Structural characterization of neutral glycosphingolipids using high-performance liquid chromatography-electrospray ionization mass spectrometry with a repeated high-speed polarity and MSn switching system

Mass Spectrometry of Neutral Glycosphingolipids

This chapter describes the protocols for mass spectrometry (MS) applied to the structural characterization of neutral glycosphingolipids (GSLs) and the determination of neutral GSL contents in biological materials. The structural characterization is performed by thin layer chromatography-matrix assisted laser desorption ionization/mass spectrometry (TLC-MALDI/MS) and liquid chromatography-electrospray ionization/mass spectrometry (LC-ESI/MS) with reversed phase separation. The content determination is carried out by LC-ESI/MS with multiple reaction monitoring (MRM). These protocols provide clues for the functions of neutral GSLs at the level of a single GSL molecular species.

Simple separation of glycosphingolipids in the lower phase of a Folch's partition from crude lipid fractions using zirconium dioxide

A simple method was developed for the separation of glycosphingolipids (GSLs) from lipid mixtures, including phospholipids and cholesterol, using zirconium dioxide (zirconia, ZrO₂). Although this procedure does not incorporate a mild alkali treatment, which is commonly used for eliminating glycerophospholipids, it can be used to remove both alkali-resistant sphingomyelin and glycerophospholipids possessing ether bonds. Importantly, when GSLs were dissolved in organic solvent together with cholesterol (Chol) and phospholipids, and loaded onto ZrO₂, Chol did not bind to the ZrO₂ but both the GSLs and phospholipids did. When eluted with 5 mg/mL of 2,5-dihydroxybenzoic acid in methanol, GSLs but not phospholipids were recovered, leaving the phospholipids bound to the ZrO₂ particles. This method is particularly applicable for GSLs such as triglycosylceramides, tetraglycosylceramides and some pentaglycosylceramides, sulfatide and GM3 located in the lower phase of a Folch's partition, where significant amounts of phospholipids, Chol and neutral lipids reside along with GSLs. This method was successfully used to easily isolate GSLs from biological materials for their subsequent analysis by matrix-assisted laser desorption ionization time-of-flight mass spectrometry with high resolution.

Electrospray ionization mass spectrometry characterization of ubiquitous minor lipids and oligosaccharides in milk of the camel (Camelus dromedarius) and their inhibition of oxidative stress in human plasma

The aim of this study was to characterize minor lipids in methanol fraction extracted from raw camel milk after loading it on a water-preconditioned short C18 open column and fractionating with a gradient of methanol/water. The C18 column showed high fractionation efficiency of minor lipids, such as glycosphingolipids, lipopolysaccharides, or oligosaccharides, when compared with other constituents, in particular polysaccharides, proteins, and free fatty acids. Liquid chromatography electrospray ionization tandem mass spectrometry in negative ion mode was used to identify 21 new glycosphingolipids, lipopolysaccharides, and oligosaccharides. Electrospray ionization tandem mass spectrometry was qualified to provide relevant data for recognizing the molecular mass, glycosylation sequences, and structure of saccharide moieties for the revealed compounds. The sequence of combinations of one selected lipopolysaccharide, which was considered the backbone of the remaining lipopolysaccharides, was confirmed in a density functional theory study. The obtained results showed that the tested fraction is a rich source of glycosphingolipids, lipopolysaccharides, and oligosaccharides with antioxidant activity.

Identification of neutral and acidic glycosphingolipids in the human dermal fibroblasts

Skin fibroblasts are recognized as a valuable model of primary human cells able of mirroring the chronological and biological aging. Here, a lipidomic study of glycosphingolipids (GSL) occurring in the easily accessible human dermal fibroblasts (HDF) is presented. Reversed-phase liquid chromatography with negative electrospray ionization (RPLC-ESI) coupled to either orbitrap or linear ion-trap multiple-stage mass spectrometry was applied to characterize GSL in commercially adult and neonatal primary human fibroblast cells and in skin samples taken from an adult volunteer. Collision-induced dissociation in negative ion mode allowed us to get information on the monosaccharide number and ceramide composition, whereas tandem mass spectra on the ceramide anion was useful to identify the sphingoid base. Nearly sixty endogenous GSL species were successfully recognized, namely 33 hexosyl-ceramides (i.e., HexCer, Hex₂Cer and Hex₃Cer) and 24 gangliosides as monosialic acid GM1, GM2 and GM3, along with 5 globosides Gb4. An average content of GSLs was attained and the most representative GSL in skin fibroblasts were Hex₃Cer, also known as Gb3Cer, followed by Gb4, HexCer and Hex₂Cer , while gangliosides were barely quantifiable. The most abundant GSLs in the examined cell lines share the same ceramide base (i.e. d18:1) and the relative content was d18:1/24:1 > d18:1/24:0 > d18:1/16:0 > d18:1/22:0.

