Measurement of oxidative damage to DNA in nanomaterial exposed cells and animals

Pilot Study of Acute and Subchronic Oral Toxicological Biosafety Evaluation of Resorcinol-Formaldehyde Aerogel Nanomaterial in Kunming Mice

Resorcinol-formaldehyde aerogel (RFa) is a unique nanomaterial composed of polymer nanoparticles with a three-dimensional network structure. Our previous studies have demonstrated its application in the separation and purification of alkaloids, and we are exploring its application potential as the drug delivery carrier. Therefore, it is necessary to comprehensively understand the in vivo toxicity profile of RFa and evaluate its oral biosafety. In this work, we systematically evaluated the in vivo acute toxicity and subchronic oral toxicity of RFa in both male and female Kunming mice. During the 14-day acute toxicity test, the dose administered (M = 580 mg/kg) was converted from the clinical dose of adsorbed alkaloids on RFa. The mice were gavaged only once and were observed continuously for 14 days. There were no abnormalities, and pathological changes in the major organs (heart, liver, spleen, lungs, kidneys, testes, and ovaries) were detected, followed by the 12-week subchronic toxicity test at the dose of 1/4M, 1/2M, and M. All mice were administered orally once daily and regularly observed throughout the experimental period. As a result, no abnormalities were found in body weights, food intake, and organ coefficients. Tissue section revealed no pathological changes in the major organs. In addition, there were no significant differences in hematological, blood biochemical, and coagulation parameters in both male and female mice compared to control group. These results showed that RFa was well tolerated at these dosage levels and did not cause significant toxic effects in Kunming mice. This study, as part of a broad research program on the biosafety of aerogel nanomaterials, provided the biosafety assurance for the subsequent study of RFa in biomedical applications.

New methodological developments for testing the in vitro genotoxicity of nanomaterials: Comparison of 2D and 3D HepaRG liver cell models and classical and high throughput comet assay formats

Nanomaterials (NMs) are defined as materials with at least one external dimension below 100 nm. Their small size confers them interesting unique physico-chemical properties, hence NMs are increasingly used in a diversity of applications. However, the specific properties of NMs could also make them more harmful than their bulk counterparts. Therefore, there is a crucial need to deliver efficient NM hazard assessment in order to sustain the responsible development of nanotechnology. This study analysed the genotoxic potential of several NMs: one titanium dioxide (TiO2) and two zinc oxide NMs (ZnO) that were tested up to 100 μg/mL on 2D and 3D hepatic HepaRG models. Genotoxicity analysis was performed comparing the alkaline comet assay in classical and high throughput formats. Moreover, oxidative DNA lesions were investigated with the Fpg-modified comet assay. Results showed that TiO2 NMs were not cytotoxic and not genotoxic in either cell model, although a small increase in the % tail DNA was observed in 3D HepaRG cells at 100 μg/mL in the classical format. The two ZnO NMs (ZnO S. NMs a commercial suspension and NM110 provided by the European Union Joint Research Centre) induced a concentration-dependent increase in cytotoxicity that was more pronounced in the 2D (>20% cytotoxicity was observed for ZnO S. at concentrations greater than 25 μg/mL, and for NM 110 at 50 μg/mL) than in the 3D model (more than 20% cytotoxicity for ZnO S. NMs at 50 μg/mL). While ZnO S. NMs induced DNA damage associated with cytotoxicity (at 25 and 50 μg/mL in 2D and 50 μg/mL in 3D), NM110 showed a clear genotoxic effect at non-cytotoxic concentrations (25 μg/mL in 2D and at 25 and 50 μg/mL in 3D). No major differences could be observed in the comet assay in the presence or absence of the Fpg enzyme. High throughput analysis using CometChip® mostly confirmed the results obtained with the classical format, and even enhanced the detection of genotoxicity in the 3D model. In conclusion, this study demonstrated that new approach methodologies (NAMs), 3D models and the high throughput format for the comet assay, were more efficient in the detection of genotoxic effects, and are therefore promising approaches to improve hazard assessment of NMs.

Gastrointestinal tract exposure to particles and DNA damage in animals: A review of studies before, during and after the peak of nanotoxicology

Humans ingest particles and fibers on daily basis. Non-digestible carbohydrates are beneficial to health and food additives are considered safe. However, titanium dioxide (E171) has been banned in the European Union because the European Food Safety Authority no longer considers it non-genotoxic. Ingestion of microplastics and nanoplastics are novel exposures; their potential hazardous effects to humans have been under the radar for many years. In this review, we have assessed the association between oral exposure to man-made particles/fibers and genotoxicity in gastrointestinal tract cells and secondary tissues. We identified a total of 137 studies on oral exposure to particles and fibers. This was reduced to 49 papers with sufficient quality and relevance, including exposures to asbestos, diesel exhaust particles, titanium dioxide, silver nanoparticles, zinc oxide, synthetic amorphous silica and certain other nanomaterials. Nineteen studies show positive results, 25 studies show null results, and 5 papers show equivocal results on genotoxicity. Recent studies seem to show null effects, whereas there is a higher proportion of positive genotoxicity results in early studies. Genotoxic effects seem to cluster in studies on diesel exhaust particles and titanium dioxide, whereas studies on silver nanoparticles, zinc oxide and synthetic amorphous silica seem to show mainly null effects. The most widely used genotoxic tests are the alkaline comet assay and micronucleus assay. There are relatively few results on genotoxicity using reliable measurements of oxidatively damaged DNA, DNA double strand breaks (γH2AX assay) and mutations. In general, evidence suggest that oral exposure to particles and fibers is associated with genotoxicity in animals.

Nanoplastics from ground polyethylene terephthalate food containers: Genotoxicity in human lung epithelial A549 cells

The ubiquitous pollution of plastic particles in most environmental matrices leads to concern about any potential adverse effects on human health. Most studies on the toxicological effect of nanoplastics has focused on standard particles of polystyrene. In reality humans are exposed to a large variety of different types and sizes of plastic material via oral intake and inhalation. In this study, we investigated the effect of polyethylene terephthalate (PET) nanoplastic particles from ground food containers from a supermarket. The aim was to investigate a possible link between exposure to PET nanoplastics and genotoxic response in a cell model of the human airway epithelial (A549) cells. Further, we investigated the combined effect of PET and chemicals known to alter the cellular redox state, as a model of partially compromised antioxidant defense system. DNA damage was assessed by the alkaline comet assay. The ground PET nanoplastics have a mean hydrodynamic diameter of 136 nm in water. The results showed that PET exposure led to increased reactive oxygen species production (approximately 30 % increase compared to unexposed cells). In addition, exposure to PET nanoplastic increased the level of DNA strand breaks (net increase = 0.10 lesions/106 base pair, 95 % confidence interval: 0.01, 0.18 lesions/106 base pair). Pre- or post-exposure to hydrogen peroxide or buthionine sulfoximine did not lead to a higher level of DNA damage. Overall, the study shows that exposure to PET nanoplastics increases both intracellular reactive oxygen production and DNA damage in A549 cells.

Long-term cryopreservation of potassium bromate positive assay controls for measurement of oxidatively damaged DNA by the Fpg-modified comet assay: results from the hCOMET ring trial

The formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay is widely used for the measurement of oxidatively generated damage to DNA. However, there has not been a recommended long-term positive control for this version of the comet assay. We have investigated potassium bromate as a positive control for the Fpg-modified comet assay because it generates many Fpg-sensitive sites with a little concurrent generation of DNA strand breaks. Eight laboratories used the same procedure for the treatment of monocytic THP-1 cells with potassium bromate (0, 0.5, 1.5, and 4.5 mM) and subsequent cryopreservation in a freezing medium consisting of 50% foetal bovine serum, 40% RPMI-1640 medium, and 10% dimethyl sulphoxide. The samples were analysed by the Fpg-modified comet assay three times over a 3-year period. All laboratories obtained a positive concentration-response relationship in cryopreserved samples (linear regression coefficients ranging from 0.79 to 0.99). However, there was a wide difference in the levels of Fpg-sensitive sites between the laboratory with the lowest (4.2% Tail DNA) and highest (74% Tail DNA) values in THP-1 cells after exposure to 4.5 mM KBrO3. In an attempt to assess sources of inter-laboratory variation in Fpg-sensitive sites, comet images from one experiment in each laboratory were forwarded to a central laboratory for visual scoring. There was high consistency between measurements of %Tail DNA values in each laboratory and the visual score of the same comets done in the central laboratory (r = 0.98, P < 0.001, linear regression). In conclusion, the results show that potassium bromate is a suitable positive comet assay control.

