Analysis of phospholipid species in rat peritoneal surface layer by liquid chromatography/electrospray ionization ion-trap mass spectrometry

Sphingolipids as prognostic biomarkers of neurodegeneration, neuroinflammation, and psychiatric diseases and their emerging role in lipidomic investigation methods

Lipids play an important role in neurodegeneration, neuroinflammation, and psychiatric disorders and an imbalance in sphingolipid levels is associated with disease. Although early diagnosis and intervention of these disorders would clearly have favorable long-term outcomes, no diagnostic tests currently exist that can accurately identify people at risk. Reliable prognostic biomarkers that are easily accessible would be beneficial to determine therapy and treatment response in clinical trials. Recent advances in lipidomic investigation methods have greatly progressed the knowledge of sphingolipids in neurodegenerative and psychiatric disorders over the past decades although more longitudinal studies are needed to understand its exact role in these disorders to be used as potential tools in the clinic. In this review, we give an overview of the current knowledge of sphingolipids in neurodegenerative and psychiatric disorders and explore recent advances in investigation methods. Finally, the potential of sphingolipid metabolism products and signaling molecules as potential biomarkers for diagnosis, prognostic, or surrogate markers of treatment response is discussed.

Lipidomics applications for disease biomarker discovery in mammal models

Lipidomics is a lipid-targeted metabolomics approach focusing on comprehensive analysis of all lipids with which they interact in biology systems. Recent technological advances in MS and chromatography have greatly enhanced the developments and applications of metabolic profiling of diverse lipids in complex biological samples. Lipidomics will not only provide insights into the specific functions of lipid species in health and disease, but will also identify potential biomarkers for establishing preventive or therapeutic programs for human disease. In this review, recent applications of lipidomics to understand animal models of disease such as metabolic syndromes, neurodegenerative diseases, cancer and infectious diseases are considered. We also discuss the lipidomics for the future perspectives and their potential problems.

Ionic liquid matrix-based dispersive liquid-liquid microextraction for enhanced MALDI-MS analysis of phospholipids in soybean

Ionic liquid matrix (ILM) is found to be a very versatile substance for analysis of broad range of organic molecules in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) due to good solubility for a variety of analytes, formation of homogenous crystals and high vacuum stability of the matrix. In the present work, an ILM, cyno-4-hydroxycinnamic acid-butylamine (CHCAB) was employed in dispersive liquid-liquid microextraction (DLLME) as sample probe and matrix for extraction and ionization of phospholipids from food samples (soybean) prior to MALDI-MS analysis. With the employed technique, 8-125 fold improvement in signal intensity and limit of detection were achieved for the analysis of phospholipids. The best extraction efficiency of phospholipids in ILM-DLLME was obtained with 5min extraction time in presence 30mg/mL CHCAB and 1.2% NaCl using chloroform as an extracting solvent and methanol as a dispersing solvent. Further, the developed ILM-DLLME procedure has been successfully applied for the analysis of phospholipids in soybean samples in MALDI-MS.

Lipid and lipid mediator profiling of human synovial fluid in rheumatoid arthritis patients by means of LC-MS/MS

Human synovial fluid (SF) provides nutrition and lubrication to the articular cartilage. Particularly in arthritic diseases, SF is extensively accumulating in the synovial junction. During the last decade lipids have attracted considerable attention as their role in the development and resolution of diseases became increasingly recognized. Here, we describe a capillary LC-MS/MS screening platform that was used for the untargeted screening of lipids present in human SF of rheumatoid arthritis (RA) patients. Using this platform we give a detailed overview of the lipids and lipid-derived mediators present in the SF of RA patients. Almost 70 different lipid components from distinct lipid classes were identified and quantification was achieved for the lysophosphatidylcholine and phosphatidylcholine species. In addition, we describe a targeted LC-MS/MS lipid mediator metabolomics strategy for the detection, identification and quantification of maresin 1, lipoxin A(4) and resolvin D5 in SF from RA patients. Additionally, we present the identification of 5S,12S-diHETE as a major marker of lipoxygenase pathway interactions in the investigated SF samples. These results are the first to provide a comprehensive approach to the identification and profiling of lipids and lipid mediators present in SF and to describe the presence of key anti-inflammatory and pro-resolving lipid mediators identified in SF from RA patients.

