Interactions of perfluorooctanoic acid and perfluorooctanesulfonic acid with serum albumins by native mass spectrometry, fluorescence and molecular docking

Quantitative cross-species comparison of serum albumin binding of per- and polyfluoroalkyl substances from five structural classes

Per- and polyfluoroalkyl substances (PFAS) are a class of over 8000 chemicals, many of which are persistent, bioaccumulative, and toxic to humans, livestock, and wildlife. Serum protein binding affinity is instrumental in understanding PFAS toxicity, yet experimental binding data is limited to only a few PFAS congeners. Previously, we demonstrated the usefulness of a high-throughput, in vitro differential scanning fluorimetry assay for determination of relative binding affinities of human serum albumin for 24 PFAS congeners from 6 chemical classes. In the current study, we used this assay to comparatively examine differences in human, bovine, porcine, and rat serum albumin binding of 8 structurally informative PFAS congeners from 5 chemical classes. With the exception of the fluorotelomer alcohol 1H, 1H, 2H, 2H-perfluorooctanol (6:2 FTOH), each PFAS congener bound by human serum albumin was also bound by bovine, porcine, and rat serum albumin. The critical role of the charged functional headgroup in albumin binding was supported by the inability of albumin of each species tested to bind 6:2 FTOH. Significant interspecies differences in serum albumin binding affinities were identified for each of the bound PFAS congeners. Relative to human albumin, perfluoroalkyl carboxylic and sulfonic acids were bound with greater affinity by porcine and rat serum albumin, and the perfluoroalkyl ether acid congener bound with lower affinity to porcine and bovine serum albumin. These comparative affinity data for PFAS binding by serum albumin from human, experimental model, and livestock species reduce critical interspecies uncertainty and improve accuracy of predictive bioaccumulation and toxicity assessments for PFAS.

Modulating the ion-transfer electrochemistry of perfluorooctanoate with serum albumin and β-cyclodextrin

Per- and polyfluoroalkyl substances (PFAS) are durable synthetic pollutants that persist in the environment and resist biodegradation. Ion-transfer electrochemistry at aqueous-organic interfaces is a simple strategy for the detection of ionised PFAS. Herein, we investigate the modulation of the ion transfer voltammetry of perfluorooctanoate (PFOA) at liquid-liquid micro-interface arrays by aqueous phase bovine serum albumin (BSA) or β-cyclodextrin (β-CD) and examine the determination of association constants for these binding interactions. By tracking the ion transfer current due to ionised, uncomplexed PFOA as a function of BSA or β-CD concentration, titration curves are produced. Fitting of a binding isotherm to these data provides the association constants. The association constant of PFOA with the BSA determined in this way was ca. 105 M-1 assuming a 1 : 1 binding. Likewise, the association constant for PFOA with β-CD was ca. 104 M-1 for a 1 : 1 β-CD-PFOA complex. Finally, the simultaneous effect of both BSA and β-CD on the ion transfer voltammetry of PFOA was studied, showing clearly that PFOA bound to BSA is released (de-complexed) upon addition of β-CD. The results presented here show ion transfer voltammetry as a simple strategy for the study of molecular and biomolecular binding of ionised PFAS and is potentially useful in understanding the affinity of different PFAS with aqueous phase binding agents such as proteins and carbohydrates.

Potential toxic effects of perfluorobutanesulfonyl fluoride analysis based on multiple-spectroscopy techniques and molecular modelling analysis

Perfluorobutanesulfonyl fluoride (PBSF) has been used in the manufacture of fluorochemicals. Since PBSF is not biodegradable, the predicted environmental levels of PBSF are also expected to rise over time. In recent years, there has been a rise in the levels of PBSF in humans. In order to clarify the impact of PBSF on the accumulation of substances in the human body, we examined the interaction mechanism between PBSF and bovine serum albumin (BSA). To investigate the interaction mechanism between PBSF and BSA, we utilized a range of methods including UV-visible spectrophotometry, fluorescence spectroscopy, circular dichroism, molecular docking simulation, and molecular dynamics (MD) simulation. The inherent fluorescence of BSA was effectively suppressed by PBSF through fluorescence quenching analysis, using a static mechanism. The Ka value of 1.34 × 105 mol-1 L indicated a strong binding between PBSF and BSA. Further analysis of the interaction between PBSF and BSA involved examining thermodynamic parameters, fluorescence resonance energy transfer, and conducting other theoretical calculations. These investigations produced results that were in strong accordance with the experimental observations. The participation of hydrophobic interactions between BSA and PBSF was uncovered through molecular docking and MD simulation investigations. Furthermore, this investigation explored the impact of copper ions (Cu2+) and calcium ions (Ca2+) on the interaction between PBSF and BSA, establishing a vital basis for comprehending the mechanism by which PBSF affects proteins in the human surroundings.

Binding Affinity and Mechanism of Six PFAS with Human Serum Albumin: Insights from Multi-Spectroscopy, DFT and Molecular Dynamics Approaches

Per- and Polyfluoroalkyl Substances (PFAS) bioaccumulate in the human body, presenting potential health risks and cellular toxicity. Their transport mechanisms and interactions with tissues and the circulatory system require further investigation. This study investigates the interaction mechanisms of six PFAS with Human Serum Albumin (HSA) using multi-spectroscopy, DFT and a molecular dynamics approach. Multi-spectral analysis shows that perfluorononanoic acid (PFNA) has the best binding capabilities with HSA. The order of binding constants (298 K) is as follows: "Perfluorononanoic Acid (PFNA, 7.81 × 106 L·mol-1) > Perfluoro-2,5-dimethyl-3,6-dioxanonanoic Acid (HFPO-TA, 3.70 × 106 L·mol-1) > Perfluorooctanoic Acid (PFOA, 2.27 × 105 L·mol-1) > Perfluoro-3,6,9-trioxadecanoic Acid (PFO3DA, 1.59 × 105 L·mol-1) > Perfluoroheptanoic Acid (PFHpA, 4.53 × 103 L·mol-1) > Dodecafluorosuberic Acid (DFSA, 1.52 × 103 L·mol-1)". Thermodynamic analysis suggests that PFNA and PFO3DA's interactions with HSA are exothermic, driven primarily by hydrogen bonds or van der Waals interactions. PFHpA, DFSA, PFOA, and HFPO-TA's interactions with HSA, on the other hand, are endothermic processes primarily driven by hydrophobic interactions. Competitive probe results show that the main HSA-PFAS binding site is in the HSA structure's subdomain IIA. These findings are also consistent with the findings of molecular docking. Molecular dynamics simulation (MD) analysis further shows that the lowest binding energy (-38.83 kcal/mol) is fund in the HSA-PFNA complex, indicating that PFNA binds more readily with HSA. Energy decomposition analysis also indicates that van der Waals and electrostatic interactions are the main forces for the HSA-PFAS complexes. Correlation analysis reveals that DFT quantum chemical descriptors related to electrostatic distribution and characteristics like ESP and ALIE are more representative in characterizing HSA-PFAS binding. This study sheds light on the interactions between HSA and PFAS. It guides health risk assessments and control strategies against PFAS, serving as a critical starting point for further public health research.

