High-throughput comet assay using 96 minigels

In vitro Safety Assessment of Extracts and Compounds From Plants as Sunscreen Ingredients

This work investigated the safety of extracts obtained from plants growing in Colombia, which have previously shown UV-filter/antigenotoxic properties. The compounds in plant extracts obtained by the supercritical fluid (CO2) extraction method were identified using gas chromatography coupled to mass spectrometry (GC/MS) analysis. Cytotoxicity measured as cytotoxic concentration 50% (CC50) and genotoxicity of the plant extracts and some compounds were studied in human fibroblasts using the trypan blue exclusion assay and the Comet assay, respectively. The extracts from Pipper eriopodon and Salvia aratocensis species and the compound trans-β-caryophyllene were clearly cytotoxic to human fibroblasts. Conversely, Achyrocline satureioides, Chromolaena pellia, and Lippia origanoides extracts were relatively less cytotoxic with CC50 values of 173, 184, and 89 μg/mL, respectively. The C. pellia and L. origanoides extracts produced some degree of DNA breaks at cytotoxic concentrations. The cytotoxicity of the studied compounds was as follows, with lower CC50 values representing the most cytotoxic compounds: resveratrol (91 μM) > pinocembrin (144 μM) > quercetin (222 μM) > titanium dioxide (704 μM). Quercetin was unique among the compounds assayed in being genotoxic to human fibroblasts. Our work indicates that phytochemicals can be cytotoxic and genotoxic, demonstrating the need to establish safe concentrations of these extracts for their potential use in cosmetics.

An ecotoxicological assessment of a strigolactone mimic used as the active ingredient in a plant biostimulant formulation

A risk assessment on the aquatic toxicity of the plant biostimulant strigolactone mimic (2-(4-methyl-5-oxo-2,5-dihydro-furan-2-yloxy)-benzo[de]isoquinoline-1,3-dione (SL-6) was performed using a suite of standardised bioassays representing different trophic groups and acute and chronic endpoints. In freshwater, three trophic groups of algae, crustacea and fish were used. Whilst in seawater, algae (unicellular and macroalgae), Crustacea and Mollusca were employed. In addition, the genotoxicity of SL-6 was determined with the comet assessment performed on unicellular marine algae, oysters, and fish embryos. This was the first time ecotoxicity tests have been performed on SL-6. In freshwater, the lowest LOEC was measured in the unicellular algae at 0.31 mg/L SL-6. Although, similar LOEC values were found for embryo malformations and impacts on hatching rate in zebrafish (LOEC 0.31-0.33 mg/L). Consistent malformations of pericardial and yolk sac oedemas were identified in the zebrafish embryos at 0.31 mg/L. In marine species, the lowest LOEC was found for both Tisbe battagliai mortality and microalgae growth at an SL-6 concentration of 1.0 mg/L. Significant genotoxicity was observed above control levels at 0.0031 mg/L SL-6 in the unicellular algae and 0.001 mg/L SL-6 in the oyster and zebrafish larvae. When applying the simple risk assessment, based on the lowest NOECs and appropriate assessment factors, the calculated predicted no effect concentration (PNEC), for the ecotoxicity and the genotoxicity tests were 1.0 µg/L and 0.01 µg/L respectively.

Further development of CometChip technology to measure DNA damage in vitro and in vivo: Comparison with the 2 gels/slide format of the standard and enzyme-modified comet assay

DNA damage plays a pivotal role in carcinogenesis and other diseases. The comet assay has been used for more than three decades to measure DNA damages. The 1-2 gels/slide format is the most used version of the assay. In 2010, a high throughput 96 macrowell format with a spatially encoded array of microwells patterned in agarose was developed, called the CometChip. The commercial version (CometChip®) has been used for the in vitro standard version of the comet assay (following the manufacturer's protocol), although it has not been compared directly with the 2 gels/slide format. The aim of this work is to developed new protocols to allow use of DNA repair enzymes as well as the analysis of in vivo frozen tissue samples in the CometChip®, to increase the throughput, and to compare its performance with the classic 2 gels/slide format. We adapted the manufacturer's protocol to allow the use of snap frozen tissue samples, using male Wistar rats orally dosed with methyl methanesulfonate (MMS, 200 mg/kg b.w.), and to detect altered nucleobases using DNA repair enzymes, with TK6 cells treated with potassium bromate (KBrO3, 0-4 mM, 3 h) and formamidopyrimidine DNA glycosylase (Fpg) as the enzyme. Regarding the standard version of the comet, we performed thee comparison of the 2 gel/slide and CometChip® format (using the the manufacturer's protocol), using TK6 cells with MMS (100-800 µM, 1 h) and hydrogen peroxide (H2O2, 7.7-122.5 µM, 5 min) as testing compounds. In all cases the CometChip® was performed along with the 2 gels/slide format. Results obtained were comparable and the CometChip® is a good alternative to the 2 gels/slide format when a higher throughput is required.

Development of a Novel, Automated High-Throughput Device for Performing the Comet Assay

A comet assay is a trusted and widely used method for assessing DNA damage in individual eukaryotic cells. However, it is time-consuming and requires extensive monitoring and sample manipulation by the user. This limits the throughput of the assay, increases the risk of errors, and contributes to intra- and inter-laboratory variability. Here, we describe the development of a device which automates high throughput sample processing for a comet assay. This device is based upon our patented, high throughput, vertical comet assay electrophoresis tank, and incorporates our novel, patented combination of assay fluidics, temperature control, and a sliding electrophoresis tank to facilitate sample loading and removal. Additionally, we demonstrated that the automated device performs at least as well as our "manual" high throughput system, but with all the advantages of a fully "walkaway" device, such as a decreased need for human involvement and a decreased assay run time. Our automated device represents a valuable, high throughput approach for reliably assessing DNA damage with the minimal operator involvement, particularly if combined with the automated analysis of comets.

Measuring DNA modifications with the comet assay: a compendium of protocols

The comet assay is a versatile method to detect nuclear DNA damage in individual eukaryotic cells, from yeast to human. The types of damage detected encompass DNA strand breaks and alkali-labile sites (e.g., apurinic/apyrimidinic sites), alkylated and oxidized nucleobases, DNA-DNA crosslinks, UV-induced cyclobutane pyrimidine dimers and some chemically induced DNA adducts. Depending on the specimen type, there are important modifications to the comet assay protocol to avoid the formation of additional DNA damage during the processing of samples and to ensure sufficient sensitivity to detect differences in damage levels between sample groups. Various applications of the comet assay have been validated by research groups in academia, industry and regulatory agencies, and its strengths are highlighted by the adoption of the comet assay as an in vivo test for genotoxicity in animal organs by the Organisation for Economic Co-operation and Development. The present document includes a series of consensus protocols that describe the application of the comet assay to a wide variety of cell types, species and types of DNA damage, thereby demonstrating its versatility.

Assessing testicular germ cell DNA damage in the comet assay; introduction of a proof-of-concept

The in vivo comet assay is widely used to measure genotoxicity; however, the current OECD test guideline (TG 489) does not recommend using the assay to assess testicular germ cells, due to the presence of testicular somatic cells. An adapted approach to specifically assess testicular germ cells within the comet assay is certainly warranted, considering regulatory needs for germ cell-specific genotoxicity data in relation to the increasing global production of and exposure to potentially hazardous chemicals. Here, we provide a proof-of-concept to selectively analyze round spermatids and primary spermatocytes, distinguishing them from other cells of the testicle. Utilizing the comet assay recordings of DNA content (total fluorescence intensity) and DNA damage (% tail intensity) of individual comets, we developed a framework to distinguish testicular cell populations based on differences in DNA content/ploidy and appearance. Haploid round spermatid comets are identified through (1) visual inspection of DNA content distributions, (2) setting DNA content thresholds, and (3) modeling DNA content distributions using a normal mixture distribution function. We also describe an approach to distinguish primary spermatocytes during comet scoring, based on their high DNA content and large physical size. Our concept allows both somatic and germ cells to be analyzed in the same animal, adding a versatile, sensitive, rapid, and resource-efficient assay to the limited genotoxicity assessment toolbox for germ cells. An adaptation of TG 489 facilitates accumulation of valuable information regarding distribution of substances to germ cells and their potential for inducing germ cell gene mutations and structural chromosomal aberrations.

