Effects of short-term in vivo exposure to polybrominated diphenyl ethers on thyroid hormones and hepatic enzyme activities in weanling rats

Toxicity of Bromkal 70-5DE, a technical mixture of polybrominated diphenyl ethers, following 28 d of oral exposure in rats and impact of analysed impurities

The subacute toxicity of a commercial polybrominated diphenyl ether (PBDE) preparation, Bromkal 70-5DE, was investigated. In addition to a vehicle control, the mixture was given orally to male and female Sprague-Dawley rats for 28 d at three dose levels; 2.5, 25 and 250 mg kg(-1) b.w.d(-1). The observed effects include increased hepatic EROD activity (from 2.5 mg kg(-1)d(-1)); increased liver weight (males), increased PROD activity and depletion of hepatic retinoids (from 25 mg kg(-1)d(-1)); and increased liver weight (females), marked histological changes in the liver and lungs, as well as increased serum parameters such as total protein, cholesterol and albumin (from 250 mg kg(-1)d(-1)). Chemical analysis of the PBDE mixture with gas chromatography/mass spectrometry (GS/MS) showed impurities of polybrominated dibenzofurans and to a lesser extent dibenzodioxins, in total levels of about 7.0 microg g(-1) of Bromkal technical mixture. The animals were thereby exposed to an estimated dose of dioxin-like equivalents corresponding to 1.3-131 ng TEQ kg(-1) b.w.d(-1). It cannot be ruled out that this level of impurities can explain the hepatic EROD induction and hepatic retinoid depletion, which are considered typical markers of toxicity mediated via the aryl hydrocarbon receptor (AhR).

The effect of short-term intoxication of rats with pentabromodiphenyl ether (in mixture mimic commercial products)

Until quite recently, pentabromodiphenyl ether (PentaBDE) was most commonly used as a flame retardant. Due to the considerably long atmospheric half-life of PentaBDE and its contribution to environmental pollution, it is categorized as a persistent organic pollutant (POP). As the data on the toxicity of PentaBDE is rather scarce, its potential acute toxicity was the subject of this study. PentaBDE was administered intragastrically to female rats, in a single dose (25, 200 or 2000 mg/kg b.w.). PentaBDE administered to rats disturbed redox homeostasis, which was manifested by lower total antioxidant status (TAS) in serum and by higher liver glutathione reduced (GSH) concentration. The toxic effect of PentaBDE intensified lipid peroxidation. On histopathological examination, administration of the highest PentaBDE dose (2000 mg/kg b.w.) was seen to induce symptoms of fatty liver. PentaBDE caused an increase in relative liver mass, cytochromes P-450 (after two highest doses), a dose-dependent increase in the activity of CYP lA (12-26 fold) and CYP 2B (5-6 fold) as well as the levels of CYP lAl (16-50 fold) and CYP 4A (2-3 fold) in liver.

Exposure to DE-71 alters thyroid hormone levels and gene transcription in the hypothalamic-pituitary-thyroid axis of zebrafish larvae

Polybrominated diphenyl ethers (PBDEs) have the potential to disrupt thyroid hormone homeostasis, but the molecular mechanisms underlying this process have not yet been clarified. In the present study, zebrafish (Danio rerio) embryos were exposed to a low concentration (0, 1, 3, and 10microg/L) of DE-71 from fertilization to 14 days thereafter. The whole-body content of thyroid hormone and transcription of genes in the hypothalamic-pituitary-thyroid (HPT) axis were analyzed. Exposure to up to 10microg/L of DE-71 significantly reduced thyroxine (T4) levels and significantly upregulated the transcription of corticotrophin-releasing hormone (CRH) and thyroid-stimulating hormone (TSHbeta) genes in a concentration-dependent manner. The transcription of genes involved in the synthesis of TH proteins, sodium/iodide symporter (Slc5a5), and thyroglobulin (TG) and the transcription of marker genes associated with early thyroid development (Pax8 and Nkx2.1) were significantly upregulated upon DE-71 exposure. The expression of thyronine deiodinase (Deio1 and Deio2) mRNAs was also significantly upregulated, possibly as a compensatory response to the decreased T4 levels. However, DE-71 exposure resulted in the downregulation of transthyretin (TTR) gene transcription and did not affect the transcription of thyroid hormone receptors (TRs). Exposure to DE-71 significantly induced the transcription of the uridinediphosphate-glucuronosyltransferase (UGT1ab) gene. The results of our study confirmed the reliability of the zebrafish larvae as models for assessment of the developmental toxicity of PBDEs and transcription of genes of the HPT axis can evaluate the potential mechanisms of thyroid disruption.

Developing a biomonitoring educational pamphlet for potential participants in a breast milk biomonitoring study

Over the past decade, biomonitoring research initiatives in the United States have increased because of growing concern over the accumulation of environmental chemicals in the human body. One matrix that has become a viable biological sample for estimating human exposure to environmental chemicals is breast milk. However, breast milk biomonitoring research can induce anxiety and confusion about breastfeeding if communication is lacking between researchers, community partners, and participants. To bridge this communication gap, an informative, reassuring 8-page pamphlet was developed to educate community partners and potential participants about research on 1 class of environmental chemicals-polybrominated diphenyl ethers. Not only did the pamphlet assist in participant recruitment, but it forged positive relationships with valuable community partners.

PBDE concentrations in women's serum and fecundability

BACKGROUND

Exposure to polybrominated diphenyl ether (PBDE) flame retardants is widespread, with 97% of Americans having detectable levels. Although PBDEs have been associated with reproductive and hormonal effects in animals, no human studies have examined their association with fertility.

OBJECTIVES

This study was designed to determine whether maternal concentrations of PBDEs in serum collected during pregnancy are associated with time to pregnancy and menstrual cycle characteristics.

METHODS

Pregnant women (n = 223) living in a low-income, predominantly Mexican-immigrant community in California were interviewed to determine how many months they took to become pregnant. Blood samples were collected and analyzed for PBDEs. PBDE concentrations were lipid adjusted and log10 transformed. Analyses were limited to PBDE congeners detected in > 75% of the population (BDEs 47, 99, 100, 153). Cox proportional hazards models modified for discrete time were used to obtain fecundability odds ratios (fORs) for the association of PBDEs and time to pregnancy.

RESULTS

We detected all four congeners in > 97% of women. Increasing levels of BDEs 47, 99, 100, 153 and the sum of these four congeners were all associated with longer time to pregnancy. We observed significantly reduced fORs for BDE-100 [adjusted fOR = 0.6; 95% confidence interval (CI), 0.4-0.9], BDE-153 (adjusted fOR = 0.5; 95% CI, 0.3-0.8), and the sum of the four congeners (adjusted fOR = 0.7; 95% CI, 0.5-1.0). PBDEs were not associated with menstrual cycle characteristics.

CONCLUSIONS

We found significant decreases in fecundability associated with PBDE exposure in women. Future studies are needed to replicate and confirm this finding.

Bioaccumulation behavior of polybrominated diphenyl ethers (PBDEs) in the freshwater food chain of Baiyangdian lake, north China

Polybrominated diphenyl ethers (PBDEs) are of great environmental concern due to bioaccumulation in different food chains. Trophodynamics of PBDEs in freshwater food chain is an important criterion for assessing their ecological risk. In the study, PBDEs were analyzed in sixteen aquatic species collected from Baiyangdian Lake, North China. The concentrations of nine PBDE congeners (BDE-28, -47, -66, -99, -100, -85, -153, -154, and -183) in aquatic organisms ranged from 3.4 to 160.2ng/g lipid weight. BDE-47 was the predominant PBDE congener in most samples except for river snails and swan mussels. BDE-209 was detected in 50% of biota samples, which indicated the bioavailability of BDE209. Correlation between lipid-normalized concentrations of PBDEs and trophic levels determined by stable isotope nitrogen technologies confirmed that PBDEs were biomagnified in the freshwater food chain. The trophic magnification factors (TMFs) ranged from 1.3 to 2.1 for PBDE congeners, greater than one, indicating the biomagnification potential for the PBDE congeners in the freshwater food chain. The relationship between TMFs and Log K(ow) (octanol-water partition coefficient) indicated that the phenomenon of trophic magnification for lowly brominated congeners was obvious in the freshwater food chain.

