Neurotoxic effects of perfluoroalkyl acids: Neurobehavioral deficit and its molecular mechanism

Prenatal exposure to per- and polyfluoroalkyl substances and child behavioral problems

BACKGROUND

Prenatal exposure to per- and polyfluoroalkyl substances (PFAS) may adversely affect child behaviors; however, findings of epidemiologic studies are inconsistent. We examined prenatal PFAS exposure in association with child behavioral problems.

METHODS

Participants were 177 mother-child pairs from MARBLES (Markers of Autism Risk in Babies - Learning Early Signs), a cohort with elevated familial likelihood of autism spectrum disorder (ASD). We quantified nine PFAS in maternal serum (1-3 samples per mother) collected from the 1st to 3rd trimesters of pregnancy. Child behavioral problems were assessed at 3 years of age using the Child Behavior Checklist (CBCL), developed to test for various behavioral problems of children. We examined associations of the CBCL scores with individual PFAS concentrations and with their mixture using negative binomial regression and weighted quantile sum regression models.

RESULTS

Higher prenatal perfluorononanoate (PFNA) concentrations were associated with higher scores of externalizing problems [β = 0.16, 95% CI (0.01, 0.32)] and aggressive behavior [β = 0.17 (0.01, 0.32)]. Higher PFNA, perfluorooctane sulfonate (PFOS), and perfluorodecanoate (PFDA) were associated with higher scores of sleep problems [β = 0.34 (0.15, 0.54) for PFNA, β = 0.20 (0.02, 0.37) for PFOS, and β = 0.19 (0.00, 0.37) for PFDA]. No significant associations observed for typically developing children, whereas PFOS, PFNA, and PFDA were associated with several behavioral problems among children diagnosed with ASD or other neurodevelopmental concerns. Exposure to a mixture of PFAS was associated with higher scores of sleep problems and aggressive behavior, mostly contributed by PFNA and PFDA.

CONCLUSIONS

Our study showed that prenatal exposure to some PFAS could increase child behavioral problems at 3 years of age. However, our results should be interpreted with caution because we relied on data from a cohort with increased familial likelihood of ASD and thereby had more behavioral problems.

Metabolic, neurotoxic and immunotoxic effects of PFAAs and their mixtures on the proteome of the head kidney and plasma from rainbow trout (Oncorhynchus mykiss)

PFAAs (Perfluoroalkyl acids) are a class of bioaccumulative, persistent and ubiquitous environmental contaminants which primarily occupy the hydrosphere and its sediments. Currently, a paucity of toxicological information exists for short chain PFAAs and complex mixtures. In order to address these knowledge gaps, we performed a 3-week, aqueous exposure of rainbow trout to 3 different concentrations of a PFAA mixture (50, 100 and 500 ng/L) modeled after the composition determined in Lake Ontario. We conducted an additional set of exposures to individual PFAAs (25 nM each of PFOS (12,500 ng/L), PFOA (10,300 ng/L), PFBS (7500 ng/L) or PFBA (5300 ng/L) to evaluate differences in biological response across PFAA congeners. Untargeted proteomics and phosphorylated metabolomics were conducted on the blood plasma and head kidney tissue to evaluate biological response. Plasma proteomic responses to the mixtures revealed several unexpected outcomes including Similar proteomic profiles and biological processes as the PFOS exposure regime while being orders of magnitude lower in concentration and an atypical dose response in terms of the number of significantly altered proteins (FDR < 0.1). Biological pathway analysis revealed the low mixture, medium mixture and PFOS to significantly alter (FDR < 0.05) a number of processes including those involved in lipid metabolism, oxidative stress and the nervous system. We implicate plasma increases in PPARD and PPARG as being directly related to these biological processes as they are known to be important regulators in all 3 processes. In contrast to the blood plasma, the high mixture and PFOA exposure regimes caused the greatest change to the head kidney proteome, altering many proteins being involved in lipid metabolism, oxidative stress and inflammation. Our findings support the pleiotropic effect PFAAs have on aquatic organisms at environmentally relevant doses including those on PPAR signaling, metabolic dysregulation, immunotoxicity and neurotoxicity.

Early-life perfluorooctanoic acid exposure disrupts the function of dopamine transporter protein with glycosylation changes implicating the links between decreased dopamine levels and disruptive behaviors in larval zebrafish

Exposure to perfluorooctanoic acid (PFOA) during early embryonic development is associated with the increased risk of developmental neurotoxicity and neurobehavioral disorders in children. In our previous study, we demonstrated that exposure to PFOA affected locomotor activity and disrupted dopamine-related gene expression in zebrafish larvae. Consequently, we continue to study the dopaminergic system with a focus on dopamine levels and dopamine's effect on behaviors in relation to PFOA exposure. In the present study, we found a decrease in dopamine levels in larval zebrafish. We studied the dopamine transporter (DAT) protein, which is responsible for regulating dopamine levels through the reuptake of dopamine in neuronal cells. We demonstrated that exposure to PFOA disrupted the glycosylation process of DAT, inhibited its uptake function, and induced endoplasmic reticulum (ER) stress in dopaminergic cells. Besides, we conducted a light-dark preference test on larval zebrafish and observed anxiety/depressive-like behavioral changes following exposure to PFOA. Dopamine is one of the most prominent neurotransmitters that significantly influences human behavior, with low dopamine levels being associated with impairments such as anxiety and depression. The anxiety-like response in zebrafish larvae exposure to PFOA implies the link with the reduced dopamine levels. Taken together, we can deduce that glycosylation changes in DAT lead to dysfunction of DAT to regulate dopamine levels, which in turn alters behavior in larval zebrafish. Therefore, alternation in dopamine levels may play a pivotal role in the development of anxiety/depressive-like behavioral changes induced by PFOA.

