Rationale of genotoxicity testing of nanomaterials: regulatory requirements and appropriateness of available OECD test guidelines

The State of the Art and Challenges of In Vitro Methods for Human Hazard Assessment of Nanomaterials in the Context of Safe-by-Design

The Safe-by-Design (SbD) concept aims to facilitate the development of safer materials/products, safer production, and safer use and end-of-life by performing timely SbD interventions to reduce hazard, exposure, or both. Early hazard screening is a crucial first step in this process. In this review, for the first time, commonly used in vitro assays are evaluated for their suitability for SbD hazard testing of nanomaterials (NMs). The goal of SbD hazard testing is identifying hazard warnings in the early stages of innovation. For this purpose, assays should be simple, cost-effective, predictive, robust, and compatible. For several toxicological endpoints, there are indications that commonly used in vitro assays are able to predict hazard warnings. In addition to the evaluation of assays, this review provides insights into the effects of the choice of cell type, exposure and dispersion protocol, and the (in)accurate determination of dose delivered to cells on predictivity. Furthermore, compatibility of assays with challenging advanced materials and NMs released from nano-enabled products (NEPs) during the lifecycle is assessed, as these aspects are crucial for SbD hazard testing. To conclude, hazard screening of NMs is complex and joint efforts between innovators, scientists, and regulators are needed to further improve SbD hazard testing.

DNA Oxidative Damage as a Sensitive Genetic Endpoint to Detect the Genotoxicity Induced by Titanium Dioxide Nanoparticles

The genotoxicity of nanomaterials has attracted great attention in recent years. As a possible occupational carcinogen, the genotoxic effects and underlying mechanisms of titanium dioxide nanoparticles (TiO2 NPs) have been of particular concern. In this study, the effect of TiO2 NPs (0, 25, 50 and 100 µg/mL) on DNA damage and the role of oxidative stress were investigated using human bronchial epithelial cells (BEAS-2B) as an in vitro model. After detailed characterization, the cytotoxicity of TiO2 NPs was detected. Through transmission electron microscopy (TEM), we found that TiO2 NPs entered the cytoplasm but did not penetrate deep into the nucleus of cells. The intracellular levels of reactive oxygen species (ROS) significantly increased in a dose-dependent manner and the ratios of GSH/GSSG also significantly decreased. The results of the normal comet assay were negative, while the Fpg-modified comet assay that specifically detected DNA oxidative damage was positive. Meanwhile, N-acetyl-L-cysteine (NAC) intervention inhibited the oxidative stress and genotoxicity induced by TiO2 NPs. Therefore, it was suggested that TiO2 NPs could induce cytotoxicity, oxidative stress and DNA oxidative damage in BEAS-2B cells. DNA oxidative damage may be a more sensitive genetic endpoint to detect the genotoxicity of TiO2 NPs.

Nanosafety: An Evolving Concept to Bring the Safest Possible Nanomaterials to Society and Environment

The use of nanomaterials has been increasing in recent times, and they are widely used in industries such as cosmetics, drugs, food, water treatment, and agriculture. The rapid development of new nanomaterials demands a set of approaches to evaluate the potential toxicity and risks related to them. In this regard, nanosafety has been using and adapting already existing methods (toxicological approach), but the unique characteristics of nanomaterials demand new approaches (nanotoxicology) to fully understand the potential toxicity, immunotoxicity, and (epi)genotoxicity. In addition, new technologies, such as organs-on-chips and sophisticated sensors, are under development and/or adaptation. All the information generated is used to develop new in silico approaches trying to predict the potential effects of newly developed materials. The overall evaluation of nanomaterials from their production to their final disposal chain is completed using the life cycle assessment (LCA), which is becoming an important element of nanosafety considering sustainability and environmental impact. In this review, we give an overview of all these elements of nanosafety.

Physiological homeostasis alteration and cellular structure damage of Chlorella vulgaris exposed to silver nanoparticles with various microstructural morphologies

The toxicity of silver nanoparticles (AgNPs) with a single morphology to aquatic organisms has been well demonstrated in the past decade, but few studies have been carried out to evaluate the differences in toxicity among AgNPs with various microstructural morphologies. In this work, C. vulgaris was used as the tested organism to examine the differences in toxic effects among AgNSs, AgNCs, and AgPLs at concentrations of 0.5, 1.0, 2.0, and 5.0 mg/L. The results showed that the cell density and chlorophyll a content of C. vulgaris decreased when the dose of AgNPs was increased, while the inhibiting effects that were caused by AgPLs were stronger than those that were caused by AgNCs and AgNSs. Under short-term exposure to AgPLs, the ROS content was significantly higher than those under exposure to AgNCs and AgNSs, while the MDA content fluctuated without obvious regularity. The dose of AgPLs affected the antioxidative enzyme activity and lipid peroxidation more obviously than those of AgNSs and AgNCs. The superoxide dismutase and catalase contents in the former case were distinctly higher than those in the latter cases. Consequently, the cell apoptosis rate under exposure to AgPLs reached 83%, which was higher than those under exposure to AgNSs (50%) and AgNCs (71%). This work shows that the level of toxicity to C. vulgaris was in the order of AgPLs > AgNCs > AgNSs. The obtained results demonstrate that the microstructural morphologies of AgNPs determined their potential toxicity.

