Effect of long- and short-chain perfluorinated compounds on cultured thyroid cells viability and response to TSH

Do PFCAs drive the establishment of thyroid cancer microenvironment? Effects of C6O4, PFOA and PFHxA exposure in two models of human thyroid cells in primary culture

BACKGROUND

Exposure to environmental pollutants is suspected to be one of the potential causes accounting for the increase in thyroid cancer (TC) incidence worldwide. Among the ubiquitous pollutants, per-polyfluoroalkyl substances (PFASs), were demonstrated to exert thyroid disrupting effects. Perfluoroalkyl carboxylates (PFCAs) represent a subgroup of PFAS and include perfluoro carboxylic acids (PFOA and PFHxA) and perfluoropolyether carboxylic acid (C6O4). The potential relationship between exposure to PFCAs and TC was not yet fully elucidated. This in vitro study investigated whether certain PFCAs (C6O4, PFOA, and PFHxA) can influence the composition of TC microenvironment.

METHODS

Two models of normal thyroid cells in primary cultures: Adherent (A-NHT) and Spheroids (S-NHT) were employed. A-NHT and S-NHT were exposed to C6O4, PFOA or PFHxA (0; 0.01; 0.1, 1; 10; 100; 1000 ng/mL) to assess viability (WST-1 and AV/PI assay), evaluate spherification index (SI) and volume specifically in S-NHT. CXCL8 and CCL2 (mRNA and protein), and EMT-related genes were assessed in both models after exposure to PFCAs.

RESULTS

PFHxA reduced the viability of both A-NHT and S-NHT. None of the PFCAs interfered with the volume or spherification process in S-NHT. CXCL8 and CCL2 mRNA and protein levels were differently up-regulated by each PFCAs, being PFOA and PFHxA the stronger inducers. Moreover, among the tested PFCAs, PFHxA induced a more consistent increase in the mRNA levels of EMT-related genes.

CONCLUSIONS

This is the first evaluation of the effects of exposure to PFCAs on factors potentially involved in establishing the TC microenvironment. PFHxA modulated the TC microenvironment at three levels: cell viability, pro-tumorigenic chemokines, and EMT-genes. The results provide further evidence of the pro-tumorigenic effect of PFOA. On the other hand, a marginal effect was observed for C6O4 on pro-tumorigenic chemokines.

Perfluorooctane sulfonate (PFOS) and its selected analogs induce various cell death types in peripheral blood mononuclear cells

The perfluoalkyl substance (PFASs) perfluorooctane sulfonate (PFOS) has been widely used in industry. However, PFOS is a persistent organic pollutant and has been gradually replaced by its short-chain analogs, perfluorohexane sulfonate (PFHxS) and perfluorobutane sulfonate (PFBS). PFASs are extremely persistent and are very frequently detected among the general population. The aim of the study was to determine the effect of selected PFASs on peripheral blood mononuclear cells (PBMCs) and the mechanisms of their action. PBMCs were exposed to PFOS, PFBS and PFHxS at concentrations ranging from 0.02 to 400 μM for 24 h, they were then tested for viability, apoptosis (changes in cytosolic calcium ions level and caspase-3, -8 and -9 activation), ferroptosis (changes in chelatable iron ions level and lipid peroxidation), and autophagy (LC3-II and Raptor level assay). PFOS exposure decreased cell viability, increased calcium ion level and caspase-8 activation; it also enhanced lipid peroxidation and increased the intracellular pool of chelatable iron ions as well as LC3-II protein content. In contrast, short-chain PFBS and PFHxS induced significant changes in the markers of apoptosis but had no substantial impact on ferroptosis or autophagy markers over a wide range of concentrations. Our results indicate that only PFOS demonstrated pro-ferroptotic and pro-autophagic potential but observed changes occurred at relatively high exposure. A short-chain substitute (PFBS) exhibited strong pro-apoptotic potential at concentrations related to occupational exposure. While the short-chain PFASs strongly affected the mitochondrial pathway of apoptosis, apoptosis itself was only induced by PFBS via the intrinsic and extrinsic pathways. It seems that the length of the carbon chain in PFASs appears to determine the cell death mechanisms activated in human PBMCs following exposure. Our findings provide a new insight into the immune toxicity mechanism induced by these compounds.

