Identification and Quantitation of C═C Location Isomers of Unsaturated Fatty Acids by Epoxidation Reaction and Tandem Mass Spectrometry

Abstract

Unsaturated fatty acids (FAs) serve as nutrients, energy sources, and signaling molecules for organisms, which are the major components for a large variety of lipids. However, structural characterization and quantitation of unsaturated FAs by mass spectrometry remain an analytical challenge. Here, we report the coupling of epoxidation reaction of the C═C in unsaturated FAs and tandem mass spectrometry (MS) for rapid and accurate identification and quantitation of C═C isomers of FAs in a shotgun lipidomics approach. Epoxidation of the C═C leads to the production of an epoxide which, upon collision induced dissociation (CID), produces abundant diagnostic ions indicative of the C═C location. The total intensity of the same set of diagnostic ions for one specific FA C═C isomer was also used for its relative and absolute quantitation. The simple experimental setup, rapid reaction kinetics (<2 min), high reaction yield (>90% for monounsaturated FAs), and easy-to-interpret tandem MS spectra enable a promising methodology particularly for the analysis of unsaturated FAs in complex biological samples such as human plasma and animal tissues.

An On‐Tissue Paternò–Büchi Reaction for Localization of Carbon–Carbon Double Bonds in Phospholipids and Glycolipids by Matrix‐Assisted Laser‐Desorption–Ionization Mass‐Spectrometry Imaging

“…In combination with electrospray ionization (ESI‐)MS, several techniques have recently emerged that exploit chemical derivatization of C=C bonds and subsequent generation of diagnostic fragments in a CID experiment. These include ozone‐induced dissociation (OzID) of selected ions within a collision cell, epoxidation reaction with acetone enabled by a cold plasma, and on‐line Paternò–Büchi (PB) photo‐derivatization . Very recently, a combination of MALDI‐MSI and CID/OzID, performed in the linear ion trap of a modified MALDI‐LTQ Orbitrap Elite mass spectrometer, was used to visualize the distributions of db‐ and sn ‐positional isomers of several phosphatidylcholines (PC) in mouse brain .…”

A lipidomic workflow capable of resolving sn- and CC location isomers of phosphatidylcholines

“…16,17 Localization of C]C has been recently achieved by paring C]C derivatization with subsequent MS/MS via CID, such as the Paternò-Büchì (PB) reaction 18,19 and epoxidation reaction. [20][21][22] These approaches are capable of determining C]C locations in various classes of lipids but they cannot provide information on the sn-positions of fatty acyls. Several MS/MS techniques utilizing ion activation/dissociation other than CID or combined with CID turn out to be quite informative for obtaining both sn-position and (or) C]C location from GPs.…”

Large-scale lipid analysis with C=C location and sn-position isomer resolving power

“…GPs, for instance, have five levels in terms of structure information, including lipid class, fatty acyl identities, fatty acyl sn-positions, and C=C location/geometry (viz cis/trans) in the fatty acyl. Successful attempts for determining C=C locations [22][23][24][25][26][27][28] in fatty acyls or their sn-positions 28,29 have already been reported for MS analysis, enabling characterization of detailed structure moieties and identification of lipid structure isomers. An extremely useful feature offered by lipid isomer analysis, is the relative quantitation achieved at high precisions without requiring the use of lipid standards, which is not readily available 25,26 .…”

“…Ozone-induced dissociation (OzID) [31][32][33] and ultraviolet photodissociation (UVPD) 28 have been used to determine both sn-positions and C=C locations in GPs. By coupling photochemical (Paternò-Bǜchi, PB) reaction with tandem MS (MS/MS), we have systematically demonstrated the qualitative and quantitative analysis of lipids with C=C specificity from complex biological samples [25][26][27]34,35 . PB reaction converts the C=C to an oxetane which can be preferentially fragmented by low-energy collisioninduced dissociation (CID).…”