Genotoxicity by rapeseed methyl ester and hydrogenated vegetable oil combustion exhaust products in lung epithelial (A549) cells

Biofuel is an attractive substitute for petrodiesel because of its lower environmental footprint. For instance, the polycyclic aromatic hydrocarbons (PAH) emission per fuel energy content is lower for rapeseed methyl ester (RME) than for petrodiesel. This study assesses genotoxicity by extractable organic matter (EOM) of exhaust particles from the combustion of petrodiesel, RME, and hydrogenated vegetable oil (HVO) in lung epithelial (A549) cells. Genotoxicity was assessed as DNA strand breaks by the alkaline comet assay. EOM from the combustion of petrodiesel and RME generated the same level of DNA strand breaks based on the equal concentration of total PAH (i.e. net increases of 0.13 [95% confidence interval (CI): 0.002, 0.25, and 0.12 [95% CI: 0.01, 0.24] lesions per million base pairs, respectively). In comparison, the positive control (etoposide) generated a much higher level of DNA strand breaks (i.e. 0.84, 95% CI: 0.72, 0.97) lesions per million base pairs. Relatively low concentrations of EOM from RME and HVO combustion particles (<116 ng/ml total PAH) did not cause DNA strand breaks in A549 cells, whereas benzo[a]pyrene and PAH-rich EOM from petrodiesel combusted using low oxygen inlet concentration were genotoxic. The genotoxicity was attributed to high molecular weight PAH isomers with 5-6 rings. In summary, the results show that EOM from the combustion of petrodiesel and RME generate the same level of DNA strand breaks on an equal total PAH basis. However, the genotoxic hazard of engine exhaust from on-road vehicles is lower for RME than petrodiesel because of lower PAH emission per fuel energy content.

Airway and systemic biomarkers of health effects after short-term exposure to indoor ultrafine particles from cooking and candles - A randomized controlled double-blind crossover study among mild asthmatic subjects

BACKGROUND

There is insufficient knowledge about the systemic health effects of exposure to fine (PM_2.5) and ultrafine particles emitted from typical indoor sources, including cooking and candlelight burning. We examined whether short-term exposure to emissions from cooking and burning candles cause inflammatory changes in young individuals with mild asthma. Thirty-six non-smoking asthmatics participated in a randomized controlled double-blind crossover study attending three exposure sessions (mean PM_2.5 µg/m³_; polycyclic aromatic hydrocarbons ng/m³): (a) air mixed with emissions from cooking (96.1; 1.1), (b) air mixed with emissions from candles (89.8; 10), and (c) clean filtered air (5.8; 1.0). Emissions were generated in an adjacent chamber and let into a full-scale exposure chamber where participants were exposed for five hours. Several biomarkers were assessed in relation to airway and systemic inflammatory changes; the primary outcomes of interest were surfactant Protein-A (SP-A) and albumin in droplets in exhaled air - novel biomarkers for changes in the surfactant composition of small airways. Secondary outcomes included cytokines in nasal lavage, cytokines, C-reactive protein (CRP), epithelial progenitor cells (EPCs), genotoxicity, gene expression related to DNA-repair, oxidative stress, and inflammation, as well as metabolites in blood. Samples were collected before exposure start, right after exposure and the next morning.

RESULTS

SP-A in droplets in exhaled air showed stable concentrations following candle exposure, while concentrations decreased following cooking and clean air exposure. Albumin in droplets in exhaled air increased following exposure to cooking and candles compared to clean air exposure, although not significant. Oxidatively damaged DNA and concentrations of some lipids and lipoproteins in the blood increased significantly following exposure to cooking. We found no or weak associations between cooking and candle exposure and systemic inflammation biomarkers including cytokines, CRP, and EPCs.

CONCLUSIONS

Cooking and candle emissions induced effects on some of the examined health-related biomarkers, while no effect was observed in others; Oxidatively damaged DNA and concentrations of lipids and lipoproteins were increased in blood after exposure to cooking, while both cooking and candle emissions slightly affected the small airways including the primary outcomes SP-A and albumin. We found only weak associations between the exposures and systemic inflammatory biomarkers. Together, the results show the existence of mild inflammation following cooking and candle exposure.

Exposure to nanoplastic particles and DNA damage in mammalian cells

There is concern about human exposure to nanoplastics from intentional use or degradation of plastics in the environment. This review assesses genotoxic effects of nanoplastics, defined as particles with a primary size of less than 1000 nm. The majority of results on genotoxicity come from studies on polystyrene (PS) particles in mammalian cell cultures. Most studies have measured DNA strand breaks (standard comet assay), oxidatively damaged DNA (Fpg-modified comet assay) and micronuclei. Twenty-nine out of 60 results have shown statistically significant genotoxic effects by PS exposure in cell cultures. A statistical analysis indicates that especially modified PS particles are genotoxic (odds ratio = 8.6, 95 % CI: 1.6, 46) and immune cells seems to be more sensitive to genotoxicity than other cell types such as epithelial cells (odds ratio = 8.0, 95 % CI: 1.6, 39). On the contrary, there is not a clear association between statistically significant effects in genotoxicity tests and the primary size of PS particles, (i.e. smaller versus larger than 100 nm) or between the type of genotoxic endpoint (i.e. repairable versus permanent DNA lesions). Three studies of PS particle exposure in animals have shown increased level of DNA strand breaks in leukocytes and prefrontal cortex cells. Nanoplastics from polyethylene, propylene, polyvinyl chloride and polyethylene terephthalate have been investigated in very few studies and it is currently not possible to draw conclusion about their genotoxic hazard. In summary, there is some evidence suggesting that PS particles may be genotoxic in mammalian cells.

Do cytotoxicity and cell death cause false positive results in the in vitro comet assay?

The comet assay is used to measure DNA damage induced by chemical and physical agents. High concentrations of test agents may cause cytotoxicity or cell death, which may give rise to false positive results in the comet assay. Systematic studies on genotoxins and cytotoxins (i.e. non-genotoxic poisons) have attempted to establish a threshold of cytotoxicity or cell death by which DNA damage results measured by the comet assay could be regarded as a false positive result. Thresholds of cytotoxicity/cell death range from 20% to 50% in various publications. Curiously, a survey of the latest literature on comet assay results from cell culture studies suggests that one-third of publications did not assess cytotoxicity or cell death. We recommend that it should be mandatory to include results from at least one type of assay on cytotoxicity, cell death or cell proliferation in publications on comet assay results. A combination of cytotoxicity (or cell death) and proliferation (or colony forming efficiency assay) is preferable in actively proliferating cells because it covers more mechanisms of action. Applying a general threshold of cytotoxicity/cell death to all types of agents may not be applicable; however, 25% compared to the concurrent negative control seems to be a good starting value to avoid false positive comet assay results. Further research is needed to establish a threshold value to distinguish between true and potentially false positive genotoxic effects detected by the comet assay.

