The bioaccumulation and biodistribution of poly- and perfluoroalkyl substances (PFASs) is based on how strongly they bind to proteins and the extent to which they partition into lipid phases. Neither protein binding nor lipid partitioning alone adequately describe the biological fate of PFASs; the fate is based on a combination of binding and partitioning where the prevalence of each mechanism is determined by the physicochemical properties of PFASs and the environmental conditions, such as electrolyte concentration and temperature. Such information is scarce, particularly for series of PFASs within and across classifications (e.g. carboxylates versus sulfonates) and specifically in the context of protein binding and lipid partitioning. This presentation will describe our work using an array of experimental techniques to gain a deeper mechanistic understanding of PFAS binding to proteins and partitioning into lipids phases. PFAS concentration in blood is an indicator of exposure, therefore bovine serum albumin (BSA) was used as a model protein to examine binding based on fluorescence spectroscopy, fluorine nuclear magnetic resonance spectroscopy (19F-NMR), and differential scanning calorimetry. Multiple PFAS carbon chain lengths (C6-C10 for carboxylates and C6-C8 for sulfonates) were examined to extrapolate beyond the legacy compounds perfluorooctanoic acid (PFOA) and perfluorosulfonate (PFOS). We established binding relationships for PFAS chain length and temperature, and showed that protein conformational changes play a clear role in determining the extent of entropic binding. Further, by employing C6-C10 hydrocarbon analogs, it was discovered that binding of PFAS is mechanistically different and much stronger than that of the hydrocarbons. PFASs are known to accumulate in fatty tissues and partition into cellular membranes. Therefore, a lipid bilayer permeability assay was used to examine PFAS solution-diffusion, the parallel artificial membrane permeability assay (PAMPA) modelling the human gastrointestinal tract. Fluorescence anisotropy was then used to determine the extent of membrane partitioning and disruption induced by PFAS partitioning. The variables used to study protein binding were examined for membrane permeability, allowing us to identify correlations comparing the prevalence of binding, permeability, and partitioning. This work provides a framework for comprehensively examining protein binding and lipid partitioning in complex systems.

Protein pairing and lipid linking: Mechanistic studies reveal the effects of environmental conditions and PFAS mixtures

2019 Spring National Meeting

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