The interaction of perfluorooctane sulfonate with hemoproteins and its relevance to molecular toxicology

Perfluorooctane sulfonate (PFOS), a representative of perfluorinated compounds in industrial and commercial products, has posed a great threat to animals and humans via environmental exposure and dietary consumption. Herein, we investigated the effects of PFOS binding on the redox state and stability of two hemoproteins (hemoglobin (Hb) and myoglobin (Mb)). Fluorescence spectroscopy, circular dichroism and UV-vis absorption spectroscopy demonstrated that PFOS could induce the conformational changes of proteins along with the exposure of heme cavity and generation of hemichrome, which resulted in the increased release of free hemin. After that, free hemin liberated from hemoproteins led to reactive oxygen species formation, lipid peroxidation, cell membrane damage and loss of cell viability in vascular endothelial cells, while neither Hb nor Mb did show cytotoxicity. Chemical inhibitors of ferroptosis effectively mitigated hemin-caused toxicity, identifying the hemin-dependent ferroptotic cell death mechanisms. These data demonstrated that PFOS posed a potential threat of toxicity through a mechanism which involved its binding to hemoproteins, decreased oxygen transporting capacity, and increased hemin release. Altogether, our findings elucidate the binding mechanisms of PFOS with two hemoproteins, as well as possible risks on vascular endothelial cells, which would have important implications for the human and environmental toxicity of PFOS.

An integrated assessment of ecological and human health risks of per- and polyfluoroalkyl substances through toxicity prediction approaches

Per- and polyfluoroalkyl substances (PFAS) are also known as "forever chemicals" due to their persistence and ubiquitous environmental distribution. This review aims to summarize the global PFAS distribution in surface water and identify its ecological and human risks through integrated assessment. Moreover, it provides a holistic insight into the studies highlighting the human biomonitoring and toxicological screening of PFAS in freshwater and marine species using quantitative structure-activity relationship (QSAR) based models. Literature showed that PFOA and PFOS were the most prevalent chemicals found in surface water. The highest PFAS levels were reported in the US, China, and Australia. The TEST model showed relatively low LC50 of PFDA and PFOS for Pimephales promelas (0.36 and 0.91 mg/L) and high bioaccumulation factors (518 and 921), revealing an elevated associated toxicity. The risk quotients (RQs) values for P. promelas and Daphnia magna were found to be 269 and 23.7 for PFOS. Studies confirmed that long-chain PFAS such as PFOS and PFOA undergo bioaccumulation in aquatic organisms and induce toxicological effects such as oxidative stress, transgenerational epigenetic effects, disturbed genetic and enzymatic responses, perturbed immune system, hepatotoxicity, neurobehavioral toxicity, altered genetic and enzymatic responses, and metabolism abnormalities. Human biomonitoring studies found the highest PFOS, PFOA, and PFHxS levels in urine, cerebrospinal fluid, and serum samples. Further, long-chain PFOA and PFOS exposure create severe health implications such as hyperuricemia, reduced birth weight, and immunotoxicity in humans. Molecular docking analysis revealed that short-chain PFBS (-11.84 Kcal/mol) and long-chain PFUnDA (-10.53 Kcal/mol) displayed the strongest binding interactions with human serum albumin protein. Lastly, research challenges and future perspectives for PFAS toxicological implications were also discussed, which helps to mitigate associated pollution and ecological risks.

Investigation of the Binding Fraction of PFAS in Human Plasma and Underlying Mechanisms Based on Machine Learning and Molecular Dynamics Simulation

More than 7000 per- and polyfluorinated alkyl substances (PFAS) have been documented in the U.S. Environmental Protection Agency's CompTox Chemicals database. These PFAS can be used in a broad range of industrial and consumer applications but may pose potential environmental issues and health risks. However, little is known about emerging PFAS bioaccumulation to assess their chemical safety. This study focuses specifically on the large and high-quality data set of fluorochemicals from the related environmental and pharmaceutical chemicals databases, and machine learning (ML) models were developed for the classification prediction of the unbound fraction of compounds in plasma. A comprehensive evaluation of the ML models shows that the best blending model yields an accuracy of 0.901 for the test set. The predictions suggest that most PFAS (∼92%) have a high binding fraction in plasma. Introduction of alkaline amino groups is likely to reduce the binding affinities of PFAS with plasma proteins. Molecular dynamics simulations indicate a clear distinction between the high and low binding fractions of PFAS. These computational workflows can be used to predict the bioaccumulation of emerging PFAS and are also helpful for the molecular design of PFAS to prevent the release of high-bioaccumulation compounds into the environment.

Serum albumin mitigated perfluorooctane sulfonate-induced cytotoxicity by affecting the cellular responses

During the wide applications of perfluorinated materials such as perfluorooctane sulfonate (PFOS) in commercial and industrial products, the potential toxicity of these engineered compounds has attracted more and more attention. As a typical environmental pollutant, PFOS could preferentially bind to albumin protein in vivo. However, the role of protein-PFOS interactions in the cytotoxicity of PFOS was not stressed enough. Herein, we investigated the interactions of PFOS with human serum albumin (HSA, the most abundant protein in human plasma) using both experimental and theoretical approaches. It was demonstrated that PFOS could mainly bind to the Sudlow site I of HSA to generate HSA-PFOS complex through hydrogen bonds and van der Waals forces. Toxicity assays with endothelial cells illustrated that the binding of HSA could significantly attenuate the intracellular uptake and subcellular distribution of PFOS, thereby inhibiting the formation of reactive oxygen species and toxicity for those HSA-bound PFOS. Similarly, the presence of fetal bovine serum in the cell culture media greatly reduced PFOS-caused cytotoxicity. Conclusively, our study reveals that the binding of albumin protein to PFOS could mitigate its toxicity by the modulation of cellular responses. The formation of protein-complexed contaminants would significantly reduce the bioavailability of these chemicals and subsequently mitigate their environmental toxicology to the human health.

Trends in Serum Per- and Polyfluoroalkyl Substance (PFAS) Concentrations in Teenagers and Adults, 1999-2018 NHANES

Some types of per- and poly-fluoroalkyl substances (PFAS) have been banned over the last two decades, but millions of Americans continue to have exposure to the compounds through drinking water and consumer products. Therefore, understanding the changes in serum PFAS concentrations after their limited use is necessary to protect public health. In this study, we evaluated trends of serum PFAS compounds (PFOS, PFOA, PFHxS, PFDA, and PFNA) to determine their distribution among the United States general population. We analyzed serum concentrations of PFAS measured from random subsamples of the National Health and Nutrition Examination Survey (NHANES) participants. The study results demonstrated that demographic factors such as race/ethnicity, age, and sex may influence the levels of serum PFAS over time. Adults, males, Asians, Non-Hispanic Blacks, and Non-Hispanic Whites had high risks of exposure to the selected PFAS. Overall, serum PFAS levels declined continuously in the studied population from 1999 to 2018. Among the studied population, PFOS and PFDA were the most and least prevalent PFAS in blood serum, respectively. Serum levels of PFDA, PFOA, and PFHxS showed upward trends in at least one racial/ethnic group after 2016, which underscores the need for continuous biomonitoring of PFAS levels in humans and the environment.