Perfluorooctanesulfonic acid (PFOS) disrupts cadherin-16 in the developing rat thyroid gland

Perfluorooctanesulfonic acid (PFOS) can disrupt the thyroid hormone (TH) system in rodents, potentially affecting perinatal growth and neurodevelopment. Some studies also suggest that gestational exposure to PFOS can lead to lower TH levels throughout life, indicating that PFOS may compromise thyroid gland development. To address this question, we utilized a rat thyroid gland ex vivo culture system to study direct effects of PFOS on the developing thyroid. No significant changes to follicular structure or size were observed with 1 µM or 10 µM PFOS exposure. However, the transcription factor Foxe1, together with Tpo and Lrp2, were upregulated, whereas the key transcription factor Pax8 and its downstream target gene Cdh16 were significantly downregulated at the transcript level, observed with both RT-qPCR and RNAscope. Notably, Cdh16 expression was not uniformly downregulated across Cdh16-postive cells, but instead displayed a patchy expression pattern across the thyroid gland. This is a significant change in expression pattern compared to control thyroids where Cdh16 is expressed relatively uniformly. The disrupted expression pattern was also seen at the protein level. This suggests that PFOS exposure can impact follicular growth and structure. Compromised follicle integrity, if irreversible, could help explain reduced TH synthesis postnatally. This view is supported by observed changes to Tpo and Lrp2 expression, two factors that play a role in TH synthesis.

Perfluorooctanoic acid disrupts thyroid-specific genes expression and regulation via the TSH-TSHR signaling pathway in thyroid cells

Perfluorooctanoic acid (PFOA) is a highly persistent and widespread chemical in the environment with endocrine disruption effects. Although it has been reported that PFOA can affect multiple aspects of thyroid function, the exact mechanism by which it reduces thyroxine levels has not yet been elucidated. In this study, FRTL-5 rat thyroid follicular cells were used as a model to study the toxicity of PFOA to the genes related to thyroid hormone synthesis and their regulatory network. Our results reveal that PFOA interfered with the phosphorylation of the cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB) induced by thyroid-stimulating hormone (TSH), as well as the transcription levels of paired box 8 (PAX8), thyroid transcription factor 1 (TTF1), sodium/iodide cotransporter (NIS), thyroglobulin (TG), and thyroid peroxidase (TPO). However, the above outcomes can be alleviated by enhancing cAMP production with forskolin treatment. Further investigations showed that PFOA reduced the mRNA level of TSH receptor (TSHR) and impaired its N-glycosylation, suggesting that PFOA has disrupting effects on both transcriptional regulation and post-translational regulation. In addition, PFOA increased endoplasmic reticulum (ER) stress and decreased ER mass in FRTL-5 cells. Based on these findings, it can be inferred that PFOA disrupts the TSH-activated cAMP signaling pathway by inhibiting TSHR expression and its N-glycosylation. We propose that this mechanism may contribute to the decrease in thyroid hormone levels caused by PFOA. Our study sheds light on the molecular mechanism by which PFOA can disrupt thyroid function and provides new insights and potential targets for interventions to counteract the disruptive effects of PFOA.

PFOA, PFHxA and C6O4 differently modulate the expression of CXCL8 in normal thyroid cells and in thyroid cancer cell lines

Industrial chemical PFAS are persistent pollutants. Long chain PFAS were taken out of production due to their risk for human health, however, new congeners PFAS have been introduced. The in vitro effects of the long-chain PFOA, the short-chain PFHxA and the new-generation C6O4 were evaluated in normal and in thyroid cancer cell lines in terms of cell viability and proliferation, and secretion of a pro-tumorigenic chemokine (CXCL8), both at the mRNA and at the protein level. The Nthy-ory 3-1 normal-thyroid cell line, the TPC-1 and the 8505C (RET/PTC rearranged and BRAFV600e mutated, respectively) thyroid-cancer cell lines were exposed to increasing concentrations of each PFAS in a time-course. We evaluated viability using WST-1 (confirmed by AnnexinV/PI) and proliferation using the cristal-violet test. To evaluate CXCL8 mRNA we used RT-PCR and measured CXCL8 in the supernatants by ELISA. The exposure to none PFAS did not affect thyroid cells viability (except for a reduction of 8505C cells viability after 144 h) or proliferation. Individual PFAS differently modulated CXCL8 mRNA and protein level. PFOA increased CXCL8 both at mRNA and protein level in the three cell lines; PFHxA increased CXCL8 mRNA in the three cell lines, but increased the protein only in TPC-1 cells; C6O4 increased the CXCL8 mRNA only in thyroid cancer cell lines, but never increased the CXCL8 protein. The results of the present study indicate that the in vitro exposure to different PFAS may modulate both at the mRNA and secreted protein levels of CXCL8 in normal and cancer thyroid cells. Strikingly different effects emerged according to the specific cell type and to the targeted analyte (CXCL8 mRNA or protein).