Polycyclic aromatic hydrocarbons (PAHs): Updated aspects of their determination, kinetics in the human body, and toxicity

Polycyclic aromatic hydrocarbons (PAHs) are legacy pollutants of considerable public health concern. Polycyclic aromatic hydrocarbons arise from natural and anthropogenic sources and are ubiquitously present in the environment. Several PAHs are highly toxic to humans with associated carcinogenic and mutagenic properties. Further, more severe harmful effects on human- and environmental health have been attributed to the presence of high molecular weight (HMW) PAHs, that is PAHs with molecular mass greater than 300 Da. However, more research has been conducted using low molecular weight (LMW) PAHs). In addition, no HMW PAHs are on the priority pollutants list of the United States Environmental Protection Agency (US EPA), which is limited to only 16 PAHs. However, limited analytical methodologies for separating and determining HMW PAHs and their potential isomers and lack of readily available commercial standards make research with these compounds challenging. Since most of the PAH kinetic data originate from animal studies, our understanding of the effects of PAHs on humans is still minimal. In addition, current knowledge of toxic effects after exposure to PAHs may be underrepresented since most investigations focused on exposure to a single PAH. Currently, information on PAH mixtures is limited. Thus, this review aims to critically assess the current knowledge of PAH chemical properties, their kinetic disposition, and toxicity to humans. Further, future research needs to improve and provide the missing information and minimize PAH exposure to humans.

Calibration of the comet assay using ionising radiation

Several trials have attempted to identify sources of inter-laboratory variability in comet assay results, aiming at achieving more equal responses. Ionising radiation induces a defined level of DNA single-strand breaks (per dose/base pairs) and is used as a reference when comparing comet results but relies on accurately determined radiation doses. In this ring test we studied the significance of dose calibrations and comet assay protocol differences, with the object of identifying causes of variability and how to deal with them. Eight participating laboratories, using either x-ray or gamma radiation units, measured dose rates using alanine pellet dosimeters that were subsequently sent to a specialised laboratory for analysis. We found substantial deviations between calibrated and nominal (uncalibrated) dose rates, with up to 46% difference comparing highest and lowest values. Three additional dosimetry systems were employed in some laboratories: thermoluminescence detectors and two aqueous chemical dosimeters. Fricke's and Benzoic Acid dosimetry solutions gave reliable quantitative dose estimations using local equipment. Mononuclear cells from fresh human blood or mammalian cell lines were irradiated locally with calibrated (alanine) radiation doses and analysed for DNA damage using a standardised comet assay protocol and a lab-specific protocol. The dose response of eight laboratories, calculated against calibrated radiation doses, was linear with slope variance CV= 29% with the lab-specific protocol, reduced to CV= 16% with the standard protocol. Variation between laboratories indicate post-irradiation repair differences. Intra-laboratory variation was very low judging from the dose response of 8 donors (CV=4%). Electrophoresis conditions were different in the lab-specific protocols explaining some dose response variations which were reduced by systematic corrections for electrophoresis conditions. The study shows that comet assay data obtained in different laboratories can be compared quantitatively using calibrated radiation doses and that systematic corrections for electrophoresis conditions are useful.

The miniaturized enzyme-modified comet assay for genotoxicity testing of nanomaterials

The in vitro comet assay is a widely applied method for investigating genotoxicity of chemicals including engineered nanomaterials (NMs). A big challenge in hazard assessment of NMs is possible interference between the NMs and reagents or read-out of the test assay, leading to a risk of biased results. Here, we describe both the standard alkaline version of the in vitro comet assay with 12 mini-gels per slide for detection of DNA strand breaks and the enzyme-modified version that allows detection of oxidized DNA bases by applying lesion-specific endonucleases (e.g., formamidopyrimidine DNA glycosylase or endonuclease III). We highlight critical points that need to be taken into consideration when assessing the genotoxicity of NMs, as well as basic methodological considerations, such as the importance of carrying out physicochemical characterization of the NMs and investigating uptake and cytotoxicity. Also, experimental design-including treatment conditions, cell number, cell culture, format and volume of medium on the plate-is crucial and can have an impact on the results, especially when testing NMs. Toxicity of NMs depends upon physicochemical properties that change depending on the environment. To facilitate testing of numerous NMs with distinct modifications, the higher throughput miniaturized version of the comet assay is essential.

Differences in Trophic Level, Contaminant Load, and DNA Damage in an Urban and a Remote Herring Gull (Larus argentatus) Breeding Colony in Coastal Norway

Herring gulls (Larus argentatus) are opportunistic feeders, resulting in contaminant exposure depending on area and habitat. We compared contaminant concentrations and dietary markers between two herring gull breeding colonies with different distances to extensive human activity and presumed contaminant exposure from the local marine diet. Furthermore, we investigated the integrity of DNA in white blood cells and sensitivity to oxidative stress. We analyzed blood from 15 herring gulls from each colony-the urban Oslofjord near the Norwegian capital Oslo in the temperate region and the remote Hornøya island in northern Norway, on the Barents Sea coast. Based on d¹³ C and d³⁴ S, the dietary sources of urban gulls differed, with some individuals having a marine and others a more terrestrial dietary signal. All remote gulls had a marine dietary signal and higher relative trophic level than the urban marine feeding gulls. Concentrations (mean ± standard deviation [SD]) of most persistent organic pollutants, such as polychlorinated biphenyl ethers (PCBs) and perfluorooctane sulfonic acid (PFOS), were higher in urban marine (PCB153 17 ± 17 ng/g wet weight, PFOS 25 ± 21 ng/g wet wt) than urban terrestrial feeders (PCB153 3.7 ± 2.4 ng/g wet wt, PFOS 6.7 ± 10 ng/g wet wt). Despite feeding at a higher trophic level (d¹⁵ N), the remote gulls (PCB153 17 ± 1221 ng/g wet wt, PFOS 19 ± 1421 ng/g wet wt) were similar to the urban marine feeders. Cyclic volatile methyl siloxanes were detected in only a few gulls, except for decamethylcyclopentasiloxane in the urban colony, which was found in 12 of 13 gulls. Only hexachlorobenzene was present in higher concentrations in the remote (2.6 ± 0.42 ng/g wet wt) compared with the urban colony (0.34 ± 0.33 ng/g wet wt). Baseline and induced DNA damage (doublestreak breaks) was higher in urban than in remote gulls for both terrestrial and marine feeders. Environ Toxicol Chem 2022;41:2466-2478. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

NEIL1 and NEIL2 DNA glycosylases modulate anxiety and learning in a cooperative manner in mice

Oxidative DNA damage in the brain has been implicated in neurodegeneration and cognitive decline. DNA glycosylases initiate base excision repair (BER), the main pathway for oxidative DNA base lesion repair. NEIL1 and NEIL3 DNA glycosylases affect cognition in mice, while the role of NEIL2 remains unclear. Here, we investigate the impact of NEIL2 and its potential overlap with NEIL1 on behavior in knockout mouse models. Neil1^-/-Neil2^-/- mice display hyperactivity, reduced anxiety and improved learning. Hippocampal oxidative DNA base lesion levels are comparable between genotypes and no mutator phenotype is found. Thus, impaired canonical repair is not likely to explain the altered behavior. Electrophysiology suggests reduced axonal activation in the hippocampal CA1 region in Neil1^-/-Neil2^-/- mice and lack of NEIL1 and NEIL2 causes dysregulation of genes in CA1 relevant for synaptic function. We postulate a cooperative function of NEIL1 and NEIL2 in genome regulation, beyond canonical BER, modulating behavior in mice.

