Maternal transfer of F-53B inhibited neurobehavior in zebrafish offspring larvae and potential mechanisms: Dopaminergic dysfunction, eye development defects and disrupted calcium homeostasis

Diltiazem disrupts Ca2+-homeostasis and exerts immunotoxic effects on a marine bivalve mollusc, the blood clam (Tegillarca granosa)

The prevalence of pharmaceutical residues like diltiazem in environments raises concerns over their potential threat to non-target organisms. While the immune system poses as a potential target, little is known about the immunotoxicity of diltiazem to aquatic species such as bivalve molluscs. In this study, the binding affinity of diltiazem to the calcium channels of several aquatic species was evaluated by molecular docking. Taking blood clam as a representative, the impacts of diltiazem on Ca2+-homeostasis and immune parameters were also assessed. Our results illustrated diltiazem exhibit a high binding affinity to calcium channels of representative aquatic species. Moreover, Ca2+-homeostasis in the haemocytes of blood clam was significantly disrupted by 4-week exposure to diltiazem. Additionally, apart from exhibiting significantly lower survival rates upon pathogenic challenge, diltiazem-exposed blood clams also suffered markedly impaired immune-related hematic parameters and lower levels of immune factors. Furthermore, diltiazem exposure generally altered the expression of key Ca2+-homeostasis and immune-related genes. Collectively, our data suggest that diltiazem at environmentally relevant concentrations could severely undermine the immunity of blood clam by disrupting Ca2+-homeostasis. Given the high binding affinities of diltiazem to calcium channels of diverse aquatic species and the critical role of Ca2+-homeostasis, the far-reaching impacts of diltiazem pollution on non-target aquatic species warrant closer attention and monitoring.

Neurodevelopmental toxicity and mechanism of chlorinated polyfluoroalkyl ether sulfonate alternative F-53B in pubertal male rats

F-53B, a substitute for perfluorooctane sulfonate (PFOS), has attracted considerable concerns due to its frequent detection in environment matrices. However, the potential health risks to mammals, especially neurodevelopmental toxicity, remain unclear. In this study, 3-week-old pubertal male rats were exposed to F-53B at concentrations of 0, 0.15, 1.5, and 15 μg/kg for 3 weeks continuously. Diminished cognitive abilities were observed by morris water maze (MWM) test, F-53B exposure increased the escape latency and decreased the time spent in the target quadrant of rats. Furthermore, F-53B significantly altered neurotransmitter levels in the hippocampus. Molecular docking studies indicated that F-53B might bind to metabotropic glutamate receptor 5 (mGluR5), potentially entering neurons and causing further neurotoxicity. qRT-PCR and western blot analyses were used to assess the expression of genes and proteins related to calcium pathways. Results revealed that F-53B exposure downregulated mRNA expression of ryanodine receptors (RyRs) and the phosphorylation of inositol trisphosphate receptors (IP3Rs), while upregulating sarco/endoplasmic reticulum Ca2+-ATPase2 (SERCA2) levels. F-53B inhibits the IP3/Ca2+ signaling pathway in the rat hippocampus, which may affect ER Ca2+ storage and release functions. Additionally, F-53B reduced the phosphorylation of IP3R, Ca2+/calmodulin-dependent protein kinase II (CaMKII), extracellular signal-regulated kinase 1 and 2 (ERK1/2), and cAMP response element binding protein (CREB), potentially impairing synaptic plasticity and long-term potentiation (LTP), leading to learning and memory deficits. This study reveals that F-53B induced neurodevelopmental toxicity linked to calcium pathway disruption and provides new insight into the potential long-term hazards of F-53B.

Neurodevelopmental effects of exposure to environmentally relevant concentrations of perfluorooctane sulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS) and 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) on larval zebrafish: Multi-omics and neuropathology perspective

Previous studies have shown that perfluorooctane sulfonic acid (PFOS) and its new substitutes perfluorobutanesulfonic acid (PFBS) and 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) were associated with neurological abnormalities. However, many of these were conducted at concentrations higher than environmental levels, thus causing overt toxicity. This study employed multi-omics (transcriptomics and targeted metabolomics), morphological, behavioral and neuropathological methods to assess zebrafish embryos exposed to environmentally relevant concentrations (ERC) (10 and 100 ng/L), aiming to better elucidate the key molecular mechanisms that induce neurotoxic effects at ERC. Early development indicators and behavioral analyses showed that these three substances negatively impacted zebrafish development and inhibited locomotor behavior. Neuropathology and transcriptomics indicated that they disrupted visual phototransduction and lysosomal pathways, leading to the destruction of Nissl bodies, myelin sheaths and retinal structures, which were related to the abnormal transcription of relevant genes. Furthermore, targeted metabolomics demonstrated that they caused neurotoxicity by increasing the content of kynurenine and decreasing the content of asparagine and histidine. These findings indicated that they had similar neurotoxic effects, but the mechanisms may differ slightly. Collectively, this study will provide novel insights into understanding the mechanisms by which ERC of PFOS and its substitutes produce neurodevelopmental toxicity.

