Comparison of gene expression methods to identify genes responsive to perfluorooctane sulfonic acid

Covalent binding of fluorotelomer unsaturated aldehydes (FTUALs) and carboxylic acids (FTUCAs) to proteins

Fluorotelomer unsaturated carboxylic acids and aldehydes (FTUCAs and FTUALs) are intermediate compounds that form from the biotransformation of fluorotelomer-based compounds. Previous evidence that FTUCAs and FTUALs bind to biological nucleophiles has indicated that protein binding might give rise to toxicity resulting from protein function disruption. The current study assesses the reactivity of FTUALs and FTUCAs by probing the covalent interactions of FTUALs and FTUCAs with proteins present in rat liver microsomes and bovine blood plasma. The FTUALs exhibited significant levels of protein covalent binding, with binding levels ranging from 20.1 (±2.8)% to 71.3 (±19.5)% in microsomes and 24.0 (±1.5)% to 82.5 (±14.0)% in blood plasma. By contrast, the FTUCAs did not exhibit any apparent covalent binding. Bovine serum albumin (BSA) was extracted and isolated from the plasma after incubation of 8:2 FTUAL (5-100 μM). Electrospray ionization mass spectrometry (ESI-MS) was used to investigate the stoichiometry of 8:2 FTUAL covalently bound to BSA; three measurable FTUAL adducts were formed with BSA. To compare the percent binding results from the FTUAL microsome incubation experiments, 8:2 FTOH was incubated in microsomes to determine the protein binding associated with the biotransformation of 8:2 FTOH. Results from this study showed that the biotransformation of 8:2 FTOH yielded 26.1 (±3.0)% binding, and was statistically similar to the percent binding associated with 8:2 FTUAL exposure (p > 0.05), indicating that the binding of 8:2 FTUAL to proteins might be a primary fate in the biotransformation of 8:2 FTOH.

Transcriptional effects of perfluorinated compounds in rat hepatoma cells

Perfluorooctanesulfonate (PFOS) is the terminal degradation product of many commercially used perfluorinated compounds, and most of the toxicity testing to date has focused on its potential biological effects. While PFOS has been extensively studied, other PFCs including replacement chemicals such as perfluorobutanesulfonate (PFBS) and perfluorobutyric acid (PFBA), have not been well characterized. Despite the relative lack of data available on these other PFCs it has been assumed that they will cause similar or lesser effects than PFOS. This study compared the effects of 10 PFCs routinely found in the environment on mRNA abundance of 7 genes related to processes known to be affected by PFOS, such as fatty acid and cholesterol synthesis, and thyroid development. Rat H4IIE hepatoma cells were exposed and changes in mRNA abundance were quantified by real-time PCR. Significant changes in mRNA abundance were observed. The effects caused by the shorter chain replacement chemicals differed significantly from those caused by PFOS or PFOA. Furthermore, not all of the PFCs caused the same effects, and changes could not simply be attributed to chain-length or functional group. These differences could mean that these replacement chemicals do not act through the same mechanisms as the more studied PFOS and PFOA.

Chronic toxicity of fluorotelomer acids to Daphnia magna and Chironomus dilutus

Saturated and unsaturated fluorotelomer carboxylic acids (fluorotelomer acids: FTAs) represent important intermediates in the degradation of fluorotelomer alcohols to perfluorinated carboxylic acids (PFCAs). Recent studies have detected FTAs at low concentrations (ng/L) in precipitation and surface waters; however, information regarding chronic toxicity is lacking. The present study assessed the chronic toxicity of the 8:2 saturated fluorotelomer carboxylic acid (8:2 FTCA) to Chironomus dilutus and the 10:2 saturated and unsaturated fluorotelomer carboxylic acids (10:2 FTCA and 10:2 fluorotelomer unsaturated carboxylic acid [FTuCA]) to Daphnia magna in separate life-cycle tests. In D. magna tests the FTCA was consistently more toxic than the FTuCA. Lethal concentrations (LC50s) were 150 and >60 microg/L for FTuCA and FTCA, respectively. Reproduction was significantly reduced relative to the controls, with respective median effective concentrations (EC50s) for time to first brood and mean number of offspring/female of 287 and 214 microg/L for FTuCA and 50 and 48 microg/L for FTCA. In tests with C. dilutus, EC50s for survival and growth at 20 d were 2,610 and 1,250 microg/L. Total emergence and time to first emergence, the most sensitive endpoints, yielded EC50s of 440 and 890 microg/L. Few adults emerged and no reproduction occurred at the two highest concentrations (600 and 1540 microg/L). Mean number of eggs/female was not affected. These results represent the first chronic toxicity data for FTCAs and additional evidence that FTCAs are more toxic than some PFCAs. While the results indicate that current environmental concentrations of FTAs likely pose negligible risk to aquatic biota, additional quantification of FTAs in surface waters and assessment of their toxicity is needed before meaningful assessments of potential risks to aquatic biota are possible.