Desorption electrospray ionization then MALDI mass spectrometry imaging of lipid and protein distributions in single tissue sections

Imaging mass spectrometry (MS) is a powerful technique for mapping the spatial distributions of a wide range of chemical compounds simultaneously from a tissue section. Co-localization of the distribution of individual molecular species, including particular lipids and proteins, and correlation with the morphological features of a single tissue section are highly desirable for comprehensive tissue analysis and disease diagnosis. We now report on the use, in turn, of desorption electrospray ionization (DESI), matrix assisted laser desorption ionization (MALDI), and then optical microscopy to image lipid and protein distributions in a single tissue section. This is possible through the use of histologically compatible DESI solvent systems, which allow for sequential analyses of the same section by DESI then MALDI. Hematoxylin and eosin (H&E) staining was performed on the same section after removal of the MALDI matrix. This workflow allowed chemical information to be unambiguously matched to histological features in mouse brain tissue sections. The lipid sulfatide (24:1), detected at m/z 888.8 by DESI imaging, was colocalized with the protein MBP isoform 8, detected at m/z 14117 by MALDI imaging, in regions corresponding to the corpus callosum substructure of the mouse brain, as confirmed in the H&E images. Correlation of lipid and protein distributions with histopathological features was also achieved for human brain cancer samples. Higher tumor cell density was observed in regions demonstrating higher relative abundances of oleic acid, detected by DESI imaging at m/z 281.4, and the protein calcyclin, detected by MALDI at m/z 10085, for a human glioma sample. Since correlation between molecular signatures and disease state can be achieved, we expect that this methodology will significantly enhance the value of MS imaging in molecular pathology for diagnosis.

Identification and quantification of phosphatidylcholines containing very-long-chain polyunsaturated fatty acid in bovine and human retina using liquid chromatography/tandem mass spectrometry

The retina is one of the vertebrate tissues with the highest content in polyunsaturated fatty acids (PUFA). A large proportion of retinal phospholipids, especially those found in photoreceptor membranes, are dipolyunsaturated molecular species. Among them, dipolyunsaturated phosphatidylcholine (PC) molecular species are known to contain very-long-chain polyunsaturated fatty acids (VLC-PUFA) from the n-3 and n-6 series having 24-36 carbon atoms (C24-C36) and four to six double bonds. Recent interest in the role played by VLC-PUFA arose from the findings that a protein called elongation of very-long-chain fatty acids 4 (ELOVL4) is involved in their biosynthesis and that mutations in the ELOVL4 gene are associated with Stargardt-like macular dystrophy (STD3), a dominantly inherited juvenile macular degeneration leading to vision loss. The aim of the present study was to develop an HPLC-ESI-MS/MS method for the structural characterisation and the quantification of dipolyunsaturated PC molecular species containing VLC-PUFA and validate this methodology on retinas from bovines and human donors. Successful separation of phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), PC, lyso-phosphatidylcholine (LPC) and sphingomyelin (SM) was achieved using a silica gel column and a gradient of hexane/isopropanol/water containing ammonium formate as a mobile phase. A complete structural characterisation of intact phosphatidylcholine species was obtained by collision-induced dissociation (CID) in the negative mode. Fatty acid composition and distribution can be clearly assigned based on the intensity of sn-2/sn-1 fragment ions. The PC species were characterised on bovine retina, 28 of which were dipolyunsaturated PC species containing one VLC-PUFA (C24-C36) with three to six double bonds. VLC-PUFA was always in the sn-1 position while PUFA at the sn-2 position was exclusively docosahexaenoic acid (DHA, C22:6n-3). Most of these VLC-PUFA-containing dipolyunsaturated PCs were detected and quantified in human retinas. The quantitative analysis of the different PC molecular species was performed in the positive mode using precursor ion scanning of m/z 184 and 14:0/14:0-PC and 24:0/24:0-PC as internal standards. The relationship between the MS peak intensities of different PC species and their carbon chain length was included for calibration. The main compounds represented were those having VLC-PUFA with 32 carbon atoms (C32:3, C32:4, C32:5 and C32:6) and 34 carbon atoms (C34:3, C34:4, C34:5 and C34:6). Dipolyunsaturated PCs with 36:5 and 36:6 were detected but in smaller quantities. In conclusion, this new HPLC-ESI-MS/MS method is sensitive and specific enough to structurally characterise and quantify all molecular PC species, including those esterified with VLC-PUFA. This technique is valuable for a precise characterisation of PC molecular species containing VLC-PUFA in retina and may be useful for a better understanding of the pathogenesis of STD3.

