Developmental exposure to a POPs mixture or PFOS increased body weight and reduced swimming ability but had no effect on reproduction or behavior in zebrafish adults

Reviewing the use of zebrafish for the detection of neurotoxicity induced by chemical mixtures through the analysis of behaviour

The knowledge and assessment of mixtures of chemical pollutants in the aquatic environment is a complex issue that is often challenging to address. In this review, we focused on the use of zebrafish (Danio rerio), a vertebrate widely used in biomedical research, as a model for detecting the effects of chemical mixtures with a focus on behaviour. Our aim was to summarize the current status of the ecotoxicological research in this sector. Specifically, we limited our research to the period between January 2012 and September 2023, including only those works aimed at detecting neurotoxicity through behavioural endpoints, utilizing zebrafish at one or more developmental stages, from egg to adult. Additionally, we gathered the findings for every group of chemicals involved and summarised data from all the works we included. At the end of the screening process 101 papers were considered eligible for inclusion. Results show a growing interest in zebrafish at all life stages for this kind of research in the last decade. Also, a wide variety of different assays, involving different senses, was used in the works we surveyed, with exposures ranging from acute to chronic. In conclusion, the results of this study show the versatility of zebrafish as a model for the detection of mixture toxicity although, for what concerns behavioural analysis, the lack of standardisation of methods and endpoints might still be limiting.

Association between prenatal exposure to per- and polyfluoroalkyl substances and infant anthropometry: A prospective cohort study

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic organic chemicals with potential endocrine-disrupting effects, and have been found to impair the physical growth of offspring in both experimental and epidemiological studies. We aimed to investigate the effects of prenatal PFAS exposure on repeated measurements of multiple anthropometric indicators in infants.

METHOD

PFAS were measured in serum samples collected from pregnant women at 12-16 gestational weeks. We calculated z-scores for the weight-for-age (WAZ), weight-for-length (WLZ), head circumference-for-age (HCZ), arm circumference-for-age (ACZ), triceps skinfold-for-age (TSZ), and subscapular skinfold-for-age (SSZ) at birth, 6 months, and 12 months of age according to the child growth standards of the World Health Organization (WHO) for anthropometric indicators. A total of 964 mother-infant pairs were included. A multivariate linear regression was performed to examine the associations between prenatal PFAS concentrations and anthropometric indicators at each time point. A generalized estimating equation (GEE) model was used to examine the longitudinal effects of PFAS exposure on repeated measurements of anthropometric indicators. Ultimately, a Bayesian kernel machine regression (BKMR) model was used to assess the joint effects of the PFAS mixture on anthropometric indicators.

RESULTS

In GEE models, perfluorododecanoic acid (PFDoA) in the high tertile group was associated with increased WAZ/WLZ, with β values (95% confidence intervals (CI)) of 0.12 (0.00, 0.23) and 0.18 (0.03, 0.32), respectively. Perfluorononanoic acid (PFNA) was associated with increased ACZ in the middle and high tertile groups. The BKMR models also presented the associations of the PFAS mixture with increased WAZ/WLZ throughout infancy, with more profound effects in females. Meanwhile, a pattern of inverse associations was observed between the perfluorooctanoic acid (PFOA) concentrations in the high tertile group and decreased WAZ, WLZ, and HCZ in males. In addition, the associations between PFAS and increased TSZ/SSZ at birth were identified by both linear regression and BKMR models.

CONCLUSION

Prenatal PFAS exposure (PFNA and PFDoA) was associated with increased infant anthropometry, especially in female infants, while prenatal PFOA exposure was associated with decreased weight, and head and arm circumference in male infants. The findings indicate that prenatal PFAS exposure may impair the growth trajectory of offspring.

