Harmonized Cross-Species Assessment of Endocrine and Metabolic Disruptors by Ecotox FACTORIAL Assay

Nuclear hormone receptors control fundamental processes of human fetal neurodevelopment: Basis for endocrine disruption assessment

Despite growing awareness of endocrine disrupting chemicals (EDCs), knowledge gaps remain regarding their effects on human brain development. EDC risk assessment focuses primarily on EATS modalities (estrogens, androgens, thyroid hormones, and steroidogenesis), overlooking the broader range of hormone receptors expressed in the developing brain. This limits the evaluation of chemicals for their potential to cause endocrine disruption-mediated developmental neurotoxicity (ED-DNT). The Neurosphere Assay, an in vitro test method for developmental neurotoxicity (DNT) evaluation, is an integral component of the DNT in vitro testing battery, which has been used to screen a broad domain of environmental chemicals. Here, we define the endocrine-related applicability domain of the Neurosphere Assay by assessing the impact and specificity of 14 hormone receptors on seven key neurodevelopmental processes (KNDPs), neural progenitor cell (NPC) proliferation, migration of radial glia, neurons, and oligodendrocytes, neurite outgrowth, and differentiation of neurons and oligodendrocytes. Comparative analyses in human and rat NPCs of both sexes revealed species- and sex-specific responses. Mechanistic insights were obtained through RNA sequencing and agonist/antagonist co-exposures. Most receptor agonists modulated KNDPs at concentrations in the range of physiologically relevant hormone concentrations. Phenotypic effects induced by glucocorticoid receptor (GR), liver X receptor (LXR), peroxisome proliferator-activated receptor beta/delta (PPARβδ), retinoic acid receptor (RAR) and retinoid X receptor (RXR) activation were counteracted by receptor antagonists, confirming specificity. Transcriptomics highlighted receptor crosstalk and the involvement of conserved developmental pathways (e.g. Notch and Wnt). Species comparisons identified limited concordance in hormone receptor-regulated KNDPs between human and rat NPCs. This study presents novel findings on cellular and molecular hormone actions in human fetal NPCs, highlights major species differences, and illustrates the Neurosphere Assay's relevance for detecting endocrine MoAs, supporting its application in human-based ED-DNT risk assessment.

Burnt Plastic (Pyroplastic) from the M/V X-Press Pearl Ship Fire and Plastic Spill Contain Compounds That Activate Endocrine and Metabolism-Related Human and Fish Transcription Factors

In May 2021, the M/V X-Press Pearl ship fire disaster led to the largest maritime spill of resin pellets (nurdles) and burnt plastic (pyroplastic). Field samples collected from beaches in Sri Lanka nearest to the ship comprised nurdles and pieces of pyroplastic. Three years later, the toxicity of the spilled material remains unresolved. To begin understanding its potential toxicity, solvent extracts of the nurdles and pyroplastic were screened for their bioactivity by several Attagene FACTORIAL bioassays (TF, NR, and AquaTox), which measured the activity of a combined 70 human transcription factor response elements and nuclear receptors and 6 to 7 nuclear receptors for each of three phylogenetically distinct fish species. Extracts of the pyroplastics robustly activated end points for the human aryl hydrocarbon receptor (AhR), estrogen receptor (ER), pregnane X receptor (PXR), peroxisome proliferator-activated receptor (PPAR), retinoid X receptor (RXR), and oxidative stress (NRF2) and had the potential for activation of several others. The bioactivity profile of the pyroplastics was most similar (similarity score = 0.96) to that of probable human carcinogens benzo[b]fluoranthene and benzo[k]fluoranthene despite the extracts being a complex mixture of thousands of compounds. The activity diminished only slightly for extracts of pyroplastic collected eight months after the spill. The AquaTox FACTORIAL bioassay measured the activation of ERα, ERβ, androgen receptor (AR), PPARα, PPARγ, and RXRβ for human, zebrafish (Danio rerio), Japanese medaka (Oryzias latipes), and rainbow trout (Oncorhynchus mykiss), revealing species-specific sensitivities to the chemicals associated with the pyroplastics. These findings provide needed information to guide long-term monitoring efforts, make hazard assessments of the spilled material, and direct further research on pyroplastic, an emerging global contaminant.

