The PFOS disturbed immunomodulatory functions via nuclear Factor-κB signaling in liver of zebrafish (Danio rerio)

Per- and polyfluoroalkyl substances alter innate immune function: evidence and data gaps

Per- and polyfluoroalkyl substances (PFASs) are a large class of compounds used in a variety of processes and consumer products. Their unique chemical properties make them ubiquitous and persistent environmental contaminants while also making them economically viable and socially convenient. To date, several reviews have been published to synthesize information regarding the immunotoxic effects of PFASs on the adaptive immune system. However, these reviews often do not include data on the impact of these compounds on innate immunity. Here, current literature is reviewed to identify and incorporate data regarding the effects of PFASs on innate immunity in humans, experimental models, and wildlife. Known mechanisms by which PFASs modulate innate immune function are also reviewed, including disruption of cell signaling, metabolism, and tissue-level effects. For PFASs where innate immune data are available, results are equivocal, raising additional questions about common mechanisms or pathways of toxicity, but highlighting that the innate immune system within several species can be perturbed by exposure to PFASs. Recommendations are provided for future research to inform hazard identification, risk assessment, and risk management practices for PFASs to protect the immune systems of exposed organisms as well as environmental health.

Nanoscale exopolymer reassembly-trap mechanism determines contrasting PFOS exposure patterns in aquatic animals with different feeding habitats: A nano-visualization study

The behavior and fate of PFOS (perfluorooctanesulfonate) in the aquatic environment have received great attention due to its high toxicity and persistence. The nanoscale supramolecular mechanisms of interaction between PFOS and ubiquitous EPS (exopolymers) remain unclear though EPS have been widely-known to influence the bioavailability of PFOS. Typically, the exposure patterns of PFOS in aquatic animals changed with the EPS-PFOS interaction are not fully understood. This study hypothesized that PFOS exposure and accumulation pathways depended on the PFOS-EPS interactive assembly behavior and animal species. Two model animals, zebrafish and chironomid larvae, with different feeding habitats were chosen for the exposure and accumulation tests at the environmental concentrations of PFOS in the absence and presence of EPS. It was found that PFOS triggered the self-assembly of EPS to form large aggregates which significantly trapped PFOS. PFOS accumulation was significantly promoted in zebrafish but drastically reduced in chironomid larvae because of the nanoscale interactive assembly between EPS and PFOS. The decreased dermal uptake but increased oral uptake of PFOS by zebrafish with large mouthpart size could be ascribed to the increased ingestion of PFOS-enriched EPS aggregates as food. For the chironomid larvae with small mouthpart size, the PFOS-EPS assemblies reduced the dermal, oral and intestinal uptake of PFOS. The nano-visualization evidences confirmed that the PFOS-enriched EPS-PFOS assemblies blocked PFOS penetration through skin of both animals. These findings provide novel knowledge about the ecological risk of PFOS in aquatic environments.

Immunotoxicity of legacy and alternative per- and polyfluoroalkyl substances on zebrafish larvae

Hexafluoropropylene oxide dimer acid (HFPO-DA) and perfluoroethylcyclohexane sulfonate (PFECHS) are increasingly used as alternatives for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). However, their immunotoxicity and underlying molecular mechanisms remain poorly understood. Here, to assess immunotoxic effects, zebrafish embryos were exposed to environmentally relevant concentrations of PFOA, PFOS, HFPO-DA, and PFECHS for four days. Results revealed that all four per- and polyfluoroalkyl substances (PFAS) resulted in decreased heart rate and spontaneous movement, and induced oxidative stress in zebrafish larvae. Notably, HFPO-DA exhibited more severe oxidative stress than PFOA. Immune dysfunction was observed, characterized by elevated cytokine, complement factor, nitric oxide, and neutrophil content, along with a significant decrease in lysozyme content. Transcriptomic analysis revealed the activation of Toll-like receptor (TLR)/NOD-like receptor (NLR)/RIG-I-like receptor (RLR) and associated downstream genes, indicating their pivotal role in PFAS-induced immunomodulation. Molecular docking simulations demonstrated stable interactions between PFAS and key receptors (TLR2, NOD2 and RIG-I). Overall, HFPO-DA and PFECHS exhibited immunotoxic effects in zebrafish larvae similar to legacy PFAS, providing important information for understanding the toxic mode of action of these emerging alternatives.

Chronic environmental level exposure to perfluorooctane sulfonate overshadows graphene oxide to induce apoptosis through activation of the ROS-p53-caspase pathway in marine medaka Oryzias melastigma

The widespread occurrence of perfluorooctane sulfonate (PFOS) and the mass production and application of graphene oxide (GO) lead to their inevitable release and interaction in the environment, which may enhance associated toxic impacts on aquatic organisms. This study elucidates the induction of apoptosis by 60-day chronic single and mixture exposures to environmentally relevant levels of PFOS (0.5 μg/L and 5 μg/L) and GO (1 mg/L) in adult marine medaka Oryzias melastigma. Results showed a significant increase (p < 0.05) in reactive oxygen species (ROS) levels, the apoptotic positive rate in livers, and activities of caspases 3, 8, and 9 in all treated groups compared to the control. PFOS individual and PFOS-GO combined exposures significantly impacted fish growth, upregulated expressions of six apoptosis-related genes including p53, apaf1, il1b, tnfa, bcl2l1, bax, as well as enriched cell cycle and p53 signaling pathways (transcriptomic analysis) related to apoptosis compared to control group. Besides higher ROS production, GO also had a higher binding affinity to proteins than PFOS, especially to caspase 8 as revealed by molecular docking. Overall, PFOS induced ROS-p53-caspase apoptosis pathway through multi-gene regulation during single or mixture exposure, while GO single exposure induced apoptosis through tissue damage and ROS-caspase pathway activation and direct docking with caspase 8 to activate the caspase cascade. Under co-exposure, the PFOS-induced apoptotic pathway overshadowed the GO-induced pathway, due to competition for limited active sites on caspases. These findings will contribute to a better understanding of the apoptosis mechanism and ecological risks of nanomaterials and per- and polyfluoroalkyl substances in marine ecosystems.

