Evaluation of relative effect potencies (REPs) for dioxin-like compounds to derive systemic or human-specific TEFs to improve human risk assessment

Species differences in specific ligand-binding affinity and activation of AHR: The biological basis for calculation of relative effective potencies and toxic equivalence factors

In 2022 the World Health Organization (WHO) published updated 'Toxic Equivalence Factors' (TEFs) for a wide variety of chlorinated dioxins, dibenzofurans and PCBs [collectively referred to as 'dioxin-like chemicals'; DLCs) that interact with the aryl hydrocarbon receptor (AHR)]. Their update used sophisticated statistical analysis of hundreds of published studies that reported estimation of 'Relative Effective Potency' (REP) values for individual DLC congeners. The weighting scheme used in their assessment of each study favored in vivo over in vitro studies and was based largely on rodent studies. In this Commentary, we highlight the large body of published studies that demonstrate large species differences in AHR-ligand activation and provide supporting evidence for our position that the WHO 2022 TEF values intended for use in human risk assessment of DLC mixtures will provide highly misleading overestimates of 'Toxic Equivalent Quotients' (TEQs), because of well-recognized striking differences in AHR ligand affinities between rodent (rat, mouse) and human. The data reviewed in our Commentary support the position that human tissue-derived estimates of REP/TEF values for individual DLC congeners, although uncertain, will provide much better, more realistic estimates of potential activation of the human AHR, when exposure to complex DLC mixtures occurs.

A Physiologically Based Pharmacokinetic (PBPK) Modeling Framework for Mixtures of Dioxin-like Compounds

Humans are exposed to persistent organic pollutants, such as dioxin-like compounds (DLCs), as mixtures. Understanding and predicting the toxicokinetics and thus internal burden of major constituents of a DLC mixture is important for assessing their contributions to health risks. PBPK models, including dioxin models, traditionally focus on one or a small number of compounds; developing new or extending existing models for mixtures often requires tedious, error-prone coding work. This lack of efficiency to scale up for multi-compound exposures is a major technical barrier toward large-scale mixture PBPK simulations. Congeners in the DLC family, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), share similar albeit quantitatively different toxicokinetic and toxicodynamic properties. Taking advantage of these similarities, here we reported the development of a human PBPK modeling framework for DLC mixtures that can flexibly accommodate an arbitrary number of congeners. Adapted from existing TCDD models, our mixture model contains the blood and three diffusion-limited compartments-liver, fat, and rest of the body. Depending on the number of congeners in a mixture, varying-length vectors of ordinary differential equations (ODEs) are automatically generated to track the tissue concentrations of the congeners. Shared ODEs are used to account for common variables, including the aryl hydrocarbon receptor (AHR) and CYP1A2, to which the congeners compete for binding. Binary and multi-congener mixture simulations showed that the AHR-mediated cross-induction of CYP1A2 accelerates the sequestration and metabolism of DLC congeners, resulting in consistently lower tissue burdens than in single exposure, except for the liver. Using dietary intake data to simulate lifetime exposures to DLC mixtures, the model demonstrated that the relative contributions of individual congeners to blood or tissue toxic equivalency (TEQ) values are markedly different than those to intake TEQ. In summary, we developed a mixture PBPK modeling framework for DLCs that may be utilized upon further improvement as a quantitative tool to estimate tissue dosimetry and health risks of DLC mixtures.

Dermal Exposure to Hazardous Chemicals in Baby Diapers: A Re-Evaluation of the Quantitative Health Risk Assessment Conducted by The French Agency for Food, Environmental and Occupational Health and Safety (ANSES)

