Influence of Perfluorinated Compounds on the Properties of Model Lipid Membranes

PFAS fluidize synthetic and bacterial lipid monolayers based on hydrophobicity and lipid charge

Poly- and Perfluoroalkyl substances (PFASs) are pollutants of emerging concern that persist in nature and pose environmental health and safety risks. PFAS disrupt biological membranes resulting in cellular inhibition, but the mechanism of disruption and the role of lipid composition remain unclear. We examine the role of phospholipid saturation and headgroup charge on the interactions between PFASs and phospholipid monolayers comprised of synthetic phosphocholine (PC) and phosphoglycerol (PG) lipids and prepared from bacteria membrane extracts rich in PG lipids from an environmentally relevant marine bacterium Alcanivorax borkumensis. When deposited on a buffered subphase containing PFAS, PFAS mixed within and fluidized zwitterionic and net-anionic monolayers leading to increases in monolayer compressibility that were driven by a combination of PFAS hydrophobicity and monolayer charge density. Differences in the monolayer response using saturated or unsaturated lipids are attributed to the ability of the unsaturated lipids to accommodate PFAS within 'void space' arising from the bent lipid tails. Similar fluidization and compressibility behavior were also observed in A. borkumensis lipid monolayers. This work provides new insight into PFAS partitioning into bacterial membranes and the effect PFAS have on the physicomechanical properties of zwitterionic and charged lipid monolayers.

Headgroup-Specific Interaction of Biological Lipid Monolayer/Water Interface with Perfluorinated Persistent Organic Pollutant (f-POP): As Observed with Interface-Selective Vibrational Spectroscopy

Perfluoro compounds are widely used in various manufacturing processes, which leads to their bioaccumulation and subsequent adverse effects on human health. Using interface-selective vibrational spectroscopy (heterodyne-detected vibrational sum frequency generation (HD-VSFG)), we have elucidated the molecular mechanism of the perturbation of lipid monolayers on the water surface using a prototype perfluorinated persistent organic pollutant, perfluoroheptanoic acid (PFHA). PFHA disrupts the well-ordered all-trans conformation of a cationic lipid (1,2-dipalmitoyl-3-trimethylammonium propane (DPTAP)) monolayer and reduces the interfacial electric field at the lipid/water interface. In contrast, the hydrophobic packing of an anionic lipid (1,2-dipalmitoyl-sn-glycero-3-phospoglycerol (DPPG)) monolayer remains largely unaffected in the presence of PFHA, though the interfacial electric field is reduced. For a zwitterionic lipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC))/water interface, both alkyl chain ordering and interfacial electric field are fairly perturbed by PFHA. Lipid headgroup-specific interaction of PFHA and the repulsive interaction of oleophobic fluoroalkyl chain with the lipid alkyl chains govern these distinct perturbations of the lipid monolayers on the water surface.

Interactions of particulate matter and pulmonary surfactant: Implications for human health

Particulate matter (PM), which is the primary contributor to air pollution, has become a pervasive global health threat. When PM enters into a respiratory tract, the first body tissues to be directly exposed are the cells of respiratory tissues and pulmonary surfactant. Pulmonary surfactant is a pivotal component to modulate surface tension of alveoli during respiration. Many studies have proved that PM would interact with pulmonary surfactant to affect the alveolar activity, and meanwhile, pulmonary surfactant would be adsorbed to the surface of PM to change the toxic effect of PM. This review focuses on recent studies of the interactions between micro/nanoparticles (synthesized and environmental particles) and pulmonary surfactant (natural surfactant and its models), as well as the health effects caused by PM through a few significant aspects, such as surface properties of PM, including size, surface charge, hydrophobicity, shape, chemical nature, etc. Moreover, in vitro and in vivo studies have shown that PM leads to oxidative stress, inflammatory response, fibrosis, and cancerization in living bodies. By providing a comprehensive picture of PM-surfactant interaction, this review will benefit both researchers for further studies and policy-makers for setting up more appropriate regulations to reduce the adverse effects of PM on public health.

