Use of metal oxide nanoparticle band gap to develop a predictive paradigm for oxidative stress and acute pulmonary inflammation

Dynamics of sub-lethal effects of nano-CuO on the microalga Chlamydomonas reinhardtii during short-term exposure

Though nano-CuO has been classified as toxic toward aquatic microorganisms and its use in various applications is expected to increase in near future, its ecotoxicity is currently poorly understood. The aim of this study was to investigate the mechanisms of nano-CuO toxicity based on the paradigm of oxidative stress, the dynamics of response over 24h, and the modulating effect of exposure conditions on toxicity and responses. To this end, the model microalga Chlamydomonas reinhardtii was exposed to 10mgL(-1) nano-CuO in five different exposure media, including two different growth media, two Good's buffers, and natural lake water. The measured endpoints included cell growth, morphological aspect, chlorophyll autofluorescence, oxidative stress, and membrane permeabilization. The results suggest that agglomerated nano-CuO is toxic and that exposure media are decisive in whether or not particles or free Cu ions are the main mediators of toxicity. A significant particle effect was only observed in the Good's buffer 3-(N-morpholino) propanesulfonic acid. However, nano-CuO particles especially influenced the dynamics of response early in exposure, between 0h and 5h, suggesting that an adaptation to particle stress may occur or that particles modify the bioavailability of the free Cu ions in early exposure.

A decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping)

The European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) 'Nano Task Force' proposes a Decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping) that consists of 3 tiers to assign nanomaterials to 4 main groups, to perform sub-grouping within the main groups and to determine and refine specific information needs. The DF4nanoGrouping covers all relevant aspects of a nanomaterial's life cycle and biological pathways, i.e. intrinsic material and system-dependent properties, biopersistence, uptake and biodistribution, cellular and apical toxic effects. Use (including manufacture), release and route of exposure are applied as 'qualifiers' within the DF4nanoGrouping to determine if, e.g. nanomaterials cannot be released from a product matrix, which may justify the waiving of testing. The four main groups encompass (1) soluble nanomaterials, (2) biopersistent high aspect ratio nanomaterials, (3) passive nanomaterials, and (4) active nanomaterials. The DF4nanoGrouping aims to group nanomaterials by their specific mode-of-action that results in an apical toxic effect. This is eventually directed by a nanomaterial's intrinsic properties. However, since the exact correlation of intrinsic material properties and apical toxic effect is not yet established, the DF4nanoGrouping uses the 'functionality' of nanomaterials for grouping rather than relying on intrinsic material properties alone. Such functionalities include system-dependent material properties (such as dissolution rate in biologically relevant media), bio-physical interactions, in vitro effects and release and exposure. The DF4nanoGrouping is a hazard and risk assessment tool that applies modern toxicology and contributes to the sustainable development of nanotechnological products. It ensures that no studies are performed that do not provide crucial data and therefore saves animals and resources.

Colorimetric detection of catalytic reactivity of nanoparticles in complex matrices

There is a need for new methodologies to quickly assess the presence and reactivity of nanoparticles (NPs) in commercial, environmental, and biological samples since current detection techniques require expensive and complex analytical instrumentation. Here, we investigate a simple and portable colorimetric detection assay that assesses the surface reactivity of NPs, which can be used to detect the presence of NPs, in complex matrices (e.g., environmental waters, serum, urine, and in dissolved organic matter) at as low as part per billion (ppb) or ng/mL concentration levels. Surface redox reactivity is a key emerging property related to potential toxicity of NPs with living cells, and is used in our assays as a key surrogate for the presence of NPs and a first tier analytical strategy toward assessing NP exposures. We detect a wide range of metal (e.g., Ag and Au) and oxide (e.g., CeO2, SiO2, VO2) NPs with a diameter range of 5 to 400 nm and multiple capping agents (tannic acid (TA), polyvinylpyrrolidone (PVP), branched polyethylenimine (BPEI), polyethylene glycol (PEG)). This method is sufficiently sensitive (ppb levels) to measure concentrations typically used in toxicological studies, and uses inexpensive, commercially available reagents.

Indium oxide (In2O3) nanoparticles induce progressive lung injury distinct from lung injuries by copper oxide (CuO) and nickel oxide (NiO) nanoparticles

Indium is an essential element in the manufacture of liquid crystal displays and other electronic devices, and several forms of indium compounds have been developed, including nanopowders, films, nanowires, and indium metal complexes. Although there are several reports on lung injury caused by indium-containing compounds, the toxicity of nanoscale indium oxide (In2O3) particles has not been reported. Here, we compared lung injury induced by a single exposure to In2O3 nanoparticles (NPs) to that caused by benchmark high-toxicity nickel oxide (NiO) and copper oxide (CuO) NPs. In2O3 NPs at doses of 7.5, 30, and 90 cm(2)/rat (50, 200, and 600 µg/rat) were administered to 6-week-old female Wistar rats via pharyngeal aspiration, and lung inflammation was evaluated 1, 3, 14, and 28 days after treatment. Neutrophilic inflammation was observed on day 1 and worsened until day 28, and severe pulmonary alveolar proteinosis (PAP) was observed on post-aspiration days 14 and 28. In contrast, pharyngeal aspiration of NiO NPs showed severe neutrophilic inflammation on day 1 and lymphocytic inflammation with PAP on day 28. Pharyngeal aspiration of CuO NPs showed severe neutrophilic inflammation on day 1, but symptoms were completely resolved after 14 days and no PAP was observed. The dose of In2O3 NPs that produced progressive neutrophilic inflammation and PAP was much less than the doses of other toxic particles that produced this effect, including crystalline silica and NiO NPs. These results suggest that occupational exposure to In2O3 NPs can cause severe lung injury.

