A whole life cycle assessment on effects of waterborne PBDEs on gene expression profile along the brain–pituitary–gonad axis and in the liver of zebrafish

Enviro Toxic and Chemistry

et al. 2014

The objective of the present study was to investigate the impact of polybrominated diphenyl ethers (PBDEs) on fish reproduction over 2 generations. Zebrafish (Danio rerio) embryos (F0) were exposed to low concentrations (3 mg/L, 10 mg/L, and 30 mg/ L) of the PBDE mixture DE-71 until they were sexually mature, and steroid hormone production, expression of genes involved in steroidogenesis, gonadal development, and gamete characteristics were examined. Exposure of female zebrafish to DE-71 resulted in lower estradiol production and downregulation of cytochrome P450 aromatase mRNA. In males, exposure to DE-71 resulted in greater testosterone production and greater cytochrome P450 c17 a-hydroxylase,17,20-lase mRNA expression. Moreover, hepatic vitellogenin mRNA and estrogenic receptor b gene transcription were downregulated in females and males. Expression of the follicle-stimulating hormone b gene in the pituitary was upregulated, and the expression of luteinizing hormone b was downregulated in both sexes. Histological examination showed inhibition of oocyte maturation in females and retarded spermiation in males. The average number of eggs (F1) produced was also reduced. Additionally, exposure of F0 embryos to DE-71 did not result in developmental toxicity, whereas delayed hatching, reduced survival, and decreased growth were observed in the F1 embryos derived from parent fish exposed to DE-71. Therefore, long-term exposure to low concentrations of PBDEs in zebrafish could cause reproductive impairment, suggesting that PBDEs might have significant adverse effects on fish population in the highly PBDEs-contaminated aquatic environment. Environ Toxicol Chem 2014;33:1354-1362. # 2014 SETAC

Section: Discussionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 90%

Endocrine disruption and reproduction impairment in zebrafish after long‐term exposure to DE‐71

Liu

Enviro Toxic and Chemistry

et al. 2014

“…18,19 In the present study, chronic exposure to DCOIT induced a significant upregulation of mGnRH rather than sGnRH, another subunit examined, probably as a consequence of the physiologically closer correlation of mGnRH with endocrine regulation in marine medaka.…”

Section: ■ Discussionmentioning

confidence: 42%

Chronic Exposure of Marine Medaka (Oryzias melastigma) to 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) Reveals Its Mechanism of Action in Endocrine Disruption via the Hypothalamus-Pituitary-Gonadal-Liver (HPGL) Axis

Zhang

Rui³

et al. 2016

Environ. Sci. Technol.

In this study, marine medaka (Oryzias melastigma) were chronically exposed for 28 days to environmentally realistic concentrations of 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) (0, 0.76, 2.45, and 9.86 μg/L), the active ingredient in commercial antifouling agent SeaNine 211. Alterations of the hypothalamus-pituitary–gonadal-liver (HPGL) axis were investigated across diverse levels of biological organization to reveal the underlying mechanisms of its endocrine disruptive effects. Gene transcription analysis showed that DCOIT had positive regulatory effects mainly in male HPGL axis with lesser extent in females. The stimulated steroidogenic activities resulted in increased concentrations of steroid hormones, including estradiol (E2), testosterone (T), and 11-KT-testosterone (11-KT), in the plasma of both sexes, leading to an imbalance in hormone homeostasis and increased E2/T ratio. The relatively estrogenic intracellular environment in both sexes induced the hepatic synthesis and increased the liver and plasma content of vitellogenin (VTG) or choriogenin. Furthermore, parental exposure to DCOIT transgenerationally impaired the viability of offspring, as supported by a decrease in hatching and swimming activity. Overall, the present results elucidated the estrogenic mechanisms along HPGL axis for the endocrine disruptive effects of DCOIT. The reproductive impairments of DCOIT at environmentally realistic concentrations highlights the need for more comprehensive investigations of its potential ecological risks.

“…The differential responses we observed may reflect differences in life stage and exposure conditions, including the presence of 6‐OH‐BDE‐47 and 2,4,6‐TBP in the exposure mixture along with DE‐71. In addition to effects on thyroid homeostasis, long‐term exposure to DE‐71 can elicit reproductive effects through altered sex ratios, decreased gamete quality, and altered steroidogenesis . Reproductive endpoints were not evaluated in the present study, so further studies are needed to discern potential effects of PBDE/OH‐BDE mixtures on reproductive maturation.…”

Section: Discussionmentioning

confidence: 96%

Exposure to a PBDE/OH‐BDE mixture alters juvenile zebrafish (Danio rerio) development

Macaulay

Chernick

Enviro Toxic and Chemistry

et al. 2016

Polybrominated diphenyl ethers (PBDEs) and halogenated phenolic compounds (e.g., hydroxylated BDEs (OH-BDEs)) arecontaminants detected together frequently in human tissues, and are structurally similar to thyroid hormones (TH). THs partially mediate metamorphic transitions between life stages in zebrafish, making this a critical developmental window which may be uniquely vulnerable to chemicals disrupting thyroid signaling. In this study, zebrafish were exposed to 6-OH-BDE-47 (30 nM) alone or to a low (30 μg/L) or high dose (600 μg/L) mixture of PentaBDEs, 6-OH-BDE-47 (0.5–6 μg/L), & 2,4,6 tribromophenol (TBP) (5–100 μg/L) during juvenile development (9–23 days post fertilization; dpf) and evaluated for developmental endpoints mediated by TH signaling. Fish were sampled at three time points and examined for developmental and skeletal morphology, apical thyroid and skeletal gene markers, and modifications in swimming behavior (as adults). Exposure to the high mixture resulted in > 85% mortality within one week of exposure, despite being below reported acute toxicity thresholds for individual congeners. The low mixture and 6-OH-BDE-47 groups exhibited reductions in body length and delayed maturation, specifically relating to swim bladder,?, fin, and pigmentation development. Reduced skeletal ossification was also observed in 6-OH-BDE-47 treated fish. Assessment of thyroid and osteochondral gene regulatory networks demonstrated significantly increased expression of genes that regulate skeletal development and THs. Overall, these results indicate that exposures to PBDEs/OH-BDEs mixtures adversely impact zebrafish maturation during metamorphosis.