Chronic exposure to perfluorooctane sulfonate induces behavior defects and neurotoxicity through oxidative damages, in vivo and in vitro

Versatility of Caenorhabditis elegans as a Model Organism for Evaluating Foodborne Neurotoxins and Food Bioactive Compounds in Nutritional Neuroscience

Epidemiological evidence has shown that the regular ingestion of vegetables and fruits is associated with reduced risk of developing chronic diseases. The introduction of the 3Rs (replacement, reduction, and refinement) principle into animal experiments has led to the use of valid, cost-effective, and efficient alternative and complementary invertebrate animal models which are simpler and lower in the phylogenetic hierarchy. Caenorhabditis elegans (C. elegans), a nematode with a much simpler anatomy and physiology compared to mammals, share similarities with humans at the cellular and molecular levels, thus making it a valid model organism in neurotoxicology. This review explores the versatility of C. elegans in elucidating the neuroprotective mechanisms elicited by food bioactive compounds against neurotoxic effects of food- and environmental-related contaminants. Several signaling pathways linked to the molecular basis of neuroprotection exerted by bioactive compounds in chemically induced or transgenic C. elegans models of neurodegenerative diseases are also discussed. Specifically, the modulatory effects of bioactive compounds on the DAF-16/FoxO and SKN-1/Nrf2 signaling pathways, stress resistance- and autophagy-related genes, and antioxidant defense enzyme activities were highlighted. Altogether, C. elegans represent a valuable model in nutritional neuroscience for the identification of promising neuroprotective agents and neurotherapeutic targets which could help in overcoming the limitations of current therapeutic agents for neurotoxicity and neurodegenerative diseases.

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.

Perfluorooctane sulfonic acid: a possible risk factor of endothelial dysfunction based on in silico and in vitro studies

Perfluorooctane sulfonic acid (PFOS) is a fluorinated chemical utilized in a variety of industrial and household products. PFOS has been detected in human serum and is associated with multiple human adverse health effects. Epidemiological evidence has linked PFOS exposure to endothelial dysfunction, which is a key contributor to atherosclerosis. However, the underlying mechanisms of PFOS-induced endothelial dysfunction associated atherosclerosis has not been investigated. In the present study, human microvascular endothelial cells (HMEC-1) exposed to PFOS (15 μM) for 72 h, mimicking long-term exposure. We further employed integrated RNA-sequencing (RNA-seq) and transcriptomic analysis to identify differentially expressed genes (DEGs) for biological alterations: gene ontology (GO), pathway enrichment analysis (KEGG), protein-protein interaction network and modular clustering analysis. Furthermore, the Metascape database was used for disease association, tissue specificity, and transcription factor analysis. Hub genes were verified using atherosclerosis patient data sets from the GEO dataset. Alteration of hub genes in patients was then validated using immunoblotting and ELISA. Our results revealed that PFOS altered amino acid biosynthesis, lipid metabolism and induced the ER-stress response through the HRI/eIF2α/ATF4 pathway, leading to endothelial dysfunction. Interestingly, we found that PFOS induced inflammation by increasing COX-2, ICAM-1 and IL-6 expression through NF-κB and JAK2/STAT3 pathway in endothelial cells. Moreover, up-regulated C/EBPβ and ATF4 were observed in both patients and PFOS-exposed endothelium, which may use as an early biomarker and may have a potential role in PFOS-induced endothelial dysfunction. These findings provide novel insight into the underlying molecular mechanisms of PFOS-induced endothelial dysfunction associated with atherosclerosis.

Per- and polyfluoroalkyl substances in environment and potential health impacts: Sources, remediation treatment and management, policy guidelines, destructive technologies, and techno-economic analysis

Per- and polyfluoroalkyl Substances (PFAS), also known as forever chemicals and ubiquitous persistence, pose significant public health challenges due to their potential toxicity, particularly in drinking water and soil contamination. However, PFAS occurrence and their concentrations in different environmental matrices vary globally, but factors influencing trends, transport, fate, toxicity, and interactions with co-contaminants remain largely unexplored. Therefore, this review critically examines the state-of-the-art worldwide PFAS sources, distribution, and pathways, and evaluates how PFASs are processed in wastewater treatment, generally, which causes severe problems with the quality and safety of drinking water. Importantly, the review also underscores health issues due to PFAS consumption and recent research trends on developing effective treatment strategies to manage PFAS contamination. Potential effects of PFAS were linked to urban land use and the proportion of wastewater effluent in streamflow. Besides, major emphasis was provided on challenges for conventional treatment, destructive technologies, environmental accumulation, precursor transformation, and cost-investment related to PFAS removal technologies. To combat PFAS contamination, this review proposes a framework that promotes the comprehensive identification of prevalent compounds, with a focus on their eradication through knowledge-based and targeted analysis. Additionally, it explores the ongoing debate surrounding PFAS laws and legal frameworks, offering ideas for enhancing contamination management. Lastly, this review provides a strategic plan for improving response and preparedness, serving as a foundation for addressing future environmental challenges and informing health risk assessments.

Toxicity of Per- and Polyfluoroalkyl Substances and Their Substitutes to Terrestrial and Aquatic Invertebrates-A Review

Per- and polyfluoroalkyl substances (PFASs) have been widely used in daily life but they cause certain impacts on the environment due to their unique carbon-fluorine chemical bonds that are difficult to degrade in the environment. Toxicological studies on PFASs and their alternatives have mainly focused on vertebrates, while terrestrial and aquatic invertebrates have been studied to a lesser extent. As invertebrates at the bottom of the food chain play a crucial role in the whole ecological chain, it is necessary to investigate the toxicity of PFASs to invertebrates. In this paper, the progress of toxicological studies on PFASs and their alternatives in terrestrial and aquatic invertebrates is reviewed, and the accumulation of PFASs, their toxicity in invertebrates, as well as the neurotoxicity and toxicity to reproduction and development are summarized. This provides a reference to in-depth studies on the comprehensive assessment of the toxicity of PFASs and their alternatives, promotes further research on PFASs in invertebrates, and provides valuable recommendations for the use and regulation of alternatives to PFASs.

Effect of Per and Poly-Fluoroalkyl Substances on Pregnancy and Child Development

BACKGROUND

Childhood obesity is significantly influenced by maternal exposure to Per and Poly-Fluoroalkyl Substances (PFAS) during pregnancy. PFAS exposure occurs through the Peroxisome Proliferator-Activated Receptor (PPAR-γ) receptor, leading to increased fat deposition and profound health effects in child growth and development. Despite ongoing investigations, the relationship between maternal serum PFAS concentration and child obesity requires further exploration.

OBJECTIVE

This study aimed to review the possible effects of Per and poly-fluoroalkyl substances exposure and their mechanism in overweight/obese children from pregnant ladies.

METHODS

A detailed literature survey was conducted using online databases, including Science Direct, Google Scholar, Scopus, Cochrane, and PubMed. The study focused on the diverse effects of PFAS on maternal and child health, with particular emphasis on neurological complications.

RESULTS

Child growth development depends upon breastfeeding and placenta health, which is disrupted by PFAS exposure, ultimately destroying the body mass index of the child. Neurotoxicity testing utilized the SH-SY5Y human-derived cell line as an in vitro model, revealing PFAS-induced increases in adipocyte number, reduced cell size, altered lipid conglomeration, increased adiposity, and changes in liver function. in vivo studies in mice and human cell lines indicated PPAR-γ and ER-α activation, leading to adiposity and weight gain through Estrogen signaling and Lipid metabolism. PFAS concentrations positively correlated in maternal sera, analyzed by liquid chromatography/quadrupole mass spectrometry.