Bioaccumulation and biotransformation of decabromodiphenyl ether and effects on daily growth in juvenile lake whitefish (Coregonus clupeaformis)

Decabromodiphenyl ether (BDE 209) is the main congener in the commonly used commercial flame retardant mixture, "deca-BDE". There is evidence showing that fish can debrominate BDE 209 into potentially more toxic congeners. The objective of this study was to evaluate BDE 209 uptake and its potential effects on juvenile lake whitefish (Coregonus clupeaformis). Lake whitefish were fed BDE 209 at four nominal concentrations (control, 0.1, 1, and 2 microg/g-diet) for 30 days. Livers and carcasses were analyzed for 11 polybrominated diphenyl ether (PBDE) congeners (BDE 47, 99, 100, 153, 154, 196, 197, 206, 207, 208, and 209) and daily otolith increment width was measured as an estimate of growth before and after exposure. Four congeners (BDE 206, 207, 208, and 209) were detected in livers and carcasses. Hepatic BDE 209 concentrations in the 1 and 2 microg/g treatments were significantly higher than in the control group (1.25 and 5.80 nmol/g-lipid compared to 0.183 nmol/g-lipid). The concentration of BDE 209 detected in the tissues of the control group resulted from BDE 209 in the base diets. Concentrations of all congeners from the 1 and 2 microg/g groups were higher in livers than carcasses, indicating the liver was the primary organ of BDE 209 accumulation. Compared to the fraction in diets, the molar fraction of BDE 209 was lower in livers and carcasses, whereas the fractions of BDE 206, 207, and 208 were higher. These different distributions of PBDE congeners resulted from differential adsorption and metabolism. One congener, BDE 206, could be a major metabolite from BDE 209 debromination. Otolith increment widths were narrower in fish from the highest diet concentration administered, suggesting BDE 209 may have affected growth rates. In conclusion, this in vivo study with lake whitefish showed that BDE 209 was debrominated into lower PBDE congeners and that exposure to 2 microg/g may have affected fish growth.

Bioaccumulation and biomagnification of polybrominated diphenyl ethers in a food web of Lake Michigan

Polybrominated diphenyl ethers are hydrophobic chemicals and can biomagnify in food chains. Little is known about the biomagnification of PBDEs in the Lake Michigan food web. Plankton, Diporeia, lake whitefish, lake trout, and Chinook salmon were collected from Lake Michigan in 2006 between April and August. Fish liver and muscle and whole invertebrates were analyzed for six PBDEs (BDE-47, 99, 100, 153, 154, and 209). Carbon and nitrogen stable isotope ratios (delta(13)C and delta(15)N) were also quantified in order to establish the trophic structure of the food web. Geometric means of Sigma PBDE concentrations in fish ranged from 0.562 to 1.61 microg/g-lipid. BDE-209 concentrations ranged from 0.184 to 1.23 microg/g-lipid in all three fish species. Sigma BDE-47, 99, and 209 comprised 80-94% of Sigma PBDE molar concentration. Within each fish species, there were no significant differences in PBDE concentrations between liver and muscle. The highest concentration of BDE-209 (144 microg/g-lipid) was detected in Diporeia. Based on analysis of delta(15)N and PBDE concentrations, BDE-47 and 100 were found to biomagnify, whereas BDE-209 did not. A significant negative correlation between BDE-209 and trophic level was found in this food web. Biomagnification factors were also calculated and again BDE-47 and 100 biomagnified between food web members whereas BDE-209 did not. Diporeia could be one of the main dietary sources of BDE-209 for fish in Lake Michigan; BDE-47 and 100 biomagnified within this food chain; the concentration of BDE-209 decreased at higher trophic levels, suggesting partial uptake and/or biotransformation of BDE-209 in the Lake Michigan food web.

Contaminant blubber burdens in Atlantic bottlenose dolphins (Tursiops truncatus) from two southeastern US estuarine areas: concentrations and patterns of PCBs, pesticides, PBDEs, PFCs, and PAHs

Polychlorinated biphenyls (PCBs), chlorinated pesticides (i.e., dichlorodiphenyltrichloroethane (DDT) and its metabolites, chlordanes (CHLs), dieldrin, hexachlorobenzene (HCB), and mirex), polybrominated diphenyl ethers (PBDEs), perfluorinated chemicals (PFCs), and polyaromatic hydrocarbons (PAHs) were measured in blubber biopsy samples collected from 139 wild bottlenose dolphins (Tursiops truncatus) during 2003-2005 in Charleston (CHS), SC and the Indian River Lagoon (IRL), FL. Dolphins accumulated a similar suite of contaminants with summation operatorPCB dominating (CHS 64%, IRL 72%), followed by summation operatorDDT (CHS 20%, IRL 17%), summation operatorCHLs (CHS 7%; IRL 7%), summation operatorPBDE (CHS 4%, IRL 2%), PAH at 2%, and dieldrin, PFCs and mirex each 1% or less. Together summation operatorPCB and summation operatorDDT concentrations contributed approximately 87% of the total POCs measured in blubber of adult males. summation operatorPCBs in adult male dolphins exceed the established PCB threshold of 17mg/kg by a 5-fold order of magnitude with a 15-fold increase for many animals; 88% of the dolphins exceed this threshold. For male dolphins, CHS (93,980ng/g lipid) had a higher summation operatorPCBs geomean compared to the IRL (79,752ng/g lipid) although not statistically different. In adult males, the PBDE geometric mean concentration was significantly higher in CHS (5920ng/g lipid) than the IRL (1487ng/g). Blubber summation operatorPFCs concentrations were significantly higher in CHS dolphins. In addition to differences in concentration of PCB congeners, summation operatorPBDE, TEQ, summation operatorCHLs, mirex, dieldrin, and the ratios summation operatorDDE/ summation operatorDDT and trans-nonachlor/cis-nonachlor were the most informative for discriminating contaminant loads in these two dolphin populations. Collectively, the current summation operatorPCB, summation operatorDDT, and summation operatorPBDEs blubber concentrations found in CHS dolphins are among the highest reported values in marine mammals. Both dolphin populations, particularly those in CHS, carry a suite of organic chemicals at or above the level where adverse effects have been reported in wildlife, humans, and laboratory animals warranting further examination of the potential adverse effects of these exposures.

POP levels in breast milk and maternal serum and thyroid hormone levels in mother-child pairs from Uppsala, Sweden

In experimental studies, it has frequently been observed that the homeostasis of thyroid hormones (THs) is affected by exposure to persistent organic pollutants (POPs), such as dioxins and PCBs. In man, similar effects have been indicated in several epidemiological studies. In order to investigate the possible effect on THs at low background exposures found among the Swedish population the following study was performed. Primiparous women (n=395) in the Uppsala region were recruited between 1996 and 1999. Of these, 325 mothers agreed to donate a serum sample in late pregnancy and breast milk was obtained from 211 women 3 weeks after delivery. Babies were sampled for blood at 3 weeks (n=150) and 3 months (n=115) after birth. In connection to the sampling, questions on personal characteristics were asked. Levels of low (tri- to penta-) chlorinated PCB, di-ortho PCB, p,p'-DDE, (mono-ortho) PCB TEQ and PCDD/DF TEQ were monitored in breast milk and in mother's blood (not PCDD/DF). The results showed that the measured TH levels (thyroid-stimulating hormone - TSH, total tri-iodothyronine - TT3, free thyroxine - FT4) in mothers and children were within the reference range. Some significant associations were seen between POP exposures and TH levels in mother or child after simple regression analysis. Following adjustment for important confounding factors, the significant associations mostly disappeared. However, significantly decreasing TT3 levels with increasing prenatal low-chlorinated PCB exposure were still seen in 3 week old children, and on TT3 in mothers exposed to PCDD/DF. In conclusion, the study clearly shows the importance of adjustment for important confounding factors in the analysis of possible associations between POP exposure and hormonal effects. The remaining associations are weak in both children and mothers and the clinical consequences of these alterations are uncertain. When comparing studies that investigate associations between TH levels and POP levels during the perinatal stage, no obvious between-study concordance was seen regarding the critical dose for hormonal effects to occur.

