Development of a Gestational and Lactational Physiologically Based Pharmacokinetic (PBPK) Model for Perfluorooctane Sulfonate (PFOS) in Rats and Humans and Its Implications in the Derivation of Health-Based Toxicity Values

Hexafluoropropylene Oxide Trimer Acid Is an Unsafe Substitute to Perfluorooctanoic Acid Due to Its Remarkable Liver Accumulation in Mice Disclosed by Comprehensive Toxicokinetic Models

Hexafluoropropylene oxide trimer acid (HFPO-TA, C2F5(CF2OCF(CF3))2COOH) is widely used as an alternative to perfluorooctanoic acid (PFOA), but whether it is a safe alternative requires further evaluation. In this study, male mice were exposed to three dosages (0.56, 2.8, and 14 mg/kg) of HFPO-TA via single oral gavage or intravenous injection for 28 days. HFPO-TA was rapidly absorbed into the blood and tissues within 15 min postexposure, with a volume of distribution approximately 3 times higher than PFOA, indicating a greater propensity for tissue distribution. Notably, HFPO-TA was distinctly more accumulated in liver compared to plasma and other tissues and very poorly excreted, with only 2.23% in urine and 7.26% in feces on the 21st day after oral exposure. A physiologically based toxicokinetic model, extrapolated to long-term low-dose exposure, revealed a lower bile clearance rate (8-fold) and higher liver partition coefficient (7-fold) than PFOA, and a higher hepatic first-pass effect of HFPO-TA (5-fold) than PFOA, contributing to its remarkable liver accumulation (5-fold). Molecular docking analysis reveals strong binding affinity of HFPO-TA with typical enterohepatic circulation transport proteins due to its strong hydrophobicity, flexible chain structure, and formation of additional hydrogen bonds, favoring HFPO-TA accumulation in the liver. The results suggest that HFPO-TA may not be a safe substitute for legacy PFAS, and further human exposure risk assessments are warranted.

An in vitro and machine learning framework for quantifying serum albumin binding of per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of anthropogenic chemicals; many are persistent, bioaccumulative, and mobile in the environment. Worldwide, PFAS bioaccumulation causes serious adverse health impacts, yet the physiochemical determinants of bioaccumulation and toxicity for most PFAS are not well understood, largely due to experimental data deficiencies. As most PFAS are proteinophilic, protein binding is a critical parameter for predicting PFAS bioaccumulation and toxicity. Among these proteins, human serum albumin (HSA) is the predominant blood transport protein for many PFAS. We previously demonstrated the utility of an in vitro differential scanning fluorimetry assay for determining relative HSA binding affinities for 24 PFAS. Here, we report HSA affinities for 65 structurally diverse PFAS from 20 chemical classes. We leverage these experimental data, and chemical/molecular descriptors of PFAS, to build 7 machine learning classifier algorithms and 9 regression algorithms, and evaluate their performance to identify the best predictive binding models. Evaluation of model accuracy revealed that the top-performing classifier model, logistic regression, had an AUROC (area under the receiver operating characteristic curve) statistic of 0.936. The top-performing regression model, support vector regression, had an R2 of 0.854. These top-performing models were then used to predict HSA-PFAS binding for chemicals in the EPAPFASINV list of 430 PFAS. These developed in vitro and in silico methodologies represent a high-throughput framework for predicting protein-PFAS binding based on empirical data, and generate directly comparable binding data of potential use in predictive modeling of PFAS bioaccumulation and other toxicokinetic endpoints.

Development of a Physiologically Based Pharmacokinetic (PBPK) Model for F-53B in Pregnant Mice and Its Extrapolation to Humans

Chlorinated polyfluorinated ether sulfonic acid (F-53B), a commonly utilized alternative for perfluorooctane sulfonate, was detected in pregnant women and cord blood recently. However, the lack of detailed toxicokinetic information poses a significant challenge in assessing the human risk assessment for F-53B exposure. Our study aimed to develop a physiologically based pharmacokinetic (PBPK) model for pregnant mice, based on toxicokinetic experiments, and extrapolating it to humans. Pregnant mice were administered 80 μg/kg F-53B orally and intravenously on gestational day 13. F-53B concentrations in biological samples were analyzed via ultraperformance liquid chromatography-mass spectrometry. Results showed the highest F-53B accumulation in the brain, followed by the placenta, amniotic fluid, and liver in fetal mice. These toxicokinetic data were applied to F-53B PBPK model development and evaluation, and Monte Carlo simulations were used to characterize the variability and uncertainty in the human population. Most of the predictive values were within a 2-fold range of experimental data (>72%) and had a coefficient of determination (R2) greater than 0.68. The developed mouse model was then extrapolated to the human and evaluated with human biomonitoring data. Our study provides an important step toward improving the understanding of toxicokinetics of F-53B and enhancing the quantitative risk assessments in sensitive populations, particularly in pregnant women and fetuses.

