Analyzing a metabolite level in a tissue sample using DESI
The invention generally relates to methods for analyzing a metabolite level in a sample. In certain embodiments, methods of the invention may involve obtaining a sample, analyzing the sample using a mass spectrometry technique to determine a level of at least one metabolite in the sample, and correlating the metabolite level with an originating source of the sample, thereby analyzing the sample.
1. A method for analyzing a tissue section, the method comprising:
depositing the tissue section onto a substrate, wherein the tissue section comprises at least one metabolite indicative of a cancer and a plurality of reference molecules that are not associated with the cancer;
conducting a desorption electrospray ionization (DESI) technique on one or more locations of the tissue section in order to desorb the at least one metabolite and the plurality of reference molecules from the one or more locations of the tissue section and direct the at least one metabolite and the plurality of reference molecules into a mass spectrometer to thereby generate a mass spectral signal of the at least one metabolite and a plurality of reference mass spectral signals at the one or more locations;
normalizing the mass spectral signal of the at least one metabolite at the one or more locations to a combination of the plurality of reference mass spectral signals from the tissue section in order to obtain a relative abundance of the at least one metabolite at the one or more locations within the tissue section; and
producing a mass spectral image of the tissue section that comprises a relative abundance of the at least one metabolite at the one or more locations within the tissue section, wherein the relative abundance of the at least one metabolite at the one or more locations within the tissue section is indicative of locations of cancerous tissue or non-neoplastic tissue within the tissue section.
2. The method according to claim 1 , wherein the DESI technique uses a solvent that does not destroy native tissue morphology of the tissue section, and wherein the solvent comprises dimethylformamide (DMF), acetonitrile (ACN), tetrahydrofuran (THF) or methanol (MeOH):chloroform (CHCl 3 ).
3. The method according to claim 2 , wherein the solvent further comprises at least one of ethanol (EtOH), water (H 2 O), and acetonitrile (ACN).
4. The method according to claim 2 , further comprising performing a histochemistry analysis technique on the tissue sample.
5. The method according to claim 4 , wherein the histochemistry analysis technique is H&E staining or immunohistochemistry.
6. The method according to claim 4 , further comprising producing an optical image of the tissue section based on data from the histochemistry analysis technique.
7. The method according to claim 6 , further comprising overlaying the mass spectral image of the tissue section onto the optical image of the tissue section.
8. The method according to claim 1 , wherein the solvent is selected from the group consisting of: acetonitrile (ACN):ethanol (EtOH); and acetonitrile (ACN):chloroform (CHCl 3 ).
9. The method according to claim 1 , wherein the plurality of reference molecules are lipids.
10. The method according to claim 1 , wherein the DESI technique is performed without prior sample preparation.
11. The method according to claim 1 , wherein the tissue section is from a frozen tissue sample.
12. The method according to claim 1 , wherein the tissue section is a human tissue section.
13. The method according to claim 12 , wherein the human tissue section is a distribution of cells and extracellular matrix that is spread on the substrate.
14. The method according to claim 12 , wherein the human tissue section comprises at least a portion of a tumor.
15. The method according to claim 14 , further comprising defining one or more tumor margins based on the mass spectral image of the tissue section.
16. The method according to claim 1 , wherein the DESI technique is performed in a negative ion mode.