Toxicity of CeO2 nanoparticles - the effect of nanoparticle properties

Conflicting reports on the toxicity of CeO2 nanomaterials have been published in recent years, with some studies finding CeO2 nanoparticles to be toxic, while others found it to have protective effects against oxidative stress. To investigate the possible reasons for this, we have performed a comprehensive study on the physical and chemical properties of nanosized CeO2 from three different suppliers as well as CeO2 synthesized by us, and tested their toxicity. For toxicity tests, we have studied the effects of CeO2 nanoparticles on a Gram-negative bacterium Escherichia coli in the dark, under ambient and UV illuminations. We have also performed toxicity tests on the marine diatom Skeletonema costatum under ambient and UV illuminations. We found that the CeO2 nanoparticle samples exhibited significantly different toxicity, which could likely be attributed to the differences in interactions with cells, and possibly to differences in nanoparticle compositions. Our results also suggest that toxicity tests on bacteria may not be suitable for predicting the ecotoxicity of nanomaterials. The relationship between the toxicity and physicochemical properties of the nanoparticles is explicitly discussed in the light of the current results.

Evaluation of zinc oxide nanoparticles toxicity on marine algae chlorella vulgaris through flow cytometric, cytotoxicity and oxidative stress analysis

The increasing industrial use of nanomaterials during the last decades poses a potential threat to the environment and in particular to organisms living in the aquatic environment. In the present study, the toxicity of zinc oxide nanoparticles (ZnO NPs) was investigated in Marine algae Chlorella vulgaris (C. vulgaris). High zinc dissociation from ZnONPs, releasing ionic zinc in seawater, is a potential route for zinc assimilation and ZnONPs toxicity. To examine the mechanism of toxicity, C. vulgaris were treated with 50mg/L, 100mg/L, 200mg/L and 300 mg/L ZnO NPs for 24h and 72h. The detailed cytotoxicity assay showed a substantial reduction in the viability dependent on dose and exposure. Further, flow cytometry revealed the significant reduction in C. vulgaris viable cells to higher ZnO NPs. Significant reductions in LDH level were noted for ZnO NPs at 300 mg/L concentration. The activity of antioxidant enzyme superoxide dismutase (SOD) significantly increased in the C. vulgaris exposed to 200mg/L and 300 mg/L ZnO NPs. The content of non-enzymatic antioxidant glutathione (GSH) significantly decreased in the groups with a ZnO NPs concentration of higher than 100mg/L. The level of lipid peroxidation (LPO) was found to increase as the ZnO NPs dose increased. The FT-IR analyses suggested surface chemical interaction between nanoparticles and algal cells. The substantial morphological changes and cell wall damage were confirmed through microscopic analyses (FESEM and CM).

Sulfidation as a natural antidote to metallic nanoparticles is overestimated: CuO sulfidation yields CuS nanoparticles with increased toxicity in medaka (Oryzias latipes) embryos

Sulfidation is considered as a natural antidote to toxicity of metallic nanoparticles (NPs). The detoxification contribution from sulfidation, however, may vary depending on sulfidation mechanisms. Here we present the dissolution-precipitation instead of direct solid-state-shell mechanism to illustrate the process of CuO-NPs conversion to CuS-NPs in aqueous solutions. Accordingly, the CuS-NPs at environmentally relevant concentrations showed much stronger interference on Japanese medaka (Oryzias latipes) embryo hatching than CuO-NPs, which was probably due to elevated free copper ions released from CuS-NPs, leading to significant increase in oxidative stress and causing toxicity in embryos. The larval length was significantly reduced by CuS-NPs, however, no other obviously abnormal morphological features were identified in the hatched larvae. Co-introduction of a metal ion chelator [ethylene diamine tetraacetic acid (EDTA)] could abolish the hatching inhibition induced by CuS-NPs, indicating free copper ions released from CuS-NPs play an important role in hatching interference. This work documents for the first time that sulfidation as a natural antidote to metallic NPs is being overestimated, which has far reaching implications for risk assessment of metallic NPs in aquatic environment.

Genotoxicity of metal oxide nanomaterials: review of recent data and discussion of possible mechanisms

Nanotechnology has rapidly entered into human society, revolutionized many areas, including technology, medicine and cosmetics. This progress is due to the many valuable and unique properties that nanomaterials possess. In turn, these properties might become an issue of concern when considering potentially uncontrolled release to the environment. The rapid development of new nanomaterials thus raises questions about their impact on the environment and human health. This review focuses on the potential of nanomaterials to cause genotoxicity and summarizes recent genotoxicity studies on metal oxide/silica nanomaterials. Though the number of genotoxicity studies on metal oxide/silica nanomaterials is still limited, this endpoint has recently received more attention for nanomaterials, and the number of related publications has increased. An analysis of these peer reviewed publications over nearly two decades shows that the test most employed to evaluate the genotoxicity of these nanomaterials is the comet assay, followed by micronucleus, Ames and chromosome aberration tests. Based on the data studied, we concluded that in the majority of the publications analysed in this review, the metal oxide (or silica) nanoparticles of the same core chemical composition did not show different genotoxicity study calls (i.e. positive or negative) in the same test, although some results are inconsistent and need to be confirmed by additional experiments. Where the results are conflicting, it may be due to the following reasons: (1) variation in size of the nanoparticles; (2) variations in size distribution; (3) various purities of nanomaterials; (4) variation in surface areas for nanomaterials with the same average size; (5) differences in coatings; (6) differences in crystal structures of the same types of nanomaterials; (7) differences in size of aggregates in solution/media; (8) differences in assays; (9) different concentrations of nanomaterials in assay tests. Indeed, due to the observed inconsistencies in the recent literature and the lack of adherence to appropriate, standardized test methods, reliable genotoxicity assessment of nanomaterials is still challenging.