The potential of selected brominated flame retardants to affect neurological development

Various brominated flame retardants (BFR), including polybrominated diphenyl ether (PBDE) congeners, hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), are commonly used in household items and electronics and have been detected in the environment and/or the bodily fluids of people, including children. Some studies in animals suggest that exposure to PBDE congeners, HBCD, or TBBPA during the perinatal period may affect locomotor activity and/or memory and learning. Epidemiological studies showing similar effects in humans, however, are lacking. To assess whether an association exists between perinatal exposure and development of consistent neurobehavioral alterations, published animal studies investigating perinatal exposure to PBDE congeners, HBCD, or TBBPA with specific neurobehavioral evaluations-particularly, assessments of motor activity-were reviewed for consistency of results. Our analysis shows that although the majority of studies suggest that perinatal exposure affects motor activity, the effects observed were not consistent. This lack of consistency includes the type of motor activity (locomotion, rearing, or total activity) affected, the direction (increase or decrease) and pattern of change associated with exposure, the existence of a dose response, the permanency of findings, and the possibility of gender differences in response. Interestingly, Good Laboratory Practices (GLP)-compliant studies that followed U.S. Environmental Protection Agency (EPA)/Organization for Economic Cooperation and Development (OECD) guidelines for developmental neurotoxicity testing found no adverse effects associated with exposure to PBDE209, HBCD, or TBBPA at doses that were orders of magnitude higher and administered over longer durations than those used in the other studies examined herein. The lack of consistency across studies precludes establishment of a causal relationship between perinatal exposure to these substances and alterations in motor activity.

Global gene expression analysis in the livers of rat offspring perinatally exposed to low doses of 2,2',4,4'-tetrabromodiphenyl ether

BACKGROUND

Polybrominated diphenyl ethers are a group of flame-retardant chemicals appearing increasingly in the environment. Their health effects and mechanisms of toxicity are poorly understood.

OBJECTIVES

We screened for the sensitive effects and mechanisms of toxicity of 2,2 ,4,4 -tetra-bromodiphenyl ether (BDE-47) by analyzing the gene expression profile in rats exposed to doses comparable to human exposure.

METHODS

Wistar dams were exposed to vehicle or BDE-47 (0.002 and 0.2 mg/kg body weight) every fifth day from gestation day 15 to postnatal day 20 by injections to caudal vein. Total RNA was extracted from the livers of pups and hybridized to the whole-genome RNA expression micro-arrays. The list of genes 2-fold differentially expressed was exported to PANTHER and Ingenuity Systems for analysis of enriched ontology groups and molecular pathways.

RESULTS

Oxidoreductase and transferase protein families were enriched in exposed rats as were these biological process categories: carbohydrate metabolism; electron transport; and lipid, fatty acid, and steroid metabolism. Four signaling pathways (cascades of activation of drug-metabolizing enzymes) and 10 metabolic pathways were significantly enriched. Drug-metabolizing enzymes appear to be regulated by BDE-47 through an aryl hydrocarbon receptor-independent mechanism. Direct interaction with retinoid X receptor or its upstream cascade may be involved. The main metabolic effects consisted of activation of metabolic pathways: alpha- and omega-oxidation of fatty acids, glycolysis, and starch hydrolysis.

CONCLUSIONS

Altered expression of genes involved in metabolic and signaling pathways and functions of the organism occurs after perinatal exposure of rat offspring to BDE-47 at doses relevant for the general population.

Anthropogenic and naturally-produced organobrominated compounds in marine mammals from Brazil

Liver samples from 51 cetaceans, comprising 10 species, stranded between 1994 and 2006 in a highly industrialized and urbanized region in Southeast Brazil, were analyzed for polybrominated diphenyl ethers (PBDEs) and methoxylated-PBDEs (MeO-PBDEs). A concentration range of PBDEs (3-5960ng/g lw) similar to that observed in Northern Hemisphere dolphins was found. MeO-PBDE concentrations in continental shelf (CS) dolphins from Brazil are among the highest detected to date in cetaceans (up to 250microg/g lw). Higher SigmaMeO-PBDE concentrations were measured in CS and oceanic dolphins than in estuarine dolphins. The SigmaPBDE/SigmaMeO-PBDE ratio varied significantly ranging from a mean value of 7.12 to 0.08 and 0.01 for estuarine, CS and oceanic species, respectively. A positive correlation was observed between SigmaPBDE and year of stranding of male estuarine dolphins (Sotalia guianensis), which suggests temporal variation in the exposure. Placental transfer of organobrominated compounds was also evidenced in S. guianensis.

Occurrence of polybrominated diphenyl ethers in fish and shellfish downstream from electronic-waste recycling plants

We measured 39 polybrominated diphenyl ethers (PBDEs) in the muscle tissue of three species of fish (Sciaenops ocellatus, Sparus macrocephalus, and Lateolabraxjaponicus) and four species of shellfish (Tegillarca granosa, Cyclina sinensis, Sinonovacula constricta, and Ostrea cucullata) that were collected downstream of electronic-waste recycling plants in Taizhou, China. A total of 24 PBDE congeners (PBDE24) in the samples were detected. The sigma PBDE24 (total PBDE) ranged from 545.4 to 1688.7 ng/kg ww (wet weight). The mean sigma PBDE24 concentration was 1382.6 ng/kg ww in fish and 858.1 ng/kg ww in shellfish. The lower brominated congeners were detected at relatively high concentrations in all species. The penta-products, produced from e-waste, were found at relatively low levels. A principal component analysis suggested a significant correlation among di-, tri-, tetra-, and hepta-BDEs for the three species of fish. Similarly, we found a significant correlation between mono- and tri-BDEs in the shellfish. Our results suggested that the processes of PBDE metabolism and elimination were similar in both fish and shellfish. In addition, the primary source of PBDEs appeared to be from the debromination of high brominated PBDEs.

Toxicity of penta- and decabromodiphenyl ethers after repeated administration to rats: a comparative study

Until recently, pentabromodiphenyl (PentaBDE) and decabromodiphenyl (DecaBDE) ethers were commonly used as flame retardants in a wide array of products, mostly in the production of plastics utilized in the electric, electronic and textile industries. The aim of this study was to compare the toxicity of PentaBDE and DecaBDE after their repeated (7-28 days) intragastric administration to rats. The compounds were given at doses of 2, 8, 40 or 200 mg/kg/day (PentaBDE) and 10, 100 or 1,000 mg/kg/day (DecaBDE). The repeated administration of PentaBDE disturbed redox homeostasis, which was manifested by lower total antioxidant status and increased activity of glutathione reductase in serum and higher concentrations of glutathione reduced and malondialdehyde in the liver. The occurrence of these effects was not observed after DecaBDE administration. The results of histopathological examination showed fatty degeneration after administration of the highest dose of PentaBDE. The repeated administration of PentaBDE also caused the increase in relative liver mass, dose-dependent increase in the activity of CYP 1A (EROD) and CYP 2B (PROD), 7-12- and 2-8-fold, respectively, as well as enhanced level of CYP 1A1 (5-30-fold) and CYP 4A (2-4.5-fold). The administration of DecaBDE induced much less pronounced changes: a maximum 2.8-fold increase in the activity of CYP 1A, a twofold increase in CYP 2B, and no alterations in other parameters under study. Contrary to DecaBDE, PentaBDE disturbed redox homeostasis, and induced liver microsomal enzymes. Fatty degeneration in liver caused by this compound was also found.