Biocompatibility and Cytotoxicity of Gold Nanoparticles: Recent Advances in Methodologies and Regulations

Recent advances in the synthesis of metal nanoparticles (MeNPs), and more specifically gold nanoparticles (AuNPs), have led to tremendous expansion of their potential applications in different fields, ranging from healthcare research to microelectronics and food packaging. The properties of functionalised MeNPs can be fine-tuned depending on their final application, and subsequently, these properties can strongly modulate their biological effects. In this review, we will firstly focus on the impact of MeNP characteristics (particularly of gold nanoparticles, AuNPs) such as shape, size, and aggregation on their biological activities. Moreover, we will detail different in vitro and in vivo assays to be performed when cytotoxicity and biocompatibility must be assessed. Due to the complex nature of nanomaterials, conflicting studies have led to different views on their safety, and it is clear that the definition of a standard biosafety label for AuNPs is difficult. In fact, AuNPs' biocompatibility is strongly affected by the nanoparticles' intrinsic characteristics, biological target, and methodology employed to evaluate their toxicity. In the last part of this review, the current legislation and requirements established by regulatory authorities, defining the main guidelines and standards to characterise new nanomaterials, will also be discussed, as this aspect has not been reviewed recently. It is clear that the lack of well-established safety regulations based on reliable, robust, and universal methodologies has hampered the development of MeNP applications in the healthcare field. Henceforth, the international community must make an effort to adopt specific and standard protocols for characterisation of these products.

AC/DC magnetic device for safe medical use of potentially harmful magnetic nanocarriers

Continuing our previous research work on a drug delivery system based on combined AC/DC magnetic fields, we have developed a prototype AC/DC magnetic syringe device for stimulation of drug release from drug carriers, with the options of injecting/removing drug carriers. The porous Fe₃O₄ carrier, in a dose-dependent manner, causes acute oxidative damage and reduces the viability of differentiated SH-SY5Y human neuroblastoma cells, indicating the necessity for its removal once it reaches the therapeutic concentration at the target tissue. The working mechanism of the device consists of three simple steps. First, direct injection of the drug adsorbed on the surface of a carrier via a needle inserted into the targeted area. The second step is stimulation of drug release using a combination of AC magnetic field (a coil magnetised needle with AC current) and permanent magnets (DC magnetic lens outside of the body), and the third step is removal of the drug carriers from the injected area after the completion of drug release by magnetising the tip of the needle with DC current. Removing the drug carriers allows us to avoid possible acute and long term side effects of the drug carriers in the patient's body, as well as any potential response of the body to the drug carriers.

Recent advances in the applications of nano-agrochemicals for sustainable agricultural development

Modern agricultural practices have triggered the process of agricultural pollution. This process can cause the degradation of eco-systems, land, and environment owing to the modern-day by-products of agriculture. The substantial use of chemical fertilizers, pesticides, and, contaminated water for irrigation cause further damage to agriculture. The current scenario of the agriculture and food sector has therefore become unsustainable. Nanotechnology has provided innovative and resourceful frontiers to the agriculture sector by contributing practical applications in conventional agricultural ways and practices. There is a large possibility that agri-nanotechnology can have a significant impact on the sustainable agriculture and crop growth. Recent research has shown the potential of nanotechnology in improving the agriculture sector by enhancing the efficiency of agricultural inputs and providing solutions to agricultural problems for improving food productivity and security. The prospective use of nanoscale agrochemicals such as nanofertilizers, nanopesticides, nanosensors, and nanoformulations in agriculture has transformed traditional agro-practices, making them more sustainable and efficient. However, the application of these nano-products in real field situations raises concern about nanomaterial safety, exposure levels, and toxicological repercussions to the environment and human health. The present review gives an insight into recent advancements in nanotechnology-based agrochemicals that have revolutionized the agriculture sector. Further, the implementation barriers related to the nanomaterial use in agriculture, their commercialization potential, and the need for policy regulations to assess possible nano-agricultural risks are also discussed.

Nanotoxicological study of downconversion Y2 O3 :Eu3+ luminescent nanoparticles functionalized with folic acid for cancer cells bioimaging

Luminescent lanthanide downconversion nanoparticles (DCNPs) provide a combination of high luminescence intensity, sharp emission peaks with narrow bandwidth and a large Stokes' shift, leading to high-performance biomedical applications mainly for imaging. The purpose of this study is to present a nanotoxicological study of DCNPs Y₂ O₃ codoped with Eu³⁺ and functionalized with folic acid (FA). These assessments include cytotoxicity, genotoxicity, hemocompatibility, and in vitro inflammatory studies. We demonstrated by flow cytometry and confocal microscope the internalization of FA-DCNPs in breast cancer and melanoma cells. They were synthesized by sol-gel method and coated with a thin silica shell to make them biocompatible; also they were functionalized with amino groups and FA ligands that bind to the folate receptors (FR) located on the surface of the cancer cells studied. This functionalization enables the DCNPs to be internalized into the cancer cells via endocytosis by the conjugation FA-FR. The DCNPs were characterized with transmission electron microscope, Fourier transform infrared spectroscopy and photoluminescence. The nanotoxicological assessments demonstrated that both nanoparticles (bare and functionalized) are no cytotoxic and no genotoxic at the tested concentrations (0.01-20 μg/mL) in three cell lines (breast, skin cancer, and osteoblasts). Also they are hemocompatible and do not exert nitric oxide production in vitro by macrophages. The FA-DCNPs were clearly localized into the cell cytoplasm with bright red luminescence. Thus, herein we present a complete nanotoxicological study of FA-DCNPs Y₂ O₃ codoped with Eu³⁺ and we conclude that these nanoparticles are biocompatible and can be further used for cancer cells bioimaging.