Contribution of Continued Dermal Exposure of PFAS-Containing Sunscreens to Internal Exposure: Extrapolation from In Vitro and In Vivo Tests to Physiologically Based Toxicokinetic Models

Per- and polyfluoroalkyl substances (PFASs) are widely present in sunscreen products as either active ingredients or impurities. They may penetrate the human skin barrier and then pose potential health risks. Herein, we aimed to develop a physiologically based toxicokinetic (PBTK) model capable of predicting the body loading of PFASs after repeated, long-term dermal application of commercial sunscreens. Ten laboratory-prepared sunscreens, generally falling into two categories of water-in-oil (W/O) and oil-in-water (O/W) sunscreens, were subject to in vitro percutaneous penetration test to assess the impacts of four sunscreen ingredients on PFAS penetration. According to the results, two sunscreen formulas representing W/O and O/W types that mostly enhanced PFAS dermal absorption were then selected for a subsequent 30 day in vivo exposure experiment in mice. PBTK models were successfully established based on the time-dependent PFAS concentrations in mouse tissues (R2 = 0.885-0.947) and validated through another 30 day repeated exposure experiment in mice using two commercially available sunscreens containing PFASs (R2 = 0.809-0.835). The PBTK model results suggest that applying sunscreen of the same amount on a larger skin area is more conducive to PFAS permeation, thus enhancing the exposure risk. This emphasizes the need for caution in practical sunscreen application scenarios, particularly during the summer months.

Quantitative cross-species comparison of serum albumin binding of per- and polyfluoroalkyl substances from five structural classes

Per- and polyfluoroalkyl substances (PFAS) are a class of over 8000 chemicals, many of which are persistent, bioaccumulative, and toxic to humans, livestock, and wildlife. Serum protein binding affinity is instrumental in understanding PFAS toxicity, yet experimental binding data is limited to only a few PFAS congeners. Previously, we demonstrated the usefulness of a high-throughput, in vitro differential scanning fluorimetry assay for determination of relative binding affinities of human serum albumin for 24 PFAS congeners from 6 chemical classes. In the current study, we used this assay to comparatively examine differences in human, bovine, porcine, and rat serum albumin binding of 8 structurally informative PFAS congeners from 5 chemical classes. With the exception of the fluorotelomer alcohol 1H, 1H, 2H, 2H-perfluorooctanol (6:2 FTOH), each PFAS congener bound by human serum albumin was also bound by bovine, porcine, and rat serum albumin. The critical role of the charged functional headgroup in albumin binding was supported by the inability of albumin of each species tested to bind 6:2 FTOH. Significant interspecies differences in serum albumin binding affinities were identified for each of the bound PFAS congeners. Relative to human albumin, perfluoroalkyl carboxylic and sulfonic acids were bound with greater affinity by porcine and rat serum albumin, and the perfluoroalkyl ether acid congener bound with lower affinity to porcine and bovine serum albumin. These comparative affinity data for PFAS binding by serum albumin from human, experimental model, and livestock species reduce critical interspecies uncertainty and improve accuracy of predictive bioaccumulation and toxicity assessments for PFAS.

Physiologically based toxicokinetic modelling of Tri(2-chloroethyl) phosphate (TCEP) in mice accounting for multiple exposure routes

Exposure routes are important for health risk assessment of chemical risks. The application of physiologically based toxicokinetic (PBTK) models to predict concentrations in vivo can determine the effects of harmful substances and tissue accumulation on the premise of saving experimental costs. In this study, Tri(2-chloroethyl) phosphate (TCEP), an organophosphate ester (OPE), was used as an example to study the PBTK model of mice exposed to different exposure doses by multiple routes. Different routes of exposure (gavage and intradermal injection) can cause differences in the concentration of chemicals in the organs. TCEP that enters the body through the mouth is mainly concentrated in the gastrointestinal tract and liver. However, the concentrations of chemicals that enter the skin into the mice are higher in skin, rest of body, and blood. In addition, TCEP was absorbed and accumulated very rapidly in mice, within half an hour after a single exposure. We have successfully established a mouse PBTK model of the TCEP accounting for multiple exposure Routes and obtained a series of kinetic parameters. The model includes blood, liver, kidney, stomach, intestine, skin, and rest of body compartments. Oral and dermal exposure route was considered for PBTK model. The PBTK model established in this study has a good predictive ability. More than 70% of the predicted values deviated from the measured values by less than 5-fold. In addition, we extrapolated the model to humans. A human PBTK model is built. We performed a health risk assessment for world populations based on human PBTK model. The risk of TCEP in dust is greater through mouth than through skin. The risk of TCEP in food of Chinese population is greater than dust.

Exploring Route-Specific Pharmacokinetics of PFAS in Mice by Coupling in Vivo Tests and Physiologically Based Toxicokinetic Models

BACKGROUND

Oral ingestion, inhalation, and skin contact are important exposure routes for humans to uptake per- and polyfluoroalkyl substances (PFAS). However, nasal and dermal exposure to PFAS remains unclear, and accurately predicting internal body burden of PFAS in humans via multiple exposure pathways is urgently required.

