Bisphenol S exposure alters behavioral parameters in adult zebrafish and offspring

Bisphenol F and Bisphenol S exposure during development reduce neuronal ganglia integrity and change behavioral profile of Drosophila melanogaster larvae

The behavior and neuronal ganglia integrity of Drosophila melanogaster larvae exposed to Bisphenol F (BPF) and Bisphenol S (BPS) (0.25, 0.5 and 1 mM) was evaluated. Larvae exposed to BPF and BPS (0.5 and 1 mM) showed hyperactivity, reduced decision-making capacity and were not responsive to touch (no sensitivity to physical stimuli). There was also a reduction in the tunneling capacity induced by 1 mM of BPF and BPS (innate behaviors for survival). Behaviors resulting from changes in neuronal functioning, thermotaxis and phototaxis showed that BPS was more harmful compared to BPF. Furthermore, the concentration of 1 mM BPS generated greater damage to neuronal ganglia when compared to BPF. This difference may be related to the LC50 of the 10.04 mM BPS and 15.07 mM BPF. However, these behavioral changes presented by the larvae here are characteristic of those presented in neurodevelopmental disorders. Our findings are novel and refute the possibility that BPF and BPS are safer alternatives.

Maternal exposure to bisphenol S reduces anxiety and impairs collective antipredator behavior of male zebrafish (Danio rerio) offspring through dysregulation of their serotonergic system

Bisphenol S (BPS) is a common endocrine-disrupting chemical globally used in several consumer and industrial products. Although previous studies suggested that BPS induces multiple effects in exposed organisms, very little is known about its intergenerational effect on offspring behavior and/or the potential underlying mechanisms. To this end, adult female zebrafish Danio rerio were exposed to BPS (0, 10, 30 µg/L) and 1 µg/L of 17-β-estradiol (E2) as a positive control for 60 days. Afterwards, female fish were bred with untreated males, and their offspring were raised to 6 months old in control water. Maternal exposure to BPS decreased male offspring anxiety and antipredator behaviors while boldness remained unaffected. Specifically, maternal exposure to 10 and 30 µg/L BPS and 1 µg/L E2 were found to impact male offspring anxiety levels as they decreased the total time that individuals spent in the dark zone in the light/dark box test and increased the total track length in the center of the open field test. In addition, maternal exposure to all concentrations of BPS and E2 disrupted antipredator responses of male offspring by decreasing shoal cohesion in the presence of chemical alarm cues derived from conspecifics, which communicated high risk. To elucidate the possible molecular mechanism underlying these neuro-behavioral effects of BPS, we assessed the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter and monoamine oxidase (MAO). The impaired anxiety and antipredator responses were associated with reduced levels of 5-HT1A subtype and MAO mRNA expression within the brain of adult male offspring. Collectively, the results of this study demonstrate that maternal exposure to environmental concentrations of BPS can interfere with the serotonergic signaling pathway in the developing brain, subsequently leading to the onset of a suite of behavioral deficits in adult offspring.

A latest progress in the study of fish behavior: cross-generational effects of behavior under pollution pressure and new technologies for behavior monitoring

With the development of agriculture and industry, an increasing number of pollutants are being discharged into the aquatic environment. These pollutants can harm aquatic life. The behavioral characteristics of animals are an external manifestation of their internal mechanisms. Changes in behavior reflect damage and changes in the internal mechanisms. Environmental pollution may lead to behavioral changes not only in the parental generation but also in the offspring that has not been exposed to the pollutants. That is, the intrinsic mechanism that leads to behavioral changes is inheritable. Fish are representative species of aquatic organisms and are commonly used in various research studies. The behavior of fish has also received extensive attention, and the monitoring technology for fish behavior has developed rapidly. This article summarizes the development process of behavior monitoring technology and introduces some of the latest technologies for studying fish behavior. This article also summarizes the intergenerational effects of pollutants on fish behavior, as well as the potential intrinsic and genetic mechanisms that may lead to behavioral changes. This article provides a reference for future relevant neurobehavioral studies.

