High performance liquid chromatography-tandem mass spectrometry of phospholipid molecular species in eggs from hens fed diets enriched in seal blubber oil

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.

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.

High-performance liquid chromatography method for quantifying sphingomyelin in rat brain

A rapid, reproducible and accurate high-performance liquid chromatographic (HPLC) method for the quantitative determination of sphingomyelin in rat brain was developed and validated using normal-phase silica gel column, acetonitrile-methanol-water (65:18:17 (v/v)) at a flow rate of 1 ml/min, isocratic elution, UV detection at 207 nm and 1,2-dimyristoyl-sn-glycero-3-phosphocholine as an internal standard. Total run time was 10.0 min. The calibration curve was linear over the range of 0.025-0.4 mg/ml sphingomyelin (R2>0.99). The intra-day coefficient of variation ranged from 1.4% to 2.2%. The average inter-day coefficient of variation over a period of 4 days was 3.1%. The practical limit of detection was 0.005 mg/ml with a quantification limit of 0.01 mg/ml.

Simultaneous analysis of glycolipids and phospholids molecular species in avocado (Persea americana Mill) fruit

The molecular species of phospholipids (PLs) and glycolipids (GLs) were simultaneously characterized in the pulp and almond of the avocado fruit (Persea americana Mill) of four varieties by means of high performance liquid chromatography-electrospray ionisation ion-trap tandem mass spectrometry. In the pulp, the predominant species of monoglycosyldiglycerides (MGD) were m/z 796.6 (oleic/linolenic and linoleic/linoleic acids) and m/z 800.4 (stearic/linoleic and oleic/oleic acids). One of the main diglycosyldiglycerides (DGD) both in the pulp and almond was m/z 958.5 (oleic/linolenic); however, the pulp was also rich of m/z 962.4 (oleic/oleic), whereas in the almond, m/z 934.5 (palmitic/linoleic and palmitoleic/oleic) and m/z 960.5 (oleic/linoleic and stearic/linolenic) were more abundant. In the almond, the main PL classes (phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI)) contained always palmitic/linoleic acids. Alpha-linolenic acid was contained as MGD (linolenic/linolenic) and DGD (linolenic/linolenic), more present in the pulp than in the almond. The major molecular species of glycocerebrosides (GCer) in the pulp and almond carried hydroxy-palmitic acid (C(16h:0))/4,8-sphyngadienine (d(18:2)).

Structure-specific, quantitative methods for analysis of sphingolipids by liquid chromatography-tandem mass spectrometry: "inside-out" sphingolipidomics

Due to the large number of highly bioactive subspecies, elucidation of the roles of sphingolipids in cell structure, signaling, and function is beginning to require that one perform structure-specific and quantitative (i.e., "sphingolipidomic") analysis of all individual subspecies, or at least of those are relevant to the biologic system of interest. As part of the LIPID MAPS Consortium, methods have been developed and validated for the extraction, liquid chromatographic (LC) separation, and identification and quantitation by electrospray ionization (ESI), tandem mass spectrometry (MS/MS) using an internal standard cocktail that encompasses the signaling metabolites (e.g., ceramides, ceramide 1-phosphates, sphingoid bases, and sphingoid base 1-phosphates) as well as more complex species (sphingomyelins, mono- and di-hexosylceramides). The number of species that can be analyzed is growing rapidly with the addition of sulfatides and other complex sphingolipids as more internal standards become available. This review describes these methods as well as summarizes others from the published literature. Sphingolipids are an amazingly complex family of compounds that are found in all eukaryotes as well as some prokaryotes and viruses. The size of the sphingolipidome (i.e., all of the individual molecular species of sphingolipids) is not known, but must be immense considering mammals have over 400 headgroup variants (for a listing, see http://www.sphingomap.org), each of which is comprised of at least a few-and, in some cases, dozens-of lipid backbones. No methods have yet been developed that can encompass so many different compounds in a structurally specific and quantitative manner. Nonetheless, it is possible to analyze useful subsets of the sphingolipidome, such as the backbone sphingolipids involved in signaling (sphingoid bases, sphingoid base 1-phosphates, ceramides, and ceramide 1-phosphates) and metabolites at important branchpoints, such as the partitioning of ceramide into sphingomyelins, glucosylceramides, galactosylceramides, and ceramide 1-phosphate versus turnover to the backbone sphingoid base. This review describes methodology that has been developed as part of the LIPID MAPS Consortium (www.lipidmaps.org) as well as other methods that can be used for sphingolipidomic analysis to the extent that such is currently feasible. The focus of this review is primarily mammalian sphingolipids; hence, if readers are interested in methods to study other organisms, they should consult the excellent review by Stephen Levery in another volume of Methods in Enzymology (Levery, 2005), which covers additional species found in plants, fungi, and other organisms. It should be noted from the start that although many analytical challenges remain in the development of methods to analyze the full "sphingolipidome," the major impediment to progress is the limited availability of reliable internal standards for most of the compounds of interest. Because it is an intrinsic feature of mass spectrometry that ion yields tend to vary considerably among different compounds, sources, methods, and instruments, an analysis that purports to be quantitative will not be conclusive unless enough internal standards have been added to correct for these variables. Ideally, there should be some way of standardizing every compound in the unknown mixture; however, that is difficult, if not impossible, to do because the compounds are not available, and the inclusion of so many internal standards generates a spectrum that may be too complex to interpret. Therefore, a few representative internal standards are usually added, and any known differences in the ion yields of the analytes of interest versus the spiked standard are factored into the calculations. Identification of appropriate internal standards has been a major focus of the LIPID MAPS Consortium, and the methods described in this review are based on the development of a certified (i.e., compositionally and quantitatively defined by the supplier) internal standard cocktail that is now commercially available (Avanti Polar Lipids, Alabaster, AL). For practical and philosophical reasons, an internal standard cocktail was chosen over the process of an investigator adding individual standards for only the analytes of interest. On the practical level, addition of a single cocktail minimizes pipetting errors as well as keeping track of whether each internal standard is still usable (e.g., has it degraded while in solution?). Philosophically, the internal standard cocktail was chosen because an underlying premise of systems analysis asserts that, due to the high relevancy of unexpected interrelationships involving more distant components, one can only understand a biological system when factors outside the primary focus of the experiment have also been examined. Indeed, the first payoffs of "omics" and systems approaches involve the discoveries of interesting compounds in unexpected places when a "sphingolipidomic" analytical method was being used as routine practice instead of a simpler method that would have only measured the compound initially thought to be important (Zheng et al., 2006). Thus, routine addition of a broad internal standard cocktail at the outset of any analysis maximizes the opportunity for such discoveries, both at the time the original measurements are made and when one decides to return to the samples later, which can fortunately be done for many sphingolipids because they remain relatively stable in storage.