Short-term exposure to triclosan decreases thyroxine in vivo via upregulation of hepatic catabolism in Young Long-Evans rats

Triclosan (5-chloro-2-(2,4-dichlorophenoxy)-phenol) is a chlorinated phenolic antibacterial compound found in consumer products. In vitro human pregnane X receptor activation, hepatic phase I enzyme induction, and decreased in vivo total thyroxine (T4) suggest adverse effects on thyroid hormone homeostasis. Current research tested the hypothesis that triclosan decreases circulating T4 via upregulation of hepatic catabolism and transport. Weanling female Long-Evans rats received triclosan (0-1000 mg/kg/day) by gavage for 4 days. Whole blood and liver were collected 24 h later. Total serum T4, triiodothyronine (T3), and thyroid-stimulating hormone (TSH) were measured by radioimmunoassay. Hepatic microsomal assays measured ethoxyresorufin-O-deethylase, pentoxyresorufin-O-deethylase (PROD), and uridine diphosphate glucuronyltransferase enzyme activities. The messenger RNA (mRNA) expression of cytochrome P450s 1a1, 2b1/2, and 3a1/23; UGTs 1a1, 1a6, and 2b5; sulfotransferases 1c1 and 1b1; and hepatic transporters Oatp1a1, Oatp1a4, Mrp2, and Mdr1b was measured by quantitative reverse transcriptase PCR. Total T4 decreased dose responsively, down to 43% of control at 1000 mg/kg/day. Total T3 was decreased to 89 and 75% of control at 300 and 1000 mg/kg/day. TSH did not change. Triclosan dose dependently increased PROD activity up to 900% of control at 1000 mg/kg/day. T4 glucuronidation increased nearly twofold at 1000 mg/kg/day. Cyp2b1/2 and Cyp3a1/23 mRNA expression levels were induced twofold and fourfold at 300 mg/kg/day. Ugt1a1 and Sult1c1 mRNA expression levels increased 2.2-fold and 2.6-fold at 300 mg/kg/day. Transporter mRNA expression levels were unchanged. These data denote important key events in the mode of action for triclosan-induced hypothyroxinemia in rats and suggest that this effect may be partially due to upregulation of hepatic catabolism but not due to mRNA expression changes in the tested hepatic transporters.

In Vivo Acute Exposure to Polychlorinated Biphenyls: Effects on Free and Total Thyroxine in Rats

Hypothyroxinemia in rats has been well documented as a result of exposure to polychlorinated biphenyls (PCBs). Hypothetical mechanisms include induction of hepatic catabolic enzymes and cellular hormone transporters, and/or interference with plasma transport proteins. We hypothesized that if thyroxine displacement from transport proteins by PCBs occurs in vivo, it would result in increased free thyroxine (FT4). This study investigates the effects of a single oral dose of 2,2’,4,4’,5,5'-hexachlorobiphenyl (PCB 153 at 60 mg/kg) or 3,3’,4,4’,5,5'-hexachlorobiphenyl (PCB 169 at 1 mg/kg) on rats at 28 or 76 days of age. Total thyroxine (TT4) and FT4 were measured at 0.5, 1, 2, 4, 8, 24, or 48 hours post -dosing. Microsomal ethoxy- and pentoxy-resorufin-O-deethylase (EROD and PROD) activity and uridine diphosphoglucuronosyl transferase (UGT) activity were determined. No significant increase in TT4 or FT4 concentrations was seen at any time point. PCB 153 significantly decreased TT4 and FT4 in young and adult rats, with young rats showing a time-by-treatment interaction from 2 to 48 hours post -dosing in serum FT4. With PCB 169 exposure, young rats showed a decrease in FT4 only, whereas adult rats showed decreases in TT4 only. Hepatic EROD and PROD activities were both dramatically increased following PCB 169 and 153, respectively. Uridine diphosphoglucuronosyl transferase activity was increased only after PCB 169 exposure. These data demonstrate that neither PCB 153 nor PCB169 increased FT4, which supports the conclusion that these PCBs do not displace thyroxine from serum TTR, or if it does occur, there is no subsequent increase in serum FT4 in vivo.

Environmental chemicals and thyroid function: an update

PURPOSE OF REVIEW

To overview the effects of endocrine disrupters on thyroid function.

RECENT FINDINGS

Studies in recent years have revealed thyroid-disrupting properties of many environmentally abundant chemicals. Of special concern is the exposure of pregnant women and infants, as thyroid disruption of the developing fetus may have deleterious effects on neurological outcome. Evidence is reviewed for the following groups of chemicals: polychlorinated biphenyls, dioxins, flame retardants, pesticides, perfluorinated chemicals, phthalates, bisphenol A and ultraviolet filters. Chemicals may exert thyroid effects through a variety of mechanisms of action, and some publications have focused on elucidating the mechanisms of specific (groups of) chemicals.

SUMMARY

A large variety of ubiquitous chemicals have been shown to have thyroid-disrupting properties, and the combination of mechanistic, epidemiological and exposure studies indicates that the ubiquitous human and environmental exposure to industrial chemicals may impose a serious threat to human and wildlife thyroid homeostasis. Currently, available evidence suggests that authorities need to regulate exposure to thyroid-disrupting chemicals of pregnant women, neonates and small children in order to avoid potential impairment of brain development. Future studies will indicate whether adults also are at risk of thyroid damage due to these chemicals.

Components of plastic: experimental studies in animals and relevance for human health

Components used in plastics, such as phthalates, bisphenol A (BPA), polybrominated diphenyl ethers (PBDE) and tetrabromobisphenol A (TBBPA), are detected in humans. In addition to their utility in plastics, an inadvertent characteristic of these chemicals is the ability to alter the endocrine system. Phthalates function as anti-androgens while the main action attributed to BPA is oestrogen-like activity. PBDE and TBBPA have been shown to disrupt thyroid hormone homeostasis while PBDEs also exhibit anti-androgen action. Experimental investigations in animals indicate a wide variety of effects associated with exposure to these compounds, causing concern regarding potential risk to human health. For example, the spectrum of effects following perinatal exposure of male rats to phthalates has remarkable similarities to the testicular dysgenesis syndrome in humans. Concentrations of BPA in the foetal mouse within the range of unconjugated BPA levels observed in human foetal blood have produced effects in animal experiments. Finally, thyroid hormones are essential for normal neurological development and reproductive function. Human body burdens of these chemicals are detected with high prevalence, and concentrations in young children, a group particularly sensitive to exogenous insults, are typically higher, indicating the need to decrease exposure to these compounds.

Thyroid function and plasma concentrations of polyhalogenated compounds in Inuit adults

BACKGROUND

Several ubiquitous polyhalogenated compounds (PHCs) have been shown to alter thyroid function in animal and in vitro studies. So far, epidemiologic studies have focused on the potential effect of a small number of them, namely, polychlorinated biphenyls (PCBs) and some organochlorines (OCs), without paying attention to other important PHCs.

OBJECTIVES

We investigated the relationship between exposure to several PHCs and thyroid hormone homeostasis in Inuit adults from Nunavik.

METHODS

We measured thyroid parameters [thyroid-stimulating-hormone (TSH), free thyroxine (fT(4)), total triiodothyronine (tT(3)), and thyroxine-binding globulin (TBG)] and concentrations of 41 contaminants, including PCBs and their metabolites, organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), perfluorooctanesulfonate (PFOS), and a measure of dioxin-like compounds, detected in plasma samples from Inuit adults (n = 623).

RESULTS

We found negative associations between tT(3) concentrations and levels of 14 PCBs, 7 hydroxylated PCBs (HO-PCBs), all methylsulfonyl metabolites of PCBs (MeSO(2)-PCBs), and 2 OCPs. Moreover, we found negative associations between fT(4) levels and hexachlorobenzene concentrations. TBG concentrations were inversely related to 8 PCBs, 5 HO-PCBs, and 3 OCPs. Exposure to BDE-47 was positively related to tT (3), whereas PFOS concentrations were negatively associated with TSH, tT(3,) and TBG and positively with fT(4) concentrations.