Lipid profiling of rat peritoneal surface layers by online normal- and reversed-phase 2D LC QToF-MS

An online, two-dimensional (2D) liquid chromatography (LC) quadrupole time-of-flight mass spectrometry (QToF-MS) method was developed for lipid profiling of rat peritoneal surface layers, in which the lipid classes and species could be simultaneously separated in one injection with a significantly increased sensitivity. Different lipid classes were separated on a normal-phase column in the first dimension and lipid molecular species were separated on a reversed-phase column in the second dimension, so that the ion suppression effects were reduced while the detection sensitivity was improved. Identified were 721 endogenous lipid species from 12 lipid classes, in which 415 structures were confirmed using tandem mass spectra, and the other 306 lipid molecular species were identified by accurate masses. The linearity, limit of detection, and repeatability were all satisfactory. The method was applied to the investigation of the lipid changes in rat peritoneal surface layer after peritoneal dialysis, and 32 potential lipid biomarkers were identified, as their concentrations in the dosed group were 2.2-12.5 times of those in the control group. The results revealed that this 2D LC-MS system was a promising tool for lipid profiling of complex biological samples.

The Alterations of Erythrocyte Phospholipids in Type 2 Diabetes Observed after Oral High-Fat Meal Loading: The FTIR Spectroscopic and Mass Spectrometric Studies

Little is known about the postprandial remodelling of erythrocytes phospholipids (PLs) in type 2 diabetics (T2DM). Therefore, this study aims to compare the alterations of erythrocyte PLs in T2DM to those of healthy subjects after ingestion of a high-fat meal. Eleven T2DM and ten healthy subjects underwent a high-fat meal loading. Erythrocytes were isolated from blood obtained after fasting and 4 h after the meal. Fourier Transform Infrared (FTIR) spectroscopy was initially used to screen erythrocyte PLs by monitoring C-H stretching vibrations. Phosphatidylcholine (PC) molecular species were further investigated by Liquid Chromatography-Electrospray Ionisation-Mass Spectrometry (LC-ESI-MS). For the control group, FTIR revealed postprandial changes in C-H stretching vibrations, particularly of the olefinic band. These findings were supported by LC-ESI-MS data, showing marked changes in PC molecular species, especially of the PC34:1 (where 34 and 1 mean the summed number of carbons and double bonds, respectively). However, similar changes of those were not apparent in the T2DM group. Our results reveal marked postprandial alterations of erythrocyte PC species in healthy subjects whereas only mild alterations are observed in T2DM. The discrepant effects of high-fat meal loading suggest abnormal PC remodelling in the diabetic erythrocyte that may affect its membrane fluidity and integrity.

Plasma phospholipid metabolic profiling and biomarkers of rats following radiation exposure based on liquid chromatography-mass spectrometry technique

Lipidomics, a prominent area of metabolomics, utilizes novel analytical methodologies to study the extensive classes of lipid molecules, changes in lipid metabolism and lipid-mediated signaling processes. In this paper, the phospholipid metabolic profiles changes and potential biomarker identification in the rats plasma after gamma-irradiation exposure were investigated by coupling high performance liquid chromatography-mass spectrometry technology to multivariate statistical analysis. Orthogonal partial least-squares to latent structures discriminate analysis (OPLS-DA) was used to find the potential plasma phospholipids biomarkers of rats for radiation exposure. According to the corresponding tandem mass spectrometric results, potential biomarkers were identified. After exposure to gamma-rays, phosphatidylethanolamine and phosphatidylserine showed a marked increase, and phosphatidylcholine, sphingomyelin and lysophosphatidylcholine followed the same trend, although their rise was not significant. The results suggested that radiated rats had a phospholipid metabolic abnormality, which could be an alternative way to assess the radiaton exposure. The biomarkers may involve a radiation-induced apoptosis pathway and represent a promising target for discovery new radioprotective drugs and radiosensitizers.

A simple and universal method for the separation and identification of phospholipid molecular species

One of the major challenges in lipidomics is to obtain as much information about the lipidome as possible. Here, we present a simple yet universal high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method to separate molecular species of all phospholipid classes in one single run. The method is sensitive, robust and allows lipid profiling using full scan mass spectrometry, as well as lipid class specific scanning in positive and negative ionisation mode. This allows high-throughput processing of samples for lipidomics, even if different types of MS analysis are required. Excellent separation of isobaric and even isomeric species is achieved, and original levels of lyso-lipids can be determined without interference from lyso-lipids formed from diacyl species by source fragmentation. As examples of application of this method, more than 400 phospholipid species were identified and quantified in crude phospholipid extracts from rat liver and the parasitic helminth Schistosoma mansoni.

