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. 2017 Jan 3;89(1):576-580.
doi: 10.1021/acs.analchem.6b04185. Epub 2016 Dec 20.

Precast Gelatin-Based Molds for Tissue Embedding Compatible with Mass Spectrometry Imaging

Emily L Gill  1 , Richard A Yost  1   2 , Vinata Vedam-Mai  3 , Timothy J Garrett  2
Affiliations

Precast Gelatin-Based Molds for Tissue Embedding Compatible with Mass Spectrometry Imaging

Emily L Gill et al. Anal Chem. .

Abstract

Preparation of tissue for matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) generally involves embedding the tissue followed by freezing and cryosectioning, usually between 5 and 25 μm thick, depending on the tissue type and the analyte(s) of interest. The brain is approximately 60% fat; it therefore lacks rigidity and poses structural preservation challenges during sample preparation. Histological sample preparation procedures are generally transferable to MALDI-MSI; however, there are various limitations. Optimal cutting temperature compound (OCT) is commonly used to embed and mount fixed tissue onto the chuck inside the cryostat during cryosectioning. However, OCT contains potential interferences that are detrimental to MALDI-MSI, while fixation is undesirable for the analysis of some analytes either due to extraction or chemical modification (i.e., polar metabolites). Therefore, a method for both fixed and fresh tissue compatible with MALDI-MSI and histology is desirable to increase the breadth of analyte(s), maintain the topographies of the brain, and provide rigidity to the fragile tissue while eliminating background interference. The method we introduce uses precast gelatin-based molds in which a whole mouse brain is embedded, flash frozen, and cryosectioned in preparation for mass spectrometry imaging (MSI).

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Figures

Figure 1
Figure 1
Fresh mouse brain tissue (A) thaw mounted onto a glass slide along with 15% gelatin and (B) the precast mold mounted onto the chuck inside the cryostat using OCT.
Figure 2
Figure 2
Mouse brain tissue (A) flash frozen in liquid nitrogen with no embedding procedure, (B) flash frozen in liquid nitrogen and embedded inside one half of the precast mold, (C) a fresh mouse brain inside the precast mold with added 15% gelatin and (D) a PFA fixed mouse brain inside the precast mold.
Figure 3
Figure 3
MALDI mass spectra of (A) DHB matrix only (m/z 273 [2DHB+H-2H2O]+). and (B) a section of the precast mold coated in DHB showing poor spectral intensity.
Figure 4
Figure 4
MALDI-MSI of a mouse brain coronal section (A) the phospholipid region and (B) MSI images of phosphatidylcholine [PC 38:4 + Na]+ at m/z 832, phosphatidylcholine [PC 36:1 + Na]+ at m/z 810, and phosphatidylcholine [PC 38:6 + Na]+ at m/z 828.
See this image and copyright information in PMC

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