An Alternative Method for Quantitative Mass Spectrometry Imaging (<i>q</i>-MSI) of Dopamine Utilizing Fragments of Animal Tissue

Abstract

Mass spectrometry imaging (MSI) is a well-known method for the ionization of molecules on tissue sections and the visualization of their localization. Recently, different sample preparation methods and new instruments have been used for MSI, and different molecules are becoming visible. On the other hand, although several quantification methods ( q -MSI) have been proposed, there is still room for the development of a simplified procedure. Here, we have attempted to develop a reproducible and reliable quantification method using a calibration curve prepared from tissue debris of a frozen section of a sample when we trim the frozen blocks. We discuss the reproducibility of this method across different sample lots and the effect of the biological matrix (ion suppression) on our results. The quantitative performance was evaluated in terms of accuracy and relative standard deviation, and the reliability of the quantitative values obtained by matrix-assisted laser desorption/ionization-MSI was further evaluated by enzyme-linked immunosorbent assay (ELISA). Our q -MSI method for the quantification of dopamine in mouse brain tissue was found to be highly linear, accurate, and precise. The quantitative values obtained by MSI were found to be highly comparable (>85% similarity) to the results obtained by ELISA from the same tissue extracts.

Exploiting Differential Signal Filtering (DSF) and Image Structure Filtering (ISF) Methods for Untargeted Mass Spectrometry Imaging of Bacterial Metabolites

“…The average spectrum corresponding to the coculture condition was then investigated to look for signals specifically induced by the interaction between bacteria with a high confidence level. For this purpose, the following criteria were required to postulate the specificity of a signal implied during the interaction: The ion must be exclusively present in the mass spectra of the tested condition (interaction). The resulting ion image had to be recorded in a minimum of 4 out of 5 biological replicates; the topological coherence of the ion image structures was visually assessed by the operator. MSI is generally speaking not a quantitative method, especially considering the label-free techniques, despite substantial efforts focusing on tissue sections during the last years. − In the absence of a quantitative method that could operate directly on agar media, we decided to retain the signals detected only during the interaction between the bacteria. Consequently, we omitted the signals variation linked to the overexpression or repression of the compounds, initiated by the coculture conditions, but in return, we preserved our data from biases and ambiguities.…”