In January 2019, the French Agency for Food, Environmental and Occupational Health and Safety (ANSES) published an opinion on risks related to the presence of hazardous chemicals in infant diapers. ANSES found that health reference values were largely exceeded for polycyclic aromatic hydrocarbons (PAHs), dioxins (PCCD/Fs) and dioxin-like polychlorobiphenyls (DL-PCBs). The levels of formaldehyde and some fragrances were also considered potentially unsafe. Therefore, ANSES concluded that actions have to be taken to restrict levels of these contaminants in diapers. Under the exposure scenario deemed the most reliable by ANSES, estimates of cancer risks of the most potent PAHs detected in diapers exceeded 10⁻³ and hazard quotients for neurobehavioral effects attained values up to 66. Regarding dioxins and DL-PCBs, ANSES derived a hazard quotient of 12 for the risk of decreased sperm count at adult age. The aim of this study was to examine whether the exposure and risk assessment conducted by ANSES contained potential flaws that could explain such a high exceedance of health reference values. This study also put into perspective the exposure from diapers with that from breast milk whose benefits for children’s health are undisputable despite contamination by PAHs, dioxins and DL-PCB_S.

Issues in the hazard and risk assessment of perfluoroalkyl substance mixtures

In its 2020 Scientific Opinion on the Risk to human health related to the presence of perfluoroalkyl substances in food, EFSA had to tackle the challenging task to evaluate the risk(s) posed by the potential presence of per- and polyfluoroalkyl substances (PFAS). The assessment had to cover 27 perfluoroalkyl carboxylates (PFCAs) and sulfonates (PFSAs) of variable chain length (C4-C18). Grouping such a large number of structurally diverse compounds - many with a limited exposure and absent toxicity database - is a complex task. Our commentary summarizes some of the issues and pitfalls in this assessment.

Dioxins and dioxin-like PCBs in buffalo milk from the Campania region (Italy): Decreasing trend and baseline assessment over 10 years (2008-2018)

Polychlorodibenzo-p-dioxins, polychlorodibenzo-furans (PCDD/Fs) and dioxin-like polychlorobiphenyls (DL-PCBs) enter the food chain from the environment. In this study, we report the 2008-2018 time-trends in the PCDD/F and DL-PCB contamination of milk from buffaloes fed on local forage in rural areas of the Campania region. Validated according to QA/QC criteria, the dataset (N = 808 on a total of 2068 samples, after excluding follow-up results and outliers) was computed on the upper-bound value pg WHO-TEQ₂₀₀₅ g^-1fat. We assessed time-trends and assayed baseline contamination levels, which displayed log-normal distribution. A significant decreasing trend (p < 0.01) was observed from 2008 to 2009 and 2010; the P50-P95 range fell from 2.37-8.48 pg WHO-TEQ₂₀₀₅ g^-1fat (N = 393) in 2008 to 1.73-4.61 in 2009 (N = 86) and to 0.67-1.46 in 2010 (N = 42). From 2010 to 2018 (N = 329), no significant variation was found among years and the related dataset fitted a log-normal distribution (p < 0.05). Occurrence descriptors indicated that the baseline contamination of dairy products (mean = 0.54; P50-P95 = 0.47-1.24) in the Campania Region was well below the EU regulatory limit in force (5.5 pg WHO-TEQ₂₀₀₅ g^-1fat). Given the Tolerable Weekly Intake of 2 pg WHO-TEQ kg^-1 body weight (bw) proposed by the EFSA for PCDD/Fs and DL-PCBs, this level of baseline contamination is discussed with regard to the orientation of food safety and food security risk connected with buffalo mozzarella cheese production.

Occurrence and spatial distribution of dioxin and dioxin-like compounds in topsoil of Taranto (Apulia, Italy) by GC-MS analysis and DR-CALUX® bioassay

