Implementation of alternative test strategies for the safety assessment of engineered nanomaterials

Bridging the gap: Innovative human-based in vitro approaches for nanomaterials hazard assessment and their role in safe and sustainable by design, risk assessment, and life cycle assessment

The application of nanomaterials in industry and consumer products is growing exponentially, which has pressed the development and use of predictive human in vitro models in pre-clinical analysis to closely extrapolate potential toxic effects in vivo. The conventional cytotoxicity investigation of nanomaterials using cell lines from cancer origin and culturing them two-dimensionally in a monolayer without mimicking the proper pathophysiological microenvironment may affect a precise prediction of in vitro effects at in vivo level. In recent years, complex in vitro models (also belonging to the new approach methodologies, NAMs) have been established in unicellular to multicellular cultures either by using cell lines, primary cells or induced pluripotent stem cells (iPSCs), and reconstituted into relevant biological dimensions mimicking in vivo conditions. These advanced in vitro models retain physiologically reliant exposure scenarios particularly appropriate for oral, dermal, respiratory, and intravenous administration of nanomaterials, which have the potential to improve the in vivo predictability and lead to reliable outcomes. In this perspective, we discuss recent developments and breakthroughs in using advanced human in vitro models for hazard assessment of nanomaterials. We identified fit-for-purpose requirements and remaining challenges for the successful implementation of in vitro data into nanomaterials Safe and Sustainable by Design (SSbD), Risk Assessment (RA), and Life Cycle Assessment (LCA). By addressing the gap between in vitro data generation and the utility of in vitro data for nanomaterial safety assessments, a prerequisite for SSbD approaches, we outlined potential key areas for future development.

Harmonization Risks and Rewards: Nano-QSAR for Agricultural Nanomaterials

This comprehensive review explores the emerging landscape of Nano-QSAR (quantitative structure-activity relationship) for assessing the risk and potency of nanomaterials in agricultural settings. The paper begins with an introduction to Nano-QSAR, providing background and rationale, and explicitly states the hypotheses guiding the review. The study navigates through various dimensions of nanomaterial applications in agriculture, encompassing their diverse properties, types, and associated challenges. Delving into the principles of QSAR in nanotoxicology, this article elucidates its application in evaluating the safety of nanomaterials, while addressing the unique limitations posed by these materials. The narrative then transitions to the progression of Nano-QSAR in the context of agricultural nanomaterials, exemplified by insightful case studies that highlight both the strengths and the limitations inherent in this methodology. Emerging prospects and hurdles tied to Nano-QSAR in agriculture are rigorously examined, casting light on important pathways forward, existing constraints, and avenues for research enhancement. Culminating in a synthesis of key insights, the review underscores the significance of Nano-QSAR in shaping the future of nanoenabled agriculture. It provides strategic guidance to steer forthcoming research endeavors in this dynamic field.

Safety Assessment of Nanomaterials in Cosmetics: Focus on Dermal and Hair Dyes Products

Nanomaterials use in cosmetics is markedly enhancing, so their exposure and toxicity are important parameters to consider for their risk assessment. This review article provides an overview of the active cosmetic ingredients used for cosmetic application, including dermal cosmetics and also hair dye cosmetics, as well as their safety assessment, enriched with a compilation of the safety assessment tests available to evaluate the different types of toxicity. In fact, despite the increase in research and the number of papers published in the field of nanotechnology, the related safety assessment is still insufficient. To elucidate the possible effects that nanosized particles can have on living systems, more studies reproducing similar conditions to what happens in vivo should be conducted, particularly considering the complex interactions of the biological systems and active cosmetic ingredients to achieve newer, safer, and more efficient nanomaterials. Toward this end, ecological issues and the toxicological pattern should also be a study target.

A Systematic Review on the Hazard Assessment of Amorphous Silica Based on the Literature From 2013 to 2018

Background

Nanomaterials are suspected of causing health problems, as published studies on nanotoxicology indicate. On the other hand, some of these materials, such as nanostructured pyrogenic and precipitated synthetic amorphous silica (SAS) and silica gel, have been used for decades without safety concerns in industrial, commercial, and consumer applications. However, in addition to many in vivo and in vitro studies that have failed to demonstrate the intrinsic toxicity of SAS, articles periodically emerge, in which biological effects of concern have been described. Even though most of these studies do not meet high-quality standards and do not always use equivalent test materials or standardized test systems, the results often trigger substance re-evaluation. To put the results into perspective, an extensive literature study was carried out and an example of amorphous silica will be used to try to unravel the reliability from the unreliable results.

Methods

A systematic search of studies on nanotoxicological effects has been performed covering the years 2013 to 2018. The identified studies have been evaluated for their quality regarding material and method details, and the data have been curated and put into a data collection. This review deals only with investigations on amorphous silica.

Results

Of 18,162 publications 1,217 have been selected with direct reference to experiments with synthetically produced amorphous silica materials. The assessment of these studies based on defined criteria leads to a further reduction to 316 studies, which have been included in this systematic review. Screening for quality with well-defined quantitative criteria following the GUIDE nano concept reveals only 27.3% has acceptable quality. Overall, the in vitro and in vivo data showed low or no toxicity of amorphous silica. The data shown do not support the hypothesis of dependency of biological effects on the primary particle size of the tested materials.

Conclusion

This review demonstrates the relatively low quality of most studies published on nanotoxicological issues in the case of amorphous silica. Moreover, mechanistic studies are often passed off or considered toxicological studies. In general, standardized methods or the Organization for Economic Cooperation and Development (OECD) guidelines are rarely used for toxicological experiments. As a result, the significance of the published data is usually weak and must be reevaluated carefully before using them for regulatory purposes.

