Mathematical Model-Assisted UHPLC-MS/MS Method for Global Profiling and Quantification of Cholesteryl Esters in Hyperlipidemic Golden Hamsters

A study on cholesterol-cholesteryl ester metabolic homeostasis and drug intervention in hyperlipidemic hamsters using UHPLC-MS/MS

Hyperlipidemia is a global metabolic disorder characterized by dysregulation of lipid metabolism. This dysregulation is closely associated with the altered homeostasis of cholesterol-cholesteryl ester (CE) metabolism in systemic circulation, and some organs. Additionally, the relationship between oxidized cholesteryl ester (oxCE) and the disease has also gained attention. Currently, there is a lack of comprehensive research on the alterations in cholesterol-CE metabolism in the context of hyperlipidemia, as well as the characteristics of lipid-lowering agents in regulating this metabolic state. Therefore, 40 oxCEs were identified in the hamster liver sample, and novel ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) methods were established for simultaneous analysis of cholesterol, 57 CEs, and 40 oxCEs in the serum, liver, adipose tissue, and intestine of hyperlipidemic hamsters. This study investigated the metabolic alterations between cholesterol-CE/oxCE in hyperlipidemic hamsters and those treated with lipid-lowering agents, including the Niemann-Pick-C1 like-1 protein (NPC1L1) inhibitor ezetimibe and the acyl coenzyme A: cholesterol acyltransferase (ACAT) inhibitor avasimibe. The study findings demonstrate metabolic disorders in cholesterol-CE/oxCE homeostasis in hyperlipidemic hamsters. Lipid-lowering agent therapy can improve the metabolic dysregulation caused by hyperlipidemia, with distinct characteristics: ezetimibe is more effective in reducing cholesterol, while avasimibe is more effective in reducing CEs/oxCEs. Eight potential biomarkers indicating the dysregulation of cholesterol-CE metabolism caused by hyperlipidemia and its improvement by lipid-lowering agents have been identified in the serum. This study offers new insights into the hyperlipidemia pathophysiology and the mechanisms of lipid-lowering agents from a novel perspective on cholesterol-CE/oxCE metabolic homeostasis.

Clinical advances in analytical profiling of signature lipids: implications for severe non-communicable and neurodegenerative diseases

BACKGROUND

Lipids play key roles in numerous biological processes, including energy storage, cell membrane structure, signaling, immune responses, and homeostasis, making lipidomics a vital branch of metabolomics that analyzes and characterizes a wide range of lipid classes. Addressing the complex etiology, age-related risk, progression, inflammation, and research overlap in conditions like Alzheimer's Disease, Parkinson's Disease, Cardiovascular Diseases, and Cancer poses significant challenges in the quest for effective therapeutic targets, improved diagnostic markers, and advanced treatments. Mass spectrometry is an indispensable tool in clinical lipidomics, delivering quantitative and structural lipid data, and its integration with technologies like Liquid Chromatography (LC), Magnetic Resonance Imaging (MRI), and few emerging Matrix-Assisted Laser Desorption Ionization- Imaging Mass Spectrometry (MALDI-IMS) along with its incorporation into Tissue Microarray (TMA) represents current advances. These innovations enhance lipidomics assessment, bolster accuracy, and offer insights into lipid subcellular localization, dynamics, and functional roles in disease contexts.

AIM OF THE REVIEW

The review article summarizes recent advancements in lipidomic methodologies from 2019 to 2023 for diagnosing major neurodegenerative diseases, Alzheimer's and Parkinson's, serious non-communicable cardiovascular diseases and cancer, emphasizing the role of lipid level variations, and highlighting the potential of lipidomics data integration with genomics and proteomics to improve disease understanding and innovative prognostic, diagnostic and therapeutic strategies.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Clinical lipidomic studies are a promising approach to track and analyze lipid profiles, revealing their crucial roles in various diseases. This lipid-focused research provides insights into disease mechanisms, biomarker identification, and potential therapeutic targets, advancing our understanding and management of conditions such as Alzheimer's Disease, Parkinson's Disease, Cardiovascular Diseases, and specific cancers.

