Multiple Lipid Species Research Articles

Multivariate genetic analysis of human plasma triacylglycerols and diacylglycerols and their link to cardiovascular disease

Background and Aims: Human plasma lipidome, composed of thousands of lipid species, captures information beyond traditional lipids. Genome-wide association studies (GWAS) of individual lipid species (univariate analysis) have identified many lipid-associated loci, however multivariate analysis of multiple lipid species improves statistical power and could help identify additional lipid loci. We performed multivariate analysis using lipidome data.

Fabricating Multi-Component Lipid Nanotube Networks Using the Gliding Kinesin Motility Assay.

Lipid nanotube (LNT) networks represent an in vitro model system for studying molecular transport and lipid biophysics with relevance to the ubiquitous lipid tubules found in eukaryotic cells. However, in vivo LNTs are highly non-equilibrium structures that require chemical energy and molecular motors to be assembled, maintained, and reorganized. Furthermore, the composition of in vivo LNTs is complex, comprising of multiple different lipid species. Typical methods to extrude LNTs are both time- and labor-intensive, and they require optical tweezers, microbeads, and micropipettes to forcibly pull nanotubes from giant lipid vesicles. Presented here is a protocol for the gliding motility assay (GMA), in which large scale LNT networks are rapidly generated from giant unilamellar vesicles (GUVs) using kinesin-powered microtubule motility. Using this method, LNT networks are formed from a wide array of lipid formulations that mimic the complexity of biological LNTs, making them increasingly useful for in vitro studies of lipid biophysics and membrane-associated transport. Additionally, this method is capable of reliably producing LNT networks in a short time (<30 min) using commonly used laboratory equipment. LNT network characteristics such as length, width, and lipid partitioning are also tunable by altering the lipid composition of the GUVs used for fabricating the networks.

Spontaneous lipid binding to the nicotinic acetylcholine receptor in a native membrane.

The nicotinic acetylcholine receptor (nAChR) and other pentameric ligand-gated ion channels are native to neuronal membranes with an unusual lipid composition. While it is well-established that these receptors can be significantly modulated by lipids, the underlying mechanisms have been primarily studied in model membranes with few lipid species. Here, we use coarse-grained molecular dynamics simulation to probe specific binding of lipids in a complex quasi-neuronal membrane. We ran a total of 50 μs of simulations of a single nAChR in a membrane composed of 36 species of lipids. Competition between multiple lipid species produces a complex distribution. We find that overall, cholesterol selects for concave inter-subunit sites and polyunsaturated fatty acids select for convex M4 sites, while monounsaturated and saturated lipids are unenriched in the nAChR boundary. We propose the "density-threshold affinity" as a metric calculated from continuous density distributions, which reduces to a standard affinity in two-state binding. We find that the density-threshold affinity for M4 weakens with chain rigidity, which suggests that flexible chains may help relax packing defects caused by the conical protein shape. For any site, PE headgroups have the strongest affinity of all phospholipid headgroups, but anionic lipids still yield moderately high affinities for the M4 sites as expected. We observe cooperative effects between anionic headgroups and saturated chains at the M4 site in the inner leaflet. We also analyze affinities for individual anionic headgroups. When combined, these insights may reconcile several apparently contradictory experiments on the role of anionic phospholipids in modulating nAChR.

Biophysical impact of sphingosine and other abnormal lipid accumulation in Niemann-Pick disease type C cell models

Niemann-Pick disease type C (NPC) is a complex and rare pathology, which is mainly associated to mutations in the NPC1 gene. This disease is phenotypically characterized by the abnormal accumulation of multiple lipid species in the acidic compartments of the cell. Due to the complexity of stored material, a clear molecular mechanism explaining NPC pathophysiology is still not established. Abnormal sphingosine accumulation was suggested as the primary factor involved in the development of NPC, followed by the accumulation of other lipid species. To provide additional mechanistic insight into the role of sphingosine in NPC development, fluorescence spectroscopy and microscopy were used to study the biophysical properties of biological membranes using different cellular models of NPC. Addition of sphingosine to healthy CHO-K1 cells, in conditions where other lipid species are not yet accumulated, caused a rapid decrease in plasma membrane and lysosome membrane fluidity, suggesting a direct effect of sphingosine rather than a downstream event. Changes in membrane fluidity caused by addition of sphingosine were partially sustained upon impaired trafficking and metabolization of cholesterol in these cells, and could recapitulate the decrease in membrane fluidity observed in NPC1 null Chinese Hamster Ovary (CHO) cells (CHO-M12) and in cells with pharmacologically induced NPC phenotype (treated with U18666A). In summary, these results show for the first time that the fluidity of the membranes is altered in models of NPC and that these changes are in part caused by sphingosine, supporting the role of this lipid in the pathophysiology of NPC.