Nanomaterials in hair care and treatment

Hair care and treatment has evolved significantly through the years as new formulations are continuously being explored in an attempt to meet the demand in cosmetic and medicinal fields. While standard hair care procedures include hair washing, aimed at hair cleansing and maintenance, as well as hair dyeing and bleaching formulations for hair embellishment, modern hair treatments are mainly focused on circumventing hair loss conditions, strengthening hair follicle properties and treat hair infestations. In this regard, active compounds (ACs) included in hair cosmetic formulations include a vast array of hair cleansing and hair dye molecules, and typical hair treatments include anti-hair loss ACs (e.g. minoxidil and finasteride) and anti-lice ACs (e.g. permethrin). However, several challenges still persist, as conventional AC formulations exhibit sub-optimal performance and some may present toxicity issues, calling for an improved design of formulations regarding both efficacy and safety. More recently, nano-based strategies encompassing nanomaterials have emerged as promising tailored approaches to improve the performance of ACs incorporated into hair cosmetics and treatment formulations. The interest in using these nanomaterials is based on account of their ability to: (1) increase stability, safety and biocompatibility of ACs; (2) maximize hair affinity, contact and retention, acting as versatile biointerfaces; (3) enable the controlled release of ACs in both hair and scalp, serving as prolonged AC reservoirs; besides offering (4) hair follicle targeting features attending to the possibility of surface tunability. This review covers the breakthrough of nanomaterials for hair cosmetics and hair treatment, focusing on organic nanomaterials (polymer-based and lipid-based nanoparticles) and inorganic nanomaterials (nanosheets, nanotubes and inorganic nanoparticles), as well as their applications, highlighting their potential as innovative multifunctional nanomaterials towards maximized hair care and treatment. STATEMENT OF SIGNIFICANCE: This manuscript is focused on reviewing the nanotechnological strategies investigated for hair care and treatment so far. While conventional formulations exhibit sub-optimal performance and some may present toxicity issues, the selection of improved and suitable nanodelivery systems is of utmost relevance to ensure a proper active ingredient release in both hair and scalp, maximize hair affinity, contact and retention, and provide hair follicle targeting features, warranting stability, efficacy and safety. This innovative manuscript highlights the advantages of nanotechnology-based approaches, particularly as tunable and versatile biointerfaces, and their applications as innovative multifunctional nanomaterials towards maximized hair care and treatment.

Engineered Nanomaterials: The Challenges and Opportunities for Nanomedicines

The emergence of nanotechnology as a key enabling technology over the past years has opened avenues for new and innovative applications in nanomedicine. From the business aspect, the nanomedicine market was estimated to worth USD 293.1 billion by 2022 with a perception of market growth to USD 350.8 billion in 2025. Despite these opportunities, the underlying challenges for the future of engineered nanomaterials (ENMs) in nanomedicine research became a significant obstacle in bringing ENMs into clinical stages. These challenges include the capability to design bias-free methods in evaluating ENMs' toxicity due to the lack of suitable detection and inconsistent characterization techniques. Therefore, in this literature review, the state-of-the-art of engineered nanomaterials in nanomedicine, their toxicology issues, the working framework in developing a toxicology benchmark and technical characterization techniques in determining the toxicity of ENMs from the reported literature are explored.

Kolaviron via anti-inflammatory and redox regulatory mechanisms abates multi-walled carbon nanotubes-induced neurobehavioral deficits in rats

Exposure to multi-walled carbon nanotubes (MWCNTs) reportedly elicits neurotoxic effects. Kolaviron is a phytochemical with several pharmacological effects namely anti-oxidant, anti-inflammatory, and anti-genotoxic activities. The present study evaluated the neuroprotective mechanism of kolaviron in rats intraperitoneally injected with MWCNTs alone at 1 mg/kg body weight or orally co-administered with kolaviron at 50 and 100 mg/kg body weight for 15 consecutive days. Following exposure, neurobehavioral analysis using video-tracking software during trial in a novel environment indicated that co-administration of both doses of kolaviron significantly (p < 0.05) enhanced the locomotor, motor, and exploratory activities namely total distance traveled, maximum speed, total time mobile, mobile episode, path efficiency, body rotation, absolute turn angle, and negative geotaxis when compared with rats exposed to MWCNTs alone. Further, kolaviron markedly abated the decrease in the acetylcholinesterase activity and antioxidant defense system as well as the increase in oxidative stress and inflammatory biomarkers induced by MWCNT exposure in the cerebrum, cerebellum, and mid-brain of rats. The amelioration of MWCNT-induced neuronal degeneration in the brain structures by kolaviron was verified by histological and morphometrical analyses. Taken together, kolaviron abated MWCNT-induced neurotoxicity via anti-inflammatory and redox regulatory mechanisms.

Metal-Based Nanostructures/PLGA Nanocomposites: Antimicrobial Activity, Cytotoxicity, and Their Biomedical Applications

Among the different synthetic polymers developed for biomedical applications, poly(lactic-co-glycolic acid) (PLGA) has attracted considerable attention because of its excellent biocompatibility and biodegradability. Nanocomposites based on PLGA and metal-based nanostructures (MNSs) have been employed extensively as an efficient strategy to improve the structural and functional properties of PLGA polymer. The MNSs have been used to impart new properties to PLGA, such as antimicrobial properties and labeling. In the present review, the different strategies available for the fabrication of MNS/PLGA nanocomposites and their applications in the biomedical field will be discussed, beginning with a description of the preparation routes, antimicrobial activity, and cytotoxicity concerns of MNS/PLGA nanocomposites. The biomedical applications of these nanocomposites, such as carriers and scaffolds in tissue regeneration and other therapies are subsequently reviewed. In addition, the potential advantages of using MNS/PLGA nanocomposites in treatment illnesses are analyzed based on in vitro and in vivo studies, to support the potential of these nanocomposites in future research in the biomedical field.

The Hemocompatibility of Nanoparticles: A Review of Cell-Nanoparticle Interactions and Hemostasis

Understanding cell-nanoparticle interactions is critical to developing effective nanosized drug delivery systems. Nanoparticles have already advanced the treatment of several challenging conditions including cancer and human immunodeficiency virus (HIV), yet still hold the potential to improve drug delivery to elusive target sites. Even though most nanoparticles will encounter blood at a certain stage of their transport through the body, the interactions between nanoparticles and blood cells is still poorly understood and the importance of evaluating nanoparticle hemocompatibility is vastly understated. In contrast to most review articles that look at the interference of nanoparticles with the intricate coagulation cascade, this review will explore nanoparticle hemocompatibility from a cellular angle. The most important functions of the three cellular components of blood, namely erythrocytes, platelets and leukocytes, in hemostasis are highlighted. The potential deleterious effects that nanoparticles can have on these cells are discussed and insight is provided into some of the complex mechanisms involved in nanoparticle-blood cell interactions. Throughout the review, emphasis is placed on the importance of undertaking thorough, all-inclusive hemocompatibility studies on newly engineered nanoparticles to facilitate their translation into clinical application.