Total fluorine, extractable organic fluorine, perfluorooctane sulfonate and other related fluorochemicals in liver of Indo-Pacific humpback dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) from South China

The concentrations of 10 PFCs (perfluorinated compounds: PFOS, PFHxS, PFOSA, N-EtFOSA, PFDoDA, PFUnDA, PFDA, PFNA, PFOA, and PFHpA) were measured in liver samples of Indo-Pacific humpback dolphins (Sousa chinensis) (n=10) and finless porpoises (Neophocaena phocaenoides) (n=10) stranded in Hong Kong between 2003 and 2007. PFOS was the dominant PFC in the tissues at concentrations ranging at 26-693 ng/g ww in dolphins and 51.3-262 ng/g ww in porpoises. A newly developed combustion ion chromatography for fluorine was applied to measure total fluorine (TF) and extractable organic fluorine (EOF) in these liver samples to understand PFC contamination using the concept of mass balance analysis. Comparisons between the amounts of known PFCs and EOF in the livers showed that a large proportion (approximately 70%) of the organic fluorine in both species is of unknown origin. These investigations are critical for a comprehensive assessment of the risks of these compounds to humans and other receptors.

Perfluoroalkyl Acids: A Review of Monitoring and Toxicological Findings

In recent years, human and wildlife monitoring studies have identified perfluoroalkyl acids (PFAA) worldwide. This has led to efforts to better understand the hazards that may be inherent in these compounds, as well as the global distribution of the PFAAs. Much attention has focused on understanding the toxicology of the two most widely known PFAAs, perfluorooctanoic acid, and perfluorooctane sulfate. More recently, research was extended to other PFAAs. There has been substantial progress in understanding additional aspects of the toxicology of these compounds, particularly related to the developmental toxicity, immunotoxicity, hepatotoxicity, and the potential modes of action. This review provides an overview of the recent advances in the toxicology and mode of action for PFAAs, and of the monitoring data now available for the environment, wildlife, and humans. Several avenues of research are proposed that would further our understanding of this class of compounds.

The applicability of biomonitoring data for perfluorooctanesulfonate to the environmental public health continuum

Perfluorooctanesulfonate and its salts (PFOS) are derived from perfluorooctanesulfonyl fluoride, the basic chemical building block for many sulfonyl-based fluorochemicals used as surfactants and for their repellent properties. PFOS is highly persistent in the environment and has a long serum elimination half-life in both animals and humans. PFOS has been detected globally in the environment and in blood serum in various populations throughout the world, with the majority of human sampling done in the United States and Japan. The mechanisms and pathways leading to the presence of PFOS in human blood are not well characterized but likely involve both direct exposures to PFOS or chemicals and materials that can degrade to PFOS, either in the environment or from industrial and commercial uses. In 2000 the 3M Company, a major manufacturer, announced a phaseout of PFOS-related materials. Animal studies indicate that PFOS is well absorbed orally and distributes mainly in blood serum and the liver. Several repeat-dose toxicology studies in animals consistently demonstrated that the liver is the primary target organ. In addition there is a steep dose response for mortality in sexually mature rats and primates as well as in neonatal rats and mice exposed in utero. Several biomonitoring research needs that have been identified on PFOS include additional data from general populations pertaining to other matrices besides blood; matched serum and urine samples from humans and research animals; and comparison of whole blood, serum, and plasma concentrations from the same individuals.

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.