An investigation of the effects of chain length and ionic head group on perfluoroalkyl acid binding to human serum albumin

Perfluoroalkyl acids (PFAAs) are a class of contaminants of emerging concern (CECs) and have been a rising local issue due to the water contamination of Hoosick Falls, NY, and Bennington, VT, among other local communities. They also have been designated as PBTs (persistent, bioaccumulative and toxic), which is concerning since they are found in a wide variety of consumer products ranging from non-stick coatings to fire-fighting foam. Unlike other CECs, PFAAs bioaccumulate in areas of high protein concentration due to their unique properties of being both lipophobic and hydrophobic, causing them to accumulate in areas such as the kidneys, liver and blood; therefore, it is vital to study PFAA-protein interactions. Human Serum Albumin (HSA) is used as the model protein in PFAA-protein binding since it is the most abundant protein in the blood and is involved in the reversible binding and transport of exogenous and endogenous ligands. Previous research on PFAAs have lacked a systematic method of studying the binding of PFAA to HSA, have had conflicting data and have only focused on the medium-chain length PFAAs. Relatively few studies have focused on determining a relationship between PFAA chain length and ionic head group to HSA binding. In this study binding affinities for short-, medium- and long-chain perfluorocarboxylates and perfluorosulfonates (ranging from 4 to 12 carbons) were determined in order to understand the relationship between PFAA chain length and ionic head group. These results were obtained using a systematic equilibrium dialysis method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) that selectively determined PFAA binding affinities. The results show that all PFAAs studied bind to HSA according to a two-class binding model, regardless of chain length or ionic head group, and the short-chain PFAAs bind only moderately weaker than the medium- and long-chain PFAAs, which raises concern over whether or not the short-chain PFAA replacements are any safer than their predecessors.