OBJECTIVES

We aimed to develop multiple physiologically based toxicokinetic (PBTK) models to unveil the route-specific pharmacokinetics and bioavailability of PFAS via respective oral, nasal, and dermal exposure pathways using a mouse model and sought to predict the internal concentrations in various tissues through multiple exposure routes and extrapolate it to humans.

METHODS

Mice were administered the mixed solution of perfluorohexane sulfonate, perfluorooctane sulfonate, and perfluorooctanoic acid through oral, nasal, and dermal exposure separately or jointly. The time-dependent concentrations of PFAS in plasma and tissues were determined to calibrate and validate the individual and combined PBTK models, which were applied in single- and repeated-dose scenarios.

RESULTS

The developed route-specific PBTK models successfully simulated the tissue concentrations of PFAS in mice following single or joint exposure routes as well as long-term repeated dose scenarios. The time to peak concentration of PFAS in plasma via dermal exposure was much longer (34.1-83.0 h) than that via nasal exposure (0.960 h). The bioavailability of PFAS via oral exposure was the highest (73.2%-98.0%), followed by nasal (33.9%-66.8%) and dermal exposure (4.59%-7.80%). This model was extrapolated to predict internal levels in human under real environment.

DISCUSSION

Based on these data, we predict the following: PFAS were absorbed quickly via nasal exposure, whereas a distinct hysteresis effect was observed for dermal exposure. Almost all the PFAS to which mice were exposed via gastrointestinal route were absorbed into plasma, which exhibited the highest bioavailability. Exhalation clearance greatly depressed the bioavailability of PFAS via nasal exposure, whereas the lowest bioavailability in dermal exposure was because of the interception of PFAS within the skin layers. https://doi.org/10.1289/EHP11969.

Quantitative Cross-Species Comparison of Serum Albumin Binding of Per- and Polyfluoroalkyl Substances from Five Structural Classes

Per- and polyfluoroalkyl substances (PFAS) are a class of over 8,000 chemicals that are persistent, bioaccumulative, and toxic to humans, livestock, and wildlife. Serum protein binding affinity is instrumental in understanding PFAS toxicity, yet experimental binding data is limited to only a few PFAS congeners. Previously, we demonstrated the usefulness of a high-throughput, in vitro differential scanning fluorimetry assay for determination of relative binding affinities of human serum albumin for 24 PFAS congeners from 6 chemical classes. In the current study, we used this differential scanning fluorimetry assay to comparatively examine differences in human, bovine, porcine, and rat serum albumin binding of 8 structurally informative PFAS congeners from 5 chemical classes. With the exception of the fluorotelomer alcohol 1H,1H,2H,2H-perfluorooctanol (6:2 FTOH), each PFAS congener bound by human serum albumin was also bound by bovine, porcine, and rat serum albumin. The critical role of the charged functional headgroup in albumin binding was supported by the inability of serum albumin of each species tested to bind 6:2 FTOH. Significant interspecies differences in serum albumin binding affinities were identified for each of the bound PFAS congeners. Relative to human albumin, perfluoroalkyl carboxylic and sulfonic acids were bound with greater affinity by porcine and rat serum albumin, and perfluoroalkyl ether congeners bound with lower affinity to porcine and bovine serum albumin. These comparative affinity data for PFAS binding by serum albumin from human, experimental model and livestock species reduce critical interspecies uncertainty and improve accuracy of predictive toxicity assessments for PFAS.

In vitro to in vivo extrapolation for predicting human equivalent dose of phenolic endocrine disrupting chemicals: PBTK model development, biological pathways, outcomes and performance

In vitro to in vivo (IVIVE) leverages in vitro high-throughput biological responses to predict the corresponding in vivo exposures and further estimate the human safe dose. However, for phenolic endocrine disrupting chemicals (EDCs) linked with complicated biological pathways and adverse outcomes (AO), such as bisphenol A (BPA) and 4-nonylphenol (4-NP), plausible estimation of human equivalent doses (HED) by IVIVE approaches considering various biological pathways and endpoints is still challenging. To explore the capabilities and limitations of IVIVE, this study conducted physiologically based toxicokinetic (PBTK)-IVIVE approaches to derive pathway-specific HEDs using BPA and 4-NP as examples. In vitro HEDs of BPA and 4-NP varied in different adverse outcomes, pathways, and testing endpoints and ranged from 0.0013 to 1.0986 mg/kg bw/day and 0.0551 to 1.7483 mg/kg bw/day, respectively. In vitro HEDs associated with reproductive AOs initiated by PPARα activation and ER agonism were the most sensitive. Model verification suggested the potential of using effective in vitro data to determine reasonable approximation of in vivo HEDs for the same AO (fold differences of most AOs ranged in 0.14-2.74 and better predictions for apical endpoints). Furthermore, system-specific parameters of cardiac output and its fraction, body weight, as well as chemical-specific parameters of partition coefficient and liver metabolic were most sensitive for the PBTK simulations. The results indicated that the application of fit for-purpose PBTK-IVIVE approach could provide credible pathway-specific HEDs and contribute to high throughput prioritization of chemicals in a more realistic scenario.

