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According to European regulations, migration from food packaging must be safe. However, currently, there is no consensus on how to evaluate its safety, especially for non-intentionally added substances (NIAS). The intensive and laborious approach, involving identification and then quantification of all migrating substances followed by a toxicological evaluation, is not practical or feasible. In alignment with the International Life Sciences Institute (ILSI) and the European Union (EU) guidelines on packaging materials, efforts are focused on combining data from analytics, bioassays and in silico toxicology approaches for the risk assessment of packaging materials. Advancement of non-targeted screening approaches using both analytical methods and in vitro bioassays is key. A protocol was developed for the chemical and biological screening of migrants from coated metal packaging materials. This protocol includes guidance on sample preparation, migrant simulation, chemical analysis using liquid chromatography (LC-MS) and validated bioassays covering endocrine activity, genotoxicity and metabolism-related targets. An inter-laboratory study was set-up to evaluate the consistency in biological activity and analytical results generated between three independent laboratories applying the developed protocol and guidance. Coated packaging metal panels were used in this case study. In general, the inter-laboratory chemical analysis and bioassay results displayed acceptable consistency between laboratories, but technical differences led to different data interpretations (e.g., cytotoxicity, cell passages, chemical analysis). The study observations with the greatest impact on the quality of the data and ultimately resulting in discrepancies in the results are given and suggestions for improvement of the protocol are made (e.g., sample preparation, chemical analysis approaches). Finally, there was agreement on the need for an aligned protocol to be utilized by qualified laboratories for chemical and biological analyses, following best practices and guidance for packaging safety assessment of intentionally added substances (IAS) and NIAS to avoid inconsistency in data and the final interpretation.

Acute toxicity in silico models are being used to support an increasing number of application areas including (1) product research and development, (2) product approval and registration as well as (3) the transport, storage and handling of chemicals. The adoption of such models is being hindered, in part, because of a lack of guidance describing how to perform and document an in silico analysis. To address this issue, a framework for an acute toxicity hazard assessment is proposed. This framework combines results from different sources including in silico methods and in vitro or in vivo experiments. In silico methods that can assist the prediction of in vivo outcomes (i.e., LD 50 ) are analyzed concluding that predictions obtained using in silico approaches are now well-suited for reliably supporting assessment of LD 50 -based acute toxicity for the purpose of GHS classification. A general overview is provided of the endpoints from in vitro studies commonly evaluated for predicting acute toxicity (e.g., cytotoxicity/cytolethality as well as assays targeting specific mechanisms). The increased understanding of pathways and key triggering mechanisms underlying toxicity and the increased availability of in vitro data allow for a shift away from assessments solely based on endpoints such as LD 50 , to mechanism-based endpoints that can be accurately assessed in vitro or by using in silico prediction models. This paper also highlights the importance of an expert review of all available information using weight-of-evidence considerations and illustrates, using a series of diverse practical use cases, how in silico approaches support the assessment of acute toxicity.

Neurotoxicology is the study of adverse effects on the structure or function of the developing or mature adult nervous system following exposure to chemical, biological, or physical agents. The development of more informative alternative methods to assess developmental (DNT) and adult (NT) neurotoxicity induced by xenobiotics is critically needed. The use of such alternative methods including in silico approaches that predict DNT or NT from chemical structure (e.g., statistical-based and expert rule-based systems) is ideally based on a comprehensive understanding of the relevant biological mechanisms. This paper discusses known mechanisms alongside the current state of the art in DNT/NT testing. In silico approaches available today that support the assessment of neurotoxicity based on knowledge of chemical structure are reviewed, and a conceptual framework for the integration of in silico methods with experimental information is presented. Establishing this framework is essential for the development of protocols, namely standardized approaches, to ensure that assessments of NT and DNT based on chemical structures are generated in a transparent, consistent, and defendable manner., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dr. Myatt reports grants from NIH during the conduct of the study; and FDA’s Center for Drug Evaluation and Research (CDER) and Leadscope Inc. (an Instem company) are parties to a formal Research Collaboration Agreement (RCA).

