Development and application of a UHPLC-MS/MS metabolomics based comprehensive systemic and tissue-specific screening method for inflammatory, oxidative and nitrosative stress

Nitro fatty acids: A comprehensive review on analytical methods and levels in health and disease

Nitro fatty acids (NO2-FAs) are biologically active compounds produced from the reaction of unsaturated fatty acids with reactive nitrogen species (RNS). Due to their electrophilic nature, these endogenously produced metabolites can react with nucleophilic targets, producing a spectrum of modulatory and protective effects. Determination of NO2-FAs in biological samples is challenging due to their low nanomolar to picomolar endogenous concentrations, indistinct metabolism, and distribution in many tissues and biofluids. Several attempts have been made to develop precise, standardized, and efficient methodologies for assessing physiological and pathophysiological processes to overcome the difficulties associated with their measurement. This review discusses those approaches utilizing liquid chromatography tandem mass spectrometry (LC‒MS/MS) and gas chromatography tandem mass spectrometry (GC‒MS/MS) for the quantification of NO2-FAs, in addition to a summary of their laboratory synthesis and extraction from biological samples. Clinical associations with different pathological conditions, including hyperlipidaemia, cardiac ischemia and herpes simplex type 2 viral infection (HSV-2), are also discussed.

Association of oxidative stress and inflammatory metabolites with Alzheimer's disease cerebrospinal fluid biomarkers in mild cognitive impairment

BACKGROUND

Isoprostanes and prostaglandins are biomarkers for oxidative stress and inflammation. Their role in Alzheimer's disease (AD) pathophysiology is yet unknown. In the current study, we aim to identify the association of isoprostanes and prostaglandins with the Amyloid, Tau, Neurodegeneration (ATN) biomarkers (Aβ-42, p-tau, and t-tau) of AD pathophysiology in mild cognitive impairment (MCI) subjects.

METHODS

Targeted metabolomics profiling was performed using liquid chromatography-mass spectrometry (LCMS) in 147 paired plasma-CSF samples from the Ace Alzheimer Center Barcelona and 58 CSF samples of MCI patients from the Mannheim/Heidelberg cohort. Linear regression was used to evaluate the association of metabolites with CSF levels of ATN biomarkers in the overall sample and stratified by Aβ-42 pathology and APOE genotype. We further evaluated the role of metabolites in MCI to AD dementia progression.

RESULTS

Increased CSF levels of PGF2α, 8,12-iso-iPF2α VI, and 5-iPF2α VI were significantly associated (False discovery rate (FDR) < 0.05) with higher p-tau levels. Additionally, 8,12-iso-iPF2α VI was associated with increased total tau levels in CSF. In MCI due to AD, PGF2α was associated with both p-tau and total tau, whereases 8,12-iso-iPF2α VI was specifically associated with p-tau levels. In APOE stratified analysis, association of PGF2α with p-tau and t-tau was observed in only APOE ε4 carriers while 5-iPF2α VI showed association with both p-tau and t-tau in APOE ε33 carriers. CSF levels of 8,12- iso-iPF2α VI showed association with p-tau and t-tau in APOE ε33/APOE ε4 carriers and with t-tau in APOE ε3 carriers. None of the metabolites showed evidence of association with MCI to AD progression.

CONCLUSIONS

Oxidative stress (8,12-iso-iPF2α VI) and inflammatory (PGF2α) biomarkers are correlated with biomarkers of AD pathology during the prodromal stage of AD and relation of PGF2α with tau pathology markers may be influenced by APOE genotype.

A Targeted, Bioinert LC-MS/MS Method for Sensitive, Comprehensive Analysis of Signaling Lipids

Signaling lipids are key players in cellular processes. Despite their importance, no method currently allows their comprehensive monitoring in one analytical run. Challenges include a wide dynamic range, isomeric and isobaric species, and unwanted interaction along the separation path. Herein, we present a sensitive and robust targeted liquid chromatography-mass spectrometry (LC-MS/MS) approach to overcome these challenges, covering a broad panel of 17 different signaling lipid classes. It involves a simple one-phase sample extraction and lipid analysis using bioinert reversed-phase liquid chromatography coupled to targeted mass spectrometry. The workflow shows excellent sensitivity and repeatability in different biological matrices, enabling the sensitive and robust monitoring of 388 lipids in a single run of only 20 min. To benchmark our workflow, we characterized the human plasma signaling lipidome, quantifying 307 endogenous molecular lipid species. Furthermore, we investigated the signaling lipidome during platelet activation, identifying numerous regulations along important lipid signaling pathways. This highlights the potential of the presented method to investigate signaling lipids in complex biological systems, enabling unprecedentedly comprehensive analysis and direct insight into signaling pathways.