DNA methyltransferase 1 deficiency improves macrophage motility and wound healing by ameliorating cholesterol accumulation

Healing of the cutaneous wound requires macrophage recruitment at the sites of injury, where chemotactic migration of macrophages toward the wound is regulated by local inflammation. Recent studies suggest a positive contribution of DNA methyltransferase 1 (Dnmt1) to macrophage pro-informatory responses; however, its role in regulating macrophage motility remains unknown. In this study, myeloid-specific depletion of Dnmt1 in mice promoted cutaneous wound healing and de-suppressed the lipopolysaccharides (LPS)-inhibited macrophage motility. Dnmt1 inhibition in macrophages eliminated the LPS-stimulated changes in cellular mechanical properties in terms of elasticity and viscoelasticity. LPS increased the cellular accumulation of cholesterol in a Dnmt1-depedent manner; cholesterol content determined cellular stiffness and motility. Lipidomic analysis indicated that Dnmt1 inhibition altered the cellular lipid homeostasis, probably through down-regulating the expression of cluster of differentiation 36 CD36 (facilitating lipid influx) and up-regulating the expression of ATP-binding cassette transporter ABCA1 (mediating lipid efflux) and sterol O-acyltransferase 1 SOAT1 (also named ACAT1, catalyzing the esterification of cholesterol). Our study revealed a Dnmt1-dependent epigenetic mechanism in the control of macrophage mechanical properties and the related chemotactic motility, indicating Dnmt1 as both a marker of diseases and a potential target of therapeutic intervention for wound healing.

Analysis of Phospholipids in Digestion Using Hybrid IDA and SWATH Acquisition: An Example for Krill Oil

The composition and digestion of phospholipid-rich foods have important effects on the health of the body. Herein, a model-assisted liquid chromatography coupling mass spectrometry (LC-MS) method was established to analyze the phosphatidylcholine (PC) and lyso-phosphatidylcholine (LPC) species in krill oil before and after digestion. According to the confirmed PC and LPC species in the IDA (information dependent acquisition) results, three categories of mathematical models were set up, involving the retention time (RT), carbon number and unsaturation degree of the fatty acyl chain. All of the regression coefficient values (R²) were greater than 0.90, showing satisfactory fitting results. On this basis, using the computationally created precursor ion mass of PC and LPC species, 12 extra PC species and 4 LPC species were found in the SWATH (sequential windowed acquisition of all theoretical fragment ions) results. The PC and LPC compositions in the final digestive products had obvious differences among the different krill oils with different phospholipid content. Furthermore, more than half of the LPC species in the final digestive products were newly generated, indicating that LPC was one of basic constituents in the digestive products of krill oil. In conclusion, model-assisted hybrid IDA and SWATH acquisition has excellent detection performance, contributing to deep studies of the formations and functions of phospholipids.

Sea Cucumber Phospholipids Regulate Cholesterol Metabolism in High-Fat Diet-induced ApoE-/- Mice

BACKGROUND

Sea cucumber phospholipids, marine-derived lipids with high nutritional functions, have been proven to exhibit various biological activities. However, it is unclear how sea cucumber phospholipids regulate cholesterol (Chol) metabolism in atherosclerosis (AS).

OBJECTIVE

This study aimed to investigate the effects and mechanism of sea cucumber phospholipids on the metabolism of Chol and cholesterol esters (CE) in ApoE^-/- mice, including plasmenyl phosphatidylethanolamine (PE-P) and plasmanyl phosphatidylcholine (PC-O).

METHODS

Male ApoE^-/- mice were fed with chow diet, high-fat diet (HFD), and high-fat diet supplemented with PC-O or PE-P, respectively. We integrated a targeted lipidomics strategy to classify and compare the cholesteryl esters according to their fatty acid types, then analyzed the individual cholesteryl ester molecular species in the liver and serum of mice. Furthermore, the Chol metabolism-related genes and pathways were analyzed in high-fat-induced ApoE^-/- mice.

RESULTS

Biochemical analysis showed that sea cucumber phospholipids significantly inhibit the generation of arterial plaque in ApoE^-/- mice. Compared with the HFD group, PE-P significantly reduced the contents of saturated fatty acid-cholesterol esters (SFA-CE) and monounsaturated fatty acid-cholesterol esters (MUFA-CE) in mice liver (P < 0.05), whereas PC-O particularly upregulated CE20:5 and CE22:6 in serum of mice (P < 0.001). Furthermore, PC-O and PE-P inhibited the Chol synthesis pathway (Cyp7A1 and Cyp27A1), as well as promoted the catabolism of Chol by upregulating gene expressions of bile acid synthesis (Abcb11) and lysosomal activity (Lamp1), respectively.

CONCLUSIONS

Sea cucumber phospholipids could ameliorate the AS symptoms by regulating Chol metabolism.

Berberine is a potential alternative for metformin with good regulatory effect on lipids in treating metabolic diseases

Metformin (MTF) and berberine (BBR) share several therapeutic benefits in treating metabolic-related disorders. However, as the two agents have very different chemical structure and bioavailability in oral route, the goal of this study is to learn their characteristics in treating metabolic disorders. The therapeutic efficacy of BBR and MTF was systemically investigated in the high fat diet feeding hamsters and/or ApoE^(-/-) mice; in parallel, gut microbiota related mechanisms were studied for both agents. We discovered that, although both two drugs had almost identical effects on reducing fatty liver, inflammation and atherosclerosis, BBR appeared to be superior over MTF in alleviating hyperlipidemia and obesity, but MTF was more effective than BBR for the control of blood glucose. Association analysis revealed that the modulation of intestinal microenvironment played a crucial role in the pharmacodynamics of both drugs, in which their respective superiority on the regulation of gut microbiota composition and intestinal bile acids might contribute to their own merits on lowering glucose or lipids. This study shows that BBR may be a good alternative for MTF in treating diabetic patients, especially for those complicated with dyslipidemia and obesity.