A continuous in silico learning strategy to identify safety liabilities in compounds used in the leather and textile industry

There is a widely recognized need to reduce human activity's impact on the environment. Many industries of the leather and textile sector (LTI), being aware of producing a significant amount of residues (Keßler et al. 2021; Liu et al. 2021), are adopting measures to reduce the impact of their processes on the environment, starting with a more comprehensive characterization of the chemical risk associated with the substances commonly used in LTI. The present work contributes to these efforts by compiling and toxicologically annotating the substances used in LTI, supporting a continuous learning strategy for characterizing their chemical safety. This strategy combines data collection from public sources, experimental methods and in silico predictions for characterizing four different endpoints: CMR, ED, PBT, and vPvB. We present the results of a prospective validation exercise in which we confirm that in silico methods can produce reasonably good hazard estimations and fill knowledge gaps in the LTI chemical space. The proposed protocol can speed the process and optimize the use of resources including the lives of experimental animals, contributing to identifying potentially harmful substances and their possible replacement by safer alternatives, thus reducing the environmental footprint and impact on human health.

Efficacy and mechanism of lipoic acid in the treatment of reproductive injury caused by perfluorooctanoic acid

Environmental pollutants, including perfluorooctanoic acid (PFOA), cause severe reproductive damage to humans and animals. Lipoic acid (LA) is a strong antioxidant that alleviates the oxidative damage caused by heavy metals, environmental toxicants, chemical poisons, etc. Therefore, the present study investigated the curative effect and mechanism of LA in treating spermatogenesis dysfunction caused by PFOA. A rat reproductive injury model was established by gavage of PFOA for consecutive 30 days and then rats were treated with different doses of LA for 42 days. The effects were assessed by ELISA, western blotting, H&E staining and immunofluorescence staining. The results demonstrated that LA had ameliorating effects on PFOA-induced reproductive injury in rats, it increased the sperm counts, and the levels of serum succinate dehydrogenase, lactate dehydrogenase, glutathione peroxidase and superoxide dismutase returned to normal levels following LA treatment. In addition, LA promoted the expression of estradiol, reduced the expression of serum sex hormones, such as follicle-stimulating hormone, androgen receptor (AR) and malondialdehyde in the testes, and restored the structure of seminiferous tubules. Its therapeutic mechanisms include regulating the testicular oxidative stress pathway and hypothalamic-pituitary-testis axis.

Association of per- and polyfluoroalkyl substances with thyroid homeostasis during pregnancy in the SELMA study

OBJECTIVES

To investigate the association of exposure to per- and polyfluoroalkyl substances (PFAS) during early pregnancy with markers of the maternal thyroid system.

METHODS

Serum concentrations of seven PFAS as well as thyroid stimulating hormone (TSH), free and total thyroxine (FT4 and TT4), free and total triiodothyronine (FT3 and TT3) were measured in pregnant women in early pregnancy in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study. Outcomes were concentrations of TSH and thyroid hormones, FT4/FT3 or TT4/TT3 ratios, TSH/FT4 ratio as a marker of the negative feedback loop, TT4/FT4 or TT3/FT3 ratios as markers of the binding of thyroid hormones to binding proteins.