CONCLUSION

Exposure to several PHCs was associated with modifications of the thyroid parameters in adult Inuit, mainly by reducing tT(3) and TBG circulating concentrations. The effects of PFOS and BDE-47 on thyroid homeostasis require further investigation because other human populations display similar or higher concentrations of these chemicals.

Patterns and concentration levels of polybrominated diphenyl ethers (PBDEs) in placental tissue of women in Denmark

The levels and congener patterns of PBDEs were investigated in human placental samples in Denmark. The median concentrations of sigmaPBDE(tri-hepta) and BDE-209 in the 50 samples were 1.22 and 1.14 ng g(-1) lw, respectively, with the total sum ranging from 0.51 to 17.1 ng g(-1) lw, which is similar to previous placental studies. The PBDE content in placental tissue was dominated by BDE-209, which accounted for approximately 50% of the total amount of PBDEs. BDE-47, -99, and -153 were detected in all samples. Approximately equal amounts of BDE-47 and BDE-153 were observed in the placental tissue, which is in agreement with previous European studies of human serum. Principal Component Analysis (PCA) was performed to analyze congener patterns within and between mothers. The loading plot showed groupings of the measured PBDE variables in three groups, representative of Penta-, Octa- and Deca-BDE technical mixtures. Congeners representing the individual technical mixtures were close to orthogonal or inversely correlated, indicating variation in the congener patterns of internal exposure corresponding to the patterns of technical mixtures used in products. Visualisation of the participant objects according to body mass index (BMI), revealed inherent congener patterns (19% X-variance) showing increased frequency for participants within the highest BMI group to have elevated concentrations of BDE-209 in the placental tissue.

Nuclear hormone receptor activity of polybrominated diphenyl ethers and their hydroxylated and methoxylated metabolites in transactivation assays using Chinese hamster ovary cells

BACKGROUND

An increasing number of studies are reporting the existence of polybrominated diphenyl ethers (PBDEs) and their hydroxylated (HO) and methoxylated (MeO) metabolites in the environment and in tissues from wildlife and humans.

OBJECTIVE

Our aim was to characterize and compare the agonistic and antagonistic activities of principle PBDE congeners and their HO and MeO metabolites against human nuclear hormone receptors.

METHODS

We tested the hormone receptor activities of estrogen receptor alpha (ERalpha), ERbeta, androgen receptor (AR), glucocorticoid receptor (GR), thyroid hormone receptor alpha(1) (TRalpha(1)), and TRbeta(1) against PBDE congeners BDEs 15, 28, 47, 85, 99, 100, 153, and 209, four para-HO-PBDEs, and four para-MeO-PBDEs by highly sensitive reporter gene assays using Chinese hamster ovary cells.

RESULTS

Of the 16 compounds tested, 6 and 2 showed agonistic activities in the ERalpha and ERbeta assays, respectively, and 6 and 6 showed antagonistic activities in these assays. 4'-HO-BDE-17 showed the most potent estrogenic activity via ERalpha/beta, and 4'-HO-BDE-49 showed the most potent anti estrogenic activity via ERalpha/beta. In the AR assay, 13 compounds showed antagonistic activity, with 4'-HO-BDE-17 in particular inhibiting AR-mediated transcriptional activity at low concentrations in the order of 10(-8) M. In the GR assay, seven compounds, including two HO-PBDEs and two MeO-PBDEs, showed weak antagonistic activity. In the TRalpha(1) and TRbeta(1) assays, only 4-HO-BDE-90 showed weak antagonistic activity.

CONCLUSIONS

Taken together, these results suggest that PBDEs and their metabolites might have multiple endocrine-disrupting effects via nuclear hormone receptors, and para-HO-PBDEs, in particular, possess more potent receptor activities compared with those of the parent PBDEs and corresponding para-MeO-PBDEs.

Technical pentabromodiphenyl ether and hexabromocyclododecane as activators of the pregnane-X-receptor (PXR)

Technical pentabrominated diphenyl ether (pentaBDE mix) is a mixture of polybrominated diphenyl ethers (PBDEs) which has been widely used as a flame retardant. Since its ban in several countries it has been replaced by other brominated flame retardants such as hexabromocyclododecane (HBCD). Both certain PBDE congeners and HBCD are present in environmental and human samples reflecting their persistent and bioaccumulative properties. PentaBDE mix and HBCD have recently been found to induce cytochrome P450 (CYP) 3 enzymes in rat liver. In this study we tested both technical pentaBDE mix and HBCD for their potency to induce CYP3A enzymes in rat hepatocytes in primary culture, and in rat H4IIE and human HepG2 hepatoma cells. In rat hepatocytes, HBCD was a more effective CYP3A1 inducer than pentaBDE mix, being less effective, however, than the prototype inducer dexamethasone. In human HepG2 cells, both compounds and the prototype inducer rifampicin were about equally effective. In contrast, in HepG2 cells, HBCD failed to induce luciferin-PFBE dealkylase, a common catalytic activity of a number of CYP3A enzymes, possibly reflecting enzyme inhibition. A significant induction of catalytic activity was observed in rat hepatocytes with both compounds. Analysis of a XREM-driven reporter gene activity in transfected cells confirmed that both compounds act as agonists of the human and rat pregnane-X-receptor, which was detectable in all cell types used.

Polybrominated diphenyl ether-associated alterations in cell biochemistry as determined by attenuated total reflection Fourier-transform infrared spectroscopy: a comparison with DNA-reactive and/or endocrine-disrupting agents

Whether polybrominated diphenyl ethers (PBDEs) induce effects in target cells is increasingly important given that their environmental burdens are rising. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy can be used to biochemically signature cells based on the notion that a detailed "biochemical-cell fingerprint" in the form of an infrared (IR) spectrum is derived. By employing subsequent computational approaches such as principal component analysis (PCA) and/or linear discriminant analysis (LDA), data reduction is achieved to allow for the identification of wavenumber-related biomarkers of effect Clustering of similar spectra (or scores) away from dissimilar ones highlights the variance responsible for discriminating classes. Discriminating biomarkers might include protein conformational changes, structural alterations to DNA/RNA, glycogen content, or protein phosphorylation. Employing this approach, we investigated in MCF-7 cells the dose-related effects of PBDEs (congeners 47, 153, 183, and 209), benzo[a]pyrene (B[a]P), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PHIP), 17beta-Oestradiol (E2), or lindane (gamma-hexachlorocyclohexane). Cultures concentrated in G0/G1- or S-phases were treated for 24 h. Following treatment MCF-7 cells were fixed and applied to IR reflective Low-E windows for interrogation using ATR-FTIR spectroscopy. At concentrations as low as 10(-12) M in culture, significant separation (P < or = 0.05) of PBDE-treated and vehicle control cell populations was noted. In some cases this was associated with alterations in lipid or the secondary structure of proteins; with DNA-reactive compounds (e.g., B[a]P), variance was primarily noted in the DNA/RNA region. This study points to a novel nondestructive approach capable of identifying contaminant effects at environmental concentrations in target cells.

Polybrominated diphenyl ethers in human gestational membranes from women in southeast Michigan

Polybrominated diphenyl ethers (PBDEs) have been incorporated into many consumer products as flame retardants. Due to their persistence and ability to bioaccumulate, PBDEs are ubiquitous in human blood and breast milk samples from industrialized nations. Although there exists a potential for environmental pollutants such as PBDEs to adversely impact birth outcomes and perinatal health, reports of PBDE levels in human reproductive tissues are limited. The aim of the current study is to evaluate the total levels and congener-specific profiles of PBDEs from human extraplacental gestational membranes. Gestational membranes from five term pregnancies were obtained from nonlaboring caesarian deliveries at the University of Michigan Women's Hospital Birth Center. Duplicate samples were extracted and analyzed by GC-MS for twenty-one PBDE congeners. Total PBDE loading was 17.4 +/- 3.9 pg/g tissue (5.62 +/- 1.28 ng/g lipid). Seventy-eight percent of the total measurable PBDE loading was due to BDEs 47, 49, 99, 100, and 153, with measured values of 3.63, 3.15, 3.05, 1.74, and 1.90 pg/g tissue (1170, 1018, 983, 561, and 612 pg/g lipid), respectively. The remaining 28% comprised BDEs 17, 28, 66, 71, 85, and 154. No octa-, nona-, or deca-BDEs were identified. Although previously unreported in the human gestational compartment BDE 49 comprised 17% of the total PBDE level. This work establishes baseline accumulated levels of PBDEs in gestational membranes of women in Southeast Michigan.

