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.

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.

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.

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.

Metabolomic profiles in relation to benchmark polycyclic aromatic compounds (PACs) and trace elements in two seabird species from Arctic Canada.

While exposure of birds to oil-related contaminants has been documented, the related adverse effects this exposure has on Arctic marine birds remain unexplored. Metabolomics can play an important role to explore biologically relevant metabolite biomarkers in relation to different stressors, even at benchmark levels of contamination. The aim of this study was to characterize the metabolomics profiles in relation to polycyclic aromatic compounds (PACs) and trace elements in the liver of two seabird species in the Canadian Arctic.

Cross-Model Comparison of Transcriptomic Dose-Response of Short-Chain Chlorinated Paraffins.

Short-chain chlorinated paraffins (SCCPs) have attracted attention because of their toxicological potential in humans and wildlife at environmentally relevant doses. However, limited information is available regarding mechanistic differences across species in terms of the biological pathways that are impacted by SCCP exposure. Here, a concentration-dependent reduced human transcriptome (RHT) approach was conducted to evaluate 15 SCCPs in HepG2 cells and compared with our previous results using a reduced zebrafish transcriptome (RZT) approach in zebrafish embryos (ZFEs).

Concentration- and time-dependent induction of Cyp1a and DNA damage response by benzo(a)pyrene in LMH three-dimensional spheroids.

In vitro liver toxicity tests performed using cell lines cultured as two-dimensional (2D) monolayer have limited CYP450 activity and may be inadequate for screening chemicals that require activation to exert toxicity. Metabolic competence is greatly improved using three-dimensional (3D) cell culture. In this study, Cyp1a induction, and subsequent DNA damage response induced by benzo(a)pyrene (BaP) were compared in 2D monolayer cells and 3D spheroids of the chicken hepatic cell line, LMH.

Effects of two Bisphenol A replacement compounds, 1,7-bis (4-hydroxyphenylthio)-3,5-dioxaheptane and Bisphenol AF, on development and mRNA expression in chicken embryos.

Concerns about the estrogenic properties of Bisphenol A (BPA) have led to increased efforts to find BPA replacements. 1,7-bis(4-Hydroxyphenylthio)-3,5-dioxaheptane (DD-70) and 4,4'-(hexafluoroisopropylidene) diphenol (bisphenol AF, BPAF) are two potential chemical substitutes for BPA; however, toxicity data for these chemicals in avian species are limited. To determine effects on avian embryonic viability, development, and hepatic mRNA expression at two distinct developmental periods (mid-incubation [day 11] and term [day 20]), two egg injection studies were performed.

In Vitro Screening of 21 Bisphenol A Replacement Alternatives: Compared with Bisphenol A, the Majority of Alternatives Are More Cytotoxic and Dysregulate More Genes in Avian Hepatocytes.

An avian in vitro screening approach was used to determine the effects of 21 bisphenol A (BPA) alternatives. Cytotoxicity and dysregulation of genes associated with estrogen response and other toxicologically relevant pathways evoked by these alternatives were compared with BPA. Most of the BPA alternatives (15/21) were equally or more cytotoxic than BPA in chicken embryonic hepatocytes; variability in cell viability was associated with chemical structure and the log octanol-water partition coefficient (logP) values.

Toxicity Screening of Bisphenol A Replacement Compounds: Cytotoxicity and mRNA Expression in Primary Hepatocytes of Chicken and Double-Crested Cormorant.

A market for bisphenol A (BPA) replacement compounds has emerged as a result of restrictions on the use of BPA. Some of these compounds have been detected in the environment; however, little is known about their toxicological properties. In the present study, an avian in vitro toxicogenomic approach was used to compare the effects of 5 BPA alternatives.

Chemically induced mutations in a MutaMouse reporter gene inform mechanisms underlying human cancer mutational signatures.