Survival, Growth, and Reproduction Responses in a Three-Generation Exposure of the Zebrafish (Danio rerio) to Perfluorooctane Sulfonate

A prior multigenerational perfluorooctane sulfonic acid (PFOS) exposure investigation in zebrafish reported adverse effects at 0.734 µg/L, among the lowest aquatic effect levels for PFOS reported to date. The present three-generation PFOS exposure quantified survival, growth, reproduction, and vitellogenin (VTG; egg yolk protein) responses in zebrafish, incorporating experimental design and procedural improvements relative to the earlier study. Exposures targeting 0.1, 0.6, 3.2, 20, and 100 µg/L in parental (P) and first filial (F1) generations lasted for 180 days post fertilization (dpf) and the second filial generation (F2) through 16 dpf. Survival decreased significantly in P and F2 generation exposures, but not in F1, at the highest PFOS treatment (100 µg/L nominal, 94-205 µg/L, measured). Significant adverse effects on body weight and length were infrequent, of low magnitude, and occurred predominantly at the highest exposure treatment. Finally, PFOS had no significant effects on P or F1 egg production and survival or whole-body VTG levels in P or F1 male fish. Overall, the predominance and magnitude of adverse PFOS effects at <1 µg/L reported in prior research were largely nonrepeatable in the present study. In contrast, the present study indicated a threshold for ecologically relevant adverse effects in zebrafish at 117 µg/L (SE 8 µg/L, n = 10) for survival and 47 µg/L (SE 11 µg/L, n = 19) for all statistically significant negative effects observed. Environ Toxicol Chem 2024;43:115-131. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Early life exposure to perfluorooctanesulfonate (PFOS) impacts vital biological processes in Xenopus laevis: Integrated morphometric and transcriptomic analyses

Perfluorooctanesulfonate (PFOS) is a ubiquitous environmental pollutant associated with increasing health concerns and environmental hazards. Toxicological analyses of PFOS exposure are hampered by large interspecies variations and limited studies on the mechanistic details of PFOS-induced toxicity. We investigated the effects of PFOS exposure on Xenopus laevis embryos based on the reported developmental effects in zebrafish. X. laevis was selected to further our understanding of interspecies variation in response to PFOS, and we built upon previous studies by including transcriptomics and an assessment of ciliogenic effects. Midblastula-stage X. laevis embryos were exposed to PFOS using the frog embryo teratogenesis assay Xenopus (FETAX). Results showed teratogenic effects of PFOS in a time- and dose-dependent manner. The morphological abnormalities of skeleton deformities, a small head, and a miscoiled gut were associated with changes in gene expression evidenced by whole-mount in situ hybridization and transcriptomics. The transcriptomic profile of PFOS-exposed embryos indicated the perturbation in the expression of genes associated with cell death, and downregulation in adenosine triphosphate (ATP) biosynthesis. Moreover, we observed the effects of PFOS exposure on cilia development as a reduction in the number of multiciliated cells and changes in the directionality and velocity of the cilia-driven flow. Collectively, these data broaden the molecular understanding of PFOS-induced developmental effects, whereby ciliary dysfunction and disrupted ATP synthesis are implicated as the probable modes of action of embryotoxicity. Furthermore, our findings present a new challenge to understand the links between PFOS-induced developmental toxicity and vital biological processes.

Comparing Ocular Toxicity of Legacy and Alternative Per- and Polyfluoroalkyl Substances in Zebrafish Larvae

Studies comparing the ocular toxicity potential between legacy and alternative PFAS are lacking. To address this research gap, zebrafish larvae were exposed to both legacy PFAS (i.e., perfluorooctanesulfonic acid [PFOS] and perfluorooctanoic acid [PFOA]) and their corresponding alternatives (i.e., perfluorobutanesulfonic acid [PFBS] and perfluorobutanoic acid [PFBA]). Alterations in their visual behaviors, such as phototactic and optomotor responses (OMR), were assessed at sublethal concentrations. Gene expression variations in visual function-associated pathways were also measured. Visual behavioral assessment revealed that PFOS exposure resulted in concentration-dependent reductions in phototactic responses at 10-1000 μg/L, with PFOA exerting reduction effects only at 100 mg/L. However, their two alternatives had no effect at all tested concentrations. Following an improved contrast-OMR (C-OMR) assessment, PFOS decreased the OMR to a water flow stimulus at 10, 100, and 1000 μg/L. The gene expression analysis revealed that PFOS exposure markedly downregulated most genes involved in the opsins in the photoreceptor and phototransduction cascade, which explains the observed visual behavior changes well. Our findings indicate that PFOS is the most likely PFAS to cause visual toxicity, with PFOA present but less likely, and their substitutes, PFBS and PFBA, cannot be classified as visually toxic to zebrafish.