Metabolism of polybrominated diphenyl ethers (PBDEs) by human hepatocytes in vitro

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are flame-retardant chemicals that accumulate in human tissues and are potential toxicants. Concentrations of PBDEs in human tissues have increased recently, and body burdens in the U.S. and Canadian populations are higher than in any other region.

OBJECTIVES

Although metabolism in animal laboratory studies has been examined, no studies have explored the metabolism of these contaminants in human tissues. We undertook this study to determine whether PBDEs could be metabolized by human liver cells in vitro and to identify what types of metabolites are formed.

METHODS

We exposed hepatocytes from three different donors (two cryopreserved batches and one fresh batch) to solutions containing 10 muM of either of two environmentally relevant and prominent PBDE congeners-BDE-99 or BDE-209-for periods of 24-72 hr. We also conducted gene expression analysis to provide information on potential induction of xenobiotic metabolizing enzymes.

RESULTS

Exposing hepatocytes to BDE-99 resulted in the formation of 2,4,5-tribromo phenol, two monohydroxylated pentabrominated diphenyl ether metabolites, and a yet unidentified tetrabrominated metabolite. No hydroxylated or debrominated metabolites were observed in the cells exposed to BDE-209. This suggests that BDE-209 was not metabolized, that nonextractable, covalently protein-bound metabolites were formed, or that the exposure time was not long enough for BDE-209 to diffuse into the cell to be metabolized. However, we observed up-regulation of genes encoding for cytochrome P450 monooxygenase (CYP) 1A2, CYP3A4, deiodinase type 1, and glutathione S-transferase M1 in hepatocyes exposed to both BDE-99 and BDE-209.

CONCLUSIONS

Our in vitro results suggest that the human liver will likely metabolize some BDE congeners (e.g., BDE-99) in vivo. These metabolites have been shown to elicit greater toxicity than the parent BDE congeners in laboratory bioassays; thus, more research on body burdens and human health effects from these metabolites are warranted.

Dietary exposure to 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47) alters thyroid status and thyroid hormone-regulated gene transcription in the pituitary and brain

BACKGROUND

Polybrominated diphenyl ether (PBDE) flame retardants have been implicated as disruptors of the hypothalamic-pituitary-thyroid axis. Animals exposed to PBDEs may show reduced plasma thyroid hormone (TH), but it is not known whether PBDEs impact TH-regulated pathways in target tissues.

OBJECTIVE

We examined the effects of dietary exposure to 2,2',4,4'-tetrabromodiphenyl ether (PBDE-47)-commonly the highest concentrated PBDE in human tissues-on plasma TH levels and on gene transcripts for glycoprotein hormone alpha-subunit (GPHalpha) and thyrotropin beta-subunit (TSHbeta) in the pituitary gland, the auto-induced TH receptors alpha and beta in the brain and liver, and the TH-responsive transcription factor basic transcription element-binding protein (BTEB) in the brain.

METHODS

Breeding pairs of adult fathead minnows (Pimephales promelas) were given dietary PBDE-47 at two doses (2.4 microg/pair/day or 12.3 microg/pair/day) for 21 days.

RESULTS

Minnows exposed to PBDE-47 had depressed plasma thyroxine (T(4)), but not 3,5,3'-triiodothyronine (T(3)). This decline in T(4) was accompanied by elevated mRNA levels for TStHbeta (low dose only) in the pituitary. PBDE-47 intake elevated transcript for TH receptor alpha in the brain of females and decreased mRNA for TH receptor beta in the brain of both sexes, without altering these transcripts in the liver. In males, PBDE-47 exposure also reduced brain transcripts for BTEB.

CONCLUSIONS

Our results indicate that dietary exposure to PBDE-47 alters TH signaling at multiple levels of the hypothalamic-pituitary-thyroid axis and provide evidence that TH-responsive pathways in the brain may be particularly sensitive to disruption by PBDE flame retardants.

Hormone disruption by PBDEs in adult male sport fish consumers

BACKGROUND

Persistent pollutants, such as polychlorinated biphenyls (PCBs), affect endocrine function. Human exposure to polybrominated diphenyl ethers (PBDEs), which are similar in structure to PCBs, has increased recently, but health effects have not been well studied.

OBJECTIVES

Our goal in this study was to determine whether PBDE body burdens are related to thyroid and steroid hormone levels, thyroid antibodies, and thyroid disease in a cohort of frequent and infrequent adult male sport fish consumers.

METHODS

We tested serum from 405 adult males for PBDE congeners, PCB congeners, testosterone, sex-hormone-binding globulin (SHBG), SHBG-bound testosterone, thyroglobulin antibodies, and the thyroid hormones thyroxine (T(4)), triiodothyronine (T(3)), thyroid-stimulating hormone (TSH), and T(4)-binding globulin (TBG). We collected data on demographics, fish consumption, medical diseases, and medication use.

RESULTS

The median sum of PBDEs was 38 ng/g lipid. In 308 men without thyroid disease or diabetes, PBDEs were positively related to measures of T(4) and reverse T(3) and inversely related to total T(3) and TSH. PBDEs were positively related to the percentage of T(4) bound to albumin, and inversely related to the percentage of T(4) bound to TBG. Associations of BDE congeners with hormones varied. BDE-47 was positively associated with testosterone levels. Participants with PBDEs over the 95th percentile were more likely to have thyroglobulin antibodies, although high PBDE exposure was not associated with thyroid disease. PBDE effects were independent of PCB exposure and sport fish consumption.

CONCLUSIONS

PBDE exposure, at levels comparable with those of the general U.S. population, was associated with increased thyroglobulin antibodies and increased T(4) in adult males.

Chronic postnatal DE-71 exposure: effects on learning, attention and thyroxine levels

Polybrominated diphenyl ethers (PBDEs) are ubiquitous, bioaccumulative flame retardants. Much remains to be learned about their developmental toxicological properties, particularly with regards to chronic exposure. In two experiments, male Long-Evans rats ingested the commercial pentaBDE mixture DE-71 from birth onward, first through the milk of lactating dams (who ingested 5 or 7.5 mg DE-71/day in a custom-mixed chow), then directly via chow consumption (at a dose of 3 or 4.5 mg/day). Control rats consumed the same brand of chow without DE-71. As adults, the rats were assessed for learning and attention using a series of five-choice serial reaction time tasks. A challenge with the muscarinic cholinergic antagonist scopolamine (0, 0.01, 0.03, or 0.05 mg/kg injected s.c.) was conducted on the final attention task. Serum total thyroxine (T4) levels were obtained at the end of testing. Total T4 was significantly lower in both DE-71 groups than in controls. Visual discrimination learning was unaffected by DE-71, but rats ingesting 4.5 mg/day DE-71 demonstrated significant impairments in sustained attention and inhibitory control, as evidenced by increased premature responding and decreased accuracy of responding in Attention Task 1. However, the DE-71-exposed rats did not respond differentially to the effects of scopolamine on attention compared to controls. These effects of chronic developmental DE-71 exposure differ from effects seen with brief postnatal exposure, suggesting that more research needs to be done on the more environmentally relevant chronic exposure model.

