Mutagenicity of cytochrome P450 2E1 substrates in the Ames test with the metabolic competent S. typhimurium strain YG7108pin3ERb5

The food contaminant acetamide is not an in vivo clastogen, aneugen, or mutagen in rodent hematopoietic tissue

Acetamide (CAS 60-35-5) is classified by IARC as a Group 2B, possible human carcinogen, based on the induction of hepatocellular carcinomas in rats following chronic exposure to high doses. Recently, acetamide was found to be present in a variety of human foods, warranting further investigation. The regulatory body JECFA has previously noted conflicting reports on acetamide's ability to induce micronuclei (MN) in mice in vivo. To better understand the potential in vivo genotoxicity of acetamide, we performed acute MN studies in rats and mice, and a subchronic study in rats, the target species for liver cancer. In the acute exposure, animals were gavaged with water vehicle control, 250, 1000, or 2000 mg/kg acetamide, or the positive control (1 mg/kg mitomycin C). In the subchronic assay, bone marrow of rats gavaged at 1000 mg/kg/day (limit dose) for 28 days was evaluated. Both acute and subchronic exposures showed no change in the ratio of polychromatic to total erythrocytes (P/E) at any dose, nor was there any increase in the incidence of micronucleated polychromatic erythrocytes (MN-PCE). Potential mutagenicity of acetamide was evaluated in male rats gavaged with vehicle control or 1500 mg/kg/day acetamide using the in vivoPig-a gene mutation assay. There was no increase in mutant red blood cells or reticulocytes in acetamide-treated animals. In both acute and sub-chronic studies, elevated blood plasma acetamide in treated animals provided evidence of systemic exposure. We conclude based on this study that acetamide is not clastogenic, aneugenic, or mutagenic in vivo in rodent hematopoietic tissue warranting a formal regulatory re-evaluation.

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In vivo micronucleus tests with acetamide in mice and rats.

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Acetamide blood plasma levels demonstrated evidence of exposure.

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Acetamide does not induce micronuclei in rats and mice.

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Acetamide does not increase mutations in the rat Pig-a gene mutation assay.

Systematic Review of Toxicity Removal by Advanced Wastewater Treatment Technologies via Ozonation and Activated Carbon

Upgrading wastewater treatment plants (WWTPs) with advanced technologies is one key strategy to reduce micropollutant emissions. Given the complex chemical composition of wastewater, toxicity removal is an integral parameter to assess the performance of WWTPs. Thus, the goal of this systematic review is to evaluate how effectively ozonation and activated carbon remove in vitro and in vivo toxicity. Out of 2464 publications, we extracted 46 relevant studies conducted at 22 pilot or full-scale WWTPs. We performed a quantitative and qualitative evaluation of in vitro (100 assays) and in vivo data (20 species), respectively. Data is more abundant on ozonation (573 data points) than on an activated carbon treatment (162 data points), and certain in vitro end points (especially estrogenicity) and in vivo models (e.g., daphnids) dominate. The literature shows that while a conventional treatment effectively reduces toxicity, residual effects in the effluents may represent a risk to the receiving ecosystem on the basis of effect-based trigger values. In general, an upgrade to ozonation or activated carbon treatment will significantly increase toxicity removal with similar performance. Nevertheless, ozonation generates toxic transformation products that can be removed by a post-treatment. By assessing the growing body of effect-based studies, we identify sensitive and underrepresented end points and species and provide guidance for future research.

