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The field of lipidomics has been significantly advanced by mass spectrometric analysis. The distinction and quantitation of the unsaturated lipid isomers, however, remain a long-standing challenge. In this study, we have developed an analytical tool for both identification and quantitation of lipid C=C location isomers from complex mixtures using online Paternò–Büchi reaction coupled with tandem mass spectrometry (MS/MS). The potential of this method has been demonstrated with an implementation into shotgun lipid analysis of animal tissues. Among 96 of the unsaturated fatty acids and glycerophospholipids identified from rat brain tissue, 50% of them were found as mixtures of C=C location isomers; for the first time, to our knowledge, the quantitative information of lipid C=C isomers from a broad range of classes was obtained. This method also enabled facile cross-tissue examinations, which revealed significant changes in C=C location isomer compositions of a series of fatty acids and glycerophospholipid (GP) species between the normal and cancerous tissues.

Lipids play a pivotal role in biological processes and lipid analysis by mass spectrometry (MS) has significantly advanced lipidomic studies. While the structure specificity of lipid analysis proves to be critical for studying the biological functions of lipids, current mainstream methods for large-scale lipid analysis can only identify the lipid classes and fatty acyl chains, leaving the C=C location and sn -position unidentified. In this study, combining photochemistry and tandem MS we develop a simple but effective workflow to enable large-scale and near-complete lipid structure characterization with a powerful capability of identifying C=C location(s) and sn -position(s) simultaneously. Quantitation of lipid structure isomers at multiple levels of specificity is achieved and different subtypes of human breast cancer cells are successfully discriminated. Remarkably, human lung cancer tissues can only be distinguished from adjacent normal tissues using quantitative results of both lipid C=C location and sn -position isomers. Coupling photochemical derivatization with tandem mass spectrometry enables C=C-isomer resolved lipidomics. Here, the authors further develop this approach into a shotgun lipidomics workflow that allows simultaneous characterization of lipid C=C locations and sn -positions in complex biological samples.

Lipid peroxidation plays an important role in physiological and pathophysiological conditions; it occurs mainly in the vicinity of the membrane. Glycerophospholipids are indispensable for normal structure of membranes. Lipid mediators are final products of lipid peroxidation. Glycerophospholipids as a source of lipid mediators are closely related with lipid mediators in lipid peroxidation process. This study developed a strategy for simultaneous analysis of glycerophospholipids and lipid mediators in a sample based on a secondary extraction scheme. Due to differences in physicochemical properties of glycerophospholipids and lipid mediators, we used different solvents and methods to extract glycerophospholipids and lipid mediators based on a sample. In addition, we compared three methods of extracting glycerophospholipids to select the best extraction method. In this study, a UPLC-MRM absolute quantification strategy for three deuterated internal standards of lipid mediator was established. The calibration range of all standards is linear, and the correlation coefficients are greater than 0.999. Quantitative range, precision, and accuracy of all analytes–based analysis method meet requirements of method validation. And the accuracy and precision of this method for glycerophospholipids meet the requirements of method verification. It is satisfactory to apply this method in the analysis of the changes of enzymes in lipid peroxidation during the treatment of asthma with dexamethasone. The quantitative results of phospholipids and lipid mediators in mouse lung tissue were obtained by this method, indicating that dexamethasone may inhibit the activity of phospholipase As enzyme and thus slow down the lipid peroxidation process. This work may be of great significance for exploring the changes of enzymes in lipid peroxidation metabolism. Graphical Abstract

The high spatial resolution of secondary ion mass spectrometry and the high resolving power of the Orbitrap mass spectrometer are combined in a single imaging platform, the 3D OrbiSIMS. The instrument's capabilities for resolving lipids and neurotransmitters in the brain with subcellular spatial resolution, and a drug in a single cell in three dimensions is demonstrated. We report the development of a 3D OrbiSIMS instrument for label-free biomedical imaging. It combines the high spatial resolution of secondary ion mass spectrometry (SIMS; under 200 nm for inorganic species and under 2 μm for biomolecules) with the high mass-resolving power of an Orbitrap (>240,000 at m/z 200). This allows exogenous and endogenous metabolites to be visualized in 3D with subcellular resolution. We imaged the distribution of neurotransmitters—gamma-aminobutyric acid, dopamine and serotonin—with high spectroscopic confidence in the mouse hippocampus. We also putatively annotated and mapped the subcellular localization of 29 sulfoglycosphingolipids and 45 glycerophospholipids, and we confirmed lipid identities with tandem mass spectrometry. We demonstrated single-cell metabolomic profiling using rat alveolar macrophage cells incubated with different concentrations of the drug amiodarone, and we observed that the upregulation of phospholipid species and cholesterol is correlated with the accumulation of amiodarone.