Development and application of an interactive generic physiologically based pharmacokinetic (igPBPK) model for adult beef cattle and lactating dairy cows to estimate tissue distribution and edible tissue and milk withdrawal intervals for per- and polyfluoroalkyl substances (PFAS)

Humans can be exposed to per- and polyfluoroalkyl substances (PFAS) through dietary intake from milk and edible tissues from food animals. This study developed a physiologically based pharmacokinetic (PBPK) model to predict tissue and milk residues and estimate withdrawal intervals (WDIs) for multiple PFAS including PFOA, PFOS and PFHxS in beef cattle and lactating dairy cows. Results showed that model predictions were mostly within a two-fold factor of experimental data for plasma, tissues, and milk with an estimated coefficient of determination (R2) of >0.95. The predicted muscle WDIs for beef cattle were <1 day for PFOA, 449 days for PFOS, and 69 days for PFHxS, while the predicted milk WDIs in dairy cows were <1 day for PFOA, 1345 days for PFOS, and zero day for PFHxS following a high environmental exposure scenario (e.g., 49.3, 193, and 161 ng/kg/day for PFOA, PFOS, and PFHxS, respectively, for beef cattle for 2 years). The model was converted to a web-based interactive generic PBPK (igPBPK) platform to provide a user-friendly dashboard for predictions of tissue and milk WDIs for PFAS in cattle. This model serves as a foundation for extrapolation to other PFAS compounds to improve safety assessment of cattle-derived food products.

A physiologically based pharmacokinetic model to optimize the dosage regimen and withdrawal time of cefquinome in pigs

Cefquinome is widely used to treat respiratory tract diseases of swine. While extra-label dosages of cefquinome could improve clinical efficacy, they might lead to excessively high residues in animal-derived food. In this study, a physiologically based pharmacokinetic (PBPK) model was calibrated based on the published data and a microdialysis experiment to assess the dosage efficiency and food safety. For the microdialysis experiment, in vitro/in vivo relative recovery and concentration-time curves of cefquinome in the lung interstitium were investigated. This PBPK model is available to predict the drug concentrations in the muscle, kidney, liver, plasma, and lung interstitial fluid. Concentration-time curves of 1000 virtual animals in different tissues were simulated by applying sensitivity and Monte Carlo analyses. By integrating pharmacokinetic/pharmacodynamic target parameters, cefquinome delivered at 3-5 mg/kg twice daily is advised for the effective control of respiratory tract infections of nursery pig, which the bodyweight is around 25 kg. Based on the predicted cefquinome concentrations in edible tissues, the withdrawal interval is 2 and 3 days for label and the extra-label doses, respectively. This study provides a useful tool to optimize the dosage regimen of cefquinome against respiratory tract infections and predicts the concentration of cefquinome residues in edible tissues. This information would be helpful to improve the food safety and guide rational drug usage.

A State-of-the-Science Review of Interactions of Per- and Polyfluoroalkyl Substances (PFAS) with Renal Transporters in Health and Disease: Implications for Population Variability in PFAS Toxicokinetics

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in the environment and have been shown to cause various adverse health impacts. In animals, sex- and species-specific differences in PFAS elimination half-lives have been linked to the activity of kidney transporters. However, PFAS molecular interactions with kidney transporters are still not fully understood. Moreover, the impact of kidney disease on PFAS elimination remains unclear.

OBJECTIVES

This state-of-the-science review integrated current knowledge to assess how changes in kidney function and transporter expression from health to disease could affect PFAS toxicokinetics and identified priority research gaps that should be addressed to advance knowledge.

METHODS

We searched for studies that measured PFAS uptake by kidney transporters, quantified transporter-level changes associated with kidney disease status, and developed PFAS pharmacokinetic models. We then used two databases to identify untested kidney transporters that have the potential for PFAS transport based on their endogenous substrates. Finally, we used an existing pharmacokinetic model for perfluorooctanoic acid (PFOA) in male rats to explore the influence of transporter expression levels, glomerular filtration rate (GFR), and serum albumin on serum half-lives.

RESULTS

The literature search identified nine human and eight rat kidney transporters that were previously investigated for their ability to transport PFAS, as well as seven human and three rat transporters that were confirmed to transport specific PFAS. We proposed a candidate list of seven untested kidney transporters with the potential for PFAS transport. Model results indicated PFOA toxicokinetics were more influenced by changes in GFR than in transporter expression.

DISCUSSION

Studies on additional transporters, particularly efflux transporters, and on more PFAS, especially current-use PFAS, are needed to better cover the role of transporters across the PFAS class. Remaining research gaps in transporter expression changes in specific kidney disease states could limit the effectiveness of risk assessment and prevent identification of vulnerable populations. https://doi.org/10.1289/EHP11885.

Community-facing toxicokineticmodels to estimate PFAS serum levels based on life history and drinking water exposures

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are drinking water contaminants. Tools to assess the potential body burden associated with drinking PFAS-contaminated water may be helpful for public health assessment of exposed communities.

