Human detoxification of perfluorinated compounds

Individual and joint associations of per- and polyfluoroalkyl substances (PFAS) with gallstone disease in adults: A cross-sectional study

Disturbances in the enterohepatic circulation are important biological mechanisms for causing gallstones and also have important effects on the metabolism of Per- and polyfluoroalkyl substances (PFAS). Moreover, PFAS is associated with sex hormone disorder which is another important cause of gallstones. However, it remains unclear whether PFAS is associated with gallstones. In this study, we used logistic regression, restricted cubic spline (RCS), quantile g-computation (qg-comp), Bayesian kernel machine regression (BKMR), and subgroup analysis to assess the individual and joint associations of PFAS with gallstones and effect modifiers. We observed that the individual associations of perfluorodecanoic acid (PFDeA) (OR: 0.600, 95% CI: 0.444 to 0.811), perfluoroundecanoic acid (PFUA) (OR: 0.630, 95% CI: 0.453 to 0.877), n-perfluorooctane sulfonic acid (n-PFOS) (OR: 0.719, 95% CI: 0.571 to 0.906), and perfluoromethylheptane sulfonic acid isomers (Sm-PFOS) (OR: 0.768, 95% CI: 0.602 to 0.981) with gallstones were linearly negative. Qg-comp showed that the PFAS mixture (OR: 0.777, 95% CI: 0.514 to 1.175) was negatively associated with gallstones, but the difference was not statistically significant, and PFDeA had the highest negative association. Moreover, smoking modified the association of perfluorononanoic acid (PFNA) with gallstones. BKMR showed that PFDeA, PFNA, and PFUA had the highest groupPIP (groupPIP = 0.93); PFDeA (condPIP = 0.82), n-perfluorooctanoic acid (n-PFOA) (condPIP = 0.68), and n-PFOS (condPIP = 0.56) also had high condPIPs. Compared with the median level, the joint association of the PFAS mixture with gallstones showed a negative trend; when the PFAS mixture level was at the 70th percentile or higher, they were negatively associated with gallstones. Meanwhile, when other PFAS were fixed at the 25th, 50th, and 75th percentiles, PFDeA had negative associations with gallstones. Our evidence emphasizes that PFAS is negatively associated with gallstones, and more studies are needed in the future to definite the associations of PFAS with gallstones and explore the underlying biological mechanisms.

Personal Strategies to Reduce the Cardiovascular Impacts of Environmental Exposures

Ubiquitous environmental exposures increase cardiovascular disease risk via diverse mechanisms. This review examines personal strategies to minimize this risk. With regard to fine particulate air pollution exposure, evidence exists to recommend the use of portable air cleaners and avoidance of outdoor activity during periods of poor air quality. Other evidence may support physical activity, dietary modification, omega-3 fatty acid supplementation, and indoor and in-vehicle air conditioning as viable strategies to minimize adverse health effects. There is currently insufficient data to recommend specific personal approaches to reduce the adverse cardiovascular effects of noise pollution. Public health advisories for periods of extreme heat or cold should be observed, with limited evidence supporting a warm ambient home temperature and physical activity as strategies to limit the cardiovascular harms of temperature extremes. Perfluoroalkyl and polyfluoroalkyl substance exposure can be reduced by avoiding contact with perfluoroalkyl and polyfluoroalkyl substance-containing materials; blood or plasma donation and cholestyramine may reduce total body stores of perfluoroalkyl and polyfluoroalkyl substances. However, the cardiovascular impact of these interventions has not been examined. Limited utilization of pesticides and safe handling during use should be encouraged. Finally, vasculotoxic metal exposure can be decreased by using portable air cleaners, home water filtration, and awareness of potential contaminants in ground spices. Chelation therapy reduces physiological stores of vasculotoxic metals and may be effective for the secondary prevention of cardiovascular disease.

Association between serum perfluoroalkyl substances concentrations and non-alcoholic fatty liver disease among Korean adults: a cross-sectional study using the National Environmental Health Survey cycle 4

Background

Perfluoroalkyl substances (PFAS) are widely used in industry and daily life due to their useful properties. They have a long half-life, accumulate in the body, and there is evidence that they are associated with biomarkers of lipid metabolism and liver damage. This may suggest non-alcoholic fatty liver disease (NAFLD) caused by PFAS. However, since there has been no study analyzing the relationship between PFAS and NAFLD in the entire population in Korea. We sought to confirm the relationship between serum PFAS concentration and NAFLD prevalence in Korean adults using the Korean National Environmental Health Survey (KoNEHS) cycle 4.

Methods

The study was conducted on 2,529 subjects in 2018-2019 among KoNEHS participants. For the diagnosis of NAFLD, the hepatic steatosis index (HSI) was used, and the geometric mean and concentration distribution of serum PFAS were presented. Logistic regression was performed to confirm the increase in the risk of NAFLD due to changes in PFAS concentration, and the odds ratio and 95% confidence interval (CI) were calculated.

Results

In both adjusted and unadjusted models, an increased odds ratio was observed with increasing serum concentrations of total PFAS and perfluorooctane sulfonate (PFOS) in the non-obese group. In the adjusted model, the odds ratios for serum total PFAS and PFOS were 6.401 (95% CI: 1.883-21.758) and 7.018 (95% CI: 2.688-18.319).

Conclusions

In this study, a higher risk of NAFLD based on HSI was associated with serum total PFAS, PFOS in non-obese group. Further research based on radiological or histological evidence for NAFLD diagnosis and long-term prospective studies are necessary. Accordingly, it is necessary to find ways to reduce exposure to PFAS in industry and daily life.

Substantial decrease of PFAS with anion exchange resin treatment - A clinical cross-over trial

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are heat and stain resisting chemicals. They are persistent, bioaccumulating and spread ubiquitously. Many hotspots where humans are exposed to high levels of PFAS have been reported. A few small observational studies in humans suggest that treatment with an Anion Exchange Resin (AER) decreases serum PFAS. This first clinical controlled crossover study aimed to assess whether AER decreases perfluorooctanesulfonic acid (PFOS) in highly exposed adults.

METHODS

An open label 1:1 randomized treatment sequence crossover study with allocation to oral AER (cholestyramine 4 g three times daily) or observation for 12 weeks was conducted among citizens from a PFAS hotspot. Main inclusion criteria was serum PFOS > 21 ng/mL. Primary endpoint was change in serum PFOS levels between treatment and observational period.

RESULTS

In total, 45 participants were included with a mean age of 50 years (SD 13). Serum PFOS baseline median was 191 ng/mL (IQR: 129-229) and decreased with a mean of 115 ng/mL (95 % CI: 89-140) on treatment, and 4.3 ng/mL in observation period corresponding to a decrease of 60 % (95 % CI: 53-67; p < 0.0001). PFHxS, PFOA, PFNA and PFDA decreased during treatment between 15 and 44 %. No serious adverse events were reported.

CONCLUSIONS

Oral treatment with AER significantly lowered serum PFOS concentrations suggesting a possible treatment for enhancing elimination of PFOS in highly exposed adults.

Microfluidic Chip-Based Modeling of Three-Dimensional Intestine-Vessel-Liver Interactions in Fluorotelomer Alcohol Biotransformation

Plyfluoroalkyl substance (PFAS), featured with incredible persistence and chronic toxicity, poses an emerging ecological and environmental crisis. Although significant progress has been made in PFAS metabolism in vivo, the underlying mechanism of metabolically active organ interactions in PFAS bioaccumulation remains largely unknown. We developed a microfluidic-based assay to recreate the intestine-vessel-liver interface in three dimensions, allowing for high-resolution, real-time images and precise quantification of intestine-vessel-liver interactions in PFAS biotransformation. In contrast to the scattered arrangement of vascular endothelium on the traditional d-polylysine-modified two-dimensional (2D) plate, the microtubules in our three-dimensional (3D) platform formed a dense honeycomb network through the ECM, with longer tubular structures. Additionally, the slope culture of epithelial cells in our platform exhibited a closely arranged and thicker cell layer than the planar culture. To dynamically monitor the metabolic crosstalk in the intestinal-vascular endothelium-liver interaction under exposure to fluorotelomer alcohols (FTOHs), we combined the chip with a solid-phase extraction-mass spectrometry (SPE-MS) system. Our findings revealed that endothelial cells were involved in the metabolic process of FTOHs. The transformation of intestinal epithelial and hepatic epithelial cells produces toxic metabolite fluorotelomer carboxylic acids (FTCAs), which circulate to endothelial cells and affect angiogenesis. This system shows promise as an enhanced surrogate model and platform for studying pollutant exposure as well as for biomedical and pharmaceutical research.