Hepatotoxicity is one of the most frequently observed adverse effects resulting from exposure to a xenobiotic. For example, in pharmaceutical research and development it is one of the major reasons for drug withdrawals, clinical failures, and discontinuation of drug candidates. The development of faster and cheaper methods to assess hepatotoxicity that are both more sustainable and more informative is critically needed. The biological mechanisms and processes underpinning hepatotoxicity are summarized and experimental approaches to support the prediction of hepatotoxicity are described, including toxicokinetic considerations. The paper describes the increasingly important role of in silico approaches and highlights challenges to the adoption of these methods including the lack of a commonly agreed upon protocol for performing such an assessment and the need for in silico solutions that take dose into consideration. A proposed framework for the integration of in silico and experimental information is provided along with a case study describing how computational methods have been used to successfully respond to a regulatory question concerning non-genotoxic impurities in chemically synthesized pharmaceuticals.

The kidneys, heart and lungs are vital organ systems evaluated as part of acute or chronic toxicity assessments. New methodologies are being developed to predict these adverse effects based on in vitro and in silico approaches. This paper reviews the current state of the art in predicting these organ toxicities. It outlines the biological basis, processes and endpoints for kidney toxicity, pulmonary toxicity, respiratory irritation and sensitization as well as functional and structural cardiac toxicities. The review also covers current experimental approaches, including off-target panels from secondary pharmacology batteries. Current in silico approaches for prediction of these effects and mechanisms are described as well as obstacles to the use of in silico methods. Ultimately, a commonly accepted protocol for performing such assessment would be a valuable resource to expand the use of such approaches across different regulatory and industrial applications. However, a number of factors impede their widespread deployment including a lack of a comprehensive mechanistic understanding, limited in vitro testing approaches and limited in vivo databases suitable for modeling, a limited understanding of how to incorporate absorption, distribution, metabolism, and excretion (ADME) considerations into the overall process, a lack of in silico models designed to predict a safe dose and an accepted framework for organizing the key characteristics of these organ toxicants., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Glenn J Myatt reports financial support was provided by National Institutes of Health.

The assessment of skin sensitization has evolved over the past few years to include in vitro assessments of key events along the adverse outcome pathway and opportunistically capitalize on the strengths of in silico methods to support a weight of evidence assessment without conducting a test in animals. While in silico methods vary greatly in their purpose and format; there is a need to standardize the underlying principles on which such models are developed and to make transparent the implications for the uncertainty in the overall assessment. In this contribution, the relationship between skin sensitization relevant effects, mechanisms, and endpoints are built into a hazard assessment framework. Based on the relevance of the mechanisms and effects as well as the strengths and limitations of the experimental systems used to identify them, rules and principles are defined for deriving skin sensitization in silico assessments. Further, the assignments of reliability and confidence scores that reflect the overall strength of the assessment are discussed. This skin sensitization protocol supports the implementation and acceptance of in silico approaches for the prediction of skin sensitization., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

In silico toxicology (IST) approaches to rapidly assess chemical hazard, and usage of such methods is increasing in all applications but especially for regulatory submissions, such as for assessing chemicals under REACH as well as the ICH M7 guideline for drug impurities. There are a number of obstacles to performing an IST assessment, including uncertainty in how such an assessment and associated expert review should be performed or what is fit for purpose, as well as a lack of confidence that the results will be accepted by colleagues, collaborators and regulatory authorities. To address this, a project to develop a series of IST protocols for different hazard endpoints has been initiated and this paper describes the genetic toxicity in silico (GIST) protocol. The protocol outlines a hazard assessment framework including key effects/mechanisms and their relationships to endpoints such as gene mutation and clastogenicity. IST models and data are reviewed that support the assessment of these effects/mechanisms along with defined approaches for combining the information and evaluating the confidence in the assessment. This protocol has been developed through a consortium of toxicologists, computational scientists, and regulatory scientists across several industries to support the implementation and acceptance of in silico approaches., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