Cholesterol-like Condensing Effect of Perfluoroalkyl Substances on a Phospholipid Bilayer

To understand the potential cytotoxicity of perfluoroalkyl substances (PFAS), we study their interactions with a model phospholipid bilayer membrane using molecular dynamics (MD) simulations. Four typical PFAS molecules are investigated, including perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and perfluorohexane sulfonate (PFHxS). All of these PFAS molecules are found to spontaneously penetrate the lipid bilayer within a short simulation time (a few nanoseconds). During the penetration process, further free-energy analysis reveals that a PFAS molecule encounters an energy barrier at the bilayer/water interface. To overcome this free-energy barrier, the PFAS molecule flips itself at the interface. We further investigate the influence of embedded PFAS molecules on the membrane properties. All of the embedded PFAS molecules are found to produce a cholesterol-like condensing effect on the lipid bilayer, which includes increases of the order parameters of lipid tails and the thickness of the lipid bilayer and a decrease of area per lipid. Moreover, the PFAS molecules are found to form hydrogen bonds with oxygen atoms at three different positions of a lipid molecule. Our work reveals the penetration pathway of PFAS molecules entering into a lipid bilayer. In addition, the cholesterol-like condensing effect induced by embedded PFAS molecules on model membranes is systematically investigated and discussed. Our simulations can help understand the physical mechanisms of PFAS cytotoxicity.

Monolayer behavior of pure F-DPPC and mixed films with DPPC studied by epifluorescence microscopy and infrared reflection absorption spectroscopy

The monolayer behavior of a l-DPPC derivative with a single fluorination in one of its terminal methyl groups (F-DPPC) at air-water interface was investigated by epifluorescence microscopy and infrared reflection absorption spectroscopy (IRRAS). Epifluorescence microscopy was utilized to study the shape and morphology of liquid-condensed (LC) domains observed upon compression of the film. IRRAS was employed for the determination of chain order and orientation. The shapes of LC-domains in a monolayer of F-DPPC are more dependent on the rate of compression than those of DPPC. The LC domains of F-DPPC display pronounced fractal growth patterns depending on the compression speed. The evolution of LC domain occurs under dominating electrostatic dipolar forces in F-DPPC. IRRAS measurements with the analysis of the frequency of the methylene stretching vibrations as a function of film compression show that the acyl chains in an F-DPPC monolayer in the LE-phase are more disordered than those in a DPPC film. The reason for the higher chain disorder in LE phase F-DPPC monolayers is a back folding of the fluorinated sn-2 chain terminus towards the air-water interface leading to larger molecular area requirement. Angular dependent IRRA spectra of monolayers at a surface pressure of 30 mN m^-1 show that in the LC phase DPPC and F-DPPC exhibit a similar tilt of the acyl chains of ca. 28-30 ° relative to the surface normal. F-DPPC is ideally miscible with l-DPPC-d₆₂ having the same chirality, as indicated by epifluorescence images and by IRRAS. However, the LC domains in an equimolar mixture of d-DPPC and F-DPPC having opposite chirality show multi-lobed complex domain patterns indicating chiral phase separation within LC domains.

An acute exposure to perfluorooctanoic acid causes non-reversible plasma membrane injury in HeLa cells

Health and environmental risks regarding perfluorooctanoic acid, a well-known perfluorinated compound, are still a subject of great concern. Ubiquitous exposure and disparity of results make it difficult to determine the underlying mechanism of action, especially at the cellular level. This study proposes an experimental design to assess the reversibility of adverse effects after a one-time exposure to the compound, in comparison with other more conventional timings. Complementary endpoints including total protein content, neutral red uptake and MTT reduction tests along with division rates and microscopic observations were evaluated in HeLa cells. In addition, PFOA quantification inside the cells was performed. The cellular effects exerted after 24 h exposure to perfluorooctanoic acid are non-reversible after a 48 h recovery period. In addition, we describe for the first time the induction of plasma membrane blebbing and the activation of membrane repair mechanisms after recovery from non-cytotoxic treatments with the compound. This experimental design has provided relevant information regarding the toxicity of this perfluorinated compound, relating all the adverse effects detected to its interaction with the plasma membrane.

