Interpretation of in vitro concentration-response data for risk assessment and regulatory decision-making: Report from the 2022 IWGT quantitative analysis expert working group meeting

Quantitative risk assessments of chemicals are routinely performed using in vivo data from rodents; however, there is growing recognition that non-animal approaches can be human-relevant alternatives. There is an urgent need to build confidence in non-animal alternatives given the international support to reduce the use of animals in toxicity testing where possible. In order for scientists and risk assessors to prepare for this paradigm shift in toxicity assessment, standardization and consensus on in vitro testing strategies and data interpretation will need to be established. To address this issue, an Expert Working Group (EWG) of the 8th International Workshop on Genotoxicity Testing (IWGT) evaluated the utility of quantitative in vitro genotoxicity concentration-response data for risk assessment. The EWG first evaluated available in vitro methodologies and then examined the variability and maximal response of in vitro tests to estimate biologically relevant values for the critical effect sizes considered adverse or unacceptable. Next, the EWG reviewed the approaches and computational models employed to provide human-relevant dose context to in vitro data. Lastly, the EWG evaluated risk assessment applications for which in vitro data are ready for use and applications where further work is required. The EWG concluded that in vitro genotoxicity concentration-response data can be interpreted in a risk assessment context. However, prior to routine use in regulatory settings, further research will be required to address the remaining uncertainties and limitations.

Establishing a quantitative framework for regulatory interpretation of genetic toxicity dose-response data: Margin of exposure case study of 48 compounds with both in vivo mutagenicity and carcinogenicity dose-response data

Quantitative relationships between carcinogenic potency and mutagenic potency have been previously examined using a benchmark dose (BMD)-based approach. We extended those analyses by using human exposure data for 48 compounds to calculate carcinogenicity-derived and genotoxicity-derived margin of exposure values (MOEs) that can be used to prioritize substances for risk management. MOEs for 16 of the 48 compounds were below 10,000, and consequently highlighted for regulatory concern. Of these, 15 were highlighted using genotoxicity-derived (micronucleus [MN] dose-response data) MOEs. A total of 13 compounds were highlighted using carcinogenicity-derived MOEs; 12 compounds were overlapping. MOEs were also calculated using transgenic rodent (TGR) mutagenicity data. For 10 of the 12 compounds examined using TGR data, the results similarly revealed that mutagenicity-derived MOEs yield regulatory decisions that correspond with those based on carcinogenicity-derived MOEs. The effect of benchmark response (BMR) on MOE determination was also examined. Reinterpretation of the analyses using a BMR of 50% indicated that four out of 15 compounds prioritized using MN-derived MOEs based on a default BMR of 5% would have been missed. The results indicate that regulatory decisions based on in vivo genotoxicity dose-response data would be consistent with those based on carcinogenicity dose-response data; in some cases, genotoxicity-based decisions would be more conservative. Going forward, and in the absence of carcinogenicity data, in vivo genotoxicity assays (MN and TGR) can be used to effectively prioritize substances for regulatory action. Routine use of the MOE approach necessitates the availability of reliable human exposure estimates, and consensus regarding appropriate BMRs for genotoxicity endpoints.

Utility of a next-generation framework for assessment of genomic damage: A case study using the pharmaceutical drug candidate etoposide

We present a hypothetical case study to examine the use of a next-generation framework developed by the Genetic Toxicology Technical Committee of the Health and Environmental Sciences Institute for assessing the potential risk of genetic damage from a pharmaceutical perspective. We used etoposide, a genotoxic carcinogen, as a representative pharmaceutical for the purposes of this case study. Using the framework as guidance, we formulated a hypothetical scenario for the use of etoposide to illustrate the application of the framework to pharmaceuticals. We collected available data on etoposide considered relevant for assessment of genetic toxicity risk. From the data collected, we conducted a quantitative analysis to estimate margins of exposure (MOEs) to characterize the risk of genetic damage that could be used for decision-making regarding the predefined hypothetical use. We found the framework useful for guiding the selection of appropriate tests and selecting relevant endpoints that reflected the potential for genetic damage in patients. The risk characterization, presented as MOEs, allows decision makers to discern how much benefit is critical to balance any adverse effect(s) that may be induced by the pharmaceutical. Interestingly, pharmaceutical development already incorporates several aspects of the framework per regulations and health authority expectations. Moreover, we observed that quality dose response data can be obtained with carefully planned but routinely conducted genetic toxicity testing. This case study demonstrates the utility of the next-generation framework to quantitatively model human risk based on genetic damage, as applicable to pharmaceuticals.

Heritable hazards of smoking: Applying the "clean sheet" framework to further science and policy

All the cells in our bodies are derived from the germ cells of our parents, just as our own germ cells become the bodies of our children. The integrity of the genetic information inherited from these germ cells is of paramount importance in establishing the health of each generation and perpetuating our species into the future. There is a large and growing body of evidence strongly suggesting the existence of substances that may threaten this integrity by acting as human germ cell mutagens. However, there generally are no absolute regulatory requirements to test agents for germ cell effects. In addition, the current regulatory testing paradigms do not evaluate the impacts of epigenetically mediated intergenerational effects, and there is no regulatory framework to apply new and emerging tests in regulatory decision making. At the 50th annual meeting of the Environmental Mutagenesis and Genomics Society held in Washington, DC, in September 2019, a workshop took place that examined the heritable effects of hazardous exposures to germ cells, using tobacco smoke as the example hazard. This synopsis provides a summary of areas of concern regarding heritable hazards from tobacco smoke exposures identified at the workshop and the value of the Clean Sheet framework in organizing information to address knowledge and testing gaps.

Utility of a next generation framework for assessment of genomic damage: A case study using the industrial chemical benzene

We recently published a next generation framework for assessing the risk of genomic damage via exposure to chemical substances. The framework entails a systematic approach with the aim to quantify risk levels for substances that induce genomic damage contributing to human adverse health outcomes. Here, we evaluated the utility of the framework for assessing the risk for industrial chemicals, using the case of benzene. Benzene is a well-studied substance that is generally considered a genotoxic carcinogen and is known to cause leukemia. The case study limits its focus on occupational and general population health as it relates to benzene exposure. Using the framework as guidance, available data on benzene considered relevant for assessment of genetic damage were collected. Based on these data, we were able to conduct quantitative analyses for relevant data sets to estimate acceptable exposure levels and to characterize the risk of genetic damage. Key observations include the need for robust exposure assessments, the importance of information on toxicokinetic properties, and the benefits of cheminformatics. The framework points to the need for further improvement on understanding of the mechanism(s) of action involved, which would also provide support for the use of targeted tests rather than a prescribed set of assays. Overall, this case study demonstrates the utility of the next generation framework to quantitatively model human risk on the basis of genetic damage, thereby enabling a new, innovative risk assessment concept. Environ. Mol. Mutagen. 61:94-113, 2020. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Application of the adverse outcome pathway framework to genotoxic modes of action