The aim of the present study was to assess the occurrence and spatial distribution of PCDD/Fs and dioxin-like compounds in topsoils of Taranto (Apulia Region), one of the most heavily industrialized and contaminated area of Southern Italy. A combined approach of chemical analysis by GC-MS/MS and AhR reporter gene bioassay was applied in a subset of topsoil samples (n = 20) collected in 2017-18 from ten sites embracing three levels of risk (from high to low) in the framework of a large survey inside Taranto municipality. TCDD-BEQs and GC-MS/MS TEQ_WHO and TEQ_THEORETICAL revealed a decreasing trend with the distance from main industrial settings and landfill areas. A strong correlation between TCDD-BEQs and TEQ_WHO values (R² = 0.85) and TEQ_THEORETICAL (R² = 0.88) was also found. In 3 out of 10 topsoil investigated, BEQs and TEQ_{WHO/THEORETICAL} resulted above Italian National Regulatory Limits for ∑PCDD/Fs in green, private and recreational used soils (10 ng TEQ/kg d.w. D.Lgs 152/2006) and for ∑PCDD/F/dl-PCBs in agricultural and farming soil (6 ng TEQ/kg d.w. D.M. 46/2019). GC-MS/MS pattern revealed the highest prevalence of dl-PCBs in 6 out of 10 sites, followed by PCDFs and PCDDs. Those sites are all located in proximity of main industrial steel and iron ore sinter plant, steel plant's landfills and illegal dumping sites. An update on occurrence and spatial distribution of PCDD/Fs and dl-PCBs contamination of Taranto urban soils was obtained and the DR-CALUX® bioassay was further recommended as a suitable screening tool for environmental and human risk assessment.

Risk Assessment of Per- and Polyfluoroalkyl Substance Mixtures: A Relative Potency Factor Approach

Per- and polyfluoroalkyl substances (PFAS) often occur together as contamination in exposure media such as drinking water or food. The relative potency factor (RPF) methodology facilitates the risk assessment of mixture exposure. A database of liver endpoints was established for 16 PFAS, using data with the same species (rat), sex (male), and exposure route (oral) and comparable exposure duration (42-90 d). Dose-response analysis was applied to derive the relative potencies of 3 perfluoroalkyl sulfonic acids (perfluorobutane sulfonic acid, perfluorohexane sulfonic acid, perfluorooctane sulfonic acid), 8 perfluoroalkyl carboxylic acids (perfluorobutanoic acid, perfluorohexanoic acid, perfluorononanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotetradecanoic acid, perfluorohexadecanoic acid, perfluorooctadecanoic acid), 2 perfluoroalkyl ether carboxylic acids (tetrafluoro-2-[heptafluoropropoxy]propanoic acid, 3H-perfluoro-3-[(3-methoxy-propoxy)propanoic acid]), and 2 fluorotelomer alcohols (6:2 FTOH, 8:2 FTOH) compared to perfluorooctanoic acid (PFOA), based on liver effects. In addition, the RPFs of 7 other perfluoroalkyl acids were estimated based on read-across. This resulted in the relative potencies of 22 PFAS compared to the potency of index compound PFOA. The obtained RPFs can be applied to measured PFAS quantities, resulting in the sum of PFOA equivalents in a mixture. This sum can be compared with an established PFOA concentration limit (e.g., in drinking water or food) or an external health-based guidance value (e.g., tolerable daily intake, acceptable daily intake, or reference dose) to estimate the risk resulting from direct oral exposure to mixtures. Assessing mixture exposure is particularly relevant for PFAS, with omnipresent exposure in our daily lives. Environ Toxicol Chem 2021;40:859-870. © 2020 SETAC.

Induction of AhR transactivation by PBDD/Fs and PCDD/Fs using a novel human-relevant, high-throughput DRhuman CALUX reporter gene assay

Polychlorinated dioxins and dibenzofurans (PCDD/Fs) are highly toxic contaminants that are strictly regulated and monitored in the environment and food to reduce human exposure. Recently, the increasing occurrence of polybrominated dioxins and dibenzofurans (PBDD/Fs) in the environment is raising concerns about the impact on human health by the combined exposure to chlorinated and brominated analogues of dioxins. Toxicological properties of PBDD/Fs relative to PCDD/Fs have not been firmly established, and brominated dioxins are not included in routine monitoring programs. In this study, we set out to determine human-relevant congener-specific potency values for a range of brominated and chlorinated dioxin congeners, based on their aryl hydrocarbon receptor (AhR)-mediated mode of toxic action. Transactivation of the AhR was measured using dioxin-responsive (DR) CALUX reporter gene assays. Because of known species-differences in dioxin-mediated toxicity, we developed and used a HepG2 human liver cell-based DR human CALUX assay that is a variant of the rodent-based DR CALUX. The assay was found to be highly inducible and stable, with low variations between independent measurements. Using both DR CALUX assays in an automated high-throughput mode we found that overall PBDD/Fs were as potent as PCDD/Fs in inducing AhR transactivation, but congener-specific differences were observed. We also observed species-specific differences in sensitivity and potency when comparing DR human REP values to those obtained in the rat-based DR CALUX. Finally, we observed significant differences between WHO-TEF values and DR human REP values, suggesting that actual WHO-TEF values may underestimate the hazards associated with exposure of humans to dioxins.