Systematic review on primary and secondary genotoxicity of carbon black nanoparticles in mammalian cells and animals

Carbon black exposure causes oxidative stress, inflammation and genotoxicity. The objective of this systematic review was to assess the contributions of primary (i.e. direct formation of DNA damage) and secondary genotoxicity (i.e., DNA lesions produced indirectly by inflammation) to the overall level of DNA damage by carbon black. The database is dominated by studies that have measured DNA damage by the comet assay. Cell culture studies indicate a genotoxic action of carbon black, which might be mediated by oxidative stress. Many in vivo studies originate from one laboratory that has investigated the genotoxic effects of Printex 90 in mice by intra-tracheal instillation. Meta-analysis and pooled analysis of these results demonstrate that Printex 90 exposure is associated with a slightly increased level of DNA strand breaks in bronchoalveolar lavage cells and lung tissue. Other types of genotoxic damage have not been investigated as thoroughly as DNA strand breaks, although there is evidence to suggest that carbon black exposure might increase the mutation frequency and cytogenetic endpoints. Stratification of studies according to concurrent inflammation and DNA damage does not indicate that carbon black exposure gives rise to secondary genotoxicity. Even substantial pulmonary inflammation is at best only associated with a weak genotoxic response in lung tissue. In conclusion, the review indicates that nanosized carbon black is a weak genotoxic agent and this effect is more likely to originate from a primary genotoxic mechanism of action, mediated by e.g., oxidative stress, than inflammation-driven (secondary) genotoxicity.

Continuous ZnO nanoparticle exposure induces melanoma-like skin lesions in epidermal barrier dysfunction model mice through anti-apoptotic effects mediated by the oxidative stress–activated NF-κB pathway

Background

Increasing interest in the hazardous properties of zinc oxide nanoparticles (ZnO NPs), commonly used as ultraviolet filters in sunscreen, has driven efforts to study the percutaneous application of ZnO NPs to diseased skin; however, in-depth studies of toxic effects on melanocytes under conditions of epidermal barrier dysfunction remain lacking.

Methods

Epidermal barrier dysfunction model mice were continuously exposed to a ZnO NP-containing suspension for 14 and 49 consecutive days in vivo. Melanoma-like change and molecular mechanisms were also verified in human epidermal melanocytes treated with 5.0 µg/ml ZnO NPs for 72 h in vitro.

Results

ZnO NP application for 14 and 49 consecutive days induced melanoma-like skin lesions, supported by pigmented appearance, markedly increased number of melanocytes in the epidermis and dermis, increased cells with irregular nuclei in the epidermis, recruited dendritic cells in the dermis and dysregulated expression of melanoma-associated gene Fkbp51, Trim63 and Tsp 1. ZnO NPs increased oxidative injury, inhibited apoptosis, and increased nuclear factor kappa B (NF-κB) p65 and Bcl-2 expression in melanocytes of skin with epidermal barrier dysfunction after continuously treated for 14 and 49 days. Exposure to 5.0 µg/ml ZnO NPs for 72 h increased cell viability, decreased apoptosis, and increased Fkbp51 expression in melanocytes, consistent with histological observations in vivo. The oxidative stress–mediated mechanism underlying the induction of anti-apoptotic effects was verified using the reactive oxygen species scavenger N-acetylcysteine.

Conclusions

The entry of ZnO NPs into the stratum basale of skin with epidermal barrier dysfunction resulted in melanoma-like skin lesions and an anti-apoptotic effect induced by oxidative stress, activating the NF-κB pathway in melanocytes.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01308-w.

Measurement of oxidatively damaged DNA in mammalian cells using the comet assay: Reflections on validity, reliability and variability

The comet assay is a simple technique for measurements of low levels of DNA damage and repair in single cells. However, there is variation in background levels of DNA damage in peripheral blood mononuclear cells (PBMCs). This variation has been documented by inter-laboratory ring-trials where identical samples have been analysed in different laboratories using the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay. The coefficient of variation of background levels of Fpg-sensitive sites was 128 % in the first inter-laboratory validation trial called European Standards Committee on Oxidative DNA Damage. The variation was reduced to 44 % by the end of the project. Subsequent ring-trials by the European Comet Assay Validation Group showed similar inter-laboratory variation in Fpg-sensitive sites in PBMCs (45 %). The lowest inter-laboratory variation in Fpg-sensitive sites in PBMCs was 12 % when using calibration to standardize comet assay descriptors. Introduction of standard comet assay procedures was surprisingly unsuccessful as certain laboratories experienced technical problems using unaccustomed assay conditions. This problem was alleviated by using flexible assay standard conditions rather than a standard protocol in a ring-trial by the hCOMET group. The approach reduced technical problems, but the inter-laboratory variation in Fpg-sensitive sites was not reduced. The ring-trials have not pinpointed specific assay steps as major determinants of the variation in DNA damage levels. It is likely that small differences in several steps cause inter-laboratory variation. Although this variation in reported DNA damage levels causes concern, ring-trials have also shown that the comet assay is a reliable tool in biomonitoring studies.

Biomarkers of DNA Oxidation Products: Links to Exposure and Disease in Public Health Studies

Environmental exposure can increase the production of reactive oxygen species and deplete cellular antioxidants in humans, resulting in oxidatively generated damage to DNA that is both a useful biomarker of oxidative stress and indicator of carcinogenic hazard. Methods of oxidatively damaged DNA analysis have been developed and used in public health research since the 1990s. Advanced techniques detect specific lesions, but they might not be applicable to complex matrixes (e.g., tissues), small sample volume, and large-scale studies. The most reliable methods are characterized by (1) detecting relevant DNA oxidation products (e.g., premutagenic lesions), (2) not harboring technical problems, (3) being applicable to complex biological mixtures, and (4) having the ability to process a large number of samples in a reasonable period of time. Most effort has been devoted to the measurements of 8-oxo-7,8-dihydro-2'-deoxyguanine (8-oxodG), which can be analyzed by chromatographic, enzymic, and antibody-based methods. Results from validation trials have shown that certain chromatographic and enzymic assays (namely the comet assay) are superior techniques. The enzyme-modified comet assay has been popular because it is technically simpler than chromatographic assays. It is widely used in public health studies on environmental exposures such as outdoor air pollution. Validated biomarker assays on oxidatively damaged DNA have been used to fill knowledge gaps between findings in prospective cohort studies and hazards from contemporary sources of air pollution exposures. Results from each of these research fields feed into public health research as approaches to conduct primary prevention of diseases caused by environmental or occupational agents.

Current approaches for the exploration of antimicrobial activities of nanoparticles

Infectious diseases of bacterial and viral origins contribute to substantial mortality worldwide. Collaborative efforts have been underway between academia and the industry to develop technologies for a more effective treatment for such diseases. Due to their utility in various industrial applications, nanoparticles (NPs) offer promising potential as antimicrobial agents against bacterial and viral infections. NPs have been established to possess potent antimicrobial activities against various types of pathogens due to their unique characteristics and cell-damaging ability through several mechanisms. The recently accepted antimicrobial mechanisms possessed by NPs include metal ion release, oxidative stress induction, and non-oxidative mechanisms. Another merit of NPs lies in the low likelihood of the development of microbial tolerance towards NPs, given the multiple simultaneous mechanisms of action against the pathogens targeting numerous gene mutations in these pathogens. Moreover, NPs provide a fascinating opportunity to curb microbial growth before infections: this outstanding feature has led to their utilization as active antimicrobial agents in different industrial applications, e.g. the coating of medical devices, incorporation in food packaging, promoting wound healing and encapsulation with other potential materials for wastewater treatment. This review discusses the progress and achievements in the antimicrobial applications of NPs, factors contributing to their actions, mechanisms underlying their efficiency, and risks of their applications, including the antimicrobial action of metal nanoclusters (NCs). The review concludes with a discussion of the restrictions on present studies and future prospects of nanotechnology-based NPs development.

