Rapid effects of the aromatase inhibitor fadrozole on steroid production and gene expression in the ovary of female fathead minnows (Pimephales promelas).

Cytochrome P450 aromatase catalyzes conversion of C19 androgens to C18 estrogens and is critical for normal reproduction in female vertebrates. Fadrozole is a model aromatase inhibitor that has been shown to suppress estrogen production in the ovaries of fish. However, little is known about the early impacts of aromatase inhibition on steroid production and gene expression in fish.

A study of temporal effects of the model anti-androgen flutamide on components of the hypothalamic-pituitary-gonadal axis in adult fathead minnows.

The aim of this study was to investigate temporal changes in the hypothalamic-pituitary-gonadal (HPG) axis of fathead minnows (Pimephales promelas) treated with the model androgen receptor (AR) antagonist flutamide. Reproductively-mature fish were exposed in a flow-through test to analytically-confirmed concentrations of either 50 or 500μg flutamide/L for 8 d, followed by an 8-d recovery period in clean water. Fish were sampled at 1, 2, 4 and 8days during each phase of the experiment.

Effects of the antimicrobial contaminant triclocarban, and co-exposure with the androgen 17β-trenbolone, on reproductive function and ovarian transcriptome of the fathead minnow (Pimephales promelas).

Triclocarban (TCC) is an antimicrobial agent routinely detected in surface waters that has been hypothesized to interact with the vertebrate endocrine system. The present study examined the effects of TCC alone and in combination with the model endocrine disruptor 17β-trenbolone (TRB) on fish reproductive function. Adult Pimephales promelas were continuously exposed to either 1 µg TCC/L or 5 µg TCC/L, to 0.

Integrated assessment of runoff from livestock farming operations: Analytical chemistry, in vitro bioassays, and in vivo fish exposures.

Animal waste from livestock farming operations can contain varying levels of natural and synthetic androgens and/or estrogens, which can contaminate surrounding waterways. In the present study, surface stream water was collected from 6 basins containing livestock farming operations. Aqueous concentrations of 12 hormones were determined via chemical analyses.

An inexpensive, temporally integrated system for monitoring occurrence and biological effects of aquatic contaminants in the field.

Assessment of potential risks of complex contaminant mixtures in the environment requires integrated chemical and biological approaches. In support of the US Great Lakes Restoration Initiative, the US Environmental Protection Agency lab in Duluth, MN, is developing these types of methods for assessing possible risks of aquatic contaminants in near-shore Great Lakes (USA) sites. One component involves an exposure system for caged fathead minnow (Pimephales promelas) adults suitable for the wide range of habitat and deployment situations encountered in and around the Great Lakes.

Cross-species sensitivity to a novel androgen receptor agonist of potential environmental concern, spironolactone.

Spironolactone is a pharmaceutical that in humans is used to treat conditions like hirsutism, various dermatologic afflictions, and female-pattern hair loss through antagonism of the androgen receptor. Although not routinely monitored in the environment, spironolactone has been detected downstream of a pharmaceutical manufacturer, indicating a potential for exposure of aquatic species. Furthermore, spironolactone has been reported to cause masculinization of female western mosquitofish, a response indicative of androgen receptor activation.

Effects of the insecticide fipronil on reproductive endocrinology in the fathead minnow.

Gamma-aminobutyric acid (GABA) and GABA receptors play an important role in neuroendocrine regulation in fish. Disruption of the GABAergic system by environmental contaminants could interfere with normal regulation of the hypothalamic-pituitary-gonadal axis, leading to impaired fish reproduction. The present study used a 21-d fathead minnow (Pimephales promelas) reproduction assay to investigate the reproductive toxicity of fipronil (FIP), a broad-spectrum phenylpyrazole insecticide that acts as a noncompetitive blocker of GABA receptor-gated chloride channels.

Developing predictive approaches to characterize adaptive responses of the reproductive endocrine axis to aromatase inhibition: I. Data generation in a small fish model.

Adaptive or compensatory responses to chemical exposure can significantly influence in vivo concentration-duration-response relationships. This study provided data to support development of a computational dynamic model of the hypothalamic-pituitary-gonadal axis of a model vertebrate and its response to aromatase inhibitors as a class of endocrine active chemicals. Fathead minnows (Pimephales promelas) were either exposed to the aromatase inhibitor fadrozole (0.

Propiconazole inhibits steroidogenesis and reproduction in the fathead minnow (Pimephales promelas).

