A nontargeted screening method for covalent DNA adducts and DNA modification selectivity using liquid chromatography-tandem mass spectrometry

Abstract

A method for nontargeted screening for covalent DNA adducts was developed using combination of neutral loss scan and product ion scan in a hybrid linear-ion-trap - triple quadrupole mass spectrometer system. DNA 2′-deoxynucleosides and adducts eluted from liquid chromatography were first analyzed in neutral loss mode to screen for the neutral loss of the deoxyribose moiety ([M+H-116]+) from the protonated molecular ion ([M+H]+). The product ion scan was subsequently used to elucidate the structures for the molecular ions observed from the peaks in the neutral loss scan chromatogram. The synthesized DNA adducts were used to evaluate the developed method by reaction of 20-mer DNA oligonucleotide with two direct agents respectively, specifically phenyl glycidyl ether and styrene-7,8-oxide. The modification selectivity of two compounds to the four nitrogenous bases on DNA sequence was also investigated in this study. The results showed that the two compounds had different modification selectivity to the four bases. Both compounds could modify all four nitrogenous bases (i.e. adenine, guanine, thymine, and cytosine) on DNA sequences to form various covalent DNA adducts. While phenyl glycidyl ether modified almost all of thymidine on DNA sequence, styrene-7,8-oxide, on the other hand, modified only a small portion of thymidine. The developed method proved possibly a potential tool for screening of unknown DNA adducts as exposure biomarkers of contaminants to human in the environment.