Current situation on the availability of nanostructure-biological activity data

Recent developments in nanotechnology have not only increased the number of nanoproducts on the market, but also raised concerns about the safety of engineered nanomaterials (ENMs) for human health and the environment. As the production and use of ENMs increase, we are approaching the point at which it is impossible to individually assess the toxicity of a vast number of ENMs. Therefore, it is desirable to use time-effective computational methods, such as the quantitative structure-activity relationship (QSAR) models, to predict the toxicity of ENMs. However, the accuracy of the nano-(Q)SARs is directly tied to the quality of the data from which the model is estimated. Although the amount of available nanotoxicity data is insufficient for generating robust nano-(Q)SAR models in most cases, there are a handful of studies that provide appropriate experimental data for (Q)SAR-like modelling investigations. The aim of this study is to review the available literature data that are particularly suitable for nano-(Q)SAR modelling. We hope that this paper can serve as a starting point for those who would like to know more about the current availability of experimental data on the health effects of ENMs for future modelling purposes.

The biomechanisms of metal and metal-oxide nanoparticles' interactions with cells

Humans are increasingly exposed to nanoparticles (NPs) in medicine and in industrial settings, where significant concentrations of NPs are common. However, NP interactions with and effects on biomolecules and organisms have only recently been addressed. Within we review the literature regarding proposed modes of action for metal and metal-oxide NPs, two of the most prevalent types manufactured. Iron-oxide NPs, for instance, are used as tracers for magnetic resonance imaging of oncological tumors and as vehicles for therapeutic drug delivery. Factors and theories that determine the physicochemical and biokinetic behaviors of NPs are discussed, along with the observed toxicological effects of NPs on cells. Key thermodynamic and kinetic models that explain the sources of energy transfer from NPs to biological targets are summarized, in addition to quantitative structural activity relationship (QSAR) modeling efforts. Future challenges for nanotoxicological research are discussed. We conclude that NP studies based on cell culture are often inconsistent and underestimate the toxicity of NPs. Thus, the effect of NPs needs to be examined in whole animal systems.

Toxicity of metal oxide nanoparticles in Escherichia coli correlates with conduction band and hydration energies

Metal oxide nanoparticles (MOx NPs) are used for a host of applications, such as electronics, cosmetics, construction, and medicine, and as a result, the safety of these materials to humans and the environment is of considerable interest. A prior study of 24 MOx NPs in mammalian cells revealed that some of these materials show hazard potential. Here, we report the growth inhibitory effects of the same series of MOx NPs in the bacterium Escherichia coli and show that toxicity trends observed in E. coli parallel those seen previously in mammalian cells. Of the 24 materials studied, only ZnO, CuO, CoO, Mn2O3, Co3O4, Ni2O3, and Cr2O3 were found to exert significant growth inhibitory effects; these effects were found to relate to membrane damage and oxidative stress responses in minimal trophic media. A correlation of the toxicological data with physicochemical parameters of MOx NPs revealed that the probability of a MOx NP being toxic increases as the hydration enthalpy becomes less negative and as the conduction band energy approaches those of biological molecules. These observations are consistent with prior results observed in mammalian cells, revealing that mechanisms of toxicity of MOx NPs are consistent across two very different taxa. These results suggest that studying nanotoxicity in E. coli may help to predict toxicity patterns in higher organisms.

Novel approach for efficient predictions properties of large pool of nanomaterials based on limited set of species: nano-read-across

Creating suitable chemical categories and developing read-across methods, supported by quantum mechanical calculations, can be an effective solution to solving key problems related to current scarcity of data on the toxicity of various nanoparticles. This study has demonstrated that by applying a nano-read-across, the cytotoxicity of nano-sized metal oxides could be estimated with a similar level of accuracy as provided by quantitative structure-activity relationship for nanomaterials (nano-QSAR model(s)). The method presented is a suitable computational tool for the preliminary hazard assessment of nanomaterials. It also could be used for the identification of nanomaterials that may pose potential negative impact to human health and the environment. Such approaches are especially necessary when there is paucity of relevant and reliable data points to develop and validate nano-QSAR models.

Toxicity of metal oxide nanoparticles: mechanisms, characterization, and avoiding experimental artefacts

Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non-toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity.

Self-assembled serum albumin–poly(l-lactic acid) nanoparticles: a novel nanoparticle platform for drug delivery in cancer

A new protein–hydrophobic polymeric nanoparticle platform BSA–PLLA NPs has been prepared. A large amount of BA was well encapsulated into the BSA–PLLA NPs. Moreover, the BSA–PLLA/BA NPs shows excellent antitumor activity.

Sulfidation modulates the toxicity of biogenic copper nanoparticles

First report to show sulfidation reduces CuNP toxicity in vivo. Sulfidation lowered oxidative stress and liver pathology, protected biochemical components, prevented micronucleus formation – strategy for reducing environmental impact of nanoparticles.

Manganese Oxides in Heterogeneous (Photo)Catalysis: Possibilities and Challenges

The aim to develop active photocatalysts based on abundant elements for solar energy conversion reactions has sparked wide interest in manganese oxides as visible light-absorbing alternative to TiO

Causal inference methods to assist in mechanistic interpretation of classification nano-SAR models

Causal inference methods are helpful with finding possible biological mechanisms of nanoparticles' toxicity.

Use of a lipid-coated mesoporous silica nanoparticle platform for synergistic gemcitabine and paclitaxel delivery to human pancreatic cancer in mice