Increased Cardiovascular Risk Associated with Chemical Sensitivity to Perfluoro-Octanoic Acid: Role of Impaired Platelet Aggregation

Perfluoro–alkyl substances (PFAS), particularly perfluoro–octanoic acid (PFOA), are persisting environmental chemicals showing bioaccumulation in human tissues. Recently, exposure to PFAS has been associated with increased prevalence of cardiovascular diseases (CVDs). However, a causal role of PFAS in atherosclerosis pathogenesis is under-investigated. Here, we investigated the effect of PFOA exposure on platelets’ function, a key player in atherosclerosis process. PFOA accumulation in platelets was evaluated by liquid chromatography-mass spectrometry. Changes in platelets’ membrane fluidity and activation after dose-dependent exposure to PFOA were evaluated by merocyanine 540 (MC540) and anti P-Selectin immune staining at flow cytometry, respectively. Intracellular calcium trafficking was analyzed with Fluo4M probe, time-lapse live imaging. Platelets’ aggregation state was also evaluated with Multiplate^® aggregometry analyzer in 48 male subjects living in a specific area of the Veneto region with high PFAS environmental pollution, and compared with 30 low-exposure control subjects. Platelets’ membrane was the major target of PFOA, whose dose-dependent accumulation was associated in turn with increased membrane fluidity, as expected by a computational model; increased activation at resting condition; and both calcium uptake and aggregation upon activation. Finally, exposed subjects had higher serum and platelets levels of PFOA, together with increased aggregation parameters at Multiplate^®, compared with controls. These data help to explain the emerging association between PFAS exposure and CVD.

Fluorocarbon Exposure Mode Markedly Affects Phospholipid Monolayer Behavior at the Gas/Liquid Interface: Impact on Size and Stability of Microbubbles

Although most phospholipid-shelled microbubbles (MBs) investigated for medical applications are stabilized by a fluorocarbon (FC) gas, information on the interactions between the phospholipid and FC molecules at the gas/water interface remains scarce. We report that the procedure of introduction of perfluorohexane (F-hexane), that is, either in the gas phase above dimyristoylphosphatidylcholine (DMPC) or dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers, or in the aqueous subphase, radically affects the compression isotherms. When introduced in the gas phase, F-hexane is rapidly incorporated in the interfacial film, but is also readily desorbed upon compression and eventually totally expelled from the phospholipid monolayers. By contrast, when introduced in the aqueous phase, F-hexane remains trapped at the interface. These dissimilar outcomes demonstrate that the phospholipid monolayer acts as a barrier that effectively hinders the transfer of the FC across the interfacial film. F-hexane was also found to significantly accelerate the adsorption kinetics of the phospholipids at the gas/water interface and to lower the interfacial tension, as assessed by bubble profile analysis tensiometry. The extent of these effects is more pronounced when F-hexane is provided from the gas phase. The size and stability characteristics of DMPC- and DPPC-shelled microbubbles were also found to depend on how the FC is introduced. As compared to reference MBs prepared under nitrogen only, introduction of F-hexane always causes a decrease in MB mean radius. However, while for DMPC this decrease depends on the F-hexane introduction procedure, it is independent from the procedure and most pronounced (from ∼2.0 μm to ∼1.0 μm) for DPPC. Introducing the FC in the gas phase has the strongest effect on MB half-life (t_1/2 = ∼1.8 and 6.8 h for DMPC and DPPC, respectively), as compared to when it is delivered through the aqueous phase (∼0.8 and ∼1.7 h). Fluorocarbonless reference DMPC and DPPC bubbles had a half-life of ∼0.5 and 0.8 h, respectively. The effects of F-hexane on MB characteristics are discussed with regard to the interactions between phospholipids and F-hexane and monolayer fluidization effect, as revealed by the Langmuir and tensiometric studies.

Contribution of Molecular Structure to Self-Assembling and Biological Properties of Bifunctional Lipid-Like 4-(N-Alkylpyridinium)-1,4-Dihydropyridines

