An evaluation of Salmonella (Ames) test data in the published literature: application of statistical procedures and analysis of mutagenic potency

Validation of the 3D reconstructed human skin Comet assay, an animal-free alternative for following-up positive results from standard in vitro genotoxicity assays

As part of the safety assessment process, all industrial sectors employ genotoxicity test batteries, starting with well-established in vitro assays. However, these batteries have limited predictive capacity for the in vivo situation, which may result in unnecessary follow-up in vivo testing or the loss of promising substances where animal tests are prohibited or not desired. To address this, a project involving regulators, academia and industry was established to develop and validate in vitro human skin-based genotoxicity assays for topically exposed substances, such as cosmetics ingredients. Here, we describe the validation of the 3D reconstructed skin (RS) Comet assay. In this multicenter study, chemicals were applied topically three times to the skin over 48 h. Isolated keratinocytes and fibroblasts were transferred to slides before electrophoresis and the resulting comet formation was recorded as % tail DNA. Before decoding, results of the validation exercise for 32 substances were evaluated by an independent statistician. There was a high predictive capacity of this assay when compared to in vivo outcomes, with a sensitivity of 77 (80)%, a specificity of 88 (97)% and an overall accuracy of 83 (92)%. The numbers reflect the calls of the performing laboratories in the coded phase, whereas those in parenthesis reflect calls according to the agreed evaluation criteria. Intra- and inter-laboratory reproducibility was also very good, with a concordance of 93 and 88%, respectively. These results generated with the Phenion® Full-Thickness skin model demonstrate its suitability for this assay, with reproducibly low background DNA damage and sufficient metabolic capacity to activate pro-mutagens. The validation outcome supports the use of the RS Comet assay to follow up positive results from standard in vitro genotoxicity assays when the expected route of exposure is dermal. Based on the available data, the assay was accepted recently into the OECD test guideline development program.

Important considerations for the validation of QSAR models for in vitro mutagenicity

While high-level performance metrics generated from the validation of quantitative structure-activity relationship (QSAR) systems can provide valuable information on how well these models perform and where they need to be improved, they require appropriate interpretation. There is no universal performance metric which will answer all of the questions a user might ask relating to a model, and therefore, a combination of metrics should usually be considered. Furthermore, results may vary according to the chemical space being used to validate a model, and, in some cases, it may be the validation data which is lacking or ambiguous rather than the prediction being made. Finally, users also need to consider the interpretability of the predictions being made, alongside the accuracy of the predictions. In this paper, we will discuss these important considerations in more detail within the context of the results obtained at Lhasa Limited as part of the National Institute of Health Sciences (NIHS) QSAR challenge project.

Principles and procedures for handling out-of-domain and indeterminate results as part of ICH M7 recommended (Q)SAR analyses

The International Council for Harmonization (ICH) M7 guideline describes a hazard assessment process for impurities that have the potential to be present in a drug substance or drug product. In the absence of adequate experimental bacterial mutagenicity data, (Q)SAR analysis may be used as a test to predict impurities' DNA reactive (mutagenic) potential. However, in certain situations, (Q)SAR software is unable to generate a positive or negative prediction either because of conflicting information or because the impurity is outside the applicability domain of the model. Such results present challenges in generating an overall mutagenicity prediction and highlight the importance of performing a thorough expert review. The following paper reviews pharmaceutical and regulatory experiences handling such situations. The paper also presents an analysis of proprietary data to help understand the likelihood of misclassifying a mutagenic impurity as non-mutagenic based on different combinations of (Q)SAR results. This information may be taken into consideration when supporting the (Q)SAR results with an expert review, especially when out-of-domain results are generated during a (Q)SAR evaluation.

Transformation products in the water cycle and the unsolved problem of their proactive assessment: A combined in vitro/in silico approach

Transformation products (TPs) emerging from incomplete degradation of micropollutants in aquatic systems can retain the biological activity of the parent compound, or may even possess new unexpected toxic properties. The chemical identities of these substances remain largely unknown, and consequently, the risks caused by their presence in the water cycle cannot be assessed thoroughly. In this study, a combined approach for the proactive identification of hazardous elements in the chemical structures of TPs, comprising analytical, bioanalytical and computational methods, was assessed by the example of the pharmaceutically active micropollutant propranolol (PPL). PPL was photo-transformed using ultraviolet (UV) irradiation and 115 newly formed TPs were monitored in the reaction mixtures by LC-MS analysis. The reaction mixtures were screened for emerging effects using a battery of in vitro bioassays and the occurrence of cytotoxic and mutagenic activities in bacteria was found to be significantly correlated with the occurrence of specific TPs during the treatment process. The follow-up analysis of structure-activity-relationships further illustrated that only small chemical transformations, such as the hydroxylation or the oxidative opening of an aromatic ring system, could substantially alter the biological effects of micropollutants in aquatic systems. In conclusion, more efforts should be made to prevent the occurrence and transformation of micropollutants in the water cycle and to identify the principal degradation pathways leading to their toxicological activation. With regard to the latter, the judicious combination of bioanalytical and computational tools represents an appealing approach that should be developed further.

