Search

Aneuploidy is characterized by the presence of an abnormal number of chromosomes and is a common hallmark of cancer. However, exposure to aneugenic compounds does not necessarily lead to cancer. Aneugenic compounds are mainly identified using the in vitro micronucleus assay but this assay cannot standardly discriminate between aneugens and clastogens and cannot be used to identify the exact mode-of-action (MOA) of aneugens; tubulin stabilization, tubulin destabilization, or inhibition of mitotic kinases. To improve the classification of aneugenic substances and determine their MOA, we developed and validated the TubulinTracker assay that uses a green fluorescent protein-tagged tubulin reporter cell line to study microtubule stability using flow cytometry. Combining the assay with a DNA stain also enables cell cycle analysis. Substances whose exposure resulted in an accumulation of cells in G2/M phase, combined with increased or decreased tubulin levels, were classified as tubulin poisons. All known tubulin poisons included were classified correctly. Moreover, we correctly classified compounds, including aneugens that did not affect microtubule levels. However, the MOA of aneugens not affecting tubulin stability, such as Aurora kinase inhibitors, could not be identified. Here, we show that the TubulinTracker assay can be used to classify microtubule stabilizing and destabilizing compounds in living cells. This insight into the MOA of aneugenic agents is important, eg, to support a weight-of-evidence approach for risk assessment, and the classification as an aneugen as opposed to a clastogen or mutagen, has a big impact on the assessment. [ABSTRACT FROM AUTHOR]

The regulatory 2D in vitro micronucleus (MN) assay is part of a battery of tests, used to test for genotoxicity of new and existing compounds before they are assessed in vivo (ICH S2). The 2D MN assay consists of a monolayer of cells, whereas the in vivo bone marrow (BM) setting comprises a multicellular environment within a three-dimensional extracellular matrix. Although the in vitro MN assay follows a robust protocol set out by the Organisation for Economic Co-operation and Development (OECD) to comply with regulatory bodies, some compounds have been identified as negative genotoxicants within the in vitro MN assay but marginally positive when assessed in vivo. The glucocorticoids, which are weakly positive in vivo , have generally been suggested to pose no long-term carcinogenic risk; however, for novel compounds of unknown activity, improved prediction of genotoxicity is imperative. To help address this observation, we describe a novel 3D in vitro assay which aims to replicate the results seen within the in vivo BM microenvironment. AlgiMatrix scaffolds were optimized for seeding with HS-5 human BM stromal cells as a BM microenvironment, to which the human lymphoblast cell line TK6 was added. An MN assay was performed aligning with the 2D regulatory assay protocol. Utilizing this novel 3D in vitro model of the BM, known genotoxicants (mitomycin C, etoposide, and paclitaxel), a negative control (caffeine), and in vivo positive glucocorticoids (dexamethasone and prednisolone) were investigated for the induction of MN. It was found, in agreement with historical in vivo data, that the model could accurately predict the in vivo outcome of the glucocorticoids, unlike the regulatory 2D in vitro MN assay. These preliminary results suggest our 3D MN assay may better predict the outcome of in vivo MN tests, compared with the standard 2D assay. [ABSTRACT FROM AUTHOR]

Background: Recent scientific advances in cancer research have led to the development of immunomodulatory and molecularly targeted drugs with better safety profiles than chemotherapeutics, which makes it possible to include healthy volunteers (HVs) in clinical trials. In this study, we aimed to identify the number of marketing authorization applications (MAAs) that enrolled HVs in a clinical trial and to identify the number of anticancer drugs that were given to HVs despite a positive genotoxic finding. In addition, we evaluated the dose of anticancer drugs administered to HVs and the justification for proceeding with HV studies despite a positive genotoxic finding. Methods: Publicly available information from the European Medicines Agency (EMA) website was used for this study. Anticancer drugs were identified using the human medicines highlights published by EMA between January 2010 and December 2019. EPARs were used to collect general information of the anticancer drugs, details on genotoxicity studies, and the enrollment of HVs in clinical trials. Results: We identified 71 MAAs for small molecule anticancer drugs with a positive or negative CHMP opinion in the EU. Forty-eight anticancer drugs were studied in HVs, of which 12 anticancer drugs were administered to HVs despite positive genotoxic findings in the standard battery. Systematic and extensive genetic toxicology screening demonstrated the absence of genotoxic risks to the cell system. Conclusion: We showed that despite a positive genotoxic finding, comprehensive genetic toxicology testing demonstrated the absence of risks to the cell system at the human exposure dose. Therefore, these anticancer drugs posed no harm to HVs. [ABSTRACT FROM AUTHOR]

