Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Chemistry

Supervisor

Yeung, Ken

2nd Supervisor

Whitehead, Shawn

Co-Supervisor

Abstract

Matrix assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) is largely performed on fresh frozen tissue whereas clinical tissue samples stored long term are fixed in formalin, and the fixation process is thought to cause signal suppression for lipid molecules. Studies show that fresh frozen brain tissue sections washed with ammonium formate (AF) solution prior to matrix application in the MALDI-IMS procedure display an increase in signal intensity and sensitivity for lipid molecules while maintaining molecular spatial distribution. Work in this thesis compares MALDI data of ganglioside molecules from fresh frozen and post-fixed rat brain samples, and post-fixed human brain samples washed with AF. Results demonstrate that MALDI-IMS spectra for gangliosides are significantly enhanced in fresh frozen rat brain, formalin-fixed rat brain and formalin fixed human brain samples washed with AF. This method will allow for analysis of gangliosides from formalin-fixed clinical samples, which can open additional avenues for neurodegenerative disease research.

Summary for Lay Audience

Matrix assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) is used to analyze molecules directly on tissue samples providing information about molecules present in the samples and where they are located. Tissue samples are often stored frozen or in a chemical solution called formalin, currently frozen tissue is largely used for MALDI as the chemical storage is thought to interfere with some types of molecules within tissue samples, such as lipid molecules. Some studies have demonstrated that molecules in frozen tissue can be better detected if the tissue is washed with ammonium formate (AF) before MALDI is performed, this method not only improves detection but also retains the location of molecules within the samples. This work aims to see if gangliosides, a lipid found in the brain, in human tissue stored in formalin can be analysed in MALDI imaging by comparing results from frozen and formalin rat brains and human brain samples washed with AF. Results show that MALDI data for gangliosides was improved in all types of tissue tested through the use of an AF wash. Images generated from MALDI were shown with molecule location retained after tissue washing. These results show that this method will allow for gangliosides to be analysed in samples stored in formalin in a clinical setting which can offer new research opportunities with neurodegenerative diseases.

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