Electrospray mass spectrometry of phospholipids

Electron-induced dissociation (EID) for structure characterization of glycerophosphatidylcholine: determination of double-bond positions and localization of acyl chains

Glycerophospholipids are a highly abundant and diverse collection of biologically relevant lipids, and distinction between isomeric and isobaric species is a fundamental aspect for confident identification. The ability to confidently assign a unique structure to a glycerophospholipid of interest is dependent on determining the number and location of the points of unsaturation and assignment of acyl chain position. The use of high-energy electrons (>20 eV) to induce gas-phase dissociation of intact precursor ions results in diagnostic product ions for localizing double-bond positions and determining acyl chain assignment. We describe a high-resolution, tandem mass spectrometry method for structure characterization of glycerophospholipids using electron-induced dissociation (EID). Furthermore, the inclusion of nomenclature to systematically assign bond cleavage sites with acyl chain position and double-bond location enables a uniform platform for lipid identification. The EID methodology detailed here combines novel application of an electron-based dissociation technique with high-resolution mass spectrometry that facilitates a new experimental approach for lipid biomarker discovery and validation.

RADICAL-INDUCED FRAGMENTATION OF PHOSPHOLIPID CATIONS USING METASTABLE ATOM-ACTIVATED DISSOCIATION MASS SPECTROMETRY (MAD-MS)

The fragmentation pattern of several protonated 1+ phosphatidylcholines (PCs) were studied using low energy collision induced dissociation (CID) and helium metastable atom-activated dissociation (He-MAD). He-MAD of the protonated compounds produced a dominant phosphocholine head group at m/z 184 as well as typical sn-1 and sn-2 glycerol fragments such as [M+H-R_x-1CHC=O]⁺ and [M+H-R_x-1CO₂H]⁺. Within the aliphatic chain, He-MAD showed fragments consistent with high-energy collision induced dissociation (HE-CID) and products/pathways consistent with Penning ionization of the 1+ precursor ions to their respective radical dications. These Penning ionization products included both singly and doubly charged radical fragments, and the fragment ions are related to the number and position of double bonds in the acyl chains. Fragments created through HE-CID-like fragmentation followed classic charge remote fragmentation pathways including ladder-like fragmentation along the acyl chain, except for additional or missing peaks due to predictable rearrangement reactions. He-MAD therefore shows utility in being able to effectively fragment singly charged lipids into a variety of useful product ions using both radical and high-energy processes in the confines of a 3D ion trap.

Gas-Phase Chemical Separation of Phosphatidylcholine and Phosphatidylethanolamine Cations via Charge Inversion Ion/Ion Chemistry

The [M + H](+) cations formed upon electrospray ionization of the glycerophospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE) show distinct reactivities upon gas-phase reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). PC cations undergo charge inversion via adduct formation with subsequent methyl cation and proton transfer to the acid to yield [PC - CH3](-) anions. These demethylated PC anions fragment upon ion trap collision-induced dissociation (CID) to yield products that reveal fatty acid chain lengths and degrees of unsaturation. PE cations, on the other hand, undergo charge inversion via double proton transfer to the two carboxylate moieties in doubly deprotonated PDPA to yield [PE - H](-) anions. These anions also fragment upon ion trap CID to yield product ions indicative of chain lengths and degrees of unsaturation in the fatty acyl moieties. Advantage is taken of this distinct reactivity to separate isomeric and isobaric PC and PE cations present in mass spectra of lipid mixtures. A cation precursor ion population containing a mixture of PE and PC cations is mass-selected and subjected to ion/ion charge inversion reactions that result in separation of PC and PE anions into different mass-to-charge ratios. Mass selection and subsequent ion trap CID of the lipid anions allows for the characterization of the isomeric lipids within each subclass. The charge inversion approach described here is demonstrated to provide increased signal-to-noise ratios for detection of PCs and PEs relative to the standard negative ionization approach as well as improved mixture analysis performance.

Sex-specific cardiac cardiolipin remodelling after doxorubicin treatment

Background

Imbalance in lipid metabolism and membrane lipid homeostasis has been observed in numerous diseases including heart failure and cardiotoxicity. Growing evidence links phospholipid alterations especially cardiolipins (CLs) to defects in mitochondrial function and energy metabolism in heart failure. We have shown recently that doxorubicin cardiotoxicity is more severe in male than female Wistar rats. We aimed to study whether this sex specificity is linked to differences in cardiac phospholipid profiles.

Results

Adult male and female rats were injected 2 mg/kg doxorubicin weekly for 7 weeks. Cardiac phospholipid molecular species were determined by liquid chromatography coupled with mass spectrometry fragmentation (LC)/MSⁿ. Sex difference in phosphatidylethanolamine and phosphatidylcholine species containing docosahexaenoic and docosapentaenoic acyl chains was observed, females having more than males. In both sexes, doxorubicin induced an important loss of the main CL(18:2)₄, while the level of monolysocardiolipin MLCL(18:2)₃ remained stable. However, a severe remodelling appeared in treated rats with the longest CL acyl chains in doxorubicin-treated females, which might compensate for the loss of tetra-linoleoyl CL. The level of oxidized cardiolipin was not particularly increased after doxorubicin treatment. Finally, expression of genes involved in the biosynthesis of fatty acid appeared to be decreased in doxorubicin-treated males.

