Enantioselective ultra-high performance liquid chromatography-tandem mass spectrometry method based on sub-2µm particle polysaccharide column for chiral separation of oxylipins and its application for the analysis of autoxidized fatty acids and platelet releasates.

Abstract

Oxylipins, the oxidation products of polyunsaturated fatty acids, are important signaling molecules in living organisms. Some of them have pro-inflammatory properties, while others act as pro-resolving agents. Oxylipins also play a major role in platelet biology and the progression of thrombo-inflammation. Depending on their structure, they may be pro-thrombotic or anti-thrombotic. For an unbiased biological interpretation, a detailed analysis of a broad spectrum of oxylipins including their stereoisomers is necessary. In our work, we developed for the first time an enantioselective UHPLC-ESI-MS/MS assay which allows quantifying individual oxylipin enantiomers. The assay made use of a sub-2µm particle-based amylose-(3,5-dimethylphenylcarbamate) chiral stationary phase (Chiralpak IA-U) under MS-compatible reversed-phase conditions. It covered 19 enantiomeric pairs of oxylipins and one diasteromeric pair of a lipid mediator: 2 pairs of hydroxyoctadecadienoic acids (HODE), 6 pairs of hydroxyeicosatetraenoic acids (HETE), 5 pairs of hydroxyeicosapentaenoic acids (HEPE), 3 pairs of hydroxydocosahexaenoic acids (HDoHE) and one pair of each: resolvins D1, hydroxyeicosatrienoic acid (HETrE), hydroxyoctadecatrienoic acid (HOTrE) and dihydroxyeicosatetraenoic acid (DiHETE). The new method is fast and showed outstanding peak resolution for most of the isomeric pairs. Excellent method sensitivity (average LOD was equal to 2.7 pg on column) was obtained by using a triple quadrupole instrument as a detector in a targeted, selected reaction monitoring (SRM) mode. The applicability of the method was verified by preliminary validation. It was then applied to analyze oxylipins produced by autoxidation of polyunsaturated fatty acids (PUFA) in air. Multiple oxylipins were found in each of the samples as racemic mixtures and served as reference substances for identification. Finally, the new enantioselective UHPLC method was applied to analyze releasates from platelets in resting state, and following activation with thrombin. The highest abundant oxylipin in the platelet releasate was 12(S)-HETE, but many other oxylipins were found in the thrombin activated samples, usually as single enantiomers (e.g. 12(S)-HEPE, 11(R)-HETE, 9(R)-HODE, 13-(S)-HODE, 14(S)-HDoHE). The latter was detected at about similar concentration in resting platelet releasates as well. 15-HETE showed elevated levels for both R-and S-enantiomers in releasates of thrombin-activated platelets. 12-HETrE was found presumably as both enantiomers, however, retention time inconsistencies indicate that the R-enantiomer is actually a different compound, maybe another constitutional isomer with different double-bond configuration.