CONCLUSION

PFAS, with a long half-life of 3.5-8.5 years, is commonly found in the serum of pregnant women, crossing the placenta barrier. This exposure disrupts placental homeostasis, negatively impacting mechanisms of action and potentially leading to deterioration in pregnancy and child health. Further research is needed to comprehensively understand the complex interplay between PFAS exposure and its implications for maternal and child well-being.

Impact of Short-Chain Perfluoropropylene Oxide Acids on Biochemical and Behavioural Parameters in Eisenia fetida (Savigny, 1826)

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent organic pollutants that pose a growing threat to environmental and human health. Soil acts as a long-term reservoir for PFAS, potentially impacting soil biodiversity and ecosystem function. Earthworms, as keystone species in soil ecosystems, are particularly vulnerable to PFAS exposure. In this study, we investigated the sublethal effects of three short-chain (C4-C6) next-generation perfluoropropylene oxide acids (PFPOAs) on the earthworm Eisenia fetida, using a legacy perfluoroalkyl carboxylic acid (PFCA), perfluorooctanoic acid (PFOA), as a reference. We assessed a suite of biochemical endpoints, including markers for oxidative stress (catalase and superoxide dismutase activity), immunity (phenol oxidase activity), neurotoxicity (acetylcholinesterase activity), and behavioural endpoints (escape test). Results indicate that all tested PFAS, even at sub-micromolar concentrations, elicited significant effects across multiple physiological domains. Interestingly, HFPO-DA demonstrated the most substantial impact across all endpoints tested, indicating broad and significant biochemical and neurotoxic effects. Our findings underscore the potential risks of both legacy and emerging PFAS to soil ecosystems, emphasising the need for further research to understand the long-term consequences of PFAS contamination.

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.

PFOS Elicits Cytotoxicity in Neuron Through Astrocyte-Derived CaMKII-DLG1 Signaling In Vitro Rat Hippocampal Model

Both epidemiological investigation and animal experiments demonstrated that pre-/postnatal exposure to perfluorooctane sulfonic acid (PFOS) could induce neurodevelopmental disorders. Previous studies showed that astrocyte was involved in PFOS-induced neurotoxicity, while little information is available. In the present study, the role of astrocyte-derived calmodulin-dependent protein kinase II (CaMKII)-phosphorylated discs large homolog 1 (DLG1) signaling in PFOS eliciting cytotoxicity in neuron was explored with primary cultured hippocampal astrocyte and neuron. The application of PFOS showed a decreased cell viability, synapse length and glutamate transporter 1 (GLT-1) expression, but an increased CaMKII, DLG1 and cyclic AMP response element binding protein (CREB) expression in primary cultured astrocyte. With 2-(2-hydroxyethylamino)-6-aminohexylcarbamic acid tert-butyl ester-9-isopropylpurine (CK59), the CaMKII inhibitor, the disturbed cell viability and molecules induced by PFOS could be alleviated (CREB expression was excluded) in astrocytes. The cytotoxic effect of neuron exposed to astrocyte conditional medium collected from PFOS (PFOS-ACM) pretreated with CK59 was also decreased. These results indicated that PFOS mediated GLT-1 expression through astrocyte-derived CaMKII-DLG signaling, which might be associated with injuries on neurons. The present study gave an insight in further exploration of mechanism in PFOS-induced neurotoxicity.

Perfluorooctanoic acid inhibits androgen biosynthesis in rat immature Leydig cells

Perfluorooctanoic acid (PFOA) is a commonly used short-chain synthetic perfluoroalkyl agent. Immature Leydig cells (ILCs) are localized in the testis and responsible for androgen biosynthesis and metabolism. Although PFOA shows toxicity in the reproductive system, it is not clear if it disrupts the function of ILCs. In the present study, primary ILCs were isolated from 35-day-old rats and exposed to a range of PFOA concentrations (0, 0.01, 0.1, or 1 μM). It was determined that 0.1 or 1 μM PFOA reduced total androgen biosynthesis in ILCs. Specifically, 22R-hydroxycholesterol (22R), and pregnenolone (P5) mediated androgen biosynthesis were reduced by 0.1 μM PFOA. PFOA also selectively downregulated mRNA and protein expressions of steroidogenic enzymes including LHCGR, CYP11A1, 3β-HSD1, and NR5A1 at 0.01, 0.1, or 1 μM. Further analysis revealed that 0.1 μM PFOA inhibited CYP11A1 and 3β-HSD1 enzyme activities. However, PFOA did not significantly affect androgen metabolism and turnover under any of the conditions tested. And PFOA gavaging to 35-day-old rats at 5 or 10 mg/kg for 7 or 14 days also reduced serum androgen levels secreted by ILCs. Moreover, PFOA gavaging also downregulated the mRNA and protein expression levels of LHCGR, CYP11A1, 3β-HSD1, and NR5A1 in vivo. Taken together, these findings suggest that PFOA inhibits androgen biosynthesis in ILCs by selectively targeting key enzymes in the synthesis pathway.

Environmental impacts, exposure pathways, and health effects of PFOA and PFOS

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals that have been widely utilized in various industries since the 1940s, and have now emerged as environmental contaminants. In recent years, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have been restricted and replaced with several alternatives. The high persistence, bioaccumulation, and toxicity of these substances have contributed to their emergence as environmental contaminants, and several aspects of their behavior remain largely unknown and require further investigation. The trace level of PFAS makes the development of a monitoring database challenging. Additionally, the potential health issues associated with PFAS are not yet fully understood due to ongoing research and inadequate evidence (experimental and epidemiological studies), especially with regard to the combined effects of exposure to PFAS mixtures and human health risks from drinking water consumption. This in-depth review offers unprecedented insights into the exposure pathways and toxicological impacts of PFAS, addressing critical knowledge gaps in their behaviors and health implications. It presents a comprehensive NABC-Needs, Approach, Benefits, and Challenges-analysis to guide future strategies for the sustainable monitoring and management of these pervasive environmental contaminants.

Effects of postnatal exposure to phthalate, bisphenol a, triclosan, parabens, and per- and poly-fluoroalkyl substances on maternal postpartum depression and infant neurodevelopment: a korean mother-infant pair cohort study

Exposure to endocrine-disrupting chemicals (EDCs) can promote infant neurodevelopmental impairment and maternal postpartum depression (PPD). However, the associations between lactation exposure to EDCs, maternal PPD, and infant neurodevelopment are unclear. Hence, we investigated these relationships in infants aged 36-42 months. We recruited 221 Korean mothers and analyzed 29 EDCs. The Edinburgh Postnatal Depression Scale (EPDS) was used to assess maternal PPD. Bayley scales of infant development; the Swanson, Nolan, and Pelham rating scale (SNAP); and the Child Behavior Checklist (CBCL) were used to assess neurodevelopment in infants exposed to the top 30% of EDC over three years. Multiple regression analyses were adjusted for maternal age, pre-pregnancy body mass index, education, income, employment, residence, and infant age and sex. The rates of infants with clinically abnormal diagnoses on neurologic developmental tests (Balyey, SNAP, and CBCL scales) ranged from 7.7 to 38.5% in this study, with the motor and hyperactivity/impulsivity areas scoring the highest among 65 boys and girls. Mono-2-ethylhexyl phthalate (MEHP) and mono-isononyl phthalate (MiNP) levels in breast milk significantly correlated with infant inattention and hyperactivity. Perfluorononanoic acid (PFNA) and perfluorooctyl sulfonate (PFOS) levels correlated significantly with motor development of BSID-III and total CBCL score which mean infant might have lower developmental status. EDC concentrations in breast milk were not associated with maternal PPD. Overall, lactational exposure to EDCs during the postpartum period can exert a negative effect on maternal PPD and infant neurodevelopment.

