Liquid chromatography-tandem mass spectrometry analysis of the DNA adducts of aristolochic acids.

Electrophilic attack of aristolactam-nitrenium ion by the C7 position to the exocyclic amino group in the DNA bases led to the formation of the major adducts. In this study, liquid chromatography coupled with electrospray ionization tandem mass spectrometry was applied to the study of DNA adducts of aristolochic acid (AA). When DNA (bases and CT-DNA) was incubated with AA, dG-AAI, dG-AAII, dA-AAI, dA-AAII, dC-AAI, and dC-AAII were detected and characterized. The dC adducts of AA were identified for the first time. The soft ionization technology allowed detection of the intact DNA adducts. High-resolution MS and MS-MS capabilities of a quadrupole time-of-flight mass spectrometer were shown to be efficient for DNA adducts analysis. DNA-AA adducts showed characteristic fragmentation patterns in MS-MS analysis. The dissociative loss of 116 Da from the DNA-AA adducts, which resulted from internal hydrogen transfer and cleavage at the C-N glycosidic bond, provided a characteristic fragment for the structural elucidation.