Inhalation of hydrogenated vegetable oil combustion exhaust and genotoxicity responses in humans

Biofuels from vegetable oils or animal fats are considered to be more sustainable than petroleum-derived diesel fuel. In this study, we have assessed the effect of hydrogenated vegetable oil (HVO) exhaust on levels of DNA damage in peripheral blood mononuclear cells (PBMCs) as primary outcome, and oxidative stress and inflammation as mediators of genotoxicity. In a randomized cross-over study, healthy humans were exposed to filtered air, inorganic salt particles, exhausts from combustion of HVO in engines with aftertreatment [i.e. emission with nitrogen oxides and low amounts of particulate matter less than 2.5 µm (approximately 1 µg/m³)], or without aftertreatment (i.e. emission with nitrogen oxides and 93 ± 13 µg/m³ of PM_2.5). The subjects were exposed for 3 h and blood samples were collected before, within 1 h after the exposure and 24 h after. None of the exposures caused generation of DNA strand breaks and oxidatively damaged DNA, or affected gene expression of factors related to DNA repair (Ogg1), antioxidant defense (Hmox1) or pro-inflammatory cytokines (Ccl2, Il8 and Tnfa) in PBMCs. The results from this study indicate that short-term HVO exhaust exposure is not associated with genotoxic hazard in humans.

Validation of the in vitro comet assay for DNA cross-links and altered bases detection

Mechanistic toxicology is gaining weight for human health risk assessment. Different mechanistic assays are available, such as the comet assay, which detects DNA damage at the level of individual cells. However, the conventional alkaline version only detects strand breaks and alkali-labile sites. We have validated two modifications of the in vitro assay to generate mechanistic information: (1) use of DNA-repair enzymes (i.e., formamidopyrimidine DNA glycosylase, endonuclease III, human 8-oxoguanine DNA glycosylase I and human alkyladenine DNA glycosylase) for detection of oxidized and alkylated bases as well as (2) a modification for detecting cross-links. Seven genotoxicants with different mechanisms of action (potassium bromate, methyl methanesulfonate, ethyl methanesulfonate, hydrogen peroxide, cisplatin, mitomycin C, and benzo[a]pyrene diol epoxide), as well as a non-genotoxic compound (dimethyl sulfoxide) and a cytotoxic compound (Triton X-100) were tested on TK-6 cells. We were able to detect with high sensitivity and clearly differentiate oxidizing, alkylating and cross-linking agents. These modifications of the comet assay significantly increase its sensitivity and its specificity towards DNA lesions, providing mechanistic information regarding the type of damage.

EFSA Scientific Committee, More S, Bampidis V, Benford D, Bragard C, Halldorsson T, Hernández‐Jerez A, Hougaard Bennekou S, Koutsoumanis K, Lambré C, Machera K, Naegeli H, Nielsen S, Schlatter J, Schrenk D, Silano (deceased) V, Turck D, Younes M, Castenmiller J, Chaudhry Q, Cubadda F, Franz R, Gott D, Mast J, Mortensen A, Oomen AG, Weigel S, Barthelemy E, Rincon A, Tarazona J, Schoonjans R. Guidance on risk assessment of nanomaterials to be applied in the food and feed chain: human and animal health

The EFSA has updated the Guidance on risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain, human and animal health. It covers the application areas within EFSA's remit, including novel foods, food contact materials, food/feed additives and pesticides. The updated guidance, now Scientific Committee Guidance on nano risk assessment (SC Guidance on Nano-RA), has taken account of relevant scientific studies that provide insights to physico-chemical properties, exposure assessment and hazard characterisation of nanomaterials and areas of applicability. Together with the accompanying Guidance on Technical requirements for regulated food and feed product applications to establish the presence of small particles including nanoparticles (Guidance on Particle-TR), the SC Guidance on Nano-RA specifically elaborates on physico-chemical characterisation, key parameters that should be measured, methods and techniques that can be used for characterisation of nanomaterials and their determination in complex matrices. The SC Guidance on Nano-RA also details aspects relating to exposure assessment and hazard identification and characterisation. In particular, nanospecific considerations relating to in vitro/in vivo toxicological studies are discussed and a tiered framework for toxicological testing is outlined. Furthermore, in vitro degradation, toxicokinetics, genotoxicity, local and systemic toxicity as well as general issues relating to testing of nanomaterials are described. Depending on the initial tier results, additional studies may be needed to investigate reproductive and developmental toxicity, chronic toxicity and carcinogenicity, immunotoxicity and allergenicity, neurotoxicity, effects on gut microbiome and endocrine activity. The possible use of read-across to fill data gaps as well as the potential use of integrated testing strategies and the knowledge of modes or mechanisms of action are also discussed. The Guidance proposes approaches to risk characterisation and uncertainty analysis.

Potassium bromate as positive assay control for the Fpg-modified comet assay

The comet assay is a popular assay in biomonitoring studies. DNA strand breaks (or unspecific DNA lesions) are measured using the standard comet assay. Oxidative stress-generated DNA lesions can be measured by employing DNA repair enzymes to recognise oxidatively damaged DNA. Unfortunately, there has been a tendency to fail to report results from assay controls (or maybe even not to employ assay controls). We believe this might have been due to uncertainty as to what really constitutes a positive control. It should go without saying that a biomonitoring study cannot have a positive control group as it is unethical to expose healthy humans to DNA damaging (and thus potentially carcinogenic) agents. However, it is possible to include assay controls in the analysis (here meant as a cryopreserved sample of cells i.e. included in each experiment as a reference sample). In the present report we tested potassium bromate (KBrO3) as a positive comet assay control for the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay. Ten laboratories used the same procedure for treatment of monocytic THP-1 cells with KBrO3 (0.5, 1.5 and 4.5 mM for 1 h at 37°C) and subsequent cryopreservation. Results from one laboratory were excluded in the statistical analysis because of technical issues in the Fpg-modified comet assay. All other laboratories found a concentration-response relationship in cryopreserved samples (regression coefficients from 0.80 to 0.98), although with different slopes ranging from 1.25 to 11.9 Fpg-sensitive sites (%DNA in tail) per 1 mM KBrO3. Our results demonstrate that KBrO3 is a suitable positive comet assay control.

Genotoxicity of multi-walled carbon nanotube reference materials in mammalian cells and animals

Carbon nanotubes (CNTs) were the first nanomaterials to be evaluated by the International Agency for Research on Cancer (IARC). The categorization as possibly carcinogenic agent to humans was only applicable to multi-walled carbon nanotubes called MWCNT-7. Other types of CNTs were not classifiable because of missing data and it was not possible to pinpoint unique CNT characteristics that cause cancer. Importantly, the European Commission's Joint Research Centre (JRC) has established a repository of industrially manufactured nanomaterials that encompasses at least four well-characterized MWCNTs called NM-400 to NM-403 (original JRC code). This review summarizes the genotoxic effects of these JRC materials and MWCNT-7. The review consists of 36 publications with results on cell culture experiments (22 publications), animal models (9 publications) or both (5 publications). As compared to the publications in the IARC monograph on CNTs, the current database represents a significant increase as there is only an overlap of 8 publications. However, the results come mainly from cell cultures and/or measurements of DNA strand breaks by the comet assay and the micronucleus assay (82 out of 97 outcomes). A meta-analysis of cell culture studies on DNA strand breaks showed a genotoxic response by MWCNT-7, less consistent effect by NM-400 and NM-402, and least consistent effect by NM-401 and NM-403. Results from other in vitro tests indicate strongest evidence of genotoxicity for MWCNT-7. There are too few observations from animal models and humans to make general conclusions about genotoxicity.

Measurement of DNA damage with the comet assay in high-prevalence diseases: current status and future directions

The comet assay is widely used in studies on genotoxicity testing, human biomonitoring and clinical studies. The simple version of the assay detects a mixture of DNA strand breaks and alkali-labile sites; these lesions are typically described as DNA strand breaks to distinguish them from oxidatively damaged DNA that are measured with the enzyme-modified comet assay. This review assesses the association between high-prevalence diseases in high-income countries and DNA damage measured with the comet assay in humans. The majority of case-control studies have assessed genotoxicity in white blood cells. Patients with coronary artery disease, diabetes, kidney disease, chronic obstructive pulmonary disease and Alzheimer's disease have on average 2-fold higher levels of DNA strand breaks compared with healthy controls. Patients with coronary artery disease, diabetes, kidney disease and chronic obstructive pulmonary disease also have 2- to 3-fold higher levels of oxidatively damaged DNA in white blood cells than controls, although there is not a clear difference in DNA damage levels between the different diseases. Case-control studies have shown elevated levels of DNA strand breaks in patients with breast cancer, whereas there are only few studies on colorectal and lung cancers. At present, it is not possible to assess if these neoplastic diseases are associated with a different level of DNA damage compared with non-neoplastic diseases.

