Mass spectrometric identification of molecular species of phosphatidylcholine and lysophosphatidylcholine extracted from shark liver

Shotgun lipidomics reveals the changes in phospholipids of brown rice during accelerated aging

Brown rice exhibits higher nutritional value and attracts more and more attentions; however, the change in phospholipid molecular species in brown rice during aging is poorly understood. In this study, shotgun lipidomics was employed to investigate the changes in phospholipid molecular species in four brown rice varieties (two japonica rice and two indica rice) during accelerated aging. A total of 64 phospholipid molecular species were identified, and most of them were rich in polyunsaturated fatty acids. For japonica rice, phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylglycerol (PG) gradually decreased during accelerated aging. However, the content of PC, PE, and PG in indica rice showed no difference during accelerated aging. Significantly different phospholipid molecular species from four brown rice were screened during accelerated aging. Based on these significantly different phospholipids, the metabolic pathways including glycerophospholipid metabolism and linoleic acid metabolism during accelerated aging were depicted. The findings from this study could be helpful in explaining the impact of accelerated aging on phospholipids of brown rice, and offer an understanding on relationships between phospholipids degradation and brown rice deterioration.

Applications of lipidomics in marine organisms: Progresses, challenges and future perspectives

Marine ecosystems comprise a high diversity of life forms, such as algae, invertebrates, and vertebrates. These organisms have adapted their physiology according to the conditions of the environments in which...

Impact of air-frying on the plasmalogens deterioration and oxidation in oyster revealed by mild acid hydrolysis and HILIC-MS-based lipidomics analysis

Oyster is rich in plasmalogens that are ether phospholipids with biological functions to human body. Air-frying is a popular technique for preparing delicious oyster but makes the plasmalogens vulnerable to oxidation. In this study, the effect of air-frying processing on plasmalogens oxidation was studied by lipidomic approach. Plasmalogens were always mixed with normal phospholipids, thus the lipid extract was treated with mild acid hydrolysis to rapidly degrade plasmalogens owing to the acid lability of vinyl ether linkage at sn-1 position. After hydrophilic interaction chromatography MS/MS analysis, there were three plasmalogen classes, plasmanylcholine, plasmanylethanolamine, and plasmanylinositol, completely separated, and each plasmalogen molecular species was identified and quantified. It indicated that the content of plasmalogens underwent an obvious decrease during the air-frying process. To weaken such effect, the influence of air-frying temperature was further inspected by multivariate statistical analyses. The main variables, including the ions of m/z 756.4927, 784.5486, 828.5812, etc., were revealed by unsupervised principle component analysis, supervised orthogonal partial least-square analysis, and variable importance in projection plot. As a conclusion, air-frying has health benefits in reducing fat content but destructive to plasmalogens, thus interventions are recommended to prevent the degradation of plasmalogens.

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.

TiO₂/SiO₂ core-shell composite-based sample preparation method for selective extraction of phospholipids from shrimp waste followed by hydrophilic interaction chromatography coupled with quadrupole time-of-flight/mass spectrometry analysis

A solid-phase extraction (SPE) procedure, using titania-coated silica (TiO2/SiO2) core-shell composites as the sorbent, combined with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for extraction, visualization, and quantification of phospholipids in shrimp waste (Litopenaeus vannamei). The SPE protocol was optimized, and the best conditions were pH 5 of the loading solvent, 10% aqueous methanol as the washing solvent, and 1.0 mL of chloroform/methanol (1:2, v/v) as eluting solvents. Afterward, the eluate was separated on a diol hydrophilic interaction chromatography (HILIC) column. A total of 69 phospholipid species were identified and determined. The results indicated that, in comparison to previously published methods, this strategy was cost-effective and efficient in extraction, characterization, and determination of phospholipids. Meanwhile, phospholipids were abundant in shrimp waste, most of which contained unsaturated fatty acyl chains, such as 18:3 [α-linolenic acid (ALA)], 20:5 [eicosapentaenoic acid (EPA)], and 22:6 [docosahexaenoic acid (DHA)]. The successful application of this strategy paves the way for full use of traditionally discarded shrimp wastes.

