Studies on molecular species of choline and ethanolamine glycerophospholipids obtained from rat brain myelin and synaptosomes by gas-liquid chromatography mass spectrometry

In situ structural characterization of glycerophospholipids and sulfatides in brain tissue using MALDI-MS/MS

Lipids are major structural components of biomembranes. Negatively charged species such as phosphatidylinositol, phosphatidylserine, sulfatides, and the zwitterionic phosphatidylethanolamines are major components of the cytoplasmic surface of the cellular membrane lipid bilayer and play a key role in several receptors signaling functions. Lipids are not just involved in metabolic and neurological diseases; negatively charged lipids in particular play crucial roles in physiological events such as signal transduction, receptors, and enzymatic activation, as well as storage and release of therapeutic drugs and toxic chemicals in the body. Due to the importance of their role in signaling, the field of lipidomics has rapidly expanded in recent years. In the present study, direct probing of tissue slices with negative ion mode matrix assisted laser desorption/ionization mass spectrometry was employed to profile the distribution of lipids in the brain. In total, 32 lipid species consisting of phosphatidylethanolamines, phosphatidylglycerol, phosphatidylinositols, phosphatidylserines, and sulfatides were assigned. To confirm the structure of lipid species, MALDI-MS/MS analysis was conducted. Product-ion spectra obtained in negative ion mode allow for the assignment of the head groups and the fatty acid chains for the lipid species.

Tandem mass spectrometry of negative ions from choline phospholipid molecular species related to platelet activating factor

Fast atom bombardment mass spectrometry of choline phospholipids produces negative ions characteristic of the intact molecule and tandem mass spectrometry of collision-induced decomposition of M-15 anions characterizes both the identity and substituent position of radyl groups. Certain choline phospholipid molecular species which may be of special interest in the generation of platelet activating factor contain a highly unsaturated fatty acyl substituent at sn-2 and an ether radyl group at sn-1; other choline phospholipid molecular species which contain esterified arachidonic acid are of interest as potential sources of arachidonate for eicosanoid biosynthesis. Collisional activated decomposition of 1-hexadecanoyl-2-arachidonoyl-sn-glycero-phosphocholine produce abundant carboxylate anions at m/z 303 (arachidonate) and m/z 255 (hexadecanoate) in a ratio of 3:1, diagnostic for the sn-2 arachidonoyl position. The ether analog, 1-O-hexadecyl-2-arachidonoyl glycerophosphocholine, produces only one collision-induced dissociation ion at m/z 303 and no product ions corresponding to the ether substituent at sn-1. Molecular weight information from the M-15 ion combined with the CID generated carboxylate anions completely characterize these important phospholipids. Precursor ion studies of M-15 anions from glycero-phosphocholine lipids indicate that this ion is derived directly from a unique adduct ion formed by attachment of the molecular species to a matrix alkoxide ion, neutralizing the positive charge of the quaternary choline nitrogen. Decomposition of this adduct ion yields a methylated matrix molecule and the nominal M-15 ion.

Effect of 17 beta-estradiol on PAF and prostaglandin levels in oophorectomized rat uterus

The effects of 17 beta-estradiol on the levels of platelet-activating factor (PAF) and prostaglandins and their precursor phospholipid in the uterus of oophorectomized rats were studied. Oophorectomy results in the decrease in the uterine PAF level to one-third of that in natural estrus. This level was recovered by subcutaneous administration of 17 beta-estradiol. The level of uterine phospholipids, which are rich in arachidonic acid, was significantly decreased by estradiol treatment. More arachidonate-PC was depleted than arachidonate-PE. The molecular structure was confirmed by gas chromatography-mass spectrometry. The amount of PGF2 alpha in the oophorectomized uterine tissue was 10-times that of PAF, but like the latter, increased 3-4 times on estradiol treatment. The chemical structures of PAF and PGF2 alpha formed on estradiol treatment were confirmed by mass spectrometry. The present data strongly suggest a correlation between the formations of PAF and PGF2 alpha, and indicate that estradiol may regulate the physiological formations of PAF and PGs in non-pregnant rat uterus.

Calcium-dependent incorporation of choline into phosphatidylcholine (PC) by base-exchange in rat brain membranes occurs preferentially with phospholipid substrates containing docosahexaenoic acid (22:6(n-3))

The fatty acid composition of phosphatidylcholine (PC) formed by base-exchange was examined in rat brain membranes in vitro. The free choline incorporated into subspecies of PC by this phospholipase-D type activity can be distinguished from that which might enter indirectly via the last enzyme of the de novo pathway for phospholipid biosynthesis, cholinephosphotransferase, by its ionic requirements. Choline base-exchange in lysed synaptosomes is optimal when assayed at extracellular (mM) calcium concentrations and is blocked by magnesium. As much as 40% of the choline incorporated by base-exchange into rat brain membranes was recovered in subspecies of PC, representing no more than 10% of the total PC pool, which contained docosahexaenoic acid (22:6(n-3)). Docosahexaenoic acid is enriched in electrically-excitable membranes and its content in phospholipids of rat and human brain change during early development and increase with age.