METHODS

We implemented a suite of one-compartment toxicokinetic models using extensively calibrated toxicokinetic parameters (half-life and volume of distribution). We implemented the models both in the R programming language for research purposes, and as a web estimator for the general public (built in typescript.js). These models simulate exposure to PFAS water concentrations for individuals with varying characteristics such as age, sex, weight, and breastfeeding history. The models account for variability and uncertainty in parameter inputs to produce Monte Carlo-based estimates of serum concentration. For children, the models additionally account for gestational exposure, lactational exposure, and potential exposure through formula feeding. For adults who have borne children, the models account for clearance through birth and breastfeeding. We ran simulations of individuals with known PFAS water and serum concentrations to evaluate the model. We then compared the predicted serum PFAS concentrations to measured data.

RESULTS

The models accurately estimate individual-level serum levels for each PFAS for most adults within ½ order of magnitude. We found that the models somewhat overestimated serum concentrations for children in the tested locations, and that these overestimates are generally within an order of magnitude.

DISCUSSION

This paper presents scientifically robust models that allow users to estimate serum PFAS concentrations based on known PFAS water concentrations and physiologic information. However, accuracy in historical water concentration inputs, exposure from non-drinking water sources, and life-history characteristics of individuals present a complex problem for individual estimation. Additional refinements to the model suite to improve the prediction of individual results may consist of including duration of exposure and additional life-history characteristics.

Determinants of maternal and neonatal PFAS concentrations: a review

Per- and polyfluoroalkyl substances (PFAS) are used for their properties such as stain and water resistance. The substances have been associated with adverse health outcomes in both pregnant mothers and infants, including pre-eclampsia and low birthweight. A growing body of research suggests that PFAS are transferred from mother to fetus through the placenta, leading to in utero exposure. A systematic review was performed using the PubMed database to search for studies evaluating determinants of PFAS concentrations in blood matrices of pregnant mothers and neonates shortly after birth. Studies were included in this review if an observational study design was utilized, exposure to at least one PFAS analyte was measured, PFAS were measured in maternal or neonatal matrices, at least one determinant of PFAS concentrations was assessed, and results such as beta estimates were provided. We identified 35 studies for inclusion in the review and evaluated the PFAS and determinant relationships among the factors collected in these studies. Parity, breastfeeding history, maternal race and country of origin, and household income had the strongest and most consistent evidence to support their roles as determinants of certain PFAS concentrations in pregnant mothers. Reported study findings on smoking status, alcohol consumption, and pre-pregnancy body mass index (BMI) suggest that these factors are not important determinants of PFAS concentrations in pregnant mothers or neonates. Further study into informative factors such as consumer product use, detailed dietary information, and consumed water sources as potential determinants of maternal or neonatal PFAS concentrations is needed. Research on determinants of maternal or neonatal PFAS concentrations is critical to estimate past PFAS exposure, build improved exposure models, and further our understanding on dose-response relationships, which can influence epidemiological studies and risk assessment evaluations. Given the potential for adverse outcomes in pregnant mothers and neonates exposed to PFAS, it is important to identify and understand determinants of maternal and neonatal PFAS concentrations to better implement public health interventions in these populations.

Microbial biotransformation mechanisms of PFPiAs in soil unveiled by metagenomic analysis

As alternatives of long-chain PFASs (Poly- and perfluoroalkyl substances), perfluoroalkyl phosphinic acids (PFPiAs) are increasingly observed in the environment, but their environmental behaviors have not been well understood. Here, the microbial biotransformation of C6/C6 and C8/C8 PFPiA in two soils (Soil N and Y) was investigated. After 252 d and 330 d of incubation with PFPiAs in Soil N and Y respectively, the levels of PFPiAs decreased distinctly, accompanied by the increasing perfluorohexaphosphonic acid (PFHxPA) or perfluorooctanophosphonic acid (PFOPA) formation, magnifying PFPiAs were susceptible to C-P cleavage, which was also confirmed by the density functional theory calculations. The half-lives of the PFPiAs were longer than one year, while generally shorter in Soil N than in Soil Y and that of C6/C6 was shorter than C8/C8 PFPiA (392 d and 746 d in Soil N, and 603 and 1155 d in Soil Y, respectively). Metagenomic sequencing analysis revealed that Proteobacteria as the primary host of the potential functional genes related to CP bond cleavage might be the crucial phyla contributing to the biotransformation of PFPiAs. Meanwhile, the more intensive interactions between the microbes in Soil N consistently contribute to its greater capacity for transforming PFPiAs.