Different metabolic profiles of K1 serotype and non-serotype K1 and K2 Klebsiella pneumoniae isolates in oral infection mice model

K1 or K2 serotype Klebsiella pneumoniae isolate caused clinical pyogenic liver abscess (KLA) infection is prevalent in many areas. It has been identified that K1 or K2 serotype K. pneumoniae isolates caused KLA infection in mice by oral inoculation. In our study, K1 serotype K. pneumoniae isolate Kp1002 with hypermucoviscosity (HV)-positive phenotype caused KLA infection in C57BL/6 mice by oral inoculation. Simultaneously, non-serotype K1 and K2 isolate Kp1014 with HV-negative phenotype failed to cause KLA infection in the same manner. It seems that gastrointestinal tract translocation is the pathway by which K1 or K2 serotype K. pneumoniae caused KLA infection. Liquid chromatography-tandem mass spectrometry was used to further analyze metabolic profile changes in mice with KLA infection. Data showed that after Kp1002 or Kp1014 oral inoculation, serum Phosphatidylcholine (PC) and Lysophosphatidylcholine (LPC) levels significantly changed in mice. Some PC and LPC molecules showed changes both in the Kp1002 KLA group and the Kp1014 no-KLA group compared with the control group. The level of 18:1/18:2-PC significantly changed in the Kp1002 KLA group compared with the control group, but showed no change between the Kp1014 no-KLA group and the control group. The level of 18:1/18:2-PC might have been particularly affected by KLA infection caused by K1 serotype K. pneumoniae Kp1002. It may be a potential biomarker for KLA infection.

Lipidomic fingerprint of almonds (Prunus dulcis L. cv Nonpareil) using TiO₂ nanoparticle based matrix solid-phase dispersion and MALDI-TOF/MS and its potential in geographical origin verification

A matrix solid-phase dispersion (MSPD) procedure with titanium dioxide (TiO2) nanoparticles (NP) as sorbent was developed for the selective extraction of phospholipids from almond samples, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF/MS) was employed for analysis. A remarkable increase in the signals of phospholipid accompanied by a decrease in those of triacylglycerols and diacylglycerols was observed in the relevant mass spectra. The proposed method was applied to five batches of almonds originating from four geographical areas, whereas principal component analysis (PCA) was utilized to normalize the relative amounts of the identified phospholipid species. The results indicated that the lipidomic fingerprint of almonds was successfully established by the negative ion mode spectrum, and the ratio of m/z 833.6 to 835.6 as well as m/z 821.6 could be introduced as potential markers for the differentiation of the tested almonds with different geographical origins. The whole method is of great promise for selective separation of phospholipids from nonphospholipids, especially the glycerides, and superior in fast screening and characterization of phospholipids in almond samples.

A mass spectrometric study for comparative analysis and evaluation of metabolite recovery from plasma by various solvent systems

A solvent system that extracts a maximum number of metabolites belonging to diverse chemical classes from complex biofluids, such as plasma, may offer useful inputs to understand the metabolic and physiological state of an individual. The present study compared seven solvent systems for extraction of metabolites from plasma. The extracts were analyzed by mass spectrometry (MS) and MS/MS (MS2) using a quadrupole time-of-flight liquid chromatography/MS system in positive and negative modes of ionization. Metabolites with molecular mass below 400 were identified using Human Metabolome Database MS2 and MS search interfaces. The acetone/isopropanol (2:1) system yielded promising results in positive ionization mode, as the maximum number of MS and MS2 features was detected in the extract. It was found to be superior in extraction of various classes of metabolites, especially organic acids, nucleosides and nucleoside derivatives, and heterocyclic molecules. Glycerophosphocholines in the mass range of 400-700 were found to be efficiently extracted by the methanol/chloroform/water (8:1:1) system. In negative mode as well, the maximum number of MS2 features was detected in methanol/chloroform/water and acetone/isopropanol extracts. The fingerprints of molecular features obtained in the negative and positive modes differed from each other to a significant extent.