A comprehensive UHPLC-MS/MS method for metabolomics profiling of signaling lipids: Markers of oxidative stress, immunity and inflammation

Signaling lipids (SLs) play a crucial role in various signaling pathways, featuring diverse lipid backbone structures. Emerging evidence showing the biological significance and biomedical values of SLs has strongly spurred the advancement of analytical approaches aimed at profiling SLs. Nevertheless, the dramatic differences in endogenous abundances across lipid classes as well as multiple isomers within the same lipid class makes the development of a generic analytical method challenging. A better analytical method that combines comprehensive coverage and high sensitivity is needed to enable us to gain a deeper understanding of the biochemistry of these molecules in health and disease. In this study, we developed a fast and comprehensive targeted ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for profiling SLs. The platform enables analyses of 260 metabolites covering oxylipins (isoprostanes, prostaglandins and other oxidized lipids), free fatty acids, lysophospholipids, sphingoid bases (C16, C18), platelet activating factors (C16, C18), endocannabinoids and bile acids. Various validation parameters including linearity, limit of detection, limit of quantification, extraction recovery, matrix effect, intra-day and inter-day precision were used to characterize this method. Metabolite quantitation was successfully achieved in both NIST Standard Reference Material for human plasma (NIST SRM 1950) and pooled human plasma, with 109 and 144 metabolites quantitated. The quantitation results in NIST SRM 1950 plasma demonstrated good correlations with certified or previously reported values in published literature. This study introduced quantitative data for 37 SLs for the first time. Metabolite concentrations measured in NIST SRM 1950 will serve as essential reference data for facilitating interlaboratory comparisons. The methodology established here will be the cornerstone for in-depth profiling of signaling lipids across diverse biological samples and contexts.

Biomarkers for assessing pain and pain relief in the neonatal intensive care unit

Newborns admitted to the neonatal intensive care unit (NICU) regularly undergo painful procedures and may face various painful conditions such as postoperative pain. Optimal management of pain in these vulnerable preterm and term born neonates is crucial to ensure their comfort and prevent negative consequences of neonatal pain. This entails accurate and timely identification of pain, non-pharmacological pain treatment and if needed administration of analgesic therapy, evaluation of treatment effectiveness, and monitoring of adverse effects. Despite the widely recognized importance of pain management, pain assessment in neonates has thus far proven to be a challenge. As self-report, the gold standard for pain assessment, is not possible in neonates, other methods are needed. Several observational pain scales have been developed, but these often rely on snapshot and largely subjective observations and may fail to capture pain in certain conditions. Incorporation of biomarkers alongside observational pain scores holds promise in enhancing pain assessment and, by extension, optimizing pain treatment and neonatal outcomes. This review explores the possibilities of integrating biomarkers in pain assessment in the NICU.

Scavenger Receptor BI Deficiency in Mice Is Associated With Plasma Ceramide and Sphingomyelin Accumulation and a Reduced Cholesteryl Ester Fatty Acid Length and Unsaturation Degree

Objective

Scavenger receptor class B type I (SR-BI) is primarily known for its role in the selective uptake of cholesteryl esters (CEs) from high-density lipoproteins (HDLs). Here we investigated whether SR-BI deficiency is associated with other potentially relevant changes in the plasma lipidome than the established effect of HDL-cholesterol elevation.

Methods

Targeted ultra-high-performance liquid chromatography-tandem mass spectrometry was utilized to measure lipid species in plasma from female wild-type and SR-BI knockout mice.

Results

SR-BI deficiency was associated with a reduction in the average CE fatty acid length (-2%; p<0.001) and degree of CE fatty acid unsaturation (-18%; p<0.001) due to a relative shift from longer, polyunsaturated CE species CE (20:4), CE (20:5), and CE (22:6) towards the mono-unsaturated CE (18:1) species. Sphingomyelin (SM) levels were 64% higher (p<0.001) in SR-BI knockout mice without a parallel change in (lyso)phosphatidylcholine (LPC) concentrations, resulting in an increase in the SM/LPC ratio from 0.102±0.005 to 0.163±0.003 (p<0.001). In addition, lower LPC lengths (-5%; p<0.05) and fatty acid unsaturation degrees (-20%; p<0.01) were detected in SR-BI knockout mice. Furthermore, SR-BI deficiency was associated with a 4.7-fold increase (p<0.001) in total plasma ceramide (Cer) levels, with a marked >9-fold rise (p<0.001) in Cer (d18:1/24:1) concentrations.

Conclusion

We have shown that SR-BI deficiency in mice not only impacts the CE concentrations, length, and saturation index within the plasma compartment, but is also associated with plasma accumulation of several Cer and SM species that may contribute to the development of specific hematological and metabolic (disease) phenotypes previously detected in SR-BI knockout mice.

Multi-omics reveal neuroprotection of Acer truncatum Bunge Seed extract on hypoxic-ischemia encephalopathy rats under high-altitude

Hypoxic-ischemic encephalopathy (HIE) at high-altitudes leads to neonatal mortality and long-term neurological complications without effective treatment. Acer truncatum Bunge Seed extract (ASO) is reported to have effect on cognitive improvement, but its molecular mechanisms on HIE are unclear. In this study, ASO administration contributed to reduced neuronal cell edema and improved motor ability in HIE rats at a simulated 4500-meter altitude. Transcriptomics and WGCNA analysis showed genes associated with lipid biosynthesis, redox homeostasis, neuronal growth, and synaptic plasticity regulated in the ASO group. Targeted and untargeted-lipidomics revealed decreased free fatty acids and increased phospholipids with favorable ω-3/ω-6/ω-9 fatty acid ratios, as well as reduced oxidized glycerophospholipids (OxGPs) in the ASO group. Combining multi-omics analysis demonstrated FA to FA-CoA, phospholipids metabolism, and lipid peroxidation were regulated by ASO treatment. Our results illuminated preliminary metabolism mechanism of ASO ingesting in rats, implying ASO administration as potential intervention strategy for HIE under high-altitude.