Perinatal exposure to PFOS and sustained high-fat diet promote neurodevelopmental disorders via genomic reprogramming of pathways associated with neuromotor development

Perfluorooctanesulfonic acid (PFOS) is a neurotoxic widespread organic contaminant which affects several brain functions including memory, motor coordination and social activity. PFOS has the ability to traverse the placenta and the blood brain barrier (BBB) and cause weight gain in female mice. It's also known that obesity and consumption of a high fat diet have negative effects on the brain, impairs cognition and increases the risk for the development of dementia. The combination effect of developmental exposure to PFOS and the intake of a high-fat diet (HFD) has not been explored. This study investigates the effect of PFOS and /or HFD on weight gain, behavior and transcriptomic and proteomic analysis of adult brain mice. We found that female mice exposed to PFOS alone showed an increase in weight, while HFD expectedly increased body weight. The combination of HFD and PFOS exacerbated generalized behavior such as time spent in the center and rearing, while PFOS alone impacted the distance travelled. These results suggest that PFOS exposure may promote hyperactivity. The combination of PFOS and HFD alter social behavior such as rearing and withdrawal. Although HFD interfered with memory retrieval, biomarkers of dementia did not change except for total Tau and phosphorylated Tau. Tau was impacted by either or both PFOS exposure and HFD. Consistent with behavioral observations, global cerebral transcriptomic analysis showed that PFOS exposure affects calcium signaling, MAPK pathways, ion transmembrane transport, and developmental processes. The combination of HFD with PFOS enhances the effect of PFOS in the brain and affects pathways related to ER stress, axon guidance and extension, and neural migration. Proteomic analysis showed that HFD enhances the impact of PFOS on inflammatory pathways, regulation of cell migration and proliferation, and MAPK signaling pathways. Overall, these data show that PFOS combined with HFD may reprogram the genome and modulate neuromotor development and may promote symptoms linked to attention deficit-hyperactivity disorders (ADHD) and autism spectrum disorders (ASD). Future work will be needed to confirm these connections.

Optimization for the analysis of 42 per- and polyfluorinated substances in human plasma: A high-throughput method for epidemiological studies

There is an increasing awareness about the presence of per- and polyfluoroalkyl substances (PFAS) in many environmental and biological compartments, including human biofluids and tissues. However, the increase of PFAS replacements, including alternatives with shorter chain or less bioaccumulative potential, has broaden the exposure and the need for wider identification procedures. Moreover, the low volumes available for human blood or plasma, and the high number of samples needed to assess adequately epidemiologic studies, require particularly fast, reproducible and, if possible, miniaturized protocols. Therefore, accurate and robust analytical methods are still needed to quantify the PFAS's burden in humans and to understand potential health risks. In this study, we have developed and validated the analysis of 42 PFAS in human plasma by means of a Captiva 96-well micro extraction plate and a LC-q-Orbitrap. For the optimization of the analytical workflow, three extraction/clean-up methods were tested, and the selected one was validated using spiked artificial and bovine plasma at four concentration levels. The final method showed high absolute recoveries for the 42 PFAS, ranging from 52% to 130%, instrumental detection limits between 0.001-0.6 ng mL-1, overall good precision (CV < 20% for most of the PFAS) and a low uncertainty (< 30% of relative expanded deviation, k = 2). The method was further validated both with the NIST plasma Standard Reference Material 1950, showing that the accuracy of the provided results was between 63%-101%, and by the proficiency test arranged by the Arctic Monitoring Assessment Program (AMAP, 2022) obtaining satisfactory results within 95% confidence interval of the assigned value.

Effects of subchronic exposure of perfluorooctane sulfonate on cognitive function of mice and its mechanism

Perfluorooctane sulfonate (PFOS) is an emerging persistent organic pollutant, and its potential impact on cognitive function remains unclear. We adopted the C57BL/6J mouse model to investigate the effect of PFOS on cognitive function, as well as the underlying mechanisms. Subchronic exposure was performed by administering PFOS via drinking water for 6 months (at doses of 0, 0.2, and 2.0 mg/kg/day), starting from 10.5 months old. The object recognition ability was tested at 2, 4, and 6 months of exposure, and spatial learning and memory were assessed at endpoint. The apoptosis of neurons and astrocytes in the cortex and hippocampus was analyzed, as well as the potential apoptotic signaling pathways. Our results showed that exposure to PFOS for 6 months caused a decrease in object recognition ability and a decline in learning and spatial memory. PFOS selectively increased apoptosis in neurons of the cerebral cortex and specifically activated the endoplasmic reticulum stress PERK/CHOP signaling pathway. In conclusion, our results confirmed that subchronic exposure to PFOS can lead to cognitive impairment in mice, which might be closely associated with the specific activation of an endoplasmic reticulum stress-induced pro-apoptosis pathway in the cerebral cortex neurons.