Recently, a commercial albumin-bound paclitaxel (PTX) nanocarrier (Abraxane) was approved as the first new drug for pancreatic ductal adenocarcinoma in almost a decade. PTX improves the pharmaceutical efficacy of the first-line pancreatic cancer drug, gemcitabine (GEM), through suppression of the tumor stroma and inhibiting the expression of the GEM-inactivating enzyme, cytidine deaminase (CDA). We asked, therefore, whether it was possible to develop a mesoporous silica nanoparticle (MSNP) carrier for pancreatic cancer to co-deliver a synergistic GEM/PTX combination. High drug loading was achieved by a custom-designed coated lipid film technique to encapsulate a calculated dose of GEM (40 wt %) by using a supported lipid bilayer (LB). The uniform coating of the 65 nm nanoparticles by a lipid membrane allowed incorporation of a sublethal amount of hydrophobic PTX, which could be co-delivered with GEM in pancreatic cells and tumors. We demonstrate that ratiometric PTX incorporation and delivery by our LB-MSNP could suppress CDA expression, contemporaneous with induction of oxidative stress as the operating principle for PTX synergy. To demonstrate the in vivo efficacy, mice carrying subcutaneous PANC-1 xenografts received intravenous (IV) injection of PTX/GEM-loaded LB-MSNP. Drug co-delivery provided more effective tumor shrinkage than GEM-loaded LB-MSNP, free GEM, or free GEM plus Abraxane. Comparable tumor shrinkage required coadministration of 12 times the amount of free Abraxane. High-performance liquid chromatography analysis of tumor-associated GEM metabolites confirmed that, compared to free GEM, MSNP co-delivery increased the phosphorylated DNA-interactive GEM metabolite 13-fold and decreased the inactivated and deaminated metabolite 4-fold. IV injection of MSNP-delivered PTX/GEM in a PANC-1 orthotopic model effectively inhibited primary tumor growth and eliminated metastatic foci. The enhanced in vivo efficacy of the dual delivery carrier could be achieved with no evidence of local or systemic toxicity. In summary, we demonstrate the development of an effective LB-MSNP nanocarrier for synergistic PTX/GEM delivery in pancreatic cancer.

One-pot and facile synthesis of anti-biofouling polymer-modified gadolinium-based nanoprobes for dual-modal imaging and long-lasting tracking

PEGylated gadolinium hydroxycarbonate nanoparticles have been designed and synthesized via a one-pot facile route and successfully applied as high-performance dual-modal contrast agents for X-ray CT and MR imaging.

Genotoxicity, potential cytotoxicity and cell uptake of titanium dioxide nanoparticles in the marine fish Trachinotus carolinus (Linnaeus, 1766)

Nanoparticles have physicochemical characteristics that make them useful in areas such as science, technology, medicine and in products of everyday use. Recently the manufacture and variety of these products has grown rapidly, raising concerns about their impact on human health and the environment. Adverse effects of exposure to nanoparticles have been reported for both terrestrial and aquatic organisms, but the toxic effects of the substances on marine organisms remain poorly understood. The main aim of this study was to evaluate the genotoxicity of TiO2-NP in the marine fish Trachinotus carolinus, through cytogenotoxic methods. The fish received two different doses of 1.5 μg and 3.0 μg-TiO2-NP g(-1) by intraperitoneal injection. Blood samples were collected to analyze erythrocyte viability using the Trypan Blue exclusion test, comet assay (pH>13), micronucleus (MN) and other erythrocyte nuclear abnormalities (ENA) 24, 48 and 72 h after injection. The possible cell uptake of TiO2-NP in fish injected with the higher dose was investigated after 72 h using transmission electron microscopy (TEM). The results showed that TiO2-NP is genotoxic and potentially cytotoxic for this species, causing DNA damage, inducing the formation of MN and other ENA, and decreasing erythrocyte viability. TEM examination revealed that cell uptake of TiO2-NP was mainly in the kidney, liver, gills and to a lesser degree in muscle. To the extent of the authors' knowledge, this is the first in vivo study of genotoxicity and other effects of TiO2-NP in a marine fish.

Inflammatory response of lung macrophages and epithelial cells after exposure to redox active nanoparticles: effect of solubility and antioxidant treatment

The effects of an exposure to three mass-produced metal oxide nanoparticles-similar in size and specific surface area but different in redox activity and solubility-were studied in rat alveolar macrophages (MAC) and epithelial cells (AEC). We hypothesized that the cell response depends on the particle redox activity and solubility determining the amount of reactive oxygen species formation (ROS) and subsequent inflammatory response. MAC and AEC were exposed to different amounts of Mn3O4 (soluble, redox-active), CeO2 (insoluble, redox-active), and TiO2 (insoluble, redox-inert) up to 24 h. Viability and inflammatory response were monitored with and without coincubation of a free-radical scavenger (trolox). In MAC elevated ROS levels, decreased metabolic activity and attenuated inflammatory mediator secretion were observed in response to Mn3O4. Addition of trolox partially resolved these changes. In AEC, decreased metabolic activity and an attenuated inflammatory mediator secretion were found in response to CeO2 exposure without increased production of ROS, thus not sensitive to trolox administration. Interestingly, highly redox-active soluble particles did not provoke an inflammatory response. The data reveal that target and effector cells of the lung react in different ways to particle exposure making a prediction of the response depending on redox activity and intracellular solubility difficult.

Comparative lung toxicity of engineered nanomaterials utilizing in vitro, ex vivo and in vivo approaches

Background

Although engineered nanomaterials (ENM) are currently regulated either in the context of a new chemical, or as a new use of an existing chemical, hazard assessment is still to a large extent reliant on information from historical toxicity studies of the parent compound, and may not take into account special properties related to the small size and high surface area of ENM. While it is important to properly screen and predict the potential toxicity of ENM, there is also concern that current toxicity tests will require even heavier use of experimental animals, and reliable alternatives should be developed and validated. Here we assessed the comparative respiratory toxicity of ENM in three different methods which employed in vivo, in vitro and ex vivo toxicity testing approaches.

Methods

Toxicity of five ENM (SiO₂ (10), CeO₂ (23), CeO₂ (88), TiO₂ (10), and TiO₂ (200); parentheses indicate average ENM diameter in nm) were tested in this study. CD-1 mice were exposed to the ENM by oropharyngeal aspiration at a dose of 100 μg. Mouse lung tissue slices and alveolar macrophages were also exposed to the ENM at concentrations of 22–132 and 3.1-100 μg/mL, respectively. Biomarkers of lung injury and inflammation were assessed at 4 and/or 24 hr post-exposure.

Results

Small-sized ENM (SiO₂ (10), CeO₂ (23), but not TiO₂ (10)) significantly elicited pro-inflammatory responses in mice (in vivo), suggesting that the observed toxicity in the lungs was dependent on size and chemical composition. Similarly, SiO₂ (10) and/or CeO₂ (23) were also more toxic in the lung tissue slices (ex vivo) and alveolar macrophages (in vitro) compared to other ENM. A similar pattern of inflammatory response (e.g., interleukin-6) was observed in both ex vivo and in vitro when a dose metric based on cell surface area (μg/cm²), but not culture medium volume (μg/mL) was employed.