In May 2017, the Health and Environmental Sciences Institute's Genetic Toxicology Technical Committee hosted a workshop to discuss whether mode of action (MOA) investigation is enhanced through the application of the adverse outcome pathway (AOP) framework. As AOPs are a relatively new approach in genetic toxicology, this report describes how AOPs could be harnessed to advance MOA analysis of genotoxicity pathways using five example case studies. Each of these genetic toxicology AOPs proposed for further development includes the relevant molecular initiating events, key events, and adverse outcomes (AOs), identification and/or further development of the appropriate assays to link an agent to these events, and discussion regarding the biological plausibility of the proposed AOP. A key difference between these proposed genetic toxicology AOPs versus traditional AOPs is that the AO is a genetic toxicology endpoint of potential significance in risk characterization, in contrast to an adverse state of an organism or a population. The first two detailed case studies describe provisional AOPs for aurora kinase inhibition and tubulin binding, leading to the common AO of aneuploidy. The remaining three case studies highlight provisional AOPs that lead to chromosome breakage or mutation via indirect DNA interaction (inhibition of topoisomerase II, production of cellular reactive oxygen species, and inhibition of DNA synthesis). These case studies serve as starting points for genotoxicity AOPs that could ultimately be published and utilized by the broader toxicology community and illustrate the practical considerations and evidence required to formalize such AOPs so that they may be applied to genetic toxicity evaluation schemes. Environ. Mol. Mutagen. 61:114-134, 2020. © 2019 Wiley Periodicals, Inc.

Next generation testing strategy for assessment of genomic damage: A conceptual framework and considerations

For several decades, regulatory testing schemes for genetic damage have been standardized where the tests being utilized examined mutations and structural and numerical chromosomal damage. This has served the genetic toxicity community well when most of the substances being tested were amenable to such assays. The outcome from this testing is usually a dichotomous (yes/no) evaluation of test results, and in many instances, the information is only used to determine whether a substance has carcinogenic potential or not. Over the same time period, mechanisms and modes of action (MOAs) that elucidate a wider range of genomic damage involved in many adverse health outcomes have been recognized. In addition, a paradigm shift in applied genetic toxicology is moving the field toward a more quantitative dose-response analysis and point-of-departure (PoD) determination with a focus on risks to exposed humans. This is directing emphasis on genomic damage that is likely to induce changes associated with a variety of adverse health outcomes. This paradigm shift is moving the testing emphasis for genetic damage from a hazard identification only evaluation to a more comprehensive risk assessment approach that provides more insightful information for decision makers regarding the potential risk of genetic damage to exposed humans. To enable this broader context for examining genetic damage, a next generation testing strategy needs to take into account a broader, more flexible approach to testing, and ultimately modeling, of genomic damage as it relates to human exposure. This is consistent with the larger risk assessment context being used in regulatory decision making. As presented here, this flexible approach for examining genomic damage focuses on testing for relevant genomic effects that can be, as best as possible, associated with an adverse health effect. The most desired linkage for risk to humans would be changes in loci associated with human diseases, whether in somatic or germ cells. The outline of a flexible approach and associated considerations are presented in a series of nine steps, some of which can occur in parallel, which was developed through a collaborative effort by leading genetic toxicologists from academia, government, and industry through the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) Genetic Toxicology Technical Committee (GTTC). The ultimate goal is to provide quantitative data to model the potential risk levels of substances, which induce genomic damage contributing to human adverse health outcomes. Any good risk assessment begins with asking the appropriate risk management questions in a planning and scoping effort. This step sets up the problem to be addressed (e.g., broadly, does genomic damage need to be addressed, and if so, how to proceed). The next two steps assemble what is known about the problem by building a knowledge base about the substance of concern and developing a rational biological argument for why testing for genomic damage is needed or not. By focusing on the risk management problem and potential genomic damage of concern, the next step of assay(s) selection takes place. The work-up of the problem during the earlier steps provides the insight to which assays would most likely produce the most meaningful data. This discussion does not detail the wide range of genomic damage tests available, but points to types of testing systems that can be very useful. Once the assays are performed and analyzed, the relevant data sets are selected for modeling potential risk. From this point on, the data are evaluated and modeled as they are for any other toxicology endpoint. Any observed genomic damage/effects (or genetic event(s)) can be modeled via a dose-response analysis and determination of an estimated PoD. When a quantitative risk analysis is needed for decision making, a parallel exposure assessment effort is performed (exposure assessment is not detailed here as this is not the focus of this discussion; guidelines for this assessment exist elsewhere). Then the PoD for genomic damage is used with the exposure information to develop risk estimations (e.g., using reference dose (RfD), margin of exposure (MOE) approaches) in a risk characterization and presented to risk managers for informing decision making. This approach is applicable now for incorporating genomic damage results into the decision-making process for assessing potential adverse outcomes in chemically exposed humans and is consistent with the ILSI HESI Risk Assessment in the 21st Century (RISK21) roadmap. This applies to any substance to which humans are exposed, including pharmaceuticals, agricultural products, food additives, and other chemicals. It is time for regulatory bodies to incorporate the broader knowledge and insights provided by genomic damage results into the assessments of risk to more fully understand the potential of adverse outcomes in chemically exposed humans, thus improving the assessment of risk due to genomic damage. The historical use of genomic damage data as a yes/no gateway for possible cancer risk has been too narrowly focused in risk assessment. The recent advances in assaying for and understanding genomic damage, including eventually epigenetic alterations, obviously add a greater wealth of information for determining potential risk to humans. Regulatory bodies need to embrace this paradigm shift from hazard identification to quantitative analysis and to incorporate the wider range of genomic damage in their assessments of risk to humans. The quantitative analyses and methodologies discussed here can be readily applied to genomic damage testing results now. Indeed, with the passage of the recent update to the Toxic Substances Control Act (TSCA) in the US, the new generation testing strategy for genomic damage described here provides a regulatory agency (here the US Environmental Protection Agency (EPA), but suitable for others) a golden opportunity to reexamine the way it addresses risk-based genomic damage testing (including hazard identification and exposure). Environ. Mol. Mutagen. 58:264-283, 2017. © 2016 The Authors. Environmental and Molecular Mutagenesis Published by Wiley Periodicals, Inc.

Perfluorooctane Sulfonate Plasma Half-Life Determination and Long-Term Tissue Distribution in Beef Cattle (Bos taurus)

Perfluorooctane sulfonate (PFOS) is used in consumer products as a surfactant and is found in industrial and consumer waste, which ends up in wastewater treatment plants (WWTPs). PFOS does not breakdown during WWTP processes and accumulates in the biosolids. Common practices include application of biosolids to pastures and croplands used for feed, and as a result, animals such as beef cattle are exposed to PFOS. To determine plasma and tissue depletion kinetics in cattle, 2 steers and 4 heifers were dosed with PFOS at 0.098 mg/kg body weight and 9.1 mg/kg, respectively. Plasma depletion half-lives for steers and heifers were 120 ± 4.1 and 106 ± 23.1 days, respectively. Specific tissue depletion half-lives ranged from 36 to 385 days for intraperitoneal fat, back fat, muscle, liver, bone, and kidney. These data indicate that PFOS in beef cattle has a sufficiently long depletion half-life to permit accumulation in edible tissues.