Systematic review of physiologically based kinetic lactation models for transfer of xenobiotic compounds to milk

Lactational elimination has been described mathematically for nearly 50 years. Over 40 published articles, containing >50 physiologically based kinetic (PBK) lactation models were included in the systematic review. These PBK models described the lactational elimination of xenobiotic compounds in humans, rats, mice, and dairy cows and goats. A total of 78 compounds have been modelled, ranging from industrial chemicals, pesticides, to pain medication, antibiotics, and caffeine. Few models included several species or compounds, and models were thus generally not translational or generic. Three dairy cow models mechanistically described the intramammary disposition of pharmaceuticals after intramammary administration, including volume changes caused by milking, while empirically describing the remaining pharmacokinetics. The remaining models were semi- or whole body PBK models, describing long-term exposure of environmental pollutants, or short-term exposure of pharmaceuticals. The absolute majority described the disposition to the mammary gland or milk with perfusion limited compartments, but permeability limited models were available as well. With long-term exposure, models often included changes in milk volume and/or consumption by the offspring, and changes in body weight of offspring. Periodic emptying of the mammary gland, as with feeding or milking, was sparsely applied. Rodent models used similar physiological parameters, while values of physiological parameters applied in human models could range widely. When milk composition was included in the models, it most often included the fat content. The review gives an extensive overview of the applied functions and modelling strategies of PBK lactation models.

Human health risk assessment of 6:2 Cl-PFESA through quantitative in vitro to in vivo extrapolation by integrating cell-based assays, an epigenetic key event, and physiologically based pharmacokinetic modeling

Human health risk assessment of chemicals is essential but often relies on time-consuming and animal and labor-extensive procedures. Here, we develop a population-based, quantitative in vitro to in vivo extrapolation (QIVIVE) approach which depended on cellular effects monitored by in vitro assays, considered chemical internal concentration determined by LC-MS/MS, extrapolated into in vivo target tissue concentration through physiologically based pharmacokinetic (PBPK) modelling, and assessed populational health risk using in silico modelling. By applying this QIVIVE approach to 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA), as a representative of the emerging pollutants, we find that 6:2 Cl-PFESA disturbed lipid homeostasis in HepG2 cells through enhancement of lipid accumulation and fatty acid β-oxidation, during which miR-93-5p served as a key event towards toxicity and thus, could serve as an efficient toxicity marker for risk assessment; further, the disruption potency of lipid homeostasis of 6:2 Cl-PFESA for the most of studied populations in China might be of moderate concern. Together, our approach improved the reliability of QIVIVE during human health risk assessment, which can readily be used for other chemicals.

Emerging and Legacy Perfluoroalkyl Substances in Breastfed Chinese Infants: Renal Clearance, Body Burden, and Implications

BACKGROUND

Human breast milk is a primary route of exposure to perfluoroalkyl substances (PFAS) in infants. To understand the associated risks, the occurrence of PFAS in human milk and the toxicokinetics of PFAS in infants need to be addressed.

OBJECTIVES

We determined levels of emerging and legacy PFAS in human milk and urine samples from Chinese breastfed infants, estimated renal clearance, and predicted infant serum PFAS levels.

METHODS

In total, human milk samples were collected from 1,151 lactating mothers in 21 cities in China. In addition, 80 paired infant cord blood and urine samples were obtained from two cities. Nine emerging PFAS and 13 legacy PFAS were analyzed in the samples using ultra high-performance liquid chromatography tandem mass spectrometry. Renal clearance rates (CLrenals) of PFAS were estimated in the paired samples. PFAS serum concentrations in infants (<1 year of age) were predicted using a first-order pharmacokinetic model.

RESULTS

All nine emerging PFAS were detected in human milk, with the detection rates of 6:2 Cl-PFESA, PFMOAA, and PFO5DoDA all exceeding 70%. The level of 6:2 Cl-PFESA in human milk (median concentration=13.6 ng/L) ranked third after PFOA (336 ng/L) and PFOS (49.7 ng/L). The estimated daily intake (EDI) values of PFOA and PFOS exceeded the reference dose (RfD) of 20 ng/kg BW per day recommended by the U.S. Environmental Protection Agency in 78% and 17% of breastfed infant samples, respectively. 6:2 Cl-PFESA had the lowest infant CLrenal (0.009mL/kg BW per day), corresponding to the longest estimated half-life of 49 y. The average half-lives of PFMOAA, PFO2HxA, and PFO3OA were 0.221, 0.075, and 0.304 y, respectively. The CLrenals of PFOA, PFNA, and PFDA were slower in infants than in adults.

CONCLUSIONS

Our results demonstrate the widespread occurrence of emerging PFAS in human milk in China. The relatively high EDIs and half-lives of emerging PFAS suggest potential health risks of postnatal exposure in newborns. https://doi.org/10.1289/EHP11403.

