Mechanisms of extrahepatic tumor induction by peroxisome proliferators in male CD rats

A critical review of perfluorooctanoate and perfluorooctanesulfonate exposure and cancer risk in humans

Perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) are ubiquitous synthetic chemicals with no known effect on human cancer development. This article systematically and critically reviews the epidemiologic evidence regarding the association between PFOA and PFOS exposure and cancer risk in humans. Eighteen epidemiologic studies - eight of PFOA, four of PFOS, and six of both PFOA and PFOS - have estimated associations of exposure to these chemicals with cancer incidence or mortality, with studies equally divided between occupational and nonoccupational settings. Although some statistically significant positive associations have been reported, for example, with cancers of the prostate, kidney, testis, and thyroid, the majority of relative risk estimates for both PFOA and PFOS have been between 0.5 and 2.0 (with 95% confidence intervals including 1.0), inconsistently detected across studies, counterbalanced by negative associations, not indicative of a monotonic exposure-response relationship, and not coherent with toxicological evidence in animals, in which the primary target organs are the liver, testis (Leydig cells), and pancreas (acinar cells). Many positive associations with PFOA exposure were detected in community settings without occupational exposure and were not supported by results in exposed workers. Given that occupational exposure to PFOA and PFOS is one to two orders of magnitude higher than environmental exposure, the discrepant positive findings are likely due to chance, confounding, and/or bias. Taken together, the epidemiologic evidence does not support the hypothesis of a causal association between PFOA or PFOS exposure and cancer in humans.

Pathology review of proliferative lesions of the exocrine pancreas in two chronic feeding studies in rats with ammonium perfluorooctanoate

Two chronic dietary studies, conducted years apart, with ammonium perfluorooctanoate (APFO) in Sprague Dawley rats have been previously reported. Although both included male 300 ppm dietary dose groups, only the later study, conducted in 1990–1992 by Biegel et al., reported an increase in proliferative lesions (hyperplasia and adenoma) of the acinar pancreas. An assessment of the significance of the differences between both studies requires careful consideration of: the diagnostic criteria for proliferative acinar cell lesions of the rat pancreas (for example, the diagnosis of pancreatic acinar cell hyperplasia versus adenoma is based on the two-dimensional size of the lesion rather than distinct morphological differences); the basis for those criteria in light of their relevance to biological behavior; and the potential diagnostic variability between individual pathologists for difficult-to-classify lesions. A pathology peer review of male exocrine pancreatic tissues from the earlier study, conducted in 1981–1983 by Butenhoff et al., was undertaken. This review identified an increase in acinar cell hyperplasia but not adenoma or carcinoma in the earlier study. Both studies observed a proliferative response in the acinar pancreas which was more pronounced in the study by Biegel et al. Definitive reasons for the greater incidence of proliferative lesions in the later study were not identified, but some possible explanations are presented herein. The relevance of this finding to human risk assessment, in the face of differences in the biological behavior of human and rat pancreatic proliferative lesions and the proposed mechanism of formation of these lesions, are questionable.

The physiological role of arcuate kisspeptin neurons in the control of reproductive function in female rats

Kisspeptin plays a pivotal role in pubertal onset and reproductive function. In rodents, kisspeptin perikarya are located in 2 major populations: the anteroventral periventricular nucleus and the hypothalamic arcuate nucleus (ARC). These nuclei are believed to play functionally distinct roles in the control of reproduction. The anteroventral periventricular nucleus population is thought to be critical in the generation of the LH surge. However, the physiological role played by the ARC kisspeptin neurons remains to be fully elucidated. We used bilateral stereotactic injection of recombinant adeno-associated virus encoding kisspeptin antisense into the ARC of adult female rats to investigate the physiological role of kisspeptin neurons in this nucleus. Female rats with kisspeptin knockdown in the ARC displayed a significantly reduced number of both regular and complete oestrous cycles and significantly longer cycles over the 100-day period of the study. Further, kisspeptin knockdown in the ARC resulted in a decrease in LH pulse frequency. These data suggest that maintenance of ARC-kisspeptin levels is essential for normal pulsatile LH release and oestrous cyclicity.

Perfluorinated compounds: emerging POPs with potential immunotoxicity

Perfluorinated compounds (PFCs) have been recognized as an important class of environmental contaminants commonly detected in blood samples of both wildlife and humans. These compounds have been in use for more than 60 years as surface treatment chemicals, polymerization aids, and surfactants. They possess a strong carbon-fluorine bond, which leads to their environmental persistence. There is evidence from both epidemiology and laboratory studies that PFCs may be immunotoxic, affecting both cell-mediated and humoral immunity. Reported effects of PFCs include decreased spleen and thymus weights and cellularity, reduced specific antibody production, reduced survival after influenza infection, and altered cytokine production. Immunosuppression is a critical effect associated with exposure to PFCs, as it has been reported to reduce antibody responses to vaccination in children. Mounting evidence suggests that immunotoxicity in experimental animals can occur at serum concentrations below, within, or just above the reported range for highly exposed humans and wildlife. Considering bioaccumulation and exposure to multiple PFCs, the risk of immunotoxicity for humans and wildlife cannot be discounted. This review will discuss current and recently published work exploring the immunomodulatory effects of PFCs in experimental animals and humans.

Relationship of Body Weight Parameters with the Incidence of Common Spontaneous Tumors in Tg.rasH2 Mice

The mechanistic relationship between increased food consumption, increased body weights, and increased incidence of tumors has been well established in 2-year rodent models. Body weight parameters such as initial body weights, terminal body weights, food consumption, and the body weight gains in grams and percentages were analyzed to determine whether such relationship exists between these parameters with the incidence of common spontaneous tumors in Tg.rasH2 mice. None of these body weight parameters had any statistically significant relationship with the incidence of common spontaneous tumors in Tg.rasH2 males, namely lung tumors, splenic hemangiosarcomas, nonsplenic hemangiosarcomas, combined incidence of all hemangiosarcomas, and Harderian gland tumors. These parameters also did not have any statistically significant relationship with the incidence of lung and Harderian gland tumors in females. However, in females, increased initial body weights did have a statistically significant relationship with the nonsplenic hemangiosarcomas, and increased terminal body weights did have a statistically significant relationship with the incidence of splenic hemangiosarcomas, nonsplenic hemangiosarcomas, and the combined incidence of all hemangiosarcomas. In addition, increased body weight gains in grams and percentages had a statistically significant relationship with the combined incidence of all hemangiosarcomas in females, but not separately with splenic and nonsplenic hemangiosarcomas.

Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPARα) as a case study

Several therapeutic agents and industrial chemicals induce liver tumors in rodents through the activation of the peroxisome proliferator-activated receptor alpha (PPARα). The cellular and molecular events by which PPARα activators induce rodent hepatocarcinogenesis has been extensively studied and elucidated. This review summarizes the weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis and identifies gaps in our knowledge of this MOA. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators including a phthalate ester plasticizer di(2-ethylhexyl) phthalate (DEHP) and the drug gemfibrozil. While biologically plausible in humans, the hypothesized key events in the rodent MOA, for PPARα activators, are unlikely to induce liver tumors in humans because of toxicodynamic and biological differences in responses. This conclusion is based on minimal or no effects observed on growth pathways, hepatocellular proliferation and liver tumors in humans and/or species (including hamsters, guinea pigs and cynomolgous monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Overall, the panel concluded that significant quantitative differences in PPARα activator-induced effects related to liver cancer formation exist between rodents and humans. On the basis of these quantitative differences, most of the workgroup felt that the rodent MOA is "not relevant to humans" with the remaining members concluding that the MOA is "unlikely to be relevant to humans". The two groups differed in their level of confidence based on perceived limitations of the quantitative and mechanistic knowledge of the species differences, which for some panel members strongly supports but cannot preclude the absence of effects under unlikely exposure scenarios.

Perfluorooctanoic acid (PFOA) exposures and incident cancers among adults living near a chemical plant

BACKGROUND

Perfluorooctanoic acid (PFOA) is a synthetic chemical ubiquitous in the serum of U.S. residents. It causes liver, testicular, and pancreatic tumors in rats. Human studies are sparse.

OBJECTIVE

We examined cancer incidence in Mid-Ohio Valley residents exposed to PFOA in drinking water due to chemical plant emissions.

METHODS

The cohort consisted of adult community residents who resided in contaminated water districts or worked at a local chemical plant. Most participated in a 2005-2006 baseline survey in which serum PFOA was measured. We interviewed the cohort in 2008-2011 to obtain further medical history. Retrospective yearly PFOA serum concentrations were estimated for each participant from 1952 through 2011. Self-reported cancers were validated through medical records and cancer registry review. We estimated the association between cancer and cumulative PFOA serum concentration using proportional hazards models.

RESULTS

Participants (n = 32,254) reported 2,507 validated cancers (21 different cancer types). Estimated cumulative serum PFOA concentrations were positively associated with kidney and testicular cancer [hazard ratio (HR) = 1.10; 95% CI: 0.98, 1.24 and HR = 1.34; 95% CI: 1.00, 1.79, respectively, for 1-unit increases in ln-transformed serum PFOA]. Categorical analyses also indicated positive trends with increasing exposures for both cancers: for kidney cancer HRs for increasing exposure quartiles were 1.0, 1.23, 1.48, and 1.58 (linear trend test p = 0.18) and for testicular cancer, HRs were 1.0, 1.04, 1.91, 3.17 (linear trend test p = 0.04).

CONCLUSIONS

PFOA exposure was associated with kidney and testicular cancer in this population. Because this is largely a survivor cohort, findings must be interpreted with caution, especially for highly fatal cancers such as pancreatic and lung cancer.

Perfluorooctanoic acid induces apoptosis through the p53-dependent mitochondrial pathway in human hepatic cells: a proteomic study

Perfluorooctanoic acid (PFOA) is one of the most commonly used perfluorinated compounds, and exposure to it has been associated with a number of adverse health effects. However, the molecular mechanisms involved in PFOA toxicity are still not well characterized. In the present study, flow cytometry analysis revealed that PFOA induced oxidative stress, cell cycle arrest and apoptosis in human non-tumor hepatic cells (L-02). Furthermore, we investigated the alterations in protein profile within L-02 cells exposed to PFOA, aiming to explore the mechanisms underlying PFOA hepatotoxicity on the proteome level. Of the 28 proteins showing significant differential expression in response to PFOA, 24 were down-regulated and 4 were up-regulated. This proteomic study proposed that the inhibition of some proteins, including GRP78, HSP27, CTSD and hnRNPC may be involved in the activation of p53, which consequently triggered the apoptotic process in L-02 cells. Induction of apoptosis via the p53-dependent mitochondrial pathway is further suggested as one of the key toxicological events occurring in L-02 cells under PFOA stress. We hope these data will shed new light on the molecular mechanisms responsible for PFOA-mediated toxicity in human liver cells, and from such studies useful biomarkers indicative of PFOA exposure could be developed.

Formation of perfluorinated surfactants from precursors by indigenous microorganisms in groundwater

The formation of perfluorinated surfactants (PFSs) from their precursors in waters is of concern. In this study, the formation of PFSs through biodegradation of precursors was measured in incubation tests. Indigenous microorganisms in groundwater were able to biodegrade perfluorooctane sulfonamide (FOSA) to yield perfluorooctane sulfonate (PFOS). The addition of nutrients and soil promoted the formation. A 42-d incubation test using sources of groundwater recharge showed that PFOS, perfluorooctanoate, and perfluorononanoate were significantly and remarkably (⩾1.5×) formed from precursors in street runoff through biodegradation, but not in rainwater or wastewater effluent. Significant formation of PFSs from precursors in street runoff was observed.