Biological effects of combustion-derived particles from different biomass sources on human bronchial epithelial cells

Combustion-derived particles (CDPs), in particular from traffic, are regarded as a central contributor for adverse health effects linked to air pollution. Recently, also biomass burning has been recognized as an important source for CDPs. Here, the effects of CDPs (PM₁₀) originating from burning of pellet, charcoal and wood on key processes associated to lung carcinogenesis were explored. Human bronchial epithelial cells (HBEC3-KT) were exposed to 2.5 μg/cm² of CDPs for 24 h and biological effects were examined in terms of cytotoxicity, inflammation, epithelial to mesenchymal transition (EMT)-related effects, DNA damage and genotoxicity. Reduced cell migration, inflammation and modulation of various PM-associated genes were observed mainly after exposure to wood and pellet. In contrast, only particles from pellet burning induced alteration in cell proliferation and DNA damage, which resulted in cell cycle alterations. Charcoal instead, appeared in general less effective in inducing pro-carcinogenic effects. These results illustrate differences in the toxicological profile due to the CDPs source. The different chemical compounds adsorbed on CDPs seemed to be central for particle properties, leading to an activation of various cellular signaling pathways involved in early steps of cancer progression.

Effect of cryopreservation on DNA damage and DNA repair activity in human blood samples in the comet assay

The comet assay is a commonly used method to determine DNA damage and repair activity in many types of samples. In recent years, the use of the comet assay in human biomonitoring became highly attractive due to its various modified versions, which may be useful to determine individual susceptibility in blood samples. However, in human biomonitoring studies, working with large sample numbers that are acquired over an extended time period requires some additional considerations. One of the most important issues is the storage of samples and its effect on the outcome of the comet assay. Another important question is the suitability of different blood preparations. In this study, we analysed the effect of cryopreservation on DNA damage and repair activity in human blood samples. In addition, we investigated the suitability of different blood preparations. The alkaline and FPG as well as two different types of repair comet assay and an in vitro hydrogen peroxide challenge were applied. Our results confirmed that cryopreserved blood preparations are suitable for investigating DNA damage in the alkaline and FPG comet assay in whole blood, buffy coat and PBMCs. Ex vivo hydrogen peroxide challenge yielded its optimal effect in isolated PBMCs. The utilised repair comet assay with either UVC or hydrogen peroxide-induced lesions and an aphidicolin block worked well in fresh PBMCs. Cryopreserved PBMCs could not be used immediately after thawing. However, a 16-h recovery with or without mitotic stimulation enabled the application of the repair comet assay, albeit only in a surviving cell fraction.

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.

B-Comet Assay (Comet Assay on Buccal Cells) for the Evaluation of Primary DNA Damage in Human Biomonitoring Studies

Many subjects perceive venous blood collection as too invasive, and thus moving to better-accepted procedures for leukocytes collection might be crucial in human biomonitoring studies (e.g., biomonitoring of occupational or residential exposure to genotoxins) management. In this context, primary DNA damage was assessed in buccal lymphocytes (BLs), fresh whole venous, and capillary blood leukocytes, and compared with that in peripheral blood lymphocytes (PBLs)—the most frequently used cells—in 15 young subjects. Mouthwashes were collected after the volunteers rinsed their mouths with normal saline, and BLs were isolated by density gradient centrifugation. Blood samples were collected by venipuncture or by lancet. Anthropometric and lifestyle information was obtained by the administration of a structured questionnaire. As shown in the Bland-Altman plots, the level of agreement between BLs and PBLs lied within the accepted range, we thus enrolled a wider population (n = 54) to assess baseline DNA damage in BLs. In these cells, mean values of tail length (µm), tail intensity (%), and tail moment were 25.7 ± 0.9, 6.7 ± 0.4 and 1.0 ± 0.1, respectively. No significant association was observed between sex and smoking habit with any of the DNA damage parameters. Conversely, underweight subjects displayed significantly higher genomic instability compared with normal weight group (p < 0.05). In conclusion, we successfully managed to set up and update a non-invasive and well-accepted procedure for the isolation of BLs from saliva that could be useful in upcoming biomonitoring studies.

The enzyme-modified comet assay: Past, present and future

The enzyme-modified comet assay was developed in order to detect DNA lesions other than those detected by the standard version (single and double strand breaks and alkali-labile sites). Various lesion-specific enzymes, from the DNA repair machinery of bacteria and humans, have been combined with the comet assay, allowing detection of different oxidized and alkylated bases as well as cyclobutane pyrimidine dimers, mis-incorporated uracil and apurinic/apyrimidinic sites. The enzyme-modified comet assay has been applied in different fields - human biomonitoring, environmental toxicology, and genotoxicity testing (both in vitro and in vivo) - as well as in basic research. Up to now, twelve enzymes have been employed; here we describe the enzymes and give examples of studies in which they have been applied. The bacterial formamidopyrimidine DNA glycosylase (Fpg) and endonuclease III (EndoIII) have been extensively used while others have been used only rarely. Adding further enzymes to the comet assay toolbox could potentially increase the variety of DNA lesions that can be detected. The enzyme-modified comet assay can play a crucial role in the elucidation of the mechanism of action of both direct and indirect genotoxins, thus increasing the value of the assay in the regulatory context.

Fluorescence Sheds Light on DNA Damage, DNA Repair, and Mutations

DNA damage can lead to carcinogenic mutations and toxicity that promotes diseases. Therefore, having rapid assays to quantify DNA damage, DNA repair, mutations, and cytotoxicity is broadly relevant to health. For example, DNA damage assays can be used to screen chemicals for genotoxicity, and knowledge about DNA repair capacity has applications in precision prevention and in personalized medicine. Furthermore, knowledge of mutation frequency has predictive power for downstream cancer, and assays for cytotoxicity can predict deleterious health effects. Tests for all of these purposes have been rendered faster and more effective via adoption of fluorescent readouts. Here, we provide an overview of established and emerging cell-based assays that exploit fluorescence for studies of DNA damage and its consequences.

Genotoxicity of Nanomaterials: Advanced In Vitro Models and High Throughput Methods for Human Hazard Assessment-A Review

Changes in the genetic material can lead to serious human health defects, as mutations in somatic cells may cause cancer and can contribute to other chronic diseases. Genotoxic events can appear at both the DNA, chromosomal or (during mitosis) whole genome level. The study of mechanisms leading to genotoxicity is crucially important, as well as the detection of potentially genotoxic compounds. We consider the current state of the art and describe here the main endpoints applied in standard human in vitro models as well as new advanced 3D models that are closer to the in vivo situation. We performed a literature review of in vitro studies published from 2000-2020 (August) dedicated to the genotoxicity of nanomaterials (NMs) in new models. Methods suitable for detection of genotoxicity of NMs will be presented with a focus on advances in miniaturization, organ-on-a-chip and high throughput methods.