Altered methionine-sulfone levels are associated with impaired growth in HIV-exposed-uninfected children

OBJECTIVE

To determine immune-metabolic dysregulation in children born to women living with HIV.

METHODS

Longitudinal immune-metabolomic analyses of plasma of 32 pregnant women with HIV (WHIV) and 12 uninfected women and their children up to 1.5 years of age were performed.

RESULTS

Using liquid chromatography-mass spectrometry and a multiplex bead assay, 280 metabolites (57 amino acids, 116 positive lipids, 107 signalling lipids) and 24 immune mediators (e.g. cytokines) were quantified. combinational antiretroviral therapy (cART) exposure was categorized as cART initiation preconception (long), cART initiation postconception up to 4 weeks before birth (medium) and cART initiation within 3 weeks of birth (short). Plasma metabolite profiles differed between HIV-exposed-uninfected (HEU)-children with long cART exposure compared to HIV-unexposed-children (HUU). Specifically, higher levels of methionine-sulfone, which is associated with oxidative stress, were detected in HEU-children with long cART exposure compared to HUU-children. High infant methionine-sulfone levels were reflected by high prenatal plasma levels in the mother. Increased methionine-sulfone levels in the children were associated with decreased growth, including both weight and length.

CONCLUSION

These findings based on longitudinal data demonstrate that dysregulation of metabolite networks associated with oxidative stress in children born to WHIV is associated with restricted infant growth.

1α,25-Dihydroxyvitamin D3 Improves Follicular Development and Steroid Hormone Biosynthesis by Regulating Vitamin D Receptor in the Layers Model

1α,25-Dihydroxyvitamin D₃ (VitD₃) is the active form of vitamin D, and it regulates gene expression and protein synthesis in mammalian follicle development. However, the function of VitD₃ in the follicular development of layers remains unclear. This study investigated, through in vivo and in vitro experiments, the effects of VitD₃ on follicle development and steroid hormone biosynthesis in young layers. In vivo, ninety 18-week-old Hy-Line Brown laying hens were randomly divided into three groups for different treatments of VitD₃ (0, 10, and 100 μg/kg). VitD₃ supplementation promoted follicle development, increasing the number of small yellow follicles (SYFs) and large yellow follicles (LYFs) and the thickness of the granulosa layer (GL) of SYFs. Transcriptome analysis revealed that VitD₃ supplementation altered gene expression in the ovarian steroidogenesis, cholesterol metabolism, and glycerolipid metabolism signaling pathways. Steroid hormone-targeted metabolomics profiling identified 20 steroid hormones altered by VitD₃ treatment, with 5 being significantly different among the groups. In vitro, it was found that VitD₃ increased cell proliferation, promoted cell-cycle progression, regulated the expression of cell-cycle-related genes, and inhibited the apoptosis of granulosa cells from pre-hierarchical follicles (phGCs) and theca cells from prehierarchical follicles (phTCs). In addition, the steroid hormone biosynthesis-related genes, estradiol (E2) and progesterone (P4) concentrations, and vitamin D receptor (VDR) expression level was significantly altered by VitD₃. Our findings identified that VitD₃ altered the gene expression related to steroid metabolism and the production of testosterone, estradiol, and progesterone in the pre-hierarchical follicles (PHFs), resulting in positive effects on poultry follicular development.

Understanding the Functional Role of the Microbiome and Metabolome in Asthma

PURPOSE OF REVIEW

Asthma is a heterogenous respiratory disease characterized by airway inflammation and obstruction. However, the causes of asthma are unknown. Several studies have reported microbial and metabolomic dysbiosis in asthmatic patients; but, little is known about the functional role of the microbiota or the host-microbe metabolome in asthma pathophysiology. Current multi-omic studies are linking both the metabolome and microbiome in different organ systems to help identify the interactions involved in asthma, with the goal of better identifying endotypes/phenotypes, causal links, and potential targets of treatment. This review thus endeavors to explore the benefits of and current advances in studying microbiome-metabolome interactions in asthma.

RECENT FINDINGS

This is a narrative review of the current state of research surrounding the interaction between the microbiome and metabolome and their role in asthma. Associations with asthma onset, severity, and phenotype have been identified in both the microbiome and the metabolome, most frequently in the gut. More recently, studies have begun to investigate the role of the respiratory microbiome in airway disease and its association with the systemic metabolome, which has provided further insights into its role in asthma phenotypes. This review also identifies gaps in the field in understanding the direct link between respiratory microbiome and metabolome, hypothesizes the benefits for conducting such studies in the future for asthma treatment and prevention, and identifies current analytical limitations that need to be addressed to advance the field. This is a comprehensive review of the current state of research on the interaction between the microbiome and metabolome and their role in asthma.