Measurement of Oxidatively Induced DNA Damage in Caenorhabditis elegans with High-Salt DNA Extraction and Isotope-Dilution Mass Spectrometry

Caenorhabditis elegans is used extensively as a medical and toxicological model organism. However, little is known about background levels of oxidatively induced DNA damage in the nematode or how culturing methods affect DNA damage levels. The tough C. elegans cuticle makes it challenging to extract genomic DNA without harsh procedures that can artifactually increase DNA damage. Therefore, a mild extraction protocol based on enzymatic digestion of the C. elegans cuticle with high-salt phase-separation of DNA has been developed and optimized. This method allows for efficient extraction of >50 μg DNA using a minimum of 250000 nematodes grown in liquid culture. The extracted DNA exhibited acceptable RNA levels (<10% contamination), functionality in polymerase chain reaction assays, and reproducible DNA fragmentation. Gas chromatography/tandem mass spectrometry (GC-MS/MS) with isotope-dilution measured lower lesion levels in high-salt extracts than in phenol extracts. Phenolic extraction produced a statistically significant increase in 8-hydroxyguanine, a known artifact, and additional artifactual increases in 2,6-diamino-4-hydroxy-5-formamidopyrimidine, 4,6-diamino-5-formamidopyrimidine, and 8-hydroxyadenine. The high-salt DNA extraction procedure utilizes green solvents and reagents and minimizes artifactual DNA damage, making it more suitable for molecular and toxicological studies in C. elegans. This is, to our knowledge, the first use of GC-MS/MS to measure multiple 8,5'-cyclopurine-2'-deoxynucleosides in a toxicologically important terrestrial organism.

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.

Lignin for Nano- and Microscaled Carrier Systems: Applications, Trends, and Challenges

To liberate society from its dependence on fossil-based fuels and materials it is pivotal to explore components of renewable plant biomass in applications that benefit from their intrinsic biodegradability, safety, and sustainability. Lignin, a byproduct of the pulp and paper industry, is a plausible material for carrying various types of cargo in small- and large-scale applications. Herein, possibilities and constraints regarding the physical-chemical properties of the lignin source as well as modifications and processing required to render lignins suitable for the loading and release of pesticides, pharmaceuticals, and biological macromolecules is reviewed. In addition, the technical challenges, regulatory and toxicological aspects, and future research needed to realize some of the promises that nano- and microscaled lignin materials hold for a sustainable future are critically discussed.

A high throughput imaging database of toxicological effects of nanomaterials tested on HepaRG cells

The large amount of existing nanomaterials demands rapid and reliable methods for testing their potential toxicological effect on human health, preferably by means of relevant in vitro techniques in order to reduce testing on animals. Combining high throughput workflows with automated high content imaging techniques allows deriving much more information from cell-based assays than the typical readouts (i.e. one measurement per well) with optical plate-readers. We present here a dataset including data based on a maximum of 14 different read outs (including viable cell count, cell membrane permeability, apoptotic cell death, mitochondrial membrane potential and steatosis) of the human hepatoma HepaRG cell line treated with a large set of nanomaterials, coatings and supernatants at different concentrations. The database, given its size, can be utilized in the development of in silico hazard assessment and prediction tools or can be combined with toxicity results from other in vitro test systems.

Overview of the blood compatibility of nanomedicines: A trend analysis of in vitro and in vivo studies

As nanomedicines have the potential to address many currently unmet medical needs, the early identification of regulatory requirements that could hamper a smooth translation of nanomedicines from the laboratory environment to clinical applications is of utmost importance. The blood system is especially relevant as many nanomedicinal products that are currently under development are designed for intravenous administration and cells of the blood system will be among the first biological systems exposed to the injected nanomedicine. This review collects and summarizes the current knowledge related to the blood compatibility of nanomedicines and nanomaterials with a potential use in biomedical applications. Different types of nanomedicines were analyzed for their toxicity to the blood system, and the role of their physicochemical properties was further elucidated. Trends were identified related to: (a) the nature of the most frequently occurring blood incompatibilities such as thrombogenicity and complement activation, (b) the contribution of physicochemical properties to these blood incompatibilities, and (c) the similarities between data retrieved from in vivo and in vitro studies. Finally, we provide an overview of available standards that allow evaluating the compatibility of a material with the blood system. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Therapeutic Approaches and Drug Discovery > Emerging Technologies Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Multi-omics analysis of ten carbon nanomaterials effects highlights cell type specific patterns of molecular regulation and adaptation

New strategies to characterize the effects of engineered nanomaterials (ENMs) based on omics technologies are emerging. However, given the intricate interplay of multiple regulatory layers, the study of a single molecular species in exposed biological systems might not allow the needed granularity to successfully identify the pathways of toxicity (PoT) and, hence, portraying adverse outcome pathways (AOPs). Moreover, the intrinsic diversity of different cell types composing the exposed organs and tissues in living organisms poses a problem when transferring in vivo experimentation into cell-based in vitro systems. To overcome these limitations, we have profiled genome-wide DNA methylation, mRNA and microRNA expression in three human cell lines representative of relevant cell types of the respiratory system, A549, BEAS-2B and THP-1, exposed to a low dose of ten carbon nanomaterials (CNMs) for 48 h. We applied advanced data integration and modelling techniques in order to build comprehensive regulatory and functional maps of the CNM effects in each cell type. We observed that different cell types respond differently to the same CNM exposure even at concentrations exerting similar phenotypic effects. Furthermore, we linked patterns of genomic and epigenomic regulation to intrinsic properties of CNM. Interestingly, DNA methylation and microRNA expression only partially explain the mechanism of action (MOA) of CNMs. Taken together, our results strongly support the implementation of approaches based on multi-omics screenings on multiple tissues/cell types, along with systems biology-based multi-variate data modelling, in order to build more accurate AOPs.

Implementation of Safe-by-Design for Nanomaterial Development and Safe Innovation: Why We Need a Comprehensive Approach

Manufactured nanomaterials (MNMs) are regarded as key components of innovations in various fields with high potential impact (e.g., energy generation and storage, electronics, photonics, diagnostics, theranostics, or drug delivery agents). Widespread use of MNMs raises concerns about their safety for humans and the environment, possibly limiting the impact of the nanotechnology-based innovation. The development of safe MNMs and nanoproducts has to result in a safe as well as functional material or product. Its safe use, and disposal at the end of its life cycle must be taken into account too. However, not all MNMs are similarly useful for all applications, some might bear a higher hazard potential than others, and use scenarios could lead to different exposure probabilities. To improve both safety and efficacy of nanotechnology, we think that a new proactive approach is necessary, based on pre-regulatory safety assessment and dialogue between stakeholders. On the basis of the work carried out in different European Union (EU) initiatives, developing and integrating MNMs Safe-by-Design and Trusted Environments (NANoREG, ProSafe, and NanoReg2), we present our point of view here. This concept, when fully developed, will allow for cost effective industrial innovation, and an exchange of key information between regulators and innovators. Regulators are thus informed about incoming innovations in good time, supporting a proactive regulatory action. The final goal is to contribute to the nanotechnology governance, having faster, cheaper, effective, and safer nano-products on the market.