Shotgun lipidomics strategy for fast analysis of phospholipids in fisheries waste and its potential in species differentiation

An efficient shotgun lipidomics strategy was established and optimized for fast phospholipid profiling of viscera from three fish species: Lateolabrax japonicas, Ctenopharyngodon idellus, and Carassius auratus. This strategy relies on direct infusion of total lipid extracts into a tandem mass spectrometer without additional separation of the individual molecular species. Four classes of phospholipids, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), and phosphatidylserine (PS), were analyzed, and at least 81 molecular species of phospholipids were identified, including 34 species of PC, 24 species of PE, 12 species of PS, and 11 species of PI, in both positive- and negative-ion electrospray ionization mode. The results show that fish viscera, which are traditionally discarded as fisheries wastes, are nutritional in phospholipids with total contents of the four detected phospholipid classes ranging from 1.52 to 3.29 mg/g in the three tested fish species. Regardless of the tested fish species, PC and PE are the dominant phospholipid classes, followed by PI and PS. Furthermore, principal component analysis (PCA) was applied to normalize the relative amounts of the identified phospholipid species. The results demonstrate that PS 18:0/22:6, PI 18:0/20:4, and PI 18:0/20:5 were the main contributors of cumulative value and could be used as an indicator for fish species differentiation. This shotgun lipidomics method was >10 times faster than traditional methods, because no chromatographic separation was needed. The successful application of this strategy paves the way for full utilization of traditionally discarded fisheries wastes and provides an alternative means for fish species differentiation.

Structural elucidation of molecular species of pacific oyster ether amino phospholipids by normal-phase liquid chromatography/negative-ion electrospray ionization and quadrupole/multiple-stage linear ion-trap mass spectrometry

Although marine oysters contain abundant amounts of ether-linked aminophospholipids, the structural identification of the various molecular species has not been reported. We developed a normal-phase silica liquid chromatography/negative-ion electrospray ionization/quadrupole multiple-stage linear ion-trap mass spectrometric (NPLC-NI-ESI/Q-TRAP-MS(3)) method for the structural elucidation of ether molecular species of serine and ethanolamine phospholipids from marine oysters. The major advantages of the approach are (i) to avoid incorrect selection of isobaric precursor ions derived from different phospholipid classes in a lipid mixture, and to generate informative and clear MS(n) product ion mass spectra of the species for the identification of the sn-1 plasmanyl or plasmenyl linkages, and (ii) to increase precursor ion intensities by "concentrating" lipid molecules of each phospholipid class for further structural determination of minor molecular species. Employing a combination of NPLC-NI-ESI/MS(3) and NPLC-NI-ESI/MS(2), we elucidated, for the first time, the chemical structures of docosahexaenoyl and eicosapentaenoyl plasmenyl phosphatidylserine (PS) species and differentiated up to six isobaric species of diacyl/alkylacyl/alkenylacyl phosphatidylethanolamine (PE) in the US pacific oysters. The presence of a high content of both omega-3 plasmenyl PS/plasmenyl PE species and multiple isobaric molecular species isomers is the noteworthy characteristic of the marine oyster. The simple and robust NPLC-NI-ESI/MS(n)-based methodology should be particularly valuable in the detailed characterization of marine lipid dietary supplements with respect to omega-3 aminophospholipids.

