Project description:Current methods to support chemical hazard assessment face significant challenges given the rapidly growing number of compounds of emerging concern (CEC) requiring assessment. Standard testing strategies rely upon live animal testing, which are time-consuming, expensive, and ethically questionable. These concerns serve as an impetus to develop new approach methodologies (NAMs) that do not rely on live animal tests. This study explored the application of the molecular benchmark dose (BMD) approach in a 7-day embryo-larval fathead minnow (FHM) assay to derive determine transcriptomic points-of-departure (tPODs) which can be useds to predict apical BMDs of fluoxetine (FLX), a highly prescribed and potent selective serotonin reuptake inhibitor frequently detected in surface waters. Fertilized FHM embryos were exposed to graded concentrations of FLX (confirmed at <LOD, 0.19, 0.74, 3.38, 10.2, 47.5 µg/L) for 32 days. Subsets of fish were subjected to omics and locomotor analyses at 7 days post-fertilization (dpf) and to histological and biometric measurements at 32 dpf. Enrichment analyses of transcriptomics and proteomics data revealed significant perturbations in gene sets associated with serotonergic and axonal functions. BMD analysis resulted in tPOD values of 0.56 µg/L (median of the 20 most sensitive gene-level BMDs), 5.0 µg/L (tenth percentile of all gene-level BMDs), 7.51 µg/L (mode of the first peak of all gene-level BMDs) , and 5.66 µg/L (pathway-level BMD). These tPODs are protective of apical locomotor and reduced weight effects (LOEC of 10.2 µg/L) observed in this study and are well within the range of chronic apical BMDs of FLX reported in the literature. Furthermore, the distribution of gene-level BMDs followed a bimodal pattern, revealing disruption of sensitive neurotoxic pathways at low concentrations and metabolic pathway perturbations at higher concentrations. This is one of the first studies to derive tPODs for FLX using a short-term embryo assay at a life stage not considered to be a live animal under current legislations.

Project description:Fluoxetine (FLX) is the most common selective serotonin reuptake inhibitor pharmaceutical used for the treatment of psychological disorders such as depression and anxiety. Increased prescription use of FLX by human populations has led to its pseudo-persistence in effluent-receiving waterways. Despite emerging concerns of FLX becoming a potential threat to the aquatic environment, there is currently limited information on effects of FLX on aquatic wildlife, including its specific mechanism of action and associated toxicity pathways in fish. The main goal of this study was to identify and validate key molecular toxicity pathways that are predictive of apical endpoints induced by exposure to FLX using the fathead minnow (Pimephales promelas), a model species common to North American freshwater systems. Adult fathead minnows were exposed to three concentrations of FLX (2.42, 10.7, and 56.7 µg/L) and a control for 21 days. After 96 hours, a subset of fish was sampled, and liver and brain tissue were collected to characterize molecular toxicity pathways using whole transcriptome and proteome analyses. In addition, at the end of the 21-day exposure, individuals were assessed for apical outcomes of regulatory relevance including histopathology and fecundity. Differential gene expression observed in the liver of fish exposed to the highest FLX treatment and revealed dysregulation of pathways associated with biosynthesis and metabolism of fatty acids, which may be an upstream molecular response that led to lipid-type vacuolation of hepatocytes, as observed in the histology analysis. Whole proteome analysis of the same fish revealed dysregulation of PPAR signalling, which may be associated with the enrichment of lipid-related pathways observed in the transcriptome. In addition, there was an indication of pathway enrichment of transcription- and translation-related pathways in the proteome. Common dysregulated genes in the brain of the treated fish were related to cellular signalling processes that are influenced by serotonin levels and shown to be involved in reproductive behaviour and, in turn, reproductive success. This was confirmed through a significant decrease in fecundity following the 21-day exposure. Pathways to measurable adverse outcomes are complex, however, this research does provide some important clues to the mechanistic toxicity that FLX inflicts.