Applications of CometChip for Environmental Health Studies

Environmental exposures have long been known to impact public health and safety. For example, exposures to airborne particulates, heavy metals in water, or certain industrial chemicals can contribute to aging and to risk of developing cancer and other diseases. Environmental factors can impact health in a variety of ways, but a key concern is DNA damage, which can lead to mutations that cause cancer. Cancer can take years to develop following chemical exposure; however, one way to predict carcinogenicity in a more practical time frame is by studying the chemical's ability to induce DNA damage. The comet assay (or single-cell gel electrophoresis assay) has been used successfully for genotoxicity testing. The comet assay allows for the detection of DNA strand breaks via analysis of DNA migration during electrophoresis. Previously, the Engelward laboratory, in collaboration with the Bhatia laboratory, developed the CometChip for measurements of DNA damage and repair. The CometChip is a high-throughput comet assay that improves user reproducibility and significantly shortens total assay time. Here, we describe how the high-throughput CometChip platform can be used to measure DNA damage in established cell lines, animal models, and human samples. We also discuss technical challenges associated with these studies and provide recommendations on how to achieve optimal results for researchers interested in adopting this assay.

Systems chemo-biology analysis of DNA damage response and cell cycle effects induced by coal exposure

Cell cycle alterations are among the principle hallmarks of cancer. Consequently, the study of cell cycle regulators has emerged as an important topic in cancer research, particularly in relation to environmental exposure. Particulate matter and coal dust around coal mines have the potential to induce cell cycle alterations. Therefore, in the present study, we performed chemical analyses to identify the main compounds present in two mineral coal samples from Colombian mines and performed systems chemo-biology analysis to elucidate the interactions between these chemical compounds and proteins associated with the cell cycle. Our results highlight the role of oxidative stress generated by the exposure to the residues of coal extraction, such as major inorganic oxides (MIOs), inorganic elements (IEs) and polycyclic aromatic hydrocarbons (PAH) on DNA damage and alterations in the progression of the cell cycle (blockage and/or delay), as well as structural dysfunction in several proteins. In particular, IEs such as Cr, Ni, and S and PAHs such as benzo[a]pyrene may have influential roles in the regulation of the cell cycle through DNA damage and oxidative stress. In this process, cyclins, cyclin-dependent kinases, zinc finger proteins such as TP53, and protein kinases may play a central role.

Comet assay on one- and two-cell mouse embryos

DNA damage quantified as the comet tail length was assessed using in vitro and in vivo comet assay on one- and two-cell mouse embryos obtained by natural mating. The use of a protocol with three layers of agarose reduces the embryo loss and makes it possible to study a small number of embryos. A significantly lower level of basal, but not induced DNA damage was found in embryos with cleaved zona pellucida compared to embryos with intact zona pellucida. There were no significant differences in the length of the comet's tail between embryos lysed in different lysis solutions, both in cases of basal and induced DNA damage. A significant increase in the comet tail length was detected in one-cell embryos of mice treated with methyl methanesulfonate and etoposide compared to the control. The data show that DNA damage induced in maternal germ cells persists, which can be detected in embryos using the comet assay.

Novel approach for the detection of alkylated bases using the enzyme-modified comet assay

The enzyme-modified comet assay is widely used for the detection of oxidized DNA lesions. Here we describe for the first time the use of the human alkyladenine DNA glycosylase (hAAG) for the detection of alkylated bases. hAAG was titrated using untreated and methyl methanesulfonate (MMS)-treated TK-6 cells. The hAAG-modified comet assay was compared to the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay, widely used to detect oxidized lesions but that also detects ring-opened purines derived from some alkylated lesions, using cells treated with potassium bromate (oxidizing agent) or MMS. Moreover, neutral and alkaline lysis conditions were used to determine the nature of detected lesions. When alkaline lysis was employed (condition normally used), the level of hAAG-sensitive sites was higher than the Fpg-sensitive sites in MMS-treated cells and hAAG, unlike Fpg, did not detect oxidized bases. After neutral lysis, Fpg did not detect MMS-induced lesions; however, results obtained with hAAG remained unchanged. As expected, Fpg detected oxidized purines and imidazole ring-opened purines, derived from N7-methylguanines under alkaline conditions. It seems that hAAG detected N7-methylguanines, the ring-opened purines derived at high pH, and 3-methlyladenines. Specificity of hAAG towards different DNA lesions was evaluated using a multiplex oligonucleotide-cleavage assay, confirming the ability of hAAG to detect ethenoadenines and hypoxanthine. The hAAG-modified comet assay is a new tool for the detection of alkylated bases.

Gamma radiation induces life stage-dependent reprotoxicity in Caenorhabditis elegans via impairment of spermatogenesis

The current study investigated life stage, tissue and cell dependent sensitivity to ionizing radiation of the nematode Caenorhabditis elegans. Results showed that irradiation of post mitotic L4 stage larvae induced no significant effects with respect to mortality, morbidity or reproduction at either acute dose ≤6 Gy (1500 mGy·h^-1) or chronic exposure ≤15 Gy (≤100 mGy·h^-1). In contrast, chronic exposure from the embryo to the L4-young adult stage caused a dose and dose-rate dependent reprotoxicity with 43% reduction in total brood size at 6.7 Gy (108 mGy·h^-1). Systematic irradiation of the different developmental stages showed that the most sensitive life stage was L1 to young L4. Exposure during these stages was associated with dose-rate dependent genotoxic effects, resulting in a 1.8 to 2 fold increase in germ cell apoptosis in larvae subjected to 40 or 100 mGy·h^-1, respectively. This was accompanied by a dose-rate dependent reduction in the number of spermatids, which was positively correlated to the reprotoxic effect (0.99, PCC). RNAseq analysis of nematodes irradiated from L1 to L4 stage revealed a significant enrichment of differentially expressed genes related to both male and hermaphrodite reproductive processes. Gene network analysis revealed effects related to down-regulation of genes required for spindle formation and sperm meiosis/maturation, including smz-1, smz-2 and htas-1. Furthermore, the expression of a subset of 28 set-17 regulated Major Sperm Proteins (MSP) required for spermatid production was correlated (R² 0.80) to the reduction in reproduction and the number of spermatids. Collectively these observations corroborate the impairment of spermatogenesis as the major cause of gamma radiation induced life-stage dependent reprotoxic effect. Furthermore, the progeny of irradiated nematodes showed significant embryonal DNA damage that was associated with persistent effect on somatic growth. Unexpectedly, these nematodes maintained much of their reproductive capacity in spite of the reduced growth.

Evaluation of the Major Steps in the Conventional Protocol for the Alkaline Comet Assay

Single cell gel electrophoresis, also known as the comet assay, has become a widespread DNA damage assessment tool due to its sensitivity, adaptability, low cost, ease of use, and reliability. Despite these benefits, this assay has shortcomings, such as long assay running time, the manipulation of multiple slides, individually, through numerous process steps, the challenge of working in a darkened environment, and reportedly considerable inter- and intra-laboratory variation. All researchers typically perform the comet assay based upon a common core approach; however, it appears that some steps in this core have little proven basis, and may exist, partly, out of convenience, or dogma. The aim of this study was to critically re-evaluate key steps in the comet assay, using our laboratory's protocol as a model, firstly to understand the scientific basis for why certain steps in the protocol are performed in a particular manner, and secondly to simplify the assay, and decrease the cost and run time. Here, the shelf life of the lysis and neutralization buffers, the effect of temperature and incubation period during the lysis step, the necessity for drying the slides between the electrophoresis and staining step, and the need to perform the sample workup and electrophoresis steps under subdued light were all evaluated.