Comparative in vitro toxicity of nitrosamines and nitramines associated with amine-based carbon capture and storage

Amine-based CO2 capture is a prime contender for the first full-scale implementation of CO2 capture at fossil fuel-fired power plants postcombustion. However, the formation of potentially carcinogenic N-nitrosamines and N-nitramines from reactions of flue gas NOx with the amines presents a potential risk for contaminating airsheds and drinking water supplies. Setting regulatory emission limits is hampered by the dearth of toxicity information for the N-nitramines. This study employed quantitative in vitro bioassays for mutagenicity in Salmonella typhimurium, and chronic cytotoxicity and acute genotoxicity in Chinese hamster ovary (CHO) cells to compare the toxicity of analogous N-nitrosamines and N-nitramines relevant to CO2 capture. Although the rank order was similar for genotoxicity in CHO cells and mutagenicity in S. typhimurium, the Salmonella assay was far more sensitive. In general, mutagenicity was higher with S9 hepatic microsomal activation. The rank order of mutagenicity was N-nitrosodimethylamine (NDMA)>N-nitrosomorpholine>N-nitrodimethylamine>1,4-dinitrosopiperazine>N-nitromorpholine>1,4-dinitropiperazine>N-nitromonoethanolamine>N-nitrosodiethanolamine>N-nitrodiethanolamine. 1-Nitrosopiperazine and 1-nitropiperazine were not mutagenic. Overall, N-nitrosamines were ∼15-fold more mutagenic than their N-nitramine analogues.

Genotoxicity Assessment of Erythritol by Using Short-term Assay

Erythritol is a sugar alcohol that is widely used as a natural sugar substitute. Thus, the safety of its usage is very important. In the present study, short-term genotoxicity assays were conducted to evaluate the potential genotoxic effects of erythritol. According to the OECD test guidelines, the maximum test dose was 5,000 μg/plate in bacterial reverse mutation tests, 5,000 μg/ml in cell-based assays, and 5,000 mg/kg for in vivo testing. An Ames test did not reveal any positive results. No clastogenicity was observed in a chromosomal aberration test with CHL cells or an in vitro micronucleus test with L5178Y tk^+/− cells. Erythritol induced a marginal increase of DNA damage at two high doses by 24 hr of exposure in a comet assay using L5178Y tk^+/− cells. Additionally, in vivo micronucleus tests clearly demonstrated that oral administration of erythritol did not induce micronuclei formation of the bone marrow cells of male ICR mice. Taken together, our results indicate that erythritol is not mutagenic to bacterial cells and does not cause chromosomal damage in mammalian cells either in vitro or in vivo.

Safety studies conducted on a sanitizing agent containing benzalkonium chloride

Free N Clear is a sanitizing agent composed of United States Pharmacopeial Convention grade benzalkonium chloride (BAC), acetic acid, and methylparaben. Free N Clear is proposed for use as a sanitizing agent at a 1: 50 dilution (2% solution), which contains approximately 100 ppm BAC. As part of a program to assess its safety, a 2% solution of Free N Clear (diluted Free N Clear) was administered by gavage to Sprague-Dawley rats for 91d and tested for genetic toxicity in vitro and in vivo. In the 91d study, the no observable adverse-effect level of diluted Free N Clear in male and female Sprague-Dawley rats is 5000 mg/kg bw/day, the highest dose administered. Diluted Free N Clear was not mutagenic in a bacterial reverse mutation assay that tested concentrations extending into the toxic range, and did not increase the frequency of micronucleated polychromatic erythrocytes in bone marrow cells of male or female Sprague-Dawley rats when tested at the maximum permissible dose volume of 20 mL/kg bw. The results support safety of Free N Clear, when used at the concentration proposed for use.

PRACTICAL APPLICATION

The significance of these findings will allow for the development of Free N Clear as a potential sanitizing agent for food.

International round-robin study on the Ames fluctuation test

An international round-robin study on the Ames fluctuation test [ISO 11350, 2012], a microplate version of the classic plate-incorporation method for the detection of mutagenicity in water, wastewater and chemicals was performed by 18 laboratories from seven countries. Such a round-robin study is a precondition for both the finalization of the ISO standardization process and a possible regulatory implementation in water legislation. The laboratories tested four water samples (spiked/nonspiked) and two chemical mixtures with and without supplementation of a S9-mix. Validity criteria (acceptable spontaneous and positive control-induced mutation counts) were fulfilled by 92-100%, depending on the test conditions. A two-step method for statistical evaluation of the test results is proposed and assessed in terms of specificity and sensitivity. The data were first subjected to powerful analysis of variance (ANOVA) after an arcsine-square-root transformation to detect significant differences between the test samples and the negative control (NC). A threshold (TH) value based on a pooled NC was then calculated to exclude false positive test results. Statistically, positive effects observed by the William's test were considered negative, if the mean of all replicates of a sample did not exceed the calculated TH. By making use of this approach, the overall test sensitivity was 100%, and the test specificity ranged from 80 to 100%.

