Background: Since its introduction 10 years ago by Caprioli and associates, MALDI mass spectrometry imaging has enabled spatial analysis of drugs, lipids, peptides, and polypeptides. In polypeptides, the detectable mass range is limited to small proteins with a mass less than 25 kDa. This is a limitation, as many proteins, including cytokines, growth factors, enzymes, and receptors have molecular weights, exceeding 25 kDa. In the present work, we report the development of a novel strategy to observe higher mass proteins up to 30 kDa.
Material/Methods: We investigated the development of sample preparation methods based on hexafluoroisopropanol (1,1,1,3,3,3-hexaluoro-2-propanol) and 2,2,2-trifluoroethanol solvents for protein solubilization optimized for high-mass proteins.
Results: We were, for the first time in mass spectrometry imaging, able to detect to proteins up to 70 kDa directly from tissue. These developments indicate future avenues by which the sensitivity of protein mass spectrometry imaging can be further improved. We applied these developments to ovarian cancer and demonstrate that protein are similar to that which can be obtained using 2D gel based analyses.
Conclusions: Increasing the possibility of detecting proteins and high-mass proteins is key for developing direct tissue proteomics and especially any potential functional investigation. These data will open the door of a novel step in mass spectrometry imaging.

Keywords: Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization - methods, Proteomics, Proteins - chemistry, Propanols, Ovarian Neoplasms - metabolism, Neoplasm Proteins - metabolism, Molecular Weight, Brain - metabolism, Tissue Extracts - metabolism, Trifluoroethanol, Tumor Markers, Biological - analysis