Integrative multi-omics reveals analogous developmental neurotoxicity mechanisms between perfluorobutanesulfonic acid and perfluorooctanesulfonic acid in zebrafish

The molecular mechanism of perfluorobutanesulfonic acid (PFBS), an alternative to legacy perfluorooctanesulfonic acid (PFOS), is not fully understood yet. Therefore, we conducted a developmental toxicity evaluation on zebrafish embryos exposed to PFBS and PFOS and assessed neurobehavioral changes at concentrations below each point of departure (POD) determined by embryonic mortality. Using transcriptomics, proteomics, and metabolomics, biomolecular perturbations in response to PFBS were profiled and then integrated for comparison with those for PFOS. Although PFBS (7525.47 μM POD) was approximately 700 times less toxic than PFOS (11.42 μM POD), altered neurobehavior patterns and affected kinds of endogenous neurochemicals were similar between PFBS and PFOS at the corresponding POD-based concentrations. Multi-omics analysis revealed that the PFBS neurotoxicity mechanism was associated with oxidative stress, lipid metabolism, and glycolysis/glucogenesis. The commonalities in developmental neurotoxicity-related mechanisms between PFBS and PFOS interconnected by knowledge-based integration of multi-omics included the calcium signaling pathway, lipid homeostasis, and primary bile acid biosynthesis. Despite being less toxic than PFOS, PFBS exhibited similar dysregulated molecular mechanisms, suggesting that chain length differences do not affect the intrinsic toxicity mechanism. Overall, carefully managing potential toxicity of PFBS can secure its status as an alternative to PFOS.

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.

Plasma concentrations of per- and polyfluoroalkyl substances are associated with perturbations in lipid and amino acid metabolism

Exposure to per- and polyfluoroalkyl substances (PFAS) through the environment can lead to harmful health outcomes and the development of disease. However, little is known about how PFAS impact underlying biology that contributes to these adverse health effects. The metabolome represents the end product of cellular processes and has been used previously to understand physiological changes that lead to disease. In this study, we investigated whether exposure to PFAS was associated with the global, untargeted metabolome. In a cohort of 459 pregnant mothers and 401 children, we quantified plasma concentrations of six individual PFAS- PFOA, PFOS, PFHXS, PFDEA, and PFNA- and performed plasma metabolomic profiling by UPLC-MS. In adjusted linear regression analysis, we found associations between plasma PFAS and perturbations in lipid and amino acid metabolites in both mothers and children. In mothers, metabolites of 19 lipid pathways and 8 amino acid pathways were significantly associated with PFAS exposure at an FDR<0.05 threshold; in children, metabolites of 28 lipid pathways and 10 amino acid pathways exhibited significant associations at FDR<0.05 with PFAS exposure. Our investigation found that metabolites of the Sphingomyelin, Lysophospholipid, Long Chain Polyunsaturated Fatty Acid (n3 and n6), Fatty Acid- Dicarboxylate, and Urea Cycle showed the most significant associations with PFAS, suggesting these may be particular pathways of interest in the physiological response to PFAS. To our knowledge, this is the first study to characterize associations between the global metabolome and PFAS across multiple periods in the life course to understand impacts on underlying biology, and the findings presented here are relevant in understanding how PFAS disrupt normal biological function and may ultimately give rise to harmful health effects.

Prenatal Exposure to Legacy and Alternative Per- and Polyfluoroalkyl Substances and Neuropsychological Development Trajectories over the First 3 Years of Life

The neurotoxic effects of prenatal exposure to per- and polyfluoroalkyl substances (PFAS) on offspring animals are well-documented. However, epidemiological evidence for legacy PFAS is inconclusive, and for alternative PFAS, it is little known. In this investigation, we selected 718 mother-child pairs from the Chinese Maoming Birth Cohort Study and measured 17 legacy and alternative PFAS in the third-trimester serum. Neuropsychological developments (communication, gross motor function, fine motor function, problem solving ability, and personal-social skills) were assessed at 3, 6, 12, 18, 24, and 36 months using the Ages and Stages Questionnaires 3rd edition. Trajectories of each subscale were classified into persistently low and persistently high groups via group-based trajectory modeling. Logistic regression and grouped weighted quantile sum were fitted to assess the potential effects of individual PFAS and their mixtures, respectively. Higher linear PFHxS levels were associated with elevated odds for the persistently low trajectories of communication (OR = 1.73; 95% CI: 1.12, 2.66) and problem solving ability (OR = 2.11; 95% CI: 1.14, 3.90). Similar findings were observed for linear PFOS, 1m-PFOS, PFDA, PFDoDA, PFUnDA, and legacy PFAS mixture. However, no association was observed for alternative PFAS and their mixture. We provided insights into the longitudinal links between prenatal legacy/alternative PFAS exposure and neuropsychological development trajectories over the first 3 years of life.

Tissue-specific accumulation, depuration, and effects of perfluorooctanoic acid on fish: Influences of aqueous pH and sex

Perfluorooctanoic acid (PFOA) is widely distributed in nature, particularly in aquatic environments. Its bioaccumulation and toxicity in aquatic organisms can be affected by both the chemical status of PFOA in water and the physiology of the organism. However, research on the patterns of these effects is scarce. In this study, we investigated the influence of aqueous pH (pH 6, acidic; pH 7.5, neutral; pH 9, basic) and fish sex on PFOA uptake, clearance, and biochemical effects in crucian carp (C. auratus) using flow-through exposure. In the 17-d kinetic experiment, PFOA bioaccumulation adhered to a uniform first-order model in which PFOA uptake rates from water to blood and liver in acidic conditions were faster than those in other conditions, indicating possible acidic pH influence on PFOA uptake. PFOA clearance rates in these compartments of males were slower than in females, which was attributed to the notably stronger expression of Oat2 (organic anion transporter 2, responsible for reabsorption) in the kidneys of males. Similar responses were observed for peroxisome proliferation-related biomarkers at different pH levels and in different sexes. These biochemical responses were driven by the internal concentrations of PFOA. The inhibition acetylcholinesterase activity in the fish brain was closely linked to changes in P-glycoprotein content, demonstrating a protective relationship. Collectively, an aqueous pH lower than 7.5 might affect the uptake of PFOA by fish. The clearance discrepancies between the sexes highlight the importance of anion carriers for ionizable organic compounds in aquatic organisms.

