Considerations for the Use of Mutation as a Regulatory Endpoint in Risk Assessment

The North-western Italy air quality monitoring network: Improving experience of PM2.5 assessment with mutagenicity assay

The finest fraction of Particulate Matter (PM2.5) carries a large number of pollutants, some of which are assessed as genotoxic, such as some Polycyclic Aromatic Hydrocarbons (PAHs). In many countries, PM2.5 in combination with some PAHs are monitored to assess the concentrations of pollutants, while the air quality is rarely assessed by means of biological assays. Epidemiological studies have demonstrated a significant correlation between these two pollutants and human adverse effects, in particular on the respiratory system. Nevertheless, other air pollutants can induce a biological effect and the cumulative effect of the PM2.5 complex mixture may not be easily deduced by PM2.5 and PAH levels. This study aimed to combine the legislative monitoring of PM2.5 with the study of its mutagenicity. During a full year, daily air samples were collected in nine sites of the North-western Italy air quality monitoring network (Piedmont Region) and PM2.5 and PAH concentrations were assessed. Monthly pooled organic extracts were tested with the Salmonella assay using TA98 and TA100 strains, with and without metabolic activation (±S9), and using TA98NR and YG1021 strains. In all sites, a positive response was observed for TA98 and TA100 especially without S9. A significant mutagenic seasonal variation was detected, with higher mutagenicity in winter and lower responses in summer (average total mutagenicity ratio 27:1). The response of TA98NR and YG1021 compared with TA98 suggested a significant contribution of nitro-compounds to the mutagenicity. No significant differences were found between urban background and rural sites denoting the spread of pollution. A mutagenicity increase, 1.28 Total Mutagenicity Factor/20 m³, was observed for each PM2.5 μg increment. PAH levels and corresponding Toxic Equivalent Factors were highly correlated to mutagenicity results. This work confirms that complex environmental mixtures can be appropriately assessed through the implementation of physical-chemical analyzes with bioassays able to evaluate synergistic and antagonistic effects, especially for highest and lowest pollution settings.

Genotoxicity as a toxicologically relevant endpoint to inform risk assessment: A case study with ethylene oxide

The purpose of the present investigation is to analyze the in vivo genotoxicity dose-response data of ethylene oxide (EO) and the applicability of the derived point-of-departure (PoD) values when estimating permitted daily exposure (PDE) values. A total of 40 data sets were identified from the literature, and benchmark dose analyses were conducted using PROAST software to identify a PoD value. Studies employing the inhalation route of exposure and assessing gene or chromosomal mutations and chromosomal damage in various tissues were considered the most relevant for assessing risk from EO, since these effects are likely to contribute to adverse health consequences in exposed individuals. The PoD estimates were screened for precision and the values were divided by data-derived adjustment factors. For gene mutations, the lowest PDE was 285 parts per trillion (ppt) based on the induction of lacI mutations in the testes of mice following 48 weeks of exposure to EO. The corresponding lowest PDE value for chromosomal mutations was 1,175 ppt for heritable translocations in mice following 8.5 weeks of EO exposure. The lowest PDE for chromosomal aberrations was 238 ppt in the mouse peripheral blood lymphocytes following 48 weeks of inhalation exposure. The diverse dose-response data for EO-induced genotoxicity enabled the derivation of PoDs for various endpoints, tissues, and species and identified 238 ppt as the lowest PDE in this retrospective analysis.

