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

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.