Plasma Lipidomic Profiles and Risk of Diabetes: 2 Prospective Cohorts of HIV-Infected and HIV-Uninfected Individuals.

Antiretroviral therapy (ART) use is associated with disrupted lipid and glucose metabolism in people with HIV infection. We aimed to identify plasma lipid species associated with risk of diabetes in the context of HIV infection. We profiled 211 plasma lipid species in 491 HIV-infected and 203 HIV-uninfected participants aged 35 to 55 years from the Women's Interagency HIV Study and the Multicenter AIDS Cohort Study. Cox proportional hazards model was used to examine associations between baseline lipid species and incident diabetes (166 diabetes cases were identified during a median follow-up of 12.6 years). We identified 11 lipid species, representing independent signals for 8 lipid classes/subclasses, associated with risk of diabetes (P < 0.05 after FDR correction). After adjustment for multiple covariates, cholesteryl ester (CE) (22:4), lysophosphatidylcholine (LPC) (18:2), phosphatidylcholine (PC) (36:4), phosphatidylcholine plasmalogen (34:3), and phosphatidylethanolamine (PE) (38:2) were associated with decreased risk of diabetes (HRs = 0.70 to 0.82 per SD increment), while diacylglycerol (32:0), LPC (14:0), PC (38:3), PE (36:1), and triacylglycerol (50:1) were associated with increased risk of diabetes (HRs = 1.26 to 1.56 per SD increment). HIV serostatus did not modify any lipid-diabetes associations; however, most of these lipid species were positively associated with HIV and/or ART use, including 3 diabetes-decreased ( CE [22:4], LPC [18:2], PE [38:2]) and all 5 diabetes-increased lipid species. This study identified multiple plasma lipid species associated with incident diabetes. Regardless of the directions of their associations with diabetes, most diabetes-associated lipid species were elevated in ART-treated people with HIV infection. This suggests a complex role of lipids in the link between ART and diabetes in HIV infection.

High Glucosylceramides and Low Anandamide Contribute to Sensory Loss and Pain in Parkinson's Disease.

Parkinson's disease (PD) causes chronic pain in two-thirds of patients, in part originating from sensory neuropathies. The aim of the present study was to describe the phenotype of PD-associated sensory neuropathy and to evaluate its associations with lipid allostasis, the latter motivated by recent genetic studies associating mutations of glucocerebrosidase with PD onset and severity. Glucocerebrosidase catalyzes the metabolism of glucosylceramides. We used quantitative sensory tests, pain ratings, and questionnaires and analyzed plasma levels of multiple bioactive lipid species using targeted lipidomic analyses. The study comprised 2 sets of patients and healthy controls: the first 128 Israeli PD patients and 224 young German healthy controls for exploration, the second 50/50 German PD patients and matched healthy controls for deeper analyses. The data showed a 70% prevalence of PD pain and sensory neuropathies with a predominant phenotype of thermal sensory loss plus mechanical hypersensitivity. Multivariate analyses of lipids revealed major differences between PD patients and healthy controls, mainly originating from glucosylceramides and endocannabinoids. Glucosylceramides were increased, whereas anandamide and lysophosphatidic acid 20:4 were reduced, stronger in patients with ongoing pain and with a linear relationship with pain intensity and sensory losses, particularly for glucosylceramide 18:1 and glucosylceramide 24:1. Our data suggest that PD-associated sensory neuropathies and PD pain are in part caused by accumulations of glucosylceramides, raising the intriguing possibility of reducing PD pain and sensory loss by glucocerebrosidase substituting or refolding approaches. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

376-P: Analysis of the Fasting and Postprandial Plasma Metabolome Reveals Metabolic Signatures of Postbariatric Hypoglycemia