National inventory of perfluoroalkyl substances in archived U.S. biosolids from the 2001 EPA National Sewage Sludge Survey

Using liquid chromatography tandem mass spectrometry, we determined the first nationwide inventories of 13 perfluoroalkyl substances (PFASs) in U.S. biosolids via analysis of samples collected by the U.S. Environmental Protection Agency in the 2001 National Sewage Sludge Survey. Perfluorooctane sulfonate [PFOS; 403 ± 127 ng/g dry weight (dw)] was the most abundant PFAS detected in biosolids composites representing 32 U.S. states and the District of Columbia, followed by perfluorooctanoate [PFOA; 34 ± 22 ng/g dw] and perfluorodecanoate [PFDA; 26 ± 20 ng/g dw]. Mean concentrations in U.S. biosolids of the remaining ten PFASs ranged between 2 and 21 ng/g dw. Interestingly, concentrations of PFOS determined here in biosolids collected prior to the phase-out period (2002) were similar to levels reported in the literature for recent years. The mean load of ∑PFASs in U.S. biosolids was estimated at 2749-3450 kg/year, of which about 1375-2070 kg is applied on agricultural land and 467-587 kg goes to landfills as an alternative disposal route. This study informs the risk assessment of PFASs by furnishing national inventories of PFASs occurrence and environmental release via biosolids application on land.

In vitro toxicological characterization of perfluorinated carboxylic acids with different carbon chain lengths

Perfluorooctanoic acid (PFOA) is in use for the production of fluoropolymers (PFT). Due to its toxic properties it was proposed to replace the substance in its industrial applications by homologous compounds with shorter carbon chain length that were supposed to be less toxic compared to PFOA, however, the smaller PFOA homologs are poorly characterized so far. In this study we have conducted a comparative analysis of the toxicity of perfluorinated carboxylic acids (PFCA) with a carbon chain length ranging from four to twelve carbon atoms. By using the human hepatocarcinoma cell line HepG2 as an in vitro model for human hepatocytes we could show a positive correlation between the carbon chain length of the respective PFCA and its cytotoxicity. There was, however, no indication of an apoptotic mechanism for cytotoxicity. All PFCA under investigation were negative in two independent genotoxicity assays. As PFOA, being a well-known peroxisome proliferator, the other PFCA tested in this study were also shown to activate human peroxisome proliferator-activated receptor alpha (PPARα) with PFOA having the highest potential of PPARα activation. Moreover, the compounds showed weak potential to activate PPARγ and hardly activated PPARδ. Taken together, the in vitro study revealed that PFCA with a shorter carbon chain length seem to be less toxic than PFOA.

Cellular response of freshwater green algae to perfluorooctanoic acid toxicity

Perfluorooctanoic acid (PFOA) is a kind of persistent organic pollutants and its aquatic eco-toxicity has attracted wide attention; however, the mechanism involved in its toxicity as well as the cell response against PFOA have not been well established. Herein, using single-celled green algae Chlorella pyrenoidosa and Selenastrum capricornutum at the logarithmic growth stage as test organisms, we studied the toxic effects of PFOA on the cell permeability, The 96 h-EC(50) values of PFOA for C. pyrenoidosa and S. capricornutum were 207.46 mg L(-1) and 190.99 mg L(-1), respectively, lower than the 96 h-EC(50) values reported in the literatures. After 96 h of PFOA exposure, the permeability of the cell membranes of both algae was significantly decreased, and the chlorophyll concentration mirrored the trends of algal growth. In both algal species, after a 192-h exposure to a low concentration of PFOA, the activities of superoxide dismutase and catalase were greater than those of the control. At higher concentrations of PFOA, activities of superoxide dismutase and catalase were strongly inhibited. These results indicate that long-term exposure to low levels of PFOA may induce excessive generation of reactive oxygen species in algal cells, causing oxidative damage to cells.

River water contaminated with perfluorinated compounds potentially posing the greatest risk to young children

Although, humans are exposed to perflourinated compounds (PFCs) from various media, water consumption could be an important source for the residents living near to contaminated areas. Since comprehensive multimedia exposure model has not been developed for PFCs, assessment of the potential risk due to exposure to PFCs through direct water consumption could be a conservative estimate. The human health risks derived from the exposure to PFCs through water consumption were assessed for different age groups of general population in Taiwan using probabilistic approach. Based on available data on concentrations of PFCs in river water, exposure to PFOS, PFOA and PFDA via water consumption for different age groups were calculated using deterministic and probabilistic risk assessment methods. The oral non-cancer risks from PFOS, PFOA and their combination, expressed as a Hazard Index (HI), was determined by comparing oral exposure dose (through water intake) with the oral Reference Dose (RfD). The average exposure to PFOS, PFOA and PFDA via water consumption for adults ranged from 0.16 to 220.15, 0.43 to 12.5 and 0.43 to 2.36 ng kg-bw(-1) d(-1) and for children 0.13-354.3, 0.35-20.17 and 0.35-3.79 ng kg-bw(-1) d(-1), respectively. Probabilistic values of total HIs for all age groups reside near to Keya River exceed the RfD 2.4-4.8 times, corresponding mainly to PFOS with a percentage of 97%. In conclusions, children aged 1-3 years old and the residents reside near to Keya River are at the highest risk of exposure to PFCs via water consumption.

Perfluorooctanoic acid induced-developmental cardiotoxicity: are peroxisome proliferator activated receptor α (PPARα) and bone morphorgenic protein 2 (BMP2) pathways involved?

Perfluorooctanoic acid (PFOA) is an environmental contaminant known to induce developmental toxicity in animal models through activation of the peroxisome proliferator-activated receptor α (PPARα). Previously, it was demonstrated that in ovo exposure to PFOA induced cardiotoxicity in chicken embryos and hatchlings. To investigate potential PPARα-mediated mechanisms, fertile chicken eggs were injected prior to incubation with WY 14,643, a PPARα agonist. Cardiac morphology and function were evaluated in late-stage embryos and hatchlings. Histologically, unlike PFOA, WY 14,643 did not induce thinning of the right ventricular wall. Via echocardiography, however, WY 14,643 induced effects similar to those of PFOA, including increased left ventricular wall thickness and mass, elevated heart rate, ejection fraction, fractional shortening, and decreased stroke volume. Additionally, to investigate mechanisms associated with early heart development, a separate group of fertile chicken eggs was injected prior to incubation with PFOA or WY 14,643 and in early-stage embryos, gene expression and protein concentration associated with the bone morphogenic protein (BMP2) pathway were determined. Although changes were not statistically consistent among doses, expression of BMP2, Nkx2.5, and GATA4 mRNA in early embryos was altered by PFOA exposure; however, protein concentrations of these targets were not markedly altered by either PFOA or WY 14,643. Protein levels of pSMAD1/5, a transcriptional regulator stimulated by BMPs, were altered by both PFOA and WY 14,643, but in different directions; PFOA reduced cytoplasmic pSMAD1/5, whereas WY 14,643 decreased nuclear pSMAD1/5. Taken together, these data suggest that developmental cardiotoxicity induced by PFOA likely involves both PPARα and BMP2 pathways.