RESULTS

The study population comprised 2,008 women with median (95% range) gestational age of 10 (6-14) weeks. There was no association between PFAS and TSH. Higher PFNA, PFDA, PFHpA and PFOA levels were associated with a higher FT4 (largest effect estimate for PFDA: β [95% CI]: 0.27 [0.10 to 0.45], P = 0.002). Higher PFUnDA levels, but no other PFAS, were associated with a lower FT3 (β [95% CI]: -0.05 [-0.09 to -0.01], P = 0.005). Higher PFUnDA levels were associated with lower TT4 (β [95% CI]: -1.58 [-3.07 to -0.09]) and there was an inverted U-shaped association of PFOS with TT4 (P = 0.03). Higher PFDA, PFUnDA, PFHpA levels were associated with a lower TT3. Overall, higher PFAS concentrations were associated with a higher FT4/FT3 ratio and a higher TT4/TT3 ratio. There was no association of PFAS with the TSH/FT4 ratio. Higher concentrations of several PFAS were associated with lower TT4/FT4 and TT3/FT3 ratios.

CONCLUSIONS

These findings translate results from experimental studies suggesting that exposure to PFAS may interfere with the thyroid system during pregnancy. Further experimental studies should take into account human evidence to better understand the potential underlying mechanisms of thyroid disruption by PFAS exposure.

Lack of interaction of the fluorosurfactant C6O4 with human renal transporters: In vitro/in silico analysis

C6O4 is a water soluble perfluoroether carboxylic acid ammonium salt used as surfactant in the synthesis of fluoropolymers. Available experimental data in rats exposed by the oral route indicate it is eliminated in urine. Previous studies with various linear perfluorocarboxylic acids have suggested that these compounds are substrates of renal membrane transporters in rats and humans, and that the interaction with basal and apical membrane transporters can influence the elimination kinetic by these organisms and explain, in part, the observed differences in the respective half-lives. In particular, apical transporters may contribute to the reuptake of these exogenous compounds from the tubule lumen. The present study was designed to investigate the uptake of C6O4 in two renal cell lines transiently transfected with the human apical membrane transporters, organic anion transporter 4 (OAT4), and urate transporter 1 (URAT1). The uptake of the linear perfluorohexanoic acid (PFC6) was evaluated in parallel. While the uptake of the conjugated steroid estrone-3-sulfate (E3S), a known substrate for renal transporters, and of PFC6 was clearly observed in both cell types transfected with either OAT4 or URAT1, no significant uptake of C6O4 was measured under the same test conditions. The results of the transporter's functionality measured in vitro were consistent with molecular docking simulations. Both outward and inward models of the transporters showed a reduced interaction between C6O4 and URAT1 or OAT4. In contrast, more stable interactions were predicted for PFC6 and PFOA, as well as for the E3S substrate, as shown by the respective docking scores reflecting the binding strength and by the poses assumed in the transporter channels. Altogether, the in vitro and in silico modeling results showed a low reuptake potential and limited interactions of C6O4 molecule with two human apical membrane transporters, contrasting with the more efficient reuptake of PFC6 from the tubule lumen. These results suggest reabsorption from the proximal tubule by apical renal transporters is not likely to interfere with the elimination pathway of C6O4 in humans.

Early Warnings by Liver Organoids on Short- and Long-Chain PFAS Toxicity

Short-chain per-fluoroalkyl substances (PFAS) have replaced long-chains in many applications, however the toxicity and its mode of action and interactions due to the large number of these compounds and their mixtures is still poorly understood. The paper aims to compare the effects on mouse liver organoids (target organ for bioaccumulation) of two long-chain PFAS (perfluorooctane sulfonate -PFOS-, perfluorooctanoic acid -PFOA) and two short-chain PFAS commonly utilized in the industry (heptafluorobutyric acid -HFBA-, Pentafluoropropionic anhydride-PFPA) to identify the mode of action of these classes of contaminants. Cytomorphological aberrations and ALT/GDH enzyme disruption were identified but no acute toxicity endpoint neither apoptosis was detected by the two tested short-chain PFAS. After cytomorphological analysis, it is evident that short-chain PFAS affected organoid morphology inducing a reduction of cytostructural complexity and aberrant cytological features. Conversely, EC50 values of 670 ± 30 µM and 895 ± 7 µM were measured for PFOS and PFOA, respectively, together with strong ALT/GDH enzyme disruption, caspase 3 and 7 apoptosis activation and deep loss of architectural complexity of organoids in the range of 500–1000 µM. Eventually, biochemical markers and histology analysis confirmed the sensitivity of organoid tests that could be used as a fast and reproducible platform to test many PFAS and mixtures saving time and at low cost in comparison with in vivo tests. Organoids testing could be introduced as an innovative platform to assess the toxicity to fast recognize potentially dangerous pollutants.

