Waterborne exposure to bisphenol F causes thyroid endocrine disruption in zebrafish larvae

Evaluation of thyroid-disrupting effects of bisphenol F and bisphenol S on zebrafish (Danio rerio) using anti-transthyretin monoclonal antibody-based immunoassays

The thyroid disrupting chemicals (TDCs) have raised great concerns due to their adverse impacts on thyroid hormones (THs). In this study, we investigated the thyroid-disrupting effects of bisphenol F (BPF) and bisphenol S (BPS), two major BPA substitutes, on adult zebrafish (Danio rerio). Firstly, anti-transthyretin (TTR) monoclonal antibody (anti-TTR mAb) was prepared and used to establish an indirect ELISA, which had a working range of 15.6∼1000 ng/mL of a detection limit of 6.1 ng/mL. The immunoassays based on anti-TTR mAb showed that exposure to BPF (10 and 100 μg/L) and BPS (100 μg/L) significantly elevated the levels of TTR protein in the plasma, liver, and brain tissues. Moreover, immunofluorescence showed that 100 μg/L BPF and BPS induced the production of TTR protein in liver and brain tissues. In addition, BPF and BPS increased THs levels and damaged thyroid tissue structure in adult female zebrafish. Especially, 100 μg/L BPF significantly increased T4 and T3 levels by 2.05 and 1.14 times, and induced pathological changes of thyroid follicles. The changes in the expression levels of genes involved in the hypothalamus-pituitary-thyroid (HPT) axis further illustrated that BPF and BPS had significant adverse effects on THs homeostasis and thyroid function in zebrafish. Therefore, TTR immunoassays could be used for the evaluation of thyroid-disrupting effects in fish and BPF exhibited greater disruption than BPS.

Maternal bisphenols exposure and thyroid function in children: a systematic review and meta-analysis

Background

Evidence from animal experiments and epidemiological studies has reported controversial results about the effects of prenatal bisphenols (BPs) exposure on childhood thyroid function. This study aims to explore the associations of prenatal exposure to BPs with thyroid-related hormones (THs) in newborns and early childhood, with a particular focus on the sex-dependent and exposure level effects.

Methods

Correlated studies were systematically searched from PubMed, Web of Science, Medline, Cochrane, and Embase until February 21, 2024. The exposures assessed include bisphenol A (BPA), bisphenol F (BPF), bisphenol S (BPS), bisphenol AF (BPAF), and tetrachlorobisphenol A (TCBPA). THs measured were thyroid stimulating hormone (TSH), total tri-iodothyronine (TT3), total thyroxine (TT4), free tri-iothyronine (FT3), and free thyroxine (FT4). Effect estimates were quantified using coefficients from multivariable regression models. Statistical analyses were completed using Stata 16.0. The methodological quality of the included studies was evaluated using the Newcastle-Ottawa Scale (NOS).

Results

Eleven cohort studies comprising 5,363 children were included in our meta-analysis. Prenatal bisphenol concentrations were statistically significant related to alterations in thyroid hormones in children, exclusively in female offspring, including reduced TSH (β = -0.020, 95% CI: -0.036, -0.005) and increased TT3 levels (β = 0.011, 95% CI: 0.001, 0.021), and exposure to high concentration of bisphenols (>1.5 ug/g creatinine) significantly reduced FT3 levels in children (β = -0.011, 95% CI: -0.020, -0.003).

Conclusion

Prenatal bisphenol exposure is linked to alterations in thyroid hormone levels in girls, necessitating enhanced measures to control bisphenol exposure levels during pregnancy for child health protection.

Systematic Review Registration

https://inplasy.com, identifier INPLASY202450129.

Bisphenol-F and Bisphenol-S (BPF and BPS) Impair the Stemness of Neural Stem Cells and Neuronal Fate Decision in the Hippocampus Leading to Cognitive Dysfunctions

Neurogenesis occurs throughout life in the hippocampus of the brain, and many environmental toxicants inhibit neural stem cell (NSC) function and neuronal generation. Bisphenol-A (BPA), an endocrine disrupter used for surface coating of plastic products causes injury in the developing and adult brain; thus, many countries have banned its usage in plastic consumer products. BPA analogs/alternatives such as bisphenol-F (BPF) and bisphenol-S (BPS) may also cause neurotoxicity; however, their effects on neurogenesis are still not known. We studied the effects of BPF and BPS exposure from gestational day 6 to postnatal day 21 on neurogenesis. We found that exposure to non-cytotoxic concentrations of BPF and BPS significantly decreased the number/size of neurospheres, BrdU+ (proliferating NSC marker) and MAP-2+ (neuronal marker) cells and GFAP+ astrocytes in the hippocampus NSC culture, suggesting reduced NSC stemness and self-renewal and neuronal differentiation and increased gliogenesis. These analogs also reduced the number of BrdU/Sox-2+, BrdU/Dcx+, and BrdU/NeuN+ co-labeled cells in the hippocampus of the rat brain, suggesting decreased NSC proliferation and impaired maturation of newborn neurons. BPF and BPS treatment increases BrdU/cleaved caspase-3+ cells and Bax-2 and cleaved caspase protein levels, leading to increased apoptosis in hippocampal NSCs. Transmission electron microscopy studies suggest that BPF and BPS also caused degeneration of neuronal myelin sheath, altered mitochondrial morphology, and reduced number of synapses in the hippocampus leading to altered cognitive functions. These results suggest that BPF and BPS exposure decreased the NSC pool, inhibited neurogenesis, induced apoptosis of NSCs, caused myelin degeneration/synapse degeneration, and impaired learning and memory in rats.

The association between prenatal bisphenol F exposure and infant neurodevelopment: The mediating role of placental estradiol

BACKGROUND

There are limited population studies on the neurodevelopmental effects of bisphenol F (BPF), a substitute for bisphenol A. Furthermore, the role of placental estradiol as a potential mediator linking these two factors remains unclear.

OBJECTIVE

To examine the association between maternal prenatal BPF exposure and infant neurodevelopment in a prospective cohort study and to explore the mediating effects of placental estradiol between BPF exposure and neurodevelopment in a nested case-control study.

METHODS

The prospective cohort study included 1077 mother-neonate pairs from the Wuhu city cohort study in China. Maternal BPF was determined using the liquid/liquid extraction and Ultra-performance liquid chromatography tandem mass spectrometry method. Children's neurodevelopment was assessed at ages 3, 6, and 12 months using Ages and Stages Questionnaires. The nested case-control study included 150 neurodevelopmental delay cases and 150 healthy controls. Placental estradiol levels were measured using enzyme-linked immunosorbent assay kits. Generalized estimating equation models and robust Poisson regression models were used to examine the associations between BPF exposure and children's neurodevelopment. In the nested case-control study, causal mediation analysis was conducted to assess the role of placental estradiol as a mediator in multivariate models.

RESULTS

In the prospective cohort study, the pregnancy-average BPF concentration was positively associated with developmental delays in gross-motor, fine-motor, and problem-solving ( ORtotal ASQ: 1.14(1.05, 1.25), ORgross-motor: 1.22(1.10, 1.36), ORfine-motor: 1.19(1.07, 1.31), ORproblem-solving: 1.11(1.01, 1.23)). After sex-stratified analyses, pregnancy-average BPF concentration was associated with an increased risk of neurodevelopmental delays in the gross-motor (ORgross-motor:1.30(1.12, 1.51)) and fine-motor (ORfine-motor: 1.22(1.06, 1.40)) domains in boys. In the nested case-control study, placental estradiol mediated 16.6% (95%CI: 4.4%, 35.0%) of the effects of prenatal BPF exposure on developmental delay.

CONCLUSIONS

Our study supports an inverse relationship between prenatal BPF exposure and child neurodevelopment in infancy, particularly in boys. Decreased placental estradiol may be an underlying biological pathway linking prenatal BPF exposure to neurodevelopmental delay in offspring.

Bisphenol analogues in infant foods in south China and implications for infant exposure

Bisphenol analogues (BPs) are commonly used as modifiers, stabilizers and photo-initiators in polymer materials, including those used in food packaging. Compared to adults, infants are more sensitive to chemicals because their bodies are growing and not fully developed. Therefore, it is essential to determine the concentrations of BPs in common infant foods to assess infant exposure and prevent hazards. We collected 54 infant formula (IF) samples, 90 complementary food (CMF) samples and 62 breastmilk samples from breastfeeding women in south China. Tandem mass spectrometry coupled to liquid chromatography separation (HPLC-MS/MS) was used to detect the concentrations of 8 BPs in the three types of food samples. The estimated daily intake (EDI) of infants was also assessed. The results showed that the detection frequency of bisphenol F (BPF), bisphenol S (BPS), bisphenol AF (BPAF) and bisphenol AP (BPAP) were relatively high among the different infant foods. BPF, BPP and BPS were predominant among the detected BPs. The lowest 95th EDI for BPA was 0.67 ng kg-bw-1 day-1, exceeding the tolerable daily intake (TDI) limit for BPA set by the European Food Safety Authority in 2023. Thus, BP exposure is a significant risk to infants. More attention should be paid to the presence of BPs in daily use products and food, and intake limits should be set for BPs other than BPA.

Combined toxicity of aflatoxin B1 and tebuconazole to the embryo development of zebrafish (Danio rerio)

Mycotoxins and pesticides are pervasive elements within the natural ecosystem. Furthermore, many environmental samples frequently exhibit simultaneous contamination by multiple mycotoxins and pesticides. Nevertheless, a significant portion of previous investigations has solely reported the occurrence and toxicological effects of individual chemicals. Global regulations have yet to consider the collective impacts of mycotoxins and pesticides. In our present study, we undertook a comprehensive analysis of multi-level endpoints to elucidate the combined toxicity of aflatoxin B1 (AFB1) and tebuconazole (TCZ) on zebrafish (Danio rerio). Our findings indicated that AFB1 (with a 10-day LC50 value of 0.018 mg L-1) exhibits higher toxicity compared to TCZ (with a 10-day LC50 value of 2.1 mg L-1) toward D. rerio. The co-exposure of AFB1 and TCZ elicited synergistic acute responses in zebrafish. The levels of GST, CYP450, SOD, and Casp-9 exhibited significant variations upon exposure to AFB1, TCZ, and their combined mixture, in contrast to the control group. Additionally, eight genes, namely cat, cxcl-cic, il-1β, bax, apaf-1, trβ, ugtlab, and vtg1, displayed marked alterations when exposed to the chemical mixture as opposed to individual substances. Therefore, further exploration of the underlying mechanisms governing joint toxicity is imperative to establish a scientific basis for evaluating the risk associated with the combined effects of AFB1 and TCZ. Moreover, it is essential to thoroughly elucidate the organ system toxicity triggered by the co-occurrence of mycotoxins and pesticides.