Significant Variability in the Developmental Toxicity of Representative Perfluoroalkyl Acids as a Function of Chemical Speciation

Current toxicological data of perfluoroalkyl acids (PFAAs) are disparate under similar exposure scenarios. To find the cause of the conflicting data, this study examined the influence of chemical speciation on the toxicity of representative PFAAs, including perfluorooctanoic acid (PFOA), perfluorobutane carboxylic acid (PFBA), and perfluorobutanesulfonic acid (PFBS). Zebrafish embryos were acutely exposed to PFAA, PFAA salt, and a pH-negative control, after which the developmental impairment and mechanisms were explored. The results showed that PFAAs were generally more toxic than the corresponding pH control, indicating that the embryonic toxicity of PFAAs was mainly caused by the pollutants themselves. In contrast to the high toxicity of PFAAs, PFAA salts only exhibited mild hazards to zebrafish embryos. Fingerprinting the changes along the thyroidal axis demonstrated distinct modes of endocrine disruption for PFAAs and PFAA salts. Furthermore, biolayer interferometry monitoring found that PFOA and PFBS acids bound more strongly with albumin proteins than did their salts. Accordingly, the acid of PFAAs accumulated significantly higher concentrations than their salt counterparts. The present findings highlight the importance of chemical forms to the outcome of developmental toxicity, calling for the discriminative risk assessment and management of PFAAs and salts.

Computational Modeling of Human Serum Albumin Binding of Per- and Polyfluoroalkyl Substances Employing QSAR, Read-Across, and Docking

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals in widespread use that have been shown to be toxic to wildlife and humans. Human serum albumin (HSA) is a known transport protein that binds PFAS at various sites, leading to bioaccumulation and long-term toxicity. In silico tools like quantitative structure-activity relationship (QSAR), read-across, and quantitative read-across structure-property relationship (q-RASPR) are proven techniques for modeling chemical toxicity based on experimental data which can be used to predict the toxicity of untested and new chemicals, while at the same time, help to identify the major features responsible for toxicity. Classification-based and regression-based QSAR models are employed in the present study to predict the binding affinities of 24 PFAS to HSA. Regression-based QSAR models revealed that the packing density index (PDI) and quantitative estimation of drug-likeness (QED) descriptors were both positively correlated with higher binding affinity, while the classification-based QSAR model showed the average connectivity index of order 4 (X4A) descriptor was inversely correlated with binding affinity. Whereas molecular docking studies suggested that PFAS with the highest binding affinity to HSA create hydrogen bonds with Arg348 and salt bridges with Arg348 and Arg485, PFAS with lower binding affinity either showed no interactions with either amino acid or only interactions with Arg348. Among the studied PFAS, perfluoroalkyl acids (PFAA) with large carbon chain length (>C10) have one of the lowest binding affinities, compared to PFAA with carbon chain length ranging from 7 to 9, which showed the highest affinity to HSA. Generalized Read-Across (GenRA) was used to predict toxicity outcomes for the top five highest binding affinity PFAS based on 10 structural analogs for each and found that all are predicted as being chronic to sub-chronically toxic to HSA. The developed in silico models presented in this work can provide a framework for designing PFAS alternatives, screening compounds currently in use, and for the study of PFAS mixture toxicity, which is an area of intense research.

Binding of serum albumin to perfluorooctanoic acid reduced cytotoxicity

With the ubiquitous applications of perfluorinated compounds such as perfluorooctanoic acid (PFOA) in industrial and commercial products, the toxicity of these engineered materials in environmental and public health is received growing attention. As a typical organic pollutant, PFOA has been extensively found in wildlife and human bodies, and can preferentially bind to serum albumin in vivo. However, the importance of protein-PFOA interactions on the cytotoxicity of PFOA could not be stressed enough. In this study, we used both experimental and theoretical approaches, to investigate the interactions of PFOA with bovine serum albumin (BSA, the most abundant protein in blood). It was found that PFOA could mainly interact with Sudlow site I of BSA to form BSA-PFOA complex, in which van der Waals forces and hydrogen bonds played dominant roles. Moreover, the strong binding of BSA could greatly alter the cellular uptake and distribution of PFOA in human endothelial cells, and result in the decreases of reactive oxygen species formation and cytotoxicity for these BSA-coated PFOA. Consistently, the addition of fetal bovine serum into cell culture medium also significantly mitigated PFOA-induced cytotoxicity, which was attributed to the extracellular complexation between PFOA and serum proteins. Altogether, our study demonstrates that the binding of serum albumin to PFOA could reduce its toxicity by affecting the cellular responses.

Can blood proteome diversity among fish species help explain perfluoroalkyl acid trophodynamics in aquatic food webs?

Per- and polyfluoroalkyl substances (PFAS) are a diverse family of industrially significant synthetic chemicals infamous for extreme environmental persistence and global environmental distribution. Many PFAS are bioaccumulative and biologically active mainly due to their tendency to bind with various proteins. These protein interactions are important in determining the accumulation potential and tissue distribution of individual PFAS. Trophodynamics studies including aquatic food webs present inconsistent evidence for PFAS biomagnification. This study strives to identify whether the observed variability in PFAS bioaccumulation potential among species could correspond with interspecies protein composition differences. Specifically, this work compares the perfluorooctane sulfonate (PFOS) serum protein binding potential and the tissue distribution of ten perfluoroalkyl acids (PFAAs) detected in alewife (Alosa pseudoharengus), deepwater sculpin (Myoxocephalus thompsonii), and lake trout (Salvelinus namaycush) of the Lake Ontario aquatic piscivorous food web. These three fish sera and fetal bovine reference serum all had unique total serum protein concentrations. Serum protein-PFOS binding experiments showed divergent patterns between fetal bovine serum and fish sera, suggesting potentially two different PFOS binding mechanisms. To identify interspecies differences in PFAS-binding serum proteins, fish sera were pre-equilibrated with PFOS, fractionated by serial molecular weight cut-off filter fractionation, followed by liquid chromatography-tandem mass spectrometry analysis of the tryptic protein digests and the PFOS extracts of each fraction. This workflow identified similar serum proteins for all fish species. However, serum albumin was only identified in lake trout, suggesting apolipoproteins are likely the primary PFAA transporters in alewife and deepwater sculpin sera. PFAA tissue distribution analysis provided supporting evidence for interspecies variations in lipid transport and storage, which may also contribute to the varied PFAA accumulation in these species. Proteomics data are available via ProteomeXchange with identifier PXD039145.

A Review on Per- and Polyfluoroalkyl Substances in Pregnant Women: Maternal Exposure, Placental Transfer, and Relevant Model Simulation

Per- and polyfluoroalkyl substances (PFASs) are important and ubiquitous environmental contaminants worldwide. These novel contaminants can enter human bodies via various pathways, subsequently posing risks to the ecosystem and human health. The exposure of pregnant women to PFASs might pose risks to the health of mothers and the growth and development of fetuses. However, little information is available about the placental transfer of PFASs from mothers to fetuses and the related mechanisms through model simulation. In the present study, based upon a review of previously published literature, we initially summarized the exposure pathways of PFASs in pregnant women, factors affecting the efficiency of placental transfer, and mechanisms associated with placental transfer; outlined simulation analysis approaches using molecular docking and machine learning to reveal the mechanisms of placental transfer; and finally highlighted future research emphases that need to be focused on. Consequently, it was notable that the binding of PFASs to proteins during placental transfer could be simulated by molecular docking and that the placental transfer efficiency of PFASs could also be predicted by machine learning. Therefore, future research on the maternal-fetal transfer mechanisms of PFASs with the benefit of simulation analysis approaches is warranted to provide a scientific basis for the health effects of PFASs on newborns.

