Effect of reducing the top concentration used in the in vitro chromosomal aberration test in CHL cells on the evaluation of industrial chemical genotoxicity

Toxicity associated with long term use of aluminum cookware in mice: A systemic, genetic and reproductive perspective

Studies on the toxic effects of cooking with aluminum pots are limited and none of them have explored its impact on the genetic material in germ and somatic cells. Therefore, this study investigated the cytogenotoxic effect of boiled water from new, 3- and 6-year old aluminum pots in germ and somatic cells viz-a-vis mouse sperm morphology test and sperm count; and the bone marrow micronucleus test. The mice were allowed to freely drink the boiled water from the different aluminum pots for 3, 4, and 5 weeks. The heavy metal analysis showed that As, Pb, Cd, and Al were present in the boiled water samples at different concentrations with the 6-year old pot having the highest concentrations of Pb, Cd, and Al. There were duration of exposure and age of pot-dependent significant increase in abnormal sperm cells and a significant decrease total mean sperm count of exposed mice. Similarly, there was a statistically significant increase in micronucleated polychromatic erythrocytes and nuclear abnormalities in the exposed mice that increased dependently upon the age of the cookware. Finally there were significantly increased activities of serum AST and ALT; and the liver concentrations of MDA, SOD and CAT in boiled water exposed mice. The findings of this study revealed that boiled water from aluminum pots is capable of inducing cytotoxic and genotoxic effects, especially as the pot ages.

In Silico Model for Chemical-Induced Chromosomal Damages Elucidates Mode of Action and Irrelevant Positives

In silico tools to predict genotoxicity have become important for high-throughput screening of chemical substances. However, current in silico tools to evaluate chromosomal damage do not discriminate in vitro-specific positives that can be followed by in vivo tests. Herein, we establish an in silico model for chromosomal damages with the following approaches: (1) re-categorizing a previous data set into three groups (positives, negatives, and misleading positives) according to current reports that use weight-of-evidence approaches and expert judgments; (2) utilizing a generalized linear model (Elastic Net) that uses partial structures of chemicals (organic functional groups) as explanatory variables of the statistical model; and (3) interpreting mode of action in terms of chemical structures identified. The accuracy of our model was 85.6%, 80.3%, and 87.9% for positive, negative, and misleading positive predictions, respectively. Selected organic functional groups in the models for positive prediction were reported to induce genotoxicity via various modes of actions (e.g., DNA adduct formation), whereas those for misleading positives were not clearly related to genotoxicity (e.g., low pH, cytotoxicity induction). Therefore, the present model may contribute to high-throughput screening in material design or drug discovery to verify the relevance of estimated positives considering their mechanisms of action.

In Vitro Cytogenetic Assays: Chromosomal Aberrations and Micronucleus Tests

Chromosome damage is a very important indicator of genetic damage relevant to environmental and clinical studies. Detailed descriptions of the protocols used for detection of chromosomal aberrations induced by genotoxic agents in vitro both in the presence or absence of rat liver-derived metabolizing systems are given in this chapter. Structural chromosomal aberrations that can be observed and quantified at metaphases are described here. For the detection of chromosomal damage (fragments or whole chromosome) in interphase, the micronucleus test can be used, and a description of this test is also presented. Criteria for determining a positive result using appropriate statistical methods are described.

Genotoxicity evaluation of titanium dioxide nanoparticles using the mouse lymphoma assay and the Ames test

Titanium dioxide nanoparticles (TiO₂-NPs) are widely used in the cosmetics, health, and food industries, but their safety and genotoxicity remain a matter of debate. We investigated whether TiO₂-NPs could induce gene mutations in mouse lymphoma L5178Y cells and Salmonella typhimurium strains TA97a, TA98, TA100, TA102, and TA1535. Following preliminary tests, 2 mg/mL for the mouse lymphoma gene mutation assay and 1.25 mg/plate for the in vitro bacterial reverse mutation assay (Ames test) were selected as the highest concentrations. Exposure to TiO2-NPs for 4 or 24 h with or without S9 metabolic activation did not increase mutation frequency for any of the concentrations tested in L5178Y cells. In the Ames test, TiO₂-NPs did not induce reverse mutation in the bacterial strains. No positive mutagenic responses were observed in either test system, and therefore we cannot classify TiO₂-NPs as mutagenic; further testing will be required to determine conclusively whether TiO₂-NPs are genotoxic.

