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Hidradenitis suppurativa (HS) is an inflammatory skin condition that is often considered a systemic disease due to its association with metabolic comorbidity.In this study, we aimed to identify differences in plasma lipidomic profiles between HS patients and control subjects.HS patients were recruited from a tertiary dermatological centre and demographic and comorbidity matched controls from the general population. A targeted lipidomic approach was performed to characterize over 700 lipid species representing 35 lipid classes/sub-classes. Linear regression models adjusted for confounding factors were used to compare the plasma lipidomic profiles of HS patients to controls. Ordinal regression models were used to study the association of lipids with disease activity and severity scores.60 HS patients and 73 control subjects were recruited. Differential levels (p 0.05) of 32 lipid species in HS patients compared to controls were observed, including a decrease in the long chain base d19:1 containing ceramides, and elevation of hydroxyeicosatetraenoic acid (HETE) and dihydroxyeicosatrienoic acid (DHET) oxylipins. These lipids along with several other molecules showed associations with Hurley, HS-PGA and disease activity scores.This study found mild changes in plasma lipidomic profiles, consistent with previous studies showing attenuated metabolomic changes in plasma as opposed to lesional skin. However, a number of lipid species were associated with increasing activity and severity of the disease. Further, the significant lipid species within the same class showed consistent trends of increase or decrease in HS as compared to controls.

Aims/hypothesis We sought to subtype South East Asian patients with type 2 diabetes by de novo cluster analysis on clinical variables, and to determine whether the novel subgroups carry distinct genetic and lipidomic features as well as differential cardio-renal risks. Methods Analysis by k-means algorithm was performed in 687 participants with recent-onset diabetes in Singapore. Genetic risk for beta cell dysfunction was assessed by polygenic risk score. We used a discovery–validation approach for the lipidomics study. Risks for cardio-renal complications were studied by survival analysis. Results Cluster analysis identified three novel diabetic subgroups, i.e. mild obesity-related diabetes (MOD, 45%), mild age-related diabetes with insulin insufficiency (MARD-II, 36%) and severe insulin-resistant diabetes with relative insulin insufficiency (SIRD-RII, 19%). Compared with the MOD subgroup, MARD-II had a higher polygenic risk score for beta cell dysfunction. The SIRD-RII subgroup had higher levels of sphingolipids (ceramides and sphingomyelins) and glycerophospholipids (phosphatidylethanolamine and phosphatidylcholine), whereas the MARD-II subgroup had lower levels of sphingolipids and glycerophospholipids but higher levels of lysophosphatidylcholines. Over a median of 7.3 years follow-up, the SIRD-RII subgroup had the highest risks for incident heart failure and progressive kidney disease, while the MARD-II subgroup had moderately elevated risk for kidney disease progression. Conclusions/interpretation Cluster analysis on clinical variables identified novel subgroups with distinct genetic, lipidomic signatures and varying cardio-renal risks in South East Asian participants with type 2 diabetes. Our study suggests that this easily actionable approach may be adapted in other ethnic populations to stratify the heterogeneous type 2 diabetes population for precision medicine. Graphical abstract

The lysosome is central to the degradation of proteins, carbohydrates, and lipids and their salvage back to the cytosol for reutilization. Lysosomal transporters for amino acids, sugars, and cholesterol have been identified, and the metabolic fates of these molecules in the cytoplasm have been elucidated. Remarkably, it is not known whether lysosomal salvage exists for glycerophospholipids, the major constituents of cellular membranes. By using a transport assay screen against orphan lysosomal transporters, we identified the major facilitator superfamily protein Spns1 that is ubiquitously expressed in all tissues as a proton-dependent lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE) transporter, with LPC and LPE being the lysosomal breakdown products of the most abundant eukaryotic phospholipids, phosphatidylcholine and phosphatidylethanolamine, respectively. Spns1 deficiency in cells, zebrafish embryos, and mouse liver resulted in lysosomal accumulation of LPC and LPE species with pathological consequences on lysosomal function. Flux analysis using stable isotope-labeled phospholipid apolipoprotein E nanodiscs targeted to lysosomes showed that LPC was transported out of lysosomes in an Spns1-dependent manner and re-esterified back into the cytoplasmic pools of phosphatidylcholine. Our findings identify a phospholipid salvage pathway from lysosomes to the cytosol that is dependent on Spns1 and critical for maintaining normal lysosomal function.

Major Facilitator Superfamily Domain containing 2a (Mfsd2a) is a sodium-dependent lysophosphatidylcholine (LPC) transporter expressed at the blood–brain barrier that constitutes the main pathway by which the brain obtains omega-3 fatty acids, such as docosahexanoic acid. Mfsd2a deficiency in humans results in severe microcephaly, underscoring the importance of LPC transport by Mfsd2a for brain development. Biochemical studies and recent cryo-electron microscopy (cryo-EM) structures of Mfsd2a bound to LPC suggest that Mfsd2a transports LPC via an alternating access mechanism between outward-facing and inward-facing conformational states in which the LPC inverts during transport between the outer and inner leaflet of a membrane. However, direct biochemical evidence of flippase activity by Mfsd2a has not been demonstrated and it is not understood how Mfsd2a could invert LPC between the outer and inner leaflet of the membrane in a sodium-dependent manner. Here, we established a unique in vitro assay using recombinant Mfsd2a reconstituted in liposomes that exploits the ability of Mfsd2a to transport lysophosphatidylserine (LPS) coupled with a small molecule LPS binding fluorophore that allowed for monitoring of directional flipping of the LPS headgroup from the outer to the inner liposome membrane. Using this assay, we demonstrate that Mfsd2a flips LPS from the outer to the inner leaflet of a membrane bilayer in a sodium-dependent manner. Furthermore, using cryo-EM structures as guides together with mutagenesis and a cell-based transport assay, we identify amino acid residues important for Mfsd2a activity that likely constitute substrate interaction domains. These studies provide direct biochemical evidence that Mfsd2a functions as a lysolipid flippase.