A Sample Preparation Method for the Simultaneous Profiling of Signaling Lipids and Polar Metabolites in Small Quantities of Muscle Tissues from a Mouse Model for Sarcopenia

The metabolic profiling of a wide range of chemical classes relevant to understanding sarcopenia under conditions in which sample availability is limited, e.g., from mouse models, small muscles, or muscle biopsies, is desired. Several existing metabolomics platforms that include diverse classes of signaling lipids, energy metabolites, and amino acids and amines would be informative for suspected biochemical pathways involved in sarcopenia. The sample limitation requires an optimized sample preparation method with minimal losses during isolation and handling and maximal accuracy and reproducibility. Here, two developed sample preparation methods, BuOH-MTBE-Water (BMW) and BuOH-MTBE-More-Water (BMMW), were evaluated and compared with previously reported methods, Bligh-Dyer (BD) and BuOH-MTBE-Citrate (BMC), for their suitability for these classes. The most optimal extraction was found to be the BMMW method, with the highest extraction recovery of 63% for the signaling lipids and 81% for polar metabolites, and an acceptable matrix effect (close to 1.0) for all metabolites of interest. The BMMW method was applied on muscle tissues as small as 5 mg (dry weight) from the well-characterized, prematurely aging, DNA repair-deficient Ercc1^∆/- mouse mutant exhibiting multiple-morbidities, including sarcopenia. We successfully detected 109 lipids and 62 polar targeted metabolites. We further investigated whether fast muscle tissue isolation is necessary for mouse sarcopenia studies. A muscle isolation procedure involving 15 min at room temperature revealed a subset of metabolites to be unstable; hence, fast sample isolation is critical, especially for more oxidative muscles. Therefore, BMMW and fast muscle tissue isolation are recommended for future sarcopenia studies. This research provides a sensitive sample preparation method for the simultaneous extraction of non-polar and polar metabolites from limited amounts of muscle tissue, supplies a stable mouse muscle tissue collection method, and methodologically supports future metabolomic mechanistic studies of sarcopenia.

PRMT3 inhibitor SGC707 reduces triglyceride levels and induces pruritus in Western-type diet-fed LDL receptor knockout mice

Protein arginine methyltransferase 3 (PRMT3) is a co-activator of liver X receptor capable of selectively modulating hepatic triglyceride synthesis. Here we investigated whether pharmacological PRMT3 inhibition can diminish the hepatic steatosis extent and lower plasma lipid levels and atherosclerosis susceptibility. Hereto, male hyperlipidemic low-density lipoprotein receptor knockout mice were fed an atherogenic Western-type diet and injected 3 times per week intraperitoneally with PRMT3 inhibitor SGC707 or solvent control. Three weeks into the study, SGC707-treated mice developed severe pruritus and scratching-associated skin lesions, leading to early study termination. SGC707-treated mice exhibited 50% lower liver triglyceride stores as well as 32% lower plasma triglyceride levels. Atherosclerotic lesions were virtually absent in all experimental mice. Plasma metabolite analysis revealed that levels of taurine-conjugated bile acids were ~ threefold increased (P < 0.001) in response to SGC707 treatment, which was paralleled by systemically higher bile acid receptor TGR5 signalling. In conclusion, we have shown that SGC707 treatment reduces hepatic steatosis and plasma triglyceride levels and induces pruritus in Western-type diet-fed LDL receptor knockout mice. These findings suggest that pharmacological PRMT3 inhibition can serve as therapeutic approach to treat non-alcoholic fatty liver disease and dyslipidemia/atherosclerosis, when unwanted effects on cholesterol and bile acid metabolism can be effectively tackled.

Nitro Fatty Acids (NO2-FAs): An Emerging Class of Bioactive Fatty Acids

Unsaturated nitro fatty acids (NO₂-FAs) constitute a category of molecules that may be formed endogenously by the reaction of unsaturated fatty acids (UFAs) with secondary species of nitrogen monoxide and nitrite anions. The warhead of NO₂-FAs is a nitroalkene moiety, which is a potent Michael acceptor and can undergo nucleophilic attack from thiol groups of biologically relevant proteins, showcasing the value of these molecules regarding their therapeutic potential against many diseases. In general, NO₂-FAs inhibit nuclear factorκ-B (NF-κB), and simultaneously they activate nuclear factor (erythroid derived)-like 2 (Nrf2), which activates an antioxidant signaling pathway. NO₂-FAs can be synthesized not only endogenously in the organism, but in a synthetic laboratory as well, either by a step-by-step synthesis or by a direct nitration of UFAs. The step-by-step synthesis requires specific precursor compounds and is in position to afford the desired NO₂-FAs with a certain position of the nitro group. On the contrary, the direct nitration of UFAs is not a selective methodology; thus, it affords a mixture of all possible nitro isomers.

A Microfluidics-Based Screening Tool to Assess the Impact of Blood Plasma Factors on Microvascular Integrity

This study provides a method to assess the impact of circulating plasma factors on microvascular integrity by using a recently developed microvessel-on-a-chip platform featuring the human endothelium that is partly surrounded by the extracellular matrix. The system is high-throughput, which allows parallel analysis of organ-level microvessel pathophysiology, including vascular leakage. Ethylenediaminetetraacetic acid plasma samples are mixed with inhibitors for recalcification of the plasma samples to avoid activation of the coagulation- or complement system. Moreover, the assay is validated by spiking vascular endothelial growth factor, histamine, or tumor necrosis factor alpha to recalcified plasma and confirms their modulation of microvessel barrier function at physiologically relevant concentrations. Finally, this study shows that perfusing the microvessels with recalcified plasma samples of coronavirus disease-2019 patients, with a confirmed proinflammatory profile, results in markedly increased leakage of the microvessels. The assay provides opportunities for diagnostic screening of inflammatory or endothelial disrupting plasma factors associated with endothelial dysfunction.