Caspase-8 promotes NLRP3 inflammasome activation mediates eye development defects in zebrafish larvae exposed to perfulorooctane sulfonate (PFOS)

Epidemiological evidence showed that serum high perfluorooctane sulfonate (PFOS) levels are associated with multiple eye related diseases, but the potential underlying molecular mechanisms remain poorly understood. Zebrafish and photoreceptor cell (661w) models were used to investigate the molecular mechanism of PFOS induced eye development defects. Our results showed a novel molecular mechanism of PFOS-induced inflammation response-mediated photoreceptor cell death associated with eye development defects. Inhibition of Caspase-8 activation significantly decreased photoreceptor cell death in PFOS exposure. Mechanistically, Toll-like receptor 4 (TLR4) mediates activation of Caspase-8 promote activation of NLR family pyrin domain-containing 3 (NLRP3) inflammasome to elicit maturation of interleukin-1 beta (IL-1β) via Caspase-1 activation, facilitating photoreceptor cell inflammation damage in PFOS exposure. In addition, we also made a novel finding that Caspase-3 activation was increased via Caspase-8 activation and directly intensified cell death. Our results show the important role of Caspase-8 activation in PFOS induced eye development defects and highlight Caspase-8 mediated activation of the NLRP3 inflammation triggers activation of Caspase-1 and promote the maturation of IL-1β in retinal inflammatory injury.

Genotoxicity and cytotoxicity assessment of 'forever chemicals' in zebrafish (Danio rerio)

Per- and polyfluoroalkyl substances (PFAS) comprise many chemicals with strong carbon-carbon and carbon-fluorine bonds and have extensive industrial applications in manufacturing several consumer products. The solid covalent bonding makes them more persistent in the environment and stays away from all types of degradation, naming them 'forever chemicals.' Zebrafish (Danio rerio) was used to evaluate the genotoxic and cytotoxic effects of legacy PFAS, Perfluorooctane sulfonate (PFOS), and its alternatives, such as Perfluoro-2-methyl-3-oxahexanoic acid ammonium (GenX) and 7H-Perfluoro-3,6-dioxa-4-methyl-octane-1-sulfonic acid (Nafion by-product 2 [NBP2]) upon single and combined exposure at an environmental concentration of 10 µg/L for 48-h. Erythrocyte micronucleus cytome assay (EMNCA) revealed an increased frequency of micronuclei (MN) in fish erythrocytes with a significant increase in NBP2-treated fish. The order of genotoxicity noticed was NBP2 > PFOS > Mixture > GenX in D. rerio. Fish exposed to PFOS and its alternatives in single and combined experiments did not cause any significant difference in nuclear abnormalities. However, PFOS and combined exposure positively inhibit cytokinesis, resulting in an 8.16 and 7.44-fold-change increase of binucleated cells. Besides, statistically, increased levels of reactive oxygen species (ROS) and malondialdehyde (MDA) content indicate oxidative stress in D. rerio. In addition, 'forever chemicals' resulted in cytotoxicity, as evident through changes in nucleus width to the erythrocyte length in NBP2 and mixture exposure groups. The findings revealed that PFAS alternative NBP2 is more toxic than PFOS in inducing DNA damage and cytotoxicity. In addition, all three tested 'forever chemicals' induced ROS and lipid peroxidation after individual and combined exposure. The present work is the first to concern the genotoxicity and cytotoxicity of 'forever chemicals' in the aquatic vertebrate D. rerio.

PFOS Exposure Promotes Hepatotoxicity in Quails by Exacerbating Oxidative Stress and Inflammation-Induced Apoptosis through Activating TLR4/MyD88/NF-κb Signaling

PFOS is a ubiquitous pollutant garnering considerable attention due to its deleterious effects on both human and animal health. Given the poultry industry's intimate link with human health, investigating PFOS's impact on quails is crucial. PFOS readily accumulates in the liver, causing hepatotoxicity, yet its molecular mechanisms remain elusive. In our study, we fed quail diets contaminated with varying PFOS concentrations (12.5, 25, and 50 mg/kg) and observed dose-dependent liver damage in quails. The results show that PFOS damages mitochondrial structure, increases ROS levels, and downregulates antioxidants to promote oxidative stress damage in hepatocytes. PFOS also upregulated pro-inflammatory molecules (TNF-α, IL-1β, and IL-6) while downregulating the anti-inflammatory factor IL-10, activating the TLR4//MyD88/NF-κB signaling pathway, thereby potentiating liver inflammation. Then, oxidative stress and inflammation by PFOS induce apoptosis in quail hepatocytes through the mitochondrial pathway, with severity closely related to hepatotoxicity. In conclusion, PFOS induces mitochondrial apoptosis by exacerbating oxidative stress and inflammation by activating the TLR4/MyD88/NF-κB signaling pathway, ultimately leading to hepatotoxicity in quails.

A comparative review of the toxicity mechanisms of perfluorohexanoic acid (PFHxA) and perfluorohexanesulphonic acid (PFHxS) in fish

Industrial and consumer goods contain diverse perfluoroalkyl substances (PFAS). These substances, like perfluorohexanoic acid (PFHxA) and perfluorohexanesulphonic acid (PFHxS), are under increased scrutiny due to their potential toxicity to aquatic organisms. However, our understanding of their biological impacts and mechanisms of action remains limited. The objectives of this review were to compare data for levels of PFHxA and PFHxS in aquatic environments and fish tissues, as well as toxicity mechanisms related to morphological, endocrine, metabolic, and behavioral endpoints. A computational assessment was also performed to identify putative mechanisms of toxicity and to characterize exposure biomarkers. Studies have shown that both PFHxA and PFHxS residues are present in diverse marine and freshwater fish tissues, suggesting the importance of monitoring these PFAS in aquatic organisms. In fish tissues, these chemicals have been reported to be as high as 37.5 ng/g for PFHxA and 1290 ng/g for PFHxS, but their persistence in aquatic environments and degradation in tissues requires further study. In terms of mechanisms of toxicity, both oxidative stress and endocrine disruption have been reported. Based on evidence for endocrine disruption, we modeled interactions of estrogen and androgen receptors of several fish species with PFHxA and PFHxS. Molecular docking revealed that PFHxS has a stronger affinity for interacting with the estrogen and androgen receptors of fish compared to PFHxA and that estrogen and androgen receptors of fathead minnow, zebrafish, Atlantic salmon, and largemouth bass show comparable binding affinities for each chemical except for salmon Esr2b, which was predicted to have lower affinity for PFHxA relative to Esr2a. While mechanistic data are lacking in fish in general for these chemicals, a computational approach revealed that PFHxA can perturb the endocrine system, nervous system, and is linked to changes in kidney and liver weight. Proteins associated with PFHxA and PFHxS exposures in fish include those related to lipid and glucose regulation, reproductive proteins like KISS metastasis suppressor, and proteins associated with the immune system (specifically RAG1, RAG2), all of which are potential biomarkers of exposure. Taken together, we synthesize current knowledge regarding the environmental fate and ecotoxicology of PFHxA/PFHxS in fish species.