An Update on the Content of Fatty Acids, Dioxins, PCBs and Heavy Metals in Farmed, Escaped and Wild Atlantic Salmon (Salmo salar L.) in Norway

In this paper, we present updated data on proximate composition, amino acid, and fatty acid composition, as well as concentrations of dioxins, polychlorinated biphenyls (PCBs), and selected heavy metals, in fillets from farmed (n = 20), escaped (n = 17), and wild (n = 23) Atlantic salmon (Salmo salar L.). The concentrations of dioxins (0.53 ± 0.12 pg toxic equivalents (TEQ)/g), dioxin-like PCBs (0.95 ± 0.48 pg TEQ/g), mercury (56.3 ± 12.9 µg/kg) and arsenic (2.56 ± 0.87 mg/kg) were three times higher in wild compared to farmed salmon, but all well below EU-uniform maximum levels for contaminants in food. The six ICES (International Council for the Exploration of the Sea) PCBs concentrations (5.09 ± 0.83 ng/g) in wild salmon were higher than in the farmed fish (3.34 ± 0.46 ng/g). The protein content was slightly higher in wild salmon (16%) compared to the farmed fish (15%), and the amount of essential amino acids were similar. The fat content of farmed salmon (18%) was three times that of the wild fish, and the proportion of marine long-chain omega-3 fatty acids was a substantially lower (8.9 vs. 24.1%). The omega-6 to omega-3 fatty acid ratio was higher in farmed than wild salmon (0.7 vs. 0.05). Both farmed and wild Atlantic salmon are still valuable sources of eicosapentaenoic acid and docosahexaenoic acid. One 150 g portion per week will contribute to more (2.1 g and 1.8 g) than the recommended weekly intake for adults.

Cardiovascular Effects of Polychlorinated Biphenyls and Their Major Metabolites

BACKGROUND

Xenobiotic metabolism is complex, and accounting for bioactivation and detoxification processes of chemicals remains among the most challenging aspects for decision making with in vitro new approach methods data.

OBJECTIVES

Considering the physiological relevance of human organotypic culture models and their utility for high-throughput screening, we hypothesized that multidimensional chemical-biological profiling of chemicals and their major metabolites is a sensible alternative for the toxicological characterization of parent molecules vs. metabolites in vitro.

METHODS

In this study, we tested 25 polychlorinated biphenyls (PCBs) [PCB 3, 11, 52, 126, 136, and 153 and their relevant metabolites (hydroxylated, methoxylated, sulfated, and quinone)] in concentration-response (10 nM-100μM) for effects in human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) and endothelial cells (ECs) (iPSC-derived and HUVECs). Functional phenotypic end points included effects on beating parameters and intracellular Ca2+ flux in CMs and inhibition of tubulogenesis in ECs. High-content imaging was used to evaluate cytotoxicity, mitochondrial integrity, and oxidative stress.

RESULTS

Data integration of a total of 19 physicochemical descriptors and 36 in vitro phenotypes revealed that chlorination status and metabolite class are strong predictors of the in vitro cardiovascular effects of PCBs. Oxidation of PCBs, especially to di-hydroxylated and quinone metabolites, was associated with the most pronounced effects, whereas sulfation and methoxylation of PCBs resulted in diminished bioactivity.

DISCUSSION

Risk characterization analysis showed that although in vitro derived effective concentrations exceeded the levels measured in the general population, risks cannot be ruled out due to the potential for population variability in susceptibility and the need to fill data gaps using read-across approaches. This study demonstrated a strategy for how in vitro data can be used to characterize human health risks from PCBs and their metabolites. https://doi.org/10.1289/EHP7030.

