UV MALDI-TOF-TOF-MS and ESI-Q-TOF-MS for the analysis of DNA nucleotides and their photoproducts

IVANA K. LEVY; M. MICAELA GONZALEZ; ERRA-BALSELLS, ROSA; FRANCO M. CABRERIZO

Congreso; Segundo Congreso Argentino de Espectrometría de Masa (II CAEM); 2014

UV MALDI-TOF-TOF-MS is a very powerful technique usually used for determination of macromolecules such as oligonucleotides, proteins, peptides, among others. However, there are a few examples of UV MALDI-TOF-TOF-MS successful applications for small molecules due to the reduced sensitivity caused by matrix signals and/or clusters and low analyzers resolution. In addition, although ESI and MALDI both are soft ionization techniques, ESI as atmospheric pressure ionization (API) could promote analyte oxidation and both cleavages of low thermo stable biomolecules as nucleotides. Moreover, in some cases, the direct absorption of the UV laser radiation by the analytes could induce photoreactions during the experiment UV MALDI. In this context, a very careful study must be performed to interpret signals of labile small molecules. In this work, we analyzed samples of three different 2´-deoxynucleotides 5´-monophosphate or dNMP: (2´-deoxyguanosine 5´-monophosphate (dGMP), 2´-deoxyadenosine 5´-monophosphate (dAMP) and 2´-deoxycytidine 5´-monophosphate (dCMP)) and one nucleotide (thymidine 5´-monophosphate (TMP)) using different matrix (3-hydroxypicolinic acid (3-HPA), norharmane (nHo), 2´,4´,6´-trihydroxyacetophenone (THAP), etc.) by UV MALDI-TOF-MS. Relevant results were compared by ESI-Q-TOF-MS. Additionally, the photoproducts generated in the photosensitized (UVA) oxidation of dNMP, by norharmane in aqueous phase, were investigated and characterized by mean of ESI-MS and UV-LDI-TOF-MS. The aim of these experiments was the searching for particular biomarkers of UVA photosensitized oxidative stress, which could be specifically detected by both MS techniques. In all cases, although mass spectra of UV MALDI and ESI were quite similar, clear differences were observed: e.g., ESI mass spectra showed characteristic ionic fragments of nucleotides, and some were also observed by MALDI-MS analysis. These results suggest that both techniques should be used in a complementary way. The analysis of the irradiated samples allowed assigning signals for several types of photoproducts. E.g., in the case of dGMP, one of the major target for DNA oxidation due to its lowest oxidation potential, diagnostic signals related to 8-oxo-7,8-dihydro-2´-guanine (8-oxoG), spiroiminodihydantoin (Sp), guanidinohydantoin (Gh), 2,2,4-triamino-5(2H)-oxazolone (Ox), dehydroguanidinohydantoin (DGh), 6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG), among others moieties, could be clearly detected.