Adverse Outcome Pathway (AOP) Coaching Program-How it functions and contributes to a more harmonized approach to AOP development and construction of AOP networks with regulatory utility.

The Adverse Outcome Pathway (AOP) framework contributes to understanding how specific and measurable biological perturbations cause adverse effects on human and environmental health. Recognizing the value of AOPs to support regulatory decisions around the world, the Organisation for Economic Co-operation and Development (OECD) launched the AOP Programme in 2012, which sought to promote and guide the development of AOPs to ensure their suitability for the downstream applications in the context of regulatory safety assessment. OECD published the initial guidance on AOP development and assessment in 2013, which has been expanded as practices have evolved and matured.

Avian-Specific Evidence for an Estrogen Receptor Agonism Adverse Outcome Pathway Based on Chicken Embryos and LMH 3D Spheroids Exposed to Ethinylestradiol and Bisphenol A.

Several adverse outcome pathways (AOPs) describe the effects of endocrine disrupting compounds on estrogen signaling. Substantial data support an AOP related to estrogen receptor (ER) antagonism, leading to decreased fecundity in fish. In this study, data were generated for an ER agonism AOP leading to reduced fecundity in avian species (AOP537).

Gene Set Enrichment Analysis in Zebrafish Embryos Is Susceptible to False-Positive Results in the Absence of Differentially Expressed Genes.

High-throughput gene expression studies commonly employ pathway analyses to infer biological meaning from lists of differentially expressed genes (DEGs). In toxicology and pharmacology studies, treatment groups are analysed against vehicle controls to identify DEGs and altered pathways. Previously, we empirically quantified false-positive rates of DEGs in gene expression data from pools of vehicle-treated zebrafish embryos to determine appropriate study designs (sample and pool size).

Development and characterization of a double-crested cormorant hepatic cell line, DCH22, for chemical screening.

There are currently no available cell lines for the ecologically relevant colonial waterbird species, the double-crested cormorant (DCCO). DCCOs are high trophic level aquatic birds that are used for routine contaminant monitoring programs in the Laurentian Great Lakes and marine coasts of Canada. Developing a DCCO cell line for toxicological screening will ideally provide improved understanding of the effects of environmental chemicals given the large differences in sensitivity between laboratory and wild avian species.

Comparison of gene expression and polycyclic aromatic compound profiles in hepatic tissue of black guillemot (Cepphus grylle) collected from an oil spill site and a non-spill site in the Arctic.

Economic development, marine transportation, and oil exploration are all activities that are increasing in the Arctic region, and there is concern regarding increased oil-related contaminants entering this sensitive environment. Polycyclic aromatic compounds (PACs) are the main chemical constituents in oil-related contaminants and have been detected in wildlife species following both acute and chronic exposure. In 2020, an oil spill occurred in Kaikopok Bay near Postville, NL, Canada.

Association of Hepatic Gene Expression with Chemical Concentrations in Wild-Collected Double-Crested Cormorant Embryos using an EcoToxChip Gene Array.

Contaminant monitoring programs use wild bird eggs, but determining whether measured concentrations elicit adverse effects relies on extrapolation from toxicity studies with avian model species. Here, we directly evaluated the relationships between whole embryo contaminant concentrations and mRNA expression in liver tissue of the double-crested cormorant (). Eggs collected from three North American sites (one from Lake Erie and two from the Salish Sea) were artificially incubated until pipping.

Bioinformatic workflows for deriving transcriptomic points of departure: current status, data gaps, and research priorities.

There is a pressing need to increase the efficiency and reliability of toxicological safety assessment for protecting human health and the environment. Although conventional toxicology tests rely on measuring apical changes in vertebrate models, there is increasing interest in the use of molecular information from animal and in vitro studies to inform safety assessment. One promising and pragmatic application of molecular information involves the derivation of transcriptomic points of departure (tPODs).

Contribution of emissions from the oil sands activities in Alberta, Canada to atmospheric concentration and deposition of nitrogen and sulfur species at a downwind site.

Oil sands activities in the Athabasca Oil Sands Region in Alberta, Canada, are large sources of atmospheric NO and SO. This study investigated the impact of oil sands emissions on the atmospheric deposition of nitrogen and sulfur species at a downwind site, about 350 km from the oil sands facilities. Measurement data are from the Canadian Air and Precipitation Monitoring Network (CAPMoN) from 2015 to 2019, including ambient concentrations of HNO, pNO, NO, pNH, NH, SO, pSO and base cations, as well as concentrations of NO, SO, NH, and base cations in precipitation.

Transcriptomic point of departure determination: a comparison of distribution-based and gene set-based approaches.

A key step in assessing the potential human and environmental health risks of industrial and agricultural chemicals is to determine the toxicity point of departure (POD), which is the highest dose level that causes no adverse effect. Transcriptomic POD (tPOD) values have been suggested to accurately estimate toxicity POD values. One step in the most common approach for tPOD determination involves mapping genes to annotated gene sets, a process that might lead to substantial information loss particularly in species with poor gene annotation.

Empirical Characterization of False Discovery Rates of Differentially Expressed Genes and Transcriptomic Benchmark Concentrations in Zebrafish Embryos.

High-throughput transcriptomics (HTTr) is increasingly applied to zebrafish embryos to survey the toxicological effects of environmental chemicals. Before the adoption of this approach in regulatory testing, it is essential to characterize background noise in order to guide experimental designs. We thus empirically quantified the HTTr false discovery rate (FDR) across different embryo pool sizes, sample sizes, and concentration groups for toxicology studies.

Wildlife ecological risk assessment in the 21st century: Promising technologies to assess toxicological effects.

Despite advances in toxicity testing and the development of new approach methodologies (NAMs) for hazard assessment, the ecological risk assessment (ERA) framework for terrestrial wildlife (i.e., air-breathing amphibians, reptiles, birds, and mammals) has remained unchanged for decades.

