New developments in the evolution and application of the WHO/IPCS framework on mode of action/species concordance analysis

A pragmatic workflow for human relevance assessment of toxicological pathways and associated new approach methodologies

Currently, safety assessments of chemical substances are predominantly based on animal data. Multiple considerations call for the use of alternative testing strategies that are based on new approach methodologies (NAMs). However, the human relevance of these testing strategies is usually uncertain. This necessitates a harmonized and accepted workflow for assessing their applicability for regulatory purposes. This report proposes such a workflow, applicable for assessing the human relevance of a toxicological pathway and the relevance of NAMs related to the different components of the pathway. The workflow starts with an established toxicological pathway, of which the adverse outcome is relevant for human health risk assessment and that has sufficient weight of evidence. Human relevance is assessed through three main questions, related to the different components (steps) of the pathway, the pathology of human syndromes that have a similar adverse outcome, and quantitative aspects. The latter comprise both interspecies differences and in vitro - in vivo differences. The combined evidence is scored as 'strong', 'moderate' or 'weak' support of human relevance, based on expert judgement. The workflow developed was tested in a case study, through application to an AOP describing craniofacial malformations after in utero exposure to triazoles. Based on evidence collected for two of the three main questions, the case study provided moderate to strong support for human relevance of both the various components of the AOP and its associated NAMs. Furthermore, it demonstrated that the workflow is a promising approach that allows for a more transparent scientific evaluation of human relevance of toxicological pathways and associated NAMs. Therefore, despite some areas for improvement, we consider the workflow an important step forward for application of AOPs and related NAMs in human health risk assessment.

Mode of action analysis for rat thyroid gland follicular cell tumor formation by MGK-264 and human relevance

MGK-264 (N-(2-ethylhexyl)-5-norborene-2.3-dicarboximide or N-octyl bicycloheptene dicarboximide), an insecticidal synergist, produced thyroid gland follicular cell (TFC) tumors in male Sprague-Dawley (SD) rats in a carcinogenicity study. The purpose of this study was to evaluate the possible mode of action (MoA) for TFC tumor induction by MGK-264 and its relevance to humans. In short-term in vivo studies, the treatment of male SD rats with MGK-264 resulted in induction of hepatic UDPglucuronosyltransferase (UGT) activity towards thyroxine (T4) as substrate (UGT activity), a decrease in serum T4 levels, an increase in serum thyroid stimulating hormone levels, and TFC hypertrophy at MGK-264 dose levels where TFC tumors were noted in the carcinogenicity study. Other possible MoAs such as genotoxicity, thyroperoxidase inhibition, and sodium/iodide symporter inhibition were excluded. Therefore, it is reasonable to conclude that MGK-264 has mitogenic activity on TFCs via induction of hepatic UGT activity followed by perturbation of the hypothalamus-pituitary-thyroid axis, similar to other hepatic xenobiotic enzyme inducers like phenobarbital. Literature data demonstrates that there are marked species differences between rats and humans in the effects of hepatic xenobiotic enzyme inducers on thyroid hormones and the thyroid gland. Overall, the proposed MoA for MGK-264-induced rat TFC tumor formation is considered quantitatively not plausible for humans.

A proposal of criteria to support the EU classification on endocrine disruption for the thyroid modality and their application to four data-rich case studies

Recently, the European Commission has implemented hazard categories to classify substances as endocrine disruptors for human health, i.e. ED HH 1 or ED HH 2, depending on the weight-of-evidence. However, specific guidance on how to differentiate between the two is unavailable. This article presents the CropLife Europe (CLE) proposal for a structured approach to support the ED HH classification for the thyroid modality. Further, the Thyroid Function-Related Neurodevelopmental Toxicity Testing and Assessment Scheme (Thyroid-NDT-TAS) has been modified in view of the new classification. Application of the CLE proposal and the modified Thyroid-NDT-TAS is illustrated in four case studies covering active substances in plant protection products that showed thyroid- and liver-related effects in laboratory animal studies (pyrimethanil, boscalid, metribuzin, ethiprole). For all four substances, there is strong and consistent evidence that the thyroid-related endocrine activity in rats is liver enzyme induction-mediated, a mode-of-action that is of questionable relevance to humans. In vitro species comparisons (unavailable for pyrimethanil) further confirm non-relevance to humans. However, pyrimethanil (and boscalid) did not elicit developmental neurotoxicity in rats. For pyrimethanil, boscalid and ethiprole, the overall weight-of-evidence determination yields the conclusion "no ED HH via the thyroid modality". For metribuzin, category ED HH 2 may be triggered due to uncertainties related to its database. The case studies underline that expert judgement is required to assess overall effect patterns, to balance the available evidence and to conclude on classification as ED HH 1, ED HH 2 or no ED HH via the thyroid modality.

Systematic evaluation of the evidence base on methyl tert-butyl ether supporting a lack of concern for carcinogenic hazard in humans based on animal cancer studies and mechanistic data

Methyl tert-butyl ether (MTBE) is a high-octane fuel component that helps gasoline burn cleaner and reduces automobile emissions. In 1999, the International Agency for Research on Cancer (IARC) categorized MTBE as "not classifiable" regarding human carcinogenicity. Since then, additional studies have been published that substantially added to the evidence base to examine the carcinogenic potential of MTBE in humans. A systematic literature search and review was conducted to identify mechanistic data, as well as studies investigating cancer in MTBE-exposed humans and experimental animals. Critical appraisal was performed for relevant studies with mechanistic data organized and evaluated within Key Characteristics of Carcinogens (KCCs). Three standard animal cancer bioassays showed a low incidence of hepatocellular adenomas in female mice (inhalation exposure), with renal adenomas/carcinoma (inhalation) and brain tumors (drinking water) in male rats exposed to high concentrations of MTBE. Evidence extracted from the literature demonstrate that the mechanism of male rat renal tumors does not operate in humans. Review of the strength of mechanistic data was based on activity, relevancy, and reliability, with information-dense KCC2-is genotoxic, and KCC10-alters cell proliferation, cell death, and nutrient supply, together supporting that MTBE is unlikely to be a carcinogenic hazard to humans.

A critical evaluation of rodent carcinogenicity studies on butyl methacrylate demonstrates a lack of carcinogenic potential

Assessments of a chemical agent's carcinogenicity based on rodent bioassays rely on their appropriate interpretation. This involves attention to study details, including reliable histopathologic diagnoses, and proper statistical analyses, including consideration of multiple comparisons, concurrent and historical controls. A major factor is evaluation of their likely mode of action and the human relevance of any identified tumors. We present a critical evaluation of the assessment of the 2-year inhalation bioassays of n-butyl methacrylate (n-BMA) in rats and mice performed by the Japan Bioassay Research Center (JBRC) and an assessment of the International Agency for Research on Cancer (IARC) review and classification as Group 2B, possible human carcinogen. The tumors of concern for assessment of its carcinogenicity included mononuclear cell leukemia (MCL) in male rats, thyroid C-cell tumors in female rats, liver tumors and histiocytic sarcomas in male mice, and hemangiosarcomas in female mice. Our review of these studies raises concerns regarding the accuracy of histopathology diagnoses and human relevance of MCL. Most critically, the statistical evaluation/interpretation of all tumor types indicates no carcinogenic effects, since the frequency of increases (at p < 0.05) in tumor incidences in the study is totally consistent with chance expectation (i.e. not treatment related). Furthermore, the plausibility of n-BMA being carcinogenic is questionable since it is non-genotoxic, and the weight of evidence including read-across to the close structural analog methyl methacrylate indicates no concern for cancer. After thorough review of these bioassays, we conclude that there is no convincing evidence of carcinogenicity for n-BMA, contrary to the conclusion of the JBRC and the decision by the IARC.

Adverse Outcome Pathways Mechanistically Describing Hepatotoxicity

Adverse outcome pathways (AOPs) describe toxicological processes from a dynamic perspective by linking a molecular initiating event to a specific adverse outcome via a series of key events and key event relationships. In the field of computational toxicology, AOPs can potentially facilitate the design and development of in silico prediction models for hazard identification. Various AOPs have been introduced for several types of hepatotoxicity, such as steatosis, cholestasis, fibrosis, and liver cancer. This chapter provides an overview of AOPs on hepatotoxicity, including their development, assessment, and applications in toxicology.

