Sex differences, growth, reproduction and zinc ion homeostasis of zebrafish after chronic dietary l-selenomethionine exposure.

Several mechanisms regarding the developmental and reproductive toxicity of l -selenomethionine (SeMet) in freshwater fish have been widely reported. However, limited information was available on endocrine-disrupting effects of SeMet. In this study, zebrafish larvae (day 24 post-fertilization) were exposed to environmentally-relevant levels of dietary SeMet (control, 1.11 ± 0.11, 3.59 ± 0.20, 10.80 ± 0.52, 29.19 ± 0.46, and 58.63 ± 0.70 μg Se/g d.w. diet) for 90 days until sexual maturity. For the first time, a gender difference in the effect of SeMet on body mass of zebrafish was observed. The lowest observed adverse effect level (LOAEL) in male was 10.80 ± 0.52 μg Se/g d.w., while it was 29.19 ± 0.46 μg Se/g d.w. in female. Chronic exposure to dietary SeMet reduced the percentage of early vitellogenic oocyte in female and the percentage of spermatid in male by inhibiting the growth hormone/insulin-like growth factors (GH/IGFs) and hypothalamus-pituitary-gonad (HPG) systems, which was characterized by significant decreases in the transcriptional levels of gh , igf1 , era , and ar. Se content in the liver of male was significantly higher than that in female when dietary Se level reached 10.80 ± 0.52 μg Se/g d.w.. Furthermore, the zinc content in the livers and gonads of both female and male treated with 29.19 ± 0.46 and 58.63 ± 0.70 μg Se/g d.w. diets was significantly reduced. Reduction of zinc ion not only led to the significantly upregulated transcriptional levels of zip1 and znt2 , but also downregulated transcriptional levels of znf219l and sp7. In summary, this study provides a new evidence that chronic exposure to high level of dietary SeMet (≥10.80 μg Se/g d.w.) could impair the development and reproduction of zebrafish with gender difference by interfering the GH/IGFs and HPG systems. Moreover, disruption of zinc ion homeostasis might exacerbate the toxicity of Se to zebrafish. Image 1 • The LOAEL in male was 10.80 μg Se/g, while it was 29.19 μg Se/g in female. • SeMet impaired growth and reproduction by interfering GH/IGFs and HPG systems. • Chronic exposure to high level of dietary SeMet disrupted zinc ion homeostasis. [ABSTRACT FROM AUTHOR]