Nuclear envelope (NE) expansion must be controlled to maintain nuclear shape and function. The nuclear membrane expands massively during ‘closed’ mitosis, enabling chromosome segregation within an intact NE. Phosphatidic acid (PA) and diacylglycerol (DG) can both serve as biosynthetic precursors for membrane lipid synthesis. How they are regulated in time and space and what are the implications of changes in their flux for mitotic fidelity is largely unknown. Using genetically encoded PA and DG probes, we show that DG is depleted from the inner nuclear membrane during mitosis in the fission yeast Schizosaccharomyces pombe, but PA does not accumulate, indicating that it is rerouted to membrane synthesis. We demonstrate that DG-to-PA conversion catalysed by the diacylglycerol kinase Dgk1 and direct glycerophospholipid synthesis from DG by diacylglycerol cholinephosphotransferase / ethanolaminephosphotransferase Ept1 reinforce NE expansion. We conclude that DG consumption through both de novo and the Kennedy pathways fuels a spike in glycerophospholipid biosynthesis, controlling NE expansion, and ultimately, mitotic fidelity.

Supplemental Digital Content is available in the text., Objective: While the risk of acute coronary events has been associated with biological variability of circulating cholesterol, the association with variability of other atherogenic lipids remains less understood. We evaluated the longitudinal variability of 284 lipids and investigated their association with asymptomatic coronary atherosclerosis. Approach and Results: Circulating lipids were extracted from fasting blood samples of 83 community-sampled symptom-free participants (age 41–75 years), collected longitudinally over 6 months. Three types of coronary plaque volume (calcified, lipid-rich, and fibrotic) were quantified using computed tomography coronary angiogram. We first deconvoluted between-subject (CVg) and within-subject (CVw) lipid variabilities. We then tested whether the mean lipid abundance was different across groups categorized by Framingham risk score and plaques phenotypes (lipid-rich, fibrotic, and calcified). Finally, we investigated whether visit-to-visit variability of each lipid was associated with plaque burden. Most lipids (72.5%) exhibited higher CVg than CVw. Among the lipids (n=145) with 1.2-fold higher CVg than CVw, 26 species including glycerides and ceramides were significantly associated with Framingham risk score and the 3 plaque phenotypes (false discovery rate

Accumulation of sphingolipids, especially sphingosines, in the lysosomes is attributed to the pathogenesis of several lysosomal storage diseases. In search for a lysosomal protein that mediates the release of sphingosines, we identified SPNS1 which shares the highest homology to SPNS2, a sphingosine-1-phosphate (S1P) transporter. We generated knockout cells and mice forSpns1and employed lipidomics and metabolomics to identify SPNS1 ligands. We found that knockouts ofSpns1resulted in the accumulation of sphingolipids, including sphingosines in embryonic brains and cell lines. These results suggest that deficiency of SPNS1 affects the clearance of sphingolipids in lysosomes. Biochemical assays demonstrated that sphingosines released from lysosomes required SPNS1. Furthermore, by performing a comprehensive analysis of metabolites from livers of postnatalSpns1knockout mice (gSpns1-cKO), we detected a striking accumulation of lysoglycerophospholipids including LPC, LPE, LPG, and lysoplasmalogens. Interestingly, the release of these lysoglycerophospholipids also required SPNS1. Global knockout ofSpns1(gSpns1-KO) resulted in embryonic lethality between E12.5-E13.5 with developmental defects. Postnatal deletion ofSpns1in mice caused lipid accumulation in the lysosomes and pathological conditions reminiscent of lysosomal storage diseases. These results reveal a critical molecular role of SPNS1 as a transporter for lysosphingolipids and lysoglyerophospholipids from the lysosomes and link its physiological functions with lysosomal storage diseases.SignificancePhospholipids, including glycerophospholipids and sphingolipids, are delivered to the lysosomes for recycling. The hydrolysis of these lipids by lysosomal enzymes generates the corresponding lysoglycerophospholipids, such as lysophosphatidylcholine and lysosphingolipids, such as sphingosine, which are believed to be exported out of the lysosomes for recycling in the cytoplasm. However, it is unknown how these lysophospholipids are released from the lysosomes. The current study utilized genetic knockout models in combination with mass spectrometry analysis of complex phospholipids and sphingolipids to characterize the roles of an orphan lysosomal transporter, namely SPNS1. These findings show that deficiency of SPNS1 results in the accumulation of lysophospholipids in cells and animal tissues and that the transporter is required to transport both lysoglycerophospholipids and lysosphingolipids out of the lysosomes. SPNS1 is critical for early development in mice. Ablation of SPNS1 at postnatal life causes pathological conditions reminiscent of lysosomal storage diseases in mice. These findings reveal the molecular functions of SPNS1 as a lysophospholipid transporter and provide a foundation for studying the transport of these lysolipids in lysosomal storage diseases.

In recent decades, mass spectrometry-based lipidomics has provided a fertile environment for scientific investigations of biochemical and mechanistic processes in biological systems. Notably, this approach has been used to characterize physiological and pathological processes relevant to the central nervous system by identifying changes in the sphingolipid content in the brain, cerebral spinal fluid, and blood plasma. However, despite a preponderance of studies identifying correlations between specific lipids and disease progression, this powerful resource has not yet substantively translated into clinically useful diagnostic assays. Part of this gap may be explained by insufficient depth of the lipidomic profiles in many studies, by lab-to-lab inconsistencies in methodology, and a lack of absolute quantification. These issues limit the identification of specific molecular species and the harmonization of results across independent studies. In this chapter, we contextualize these issues with recent reports identifying correlations between brain lipids and neurological diseases, and we describe the workflow our group has optimized for analysis of the blood plasma sphingolipidome, adapted to the characterization of the human brain tissue.