EFSA Scientific Committee, Bennekou SH, Allende A, Bearth A, Casacuberta J, Castle L, Coja T, Crépet A, Halldorsson T, Hoogenboom L(R, Knutsen H, Koutsoumanis K, Lambré C, Nielsen S, Turck D, Civera AV, Villa R, Zorn H, Bampidis V, Castenmiller J, Chagnon M, Cottrill B, Darney K, Gropp J, Puente SL, Rose M, Vinceti M, Bastaki M, Gergelová P, Greco L, Innocenti ML, Janossy J, Lanzoni A, Terron A, Benford D. Risks to human and animal health from the presence of bromide in food and feed

The European Commission mandated EFSA to assess the toxicity of bromide, the existing maximum residue levels (MRLs), and possible transfer from feed into food of animal origin. The critical effects of bromide in experimental animals are on the thyroid and central nervous system. Changes in thyroid hormone homeostasis could result in neurodevelopmental toxicity, among other adverse effects. Changes in thyroid hormone concentrations and neurophysiological parameters have also been observed in experimental human studies, but the evidence was limited. Dose-response modelling of decreased blood thyroxine concentrations in rats resulted in a reference point of 40 mg/kg body weight (bw) per day. The Scientific Committee established a tolerable daily intake (TDI) of 0.4 mg/kg bw per day and an acute reference dose (ARfD) of 0.4 mg/kg bw per day to protect against adverse neurodevelopmental effects. The TDI value is supported by the results of experimental human studies with a NOAEL of 4 mg/kg bw per day and 10-fold interindividual variability. The TDI and ARfD are considered as conservative with 90% certainty. Insufficient evidence related to the toxicological effects of bromide was available for animals, with the exception of dogs. Therefore, the reference point of 40 mg/kg bw per day was extrapolated to maximum safe concentrations of bromide in complete feed for other animal species. Bromide can transfer from feed to food of animal origin, but, from the limited data, it was not possible to quantify the transfer rate. Monitoring data exceeded the current MRLs for some food commodities, generally with a low frequency. A conservative safety screening of the MRLs indicated that the TDI and ARfD are exceeded for some EU diets. Dietary exposure assessment for animals was not feasible due to insufficient data. The Scientific Committee recommends data be generated to allow robust dietary exposure assessments in the future, and data that support the risk assessment.

Mode of action Criteria for selection of the critical effect and safe dose range for PFOA by the Alliance for risk assessment

In response to the current disparity in risk assessment values for PFOA from different agencies and countries, an international effort facilitated by the Alliance for Risk Assessment (ARA) was recently undertaken to characterize the range of scientifically supportable safe dose estimates. In this assessment (Burgoon et al., 2023), an evaluation of the evidence regarding the potential modes of action (MOA) for PFOA toxicity was performed first, so that it could be used to inform subsequent decisions regarding potential critical effects and studies. This review describes the evidence considered in the MOA evaluations that were performed as part of the ARA effort. The overall conclusions of this evaluation are that the available mechanistic data do not support any conclusion that reported epidemiological associations of blood concentrations of PFOA as low as 10 ng/mL with various health effects should be considered causal. It is more likely that the reported associations may instead reflect reverse causality/pharmacokinetic confounding. These conclusions are consistent with the opinions of the World Health Organization (WHO, 2022).

Commentary: Understanding IARC's PFOA and PFOS carcinogenicity assessments

In November 2023, the International Agency for Research on Cancer (IARC) classified PFOA as "carcinogenic to humans" (Group 1) and PFOS as "possibly carcinogenic to humans" (Group 2B). We evaluated these classifications, considering the epidemiology, experimental animal, and mechanistic evidence. It is our opinion that the IARC Working Group overstated the available evidence for the carcinogenicity of PFOA and PFOS. Epidemiology studies have shown weak and inconsistent associations across studies. Studies reporting increased incidences of tumors in experimental animals exposed to PFOA or PFOS had statistically significant results that were driven by the presence of benign adenomas. The IARC Working Group used the key characteristics of carcinogens (KCCs, which comprise 10 chemical and/or biological properties of known human carcinogens) approach to upgrade the carcinogenicity classifications for PFOA and PFOS from initially lower classifications that were based on the strength of the epidemiology and experimental animal evidence. However, this is not a robust assessment of mechanistic evidence, as it fails to consider the quality, external validity, and relevance of the evidence. Rather than use the KCCs as a checklist of potential carcinogenic mechanisms, IARC should use a rigorous method to evaluate the plausibility and human relevance of mechanistic evidence.

Comprehensive analysis of adverse outcome pathway, potency, human exposure supports carcinogenicity of polyhexamethylene guanidine phosphate in lung cancer

In this study, we investigated the potential mechanisms by which polyhexamethylene guanidine phosphate (PHMG-p), a known respiratory irritant, may contribute to lung cancer development. Using the adverse outcome pathway (AOP) framework, we analyzed established databases (such as AOP-Wiki) and employed AI tools (AOP-helpFinder) to identify key events (KEs) associated with lung carcinogenesis. Our analysis indicates that chronic inhalation of PHMG-p triggers a non-genotoxic pathway, characterized by cell membrane disruption, inflammation, and oxidative stress, with a point of departure (POD) of 0.0018 mg/m³, suggesting carcinogenic potential. Additionally, a human exposure assessment revealed that most claimants were exposed to PHMG-p levels exceeding the estimated inhalation reference concentration (RfC) of 0.018 µg/m³. While downstream KEs, such as DNA damage, mutation, and cell proliferation, require further investigation, our findings, supported by the AOP framework and potency and exposure assessments, strongly suggest that PHMG-p exposure could induce lung cancer in individuals affected by humidifier disinfectants. These results underscore the importance of a comprehensive risk assessment approach for evaluating the carcinogenicity of PHMG-p.

Incorporating a weight-of-evidence approach into a tiered assessment for chemicals management, with emphasis on program development and applications in developing countries and emerging economies

A flexible approach is described for incorporating a weight-of-evidence (WoE) methodology into a tiered ecological risk assessment (ERA)/management framework for chemicals. The approach is oriented toward informing decisions about chemicals. Communication is regarded as a critical component of the risk assessment process. The paper resulted from insights gained from seven ERA workshops held by SETAC (Society of Environmental Toxicology and Chemistry, www.setac.org) in the Asia-Pacific, African, and Latin American regions. Formal ERA methods are not fully developed or applied in many of these countries and assessments often begin with tables of risk values and test methods from countries where ERA is already implemented. While appropriate and sometimes necessary, workshop participants had questions about the reliability and relevance of using this information for regionally specific ecosystems with different receptors, fate processes, and exposure characteristics. The idea that an assessment of reliability and relevance of available information and the need for additional information was necessary at an early stage of the assessment process was considered. The judgment of reliability and relevance is central to WoE approaches along with the identification of information needs and the integration of such information. The need to engage in WoE considerations early and throughout the assessment process indicates that a tiered approach is appropriate for unifying the evaluation process in a consistent way from early screening-level steps to later more involved evaluations. The approach outlined in this article is complementary to WoE guidance developed by the Organization for Economic Co-operation and Development and many national guidance documents. To link assessments of risk to management decisions, emphasis is given to communications at each tier between the risk assessor (technical side) and the decision-makers (policy and regulatory side). Tools and information sources are suggested for each tier and suggestions are meant to be illustrative and not prescriptive. Integr Environ Assess Manag 2024;20:2312-2325. © 2024 SETAC.

E-waste: mechanisms of toxicity and safety testing

Currently, information on the toxicity profile of the majority of the identified e-waste chemicals, while extensive and growing, is admittedly fragmentary, particularly at the cellular and molecular levels. Furthermore, the toxicity of the chemical mixtures likely to be encountered by humans during and after informal e-waste recycling, as well as their underlying mechanisms of action, is largely unknown. This review paper summarizes state-of-the-art knowledge of the potential underlying toxicity mechanisms associated with e-waste exposures, with a focus on toxic responses connected to specific organs, organ systems, and overall effects on the organism. To overcome the complexities associated with assessing the possible adverse outcomes from exposure to chemicals, a growing number of new approach methodologies have emerged in recent years, with the long-term objective of providing a human-based and animal-free system that is scientifically superior to animal testing, more effective, and acceptable. This encompasses a variety of techniques, typically regarded as alternative approaches for determining chemical-induced toxicities and holds greater promise for a better understanding of key events in the metabolic pathways that mediate known adverse health outcomes in e-waste exposure scenarios. This is crucial to establishing accurate scientific knowledge on mixed e-waste chemical exposures in shorter time frames and with greater efficacy, as well as supporting the need for safe management of hazardous chemicals. The present review paper discusses important gaps in knowledge and shows promising directions for mechanistically anchored effect-based monitoring strategies that will contribute to the advancement of the methods currently used in characterizing and monitoring e-waste-impacted ecosystems.

