Research Article

Optimization of MALDI tissue imaging and correlation with immunohistochemistry in rat kidney sections

Cassie Gregson

Staffordshire University

Received:

29 Sep 2008

Accepted:

18 Dec 2008

Published:

29 Apr 2009

Volume:

2

Issue:

2

Keywords:

MALDI, MALDI imaging, mass spectrometry

Abstract:

Cancer is responsible for approximately 6.7 million deaths and 10.9 million newly diagnosed cases worldwide per year. Currently, the definitive diagnosis of a tissue or cell sample is determined by molecular pathology and histochemical techniques, which assess tumour type, grade and stage. This information also allows for the diagnosis, prognosis and available treatment options to be established. In addition, immunohistochemistry (IHC) in combination with histochemistry is used to determine the surgical margin status of tumours, which can be correlated to the likelihood of recurrence. Matrix-assisted laser desorption/ionization (MALDI) imaging is a mass spectrometry profiling technique, which can be used to simultaneously identify multiple species within a tissue section. The array format of the acquisition allows for the creation of an image that is viewed in a similar way to an IHC section. MALDI imaging could potentially provide an alternative diagnostic assay that could be used to provide cancer prognosis. To assess the suitability of MALDI imaging for this application, sample preparation and MALDI imaging methodology were developed using α2u-globulin as an example protein. This protein is known to be preferably expressed in the kidneys of male rats allowing a proof-of-principle study to be performed comparing the expression levels and localization between male and female rat kidney sections. The expression of α2u-globulin was localized to the cortex region of the kidney, with the levels of α2u-globulin shown to be significantly higher in the male than the female kidney sections. These findings were validated by comparison with IHC data. The proof-of-principle study therefore demonstrated that MALDI imaging could be a potential alternative to current molecular pathology and histochemical techniques for the determination of tumour type, grade and stage as well as the determination of surgical margin status.