The bacterial cell membrane is an interface for cell envelope synthesis, protein secretion, virulence factor assembly and a target for host cationic antimicrobial peptides (CAMPs). To resist CAMP killing, several Gram-positive pathogens encode the multiple peptide resistance factor (MprF) enzyme that covalently attaches cationic amino acids to anionic phospholipids in the cell membrane. WhileE. faecalisencodes twomprFparalogs, MprF2 plays a dominant role in conferring resistance to killing by the CAMP human β-defensin 2 (hBD-2) inE. faecalisstrain OG1RF. The goal of the current study is to understand the broader lipidomic and functional roles ofE. faecalis mprF. We analyzed the lipid profiles of parental wild type andmprFmutant strains and show that while ∆mprF2and ∆mprF1∆mprF2mutants completely lacked cationic lysyl-phosphatidylglycerol (L-PG), the ∆mprF1mutant synthesized ∼70% of L-PG compared to the parent. Unexpectedly, we also observed a significant reduction of PG in ∆mprF2and ∆mprF1∆mprF2. In themprFmutants, particularly ∆mprF1∆mprF2, the decrease in L-PG and PG is compensated by an increase in the phosphorus-containing lipid, GPDGDAG, and D-ala-GPDGDAG. These changes were accompanied by a downregulation ofde novofatty acid biosynthesis and an accumulation of long-chain acyl-acyl carrier proteins (long-chain acyl-ACPs), suggesting that the suppression of fatty acid biosynthesis was mediated by the transcriptional repressor FabT. Growth in chemically defined media lacking fatty acids revealed severe growth defects in the ∆mprF1∆mprF2mutant strain, but not the single mutants, which was partially rescued through supplementation with palmitic and stearic acids. Changes in lipid homeostasis correlated with lower membrane fluidity, impaired protein secretion, and increased biofilm formation in both ∆mprF2and ∆mprF1∆mprF2, compared to wild type and ∆mprF1. Collectively, our findings reveal a previously unappreciated role formprFin global lipid regulation and cellular physiology, which could facilitate the development of novel therapeutics targeting MprF.Significance StatementThe cell membrane plays a pivotal role in protecting bacteria against external threats, such as antibiotics. Cationic phospholipids such as lysyl-phosphatidyglycerol (L-PG) resist the action of cationic antimicrobial peptides through electrostatic repulsion. Here we demonstrate that L-PG depletion has several unexpected consequences inEnterococcus faecalis, including a reduction of phosphatidylglycerol (PG), enrichment of a phosphorus-containing lipid, reduced fatty acid synthesis accompanied by an accumulation of long-chain acyl-acyl carrier proteins (long chain acyl-ACPs), lower membrane fluidity, and impaired secretion. These changes are not deleterious to the organism as long as exogenous fatty acids are available for uptake from the culture medium. Our findings suggest an adaptive mechanism involving compensatory changes across the entire lipidome upon removal of a single phospholipid modification. Such adaptations must be considered when devising antimicrobial strategies that target membrane lipids.

Macrophage activation in response to stimulation of Toll-like receptor 4 (TLR4) provides a paradigm for investigating energy metabolism that regulates the inflammatory response. TLR4-mediated pro-inflammatory macrophage activation is characterized by increased glycolysis and altered mitochondrial metabolism, supported by selective amino acid uptake and/or usage. Fatty acid metabolism remains as a highly complex rewiring that accompanies classical macrophage activation. TLR4 activation leads to de novo synthesis of fatty acids, which flux into sphingolipids, complex lipids that form the building blocks of eukaryotic cell membranes and regulate cell function. Here, we review the importance of TLR4-mediated de novo synthesis of membrane sphingolipids in macrophages. We first highlight fatty acid metabolism during TLR4-driven macrophage immunometabolism. We then focus on the temporal dynamics of sphingolipid biosynthesis and emphasize the modulatory role of some sphingolipid species (i.e. sphingomyelins, ceramides and glycosphingolipids) on the pro-inflammatory and pro-resolution phases of LPS/TLR4 activation in macrophages.

Lipids are crucial components of cellular function owing to their role in membrane formation, intercellular signaling, energy storage, and homeostasis maintenance. In the brain, lipid dysregulations have been associated with the etiology and progression of neurodegeneration and other neurological pathologies. Hence, brain lipids are emerging as important potential targets for the early diagnosis and prognosis of neurological diseases. This review aims to highlight the significance and usefulness of lipidomics in diagnosing and treating brain diseases. We explored lipid alterations associated with brain diseases, paying attention to organ-specific characteristics and the functions of brain lipids. As the recent advances in brain lipidomics would have been impossible without advances in analytical techniques, we provide up-to-date information on mass spectrometric approaches and integrative analysis with other omic approaches. Last, we present the potential applications of lipidomics combined with artificial intelligence techniques and interdisciplinary collaborative research for treating brain diseases with clinical heterogeneities.

Asians are underrepresented across many omics databases, thereby limiting the potential of precision medicine in nearly 60% of the global population. As such, there is a pressing need for multi-omics derived quantitative trait loci (QTLs) to fill the knowledge gap of complex traits in populations of Asian ancestry. Here, we provide the first blood-based multi-omics analysis of Asian pregnant women, constituting high-resolution genotyping (N = 1079), DNA methylation (N = 915) and transcriptome profiling (N = 238). Integrative omics analysis identified 219 154 CpGs associated with cis-DNA methylation QTLs (meQTLs) and 3703 RNAs associated with cis-RNA expression QTLs (eQTLs). Ethnicity was the largest contributor of inter-individual variation across all omics datasets, with 2561 genes identified as hotspots of this variation; 395 of these hotspot genes also contained both ethnicity-specific eQTLs and meQTLs. Gene set enrichment analysis of these ethnicity QTL hotspots showed pathways involved in lipid metabolism, adaptive immune system and carbohydrate metabolism. Pathway validation by profiling the lipidome (~480 lipids) of antenatal plasma (N = 752) and placenta (N = 1042) in the same cohort showed significant lipid differences among Chinese, Malay and Indian women, validating ethnicity-QTL gene effects across different tissue types. To develop deeper insights into the complex traits and benefit future precision medicine research in Asian pregnant women, we developed iMOMdb, an open-access database.

