Mass spectrometry images acylcarnitines, phosphatidylcholines, and sphingomyelin in MDA-MB-231 breast tumor models

Kamila Chughtai,Lu Jiang,Tiffany R Greenwood,Kristine Glunde,Ron M.A Heeren

doi:10.1194/jlr.m027961

Abstract

The lipid compositions of different breast tumor microenvironments are largely unknown due to limitations in lipid imaging techniques. Imaging lipid distributions would enhance our understanding of processes occurring inside growing tumors, such as cancer cell proliferation, invasion, and metastasis. Recent developments in MALDI mass spectrometry imaging (MSI) enable rapid and specific detection of lipids directly from thin tissue sections. In this study, we performed multimodal imaging of acylcarnitines, phosphatidylcholines (PC), a lysophosphatidylcholine (LPC), and a sphingomyelin (SM) from different microenvironments of breast tumor xenograft models, which carried tdTomato red fluorescent protein as a hypoxia-response element-driven reporter gene. The MSI molecular lipid images revealed spatially heterogeneous lipid distributions within tumor tissue. Four of the most-abundant lipid species, namely PC(16:0/16:0), PC(16:0/18:1), PC(18:1/18:1), and PC(18:0/18:1), were localized in viable tumor regions, whereas LPC(16:0/0:0) was detected in necrotic tumor regions. We identified a heterogeneous distribution of palmitoylcarnitine, stearoylcarnitine, PC(16:0/22:1), and SM(d18:1/16:0) sodium adduct, which colocalized primarily with hypoxic tumor regions. For the first time, we have applied a multimodal imaging approach that has combined optical imaging and MALDI-MSI with ion mobility separation to spatially localize and structurally identify acylcarnitines and a variety of lipid species present in breast tumor xenograft models.

Highlights

The lipid compositions of different breast tumor microenvironments are largely unknown due to limitations in lipid imaging techniques
We have demonstrated that the incorporation of mass spectrometry imaging (MSI) into a multimodal imaging approach revealed the molecular complexity of tumor tissue at an unprecedented level
Bright-field microscopy visualized the shape of the tumor, fluorescence microscopy outlined the position of hypoxic tumor regions, and histochemical staining revealed the localization of necrotic tumor tissue

Summary

Introduction

The lipid compositions of different breast tumor microenvironments are largely unknown due to limitations in lipid imaging techniques. Recent developments in MALDI mass spectrometry imaging (MSI) enable rapid and specific detection of lipids directly from thin tissue sections. We have applied a multimodal imaging approach that has combined optical imaging and MALDI-MSI with ion mobility separation to spatially localize and structurally identify acylcarnitines and a variety of lipid species present in breast tumor xenograft models.—Chughtai, K., L. MALDI mass spectrometry imaging (MSI) can detect, localize, and identify multiple biologically relevant molecules directly from thin tissue sections without the necessity for any labeling [1]. An additional advantage of MSI is its compatibility with other imaging techniques such as optical bright field and fluorescence microscopy Such a multimodal approach is useful for analyzing the molecular composition of complex, heterogeneous tumor tissue, which comprises several distinct tumor microenvironments.

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Conclusion