Combined Effects of Fluoride and Dietary Seleno-L-Methionine at Environmentally Relevant Concentrations on Female Zebrafish (Danio rerio) Liver: Histopathological Damages, Oxidative Stress and Inflammation

Fluoride, a global environmental pollutant, is ubiquitous in aquatic environments and coexists with selenium, which can cause complex effects on exposed organisms. However, data on the interaction of fluoride and selenium remain scarce. In this study, female zebrafish (Danio rerio) were exposed to fluoride (80 mg/L sodium fluoride) and/or dietary selenomethionine (Se-Met) for 30, 60 and 90 days, the effects on the liver of zebrafish were investigated. The results indicated that an increase in fluoride burden, inhibited growth and impaired liver morphology were recorded after fluoride exposure. Furthermore, fluoride alone caused oxidative stress and inflammation in the liver, as reflected by the increase in ROS and MDA contents, the reduction of anti-oxidative enzymes, the altered immune related enzymes (ACP, AKP, LZM and MPO) and the expression of IL-6, IL-1β, TNF-α, IL-10 and TGF-β. In contrast, co-exposure to fluoride and Se-Met decreased fluoride burden and restored growth. Furthermore, dietary Se-Met alleviated oxidative stress, inflammation and impaired morphology in liver trigger by fluoride. However, dietary Se-Met alone increased the activities of SOD and CAT. These results demonstrate that the protective effect of dietary Se-Met against chronic fluoride toxicity at a certain level.

A review of cumulative toxic effects of environmental endocrine disruptors on the zebrafish immune system: Characterization methods, toxic effects and mechanisms

Environmental endocrine disrupting chemicals (EDCs), are a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Currently, in addition to neurological, endocrine, developmental and reproductive toxicity, ecotoxicology studies on immunotoxicity are receiving increasing attention. In this review, the composition of immune system of zebrafish, the common indicators of immunotoxicity, the immunotoxicity of EDCs and their molecular mechanism were summarized. We reviewed the immunotoxicity of EDCs on zebrafish mainly in terms of immune organs, immunocytes, immune molecules and immune functions, meanwhile, the possible molecular mechanisms driving these effects were elucidated in terms of endocrine disruption, dysregulation of signaling pathways, and oxidative damage. Hopefully, this review will provide a reference for further investigation of the immunotoxicity of EDCs.

Hepatotoxic response of perfluorooctane sulfonamide (PFOSA) in early life stage zebrafish (Danio rerio) is greater than perfluorooctane sulfonate (PFOS)

Perfluorooctane sulfonamide (PFOSA), a typical perfluorooctane sulfonate precursor (PreFOS), has been detected in the aquatic environment globally. However, the effects of PFOSA at levels measured in the environment have not been well characterized in aquatic organisms. In this study, we evaluated the transcriptional, biochemical, histopathological, and morphological effects of PFOSA to characterize the underlying mechanisms of toxicity by using a universal model in aquatic ecotoxicology, zebrafish (Danio rerio). Transcriptional changes in PFOSA-exposed zebrafish predicted hepatic fibrosis and associated immune function. Subsequent, sublethal impacts were observed, which included significant alterations in liver-specific protein levels, increased immune cell numbers, and liver pathological structural damage. In addition, we compared the effects caused by PFOSA and perfluorooctane sulfonate (PFOS) at the same exposure concentration and found a greater hepatotoxic effect of PFOSA relative to PFOS, indicating that the adverse impacts of PFOSA may be more severe. This was the first study to comparatively explore the hepatotoxic response of PFOSA and PFOS in aquatic organisms, which can be used for ecological risk assessments of PreFOS compounds.

Establishing Chronic Toxicity Effect Levels for Zebrafish (Danio rerio) Exposed to Perfluorooctane Sulfonate

Zebrafish (Danio rerio) are among the aquatic species most sensitive to perfluorooctane sulfonate (PFOS). Environmental regulatory agencies and researchers use effect benchmarks from laboratory zebrafish PFOS toxicity studies in PFOS-spiked water to calculate PFOS aquatic life criteria. Threshold values as low as 0.7 µg/L (identified in an early, limited scope study) have been used in criteria derivation and site-specific aquatic ecological risk assessments. The present study reviews PFOS effects benchmarks for lethality, growth, and reproduction endpoints from more than 20 zebrafish toxicity studies, including a recent multigenerational study conducted by the United States Army Corps of Engineers Engineer Research & Development Center. Our review of 12 key studies examining long-term, chronic exposures (including multigenerational exposures of 300 days or more) indicated that 0.7 µg/L should not be used as a conservative screening threshold given that effects could not be repeated at this concentration by the recent enhanced multigenerational study. Based on this finding and multiple chronic sublethal studies on PFOS in zebrafish, chronic effects on lethality, growth, and reproduction occur at concentrations two orders of magnitude higher than 0.7 µg/L. Overall, the present review indicates a no-effect screening level of 31 µg/L and a low-effect screening level of 96 µg/L should be used to develop PFOS aquatic life criteria and to inform site-specific ecological risk assessments that are charged with evaluating risks to freshwater fish. Environ Toxicol Chem 2024;43:7-18. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

A study on the effectiveness of sodium selenite in treating cadmium and perfluoro octane sulfonic (PFOS) poisoned zebrafish (Danio rerio)

Perfluoro octane sulfonate (PFOS) and cadmium (Cd) are toxic elements in the environment. As a micronutrient trace element, selenium (Se) can mitigate the adverse effects induced by PFOS and Cd. However, few studies have examined the correlation between Se, PFOS and Cd in fish. The present study focused on the antagonistic effects of Se on PFOS+Cd-induced accumulation in the liver of zebrafish. The fish was exposed to PFOS (0.08mg/L), Cd (1mg/L), PFOS+ Cd (0.08 mg/L PFOS+1 mg/L Cd), L-Se (0.07mg/L Sodium selenite +0.08mg/L PFOS+1mg/L Cd), M-Se (0.35mg/L Sodium selenite + 0.08mg/L PFOS+ 1 mg/L Cd), H-Se (1.75 mg/L Sodium selenite + 0.08 mg/L PFOS+ 1mg/L Cd) for 14d. The addition of selenium to fish exposed to PFOS and Cd has been found to have significant positive effects. Specifically, selenium treatments can alleviate the adverse effects of PFOS and Cd on fish growth, with a 23.10% improvement observed with the addition of T6 compared to T4. In addition, selenium can alleviate the negative effects of PFOS and Cd on antioxidant enzymes in zebrafish liver, thus reducing the liver toxicity caused by PFOS and Cd. Overall, the supplementation of selenium can reduce the health risks to fish and mitigate the injuries caused by PFOS and Cd in zebrafish.