The present publication surveys several applications of in silico (i.e., computational) toxicology approaches across different industries and institutions. It highlights the need to develop standardized protocols when conducting toxicity-related predictions. This contribution articulates the information needed for protocols to support in silico predictions for major toxicological endpoints of concern (e.g., genetic toxicity, carcinogenicity, acute toxicity, reproductive toxicity, developmental toxicity) across several industries and regulatory bodies. Such novel in silico toxicology (IST) protocols, when fully developed and implemented, will ensure in silico toxicological assessments are performed and evaluated in a consistent, reproducible, and well-documented manner across industries and regulatory bodies to support wider uptake and acceptance of the approaches. The development of IST protocols is an initiative developed through a collaboration among an international consortium to reflect the state-of-the-art in in silico toxicology for hazard identification and characterization. A general outline for describing the development of such protocols is included and it is based on in silico predictions and/or available experimental data for a defined series of relevant toxicological effects or mechanisms. The publication presents a novel approach for determining the reliability of in silico predictions alongside experimental data. In addition, we discuss how to determine the level of confidence in the assessment based on the relevance and reliability of the information., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Hexabromocyclododecane (HBCD) is a high production volume brominated flame retardant added to building insulation foams, electronics, and textiles. HBCD is a commercial mixture (CM-HBCD) composed of three main stereoisomers: α-HBCD (10%), β-HBCD (10%), and γ-HBCD (80%). A shift from the dominant stereoisomer γ-HBCD to α-HBCD is detected in humans and wildlife., Objectives: Considering CM-HBCD has been implicated in neurodevelopment and endocrine disruption, with expected metabolism perturbations, we performed metabolomics on mice serum obtained during a window-of-developmental neurotoxicity to draw correlations between early-life exposures and developmental outcomes and to predict health risks., Methods: Six female C57BL/6 mice at postnatal day (PND) 10 were administered a single gavage dose of α-, γ-, or CM-HBCD at 3, 10, and 30 mg/kg. Nuclear magnetic resonance metabolomics was used to analyze 60 μL serum aliquots of blood collected 4 days post-oral exposure., Results: Infantile mice exposed to α-, γ-, or CM-HBCD demonstrated differences in endogenous metabolites by treatment and dose groups, including metabolites involved in glycolysis, gluconeogenesis, lipid metabolism, citric acid cycle, and neurodevelopment. Ketone bodies, 3-hydroxybutyrate, and acetoacetate, were nonstatistically elevated, when compared with mean control levels, in all treatment and dose groups, while glucose, pyruvate, and alanine varied. Acetoacetate was significantly increased in the 10 mg/kg α-HBCD and was nonsignificantly decreased with CM-HBCD. A third ketone body, acetone, was significantly lower in the 30 mg/kg α-HBCD group with significant increases in pyruvate at the same treatment and dose group. Metabolites significant in differentiating treatment and dose groups were also identified, including decreases in amino acids glutamate (excitatory neurotransmitter in learning and memory) and phenylalanine (neurotransmitter precursor) after α-HBCD and γ-HBCD exposure, respectively., Conclusions: We demonstrated that 4 days following a single neonatal oral exposure to α-, γ-, and CM-HBCD resulted in different serum metabolomic profiles, indicating stereoisomer- and mixture-specific effects and possible mechanisms of action.

An essential metal hypothesis for neurodegenerative disease suggests an alteration in metal homeostasis contributing to the onset and progression of disease. Similar associations have been proposed for nonessential metals. To examine the relationship between metal levels in brain tissue and ventricular fluid (VF), postmortem samples of frontal cortex (FC) and VF from Alzheimer's disease (AD) cases and nondemented elderly subjects were analyzed for arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), tin (Sn), vanadium (V), and zinc (Zn) using inductively coupled plasma sector field mass spectrometry. All metals, with exception of equivalent Pb levels, were lower in the VF, compared to FC. Within-subject comparisons demonstrated that VF levels were not representative of levels within brain tissue. The essential metals Cu, Fe, and Zn were found highest in both compartments. Cd, Hg, and V levels in the VF were below the limit of quantification. In AD cases, FC levels of Fe were higher and As and Cd were lower than levels in controls, while levels of As in the VF were higher. Parameter estimates for FC metal levels indicated an association of Braak stage and higher Fe levels and an association of Braak stage and lower As, Mn, and Zn levels. The data showed no evidence of an accumulation of nonessential metals within the AD brain and, with the exception of As, showed no significant shift in the ratio of FC to VF levels to indicate differential clearance., (Published by Oxford University Press on behalf of the Society of Toxicology 2015. This work is written by US Government employees and is in the public domain in the US.)