Risk Assessment and Risk Minimization in Nanomedicine: A Need for Predictive, Alternative, and 3Rs Strategies

The use of nanomaterials in medicine has grown very rapidly, leading to a concern about possible health risks. Surely, the application of nanotechnology in medicine has many significant potentialities as it can improve human health in at least three different ways: by contributing to early disease diagnosis, improved treatment outcomes and containment of health care costs. However, toxicology or safety assessment is an integral part of any new medical technology and the nanotechnologies are no exception. The principle aim of nanosafety studies in this frame is to enable safer design of nanomedicines. The most urgent need is finding and validating novel approaches able to extrapolate acute in vitro results for the prediction of chronic in vivo effects and to this purpose a few European initiatives have been launched. While a "safe-by-design" process may be considered as utopic, "safer-by-design" is probably a reachable goal in the field of nanomedicine.

How the toxicity of nanomaterials towards different species could be simultaneously evaluated: a novel multi-nano-read-across approach

Application of predictive modeling approaches can solve the problem of missing data. Numerous studies have investigated the effects of missing values on qualitative or quantitative modeling, but only a few studies have discussed it for the case of applications in nanotechnology-related data. The present study is aimed at the development of a multi-nano-read-across modeling technique that helps in predicting the toxicity of different species such as bacteria, algae, protozoa, and mammalian cell lines. Herein, the experimental toxicity of 184 metal and silica oxide (30 unique chemical types) nanoparticles from 15 datasets is analyzed. A hybrid quantitative multi-nano-read-across approach that combines interspecies correlation analysis and self-organizing map analysis is developed. In the first step, hidden patterns of toxicity among nanoparticles are identified using a combination of methods. Subsequently, the developed model based on categorization of the toxicity of the metal oxide nanoparticle outcomes is evaluated via the combination of supervised and unsupervised machine learning techniques to determine the underlying factors responsible for the toxicity.

The inflammatory response to silver and titanium dioxide nanoparticles in the central nervous system

Despite the increasing number of neurotoxicological studies on metal-containing nanoparticles (NPs), the NP-induced neuroinflammation has not yet been well understood. This review provides a comprehensive understanding of inflammatory responses to two typical metal-containing NPs, namely silver NPs (Ag-NPs) and titanium dioxide NPs (TiO₂-NPs). Ag-NPs and TiO₂-NPs could translocate into the CNS through damaged blood-brain barrier, nerve afferent signaling and eye-to-brain ways, and even cell uptake. NPs could stimulate the activation of glial cells to release proinflammatory cytokines and generate reactive oxygen species and nitric oxide production, resulting in the neuroinflammation. The potential mechanisms of Ag-NPs and TiO₂-NPs causing inflammation are complex, including several immune response relevant signaling pathways. Some parameters governing their ability to cause neuroinflammation are presented as well.

Nanomaterial libraries and model organisms for rapid high-content analysis of nanosafety

Safety analysis of engineered nanomaterials (ENMs) presents a formidable challenge regarding environmental health and safety, due to their complicated and diverse physicochemical properties. Although large amounts of data have been published regarding the potential hazards of these materials, we still lack a comprehensive strategy for their safety assessment, which generates a huge workload in decision-making. Thus, an integrated approach is urgently required by government, industry, academia and all others who deal with the safe implementation of nanomaterials on their way to the marketplace. The rapid emergence and sheer number of new nanomaterials with novel properties demands rapid and high-content screening (HCS), which could be performed on multiple materials to assess their safety and generate large data sets for integrated decision-making. With this approach, we have to consider reducing and replacing the commonly used rodent models, which are expensive, time-consuming, and not amenable to high-throughput screening and analysis. In this review, we present a ‘Library Integration Approach’ for high-content safety analysis relevant to the ENMs. We propose the integration of compositional and property-based ENM libraries for HCS of cells and biologically relevant organisms to be screened for mechanistic biomarkers that can be used to generate data for HCS and decision analysis. This systematic approach integrates the use of material and biological libraries, automated HCS and high-content data analysis to provide predictions about the environmental impact of large numbers of ENMs in various categories. This integrated approach also allows the safer design of ENMs, which is relevant to the implementation of nanotechnology solutions in the pharmaceutical industry.

Redox-active nanomaterials for nanomedicine applications

Nanomedicine utilizes the remarkable properties of nanomaterials for the diagnosis, treatment, and prevention of disease. Many of these nanomaterials have been shown to have robust antioxidative properties, potentially functioning as strong scavengers of reactive oxygen species. Conversely, several nanomaterials have also been shown to promote the generation of reactive oxygen species, which may precipitate the onset of oxidative stress, a state that is thought to contribute to the development of a variety of adverse conditions. As such, the impacts of nanomaterials on biological entities are often associated with and influenced by their specific redox properties. In this review, we overview several classes of nanomaterials that have been or projected to be used across a wide range of biomedical applications, with discussion focusing on their unique redox properties. Nanomaterials examined include iron, cerium, and titanium metal oxide nanoparticles, gold, silver, and selenium nanoparticles, and various nanoscale carbon allotropes such as graphene, carbon nanotubes, fullerenes, and their derivatives/variations. Principal topics of discussion include the chemical mechanisms by which the nanomaterials directly interact with biological entities and the biological cascades that are thus indirectly impacted. Selected case studies highlighting the redox properties of nanomaterials and how they affect biological responses are used to exemplify the biologically-relevant redox mechanisms for each of the described nanomaterials.