An optimized comet-based in vitro DNA repair assay to assess base and nucleotide excision repair activity

This optimized protocol (including links to instruction videos) describes a comet-based in vitro DNA repair assay that is relatively simple, versatile, and inexpensive, enabling the detection of base and nucleotide excision repair activity. Protein extracts from samples are incubated with agarose-embedded substrate nucleoids ('naked' supercoiled DNA) containing specifically induced DNA lesions (e.g., resulting from oxidation, UVC radiation or benzo[a]pyrene-diol epoxide treatment). DNA incisions produced during the incubation reaction are quantified as strand breaks after electrophoresis, reflecting the extract's incision activity. The method has been applied in cell culture model systems, human biomonitoring and clinical investigations, and animal studies, using isolated blood cells and various solid tissues. Once extracts and substrates are prepared, the assay can be completed within 2 d.

Inflammation, oxidative stress and genotoxicity responses to biodiesel emissions in cultured mammalian cells and animals

Biodiesel fuels are alternatives to petrodiesel, especially in the transport sector where they have lower carbon footprint. Notwithstanding the environmental benefit, biodiesel fuels may have other toxicological properties than petrodiesel. Particulate matter (PM) from petrodiesel causes cancer in the lung as a consequence of delivery of genotoxic polycyclic aromatic hydrocarbons, oxidative stress and inflammation. We have reviewed articles from 2002 to 2019 (50% of the articles since 2015) that have described toxicological effects in terms of genotoxicity, oxidative stress and inflammation of biodiesel exhaust exposure in humans, animals and cell cultures. The studies have assessed first generation biodiesel from different feedstock (e.g. rapeseed and soy), certain second generation fuels (e.g. waste oil), and hydrogenated vegetable oil. It is not possible to rank the potency of toxicological effects of specific biodiesel fuels. However, exposure to biodiesel exhaust causes oxidative stress, inflammation and genotoxicity in cell cultures. Three studies in animals have not indicated genotoxicity in lung tissue. The database on oxidative stress and inflammation in animal studies is larger (13 studies); ten studies have reported increased levels of oxidative stress biomarkers or inflammation, although the effects have been modest in most studies. The cell culture and animal studies have not consistently shown a different potency in effect between biodiesel and petrodiesel exhausts. Both increased and decreased potency have been reported, which might be due to differences in feedstock or combustion conditions. In conclusion, combustion products from biodiesel and petrodiesel fuel may evoke similar toxicological effects on genotoxicity, oxidative stress and inflammation.

Telomere length and genotoxicity in the lung of rats following intragastric exposure to food-grade titanium dioxide and vegetable carbon particles

Vegetable carbon (E153) and titanium dioxide (E171) are widely used as black and white food colour additives. The aim of this study was to assess gastrointestinal tight junction and systemic genotoxic effects in rats following exposure to E153 and E171 for 10 weeks by oral gavage once a week. The expression of tight junction proteins was assessed in intestinal tissues. Levels of DNA strand breaks, oxidatively damaged DNA and telomere length were assessed in secondary organs. Hydrodynamic suspensions of E153 and E173 indicated mean particles sizes of 230 and 270 nm, respectively, and only E153 gave rise to intracellular production of reactive oxygen species in colon epithelial (Caco-2) cells. Rats exposed to E153 (6.4 mg/kg/week) or E171 (500 mg/kg/week) had decreased gene expression of the tight junction protein TJP1 (P < 0.05). E153 (6.4 mg/kg/week) also decreased OCLN (P < 0.05) in the colon and occludin protein expression in the small intestine (P < 0.05). Furthermore, E153 or E171 exposed rats had shorter telomeres in the lung (P < 0.05). Plasma from particle-exposed rats also produced telomere shortening in cultured lung epithelial cells. There were unaltered levels of oxidatively damaged DNA in the liver and lung and no changes in the DNA repair activity of oxidatively damaged DNA in the lung. Altogether, these results indicate that intragastric exposure to E153 and E171 is associated with reduced tight junction protein expression in the intestinal barrier and telomere length shortening in the lung in rats.

Pulmonary toxicity of Fe2O3, ZnFe2O4, NiFe2O4 and NiZnFe4O8 nanomaterials: Inflammation and DNA strand breaks

Exposure to metal oxide nanomaterials potentially occurs at the workplace. We investigated the toxicity of two Fe-oxides: Fe₂O₃ nanoparticles and nanorods; and three MFe₂O₄ spinels: NiZnFe₄O₈, ZnFe₂O₄, and NiFe₂O₄ nanoparticles. Mice were dosed 14, 43 or 128 μg by intratracheal instillation. Recovery periods were 1, 3, or 28 days. Inflammation - neutrophil influx into bronchoalveolar lavage (BAL) fluid - occurred for Fe₂O₃ rods (1 day), ZnFe₂O₄ (1, 3 days), NiFe₂O₄ (1, 3, 28 days), Fe₂O₃ (28 days) and NiZnFe₄O₈ (28 days). Conversion of mass-dose into specific surface-area-dose showed that inflammation correlated with deposited surface area and consequently, all these nanomaterials belong to the so-called low-solubility, low-toxicity class. Increased levels of DNA strand breaks were observed for both Fe₂O₃ particles and rods, in BAL cells three days post-exposure. To our knowledge, this is, besides magnetite (Fe₃O₄), the first study of the pulmonary toxicity of MFe₂O₄ spinel nanomaterials.

Effect of combustion-derived particles on genotoxicity and telomere length: A study on human cells and exposed populations

Particulate matter (PM) from combustion processes has been associated with oxidative stress to DNA, whereas effects related to telomere dysfunction are less investigated. We collected air-borne PM from a passenger cabin of a diesel-propelled train and at a training facility for smoke diving exercises. Effects on oxidative stress biomarkers, genotoxicity measured by the comet assay and telomere length in PM-exposed A549 cells were compared with the genotoxicity and telomere length in peripheral blood mononuclear cells (PBMCs) from human volunteers exposed to the same aerosol source. Although elevated levels of DNA strand breaks and oxidatively damaged DNA in terms of Fpg-sensitive sites were observed in PBMCs from exposed humans, the PM collected at same locations did not cause genotoxicity in the comet assay in A549 cells. Nevertheless, A549 cells displayed telomere length shortening after four weeks exposure to PM. This is in line with slightly shorter telomere length in PBMCs from exposed humans, although it was not statistically significant. In conclusion, the results indicate that genotoxic potency measured by the comet assay of PM in A549 cells may not predict genotoxicity in exposed humans, whereas telomere length measurements may be a novel indicator of genotoxic stress in cell cultures and humans.

Hazard assessment of small-size plastic particles: is the conceptual framework of particle toxicology useful?

Humans are exposed to plastic particles, but there are no studies on environmental plastics in cell cultures or animals. The toxicological understanding arises from model particles like polystyrene, polyethylene or non-plastic particles like food-grade titanium dioxide. The majority of studies on polystyrene particles show toxicological effects on measures of oxidative stress, inflammation, mitochondrial dysfunction, lysosomal dysfunction and apoptosis. The toxic effects in cell cultures mainly occur at high concentrations. Polyethylene particles seem to generate inflammatory reactions, whereas other toxicological effects have not been assessed. There are very few studies on effects of polystyrene particles in animal models and these have not demonstrated overt indices of toxicity. Studies in animals are the likely way for hazard assessment of micro- or nanoplastics. However, co-culture systems that mimic the complex architecture of mammalian tissues can cost-efficiently determine the hazards of micro- and nanoplastics. Future studies should include low doses of micro- and nanoplastic particles, which are more relevant in the assessment of health risk than the extrapolation of effects from high doses to realistic doses. Based on studies on model particles, environmental exposure to micro- and nanoplastic particles may be a hazard to human health.