Peripheral blood mononuclear cells (PBMCs), including lymphocytes, are important components of the human immune system. These cells contain a diverse array of lipids, primarily glycerophospholipids (GPs) and sphingolipids (SPs), which play essential roles in cellular structure, signaling, and programmed cell death. This study presents a detailed analysis of GP and SP profiles in human PBMC samples using tandem mass spectrometry (MS/MS). Hydrophilic interaction liquid chromatography (HILIC) and electrospray ionization (ESI) coupled with linear ion-trap MS/MS were employed to investigate the diagnostic fragmentation patterns that aided in determining regiochemistry in complex lipid extracts. Specifically, the study explored the fragmentation patterns of various lipid species, including phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), their plasmalogen and lyso forms, phosphatidylserines (PSs), phosphatidylinositols (PIs), phosphatidylglycerols (PGs), sphingomyelins (SMs), and dihexosylceramides (Hex2Cer). Our comprehensive analysis led to the characterization of over 200 distinct lipid species, significantly expanding our understanding of PBMC lipidome complexity. A freely available spreadsheet tool for simulating MS/MS spectra of GPs is provided, enhancing the accessibility and reproducibility of this research. This study advances our knowledge of PBMC lipidomes and establishes a robust analytical framework for future investigations in lipidomics.

A lipidome comprises thousands of lipid species, many of which are isomers and isobars. Liquid chromatography-tandem mass spectrometry (LC-MS/MS), although widely used for lipidomic profiling, faces challenges in differentiating lipid isomers. Herein, we address this issue by leveraging the orthogonal separation capabilities of hydrophilic interaction liquid chromatography (HILIC) and trapped ion mobility spectrometry (TIMS). We further integrate isomer-resolved MS/MS methods onto HILIC-TIMS, which enable pinpointing double bond locations in phospholipids and sn -positions in phosphatidylcholine. This system profiles phospholipids at multiple structural levels with short analysis time (<10 min per LC run), high sensitivity (nM detection limit), and wide coverage, while data analysis is streamlined using a home-developed software, LipidNovelist. Notably, compared to our previous report, the system doubles the coverage of phospholipids in bovine liver and reveals uncanonical desaturation pathways in RAW 264.7 macrophages. Relative quantitation of the double bond location isomers of phospholipids and the sn -position isomers of phosphatidylcholine enables the phenotyping of human bladder cancer tissue relative to normal control, which would be otherwise indistinguishable by traditional profiling methods. Our research offers a comprehensive solution for lipidomic profiling and highlights the critical role of isomer analysis in studying lipid metabolism in both healthy and diseased states. The existence of large number of isomers poses challenges for lipidomic analysis. The authors integrate hydrophilic interaction liquid chromatography, trapped ion mobility, and isomer-resolved MS/MS into a single system, enabling deep profiling of phospholipidomes at fast speed and wide coverage.

Diacyl glycerophospholipids (GPs) belong to the most abundant lipid species in living organisms and consist of a glycerol backbone with fatty acyl groups in sn-1 and sn-2 and a polar head group in the sn-3 position. Regioisomeric mixed diacyl GPs have the same fatty acyl composition but differ in their allocation to sn-1 or sn-2 of the glycerol unit. In-depth analysis of regioisomeric mixed diacyl GP species composed of fatty acyl moieties that are similar in length and degree of saturation typically requires either chemical derivatization or sophisticated analytical instrumentation, since these types of regioisomers are not well resolved under standard ultra-performance liquid chromatography (UPLC) conditions. Here, we introduce a simple and fast method for diacyl GP regioisomer analysis employing UPLC tandem mass spectrometry (MS/MS). This GP regioisomer analysis is based both on minor chromatographic retention time shifts and on major differences in relative abundances of the two fatty acyl anion fragments observed in MS/MS. To monitor these differences with optimal precision, MS/MS spectra are recorded continuously over the UPLC elution profile of the lipid species of interest. Quantification of relative abundances of the regioisomers was performed by algorithms that we have developed for this purpose. The method was applied to commercially available mixed diacyl GP standards and to total lipid extracts of Escherichia coli (E. coli) and bovine liver. To validate our results, we determined regioisomeric ratios of phosphatidylcholine (PC) standards using phospholipase A2-specific release of fatty acids from the sn-2 position of the glycerol backbone. Our results show that most analyzed mixed diacyl GPs of biological origin exhibit significantly higher regioisomeric purity than synthetic lipid standards. In summary, this method can be implemented in routine LC-MS/MS-based lipidomics workflows without the necessity for additional chemical additives, derivatizations, or instrumentation.

