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EVALUATION OF THE MODEL ANTI-ANDROGEN FLUTAMIDE FOR ASSESSING THE MECHANISTIC BASIS OF RESPONSES TO AN ANDROGEN IN THE FATHEAD MINNOW (JOURNAL ARTICLE)
Citation:
ANKLEY, G. T., D. L. DEFOE, M. D. KAHL, K. M. JENSEN, E. A. MAKYNEN, A. L. MIRACLE, P. C. HARTIG, V. S. WILSON, L. E. GRAY, AND M. C. CARDON. EVALUATION OF THE MODEL ANTI-ANDROGEN FLUTAMIDE FOR ASSESSING THE MECHANISTIC BASIS OF RESPONSES TO AN ANDROGEN IN THE FATHEAD MINNOW (JOURNAL ARTICLE). ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 38(23):6322-6327, (2004).
Impact/Purpose:
The indeterminate condition of exposure indicator research stands to change markedly with the ability to connect molecular biological technologies with cellular or tissue effects and outcomes. Three focal areas of ecological research aim to develop a sequence of approaches where "the earliest recognizable signatures of exposure" (i.e., unique patterns of up- and down-regulated genes and proteins) are identified for numerous stressors, demonstrable in case studies and incorporated into Agency, State and Regional studies supported by EMAP and other programs.
Area 1, Computational Toxicology Research: Exposure assessment has historically been based on use of chemical analysis data to generate exposure models. While biological activity of chemicals has been recognized to be important for exposure risk assessments, measurement of such activity has been limited to whole organism toxicity tests. Use of molecular approaches will:
improve extrapolation between components of source-to-outcome continuum (source , exposure , dose , effect , outcome)
Using a systems modeling approach, gene and protein expression data, in small fish models (fathead minnow and zebrafish), will be integrated with metabolomic and histopathological data. This will assist in prediction of environmental transformation and chemical effects based on structural characteristics, and enhance quantitative risk assessments, including areas of uncertainty such as a basis for extrapolation of effects of endocrine disrupting chemicals, interspecies extrapolation, complex chemical mixtures and dose-response assessment.
Area 2, Ecological Research-Environmental Diagnostics: Development of molecular diagnostic indicators contributes to several of the GPRA Diagnostic Research Goals. Methods will employ DNA microarray technology and expression proteomics, focusing on species of relevance to aquatic ecosystem risk assessment. Significantly, these diagnostic indicators will open the door to understanding subcellular interactions resulting from exposure to complex chemical mixtures.
define relationship between genetic disposition of populations and degree/specificity of stressor-specific gene transcriptional response in aquatic organisms (fish and invertebrates)
identify of chemical mixture induced transcriptional "patterns" using microarrays and hyperspectral scanning - via collaboration with DOE Sandia National Labs
apply molecular indicators to watershed level stressor study, including pilot studies with targeted pesticides and toxins indicators
develop molecular indicators of exposure for invertebrates (Daphnia, Lumbriculus, Chironomus)
Area 3, Exposure Research in Endocrine Disruptors:
Subobjective 1: Develop exposure methods, measurement protocols, and models for assessment of risk management practices of endocrine disrupting compounds. As risk management approaches are identified and developed, there will be a need to identify, adapt and develop bioassay screening tools and other analytical methods to assess their efficacy. Measurements research will be performed to define management needs. This effort will entail cross-lab participation from NRMRL, NERL and NHEERL.
Subobjective 2: Determine extent of environmental and human exposures to EDCs, characterize sources and factors influencing these exposures, develop and evaluate risk management strategies to reduce exposures. In order to develop effective risk management strategies, it is important to understand the extent of exposures to endocrine disrupting compounds and factors influencing source-to-exposure-to-dose relationships.
apply molecular indicators of exposure to estrogenic compounds in selected wastewater treatment plants located in ten USEPA Regions
identify differential gene expression following exposure of fathead minnows to environmental androgens and androgen-like compounds
apply molecular indicators of exposu
Description:
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 which 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 172-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.