Haem-Mediated Albumin Biosensing: Towards Voltammetric Detection of PFOA

The haem group is a promising redox probe for the design of albumin-based voltammetric sensors. Among the endogenous ligands carried by human serum albumin (hSA), haem is characterised by a reversible redox behaviour and its binding kinetics strongly depend on hSA's conformation, which, in turn, depends on the presence of other ligands. In this work, the potential applicability of haem, especially hemin, as a redox probe was first tested in a proof-of-concept study using perfluorooctanoic acid (PFOA) as model analyte. PFOA is known to bind hSA by occupying Sudlow's I site (FA7) which is spatially related to the haem-binding site (FA1). The latter undergoes a conformational change, which is expected to affect hemin's binding kinetics. To verify this hypothesis, hemin:albumin complexes in the presence/absence of PFOA were first screened by UV-Vis spectroscopy. Once the complex formation was verified, haem was further characterised via electrochemical methods to estimate its electron transfer kinetics. The hemin:albumin:PFOA system was studied in solution, with the aim of describing the multiple equilibria at stake and designing an electrochemical assay for PFOA monitoring. This latter could be integrated with protein-based bioremediation approaches for the treatment of per- and polyfluoroalkyl substances polluted waters. Overall, our preliminary results show how hemin can be applied as a redox probe in albumin-based voltammetric sensing strategies.

Changes in perfluoroalkyl substances (PFAS) concentrations in human milk over the course of lactation: A study in Ronneby mother-child cohort

BACKGROUND

Little is known about how PFAS concentrations in human milk change over the course of lactation, although this is an important determinant of cumulative infant exposure from breastfeeding.

OBJECTIVE

To estimate changes in PFAS concentrations in human milk over the course of lactation in a population with a wide range of exposure from background-to high-exposed.

METHODS

We measured PFAS concentrations in colostrum and mature milk samples from women in the Ronneby Mother-Child Cohort. For each PFAS, we estimated the change in concentration from colostrum collected 3-4 days postpartum to mature milk collected 4-12 weeks postpartum using linear mixed-effects models. We evaluated whether this estimated change varied by quartiles of colostrum concentrations. In a subset of mothers with at least three mature milk samples, we estimated the change in concentration per month over the first eight months of lactation.

RESULTS

Our study included 77 mother-child pairs, of whom 74 had colostrum and initial mature milk samples and 11 had three or more repeated samples. The concentration change from colostrum to mature milk varied by PFAS. While PFOS increased by 21% (95% CI: 8.9, 35), PFOA decreased by 17% (95% CI: -28, -3.5) and PFHxS decreased by 12% (95% CI: -24, 3.3). In addition, PFAS concentrations tended to increase in women with lower colostrum levels, but decreased or remained the same in women with high colostrum concentrations. When we estimated changes over the course of lactation, we found that PFOA concentrations decreased the most (-12% per month; 95% CI: -22, -1.5), whereas PFHxS and PFOS showed small nonsignificant decreases.

CONCLUSIONS

Models for cumulative infancy exposure from breastfeeding need to account for differences in concentration trajectories by PFAS and possibly by maternal exposure level. Additional research is needed to evaluate the relative exposure from breastfeeding vs prenatal exposure, especially in highly exposed communities where breastfeeding guidance is urgently needed.

Uptake, distribution, and depuration of emerging per- and polyfluoroalkyl substances in mice: Role of gut microbiota

The bioaccumulation and fate in mammals of hexafluoropropylene oxide trimer acid (HFPO-TA) and hexafluoropropylene oxide dimer acid (HFPO-DA), as major alternatives for perfluorooctanoate (PFOA), have rarely been reported. In addition, the role of gut microbiota was greatly understudied. In this study, the uptake, distribution, and depuration of HFPO-TA, HFPO-DA, and PFOA were investigated by exposure to mice for 14 days, followed by a clearance period of 7 days. The patterns of tissue distribution and depuration kinetics of HFPO-TA and PFOA were similar, but different from HFPO-DA. Liver was the main deposition organ for HFPO-TA and PFOA, making contributions of 58.8 % and 59.1 % to the total mass recovered on day 14. Depuration of HFPO-DA was more rapid than HFPO-TA and PFOA. Approximately 95.3 % of HFPO-DA in liver was eliminated on day 21 compared with day 14. While the clearance rates of HPFO-TA and PFOA were only 6.1 % and 13.9 % on day 21. The comparison between normal and pseudo germ-free mice (GM) was also conducted to investigate the effect of gut microbial on in vivo absorption of the three per- and polyfluoroalkyl substances (PFASs). Significantly higher (p < 0.05) concentrations of all the three PFASs were observed in most organs and tissues of GM compared with NC group. An analysis of gut microbiota showed that the higher absorption of PFASs in GM group may be attributed to the increase of intestinal permeability (as indicated by the decrease of tight junction protein expression), which were induced by the change of lachnospiraceae abundance. The result highlighted the importance of gut microbiota in absorption and health risk evaluation of emerging PFASs.

Investigation of the Interaction between Human Serum Albumin and Branched Short-Chain Perfluoroalkyl Compounds

The current trend dealing with the production of per- and polyfluoroalkyl substances (PFASs) involves the shifting toward branched short-chain fluorinated compounds known as new-generation PFASs. A key aspect to be clarified, to address the adverse health effects associated with the exposure to PFASs, is their binding mode to human serum albumin (hSA), the most abundant protein in plasma. In this study, we investigated the interaction between hSA and two representative branched short-chain PFASs, namely, HPFO-DA and C6O4. In-solution studies revealed that both compounds bind hSA with affinities and stoichiometries lower than that of the legacy long-chain perfluoroalkyl compound PFOA. Competition experiments using hSA-binding drugs with known site-selectivity revealed that both HPFO-DA and C6O4 bound to pockets located in subdomain IIIA. The crystal structure of hSA in complex with HPFO-DA unveiled the presence of two binding sites. The characterization and direct comparison of hSA interactions with new-generation PFASs may be key elements for the understanding of the toxicological impact of these compounds.

Elucidating the molecular mechanisms of perfluorooctanoic acid-serum protein interactions by structural mass spectrometry

Perfluorooctanoic acid (PFOA) is a persistent environmental pollutant and will continually accumulate in blood due to its chemical inertness and strong interaction with serum proteins, especially serum albumin (SA), inducing highly adverse health risks. However, the molecular mechanisms of dynamic interactions between PFOA with serum proteins remain unclear, limiting the development of potential therapeutic strategies. Herein, we developed an integrated structural strategy to systematically profile the molecular details of dynamic interactions among PFOA, SA, and β-cyclodextrin (β-CD) by combing native mass spectrometry (nMS), lysine reactivity profiling (LRP), and molecular docking (MD) simulation. The SA site 1, site 2 pockets, and cleft nearby are observed as the primary interaction regions of PFOA. Further, β-CD can disrupt the PFOA combinations with bovine SA regions around sites Lys20, Lys280, Lys350, and Lys431-Lys439, with an overall reversing efficiency of about 26% at an identical concentration to PFOA. The interactome of PFOA with complex human serum proteins is globally profiled with molecular interaction details, including human serum albumin, apolipoprotein A-I, alpha-2-macroglobulin, and complement C3. Our results reveal molecular insights into the detail of the interaction between PFOA and serum proteins, beneficial to understanding PFOA toxicology.