Embryonic exposure to PFAS causes long-term, compound-specific behavioral alterations in zebrafish

Per- and polyfluoroalkyl substances (PFAS) are commonly used as surfactants and coatings for industrial processes and consumer products. These compounds have been increasingly detected in drinking water and human tissue, and concern over their potential effects on health and development is growing. However, relatively little data are available for their potential impacts on neurodevelopment and the degree to which different compounds within this class may differ from one another in their neurotoxicity. The present study examined the neurobehavioral toxicology of two representative compounds in a zebrafish model. Zebrafish embryos were exposed to 0.1-100uM perfluorooctanoic acid (PFOA) or 0.01-1.0uM perfluorooctanesulfonic acid (PFOS) from 5 to 122 h post-fertilization. These concentrations were below threshold for producing increased lethality or overt dysmorphologies, and PFOA was tolerated at a concentration 100× higher than PFOS. Fish were maintained to adulthood, with behavioral assessments at 6 days, 3 months (adolescence) and 8 months of age (adulthood). Both PFOA and PFOS caused behavioral changes in zebrafish, but PFOS and PFOS produced strikingly different phenotypes. PFOA was associated with increased larval motility in the dark (100uM), and enhanced diving responses in adolescence (100uM) but not adulthood. PFOS was associated with a reversed light-dark response in the larval motility test (0.1-1uM), whereby the fish were more active in the light than the dark. PFOS also caused time-dependent changes in locomotor activity in the novel tank test during adolescence (0.1-1.0uM) and an overall pattern of hypoactivity in adulthood at the lowest concentration (0.01uM). Additionally, the lowest concentration of PFOS (0.01uM) reduced acoustic startle magnitude in adolescence, but not adulthood. These data suggest that PFOS and PFOA both produce neurobehavioral toxicity, but these effects are quite distinct from one another.

Nafion by-product 2 disturbs lipid homeostasis in zebrafish embryo

As a novel polyfluoroalkyl substance, Nafion by-product 2 (Nafion BP2) has been detected widely in environmental matrix as well as human samples. However, its toxicity remains poorly recognized. Here, we investigated the toxic effects of Nafion BP2 by use of zebrafish model and highlighted its toxicity on lipid homeostasis. Large sized-lipid droplets (LDs) have been revealed to gather in pericardium and anterior yolk sac region of zebrafish larvae by Oil Red O staining after a 120 h Nafion BP2 exposure. Meanwhile, the total cholesterol (TC) concentrations were significantly disrupted. Lipidomic analysis uncovered a dramatical alterations on lipid profiles. Significant reductions were observed for a set of lipids including phosphatidylinositol (PI), phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingolipid (SM) and triglyceride (TG) in zebrafish. Transcriptome analyses further confirmed genes involved in LDs biosynthesis, lipid transportation and lipid metabolism, were significantly disrupted. Especially for APOA4 and CIDEC genes, fold changes (Log2 FC) of gene expression level by up to 17.8 and 3.5, respectively, were observed. Together, these findings demonstrated the disturbance of Nafion BP2 on lipid homeostasis of zebrafish and provided an unprecedented insight into the health risk assessments of emerging fluorochemicals.

Perfluorooctane sulfonic acid (PFOS) exposures interfere with behaviors and transcription of genes on nervous and muscle system in zebrafish embryos

Perfluorooctane sulfonic acid (PFOS) has been widely detected in environment and organisms. PFOS has been identified as the driving agent for the behavioral changes of zebrafish larvae, while the underlying molecular mechanism remains unclear. In this study, zebrafish embryos/larvae were exposed to 0, 0.04, 0.1, 0.4 and 1 μM PFOS for 166 h. The locomotor behaviors and the mRNA transcription of genes in neuromuscular system were detected. Exposure to PFOS did not affect the hatching/death rates and body length, but increased the heart beat rates and frequency of spontaneous tail coiling. Locomotor behavior in zebrafish larvae of 0.4 and 1 μM PFOS groups were increased in the light condition. Additionally, the levels of acetylcholine (Ach) in 0.4 μM PFOS group and dopamine (DA) in 0.1, 0.4 and 1 μM PFOS groups were found to be significantly increased. The expression of genes related to the synthesis and decomposition of ACh，the synthesis and receptor of DA, and fosab was increased in the different PFOS treatment groups, while the expression of all the other genes of the neuromuscular system were significantly reduced. The findings of this investigation demonstrated that PFOS exposure may alter the locomotor behavior of zebrafish through disrupting the expressions of genes in neuromuscular system. The disturbed process of neurotransmitter transmission and muscle contraction caused by PFOS may be the dominant mechanism of hyperactivity in zebrafish.

