LC-MS/MS Analysis of Lipid Oxidation Products in Blood and Tissue Samples

A Critical Overview of HPLC-MS-Based Lipidomics in Determining Triacylglycerol and Phospholipid in Foods

With the current advancement in mass spectrometry (MS)-based lipidomics, the knowledge of lipidomes and their diverse roles has greatly increased, enabling a deeper understanding of the action of bioactive lipid molecules in plant- and animal-based foods. This review provides in-depth information on the practical use of MS techniques in lipidomics, including lipid extraction, adduct formation, MS analysis, data processing, statistical analysis, and bioinformatics. Moreover, this contribution demonstrates the effectiveness of MS-based lipidomics for identifying and quantifying diverse lipid species, especially triacylglycerols and phospholipids, in foods. Further, it summarizes the wide applications of MS-based lipidomics in food science, such as for assessing food processing methods, detecting food adulteration, and measuring lipid oxidation in foods. Thus, MS-based lipidomics may be a useful method for identifying the action of individual lipid species in foods.

Effects of Different Storage Conditions on Lipid Stability in Mice Tissue Homogenates

Lipids are biomolecules involved in numerous (patho-)physiological processes and their elucidation in tissue samples is of particular interest. However, tissue analysis goes hand in hand with many challenges and the influence of pre-analytical factors can intensively change lipid concentrations ex vivo, compromising the results of the whole research project. Here, we study the influence of pre-analytical factors on lipid profiles during the processing of homogenized tissues. Homogenates from four different mice tissues (liver, kidney, heart, spleen) were stored at room temperature as well as in ice water for up to 120 min and analyzed via ultra-high-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS). Lipid class ratios were calculated since their suitability as indicators for sample stability has been previously illustrated. Only approx. 40% of lipid class ratios were unchanged after 35 min, which was further reduced to 25% after 120 min during storage at room temperature. In contrast, lipids in tissue homogenates were generally stable when samples were kept in ice water, as more than 90% of investigated lipid class ratios remained unchanged after 35 min. Ultimately, swift processing of tissue homogenates under cooled conditions represents a viable option for lipid analysis and pre-analytical factors require more attention to achieve reliable results.

Untargeted lipidomics analysis of Mori Fructus polysaccharide on acute alcoholic liver injury in mice using ultra performance liquid chromatography-quadrupole-orbitrap-high resolution mass spectrometry

ETHNOPHARMACOLOGICAL RELEVANCE

Mori Fructus (MF) is a traditional Chinese medicine with long application history, which has protective effects on liver diseases. Mori Fructus polysaccharide (MFP) is one of the active ingredients of MF and possesses therapeutic effects against acute alcoholic liver injury. Recent researches have reported that the therapeutic effects of MFP might be related to the regulation of several lipid metabolic pathways. However, the mechanism of lipid metabolism was still unclear.

AIM OF THE STUDY

This study aimed to investigate the regulatory effect of MFP on lipid metabolism in mice with acute alcoholic liver injury, and to enrich the application of its hepatoprotective effect.

MATERIALS AND METHODS

Fifty Specific Pathogen Free (SPF) Kunming (KM) male mice were divided into five groups randomly, including normal control group, model group, bifendate positive group (220 mg/ kg), MFPA1 group (50 mg/ kg) and MFPB1 group (50 mg/ kg). A model of acute alcoholic liver injury was established by treating the mice with ethanol. The liver sections were processed and histopathological changes was observed with hematoxylin and eosin staining. The secretion levels of biochemical indexes in the liver and serum were assayed by ELISA. The untargeted lipidomics analysis was performed on a Q Exactive Focus quadrupole orbitrap high resolution mass spectrometry coupled with a Dionex Ultimate 3000 RSLC (HPG) ultra-performance liquid chromatography (UPLC-Q-Orbitrap-HRMS) system (Thermo Fisher Scientific), with a HESI ionization source.

