Ammonium perchlorate: serum dosimetry, neurotoxicity, and resilience of the neonatal rat thyroid system.

The environmental contaminant perchlorate impairs the synthesis of thyroid hormones by reducing iodine uptake into the thyroid gland. Despite this known action, moderate doses of perchlorate do not significantly alter serum thyroid hormone in rat pups born to exposed dams. We examined perchlorate dosimetry and responsivity of the thyroid gland and brain in offspring following maternal exposure to perchlorate. Pregnant rat dams were delivered perchlorate in drinking water (0, 30, 100, 300, 1000 ppm) from gestational day 6 to postnatal day (PN) 21. Perchlorate was present in the placenta, milk, and serum, the latter declining in pups over the course of lactation. Serum and brain thyroid hormone were reduced in pups at birth but recovered to control levels by PN2. Dramatic upregulation of Nis was observed in the thyroid gland of the exposed pup. Despite the return of serum thyroid hormone to control levels by PN2, expression of several TH-responsive genes was altered in the PN14 pup brain. Contextual fear learning was unimpaired in the adults, supporting previous reports. Declining levels of serum perchlorate and a profound upregulation of Nis gene expression in the thyroid gland are consistent with the rapid return to the euthyroid state in the neonate. However, despite this recovery, thyroid hormone insufficiencies in serum and brain beginning in utero and present at birth appear sufficient to alter TH action in the fetus and subsequent trajectory of brain development. Biomarkers of that altered trajectory remain in the brain of the neonate, demonstrating that perchlorate is not devoid of effects on the developing brain.

An improved multicellular human organoid model for the study of chemical effects on palatal fusion.

BACKGROUND: Tissue fusion is a mechanism involved in the development of the heart, iris, genital tubercle, neural tube, and palate during embryogenesis. Failed fusion of the palatal shelves could result in cleft palate (CP), a common birth defect. Organotypic models constructed of human cells offer an opportunity to investigate developmental processes in the human. Previously, our laboratory developed an organoid model of the human palate that contains human mesenchyme and epithelial progenitor cells to study the effects of chemicals on fusion. METHODS: Here, we developed an organoid model more representative of the embryonic palate that includes three cell types: mesenchyme, endothelial, and epithelial cells. We measured fusion by a decrease in epithelial cells at the contact point between the organoids and compared the effects of CP teratogens on fusion and toxicity in the previous and current organoid models. We further tested additional suspect teratogens in our new model. RESULTS: We found that the three-cell-type model is more sensitive to fusion inhibition by valproic acid and inhibitors of FGF, BMP, and TGFßRI/II. In this new model, we tested other suspect CP teratogens and found that nocodazole, topiramate, and Y27632 inhibit fusion at concentrations that do not induce toxicity. CONCLUSION: This sensitive human three-cell-type organotypic model accurately evaluates chemicals for cleft palate teratogenicity.

Gestational Exposure to Perchlorate in the Rat: Thyroid Hormones in Fetal Thyroid Gland, Serum, and Brain.

Iodine is essential for the production of thyroid hormones. Perchlorate is an environmental contaminant that interferes with iodine uptake into the thyroid gland to reduce thyroid hormone synthesis. As thyroid hormones are critical for brain development, exposure to perchlorate during pregnancy is of concern for the developing fetal brain. In this study, we (1) define profiles of thyroid hormone in the maternal and fetal compartments of pregnant rats in response to inhibition of the sodium-iodide symporter (NIS) by perchlorate and (2) expand inquiry previously limited to serum to include fetal thyroid gland and brain. Perchlorate was added to the drinking water (0, 1, 30, 300, and 1000 ppm) of pregnant rat dams from gestational days (GD) 6-20. On GD20, blood, thyroid gland, and brain were collected from the fetus and dam for thyroid hormone and molecular analyses. Thyroid gland and serum thyroid hormones were dose-dependently reduced, with steeper declines evident in the fetus than in the dam. The thyroid gland revealed perturbations of thyroid hormone-action with greater sensitivity in the fetus than the dam. Thyroid hormones and thyroid hormone-responsive gene expression were reduced in the fetal cortex portending effects on brain development. These findings are the first quantitative assessments of perchlorate-induced deficits in the fetal thyroid gland and fetal brain. We provide a conceptual framework to develop a quantitative NIS adverse outcome pathway for serum thyroid hormone deficits and the potential to impact the fetal brain. Such a framework may also serve to facilitate the translation of in vitro bioactivity to the downstream in vivo consequences of NIS inhibition in the developing fetus.