Approaches for identifying germ cell mutagens: Report of the 2013 IWGT workshop on germ cell assays(☆)

This workshop reviewed the current science to inform and recommend the best evidence-based approaches on the use of germ cell genotoxicity tests. The workshop questions and key outcomes were as follows. (1) Do genotoxicity and mutagenicity assays in somatic cells predict germ cell effects? Limited data suggest that somatic cell tests detect most germ cell mutagens, but there are strong concerns that dictate caution in drawing conclusions. (2) Should germ cell tests be done, and when? If there is evidence that a chemical or its metabolite(s) will not reach target germ cells or gonadal tissue, it is not necessary to conduct germ cell tests, notwithstanding somatic outcomes. However, it was recommended that negative somatic cell mutagens with clear evidence for gonadal exposure and evidence of toxicity in germ cells could be considered for germ cell mutagenicity testing. For somatic mutagens that are known to reach the gonadal compartments and expose germ cells, the chemical could be assumed to be a germ cell mutagen without further testing. Nevertheless, germ cell mutagenicity testing would be needed for quantitative risk assessment. (3) What new assays should be implemented and how? There is an immediate need for research on the application of whole genome sequencing in heritable mutation analysis in humans and animals, and integration of germ cell assays with somatic cell genotoxicity tests. Focus should be on environmental exposures that can cause de novo mutations, particularly newly recognized types of genomic changes. Mutational events, which may occur by exposure of germ cells during embryonic development, should also be investigated. Finally, where there are indications of germ cell toxicity in repeat dose or reproductive toxicology tests, consideration should be given to leveraging those studies to inform of possible germ cell genotoxicity.

Derivation of point of departure (PoD) estimates in genetic toxicology studies and their potential applications in risk assessment

Genetic toxicology data have traditionally been employed for qualitative, rather than quantitative evaluations of hazard. As a continuation of our earlier report that analyzed ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS) dose-response data (Gollapudi et al., 2013), here we present analyses of 1-ethyl-1-nitrosourea (ENU) and 1-methyl-1-nitrosourea (MNU) dose-response data and additional approaches for the determination of genetic toxicity point-of-departure (PoD) metrics. We previously described methods to determine the no-observed-genotoxic-effect-level (NOGEL), the breakpoint-dose (BPD; previously named Td), and the benchmark dose (BMD10 ) for genetic toxicity endpoints. In this study we employed those methods, along with a new approach, to determine the non-linear slope-transition-dose (STD), and alternative methods to determine the BPD and BMD, for the analyses of nine ENU and 22 MNU datasets across a range of in vitro and in vivo endpoints. The NOGEL, BMDL10 and BMDL1SD PoD metrics could be readily calculated for most gene mutation and chromosomal damage studies; however, BPDs and STDs could not always be derived due to data limitations and constraints of the underlying statistical methods. The BMDL10 values were often lower than the other PoDs, and the distribution of BMDL10 values produced the lowest median PoD. Our observations indicate that, among the methods investigated in this study, the BMD approach is the preferred PoD for quantitatively describing genetic toxicology data. Once genetic toxicology PoDs are calculated via this approach, they can be used to derive reference doses and margin of exposure values that may be useful for evaluating human risk and regulatory decision making.

Review of various approaches for assessing public health risks in regulatory decision making: choosing the right approach for the problem

Stakeholders in the public health risk analysis community can possess differing opinions about what is meant by "conduct a risk assessment." In reality, there is no one-size-fits-all risk assessment that can address all public health issues, problems, and regulatory needs. Although several international and national organizations (e.g., Codex Alimentarius Commission, Office International des Epizooties, Food and Agricultural Organization, World Health Organization, National Research Council, and European Food Safety Authority) have addressed this issue, confusion remains. The type and complexity of a risk assessment must reflect the risk management needs to appropriately inform a regulatory or nonregulatory decision, i.e., a risk assessment is ideally "fit for purpose" and directly applicable to risk management issues of concern. Frequently however, there is a lack of understanding by those not completely familiar with risk assessment regarding the specific utility of different approaches for assessing public health risks. This unfamiliarity can unduly hamper the acceptance of risk assessment results by risk managers and may reduce the usefulness of such results for guiding public health policies, practices, and operations. Differences in interpretation of risk assessment terminology further complicate effective communication among risk assessors, risk managers, and stakeholders. This article provides an overview of the types of risk assessments commonly conducted, with examples primarily from the food and agricultural sectors, and a discussion of the utility and limitations of these specific approaches for assessing public health risks. Clarification of the risk management issues and corresponding risk assessment design needs during the formative stages of the risk analysis process is a key step for ensuring that the most appropriate assessment of risk is developed and used to guide risk management decisions.

Distribution and excretion of perfluorooctane sulfonate (PFOS) in beef cattle (Bos taurus)

Perfluorooctane sulfonate (PFOS), a perfluoroalkyl surfactant used in many industrial products, is present in industrial wastes and in wastewater treatment plant biosolids. Biosolids are commonly applied to pastures and crops used for animal feed; consequently, PFOS may accumulate in the edible tissues of grazing animals or in animals exposed to contaminated feeds. There are no data on the absorption, distribution, and excretion of PFOS in beef cattle, so a 28-day study was conducted to determine these parameters for PFOS in three Lowline Angus steers given a single oral dose of PFOS at approximately 8 mg/kg body weight. PFOS concentrations were determined by liquid chromatography-tandem mass spectrometry in multiple tissue compartments. The major route of excretion was in the feces (11 ± 1.3% of the dose, mean ± standard deviation) with minimal PFOS elimination in urine (0.5 ± 0.07% of the dose). At day 28 the mean plasma concentration remained elevated at 52.6 ± 3.4 μg/mL, and it was estimated that 35.8 ± 4.3% of the dose was present in the plasma. Plasma half-lives could not be calculated due to multiple peaks caused by apparent redistributions from other tissues. These data indicate that after an acute exposure PFOS persists and accumulates in edible tissues. The largest PFOS body burdens were in the blood (∼36%), carcass remainder (5.7 ± 1.6%), and the muscle (4.3 ± 0.6%). It was concluded that PFOS would accumulate in edible tissues of beef, which could be a source of exposure for humans.

Dietary estimates of dioxins consumed in U.S. Department of Agriculture-regulated meat and poultry products

The U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) examined whether levels of dioxin-like compounds (DLCs) measured in FSIS-regulated meat and poultry products indicate possible concern for U.S. public health based on usual and recommended consumption patterns of meat and poultry for the U.S. population. The FSIS estimated daily dietary exposures and compared them with the reference dose (RfD) established by the U.S. Environmental Protection Agency (EPA) for potential noncancer risks from 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), assuming that all measured DLCs were represented by the RfD (i.e., not just TCDD alone). The estimates indicate that a typical U.S. adult daily exposure of DLCs from FSIS-regulated products is below the EPA-established RfD. Only children consuming chronic average daily servings of meat or poultry products containing the highest measured levels of DLCs may exceed the RfD. If one follows the recommendations from the 2010 Dietary Guidelines for Americans, all expected exposures to DLCs from FSIS-regulated products are estimated to be well below the RfD.