Conazoles are designed to inhibit cytochrome P450 (CYP) 14α-demethylase, an enzyme key to fungal cell wall formation. In vertebrates, conazoles may inhibit other CYPs, potentially disrupting processes like sex steroid synthesis. Propiconazole is a current-use pesticide that is among the first chemicals being tested in the U.

Effects of gemfibrozil on lipid metabolism, steroidogenesis, and reproduction in the fathead minnow (Pimephales promelas).

Fibrates are a class of pharmaceuticals that indirectly modulate cholesterol biosynthesis through effects on peroxisome proliferator-activated receptors. Gemfibrozil is a fibrate that has been detected in wastewater treatment plant influents, effluents, and drinking water. The objective of the present study was to assess the potential physiological and reproductive impacts of gemfibrozil on fathead minnows (Pimephales promelas).

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.

A time-course analysis of effects of the steroidogenesis inhibitor ketoconazole on components of the hypothalamic-pituitary-gonadal axis of fathead minnows.

The objective of this study was to evaluate temporal effects of the model steroidogenesis inhibitor ketoconazole (KTC) on aspects of reproductive endocrine function controlled by the hypothalamic-pituitary-gonadal (HPG) axis in the fathead minnow (Pimephales promelas). Ketoconazole inhibits the activity of two cytochrome P450s (CYPs) key to sex steroid production in vertebrates, CYP11a (cholesterol side chain cleavage) and CYP17 (c17α-hydroxylase/17, 20-lyase). Sexually mature fish were exposed to water-borne KTC (30 or 300 μg/L) in a flow-through system for up to 8d, following which animals were allowed to recover in clean water.

Effects of a glucocorticoid receptor agonist, dexamethasone, on fathead minnow reproduction, growth, and development.

Synthetic glucocorticoids are pharmaceutical compounds prescribed in human and veterinary medicine as anti-inflammatory agents and have the potential to contaminate natural watersheds via inputs from wastewater treatment facilities and confined animal-feeding operations. Despite this, few studies have examined the effects of this class of chemicals on aquatic vertebrates. To generate data to assess potential risk to the aquatic environment, we used fathead minnow 21-d reproduction and 29-d embryo-larvae assays to determine reproductive toxicity and early-life-stage effects of dexamethasone.

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 (Pimephales promelas) and zebrafish (Danio rerio), 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.

Temporal evaluation of effects of a model 3β-hydroxysteroid dehydrogenase inhibitor on endocrine function in the fathead minnow.

Inhibition of enzymes involved in the synthesis of sex steroids can substantially impact developmental and reproductive processes controlled by the hypothalmic-pituitary-gonadal (HPG) axis. A key steroidogenic enzyme that has received little attention from a toxicological perspective is 3β-hydroxysteroid dehydrogenase (3β-HSD). In these studies, we exposed reproductively-active fathead minnows (Pimephales promelas) to the model 3β-HSD inhibitor trilostane at two test concentrations (300 and 1,500 µg/L) over a 16-d period that included both 8-d exposure and 8-d recovery phases.

Effects of a short-term exposure to the fungicide prochloraz on endocrine function and gene expression in female fathead minnows (Pimephales promelas).

Prochloraz is a fungicide known to cause endocrine disruption through effects on the hypothalamic-pituitary-gonadal (HPG) axis. To determine the short-term impacts of prochloraz on gene expression and steroid production, adult female fathead minnows (Pimephales promelas) were exposed to the chemical (0 or 300 μg/L) for a time-course of 6, 12 and 24 h. Consistent with inhibition of cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17) and aromatase (CYP19), known molecular targets of prochloraz, plasma 17β-estradiol (E2) was reduced within 6 h.

Use of gene expression, biochemical and metabolite profiles to enhance exposure and effects assessment of the model androgen 17β-trenbolone in fish.

The impact of exposure by water to a model androgen, 17β-trenbolone (TRB), was assessed in fathead minnows using an integrated molecular approach. This included classical measures of endocrine exposure such as impacts on testosterone (T), 17β-estradiol (E2), and vitellogenin (VTG) concentrations in plasma, as well as determination of effects on the hepatic metabolome using proton nuclear magnetic resonance spectroscopy. In addition, the rates of production of T and E2 in ovary explants were measured, as were changes in a number of ovarian gene transcripts hypothesized to be relevant to androgen exposure.

Impacts of an anti-androgen and an androgen/anti-androgen mixture on the metabolite profile of male fathead minnow urine.