PFAS Exposures and the Human Metabolome: A Systematic Review of Epidemiological Studies

Purpose of Review

There is a growing interest in understanding the health effects of exposure to per- and polyfluoroalkyl substances (PFAS) through the study of the human metabolome. In this systematic review, we aimed to identify consistent findings between PFAS and metabolomic signatures. We conducted a search matching specific keywords that was independently reviewed by two authors on two databases (EMBASE and PubMed) from their inception through July 19, 2022 following PRISMA guidelines.

Recent Findings

We identified a total of 28 eligible observational studies that evaluated the associations between 31 different PFAS exposures and metabolomics in humans. The most common exposure evaluated was legacy long-chain PFAS. Population sample sizes ranged from 40 to 1,105 participants at different stages across the lifespan. A total of 19 studies used a non-targeted metabolomics approach, 7 used targeted approaches, and 2 included both. The majority of studies were cross-sectional (n = 25), including four with prospective analyses of PFAS measured prior to metabolomics.

Summary

Most frequently reported associations across studies were observed between PFAS and amino acids, fatty acids, glycerophospholipids, glycerolipids, phosphosphingolipids, bile acids, ceramides, purines, and acylcarnitines. Corresponding metabolic pathways were also altered, including lipid, amino acid, carbohydrate, nucleotide, energy metabolism, glycan biosynthesis and metabolism, and metabolism of cofactors and vitamins. We found consistent evidence across studies indicating PFAS-induced alterations in lipid and amino acid metabolites, which may be involved in energy and cell membrane disruption.

Ultra-sensitive SERS detection of perfluorooctanoic acid based on self-assembled p-phenylenediamine nanoparticle complex

PFOA is a representative perfluorinated compound that is used as a surfactant in various industrial fields. However, because PFOA has severe side effects due to its strong toxicity, such as carcinogenesis, liver damage, and immune system damage, it is crucial to enable PFOA detection with high sensitivity. Herein, we developed a perfluorooctanoic acid (PFOA) surface-enhanced Raman scattering (SERS) sensor using self-assembled p-phenylenediamine (SAp-PD) nanoparticles and an Ag SERS substrate. For the ultra-sensitive detection of PFOA, we synthesized and optimized SAp-PD, which shows a decrease in SERS intensities when reacting with PFOA. Using the Ag nanograss SERS substrate, the change in intensity that resulted from the SAp-PD and PFOA reaction was amplified. Consequently, we detected the 1.28 pM (detection limit) of PFOA in distilled water. Moreover, PFOA molecules were successfully detected in samples of the PFOA-coated frying pan and rice extraction at concentrations up to 1.69 nM and 10.3 μM, respectively.

Per- and polyfluoroalkyl substances (PFAS) inhibit cytochrome P450 CYP3A7 through direct coordination to the heme iron and water displacement

Per- and polyfluoroalkyl substances (PFAS) are a chemical class of highly stable, fluorinated compounds popular for use in a variety of consumer products. PFAS environmental persistence in drinking water contributes to acute exposure in humans and subsequent bioaccumulation of the compounds in the liver and lung tissue. Prenatal PFAS exposure has been associated with lowered birth weight, premature birth, and developmental defects including cranio-facial abnormalities. The cytochrome P450 enzyme CYP3A7 is responsible for facilitating a variety of reactions essential for proper fetal development in humans. In addition to drug metabolism, CYP3A7 is responsible for metabolizing endogenous ligands in the developing human liver, including the steroid precursor dehydroepiandrosterone 3-sulfate (DHEA-S), essential for estriol synthesis during pregnancy, along with the morphogen all-trans-retinoic acid (atRA). Interference with estriol synthesis during pregnancy, as well as atRA clearance, is known to result in similar effects associated with prenatal PFAS exposure including lowered birth weight, premature birth, and developmental defects. We hypothesized that PFAS compounds bind to the CYP3A7 enzyme resulting in its inhibition. We implemented a series of binding studies using spectral characterization of six PFAS compounds (PFOA, PFOS, GenX, PFNA, PFNS, and PFHxS), and evaluated their interactions with recombinant CYP3A7. In addition, we screened PFAS for their ability to inhibit CYP3A7 oxidative activity using dibenzylfluorescein, a fluorescent probe, and DHEA-S, an endogenous substrate of CYP3A7. Our data demonstrate that of the six PFAS tested, PFOA, PFOS, PFNA, and PFHxS bind to and inhibit CYP3A7.

Effect of lifestyle-based lipid lowering interventions on the relationship between circulating levels of per-and polyfluoroalkyl substances and serum cholesterol

Exposure to certain per-and polyfluoroalkyl substances (PFAS) has been shown to be positively associated with total and/or low-density lipoprotein cholesterol. Examining this association in lipid lowering interventions may provide additional evidence linking PFAS to cardiovascular risk. We examined the relationship of 6 PFAS with cholesterol in a 6-month lifestyle-based intervention. We quantitated PFAS in 350 individuals at baseline and post intervention and examined associations of PFAS with cholesterol before and after intervention. Food frequency questionnaires and GIS analyses were used to investigate PFAS hotspots and possible exposure routes. Cholesterol significantly decreased following intervention and in parallel, PFOS, PFOA, PFHxS, and PFHpA significantly decreased. PFOS was positively correlated with total cholesterol only post-intervention. We observed that PFOS was distributed among both non-albumin and albumin lipoprotein fractions pre-intervention, but entirely in albumin fraction post-intervention. Our results indicate that lipid-lowering via lifestyle modification may impact on circulating levels or distribution of PFAS.

Is the cholesterol-perfluoroalkyl substance association confounded by dietary fiber intake?: a Bayesian analysis of NHANES data with adjustment for measurement error in fiber intake

BACKGROUND

Serum concentrations of total cholesterol and related lipid measures have been associated with serum concentrations of per- and polyfluoroalkyl substances (PFAS) in humans, even among those with only background-level exposure to PFAS. Fiber is known to decrease serum cholesterol and a recent report based on National Health and Nutrition Examination Survey (NHANES) showed that PFAS and fiber are inversely associated. We hypothesized that confounding by dietary fiber may account for some of the association between cholesterol and PFAS.

METHODS

We implemented a Bayesian correction for measurement error in estimated intake of dietary fiber to evaluate whether fiber confounds the cholesterol-PFAS association. The NHANES measure of diet, two 24-h recalls, allowed calculation of an estimate of the "true" long-term fiber intake for each subject. We fit models to the NHANES data on serum cholesterol and serum concentration of perfluorooctanoic acid (PFOA) and two other PFAS for 7,242 participants in NHANES.

RESULTS

The Bayesian model, after adjustment for soluble fiber intake, suggested a decrease in the size of the coefficient for PFOA by 6.4% compared with the fiber-unadjusted model.

CONCLUSIONS

The results indicated that the association of serum cholesterol with PFAS was not substantially confounded by fiber intake.

Food grown on fire stations as a potential pathway for firefighters' exposure to per- and poly-fluoroalkyl substances (PFAS)

Human exposure to per- and polyfluoroalkyl substances also known as PFAS is an ongoing occupational and environmental health problem. This study seeks to characterise multiple pathways for firefighters' exposure to PFAS. PFAS were analysed in 688 environmental samples such as eggs, fruits, vegetables, dust, soil, surface swabs, appliance washes and water obtained from fire stations. Relevant exposure pathways were identified and daily intake levels were estimated using PFAS concentrations and exposure factors relevant to firefighters. Five PFAS including perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid (PFHxS), 6:2 fluorotelomer sulfonate (6:2 FTS), and 8:2 fluorotelomer sulfonic acid (8:2 FTS) were frequently detected in the samples. Based on the median concentrations in each sample type, PFOS was the most abundant contaminant in eggs (80%), fruits (52%), dust (81%), surface swab (66%), soil (83%) and appliance wash (31%) samples. On the other hand, PFHxS was most abundant in vegetables (77%) and 8:2 FTS in water (58%). The intake estimation results show that dietary exposure from ingestion of foods produced on fire stations was the predominant exposure pathway, representing 82% and 62% of firefighters' total PFAS intake under typical and worst-case exposure scenarios, respectively. Incidental ingestion and dermal absorption of PFAS in dust contributed 15% for typical and 34% for worst-case exposure scenarios. The relative contributions from incidental ingestion and dermal absorption of PFAS in soil and appliance washes were insignificant. Overall, the study identifies multiple exposure pathways relevant to career firefighters including consumption of food grown on fire stations, which has not previously been recognised within the occupational exposure context. The results suggest exposure control strategies that target foods produced on fire stations could substantially reduce firefighters' exposure to PFAS.