The design of nanoparticle delivery materials possessing biological activities is an attractive strategy for the development of various therapies. In this study, 11 cationic amphiphilic 4-(N-alkylpyridinium)-1,4-dihydropyridine (1,4-DHP) derivatives differing in alkyl chain length and propargyl moiety/ties number and position were selected for the study of their self-assembling properties, evaluation of their cytotoxicity in vitro and toxicity on microorganisms, and the characterisation of their interaction with phospholipids. These lipid-like 1,4-DHPs have been earlier proposed as promising nanocarriers for DNA delivery. We have revealed that the mean diameter of freshly prepared nanoparticles varied from 58 to 513 nm, depending upon the 4-(N-alkylpyridinium)-1,4-DHP structure. Additionally, we have confirmed that only nanoparticles formed by 4-(N-dodecylpyridinium)-1,4-DHP derivatives 3 and 6, and by 4-(N-hexadecylpyridinium)-1,4-DHP derivatives 10 and 11 were stable after two weeks of storage. The nanoparticles of these compounds were found to be homogenous in size distribution, ranging from 124 to 221 nm. The polydispersity index (PDI) values of 1,4-DHPs samples 3, 6, 10, and 11 were in the range of 0.10 to 0.37. We also demonstrated that the nanoparticles formed by 4-(N-dodecylpyridinium)-1,4-DHP derivatives 3, 6, and 9, and 4-(N-hexadecylpyridinium)-1,4-DHP derivatives 10 and 11 had zeta-potentials from +26.07 mV (compound 6) to +62.80 mV (compound 11), indicating a strongly positive surface charge and confirming the relative electrostatic stability of these nanoparticle solutions. Transmission electron microscopy (TEM) images of nanoaggregates formed by 1,4-DHPs 3 and 11 confirmed liposome-like structures with diameters around 70 to 170 nm. The critical aggregation concentration (CAC) value interval for 4-(N-alkylpyridinium)-1,4-DHP was from 7.6 µM (compound 11) to 43.3 µM (compound 6). The tested 4-(N-alkylpyridinium)-1,4-DHP derivatives were able to quench the fluorescence of the binary 1,6-diphenyl-1,3,5-hexatriene (DPH)—1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) system, demonstrating hydrophobic interactions of 1,4-DHPs with phospholipids. Thus, 4-(N-dodecylpyridinium)-1,4-DHP derivative 3 quenched the fluorescence of the DPH–DPPC system more efficiently than the other 4-(N-alkylpyridinium)-1,4-DHP derivatives. Likewise the compound 3, also 4-(N-dodecylpyridinium)-1,4-DHP derivative 9 interacted with the phospholipids. Moreover, we have established that increasing the length of the alkyl chain at the quaternised nitrogen of the 4-(N-alkylpyridinium)-1,4-DHP molecule or the introduction of propargyl moieties in the 1,4-DHP molecule significantly influences the cytotoxicity on HT-1080 (human fibrosarcoma) and MH-22A (mouse hepatocarcinoma) cell lines, as well as the estimated basal cytotoxicity. Additionally, it was demonstrated that the toxicity of the 4-(N-alkylpyridinium)-1,4-DHP derivatives on the Gram-positive and Gram-negative bacteria species and eukaryotic microorganism depended on the presence of the alkyl chain length at the N-alkyl pyridinium moiety, as well as the number of propargyl groups. These lipid-like compounds may be proposed for the further development of drug formulations to be used in cancer treatment.

Phospholipid Levels Predict the Tissue Distribution of Poly- and Perfluoroalkyl Substances in a Marine Mammal

Exposure to poly- and perfluoroalkyl substances (PFASs) has been linked to many negative health impacts in humans and wildlife. Unlike neutral hydrophobic organic pollutants, many PFASs are ionic and have been hypothesized to accumulate in both phospholipids and protein-rich tissues. Here we investigate the role of phospholipids for PFAS accumulation by analyzing associations among concurrent measurements of phospholipid, total protein, total lipid and 24 PFASs in the heart, muscle, brain, kidney, liver, blubber, placenta and spleen of North Atlantic pilot whales (Globicephala melas). The sum of 24 PFASs ( ∑ 24 PFAS ) was highest in the liver (median 260 ng g^-1; interquartile range (IQR) 216-295 ng g^-1) and brain (86.0; IQR 54.5-91.3 ng g^-1), while phospholipid levels were highest in brain. The relative abundance of PFASs in the brain greatly increases with carbon chain lengths of 10 or greater, suggesting shorter-chained compounds may cross the blood-brain barrier less efficiently. Phospholipids were significant predictors of the tissue distribution of the longest-chained PFASs: perfluorodecanesulfonate (PFDS), perfluorododecanoate (PFDoA), perfluorotridecanoate (PFTrA), and perfluorotetradecanoic acid (PFTA) (r_s = 0.5-0.6). In all tissues except the brain, each 1 mg g^-1 increase in phospholipids led to a 12%-25% increase in the concentration of each PFAS. We conclude that partitioning to phospholipids is an important mechanism of bioaccumulation for long-chained PFASs in marine mammals.