Health effects of exposure to diesel exhaust in diesel-powered trains

BACKGROUND

Short-term controlled exposure to diesel exhaust (DE) in chamber studies have shown mixed results on lung and systemic effects. There is a paucity of studies on well-characterized real-life DE exposure in humans. In the present study, 29 healthy volunteers were exposed to DE while sitting as passengers in diesel-powered trains. Exposure in electric trains was used as control scenario. Each train scenario consisted of three consecutive days (6 h/day) ending with biomarker samplings.

RESULTS

Combustion-derived air pollutants were considerably higher in the passenger carriages of diesel trains compared with electric trains. The concentrations of black carbon and ultrafine particles were 8.5 μg/m³ and 1.2-1.8 × 10⁵ particles/cm³ higher, respectively, in diesel as compared to electric trains. Net increases of NOx and NO₂ concentrations were 317 μg/m³ and 36 μg/m³. Exposure to DE was associated with reduced lung function and increased levels of DNA strand breaks in peripheral blood mononuclear cells (PBMCs), whereas there were unaltered levels of oxidatively damaged DNA, soluble cell adhesion molecules, acute phase proteins in blood and urinary excretion of metabolites of polycyclic aromatic hydrocarbons. Also the microvascular function was unaltered. An increase in the low frequency of heart rate variability measures was observed, whereas time-domain measures were unaltered.

CONCLUSION

Exposure to DE inside diesel-powered trains for 3 days was associated with reduced lung function and systemic effects in terms of altered heart rate variability and increased levels of DNA strand breaks in PBMCs compared with electric trains.

TRIAL REGISTRATION

ClinicalTrials.Gov ( NCT03104387 ). Registered on March 23rd 2017.

The safety of tattoo inks: Possible options for a common regulatory framework

Tattoo prevalence has been increasing in the last 25 years, but specific regulations on tattoo inks are still missing. In the European Union, no supranational regulation is available and only few national provisions cover them. In the United States, tattoo inks are classified as cosmetics but are not approved for injection into the dermis. Health risks for consumers may derive from microbiological contamination and the presence of toxic substances or nanomaterials. However, current regulations and non-binding recommendations, where present, only address the microbiological and chemical risks, completely overlooking nanotoxicity. The aim of this paper is to promote awareness of the risks associated with tattoo inks and the nanomaterials contained therein. In particular, the need for a harmonised regulation or, at least, a set of minimal requirements is highlighted to improve the safety of tattoo inks and market surveillance by regulatory authorities.

Influence of dispersion medium on nanomaterial-induced pulmonary inflammation and DNA strand breaks: investigation of carbon black, carbon nanotubes and three titanium dioxide nanoparticles

Intratracheal instillation serves as a model for inhalation exposure. However, for this, materials are dispersed in appropriate media that may influence toxicity. We tested whether different intratracheal instillation dispersion media influence the pulmonary toxicity of different nanomaterials. Rodents were intratracheally instilled with 162 µg/mouse/1620 µg/rat carbon black (CB), 67 µg/mouse titanium dioxide nanoparticles (TiO₂) or 54 µg/mouse carbon nanotubes (CNT). The dispersion media were as follows: water (CB, TiO₂); 2% serum in water (CB, CNT, TiO₂); 0.05% serum albumin in water (CB, CNT, TiO₂); 10% bronchoalveolar lavage fluid in 0.9% NaCl (CB), 10% bronchoalveolar lavage (BAL) fluid in water (CB) or 0.1% Tween-80 in water (CB). Inflammation was measured as pulmonary influx of neutrophils into bronchoalveolar fluid, and DNA damage as DNA strand breaks in BAL cells by comet assay. Inflammation was observed for all nanomaterials (except 38-nm TiO₂) in all dispersion media. For CB, inflammation was dispersion medium dependent. Increased levels of DNA strand breaks for CB were observed only in water, 2% serum and 10% BAL fluid in 0.9% NaCl. No dispersion medium-dependent effects on genotoxicity were observed for TiO₂, whereas CNT in 2% serum induced higher DNA strand break levels than in 0.05% serum albumin. In conclusion, the dispersion medium was a determinant of CB-induced inflammation and genotoxicity. Water seemed to be the best dispersion medium to mimic CB inhalation, exhibiting DNA strand breaks with only limited inflammation. The influence of dispersion media on nanomaterial toxicity should be considered in the planning of intratracheal investigations.

The enzyme-modified comet assay: Enzyme incubation step in 2 vs 12-gels/slide systems

The enzyme-modified comet assay is a commonly used method to detect specific DNA lesions. However, still a lot of errors are made by many users, leading to dubious results and even misinterpretations. This technical note describes some critical points in the use of the enzyme-modified comet assay, such as the enzyme concentration, the time of incubation, the format used and the equipment. To illustrate the importance of these conditions/parameters, titration experiments of formamidopyrimidine DNA glycosylase (Fpg) were performed using the 2 gels/slide and the 12 minigels/slide formats (plus the 12-Gel Comet Assay Unit™). Incubation times of 15 and 30 min, and 1 h were used. Results showed that the 12 minigels/slide system requires a lower volume and concentration of Fpg. A longer time of incubation has a bigger impact when using such format. Moreover, the paper describes how to perform and interpret a titration experiment when using the enzyme-modified comet assay.

Association between polycyclic aromatic hydrocarbon exposure and peripheral blood mononuclear cell DNA damage in human volunteers during fire extinction exercises

This study investigated a number of biomarkers, associated with systemic inflammation as well as genotoxicity, in 53 young and healthy subjects participating in a course to become firefighters, while wearing personal protective equipment (PPE). The exposure period consisted of a 3-day training course where the subjects participated in various live-fire training exercises. The subjects were instructed to extinguish fires of either wood or wood with electrical cords and mattresses. The personal exposure was measured as dermal polycyclic aromatic hydrocarbon (PAH) concentrations and urinary excretion of 1-hydroxypyrene (1-OHP). The subjects were primarily exposed to particulate matter (PM) in by-stander positions, since the self-contained breathing apparatus effectively prevented pulmonary exposure. There was increased dermal exposure to pyrene (68.1%, 95% CI: 52.5%, 83.8%) and sum of 16 polycyclic aromatic hydrocarbons (ƩPAH; 79.5%, 95% CI: 52.5%, 106.6%), and increased urinary excretion of 1-OHP (70.4%, 95% CI: 52.5%; 106.6%) after the firefighting exercise compared with the mean of two control measurements performed 2 weeks before and 2 weeks after the firefighting course, respectively. The level of Fpg-sensitive sites in peripheral blood mononuclear cells (PBMCs) was increased by 8.0% (95% CI: 0.02%, 15.9%) compared with control measurements. The level of DNA strand breaks was positively associated with dermal exposure to pyrene and ƩPAHs, and urinary excretion of 1-OHP. Fpg-sensitive sites were only associated positively with PAHs. Biomarkers of inflammation and lung function showed no consistent response. In summary, the study demonstrated that PAH exposure during firefighting activity was associated with genotoxicity in PBMCs.

The comet assay: ready for 30 more years

During the last 30 years, the comet assay has become widely used for the measurement of DNA damage and repair in cells and tissues. A landmark achievement was reached in 2016 when the Organization for Economic Co-operation and Development adopted a comet assay guideline for in vivo testing of DNA strand breaks in animals. However, the comet assay has much more to offer than being an assay for testing DNA strand breaks in animal organs. The use of repair enzymes increases the range of DNA lesions that can be detected with the assay. It can also be modified to measure DNA repair activity. Still, despite the long-term use of the assay, there is a need for studies that assess the impact of variation in specific steps of the procedure. This is particularly important for the on-going efforts to decrease the variation between experiments and laboratories. The articles in this Special Issue of Mutagenesis cover important technical issues of the comet assay procedure, nanogenotoxicity and ionising radiation sensitivity on plant cells. The included biomonitoring studies have assessed seasonal variation and certain predictors for the basal level of DNA damage in white blood cells. Lastly, the comet assay has been used in studies on genotoxicity of environmental and occupational exposures in human biomonitoring studies and animal models. Overall, the articles in this Special Issue demonstrate the versatility of the comet assay and they hold promise that the assay is ready for the next 30 years.