One severe complication of gastrointestinal and bariatric surgery is post-bariatric hypoglycemia (PBH). Affected patients may develop severe hypoglycemia, typically 1-3 hours after meals. While exaggerated postprandial incretin hormone and insulin secretion has been implicated, additional contributors to hypoglycemia remain uncertain. We performed untargeted semiquantitative metabolomic analysis of plasma samples collected in the fasting state and at 30 and 120 minutes after a liquid mixed meal (Ensure) in 13 individuals with PBH post-RYGB, 10 asymptomatic post-RYGB, and 8 overweight/obese individuals without history of gastrointestinal surgery. Multiple analytes were reduced in the fasting state in PBH, including 10 amino acids (Leu, Ile, Val, Ala, Phe, Tyr, Met, Trp, Thr, Asn, nominal p&amp;lt;0.05 vs. asymptomatic, FC -1.2 to -1.4), multiple lipid species (C22:6 LPC, C22:6 LPE, C20:4 LPE, C56:7 TAG, C54:5 TAG, C50:5 TAG, p&amp;lt;0.05 vs. asymptomatic,FC -1.3 to -1.5). We also observed robust reduction (2-10 fold, p&amp;lt;0.05) in multiple tryptophan pathway metabolites, including kynurenic acid, xanthurenate, and serotonin. Markers of insulin resistance and T2D risk, such as 2-aminoadipate and alpha-hydroxybutyrate, and multiple B complex vitamins (B3, B5, B6) were also decreased in PBH in the fasting state. By contrast, tricarboxylic acid (TCA) cycle intermediates such as aconitate, isocitrate, succinate and malate and the ketone beta-hydroxybutyrate were all increased in PBH (p&amp;lt;0.05). In summary, we identify several metabolic signatures of PBH including reduction in multiple circulating AA, lipid species, and tryptophan intermediates as well as increased TCA cycle intermediates. Together these could potentially contribute to alterations in glucose metabolic flux in both the fasting and postprandial state in individuals with PBH. Disclosure R. Ferraz-Bannitz: None. C.M. Mulla: None. J. Dreyfuss: None. H. Pan: None. M. Patti: Consultant; Self; Fractyl Laboratories, Inc. Research Support; Self; Dexcom, Inc., Xeris Pharmaceuticals, Inc. Other Relationship; Self; Academy of Nutrition and Dietetics, American Diabetes Association, American Society of Metabolic and Bariatric Surgery, Endocrine Society, Insulet Corporation, King Abdullah International Medical Research Center, SUNY Downstate. Funding National Institutes of Health (R01DK121995, P30DK046200)

Defining how multiple lipid species interact with inward rectifier potassium (Kir2) channels

Protein-lipid interactions are a key element of the function of many integral membrane proteins. These potential interactions should be considered alongside the complexity and diversity of membrane lipid composition. Inward rectifier potassium channel (Kir) Kir2.2 has multiple interactions with plasma membrane lipids: Phosphatidylinositol (4, 5)-bisphosphate (PIP2) activates the channel; a secondary anionic lipid site has been identified, which augments the activation by PIP2; and cholesterol inhibits the channel. Molecular dynamics simulations are used to characterize in molecular detail the protein-lipid interactions of Kir2.2 in a model of the complex plasma membrane. Kir2.2 has been simulated with multiple, functionally important lipid species. From our simulations we show that PIP2 interacts most tightly at the crystallographic interaction sites, outcompeting other lipid species at this site. Phosphatidylserine (PS) interacts at the previously identified secondary anionic lipid interaction site, in a PIP2 concentration-dependent manner. There is interplay between these anionic lipids: PS interactions are diminished when PIP2 is not present in the membrane, underlining the need to consider multiple lipid species when investigating protein-lipid interactions.

Brain region-specific amyloid plaque-associated myelin lipid loss, APOE deposition and disruption of the myelin sheath in familial Alzheimer's disease mice.