Killing two birds with one stone: Pregnancy is a sensitive window for endocrine effects on both the mother and the fetus

Pregnancy is a complex process requiring tremendous physiological changes in the mother in order to fulfill the needs of the growing fetus, and to give birth, expel the placenta and nurse the newborn. These physiological modifications are accompanied with psychological changes, as well as with variations in habits and behaviors. As a result, this period of life is considered as a sensitive window as impaired functional and physiological changes in the mother can have short- and long-term impacts on her health. In addition, dysregulation of the placenta and of mechanisms governing placentation have been linked to chronic diseases later-on in life for the fetus, in a concept known as the Developmental Origin of Health and Diseases (DOHaD). This concept stipulates that any change in the environment during the pre-conception and perinatal (in utero life and neonatal) period to puberty, can be "imprinted" in the organism, thereby impacting the health and risk of chronic diseases later in life. Pregnancy is a succession of events that is regulated, in large part, by hormones and growth factors. Therefore, small changes in hormonal balance can have important effects on both the mother and the developing fetus. An increasing number of studies demonstrate that exposure to endocrine disrupting compounds (EDCs) affect both the mother and the fetus giving rise to growing concerns surrounding these exposures. This review will give an overview of changes that happen during pregnancy with respect to the mother, the placenta, and the fetus, and of the current literature regarding the effects of EDCs during this specific sensitive window of exposure.

Effect of Enterohepatic Circulation on the Accumulation of Per- and Polyfluoroalkyl Substances: Evidence from Experimental and Computational Studies

The pharmacokinetic characteristics of per- and polyfluoroalkyl substances (PFAS) affect their distribution and bioaccumulation in biological systems. The enterohepatic circulation leads to reabsorption of certain chemicals from bile back into blood and the liver and thus influences their elimination, yet its influence on PFAS bioaccumulation remains unclear. We explored the role of enterohepatic circulation in PFAS bioaccumulation by examining tissue distribution of various PFAS in wild fish and a rat model. Computational models were used to determine the reabsorbed fractions of PFAS by calculating binding affinities of PFAS for key transporter proteins of enterohepatic circulation. The results indicated that higher concentrations were observed in blood, the liver, and bile compared to other tissues for some PFAS in fish. Furthermore, exposure to a PFAS mixture on the rat model showed that the reabsorption phenomenon appeared during 8-12 h for most long-chain PFAS. Molecular docking calculations suggest that PFAS can bind to key transporter proteins via electrostatic and hydrophobic interactions. Further regression analysis adds support to the hypothesis that binding affinity of the apical sodium-dependent bile acid transporter is the most important variable to predict the human half-lives of PFAS. This study demonstrated the critical role of enterohepatic circulation in reabsorption, distribution, and accumulation of PFAS.

Biological Utility of Fluorinated Compounds: from Materials Design to Molecular Imaging, Therapeutics and Environmental Remediation

The applications of fluorinated molecules in bioengineering and nanotechnology are expanding rapidly with the controlled introduction of fluorine being broadly studied due to the unique properties of C-F bonds. This review will focus on the design and utility of C-F containing materials in imaging, therapeutics, and environmental applications with a central theme being the importance of controlling fluorine-fluorine interactions and understanding how such interactions impact biological behavior. Low natural abundance of fluorine is shown to provide sensitivity and background advantages for imaging and detection of a variety of diseases with ¹⁹F magnetic resonance imaging, ¹⁸F positron emission tomography and ultrasound discussed as illustrative examples. The presence of C-F bonds can also be used to tailor membrane permeability and pharmacokinetic properties of drugs and delivery agents for enhanced cell uptake and therapeutics. A key message of this review is that while the promise of C-F containing materials is significant, a subset of highly fluorinated compounds such as per- and polyfluoroalkyl substances (PFAS), have been identified as posing a potential risk to human health. The unique properties of the C-F bond and the significant potential for fluorine-fluorine interactions in PFAS structures necessitate the development of new strategies for facile and efficient environmental removal and remediation. Recent progress in the development of fluorine-containing compounds as molecular imaging and therapeutic agents will be reviewed and their design features contrasted with environmental and health risks for PFAS systems. Finally, present challenges and future directions in the exploitation of the biological aspects of fluorinated systems will be described.

Perfluoroalkyl Carboxylic Acids Interact with the Human Bile Acid Transporter NTCP

Na⁺/taurocholate cotransporting polypeptide (NTCP) is important for the enterohepatic circulation of bile acids, which has been suggested to contribute to the long serum elimination half-lives of perfluoroalkyl substances in humans. We demonstrated that some perfluoroalkyl sulfonates are transported by NTCP; however, little was known about carboxylates. The purpose of this study was to determine if perfluoroalkyl carboxylates would interact with NTCP and potentially act as substrates. Sodium-dependent transport of [³H]-taurocholate was measured in human embryonic kidney cells (HEK293) stably expressing NTCP in the absence or presence of perfluoroalkyl carboxylates with varying chain lengths. PFCAs with 8 (PFOA), 9 (PFNA), and 10 (PFDA) carbons were the strongest inhibitors. Inhibition kinetics demonstrated competitive inhibition and indicated that PFNA was the strongest inhibitor followed by PFDA and PFOA. All three compounds are transported by NTCP, and kinetics experiments revealed that PFOA had the highest affinity for NTCP with a K_m value of 1.8 ± 0.4 mM. The K_m value PFNA was estimated to be 5.3 ± 3.5 mM and the value for PFDA could not be determined due to limited solubility. In conclusion, our results suggest that, in addition to sulfonates, perfluorinated carboxylates are substrates of NTCP and have the potential to interact with NTCP-mediated transport.

Temporal trends of concentrations of per- and polyfluoroalkyl substances among adults with overweight and obesity in the United States: Results from the Diabetes Prevention Program and NHANES

BACKGROUND

Understanding the temporal trends and change of concentrations of per- and polyfluoroalkyl substances (PFAS) is important to evaluate the health impact of PFAS at both the individual- and population-level, however, limited information is available for pre-diabetic adults in the U.S.

OBJECTIVES

Determine trends and rate of change of plasma PFAS concentrations in overweight or obese U.S. adults and evaluate variation by sex, race/ethnicity, and age.

METHODS

We described temporal trends of plasma PFAS concentrations using samples collected in 1996-1998, 1999-2001, and 2011-2012 from 957 pre-diabetic adults enrolled in the Diabetes Prevention Program (DPP) trial and Outcomes Study (DPPOS) and compared to serum concentrations from the National Health and Nutrition Examination Survey (NHANES 1999-2000, 2003-2016, adults with BMI ≥ 24 kg/m²). We examined associations between participants' characteristics and PFAS concentrations and estimated the rate of change using repeated measures in DPP/DPPOS assuming a first-order elimination model.

RESULTS

Longitudinal measures of PFAS concentrations in DPP/DPPOS individuals were comparable to NHANES cross-sectional populational means. Plasma concentrations of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid, perfluorohexanesulfonic acid (PFHxS), N-ethyl-perfluorooctane sulfonamido acetic acid (EtFOSAA), and N-methylperfluorooctane sulfonamido acetic acid (MeFOSAA) started to decline after the year 2000 and concentrations of perfluorononanoic acid (PFNA) increased after 2000 and, for NHANES, decreased after 2012. We consistently observed higher PFOS, PFHxS and PFNA among male, compared to female, and higher PFOS and PFNA among Black, compared to white, participants. The estimated time for concentrations to decrease by half ranged from 3.39 years for EtFOSAA to 17.56 years for PFHxS.

DISCUSSION

We observed a downward temporal trend in plasma PFOS concentrations that was consistent with the timing for U.S. manufacturers' phaseout. Male and Black participants consistently showed higher PFOS and PFNA than female and white participants, likely due to differences in exposure patterns, metabolism or elimination kinetics.

Why is elevation of serum cholesterol associated with exposure to perfluoroalkyl substances (PFAS) in humans? A workshop report on potential mechanisms

Serum concentrations of cholesterol are positively correlated with exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in humans. The associated change in cholesterol is small across a broad range of exposure to PFOA and PFOS. Animal studies generally have not indicated a mechanism that would account for the association in humans. The extent to which the relationship is causal is an open question. Nonetheless, the association is of particular importance because increased serum cholesterol has been considered as an endpoint to derive a point of departure in at least one recent risk assessment. To gain insight into potential mechanisms for the association, both causal and non-causal, an expert workshop was held Oct 31 and Nov 1, 2019 to discuss relevant data and propose new studies. In this report, we summarize the relevant background data, the discussion among the attendees, and their recommendations for further research.