Perfluorooctanoic acid (PFOA), an emerging drinking water contaminant: a critical review of recent literature

Perfluorooctanoic acid (PFOA) is an anthropogenic contaminant that differs in several ways from most other well-studied organic chemicals found in drinking water. PFOA is extremely resistant to environmental degradation processes and thus persists indefinitely. Unlike most other persistent and bioaccumulative organic pollutants, PFOA is water-soluble, does not bind well to soil or sediments, and bioaccumulates in serum rather than in fat. It has been detected in finished drinking water and drinking water sources impacted by releases from industrial facilities and waste water treatment plants, as well as in waters with no known point sources. However, the overall occurrence and population exposure from drinking water is not known. PFOA persists in humans with a half-life of several years and is found in the serum of almost all U.S. residents and in populations worldwide. Exposure sources include food, food packaging, consumer products, house dust, and drinking water. Continued exposure to even relatively low concentrations in drinking water can substantially increase total human exposure, with a serum:drinking water ratio of about 100:1. For example, ongoing exposures to drinking water concentrations of 10 ng/L, 40 ng/L, 100 ng/L, or 400 ng/L are expected to increase mean serum levels by about 25%, 100%, 250%, and 1000%, respectively, from the general population background serum level of about 4 ng/mL. Infants are potentially a sensitive subpopulation for PFOA's developmental effects, and their exposure through breast milk from mothers who use contaminated drinking water and/or from formula prepared with contaminated drinking water is higher than in adults exposed to the same drinking water concentration. Numerous health endpoints are associated with human PFOA exposure in the general population, communities with contaminated drinking water, and workers. As is the case for most such epidemiology studies, causality for these effects is not proven. Unlike most other well-studied drinking water contaminants, the human dose-response curve for several effects appears to be steepest at the lower exposure levels, including the general population range, with no apparent threshold for some endpoints. There is concordance in animals and humans for some effects, while humans and animals appear to react differently for other effects such as lipid metabolism. PFOA was classified as "likely to be carcinogenic in humans" by the USEPA Science Advisory Board. In animal studies, developmental effects have been identified as more sensitive endpoints for toxicity than carcinogenicity or the long-established hepatic effects. Notably, exposure to an environmentally relevant drinking water concentration caused adverse effects on mammary gland development in mice. This paper reviews current information relevant to the assessment of PFOA as an emerging drinking water contaminant. This information suggests that continued human exposure to even relatively low concentrations of PFOA in drinking water results in elevated body burdens that may increase the risk of health effects.

Transcription of genes involved in fat metabolism in chicken embryos exposed to the peroxisome proliferator-activated receptor alpha (PPARα) agonist GW7647 or to perfluorooctane sulfonate (PFOS) or perfluorooctanoic acid (PFOA)

Perfluoroalkyl acids (PFAAs) such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are developmental toxicants in various animal classes, including birds. Both compounds interact with peroxisome proliferator-activated receptors (PPARs), but it is not known whether activation of PPARs is involved in their embryo toxicity in birds. We exposed chicken embryos via egg injection at a late developmental stage to GW7647, a potent PPARα agonist in mammals, and to PFOS or PFOA. Mortality was induced by PFOS and PFOA but not by GW7647. Transcripts of a number of genes activated by PPARα agonists in mammals were analyzed in liver and kidney of 18-day-old embryos. Several of the genes were induced in both liver and kidney following exposure to GW7647. Treatment with PFOA resulted in induction of acyl-coenzyme A oxidase mRNA in liver, whereas none of the genes were significantly induced by PFOS treatment. No up-regulation of gene transcription was found in kidney following treatment with PFOS or PFOA. Principal component analysis showed that PFOA caused an mRNA expression pattern in liver more similar to the pattern induced by GW7647 than PFOS did. Our findings do not support that the embryo mortality by PFOS and PFOA in chicken embryos involves PPARα activation.

Chronic dietary toxicity and carcinogenicity study with ammonium perfluorooctanoate in Sprague-Dawley rats

In order to assess the potential chronic toxicity and tumorigenicity of ammonium perfluorooctanoate (APFO), a 2-year dietary study was conducted with male and female rats fed 30 ppm or 300 ppm (approximately 1.5 and 15 mg/kg). In males fed 300 ppm, mean body weights were lower across most of the test period and survival in these rats was greater than that seen either in the 30 ppm or the control group. Non-neoplastic effects were observed in liver in rats fed 300 ppm and included elevated liver weight, an increase in the incidence of diffuse hepatocellular hypertrophy, portal mononuclear cell infiltration, and mild hepatocellular vacuolation without an increase in hepatocellular necrosis. Mean serum activities of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase were elevated up to three times the control means, primarily at the 300 ppm dose. A significant increase in Leydig cell tumors of the testes was seen in the males fed 300 ppm, and tumors of the liver and acinar pancreas, which are often observed in rats from chronic exposure to peroxisome proliferating agents, were not observed in this study. All other tumor types were those seen spontaneously in rats of this stock and age and were not associated with feeding of APFO.

Perfluorooctanoic acid induces gene promoter hypermethylation of glutathione-S-transferase Pi in human liver L02 cells

Perfluorooctanoic acid (PFOA) is one of the most commonly used perfluorinated compounds. Being a persistent environmental pollutant, it can accumulate in human tissues via various exposure routes. PFOA may interfere in a toxic fashion on the immune system, liver, development, and endocrine systems. In utero human exposure had been associated with cord serum global DNA hypomethylation. In light of this, we investigated possible PFOA-induced DNA methylation alterations in L02 cells in order to shed light into its epigenetic-mediated mechanisms of toxicity in human liver. L02 cells were exposed to 5, 10, 25, 50 or 100 mg/L PFOA for 72h. Global DNA methylation levels were determined by LC/ESI-MS, glutathione-S-transferase Pi (GSTP) gene promoter DNA methylation was investigated by methylation-specific polymerase chain reaction (PCR) with bisulfite sequencing, and consequent mRNA expression levels were measured with quantitative real-time reverse transcriptase PCR. A dose-related increase of GSTP promoter methylation at the transcription factor specificity protein 1 (SP1) binding site was observed. However, PFOA did not significantly influence global DNA methylation; nor did it markedly alter the promoter gene methylation of p16 (cyclin-dependent kinase inhibitor 2A), ERα (estrogen receptor α) or PRB (progesterone receptor B). In addition, PFOA significantly elevated mRNA transcript levels of DNMT3A (which mediates de novo DNA methylation), Acox (lipid metabolism) and p16 (cell apoptosis). Considering the role of GSTP in detoxification, aberrant methylation may be pivotal in PFOA-mediated toxicity response via the inhibition of SP1 binding to GSTP promoter.