OrganoPlate Micro-fluidic Microvessel Culture and Analysis

The endothelial cells from the microvasculature are key drivers and targets of inflammatory and thrombotic processes in microvascular diseases. The study of bioactive lipids in inflammatory processes has been largely based on two-dimensional endothelial cell cultures. Three-dimensional microvessels-on-a-chip provides an opportunity to monitor the inflammatory phenotype of human microvessels in a more physiological-relevant environment. This protocol describes the culture of endothelial cells as three-dimensional microvessels in the OrganoPlate. The microvessels are treated with tumor necrosis factor alpha to induce inflammation. The collection of samples from the microvessels is optimized for measuring bioactive lipids with liquid chromatography-mass spectrometry, providing a more informative metabolic readout as compared with functional assays.

Targeting Xanthine Oxidase by Natural Products as a Therapeutic Approach for Mental Disorders

Mental disorders comprise diverse human pathologies, including depression, bipolar affective disorder, schizophrenia, and dementia that affect millions of people around the world. The causes of mental disorders are unclear, but growing evidence suggests that oxidative stress and the purine/adenosine system play a key role in their development and progression. Xanthine oxidase (XO) is a flavoprotein enzyme essential for the catalysis of the oxidative hydroxylation of purines -hypoxanthine and xanthine- to generate uric acid. As a consequence of the oxidative reaction of XO, reactive oxygen species (ROS) such as superoxide and hydrogen peroxide are produced and, further, contribute to the pathogenesis of mental disorders. Altered XO activity has been associated with free radical-mediated neurotoxicity inducing cell damage and inflammation. Diverse studies reported a direct association between an increased activity of XO and diverse mental diseases including depression or schizophrenia. Small-molecule inhibitors, such as the well-known allopurinol, and dietary flavonoids, can modulate the XO activity and subsequent ROS production. In the present work, we review the available literature on XO inhibition by small molecules and their potential therapeutic application in mental disorders. In addition, we discuss the chemistry and molecular mechanism of XO inhibitors, as well as the use of structure-based and computational methods to design specific inhibitors with the capability of modulating XO activity.

Mechanism of action and potential applications of selective inhibition of microsomal prostaglandin E synthase-1-mediated PGE2 biosynthesis by sonlicromanol's metabolite KH176m

Increased prostaglandin E2 (PGE₂) levels were detected in mitochondrial disease patient cells harboring nuclear gene mutations in structural subunits of complex I, using a metabolomics screening approach. The increased levels of this principal inflammation mediator normalized following exposure of KH176m, an active redox-modulator metabolite of sonlicromanol (KH176). We next demonstrated that KH176m selectively inhibited lipopolysaccharide (LPS) or interleukin-1β (IL-1β)-induced PGE₂ production in control skin fibroblasts. Comparable results were obtained in the mouse macrophage-like cell line RAW264.7. KH176m selectively inhibited mPGES-1 activity, as well as the inflammation-induced expression of mPGES-1. Finally, we showed that the effect of KH176m on mPGES-1 expression is due to the inhibition of a PGE₂-driven positive feedback control-loop of mPGES-1 transcriptional regulation. Based on the results obtained we discuss potential new therapeutic applications of KH176m and its clinical stage parent drug candidate sonlicromanol in mitochondrial disease and beyond.

Association of lysophosphatidic acids with cerebrospinal fluid biomarkers and progression to Alzheimer's disease

Background

Lysophosphatidic acids (LPAs) are bioactive signaling phospholipids that have been implicated in Alzheimer’s disease (AD). It is largely unknown whether LPAs are associated with AD pathology and progression from mild cognitive impairment (MCI) to AD.

Methods

The current study was performed on cerebrospinal fluid (CSF) and plasma samples of 182 MCI patients from two independent cohorts. We profiled LPA-derived metabolites using liquid chromatography-mass spectrometry. We evaluated the association of LPAs with CSF biomarkers of AD, Aβ-42, p-tau, and total tau levels overall and stratified by APOE genotype and with MCI to AD progression.

Results

Five LPAs (C16:0, C16:1, C22:4, C22:6, and isomer-LPA C22:5) showed significant positive association with CSF biomarkers of AD, Aβ-42, p-tau, and total tau, while LPA C14:0 and C20:1 associated only with Aβ-42 and alkyl-LPA C18:1, and LPA C20:1 associated with tau pathology biomarkers. Association of cyclic-LPA C16:0 and two LPAs (C20:4, C22:4) with Aβ-42 levels was found only in APOE ε4 carriers. Furthermore, LPA C16:0 and C16:1 also showed association with MCI to AD dementia progression, but results did not replicate in an independent cohort.