Generation and application of a Tg(cyp1a:egfp) transgenic marine medaka (Oryzias melastigma) line as an in vivo assay to sensitively detect dioxin-like compounds in the environment

Large-range environmental pollution by dioxin and dioxin-like compounds (DLCs) is becoming a serious problem. To establish an in vivo method for the detection of DLCs in seawater, a Tg(cyp1a-12DRE:egfp) transgenic marine medaka (Oryzias melastigma) line was first developed with the modified cyp1a-12DRE promoter driving enhanced green fluorescent protein (EGFP) expression using Tol2 transgenesis technology. With increasing concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), the EGFP fluorescence intensity increased significantly. The Tg(cyp1a-12DRE:egfp) medaka possessed high sensitivity (limit of detection of 1 ng/L TCDD) and specificity and low background. This transgenic line is capable of detecting DLCs in environmental seawater in which the concentration of DLCs is at least 0.12207 ng/L TCDD after sample enrichment. The fluorescence-toxic equivalency (TEQ) values from EGFP intensity were closely correlated with the chemical-TEQ values obtained from chemical analyses. Furthermore, the Tg(cyp1a-12DRE:egfp) medaka can directly detect DLCs in seawater samples after a serious pollution accident and screen unknown aryl hydrocarbon receptor (AhR) agonists for risk assessment. For the first time, a convenient method has been established that sensitively and specifically responds to DLCs using the Tg(cyp1a-12DRE:egfp) marine medaka, which could be a highly efficient tool for detecting seawater DLCs in the future.

The Ah Receptor: Adaptive Metabolism, Ligand Diversity, and the Xenokine Model

The Ah receptor (AHR) has been studied for almost five decades. Yet, we still have many important questions about its role in normal physiology and development. Moreover, we still do not fully understand how this protein mediates the adverse effects of a variety of environmental pollutants, such as the polycyclic aromatic hydrocarbons (PAHs), the chlorinated dibenzo-p-dioxins ("dioxins"), and many polyhalogenated biphenyls. To provide a platform for future research, we provide the historical underpinnings of our current state of knowledge about AHR signal transduction, identify a few areas of needed research, and then develop concepts such as adaptive metabolism, ligand structural diversity, and the importance of proligands in receptor activation. We finish with a discussion of the cognate physiological role of the AHR, our perspective on why this receptor is so highly conserved, and how we might think about its cognate ligands in the future.

Relative Effect Potency Estimates for Dioxin-Like Compounds in Pregnant Women with Gestational Diabetes Mellitus and Blood Glucose Outcomes Based on a Nested Case-control Study

To improve the applicability of the toxic equivalents principle for human health risk assessment, systemic relative effect potencies (REPs) for dioxin-like compounds (DLCs) deriving from human in vivo data are required. A prospective nested case-control study was performed to determine REPs from the human serum concentration of DLCs using gestational diabetes mellitus (GDM) and fasting blood glucose (FBG) as the end points of concern. Serum concentration of 29 DLCs from 77 cases and 154 controls were measured. Logistic and linear regression were used to estimate the effects of individual congeners on GDM and FBG, respectively. The REPs based on GDM and FBG were calculated from the ratios of regression coefficients, β_i (DLCs)/β_TCDD. Two sets of consistent human serum-based REPs, that is, GDM-REP and FBG-REP, were established and largely agree with REPs from other human studies. These human-serum REPs show much smaller variation compared to the 4 to 5 orders of magnitude span in REPs database for the present WHO-TEF determination. Moreover, the established REPs fitted well with WHO-TEFs, especially for polychlorinated dibenzo- p-dioxins, furans. These REPs reflecting real human exposure scenarios exhibited validity and could be used to improve health risk assessment of human body burden of DLCs.

