MALDI DIRECT ANALYSIS AND IMAGING OF FROZEN VERSUS FFPE TISSUES: WHAT STRATEGY FOR WHICH SAMPLE?
Résumé
Various preservation methods can be used for keeping tissues depending on the organism and nature of the tissue. Tissue preservation techniques determine what structures are preserved. Thus, tissue fixation followed by embedding in paraffin is known to improve tissue conservation for long period. However, frozen tissues are much easier to handle for retrieving molecular information's especially on proteins. In this context, we first used frozen samples and were interested in finding better suited matrices for MALDI-MSI. So called Solid Ionic Matrices were found to be of great interest for such applications. These matrices present greater shot to shot reproducibility, increased intensity and number of detected peptides and lower ablation. Concerning FPE samples, the ones fixed in formalin were studied. For FFPE samples, direct tissue analysis reveals cross-linking reaction induced by formalin fixation, resulting in great difficulty for obtaining molecular information on proteins. A different strategy has, then, to be used, involving in situ enzymatic digestion. Using automatic micro-deposition and creating a raster of micro area, for the enzymatic digestion and the matrix deposition steps, allows the performance of MALDI-MSI. This new approach has increased the potential of MALDI-MSI by making the technique useful for the imaging of a wider range of tissue and could lead to several clinical applications.