In Vitro Transformation of Human Bronchial Epithelial Cells by Diesel Exhaust Particles: Gene Expression Profiling and Early Toxic Responses

Occupational exposure to diesel exhaust may cause lung cancer in humans. Mechanisms include DNA-damage and inflammatory responses. Here, the potential of NIST SRM2975 diesel exhaust particles (DEP) to transform human bronchial epithelial cells (HBEC3) in vitro was investigated. Long-term exposure of HBEC3 to DEP led to increased colony growth in soft agar. Several DEP-transformed cell lines were established and based on the expression of epithelial-to-mesenchymal-transition (EMT) marker genes, one of them (T2-HBEC3) was further characterized. T2-HBEC3 showed a mesenchymal/fibroblast-like morphology, reduced expression of CDH1, and induction of CDH2 and VIM. T2-HBEC3 had reduced migration potential compared with HBEC3 and little invasion capacity. Gene expression profiling showed baseline differences between HBEC3 and T2-HBEC3 linked to lung carcinogenesis. Next, to assess differences in sensitivity to DEP between parental HBEC3 and T2-HBEC3, gene expression profiling was carried out after DEP short-term exposure. Results revealed changes in genes involved in metabolism of xenobiotics and lipids, as well as inflammation. HBEC3 displayed a higher steady state of IL1B gene expression and release of IL-1β compared with T2-HBEC3. HBEC3 and T2-HBEC3 showed similar susceptibility towards DEP-induced genotoxic effects. Liquid-chromatography-tandem-mass-spectrometry was used to measure secretion of eicosanoids. Generally, major prostaglandin species were released in higher concentrations from T2-HBEC3 than from HBEC3 and several analytes were altered after DEP-exposure. In conclusion, long-term exposure to DEP-transformed human bronchial epithelial cells in vitro. Differences between HBEC3 and T2-HBEC3 regarding baseline levels and DEP-induced changes of particularly CYP1A1, IL-1β, PGE2, and PGF2α may have implications for acute inflammation and carcinogenesis.

Genotoxic Response and Mortality in 3 Marine Copepods Exposed to Waterborne Copper

Copper (Cu) is an essential trace metal, but may also be toxic to aquatic organisms. Although many studies have investigated the cytotoxicity of Cu, little is known about the in vivo genotoxic potential of Cu in marine invertebrates. We investigated the genotoxicity of Cu in 2 pelagic calanoid copepods, Acartia tonsa and Temora longicornis, and the intertidal harpacticoid copepod Tigriopus brevicornis by exposing them for 6 and 72 h to waterborne Cu (0, 6, and 60 µg Cu/L). A subsequent 24-h period in filtered seawater was used to investigate delayed effects or recovery. Genotoxicity was evaluated as DNA strand breaks in individual copepods using the comet assay. Copper did not increase DNA strand breaks in any of the species at any concentration or time point. The treatment did, however, cause 100% mortality in A. tonsa following exposure to 60 µg Cu/L. Acartia tonsa and T. longicornis were more susceptible to Cu-induced mortality than the benthic harpacticoid T. brevicornis, which appeared to be unaffected by the treatments. The results show major differences in Cu susceptibility among the 3 copepods and also that acute toxicity of Cu to A. tonsa is not directly associated with genotoxicity. We also show that the comet assay can be used to quantify genotoxicity in individual copepods. Environ Toxicol Chem 2019;38:2224-2232. © 2019 SETAC.

Evaluation of oxidative and methylating DNA damage in painters occupationally exposed to organic solvents and paints

Introduction: The exposure to organic solvents and paints has been associated with genotoxicity and a greater risk of neoplasms. However, the type of DNA damage induced in humans by the exposure to these compounds, which would help explain the mechanisms of their genotoxicity, is still not fully characterized. Due to inadequate practices of occupational safety, car painters in the informal sector are a highly exposed group to organic solvents and paints. Objective: To identify the oxidative and methylating damage in the DNA of lymphocytes of car painters exposed to organic solvents and paints. Materials and methods: Isolated peripheral blood lymphocytes from 62 painters and 62 unexposed subjects were analyzed by the modified high-throughput comet assay with the Fpg and AlkA enzymes. The categories used for the evaluation of the DNA damage were basal damage (without enzymes), oxidative and methylating damage. The measurement parameter used to establish the damage was the percentage of DNA in the tail. Results: The percentage of DNA in the tail was higher in the exposed group compared to the unexposed group (p<0.05). In the exposed group, this percentage was higher in the oxidative damage category than the baseline (16.50 vs. 12.87; p<0.001), whereas methylating damage did not show significant differences (14.00 vs. 12.87; p>0.05). Conclusion: In this study, exposure to organic solvents and paints was associated with an increase in oxidative lesions in the DNA of car painters’ lymphocytes, such as the production of 8-oxodG and other formamidopyrimidine products which are considered highly mutagenic.

Technical recommendations to perform the alkaline standard and enzyme-modified comet assay in human biomonitoring studies

The comet assay (single cell gel electrophoresis) is widely used as a biomonitoring tool to assess DNA damage - strand breaks, as well as oxidised bases; it can also be adapted to measure DNA repair. It is based on the ability of breaks in the DNA to relax supercoiling, allowing DNA loops to extend from the nuclear core (nucleoid) under an electric field to form a comet-like tail. Most commonly, it is applied to white blood cells. The range of detection is between a few hundred breaks per cell and a few thousand, encompassing levels of damage that can be repaired and tolerated by human cells. Its applications include monitoring various diseases, studying the influence of nutrition on DNA stability, and investigating effects of environmental and occupational mutagens. Here we address the issue of inter-laboratory variation in comet assay results. This variation is largely due to differences in methods. Imposing a standard protocol is not practical, but users should be aware of the crucial parameters that affect performance of the assay. These include the concentration of agarose in which the cells are embedded; the duration of cell lysis, and of enzyme incubation when oxidised bases are being measured; the duration of alkaline unwinding; the duration of electrophoresis and the voltage gradient applied; and the method used to score the comets. Including reference standards in each experiment allows experimental variability to be monitored - and if variation is not extreme, results can be normalised using reference standard values. Reference standards are also essential for inter-laboratory comparison. Finally, we offer recommendations which, we believe, will limit variability and increase the usefulness of this assay in molecular epidemiology.

Lung effects of 7- and 28-day inhalation exposure of rats to emissions from 1st and 2nd generation biodiesel fuels with and without particle filter - The FuelHealth project

Increased use of 1st and 2nd generation biofuels raises concerns about health effects of new emissions. We analyzed cellular and molecular lung effects in Fisher 344 rats exposed to diesel engine exhaust emissions (DEE) from a Euro 5-classified diesel engine running on B7: petrodiesel fuel containing 7% fatty acid methyl esters (FAME), or SHB20 (synthetic hydrocarbon biofuel): petrodiesel fuel containing 7% FAME and 13% hydrogenated vegetable oil. The Fisher 344 rats were exposed for 7 consecutive days (6 h/day) or 28 days (6 h/day, 5 days/week), both with and without diesel particle filter (DPF) treatment of the exhaust in whole body exposure chambers (n = 7/treatment). Histological analysis and analysis of cytokines and immune cell numbers in bronchoalveolar lavage fluid (BALF) did not reveal adverse pulmonary effects after exposure to DEE from B7 or SHB20 fuel. Significantly different gene expression levels for B7 compared to SHB20 indicate disturbed redox signaling (Cat, Hmox1), beta-adrenergic signaling (Adrb2) and xenobiotic metabolism (Cyp1a1). Exhaust filtration induced higher expression of redox genes (Cat, Gpx2) and the chemokine gene Cxcl7 compared to non-filtered exhaust. Exposure time (7 versus 28 days) also resulted in different patterns of lung gene expression. No genotoxic effects in the lungs were observed. Overall, exposure to B7 or SHB20 emissions suggests only minor effects in the lungs.