Impact of endocrine disruptors on peripheral blood mononuclear cells in vitro: role of gender

Humans can be exposed to endocrine disruptors (EDs) in numerous ways. EDs can interfere with endogenous hormones at different levels, resulting in numerous adverse human health outcomes, including immunotoxicity. In this regard, this study aimed to investigate in vitro the possible effects of EDs on immune cells and possible gender differences. Peripheral blood mononuclear cells from healthy humans, both males and females, were exposed to 6 different EDs, namely atrazine (herbicide), cypermethrin (insecticide), diethyl phthalate (plasticizer), 17α-ethynylestradiol (contraceptive drug), perfluorooctanesulfonic acid (persistent organic pollutant), and vinclozolin (fungicide). We evaluated the effect of EDs on RACK1 (receptor for activated C kinase 1) expression, considering it as a bridge between the endocrine and the immune system, and putatively used as screening tool of immunotoxic effects of EDs. The exposure to EDs resulted at different extent in alteration in RACK1 expression, pro-inflammatory activity, natural killer lytic ability, and lymphocyte differentiation, with sex-related differences. In particular, diethyl phthalate and perfluorooctanesulfonic acid resulted the most active EDs tested, with gender differences in terms of effects and magnitude. The results from our study evidenced the ability of EDs to directly affect immune cells.

Combined Effects of Fluoride and Dietary Seleno-L-methionine at Environmentally Relevant Concentrations on Female Zebrafish (Danio rerio) Liver: Histopathological Damages, Oxidative Stress and Inflammation

Fluoride, a global environmental pollutant, is ubiquitous in aquatic environments and coexists with selenium, which can cause complex effects on exposed organisms. However, data on the interaction of fluoride and selenium remain scarce. In this study, female zebrafish (Danio rerio) were exposed to fluoride (80 mg/L sodium fluoride) and/or dietary selenomethionine for 30, 60 and 90 days, the effects on the liver of zebrafish were investigated. The results indicated that an increase in fluoride burden, inhibited growth and impaired liver morphology were recorded after fluoride exposure. Furthermore, fluoride alone caused oxidative stress and inflammation in the liver, as reflected by the increase in ROS and MDA contents, the reduction of anti-oxidative enzymes, the altered immune related enzymes (ACP, AKP, LZM and MPO) and the expression of IL-6, IL-1β, TNF-α, IL-10 and TGF-β. In contrast, co-exposure to fluoride and Se-Met decreased fluoride burden and restored growth. Furthermore, dietary Se-Met alleviated oxidative stress, inflammation and impaired morphology in liver trigger by fluoride. However, dietary Se-Met alone increased the activities of SOD and CAT. These results demonstrate that the protective effect of dietary Se-Met against chronic fluoride toxicity at a certain level.

Cannabidiol alleviates perfluorooctane sulfonate-induced macrophage extracellular trap mediate inflammation and fibrosis in mice liver

As a new type of persistent organic pollutant, perfluorooctane sulphonate (PFOS) has received extensive attention worldwide. Cannabidiol (CBD) is a non-psychoactive natural cannabinoid extract that has been proved to have antioxidation, regulation of inflammation and other functions. However, the effects of PFOS on liver injury and whether CBD can alleviate PFOS-induced liver injury are still unclear. Therefore, in this study, we used CBD (10 mg/kg) and/or PFOS (5 mg/kg) to intraperitoneally inject mice for 30 days. We found that PFOS exposure led to inflammatory infiltration in the liver of mice, increased the formation of macrophage extracellular trap (MET), and promoted fibrosis. In vitro, we established a coculture system of RAW264.7, AML12 and LX-2 cells, and treated them with CBD (10 μM) and/or PFOS (200 μM). The results showed that PFOS could also induce the expression of MET, inflammation and fibrosis marker genes in vitro. Coiled-coil domain containing protein 25 (CCD25), as a MET-DNA sensor, was used to investigate its ability to regulate inflammation and fibrosis, we knocked down CCDC25 and its downstream proteins (integrin-linked kinase, ILK) by siRNA technology, and used QNZ to inhibit NF-κB pathway. The results showed that the knockdown of CCDC25 and ILK and the inhibition of NF-κB pathway could inhibit MET-induced inflammation and fibrosis marker gene expression. In summary, we found that PFOS-induced MET can promote inflammation and fibrosis through the CCDC25-ILK-NF-κB signaling axis, while the treatment of CBD showed a protective effect, and it is proved by Macromolecular docking that this protective effect is achieved by combining CBD with peptidylarginine deiminase 4 (PAD4) to alleviate the release of MET. Therefore, regulating the formation of MET and the CCDC25-ILK-NF-κB signaling axis is an innovative treatment option that can effectively reduce hepatotoxicity. Our study reveals the mechanism of PFOS-induced hepatotoxicity and provides promising insights into the protective role of CBD in this process.

Transcriptional investigation of the toxic mechanisms of perfluorooctane sulfonate in rats based on an RNA-Seq approach

Perfluorooctane sulfonate (PFOS) was widely used in industrial applications before it was listed as a persistent organic pollutant by the Conference of the Parties in the Stockholm Convention in 2009. Although the potential toxicity of PFOS has been studied, its toxic mechanisms remain largely undefined. Here, we investigated novel hub genes and pathways affected by PFOS to gain new conceptions of the toxic mechanisms of PFOS. Reduced body weight gain and abnormal ultra-structures in the liver and kidney tissues were spotted in PFOS-exposed rats, indicating successful establishment of the PFOS-exposed rat model. The transcriptomic alterations of blood samples upon PFOS exposure were analysed using RNA-Seq. GO analysis indicates that the differentially expressed gene-enriched GO terms are related to metabolism, cellular processes, and biological regulation. Kyoto encyclopaedia of gene and genomes (KEGG) and gene set enrichment analysis (GSEA) were conducted to identify six key pathways: spliceosome, B cell receptor signalling pathway, acute myeloid leukaemia, protein processing in the endoplasmic reticulum, NF-kappa B signalling pathway, and Fc gamma R-mediated phagocytosis. The top 10 hub genes were screened from a protein-protein interaction network and verified via quantitative real-time polymerase chain reaction. The overall pathway network and hub genes may provide new insights into the toxic mechanisms of PFOS exposure states.