Cytogenetic and genotoxic effects of 2-chlorophenol on Allium cepa L. root meristem cells

2-Chlorophenol (2-CP), a class of chlorinated organic pollutants like other chlorophenols, is used as intermediate in the synthesis of the higher chlorinated congeners, certain dyes, preservatives, herbicides, fungicides, and plastics. In this study, cytotoxic and genotoxic effects of 2-CP were investigated on the root meristem cells of Allium cepa for its effects on root growth, mitotic index (MI), mitotic phases, chromosomal abnormalities (CAs), and DNA damage by using Allium anaphase-telophase and Comet assays. EC₅₀ of 2-CP value was determined as approximately 25 mg/L by Allium root growth inhibition test. Three concentrations of 2-CP (12.5, 25, and 50 mg/L), distilled water (negative control), and methyl methane sulfonate (MMS, 10 mg/L, positive control) were applied to onion stem cells under different exposure periods (24, 48, 72, and 96 h). All the applied doses of 2-CP slightly decreased MIs. 2-CP induced total CAs such as disturbed anaphase-telophase, chromosome laggards, stickiness, and bridges and also DNA damage at significant levels. These results demonstrate that 2-CP has genotoxic effects in A. cepa root meristematic cells.

The research of genetic toxicity of β-phellandrene

β-Phellandrene, a plant extract, can be used as natural pesticides and synthetic materials. As a factor that human may be exposed to, the toxicity information about β-phellandrene is scared at present. This study focused on the genetic toxicity of β-phellandrene. The genetic toxicity of β-phellandrene was evaluated by micronucleus test, comet assay, Ames test, and chromosomal aberration test. In this study, 2850, 1425, 712.5mg/kg β-phellandrene were used in vivo experiments (comet assay and micronucleus test). For Ames test, pure β-phellandrene and different concentrations were used in the experiment. According to the results of cell viability assay (MTT test), the concentration of chromosomal aberration test was formulated. The result of comet assay showed that β-phellandrene can significantly induce DNA damage at the dosage of 1425 and 2850mg/kg. While the results of Micronucleus test and chromosome aberration test showed that β-phellandrene does not lead to apparently genetic toxicity on chromosome level. Ames tests suggest that β-phellandrene had the ability to increase gene mutation with or without S9 mixture. So, it could be drawn that β-phellandrene would have certain genetic toxicity, and the toxicity is reflected as DNA strand breaks and mutation. This study filled the lack of genetic toxicity study of β-phellandrene, and enriched information for risk assessment for β-phellandrene.

Regulatory requirements for genotoxicity assessment of plant protection product active ingredients, impurities, and metabolites

Active ingredients in plant protection products are subject to rigorous safety assessment during their development, including assessment of genotoxicity. Plant protection products are used for agriculture in multiple regions and for the registration of active ingredients it is necessary to satisfy the data requirements of these different regions. There are no overarching global agreements on which genotoxicity studies need to be conducted to satisfy the majority of regulatory authorities. The implementation of new OECD guidelines for the in vitro micronucleus, transgenic rodent somatic and germ cell gene mutation and in vivo comet assays, as well as the revision of a number of other OECD test guidelines has resulted in some changes to data requirements. This review describes the genotoxicity data requirements for chemical active ingredients as well as biologicals, microbials, ground water metabolites, metabolites, and impurities in a number of regions. Similarities and differences are highlighted. Environ. Mol. Mutagen. 58:325-344, 2017. © 2017 Wiley Periodicals, Inc.

International regulatory requirements for genotoxicity testing for pharmaceuticals used in human medicine, and their impurities and metabolites

The process of developing international (ICH) guidelines is described, and the main guidelines reviewed are the ICH S2(R1) guideline that includes the genotoxicity test battery for human pharmaceuticals, and the ICH M7 guideline for assessing and limiting potentially mutagenic impurities and degradation products in drugs. Key aspects of the guidelines are reviewed in the context of drug development, for example the incorporation of genotoxicity assessment into non-clinical toxicity studies, and ways to develop and assess weight of evidence. In both guidelines, the existence of "thresholds" or non-linear dose responses for genotoxicity plays a part in the strategies. Differences in ICH S2(R1) protocol recommendations from OECD guidelines are highlighted and rationales explained. The use of genotoxicity data during clinical development and in assessment of carcinogenic potential is also described. There are no international guidelines on assessment of potentially genotoxic metabolites, but some approaches to safety assessment are discussed for these. Environ. Mol. Mutagen. 58:296-324, 2017. © 2017 Wiley Periodicals, Inc.

