Use of mTRAQ derivatization reagents on tissues for imaging neurotransmitters by MALDI imaging mass spectrometry: the triple spray method

Toshimasa Ito,Masashi Hiramoto

doi:10.1007/s00216-019-02052-1

Abstract

During drug development, matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry is used for visually elucidating the distribution of substances such as biomarkers, candidate compounds, and metabolites in the tissues. However, it is difficult to make relative comparisons between tissue sections and there are still many challenges. Here, we report a new method of “triple spray” for the comparison of analyte distribution in multiple tissue slices. This method targets amino acids and amines, and it incorporates the application of the internal standard in the on-tissue derivatization step. With further development, it has the potential to alleviate problems caused by the matrix effect. Initially, we measured three serial sections of rat brain to verify the efficacy of this method. In the hypothalamus, where gamma-aminobutyric acid (GABA) is known to be present in high concentration, the GABA levels of the three serial section showed little variation (CV = 1.62%). Subsequently, we compared the GABA level in the brain between stroke-prone spontaneous hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats with three individuals each. It showed significant differences between these models at the pre-selected region of interest (p < 0.05). Our results show that the triple spray allows for relative comparison among multiple tissue slices with high reproducibility.Graphical abstract

Highlights

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging can visualize the distribution of various biomolecules with high spatial resolution on the order of micrometers, leading to application into many fields, including the use in drug development [1]
We focused on quantitatively evaluating gamma-aminobutyric acid (GABA) because it is an important neurotransmitter and there are many reported cases in the MALDI mass spectrometry imaging field [18, 19]
Peak intensity of endogenous GABA labeled with mTRAQΔ0 was normalized by that of GABA standard solution labeled with mTRAQΔ4 in order to generate the images and values without the factor of ion suppression

Summary

Introduction

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging can visualize the distribution of various biomolecules with high spatial resolution on the order of micrometers, leading to application into many fields, including the use in drug development [1]. It is attractive to be able to detect compounds such as biomarkers [2], administered drug, and its metabolite [3] without the use of radioisotope or antibody label One disadvantage of this method is the reliance on the analyte to be ionizable. One method conducts direct addition of the standard curve samples onto the tissue [8] and another uses sliced frozen homogenate sample spiked with the analyte standard solution as the standard curve sample [9], which can be effective for tissues with equal ion suppression across the tissue, such as liver tissues.

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