Immunotoxicity and Transcriptome Analyses of Zebrafish (Danio rerio) Embryos Exposed to 6:2 FTSA

As a new alternative to perfluorooctane sulfonic acid (PFOS), 6:2 fluorotelomer sulfonic acid (6:2 FTSA) has been widely produced and used in recent years, and its concentration and frequency of detection in the aquatic environment and aquatic organisms are increasing. However, studies of its toxicity in aquatic biological systems are alarmingly scarce, and the relevant toxicological information needs to be improved. In this study, we investigated AB wild-type zebrafish (Danio rerio) embryos subjected to acute 6:2 FTSA exposure for immunotoxicity using immunoassays and transcriptomics. Immune indexes showed significant decreases in SOD and LZM activities, but no significant change in NO content. Other indexes (TNOS, iNOS, ACP, AKP activities, and MDA, IL-1β, TNF-α, NF-κB, TLR4 content) all showed significant increases. These results indicated that 6:2 FTSA induced oxidative stress and inflammatory responses in zebrafish embryos and exhibited immunotoxicity. Consistently, transcriptomics showed that genes involved in the MAPK, TLR and NOD-like receptor signaling pathways (hsp70, hsp701, stat1b, irf3, cxcl8b, map3k8, il1b, tnfa and nfkb) were significantly upregulated after 6:2 FTSA exposure, suggesting that 6:2 FTSA might induce immunotoxicity in zebrafish embryos through the TLR/NOD-MAPK pathway. The results of this study indicate that the safety of 6:2 FTSA should be examined further.

A systematic evidence map of chronic inflammation and immunosuppression related to per- and polyfluoroalkyl substance (PFAS) exposure

BACKGROUND

The ability to induce chronic inflammation and immunosuppression are two key characteristics of carcinogens and important forms of immunotoxicity. The National Toxicology Program (NTP) evaluated the immunotoxicity of two per- and polyfluoroalkyl substances (PFASs), PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate), in 2016. However, the potential pro-inflammatory and immunosuppressive effects of other PFASs remain largely uncharacterized.

METHODS

We developed an expanded set of search terms pertaining to the chronic inflammatory and immunosuppressive effects of PFASs based on those of the International Agency for Research on Cancer (IARC) and NTP. To confirm searching effectiveness and scope, we compared our search term results with those of IARC and NTP for both PFASs and two other known carcinogens, chromium (VI) and benzene. Systematic evidence maps (SEMs) were also produced using Tableau to visualize the distribution of study numbers and types reporting immunotoxic effects and specific biomarkers elicited by PFAS exposures.

RESULTS

In total, 1155 PFAS studies were retrieved, of which 321 qualified for inclusion in our dataset. Using our search terms, we identified a greater number of relevant studies than those obtained using IARC and NTP's search terms. From the SEM findings, increased cytokine production strengthened an association between PFAS exposure and chronic inflammation, and decreased B-cell activation and altered levels of T-cell subtypes and immunoglobulins confirmed PFAS-induced immunosuppression.

CONCLUSION

Our SEM findings confirm that several PFASs commonly found in both in the environment, including those that are lesser-known, may induce immunosuppression and chronic inflammation, two key characteristics of carcinogens. This approach, including development of search terms, study screening process, data coding, and evidence mapping visualizations, can be applied to other key characteristics of chemical carcinogens.

Consideration of pathways for immunotoxicity of per- and polyfluoroalkyl substances (PFAS)

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are of public health concern, because of their ubiquitous and extremely persistent occurrence, and depending on their structure, their bio-accumulative, mobile and toxic properties. Human health effects associated with exposure to PFAS include adverse effects on the immune system. In 2020, EFSA (the European Food Safety Authority) defined adverse effects on the immune system as the most critical effect for human health risk assessment, based on reduced antibody responses to childhood vaccines and similar effects observed in experimental animal studies. Likewise, the U.S. EPA (Environmental Protection Agency) considers PFAS-induced immunotoxicity, especially in children, as the critical effect for risk assessment. However, the mechanisms by which antibody concentrations are impacted are not completely understood. Furthermore, other targets of the immune system functions have been reported in the literature.

OBJECTIVE

The aim of this review is to explore PFAS-associated immune-related effects. This includes, relevant mechanisms that may underlie the observed effects on the immune system, immunosuppression as well as immunoenhancement, such as i) modulation of cell signalling and nuclear receptors, such as NF-κB and PPARs; ii) alteration of calcium signalling and homoeostasis in immune cells; iii) modulation of immune cell populations; iv) oxidative stress and v) impact on fatty acid metabolism & secondary effects on the immune system.

METHODS

A literature research was conducted using three databases (Web of Science, PubMed, and Scopus), which were searched in July 2021 for relevant studies published in the time frame from 2018 to 2021. In total, 487 publications were identified as potentially eligible and following expert-based judgement, articles relevant for mechanisms of PFAS induced immunotoxicity are discussed.

CONCLUSIONS

Taken together, we show that there is substantial evidence from both in vitro and in vivo experimental as well as epidemiological studies, supporting that various PFAS, not only PFOA and PFOS, affect multiple aspects of the immune system. Timing of exposure is critical, because the developing immune system is especially vulnerable to toxic insults, resulting in a higher risk of particularly adverse immune effects but also other organs later in life.

Alleviating effects of essential oil from Artemisia vulgaris on enteritis in zebrafish via modulating oxidative stress and inflammatory response

Artemisia vulgaris (A. vulgaris) is a traditional Chinese medicine widely distributed in China and contains many bioactive compounds with pharmacological effects. However, the anti-inflammatory effects and mechanism of essential oil from A. vulgaris on enteritis in fish are still unclear. In this study, in order to elucidate the underlying mechanism of essential oil from A. vulgaris on zebrafish enteritis, zebrafish were used for establishing animal models to observe the histopathological changes of intestines, determine the activities of immune-related enzymes and oxidative stress indicators, and the mRNA expression of genes in MyD88/TRAF6/NF-KB signaling pathways. The results showed that different doses of A. vulgaris essential oil could effectively alleviate zebrafish enteritis in a dose- and time-dependent manner by improving the intestinal histopathological damage, decreasing the intestinal oxidative stress, repairing the intestinal immune ability, changing the expression levels of IL-1β, IL-10 and genes in MyD88/TRAF6/NF-κB pathway. In addition, co-treatment with oxazolone and MyD88 inhibitor could alleviate the morphological damage, the induction of oxidative stress, and the levels of immune-related enzymes and the mRNA expression of genes in MyD88/TRAF6/NF-κB signaling pathway. Moreover, essential oil from A. vulgaris had more significantly therapeutic effects on enteritis of male zebrafish than that of female zebrafish. This result will clarify the therapeutic effect and anti-inflammatory mechanism of essential oil from A. vulgaris on zebrafish enteritis, and provide a theoretical basis for further research on the rationality of A. vulgaris to replace feed antibiotics.