Systemic PFOS and PFOA exposure and disturbed lipid homeostasis in humans: what do we know and what not?

Associations between per- and polyfluoroalkyl substances (PFASs) and increased blood lipids have been repeatedly observed in humans, but a causal relation has been debated. Rodent studies show reverse effects, i.e. decreased blood cholesterol and triglycerides, occurring however at PFAS serum levels at least 100-fold higher than those in humans. This paper aims to present the main issues regarding the modulation of lipid homeostasis by the two most common PFASs, PFOS and PFOA, with emphasis on the underlying mechanisms relevant for humans. Overall, the apparent contrast between human and animal data may be an artifact of dose, with different molecular pathways coming into play upon exposure to PFASs at very low versus high levels. Altogether, the interpretation of existing rodent data on PFOS/PFOA-induced lipid perturbations with respect to the human situation is complex. From a mechanistic perspective, research on human liver cells shows that PFOS/PFOA activate the PPARα pathway, whereas studies on the involvement of other nuclear receptors, like PXR, are less conclusive. Other data indicate that suppression of the nuclear receptor HNF4α signaling pathway, as well as perturbations of bile acid metabolism and transport might be important cellular events that require further investigation. Future studies with human-relevant test systems would help to obtain more insight into the mechanistic pathways pertinent for humans. These studies shall be designed with a careful consideration of appropriate dosing and toxicokinetics, so as to enable biologically plausible quantitative extrapolations. Such research will increase the understanding of possible perturbed lipid homeostasis related to PFOS/ PFOA exposure and the potential implications for human health.

Perfluoroalkyl substance excretion: Effects of organic anion-inhibiting and resin-binding drugs in a community setting

BACKGROUND

Longer serum half-lives of perfluoroalkyl substances (PFAS) in humans compared to other species has been attributed to differences in the activity of organic anion transporters (OAT).

METHODS

Among 56,175 adult participants in the community-based C8 Health Project, 23 subjects were taking the uricosuric OAT-inhibitor probenecid, and 36 subjects were taking the bile acid sequestrant cholestyramine. In regression models of log transformed serum PFAS, medication effects were estimated in terms of mean ratios, adjusting for age, gender, BMI, estimated glomerular filtration rate (eGFR) and water-district of residence.

RESULTS

Probenecid was associated with modest, but not statistically significant increases in serum PFAS concentrations. In contrast, cholestyramine significantly lowered serum PFAS concentrations, notably for perfluorooctane sulfonic acid (PFOS).

CONCLUSIONS

The effectiveness of cholestyramine in a community setting supports the importance of gastrointestinal physiology for PFAS excretion kinetics, especially for PFOS. We did not find clear evidence that probenecid, an inhibitor of OAT, affects PFAS clearance.

Endocrine Disrupting Chemicals and Reproductive Health in Boys and Men

Male reproductive health has declined as indicated by increasing rates of cryptorchidism, i.e., undescended testis, poor semen quality, low serum testosterone level, and testicular cancer. Exposure to endocrine disrupting chemicals (EDCs) has been proposed to have a role in this finding. In utero exposure to antiandrogenic EDCs, particularly at a sensitive period of fetal testicular development, the so-called 'masculinization programming window (MPW)', can disturb testicular development and function. Low androgen effect during the MPW can cause both short- and long-term reproductive disorders. A concurrent exposure to EDCs may also affect testicular function or damage testicular cells. Evidence from animal studies supports the role of endocrine disrupting chemicals in development of male reproductive disorders. However, evidence from epidemiological studies is relatively mixed. In this article, we review the current literature that evaluated relationship between prenatal EDC exposures and anogenital distance, cryptorchidism, and congenital penile abnormality called hypospadias. We review also studies on the association between early life and postnatal EDC exposure and semen quality, hypothalamic-pituitary-gonadal axis hormone levels and testicular cancer.

The concentration of several perfluoroalkyl acids in serum appears to be reduced by dietary fiber

Fiber-rich food intake has been associated with lower serum concentrations of perfluoroalkyl substances (PFAS) in some studies and dietary fiber was related to lower serum PFAS in a recent study. Given the previous epidemiologic data suggesting that fiber might decrease serum PFAS concentrations, we examined the relation of serum PFAS concentrations to intake of dietary fiber in National Health and Nutrition Examination Survey (NHANES) data. We examined the PFAS-fiber association among 6482 adults who participated in the NHANES, 2005-2016. Fiber intake was estimated based on two 24-hour diet recalls. We adjusted the models for determinants of PFAS and potentially confounding factors such as intake of foods reported to increase PFAS exposure. Results were expressed as the percent difference in PFAS concentration per interquartile range (IQR) increase in fiber (and 95 percent confidence interval), and the NHANES sampling parameters were used to make the results generalizable to the U.S. The adjusted percent difference in perfluorooctanoic acid (PFOA) per IQR increase in fiber was -3.64 (-6.15, -1.07); for perfluorooctane sulfonic acid (PFOS) was -6.69 (-9.57, -3.73), and for perfluorononanoic acid (PFNA) was -8.36 (-11.33, -5.29). These results suggest that dietary fiber increases the gastrointestinal excretion of PFOA, PFOS, and PFNA. Because fiber also lowers serum cholesterol, in some studies of the serum cholesterol-PFAS relationship confounding by fiber may be worth evaluating.

Assessment of the Emerging Threat Posed by Perfluoroalkyl and Polyfluoroalkyl Substances to Male Reproduction in Humans

Per-fluoroalkyl and polyfluoroalkyl substances (PFAS) are a diverse group of synthetic fluorinated chemicals used widely in industry and consumer products. Due to their extensive use and chemical stability, PFAS are ubiquitous environmental contaminants and as such, form an emerging risk factor for male reproductive health. The long half-lives of PFAS is of particular concern as the propensity to accumulate in biological systems prolong the time taken for excretion, taking years in many cases. Accordingly, there is mounting evidence supporting a negative association between PFAS exposure and an array of human health conditions. However, inconsistencies among epidemiological and experimental findings have hindered the ability to definitively link negative reproductive outcomes to specific PFAS exposure. This situation highlights the requirement for further investigation and the identification of reliable biological models that can inform health risks, allowing sensitive assessment of the spectrum of effects of PFAS exposure on humans. Here, we review the literature on the biological effects of PFAS exposure, with a specific focus on male reproduction, owing to its utility as a sentinel marker of general health. Indeed, male infertility has increasingly been shown to serve as an early indicator of a range of co-morbidities such as coronary, inflammatory, and metabolic diseases. It follows that adverse associations have been established between PFAS exposure and the incidence of testicular dysfunction, including pathologies such as testicular cancer and a reduction in semen quality. We also give consideration to the mechanisms that render the male reproductive tract vulnerable to PFAS mediated damage, and discuss novel remediation strategies to mitigate the negative impact of PFAS contamination and/or to ameliorate the PFAS load of exposed individuals.

Diet as an Exposure Source and Mediator of Per- and Polyfluoroalkyl Substance (PFAS) Toxicity

Per- and polyfluoroalkyl substances (PFAS) are ubiquitously found in the environment due to their widespread commercial use and high chemical stability. Humans are exposed primarily through ingestion of contaminated water and food and epidemiological studies over the last several decades have shown that PFAS levels are associated with adverse chronic health effects, including cardiometabolic disorders such as hyperlipidemia and non-alcoholic fatty liver disease. Perhaps the most well-established effects, as demonstrated in animal studies and human epidemiological studies, are the metabolic alterations PFAS exposure can lead to, especially on lipid homeostasis and signaling. This altered lipid metabolism has often been linked to conditions such as dyslipidemia, leading to fatty liver disease and steatosis. Western diets enriched in high fat and high cholesterol containing foods may be an important human exposure route of PFAS and may also act as an important modulator of associated toxicities. In fact, the chemical structure of PFAS resemble fatty acids and may activate some of the same signaling cascades critical for endogenous metabolism. In this review we aim to outline known dietary exposure sources of PFAS, describe the detrimental metabolic health effects associated with PFAS exposure, and focus on studies examining emerging interaction of dietary effects with PFAS exposure that further alter the dysregulated metabolic state.

Associations between perfluoroalkyl substances and lipid profile in a highly exposed young adult population in the Veneto Region

BACKGROUND

Residents of a large area of the Veneto Region (North-Eastern Italy) were exposed for decades to drinking water contaminated by perfluoroalkyl substances (PFAS). PFAS have been consistently associated with raised serum lipids, mainly in cross-sectional studies and in background exposure contexts, but the shape of the dose-response relationships has been poorly investigated. The objectives of our study were to evaluate the association between serum PFAS and serum lipids and their dose-response patterns in a large exposed population.