Endocrine disruption assessment in aquatic vertebrates - Identification of substance-induced thyroid-mediated effect patterns

According to the World Health Organisation and European Commission definitions, substances shall be considered as having endocrine disrupting properties if they show adverse effects, have endocrine activity and the adverse effects are a consequence of the endocrine activity (using a weight-of-evidence approach based on biological plausibility), unless the adverse effects are not relevant to humans or non-target organisms at the (sub)population level. To date, there is no decision logic on how to establish endocrine disruption via the thyroid modality in non-mammalian vertebrates. This paper describes an evidence-based decision logic compliant with the integrated approach to testing and assessment (IATA) concept, to identify thyroid-mediated effect patterns in aquatic vertebrates using amphibians as relevant models for thyroid disruption assessment. The decision logic includes existing test guidelines and methods and proposes detailed considerations on how to select relevant assays and interpret the findings. If the mammalian dataset used as the starting point indicates no thyroid concern, the Xenopus Eleutheroembryonic Thyroid Assay allows checking out thyroid-mediated activity in non-mammalian vertebrates, whereas the Amphibian Metamorphosis Assay or its extended, fixed termination stage variant inform on both thyroid-mediated activity and potentially population-relevant adversity. In evaluating findings, the response patterns of all assay endpoints are considered, including the direction of changes. Thyroid-mediated effect patterns identified at the individual level in the amphibian tests are followed by mode-of-action and population relevance assessments. Finally, all data are considered in an overarching weight-of-evidence evaluation. The logic has been designed generically and can be adapted, e.g. to accommodate fish tests once available for thyroid disruption assessments. It also ensures that all scientifically relevant information is considered, and that animal testing is minimised. The proposed decision logic can be included in regulatory assessments to facilitate the conclusion on whether substances meet the endocrine disruptor definition for the thyroid modality in non-mammalian vertebrates.

A UK framework for the assessment and integration of different scientific evidence streams in chemical risk assessment

BACKGROUND

Few methods are available for transparently combining different evidence streams for chemical risk assessment to reach an integrated conclusion on the probability of causation. Hence, the UK Committees on Toxicity (COT) and on Carcinogenicity (COC) have reviewed current practice and developed guidance on how to achieve this in a transparent manner, using graphical visualisation.

METHODS/APPROACH

All lines of evidence, including toxicological, epidemiological, new approach methodologies, and mode of action should be considered, taking account of their strengths/weaknesses in their relative weighting towards a conclusion on the probability of causation. A qualitative estimate of the probability of causation is plotted for each line of evidence and a combined estimate provided.

DISCUSSION/CONCLUSIONS

Guidance is provided on integration of multiple lines of evidence for causation, based on current best practice. Qualitative estimates of probability for each line of evidence are plotted graphically. This ensures a deliberative, consensus conclusion on likelihood of causation is reached. It also ensures clear communication of the influence of the different lines of evidence on the overall conclusion on causality. Issues on which advice from the respective Committees is sought varies considerably, hence the guidance is designed to be sufficiently flexible to meet this need.

Associations between Ethylene Oxide Exposure and Liver Function in the US Adult Population

BACKGROUND

Ethylene oxide, a reactive epoxy compound, has been widely used in various industries for many years. However, evidence of the combined toxic effects of ethylene oxide exposure on the liver is still lacking.

METHODS

We analyzed the merged data from the National Health and Nutrition Examination Survey (NHANES) from 2013 to 2016. Ultimately, 4141 adults aged 18 and over were selected as the sample. We used linear regression to explore the association between blood ethylene oxide and LFT indicators.

RESULTS

The weighted linear regression model showed that HbEO is positively correlated with ALP (β = 2.61, 95% CI 1.97, 3.24, p < 0.0001), GGT (β = 5.75, 95% CI 4.46, 7/05, p < 0.0001), ALT (β = 0.50, 95% CI 0.09, 0.90, p = 0.0158), and AST (β = 0.71, 95% CI 0.44, 0.98, p < 0.0001) and negatively correlated with TBIL (β = -0.30, 95% CI -0.43, -0.16, p < 0.0001).

CONCLUSIONS

Ethylene oxide exposure is significantly associated with changes in liver function indicators among adults in the United States. Future work should further examine these relationships.

Mode of action analysis for fluxapyroxad-induced rat liver tumour formation: evidence for activation of the constitutive androstane receptor and assessment of human relevance

The fungicide fluxapyroxad (BAS 700 F) has been shown to significantly increase the incidence of liver tumours in male Wistar rats at dietary levels of 1500 and 3000 ppm and in female rats at a dietary level of 3000 ppm via a non-genotoxic mechanism. In order to elucidate the mode of action (MOA) for fluxapyroxad-induced rat liver tumour formation a series of in vivo and in vitro investigative studies were undertaken. The treatment of male and female Wistar rats with diets containing 0 (control), 50, 250, 1500 and 3000 ppm fluxapyroxad for 1, 3, 7 and 14 days resulted in a dose-dependent increases in relative weight at 1500 and 3000 ppm from day 3 onwards in both sexes, with an increase in relative liver weight being also observed in male rats given 250 ppm fluxapyroxad for 14 days. Examination of liver sections revealed a centrilobular hepatocyte hypertrophy in some fluxapyroxad treated male and female rats. Hepatocyte replicative DNA synthesis (RDS) was significantly increased in male rats given 1500 and 3000 ppm fluxapyroxad for 3 and 7 days and in female rats given 50-3000 ppm fluxapyroxad for 7 days and 250-3000 ppm fluxapyroxad for 3 and 14 days; the maximal increases in RDS in both sexes being observed after 7 days treatment. The treatment of male and female Wistar rats with 250-3000 ppm fluxapyroxad for 14 days resulted in significant increases in hepatic microsomal total cytochrome P450 (CYP) content and CYP2B subfamily-dependent enzyme activities. Male Wistar rat hepatocytes were treated with control medium and medium containing 1-100 μM fluxapyroxad or 500 μM sodium phenobarbital (NaPB) for 4 days. Treatment with fluxapyroxad and NaPB increased CYP2B and CYP3A enzyme activities and mRNA levels but had little effect on markers of CYP1A and CYP4A subfamily enzymes and of the peroxisomal fatty acid β-oxidation cycle. Hepatocyte RDS was significantly increased by treatment with fluxapyroxad, NaPB and 25 ng/ml epidermal growth factor (EGF). The treatment of hepatocytes from two male human donors with 1-100 μM fluxapyroxad or 500 μM NaPB for 4 days resulted in some increases in CYP2B and CYP3A enzyme activities and CYP mRNA levels but had no effect on hepatocyte RDS, whereas treatment with EGF resulted in significant increase in RDS in both human hepatocyte preparations. Hepatocytes from male Sprague-Dawley wild type (WT) and constitutive androstane receptor (CAR) knockout (CAR KO) rats were treated with control medium and medium containing 1-16 μM fluxapyroxad or 500 μM NaPB for 4 days. While both fluxapyroxad and NaPB increased CYP2B enzyme activities and mRNA levels in WT hepatocytes, only minor effects were observed in CAR KO rat hepatocytes. Treatment with both fluxapyroxad and NaPB only increased RDS in WT and not in CAR KO rat hepatocytes, whereas treatment with EGF increased RDS in both WT and CAR KO rat hepatocytes. In conclusion, a series of in vivo and in vitro investigative studies have demonstrated that fluxapyroxad is a CAR activator in rat liver, with similar properties to the prototypical CAR activator phenobarbital. A robust MOA for fluxapyroxad-induced rat liver tumour formation has been established. Based on the lack of effect of fluxapyroxad on RDS in human hepatocytes, it is considered that the MOA for fluxapyroxad-induced liver tumour formation is qualitatively not plausible for humans.