Bisphenol analogues induce thyroid dysfunction via the disruption of the thyroid hormone synthesis pathway

Bisphenol analogues are widely used in industrial and daily-use consumer products having imperfect thyroid hormones (THs) structures. Widespread exposure interferes with thyroid-related health outcomes in human. The mechanisms of disruption on TH synthesis and subsequent thyroid dysfunction by different bisphenol analogues remain unclear. Here, we evaluated bisphenol-induced thyroid endocrine disruption in C57BL/6 mice at doses of 0.002, 0.02, 2, and 20 mg/kg body weight/day (BW/d) for five consecutive weeks. Administration of 20 mg/kg BW/d bisphenol S (BPS) and 2 mg/kg BW/d tetrabromobisphenol S (TBBPS) significantly increased serum thyrotropin (TSH) levels to 1.21-fold and 1.20-fold of control group, respectively, indicating that bisphenols induced thyroid dysfunction in mice. Height of the thyroid follicle epithelium significantly increased to 1.27-, 1.24-, 1.26-, and 1.36-fold compared to control group with BPA, BPS, TBBPA, and TBBPS at 20 mg/kg BW/d, respectively, indicating impairment of the thyroid gland structure, and TBBPS showed potent effect. Exposure to bisphenol analogues of 0.02 mg/kg BW/d downregulated the protein expression levels of thyrotropin receptor, the sodium/iodide symporter, thyroperoxidase. The TH-dependent effects were further determined using the T-Screen assay at 10-11 M to 10-5 M concentrations. Bisphenol analogues significantly decreased TH-dependent GH3 cell proliferation, indicating the antagonistic activity of bisphenol analogues. The gene responsible for THs synthesis of thyrotropin releasing hormone receptor and TSH were upregulated, but downregulation of thyroid receptor β was observed. Our results suggest that bisphenol analogues distinctly induce thyroid dysfunction via TH synthesis, implying adverse effect of bisphenol analogues on TH homeostasis and subsequent physiological processes.

Fluorene-9-bisphenol affects the terminal differentiation of mouse embryonic bodies

Fluorene-9-bisphenol (BHPF) has recently attracted interest as it is increasingly used in industrial settings as a substitute for Bisphenol A (BPA). However, the effects of BHPF exposure on embryonic stem cell (ESC) self-renewal, pluripotency, and differentiation remain poorly understood. This study investigates the impacts of BHPF on mouse embryonic stem cells (mESCs) and embryonic bodies (EBs). Our results reveal that BHPF exposure leads to a morphological shift in mESCs, reducing the percentage of dome-shaped colonies and indicating loss of self-renewal and pluripotency. BHPF exposure also appeared to affect the early stages of EB formation and their growth dynamics, with a reduction in EB numbers and an increase in their size. Subsequent gene expression analysis revealed that BHPF exposure led to increased expression of the inflammatory gene Il6, indicating a potential stress response. Furthermore, BHPF affected the terminal differentiation pathway, modulating the expression of 16 genes associated with distinct cell types, including lymphatic endothelium, keratinocyte epithelium, pancreatic beta cells, macrophages, monocytes, T-cells, neurons, retinal ganglion cells, nephrons proximal tubule cells, and cardiomyocytes. These findings offer insights into the impact of BHPF on ESC biology and suggest potential implications for developmental and neurodegenerative disorders. Future work should focus on elucidating the underlying mechanisms of BHPF-mediated effects on stem cell function. This may offer new perspectives for understanding the health impacts of environmental exposure to BHPF.

Transcriptome Analysis of the Developmental Effects of Bisphenol F Exposure in Chinese Medaka (Oryzias sinensis)

Bisphenol F (BPF) has been used in the syntheses of polymers, which are widely used in coatings, varnishes, adhesives, and other plastics. During the past decades, BPF contamination in the aquatic environment has dramatically increased due to its release from manmade products. Concerns have driven much attention to whether it may adversely impact aquatic lives or human beings. The present study performed an acute toxic exposure experiment and a 15 d developmental exposure of BPF at environmental concentrations (20, 200, and 2000 ng/L) using Chinese medaka (Oryzias sinensis). In the acute toxic exposure, the LC₅₀ of BPF to Chinese medaka is 87.90 mg/L at 96 h. Developmental exposure induced a significant increase in the frequency of larvae with abnormalities in the 2000 ng/L BPF group compared to the control group. Transcriptomic analysis of the whole larvae revealed 565 up-regulated and 493 down-regulated genes in the 2000 ng/L BPF exposure group. Analysis of gene ontology and KEGG pathways enrichments indicated endocrine disorders to be associated with BPF-induced developmental toxicity. The present results suggest that BPF is developmentally toxic at 2000 ng/L concentration in Chinese medaka and causes endocrine-related aberrations in the transcriptional network of genes.

Genetic background in the rat affects endocrine and metabolic outcomes of bisphenol F exposure

Environmental bisphenol compounds like bisphenol F (BPF) are endocrine-disrupting chemicals (EDCs) affecting adipose and classical endocrine systems. Genetic factors that influence EDC exposure outcomes are poorly understood and are unaccounted variables that may contribute to the large range of reported outcomes in the human population. We previously demonstrated that BPF exposure increased body growth and adiposity in male N/NIH heterogeneous stock (HS) rats, a genetically heterogeneous outbred population. We hypothesize that the founder strains of the HS rat exhibit EDC effects that were strain- and sex-dependent. Weanling littermate pairs of male and female ACI, BN, BUF, F344, M520, and WKY rats randomly received either vehicle (0.1% EtOH) or 1.125 mg BPF/l in 0.1% EtOH for 10 weeks in drinking water. Body weight and fluid intake were measured weekly, metabolic parameters were assessed, and blood and tissues were collected. BPF increased thyroid weight in ACI males, thymus and kidney weight in BUF females, adrenal weight in WKY males, and possibly increased pituitary weight in BN males. BUF females also developed a disruption in activity and metabolic rate with BPF exposure. These sex- and strain-specific exposure outcomes illustrate that HS rat founders possess diverse bisphenol-exposure risk alleles and suggest that BPF exposure may intensify inherent organ system dysfunction existing in the HS rat founders. We propose that the HS rat will be an invaluable model for dissecting gene EDC interactions on health.

Different types of bisphenols alter ovarian steroidogenesis: Special attention to BPA

Endocrine disruptors such as bisphenol A (BPA) and some of its analogues, including BPS, BPAF, and BPE, are used extensively in the manufacture of plastics. These synthetic chemicals could seriously alter the functionality of the female reproductive system. Although the number of studies conducted on other types of bisphenols is smaller than the number of studies on BPA, the purpose of this review study was to evaluate the effects of bisphenol compounds, particularly BPA, on hormone production and on genes involved in ovarian steroidogenesis in both in vitro (human and animal cell lines) and in vivo (animal models) studies. The current data show that exposure to bisphenol compounds has adverse effects on ovarian steroidogenesis. For example, BPA, BPS, and BPAF can alter the normal function of the hypothalamic-pituitary-gonadal (HPG) axis by targeting kisspeptin neurons involved in steroid feedback signals to gonadotropin-releasing hormone (GnRH) cells, resulting in abnormal production of LH and FSH. Exposure to BPA, BPS, BPF, and BPB had adverse effects on the release of some hormones, namely 17-β-estradiol (E2), progesterone (P4), and testosterone (T). BPA, BPE, BPS, BPF, and BPAF are also capable of negatively altering the transcription of a number of genes involved in ovarian steroidogenesis, such as the steroidogenic acute regulatory protein (StAR, involved in the transfer of cholesterol from the outer to the inner mitochondrial membrane, where the steroidogenesis process begins), cytochrome P450 family 17 subfamily A member 1 (Cyp17a1, which is involved in the biosynthesis of androgens such as testosterone), 3 beta-hydroxysteroid dehydrogenase enzyme (3β-HSD, involved in the biosynthesis of P4), and cytochrome P450 family 19 subfamily A member 1 (Cyp19a1, involved in the biosynthesis of E2). Exposure to BPA, BPB, BPF, and BPS at prenatal or prepubertal stages could decrease the number of antral follicles by activating apoptosis and autophagy pathways, resulting in decreased production of E2 and P4 by granulosa cells (GCs) and theca cells (TCs), respectively. BPA and BPS impair ovarian steroidogenesis by reducing the function of some important cell receptors such as estrogens (ERs, including ERα and ERβ), progesterone (PgR), the orphan estrogen receptor gamma (ERRγ), the androgen receptor (AR), the G protein-coupled estrogen receptor (GPER), the FSHR (follicle-stimulating hormone receptor), and the LHCGR (luteinizing hormone/choriogonadotropin receptor). In animal models, the effects of bisphenol compounds depend on the type of animals, their age, and the duration and dose of bisphenols, while in cell line studies the duration and doses of bisphenols are the matter.