Thyroid Disruptors: Extrathyroidal Sites of Chemical Action and Neurodevelopmental Outcome-An Examination Using Triclosan and Perfluorohexane Sulfonate.

Many xenobiotics are identified as potential thyroid disruptors due to their action to reduce circulating levels of thyroid hormone, most notably thyroxine (T4). Developmental neurotoxicity is a primary concern for thyroid disrupting chemicals yet correlating the impact of chemically induced changes in serum T4 to perturbed brain development remains elusive. A number of thyroid-specific neurodevelopmental assays have been proposed, based largely on the model thyroid hormone synthesis inhibitor propylthiouracil (PTU). This study examined whether thyroid disrupting chemicals acting distinct from synthesis inhibition would result in the same alterations in brain as expected with PTU. The perfluoroalkyl substance perfluorohexane sulfonate (50 mg/kg/day) and the antimicrobial Triclosan (300 mg/kg/day) were administered to pregnant rats from gestational day 6 to postnatal day (PN) 21, and a number of PTU-defined assays for neurotoxicity evaluated. Both chemicals reduced serum T4 but did not increase thyroid stimulating hormone. Both chemicals increased expression of hepatic metabolism genes, while thyroid hormone-responsive genes in the liver, thyroid gland, and brain were largely unchanged. Brain tissue T4 was reduced in newborns, but despite persistent T4 reductions in serum, had recovered in the PN6 pup brain. Neither treatment resulted in a low dose PTU-like phenotype in either brain morphology or neurobehavior, raising questions for the interpretation of serum biomarkers in regulatory toxicology. They further suggest that reliance on serum hormones as prescriptive of specific neurodevelopmental outcomes may be too simplistic and to understand thyroid-mediated neurotoxicity we must expand our thinking beyond that which follows thyroid hormone synthesis inhibition.

Evaluating thyroid hormone disruption: investigations of long-term neurodevelopmental effects in rats after perinatal exposure to perfluorohexane sulfonate (PFHxS).

Thyroid hormones are critical for mammalian brain development. Thus, chemicals that can affect thyroid hormone signaling during pregnancy are of great concern. Perfluorohexane sulfonate (PFHxS) is a widespread environmental contaminant found in human serum, breastmilk, and other tissues, capable of lowering serum thyroxine (T4) in rats. Here, we investigated its effects on the thyroid system and neurodevelopment following maternal exposure from early gestation through lactation (0.05, 5 or 25 mg/kg/day PFHxS), alone or in combination with a mixture of 12 environmentally relevant endocrine disrupting compounds (EDmix). PFHxS lowered thyroid hormone levels in both dams and offspring in a dose-dependent manner, but did not change TSH levels, weight, histology, or expression of marker genes of the thyroid gland. No evidence of thyroid hormone-mediated neurobehavioral disruption in offspring was observed. Since human brain development appear very sensitive to low T4 levels, we maintain that PFHxS is of potential concern to human health. It is our view that current rodent models are not sufficiently sensitive to detect adverse neurodevelopmental effects of maternal and perinatal hypothyroxinemia and that we need to develop more sensitive brain-based markers or measurable metrics of thyroid hormone-dependent perturbations in brain development.

A Three-Dimensional Organoid Culture Model to Assess the Influence of Chemicals on Morphogenetic Fusion.