Transplacental docosahexaenoic-acid (DHA) supply for fetal development is regulated by placental DHA-lipid metabolism. Both maternal diabetes and obesity are linked to possible decreased fetal circulating DHA and increased placental DHA-lipids. Since myo-inositol is a promising intervention for gestational diabetes (GDM), we aimed to determine whether myo-inositol could rectify perturbations in placental DHA metabolism associated with maternal increasing glycemia and obesity and examine links with birthweight. Term placental villous explants from 17 women representing a range of BMIs and mid-gestational glycemia, were incubated with 13C-labeled-DHA for 48 h, in 0.3 µmol/L (control) or 60 µmol/L myo-inositol. Individual newly synthesized 13C-DHA-labeled lipid species were quantified by liquid-chromatography-mass-spectrometry. Compared with controls, incubation with myo-inositol decreased most 13C-DHA-lipids in placental explants from women with higher BMI or higher glycemia, but increased 13C-DHA-lipids with normal BMI or lower glycemia. Myo-inositol also increased 13C-DHA-labeled lipids in cases of lower birthweight centile, but induced decreases at higher centiles. Myo-inositol therefore lowered DHA-lipids in placenta with high basal placental DHA-lipid production (higher BMI and glycemia) but increased DHA-lipids where basal processing capacity is low. Myo-inositol thus moderates placental DHA metabolism towards a physiological mean which may in turn moderate birthweight.

The rapid increase in lipidomic data has triggered a community-based movement to develop guidelines and minimum requirements for generating, reporting and publishing lipidomic data. The creation of a dynamic checklist summarizing key details of lipidomic analyses using a common language has the potential to harmonize the field by improving both traceability and reproducibility.

In the case of many bacteria, such as

SUMMARYDefects in insulin processing and granule maturation are linked to pancreatic beta-cell failure during type 2 diabetes (T2D). Phosphatidylinositol transfer protein alpha (PITPNA) stimulates activity of phosphatidylinositol (PtdIns) 4-OH kinase to produce sufficient PtdIns-4-phosphate (PtdIns-4-P) in the trans-Golgi network to promote insulin granule maturation. PITPNA in beta-cells of T2D human subjects is markedly reduced suggesting its depletion accompanies beta-cell dysfunction. Conditional deletion of Pitpna in the beta-cells of Ins-Cre;Pitpnaflox/flox mice leads to hyperglycemia resulting from decreased glucose-stimulated insulin secretion (GSIS) and reduced pancreatic beta-cell mass. Furthermore, PITPNA silencing in human islets confirmed its role in PtdIns-4-P synthesis and led to impaired insulin granule maturation and docking, GSIS, and proinsulin processing with evidence of ER stress. Restoration of PITPNA in islets of T2D human subjects reversed these beta-cell defects and identify PITPNA as a critical target linked to beta-cell failure in T2D.

We recently discovered that Mfsd2b, which is the S1P exporter found in blood cells. Here, we report that Mfsd2b is critical for the release of all S1P species in both resting and activated platelets. We show that resting platelets store S1P in the cytoplasm. After activation, this S1P pool is delivered to the plasma membrane, where Mfsd2b is predominantly localized for export. Employing knockout mice of Mfsd2b, we reveal that platelets contribute a minor amount of plasma S1P. Nevertheless, Mfsd2b deletion in whole body or platelets impairs platelet morphology and functions. In particular, Mfsd2b knockout mice show significantly reduced thrombus formation. We show that loss of Mfsd2b affects intrinsic platelet functions as part of remarkable sphingolipid accumulation. These findings indicate that accumulation of sphingolipids including S1P by deletion of Mfsd2b strongly impairs platelet functions, which suggests that the transporter may be a target for the prevention of thrombotic disorders., The mechanisms by which platelets release sphingosine-1-phosphate (S1P) is not well characterized. Here the authors show that Mfsd2b is required for S1P release from both resting and activated platelets and that deletion of Mfsd2b impairs thrombotic functions of platelets.

BackgroundPrognostic biomarkers for patients admitted for a myocardial infarction (MI) episode are of great interest for risk stratification and follow-up care after discharge. Multi-omics analysis is a standard approach for the discovery of diagnostic and prognostic biomarkers, but few studies have evaluated the prognostic potential of molecular markers in combination with echocardiographic imaging variables.MethodsWe measured the plasma proteome and lipidome in patients discharged from an acute MI and followed for secondary outcomes in New Zealand for a median time of 4.85 years (CDCS, N=741 for network inference, N=464 for predictive analysis) and in Singapore for a median time of 2.0 years (IMMACULATE, N=190 for validation). Using a network-based integrative analysis framework iOmicsPASS+, we mapped proteins, lipids, echocardiographic imaging variables and clinical biomarkers to a unified network and identified predictive subnetwork signatures of major adverse cardiac events (MACE) and heart failure hospitalization (HFH) in CDCS, with validation in IMMACULATE.ResultsSpecific plasma proteins and lipids showed direct connections to cardiac imaging variables in the network. The gold standard biomarker, NT-proBNP, remained one of the best prognostic marker of MACE and HFH, but a number of plasma proteins involved in extracellular matrix organization, chemotaxis, inflammation, and apoptosis were also strong predictors of both outcomes. Hub proteins of subnetwork signatures were enriched in the heart, arteries, kidneys, liver and lungs. BMP10, CAPG, EFEMP1, FSTL3, RSPO4, and RELT were those directly connected to the echocardiographic variables and natriuretic peptides. In particular, EFEMP1 and FSTL3 in combination with diastolic function (E/e’) were strongly predictive of HFH in both CDCS (AUC 0.78, 95%CI 0.72-0.83) and IMMACULATE (AUC 0.72, 0.61-0.84).ConclusionsOur integrative analysis revealed competing signatures beyond established biomarkers of post-MI HFH, comprised of plasma proteins correlated with impaired diastolic function after the primary MI episode.