Conclusion

Exposure to ENM induced acute lung inflammatory effects in a size- and chemical composition-dependent manner. The cell culture and lung slice techniques provided similar profiles of effect and help bridge the gap in our understanding of in vivo, ex vivo, and in vitro toxicity outcomes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-014-0047-3) contains supplementary material, which is available to authorized users.

From basic physics to mechanisms of toxicity: the "liquid drop" approach applied to develop predictive classification models for toxicity of metal oxide nanoparticles

Many metal oxide nanoparticles are able to cause persistent stress to live organisms, including humans, when discharged to the environment. To understand the mechanism of metal oxide nanoparticles' toxicity and reduce the number of experiments, the development of predictive toxicity models is important. In this study, performed on a series of nanoparticles, the comparative quantitative-structure activity relationship (nano-QSAR) analyses of their toxicity towards E. coli and HaCaT cells were established. A new approach for representation of nanoparticles' structure is presented. For description of the supramolecular structure of nanoparticles the "liquid drop" model was applied. It is expected that a novel, proposed approach could be of general use for predictions related to nanomaterials. In addition, in our study fragmental simplex descriptors and several ligand-metal binding characteristics were calculated. The developed nano-QSAR models were validated and reliably predict the toxicity of all studied metal oxide nanoparticles. Based on the comparative analysis of contributed properties in both models the LDM-based descriptors were revealed to have an almost similar level of contribution to toxicity in both cases, while other parameters (van der Waals interactions, electronegativity and metal-ligand binding characteristics) have unequal contribution levels. In addition, the models developed here suggest different mechanisms of nanotoxicity for these two types of cells.

The Yin: An adverse health perspective of nanoceria: uptake, distribution, accumulation, and mechanisms of its toxicity

This critical review evolved from a SNO Special Workshop on Nanoceria panel presentation addressing the toxicological risks of nanoceria: accumulation, target organs, and issues of clearance; how exposure dose/concentration, exposure route, and experimental preparation/model influence the different reported effects of nanoceria; and how can safer by design concepts be applied to nanoceria? It focuses on the most relevant routes of human nanoceria exposure and uptake, disposition, persistence, and resultant adverse effects. The pulmonary, oral, dermal, and topical ocular exposure routes are addressed as well as the intravenous route, as the latter provides a reference for the pharmacokinetic fate of nanoceria once introduced into blood. Nanoceria reaching the blood is primarily distributed to mononuclear phagocytic system organs. Available data suggest nanoceria's distribution is not greatly affected by dose, shape, or dosing schedule. Significant attention has been paid to the inhalation exposure route. Nanoceria distribution from the lung to the rest of the body is less than 1% of the deposited dose, and from the gastrointestinal tract even less. Intracellular nanoceria and organ burdens persist for at least months, suggesting very slow clearance rates. The acute toxicity of nanoceria is very low. However, large/accumulated doses produce granuloma in the lung and liver, and fibrosis in the lung. Toxicity, including genotoxicity, increases with exposure time; the effects disappear slowly, possibly due to nanoceria's biopersistence. Nanoceria may exert toxicity through oxidative stress. Adverse effects seen at sites distal to exposure may be due to nanoceria translocation or released biomolecules. An example is elevated oxidative stress indicators in the brain, in the absence of appreciable brain nanoceria. Nanoceria may change its nature in biological environments and cause changes in biological molecules. Increased toxicity has been related to greater surface Ce3+, which becomes more relevant as particle size decreases and the ratio of surface area to volume increases. Given its biopersistence and resulting increased toxicity with time, there is a risk that long-term exposure to low nanoceria levels may eventually lead to adverse health effects. This critical review provides recommendations for research to resolve some of the many unknowns of nanoceria's fate and adverse effects.

Comparative iron oxide nanoparticle cellular dosimetry and response in mice by the inhalation and liquid cell culture exposure routes

Background

Toxicity testing the rapidly growing number of nanomaterials requires large scale use of in vitro systems under the presumption that these systems are sufficiently predictive or descriptive of responses in in vivo systems for effective use in hazard ranking. We hypothesized that improved relationships between in vitro and in vivo models of experimental toxicology for nanomaterials would result from placing response data in vitro and in vivo on the same dose scale, the amount of material associated with cells.

Methods

Balb/c mice were exposed nose-only to an aerosol (68.6 nm CMD, 19.9 mg/m³, 4 hours) generated from of 12.8 nm superparamagnetic iron oxide particles (SPIO). Target cell doses were calculated, histological evaluations conducted, and biomarkers of response were identified by global transcriptomics. Representative murine epithelial and macrophage cell types were exposed in vitro to the same material in liquid suspension for four hours and levels of nanoparticle regulated cytokine transcripts identified in vivo were quantified as a function of measured nanoparticle cellular dose.

Results

Target tissue doses of 0.009-0.4 μg SPIO/cm² in lung led to an inflammatory response in the alveolar region characterized by interstitial inflammation and macrophage infiltration. In vitro, higher target tissue doses of ~1.2-4 μg SPIO/ cm² of cells were required to induce transcriptional regulation of markers of inflammation, CXCL2 & CCL3, in C10 lung epithelial cells. Estimated in vivo macrophage SPIO nanoparticle doses ranged from 1-100 pg/cell, and induction of inflammatory markers was observed in vitro in macrophages at doses of 8-35 pg/cell.

Conclusions

Application of target tissue dosimetry revealed good correspondence between target cell doses triggering inflammatory processes in vitro and in vivo in the alveolar macrophage population, but not in the epithelial cells of the alveolar region. These findings demonstrate the potential for target tissue dosimetry to enable the more quantitative comparison of in vitro and in vivo systems and advance their use for hazard assessment and extrapolation to humans. The mildly inflammogentic cellular doses experienced by mice were similar to those calculated for humans exposed to the same material at the existing permissible exposure limit of 10 mg/m³ iron oxide (as Fe).