There is emerging evidence that amyloid beta (Aβ) aggregates forming neuritic plaques lead to impairment of the lipid-rich myelin sheath and glia. In this study, we examined focal myelin lipid alterations and the disruption of the myelin sheath associated with amyloid plaques in a widely used familial Alzheimer's disease (AD) mouse model; 5xFAD. This AD mouse model has Aβ42 peptide-rich plaque deposition in the brain parenchyma. Matrix-assisted laser desorption/ionization imaging mass spectrometry of coronal brain tissue sections revealed focal Aβ plaque-associated depletion of multiple myelin-associated lipid species including sulfatides, galactosylceramides, and specific plasmalogen phopshatidylethanolamines in the hippocampus, cortex, and on the edges of corpus callosum. Certain phosphatidylcholines abundant in myelin were also depleted in amyloid plaques on the edges of corpus callosum. Further, lysophosphatidylethanolamines and lysophosphatidylcholines, implicated in neuroinflammation, were found to accumulate in amyloid plaques. Double staining of the consecutive sections with fluoromyelin and amyloid-specific antibody revealed amyloid plaque-associated myelin sheath disruption on the edges of the corpus callosum which is specifically correlated with plaque-associated myelin lipid loss only in this region. Further, apolipoprotein E, which is implicated in depletion of sulfatides in AD brain, is deposited in all the Aβ plaques which suggest apolipoprotein E might mediate sulfatide depletion as a consequence of an immune response to Aβ deposition. This high-spatial resolution matrix-assisted laser desorption/ionization imaging mass spectrometry study in combination with (immuno) fluorescence staining of 5xFAD mouse brain provides new understanding of morphological, molecular and immune signatures of Aβ plaque pathology-associated myelin lipid loss and myelin degeneration in a brain region-specific manner. Read the Editorial Highlight for this article on page 7.

Lipidome-wide 13C flux analysis: a novel tool to estimate the turnover of lipids in organisms and cultures

Lipid metabolism plays an important role in the regulation of cellular homeostasis. However, because it is difficult to measure the actual rates of synthesis and degradation of individual lipid species, lipid compositions are often used as a surrogate to evaluate lipid metabolism even though they provide only static snapshots of the lipodome. Here, we designed a simple method to determine the turnover rate of phospholipid and acylglycerol species based on the incorporation of 13C6-glucose combined with LC-MS/MS. We labeled adult Drosophila melanogaster with 13C6-glucose that incorporates into the entire lipidome, derived kinetic parameters from mass spectra, and studied effects of deletion of CG6718, the fly homolog of the calcium-independent phospholipase A2β, on lipid metabolism. Although 13C6-glucose gave rise to a complex pattern of 13C incorporation, we were able to identify discrete isotopomers in which 13C atoms were confined to the glycerol group. With these isotopomers, we calculated turnover rate constants, half-life times, and fluxes of the glycerol backbone of multiple lipid species. To perform these calculations, we estimated the fraction of labeled molecules in glycerol-3-phosphate, the lipid precursor, by mass isotopomer distribution analysis of the spectra of phosphatidylglycerol. When we applied this method to D. melanogaster, we found a range of lipid half-lives from 2 to 200 days, demonstrated tissue-specific fluxes of individual lipid species, and identified a novel function of CG6718 in triacylglycerol metabolism. This method provides fluxomics-type data with significant potential to improve the understanding of complex lipid regulation in a variety of research models.

Icosabutate Exerts Beneficial Effects Upon Insulin Sensitivity, Hepatic Inflammation, Lipotoxicity, and Fibrosis in Mice.

Icosabutate is a structurally engineered eicosapentaenoic acid derivative under development for nonalcoholic steatohepatitis (NASH). In this study, we investigated the absorption and distribution properties of icosabutate in relation to liver targeting and used rodents to evaluate the effects of icosabutate on glucose metabolism, insulin resistance, as well as hepatic steatosis, inflammation, lipotoxicity, and fibrosis. The absorption, tissue distribution, and excretion of icosabutate was investigated in rats along with its effects in mouse models of insulin resistance (ob/ob) and metabolic inflammation/NASH (high‐fat/cholesterol‐fed APOE*3Leiden.CETP mice) and efficacy was compared with synthetic peroxisome proliferator‐activated receptor α (PPAR‐α) (fenofibrate) and/or PPAR‐γ/(α) (pioglitazone and rosiglitazone) agonists. Icosabutate was absorbed almost entirely through the portal vein, resulting in rapid hepatic accumulation. Icosabutate demonstrated potent insulin‐sensitizing effects in ob/ob mice, and unlike fenofibrate or pioglitazone, it significantly reduced plasma alanine aminotransferase. In high‐fat/cholesterol‐fed APOE*3Leiden.CETP mice, icosabutate, but not rosiglitazone, reduced microvesicular steatosis and hepatocellular hypertrophy. Although both rosiglitazone and icosabutate reduced hepatic inflammation, only icosabutate elicited antifibrotic effects in association with decreased hepatic concentrations of multiple lipotoxic lipid species and an oxidative stress marker. Hepatic gene‐expression analysis confirmed the changes in lipid metabolism, inflammatory and fibrogenic response, and energy metabolism, and revealed the involved upstream regulators. In conclusion, icosabutate selectively targets the liver through the portal vein and demonstrates broad beneficial effects following insulin sensitivity, hepatic microvesicular steatosis, inflammation, lipotoxicity, oxidative stress, and fibrosis. Icosabutate therefore offers a promising approach to the treatment of both dysregulated glucose/lipid metabolism and inflammatory disorders of the liver, including NASH.