Comparison of in vitro micronucleus and gene mutation assay results for p53-competent versus p53-deficient human lymphoblastoid cells

The high frequency of false or irrelevant positive results in in vitro mammalian cell genotoxicity tests is a critical concern for regulators. Here, we tested whether such results may be due to the mammalian cells used in the tests being deficient in p53, which is involved in the maintenance of genomic stability. We compared the in vitro responses of two human lymphoblastoid cell lines derived from the same progenitor cell-p53-competent (TK6) and p53-deficient (WTK-1) cells-in a micronucleus (MN) test and a thymidine kinase gene (TK) mutation assay. We tested 14 chemicals including three mutagens and 11 clastogens and spindle poisons. The three mutagens evoked clear positive responses in both assays in both cell lines. The responses to the clastogens and spindle poisons, on the other hand, depended on the assay endpoint and/or the cell line. Most of clastogens and spindle poisons were positive in the MN test in both cell lines. In the TK mutation assay, on the other hand, WTK-1 cells but not TK6 cells detected spindle poisons, which may have been due to the disturbance of the spindle checkpoint and lack of apoptosis in the p53-deficient cells. Some chemicals that induced chromosome aberrations in rodent cells were negative in both TK6 and WTK-1 cells, indicating that a species-specific factor rather than p53 status was associated with the response. In conclusion, the p53 status did not seriously influence the MN test results but it did influence the TK mutation assay results.

Umbuzeiro G, DeMarini DM. The Salmonella mutagenicity assay: the stethoscope of genetic toxicology for the 21st century

OBJECTIVES

According to the 2007 National Research Council report Toxicology for the Twenty-First Century, modern methods (e.g., "omics," in vitro assays, high-throughput testing, computational methods) will lead to the emergence of a new approach to toxicology. The Salmonella mammalian microsome mutagenicity assay has been central to the field of genetic toxicology since the 1970s. Here we document the paradigm shifts engendered by the assay, the validation and applications of the assay, and how the assay is a model for future in vitro toxicology assays.

DATA SOURCES

We searched PubMed, Scopus, and Web of Knowledge using key words relevant to the Salmonella assay and additional genotoxicity assays.

DATA EXTRACTION

We merged the citations, removing duplicates, and categorized the papers by year and topic.

DATA SYNTHESIS

The Salmonella assay led to two paradigm shifts: that some carcinogens were mutagens and that some environmental samples (e.g., air, water, soil, food, combustion emissions) were mutagenic. Although there are > 10,000 publications on the Salmonella assay, covering tens of thousands of agents, data on even more agents probably exist in unpublished form, largely as proprietary studies by industry. The Salmonella assay is a model for the development of 21st century in vitro toxicology assays in terms of the establishment of standard procedures, ability to test various agents, transferability across laboratories, validation and testing, and structure-activity analysis.

CONCLUSIONS

Similar to a stethoscope as a first-line, inexpensive tool in medicine, the Salmonella assay can serve a similar, indispensable role in the foreseeable future of 21st century toxicology.

Genotoxicity Studies on Carrageenan: Short-term In Vitro Assays

Carrageenan is a naturally-occurring sulfated polygalactan which has been widely used in the dairy industry and a gelling agent in non-dairy products. In this study, four short-term in vitro genotoxicity assays were investigated to evaluate the potential genotoxic effects of carrageenan. The mutagenic-ity of carrageenan was evaluated up to a maximum dose of 5 mg/plate in Ames test. There was no increase in the number of revertant colonies compared to its negative control at any dose in all of strains tested. To assess clastogenic effect, the in vitro chromosomal aberration assay was performed using Chinese hamster lung cells. Carrageenan was not considered to be clastogenic in this assay at up to the highest feasible concentration which could be evaluated. The in vitro comet assay and micronucleus test results obtained on L5178Y cells also revealed that carrageenan has no genotoxicity potential, although there was a marginal increase in micronuclei frequencies and DNA damage in the respective micronucleus and comet assays. Taken together, our results indicate that carrageenan was not genotoxic based on four in vitro genotoxicity results.

In Vitro Studies on the Genotoxic Effects of Wood Smoke Flavors

Smoke flavors based on the thermal decomposition of wood have been applied to a variety of food products as an alternative for traditional smoking. Despite its increasing use, the available genotoxicity data on wood smoke flavors (WSF) are still controversial. Thus, potential genotoxic effects of WSF in four short-term in vitro genotoxicity assays were investigated, which included the Ames assay, chromosomal aberration assay, micronucleus test and the alkaline comet assay. WSF did not cause any mutation in the Ames assay using five tester strains at six concentrations of 0.16, 0.31, 0.63, 1.25, 2.5 and 5 µl/plate. To assess clastogenic effect, the in vitro chromosomal aberration assay was performed using Chinese hamster lung cells. No statistically significant increase in the number of metaphases with structural aberrations was observed at the concentrations of 1.25, 2.5, and 5 µl/ml. The in vitro comet assay and micronucleus test results obtained on L5178Y cells also revealed that WSF has no genotoxicity potential, although there was a marginal increase in micronuclei frequencies and DNA damage in the respective micronucleus and comet assays. Taken together, based on the results obtained from these four in vitro studies, it is concluded that WSF is not a mutagenic agent in bacterial cells and causes no chromosomal and DNA damage in mammalian cells in vitro.