Concentration dependence of human and mouse aryl hydrocarbon receptor responsiveness to polychlorinated biphenyl exposures: Implications for aroclor mixtures

1. Aryl hydrocarbon receptor (AhR) ligands, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyls (PCBs), are endocrine disrupting chemicals associated with nonalcoholic fatty liver disease. This study documents the species-specific differences between mouse (high affinity mAhR) and human AhR (hAhR) activation by PCB congeners and Aroclor mixtures. 2. AhR activation by TCDD or PCBs 77, 81, 114, 114, 126, and 169 was measured using luciferase reporter constructs transfected into either Hepa1c1c7 mouse or HepG2 human liver cell lines. The EC₅₀ values were lower in Hepa1c1c7 cells than HepG2 cells for all compounds tested except PCB 81. The results for TCDD and PCB 126 were validated in primary human and mouse hepatocytes by measuring CYP1A1 gene transcript levels. 3. Because humans are exposed to PCB mixtures, several mixtures (Aroclors 1254; 1260; and 1260 + 0.1% PCB126 each at 10 µg/ml) were then tested. Neither Aroclor 1254 nor Aroclor 1260 increased luciferase activity by the transfected AhR reporter construct. The Aroclor 1260 + 0.1% PCB 126 mixture induced mAhR-mediated transactivation, but not hAhR activation in cell lines. 4. In summary, significant concentration-dependent differences exist between human and mouse AhR activation by PCBs. Relative effect potencies differed, in some cases, from published toxic equivalency factors.

Risk for animal and human health related to the presence of dioxins and dioxin-like PCBs in feed and food

The European Commission asked EFSA for a scientific opinion on the risks for animal and human health related to the presence of dioxins (PCDD/Fs) and DL-PCBs in feed and food. The data from experimental animal and epidemiological studies were reviewed and it was decided to base the human risk assessment on effects observed in humans and to use animal data as supportive evidence. The critical effect was on semen quality, following pre- and postnatal exposure. The critical study showed a NOAEL of 7.0 pg WHO2005-TEQ/g fat in blood sampled at age 9 years based on PCDD/F-TEQs. No association was observed when including DL-PCB-TEQs. Using toxicokinetic modelling and taking into account the exposure from breastfeeding and a twofold higher intake during childhood, it was estimated that daily exposure in adolescents and adults should be below 0.25 pg TEQ/kg bw/day. The CONTAM Panel established a TWI of 2 pg TEQ/kg bw/week. With occurrence and consumption data from European countries, the mean and P95 intake of total TEQ by Adolescents, Adults, Elderly and Very Elderly varied between, respectively, 2.1 to 10.5, and 5.3 to 30.4 pg TEQ/kg bw/week, implying a considerable exceedance of the TWI. Toddlers and Other Children showed a higher exposure than older age groups, but this was accounted for when deriving the TWI. Exposure to PCDD/F-TEQ only was on average 2.4- and 2.7-fold lower for mean and P95 exposure than for total TEQ. PCDD/Fs and DL-PCBs are transferred to milk and eggs, and accumulate in fatty tissues and liver. Transfer rates and bioconcentration factors were identified for various species. The CONTAM Panel was not able to identify reference values in most farm and companion animals with the exception of NOAELs for mink, chicken and some fish species. The estimated exposure from feed for these species does not imply a risk.

Epidermal Growth Factor Receptor Signaling Disruption by Endocrine and Metabolic Disrupting Chemicals

The purpose of this study is to identify an environmentally relevant shared receptor target for endocrine and metabolism disrupting chemical pollutants. A feature of the tested chemicals was that they induced Cyp2b10 in vivo implicating activation of the constitutive androstane receptor (CAR). Recent studies suggest that these compounds could be indirect CAR activators via epidermal growth factor receptor (EGFR) inhibition. Assays included a CAR activity reporter assay, EGF endocytosis assay, and EGFR phosphorylation assay. Docking simulations were used to identify putative binding sites for environmental chemicals on the EGFR. Whole-weight and lipid-adjusted serum mean pollutant exposures were determined using data from the National Health and Examination Survey (NHANES) and compared with the IC50 values determined in vitro. Chlordane, trans-nonachlor, PCB-126, PCB-153, and atrazine were the most potent EGFR inhibitors tested. PCB-126, PCB-153, and trans-nonachlor appeared to be competitive EGFR antagonists as they displaced bound EGF from EGFR. However, atrazine acted through a different mechanism and could be an EGFR tyrosine kinase inhibitor. EGFR inhibition relative effect potencies were determined for these compounds. In NHANES, serum concentrations of trans-nonachlor, PCB-126, and PCB-153 greatly exceeded their calculated IC50 values. A common mechanism of action through EGFR inhibition for three diverse classes of metabolic disrupting chemicals was characterized by measuring inhibition of EGFR phosphorylation and EGF-EGFR endocytosis. Based on NHANES data, EGFR inhibition may be an environmentally relevant mode of action for some PCBs, pesticides, and herbicides.