Genotoxicity Assessment of Nanomaterials: Recommendations on Best Practices, Assays, and Methods

Nanomaterials (NMs) present unique challenges in safety evaluation. An international working group, the Genetic Toxicology Technical Committee of the International Life Sciences Institute's Health and Environmental Sciences Institute, has addressed issues related to the genotoxicity assessment of NMs. A critical review of published data has been followed by recommendations on methods alterations and best practices for the standard genotoxicity assays: bacterial reverse mutation (Ames); in vitro mammalian assays for mutations, chromosomal aberrations, micronucleus induction, or DNA strand breaks (comet); and in vivo assays for genetic damage (micronucleus, comet and transgenic mutation assays). The analysis found a great diversity of tests and systems used for in vitro assays; many did not meet criteria for a valid test, and/or did not use validated cells and methods in the Organization for Economic Co-operation and Development Test Guidelines, and so these results could not be interpreted. In vivo assays were less common but better performed. It was not possible to develop conclusions on test system agreement, NM activity, or mechanism of action. However, the limited responses observed for most NMs were consistent with indirect genotoxic effects, rather than direct interaction of NMs with DNA. We propose a revised genotoxicity test battery for NMs that includes in vitro mammalian cell mutagenicity and clastogenicity assessments; in vivo assessments would be added only if warranted by information on specific organ exposure or sequestration of NMs. The bacterial assays are generally uninformative for NMs due to limited particle uptake and possible lack of mechanistic relevance, and are thus omitted in our recommended test battery for NM assessment. Recommendations include NM characterization in the test medium, verification of uptake into target cells, and limited assay-specific methods alterations to avoid interference with uptake or endpoint analysis. These recommendations are summarized in a Roadmap guideline for testing.

Evaluation of genotoxicity and coumarin production in conventional and organic cultivation systems of Mikania glomerata Spreng

Mikania glomerata Sprengel, popularly known as "guaco," is used in Brazilian folk medicine for several inflammatory and allergic conditions. Besides, the popular use "guaco" is indicated by the Brazilian Ministry of Health as a safe and effective herbal medicine. The biological activity of M. glomerata extracts is due to the presence of the coumarins, a large family of phenolic substances found in plants and is made of fused benzene and α-pyrone rings. Considering that there are few data on the biological effects of the extracts of M. glomerata, mainly in genetic level, this work aims to evaluate, in vitro, the genotoxicity and coumarin production in M. glomerata in conventional and organic growing. The data showed that the organic culture system showed double the concentration of coumarin being significantly more productive than the conventional system. Besides, the results of comet assay suggest that extracts of M. glomerata cultivated in a conventional system was genotoxic, increased DNA damage levels while the organic extracts seem to have antigenotoxic effect possibly due to the concentration of coumarins. Additional biochemical investigations are necessary to elucidate the mechanisms of action of M. glomerata extracts, which were found to have a role in protection against DNA damage.

In Vitro Approaches for Assessing the Genotoxicity of Nanomaterials

Genotoxicity is associated with serious health effects and includes different types of DNA lesions, gene mutations, structural chromosome aberrations involving breakage and/or rearrangements of chromosomes (referred to as clastogenicity) and numerical chromosome aberrations (referred to as aneuploidy). Assessing the potential genotoxic properties of chemicals, including nanomaterials (NMs), is a key element in regulatory safety assessment. State-of-the-art genotoxicity testing includes a battery of assays covering gene mutations, structural and numerical chromosome aberrations. Typically various in vitro assays are performed in the first tier. It is not very likely that NMs may induce as yet unknown types of genotoxic damage beyond what is already known for chemicals. Thus, principles of genotoxicity testing as established for chemicals should be applicable to NMs as well. However, established test guidelines (i.e., OECD TG) may require adaptations for NM testing, as currently under discussion at the OECD. This chapter gives an overview of genotoxicity testing of NMs in vitro based on experiences from various research projects. We recommend a combination of a mammalian gene mutation assay (at either Tk or HPRT locus), the in vitro comet assay, and the cytokinesis-block micronucleus assay, which are discussed in detail here. In addition we also include the Cell Transformation Assay (CTA) as a promising novel test for predicting NM-induced cell transformation in vitro.

Ecotoxicity of different-shaped silver nanoparticles: Case of zebrafish embryos

As the worldwide application of silver nanomaterials in commercial products increases every year, and concern about the environmental risks of such nanoparticles also grows. A clear understanding of how different characteristics of nanoparticles contribute in their toxic behavior to organisms are imperative for predicting and control nanotoxicity. Within our research, we investigated the toxic effect of two types of silver nanoparticles (spherical and flat Ag nanoparticles) on zebrafish (Danio rerio) embryos. Particular interest was paid to proper characterization of Ag nanoparticles initially and during the experiment. A proper test medium was found and used for ecotoxicity evaluation. The behavior of flat silver nanoparticles with respect to embryos of zebrafish was analyzed and compared to the ecotoxicity of silver ionic form (AgNO₃). Both types of nanoparticles showed a more pronounced toxic effect to Danio rerio embryos than silver ions (AgNO₃), while silver nanoplates were more harmful than Ag nanospheres. While previous investigations showed that toxicity of Ag nanoparticles can be explained by the presence of Ag⁺ in solution of silver nanoparticles, our results demonstrate that the harmful effects of nanosilver may be associated with silver nanoparticles themselves than with ionic silver released into solution.

Bioengineering a non-genotoxic vector for genetic modification of mesenchymal stem cells

Vectors used for stem cell transfection must be non-genotoxic, in addition to possessing high efficiency, because they could potentially transform normal stem cells into cancer-initiating cells. The objective of this research was to bioengineer an efficient vector that can be used for genetic modification of stem cells without any negative somatic or genetic impact. Two types of multifunctional vectors, namely targeted and non-targeted were genetically engineered and purified from E. coli. The targeted vectors were designed to enter stem cells via overexpressed receptors. The non-targeted vectors were equipped with MPG and Pep1 cell penetrating peptides. A series of commercial synthetic non-viral vectors and an adenoviral vector were used as controls. All vectors were evaluated for their efficiency and impact on metabolic activity, cell membrane integrity, chromosomal aberrations (micronuclei formation), gene dysregulation, and differentiation ability of stem cells. The results of this study showed that the bioengineered vector utilizing VEGFR-1 receptors for cellular entry could transfect mesenchymal stem cells with high efficiency without inducing genotoxicity, negative impact on gene function, or ability to differentiate. Overall, the vectors that utilized receptors as ports for cellular entry (viral and non-viral) showed considerably better somato- and genosafety profiles in comparison to those that entered through electrostatic interaction with cellular membrane. The genetically engineered vector in this study demonstrated that it can be safely and efficiently used to genetically modify stem cells with potential applications in tissue engineering and cancer therapy.

