Matrix-assisted laser desorption-ionization imaging mass spectrometry for direct tissue analysis.

Matrix-assisted laser desorption-ionization (MALDI) imaging mass spectrometry (IMS) is a powerful tool in histopathological characterization and represents a modern analytical technique, enabling two-dimensional detection of molecular components of biological samples. Using this method, it is possible to investigate the spatial distribution of proteins, lipids, carbohydrates, cholesterols, nucleic acids, phospholipids, and small molecules in biological systems by in-situ analysis of cell cultures and tissue sections. Recently, MALDI-IMS has become an essential tool for tissue analyses in life science applications, offering global analysis of tissue samples. An advantage of this imaging technique is the acquisition of local molecular expression profiles up to the microscopic level, while maintaining the topographic integrity of the tissue by avoiding time-consuming extraction, purification, or separation steps, respectively. With MALDI-IMS it is possible to determine the distribution of hundreds of unknown compounds in a single measurement, allowing rapid probing of the tissues' biochemistry. Moreover, MALDI-IMS results include qualitative and semiquantitative information, providing unique chemi-morphological information about the tissue status, which represents an important benefit for future analytical interpretation of pathological changes of a tissue. This article summarizes the most recent advances in sample preparation, instrumentation, and data-processing techniques for MALDI-IMS

MALDI-MS tissue imaging identification of biliverdin reductase B overexpression in prostate cancer.

[object Object]: New biomarkers are needed to improve the specificity of prostate cancer detection and characterisation of individual tumors. In a proteomics profiling approach using MALDI-MS tissue imaging on frozen tissue sections, we identified discriminating masses. Imaging analysis of cancer, non-malignant benign epithelium and stromal areas of 15 prostatectomy specimens in a test and 10 in a validation set identified characteristic m/z peaks for each tissue type, e.g. m/z 10775 for benign epithelial, m/z 6284 and m/z 6657.5 for cancer and m/z 4965 for stromal tissue. A 10-fold cross-validation analysis showed highest discriminatory ability to separate tissue types for m/z 6284 and m/z 6657.5, both overexpressed in cancer, and a multicomponent mass peak cluster at m/z 10775-10797.4 overexpressed in benign epithelial tissue. ROC AUC values for these three masses ranged from 0.85 to 0.95 in the discrimination of malignant and non-malignant tissue. To identify the underlying proteins, prostate whole tissue extract was separated by nano-HPLC and subjected to MALDI TOF/TOF analysis. Proteins in fractions containing discriminatory m/z masses were identified by MS/MS analysis and candidate marker proteins subsequently validated by immunohistochemistry (IHC). Biliverdin reductase B (BLVRB) turned out to be overexpressed in PCa tissue. BIOLOGICAL SIGNIFICANCE: In this study on cryosections of radical prostatectomies of prostate cancer patients, we performed a MALDI-MS tissue imaging analysis and a consecutive protein identification of significant m/z masses by nano-HPLC, MALDI TOF/TOF and MS/MS analysis. We identified BLVRB as a potential biomarker in the discrimination of PCa and benign tissue, also suggesting BVR as a feasible therapeutic target