Lipidomics is developing as an important area in biomedical and clinical research. Reliable quantification of lipid species is required for clinical translation of lipidomic studies. Hydrophilic interaction chromatography (HILIC), normal-phase liquid chromatography (NPLC), and supercritical fluid chromatography (SFC) are commonly used techniques in lipidomics and provide class-based separation of lipids. While co-elution of lipid species and their internal standards is an advantage for accurate quantification, it leads to isotopic overlap between species of the same lipid class. In shotgun lipidomics, isotopic correction is typically done based on elemental formulas of precursor ions. In multiple reaction monitoring (MRM) analyses, however, this approach should not be used, as the overall contribution of heavy isotopes to the MRM transitions' intensities depends on their location in the molecule with respect to the fragmentation pattern. We present an algorithm, provided in the R programming language, for isotopic correction in class-based separation using MRM, extracting relevant structural information from MRM transitions to apply adequate isotopic correction factors. Using standards, we show that our algorithm accurately estimates the isotopic contribution of isotopologues to MRM transitions' measured intensities. Using human plasma as an example, we demonstrate the necessity of adequate isotopic correction for accurate quantitation of lipids measured by MRM with class-based chromatographic separation. We show that over a third of the measured phosphatidylcholine species had their intensity corrected by more than 10%. This isotopic correction algorithm and R-implemented application enable a more accurate quantification of lipids in class-based separation-MRM, a prerequisite for successful translation of lipidomic applications.

Contamination from the polymeric material released by vial caps used for sample introduction in liquid chromatography can significantly affect the signal of the analyte of interest. In particular, repeated injections from the same sample vial can enhance this suppressing effect. Multiple injections of the same sample are often used in metabolomics and lipidomics during routine analyses. Here we demonstrate how the presence of contaminant polymers, originating from the vial closures, significantly influences the estimation of the relative amount of endogenous lipids in human plasma. Furthermore, this can negatively impact other operations in mass spectrometric analysis, such as instrument equilibration and tuning or the common use of technical replicates to improve confidence in data interpretation. Our observations provide critical information on how to improve future analyses through the use of appropriate vial caps, solvents, chromatographic separations and equipment.

Purpose Trabeculectomy surgery could affect ocular surface disease (OSD) in several ways, through cessation of long term glaucoma eyedrops, exposure to operative mitomycin C and post-operative eyedrops including corticosteroids and aminoglycosides and reduction in eyelid hygiene measures. Previously we showed the relevance of tear lipid mediators (also referred oxylipins) in OSD. Here, we aim to evaluate changes of these lipids in a post-trabeculectomy cohort. Methods Patients undergoing trabeculectomy were prospectively evaluated and had tear collected using Schirmer's strips, preoperatively and postoperatively at 0.5, 1.0 and 3.0 years. Lipid mediators were analyzed using liquid chromatography mass spectrometry. Results The normalized concentrations of 40 lipid mediators were between 0.1 and 8.0 ng/mL, whereas docosahexaenoic acid (DHA), Arachidonic acid (AA) and eicosapentaenoic acid (EPA) ranged up to a few hundred ng/mL. The concentrations of lipid mediators, except DHA, EPA, and thromboxane (TXB1), showed reduction after surgery. At the last visit, these lipids were significantly reduced by 1/3 to ½, compared to pre-operative values: 8-HETE, 15-HETE, 15-oxoETE, 11-HDoHE, 17-HDoHE, and 20-OH-LTB4. To examine collective changes of lipids, clustering analysis revealed 10 groups of lipids consistent with known metabolic pathways. Results An increase in the level of 2,3-dinor-8-isoPGF2α between 0 and 0.5 year was associated with inferior corneal staining at 0.5 year. In 14 patients who required post-operative needling, six lipid mediators were found to be significantly higher at 1.0 year compared to non-needled patients. Conclusions In this 3-years study, trabeculectomy reduced the tear level of pro-inflammatory lipid mediators. Patients who required needling of the bleb to maintain surgical success may have a chronic underlying inflammatory process associated with fibrosis.

SignificanceWith obesity on the rise, there is a growing appreciation for intracellular lipid droplet (LD) regulation. Here, we show how saturated fatty acids (SFAs) reduce fat storage-inducing transmembrane protein 2 (FIT2)-facilitated, pancreatic β cell LD biogenesis, which in turn induces β cell dysfunction and death, leading to diabetes. This mechanism involves direct acylation of FIT2 cysteine residues, which then marks the FIT2 protein for endoplasmic reticulum (ER)-associated degradation. Loss of β cell FIT2 and LDs reduces insulin secretion, increases intracellular ceramides, stimulates ER stress, and exacerbates diet-induced diabetes in mice. While palmitate and stearate degrade FIT2, unsaturated fatty acids such as palmitoleate and oleate do not, results of which extend to nutrition and diabetes. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) Published version This work was supported by the Singapore Ministry of Education grants under its Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2015-T2-2-087 and MOE2018-T2-1-085 to Y.A.) and Tier 1 (2017-T1-001-220 and 2019-T1-001-059 to Y.A.); the LKCMedicine, Nanyang Technological University Singapore Start-up Grant (P.-O.B.); and the LKCMedicine Healthcare Research Fund (Diabetes Research), established through the generous support of alumni of Nanyang Technological University, Singapore (Y.A.). Q.W.C.H. is supported by the Nanyang President’s Graduate Scholarship award, Nanyang Technological University, Singapore. J.N.F. is supported by Singapore National Research Foundation Fellowship award (NRF-NRFF2016-03). Work in the M.R.W. and F.T. laboratories is supported by grants from the National University of Singapore via the Life Sciences Institute, the National Research Foundation (NRF; NRFI2015-05 and NRFSBP-P4) and the NRF and Agency for Science, Technology and Research (A*STAR) Industry Alignment Fund–Industry Collaborative Project I1901E0040. N.T. is supported by the 1.3.5 Project for Disciplines of Excellence grant, West China Hospital, Sichuan University (ZYGD18017). P.-O.B. is supported by the grants from the Swedish Research Council, the Family Erling-Persson Foundation, the Novo Nordisk Foundation, the Stichting af Jochnick Foundation, the Swedish Diabetes Association, the Scandia Insurance Company Ltd., the Diabetes Research and Wellness Foundation, Berth von Kantzow’s Foundation, the Strategic Research Program in Diabetes at Karolinska Institutet, the ERC-2018-AdG 834860 EYELETS, and the Center of Excellence–International Collaboration Initiative Grant (139180012, China). X.Z. is currently sup-ported by the National Natural Science Foundation of China grant (82070846). G.A.R. was supported by the Wellcome Trust Investigator (WT212625/Z/18/Z) Award, the Medical Research Council Programme grant (MR/R022259/1), and the European Union Horizon2020 research and innovation programme via the Innovative Medicines Initiative 2 Joint Undertaking under Grant Agreement No. 115881 (RHAPSODY).