In vitro genotoxicity testing plays an important role in chemical risk assessment. The human B-lymphoblastoid cell line TK6 is widely used as a standard cell line for regulatory safety evaluations. Like many other mammalian cell lines, TK6 cells have limited metabolic capacity; therefore, usually require a source of exogenous metabolic activation for use in genotoxicity testing. Previously, we developed a set of TK6-derived cell lines that individually express one of fourteen cytochrome P450s (CYPs). In the present study, we surveyed a panel of major Phase II drug-metabolizing enzymes to characterize their baseline expression in TK6 cells. These results may serve as a reference enzymatic profile of this commonly used cell line. [ABSTRACT FROM AUTHOR]

Accuracy, sensitivity, simplicity, reproducibility, and low-cost are desirable requirements for genotoxicity assessment techniques. Here we describe a simple electrophoretic assay for genomic DNA lesions quantification (EAsy-GeL) based on subjecting DNA samples to rapid unwinding/renaturation treatments and neutral agarose gel electrophoresis. The experiments performed in this work involved different biological samples exposed to increasing environmental-simulated doses of ultraviolet-B (UVB) radiation, such as Escherichia coli, human leukocytes, and isolated human genomic DNA. DNA extraction was carried out using a universal and low-cost protocol, which takes about 4 h. Before electrophoresis migration, DNA samples were kept into a neutral buffer to detect double-strand breaks (DSBs) or subjected to a 5-min step of alkaline unwinding and neutral renaturation to detect single-strand breaks (SSBs) or incubated with the DNA repair enzyme T4-endonuclease V for the detection of cyclobutane pyrimidine dimers (CPDs) before the 5-min step of DNA unwinding/renaturation. Then, all DNA samples were separated by neutral agarose gel electrophoresis, the DNA average length of each lane was calculated through the use of free software, and the frequency of DNA breaks per kbp was determined by a simple rule of three. Dose-response experiments allowed the quantification of different levels of DNA damage per electrophoretic run, varying from a constant and low amount of DSBs/SSBs to high and dose-dependent levels of CPDs. Compared with other assays based on alkaline unwinding and gel electrophoresis, EAsy-GeL has important advantages for both environmental monitoring and laboratory testing purposes. The simplicity and applicability of this protocol to other types of DNA lesions, biological models, and agents make it ideal for genotoxicity, DNA repair studies, as well as for assessing exposure risks to ecosystems and human health.

The human lymphoblastoid cell line TK6 stands out as the most widely employed human cell line in genotoxicity testing, as recommended by various testing guidelines for in vitro assessments. Nevertheless, like many testing cell lines, TK6 lacks functional phase I drug-metabolizing enzymes crucial for chemical genotoxicity evaluations. This protocol introduces a lentivirus-based methodology for establishing a panel of TK6-derived cell lines, each expressing one of 14 cytochrome P450s (CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A5, and CYP3A7). The utilization of a lentiviral expression system ensures stable transduction, offering notable advantages such as sustained transgene expression, high transduction efficiency, positive selection feasibility, and user-friendly application. Additionally, we present a detailed procedure for validating the enhanced expression of each CYP in the established cell lines through real-time PCR, western blotting, and mass spectrometry analysis. Lastly, we exemplify the application of these CYP-expressing TK6 cell lines in genotoxicity testing, employing a flow-cytometry-based in vitro micronucleus test. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Lentivirus production and transduction for TK6 cells Support Protocol: Selecting a single clone of CYP-expressing TK6 cells Basic Protocol 2: Validation of CYP expression in TK6 cell lines Basic Protocol 3: Application of transduced cell lines in flow-cytometry-based micronucleus assay., (Published 2024. This article is a U.S. Government work and is in the public domain in the USA.)