A 2024 inventory of test methods relevant to thyroid hormone system disruption for human health and environmental regulatory hazard assessment

Thyroid hormone system disruption (THSD) is a growing concern in chemical hazard assessment due to its impact on human and environmental health and the scarce methods available for assessing the THSD potential of chemicals. In particular, the general lack of validated in silico and in vitro methods for assessing THS activity is of high concern. This manuscript provides an inventory of test methods relevant to THSD. Building on the Organisation for Economic Co-operation and Development (OECD) Guidance Document 150 and recent international developments, we highlight progress in in silico and in vitro methods, as well as in vivo assays. The provided inventory categorizes available methods according to the levels of the OECD Conceptual Framework, with an assessment of the validation status of each method. At Level 1, 12 in silico models that have been statistically validated and are directly related to THSD have been identified. At Level 2, 67 in vitro methods have been listed including those assessed in key initiatives such as the European Union Network of Laboratories for the Validation of Alternative Methods (EU-NETVAL) validation study to identify potential thyroid disruptors. At Levels 3-5, THSD-sensitive endpoints are being included in existing fish-based OECD Test Guidelines to complement amphibian assays. In total, the inventory counts 108 entries comprising established methods (e.g., OECD Test Guidelines) as well as citable methods that are under further development and in some cases are ready for validation or in the initial stages of validation. This work aims to support the ongoing development of strategies for regulatory hazard assessment, such as integrated approaches to testing and assessment (IATAs), for endocrine disruptors, addressing critical gaps in the current testing landscape for THSD in both human and environmental health contexts.

Human and fish differences in steroid receptors activation: A review

Steroid receptors (SRs) are transcription factors activated by steroid hormones (SHs) that belong to the nuclear receptors (NRs) superfamily. Several studies have shown that SRs are targets of endocrine disrupting chemicals (EDCs), widespread substances in the environment capable of interfering with the endogenous hormonal pathways and causing adverse health effects in living organisms and/or their progeny. Cell lines with SRs reporter gene are currently used for in vitro screening of large quantities of chemicals with suspected endocrine-disrupting activities. However, most of these cell lines express human SRs and therefore the toxicological data obtained are also extrapolated to non-mammalian species. In parallel, in vivo tests have recently been developed on fish species whose data are also extrapolated to mammalian species. As some species-specific differences in SRs activation by natural and synthetic chemicals have been recently reported, the aim of this review is to summarize those between human and fish SRs, as representatives of mammalian and non-mammalian toxicology, respectively. Overall, this literature study aims to improve inter-species extrapolation of toxicological data on EDCs and to understand which reporter gene cell lines expressing human SRs are relevant for the assessment of effects in fish and whether in vivo tests on fish can be properly used in the assessment of adverse effects on human health.

Linking Mechanistic Effects of Pharmaceuticals and Personal Care Products to Ecologically Relevant Outcomes: A Decade of Progress

There are insufficient toxicity data to assess the ecological risks of many pharmaceuticals and personal care products (PPCPs). While data limitations are not uncommon for contaminants of environmental concern, PPCPs are somewhat unique in that an a priori understanding of their biological activities in conjunction with measurements of molecular, biochemical, or histological responses could provide a foundation for understanding mode(s) of action and predicting potential adverse apical effects. Over the past decade significant progress has been made in the development of new approach methodologies (NAMs) to efficiently quantify these types of endpoints using computational models and pathway-based in vitro and in vivo assays. The availability of open-access knowledgebases to curate biological response (including NAM) data and sophisticated bioinformatics tools to help interpret the information also has significantly increased. Finally, advances in the development and implementation of the adverse outcome pathway framework provide the critical conceptual underpinnings needed to translate NAM data into predictions of the ecologically relevant outcomes required by risk assessors and managers. The evolution and convergence of these various data streams, tools, and concepts provides the basis for a fundamental change in how ecological risks of PPCPs can be pragmatically assessed. Environ Toxicol Chem 2024;43:537-548. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Weight of evidence for cross-species conservation of androgen receptor-based biological activity