Nanoparticles in dentistry

OBJECTIVE

Nanoparticles having a size from 1 to 100nm are present in nature and are successfully used in many products of daily life. Nanoparticles are also embedded per se or as byproducts from milling processes of larger filler particles in many dental materials.

METHODS AND RESULTS

Recently, possible adverse effects of nanoparticles have gained increased interest with the lungs being a main target organ. Exposure to nanoparticles in dentistry may occur in the dental laboratory, by processing gypsum type products or by grinding and polishing materials. In the dental practice virtually no exposure to nanoparticles occurs when handling unset materials. However, nanoparticles are produced by intraoral adjustment of set restorative materials through grinding/polishing regardless whether they contain nanoparticles or not. Nanoparticles may also be produced through wear of restorations or released from dental implants and they enter the environment when removing restorations. The risk for dental technicians is taken care of by legal regulations. Based on model worst case mass-based calculations, the exposure of dental practice personnel and patients to nanoparticles through intraoral grinding/polishing and wear is low to negligible. Accordingly, the additional risk due to nanoparticles exposure from present materials is considered to be low. However, more research is needed, especially on vulnerable groups (asthma or COPD). An assessment of risks for the environment is not possible due to the lack of data.

SIGNIFICANCE

Measures to reduce exposure to nanoparticles include intraorally grinding/polishing using water coolants, proper sculpturing to reduce the need for grinding and sufficient ventilation of treatment areas.

Toxicity of nanomaterials found in human environment

The US National Nanotechnology Initiative (NNI) defines nanotechnology as “the understanding and control of matter at dimensions between approximately 1 and 100 nm, where unique phenomena enable novel applications.” Recent scientific reports available in the literature clearly demonstrate the potential benefits of nanotechnology in consumer and industrial products. More and more nanomaterials are expected to be used in consumer products. This is expected to lead to increased human exposure to nanomaterials in their daily lives. Therefore, the effect of nanomaterials present in human environment is an area of increasing scientific interest. The information presented in this review is obtained from the current literature. It indicates that nanomaterials found in human environment may have potential for toxicological effects. However, the current literature on toxicological effects of nanomaterials is diverse. The current data are presented from studies without harmonization. These studies have used different in vitro and in vivo test models, different sources of test nanomaterials, different methods for nanomaterial characterization, and different experimental conditions. Therefore, these data are hard to interpret. More research on nanomaterial characterization, biological interaction, toxicity, and health effects is needed. The test methods need to be validated. Positive and negative controls for nanotoxicity need to be identified. Toxicity data harmonization needs to be done. Therefore, general information is not currently available for risk evaluation of certain nanomaterials that might be present in consumer products or that may enter into the market in future. Standardized and validated methods are necessary for toxicity assessment of nanomaterials. Therefore, in the absence of standardized validated methods any specific regulatory testing requirements for nanomaterials are currently premature. We conclude that the benefits of nanomaterials found currently in human environment are many, but their overall adverse effects on human health are limited.

Immunotoxicity, genotoxicity and epigenetic toxicity of nanomaterials: New strategies for toxicity testing?

The unique properties of nanomaterials (NMs) are beneficial in numerous industrial and medical applications. However, they could also induce unintended effects. Thus, a proper strategy for toxicity testing is essential in human hazard and risk assessment. Toxicity can be tested in vivo and in vitro; in compliance with the 3Rs, alternative strategies for in vitro testing should be further developed for NMs. Robust, standardized methods are of great importance in nanotoxicology, with comprehensive material characterization and uptake as an integral part of the testing strategy. Oxidative stress has been shown to be an underlying mechanism of possible toxicity of NMs, causing both immunotoxicity and genotoxicity. For testing NMs in vitro, a battery of tests should be performed on cells of human origin, either cell lines or primary cells, in conditions as close as possible to an in vivo situation. Novel toxicity pathways, particularly epigenetic modification, should be assessed along with conventional toxicity testing methods. However, to initiate epigenetic toxicity screens for NM exposure, there is a need to better understand their adverse effects on the epigenome, to identify robust and reproducible causal links between exposure, epigenetic changes and adverse phenotypic endpoints, and to develop improved assays to monitor epigenetic toxicity.

Genotoxicity of metal based engineered nanoparticles in aquatic organisms: A review

Engineered nanoparticles (ENPs) are an emerging class of environmental contaminants, but are generally found in very low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. In this review, we: (i) highlight key mechanisms of metal-based ENP-induced genotoxicity, (ii) identify key nanoparticle and environmental factors which influence the observed genotoxic effects, and (iii) highlight the challenges involved in interpreting reported data and provide recommendations on how these challenges might be addressed. We review the application of eight different genotoxicity assays, where the Comet Assay is generally preferred due to its capacity to detect low levels of DNA damage. Most ENPs have been shown to cause genotoxic responses; e.g., DNA or/and chromosomal fragmentation, or DNA strand breakage, but at unrealistic high concentrations. The genotoxicity of the ENPs was dependent on the inherent physico-chemical properties (e.g. size, coating, surface chemistry, e.tc.), and the presence of co-pollutants. To enhance the value of published genotoxicity data, the role of environmental processes; e.g., dissolution, aggregation and agglomeration, and adsorption of ENPs when released in aquatic systems, should be included, and assay protocols must be standardized. Such data could be used to model ENP genotoxicity processes in open environmental systems.