Glioma is associated with exposure to legacy and alternative per- and polyfluoroalkyl substances

Data on the occurrences of legacy and alternative per- and polyfluoroalkyl substances (PFASs) in glioma are scarce. It remains unclear if PFASs exposure is related to the prevalence of glioma. A total of 137 glioma and 40 non-glioma brain tissue samples from patients recruited from the Nanfang Hospital, South China were analyzed for 17 PFAS compounds. Perfluorohexanoic acid, perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorooctane sulfonamide (FOSA), and 6:2 chlorinated polyfluorinated ether sulfonate were frequently detected (> 60 %) in glioma. The total concentrations (range; median) of 17 PFASs in glioma (0.20-140; 3.1 ng g^-1) were slightly higher than those in non-glioma (0.35-32; 2.2 ng g^-1), but without statistical significance. The PFAS concentrations in males were statistically higher (p < 0.05) than those in females. Elevated glioma grades were associated with higher concentrations of PFOA, PFOS, and FOSA. Positive correlations were observed between PFAS concentrations (especially for PFOA) and Ki-67 or P53 expression, pathological molecular markers of glioma. Our findings suggested that exposure to PFASs might increase the probability to develop glioma. This is the first case study demonstrating associations between PFASs exposure and brain cancer. More evidences and potential pathogenic mechanisms warranted further investigations.

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.

Neurotransmission Targets of Per- and Polyfluoroalkyl Substance Neurotoxicity: Mechanisms and Potential Implications for Adverse Neurological Outcomes

Per- and polyfluoroalkyl substances (PFAS) are a group of persistent environmental pollutants that are ubiquitously found in the environment and virtually in all living organisms, including humans. PFAS cross the blood-brain barrier and accumulate in the brain. Thus, PFAS are a likely risk for neurotoxicity. Studies that measured PFAS levels in the brains of humans, polar bears, and rats have demonstrated that some areas of the brain accumulate greater amounts of PFAS. Moreover, in humans, there is evidence that PFAS exposure is associated with attention-deficit/hyperactivity disorder (ADHD) in children and an increased cause of death from Parkinson's disease and Alzheimer's disease in elderly populations. Given possible links to neurological disease, critical analyses of possible mechanisms of neurotoxic action are necessary to advance the field. This paper critically reviews studies that investigated potential mechanistic causes for neurotoxicity including (1) a change in neurotransmitter levels, (2) dysfunction of synaptic calcium homeostasis, and (3) alteration of synaptic and neuronal protein expression and function. We found growing evidence that PFAS exposure causes neurotoxicity through the disruption of neurotransmission, particularly the dopamine and glutamate systems, which are implicated in age-related psychiatric illnesses and neurodegenerative diseases. Evaluated research has shown there are highly reproduced increased glutamate levels in the hippocampus and catecholamine levels in the hypothalamus and decreased dopamine in the whole brain after PFAS exposure. There are significant gaps in the literature relative to the assessment of the nigrostriatal system (striatum and ventral midbrain) among other regions associated with PFAS-associated neurologic dysfunction observed in humans. In conclusion, evidence suggests that PFAS may be neurotoxic and associated with chronic and age-related psychiatric illnesses and neurodegenerative diseases. Thus, it is imperative that future mechanistic studies assess the impact of PFAS and PFAS mixtures on the mechanism of neurotransmission and the consequential functional effects.

PFOS-induced thyroid hormone system disrupted rats display organ-specific changes in their transcriptomes

Perfluorooctanesulfonic acid (PFOS) is a persistent anthropogenic chemical that can affect the thyroid hormone system in humans and animals. In adults, thyroid hormones (THs) are regulated by the hypothalamic-pituitary-thyroid (HPT) axis, but also by organs such as the liver and potentially the gut microbiota. PFOS and other xenobiotics can therefore disrupt the TH system at various locations and through different mechanisms. To start addressing this, we exposed adult male rats to 3 mg PFOS/kg/day for 7 days and analysed effects on multiple organs and pathways simultaneously by transcriptomics. This included four primary organs involved in TH regulation, namely hypothalamus, pituitary, thyroid, and liver. To investigate a potential role of the gut microbiota in thyroid hormone regulation, two additional groups of animals were dosed with the antibiotic vancomycin (8 mg/kg/day), either with or without PFOS. PFOS exposure decreased thyroxine (T4) and triiodothyronine (T3) without affecting thyroid stimulating hormone (TSH), resembling a state of hypothyroxinemia. PFOS exposure resulted in 50 differentially expressed genes (DEGs) in the hypothalamus, 68 DEGs in the pituitary, 71 DEGs in the thyroid, and 181 DEGs in the liver. A concomitant compromised gut microbiota did not significantly change effects of PFOS exposure. Organ-specific DEGs did not align with TH regulating genes; however, genes associated with vesicle transport and neuronal signaling were affected in the hypothalamus, and phase I and phase II metabolism in the liver. This suggests that a decrease in systemic TH levels may activate the expression of factors altering trafficking, metabolism and excretion of TH. At the transcriptional level, little evidence suggests that the pituitary or thyroid gland is involved in PFOS-induced TH system disruption.

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.

Non-targeted metabolomics and associations with per- and polyfluoroalkyl substances (PFAS) exposure in humans: A scoping review

OBJECTIVE

To summarize the application of non-targeted metabolomics in epidemiological studies that assessed metabolite and metabolic pathway alterations associated with per- and polyfluoroalkyl substances (PFAS) exposure.

