The use of 1,5-diaminonaphthalene for matrix-assisted laser desorption/ionization mass spectrometry imaging of brain in neurodegenerative disorders.

The selection of a suitable matrix and deposition technique constitutes a critical step in successful matrix-assisted laser desorption/ionization mass spectrometry imaging measurement. In the present work, we compared three techniques of matrix deposition, specifically, sublimation and spraying of 1,5-diaminonaphthalene with two automatic sprayers, ImagePrep and iMatrixSpray. The studied methods were evaluated in experiments for the analysis of lipid composition in the brains of two mouse models of neurodegeneration: APP/PS1 mice with plaques of amyloid β (Aβ) peptides and THY-Tau22 mice with pathologically hyperphosphorylated Tau protein, two hallmarks of Alzheimer's disease-like pathology. The sublimation method provided irreproducible results because of significant matrix loss due to the high vacuum in the ion source and laser irradiation. In contrast, the ImagePrep and iMatrixSpray provided stable film of the matrix. The deposited matrix was stable during the measurement, and highly reproducible datasets were obtained. Both spraying methods yielded similar results with approximately the same number of detected lipids and comparable signal intensity. However, iMatrixSpray has two main advantages: a faster matrix deposition and the formation of smaller matrix crystals leading to better spatial resolution. In the APP/PS1 mouse model at an age of 6 months, we found colocalization of Aβ plaques with different phospholipids, sphingolipids and lysophospholipids. We did not find a difference in lipid composition between the THY-Tau22 mice and the wild-type controls. The results indicate that hyperphosphorylation of tau protein in the THY-Tau22 mouse model at the age of 6 months is not accompanied with a significant change in lipid content in the brain. However, considering limitations of the used method, a definitive conclusion in this respect will need further research.