Derivatization Strategy for Simultaneous Molecular Imaging of Phospholipids and Low-Abundance Free Fatty Acids in Thyroid Cancer Tissue Sections

Abstract

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) has been applied in many fields for detecting and imaging a variety of metabolites. In cancer research, this fast-growing imaging method also helps to elucidate the connection between the changes of metabolites in the microenvironment and the proliferation and survival of cancer cells. Free fatty acids (FFAs) are a vital building block of phospholipids (PLs) that can serve as a second cellular messenger and provide nutrients in the cancer microenvironment. The metabolism process of FFAs and PLs is highly relevant to the initiation and progression of different cancers. To better understand the metabolism process in cancer tissues, simultaneously detecting and imaging FFAs and PLs is essential. Despite the crucial developments that have been performed in the field of lipids imaging, FFAs and PLs have rarely been detected and imaged simultaneously in positive ion mode with good detection sensitivity. In this work, an on-tissue derivatization method was used to add a permanently quaternary amine onto FFAs; then, the FFAs and PLs were simultaneously imaged in positive ion mode. The derivatized FFAs are suitable for detection in positive ion mode. In comparison with the traditional matrix and the previous derivatization method, our derivatization reagent has a higher sensitivity for imaging FFAs. In addition, for simultaneous imaging analysis of FFAs and PLs, the number of imaged FFAs and PLs is greater than that with the previous on-tissue derivatization method. This high-sensitivity on-tissue derivatization method was applied to detect and image PLs and fatty acids in thyroid cancer tissues. In the MSI experiment, FFA derivatives and PLs were imaged while molecular localization and tissue integrity were maintained. Meanwhile, the correlation between PLs and FFAs was also studied, and the results showed that the correlations between saturated FFAs of C16:0 and C18:0 and PLs are better than the correlations of unsaturated FFAs with PLs.

Validation of MALDI-MS imaging data of selected membrane lipids in murine brain with and without laser postionization by quantitative nano-HPLC-MS using laser microdissection

“…While in the analysis of extracted analyte upstream separation techniques like high performance liquid chromatography (HPLC) can be used to reduce sample complexity and omit ISE, MALDI-MSI inherently handles unseparated samples. In order to reduce ISE for the targeted analysis of certain heavily suppressed analyte classes, on tissue enzymatic digestion to deplete suppressing substances and on tissue derivatization to increase sensitivity for a certain analyte class have been successfully employed [22][23][24]. In a different approach, laser-induced postionization in a fine vacuum MALDI ion source (MALDI-2) has shown promising first results pointing towards a reduction in ISE in the analysis of membrane lipids [15,[25][26][27].…”

Recent developments of novel matrices and on-tissue chemical derivatization reagents for MALDI-MSI

“…With DMPI Wang and coworkers [88] synthesized N,Ndimethylpiperazine iodide (DMPI) using CH 3 I and Nmethylpiperazine. 2-(7-Azabenzotriazol-1-yl)-N,N,N´,N´tetramethyluronium hexafluorophosphate (HATU) was used in this work to generate active esters from carboxylic acids derived from fatty acids such as C16:0 and C18:0.…”

Glass Surface as Strong Base, ‘Green’ Heterogeneous Catalyst and Degradation Reagent

“…The finding that biomolecules such as glutathione and acetylcholine can undergo significant amounts of chemical degradation when in contact with glass surfaces, raises awareness of the possible significance of the phenomenon considering that many important biomolecules are stored in solution in glass containers. Considering the importance of phospholipids in many practical aspects of chemistry 44,45 including mRNA-based COVID-19 vaccine, 46 we chose to study three types of phospholipids in detail: zwitterionic phosphocholine (PC) and zwitterionic phosphoethanolamine (PE) as well as negatively charged phosphatidylglycerol (PG).…”