Invisible Hand behind Female Reproductive Disorders: Bisphenols, Recent Evidence and Future Perspectives

Reproductive disorders are considered a global health problem influenced by physiological, genetic, environmental, and lifestyle factors. The increased exposure to bisphenols, a chemical used in large quantities for the production of polycarbonate plastics, has raised concerns regarding health risks in humans, particularly their endocrine-disrupting effects on female reproductive health. To provide a basis for future research on environmental interference and reproductive health, we reviewed relevant studies on the exposure patterns and levels of bisphenols in environmental matrices and humans (including susceptible populations such as pregnant women and children). In addition, we focused on in vivo, in vitro, and epidemiological studies evaluating the effects of bisphenols on the female reproductive system (the uterus, ovaries, fallopian tubes, and vagina). The results indicate that bisphenols cause structural and functional damage to the female reproductive system by interfering with hormones; activating receptors; inducing oxidative stress, DNA damage, and carcinogenesis; and triggering epigenetic changes, with the damaging effects being intergenerational. Epidemiological studies support the association between bisphenols and diseases such as cancer of the female reproductive system, reproductive dysfunction, and miscarriage, which may negatively affect the establishment and maintenance of pregnancy. Altogether, this review provides a reference for assessing the adverse effects of bisphenols on female reproductive health.

Structure-based developmental toxicity and ASD-phenotypes of bisphenol A analogues in embryonic zebrafish

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that has become more prevalent in recent years. Environmental endocrine disruptor bisphenol A (BPA) has been linked to ASD. BPA analogues (BPs) are structure-modified substitutes widely used as safer alternatives in consumer products, yet few studies have explored the developmental neurotoxicity (DNT) of BPA analogues. In the present study, we used the larval zebrafish model to assess the DNT effects of BPA and its analogues. Our results showed that many BPA analogues are more toxic than BPA in the embryonic zebrafish assay regarding teratogenic effect and mortality, which may partially due to differences in lipophilicity and/or different substitutes of structural function groups such as CF3, benzene, or cyclohexane. At sublethal concentrations, zebrafish embryos exposed to BPA or BPs also displayed reduced prosocial behavior in later larval development, evidenced by increased nearest neighbor distance (NND) and the interindividual distance (IID) in shoaling, which appears to be structurally independent. An in-depth analysis of BPA, bisphenol F (BPF), and bisphenol S (BPS) revealed macrocephaly and ASD-like behavioral deficits resulting from exposures to sublethal concentrations of these chemicals. The ASD-like behavioral deficits were characterized by hyperactivity, increased anxiety-like behavior, and decreased social contact. Mechanistically, accelerated neurogenesis that manifested by increased cell proliferation, the proportion of newborn mature neurons, and the number of neural stem cells in proliferation, as well as upregulated genes related to the K⁺ channels, may have contributed to the observed ASD-like morphological and behavioral alterations. Our findings indicate that BPF and BPS may also pose significant risks to ASD development in humans and highlight the importance of a comprehensive assessment of DNT effects for all BPA analogues in the future.

Bisphenol S Impairs Behaviors through Disturbing Endoplasmic Reticulum Function and Reducing Lipid Levels in the Brain of Zebrafish

The number of neurotoxic pollutants is increasing, but their mechanism of action is unclear. Here, zebrafish were exposed to 0, 1, 10, and 100 μg/L bisphenol S (BPS) for different durations beginning at 2 h postfertilization (hpf) to explore the neurotoxic mechanisms of BPS. Zebrafish larvae exposed to BPS displayed abnormal neurobehaviors. At 48 and 120 hpf, BPS inhibited yolk lipid consumption and reduced the lipid distribution in the zebrafish brain. Moreover, BPS downregulated the mRNA levels of genes involved in fatty acid elongation in the endoplasmic reticulum (ER) and activated ER stress pathways at 48 and 120 hpf, and KEGG analysis after RNA-seq showed that the protein processing pathway in the ER was significantly enriched after BPS exposure. Exposure to ER toxicants (thapsigargin and tunicamycin), two positive controls, induced neurotoxic effects on zebrafish embryos and larvae similar to those of BPS exposure. These data suggested that BPS and ER toxicants disturbed ER function and reduced brain lipid levels. Continued exposure to BPS into adulthood not only inhibited brain fatty acid elongation and ER function but also caused abnormal swelling of the ER in zebrafish. Our data provide new insights into the neurotoxic mechanism of BPS.

Environmental concentrations of 2, 4-DTBP cause immunotoxicity in zebrafish (Danio rerio) and may elicit ecological risk to wildlife