Stabilization of Liposomes by Perfluorinated Compounds

Perfluorinated compounds (PFCs) are emerging persistent environmental contaminants that may be toxic to animals and humans. To gain fundamental insights into the mechanism of their toxicity, the interactions of phosphocholine (PC) liposomes as model membranes were studied with three types of PFCs, including perfluorooctanoic acid, perfluorooctane sulfonate, and perfluorohexanesulfonic acid potassium salt, together with three common surfactants: sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and sodium 1-heptanesulfonate (SHS). The interactions were systematically characterized by zeta potential measurement, dynamic light scattering, negative-stain transmission electron microscopy, and fluorescence spectroscopy. Unmodified liposomes, calcein-loaded liposomes, and Laurdan dye-embedded liposomes were all tested. By gradually increasing the temperature, the three PFCs and SHS decreased the leakage of calcein-loaded 1,2-dipalmitoyl-sn-glycero-3-phosphocholine liposomes, whereas SDS and CTAB increased the leakage. The PFCs that affected the lipid membranes stronger than SHS were attributable to their perfluoroalkyl carbon chains. Packing of the lipids was further studied using Laurdan dye as a probe. Calcein leakage tests also indicated that PFCs inhibited lipid membrane leakage induced by inorganic nanoparticles such as silica and gold nanoparticles. This study confirmed the similar effect of the PFCs as cholesterol in affecting membrane properties and would be helpful for understanding the interaction mechanism of PFCs and cell membranes.

Partitioning and Accumulation of Perfluoroalkyl Substances in Model Lipid Bilayers and Bacteria

Perfluoroalkyl substances (PFAS) are ubiquitous and persistent environmental contaminants, yet knowledge of their biological effects and mechanisms of action is limited. The highest aqueous PFAS concentrations are found in areas where bacteria are relied upon for functions such as nutrient cycling and contaminant degradation, including fire-training areas, wastewater treatment plants, and landfill leachates. This research sought to elucidate one of the mechanisms of action of PFAS by studying their uptake by bacteria and partitioning into model phospholipid bilayer membranes. PFAS partitioned into bacteria as well as model membranes (phospholipid liposomes and bilayers). The extent of incorporation into model membranes and bacteria was positively correlated to the number of fluorinated carbons. Furthermore, incorporation was greater for perfluorinated sulfonates than for perfluorinated carboxylates. Changes in zeta potential were observed in liposomes but not bacteria, consistent with PFAS being incorporated into the phospholipid bilayer membrane. Complementary to these results, PFAS were also found to alter the gel-to-fluid phase transition temperature of phospholipid bilayers, demonstrating that PFAS affected lateral phospholipid interactions. This investigation compliments other studies showing that sulfonated PFAS and PFAS with more than seven fluorinated carbons have a higher potential to accumulate within biota than carboxylated and shorter-chain PFAS.

Cholesterol-like effects of a fluorotelomer alcohol incorporated in phospholipid membranes

Fluorocarbon amphiphiles are anthropogenic substances widely used in diverse applications such as food packaging, clothing or cookware. Due to their widespread use and non-biodegradability, these chemicals are now ubiquitous in the natural world with high propensity to bioaccumulate in biological membranes, wherein they may affect microscopic properties. Here, we test the hypothesis that a typical fluorocarbon amphiphile can affect lipid membranes similarly to cholesterol by investigating the effect of 1H,1H,2H,2H-perfluoro-1-decanol (8:2 FTOH) on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membranes. Using solid-state nuclear magnetic resonance spectroscopy, differential scanning calorimetry and confocal microscopy, we present a consistent set of independent experimental evidences supporting this hypothesis, namely that upon incorporation of 8:2 FTOH, (i) a condensing effect on the acyl chains occurs in the fluid phase, (ii) coexistence of two membrane phases is observed below melting, and (iii) the melting temperature of DPPC varies no more than approximately ±1 °C up to a concentration of 40 mol% of 8:2 FTOH. The condensing effect is quantified by means of advanced dipolar recoupling solid-state NMR experiments and is found to be of approximately half the magnitude of the cholesterol effect at the same concentration.