Conclusions

These results emphasize for the first time the cardiac remodelling in the phospholipid classes after doxorubicin treatment. These observations suggest that doxorubicin has a sex-specific impact on the heart phospholipidome especially on cardiolipin, an essential mitochondrial lipid. Further studies are needed to better understand the roles of lipids in the anthracycline cardiotoxicity and sex differences, but phospholipid cardioprotection seems a valuable new additive therapeutic strategy for anthracycline cardiotoxicity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-015-0039-5) contains supplementary material, which is available to authorized users.

Unravelling polar lipids dynamics during embryonic development of two sympatric brachyuran crabs (Carcinus maenas and Necora puber) using lipidomics

Embryogenesis is an important stage of marine invertebrates with bi-phasic life cycles, as it conditions their larval and adult life. Throughout embryogenesis, phospholipids (PL) play a key role as an energy source, as well as constituents of biological membranes. However, the dynamics of PL during embryogenesis in marine invertebrates is still poorly studied. The present work used a lipidomic approach to determine how polar lipid profiles shift during embryogenesis in two sympatric estuarine crabs, Carcinus maenas and Necora puber. The combination of thin layer chromatography, liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry allowed us to achieve an unprecedented resolution on PL classes and molecular species present on newly extruded embryos (stage 1) and those near hatching (stage 3). Embryogenesis proved to be a dynamic process, with four PL classes being recorded in stage 1 embryos (68 molecular species in total) and seven PL classes at stage 3 embryos (98 molecular species in total). The low interspecific difference recorded in the lipidomic profiles of stage 1 embryos appears to indicate the existence of similar maternal investment. The same pattern was recorded for stage 3 embryos revealing a similar catabolism of embryonic resources during incubation for both crab species.

Potential Adverse Effects of Prolonged Sevoflurane Exposure on Developing Monkey Brain: From Abnormal Lipid Metabolism to Neuronal Damage

Sevoflurane is a volatile anesthetic that has been widely used in general anesthesia, yet its safety in pediatric use is a public concern. This study sought to evaluate whether prolonged exposure of infant monkeys to a clinically relevant concentration of sevoflurane is associated with any adverse effects on the developing brain. Infant monkeys were exposed to 2.5% sevoflurane for 9 h, and frontal cortical tissues were harvested for DNA microarray, lipidomics, Luminex protein, and histological assays. DNA microarray analysis showed that sevoflurane exposure resulted in a broad identification of differentially expressed genes (DEGs) in the monkey brain. In general, these genes were associated with nervous system development, function, and neural cell viability. Notably, a number of DEGs were closely related to lipid metabolism. Lipidomic analysis demonstrated that critical lipid components, (eg, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol) were significantly downregulated by prolonged exposure of sevoflurane. Luminex protein analysis indicated abnormal levels of cytokines in sevoflurane-exposed brains. Consistently, Fluoro-Jade C staining revealed more degenerating neurons after sevoflurane exposure. These data demonstrate that a clinically relevant concentration of sevoflurane (2.5%) is capable of inducing and maintaining an effective surgical plane of anesthesia in the developing nonhuman primate and that a prolonged exposure of 9 h resulted in profound changes in gene expression, cytokine levels, lipid metabolism, and subsequently, neuronal damage. Generally, sevoflurane-induced neuronal damage was also associated with changes in lipid content, composition, or both; and specific lipid changes could provide insights into the molecular mechanism(s) underlying anesthetic-induced neurotoxicity and may be sensitive biomarkers for the early detection of anesthetic-induced neuronal damage.

Differentiation of Whole Grain from Refined Wheat (T. aestivum) Flour Using Lipid Profile of Wheat Bran, Germ, and Endosperm with UHPLC-HRAM Mass Spectrometry

A comprehensive analysis of wheat lipids from milling fractions of bran, germ, and endosperm was performed using ultrahigh-performance liquid chromatography-high-resolution accurate-mass multistage mass spectrometry (UHPLC-HRAM-MS(n)) with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in both positive and negative modes. About 155 lipid compounds, including free fatty acids (FA), oxylipins, alk(en)ylresorcinols (ARs), γ-oryzanol, sphingolipids, triglycerides (TGs), diglycerides (DGs), phospholipids, and galactolipids were characterized from the three milling fractions. Galactolipids and phospholipids were proposed to be potential discriminatory compounds for refined flour, whereas γ-oryzanols, ARs, TGs, and DGs could distinguish whole wheat flour from a refined one based on principal component analysis (PCA).