Insights into the impacts of dissolved organic matter of different origins on bioaccumulation and translocation of per- and polyfluoroalkyl substances (PFASs) in wheat

Per- and polyfluoroalkyl substances (PFASs) have been found to be widely present in soil. Dissolved organic matter (DOM) in soil are supposed to greatly affect the bioavailability of PFASs in soil. Herein, hydroponic experiments were conducted to understand the impacts of two kinds of typical DOM, bovine serum albumin (BSA) and humic acid (HA), on the uptake and translocation of legacy PFASs and their emerging alternatives, perfluorooctane sulfonic acid (PFOS), perfluorooctane acid (PFOA), perfluorohexane sulfonic (PFHxS) and 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA) in wheat (Triticum aestivum L.). The results indicated that both HA and BSA significantly inhibited the bioaccumulation and translocation of PFASs in the roots and shoots of wheat, and the impacts of BSA were greater than HA. This difference was explained by the greater binding affinities of the four PFASs with BSA than with HA, as evidenced by the equilibrium dialysis and isothermal titration calorimetry (ITC) analyses. It was noting that inhibition impacts of the BSA-HA mixture (1:1) were lower than BSA alone. The results of Fourier transform infrared (FT-IR) spectroscopy and excitation-emission matrix (EEM) fluorescence spectroscopy suggested that HA could bind with the fluorescent tryptophan residues in BSA greatly, competing the binding sites with PFASs and forming a cover on the surface of BSA. As a result, the binding of PFASs with BSA-HA complex was much lower than that with BSA, but close to HA. The results of this study shed light on the impacts of DOM in soil on the bioaccumulation and translocation of PFASs in plants.

The transplacental transfer efficiency of per- and polyfluoroalkyl substances (PFAS): a first meta-analysis

Per- and polyfluorinated substances (PFAS), ubiquitously present in the environment and biota, are transferred to the fetus via the placenta. PFAS can be distinguished, among other things, by their different carbon chain lengths and functional groups. The aim of this study was to provide comprehensive evidence on PFAS transfer rates across the human placental barrier by means of a meta-analysis based upon a systematic review. The available literature up to April 2021 was reviewed and transplacental transfer efficiencies (TTEs) of PFAS assessed. A total of 39 studies reporting data on 20 PFAS were included in the systematic review. Of these, 20 studies with data on 19 compounds were included in the meta-analysis. Comprehensive Meta-Analysis (CMA v3.0) was used for quantitative, statistical analyses with random effects models. A curvilinear relationship was found with short and long chains of perfluorocarboxylic acids (PFCAs) exhibiting higher TTE than compounds with intermediate chain length. Among the less well studied PFAS, perfluorohexanoic acid (PFHxA), 6:2 fluorotelomersulfonic acid (6:2 FTS) and perfluorobutanoic acid (PFBA) stood out the most with a high TEEs. The dependence of TTEs on chain length and functional group is clearly shown in this first meta-analysis on PFAS transfer across the human placenta. More data on effects of less well studied PFAS in pregnant women and neonates are needed to assess the potential risk for fetal exposure.

Temporal trends, 2000-2017, of perfluoroalkyl acid (PFAA) concentrations in serum of Swedish adolescents

Per- and polyfluoroalkyl substances (PFAS) have been extensively used as surfactants because of their high stability and good water/oil-repellent properties. PFASs, especially perfluoroalkyl acids (PFAAs), have long biological half-lives, and exposure may cause adverse health effects in humans. We assessed temporal trends of concentrations of eight PFAAs in serum of Swedish adolescents (age 16-21 years) from the general population, and estimated the stability of PFAAs and serum samples after 6 years of storage. Repeated cross-sectional sampling was performed on five occasions (covering in total 1213 individuals, 83% males) in southern Sweden between 2000 and 2017. We analyzed serum for perfluorohexane sulfonic acid (PFHxS), perfluorooctane sulfonic acid (PFOS), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), and perfluorododecanoic acid (PFDoDA) using liquid chromatography-tandem mass spectrometry. We assessed time trends using linear regression, long-term stability was assessed by reanalyzing samples collected 2013, and the comparison was done using Pearson correlation and Bland-Altman plots. PFHxS, PFOS, and PFOA decreased by 6.7% (CI: -7.0, -6.3%), 12.6% (CI: -12.9, -12.3%), and 6.5% (CI: -6.8, -6.1%) per year, respectively, and year of sampling explained 48-81% of the variation in concentrations. PFNA and PFDA seemed to increase up to 2009 and decrease thereafter. The trends were consistent after sensitivity analyses excluding women. Strong correlations of 94-97% were observed for concentrations of all compounds, except PFHxS, after storage. The observed trends closely followed the timing of manufacturers' voluntary phase-out initiatives, and of regulatory measures governing the compounds implemented in the EU and USA. This indicates that these actions mitigated the population's exposure to PFHxS, PFOS, and PFOA and, in recent years, to PFNA and PFDA, in southern Sweden. Furthermore, the results suggest that PFAAs remain stable in serum samples after long-term storage.

Prenatal perfluoroalkyl substance exposure and neuropsychological development throughout childhood: The INMA Project

BACKGROUND

Perfluoroalkyl substances (PFASs) have been related to neurodevelopmental toxicity in animals. However, human studies are inconclusive.

OBJECTIVES

To evaluate the association between prenatal PFAS exposure and neuropsychological development during childhood.

METHODS

1240 mother-child pairs from the Spanish INMA Project were analyzed. Perfluorohexanesulfonic acid (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorononanoic acid (PFNA) were measured in first-trimester maternal plasma. Neuropsychological development was assessed at 14 months, 4-5 and 7 years covering four domains: general cognitive, general motor, attention, and working memory. Associations were studied by means of multivariable regression analyses.

RESULTS

PFHxS, PFOA, PFOS, and PFNA medians were: 0.6, 2.4, 6.1, and 0.7 ng/mL. Higher PFAS prenatal exposure was associated with worse motor development at 14 months, especially in the case of PFHxS (β[95%CI]: -1.49[-2.73, -0.24]) and to a lesser extent PFOS (-1.25[-2.62, 0.12]). There was also a marginal positive association between general cognitive development at 4-5 years and PFOS (1.17[-0.10, 2.43]) and PFNA (0.99[-0.13, 2.12]). No clear associations for other neuropsychological outcomes or any sex differences were found.

DISCUSSION

This study shows no clear-cut evidence of an association between prenatal PFAS exposure and adverse neuropsychological development in children up to the age of 7 years.

Native mass spectrometry for the design and selection of protein bioreceptors for perfluorinated compounds

Biosensing platforms are answering the increasing demand for analytical tools for environmental monitoring of small molecules, such as per- and polyfluoroalkyl substances (PFAS). By transferring toxicological findings in bioreceptor design we can develop innovative pathways for biosensor design. Indeed, toxicological studies provide fundamental information about PFAS-biomolecule complexes that can help evaluate the applicability of the latter as bioreceptors. The toolbox of native mass spectrometry (MS) can support this evaluation, as shown by the two case studies reported in this work. The analysis of model proteins' (i.e. albumin, haemoglobin, cytochrome c and neuroglobin) interactions with well-known PFAS, such as perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), demonstrated the potential of this native MS screening approach. In the first case study, untreated albumin and delipidated albumin were compared in the presence and absence of PFOA confirming that the delipidation step increases albumin affinity for PFOA without affecting protein stability. In the second case study, the applicability of our methodology to identify potential bioreceptors for PFOS/PFOA was extended to other proteins. Structurally related haemoglobin and neuroglobin revealed a 1 : 1 complex, whereas no binding was observed for cytochrome c. These studies have value as a proof-of-concept for a general application of native MS to identify bioreceptors for toxic compounds.

