Intraperitoneally injected d11-11(12)-epoxyeicosatrienoic acid is rapidly incorporated and esterified within rat plasma and peripheral tissues but not the brain.

Epoxyeicosatrienoic acids (EpETrEs) are bioactive lipid mediators of arachidonic acid cytochrome P450 oxidation. In vivo, the free (unbound) form of EpETrEs regulate multiple processes including blood flow, angiogenesis and inflammation resolution. Free EpETrEs are thought to rapidly degrade via soluble epoxide hydrolase (sEH); yet, in many tissues, the majority of EpETrEs are esterified to complex lipids (e.g. phospholipids) suggesting that esterification may play a major role in regulating free, bioactive EpETrE levels. This hypothesis was tested by quantifying the metabolism of intraperitoneally injected free d11-11(12)-Epoxyeicosatrienoic acid (d11-11(12)-EpETrE) in male and female rats. Plasma and tissues (liver, adipose and brain) were obtained 3 to 4 min later and assayed for d11-11(12)-EpETrE and its sEH metabolite, d11-11,12-dihydroxyeicosatrienoic acid (d11-11,12-diHETrE) in both the free and esterified lipid fractions. In both males and females, the majority of injected tracer was recovered in liver followed by plasma and adipose. No tracer was detected in the brain, indicating that brain levels are maintained by endogenous synthesis from precursor fatty acids. In plasma, liver, and adipose, the majority (>54 %) of d11-11(12)-EpETrE was found esterified to phospholipids or neutral lipids (triglycerides and cholesteryl esters). sEH-derived d11-11,12-diHETrE was not detected in plasma or tissues, suggesting negligible conversion within the 3-4 min period post tracer injection. This study shows that esterification is the main pathway regulating free 11(12)-EpETrE levels in vivo.

Induction of ferroptosis in human keratinocyte HaCaT cells by squalene hydroperoxide: Possible prevention of skin ferroptosis by botanical extracts.

Ever since the proposal of ferroptosis, it has been studied as a nonapoptotic cell death caused by iron ion-dependent phospholipid (PL) peroxidation. We previously showed that treatment of human hepatoma cell line HepG2 with prepared PL hydroperoxide (PLOOH) resulted in ferroptosis. However, in human sebum, the major hydroperoxide is not PLOOH but squalene hydroperoxide (SQOOH), and to our knowledge, it is not established yet whether SQOOH induces ferroptosis in the skin. In this study, we synthesized SQOOH and treated human keratinocyte HaCaT cells with SQOOH. The results showed that SQOOH induces ferroptosis in HaCaT cells in the same way that PLOOH causes ferroptosis in HepG2 cells. Some natural antioxidants (botanical extracts) could inhibit the ferroptosis in both the cell types. Consequently, future research focus would revolve around the involvement of SQOOH-induced ferroptosis in skin pathologies as well as the prevention and treatment of skin diseases through inhibition of ferroptosis by botanical extracts.

Analysis of docosahexaenoic acid hydroperoxide isomers in mackerel using liquid chromatography-mass spectrometry.

Docosahexaenoic acid (DHA) is mostly esterified in food and is easily oxidized by exposure to heat or light. Hydroperoxide positions of DHA mono-hydroperoxide (DHA;OOH) provide information on oxidation mechanisms (e.g., radical- or singlet oxygen oxidation), yet direct identification of esterified DHA;OOH isomers has not been achieved. We previously accomplished the direct analysis of free DHA;OOH isomers with liquid chromatography-mass spectrometry (LC-MS/MS). In this study, we developed an LC-MS/MS method for direct analysis of esterified DHA;OOH based on our previous study. The developed method was capable of distinguishing esterified DHA;OOH isomers in raw- and oxidized mackerel. The result suggested that radical oxidation of esterified DHA can progress even in refrigeration. Different transitions were observed depending on the oxidation mechanism and lipid class. The analytical method and insights obtained in this study would be valuable to further understand and effectively prevent DHA oxidation in food products.