A systematic study of lipids – from ESI analysis to MALDI Imaging using a 7T FT-ICR instrument

Abstract

Lipids are essential molecules for cellular signaling, metabolism, and key components of our cells. At the skin level, exposure to solar radiation, high oxygen levels, and environmental pollutants leads to premature skin aging, tissue inflammation, and photocarcinogenesis. This oxidative stress activates cutaneous lipoxygenases or causes nonenzymatic lipid peroxidation, thus forming oxidized lipids (oxLipS). These oxLipS are crucial components in events like cellular senescence. We present a systematic investigation of lipids and their non-enzymtic oxidation products generated in a controlled environment by reactive oxygen species (ROS) after UV exposure. Untargeted OxLipS analysis was performed on a dual-source ESI/MALDI 7T scimaX FTICR MRMS (Bruker). ESI provides high throughput and high sensitivity, while the MALDI Imaging platform (MSI) complements with the spatial localization. A lipid standard solution (LipS), containing 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PAPC) and not UV affected references 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dinonanoyl-sn-glycero-3-phosphocholine (DNPC) in chloroform were exposed to solar-like conditions (UVA radiation). Direct infusion ESI experiments of the LipS generated crucial information on oxLipS species produced by ROS formed in solution. Accurate, high-resolution MS data allowed identification of known and newly formed species via database search (LipidMAPS). A tentative structural assignment was performed for m/z values not found in the database. Skin biopsies were mounted on ITO slides for MALDI MSI. Different sample preparation methods (sublimation, spraying) after tissue washing have been investigated, and instrument parameters adapted for optimized FT ICR imaging [1,2]. Selected m/z values were compared between ESI and MALDI, thus aiding the translation of ex vivo experiments to in vivo MALDI MSI results. Here, several oxLipS were localized, visualized, and identified in skin section samples. The different sample preparation approaches allowed us to further improve and develop a method for oxLipS investigation in skin tissue section via MALDI MSI.