Perspectives from the NanoSafety Modelling Cluster on the validation criteria for (Q)SAR models used in nanotechnology

Nanotechnology and the production of nanomaterials have been expanding rapidly in recent years. Since many types of engineered nanoparticles are suspected to be toxic to living organisms and to have a negative impact on the environment, the process of designing new nanoparticles and their applications must be accompanied by a thorough risk analysis. (Quantitative) Structure-Activity Relationship ([Q]SAR) modelling creates promising options among the available methods for the risk assessment. These in silico models can be used to predict a variety of properties, including the toxicity of newly designed nanoparticles. However, (Q)SAR models must be appropriately validated to ensure the clarity, consistency and reliability of predictions. This paper is a joint initiative from recently completed European research projects focused on developing (Q)SAR methodology for nanomaterials. The aim was to interpret and expand the guidance for the well-known "OECD Principles for the Validation, for Regulatory Purposes, of (Q)SAR Models", with reference to nano-(Q)SAR, and present our opinions on the criteria to be fulfilled for models developed for nanoparticles.

Cell-based cytotoxicity assays for engineered nanomaterials safety screening: exposure of adipose derived stromal cells to titanium dioxide nanoparticles

BACKGROUND

Increasing production of nanomaterials requires fast and proper assessment of its potential toxicity. Therefore, there is a need to develop new assays that can be performed in vitro, be cost effective, and allow faster screening of engineered nanomaterials (ENMs).

RESULTS

Herein, we report that titanium dioxide (TiO2) nanoparticles (NPs) can induce damage to adipose derived stromal cells (ADSCs) at concentrations which are rated as safe by standard assays such as measuring proliferation, reactive oxygen species (ROS), and lactate dehydrogenase (LDH) levels. Specifically, we demonstrated that low concentrations of TiO2 NPs, at which cellular LDH, ROS, or proliferation profiles were not affected, induced changes in the ADSCs secretory function and differentiation capability. These two functions are essential for ADSCs in wound healing, energy expenditure, and metabolism with serious health implications in vivo.

CONCLUSIONS

We demonstrated that cytotoxicity assays based on specialized cell functions exhibit greater sensitivity and reveal damage induced by ENMs that was not otherwise detected by traditional ROS, LDH, and proliferation assays. For proper toxicological assessment of ENMs standard ROS, LDH, and proliferation assays should be combined with assays that investigate cellular functions relevant to the specific cell type.

Pro-Inflammatory and Pro-Fibrogenic Effects of Ionic and Particulate Arsenide and Indium-Containing Semiconductor Materials in the Murine Lung

We have recently shown that the toxicological potential of GaAs and InAs particulates in cells is size- and dissolution-dependent, tending to be more pronounced for nano- vs micron-sized particles. Whether the size-dependent dissolution and shedding of ionic III-V materials also apply to pulmonary exposure is unclear. While it has been demonstrated that micron-sized III-V particles, such as GaAs and InAs, are capable of inducing hazardous pulmonary effects in an occupational setting as well as in animal studies, the effect of submicron particles (e.g., the removal of asperities during processing of semiconductor wafers) is unclear. We used cytokine profiling to compare the pro-inflammatory effects of micron- and nanoscale GaAs and InAs particulates in cells as well as the murine lung 40 h and 21 days after oropharyngeal aspiration. Use of cytokine array technology in macrophage and epithelial cell cultures demonstrated a proportionally higher increase in the levels of matrix metalloproteinase inducer (EMMPRIN), macrophage migration inhibitory factor (MIF), and interleukin 1β (IL-1β) by nanosized (n) GaAs and n-InAs as well as As(III). n-GaAs and n-InAs also triggered higher neutrophil counts in the bronchoalveolar lavage fluid (BALF) of mice than micronscale particles 40 h post-aspiration, along with increased production of EMMPRIN and MIF. In contrast, in animals sacrificed 21 days after exposure, only n-InAs induced fibrotic lung changes as determined by increased lung collagen as well as increased levels of TGF-β1 and PDGF-AA in the BALF. A similar trend was seen for EMMPRIN and matrix metallopeptidase (MMP-9) levels in the BALF. Nano- and micron-GaAs had negligible subacute effects. Importantly, the difference between the 40 h and 21 days data appears to be biopersistence of n-InAs, as demonstrated by ICP-OES analysis of lung tissue. Interestingly, an ionic form of In, InCl₃, also showed pro-fibrogenic effects due to the formation of insoluble In(OH)₃ nanostructures. All considered, these data indicate that while nanoscale particles exhibit increased pro-inflammatory effects in the lung, most effects are transient, except for n-InAs and insoluble InCl₃ species that are biopersistent and trigger pro-fibrotic effects. These results are of potential importance for the understanding the occupational health effects of III-V particulates.

Systems Biology to Support Nanomaterial Grouping

The assessment of potential health risks of engineered nanomaterials (ENMs) is a challenging task due to the high number and great variety of already existing and newly emerging ENMs. Reliable grouping or categorization of ENMs with respect to hazards could help to facilitate prioritization and decision making for regulatory purposes. The development of grouping criteria, however, requires a broad and comprehensive data basis. A promising platform addressing this challenge is the systems biology approach. The different areas of systems biology, most prominently transcriptomics, proteomics and metabolomics, each of which provide a wealth of data that can be used to reveal novel biomarkers and biological pathways involved in the mode-of-action of ENMs. Combining such data with classical toxicological data would enable a more comprehensive understanding and hence might lead to more powerful and reliable prediction models. Physico-chemical data provide crucial information on the ENMs and need to be integrated, too. Overall statistical analysis should reveal robust grouping and categorization criteria and may ultimately help to identify meaningful biomarkers and biological pathways that sufficiently characterize the corresponding ENM subgroups. This chapter aims to give an overview on the different systems biology technologies and their current applications in the field of nanotoxicology, as well as to identify the existing challenges.

Detection of Endotoxin Contamination of Graphene Based Materials Using the TNF-α Expression Test and Guidelines for Endotoxin-Free Graphene Oxide Production

Nanomaterials may be contaminated with bacterial endotoxin during production and handling, which may confound toxicological testing of these materials, not least when assessing for immunotoxicity. In the present study, we evaluated the conventional Limulus amebocyte lysate (LAL) assay for endotoxin detection in graphene based material (GBM) samples, including graphene oxide (GO) and few-layered graphene (FLG). Our results showed that some GO samples interfered with various formats of the LAL assay. To overcome this problem, we developed a TNF-α expression test (TET) using primary human monocyte-derived macrophages incubated in the presence or absence of the endotoxin inhibitor, polymyxin B sulfate, and found that this assay, performed with non-cytotoxic doses of the GBM samples, enabled unequivocal detection of endotoxin with a sensitivity that is comparable to the LAL assay. FLG also triggered TNF-α production in the presence of the LPS inhibitor, pointing to an intrinsic pro-inflammatory effect. Finally, we present guidelines for the preparation of endotoxin-free GO, validated by using the TET.

