Analysis of Eicosanoids

A simpler practice to analyze bile acids is to use negative-ion FAB-MS [53,54]. A Sep-Pak Cig cartridge can be used to isolate bile acids (e.g., from urine sample) prior to FAB-MS analysis. Currently, ESI-MS has largely supplemented FAB-MS to analyze polar bile acids. The coupling of ESI with MS/MS provides an additional level of specificity. For example, neutral-loss scans for 36 and 54 Da can detect di- and trihydroxy bile acids. LC/ESI-MS can be used for the sensitive detection of bile acids in biological extracts. Recently, cholic acid, chenodeoxycholic acid, and deoxycholic acid have been detected in the cytoplasmic fraction from a rat brain [55]. 

Leukotrienes (LTs) are lipid mediators derived enzymatically from arachidonic acid. Structurally, these eicosanoids contain a conjugated triene functionality. LTB4 and LTC4 are the two important leukotrienes. Mass spectrometry has played 

Many other eicosanoids, such as thromboxanes, lipoxins, 0x0 eicosanoids, hydroperoxy eicosanoids, hydroxyeicosatetraenoic acids, epoxyeicosatetraenoic acids, and isoprostanes, are also biologically active molecules. ESI has emerged as an efficient ionization method for these classes of eicosanoids. An abundant carboxylate anion is produced in the negative-ion ESI mode [59]. Low-energy CID of the ESI-produced [M — H] ions of these molecular species produces structurally distinct ions for these disparate molecular species. 

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Brash, A.R. and Hawkins, D.J. 1990. High-performance liquid chromatography for chiral analysis of eicosanoids. Methods Enzymol. 187 187-195. 

The LC-MS analysis of these compounds is briefly reviewed in this section. Balazy [33] reviewed the analysis of eicosanoids in terms of targeted lipidomics. 

Next to these more fundamental studies on the structural characterization of eicosanoids, LC-MS was applied in the qualitative and/or quantitative analysis of eicosanoids in biological systems. Some selected examples are briefly reviewed. 

Mesaros C, Lee SH, Blair I A. Targeted quantitative analysis of eicosanoid lipids in biological samples using liquid chromatography—tandem mass spectrometry. J Chromatogr B 2009 877 2736-2745. 

Buczynski, M.W., Dumlao, D.S. and Dennis, E.A. (2009) Thematic review series Pro-teomics. An integrated omics analysis of eicosanoid biology. J. Lipid Res. 50,1015-1038. 

Methodological Problems in the Analysis of Eicosanoid Production in Brain 19... 

The absolute stereochemistries for both compounds were determined by CD analysis of the p-bromobenzoate derivatives. Two other eicosanoids were also isolated from whole animals [198], The trihydroxylated oxylipin 8jR,11S,12R-trihydroxyeicosa-5Z,9 ,14Z,17Z-tetraenoic acid (trioxilin A4,150) was detected in, or isolated from, five starfish species P. miniata, Dermasterias imbricata, Pycnopodia helianthoides, Culcita novaeguinea, and Nardoa tubercolata. Its structure was determined by H and 13C NMR and FAB-MS analyses of the natural product and of an acetonide derivative. The co6 analog of this compound (151) was isolated only from P. helianthoides. The relative stereochemistry in these metabolites (150, 151) was established from a comparison of NMR shifts with malyngic acid, a trihydroxylated C18 compound isolated from Lyngbya majuscula, while the absolute stereochemistry was proposed on the basis of the earlier isolation of 8R-HETE from P. miniata. 

Griffiths et al. [36] described the analysis of HETE and diHETE by ESI-MS-MS of [M-H] on a sector-time-of-flight hybrid instrument equipped with a focal-plane detector. The HETE and diHETE could be analysed in underivatized form at the pmol level. The MS-MS spectra allow differentiation of isomeric eicosanoids. 

Margalit et al. [48] reported the simultaneous quantitative analysis of 14 eicosanoids in biological samples using column-bypass negative-ion ESI-MS in SRM mode. Detection limits ranged from 0.5 pg for TXBj to 10 pg for 6-keto PGF, . 

The newer MS techniques, such as FAB/MS, TS/MS and ES/MS, allow the analysis of non-derivatized products. The combination of these techniques with MS/MS has also facilitated the identification of eicosanoids. 

The objective of this contribution is to discuss still another method for the analysis of the prostanoids and similar compounds (the eicosanoids")/ used by other investigators to a limited extent compared with the three assays mentioned above, namely gas chromatography with electron-capture detection (GC-EC). 

Analysis of individual lipid species of a class in the Lipid MAPS protocols was largely developed based on reversed-phase LC-MS. For example, in the protocol for eicosanoid analysis, a C18 column (250 X 2.1 mm) was employed and a specific gradient from mobile phase A (water-acetonitrile-formic acid, 63 37 0.02, v/v/v) to B (acetonitrile-isopropanol, 50 50, v/v) was applied [71]. Individual eicosanoid species were detected by using the MRM approach and quantified in comparison to the relevant internal standard. 

Chiral chromatography is widely used for the resolution of chiral isomers of eicosanoids and enantiomeric isomers of di- and monoacylglycerols. The technique and its applications were extensively reviewed by Prof. Ian Blair in relation to the targeted analysis of these lipid classes and individual species employing LC-MS [87-89]. 

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