Quantitation of N 6 ‑Formyl-lysineAdduct Following Aristolochic Acid Exposure in Cells and Rat Tissuesby Liquid Chromatography-Tandem Mass Spectrometry Coupled with StableIsotope-Dilution Method

N6-Formyl-lysine (FLys) is an abundant and lasting protein adduct formed when formaldehyde generated by nitrosative/oxidative stress and inflammation reacts with lysine residues. It is believed that the post-translational N6-formylation of lysine is associated with a variety of pathological processes and human diseases. Thus, FLys may serve well as a dosimetric biomarker for exposure to formaldehyde and other oxidative stress-inducing toxicants. However, since current methods for FLys determination are tedious and time-consuming, we developed and validated an aqueous normal phase liquid chromatography-tandem mass spectrometry (LC-MS/MS) coupled with isotope-dilution method for the rigorous quantification of FLys with enhanced sensitivity and selectivity. After validating the accuracy and precision of the method with a synthetic peptide containing FLys, the method was applied to quantitate the concentration-dependent formation of FLys in cells exposed to formaldehyde and Fe2+-EDTA, an OH radical-mediated o...