Interacted toxic mechanisms of ochratoxin A and tricyclazole on the zebrafish (Danio rerio)

Despite the current efforts to identify the mixtures of chemical pollutants, they are often "binned" into their corresponding pollutant groups. Limited studies have investigated complex mixtures of chemical pollutants co-occurring across different groups. The combined toxic impacts of several substances become a critical consideration in toxicology because chemical combinations can exert a greater deleterious effect than the single components in the mixture. In the current work, we assessed the joint impacts of ochratoxin A and tricyclazole on the zebrafish (Danio rerio) embryos and explored their underlying signaling pathways. Ochratoxin A displayed higher toxicity than tricyclazole, with a 10-day LC₅₀ of 0.16 mg L^-1, whereas that for tricyclazole was 1.94 mg L^-1. The combination of ochratoxin A and tricyclazole exhibited a synergistic impact on D. rerio. The activities of detoxification enzymes GST and CYP450, as well as apoptosis-associated enzyme caspase 3, were distinctly changed in most individual and mixture exposures comparing to the untreated group. Upon both individual and mixture exposures, more dramatic variations were detected in the expressions of nine genes, such as the apoptosis genes cas3 and bax, antioxidant gene mn-sod, immunosuppression gene il-1β, and the endocrine system genes trα, dio1, trβ, ugtlab, and crh, compared with the untreated group. These findings suggested that the simultaneous exposure to low doses of mycotoxins and pesticides in food commodities was more toxic than predicted from the individual chemicals. Considering the frequent co-occurrence of mycotoxins and pesticides in the diet, this synergy should be considered in future assessments.

Prenatal bisphenol exposure and intelligence quotient in children at six years of age: A prospective cohort study

The effects of prenatal bisphenol A (BPA) exposure on children's cognitive development have been reported; however, relevant evidence on BPA analogues was limited, with rare evidence of the joint effect of their mixture. Among 424 mother-offspring pairs from the Shanghai-Minhang Birth Cohort Study, maternal urinary concentrations of five bisphenols (BPs) were quantified, and children's cognitive function was assessed by the Wechsler Intelligence Scale at six years of age. We assessed the associations of prenatal exposure to individual BPs with children's intelligence quotient (IQ) and analyzed the joint effect of BPs mixture by the Quantile g-computation model (QGC) and Bayesian kernel machine regression model (BKMR). QGC models showed that higher maternal urinary BPs mixture concentrations were associated with lower scores among boys in a non-linear way; however, no association was observed in girls. For individual effects, BPA and BPF were associated with decreased IQ scores in boys and were identified as important contributors to the joint effect of BPs mixture. However, associations of BPA with increased IQ scores in girls, and TCBPA with increased IQ scores in both sexes were observed. Our findings suggested prenatal exposure to BPs mixture may affect children's cognitive function in a sex-specific pattern and provided evidence of the neurotoxicity of BPA and BPF.

Estrogenic and non-estrogenic effects of bisphenol A and its action mechanism in the zebrafish model: An overview of the past two decades of work

Bisphenol A (BPA) is the most simple and predominant component of the Bisphenol family. BPA is widely present in the environment and the human body as a result of its extensive usage in the plastic and epoxy resins of consumer goods like water bottles, food containers, and tableware. Since the 1930s, when BPA's estrogenic activity was first observed, and it was labeled as a "mimic hormone of E2", studies on the endocrine-disrupting effects of BPA then have been widely conducted. As a top vertebrate model for genetic and developmental studies, the zebrafish has caught tremendous attention in the past two decades. By using the zebrafish, the negative effects of BPA either through estrogenic signaling pathways or non-estrogenic signaling pathways were largely found. In this review, we tried to draw a full picture of the current state of knowledge on the estrogenic and non-estrogenic effects of BPA with their mechanisms of action through the zebrafish model of the past two decades, which may help to fully understand the endocrine-disrupting effects of BPA and its action mechanism, and give a direction for the future studies.

Impacts of co-exposure to zearalenone and trifloxystrobin on the enzymatic activity and gene expression in zebrafish

Although humans and animals are usually exposed to combinations of toxic substances, little is known about the interactive toxicity of mycotoxins and farm chemicals. Therefore, we can not precisely evaluate the health risks of combined exposure. In the present work, using different approaches, we examined the toxic impacts of zearalenone and trifloxystrobin on zebrafish (Danio rerio). Our findings showed that the lethal toxicity of zearalenone to embryonic fish with a 10-day LC₅₀ of 0.59 mg L^-1 was lower than trifloxystrobin (0.037 mg L^-1). Besides, the mixture of zearalenone and trifloxystrobin triggered acute synergetic toxicity to embryonic fish. Moreover, the contents of CAT, CYP450, and VTG were distinctly altered in most single and combined exposures. Transcriptional levels of 23 genes involved in the oxidative response, apoptosis, immune, and endocrine systems were determined. Our results implied that eight genes (cas9, apaf-1, bcl-2, il-8, trb, vtg1, erβ1, and tg) displayed greater changes when exposed to the mixture of zearalenone and trifloxystrobin compared with the corresponding individual chemicals. Our findings indicated that performing the risk assessment based on the combined impact rather than the individual dosage response of these chemicals was more accurate. Nevertheless, further investigations are still necessary to reveal the modes of action of mycotoxin and pesticide combinations and alleviate their effects on human health.

BPA and its alternatives BPF and BPAF exaggerate hepatic lipid metabolism disorders in male mice fed a high fat diet

Alternatives to Bisphenol A (BPA), such as BPF and BPAF, have found increasing industrial applications. However, toxicological research on these BPA analogues remains limited. This study aimed to investigate the effects of BPA, BPF, and BPAF exposure on hepatotoxicity in mice fed with high-fat diets (HFD). Male mice were exposed to the bisphenols at a dose of 0.05 mg per kg body weight per day (mg/kg bw/day) for eight consecutive weeks, or 5 mg/kg bw/day for the first week followed by 0.05 mg/kg bw/day for seven weeks under HFD. The low dose (0.05 mg/kg bw/day) was corresponding to the tolerable daily intake (TDI) of BPA and the high dose (5 mg/kg bw/day) was corresponding to its no observed adverse effect level (NOAEL). Biochemical analysis revealed that exposure to these bisphenols resulted in liver damage. Metabolomics analysis showed disturbances of fatty acid and lipid metabolism in bisphenol-exposed mouse livers. BPF and BPAF exposure reduced lipid accumulation in HFD mouse liver by lowering glyceride and cholesterol levels. Transcriptomics analysis demonstrated that expression levels of genes related to fatty acid synthesis and metabolism were changed, which might be related to the activation of the PPAR signaling pathway. Besides, a feedback regulation mechanism might exist to maintain hepatic metabolic homeostasis. For the first time, this study demonstrated the effects of BPF and BPAF exposure in HFD-mouse liver. Considering the reality of the high prevalence of obesity nowadays and the ubiquitous environmental distribution of bisphenols, this study provides insight and highlights the adverse effects of BPA alternatives, further contributing to the consideration of the safe use of such compounds.

Bisphenol S disrupts opsins gene expression and impairs the light-sensing function via antagonizing TH-TRβ signaling pathway in zebrafish larvae

Bisphenol S (BPS) is extensively used in "bisphenol A-free" products such as baby bottles. Although the visual toxicity of BPS has been reported, the underlying mechanism was largely unknown. In the present study, zebrafish were exposed to 0, 4 and 400 nM BPS from 2 h post-fertilization (hpf) to 120 hpf to further explore the thyroid disruption mechanism underlying the BPS induced impairment of visual function. The results showed that BPS decreased T3 levels in larval eyes, induced retinal expression of thyroid hormone receptor β (TRβ), and thereby down-regulated the expression of TH-mediated opsin genes (opn1lw1, opn1lw2, opn1mw1, opn1mw2, opn1mw3, and opn1sw2) and impaired subsequent phototransduction pathways, leading to decreased visually mediated phototactic response and body color adaptation but stimulated visual motor response (VMR). Combining exposure of exogenous T3 or 1-850 (antagonist for TRβ) with BPS could partly compensate the inhibited expression of opsin genes (opn1mw2, opn1lw1, and opn1lw2) and alleviate the hyperactivity of larval VMR caused by BPS alone, suggesting that BPS disrupted the opsins expression and also light-sensing function via antagonizing TH-TRβ signaling pathway. This study underlined the importance of TH signaling in regulating the proper vision and proposed a novel mechanism for the visual toxicity of BPS.

Transient developmental exposure to low doses of bisphenol F negatively affects neurogliogenesis and olfactory behaviour in adult mice

Neural stem cells in the murine subventricular zone (SVZ) reactivate during postnatal development to generate neurons and glia throughout adulthood. We previously demonstrated that a postnatal thyroid hormone (TH) peak orchestrates this remodelling, rendering this process vulnerable to endocrine disruption. We exposed mice to 2 or 200 µg/kg bw/day of the bisphenol A-replacement and suspected TH-disruptor bisphenol F (BPF) in the drinking water, from embryonic day 15 to postnatal day 21 (P21). In parallel, one group was exposed to the TH-synthesis blocker propylthiouracil (0.15 % PTU). In contrast to PTU, BPF exposure did not affect serum TH levels at P15, P21 or P60. RNA-seq on dissected SVZs at P15 revealed dysregulated neurodevelopmental genes in all treatments, although few overlapped amongst the conditions. We then investigated the phenotype at P60 to analyse long-term consequences of transient developmental exposure. As opposed to hypothyroid conditions, and despite dysregulated oligodendrogenesis-promoting genes in the P15 SVZ exposed to the highest dose of BPF, immunostainings for myelin and OLIG2/CC1 showed no impact on global myelin content nor oligodendrocyte maturation in the P60 corpus callosum, apart from a reduced thickness. The highest dose did reduce numbers of newly generated SVZ-neuroblasts with 22 %. Related to this were behavioural alterations. P60 mice previously exposed to the highest BPF dose memorized an odour less well than control animals did, although they performed better than PTU-exposed animals. All mice could discriminate new odours, but all exposed groups showed less interest in social odours. Our data indicate that perinatal exposure to low doses of BPF disrupts postnatal murine SVZ remodelling, and lowers the adult neuron/oligodendroglia output, even after exposure had been absent for 40 days. These anomalies warrant further investigation on the potential harm of alternative bisphenol compounds for human foetal brain development.

