Mechanistic Insights into 1,2-bis(2,4,6-tribromophenoxy)ethane-Induced Male Reproductive Toxicity in Zebrafish.

The novel brominated flame retardant, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), has increasingly been detected in environmental and biota samples. However, limited information is available regarding its toxicity, especially at environmentally relevant concentrations. In the present study, adult male zebrafish were exposed to varying concentrations of BTBPE (0, 0.01, 0.1, 1, and 10 µg/L) for 28 days. The results demonstrated underperformance in mating behavior and reproductive success of male zebrafish when paired with unexposed females. Additionally, a decline in sperm quality was confirmed in BTBPE-exposed male zebrafish, characterized by decreased total motility, decreased progressive motility, and increased morphological malformations. To elucidate the underlying mechanism, an integrated proteomic and phosphoproteomic analysis was performed, revealing a predominant impact on mitochondrial functions at the protein level and a universal response across different cellular compartments at the phosphorylation level. Ultrastructural damage, increased expression of apoptosis-inducing factor, and disordered respiratory chain confirmed the involvement of mitochondrial impairment in zebrafish testes. These findings not only provide valuable insights for future evaluations of the potential risks posed by BTBPE and similar chemicals but also underscore the need for further research into the impact of mitochondrial dysfunction on reproductive health.

Integrated Studies on Male Reproductive Toxicity of Bis(2-ethylhexyl)-tetrabromophthalate: in Silico, in Vitro, ex Vivo, and in Vivo.

Bis(2-ethylhexyl)tetrabromophthalate (TBPH) has been widely detected in the environment and organisms; thus, its toxic effects on male reproduction were systematically studied. First, we found that TBPH can stably bind to the androgen receptor (AR) based on in silico molecular docking results and observed an antagonistic activity, but not agonistic activity, on the AR signaling pathway using a constructed AR-GRIP1 yeast assay. Subsequently, we validated the adverse effects on male germ cells by observing inhibited androgen production and proliferation in Leydig cells upon in vitro exposure and affected general motility and motive tracks of zebrafish sperm upon ex vivo exposure. Finally, the in vivo reproductive toxicity was demonstrated in male zebrafish by reduced mating behavior in F0 generation when paired with unexposed females and abnormal development of their offspring. In addition, reduced sperm motility and impaired germ cells in male zebrafish were also observed, which may be related to the disturbed homeostasis of sex hormones. Notably, the specifically suppressed AR in the brain provides further evidence for the antagonistic effects as above-mentioned. These results confirmed that TBPH affected male reproduction through a classical nuclear receptor-mediated pathway, which would be helpful for assessing the ecological and health risks of TBPH.

Evaluation and Mechanistic Study of Transgenerational Neurotoxicity in Zebrafish upon Life Cycle Exposure to Decabromodiphenyl Ethane (DBDPE).

The novel brominated flame retardant decabromodiphenyl ethane (DBDPE) has become a ubiquitous emerging pollutant in the environment, which may evoke imperceptible effects in humans or wild animals. Hence in this study, zebrafish embryos were exposed to DBDPE (0, 0.1, 1, and 10 nM) until sexual maturity (F0), and F1 and F2 generations were cultured without further exposure to study the multi- and transgenerational toxicity and underlying mechanism. The growth showed sex-different changing profiles across three generations, and the social behavior confirmed transgenerational neurotoxicity in adult zebrafish upon life cycle exposure to DBDPE. Furthermore, maternal transfer of DBDPE was not detected, whereas parental transfer of neurotransmitters to zygotes was specifically disturbed in F1 and F2 offspring. A lack of changes in the F1 generation and opposite changing trends in the F0 and F2 generations were observed in a series of indicators for DNA damage, DNA methylation, and gene transcription. Taken together, life cycle exposure to DBDPE at environmentally relevant concentrations could induce transgenerational neurotoxicity in zebrafish. Our findings also highlighted potential impacts on wild gregarious fish, which would face higher risks from predators.

Evidence for Adverse Effects on Liver Development and Regeneration in Zebrafish by Decabromodiphenyl Ethane.

Decabromodiphenyl ethane (DBDPE), a ubiquitous emerging pollutant, could be enriched in the liver of organisms, but its effects and mechanisms on liver development and regeneration remain largely unknown. In the present study, we first investigated the adverse effects on liver development and found decreased area and intensity of fluorescence in transgenic zebrafish larvae exposed to DBDPE; further results in wild-type zebrafish larvae revealed a possible mechanism involving disturbed MAPK/Fox O signaling pathways and cell cycle arrest as indicated by decreased transcription of growth arrest and DNA-damage-inducible beta a (gadd45ba). Subsequently, an obstructed recovery process of liver tissue after partial hepatectomy was characterized by the changing profiles of ventral lobe-to-intestine ratio in transgenic female adults upon DBDPE exposure; further results confirmed the adverse effects on liver regeneration by the alterations of the hepatic somatic index and proliferating cell nuclear antigen expression in wild-type female adults and also pointed out a potential role of a disturbed signaling pathway involving cell cycles and glycerolipid metabolism. Our results not only provided novel evidence for the hepatotoxicity and underlying mechanism of DBDPE but also were indicative of subsequent ecological and health risk assessment.