METHODS

A cross-sectional study was conducted in 16,224 individuals aged 20-39 years recruited in the regional health surveillance program. 15,720 subjects were analysed after excluding pregnant women (n = 327), participants reporting use of cholesterol lowering medications (n = 67) or with missing information on the selected covariates (n = 110). Twelve PFAS were measured by HPLC-MS in serum; three (PFOA, PFOS and PFHxS) were quantifiable in at least 50% of samples. Non-fasting serum total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and triglycerides were measured by enzymatic assays in automated analysers and low-density lipoprotein cholesterol (LDL-C), non-HDL cholesterol and total/HDL cholesterol ratio were calculated. The associations between natural log (ln) transformed PFAS and lipids were assessed through generalized additive models using linear regression and smoothing thin plate splines, adjusted for potential confounders.

RESULTS

There were strong positive associations between the ln-transformed PFOA, PFOS, and PFHxS and TC, HDL-C, and LDL-C, and between ln PFOA and PFHxS and triglycerides. Each ln-increase in PFOA was associated with an increase of 1.94 mg/dL (95% CI 1.48-2.41) in TC, with 4.99 mg/dL (CI 4.12-5.86) for PFOS and 2.02 mg/dL (CI 1.45-2.58) for PFHxS.

CONCLUSIONS

Investigation of the shape of exposure-response associations using splines showed a positive association with the largest increases per unit of PFAS in cholesterol levels occurring at the lower range of PFAS concentrations for each compound.

Metabolism of mono-(2-ethylhexyl) phthalate in Arabidopsis thaliana: Exploration of metabolic pathways by deuterium labeling

Mono-(2-ethylhexyl) phthalate (MEHP) is the primary monoester transformation product of the commonly used plasticizer, di-2-ethylhexyl phthalate (DEHP), and has been frequently detected in various environmental compartments (e.g., soil, biosolids, plants). Plants growing in contaminated soils can take up MEHP, and consumption of the contaminated plants may result in unintended exposure for humans and other organisms. The metabolism of MEHP in plants is poorly understood, but critical for evaluating the potential human and environmental health risks. The present study represents the first attempt to explore the metabolic fate of MEHP in plants. We used Arabidopsis thaliana cells as a plant model and explored metabolic pathways of MEHP using deuterium stable isotope labelling (SIL) coupled with time-of-flight high resolution mass spectrometer (TOF-HRMS). A. thaliana rapidly took up MEHP from the culture medium and mediated extensive metabolism of MEHP. Combining SIL with TOF-HRMS analysis was proved as a powerful method for identification of unknown MEHP metabolites. Four phase Ⅰ and three phase Ⅱ metabolites were confirmed or tentatively identified. Based on the detected transformation products, hydroxylation, oxidation, and malonylation are proposed as the potential MEHP metabolism pathways. In cells, the maximum fraction of each transformation product accounted for 2.8-56.5% of the total amount of metabolites during the incubation. For individual metabolites, up to 2.9-100% was found in the culture medium, suggesting plant excretion. The results in the cell culture experiments were further confirmed in cabbage and A. thaliana seedlings. The findings suggest active metabolism of MEHP in plants and highlight the need to include metabolites in refining environmental risk assessment of plasticizers in the agro-food systems.

Serum Half-Lives for Short- and Long-Chain Perfluoroalkyl Acids after Ceasing Exposure from Drinking Water Contaminated by Firefighting Foam

BACKGROUND

Firefighting foam-contaminated ground water, which contains high levels of perfluoroalkyl substances (PFAS), is frequently found around airports. In 2018 it was detected that employees at a municipal airport in northern Sweden had been exposed to high levels of short-chain PFAS along with legacy PFAS (i.e., PFOA, PFHxS, and PFOS) through drinking water.

OBJECTIVES

In this study, we aimed to describe the PFAS profile in drinking water and biological samples (paired serum and urine) and to estimate serum half-lives of the short-chain PFAS together with legacy PFAS.

METHODS

Within 2 weeks after provision of clean water, blood sampling was performed in all 26 airport employees. Seventeen of them were then followed up monthly for 5 months. PFHxA, PFHpA, PFBS, PFPeS, and PFHpS together with legacy PFAS in water and biological samples were quantified using LC/MS/MS. Half-lives were estimated by assuming one compartment, first-order elimination kinetics.

RESULTS

The proportions of PFHxA, PFHpA, and PFBS were higher in drinking water than in serum. The opposite was found for PFHxS and PFOS. The legacy PFAS accounted for about 50% of total PFAS in drinking water and 90% in serum. Urinary PFAS levels were very low compared with serum. PFBS showed the shortest half-life {average 44 d [95% confidence interval (CI): 37, 55 d]}, followed by PFHpA [62 d (95% CI: 51, 80 d)]. PFPeS and PFHpS showed average half-lives as 0.63 and 1.46 y, respectively. Branched PFOS isomers had average half-lives ranging from 1.05 to 1.26 y for different isomers. PFOA, PFHxS, and linear PFOS isomers showed average half-lives of 1.77, 2.87, and 2.93 y, respectively.

DISCUSSION

A general pattern of increasing half-lives with increasing chain length was observed. Branched PFOS isomers had shorter half-lives than linear PFOS isomers. https://doi.org/10.1289/EHP6785.

Per- and polyfluoroalkyl substances and blood lipid levels in pre-diabetic adults-longitudinal analysis of the diabetes prevention program outcomes study

Exposure to per- and polyfluoroalkyl substances (PFASs) may interfere with lipid regulation. However, most previous studies were cross-sectional with the risk of reverse causation, suggesting a need for long-term prospective studies. We examined the relationship of baseline plasma PFAS concentrations with repeated measures of blood lipids. We included 888 prediabetic adults from the Diabetes Prevention Program (DPP) and DPP Outcomes Study, who had measurements of 6 plasma PFAS concentrations at baseline (1996-1999) and repeated measures of blood lipids over 15 years of follow-up, and were initially randomized to placebo or a lifestyle intervention. We used linear regression to examine cross-sectional associations of PFAS concentrations and lipid levels at baseline, and evaluated prospective risks of hypercholesterolemia and hypertriglyceridemia using Cox proportional hazard models, and tested for effect modification by study arm. Participants (65.9% female, 57.0% White, 65.9% aged 40-59 years) had comparable PFAS concentrations [e.g., median (IQR) perfluorooctanoic acid (PFOA) 4.9 ng/mL (3.2)] with the general U.S. population in 1999-2000. We observed higher total cholesterol at baseline per doubling of PFOA (β: 6.1 mg/dL, 95% CI: 3.1, 9.04), perfluorohexane sulfonic acid (PFHxS, β: 2.2 mg/dL, 95% CI: 0.2, 4.3), and perfluorononanoic acid (PFNA, β: 2.9 mg/dL, 95% CI: 0.7, 5.0). Prospectively, baseline concentrations of several PFASs, including PFOA, PFOS, PFHxS and PFNA, predicted higher risks of incident hypercholesterolemia and hypertriglyceridemia, but only in the placebo group and not the lifestyle intervention group. For example, participants in the placebo group with PFOA concentration > median (4.9 ng/mL) were almost twice as likely (HR: 1.90, 95% CI: 1.25, 2.88) to develop hypertriglyceridemia compared to those ≤median. Findings suggest adverse effects of some PFASs on lipid profiles in prediabetic adults. However, the detrimental effect was attenuated with a lifestyle intervention.

Toxicokinetics of perfluorobutane sulfonate (PFBS), perfluorohexane-1-sulphonic acid (PFHxS), and perfluorooctane sulfonic acid (PFOS) in male and female Hsd:Sprague Dawley SD rats after intravenous and gavage administration

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In rats, the half-life of perfluoroalkyl sulfonic acids decreased with shorter chain lengths.

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Sex differences in kinetics were found for PFBS and PFHxS but not PFOS.

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Perfluoroalkyl sulfonic acids were highly present in the liver but not the brain.