Male and female fathead minnows (Pimephales promelas, FHM) were exposed via water to 20 or 200 microg/L of cyproterone acetate (CA), a model androgen receptor (AR) antagonist. FHM were also exposed to 500 ng/L of 17beta-trenbolone (TB), a model AR agonist, and to mixtures of TB with both concentrations of CA. The urine metabolite profile (as measured by 1H NMR spectroscopy) of male FHM exposed to the high concentration of CA was markedly different from that of controls, and this difference was less for males coexposed to the associated TB+CA mixture.

Use of chemical mixtures to differentiate mechanisms of endocrine action in a small fish model.

Various assays with adult fish have been developed to identify potential endocrine-disrupting chemicals (EDCs) which may cause toxicity via alterations in the hypothalamic-pituitary-gonadal (HPG) axis. These assays can be sensitive and highly diagnostic for key mechanisms such as agonism of the estrogen and androgen receptors (ERs, ARs) and inhibition of steroid synthesis. However, most of the tests do not unambiguously identify AR antagonists.

II: Effects of a dopamine receptor antagonist on fathead minnow dominance behavior and ovarian gene expression in the fathead minnow and zebrafish.

Neurotransmitters such as dopamine play an important role in reproductive behaviors and signaling. Neuroendocrine-active chemicals in the environment have potential to interfere with and/or alter these processes. A companion study with the dopamine 2 receptor antagonist, haloperidol, found no evidence of a direct effect of the chemical on fish reproduction.

I. Effects of a dopamine receptor antagonist on fathead minnow, Pimephales promelas, reproduction.

Neurotransmitters such as dopamine play an important role in regulating fish reproduction. However, the potential for neuroendocrine active chemicals to disrupt fish reproduction has not been well studied, despite emerging evidence of their discharge into aquatic environments. This study is the first to apply the fathead minnow 21 d reproduction assay developed for the US Endocrine Disruptor Screening Program to evaluate the reproductive toxicity of a model neuroendocrine active chemical, the dopamine 2 receptor antagonist, haloperidol.

Dynamic nature of alterations in the endocrine system of fathead minnows exposed to the fungicide prochloraz.

The vertebrate hypothalamic-pituitary-gonadal (HPG) axis is controlled through various feedback mechanisms that maintain a dynamic homeostasis in the face of changing environmental conditions, including exposure to chemicals. We assessed the effects of prochloraz on HPG axis function in adult fathead minnows (Pimephales promelas) at multiple sampling times during 8-day exposure and 8-day depuration/recovery phases. Consistent with one mechanism of action of prochloraz, inhibition of cytochrome P450 (CYP) 19 aromatase activity, the fungicide depressed ex vivo ovarian production and plasma concentrations of 17beta-estradiol (E2) in female fish.

Direct effects, compensation, and recovery in female fathead minnows exposed to a model aromatase inhibitor.

Background: Several chemicals in the environment have the potential to inhibit aromatase, an enzyme critical to estrogen synthesis.

Objectives: The objective of this study was to provide a detailed characterization of molecular and biochemical responses of female fathead minnows to a model aromatase inhibitor, fadrozole (FAD).

Methods: Fish were exposed via water to 0, 3, or 30 microg FAD/L for 8 days and then held in clean water for 8 days, with samples collected at four time points during each 8-day period.

Effects of a 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane, on the fathead minnow reproductive axis.

A number of environmental contaminants and plant flavonoid compounds have been shown to inhibit the activity of 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3beta-HSD). Because 3beta-HSD plays a critical role in steroid hormone synthesis, inhibition of 3beta-HSD represents a potentially important mode of endocrine disruption that may cause reproductive dysfunction in fish or other vertebrates. The objective of this study was to test the hypothesis that exposure to the model 3beta-HSD inhibitor, trilostane, would adversely affect reproductive success of the fathead minnow (Pimephales promelas).

Reproductive toxicity of vinclozolin in the fathead minnow: confirming an anti-androgenic mode of action.

The objective of the present study was to characterize responses of the reproductive endocrine system of the fathead minnow (Pimephales promelas) to the fungicide vinclozolin (VZ), using a 21-d reproduction assay, and a shorter-term (approximately two weeks) test in which fish were cotreated with the VZ (a putative anti-androgen) and the androgen 17beta-trenbolone (TB). Effects on fecundity, gonadal histology, secondary sexual characteristics, reproductive hormones, and relative abundance of androgen receptor (AR) and 11beta-hydroxysteroid dehydrogenase (11betaHSD) mRNA transcripts were evaluated in one or both of these studies. Fecundity of VZ-exposed fish was decreased in a concentration-dependent manner in the 21-d test, culminating in complete reproductive failure at a concentration of 700 microg/L.