Cell line‐based in vitro testing has been widely used as an important component of the genotoxicity testing battery; however, the use of cell lines is constrained by several limitations, including the genetic drift and variability. A study recently reported in the literature comprehensively examined genomic changes in a large number of cell lines and reported extensive genetic variations within the same cell lines across passage numbers and laboratories, even for single‐cell derived subclones. The primary objective of this communication is to raise awareness and stimulate discussion within the genotoxicity testing community of the extent of genetic variability of cell lines in general and how these variables could potentially influence the results and reproducibility of genotoxicity testing. Meanwhile, some recommendations for good cell culture practices are highlighted to mitigate, at least to some extent, the concern about genetic variation. Environ. Mol. Mutagen. 60:559–562, 2019. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The problem of the currently used routine genotoxicity tests is relatively low predictivity of in vitro tests for in vivo genotoxicity and carcinogenicity. An important reason is considered to be inadequate expression of xenobiotic-metabolizing enzymes in indicator cell lines. The aim of our study was to generate metabolically active differentiated hepatic progenies (hDHP) from human adipose tissue-derived mesenchymal stem cells (hASC) for genotoxicity testing. hDHP, generated using a three-step hepatic differentiation procedure, expressed hepatic properties such as glycogen storage and albumin secretion. The results of the comet assay demonstrated comparable sensitivity of hASC and hDHP to detect DNA damage induced by a direct acting genotoxic agent tert-butylhydroperoxide. Exposure to model indirect acting genotoxins benzo(a)pyrene, aflatoxin B1, and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine did not induce DNA damage in hASC, while hDHP cells detected DNA damage induced by benzo(a)pyrene and aflatoxin B1, indicating their metabolic activity. The gene and protein expression analysis confirmed the presence of key enzymes involved in metabolism of the three genotoxins in hDHP cells. Moreover, the exposure of hDHP to the model pro-carcinogens altered the expression of selected metabolic genes. hDHP were further immortalized with hTERT transfection, resulting in a stable cell line that can be matured to metabolically active hDHP ready for genotoxicity testing in only 2 weeks. The advantage of these immortalized cells is their prolonged replicative life span and consequently limitless supply of hDHP cells. We conclude that hDHP cells have a great potential for the application in the routine genotoxicity testing and are therefore worth further investigations. [ABSTRACT FROM AUTHOR]

Resumo Justificativa e objetivos Os Resíduos de Gases Anestésicos (RGA) presentes no ar ambiente das Salas de Operação (SO) são associados a riscos ocupacionais diversos. O presente artigo propõe‐se a discorrer sobre exposição ocupacional aos RGA e seu impacto em profissionais expostos, com ênfase em danos genéticos e estresse oxidativo. Conteúdo Apesar do surgimento de anestésicos inalatórios mais seguros, a exposição ocupacional aos RGA ainda é preocupação atual. Fatores relacionados às técnicas anestésicas e estação de anestesia, além da ausência de sistema de exaustão de gases em SO, contribuem para poluição anestésica. Para minimizar os riscos à saúde em profissionais expostos, recomendam‐se limites máximos de exposição. Entretanto, em países em desenvolvimento, ainda carece a mensuração de RGA e de regulamentação frente à exposição ocupacional aos RGA. Os RGA são capazes de induzir danos no material genético, como danos no DNA avaliados pelo teste do cometa e aumento na frequência de micronúcleos em profissionais com exposição prolongada. O estresse oxidativo também é associado à exposição aos RGA por induzir lipoperoxidação, danos oxidativos no DNA e comprometimento do sistema antioxidante em profissionais expostos. Conclusões Por tratar‐se de questão de saúde pública, é imprescindível reconhecer os riscos ocupacionais relacionados aos RGA, inclusive genotoxicidade, mutagenicidade e estresse oxidativo. Urge a necessidade de mensuração dos RGA para conhecimento desses valores nas SO, especialmente em países em desenvolvimento, de normatização das concentrações máximas seguras de RGA nas SO, além de se adotarem práticas de educação com conscientização dos profissionais expostos. Background and objectives The waste anesthetic gases (WAGs) present in the ambient air of operating rooms (OR), are associated with various occupational hazards. This paper intends to discuss occupational exposure to WAGs and its impact on exposed professionals, with emphasis on genetic damage and oxidative stress. Content Despite the emergence of safer inhaled anesthetics, occupational exposure to WAGs remains a current concern. Factors related to anesthetic techniques and anesthesia workstations, in addition to the absence of a scavenging system in the OR, contribute to anesthetic pollution. In order to minimize the health risks of exposed professionals, several countries have recommended legislation with maximum exposure limits. However, developing countries still require measurement of WAGs and regulation for occupational exposure to WAGs. WAGs are capable of inducing damage to the genetic material, such as DNA damage assessed using the comet assay and increased frequency of micronucleus in professionals with long‐term exposure. Oxidative stress is also associated with WAGs exposure, as it induces lipid peroxidation, oxidative damage in DNA, and impairment of the antioxidant defense system in exposed professionals. Conclusions The occupational hazards related to WAGs including genotoxicity, mutagenicity and oxidative stress, stand as a public health issue and must be acknowledged by exposed personnel and responsible authorities, especially in developing countries. Thus, it is urgent to stablish maximum safe limits of concentration of WAGs in ORs and educational practices and protocols for exposed professionals. [ABSTRACT FROM AUTHOR]