Social disparities in exposures to bisphenol A and polyfluoroalkyl chemicals: a cross-sectional study within NHANES 2003-2006

BACKGROUND

Bisphenol A (BPA) and polyfluoroalkyl chemicals (PFCs) are suspected endocrine disrupting compounds known to be ubiquitous in people's bodies. Population disparities in exposure to these chemicals have not been fully characterized.

METHODS

We analyzed data from the 2003-2006 National Health and Nutrition Examination Survey. Using multivariable linear regression we examined the association between urinary concentrations of BPA, serum concentrations of four PFCs, and multiple measures of socioeconomic position (SEP): family income, education, occupation, and food security. We also examined associations with race/ethnicity.

RESULTS

All four PFCs were positively associated with family income, whereas BPA was inversely associated with family income. BPA concentrations were higher in people who reported very low food security and received emergency food assistance than in those who did not. This association was particularly strong in children: 6-11 year-olds whose families received emergency food had BPA levels 54% higher (95% CI, 13 to 112%) than children of families who did not. For BPA and PFCs we saw smaller and less consistent associations with education and occupation. Mexican Americans had the lowest concentrations of any racial/ethnic group of both types of chemicals; for PFCs, Mexican Americans not born in the U.S. had much lower levels than those born in the U.S.

CONCLUSIONS

People with lower incomes had higher body burdens of BPA; the reverse was true for PFCs. Family income with adjustment for family size was the strongest predictor of chemical concentrations among the different measures of SEP we studied. Income, education, occupation, and food security appear to capture different aspects of SEP that may be related to exposure to BPA and PFCs and are not necessarily interchangeable as measures of SEP in environmental epidemiology studies. Differences by race/ethnicity were independent of SEP.

Perflurooctanoic acid induces developmental cardiotoxicity in chicken embryos and hatchlings

Perfluorooctanoic acid (PFOA) is a widespread environmental contaminant that is detectable in serum of the general U.S. population. PFOA is a known developmental toxicant that induces mortality in mammalian embryos and is thought to induce toxicity via interaction with the peroxisome proliferator activated receptor alpha (PPARα). As the cardiovascular system is crucial for embryonic survival, PFOA-induced effects on the heart may partially explain embryonic mortality. To assess impacts of PFOA exposure on the developing heart in an avian model, we used histopathology and immunohistochemical staining for myosin to assess morphological alterations in 19-day-old chicken embryo hearts after PFOA exposure. Additionally, echocardiography and cardiac myofibril ATPase activity assays were used to assess functional alterations in 1-day-old hatchling chickens following developmental PFOA exposure. Overall thinning and thinning of a dense layer of myosin in the right ventricular wall were observed in PFOA-exposed chicken embryo hearts. Alteration of multiple cardiac structural and functional parameters, including left ventricular wall thickness, left ventricular volume, heart rate, stroke volume, and ejection fraction were detected with echocardiography in the exposed hatchling chickens. Assessment of ATPase activity indicated that the ratio of cardiac myofibril calcium-independent ATPase activity to calcium-dependent ATPase activity was not affected, which suggests that developmental PFOA exposure may not affect cardiac energetics. In summary, structural and functional characteristics of the heart appear to be developmental targets of PFOA, possibly at the level of cardiomyocytes. Additional studies will investigate mechanisms of PFOA-induced developmental cardiotoxicity.

Mode of Action analysis of perfluorooctanoic acid (PFOA) tumorigenicity and Human Relevance

Perfluorooctanoic acid (PFOA) is an environmentally persistent chemical used in the manufacturing of a wide array of industrial and commercial products. PFOA has been shown to induce tumors of the liver, testis and pancreas (tumor triad) in rats following chronic dietary administration. PFOA belongs to a group of compounds that are known to activate the PPARα receptor. The PPARα activation Mode of Action was initially addressed in 2003 [9] and further refined in subsequent reviews [92-94]. In the intervening time, additional information on PFOA effects as well as a further refinement of the Mode of Action framework warrants a re-examination of this compound for its cancer induction Mode of Action. This review will address the rodent (rat) cancer data and cancer Mode of Action of PFOA for tumors of the liver, testes and pancreas.

In vitro characterization of the immunotoxic potential of several perfluorinated compounds (PFCs)

We have previously shown that PFOA and PFOS directly suppress cytokine secretion in immune cells, with different mechanisms of action. In particular, we have demonstrated a role for PPAR-α in PFOA-induced immunotoxicity, and that PFOS has an inhibitory effect on LPS-induced I-κB degradation. These studies investigate the immunomodulatory effects of four other PFCs, namely PFBS, PFOSA, PFDA, and fluorotelomer using in vitro assays. The release of the pro-inflammatory cytokines IL-6 and TNF-α was evaluated in lipolysaccharide (LPS)-stimulated human peripheral blood leukocytes (hPBL) and in the human promyelocytic cell line THP-1, while the release of IL-10 and IFN-γ was evaluated in phytohemagglutinin (PHA)-stimulated hPBL. All PFCs suppressed LPS-induced TNF-α production in hPBL and THP-1 cells, while IL-6 production was suppressed by PFOSA, PFOS, PFDA and fluorotelomer. PFBS, PFOSA, PFOS, PFDA and fluorotelomer inhibited PHA-induced IL-10 release, while IFN-γ secretion was affected by PFOSA, PFOS, PFDA and fluorotelomer. Leukocytes obtained from female donors appear to be more sensitive to the in vitro immunotoxic effects of PFCs when their responses are compared to the results obtained using leukocytes from male donors. Mechanistic investigations demonstrated that inhibition of TNF-α release in THP-1 cells occurred at the transcriptional level. All PFCs, including PFOA and PFOS, decreased LPS-induced NF-κB activation. With the exception of PFOA, none of the PFCs tested was able to activate PPARα driven transcription in transiently transfected THP-1 cells, excluding a role for PPARα in the immunomodulation observed. PFBS and PFDA prevented LPS-induced I-κB degradation. Overall, these studies suggest that PFCs affect NF-κB activation, which directly suppresses cytokine secretion by immune cells. Our results indicate that PFOA is the least active of the PFCs examined followed by PFBS, PFDA, PFOS, PFOSA and fluorotelomer.