RECENT FINDINGS

Eleven human studies published before April 1st, 2021 were identified through database searches (PubMed, Dimensions, Web of Science Core Collection, Embase, Scopus), and citation chaining (Citationchaser). The sample sizes of these studies ranged from 40 to 965, involving children and adolescents (n = 3), non-pregnant adults (n = 5), or pregnant women (n = 3). High-resolution liquid chromatography-mass spectrometry was the primary analytical platform to measure both PFAS and metabolome. PFAS were measured in either plasma (n = 6) or serum (n = 5), while metabolomic profiles were assessed using plasma (n = 6), serum (n = 4), or urine (n = 1). Four types of PFAS (perfluorooctane sulfonate(n = 11), perfluorooctanoic acid (n = 10), perfluorohexane sulfonate (n = 9), perfluorononanoic acid (n = 5)) and PFAS mixtures (n = 7) were the most studied. We found that alterations to tryptophan metabolism and the urea cycle were most reported PFAS-associated metabolomic signatures. Numerous lipid metabolites were also suggested to be associated with PFAS exposure, especially key metabolites in glycerophospholipid metabolism which is critical for biological membrane functions, and fatty acids and carnitines which are relevant to the energy supply pathway of fatty acid oxidation. Other important metabolome changes reported included the tricarboxylic acid (TCA) cycle regarding energy generation, and purine and pyrimidine metabolism in cellular energy systems.

CONCLUSIONS

There is growing interest in using non-targeted metabolomics to study the human physiological changes associated with PFAS exposure. Multiple PFAS were reported to be associated with alterations in amino acid and lipid metabolism, but these results are driven by one predominant type of pathway analysis thus require further confirmation. Standardizing research methods and reporting are recommended to facilitate result comparison. Future studies should consider potential differences in study methodology, use of prospective design, and influence from confounding bias and measurement errors.

Uptake of perfluoroalkyl substances, pharmaceuticals, and parabens by oyster mushrooms (Pleurotus ostreatus) and exposure risk in human consumption

Organic micropollutants (MPs) pose potential threats to environmental ecosystems and human health. This study investigated uptake of perfluoroalkyl substances (PFASs), pharmaceuticals, and paraben by edible oyster mushrooms (Pleurotus ostreatus), cultivated on spiked growth substrate. Concentrations of pharmaceuticals and paraben in substrate showed a decreasing trend over a 20-day harvesting period, whereas PFAS concentrations were variable over the harvesting period. However, only propylparaben, clarithromycin, and PFASs were detected in fruiting bodies of oyster mushroom. Uptake of PFASs by oyster mushroom fruit bodies was negatively correlated with perfluorocarbon chain length. An impact of MPs on fungal colonization was observed, with decreased respiration in treatments with the highest concentration of MPs, but production of fruiting bodies was not affected by exposure level. The potential human risk from ingestion of MPs was evaluated for oyster mushrooms exposed to the highest concentration of MPs in substrate, based on acceptable daily intake (ADI).

The association between maternal perfluoroalkyl substances exposure and early attention deficit hyperactivity disorder in children: a systematic review and meta-analysis

Some studies have shown that maternal exposure to perfluoroalkyl substances (PFASs) may be associated with early attention deficit hyperactivity disorder (ADHD) in children. The purpose of this systematic review and meta-analysis is to verify this association by reviewing existing studies and to provide a strong basis for preventing ADHD. The researchers searched electronic databases such as PubMed, Science Direct, Scopus, Google Scholar, Web of Science, and Embase for all studies published before October 2020. Finally, we included nine articles for analysis. Our meta-analysis showed that maternal exposure to PFASs was not significantly associated with the prevalence rate of early childhood ADHD (perfluorooctanoic acid (PFOA), odds ratio (OR) = 1.00, 95% confidence interval (95% CI) = 0.75-1.25; perfluorooctane sulfonate (PFOS), OR = 1.01, 95% CI = 0.88-1.14; perfluorohexane sulfonate (PFHxS), OR = 1.08, 95% CI = 0.80-1.09; perfluorononanoic acid (PFNA), OR = 1.13, 95% CI = 0.99-1.28; perfluorodecanoic acid (PFDA), OR = 1.23, 95% CI = 0.15-2.32). Due to significant heterogeneity, we subsequently performed subgroup analysis and sensitivity analysis. Through subgroup analysis, we found that PFOS concentration of children's blood and the prevalence rate of early childhood ADHD were statistically positively correlated, and there was also a positive correlation between PFOS exposure and the prevalence rate of early childhood ADHD in the America. Moreover, there was also a statistically positive correlation between PFNA concentration in maternal blood and the prevalence rate of early childhood ADHD. Sensitivity analysis showed that the final results did not change much, the sensitivity was low, and the results were relatively stable. In conclusion, a causal relationship between maternal PFASs exposure and ADHD in children was unlikely. Among them, PFOS, PFNA, and ADHD might have positive associations worthy of further investigation.

Perfluoroalkyl Substances in the Western Tropical Atlantic Ocean

The dispersion of perfluoroalkyl substances (PFAS) in surface and deep-water profiles (down to 5845 m deep) was evaluated through the Western Tropical Atlantic Ocean (TAO) between 15°N and 23°S. The sum concentrations for eight quantifiable PFAS (∑₈PFAS) in surface waters ranged from 11 to 69 pg/L, which is lower than previously reported in the same area as well as in higher latitudes. Perfluoroalkyl carboxylic acids (PFCAs) were the predominant PFASs present in the Western TAO. The 16 surface samples showed variable PFAS distributions, with the predominance of perfluorooctanoic acid (PFOA) along the transect (67%; 11 ± 8 pg/L) and detection of perfluoroalkyl sulfonic acids (PFSAs) only in the Southern TAO. Perfluoroheptanoic acid (PFHpA) was often detected in the vertical profiles. PFAS distribution patterns (i.e., profiles and concentrations) varied with depth throughout the TAO latitudinal sectors (North, Equator, South Atlantic, and in the Brazilian coastal zone). Vertical profiles in coastal samples displayed decreasing PFAS concentrations with increasing depth, whereas offshore samples displayed higher PFAS detection frequencies in the intermediate water masses. Together with the surface currents and coastal upwelling, the origin of the water masses was an important factor in explaining PFAS concentrations and profiles in the TAO.

