The effect of sample age on the metabolic information extracted from formalin-fixed and paraffin embedded tissue samples using desorption electrospray ionization mass spectrometry imaging

Olof Gerdur Isberg; Yuchen Xiang; Sigridur Klara Bodvarsdottir; Jon Gunnlaugur Jonasson; Margret Thorsteinsdottir; Zoltan Takats

doi:10.1016/j.jmsacl.2021.10.004

The effect of sample age on the metabolic information extracted from formalin-fixed and paraffin embedded tissue samples using desorption electrospray ionization mass spectrometry imaging

J Mass Spectrom Adv Clin Lab. 2021 Oct 28:22:50-55. doi: 10.1016/j.jmsacl.2021.10.004. eCollection 2021 Nov.

Authors

Olof Gerdur Isberg^{1

2

3}, Yuchen Xiang¹, Sigridur Klara Bodvarsdottir³, Jon Gunnlaugur Jonasson^{4

5}, Margret Thorsteinsdottir^{2

3}, Zoltan Takats¹

Affiliations

¹ Department of Metabolism, Digestion and Reproduction, Faculty of Medicine, Imperial College London, London SW7 2AZ, United Kingdom.
² Faculty of Pharmaceutical Sciences, University of Iceland, Hofsvallagata 53, 107 Reykjavik, Iceland.
³ Biomedical Center, University of Iceland, Reykjavik, Iceland.
⁴ Pathology, Landspitali-National University Hospital, Reykjavik, Iceland.
⁵ Faculty of Medicine, University of Iceland, Reykjavik, Iceland.

Abstract

Background: Metabolites, especially lipids, have been shown to be promising therapeutic targets. In conjugation with genes and proteins they can be used to identify phenotypes of disease and support the development of targeted treatments. The majority of clinically collected tissue samples are stored in formalin-fixed and paraffin embedded (FFPE) blocks due to their tissue conservation ability and indefinite storage capacity. For metabolic analysis, however, fresh frozen (FF) samples are currently preferred over FFPE samples due to concerns of metabolic information being lost when preparing the samples. With little or no sample preparation, desorption electrospray ionisation mass spectrometry imaging (DESI-MSI) allows for the study of spatial as well as spectral information. Methods: DESI-MSI analysis was performed on FFPE breast cancer tissue microarray samples from 213 patients collected between the years 1935-2013. Logistic regression (LR) models were built to classify samples based on age and FF samples were used for feature validation. Results: LR models developed on the FFPE samples achieved an average classification accuracy of 96% when predicting their age with a 10-year grouping. Closer examination of the metabolic change over time revealed that the mean signal intensities for the lower mass range (100 - 500 m/z) linearly decrease over time, while the mean intensities for the higher mass range (500 - 900 m/z), remained relatively constant. Conclusions: In our samples, which span over 70 years, sample age has a weak yet quantifiable impact on metabolite content in FFPE samples, while the higher mass range is seemingly unaffected. FFPE samples thus provide an alternative avenue for metabolic analysis of lipids.

Keywords: DESI-MSI; FFPE; Lipids; Mass spectrometry imaging; Sample age.