Titanium dioxide nanoparticles: an in vitro study of DNA binding, chromosome aberration assay, and comet assay

Engineered titanium dioxide nanoparticles (TiO2 NPs) are extensively used in cosmetic, pharmaceutical and other industries globally due to their unique properties, which has raised concern for biosafety. Genotoxicity assessment is an important part of biosafety evaluation; we report in vitro cytogenetic assays for NPs considering their unique physicochemical characteristics to fill the gap of laboratory data regarding biological safety along with mechanistic study for mode of interaction of NP with genetic material. Comet and chromosome aberration assay (CA assay) using short-term human peripheral blood cultures following exposure to TiO2 NPs; along with physicochemical parameters for stability of nano form in cultures; and DNA binding activity were carried out. The dynamic light scattering and zeta potential measurements revealed mono dispersion in media. The fluorescence spectroscopy for binding affinity of TiO2 NPs and human genomic DNA showed binding constant (Kb), 4.158 × 106 M-1 indicating strong binding affinity and negative ΔG0 value suggesting spontaneous DNA binding supporting its genotoxic potential. Following in vitro exposure to TiO2 NPs for 24 h, the cultures were analyzed for comet and CA assays, which showed significant results (p < 0.05) for % DNA intensity in tail, Olive Tail Moment and frequency of Chromosomal aberrations (CA) at 75 and 125 μM but not at 25 μM.

Emerging metrology for high-throughput nanomaterial genotoxicology

The rapid development of the engineered nanomaterial (ENM) manufacturing industry has accelerated the incorporation of ENMs into a wide variety of consumer products across the globe. Unintentionally or not, some of these ENMs may be introduced into the environment or come into contact with humans or other organisms resulting in unexpected biological effects. It is thus prudent to have rapid and robust analytical metrology in place that can be used to critically assess and/or predict the cytotoxicity, as well as the potential genotoxicity of these ENMs. Many of the traditional genotoxicity test methods [e.g. unscheduled DNA synthesis assay, bacterial reverse mutation (Ames) test, etc.,] for determining the DNA damaging potential of chemical and biological compounds are not suitable for the evaluation of ENMs, due to a variety of methodological issues ranging from potential assay interferences to problems centered on low sample throughput. Recently, a number of sensitive, high-throughput genotoxicity assays/platforms (CometChip assay, flow cytometry/micronucleus assay, flow cytometry/γ-H2AX assay, automated 'Fluorimetric Detection of Alkaline DNA Unwinding' (FADU) assay, ToxTracker reporter assay) have been developed, based on substantial modifications and enhancements of traditional genotoxicity assays. These new assays have been used for the rapid measurement of DNA damage (strand breaks), chromosomal damage (micronuclei) and for detecting upregulated DNA damage signalling pathways resulting from ENM exposures. In this critical review, we describe and discuss the fundamental measurement principles and measurement endpoints of these new assays, as well as the modes of operation, analytical metrics and potential interferences, as applicable to ENM exposures. An unbiased discussion of the major technical advantages and limitations of each assay for evaluating and predicting the genotoxic potential of ENMs is also provided.

Effect of surface coating on the biocompatibility and in vivo MRI detection of iron oxide nanoparticles after intrapulmonary administration

Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted special attention as novel nanoprobes capable of improving both the therapy and diagnosis of lung diseases. For safe prospective clinical applications, their biocompatibility has to be assessed after intrapulmonary administration. This study was therefore conducted to understand the biological impact of SPIONs and their further surface-functionalization with polyethylene glycol (PEG) having either negative (i.e. carboxyl) or positive (i.e. amine) terminal in a 1-month longitudinal study following acute and sub-acute exposures. Noninvasive free-breathing MR imaging protocols were first optimized to validate SPIONs detection in the lung and investigate possible subsequent systemic translocation to abdominal organs. Pulmonary Magnetic Resonance Imaging (MRI) allowed successful in vivo detection of SPIONs in the lung using ultra-short echo time sequence. Following high-dose lung administration, MR imaging performed on abdominal organs detected transient accumulation of SPIONs in the liver. Iron quantification using Inductive coupled plasma - Mass mass spectroscopy (ICP-MS) confirmed MRI readouts. Oxidative stress induction and genotoxicity were then conducted to evaluate the biocompatibility of SPIONs with their different formulations in a mouse model. A significant increase in lipid peroxidation was observed in both acute and sub-acute sets and found to regress in a time-dependent manner. PEG functionalized SPIONs revealed a lower effect with no difference between both terminal modifications. Genotoxicity assessments revealed an increase in DNA damage and gene expression of CCL-17 and IL-10 biomarkers following SPIONs administration, which was significantly higher than surface-modified nanoparticles and decreased in a time-dependent manner. However, SPIONs with carboxyl terminal showed a slightly prominent effect compared to amine modification.

Development of nanotoxicology: implications for drug delivery and medical devices

Current nanotoxicology research suffers from suboptimal in vitro models, lack of in vitro–in vivo correlations, variability within in vitro protocols, deficits in both material purity and physicochemical characterization. Reliable nanomaterial toxicity and mechanistic insights are required for health and toxicity risk assessments. Much in vitro toxicological data is inconclusive in designating whether nanomaterials for drug delivery and medical device implants are truly safe. A critique is presented to analyze the interface between toxicology and nanopharmaceuticals. Deficiencies of existing practices in toxicology are reviewed and useful emerging techniques (e.g., lab-on-a-chip, tissue engineering, atomic force microscopy, high-content analysis) are highlighted. Cross-fertilization between disciplines will aid development of biocompatible delivery and implant platforms while improvements are being suggested for better translation of nanotoxicology.