Xenobiotics such as phenobarbital, 2,3,7,8-tetrachlorodibenzo-p-dioxin, and Aroclor 1254 significantly suppress the activity of a key gluconeogenic and glyceroneogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), suggesting that xenobiotics disrupt hepatic glucose and fat metabolism. The effects of polybrominated diphenyl ethers (PBDE), a family of synthetic flame-retardant chemicals, on PEPCK activity is unknown. This study investigated the effect of DE-71, a commercial PBDE mixture, on PEPCK enzyme kinetics. Forty-eight 1-mo-old male Wistar rats were gavaged daily with either corn oil or corn oil containing 14 mg/kg DE-71 for 3, 14, or 28 d (n = 8/group). At each time point, fasting plasma glucose, insulin, and C-peptide were measured and hepatic PEPCK activity, lipid content, and three cytochrome P-450 enzymes (CYP1A, -2B, and -3A) were assayed. PBDE treatment for 28 d significantly decreased PEPCK Vmax ( μ mol/min/g liver weight) by 43% and increased liver lipid by 20%, compared to control. CYP1A, -2B, and -3A Vmax values were enhanced by 5-, 6-, and 39-fold, respectively, at both 14 and 28 d in treated rats compared to control. There was a significant inverse and temporal correlation between CYP3A and PEPCK Vmax for the treatment group. Fasting plasma glucose, insulin, and C-peptide levels were not markedly affected by treatment, but the glucose:insulin ratio was significantly higher in treated compared to control rats. Data suggest that in vivo PBDE treatment compromises liver glucose and lipid metabolism, and may influence whole-body insulin sensitivity.

The metabolism of α- and γ-hexabromocyclododecane (HBCD) was investigated in adult C57BL/6 female mice. α- or γ-[(14)C]HBCD (3 mg/kg bw) was orally administered with subsequent urine and feces collection for 4 consecutive days; a separate group of mice was dosed and sacrificed 3 h postexposure to investigate tissue metabolite levels. Extractable and nonextractable HBCD metabolites were quantitated in liver, blood, fat, brain, bile, urine, and feces and characterized by LC/MS (ESI-). Metabolites identified were distinct between the two stereoisomers. In mice exposed to α-HBCD, four hydroxylated metabolites were detected in fecal extracts, and one of these metabolite isomers was consistently characterized in liver, brain, and adipose tissue extracts. In contrast, fecal extracts from mice exposed to γ-HBCD contained multiple isomers of monohydroxy-pentabromocyclododecene, dihydroxy-pentabromocyclododecene, and dihydroxy-pentabromocyclododecadiene, while in liver and adipose tissues extracts only a single monohydroxy-pentabromocyclododecane metabolite was observed. Both stereoisomers were transformed to metabolites which formed covalent bonds to proteins and/or lipids in the gut as suggested by high fecal nonextractables. The presence of tissue- and excreta-specific metabolic products after in vivo exposure to the two main HBCD stereoisomers supports previous toxicokinetic studies indicating that these two stereoisomers are biologically distinct. The distinct metabolic products identified in this study have the potential to aid in the identification of stereoisomer-specific HBCD exposures in future biomonitoring studies.

Background: Hexabromocyclododecane (HBCD) is a brominated flame retardant used in polystyrene foams in thermal insulation and electrical equipment. The HBCD commercial mixture consists mainly of α, β, and γ stereoisomers. Health concerns of HBCD exposure include alterations in immune and reproductive systems, neurotoxic effects, and endocrine disruption. Stereoisomer-specific levels of HBCD have not been measured previously in U.S. food., Objectives: We measured HBCD stereoisomer levels in U.S. foods from Dallas, Texas, supermarkets., Methods: Convenience samples of commonly consumed foods were purchased from supermarkets in Dallas in 2009-2010. Food samples included a wide variety of lipid-rich foods: fish, peanut butter, poultry, pork, and beef. Thirty-six individual food samples were collected in 2010 and analyzed for α-, β-, and γ-HBCD stereoisomers using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Ten pooled food samples previously collected in 2009 for a study of total HBCD levels using gas chromatography-mass spectrometry (GC-MS), were reanalyzed for α-, β-, and γ-HBCD stereoisomers using LC-MS/MS., Results: Of the 36 measured individual foods, 15 (42%) had detectable levels of HBCD. Median (ranges) of α- and γ-HBCD concentrations were 0.003 (< 0.005-1.307) and 0.005 (< 0.010-0.143) ng/g wet weight (ww), respectively; β-HBCD was present in three samples with a median (range) of 0.003 (< 0.005-0.019) ng/g ww. Median levels (range) for α-, β-, and γ-HBCD, in pooled samples were 0.077 (0.010-0.310), 0.008 (< 0.002-0.070), and 0.024 (0.012-0.170) ng/g ww, respectively., Conclusions: α-HBCD was detected most frequently and at highest concentrations, followed by γ-, and then β-HBCD, in food samples from Dallas, Texas. Food may be a substantial contributor to the elevated α-HBCD levels observed in humans. These data suggest that larger and more representative sampling should be conducted.

