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Characterization of adducts formed between human serum albumin and the butadiene metabolite epoxybutanediol.

1,3-Butadiene (BD) has been classified as a potential human carcinogen. It occurs in the environment as well as in industrial settings. In humans, BD is readily metabolized to reactive epoxides (e.g. 1,2-epoxy-3,4-butanediol). In this study, conjugates between human serum albumin (HSA) and EBD were synthesized (molar ratios of 1:600, 1:1 and 1:0.1; HSA/EBD) under physiological conditions. The 1:600 conjugate and a blank HSA sample were digested with trypsin to obtain specific peptides that were fractionated by preparative liquid chromatography (LC). The fractions were analyzed using nanoelectrospray quadrupole time-of-flight mass spectrometry (nanoES-QqTOFMS). Adducted HSA tryptic peptides were identified and the adducted amino acid residues were identified by sequence analysis based on tandem mass spectrometry (MS/MS). A total of 26 2,3,4-trihydroxybutyl (THB) adducts were identified on 23 tryptic peptides in the HSA/EBD conjugate. The adducted amino acids were the N-terminal aspartic acid residue, six glutamic acid residues, five histidine residues and 14 lysine residues. Results from the nanoES-QqTOFMS experiments were used to set up a more sensitive liquid chromatographic/mass spectrometric (LC/MS) analysis using selected reaction monitoring. Eight of the adducted peptides could be detected in tryptic digests of the 1:0.1 HSA/EBD conjugate.