The structural organization of seed oil bodies could explain the contrasted oil extractability observed in two rapeseed genotypes

The protein, phospholipid and sterol composition of the oil body surface from the seeds of two rapeseed genotypes was compared in order to explain their contrasted oil extractability. In the mature seeds of oleaginous plants, storage lipids accumulate in specialized structures called oil bodies (OBs). These organelles consist of a core of neutral lipids surrounded by a phospholipid monolayer in which structural proteins are embedded. The physical stability of OBs is a consequence of the interactions between proteins and phospholipids. A detailed study of OB characteristics in mature seeds as well as throughout seed development was carried out on two contrasting rapeseed genotypes Amber and Warzanwski. These two accessions were chosen because they differ dramatically in (1) crushing ability, (2) oil extraction yield and, (3) the stability of purified OBs. Warzanwski has higher crushing ability, better oil extraction yield and less stable purified OBs than Amber. OB morphology was investigated in situ using fluorescence microscopy, transmission electron microscopy and pulsed field gradient NMR. During seed development, OB diameter first increased and then decreased 30 days after pollination in both Amber and Warzanwski embryos. In mature seeds, Amber OBs were significantly smaller. The protein, phospholipid and sterol composition of the hemi-membrane was compared between the two accessions. Amber OBs were enriched with H-oleosins and steroleosins, suggesting increased coverage of the OB surface consistent with their higher stability. The nature and composition of phospholipids and sterols in Amber OBs suggest that the hemi-membrane would have a more rigid structure than that of Warzanwski OBs.

Oxidative lipidomics coming of age: advances in analysis of oxidized phospholipids in physiology and pathology

SIGNIFICANCE

Oxidized phospholipids are now well recognized as markers of biological oxidative stress and bioactive molecules with both pro-inflammatory and anti-inflammatory effects. While analytical methods continue to be developed for studies of generic lipid oxidation, mass spectrometry (MS) has underpinned the advances in knowledge of specific oxidized phospholipids by allowing their identification and characterization, and it is responsible for the expansion of oxidative lipidomics.

RECENT ADVANCES

Studies of oxidized phospholipids in biological samples, from both animal models and clinical samples, have been facilitated by the recent improvements in MS, especially targeted routines that depend on the fragmentation pattern of the parent molecular ion and improved resolution and mass accuracy. MS can be used to identify selectively individual compounds or groups of compounds with common features, which greatly improves the sensitivity and specificity of detection. Application of these methods has enabled important advances in understanding the mechanisms of inflammatory diseases such as atherosclerosis, steatohepatitis, leprosy, and cystic fibrosis, and it offers potential for developing biomarkers of molecular aspects of the diseases.

CRITICAL ISSUES AND FUTURE DIRECTIONS

The future in this field will depend on development of improved MS technologies, such as ion mobility, novel enrichment methods and databases, and software for data analysis, owing to the very large amount of data generated in these experiments. Imaging of oxidized phospholipids in tissue MS is an additional exciting direction emerging that can be expected to advance understanding of physiology and disease.

Lipidomic profiling of mastoid bone and tissue from patients with chronic otomastoiditis

Introduction Chronic otomastoiditis causes pain, otorrhea, and hearing loss resulting from the growth of tissue within the normally hollow mastoid cavity.

Objectives In this report, we used a lipidomics approach to profile major mastoid bone and tissue lipids from patients with and without otomastoiditis.

Methods The bone dust created during mastoidectomy, as well as the mastoid tissue, was analyzed from seven patients. Bone dust was also collected and analyzed in an additional four otologic cases (parotidectomy requiring mastoidectomy). Samples were subjected to a modified Bligh/Dyer lipid extraction, then high-performance thin-layer chromatography (HPTLC), combined gas chromatography/electron impact-mass spectrometry (GC/EI-MS), and flow-injection/electrospray ionization-tandem mass spectrometry (FI/ESI-MSMS). Data were analyzed for identification and profiling of major lipid components.

Results HPTLC revealed the presence of various lipid classes, including phosphatidylcholines, cholesterol, and triacylglycerols. GC/EI-MS analysis revealed the presence of cholesterol and several fatty acids. FI/ESI-MSMS analysis revealed a host of phosphatidylcholines, phosphatidylethanolamines, and cholesteryl esters.

Conclusion We used a lipidomics approach to develop an efficient (both in time and tissue amount) methodology for analysis of these tissues, identify the most abundant and common lipid species, and create a base of knowledge from which more focused endeavors in biomarker discovery can emerge. In an effort toward improved patient categorization and individualized intervention, the ultimate goal of this work is to correlate these lipid molecules to disease state and progression. This is the first reported study of its kind on these tissues.