DNA repair as a human biomonitoring tool: Comet assay approaches

The comet assay offers the opportunity to measure both DNA damage and repair. Various comet assay based methods are available to measure DNA repair activity, but some requirements should be met for their effective use in human biomonitoring studies. These conditions include i) robustness of the assay, ii) sources of inter- and intra-individual variability must be known, iii) DNA repair kinetics should be assessed to optimize sampling timing; and iv) DNA repair in accessible surrogate tissues should reflect repair activity in target tissues prone to carcinogenic effects. DNA repair phenotyping can be performed on frozen and fresh samples, and is a more direct measurement than genomic or transcriptomic approaches. There are mixed reports concerning the regulation of DNA repair by environmental and dietary factors. In general, exposure to genotoxic agents did not change base excision repair (BER) activity, whereas some studies reported that dietary interventions affected BER activity. On the other hand, in vitro and in vivo studies indicated that nucleotide excision repair (NER) can be altered by exposure to genotoxic agents, but studies on other life style related factors, such as diet, are rare. Thus, crucial questions concerning the factors regulating DNA repair and inter-individual variation remain unanswered. Intra-individual variation over a period of days to weeks seems limited, which is favourable for DNA repair phenotyping in biomonitoring studies. Despite this reported low intra-individual variation, timing of sampling remains an issue that needs further investigation. A correlation was reported between the repair activity in easily accessible peripheral blood mononuclear cells (PBMCs) and internal organs for both NER and BER. However, no correlation was found between tumour tissue and blood cells. In conclusion, although comet assay based approaches to measure BER/NER phenotypes are feasible and promising, more work is needed to further optimize their application in human biomonitoring and intervention studies.

Nephrotoxicity: Topical issue

Drug-induced kidney injury is one of the most significant adverse events and dose limiting factor in chemotherapy as well a major cause of prospective drug attrition during pharmaceutical development. Moreover, kidney injury can also occur as a consequence of exposures to environmental xenobiotics such as heavy metals, fungal toxins and nanomaterials. The lack of adequate in vitro human kidney models that mimic more realistically the in vivo conditions and the absence of suitable and robust, cost-effective and predictive cell-based in vitro assays contribute to an underestimation of the kidney toxic potential of new drugs and xenobiotics. Therefore, a rapid screening system capable to detect potential nephrotoxicity at early stages of drug discovery is an urgent need. Here we provide an overview of human cell lines currently used as a surrogate in vitro kidney models in nephrotoxicity studies, including their advantages and limitations. In addition, the capacity of the single cell gel electrophoresis (SCGE)/comet assay as a potential tool in kidney toxicants screening is discussed. Despite a limited number of studies using the comet assay to evaluate the drug-induced kidney damage potential, a considerable variability in SCGE methodology (e.g. lysis, unwinding, and electrophoresis conditions) has been observed. Before the comet assay can be included in nephrotoxicity testing, a basic guideline has to be developed. To test its feasibility, additional in vitro experiments including inter-laboratory validation studies based on this guideline have to be performed.

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.

Using the comet assay and lysis conditions to characterize DNA lesions from the acrylamide metabolite glycidamide

The alkaline comet assay and a cell-free system were used to characterise DNA lesions induced by treatment with glycidamide (GA), a metabolite of the food contaminant acrylamide. DNA lesions induced by GA were sensitively detected when the formamidopyrimidine-DNA-glycosylase (Fpg) enzyme was included in the comet assay. We used LC-MS to characterise modified bases from GA-treated naked DNA with and without subsequent Fpg treatment. N7-GA-Guanine and N3-GA-Adenine aglycons were detected in the supernatant showing some depurination of adducted bases; treatment of naked DNA with Fpg revealed no further increase in the adduct yield nor occurrence of other adducted nucleobases. We treated human lymphocytes with GA and found large differences in DNA lesion levels detected with Fpg, depending on the duration and the pH of the lysis step. These lysis-dependent variations in GA-induced Fpg sensitive sites paralleled those observed after treatment of cells with methyl methane sulfonate (MMS). On the other hand, oxidative lesions (8-oxoGuanine) induced by a photoactive compound (Ro 12-9786) plus light, and also DNA strand breaks induced by X-rays, were detected largely independently of the lysis conditions. The results suggest that the GA-induced lesions are predominantly N7-GA-dG adducts slowly undergoing imidazole ring opening at pH 10 as in the standard lysis procedure; such structures are substrate for Fpg leading to strand breaks. The data suggest that the characteristic alkaline lysis dependence of some DNA lesions may be used to study specific types of DNA modifications. The comet assay is increasingly used in regulatory testing of chemicals; in this context, lysis-dependent variations represent a novel approach to obtain insight in the molecular nature of a genotoxic insult.

Comparative toxicity of selected PAHs in rainbow trout hepatocytes: genotoxicity, oxidative stress and cytotoxicity

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in aquatic ecosystems, which may have potentially toxic effects on organisms. In this study occurrence of DNA strand breaks, oxidative stress, and cytotoxicity were investigated in rainbow trout hepatocytes following in vitro exposure for 24 h to four PAHs (0.01-10 µM): naphthalene, fluoranthene, pyrene, and benzo[a]pyrene (B[a]P). The exposed hepatocytes were analyzed for DNA strand breaks using the comet assay and for antioxidant status by measuring intracellular glutathione (GSH) content using the fluorescent probe mBCl. The cytotoxicity of PAHs was assessed using the fluorescent probe CFDA-AM. The results showed that fluoranthene, pyrene, and B[a]P were genotoxic at all exposure concentrations, whereas naphthalene was genotoxic at concentrations ≥0.1 µM. All treatments reduced the intracellular concentrations of GSH for all four PAHs, except 10 µM of B[a]P, suggesting that some level of oxidative stress was present. The cytotoxic effect was observed for naphthalene at concentrations ≥0.1 µM and pyrene at all exposure concentrations, whereas fluoranthene and B[a]P were not cytotoxic at the tested concentrations. The study shows that low-molecular-weight PAHs may cause DNA strand breaks as high-molecular-weight PAHs do in fish tissue. In addition, two- to five-ring PAHs can induce oxidative stress and cytotoxicity.

Validation of Gelbond® high-throughput alkaline and Fpg-modified comet assay using a linear mixed model

Even if the comet assay has been widely used for decades, there is still a need for controlled studies and good mathematical models to assess the variability of the different versions of this assay and in particular to assess potential intra-experimental variability of the high-throughput comet assay. To address this point, we further validate a high-throughput comet assay that uses hydrophilic polyester film (Gelbond®). Experiments were performed using human peripheral blood mononuclear cells (PBMC) either untreated or treated with different concentration of MMS (methyl methanesulfonate). A positive control for the Fpg (Formamidopyrimidine DNA glycosylase)-modified comet assay (Ro 19-8022 with light) was also included. To quantify the sources of variability of the assay, including intradeposit variability, instead of summarizing DNA damage on 50 cells from a deposit by the mean or median of their percentage DNA tail, we analyzed all logit-transformed data with a linear mixed model. The main source of variation in our experimental data is between cells within the same deposit, suggesting genuine variability in the response of the cells rather than variation caused by technical treatment of cell samples. The second source of variation is the inter-experimental variation (day-to-day experiment); the coefficient of this variation for the control was 13.6%. The variation between deposits in the same experiment is negligible. Moreover, there is no systematic bias because of the position of samples on the Gelbond^® film nor the position of the films in the electrophoresis tank. This high-throughput comet assay is thus reliable for various applications. Environ. Mol. Mutagen. 59:595-602, 2018. © 2018 Wiley Periodicals, Inc.