Lipid peroxidation and oxidative stress responses of salmon fed a diet containing perfluorooctane sulfonic- or perfluorooctane carboxylic acids

The present study was conducted to evaluate the effects of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on lipid β-oxidation and oxidative stress responses in Atlantic salmon liver and kidney tissues. We quantified changes in the expression levels of peroxisome proliferator-activated receptors (PPARs) and acyl-CoA oxidase (ACOX1) enzyme whose transcription is induced by PPARs. In addition, we analyzed gene expression patterns for enzymatic antioxidants (superoxide dismutase: SOD, catalase: CAT and glutathione peroxidase: GPx). Thiobarbituric acid reactive substances (TBARS) were analyzed as a measure for lipid peroxidation. Juvenile Atlantic salmon were repeatedly force-fed food spiked with PFOA or PFOS at 0.2mg/kg, and samples were collected after 0, 2, 5 and 8 days and after a 7 days recovery period. Our data showed that exposure of salmon to PFOS or PFOA produced changes (either increased or decreased) in mRNA expression for PPARs, ACOX1, oxidative stress responses and lipid peroxidation (TBARS) and these responses showed marked organ differences, associated with tissue bioaccumulation patterns and dependent on exposure time. Given that a classical reaction during reactive oxygen species (ROS)-induced damage involves the peroxidation of lipids, our study demonstrates that salmon continuously exposed to dietary PFOS or PFOA dose showed alteration in peroxisomal responses and oxidative stress responses, with higher severity in the kidney, compared to liver. Overall, our data suggest that ROS-mediated oxidative damage maybe a significant and putative toxic effect of PFOA and PFOS in fish as has been reported in mammals.

Levels, temporal trends, and tissue distribution of perfluorinated surfactants in freshwater fish from Asian countries

Perfluorinated surfactants (PFSs) in Asian freshwater fish species were analyzed to investigate tissue distribution, temporal trends, extent of pollution, and level of PFS exposure through food intake. Freshwater fish species, namely carp, snakehead, and catfish, were collected in Japan, Vietnam, India, Malaysia, and Thailand, and 10 PFSs, including perfluorooctanesulfonate (PFOS) and perfluorooctanoate, were analyzed by liquid chromatography-tandem mass spectrometry. PFSs in carp in Tokyo were more concentrated in kidneys (Σ10 PFSs = 257 ± 95 ng/g wet weight [ww]) and livers (119 ± 36 ng/g ww) than in ovaries (43 ± 2 ng/g ww) and muscles (24 ± 17 ng/g ww). Concentrations of PFOS and its precursor, perfluorooctane sulfonamide, in livers of carp and in waters in Tokyo showed a dramatic decrease during the last decade, probably because of 3 M's phasing-out of the manufacture of perfluorooctanesulfonyl-fluoride-based products in 2000. In contrast, continuing contamination by long-chain perfluorocarboxylates (PFCAs) with ≥ 9 fluorinated carbons was seen in multiple media, suggesting that these compounds continue to be emitted. PFS concentrations in freshwater fish species in tropical Asian countries were generally lower than those in developed countries, such as Japan, e.g., for PFOS in muscle, Vietnam < 0.05-0.3 ng/g ww; India < 0.05-0.2 ng/g ww; Malaysia < 0.05-0.2 ng/g ww; Thailand < 0.05 ng/g ww; and Japan (Tokyo) = 5.1-22 ng/g ww. Daily intake of short-chain PFCAs with ≤ 8 fluorinated carbons from freshwater fish species in Japan was approximately one order of magnitude lower than that from drinking water, whereas daily intake of PFOS and long-chain PFCAs with ≥ 9 fluorinated carbons from freshwater fish species was comparable with or greater than that from drinking water. Because the risk posed by exposure to these compounds through intake of fish species is a matter of concern, we recommend the continued monitoring of PFS levels in Asian developing countries.

Why toxic equivalency factors are not suitable for perfluoroalkyl chemicals

The pervasive nature of perfluoroalkyl chemicals in the environment has generated considerable interest for developing new strategies for risk assessment. In experimental animal models, exposure to perfluoroalkyl chemicals can cause developmental toxicity and hepatotoxicity. Peroxisome proliferator-activated receptor-α (PPARα) is required to mediate some but not all of these effects. Since PPARα has a role in mediating some of these effects, and there is some overlap in the type of toxicities elicited by perfluoroalkyl chemicals, it has been suggested that a scaling system analogous to the toxic equivalency factor (TEF) system used for polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), and polychlorinated biphenyls (PCB) could be used for perfluoroalkyl chemicals. However, evidence suggests that perfluoroalkyl chemicals can activate/interfere with other receptors, and there is reason to suggest the possibility of species differences in the response mediated by different receptors as well as qualitative differences in toxicities elicited by perfluoroalkyl chemicals. These differences and other data gaps preclude the development of a TEF approach for perfluoroalkyl chemicals.