Hexabromocyclododecane (HBCD) is a mixture of three stereoisomers alpha (α), beta (β), and gamma (γ). γ-HBCD dominates the mixture (∼70%), and despite α-HBCD's minor contribution to global HBCD production and usage (∼10%), it is the dominant congener found in most biotic samples worldwide. Evidence of toxicity and lack of stereoisomer studies drives the importance of understanding HBCD toxicokinetics in potentially susceptible populations. The majority of public health concern has focused on hazardous effects resulting from exposure of infants and young children to HBCD due to reports on adverse developmental effects in rodent studies, in combination with human exposure estimates suggesting that nursing infants and young children have the highest exposure to HBCD. This study was designed to investigate differences in the disposition of both γ-HBCD and α-HBCD in infantile mice reported to be susceptible to the HBCD commercial mixture. The tissue distribution of α-[(14)C]HBCD- and γ-[(14)C]HBCD-derived radioactivity was monitored in C57BL/6 mice following a single oral dose of either compound (3 mg/kg) after direct gavage at postnatal day 10. Mice were held up to 7 days in shoebox cages after which pups were sacrificed, tissue collected, and internal dosimetry was measured. Developing mice exposed to α-HBCD had an overall higher body burden than γ-HBCD at every time point measured; at 4 days postexposure, they retained 22% of the α-HBCD administered dose, whereas pups exposed to γ-HBCD retained 10%. Total body burden in infantile mice after exposure to γ-HBCD was increased 10-fold as compared with adults. Similarly, after exposure to α-HBCD, infantile mice contained 2.5-fold higher levels than adult. These differences lead to higher concentrations of the HBCD diastereomers at target tissues during critical windows of development. The results indicate that the toxicokinetics of the two HBCD diastereomers differ between developing and adult mice; whereas distribution patterns are similar, concentrations of each HBCD diastereomer's-derived radioactivity are higher in the pup's liver, fat, kidney, brain, blood, muscle, and lungs than in the adult's. This study suggests that developmental stage may be a risk factor for the harmful effects of α-HBCD and γ-HBCD, when developing animals may be more sensitive to effects and have increased body burden.

Alpha-hexabromocyclododecane (α-HBCD) is an emerging persistent organic pollutant present in the hexabromocyclododecane (HBCD) commercial mixture. HBCD is used as an additive flame retardant in a wide variety of household consumer products. Three main stereoisomers, alpha (α), beta (β), and gamma (γ), comprise roughly 10, 10, and 80% of the mixture, respectively. Despite its small contribution to HBCD global production and usage, α-HBCD is the major stereoisomer found in wildlife and human tissues including breast milk and blood in North America, European Union, and Asia. No mammalian or human data are currently available regarding the toxicokinetics of α-HBCD. This study was conducted in an effort to fully characterize the absorption, distribution, metabolism, and elimination of α-HBCD following a single and repeated exposure with respect to dose, time, and route of administration in female C57BL/6 mice. Results indicate that ∼90% of the administered dose (3 mg/kg) was absorbed after oral exposure. Disposition was (1) dictated by lipophilicity, as adipose, liver, muscle, and skin were major depots and (2) was dose dependent with nonlinear accumulation at higher doses. Elimination, both whole-body and from individual tissues, was biphasic. α-HBCD-derived radioactivity was excreted in the feces as parent and metabolites, whereas urine only contained metabolites. Presence of polar metabolites in the blood and urine were a major factor in determining the rapid initial whole-body half-life after a single oral exposure. Initial half-lives were ∼1-3 days and much longer terminal half-lives of 17 days were observed, suggesting the potential for α-HBCD bioaccumulation. A 10-day repeated study supports α-HBCD bioaccumulation potential. Stereoisomerization previously observed after exposure to γ-HBCD was not seen after exposure of α-HBCD. The toxicokinetic behavior reported here has important implications for the extrapolation of toxicological studies of the commercial HBCD mixture to the assessment of risk of α-HBCD which is the major stereoisomer found in wildlife and people.