Behavioral effects of early-life exposure to perfluorooctanoic acid might synthetically link to multiple aspects of dopaminergic neuron development and dopamine functions in zebrafish larvae

Perfluorooctanoic acid (PFOA) is known as an environmental endocrine disruptor and has developmental neurotoxicity that could be associated with behavior changes in human and animal studies. Previous studies have shown that PFOA might affect the dopaminergic nervous system. However, the mode of action underlying the effects of PFOA remains poorly understood. Our study used zebrafish as an animal model to investigate the effects of early-life PFOA exposure on dopaminergic neuron development and dopamine functions in zebrafish larvae. Zebrafish fertilized eggs were exposed to different concentrations of PFOA (0, 10, 100, 1000 μg/L). After exposure to PFOA for 7 days, the locomotor activity of zebrafish was decreased; the mRNA levels of nuclear receptor subfamily 4 group a member 2b (nr4a2b), paired box 2 and 5 (pax2, pax5), tyrosine hydroxylase 1/2 (th1/th2) and dopamine transporter (dat) were increased; mRNA and protein level of mesencephalic astrocyte-derived neurotrophic factor (manf) were decreased. Neural cell proliferation in the preoptic area of hypothalamus was increased. In conclusion, dopaminergic neuron development might be one of the targets of early-life PFOA exposure. The neurobehavior changes induced by PFOA exposure might link to multiple aspects of dopaminergic neuron development and dopamine functions in zebrafish larvae.

Perfluorononanoic acid impedes mouse oocyte maturation by inducing mitochondrial dysfunction and oxidative stress

Perfluorononanoic acid (PFNA), a member of PFAS, is frequently detected in human blood and tissues, even in follicular fluid of women. The exposure of PFNA, but not PFOA and PFOS, is positively correlated with miscarriage and increased time to pregnancy. Toxicological studies indicated that PFNA exposure is associated with immunotoxicity, hepatotoxicity, developmental toxicity, and reproductive toxicity in animals. However, there is little information regarding the toxic effects of PFNA on oocyte maturation. In this study, we investigated the toxic effects of PFNA exposure on mouse oocyte maturation in vitro. Our results showed that 600 μM PFNA significantly inhibited germinal vesicle breakdown (GVBD) and polar body extrusion (PBE) in mouse oocytes. Our further study revealed that PFNA induced abnormal metaphase I (MI) spindle assembly, evidenced by malformed spindles and mislocalization of p-ERK1/2 in PFNA-treated oocytes. We also found that PFNA induced abnormal mitochondrial distribution and increased mitochondrial membrane potential. Consequently, PFNA increased reactive oxygen species (ROS) levels, leading to oxidative stress, DNA damage, and eventually early-stage apoptosis in oocytes. In addition, after 14 h culture, PFNA disrupted the formation of metaphase II (MII) spindle in most PFNA-treated oocytes with polar bodies. Collectively, our results indicate that PFNA interferes with oocyte maturation in vitro via disrupting spindle assembly, damaging mitochondrial functions, and inducing oxidative stress, DNA damage, and early-stage apoptosis.

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.

Chemical Aspects of Human and Environmental Overload with Fluorine

Over the last 100-120 years, due to the ever-increasing importance of fluorine-containing compounds in modern technology and daily life, the explosive development of the fluorochemical industry led to an enormous increase of emission of fluoride ions into the biosphere. This made it more and more important to understand the biological activities, metabolism, degradation, and possible environmental hazards of such substances. This comprehensive and critical review focuses on the effects of fluoride ions and organofluorine compounds (mainly pharmaceuticals and agrochemicals) on human health and the environment. To give a better overview, various connected topics are also discussed: reasons and trends of the advance of fluorine-containing pharmaceuticals and agrochemicals, metabolism of fluorinated drugs, withdrawn fluorinated drugs, natural sources of organic and inorganic fluorine compounds in the environment (including the biosphere), sources of fluoride intake, and finally biomarkers of fluoride exposure.

Perfluoroalkyl substances and cognitive function in older adults: Should we consider non-monotonic dose-responses and chronic kidney disease?

BACKGROUND

Although potential neurotoxicity of perfluoroalkyl and polyfluoroalkyl substances (PFAS) is suggested, previous epidemiologic studies have reported a 'protective' association between serum PFAS concentration and cognition function. Poor outcome assessment, residual confounding, non-monotonic dose-responses (NMDRs), and the role of reduced kidney function in PFAS excretion may be alternative explanations of these findings.

OBJECTIVES

We examined the association of perfluoroalkyls with cognitive functions assessed using the Consortium to Establish a Registry for Alzheimer's Disease word learning and recall; the Animal Fluency; and the Digit Symbol Substitution tests.

METHODS

We included 903 adults aged ≥60 years from the National Health and Nutrition Examination Survey (NHANES) 2011-2014. We computed a composite z-score as an average of four individual cognitive z-scores and used it as the outcome. Linear and generalized additive models were used to evaluate linear and non-linear associations.