Background There has been ongoing research impetus to uncover novel blood-based diagnostic and prognostic biomarkers for Alzheimer’s disease (AD), vascular dementia (VaD), and related cerebrovascular disease (CEVD)-associated conditions within the spectrum of vascular cognitive impairment (VCI). Sphingosine-1-phosphates (S1Ps) are signaling lipids which act on the S1PR family of cognate G-protein-coupled receptors and have been shown to modulate neuroinflammation, a process known to be involved in both neurodegenerative and cerebrovascular diseases. However, the status of peripheral S1P in AD and VCI is at present unclear. Methods We obtained baseline bloods from individuals recruited into an ongoing longitudinal cohort study who had normal cognition (N = 80); cognitive impairment, no dementia (N = 160); AD (N = 113); or VaD (N = 31), along with neuroimaging assessments of cerebrovascular diseases. Plasma samples were processed for the measurements of major S1P species: d16:1, d17:1, d18:0, and d18:1, along with pro-inflammatory cytokines interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF). Furthermore, in vitro effects of S1Ps on cytokine expression were also studied in an astrocytoma cell line and in rodent primary astrocytes. Results Of the S1Ps species measured, only d16:1 S1P was significantly reduced in the plasma of VaD, but not AD, patients, while the d18:1 to d16:1 ratios were increased in all cognitive subgroups (CIND, AD, and VaD). Furthermore, d18:1 to d16:1 ratios correlated with levels of IL-6, IL-8, and TNF. In both primary astrocytes and an astroglial cell line, treatment with d16:1 or d18:1 S1P resulted in the upregulation of mRNA transcripts of pro-inflammatory cytokines, with d18:1 showing a stronger effect than d16:1. Interestingly, co-treatment assays showed that the addition of d16:1 reduced the extent of d18:1-mediated gene expression, indicating that d16:1 may function to “fine-tune” the pro-inflammatory effects of d18:1. Conclusion Taken together, our data suggest that plasma d16:1 S1P may be useful as a diagnostic marker for VCI, while the d18:1 to d16:1 S1P ratio is an index of dysregulated S1P-mediated immunomodulation leading to chronic inflammation-associated neurodegeneration and cerebrovascular damage.

Platinum-based therapeutics are used to manage many forms of cancer, but frequently result in peripheral neuropathy. Currently, the only option available to attenuate chemotherapy-induced neuropathy is to limit or discontinue this treatment. Sphingosine 1-phosphate (S1P) is a lipid-based signaling molecule involved in neuroinflammatory processes by interacting with its five cognate receptors: S1P1–5. In this study, using a combination of drug pharmacodynamic analysis in human study participants, disease modeling in rodents, and cell-based assays, we examined whether S1P signaling may represent a potential target in the treatment of chemotherapy-induced neuropathy. To this end, we first investigated the effects of platinum-based drugs on plasma S1P levels in human cancer patients. Our analysis revealed that oxaliplatin treatment specifically increases one S1P species, d16:1 S1P, in these patients. Although d16:1 S1P is an S1P2 agonist, it has lower potency than the most abundant S1P species (d18:1 S1P). Therefore, as d16:1 S1P concentration increases, it is likely to disproportionately activate proinflammatory S1P1 signaling, shifting the balance away from S1P2. We further show that a selective S1P2 agonist, CYM-5478, reduces allodynia in a rat model of cisplatin-induced neuropathy and attenuates the associated inflammatory processes in the dorsal root ganglia, likely by activating stress-response proteins, including ATF3 and HO-1. Cumulatively, the findings of our study suggest that the development of a specific S1P2 agonist may represent a promising therapeutic approach for the management of chemotherapy-induced neuropathy.

Quantitative MS of human plasma lipids is a promising technology for translation into clinical applications. Current MS-based lipidomic methods rely on either direct infusion (DI) or chromatographic lipid separation methods (including reversed phase and hydrophilic interaction LC). However, the use of lipid markers in laboratory medicine is limited by the lack of reference values, largely because of considerable differences in the concentrations measured by different laboratories worldwide. These inconsistencies can be explained by the use of different sample preparation protocols, method-specific calibration procedures, and other experimental and data-reporting parameters, even when using identical starting materials. Here, we systematically investigated the roles of some of these variables in multiple approaches to lipid analysis of plasma samples from healthy adults by considering: 1) different sample introduction methods (separation vs. DI methods); 2) different MS instruments; and 3) between-laboratory differences in comparable analytical platforms. Each of these experimental variables resulted in different quantitative results, even with the inclusion of isotope-labeled internal standards for individual lipid classes. We demonstrated that appropriate normalization to commonly available reference samples (i.e., "shared references") can largely correct for these systematic method-specific quantitative biases. Thus, to harmonize data in the field of lipidomics, in-house long-term references should be complemented by a commonly available shared reference sample, such as NIST SRM 1950, in the case of human plasma.

