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

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 5-25 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, whilst 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 whilst 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).

Sample preparation strategies for high‐throughput mass spectrometry imaging of primary tumor organoids

“…A thin white line is included in the figure to outline the Matrigel hydrogel boundary within the embedded gelatin. Gelatin is considered an MSI compatible material for small molecule and lipid analysis . Supporting Information Table S1) contains a list of all background peaks detected from the Matrigel, which are also found in the organoids themselves.…”

Emerging applications in mass spectrometry imaging; enablers and roadblocks

“…Embedding several tissues from the same study has also proven beneficial for reducing sample preparation time and preventing molecular changes via "freezer burn" to tissue sections in the cryostat. 29 MSI compatible materials that do not interfere with analysis include gelatin 30 and carboxymethylcellulose (CMC). 31 Alternatively, poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA) was specifically developed for MSI, as it is liquid at -8 °C.…”

Trends in mass spectrometry imaging for cardiovascular diseases

“…The typical section thickness varies between 10 and 20 μm to avoid cracking or excessive drying times. Fragile cardiovascular tissue can be supported during sectioning with an embedding medium, for example, gelatin [ 18 , 19 ] or carboxymethyl cellulose [ 20 , 21 ]. The use of optimal cutting temperature (OCT) compound is not recommended due to possible polymeric contamination of the MS spectra [ 22 ] that obscure some of the relevant molecular details.…”