Prenatal Exposure to Perfluoroalkyl Substances and Cognitive and Neurobehavioral Development in Children at 6 Years of Age

Epidemiological evidence regarding the effects of prenatal exposure to perfluoroalkyl substances (PFASs) on neurodevelopment in children is inconclusive. In 449 mother-child pairs from the Shanghai-Minhang Birth Cohort Study, we measured the concentrations of 11 PFASs in maternal plasma samples obtained at 12-16 weeks of gestation. We assessed children's neurodevelopment at 6 years of age by the fourth edition of the Chinese Wechsler Intelligence Scale for Children and Child Behavior Checklist for ages 6-18. We evaluated the association between prenatal exposure to PFASs and children's neurodevelopment and the effect modification of maternal dietary factors during pregnancy and the child's sex. We found that prenatal exposure to multiple PFASs was associated with increased scores for attention problems, and the individual effect of perfluorooctanoic acid (PFOA) was statistically significant. However, no statistically significant association between PFASs and cognitive development was observed. Additionally, we found the effect modification of maternal nut intake and child's sex. In conclusion, this study suggests that prenatal exposure to PFASs was associated with more attention problems, and maternal nut intake during pregnancy may alter the potential effect of PFASs. However, these findings were exploratory because of multiple testing and the relatively small sample size.

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.

Nutritional Modulation of Associations between Prenatal Exposure to Persistent Organic Pollutants and Childhood Obesity: A Prospective Cohort Study

BACKGROUND

Prenatal exposure to persistent organic pollutants (POPs) may contribute to the development of childhood obesity and metabolic disorders. However, little is known about whether the maternal nutritional status during pregnancy can modulate these associations.

OBJECTIVES

The main objective was to characterize the joint associations and interactions between prenatal levels of POPs and nutrients on childhood obesity.

METHODS

We used data from to the Spanish INfancia y Medio Ambiente-Environment and Childhood (INMA) birth cohort, on POPs and nutritional biomarkers measured in maternal blood collected at the first trimester of pregnancy and child anthropometric measurements at 7 years of age. Six organochlorine compounds (OCs) [dichlorodiphenyldichloroethylene, hexachlorobenzene (HCB), β-hexachlorocyclohexane (β-HCH) and polychlorinated biphenyls 138, 153, 180] and four per- and polyfluoroalkyl substances (PFAS) were measured. Nutrients included vitamins (D, B12, and folate), polyunsaturated fatty acids (PUFAs), and dietary carotenoids. Two POPs-nutrients mixtures data sets were established: a) OCs, PFAS, vitamins, and carotenoids (n=660), and b) OCs, PUFAs, and vitamins (n=558). Joint associations of mixtures on obesity were characterized using Bayesian kernel machine regression (BKMR). Relative importance of biomarkers and two-way interactions were identified using gradient boosting machine, hierarchical group lasso regularization, and BKMR. Interactions were further characterized using multivariate regression models in the multiplicative and additive scale.

RESULTS

Forty percent of children had overweight or obesity. We observed a positive overall joint association of both POPs-nutrients mixtures on overweight/obesity risk, with HCB and vitamin B12 the biomarkers contributing the most. Recurrent interactions were found between HCB and vitamin B12 across screening models. Relative risk for a natural log increase of HCB was 1.31 (95% CI: 1.11, 1.54, pInteraction=0.02) in the tertile 2 of vitamin B12 and in the additive scale a relative excess risk due to interaction of 0.11 (95% CI: 0.02, 0.20) was found. Interaction between perfluorooctane sulfonate and β-cryptoxanthin suggested a protective effect of the antioxidant on overweight/obesity risk.

CONCLUSION

These results support that maternal nutritional status may modulate the effect of prenatal exposure to POPs on childhood overweight/obesity. These findings may help to develop a biological hypothesis for future toxicological studies and to better interpret inconsistent findings in epidemiological studies. https://doi.org/10.1289/EHP11258.

Effects of perfluorooctane sulfonate (PFOS) on cognitive behavior and autophagy of male mice

Perfluorooctane sulfonate (PFOS), an emerging environmental pollutant, is reported to cause neurotoxicity in animals and humans, but its underlying mechanisms are still unclear. We used in vivo models to investigate the effects of PFOS on cognition-related behaviors and related mechanisms. After 45 days of intragastric administration of PFOS (2 mg/kg or 8 mg/kg) in 7-week-old C57BL/6 mice, muscle strength, cognitive function and anxiety-like behavior were evaluated by a series of behavioral tests. The underling mechanisms of PFOS on impaired behaviors were evaluated by HE/Nissl staining, electron microscopy observation and western blot analysis. The results indicated that PFOS-exposed mice exhibited significant cognitive impairment, anxiety, neuronal degeneration and the abnormities of synaptic ultrastructure in the cortex and hippocampus. Western blot analysis indicated that PFOS exposure increased microtubule-associated protein light chain 3 (LC3) and decreased p62 protein levels, which may be associated with activation of autophagy leading to neuron damage. In summary, our results suggest that chronic exposure to PFOS adversely affects cognitive-related behavior in mice. These findings provide new mechanistic insights into PFOS-induced neurotoxicity.

A Critical Review and Meta-Analysis of Impacts of Per- and Polyfluorinated Substances on the Brain and Behavior

Per- and polyfluoroalkyl substances (PFAS) are a class of structurally diverse synthetic organic chemicals that are chemically stable, resistant to degradation, and persistent in terrestrial and aquatic environments. Widespread use of PFAS in industrial processing and manufacturing over the last 70 years has led to global contamination of built and natural environments. The brain is a lipid rich and highly vascularized organ composed of long-lived neurons and glial cells that are especially vulnerable to the impacts of persistent and lipophilic toxicants. Generally, PFAS partition to protein-rich tissues of the body, primarily the liver and blood, but are also detected in the brains of humans, wildlife, and laboratory animals. Here we review factors impacting the absorption, distribution, and accumulation of PFAS in the brain, and currently available evidence for neurotoxic impacts defined by disruption of neurochemical, neurophysiological, and behavioral endpoints. Emphasis is placed on the neurotoxic potential of exposures during critical periods of development and in sensitive populations, and factors that may exacerbate neurotoxicity of PFAS. While limitations and inconsistencies across studies exist, the available body of evidence suggests that the neurobehavioral impacts of long-chain PFAS exposures during development are more pronounced than impacts resulting from exposure during adulthood. There is a paucity of experimental studies evaluating neurobehavioral and molecular mechanisms of short-chain PFAS, and even greater data gaps in the analysis of neurotoxicity for PFAS outside of the perfluoroalkyl acids. Whereas most experimental studies were focused on acute and subchronic impacts resulting from high dose exposures to a single PFAS congener, more realistic exposures for humans and wildlife are mixtures exposures that are relatively chronic and low dose in nature. Our evaluation of the available human epidemiological, experimental, and wildlife data also indicates heightened accumulation of perfluoroalkyl acids in the brain after environmental exposure, in comparison to the experimental studies. These findings highlight the need for additional experimental analysis of neurodevelopmental impacts of environmentally relevant concentrations and complex mixtures of PFAS.