Main issues addressed in the 2014-2015 revisions to the OECD Genetic Toxicology Test Guidelines

The Organization for Economic Cooperation and Development (OECD) recently revised the test guidelines (TGs) for genetic toxicology. This article describes the main issues addressed during the revision process, and the new and consistent recommendations made in the revised TGs for: (1) demonstration of laboratory proficiency; (2) generation and use of robust historical control data; (3) improvement of the statistical power of the tests; (4) selection of top concentration for in vitro assays; (5) consistent data interpretation and determination of whether the result is clearly positive, clearly negative or needs closer consideration; and, (6) consideration of 3R's for in vivo assay design. The revision process resulted in improved consistency among OECD TGs (including the newly developed ones) and more comprehensive recommendations for the conduct and the interpretation of the assays. Altogether, the recommendations made during the revision process should improve the efficiency, by which the data are generated, and the quality and reliability of test results. Environ. Mol. Mutagen. 58:284-295, 2017. © 2017 Wiley Periodicals, Inc.

Evaluation of toxicity and genotoxicity of 2-chlorophenol on bacteria, fish and human cells

Due to the extensive use of chlorophenols (CPs) in anthropogenic activities, 2-Chlorophenol (2-CP), among other CPs, can enter aquatic ecosystems and can be harmful to a variety of organisms, including bacteria, fish and humans, that are exposed directly and/or indirectly to such contaminated environments. Based on the existing knowledge and in order to move a step forward, the purpose of this study is to investigate the toxic and mainly the genotoxic effects of 2-CP using a combination of bioassays. The tests include the marine bacterium Vibrio fischeri and micronuclei induction in the erythrocytes of Carassius auratus as well as in cultured human lymphocytes. The results obtained reveal that 2-CP is able to induce dose-dependent toxic and genotoxic effects on the selected tested concentrations under the specific experimental conditions.

A retrospective evaluation method for in vitro mammalian genotoxicity tests using cytotoxicity index transformation formulae

Although in vitro chromosomal aberration tests and micronucleus tests have been widely used for genotoxicity evaluation, false-positive results have been reported under strong cytotoxic conditions. To reduce false-positive results, the new Organization for Economic Co-operation and Development (OECD) test guideline (TG) recommends the use of a new cytotoxicity index, relative increase in cell count or relative population doubling (RICC/RPD), instead of the traditionally used index, relative cell count (RCC). Although the use of the RICC/RPD may result in different outcomes and require re-evaluation of tested substances, it is impractical to re-evaluate all existing data. Therefore, we established a method to estimate test results from existing RCC data. First, we developed formulae to estimate RICC/RPD from RCC without cell counts by considering cell doubling time and experiment time. Next, the accuracy of the cytotoxicity index transformation formulae was verified by comparing estimated RICC/RPD and measured RICC/RPD for 3 major chemicals associated with false-positive genotoxicity test results: ethyl acrylate, eugenol and p-nitrophenol. Moreover, 25 compounds with false-positive in vitro chromosomal aberration (CA) test results were re-evaluated to establish a retrospective evaluation method based on derived estimated RICC/RPD values. The estimated RICC/RPD values were in good agreement with the measured RICC/RPD values for every concentration and chemical, and the estimated RICC suggested the possibility that 12 chemicals (48%) with previously judged false-positive results in fact had negative results. Our method enables transformation of RCC data into RICC/RPD values with a high degree of accuracy and will facilitate comprehensive retrospective evaluation of test results.

Genotoxicity of pyrroloquinoline quinone (PQQ) disodium salt (BioPQQ™)

The genotoxic potential of pyrroloquinoline quinone (PQQ) disodium salt (BioPQQ™) was evaluated in a battery of genotoxicity tests. The results of the bacterial mutation assay (Ames test) were negative. Weak positive results were obtained in 2 separate in vitro chromosomal aberration test in Chinese hamster lung (CHL) fibroblasts. Upon testing in an in vitro chromosomal aberration test in human peripheral blood lymphocytes, no genotoxic activity of PQQ was noted. In the in vivo micronucleus assay in mice, PQQ at doses up to 2,000 mg/kg body weight demonstrated that no genotoxic effects are expressed in vivo in bone marrow erythrocytes. The weak responses in the in vitro test CHL cells were considered of little relevance under conditions of likely human exposure. PQQ disodium was concluded to have no genotoxic activity in vivo.