Metabolite changes during the life history of Porphyra haitanensis

Plant metabolomics is essentially the comprehensive analysis of complex metabolites of plant extracts. Metabolic fingerprinting is an important part of plant metabolomics research. In this study, metabolic fingerprinting of different stages of the life history of the red alga Porphyra haitanensis was performed. The stages included conchocelis filaments, sporangial branchlets, conchosporangia, discharged conchospores and conchosporangial branchlets after conchospore discharge. Metabolite extracts were analysed with ultra-performance liquid chromatography coupled with electrospray ionisation quadrupole-time of flight mass spectrometry. Analyses profiles were subjected to principal components analysis and orthogonal projection to latent structures discriminant analysis using the SIMCA-P software for biomarker selection and identification. Based on the MS/MS spectra and data from the literature, potential biomarkers, mainly of phosphatidylcholine and lysophosphatidylcholine, were identified. Identification of these biomarkers suggested that plasma membrane phospholipids underwent major changes during the life history of P. haitanensis. The levels of phosphatidylcholine and lysophosphatidylcholine increased in sporangial branchlets and decreased in discharged conchospores. Moreover, levels of sphingaine (d18:0) decreased in sporangial branchlets and increased in discharged conchospores, which indicates that membrane lipids were increasingly synthesised as energy storage in sporangial branchlets, while energy was consumed in sporangial branchlets to discharged conchospores. A metabolomic study of different growth phases of P. haitanensis will enhance our understanding of its physiology and ecology.

Ion/ion reactions with "onium" reagents: an approach for the gas-phase transfer of organic cations to multiply-charged anions

The use of ion/ion reactions to effect gas-phase alkylation is demonstrated. Commonly used fixed-charge "onium" cations are well-suited for ion/ion reactions with multiply deprotonated analytes because of their tendency to form long-lived electrostatic complexes. Activation of these complexes results in an SN2 reaction that yields an alkylated anion with the loss of a neutral remnant of the reagent. This alkylation process forms the basis of a general method for alkylation of deprotonated analytes generated via electrospray, and is demonstrated on a variety of anionic sites. SN2 reactions of this nature are demonstrated empirically and characterized using density functional theory (DFT). This method for modification in the gas phase is extended to the transfer of larger and more complex R groups that can be used in later gas-phase synthesis steps. For example, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) is used to transfer a carbodiimide functionality to a peptide anion containing a carboxylic acid. Subsequent activation yields a selective reaction between the transferred carbodiimide group and a carboxylic acid, suggesting the carbodiimide functionality is retained through the transfer process. Many different R groups are transferable using this method, allowing for new possibilities for charge manipulation and derivatization in the gas phase.

In situ analysis of soybeans and nuts by probe electrospray ionization mass spectrometry

The probe electrospray ionization (PESI) is an ESI-based ionization technique that generates electrospray from the tip of a solid metal needle. In the present work, we describe the PESI mass spectra obtained by in situ measurement of soybeans and several nuts (peanuts, walnuts, cashew nuts, macadamia nuts and almonds) using different solid needles as sampling probes. It was found that PESI-MS is a valuable approach for in situ lipid analysis of these seeds. The phospholipid and triacylglycerol PESI spectra of different nuts and soybean were compared by principal component analysis (PCA). PCA shows significant differences among the data of each family of seeds. Methanolic extracts of nuts and soybean were exposed to air and sunlight for several days. PESI mass spectra were recorded before and after the treatment. Along the aging of the oil (rancidification), the formation of oxidated species with variable number of hydroperoxide groups could be observed in the PESI spectra. The relative intensity of oxidated triacylglycerols signals increased with days of exposition. Monitoring sensitivity of PESI-MS was high. This method provides a fast, simple and sensitive technique for the analysis (detection and characterization) of lipids in seed tissue and degree of oxidation of the oil samples.

Making methods rugged for regulated bioanalysis

Methods started in discovery are optimized as they progress through preclinical and clinical development. Making a robust assay includes testing individual steps for consistency and points of failure. Assays may be transferred, optimized and revalidated several times. A rugged assay will not only meet regulatory requirements, but will execute with a low failure rate and confirm results under repeat analysis. Challenging aspects such as differential recovery, sample stabilization, resolution of isomers or conjugate analysis must be tackled and made routine. The proper selection of the IS can overcome limitations. It is best to know the potential points of failure before a study has started, but lessons learned from each study also provide invaluable insights to improve assay ruggedness.

Comparison and characterization of soybean and sunflower lecithins used for chocolate production by high-performance thin-layer chromatography with fluorescence detection and electrospray mass spectrometry

The scarce availability of nongenetically modified soybeans on the world market represents a growing problem for food manufacturers. Hence, in this study the effects of substituting soybean with sunflower lecithin were investigated with regard to chocolate production. The glycerophospholipid pattern of the different lecithin samples was investigated by high-performance thin-layer chromatography fluorescence detection (HPTLC-FLD) and by HPTLC-positive ion electrospray ionization mass spectrometry (ESI(+)-MS) via the TLC-MS Interface and by scanning HPTLC-matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOFMS). Especially, the contents of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were of interest due to the influencing effects of these two glycerophospholipids on the rheological parameters of chocolate production. The lecithin substitution led to only slight differences in the rheological parameters of milk and dark chocolate. Limits of detection (LODs) and limits of quantification (LOQs) of seven glycerophospholipids were studied for three detection modes. Mean LODs ranged from 8 to 40 mg/kg for HPTLC-FLD and, using a single-quadrupole MS, from 10 to 280 mg/kg for HPTLC-ESI(+)-MS as well as from 15 to 310 mg/kg for HPTLC-FLD-ESI(+)-MS recorded after derivatization with the primuline reagent.