Alcohol is the most popular legal drug used in our society today, and its consumption by pregnant women remains an important public health problem. Gestational alcohol consumption can result in a continuum of adverse fetal outcomes known as fetal alcohol spectrum disorder (FASD). Effective strategies are needed to prevent the increasing adoption of risky drinking behaviors. Because ethanol itself is only measurable for a few hours after ethanol intake in conventional matrices including blood, urine, and sweat, these matrices are only useful to detect recent ethanol exposure. Since approximately early 2000, the non-oxidative ethanol metabolites have received increasing attention because of their specificity and, in some cases, wide time window of detection in non-conventional matrices including hair and meconium. In the attempt to update analytical methods for the determination of non-oxidative markers of alcohol, the objective of this study is to review published studies that measure fatty-acid ethyl esters (FAEE), ethyl glucuronide (EtG), and phosphatidylethanol (PEth) in alternative biological matrices, focusing on the extraction and detection methods and full analytical conditions used.

Lipids are a major component of heart tissue and perform several important functions such as energy storage, signaling, and as building blocks of biological membranes. The heart lipidome is quite diverse consisting of glycerophospholipids such as phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), phosphatidylinositols (PIs), phosphatidylglycerols (PGs), cardiolipins (CLs), and glycerolipids, mainly triacylglycerols (TAGs). In this study, mass spectrometry imaging (MSI) enabled by matrix implantation of ionized silver nanoparticles (AgNP) was used to map several classes of lipids in heart tissue. The use of AgNP matrix implantation was motivated by our previous work showing that implantation doses of only 10 14 /cm 2 of 2 nm gold nanoparticulates into the first 10 nm of the near surface of the tissue enabled detection of most brain lipids (including neutral lipid species such as cerebrosides) more efficiently than traditional organic MALDI matrices. Herein, a similar implantation of 500 eV AgNP − across the entire heart tissue section results in a quick, reproducible, solvent-free, uniform matrix concentration of 6 nm AgNP residing near the tissue surface. MALDI-MSI analysis of either positive or negative ions produce high-quality images of several heart lipid species. In negative ion mode, 24 lipid species [16 PEs, 4 PIs, 1 PG, 1 CL, 2 sphingomyelins (SMs)] were imaged. Positive ion images were also obtained from 29 lipid species (10 PCs, 5 PEs, 5 SMs, 9 TAGs) with the TAG species being heavily concentrated in vascular regions of the heart.

Background Distiller’s grains (DG), a major by-product of the Chinese Baijiu industry, represent an inexpensive yet high-quality protein raw material. Previous studies have shown that probiotics-fermented distiller's grains (FDG) hold the potential to serve as an effective livestock feed resource. However, the impacts of feeding FDG-based diets on rumen enzyme activities, rumen microbial communities and metabolism in finishing cattle, along with their underlying regulatory mechanisms, remain poorly understood. Results After 45 days of feeding FDG diets, rumen enzyme activities increased significantly. Feeding 10% FDG diets increased the relative abundance of the bacterial genus Prevotella_1 and the fungal genera Candida , Mucor , and Scedosporium in the rumen. Conversely, the relative abundances of bacterial genera Veillonellaceae UCG-001 and Candidatus Saccharimonas , as well as fungal genus Talaromyces , were reduced notably in the rumen following FDG diet supplementation. Compared to the FDG-10% group, the FDG-20% group exhibited a higher relative abundance of the beneficial bacterial genus Bifidobacterium and the fungal genus Plectosphaerella . Non-targeted metabolomic analysis indicated that the differential metabolites were primarily categorized as benzenoids, lipids and lipid-like molecules, and organic acids and derivatives, which were significantly enriched in the neuroactive ligand-receptor interaction and taste transduction metabolic pathways. Untargeted lipidomic analysis further demonstrated that feeding 20% FDG diets elevated the levels of glycerophospholipids in the rumen. Spearman analysis identified the correlations between specific bacterial and fungal genera and rumen enzyme activities, differential metabolites, and lipids. Conclusions These results suggest that feeding FDG diets potentially improves rumen enzyme activities and up-regulates the levels of glycerophospholipids in the rumen, which may be associated with the alterations in specific rumen microbiota involved in degrading cellulose. Of these, 20% FDG replacement emerges as a better dose within the range of FDG additions in this study. 5dSr_AZjUZngmyDcHFEQW9 Video Abstract Graphical Abstract