Cross-species applicability of an adverse outcome pathway network for thyroid hormone system disruption.

Thyroid hormone system disrupting compounds are considered potential threats for human and environmental health. Multiple adverse outcome pathways (AOPs) for thyroid hormone system disruption (THSD) are being developed in different taxa. Combining these AOPs results in a cross-species AOP network for THSD which may provide an evidence-based foundation for extrapolating THSD data across vertebrate species and bridging the gap between human and environmental health.

Accounting for Non-Detects: Application to Satellite Ammonia Observations.

Presented is a methodology to explicitly identify and account for cloud-free satellite measurements below a sensor's measurement detection level. These low signals can often be found in satellite observations of minor atmospheric species with weak spectral signals (e.g.

A Transformative Vision for an Omics-Based Regulatory Chemical Testing Paradigm.

Use of molecular data in human and ecological health risk assessments of industrial chemicals and agrochemicals has been anticipated by the scientific community for many years; however, these data are rarely used for risk assessment. Here, a logic framework is proposed to explore the feasibility and future development of transcriptomic methods to refine and replace the current apical endpoint-based regulatory toxicity testing paradigm. Four foundational principles are outlined and discussed that would need to be accepted by stakeholders prior to this transformative vision being realized.

Reactive Oxygen Species in the Adverse Outcome Pathway Framework: Toward Creation of Harmonized Consensus Key Events.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are formed as a result of natural cellular processes, intracellular signaling, or as adverse responses associated with diseases or exposure to oxidizing chemical and non-chemical stressors. The action of ROS and RNS, collectively referred to as reactive oxygen and nitrogen species (RONS), has recently become highly relevant in a number of adverse outcome pathways (AOPs) that capture, organize, evaluate and portray causal relationships pertinent to adversity or disease progression. RONS can potentially act as a key event (KE) in the cascade of responses leading to an adverse outcome (AO) within such AOPs, but are also known to modulate responses of events along the AOP continuum without being an AOP event itself.

A Case Study on Integrating a New Key Event Into an Existing Adverse Outcome Pathway on Oxidative DNA Damage: Challenges and Approaches in a Data-Rich Area.

Adverse outcome pathways (AOPs) synthesize toxicological information to convey and weigh evidence in an accessible format. AOPs are constructed in modules that include key events (KEs) and key event relationships (KERs). This modular structure facilitates AOP expansion and network development.

Microsatellite mutation frequencies in river otters (Lontra Canadensis) from the Athabasca Oil Sands region are correlated to polycyclic aromatic compound tissue burden.

Mining activities in the Athabasca oil sands region (AOSR) have contributed to an increase of polycyclic aromatic compounds (PACs) locally. However, many PACs found in the AOSR, and the combined effects of PAC mixtures have not been evaluated for genotoxicity in wildlife. Here, we examine whether mutation frequencies in AOSR river otters are correlated to PAC tissue burdens.

Toxicity screening of bisphenol A replacement compounds: cytotoxicity and mRNA expression in LMH 3D spheroids.

Previously, we showed that the chicken LMH cell line cultured as 3D spheroids may be a suitable animal free alternative to primary chicken embryonic hepatocytes (CEH) for avian in vitro chemical screening. In this study, cytotoxicity and mRNA expression were determined in LMH 3D spheroids following exposure to bisphenol A (BPA), five BPA replacement compounds (BPF, TGSH, DD-70, BPAF, BPSIP), and 17β estradiol (E2). Results were compared to an earlier study that evaluated the same endpoints for these chemicals in CEH.

Cytotoxic and Transcriptomic Effects in Avian Hepatocytes Exposed to a Complex Mixture from Air Samples, and Their Relation to the Organic Flame Retardant Signature.

Assessing complex environmental mixtures and their effects is challenging. In this study, we evaluate the utility of an avian in vitro screening approach to determine the effects of passive air sampler extracts collected from different global megacities on cytotoxicity and gene expression. Concentrations of a suite of organic flame retardants (OFRs) were quantified in extracts from a total of 19 megacities/major cities in an earlier study, and levels were highly variable across sites.

Developmental and Hepatic Gene Expression Changes in Chicken Embryos Exposed to p-Tert-Butylphenyl Diphenyl Phosphate and Isopropylphenyl Phosphate via Egg Injection.

Organophosphate flame retardants (OPFRs) are used in a variety of products such as clear coats, resins, and plastics; however, research into their toxicological effects is limited. p-Tert-butylphenyl diphenyl phosphate (BPDP) and isopropylphenyl phosphate (IPPP) are two OPFRs that were prioritized for whole-animal toxicological studies based on observed effects in cultured avian hepatocytes in a previous study. The present study investigates the toxicity of BPDP and IPPP in chicken embryos at different developmental stages by evaluating morphological and gene expression endpoints.

Temporal change and the influence of climate and weather factors on mercury concentrations in Hudson Bay polar bears, caribou, and seabird eggs.

Temporal trends of mercury in Arctic wildlife are inconsistent within and between species and are often insignificant, which limits data interpretation. Recent multivariate analyses have shown that weather and climate factors (e.g.

A Pragmatic Approach to Adverse Outcome Pathway Development and Evaluation.

The adverse outcome pathway (AOP) framework provides a practical means for organizing scientific knowledge that can be used to infer cause-effect relationships between stressor events and toxicity outcomes in intact organisms. It has reached wide acceptance as a tool to aid chemical safety assessment and regulatory toxicology by supporting a systematic way of predicting adverse health outcomes based on accumulated mechanistic knowledge. A major challenge for broader application of the AOP concept in regulatory toxicology, however, has been developing robust AOPs to a level where they are peer reviewed and accepted.