Lipidomic analysis of plasma, erythrocytes and lipoprotein fractions of cardiovascular disease patients using UHPLC/MS, MALDI-MS and multivariate data analysis

Differences among lipidomic profiles of healthy volunteers, obese people and three groups of cardiovascular disease (CVD) patients are investigated with the goal to differentiate individual groups based on the multivariate data analysis (MDA) of lipidomic data from plasma, erythrocytes and lipoprotein fractions of more than 50 subjects. Hydrophilic interaction liquid chromatography on ultrahigh-performance liquid chromatography (HILIC-UHPLC) column coupled with electrospray ionization mass spectrometry (ESI-MS) is used for the quantitation of four classes of polar lipids (phosphatidylethanolamines, phosphatidylcholines, sphingomyelins and lysophosphatidylcholines), normal-phase UHPLC-atmospheric pressure chemical ionization MS (NP-UHPLC/APCI-MS) is applied for the quantitation of five classes of nonpolar lipids (cholesteryl esters, triacylglycerols, sterols, 1,3-diacylglycerols and 1,2-diacylglycerols) and the potential of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is tested for the fast screening of all lipids without a chromatographic separation. Obtained results are processed by unsupervised (principal component analysis) and supervised (orthogonal partial least squares) MDA approaches to highlight the largest differences among individual groups and to identify lipid molecules with the highest impact on the group differentiation.

Characterization of Lipids and Proteins Associated to the Cell Wall of the Acapsular Mutant Cryptococcus neoformans Cap 67

Cryptococcus neoformans is an opportunistic human pathogen that causes life-threatening meningitis. In this fungus, the cell wall is exceptionally not the outermost structure due to the presence of a surrounding polysaccharide capsule, which has been highly studied. Considering that there is little information about C. neoformans cell wall composition, we aimed at describing proteins and lipids extractable from this organelle, using as model the acapsular mutant C. neoformans cap 67. Purified cell wall preparations were extracted with either chloroform/methanol or hot sodium dodecyl sulfate. Total lipids fractionated in silica gel 60 were analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS), while trypsin digested proteins were analyzed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). We detected 25 phospholipid species among phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidic acid. Two glycolipid species were identified as monohexosyl ceramides. We identified 192 noncovalently linked proteins belonging to different metabolic processes. Most proteins were classified as secretory, mainly via nonclassical mechanisms, suggesting a role for extracellular vesicles (EV) in transwall transportation. In concert with that, orthologs from 86% of these proteins have previously been reported both in fungal cell wall and/or in EV. The possible role of the presently described structures in fungal-host relationship is discussed.

Overexpression of Lysophosphatidylcholine Acyltransferase 1 and Concomitant Lipid Alterations in Gastric Cancer

BACKGROUND

The involvement of lipids in carcinogenic and developmental processes has been reported in some malignancies, but their roles in gastric cancer remain to be analyzed. In this study, we compared the lipid content of gastric cancer tissue and adjacent nonneoplastic mucosa using imaging mass spectrometry.

METHODS

Mass spectra were acquired from 12 sections of human gastric cancer tissue and adjacent nonneoplastic mucosa using a matrix-assisted laser desorption-ionization time-of-flight tandem mass spectrometry type mass spectrometer equipped with a 355 nm Nd:YAG laser. Protein expression of lysophosphatidylcholine acyltransferase 1 (LPCAT1), which converts lysophosphatidylcholine (LPC) to phosphatidylcholine (PC) in the presence of acyl-CoA in Lands' cycle, was immunohistochemically analyzed in 182 gastric cancer specimens.

RESULTS

The averaged mass spectra from the cancer tissue and nonneoplastic mucosa were identical. Most of the signals that differed between cancer tissue and nonneoplastic mucosa corresponded to phospholipids, the majority of which were PC and LPC. Two signals, m/z 798.5 and 496.3, were higher and lower, respectively, in cancer tissues, predominantly in differentiated adenocarcinoma. A database search enabled identification of the ions at m/z 798.5 and m/z 496.3 as potassium-adducted PC (16:0/18:1) and proton-adducted LPC (16:0), respectively. Immunohistochemical analysis revealed that LPCAT1 was highly expressed in cancer lesions compared to nonneoplastic mucosa, predominantly in differentiated adenocarcinoma. LPCAT1 expression levels correlated positively with tumor differentiation and negatively with tumor depth, lymph node metastasis, and tumor stage.

CONCLUSIONS

Overexpressed LPCAT1 protein in gastric mucosa appears to play important roles in the tumorigenic process of gastric cancer by converting LPC to PC.

Applications of mass spectrometry for cellular lipid analysis

Mass spectrometric analysis of cellular lipids is an enabling technology for lipidomics, which is a rapidly-developing research field. In this review, we briefly discuss the principles, advantages, and possible limitations of electrospray ionization (ESI) and matrix assisted laser desorption/ionization (MALDI) mass spectrometry-based methodologies for the analysis of lipid species. The applications of these methodologies to lipidomic research are also summarized.