First insights into the formation and long-term dynamic behaviors of nonextractable perfluorooctanesulfonate and its alternative 6:2 chlorinated polyfluorinated ether sulfonate residues in a silty clay soil

Per- and polyfluoroalkyl substances (PFAS) are persistent and toxic contaminants that are ubiquitous in the environment. They can incorporate into soil as nonextractable residues (NER) which are not detectable with conventional analytical protocols but are still possible to remobilize with changes of surrounding conditions, and thus will be bioavailable again. Therefore, there is a need to investigate thoroughly the long-term fate of NER-PFAS. In this study, a 240-day incubation of perfluorooctanesulfonate (PFOS) and its alternative 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) in a silty clay topsoil was carried out. Solvent extraction, alkaline hydrolysis and sequential chemical degradation were applied on periodically sampled soil to obtain extractable, moderately bound and deeply bound PFAS, respectively. The results confirmed the formation of NER of both compounds but with different preferences of incorporating mechanisms. NER-PFOS was formed predominantly by covalent binding (via head group) and strong adsorption (via tail group). The formation of NER-F-53B was mainly driven by physical entrapment. Both bound compounds within the incubation period showed three-stage behaviors including an initial period with slight release followed by a (re) incorporating stage and a subsequent remobilizing stage. This work provides some first insights on the long-term dynamic behaviors of nonextractable PFAS and will be conducive to their risk assessment and remediation (e.g. estimating potential NER-PFAS level based on their free extractable level, and selecting remediation methods according to their prevailing binding mechanisms).

In-Vitro and In-Silico Assessment of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) Binding to Human Serum Albumin

Drinking water contaminated by fluorosurfactant-based aqueous film-forming foams (AFFF) is a source of human exposure to poly- and perfluoroalkyl substances (PFAS). However, assessment of bioaccumulation potentials of diverse PFAS in commercial products such as AFFF have been insufficient and challenging, especially due to a lack of analytical standards. Here we explore the value of suspect screening, equilibrium dialysis, and molecular-docking simulations to identify potentially bioaccumulative PFAS. We exposed human serum albumin (HSA) protein to dilutions of a legacy AFFF produced by 3M in 1999 using equilibrium dialysis and screened in-vitro protein-binding affinities using high-resolution mass spectrometry (HRMS). Through suspect screening, we identified 32 PFAS and 18 hydrocarbon surfactants in the AFFF that bound to HSA. Quantification of noncovalent association constants for 26 PFAS standards confirmed that many PFAS, including the short-chain perfluoropropane sulfonic acid (log Ka= 4.1 ± 0.2 M-1), exhibit strong binding affinities with HSA. At least five PFAS in AFFF (including three PFAS with less than five perfluorocarbons) remained bound to the precipitated HSA pellet after extensive solvent washing-an indication of high PFAS binding potential. Three PFAS (PFBS, PFOS, and PFOA) were confirmed in the protein pellet with analytical standards and quantified after acid digestion-this sample fraction accounted for 5 to 20% of each compound mass in the sample. We calculated pseudo-bioconcentration factors (BCFpseudo) for PFAS that suspect screening flagged as noncovalently bound or potentially covalently bound. Most PFAS exhibiting high BCFpseudo, especially those with seven perfluorocarbons, contained a carboxylic acid or a sulfonic acid. Finally, we used molecular docking to simulate HSA binding affinities for 62 ligands (26 PFAS targets, 18 PFAS qualified in AFFF, and 18 hydrocarbon surfactants qualified in AFFF). We found that molecular docking can effectively separate HSA-binding and -nonbinding compounds in AFFF. In-vitro and in-silico approaches described in this study provide replicable, high-throughput workflows for assessing bioaccumulation potentials of diverse PFAS in commercial products.

Perfluoroalkyl Acid Binding with Peroxisome Proliferator-Activated Receptors α, γ, and δ, and Fatty Acid Binding Proteins by Equilibrium Dialysis with a Comparison of Methods

The biological impacts of per- and polyfluorinated alkyl substances (PFAS) are linked to their protein interactions. Existing research has largely focused on serum albumin and liver fatty acid binding protein, and binding affinities determined with a variety of methods show high variability. Moreover, few data exist for short-chain PFAS, though their prevalence in the environment is increasing. We used molecular dynamics (MD) to screen PFAS binding to liver and intestinal fatty acid binding proteins (L- and I-FABPs) and peroxisome proliferator activated nuclear receptors (PPAR-α, -δ and -γ) with six perfluoroalkyl carboxylates (PFCAs) and three perfluoroalkyl sulfonates (PFSAs). Equilibrium dissociation constants, KDs, were experimentally determined via equilibrium dialysis (EqD) with liquid chromatography tandem mass spectrometry for protein-PFAS pairs. A comparison was made between KDs derived from EqD, both here and in literature, and other in vitro approaches (e.g., fluorescence) from literature. EqD indicated strong binding between PPAR-δ and perfluorobutanoate (0.044 ± 0.013 µM) and perfluorohexane sulfonate (0.035 ± 0.0020 µM), and between PPAR-α and perfluorohexanoate (0.097 ± 0.070 µM). Unlike binding affinities for L-FABP, which increase with chain length, KDs for PPARs showed little chain length dependence by either MD simulation or EqD. Compared with other in vitro approaches, EqD-based KDs consistently indicated higher affinity across different proteins. This is the first study to report PPARs binding with short-chain PFAS with KDs in the sub-micromolar range.

Unveiling the binding mode of perfluorooctanoic acid to human serum albumin

Perfluorooctanoic acid (PFOA) is a toxic compound that is absorbed and distributed throughout the body by noncovalent binding to serum proteins such as human serum albumin (hSA). Though the interaction between PFOA and hSA has been already assessed using various analytical techniques, a high resolution and detailed analysis of the binding mode is still lacking. We report here the crystal structure of hSA in complex with PFOA and a medium-chain saturated fatty acid (FA). A total of eight distinct binding sites, four occupied by PFOAs and four by FAs, have been identified. In solution binding studies confirmed the 4:1 PFOA-hSA stoichiometry and revealed the presence of one high and three low affinity binding sites. Competition experiments with known hSA-binding drugs allowed locating the high affinity binding site in sub-domain IIIA. The elucidation of the molecular basis of the interaction between PFOA and hSA might provide not only a better assessment of the absorption and elimination mechanisms of these compounds in vivo but also have implications for the development of novel molecular receptors for diagnostic and biotechnological applications.

Dominant entropic binding of perfluoroalkyl substances (PFASs) to albumin protein revealed by 19F NMR

Mechanistic insight into protein binding by poly- and perfluoroalkyl substances (PFASs) is critical to understanding how PFASs distribute and accumulate within the body and to developing predictive models within and across classes of PFASs. Fluorine nuclear magnetic resonance spectroscopy (19F NMR) has proven to be a powerful, yet underutilized tool to study PFAS binding; chemical shifts of each fluorine group reflect the local environment along the length of the PFAS molecule. Using bovine serum albumin (BSA), we report dissociation constants, Kd, for four common PFASs well below reported critical micelle concentrations (CMCs) - perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and perfluorooctanesulfonic acid (PFOS) - as a function of temperature in phosphate buffered saline. Kd values were determined based on the difluoroethyl group adjacent to the anionic headgroups and the terminal trifluoromethyl groups. Our results indicate that the hydrophobic tails exhibit greater binding affinity relative to the headgroup, and that the binding affinities are generally consistent with previous results showing that greater PFAS hydrophobicity leads to greater protein binding. However, the binding mechanism was dominated by entropic hydrophobic interactions attributed to desolvation of the PFAS tails within the hydrophobic cavities of the protein and on the surface of the protein. In addition, PFNA appears to form hemimicelles on the protein surfaces below reported CMC values. This work provides a renewed approach to utilizing 19F NMR for PFAS-protein binding studies and a new perspective on the role of solvent entropy.