Quantitative approaches for assessing dose-response relationships in genetic toxicology studies

Genetic toxicology studies are required for the safety assessment of chemicals. Data from these studies have historically been interpreted in a qualitative, dichotomous "yes" or "no" manner without analysis of dose-response relationships. This article is based upon the work of an international multi-sector group that examined how quantitative dose-response relationships for in vitro and in vivo genetic toxicology data might be used to improve human risk assessment. The group examined three quantitative approaches for analyzing dose-response curves and deriving point-of-departure (POD) metrics (i.e., the no-observed-genotoxic-effect-level (NOGEL), the threshold effect level (Td), and the benchmark dose (BMD)), using data for the induction of micronuclei and gene mutations by methyl methanesulfonate or ethyl methanesulfonate in vitro and in vivo. These results suggest that the POD descriptors obtained using the different approaches are within the same order of magnitude, with more variability observed for the in vivo assays. The different approaches were found to be complementary as each has advantages and limitations. The results further indicate that the lower confidence limit of a benchmark response rate of 10% (BMDL(10) ) could be considered a satisfactory POD when analyzing genotoxicity data using the BMD approach. The models described permit the identification of POD values that could be combined with mode of action analysis to determine whether exposure(s) below a particular level constitutes a significant human risk. Subsequent analyses will expand the number of substances and endpoints investigated, and continue to evaluate the utility of quantitative approaches for analysis of genetic toxicity dose-response data.

Absorption and excretion of 14C-perfluorooctanoic acid (PFOA) in Angus cattle (Bos taurus)

Perfluoroalkyl substances (PFASs), such as perfluorooctanoic acid (PFOA), are environmentally persistent industrial chemicals often found in biosolids. Application of these biosolids to pastures raises concern about the accumulation of PFOA in the edible tissues of food animals. Because data on the absorption, distribution, metabolism, and excretion (ADME) of PFOA in cattle were unavailable, a study was conducted to determine pharmacokinetic parameters following a single oral exposure (1 mg/kg body weight of (14)C-PFOA) in four Lowline Angus steers. Radiocarbon was quantified in blood, urine, and feces for 28 days and in tissues at the time of slaughter (28 days) by liquid scintillation counting (LSC) or by combustion analysis with LSC with confirmation by liquid chromatography-tandem mass spectrometry (LC-MS/MS). (14)C-PFOA was completely absorbed and excreted (100.7 ± 3.3% recovery) in the urine within 9 days of dosing. The plasma elimination half-life was 19.2 ± 3.3 h. No (14)C-PFOA-derived radioactivity was detected in edible tissues. Although PFOA was rapidly absorbed, it was also rapidly excreted by steers and did not persist in edible tissues, suggesting meat from cattle exposed to an acute dose of PFOA is unlikely to be a major source of exposure to humans.

Follow-up actions from positive results of in vitro genetic toxicity testing

Appropriate follow-up actions and decisions are needed when evaluating and interpreting clear positive results obtained in the in vitro assays used in the initial genotoxicity screening battery (i.e., the battery of tests generally required by regulatory authorities) to assist in overall risk-based decision making concerning the potential effects of human exposure to the agent under test. Over the past few years, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute (HESI) Project Committee on the Relevance and Follow-up of Positive Results in In Vitro Genetic Toxicity (IVGT) Testing developed a decision process flow chart to be applied in case of clear positive results in vitro. It provides for a variety of different possibilities and allows flexibility in choosing follow-up action(s), depending on the results obtained in the initial battery of assays and available information. The intent of the Review Subgroup was not to provide a prescriptive testing strategy, but rather to reinforce the concept of weighing the totality of the evidence. The Review Subgroup of the IVGT committee highlighted the importance of properly analyzing the existing data, and considering potential confounding factors (e.g., possible interactions with the test systems, presence of impurities, irrelevant metabolism), and chemical modes of action when analyzing and interpreting positive results in the in vitro genotoxicity assays and determining appropriate follow-up testing. The Review Subgroup also examined the characteristics, strengths, and limitations of each of the existing in vitro and in vivo genotoxicity assays to determine their usefulness in any follow-up testing.

Application of quantitative microbial risk assessments for estimation of risk management metrics: Clostridium perfringens in ready-to-eat and partially cooked meat and poultry products as an example

The U.S. Department of Agriculture, Food Safety and Inspection Service is exploring quantitative risk assessment methodologies to incorporate the use of the Codex Alimentarius' newly adopted risk management metrics (e.g., food safety objectives and performance objectives). It is suggested that use of these metrics would more closely tie the results of quantitative microbial risk assessments (QMRAs) to public health outcomes. By estimating the food safety objective (the maximum frequency and/or concentration of a hazard in a food at the time of consumption) and the performance objective (the maximum frequency and/or concentration of a hazard in a food at a specified step in the food chain before the time of consumption), risk managers will have a better understanding of the appropriate level of protection (ALOP) from microbial hazards for public health protection. We here demonstrate a general methodology that allows identification of an ALOP and evaluation of corresponding metrics at appropriate points in the food chain. It requires a two-dimensional probabilistic risk assessment, the example used being the Monte Carlo QMRA for Clostridium perfringens in ready-to eat and partially cooked meat and poultry products, with minor modifications to evaluate and abstract required measures. For demonstration purposes, the QMRA model was applied specifically to hot dogs produced and consumed in the United States. Evaluation of the cumulative uncertainty distribution for illness rate allows a specification of an ALOP that, with defined confidence, corresponds to current industry practices.

Genomics-based food-borne pathogen testing and diagnostics: possibilities for the U.S. Department of Agriculture's Food Safety and Inspection Service

The use of genomic technologies at the U.S. Department of Agriculture could enhance inspection, monitoring, and risk assessment capabilities within its Food Safety and Inspection Service (FSIS). Molecular assays capable of detecting hundreds of microbial DNA sequences within a single food sample that identify food-borne pathogens of concern and characterize their traits most relevant to human health risk are of great interest for FSIS. For example, a high-density assay, or combination of assays, could screen FSIS inspected food for pathogens relevant to public health (e.g., Salmonella, Listeria, and toxic E. coli) as well as their associated virulence factors and antibiotic resistance genes. Because most genotype assays can be completed in one working day with a minimum of reagents, use of such assays could potentially save FSIS a significant amount of cost/time for analyses. Further, a genotype assay can detect specific microbial traits relevant to human health risk based on the DNA sequence of toxin producing genes, antibiotic resistance alleles, and more. By combining rapid analysis with specific data on human health risks, information from such high-density genotype assays could provide expanded support for test and hold situations, recalls, outbreak management, and microbial risk assessments (e.g., provide data needed for food-borne illness source attribution). Environ. Mol. Mutagen.

Use of genetic toxicology information for risk assessment

Genetic toxicology data are used worldwide in regulatory decision-making. On the 25th anniversary of Environmental and Molecular Mutagenesis, we think it is important to provide a brief overview of the currently available genetic toxicity tests and to outline a framework for conducting weight-of-the-evidence (WOE) evaluations that optimize the utility of genetic toxicology information for risk assessment. There are two major types of regulatory decisions made by agencies such as the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA): (1) the approval and registration of pesticides, pharmaceuticals, medical devices, and medical-use products, and (2) the setting of standards for acceptable exposure levels in air, water, and food. Genetic toxicology data are utilized for both of these regulatory decisions. The current default assumption for regulatory decisions is that chemicals that are shown to be genotoxic in standard tests are, in fact, capable of causing mutations in humans (in somatic and/or germ cells) and that they contribute to adverse health outcomes via a "genotoxic/mutagenic" mode of action (MOA). The new EPA Guidelines for Carcinogen Risk Assessment [Guidelines for Carcinogen Risk Assessment, USEPA, 2005, EPA Publication No. EPA/630/P-03/001F] emphasize the use of MOA information in risk assessment and provide a framework to help identify a possible mutagenic and/or nonmutagenic MOA for potential adverse effects. An analysis of the available genetic toxicity data is now, more than ever, a key component to consider in the derivation of an MOA for characterizing observed adverse health outcomes such as cancer. We provide our perspective and a two-step strategy for evaluating genotoxicity data for optimal use in regulatory decision-making. The strategy includes integration of all available information and provides, first, for a WOE analysis as to whether a chemical is a mutagen, and second, whether an adverse health outcome is mediated via a mutagenic MOA.