Molecular species of choline and ethanolamine phospholipids in rat cerebellum during development

The molecular species composition of rat cerebellar phospholipid subclasses has been studied by HPLC after phospholipase C treatment and dinitrophenyl derivatization. During rat cerebellum development (3-90 days postpartum), cholinephosphoglycerides and ethanolamine phosphoglycerides represented approximately 80% of all phospholipids, with their relative amount changing after 1 month. Among ethanolamine phosphoglycerides, the molar ratio of diacylglycerophosphoethanolamine (diacylGPE) to alkenylacylGPE decreased from approximately 1.4 at 3 days to approximately 0.5 after 10 days. The phospholipids investigated contained up to 12 different molecular species. The rate of accumulation of the various molecular species of diacylglycerophosphocholine (diacylGPC), diacylGPE, and alkenylacylGPE during cerebellar development allowed a classification into three main groups. The overall increase of the molecular species of the first group (6-diacylGPC, 5-diacylGPE, and 4-alkenylacylGPE) was approximately 18-fold between 3 and 90 days, with a faster rate of accumulation between 3 and 30 days. Those of the second group (3-diacylGPC, 5-diacylGPE, and 5-akenylacylGPE) increased by approximately 45-fold during the same developmental period, at a slow rate before day 15 and a faster one thereafter. The molecular species of the third group (3-alkenylacylGPE) increased by greater than 250-fold between 3 and 90 days, at a very slow rate before day 21 and more quickly thereafter. The different rates of accumulation of the components of the three groups during cerebellar development suggest a preferential location of the first group in membranes of neuronal perikaryons, glial cells, and synaptosomal structures. Those of the second group appear to be located in both synaptosomal membranes and myelin sheets, and those of the third group can be considered as myelin markers.

Analysis of a specific oxygenation reaction of soybean lipoxygenase-1 with fatty acids esterified in phospholipids

Soybean lipoxygenase was reacted with phosphatidylcholine (at pH 9, with 10 mM deoxycholate), and the oxygenation products were analyzed by high-pressure liquid chromatography, UV, gas chromatography-mass spectrometry (GC-MS), and NMR. The structures of the intact glycerolipid products were established by GC-MS of diglycerides recovered by phospholipase C hydrolysis and by proton NMR of the intact phosphatidylcholine. These analyses, together with analyses of the transesterified fatty acids, indicated that arachidonyl and linoleoyl moieties in the phosphatidylcholine were converted exclusively to the 15(S)-hydroperoxy-5(Z),8(Z),11(Z),13(E)-eicosatetraenoate and 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate analogues, respectively. Control experiments proved that the intact phospholipid (and not hydrolyzed/reesterified fatty acid) was the true substrate of the oxygenation reaction. Phosphatidylethanolamine and phosphatidylinositol lipids were also substrates for specific oxygenation by the soybean lipoxygenase. The results provide concrete evidence that fatty acids esterified in phospholipid can be subject to highly specific oxygenation by a lipoxygenase enzyme.

Strategy of glycerolipid separation and quantitation by complementary analytical techniques. Plenary lecture

Although improved systems for chromatographic resolution continue to be developed there is good reason to believe that no single method will be capable fo complete separation of all lipid mixtures including the geometric, positional and stereochemical isomers in each molecular species. Furthermore, the chromatographic systems giving the highest resolution usually yield the least complete recoveries of components and require separate procedures of quantitation. It is therefore necessary to develop appropriate strategies that yield the required resolution as a result of consecutive application of complementary analytical techniques. At the present time, the original combination of thin-layer and gas--liquid chromatography has been joined by the combination of thin-layer and liquid, and liquid and gas--liquid chromatography with both liquid and gas--liquid chromatography being frequently coupled to mass spectrometry with computerized data processing. Internal standardization with hydrogen flame ionization provides a simple quantitative detection for gas chromatography, while mass spectrometry serves a similar purpose in liquid chromatography, although a much more extensive calibration may be required for quantitation. Special advantages for both separation and quantitation of most neutral lipid mixtures are derived from enzymic and chemical modification of the samples prior to chromatography. With imaginative work-up of samples, superior qualitative and quantitative results can frequently be obtained by appropriate combination of chromatographic techniques of limited resolving power.