Re-evaluating the Significance of Estrone as an Environmental Estrogen

Studies worldwide have demonstrated the occurrence of feminized male fish at sites impacted by human and animal wastes. A variety of chemicals could contribute to this phenomenon, but those receiving the greatest attention in terms of research and monitoring have been 17β-estradiol (β-E2) and 17α-ethinylestradiol, due both to their prevalence in the environment and strong estrogenic potency. A third steroid, estrone (E1), also can occur at high concentrations in surface waters but generally has been of lesser concern due to its relatively lower affinity for vertebrate estrogen receptors. In an initial experiment, male fathead minnow (<i>Pimephales promelas</i>) adults were exposed for 4-d to environmentally relevant levels of waterborne E1, which resulted in plasma β-E2 concentrations similar to those found in reproductively active females. In a second exposure we used ¹³C-labeled E1, together with liquid chromatography-tandem mass spectrometry, to demonstrate that elevated β-E2 measured in the plasma of the male fish was indeed derived from the external environment, most likely via a conversion catalyzed by one or more 17β-hydroxysteroid dehydrogenases. The results of our studies suggest that the potential impact of E1 as an environmental estrogen currently is underestimated

Re-evaluating the Significance of Estrone as an Environmental Estrogen

Studies worldwide have demonstrated the occurrence of feminized male fish at sites impacted by human and animal wastes. A variety of chemicals could contribute to this phenomenon, but those receiving the greatest attention in terms of research and monitoring have been 17β-estradiol (β-E2) and 17α-ethinylestradiol, due both to their prevalence in the environment and strong estrogenic potency. A third steroid, estrone (E1), also can occur at high concentrations in surface waters but generally has been of lesser concern due to its relatively lower affinity for vertebrate estrogen receptors. In an initial experiment, male fathead minnow (<i>Pimephales promelas</i>) adults were exposed for 4-d to environmentally relevant levels of waterborne E1, which resulted in plasma β-E2 concentrations similar to those found in reproductively active females. In a second exposure we used ¹³C-labeled E1, together with liquid chromatography-tandem mass spectrometry, to demonstrate that elevated β-E2 measured in the plasma of the male fish was indeed derived from the external environment, most likely via a conversion catalyzed by one or more 17β-hydroxysteroid dehydrogenases. The results of our studies suggest that the potential impact of E1 as an environmental estrogen currently is underestimated

Short-Term Study Investigating the Estrogenic Potency of Diethylstilbesterol in the Fathead Minnow (Pimephales promelas)

Diethylstilbestrol (DES) is a synthetic estrogen that has been banned for use in humans, but still is employed in livestock and aquaculture operations in some parts of the world. Detectable concentrations of DES in effluent and surface waters have been reported to range from slightly below 1 to greater than 10 ng/L. Little is known, however, concerning the toxicological potency of DES in fish. In this study, sexually mature fathead minnows (Pimephales promelas) of both sexes were exposed to 1, 10, or 100 ng of DES/L of water in a flow-through system. Tissue concentrations of DES and changes in a number of estrogen-responsive end points were measured in the fish at the end of a 4 d exposure and after a 4 d depuration/recovery period in clean water. Accumulation of DES was sex-dependent, with females exhibiting higher tissue residues than males after the 4 d exposure. The observed bioconcentration of DES in the fish was about 1 order of magnitude lower than that predicted on the basis of the octanol–water partition coefficient of the chemical, suggesting relatively efficient metabolic clearance by the fish. Exposure to 1, 10, or 100 ng of DES/L caused decreased testis weight and morphological demasculinization of males (regression of dorsal nuptial tubercles). Diethylstilbesterol induced plasma vitellogenin (VTG) in both sexes at water concentrations ≥10 ng/L; this response (especially in males) persisted through the end of the 4 d recovery period. Hepatic transcripts of VTG and estrogen receptor-α also were affected at DES concentrations ≥10 ng/L. Evaluation of transcript profiles in the liver of females using a 15K-gene fathead minnow microarray revealed a concentration-dependent change in gene expression, with mostly up-regulated transcripts after the exposure and substantial numbers of down-regulated gene products after depuration. Genes previously identified as vitellogenesis-related and regulated by 17β-estradiol were significantly enriched among those differentially expressed following exposure to DES. Overall, our studies show that DES causes a range of responses in fish at water concentrations comparable to those reported in the environment and that in vivo potency of the estrogen is on par with that of the better-studied estrogenic contaminant 17α-ethinylestradiol

Ecotoxicogenomics to Support Ecological Risk Assessment: A Case Study with Bisphenol A in Fish