Effects of decabrominated diphenyl ether (DBDE) on developmental immunotoxicity in offspring mice

Decabrominated diphenyl ether (DBDE), a representative brominated flame retardant ubiquitous in the environment, is suspected of being hazardous to humans. We evaluated the developmental immunotoxicity of DBDE by an assay system using respiratory syncytial virus (RSV) infection in offspring mice. Pregnant mice were continuously exposed to DBDE (10, 100, 1000, or 10,000ppm) in the diet from gestation day 10 to weaning on postnatal day 21. Offspring mice born to these dams were intranasally infected with RSV. Virus titers in the lungs of RSV-infected offspring exposed perinatally to DBDE increased dose-dependently compared with the control. The level of interferon-γ in the bronchoalveolar lavage fluids and gene expression of the chemokine RANTES in the lungs were also significantly elevated in offspring mice exposed to DBDE. Histopathological analysis revealed that pneumonia in the lungs of offspring mice exposed to 10,000ppm of DBDE was exacerbated compared with the control. These results indicate that DBDE is a developmental immunotoxic agent.

An overview of policies for managing polybrominated diphenyl ethers (PBDEs) in the Great Lakes basin

The Great Lakes are an important environmental and economic resource for Canada and the United States. The ecological integrity of the Great Lakes, however, is becoming increasingly threatened by a number of persistent, bio-accumulative and harmful chemicals that enter the Great Lakes ecosystem through fluvial and atmospheric deposition. Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardant, are among such chemicals, whose concentration in the Great Lakes has greatly increased in recent years. Despite growing concern over the possible health and environmental effects of these compounds, only four of the eight Great Lakes states have enacted regulations to ban/restrict the use of PBDE while the two Canadian Great Lakes provinces are yet to endorse any regulation. Of the three main commercial PBDE mixtures (pentaBDE, octaBDE and decaBDE), penta- and octaBDE are no longer manufactured or imported into the United States and Canada. DecaBDE, however, still finds use in a variety of products. In the present paper, the authors review the current regulations and policies for managing PBDEs in the Great Lakes jurisdictions and briefly review commercially available non-bromine chemical alternatives to PBDE. As these alternatives are comparatively more expensive than PBDE, future adoption of more eco-friendly flame retardants by the polymer industry will likely depend on stricter legislation regulating the use of PBDE and/or an increased public demand for PBDE-free products.

Effects of perinatal PBDE exposure on hepatic phase I, phase II, phase III, and deiodinase 1 gene expression involved in thyroid hormone metabolism in male rat pups

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.

The effects of triclosan on puberty and thyroid hormones in male Wistar rats

Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is a potent antibacterial and antifungal compound that is widely used in personal care products, plastics, and fabrics. Recently triclosan has been shown to alter endocrine function in a variety of species. The purpose of this study was to determine effects of triclosan on pubertal development and thyroid hormone concentrations in the male rat. Weanling rats were exposed to 0, 3, 30, 100, 200, or 300 mg/kg of triclosan by oral gavage from postnatal day (PND) 23 to 53. Preputial separation (PPS) was examined beginning on PND 33. Rats were killed on PND 53, organ weights were recorded and serum was collected for subsequent analysis. Triclosan did not affect growth or the onset of PPS. Serum testosterone was significantly decreased at 200 mg/kg, however no effects were observed on androgen-dependent reproductive tissue weights. Triclosan significantly decreased total serum thyroxine (T4) in a dose-dependent manner at 30 mg/kg and higher (no observed effect level of 3 mg/kg). Triiodothyronine (T3) was significantly decreased only at 200 mg/kg, but thyroid stimulating hormone was not statistically different at any dose. Liver weights were significantly increased at 100 mg/kg triclosan and above suggesting that the induction of hepatic enzymes may have contributed to the altered T4 and T3 concentrations, but it does not appear to correlate with the T4 dose-response. This study demonstrates that triclosan exposure does not alter androgen-dependent tissue weights or onset of PPS; however, triclosan exposure significantly impacts thyroid hormone concentrations in the male juvenile rat.

Detection of polybrominated diphenyl ethers in herring gull (Larus argentatus) brains: effects on mRNA expression in cultured neuronal cells

In recent years, polybrominated diphenyl ethers (PBDEs) have been detected at increasing levels in the environment due to their widespread use as flame retardants. PBDEs can affect thyroid hormone homeostasis and the cholinergic neurotransmitter system. In this study, several PBDE congeners were detected in whole brain samples and neuronal cells of herring gulls (Larus argentatus). A herring gull neuronal cell culture method was used to determine the effects of PBDEs on cytotoxicity and mRNA expression. Real-time RT-PCR assays were developed for genes associated with the thyroid hormone pathway (thyroid hormone receptors [TR alpha and beta], transthyretin [TTR]), and the cholinergic system (neuronal nicotinic acetylcholine receptor alpha-7 [nAChR alpha-7]). Administration of T3 resulted in a significant up-regulation of the two TRs and a significant down-regulation of TTR. TTR was also down-regulated by the commercial penta-BDE mixture, DE-71. In contrast, neither DE-71, nor BDE-47, -99, or -100 altered the mRNA levels of the TRs or nAChR alpha-7. The in vitro approach was a relevant model system for assessing the effects of PBDEs on cytotoxicity and mRNA expression. Herring gull neuronal cells were responsive to both T3 and PBDEs although, receptors associated with two predicted mechanisms of PBDE action were not effective molecular biomarkers of exposure.

Current and Potential Rodent Screens and Tests for Thyroid Toxicants

This article reviews current rodent screens and tests to detect thyroid toxicants. Many points of disruption for thyroid toxicants are outlined and include: (a) changes in serum hormone level; (b) thyroperoxidase inhibitors; (c) the perchlorate discharge test; (d) inhibitors of iodide uptake; (e) effects on iodothyronine deiodinases; (f) effects on thyroid hormone action; and (g) role of binding proteins (e.g., rodent transthyretin). The major thyroid endpoints currently utilized in existing in vivo assay protocols of the Organization for Economic Cooperation and Development (OECD), Japanese researchers, and U.S. Environmental Protection Agency (EPA) include thyroid gland weight, histopathology, circulating thyroid hormone measurements, and circulating thyroid-stimulating hormone (TSH). These endpoints can be added into the existing in vivo assays for reproduction, development, and neurodevelopment that are outlined in this chapter. Strategic endpoints for possible addition to existing protocols to detect effects on developmental and adult thyroid endpoints are discussed. Many of these endpoints for detecting thyroid system disruption require development and additional research before they can be considered in existing assays. Examples of these endpoints under development include computer-assisted morphometry of the brain and evaluation of treatment-related changes in gene expression, thyrotropin-releasing hormone (TRH) and TSH challenge tests, and tests to evaluate thyroid hormone (TH)-dependent developmental events, especially in the rodent brain (e.g., measures of cerebellar and cortical proliferation, differentiation, migration, apoptosis, planimetric measures and gene expression, and oligodendrocyte differentiation). Finally, TH-responsive genes and proteins as well as enzyme activities are being explored. Existing in vitro tests are also reviewed, for example, thyroid hormone (TH) metabolism, receptor binding, and receptor activation assays, and their restrictions are described. The in vivo assays are currently the most appropriate for understanding the potential effects of a thyroid toxicant on the thyroid system. The benefits and potential limitations of the current in vivo assays are listed, and a discussion of the rodent thyroid system in the context of human health is touched upon. Finally, the importance of understanding the relationship between timing of exposure, duration of dose, and time of acquisition of the endpoints in interpreting the results of the in vivo assays is emphasized.

Overview of toxicological aspects of polybrominated diphenyl ethers: a flame-retardant additive in several consumer products

Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants due to their long half-life and widespread use as flame retardants in several consumer products, including plastics. In addition to other actions, these compounds are characterized as thyroid hormone disruptors. Thyroid hormones affect the function of nearly all tissues via their effects on cellular metabolism and the essential roles they play in differentiation and growth. Interference with thyroid hormone homeostasis by these environmental compounds, therefore, has the potential to impact development and every system in the body. Their presence in human breast milk is particularly troubling due to exposure of nursing children. The last trimester of pregnancy up to 2 years of age corresponds to a time of rapid neurodevelopment and represents a period of vulnerability to environmental insults. Rodent studies indicate that PBDEs may act as developmental neurotoxicants and effects on the reproductive system have been reported as well. Concerns exist regarding possible impacts of exposure, in particular ones which occur during development, on human health. This paper is part of a series of articles regarding contaminants in plastic and provides an overview regarding PBDEs, a class of flame-retardant additives to plastic. PBDEs possess a similar structure to the polychlorinated biphenyls (PCBs) previously used as lubricants in electrical generators and transformers until production was prohibited approximately 25 years ago. Parallels between the two compounds will be briefly made and in particular, as more epidemiological studies on PCBs are available than on PBDEs, a few examples concerning thyroid homeostasis, cognitive function and sexually dimorphic behavior in humans will be mentioned.

