the primary protein component of the complex PC (ie, BSA). Alterations in cellular–NP uptake/interactions may be driven through cell surface receptor recognition of protein constituents that make up the PC rather than the physicochemical differences in AgNPs.

Influence of carbon nanomaterial defects on the formation of protein corona

In any physiological media, carbon nanomaterials (CNM) strongly interact with biomolecules leading to the formation of biocorona, which subsequently dictate the physiological response and the fate of CNMs. Defects in CNMs play an important role not only in material properties but also in the determination of how materials interact at the nano-bio interface. In this article, we probed the influence of defect-induced hydrophilicity on the biocorona formation using micro-Raman, photoluminescence, infrared spectroscopy, electrochemistry, and molecular dynamics simulations. Our results show that the interaction of proteins (albumin and fibrinogen) with CNMs is strongly influenced by charge-transfer between them, inducing protein unfolding which enhances conformational entropy and higher protein adsorption.

Comparison of 20 nm silver nanoparticles synthesized with and without a gold core: Structure, dissolution in cell culture media, and biological impact on macrophages

Widespread use of silver nanoparticles raises questions of environmental and biological impact. Many synthesis approaches are used to produce pure silver and silver-shell gold-core particles optimized for specific applications. Since both nanoparticles and silver dissolved from the particles may impact the biological response, it is important to understand the physicochemical characteristics along with the biological impact of nanoparticles produced by different processes. The authors have examined the structure, dissolution, and impact of particle exposure to macrophage cells of two 20 nm silver particles synthesized in different ways, which have different internal structures. The structures were examined by electron microscopy and dissolution measured in Rosewell Park Memorial Institute media with 10% fetal bovine serum. Cytotoxicity and oxidative stress were used to measure biological impact on RAW 264.7 macrophage cells. The particles were polycrystalline, but 20 nm particles grown on gold seed particles had smaller crystallite size with many high-energy grain boundaries and defects, and an apparent higher solubility than 20 nm pure silver particles. Greater oxidative stress and cytotoxicity were observed for 20 nm particles containing the Au core than for 20 nm pure silver particles. A simple dissolution model described the time variation of particle size and dissolved silver for particle loadings larger than 9 μg/ml for the 24-h period characteristic of many in-vitro studies.

Silver nanoparticle protein corona and toxicity: a mini-review

Silver nanoparticles are one of the most important materials in the nanotechnology industry. Additionally, the protein corona is emerging as a key entity at the nanobiointerface; thus, a comprehensive understanding of the interactions between proteins and silver nanoparticles is imperative. Therefore, literature reporting studies involving both single molecule protein coronas (i.e., bovine and human serum albumin, tubulin, ubiquitin and hyaluronic-binding protein) and complex protein coronas (i.e., fetal bovine serum and yeast extract proteins) were selected to demonstrate the effects of protein coronas on silver nanoparticle cytotoxicity and antimicrobial activity. There is evidence that distinct and differential protein components may yield a "protein corona signature" that is related to the size and/or surface curvature of the silver nanoparticles. Therefore, the formation of silver nanoparticle protein coronas together with the biological response to these coronas (i.e., oxidative stress, inflammation and cytotoxicity) as well as other cellular biophysicochemical mechanisms (i.e., endocytosis, biotransformation and biodistribution) will be important for nanomedicine and nanotoxicology. Researchers may benefit from the information contained herein to improve biotechnological applications of silver nanoparticles and to address related safety concerns. In summary, the main aim of this mini-review is to highlight the relationship between the formation of silver nanoparticle protein coronas and toxicity.

Investigation of cellular responses upon interaction with silver nanoparticles

In order for nanoparticles (NPs) to be applied in the biomedical field, a thorough investigation of their interactions with biological systems is required. Although this is a growing area of research, there is a paucity of comprehensive data in cell-based studies. To address this, we analyzed the physicomechanical responses of human alveolar epithelial cells (A549), mouse fibroblasts (NIH3T3), and human bone marrow stromal cells (HS-5), following their interaction with silver nanoparticles (AgNPs). When compared with kanamycin, AgNPs exhibited moderate antibacterial activity. Cell viability ranged from ≤80% at a high AgNPs dose (40 µg/mL) to >95% at a low dose (10 µg/mL). We also used atomic force microscopy-coupled force spectroscopy to evaluate the biophysical and biomechanical properties of cells. This revealed that AgNPs treatment increased the surface roughness (P<0.001) and stiffness (P<0.001) of cells. Certain cellular changes are likely due to interaction of the AgNPs with the cell surface. The degree to which cellular morphology was altered directly proportional to the level of AgNP-induced cytotoxicity. Together, these data suggest that atomic force microscopy can be used as a potential tool to develop a biomechanics-based biomarker for the evaluation of NP-dependent cytotoxicity and cytopathology.

