• Tissue Lipid Analysis via MALDI Imaging (MALDI-IMS)

      Feldman, Steven G.; Scott, Alison June; Ernst, Robert K. (2013-04-11)
      Mammalian tissue contains a complex array of lipids and membrane components. Analysis is typically accomplished by one of many histological methods, such as Hematoxylin and Eosin (H&E) stain, immunohistochemistry (IHC) and in situ hybridization (ISH). However, a limitation of most techniques is a requirement for prior knowledge of the targets of interest. Mass spectrometry (MS) coupled assays are useful for their inherent speed and accuracy. Hyphenated MS techniques, such as MALDI-TOF MS (Matrix Assisted Laser Desorption Ionization-Time of Flight) have been developed for rapid analysis of complex biological samples. MALDI-TOF MS lends itself to tissue slices because it does not require pure samples and can offer de novo discovery of sample components. Here we show the coupling of this technique with histological staining for the investigation of lipids and their localization within mouse kidney tissue slices. This method is shown to be extensible through the incorporation of LIFT (MS/MS) wherein a specific peak of known molecular weight is exposed to a high energy laser which causes reliable and reproducible fragmentation based on bond energies within the molecule. As such, aspects of the target molecule from a class (eg phospholipids) down to side chains can be identified allowing the fullscale investigation of major tissue components. In a proof of concept study, pure standards of the major phospholipids phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) were subjected to LIFT, to confirm structures. Subsequently, MALDI-IMS applied to tissue slices reveals abundant peaks in the range of predicted phospholipids. These results will be analyzed to confirm these tissue phospholipids. MALDI-TOF MS coupled with LIFT presents a novel way of looking at tissue without prior knowledge of its constituents as it allows for analysis in the absence of traditional reagents such as antibodies or nucleic acid probes.