Interspecies scaling of toxicity reference values in human health versus ecological risk assessments: A critical review

Risk assessments that focus on anthropogenic chemicals in environmental media-whether considering human health or ecological effects-often rely on toxicity data from experimentally studied species to estimate safe exposures for species that lack similar data. Current default extrapolation approaches used in both human health risk assessments and ecological risk assessments (ERAs) account for differences in body weight between the test organisms and the species of interest, but the two default approaches differ in important ways. Human health risk assessments currently employ a default based on body weight raised to the three-quarters power. Ecological risk assessments for wildlife (i.e., mammals and birds) are typically based directly on body weight, as measured in the test organism and receptor species. This review describes differences in the experimental data underlying these default practices and discusses the many factors that affect interspecies variability in chemical exposures. The interplay of these different factors can lead to substantial departures from default expectations. Alternative methodologies for conducting more accurate interspecies extrapolations in ERAs for wildlife are discussed, including tissue-based toxicity reference values, physiologically based toxicokinetic and/or toxicodynamic modeling, chemical read-across, and a system of categorical defaults based on route of exposure and toxic mode of action. Integr Environ Assess Manag 2024;20:749-764. © 2023 SETAC.

Evaluation of neural reflex activation as a potential mode of action for respiratory and cardiovascular effects of fine particulate matter

OBJECTIVES

Mortality from respiratory and cardiovascular health conditions contributes largely to the total mortality that has been associated with exposure to PM2.5 in epidemiology studies. A mode of action (MoA) for these underlying morbidities has not been established, but it has been proposed that some effects of PM2.5 occur through activation of neural reflexes.

MATERIALS AND METHODS

We critically reviewed the experimental studies of PM2.5 (including ambient PM2.5, diesel exhaust particles, concentrated ambient particles, diesel exhaust, and cigarette smoke) and neural reflex activation, and applied the principles of the International Programme on Chemical Safety (IPCS) MoA/human relevance framework to assess whether they support a biologically plausible and human-relevant MoA by which PM2.5 could contribute to cardiovascular and respiratory causes of death. We also considered whether the evidence from these studies supports a non-threshold MoA that operates at low, human-relevant PM2.5 exposure concentrations.

RESULTS AND DISCUSSION

We found that the proposed MoA of neural reflex activation is biologically plausible for PM2.5-induced respiratory effects at high exposure levels used in experimental studies, but further studies are needed to fill important data gaps regarding the relevance of this MoA to humans at lower PM2.5 exposure levels. A role for the proposed MoA in PM2.5-induced cardiovascular effects is plausible for some effects but not others.

CONCLUSIONS

Further studies are needed to determine whether neural reflex activation is the MoA by which PM2.5 could cause either respiratory or cardiovascular morbidities in humans, particularly at the ambient concentrations associated with total mortality in epidemiology studies.

European Food Safety Authority (EFSA), Crivellente F, Hernández‐Jerez AF, Lanzoni A, Metruccio F, Mohimont L, Nikolopoulou D, Castoldi AF. Specific effects on the thyroid relevant for performing a dietary cumulative risk assessment of pesticide residues: 2024 update

EFSA updated its previous work on the establishment of specific effects that are considered relevant for grouping pesticide residues targeting the thyroid and for performing the retrospective assessment of dietary cumulative risk (CRA). The two specific effects already selected in 2019 leading to the two cumulative assessment groups (CAGs) 'hypothyroidism' and 'C-cell hypertrophy, hyperplasia and neoplasia' were reconfirmed. Compared to 2019, the list of indicators that can be used to identify these specific effects was refined to only include histopathological changes. In a second phase of the work, data will be extracted on indicators of the specific effects from the dossiers on active substances (a.s.) used as plant protection products. The criteria for including a.s. into CAGs were also updated, together with the hazard characterisation methodology and the lines of evidence for assessing CAG-membership probabilities. The tasks related to the data extraction and the establishment of the CAGs on hypothyroidism and on C-cell hypertrophy, hyperplasia and neoplasia are beyond the scope of this report. This part of the CRA process has been outsourced and will be the subject of a separate report.

Ten years of using key characteristics of human carcinogens to organize and evaluate mechanistic evidence in IARC Monographs on the identification of carcinogenic hazards to humans: Patterns and associations

Systematic review and evaluation of mechanistic evidence using the Key Characteristics approach was proposed by the International Agency for Research on Cancer (IARC) in 2012 and used by the IARC Monographs Working Groups since 2015. Key Characteristics are 10 features of agents known to cause cancer in humans. From 2015 to 2022, a total of 19 Monographs (73 agents combined) used Key Characteristics for cancer hazard classification. We hypothesized that a retrospective analysis of applications of the Key Characteristics approach to cancer hazard classification using heterogenous mechanistic data on diverse agents would be informative for systematic reviews in decision-making. We extracted information on the conclusions, data types, and the role mechanistic data played in the cancer hazard classification from each Monograph. Statistical analyses identified patterns in the use of Key Characteristics, as well as trends and correlations among Key Characteristics, data types, and ultimate decisions. Despite gaps in data for many agents and Key Characteristics, several significant results emerged. Mechanistic data from in vivo animal, in vitro animal, and in vitro human studies were most impactful in concluding that an agent could cause cancer via a Key Characteristic. To exclude the involvement of a Key Characteristic, data from large-scale systematic in vitro testing programs such as ToxCast, were most informative. Overall, increased availability of systemized data streams, such as human in vitro data, would provide the basis for more confident and informed conclusions about both positive and negative associations and inform expert judgments on cancer hazard.

Procedural application of mode-of-action and human relevance analysis: styrene-induced lung tumors in mice

Risk assessment of human health hazards has traditionally relied on experiments that use animal models. Although exposure studies in rats and mice are a major basis for determining risk in many cases, observations made in animals do not always reflect health hazards in humans due to differences in biology. In this critical review, we use the mode-of-action (MOA) human relevance framework to assess the likelihood that bronchiolar lung tumors observed in mice chronically exposed to styrene represent a plausible tumor risk in humans. Using available datasets, we analyze the weight-of-evidence 1) that styrene-induced tumors in mice occur through a MOA based on metabolism of styrene by Cyp2F2; and 2) whether the hypothesized key event relationships are likely to occur in humans. This assessment describes how the five modified Hill causality considerations support that a Cyp2F2-dependent MOA causing lung tumors is active in mice, but only results in tumorigenicity in susceptible strains. Comparison of the key event relationships assessed in the mouse was compared to an analogous MOA hypothesis staged in the human lung. While some biological concordance was recognized between key events in mice and humans, the MOA as hypothesized in the mouse appears unlikely in humans due to quantitative differences in the metabolic capacity of the airways and qualitative uncertainties in the toxicological and prognostic concordance of pre-neoplastic and neoplastic lesions arising in either species. This analysis serves as a rigorous demonstration of the framework's utility in increasing transparency and consistency in evidence-based assessment of MOA hypotheses in toxicological models and determining relevance to human health.

SDHi fungicides: An example of mitotoxic pesticides targeting the succinate dehydrogenase complex

Succinate dehydrogenase inhibitors (SDHi) are fungicides used to control the proliferation of pathogenic fungi in crops. Their mode of action is based on blocking the activity of succinate dehydrogenase (SDH), a universal enzyme expressed by all species harboring mitochondria. The SDH is involved in two interconnected metabolic processes for energy production: the transfer of electrons in the mitochondrial respiratory chain and the oxidation of succinate to fumarate in the Krebs cycle. In humans, inherited SDH deficiencies may cause major pathologies including encephalopathies and cancers. The cellular and molecular mechanisms related to such genetic inactivation have been well described in neuroendocrine tumors, in which it induces an oxidative stress, a pseudohypoxic phenotype, a metabolic, epigenetic and transcriptomic remodeling, and alterations in the migration and invasion capacities of cancer cells, in connection with the accumulation of succinate, an oncometabolite, substrate of the SDH. We will discuss recent studies reporting toxic effects of SDHi in non-target organisms and their implications for risk assessment of pesticides. Recent data show that the SDH structure is highly conserved during evolution and that SDHi can inhibit SDH activity in mitochondria of non-target species, including humans. These observations suggest that SDHi are not specific inhibitors of fungal SDH. We hypothesize that SDHi could have toxic effects in other species, including humans. Moreover, the analysis of regulatory assessment reports shows that most SDHi induce tumors in animals without evidence of genotoxicity. Thus, these substances could have a non-genotoxic mechanism of carcinogenicity that still needs to be fully characterized and that could be related to SDH inhibition. The use of pesticides targeting mitochondrial enzymes encoded by tumor suppressor genes raises questions on the risk assessment framework of mitotoxic pesticides. The issue of SDHi fungicides is therefore a textbook case that highlights the urgent need for changes in regulatory assessment.