Effects of bisphenol A (BPA) on ovarian transcript profiles as well as targeted end points with endocrine/reproductive relevance were examined in two fish species, fathead minnow (<i>Pimephales promelas</i>) and zebrafish (<i>Danio rerio</i>), exposed in parallel using matched experimental designs. Four days of waterborne exposure to 10 μg BPA/L caused significant vitellogenin induction in both species. However, zebrafish were less sensitive to effects on hepatic gene expression and steroid production than fathead minnow and the magnitude of vitellogenin induction was more modest (i.e., 3-fold compared to 13 000-fold in fathead minnow). The concentration–response at the ovarian transcriptome level was nonmonotonic and violated assumptions that underlie proposed methods for estimating hazard thresholds from transcriptomic results. However, the nonmonotonic profile was consistent among species and there were nominal similarities in the functions associated with the differentially expressed genes, suggesting potential activation of common pathway perturbation motifs in both species. Overall, the results provide an effective case study for considering the potential application of ecotoxicogenomics to ecological risk assessments and provide novel comparative data regarding effects of BPA in fish

Prioritization of Contaminants of Emerging Concern in Wastewater Treatment Plant Discharges Using Chemical:Gene Interactions in Caged Fish

We examined whether contaminants present in surface waters could be prioritized for further assessment by linking the presence of specific chemicals to gene expression changes in exposed fish. Fathead minnows were deployed in cages for 2, 4, or 8 days at three locations near two different wastewater treatment plant discharge sites in the Saint Louis Bay, Duluth, MN and one upstream reference site. The biological impact of 51 chemicals detected in the surface water of 133 targeted chemicals was determined using biochemical endpoints, exposure activity ratios for biological and estrogenic responses, known chemical:gene interactions from biological pathways and knowledge bases, and analysis of the covariance of ovary gene expression with surface water chemistry. Thirty-two chemicals were significantly linked by covariance with expressed genes. No estrogenic impact on biochemical endpoints was observed in male or female minnows. However, bisphenol A (BPA) was identified by chemical:gene covariation as the most impactful estrogenic chemical across all exposure sites. This was consistent with identification of estrogenic effects on gene expression, high BPA exposure activity ratios across all test sites, and historical analysis of the study area. Gene expression analysis also indicated the presence of nontargeted chemicals including chemotherapeutics consistent with a local hospital waste stream. Overall impacts on gene expression appeared to be related to changes in treatment plant function during rain events. This approach appears useful in examining the impacts of complex mixtures on fish and offers a potential route in linking chemical exposure to adverse outcomes that may reduce population sustainability

Ecotoxicogenomics to Support Ecological Risk Assessment: A Case Study with Bisphenol A in Fish

Effects of bisphenol A (BPA) on ovarian transcript profiles as well as targeted end points with endocrine/reproductive relevance were examined in two fish species, fathead minnow (<i>Pimephales promelas</i>) and zebrafish (<i>Danio rerio</i>), exposed in parallel using matched experimental designs. Four days of waterborne exposure to 10 μg BPA/L caused significant vitellogenin induction in both species. However, zebrafish were less sensitive to effects on hepatic gene expression and steroid production than fathead minnow and the magnitude of vitellogenin induction was more modest (i.e., 3-fold compared to 13 000-fold in fathead minnow). The concentration–response at the ovarian transcriptome level was nonmonotonic and violated assumptions that underlie proposed methods for estimating hazard thresholds from transcriptomic results. However, the nonmonotonic profile was consistent among species and there were nominal similarities in the functions associated with the differentially expressed genes, suggesting potential activation of common pathway perturbation motifs in both species. Overall, the results provide an effective case study for considering the potential application of ecotoxicogenomics to ecological risk assessments and provide novel comparative data regarding effects of BPA in fish

Ecotoxicogenomics to Support Ecological Risk Assessment: A Case Study with Bisphenol A in Fish

Effects of bisphenol A (BPA) on ovarian transcript profiles as well as targeted end points with endocrine/reproductive relevance were examined in two fish species, fathead minnow (<i>Pimephales promelas</i>) and zebrafish (<i>Danio rerio</i>), exposed in parallel using matched experimental designs. Four days of waterborne exposure to 10 μg BPA/L caused significant vitellogenin induction in both species. However, zebrafish were less sensitive to effects on hepatic gene expression and steroid production than fathead minnow and the magnitude of vitellogenin induction was more modest (i.e., 3-fold compared to 13 000-fold in fathead minnow). The concentration–response at the ovarian transcriptome level was nonmonotonic and violated assumptions that underlie proposed methods for estimating hazard thresholds from transcriptomic results. However, the nonmonotonic profile was consistent among species and there were nominal similarities in the functions associated with the differentially expressed genes, suggesting potential activation of common pathway perturbation motifs in both species. Overall, the results provide an effective case study for considering the potential application of ecotoxicogenomics to ecological risk assessments and provide novel comparative data regarding effects of BPA in fish