12 research outputs found
Shotgun Approach for Quantitative Imaging of Phospholipids Using Nanospray Desorption Electrospray Ionization Mass Spectrometry
Mass spectrometry imaging (MSI) has
been extensively used for determining
spatial distributions of molecules in biological samples, and there
is increasing interest in using MSI for quantification. Nanospray
desorption electrospray ionization (nano-DESI) is an ambient MSI technique
where a solvent is used for localized extraction of molecules followed
by nanoelectrospray ionization. Doping the nano-DESI solvent with
carefully selected standards enables online quantification during
MSI experiments. In this proof-of-principle study, we demonstrate
that
this quantification approach can be extended to provide shotgun-like
quantification of phospholipids in thin brain tissue sections. Specifically,
two phosphatidylcholine (PC) standards were added to the nano-DESI
solvent for simultaneous imaging and quantification of 22 endogenous
PC species observed in nano-DESI MSI. Furthermore, by combining the
quantitative data obtained in the individual pixels, we demonstrate
quantification of these PC species in seven different regions of a
rat brain tissue section
Representative pressure-volume curves made from the total volume from the volume maps and average tracheal pressure.
<p>Data are from three different rats, one from each dose group.</p
An example of finite element discretization of an image.
<p>An example of finite element discretization of an image.</p
Average landmark displacement (in pixels, red) and the percentage of misregistered landmarks (blue) for the five cases shown in Figure 1.
<p>The red dashed line indicates the observer’s average “click error”.</p
Comparison of the average ventilator-measured volume and the total volume from the volume maps for six untreated rats, plotted as a function of tracheal pressure.
<p>Error bars represent the standard deviation of the mean ventilator volume and tracheal pressure over the entire imaging experiment.</p
Examples of image processing for registration testing.
<p>A) Original image. B) Image with bones removed. C) Image with all background masked. D) Same as C, with Gaussian filter applied prior to masking. E) Same as D, with contrast enhancement applied.</p
Block diagram illustrating the data processing flow.
<p>Block diagram illustrating the data processing flow.</p
Imaging Nicotine in Rat Brain Tissue by Use of Nanospray Desorption Electrospray Ionization Mass Spectrometry
Imaging mass spectrometry offers simultaneous spatially
resolved
detection of drugs, drug metabolites, and endogenous substances in
a single experiment. This is important when evaluating effects of
a drug on a complex organ system such as the brain, where there is
a need to understand how regional drug distribution impacts function.
Nanospray desorption electrospray ionization, nano-DESI, is a new
ambient technique that enables spatially resolved analysis of a variety
of samples without special sample pretreatment. This study introduces
an experimental approach for accurate spatial mapping of drugs and
metabolites in tissue sections by nano-DESI imaging. In this approach,
an isotopically labeled standard is added to the nano-DESI solvent
to compensate for matrix effects and ion suppression. The analyte
image is obtained by normalizing the analyte signal to the signal
of the standard in each pixel. We demonstrate that the presence of
internal standard enables online quantification of analyte molecules
extracted from tissue sections. Ion images are subsequently mapped
to the anatomical brain regions in the analyzed section by use of
an atlas mesh deformed to match the optical image of the section.
Atlas-based registration accounts for the physical variability between
animals, which is important for data interpretation. The new approach
was used for mapping the distribution of nicotine in rat brain tissue
sections following in vivo drug administration. We demonstrate the
utility of nano-DESI imaging for sensitive detection of the drug in
tissue sections with subfemtomole sensitivity in each pixel of a 27
μm × 150 μm area. Such sensitivity is necessary for
spatially resolved detection of low-abundance molecules in complex
matrices
Automated Platform for High-Resolution Tissue Imaging Using Nanospray Desorption Electrospray Ionization Mass Spectrometry
An automated platform has been developed for acquisition
and visualization of mass spectrometry imaging (MSI) data using nanospray
desorption electrospray ionization (nano-DESI). The new system enables
robust operation of the nano-DESI imaging source over many hours by
precisely controlling the distance between the sample and the nano-DESI
probe. This is achieved by mounting the sample holder onto an automated <i>XYZ</i> stage, defining the tilt of the sample plane, and recalculating
the vertical position of the stage at each point. This approach is
useful for imaging of relatively flat samples such as thin tissue
sections. Custom software called MSI QuickView was developed for visualization
of large data sets generated in imaging experiments. MSI QuickView
enables fast visualization of the imaging data during data acquisition
and detailed processing after the entire image is acquired. The performance
of the system is demonstrated by imaging rat brain tissue sections.
Low background noise enables simultaneous detection of lipids and
metabolites in the tissue section. High-resolution mass analysis combined
with tandem mass spectometry (MS/MS) experiments enabled identification
of the observed species. In addition, the high dynamic range (>2000)
of the technique allowed us to generate ion images of low-abundance
isobaric lipids. A high-spatial resolution image was acquired over
a small region of the tissue section revealing the distribution of
an abundant brain metabolite, creatine, on the boundary between the
white and gray matter. The observed distribution is consistent with
the literature data obtained using magnetic resonance spectroscopy
Multimodal MSI in Conjunction with Broad Coverage Spatially Resolved MS<sup>2</sup> Increases Confidence in Both Molecular Identification and Localization
One critical aspect
of mass spectrometry imaging (MSI) is the need
to confidently identify detected analytes. While orthogonal tandem
MS (e.g., LC–MS<sup>2</sup>) experiments from sample extracts
can assist in annotating ions, the spatial information about these
molecules is lost. Accordingly, this could cause mislead conclusions,
especially in cases where isobaric species exhibit different distributions
within a sample. In this Technical Note, we employed a multimodal
imaging approach, using matrix assisted laser desorption/ionization
(MALDI)-MSI and liquid extraction surface analysis (LESA)-MS<sup>2</sup>I, to confidently annotate and localize a broad range of metabolites
involved in a tripartite symbiosis system of moss, cyanobacteria,
and fungus. We found that the combination of these two imaging modalities
generated very congruent ion images, providing the link between highly
accurate structural information onfered by LESA and high spatial resolution
attainable by MALDI. These results demonstrate how this combined methodology
could be very useful in differentiating metabolite routes in complex
systems