Neurobehavioral response in zebrafish exposed to perfluorooctane sulfonate and its substitutes: Underestimated ecological risks

Perfluorooctane sulfonate (PFOS) is a persistent environmental contaminant with adverse effects. Alongside PFOS, its substitutes, such as 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and 6:2 fluorotelomer sulfonic acid (6:2 FTSA), are frequently detected in aquatic environments. While the effects of PFOS and its substitutes on the aquatic organism behavior have been observed, the underlying mechanisms of these effects remain poorly understood. In this study, an online biological monitoring system was utilized to investigate the behavioral effects of 7-day exposure to PFOS, F-53B, and 6:2 FTSA in adult zebrafish (Danio rerio), and assess alterations in neurotoxicity-related biomarker levels. Results demonstrate that exposure to PFOS, F-53B, and 6:2 FTSA significantly reduced the behavioral strength (BS) and the amplitude of circadian rhythm in zebrafish. Notably, PFOS and 6:2 FTSA exposure induced circadian rhythm phase shifts. Furthermore, acetylcholinesterase (AChE) activity and dopamine (DA)/melatonin (MT) levels showed significant reductions consistent with BS alterations across all exposure groups. Molecular docking analysis revealed that PFOS, F-53B, and 6:2 FTSA exhibited significant binding affinities to related receptors. Among the three pollutants, F-53B exerted the most pronounced effects on BS values, circadian rhythm amplitude, and levels of related biomarkers. In contrast, 6:2 FTSA displayed the most significant impact on circadian rhythm phase shifts. These findings suggest that the effects and the underlying mechanisms of PFOS and its substitutes on zebrafish behavior may vary. A comprehensive evaluation of the neurotoxicity of PFOS substitutes for aquatic organisms is required to prevent underestimation of their potential risks.

Mechanistic insights into the neurotoxicity of F53B: Effects on metabolic dysregulation and apoptosis of dopaminergic neurons

F53B (6:2 chlorinated polyfluorinated ether sulfonate), a substitute for perfluorooctane sulfonate (PFOS), is widely used as a chromium mist inhibitor in the electroplating industry. However, significant concern has arisen owing to its biological toxicity. Several studies on F53B toxicity in mammals have focused on hepatotoxicity, immunotoxicity, developmental toxicity, and reproductive toxicity, while its neurotoxic effects, especially in relation to neurodegenerative diseases such as Parkinson's disease (PD), remain unclear. In this study, we investigated the neurotoxic effects of F53B on dopaminergic neurons and explored its potential risk associated with PD in a cellular model. Potential target prediction and validation experiments demonstrated that F53B induced apoptosis in dopaminergic neurons. We also discovered that F53B triggered oxidative stress and inflammatory responses, and stimulated nitric oxide (NO) generation in the PD cellular model. Subsequently, untargeted metabolomics and lipidomics approaches were integrated to explore the molecular mechanisms underlying the response of dopaminergic neurons to F53B exposure. The results suggested that F53B disrupted arginine and proline metabolism, energy metabolism, and caused lipid dysregulation, particularly promoting the hydrolysis of sphingomyelin (SM) into ceramide (Cer). Overall, this study provides evidence that F53B exposure could increase the potential risk of PD and offers novel insights into its neurotoxicity mechanisms.