The mutagenic hazards of aquatic sediments: a review

Sediments are the sink for particle-sorbed contaminants in aquatic systems and can serve as a reservoir of toxic contaminants that continually threaten the health and viability of aquatic biota. This work is a comprehensive review of published studies that investigated the genotoxicity of sediments in rivers, lakes and marine habitats. The Salmonella mutagenicity test is the most frequently used assay and accounts for 41.1% of the available data. The Salmonella data revealed mutagenic potency values for sediment extracts (in revertants per gram dry weight) that spans over seven orders of magnitude from not detectable to highly potent (10(5) rev/g). Analyses of the Salmonella data (n=510) showed significant differences between rural, urban/industrial, and heavily contaminated (e.g., dump) sites assessed using TA98 and TA100 with S9 activation. Additional analyses showed a significant positive correlation between Salmonella mutagenic potency (TA98 and TA100 with S9) and PAH contamination (r2=0.19-0.68). The second and third most commonly used assays for the analysis of sediments and sediment extracts are the SOS Chromotest (9.2%) and the Mutatox assays (7.8%), respectively. These assays are frequently used for rapid initial screening of collected samples. A variety of other in vitro endpoints employing cultured fish and mammalian cells have been used to investigate sediment genotoxic activity. Endpoints investigated include sister chromatid exchange frequency, micronucleus frequency, chromosome aberration frequency, gene mutation at tk and hprt loci, unscheduled DNA synthesis, DNA adduct frequency, and DNA strand break frequency. More complex in vivo assays have documented a wide range of effects including neoplasms and preneoplastic lesions in fish and invertebrate exposed ex situ. Although costly and time consuming, these assays have provided definitive evidence linking sediment contamination and a variety of genotoxic and carcinogenic effects observed in situ.

A comparative assessment of Boise, Idaho, ambient air fine particle samples using the plate and microsuspension Salmonella mutagenicity assays

The primary objective of this study is to characterize the genotoxic potential of the ambient air aerosols collected within an air shed impacted primarily by wood smoke and automotive emissions. The study also examines the relative merits of a microsuspension assay and the standard plate assay for monitoring the presence of airborne particle-bound mutagens. Wintertime ambient air particulate samples collected from Boise, Idaho, USA, were shown to contain extractable organic matter that is mutagenic in the Salmonella typhimurium microsuspension and plate-incorporation assays. Differences in the results from the primary sites, auxiliary sites and the background site demonstrate that the particle-bound mutagens are not evenly distributed within the air shed and are more associated with the location of sampling than with the time of sampling or the type of bioassay used to evaluate the samples. This study also demonstrates that the bioassay protocol used in such studies should depend upon the characteristics of the air shed's mutagens and the purpose of the study. For example, the microsuspension assay gave somewhat more variable results between samples but was approximately threefold more sensitive than the plate assay. When strain TA98 was used in the microsuspension assay, the mutagenic response was greater without an exogenous activation system. The reverse was true for the plate assay in which the use of an exogenous activation system increased the mutagenicity response. TA100 in the microsuspension assay provided results comparable to those with TA98. This is important because TA100 can also be used to bioassay semivolatile and volatile organics associated with ambient air mutagenicity. This, in turn, allows a comparison of the mutagenicity of organics collected by differing methods due to their volatility. Future studies should be directed toward correlation of mutagenicity results with other analytical results in order to further develop methods for better characterization of the genotoxicity of ambient air.

Use of alkaline Comet assay to assess DNA repair after m-THPC-PDT

Photodynamic therapy (PDT) with Photofrin has already been authorized for certain applications in Japan, the USA and France, and powerful second-generation sensitizers such as meta-(tetrahydroxyphenyl) chlorin (m-THPC) are now being considered for approval. Although sensitizers are likely to localize within the cytoplasm or the plasma membrane, nuclear membrane can be damaged at an early stage of photodynamic reaction, resulting in DNA lesions. Thus, it is of critical importance to assess the safety of m-THPC-PDT, which would be used mainly against early well-differentiated cancers. In this context, m-THPC toxicity and phototoxicity were studied by a colorimetric MTT assay on C6 cells to determine the LD50 (2.5 microg/ml m-THPC for 10 J/cm2 irradiation and 1 microg/ml for 25 J/cm2 irradiation) and PDT doses inducing around 25% cell death. Single-cell electrophoresis (a Comet assay with Tail Moment calculation) was used to evaluate DNA damage and repair in murine glioblastoma C6 cells after LD25 or higher doses for assays of PDT. These results were correlated with m-THPC nuclear distribution by confocal microspectrofluorimetry. m-THPC failed to induce significant changes in the Tail Moment of C6 cells in the absence of light, whereas m-THPC-PDT induced DNA damage immediately after irradiation. The Tail Moment increase was not linear (curve slope being 43 for 0-1 microg/ml m-THPC and 117 for 1-3 microg/ml), but the mean value increased with the light dose (0, 10 or 25 J/cm2) and incubation time (every hour from 1 to 4 h) for an incubation with m-THPC 1 microg/ml. However, cultured murine glioblastoma cells were capable of significant DNA repair after 4 h, and no residual DNA damage was evident after 24-h post-treatment incubation at 37 degrees C. An increase in the light dose appeared to be less genotoxic than an increase in the m-THPC dose for similar toxicities. Our results indicate that m-THPC PDT appears to be a safe treatment since DNA repair seemed to not be impaired and DNA damage occurred only with lethal PDT doses. However, the Comet assay cannot give us the certainty that no mutation, photoadducts or oxidative damage have been developed so this point would be verified with another mutagenicity assay.