RESULTS

It was observed that abnormal glutamic-pyruvic transaminase enzyme (ALT), glutamic-oxaloacetic aminotransferase (AST), triglyceride (TG), superoxide dismutase (SOD), and malondialdehyde (MDA) concentrations were ameliorated after irrigation of MFP or bifendate. Histopathology examination showed that intragastric infusion of MFP can be helpful in the repair of damaged liver in mice. The multivariate analysis of hepatic lipids showed segregation of ethanol-fed groups from the normal controls. After the comparison of mass spectra, 10 lipids were found to have different content in the normal control group and the model group. Differential lipids that were increased by ethanol exposure included fatty acids, phosphatidylcholine, and lyso-phosphatidylethanolamine, whereas lyso-phosphatidylcholine decreased. Among them, 4 lipids almost returned to the level of normal mice after MFP treatment.

CONCLUSION

The therapeutic effect of MFP on acute alcoholic liver injury may be achieved by regulating a variety of metabolic pathways, including linoleic acid metabolism, α - linolenic acid metabolism, and glycerolphospholipid metabolism. These results revealed that MFP efficiently exerted hepatoprotective benefits, and its potential effect was associated with the amelioration of lipid metabolism.

Moving forward with isoprostanes, neuroprostanes and phytoprostanes: where are we now?

Polyunsaturated fatty acids (PUFAs) are essential components in eukaryotic cell membrane. They take part in the regulation of cell signalling pathways and act as precursors in inflammatory metabolism. Beside these, PUFAs auto-oxidize through free radical initiated mechanism and release key products that have various physiological functions. These products surfaced in the early nineties and were classified as prostaglandin isomers or isoprostanes, neuroprostanes and phytoprostanes. Although these molecules are considered robust biomarkers of oxidative damage in diseases, they also contain biological activities in humans. Conceptual progress in the last 3 years has added more understanding about the importance of these molecules in different fields. In this chapter, a brief overview of the past 30 years and the recent scope of these molecules, including their biological activities, biosynthetic pathways and analytical approaches are discussed.

Enrichment of alpha-linolenic acid in rodent diet reduced oxidative stress and inflammation during myocardial infarction

Myocardial infarction (MI) is an irreversible event caused by cardiac ischemia and may be fatal. Studies reported that increased intake of n-3 polyunsaturated fatty acids (PUFA) namely, eicosapentaenoic acid and docosahexaenoic acid reduce the risk of cardiovascular disease and lower the incidence of MI. Nonetheless, the cardioprotective effect of plant n-3-PUFA such as α-linolenic acid (ALA) in the diet is not conclusive. In this study, Sprague Dawley rats were supplemented with isocaloric diets enriched with ALA rich flaxseed (FS) and flaxseed oil (FSO), and normal chow (Control) for 4 weeks. MI was induced by isoproterenol (ISO) injection. Results showed that all ALA-enriched diets displayed cardioprotection against MI. The heart to body weight ratio, plasma LDH activity and plasma cTnI were reduced compared to ISO and was prominent in FS diet. ALA and EPA were up-regulated in both tissues and plasma by ALA-diets compared to Control and remained higher than ISO groups. Notably, LOX-mediated HETEs decreased whereas LOX-mediated HDHAs were elevated in both tissues and plasma of ALA-enriched diets compared to ISO. In addition, non-enzymatic oxidized products from arachidonic acid including 15-F_2t-IsoP were reduced in both tissues and plasma of MI rats supplemented with ALA-enriched diets while those from n-3 PUFAs including F₄-NeuroPs, PhytoPs and PhytoFs were elevated compared to control. ALA-enriched diets particularly flaxseed reduced gene expressions of inflammatory cytokines namely IL-1β, IL-6 and TNFα and prevented the down regulation of antioxidant catalase in the heart tissues. In conclusion ALA-enriched diets potentially exerted cardioprotection through the regulation of anti-inflammatory and anti-oxidative mediators from n-3 PUFA autooxidation.

Lactobacillus rhamnosus GG and Oat Beta-Glucan Regulated Fatty Acid Profiles along the Gut-Liver-Brain Axis of Mice Fed with High Fat Diet and Demonstrated Antioxidant and Anti-Inflammatory Potentials

SCOPE

This study takes a novel approach to investigate the anti-inflammatory and antioxidant effects of prebiotic oat beta-glucan (OAT) and the probiotic Lactobacillus rhamnosus GG (LGG) against high-fat diets (HFD) by examining the fatty acid profiles in the gut-liver-brain axis.