Deep mining and quantification of oxidized cholesteryl esters discovers potential biomarkers involved in breast cancer by liquid chromatography-mass spectrometry

Oxidized cholesteryl ester (OxCE) is produced by the oxidation of cholesteryl ester (CE) in the cores of lipoproteins. OxCE production and oxidative stress have been largely associated with breast cancer. Herein, we developed a novel reverse-phase liquid chromatography coupling quadrupole time-of-flight mass spectrometry (RPLC‒Q-TOF‒MS) method based on the iterative acquisition mode and used the MS/MS mode for deep mining and simultaneous quantification of cholesterol (Chol), CEs and OxCEs in human serum. A mathematical model was used to globally profile 57 molecular species of both CEs and OxCEs in the serum of both healthy volunteers and patients with breast cancer, and the qualitative results were verified based on the retention regularity. An abnormal elevation of OxCEs was found in serum samples of breast cancer patients, where OxCEs were produced by the oxidation of the fatty acyl chain of CE (20:4), such as CE (20:1)+3O, CE (20:2)+2O and CE (20:3)+O, which could be regarded as biomarkers. This comprehensive method for the global profiling of Chol, OxCEs and CEs sheds light on the role OxCEs and CEs play in breast cancer and has enabled the discovery of breast cancer biomarkers.

Absolute Quantification of Acylcarnitines Using Integrated Tmt-PP Derivatization-Based LC-MS/MS and Quantitative Analysis of Multi-Components by a Single Marker Strategy

Acylcarnitines (ACs) play important roles in the fatty acid β-oxidation and are considered as diagnostic markers for many diseases. Accurate determination of ACs remains challenging due to their low abundance, high structure diversity, and limited availability of standard compounds. In this study, microwave-assisted Tmt-PP (p-[3,5-(dimethylamino)-2,4,6-triazine] benzene-1-sulfonyl piperazine) derivatization was utilized to facilitate the liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) determination of ACs. The result indicated that Tmt-PP labeling enables the prediction of the retention time and MS response of ACs and enhances their MS response up to 4 times. The introduction of the microwave during the derivatization procedure greatly improved the reaction efficiency, demonstrated by the shortened reaction time from 90 to 1 min. Furthermore, we applied a strategy named quantitative analysis of multi-components by a single marker (QAMS) for the assay of 26 ACs with only 5 AC standards, solving the standard availability issue to a large extent. The established workflow was applied to discover dysregulated ACs in xenograft colon cancer mice, and the quantification results were highly comparable with traditional methods where there were the corresponding standards for each AC. Our study demonstrated that chemical derivatization-based LC-MS/MS integrated with the QAMS strategy is robust for the identification and quantification of ACs and has great potential in targeted metabolomics study.

A simulated strategy for analysis of Short- to Long- chain fatty acids in mouse serum beyond chemical standards

Broadening coverage in fatty acid (FA) analysis benefits the understanding of metabolic regulation in biological system. However, the limited access of chemical standards makes it challenging. In this work, we introduced a simulation assisted strategy to analyze short-, medium-, long- and very-long-chain fatty acids beyond the use of chemical standards. This targeted analysis in selected reaction monitoring (SRM) mode incorporated 3-nitrophenylhydrazine derivatization and mathematical simulation of ion transitions, collision energies, RF values and retention times to identify and quantify the fatty acids without chemical standards. Serum analysis using high resolution mass spectrometry coupled with paired labeling was employed to refine the computational retention times. Based on the simulation, 116 free fatty acids from C1 to C24 were covered in a single analysis on use of 34 standard chemicals. Background interference is commonly observed in fatty acid analysis. For certain fatty acids, e.g. acetic acid or palmitic acid, reliable quantitation is largely restricted by contamination level instead of detection limit. Therefore, the background interference and quantifiable serum volume required for each fatty acid were also evaluated. At least 20 µL serum was suggested to cover most molecules. Using this approach, a total of 66 free fatty acids with various chain lengths and saturations were detected in NTCP knockout mice serum, of which 34 FAs were confirmed by chemical standards and 32 FAs were potentially assigned based on the simulation. Gender dependent fatty acid regulation was observed by NTCP knockout. This work provides a unique strategy that enables to broaden the fatty acid coverage with the absence of chemical standards and is applicable to other derivatizations.