Perfluorinated alkyl substances (PFAS) are persistent contaminants that have been detected in the environment and in humans. With the PFAS chemical class, there are perfluorinated alkyl acids, many of which have been associated with certain toxicities. Because toxicity testing cannot feasibly be conducted for each individual PFAS, the National Toxicology Program (NTP) designed studies to compare toxicities across different subclasses of PFAS and across PFAS of different chain lengths to better understand the structure-toxicity relationship. Pharmacokinetic studies were conducted in parallel to these toxicity studies to facilitate comparisons across PFAS and to provide context for human relevance. Here, the toxicokinetic parameters of perfluorobutane sulfonate (PFBS), perfluorohexane-1-sulphonic acid (PFHxS), or perfluorooctane sulfonate (PFOS) after a single intravenous or gavage administration in male and female Hsd:Sprague-Dawley rats are reported. Concentrations of these PFAS were measured in the liver, kidney, and brain. Plasma half-life increased with longer chain length after gavage administration: PFBS- males averaged 3.3 h, females 1.3 h; PFHxS- males averaged 16.3 days, females 2.1 days; PFOS- males and females averaged ˜ 20 days. There were dose-dependent changes in clearance and systemic exposure for all administered chemicals and the direction of change was different in PFOS compared to the others. Liver:plasma ratios of PFOS were the highest followed by PFHxS and PFBS, while brain:plasma ratios were low in all three sulfonates. Sex differences in plasma half-life and tissue distribution were observed for PFBS and PFHxS, but not PFOS. These data provide a direct comparison of the kinetics of three different perfluoroalkyl sulfonic acids and allow for the contextualization of toxicity data in rats for human risk assessment of this chemical class.

Zeolite Clinoptilolite: Therapeutic Virtues of an Ancient Mineral

Zeolites are porous minerals with high absorbency and ion-exchange capacity. Their molecular structure is a dense network of AlO4 and SiO4 that generates cavities where water and other polar molecules or ions are inserted/exchanged. Even though there are several synthetic or natural occurring species of zeolites, the most widespread and studied is the naturally occurring zeolite clinoptilolite (ZC). ZC is an excellent detoxifying, antioxidant and anti-inflammatory agent. As a result, it is been used in many industrial applications ranging from environmental remediation to oral applications/supplementation in vivo in humans as food supplements or medical devices. Moreover, the modification as micronization of ZC (M-ZC) or tribomechanically activated zeolite clinoptilolite (TMAZ) or furthermore as double tribomechanically activated zeolite clinoptilolite (PMA-ZC) allows improving its benefits in preclinical and clinical models. Despite its extensive use, many underlying action mechanisms of ZC in its natural or modified forms are still unclear, especially in humans. The main aim of this review is to shed light on the geochemical aspects and therapeutic potentials of ZC with a vision of endorsing further preclinical and clinical research on zeolites, in specific on the ZC and its modified forms as a potential agent for promoting human brain health and overall well-being.

Biomonitoring PFAAs in blood and semen samples: Investigation of a potential link between PFAAs exposure and semen mobility in China

Perfluoroalkyl acids (PFAAs) have been suspected to act as endocrine disruptors and adversely affect human reproductive health. We aimed to investigate the association between PFAAs in blood and semen, explore a potential link between PFAAs exposure and semen quality in the population of the Pearl River Delta (PRD) region in China, one of the "world factories". The monitoring results demonstrated that the population (103 male participants) from the PRD region in this study had higher PFAAs levels in blood and semen than some other areas in China. PFOS was found at the highest mean concentrations of 118.16 ng/mL in blood and 5.31 ng/mL in semen among the nine PFAAs. Significant associations were found between concentrations of several analytes in blood and semen, including Σ₉ PFAAs (r = 0.475, P < .01), PFOA (r = 0.215, P = .029), PFHS (r = 0.458, P < .01) and PFOS (r = 0.981, P < .01). BMI was the most important factor to PFAAs, but there was no significant difference in PFAAs concentrations in blood and semen collected from participants with different smoking and drinking habits, education background and occupations. Negative correlations were significantly observed between sperm motility and PFBA, PFPeA, PFHxA, PFBS, PFOA, PFHS, PFOS and Σ₉PFAAs in semen. Therefore, exposure to PFAAs may result in a decline in semen mobility in participants from the PRD region.

Organic Anion Transporting Polypeptides Contribute to the Disposition of Perfluoroalkyl Acids in Humans and Rats

Perfluoroalkyl sulfonates (PFSAs) such as perfluorohexane sulfonate (PFHxS) and perfluorooctane sulfonate (PFOS) have very long serum elimination half-lives in humans, and preferentially distribute to serum and liver. The enterohepatic circulation of PFHxS and PFOS likely contributes to their extended elimination half-lives. We previously demonstrated that perfluorobutane sulfonate (PFBS), PFHxS, and PFOS are transported into hepatocytes both in a sodium-dependent and a sodium-independent manner. We identified Na+/taurocholate cotransporting polypeptide (NTCP) as the responsible sodium-dependent transporter. Furthermore, we demonstrated that the human apical sodium-dependent bile salt transporter (ASBT) contributes to the intestinal reabsorption of PFOS. However, so far no sodium-independent uptake transporters for PFSAs have been identified in human hepatocytes or enterocytes. In addition, perfluoroalkyl carboxylates (PFCAs) with 8 and 9 carbons were shown to preferentially distribute to the liver of rodents; however, no rat or human liver uptake transporters are known to transport these PFCAs. Therefore, we tested whether PFBS, PFHxS, PFOS, and PFCAs with 7-10 carbons are substrates of organic anion transporting polypeptides (OATPs). We used CHO and HEK293 cells to demonstrate that human OATP1B1, OATP1B3, and OATP2B1 can transport PFBS, PFHxS, PFOS, and the 2 PFCAs (C8 and C9). In addition, we show that rat OATP1A1, OATP1A5, OATP1B2, and OATP2B1 transport all 3 PFSAs. In conclusion, our results suggest that besides NTCP and ASBT, OATPs also are capable of contributing to the enterohepatic circulation and extended human serum elimination half-lives of the tested perfluoroalkyl acids.

Half-lives of PFOS, PFHxS and PFOA after end of exposure to contaminated drinking water

Background

Municipal drinking water contaminated with perfluorinated alkyl acids had been distributed to one-third of households in Ronneby, Sweden. The source was firefighting foam used in a nearby airfield since the mid-1980s. Clean water was provided from 16 December 2013.

Objective

To determine the rates of decline in serum perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), and their corresponding half-lives.

Methods

Up to seven blood samples were collected between June 2014 and September 2016 from 106 participants (age 4–84 years, 53% female).

Results

Median initial serum concentrations were PFHxS, 277 ng/mL (range 12–1660); PFOS, 345 ng/mL (range 24–1500); and PFOA, 18 ng/mL (range 2.4–92). The covariate-adjusted average rates of decrease in serum were PFHxS, 13% per year (95% CI 12% to 15%); PFOS, 20% per year (95% CI 19% to 22%); and PFOA, 26% per year (95% CI 24% to 28%). The observed data are consistent with a first-order elimination model. The mean estimated half-life was 5.3 years (95% CI 4.6 to 6.0) for PFHxS, 3.4 years (95% CI 3.1 to 3.7) for PFOS and 2.7 years (95% CI 2.5 to 2.9) for PFOA. The interindividual variation of half-life was around threefold when comparing the 5th and 95th percentiles. There was a marked sex difference with more rapid elimination in women for PFHxS and PFOS, but only marginally for PFOA.

Conclusions

The estimated half-life for PFHxS was considerably longer than for PFOS and PFOA. For PFHxS and PFOS, the average half-life is shorter than the previously published estimates. For PFOA the half-life is in line with the range of published estimates.

Historical human exposure to perfluoroalkyl acids in the United States and Australia reconstructed from biomonitoring data using population-based pharmacokinetic modelling

Perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS) and perfluorohexanesulfonic acid (PFHxS) are found in the blood of humans and wildlife worldwide. Since the beginning of the 21st century, a downward trend in the human body burden, especially for PFOS and PFOA, has been observed while there is no clear temporal trend in wildlife. The inconsistency between the concentration decline in human serum and in wildlife could be indicative of a historical exposure pathway for humans linked to consumer products that has been reduced or eliminated. In this study, we reconstruct the past human exposure trends in two different regions, USA and Australia, by inferring the historical intake from cross-sectional biomonitoring data of PFOS, PFOA and PFHxS using a population-based pharmacokinetic model. For PFOS in the USA, the reconstructed daily intake peaked at 4.5ng/kg-bw/day between 1988 and 1999 while in Australia it peaked at 4.0ng/kg-bw/day between 1984 and 1996. For PFOA in the USA and Australia, the peak reconstructed daily intake was 1.1ng/kg-bw/day in 1995 and 3.6ng/kg-bw/day in 1992, respectively, and started to decline in 2000 and 1995, respectively. The model could not be satisfactorily fitted to the biomonitoring data for PFHxS within reasonable boundaries for its intrinsic elimination half-life, and thus reconstructing intakes of PFHxS was not possible. Our results indicate that humans experienced similar exposure levels and trends to PFOS and PFOA in the USA and Australia. Our findings support the hypothesis that near-field consumer product exposure pathways were likely dominant prior to the phase-out in industrialized countries. The intrinsic elimination half-life, which represents elimination processes that are common for all humans, and elimination processes unique to women (i.e., menstruation, cord-blood transfer and breastfeeding) were also investigated. The intrinsic elimination half-lives for PFOS and PFOA derived from model fitting for men were 3.8 and 2.4years, respectively, for the USA, and 4.9 and 2years respectively for Australia. Our results show that menstruation is a depuration pathway for PFOA for women, similarly but to a lesser extent compared to previous reports for PFOS. However menstruation, cord-blood transfer and breastfeeding together do not fully explain the apparently more rapid elimination of PFOA and PFOS by women compared to men; the intrinsic elimination half-lives in women were up to 13% lower for PFOS and up to 12% lower for PFOA compared to the corresponding half-lives in men.