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0046-4) contains supplementary material, which is available to authorized users.

Effects of water and cell culture media on the physicochemical properties of ZnMgO nanoparticles and their toxicity toward mammalian cells

ZnMgO nanoparticles have shown potential for medical applications as an efficient antibacterial agent. In this work, we investigate the effect of water and two commonly used cell culture media on the physicochemical properties of ZnMgO nanoparticles in correlation with their cytotoxicity. In vacuum, ZnMgO nanopowder consists of MgO (nanocubes) and ZnO (nanotetrapods and nanorods) particles. Upon exposure to water or the Luria-Bertani solution, ZnO characteristic shapes were not observable while MgO nanocubes transformed into octahedral form. In addition, water caused morphological alternations in form of disordered and fragmented structures. This effect was directly reflected in UV/vis absorption properties of ZnMgO, implying that formation of new states within the band gap of ZnO and redistribution of specific sites on MgO surfaces occurs in the presence of water. In mammalian culture cell medium, ZnMgO nanoparticles were shapeless, agglomerated, and coated with surrounding proteins. Serum albumin was found to adsorb as a major but not the only protein. Adsorbed albumin mainly preserved its α-helix secondary structure. Finally, the cytotoxicity of ZnMgO was shown to strongly depend on the environment: in the presence of serum proteins ZnMgO nanopowder was found to be safe for mammalian cells while highly toxic in a serum-free medium or a medium containing only albumin. Our results demonstrate that nanostructured ZnMgO reaches living cells with modified morphology and surface structure when compared to as-synthesized particles kept in vacuum. In addition, its biocompatibility can be modulated by proteins from biological environment.

Promoting cell proliferation using water dispersible germanium nanowires

Group IV Nanowires have strong potential for several biomedical applications. However, to date their use remains limited because many are synthesised using heavy metal seeds and functionalised using organic ligands to make the materials water dispersible. This can result in unpredicted toxic side effects for mammalian cells cultured on the wires. Here, we describe an approach to make seedless and ligand free Germanium nanowires water dispersible using glutamic acid, a natural occurring amino acid that alleviates the environmental and health hazards associated with traditional functionalisation materials. We analysed the treated material extensively using Transmission electron microscopy (TEM), High resolution-TEM, and scanning electron microscope (SEM). Using a series of state of the art biochemical and morphological assays, together with a series of complimentary and synergistic cellular and molecular approaches, we show that the water dispersible germanium nanowires are non-toxic and are biocompatible. We monitored the behaviour of the cells growing on the treated germanium nanowires using a real time impedance based platform (xCELLigence) which revealed that the treated germanium nanowires promote cell adhesion and cell proliferation which we believe is as a result of the presence of an etched surface giving rise to a collagen like structure and an oxide layer. Furthermore this study is the first to evaluate the associated effect of Germanium nanowires on mammalian cells. Our studies highlight the potential use of water dispersible Germanium Nanowires in biological platforms that encourage anchorage-dependent cell growth.

High content analysis provides mechanistic insights on the pathways of toxicity induced by amine-modified polystyrene nanoparticles

The fast-paced development of nanotechnology needs the support of effective safety testing. We have developed a screening platform measuring simultaneously several cellular parameters for exposure to various concentrations of nanoparticles (NPs). Cell lines representative of different organ cell types, including lung, endothelium, liver, kidney, macrophages, glia, and neuronal cells were exposed to 50 nm amine-modified polystyrene (PS-NH₂) NPs previously reported to induce apoptosis and to 50 nm sulphonated and carboxyl-modified polystyrene NPs that were reported to be silent. All cell lines apart from Raw 264.7 executed apoptosis in response to PS-NH₂ NPs, showing specific sequences of EC50 thresholds; lysosomal acidification was the most sensitive parameter. Loss of mitochondrial membrane potential and plasma membrane integrity measured by High Content Analysis resulted comparably sensitive to the equivalent OECD-recommended assays, allowing increased output. Analysis of the acidic compartments revealed good cerrelation between size/fluorescence intensity and dose of PS-NH₂ NPs applied; moreover steatosis and phospholipidosis were observed, consistent with the lysosomal alterations revealed by Lysotracker green; similar responses were observed when comparing astrocytoma cells with primary astrocytes. We have established a platform providing mechanistic insights on the response to exposure to nanoparticles. Such platform holds great potential for in vitro screening of nanomaterials in highthroughput format.

Biosynthesis of stable antioxidant ZnO nanoparticles by Pseudomonas aeruginosa rhamnolipids

During the last several years, various chemical methods have been used for synthesis of a variety of metal nanoparticles. Most of these methods pose severe environmental problems and biological risks; therefore the present study reports a biological route for synthesis of zinc oxide nanoparticles using Pseudomonas aeruginosa rhamnolipids (RLs) (denoted as RL@ZnO) and their antioxidant property. Formation of stable RL@ZnO nanoparticles gave mostly spherical particles with a particle size ranging from 35 to 80 nm. The RL@ZnO nanoparticles were characterized by UV-visible (UV–vis) spectroscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), and thermal gravimetric analysis. The UV–vis spectra presented a characteristic absorbance peak at ∼360 nm for synthesized RL@ZnO nanoparticles. The XRD spectrum showed that RL@ZnO nanoparticles are crystalline in nature and have typical wurtzite type polycrystals. Antioxidant potential of RL@ZnO nanoparticles was assessed through 2,2–diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, and superoxide anion free radicals with varying concentration and time of the storage up to 15 months, while it was found to decline in bare ZnO nanoparticles. Similarly, the inhibitory effects on β-carotene oxidation and lipid peroxidation were also observed. These results elucidate the significance of P. aeruginosa RL as effective stabilizing agents to develop surface protective ZnO nanoparticles, which can be used as promising antioxidants in biological system.