Impact of Silver and Iron Nanoparticle Exposure on Cholesterol Uptake by Macrophages

Macrophages are central to the development of atherosclerosis by absorbing lipids, promoting inflammation, and increasing plaque deposition. Nanoparticles (NPs) are becoming increasingly common in biomedical applications thereby increasing exposure to the immune and vascular systems. This project investigated the influence of NPs on macrophage function and specifically cholesterol uptake. Macrophages were exposed to 20 nm silver NPs (AgNPs), 110 nm AgNPs, or 20 nm Fe3O4NPs for 2 h and NP uptake, cytotoxicity, and subsequent uptake of fluorescently labeled cholesterol were assessed. Macrophage uptake of NPs did not induce cytotoxicity at concentrations utilized (25 μg/mL); however, macrophage exposure to 20 nm AgNPs reduced subsequent uptake of cholesterol. Further, we assessed the impact of a cholesterol-rich environment on macrophage function following NP exposure. In these sets of experiments, macrophages internalized NPs, exhibited no cytotoxicity, and altered cholesterol uptake. Alterations in the expression of scavenger receptor-B1 following NP exposure, which likely influences cholesterol uptake, were observed. Overall, NPs alter cholesterol uptake, which may have implications in the progression of vascular or immune mediated diseases. Therefore, for the safe development of NPs for biomedical applications, it is necessary to understand their impact on cellular function and biological interactions in underlying disease environments.

Biomolecular corona on nanoparticles: a survey of recent literature and its implications in targeted drug delivery

Achieving controlled cellular responses of nanoparticles (NP) is critical for the successful development and translation of NP-based drug delivery systems. However, precise control over the physicochemical and biological properties of NPs could become convoluted, diminished, or completely lost as a result of the adsorption of biomolecules to their surfaces. Characterization of the formation of the "biomolecular" corona has thus received increased attention due to its impact on NP and protein structure as well as its negative effect on NP-based targeted drug delivery. This review presents a concise survey of the recent literature concerning the importance of the NP-biomolecule corona and how it can be utilized to improve the in vivo efficacy of targeted delivery systems.

Formation of a protein corona on silver nanoparticles mediates cellular toxicity via scavenger receptors

Addition of a protein corona (PC) or protein adsorption layer on the surface of nanomaterials following their introduction into physiological environments may modify their activity, bio-distribution, cellular uptake, clearance, and toxicity. We hypothesize that silver nanoparticles (AgNPs) will associate with proteins common to human serum and cell culture media forming a PC that will impact cell activation and cytotoxicity. Furthermore, the role of scavenger receptor BI (SR-BI) in mediating this toxicity was evaluated. Citrate-suspended 20 nm AgNPs were incubated with human serum albumin (HSA), bovine serum albumin (BSA), high-density lipoprotein (HDL), or water (control) to form a PC. AgNPs associated with each protein (HSA, BSA, and HDL) forming PCs as assessed by electron microscopy, hyperspectral analysis, ζ-potential, and hydrodynamic size. Addition of the PC decreased uptake of AgNPs by rat lung epithelial and rat aortic endothelial cells. Hyperspectral analysis demonstrated a loss of the AgNP PC following internalization. Cells demonstrated concentration-dependent cytotoxicity following exposure to AgNPs with or without PCs (0, 6.25, 12.5, 25 or 50 μg/ml). All PC-coated AgNPs were found to activate cells by inducing IL-6 mRNA expression. A small molecule SR-BI inhibitor was utilized to determine the role of SR-BI in the observed effects. Pretreatment with the SR-BI inhibitor decreased internalization of AgNPs with or without PCs, and reduced both cytotoxicity and IL-6 mRNA expression. This study characterizes the formation of a PC on AgNPs and demonstrates its influence on cytotoxicity and cell activation through a cell surface receptor.

Potential of hyperspectral imaging microscopy for semi-quantitative analysis of nanoparticle uptake by protozoa