Producing Fluorine- and Lubricant-Free Flexible Pathogen- and Blood-Repellent Surfaces Using Polysiloxane-Based Hierarchical Structures

High-touch surfaces are known to be a major route for the spread of pathogens in healthcare and public settings. Antimicrobial coatings have, therefore, garnered significant attention to help mitigate the transmission of infectious diseases via the surface route. Among antimicrobial coatings, pathogen-repellent surfaces provide unique advantages in terms of safety in public settings such as instant repellency, affordability, biocompatibility, and long-term stability. While there have been many advances in the fabrication of biorepellent surfaces in the past two decades, this area of research continues to suffer challenges in scalability, cost, compatibility with high-touch applications, and performance for pathogen repellency. These features are critical for high-touch surfaces to be used in public settings. Additionally, the environmental impact of manufacturing repellent surfaces remains a challenge, mainly due to the use of fluorinated coatings. Here, we present a flexible hierarchical coating with straightforward and cost-effective manufacturing without the use of fluorine or a lubricant. Hierarchical surfaces were prepared through the growth of polysiloxane nanostructures using n-propyltrichlorosilane (n-PTCS) on activated polyolefin (PO), followed by heat shrinking to induce microscale wrinkles. The developed coatings demonstrated repellency, with contact angles over 153° and sliding angles <1°. In assays mimicking touch, these hierarchical surfaces demonstrated a 97.5% reduction in transmission of Escherichia coli (E.coli), demonstrating their potential as antimicrobial coatings to mitigate the spread of infectious diseases. Additionally, the developed surfaces displayed a 93% reduction in blood staining after incubation with human whole blood, confirming repellent properties that reduce bacterial deposition.

PFAS Molecules: A Major Concern for the Human Health and the Environment

Per- and polyfluoroalkyl substances (PFAS) are a group of over 4700 heterogeneous compounds with amphipathic properties and exceptional stability to chemical and thermal degradation. The unique properties of PFAS compounds has been exploited for almost 60 years and has largely contributed to their wide applicability over a vast range of industrial, professional and non-professional uses. However, increasing evidence indicate that these compounds represent also a serious concern for both wildlife and human health as a result of their ubiquitous distribution, their extreme persistence and their bioaccumulative potential. In light of the adverse effects that have been already documented in biota and human populations or that might occur in absence of prompt interventions, the competent authorities in matter of health and environment protection, the industries as well as scientists are cooperating to identify the most appropriate regulatory measures, substitution plans and remediation technologies to mitigate PFAS impacts. In this review, starting from PFAS chemistry, uses and environmental fate, we summarize the current knowledge on PFAS occurrence in different environmental media and their effects on living organisms, with a particular emphasis on humans. Also, we describe present and provisional legislative measures in the European Union framework strategy to regulate PFAS manufacture, import and use as well as some of the most promising treatment technologies designed to remediate PFAS contamination in different environmental compartments.

Per- and poly-fluoroalkyl substances (PFAS) and female reproductive outcomes: PFAS elimination, endocrine-mediated effects, and disease

Per- and poly-fluoroalkyl substances (PFAS) are widespread environmental contaminants frequently detected in drinking water supplies worldwide that have been linked to a variety of adverse reproductive health outcomes in women. Compared to men, reproductive health effects in women are generally understudied while global trends in female reproduction rates are declining. Many factors may contribute to the observed decline in female reproduction, one of which is environmental contaminant exposure. PFAS have been used in home, food storage, personal care and industrial products for decades. Despite the phase-out of some legacy PFAS due to their environmental persistence and adverse health effects, alternative, short-chain and legacy PFAS mixtures will continue to pollute water and air and adversely influence women's health. Studies have shown that both long- and short-chain PFAS disrupt normal reproductive function in women through altering hormone secretion, menstrual cyclicity, and fertility. Here, we summarize the role of a variety of PFAS and PFAS mixtures in female reproductive tract dysfunction and disease. Since these chemicals may affect reproductive tissues directly or indirectly through endocrine disruption, the role of PFAS in breast, thyroid, and hypothalamic-pituitary-gonadal axis function are also discussed as the interplay between these tissues may be critical in understanding the long-term reproductive health effects of PFAS in women. A major research gap is the need for mechanism of action data - the targets for PFAS in the female reproductive and endocrine systems are not evident, but the effects are many. Given the global decline in female fecundity and the ability of PFAS to negatively impact female reproductive health, further studies are needed to examine effects on endocrine target tissues involved in the onset of reproductive disorders of women.

