Quantification and molecular imaging of fatty acid isomers from complex biological samples by mass spectrometry

Abstract

Elucidating the isomeric structure of free fatty acids (FAs) in biological samples is essential to comprehend their biological functions in various physiological and pathological processes. Herein, we report a novel...

Review of Recent Advances in Lipid Analysis of Biological Samples via Ambient Ionization Mass Spectrometry

“…The epoxidation reaction is another chemical derivatization strategy for the structural determination of lipids. Epoxidation using either meta-chloroperoxybenzoic acid (m-CPBA) (Figure 4A) [24] or peracetic acid (PAA) (Figure 4B) [5] coupled with CID-MS/MS to produce a diagnostic ion pair, as shown in Figure 4. Briefly, unsaturated lipids are firstly oxidized via m-CPBA or PAA to generate an epoxide; then, the epoxide product is isolated for CID-MS/MS analysis, which generates a pair of diagnostic ions for pinpointing the C = C bond location [24,25].…”

“…The method attained satisfactory linearity in a quantitative analysis of C = C bond positional FA isomers (including FA 16:1 (9Z), FA 18:1 (9Z), and FA 18:1 (11Z)) (R 2 > 0.9989), the limit of detections (LODs) and relative standard deviations (RSDs) for three tested FAs were 4.2 nM-5.6 nM and 3.4-8.9%, respectively. Furthermore, PAA epoxidation can be combined with matrix-assisted laser desorption/ionization time-of-fight/time-of-fight MS (MALDI-TOF/TOF-MS) for the spatial mapping and characterization of the C = C bond in FAs from tissue sections (Figure 4D) [5]. Although epoxidation reactions by both m-CPBA and PAA have been developed for the analysis of unsaturated lipids, PAA offers the advantage of an easy sample clean-up, owing to the high volatility of PAA, and PAA presents minimal potential side effects, such as ion suppression and MALDI matrix oxidization, during on-tissue epoxidation [5].…”

“…Furthermore, PAA epoxidation can be combined with matrixassisted laser desorption/ionization time-of-fight/time-of-fight MS (MALDI-TOF/TOF-MS) for the spatial mapping and characterization of the C=C bond in FAs from tissue sections (Figure 4D) [5]. Although epoxidation reactions by both m-CPBA and PAA have been developed for the analysis of unsaturated lipids, PAA offers the advantage of an easy sample clean-up, owing to the high volatility of PAA, and PAA presents minimal potential side effects, such as ion suppression and MALDI matrix oxidization, during ontissue epoxidation [5]. Recently, chloroauric acid (HAuCl 4 ) was added into an electrospray solvent during microdroplet mass spectrometry analysis; the resulting oxidation products could be used to identify the location of one or more C=C bonds in unsaturated lipids.…”

“…Unsaturated lipids, as a subclass of lipids, structurally differ in the types of headgroups (such as phosphatidic acids (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylinositol (PI), and phosphatidylserine (PS)), carbon-carbon double bond (C=C) locations, numbers, as well as cis/trans geometric isomerism, and the sn-position of the fatty acyl chain (Figure 1A), which complicate structural characterization [3,4]. In particular, the biological functions of lipids highly depend on their structural diversity and varying expression levels [5]. For example, the unsaturation level of lipids affects cell physiological properties (e.g., the permeability and fluidity of the cell membrane, cardiolipin remodeling, and neurotransmitter release) [6,7].…”

“…Generally, tandem mass spectrometry (MS/MS) via the collision-induced desorption (CID) method can provide a lipid head group and fatty acyl chain composition, but has limited application in directly locating the C=C positions, because low energy CID cannot obtain informative fragment ions to assign the C=C location [15][16][17]. Hence, emerging MS-based dissociation methods, including ozone-induced dissociation (OzID) [18,19], electron-induced dissociation (EID) [20], ultraviolet photodissociation (UVPD) [1,21], and selective C=C bond derivatization methods (e.g., the Paternò-Büchi (PB) reaction [22,23], meta-chloroperoxybenzoic acid (m-CPBA) epoxidation [24,25], and peracetic acid (PAA) epoxidation [5]), have been developed to elucidate the lipid structure. Traditionally, MS coupled with chromatographic approaches (such as liquid chromatography (LC)) are effective tools for the characterization of lipid isomers [26][27][28], but these methods usually require tedious sample preparations prior to MS analysis.…”