Ten Years of Using Key Characteristics of Human Carcinogens to Organize and Evaluate Mechanistic Evidence in IARC Monographs on the Identification of Carcinogenic Hazards to Humans: Patterns and Associations

Systematic review and evaluation of the mechanistic evidence only recently been instituted in cancer hazard identification step of decision-making. One example of organizing and evaluating mechanistic evidence is the Key Characteristics approach of the International Agency for Research on Cancer (IARC) Monographs on the Identification of Carcinogenic Hazards to Humans. The Key Characteristics of Human Carcinogens were proposed almost 10 years ago and have been used in every IARC Monograph since 2015. We investigated the patterns and associations in the use of Key Characteristics by the independent expert Working Groups. We examined 19 Monographs (2015-2022) that evaluated 73 agents. We extracted information on the conclusions by each Working Group on the strength of evidence for agent-Key Characteristic combinations, data types that were available for decisions, and the role mechanistic data played in the final cancer hazard classification. We conducted both descriptive and association analyses within and across data types. We found that IARC Working Groups were cautious when evaluating mechanistic evidence: for only ∼13% of the agents was strong evidence assigned for any Key Characteristic. Genotoxicity and cell proliferation were most data-rich, while little evidence was available for DNA repair and immortalization Key Characteristics. Analysis of the associations among Key Characteristics revealed that only chemical's metabolic activation was significantly co-occurring with genotoxicity and cell proliferation/death. Evidence from exposed humans was limited, while mechanistic evidence from rodent studies in vivo was often available. Only genotoxicity and cell proliferation/death were strongly associated with decisions on whether mechanistic data was impactful on the final cancer hazard classification. The practice of using the Key Characteristics approach is now well-established at IARC Monographs and other government agencies and the analyses presented herein will inform the future use of mechanistic evidence in regulatory decision-making.

Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny - Part IV: the ECETOC and CLE Proposal for a Thyroid Function-Related Neurodevelopmental Toxicity Testing and Assessment Scheme (Thyroid-NDT-TAS)

Following the European Commission Endocrine Disruptor Criteria, substances shall be considered as having endocrine disrupting properties if they (a) elicit adverse effects, (b) have endocrine activity, and (c) the two are linked by an endocrine mode-of-action (MoA) unless the MoA is not relevant for humans. A comprehensive, structured approach to assess whether substances meet the Endocrine Disruptor Criteria for the thyroid modality (EDC-T) is currently unavailable. Here, the European Centre for Ecotoxicology and Toxicology of Chemicals Thyroxine Task Force and CropLife Europe propose a Thyroid Function-Related Neurodevelopmental Toxicity Testing and Assessment Scheme (Thyroid-NDT-TAS). In Tier 0, before entering the Thyroid-NDT-TAS, all available in vivo, in vitro and in silico data are submitted to weight-of-evidence (WoE) evaluations to determine whether the substance of interest poses a concern for thyroid disruption. If so, Tier 1 of the Thyroid-NDT-TAS includes an initial MoA and human relevance assessment (structured by the key events of possibly relevant adverse outcome pathways) and the generation of supportive in vitro/in silico data, if relevant. Only if Tier 1 is inconclusive, Tier 2 involves higher-tier testing to generate further thyroid- and/or neurodevelopment-related data. Tier 3 includes the final MoA and human relevance assessment and an overarching WoE evaluation to draw a conclusion on whether, or not, the substance meets the EDC-T. The Thyroid-NDT-TAS is based on the state-of-the-science, and it has been developed to minimise animal testing. To make human safety assessments more accurate, it is recommended to apply the Thyroid-NDT-TAS during future regulatory assessments.

An Adverse Outcome Pathway Network for Chemically Induced Oxidative Stress Leading to (Non)genotoxic Carcinogenesis

Nongenotoxic (NGTX) carcinogens induce cancer via other mechanisms than direct DNA damage. A recognized mode of action for NGTX carcinogens is induction of oxidative stress, a state in which the amount of oxidants in a cell exceeds its antioxidant capacity, leading to regenerative proliferation. Currently, carcinogenicity assessment of environmental chemicals primarily relies on genetic toxicity end points. Since NGTX carcinogens lack genotoxic potential, these chemicals may remain undetected in such evaluations. To enhance the predictivity of test strategies for carcinogenicity assessment, a shift toward mechanism-based approaches is required. Here, we present an adverse outcome pathway (AOP) network for chemically induced oxidative stress leading to (NGTX) carcinogenesis. To develop this AOP network, we first investigated the role of oxidative stress in the various cancer hallmarks. Next, possible mechanisms for chemical induction of oxidative stress and the biological effects of oxidative damage to macromolecules were considered. This resulted in an AOP network, of which associated uncertainties were explored. Ultimately, development of AOP networks relevant for carcinogenesis in humans will aid the transition to a mechanism-based, human relevant carcinogenicity assessment that involves a substantially lower number of laboratory animals.

Evidential requirements for the regulatory hazard and risk assessment of respiratory sensitisers: methyl methacrylate as an example

This review addresses the need for a framework to increase the consistency, objectivity and transparency in the regulatory assessment of respiratory sensitisers and associated uncertainties. Principal issues are considered and illustrated through a case study (with methyl methacrylate). In the absence of test methods validated for regulatory use, formal documentation of the weight-of-evidence for hazard classification both at the level of integration of individual studies within lines of evidence and across a broad range of data streams was agreed to be critical for such a framework. An integrated approach is proposed to include not only occupational studies and clinical evidence for the regulatory assessment of respiratory sensitisers, but also information on structure and physical and chemical factors, predictive approaches such as structure activity analysis and in vitro and in vivo mechanistic and toxicokinetic findings. A weight-of-evidence protocol, incorporating integration of these sources of data based on predefined considerations, would contribute to transparency and consistency in the outcome of the assessment. In those cases where a decision may need to be taken on the basis of occupational findings alone, conclusions should be based on transparent weighting of relevant data on the observed prevalence of occupational asthma in various studies taking into account all relevant information including the range and nature of workplace exposures to the substance of interest, co-exposure to other chemicals and study quality.

Causal Criteria in Medical and Biological Disciplines: History, Essence, and Radiation Aspects. Report 4, Part 1: The Post-Hill Criteria and Ecolgoical Criteria

Part 1 of Report 4 is focused on the development and modifications of causal criteria after A.B. Hill (1965). Criteria from B. MacMahon et al. (1970-1996), regarded as the first textbook for modern epidemiology, were considered, and it was found that the named researchers did not offer anything new despite the frequent mention of this source in relation to the theme. A similar situation emerged with the criteria of M. Susser: the three obligatory points of this author, "Association" (or "Probability" of causality), "Time order," and "Direction of effect," are trivial, and two more special criteria, which are the development of "Popperian Epidemiology," i.e., "Surviability" of the hypothesis when it is tested by different methods (included in the refinement in Hill's criterion "Consistency of association") and "Predictive performance" of the hypothesis are more theoretical and hardly applicable for the practice of epidemiology and public health. The same restrictions apply to the similar "Popperian" criteria of D.L. Weed, "Predictability" and "Testability" of the causal hypothesis. Although the universal postulates of A.S. Evans for infectious and noninfectious pathologies can be considered exhaustive, they are not used either in epidemiology or in any other discipline practice, except for the field of infectious pathologies, which is probably explained by the complication of the ten-point complex. The little-known criteria of P. Cole (1997) for medical and forensic practice are the most important. The three parts of Hill's criterion-based approaches are important in that they go from a single epidemiological study through a cycle of studies (coupled with the integration of data from other biomedical disciplines) to re-base Hill's criteria for assessing the individual causality of an effect. These constructs complement the earlier guidance from R.E. Gots (1986) on establishing probabilistic personal causation. The collection of causal criteria and the guidelines for environmental disciplines (ecology of biota, human ecoepidemiology, and human ecotoxicology) were considered. The total dominance of inductive causal criteria, both initial and in modifications and with additions, was revealed for an apparently complete base of sources (1979-2020). Adaptations of all known causal schemes based on guidelines have been found, from Henle-Koch postulates to Hill and Susser, including in the international programs and practice of the U.S. Environmental Protection Agency. The Hill Criteria are used by the WHO and other organizations on chemical safety (IPCS) to assess causality in animal experiments for subsequent extrapolation to humans. Data on the assessment of the causality of effects in ecology, ecoepidemiology, and ecotoxicology, together with the use of Hill's criteria for animal experiments, are of significant relevance not only for radiation ecology, but also for radiobiology.