Endocrine disrupting properties of perfluorooctanoic acid

Perfluoroalkyl acids (PFAAs) have attracted attention in recent years for their environmental ubiquity, as well as their toxicity. Several PFAAs are found in human tissues globally, as humans are exposed on a daily basis through intake of contaminated food, water, and air, irrespective of proximity to industry. Perfluorooctanoic acid (PFOA) is a PFAA shown to be developmentally toxic in mice, with broad and varied health consequences that may include long-lasting effects in reproductive tissues and metabolic reprogramming. To date, the only demonstrated mode of action by which the health effects of PFOA are mediated is via the activation of the peroxisome proliferator-activated receptor alpha (PPARα). The endogenous roles for this receptor, as well as the adverse outcomes of activation by exogenous agents during development, are currently under investigation. Recent studies suggest that PFOA may alter steroid hormone production or act indirectly, via ovarian effects, as a novel means of endocrine disruption. Here we review the existing literature on the known health effects of PFOA in animal models, focusing on sensitive developmental periods. To complement this, we also present epidemiologic health data, with the caveat that these studies largely address only associations between adult exposures and outcomes, rarely focusing on endocrine-specific endpoints, susceptible subpopulations, or windows of sensitivity. Further research in these areas is needed.

Polyfluorinated compounds: past, present, and future

Interest and concern about polyfluorinated compounds (PFCs), such as perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and an increasing number of other related compounds is growing as more is learned about these ubiquitous anthropogenic substances. Many of these compounds can be toxic, and they are regularly found in the blood of animals and humans worldwide. A great deal of research has been conducted in this area, but a surprising amount remains unknown about their distribution in the environment and how people ultimately become exposed. The utility of these compounds seems to ensure their continued use in one form or another for the foreseeable future, presenting a long-term challenge to scientists, industry leaders, and public health officials worldwide.

Perfluorinated chemicals in blood of residents in Wenzhou, China

Perfluorinated compounds (PFCs) are persistent organic pollutants ubiquitously distributed in the environment and human populations. Here we report PFC concentrations in the residents of Wenzhou City, which is characterized as the 'Footwear Capital' of China. Specifically, fifty serum samples collected from workers in a leather factory, fifty-five umbilical cord serum samples and fifteen serum samples from infertile men were analyzed. PFOS was one of the most frequently detected PFCs and showed the highest level. The mean serum levels of PFOS and PFOA of workers and infertile males were higher than the cord serum. PFOS concentration in cord serum increased with increase in age of the mother. Gender differences were significant both in worker serum samples and umbilical cord samples with higher levels found in males/male fetuses. Our findings suggested that PFOS, PFOA and PFHxS were widely distributed in Wenzhou residents, but occupational exposure was not the main source for workers.

Perfluorooctanoic acid (PFOA) acts as a tumor promoter on Syrian hamster embryo (SHE) cells

Perfluorooctane sulfonate (PFOS) (C(8)F(17)SO(3)) and perfluorooctanoic acid (PFOA) (C(8)HF(15)O(2)) are synthetic chemicals widely used in industrial applications for their hydrophobic and oleophobic properties. They are persistent, bioaccumulative, and toxic to mammalian species. Their widespread distribution on earth and contamination of human serum raised concerns about long-term side effects. They are suspected to be carcinogenic through a nongenotoxic mode of action, a mechanism supported by recent findings that PFOS induced cell transformation but no genotoxicity in Syrian hamster embryo (SHE) cells. In the present study, we evaluated carcinogenic potential of PFOA using the cell transformation assay on SHE cells. The chemical was applied alone or in combination with a nontransformant concentration of benzo[a]pyrene (BaP, 0.4 μM) in order to detect PFOA ability to act as tumor initiator or tumor promoter. The results showed that PFOA tested alone in the range 3.7 × 10(-5) to 300 μM did not induce SHE cell transformation frequency in a 7-day treatment. On the other side, the combination BaP/PFOA induced cell transformation at all PFOA concentrations tested, which revealed synergistic effects. No genotoxicity of PFOA on SHE cells was detected using the comet assay after 5 and 24 h of exposure. No significant increase in DNA breakage was found in BaP-initiated cells exposed to PFOA in a 7-day treatment. The whole results showed that PFOA acts as a tumor promoter and a nongenotoxic carcinogen. Cell transformation in initiated cells was observed at concentrations equivalent to the ones found in human serum of nonoccupationally and occupationally exposed populations. An involvement of PFOA in increased incidence of cancer recorded in occupationally exposed population cannot be ruled out.

Perfluorinated compounds differentially affect steroidogenesis and viability in the human adrenocortical carcinoma (H295R) in vitro cell assay

Perfluorinated compounds (PFCs) comprise a large class of man-made chemicals of which some are persistent and present throughout the ecosystem. This raises concerns about potential harmful effects of such PFCs on humans and the environment. In order to investigate the effects of potentially harmful PFCs on steroid hormone production, human adrenocortical H295R cells were exposed to three persistent PFCs including perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and perfluorononanoic acid (PFNA) at six different concentrations (6nM to 600μM) for 48h. Exposure to 600μM PFOS resulted in a dose-responsive increase in oestradiol as well as a smaller dose-responsive increase in progesterone and testosterone secretion measured using radioimmunoassay. The aromatase activity was not significantly altered by PFOS. Only small changes in hormone secretion were detected following exposure to PFOA and PFNA. Gene expression of CYP11A, quantified using qRT-PCR was decreased by all exposure doses of PFOA, whereas HMGR expression was decreased by 60nM PFNA. The viability markedly decreased by exposure to 600μM of PFOA or PFNA, but not PFOS. Flow cytometric analysis demonstrated a significant increase in apoptosis following exposure to PFNA at the highest concentration. We conclude that PFOS is capable of altering steroidogenesis in the H295R in vitro model by a mechanism other than changes in gene expression or activity of aromatase. Additionally, PFCs appear to differentially affect cell viability with induction of cell death via apoptosis at high doses of PFNA.

Comparison and evaluation of pharmacokinetics of PFOA and PFOS in the adult rat using a physiologically based pharmacokinetic model

Perfluoroalkyl acid carboxylates and sulfonates (PFAAs) have many consumer and industrial applications. The persistence and widespread distribution of PFAAs have brought them under intense scrutiny. Limited PK data for PFAAs is available for humans; however, toxicological and pharmacokinetic data exist for rats, which can be useful for cross-species extrapolation. In this work, PBPK models were developed for adult male and female rats to describe the pharmacokinetics of PFOA and PFOS. The models contain a description of saturable renal resorption, free fraction of chemical in plasma, and saturable binding in liver. Both male and female rat models for each chemical were consistent with available PK data resulting from IV, oral, and dietary dosing regimens. Predicted plasma concentration curves followed trends observed in experimental data, and model predictions were within a factor of two of experimental values. PFOA and PFOS rat model output is sensitive to parameters governing renal resorption, indicating that renal resorption is responsible for the long-half life. These models, along with the PFAA gestation and lactation models published in this issue, will help address concerns about possible health effects due to PFAA exposure in the fetus and neonate and will be useful in comparing PK across life stages.