Bisphenols induce cardiotoxicity in zebrafish embryos: Role of the thyroid hormone receptor pathway

Bisphenols are frequently found in the environment and have been of emerging concern because of their adverse effects on aquatic animals and humans. In this study, we demonstrated that bisphenol A, S, and F (BPA, BPS, BPF) at environmental concentrations induced cardiotoxicity in zebrafish embryos. BPA decreased heart rate at 96 hpf (hours post fertilization) and increased the distance between the sinus venosus (SV) and bulbus arteriosus (BA), in zebrafish. BPF promoted heart pumping and stroke volume, shortened the SV-BAdistance, and increased body weight. Furthermore, we found that BPA increased the expression of the dio3b, thrβ, and myh7 genes but decreased the transcription of dio2. In contrast, BPF downregulated the expression of myh7 but upregulated that of thrβ. Molecular docking results showed that both BPA and BPF are predicted to bind tightly to the active pockets of zebrafish THRβ with affinities of -4.7 and -4.77 kcal/mol, respectively. However, BPS did not significantly affect dio3b, thrβ, and myh7 transcription and had a higher affinity for zebrafish THRβ (-2.13 kcal/mol). These findings suggest that although BPA, BPS, and BPF have similar structures, they may induce cardiotoxicity through different molecular mechanisms involving thyroid hormone systems. This investigation provides novel insights into the potential mechanism of cardiotoxicity from the perspective of thyroid disruption and offer a cautionary role for the use of BPA substitution.

Transcriptomic sequencing reveals the potential molecular mechanism by which Tetrabromobisphenol A bis (2-hydroxyethyl ether) exposure exerts developmental neurotoxicity in developing zebrafish (Danio rerio)

Tetrabromobisphenol A bis (2-hydroxyethyl ether) (TBBPA-DHEE) is a derivative of Tetrabromobisphenol A (TBBPA) used as an intermediate flame retardant in engineering polymers. The mechanism of neurodevelopmental toxicity of TBBPA-DHEE remains unclear due to limited toxicological data. We performed behavioral and transcriptomic analyses to assess the neurodevelopmental effects of TBBPA-DHEE on developing zebrafish and potential toxicity mechanisms. Our result shows that exposure to TBBPA-DHEE significantly increased mortality, deformity rate, and reduction in hatch rate, hatchability, and body length relative to the DMSO control. The behavior analysis indicates that TBBPA-DHEE significantly reduced the spontaneous movement of larva compared to the control. The TSH and GH levels were significantly reduced in all the exposure groups in a concentration-dependent manner relative to the DMSO control. TBBPA-DHEE exhibited a significant reduction in locomotor activity across all the exposure groups in the light/dark locomotion test. The transcriptomic analysis result shows that 579 genes were differentially expressed. KEGG analysis shows the enrichment of complement cascade, JAK-STAT signaling pathway, cytokine-cytokine interaction, and phototransduction pathway resulting in a change in mRNA expression of their genes. These observed changes in developmental endpoints, hormonal level, and alteration in mRNA expression of component genes involved in neurodevelopmental pathways could be part of the possible mechanism of the observed toxic effects of TBBPA-DHEE exposure on zebrafish. This study could reveal the possible neurodevelopmental toxicity of TBBPA-DHEE to aquatic species, which could help uncover the health implications of emerging environmental contaminants.

Associations of bisphenol exposure with thyroid hormones in pregnant women: a prospective birth cohort study in China

Bisphenols are endocrine disruptor chemicals that disrupt thyroid hormone homeostasis. However, evidence on the effects of bisphenol mixtures on thyroid hormones are insufficient. Therefore, the present study aimed to explore the effects of bisphenol substitutes and bisphenol mixtures on thyroid hormones during pregnancy. The study was conducted among 446 pregnant women in the Guangxi Zhuang Birth Cohort (GZBC), China. In multiple linear regressions, compared with the low-exposure group, bisphenol S (BPS) concentrations in the middle-exposure group led to a 10.90% (95% CI: - 18.16%, - 2.99%) decrease in triiodothyronine (T3) levels in the first trimester; tetrabromobisphenol A (TBBPA) levels in the middle-exposure group led to an 8.26% (95% CI: - 15.82%, - 0.01%) decrease in T3 levels in the first trimester; bisphenol B (BPB) levels in the middle-exposure group led to higher free thyroxine (FT4) levels (9.84%; 95% CI: 1.73%, 18.60%) in the second trimester; bisphenol F (BPF) in the middle-exposure group led to higher FT4 levels (8.59%, 95% CI: 0.53%, 17.31%) in the second trimester; and TBBPA levels in the high-exposure group led to a 9.39% (95% CI: 1.46%, 17.93%) increase in FT4 levels in the second trimester. The Bayesian kernel machine regression (BKMR) and restricted cubic spline (RCS) models showed a U-shaped dose-response relationship between bisphenol A (BPA) and free triiodothyronine (FT3) (p < 0.01) as well as BPS and FT4 (p < 0.05). Nonlinear relationships were also observed between the bisphenol mixture and FT3. Overall, maternal bisphenol exposure affected thyroid hormone levels during pregnancy. This study provides evidence that BPB, BPF, BPS, and TBBPA are unsafe substitutes for BPA, as well as the overall effect of bisphenols on adverse health in human beings.

Effects of BPZ, BPC, BPF, and BPS Exposure on Adult Zebrafish (Danio rerio): Accumulation, Oxidative Stress, and Gene Expression

As substitutes for bisphenol A (BPA), bisphenol analogs (BPs) have been found to cause endocrine disorders and induce toxic effects. The objective of this study was to evaluate the bioaccumulation and subacute toxicity of bisphenol Z (BPZ), bisphenol C (BPC), bisphenol F (BPF), and bisphenol S (BPS) to zebrafish. Five-month-old zebrafish were exposed to 1/100 LC₅₀, 1/50 LC₅₀, and 1/10 LC₅₀ of BPZ, BPC, BPF, and BPS for 13 days, respectively. Bioaccumulation, oxidative stress, and related mRNA expression in zebrafish tissues were measured on days 1, 7, and 13. After exposure, the four kinds of BPs all resulted in the accumulation of concentration and lipid peroxidation in zebrafish tissues to varying degrees. BPZ and BPC had the highest bioaccumulation level and had the greatest influence on malonic dialdehyde (MDA). In addition, the enzyme activities of superoxide dismutase (SOD), peroxidase (POD), glutathione peroxidase (GSH-PX), and the content of glutathione (GSH) in zebrafish tissues were also affected at different levels. However, the enzyme activities of SOD and POD were inactivated in zebrafish exposed to a high concentration of BPC. Further studies showed that BPs exposure down-regulated the transcription level of sod but up-regulated the relative expression levels of cat and gpx. The mRNA relative expression level of erα was not significantly changed, while the mRNA relative expression level of erβ₁ was significantly down-regulated except under BPS exposure. These results indicate that BPZ, BPC, and BPF significantly affect the expression level of the estrogen receptor (ER) in zebrafish tissues. Overall, the results suggest that exposure to waterborne BPs can cause severe oxidative stress and tissue damage in adult zebrafish that is not sufficient to kill them after 13 days of waterborne exposure. The toxicity of BPs to organisms, therefore, should be further analyzed and evaluated.

Critical review of the toxicity mechanisms of bisphenol F in zebrafish (Danio rerio): Knowledge gaps and future directions

Replacement chemicals for bisphenol A, such as bisphenol F (BPF), are detected in aquatic environments worldwide and can potentially exert negative effects on aquatic organisms. We synthesized peer-reviewed literature reporting molecular and physiological responses in zebrafish following exposure to BPF, as BPF is closely related to BPA structure and is a dominant replacement chemical in the marketplace. Global concentrations of BPF in aquatic environments were compiled and compared to physiological and behavioral impacts reported in zebrafish (e.g., developmental abnormalities, oxidative stress, immunotoxicity, endocrine disruption, and neurotoxicity). Using computational approaches, we elucidate BPF-mediated molecular networks and reveal novel biomarkers associated with BPF exposure. Functional classes of proteins including inflammatory cytokines, ATPases, peroxidases, and aromatic l-amino decarboxylases represent novel, underexplored targets of toxicity. Most revealing of this critical review is that few studies report biological responses to BPF at levels present in aquatic environments. Recommendations for future investigations based on knowledge gaps include: (1) Mechanistic studies in the central nervous system of zebrafish to address neurotoxicity; (2) Behavioral assays in zebrafish that assess the effects of BPF on anxiolytic, social, and fear-related behaviors; (3) Studies that broaden understanding of potential endocrine disrupting effects of BPF, for example insulin signaling is predicted to be sensitive to BPF exposure; (4) Studies into metabolic disruption with a focus on glutathione and aromatic amino acids, based upon pathway analysis data; (5) Studies utilizing mixture exposures with other BPA analogs to reflect environmental conditions more accurately.

Effects of tetramethyl bisphenol F on thyroid and growth hormone-related endocrine systems in zebrafish larvae

Trimethyl bisphenol F (TMBPF) has recently been used as a bisphenol A substitute in polymer coatings for metal cans containing beverages or food. This study investigated whether TMBPF disrupts the endocrine system associated with thyroid hormones and growth hormones employing zebrafish embryos and larvae. After 14 days of exposure, body weight was significantly reduced when zebrafish were exposed to a TMBPF concentration greater than 50 μg/L. The triiodothyronine levels were significantly increased, while growth hormone levels were significantly decreased in larvae exposed to 5 μg/L TMBPF. The transcription of genes associated with thyroid hormone production (trα, tpo, tg, and nis), deiodination (deio2), growth hormone production (gh1, ghrh, and ghra), and insulin-like growth factor (igf2a, igf2b, igf2r, igfbp1a, igfbp1b, igfbp2a, igfbp2b, and igfbp5a) was significantly upregulated, whereas the transcription of genes association with thyrotropin-releasing hormone (trh and trhr1) was significantly downregulated. These results suggest that hyperthyroidism, decrease in growth hormone, and regulation of genes involved in the hypothalamus-pituitary-thyroid and growth hormone/insulin-like growth factor might be responsible for the observed growth inhibition in larvae exposed to TMBPF. The bioaccumulation of TMBPF and its effects on the endocrine system after chronic exposure requires further investigation.