Are additive effects of dietary surfactants on intestinal tight junction integrity an overlooked human health risk? - A mixture study on Caco-2 monolayers

Surfactants may cause dysfunction of intestinal tight junctions (TJs), which is a common feature of intestinal autoimmune diseases. Effects of dietary surfactants on TJ integrity, measured as trans-epithelial resistance (TEER), were studied in Caco-2 cell monolayers. Cytotoxicity was assessed as apical LDH leakage. Monolayers were apically exposed for 60 min to the dietary surfactants solanine and chaconine (SC, potato glycoalkaloids, 0-0.25 mM), perfluorooctane sulfonic acid (PFOS, industrial contaminant, 0-0.8 mM), and sucrose monolaurate (SML, food emulsifier E 473, 0-2.0 mM) separately and as a mixture. Dose-response modelling of TEER EC₅₀ showed that SC were 2.7- and 12-fold more potent than PFOS and SML, respectively. The mixture was composed of 1 molar unit SC, 2.7 units PFOS and 12 units SML ("SC TEER equivalent" proportions 1:1:1). Mixture exposure (0-0.05 mM SC equivalents) dose-response modelling suggested additive action on TJ integrity. Increasing SC and SML concentrations caused increased LDH leakage, but PFOS decreased LDH leakage at intermediate exposure concentrations. In the mixture PFOS appeared to protect from extensive SC- and SML-induced LDH leakage. Complex mixtures of surfactants in food may act additively on intestinal TJ integrity, which should be considered in risk assessment of emulsifier authorisation for use in food production.

In silico approach to investigating the adsorption mechanisms of short chain perfluorinated sulfonic acids and perfluorooctane sulfonic acid on hydrated hematite surface

Short chain perfluorinated sulfonic acids (PFSAs) that were introduced as alternatives for perfluorooctane sulfonic acid (PFOS) have been widely produced and used. However, few studies have investigated the environmental process of short chain PFSAs, and the related adsorption mechanisms still need to be uncovered. The water-oxide interface is one of the major environmental interfaces that plays an important role in affecting the adsorption behaviour and transport potential of the environmental pollutant. In this study, we performed molecular dynamics simulations and quantum chemistry calculations to investigate the adsorption mechanisms of five PFSAs and their adsorption on hydrated hematite surface as well. Different to the vertical configuration reported for PFOS on titanium oxide, all PFSAs share the same adsorption configuration as the long carbon chains parallel to the surface. The formation of hydrogen bonds between F and inter-surface H helps to stabilize the unique configuration. As a result, the sorption capacity increases with increasing C-F chain length. Moreover, both calculated adsorption energy and partial density of states (PDOS) analysis demonstrate a PFSAs adsorption mechanism in between physical and chemical adsorption because the hydrogen bonds formed by the overlap of F (p) orbital and H (s) orbital are weak intermolecular interactions while the physical adsorption are mainly ascribed to the electrostatic interactions. This massive calculation provides a new insight into the pollutant adsorption behaviour, and in particular, may help to evaluate the environmental influence of pollutants.

Does perfluorooctane sulfonate (PFOS) act as chemosensitizer in zebrafish embryos?

Earlier studies have shown that perfluorooctane sulfonate (PFOS) increases the toxicity of other chemicals by enhancing their uptake by cells and tissues. The present study aimed at testing whether the underlying mechanism of enhanced uptake of chemicals by zebrafish (Danio rerio) embryos in the presence of PFOS is by interference of this compound with the cellular efflux transporter Abcb4. Modifications of uptake/clearance and toxicity of two Abcb4 substrates, the fluorescent dye rhodamine B (RhB) and vinblastine, by PFOS were evaluated using 24 and 48h post-fertilization (hpf) embryos. Upon 90min exposure of 24hpf embryos to 1μM RhB and different PFOS concentrations (3-300μM) accumulation of RhB in zebrafish was increased by up to 11.9-fold compared to controls, whereas RhB increases in verapamil treatments were 1.7-fold. Co-administration of PFOS and vinblastine in exposures from 0 to 48hpf resulted in higher vinblastine-caused mortalities in zebrafish embryos indicating increased uptake of this compound. Interference of PFOS with zebrafish Abcb4 activity was further studied using recombinant protein obtained with the baculovirus expression system. PFOS lead to a concentration-dependent decrease of the verapamil-stimulated Abcb4 ATPase activity; at higher PFOS concentrations (250, 500μM), also the basal ATPase activity was lowered indicating PFOS to be an Abcb4 inhibitor. In exposures of 48hpf embryos to a very high RhB concentration (200μM), accumulation of RhB in embryo tissue and adsorption to the chorion were increased in the presence of 50 or 100μM PFOS. In conclusion, the results indicate that PFOS acts as inhibitor of zebrafish Abcb4; however, the exceptionally large PFOS-caused effect amplitude of RhB accumulation in the 1μM RhB experiments and the clear PFOS effects in the experiments with 200μM RhB suggest that an additional mechanism appears to be responsible for the potential of PFOS to enhance uptake of Abcb4 substrates.

