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Xenobiotic-responsive Nuclear Receptors in Transcriptional Effects Upon Perfluoroalkyl Acid Exposure in Diverse Species

ABSTRACT: Humans and ecological species have been found to have detectable body burdens of a number of perfluorinated alkyl acids (PFAA) including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). In mouse and rat liver these compounds elicit transcriptional and phenotypic effects similar to peroxisome proliferator chemicals (PPC) that work through the nuclear receptor peroxisome proliferator activated receptor alpha (PPARalpha). Recent studies indicate that along with PPARalpha other nuclear receptors are required for transcriptional changes in the mouse liver after PFOA exposure including the constitutive activated receptor (CAR) and pregnane X receptor (PXR) that regulate xenobiotic metabolizing enzymes (XME). To determine the potential role of CAR/PXR in mediating effects of PFAAs in rat liver, we performed a meta-analysis of transcript profiles from published studies in which rats were exposed to PFOA or PFOS. We compared the profiles to those produced by exposure to prototypical activators of CAR (Phenobarbital (PB)), PXR (pregnenolone 16 alpha-carbonitrile (PCN)), or PPARalpha (WY-14,643 (WY)). As expected, PFOA and PFOS elicited transcript profile signatures that included many known PPARalpha target genes. Numerous XME genes were also altered by PFOA and PFOS but not WY. These genes exhibited expression changes shared with PB or PCN. Reexamination of the transcript profiles from the livers of chicken or fish exposed to PFAAs indicated that PPARalpha, CAR, and PXR orthologs were not activated. Our results indicate that PFAAs under these experimental conditions activate PPARalpha, CAR, and PXR in rats but not chicken and fish. Lastly, we discuss evidence that human populations with greater CAR expression have lower body burdens of PFAAs. Keywords: gene expression/microarray

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE14712 | GEO | 2009/02/07

SECONDARY ACCESSION(S): PRJNA112101

REPOSITORIES: GEO

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Project description:Perfluorooctane sulfonate (PFOS) is a perfluoroalkyl acid (PFAA) and a persistent environmental contaminant found in the tissues of humans and wildlife. Although blood levels of PFOS have begun to decline, health concerns remain because of the long half-life of PFOS in humans. Like other PFAAs, such as perfluorooctanoic acid (PFOA), PFOS is an activator of peroxisome proliferator-activated receptor-alpha (PPARα) and exhibits hepatocarcinogenic potential in rodents. PFOS is also a developmental toxicant in rodents where, unlike PFOA, it’s mode of action is independent of PPARα. Wild-type (WT) and PPARα-null (Null) mice were dosed with 0, 3, or 10 mg/kg/day PFOS for 7 days. Animals were euthanized, livers weighed, and liver samples collected for histology and preparation of total RNA. Gene profiling was conducted using Affymetrix 430_2 microarrays. In WT mice, PFOS induced changes that were characteristic of PPARα transactivation including regulation of genes associated with lipid metabolism, peroxisome biogenesis, proteasome activation, and inflammation. PPARα-independent changes were indicated in both WT and Null mice by altered expression of genes related to lipid metabolism, inflammation, and xenobiotic metabolism. Such results are similar to prior studies done with PFOA and are consistent with modest activation of the constitutive androstane receptor (CAR) and possibly PPARγ and/or PPARβ/δ. Unique treatment-related effects were also found in Null mice including altered expression of genes associated with ribosome biogenesis, oxidative phosphorylation and cholesterol biosynthesis. Of interest was up-regulation of Cyp7a1, a gene which is under the control of various transcription regulators. Hence, in addition to its ability to modestly activate PPARα, PFOS induces a variety of “off-target” effects as well. PPARalpha-null and wild-type male mice at 6-9 months of age were dosed by gavage for 7 consecutive days with either 0, 3, or 10 mg/kg PFOS (potassium salt) in 0.5% Tween 20. Five biological replicates consisting of individual animals were included in each dosage group. Data were compared to results previously published by our group for PFOA and Wy-14,643, a commonly used agonist of PPARalpha (Rosen et al., Toxicol Pathol. 36:592-607, 2008; GSE9796)

Project description:Background: Previously, we reported that perfluorooctanoic acid (PFOA) promotes liver cancer in manner similar to that of 17β-estradiol (E2) in rainbow trout. Also, other perfluoroalkyl acids (PFAAs) are weakly estrogenic in trout and bind the trout liver estrogen receptor (ER). Objectives: The primary objective of this study was to determine whether multiple PFAAs enhance hepatic tumorigenesis in trout, an animal model that represents human insensitivity to peroxisome proliferators. Methods: A two-stage chemical carcinogenesis model was employed in trout to evaluate PFOA, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluorooctane sulfonate (PFOS) and 8:2 fluorotelomer alcohol (8:2FtOH) as complete carcinogens or promoters of aflatoxin B1 (AFB1)- and/or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced liver cancer. A custom trout DNA microarray was used to assess hepatic transcriptional response to these dietary treatments in comparison to E2 and the classic peroxisome proliferator clofibrate (CLOF). Results: Incidence, multiplicity and size of liver tumors in trout fed diets containing E2, PFOA, PFNA and PFDA were significantly higher compared to AFB1-initiated animals fed control diet, whereas PFOS caused a minor increase in liver tumor incidence. E2 and PFOA also enhanced MNNG-initiated hepatocarcinogenesis. Pearson correlation analyses, unsupervised hierarchical clustering and principal components analyses showed that the hepatic gene expression profiles for E2 and PFOA, PFNA, PFDA and PFOS were overall highly similar, though distinct patterns of gene expression were evident for each treatment, particularly for PFNA. Conclusions: Overall, these data suggest that multiple PFAAs can promote liver cancer and that the mechanism of promotion may be similar to that for E2. A total of 40 samples were analyzed using a a dye-swap, reference sample hybridization protocol. Rainbow trout were exposed to the following experimental treatments via the diet for two weeks (number in parenthesis is assigned group #): (1) Control; (2) 5 mg/kg diet estradiol (E2); (3) 2000 mg/kg diet perfluorooctanoic acid (PFOA); (4) 2000 mg/kg diet perfluorononanoic acid (PFNA); (5) 2000 mg/kg diet perfluorodecanoic acid (PFDA); (6) 200 mg/kg diet perfluorooctane sulfonate; (7) 2000 mg/kg 8:2 fluorotelomer alcohol (FTOH); and (8) 2000 mg/kg diet clofibrate. A total of 40 total hepatic mRNA samples were analyzed using a dye-swap, reference sample hybridization protocol. A reference RNA pool was made by combining equal amounts of RNA from all control RNA samples, with one exception. A separate time-matched reference pool was utilized for group 6 samples (PFOS treatment). Five hybridizations were performed for each treatment group in the following pattern: Replicate A Cy5/Reference Cy3; Replicate A Cy3/Reference Cy 5; Replicate B Cy5/Reference Cy3; Replicate B Cy3/Reference Cy5; Replicate C Cy5/Reference Cy3. Thus, the experiment consisted of three biological replicates, for two of which were replicated technically.

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Xenobiotic-responsive Nuclear Receptors in Transcriptional Effects Upon Perfluoroalkyl Acid Exposure in Diverse Species

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