Transplacental docosahexaenoic-acid (DHA) supply for fetal development is regulated by placental DHA-lipid metabolism. Both maternal diabetes and obesity are linked to possible decreased fetal circulating DHA and increased placental DHA-lipids. Since myo-inositol is a promising intervention for gestational diabetes (GDM), we aimed to determine whether myo-inositol could rectify perturbations in placental DHA metabolism associated with maternal increasing glycemia and obesity and examine links with birthweight. Term placental villous explants from 17 women representing a range of BMIs and mid-gestational glycemia, were incubated with

Complexity is a fundamental feature of biological systems. Omics techniques like lipidomics can simultaneously quantify many thousands of molecules, thereby directly capturing the underlying biological complexity. However, this approach transfers the original biological complexity to the resulting datasets, posing challenges in data reduction and analysis. Aging is a prime example of a process that exhibits complex behaviour across multiple scales of biological organisation. The aging process is characterised by slow, cumulative and detrimental changes that are driven by intrinsic biological stochasticity and mediated through non-linear interactions and feedback within and between these levels of organization (ranging from metabolites, macromolecules, organelles and cells to tissue and organs). Only collectively and over long timeframes do these changes manifest as the exponential increases in morbidity and mortality that define biological aging, making aging a problem more difficult to study than the aetiologies of specific diseases. But aging’s time dependence can also be exploited to extract key insights into its underlying biology. Here we explore this idea by using data on changes in lipid composition across the lifespan of an organism to construct and test a LipidClock to predict biological age in the nematode Caenorhabdits elegans. The LipidClock consist of a feature transformation via Principal Component Analysis followed by Elastic Net regression and yields and Mean Absolute Error of 1.45 days for wild type animals and 4.13 days when applied to mutant strains with lifespans that are substantially different from that of wild type. Gompertz aging rates predicted by the LipidClock can be used to simulate survival curves that are in agreement with those from lifespan experiments.

Complexes formed by the alpha1 N-terminal peptide of alpha-lactalbumin and oleic acid (alpha1-oleate) interact with lipid bilayers. Plasma membrane perturbations trigger tumor cell death but normal differentiated cells are more resistant, and their plasma membranes are less strongly affected. This study examined membrane lipid composition as a determinant of tumor cell reactivity. Bladder cancer tissue showed a higher abundance of unsaturated lipids enriched in phosphatidylcholine, PC (36:4) and PC (38:4), and sphingomyelin, SM (36:1) than healthy bladder tissue, where saturated lipids predominated and the lipid extracts from bladder cancer tissue inhibited the tumoricidal effect of the complex more effectively than healthy tissue extracts. Furthermore, unsaturated PC in solution inhibited tumor cell death, and the complex interacted with giant unilamellar vesicles formed by PC, confirming the affinity of alpha1-oleate for fluid membranes enriched in PC. Quartz Crystal Microbalance with dissipation monitoring (QCM-D) detected a preference of the complex for the liquid-disordered phase, suggesting that the insertion into PC-based membranes and the resulting membrane perturbations are influenced by membrane lipid saturation. The results suggest that the membrane lipid composition is functionally important and that specific unsaturated membrane lipids may serve as "recognition motifs" for broad-spectrum tumoricidal molecules such as alpha1-oleate.

Malassezia are common components of human skin, and as the dominant human skin eukaryotic microbe, they take part in complex microbe–host interactions. Other phylogenetically related fungi (including within Ustilagomycotina) communicate with their plant host through bioactive oxygenated polyunsaturated fatty acids, generally known as oxylipins, by regulating the plant immune system to increase their virulence. Oxylipins are similar in structure and function to human eicosanoids, which modulate the human immune system. This study reports the development of a highly sensitive mass-spectrometry-based method to capture and quantify bioactive oxygenated polyunsaturated fatty acids from the human skin surface and in vitro Malassezia cultures. It confirms that Malassezia are capable of synthesizing eicosanoid-like lipid mediators in vitro in a species dependent manner, many of which are found on human skin. This method enables sensitive identification and quantification of bioactive lipid mediators from human skin that may be derived from metabolic pathways shared between skin and its microbial residents. This enables better cross-disciplinary and detailed studies to dissect the interaction between Malassezia and human skin, and to identify potential intervention points to promote or abrogate inflammation and to improve human skin health.

BackgroundThere is mounting evidence thatin uteroand early life exposures may predispose an individual to metabolic disorders in later life; and dysregulation of lipid metabolism is critical in such outcomes. However, there is limited knowledge about lipid metabolism and factors causing lipid dysregulation in early life that could result in adverse health outcomes in later life. In this study, we aim to understand the lipid metabolism in pregnancy, and from birth to four years.Methods and findingsWe performed comprehensive lipid profiling of 1074 mother-child dyads in the Barwon Infant Study (BIS), a population based pre-birth cohort and measured 776 distinct lipid species across 42 lipid classes using ultra high-performance liquid chromatography (UHPLC). We measured lipids in 1032 maternal serum samples at 28 weeks’ gestation, 893 cord serum samples at birth, 793, 735, and 511 plasma samples at six, twelve months, and four years, respectively. The lipidome differed between mother and newborn and changed markedly with increasing postnatal age. Cord serum was enriched with long chain poly-unsaturated fatty acids (LC-PUFAs), and corresponding cholesteryl esters relative to the maternal serum. Alkenyl-phosphatidylethanolamine species containing LC-PUFAs increased with postnatal age, whereas the corresponding lysophospholipids and triglycerides decreased. We performed regression analyses to investigate the associations of cord serum lipid species with birth factors: gestational age, birth weight, mode of birth and duration of labor. Majority of the cord serum lipids were strongly associated with gestational age and birth weight, with most lipids showing opposing associations. Each mode of birth showed an independent association with cord serum lipids.ConclusionsThere were marked changes in the plasma lipidome over the first four years of life. This study sheds light on lipid metabolism in infancy and early childhood and provide a framework to define the relationship between lipid metabolism and health outcomes in early childhood.Funding StatementThis work was supported by the A*STAR-NHMRC joint call funding (1711624031).