Overexpression of HexCer and LacCer containing 2-hydroxylated fatty acids in cholangiocarcinoma and the association of the increase of LacCer (d18:1-h23:0) with shorter survival of the patients

Alteration of glycosphingolipid (GSL) synthesis is observed in many types of cancer. In this study, we have analyzed the expression of sphingolipids and GSLs in cholangiocarcinoma (CCA) tissues and adjacent normal liver tissues. Neutral lipids were extracted from tissue samples using mild-alkaline treatment method followed by TLC and LC-MS analysis. The expression of ceramides, hexosylceramides (HexCer), and lactosylceramides (LacCer) was altered in CCA tissues, 61.1% (11/18) of them showing an increase whereas 38.9% (7/18) showing a decrease, compared with the adjacent normal tissue. Cers and GSLs containing 2-hydroxylated fatty acids except one LacCer molecular species were overexpressed in CCA tissues, and the increase of LacCer (d18:1-h23:0) was correlated with shorter survival of CCA patients, suggesting the involvement of GSL synthesis and fatty acid hydroxylation in progression of CCA. Taken together, we have demonstrated in this study the increase of GSL synthesis and fatty hydroxylation in CCA, which probably be used as a target for CCA treatment.

Separation of glycosphingolipids with titanium dioxide

We introduce the principle of a new technique to isolate glycosphingolipids (GSLs) from phospholipids. Neutral and acidic GSLs in organic solvent bind to titanium dioxide under neutral pH and can be eluted with 5 mg/ml of 2,5-dihydroxybenzoic acid in methanol. This special property is applicable for eliminating phospholipids, including sphingomyelin, which cannot be eliminated by a typical mild alkaline treatment. By using this technique, we demonstrated the rapid separation of minor components of GSLs, namely sulfatide and gangliosides from rabbit serum and liver, respectively. The minor GSL components were effectively purified despite both sources containing tremendous amount of phospholipids and simple lipids such as cholesterol, cholesteryl esters and triglycerides.

Glycosphingolipidomics of donkey milk by hydrophilic interaction liquid chromatography coupled to ESI and multistage MS

Hydrophilic interaction liquid chromatography coupled to negative-ion electrospray linear ion-trap multiple-stage MS (HILIC-ESI-MSⁿ , n = 2,3) was used to characterize polar lipids occurring in donkey milk. Besides the detection of abundant phospholipids, the structural characterization and content evaluation of minor glycosphingolipids (GSLs) were assessed. We report an unprecedented characterization of 11 hexosyl-ceramides (HexCer), 10 Hex₂ Cer, and 4 Hex₃ Cer. CID-MS/MS spectra in negative ion mode mainly afford information on the monosaccharide number and ceramide constitution (i.e., N-acyl residue and long-chain base), whereas MS/MS/MS spectra on the ceramide anions allow to recognize for each GSL the sphingoid base. The occurrence of sphingosine (S), sphinganine (DS), and phytosphingosine (P) was inferred from the fragmentation patterns. The milk samples exhibit a relatively high number of phytosphingosine substitutes, perhaps because of the feeding of donkeys, mainly based on pasture grass. However, the incidence of hydroxylated species on the α-carbon of the acyl chain was also revealed. The fatty acid composition of N-acyl chains showed high values of long-chain saturated fatty acids such as 20:0, 22:0, 23:0, and 24:0. An average content of GSL is also provided and three representative mono-, di-, and tri-HexCer in donkey milk are the following: HexCer 18:0/24:1 phytosphingosine nonhydroxylated [PN] at m/z 862.6 as chloride adduct [M+Cl]^- , and content 225.9 ± 2.8 μg 100 mL^-1 ; Hex₂ Cer 18:0/16:0 sphinganine nonhydroxylated [DSN] at m/z 862.7 as deprotonated adduct [M-H]^- , and content 70.8 ± 1.4 μg 100 mL^-1 ; and Hex₃ Cer 18:1/24:1 [SN] at m/z 1132.8 as [M-H]^- , and content 38.5 ± 0.7 μg 100 mL^-1 .

Sphingolipidomics: An Important Mechanistic Tool for Studying Fungal Pathogens

Sphingolipids form of a unique and complex group of bioactive lipids in fungi. Structurally, sphingolipids of fungi are quite diverse with unique differences in the sphingoid backbone, amide linked fatty acyl chain and the polar head group. Two of the most studied and conserved sphingolipid classes in fungi are the glucosyl- or galactosyl-ceramides and the phosphorylinositol containing phytoceramides. Comprehensive structural characterization and quantification of these lipids is largely based on advanced analytical mass spectrometry based lipidomic methods. While separation of complex lipid mixtures is achieved through high performance liquid chromatography, the soft - electrospray ionization tandem mass spectrometry allows a high sensitivity and selectivity of detection. Herein, we present an overview of lipid extraction, chromatographic separation and mass spectrometry employed in qualitative and quantitative sphingolipidomics in fungi.