Association of Lipidomic Profiles With Progression of Carotid Artery Atherosclerosis in HIV Infection

Lipid metabolism disruption and excess risk of cardiovascular disease (CVD) have been observed in HIV-infected individuals, but the associations among HIV infection, plasma lipidome, and CVD risk have not been well understood. To evaluate plasma lipidomic profiles and their associations with carotid artery atherosclerosis in individuals with HIV and individuals without HIV. Prospective analysis in the Women's Interagency HIV Study and Multicenter AIDS Cohort Study during a 7-year follow-up (from 2004-2006 to 2011-2013) at multicenter HIV cohorts in the United States. The study included 737 participants aged 35 to 55 years (520 with HIV and 217 without HIV) without CVD or carotid artery plaque at baseline. Data were analyzed between April 2017 and July 2019. Two hundred eleven plasma lipid species. Poisson regression was used to examine the associations of baseline lipid species with risk of plaque measured by repeated B-mode carotid artery ultrasonography imaging. Of the 737 included participants, 398 (54%) were women, 351 (48%) were African American (non-Hispanic), 156 of 737 (21%) were nonwhite Hispanic, and the mean (SD) age was 45 (6) years. After adjusting for demographic and behavioral factors, we identified 12 lipid species, representing independent signals for 10 lipid classes, associated with risk of plaque. Nine lipid species remained significant after further adjusting for conventional CVD risk factors, although many of them showed moderate to high association with conventional blood lipids (eg, total and low-density lipoprotein cholesterols and triglycerides). Cholesteryl ester (16:1) (risk ratio [RR] per standard deviation, 1.28; 95% CI, 1.08-1.52), ceramide (16:0) (RR, 1.29; 95% CI, 1.02-1.63), lysophosphatidylcholine (20:4) (RR, 1.28; 95% CI, 1.05-1.58), lysophosphatidylethanolamine (16:0) (RR, 1.28; 95% CI, 1.05-1.57), phosphatidylethanolamine (38:6) (RR, 1.33; 95% CI, 1.08-1.64), phosphatidylethanolamine-plasmalogen (36:2) (RR, 1.25; 95% CI, 1.04-1.52), phosphatidylserine-plasmalogen (36:3) (RR, 1.19; 95% CI, 1.00-1.43), and triacylglycerol (54:6) (RR, 1.26; 95% CI, 1.04-1.54) were associated with increased risk of plaque, while phosphatidylcholine (36:4) (RR, 0.65; 95% CI, 0.54-0.77) was associated with decreased risk of plaque. Most of these plaque-increased lipid species showed higher levels in individuals with HIV, particularly among individuals with HIV using antiretroviral therapy compared with individuals without HIV. Network analysis identified 9 lipid modules, and 2 modules composed of triacylglycerols and phosphatidylcholines with long and unsaturated acyl chains, respectively, showed the strongest associations with increased risk of plaque. This study identified multiple plasma lipid species associated with carotid artery atherosclerosis, and alterations in these lipid species might be associated with HIV infection and antiretroviral therapy. Our data suggest unfavorable associations of long-chain and unsaturated triacylglycerols and phosphatidylcholines with carotid artery plaque formation.

Cholesterol Acceptors Regulate the Lipidome of Macrophage Foam Cells.