Relevance of mouse lung tumors to human risk assessment

Mouse lung is a common site for chemical tumorigenicity, but the relevance to human risk remains debated. Long-term bioassays need to be assessed for appropriateness of the dose, neither exceeding Maximum Tolerated Dose (MTD) nor Kinetically based Maximum Dose (KMD). An example of the KMD issue is 1,3-dichloropropene (1,3-D), which only produced an increased incidence of lung tumors at a dose exceeding the KMD. In addition, since mouse lung tumors are common (>1% incidence), the appropriate statistical significance is p < .01. Numerous differences exist for mouse lung and tumors compared to humans, including anatomy, respiratory rate, metabolism, tumor histogenesis, and metastatic frequency. The recent demonstration of the critical role of mouse lung specific Cyp2 F2 metabolism in mouse lung carcinogenicity including styrene or fluensulfone indicates that this tumor response is not qualitatively or quantitatively relevant to humans. For non-DNA reactive and non-mutagenic carcinogens, the mode of action involves direct mitogenicity such as for isoniazid, styrene, fluensulfone, permethrin or cytotoxicity with regeneration such as for naphthalene. However, the possibility of mixed mitogenic and cytotoxic modes of action cannot always be excluded. The numerous differences between mouse and human, combined with epidemiologic evidence of no increased cancer risk for several of these chemicals make the relevance of mouse lung tumors for human cancer risk dubious.

EURL ECVAM Genotoxicity and Carcinogenicity Database of Substances Eliciting Negative Results in the Ames Test: Construction of the Database

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EURL ECVAM Consolidated Genotoxicity and Carcinogenicity Database extended.

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Negative Ames test results were compiled and reviewed.

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A database of Ames negative results was constructed.

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Database chemical space characterization was conducted.

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OFG representation of carcinogens and non-carcinogens was characterised.

The bacterial reverse mutation test (Ames test) is the most commonly used genotoxicity test; it is a primary component of the chemical safety assessment data required by regulatory agencies worldwide. Within the current accepted in vitro genotoxicity test battery, it is considered capable of revealing DNA reactivity, and identifying substances that can produce gene mutations via different mechanisms. The previously published consolidated EURL ECVAM Genotoxicity and Carcinogenicity Database, which includes substances that elicited a positive response in the Ames test, constitutes a collection of data that serves as a reference for a number of regulatory activities in the area of genotoxicity testing. Consequently, we considered it important to expand the database to include substances that fail to elicit a positive response in the Ames test, i.e., Ames negative substances. Here, we describe a curated collection of 211 Ames negative substances, with a summary of complementary data available for other genotoxicity endpoints in vitro and in vivo, plus available carcinogenicity data. A descriptive analysis of the data is presented. This includes a representation of the chemical space formed by the Ames-negative database with respect to other substances (e.g. REACH registered substances, approved drugs, pesticides, etc.) and a description of the organic functional groups found in the database. We also provide some suggestions on further analyses that could be made.

Genotoxic Assessment of the Dry Decoction of Myracrodruon urundeuva Allemão (Anacardiaceae) Leaves in Somatic Cells of Drosophila melanogaster by the Comet and SMART Assays

Medicinal plants are worldwide used as an efficient treatment of many diseases. Myracrodruon urundeuva Allemão (Anacardiaceae) is widely used Brazilian folk medicine to treat inflammations and infections of the female genital tract, conditions of the stomach and throat, and to heal wounds on the skin and mucous membranes. Several pharmacological properties of extracts and compounds isolated from M. urundeuva are found in the literature, corroborating its uses as antiulcer and gastroprotective, anti-inflammatory and analgesic, as well as antimicrobial. Despite these many uses in traditional herbal medicine, there are few reports of its toxic-genetic effect. This work aimed to investigate the genotoxic and mutagenic potential in vivo of the dry decoction of M. urundeuva leaves on somatic cells of Drosophila melanogaster, through the Comet assay and somatic mutation and recombination test (SMART). Six concentrations (0.5, 1.0, 2.0, 4.0, 8.0, and 16.0 mg/mL) were studied after feeding individuals for 24 hr in culture medium hydrated with extracts of M. urundeuva. In the Comet assay, all concentrations showed a genotoxic effect significantly higher than the negative control group, treated with distilled water. The two highest concentrations were also superior to the positive control group, treated with cyclophosphamide (1 mg/mL). In the SMART, there was a mutagenic effect at all concentrations tested, with a clear dose-dependent relationship. Both recombination and mutation account for these mutagenic effects. The set of results indicate that the dry decoction of M. urundeuva leaves is genotoxic and mutagenic for D. melanogaster under the experimental conditions of this study. Environ. Mol. Mutagen. 61:329-337, 2020. © 2019 Wiley Periodicals, Inc.