Analytical Strategy for Oxylipin Annotation by Combining Chemical Derivatization-Based Retention Index Algorithm and Feature Tandem Mass Spectrometric Fragmentation as a Biomarker Discovery Tool

Non-enantioselective, enantioselective, and two-dimensional liquid chromatography coupled with tandem mass spectrometry for the study of stereochemical disposition of oxylipins in cGMP-regulated hemin-treated platelets

Oxylipins are important low abundant signaling molecules in living organisms. In platelets they play a primary role in platelet activation and aggregation in the course of thrombotic events. In vivo, they are enzymatically synthesized by cyclooxygenases, lipoxygenases, or cytochrome P450 isoenzmes, resulting in diverse polyunsaturated fatty acid (FA) metabolites including hydroxy-, epoxy-, oxo-FAs, and endoperoxides with pro-thrombotic or anti-thrombotic effects. In a recent study, it was reported that hemin induces platelet death which was accompanied by enhanced reactive oxygen species (ROS) production (measured by flow cytometry) and lipid peroxidation (as determined by proxy using flow cytometry with BODIPY-C11 as sensor). Lipidomic studies further indicated significant changes of the platelet lipidome upon ex vivo hemin treatment, amongst others oxylipins were increased. The effect could be (at least partly) reversed by riociguat/diethylamine NONOate diethylammonium salt (DEA/NO) which modulates the soluble guanylate cyclase(sGC)-cGMP-cGMP-dependent protein kinase I(cGKI) signaling axis. In the original work, oxylipins were measured by a non-enantioselective UHPLC-tandem-MS assay which may not give the full picture whether oxylipin elevation is due to ROS or by enzymatic processes. We present here the study of the stereochemical disposition of hemin-induced platelet lipidome alterations using Chiralpak IA-U column with amylose tris(3,5-dimethylphenylcarbamate) chiral selector immobilized on 1.6 µm silica particles. It was found that the major platelet oxylipins 12-HETE, 12-HEPE and 14-HDoHE (from 12-LOX) and 12-HHT (from COX-1) were present in S-configuration indicating their enzymatic formation. On the other hand, both R and S enantiomers of 9- and 13-HODE, 11- and 15-HETE were detected, possibly due to enzyme promiscuity rather than non-specific oxidation (by ROS or autoxidation), as confirmed by multi-loop based two-dimensional LC-MS using selective comprehensive mode with achiral RPLC in the 1st dimension and chiral LC in the 2nd using a multiple heart-cutting interface. For 12-HETrE, a peak at the retention time of the R-enantiomer was ruled out as isobaric interference by 2D-LC-MS. In particular, arachidonic acid derivates 12(S)-HHT, 11(R)-HETE and 15(S)-HETE were found to be sensitive to hemin and cGMP modulation.

Revealing oxidative degradation of lipids and screening potential markers of four vegetable oils during thermal processing by pseudotargeted oxidative lipidomics

The oxidative degradation of lipids in vegetable oils during thermal processing may present a risk to human health. However, not much is known about the evolution of lipids and their non-volatile derivatives in vegetable oils under different thermal processing conditions. In the present study, a pseudotargeted oxidative lipidomics approach was developed and the evolution of lipids and their non-volatile derivatives in palm oil, rapeseed oil, soybean oil, and flaxseed oil under different thermal processing conditions was investigated. The results showed that thermal processing resulted in the oxidative degradation of TGs in vegetable oils, which generated oxTGs, DGs, and FFAs, as well as TGs with smaller molecular weights. The lower the fatty acid saturation, the more severe the oxidative degradation of vegetable oils and thermal processing at high temperatures should be avoided if possible. From the accumulation of oxTGs concentrations, the hazards during thermal processing at high temperatures were, in descending order, soybean oil, rapeseed oil, flaxseed oil, and palm oil. The non-volatile potential markers were screened in palm oil, rapeseed oil, soybean oil, and flaxseed oil for 1, 7, 5, and 2 markers related to thermal processing time, respectively. The study provided suggestions for the consumption of vegetable oils from multiple perspectives and identified markers for monitored oxidative degradation of vegetable oils.