Metal Exposure Promotes Colorectal Tumorigenesis via the Aberrant N6-Methyladenosine Modification of ATP13A3

Element contamination, including that from heavy metals, is associated with gastrointestinal tumorigenesis, but the effects and mechanisms of crucial element exposure associated with colorectal cancer remain unclear. We profiled 56 elements by ICP-MS and used logistic regression, LASSO, BKMR, and GAM to identify colorectal cancer-relevant elements. A series of biochemical experiments were performed to demonstrate the cytotoxicity and the mechanisms of malignant transformation after metal exposure. Using an elementomics approach, we first found that the metal thallium (Tl) was positively correlated with many toxic metals and was associated with a significantly increased risk of colorectal cancer. Acute exposure to Tl induced cytotoxicity and cell death by accelerating the generation of reactive oxygen species and DNA damage. Chronic exposure to Tl led to the inhibition of cell death and thereby induced the malignant transformation of normal colon cells and xenograft tumor formation in nude mice. Furthermore, we describe the first identification of a significant metal quantitative trait locus for the novel colorectal cancer susceptibility locus rs1511625 near ATP13A3. Mechanistically, Tl increased the level of aberrant N⁶-methyladenosine (m⁶A) modification of ATP13A3 via the METLL3/METTL14/ALKBH5-ATP13A3 axis to promote colorectal tumorigenesis. This study provides a basis for the development of public health strategies for reducing metal exposure among populations at high risk for colorectal cancer.

Physiologically-based toxicokinetic model for the prediction of perchlorate distribution and its application

Perchlorate is a stable and readily transportable thyroid hormone disruptor, and prevalent exposure to perchlorate through food and drinking water has raised public concern about its health effects. The physiologically based toxicokinetic (PBTK) model as a dose prediction method is effective to predict the toxicant exposure dose of an organism and helps quantitatively assess the dose-dependent relationship with toxic effects. The current study aimed to establish a multi-compartment PBTK model based on updated time-course datasets of single oral exposure to perchlorate in rats. With adjustment of the kinetic parameters, the model fitted well the toxicokinetic characteristics of perchlorate in urine, blood, and thyroid from our experiments and the literature, and the coefficient of determination (R²) between the fitting values and the experimental data in regression analysis was greater than 0.91, indicating the robustness of the current model. The results of sensitivity analysis and daily repeated exposure simulations together confirmed its effective renal clearance. According to the distribution characteristic of perchlorate, a correlation study of internal and external exposure was conducted using urinary perchlorate as a bioassay indicator. The developed multi-compartment model for perchlorate updates important toxicokinetic data and kinetic parameters, providing analytical and modeling tools for deriving total exposure levels in the short term.

Machine learning and artificial intelligence in physiologically based pharmacokinetic modeling

Physiologically based pharmacokinetic (PBPK) models are useful tools in drug development and risk assessment of environmental chemicals. PBPK model development requires the collection of species-specific physiological, and chemical-specific absorption, distribution, metabolism, and excretion (ADME) parameters, which can be a time-consuming and expensive process. This raises a need to create computational models capable of predicting input parameter values for PBPK models, especially for new compounds. In this review, we summarize an emerging paradigm for integrating PBPK modeling with machine learning (ML) or artificial intelligence (AI)-based computational methods. This paradigm includes 3 steps (1) obtain time-concentration PK data and/or ADME parameters from publicly available databases, (2) develop ML/AI-based approaches to predict ADME parameters, and (3) incorporate the ML/AI models into PBPK models to predict PK summary statistics (eg, area under the curve and maximum plasma concentration). We also discuss a neural network architecture "neural ordinary differential equation (Neural-ODE)" that is capable of providing better predictive capabilities than other ML methods when used to directly predict time-series PK profiles. In order to support applications of ML/AI methods for PBPK model development, several challenges should be addressed (1) as more data become available, it is important to expand the training set by including the structural diversity of compounds to improve the prediction accuracy of ML/AI models; (2) due to the black box nature of many ML models, lack of sufficient interpretability is a limitation; (3) Neural-ODE has great potential to be used to generate time-series PK profiles for new compounds with limited ADME information, but its application remains to be explored. Despite existing challenges, ML/AI approaches will continue to facilitate the efficient development of robust PBPK models for a large number of chemicals.

Novel insights into the mediating roles of cluster of differentiation 36 in transmembrane transport and tissue partition of per- and polyfluoroalkyl substances in mice

Transmembrane transport is important for bioaccumulation of per- and polyfluoroalkyl substances (PFASs) in organisms, but has not yet been well understood. Here, the roles of cluster of differentiation 36 (CD36) in accumulation of PFASs were investigated. CD36 was overexpressed in Escherichia coli to get CD36-BL21 strain, and the binding affinities of 20 PFASs with CD36 were determined by microscale thermophoresis, which grew up to 17.5 μM with increasing carbon chain length. Consequently, the accumulation of most PFASs was remarkably promoted in CD36-BL21 in comparison to the wild strain, and the enhancement was proportional to their binding affinities with CD36 (r = -0.96). However, this effect was depressed greatly as CD36 was inhibited by sulfo-N-succinimidyl oleate (SSO). Additionally, as the mice received SSO pretreatment before they were exposed to perfluorododecanoic acid, its accumulation in the tissues rich in CD36, such as liver, was suppressed, but increased by 1.1 times in the serum. These indicated that CD36 played critical roles in the transmembrane transport and tissue partition of PFASs in organisms. The developed relationship between liver-blood partition of PFASs and their binding affinities with intracellular proteins was distinctly improved by incorporating that with CD36 (r = -0.97).