Perfluorooctane sulfonate (PFOS) induces several behavioural defects in Caenorhabditis elegans that can also be transferred to the next generations

Perfluorooctane sulfonate (PFOS) is a well-known global persistent organic pollutant of grave concern to ecological and human health. Toxicity of PFOS to animals and humans are well studied. Although few studies have reported the behavioral effect of PFOS on nematode Caenorhabditis elegans, it's transgenerational effects were seldom studied. Therefore, we investigated the toxicity of PFOS on several behavioral responses besides bioaccumulation and transgenerational effects in C. elegans. In contrast to the several published studies, we used lower concentrations (0.5-1000 μg/L or 0.001-2.0 μM) that are environmentally relevant and reported to occur close to the contaminated areas. The 48 h median lethal concentration of PFOS was found to be 3.15 μM (1575 μg/L). PFOS (≥0.01 μM) caused severe toxicity to locomotion, and this effect was even transferred to progeny. However, after a few generations, the defect was rectified in the progeny of single-time exposed parent nematodes. Whereas, continuous exposure at 0.001 μM PFOS, no visible defects were observed in the progeny. PFOS (≥0.01 μM) also significantly decreased the brood size in a concentration-dependent manner. Besides, lifespan was affected by the higher concentration of PFOS (≥1.0 μM). These two behavioral endpoints, lifespan and reproduction defects, became less severe in the progeny. Chemotaxis plasticity was also significantly retarded by ≥ 1.0 μM PFOS compared to the control group. Results indicate that PFOS can exert severe neurobehavioral defects that can be transferred from parents to their offspring. The findings of this study have significant implications for the risk assessment of perfluorinated substances in the environment.

Combined effects of mixed per- and polyfluoroalkyl substances on the Nrf2-ARE pathway in ARE reporter-HepG2 cells

Although the Nrf2-ARE pathway plays a critical role in cellular protection against toxicity and oxidative stress from environmental chemical stressors, the association between exposure to per- and polyfluoroalkyl substances (PFAS) mixtures and the changes of Nrf2-ARE pathway remains largely unexplored. This study evaluated the potential of PFAS to induce the Nrf2-ARE pathway as individual compounds and as binary, ternary, and multicomponent mixtures in the ARE reporter-HepG2 cells and compared the mixture toxicity data to the predictions by concentration addition (CA) model. The toxicological interactions between PFAS mixture components were also determined by the model deviation ratio (MDR) between the CA predicted and mixture toxicity values. The induction of the Nrf2-ARE pathway was quantified using the luciferase system, and the endpoint assessed was the concentration that induced an induction ratio (IR) of 1.5 (EC_IR1.5). The results showed that exposures to both individual and mixed PFAS induced the Nrf2-ARE pathway in ARE reporter-HepG2 cells. Based on the MDRs, the combinations with PFOS showed synergistic interactive effects, while the combinations with PFOA showed additive effects. These results indicate that the CA model underestimated the mixture toxicity of PFAS with PFOS co-exposures and may have health risk assessment implications.

Integrative effects based on behavior, physiology and gene expression of tritiated water on zebrafish

Tritium is a water-soluble hydrogen isotope that releases beta rays during decay. In nature, tritium primarily exists as tritiated water (HTO), and its main source is nuclear power/processing plants. In recent decades, with the development of nuclear power industry, it is necessary to evaluate the impact of tritium on organisms. In this study, fertilized zebrafish embryos are treated with different HTO concentrations (3.7 × 10³ Bq/ml, 3.7 × 10⁴ Bq/ml, 3.7 × 10⁵ Bq/ml). After treatment with HTO, the zebrafish embryos developed without evident morphological changes. Nevertheless, the heart rate increased and locomotor activity decreased significantly. In addition, RNA-sequencing shows that HTO can affect gene expressions. The differentially expressed genes are enriched through many physiological processes and intracellular signaling pathways, including cardiac, cardiovascular, and nervous system development and the metabolism of xenobiotics by cytochrome P450. Moreover, the concentrations of thyroid hormones in the zebrafish decrease and the expression of thyroid hormone-related genes is disordered after HTO treatment. Our results suggest that exposure to HTO may affect the physiology and behaviors of zebrafish through physiological processes and intracellular signaling pathways and provide a theoretical basis for ecological risk assessment of tritium.

Integrated multi-omics analysis reveals the underlying molecular mechanism for developmental neurotoxicity of perfluorooctanesulfonic acid in zebrafish

Limited studies on multi-omics have been conducted to comprehensively investigate the molecular mechanism underlying the developmental neurotoxicity of perfluorooctanesulfonic acid (PFOS). In this study, the locomotor behavior of zebrafish larvae was assessed under the exposure to 0.1-20 μM PFOS based on its reported neurobehavioral effect. After the number of zebrafish larvae was optimized for proteomics and metabolomics studies, three kinds of omics (i.e., transcriptomics, proteomics, and metabolomics) were carried out with zebrafish larvae exposed to 0.1, 1, 5, and 10 μM PFOS. More importantly, a data-driven integration of multi-omics was performed to elucidate the toxicity mechanism involved in developmental neurotoxicity. In a concentration-dependent manner, exposure to PFOS provoked hyperactivity and hypoactivity under light and dark conditions, respectively. Individual omics revealed that PFOS exposure caused perturbations in the pathways of neurological function, oxidative stress, and energy metabolism. Integrated omics implied that there were decisive pathways for axonal deformation, neuroinflammatory stimulation, and dysregulation of calcium ion signaling, which are more clearly specified for neurotoxicity. Overall, our findings broaden the molecular understanding of the developmental neurotoxicity of PFOS, for which multi-omics and integrated omics analyses are efficient for discovering the significant molecular pathways related to developmental neurotoxicity in zebrafish.

Perfluorooctane sulfonate (PFOS) disturbs fatty acid metabolism in Caenorhabditis elegans: Evidence from chemical analysis and molecular mechanism exploration

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant that might induce disorders in fatty acid (FA) metabolism, but the underlying mechanisms remain unresolved. Caenorhabditis elegans (C. elegans) as a model organism can synthesize polyunsaturated FAs de novo via the polyunsaturated FA synthesis pathway. In this study, synchronized L1 C. elegans were exposed to 0, 0.01, 0.1, 0.5 and 1 μM PFOS for 72 h. Gas chromatography-mass spectrometry (GC-MS) was used to establish a sensitive and reliable analysis method for PFASs in exposed nematode, the instrument detection limits of nine fatty acid methyl esters examined ranged between 1.11 and 27.6 ng/mL, with satisfactory reproducibility (RSD < 10%) observed. Methyl pentadecanoate (C15:0) was used as an internal standard, the linearity of the calibration (0.1-10 μg/mL) nine FAs from the nematode were quantitatively analyzed. Comparing with the control group, PFOS exposure caused significantly decreased levels of C18:0 while significantly increased levels of C18:3n6. A decrease in the C18:3n6: C18:2n6 ratio was observed. Consistently, expression of the FA desaturation gene fat-3 was significantly down-regulated. These findings suggest that the FA disorder is associated with decrease in mRNA expression of Δ6-desaturase genes in C. elegans. Simultaneously, the disorders in FA metabolism were found to disrupt mitochondrial function with a reduction in ATP synthesis, as determined by the luciferase method. In summary, the results of the study provide insights into the adverse effects of PFOS on FA metabolism in living organisms.

Acute Toxicity and Transgenerational Effects of Perfluorobutane Sulfonate on Caenorhabditis elegans

Perfluorobutane sulfonate (PFBS), due to its increasing use as an alternative to perfluooctane sulfonate (PFOS), is widely detected in humans and the environment, necessitating the evaluation of its potential ecotoxicological risk. We assessed the toxicity and bioaccumulation potential of PFBS in Caenorhabditis elegans, using lethality, locomotion, reproduction, life span, growth, and chemotactic behavior as the effect parameters. In addition, a total of 6 generations of exposed parent animals were monitored for locomotion, brood, and life span behaviors. Life span and brood size were significantly reduced in parent nematodes (P0) following exposure to ≥0.1 mM PFBS, but these negative effects did not transfer to the progeny. Although there was no remarkable effect on reproduction and life span in parent worms exposed to ≤0.01 mM PFBS, multigenerational exposure at 0.0005 mM significantly affected the F4 and F5 progeny. Furthermore, 0.01 to 2.0 mM of PFBS substantially retarded the locomotion behavior of P0 worms. At higher concentrations such as 1.0 mM, this negative effect on locomotion was transferred to the next generation (F1) but later recovered from F2 progeny onward. Our findings demonstrate for the first time that chronic exposure to PFBS at higher concentrations can cause behavioral toxicity and could be transferred to the progeny. These findings have significant implications for the environmental risk assessment of PFBS. Environ Toxicol Chem 2021;40:1973-1982. © 2021 SETAC.