Over the past thirty years, the International Workshops on Genotoxicity Testing (IWGT) became one of the leading groups in the field of regulatory genotoxicology, not only due to the diversity of participants with respect to geography and professional affiliation, but also due to the unique setup of recurring IWGT meetings every four years. The hallmarks of the IWGT process have been diligent initial planning approaches of the working groups, collection of data so as to stimulate data-driven discussions and debate, and striving to reach consensus recommendations. The scientific quality of the Working Groups (WGs) has been exceptional due to the selection of highly regarded experts on each topic. As a result, the IWGT working group reports have become important documents. The deliberations and publications have provided guidance on test systems and testing protocols that have influenced the development or revision of test guidelines of the Organisation for Economic Co-operation and Development (OECD), guidance by the International Council for Harmonisation (ICH), and strategic testing or data analysis approaches in general. This article summarizes the history of the IWGT, identifies some of its major achievements, and provides an outlook for the future. [ABSTRACT FROM AUTHOR]

Present report deals with the phytotoxicity and genotoxicity of Mathura refinery wastewater and Aligarh wastewater of Northern India. The IC50 value in Allium cepa root growth inhibition test was recorded to be 0.14X and 0.10X for Mathura refinery and Aligarh industrial wastewaters, respectively. Significant decline in the survival of various Escherichia coli K12 DNA repair defective mutants was observed when the tester strains were exposed to the aforementioned samples. The order of sensitivity was invariably as: AB1157 (wild type) < AB2494 (lexA mutant) < AB2463 (recA mutant) < AB2480 (uvrA recA double mutant). These results suggested a significant amount of DNA damage within the bacterial cells exposed to test wastewaters. A. cepa genotoxicity test also demonstrated a considerable amount of chromosomal damage of A. cepa brought about by the test samples. The aberration index (A.I.) for Aligarh wastewater and refinery wastewater was recorded to be 11.2% and 14.7%, respectively, whereas the aquaguard mineral water serving as negative control displayed the A.I. value to be 2.6%. Interestingly, genotoxicity of both industrial wastewaters was reduced to a remarkable extent in presence of mannitol, the hydroxyl radical scavenger. Present study clearly indicated a distinct pattern of the chromosomal aberrations showing predominantly stickiness and stray chromosomes in case of AWW while clumping and stickiness in case of RWW, thereby affirming the genotoxicity of both test waters.

Chemical contaminants and residues are undesired chemicals occurring in consumer products such as food and drugs, at the workplace and in the environment, i.e. in air, soil and water. These compounds can be detected even at very low concentrations and lead frequently to considerable concerns among consumers and in the media. Thus it is a major challenge for modern toxicology to provide transparent and versatile tools for the risk assessment of such compounds in particular with respect to human health. Well-known examples of toxic contaminants are dioxins or mercury (in the environment), mycotoxins (from infections by molds) or acrylamide (from thermal treatment of food). The process of toxicological risk assessment of such chemicals is based on i) the knowledge of their contents in food, air, water etc., ii) the routes and extent of exposure of humans, iii) the toxicological properties of the compound, and, iv) its mode(s) of action. In this process quantitative dose-response relationships, usually in experimental animals, are of outstanding importance. For a successful risk assessment, in particular of genotoxic chemicals, several conditions and models such as the Margin of Exposure (MoE) approach or the Threshold of Toxicological Concern (TTC) concept exist, which will be discussed. [ABSTRACT FROM AUTHOR]