Hexabromocyclododecane-gamma (γ-HBCD) is the predominate diastereoisomer in the commercial HBCD mixture used as a flame retardant in a wide variety of consumer products. Three main diastereoisomers, alpha (α), beta (β), and gamma (γ), comprise the mixture. Despite the γ-diastereoisomer being the major diastereoisomer in the mixture and environmental samples, the α-diastereoisomer predominates human tissue and wildlife. This study was conducted to characterize absorption, distribution, metabolism, and excretion parameters of γ-HBCD with respect to dose and time following a single acute exposure and repeated exposure in adult female C57BL/6 mice. Results suggest that 85% of the administered dose (3 mg/kg) was absorbed after po exposure. Disposition was dose independent and did not significantly change after 10 days of exposure. Liver was the major depot (< 0.3% of dose) 4 days after treatment followed by blood, fat, and then brain. γ-HBCD was rapidly metabolized and eliminated in the urine and feces. For the first time, in vivo stereoisomerization was observed of the γ-diastereoisomer to the β-diastereoisomer in liver and brain tissues and to the α- and β-diastereoisomer in fat and feces. Polar metabolites in the blood and urine were a major factor in determining the initial whole-body half-life (1 day) after a single po exposure. Elimination, both whole-body and from individual tissues, was biphasic. Initial half-lives were approximately 1 day, whereas terminal half-lives were up to 4 days, suggesting limited potential for γ-diastereoisomer bioaccumulation. The toxicokinetic behavior reported here has important implications for the extrapolation of toxicological studies of the commercial HBCD mixture to the assessment of risk.

Previous studies demonstrated that perinatal exposure to polybrominated diphenyl ethers (PBDEs), a major class of brominated flame retardants, may affect thyroid hormone (TH) concentrations by inducing hepatic uridinediphosphate-glucoronosyltransferases (UGTs). This study further examines effects of the commercial penta mixture, DE-71, on genes related to TH metabolism at different developmental time points in male rats. DE-71 is predominately composed of PBDE congeners 47, 99, 100, 153, 154 with low levels of brominated dioxin and dibenzofuran contaminants. Pregnant Long-Evans rats were orally administered 1.7 (low), 10.2 (mid), or 30.6 (high) mg/kg/day of DE-71 in corn oil from gestational day (GD) 6 to postnatal day (PND) 21. Serum and liver were collected from male pups at PND 4, 21, and 60. Total serum thyroxine (T(4)) decreased to 57% (mid) and 51% (high) on PND 4, and 46% (mid) dose and 25% (high) on PND 21. Cyp1a1, Cyp2b1/2, and Cyp3a1 enzyme and mRNA expression, regulated by aryl hydrocarbon receptor, constitutive androstane receptor, and pregnane xenobiotic receptor, respectively, increased in a dose-dependent manner. UGT-T(4) enzymatic activity significantly increased, whereas age and dose-dependent effects were observed for Ugt1a6, 1a7, and 2b mRNA. Sult1b1 mRNA expression increased, whereas that of transthyretin (Ttr) decreased as did both the deiodinase I (D1) enzyme activity and mRNA expression. Hepatic efflux transporters Mdr1 (multidrug resistance), Mrp2 (multidrug resistance-associated protein), and Mrp3 and influx transporter Oatp1a4 mRNA expression increased. In this study the most sensitive responses to PBDEs following DE-71 exposure were CYP2B and D1 activities and Cyb2b1/2, d1, Mdr1, Mrp2, and Mrp3 gene expression. All responses were reversible by PND 60. In conclusion, deiodination, active transport, and sulfation, in addition to glucuronidation, may be involved in disruption of TH homeostasis due to perinatal exposure to DE-71 in male rat offspring.