Silver nanoparticles: correlating nanoparticle size and cellular uptake with genotoxicity

The focus of this research was to develop a better understanding of the pertinent physico-chemical properties of silver nanoparticles (AgNPs) that affect genotoxicity, specifically how cellular uptake influences a genotoxic cell response. The genotoxicity of AgNPs was assessed for three potential mechanisms: mutagenicity, clastogenicity and DNA strand-break-based DNA damage. Mutagenicity (reverse mutation assay) was assessed in five bacterial strains of Salmonella typhimurium and Echerichia coli, including TA102 that is sensitive to oxidative DNA damage. AgNPs of all sizes tested (10, 20, 50 and 100nm), along with silver nitrate (AgNO3), were negative for mutagenicity in bacteria. No AgNPs could be identified within the bacteria cells using transmission electron microscopy (TEM), indicating these bacteria lack the ability to actively uptake AgNPs 10nm or larger. Clastogenicity (flow cytometry-based micronucleus assay) and intermediate DNA damage (DNA strand breaks as measured in the Comet assay) were assessed in two mammalian white blood cell lines: Jurkat Clone E6-1 and THP-1. It was observed that micronucleus and Comet assay end points were inversely correlated with AgNP size, with smaller NPs inducing a more genotoxic response. TEM results indicated that AgNPs were confined within intracellular vesicles of mammalian cells and did not penetrate the nucleus. The genotoxicity test results and the effect of AgNO3 controls suggest that silver ions may be the primary, and perhaps only, cause of genotoxicity. Furthermore, since AgNO3 was not mutagenic in the gram-negative bacterial Ames strains tested, the lack of bacterial uptake of the AgNPs may not be the major reason for the lack of genotoxicity observed.

Growth arrest and rapid capture of select pathogens following magnetic nanoparticle treatment

Thorough understanding of magnetic nanoparticle (MNP) properties is essential for developing new theranostics. In this study, we provide evidence that non-modified magnetic iron oxide nanoparticles and their functionalized derivatives may be used to restrict growth and capture different pathogens. Coprecipitation of Fe(2+) and Fe(3+) ions in an alkaline solution was used to synthesize MNPs that subsequently were functionalized by gold and aminosilane coating. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR) were used to assess their physicochemical properties. A significant decrease of Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans outgrown from medium after addition of MNPs or their derivatives was observed during 24h culture. Measurement of optical density revealed that using MNPs, these pathogens can be quickly captured and removed (with efficiency reaching almost 100%) from purposely infected saline buffer and body fluids such as human blood plasma, serum, abdominal fluids and cerebrospinal fluids. These effects depend on nanoparticle concentration, surface chemistry, the type of pathogen, as well as the surrounding 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.

Hydrodynamic chromatography – inductively coupled plasma mass spectrometry, with post-column injection capability for simultaneous determination of nanoparticle size, mass concentration and particle number concentration (HDC-PCi-ICP-MS)

A novel, rapid method for the simultaneous determination of the size, mass concentration and particle number concentration of nanoparticle dispersions is presented.

Ultrastructural interactions and genotoxicity assay of cerium dioxide nanoparticles on mouse oocytes

Cerium dioxide nanoparticles (C(e)O₂ ENPs) are on the priority list of nanomaterials requiring evaluation. We performed in vitro assays on mature mouse oocytes incubated with C(e)O₂ ENPs to study (1) physicochemical biotransformation of ENPs in culture medium; (2) ultrastructural interactions with follicular cells and oocytes using Transmission Electron Microscopy (TEM); (3) genotoxicity of C(e)O₂ ENPs on follicular cells and oocytes using a comet assay. DNA damage was quantified as Olive Tail Moment. We show that ENPs aggregated, but their crystal structure remained stable in culture medium. TEM showed endocytosis of C(e)O₂ ENP aggregates in follicular cells. In oocytes, C(e)O₂ ENP aggregates were only observed around the zona pellucida (ZP). The comet assay revealed significant DNA damage in follicular cells. In oocytes, the comet assay showed a dose-related increase in DNA damage and a significant increase only at the highest concentrations. DNA damage decreased significantly both in follicular cells and in oocytes when an anti-oxidant agent was added in the culture medium. We hypothesise that at low concentrations of C(e)O₂ ENPs oocytes could be protected against indirect oxidative stress due to a double defence system composed of follicular cells and ZP.

Transcriptional responses of human aortic endothelial cells to nanoconstructs used in biomedical applications

Understanding the potential toxicities of manufactured nanoconstructs used for drug delivery and biomedical applications may help improve their safety. We sought to determine if surface-modified silica nanoparticles and poly(amido amine) dendrimers elicit genotoxic responses on vascular endothelial cells. The nanoconstructs utilized in this study had a distinct geometry (spheres vs worms) and surface charge, which were used to evaluate the contributions of these parameters to any potential adverse effects of these materials. Time-dependent cytotoxicity was found for surfaced-functionalized but geometrically distinct silica materials, while amine-terminated dendrimers displayed time-independent cytotoxicity and carboxylated dendrimers were nontoxic in our assays. Transcriptomic evaluation of human aortic endothelial cell (HAEC) responses indicated time-dependent gene induction following silica exposure, consisting of cell cycle gene repression and pro-inflammatory gene induction. However, the dendrimers did not induce genomic toxicity, despite displaying general cytotoxicity.

