MALDI imaging MS of phospholipids in the mouse lung Karin

Journal of Lipid Research Volume 52, 2011 1551 Copyright © 2011 by the American Society for Biochemistry and Molecular Biology, Inc. that interfere with cysteinyl-leukotriene production are frequently used in treating asthma ( 6 ). These lipid mediators are derived from the enzymatic hydrolysis of arachidonatecontaining phospholipids, probably a phospholipase A 2 , and subsequent metabolism of free arachidonic acid to the oxygenated lipid mediator. Metabolites of docosahexaenoic acid are also emerging as important mediators of infl ammation resolution in the lung ( 7 ), and likewise, the docosahexaenoate is stored in membrane phospholipids that must be hydrolyzed to generate free docosahexaenoic acid. Because these mediators act in an autocrine and paracrine manner, the specifi c localization of arachidonateand docosahexaenoate-containing phospholipid precursors plays a critical role in driving the production of docosanoids, leukotrienes, and prostaglandins at local sites in the lung. In addition to phospholipids containing polyunsaturated fatty acyl groups, abundant phospholipids in the lung are present in lung surfactant (8, 9). Chemical imaging techniques, such as immunohistochemistry and dye staining, are typically used to enable the detection and determination of the localization of biological compounds. However, the ability to image the location of specifi c lipids in tissues has been limited. Staining with Nile Red ( 10 ), Oil Red O ( 11 ), or BODIPY 493/503 ( 12 ) provides the localization of only the neutral lipids in a tissue. Antibodies for different phospholipid headgroups are available for studying their localization in tissues by immunohistochemical methods ( 13 ), but specifi c antibodies Abstract Lipid mediators are important in lung biochemistry and are derived from the enzymatic oxidation of arachidonic and docosahexaenoic acids, which are PUFAs that are present in phospholipids in cell membranes. In this study, MALDI imaging MS was used to determine the localization of arachidonateand docosahexaenoate-containing phospholipids in mouse lung. These PUFA-containing phospholipids were determined to be uniquely abundant at the lining of small and large airways, which were unequivocally identifi ed by immunohistochemistry. In addition, it was found that the blood vessels present in the lung were characterized by sphingomyelin molecular species, and lung surfactant phospholipids appeared evenly distributed throughout the lung parenchyma, indicating alveolar localization. This technique revealed unexpected high concentrations of arachidonateand docosahexaenoate-containing phospholipids lining the airways in pulmonary tissue, which could serve as precursors of lipid mediators affecting airways biology. —Berry, K. A. Z., B. Li, S. D. Reynolds, R. M. Barkley, M. A. Gijón, J. A. Hankin, P. M. Henson, and R. C. Murphy. MALDI imaging MS of phospholipids in the mouse lung. J. Lipid Res . 2011. 52: 1551–1560.