A Pragmatic Framework for the Application of New Approach Methodologies in One Health Toxicological Risk Assessment

Globally, industries and regulatory authorities are faced with an urgent need to assess the potential adverse effects of chemicals more efficiently by embracing new approach methodologies (NAMs). NAMs include cell and tissue methods (in vitro), structure-based/toxicokinetic models (in silico), methods that assess toxicant interactions with biological macromolecules (in chemico), and alternative models. Increasing knowledge on chemical toxicokinetics (what the body does with chemicals) and toxicodynamics (what the chemicals do with the body) obtained from in silico and in vitro systems continues to provide opportunities for modernizing chemical risk assessments. However, directly leveraging in vitro and in silico data for derivation of human health-based reference values has not received regulatory acceptance due to uncertainties in extrapolating NAM results to human populations, including metabolism, complex biological pathways, multiple exposures, interindividual susceptibility and vulnerable populations. The objective of this article is to provide a standardized pragmatic framework that applies integrated approaches with a focus on quantitative in vitro to in vivo extrapolation (QIVIVE) to extrapolate in vitro cellular exposures to human equivalent doses from which human reference values can be derived. The proposed framework intends to systematically account for the complexities in extrapolation and data interpretation to support sound human health safety decisions in diverse industrial sectors (food systems, cosmetics, industrial chemicals, pharmaceuticals etc.). Case studies of chemical entities, using new and existing data, are presented to demonstrate the utility of the proposed framework while highlighting potential sources of human population bias and uncertainty, and the importance of Good Method and Reporting Practices.

Updated systematic assessment of human, animal and mechanistic evidence demonstrates lack of human carcinogenicity with consumption of aspartame

Aspartame has been studied extensively and evaluated for its safety in foods and beverages yet concerns for its potential carcinogenicity have persisted, driven primarily by animal studies conducted at the Ramazzini Institute (RI). To address this controversy, an updated systematic review of available human, animal, and mechanistic data was conducted leveraging critical assessment tools to consider the quality and reliability of data. The evidence base includes 12 animal studies and >40 epidemiological studies reviewed by the World Health Organization which collectively demonstrate a lack of carcinogenic effect. Assessment of >1360 mechanistic endpoints, including many guideline-based genotoxicity studies, demonstrate a lack of activity associated with endpoints grouped to key characteristics of carcinogens. Other non-specific mechanistic data (e.g., mixed findings of oxidative stress across study models, tissues, and species) do not provide evidence of a biologically plausible carcinogenic pathway associated with aspartame. Taken together, available evidence supports that aspartame consumption is not carcinogenic in humans and that the inconsistent findings of the RI studies may be explained by flaws in study design and conduct (despite additional analyses to address study limitations), as acknowledged by authoritative bodies.

Application of AOPs to assist regulatory assessment of chemical risks - Case studies, needs and recommendations

While human regulatory risk assessment (RA) still largely relies on animal studies, new approach methodologies (NAMs) based on in vitro, in silico or non-mammalian alternative models are increasingly used to evaluate chemical hazards. Moreover, human epidemiological studies with biomarkers of effect (BoE) also play an invaluable role in identifying health effects associated with chemical exposures. To move towards the next generation risk assessment (NGRA), it is therefore crucial to establish bridges between NAMs and standard approaches, and to establish processes for increasing mechanistically-based biological plausibility in human studies. The Adverse Outcome Pathway (AOP) framework constitutes an important tool to address these needs but, despite a significant increase in knowledge and awareness, the use of AOPs in chemical RA remains limited. The objective of this paper is to address issues related to using AOPs in a regulatory context from various perspectives as it was discussed in a workshop organized within the European Union partnerships HBM4EU and PARC in spring 2022. The paper presents examples where the AOP framework has been proven useful for the human RA process, particularly in hazard prioritization and characterization, in integrated approaches to testing and assessment (IATA), and in the identification and validation of BoE in epidemiological studies. Nevertheless, several limitations were identified that hinder the optimal usability and acceptance of AOPs by the regulatory community including the lack of quantitative information on response-response relationships and of efficient ways to map chemical data (exposure and toxicity) onto AOPs. The paper summarizes suggestions, ongoing initiatives and third-party tools that may help to overcome these obstacles and thus assure better implementation of AOPs in the NGRA.

Data-driven learning of narcosis mode of action identifies a CNS transcriptional signature shared between whole organism Caenorhabditis elegans and a fish gill cell line

With the large numbers of man-made chemicals produced and released in the environment, there is a need to provide assessments on their potential effects on environmental safety and human health. Current regulatory frameworks rely on a mix of both hazard and risk-based approaches to make safety decisions, but the large number of chemicals in commerce combined with an increased need to conduct assessments in the absence of animal testing makes this increasingly challenging. This challenge is catalysing the use of more mechanistic knowledge in safety assessment from both in silico and in vitro approaches in the hope that this will increase confidence in being able to identify modes of action (MoA) for the chemicals in question. Here we approach this challenge by testing whether a functional genomics approach in C. elegans and in a fish cell line can identify molecular mechanisms underlying the effects of narcotics, and the effects of more specific acting toxicants. We show that narcosis affects the expression of neuronal genes associated with CNS function in C. elegans and in a fish cell line. Overall, we believe that our study provides an important step in developing mechanistically relevant biomarkers which can be used to screen for hazards, and which prevent the need for repeated animal or cross-species comparisons for each new chemical.

Towards achieving a modern science-based paradigm for agrochemical carcinogenicity assessment

The rodent cancer bioassay has been the standard approach to fulfill regulatory requirements for assessing human carcinogenic potential of agrochemicals, food additives, industrial chemicals, and pharmaceuticals. Decades of research have described the limitations of the rodent cancer bioassay leading to international initiatives to seek alternatives and establish approaches that modernize carcinogenicity assessment. Biologically relevant approaches can provide mechanistic information and increased efficiency for evaluating hazard and risk of chemical carcinogenicity to humans. The application of human-relevant mechanistic understanding to support new approaches to carcinogenicity assessment will be invaluable for regulatory decision-making. The present work outlines the challenges and opportunities that authorities should consider as they come together to build a roadmap that leads to global acceptance and incorporation of fit-for-purpose, scientifically defensible new approaches for human-relevant carcinogenicity assessment of agrochemicals.

Commentary: cumulative risk assessment of perfluoroalkyl carboxylic acids and perfluoralkyl sulfonic acids: what is the scientific support for deriving tolerable exposures by assembling 27 PFAS into 1 common assessment group?

This commentary proposes an approach to risk assessment of mixtures of per- and polyfluorinated alkyl substances (PFAS) as EFSA was tasked to derive a tolerable intake for a group of 27 PFAS. The 27 PFAS to be considered contain different functional groups and have widely variable physicochemical (PC) properties and toxicokinetics and thus should not treated as one group based on regulatory guidance for risk assessment of mixtures. The proposed approach to grouping is to split the 27 PFAS into two groups, perfluoroalkyl carboxylates and perfluoroalkyl sulfonates, and apply a relative potency factor approach (as proposed by RIVM) to obtain two separate group TDIs based on liver toxicity in rodents since liver toxicity is a sensitive response of rodents to PFAS. Short chain PFAS and other PFAS structures should not be included in the groups due to their low potency and rapid elimination. This approach is in better agreement with scientific and regulatory guidance for mixture risk assessment.