Project description:Metformin, along with its biotransformation product guanylurea, are commonly observed in municipal wastewaters and subsequent surface waters. Previous studies in fish have identified metformin as a potential endocrine active compound but there are inconsistencies in the literature with regard to effects. To further investigate the potential reproductive toxicity of metformin and guanylurea to fish, a series of experiments were performed with reproductively mature fathead minnows (Pimephales promelas). First, explants of mature fathead minnow ovary tissue were exposed to 0.001-100 µM metformin or guanylurea to investigate whether they can directly perturb steroidogenesis. Second, spawning pairs of fathead minnows were exposed to metformin (0.41, 4.1, 41 µg/L) or guanylurea (1.0, 10, 100 µg/L) for 23 d to assess impacts on reproduction. Lastly, male fathead minnows were exposed to 41 µg/L metformin, 100 µg/L guanylurea, or a mixture of both compounds, with samples collected over a 96 h time course to investigate potential impacts to the hepatic transcriptome or metabolome. Neither metformin or guanylurea effected estradiol or testosterone by ovary tissue exposed in vitro. In the 23 d exposure, neither compound significantly impacted transcription of endocrine-related genes in male liver or gonad, circulating steroid concentrations in male or female fish, or fecundity of spawning pairs. In the 96 h time course, 100 µg guanylurea/L elicited more differential gene expression than 41 µg metformin/L , and showed the greatest impacts after 96 h. A number of DEGs up-regulated after 24 h were subsequently down-regulated after 96 h, demonstrating time-dependent impacts of guanylurea on the liver. Overall, metformin and guanylurea did not elicit effects consistent with reproductive toxicity in adult fathead minnows at environmentally relevant concentrations. Where effects were identified using ‘omics approaches, guanylurea induced greater impacts than metformin.

Project description:Cyclooxygenase (COX) inhibition is of concern in fish because COX inhibitors (e.g., ibuprofen) are ubiquitous in aquatic systems/fish tissues, and can disrupt synthesis of prostaglandins that modulate a variety of essential biological functions including reproduction. Transcriptomic data and publicly available high throughput toxicity data were utilized to develop putative adverse outcome pathways (AOPs) for molecular initiating event (MIE) of COX inhibition. Effects of a waterborne exposure to indomethacin (IN; 100 Âµg/L), ibuprofen (IB; 200 Âµg/L) and celecoxib (CX; 20 Âµg/L) on liver metabolome and ovarian gene expression (using oligonucleotide microarrays) in sexually mature fathead minnows were examined. Metabolomic profiles of IN, IB and CX were not significantly different from control or one another. Exposure to IB and CX resulted in differential expression of comparable numbers of genes (IB = 433, CX= 545). In contrast, 2558 genes were differentially expressed in IN-treated fish. Functional analyses (canonical pathway and gene set enrichment) indicated extensive effects of IN on prostaglandin synthesis pathway, oocyte meiosis and several other processes consistent with physiological roles of prostaglandins. Transcriptomic data was congruent with apical endpoint data - IN reduced plasma prostaglandin F2 alpha concentrations, and ovarian COX activity, whereas IB and CX did not. Putative AOPs pathways for COX inhibition (MIE) leading to reproductive failure (adverse outcome) via reduction of: 1) ovulation, 2) reproductive behaviors mediated by exogenous and endogenous prostaglandins, and 3) oocyte maturation were developed. Adult fathead minnow were exposed to either 100 Âµg/L indomethacin, 200 Âµg/L ibuprofen, 20 Âµg/L celecoxib or UV-treated Lake Superior (control) water for 96 hours. After exposure, microarray analyses were conducted using the female gonads (n=7-8 per treatment) and metabolomic analyses were conducted using the livers of all the exposed fish.

Dataset Information

Comparative analysis of transcriptomic points-of-departure (tPODs) and adverse apical responses in embryo-larval fathead minnows exposed to fluoxetine

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