Assessment of the mode of action underlying development of forestomach tumors in rodents following oral exposure to ethyl acrylate and relevance to humans

Chronic repeated gavage dosing of high concentrations of ethyl acrylate (EA) causes forestomach tumors in rats and mice. For two decades, there has been general consensus that these tumors are unique to rodents because of: i) lack of carcinogenicity in other organs, ii) specificity to the forestomach (an organ unique to rodents which humans do not possess), iii) lack of carcinogenicity by other routes of exposure, and iv) obvious site of contact toxicity at carcinogenic doses. In 1986, EA was classified as possibly carcinogenic to humans by the International Agency for Research on Cancer (IARC). However, by applying a MOA analyses and human relevance framework assessment, the weight-of-evidence supports a cytotoxic MOA with the following key events: i) bolus delivery of EA to forestomach lumen and subsequent absorption, ii) cytotoxicity likely due to saturation of enzymatic detoxification, iii) chronic regenerative hyperplasia, and iv) spontaneous mutation due to increased cell replication and cell population. Clonal expansion of initiated cells thus results in late onset tumorigenesis. The key events in this 'wound and healing' MOA provide high confidence in the MOA as assessed by evolved Bradford-Hill Criteria. The weight-of-evidence supported by the proposed MOA, combined with a unique tissue that does not exist in humans, indicates that EA is highly unlikely to pose a human cancer hazard.

Safety of ethyl acrylate to be used as flavouring

The EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids (CEF Panel) was requested by the European Commission according to Art. 29 1(a) of the Regulation (EC) No 178/2002 to carry out a review of existing literature on the safety of ethyl acrylate [FL-no: 09.037] when used as a flavouring substance. Ethyl acrylate [FL-no: 09.037] was evaluated in 2010 by EFSA in FGE.71 as a flavouring substance, based on the 2006 JECFA evaluation. The Panel concluded that ethyl acrylate was of no safety concern at estimated level of intake as flavouring substance based on the Maximised Survey-Derived Daily Intake (MSDI) approach. The Panel has evaluated the new literature available and any previous assessments performed by JECFA (2006) and EFSA (2010). Moreover, new data on the use levels of ethyl acrylate as flavouring substance have been provided. For use as flavouring substance, the chronic dietary exposure estimated using the added portions exposure technique (APET), is calculated to be 3,545 μg/person per day for a 60-kg adult and 2,233 μg/person per day for a 15-kg 3-year-old child. Exposure from food contact materials may be up to 6,000 μg/person per day. The Panel considered that based on the available data, which covers all relevant genetic endpoints (i.e. gene mutations, structural and numerical chromosomal aberrations) there is no concern with respect to genotoxicity of ethyl acrylate. The Panel evaluated the available carcinogenicity studies conducted in rats and mice and agreed with the NTP evaluation (1998) concluding that the forestomach squamous cell papilloma and carcinoma observed in rodents were not relevant to humans. Additionally, there was no evidence of systemic toxicity in short-term and subchronic toxicity studies. Therefore, the Panel concluded that there is no safety concern for the use of ethyl acrylate as a flavouring substance, under the intended conditions of use.

Combinations of genotoxic tests for the evaluation of group 1 IARC carcinogens

Many of the known human carcinogens are potent genotoxins that are efficiently detected as carcinogens in human populations but certain types of compounds such as immunosuppressants, sex hormones, etc. act via non-genotoxic mechanism. The absence of genotoxicity and the diversity of modes of action of non-genotoxic carcinogens make predicting their carcinogenic potential extremely challenging. There is evidence that combinations of different short-term tests provide a better and efficient prediction of human genotoxic and non-genotoxic carcinogens. The purpose of this study is to summarize the in vivo and in vitro comet assay (CMT) results of group 1 carcinogens selected from the International Agency for Research on Cancer and to discuss the utility of the comet assay along with other genotoxic assays such as Ames, in vivo micronucleus (MN), and in vivo chromosomal aberration (CA) test. Of the 62 agents for which valid genotoxic data were available, 38 of 61 (62.3%) were Ames test positive, 42 of 60 (70%) were in vivo MN test positive and 36 of 45 (80%) were positive for the in vivo CA test. Higher sensitivity was seen in in vivo CMT (90%) and in vitro CMT (86.9%) assay. Combination of two tests has greater sensitivity than individual tests: in vivo MN + in vivo CA (88.6%); in vivo MN + in vivo CMT (92.5%); and in vivo MN + in vitro CMT (95.6%). Combinations of in vivo or in vitro CMT with other tests provided better sensitivity. In vivo CMT in combination with in vivo CA provided the highest sensitivity (96.7%).