Effect of nanoparticle stabilization and physicochemical properties on exposure outcome: acute toxicity of silver nanoparticle preparations in zebrafish (Danio rerio)

Nanotechnology has vast potential for expanded development and novel application in numerous sectors of society. With growing use and applications, substantial production volumes and associated environmental release can be anticipated. Exposure effect of nanoparticles (NP) on biological systems may be intrinsic to their physicochemical properties introducing unknown associated risk. Herein, we expand the knowledge of health and environmental impact of silver nanoparticles (AgNPs), testing the acute toxicity of 14 AgNP preparations on developing zebrafish embryos (Danio rerio). Toxicological end points, including mortality, hatching rate, and heart rate were recorded. Concentration, stabilization agent and physicochemical properties were monitored as contributing outcome factors. Our findings indicate wide ranging LC50 24 h postfertilization values (0.487 ppm (0.315, 0.744 95% CI) to 47.89 ppm (18.45, 203.49 95% CI)), and indicate surface charge and ionic dissolution as key contributory factors in AgNP exposure outcome.

Evaluation of in vitro and in vivo genotoxicity of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) have extensive potential industrial applications due to their unique physical and chemical properties; yet this also increases the chance of human and environment exposure to SWCNTs. Due to the current lack of hazardous effect information on SWNCTs, a standardized genotoxicity battery test was conducted to clarify the genetic toxicity potential of SWCNTs (diameter: 1–1.2 nm, length: ∼20 μm) according to Organization for Economic Cooperation and Development test guidelines 471 (bacterial reverse mutation test), 473 ( in vitro chromosome aberration test), and 474 ( in vivo micronuclei test) with a good laboratory practice system. The test results showed that the SWCNTs did not induce significant bacterial reverse mutations at 31.3–500 μg/plate in Salmonella typhimurium strains TA98, TA100, TA1535, and TA1537 or in Escherichia coli strain WP2uvrA, with and without a metabolic activation system. Furthermore, the in vitro chromosome aberration test showed no significant increase in structural or numerical chromosome aberration frequencies at SWCNT dose levels of 12.5–50 μg/ml in the presence and absence of metabolic activation. However, dose-dependent cell growth inhibition was found at all the SWCNT dose levels and statistically significant cytotoxic effects observed at certain concentrations in the presence and absence of metabolic activation. Finally, the SWCNTs did not evoke significant in vivo micronuclei frequencies in the polychromatic erythrocytes of an imprinting control region mice at 25–100 mg/kg. Thus, according to the results of the present study, the SWCNTs were not found to have a genotoxic effect on the in vitro and in vivo test systems.

Mechanisms of genotoxicity. A review of in vitro and in vivo studies with engineered nanoparticles

Engineered nanoparticles (NPs) are widely used in different technologies but their unique properties might also cause adverse health effects. In reviewing recent in vitro and in vivo genotoxicity studies we discuss potential mechanisms of genotoxicity induced by NPs. Various factors that may influence genotoxic response, including physico-chemical properties and experimental conditions, are highlighted. From 4346 articles on NP toxicity, 112 describe genotoxicity studies (94 in vitro, 22 in vivo). The most used assays are the comet assay (58 in vitro, 9 in vivo), the micronucleus assay (31 in vitro, 14 in vivo), the chromosome aberrations test (10 in vitro, 1 in vivo) and the bacterial reverse mutation assay (13 studies). We describe advantages and potential problems with different methods and suggest the need for appropriate methodologies to be used for investigation of genotoxic effects of NPs, in vitro and in vivo.

Appropriate in vitro methods for genotoxicity testing of silver nanoparticles

OBJECTIVES

We investigated the genotoxic effects of 40-59 nm silver nanoparticles (Ag-NPs) by bacterial reverse mutation assay (Ames test), in vitro comet assay and micronucleus (MN) assay. In particular, we directly compared the effect of cytochalasin B (cytoB) and rat liver homogenate (S9 mix) in the formation of MN by Ag-NPs.

METHODS

Before testing, we confirmed that Ag-NPs were completely dispersed in the experimental medium by sonication (three times in 1 minute) and filtration (0.2 µm pore size filter), and then we measured their size in a zeta potential analyzer. After that the genotoxicity were measured and especially, S9 mix and with and without cytoB were compared one another in MN assay.

RESULTS

Ames test using Salmonella typhimurium TA98, TA100, TA1535 and TA1537 strains revealed that Ag-NPs with or without S9 mix did not display a mutagenic effect. The genotoxicity of Ag-NPs was also evaluated in a mammalian cell system using Chinese hamster ovary cells. The results revealed that Ag-NPs stimulated DNA breakage and MN formation with or without S9 mix in a dose-dependent manner (from 0.01 µg/mL to 10 µg/mL). In particular, MN induction was affected by cytoB.

CONCLUSIONS

All of our findings, with the exception of the Ames test results, indicate that Ag-NPs show genotoxic effects in mammalian cell system. In addition, present study suggests the potential error due to use of cytoB in genotoxic test of nanoparticles.

Can the Ames test provide an insight into nano-object mutagenicity? Investigating the interaction between nano-objects and bacteria

The aim of this study was to assess the interaction of a series of well characterised nano-objects with the Gram negative bacterium Salmonella typhimurium, and how such an interaction may relate to the potential mutagenicity of nano-objects. Transmission electron microscopy showed that nano-objects (Au-PMA-ATTO NPs, CeO₂ NPs, SWCNTs and MWCNTs), as well as CAFs entered S. typhimurium. Only DEPs did not penetrate/enter the bacteria, however, were the only particle stimulus to induce any significant mutagenicity through the Ames test. Comparison with a sophisticated 3D in vitro cell model showed CAFs, DEPs, SWCNTs and MWCNTs to cause a significant increase in mammalian cell proliferation, whilst both the Au-PMA-ATTO NPs and CeO₂ NPs had not significant adverse effects. In conclusion, these results indicate that various of different nano-objects are able to penetrate the double-lipid bilayer of Gram negative bacteria, although the Ames test may not be a good indicator for nano-object mutagenicity.