Transcriptomics integrated with metabolomics reveals the effect of Bisphenol F (BPF) exposure on intestinal inflammation

As a viable alternative to Bisphenol A (BPA), Bisphenol F (BPF) has been detected in humans at comparable concentrations and detection frequencies. Emerging evidence reveals that BPF induces intestinal toxicity. However, less information is available concerning BPF and its potential effects on intestinal inflammation, which has been associated with numerous disorders. The results from the present study showed that BPF exposure triggered lipopolysaccharide (LPS)-induced explosion of pro-inflammatory cytokines interleukin-17A (IL-17A), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) and impairment of the intestinal epithelial barrier by downregulating the expression of tight junction proteins Zonula Occludens-1 (ZO-1) and Claudin-1 (CLDN1) in normal colonic epithelial cells (NCM460). A multi-omics analysis integrating the transcriptomics with metabolomics revealed an altered transcripts and metabolites profile following BPF exposure. Correlation analysis indicated that RAS Guanyl Releasing Protein 2 (RASGRP2) and Phospholipase A2 Group IVE (PLA2G4E) were positively associated with the increased serotonin which was positively associated with the stimulated IFN-γ in BPF-treated NCM460 cells. Pyrogallol, pyridoxine, and N-acetylputrescine were positively associated with IL-17A levels. Collectively, the integrative analyses demonstrated an orchestrated coordination between the inflammatory response, transcriptomic, and metabolomics changes. Data presented herein provide evidence for the possible roles of BPF in the pathogenesis of intestinal inflammation. These results illustrate the advantages of using integrative analyses of high throughput datasets for characterizing the effects and mechanisms of toxicants.

Overlooked environmental risks deriving from aqueous transformation of bisphenol alternatives: Integration of chemical and toxicological insights

Owing to the widespread prevalence and ecotoxicity of bisphenol alternatives such as bisphenol S, bisphenol F, and bisphenol AF, the past decade has witnessed the publication of a remarkable number of studies related to their transformation and remediation in natural waters. However, the reactivity, removal efficiency, transformation products (TPs), and mechanisms of such emerging pollutants by different treatment processes have not been well elucidated. Particularly, the transformation-driven environmental risks have been mostly overlooked. Therefore, we present a review to address these issues from chemical and toxicological viewpoints. Four degradation systems can be largely classified as catalytic persulfate (PS) oxidation, non-catalytic oxidation, photolysis and photocatalysis, and biodegradation. It was found that bisphenol alternatives possess distinct reactivities with different oxidizing species, with the highest performance for hydroxyl radicals. All systems exhibit superior elimination efficiency for these compounds. The inadequate mineralization suggests the formation of recalcitrant TPs, from which the overall reaction pathways are proposed. The combined experimental and in silico analysis indicates that many TPs have developmental toxicity, endocrine-disrupting effects, and genotoxicity. Notably, catalytic PS systems and non-catalytic oxidation result in the formation of coupling products as well as halogenated TPs with higher acute and chronic toxicity and lower biodegradability than the parent compounds. In contrast, photolysis and photocatalysis generate hydroxylated and bond-cleavage TPs with less toxicity. Overall, this review highlights the secondary environmental risks from the transformation of bisphenol alternatives by conventional and emerging treatment processes. Finally, future perspectives are recommended to address the knowledge gaps of these contaminants in aquatic ecosystems.

Pharmacokinetics and toxicity evaluation following oral exposure to bisphenol F

Bisphenol F is a substitute material for bisphenol A and is widely used in household products as a raw material for polycarbonate resin, epoxy resin, and plastic reinforcement. It is known to be mainly used in food containers, thermal paper for receipts, and coatings for water pipes. In some countries, bisphenol F has been detected in drinking water and human urine samples. However, due to the lack of safety evaluation data on bisphenol F, it is difficult to establish appropriate guidelines for the proper use of the substance, and social anxiety is increasing accordingly. This study investigated the use, exposure route, and distribution flow of bisphenol F, a household chemical. To determine the no-observed-adverse-effect level (NOAEL) and target organ of bisphenol F after exposure, a single-dose oral toxicity, dose-range finding (28 day oral), repeated dose toxicity (90 day oral), and genotoxicity (reverse mutation, chromosomal abnormality, in vivo micronucleus test) tests were performed. The pharmacokinetic profile was also obtained. The test results are as follows: in the pharmacokinetic study, it was confirmed that single oral exposure to BPF resulted in systemic exposure; in single oral dose toxicity test, the approximate lethal dose was found to be 4000 mg/kg and confusion and convulsion was shown in the test animals; NOAEL was determined to be 2 mg/kg/day for male and 5 mg/kg/day for female, and the no-observed-effect level (NOEL) was determined to be 2 mg/kg/day for males and 1 mg/kg/day for females, and the target organ was the small intestine; genotoxicity tests confirmed that BPF does not induce genotoxicity.

Developmental toxicity of bromoacetamide via the thyroid hormone receptors-mediated disruption of thyroid hormone homeostasis in zebrafish embryos

Bromoacetamide (BAcAm) is a nitrogenous disinfection by-product. We previously found that BAcAm induced developmental toxicity in zebrafish embryos, but the underlying mechanisms remain to be elucidated. Since thyroid hormones (THs) homeostasis is crucial to development, we hypothesized that disruption of THs homeostasis may play a role in the developmental toxicity of BAcAm. In this study, we found BAcAm exposure significantly increased mortality and malformation rate, decreased hatching rate and body length, inhibited the locomotor capacity in zebrafish embryos. BAcAm elevated TSH, T₃ and T₄ levels, down-regulated T₃/T₄ ratios, and up-regulated mRNA expression changes of THs related genes (trh, tsh, tg, nis, tpo, dio1, dio2, ugt1ab，klf9 and rho), but down-regulated mRNA expression changes of TH receptors (tr α and tr β). Up-regulated tr α and tr β mRNAs by rescue treatment confirmed that both tr α and tr β were involved in the developmental toxicity of BAcAm. In conclusion, our study indicates disruption of THs homeostasis via the thyroid hormone receptors was responsible for the developmental toxicity of BAcAm.

Disruption by stealth - Interference of endocrine disrupting chemicals on hormonal crosstalk with thyroid axis function in humans and other animals

Thyroid hormones (THs) are important regulators of growth, development, and homeostasis of all vertebrates. There are many environmental contaminants that are known to disrupt TH action, yet their mechanisms are only partially understood. While the effects of Endocrine Disrupting Chemicals (EDCs) are mostly studied as "hormone system silos", the present critical review highlights the complexity of EDCs interfering with TH function through their interactions with other hormonal axes involved in reproduction, stress, and energy metabolism. The impact of EDCs on components that are shared between hormone signaling pathways or intersect between pathways can thus extend beyond the molecular ramifications to cellular, physiological, behavioral, and whole-body consequences for exposed organisms. The comparatively more extensive studies conducted in mammalian models provides encouraging support for expanded investigation and highlight the paucity of data generated in other non-mammalian vertebrate classes. As greater genomics-based resources become available across vertebrate classes, better identification and delineation of EDC effects, modes of action, and identification of effective biomarkers suitable for HPT disruption is possible. EDC-derived effects are likely to cascade into a plurality of physiological effects far more complex than the few variables tested within any research studies. The field should move towards understanding a system of hormonal systems' interactions rather than maintaining hormone system silos.

Occurrence, distribution, and risk assessment of bisphenol analogues in Luoma Lake and its inflow rivers in Jiangsu Province, China

Bisphenol analogs (BPs) are widely used in industrial and commercial products and have been detected in surface water, sediment, sewage, and sludge. The presence of BPs in the natural environment poses threats to the aquatic ecosystem and human health. The concentration, distribution, seasonal variation, and risk assessment of BPA and BPA structural analogs including BPB, BPF, BPS, BPZ, BPAF, and BPAP in surface water and sediment during dry season and flood season in Luoma Lake and its inflow rivers in Jiangsu Province, China, were investigated in this study. The detection frequency of BPA and BPF was 100%. Although the use of BPA is restricted, BPA is still the dominant BPs in surface water and sediment. The concentration of BPs in surface water during flood season was higher than that in dry season. The concentrations of BPs in Fangting River, Zhongyun River, and Bulao River were higher than those in Luoma Lake. The average concentrations of BPs in surface water were in the order of BPA > BPF> BPS> BPB > BPZ > BPAF> BPAP. Compared with other studies, the concentration of BPs in Luoma Lake was moderate. There is no significant spatial distribution and difference in seasonal variation of BPs concentration in sediment (p > 0.05). Compared with other studies, the contamination of BPs in sediment of Luoma Lake was relatively low. Risk quotient (RQ) was used to evaluate the ecological risk of BPs in water environment, and the 17β estradiol equivalent (EEQ) method was used to estimate the estrogenic activity of BPs. The risk assessment showed no high ecological risk (RQ < 1.0) and estrogenic risk (EEQ < 1.0 ng/L) in dry season and flood season. The estimated RQ and EEQ_t indicated that the ecological and human health impacts were negligible in the short term.

Lethal and Sub-Lethal Effects and Modulation of Gene Expression Induced by T Kinase Inhibitors in Zebrafish (Danio Rerio) Embryos

Tyrosine kinase inhibitors (TKIs) are designed for targeted cancer therapy. The consumption of these drugs during the last 20 years has been constantly rising. In the zebrafish (Danio rerio) embryo toxicity test, we assessed the toxicity of six TKIs: imatinib mesylate, erlotinib, nilotinib, dasatinib, sorafenib and regorafenib. Imatinib mesylate and dasatinib induced lethal effects, while regorafenib, sorfenib and dasatinib caused a significant increase of sub-lethal effects, predominantly oedema, no blood circulation and formation of blood aggregates. The analyses of the changes in the expression of selected genes associated with the hormone system after the exposure to imatinib mesylate, dasatinib and regorafenib demonstrated that all three tested TKIs deregulated the expression of oestrogen receptor esr1, cytochrome P450 aromatase (cypa19b) and hydroxysteroid-dehydrogenase (hsd3b), regorafenib, and also thyroglobulin (tg). The expression of genes involved in the DNA damage response (gadd45 and mcm6) and apoptosis (bcl2) was deregulated only by exposure to regorafenib. The data indicate that common mechanisms, namely antiangiogenic activity and interference with steroidogenesis are involved in the TKI induced sub-lethal effects and potential hormone disrupting activity, respectively. The residues of TKIs may represent an environmental hazard; therefore, further ecotoxicological studies focusing also on the effects of their mixtures are warranted.

