75
regional differences in glucose metabolism in the brain [91]. IMS is an untargeted,
label-free technology, but can also be used to visualize the localization of targeted
metabolites such as those related to glucose metabolism. In this paper ATP, ADP,
HP and HBP were all identified to determine regional differences in metabolism
within the brain. This approach allows for direct measurement of metabolites generated through specific pathways and in specific brain regions. Then, using immunohistochemistry and Nissl staining, these regional differences can be visualized a
high spatial resolution.
MALDI IMS sample preparation differs from LC-MS methods, due to its retention of spatial information. Tissue can be sectioned and mounted onto glass slides,
then sprayed with matrix to improved ionization efficiency. This maintains the relationship of the robust chemical information provided by MS with spatial location in
the tissue, offering new correlations between the molecular makeup of the tissue
and the various regions and substructures. Overall this approach allowed for the
identification of key metabolites and gives insight into the relationship between
brain regions and pathways. Metabolites are tentatively identified by exact mass,
and then confirmed by MS
3
fragmentation experiments.
IMS showed the regional variations between areas that use glucose for glycolysis
versus areas that use glucose primarily for the pentose phosphate pathway (PPP).
For example, more of the glucose in the thalamus is entering the PPP over other
regions such as the amygdala where more glucose is utilized in other pathways such
as glycolysis. However, in white matter tracts and regions with low glycolysis and
PPP, ATP production is high. Additionally, this investigation showed an increase in
lactate during fasting that shows regional localization to specific brain substructures. Overall IMS allows for spatially resolved metabolomics, also showing the
ability to conduct high resolution metabolomics with the addition of spatial information in regions of interest to study specific pathways.
4.6.3 Other Metabolomics Methods: Nuclear
Magnetic Resonance
Previous methods described for metabolomics utilize mass spectrometry for analysis. While MS is higher in sensitivity by orders of magnitude, other technologies
such as nuclear magnetic resonance (NMR) have been growing in their applicability
to metabolomic research. NMR has a variety of advantages over MS [8]. The sample preparation for NMR is relatively easy compared to LC-MS, high experimental
reproducibility, and NMR is nondestructive for samples. One of the major benefits
of NMR, however, is the ability to quantify the metabolite levels explicitly. Due to
these advantages and the high automatability, NMR-based metabolomics has been
increasing over the last 15 years. With NMR technologies such as MRI and ssNMR,
living cells and entire organs can be analyzed due to the nondestructive nature of
NMR, applications that are currently inaccessible for MS. Ultimately the choice
between NMR and MS relies on the priorities of the experiment: high sensitivity
and more identifications, or nondestructive analysis.
4 Fundamentals of Mass Spectrometry-Based Metabolomics
regional differences in glucose metabolism in the brain [91]. IMS is an untargeted,
label-free technology, but can also be used to visualize the localization of targeted
metabolites such as those related to glucose metabolism. In this paper ATP, ADP,
HP and HBP were all identified to determine regional differences in metabolism
within the brain. This approach allows for direct measurement of metabolites generated through specific pathways and in specific brain regions. Then, using immunohistochemistry and Nissl staining, these regional differences can be visualized a
high spatial resolution.
MALDI IMS sample preparation differs from LC-MS methods, due to its retention of spatial information. Tissue can be sectioned and mounted onto glass slides,
then sprayed with matrix to improved ionization efficiency. This maintains the relationship of the robust chemical information provided by MS with spatial location in
the tissue, offering new correlations between the molecular makeup of the tissue
and the various regions and substructures. Overall this approach allowed for the
identification of key metabolites and gives insight into the relationship between
brain regions and pathways. Metabolites are tentatively identified by exact mass,
and then confirmed by MS
3
fragmentation experiments.
IMS showed the regional variations between areas that use glucose for glycolysis
versus areas that use glucose primarily for the pentose phosphate pathway (PPP).
For example, more of the glucose in the thalamus is entering the PPP over other
regions such as the amygdala where more glucose is utilized in other pathways such
as glycolysis. However, in white matter tracts and regions with low glycolysis and
PPP, ATP production is high. Additionally, this investigation showed an increase in
lactate during fasting that shows regional localization to specific brain substructures. Overall IMS allows for spatially resolved metabolomics, also showing the
ability to conduct high resolution metabolomics with the addition of spatial information in regions of interest to study specific pathways.
4.6.3 Other Metabolomics Methods: Nuclear
Magnetic Resonance
Previous methods described for metabolomics utilize mass spectrometry for analysis. While MS is higher in sensitivity by orders of magnitude, other technologies
such as nuclear magnetic resonance (NMR) have been growing in their applicability
to metabolomic research. NMR has a variety of advantages over MS [8]. The sample preparation for NMR is relatively easy compared to LC-MS, high experimental
reproducibility, and NMR is nondestructive for samples. One of the major benefits
of NMR, however, is the ability to quantify the metabolite levels explicitly. Due to
these advantages and the high automatability, NMR-based metabolomics has been
increasing over the last 15 years. With NMR technologies such as MRI and ssNMR,
living cells and entire organs can be analyzed due to the nondestructive nature of
NMR, applications that are currently inaccessible for MS. Ultimately the choice
between NMR and MS relies on the priorities of the experiment: high sensitivity
and more identifications, or nondestructive analysis.
4 Fundamentals of Mass Spectrometry-Based Metabolomics