Gamma radiation induces dose-dependent oxidative stress and transcriptional alterations in the freshwater crustacean Daphnia magna

Among aquatic organisms, invertebrate species such as the freshwater crustacean Daphnia magna are believed to be sensitive to gamma radiation, although information on responses at the individual, biochemical and molecular level is scarce. Following gamma radiation exposure, biological effects are attributed to the formation of free radicals, formation of reactive oxygen species (ROS) and subsequently oxidative damage to lipids, proteins and DNA in exposed organisms. Thus, in the present study, effects and modes of action (MoA) have been investigated in D. magna exposed to gamma radiation (dose rates: 0.41, 1.1, 4.3, 10.7, 42.9 and 106 mGy/h) after short-term exposure (24 and 48 h). Several individual, cellular and molecular endpoints were addressed, such as ROS formation, lipid peroxidation, DNA damage and global transcriptional changes. The results showed that oxidative stress is one of the main toxic effects in gamma radiation exposed D. magna, mediated by the dose-dependent increase in ROS formation and consequently oxidative damage to lipids and DNA over time. Global transcriptional analysis verified oxidative stress as one of the main MoA of gamma radiation at high dose rates, and identified a number of additional MoAs that may be of toxicological relevance. The present study confirmed that acute exposure to gamma radiation caused a range of cellular and molecular effects in D. magna exposed to intermediate dose rates, and highlights the need for assessing effects at longer and more environmentally relevant exposure durations in future studies.

Gamma irradiation during gametogenesis in young adult zebrafish causes persistent genotoxicity and adverse reproductive effects

The biological effects of gamma radiation may exert damage beyond that of the individual through its deleterious effects on reproductive function. Impaired reproductive performance can result in reduced population size over consecutive generations. In a continued effort to investigate reproductive and heritable effects of ionizing radiation, we recently demonstrated adverse effects and genomic instability in progeny of parents exposed to gamma radiation. In the present study, genotoxicity and effects on the reproduction following subchronic exposure during a gametogenesis cycle to ⁶⁰Co gamma radiation (27 days, 8.7 and 53 mGy/h, total doses 5.2 and 31 Gy) were investigated in the adult wild-type zebrafish (Danio rerio). A significant reduction in embryo production was observed one month after exposure in the 53 mGy/h exposure group compared to control and 8.7 mGy/h. One year later, embryo production was significantly lower in the 53 mGy/h group compared only to control, with observed sterility, accompanied by a regression of reproductive organs in 100% of the fish 1.5 years after exposure. Histopathological examinations revealed no significant changes in the testis in the 8.7 mGy/h group, while in 62.5% of females exposed to this dose rate the oogenesis was found to be only at the early previtellogenic stage. The DNA damage determined in whole blood, 1.5 years after irradiation, using a high throughput Comet assay, was significantly higher in the exposed groups (1.2 and 3-fold increase in 8.7 and 53 mGy/h females respectively; 3-fold and 2-fold increase in 8.7 and 53 mGy/h males respectively) compared to controls. A significantly higher number of micronuclei (4-5%) was found in erythrocytes of both the 8.7 and 53 mGy/h fish compared to controls. This study shows that gamma radiation at a dose rate of ≥ 8.7 mGy/h during gametogenesis causes adverse reproductive effects and persistent genotoxicity (DNA damage and increased micronuclei) in adult zebrafish.

Parental gamma irradiation induces reprotoxic effects accompanied by genomic instability in zebrafish (Danio rerio) embryos

Gamma radiation represents a potential health risk to aquatic and terrestrial biota, due to its ability to ionize atoms and molecules in living tissues. The effects of exposure to ⁶⁰Co gamma radiation in zebrafish (Danio rerio) were studied during two sensitive life stages: gametogenesis (F0: 53 and 8.7mGy/h for 27 days, total doses 31 and 5.2Gy) and embryogenesis (9.6mGy/h for 65h; total dose 0.62Gy). Progeny of F0 exposed to 53mGy/h showed 100% mortality occurring at the gastrulation stage corresponding to 8h post fertilization (hpf). Control and F0 fish exposed to 8.7mGy/h were used to create four lines in the first filial generation (F1): control, G line (irradiated during parental gametogenesis), E line (irradiated during embryogenesis) and GE line (irradiated during parental gametogenesis and embryogenesis). A statistically significant cumulative mortality of GE larva (9.3%) compared to controls was found at 96 hpf. E line embryos hatched significantly earlier compared to controls, G and GE (48-72 hpf). The deformity frequency was higher in G and GE, but not E line compared to controls at 72 hpf. One month after parental irradiation, the formation of reactive oxygen species (ROS) was increased in the G line, but did not significantly differ from controls one year after parental irradiation, while at the same time point it was significantly increased in the directly exposed E and GE lines from 60 to 120 hpf. Lipid peroxidation (LPO) was significantly increased in the G line one year after parental irradiation, while significant increase in DNA damage was detected in both the G and GE compared to controls and E line at 72 hpf. Radiation-induced bystander effects, triggered by culture media from tissue explants and observed as influx of Ca²⁺ ions through the cellular membrane of the reporter cells, were significantly increased in 72 hpf G line progeny one month after irradiation of the parents. One year after parental irradiation, the bystander effects were increased in the E line compared to controls, but not in progeny of irradiated parents (G and GE lines). Overall, this study showed that irradiation of parents can result in multigenerational oxidative stress and genomic instability in irradiated (GE) and non-irradiated (G) progeny of irradiated parents, including increases in ROS formation, LPO, DNA damage and bystander effects. The results therefore highlight the necessity for multi- and transgenerational studies to assess the environmental impact of gamma radiation.

Genotoxic effects of high dose rate X-ray and low dose rate gamma radiation in ApcMin/+ mice

Risk estimates for radiation-induced cancer in humans are based on epidemiological data largely drawn from the Japanese atomic bomb survivor studies, which received an acute high dose rate (HDR) ionising radiation. Limited knowledge exists about the effects of chronic low dose rate (LDR) exposure, particularly with respect to the application of the dose and dose rate effectiveness factor. As part of a study to investigate the development of colon cancer following chronic LDR vs. acute HDR radiation, this study presents the results of genotoxic effects in blood of exposed mice. CBAB6 F1 Apc+/+ (wild type) and ApcMin/+ mice were chronically exposed to estimated whole body absorbed doses of 1.7 or 3.2 Gy 60 Co-γ-rays at a LDR (2.2 mGy h-1 ) or acutely exposed to 2.6 Gy HDR X-rays (1.3 Gy min-1 ). Genotoxic endpoints assessed in blood included chromosomal damage (flow cytometry based micronuclei (MN) assay), mutation analyses (Pig-a gene mutation assay), and levels of DNA lesions (Comet assay, single-strand breaks (ssb), alkali labile sites (als), oxidized DNA bases). Ionising radiation (ca. 3 Gy) induced genotoxic effects dependent on the dose rate. Chromosomal aberrations (MN assay) increased 3- and 10-fold after chronic LDR and acute HDR, respectively. Phenotypic mutation frequencies as well as DNA lesions (ssb/als) were modulated after acute HDR but not after chronic LDR. The ApcMin/+ genotype did not influence the outcome in any of the investigated endpoints. The results herein will add to the scant data available on genotoxic effects following chronic LDR of ionising radiation. Environ. Mol. Mutagen. 58:560-569, 2017. © 2017 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

