Quantification of phospholipid molecular species by coupled gas chromatography-mass spectrometry of deuterated samples

Quantitative and wide-ranging profiling of phospholipids in human plasma by two-dimensional liquid chromatography/mass spectrometry

Normal-phase or reverse-phase liquid chromatography has been used in phospholipidomics for lipid separation prior to mass spectrometry analysis. However, separation using a single separation mode is often inadequate, as high-abundance phospholipids can mask large numbers of low-abundance lipids of interest. In order to detect and quantify low-abundance phospholipids, we present a novel two-dimensional (2D) approach for sensitive and quantitative global analysis of phospholipids. The methodology monitors individual glycerolipids and phospholipids through the use of a new quantitative normal-phase, solid-phase extraction procedure, followed by molecular characterization and relative quantification using an ion-trap Orbitrap equipped with a reverse-phase liquid chromatograph, with data processing by MS++ software. The CV (%) of the peak area of each lipid standard was less than 15% with this extraction method. When the method was applied to a liver sample, we could detect more phosphatidylserine (PS) compared to the previous method. Finally, our developed method was applied to Alzheimer's disease (AD) plasma samples. Several hundred peaks were detected from a 60 μL plasma sample. A partial-least-squares discriminant analysis (PLS-DA) plot using peak area ratio gave a unique group of PLS scores which could distinguish plasma samples of Alzheimer's disease (AD) patients from those of age-matched healthy controls.

Identification of the unsaturated oxo fatty acids in cheese

The nature and composition of the unsaturated (monoenoic) oxo fatty acids in Cheddar cheese have been re-evaluated. Following isolation by column chromatography and silver ion HPLC, the fatty acids were identified in the form of their picolinyl ester derivatives by gas chromatography–mass spectrometry. For confirmation, they were analysed similarly following deuteration of the double bonds with deuterium and Wilkinson's catalyst. Fifteen fatty acids were identified fully, only five of which corresponded to those reported in an earlier study. Isomers with double bonds in positions 5, 7, 9 and 11–15 were identified, with oxo groups in positions 8, 9, 10, 13, 16 and 17, and with chain-lengths varying from C14 to C18, but with C18 predominating.

Membrane Lipid Homeostasis

The lipid matrix of biological membranes is composed of a complex mixture of polar lipids. It has been estimated that more than 600 distinct molecular species of lipid are constituents of biological membranes. This rather remarkable feature raises the questions of why such complexity is required when barrier properties and many protein functions can be reconstituted with relatively simple lipid systems. Secondly, the molecular species composition of morphologically distinct membranes appears to be preserved within fairly narrow limits. The biochemical mechanism(s) responsible for this homeostasis are not fully understood. This review examines the origin of membrane lipid complexity, the methods that are currently employed to measure and detect lipid molecular species and the biochemical reactions associated with the turnover of membrane lipids in resting and stimulated cells.

Tanacetum (Chrysanthemum) corymbosum seed oil--a rich source of a novel conjugated acetylenic acid

A new conjugated trans,trans-diunsaturated acetylenic acid (17%), found for the first time in nature as a main component of the seed oil of Tanacetum (Chrysanthemum) corymbosum, was shown to be octadeca-8t,10t-dien-12-ynoic acid. Another already known naturally occurring acetylenic acid, crepenynic acid (10%), was found also in the seed oil. The structure of this new unusual fatty acid was confirmed by chromatographic (thin-layer chromatography, gas chromatography, high-performance liquid chromatography) and spectroscopic (infrared, ultraviolet, mass spectrometry) methods by using different chemical derivatizations (deuteration, preparation of picolinyl ester, dimethyloxazoline, and maleic anhydride adduct).

Novel di-, tri-, and tetraenoic fatty acids with bis-methylene-interrupted double-bond systems from the sponge Haliclona cinerea

Unusual fatty acids, with up to 34 carbon atoms and containing one or two bis-methylene-interrupted double-bond systems, have been identified in the sponge Haliclona cinerea from the Black Sea. These include the dienes-5,9-16:2, 7,11-18:2, 9,13-20:2, 13,17-24:2, 15,19-26:2, 17,21-28:2, 19,23-30:2 and 21,25-32:2; trienes-5,9,23-30:3, 5,9,24-31:3, 5,9,25-32:3, and 5,9,27-34:3; and the tetraenes-5,9,19,23-30:4, 5,9,21,25-32:4, and 5,9,23,27-34:4. In addition, 5,9,13-eicosatrienoic acid was present. Many of these do not appear to have been described before, and only 5,9-16:2 and 5,9,23-30:3 are found often in sponges. They were identified by using silver-ion high-performance liquid chromatography to simplify the complex mixture of fatty acids for subsequent analysis by gas chromatography-mass spectrometry as picolinyl ester derivatives. Deuteration with Wilkinson's catalyst in homogeneous solution confirmed the structures. We speculate that the di- and tetraenoic fatty acids arise by chain elongation of 5,9-hexadecadienoic acid, also a major component of the lipids, followed by further insertion of double bonds in the 5 and 9 positions. The trienes may be formed from 9-hexadecenoic acid by similar mechanisms.

