Top-down Metabolomic Approaches for Nitrogen-Containing Metabolites

Streamlining the processes that reveal heteroatom containing metabolites and their biosynthetic genes is essential in integrated metabolomics studies. These metabolites are especially targeted for their potential pharmaceutical activities. By using a Fourier-transform ion cyclotron resonance mass spectrometry (FTICR MS) instrument, we provide top-down targeted metabolomic analyses using ultrahigh-resolution liquid chromatography mass spectrometry (LC-MS), high-resolution matrix-assisted laser desorption/ionization (MALDI), and high-resolution imaging mass spectrometry (IMS) with N-15 labeling of nitrogen-containing metabolites. In this study, we efficiently extract known and unknown chemicals and spatial information from the medicinal plant Catharanthus roseus, which sources several cancer drugs. The ultrahigh-resolution LC MS analysis showed that the molecular formula of 65 N-metabolites were identified using the petals, peduncles, leaves, petioles, stems, and roots of the non- and N-15 labeled Catharanthus plants. The high resolution MALDI analysis showed the molecular formula of 64 N-metabolites using the petals, leaves, and stems of the non- and N-15-labeled Catharanthus. The chemical assignments using molecular formulas stored in databases identified known and unknown metabolites. The comparative analyses using the assigned metabolites revealed that most of the organ-specific ions are derived from unknown N-metabolites. The high-resolution IMS analysis characterized the spatial accumulation patterns of 32 N-metabolites using the buds, leaves, stems, and roots in Catharanthus. The comparative analysis using the non- and N-15-labeled IMS data showed the same spatial accumulation patterns of a non-and N-15-labeled metabolite in the organs, showing that top-down analysis can be performed even in IMS analysis.