Synthetic phenolic antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) has gained growing concerns due to relatively high concentrations in aquatic ecosystems. There are, however, significant knowledge gaps regarding its potential toxicity to aquatic organisms. In this study, zebrafish (Danio rerio) larvae were exposed to 0.01, 0.1, or 1 μM 2,4-DTBP for 6 d. Transcriptomic analysis of larvae revealed that biological processes related to anti-inflammatory function of macrophage M2 lineage were inhibited by 0.01 μM 2,4-DTBP. Decreases of transcripts related to the IL1B-MYD88-NF-κB pathway (i.e., il1b, il1rl1, myd88, irak4, irak1, traf6, ikbkg, nfkbia, nfkb) and protein levels of NF-κB in larvae intestine confirmed anti-inflammatory effects of 2,4-DTBP. Subsequently, larvae exposed to 2,4-DTBP were challenged with E. coli and showed higher survival rate, suggesting sustained activation of inflammation via LPS can be attenuated by 2,4-DTBP. Moreover, histological examination revealed that intestine barrier was compromised and there was an imbalance of intestine macrophage homeostasis. Food intake was also reduced following exposure to 0.1 and 1 μM 2,4-DTBP. In addition, a risk assessment revealed that 2,4-DTBP in surface water pose low to high ecological risks to aquatic organisms. Taken together, exposure to environmentally relevant concentrations of 2,4-DTBP could negatively affect immune response in zebrafish and may elicit ecological risk in fish population.

Bisphenol S degradation in soil and the dynamics of microbial community associated with degradation

Bisphenol S (BPS) has been widely applied as a replacement for BPA in industrial application, leading to the frequent detection in the environment. However, its impact on soil microbial communities has not been well reported. Here, effects of BPS exposure on soil microbial communities in the presence of polystyrene (PS) microplastics were revealed. Rapid degradation of BPS occurred with a degradation rate of up to 98.9 ± 0.001 % at 32 d. The presence of BPS reduced the diversity of soil microbial communities, and changed community structures. After BPS treatment, Proteobacteria, and its members Methylobacillus, Rhodobacteraceae and Mesorhizobium became dominant, and were considered as potential biomarkers indicating BPS contamination. Co-occurrence network analysis revealed the increased relationships of certain groups of microbes after BPS treatment. The resultant low stability and resilience towards environment disturbance of microbial community networks implied the biotoxicity of BPS towards soil ecosystems. The degradation and biotoxicity of BPS (p > 0.05) in soil was not affected by the presence of PS. Our findings showed that exposure to BPS could reshape soil microbial communities and impair the robustness of microbial co-occurrence networks.

Review of the toxicity and potential molecular mechanisms of parental or successive exposure to environmental pollutants in the model organism Caenorhabditis elegans

Environmental pollutants such as heavy metals, nano/microparticles, and organic compounds have been detected in a wide range of environmental media, causing long-term exposure in various organisms and even humans through breathing, contacting, ingestion, and other routes. Long-term exposure to environmental pollutants in organisms or humans promotes exposure of offspring to parental and environmental pollutants, and subsequently results in multiple biological defects in the offspring. This review dialectically summarizes and discusses the existing studies using Caenorhabditis elegans (C. elegans) as a model organism to explore the multi/transgenerational toxicity and potential underlying molecular mechanisms induced by environmental pollutants following parental or successive exposure patterns. Parental and successive exposure to environmental pollutants induces various biological defects in C. elegans across multiple generations, including multi/transgenerational developmental toxicity, neurotoxicity, reproductive toxicity, and metabolic disturbances, which may be transmitted to progeny through reactive oxygen species-induced damage, epigenetic mechanisms, insulin/insulin-like growth factor-1 signaling pathway. This review aims to arouse researchers' interest in the multi/transgenerational toxicity of pollutants and hopes to explore the possible long-term effects of environmental pollutants on organisms and even humans, as well as to provide constructive suggestions for the safety and management of emerging alternatives.

Maternal exposure to bisphenol S induces neuropeptide signaling dysfunction and oxidative stress in the brain, and abnormal social behaviors in zebrafish (Danio rerio) offspring

Recent studies show that bisphenol S (BPS) induces multiple adverse effects in exposed organisms; however, the maternal effects of BPS exposure remain poorly understood. Here, we expose adult female zebrafish to environmentally relevant concentrations of BPS (0, 1, 10, 30 μg/L) and 1 μg/L of 17-β-estradiol (E2) as a positive control for 60 days. Females were then paired with BPS-unexposed males and their offspring were raised in control water for 6 months. Maternal exposure to BPS was found to alter social behavior and anxiety response in a dose-specific manner in male offspring. Group preferences and social cohesion were significantly reduced by maternal exposure to 1 and 10 μg/L BPS, respectively. Additionally, maternal exposure to 1 and 30 μg/L BPS and E2 decreased offspring stress responses during the novel tank test. The impaired social behavior was associated with elevated arginine-vasotocin (AVT) level as well as with the altered expression of genes involved in AVT signaling pathway (AVT, avpr1aa) and enzymatic antioxidant genes (cat and Mn-sod) in the brain. Collectively, these results suggest that maternal exposure to environmentally relevant concentrations of BPS alters social behavior in zebrafish offspring, which is likely mediated by oxidative stress and disruption of neuropeptide signaling pathways in the brain.