Levels of perfluorinated acids (PFCAs) in different tissues of Lepidochelys olivacea sea turtles from the Escobilla beach (Oaxaca, Mexico)

Lepidochelys olivacea is the most abundant and globally distributed sea turtle species in the world and thus, monitoring this species for persistent organic pollutants, such as perfluorinated chemicals, is fundamental for their protection. This study was the first to evaluate the occurrence of five PFCAs (PFOA, PFNA, PFDA, PFUnA, PFDoA) in liver and blood samples of Olive Ridley turtle population from the Escobilla beach (Oaxaca, Mexico). PFDA and PFUnA were the predominant PFCs in blood samples (detected in 93% and 84% of samples, respectively) and were also present in the highest concentrations. Liver samples showed higher PFCA concentrations than whole blood samples, with PFNA and PFDA the most abundant PFCs congeners in liver samples, detected in 65% and 47% of the samples, respectively. The measured levels of contaminants in the blood samples of Lepidochelys olivacea sea turtles were compared to the levels reported in the literature for other turtle species. While linear significant correlations between PFNA, PFDA and PFUnA concentrations in blood samples and curved carapace lengths were determined, no correlation was found for PFOA, supporting the hypothesis that sea turtles could have a higher ability to eliminate this perfluorinated chemical from their blood than other PFCAs. However, we do not know if the concentrations are species or sampling areas dependent.

Association between perfluoroalkyl acids and kidney function in a cross-sectional study of adolescents

BACKGROUND

Perfluoroalkyl acids are synthetic compounds widely used in industrial and commercial applications. Laboratory studies suggest that these persistent and bioaccumulative chemicals produce oxidant stress and damage glomerular endothelial cells, raising concern regarding the impact of these compounds on renal function.

METHODS

We performed cross-sectional analyses of data 1960 participants aged 12-19 years of the 2003-2010 National Health and Nutrition Examination Surveys. PFAA exposure was assessed using levels of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid, and perfluorohexane sulfonic acid. Primary study outcomes were estimated glomerular filtration rate (eGFR) and serum uric acid.

RESULTS

While adjusting for demographics, cotinine, prehypertension, insulin resistance, body mass index, and hypercholesterolemia, adolescents in the highest PFOA and PFOS quartile had a lower eGFR, 6.84 mL/min/1.73 m(2) (95% CI: 2.19 to 11.48) and 9.69 mL/min/1.73 m(2) (95 % CI: -4.59 to 14.78), respectively, compared to the lowest quartile. Highest PFOA and PFOS quartiles were also associated with 0.21 mg/dL (95% CI: 0.056 to 0.37) and 0.19 mg/dL (95% CI: 0.032 to 0.34) increases in uric acid, respectively.

CONCLUSIONS

PFAAs are associated with a reduction in kidney function and increased uric acid levels in otherwise healthy adolescents. Reverse causation and residual confounding could explain the results. Our study results confirm and amplify previous findings, though longitudinal studies examining prenatal and childhood biomarkers in relationship with robust measures of childhood renal function are needed.

Na+/Taurocholate Cotransporting Polypeptide and Apical Sodium-Dependent Bile Acid Transporter Are Involved in the Disposition of Perfluoroalkyl Sulfonates in Humans and Rats

Among the perfluoroalkyl sulfonates (PFASs), perfluorohexane sulfonate (PFHxS), and perfluorooctane sulfonate (PFOS) have half-lives of several years in humans, mainly due to slow renal clearance and potential hepatic accumulation. Both compounds undergo enterohepatic circulation. To determine whether transporters involved in the enterohepatic circulation of bile acids are also involved in the disposition of PFASs, uptake of perfluorobutane sulfonate (PFBS), PFHxS, and PFOS was measured using freshly isolated human and rat hepatocytes in the absence or presence of sodium. The results demonstrated sodium-dependent uptake for all 3 PFASs. Given that the Na(+)/taurocholate cotransporting polypeptide (NTCP) and the apical sodium-dependent bile salt transporter (ASBT) are essential for the enterohepatic circulation of bile acids, transport of PFASs was investigated in stable CHO Flp-In cells for human NTCP or HEK293 cells transiently expressing rat NTCP, human ASBT, and rat ASBT. The results demonstrated that both human and rat NTCP can transport PFBS, PFHxS, and PFOS. Kinetics with human NTCP revealed Km values of 39.6, 112, and 130 µM for PFBS, PFHxS, and PFOS, respectively. For rat NTCP Km values were 76.2 and 294 µM for PFBS and PFHxS, respectively. Only PFOS was transported by human ASBT whereas rat ASBT did not transport any of the tested PFASs. Human OSTα/β was also able to transport all 3 PFASs. In conclusion, these results suggest that the long half-live and the hepatic accumulation of PFOS in humans are at least, in part, due to transport by NTCP and ASBT.

Phlebotomy treatment for elimination of perfluoroalkyl acids in a highly exposed family: a retrospective case-series

BACKGROUND

Perfluoroalkyl acids (PFAAs) are a family of commonly used synthetic chemicals that have become widespread environmental contaminants. In human serum, perfluorohexane sulfonate (PFHxS), perflurooctane sulfonate (PFOS), and perfluorooctanoate (PFOA) are most frequently detected, in part owing to their long elimination half-lives of between 3.8 yrs (PFOA) and 8.5 yrs (PFHxS). These PFAAs also cross the placenta and have been associated with developmental toxicity, and some are considered likely human carcinogens. Interventions to eliminate PFAAs in highly contaminated individuals would reduce future health risks, but minimal research has been conducted on methods to facilitate accelerated human clearance of these persistent substances.

METHODS

Six patients with elevated serum concentrations from a single family were treated by intermittent phlebotomy over a 4-5 year period at intervals similar to, or less frequent than what is done for routine blood donation at Canadian Blood Services. The apparent elimination half-life (HLapp) for PFHxS, PFOS, and PFOA in this treated population was calculated in each patient and compared to the intrinsic elimination half-lives (HLin) from a literature reference population of untreated fluorochemical manufacturing plant retirees (n = 26, age >55 yrs).

RESULTS

For all three PFAAs monitored during phlebotomy, HLapp in each of the family members (except the mother, who had a low rate of venesection) was significantly shorter than the geometric mean HL measured in the reference population, and in some cases were even shorter compared to the fastest eliminator in the reference population.

CONCLUSION

This study suggests significantly accelerated PFAA clearance with regular phlebotomy treatment, but the small sample size and the lack of controls in this clinical intervention precludes drawing firm conclusions. Given the minimal risks of intermittent phlebotomy, this may be an effective and safe clinical intervention to diminish the body burden of PFAAs in highly exposed people.

Gastrointestinal Elimination of Perfluorinated Compounds Using Cholestyramine and Chlorella pyrenoidosa

Background. While perfluorinated compounds (PFCs) are a family of commonly used synthetic compounds with many applications, some PFCs remain persistent within the human body due, in part, to enterohepatic recirculation and renal tubular reabsorption. With increasing recognition of potential harm to human health associated with PFC bioaccumulation, interventions to facilitate elimination of these toxicants are welcome in order to potentially preclude or overcome illness. Minimal research has been undertaken thus far on methods to accelerate human clearance of PFCs. Methods. To test for possible oral treatments to hasten PFC elimination, a group of individuals with elevated PFC levels was treated with cholestyramine (CSM) and, after a break, was subsequently treated with Chlorella pyrenoidosa (CP). Stool samples were collected from all participants (i) prior to any treatment, (ii) during treatment with CSM, and (iii) during treatment with CP. Results. With CSM treatment, significant levels of three distinct PFCs were found in all stools, while levels were mostly undetectable prior to treatment. Following treatment with oral CP, undetectable or very low levels of all PFCs were noted in each sample tested. Conclusion. CSM appears to facilitate elimination of some common PFCs and may have some role in the clinical management of patients with accrued PFCs.