The U.S. Environmental Protection Agency's Endocrine Disruptor Screening Program (EDSP) is tasked with assessing chemicals for their potential to perturb endocrine pathways, including those controlled by androgen receptor (AR). To address challenges associated with traditional testing strategies, EDSP is considering in vitro high-throughput screening assays to screen and prioritize chemicals more efficiently. The ability of these assays to accurately reflect chemical interactions in nonmammalian species remains uncertain. Therefore, a goal of the EDSP is to evaluate how broadly results can be extrapolated across taxa. To assess the cross-species conservation of AR-modulated pathways, computational analyses and systematic literature review approaches were used to conduct a comprehensive analysis of existing in silico, in vitro, and in vivo data. First, molecular target conservation was assessed across 585 diverse species based on the structural similarity of ARs. These results indicate that ARs are conserved across vertebrates and are predicted to share similarly susceptibility to chemicals that interact with the human AR. Systematic analysis of over 5000 published manuscripts was used to compile in vitro and in vivo cross-species toxicity data. Assessment of in vitro data indicates conservation of responses occurs across vertebrate ARs, with potential differences in sensitivity. Similarly, in vivo data indicate strong conservation of the AR signaling pathways across vertebrate species, although sensitivity may vary. Overall, this study demonstrates a framework for utilizing bioinformatics and existing data to build weight of evidence for cross-species extrapolation and provides a technical basis for extrapolating hAR-based data to prioritize hazard in nonmammalian vertebrate species.

Cross-species comparison of chemical inhibition of human and Xenopus iodotyrosine deiodinase

The transition to include in vitro-based data in chemical hazard assessment has resulted in the development and implementation of screening assays to cover a diversity of biological pathways, including recently added assays to interrogate chemical disruption of proteins relevant to thyroid signaling pathways. Iodotyrosine deiodinase (IYD), the iodide recycling enzyme, is one such thyroid-relevant endpoint for which a human-based screening assay has recently been developed and used to screen large libraries of chemicals. Presented here is the development of an amphibian IYD inhibition assay and its implementation to conduct a cross-species comparison between chemical inhibition of mammalian and non-mammalian IYD enzyme activity. The successful development of an amphibian IYD inhibition assay was based on demonstration of sufficient IYD enzyme activity in several tissues collected from larval Xenopus laevis. With this new assay, 154 chemicals were tested in concentration-response to provide a basis for comparison of relative chemical potency to results obtained from the human IYD assay. Most chemicals exhibited similar inhibition in both assays, with less than 25% variation in median inhibition for 120 of 154 chemicals and 85% concordance in categorization of "active" (potential IYD inhibitor) versus "inactive". For chemicals that produced 50% or greater inhibition in both assays, rank-order potency was similar, with the majority of the IC50s varying by less than 2-fold (and all within an order of magnitude). Most differences resulted from greater maximum inhibition or higher chemical potency observed with human IYD. This strong cross-species agreement suggests that results from the human-based assay would be conservatively predictive of chemical effects on amphibian IYD.

Evaluation of a multiplexed, multispecies nuclear receptor assay for chemical hazard assessment

Sensitivity to potential endocrine disrupting chemicals in the environment varies across species and is influenced by sequence conservation of their nuclear receptor targets. Here, we evaluated a multiplexed, in vitro assay testing receptors relevant to endocrine and metabolic disruption from five species. The TRANS-FACTORIAL™ system of human nuclear receptors was modified to include additional species: mouse (Mus musculus), frog (Xenopus laevis), zebrafish (Danio rerio), chicken (Gallus gallus), and turtle (Chrysemys picta). Receptors regulating endocrine function and xenobiotic recognition were included, specifically: ERα, ERβ, AR, TRα, TRβ, PPARγ and PXR. The assay, ECOTOX-FACTORIAL™, was evaluated with 191 chemicals enriched with known receptor ligands. Hierarchical clustering of potency values demonstrated strong coherence of receptor families. Interspecies comparisons of responses within a receptor family showed moderate to high concordance for potencies under 50 μM. PPARγ showed high concordance between mammalian species, 89%, but only 63% between mammalian and zebrafish. For chemicals with potencies below 1 μM, concordances were 89-100% for all receptors except PXR. Concordance showed a strong positive relationship to ligand-binding domain sequence similarity and critical amino acid residues obtained by the Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) tool. In combination with SeqAPASS, ECOTOX-FACTORIAL may provide efficient screening of important receptors to identify species of high priority for effects monitoring.