Teratogenicity and toxicity of the new BPA alternative TMBPF, and BPA, BPS, and BPAF in chick embryonic development

Bisphenol A (BPA) is a widely known, yet controversial reproductive toxin, capable of inducing reproductive, developmental, and somatic growth defects across species. Due to scientific findings and public concern, companies have developed BPA alternatives remarkably similar to BPA. However, these alternatives have had much less testing and oversight, yet they are already being mass-produced and used across industries from plastics to food-contact coatings. The newest one, tetramethyl bisphenol F (TMBPF), is the least well-studied and has never been investigated in embryological models, however it continues to be mass produced and found in various products. Here, we used the chicken embryotoxicity screening test to compare the toxicities and potencies of several BPA analogs including TMBPF. We exposed developing chicken (Gallus gallus domesticus) embryos in ovo, from embryonic day 5 to 12 (E5-12), to increasing concentrations of BPA, bisphenol S (BPS), bisphenol AF (BPAF), and TMBPF, from 0.003 to 30 μM, and analyzed their developmental and toxic effects. The bisphenols significantly impaired development, growth, and survival in a dose-dependent manner, even at low, environmentally relevant concentrations of 3-30 nM. There was severely reduced growth and developmental delay, with exposed embryos averaging half the size and weight of control vehicle-treated embryos. The most common and severe dysmorphologies were craniofacial, eye, gastrointestinal, and body pigmentation abnormalities. The bisphenols caused dose-dependent toxicity with the lowest LC₅₀s (lethal concentration with 50% survival) ever demonstrated in chick embryos, at 0.83-2.92 μM. Notably, TMBPF was the second-most toxic and teratogenic of all chemicals tested (rank order of BPAF > TMBPF > BPS > BPA). These results underscore the adverse effects of BPA replacements on early embryo development and may have implications for reproductive health and disease across species, including pregnancy exposures in humans.

Adverse effects of bisphenol B exposure on the thyroid and nervous system in early life stages of zebrafish

Bisphenol B (BPB), a widely used alternative of bisphenol A (BPA), has been detected in various environmental media and foodstuffs. However, the knowledge of the health risks about BPB is still limited. In this study, the effects of BPB on thyroid hormone homeostasis and neuronal development were evaluated by exposure of embryos 2 h post-fertilization (hpf) to BPB (0, 1, 10, 100 and 1000 μg/L) until 144 hpf. The results showed that 100 and 1000 μg/L BPB exposed larvae exhibited abnormal morphologies in phenotype and brain histological patterns. Significant decline of thyroid hormone thyroxine (T4) content and elevation of 3,5,3'-triiodothyronine (T3) content, along with the up-regulated expression of tg, trhr1, dio1, dio2, thrα, thrβ genes and down-regulated expression of tsh, ttr and trh genes in BPB exposed zebrafish larvae were observed. Moreover, locomotor activity of larvae was decreased, and the transcription of genes (e.g., elavl3, gap43, zn5, α-tubulin, syn2a and mbp) related to neuronal development were inhibited after exposure to BPB. The mechanism of neurotoxicity and thyroid disruption in zebrafish larvae induced by BPB were discussed.

Long-term low-dose oxytetracycline potentially leads to neurobehavioural changes

Trace levels of oxytetracycline (OTC)-a veterinary antibiotic and feed additive-are widespread in the environment. Studies revealed that OTC potentially impairs thyroid function, which may affect neurobehaviour; however, the impact of exposure to environmental concentrations of OTC on adult neurobehaviour is unknown. In this study, the effects of OTC on zebrafish after 30-day exposure were investigated. The total swimming distance was significantly increased under vibration and light/dark stimulation, while time spent in the white area was prolonged during the black/white preference test, indicating that the zebrafish became bolder and more impulsive under low OTC exposure. Additionally, monoamine neurotransmitter (5-hydroxytryptamine, dopamine, norepinephrine) levels were decreased and gene expression of monoamine oxidase (mao) involved in neurotransmitter metabolism was upregulated at the transcription level after OTC exposure. Because triiodothyronine (T3) levels were enhanced following exposure to OTC, we speculated that T3 may mediate OTC damage to the nervous system. Our simulated molecular docking analysis showed that OTC combined with the sodium iodide cotransporter protein may result in excessive T3 synthesis. We further exposed zebrafish to T3, and they exhibited similar behaviour to the OTC exposure group. In conclusion, environmental OTC may activate monoamine oxidase and enhance the metabolism of monoaminergic neurotransmitters via T3, thereby inducing abnormal neurobehaviour.

Short exposure to glyphosate induces locomotor, craniofacial, and bone disorders in zebrafish (Danio rerio) embryos

Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient in widely used broad-spectrum herbicides. Even though the toxicity mechanism of this herbicide in vertebrates is poorly understood, evidence suggests that glyphosate is an endocrine disruptor capable of producing morphological anomalies as well as cardiotoxic and neurotoxic effects. We used the zebrafish model to assess the effects of early life glyphosate exposure on the development of cartilage and bone tissues and organismal responses. We found functional alterations, including a reduction in the cardiac rate, significant changes in the spontaneous tail movement pattern, and defects in craniofacial development. These effects were concomitant with alterations in the level of the estrogen receptor alpha osteopontin and bone sialoprotein. We also found that embryos exposed to glyphosate presented spine deformities as adults. These developmental alterations are likely induced by changes in protein levels related to bone and cartilage formation.

Comparative toxicities of BPA, BPS, BPF, and TMBPF in the nematode Caenorhabditis elegans and mammalian fibroblast cells

Bisphenol A (BPA) is a chemical compound commonly used in the production of plastics for daily lives and industry. As BPA is well known for its adverse health effects, several alternative materials have been developed. This study comprehensively analyzed the toxicity of BPA and its three substitutes including bisphenol S (BPS), bisphenol F (BPF), and tetramethyl bisphenol F (TMBPF) on aging, healthspan, and mitochondria using an in vivo Caenorhabditis elegans (C. elegans) model animal and cultured mammalian fibroblast cells. C. elegans treated with 1 mM BPA exhibited abnormalities in the four tested parameters related to development and growth, including delayed development, decreased body growth, reduced reproduction, and abnormal tissue morphology. Exposure to the same concentration of each alternative including TMBPF, which has been proposed as a relatively safe BPA alternative, detrimentally affected at least three of these events. Moreover, all bisphenols (except BPS) remarkably shortened the organismal lifespan and increased age-related changes in neurons. Exposure to BPA and BPF resulted in mitochondrial abnormalities, such as reduced oxygen consumption and mitochondrial membrane potential. In contrast, the ATP levels were noticeably higher after treatment with all bisphenols. In mammalian fibroblast cells, exposure to increasing concentrations of all bisphenols (ranging from 50 μM to 500 μM) caused a severe decrease in cell viability in a dose-dependent manner. BPA increased ATP levels and decreased ROS but did not affect mitochondrial permeability transition pores (mPTP). Notably, TMBPF was the only bisphenol that caused a significant increase in mitochondrial ROS and mPTP opening. These results suggest that the potentially harmful physiological effects of BPA alternatives should be considered.

The possible hormetic effects of fluorene-9-bisphenol on regulating hypothalamic-pituitary-thyroid axis in zebrafish

Fluorene-9-bisphenol (BHPF) is a bisphenol A substitute, which has been introduced for the production of so-called 'bisphenol A (BPA)-free' plastics. However, it has been reported that BHPF can enter living organisms through using commercial plastic bottles and cause adverse effects. To date, the majority of the toxicologic study of BHPF focused on investigating its doses above the toxicological threshold. Here, we studied the effects of BHPF on development, locomotion, neuron differentiation of the central nervous system (CNS), and the expression of genes in the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish exposed to different doses of BHPF ranging from 1/5 of LD1 to LD50 (300, 500, 750, 1500, 3000, and 4500 nM). As a result, the possible hormetic effects of BHPF on regulating the HPT axis were revealed, in which low-dose BHPF positively affected the HPT axis while this regulation was inhibited as the dose increased. Underlying mechanism investigation suggested that BHPF disrupted myelination through affecting HPT axis including related genes expression and TH levels, thus causing neurotoxic characteristics. Collectively, this study provides the full understanding of the environmental impact of BHPF and its toxicity on living organisms, highlighting a substantial and generalized ongoing dose-response relationship with great implications for the usage and risk assessment of BHPF.

BPA and BPA alternatives BPS, BPAF, and TMBPF, induce cytotoxicity and apoptosis in rat and human stem cells

Bisphenol A (BPA) is a ubiquitous industrial chemical found in everyday plastic products and materials. Due to scientific findings on the reproductive, developmental, and cellular defects caused by BPA and heightened public awareness, manufacturers have begun to use new chemicals in place of BPA in "BPA-free" products. These alternatives are chemical analogs of BPA and include dozens of new compounds that have undergone relatively little testing and oversight, including: bisphenol S (BPS), bisphenol AF (BPAF), and the recently developed tetramethyl bisphenol F (TMBPF; the monomer of valPure V70). Here, we used adult female rat adipose-derived stem cells (rASCs) and human mesenchymal stem cells (hMSCs) to compare the toxicities and potencies of these BPA alternatives in vitro. Rat and human stem cells were exposed to BPA (1-10 μM), 17β-estradiol (E2; 10 μM), BPS (1-100 μM), BPAF (3×10^-4-30 μM), TMBPF (0.01-50 μM), or control media alone (with 0.01% ethanol) for varying time intervals from 10 min to 24 h. We found significantly decreased cell viability and massive apoptosis in rat and human stem cells treated with each BPA analog, as early as 10 min of exposure, and at low, physiologically relevant doses. BPAF showed extreme cytotoxicity in a dose-dependent manner (LC₅₀ =0.014 μM (rASCs) and 0.009 μM (hMSCs)), whereas TMBPF showed a bimodal response, with low and high concentrations being the most toxic (LC₅₀ =0.88 μM (rASCs) and 0.06 μM (hMSCs)). Activated caspase-6 levels increased in nearly all cells treated with the BPA analogs indicating the majority of cell death was due to caspase-6-mediated apoptosis. These results in both rat and human stem cells underscore the toxicity and potency of these BPA analogs, and establish a rank order of potency of: BPAF>TMBPF>BPA>BPS. Further, these and other recent findings indicate that these newer BPA analogs may be 'regrettable substitutions,' being worse than the original parent compound and lacking proper testing and regulation. This work brings to light the need for further toxicological characterization, better regulation, greater public awareness, and the development of safer, more sustainable chemicals and non-plastic products.