Transgenic rodent (TGR) models use bacterial reporter genes to quantify in vivo mutagenesis. Pairing TGR assays with next-generation sequencing (NGS) enables comprehensive mutation pattern analysis to inform mutational mechanisms. We used this approach to identify 2751 independent lacZ mutations in the bone marrow of MutaMouse animals exposed to four chemical mutagens: benzo[a]pyrene, N-ethyl-N-nitrosourea, procarbazine, and triethylenemelamine.

Toxicogenomic Assessment of Complex Chemical Signatures in Double-Crested Cormorant Embryos from Variably Contaminated Great Lakes Sites.

Using omics approaches to monitor complex environmental mixtures is challenging. Previously, we evaluated transcriptomic effects of complex organic extracts derived from avian eggs. However, there is a lack of studies using wild species that are naturally exposed to contaminant mixtures.

Evaluation of the Aryl Hydrocarbon Receptor Response in LMH 3D Spheroids.

In the present study, we investigated whether the immortalized chicken hepatocellular carcinoma cell line, leghorn male hepatoma (LMH), had a comparable aryl hydrocarbon receptor (AhR) response to primary chicken embryonic hepatocytes (CEHs) when used in a well-established assay for chemical screening and prioritization. The LMH cells were grown as 2-dimensional (2D) confluent cells and 3D spheroids to determine the optimal cell culture states for chemical screening. Cytochrome P450 1A4 and 1A5 (CYP1A) activity and gene expression were compared between CEHs and LMH cells grown in 2 culture states following exposure to the dioxin-like compound 3,3',4,4',5-pentachlorobiphenyl (PCB-126).

Transcriptomic points-of-departure from short-term exposure studies are protective of chronic effects for fish exposed to estrogenic chemicals.

Resource limitations often require risk assessors to extrapolate chronic toxicity from acute tests using assessment factors. Transcriptomic dose-response analysis following short-term exposures may provide a more reliable and biologically-based alternative for estimating chronic toxicity. Here, we demonstrate that transcriptomic dose-response analysis in fish following short-term exposure to endocrine disrupting chemicals (EDCs) provides estimates of chronic toxicity that may be used as protective points-of-departure (POD) for risk assessment.

Extracting and Benchmarking Emerging Adverse Outcome Pathway Knowledge.

As the community of toxicological researchers, risk assessors, and risk managers adopt the adverse outcome pathway (AOP) framework for organizing toxicological knowledge, the number and diversity of AOPs in the online AOP knowledgebase (KB) continues to grow. To track and investigate this growth, AOPs in the AOP-KB were assembled into a single network. Summary measures on the current state of the AOP-KB and the overall connectivity and structural features of the resulting network were calculated.

Integration of sperm DNA damage assessment into OECD test guidelines for genotoxicity testing using the MutaMouse model.

The Organisation for Economic Co-operation and Development (OECD) endorses test guidelines (TG) for identifying chemicals that are genotoxic, such as the transgenic rodent gene mutation assay (TG 488). Current OECD TG do not include assays for sperm DNA damage resulting in a critical testing gap. We evaluated the performance of the Sperm Chromatin Structure Assay (SCSA) and the Terminal Deoxynucleotidyl Transferase-Mediated Deoxyuridine Triphosphate Nick end Labeling (TUNEL) assay to detect sperm DNA damage within the recommended TG 488 protocol.

Prioritization of 10 organic flame retardants using an avian hepatocyte toxicogenomic assay.

As the number of chemicals developed and used by industry increases, the inherent limitations of traditional toxicology approaches become an unavoidable issue. To help meet the demand for toxicity evaluation, new methods, such as high-throughput toxicity screening, are currently being developed to permit rapid determination of toxic, molecular, and/or biochemical effects of a wide range of chemicals. In the present study, we demonstrate the utility of an avian in vitro toxicogenomics screening approach to determine the cytotoxic and transcriptomic effects of 10 organic flame retardants (OFRs) currently of international priority for ecological risk evaluation to prioritize and inform future toxicological studies.