Ecological risk assessment issues identified during the U.S. Environmental Protection Agency's examination of risk assessment practices

Recently, the U.S. Environmental Protection Agency examined its current risk-assessment principles and practices. As part of the examination, aspects of ecological risk-assessment practices were reviewed. Several issues related to ecological risk assessment were identified, including the use of organism-level versus population-level attributes to characterize risk, the possible opportunities associated with the increased use of probabilistic approaches for ecological risk assessment, and the notion of conservatism in estimating risks. The agency examination provides an understanding of current practices and is intended to begin a dialogue in which the risk assessment community can engage in addressing the identified issues to improve and enhance ecological risk assessment.

Genotoxicity risk assessment: a proposed classification strategy

Recent advances in genetic toxicity (mutagenicity) testing methods and in approaches to performing risk assessment are prompting a renewed effort to harmonize genotoxicity risk assessment across the world. The US Environmental Protection Agency (EPA) first published Guidelines for Mutagenicity Risk Assessment in 1986 that focused mainly on transmissible germ cell genetic risk. Somatic cell genetic risk has also been a risk consideration, usually in support of carcinogenicity assessments. EPA and other international regulatory bodies have published mutagenicity testing requirements for agents (pesticides, pharmaceuticals, etc.) to generate data for use in genotoxicity risk assessments. The scheme that follows provides a proposed harmonization approach in which genotoxicity assessments are fully developed within the risk assessment paradigm used by EPA, and sets out a process that integrates newer thinking in testing battery design with the risk assessment process. A classification strategy for agents based on inherent genotoxicity, dose-responses observed in the data, and an exposure analysis is proposed. The classification leads to an initial level of concern for genotoxic risk to humans. A total risk characterization is performed using all relevant toxicity data and a comprehensive exposure evaluation in association with the genotoxicity data. The result of this characterization is ultimately used to generate a final level of concern for genotoxic risk to humans. The final level of concern and characterized genotoxicity risk assessment are communicated to decision makers for possible regulatory action(s) and to the public.

A survey of EPA/OPP and open literature on selected pesticide chemicals. III. Mutagenicity and carcinogenicity of benomyl and carbendazim

The known aneuploidogens, benomyl and its metabolite, carbendazim (methyl 2-benzimidazole carbamate (MBC)), were selected for the third in a series of ongoing projects with selected pesticides. Mutagenicity and carcinogenicity data submitted to the US Environmental Protection Agency's (US EPA's) Office of Pesticide Programs (OPP) as part of the registration process are examined along with data from the open literature. Mutagenicity and carcinogenicity profiles are developed to provide a complete overview and to determine whether an association can be made between benomyl- and MBC-induced mouse liver tumors and aneuploidy. Since aneuploidogens are considered to indirectly affect DNA, the framework adopted by the Agency for evaluating any mode of action (MOA) for carcinogenesis is applied to the benomyl/MBC data. Both agents displayed consistent, positive results for aneuploidy induction but mostly negative results for gene mutations. Non-linear dose responses were seen both in vitro and in vivo for aneuploidy endpoints. No evidence was found suggesting that an alternative MOA other than aneuploidy may be operative. The data show that by 14 days of benomyl treatment, events associated with liver toxicity appear to set in motion the sequence of actions that leads to neoplasms. Genetic changes (as indicated by spindle impairment leading to missegregation of chromosomes, micronucleus induction and subsequent aneuploidy in bone marrow cells) can commence within 1-24h after dosing, well within the time frame for early key events. Critical steps associated with frank tumor formation in the mouse liver include hepatotoxicity, increased liver weights, cell proliferation, hypertrophy, and other steps involving hepatocellular alteration and eventual progression to neoplasms. The analysis, however, reveals weaknesses in the data base for both agents (i.e. no studies on mouse tubulin binding, no in vivo assays of aneuploidy on the target tissue (liver), and no clear data on cell proliferation relative to dose response and time dependency). The deficiencies in defining the MOA for benomyl/MBC introduce uncertainties into the analysis; consequently, benomyl/MBC induction of aneuploidy cannot be definitively linked to mouse liver carcinogenicity at this time.

A survey of EPA/OPP and open literature on selected pesticide chemicals. II. Mutagenicity and carcinogenicity of selected chloroacetanilides and related compounds

With this effort, we continue our examination of data on selected pesticide chemicals and their related analogues that have been presented to the U.S. Environmental Protection Agency's (USEPA's) Office of Pesticide Programs (OPP). This report focuses on a group of selected chloroacetanilides and a few related compounds. As part of the registration process for pesticidal chemicals, interested parties (registrants) must submit toxicity information to support the registration including both mutagenicity and carcinogenicity data. Although this information is available to the public via Freedom of Information (FOI) requests to the OPP, publication in the scientific literature allows greater dissemination and examination of the data. For this Special Issue, graphic profiles have been prepared of the mutagenicity and carcinogenicity data available in the submissions to OPP. Also, a discussion is presented about how toxicity data are used to help establish tolerances (limits of pesticide residues in foods). The mutagenicity results submitted by registrants are supplemented by data on these chemicals from the open literature to provide a full perspective of their genetic toxicology. The group of chloroacetanilides reviewed here display a consistent pattern of mutagenic activity, probably mediated via metabolites. This mutagenic activity is a mechanistically plausible factor in the development of tumors seen in experimental animals exposed to this class of chemicals.

Information requirements and regulatory approaches for heritable genetic risk assessment and risk communication

With the evolution of genetic toxicology as a scientific discipline and the formation of the Environmental Mutagen Society (EMS), much thought was given to the study of chemicals in the human environment for their mutagenic effects. The Society's goal was to promote scientific investigation and dissemination of information related to genetic toxicology. Subsequently, the concern for chemically induced genetic damage in human germ cells and its potential impact on genetic diseases was detailed in the Committee 17 Report (1975). With new information on the involvement of genetic alterations in disease and on the ramifications of possible effects of exposures to environmental mutagens, it is becoming increasingly necessary to again focus our attention on the assessment of heritable genetic effects. Clearly, strategies for communication of genetic hazard/risk assessments to exposed individuals and to those charged with regulating environmental agents need to be developed.