RESULTS

With the linearity assumption, perfluorooctanoate (PFOA) and perfluorononanoate (PFNA) were significantly positively associated with composite z-score after adjustment for age, sex, race/ethnicity, education, smoking, poverty-income ratio, health insurance, food security, alcohol, and physical activity. Smoothing plots suggested NMDRs, especially for perfluorooctane sulfonate (PFOS) with a U-shape dose-response. When restricting to participants without chronic kidney disease (CKD) (n = 613), the positive associations for PFOA and PFNA observed in the whole population diminished, whereas PFOS was inversely and significantly associated with composite z-score. Also, negative confounding effects of fish/seafood consumption seem to be substantial. Effect estimates of composite z-score were -0.055 (95% CI: -0.097, -0.012, P = 0.01) for a doubling increase in PFOS.

DISCUSSION

These findings suggest that the previous epidemiologic findings of a 'protective' association between PFAS and cognition may be explained by CKD, NMDRs and confounding by fish consumption. PFOS at the current population exposure level in the U.S. may be a risk factor for cognitive decline in older adults with normal kidney function.

Environmental neurotoxic pollutants: review

Environmental pollutants are recognized as one of the major concerns for public health and responsible for various forms of neurological disorders. Some of the common sources of environmental pollutants related to neurotoxic manifestations are industrial waste, pesticides, automobile exhaust, laboratory waste, and burning of terrestrial waste. Among various environmental pollutants, particulate matter, ultrafine particulate matter, nanoparticles, and lipophilic vaporized toxicant (acrolein) easily cross the blood-brain barrier, activate innate immune responses in the astrocytes, microglia, and neurons, and exert neurotoxicity. Growing shreds of evidence from human epidemiological studies have correlated the environmental pollutants with neuroinflammation, oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, myelin sheath disruption, and alterations in the blood-brain barrier anatomy leading to cognitive dysfunction and poor quality of life. These environmental pollutants also considerably cause developmental neurotoxicity, exhibit teratogenic effect and mental growth retardance, and reduce IQ level. Until now, the exact mechanism of pollutant-induced neurotoxicity is not known, but studies have shown interference of pollutants with the endogenous antioxidant defense system, inflammatory pathway (Nrf2/NF-kB, MAPKs/PI3K, and Akt/GSK3β), modulation of neurotransmitters, and reduction in long-term potentiation. In the current review, various sources of pollutants and exposure to the human population, developmental neurotoxicity, and molecular mechanism of different pollutants involved in the pathogenesis of different neurological disorders have been discussed.

Adverse effects of perfluoroalkyl acids on fish and other aquatic organisms: A review

Perfluoroalkyl acids (PFAAs) have been widely used in many industrial and consumer products. They have been detected ubiquitously in ambient water along with other environmental matrices, and their adverse effects on aquatic organisms have been a subject of active investigation. Here, we intended to summarize and synthesize the existing body of knowledge on PFAA toxicity through an extensive literature review, and shed light on areas where further research is warranted. PFAA toxicity appears to be influenced by the sex and developmental stages of aquatic organisms, but not significantly by exposure route. PFAA-induced aquatic toxicity could be classified as metabolism disturbance, reproduction disruption, oxidative stress, developmental toxicity, thyroid disruption, etc. At the molecular level, these responses can be initiated by key events, such as nuclear receptor activation, reactive oxygen species induction, or interaction with a membrane, followed by a cascade of downstream responses. PFAA-induced toxicity involves diverse metabolic processes, and therefore elucidating crosstalk or interactions among diverse metabolic pathways is a challenging task. In the presence of other chemicals, PFAAs can function as agonists or antagonists, resulting in different directions of combined toxicity. Therefore, mixture toxicity with other groups of chemicals is another research opportunity. Experimental evidence supports the trans-generational toxicity of PFAAs, suggesting that their long-term consequences for aquatic ecosystems should become of concern. A recent global ban of several PFAAs resulted in an increasing dependence on PFAA alternatives. The lack of sufficient toxicological information on this emerging group of chemicals warrant caution and rigorous toxicological assessments.

Omics approach reveals perturbation of metabolism and phenotype in Caenorhabditis elegans triggered by perfluorinated compounds

Perfluorinated compounds (PFCs) are widely used in consumer products because of their remarkable endurance. However, their distinct stability prolongs degradation, resulting in bioaccumulation in the environment which is a severe environmental issue. Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are principal constituents in the PFCs. In this study, the potential toxic effects of PFOS and PFOA were evaluated by adopting an in vivo animal model, Caenorhabditis elegans (C. elegans). The uptake of PFCs was confirmed by the quantification of internal concentration in C. elegans. Metabolomics and lipidomics were applied along with reproduction assay and reactive oxygen species (ROS) assay. In the C. elegans exposed to PFOS and PFOA, amino acids including phenylalanine, tyrosine, and tryptophan, were significantly affected. Also, various species that belong to glycerophospholipids and triacylglycerol were perturbed in the exposed groups. The alteration patterns of the lipidome in PFOS and PFOA treated C. elegans were significantly different. Additionally, dichlorodihydrofluorescein diacetate (H₂DCFDA)-based ROS assay revealed increased internal ROS in PFOS (1.5 fold, p-value = 0.0067) and PFOA (1.46 fold, p-value = 0.0253) groups. Decrease in reproduction was confirmed in PFOS (0.53 fold, p-value < 0.0001) and PFOA (0.69 fold, p-value = 0.0003) by counting progeny. Collectively, our findings suggest that exposure to PFCs in C. elegans leads to perturbation of various phenotypes as well as crucial amino acid and lipid metabolism.