Factors Modulating COVID-19: A Mechanistic Understanding Based on the Adverse Outcome Pathway Framework

Addressing factors modulating COVID-19 is crucial since abundant clinical evidence shows that outcomes are markedly heterogeneous between patients. This requires identifying the factors and understanding how they mechanistically influence COVID-19. Here, we describe how eleven selected factors (age, sex, genetic factors, lipid disorders, heart failure, gut dysbiosis, diet, vitamin D deficiency, air pollution and exposure to chemicals) influence COVID-19 by applying the Adverse Outcome Pathway (AOP), which is well-established in regulatory toxicology. This framework aims to model the sequence of events leading to an adverse health outcome. Several linear AOPs depicting pathways from the binding of the virus to ACE2 up to clinical outcomes observed in COVID-19 have been developed and integrated into a network offering a unique overview of the mechanisms underlying the disease. As SARS-CoV-2 infectibility and ACE2 activity are the major starting points and inflammatory response is central in the development of COVID-19, we evaluated how those eleven intrinsic and extrinsic factors modulate those processes impacting clinical outcomes. Applying this AOP-aligned approach enables the identification of current knowledge gaps orientating for further research and allows to propose biomarkers to identify of high-risk patients. This approach also facilitates expertise synergy from different disciplines to address public health issues.

Graphene oxide chronic exposure enhanced perfluorooctane sulfonate mediated toxicity through oxidative stress generation in freshwater clam Corbicula fluminea

Graphene oxide (GO), a frequently utilized graphene family nanomaterial, is inevitably released into the aquatic environment and interacts with organic pollutants, including perfluorooctane sulfonate (PFOS), a well-known persistent organic pollutant. To determine the adverse effects of GO chronic exposure on PFOS bioaccumulation and toxicity, adult freshwater bivalves, namely Asian clams (Corbicula fluminea) were treated for 28 days with PFOS (500 ng/L) and different concentrations of GO (0.2, 1, 5 mg/L) as PFOS single and GO single exposure groups, as well as PFOS-GO mixture exposure groups. Our results demonstrated that the bioaccumulation of PFOS was significantly enhanced by co-exposure in gills and visceral masses, which was 1.64-2.91 times higher in gills than in visceral masses. Both single, as well as co-exposure, caused a significant reduction in clams' siphoning behavior, compared to the controls. Further, the co-exposure significantly increased the production of reactive oxygen species (ROS), exacerbating malondialdehyde (MDA) content, enhancing superoxide dismutase (SOD) and catalase (CAT), while decreasing glutathione reductase (GR) and glutathione S-transferase (GST) enzymatic activities in clam tissues. And co-exposure significantly altered the expressions of se-gpx, sod, cyp30, hsp40, and hsp22 genes (associated with oxidative stress and xenobiotic metabolism) both in gills and visceral masses. Moreover, co-exposure caused significant histopathological changes such as cilia degradation in the gills, expansion of tubule lumens in digestive glands, and oocyte shrinkage in gonads. Finally, the enhanced integrated biomarker response (EIBR) index revealed that co-exposure to 500 ng/L PFOS + 1 mg/L/5 mg/L GO was the most stressful circumstance. Overall, our findings suggested that the presence of GO increased PFOS bioaccumulation in tissues, inducing multifaceted negative implications at molecular and behavioral levels through oxidative stress generation in Asian clams.

Adverse Effects of Perfluorooctane Sulfonate on the Liver and Relevant Mechanisms

Perfluorooctane sulfonate (PFOS) is a persistent, widely present organic pollutant. PFOS can enter the human body through drinking water, ingestion of food, contact with utensils containing PFOS, and occupational exposure to PFOS, and can have adverse effects on human health. Increasing research shows that the liver is the major target of PFOS, and that PFOS can damage liver tissue and disrupt its function; however, the exact mechanisms remain unclear. In this study, we reviewed the adverse effects of PFOS on liver tissue and cells, as well as on liver function, to provide a reference for subsequent studies related to the toxicity of PFOS and liver injury caused by PFOS.

Perfluorooctane sulfonate aggravates CCl4-induced hepatic fibrosis via HMGB1/TLR4/Smad signaling

Perfluorooctane sulfonate (PFOS) is a widespread environmental pollutant and may cause a variety of adverse health effects. The hepatotoxicity of PFOS has attracted particular attention, given the fact that the liver has one of the highest PFOS accumulations among human tissues. In this study, we revealed that subchronic PFOS exposure may exacerbate carbon tetrachloride (CCl₄ )-induced liver fibrosis in animal models. Administration with 1 mg/kg PFOS every other day for 56 days dramatically enhanced CCl₄ -mediated liver injury and hepatic stellate cell (HSC) activation. Furthermore, PFOS exposure may promote the activation of high-mobility group box 1 (HMGB1)/toll-like receptor 4 (TLR4) signaling pathway through inducing the secretion of HMGB1 from hepatocytes. PFOS exposure induced the translocation of HMGB1 from the nucleus into the cytoplasm of hepatocytes and cultured BRL-3A cells at a starting concentration of 50 μM. This process is accompanied with concurrent flux of calcium, suggesting a link between calcium signaling and HMGB1 release following PFOS exposure. Finally, we showed that PFOS-exposed conditional medium (PFOS-CM) of hepatocytes may induce the translocation of Smad2/3 in HSCs in a TLR4-dependent manner. Taken together, subchronic PFOS exposure might play a pro-fibrotic role via a HMGB1/TLR4-dependent Smad signaling in HSCs. Our findings for the first time uncovered an involvement of PFOS exposure in liver fibrosis via HMGB1/TLR4/Smad signaling.

Comparative chronic toxicities of PFOS and its novel alternatives on the immune system associated with intestinal microbiota dysbiosis in adult zebrafish

6:2 Chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) are widely used as perfluorooctane sulfonate (PFOS) alternatives in the Chinese market. Here, adult zebrafish were chronically exposed to 1 μM PFOS, F-53B, and OBS for 21 days to investigate the comparative immunotoxicity of these three per- and polyfluoroalkyl substances (PFAS). PFOS induced more severe oxidative stress in the liver than F-53B and OBS, and these three PFAS induced similar anti-inflammatory effects by repressing the expression of pro-inflammatory cytokines. The intestinal microbiota analysis showed that the relative abundance of Plesiomonas, Aeromonas, Cetobacterium, Shewanella, and Vibrio changed with the same trend in the three PFAS treatment groups. Furthermore, the PFAS increased the expression of hepcidin, muc, the immune-related genes mpo and saa, and decreased the expression of the tight junction-related gene occ in the intestine; moreover, villus height of the intestine was reduced after PFAS exposure, which indicated the functional disruption of the intestine. In particular, the significant correlation between the changed intestinal microbiota and liver and intestinal indicators also suggested the interaction between the immune system and intestinal microbiota. Taken together, our results indicate that exposure to PFOS and its alternatives F-53B and OBS can induce hepatic immunotoxicity associated with intestinal microbiota dysbiosis in adult zebrafish.