The lower alkyl methacrylates: Genotoxic profile of non-carcinogenic compounds

All of the lower alkyl methacrylates are high production chemicals with potential for human exposure. The genotoxicity of seven mono-functional alkyl esters of methacrylic acid, i.e. methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, n-, i- and t-butyl methacrylate and 2 ethyl hexyl methacrylate, as well as methacrylic acid itself, the acyl component common to all, is reviewed and compared with the lack of carcinogenicity of methyl methacrylate, the representative member of the series so evaluated. Also reviewed are the similarity of structure, chemical and biological reactivity, metabolism and common metabolic products of this group of compounds which allows a category approach for assessing genotoxicity. As a class, the lower alkyl methacrylates are universally negative for gene mutations in prokaryotes but do exhibit high dose clastogenicity in mammalian cells in vitro. There is no convincing evidence that these compounds induce genotoxic effects in vivo in either sub-mammalian or mammalian species. This dichotomy of effects can be explained by the potential genotoxic intermediates generated in vitro. This genotoxic profile of the lower alkyl methacrylates is consistent with the lack of carcinogenicity of methyl methacrylate.

Evaluating the efficiency of advanced wastewater treatment: target analysis of organic contaminants and (geno-)toxicity assessment tell a different story

At a pilot scale wastewater treatment plant ozonation and powdered activated carbon filtration were assessed for their efficacy to remove trace organic contaminants from secondary treated effluents. A chemical analysis of 16 organic compounds was accompanied by a comprehensive suite of in vitro and in vivo bioassays with the focus on genotoxicity to account for the potential formation of reactive oxidation products. In vitro experiments were performed with solid phase extracted water samples, in vivo experiments with native wastewater in a flow through test system on site at the treatment plant. The chemical evaluation revealed an efficient oxidation of about half of the selected compounds by more than 90% at an ozone dose of 0.7 g/g DOC. A lower oxidizing efficiency was observed for the iodinated X-ray contrast media (49-55%). Activated carbon treatment (20 mg/L) was less effective for the removal of most pharmaceuticals monitored. The umuC assay on genotoxicity delivered results with about 90% decrease of the effects by ozonation and slightly lower efficiency for PAC treatment. However, the Ames test on mutagenicity with the strain YG7108 revealed a consistent and ozone-dose dependent increase of mutagenicity after wastewater ozonation compared to secondary treatment. Sand filtration as post treatment step reduced the ozone induced mutagenicity only partly. Also the fish early life stage toxicity test revealed an increase in mortality after ozonation and a reduced effect after sand filtration. Only activated carbon treatment reduced the fish mortality compared to conventional treatment on control level. Likewise the in vivo genotoxicity detected with the comet assay using fish erythrocytes confirmed an increased (geno-)toxicity after ozonation, an effect decrease after sand-filtration and no toxic effects after activated carbon treatment. This study demonstrates the need for a cautious selection of methods for the evaluation of advanced (oxidative) treatment technologies and of the effectiveness of post-treatments for elimination of adverse effects caused by oxidative treatments case by case.

Amylenes do not lead to bacterial mutagenicity in contrast to structurally related epoxides

