Effects of perfluorooctanoic acid--a potent peroxisome proliferator in rat--on Morris hepatoma 7800C1 cells, a rat cell line

Bioaccumulation and uptake routes of perfluoroalkyl acids in Daphnia magna

Perfluoroalkyl acids (PFAs), one kind of emerging contaminants, have attracted great attentions in recent years. However, the study about their bioaccumulation mechanism remains scarce. In this research, the bioaccumulation of six kinds of PFAs in water flea Daphnia magna was studied. The uptake rates of PFAs in D. magna ranged from 178 to 1338 L kg(-1) d(-1), and they increased with increasing perfluoroalkyl chain length; the elimination rates ranged from 0.98 to 2.82 d(-1). The bioaccumulation factors (BAFs) of PFAs ranged from 91 to 380 L kg(-1) in wet weight after 25 d exposure; they increased with increasing perfluoroalkyl chain length and had a significant positive correlation with the n-octanol/water partition coefficients (logK(ow)) of PFAs (p<0.05). This indicated that the hydrophobicity of PFAs plays an important role in their bioaccumulation. The BAFs almost kept constant when the PFA concentrations in aqueous phase increased from 1 to 10 μg L(-1). Scenedesmus subspicatus, as the food of D. magna, did not significantly affect the bioaccumulation of PFAs by D. magna. Furthermore, the body burden of PFAs in the dead D. magna was 1.08-2.52 times higher than that in the living ones, inferring that the body surface sorption is a main uptake route of PFAs in D. magna. This study suggested that the bioaccumulation of PFAs in D. magna is mainly controlled by their partition between organisms and water; further research should be conducted to study the intrinsic mechanisms, especially the roles of protein and lipid in organisms.

Prenatal exposures to perfluorinated chemicals and anthropometric measures in infancy

Perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) are persistent chemicals that may affect growth early in life. The authors estimated the associations between maternal plasma levels of PFOS and PFOA and infants' weight, length, and body mass index development during the first year of life. Fourteen hundred women were randomly selected from the Danish National Birth Cohort among those who provided blood samples early in pregnancy and gave birth to liveborn singletons between 1996 and 2002. Weight and length information at 5 and 12 months of age was available for 1,010 children. Multiple linear regression models were used for analyses, and maternal PFOS and PFOA concentrations (ng/mL) were inversely related to children's weight in the first year of life: adjusted regression coefficients: 0.8 g (95% confidence interval(CI): 4.2, 2.6) at 5 months and 5.8 g (95% CI:10.4, 1.2) at 12 months for perfluorooctanesulfonate(PFOS); 9.4 g (95% CI: 28.6, 9.9) at 5 months and 19.0 g (95% CI: 44.9, 6.8) at 12 months for perfluorooctanoate(PFOA) [corrected]. A similar pattern was observed for body mass index measurements, and no associations with length were found. After sex stratification, the inverse associations with weight and body mass index were more pronounced in boys, and no clear association was seen for girls.

Perfluorinated compounds in whole blood samples from infants, children, and adults in China

Two hundred and forty five human blood (whole blood) samples from Chinese donors aged from 0 to 90 yrs were analyzed for 10 perfluorinated compounds (PFCs). Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were the most abundant PFCs found in blood. The median concentration of PFOS was lower in nonadults (i.e., infants, toddlers, children, and adolescents) (2.52-5.55 ng/mL) than in adults (8.07 ng/mL). However, median concentration of PFOA in nonadults (1.23-2.42 ng/mL) was higher than that found in adults (1.01 ng/mL). A significant increase in PFOS (r = 0.468, p < 0.01) and perfluorohexane sulfonate (PFHxS) (r = 0.357, p < 0.01) concentrations with age was found, while PFOA concentrations (r = -0.344, p < 0.01) were negatively correlated with age. No significant gender-related differences in PFC concentrations were found across all ages. The composition profiles of PFCs, as identified by principal component analysis, varied for each age group; this suggested differences in sources and pathways of exposure to PFCs for different age groups. Based on the blood PFC concentration, we estimated the daily intake of PFOS by adults using a one-compartment toxicokinetic model. The modeled daily intake of PFOS agreed well with the calculated daily intake via diet and indoor dust (0.74 vs 1.19 ng/kg b.w. for males, 1.20 vs 1.15 ng/kg b.w. for females) suggesting that dietary intake and dust ingestion are the major exposure routes to PFOS exposure in China. This is the first comprehensive study on PFCs in human blood from infants, toddlers, children, and adolescents in China. The data are valuable for understanding the sources and pathways of human exposure to PFCs for different age groups.