Hyperspectral imaging with enhanced darkfield microscopy (HSI-M) possesses unique advantages in its simplicity and non-invasiveness. In consideration of the urgent need for profound knowledge on the behavior and effects of engineered nanoparticles (NPs), here, we determined the capability of HSI-M for examining cellular uptake of different metal-based NPs, including nanosized metals (silver and gold, both citrate stabilized), metal oxides (copper oxide and titanium dioxide), and CdSe/ZnS core/shell quantum dots at subtoxic concentrations. Specifically, we demonstrated that HSI-M can be used to detect and semi-quantify these NPs in the ciliated protozoan Tetrahymena thermophila as a model aquatic organism. Detection and semi-quantification were achieved on the basis of spectral libraries for the NPs suspended in extracellular substances secreted by this single-celled organism, accounting for matrix effects. HSI-M was able to differentiate between NP types, provided that spectral profiles were significantly different from each other. This difference, in turn, depended upon NP type, size, agglomeration status, and position relative to the focal plane. As an exception among the NPs analyzed in this study, titanium dioxide NPs showed spectral similarities compared to cell material of unexposed control cells, leading to false positives. High biological variability resulted in highly variable uptake of NPs in cells of the same sample as well as between different exposures. We therefore encourage the development of techniques able to reduce the currently long analysis times that still hamper the acquisition of statistically strong data sets. Overall, this study demonstrates the potential and challenges of HSI-M in monitoring cellular uptake of synthetic NPs.

Autophagy as a Possible Underlying Mechanism of Nanomaterial Toxicity

The rapid development of nanotechnologies is raising safety concerns because of the potential effects of engineered nanomaterials on human health, particularly at the respiratory level. Since the last decades, many in vivo studies have been interested in the pulmonary effects of different classes of nanomaterials. It has been shown that some of them can induce toxic effects, essentially depending on their physico-chemical characteristics, but other studies did not identify such effects. Inflammation and oxidative stress are currently the two main mechanisms described to explain the observed toxicity. However, the exact underlying mechanism(s) still remain(s) unknown and autophagy could represent an interesting candidate. Autophagy is a physiological process in which cytoplasmic components are digested via a lysosomal pathway. It has been shown that autophagy is involved in the pathogenesis and the progression of human diseases, and is able to modulate the oxidative stress and pro-inflammatory responses. A growing amount of literature suggests that a link between nanomaterial toxicity and autophagy impairment could exist. In this review, we will first summarize what is known about the respiratory effects of nanomaterials and we will then discuss the possible involvement of autophagy in this toxicity. This review should help understand why autophagy impairment could be taken as a promising candidate to fully understand nanomaterials toxicity.

Vascular distribution of nanomaterials

Once considered primarily occupational, novel nanotechnology innovations, and applications have led to widespread domestic use and intentional biomedical exposures. With these exciting advances, the breadth and depth of toxicological considerations must also be expanded. The vascular system interacts with every tissue in the body, striving to maintain homeostasis. Engineered nanomaterials (ENM) have been reported to distribute in many different tissues and organs. However, these observations have tended to use approaches requiring tissue homogenization and/or gross organ analyses. These techniques, while effective in establishing presence, preclude an exact determination of where ENM are deposited within a tissue. If nanotechnology is to achieve its full potential, it is necessary to identify this exact distribution and deposition of ENM throughout the cardiovascular system, with respect to vascular hemodynamics and in vivo ENM modifications taken into account. Distinct levels of the vasculature will first be described as individual compartments. Then the vasculature will be considered as a whole. These unique compartments and biophysical conditions will be discussed in terms of their propensity to favor ENM deposition. Understanding levels of the vasculature will also be discussed. Ultimately, future studies must verify the mechanisms speculated on and presented herein.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

The nano-plasma interface: Implications of the protein corona

The interactions between nanoparticles and macromolecules in the blood plasma dictate the biocompatibility and efficacy of nanotherapeutics. Accordingly, the properties of nanoparticles and endogenous biomolecules change at the nano-plasma interface. Here, we review the implications of such changes including toxicity, immunological recognition, molecular targeting, biodistribution, intracellular uptake, and drug release. Although this interface poses several challenges for nanomedicine, it also presents opportunities for exploiting nanoparticle-protein interactions.

Molecular toxicity mechanism of nanosilver

Silver is an ancient antibiotic that has found many new uses due to its unique properties on the nanoscale. Due to its presence in many consumer products, the toxicity of nanosilver has become a hot topic. This review summarizes recent advances, particularly the molecular mechanism of nanosilver toxicity. The surface of nanosilver can easily be oxidized by O₂ and other molecules in the environmental and biological systems leading to the release of Ag⁺, a known toxic ion. Therefore, nanosilver toxicity is closely related to the release of Ag⁺. In fact, it is difficult to determine what portion of the toxicity is from the nano-form and what is from the ionic form. The surface oxidation rate is closely related to the nanosilver surface coating, coexisting molecules, especially thiol-containing compounds, lighting conditions, and the interaction of nanosilver with nucleic acids, lipid molecules, and proteins in a biological system. Nanosilver has been shown to penetrate the cell and become internalized. Thus, nanosilver often acts as a source of Ag⁺ inside the cell. One of the main mechanisms of toxicity is that it causes oxidative stress through the generation of reactive oxygen species and causes damage to cellular components including DNA damage, activation of antioxidant enzymes, depletion of antioxidant molecules (e.g., glutathione), binding and disabling of proteins, and damage to the cell membrane. Several major questions remain to be answered: (1) the toxic contribution from the ionic form versus the nano-form; (2) key enzymes and signaling pathways responsible for the toxicity; and (3) effect of coexisting molecules on the toxicity and its relationship to surface coating.