SOS chromotest results in a broader context: empirical relationships between genotoxic potency, mutagenic potency, and carcinogenic potency

Environmental monitoring requires that large numbers of samples be processed in a relatively short period of time. While microbioassays facilitate rapid testing, the results are often difficult to interpret in the broader context of human or animal health. Determining the consequences of exposure to genotoxic substances will ultimately require in situ monitoring of exposed organisms. However, it is immediately possible to construct a broad empirical framework within which available microbioassay results can be interpreted. To do this for SOS Chromotest results, we investigated the empirical relationships between SOS genotoxic potency and mutagenic potency (as measured with the Salmonella/microsome assay), as well as between genotoxic potency and carcinogenic potency (as measured using standard, chronic animal bioassays). Strong relationships were identified between; 1) genotoxic potency and mutagenic potency for 268 direct-acting substances (r2=0.76) and 2) genotoxic potency and mutagenic potency for 126 S9-activated substances (r2=0.65). Ordinary least squares regression analyses of the SOS genotoxicity-Salmonella mutagenicity relationship revealed a significant effect of SOS genotoxicity as well as differences in mutagenic potency that can be attributed to the Salmonella strain used to measure mutagenic potency. Analyses of S9-activated substances revealed a significant interaction between the SOS genotoxic potency (SOSIP) effect and the Salmonella strain effect. Two regression models relating SOS genotoxicity and Salmonella mutagenicity were used to predict the mutagenic potency of several industrial effluent extracts previously analyzed for SOS genotoxicity by White et al. [(1996): Environ Mol Mutagen 27:116-139]. Predictions are consistent with published mutagenic potency values for similar industrial waste materials. A consistent relationship was also identified between genotoxic potency and carcinogenic potency for 51 substances. Linear regression analyses revealed an effect of SOS genotoxic potency as well as differences in carcinogenic potency that may be attributable to experimental animal and route of exposure. The correlation between genotoxicity and carcinogenicity was fairly weak (maximum r value = 0.51). Previous studies revealed similar strength of association between Ames mutagenicity and carcinogenicity. Predicted carcinogenic potencies of previously examined genotoxic, industrial effluent extracts are generally low compared to the pure substances included in the data set.

Mathematical parameters for quantification of mutational responses in bacteria

This paper introduces a new parameter, derivable from dose-response data for induced mutagenesis in bacteria, that can be used to quantify mutational responses in short-term tests. We called this parameter the mutational response of the bipartite experimental system (agent plus cells). We defined it as being jointly proportional to the efficiency of the mutagen and the sensitivity of the test. We show how this quantity can be used to rank order chemical carcinogens on the basis of their mutagenicity and to determine the strength of any quantitative correlation that may exist between mutagenicity in bacteria and carcinogenicity in rodents. We find that this particular measure of mutational response for 10 direct-acting monofunctional alkylating agents correlates remarkably well with the rodent carcinogenicity of these chemicals measured in terms of their reciprocal TD50 values.

Applicability of alternative models of revertant variance to Ames-test data for 121 mutagenic carcinogens

Models of sampling variance in replicate revertant scores play a role in analyses of Ames-test data on mutagenicity in Salmonella, both in modeling the dose-response relation and in estimating initial dose-response slope or 'potency', e.g., for use in correlating mutagenic and carcinogenic potencies among different chemicals. Both generalized Poisson (GP) and negative binomial (NB) models of revertant variance have been applied in this way, but their empirical applicability has only been assessed using Ames-test data on a few chemicals. The applicability of these and related variance models was therefore assessed for 1905 such data sets pertaining to 121 putatively mutagenic carcinogens. Only approximately 50% of the data sets analyzed were found to involve a significantly positively correlated dose-response, and < 50% were found to exhibit a plausibly heterogeneous response variance regardless of dose-response correlation. Among data sets with plausibly heterogeneous variance, < 60% were found to exhibit significantly extra-Poisson variability. Among the significantly extra-Poisson data sets, most (> 75% among dose-response correlated data sets) were found to exhibit revertant variance consistent with both the GP and NB models; while the GP model was found to be somewhat more consistent with these data, the NB model more often gave a nominally better fit when both models were consistent. Implications of these results for the design of methods used to analyze Ames-test data are discussed.

Mutagenic activity detected by the Ames test in river water under the influence of petrochemical industries

The present study was carried out on the waters of the Caí River (Rio Grande do Sul, Brazil) in an area under the influence of a petrochemical industrial complex, as the continuation of a study in which the mutagenic activity of water samples was evaluated in the internal area of this complex. In the previous study, the release of inducing substances was detected, revealing the need for a full analysis of the real ecological impact of the industrial complex on the river. Water samples from different sites along the Caí River were subjected to the Ames test during a study of 20 months duration for the detection of possible mutagens. Strains TA100 and TA98 were used for initial sample screening in the presence and absence of the S9 mix at a standard dose of 2000 microliters/plate. When positive activity (values equal to twice the spontaneous mutation rate) and/or cytotoxic activity (cell survival below 60%) was detected, the dose-response relationship was studied. Thirty-four percent of the samples tested were mutagenic, with different values according to collection site. Of the total number of positive responses, 6% were obtained for samples collected at the blank site upstream from the area studied, 82% at sites closest to the industrial complex, and 12% in downstream areas. Strain TA98 was the most sensitive in assays with no metabolic activation. A low frequency of induction (2%) was observed for strain TA102. Application of the Ames test permitted the delimitation of three areas of influence of the petrochemical industrial complex, and the test proved to be adequate for the detection of contaminants from the petrochemical industry.