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.

Improved methods for evaluating the environmental impact of nanoparticle synthesis†

With the market for products containing nanoparticles growing, improvements in the efficiency of nanoparticle synthesis are poised to have significant positive economic and environmental impacts. While many metrics have been designed for measuring the efficiency of small molecule synthesis, the use of these metrics for evaluating nanoparticle preparation has not been optimized. Here a critical evaluation of various green chemistry metrics is provided as they are applied to a common set of nanoparticle synthetic methods. The effect of the nanoparticle polydispersity on the relative greenness of different synthetic methods is also examined. Using metrics modified to account for polydispersity, a case study of gold nanoparticle syntheses is provided and three different methods of preparing monodisperse gold nanoparticles are compared. Interestingly, not all of the metrics provide the same rankings for the synthetic methods. And when polydispersity is ignored, the metrics provide a different rank order of the methods, highlighting the importance of clearly defining the desired nanoparticle size range to avoid underestimating the environmental impact.

Multilaboratory evaluation of 15 bioassays for (eco)toxicity screening and hazard ranking of engineered nanomaterials: FP7 project NANOVALID

Within EU FP7 project NANOVALID, the (eco)toxicity of 7 well-characterized engineered nanomaterials (NMs) was evaluated by 15 bioassays in 4 laboratories. The highest tested nominal concentration of NMs was 100 mg/l. The panel of the bioassays yielded the following toxicity order: Ag > ZnO > CuO > TiO₂>MWCNTs > SiO₂>Au. Ag, ZnO and CuO proved very toxic in the majority of assays, assumingly due to dissolution. The latter was supported by the parallel analysis of the toxicity of respective soluble metal salts. The most sensitive tests/species were Daphnia magna (towards Ag NMs, 24-h EC₅₀=0.003 mg Ag/l), algae Raphidocelis subcapitata (ZnO and CuO, 72-h EC₅₀=0.14 mg Zn/l and 0.7 mg Cu/l, respectively) and murine fibroblasts BALB/3T3 (CuO, 48-h EC₅₀=0.7 mg Cu/l). MWCNTs showed toxicity only towards rat alveolar macrophages (EC₅₀=15.3 mg/l) assumingly due to high aspect ratio and TiO₂ towards R. subcapitata (EC₅₀=6.8 mg Ti/l) due to agglomeration of TiO₂ and entrapment of algal cells. Finally, we constructed a decision tree to select the bioassays for hazard ranking of NMs. For NM testing, we recommend a multitrophic suite of 4 in vitro (eco)toxicity assays: 48-h D. magna immobilization (OECD202), 72-h R. subcapitata growth inhibition (OECD201), 30-min Vibrio fischeri bioluminescence inhibition (ISO2010) and 48-h murine fibroblast BALB/3T3 neutral red uptake in vitro (OECD129) representing crustaceans, algae, bacteria and mammalian cells, respectively. Notably, our results showed that these assays, standardized for toxicity evaluation of “regular” chemicals, proved efficient also for shortlisting of hazardous NMs. Additional assays are recommended for immunotoxicity evaluation of high aspect ratio NMs (such as MWCNTs).

'Bio-nano interactions: new tools, insights and impacts': summary of the Royal Society discussion meeting

Bio-nano interactions can be defined as the study of interactions between nanoscale entities and biological systems such as, but not limited to, peptides, proteins, lipids, DNA and other biomolecules, cells and cellular receptors and organisms including humans. Studying bio-nano interactions is particularly useful for understanding engineered materials that have at least one dimension in the nanoscale. Such materials may consist of discrete particles or nanostructured surfaces. Much of biology functions at the nanoscale; therefore, our ability to manipulate materials such that they are taken up at the nanoscale, and engage biological machinery in a designed and purposeful manner, opens new vistas for more efficient diagnostics, therapeutics (treatments) and tissue regeneration, so-called nanomedicine. Additionally, this ability of nanomaterials to interact with and be taken up by cells allows nanomaterials to be used as probes and tools to advance our understanding of cellular functioning. Yet, as a new technology, assessment of the safety of nanomaterials, and the applicability of existing regulatory frameworks for nanomaterials must be investigated in parallel with development of novel applications. The Royal Society meeting 'Bio-nano interactions: new tools, insights and impacts' provided an important platform for open dialogue on the current state of knowledge on these issues, bringing together scientists, industry, regulatory and legal experts to concretize existing discourse in science law and policy. This paper summarizes these discussions and the insights that emerged.

Emerging systems biology approaches in nanotoxicology: Towards a mechanism-based understanding of nanomaterial hazard and risk

Engineered nanomaterials are being developed for a variety of technological applications. However, the increasing use of nanomaterials in society has led to concerns about their potential adverse effects on human health and the environment. During the first decade of nanotoxicological research, the realization has emerged that effective risk assessment of the multitudes of new nanomaterials would benefit from a comprehensive understanding of their toxicological mechanisms, which is difficult to achieve with traditional, low-throughput, single end-point oriented approaches. Therefore, systems biology approaches are being progressively applied within the nano(eco)toxicological sciences. This novel paradigm implies that the study of biological systems should be integrative resulting in quantitative and predictive models of nanomaterial behaviour in a biological system. To this end, global 'omics' approaches with which to assess changes in genes, proteins, metabolites, etc. are deployed allowing for computational modelling of the biological effects of nanomaterials. Here, we highlight omics and systems biology studies in nanotoxicology, aiming towards the implementation of a systems nanotoxicology and mechanism-based risk assessment of nanomaterials.

Activation of Proinflammatory Responses in Cells of the Airway Mucosa by Particulate Matter: Oxidant- and Non-Oxidant-Mediated Triggering Mechanisms

Inflammation is considered to play a central role in a diverse range of disease outcomes associated with exposure to various types of inhalable particulates. The initial mechanisms through which particles trigger cellular responses leading to activation of inflammatory responses are crucial to clarify in order to understand what physico-chemical characteristics govern the inflammogenic activity of particulate matter and why some particles are more harmful than others. Recent research suggests that molecular triggering mechanisms involved in activation of proinflammatory genes and onset of inflammatory reactions by particles or soluble particle components can be categorized into direct formation of reactive oxygen species (ROS) with subsequent oxidative stress, interaction with the lipid layer of cellular membranes, activation of cell surface receptors, and direct interactions with intracellular molecular targets. The present review focuses on the immediate effects and responses in cells exposed to particles and central down-stream signaling mechanisms involved in regulation of proinflammatory genes, with special emphasis on the role of oxidant and non-oxidant triggering mechanisms. Importantly, ROS act as a central second-messenger in a variety of signaling pathways. Even non-oxidant mediated triggering mechanisms are therefore also likely to activate downstream redox-regulated events.

