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Metabolite localization by atmospheric pressure high-resolution scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging in whole-body sections and individual organs of the rove beetle Paederus riparius.

ABSTRACT: Mass spectrometry imaging provides for non-targeted, label-free chemical imaging. In this study, atmospheric pressure high-resolution scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI) was used for the first time to describe the chemical distribution of the defensive compounds pederin, pseudopederin, and pederon in tissue sections (16 μm thick) of the rove beetle Paederus riparius. The whole-insect tissue section was scanned with a 20-μm step size. Mass resolution of the orbital trapping mass spectrometer was set to 100,000 at m/z 200. Additionally, organ-specific compounds were identified for brain, nerve cord, eggs, gut, ovaries, and malpighian tubules. To confirm the distribution of the specific compounds, individual organs from the insect were dissected, and MSI experiments were performed on the dissected organs. Three ganglia of the nerve cord, with a dimension of 250-500 μm, were measured with 10-μm spatial resolution. High-quality m/z images, based on high spatial resolution and high mass accuracy were generated. These features helped to assign mass spectral peaks with high confidence. Mass accuracy of the imaging experiments was <3 ppm root mean square error, and mapping of different compound classes from a single experiment was possible. This approach improved the understanding of the biochemistry of P. riparius. Concentration differences and distributions of pederin and its analogues could be visualized in the whole-insect section. Without any labeling, we assigned key lipids for specific organs to describe their location in the body and to identify morphological structures with a specificity higher than with staining or immunohistology methods.

SUBMITTER: Bhandari DR

PROVIDER: S-EPMC4357651 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:RationaleAs a powerful ambient ion source, atmospheric pressure (AP) matrix-assisted laser desorption/ionization (MALDI) enables direct analysis at atmospheric pressure/temperature and minimal sample preparation. With the increasing usage of AP-MALDI sources with Orbitrap instruments, systematic characterization of the extent of ion suppression effect (ISE) in AP-MALDI-Orbitrap mass spectrometry imaging (MSI) is desirable. Recently, a new low-pressure MALDI platform has been introduced that reportedly provided better sensitivity. While extensive research efforts have been devoted to improving spatial resolution, fewer studies focused on the characterization and sensitivity improvement of these MALDI platforms that, coupled with high-resolution Orbitraps, provide powerful strategy for MSI.MethodsWe compared the analytical performance of AP and low-pressure (subatmospheric) MALDI sources to study the effect of pressure control in the ion source. Using a model peptide/protein mixture, we systematically evaluated the factors influencing ISE. Furthermore, the effect of laser spot size was evaluated through tissue imaging analysis of lipids and neuropeptides. The effects of ion suppression and laser spot size have also been examined by comparing the number of identified molecular species during MSI analysis.ResultsSeveral key operating parameters including source pressure, laser energy, laser repetition rate, and microscopic slide coating materials were optimized to minimize the ISE. Under the optimal conditions, the subatmospheric AP-MALDI-Orbitrap platform with high spatial and mass spectral resolution enabled significantly improved coverage of several lipid and neuropeptide families in the MS analysis of mouse brain tissue sections.ConclusionsThe new SubAP-MALDI source coupled with an Orbitrap mass spectrometer was established as a viable platform for in situ endogenous biomolecular analysis with increased sensitivity compared with conventional AP-MALDI sources as evidenced by the confident identification of neuropeptides from mouse brain imaging analyses. The alleviated ISE was key to substantial performance improvement due to optimized intermediate pressure conditions and better ion collection by the ion funnel.

Dataset Information

Metabolite localization by atmospheric pressure high-resolution scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging in whole-body sections and individual organs of the rove beetle Paederus riparius.

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