Acrylamide: a review of its genotoxicity and an assessment of heritable genetic risk

An updated review of the genotoxicity studies with acrylamide is provided. Then, using data from the studies generating quantitative information concerning heritability of genetic effects, an assessment of the heritable genetic risk presented by acrylamide is presented. The review offers a discussion of the reactions and possible mechanisms of genotoxic action by acrylamide and its epoxide metabolite glycidamide. Several genetic risk approaches are discussed, including the parallelogram, direct (actually a modified direct), and doubling dose approaches. Using data from the specific-locus and heritable translocation assays, the modified direct and doubling dose approaches are utilized to quantitate genetic risk. Exposures of male parents to acrylamide via inhalation, ingestion, and dermal routes are also quantitated. With these approaches and measurements and their underlying assumptions concerning extrapolation factors (including germ cell stage specificity, DNA repair variability, locus specificity), number of human loci associated with dominant disease alleles, and spontaneous mutation rates, an assessment of heritable genetic risk for humans is calculated for the three exposure scenarios. The calculated estimates for offspring from fathers exposed to acrylamide via drinking water are up to three offspring potentially affected with induced genetic disease per 10(8) offspring. Estimates for inhalation or dermal exposures suggest higher risks for induced genetic disease in offspring from fathers exposed in occupational settings.

Ethylene thiourea (ETU). A review of the genetic toxicity studies

Ethylene thiourea (ETU) is a common contaminant, metabolite and degradation product of the fungicide class of ethylene bisdithiocarbamates (EBDCs); as such, they present possible exposure and toxicological concerns to exposed individuals. ETU has been assayed in many different tests to assess genotoxicity activity. While a great number of negative results are found in the data base, there is evidence that demonstrates ETU is capable of inducing genotoxic endpoints. These include responses for gene mutations (e.g. Salmonella), structural chromosomal alterations (e.g. aberrations in cultured mammalian cells as well as a dominant lethal assay) and other genotoxic effects (e.g. bacterial rec assay and several yeast assays). It is important to consider the magnitude of the positive responses as well as the concentrations/doses used when assessing the genotoxicity of ETU. While ETU induces a variety of genotoxic endpoints, it does not appear to be a potent genotoxic agent. For example, it is a weak bacterial mutagen in the Salmonella assay without activation in strain TA1535 at concentrations generally above 1000 micrograms/plate. Weak genotoxic activity of this sort is usually observed in most of the assays with positive results. Since ETU does not appear very potent and is not extremely toxic to test cells and organisms, it is not surprising to find that ETU does not produce consistent effects in many of the assays reviewed. Consequently, in many instances, mixed results for the same assay type are reported by different investigators, but as reviewed herein, these results may be dependent upon the test conditions in each individual laboratory. A primary shortcoming with many of the reported negative results is that the concentrations or doses used are not high enough for an adequate test for ETU activity. There are also problems with many of the negative assays generally in protocol or reporting, particularly with the in vivo studies (e.g. inappropriate sample number and/or sampling times; inadequate top dose employed). Overall, while ETU does not appear to be a potent genotoxic agent, it is capable of producing genotoxic effects (e.g. gene mutations, structural chromosomal aberrations). This provides a basis for weak genotoxic activity by ETU. Furthermore, based on a suggestive dominant lethal positive result, there may be a concern for heritable effects. Due to the many problems with the conduct and assessment of the in vivo assays, it is worth repeating in vivo cytogenetic assays and a dominant lethal assay (with acceptable test procedures and data generation) to determine if these results would continue to support a heritable mutagenicity concern.

A survey of EPA/OPP and open literature data on selected pesticide chemicals tested for mutagenicity. I. Introduction and first ten chemicals

Parties interested in registering a pesticide chemical with the U.S. Environmental Protection Agency's (USEPA's) Office of Pesticide Programs (OPP) must submit toxicity information to support the registration. Mutagenicity data are a part of the required information that must be submitted. This information is available to the public via Freedom of Information requests to the OPP. However, it is felt that this information would be more effectively and widely disseminated if presented in a published medium. Beginning with this publication, sets of mutagenicity data on pesticide chemicals will be periodically published in the Genetic Activity Profile (GAP) format. In addition, mutagenicity data extracted from the currently available open literature is also presented to provide a more complete database and to allow comparisons between the OPP-submitted data and other publicly available information.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Evaluation of the carcinogenic potential of pesticides. 4. Chloroalkylthiodicarboximide compounds with fungicidal activity

The Health Effects Division of the Office of Pesticide Programs (OPP) assessed the carcinogenic potential of three structurally related chloroalkylthiodicarboximide fungicides using a consensus peer review process and EPA's 1986 guidelines for cancer risk assessment. All of the fungicides were categorized as Group B2 (probable human) carcinogens based upon findings of an increased incidence of malignant tumors, or combined malignant and benign tumors, in multiple experiments involving different strains of mice and rats. The primary sites of tumor formation with the chloroalkylthiodicarboximide fungicides in male and/or female mice (CD-1 and B6C3F1) were the gastrointestinal tract (captan, folpet, and captafol), the lymph system (folpet and captafol), and the vascular system (captafol). The main sites of tumor formation in rats of one or both sexes (CR CD, Wistar, or F344 strains) were the kidney (Captan and captafol), uterus (captan), mammary gland and liver (captafol). In addition, positive trends for thyroid, testicular, mammary gland, and lymph node tumors were observed with folpet in the same strains of rats. All three of the compounds exhibited positive mutagenic activity in a variety of in vitro short-term tests for gene mutation, DNA repair, and chromosomal aberrations in prokaryotic and eukaryotic cells, but were not genotoxic in available studies performed under in vivo conditions. The assessment of human cancer risk for captan, folpet, and captafol was made using low-dose extrapolation models.

Mutagenicity test schemes and guidelines: U.S. EPA Office of Pollution Prevention and Toxics and Office of Pesticide Programs

New requirements for chemicals subject to mutagenicity testing from the U.S. Environmental Protection Agency (USEPA) are discussed. Also detailed are two categories in the 1986 Mutagenicity Risk Assessment Guidelines.

Genotoxicity of three pyridine compounds to L5178Y mouse lymphoma cells

The L5178Y mouse lymphoma assay was used to examine the potential mutagenicity of three halogenated pyridine compounds. Position effects of the halogen moiety and the role of metabolic activation were analyzed based on induced mutant frequency, gross chromosome aberrations, and micronuclei. Without activation, 2-chloropyridine, 3-chloropyridine, and 2-chloro-5-trifluoromethylpyridine produced a small increase in mutant frequency; only the 2-chloropyridine activity was significantly increased with activation. All three compounds were also clastogenic as demonstrated by increases in chromosome aberrations and micronuclei (except for 2-chloro-5-trifluoromethylpyridine which did not induce micronuclei either with or without activation).

Characteristics of the U.S. EPA's Office of Pesticide Programs' toxicity information databases

The United States Environmental Protection Agency's Office of Pesticide Programs (OPP) requires that data from toxicity testing be submitted to the OPP to support the registration of pesticide chemicals. Once the toxicity data are submitted, they are entered into various toxicity databases. The studies are listed in an archival database to catalog and allow retrieval of the study for review. Reviews of toxicity studies are then placed into a separate database that can be retrieved to support a regulatory position. Toxicity information for health effects other than cancer and gene mutations from chronic exposure is reviewed through a reference dose (RfD) approach, and these decisions and supporting data are entered into an RfD database. Carcinogenicity data are reviewed by a peer review process, and these decisions are entered into a newly developed database to show the regulatory decision with supporting data. The mutagenicity data are reviewed and acceptable data are entered into the Genetic Activity Profile system to catalog and display the submitted information. These databases contain the information used for hazard evaluations as part of the OPP review of pesticide chemicals.