The rodent Pig-a assay is an in vivo method for the detection of gene mutation, where lack of glycosylphosphatidylinositol-anchored proteins on the surface of circulating red blood cells (RBCs) serves as a reporter for Pig-a gene mutation. In the case of rats, the frequency of mutant phenotype RBCs is measured via fluorescent anti-CD59 antibodies and flow cytometry. The Pig-a assay meets the growing expectations for novel approaches in animal experimentation not only focusing on the scientific value of the assay but also on animal welfare aspects (3Rs principles), for example, amenable to integration into pivotal rodent 28-day general toxicology studies. However, as recommended in the Organisation for Economic Co-operation and Development Test Guidelines for genotoxicity testing, laboratories are expected to demonstrate their proficiency. While this has historically involved the extensive use of animals, here we describe an alternative approach based on a series of blood dilutions covering a range of mutant frequencies. The experiments described herein utilized either non-fluorescent anti-CD59 antibodies to provide elevated numbers of mutant-like cells, or a low volume blood sample from a single N-ethyl- N-nitrosourea treated animal. Results from these so-called reconstruction experiments from four independent laboratories showed good overall precision (correlation coefficients: 0.9979-0.9999) and accuracy (estimated slope: 0.71-1.09) of mutant cell scoring, which was further confirmed by Bland-Altman analysis. These data strongly support the use of reconstruction experiments for training purposes and demonstrating laboratory proficiency with very few animals, an ideal situation given the typically conflicting goals of demonstrating laboratory proficiency and reducing the use of animals. Environ. Mol. Mutagen. 57:678-686, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Limited information is available on the genotoxicity of simple quinoxalines, distinct from the food related carcinogenic derivatives bearing an aromatic amino group. Isolated positive results, with no apparent structure–activity relationships, were reported in earlier studies on alkyl substituted quinoxalines, raising a safety concern in some regulatory authorities in view of the potential human exposure related to their use as food flavors. In order to elucidate the genotoxic hazard posed by simple quinoxalines, in this work a random set of mono- and bi-substituted methyl, chloro- and hydroxyl- quinoxalines have been tested in an OECD-compliant bacterial reversion test (TG 471). The results obtained do not highlight any genotoxic potential in the set of quinoxalines examined, and suggest that this may be a common trait for other simple substituted quinoxalines. Earlier published positive findings were not confirmed in this work, which call for a cautious approach in the use of literature data for regulatory purpose. [ABSTRACT FROM PUBLISHER]

As a part of the 6th IWGT, an expert working group on the comet assay evaluated critical topics related to the use of the in vivo comet assay in regulatory genotoxicity testing. The areas covered were: identification of the domain of applicability and regulatory acceptance, identification of critical parameters of the protocol and attempts to standardize the assay, experience with combination and integration with other in vivo studies, demonstration of laboratory proficiency, sensitivity and power of the protocol used, use of different tissues, freezing of samples, and choice of appropriate measures of cytotoxicity. The standard protocol detects various types of DNA lesions but it does not detect all types of DNA damage. Modifications of the standard protocol may be used to detect additional types of specific DNA damage (e.g . , cross-links, bulky adducts, oxidized bases). In addition, the working group identified critical parameters that should be carefully controlled and described in detail in every published study protocol. In vivo comet assay results are more reliable if they were obtained in laboratories that have demonstrated proficiency. This includes demonstration of adequate response to vehicle controls and an adequate response to a positive control for each tissue being examined. There was a general agreement that freezing of samples is an option but more data are needed in order to establish generally accepted protocols. With regard to tissue toxicity, the working group concluded that cytotoxicity could be a confounder of comet results. It is recommended to look at multiple parameters such as histopathological observations, organ-specific clinical chemistry as well as indicators of tissue inflammation to decide whether compound-specific toxicity might influence the result. The expert working group concluded that the alkaline in vivo comet assay is a mature test for the evaluation of genotoxicity and can be recommended to regulatory agencies for use. [ABSTRACT FROM AUTHOR]

The conventional alkaline comet assay only detects DNA strand breaks and alkali-labile sites; however, with certain modifications it can also detect other lesions such as altered bases and cross-links. We internally validate the use of DNA-repair enzymes (Fpg, EndoIII, hOOG1 and hAAG) for detection of oxidized and alkylated bases, as well as a modification for detecting cross-links, using a medium-throughput version of the assay (12 minigels/slide) [1]. These modifications of the comet assay significantly increase its sensitivity and its specificity towards DNA lesions, providing valuable mechanistic information. Although all these modifications were integrated in a single assay, only one compound was evaluated per experiment. The use of the CometChip® will allow to integrate all the modifications and, moreover, to evaluate several compounds at once. To study the sensitivity of this high-throughput version of the comet assay, a comparison between the two gels/slide format and the CometChip®, following the manufacturers' protocol, was carried out. For that purpose, TK-6 cells treated with different concentrations of methyl methanesulfonate (MMS) and H2O2 were employed. Dose-response curves were obtained using both formats although small differences were found in values of % DNA in tail. The use of enzymes in combination with the CometChip® has not been explored before; however, the protocol has been adapted and Fpgsensitive site were successfully detected in TK-6 cells treated with KBrO3. The use of the CometChip® combined with different enzymes and other modifications could be an important tool for elucidating the mechanism of action of genotoxic compounds in a high-throughput manner. [1] Muruzabal D. et al. (2021) Arch Toxicol. 95: 2825-2838. doi: 10.1007/s00204-021-03102-3. [ABSTRACT FROM AUTHOR]