Arterial foam cells are central players of atherogenesis. Cholesterol acceptors, apolipoprotein A-I (apoA-I) and high-density lipoprotein (HDL), take up cholesterol and phospholipids effluxed from foam cells into the circulation. Due to the high abundance of cholesterol in foam cells, most previous studies focused on apoA-I/HDL-mediated free cholesterol (FC) transport. However, recent lipidomics of human atherosclerotic plaques also identified that oxidized sterols (oxysterols) and non-sterol lipid species accumulate as atherogenesis progresses. While it is known that these lipids regulate expression of pro-inflammatory genes linked to plaque instability, how cholesterol acceptors impact the foam cell lipidome, particularly oxysterols and non-sterol lipids, remains unexplored. Using lipidomics analyses, we found cholesterol acceptors remodel foam cell lipidomes. Lipid subclass analyses revealed various oxysterols, sphingomyelins, and ceramides, species uniquely enriched in human plaques were significantly reduced by cholesterol acceptors, especially by apoA-I. These results indicate that the function of lipid-poor apoA-I is not limited to the efflux of cholesterol and phospholipids but suggest that apoA-I serves as a major regulator of the foam cell lipidome and might play an important role in reducing multiple lipid species involved in the pathogenesis of atherosclerosis.

Altered Metabolic Profile of Triglyceride-Rich Lipoproteins in Gut-Lymph of Rodent Models of Sepsis and Gut Ischemia-Reperfusion Injury.

Triglyceride-rich lipoproteins are important in dietary lipid absorption and subsequent energy distribution in the body. Their importance in the gut-lymph may have been overlooked in sepsis, the most common cause of critical illness, and in gut ischemia-reperfusion injury, a common feature of many critical illnesses. We aimed to undertake an exploratory study of triglyceride-rich lipoprotein fractions in gut-lymph using untargeted metabolic profiling to identify altered metabolites in sepsis or gut ischemia-reperfusion. The gut-lymph was collected from rodent sham, sepsis, and gut ischemia-reperfusion models. The triglyceride-rich lipoprotein-enriched fractions isolated from the gut-lymph were subjected to a dual metabolomics analysis approach: non-polar metabolite analysis by ultra-high performance liquid chromatography-mass spectrometry and polar metabolite analysis by gas chromatography-mass spectrometry. The metabolite analysis of gut-lymph triglyceride-rich lipoprotein fractions revealed a significant increase (FDR-adjusted P value < 0.05) in myo-inositol in the sepsis group and monoacylglycerols [(18:1) and (18:2)] in gut ischemia-reperfusion. There were no significantly increased specific metabolites in the lipoprotein-enriched fractions of both sepsis and gut ischemia-reperfusion. In contrast, there was a widespread decrease in multiple lipid species in sepsis (35 out of 190; adjusted P < 0.05), but not in the gut ischemia-reperfusion. Increased levels of myo-inositol and monoacylglycerols, and decreased multiple lipid species in the gut-lymph triglyceride-rich lipoprotein fraction could be candidates for new biomarkers and/or involved in the progression of sepsis and gut ischemia-reperfusion pathobiology.

Curvature‐Induced Sorting of Lipids in Plasma Membrane Tethers

AbstractMembrane curvature controls the spatial organization and activity of cells. Lipid sorting in cell membranes can be explained by matching lipid molecular shape to regions of different curvatures. A molecular view of curvature‐induced lipid sorting is obtained using coarse‐grained molecular dynamics. A model membrane consisting of an asymmetric bilayer of multiple lipid species is simulated. Curvature is induced by pulling a tether, that is, a bilayer nanotube, from a flat membrane. Pulling is performed both from the inner and outer leaflets, corresponding to directions in and out of the cell. Redistribution of different lipid types between the tether and the bilayer is observed, leading to spatial variations in the composition of both leaflets, and, in turn, softening of the tether. Depending on the direction of pulling, the lipid distributions and the tether properties differ. Formation of a tether from the planar membrane thus induces lipid sorting without phase separation.

