Eric B. Monroe

Imaging mass spectrometry: fundamentals and applications to drug discovery.

Imaging mass spectrometry (IMS) encompasses a variety of techniques that enable the chemical imaging of analytes, which range in size from atoms and small molecules to intact proteins, directly from biological tissues. IMS is transforming specific areas in biological research with its unique combination of chemical and spatial information. Innovations in instrumentation and imaging protocols will make this approach invaluable at many stages of the drug discovery process, including pharmacological target screening and evaluating the distribution of drug and drug metabolites in cells and tissues. The fundamentals and unique methodology of IMS are discussed, along with exciting new applications to drug discovery science.

SIMS and MALDI MS imaging of the spinal cord

The application of MS to imaging, or MS imaging (MSI), allows for the direct investigation of tissue sections to identify biological compounds and determine their spatial distribution. We present an approach to MSI that combines secondary ion MS (SIMS) and MALDI MS for the imaging and analysis of rat spinal cord sections, thereby enhancing the chemical coverage obtained from an MSI experiment. The spinal cord is organized into discrete, anatomically defined areas that include motor and sensory networks composed of chemically diverse cells. The MSI data presented here reveal the spatial distribution of multiple phospholipids, proteins, and neuropeptides obtained within single, 20 μm sections of rat spinal cord. Analyte identities are initially determined by primary mass match and confirmed in follow‐up experiments using LC MS/MS from extracts of adjacent spinal cord sections. Additionally, a regional analysis of differentially localized signals serves to rapidly screen compounds of varying intensities across multiple spinal regions. These MSI analyses reveal new insights into the chemical architecture of the spinal cord and set the stage for future imaging studies of the chemical changes induced by pain, anesthesia, and drug tolerance.

Adapting the stretched sample method from tissue profiling to imaging

The characterization and localization of peptides and proteins in tissues provides information that aids in understanding their function and in characterizing disease states. Over the past decades, the use of MS for the profiling and imaging of biological compounds from tissues has evolved into a powerful modality to accomplish these studies. One recently described sampling approach, the stretched sample method (Monroe, E. B. et al.., Anal. Chem. 2006, 78, 6826–6832), places a tissue section onto an array of glass beads embedded on a Parafilm M membrane. When the membrane is stretched, it separates the tissue section into thousands of cell‐sized pieces for tissue profiling by MALDI‐MS. The physical separation between beads eliminates analyte redistribution during matrix application and allows long analyte extraction periods without loss of spatial resolution. Here, we enhance this sampling approach by introducing algorithms that enable the reconstruction of ion images from these stretched samples. As the first step, a sample‐tailored data acquisition method is devised to obtain mass spectra exclusively from the beads, thereby reducing the time, instrument resources, and data handling required for such MS imaging (MSI) experiments. Next, an image reconstruction algorithm matches data acquired from the stretched sample to the initial bead locations. The efficacy of this method is demonstrated using peptide‐coated beads with known peptide distributions and appears well‐suited to the MSI of heterogeneous tissue samples.

Chapter 13: Imaging of cells and tissues with mass spectrometry: adding chemical information to imaging.

Techniques that map the distribution of compounds in biological tissues can be invaluable in addressing a number of critical questions in biology and medicine. One of the newer methods, mass spectrometric imaging, has enabled investigation of spatial localization for a variety of compounds ranging from atomics to proteins. The ability of mass spectrometry to detect and differentiate a large number of unlabeled compounds makes the approach amenable to the study of complex biological tissues. This chapter focuses on recent advances in the instrumentation and sample preparation protocols that make mass spectrometric imaging of biological samples possible, including strategies for both tissue and single-cell imaging using the following mass spectrometric ionization methods: matrix-assisted laser desorption/ionization, secondary ion, electrospray, and desorption electrospray.

Mass spectrometric imaging of the nervous system.

Mass spectrometric imaging (MSI) integrates multiple fields of analytical and biomedical research with the goal of generating chemical maps that present the identity and location of the elements, molecules, and molecular complexes that comprise biological structures. Rapid advances in the development of MSI, which include a broad range of sampling and mass spectrometry strategies, allow the increasingly information-rich creation of chemical images of structurally complex tissues, individual cells, and even single chromosomes. Here we describe a variety of MSI techniques available to investigate the nervous system, with particular focus on the capability of MSI to examine both normal and diseased brain function. An important investigative tool, MSI offers tremendous potential in fundamental studies of brain chemistry, localization of pharmaceutical compounds, and the discovery of biomarkers for different neuropathologies.

Exploring the Sea Urchin Neuropeptide Landscape by Mass Spectrometry

AbstractNeuropeptides are essential cell-to-cell signaling messengers and serve important regulatory roles in animals. Although remarkable progress has been made in peptide identification across the Metazoa, for some phyla such as Echinodermata, limited neuropeptides are known and even fewer have been verified on the protein level. We employed peptidomic approaches using bioinformatics and mass spectrometry (MS) to experimentally confirm 23 prohormones and to characterize a new prohormone in nervous system tissue from Strongylocentrotus purpuratus, the purple sea urchin. Ninety-three distinct peptides from known and novel prohormones were detected with MS from extracts of the radial nerves, many of which are reported or experimentally confirmed here for the first time, representing a large-scale study of neuropeptides from the phylum Echinodermata. Many of the identified peptides and their precursor proteins have low homology to known prohormones from other species/phyla and are unique to the sea urchin. By pairing bioinformatics with MS, the capacity to characterize novel peptides and annotate prohormone genes is enhanced. Graphical Abstract