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Computational Model of the Fathead Minnow Hypothalamic-Pituitary-Gonadal Axis: Incorporating Protein Synthesis in Improving Predictability of Responses to Endocrine Active Chemicals
Breen, M., Dan Villeneuve, G. Ankley, D. Bencic, K. Watanabe, A. Lloyd, AND R. Conolly. Computational Model of the Fathead Minnow Hypothalamic-Pituitary-Gonadal Axis: Incorporating Protein Synthesis in Improving Predictability of Responses to Endocrine Active Chemicals. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY PART C. Elsevier Science Ltd, New York, NY, 183:36-45, (2016).
The computational model described in this manuscript is part of a quantitative adverse outcome pathway (QAOP) for endocrine disruption, specifically for aromatase inhibition and reproductive dysfunction, in fathead minnows. The manuscript describes iterative refinement of a previously published computational model. The main purposes of this work are (1) to obtain a better understanding of how environmental chemicals perturb normal reproductive biology, leading to adverse effects on fish populations, and (2) to provide a quantitative, predictive tool for support of regulatory decision-making.
There is international concern about chemicals that alter endocrine system function in humans and/or wildlife and subsequently cause adverse effects. We previously developed a mechanistic computational model of the hypothalamic-pituitary-gonadal (HPG) axis in female fathead minnows exposed to a model aromatase inhibitor, fadrozole (FAD), to predict dose-response and time-course behaviors for apical reproductive endpoints. Initial efforts to develop a computational model describing adaptive responses to endocrine stress providing good fits to empirical plasma 17β-estradiol (E2) data in exposed fish were only partially successful, which suggests that additional regulatory biology processes need to be considered. In this study, we addressed short-comings of the previous model by incorporating additional details concerning cyp19a (aromatase) protein synthesis. Predictions based on the revised model were evaluated using plasma E2 concentrations and ovarian cytochrome P450 (CYP) 19A aromatase mRNA data from two fathead minnow time-course experiments with FAD, as well as from a third 4-day study. The extended model provides better fits to measured E2 time-course concentrations, and the model accurately predicts CYP19A mRNA fold changes and plasma E2 dose-response from the 4-d concentration-response study. This study suggests that aromatase protein synthesis is an important process in the biological system to model the effects of FAD exposure.