Overview, conclusions, and recommendations of the IPCS collaborative study on complex mixtures

The International Programme on Chemical Safety (IPCS) sponsored an international collaborative study to examine the variability associated with the extraction and bioassay of standard reference materials (SRMs) that are complex environmental mixtures provided by the U.S. National Institute of Standards and Technology (NIST). The study was also intended to evaluate the feasibility of establishing bioassay reference values and ranges for the SRMs. Twenty laboratories from North America, Europe, and Japan participated in the study. As part of the mandatory core protocol, each laboratory extracted the organic material from two particulate samples and bioassayed these extracts. A coal tar polycyclic aromatic hydrocarbon (PAH) solution and two mutagenic control compounds were also subjected to bioassay without prior extraction by the participating laboratories. The bioassay used was the Salmonella/microsomal plate incorporation assay. For the optional portion of the study, a laboratory was free to use the SRMs for any type of exploratory research. The primary purpose of the required portion of the study was to estimate the intra- and inter-laboratory variability in mutagenic potencies of the test materials and to determine whether or not the NIST mixtures could be used as reference materials by others performing the Salmonella assay. Repeatability (intra-laboratory variance) of the bioassay results ranged from 16% to 88% depending on the SRM and the bioassay conditions (tester strain and metabolic activation), whereas reproducibility (inter-laboratory variance) ranged from 33% to 152%. Between-laboratory variability was the main source of variation accounting for approximately 55-95% of the total variation for the three environmental samples. Variation in the mutagenic potency of the control compounds was comparable, with the exception of 1-nitropyrene for which the reproducibility ranged from 127% to 132%. In summary, NIST SRMs provided useful materials for an international inter-laboratory study of complex mixtures. By establishing both intra- and inter-laboratory variance for the mutagenicity results for these materials, the usefulness of these SRMs as reference materials for the Salmonella bioassay was established, critical procedures within the bioassay protocol were identified, and recommendations for future efforts were delineated.

Sources of variation in the mutagenic potency of complex chemical mixtures based on the Salmonella/microsome assay

Twenty laboratories worldwide participated in a collaborative trial sponsored by the International Programme on Chemical Safety on the mutagenicity of complex mixtures as expressed in the Salmonella/microsome assay. The U.S. National Institute of Standards and Technology provided homogeneous reference samples of urban air and diesel particles and a coal tar solution to each participating laboratory, along with samples of benzo[a]pyrene and 1-nitropyrene which served as positive controls. Mutagenic potency was characterized by the slope of the initial linear component of the dose-response curve. Analysis of variance revealed significant interlaboratory variation in mutagenic potency, which accounted for 57-96% of the total variance on a logarithmic scale, depending on the sample, strain and activation conditions. Variation among replicate extractions of organic material (required for the air and diesel particles) and among replicate bioassays within the same laboratory was also appreciable. The average potencies for air and diesel particles in laboratories using Soxhlet extracts were not significantly different from those in laboratories using sonication, although there was larger interlaboratory variation for the Soxhlet method. Repeatability (which approximates the coefficient of variation within laboratories) ranged from 18 to 40% for air and diesel particles extracted using sonication, depending on the strain and activation conditions. Repeatability of Soxhlet-extracted air and diesel particles, however, ranged from about 37 to 89% including outliers and from about 11 to 31% excluding outliers. Repeatability of the coal tar sample and the 2 positive controls was in the range 18-34%. Reproducibility (which approximates the coefficient of variation between laboratories) was generally at least twice repeatability, and exceeded 100% for Soxhlet-extracted air and diesel particles, as well as 1-nitropyrene. Reanalysis of the data omitting observations of more than 1500 revertants/plate generally had little effect on these results. Elimination of outlying observations had limited impact, with the exception of Soxhlet-extracted air and diesel particles. In this case, reproducibility of bioassay results was notably improved, due largely to the omission of results for replicate extractions which varied more than 5-fold within one laboratory. Normalization of the log potency slopes for the mixtures by the corresponding slopes for benzo[a]pyrene tended to reduce this variation, although variation was increased after normalization by 1-nitropyrene. Adjustment for the percentage of organic matter extracted from the air and diesel particulate samples had little effect on variation for sonication-extracted particles, whereas variation was reduced for diesel particles and increased for air particles for Soxhlet.