Fetal bovine serum attenuating perfluorooctanoic acid-inducing toxicity to multiple human cell lines via albumin binding

Perfluorooctanoic acid (PFOA), as a typical emerging organic pollutant, can interact with serum albumin. However, it remains to characterize the binding of PFOA with serum albumin and to address the role of this interaction in related toxic effects. We aimed to characterize the interaction between PFOA and albumin for understanding the effects of this interaction on the uptake, distribution, and toxicity of PFOA in human cells. The results showed that viable cell count was significantly enhanced by addition of fetabl bovine serum (FBS) into cell culture medium with 300 μM PFOA treatment. PFOA mainly existed as complexed with FBS, at FBS concentration > 10%, which substantially reduced the absorption efficiency of all cell lines to PFOA. The majority of PFOA was accumulated in the cytosolic fraction, followed by nuclei, and mitochondria. Conclusively, our study suggests that the complexation of organic contaminants with proteins might mitigate their toxicity by reducing cellular uptake.

Covalent immobilization of delipidated human serum albumin on poly(pyrrole-2-carboxylic) acid film for the impedimetric detection of perfluorooctanoic acid

The immobilization of biomolecules at screen printed electrodes for biosensing applications is still an open challenge. To enrich the toolbox of bioelectrochemists, graphite screen printed electrodes (G-SPE) were modified with an electropolymerized film of pyrrole-2-carboxilic acid (Py-2-COOH), a pyrrole derivative rich in carboxylic acid functional groups. These functionalities are suitable for the covalent immobilization of biomolecular recognition layers. The electropolymerization was first optimized to obtain stable and conductive polymeric films, comparing two different electrolytes: sodium dodecyl sulphate (SDS) and sodium perchlorate. The G-SPE modified with Py-2-COOH in 0.1 M SDS solution showed the required properties and were further tested. A proof-of-concept study for the development of an impedimetric sensor for perfluorooctanoic acid (PFOA) was carried out using the delipidated human serum albumin (hSA) as bioreceptor. The data interpretation was supported by size exclusion chromatography and small-angle X-ray scattering (SEC-SAXS) analysis of the bioreceptor-target complex and the preliminary results suggest the possibility to further develop this biosensing strategy for toxicological and analytical studies.

Evaluation of structurally different brominated flame retardants interacting with the transthyretin and their toxicity on HepG2 cells

Brominated flame retardants (BFRs) are found at quantifiable levels in both humans and wildlife and may potentially cause a health risk. For BFRs and their derivatives, limited information regarding the relationship among the structure, binding affinity to the target protein and toxicity is currently available. In the present work, representative BFRs with different hydroxyl- or bromo-substituents, namely 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47), 3-hydroxy-2, 2', 4, 4'-tetrabromodiphenyl ether (3-OH-BDE-47) and tetrabromobisphenol A (TBBPA), were selected to investigate the interactions with transthyretin (TTR) by electrospray ionization mass spectrometry (ESI-MS) and cytotoxicity on HepG2 cells. It was noted that BDE-47 had a weak binding affinity to TTR, while 3-OH-BDE-47 and TBBPA had a stronger binding affinity than BDE-47 and thyroxine (T4). Hence, 3-OH-BDE-47 and TBBPA could affect the binding of TTR with its native ligand T₄ by competitive binding to TTR, even at equal concentrations, which might be associated with BFR toxicity of endocrine disruption. Negative cooperativity was found for 3-OH-BDE-47 and TBBPA binding to TTR, similar to T₄ with a well-established negatively cooperative binding mechanism. The tendency of toxic effects on HepG2 cells for these three BFRs was, 3-OH-BDE-47 > TBBPA > BDE-47, and this order was in good agreement with the binding ability explored by ESI-MS experiments and molecular docking simulation. The observations obtained by this study demonstrate that the binding properties of these BFRs to TTR and their cytotoxicity are correlated with structure differentials and functional substituents.

Interactions of indole alkaloids with myoglobin: A mass spectrometry based spectrometric and computational method

RATIONALE

Interactions of drug molecules and proteins play important roles in physiological and pathological processes in vivo. It is of significance to establish a reliable strategy for studying protein-drug ligand interactions and would be helpful for the design and screening of new drugs in pharmacological research.

METHODS

The interactions between four indole alkaloids (IAs) extracted from Ophiorrhiza japonica (O. japonica) and myoglobin (Mb) protein were investigated using a multi-spectrometric and computational method of native electrospray ionization mass spectrometry (native ESI-MS), hydrogen/deuterium exchange mass spectrometry (HDX-MS), circular dichroism (CD) and molecular docking (MD).

RESULTS

The IA-bound Mb complexes were analyzed using native ESI-MS, with the obtained protein-to-ligand stoichiometry at 1:1, 1:2 and 1:3. Binding constants were measured according to the interpretation of MS spectra. MD complemented MS measurements, probing the binding sites and modes of the four IAs to Mb. Analyses involving CD and HDX-MS demonstrated that exposure to IAs could affect the conformation of Mb by decreasing the α-helix content and made Mb more susceptible to HDX at the backbone.

CONCLUSIONS

A new MS-based integrated analysis method has been developed to successfully study the interactions of Mb and IAs extracted from O. japonica. The experimental and calculation results have good consistency, revealing all of the four IA molecules could bind to Mb to form 1:1, 1:2 and 1:3 Mb-IA complexes. The order of binding ability of these IAs to Mb was ophiorrhine B > compound C > ophiorrhine A > compound D. CD and HDX-MS results indicated that binding with IAs destabilizes Mb. HDX-MS analysis suggests that Mb becomes more susceptible to HDX, indicating that binding with IAs destabilizes the structure of Mb. In addition, the interaction with IAs affected the overall structure of Mb, ascribed to the decrease of α-helix content and less folding of the backbone.

Albumin is the major carrier protein for PFOS, PFOA, PFHxS, PFNA and PFDA in human plasma

Perfluoroalkyl (PFAS) substances are widespread in the environment and in organisms. The fact that exposure to PFAS is associated with elevated cholesterol levels is a major concern for human health. Previous investigations, in which bovine serum albumin was frequently studied, indicate that PFOS, PFOA and PFNA bind to serum albumin. However, it is critical to know whether these and other PFAS have a preference for the protein or the lipid fraction in native human blood fractions. For this reason, blood samples from four young healthy volunteers (two women, two men, 23-31 years old) were used for protein size separation and fractionation by the Cohn method in combination with serial ultracentrifugation. The plasma fractions were analyzed for 11 PFAS using high-performance tandem mass spectrometry (HPLC-MS/MS). Although the data are based on a small sample, they clearly show that albumin is the most important carrier protein for PFOS, PFOA, PFHxS, PFNA and PFDA in native human plasma. These five compounds have very little or no affinity for lipoproteins. The confirmation of their transport through albumin is important for the epidemiology of PFAS. The present results must be verified by the examination of a larger number of persons.