Self-recovery study of fluoride-induced ferroptosis in the liver of zebrafish (Danio rerio)

Ferroptosis plays a key role in fluorosis in aquatic organisms, but whether it is involved in fluoride-induced liver damage remains unclear. Previous studies have indicated that fluoride toxicity has the reversible tendency, but the mechanism of self-recovery after fluorosis in aquatic animals has not been elucidated. In this study, adult zebrafish and embryos were exposed to 0, 20, 40, 80 mg/L of fluoride for 30, 60 and 90 d and 3, 4 and 5 d post-fertilization (dpf), respectively. After 90 d, adult zebrafish were transferred to clean water for self-recovery of 30 d. The results showed that fluoride induced the prominent histopathologial changes in liver of adults, and the developmental delay and dark liver area in larvae. Fluoride significantly increased the iron overload, while decreased the expression levels of transferrin (tf), transferrin receptor (tfr), ferroportin (fpn), membrane iron transporter (fpn), and ferritin heavy chain (fth) in adults and larvae. Fluoride also induced the oxidative stress in adults and larvae by increasing the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), while decreasing the glutathione (GSH) content and the levels of glutathione peroxidase 4 (gpx4) and solute carrier family 7 member 11 (slc7a11). Self-recovery relieved fluoride-induced ferroptosis by reducing the histopathological damage and oxidative stress, reversing the expression levels of fth and slc7a11, Fe²⁺ metabolism and GSH synthesis. Lipid peroxidation and Fe²⁺ metabolism may be the key factor in alleviating effects of self-recovery on fluoride toxicity. Moreover, males are more sensitive than females. Our results provide a theoretical basis for studying the alleviating effects of self-recovery on fluoride toxicity and the underlying mechanism of its protective effect.

Persistent impairment of gonadal development in rare minnow (Gobiocypris rarus) after chronic exposure to chlorinated polyfluorinated ether sulfonate

The delayed and persistent adverse effects caused by developmental exposure to per- and poly-fluorinated substances are of significant concern. Juvenile rare minnows (Gobiocypris rarus), were exposed to chlorinated polyfluoroalkyl ether sulfonate (Cl-PFESA) at measured medium concentrations of 86.5 μg/L, 162 μg/L and 329 μg/L, for 4 weeks followed by 12 weeks of depuration. After 4 weeks of exposure, the body weight and length of the juvenile fish were increased compared to controls. Gene expression of gnrh3, lhβ, and cyp19a was decreased, and ar and erα were upregulated. Transcriptomic analysis revealed enrichment of multiple pathways related to gonadal development. After 12 weeks of depuration, the gonadosomatic indices were decreased in female fish in a concentration-dependent manner, with a significant decrease to 59% of control in 329 μg/L group. Histological analysis found increasing numbers of degenerating oocytes and perinucleolar oocytes, and decreasing numbers of mature vitellogenic oocytes in female fish treated by Cl-PFESA. Enlarged interstitial space of the testis was observed in the exposed male fish. Gene expression levels of gnrh3, lhβ, ar, erα, and vtg were upregulated in the adult fish. Chronic developmental exposure to Cl-PFESA caused persistent effects on gonadal development of fish, highlighting the necessity of a comprehensive ecological risk assessment.

Impact of environmental toxicants on p38- and ERK-MAPK signaling pathways in the central nervous system

There are several candidate signalling pathways that mediate the response of the central nervous system (CNS) cells to environmental toxins. However, much is still to be learned on how these pathways modulate neurotoxicity. The mitogen-activated protein kinases (MAPKs) signalling pathways, which include the extracellular signal-regulated protein kinase (ERK) and the p38-MAPK, are potentially key pathways to regulate CNS responses to environmental toxins. The pathways play leading roles in the transmission of extracellular signals into the cell nucleus, leading to cell differentiation, cell growth, and apoptosis, to name a few. Moreover, exposure to environmental toxins induces p38- and ERK-MAPK activation, which leads to oxidative stress, inflammation, and apoptosis in the CNS. Here, we provide a concise review of the recent evidence demonstrating the role of p38- and ERK-MAPK signaling pathways and their downstream targets in the CNS following exposure to environmental toxicants such as metals, organophosphorus and persistent organic pollutants.