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Identification of Androgen Receptor Antagonists in Fish Using a Simple Bioassay with the Fathead Minnow Pimephales promelas .
Citation:
JENSEN, K. M., E. J. DURHAN, M. D. KAHL, E. A. MAKYNEN, D. MARTINOVIC, D. L. VILLENEUVE, AND G. T. ANKLEY. Identification of Androgen Receptor Antagonists in Fish Using a Simple Bioassay with the Fathead Minnow Pimephales promelas . Presented at SETAC Annual Meeting, Tampa, FL, November 16 - 20, 2008.
Impact/Purpose:
Inhibition of tubercle formation by TB in female fathead minnows provides the basis for a sensitive, specific, and relatively simple assay to identify AR antagonists. Such an assay could be used to confirm MOA for a chemical suspected of possessing anti-androgenic properties, or could be used to test complex mixtures (e.g., effluents) for the presence of chemicals that interact with the AR.
Description:
Considerable effort has been expended on the development of bioassays to detect chemicals that affect endocrine function controlled by the vertebrate hypothalamic-pituitary-gonadal (HPG) axis via different mechanisms/modes of action (MOA). Antagonism of the androgen receptor (AR) is an important mechanism through which the HPG axis of fish can be affected by environmental contaminants. However, there are few in vivo tests specific for the detection of chemicals that act as AR antagonists. The suite of responses produced by these chemicals in sexually-mature fish can be somewhat ambiguous, making it difficult to diagnose this MOA as responsible for reproductive toxicity. In this presentation we describe a short-term assay with the fathead minnow which can be used to identity AR antagonists. The basis of the approach lies in evaluating the ability of test chemicals to block occurrence of an in vivo response mediated through the AR. Studies in our lab and elsewhere have shown that the synthetic androgen 17â-trenbolone (TB) binds with high affinity to fish AR(s) and masculinizes female fathead minnows causing the development of cranial nuptial tubercles, external structures which can be visually detected and easily quantified. Exposure (via the water) to several well-characterized AR antagonists (flutamide, vinclozolin, cyproterone acetate) effectively inhibited induction of nuptial tubercles in female fathead minnows simultaneously-exposed for 14 d to TB (500 µg/L). Exposure of the fish to ammonia, a common environmental contaminant with no known HPG activity, did not block TB-induced nuptial tubercle formation in females. Inhibition of tubercle formation by TB in female fathead minnows provides the basis for a sensitive, specific, and relatively simple assay to identify AR antagonists. Such an assay could be used to confirm MOA for a chemical suspected of possessing anti-androgenic properties, or could be used to test complex mixtures (e.g., effluents) for the presence of chemicals that interact with the AR.