Polarization induced electrospray ionization mass spectrometry for the analysis of liquid, viscous and solid samples

In this study, a polarization-induced electrospray ionization mass spectrometry (ESI-MS) was developed. A micro-sized sample droplet was deposited on a naturally available dielectric substrate such as a fruit or a stone, and then placed close to (~2 mm) the orifice of a mass spectrometer applied with a high voltage. Taylor cone was observed from the sample droplet, and a spray emitted from the cone apex was generated. The analyte ion signals derived from the droplet were obtained by the mass spectrometer. The ionization process is similar to that in ESI although no direct electric contact was applied on the sample site. The sample droplet polarized by the high electric field provided by the mass spectrometer initiated the ionization process. The dielectric sample loading substrate facilitated further the polarization process, resulting in the formation of Taylor cone. The mass spectral profiles obtained via this approach resembled those obtained using ESI-MS. Multiply charged ions dominated the mass spectra of peptides and proteins, whereas singly charged ions dominated the mass spectra of small molecules such as amino acids and small organic molecules. In addition to liquid samples, this approach can be used for the analysis of solid and viscous samples. A small droplet containing suitable solvent (5-10 µl) was directly deposited on the surface of the solid (or viscous) sample, placed close the orifice of mass spectrometer applied with a high voltage. Taylor cone derived from the droplet was immediately formed followed by electrospray processes to generate gas-phase ions for MS analysis. Analyte ions derived from the main ingredients of pharmaceutical tablets and viscous ointment can be extracted into the solvent droplet in situ and observed using a mass spectrometer.

Characterization of phospholipids by two-dimensional liquid chromatography coupled to in-line ozonolysis-mass spectrometry

In this study, the characterization of phospholipids (PL) was achieved by using a combination of LC/MS/MS and two-dimensional LC/MS. A HILIC LC column was used for PL class separation, while the further molecular species separation of each PL class was achieved by using online HILIC × C18 LC. The double bond positions along the fatty acyl chains of these PL molecular species were also obtained by using the combination of 2D-LC and in-line ozonolysis-MS analysis. The ozonolysis device is composed of a gas-permeable, liquid-impermeable Teflon tube passing through a glass chamber filled with ozone gas, which is then placed in-line between the 2D-LC and the mass spectrometer. The eluting PL molecules in the LC mobile phase passed through the device where they rapidly reacted with the ozone that penetrated through the tubing wall. The ozonolysis products were then detected by MS in real-time, which allowed the localization of the double bonds along the fatty acyl chains in these PL molecular species. This comprehensive method was successfully applied to an egg yolk PL extract, which revealed the detailed structures of the PL molecules.

Rapid identification of erythrocyte phospholipids in Sprague-Dawley rats by ultra high performance liquid chromatography with electrospray ionization quadrupole time-of-flight tandem mass spectrometry

A rapid, sensitive, and reliable approach for analyzing five kinds of erythrocyte phospholipids in Sprague-Dawley rats was provided by ultra high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry with MassLynx(TM) MassFragment. Improving conventional high performance liquid chromatography techniques, ultra high performance liquid chromatography integrated with quadrupole time-of-flight tandem mass spectrometry offers high sensitivity and increased analytical speed by using columns packed with sub-2 μm particles (1.7 μm), which allows a faster separation to be achieved. Through this method, 83 phospholipids were tentatively characterized based on their mass spectra and tandem mass spectra, as well as by matching the in-house formula database within a mass error of 5 ppm, including 40 phosphatidylcholines, 24 phosphatidyl ethanolamines, three phosphatidylinositols, six phosphatidylserines, and ten sphingomyelins. Our present results proved that the established method could be used to qualitatively analyze complex erythrocyte phospholipids in Sprague-Dawley rats and provide a useful data base for pharmacology and phospholipidomics to seek potential biomarkers of disease prediction.

Lipidomic profiling of sinus mucosa from patients with chronic rhinosinusitis

Sinusitis is a cause of significant morbidity, substantial healthcare costs, and negative effects on quality of life. The primary objective of this study is to characterize the previously unknown lipid profile of sinonasal mucosa from patients with chronic rhinosinusitis (CRS) and from controls. Sinus mucosa samples were analyzed from 9 CRS patients with concomitant nasal polyps, 11 CRS patients without polyps, and 12 controls. Ten lone polyp samples were also analyzed. Samples were subjected to a modified Bligh/Dyer lipid extraction, then high performance thin layer chromatography (HPTLC), combined gas chromatography/electron impact-mass spectrometry (GC/EI-MS), and flow-injection/electrospray ionization-tandem mass spectrometry (FI/ESI-MS/MS). Data was analyzed for identification and profiling of major components. HPTLC revealed an array of species reflecting the lipid complexity of the samples. GC/EI-MS revealed cholesterol and several fatty acids. FI/ESI-MSMS revealed numerous lipid species, namely a host of phosphatidylcholines, phosphatidylethanolamines, ceramides and cholesteryl esters, but no detectable amounts of phosphatidyinositols or sulfated lipids. These results are a first step to uncover unique molecular biomarkers in CRS.