Metabolic profiling in human SH-SY5Y neuronal cells exposed to perfluorooctanoic acid (PFOA)

Perfluorooctanoic acid (PFOA) is an abundant per- and polyfluoroalkyl substance (PFAS) detected in both indoor and outdoor environments. While studies suggest exposure concerns for humans, studies investigating PFOA-induced neurotoxicity are lacking. To address this gap, we exposed differentiated human SH-SY5Y cells to PFOA (0.1 μM up to 500 μM) at different time points (4, 24, 48, and 72 h) and measured cell viability, Casp3/7 activity, ATP levels, ATP synthase enzyme activity, mitochondrial membrane potential, reactive oxygen species (ROS), oxygen consumption rates for mitochondrial stress test (XFe24 Flux analyzer), glucose utilization, and global metabolome profiles to assess the potential for PFOA-induced neurotoxicity. Treatment with 10 or 100 μM PFOA did not compromise cell viability nor induce cytotoxicity to SH-SY5Y cells over a 48-hour exposure period. However, >250 μM PFOA compromised cell viability, induced cytotoxicity, and induced caspase 3/7 activity at 48 h. ATP levels were reduced in cells treated with 400 μM PFOA for 24 and 48 h, and with 100 μM PFOA and higher at 72 h. ATP synthase activity was inhibited by 250 μM PFOA but was unchanged by PFOA treatment at 200 μM or less. Conversely, mitochondrial membrane potential was reduced by >10 μM PFOA after 24 h. Total ROS was increased with 100 μM PFOA and higher after 4 h of exposure. Several mitochondria-related endpoints (basal respiration, ATP production, maximum respiration) were negatively affected at 250 μM PFOA at both 24- and 48-hour exposure, but were unaltered at concentrations of 100 μM PFOA or less. One exception was mitochondrial spare capacity, which was reduced by 100 μM PFOA after 24-hour exposure. Similarly, glycolysis, glycolytic capacity, and glycolytic reserve of SH-SY5Y cells were not altered by 10 nor 100 μM PFOA. Nontargeted metabolomics was conducted in cells treated with either 10 or 100 μM PFOA for 48 h, as these two concentrations were not cytotoxic and 28 metabolites differed among treatments. Notable was that 10 μM PFOA had little effect on the SH-SY5Y metabolome, and the metabolic profile was not statistically different from media nor solvent controls. On the other hand, 100 μM PFOA shifted the metabolic signature of the neuronal cells, leading to reduced abundance of ATP-related metabolites (adenine, nicotinamide), neurotransmitter precursors (DL-tryptophan, l-tyrosine), and metabolites that protect mitochondria during oxidative stress (betaine, orotic acid, and l-acetyl carnitine). We hypothesize that this metabolic signature may be associated with the reduced mitochondrial membrane potential observed at lower PFOA concentrations. Metabolic shifts appear to precede compromised cell viability, cytotoxicity, and apoptosis. This study generates mechanistic knowledge regarding PFOA-induced neurotoxicity, focusing on mitochondrial oxidative respiration and the neuronal metabolome.

Assessing the human health risks of per- and polyfluoroalkyl substances: A need for greater focus on their interactions as mixtures

Humans are exposed to complex mixtures of per- and polyfluoroalkyl substances (PFAS). However, human health risk assessment of PFAS currently relies on animal toxicity data derived from individual substance exposure, which may not adequately predict the risk from combined exposure due to possible interactions that can influence the overall risk. Long-chain perfluoroalkyl acids (PFAAs), particularly perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are recognised as global emerging contaminants of concern due to their ubiquitous distribution in all environmental media, wildlife, and humans, persistency, bioaccumulative-, toxic-, and human health-risk potentials. This article reviews the current understanding of the human health risks associated with PFAS exposure focusing on more recent toxicological and epidemiological studies from 2010 to 2020. The existing information on PFAA mixtures was also reviewed in an attempt to highlight the need for greater focus on their potential interactions as mixtures within the class of these chemicals. A growing number of toxicological studies have indicated several adverse health outcomes of PFAA exposure, including developmental and reproductive toxicity, neurotoxicity, hepatotoxicity, genotoxicity, immunotoxicity, thyroid disruption, and carcinogenicity. Epidemiological findings further support some of these adverse human health outcomes. However, the mechanisms underlying these adverse effects are not well defined. A few in vitro studies focusing on PFAA mixtures revealed that these compounds may act additively or interact synergistically/antagonistically depending on the species, dose level, dose ratio, and mixture components. Hence, the combined effects or potential interactions of PFAS mixtures should be considered and integrated into toxicity assessment to obtain a realistic and more refined human health risk assessment.

Effects of a human-based mixture of persistent organic pollutants on the in vivo exposed cerebellum and cerebellar neuronal cultures exposed in vitro

Exposure to persistent organic pollutants (POPs), encompassing chlorinated (Cl), brominated (Br) and perfluoroalkyl acid (PFAA) compounds is associated with adverse neurobehaviour in humans and animals, and is observed to cause adverse effects in nerve cell cultures. Most studies focus on single POPs, whereas studies on effects of complex mixtures are limited. We examined the effects of a mixture of 29 persistent compounds (Cl + Br + PFAA, named Total mixture), as well as 6 sub-mixtures on in vitro exposed rat cerebellar granule neurons (CGNs). Protein expression studies of cerebella from in vivo exposed mice offspring were also conducted. The selection of chemicals for the POP mixture was based on compounds being prominent in food, breast milk or blood from the Scandinavian human population. The Total mixture and sub-mixtures containing PFAAs caused greater toxicity in rat CGNs than the single or combined Cl/Br sub-mixtures, with significant impact on viability from 500x human blood levels. The potencies for these mixtures based on LC₅₀ values were Br + PFAA mixture > Total mixture > Cl + PFAA mixture > PFAA mixture. These mixtures also accelerated induced lipid peroxidation. Protection by the competitive N-methyl-D-aspartate (NMDA) receptor antagonist 3-((R)-2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) indicated involvement of the NMDA receptor in PFAA and Total mixture-, but not Cl mixture-induced toxicity. Gene-expression studies in rat CGNs using a sub-toxic and marginally toxic concentration ((0.4 nM-5.5 µM) 333x and (1 nM-8.2 µM) 500x human blood levels) of the mixtures, revealed differential expression of genes involved in apoptosis, oxidative stress, neurotransmission and cerebellar development, with more genes affected at the marginally toxic concentration. The two important neurodevelopmental markers Pax6 and Grin2b were downregulated at 500x human blood levels, accompanied by decreases in PAX6 and GluN2B protein levels, in cerebellum of offspring mice from mothers exposed to the Total mixture throughout pregnancy and lactation. In rat CGNs, the glutathione peroxidase gene Prdx6 and the regulatory transmembrane glycoprotein gene Sirpa were highly upregulated at both concentrations. In conclusion, our results support that early-life exposure to mixtures of POPs can cause adverse neurodevelopmental effects.

Perfluorooctane Sulfonate (PFOS) and Perfluorohexane Sulfonate (PFHxS) Alters Protein Phosphorylation, Increase ROS Levels and DNA Fragmentation during In Vitro Capacitation of Boar Spermatozoa

Simple Summary

Perfluorinated compounds are synthetic chemicals, with a wide variety of applications like firefighting foams, food packaging, additives in paper and fabrics to avoid dyes. Perfluorooctane sulfonate and perfluorohexane sulfonate are globally distributed, and contaminates air, water, food, and dust, have toxic effects and bioaccumulate. Significant levels of these compounds have found in blood serum, breast milk, and semen of occupationally exposed and unexposed people, as well as in blood serum and organs of the domestic, farm, and wild animals. The present study seeks to analyze the toxic effects and possible alterations caused by the presence of these compounds in boar sperm during the in vitro capacitation, due to their toxicity, worldwide distribution, and lack of information in spermatozoa physiology during pre-fertilization processes.

