Revealing Structure and Localization of Steroid Regioisomers through Predictive Fragmentation Patterns in Mass Spectrometry Imaging.

Identifying and mapping steroids in tissues can provide opportunities for biomarker discovery, the interrogation of disease progression, and new therapeutics. Although separation coupled to mass spectrometry (MS) has emerged as a powerful tool for studying steroids, imaging and annotating steroid isomers remains challenging. Herein, we present a new method based on the fragmentation of silver-cationized steroids in tandem MS, which produces distinctive and consistent fragmentation patterns conferring confidence in steroid annotation at the regioisomeric level without using prior derivatization, separation, or instrumental modification. In addition to predicting the structure of the steroid with isomeric specificity, the method is simple, flexible, and inexpensive, suggesting that the wider community will easily adapt to it. We demonstrate the utility of our approach by visualizing steroids and steroid isomer distributions in mouse brain tissue using silver-doped pneumatically assisted nanospray desorption electrospray ionization mass spectrometry imaging.

Single-cell metabolomics: where are we and where are we going?

Single-cell metabolomics with mass spectrometry enables a large variety of metabolites to be simultaneously detected from individual cells, without any preselection or labelling, to map phenotypes on the single cell level. Although the field is relatively young, it is steadily progressing with an increasing number of active research groups, techniques for cell sampling and ionization, tools for data analysis, and applications to answer important biomedical and environmental questions. In addition, the community shows great creativity in overcoming challenges associated with low sample volumes, a wide range of metabolite species, and large datasets. Here, we briefly discuss publications since 2019 and aim to provide the unfamiliar reader with an insight into the field and the expert reader with an update on the current status of the field.