Amylenes are unsaturated hydrocarbons (C₅H₁₀), such as 1-pentene, 2-pentene, 2-methyl-but-1-en (3-methyl-1-butene), 2-methyl-but-2-en (isopentene), and 3-methyl-but-1-en. We investigated bacterial mutagenicity of 1-pentene, 2-pentene, and 3-methyl-but-1-en in the Ames test. 2-Pentene was investigated as racemate and as pure diastereomers. We included the methyltransferase deficient Salmonella Typhimurium strain YG7108 and the application of a gas-tight preincubation to reduce the risk of false negative results. 1,2-Epoxypentane which may arise from 1-pentene was used as positive control. None of the investigated amylenes showed mutagenic effects, whereas 1,2-epoxypentane was mutagenic exceeding 100 μg per plate. An exceptional high reverse mutation in the negative control plates in the experiments with 1,2-epoxypentane was obviously caused by evaporation into the incubator which was shown by placing the control plates in a separate apparatus. No differences were seen upon use of YG7108 and its parent strain TA1535. In conclusion, 1,2-epoxypentane is most probably not a substrate of the deleted bacterial methyltransferases. The comparison of the bacterial mutagenicity of the investigated amylenes and 1,2-epoxipentane suggests that epoxidation of amylenes in the S9-mix does not proceed effectively or is counterbalanced by detoxifying reactions. The assessment of mutagenic effects of short chained aliphatic epoxides can be underestimated due to the evaporation of these compounds.

Alkylating potential of α,β-unsaturated compounds

Alkylation reactions of the nucleoside guanosine (Guo) by the α,β-unsaturated compounds (α,β-UC) acrylonitrile (AN), acrylamide (AM), acrylic acid (AA) and acrolein (AC), which can act as alkylating agents of DNA, were investigated kinetically. The following conclusions were drawn: i) The Guo alkylation mechanism by AC is different from those brought about the other α,β-UC; ii) for the first three, the following sequence of alkylating potential was found: AN > AM > AA; iii) A correlation between the chemical reactivity (alkylation rate constants) of AN, AM, and AA and their capacity to form adducts with biomarkers was found. iv) Guo alkylation reactions for AN and AM occur through Michael addition mechanisms, reversible in the first case, and irreversible in the second. The equilibrium constant for the formation of the Guo-AN adduct is K(eq) (37 °C) = 5 × 10(-4); v) The low energy barrier (≈10 kJ mol(-1)) to reverse the Guo alkylation by AN reflects the easy reversibility of this reaction and its possible correction by repair mechanisms; vi) No reaction was observed for AN, AM, and AA at pH < 8.0. In contrast, Guo alkylation by AC was observed under cellular pH conditions. The reaction rate constants for the formation of the α-OH-Guo adduct (the most genotoxic isomer), is 1.5-fold faster than that of γ-OH-Guo. vii) a correlation between the chemical reactivity of α,β-UC (alkylation rate constants) and mutagenicity was found.

Genotoxicity of acrylamide in vitro: Acrylamide is not metabolically activated in standard in vitro systems

The recent finding that acrylamide (AA), a genotoxic rodent carcinogen, is formed during the frying or baking of a variety of foods raises human health concerns. AA is known to be metabolized by cytochrome P450 2E1 (CYP2E1) to glycidamide (GA), which is responsible for AA's in vivo genotoxicity and probable carcinogenicity. In in-vitro mammalian cell tests, however, AA genotoxicity is not enhanced by rat liver S9 or a human liver microsomal fraction. In an attempt to demonstrate the in vitro expression of AA genotoxicity, we employed Salmonella strains and human cell lines that overexpress human CYP2E1. In the umu test, however, AA was not genotoxic in the CYP2E1-expressing Salmonella strain or its parental strain. Moreover, a transgenic human lymphoblastoid cell line overexpressing CYP2E1 (h2E1v2) and its parental cell line (AHH-1) both showed equally weak cytotoxic and genotoxic responses to high (>1 mM) AA concentrations. The DNA adduct N7-GA-Gua, which is detected in liver following AA treatment in vivo, was not substantially formed in the in vitro system. These results indicate that AA was not metabolically activated to GA in vitro. Thus, AA is not relevantly genotoxic in vitro, although its in vivo genotoxicity was clearly demonstrated.