Comparative Evaluation of the Effects of Legacy and New Generation Perfluoralkyl Substances (PFAS) on Thyroid Cells In Vitro

BACKGROUND

Per- and poly-fluorinated alkyl substances (PFAS) are environment-persitent emerging endocrine disrupting chemicals raising health concerns worldwide. Exposure to PFAS has been associated with the imbalance of thyroid hormones. However, available studies addressing the cell mechanism underlying thyroid disrupting feature of legacy PFAS, such as perfluoro-octanoic acid (PFOA), perfluoro-octane-sulfonic acid (PFOS), and the new generation substitutes, such as C6O4, are still lacking. In this study the potential disrupting effect of PFOA, PFOS, and C6O4 on a murine thyroid cell model was assessed.

METHODS

A rat FRTL-5 cell line was used as the normal thyroid follicular cell model. Cell iodide-uptake, induced by thyroid stimulating hormone (TSH), was used to assess the functional impact of PFAS exposure on cell function. Tetrazolium salt-based cell viability assay and merocyanine 540-based cell staining were used to address the possible involvement of cell toxicity and membrane biophysical properties on altered cell function. The possible direct interaction of PFAS with TSH-receptor (TSH-R) was investigated by computer-based molecular docking and analysis of molecular dynamics. Evaluation of intracellular cAMP levels and gene expression analysis were used to validate the direct impairment of TSH-R-mediated downstream events upon PFAS exposure.

RESULTS

Different from PFOS or C6O4, exposure to PFOA at a concentration ≥ 10 ng/mL was associated with significant impairment of the iodide uptake upon TSH stimulation (respectively: basal 100.0 ± 19.0%, CTRL + TSH 188.9 ± 7.8%, PFOA 10 ng/mL + TSH 120.4 ± 20.9%, p= 0.030 vs CTRL + TSH; PFOA 100 ng/mL + TSH 115,6 ± 12,3% p= 0.017 vs CTRL + TSH). No impairment of cell viability or membrane stability was observed. Computational analysis showed a possible direct differential interaction of C6O4, PFOA, and PFOS on a same binding site of the extracellular domain of TSH-R. Finally, exposure to PFOA was associated with a significant reduction of downstream intracellular cAMP levels and both sodium-iodide transporter and thyroperoxidase gene expression upon TSH-R stimulation.

CONCLUSIONS

Our data suggest that legacy and new generation PFAS can differentially influence TSH dependent signaling pathways through the direct interaction with TSH-R.

Varied thyroid disrupting effects of perfluorooctanoic acid (PFOA) and its novel alternatives hexafluoropropylene-oxide-dimer-acid (GenX) and ammonium 4,8-dioxa-3H-perfluorononanoate (ADONA) in vitro

Due to its potential adverse effects on human health, perfluorooctanoic acid (PFOA), one of the once widely used legacy per- and polyfluoroalkyl substances (PFASs), has been recently replaced by its novel alternatives including hexafluoropropylene-oxide-dimer-acid (GenX) and ammonium 4,8-dioxa-3H-perfluorononanoate (ADONA). These alternative PFASs are detected in water and exposed workers. PFASs can enter organs like thyroids, however, it is yet unknown whether the new alternatives are safer than PFOA. In the current study, we compared the thyroid disrupting effects of PFOA and its alternatives GenX and ADONA in vitro with both rat thyroid cell line FRTL5 and primary normal human thyroid (NHT) cells. Cells were exposed to ascendant doses of PFOA, GenX or ADONA for various incubation time and cell viability was assessed by WST-1 assay and LDH assay. The proliferation rate of survived cells was determined by crystal violet-based cell proliferation assay and MTT assay. The gene expression of thyroid hormone regulation-related genes in thyroid cells after exposure was quantified by RT-PCR and Western blot. Our data showed that both PFOA and GenX reduced thyroid cell viability in both dose and time dependent manner, with GenX being more toxic than PFOA at the same condition. Similarly, the proliferation rate of cells survived exposure to PFOA and GenX was considerably impaired, with GenX showing more profound adverse effect than PFOA. Unlike PFOA and GenX, ADONA showed no apparent adverse effects on the viability and proliferation of both thyroid cell types. Gene expression data revealed that all three PFASs altered gene expression in both thyroid cells and the altered gene expression seemed to be PFAS and cell type dependent. Taken together, our data reveal that the thyroid disrupting effects is increased in the order of GenX > PFOA > ADONA. Our findings will be beneficial for the guidance of the future usage of PFASs and development of better alternatives.

