Imaging the Unimaginable: Desorption Electrospray Ionization – Imaging Mass Spectrometry (DESI-IMS) in Natural Product Research

Abstract

Imaging mass spectrometry (IMS) has recently established itself in the field of “spatial metabolomics.” Merging the sensitivity and fast screening of high-throughput mass spectrometry with spatial and temporal chemical information, IMS visualizes the production, location, and distribution of metabolites in intact biological models. Since metabolite profiling and morphological features are combined in single images, IMS offers an unmatched chemical detail on complex biological and microbiological systems. Thus, IMS-type “spatial metabolomics” emerges as a powerful and complementary approach to genomics, transcriptomics, and classical metabolomics studies. In this review, we summarize the current state-of-the-art IMS methods with a strong focus on desorption electrospray ionization (DESI)-IMS. DESI-IMS utilizes the original principle of electrospray ionization, but in this case solvent droplets are rastered and desorbed directly on the sample surface. The rapid and minimally destructive DESI-IMS chemical screening is achieved at ambient conditions and enables the accurate view of molecules in tissues at the µm-scale resolution. DESI-IMS analysis does not require complex sample preparation and allows repeated measurements on samples from different biological sources, including microorganisms, plants, and animals. Thanks to its easy workflow and versatility, DESI-IMS has successfully been applied to many different research fields, such as clinical analysis, cancer research, environmental sciences, microbiology, chemical ecology, and drug discovery. Herein we discuss the present applications of DESI-IMS in natural product research.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

“…They were developed during the last 10-15 years in plant natural products. Using highly sensitive and reproducible analytical methods, they allow the correlation between chemical profile (qualitative or quantitative) and bioactivity data (Zampieri et al, 2017;Parrot et al, 2018;Wolfender et al, 2019) with recent progress in the field of data analysis and integration at the extract level (Wolfender et al, 2019). Finally, the group of direct phytochemical isolation approaches focuses on the comprehensive chemical characterization of the plant extract and the isolation of novel scaffolds without immediately evaluating their bioactivity.…”

Novel applications of mass spectrometry‐based metabolomics in herbal medicines and its active ingredients: Current evidence

“…Besides MALDI, other ion sources, such as desorption electrospray ionization, laser ablation electrospray ionization, and secondary ion mass spectrometry can also be used for MSI. MSI techniques have opened up new avenues in several areas of life sciences, including medicine, microbiology, and natural product chemistry (Parrot et al, ).…”

“…Besides MALDI, other ion sources, such as desorption electrospray ionization, laser ablation electrospray ionization, and secondary ion mass spectrometry can also be used for MSI. MSI techniques have opened up new avenues in several areas of life sciences, including medicine, microbiology, and natural product chemistry (Parrot et al, 2018). Sarabia et al (2018) established a high-resolution MALDI MSI platform to reveal the detailed spatial distribution of metabolites in the root of barley seedlings in response to salinity stress.…”

Herbal medicines on the spot: back to the green essentials

“…15 Imaging mass spectrometry (IMS) has been positioned itself in the field of "spatial metabolomics". 16 MALDI imaging is not routinely applicable to plant analysis since there are many difficulties in preparing the samples. However, it can provide valuable information about metabolite and tissue distribution maps.…”

“…As an example, Hypericum perforatum leaves and petals were analyzed to study the spatial distribution of hypericin and hyperforin. 16 Nuclear magnetic resonance (NMR), although less sensitive than MS, is widely employed for metabolomics and works as a complementary technique. The different strategies applied to herbal medicines could be classified as 1) conventional NMR, 2) hyphenated NMR, 3) quantitative NMR (qNMR), 4) NMR based metabolomics and 5) Diffusion ordered spectroscopy (DOSY).…”