Life-cycle exposure to BDE-47 results in thyroid endocrine disruption to adults and offsprings of zebrafish (Danio rerio)

Abstract

2,2,4',4'-Tetrabromodi-phenyl ether (BDE-47) is predominantly concentrated in humans and wildlife and disturbs thyroid hormone homeostasis. The purpose of this study was to characterize the thyroid endocrine disruption induced by life-cycle exposure to BDE-47 in adults and offspring of zebrafish (Danio rerio). We exposed zebrafish embryos at the blastula stage to different concentrations of BDE-47 (1, 5, and 10μg/L). Exposure duration was 180days until fish reached adulthood. In F0 larvae, exposure decreased survival and increased malformations at 4 dpf. Thyroid hormone concentrations did not differ significantly between the F0 larvae and controls. All exposures significantly up-regulated expression of tshß, pa8, ugt1 and tg and down-regulated ttr. Significant up-regulation of dio2 and crh was observed in the 10μg/L BDE-47 group. There was no significant difference in the growth and somatic index between F0 adults and controls. BDE-47 (10μg/L) significantly decreased whole-body content of thyroxine (T4) but significantly increased triiodothyronine (T3) in both sexes. All exposures up-regulated expression of crh, tshß, pa8, ugt1 and tg and down-regulated ttr. Exposure to 10μg/L BDE-47 significantly up-regulated dio2 and ugt1 in both sexes. BDE-47 exposure (5 and 10μg/L) significantly increased the activity of pethoxy-resorufin-O-deethylase and UDP-glucuronosyl transferase. BDE-47 (10μg/L) significantly increased activity of ethoxy- and methoxy-resorufin-O-deethylase. In F1 offspring without continued BDE-47 (10μg/L) treatment, T4 significantly decreased and T3 increased. T4 was further decreased and T3 was further increased with continued BDE-47 treatment. Continued BDE-47 exposure decreased hatching and increased malformation compared with those without BDE-47 exposure. Expression of crh, tshß, dio2, pa8, ugt1 and tg was significantly up-regulated without BDE-47 exposure and with continued exposure. With continued BDE-47 exposure, dio1 was significantly up-regulated and ttr was significantly down-regulated. All the genes showed clear differences between continued exposure to 10μg/L BDE-47 and without BDE-47 exposure. These results suggest that parental exposure to BDE-47 results in thyroid endocrine disruption in adults and offspring.

Keywords: BDE-47; Life-cycle exposure; Thyroid disruption; Zebrafish offsprings.