Identification and Imaging of Prostaglandin Isomers Utilizing MS3 Product Ions and Silver Cationization

Prostaglandins(PGs) are important lipid mediators involved inphysiological processes, such as inflammation and pregnancy. The pleiotropiceffects of the PG isomers and their differential expression from celltypes impose the necessity for studying individual isomers locallyin tissue to understand the molecular mechanisms. Currently, massspectrometry (MS)-based analytical workflows for determining the PGisomers typically require homogenization of the sample and a separationmethod, which results in a loss of spatial information. Here, we describea method exploiting the cationization of PGs with silver ions forenhanced sensitivity and tandem MS to distinguish the biologicallyrelevant PG isomers PGE(2), PGD(2), and & UDelta;12-PGD(2). The developed method utilizes characteristic product ionsin MS3 for training prediction models and is compatiblewith direct infusion approaches. We discuss insights into the fragmentationpathways of Ag+ cationized PGs during collision-induceddissociation and demonstrate the high accuracy and robustness of themodel to predict isomeric compositions of PGs. The developed methodis applied to mass spectrometry imaging (MSI) of mouse uterus implantationsites using silver-doped pneumatically assisted nanospray desorptionelectrospray ionization and indicates localization to the antimesometrialpole and the luminal epithelium of all isomers with different abundances.Overall, we demonstrate, for the first time, isomeric imaging of majorPG isomers with a simple method that is compatible with liquid-basedextraction MSI methods.