Toxicokinetics, dose-response, and risk assessment of nanomaterials: Methodology, challenges, and future perspectives

The rapid growth of nanomaterial applications has raised safety concerns for human health. A number of studies have been conducted to assess the toxicokinetics, toxicology, dose-response, and risk assessment of different nanomaterials using in vitro and in vivo animal and human models. However, current studies cannot meet the demand for efficient assessment of toxicokinetics, dose-response relationships, or the toxicological risk arising from the rapidly increasing number of newly synthesized nanomaterials. In this article, we review the methods for conducting toxicokinetics, hazard identification, dose-response, exposure, and risk assessment studies of nanomaterials, identify the knowledge gaps, and discuss the challenges remaining. We provide the rationale behind the appropriate design of nanomaterial plasma toxicokinetic and tissue distribution studies, including caveats on the interpretation and correlation of in vitro and in vivo toxicology studies. The potential of using physiologically based pharmacokinetic (PBPK) models to extrapolate toxicokinetic and toxicity findings from in vitro to in vivo and from animals to humans is discussed, and the knowledge gaps of PBPK modeling for nanomaterials are identified. While challenges still exist, there has been progress in the toxicokinetics, hazard identification, and risk assessment of nanomaterials in the past two decades. Recent advancements in the field are highlighted with relevant examples. We also share latest guidelines as well as our perspectives on future studies needed to characterize the toxicokinetics, toxicity, and dose-response relationship in support of nanomaterial risk assessment. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Environmental exposure to per- and polyfluoroalkyl substances and sleep disturbance in pregnant women: A prospective cohort study

Previous studies on the association between exposure to per- and polyfluoroalkyl substances (PFAS) and sleep patterns in pregnant women are limited. This cohort study aims to assess the associations between PFAS and sleep quality in pregnant women. Of the 4127 women who participated in the Shanghai Birth Cohort, 3174, 3070, and 2887 women in their first, second, and third trimesters of gestation, respectively, were included in our analysis. Sleep measures were taken using the Pittsburgh Sleep Quality Index questionnaire. Ten PFAS were measured in blood samples collected in early pregnancy. We first evaluate the associations between individual PFAS and sleep quality in the three trimesters. Weighted quantile sum (WQS) regression models were performed to test the overall effect of the PFAS mixture on sleep quality during the three trimesters. Longitudinal analyses throughout pregnancy were performed with generalized estimating equation models. Furthermore, the effect of the PFAS mixture on longitudinal sleep patterns was examined using longitudinal latent class analyses combined with WQS models. The single pollutant analysis suggested that most PFAS were associated with increased sleep disturbance risk, lower sleep efficiency, and shorter sleep duration in the three trimesters. Similarly, the WQS models revealed a significant association between the PFAS mixtures and elevated sleep disturbance risk in pregnant women, with perfluorobutane sulfonate acting as the predominant risk factor. Additionally, the longitudinal analysis confirmed the effects of PFAS exposure on increased sleep disturbance over time. The PFAS mixture was positively associated with higher risks of poor sleep quality and sleep medicine use [adjusted odds ratio (aOR) = 1.10; 95 % confidence interval (95%CI): 1.01, 1.20; and aOR = 1.25 (95%CI: 1.04, 1.50) respectively] throughout the three trimesters. Our study suggests that PFAS may increase the risk of sleep disturbance in pregnant women. Further studies are needed to confirm our results and elucidate potential mechanisms.

An Interactive Generic Physiologically Based Pharmacokinetic (igPBPK) Modeling Platform to Predict Drug Withdrawal Intervals in Cattle and Swine: A Case Study on Flunixin, Florfenicol and Penicillin G

Violative chemical residues in edible tissues from food-producing animals are of global public health concern. Great efforts have been made to develop physiologically based pharmacokinetic (PBPK) models for estimating withdrawal intervals (WDIs) for extralabel prescribed drugs in food animals. Existing models are insufficient to address the food safety concern as these models are either limited to 1 specific drug or difficult to be used by non-modelers. This study aimed to develop a user-friendly generic PBPK platform that can predict tissue residues and estimate WDIs for multiple drugs including flunixin, florfenicol, and penicillin G in cattle and swine. Mechanism-based in silico methods were used to predict tissue/plasma partition coefficients and the models were calibrated and evaluated with pharmacokinetic data from Food Animal Residue Avoidance Databank (FARAD). Results showed that model predictions were, in general, within a 2-fold factor of experimental data for all 3 drugs in both species. Following extralabel administration and respective U.S. FDA-approved tolerances, predicted WDIs for both cattle and swine were close to or slightly longer than FDA-approved label withdrawal times (eg, predicted 8, 28, and 7 days vs labeled 4, 28, and 4 days for flunixin, florfenicol, and penicillin G in cattle, respectively). The final model was converted to a web-based interactive generic PBPK platform. This PBPK platform serves as a user-friendly quantitative tool for real-time predictions of WDIs for flunixin, florfenicol, and penicillin G following FDA-approved label or extralabel use in both cattle and swine, and provides a basis for extrapolating to other drugs and species.