Showing papers by "Gerald T. Ankley published in 2004"

Small Fish Models for Identifying and Assessing the Effects of Endocrine-disrupting Chemicals

Abstract: Endocrine-disrupting chemicals (EDCs), particularly those that affect the hypothalamic-pituitary-gonadal (HPG) axis of vertebrates, have become a focus of regulatory screening and testing throughout the world. Small fish species, principally the fathead minnow (Pimephales promelas), Japanese medaka (Oryzias latipes), and zebrafish (Danio rerio), are used as model organisms for several of these testing programs. Fish are appropriate models for testing EDCs, not only from the perspective of existing ecological impacts, but also in terms of species extrapolation. Specifically, there is a significant degree of conservation of basic aspects of the HPG axis across vertebrates, which provides a technically robust basis for using results from fish tests to predict likely modes/mechanisms of action of potential EDCs in other vertebrates. Different experimental designs/endpoints for partial- and full-life cycle tests with fish that enable a consideration of a broad range of EDCs are described. Examples of results with specific chemicals in tests with the fathead minnow, medaka, and zebrafish are presented and discussed in terms of sensitivity and specificity for different classes of EDCs.

Evaluation of the Model Anti-androgen Flutamide for Assessing the Mechanistic Basis of Responses to an Androgen in the Fathead Minnow (Pimephales promelas)

Abstract: In this study, we characterized the effects of flutamide, a model mammalian androgen receptor (AR) antagonist, on endocrine function in the fathead minnow (Pimephales promelas), a small fish species that is widely used for testing endocrine-disrupting chemicals (EDCs). Binding assays with whole cells transiently transfected with cloned fathead minnow AR indicated that flutamide binds competitively to the receptor. However, as is true in mammalian systems, a 2-hydroxylated metabolite of flutamide binds to the AR with a much higher affinity than the parent chemical. Mixture experiments with flutamide and the androgen 17beta-trenbolone demonstrated that the anti-androgen effectively blocked trenbolone-induced masculinization (nuptial tubercle production) of female fathead minnows, indicating antagonism of an AR receptor-mediated response in vivo. Conversely, reductions in vitellogenin in trenbolone-exposed females were not blocked by flutamide, suggesting that the vitellogenin response is not directly mediated through the AR. The results of these studies provide data demonstrating the validity of using the fathead minnow as a model species for detecting EDCs that exert toxicity through interactions with the AR.

Partial life-cycle toxicity and bioconcentration modeling of perfluorooctanesulfonate in the northern leopard frog (Rana pipiens).

Abstract: A number of recent monitoring studies have demonstrated elevated concentrations of perfluorooctanesulfonate (PFOS) in humans and wildlife throughout the world. Although no longer manufactured in the United States, the global distribution and relative persistence of PFOS indicates a need to understand its potential ecological effects. Presently, little is known concerning toxicity of PFOS in chronic exposures with aquatic species. Therefore, we evaluated the effects of PFOS on survival and development of the northern leopard frog (Rana pipiens) from early embryogenesis through complete metamorphosis. Exposures were conducted via water at measured PFOS concentrations ranging from 0.03 to 10 mg/L. Animals exposed to 10 mg/L began dying within approximately two weeks of test initiation. Survival was not affected by PFOS at lower concentrations; however, time to metamorphosis was delayed and growth reduced in the 3-mg/L treatment group. Tadpoles readily accumulated PFOS directly from water. Using a one-compartment bioaccumulation model, growth was shown to have a modest impact on steady-state PFOS concentrations. Variability in observed growth rates and the possible contribution of a size-dependent decrease in PFOS elimination rate contributed uncertainty to modeling efforts. Nevertheless, fitted uptake and elimination rate constants were comparable to those determined in earlier studies with juvenile rainbow trout. Overall, our studies suggest that R. pipiens is not exceptionally sensitive to PFOS in terms of either direct toxicity or bioconcentration potential of the chemical.

Effects of methoprene, its metabolites, and breakdown products on retinoid-activated pathways in transfected cell lines.