International Commission for Protection Against Environmental Mutagens and Carcinogens. ICPEMC publication No. 18. Review of the genotoxicity and carcinogenicity of antischistosomal drugs; is there a case for a study of mutation epidemiology? Report of a task group on mutagenic antischistosomals

One of the interests of ICPEMC is to identify situations in which the possible induction of inherited defects in man by mutagen exposure could actually be studied. The large-scale use of mutagenic drugs in field programmes against schistosomiasis, mainly during the 1970's, was considered a possible case. An ICPEMC task group approached the problem by (1) updating the genetic toxicology data base for antischistosomal drugs, and (2) reviewing possible study areas. Expertise was combined from genetic toxicology, mutation epidemiology and tropical medicine. It was considered that: (a) if any, hycanthone would be the most appropriate candidate drug for study; (b) it would be virtually impossible to meet the basic requirements of an appropriate mutation epidemiology study, in endemic countries; (c) as more defined genetic endpoints would be selected (e.g. sentinel phenotypes) the required large sample sizes would seem prohibitive, since documentation on past programmes is limited and local demography would render the reliable tracking of substantial numbers of offspring of treated persons an almost impossible task; (d) in most endemic countries proper diagnosis and registration of inherited defects is largely lacking; (e) the problems encountered in demonstrating inherited effects in humans after heavy or chronic exposure to established animal mutagens such as ionizing radiation and cancer chemotherapy, in combination with the ambiguous nature of the animal germ cell data with hycanthone, do not particularly warrant large expectations; (f) since non-mutagenic antischistosomal drugs are now in use, the problem is academic and of low priority in the endemic countries whose medical and research resources are often limited. Thus, studying offspring of hycanthone-treated people to demonstrate the mutagenic potential of the drug in man is not a viable enterprise.

Genetic activity profiles in the testing and evaluation of chemical mixtures

Some knowledge of the potential genetic activity of a complex environmental mixture may be gained from an assessment of the genetic activity of its component chemicals. The expanded Genetic Activity Profile (GAP) data base provides a computer-generated graphic representation of genetic bioassay data as a function of dose of the substance tested. In addition, the Atmospheric Chemical Compound (ACC) data-base contains information on chemical structures, properties, detection methods, and sources of chemicals found in ambient air. Using the combined data bases, the quantity of an individual chemical present within a mixture or fraction of a mixture may be related to the quantity (lowest effective dose, LED) of the chemical, by itself, required to demonstrate a positive response in one or more genetic bioassays.

Genotoxic activity of organic chemicals in drinking water

The information summarized in this review provides substantial evidence for the widespread presence of genotoxins in drinking water. In many, if not most cases, the genotoxic activity can be directly attributed to the chlorination stage of drinking water treatment. The genotoxic activity appears to originate primarily from reactions of chlorine with humic substances in the source waters. Genotoxic activity in drinking water concentrates has been most frequently demonstrated using bacterial mutagenicity tests but results with mammalian cell assay systems are generally consistent with the findings from the bacterial assays. There is currently no evidence for genotoxic damage following in vivo exposures to animals. In some locations genotoxic contaminants of probable industrial and/or agricultural origin occur in the source waters and contribute substantially to the genotoxic activity of finished drinking waters. The method used for sample concentration can have an important bearing on study results. In particular, organic acids account for most of the mutagenicity of chlorinated drinking water, and their recovery from water requires a sample acidification step prior to extraction or XAD resin adsorption. Considerable work has been done to determine the identity of the compounds responsible for the mutagenicity of organic concentrates of drinking water. Recently, one class of acidic compounds, the chlorinated hydroxyfuranones, has been shown to be responsible for a major part of the mutagenic activity. Strategies for drinking water treatment that have been evaluated with respect to reduction of genotoxins in drinking water include granular activated carbon (GAC) filtration, chemical destruction, and the use of alternative means of treatment (i.e., ozone, chlorine dioxide, and monochloramine). GAC treatment has been found to be effective for removal of mutagens from drinking water even after the GAC is beyond its normal use for organic carbon removal. All disinfectant chemicals appear to have the capacity of forming mutagenic chemicals during water treatment. However, the levels of mutagenicity formed with the alternative disinfectants have been generally less than those seen with chlorine and, especially in the case of ozone, highly dependent on the source water.(ABSTRACT TRUNCATED AT 400 WORDS)

Statistical analysis of Salmonella test data and comparison to results of animal cancer tests

A quantitative framework for the analysis of results of the Salmonella (Ames) test is presented, and the relationship between mutagenesis and carcinogenesis is examined. Color graphics are used for the Salmonella data to describe variability, and trends across multiple chemicals and test conditions. Positivity in the Salmonella test, using statistical criteria to classify results, is compared to positivity in carcinogenesis bioassays for 48 chemicals tested in NCI/NTP-sponsored programs. Sensitivity of the Salmonella test across 5 tester strains was 91% (21/23), while specificity was only 36% (9/25). Results were most concordant for TA100 Aroclor-induced rat S9: sensitivity was 87%, specificity 64%. The correlation of mutagenic potency and carcinogenic potency was 0.41 (p less than 0.001) for 80 chemicals, using results from both the general published literature and the NCI/NTP-sponsored programs. After removal of 3 extreme values, the correlation was 0.24 (p = 0.04).

Scientific and cost-effectiveness criteria in selecting batteries of short-term tests

The scientific and cost-effectiveness criteria introduced in this paper can be applied to published datasets and current and proposed batteries of short-term tests. The reports in the current volume will provide a wealth of additional material for such evaluations, but more systematically obtained information will be necessary to assess both the internal and external validity of these tests. Individual tests and batteries of tests should be standardized, employ positive controls, generate results capable of quantitative analyses that may make dichotomous classification as "positive" and "negative" obsolete, be interpreted in light of mechanisms of action, and be cost-effective on a grand scale. For regulatory purposes our long-term goal should be to replace the whole animal lifetime bioassay with an appropriate and cost-effective set of short-term tests.