A material composed of kaolin with silver nanoparticles attached to its surface was developed as food supplement in feed as an alternative to the use of antibiotics. An in vitro genotoxicity evaluation of this formulation, was carried out following the strategy suggested by the EFSA guidance, composed by the mouse lymphoma assay (TG 490), the micronucleus (MN) test (TG 487) and the standard and DNAformamidopyrimidine glycosylase (Fpg) modified comet assay, obtaining negative results in all of them [1]. Negative results in in vitro studies do not usually require going forward with an in vivo evaluation, but regarding this type of complex materials, EFSA advices it since the current in vitro methods have some limitations. In this study an in vivo geno-toxicological evaluation of this material was conducted. First, a preliminary dose finding study was carried out using the following doses: 50, 300 and 2000 mg/kg b.w. For the main study, a combined strategy composed of the MN test (TG 474) and the comet assay (TG 489), integrated in a repeated dose 28-day oral toxicity study (TG 407), was performed. A NOAEL of 2000 mg of the silverkaolin formulation/kg b.w. by oral route, for 28 days was determined. The silver-kaolin formulation did not induce micronuclei in bone marrow, or DNA strand breaks or alkali labile sites in liver, spleen, kidney or duodenum at any dose. The modified Fpg comet assay did not reveal oxidized bases in the same tissues at the dose of 2000 mg/kg b.w. Silver was quantified by ICP-MS in all the target organs, confirming the negative results obtained under these conditions. [1] Rodriguez-Garraus A. et al., (2022) Nanomaterials 12: 914. doi: 10.3390/nano12060914. Financial support: project EFA 1983/16 OUTBIOTICS, co-financed by "Fondo Europeo de Desarrollo Regional" (FEDER) through the European Program of territorial cooperation POCTEFA 2014-20 (INTERREG POCTEFA). [ABSTRACT FROM AUTHOR]

Micronucleus assays are extensively used by biologists to assess genotoxicity and to monitor human exposure to genotoxic materials. As recent studies suggested that nuclear buds can be a new source of micronuclei formed in interphase, the quantification of nuclear buds, which are micronucleus like objects that are attached to the nuclei in interphase, in normal and control group is needed. Three automatic nuclear bud detection algorithms fit for different situations are proposed in this paper. One is based on ellipse fitting, one is based on a stick model and the other is based on the top-hat transform. Comparison of the three methods is also given in this paper. Experimental results showed that the proposed algorithms are all effective and efficient for nuclear bud detection. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation of guanine to 8-oxo-2′-deoxyguanosine (8-oxo-dG) is one of the most abundant and best studied oxidative DNA lesions and is commonly used as a biomarker for oxidative stress. Over the last decades, various methods for the detection of DNA oxidation products have been established and optimized. However, some of them lack sensitivity or are prone to artifact formation, while others are time-consuming, which hampers their application in screening approaches. In this study, we present a formamidopyrimidine glycosylase (Fpg)-based method to detect oxidative lesions in isolated DNA using a modified protocol of the automated version of the fluorimetric detection of alkaline DNA unwinding (FADU) method, initially developed for the measurement of DNA strand breaks (Moreno-Villanueva et al., 2009. BMC Biotechnol. 9, 39). The FADU-Fpg method was validated using a plasmid DNA model, mimicking mitochondrial DNA, and the results were correlated to 8-oxo-dG levels as measured by LC–MS/MS. The FADU-Fpg method can be applied to analyze the potential of compounds to induce DNA strand breaks and oxidative lesions, as exemplified here by treating plasmid DNA with the peroxynitrite-generating molecule Sin-1. Moreover, this method can be used to screen DNA-protective effects of antioxidant substances, as exemplified here for a small-molecule, i.e., uric acid, and a protein, i.e., manganese superoxide dismutase, both of which displayed a dose-dependent protection against the generation of oxidative DNA lesions. In conclusion, the automated FADU-Fpg method offers a rapid and reliable measurement for the detection of peroxynitrite-mediated DNA damage in a cell-free system, rendering it an ideal method for screening the DNA-protective effects of antioxidant compounds. [Copyright &y& Elsevier]

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