Conclusions

Our findings provide evidence that LPAs may contribute to early AD pathogenesis. Future studies are needed to determine whether LPAs play a role in upstream of AD pathology or are downstream markers of neurodegeneration.

Metabolic response of blood vessels to TNFα

TNFα signaling in the vascular endothelium elicits multiple inflammatory responses that drive vascular destabilization and leakage. Bioactive lipids are main drivers of these processes. In vitro mechanistic studies of bioactive lipids have been largely based on two-dimensional endothelial cell cultures that, due to lack of laminar flow and the growth of the cells on non-compliant stiff substrates, often display a pro-inflammatory phenotype. This complicates the assessment of inflammatory processes. Three-dimensional microvessels-on-a-chip models provide a unique opportunity to generate endothelial microvessels in a more physiological environment. Using an optimized targeted liquid chromatography–tandem mass spectrometry measurements of a panel of pro- and anti-inflammatory bioactive lipids, we measure the profile changes upon administration of TNFα. We demonstrate that bioactive lipid profiles can be readily detected from three-dimensional microvessels-on-a-chip and display a more dynamic, less inflammatory response to TNFα, that resembles more the human situation, compared to classical two-dimensional endothelial cell cultures.

In a range of conditions called autoimmune diseases, the immune system attacks the body rather than foreign elements. This can cause inflammation that is harmful for many organs. In particular, immune cells can produce excessive amounts of a chemical messenger called tumor necrosis factor alpha (TNFα for short), which can lead to the release of fatty molecules that damage blood vessels.

This process is normally studied in blood vessels cells that are grown on a dish, without any blood movement. However, in this rigid 2D environment, the cells become ‘stressed’ and show higher levels of inflammation than in the body. This makes it difficult to assess the exact role that TNFα plays in disease.

A new technology is addressing this issue by enabling scientist to culture blood vessels cells in dishes coated with gelatin. This allows the cells to organize themselves in 3D, creating tiny blood vessels in which fluids can flow. However, it was unclear whether these ‘microvessels-on-a-chip’ were better models to study the role of TNFα compared to cells grown on a plate.

Here, Junaid et al. compared the levels of inflammation in blood vessels cells grown in the two environments, showing that cells are less inflamed when they are cultured in 3D. In addition, when the artificial 3D-blood vessels were exposed to TNFα, they responded more like real blood vessels than the 2D models. Finally, experiments showed that it was possible to monitor the release of fatty molecules in this environment. Together, this work suggests that microvessels-on-a-chip are better models to study how TNFα harms blood vessels.

Next, systems and protocols could be develop to allow automated mass drug testing in microvessels-on-a-chip. This would help scientists to quickly screen thousands of drugs and find candidates that can protect blood vessels from TNFα.

Differences in airway microbiome and metabolome of single lung transplant recipients

Background

Recent studies suggest that alterations in lung microbiome are associated with occurrence of chronic lung diseases and transplant rejection. To investigate the host-microbiome interactions, we characterized the airway microbiome and metabolome of the allograft (transplanted lung) and native lung of single lung transplant recipients.

Methods

BAL was collected from the allograft and native lungs of SLTs and healthy controls. 16S rRNA microbiome analysis was performed on BAL bacterial pellets and supernatant used for metabolome, cytokines and acetylated proline-glycine-proline (Ac-PGP) measurement by liquid chromatography-high-resolution mass spectrometry.

Results

In our cohort, the allograft airway microbiome was distinct with a significantly higher bacterial burden and relative abundance of genera Acinetobacter & Pseudomonas. Likewise, the expression of the pro-inflammatory cytokine VEGF and the neutrophil chemoattractant matrikine Ac-PGP in the allograft was significantly higher. Airway metabolome distinguished the native lung from the allografts and an increased concentration of sphingosine-like metabolites that negatively correlated with abundance of bacteria from phyla Proteobacteria.

Conclusions

Allograft lungs have a distinct microbiome signature, a higher bacterial biomass and an increased Ac-PGP compared to the native lungs in SLTs compared to the native lungs in SLTs. Airway metabolome distinguishes the allografts from native lungs and is associated with distinct microbial communities, suggesting a functional relationship between the local microbiome and metabolome.

Analytical techniques for metabolomic studies: a review

Metabolomics is the comprehensive study of small-molecule metabolites. Obtaining a wide coverage of the metabolome is challenging because of the broad range of physicochemical properties of the small molecules. To study the compounds of interest spectroscopic (NMR), spectrometric (MS) and separation techniques (LC, GC, supercritical fluid chromatography, CE) are used. The choice for a given technique is influenced by the sample matrix, the concentration and properties of the metabolites, and the amount of sample. This review discusses the most commonly used analytical techniques for metabolomic studies, including their advantages, drawbacks and some applications.

Signaling lipids as diagnostic biomarkers for ocular surface cicatrizing conjunctivitis

Abstract

Metabolomics has been applied to diagnose diseases, predict disease progression, and design therapeutic strategies in various areas of medicine. However, it remains to be applied to the ocular surface diseases, where biological samples are often of limited quantities. We successfully performed proof-of-concept metabolomics assessment of volume-limited cytology samples from a clinical form of chronic inflammatory cicatrizing conjunctivitis, i.e., ocular MMP and discovered metabolic changes of signaling lipid mediators upon disease onset and progression. The metabolomics assessment revealed active oxylipins, lysophospholipids, fatty acids, and endocannabinoids alterations, from which potential biomarkers linked to inflammatory processes were identified. Possible underlying mechanisms such as dysregulated enzyme activities (e.g., lipoxygenases, cytochrome P450, and phospholipases) were suggested which may be considered as potential therapeutic targets in future studies.