Lipidomic analysis of cerebrospinal fluid by mass spectrometry-based methods

Lipids are natural substances found in all living organisms. Essential to the integrity of cell membranes, they also have many biological functions linked to energy storage and cell signaling, and are involved in a large number of heterogeneous diseases such as cancer, diabetes, neurological disorders, and inherited metabolic diseases. Lipids are challenging to analyze because of their huge structural diversity and numerous species. Up to now, lipid analysis has been achieved by targeted approaches focusing on selected families and relying on extraction protocols and chromatographic methods coupled to various detectors including mass spectrometry. Thanks to the technological improvements achieved in the fields of chromatography, high-resolution mass spectrometry and bioinformatics, it is possible to perform global lipidomic analyses enabling the concomitant detection, identification and relative quantification of many lipid species belonging to different families. The aim of this review is to focus on mass spectrometry-based methods to perform lipid and lipidomic analyses and on their application to the analysis of cerebrospinal fluid.

Comprehensive lipidome analysis by shotgun lipidomics on a hybrid quadrupole-orbitrap-linear ion trap mass spectrometer

Here we report on the application of a novel shotgun lipidomics platform featuring an Orbitrap Fusion mass spectrometer equipped with an automated nanoelectrospray ion source. To assess the performance of the platform for in-depth lipidome analysis, we evaluated various instrument parameters, including its high resolution power unsurpassed by any other contemporary Orbitrap instrumentation, its dynamic quantification range and its efficacy for in-depth structural characterization of molecular lipid species by quadrupole-based higher-energy collisional dissociation (HCD), and ion trap-based resonant-excitation collision-induced dissociation (CID). This evaluation demonstrated that FTMS analysis with a resolution setting of 450,000 allows distinguishing isotopes from different lipid species and features a linear dynamic quantification range of at least four orders of magnitude. Evaluation of fragmentation analysis demonstrated that combined use of HCD and CID yields complementary fragment ions of molecular lipid species. To support global lipidome analysis, we designed a method, termed MS(ALL), featuring high resolution FTMS analysis for lipid quantification, and FTMS(2) analysis using both HCD and CID and ITMS(3) analysis utilizing dual CID for in-depth structural characterization of molecular glycerophospholipid species. The performance of the MS(ALL) method was benchmarked in a comparative analysis of mouse cerebellum and hippocampus. This analysis demonstrated extensive lipidome quantification covering 311 lipid species encompassing 20 lipid classes, and identification of 202 distinct molecular glycerophospholipid species when applying a novel high confidence filtering strategy. The work presented here validates the performance of the Orbitrap Fusion mass spectrometer for in-depth lipidome analysis.

Glycerophospholipids

Glycerophospholipids are phosphodiesters of glycerol and an alcohol referred to as the polar headgroup. The two glycerol carbinol groups are typically esterified with long chain fatty acyl groups which impart hydrophobic character to these otherwise polar molecules. The simplest glycerophospholipid is phosphatidic acid which is a monophosphoester of diacylglycerol. The common polar headgroups are choline, ethanolamine, serine, inositol, and glycerol which divide the phospholipids into different classes. This chapter discusses glycerophosphocholine lipids (PC), glycerophosphoethanolamine lipids (PE), phosphatidylserine (PS), phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylglycerol (PG), bis(acyl-lysophosphatidyl)glycerol (BMP) and cardiolipin.

Determination of nonpolar and polar lipid classes in human plasma, erythrocytes and plasma lipoprotein fractions using ultrahigh-performance liquid chromatography-mass spectrometry

A novel normal-phase (NP) ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC/MS) method is developed for a separation and quantitation of nonpolar lipid classes occurring in human plasma, erythrocytes and plasma lipoprotein fractions. The baseline class separation of cholesteryl esters (CE), cholesterol, triacylglycerols (TG), regioisomers of 1,2- and 1,3-diacylglycerols (DG) and 1-monoacylglycerols (1-MG) is achieved using an optimized hexane - 2-propanol-acetonitrile mobile phase within 18min for all nonpolar lipid classes or only 9min excluding monoacylglycerols not detected in studied samples. The determination of individual nonpolar lipid classes is performed by the response factor approach and the use of dioleoyl ethylene glycol as a single internal standard. Polar lipid classes, such as phosphatidylglycerols (PG), phosphatidylethanolamines (PE), phosphatidylcholines (PC), sphingomyelins (SM) and lysophosphatidylcholines (LPC), are separated by hydrophilic interaction liquid chromatography (HILIC) using 5mmol/L aqueous ammonium acetate-methanol-acetonitrile gradient within 13minutes. The quantitation of polar lipid classes is done by a similar approach as for nonpolar lipid classes, but a different internal standard (sphingosyl PE d17:1/12:0) is used. The complementary information on fatty acyl profiles after the transesterification of the total lipid extract is obtained by gas chromatography with flame ionization detection (GC/FID). The applicability of developed methodology for fast and comprehensive characterization of blood lipidome is illustrated on samples of human plasma, erythrocytes, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) fractions.