Trenbolone growth promotant: covalent DNA binding in rat liver and in Salmonella typhimurium, and mutagenicity in the Ames test

DNA binding in vivo: [6,7-3H]beta-trenbolone (beta-TBOH) was administered p.o. and i.p. to rats. After 8 or 16 h, DNA was isolated from the livers and purified to constant specific radioactivity. Enzymatic digestion to deoxyribonucleotides and separation by HPLC revealed about 90% of the DNA radioactivity eluting in the form of possible TBOH-nucleotide adducts. The extent of this genotoxicity, expressed in units of the Covalent Binding Index, CBI = (mumol TBOH bound per mol nucleotide)/(mmol TBOH administered per kg body weight) spanned from 8 to 17, i.e. was in the range found with weak genotoxic carcinogens. Ames test: low doses of beta-TBOH increased the number of revertants in Salmonella strain TA100 reproducibly and in a dose-dependent manner. The mutagenic potency was 0.2 revertants per nmol after preincubation of the bacteria (20 min at 37 degrees C) with doses between 30 and 60 micrograms per plate (47 and 94 micrograms/ml preincubation mixture). Above this dose, the number of revertants decreased to control values, accompanied by a reduction in survival. The addition of rat liver S9 inhibited the mutagenicity. DNA binding in vitro: calf thymus DNA was incubated with tritiated beta-TBOH with and without rat liver S9. Highest DNA radioactivities were determined in the absence of the "activation" system. Addition of inactive S9 (without cofactors) reduced the DNA binding by a factor of up to 20. Intermediate results were found with active S9. DNA binding in Salmonella: beta-TBOH was irreversibly bound to DNA isolated from S. typhimurium TA100 after incubation of bacteria with [3H]beta-TBOH.

Guide for the Salmonella typhimurium/mammalian microsome tests for bacterial mutagenicity

Since its development by Dr. Bruce Ames and his coworkers, the Salmonella typhimurium/mammalian microsome mutagenicity assay has been used widely throughout the world. Many authors have suggested various modifications and made recommendations in regards to this assay. Although the recommendations of a panel of experts was published in 1979 by de Serres and Shelby, a committee of members of the Environmental Mutagen Society (EMS) initiated this effort in response to the encouragement by the American Society of Testing and Materials (Committee E47.09.01) and because of new developments within the field of microbial mutagenesis testing. Its purpose is to provide a guide for people who perform or evaluate microbial mutagenesis tests, but it is not intended for these recommendations to replace or diminish the usefulness of presently available protocols and procedures.

An interlaboratory study of an EPA/Ames/Salmonella test protocol

7 laboratories participated in a collaborative study to evaluate an EPA standard protocol for the Ames test. The study utilized Salmonella typhimurium (strains TA98 and TA100) and 3 metabolic activation levels (0%, 2%, and 10% S9 in the S9 mix). 6 pure chemicals and 2 complex mixtures were tested as coded unknowns. Ability to obtain qualitative results in agreement with published data was less (% agreement) than that reported in an earlier study (% agreement) by de Serres and Ashby (1981) in which each laboratory used its own protocol. The conclusion from analysis of the quantitative data from this interlaboratory Ames study was that both intralaboratory and interlaboratory variations were substantial. Results for the same substance varied by an order of magnitude or more (CV of 115%) when the mutagenic response was measured as the slope of the dose response in revertants/microgram. Taking interlaboratory variation into account, one chemical must be more than an order of magnitude more mutagenic than another (ratio of slopes greater than 10) to have only an even chance of finding a statistically significant difference between the two chemicals at the 5% level. Such large variations must be taken into account when evaluating Ames/Salmonella data.

The mutagenicity of bile acids using a fluctuation test

The mutagenicity of bile acids was detected by a fluctuation test using Salmonella typhimurium TA100 and TA98 as tester strains. Cholic acid, chenodeoxycholic acid, deoxycholic acid and ursodeoxycholic acid were mutagenic in this test while lithocholic acid was not. The mutagenicity of the bile acids on a molar basis was roughly one-fourth that of methyl methanesulfonate, a moderately potent mutagen. Epidemiological studies have shown a high correlation between levels of bile acids excreted and colon cancer. However, no evidence has previously been reported showing that bile acids are mutagenic. Our results suggest that bile acids may be important in the etiology of colon cancer.

Use of the Ames test in toxicology

The Salmonella/microsome assay (Ames test) is one of the most widely used short-term tests. Despite the ubiquitous presence of this assay and the large number of chemicals tested, there is still controversy over the value of Salmonella/microsome assay results in risk assessment. Understanding of the properties and performance of the test system is necessary to provide an appropriate answer to this question. Based on both theoretical and empirical considerations, the results of the assay can provide useful information to assist in the development of further studies and as part of the data which can be used in evaluating potential biological effects or projected lack of adverse effects. The value of the Salmonella/microsome assay in performing these functions is considerably enhanced by consideration of all the information which the assay data provide.