The new generation PFAS C6O4 does not produce adverse effects on thyroid cells in vitro

PURPOSE

Per- and poly-fluoroalkyl-substances (PFASs) are synthetic compounds that raised concern due to their potential adverse effects on human health. Long-chain PFAS were banned by government rules in many states, and thus, new emerging PFAS were recently introduced as substitutes. Among these, Perfluoro{acetic acid, 2-[(5-methoxy-1,3-dioxolan-4-yl)oxy]}, ammonium salt (C6O4) was recently introduced to produce a range of food contact articles and literature data about this compound are scanty. The aim of this study was to evaluate the in vitro effects of exposure to C6O4, compared with PFOA and PFOS on thyroid cells.

METHODS

FRTL5 rat-thyroid cell lines and normal human thyroid cells (NHT) were incubated with increasing concentrations of C6O4 for 24, 48, 72, and 144 h to assess cell viability by WST-1. Cell viability was confirmed by AnnexinV/PI staining. Long-chain PFAS (PFOA and PFOS) were used at same concentrations as positive controls. The proliferation of cells exposed to C6O4, PFOA, and PFOS was measured by staining with crystal violet and evaluation of optical density after incubation with SDS. Changes in ROS production by FRTL5 and NHT after exposure to C6O4 at short (10, 20, and 30 min) and long-time points (24 h) were evaluated by cytofluorimetry.

RESULTS

C6O4 exposure did not modify FRTL5 and NHT cell viability at any concentration and/or time points with no induction of necrosis/apoptosis. At difference, PFOS exposure reduced cell viability of FRTL5 while and NHT, while PFOA only in FRTL5. FRTL5 and NHT cell proliferation was reduced by incubation with by PFOA and PFOS, but not with C6O4. ROS production by NHT and FRTL5 cells was not modified after C6O4 exposure, at any time/concentration tested.

CONCLUSIONS

The present in vitro study constitutes the first evaluation of the potential adverse effects of the new emerging PFAS C6O4 in cultured rat and human thyroid cells, suggesting its safety for thyroid cells in vitro.

Adverse effects of in vitro GenX exposure on rat thyroid cell viability, DNA integrity and thyroid-related genes expression

The hexafluoropropylene-oxide-dimer-acid (GenX) is a short-chain perfluoroalkyl substance that was recently introduced following the phase out of PFOA, as an alternative for the process of polymerization. GenX was detected at high concentrations in rivers, drinking water and in sera of exposed workers and recent findings suggested its potential dangerousness for human health. Aim of the study was to assess the consequences of GenX exposure on in vitro thyroid cells with particular attention to the effects on cell-viability, proliferation, DNA-damage and in the thyroid-related genes expression. FRTL-5 rat-thyroid cell line were incubated with increasing concentrations of GenX for 24 h, 48 h and 72 h to assess cell viability by WST-1. DNA-damage was assessed by comet assay and further confirmed by micronucleus assay. The proliferation of survived cells was measured by staining with crystal violet and evaluation of its optical density after incubation with SDS. Changes in TTF-1, Pax8, Tg, TSH-R, NIS and TPO genes expression were evaluated by RT-PCR. GenX exposure reduced FRTL-5 viability in a time and dose-dependent manner (24 h: ANOVA F = 22.286; p < 0.001; 48 h: F = 43.253, p < 0.001; 72 h: F = 49.708, p < 0.001). Moreover, GenX exerted a genotoxic effect, as assessed by comet assay (significant increase in tail-length, olive-tail-moment and percentage of tail-DNA) and micronucleus assay, both at cytotoxic and non-cytotoxic concentrations. Exposure to GenX at concentrations non-cytotoxic exerted a significant lowering of the expression of the regulatory gene TTF-1 (p < 0.05 versus untreated) and higher expression of Pax-8 (p < 0.05 versus untreated) and a down-regulation of NIS (p < 0.05 versus untreated). In addition, cells survived to GenX exposure showed a reduced re-proliferation ability (24 h: ANOVA F = 11,941; p < 0,001; 48 h: F = 93.11; p < 0.001; 72 h F = 21.65; p < 0.001). The exposure to GenX produces several toxic effects on thyroid cells in vitro. GenX is able to promote DNA-damage and to affect the expression of thyroid transcription-factor genes.