Embryologic development involves cell differentiation and organization events that are unique to each tissue and organ and are susceptible to developmental toxicants. Animal models are the gold standard for identifying putative teratogens, but the limited throughput of developmental toxicological studies in animals coupled with the limited concordance between animal and human teratogenicity motivates a different approach. In vitro organoid models can mimic the three-dimensional (3D) morphogenesis of developing tissues and can thus be useful tools for studying developmental toxicology. Common themes during development like the involvement of epithelial-mesenchymal transition and tissue fusion present an opportunity to develop in vitro organoid models that capture key morphogenesis events that occur in the embryo. We previously described organoids composed of human stem and progenitor cells that recapitulated the cellular features of palate fusion, and here we further characterized the model by examining pharmacological inhibitors targeting known palatogenesis and epithelial morphogenesis pathways as well as 12 cleft palate teratogens identified from rodent models. Organoid survival was dependent on signaling through EGF, IGF, HGF, and FGF pathways, and organoid fusion was disrupted by inhibition of BMP signaling. We observed concordance between the effects of EGF, FGF, and BMP inhibitors on organoid fusion and epithelial cell migration in vitro, suggesting that organoid fusion is dependent on epithelial morphogenesis. Three of the 12 putative cleft palate teratogens studied here (theophylline, triamcinolone, and valproic acid) significantly disrupted in vitro organoid fusion, while tributyltin chloride and all-trans retinoic acid were cytotoxic to fusing organoids. The study herein demonstrates the utility of the in vitro fusion assay for identifying chemicals that disrupt human organoid morphogenesis in a scalable format amenable to toxicology screening.

Nicotine preloading for smoking cessation: the Preloading RCT.

BACKGROUND: Nicotine preloading means using nicotine replacement therapy prior to a quit date while smoking normally. The aim is to reduce the drive to smoke, thereby reducing cravings for smoking after quit day, which are the main cause of early relapse. A prior systematic review showed inconclusive and heterogeneous evidence that preloading was effective and little evidence of the mechanism of action, with no cost-effectiveness data. OBJECTIVES: To assess (1) the effectiveness, safety and tolerability of nicotine preloading in a routine NHS setting relative to usual care, (2) the mechanisms of the action of preloading and (3) the cost-effectiveness of preloading. DESIGN: Open-label randomised controlled trial with examination of mediation and a cost-effectiveness analysis. SETTING: NHS smoking cessation clinics. PARTICIPANTS: People seeking help to stop smoking. INTERVENTIONS: Nicotine preloading comprised wearing a 21 mg/24 hour nicotine patch for 4 weeks prior to quit date. In addition, minimal behavioural support was provided to explain the intervention rationale and to support adherence. In the comparator group, participants received equivalent behavioural support. Randomisation was stratified by centre and concealed from investigators. MAIN OUTCOME MEASURES: The primary outcome was 6-month prolonged abstinence assessed using the Russell Standard. The secondary outcomes were 4-week and 12-month abstinence. Adverse events (AEs) were assessed from baseline to 1 week after quit day. In a planned analysis, we adjusted for the use of varenicline (Champix®; Pfizer Inc., New York, NY, USA) as post-cessation medication. Cost-effectiveness analysis took a health-service perspective. The within-trial analysis assessed health-service costs during the 13 months of trial enrolment relative to the previous 6 months comparing trial arms. The base case was based on multiple imputation for missing cost data. We modelled long-term health outcomes of smoking-related diseases using the European-study on Quantifying Utility of Investment in Protection from Tobacco (EQUIPT) model. RESULTS: In total, 1792 people were eligible and were enrolled in the study, with 893 randomised to the control group and 899 randomised to the intervention group. In the intervention group, 49 (5.5%) people discontinued preloading prematurely and most others used it daily. The primary outcome, biochemically validated 6-month abstinence, was achieved by 157 (17.5%) people in the intervention group and 129 (14.4%) people in the control group, a difference of 3.02 percentage points [95% confidence interval (CI) -0.37 to 6.41 percentage points; odds ratio (OR) 1.25, 95% CI 0.97 to 1.62; p = 0.081]. Adjusted for use of post-quit day varenicline, the OR was 1.34 (95% CI 1.03 to 1.73; p = 0.028). Secondary abstinence outcomes were similar. The OR for the occurrence of serious AEs was 1.12 (95% CI 0.42 to 3.03). Moderate-severity nausea occurred in an additional 4% of the preloading group compared with the control group. There was evidence that reduced urges to smoke and reduced smoke inhalation mediated the effect of preloading on abstinence. The incremental cost-effectiveness ratio at the 6-month follow-up for preloading relative to control was £710 (95% CI -£13,674 to £23,205), but preloading was dominant at 12 months and in the long term, with an 80% probability that it is cost saving. LIMITATIONS: The open-label design could partially account for the mediation results. Outcome assessment could not be blinded but was biochemically verified. CONCLUSIONS: Use of nicotine-patch preloading for 4 weeks prior to attempting to stop smoking can increase the proportion of people who stop successfully, but its benefit is undermined because it reduces the use of varenicline after preloading. If this latter effect could be overcome, then nicotine preloading appears to improve health and reduce health-service costs in the long term. Future work should determine how to ensure that people using nicotine preloading opt to use varenicline as cessation medication. TRIAL REGISTRATION: Current Controlled Trials ISRCTN33031001. FUNDING: This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 41. See the NIHR Journals Library website for further project information.