Causation by Diesel Exhaust Particles of Endothelial Dysfunctions in Cytotoxicity, Pro-inflammation, Permeability, and Apoptosis Induced by ROS Generation

Epidemiological studies suggest that an increase of diesel exhaust particles (DEP) in ambient air corresponds to an increase in hospital-recorded myocardial infarctions within 48 h after exposure. Among the many theories to explain this data are endothelial dysfunction and translocation of DEP into vasculature. The mechanisms for such DEP-induced vascular permeability remain unknown. One of the major mechanisms underlying the effects of DEP is suggested to be oxidative stress. Experiments have shown that DEP induce the generation of reactive oxygen species (ROS), such as superoxide anion and H₂O₂ in the HUVEC tube cells. Transcription factor Nrf2 is translocated to the cell nucleus, where it activates transcription of the antioxidative enzyme HO-1 and sequentially induces the release of vascular permeability factor VEGF-A. Furthermore, a recent study shows that DEP-induced intracellular ROS may cause the release of pro-inflammatory TNF-α and IL-6, which may induce endothelial permeability as well by promoting VEGF-A secretion independently of HO-1 activation. These results demonstrated that the adherens junction molecule, VE-cadherin, becomes redistributed from the membrane at cell-cell borders to the cytoplasm in response to DEP, separating the plasma membranes of adjacent cells. DEP were occasionally found in endothelial cell cytoplasm and in tube lumen. In addition, the induced ROS is cytotoxic to the endothelial tube-like HUVEC. Acute DEP exposure stimulates ATP depletion, followed by depolarization of their actin cytoskeleton, which sequentially inhibits PI3K/Akt activity and induces endothelial apoptosis. Nevertheless, high-dose DEP augments tube cell apoptosis up to 70 % but disrupts the p53 negative regulator Mdm2. In summary, exposure to DEP affects parameters influencing vasculature permeability and viability, i.e., oxidative stress and its upregulated antioxidative and pro-inflammatory responses, which sequentially induce vascular permeability factor, VEGF-A release and disrupt cell-cell junction integrity. While exposure to a low dose of DEP actin triggers cytoskeleton depolarization, reduces PI3K/Akt activity, and induces a p53/Mdm2 feedback loop, a high dose causes apoptosis by depleting Mdm2. Addition of ROS scavenger N-acetyl cysteine suppresses DEP-induced oxidative stress efficiently and reduces subsequent damages by increasing endogenous glutathione.

Hardy A, Benford D, Halldorsson T, Jeger MJ, Knutsen HK, More S, Naegeli H, Noteborn H, Ockleford C, Ricci A, Rychen G, Schlatter JR, Silano V, Solecki R, Turck D, Younes M, Chaudhry Q, Cubadda F, Gott D, Oomen A, Weigel S, Karamitrou M, Schoonjans R, Mortensen A. Guidance on risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain: Part 1, human and animal health

The European Food Safety Authority has produced this Guidance on human and animal health aspects (Part 1) of the risk assessment of nanoscience and nanotechnology applications in the food and feed chain. It covers the application areas within EFSA's remit, e.g. novel foods, food contact materials, food/feed additives and pesticides. The Guidance takes account of the new developments that have taken place since publication of the previous Guidance in 2011. Potential future developments are suggested in the scientific literature for nanoencapsulated delivery systems and nanocomposites in applications such as novel foods, food/feed additives, biocides, pesticides and food contact materials. Therefore, the Guidance has taken account of relevant new scientific studies that provide more insights to physicochemical properties, exposure assessment and hazard characterisation of nanomaterials. It specifically elaborates on physicochemical characterisation of nanomaterials in terms of how to establish whether a material is a nanomaterial, the key parameters that should be measured, the methods and techniques that can be used for characterisation of nanomaterials and their determination in complex matrices. It also details the aspects relating to exposure assessment and hazard identification and characterisation. In particular, nanospecific considerations relating to in vivo/in vitro toxicological studies are discussed and a tiered framework for toxicological testing is outlined. It describes in vitro degradation, toxicokinetics, genotoxicity as well as general issues relating to testing of nanomaterials. Depending on the initial tier results, studies may be needed to investigate reproductive and developmental toxicity, immunotoxicity, allergenicity, neurotoxicity, effects on gut microbiome and endocrine activity. The possible use of read‐across to fill data gaps as well as the potential use of integrated testing strategies and the knowledge of modes/mechanisms of action are also discussed. The Guidance proposes approaches to risk characterisation and uncertainty analysis, and provides recommendations for further research in this area.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2018.EN-1430/full

Sensitive detection of DNA oxidation damage induced by nanomaterials

From a toxicological point of view, nanomaterials are of interest; because - on account of their great surface area relative to mass - they tend to be more reactive than the bulk chemicals from which they are derived. They might in some cases have the potential to damage DNA directly, or could act via the induction of oxidative stress. The comet assay (single cell gel electrophoresis) is widely used to measure DNA strand breaks and also oxidised bases, by including in the procedure digestion with lesion-specific enzymes such as formamidopyrimidine DNA glycosylase (which converts oxidised purines to breaks) or endonuclease III (recognising oxidised pyrimidines). We summarise reports in which these enzymes have been used to study a variety of nanomaterials in diverse cell types. We also stress that it is important to carry out tests of cell viability alongside the genotoxicity assay, since cytotoxicity can lead to adventitious DNA damage. Different concentrations of nanomaterials should be investigated, concentrating on a non-cytotoxic range; and incubating for short and longer periods can give valuable information about the mode of damage induction. The use of lesion-specific enzymes can substantially enhance the sensitivity of the comet assay in detecting genotoxic effects.

Identification of Gene Transcription Start Sites and Enhancers Responding to Pulmonary Carbon Nanotube Exposure in Vivo

Increased use of nanomaterials in industry, medicine, and consumer products has raised concerns over their toxicity. To ensure safe use of nanomaterials, understanding their biological effects at the molecular level is crucial. In particular, the regulatory mechanisms responsible for the cascade of genes activated by nanomaterial exposure are not well-characterized. To this end, we profiled the genome-wide usage of gene transcription start sites and linked active enhancer regions in lungs of C57BL/6 mice 24 h after intratracheal instillation of a single dose of the multiwalled carbon nanotube (MWCNT) Mitsui-7. Our results revealed a massive gene regulatory response, where expression of key inflammatory genes (e.g., Csf3, Il24, and Fgf23) was increased >100-fold 24 h after Mitsui-7 exposure. Many of the Mitsui-7-responsive transcription start sites were alternative transcription start sites for known genes, and the number of alternative transcription start sites used in a given gene was correlated with overall Mitsui-7 response. Strikingly, genes that were up-regulated after Mitsui-7 exposure only through their main annotated transcription start site were linked to inflammatory and defense responses, while genes up-regulated only through alternative transcription start sites were functionally heterogeneous and not inflammation-associated. Furthermore, we identified almost 12 000 active enhancers, many of which were Mitsui-7-responsive, and we identified similarly responding putative target genes. Overall, our study provides the location and activity of Mitsui-7-induced enhancers and transcription start sites, providing a useful resource for targeted experiments elucidating the biological effects of nanomaterials and the identification of biomarkers for early detection of MWCNT-induced inflammation.