Quantitative analysis of the relationship of derivatization reagents and detection sensitivity of electrospray ionization-triple quadrupole tandem mass spectrometry: Hydrazines as prototypes

Chemical derivatization-assisted electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQ-MS) has become an efficient tool for the quantification of low-molecular-weight molecules. Many studies found that the derivatives of the same analytes derivatized by different derivatization reagents with the same reaction group had different detection sensitivity, even under the same conditions of electrospray ionization-mass spectrometry (ESI-MS). This phenomenon was suggested to be caused by the different modifying groups in the derivatization reagents. However, there is still a lack of systematic study on how modifying groups in the derivatization reagents affect the detection sensitivity of their corresponding derivatives of analytes, especially theoretical investigations. In this study, we employed a quantitative structure-activity relationship (QSAR) modeling approach to explore the relationship between modifying group structures and the detection sensitivity of derivatization reagents and their derivatives during ESI-MS detection. A total of 110 derivatization reagents of the hydrazine family and their hexanal derivatives (substituted hydrazones) were selected as the prototypes to construct QSAR models. The established models suggested that several molecular descriptors, related to hydrophobicity, electronegativity, and molecular shape, were related to the detection sensitivity of hexanal derivatives induced by different modifying groups in the derivatization reagents. Besides, we found that the detection sensitivity of compounds detected in selected ion mode (SIM) showed a positive correlation with that obtained in multiple reaction monitoring mode (MRM), and the ionization efficiency was the key factor on the detection sensitivity in both modes.

Recent advances in analytical strategies for mass spectrometry-based lipidomics

Lipids are vital biological molecules and play multiple roles in cellular function of mammalian organisms such as cellular membrane anchoring, signal transduction, material trafficking and energy storage. Driven by the biological significance of lipids, lipidomics has become an emerging science in the field of omics. Lipidome in biological systems consists of hundreds of thousands of individual lipid molecules that possess complex structures, multiple categories, and diverse physicochemical properties assembled by different combinations of polar headgroups and hydrophobic fatty acyl chains. Such structural complexity poses a huge challenge for comprehensive lipidome analysis. Thanks to the great innovations in chromatographic separation techniques and the continuous advances in mass spectrometric detection tools, analytical strategies for lipidomics have been highly diversified so that the depth and breadth of lipidomics have been greatly enhanced. This review will present the current state of mass spectrometry-based analytical strategies including untargeted, targeted and pseudotargeted lipidomics. Recent typical applications of lipidomics in biomarker discovery, pathogenic mechanism and therapeutic strategy are summarized, and the challenges facing to the field of lipidomics are also discussed.

Advances in lipidomics

The present article examines recently published literature on lipids, mainly focusing on research involving glycero-, glycerophospho- and sphingo-lipids. The primary aim is identification of distinct profiles in biologic lipidomic systems by ultra-high-performance liquid chromatography (UHPLC) coupled with mass spectrometry (MS, tandem MS) with multivariate data analysis. This review specifically targets lipid biomarkers and disease pathway mechanisms in humans and artificial targets. Different specimen matrices such as primary blood derivatives (plasma, serum, erythrocytes, and blood platelets), faecal matter, urine, as well as biologic tissues (liver, lung and kidney) are highlighted.

Profiling of Cholesteryl Esters by Coupling Charge-Tagging Paternò-Büchi Reaction and Liquid Chromatography-Mass Spectrometry

The profile of cholesteryl esters (CEs) is increasingly used in metabolic disease monitoring due to the roles of CE in regulating the cholesterol level. While electrospray ionization-tandem mass spectrometry is routinely applied for the identification and quantitation of CE, it has a limitation of not being able to provide the location of carbon-carbon double bond (C═C) within unsaturated fatty acyls. In this study, we paired offline 2-acetylpyridine (2-AP) Paternò-Büchi (PB) reaction and reversed-phase liquid chromatography-tandem mass spectrometry to achieve highly sensitive and structural informative CE analysis from complex mixtures. The 2-AP PB reactions of CE standards provided 20-30% conversion but resulted in enhanced ion signal relative to that of intact CE detected as ammonium adduct ions. MS/MS of 2-AP derivatized CE via collision-induced dissociation produced two abundant diagnostic ions for each C═C in a fatty acyl, leading to both sensitive identification and quantitation of C═C location isomers. Twelve saturated and twenty-seven unsaturated CEs were profiled in pooled human plasma; of the latter group, relative quantitation of 6 groups of C═C location isomers was achieved. A dehydrocholesteryl ester, DHE 18:2 (Δ9,12), was confidently differentiated from coexisting compositional isomers: CE 18:3 (Δ9,12,15) and CE 18:3 (Δ6,9,12). The above results represented improved CE coverage at the C═C location level over those reported by gas chromatography MS or acetone PB-MS/MS methods.