Genotoxicity in mouse lymphoma cells of chemicals capable of Michael addition

Over the past several years, we have been evaluating the mutagenicity and clastogenicity of compounds capable of Michael-type reactions. These compounds, including acrylamide, several acrylate and methacrylate esters, vinyl sulfones, and phorone, have been evaluated using TK+/- -3.7.2C mouse lymphoma cells. Mutagenic chemicals induced increases in the number of small colony tk- deficient mutants. This suggested a clastogenic mechanism which was confirmed by demonstrating increases in aberrations and micronucleus frequencies in cultured cells. Vinyl sulfone was found to be the most effective chemical mutagen with induction of genotoxic effects at concentrations as low as 0.25 microgram/ml. The other compounds also produced positive results, but at higher concentrations. Since these compounds are known to deplete glutathione, phorone, a model glutathione depleter, was examined and found to produce similar effects as the other compounds in mouse lymphoma cells. These results suggest that the direct-acting Michael-type reaction has activity relevant to producing a genotoxic effect. Since acrylamide has been found to be a potent germ cell mutagen, this mechanism may be also relevant in the induction of heritable mutagenic risk.

Considerations in the U.S. Environmental Protection Agency's testing approach for mutagenicity

OPP: This paper provides the rationale and support for the decisions the OPP will make in requiring and reviewing mutagenicity information. The regulatory requirement for mutagenicity testing to support a pesticide registration is found in the 40 CFR Part 158. The guidance as to the specific mutagenicity testing to be performed is found in the OPP's Pesticide Assessment Guidelines, Subdivision F, Hazard Evaluation: Human and Domestic Animals (referred to as the Subdivision F guideline). A revised Subdivision F guideline has been presented that becomes the current guidance for submitters of mutagenicity data to the OPP. The decision to revise the guideline was the result of close examination of the version published in 1982 and the desire to update the guidance based on developments since then and current state-of-the-science. After undergoing Agency and public scrutiny, the revised guideline is to be published in 1991. The revised guideline consists of an initial battery of tests (the Salmonella assay, an in vitro mammalian gene mutation assay and an in vivo cytogenetics assay which may be either a bone marrow assay for chromosomal aberrations or for micronuclei formation) that should provide an adequate initial assessment of the potential mutagenicity of a chemical. Follow-up testing to clarify results from the initial testing may be necessary. After this information as well as all other relevant information is obtained, a weight-of-evidence decision will be made about the possible mutagenicity concern a chemical may present. Testing to pursue qualitative and/or quantitative evidence for assessing heritable risk in relation to human beings will then be considered if a mutagenicity concern exists. This testing may range from tests for evidence of gonadal exposure to dominant lethal testing to quantitative tests such as the specific locus and heritable translocation assays. The mutagenicity assessment will be performed in accordance with the Agency's Mutagenicity Risk Assessment Guidelines. The mutagenicity data would also be used in the weight-of-evidence consideration for the potential carcinogenicity of a chemical in accordance with the Agency's Carcinogen Risk Assessment Guidelines. In instances where there are triggers for carcinogenicity testing, mutagenicity data may be used as one of the triggers after a consideration of available information. It is felt that the revised Subdivision F guideline will provide appropriate, and more specific, guidance concerning the OPP approach to mutagenicity testing for the registration of a pesticide. It also provides a clearer understanding of how the OPP will proceed with its evaluation and decision making concerning the potential heritable effects of a test chemical.(ABSTRACT TRUNCATED AT 400 WORDS)

An evaluation of the roles of mammalian cell mutation assays in the testing of chemical genotoxicity

The present status of the applicability of mammalian cell gene mutation assays in the safety evaluation of industrial chemicals is evaluated from the industrial and regulatory point of view, with emphasis being placed on the CHO/HGPRT and mouse lymphoma tk +/- assays. The CHO/HGPRT assay was concluded to be a highly specific assay, but it might be less sensitive to mutagens that mainly induced large deletions. The mouse lymphoma assay was concluded to be sensitive, but it might have a lower specificity due to experimental artifacts such as pH and osmolality changes. Mammalian gene mutation assays, when conducted within their limitations, are concluded to be valuable in safety evaluation, providing results complementary to the Ames test and cytogenetic assays.

Cytogenetic studies of ethyl acrylate using C57BL/6 mice

The clastogenicity of ethyl acrylate (EA) was examined in vivo by injecting i.p. five male C57BL/6 mice per dose group with either 125, 250, 500 or 1000 mg/kg EA dissolved in saline. Controls received solvent only. Acrylamide (100 mg/kg), because of its similarity in structure and mode of action to EA, was used as a positive control. Twenty-four hours after injection, the animals were anesthetized and the spleens aseptically removed. Splenocytes were isolated on density gradients and cultured with concanavalin A to stimulate cell division. In half the cultures bromodeoxyuridine was added at 21 h for analysis of chromosome aberrations (CAs) in first division cells and sister chromatid exchange (SCE) in second division cells. In the remaining cultures cytochalasin B was added to produce binucleated cells for scoring of micronuclei (MN). There was no significant increase in SCE or CAs at any of the doses of EA examined. At the highest dose examined (1000 mg/kg), EA did cause a small but significant increase in binucleated cell MN. Acrylamide caused an increase in MN and SCEs in splenocytes. Because others have found EA to be clastogenic in vitro, isolated splenocytes were exposed to a wide range of concentrations of EA during the G0 stage of the cell cycle or 23 h after mitogen stimulation during the late G1 or early S phase of the cell cycle. Although EA was toxic for both exposure regimens, significant increases in chromatid-type aberrations were found only when the target cells were treated 23 h after mitogenic stimulation. No statistically significant increase in SCE frequency was found after either treatment regimen. These data suggest that EA is only clastogenic at near toxic concentrations during a specific stage of the cell cycle.

Comparison of mutagenicity results for nine compounds evaluated at the hgprt locus in the standard and suspension CHO assays

The Chinese hamster ovary (CHO) assay, which measures newly induced mutations at the hypoxanthine-guanine phosphoribosyltransferase (hgprt) locus, has been widely used for mutagenesis testing. The insensitivity of the standard assay to some genotoxic agents has been speculated to be due to the relatively small number of cells used in the assay. In the present study, we have compared the standard monolayer assay with a suspension adapted CHO assay that uses cell numbers comparable to that of the L5178Y mouse lymphoma assay. Nine compounds, ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), 2-methoxy-6-chloro-9-[3-(ethyl-2-chloroethyl)-aminopropylamino]-acridine 2HCl (ICR 170), methyl acrylate, ethyl acrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, 2-ethylhexyl acrylate and dicyclopentenyloxyethyl methacrylate were evaluated in the monolayer and suspension assays. Both assays gave the same overall qualitative results for the test compounds. There were some quantitative differences in the mutant frequency for the three compounds found to be mutagenic (EMS, MMS and ICR 170). The acrylates (many of which appear to exert their genotoxic effect through a clastogenic mechanism) were negative in both test systems. The use of the suspension assay did not improve the ability of the hgprt locus to detect the genotoxicity of the acrylates. Thus, increasing the number of cells does not improve the ability of the CHO/HGPRT assay to detect compounds that act primarily by a clastogenic mechanism.