A new class of perfluorinated acid contaminants: primary and secondary substituted perfluoroalkyl sulfonamides are acidic at environmentally and toxicologically relevant pH values

The SPARC software program was validated for nitrogen-hydrogen acidity constant estimation of primary and secondary sulfonamides against a broad suite of substituted derivatives with experimental datasets in water and dimethylsulfoxide solvent systems and across a wide pK(a) range. Following validation, amidic proton pK(a) values were estimated for all C(1) through C(8) congeners of five major perfluoroalkyl sulfonamide classes: unsubstituted sulfonamides, N-methyl and N-ethyl sulfonamides, sulfonamidoethanols, and sulfonamidoacetates. Branching of the perfluoroalkyl chain is expected to have substantial impacts on amide moiety acidity in these contaminant groups, with intrahomologue variability of up to four pK(a) units and increasing pK(a) values with both increasing chain branching and greater proximity of the chain branching to the sulfonamide head group. Perfluoroalkyl chain length is not predicted to have a substantial influence on sulfonamide acidity. The predicted pK(a) values and variability are anticipated to have substantial impacts on the environmental partitioning and degradation of these compounds, as well as the modes and magnitudes of toxicological effects. Substantial pH dependent isomeric fractionation of perfluoroalkyl sulfonamides is expected both in situ and in vivo, necessitating the incorporation of amide group acidities in multimedia environmental models and pharmacokinetic studies.

High-dose, short-term exposure of mice to perfluorooctanesulfonate (PFOS) or perfluorooctanoate (PFOA) affects the number of circulating neutrophils differently, but enhances the inflammatory responses of macrophages to lipopolysaccharide (LPS) in a similar fashion

Having found previously that high-dose, short-term dietary exposure of mice to perfluorooctanesulfonate (PFOS) or perfluorooctanoate (PFOA) suppresses adaptive immunity, in the present study we characterize the effects of these fluorochemicals on the innate immune system. Male C57BL/6 mice receiving 0.02% (w/w) PFOS or PFOA in their diet for 10 days exhibited a significant reduction in the numbers of total white blood cells (WBC), involving lymphopenia in both cases, but neutropenia only in response to treatment with PFOA. Moreover, both compounds also markedly reduced the number of macrophages (CD11b(+) cells) in the bone marrow, but not in the spleen or peritoneal cavity. The ex vivo production of tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6) by peritoneal macrophages isolated from animals treated with PFOA or PFOS was increased modestly. Moreover, both fluorochemicals markedly enhanced the ex vivo production of these same cytokines by peritoneal and bone marrow macrophages stimulated either in vitro or in vivo with lipopolysaccharide (LPS); whereas there was no such effect on splenic macrophages. The serum levels of these inflammatory cytokines observed in response to in vivo stimulation with LPS were elevated substantially by prior exposure to PFOA, but not by PFOS. None of these parameters of innate immunity were altered in animals receiving a dietary dose of these compounds that was 20-fold lower (0.001%, w/w). These findings reveal that in addition to suppressing adaptive immunity, high-dose, short-term exposure of mice to either PFOS or PFOA augments inflammatory responses to LPS, a potent activator of innate immunity.

