Silver nanoparticles as matrix for MALDI FTICR MS profiling and imaging of diverse lipids in brain

Owing to the diversity of lipids, profiling and imaging multiple classes of lipids in one analysis by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) is a great challenge. In this work, polyvinylpyrrolidone (PVP) capped silver nanoparticles (AgNPs) was used as the matrix for MALDI MSI for the first time to simultaneously analyze 10 classes of lipids from the brain. This analysis included fatty acids and their derivatives, sterols, CPAs, LPA and PAs, LPE and PEs, LPC and PCs, PS, Cers, SMs, and MAGs and DAGs, and other small metabolites. Owing to the abundant silver ions on the surface of PVP-capped AgNPs, compounds with poor ionization efficiency such as FAs and sterols can be detected. The PVP-capped AgNPs based MALDI MSI analysis of mouse brain showed that lipid distributions in the substructures of the mouse brain can be connected with their biological functions. The brain lipids in rats with middle cerebral artery occlusion (MCAO) were also investigated. Most unsaturated FAs, prostaglandins, CPAs, vitamin A, neuraminic acid, 5-OH-tryptophan and the K⁺ adducts of most phospholipids (PAs, LPE, PEs, PCs, PS) and SMs were extremely down regulated in the ischemic region and saturated FA, Cers, hexanoylcarnitine, stearaldehyde, the Na⁺ adduct of phospholipids (LPA, PAs, LPE, PEs, LPC, PCs) and SMs were highly expressed in the damaged section. These novel findings could be very significant for elucidating the disease mechanism. MALDI MSI using PVP-capped AgNPs as a matrix can be a powerful tool in histopathology and pathology studies.