Transplacental Transfer of Per- and Polyfluoroalkyl Substances Identified in Paired Maternal and Cord Sera Using Suspect and Nontarget Screening

Novel per- and polyfluoroalkyl substances (PFASs) in various environmental media have attracted increasing attention; however, the information regarding PFASs exposure in pregnant women and fetuses is insufficient. In this study, we built and applied suspect and nontarget screening strategies based on the mass difference of the CF₂, CF₂O, and CH₂CF₂ units to select potential novel PFASs from 117 paired maternal and cord sera. In total, 10 legacy PFASs and 19 novel PFASs from 10 classes were identified to be above confidence levels 3, among which 14 were not previously reported in human serum. Novel PFASs accounted for a considerable percentage of total PFASs in pregnant women and can be transferred to fetuses at non-negligible concentrations (i.e., 27.9% and 30.3% of total PFAS intensities in maternal and cord sera, respectively). The transplacental transfer efficiency (TTE) of PFASs showed a U-shape trend in the series of perfluoroalkyl carboxylic acids, perfluoroalkyl sulfonic acids, and unsaturated perfluorinated alcohols. The TTE of novel PFASs is suggested to be structure-dependent, based on a flexible docking experiment. This study provides comprehensive TTE information on legacy and novel PFASs for the first time, and additional toxicity studies are needed to evaluate the risk of novel PFASs further.

Novel remediation of per- and polyfluoroalkyl substances (PFASs) from contaminated groundwater using Cannabis Sativa L. (hemp) protein powder

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are a group of environmentally persistent, man-made chemicals used in many industrial products and everyday consumer items. Of the plant proteins trialled, those of hemp (Cannabis sativa L.) were found to be far superior for PFAS removal than the next best protein, soy. The use of hemp plant proteins as a possible pump-and-treat solution to PFAS remediation from groundwater has been successfully demonstrated with very good removals (>98%) of the main contaminants of PFOS and PFHxS in approximately 1 h of contact time, with salinity enhancing removal of short chain PFAS. Changes to the secondary structure of hemp proteins was found using FTIR spectroscopy analysis and calculated based on the integrated areas of the amide I component bands. The amount of β-turns increased from ∼9.3% (control) to 44.1% (undiluted groundwater); with a decrease in random coils (25.6-8.6%); α-helix (19.3-8.6%) and β-sheets (38.8-23.1%). These changes indicate that hemp proteins partially unfold during the reaction with PFAS with other FTIR evidence suggesting sorption at hydrophobic sites of the protein as well as with the side chains of the amino acids aspartic and glutamic acid. The absence of these side chains in soy protein, as evidenced from FTIR and amino acid analysis, being part of the reason why soy removed less (approx. half) of the Σ(PFHxS + PFOS) load when compared to hemp. The findings reported here will lead to new, environmentally friendly methods for PFAS remediation.

Membrane-Water Partition Coefficients to Aid Risk Assessment of Perfluoroalkyl Anions and Alkyl Sulfates

This study determined the sorption affinity to artificial phospholipid membranes ( K_MW) for series of perfluorinated carboxylates (PFCAs), perfluorinated sulfonates (PFSAs), alkyl sulfates (C _xSO₄), and 1-alkanesulfonates (C _xSO₃). A sorbent dilution assay with solid supported lipid membranes (SSLM) showed consistent CF₂ unit increments of 0.59, and CH₂ unit increments of 0.53, for the log K_MW of perfluorinated and hydrogenated anions, respectively. PFSAs sorbed 0.90 log units stronger than analogue PFCAs; C _xSO₄ sorbed 0.75 log units stronger than analogue C _xSO₃ anions. The log K_MW values for the octyl analogues increase in the order H(CH₂)₈SO₃^- (1.74) < H(CH₂)₈SO₄^- (2.58) < F(CF₂)₈CO₂^- (PFNA, 4.04) < F(CF₂)₈SO₃^- (PFOS, 4.88). Intrinsic partition ratios determined on a phospholipid coated HPLC column (IAM-HPLC) closely aligned with SSLM K_MW values. COSMO-RS based molecular calculations of K_MW aligned with SSLM K_MW values for hydrogenated anions with C₈-C₁₄ alkyl chains but strongly underestimated CF₂ and CH₂ unit increments for C₄-C₈ based anions. Dividing the critical narcotic membrane burden of 100 mmol/kg by the experimental K_MW predicts lethal baseline toxicity concentrations (LC_50,narc). The LC_50,narc coincides with the lowest reported acute LC₅₀ values for several anionic surfactants but were on average about an order of magnitude lower.

Capillary electrophoresis-based approaches for the study of affinity interactions combined with various sensitive and nontraditional detection techniques

Nearly all processes in living organisms are controlled and regulated by the synergy of many biomolecule interactions involving proteins, peptides, nucleic acids, nucleotides, saccharides, and small molecular weight ligands. There is growing interest in understanding them, not only for the purposes of interactomics as an essential part of system biology, but also in their further elucidation in disease pathology, diagnostics, and treatment. The necessity of detailed investigation of these interactions leads to the requirement of laboratory methods characterized by high efficiency and sensitivity. As a result, many instrumental approaches differing in their fundamental principles have been developed, including those based on capillary electrophoresis. Although capillary electrophoresis offers numerous advantages for such studies, it still has one serious limitation, its poor concentration sensitivity with the most commonly used detection method-ultraviolet-visible spectrometry. However, coupling capillary electrophoresis with a more sensitive detector fulfils the above-mentioned requirement. In this review, capillary electrophoresis combined with fluorescence, mass spectrometry, and several nontraditional detection techniques in affinity interaction studies are summarized and discussed, together with the possibility of conducting these measurements in microchip format.

Determination of interactions between human serum albumin and niraparib through multi-spectroscopic and computational methods

The interactions between 2-{4-[(3S)-piperidin-3-yl] phenyl}-2H-indazole-7-carboxamide (niraparib) and human serum albumin (HSA) were investigated through fluorescence and computational studies. Fluorescence experiments showed that the static quenching mechanism and the binding constant of the HSA-niraparib system at a single binding site was approximately 4 × 10⁴ L mol^-1. Thermodynamic constants indicated that the binding of niraparib to HSA was mainly driven by electrostatic interactions. Competition experiments and molecular docking simulations revealed that niraparib bound to site III of HSA. Synchronous fluorescence and Fourier transform infrared spectroscopy (FT-IR) results suggested that interactions between niraparib and HSA could affect the conformation and microenvironment of HSA. Circular dichroism (CD) measurements revealed that the α-helix contents of HSA negligibly increased after binding with niraparib. Molecular dynamics simulations demonstrated the stability of the binary HSA-niraparib system and confirmed that electrostatic forces accounted for the dominant contribution to system energy between HSA and niraparib.

MS methods to study macromolecule-ligand interaction: Applications in drug discovery

The interaction of small compounds (i.e. ligands) with macromolecules or macromolecule assemblies (i.e. targets) is the mechanism of action of most of the drugs available today. Mass spectrometry is a popular technique for the interrogation of macromolecule-ligand interactions and therefore is also widely used in drug discovery and development. Thanks to its versatility, mass spectrometry is used for multiple purposes such as biomarker screening, identification of the mechanism of action, ligand structure optimization or toxicity assessment. The evolution and automation of the instruments now allows the development of high throughput methods with high sensitivity and a minimized false discovery rate. Herein, all these approaches are described with a focus on the methods for studying macromolecule-ligand interaction aimed at defining the structure-activity relationships of drug candidates, along with their mechanism of action, metabolism and toxicity.