A Collaborative Initiative to Establish Genomic Biomarkers for Assessing Tumorigenic Potential to Reduce Reliance on Conventional Rodent Carcinogenicity Studies

There is growing recognition across broad sectors of the scientific community that use of genomic biomarkers has the potential to reduce the need for conventional rodent carcinogenicity studies of industrial chemicals, agrochemicals, and pharmaceuticals through a weight-of-evidence approach. These biomarkers fall into 2 major categories: (1) sets of gene transcripts that can identify distinct tumorigenic mechanisms of action; and (2) cancer driver gene mutations indicative of rapidly expanding growth-advantaged clonal cell populations. This call-to-action article describes a collaborative approach launched to develop and qualify biomarker gene expression panels that measure widely accepted molecular pathways linked to tumorigenesis and their activation levels to predict tumorigenic doses of chemicals from short-term exposures. Growing evidence suggests that application of such biomarker panels in short-term exposure rodent studies can identify both tumorigenic hazard and tumorigenic activation levels for chemical-induced carcinogenicity. In the future, this approach will be expanded to include methodologies examining mutations in key cancer driver gene mutation hotspots as biomarkers of both genotoxic and nongenotoxic chemical tumor risk. Analytical, technical, and biological validation studies of these complementary genomic tools are being undertaken by multisector and multidisciplinary collaborative teams within the Health and Environmental Sciences Institute. Success from these efforts will facilitate the transition from current heavy reliance on conventional 2-year rodent carcinogenicity studies to more rapid animal- and resource-sparing approaches for mechanism-based carcinogenicity evaluation supporting internal and regulatory decision-making.

Adverse Outcome Pathway for Antimicrobial Quaternary Ammonium Compounds

Quaternary ammonium compounds (QACs) or quats are a large class of antimicrobial chemicals used in households and institutions as sanitizers and disinfectants. These chemicals are utilized as food processing sanitizers, algicides, in the process of water treatment, and preservatives in cosmetics. The aim of this study was to determine an Adverse Outcome Pathway (AOP) whereby two widely used QACs, alkyl dimethyl benzyl ammonium chloride (ADBAC) and didecyl dimethyl ammonium chloride (DDAC), may result in respiratory tract and gastrointestinal tract effects. When inhaled or ingested, these QACs are incorporated into the epithelial cell membrane at the point of contact. With sufficient dosage, the epithelial membrane is disrupted, reducing its fluidity, and releasing cellular contents. Further, ADBAC and DDAC might disrupt mitochondrial functions leading to decreased ATP production. Both events might lead to cell death, either attributed to direct lysis, necrosis, or apoptosis. Pro-inflammatory mediators are recruited to the tissue, inducing inflammation, edema, and excess mucus production. The primary tissue-level adverse outcome is epithelial degeneration and dysplasia. Most important, no apparent metabolism or distribution is involved in QAC action. Based upon this knowledge, it is suggested to replace default Uncertainty Factors for risk assessments with a set of Data Derived Extrapolation Factors.

Concept for the Evaluation of Carcinogenic Substances in Population-Based Human Biomonitoring

The Human Biomonitoring (HBM) Commission at the German Environment Agency holds the opinion that for environmental carcinogens for which no exposure levels can be assumed and are harmless to health, health-based guidance values corresponding to the classical definition of the HBM-I or HBM-II value cannot be established. Therefore, only reference values have been derived so far for genotoxic carcinogens from exposure data of the general population or subpopulations. The concept presented here opens up the possibility of performing health risk assessments of carcinogenic substances in human biomonitoring, and thus goes decisively beyond the purely descriptive statistical reference value concept. Using the presented method, quantitative dose descriptors of internal exposure can be derived from those of external exposure, provided that sufficient toxicokinetic information is available. Dose descriptors of internal exposure then allow the simple estimate of additional lifetime cancer risks for measured biomarker concentrations or, conversely, of equivalent concentrations for selected risks, such as those considered as tolerable for the general population. HBM data of chronic exposures to genotoxic carcinogens can thus be used to assess the additional lifetime cancer risk referring to the general population and to justify and prioritize risk management measures.

Beyond pharmaceuticals: Fit-for-purpose new approach methodologies for environmental cardiotoxicity testing

Environmental factors play a substantial role in determining cardiovascular health, but data informing the risks presented by environmental toxicants is insufficient. In vitro new approach methodologies (NAMs) offer a promising approach with which to address the limitations of traditional in vivo and in vitro assays for assessing cardiotoxicity. Driven largely by the needs of pharmaceutical toxicity testing, considerable progress in developing NAMs for cardiotoxicity analysis has already been made. As the scientific and regulatory interest in NAMs for environmental chemicals continues to grow, a thorough understanding of the unique features of environmental cardiotoxicants and their associated cardiotoxicities is needed. Here, we review the key characteristics of as well as important regulatory and biological considerations for fit-for-purpose NAMs for environmental cardiotoxicity. By emphasizing the challenges and opportunities presented by NAMs for environmental cardiotoxicity we hope to accelerate their development, acceptance, and application.

Ecotoxicological impacts caused by high demand surfactants in Latin America and a technological and innovative perspective for their substitution

Nowadays, water pollution represents a great concern due to population growth, industrialization, and urbanization. Every day hazardous chemical products for humans and aquatic organisms are disposed of arbitrarily from homes and industries. Even though detergents are considered an essential market, there is evidence of environmental impacts caused by surfactants like nonylphenol ethoxylate (NPE) and linear alkylbenzene sulfonates (LAS). Regulations about maximum allowable concentrations in sewage, surface water, and drinking water are scarce or null, mostly in developing countries like Latin American countries. Therefore, this review explores these two common toxic surfactants (NPE and LAS) and proposes a technological, innovative, and ecological perspective on detergents. Also, it establishes a starting point for industries to minimize adverse effects on humans and environmental health caused by these compounds.

Quantification of Hepatocellular Mitoses in a Toxicological Study in Rats Using a Convolutional Neural Network

Convolutional neural networks (CNNs) have been recognized as valuable tools for rapid quantitative analysis of morphological changes in toxicologic histopathology. We have assessed the performance of CNN-based (Halo-AI) mitotic figure detection in hepatocytes in comparison with detection by pathologists. In addition, we compared with Ki-67 and 5-bromodesoxyuridin (BrdU) immunohistochemistry labeling indices (LIs) obtained by image analysis. Tissues were from an exploratory toxicity study with a glycogen synthase kinase-3 (GSK-3) inhibitor. Our investigations revealed that (1) the CNN achieved similarly accurate but faster results than pathologists, (2) results of mitotic figure detection were comparable to Ki-67 and BrdU LIs, and (3) data from different methods were only moderately correlated. The latter is likely related to differences in the cell cycle component captured by each method. This highlights the importance of considering the differences of the available methods upon selection. Also, the pharmacology of our test item acting as a GSK-3 inhibitor potentially reduced the correlation. We conclude that hepatocyte cell proliferation assessment by CNNs can have several advantages when compared with the current gold standard: it relieves the pathologist of tedious routine tasks and contributes to standardization of results; the CNN algorithm can be shared and iteratively improved; it can be performed on routine histological slides; it does not require an additional animal experiment and in this way can contribute to animal welfare according to the 3R principles.

Rethinking chronic toxicity and carcinogenicity assessment for agrochemicals project (ReCAAP): A reporting framework to support a weight of evidence safety assessment without long-term rodent bioassays

Rodent cancer bioassays have been long-required studies for regulatory assessment of human cancer hazard and risk. These studies use hundreds of animals, are resource intensive, and certain aspects of these studies have limited human relevance. The past 10 years have seen an exponential growth of new technologies with the potential to effectively evaluate human cancer hazard and risk while reducing, refining, or replacing animal use. To streamline and facilitate uptake of new technologies, a workgroup comprised of scientists from government, academia, non-governmental organizations, and industry stakeholders developed a framework for waiver rationales of rodent cancer bioassays for consideration in agrochemical safety assessment. The workgroup used an iterative approach, incorporating regulatory agency feedback, and identifying critical information to be considered in a risk assessment-based weight of evidence determination of the need for rodent cancer bioassays. The reporting framework described herein was developed to support a chronic toxicity and carcinogenicity study waiver rationale, which includes information on use pattern(s), exposure scenario(s), pesticidal mode-of-action, physicochemical properties, metabolism, toxicokinetics, toxicological data including mechanistic data, and chemical read-across from similar registered pesticides. The framework could also be applied to endpoints other than chronic toxicity and carcinogenicity, and for chemicals other than agrochemicals.