Abstract

Perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) are toxic and bioaccumulative, included in the Stockholm Convention’s list as persistent organic pollutants. Due to their toxicity, worldwide distribution, and lack of information in spermatozoa physiology during pre-fertilization processes, the present study seeks to analyze the toxic effects and possible alterations caused by the presence of these compounds in boar sperm during the in vitro capacitation. The spermatozoa capacitation was performed in supplemented TALP-Hepes media and mean lethal concentration values of 460.55 μM for PFOS, and 1930.60 μM for PFHxS were obtained. Results by chlortetracycline staining showed that intracellular Ca²⁺ patterns bound to membrane proteins were scarcely affected by PFOS. The spontaneous acrosome reaction determined by FITC-PNA was significantly reduced by PFOS and slightly increased by PFHxS. Both toxic compounds significantly alter the normal capacitation process from 30 min of exposure. An increase in ROS production was observed by flow cytometry and considerable DNA fragmentation by the comet assay. The immunocytochemistry showed a decrease of tyrosine phosphorylation in proteins of the equatorial and acrosomal zone of the spermatozoa head. In conclusion, PFOS and PFHxS have toxic effects on the sperm, causing mortality and altering vital parameters for proper sperm capacitation.

Perfluorooctane sulfonate enhances mRNA expression of PPARγ and ap2 in human mesenchymal stem cells monitored by long-retained intracellular nanosensor

Perfluorooctane sulfonate (PFOS) has been widely used as a surface coating for household products. It still exists in living environments despite being restricted, due to its bioaccumulation and long half-life. Studies have shown that PFOS has the ability to induce adipogenic differentiation of human cells. Human mesenchymal stem cells (hMSCs) distributed within the adipose tissue might be a potential target of accumulated PFOS. However, traditional end-point toxicity assays failed to examine the subtle changes of cellular function exposed to low-dose persistent organic pollutants in real time. In the present work, highly sensitive and long-retained (more than 30 days) fluorescence based polymeric nanosensors were developed and employed for real-time assessment of cellular functions. hMSCs were engineered with sensor molecules encapsulated poly (lactic-co-glycolic acid) (PLGA) particles. Once internalized by hMSCs, PLGA particles continuously release and replenish sensor molecules to cytoplasm, resulting in prolonged fluorescence signal against photo bleaching and dilution by exocytosis. With this method, the dynamic changes of viability, ROS induction, and adipogenic differentiation related mRNA expression of hMSCs were monitored. PFOS with the concentration as low as 0.1 μM can induce cellular ROS and enhance the PPARγ and ap2 mRNA expression, suggesting the effect on promoting adipogenic differentiation of hMSCs.

Combined effects and toxicological interactions of perfluoroalkyl and polyfluoroalkyl substances mixtures in human liver cells (HepG2)

The combined effects and toxicological interactions of perfluoroalkyl and polyfluoroalkyl substances (PFAS) mixtures remain largely unknown even though they occur as complex mixtures in the environment. This study investigated the toxicity of individual and combined PFAS to human liver cell line (HepG2). The Combination Index (CI)-isobologram equation method was used to determine the toxicological interactions of PFAS in binary, ternary and multi-component mixtures. The results indicated that the cytotoxicity of individual PFAS to HepG2 cells increased with increasing carbon chain lengths when separated into non-sulfonated and sulfonated groups. The respective cytotoxicity of PFAS is in the order of PFDA > PFNA > PFOA > PFHpA for perfluoroalkyl carboxylic acids and in the order of PFOS > PFHxS for perfluoroalkane sulfonic acids. The toxicological interaction of PFOS and PFOA with other PFAS clearly showed a different pattern of combined toxicity in HepG2 Cells. The binary, ternary, and multi-component combinations of PFOS with PFOA, PFNA, PFDA, PFHxS, and PFHpA displayed synergistic interactions for almost all inhibitory effect levels tested, whereas, either synergistic or antagonistic effect was observed in mixtures with PFOA. Overall, the pattern of interactions of PFAS mixtures is predominated by synergism, especially at low to medium effect levels; the exceptions to this were the antagonistic interactions found in mixture with PFOA, PFHxS, and PFHpA. These cytotoxicity results may have an implication on the health risk assessment of PFAS mixtures.

Per- and Polyfluoroalkyl Substances (PFAS) Neurotoxicity in Sentinel and Non-Traditional Laboratory Model Systems: Potential Utility in Predicting Adverse Outcomes in Human Health

Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals that were widely used in manufacturing and are now present in the environment throughout the world. It is known that various PFAS are quantifiable in human in blood, but potential adverse health outcomes remain unclear. Sentinel and non-traditional model species are useful to study potential toxicity of PFAS in order to understand the relationship between environmental and human health. Here, we present a critical review of studies on the neurotoxicity of PFAS in sentinel and non-traditional laboratory model systems, including Caenorhabditis elegans (nematode), Dugesia japonica (planarian), Rana pipiens (frogs), Danio rerio and Oryzias melastigma (fish), and Ursus maritimus (polar bears). PFAS have been implicated in developmental neurotoxicity in non-traditional and traditional model systems as well as sentinel species, including effects on neurotransmitter levels, especially acetylcholine and its metabolism. However, further research on the mechanisms of toxicity needs to be conducted to determine if these chemicals are affecting organisms in a similar manner. Overall, findings tend to be similar among the various species, but bioaccumulation may vary, which needs to be taken into account in future studies by quantifying target organ concentrations of PFAS to better compare different species. Furthermore, data on the majority of PFAS is lacking in neurotoxicity testing, and additional studies are needed to corroborate findings thus far.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) acutely affect human α1β2γ2L GABAA receptor and spontaneous neuronal network function in vitro

Concerns about the neurotoxic potential of polyfluoroalkyl substances (PFAS) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) increase, although their neurotoxic mechanisms of action remain debated. Considering the importance of the GABA_A receptor in neuronal function, we investigated acute effects of PFAS on this receptor and on spontaneous neuronal network activity. PFOS (Lowest Observed Effect Concentration (LOEC) 0.1 µM) and PFOA (LOEC 1 µM) inhibited the GABA-evoked current and acted as non-competitive human GABA_A receptor antagonists. Network activity of rat primary cortical cultures increased following exposure to PFOS (LOEC 100 µM). However, exposure of networks of human induced pluripotent stem cell (hiPSC)-derived neurons decreased neuronal activity. The higher sensitivity of the α₁β₂γ_2L GABA_A receptor for PFAS as compared to neuronal networks suggests that PFAS have additional mechanisms of action, or that compensatory mechanisms are at play. Differences between rodent and hiPSC-derived neuronal networks highlight the importance of proper model composition. LOECs for PFAS on GABA_A receptor and neuronal activity reported here are within or below the range found in blood levels of occupationally exposed humans. For PFOS, LOECs are even within the range found in human serum and plasma of the general population, suggesting a clear neurotoxic risk.