Metabonomic profiles discriminate hepatocellular carcinoma from liver cirrhosis by ultraperformance liquid chromatography-mass spectrometry

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and usually develops in patients with liver cirrhosis (LC). Biomarkers that discriminate HCC from LC are important but are limited. In the present study, an ultraperformance liquid chromatography-mass spectrometry (UPLC-MS)-based metabonomics approach was used to characterize serum profiles from HCC (n = 82), LC (n = 48), and healthy subjects (n = 90), and the accuracy of UPLC-MS profiles and alpha-fetoprotein (AFP) levels were compared for their use in HCC diagnosis. By multivariate data and receiver operating characteristic curves analysis, metabolic profiles were capable of discriminating not only patients from the controls but also HCC from LC with 100% sensitivity and specificity. Thirteen potential biomarkers were identified and suggested that there were significant disturbances of key metabolic pathways, such as organic acids, phospholipids, fatty acids, bile acids, and gut flora metabolism, in HCC patients. Canavaninosuccinate was first identified as a metabolite that exhibited a significant decrease in LC and an increase in HCC. In addition, glycochenodeoxycholic acid was suggested to be an important indicator for HCC diagnosis and disease prognosis. UPLC-MS signatures, alone or in combination with AFP levels, could be an efficient and convenient tool for early diagnosis and screening of HCC in high-risk populations.

Tracking phospholipid profiling of muscle from Ctennopharyngodon idellus during storage by shotgun lipidomics

This paper aims to study phospholipid (PL) profiling of muscle from Ctenopharyngodon idellus during room-temperature storage for 72 h by direct-infusion electrospray ionization tandem mass spectrometry (ESI-MS/MS). Five classes of PLs, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), and sphingomyelin (SM), were analyzed. At least 110 molecular species of PLs were identified, including 32 species of PC, 34 species of PE, 24 species of PS, 18 species of PI, and 2 species of SM. The result showed that oxidation and hydrolysis are the two main causes for the deterioration of PLs in fish muscle during storage. Most content of PL molecular species increased and then decreased gradually. However, some special PE molecular species with former low abundance, such as PE 32:1, PE 34:2, and PE 34:1, emerged during the storage in quantity. It indicated that those PE molecular species may come from the microbe bred in the muscle. This phenomenon was found and discussed for the first time. The possible relevance between the emergence of these special PE molecular species and the freshness of the fish muscle during storage will be investigated in further studies.

Lysophosphatidylcholine containing docosahexaenoic acid at the sn-1 position is anti-inflammatory

Lysophosphatidylcholine is known to be a lipid mediator in various cellular responses. In this study, we examined the anti-inflammatory actions of lysophosphatidylcholine containing docosahexaenoic acid esterified at the sn-1 position. First, in RAW 264.7 cells, DHA-lysoPtdCho suppressed the LPS-induced formation of NO concentration-dependently. However, ARA-lysoPtdCho showed a partial suppression, and LNA-lysoPtdCho had no significant effect. Additionally, DHA-lysoPtdCho also reduced the level of TNF-alpha or IL-6, but not PGE(2). In animal experiments, the i.v. administration of ARA-lysoPtdCho (150 or 500 mug/kg) prevented zymosan A-induced plasma leakage remarkably with a maximal efficacy (Emax) of 50%, in contrast to no effect with LNA-lysoPtdCho. Remarkably, DHA-lysoPtdCho suppressed zymosan A-induced plasma leakage with an ED(50) value of 46 mug/kg and an Emax value of around 95%. Additionally, mechanistic studies indicated that the anti-inflammatory action of DHA-lysoPtdCho was partially related to the reduced formation of LTC(4,) TNF-alpha, and IL-6. When the interval time between lysoPtdCho administration and zymosan A challenge was extended up to 2 h, such a suppressive action of DHA-lysoPtdCho was augmented, suggesting that a DHA-lysoPtdCho metabolite is important for anti-inflammatory action. In support of this, 17-HPDHA-lysoPtdCho showed a greater anti-inflammatory action than DHA-lysoPtdCho. Furthermore, a similar anti-inflammatory action was also observed with i.p. administration of DHA-lysoPtdCho or a 17(S)-hydroperoxy derivative. Additionally, oral administration of DHA-lysoPtdCho also expressed a significant anti-inflammatory action. Taken together, it is proposed that DHA-lysoPtdCho and its metabolites may be anti-inflammatory lipids in vivo systems.