Advancement in Atopic Dermatitis Research Through the Use of a Novel Skin Tape Strip Mass Spectrometry Based Processing Protocol

Allergic skin diseases, including Atopic Dermatitis (AD), severely impair the quality of life of affected patients. AD development is linked to a damaged skin barrier function that can precede clinical AD manifestations by many months. Currently there are no effective tools to predict the development of AD or to characterize the efficacy of applied therapy. Therefore, novel approaches to advance mechanistic understanding of AD as well as clinical management of AD and related skin diseases are needed.We have developed a novel protocol that allows the assessment of skin stratum corneum lipid species and filaggrin breakdown products using minimally invasive tape stripping in combination with liquid chromatography tandem mass spectrometry. Our approach requires only two tape strips to provide quantitative data on multiple lipid species as well as on the degradation products of filaggrin, a major skin protein responsible for skin barrier, pH and moisturizing properties. The hallmark of our approach is in the ability to normalize targeted mass spectrometric data per sample total protein content that was never done before. Our approach also allows to use the same sample for proteomics studies. We have applied our novel protocol to evaluate the difference between lesional and non‐lesional stratum corneum of AD subjects and to compare AD subjects with healthy individuals. The comparison of stratum corneum from 25 healthy adult subjects and 30 AD adult patients using our methodology confirmed previously known information about the shift towards short chain ceramide species in AD lesional skin and also revealed novel factors associated with AD development. Thus, total levels of sphingomyelins, and especially those with short chain fatty acids, were found to be increased several fold in atopic lesional skin. Furthermore, lysophosphatidylcholines demonstrated a profound redistribution towards the prevalence of short chain species not only in lesional but also in non‐lesional skin of AD subjects. These novel findings suggest a global shift in fatty acid biosynthesis that might be triggered by hyperactivated type 2 immune response. In fact, the RNAseq analysis performed on stratum corneum from same subjects revealed the downregulation of expression of fatty acid elongases ELOVL3 and ELOVL6 that may explain the observed global redistribution of the long chain and short chain lipids. Furthermore, the modeling of the effect of type 2 cytokines on sphingolipids using human differentiated keratinocytes in vitro confirmed the ability of type 2 cytokines IL‐4 and IL‐13 to provoke similar changes in sphingolipids. Our current ongoing studies further validate the power of the developed methodology and the value of lysophosphatidylcholines as biomarkers of atopic disease.In conclusion, skin tape stripping in conjunction with our unique processing protocol and targeted mass spectrometric methodology opens novel possibilities in clinical research by unveiling novel biomarkers of skin diseases and by allowing clinical studies in the skin using minimally invasive methodology.Support or Funding InformationNIH/NIAID grant U19 AI117673, NIH/NIAMS grant R01 AR41256This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Screening of stationary phase selectivities for global lipid profiling by ultrahigh performance supercritical fluid chromatography

The performance of seven sub-2-μm particle packed columns (2-picolylamine, 2-PIC; charged surface hybrid fluoro-phenyl, CSH-FP; high strength silica C18 SB, HSS-C18; diethylamine, DEA; 1-aminoanthracene, 1-AA; high density diol and ethylene bridged hybrid; BEH) was examined for lipid separation in ultra-high performance supercritical fluid chromatography (UHPSFC) coupled to quadrupole time-of-flight mass spectrometry. Based on the results of the column screening a method for profiling of multiple lipid species from the major lipid classes was developed.Stationary phases containing β-hydroxy amines, i.e. 1-AA, DEA and 2-PIC, yielded strong retention and poor peak shapes of zwitterionic lipids with primary amine groups, such as phosphatidylserines, phosphatidylethanolamines and its lyso forms. The BEH and HSS-C18 columns showed strong retention of polar and nonpolar lipids, respectively. The Diol column retained the majority of major lipid classes and also produced symmetric peaks. In addition, this column also produced the highest resolution within and between major lipid classes. An injection solvent composed of methanol:chloroform (1:2, v:v) and the addition of 20 mM ammonium formate in the mobile phase improved chromatographic separation and mass spectrometry detection in comparison to ammonium acetate or absence of additive. Finally, chromatographic and mass spectrometric parameters were optimized for the Diol column using a design of experiments approach. The separation mechanism on the Diol column depended on the lipid functionality and the length and degree of unsaturation of the acyl groups. The developed method could resolve 18 lipid classes and multiple lipids within each class, from blood serum and brain tissue in 11 min.

An Integrated Lipidomics and Phenotype Study Reveals Protective Effect and Biochemical Mechanism of Traditionally Used Alisma orientale Juzepzuk in Chronic Kidney Disease.