Evaluation of the human hazard of the liver and lung tumors in mice treated with permethrin based on mode of action

The non-genotoxic synthetic pyrethroid insecticide permethrin produced hepatocellular adenomas and bronchiolo-alveolar adenomas in female CD-1 mice, but not in male CD-1 mice or in female or male Wistar rats. Studies were performed to evaluate possible modes of action (MOAs) for permethrin-induced female CD-1 mouse liver and lung tumor formation. The MOA for liver tumor formation by permethrin involves activation of the peroxisome proliferator-activated receptor alpha (PPARα), increased hepatocellular proliferation, development of altered hepatic foci, and ultimately liver tumors. This MOA is similar to that established for other PPARα activators and is considered to be qualitatively not plausible for humans. The MOA for lung tumor formation by permethrin involves interaction with Club cells, followed by a mitogenic effect resulting in Club cell proliferation, with prolonged administration producing Club cell hyperplasia and subsequently formation of bronchiolo-alveolar adenomas. Although the possibility that permethrin exposure may potentially result in enhancement of Club cell proliferation in humans cannot be completely excluded, there is sufficient information on differences in basic lung anatomy, physiology, metabolism, and biologic behavior of tumors in the general literature to conclude that humans are quantitatively less sensitive to agents that increase Club cell proliferation and lead to tumor formation in mice. The evidence strongly indicates that Club cell mitogens are not likely to lead to increased susceptibility to lung tumor development in humans. Overall, based on MOA evaluation it is concluded that permethrin does not pose a tumorigenic hazard for humans, this conclusion being supported by negative data from permethrin epidemiological studies.

Beyond AOPs: A Mechanistic Evaluation of NAMs in DART Testing

New Approach Methodologies (NAMs) promise to offer a unique opportunity to enable human-relevant safety decisions to be made without the need for animal testing in the context of exposure-driven Next Generation Risk Assessment (NGRA). Protecting human health against the potential effects a chemical may have on embryo-foetal development and/or aspects of reproductive biology using NGRA is particularly challenging. These are not single endpoint or health effects and risk assessments have traditionally relied on data from Developmental and Reproductive Toxicity (DART) tests in animals. There are numerous Adverse Outcome Pathways (AOPs) that can lead to DART, which means defining and developing strict testing strategies for every AOP, to predict apical outcomes, is neither a tenable goal nor a necessity to ensure NAM-based safety assessments are fit-for-purpose. Instead, a pragmatic approach is needed that uses the available knowledge and data to ensure NAM-based exposure-led safety assessments are sufficiently protective. To this end, the mechanistic and biological coverage of existing NAMs for DART were assessed and gaps to be addressed were identified, allowing the development of an approach that relies on generating data relevant to the overall mechanisms involved in human reproduction and embryo-foetal development. Using the knowledge of cellular processes and signalling pathways underlying the key stages in reproduction and development, we have developed a broad outline of endpoints informative of DART. When the existing NAMs were compared against this outline to determine whether they provide comprehensive coverage when integrated in a framework, we found them to generally cover the reproductive and developmental processes underlying the traditionally evaluated apical endpoint studies. The application of this safety assessment framework is illustrated using an exposure-led case study.

Towards a qAOP framework for predictive toxicology - Linking data to decisions

The adverse outcome pathway (AOP) is a conceptual construct that facilitates organisation and interpretation of mechanistic data representing multiple biological levels and deriving from a range of methodological approaches including in silico, in vitro and in vivo assays. AOPs are playing an increasingly important role in the chemical safety assessment paradigm and quantification of AOPs is an important step towards a more reliable prediction of chemically induced adverse effects. Modelling methodologies require the identification, extraction and use of reliable data and information to support the inclusion of quantitative considerations in AOP development. An extensive and growing range of digital resources are available to support the modelling of quantitative AOPs, providing a wide range of information, but also requiring guidance for their practical application. A framework for qAOP development is proposed based on feedback from a group of experts and three qAOP case studies. The proposed framework provides a harmonised approach for both regulators and scientists working in this area.

Evaluation of human relevance of Nicofluprole-induced rat thyroid disruption

Nicofluprole is a novel insecticide of the phenylpyrazole class conferring selective antagonistic activity on insect GABA receptors. After repeated daily dietary administration to Wistar rats for 28/90 days, Nicofluprole induced increases in thyroid (and liver) weight, associated with histopathology changes. Nicofluprole did not inhibit thyroid peroxydase nor sodium/iodide symporter, two key players in the biosynthesis of thyroid hormones, indicating the absence of a direct thyroid effect. The results seen in rats suggested a mode of action of Nicofluprole driven by the molecular initiating event of CAR/PXR nuclear receptor activation in livers, with key events of increases in liver weight and hypertrophy, decreasing circulatory thyroid hormones, a compensatory increase in TSH release and follicular cell hypertrophy. To explore the relevance of these changes to humans, well established in vitro rat and human sandwich-cultured hepatocytes were exposed to Nicofluprole up to 7 days. A concentration-dependent CYP3A induction (PXR-activation), an increase in T4-glucuronoconjugation accompanied by UGT1A/2B inductions was observed in rat but not in human hepatocytes. The inductions seen with Nicofluprole in rat (in vivo and in vitro in hepatocytes) that were absent in human hepatocytes represent another example of species-selectivity of nuclear CAR/PXR receptor activators. Importantly, the different pattern observed in rat and human models demonstrate that Nicofluprole-related thyroid effects observed in the rat are with no human relevance.

EFSA Scientific Committee, More SJ, Bampidis V, Benford D, Bragard C, Hernandez‐Jerez A, Bennekou SH, Halldorsson TI, Koutsoumanis KP, Lambré C, Machera K, Naegeli H, Nielsen SS, Schlatter JR, Schrenk D, Silano V, Turck D, Younes M, Benfenati E, Crépet A, Te Biesebeek JD, Testai E, Dujardin B, Dorne JLCM, Hogstrand C. Guidance Document on Scientific criteria for grouping chemicals into assessment groups for human risk assessment of combined exposure to multiple chemicals

This guidance document provides harmonised and flexible methodologies to apply scientific criteria and prioritisation methods for grouping chemicals into assessment groups for human risk assessment of combined exposure to multiple chemicals. In the context of EFSA's risk assessments, the problem formulation step defines the chemicals to be assessed in the terms of reference usually through regulatory criteria often set by risk managers based on legislative requirements. Scientific criteria such as hazard-driven criteria can be used to group these chemicals into assessment groups. In this guidance document, a framework is proposed to apply hazard-driven criteria for grouping of chemicals into assessment groups using mechanistic information on toxicity as the gold standard where available (i.e. common mode of action or adverse outcome pathway) through a structured weight of evidence approach. However, when such mechanistic data are not available, grouping may be performed using a common adverse outcome. Toxicokinetic data can also be useful for grouping, particularly when metabolism information is available for a class of compounds and common toxicologically relevant metabolites are shared. In addition, prioritisation methods provide means to identify low-priority chemicals and reduce the number of chemicals in an assessment group. Prioritisation methods include combined risk-based approaches, risk-based approaches for single chemicals and exposure-driven approaches. Case studies have been provided to illustrate the practical application of hazard-driven criteria and the use of prioritisation methods for grouping of chemicals in assessment groups. Recommendations for future work are discussed.

Club Cells Are the Primary Target for Permethrin-Induced Mouse Lung Tumor Formation

Permethrin has been shown to increase lung adenomas in female CD-1 mice, but not in male mice or Wistar rats. The proposed mode of action (MOA) for permethrin-induced female mouse lung tumor formation involves morphological changes in Club cells; increased Club cell proliferation; increased Club cell hyperplasia, and lung tumor formation. In this study, the treatment of female CD-1 mice with tumorigenic doses (2500 and 5000 ppm) of permethrin, but not with a nontumorigenic dose (20 ppm), for 14 and/or 28 days increased Club cell replicative DNA synthesis. Global gene expression analysis of female mouse lung samples demonstrated that permethrin treatment up-regulated 3 genes associated with cell proliferation, namely aldehyde dehydrogenase 3a1 (Aldh3a1), oxidative stress-induced growth inhibitor 1, and thioredoxin reductase 1. Treatment with 2500 and 5000 ppm, but not 20 ppm, permethrin for 7 days produced significant increases in mRNA levels of these 3 genes. Immunohistochemical analysis demonstrated that Club cell secretory protein, CYP2F2, and ALDH3A1 colocalized in Club cells; confirmed by flow cytometry analysis of lung cells employing KI67 as a cell proliferation marker. Overall, the present data extend the proposed MOA by demonstrating that Club cells are the primary initial target of permethrin administration in female mouse lungs. As humans are quantitatively much less sensitive to agents that increase Club cell proliferation and lung tumor formation in mice, it is most likely that permethrin could not produce lung tumors in humans. This conclusion is supported by available negative epidemiological data from several studies.