Rational design of gold nanoparticle toxicology assays: a question of exposure scenario, dose and experimental setup

Many studies have evaluated the toxicity of gold nanoparticles, although reliable predictions based on these results are rare. In order to overcome this problem, this article highlights strategies to improve comparability and standardization of nanotoxicological studies. To this end, it is proposed that we should adapt the nanomaterial to the addressed exposure scenario, using ligand-free nanoparticle references in order to differentiate ligand effects from size effects. Furthermore, surface-weighted particle dosing referenced to the biologically relevant parameter (e.g., cell number or organ mass) is proposed as the gold standard. In addition, it is recommended that we should shift the focus of toxicological experiments from ‘live–dead’ assays to the assessment of cell function, as this strategy allows observation of bioresponses at lower doses that are more relevant for in vivo scenarios.

Association rule mining of cellular responses induced by metal and metal oxide nanoparticles

Relationships among fourteen different biological responses (including ten signaling pathway activities and four cytotoxicity effects) of murine macrophage (RAW264.7) and bronchial epithelial (BEAS-2B) cells exposed to six metal and metal oxide nanoparticles (NPs) were analyzed using both statistical and data mining approaches. Both the pathway activities and cytotoxicity effects were assessed using high-throughput screening (HTS) over an exposure period of up to 24 h and concentration range of 0.39-200 mg L(-1). HTS data were processed by outlier removal, normalization, and hit-identification (for significantly regulated cellular responses) to arrive at reliable multiparametric bioactivity profiles for the NPs. Association rule mining was then applied to the bioactivity profiles followed by a pruning process to remove redundant rules. The non-redundant association rules indicated that "significant regulation" of one or more cellular responses implies regulation of other (associated) cellular response types. Pairwise correlation analysis (via Pearson's χ(2) test) and self-organizing map clustering of the different cellular response types indicated consistency with the identified non-redundant association rules. Furthermore, in order to explore the potential use of association rules as a tool for data-driven hypothesis generation, specific pathway activity experiments were carried out for ZnO NPs. The experimental results confirmed the association rule identified for the p53 pathway and mitochondrial superoxide levels (via MitoSox reagent) and further revealed that blocking of the transcriptional activity of p53 lowered the MitoSox signal. The present approach of using association rule mining for data-driven hypothesis generation has important implications for streamlining multi-parameter HTS assays, improving the understanding of NP toxicity mechanisms, and selection of endpoints for the development of nanomaterial structure-activity relationships.

Exposure of cerium oxide nanoparticles to kidney bean shows disturbance in the plant defense mechanisms

Overwhelming use of engineered nanoparticles demands rapid assessment of their environmental impacts. The transport of cerium oxide nanoparticles (nCeO2) in plants and their impact on cellular homeostasis as a function of exposure duration is not well understood. In this study, kidney bean plants were exposed to suspensions of ∼ 8 ± 1 nm nCeO2 (62.5 to 500 mg/L) for 15 days in hydroponic conditions. Plant parts were analyzed for cerium accumulation after one, seven, and 15 days of nCeO2 exposure. The primary indicators of stress like lipid peroxidation, antioxidant enzyme activities, total soluble protein and chlorophyll contents were studied. Cerium in tissues was localized using scanning electron microscopy and synchrotron μ-XRF mapping, and the chemical forms were identified using μ-XANES. In the root epidermis, cerium was primarily shown to exist as nCeO2, although a small fraction (12%) was biotransformed to Ce(III) compound. Cerium was found to reach the root vascular tissues and translocate to aerial parts with time. Upon prolonged exposure to 500 mg nCeO2/L, the root antioxidant enzyme activities were significantly reduced, simultaneously increasing the root soluble protein by 204%. In addition, leaf's guaiacol peroxidase activity was enhanced with nCeO2 exposure in order to maintain cellular homeostasis.

Cytotoxicity of ZnO Nanoparticles Can Be Tailored by Modifying Their Surface Structure: A Green Chemistry Approach for Safer Nanomaterials

ZnO nanoparticles (NP) are extensively used in numerous nanotechnology applications; however, they also happen to be one of the most toxic nanomaterials. This raises significant environmental and health concerns and calls for the need to develop new synthetic approaches to produce safer ZnO NP, while preserving their attractive optical, electronic, and structural properties. In this work, we demonstrate that the cytotoxicity of ZnO NP can be tailored by modifying their surface-bound chemical groups, while maintaining the core ZnO structure and related properties. Two equally sized (9.26 ± 0.11 nm) ZnO NP samples were synthesized from the same zinc acetate precursor using a forced hydrolysis process, and their surface chemical structures were modified by using different reaction solvents. X-ray diffraction and optical studies showed that the lattice parameters, optical properties, and band gap (3.44 eV) of the two ZnO NP samples were similar. However, FTIR spectroscopy showed significant differences in the surface structures and surface-bound chemical groups. This led to major differences in the zeta potential, hydrodynamic size, photocatalytic rate constant, and more importantly, their cytotoxic effects on Hut-78 cancer cells. The ZnO NP sample with the higher zeta potential and catalytic activity displayed a 1.5-fold stronger cytotoxic effect on cancer cells. These results suggest that by modifying the synthesis parameters/conditions and the surface chemical structures of the nanocrystals, their surface charge density, catalytic activity, and cytotoxicity can be tailored. This provides a green chemistry approach to produce safer ZnO NP.

Towards understanding mechanisms governing cytotoxicity of metal oxides nanoparticles: hints from nano-QSAR studies

The production of nanomaterials increases every year exponentially and therefore the probability these novel materials that they could cause adverse outcomes for human health and the environment also expands rapidly. We proposed two types of mechanisms of toxic action that are collectively applied in a nano-QSAR model, which provides governance over the toxicity of metal oxide nanoparticles to the human keratinocyte cell line (HaCaT). The combined experimental-theoretical studies allowed the development of an interpretative nano-QSAR model describing the toxicity of 18 nano-metal oxides to the HaCaT cell line, which is a common in vitro model for keratinocyte response during toxic dermal exposure. The comparison of the toxicity of metal oxide nanoparticles to bacteria Escherichia coli (prokaryotic system) and a human keratinocyte cell line (eukaryotic system), resulted in the hypothesis that different modes of toxic action occur between prokaryotic and eukaryotic systems.