Reduction of pulmonary toxicity of metal oxide nanoparticles by phosphonate-based surface passivation

BACKGROUND

The wide application of engineered nanoparticles has induced increasing exposure to humans and environment, which led to substantial concerns on their biosafety. Some metal oxides (MOx) have shown severe toxicity in cells and animals, thus safe designs of MOx with reduced hazard potential are desired. Currently, there is a lack of a simple yet effective safe design approach for the toxic MOx. In this study, we determined the key physicochemical properties of MOx that lead to cytotoxicity and explored a safe design approach for toxic MOx by modifying their hazard properties.

RESULTS

THP-1 and BEAS-2B cells were exposed to 0-200 μg/mL MOx for 24 h, we found some toxic MOx including CoO, CuO, Ni2O3 and Co3O4, could induce reactive oxygen species (ROS) generation and cell death due to the toxic ion shedding and/or oxidative stress generation from the active surface of MOx internalized into lysosomes. We thus hypothesized that surface passivation could reduce or eliminate the toxicity of MOx. We experimented with a series of surface coating molecules and discovered that ethylenediamine tetra (methylene phosphonic acid) (EDTMP) could form stable hexadentate coordination with MOx. The coating layer can effectively reduce the surface activity of MOx with 85-99% decrease of oxidative potential, and 65-98% decrease of ion shedding. The EDTMP coated MOx show negligible ROS generation and cell death in THP-1 and BEAS-2B cells. The protective effect of EDTMP coating was further validated in mouse lungs exposed to 2 mg/kg MOx by oropharyngeal aspiration. After 40 h exposure, EDTMP coated MOx show significant decreases of neutrophil counts, lactate dehydrogenase (LDH) release, MCP-1, LIX and IL-6 in bronchoalveolar lavage fluid (BALF), compared to uncoated particles. The haematoxylin and eosin (H&E) staining results of lung tissue also show EDTMP coating could significantly reduce the pulmonary inflammation of MOx.

CONCLUSIONS

The surface reactivity of MOx including ion shedding and oxidative potential is the dominated physicochemical property that is responsible for the cytotoxicity induced by MOx. EDTMP coating could passivate the surface of MOx, reduce their cytotoxicity and pulmonary hazard effects. This coating would be an effective safe design approach for a broad spectrum of toxic MOx, which will facilitate the safe use of MOx in commercial nanoproducts.

Evaluating the mechanistic evidence and key data gaps in assessing the potential carcinogenicity of carbon nanotubes and nanofibers in humans

In an evaluation of carbon nanotubes (CNTs) for the IARC Monograph 111, the Mechanisms Subgroup was tasked with assessing the strength of evidence on the potential carcinogenicity of CNTs in humans. The mechanistic evidence was considered to be not strong enough to alter the evaluations based on the animal data. In this paper, we provide an extended, in-depth examination of the in vivo and in vitro experimental studies according to current hypotheses on the carcinogenicity of inhaled particles and fibers. We cite additional studies of CNTs that were not available at the time of the IARC meeting in October 2014, and extend our evaluation to include carbon nanofibers (CNFs). Finally, we identify key data gaps and suggest research needs to reduce uncertainty. The focus of this review is on the cancer risk to workers exposed to airborne CNT or CNF during the production and use of these materials. The findings of this review, in general, affirm those of the original evaluation on the inadequate or limited evidence of carcinogenicity for most types of CNTs and CNFs at this time, and possible carcinogenicity of one type of CNT (MWCNT-7). The key evidence gaps to be filled by research include: investigation of possible associations between in vitro and early-stage in vivo events that may be predictive of lung cancer or mesothelioma, and systematic analysis of dose-response relationships across materials, including evaluation of the influence of physico-chemical properties and experimental factors on the observation of nonmalignant and malignant endpoints.

Impact of nanoparticles on DNA repair processes: current knowledge and working hypotheses

The potential health effects of exposure to nanomaterials (NMs) is currently heavily studied. Among the most often reported impact is DNA damage, also termed genotoxicity. While several reviews relate the DNA damage induced by NMs and the techniques that can be used to prove such effects, the question of impact of NMs on DNA repair processes has never been specifically reviewed. The present review article proposes to fill this gap of knowledge by critically describing the DNA repair processes that could be affected by nanoparticle (NP) exposure, then by reporting the current state of the art on effects of NPs on DNA repair, at the level of protein function, gene induction and post-transcriptional modifications, and taking into account the advantages and limitations of the different experimental approaches. Since little is known about this impact, working hypothesis for the future are then proposed.

Repair activity of oxidatively damaged DNA and telomere length in human lung epithelial cells after exposure to multi-walled carbon nanotubes

One type of carbon nanotubes (CNTs) (MWCNT-7, from Mitsui) has been classified as probably carcinogenic to humans, however insufficient data does not warrant the same classification for other types of CNTs. Experimental data indicate that CNT exposure can result in oxidative stress and DNA damage in cultured cells, whereas these materials appear to induce low or no mutagenicity. Therefore, the present study aimed to investigate whether in vitro exposure of cultured airway epithelial cells (A549) to multi-walled CNTs (MWCNTs) could increase the DNA repair activity of oxidatively damaged DNA and drive the cells toward replicative senescence, assessed by attrition of telomeres. To investigate this, H₂O₂ and KBrO₃ were used to induce DNA damage in the cells and the effect of pre-exposure to MWCNT tested for a change in repair activity inside the cells or in the extract of treated cells. The effect of MWCNT exposure on telomere length was investigated for concentration and time response. We report a significantly increased repair activity in A549 cells exposed to MWCNTs compared to non-exposed cells, suggesting that DNA repair activity may be influenced by exposure to MWCNTs. The telomere length was decreased at times longer than 24h, but this decrease was not concentration dependent. The results suggest that the seemingly low mutagenicity of CNTs in cultured cells may be associated with an increased DNA repair activity and a replicative senescence, which may counteract the manifestation of DNA lesions to mutations.

In vitro toxicity of cationic micelles and liposomes in cultured human hepatocyte (HepG2) and lung epithelial (A549) cell lines

The aim of this study was to compare the effects of cationic micelle and liposome drug delivery systems on liver and lung cells in a toxicological in vitro screening model, with observations on cytotoxicity and genotoxicity. A screening battery was established for assessment of a broad range of parameters related to adverse effects. Clear concentration response effects were observed related to impairment of mitochondrial function, membrane integrity and oxidative stress markers, but no effect was observed on genotoxicity. The adverse effects were highest for the liposomes. The High Content Screening seems optimal for initial screening of adverse effects, and combined with standard cytotoxicity measurements initial screening can be performed for predictive toxicological screening.

Influence of multi-walled carbon nanotubes on the cognitive abilities of Wistar rats

Studies of the neurobehavioral effects of carbon nanomaterials, particularly those of multi-walled carbon nanotubes (MWCNTs), have concentrated on cognitive effects, but data are scarce. The aim of this study was to assess the influence of MWCNTs on a number of higher nervous system functions of Wistar rats. For a period of 10 days, two experimental groups were fed with MWCNTs of different diameters (MWCNT-1 group, 8-10 nm; MWCNT-2 group, 18-20 nm) once a day at a dosage of 500 mg/kg. In the open-field test, reductions of integral indications of researching activity were observed for the two MWCNT-treated groups, with a parallel significant (P<0.01) increase in stress levels for these groups compared with the untreated control group. In the elevated plus-maze test, integral indices of researching activity in the MWCNT-1 and MWCNT-2 groups reduced by day 10 by 51 and 62%, respectively, while rat stress levels remained relatively unchanged. In the universal problem solving box test, reductions in motivation and energy indices of researching activity were observed in the two experimental groups. Searching activity in the MWCNT-1 group by day 3 was reduced by 50% (P<0.01) and in the MWCNT-2 group the relevant reduction reached 11.2%. By day 10, the reduction compared with controls, was 64% (P<0.01) and 58% (P<0.01) for the MWCNT-1 and MWCNT-2 groups, respectively. In conclusion, a series of specific tests demonstrated that MWCNT-treated rats experienced a significant reduction of some of their cognitive abilities, a disturbing and worrying finding, taking into consideration the continuing and accelerating use of carbon nanotubes in medicine and science.