Thyroid Hormone Disruption in the Fetal and Neonatal Rat: Predictive Hormone Measures and Bioindicators of Hormone Action in the Developing Cortex.

Adverse neurodevelopmental consequences remain a primary concern when evaluating the effects of thyroid hormone (TH) disrupting chemicals. Though the developing brain is a known target of TH insufficiency, the relationship between THs in the serum and the central nervous system is not well characterized. To address this issue, dose response experiments were performed in pregnant rats using the goitrogen propylthiouracil (PTU) (dose range 0.1-10 ppm). THs were quantified in the serum and brain of offspring at gestational day 20 (GD20) and postnatal day 14 (PN14), two developmental stages included in OECD and EPA regulatory guideline/guidance studies. From the dose response data, the quantitative relationships between THs in the serum and brain were determined. Next, targeted gene expression analyses were performed in the fetal and neonatal cortex to test the hypothesis that TH action in the developing brain is linked to changes in TH concentrations within the tissue. Results show a significant reduction of T4/T3 in the serum and brain of the GD20 fetus in response to low doses of PTU; interestingly, very few genes were significantly different at any dose tested. In the PN14 pup significant reductions of T4/T3 in the serum and brain were also detected; however, twelve transcriptional targets were identified in the neonatal cortex that correlated well with reduced brain THs. These results show that serum T4 is a good predictor of brain THs, and offer several target genes that could serve as pragmatic readouts of T4/T3 dysfunction within the PN14 cortex.

Engineering human cell spheroids to model embryonic tissue fusion in vitro.

Epithelial-mesenchymal interactions drive embryonic fusion events during development, and perturbations of these interactions can result in birth defects. Cleft palate and neural tube defects can result from genetic defects or environmental exposures during development, yet very little is known about the effect of chemical exposures on fusion events during human development because of a lack of relevant and robust human in vitro assays of developmental fusion behavior. Given the etiology and prevalence of cleft palate and the relatively simple architecture and composition of the embryonic palate, we sought to develop a three-dimensional culture system that mimics the embryonic palate and could be used to study fusion behavior in vitro using human cells. We engineered size-controlled human Wharton's Jelly stromal cell (HWJSC) spheroids and established that 7 days of culture in osteogenesis differentiation medium was sufficient to promote an osteogenic phenotype consistent with embryonic palatal mesenchyme. HWJSC spheroids supported the attachment of human epidermal keratinocyte progenitor cells (HPEKp) on the outer spheroid surface likely through deposition of collagens I and IV, fibronectin, and laminin by mesenchymal spheroids. HWJSC spheroids coated in HPEKp cells exhibited fusion behavior in culture, as indicated by the removal of epithelial cells from the seams between spheroids, that was dependent on epidermal growth factor signaling and fibroblast growth factor signaling in agreement with palate fusion literature. The method described here may broadly apply to the generation of three-dimensional epithelial-mesenchymal co-cultures to study developmental fusion events in a format that is amenable to predictive toxicology applications.

Perfluoroalkyl acids-induced liver steatosis: Effects on genes controlling lipid homeostasis.

