3-Aminophthalhydrazide (Luminol) As a Matrix for Dual-Polarity MALDI MS Imaging

Abstract

In many aspects of the matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) technique, the discovery of new MALDI matrixes has been a major task for the improvement of ionization efficiency, signal intensity, and molecular coverage. In this work, five analog compounds, including phthalhydrazide, 3-aminophthalhydrazide (3-APH or luminol) and its sodium salt, 4-aminophthalhydrazide (4-APH), and 3-nitrophthalhydrazide (3-NPH) were evaluated as potential matrixes for MALDI Fourier-transform ion cyclotron resonance (FTICR) MSI of metabolites in mouse brain tissue. The five candidate MALDI matrixes were mainly evaluated according to the solid-state ultraviolet absorption, the ion yields and species, and the dual-polarity detection. Among the five candidate matrixes, 3-APH and its sodium salt enabled the detection of endogenous metabolites better than the three other candidates in dual polarities. The best results were observed with 3-APH. Compared with commonly used MALDI matrixes such as 2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, and 9-aminoacridine, 3-APH exhibited superior performance in dual polarity MALDI MSI, higher sensitivity, broader molecular coverage, and lower background noise. The use of 3-APH led to on-tissue MALDI FTICR MSI of 159 and 207 mouse brain metabolites in the positive and negative ion modes, respectively. Among these metabolites, nucleotides, fatty acids, glycerolipids, glycerophospholipids, sphingolipids, and saccharolipids are included. 3-APH was further used for MALDI FTICR MSI of metabolic responses to ischemia-induced disturbances in mouse brain subjected to middle cerebral artery occlusion (MCAO), thus revealing the alteration of 105 metabolites in the ipsilateral hemispheres. This further emphasizes the great potential of 3-APH as a matrix for the localization of biomarkers in brain diseases.

Developing IR-780 as a Novel Matrix for Enhanced MALDI MS Imaging of Endogenous High-Molecular-Weight Lipids in Brain Tissues

“…Furthermore, IR-780 far surpassed DHB and 9-AA in the imaging of high-MW lipids in adjacent horizontal tissue sections (Figure S8). To our knowledge, this is the first time to realize the simultaneous imaging of PPIs, CLs, and GGs from rat brain sections by MALDI MS without pretreatment. ,,− Besides, IR-780 matrix was utilized for the analyses of heart and kidney tissues of rats. PI, PIP 2 , STs, CLs, and GGs could be detected with good signal responses both in heart and kidney tissue sections (Figure S9), indicating that IR-780 could serve as a powerful matrix for imaging of high-MW lipids in diverse animal tissues.…”

Unravel the Local Complexity of Biological Environments by MALDI Mass Spectrometry Imaging

“…In this context, MSI of brain tissue plays a crucial role not only in neurobiology but also in tissue sample preparation development. Many studies evaluated the performance of a novel MALDI MSI method, e.g., evaluation of a new matrix, or instrumental setup by analyzing animal brain tissue and mapping specific histological regions [28,90,91].…”

“…It is known that different classes of phospholipids, distinguished by their head group, are localized in different brain regions. For example, the glycerophosphoserine (PS) (22:6/22:6) was revealed by nanostructure initiator MALDI MSI to be abundant in the cerebellum region of the mouse brain [90]. The PS (34:0) was detected in negative mode mainly in the cortex and hypothalamus.…”

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

“…3-Aminophthalhydrazide (3-APH, also known as luminol) is a commercially available and very effective chemiluminescent substrate. 3-APH was evaluated by Li and coworkers [37] as a dual-polarity matrix with superior performance than common matrices such as 2,5-DHB, CHCA, and 9-AA. 3-APH was able to detect and give a spatial distribution of 159 and 207 metabolites in the mouse brain in the positive and negative ion modes, respectively.…”