Abstract: Mthoprene (isopropyl (2E, 4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) is an insect juvenile hormone agonist that blocks metamorphosis in some insects. Recent evidence suggests that a metabolite, methoprene acid, activates vertebrate retinoid X receptors (RXRs), and may interfere with retinoic acid-regulated developmental processes. Methoprene, methoxy-methoprene acid, and two major breakdown products were tested for their ability to interfere with retinoid-regulated pathways when using transfected cells. The CV-1 cells were transiently transfected with genes encoding RXRs and response elements attached to luciferase reporters, and retinoic acid-sensitive F9 cells were stably transfected with retinoic acid receptor (RAR)/RXR response elements attached a lacZ reporter (Sil-REM/β-gal-NEO). Experiments confirmed that methoxy-methoprene acid acted as a ligand for RXRs and was capable of activating transcription through RAR/RXR response elements. However, neither methoprene nor the breakdown products, 7-methoxycitronellal and 7-methoxycitronellic acid, activated transcription in transfected CV-1 or F9 cells. Methoprene and methoxy-methoprene acid may interfere with the conversion of all-trans-retinol and all-trans-retinaldehyde to all-trans-retinoic acid in the F9-derived cell line. Methoprene was as effective as the retinol dehydrogenase inhibitor citral in blocking the retinol-induced transcription of RAR/RXR-regulated reporter genes, whereas methoxy-methoprene acid blocked transcription stimulated by retinaldehyde.

Evaluation of bioaccumulation and photo-induced toxicity of fluoranthene in larval and adult life-stages of Chironomus tentans

Abstract: Laboratory sediment tests were conducted to evaluate the bioaccumulation and photo-induced toxicity of fluoranthene in larval and adult life-stages of the midge, Chironomus tentans In the first of 2 experiments, fourth-instar and adult C tentans exposed to spiked sediments (204 μg fluoranthene/g dry weight) were collected for determination of fluoranthene tissue concentrations and toxicity after ultraviolet (UV) radiation treatment in the absence of sediment (water-only) Fluoranthene tissue concentrations in larvae collected after a 72-hour exposure period were 7 times greater than concentrations in adults collected on emergence from the same spiked sediments Fluoranthene-exposed adults were tolerant of UV exposure (100% survival after 7 hours), whereas larvae were sensitive (0% survival after 1 hour) In the second experiment, C tentans larvae were exposed for 96 hours to 2 sediment treatments (170 and 54 μg fluoranthene/g dry weight), after which fluoranthene tissue concentrations were determined and UV exposures conducted under water-only versus sediment conditions Exposure to UV radiation, in conjunction with sediment, provided larvae with significant protection from photo-induced toxicity compared with the water-only exposure Adults that emerged from the 2 sediment treatments were also analyzed for fluoranthene tissue residues and exposed to UV radiation Fluoranthene tissue residues were higher in adult female than in adult male midges, but exuviae from both sexes contained higher fluoranthene concentrations than whole-body tissue, thus demonstrating that the molting process is a possible detoxification mechanism Consistent with the greater tissue residue concentrations, female midges demonstrated a significant decrease in survival under UV exposure compared with male midges These studies indicated that both the burrowing behavior of the larvae and the elimination of fluoranthene in molted exuviae are protective mechanisms against photo-enhanced PAH toxicity in this species

Rapid Communication Modeling impacts on populations: fathead minnow (Pimephales promelas) exposure to the endocrine disruptor 17b-trenbolone as a case study

Abstract: Evaluation of population-level impacts is critical to credible ecological risk assessments. In this study, a predictive model was developed to translate changes in fecundity of the fathead minnow (Pimephales promelas) in a short-term laboratory toxicity test to alterations in population growth rate. The model uniquely combines a Leslie population projection matrix and the logistic equation. Application of the model requires only a life table for the organism of interest, a measure of carrying capacity for the given population, and an estimation of the effect of a stressor on vital rates. The model was applied to investigate population dynamics for fathead minnow exposed to the androgen receptor agonist 17b-trenbolone. Organismal-level responses for fathead minnows exposed to varying levels of 17b-trenbolone were used to determine projected alterations in a population existing in a small body of water containing varying concentrations of the androgen. Fathead minnow populations occurring at carrying capacity and subsequently exposed to 0.027mg/L of 17b-trenbolone exhibited a 51% projected decrease in average population size after 2 years of exposure. Populations at carrying capacity exposed to concentrations of 17b-trenbolone X0.266mg/L exhibited a 93% projected decrease in average population size after 2 years of exposure. Overall, fathead minnow populations exposed to continued concentrations of 17b-trenbolone equal to or greater than 0.027mg/L were projected to have average equilibrium population sizes that approached zero. Published by Elsevier Inc.