Transcriptional effects of PFOS in isolated hepatocytes from Atlantic salmon Salmo salar L

The main aim of the current in vitro experiment was to search for makers for PFOS exposure in isolated hepatocytes from Atlantic salmon Salmo salar, based on genes responding to PFOS exposure in other animals. Primary cell cultures of hepatocytes were exposed to four concentrations of PFOS (2.1-6.2-15.1-25.0 mg/L) for 24 and 48 h and the transcriptional levels of 12 genes encoding proteins known to respond to PFOS were quantified with real-time RT-PCR. The 12 examined genes were caspase 3B (apoptosis), GSH-Px and HSP70 (cellular stress), CYP1A, CYP3A, GST and UGT (P450 and phase II enzymes), acyl-CoA oxidase, PPARalpha, PPARbeta and PPARgamma (lipid metabolism) and Na(+)-K(+)-ATPase (ion regulation). Most of the studied genes responded in a dose-dependent manner to PFOS exposure, although the transcriptional differences in general where small with regard to fold change. Our results clearly suggest that PFOS exposure enhanced cellular stress in the examined cells, even though the exact mechanisms behind this stress remain unknown. The results from this in vitro experiment showed that genes known to be affected by PFOS exposure in other species also were induced in hepatocytes of Atlantic salmon, giving us the rationale to expand to testing the actual in vivo magnitude of effect in Atlantic salmon exposed to PFOS at doses usually seen in nature/diets.

Genotoxic risk and oxidative DNA damage in HepG2 cells exposed to perfluorooctanoic acid

Perfluorooctanoic acid (C8HF15O2, PFOA) is widely used in various industrial fields for decades and it is environmentally bioaccumulative. PFOA is known as a potent hepatocarcinogen in rodents. But it is not yet clear whether it is also carcinogenic in humans, and the genotoxic effects of PFOA on human cells have not yet been examined. In this study, the genotoxic potential of PFOA was investigated in human hepatoma HepG2 cells in culture using single cell gel electrophoresis (SCGE) assay and micronucleus (MN) assay. In order to clarify the underlying mechanism(s) we measured the intracellular generation of reactive oxygen species (ROS) using dichlorofluorescein diacetate as a fluorochrome. The level of oxidative DNA damage was evaluated by immunocytochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG) in PFOA-treated HepG2 cells. PFOA at 50-400 microM caused DNA strand breaks and at 100-400 microM MN in HepG2 cells both in a dose-dependent manner. Significantly increased levels of ROS and 8-OHdG were observed in these cells. We conclude that PFOA exerts genotoxic effects on HepG2 cells, probably through oxidative DNA damage induced by intracellular ROS.

Gene Expression Profiles in Rat Liver Treated With Perfluorooctanoic Acid (PFOA)

Perfluorooctanoic acid (PFOA; Pentadecafluorooctanoic acid) is widely used in various industrial applications. It is persistent in the environment and does not appear to undergo further degradation or transformation. PFOA is found in tissues including blood of wildlife and humans; however, the environmental fate and biological effects of PFOA remain unclear. Microarray techniques of gene expression have become a powerful approach for exploring the biological effects of chemicals. Here, the Affymetrix, Inc. rat genome 230 2.0 GeneChip was used to identify alterations in gene regulation in Sprague-Dawley rats treated with five different concentrations of PFOA. Male rats were exposed by daily gavage to 1, 3, 5, 10, or 15 mg PFOA/kg, body weight (bw)/day for 21 days and at the end of the exposure, liver was isolated and total liver RNA were used for the gene chip analysis. Over 500 genes, whose expression was significantly (p < 0.0025) altered by PFOA at two-fold changes compared to control, were examined. The effects were dose-dependent with exposure to 10 mg PFOA/kg, bw/day, causing alteration in expression of the greatest number of genes (over 800). Approximately 106 genes and 38 genes were consistently up- or down-regulated, respectively, in all treatment groups. The largest categories of induced genes were those involved in transport and metabolism of lipids, particularly fatty acids. Other induced genes were involved in cell communication, adhesion, growth, apoptosis, hormone regulatory pathways, proteolysis and peptidolysis and signal transduction. The genes expression of which was suppressed were related to transport of lipids, inflammation and immunity, and especially cell adhesion. Several other genes involved in apoptosis; regulation of hormones; metabolism; and G-protein coupled receptor protein signaling pathways were significantly suppressed.