Modulation of ammonium perfluorooctanoate-induced hepatic damage by genetically different PPARα in mice

Perfluorooctanoic acid is a ligand for peroxisome proliferator-activated receptor (PPARα). Ammonium perfluorooctanoate (APFO) at 0.1 and 0.3 mg/kg doses activated mouse PPARα, but not human PPARα. This study aimed to clarify whether milligram-order APFO can activate human PPARα, and the receptor is involved in APFO-induced chronic hepatic damage. Male Sv/129 wild-type (mPPARα), Pparα-null, and humanized PPARα (hPPARα) mice (8 weeks old) were divided into three groups. The first was treated with water and the other two with 1.0 and 5.0 mg/kg APFO for 6 weeks, orally, respectively. Both doses activated mouse and human PPARα to a similar or lower degree in the latter. APFO dose dependently increased hepatic triglyceride levels in Pparα-null and hPPARα mice, but conversely decreased those in mPPARα ones. APFO-induced hepatic damage differed markedly among the three genotyped groups: single-cell necrosis was observed in all genotyped mice; inflammatory cells and macrovesicular steatosis only in Pparα-null mice; and microvesicular steatosis and hydropic degenerations in hPPARα and Pparα-null mice. The molecular mechanism underlying these differences may be attributable to those of gene expressions involved in lipid homeostasis (PPARα, β- and ω-oxidation enzymes, and diacylglycerol acyltransferases) and uncoupling protein 2. Thus, milligram-order APFO activated both mouse and human PPARα in a different manner, which may reflect histopathologically different types of hepatic damage.

Prenatal perfluorooctanoic acid exposure in CD-1 mice: low-dose developmental effects and internal dosimetry

Perfluorooctanoic acid (PFOA) is an environmental contaminant that causes adverse developmental effects in laboratory animals. To investigate the low-dose effects of PFOA on offspring, timed-pregnant CD-1 mice were gavage dosed with PFOA for all or half of gestation. In the full-gestation study, mice were administered 0, 0.3, 1.0, and 3.0 mg PFOA/kg body weight (BW)/day from gestation days (GD) 1-17. In the late-gestation study, mice were administered 0, 0.01, 0.1, and 1.0 mg PFOA/kg BW/day from GD 10-17. Exposure to PFOA significantly (p < 0.05) increased offspring relative liver weights in all treatment groups in the full-gestation study and in the 1.0 mg PFOA/kg group in the late-gestation study. In both studies, the offspring of all PFOA-treated dams exhibited significantly stunted mammary epithelial growth as assessed by developmental scoring. At postnatal day 21, mammary glands from the 1.0 mg/kg GD 10-17 group had significantly less longitudinal epithelial growth and fewer terminal end buds compared with controls (p < 0.05). Evaluation of internal dosimetry in offspring revealed that PFOA concentrations remained elevated in liver and serum for up to 6 weeks and that brain concentrations were low and undetectable after 4 weeks. These data indicate that PFOA-induced effects on mammary tissue (1) occur at lower doses than effects on liver weight in CD-1 mice, an observation that may be strain specific, and (2) persist until 12 weeks of age following full-gestational exposure. Due to the low-dose sensitivity of mammary glands to PFOA in CD-1 mice, a no observable adverse effect level for mammary developmental delays was not identified in these studies.

Impact of perfluorooctanesulfonate and perfluorooctanoic acid on human peripheral leukocytes

Perfluorinated compounds (PFCs), such as perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA), are xenobiotics that can be detected worldwide in the environment, wildlife, and humans. So far, the immunotoxicity of PFCs has only been investigated in rodents, but not in humans. In this study, we explore the impact of PFOS and PFOA on selected functions of human leukocytes in vitro. PFOS induced a significant decrease of natural killer-cell activity and reduced the release of the pro-inflammatory cytokine TNF-α following lipopolysaccharide (LPS)-stimulation. Furthermore, the plasma PFOS concentrations (2.09-8.98 ng/ml) found in our study subjects correlated positively with the LPS-stimulated IL-6 release. PFOA augmented significantly calcitriol-induced monocytic differentiation of the HL-60 cell line. Additionally, there was a significant linear relationship between LPS-stimulated TNF-α and IL-6 release, and the plasma PFOA (1.20-6.92ng/ml) concentrations of the study subjects. In conclusion, the investigated PFCs affect human immune cells mainly with regard to natural killer-cell cytotoxicity and the pro-inflammatory cytokine release by stimulated macrophages.

Xenobiotic metabolism, disposition, and regulation by receptors: from biochemical phenomenon to predictors of major toxicities

To commemorate the 50th anniversary of the Society of Toxicology, this special edition article reviews the history and current scope of xenobiotic metabolism and transport, with special emphasis on the discoveries and impact of selected "xenobiotic receptors." This overall research realm has witnessed dynamic development in the past 50 years, and several of the key milestone events that mark the impressive progress in these areas of toxicological sciences are highlighted. From the initial observations regarding aspects of drug metabolism dating from the mid- to late 1800's, the area of biotransformation research witnessed seminal discoveries in the mid-1900's and onward that are remarkable in retrospect, including the discovery and characterization of the phase I monooxygenases, the cytochrome P450s. Further research uncovered many aspects of the biochemistry of xenobiotic metabolism, expanding to phase II conjugation and phase III xenobiotic transport. This led to hallmark developments involving integration of genomic technologies to elucidate the basis for interindividual differences in response to xenobiotic exposures and discovery of nuclear and soluble receptor families that selectively "sense" the chemical milieu of the mammalian cell and orchestrate compensatory changes in gene expression programming to accommodate complex xenobiotic exposures. This review will briefly summarize these developments and investigate the expanding roles of xenobiotic receptor biology in the underlying basis of toxicological response to chemical agents.