Biological Responses to Engineered Nanomaterials: Needs for the Next Decade

The interaction of nanomaterials with biomolecules, cells, and organisms is an enormously vital area of current research, with applications in nanoenabled diagnostics, imaging agents, therapeutics, and contaminant removal technologies. Yet the potential for adverse biological and environmental impacts of nanomaterial exposure is considerable and needs to be addressed to ensure sustainable development of nanomaterials. In this Outlook four research needs for the next decade are outlined: (i) measurement of the chemical nature of nanomaterials in dynamic, complex aqueous environments; (ii) real-time measurements of nanomaterial-biological interactions with chemical specificity; (iii) delineation of molecular modes of action for nanomaterial effects on living systems as functions of nanomaterial properties; and (iv) an integrated systems approach that includes computation and simulation across orders of magnitude in time and space.

Comprehensive In Vitro Toxicity Testing of a Panel of Representative Oxide Nanomaterials: First Steps towards an Intelligent Testing Strategy

Nanomaterials (NMs) display many unique and useful physico-chemical properties. However, reliable approaches are needed for risk assessment of NMs. The present study was performed in the FP7-MARINA project, with the objective to identify and evaluate in vitro test methods for toxicity assessment in order to facilitate the development of an intelligent testing strategy (ITS). Six representative oxide NMs provided by the EC-JRC Nanomaterials Repository were tested in nine laboratories. The in vitro toxicity of NMs was evaluated in 12 cellular models representing 6 different target organs/systems (immune system, respiratory system, gastrointestinal system, reproductive organs, kidney and embryonic tissues). The toxicity assessment was conducted using 10 different assays for cytotoxicity, embryotoxicity, epithelial integrity, cytokine secretion and oxidative stress. Thorough physico-chemical characterization was performed for all tested NMs. Commercially relevant NMs with different physico-chemical properties were selected: two TiO₂ NMs with different surface chemistry – hydrophilic (NM-103) and hydrophobic (NM-104), two forms of ZnO – uncoated (NM-110) and coated with triethoxycapryl silane (NM-111) and two SiO₂ NMs produced by two different manufacturing techniques – precipitated (NM-200) and pyrogenic (NM-203). Cell specific toxicity effects of all NMs were observed; macrophages were the most sensitive cell type after short-term exposures (24-72h) (ZnO>SiO₂>TiO₂). Longer term exposure (7 to 21 days) significantly affected the cell barrier integrity in the presence of ZnO, but not TiO₂ and SiO₂, while the embryonic stem cell test (EST) classified the TiO₂ NMs as potentially ‘weak-embryotoxic’ and ZnO and SiO₂ NMs as ‘non-embryotoxic’. A hazard ranking could be established for the representative NMs tested (ZnO NM-110 > ZnO NM-111 > SiO₂ NM-203 > SiO₂ NM-200 > TiO₂ NM-104 > TiO₂ NM-103). This ranking was different in the case of embryonic tissues, for which TiO₂ displayed higher toxicity compared with ZnO and SiO₂. Importantly, the in vitro methodology applied could identify cell- and NM-specific responses, with a low variability observed between different test assays. Overall, this testing approach, based on a battery of cellular systems and test assays, complemented by an exhaustive physico-chemical characterization of NMs, could be deployed for the development of an ITS suitable for risk assessment of NMs. This study also provides a rich source of data for modeling of NM effects.

Comparative cellular toxicity of titanium dioxide nanoparticles on human astrocyte and neuronal cells after acute and prolonged exposure

Although in the last few decades, titanium dioxide nanoparticles (TiO₂NPs) have attracted extensive interest due to their use in wide range of applications, their influences on human health are still quite uncertain and less known. Evidence exists indicating TiO₂NPs ability to enter the brain, thus representing a realistic risk factor for both chronic and accidental exposure with the consequent needs for more detailed investigation on CNS. A rapid and effective in vitro test strategy has been applied to determine the effects of TiO₂NPs anatase isoform, on human glial (D384) and neuronal (SH-SY5Y) cell lines. Toxicity was assessed at different levels: mitochondrial function (by MTT), membrane integrity and cell morphology (by calcein AM/PI staining) after acute exposure (4-24-48 h) at doses from 1.5 to 250 μg/ml as well as growth and cell proliferation (by clonogenic test) after prolonged exposure (7-10 days) at sub-toxic concentrations (from 0.05 to 31 μg/ml). The cytotoxic effects of TiO₂NPs were compared with those caused by TiO₂ bulk counterpart treatment. Acute TiO₂NP exposure produced (i) dose- and time-dependent alterations of the mitochondrial function on D384 and SH-SY5Y cells starting at 31 and 15 μg/ml doses, respectively, after 24h exposure. SH-SY5Y were slightly more sensitive than D384 cells; and (ii) cell membrane damage occurring at 125 μg/ml after 24h exposure in both cerebral cells. Comparatively, the effects of TiO₂ bulk were less pronounced than those induced by nanoparticles in both cerebral cell lines. Prolonged exposure indicated that the proliferative capacity (colony size) was compromised at the extremely low TiO₂NP doses namely 1.5 μg/ml and 0.1 μg/ml for D384 and SH-SY5Y, respectively; cell sensitivity was still higher for SH-SY5Y compared to D384. Colony number decrease (15%) was also evidenced at ≥0.2 μg/ml TiO₂NP dose. Whereas, TiO₂ bulk treatment affected cell morphology only. TiO₂ internalization in SH-SY5Y and D384 cells was appreciated using light microscopy. These findings indicated, that (i) human cerebral SH-SY5Y and D384 cell lines exposed to TiO₂NPs were affected not only after acute but even after prolonged exposure at particularly low doses (≥ 0.1 μg/ml), (ii) these in vitro critical doses were comparable to literature brain Ti levels detected in lab animal intranasally administered with TiO₂NP and associated to neurotoxic effects. In summary, the applied cell-based screening platform seems to provide effective means to initial evaluation of TiO₂NP toxicity on CNS.