Prenatal exposure to bisphenols and cognitive function in children at 7 years of age in the Swedish SELMA study

BACKGROUND

Experimental evidence demonstrates that exposure to bisphenol A (BPA), and the recently introduced alternatives bisphenol S (BPS) and bisphenol F (BPF) alter normal neurodevelopment. More research is needed to evaluate the associations between exposure to individual BPA alternatives and neurodevelopmental outcomes in humans.

OBJECTIVE

The present study aimed at examining the individual associations between prenatal BPA, BPS and BPF exposure and cognitive outcomes in children at age 7 years.

METHOD

Women were enrolled in the Swedish Environmental Longitudinal Mother and Child, Asthma and Allergy (SELMA) study, at gestational median week 10.0, and their children were examined for cognitive function at 7 years of age (N = 803). Maternal urinary BPA, BPS, and BPF concentrations were measured at enrollment and childreńs cognitive function at the age of 7 years was measured using the Wechsler Intelligence Scale for Children IV (WISC-IV).

RESULTS

All three bisphenols were detected in over 90% of the women, where BPA had the highest geometric mean concentrations (1.55 ng/mL), followed by BPF (0.16 ng/mL) and BPS (0.07 ng/mL). Prenatal BPF exposure was associated with decreased full scale IQ (β = -1.96, 95%CI; -3.12; -0.80), as well as with a decrease in all four sub scales covering verbal comprehension, perceptual reasoning, working memory and processing speed. This association corresponded to a 1.6-point lower IQ score for an inter-quartile-range (IQR) change in prenatal BPF exposure (IQR = 0.054-0.350 ng/mL). In sex-stratified analyses, significant associations with full scale IQ were found for boys (β = -2.86, 95%CI; -4.54; -1.18), while the associations for girls did not reach significance (β = -1.38, 95%CI; -2.97; 0.22). No significant associations between BPA nor BPS and cognition were found.

DISCUSSION

Prenatal exposure to BPF was significantly associated with childreńs cognitive function at 7 years. Since BPF is replacing BPA in numerous consumer products globally, this finding urgently call for further studies.

Toxicity Screening of Bisphenol A Replacement Compounds: Cytotoxicity and mRNA Expression in Primary Hepatocytes of Chicken and Double-Crested Cormorant

A market for bisphenol A (BPA) replacement compounds has emerged as a result of restrictions on the use of BPA. Some of these compounds have been detected in the environment; however, little is known about their toxicological properties. In the present study, an avian in vitro toxicogenomic approach was used to compare the effects of 5 BPA alternatives. Cell viability and mRNA expression were compared in primary embryonic hepatocytes of chicken (CEH) and double-crested cormorant (DCEH) exposed to 4,4'-(propane-2,2-diyl) diphenol (BPA), bis (4-hydroxyphenyl) methane (BPF), bis (3-allyl-4-hydroxyphenyl) sulfone (TGSH), 7-bis (4-hydroxyphenylthio)-3,5-dioxaheptane (DD-70), 2,2-bis (4-hydroxyphenyl) hexafluoropropane (BPAF), and 4-hydroxyphenyl 4-isoprooxyphenylsulfone (BPSIP). Changes in gene expression were determined using 2 polymerase chain reaction (PCR) arrays: 1) species-specific ToxChips that contain genes representing toxicologically relevant pathways, and 2) chicken-specific AestroChip that measures estrogen responsive genes. In CEH and DCEH, BPA alternatives TGSH, DD-70, and BPAF were most cytotoxic. Some of the replacement compounds changed the expression of genes related to xenobiotic metabolism, bile acid, and cholesterol regulation. The rank order based on the number of genes altered on the chicken ToxChip array was TGSH > DD-70 > BPAF = BPF > 17β estradiol (E2) > BPSIP > BPA. On the cormorant ToxChip array, BPSIP altered the greatest number of genes. Based on the chicken AestroChip data, BPSIP and BPF were slightly estrogenic. These results suggest that the replacement compounds have comparable or even greater toxicity than BPA and act via different mechanisms. Environ Toxicol Chem 2021;40:1368-1378. © 2021 Her Majesty the Queen in Right of Canada. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Comparative Neurodevelopment Effects of Bisphenol A and Bisphenol F on Rat Fetal Neural Stem Cell Models

Bisphenol A (BPA) is considered as one of the most extensively synthesized and used chemicals for industrial and consumer products. Previous investigations have established that exposure to BPA has been linked to developmental, reproductive, cardiovascular, immune, and metabolic effects. Several jurisdictions have imposed restrictions and/or have banned the use of BPA in packaging material and other consumer goods. Hence, manufacturers have replaced BPA with its analogues that have a similar chemical structure. Some of these analogues have shown similar endocrine effects as BPA, while others have not been assessed. In this investigation, we compared the neurodevelopmental effects of BPA and its major replacement Bisphenol F (BPF) on rat fetal neural stem cells (rNSCs). rNSCs were exposed to cell-specific differentiation media with non-cytotoxic doses of BPA or BPF at the range of 0.05 M to 100 M concentrations and measured the degree of cell proliferation, differentiation, and morphometric parameters. Both of these compounds increased cell proliferation and impacted the differentiation rates of oligodendrocytes and neurons, in a concentration-dependent manner. Further, there were concentration-dependent decreases in the maturation of oligodendrocytes and neurons, with a concomitant increase in immature oligodendrocytes and neurons. In contrast, neither BPA nor BPF had any overall effect on cellular proliferation or the cytotoxicity of astrocytes. However, there was a concentration-dependent increase in astrocyte differentiation and morphological changes. Morphometric analysis for the astrocytes, oligodendrocytes, and neurons showed a reduction in the arborization. These data show that fetal rNSCs exposed to either BPA or BPF lead to comparable changes in the cellular differentiation, proliferation, and arborization processes.

In vitro effects of bisphenol F on antioxidant system indicators in the isolated hepatocytes of rainbow trout (Oncorhyncus mykiss)

Bisphenol F (BPF) has been used frequently in the plastics industry and the production of daily consumer products as an alternative to bisphenol A (BPA). It was aimed herein to determine the cytotoxic effects of BPF on hepatocytes isolated from the liver of rainbow trout (Oncorhyncus mykiss) using lactate dehydrogenase (LDH) assay and antioxidant defence system indicators. The cultured hepatocytes were exposed to seven concentrations (0, 15.63, 31.25, 62.50, 125, 250, and 500 µM) of BPF for 24 h. According to the LDH assay, the percentage of cytotoxicity was increased dose dependently in the cells. The malondialdehyde content, which is indicative of lipid peroxidation, was increased significantly at BPF concentrations between 15.63 and 250 µM, whereas it remained unchanged with a concentration of 500 µM. The activities of superoxide dismutase were increased, while those of catalase were decreased with all of the BPF concentrations. Elevated levels of reduced glutathione content were determined with BPF concentrations between 15.63 and 250 µM, but decreased significantly with a concentration of 500 µM. Significant increases in the activities of the glutathione peroxidase were found in hepatocytes treated with BPF at concentrations of 31.25 to 500 µM. GST activity was only significantly increased with a BPF concentration of 250 µM. The results showed that the toxic mechanism of BPF was mainly based on cell membrane damage and oxidative stress, which have an influence on antioxidant defences. Therefore, BPF should be reconsidered as a safe alternative instead of BPA in the manufacturing of industrial or daily products.

Crosstalk of cholinergic pathway on thyroid disrupting effects of the insecticide chlorpyrifos in zebrafish (Danio rerio)

Chlorpyrifos is a widely used organophosphate insecticide and ubiquitously detected in the environment. However, little attention has been paid to its endocrine disrupting effect to non-target organisms. In the present study, zebrafish was exposed to 13 and 65 μg/L of chlorpyrifos for 7 and 10 days to determine the induced neurotoxicity and the alteration of thyroid metabolism. The 120 h LC₅₀ and LC₁₀ of chlorpyrifos was estimated as 1.35 mg/L and 0.62 mg/L based on the acute embryo toxicity assay, respectively. The acetylcholinesterase (AChE) inhibitory was detected by 13 μg/L chlorpyrifos and could be reversed by the co-exposure of 100 and 1000 μg/L anticholinergic agent atropine. For thyroid hormone level, 13 and 65 μg/L of chlorpyrifos induced increased free T₃ levels in 10 dpf (days post-fertilization). The expression of thyroid related genes in 7 and 10 dpf exposed zebrafish were measured by the quantitative Real-Time PCR (qRT-PCR) assay. The mRNA expression of tshba, thrb, crhb, ttr, tpo, ugt1ab and slc5a5 had significant change. However, the alterations of thyroid hormone and mRNA expression could be partly rescued by the addition of atropine. The molecular docking of chlorpyrifos and T₃ to the thyroid receptor β in zebrafish using homology modelling and CDOCKER procedures shown weaker binding ability of chlorpyrifos compared to T₃. Therefore, we concluded that the disturbance of thyroid signaling in zebrafish might arise from the developmental neurotoxicity induced by chlorpyrifos.