Cell-based genotoxicity testing : genetically modified and genetically engineered bacteria in environmental genotoxicology

Genotoxicity test systems that are based on bacteria display an important role in the detection and assessment of DNA damaging chemicals. They belong to the basic line of test systems due to their easy realization, rapidness, broad applicability, high sensitivity and good reproducibility. Since the development of the Salmonella microsomal mutagenicity assay by Ames and coworkers in the early 1970s, significant development in bacterial genotoxicity assays was achieved and is still a subject matter of research. The basic principle of the mutagenicity assay is a reversion of a growth inhibited bacterial strain, e.g., due to auxotrophy, back to a fast growing phenotype (regain of prototrophy). Deeper knowledge of the -mutation events allows a mechanistic understanding of the induced DNA-damage by the utilization of base specific tester strains. Collections of such specific tester strains were extended by genetic engineering. Beside the reversion assays, test systems utilizing the bacterial SOS-response were invented. These methods are based on the fusion of various SOS-responsive promoters with a broad variety of reporter genes facilitating numerous methods of signal detection. A very important aspect of genotoxicity testing is the bioactivation of -xenobiotics to DNA-damaging compounds. Most widely used is the extracellular metabolic activation by making use of rodent liver homogenates. Again, genetic engineering allows the construction of highly sophisticated bacterial tester strains with significantly enhanced sensitivity due to overexpression of enzymes that are involved in the metabolism of xenobiotics. This provides mechanistic insights into the toxification and detoxification pathways of xenobiotics and helps explaining the chemical nature of hazardous substances in unknown mixtures. In summary, beginning with "natural" tester strains the rational design of bacteria led to highly specific and sensitive tools for a rapid, reliable and cost effective -genotoxicity testing that is of outstanding importance in the risk assessment of compounds (REACH) and in ecotoxicology.

Inhibition of rat testicular nuclear kinesins (krp2; KIFC5A) by acrylamide as a basis for establishing a genotoxicity threshold

Acrylamide is a toxic substance that induces a variety of cellular responses including neurotoxicity, male reproductive toxicity, tumorigenicity, clastogenicity, and DNA alkylation. Evidence is provided that inhibition of the microtubule motor protein kinesin is responsible for acrylamide-induced clastogenicity and aneuploidy. Two kinesin motors, KIFC5A and KRP2, which are responsible for spindle assembly and disassembly of kinetochore MT, respectively, are inhibited by acrylamide. The inhibitory concentration for a response is below the levels shown to adversely affect the cytogenetic parameters. The relative contribution of these inhibitions compared to DNA alkylation is considered. The implications of inhibition of these kinesins as the site of action of acrylamide with regard to risk assessment are substantial as this event will have a threshold and a safe level of acrylamide can be determined.

Synergistic metabolic toxicity screening using microsome/DNA electrochemiluminescent arrays and nanoreactors

Platforms based on thin enzyme/DNA films were used in two-tier screening of chemicals for reactive metabolites capable of producing toxicity. Microsomes were used for the first time as sources of cytochrome (cyt) P450 enzymes in these devices. Initial rapid screening involved electrochemiluminescent (ECL) arrays featuring spots containing ruthenium poly(vinylpyridine), DNA, and rat liver microsomes or bicistronically expressed human cyt P450 2E1 (h2E1). Cyt P450 enzymes were activated via the NADPH/reductase cycle. When bioactivation of substrates in the films gives reactive metabolites, they are trapped by covalent attachment to DNA bases. The rate of increase in ECL with enzyme reaction time reflects relative DNA damage rates. "Toxic hits" uncovered by the array were studied in structural detail by using enzyme/DNA films on silica nanospheres as "nanoreactors" to provide nucleobase adducts from reactive metabolites. The utility of this synergistic approach was demonstrated by estimating relative DNA damage rates of three mutagenic N-nitroso compounds and styrene. Relative enzyme turnover rates for these compounds using ECL arrays and LC-UV-MS correlated well with TD 50 values for liver tumor formation in rats. Combining ECL array and nanoreactor/LC-MS technologies has the potential for rapid, high-throughput, cost-effective screening for reactive metabolites and provides chemical structure information that is complementary to conventional toxicity bioassays.