The coating makes the difference: acute effects of iron oxide nanoparticles on Daphnia magna

The surface of nanoparticles (NP) is often functionalized with a capping agent to increase their colloidal stability. Having a strong effect on the characteristics of NP, the coating might already determine the risk from NP to organisms and the environment. In this study identical iron oxide nanoparticles (IONP; Ø 5-6nm) were functionalized with four different coatings: ascorbate (ASC-IONP), citrate (CIT-IONP), dextran (DEX-IONP), and polyvinylpyrrolidone (PVP-IONP). Ascorbate and citrate stabilize NP via electrostatic repulsion whereas dextran and polyvinylpyrrolidone are steric stabilizers. All IONP were colloidally stable over several weeks. Their acute effects on neonates of the waterflea Daphnia magna were investigated over 96h. The highest immobilizing effect was found for ASC- and DEX-IONP. In the presence of neonates, both agglomerated or flocculated and adsorbed to the carapace and filtering apparatuses, inducing high immobilization. Lower immobilization was found for CIT-IONP. Their effect was hypothesized to partly originate from an increased release of dissolved iron and the ability to form reactive oxygen species (ROS). Furthermore, incomplete ecdysis occurred at high concentrations of ASC-, DEX-, and CIT-IONP. PVP-IONP did not induce any negative effect, although high quantities were visibly ingested by the daphnids. PVP-IONP had the highest colloidal stability without any occurring agglomeration, adsorption, or dissolution. Only strong swelling of the PVP coating was observed in medium, highly increasing the hydrodynamic diameter. Each coating caused individual effects. Toxicity cannot be correlated to hydrodynamic diameter or the kind of stabilizing forces. Effects are rather linked to decreasing colloidal stability, the release of ions from the core material or the ability to form ROS, respectively.

Emergent Properties and Toxicological Considerations for Nanohybrid Materials in Aquatic Systems

Conjugation of multiple nanomaterials has become the focus of recent materials development. This new material class is commonly known as nanohybrids or "horizon nanomaterials". Conjugation of metal/metal oxides with carbonaceous nanomaterials and overcoating or doping of one metal with another have been pursued to enhance material performance and/or incorporate multifunctionality into nano-enabled devices and processes. Nanohybrids are already at use in commercialized energy, electronics and medical products, which warrant immediate attention for their safety evaluation. These conjugated ensembles likely present a new set of physicochemical properties that are unique to their individual component attributes, hence increasing uncertainty in their risk evaluation. Established toxicological testing strategies and enumerated underlying mechanisms will thus need to be re-evaluated for the assessment of these horizon materials. This review will present a critical discussion on the altered physicochemical properties of nanohybrids and analyze the validity of existing nanotoxicology data against these unique properties. The article will also propose strategies to evaluate the conjugate materials' safety to help undertake future toxicological research on the nanohybrid material class.

Effects of an iron-based fuel-borne catalyst and a diesel particle filter on exhaust toxicity in lung cells in vitro

Metal-containing fuel additives catalyzing soot combustion in diesel particle filters are used in a widespread manner, and with the growing popularity of diesel vehicles, their application is expected to increase in the near future. Detailed investigation into how such additives affect exhaust toxicity is therefore necessary and has to be performed before epidemiological evidence points towards adverse effects of their application. The present study investigates how the addition of an iron-based fuel additive (Satacen®3, 40 ppm Fe) to low-sulfur diesel affects the in vitro cytotoxic, oxidative, (pro-)inflammatory, and mutagenic activity of the exhaust of a passenger car operated under constant, low-load conditions by exposing a three-dimensional model of the human airway epithelium to complete exhaust at the air-liquid interface. We could show that the use of the iron catalyst without and with filter technology has positive as well as negative effects on exhaust toxicity compared to exhaust with no additives: it decreases the oxidative and, compared to a non-catalyzed diesel particle filter, the mutagenic potential of diesel exhaust, but increases (pro-)inflammatory effects. The presence of a diesel particle filter also influences the impact of Satacen®3 on exhaust toxicity, and the proper choice of the filter type to be used is of importance with regards to exhaust toxicity. Figure ᅟ.

Aspect ratio plays a role in the hazard potential of CeO2 nanoparticles in mouse lung and zebrafish gastrointestinal tract

We have previously demonstrated that there is a relationship between the aspect ratio (AR) of CeO2 nanoparticles and in vitro hazard potential. CeO2 nanorods with AR ≥ 22 induced lysosomal damage and progressive effects on IL-1β production and cytotoxicity in the human myeloid cell line, THP-1. In order to determine whether this toxicological paradigm for long aspect ratio (LAR) CeO2 is also relevant in vivo, we performed comparative studies in the mouse lung and gastrointestinal tract (GIT) of zebrafish larvae. Although oropharyngeal aspiration could induce acute lung inflammation for CeO2 nanospheres and nanorods, only the nanorods with the highest AR (C5) induced significant IL-1β and TGF-β1 production in the bronchoalveolar lavage fluid at 21 days but did not induce pulmonary fibrosis. However, after a longer duration (44 days) exposure to 4 mg/kg of the C5 nanorods, more collagen production was seen with CeO2 nanorods vs nanospheres after correcting for Ce lung burden. Using an oral-exposure model in zebrafish larvae, we demonstrated that C5 nanorods also induced significant growth inhibition, a decrease in body weight, and delayed vertebral calcification. In contrast, CeO2 nanospheres and shorter nanorods had no effect. Histological and transmission electron microscopy analyses showed that the key injury mechanism of C5 was in the epithelial lining of the GIT, which demonstrated blunted microvilli and compromised digestive function. All considered, these data demonstrate that, similar to cellular studies, LAR CeO2 nanorods exhibit more toxicity in the lung and GIT, which could be relevant to inhalation and environmental hazard potential.