Interaction between hypoxia and perfluorobutane sulfonate on developmental toxicity and endocrine disruption in marine medaka embryos

The co-occurrence of hypoxia and xenobiotics is extremely common in natural environments, highlighting the necessity to elicit their interaction on aquatic toxicities. In the present study, marine medaka embryos were exposed to various concentrations (nominal 0, 1, 3.3 and 10 mg/L) of perfluorobutane sulfonate (PFBS), an environmental pollutant of emerging concern, under either normoxia (6.9 mg/L) or hypoxia (1.7 mg/L) condition. After acute exposure till 15 days post-fertilization, single or combined toxicities of PFBS and hypoxia on embryonic development (e.g., mortality, hatching and heartbeat) and endocrine systems were investigated. Sex and thyroid hormones were measured by enzyme-linked immunosorbent assay. Transcriptional changes of endocrine genes were determined by quantitative real-time PCR assays. Co-exposure to 10 mg/L PFBS and hypoxia caused a further reduction in survival rate and heart beat compared to single exposure. PFBS induced a precocious hatching, while no larvae hatched under hypoxia condition. By disturbing the balance of sex hormones, either PFBS or hypoxia single exposure produced an anti-estrogenic activity in medaka larvae. However, PFBS and hypoxia combinations reversed to estrogenic activity in co-exposed larvae. Variation in disrupting pattern may be attributed to the interactive effects on steroidogenic pathway involving diverse cytochrome P450 enzymes. Regarding thyroid system, PFBS exposure caused detriments of multiple processes along thyroidal axis (e.g., feedback regulation, synthesis and transport of thyroid hormones, receptor-mediated signaling and thyroid gland development), while hypoxia potently impaired the development and function of thyroid gland. Combinations of PFBS and hypoxia interacted to dysregulate the function of thyroid endocrine system. In summary, the present study revealed the dynamic interaction of PFBS pollutant and hypoxia on aquatic developmental toxicities and endocrine disruption. Considering the frequent co-occurrence of xenobiotics and hypoxia, current results would be beneficial to improve our understanding about their interactive mechanisms and provide baseline evidences for accurate ecological risk evaluation.

Thyroid Disrupting Effects of Old and New Generation PFAS

Per- and polyfluoroalkyl substances (PFAS) represent a group of synthetic compounds widely used in industry plants due to their low grade of degradation, surfactant properties, thermic and flame resistance. These characteristics are useful for the industrial production, however they are also potentially dangerous for human health and for the environment. PFAS are persistent pollutants accumulating in waters and soil and recoverable in foods due to their release by food packaging. Humans are daily exposed to PFAS because these compounds are ubiquitous and, when assimilated, they are difficult to be eliminated, persisting for years both in humans and animals. Due to their persistence and potential danger to health, some old generation PFAS have been replaced by newly synthesized PFAS with the aim to use alternative compounds presumably safer for humans and the environment. Yet, the environmental pollution with PFAS remains a matter of concern worldwide and led to large-scale epidemiological studies both on plants' workers and on exposed people in the general population. In this context, strong concern emerged concerning the potential adverse effects of PFAS on the thyroid gland. Thyroid hormones play a critical role in the regulation of metabolism, and thyroid function is related to cardiovascular disease, fertility, and fetal neurodevelopment. In vitro, ex vivo data, and epidemiological studies suggested that PFASs may disrupt the thyroid hormone system in humans, with possible negative repercussions on the outcome of pregnancy and fetal-child development. However, data on the thyroid disrupting effect of PFAS remain controversial, as well as their impact on human health in different ages of life. Aim of the present paper is to review recent data on the effects of old and new generation PFAS on thyroid homeostasis. To this purpose we collected information from in vitro studies, animal models, and in vivo data on exposed workers, general population, and pregnant women.