Effect of PFOA/PFOS pre-exposure on the toxicity of the herbicides 2,4-D, Atrazine, Diuron and Paraquat to a model aquatic photosynthetic microorganism

Pre-exposure to the perfluorinated compounds (PFCs) perfluorooctano sulphonate (PFOS) or perfluorooctanoic acid (PFOA) on the toxicity of four herbicides of different types and modes of action towards the self-luminescent recombinant cyanobacterium Anabaena CPB4337 was evaluated. The rationale of the approach is that both PFOS and PFOA as surfactants are known to modify cell membrane properties and pre-exposure to them might alter herbicide toxicity towards the cyanobacterium. Anabaena CPB4337 was pre-exposed during 72h to PFOS or PFOA at a concentration below their no observed effect concentration (NOEC). After pre-exposure, cells were exposed to increasing concentrations of 2,4-D Atrazine, Diuron and Paraquat and the toxicity was compared to that of non-pre-exposed ones. The data clearly showed that PFCs pre-treatment significantly altered the toxicity of the tested herbicides. However the effects resulting from PFOA and PFOS pre-exposure were not homogeneous for all the herbicides. In general PFOA pre-exposure resulted in increased herbicide toxicity except for atrazine, while PFOS pre-exposure resulted in increased toxicity for paraquat and diuron, and reduced toxicity for atrazine with no significant effect on 2,4-D toxicity. The strongest modifying effect was found for paraquat whose toxicity doubled with PFOA pre-exposure. Further analysis of membrane properties by flow cytometry revealed that both PFOA and PFOS were able to modify membrane integrity and membrane potential of Anabaena CPB4337 at the concentrations used in the pre-exposure experiments. These results reveal relevant indirect effects of PFCs pollution with eco-toxicological implications.

Perfluorooctanoic acid rigidifies a model lipid membrane

We report a combined dynamic light scattering and neutron spin-echo (NSE) study on vesicles composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine under the influence of varying amounts of perfluorooctanoic acid. We study local lipid bilayer undulations using NSE on time scales up to 200 ns. Similar to the effect evoked by cholesterol, we attribute the observed lipid bilayer stiffening to a condensing effect of the perfluorinated compound on the membrane.

Disruption of phosphatidylcholine monolayers and bilayers by perfluorobutane sulfonate

Perfluoroalkyl acids (PFAAs) are persistent environmental contaminants resistant to biological and chemical degradation due to the presence of carbon-fluorine bonds. These compounds exhibit developmental toxicity in vitro and in vivo. The mechanisms of toxicity may involve partitioning into lipid bilayers. We investigated the interaction between perfluorobutane sulfonate (PFBS), an emerging PFAA, and model phosphatidylcholine (PC) lipid assemblies (i.e., dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholine) using fluorescence anisotropy and Langmuir monolayer techniques. PFBS decreased the transition temperature and transition width of PC bilayers. The apparent membrane partition coefficients ranged from 4.9 × 10(2) to 8.2 × 10(2). The effects on each PC were comparable. The limiting molecular area of PC monolayers increased, and the surface pressure at collapse decreased in a concentration-dependent manner. The compressibility of all three PCs was decreased by PFBS. In summary, PFBS disrupted different model lipid assemblies, indicating potential for PFBS to be a human toxicant. However, the effects of PFBS are not as pronounced as those seen with longer chain PFAAs.

Gene Expression Profiling in Wild-Type and PPARα-Null Mice Exposed to Perfluorooctane Sulfonate Reveals PPARα-Independent Effects

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, its 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 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 PPARα-independent effects as well.

Partitioning of perfluorooctanoate into phosphatidylcholine bilayers is chain length-independent

The chain length dependence of the interaction of PFOA, a persistent environmental contaminant, with dimyristoyl- (DMPC), dipalmitoyl- (DPPC) and distearoylphosphatidylcholine (DSPC) was investigated using steady-state fluorescence anisotropy spectroscopy, differential scanning calorimetry (DSC) and dynamic light scattering (DLS). PFOA caused a linear depression of the main phase transition temperature T(m) while increasing the width of the phase transition of all three phosphatidylcholines. Although PFOA's effect on T(m) and the transition width decreased in the order DMPC>DPPC>DSPC, its relative effect on the phase behavior was largely independent of the phosphatidylcholine. PFOA caused swelling of DMPC but not DPPC and DSPC liposomes at 37 degrees C in the DLS experiments, which suggests that PFOA partitions more readily into bilayers in the fluid phase. These findings suggest that PFOA's effect on the phase behavior of phosphatidylcholines depends on the cooperativity and state (i.e., gel versus liquid phase) of the membrane. DLS experiments are also consistent with partial liposome solubilization at PFOA/lipid molar ratios>1, which suggests the formation of mixed PFOA-lipid micelles.

