Environmental estrogens and skeletal development disruption in the fathead minnow : A teleost model of vertebrate developmental toxicity Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rj4308719

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  • Natural and synthetic estrogenic compounds detected in surface waters have been linked to endocrine signaling disruption in several species. Endogenous estrogen contributes to cartilage and bone deposition during development in vertebrates, and is susceptible to perturbation from xenoestrogens. The goals of this work were to develop a teleost model to be used in bioassay to (a) determine the link between environmental estrogens and the morphological endpoint of vertebral abnormalities, and (b) investigate the biochemical mechanism involved in vertebral dysmorphogenesis. The hypothesis of this work is that xenobiotics with estrogenic activity adversely impact vertebral bone formation through disruption of an essential endocrine signal in bone formation, insulin-like growth factor-1 (IGF-1). Preliminary bioassay work identified the fathead minnow (Pimephales promelas) as an appropriate teleost model for investigating sublethal vertebral deformities in post-larval fish. A ranking system of relative developmental score was used to quantify the qualitative observation of skeletal development in juvenile fish. Fathead minnows were exposed to 0.1-100 pg/I 17aethinylestradiol (EE2) and 0.1-1000 pg/I bisphenol A (BPA) from egg stage to 25- 26 days post-hatch. Fish from exposure replicates were analyzed for vertebral malformations and developmental score by fluorescently staining calcified tissues. Replicates of exposed fish were also weighed and processed to quantify IGF-1 levels in whole body homogenate. MC3T3 osteoblasts were used to characterize in vitro bone cell proliferation and IGF-1, IGF-1 receptor, and estrogen receptor protein expression in response to EE2 and BPA exposure. EE2 and BPA treatment did not significantly affect protein levels in vitro, and had no significant effect on proliferation of osteoblasts in culture. However, EE2 exposure did induce an increase in vertebral deformities in vivo in fathead minnows, and a corresponding decrease in skeletal development. EE2-exposed fish also demonstrated a decrease in IGF-1 concentration that correlated to decreased weights. BPA did not cause significant changes in length, weight, or IGF-1 levels compared to control fish, nor did BPA-exposed fish demonstrate significant vertebral deformity. The results of these studies suggest skeletal development is a potential endpoint of endocrine disruption from potent environmental estrogens. Further IGF-1 and growth factor-related studies would provide a better mechanistic understanding of the etiology of vertebral dysmorphogenesis.
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