Alternate and new brominated flame retardants detected in U.S. house dust

Due to the voluntary withdrawals and/or bans on the use of two polybrominated diphenyl ether (PBDE) commercial mixtures, an increasing number of alternate flame retardant chemicals are being introduced in commercial applications. To determine if these alternate BFRs are present in indoor environments, we analyzed dust samples collected from 19 homes in the greater Boston, MA area during 2006. Using pure and commercial standards we quantified the following brominated flame retardant chemicals using GC/ECNI-MS methods: hexabromocyclododecane (sigma HBCD), bis(2,4,6,-tribromphenoxy)ethane (BTBPE), decabromodiphenyl ethane (DBDPE), and the brominated components found in Firemaster 550 (FM 550): 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) and (2-ethylhexyl)tetrabromophthalate (TBPH), the latter compound being a brominated analogue of di(2-ethylhexyl)phthalate (DEHP). The concentrations of all compounds were log-normally distributed and the largest range in concentrations was observed for HBCD (sum of all isomers), with concentrations ranging from <4.5 ng/g to a maximum of 130,200 ng/g with a median value of 230 ng/g. BTBPE ranged from 1.6 to 789 ng/g with a median value of 30 ng/g and DBDPE ranged from <10.0 to 11,070 ng/g with a median value of 201 ng/g. Of the FM 550 components, TBB ranged from <6.6 to 15,030 ng/g with a median value of 133 ng/g; whereas TBPH ranged from 1.5 to 10,630 ng/g with a median value of 142 ng/g. Furthermore, the ratio of TBB/TBPH present in the dust samples ranged from 0.05 to 50 (average 4.4), varying considerably from the ratio observed in the FM 550 commercial mixture (4:1 by mass), suggesting different sources with different chemical compositions, and/or differential fate and transport within the home. Analysis of paired dust samples collected from different rooms in the same home suggests HBCD, TBB, and TBPH are higher in dust from the main living area compared to dust collected in bedrooms; however, BTBPE and DBDPE levels were comparable between rooms. This study highlights the fact that numerous types of brominated flame retardants are present in indoor environments, raising questions about exposure to mixtures of these contaminants.

Effects of hexabromocyclododecane and polybrominated diphenyl ethers on mRNA expression in chicken (Gallus domesticus) hepatocytes

Hexabromocyclododecane (HBCD) and polybrominated diphenyl ethers (PBDEs) are additive flame retardants used in a wide range of consumer products. Both compounds have been detected in free-living avian species, but toxicological and molecular end points of exposure are limited. An in vitro approach was used to compare concentration-dependent effects of HBCD and the commercial penta-brominated diphenyl ether mixture DE-71 on cytotoxicity and mRNA expression in cultured hepatocytes derived from embryonic chickens. Neither HBCD-alpha, HBCD-technical mixture (TM), nor DE-71 effected hepatocyte viability at the highest concentrations assessed (30-100 microM). Real-time RT-PCR assays were developed to quantify changes in mRNA abundance of genes associated with chicken xenobiotic-sensing orphan nuclear receptor activation, the thyroid hormone (TH) pathway, and lipid regulation. Exposure to >or= 1 microM HBCD-alpha and HBCD-TM resulted in significant upregulation of cytochrome P450 (CYP) 2H1 (fourfold to sevenfold) and CYP3A37 (5- to 30-fold) at 24 and 36 h. In contrast, 30 microM DE-71 caused a twofold increase of CYP2H1 only. UGT1A9 expression was only upregulated by HBCD-alpha to a maximum of fourfold at >or= 1 microM. Transthyretin, thyroid hormone-responsive spot 14-alpha, and liver fatty acid-binding protein were all significantly downregulated (up to sevenfold) for cells exposed to >or= 1 microM HBCD-alpha and HBCD-TM. DE-71 also downregulated these three target genes twofold to fivefold at concentrations >or= 3 microM. Taken together, our results indicate that xenobiotic-metabolizing enzymes and genes associated with the TH pathway and lipid regulation are vulnerable to HBCD and DE-71 administration in cultured avian hepatocytes and might be useful molecular markers of exposure.

Characterization of liver toxicity in F344/N rats and B6C3F1 mice after exposure to a flame retardant containing lower molecular weight polybrominated diphenyl ethers

Lower molecular weight polybrominated diphenyl ethers (PBDEs), components of flame retardants, are found in the environment and in human and animal tissues. Toxicity studies were conducted in F344/N rats and B6C3F1 mice by administering a flame retardant containing these lower molecular weight PBDEs (BDE-47, BDE-99, BDE-100, and BDE153) by oral gavage 5 days/week for 13 weeks at doses of 0.01, 5, 50, 100 or 500mg/kg/day. Liver was the primary target organ in rats and mice. Treatment-related increases in liver weights, liver cytochrome P450 (1A1, 1A2, 2B) and UDPGT (rats only) levels, and liver lesions were seen in both rats and mice. Hepatocyte hypertrophy and vacuolization increased in incidence and severity with treatment, and occurred at levels of 50mg/kg and above in rats, and at 100mg/kg and above in mice. Liver Cyp 1A1, 1A2, and 2B levels were increased at exposure levels of 50mg/kg and above in rats and mice. In addition, treatment-related thyroid lesions occurred particularly in rats. The most sensitive parameter for PBDE toxicity was the increase in liver weights which occurred at 5mg/kg above in rats and 50mg/kg and above in mice. These results suggest that liver may be a target organ for carcinogenesis processes after long-term administration of PBDEs. A chronic PBDE study is currently being conducted by the National Toxicology Program.

A technical mixture of 2,2',4,4'-tetrabromo diphenyl ether (BDE47) and brominated furans triggers aryl hydrocarbon receptor (AhR) mediated gene expression and toxicity

Polybrominated diphenyl ethers (PBDE) are found as ubiquitous contaminants in the environment, e.g., in sediments and biota as well as in human blood samples and mother's milk. PBDEs are neuro- and developmental toxins, disturb the endocrine system and some are even carcinogenic. Structural similarities of PBDEs with dioxin-like compounds, e.g., 2,3,7,8-tetrachloro-dibenzodioxin (TCDD), have raised concern about a possible "dioxin-like" action of PBDEs. TCDD exerts its toxicity via binding to and activation of the aryl hydrocarbon receptor (AhR). AhR ligands are in contrast to PBDEs usually coplanar compounds. Thus, PBDEs are not likely to be strong AhR agonists. The aim of this study was to analyze the effects of the most abundant PBDE congener, 2,2',4,4'-tetrabromo diphenyl ether (BDE47), on AhR activity and signaling. Initially, we measured cytochrome P450 1A1 (Cyp1A1) induction as a readout for AhR activation by BDE47. Low grade purified BDE47 increased CYP1A1 levels in transformed and primary rat hepatocytes and human hepatoma cells. Chemical analysis of the BDE47 sample identified trace contaminations with brominated furans such as 2,3,7,8-tetrabromo dibenzodioxin (TBDF), which most likely were responsible for the observed activation of AhR. Subsequently, the BDE47 mixture was studied for its effect on AhR mediated toxicity and global gene expression. Indeed, in rat hepatoma cells and in zebrafish embryos the BDE47 mixture provoked changes in gene expression and toxicity similar to known AhR agonists. In addition to the dioxin-like actions, the BDE47 sample enhanced Cyp2B and Cyp3A expression suggesting that commercial PBDE mixtures, which also often contain brominated furans, may disturb cellular homeostasis at multiple levels.