Key messages

Metabolic profile of the ocular surface can be measured using impression cytology samples.

Metabolomics analysis of ocular pemphigoid is presented for the first time.

The metabolomics assessment of OCP patients revealed active oxylipins, lysophospholipids, fatty acids, and endocannabinoids alterations.

Several oxylipins are identified as diagnostic biomarkers for OCP.

Methods of the Analysis of Oxylipins in Biological Samples

Oxylipins are derivatives of polyunsaturated fatty acids and due to their important and diverse functions in the body, they have become a popular subject of studies. The main challenge for researchers is their low stability and often very low concentration in samples. Therefore, in recent years there have been developments in the extraction and analysis methods of oxylipins. New approaches in extraction methods were described in our previous review. In turn, the old analysis methods have been replaced by new approaches based on mass spectrometry (MS) coupled with liquid chromatography (LC) and gas chromatography (GC), and the best of these methods allow hundreds of oxylipins to be quantitatively identified. This review presents comparative and comprehensive information on the progress of various methods used by various authors to achieve the best results in the analysis of oxylipins in biological samples.

Feasibility of Localized Metabolomics in the Study of Pancreatic Islets and Diabetes

(1) Background: Disruption of insulin production by native or transplanted pancreatic islets caused by auto/allo-immunity leads to hyperglycemia, a serious health condition and important therapeutic challenge due to the lifelong need for exogeneous insulin administration. Early metabolic biomarkers can prompt timely interventions to preserve islet function, but reliable biomarkers are currently lacking. We explored the feasibility of "localized metabolomics" where initial biomarker discovery is made in aqueous humor samples for further validation in the circulation. (2) Methods: We conducted non-targeted metabolomic studies in parallel aqueous humor and plasma samples from diabetic and nondiabetic mice. Metabolite levels and associated pathways were compared in both compartments as well as to an earlier longitudinal dataset in hyperglycemia-progressor versus non-progressor non-obese diabetic (NOD) mice. (3) Results: We confirmed that aqueous humor samples can be used to assess metabolite levels. About half of the identified metabolites had well-correlated levels in the aqueous humor and plasma. Several plasma metabolites were significantly different between diabetic and nondiabetic animals and between males and females, and many of them were correlated with the aqueous humor. (4) Conclusions: This study provides proof-of-concept evidence that aqueous humor samples enriched with islet-related metabolites and representative of the immediate islet microenvironment following intraocular islet transplant can be used to assess metabolic changes that could otherwise be overlooked in the general circulation. The findings support localized metabolomics, with and without intraocular islet transplant, to identify biomarkers associated with diabetes and islet allograft rejection.

Discovery of bioactive nitrated lipids and nitro-lipid-protein adducts using mass spectrometry-based approaches

Nitro-fatty acids (NO₂-FA) undergo reversible Michael adduction reactions with cysteine and histidine residues leading to the post-translational modification (PTM) of proteins. This electrophilic character of NO₂-FA is strictly related to their biological roles. The NO₂-FA-induced PTM of signaling proteins can lead to modifications in protein structure, function, and subcellular localization. The nitro lipid-protein adducts trigger a series of downstream signaling events that culminates with anti-inflammatory, anti-hypertensive, and cytoprotective effects mediated by NO₂-FA. These lipoxidation adducts have been detected and characterized both in model systems and in biological samples by using mass spectrometry (MS)-based approaches. These MS approaches allow to unequivocally identify the adduct together with the targeted residue of modification. The identification of the modified proteins allows inferring on the possible impact of the NO₂-FA-induced modification. This review will focus on MS-based approaches as valuable tools to identify NO₂-FA-protein adducts and to unveil the biological effect of this lipoxidation adducts.

Profile of Phosphatidylserine Modifications under Nitroxidative Stress Conditions Using a Liquid Chromatography-Mass Spectrometry Based Approach

Nitrated lipids have been detected in vitro and in vivo, usually associated with a protective effect. While nitrated fatty acids have been widely studied, few studies reported the nitration and nitroxidation of the phospholipid classes phosphatidylcholine, and phosphatidylethanolamine. However, no information regarding nitrated and nitroxidized phosphatidylserine can be found in the literature. This work aims to identify and characterize the nitrated and nitroxidized derivatives of 1-palmitoyl-2-oleoyl-sn-3-glycero-phosphoserine (POPS), obtained after incubation with nitronium tetrafluoroborate, by liquid chromatography (LC) coupled to mass spectrometry (MS) and tandem MS (MS/MS). Several nitrated and nitroxidized products were identified, namely, nitro, nitroso, nitronitroso, and dinitro derivatives, as well as some nitroxidized species such as nitrosohydroxy, nitrohydroxy, and nitrohydroperoxy. The fragmentation pathways identified were structure-dependent and included the loss of HNO and HNO₂ for nitroso and nitro derivatives, respectively. Combined losses of PS polar head group plus HNO or HNO₂ and carboxylate anions of modified fatty acyl chain were also observed. The nitrated POPS also showed antiradical potential, demonstrated by the ability to scavenge the ABTS^●+ and DPPH^● radicals. Overall, this in vitro model of nitration based on LC-MS/MS provided additional insights into the nitrated and nitroxidized derivatives of PS and their fragmentation fingerprinting. This information is a valuable tool for targeted analysis of these modified PS in complex biological samples, to further explore the new clues on the antioxidant potential of nitrated POPS.

