Quantitative structural multiclass lipidomics using differential mobility: electron impact excitation of ions from organics (EIEIO) mass spectrometry

Takashi Baba,J.C.Yves Le Blanc,J.Larry Campbell,Paulr.S Baker,Kazutaka Ikeda

doi:10.1194/jlr.d083261

Abstract

We report a method for comprehensive structural characterization of lipids in animal tissues using a combination of differential ion mobility spectrometry (DMS) with electron-impact excitation of ions from organics (EIEIO) mass spectrometry. Singly charged lipid ions in protonated or sodiated forms were dissociated by an electron beam having a kinetic energy of 10 eV in a branched radio-frequency ion trap. We established a comprehensive set of diagnostics to characterize the structures of glycerophospholipids, sphingolipids, and acylglycerols, including glycosylated, plasmalogen, and ester forms. This EIEIO mass spectrometer was combined with DMS as a separation tool to analyze complex lipid extracts. Deuterated quantitative standards, which were added during extraction, allowed for the quantitative analysis of the lipid molecular species in various lipid classes. We applied this technique to the total lipids extracted from porcine brain, and we structurally characterized over 300 lipids (with the exception of cis/trans double-bond isomerism in the acyl chains). The structural dataset of the lipidomes, whose regioisomers were distinguished, exhibit a uniquely defined distribution of acyl chains within each lipid class; that is, sn-1 and sn-2 in the cases of glycerophospholipids or sn-2 and (sn-1, sn-3) in the cases of triacylglycerols.

Highlights

We report a method for comprehensive structural characterization of lipids in animal tissues using a combination of differential ion mobility spectrometry (DMS) with electron-impact excitation of ions from organics (EIEIO) mass spectrometry
Supplemental Material can be found at: http://www.jlr.org/content/suppl/2018/03/14/jlr.D083261.DC1 .html does not provide full structural information of lipid isomers, which is often limited to characterization of the lipid class and brutto class, which represents the head group and the combined lengths of chains and numbers of double bonds among the acyl chains
An electron beam with a kinetic energy of 10 eV was applied to positively charged lipid ions so that the electron impact excitation of ions from organics (EIEIO) spectra displayed informative fragment patterns, which identifies the lipid class, the number of double bonds and their relative positions within the chains, and regioisomerism [i.e., distinction of fatty acyl chain position on the glycerol backbone of glycerolipids (GLs) and glycerophospholipids (GPLs)]

Summary

Introduction

We report a method for comprehensive structural characterization of lipids in animal tissues using a combination of differential ion mobility spectrometry (DMS) with electron-impact excitation of ions from organics (EIEIO) mass spectrometry. Supplemental Material can be found at: http://www.jlr.org/content/suppl/2018/03/14/jlr.D083261.DC1 .html does not provide full structural information of lipid isomers, which is often limited to characterization of the lipid class and brutto class, which represents the head group and the combined lengths of chains and numbers of double bonds among the acyl chains.

Results

Conclusion