Interfacial Self-Assembly of Antimicrobial Peptide GL13K into Non-Fibril Crystalline β-Sheets

The need for new and potent antibiotics in an era of increasing multidrug resistance in bacteria has driven the search for new antimicrobial agents, including the design of synthetic antimicrobial peptides (AMPs). While a number of β-sheet forming AMPs have been proposed, their similarity to β-amyloids raises a number of concerns associated with neurodegenerative states. GL13K is an effective, synthetic AMP that selectively folds into β-sheets at anionic interfaces. Moreover, it is one of relatively few AMPs that preferentially fold into β-sheets without bridging disulfides. The interfacial activity of GL13K and its propensity to form amyloid fibrils have not been investigated. Using structural studies at the air/water interface and in the absence of anionic lipids, we demonstrate that while GL13K does form crystalline β-sheets, it does not self-assemble into fibrils. This work emphasizes the requirement for a single charged amino acid in the hydrophobic face to prevent fibril formation in synthetic peptides.

Perfluorooctane Sulfonate (PFOS) Produces Dopaminergic Neuropathology in Caenorhabditis elegans

Perfluorooctane sulfonate (PFOS) has been widely utilized in numerous industries. Due to long environmental and biological half-lives, PFOS is a major public health concern. Although the literature suggests that PFOS may induce neurotoxicity, neurotoxic mechanisms, and neuropathology are poorly understood. Thus, the primary goal of this study was to determine if PFOS is selectively neurotoxic and potentially relevant to specific neurological diseases. Nematodes (Caenorhabditis elegans) were exposed to PFOS or related per- and polyfluoroalkyl substances (PFAS) for 72 h and tested for evidence of neuropathology through examination of cholinergic, dopaminergic, gamma-amino butyric acid (GABA)ergic, and serotoninergic neuronal morphologies. Dopaminergic and cholinergic functional analyses were assessed through 1-nonanol and Aldicarb assay. Mechanistic studies assessed total reactive oxygen species, superoxide ions, and mitochondrial content. Finally, therapeutic approaches were utilized to further examine pathogenic mechanisms. Dopaminergic neuropathology occurred at lower exposure levels (25 ppm, approximately 50 µM) than required to produce neuropathology in GABAergic, serotonergic, and cholinergic neurons (100 ppm, approximately 200 µM). Further, PFOS exposure led to dopamine-dependent functional deficits, without altering acetylcholine-dependent paralysis. Mitochondrial content was affected by PFOS at far lower exposure level than required to induce pathology (≥1 ppm, approximately 2 µM). Perfluorooctane sulfonate exposure also enhanced oxidative stress. Further, mutation in mitochondrial superoxide dismutase rendered animals more vulnerable. Neuroprotective approaches such as antioxidants, PFAS-protein dissociation, and targeted (mitochondrial) radical and electron scavenging were neuroprotective, suggesting specific mechanisms of action. In general, other tested PFAS were less neurotoxic. The primary impact is to prompt research into potential adverse outcomes related to PFAS-induced dopaminergic neurotoxicity in humans.

Perfluorooctane sulfonate induces apoptosis via activation of FoxO3a and upregulation of proapoptotic Bcl-2 proteins in PC12 cells

Perfluorooctane sulfonate (PFOS), a kind of organic pollutant widely found in the environment and biota, could alter normal brain development and produce cognitive dysfunction. For the past years, the neurotoxic effects of PFOS have been shown. Recent studies have proven that PFOS can induce neuronal apoptosis and cause neurotoxicity, but the regulatory proteins referred to the process have not been clarified. In this study, PC12 cells were used to investigate the changes of the expression of apoptosis-related proteins, forkhead box O3 (FoxO3a) and pro-apoptotic Bcl-2 proteins. We detected that the levels of cleaved caspase-3 and cleaved PARP were up-regulated obviously in PFOS-treated PC12 cells by using Western blotting, and that the apoptotic rate of PC12 cells was increased significantly by using flow cytometry, verifying that PFOS could induce neuronal apoptosis. Western blot analysis and immunofluorescence revealed obvious up-regulation of the expression of FoxO3a and proapoptotic Bcl-2 proteins. In addition, knockdown of FoxO3a gene inhibited Bim expression and apoptosis. According to the data, we believe that FoxO3a may play a crucial role in PFOS-induced neurotoxicity.

Role of nitric oxide in psychostimulant-induced neurotoxicity

In recent decades, consumption of psychostimulants has been significantly increased all over the world, while exact mechanisms of neurochemical effects of psychomotor stimulants remained unclear. It is assumed that the neuronal messenger nitric oxide (NO) may be involved in mechanisms of neurotoxicity evoked by psychomotor stimulants. However, possible participation of NO in various pathological states is supported mainly by indirect evidence because of its short half-life in tissues. Aim of this review is to describe the involvement of NO and the contribution of lipid peroxidation (LPO) and acetylcholine (ACH) release in neurotoxic effects of psychostimulant drugs. NO was directly determined in brain structures by electron paramagnetic resonance (EPR). Both NO generation and LPO products as well as release of ACH were increased in brain structures following four injections of amphetamine (AMPH). Pretreatment of rats with the non-selective inhibitor of NO-synthase (NOS) N-nitro-L-arginine or the neuronal NOS inhibitor 7-nitroindazole significantly reduced increase of NO generation as well as the rise of ACH release induced by AMPH. Both NOS inhibitors injected prior to AMPH had no effect on enhanced levels of LPO products. Administration of the noncompetitive NMDA receptor antagonist dizocilpine abolished increase of both NO content and concentration of LPO products induced by of the psychostimulant drug. Dizocilpine also eliminated the influence of AMPH on the ACH release. Moreover, the neurochemical and neurotoxic effects of the psychostimulant drug sydnocarb were compared with those of AMPH. Single injection of AMPH showed a more pronounced increase in NO and TBARS levels than after an equimolar concentration of sydnocarb. The findings demonstrate the crucial role of NO in the development of neurotoxicity elicited by psychostimulants and underline the key role of NOS in AMPH-induced neurotoxicity.

Developmental exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) selectively decreases brain dopamine levels in Northern leopard frogs

Per- and polyfluoroalkyl substances (PFAS) are synthetic compounds that are a major public health concern due to widespread use, long environmental and biological half-lives, detection in most human plasma samples, and links to multiple adverse health outcomes. The literature suggests that some PFAS may be neurotoxic. However, there are major gaps in the literature with respect to how environmentally-relevant doses during development may influence the nervous system. To address this gap, we utilized a sentinel species, Northern leopard frogs (Lithobates pipiens) to determine the effects of developmental exposure to environmentally relevant perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on major neurotransmitter systems. Frog larvae at Gosner stage 25 were exposed to 10, 100, or 1000 ppb PFOS or PFOA for 30 days before neurochemical analysis. High performance liquid chromatography (HPLC) with electrochemical detection or fluorescent detection assays was used to measure neurotransmitter levels, which were normalized to protein levels in each sample. Dopamine (DA) decreased significantly in the brains of frogs treated with PFOA (1000 ppb) and PFOS (100 and 1000 ppb). Significant increases in DA turnover also resulted from PFOA and PFOS treatment. Neither PFOS, nor PFOA produced detectable alterations in serotonin (nor its metabolite), norepinephrine, gamma-amino butyric acid (GABA), glutamate, or acetylcholine. PFAS body burdens showed that PFOS accumulated relative to dose, while PFOA did not. These data suggest that DArgic neurotransmission is selectively affected in developmentally exposed amphibians and that PFAS should be evaluated for a potential role in diseases that target the DA system.

