Laser Desorption Ionization-Mass Spectrometry Imaging of Heart Tissue

Tissue imaging via laser desorption/ionization–mass spectrometry (LDI–MS) imaging was performed as previously described [21 (link),68 (link),69 (link)] in 10 µm heart sections covered by gold monolayers. LDI–MS tissue images were acquired using a MALDI-TOF UltrafleXtreme instrument with SmartBeam II Nd:YAG/355 nm laser (Bruker Daltonics, Billerica, MA, USA) and processed by using open-source software rMSI (version 0.3.1) [70 (link)] and rMSIproc (https://github.com/prafols/rMSIproc (version 0.9.1) (accessed on 2 July 2022)) [69 (link)]. The metabolites’ tentative identification was based on the exact mass of their sodium adduct according to the Human Metabolome Database, filtering metabolites with mass error Δ < 50 ppm, and the results obtained from the LC–MS/MS experiments.