High-resolution triacylglycerol mixture analysis using high-temperature gas chromatography / mass spectrometry with a polarizable stationary phase, negative ion chemical ionization, and mass-resolved chromatography

High-temperature gas chromatography/mass spectrometry (HT-GC/MS) has been employed to study the behavior of mixtures of triacylglycerol molecular species on a polarizable stationary phase (immobilized 65% phenyl methyl silicone). The use of negative ion chemical ionization (NICI) at an ion source block temperature of 300 °C overcomes problems with interpretation of electron ionization (EI) mass spectra produced during the HT-GC/MS. The NICI spectra of triacylglycerols produced under these conditions contain abundant [RCO2](-), [RCO2 - 18](-), and [RCO2 - 19](-) ions, believed to be produced by nucleophilic gas-phase ammonolysis, that are used to identify the individual fatty acid moieties associated with peaks in triacylglycerol total ion chromatograms. The polarizable stationary phase produces significantly enhanced resolution of triacylglycerol molecular species compared to hightemperature stable apolar stationary phases, such as immobilized dimethyl polysiloxanes. The resolution of complex natural mixtures of triacylglycerols can be further improved by use of the Biller-Biemann enhancement technique to produce mass-resolved chromatograms. Investigation of the mass-resolved chromatograms provides important information with regard to the factors that affect elution orders of individual triacylglycerol molecular species. The analysis of mixtures of authentic triacylglycerols by HT-GC/MS via NICI provides data that relate to the analytical limits of the technique for the analysis of triacylglycerols that bear both saturated and polyunsaturated fatty acyl moieties.

A simplified approach to the analysis of subclasses of phospholipids: application to human platelets

A procedure for the determination of the proportions of diacyl, alkenylacyl and alkylacyl subclasses of glycerophospholipids was developed. The procedure involves: (1) acid methanolysis of the phospholipid followed by Bligh/Dyer extraction of fatty acid methyl esters (FAME) derived from acyl chain types, dimethylacetals (DMA) derived from alkenyl ether chain types, and lysoalkyl phosphatidic acids (lysoalkyl-PA) derived from alkyl ether chain types; and (2) subsequent acetolysis to convert the lysoalkyl-PA to monoalkyl glycerol diacetates (MAGD). GLC analysis and quantitation (using internal standard, 21:0 FAME) of FAME, DMA and MAGD allowed calculation of the proportions of the three molecular subclasses. The methanolysis/acetolysis procedure gave an overall mean phospholipid recovery of 95 +/- 3%. Analysis of the major phospholipids in four separate preparations of fresh resting human platelets by this procedure showed the following range of molecular subclasses: phosphatidylcholine (PC), 86-92 mol % diacyl, 6-10 mol % alkylacyl and 2-3 mol % alkenylacyl; and phosphatidylethanoline (PE), 39-60 mol % diacyl, 5-8 mol % alkylacyl and 34-55 mol % alkenylacyl. The results of these subclass analyses were in general agreement with those reported in the literature.

Alterations of the composition and size of the free fatty acid pool of Tetrahymena responding to low-temperature stress

Cells of Tetrahymena mimbres (formerly T. pyriformis NT-1) in midlogarithmic growth under isothermal conditions (at 39 degrees C) contained a very small, compositionally discrete pool of free fatty acids, principally (60.6% of the total free fatty acid mass) palmitic and stearic acids. The composition, degree of unsaturation, and size of this free fatty acid pool were rapidly (15 min or less) altered in response to chilling. During the acclimation period following chilling to 15 degrees C, the size of the free fatty acid pool increased from a mean value of 15.5 nmol free fatty acid/mumol lipid phosphorus in 39 degrees C cells to 24.2 nmol free fatty acid/mumol lipid phosphorus. The degree of free fatty acid saturation rapidly increased over the initial hour following the onset of hypothermal conditions, but by 24 h the unsaturated free fatty acid/saturated free fatty acid ratio was 0.35 (equivalent to a 2.7-fold increase in unsaturation relative to 39 degrees C controls (unsaturated/saturated ratio = 0.13) and 4.4-fold greater than cells acclimated for 1 h (unsaturated/saturated ratio = 0.08)). By 24 h the percentage of palmitic and stearic acids had decreased to 45.6%. Similar, and in some instances more pronounced, changes were observed to occur in triacylglycerol-bound fatty acids. Modulation of steady-state free fatty acid composition could also be achieved by the addition of exogenous fatty acids to the growth medium. The ability to manipulate the level of intracellular free fatty acids should prove to be a valuable experimental tool in determining how specific fatty acids regulate various lipid-modifying enzymes.