METHOD AND RESULTS

HFD-fed C57BL/6N mice are supplemented with OAT and/or LGG for 17 weeks. Thereafter, mass spectrometry-based targeted lipidomics is employed to quantify short-chain fatty acids (SCFA), polyunsaturated fatty acids (PUFA), and oxidized PUFA products in the tissues. Acetate levels are suppressed by HFD in all tissues but reversed in the brain and liver by supplementation with LGG, OAT, or LGG + OAT, and in cecum content by LGG. The n-6/n-3 polyunsaturated fatty acid (PUFA) ratio is elevated by HFD in all tissues but is lowered by LGG and OAT in the cecum and the brain, and by LGG + OAT in the brain, suggesting the anti-inflammatory property of LGG and OAT. LGG and OAT synergistically, but not individually attenuate the increase in non-enzymatic oxidized products, indicating their synbiotic antioxidant property.

CONCLUSION

The regulation of the fatty acid profiles by LGG and OAT, although incomplete, but demonstrates their anti-inflammatory and antioxidant potentials in the gut-liver-brain axis against HFD.

Measurement of Enzymatic and Nonenzymatic Polyunsaturated Fatty Acid Oxidation Products in Plasma and Urine of Macular Degeneration Using LC-QTOF-MS/MS

Oxidized polyunsaturated fatty acids (PUFA) are associated to pathogenesis of diseases including cardiovascular and neurodegeneration. The novel products are not only biomarkers but also lipid mediators in gene regulation and signaling pathways. Herein, simultaneous quantitation of 28 products derived from nonenzymatic and enzymatic oxidation of PUFA i.e. 5-, 15-F_2t -isoprostanes, 7-, 17-F_2t -dihomo-isoprostanes, 7-, 17-F_2t -dihomo-isofurans, 5-, 8-, 18-F_3t -isoprostanes, 4-, 10-, 13-, 14-, 20-F_4t -neuroprostanes, 5-, 8-, 9-, 11-,12-, 15-, 20-HETE, 4-, 7-, 11-, 14-, 17-HDHA, RvE1, and NPD1 using LC-(ESI)-QTOF-MS/MS was developed. These products were measurable in a single sample and the analytical time was relative short (~15 min). Furthermore, we showed that the use of internal standards is a requisite to normalize matrix effects and preparation loss for the quantitation. Validation assays indicated the method to be robust for plasma and mid-stream urine sample analysis in particular from those of age-related macular degeneration subjects, where the accuracy of quantitation displayed good repeatability.

Combination of Lutein and Zeaxanthin, and DHA Regulated Polyunsaturated Fatty Acid Oxidation in H2O2-Stressed Retinal Cells

Photochemical and oxidative damages in retinal pigment epithelial (RPE) cells are key events in the pathogenesis of age-related macular degeneration. Polyunsaturated fatty acids (PUFA) and carotenoids are rich in retinal cells, and under oxidative stress leads to oxidation and release lipid mediators. We evaluated the impact of carotenoids (lutein, zeaxanthin) and docosahexaenoic acid (DHA) supplementation on RPE cells under oxidative stress. ARPE-19 cells were exposed to H₂O₂ after pre-treatment with lutein, zeaxanthin, DHA, lutein + zeaxanthin or lutein + zeaxanthin with DHA. The data showed H₂O₂ reduced cell viability and DHA content, while promoted catalase activity and certain oxidized PUFA products. Treatment with DHA enhanced omega-3 PUFA enzymatic oxidation namely, anti-inflammatory mediators such as hydroxy-DHA, resolvins and neuroprotection compared to control; the effects were not influenced by the carotenoids. Omega-6 PUFA oxidation, namely pro-inflammatory HETE (5-, 9-, 12 and 20-HETE), and isoprostanes (5- and 15-F_2t-IsoP and 4-F_3t-IsoP) were reduced by lutein + zeaxanthin while the addition of DHA did not further reduce these effects. We observed transcriptional regulation of 5-lipoxygenase by DHA and GPx1 and NEFEL2 by the carotenoids that potentially resulted in decreased HETEs and glutathione respectively. 4-HNE was not affected by the treatments but 4-HHE was reduced by lutein + zeaxanthin with and without DHA. To conclude, carotenoids and DHA appeared to regulate inflammatory lipid mediators while the carotenoids also showed benefits in reducing non-enzymatic oxidation of omega-6 PUFA.