A new study of the bacterial lipidome: HPTLC-MALDI-TOF imaging enlightening the presence of phosphatidylcholine in airborne Pseudomonas fluorescens MFAF76a

Lipids are major functional components of bacterial cells that play fundamental roles in bacterial metabolism and the barrier function between cells and the environment. In an effort to investigate the bacterial lipidome, we adopted a protocol using MALDI-TOF MS imaging coupled to HPTLC to screen a large number of phospholipid classes in a short span of time. With this method, phospholipids of airborne Pseudomonas fluorescens MFAF76a were visualized and identified in sample extracts (measurement accuracy below 0.1 Da, phospholipid identification by means of four characteristic fragment peaks). Via this technique, the P. fluorescens lipidome was shown to comprise three major lipid classes: phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine. The protocol described herein is simple, rapid and effective for screening of bacterial phospholipid classes. The remarkable presence of a eukaryotic phospholipid, phosphatidylcholine, was observed in P. fluorescens MFAF76a. This lipid is known to play a role in bacteria-host interactions and had not been known to be found in P. fluorescens cells.

High resolution mass spectrometry based techniques at the crossroads of metabolic pathways

The metabolome is the set of small molecular mass compounds found in biological media, and metabolomics, which refers to as the analysis of metabolome in a given biological condition, deals with the large scale detection and quantification of metabolites in biological media. It is a data driven and multidisciplinary approach combining analytical chemistry for data acquisition, and biostatistics, informatics and biochemistry for mining and interpretation of these data. Since the middle of the 2000s, high resolution mass spectrometry is widely used in metabolomics, mainly because the detection and identification of metabolites are improved compared to low resolution instruments. As the field of HRMS is quickly and permanently evolving, the aim of this work is to review its use in different aspects of metabolomics, including data acquisition, metabolite annotation, identification and quantification. At last, we would like to show that, thanks to their versatility, HRMS instruments are the most appropriate to achieve optimal metabolome coverage, at the border of other omics fields such as lipidomics and glycomics.

Metabolomic screening of regional brain alterations in the APP/PS1 transgenic model of Alzheimer's disease by direct infusion mass spectrometry

The identification of pathological mechanisms underlying to Alzheimer's disease is of great importance for the discovery of potential markers for diagnosis and disease monitoring. In this study, we investigated regional metabolic alterations in brain from the APP/PS1 mice, a transgenic model that reproduces well some of the neuropathological and cognitive deficits observed in human Alzheimer's disease. For this purpose, hippocampus, cortex, cerebellum and olfactory bulbs were analyzed using a high-throughput metabolomic approach based on direct infusion mass spectrometry. Metabolic fingerprints showed significant differences between transgenic and wild-type mice in all brain tissues, being hippocampus and cortex the most affected regions. Alterations in numerous metabolites were detected including phospholipids, fatty acids, purine and pyrimidine metabolites, acylcarnitines, sterols and amino acids, among others. Furthermore, metabolic pathway analysis revealed important alterations in homeostasis of lipids, energy management, and metabolism of amino acids and nucleotides. Therefore, these findings demonstrate the potential of metabolomic screening and the use of transgenic models for understanding pathogenesis of Alzheimer's disease.

A single step reversed-phase high performance liquid chromatography separation of polar and non-polar lipids

This paper reports a simple chromatographic system to separate lipids classes as well as their molecular species. By the use of phenyl coated silica as stationary phase in combination with a simple mobile phase consisting of methanol and water, all tested lipid classes elute within 30 min. Furthermore, a method to accurately predict retention times of specific lipid components for this type of chromatography is presented. Common detection systems were used, namely evaporative light scattering detection (ELSD), charged aerosol detection (CAD), electrospray mass spectrometry (ESI-MS), and UV detection.

Characterization of complex lipid mixtures in contaminant exposed JEG-3 cells using liquid chromatography and high-resolution mass spectrometry

The aim of this study was to develop a method based on ultra high performance liquid chromatography coupled with mass spectrometry (UHPLC-MS) for lipid profiling in human placental choriocarcinoma (JEG-3) cells. Lipids were solid-liquid extracted from JEG-3 cells using a solution of chloroform/methanol (2:1, v/v) in a simple procedure requiring minimal sample alteration. Simultaneous separation of complex lipid mixtures in their major classes was achieved with a reversed-phase (C8) UHPLC column and a mobile phase containing methanol with 1 mM ammonium formate and 0.2 % formic acid (A)/water with 2 mM ammonium formate and 0.2 % formic acid (B). Lipids were characterized using time-of-flight (TOF) and Orbitrap under full scan and positive electrospray ionization mode with both analyzers. A total of 178 species of lipids, including 37 phosphatidylcholines (PC), 32 plasmalogen PC, 9 lyso PC, 4 lyso plasmalogen PC, 30 triacylglycerols, 22 diacylglycerols, 7 cholesterol esters, 25 phosphatidylethanolamines, and 12 sphingomyelins, were identified using TOF and Orbitrap. The identification of all lipid classes was based on exact mass characterization with an error < 5 ppm. The developed methodology was applied to study lipid alterations in human placental cells against the exposure to perfluorinated chemicals (PFCs) and tributyltin (TBT).