Niclosamide Exposure at Environmentally Relevant Concentrations Efficaciously Inhibited the Growth and Disturbed the Liver-Gut Axis of Adult Male Zebrafish.

In the current study, adult male zebrafish fed a normal diet (ND) or high-fat diet (HFD) were exposed to niclosamide (NIC) at environmentally relevant concentrations to reveal the accumulation and distribution in different tissues and evaluate the effects on liver-gut axis. Chemical analysis indicated that the liver bore a greater burden of NIC compared with the brain and gonads in adult zebrafish, and the HFD-fed fish bore greater burden in their liver and brain than those ND-fed fish. The indications from body weight, growth rate, body mass index, micro-CT images, biochemical and pathological changes confirmed that NIC can efficaciously curb weight gain and improve overloads of in plasma insulin and glucose in HFD-fed zebrafish. However, the potential effects on liver-gut axis in ND-fed zebrafish were also elucidated: NIC disturbed mitochondrial energy production, inhibited the glycemic and triacylglycerol biosynthesis but promoted triacylglycerol and free fatty acid catabolism, therefore reduced lipid accumulation in hepatocytes; NIC also impaired the physical barrier, evoked inflammatory and oxidative stress and led to microbiota dysbiosis in the intestine. There findings highlighted the necessity for evaluating its potential impacts on the health of wild animals as well as human beings upon long-term exposure.

Decabromodiphenyl ethane induced hyperactivity in developing zebrafish at environmentally relevant concentrations.

Decabromodiphenyl ethane (DBDPE), a widely used novel brominated flame retardant, is gaining concerns due to rapidly increased contents in various environmental and biota samples. In the present study, zebrafish (Danio rerio) embryos were exposed to 2.91, 9.71, 29.14 and 97.12 µg/L of DBDPE until 120 h post-fertilization (hpf) to investigate the potential developmental neurotoxicity and underlying mechanisms. Chemical analysis revealed concentration-dependently increased body burdens of DBDPE in zebrafish larvae, with bioaccumulation factors (BCFs) ranging from 414 to 726. Embryonic exposure to DBDPE caused hyperactivity without affecting the development of secondary motoneuron axons and muscle fibers. However, further results implicated that DBDPE may affect the locomotor regulatory network via different mechanisms at lower and higher concentrations. On the one hand, embryonic exposure to 2.91 µg/L DBDPE transiently promoted spontaneous coiling contractions, but showed no effects on touch-response and swimming activity in zebrafish larvae. The whole-body contents of neurotransmitters were significantly decreased. Significant decreased protein abundances of α1-TUBULIN and SYN2a and molecular docking results pointed out possible interactions of DBDPE with these two proteins. However, these changes may be unconcerned with the transient hyperactivity, and the exact molecular mechanisms need further investigation. On the other hand, 29.14 and 97.12 µg/L DBDPE exposure caused longer-lasting effects in promoting spontaneous coiling contractions, and also touch-response and swimming activity. At the same time, increased ACh contents (without changes of other neurotransmitters) and ChAT activity and inhibited transcription of nAChRs were observed at higher concentrations. Molecular docking indicated direct interaction of DBDPE with ChAT. The results suggested that DBDPE induced hyperactivity at higher concentrations was probably involved with disrupted cholinergic system, with ChAT as a potential target. Given that the body burden of DBDPE in lower concentration group was comparable with those detected in wild fish, the current results may provide useful information for ecological risk assessment.

Effects of SiO2 nanoparticles on the uptake of tetrabromobisphenol A and its impact on the thyroid endocrine system in zebrafish larvae.

The coexistence of nanoparticles and organic toxicants in the environment modifies pollutant bioavailability and toxicity. This study investigated the influence of silicon dioxide nanoparticles (n-SiO2) on the uptake of tetrabromobisphenol A (TBBPA) and its impact on the thyroid endocrine system in zebrafish larvae. Zebrafish (Danio rerio) embryos were exposed to TBBPA at different concentrations (50, 100, and 200 µg/L) alone or in combination with n-SiO2 (25 mg/L) until 120 h post-fertilization (hpf). Chemical measurements showed that both TBBPA and n-SiO2 were bioconcentrated in zebrafish larvae, and the uptake of TBBPA was enhanced by n-SiO2. Furthermore, zebrafish larvae exposed to 200 µg/L TBBPA alone exhibited significantly increased T4 contents and decreased T3 contents, whereas n-SiO2 treatment alone did not have a detectable effect. Furthermore, the thyroid hormone levels changed more upon treatment with 200 µg/L TBBPA combined with 25 mg/L n-SiO2 than upon TBBPA treatment alone. Alterations in gene transcription along the related hypothalamic-pituitary-thyroid (HPT) axis were observed, and expression of the binding and transport protein transthyretin (TTR) was significantly decreased for both TBBPA alone and co-exposure with n-SiO2. Thus, the current study demonstrates that n-SiO2, even at the nontoxic concentrations, increases thyroid hormone disruption in zebrafish larvae co-exposed to TBBPA by promoting its bioaccumulation and bioavailability.