The fish early-life stage sublethal toxicity syndrome - A high-dose baseline toxicity response

A large number of toxicity studies report abnormalities in early life-stage (ELS) fish that are described here as a sublethal toxicity syndrome (TxSn_FELS) and generally include a reduced heart rate, edemas (yolk sac and cardiac), and a variety of morphological abnormalities. The TxSn_FELS is very common and not diagnostic for any chemical or class of chemicals. This sublethal toxicity syndrome is mostly observed at high exposure concentrations and appears to be a baseline, non-specific toxicity response; however, it can also occur at low doses by specific action. Toxicity metrics for this syndrome generally occur at concentrations just below those causing mortality and have been reported for a large number of diverse chemicals. Predictions based on tissue concentrations or quantitative-structure activity relationship (QSAR) models support the designation of baseline toxicity for many of the tested chemicals, which is confirmed by observed values. Given the sheer number of disparate chemicals causing the TxSn_FELS and correlation with QSAR derived partitioning; the only logical conclusion for these high-dose responses is baseline toxicity by nonspecific action and not a lock and key type receptor response. It is important to recognize that many chemicals can act both as baseline toxicants and specific acting toxicants likely via receptor interaction and it is not possible to predict those threshold doses from baseline toxicity. We should search out these specific low-dose responses for ecological risk assessment and not rely on high-concentration toxicity responses to guide environmental protection. The goal for toxicity assessment should not be to characterize toxic responses at baseline toxicity concentrations, but to evaluate chemicals for their most toxic potential. Additional aspects of this review evaluated the fish ELS teratogenic responses in relation to mammalian oral LD50s and explored potential key events responsible for baseline toxicity.

Unraveling the mechanism of long-term bisphenol S exposure disrupted ovarian lipids metabolism, oocytes maturation, and offspring development of zebrafish

Bisphenol S (BPS) acts as a xenoestrogen and disturbs the female reproductive system; however, the underlying mechanism has not been elucidated. In this study, the effect of chronic BPS exposure (1 μg/L and 100 μg/L) on ovarian lipid metabolism in zebrafish was investigated to determine its influence on adult reproductive capacity and offspring development. The results showed that long-term (240 days) exposure to BPS induced lipid accumulation in the ovaries by promoting the transport of more lipids from the circulation to the ovaries and by upregulating triacylglycerol synthesis-related genes. Significantly increased expression of cpt2, acadm, acadl, and pparα, which are involved in β-oxidation in the ovarian mitochondria, indicated that more energy was provided for oocyte maturation in exposed zebrafish ovaries. Thus, the proportion of full-grown stage oocytes in ovaries and egg reproduction were elevated at an accelerated rate, which earlier than normal reproductive cycle (8-10 days posts pawning). Moreover, the maternally BPS-exposed F1 embryos (2 h post-spawning, hpf) showed higher neutral lipid levels, impaired hatching capacity, and increased occurrence of larval deformities. All these findings demonstrated that stimulated lipid synthesis and β-oxidation in zebrafish ovaries significantly contribute to BPS-induced oocyte precociousness with subsequent effects on the development of unexposed offspring. This study provides new insight into the impact of xenoestrogens on oviparous reproduction in females and offspring development from the perspective of ovarian lipid metabolism.

The ZE-Tunnel: An Affordable, Easy-to-Assemble, and User-Friendly Benchtop Zebrafish Swim Tunnel

The popularity of zebrafish in both basic biological and biomedical research has led to an increased need for understanding their behavior. Locomotor behavior is an important outcome of different factors, such as specific genotypes or external stimuli that influence the nervous and musculoskeletal system. Locomotion can be studied by forced swimming in a swim tunnel, a device capable of generating a laminar water flow at different speeds in a chamber where zebrafish can be placed. However, commercially available swim tunnels are relatively expensive and in-house built systems are mostly presented without clear building instructions or proper validation procedures. In this study, we developed an alternative, cheap (<250 euro), and user-friendly, but customizable benchtop swim tunnel, called the "Zebrafish exercise-tunnel" (ZE-Tunnel). Detailed step-by-step instructions on how to construct the tunnel components, including the frame, mechanical, and electric components are given. The ZE-Tunnel was reliably used to exercise fish for prolonged periods and its performance was successfully validated by replicating previously published experiments on critical speed testing in zebrafish. Finally, implementation of behavioral video analysis using freely available motion-tracking software showed differences in swimming dynamics in the Chihuahua skeletal zebrafish mutant.