Persistent presence of perfluoroalkyl acids (PFAAs) in the environment is due to their extensive use in industrial and consumer products, and their slow decay. Biochemical tests in rodent demonstrated that these chemicals are potent modifiers of lipid metabolism and cause hepatocellular steatosis. However, the molecular mechanism of PFAAs interference with lipid metabolism remains to be elucidated. Currently, two major hypotheses are that PFAAs interfere with mitochondrial beta-oxidation of fatty acids and/or they affect the transcriptional activity of peroxisome proliferator-activated receptor α (PPARα) in liver. To determine the ability of structurally-diverse PFAAs to cause steatosis, as well as to understand the underlying molecular mechanisms, wild-type (WT) and PPARα-null mice were treated with perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), or perfluorohexane sulfonate (PFHxS), by oral gavage for 7days, and their effects were compared to that of PPARα agonist WY-14643 (WY), which does not cause steatosis. Increases in liver weight and cell size, and decreases in DNA content per mg of liver, were observed for all compounds in WT mice, and were also seen in PPARα-null mice for PFOA, PFNA, and PFHxS, but not for WY. In Oil Red O stained sections, WT liver showed increased lipid accumulation in all treatment groups, whereas in PPARα-null livers, accumulation was observed after PFNA and PFHxS treatment, adding to the burden of steatosis observed in control (untreated) PPARα-null mice. Liver triglyceride (TG) levels were elevated in WT mice by all PFAAs and in PPARα-null mice only by PFNA. In vitro ß-oxidation of palmitoyl carnitine by isolated rat liver mitochondria was not inhibited by any of the 7 PFAAs tested. Likewise, neither PFOA nor PFOS inhibited palmitate oxidation by HepG2/C3A human liver cell cultures. Microarray analysis of livers from PFAAs-treated mice indicated that the PFAAs induce the expression of the lipid catabolism genes, as well as those involved in fatty acid and triglyceride synthesis, in WT mice and, to a lesser extent, in PPARα-null mice. These results indicate that most of the PFAAs increase liver TG load and promote steatosis in mice We hypothesize that PFAAs increase steatosis because the balance of fatty acid accumulation/synthesis and oxidation is disrupted to favor accumulation.

The effects of perfluorinated chemicals on adipocyte differentiation in vitro.

The 3T3-L1 preadipocyte culture system has been used to examine numerous compounds that influence adipocyte differentiation or function. The perfluoroalkyl acids (PFAAs), used as surfactants in a variety of industrial applications, are of concern as environmental contaminants that are detected worldwide in human serum and animal tissues. This study was designed to evaluate the potential for PFAAs to affect adipocyte differentiation and lipid accumulation using mouse 3T3-L1 cells. Cells were treated with perfluorooctanoic acid (PFOA) (5-100 µM), perfluorononanoic acid (PFNA) (5-100 µM), perfluorooctane sulfonate (PFOS) (50-300 µM), perfluorohexane sulfonate (PFHxS) (40-250 µM), the peroxisome proliferator activated receptor (PPAR) PPARα agonist Wyeth-14,643 (WY-14,643), and the PPARγ agonist rosiglitazone. The PPARγ agonist was included as a positive control as this pathway is critical to adipocyte differentiation. The PPARα agonist was included as the PFAA compounds are known activators of this pathway. Cells were assessed morphometrically and biochemically for number, size, and lipid content. RNA was extracted for qPCR analysis of 13 genes selected for their importance in adipocyte differentiation and lipid metabolism. There was a significant concentration-related increase in cell number and decreased cell size after exposure to PFOA, PFHxS, PFOS, and PFNA. All four PFAA treatments produced a concentration-related decrease in the calculated average area occupied by lipid per cell. However, total triglyceride levels per well increased with a concentration-related trend for all compounds, likely due to the increased cell number. Expression of mRNA for the selected genes was affected by all exposures and the specific impacts depended on the particular compound and concentration. Acox1 and Gapdh were upregulated by all six compounds. The strongest overall effect was a nearly 10-fold induction of Scd1 by PFHxS. The sulfonated PFAAs produced numerous, strong changes in gene expression similar to the effects after treatment with the PPARγ agonist rosiglitazone. By comparison, the effects on gene expression were muted for the carboxylated PFAAs and for the PPARα agonist WY-14,643. In summary, all perfluorinated compounds increased cell number, decreased cell size, increased total triglyceride, and altered expression of genes associated with adipocyte differentiation and lipid metabolism.

Developmental toxicity of perfluorononanoic acid in mice.