Regulation of lipoxygenase activity by polyunsaturated lysophosphatidylcholines or their oxygenation derivatives

Lysophosphatidylcholines (lysoPCs) have been known to play a role as lipid mediators in various cellular responses. In this study, we examined whether lysoPC containing linoleoyl, arachidonoyl, or docosahexaenoyl groups or their peroxy derivatives affect lipoxygenase (LOX)-catalyzed oxygenation of native substrates. First, arachidonoyl lysoPC and docosahexaenoyl lysoPC were found to inhibit potato 5-LOX-catalyzed oxygenation of linoleic acid (LA) in a noncompetitive type with Ki values of 0.38 and 1.90 microM, respectively. Likewise, arachidonoyl lysoPC and docosahexaenoyl lysoPC also inhibited 5-LOX activity from rat basophilic leukemia cells-2H3 (RBL-2H3) with IC50 values (50% inhibitory concentration) of 18.5 +/- 3.06 and 30.6 +/- 1.06 microM, respectively. Additionally, arachidonoyl lysoPC and docosahexaenoyl lysoPC also inhibited 15-LOX activity from RBL-2H3 with IC50 values of 16.6 +/- 1.3 and 24.1 +/- 2.4 microM, respectively. In a separate experiment, where lysoPC peroxides were tested for the effect on soybean LOX-1, 15(S)-hydroperoxy-5,8,11,13-eicosatetraenoyl lysoPC and 17(S)-hydroperoxy-4,7,10,13,15,19-docosahexaenoyl lysoPC potently inhibited soybean LOX-1 activity with Ki values of 6.8 and of 1.54 microM, respectively. In contrast, 13(S)-hydroperoxy-9,11-octadecadienoyl lysoPC was observed to stimulate soybean LOX-1-catalyzed oxygenation of LA markedly with AC50 value (50% activatory concentration) of 1.5 microM. Taken together, it is proposed that lysoPCs containing polyunsaturated acyl groups or their peroxy derivatives may participate in the regulation of LOX activity in biological systems.

Oxygenation of arachidonoyl lysophospholipids by lipoxygenases from soybean, porcine leukocyte, or rabbit reticulocyte

Oxygenation of arachidonoyl lysophosphatidylcholine (lysoPC) or arachidonoyl lysophosphatidic acid (lysoPA) by lipoxygenase (LOX) was examined. The oxidized products were identified by HPLC/UV spectrophotometry/mass spectrometry analyses. Straight-phase and chiral-phase HPLC analyses indicated that soybean LOX-1 and rabbit reticulocyte LOX oxygenated arachidonoyl lysophospholipids mainly at C-15 with the S form as major enantiomer, whereas porcine leukocyte LOX oxygenated at C-12 with the S form. Next, the sequential exposure of arachidonoyl-lysoPC to soybean LOX-1 and porcine leukocyte LOX afforded two major isomers of dihydroxy derivatives with conjugated triene structure, suggesting that 15(S)-hydroperoxyeicosatetraenoyl derivatives were converted to 8,15(S)-dihydroxyeicosatetraenoyl derivatives. Separately, arachidonoyl-lysoPA, but not arachidonoyl-lysoPC, was found to be susceptible to double oxygenation by soybean LOX-1 to generate a dihydroperoxyeicosatetraenoyl derivative. Overall, arachidonoyl lysophospholipids were more efficient than arachidonic acid as LOX substrate. Moreover, the catalytic efficiency of arachidonoyl-lysoPC as substrate of three lipoxygenases was much greater than that of arachidonoyl-lysoPA or arachidonic acid. Taken together, it is proposed that arachidonoyl-lysoPC or arachidonoyl-lysoPA is efficiently oxygenated by plant or animal lipoxygenases, C12- or C15-specific, to generate oxidized products with conjugated diene or triene structure.