Identification and characterization of covalent adduct formation of fluorotelomer unsaturated carboxylic acids with histone proteins.

Fluorotelomer unsaturated carboxylic acids (FTUCAs) are intermediate compounds formed during degradation and metabolism of fluorotelomer-based compounds which are all classified as per- and polyfluoroalkyl substances (PFAS). FTUCA formation is an important conversion process, and these intermediate metabolites are crucial to the toxicity of fluorotelomer-based compounds. This study investigated non-enzymatic covalent modifications (NECMs) in vitro in histone proteins of calf thymus and Human H3.3 with 6:2 and 8:2 FTUCAs, PFOA and PFOS. Using bottom-up proteomic method, adduct chemical groups and the location of specific protein adduction sites were identified. Twelve adducted sites were identified from samples of 6:2 FTUCA (or 8:2 FTUCA) incubated with histone proteins, which included H2A, H2B, H3 and H4, after proteolytic digestion. There were two FTUCA-Cys residue adducts and ten FTUCA-His residue adducts. No covalent adducts were detectable in the assay of calf thymus histone treated with PFOA or PFOS. It was observed that concentration-dependent and time-dependent formation of adducts between the FTUCAs and histone protein, which steadily increased during incubation period. These results suggest that longer-term FTUCA exposure in organisms may result in deleterious effects and may have proteome reactivity that maybe toxicologically relevant. These adducts can also be used as biomarkers of fluorotelomer-based PFAS exposure.