Increase in omega-6 and decrease in omega-3 polyunsaturated fatty acid oxidation elevates the risk of exudative AMD development in adults with Chinese diet

Appropriate diet is essential for the regulation of age-related macular degeneration (AMD). In particular the type of dietary polyunsaturated fatty acids (PUFA) and poor antioxidant status including carotenoid levels concomitantly contribute to AMD risk. Build-up of oxidative stress in AMD induces PUFA oxidation, and a mix of lipid oxidation products (LOPs) are generated. However, LOPs are not comprehensively evaluated in AMD. LOPs are considered biomarkers of oxidative stress but also contributes to inflammatory response. In this cross-sectional case-control study, plasma omega-6/omega-3 PUFA ratios and antioxidant status (glutathione, superoxide dismutase and catalase), and plasma and urinary LOPs (41 types) were determined to evaluate its odds-ratio in the risk of developing exudative AMD (n = 99) compared to age-gender-matched healthy controls (n = 198) in adults with Chinese diet. The odds ratio of developing exudative AMD increased with LOPs from omega-6 PUFA and decreased from those of omega-3 PUFA. These observations were associated with a high plasma omega-6/omega-3 PUFA ratio and low carotenoid levels. In short, poor PUFA and antioxidant status increased the production of omega-6 PUFA LOPs such as dihomo-isoprostane and dihomo-isofuran, and lowered omega-3 PUFA LOPs such as neuroprostanes due to the high omega-6/omega-3 PUFA ratios; they were also correlated to the risk of AMD development. These findings indicate the generation of specific LOPs is associated with the development of exudative AMD.

MS-based targeted metabolomics of eicosanoids and other oxylipins: Analytical and inter-individual variabilities

Oxylipins, including the well-known eicosanoids, are potent lipid mediators involved in numerous physiological and pathological processes. Therefore, their quantitative profiling has gained a lot of attention during the last years notably in the active field of health biomarker discovery. Oxylipins include hundreds of structurally and stereochemically distinct lipid species which today are most commonly analyzed by (ultra) high performance liquid chromatography-mass spectrometry based ((U)HPLC-MS) methods. To maximize the utility of oxylipin profiling in clinical research, it is crucial to understand and assess the factors contributing to the analytical and biological variability of oxylipin profiles in humans. In this review, these factors and their impacts are summarized and discussed, providing a framework for recommendations expected to enhance the interlaboratory comparability and biological interpretation of oxylipin profiling in clinical research.

Adrenic acid non-enzymatic peroxidation products in biofluids of moderate preterm infants

Oxidative stress plays an essential role in processes of signaling and damage to biomolecules during early perinatal life. Isoprostanoids and isofuranoids from the free radical-catalyzed peroxidation of polyunsaturated fatty acids (PUFAs) are widely recognized as reliable biomarkers of oxidative stress. However, their quantification is not straightforward due to high structural similarity of the compounds formed. In this work, a semiquantitative method for the analysis of adrenic acid (AdA, C22:4 n-6) non-enzymatic peroxidation products (i.e. dihomo-isoprostanes and dihomo-isofurans) was developed. The proposed ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) method was applied to the analysis of blood plasma and urine from preterm infants providing information about AdA peroxidation.

Mass Spectrometry in Advancement of Redox Precision Medicine

Redox (portmanteau of reduction-oxidation) reactions involve the transfer of electrons between chemical species in biological processes fundamental to life. It is of outmost importance that cells maintain a healthy redox state by balancing the action of oxidants and antioxidants; failure to do so leads to a multitude of diseases including cancer, diabetes, fibrosis, autoimmune diseases, and cardiovascular and neurodegenerative diseases. From the perspective of precision medicine, it is therefore beneficial to interrogate the redox phenotype of the individual-similar to the use of genomic sequencing-in order to design tailored strategies for disease prevention and treatment. This chapter provides an overview of redox metabolism and focuses on how mass spectrometry (MS) can be applied to advance our knowledge in redox biology and precision medicine.