Identification of genes responsive to PFOS using gene expression profiling

Perfluorooctane sulfonic acid (PFOS) is widely distributed in the environment including in the tissues of wildlife and humans, however, its mechanism of action remains unclear. Here, the Affymetrix rat genome U34A genechip was used to identify alterations in gene expression due to PFOS exposure. Rat hepatoma cells were treated with PFOS at 2-50mg/L (4-100μM) for 96h. Sprague-Dawley rats were orally dosed with PFOS at 5mg/kg/day for 3 days or 3 weeks. Genes that were significantly (P <0.0025) induced were primarily genes for fatty acid metabolizing enzymes, cytochrome P450s, or genes involved in hormone regulation. Consistent expression profiles were obtained for replicate exposures, for short-term and long-term in vivo exposures, and for acute and chronic exposures. One major pathway affected by PFOS was peroxisomal fatty acid β-oxidation, which could be explained by the structural similarity between PFOS and endogenous fatty acids.

Effects of the rodent peroxisome proliferator and hepatocarcinogen, perfluorooctanoic acid, on apoptosis in human hepatoma HepG2 cells

The effects of perfluorooctanoic acid (PFOA), a potent hepatocarcinogen and peroxisome proliferator in rodents, on human cells have not yet been examined. In the present study we demonstrate that treatment of human hepatoblastoma HepG2 cells with PFOA induces apoptosis, as well as perturbs the cell cycle. This apoptosis was characterized by electron microscopy, which revealed typical nucleosomal fragmentation (also observed as a 'DNA ladder' upon electrophoresis on agarose) and was quantitated using propidium iodide staining of cellular DNA and the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. This process was dose- and time-dependent: apoptosis became manifest with 200 microM and maximal (45% of the cells) upon exposure to 450 microM PFOA for 24 h. Electrophoresis of the DNA from HepG2 cells exposed to 500 microM PFOA for 24 h or to 400 microM PFOA for 48 h revealed a smear typical of non-specific degradation. These findings indicate that in the presence of high concentrations of PFOA for long times, HepG2 cells undergo primary and secondary necrosis. Quantitation of trypan blue exclusion supported this conclusion. Flow cytometric analysis revealed that the cell cycle of HepG2 cells was perturbed by exposure to 50-150 microM PFOA. A 50 microM concentration resulted in a significant increase in the proportion of G(2)/M cells and, simultaneously, a decrease in the number of cells in the S phase, whereas treatment with 100 or 150 microM PFOA increased the proportion of cells in the G(0)/G(1) phase and decreased the number of cells in the G(2)/M and S phases. Simultaneous flow cytometric analysis of apoptosis-associated DNA strand breaks using the TUNEL procedure and of propidium iodide staining of cellular DNA revealed DNA breaks in HepG2 cells exposed to 150 microM PFOA, prior to nuclear fragmentation.

Effects of peroxisome proliferators and/or hypothyroidism on xenobiotic-metabolizing enzymes in rat testis

The objectives of the present work were to study the effects of certain peroxisome proliferators on xenobiotic-metabolizing enzyme activities in the testes of normal and hypothyroid rats, i.e. phenol sulfotransferases (pST), phenol UDP-glucuronosyl transferases (pUDPGT), glutathione transferases (GST), catalase, epoxide hydrolase (EH), glutathione peroxidase (GPX) and NAD(P)H quinone oxidoreductase (QR). Adult male rats (normal and hypothyroid) were treated for 10 days with clofibrate (0.5%), perfluorooctanoic acid (0.5%, PFOA), acetylsalisylic acid (1%, ASA) and di(2-ethylhexyl)phthalate (2%, DEHP) in their diet. The results show that treatment of normal rats with peroxisome proliferators dramatically affects the activities of xenobiotic-metabolizing enzymes (40-60% reduction). The highest effects are seen in catalase activity (50-60% with PFOA and ASA), pUDPGT (55% with PFOA), pST (55% with PFOA) and QR (50% with DEHP). These effects are not seen or are weaker after induction of hypothyroidism. Taken together, it is concluded that different classes of peroxisome proliferators have different effects on rat testicular xenobiotic-metabolizing enzymes.

