Lipid Coverage in Nanospray Desorption Electrospray Ionization Mass Spectrometry Imaging of Mouse Lung Tissues

Abstract

Lipids are a naturally occurring group of molecules that not only contribute to the structural integrity of the lung preventing alveolar collapse but also play important roles in the anti-inflammatory responses and antiviral protection. Alteration in the type and spatial localization of lipids in the lung plays a crucial role in various diseases, such as respiratory distress syndrome (RDS) in preterm infants and oxidative stress-influenced diseases, such as pneumonia, emphysema, and lung cancer following exposure to environmental stressors. The ability to accurately measure spatial distributions of lipids and metabolites in lung tissues provides important molecular insights related to lung function, development, and disease states. Nanospray desorption electrospray ionization (nano-DESI) and other ambient ionization mass spectrometry techniques enable label-free imaging of complex samples in their native state with minimal to absolutely no sample preparation. However, lipid coverage obtained in nano-DESI mass spectrometry imaging (MSI) experiments has not been previously characterized. In this work, the depth of lipid coverage in nano-DESI MSI of mouse lung tissues was compared to liquid chromatography tandem mass spectrometry (LC-MS/MS) lipidomics analysis of tissue extracts prepared using two different procedures: standard Folch extraction method of the whole lung samples and extraction into a 90% methanol/10% water mixture used in nano-DESI MSI experiments. A combination of positive and negative ionization mode nano-DESI MSI identified 265 unique lipids across 20 lipids subclasses and 19 metabolites (284 in total) in mouse lung tissues. Except for triacylglycerols (TG) species, nano-DESI MSI provided comparable coverage to LC-MS/MS experiments performed using methanol/water tissue extracts and up to 50% coverage in comparison with the Folch extractionbased whole lung lipidomics analysis. These results demonstrate the utility of nano-DESI MSI for comprehensive spatially resolved analysis of lipids in tissue sections. A combination of nano-DESI MSI and LC-MS/MS lipidomics is particularly useful for exploring changes in lipid distributions during lung development, as well as resulting from disease or exposure to environmental toxicants.

CpG preconditioning reduces accumulation of lysophosphatidylcholine in ischemic brain tissue after middle cerebral artery occlusion

“…The primary capillary delivers the solvent to the liquid bridge and the secondary capillary transfers the liquid and extracted molecules to the mass spectrometer inlet where molecules are ionized by nanoelectrospray ionization. Nano-DESI MSI [27][28][29][30] has been used to study nicotine distribution in rat brain tissue [31], metabolite diffusion from live bacterial colonies [32], imaging of lipids and metabolites in different types of tissues with moderate and high spatial resolution [33][34][35], MS/MS imaging of lipids and metabolites in mouse embryo implantation sites [36], and quantitative MSI of low abundance molecular species [37][38][39].…”

Direct Liquid Extraction and Ionization Techniques for Understanding Multimolecular Environments in Biological Systems (Secondary Publication)

“…In nano-DESI, MeOH/H2O (9:1) mixture is the preferred solvent 123,[146][147][148] . ACN/toluene/MeOH (7:3:10) was used to measure lipids 149) , and ACN/MeOH (0.1% Mass Spectrometry Advance Publication…”

“…In a comparison of lipid measurements in mouse lung tissue using nano-DESI and liquid chromatography-tandem mass spectrometry (LC-MS/MS), 147 ) the number of lipids measured by nano-DESI was about 50% of that measured by LC-MS/MS in extracts prepared using the Forch method. Although direct comparison is difficult due to the different extraction processes used for the LC-MS/MS samples, ion suppression by nano-DESI was higher because multiple lipids are ionized simultaneously and the area of the sample extracted is 100 μm 2 , which reduces the number of molecules.…”

Quantification and molecular imaging of fatty acid isomers from complex biological samples by mass spectrometry

“…Mass spectrometry (MS) is emerging as one of the most informative techniques for the study of FAs due to its superior analytical power. [7][8][9] Although signicant advancements have occurred in lipidomics research using various MS techniques including shotgun MS 10 and hyphenated chromatographic MS techniques (LC/GC-MS), 7 challenges remain in elucidating the ne structures of FA C]C bond positional isomers. Conventional low-energy collisional activation methods, such as collision-induced-dissociation (CID) tandem MS, are ineffective in recognizing the C]C bond positions in FA isomers due to the high energy required to cleave the C]C bond.…”