Cancer metabolism is associated with enhanced lipogenesis required for rapid growth and proliferation. However, the magnitude of dysregulation of diverse lipid species mostly remains to be characterized, particularly in rare cancers such as ovarian clear cell carcinoma (OCCC). Here we implemented a robust sample preparation workflow together with targeted LC-MS/MS to identify the lipidomic changes in formalin-fixed paraffin-embedded specimen from OCCC as compared to uninvolved contralateral ovarian tissue. We quantitated 342 lipid species representing 28 lipid classes. We observed differential regulation of diverse lipid species belonging to several glycerophospholipid classes and trihexosylceramide. A number of unsaturated lipid species were increased whereas saturated lipid showed a decrease in OCCC as compared to the controls. We also carried out total fatty acid analysis and observed increase in the levels of several unsaturated fatty acids with concomitant increase in the index of stearoyl-CoA desaturase (SCD) in OCCC. We confirmed the upregulation of SCD, the rate-limiting enzyme for the synthesis of monounsaturated fatty acids, by immunohistochemistry (IHC) assays. Hence, by carrying out mass spectrometry analysis of archival tissue samples, we were able to provide novel insights into the lipidomic alterations of OCCC.

Background:There is mounting evidence that in utero and early life exposures may predispose an individual to metabolic disorders in later life; and dysregulation of lipid metabolism is critical in such outcomes. However, there is limited knowledge about lipid metabolism and factors causing lipid dysregulation in early life that could result in adverse health outcomes in later life. We studied the effect of antenatal factors such as gestational age, birth weight, and mode of birth on lipid metabolism at birth; changes in the circulating lipidome in the first 4 years of life and the effect of breastfeeding in the first year of life. From this study, we aim to generate a framework for deeper understanding into factors effecting lipid metabolism in early life, to provide early interventions for those at risk of developing metabolic disorders including cardiovascular diseases.Methods:We performed comprehensive lipid profiling of 1074 mother-child dyads in the Barwon Infant Study (BIS), a population-based pre-birth cohort and measured 776 distinct lipid features across 39 lipid classes using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). We measured lipids in 1032 maternal serum samples at 28 weeks’ gestation, 893 cord serum samples at birth, 793, 735, and 511 plasma samples at 6, 12 months, and 4 years, respectively. Cord serum was enriched with long chain poly-unsaturated fatty acids (LC-PUFAs), and corresponding cholesteryl esters relative to the maternal serum. We performed regression analyses to investigate the associations of cord serum lipid species with antenatal factors: gestational age, birth weight, mode of birth and duration of labour.Results:The lipidome differed between mother and newborn and changed markedly with increasing child’s age. Alkenylphosphatidylethanolamine species containing LC-PUFAs increased with child’s age, whereas the corresponding lysophospholipids and triglycerides decreased. Majority of the cord serum lipids were strongly associated with gestational age and birth weight, with most lipids showing opposing associations. Each mode of birth showed an independent association with cord serum lipids. Breastfeeding had a significant impact on the plasma lipidome in the first year of life, with up to 17-fold increases in a few species of alkyldiaclylglycerols at 6 months of age.Conclusions:This study sheds light on lipid metabolism in infancy and early childhood and provide a framework to define the relationship between lipid metabolism and health outcomes in early childhood.Funding:This work was supported by the A*STAR-NHMRC joint call funding (1711624031).

Lipid mediators, small molecules involved in regulating inflammation and its resolution, are a class of lipids of wide interest as their levels in blood and tissues may be used to monitor health and disease states or the effect of new treatments. These molecules are present at low levels in biological samples, and an enrichment step is often needed for their detection. We describe a rapid and selective method that uses new low-cost molecularly imprinted (MIP) and non-imprinted (NIP) polymeric sorbents for the extraction of lipid mediators from plasma and tissue samples. The extraction process was carried out in solid-phase extraction (SPE) cartridges, manually packed with the sorbents. After extraction, lipid mediators were quantified by liquid chromatography–tandem mass spectrometry (LC–MSMS). Various parameters affecting the extraction efficiency were evaluated to achieve optimal recovery and to reduce non-specific interactions. Preliminary tests showed that MIPs, designed using the prostaglandin biosynthetic precursor arachidonic acid, could effectively enrich prostaglandins and structurally related molecules. However, for other lipid mediators, MIP and NIP displayed comparable recoveries. Under optimized conditions, the recoveries of synthetic standards ranged from 62% to 100%. This new extraction method was applied to the determination of the lipid mediators concentration in human plasma and mouse tissues and compared to other methods based on commercially available cartridges. In general, the methods showed comparable performances. In terms of structural specificity, our newly synthesized materials accomplished better retention of prostaglandins (PGs), hydroxydocosahexaenoic acid (HDoHE), HEPE, hydroxyeicosatetraenoic acids (HETE), hydroxyeicosatrienoic acid (HETrE), and PUFA compounds, while the commercially available Strata-X showed a higher recovery for dihydroxyeicosatetraenoic acid (diHETrEs). In summary, our results suggest that this new material can be successfully implemented for the extraction of lipid mediators from biological samples. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Sphingosine-1-phosphate (S1P) is a potent lipid mediator that is secreted by several cell types. We recently showed that Mfsd2b is an S1P transporter from hematopoietic cells that contributes approximately 50% plasma S1P. Here we report the characterization of compound deletion of Mfsd2b and Spns2, another S1P transporter active primarily in endothelial cells. Global deletion of Mfsd2b and Spns2 (global double knockout [gDKO]) results in embryonic lethality beyond embryonic day 14.5 (E14.5), with severe hemorrhage accompanied by defects of tight junction proteins, indicating that Mfsd2b and Spns2 provide S1P for signaling, which is essential for blood vessel integrity. Compound postnatal deletion of Mfsd2b and Spns2 using Mx1Cre (ctDKO-Mx1Cre) results in maximal 80% reduction of plasma S1P. ctDKO-Mx1Cre mice exhibit severe susceptibility to anaphylaxis, indicating that S1P from Mfsd2b and Spns2 is indispensable for vascular homeostasis. Our results show that S1P export from Mfsd2b and Spns2 is essential for developing and mature vasculature.