Immunotoxicity mechanisms of perfluorinated compounds PFOA and PFOS

Perfluorinated and polyfluorinated compounds (PFASs) are a class of synthetic chemical substances that are widely used in human production and life, such as fire-fighting foams, textiles and clothing, surfactants, and surface protective agents. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are the most abundant and common perfluorinated compounds in biota and humans. Currently, PFOA and PFOS have been listed in the Stockholm Convention on Persistent Organic Pollutants, and their production has been halted in many countries. However, because the high-energy carbon-fluorine bond can make it resistant to hydrolysis, photolysis, microbial degradation, and vertebrate metabolism, PFOA and PFOS show environmental persistence and bioaccumulation and hence, are of great concern to humans and wildlife. PFOA and PFOS have toxic effects on the immune system of the body. This article reviewed the effects of PFOA and PFOS on immune organs such as the spleen, bone marrow, and thymus of mice and zebrafish, and the effects on non-specific immune functions such as the skin barrier, intestinal mucosal barrier, and humoral immunity. We also reviewed the influence of specific immune functions based on cellular immunity, and further summarized the possible immune toxicity mechanisms such as AIM2 inflammasome activation, gene dysregulation, and signal pathway disorders caused by PFOA and PFOS. The aim of this review was to provide a reference for further understanding of the immunotoxicity and the responsible mechanism of PFOA and PFOS.

Polystyrene nano/microplastics induce microbiota dysbiosis, oxidative damage, and innate immune disruption in zebrafish

The toxicity of polystyrene nano/microplastics with diameter sizes of 50um and 100 nm and concentrations of 100 and 1000 μg/mL on gut microbiota, antioxidant activity and innate immune response in zebrafish was investigated. After exposure to polystyrene plastics particle, the pathological morphological changes of intestine and gills were observed, and the injury severity was related to the concentration and particle size of plastics. Significant changes in the richness and diversity of gut microbiota were observed after polystyrene plastics-exposed in zebrafish. The plastics-treated groups exhibited more substantial oxidative stress than the control group. In addition, the mRNA expression level of most pro- and anti-inflammatory factors, including IL-8, NF-κb, and IL-10, increased while the mRNA expression of TNF-α, a pro-inflammatory factor, decreased. Our results suggest that polystyrene nano/microplastics may represent a potential threat to the gut microbiota, oxidative status, and innate immunity. These results indicated that polystyrene nano/microplastics exerted size and concentration-dependent toxicity on zebrafish. The findings provide new evidence for the toxicity of polystyrene plastics on zebrafish.

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.

New compounds, old problems. The case of C6O4 - a substitute of PFOA - and its effects to the clam Ruditapes philippinarum

C6O4 (difluoro{[2,2,4,5-tetrafluoro-5-(trifluoromethoxy)-1,3-dioxolan-4-yl]oxy}acetic acid) is a new surfactant and emulsifier used as a substitute of perfluorooctanoic acid (PFOA). Recently, C6O4 has been detected in aquatic environments, but, at present, no information concerning the effects of C6O4 on aquatic species, such as bivalves, are available in the literature. Therefore, in this study we evaluated for the first time the effects of C6O4 (0.1 and 1 µg/L) and PFOA (1 µg/L) to the clam Ruditapes philippinarum. Short-term (7 days) and long-term (21 days) exposures of clams to the two compounds were carried out and numerous biomarkers were measured in haemocytes/haemolymph, as well as in gills and digestive gland. The MANOVA analysis demonstrated statistically significant effects of the independent variables "treatment", "time" and "treatment-time interaction" on the whole dataset of biomarker responses. The two-way ANOVA analysis performed for each biomarker response indicated that the two compounds affected most of the cellular and tissue parameters measured. Despite preliminary, the results obtained suggested that C6O4 - similarly to PFOA - can affect both cellular and biochemical parameters of clams.

Toxicity of gabapentin-lactam on the early developmental stage of zebrafish (Danio rerio)

Gabapentin-lactam (GBP-L) is a transformation product (TP) of gabapentin (GBP), a widely used anti-epileptic pharmaceutical. Due to its high persistence, GBP-L has been frequently detected in the surface water. However, the effects of GBP-L on aquatic organisms have not been thoroughly investigated. In the present study, zebrafish (Danio rerio) embryos as a model organism were used to study the impacts of GBP-L in terms of embryos LC₅₀, spontaneous movement at 24 hpf (hours post fertilization), heartbeat rates at 48 hpf, and body length at 72 hpf, with the concentrations of GBP-L down to 0.01 μg/L, covering its environmental concentrations. Various biomarkers from nervous, antioxidant and immune systems of zebrafish larvae were analyzed, including acetylcholinesterase, acetylcholine, dopamine, gamma-aminobutyric acid, superoxide dismutase, catalase, glutathione S-transferase, C reactive protein, and lysozyme, to assess its toxicity on these systems. RT-qPCR was then used to further verify the results and explain the toxicological mechanism at the gene level. The results demonstrated that GBP-L is much more toxic than its parent compound, and could lead to adverse impacts on the aquatic organisms even at every low concentrations.

Immunotoxicity of F53B, an alternative to PFOS, on zebrafish (Danio rerio) at different early life stages

As an alternative to perfluorooctane sulfonate (PFOS), 6:2 chlorinated polyfluorinated ether sulfonate (F53B) has emerged in the Chinese market in recent years and has been frequently detected in the aquatic environment, but its ecological risk assessment is limited. In this study, zebrafish embryos and larvae were separately exposed to F53B, and their 96-h LC₅₀ values were estimated to be 15.1 mg/L and 2.4 mg/L, respectively, suggesting that embryos were more resistant to F53B than larvae. The bioconcentration factor in larvae was basically higher than that of embryos, and the body growth of larvae was significantly affected by F53B rather than embryos, indicating that F53B may cause more severe toxicity to larvae. In addition to the excessive production of ROS and NO, the expression of many immune-related genes was increased in both embryos and larvae, but the number of dysregulated genes in larvae was more than that in embryos. Finally, the results of Point of Departure (PoD) indicated that the immunotoxicity of F53B was more sensitive to larvae than embryos at the molecular level. Our findings revealed the ecological risk of F53B by exploring the adverse effects of immunoregulation at different early life stages of zebrafish and indicated that the zebrafish larvae were more sensitive than embryos.