Persistent Endocrine-Disrupting Chemicals and Fatty Liver Disease

PURPOSE OF REVIEW

Non-alcoholic fatty liver disease (NAFLD) is the most prominent chronic liver disease in Western countries, affecting approximately 25% of the population worldwide. Sex-specific differences in the development of NAFLD are apparent. While obesity and insulin resistance are major contributors to the increasing prevalence of NAFLD, a growing body of literature suggests that exposure to persistent endocrine-disrupting chemicals (pEDCs) may also play a role. This review summarizes recent (2011 and later) scientific literature investigating exposures to pEDCs, specifically persistent organic pollutants (POPs), and NAFLD, with a focus on sex-specific associations.

RECENT FINDINGS

The overwhelming majority of studies were conducted in single-sex animal models and provide biological evidence that exposures to 2,3,7,8-tetrachlorodibenzo-p-dioxin polychlorinated biphenyls, and other POPs or POP mixtures are negatively associated with liver health. There were four cross-sectional epidemiological studies in humans that reported associations for several POPs, including polychlorinated biphenyls and perfluorinated chemicals, with elevated liver enzymes. Only one of these studies, using a sample of gastric bypass surgery patients, examined sex-specific associations of POPs and liver enzymes, finding adverse associations among women only. The noticeable lack of studies investigating how differences (i.e., biochemical, physiological, and behavioral) between men and women may influence associations of pEDCs and NAFLD represents a large research gap in environmental health. Sexual dimorphism in metabolic processes throughout the body, including the liver, is established but often overlooked in the designs and analyses of studies. Other factors identified in this review that may also act to modulate associations of environmental chemicals and NAFLD are reproductive status and dietary nutrient intakes, which also remain understudied in the literature. Despite knowledge of sexual dimorphism in the actions of pEDCs, as well as in metabolic processes related to NAFLD development, few experimental or epidemiological studies have investigated sex-dependent associations. Future studies, especially those in humans, should be designed to address this research need. Consideration of other factors, such as reproductive status, dietary intakes, and mixtures of chemicals with varying endocrine-disrupting capabilities, should be explored.

SIMONI (smart integrated monitoring) as a novel bioanalytical strategy for water quality assessment: Part i-model design and effect-based trigger values

It is virtually impossible to reliably assess water quality with target chemical analyses only. Therefore, a complementary effect-based risk assessment by bioanalyses on mixtures of bioavailable micropollutants is proposed: the Smart Integrated Monitoring (SIMONI) strategy. The goal of this strategy is to obtain more reliable information on the water quality to select optimum measures for improvement. The SIMONI strategy is 2-tiered. Tier 1 is a bioanalytical hazard identification of sites. A tier 2 ecological risk assessment is carried out only at a limited number of sites where increased hazards are detected in tier 1. Tier 2 will be customized, based on tier 1 evaluation and additional knowledge of the aquatic system. The present study focuses on the tier 1 bioanalytical hazard identification to distinguish "hot spots" of chemical pollution. First, a selection was made of relevant and cost-effective bioanalytical endpoints to cover a wide spectrum of micropollutant modes of action. Specific endpoints may indicate which classes of chemicals might cause adverse effects. Second, effect-based trigger values (EBT) were derived for these bioassays to indicate potential ecological risks. Comparison of EBT with bioassay responses should discriminate sites exhibiting different chemical hazards. Third, a model was designed to estimate the overall risks for aquatic ecosystems. The associated follow-up for risk management is a "toxicity traffic light" system: green, low hazard (no action required); orange, potential risk (further research needed); and red, high risk (mitigation measures). Thanks to cost-effectiveness, flexibility, and relevance, the SIMONI strategy has the potential to become the first bioanalytical tool to be applied in regular water quality monitoring programs. Environ Toxicol Chem 2017;36:2385-2399. © 2017 SETAC.