Quantitative analysis of a novel glucosylated phospholipid by liquid chromatography-mass spectrometry

Building upon the demonstrated presence of a new glyceroglycolipid, phosphatidylglucoside (PtdGlc), in rat embryonic brain tissues, we have developed a method to identify minute amounts of PtdGlc in cultured cells by using nano-flow high-performance liquid chromatography and negative-ion-mode electrospray linear-ion trap time-of-flight mass spectrometry (LC-MS). A normal-phase silica gel-based column enabled us to separate PtdGlc from other lipid classes. PtdGlc was identified from its tandem mass spectrometry spectrum and from its retention time in the column. Using an internal standard collection and LC-MS, we obtained the linearity of PtdGlc at a range of 6.3-800 fmol per injection. We applied this method to analyze quantitative changes in PtdGlc in C6 glioma cells after cellular differentiation into GFAP-positive glial cells. PtdGlc in C6 glioma cells consisted exclusively of C18:0/C20:0 fatty acyl chains. Differentiation induced by the addition of anti-PtdGlc antibody plus cAMP in culture medium significantly increased the glycolipid content.

Development and validation of a selective and sensitive bioanalytical procedure for the quantitative determination of gaboxadol in human plasma employing mixed mode solid phase extraction and hydrophilic interaction liquid chromatography with tandem mass spectroscopic detection

A selective and sensitive hydrophilic interaction liquid chromatography tandem mass spectrometric bioanalytical method for the quantitative determination of gaboxadol in human heparinized plasma was developed and validated. Gaboxadol and the stable isotope labeled internal standard were extracted from plasma by mixed mode solid phase extraction and analyzed on an Asahipak NH2P HPLC column with a mobile phase composed of 70% acetonitrile and 30% ammonium acetate (20 mM, pH 4). The analytes were detected by a SCIEX API 4000 triple quadropole instrument using turbo electrospray ionization and multiple reaction monitoring negative mode. The method was validated over the concentration range of 0.5-100 ng/mL. The intra-day precision of the assay, as measured by the coefficient of variation (CV%), was within 4%. The intra-day assay accuracy was found to be within 2.2% of the nominal concentration for all the standards. The average recovery of gaboxadol was about 87% and the ion suppression was approximately 8%. To eliminate late eluters including the glucuronides, a "front cut" column switching procedure was added to the chromatographic system. The effectiveness of the column switching in eliminating the absolute matrix effect caused by late eluters was demonstrated by the low variation (CV<3.5%) in the peak areas of the internal standard during the assessment of the inter-day precision and accuracy and no significant relative matrix effect was observed as illustrated by the excellent intra-day precision (CV<1.5%) from the assessment of standard samples prepared in five different lots of control plasma. The described bioanalytical method has been successfully utilized for the analysis of gaboxadol in post-dose samples (>8000) from various clinical studies. Inter-day precision and accuracy were assessed from the daily mean (n=2) of QC values from 52 runs, i.e. more than 3000 samples. The inter-day precision of the assay, based on the coefficient of variation of QC, ranged from 2.1 to 5.1%. The inter-day assay accuracy was found to be within 4% of the nominal concentration for all QC samples.

Analysis of phospholipids by NACE with on-line ESI-MS

A hyphenated method of nonaqueous capillary electrophoresis coupled to electrospray ionization mass spectrometry (NACE-ESI-MS) is described for the simultaneous analysis of phospholipids. The best results were obtained with a mixed solution of methanol/ACN (40:60 v/v) containing 20 mM ammonium acetate and 0.5% acetic acid, under the applied voltage of 30 kV and capillary temperature of 25 degrees C. ESI-MS measurements were performed in the negative mode with methanol/ACN (40:60 v/v) containing 50 mM ammonium acetate as sheath liquid at a flow rate of 2 microL/min. Different phospholipid classes have been successfully separated within 16 min, and the molecular species of every single class have been identified by using MS(2) or MS(3), which generates characteristic fragments through CID. The developed method has been applied to analyze the phospholipids extracted from rat peritoneal surface and the molecular species of phospholipid classes are presented.