The dose- and time-dependent effects of perfluorooctanoic acid on rat liver
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ABSTRACT: We reported the hepatic gene expression profiling in male Sprague-Dawley rats treated by different concentrations of perfluorooctanoic acid (PFOA) for 7, 14, and 28 days. We confirmed that PFOA induced liver tumor formation was mainly through the activation of peroxisome proliferator-activated receptor α (PPARα). We identified a panel of 7 genes (Cyp4a1, Nr1d1, Acot2, Vnn, Ehhadh, and Acot1) that might serve as the biomarkers for PPARα activation. We also meausred the apical endpoints of PPARα activation and found a good correlation with the expression level of these biomarker genes. Consitituitive androstane receptor mediated Cyp2b enzymatic activity and gene expression was also upregulated by PFOA in a dose-response manner. On the other hand, acyl hydrocarbon receptor (AhR) target gene Cyp1a2 were significantly downregulated at all time points studied. To our surprise, results of KEGG and Reactome pathway analyses suggested that PFOA did not drive the cell cycles and proliferations in the liver. While some of the DNA replication genes such as Pold2 and Mcm8 were upregulated by PFOA treatment, several key cyclin-dependent cell growth genes, including Ccnd1, Ccne2, Ccnb1, and Ccna2 were all significantly downregulated by PFOA in a dose-dependent manner, especailly at 28 days. Ingenuity Pathway Analysis also indicated that PFOA led to a suppression of liver cancer related pathways at later time points studied. These results suggest that while PFOA clearly induced PPARα activation, the increased cell growth (the second key event in the tumor mode of action), was transient and tightly regulated by feedback mechanisms. Whether such changes will eventually cause the formation of preneoplastic foci and liver tumors in rats remains unclear.
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:Exposure to PFOA during gestation altered the expression of genes related to fatty acid catabolism in both the fetal liver and lung. In the fetal liver, the effects of PFOA were robust and also included genes associated with lipid transport, ketogenesis, glucose metabolism, lipoprotein metabolism, cholesterol biosynthesis, steroid metabolism, bile acid biosynthesis, phospholipid metabolism, retinol metabolism, proteosome activation, and inflammation. These changes are consistent with activation of PPAR alpha. Non-PPAR alpha related changes were suggested as well. Keywords: gene expression, microarray,PFOA, mouse, fetus, liver
Project description:Perfluoroalkyl substances (PFAS) are man-made chemicals with suspected endocrine-disrupting properties. Exposure to perfluorooctanoic acid (PFOA) has been linked to disturbed metabolism via the liver, although the exact mechanism is not clear. Moreover, information on the metabolic effects of the new PFAS alternative GenX is limited. We tested whether low-dose exposure to PFOA and GenX induces metabolic disturbances, including NAFLD, dyslipidemia, and glucose tolerance in mice and studied the involvement of PPARα. To this end, male C57BL/6J wildtype and PPARα−/− mice were given 0.05 or 0.3 mg/kg bw/day PFOA, or 0.3 mg/kg bw/day GenX next to a high-fat diet for 20 weeks. RNA sequencing was performed on liver, next to thorough assesment of metabolic parameters. RNA sequencing revealed that whereas the effects of GenX are entirely dependent on PPARα, effects of PFOA are mostly dependent on PPARα. In the absence of PPARα, the involvement of PXR/CAR becomes more prominent. Exposure to high-dose PFOA in mice decreased body weights and increased liver weights in wildtype and PPARα−/− mice. High-dose but not low-dose PFOA reduced plasma triglycerides and cholesterol, which for triglycerides, showed PPARα dependency. PFOA and GenX increased hepatic triglycerides in a PPARα-dependent manner. Overall, we show that long-term and low-dose exposure to PFOA and GenX disrupts lipid metabolism in mice. Whereas the effects of PFOA are mediated by multiple nuclear receptors, effects of GenX are entirely mediated by PPARα. Our data underscore the potential of PFAS to disrupt metabolism by altering signaling pathways in the liver.
Project description:Exposure to PFOA during gestation altered the expression of genes related to fatty acid catabolism in both the fetal liver and lung. In the fetal liver, the effects of PFOA were robust and also included genes associated with lipid transport, ketogenesis, glucose metabolism, lipoprotein metabolism, cholesterol biosynthesis, steroid metabolism, bile acid biosynthesis, phospholipid metabolism, retinol metabolism, proteosome activation, and inflammation. These changes are consistent with activation of PPAR alpha. Non-PPAR alpha related changes were suggested as well. Experiment Overall Design: Experiment 1: High Dose: Thirty timed-pregnant CD-1 mice were orally dosed from gestation day 1-17 with either 0, 5, or 10 mg/kg/day PFOA in water. At term, fetal lung and liver were collected, total RNA prepared, and samples pooled from three fetuses per litter. Five biological replicates consisting of individual litter samples were then evaluated for treatment group using Affymetrix mouse 430_2 microarrays. Experiment Overall Design: Experiment 2: Low Dose: Thirty timed-pregnant CD-1 mice were orally dosed from gestation day 1-17 with either 0, 1, or 3 mg/kg/day PFOA in water. At term, fetal lung and liver were collected, total RNA prepared, and samples pooled from three fetuses per litter. Five biological replicates consisting of individual litter samples were then evaluated for treatment group using Affymetrix mouse 430_2 microarrays (note one microarray from the lung + 1mg/kg/day dose group was excluded from the study due to high background). Experiment Overall Design: Please note that each dose experiment had separate concurrent controls.