Dysregulation of Intestinal Health by Environmental Pollutants: Involvement of the Estrogen Receptor and Aryl Hydrocarbon Receptor.

To determine how environmental pollutants induce dysbiosis of the gut microbiota, we exposed adult zebrafish to model pollutants with varied modes of action (atrazine, estradiol, polychlorinated biphenyl [PCB]126, and PCB153) for 7 days. Subsequently, metagenomic sequencing of the intestines was performed to compare the gut microbiomes among the groups. We observed clear compound- and sex-specific responses to xenobiotic stress. Principal component analysis revealed involvement of the aryl hydrocarbon receptor (AhR) and, to a lesser extent, the estrogen receptor (ER) in the dysregulation of the intestinal microbiota. The model pollutants differentially impaired intestinal and hepatic physiological activities, as indicated by assessments of gut motility, epithelial permeability, inflammation, and oxidative stress. Correlation analysis showed that abnormal Aeromonas reproduction, especially in the PCB126 groups, was significantly positively associated with oxidative damage. Aeromonas closely interacted with Mannheimia and Blastococcus to regulate intestinal permeability. In summary, we demonstrated that ER and AhR signaling regulated the dynamics of the gut microbiota. Our findings provide new mechanistic insight into the complex interactions between the host metabolism and gut microbiota, which may contribute to the grouped assessment of environmental pollutants in future.

Endocrine disruption in Chinese rare minnow (Gobiocypris rarus) after long-term exposure to low environmental concentrations of progestin megestrol acetate.

Synthetic progestins are widely used pharmaceutical agents that have become common contaminants in the aquatic environment. The potential adverse effects of long-term exposure on aquatic wildlife, however, are not fully understood. The aim of this study was to investigate the endocrine disruption in Chinese rare minnow (Gobiocypris rarus) in response to megestrol acetate (MTA) exposure. Newly-hatched Chinese rare minnow larvae were exposed to MTA at a nominal concentration of either 1 ng/L (detected concentrations ranged from 0.18 to 0.93 ng/L) or 10 ng/L (detected concentrations ranged from 4.27 to 9.64 ng/L) for 6 months and the effects on growth, sex steroid hormones, gonadal histology, and steroidogenic genes expression were determined. After 6 months of exposure to a nominal concentration of 10 ng/L MTA, the body weight and condition factors were significantly increased in fish of both sexes. Exposure to a nominal concentration of 10 ng/L MTA significantly reduced plasma concentrations of estradiol and 11-ketotestosterone in female fish while also reducing testosterone and 11-ketotestosterone in male fish. Gonad histology revealed significantly reduced proportions of vitellogenic oocytes in female fish exposed to a nominal concentration of 10 ng/L MTA and induction of atretic follicles in female fish exposed to both nominal concentrations of MTA. The expression of cyp19a1a and cyp17a1 in the gonads was up-regulated in the ovaries while down-regulated in the testes. Our results indicate that MTA can induce endocrine disruption in Chinese rare minnow at the low concentrations found in contaminated environments. This indicates a potentially high ecological risk from MTA to fish populations in MTA-contaminated aquatic environments in China and may also in other regions.

Enhanced Bioconcentration of Bisphenol A in the Presence of Nano-TiO2 Can Lead to Adverse Reproductive Outcomes in Zebrafish.

Titanium dioxide nanoparticles (n-TiO2) and bisphenol A (BPA) are widespread environmental contaminants in the aquatic environment. We hypothesized that n-TiO2 may adsorb BPA, and thus modify its bioavailability and toxicity to aquatic organisms. In this study, the bioavailability and toxicity of BPA (0, 2, 20, 200 µg/L) was investigated in the presence of n-TiO2 (100 µg/L). The n-TiO2 sorbed BPA and the resulting nanoparticles were taken up by zebrafish, where they translocated to the liver, brain, and gonad tissues. Increased tissue burdens of both BPA and n-TiO2 were observed following coexposure, and they also caused a reduction in plasma concentrations of estradiol (E2), testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Plasma vitellogenin (VTG) concentrations were significantly increased in males and females upon exposure to BPA. Histological examination of the ovary and testes did not show obvious morphological alterations; however, inhibition of egg production was noted in the presence of n-TiO2. The results indicated that n-TiO2 acts as a carrier of BPA and enhances its bioconcentration in zebrafish, leading to endocrine disruption and impairment of reproduction.