Bonding of Butylparaben, Bis(2-ethylhexyl)-phthalate, and Perfluorooctanesulfonic Acid to DNA: Comparison with Benzo[a]pyrene Shows Low Probability for Strong Noncovalent DNA Intercalation

Parabens, phthalates, and perfluorinated compounds are pollutant compounds used in cosmetics, plastics, and fire-fighting foams. All three compounds have been studied over several years for toxicity mechanism; however, a clear view of their ability to bind to DNA has not been supplied empirically. In this work, a simulation study is done to reveal the interaction of three of these pollutants, bis(2-ethylhexyl)-phthalate (DEHP), butylparaben (BPRB), and the protonated form of perfluorooctanesulfonic acid (PFOS(H)), with DNA. The results show that the DEHP, PFOS(H), and BPRB bind with a probability of 1/5 to DNA, with respective bonding energies -23.96 kJ/mol (PFOS(H)), -94.92 kJ/mol (BPRB), and -216.52 kJ/mol (DEHP). The positive control, benzo[a]pyrene diol epoxide (BAP), which is known for its notorious DNA intercalation, binds at a rate of 3/5 simulations, with bonding energies of -6544.52, -7034.66, and -7578.67 kJ/mol. The results are compared to empirical studies and conclusively show that all these pollutants can interfere with transcription and DNA related mechanisms by forming noncovalent interactions with DNA. The results show also that these pollutants are unlikely to undergo strong noncovalent intercalation to DNA, such as BAP, and do not possess the frontier orbital profiles to undergo adduct formation. After many years of research and several unanswered questions on the action of these pollutants on DNA, a calculation on their properties hence to the DNA confirms that there is a low probability for these to undergo a strong intercalation with DNA. Literature shows however that the pollutants are strongly interfering with the protein machinery and receptors on the cell surface and are therefore still priority pollutants for ecotoxicity research.

Behavioral deficits and neural damage of Caenorhabditis elegans induced by three rare earth elements

Rare earth elements (REEs) are widely used in industry, agriculture, medicine and daily life in recent years. However, environmental and health risks of REEs are still poorly understood. In this study, neurotoxicity of trichloride neodymium, praseodymium and scandium were evaluated using nematode Caenorhabditis elegans as the assay system. Median lethal concentrations (48 h) were 99.9, 157.2 and 106.4 mg/L for NdCl₃, PrCl₃ and ScCl₃, respectively. Sublethal dose (10-30 mg/L) of these trichloride salts significantly inhibited body length of nematodes. Three REEs resulted in significant declines in locomotor frequency of body bending, head thrashing and pharyngeal pumping. In addition, mean speed and wavelength of crawling movement were significantly reduced after chronic exposure. Using transgenic nematodes, we found NdCl₃, PrCl₃ and ScCl₃ resulted in loss of dendrite and soma of neurons, and induced down-expression of dat-1::GFP and unc-47::GFP. It indicates that REEs can lead to damage of dopaminergic and GABAergic neurons. Our data suggest that exposure to REEs may cause neurotoxicity of inducing behavioral deficits and neural damage. These findings provide useful information for understanding health risk of REE materials.

Neurodevelopmental Disorders and Environmental Toxicants: Epigenetics as an Underlying Mechanism

The increasing prevalence of neurodevelopmental disorders, especially autism spectrum disorders (ASD) and attention deficit hyperactivity disorder (ADHD), calls for more research into the identification of etiologic and risk factors. The Developmental Origin of Health and Disease (DOHaD) hypothesizes that the environment during fetal and childhood development affects the risk for many chronic diseases in later stages of life, including neurodevelopmental disorders. Epigenetics, a term describing mechanisms that cause changes in the chromosome state without affecting DNA sequences, is suggested to be the underlying mechanism, according to the DOHaD hypothesis. Moreover, many neurodevelopmental disorders are also related to epigenetic abnormalities. Experimental and epidemiological studies suggest that exposure to prenatal environmental toxicants is associated with neurodevelopmental disorders. In addition, there is also evidence that environmental toxicants can result in epigenetic alterations, notably DNA methylation. In this review, we first focus on the relationship between neurodevelopmental disorders and environmental toxicants, in particular maternal smoking, plastic-derived chemicals (bisphenol A and phthalates), persistent organic pollutants, and heavy metals. We then review studies showing the epigenetic effects of those environmental factors in humans that may affect normal neurodevelopment.

Brain-Derived Neurotrophic Factor Mediated Perfluorooctane Sulfonate Induced-Neurotoxicity via Epigenetics Regulation in SK-N-SH Cells

Perfluorooctane sulfonate (PFOS), a new kind of persistent organic pollutant, is widely distributed in the environment and exists in various organisms, where it is also a neurotoxic compound. However, the potential mechanism of its neurotoxicity is still unclear. To examine the role of epigenetics in the neurotoxicity induced by PFOS, SK-N-SH cells were treated with different concentrations of PFOS or control medium (0.1% DMSO) for 48 h. The mRNA levels of DNA methyltransferases (DNMTs) and Brain-derived neurotrophic factor (BDNF), microRNA-16, microRNA-22, and microRNA-30a-5p were detected by Quantitative PCR (QPCR). Enzyme Linked Immunosorbent Assay (ELISA) was used to measure the protein levels of BDNF, and a western blot was applied to analyze the protein levels of DNMTs. Bisulfite sequencing PCR (BSP) was used to detect the methylation status of the BDNF promoter I and IV. Results of MTT assays indicated that treatment with PFOS could lead to a significant decrease of cell viability, and the treated cells became shrunk. In addition, PFOS exposure decreased the expression of BDNF at mRNA and protein levels, increased the expression of microRNA-16, microRNA-22, microRNA-30a-5p, and decreased the expression of DNMT1 at mRNA and protein levels, but increased the expression of DNMT3b at mRNA and protein levels. Our results also demonstrate that PFOS exposure changes the methylation status of BDNF promoter I and IV. The findings of the present study suggest that methylation regulation of BDNF gene promoter and increases of BDNF-related-microRNA might underlie the mechanisms of PFOS-induced neurotoxicity.

Tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloropropyl) phosphate (TCPP) induce locomotor deficits and dopaminergic degeneration in Caenorhabditis elegans

Organophosphate flame retardants (PFRs) are a new class of flame retardants. The health risks of PFRs have received attention recently. However, little is known about the potential toxicity of PFRs on the nervous system. Herein, we evaluated the neurotoxic effects of two typical PFRs, tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloropropyl) phosphate (TCPP), using Caenorhabditis elegans. Median lethal concentrations of chronic exposure (3 d) were 1578 and 857 mg L-1 for TCEP and TCPP, respectively. The sublethal dose of TCEP or TCPP significantly inhibited the body length and reduced the lifespans of nematodes. 500 mg L-1 and above of TCEP/TCPP led to a significant decline in the locomotor frequency of body bending and head thrashing. Furthermore, their exposure reduced the crawling speed and the frequency of bending oscillation of nematodes. This indicates that TCEP/TCPP induces locomotor deficits, along with Parkinsonian-like movement impairment including bradykinesia and hypokinesia. Using transgenic worms, we found that TCEP/TCPP could induce down-expression of P dat-1 and resulted in the degeneration of dopaminergic neurons, especially PDE neurons. Moreover, TCEP/TCPP induced over-expression of unc-54, which indicates the aggregation of α-synuclein in the process of degeneration. These findings suggest the neurotoxicity risks of organophosphorus flame retardants, which are associated with the locomotor deficits and dopaminergic degeneration.

Leukemia inhibitory factor stimulates steroidogenesis of rat immature Leydig cells via increasing the expression of steroidogenic acute regulatory protein

Leukemia inhibitory factor (LIF) has many physiological roles. However, its effects on Leydig cell development are still unclear. Rat immature and adult Leydig cells were cultured with different concentrations of LIF alone or in combination with luteinizing hormone (LH) for 24 h. LIF (1 and 10 ng/ml) significantly increased androgen production in immature Leydig cells, but had no effects on testosterone production in adult Leydig cells. Further studies revealed that LIF dose-dependently increased Star and Hsd17b3 expression levels in immature Leydig cells. Gene microarray revealed that the upregulation of anti-oxidative genes and Star might contribute to LIF-induced androgen production. In conclusion, LIF has stimulatory effects on androgen production in rat immature Leydig cells.