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

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

Environmentally realistic exposure to weathered North Sea oil: Sublethal effects in Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus)

With increasing oil and gas activities and transport in the Arctic, there is a need to understand how operational or accidental releases of substances affect marine organisms from a pristine environment. The aim of the current study was to describe and compare the responses of two marine fish species, Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus), following exposure to three levels (low, medium, high) of the water-soluble fraction of a North Sea crude oil for 16 days. The exposure system simulated environmental exposure by allowing clean seawater to percolate through gravel covered in weathered oil before being introduced to aquaria. Both polycyclic aromatic hydrocarbon (PAH) metabolite bile concentrations and cytochrome P4501A (CYP1A) levels and activity increased markedly in comparison with controls in both species, but there were no significant differences between the three exposures. Turbot possessed 4-5-fold higher concentrations of two PAH bile metabolites compared to Atlantic cod by day 8. In contrast, hepatic CYP1A activity in cod was consistently 2-6-fold higher than in turbot with increasing differences over the experimental period. Baseline DNA strand breaks in lymphocytes and kidney cells were low in both species, but was elevated for all treatments by day two. There were no marked indications of the treatments affecting immune functions in either species. This investigation demonstrated that there may be significant differences in responses between species receiving identical exposures and that DNA strand breaks in lymphocytes and kidney cells are sensitive to confinement stress. Data also indicate that some species, such as turbot, may adapt to treatments within days and weeks.

Baseline and oxidative DNA damage in marine invertebrates

Anthropogenic pollutants produce oxidative stress in marine organisms, directly or following generation of reactive oxygen species (ROS), potentially resulting in increased accumulation of DNA strand breaks quantified. The aim of this study is to quantify baseline levels of DNA strand breaks in marine species from four phyla and to assess relative sensitivity to oxidative stress as well as ability to recover. DNA strand breaks were determined using a formamidopyrimidine DNA glycosylase (Fpg)-amended comet assay in circulating cells from blue mussel (Mytilus edulis), shore crab (Carcinus maenas), sea star (Asterias rubens), and vase tunicate (Ciona intestinalis). Lymphocytes from Atlantic cod (Gadus morhua) were used as a reference. In addition to immediate analysis, cells from all species were exposed ex vivo to two concentrations of hydrogen peroxide (H₂O₂) at 25 or 250 μM prior to assay. Mean baseline DNA strand breaks were highest for cells from sea star (34%) followed by crab (25%), mussel (22%), tunicate (17%), and cod (14%). Circulating cells from invertebrates were markedly more sensitive to oxidative stress compared to cod lymphocytes. DNA strand breaks exceeded 80% for sea star, crab, and mussel cells following exposure to the lowest H₂O₂ concentration. There was no recovery for cells from any species following 1 hr in buffer. This study provides an in-depth analysis of DNA integrity for ecologically important species representing 4 phyla. Data indicate that circulating cells from invertebrates are more sensitive to oxidative stress than cells from fish as evidenced by DNA strand breaks. Future studies need to address the extent to which DNA strand breaks may exert consequences for body maintenance costs in marine invertebrates.

DNA damage in dab (Limanda limanda) and haddock (Melanogrammus aeglefinus) from European seas

Dab (Limanda limanda) and haddock (Melanogrammus aeglefinus) were collected from coastal and offshore locations in the Baltic (dab only), North Sea (haddock from one location only) and Iceland. Blood was analysed for DNA strand breaks using the comet assay and liver samples for DNA adduct concentrations. DNA strand breaks were at background levels in dab from the two Iceland locations and from the Dogger Bank. The highest levels were observed in dab from the Firth of Forth, Ekofisk and the German Bight. Hepatic DNA adducts in dab were highest at Ekofisk, in the Baltic and Dogger Bank, below detection limit in dab from Iceland and low in dab from the Firth of Forth and German Bight. There was large variation in DNA strand breaks between locations and individuals for haddock, particularly from Iceland. Adduct concentrations were elevated in haddock from both Iceland and the Firth of Forth. A general linear model (GLM) suggested that, in addition to location, the size of dab and its general condition contributed to explaining the observed variability in DNA strand breaks. A GLM for adducts in dab similarly allocated most of the variability to location, but with a possible contribution from CYP1A activity. There were no apparent differences between male and female dab for any of the methods. There was no obvious relationship between strand breaks and adducts in the same fish although dab from Ekofisk and Iceland had respectively high and low responses using both methods. The results from this large-scale study showed pollution-related genotoxicity for dab, that fish blood samples can be conserved prior to comet analyses and that there are clear species differences in genotoxic responses even when collected at the same location.

Tumor-associated APE1 variant exhibits reduced complementation efficiency but does not promote cancer cell phenotypes

Base excision repair (BER) is the major pathway for coping with most forms of endogenous DNA damage, and defects in the process have been associated with carcinogenesis. Apurinic/apyrimidinic endonuclease 1 (APE1) is a central participant in BER, functioning as a critical endonuclease in the processing of noncoding abasic sites in DNA. Evidence has suggested that APE1 missense mutants, as well as altered expression or localization of the protein, can contribute to disease manifestation. We report herein that the tumor-associated APE1 variant, R237C, shows reduced complementation efficiency of the methyl methanesulfonate hypersensitivity and impaired cell growth exhibited by APE1-deficient mouse embryonic fibroblasts. Overexpression of wild-type APE1 or the R237C variant in the nontransformed C127I mouse cell line had no effect on proliferation, cell cycle status, steady-state DNA damage levels, mitochondrial function, or cellular transformation. A human cell line heterozygous for an APE1 knockout allele had lower levels of endogenous APE1, increased cellular sensitivity to DNA-damaging agents, impaired proliferation with time, and a distinct global gene expression pattern consistent with a stress phenotype. Our results indicate that: (i) the tumor-associated R237C variant is a possible susceptibility factor, but not likely a driver of cancer cell phenotypes, (ii) overexpression of APE1 does not readily promote cellular transformation, and (iii) haploinsufficiency at the APE1 locus can have profound cellular consequences, consistent with BER playing a critical role in proliferating cells. Environ. Mol. Mutagen. 58:84-98, 2017. © 2017 Wiley Periodicals, Inc.

Gamma radiation at a human relevant low dose rate is genotoxic in mice

Even today, 70 years after Hiroshima and accidents like in Chernobyl and Fukushima, we still have limited knowledge about the health effects of low dose rate (LDR) radiation. Despite their human relevance after occupational and accidental exposure, only few animal studies on the genotoxic effects of chronic LDR radiation have been performed. Selenium (Se) is involved in oxidative stress defence, protecting DNA and other biomolecules from reactive oxygen species (ROS). It is hypothesised that Se deficiency, as it occurs in several parts of the world, may aggravate harmful effects of ROS-inducing stressors such as ionising radiation. We performed a study in the newly established LDR-facility Figaro on the combined effects of Se deprivation and LDR γ exposure in DNA repair knockout mice (Ogg1^−/−) and control animals (Ogg1^+/−). Genotoxic effects were seen after continuous radiation (1.4 mGy/h) for 45 days. Chromosomal damage (micronucleus), phenotypic mutations (Pig-a gene mutation of RBC^CD24−) and DNA lesions (single strand breaks/alkali labile sites) were significantly increased in blood cells of irradiated animals, covering three types of genotoxic activity. This study demonstrates that chronic LDR γ radiation is genotoxic in an exposure scenario realistic for humans, supporting the hypothesis that even LDR γ radiation may induce cancer.