Biomonitoring and Elimination of Perfluorinated Compounds and Polychlorinated Biphenyls through Perspiration: Blood, Urine, and Sweat Study

Perfluorinated compounds (PFCs) are man-made organofluorine chemicals manufactured and marketed for their stain-resistant properties. Polychlorinated biphenyls (PCBs) are anthropogenic organochlorine compounds previously used in various industrial and chemical applications prior to being banned in the Western world in the 1970s. Both PFCs and PCBs are persistent contaminants within the human organism and both have been linked to adverse health sequelae. Data is lacking on effective means to facilitate clearance of PFCs and PCBs from the body. Methods. Blood, urine, and sweat were collected from 20 individuals (10 healthy participants and 10 participants with assorted health problems) and analyzed for PFCs and PCBs using high performance liquid chromatography tandem mass spectrometry. Results. Some individual PCB congeners, but not all, were released into sweat at varying concentrations. None of the PFCs found in serum testing appeared to be excreted efficiently into perspiration. Conclusions. Induced perspiration may have some role in facilitating elimination of selected PCBs. Sweat analysis may be helpful in establishing the existence of some accrued PCBs in the human body. Sweating does not appear to facilitate clearance of accrued PFHxS (perfluorohexane sulfonate), PFOS (perfluorooctane sulfonate), or PFOA (perfluorooctanoic acid), the most common PFCs found in the human body.

Consumption of seafood, serum liver enzymes, and blood levels of PFOS and PFOA in the Japanese population

OBJECTIVE

Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) have been shown to accumulate in the human body. The purpose of the present study was to examine the factors associated with the blood levels of PFOS and PFOA.

METHODS

A cross-sectional study was performed on 307 men and 301 women (aged 16-76 years) living in 15 prefectures in Japan. Blood levels of PFOS and PFOA were measured by liquid chromatography-mass spectrometry. Hepatic enzymes (γ-GTP, GOT, and GPT) and ω-3 polyunsaturated fatty acids (DHA and EPA) levels in serum were also measured. Associations between the levels of PFOS and PFOA in blood and the intake frequency of 41 kinds of dishes, foods and beverages and the serum levels of liver enzymes and ω-3 polyunsaturated fatty acids were examined using rank correlations.

RESULTS

Frequency of intake of boiled fish in broth, sliced raw fish and coastal fish showed significant positive correlations with PFOS concentrations in blood after adjustments for potential confounders. Serum levels of GOT, GPT, DHA and EPA showed significant positive correlations with PFOS and PFOA in blood. There was also a significant regional difference in the blood levels of PFOS and 2013PFOA, with medians being highest in the Tokai/Hokuriku/Kinki region.

CONCLUSIONS

These findings suggest that the concentrations of PFOS in blood were mainly associated with fish consumption and that the levels of PFOS and PFOA were associated with the serum levels of liver enzymes in Japanese populations. Further investigations are required to clarify the reason for the regional differences in blood levels of PFOS and PFOA in Japan.

Enhanced poison elimination in critical care

Nephrologists and critical care physicians are commonly involved in the treatment of severely poisoned patients. Various techniques exist presently to enhance the elimination of poisons. Corporeal treatments occur inside of the body and include multiple-dose activated charcoal, resin binding, forced diuresis, and urinary pH alteration. Extracorporeal treatments include hemodialysis, hemoperfusion, peritoneal dialysis, continuous renal replacement therapy, exchange transfusion, and plasmapheresis. This review illustrates the potential indications and limitations in the application of these modalities as well as the pharmacological characteristics of poisons amenable to enhanced elimination.

Arsenic, cadmium, lead, and mercury in sweat: a systematic review

Arsenic, cadmium, lead, and mercury exposures are ubiquitous. These toxic elements have no physiological benefits, engendering interest in minimizing body burden. The physiological process of sweating has long been regarded as “cleansing” and of low risk. Reports of toxicant levels in sweat were sought in Medline, Embase, Toxline, Biosis, and AMED as well as reference lists and grey literature, from inception to March 22, 2011. Of 122 records identified, 24 were included in evidence synthesis. Populations, and sweat collection methods and concentrations varied widely. In individuals with higher exposure or body burden, sweat generally exceeded plasma or urine concentrations, and dermal could match or surpass urinary daily excretion. Arsenic dermal excretion was severalfold higher in arsenic-exposed individuals than in unexposed controls. Cadmium was more concentrated in sweat than in blood plasma. Sweat lead was associated with high-molecular-weight molecules, and in an interventional study, levels were higher with endurance compared with intensive exercise. Mercury levels normalized with repeated saunas in a case report. Sweating deserves consideration for toxic element detoxification. Research including appropriately sized trials is needed to establish safe, effective therapeutic protocols.

Environmental determinants of chronic disease and medical approaches: recognition, avoidance, supportive therapy, and detoxification

The World Health Organization warns that chronic, noncommunicable diseases are rapidly becoming epidemic worldwide. Escalating rates of neurocognitive, metabolic, autoimmune and cardiovascular diseases cannot be ascribed only to genetics, lifestyle, and nutrition; early life and ongoing exposures, and bioaccumulated toxicants may also cause chronic disease. Contributors to ill health are summarized from multiple perspectives--biological effects of classes of toxicants, mechanisms of toxicity, and a synthesis of toxic contributors to major diseases. Healthcare practitioners have wide-ranging roles in addressing environmental factors in policy and public health and clinical practice. Public health initiatives include risk recognition and chemical assessment then exposure reduction, remediation, monitoring, and avoidance. The complex web of disease and environmental contributors is amenable to some straightforward clinical approaches addressing multiple toxicants. Widely applicable strategies include nutrition and supplements to counter toxic effects and to support metabolism; as well as exercise and sweating, and possibly medication to enhance excretion. Addressing environmental health and contributors to chronic disease has broad implications for society, with large potential benefits from improved health and productivity.

Electromagnetic hypersensitivity: fact or fiction?

As the prevalence of wireless telecommunication escalates throughout the world, health professionals are faced with the challenge of patients who report symptoms they claim are connected with exposure to some frequencies of electromagnetic radiation (EMR). Some scientists and clinicians acknowledge the phenomenon of hypersensitivity to EMR resulting from common exposures such as wireless systems and electrical devices in the home or workplace; others suggest that electromagnetic hypersensitivity (EHS) is psychosomatic or fictitious. Various organizations including the World Health Organization as well as some nation states are carefully exploring this clinical phenomenon in order to better explain the rising prevalence of non-specific, multi-system, often debilitating symptoms associated with non-ionizing EMR exposure. As well as an assortment of physiological complaints, patients diagnosed with EHS also report profound social and personal challenges, impairing their ability to function normally in society. This paper offers a review of the sparse literature on this perplexing condition and a discussion of the controversy surrounding the legitimacy of the EHS diagnosis. Recommendations are provided to assist health professionals in caring for individuals complaining of EHS.

Sensitivity-related illness: the escalating pandemic of allergy, food intolerance and chemical sensitivity

The prevalence of allergic-related diseases, food intolerance, and chemical sensitivities in both the pediatric and adult population has increased dramatically over the last two decades, with escalating rates of associated morbidity. Conditions of acquired allergy, food intolerance and chemical hypersensitivity are frequently the direct sequelae of a toxicant induced loss of tolerance (TILT) in response to a significant initiating toxic exposure. Following the primary toxicant insult, the individuals become sensitive to low levels of diverse and unrelated triggers in their environment such as commonly encountered chemical, inhalant or food antigens. Among sensitized individuals, exposure to assorted inciting stimuli may precipitate diverse clinical and/or immune sequelae as may be evidenced by clinical symptoms as well as varied lymphocyte, antibody, or cytokine responses in some cases. Recently recognized as a mechanism of disease development, TILT and resultant sensitivity-related illness (SRI) may involve various organ systems and evoke wide-ranging physical or neuropsychological manifestations. With escalating rates of toxicant exposure and bioaccumulation in the population-at-large, an increasing proportion of contemporary illness is the direct result of TILT and ensuing SRI. Avoidance of triggers will preclude symptoms, and desensitization immunotherapy or immune suppression may ameliorate symptomatology in some cases. Resolution of SRI generally occurs on a gradual basis following the elimination of bioaccumulated toxicity and avoidance of further initiating adverse environmental exposures. As has usually been the case throughout medical history whenever new evidence regarding disease mechanisms emerges, resistance to the translation of knowledge abounds.