Study on Tissue Distribution of A Variety of Endogenous Metabolites By Air Flow Assisted Ionization-Ultra High Resolution Mass Spectrometry Imaging

As a promising new molecular imaging technique, mass spectrometry imaging (MSI) has attracted more and more attention in the field of biomedicine. A method of air flow assisted ionization-ultra high resolution mass spectrometry-based mass spectrometric imaging (AFAI-MSI) was developed to profile endogenous metabolites in rat kidney tissue in this study. Rat kidneys were collected and cut into frozen tissue sections, and then were analyzed on an AFAI-MSI system operated in positive ion mode using acetonitrile- isopropanol-water (4:4:2, V/V, 5 μL min^?1) as spray solvent, nitrogen gas as spray gas (0.6 MPa) and air as assisting gas (45 L min^?1). The mass range and resolution were set to be 70–1000 Da and 70000, respectively. As a result, a total of 38 metabolites, ranging from 10³ to 10⁷ in signal strength and belonging to different metabolite types, including organic amines, sugars, vitamins, peptides, neurotransmitters, organic acids, phospholipids, sphingolipids, glycerides, and cholesterol esters, were identified and imaged to characterize their tissue-specific distribution in kidney tissues. Some metabolites, such as choline, acetycholine, betaine, phosphocholine, and glycerolphosphocholin were found to have distinct distribution along the cortex-medulla axis, which may be involved in the formation of osmotic pressure gradient in the kidney. The proposed ultra high resolution mass spectrometry based AFAI-MSI method can work without sample pretreatment, showing high sensitivity and wide metabolite coverage, and is expected to provide a new analytical approach in the research of in situ characterization and metabolic regulation mechanism of endogenous metabolites in kidney.