Perfluorononanoic acid (PFNA) is a ubiquitous and persistent environmental contaminant. Although its levels in the environment and in humans are lower than those of perfluorooctane sulfonate (PFOS) or perfluorooctanoic acid (PFOA), a steady trend of increases in the general population in recent years has drawn considerable interest and concern. Previous studies with PFOS and PFOA have indicated developmental toxicity in laboratory rodent models. The current study extends the evaluation of these adverse outcomes to PFNA in mice. PFNA was given to timed-pregnant CD-1 mice by oral gavage daily on gestational day 1-17 at 1, 3, 5 or 10mg/kg; controls received water vehicle. Dams given 10mg/kg PFNA could not carry their pregnancy successfully and effects of this dose group were not followed. Similar to PFOS and PFOA, PFNA at 5mg/kg or lower doses produced hepatomegaly in the pregnant dams, but did not affect the number of implantations, fetal viability, or fetal weight. Mouse pups were born alive and postnatal survival in the 1 and 3mg/kg PFNA groups was not different from that in controls. In contrast, although most of the pups were also born alive in the 5mg/kg PFNA group, 80% of these neonates died in the first 10 days of life. The pattern of PFNA-induced neonatal death differed somewhat from those elicited by PFOS or PFOA. A majority of the PFNA-exposed pups survived a few days longer after birth than those exposed to PFOS or PFOA, which typically died within the first 2 days of postnatal life. Surviving neonates exposed to PFNA exhibited dose-dependent delays in eye opening and onset of puberty. In addition, increased liver weight seen in PFNA-exposed offspring persisted into adulthood and was likely related to the persistence of the chemical in the tissue. Evaluation of gene expression in fetal and neonatal livers revealed robust activation of peroxisome proliferator-activated receptor-alpha (PPARα) target genes by PFNA that resembled the responses of PFOA. Our results indicate that developmental toxicity of PFNA in mice is comparable to that of PFOS and PFOA, and that these adverse effects are likely common to perfluoroalkyl acids that persist in the body.

Comparative time course profiles of phthalate stereoisomers in mice.

More efficient models are needed to assess potential carcinogenicity hazard of environmental chemicals based on early events in tumorigenesis. Here, we investigated time course profiles for key events in an established cancer mode of action. Using a case study approach, we evaluated two reference phthalates, di(2-ethylhexyl) phthalate (DEHP) and its stereoisomer di-n-octyl phthalate (DNOP), across the span of a two-year carcinogenicity bioassay. Male B6C3F1 mice received diets with no phthalate added (control), DEHP at 0.12, 0.60, or 1.20%, or DNOP at 0.10, 0.50, or 1.00% (n = 80-83/group) for up to 104 weeks with six interim evaluations starting at week 4. Mean phthalate doses were 139, 845, and 3147 mg/kg/day for DEHP and 113, 755, and 1281 mg/kg/day for DNOP groups, respectively. Incidence and number of hepatocellular tumors (adenoma and/or carcinoma) were greater at ≥ 60 weeks for all DEHP groups with time and dose trends, whereas DNOP had no significant effects. Key events supported a peroxisome proliferator-activated receptor alpha (PPARα) mode of action for DEHP, with secondary cytotoxicity at the high dose, whereas DNOP induced modest increases in PPARα activity without proliferative or cytotoxic effects. Threshold estimates for later tumorigenic effects were identified at week 4 for relative liver weight (+24%) and PPARα activity (+79%) relative to the control group. Benchmark doses (BMDs) for these measures at week 4 clearly distinguished DEHP and DNOP and showed strong concordance with values at later time points and tumorigenic BMDs. Other target sites included testis and kidney, which showed degenerative changes at higher doses of DEHP but not DNOP. Our results highlight marked differences in the chronic toxicity profiles of structurally similar phthalates and demonstrate quantitative relationships between early bioindicators and later tumor outcomes.

Evaluation of perfluoroalkyl acid activity using primary mouse and human hepatocytes.

While perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) have been studied at length, less is known about the biological activity of other perfluoroalkyl acids (PFAAs) detected in the environment. Using a transient transfection assay developed in COS-1 cells, our group has previously evaluated a variety of PFAAs for activity associated with activation of peroxisome proliferator-activated receptor alpha (PPARα). Here we use primary heptatocytes to further assess the biological activity of a similar group of PFAAs using custom designed Taqman Low Density Arrays. Primary mouse and human hepatoyctes were cultured for 48h in the presence of varying concentrations of 12 different PFAAs or Wy14,643, a known activator of PPARα. Total RNA was collected and the expression of 48 mouse or human genes evaluated. Gene selection was based on either in-house liver microarray data (mouse) or published data using primary hepatocytes (human). Gene expression in primary mouse hepatocytes was more restricted than expected. Genes typically regulated in whole tissue by PPARα agonists were not altered in mouse cells including Acox1, Me1, Acaa1a, Hmgcs1, and Slc27a1. Cyp2b10, a gene regulated by the constitutive androstane receptor and a transcript normally up-regulated by in vivo exposure to PFAAs, was also unchanged in cultured mouse hepatocytes. Cyp4a14, Ehhadh, Pdk4, Cpt1b, and Fabp1 were regulated as expected in mouse cells. A larger group of genes were differentially expressed in human primary hepatocytes, however, little consistency was observed across compounds with respect to which genes produced a significant dose response making the determination of relative biological activity difficult. This likely reflects weaker activation of PPARα in human versus rodent cells as well as variation among individual cell donors. Unlike mouse cells, CYP2B6 was up-regulated in human hepatocytes by a number of PFAAs as was PPARδ. Rankings were conducted on the limited dataset. In mouse hepatocytes, the pattern was similar to that previously observed in the COS-1 reporter cell assay. With the exception of PFHxA, longer chain PFAA carboxylates were the most active. The pattern was similar in human hepatocytes, although PFDA and PFOS showed higher activity than previously observed while PFOA showed somewhat less activity. These data reflect inherent challenges in using primary hepatocytes to predict toxicological response.

Effects of perfluorooctanoic acid (PFOA) on expression of peroxisome proliferator-activated receptors (PPAR) and nuclear receptor-regulated genes in fetal and postnatal CD-1 mouse tissues.

PPARs regulate metabolism and can be activated by environmental contaminants such as perfluorooctanoic acid (PFOA). PFOA induces neonatal mortality, developmental delay, and growth deficits in mice. Studies in genetically altered mice showed that PPARα is required for PFOA-induced developmental toxicity. In this study, pregnant CD-1 mice were dosed orally from GD1 to 17 with water or 5mg PFOA/kg to examine PPARα, PPARß, and PPARγ expression and profile the effects of PFOA on PPAR-regulated genes. Prenatal and postnatal liver, heart, adrenal, kidney, intestine, stomach, lung, spleen, and thymus were collected at various developmental ages. RNA and protein were examined using qPCR and Western blot analysis. PPAR expression varied with age in all tissues, and in liver PPARα and PPARγ expression correlated with nutritional changes as the pups matured. As early as GD14, PFOA affected expression of genes involved in lipid and glucose homeostatic control. The metabolic disruption produced by PFOA may contribute to poor postnatal survival and persistent weight deficits of CD-1 mouse neonates.

Peroxisome proliferator-activated receptors alpha, Beta, and gamma mRNA and protein expression in human fetal tissues.

Peroxisome proliferator-activated receptors (PPARs) regulate lipid and glucose homeostasis, are targets of pharmaceuticals, and are also activated by environmental contaminants. Almost nothing is known about expression of PPARs during human fetal development. This study examines expression of PPARalpha, beta, and gamma mRNA and protein in human fetal tissues. With increasing fetal age, mRNA expression of PPARalpha and beta increased in liver, but PPARbeta decreased in heart and intestine, and PPARgamma decreased in adrenal. Adult and fetal mean expression of PPARalpha, beta, and gamma mRNA did not differ in intestine, but expression was lower in fetal stomach and heart. PPARalpha and beta mRNA in kidney and spleen, and PPARgamma mRNA in lung and adrenal were lower in fetal versus adult. PPARgamma in liver and PPARbeta mRNA in thymus were higher in fetal versus adult. PPARalpha protein increased with fetal age in intestine and decreased in lung, kidney, and adrenal. PPARbeta protein in adrenal and PPARgamma in kidney decreased with fetal age. This study provides new information on expression of PPAR subtypes during human development and will be important in evaluating the potential for the developing human to respond to PPAR environmental or pharmaceutical agonists.

Characterization of peroxisome proliferator-activated receptor alpha--independent effects of PPARalpha activators in the rodent liver: di-(2-ethylhexyl) phthalate also activates the constitutive-activated receptor.