PFOS Modulates Interactive Epigenetic Regulation in First-Trimester Human Trophoblast Cell Line HTR-8/SVneo

Organic compounds have been linked to adverse pregnancy complications. Perfluorooctanesulfonic acid (PFOS), a man-made fluorosurfactant and global pollutant, has been shown to induce oxidative stress in various cell types. Oxidative stress plays a key role in leading several placental diseases including preeclampsia (PE), gestational diabetes, spontaneous abortion, preterm labor, and intrauterine growth restriction. Recently, epigenetic regulation such as histone modifications, DNA methylation, and microRNAs (miRNAs), are shown to be associated with oxidative stress as well as pregnancy complications such as PE. However, whether PFOS exerts its detrimental effects in the placenta through epigenetics remains to be unveiled. Therefore, we aimed to investigate the effect of PFOS-induced reactive oxygen species (ROS) generation in first trimester human trophoblast cell line (HTR-8/SV_neo) and whether epigenetic regulation is involved in this process. When treated with a range of PFOS doses at 24 and 48 h, even at 10 μM, it significantly increased the ROS production and decreased gene and protein expression, respectively, of the DNA methyltransferases DNMT1 (p < 0.001; p < 0.05), DNMT3A (p < 0.001; p < 0.05), and DNMT3B (p < 0.01; p < 0.01) and the sirtuins, for example, SIRT1 (p < 0.001; p < 0.001) and SIRT3 (p < 0.001; p < 0.05), while reducing global DNA methylation (p < 0.01) and increasing protein lysine acetylation (p < 0.001) as compared to vehicle controls. Interestingly, PFOS (10 μM) significantly increased miR29-b (p < 0.01), which has been previously reported to be associated with PE. The observed epigenetic effects were shown to be dependent on the expression of miR-29b, as knockdown of miR-29b significantly alters the gene and protein expression of DNMT1, DNMT3A, DNMT3B, SIRT1, and SIRT3 and ROS production as well as global DNA methylation and protein acetylation. This study provides for the first time a novel insight into PFOS-induced ROS generation via regulation of sets of the interactive epigenetic circuit in the placenta, which may lead to pregnancy complications.

Perfluorooctanoic acid-induced toxicities in chicken embryo primary cardiomyocytes: Roles of PPAR alpha and Wnt5a/Frizzled2

Perfluorooctanoic acid (PFOA) is a widespread persistent organic pollutant and may induce developmental toxicities, including developmental cardiotoxicity. To explore the potential mechanism of developmental cardiotoxicity induced by PFOA exposure, chicken embryo primary cardiomyocytes were extracted either from chicken embryos pretreated with PFOA (2 mg/kg), or from untreated embryos and then directly exposed cells to PFOA (1, 10, 30 or 100 μg/ml) in culture. Additionally, peroxisome proliferator activated receptor alpha (PPAR alpha) silencing lentivirus was applied to the embryos on embryonic day (ED2). Cell viability was measured with CCK-8 kit, morphology was assessed with hematoxylin and eosin staining, and intracellular Ca²⁺ concentrations were determined with Fluo-4 AM probe. Western blotting was utilized to confirm PPAR alpha silencing efficiency and the protein abundance of Wnt5a and Frizzled2. The results indicated that both PFOA pretreatment and direct exposure decreased primary cardiomyocyte viability, altered cell morphology and increased intracellular Ca²⁺ concentrations. While l-carnitine co-treatment effectively abolished such changes, PPAR alpha silencing only abolished most of the changes in PFOA pretreatment group, but not in cells directly exposed to relatively high doses of PFOA. The protein abundance of Wnt5a and Frizzled2 was increased by PFOA pretreatment, while direct exposure to PFOA increased Frizzled2 abundance but decreased Wnt5a abundance. PPAR alpha silencing resulted in over 50% decrease of PPAR alpha expression level, which abolished the Wnt5a/Frizzled2 expression alterations following PFOA exposure. In conclusion, PFOA-induced primary cardiomyocyte toxicity is associated with PPAR alpha and Wnt5a/Frizzled2, in which PPAR alpha seems to play regulatory roles towards Wnt5a/Frizzled2.

Toxicokinetics of Perfluorinated Alkyl Acids Influences Their Toxic Potency in the Zebrafish Embryo ( Danio rerio)

Perfluorinated alkyl acids (PFAA) are highly persistent and bioaccumulative and have been associated with several adverse health effects. The chemical structure mainly differs in two ways: the length of the hydrophobic alkyl chain and the type of hydrophilic end group. Little is known how the chemical structure affects the toxicokinetics (TK) in different organisms. We studied the TK of four PFAA (PFOS, PFHxS, PFOA, and PFBA) with different chain lengths (4-8 carbons) and functional groups (sulfonic and carboxylic acid) in zebrafish ( Danio rerio) embryo. The time courses of the external (ambient water) and internal concentrations were determined at three exposure concentrations from 2 up to 120 h postfertilization (hpf). Three of the four PFAA showed a biphasic uptake pattern with slow uptake before hatching (around 48 hpf) and faster uptake thereafter. A two-compartment TK model adequately described the biphasic uptake pattern, suggesting that the chorion functions as an uptake barrier until 48 hpf. The bioconcentration factors (BCF) determined at 120 hpf varied widely between PFAA with averages of approximately 4000 (PFOS), 200 (PFHxS), 50 (PFOA), and 0.8 (PFBA) L kg dry weight^-1, suggesting that both the alkyl chain length and the functional group influence the TK. The differences in toxic potency were reduced by 3 orders of magnitude when comparing internal effect concentrations instead of effective external concentrations.