Resolving the glycosaminoglycan signature of ischemic stroke brain using PRM-based IR-MALDESI mass spectrometry imaging.

Stroke is the second most common cause of death in the world and a leading cause of disability. Ischemic stroke is the most common type of stroke (~87%), necessitating research into effective treatments. Chondroitin sulfate (CS) is a sulfated glycosaminoglycan (GAG) found in the central nervous system (CNS) that contains labile sulfate groups which, upon loss, leads to inaccurate structural annotations. Variable sulfation patterns have been implicated in several neurological diseases. Additionally, CS-GAG analysis is challenging due to labile sulfate groups and the presence of positional isomers. These isomers must be distinguished to develop effective targeted therapies. Currently, glycan mass spectrometry imaging (MSI) lacks soft ionization sources which impedes intact analysis of the labile sulfate modifications. Infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) is a soft ambient ionization technique capable of preserving labile species without chemical derivatization. In this work, IR-MALDESI with parallel reaction monitoring (PRM) was used to energetically resolve and characterize intact mono-sulfated CS-GAG positional isomers in healthy and ischemic stroke brain. Our results revealed that both positional isomers were upregulated in the stroke brain and their relative abundance remained constant across the tissue.