Alisma orientale Juzepzuk (AO) is widely used for various diuretic and nephropathic treatments in traditional Chinese medicines (TCM). In a clinical setting, AO is used as both a lipid-lowering and tubular interstitial fibrosis agent. However, the mechanisms of AO for the treatment of renal interstitial fibrosis and abnormal lipid metabolism are not well-understood. In this study, pharmacological and UPLC-HDMS-based lipidomic approaches were employed to investigate the lipid-lowering and tubular interstitial fibrosis effect of AO on rats with adenine-induced chronic kidney disease (CKD). Rats with CKD showed increased serum levels of creatinine and urea, tubular damage, and tubular interstitial fibrosis. Moreover, multiple lipid species were identified in CKD rats. Among these lipids, polyunsaturated fatty acid, eicosapentaenoic acid, 8,9-epoxyeicosatrienoic acid, and docosahexaenoic acid levels were significantly decreased in CKD rats compared to control rats. In CKD rats, up-regulation of the NF-κB pathway may impair polyunsaturated fatty acid metabolism, causing renal fibrosis. In addition, CKD rats showed significantly decreased diglyceride levels and increased triglyceride levels compared to the control group. Pathway over-representation analysis demonstrated that 30 metabolic pathways were associated with lipid species. AO treatment suppressed up-regulation of inflammation, and partly restored the deregulation of polyunsaturated fatty acids and glycerolipids metabolism. Our results indicated that AO treatment attenuated renal fibrosis by down-regulating inflammation, and mitigating lipid metabolism in CKD rats. In conclusion, this study has identified the therapeutic lipid-lowering and anti-fibrosis effects of AO on CKD.

Determining Double Bond Position in Lipids Using Online Ozonolysis Coupled to Liquid Chromatography and Ion Mobility-Mass Spectrometry.

The increasing focus on lipid metabolism has revealed a need for analytical techniques capable of structurally characterizing lipids with a high degree of specificity. Lipids can exist as any one of a large number of double bond positional isomers, which are indistinguishable by single-stage mass spectrometry alone. Ozonolysis reactions coupled to mass spectrometry have previously been demonstrated as a means for localizing double bonds in unsaturated lipids. Here we describe an online, solution-phase reactor using ozone produced via a low-pressure mercury lamp, which generates aldehyde products diagnostic of cleavage at a particular double bond position. This flow-cell device is utilized in conjunction with structurally selective ion mobility-mass spectrometry. The lamp-mediated reaction was found to be effective for multiple lipid species in both positive and negative ionization modes, and the conversion efficiency from precursor to product ions was tunable across a wide range (20-95%) by varying the flow rate through the ozonolysis device. Ion mobility separation of the ozonolysis products generated additional structural information and revealed the presence of saturated species in a complex mixture. The method presented here is simple, robust, and readily coupled to existing instrument platforms with minimal modifications necessary. For these reasons, application to standard lipidomic workflows is possible and aids in more comprehensive structural characterization of a myriad of lipid species.

The Hepatic Lipidome: A Gateway to Understanding the Pathogenes is of Alcohol-Induced Fatty Liver.

Chronic alcohol consumption can lead to the development of alcoholic fatty liver disease. The underlying pathogenic mechanisms however, have not been fully elucidated. Here, we review the current state of the art regarding the application of lipidomics to study alcohol's effect on hepatic lipids. It is clear that alcohol has a profound effect on the hepatic lipidome, with documented changes in the major lipid categories (i.e. fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids and prenol lipids). Alcohol's most striking effect is the marked change in the hepatic fatty acyl pool. This effect includes increased levels of 18-carbon fatty acyl chains incorporated into multiple lipid species, as well as a general shift toward increased unsaturation of fatty acyl moieties. In addition to our literature review, we also make several recommendations to consider when designing lipidomic studies into alcohol's effects. These recommendations include integration of lipidomic data with other measures of lipid metabolism, inclusion of multiple experimental time points, and presentation of quantitative data. We believe rigorous analysis of the hepatic lipidome can yield new insight into the pathogenesis of alcohol-induced fatty liver. While the existing literature has been largely descriptive, the field is poised to apply lipidomics to yield a new level of understanding on alcohol's effects on hepatic lipid metabolism.