An ISA-TAB-Nano based data collection framework to support data-driven modelling of nanotoxicology

Analysis of trends in nanotoxicology data and the development of data driven models for nanotoxicity is facilitated by the reporting of data using a standardised electronic format. ISA-TAB-Nano has been proposed as such a format. However, in order to build useful datasets according to this format, a variety of issues has to be addressed. These issues include questions regarding exactly which (meta)data to report and how to report them. The current article discusses some of the challenges associated with the use of ISA-TAB-Nano and presents a set of resources designed to facilitate the manual creation of ISA-TAB-Nano datasets from the nanotoxicology literature. These resources were developed within the context of the NanoPUZZLES EU project and include data collection templates, corresponding business rules that extend the generic ISA-TAB-Nano specification as well as Python code to facilitate parsing and integration of these datasets within other nanoinformatics resources. The use of these resources is illustrated by a "Toy Dataset" presented in the Supporting Information. The strengths and weaknesses of the resources are discussed along with possible future developments.

Emerging concepts in dendrimer-based nanomedicine: from design principles to clinical applications

Dendrimers are discrete nanostructures/nanoparticles with 'onion skin-like' branched layers. Beginning with a core, these nanostructures grow in concentric layers to produce stepwise increases in size that are similar to the dimensions of many in vivo globular proteins. These branched tree-like concentric layers are referred to as 'generations'. The outer generation of each dendrimer presents a precise number of functional groups that may act as a monodispersed platform for engineering favourable nanoparticle-drug and nanoparticle-tissue interactions. These features have attracted significant attention in medicine as nanocarriers for traditional small drugs, proteins, DNA/RNA and in some instances as intrinsically active nanoscale drugs. Dendrimer-based drugs, as well as diagnostic and imaging agents, are emerging as promising candidates for many nanomedicine applications. First, we will provide a brief survey of recent nanomedicines that are either approved or in the clinical approval process. This will be followed by an introduction to a new 'nanoperiodic' concept which proposes nanoparticle structure control and the engineering of 'critical nanoscale design parameters' (CNDPs) as a strategy for optimizing pharmocokinetics, pharmocodynamics and site-specific targeting of disease. This paradigm has led to the emergence of CNDP-directed nanoperiodic property patterns relating nanoparticle behaviour to critical in vivo clinical translation issues such as cellular uptake, transport, elimination, biodistribution, accumulation and nanotoxicology. With a focus on dendrimers, these CNDP-directed nanoperiodic patterns are used as a strategy for designing and optimizing nanoparticles for a variety of drug delivery and imaging applications, including a recent dendrimer-based theranostic nanodevice for imaging and treating cancer. Several emerging preclinical dendrimer-based nanotherapy concepts related to inflammation, neuro-inflammatory disorders, oncology and infectious and ocular diseases are reviewed. Finally we will consider challenges and opportunities anticipated for future clinical translation, nanotoxicology and the commercialization of nanomedicine.

Mechanism-based genotoxicity screening of metal oxide nanoparticles using the ToxTracker panel of reporter cell lines

BACKGROUND

The rapid expansion of manufacturing and use of nano-sized materials fuels the demand for fast and reliable assays to identify their potential hazardous properties and underlying mechanisms. The ToxTracker assay is a recently developed mechanism-based reporter assay based on mouse embryonic stem (mES) cells that uses GFP-tagged biomarkers for detection of DNA damage, oxidative stress and general cellular stress upon exposure. Here, we evaluated the ability of the ToxTracker assay to identify the hazardous properties and underlying mechanisms of a panel of metal oxide- and silver nanoparticles (NPs) as well as additional non-metallic materials (diesel, carbon nanotubes and quartz).

METHODS

The metal oxide- and silver nanoparticles were characterized in terms of agglomeration and ion release in cell medium (using photon cross correlation spectroscopy and inductively coupled plasma with optical emission spectroscopy, respectively) as well as acellular ROS production (DCFH-DA assay). Cellular uptake was investigated by means of transmission electron microscopy. GFP reporter induction and cytotoxicity of the NPs was simultaneously determined using flow cytometry, and genotoxicity was further tested using conventional assays (comet assay, γ-H2AX and RAD51 foci formation).

RESULTS

We show that the reporter cells were able to take up nanoparticles and, furthermore, that exposure to CuO, NiO and ZnO nanoparticles as well as to quartz resulted in activation of the oxidative stress reporter, although only at high cytotoxicity for ZnO. NiO NPs activated additionally a p53-associated cellular stress response, indicating additional reactive properties. Conventional assays for genotoxicity assessment confirmed the response observed in the ToxTracker assay. We show for CuO NPs that the induction of oxidative stress is likely the consequence of released Cu ions whereas the effect by NiO was related to the particles per se. The DNA replication stress-induced reporter, which is most strongly associated with carcinogenicity, was not activated by any of the tested nanoparticles.

CONCLUSIONS

We conclude that the ToxTracker reporter system can be used as a rapid mechanism-based tool for the identification of hazardous properties of metal oxide NPs. Furthermore, genotoxicity of metal oxide NPs seems to occur mainly via oxidative stress rather than direct DNA binding with subsequent replication stress.

Cancer biology, toxicology and alternative methods development go hand-in-hand

Toxicological research faces the challenge of integrating knowledge from diverse fields and novel technological developments generally in the biological and medical sciences. We discuss herein the fact that the multiple facets of cancer research, including discovery related to mechanisms, treatment and diagnosis, overlap many up and coming interest areas in toxicology, including the need for improved methods and analysis tools. Common to both disciplines, in vitro and in silico methods serve as alternative investigation routes to animal studies. Knowledge on cancer development helps in understanding the relevance of chemical toxicity studies in cell models, and many bioinformatics-based cancer biomarker discovery tools are also applicable to computational toxicology. Robotics-aided, cell-based, high-throughput screening, microscale immunostaining techniques and gene expression profiling analyses are common tools in cancer research, and when sequentially combined, form a tiered approach to structured safety evaluation of thousands of environmental agents, novel chemicals or engineered nanomaterials. Comprehensive tumour data collections in databases have been translated into clinically useful data, and this concept serves as template for computer-driven evaluation of toxicity data into meaningful results. Future 'cancer research-inspired knowledge management' of toxicological data will aid the translation of basic discovery results and chemicals- and materials-testing data to information relevant to human health and environmental safety.

Enalos InSilicoNano platform: an online decision support tool for the design and virtual screening of nanoparticles

A QNAR model, available online through Enalos InSilicoNano platform, has been developed and validated for the risk assessment of nanoparticles (NPs).