Suspended sediment exacerbates perfluorooctane sulfonate mediated toxicity through reactive oxygen species generation in freshwater clam Corbicula fluminea

Perfluorooctane sulfonate (PFOS) potentially adsorbs on the surface of suspended sediment (SPS), which can develop a toxic "pool" bioavailable to benthic organisms. In this study, the freshwater clam Corbicula fluminea was employed as a zoobenthos model to study the effects of SPS (collected from the Yellow River) on the bioaccumulation and toxicity (from the molecular level to cellular and physiological levels) caused by PFOS exposure. Besides, the enhanced integrated biomarker response (EIBR) system was applied as an index to evaluate the in-depth toxic effects of PFOS and SPS single and co-exposure at various treatment levels. Our results demonstrated that PFOS-SPS co-exposure (at sub-lethal doses of PFOS) significantly increased the bioaccumulation of PFOS, and induced the elevated levels of reactive oxygen species (ROS), the significantly increased activities of superoxide dismutase (SOD) and catalase (CAT) enzymes, the significantly increased content of malondialdehyde (MDA), and the significantly upregulated expression levels of sod, selenium-dependent glutathione peroxidase (se-gpx), heat shock protein 22 (hsp22), heat shock protein 40 (hsp40) and cytochrome P450 30 (cyp30) genes. Further, the co-exposure induced the significantly higher histopathological alterations in the gonads and digestive glands, and even elevated the inhibition of siphoning behavior in clams. In addition, the EIBR index also revealed the highest values for PFOS and SPS co-exposure, compared to the individual SPS or PFOS exposure. The results indicated that at high levels of PFOS exposure (especially at 1000 μg/L), the presence of SPS might increase the generation of ROS by influencing the bioaccumulation of PFOS, which enhanced the toxicity of PFOS to C. fluminea. These results potentially provide basic information for the comprehensive evaluation of the toxic effects of PFOS on benthos in a multi-sediment river ecosystem.

Sesamin attenuates histological alterations, oxidative stress and expressions of immune-related genes in liver of zebrafish (Danio rerio) exposed to fluoride

Sesamin is the main lignan in sesame and is reported to have many benefits and medicinal properties. However, its protective effects against fluoride-induced damage in the liver of zebrafish have not been elucidated. Our previous studies found that fluoride exposure caused damage to the liver of zebrafish. In the study, the effects of sesamin on oxidative stress and immune damage in liver of zebrafish exposed to fluoride were measured. The results indicated that fluoride exposure damaged the microstructures of liver, increased significantly the oxidative stress, decreased remarkably the activities of ACP, AKP, and LZM, and affected obviously the expressions of immune-related genes. Treatment with sesamin remarkably attenuated fluoride-induced liver damage in a dose-dependent manner, indicated by the histopathological observation. Furthermore, sesamin treatment also significantly inhibited the production of ROS and oxidative stress, such as the decrease of lipid peroxidation level and the increase of CAT and SOD activities in liver. Sesamin treatment reversed the activities of immune-related enzymes and the expressions of immune-related genes in liver exposed to fluoride. These findings suggested that sesamin could protect the liver from fluoride-induced immune damage by oxidative stress downstream-mediated changes in reversing the activities of immune-related enzymes and the expressions of immune-related genes. Taken together, sesamin plays an important role in maintaining hepatic health and preventing liver from toxic damage caused by fluoride.

Effects of dietary Cu and Zn on the accumulation, oxidative stress and the expressions of immune-related genes in the livers of Nile tilapia (Oreochromis niloticus)

Excess Cu and Zn can cause many adverse effects in fish. However, few studies have addressed the effects of dietary Cu and Zn on antioxidant physiology and immunity and the underlying mechanisms in fishes. In this study, accumulation of Cu and Zn, effects on the antioxidant enzymes and the transcriptional expressions of immune-related genes were examined in the Oreochromis niloticus fed the Cu and/or Zn enriched duckweed. The results showed that the liver and intestine had the highest accumulation of Cu²⁺ and Zn²⁺ while the muscle had the lowest accumulation of these two metals. The activities of SOD, CAT, GPx and the contents of GSH, GSSG in the liver of all treatment groups were significantly decreased compared to the control group. MDA content was significantly elevated in all treatment groups after feeding for 21 days, implying lipid peroxidation in the liver. In the Cu + Zn group, the activities of SOD, GPx and the GSSG content in the liver were significantly decreased. Compared with the Zn group, the LZM activity in the Cu + Zn group was reversed after feeding for 42 days (P < 0.05). The transcriptional expressions of immune-related genes (TNF-α, INF-γ and IL-1β) in Cu, Zn, Cu + Zn groups were significantly inhibited compared with the control group after treatment for 21 days. Compared with the Cu + Zn group, the level of INF-γ transcripts was significantly reduced in the Cu and Zn group, while the TNF-α expression was elevated after treatment for 42 days. Cu and Zn had synergistic effects on the antioxidant system. Cu has greater effects than Zn on the immunity of O. niloticus. This study demonstrates that dietary Cu and Zn may pose a potential threat to the tilapia populations.

Elevated levels of per- and polyfluoroalkyl substances in Cape Fear River Striped Bass (Morone saxatilis) are associated with biomarkers of altered immune and liver function

Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals of concern that persist in the environment. Environmental monitoring revealed high concentrations of hexafluoropropylene oxide dimer acid (HFPO-DA) and other novel PFAS in the lower Cape Fear River; however, there is limited information on PFAS exposures and effects of this contamination on aquatic biota. Serum concentrations of 23 PFAS in Striped Bass (Morone saxatilis) from the Cape Fear River (n = 58) and a reference population from an aquaculture laboratory on the Pamlico/Tar watershed (n = 29) were quantified using liquid chromatography and high-resolution mass spectrometry, and correlations between PFAS concentrations and health-related serum biomarkers were evaluated. Perfluorooctane sulfonate, the predominant PFAS in Cape Fear River Striped Bass serum, was detectable in every sample with serum concentrations reaching 977 ng/mL. Perfluorononanoic and perfluorodecanoic acid were also detected in all samples, with perfluorohexanesulfonic acid present in >98% of the samples. HFPO-DA (range <0.24-5.85 ng/mL) and Nafion byproduct 2 (range <0.2-1.03 ng/mL) were detected in 48% and 78% of samples, respectively. The mean total PFAS concentration found in domestic Striped Bass raised in well-water under controlled aquaculture conditions was 40 times lower, with HPFO-DA detected in 10% of the samples, and Nafion byproduct 2 was not detected. The elevated PFAS concentrations found in the Cape Fear River Striped Bass were associated with biomarkers of alterations in the liver and immune system.