Model and cell membrane partitioning of perfluorooctanesulfonate is independent of the lipid chain length

Perfluorooctanesulfonic acid (PFOS) is a persistent environmental pollutant that may cause adverse health effects in humans and animals by interacting with and disturbing of the normal properties of biological lipid assemblies. To gain further insights into these interactions, we investigated the effect of PFOS potassium salt on dimyristoyl- (DMPC), dipalmitoyl- (DPPC) and distearoylphosphatidylcholine (DSPC) model membranes using fluorescence anisotropy measurements and differential scanning calorimetry (DSC) and on the cell membrane of HL-60 human leukemia cells and freshly isolated rat alveolar macrophages using fluorescence anisotropy measurements. PFOS produced a concentration-dependent decrease of the main phase transition temperature (T(m)) and an increased peak width (DeltaT(w)) in both the fluorescence anisotropy and the DSC experiments, with a rank order DMPC>DPPC>DSPC. PFOS caused a fluidization of the gel phase of all phosphatidylcholines investigated, but had the opposite effect on the liquid-crystalline phase. The apparent partition coefficients of PFOS between the phosphatidylcholine bilayer and the bulk aqueous phase were largely independent of the phosphatidylcholine chain length and ranged from 4.4x10(4) to 8.8x10(4). PFOS also significantly increased the fluidity of membranes of cells. These findings suggest that PFOS readily partitions into lipid assemblies, independent of their composition, and may cause adverse biological effects by altering their fluidity in a manner that depends on the membrane cooperativity and state (e.g., gel versus liquid-crystalline phase) of the lipid assembly.

Gene expression profiling in the liver and lung of perfluorooctane sulfonate-exposed mouse fetuses: comparison to changes induced by exposure to perfluorooctanoic acid

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmental contaminants found in the tissues of humans and wildlife. They are activators of peroxisome proliferator-activated receptor-alpha (PPAR alpha) and exhibit hepatocarcinogenic potential in rats. PFOS and PFOA are also developmental toxicants in rodents and PFOS has been shown to induce pulmonary deficits in rat offspring. Pregnant CD-1 mice were dosed with 0, 5, or 10mg/kg PFOS from gestation days 1-17. Transcript profiling was conducted on the fetal liver and lung. Results were contrasted to data derived from a previous PFOA study. PFOS-dependent changes were primarily related to activation of PPAR alpha. No remarkable differences were found between PFOS and PFOA. Given that PPAR alpha signaling is required for neonatal mortality in PFOA-treated mice but not those exposed to PFOS, the neonatal mortality observed for PFOS may reflect functional deficits related to the physical properties of the chemical rather than to transcript alterations.

Polarization modulation infrared reflection-absorption spectroscopy studies of the influence of perfluorinated compounds on the properties of a model biological membrane

A combination of the Langmuir-Blodgett and Langmuir-Schaefer techniques has been used to build a 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayer at a Au(111) electrode surface with hydrogen-substituted acyl chains in the top leaflet (solution side) and deuterium-substituted acyl chains in the bottom leaflet (gold side). Polarization modulation infrared reflection-absorption spectroscopy was used to determine changes in the conformation and orientation of the acyl chains of DMPC caused by the incorporation of two selected perfluorinated compounds, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), into the top leaflet of the bilayer. The incorporation of perfluorinated compounds into the DMPC bilayer caused a broadening of the methylene peaks and a shift in the methylene band positions toward higher frequencies. In addition, the tilt angle of the acyl chains decreased in comparison to the tilt angle of a pure DMPC bilayer. The reported tilt angles were smaller upon insertion of PFOS ( approximately 24 degrees ) than in the presence of PFOA ( approximately 30 degrees ). Overall, the results show that the incorporation of the perfluorinated acids has an effect on the bilayer similar to that of cholesterol by increasing the membrane fluidity and thickness due to a decrease in the tilt angle of the acyl chains.