Adverse outcome pathway for the neurotoxicity of Per- and polyfluoroalkyl substances: A systematic review

Per- and polyfluoroalkyl substances (PFAS) are endocrine disruptors with unambiguous neurotoxic effects. However, due to variability in experimental models, population characteristics, and molecular endpoints, the elucidation of mechanisms underlying PFAS-induced neurotoxicity remains incomplete. In this review, we utilized the adverse outcome pathway (AOP) framework, a comprehensive tool for evaluating toxicity across multiple biological levels (molecular, cellular, tissue and organ, individual, and population), to elucidate the mechanisms of neurotoxicity induced by PFAS. Based on 271 studies, the reactive oxygen species (ROS) generation emerged as the molecular initiating event 1 (MIE1). Subsequent key events (KEs) at the cellular level include oxidative stress, neuroinflammation, apoptosis, altered Ca2+ signal transduction, glutamate and dopamine signaling dyshomeostasis, and reduction of cholinergic and serotonin. These KEs culminate in synaptic dysfunction at organ and tissue levels. Further insights were offered into MIE2 and upstream KEs associated with altered thyroid hormone levels, contributing to synaptic dysfunction and hypomyelination at the organ and tissue levels. The inhibition of Na+/I- symporter (NIS) was identified as the MIE2, initiating a cascade of KEs at the cellular level, including altered thyroid hormone synthesis, thyroid hormone transporters, thyroid hormone metabolism, and binding with thyroid hormone receptors. All KEs ultimately result in adverse outcomes (AOs), including cognition and memory impairment, autism spectrum disorders, attention deficit hyperactivity disorders, and neuromotor development impairment. To our knowledge, this review represents the first comprehensive and systematic AOP analysis delineating the intricate mechanisms responsible for PFAS-induced neurotoxic effects, providing valuable insights for risk assessments and mitigation strategies against PFAS-related health hazards.

Effects on Synaptic Plasticity Markers in Fetal Mice and HT22 Neurons upon F-53B Exposure: The Role of PKA Cytoplasmic Retention

Chlorinated polyfluorinated ether sulfonate (F-53B), a chromium-fog depressant widely utilized as an alternative to perfluorooctanesulfonate, can transfer from mother to fetus. Recent research has demonstrated that prenatal exposure to F-53B results in synaptic damage in weaning mice. However, the mechanism underpinning F-53B-triggered synaptic damage during fetal development remains unclear. This study aims to investigate the role of the protein kinase A (PKA)/cAMP response element-binding protein (CREB) pathway, a crucial signaling mechanism known as "synaptic switch", in the early neurotoxicity of F-53B exposure both in vivo and in vitro. Here, C57BL/6 fetal mice were subjected to exposure to F-53B (0, 4, and 40 μg/L) from gestation days (GD) 0 to 14 to evaluate nerve injury prior to delivery. HT22 neurons exposed to F-53B (0, 0.016, 0.08, 0.4, 2, and 10 μmol/L) for 24 h were utilized to elucidate the underlying mechanism. Our results demonstrated that F-53B significantly increased the fluorescence intensity of Nestin (a neural stem cell marker) in the fetal brain hippocampus (GD14). Subsequently, we found that F-53B downregulated the expression of synaptic plasticity markers (SYP, GAP43, and BDNF) in the fetal brain and HT22 neurons. Further molecular docking analysis revealed that F-53B fits into the ligand-binding pockets of PKA and CREB1. Results showed that F-53B inhibited the translocation of PKA protein from the cytoplasm to the neuronal nuclei and reduced the levels of PKA, CREB1, p-PKA(α/β/γ)-Thr197, and p-CREB1-S133 in the nucleus. Furthermore, the expression of synaptic plasticity markers altered by F-53B could be reversed by a PKA agonist and was intensified by a PKA antagonist. In summary, our findings suggest that intrauterine exposure to F-53B can weaken the expression of synaptic plasticity markers in the fetal brain, with this neurotoxicity being mediated by the cytoplasmic retention of PKA.

Development of a Physiologically Based Pharmacokinetic (PBPK) Model for F-53B in Pregnant Mice and Its Extrapolation to Humans

Chlorinated polyfluorinated ether sulfonic acid (F-53B), a commonly utilized alternative for perfluorooctane sulfonate, was detected in pregnant women and cord blood recently. However, the lack of detailed toxicokinetic information poses a significant challenge in assessing the human risk assessment for F-53B exposure. Our study aimed to develop a physiologically based pharmacokinetic (PBPK) model for pregnant mice, based on toxicokinetic experiments, and extrapolating it to humans. Pregnant mice were administered 80 μg/kg F-53B orally and intravenously on gestational day 13. F-53B concentrations in biological samples were analyzed via ultraperformance liquid chromatography-mass spectrometry. Results showed the highest F-53B accumulation in the brain, followed by the placenta, amniotic fluid, and liver in fetal mice. These toxicokinetic data were applied to F-53B PBPK model development and evaluation, and Monte Carlo simulations were used to characterize the variability and uncertainty in the human population. Most of the predictive values were within a 2-fold range of experimental data (>72%) and had a coefficient of determination (R2) greater than 0.68. The developed mouse model was then extrapolated to the human and evaluated with human biomonitoring data. Our study provides an important step toward improving the understanding of toxicokinetics of F-53B and enhancing the quantitative risk assessments in sensitive populations, particularly in pregnant women and fetuses.