Occurrence, toxicity and ecological risk of Bisphenol A analogues in aquatic environment - A review

Bisphenol analogues (BPs) have been widely applied to industry as the substitutes for bisphenol A (BPA), which have been detected frequently in surface water, sediment, sewage and sludge. The presence of BPs in natural environment could pose risks to the aquatic ecosystem and human health. This study outlined the occurrence, toxicity of BPs in aquatic environment and manifested their potential ecological risk to the aquatic ecosystem throughout the world. As for occurrence, BPA was losing its dominance, while BPs were occupying a large part, especially for bisphenol S (BPS), bisphenol F (BPF) and bisphenol AF (BPAF). In some heavily polluted areas, BPs concentration reached µg/L in aquatic environment, which in the effluent of sewage plants was higher than that in the surface water. BPs content in sludge and sediment was more than that in the aqueous phase. All BPs other than BPS and Bisphenol P (BPP) had moderate toxicity. The current data supports that exposure to BPs may have adverse effects on dysfunction of endocrine system such as thyroid hormone concentration, enzyme activity, and even cell dysfunction, gene damage and chromosomal abnormalities. According to the risk quotient (RQ), BPF shows the highest ecological risk in China, Japan and South Korea, followed by BPA and BPS. The occurrence of bisphenols and their neurotoxicity on aquatic organisms merit further investigation.

Bisphenols emerging in Norwegian and Czech aquatic environments show transthyretin binding potency and other less-studied endocrine-disrupting activities

Bisphenols are increasingly recognized as environmental pollutants with endocrine-disrupting potential. Nonetheless, the study of environmental occurrence and some endocrine-disrupting activities of some bisphenols came widely into focus of research only recently. The aims of the present study were to: 1) determine the predominant bisphenols in Norwegian sewage sludge and sediment and in Czech surface waters, and 2) characterize the binding of bisphenols to a transport protein transthyretin (TTR) and their (anti-)thyroid, (anti-)progestagenic, and (anti-)androgenic activities. High-performance liquid chromatography with atmospheric pressure chemical ionization or photoionization coupled with high resolution mass spectrometry (HPLC-APCI/APPI-HRMS) and Chemically Activated LUciferase gene eXpression (CALUX) in vitro reporter gene bioassays were used to detect the target compounds and to determine endocrine-disrupting activities, respectively. Bisphenol A (BPA), 4,4'-bisphenol F (BPF), bisphenol S (BPS), and bisphenol E (BPE) were the most frequently found compounds in municipal sewage sludge. Furthermore, bisphenol TMC (BPTMC) and bisphenol AF (BPAF) frequently occurred in sediment and surface waters, respectively. BPA was the major contributor to Ʃ of bisphenols in Norwegian sewage sludge with exception of one sample where BPF predominated. We also monitored a few bisphenols in sediment but only BPTMC was found. BPA, BPAF and BPF were the dominant bisphenols in Czech surface waters. Some bisphenols have shown TTR binding potency (BPAF = BPF > BPA = BPE) and some have displayed the following endocrine-disrupting activities: anti-thyroid (BPAF), anti-progestagenic (BPTMC > BPA = BPAF), and anti-androgenic (BPAF > BPE > BPA > BPTMC > BPF > BPS). It is noteworthy that BPAF exhibited stronger or similarly potent endocrine-disrupting activities compared to BPA. Our results provide new insights into these less-studied endocrine-disrupting activities of environmentally relevant bisphenols and may be useful in prioritizing those compounds that deserve further attention in environmental monitoring and eco-toxicological research.

Detrimental Effects of Bisphenol Compounds on Physiology and Reproduction in Fish: A Literature Review

Bisphenol-A is one of the most studied endocrine-chemicals, which is widely used all over the world in plastic manufacture. Because of its extensive use, it has become one of the most abundant chemical environmental pollutants, especially in aquatic environments. BPA is known to affect fish reproduction via estrogen receptors but many studies advocate that BPA affects almost all aspects of fish physiology. The possible modes of action include genomic, as well as and non-genomic mechanisms, estrogen, androgen, and thyroid receptor-mediated effects. Due to the high detrimental effects of BPA, various analogs of BPA are being used as alternatives. Recent evidence suggests that the analogs of BPA have similar modes of action, with accompanying effects on fish physiology and reproduction. In this review, a detailed comparison of effects produced by BPA and analogs and their mode of action is discussed.

Tralopyril induces developmental toxicity in zebrafish embryo (Danio rerio) by disrupting the thyroid system and metabolism

Tralopyril, an antifouling biocide, widely used in antifouling systems to prevent underwater equipment from biological contamination, which can pose a potential risk to aquatic organisms and human health. However, there is little information available on the toxicity of tralopyril to aquatic organisms. Herein, zebrafish (Danio rerio) were used to investigate the toxicity mechanisms of tralopyril and a series of developmental indicators, thyroid hormones, gene expression and metabolomics were measured. Results showed that tralopyril significantly decreased the heart-beat and body length of zebrafish embryos-larvae exposed to 4.20 μg/L or higher concentrations of tralopyril and also induced developmental defects including pericardial hemorrhage, spine deformation, pericardial edema, tail malformation and uninflated gas bladder. Tralopyril decreased the thyroid hormone concentrations in embryos and changed the transcriptions of the related genes (TRHR, TSHβ, TSHR, Nkx2.1, Dio1, TRα, TRβ, TTR and UGT1ab). Additionally, metabolomics analysis showed that tralopyril affected the metabolism of amino acids, energy and lipids, which was associated with regulation of thyroid system. Furthermore, this study demonstrated that alterations of endogenous metabolites induced the thyroid endocrine disruption in zebrafish following the tralopyril treatment. Therefore, the results showed that tralopyril can induce adverse developmental effects on zebrafish embryos by disrupting the thyroid system and metabolism.

Zebrafish Embryonic Exposure to BPAP and Its Relatively Weak Thyroid Hormone-Disrupting Effects

Safe endocrine-disrupting alternatives for bisphenol A (BPA) are needed because its adverse health effects have become a public concern. Some bisphenol analogues (bisphenol F and S) have been applied, but their endocrine-disrupting potential is either not negligible or weaker than that of BPA. However, the endocrine-disrupting potential of bisphenol AP (BPAP), another BPA alternative, has not yet been fully assessed. Hence, we evaluated the thyroid hormone (TH)-disrupting potency of BPAP because THs are essential endocrine hormones. Zebrafish embryos were exposed to BPAP (0, 18.2, 43.4, or 105.9 μg/L) for 120 h, and TH levels, the transcription of 16 TH-related genes, the transcriptome, development, and behavior were evaluated. In our study, a decrease in T4 level was observed only at the maximum nonlethal concentration, but significant changes in the T3 and TSHβ levels were not detected. BPAP did not cause significant changes in transcription and gene ontology enrichment related to the TH system. Developmental and behavioral changes were not observed. Despite T4 level reduction, other markers were not significantly affected by BPAP. These might indicate that BPAP has weak or negligible potency regarding TH disruption as a BPA alternative. This study might provide novel information on the TH-disrupting potential of BPAP.

Low-dose effects on thyroid disruption in zebrafish by long-term exposure to oxytetracycline

As a feed additive in agriculture, the antibiotic oxytetracycline (OTC) has become widely distributed in the natural environment, leading to the exposure of many organisms to low doses of OTC. Although OTC is clinically contraindicated in children because of its multiple side effects, the effect of exposure to low doses of environmental OTC on children is unknown, particularly during development. In this study, we investigated the effects of OTC on the thyroid endocrine system in zebrafish, through determinations of the whole-body contents of triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH) by enzyme-linked immunosorbent assay, and analysis of the mRNA expression of regulatory genes involved in the hypothalamus-pituitary-thyroid (HPT) axis using quantitative real-time polymerase chain reaction. Zebrafish embryos were exposed to OTC at environmentally relevant concentrations from 2 h to 120 days post-fertilisation. After exposure to OTC at 1,000 and 5,000 ng/L, T3 contents were significantly enhanced (37.8% and 45.1%, respectively) and TSH contents were reduced (16% and 16.3%, respectively) compared with those in the controls. The OTC-driven increase in the transcription of genes involved in thyroid synthesis (tpo and nis) may be responsible for the altered T3 levels. These data indicate that OTC may cause thyroid dysfunction and lead to reduced TSH secretion owing to enhanced negative feedback control of the HPT axis. Meanwhile, a decrease in body length, weight, and BMI and an increase in heart rate were observed with increasing OTC exposure. In conclusion, our results indicate that long-term exposure to low concentrations of OTC may alter the transcription of key genes involved in the HPT axis, as well as T3 and TSH contents, thereby disrupting the thyroid system and affecting the growth and development of zebrafish.

Changes in thyroid hormone levels and related gene expressions in embryo-larval zebrafish exposed to binary combinations of bifenthrin and acetochlor

Bifenthrin (BF) and acetochlor (AT) are widely used as an insecticide and herbicide, respectively, which are introduced to the aquatic environment as a natural result. Although the thyroid active substances may coexist in the environment, their joint effects on fish have not been identified. We examined the joint toxicity of BF and AT in zebrafish (Danio rerio) in this study. An acute lethal toxicity test indicated that the median lethal concentration (LC₅₀) values of BF and AT under 96 h treatment were 0.40 and 4.56 µmol L^-1, respectively. The binary mixture of BF + AT displayed an antagonistic effect on the acute lethal toxicity. After 14 days post fertilization (dpf) with exposure to individual pesticides at sub-lethal concentrations of, no effects were observed on the catalase (CAT) and peroxidase (POD) activities, while the binary mixtures (except for the 7.2 × 10^-3 µmol L^-1 BF + 1.2 × 10^-2 µmol L^-1 AT exposure group) significantly induced the CAT activity. The superoxide dismutase (SOD) activity and triiodothyronine (T3) level were significantly increased in all exposure groups. The thyroxine (T4) level remained unchanged after exposure to individual pesticides, but significantly increased in the 7.2 × 10^-3 µmol L^-1 BF + 1.2 × 10^-2 µmol L^-1 AT group. The expressions of the genes Dio2, TRa, TSHβ and CRH in the thyroid hormone (TH) axis were significantly up-regulated in the 7.2 × 10^-3 µmol L^-1 BF + 0.4 × 10^-2 µmol L^-1 AT group. Our data indicated that the binary mixture of BF + AT significantly altered the antioxidant enzyme activities and gene expressions in the hypothalamic-pituitary-thyroid (HPT) axis and changed the TH levels.