A new approach for the analysis of amino acid neurotransmitters in mouse brain tissues using DESI imaging

Mass spectrometry imaging using desorption electrospray ionization (DESI imaging) is a method with the potential to investigate the distribution of neurotransmitters (biogenic amines and amino acids) in brain tissues. Because of the low ionization efficiency of neurotransmitters in direct tissue analysis by DESI, neurotransmitters can be analyzed using derivatization protocols that insert a known compound into their structures through a chemical reaction due to signal suppression by lipids. In this sense, this work aims to combine a chemical derivatization protocol with DESI imaging in order to improve the analysis sensitivity of the amino acids glycine (Gly), alanine (Ala), dopamine (Dop), and gamma-aminobutyric acid (GABA) in mouse brain tissues, as well as to apply this protocol to analyze mice with Parkinson's disease. Derivatization took place using the reagent 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+) and was first investigated in a solvent to ensure the detection of the expected products. Subsequently, the brain tissue surface was subjected to the derivatization solution through spraying. Then, the tissue was analyzed by DESI, and the derivatized Gly, Ala, Dop, and GABA were detected. DESI imaging analysis demonstrated distinct spatial distributions for these derivatized amino acid neurotransmitters. The application of the protocol in brain sections from mice with Parkinson's disease demonstrated differences in the intensities and anatomical distribution for the derivatized amino acids compared with control tissues (unaffected by Parkinson's). The protocol combining derivatization with DESI imaging described in this work emerges as a potential tool for analyzing Parkinson's disease biomarkers in mouse brain tissues.