Spatial mapping and quantification of soft and hard protein coronas at silver nanocubes

Protein coronas around silver nanocubes were quantified in serum-containing media using localized surface plasmon resonances. Both soft and hard coronas showed exposure-time and concentration-dependent changes in protein surface density with time-dependent hardening. We observed spatially dependent kinetics of the corona-formation at cube edges/corners versus facets at short incubation times, where the polymer stabilization agent delayed corona hardening. The soft corona contained more protein than the hard corona at all time-points (8-fold difference with 10% serum conditions).

Bioinformatic Analysis of Differential Protein Expression in Calu-3 Cells Exposed to Carbon Nanotubes

Carbon nanomaterials are widely produced and used in industry, medicine and scientific research. To examine the impact of exposure to nanoparticles on human health, the human airway epithelial cell line, Calu-3, was used to evaluate changes in the cellular proteome that could account for alterations in cellular function of airway epithelia after 24 hexposure to 10 μg/mL and 100 ng/mLof two common carbon nanoparticles, single- and multi-wall carbon nanotubes (SWCNT, MWCNT). After exposure to the nanoparticles, label-free quantitative mass spectrometry (LFQMS) was used to study the differential protein expression. Ingenuity Pathway Analysis (IPA) was used to conduct a bioinformaticanalysis of proteins identified in LFQMS. Interestingly, after exposure to ahigh concentration (10 μg/mL; 0.4 μg/cm²) of MWCNT or SWCNT, only 8 and 13 proteins, respectively, exhibited changes in abundance. In contrast, the abundance of hundreds of proteins was altered in response to a low concentration (100 ng/mL; 4 ng/cm²) of either CNT. Of the 281 and 282 proteins that were significantly altered in response to MWCNT or SWCNT respectively, 231 proteins were the same. Bioinformatic analyses found that the proteins in common to both nanotubes occurred within the cellular functions of cell death and survival, cell-to-cell signaling and interaction, cellular assembly and organization, cellular growth and proliferation, infectious disease, molecular transport and protein synthesis. The majority of the protein changes represent a decrease in amount suggesting a general stress response to protect cells. The STRING database was used to analyze the various functional protein networks. Interestingly, some proteins like cadherin 1 (CDH1), signal transducer and activator of transcription 1 (STAT1), junction plakoglobin (JUP), and apoptosis-associated speck-like protein containing a CARD (PYCARD), appear in several functional categories and tend to be in the center of the networks. This central positioning suggests they may play important roles in multiple cellular functions and activities that are altered in response to carbon nanotube exposure.

Silver nanoparticle protein corona composition in cell culture media

The potential applications of nanomaterials as drug delivery systems and in other products continue to expand. Upon introduction into physiological environments and driven by energetics, nanomaterials readily associate proteins forming a protein corona (PC) on their surface. This PC influences the nanomaterial's surface characteristics and may impact their interaction with cells. To determine the biological impact of nanomaterial exposure as well as nanotherapeutic applications, it is necessary to understand PC formation. Utilizing a label-free mass spectrometry-based proteomics approach, we examined the composition of the PC for a set of four silver nanoparticles (AgNPs) including citrate-stabilized and polyvinlypyrrolidone-stabilized (PVP) colloidal silver (20 or 110 nm diameter). To simulate cell culture conditions, AgNPs were incubated for 1 h in Dulbecco's Modified Eagle Medium supplemented with 10% fetal bovine serum, washed, coronal proteins solubilized, and proteins identified and quantified by label-free LC-MS/MS. To determine which attributes influence PC formation, the AgNPs were characterized in both water and cell culture media with 10% FBS. All AgNPs associated a common subset of 11 proteins including albumin, apolipoproteins, keratins, and other serum proteins. 110 nm citrate- and PVP-stabilized AgNPs were found to bind the greatest number of proteins (79 and 85 respectively) compared to 20 nm citrate- and PVP-stabilized AgNPs (45 and 48 respectively), suggesting a difference in PC formation based on surface curvature. While no relationships were found for other protein parameters (isoelectric point or aliphatic index), the PC on 20 nm AgNPs (PVP and citrate) consisted of more hydrophobic proteins compared to 110 nm AgNPs implying that this class of proteins are more receptive to curvature-induced folding and crowding in exchange for an increased hydration in the aqueous environment. These observations demonstrate the significance of electrostatic and hydrophobic interactions in the formation of the PC which may have broad biological and toxicological implications.