Persistent metabolic changes in HIV-infected patients during the first year of combination antiretroviral therapy

The HIV-human metabolic relationship is a complex interaction convoluted even more by antiretroviral therapy (cART) and comorbidities. The ability of cART to undo the HIV induced metabolic dysregulation is unclear and under-investigated. Using targeted metabolomics and multiplex immune biomarker analysis, we characterized plasma samples obtained from 18 untreated HIV-1-infected adult patients and compared these to a non-HIV infected (n = 23) control population. The biogenic amine perturbations during an untreated HIV infection implicated altered tryptophan- nitrogen- and muscle metabolism. Furthermore, the lipid profiles of untreated patients were also significantly altered compared to controls. In untreated HIV infection, the sphingomyelins and phospholipids correlated negatively to markers of infection IP-10 and sIL-2R whereas a strong association was found between triglycerides and MCP-1. In a second cohort, we characterized plasma samples obtained from 28 HIV-1-infected adult patients before and 12 months after the start of cART, to investigate the immune-metabolic changes associated with cART. The identified altered immune-metabolic pathways of an untreated HIV infection showed minimal change after 12 months of cART. In conclusion, 12 months of cART impacts only mildly on the metabolic dysregulation underlying an untreated HIV infection and provide insights into the comorbidities present in virally suppressed HIV patients.

Quantification of eicosanoids and their metabolites in biological matrices: a review

The quantification of eicosanoids and their metabolites in biological samples remain an analytical challenge, even though a number of methodologies/techniques have been developed. The major difficulties encountered are related to the oxidation of eicosanoids and their low quantities in biological matrices. Among the known methodologies, liquid chromatography-mass spectrometry (LC-MS/MS) is the standard method for eicosanoid quantification in biological samples. Recently advances have improved the ability to identify and simultaneous quantitate eicosanoids in biological matrices. The present article reviews the quantitative analysis of eicosanoids in different biological matrices by LC and ultra performance liquid chromatography (UPLC)-MS/MS and discusses important aspects to be considered during the collection, sample preparation and the generation of calibration curves required for eicosanoid analysis.

Baseline metabolic profiles of early rheumatoid arthritis patients achieving sustained drug-free remission after initiating treat-to-target tocilizumab, methotrexate, or the combination: insights from systems biology

Background

We previously identified, in newly diagnosed rheumatoid arthritis (RA) patients, networks of co-expressed genes and proteomic biomarkers associated with achieving sustained drug-free remission (sDFR) after treatment with tocilizumab- or methotrexate-based strategies. The aim of this study was to identify, within the same patients, metabolic pathways important for achieving sDFR and to subsequently study the complex interactions between different components of the biological system and how these interactions might affect the therapeutic response in early RA.

Methods

Serum samples were analyzed of 60 patients who participated in the U-Act-Early trial (ClinicalTrials.gov number NCT01034137) and initiated treatment with methotrexate, tocilizumab, or the combination and who were thereafter able to achieve sDFR (n = 37); as controls, patients were selected who never achieved a drug-free status (n = 23). Metabolomic measurements were performed using mass spectrometry on oxidative stress, amine, and oxylipin platforms covering various compounds. Partial least square discriminant analyses (PLSDA) were performed to identify, per strategy arm, relevant metabolites of which the biological pathways were studied. In addition, integrative analyses were performed correlating the previously identified transcripts and proteins with the relevant metabolites.

Results

In the tocilizumab plus methotrexate, tocilizumab, and methotrexate strategy, respectively, 19, 13, and 12 relevant metabolites were found, which were subsequently used for pathway analyses. The most significant pathway in the tocilizumab plus methotrexate strategy was “histidine metabolism” (p < 0.001); in the tocilizumab strategy it was “arachidonic acid metabolism” (p = 0.018); and in the methotrexate strategy it was “arginine and proline metabolism” (p = 0.022). These pathways have treatment-specific drug interactions with metabolites affecting either the signaling of interleukin-6, which is inhibited by tocilizumab, or affecting protein synthesis from amino acids, which is inhibited by methotrexate.

Conclusion

In early RA patients treated-to-target with a tocilizumab- or methotrexate-based strategy, several metabolites were found to be associated with achieving sDFR. In line with our previous observations, by analyzing relevant transcripts and proteins within the same patients, the metabolic profiles were found to be different between the strategy arms. Our metabolic analysis further supports the hypothesis that achieving sDFR is not only dependent on predisposing biomarkers, but also on the specific treatment that has been initiated.

Trial registration

ClinicalTrials.gov, NCT01034137. Registered on January 2010

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1729-2) contains supplementary material, which is available to authorized users.