Characterization of the rat glutathione S-transferase Yc2 subunit gene, GSTA5: identification of a putative antioxidant-responsive element in the 5'-flanking region of rat GSTA5 that may mediate chemoprotection against aflatoxin B1

We have isolated and characterized genomic DNA encoding the rat glutathione S-transferase Yc2 subunit. This protein is now referred to as rGSTA5 and is noteworthy because of its high activity towards aflatoxin B1-8,9-epoxide, its marked inducibility by chemoprotectors, its sex-specific regulation, and its over-expression in hepatoma and preneoplastic nodules. The rGSTA5 gene, which was isolated on two overlapping bacteriophage lambda clones, is approx. 12 kb in length and, unlike other class Alpha genes described to date, it comprises six exons. The transcription start site has been identified 228 bp upstream from the ATG translational initiation codon, and is situated 51 bp downstream from a consensus TATA-box. Deletion analysis, using luciferase reporter constructs, has shown that the region between -177 bp and +65 bp from the transcriptional start site contains a functional promoter. Computer-assisted analysis of the upstream sequence has indicated the presence of an antioxidant-responsive element (ARE), and several elements thought to be required for tissue-specific expression of the enzyme. In addition, several putative oestrogen-responsive half sites were observed in both upstream and intronic sequences.

Synergistic induction of acyl-CoA oxidase activity, an indicator of peroxisome proliferation, by arachidonic acid and retinoic acid in Morris hepatoma 7800C1 cells

Morris hepatoma 7800C1 cells (a Wistar rat cell line) were exposed to 100 microM arachidonic acid in the medium for seven days. This treatment resulted in 150% and 60% increases (above control activities) in acyl-CoA oxidase (which catalyzes the first step in peroxisomal beta-oxidation) and catalase activities, respectively. Arachidonic acid (C20:4) can be metabolized to 20- and 19-hydroxy-arachidonic acid by cytochrome P-450IVA and it was shown that our cells are capable of forming 20-hydroxyarachidonic acid. However, 20-hydroxyarachidonic acid (0.1-0.8 microM, 4 days) had no effects on lauroyl-CoA oxidase and catalase activities in Morris hepatoma cells. Treatment of 7800C1 cells with 100 microM all-trans-retinoic acid resulted in inductions of catalase (160% above the control activity) and carnitine acetyltransferase (140% above the control activity) activities. The activity of lauroyl-CoA oxidase was often, but not always, slightly induced by treatment with all-trans-retinoic acid. When all-trans-retinoic acid was administered together with arachidonic acid, these two compounds had a synergistic effect on the induction of acyl-CoA oxidase activity (almost 700% above the control activity). However, treatment of Morris hepatoma cells with the man-made peroxisome proliferator, perfluorooctanoic acid, together with all-trans-retinoic acid did not result in any synergistic effect on this same enzyme activity. In summary, this study (1) corroborates findings from transfection experiments indicating that the heterodimer PPAR-RXR alpha activates transcription of the acyl-CoA oxidase gene using the Morris hepatoma cell line; (2) shows that arachidonic acid induces the activity of lauroyl-CoA oxidase; (3) suggests that transcription of the catalase gene is not regulated by a PPAR-RXR alpha heterodimer in this system; and (4) demonstrates that peroxisome proliferation in Morris hepatoma cells by perfluorooctanoic acid is not as dependent on the level of retinoic acid as is the same process caused by arachidonic acid.