Liver metabolic disruption induced after a single exposure to PCB126 in rats

Polychlorinated biphenyls (PCBs) have been recognized as metabolic disruptors. The liver plays a pivotal role in detoxification of an organism. Fatty liver results from altered intra-, and extra-hepatic mediators and is associated with increased glucose-related protein 78 (GRP78), commonly used as a marker for endoplasmic reticulum (ER) stress signaling. This pilot study aimed to study the effects of a single exposure on fatty liver metabolic parameters. The objective of the study is to characterize the effects of 3,3',4,4',5-pentachlorobiphenyl (PCB126) on ER stress protein chaperon GRP78 and CCAAT-enhancer-binding protein homologous protein (CHOP) and intra-hepatic mediators such as microsomal triglyceride transfer protein (MTP), sterol regulatory element-binding protein 1c (SREBP1c), and peroxisome proliferator-activated receptor alpha (PPARα), as well as extra-hepatic factors such as non-esterified fatty acid (NEFA) and tumor necrosis factor alpha (TNFα). Hepatic GRP78 mRNA and protein levels, indicating the presence of ER stress, were significantly increased following a single PCB126 exposure in rats. Intra-hepatic mechanisms such as lipoprotein secretion pathway (i.e., MTP), lipogenesis de novo (i.e., SREBP1c), and oxidation (i.e., PPARα) were altered in PCB126-treated rats. In addition, a state of inflammation measured by higher TNFα plasma levels was present in contaminated rats. These data indicate that a single injection of PCB126-modulated expression of GRP78 associated with hepatic ER stress and systemic inflammation in rats.

Relative effect potency estimates of dioxin-like activity for dioxins, furans, and dioxin-like PCBs in adults based on cytochrome P450 1A1 and 1B1 gene expression in blood

BACKGROUND

In the risk assessment of PCDDs, PCDFs, and dioxin-like (DL) PCBs, regulatory authorities support the use of the toxic equivalency factor (TEF)-scheme derived from a heterogeneous data set of the relative effect potency (REPs) estimates.

OBJECTIVES

We sought to determine REPs for dioxin-like compounds (DLCs) using expression of cytochrome P450 (CYP) 1A1 and 1B1 mRNA in human peripheral blood mononuclear cells representing two different pathways.

METHODS

We used a sex and age adjusted regression-based approach comparing the strength of association between each DLC and the cytochrome P450 (CYP) 1A1 and 1B1 mRNA expression in 320 adults residing in an organochlorine-polluted area of eastern Slovakia.

RESULTS

We calculated REPs based on CYP1A1 expression for 4 PCDDs, 8 PCDFs, and 1 PCB congener, and based on CYP1B1 expression for 5 PCDFs and 11 PCB congeners. REPs from CYP1A1 correlated with REPs previously derived from thyroid volume (ρ=0.85; p<0.001) and serum FT4 (ρ=0.77; p=0.009). The 13 log REPs from CYP1A1 correlated with log WHO-TEFs (r=0.63; p=0.015) and 11 log PCB REPs with PCB consensus toxicity factors (CTFs) for compounds with WHO-TEFs (r=0.80; p=0.003). The complete set of derived 56 log REPs correlated with the log CTFs (r=0.77; p=0.001) and log WHO-TEFs (r=0.81; p<0.001).

CONCLUSIONS

REPs calculated from thyroid and cytochrome P450 endpoints realistically reflect human exposure scenarios because they are based on human chronic and low-dose exposures. While the CYP 1A1 seems more suitable for toxicity evaluation of PCDD/Fs, the CYP 1B1 is more apt for PCDFs and PCBs and reflects different pathways.