Peroxisome proliferator chemicals (PPC) are thought to mediate their effects in rodents on hepatocyte growth and liver cancer through the nuclear receptor peroxisome proliferator-activated receptor (PPAR) alpha. Recent studies indicate that the plasticizer di-(2-ethylhexyl) phthalate (DEHP) increased the incidence of liver tumors in PPARalpha-null mice. We hypothesized that some PPC, including DEHP, induce transcriptional changes independent of PPARalpha but dependent on other nuclear receptors, including the constitutive-activated receptor (CAR) that mediates phenobarbital (PB) effects on hepatocyte growth and liver tumor induction. To determine the potential role of CAR in mediating effects of PPC, a meta-analysis was performed on transcript profiles from published studies in which rats and mice were exposed to PPC and compared the profiles to those produced by exposure to PB. Valproic acid, clofibrate, and DEHP in rat liver and DEHP in mouse liver induced genes, including Cyp2b family members that are known to be regulated by CAR. Examination of transcript changes by Affymetrix ST 1.0 arrays and reverse transcription-PCR in the livers of DEHP-treated wild-type, PPARalpha-null, and CAR-null mice demonstrated that (1) most (approximately 94%) of the transcriptional changes induced by DEHP were PPARalpha-dependent, (2) many PPARalpha-independent genes overlapped with those regulated by PB, (3) induction of genes Cyp2b10, Cyp3a11, and metallothionine-1 by DEHP was CAR dependent but PPARalpha-independent, and (4) induction of a number of genes (Cyp8b1, Gstm4, and Gstm7) was independent of both CAR and PPARalpha. Our results indicate that exposure to PPARalpha activators including DEHP leads to activation of multiple nuclear receptors in the rodent liver.

Gene expression profiling in the liver and lung of perfluorooctane sulfonate-exposed mouse fetuses: comparison to changes induced by exposure to perfluorooctanoic acid.

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmental contaminants found in the tissues of humans and wildlife. They are activators of peroxisome proliferator-activated receptor-alpha (PPAR alpha) and exhibit hepatocarcinogenic potential in rats. PFOS and PFOA are also developmental toxicants in rodents and PFOS has been shown to induce pulmonary deficits in rat offspring. Pregnant CD-1 mice were dosed with 0, 5, or 10mg/kg PFOS from gestation days 1-17. Transcript profiling was conducted on the fetal liver and lung. Results were contrasted to data derived from a previous PFOA study. PFOS-dependent changes were primarily related to activation of PPAR alpha. No remarkable differences were found between PFOS and PFOA. Given that PPAR alpha signaling is required for neonatal mortality in PFOA-treated mice but not those exposed to PFOS, the neonatal mortality observed for PFOS may reflect functional deficits related to the physical properties of the chemical rather than to transcript alterations.

Development of glucocorticoid receptor regulation in the rat forebrain: implications for adverse effects of glucocorticoids in preterm infants.

Glucocorticoids are the consensus treatment to avoid respiratory distress in preterm infants but there is accumulating evidence that these agents evoke long-term neurobehavioral deficits. Earlier, we showed that the developing rat forebrain is far more sensitive to glucocorticoid-induced disruption in the fetus than in the neonate. Feedback regulation of glucocorticoid receptors (GRs) is an essential homeostatic mechanism and we therefore examined the development of GR downregulation in the perinatal period. Pregnant rats or newborn pups were given dexamethasone daily (gestational days 17-19, postnatal days 1-3, or postnatal days 7-9), ranging from doses below that recommended for use in preterm infants (0.05 mg/kg) to therapeutic doses (0.2 or 0.8 mg/kg). Twenty-four hours after the last injection, we determined forebrain GR protein by Western blotting. Although postnatal dexamethasone treatment downregulated GRs at all doses, the fetal forebrain failed to show any decrement and instead exhibited slight GR upregulation. In controls, forebrain GR levels also showed a large increment over the course from late gestation through the second postnatal week, despite the fact that circulating glucocorticoid levels increase substantially during this period. Our results suggest that GR homeostasis develops primarily postnatally and that fetal inability to downregulate GRs in the face of exogenous glucocorticoid administration plays a role in the vulnerability of key neural circuits to developmental disruption. Since this developmental phase in the rat corresponds to the critical period in which glucocorticoids are used in preterm infants, adverse effects on brain development may be inescapable.