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.
Project description:Perfluorooctanoic acid (PFOA) is one of the most used perfluorinated compounds in numerous applications and can be detected in environmental samples from around the globe. The aquatic environment is an important site for PFOA deposit. Nevertheless, the exact mode of action and its resulting toxicological effects on aquatic organisms remain largely unknown. To gain a more extensive understanding of the mode of action of teleost PFOA toxicity, transcriptomics, proteomics, biochemical parameters and reproduction were integrated in the present study. Male and female zebrafish were exposed to nominal concentrations of 0.1; 0.5 and 1 mg/l PFOA for 4 and 28 days resulting in an accumulation which was higher in males compared to females. These gender-related differences were likely caused by different elimination rates due to distinct hormone levels and differences in transport activity by solute carriers. The general mode of action of PFOA was believed to be an increase of the mitochondrial membrane permeability which caused effects on the electron transport system at the biochemical level and resulted in alterations of the oxidative phosphorylation, oxidative stress and apoptosis at the gene transcript and protein level. As a consequence, evidence for the replacement of the affected cells and organelles to sustain tissue homeostasis was found at the molecular level. The higher energy demand, due to these adverse effects, was provided by lowering the glycogen stores. Despite this increase in metabolic expenditure, no effects on reproduction were found indicating that the fish seemed to cope with exposure to the tested concentrations of PFOA. Adult zebrafish (Danio rerio) were exposed to nominal concentrations of 0mg/l; 0.1mg/l; 1mg/l PFOA (perfluorooctanoic acid) for 28 days. Three different 25 litre aquaria per exposure concentration were used resulting in 3 biological replicates with each aquarium containing 8 male and 8 female zebrafish. The livers of 6 male fish and 6 female fish were pooled separately and snap frozen in liquid nitrogen. A reference sample was made by pooling equal amounts of RNA from all samples. A carriage wheel design was used in which all samples were connected to the reference sample and the main contrasts of interest were made directly on the same microarrays as frequently as possible. This design resulted in technical triplicates of each sample.
Project description:Perfluorooctanoic acid (PFOA) is one of the most used perfluorinated compounds in numerous applications and can be detected in environmental samples from around the globe. The aquatic environment is an important site for PFOA deposit. Nevertheless, the exact mode of action and its resulting toxicological effects on aquatic organisms remain largely unknown. To gain a more extensive understanding of the mode of action of teleost PFOA toxicity, transcriptomics, proteomics, biochemical parameters and reproduction were integrated in the present study. Male and female zebrafish were exposed to nominal concentrations of 0.1; 0.5 and 1 mg/l PFOA for 4 and 28 days resulting in an accumulation which was higher in males compared to females. These gender-related differences were likely caused by different elimination rates due to distinct hormone levels and differences in transport activity by solute carriers. The general mode of action of PFOA was believed to be an increase of the mitochondrial membrane permeability which caused effects on the electron transport system at the biochemical level and resulted in alterations of the oxidative phosphorylation, oxidative stress and apoptosis at the gene transcript and protein level. As a consequence, evidence for the replacement of the affected cells and organelles to sustain tissue homeostasis was found at the molecular level. The higher energy demand, due to these adverse effects, was provided by lowering the glycogen stores. Despite this increase in metabolic expenditure, no effects on reproduction were found indicating that the fish seemed to cope with exposure to the tested concentrations of PFOA.
Project description:In this study, we measured liver miRNA in male B6C3F1 mice exposed to a known chemical activator of the peroxisome proliferator-activated receptor alpha (PPARα) pathway, di(2-ethylhexyl) phthalate (DEHP), for 7 and 28 days at concentrations of 0, 750, 1500, 3000, or 6000 ppm in feed. At the highest dose tested, DEHP altered 61 miRNAs after 7 days and 171 miRNAs after 28 days of exposure, with 48 overlapping miRNAs between timepoints. Analysis of these 48 common miRNAs indicated enrichment in PPARα targets and other pathways related to liver injury and cancer. Four of the 10 miRNAs exhibiting a clear dose trend were linked to PPARα activation: mmu-miRs-125a-5p, -182-5p, -20a-5p, and -378a-3p.
Project description:Unlike the PPARalpha agonist W14,643, PFOA is capable of inducing effects independently of PPARa. Genes altered in the PPARalpha-null mouse following exposure to PFOA included those associated with fatty acid metabolism, inflammation, xenobiotic metabolism, and cell cycle progression. The specific signaling pathway(s) responsible for these effects is not readily apparent but it is conceivable that other members of the nuclear receptor superfamily such as PPARbeta/delta and CAR may be involved. Keywords: dose response Wild-type and PPARa-null mice were orally dosed for 7 days with either PFOA (1 or 3 mg/kg), the PPARalpha agonist WY-14,643 (50 mg/kg), or compound vehicle. Gene profiling analysis was conducted on 4 animals per group using Applied Biosystems Mouse Genome Survey Microarrays.
Project description:Unlike the PPARalpha agonist W14,643, PFOA is capable of inducing effects independently of PPARa. Genes altered in the PPARalpha-null mouse following exposure to PFOA included those associated with fatty acid metabolism, inflammation, xenobiotic metabolism, and cell cycle progression. The specific signaling pathway(s) responsible for these effects is not readily apparent but it is conceivable that other members of the nuclear receptor superfamily such as PPARbeta/delta and CAR may be involved. Keywords: dose response