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.

Accumulation features and temporal trends (2002-2015) for legacy and emerging per- and polyfluoroalkyl substances (PFASs) in finless porpoises bycaught off Korean coasts

Legacy and emerging per- and polyfluoroalkyl substances (PFASs) were measured in livers of finless porpoises (Neophocaena asiaeorientalis; n = 167) collected in Korean waters from 2002 to 2015 to investigate their occurrence, bioaccumulation feature, temporal trends, and ecotoxicological implications. Perfulorooctane sulfonate (PFOS), perfluoroundecanoate (PFUnDA), and perfluorotridecanoate (PFTrDA) were the predominant PFASs found in the porpoises. The concentration of 6:2 chlorinated polyfluoroalkyl ether sulfonate (F-53B), an alternative to PFOS, was comparable to that of PFTrDA. Perfluorooctane sulfonamide (FOSA), a precursor of PFOS, was also detected in all the porpoises examined. All PFASs, including F-53B, accumulated to higher concentrations in immature porpoises compared with mature specimens, implying substantial maternal transfer and limited metabolizing capacity for PFASs. A significant correlation was observed between PFOS and F-53B concentrations, indicating similar bioaccumulation processes. Based on prenatal exposure and toxicity, F-53B is an emerging contaminant in marine ecosystems. Significantly increasing trends were observed in the concentrations of sulfonates, carboxylates, and F-53B between 2002/2003 and 2010, whereas the FOSA concentration significantly decreased. During 2010-2015, decreasing trends were observed in the concentrations of FOSA and sulfonates, whereas concentrations of carboxylate and F-53B increased without statistical significance, likely due to a gap for the implementation of regulatory actions between sulfonates and carboxylates. Although PFOS and PFOA were found to pose little health risk to porpoises, the combined toxicological effects of other contaminants should be considered to protect populations and to mitigate PFAS contamination in marine ecosystems.

Early life exposure to F-53B induces neurobehavioral changes in developing children and disturbs dopamine-dependent synaptic signaling in weaning mice

BACKGROUND

Previous studies have shown that F-53B exposure may be neurotoxic to animals, but there is a lack of epidemiological evidence, and its mechanism needs further investigation.

METHODS

Serum F-53B concentrations and Wisconsin Card Sorting Test (WCST) were evaluated in 314 growing children from Guangzhou, China, and the association between them were analyzed. To study the developmental neurotoxicity of F-53B, experiments on sucking mice exposed via placental transfer and breast milk was performed. Maternal mice were orally exposed to 4, 40, and 400 μg/L of F-53B from postnatal day 0 (GD0) to postnatal day 21 (PND 21). Several genes and proteins related to neurodevelopment, dopamine anabolism, and synaptic plasticity were examined by qPCR and western blot, respectively, while dopamine contents were detected by ELISA kit in weaning mice.

RESULTS

The result showed that F-53B was positively associated with poor WCST performance. For example, with an interquartile range increase in F-53B, the change with 95 % confidence interval (CI) of correct response (CR), and non-perseverative errors (NPE) was -2.47 (95 % CI: -3.89, -1.05, P = 0.001), 2.78 (95 % CI: 0.79, 4.76, P = 0.007), respectively. Compared with the control group, the highest exposure group of weaning mice had a longer escape latency (35.24 s vs. 51.18 s, P = 0.034) and a lesser distance movement (34.81 % vs. 21.02 %, P < 0.001) in the target quadrant, as observed from morris water maze (MWM) test. The protein expression of brain-derived neurotrophic factor (BDNF) and growth associated protein-43 (GAP-43) levels were decreased, as compared to control (0.367-fold, P < 0.001; 0.366-fold, P < 0.001; respectively). We also observed the upregulation of dopamine transporter (DAT) (2.940-fold, P < 0.001) consistent with the trend of dopamine content (1.313-fold, P < 0.001) in the hippocampus.

CONCLUSION

Early life exposure to F-53B is associated with adverse neurobehavioral changes in developing children and weaning mice which may be modulated by dopamine-dependent synaptic plasticity.