Phase-shift, stimuli-responsive drug carriers for targeted delivery

The intersection of particles and directed energy is a rich source of novel and useful technology that is only recently being realized for medicine. One of the most promising applications is directed drug delivery. This review focuses on phase-shift nanoparticles (that is, particles of submicron size) as well as micron-scale particles whose action depends on an external-energy triggered, first-order phase shift from a liquid to gas state of either the particle itself or of the surrounding medium. These particles have tremendous potential for actively disrupting their environment for altering transport properties and unloading drugs. This review covers in detail ultrasound and laser-activated phase-shift nano- and micro-particles and their use in drug delivery. Phase-shift based drug-delivery mechanisms and competing technologies are discussed.

Silica nanoparticles administered at the maximum tolerated dose induce genotoxic effects through an inflammatory reaction while gold nanoparticles do not

While the collection of genotoxicity data and insights into potential mechanisms of action for nano-sized particulate materials (NPs) are steadily increasing, there is great uncertainty whether current standard assays are suitable to appropriately characterize potential risks. We investigated the effects of NPs in an in vivo Comet/micronucleus (MN) combination assay and in an in vitro MN assay performed with human blood. We also incorporated additional endpoints into the in vivo study in an effort to delineate primary from secondary mechanisms. Amorphous silica NPs (15 and 55 nm) were chosen for their known reactivity, while gold nano/microparticles (2, 20, and 200 nm) were selected for their wide size range and lower reactivity. DNA damage in liver, lung and blood cells and micronuclei in circulating reticulocytes were measured after 3 consecutive intravenous injections to male Wistar rats at 48, 24 and 4h before sacrifice. Gold nano/microparticles were negative for MN induction in vitro and in vivo, and for the induction of DNA damage in all tissues. Silica particles, however, caused a small but reproducible increase in DNA damage and micronucleated reticulocytes when tested at their maximum tolerated dose (MTD). No genotoxic effects were observed at lower doses, and the in vitro MN assay was also negative. We hypothesize that silica NPs initiate secondary genotoxic effects through release of inflammatory cell-derived oxidants, similar to that described for crystalline silica (quartz). Such a mechanism is supported by the occurrence of increased neutrophilic infiltration, necrosis, and apoptotic cells in the liver, and induction of inflammatory markers TNF-α and IL-6 in plasma at the MTDs. These results were fairly consistent between silica NPs and the quartz control, thereby strengthening the argument that silica NPs may act in a similar, thresholded manner. The observed profile is supportive of a secondary genotoxicity mechanism that is driven by inflammation.

New perspectives for in vitro risk assessment of multiwalled carbon nanotubes: application of coculture and bioinformatics

Nanotechnology is a rapidly expanding field with wide application for industrial and medical use; therefore, understanding the toxicity of engineered nanomaterials is critical for their commercialization. While short-term in vivo studies have been performed to understand the toxicity profile of various nanomaterials, there is a current effort to shift toxicological testing from in vivo observational models to predictive and high-throughput in vitro models. However, conventional monoculture results of nanoparticle exposure are often disparate and not predictive of in vivo toxic effects. A coculture system of multiple cell types allows for cross-talk between cells and better mimics the in vivo environment. This review proposes that advanced coculture models, combined with integrated analysis of genome-wide in vivo and in vitro toxicogenomic data, may lead to development of predictive multigene expression-based models to better determine toxicity profiles of nanomaterials and consequent potential human health risk due to exposure to these compounds.

Approaches to the safety assessment of engineered nanomaterials (ENM) in food

A systematic, tiered approach to assess the safety of engineered nanomaterials (ENMs) in foods is presented. The ENM is first compared to its non-nano form counterpart to determine if ENM-specific assessment is required. Of highest concern from a toxicological perspective are ENMs which have potential for systemic translocation, are insoluble or only partially soluble over time or are particulate and bio-persistent. Where ENM-specific assessment is triggered, Tier 1 screening considers the potential for translocation across biological barriers, cytotoxicity, generation of reactive oxygen species, inflammatory response, genotoxicity and general toxicity. In silico and in vitro studies, together with a sub-acute repeat-dose rodent study, could be considered for this phase. Tier 2 hazard characterisation is based on a sentinel 90-day rodent study with an extended range of endpoints, additional parameters being investigated case-by-case. Physicochemical characterisation should be performed in a range of food and biological matrices. A default assumption of 100% bioavailability of the ENM provides a 'worst case' exposure scenario, which could be refined as additional data become available. The safety testing strategy is considered applicable to variations in ENM size within the nanoscale and to new generations of ENM.

Responses of human cells to ZnO nanoparticles: a gene transcription study

The gene transcript profile responses to metal oxide nanoparticles was studied using human cell lines derived from the colon and skin tumors. Much of the research on nanoparticle toxicology has focused on models of inhalation and intact skin exposure, and effects of ingestion exposure and application to diseased skin are relatively unknown. Powders of nominally nanosized SiO2, TiO2, ZnO and Fe2O3 were chosen because these substances are widely used in consumer products. The four oxides were evaluated using colon-derived cell lines, RKO and CaCo-2, and ZnO and TiO2 were evaluated further using skin-derived cell lines HaCaT and SK Mel-28. ZnO induced the most notable gene transcription changes, even though this material was applied at the lowest concentration. Nano-sized and conventional ZnO induced similar responses suggesting common mechanisms of action. The results showed neither a non-specific response pattern common to all substances nor synergy of the particles with TNF-α cotreatment. The response to ZnO was not consistent with a pronounced proinflammatory signature, but involved changes in metal metabolism, chaperonin proteins, and protein folding genes. This response was observed in all cell lines when ZnO was in contact with the human cells. When the cells were exposed to soluble Zn, the genes involved in metal metabolism were induced but the genes involved in protein refoldling were unaffected. This provides some of the first data on the effects of commercial metal oxide nanoparticles on human colon-derived and skin-derived cells.