Analysis of the genotoxicity of nine acrylate/methacrylate compounds in L5178Y mouse lymphoma cells

Nine acrylate/methacrylate esters were tested for the induction of mutations, aberrations and micronuclei in cultured L5178Y mouse lymphoma cells without exogenous activation. With the exception of 2-ethylhexyl acrylate, and dicyclopentenyloxyethyl methacrylate which produced equivocal mutagenic responses, the other seven compounds (2-hydroxyethyl acrylate, dicyclopentenyloxyethyl acrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and pentaerythritol triacrylate) produced positive mutagenic responses with different potencies. For the mutagenic acrylates/methacrylates, primarily small-colony, trifluorothymidine (TFT)-resistant mutants were induced, suggesting a clastogenic mechanism that was supported by increased aberrations and micronucleus frequencies (except for trimethylolpropane trimethacrylate which was positive for aberration but not micronucleus induction). Generally, it was found that multifunctional compounds (esters with greater than 1 functional vinyl group) required lower concentrations than monofunctional compounds to induce maximal cytotoxic, mutagenic, and clastogenic responses. In addition, acrylates were generally more potent than their corresponding methacrylates. This information and these comparative activities will provide some guidance for setting priorities of concern for hazard consideration for acrylate/methacrylate ester compounds.

Differential mutant quantitation at the mouse lymphoma tk and CHO hgprt loci

Recent reports by several laboratories indicate that not all non-essential target loci are equally capable of detecting chromosomal mutations. The present study was undertaken to determine if both the tk locus in mouse lymphoma cells and the hgprt locus in Chinese hamster ovary (CHO) cells can be used to quantitate chromosomal mutations. Seven known mutagens for the tk locus were selected. These compounds were evaluated in the mouse lymphoma assay and in a suspension adapted CHO assay for their mutagenicity. In addition to the specific locus mutagenesis analysis, mouse lymphoma and CHO cells were evaluated for the frequency of gross chromosome aberrations. From these investigations, it appears that only those compounds [2-methoxy-6-chloro-9-(3-[ethyl-2-chloroethyl] aminopropylamino)-acridine-dihydrochloride (ICR 170), ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS)] that induce significant numbers of large-colony thymidine kinase (TK) mutants also induce significant numbers of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) mutants. The four acrylates evaluated (methyl acrylate, ethyl acrylate, trimethylolpropane triacrylate and tetraethyleneglycol diacrylate) induced almost exclusively small-colony TK mutants and very few if any HGPRT mutants. Aberration analysis revealed that both the mouse lymphoma and CHO cells responded to the clastogenicity of the compounds (except for ICR 170 which was not positive in CHO cells) and that neither cell line was clearly more sensitive than the other to the clastogens tested. It is significant that the four acrylates give little or no evidence of genotoxicity when evaluated using selection for HGPRT-deficient mutants, yet are clearly clastogenic to the same cells in the same experiment. These results are consistent with the hypothesis that the hgprt locus may not be useful as a marker to evaluate the clastogenic component of a genotoxic compound. The present study adds to the increasing number of studies that support the view that the hemizygous nature of the hgprt locus permits the recovery of mutations primarily affecting the function of a single gene; whereas the heterozygous nature of the tk locus permits the recovery of both single gene and chromosomal mutations.

Acrylamide: its metabolism, developmental and reproductive effects, genotoxicity, and carcinogenicity

Monomeric acrylamide is an important industrial chemical primarily used in the production of polymers and copolymers. It is also used for producing grouts and soil stabilizers. Acrylamide's neurotoxic properties have been well documented. This review will focus on pertinent information concerning other, non-neurotoxic, effects observed after exposure to acrylamide, including: its genotoxic, carcinogenic, reproductive, and developmental effects. It will also cover its absorption, metabolism, and distribution. The data show that acrylamide is capable of inducing genotoxic, carcinogenic, developmental, and reproductive effects in tested organisms. Thus, acrylamide may pose more than a neurotoxic health hazard to exposed humans. Acrylamide is a small organic molecule with very high water solubility. These properties probably facilitate its rapid absorption and distribution throughout the body. After absorption, acrylamide is rapidly metabolized, primarily by glutathione conjugation, and the majority of applied material is excreted within 24 h. Preferential bioconcentration of acrylamide and/or its metabolites is not observed although it appears to persist in tests and skin. Acrylamide can bind to DNA, presumably via a Michael addition-type reaction, which has implications for its genotoxic and carcinogenic potential. The available evidence suggests that acrylamide does not produce detectable gene mutations, but that the major concern for its genotoxicity is its clastogenic activity. This clastogenic activity has been observed in germinal tissues which suggest the possible heritability of acrylamide-induced DNA alterations. Since there is 'sufficient evidence' of carcinogenicity in experimental animals as outlined under the U.S. EPA proposed guidelines for carcinogen risk assessment, acrylamide should be categorized as a 'B2' carcinogen and therefore be considered a 'probable human carcinogen.' The very limited human epidemiological data do not provide sufficient evidence to enable one to judge the actual carcinogenic risk to humans. Acrylamide is able to cross the placenta, reach significant concentrations in the conceptus and produce direct developmental and post-natal effects in rodent offspring. It appears that acrylamide may produce neurotoxic effects in neonates from exposures not overtly toxic to the mothers. Acrylamide has an adverse effect on reproduction as evidenced by dominant lethal effects, degeneration of testicular epithelial tissue, and sperm-head abnormalities.

Comparative mutagenicity of halogenated pyridines in the Salmonella typhimurium/mammalian microsome test

The Salmonella/microsome assay with strains TA97, TA98, TA100 and TA102 was used to examine the potential mutagenicity and structure-activity of 16 mono- and di-halogenated pyridines. The chemical reactivity of the halopyridines suggests that nucleophilic displacement of halogens can occur with halogens at positions 2, 4 and 6 being displaced in addition-elimination reactions. 2-Chloropyridine gave a positive result with rat-liver metabolic activation, and 2-fluoropyridine gave equivocal results under these conditions. Mutagenic responses were also obtained with 2-chloromethyl pyridine and 3-chloromethyl pyridine, in both the presence and absence of rat-liver S9. These results suggest that the halogenated pyridines, especially with halogens at the 2-position, and singly on a methyl substituent, have mutagenic activity in the Salmonella assay.

Mutagenicity and clastogenicity of acrylamide in L5178Y mouse lymphoma cells

Acrylamide was tested without exogenous activation in L5178Y/TK+/- -3.7.2C cells for mutation at the thymidine kinase locus and for clastogenicity. Acrylamide gave a positive induced mutagenic response (approximately 70 mutants/10(6) survivors) when tested at 600-650 micrograms/ml. The highest dose tested (850 micrograms/ml) resulted in an induced mutant frequency of approximately 380 mutants/10(6) survivors (survival = 13%). Acrylamide induced almost exclusively small-colony mutants, indicating that it might be acting by a clastogenic mechanism. As predicted, acrylamide was clastogenic, inducing both chromatid and chromosome breaks and rearrangements. A clearly positive clastogenic response was observed at both the 750 micrograms/ml and 850 micrograms/ml doses, which showed 16 and 64 aberrations per 100 cells, respectively (background = 3 aberrations per 100 cells). These studies indicate that the L5178Y/TK+/- mouse lymphoma assay can detect some chromosomal mutagens (clastogens) that show little activity in other single gene mutation assays, the CHO/HPRT and Salmonella.