The importance of the mass spectral product ion structure is highlighted in quantitative assays, which typically use MRM (multiple reaction monitoring), and in the discovery of novel metabolites. Estradiol is an important sex steroid whose quantitation and metabolite identification using tandem mass spectrometry has been widely employed in numerous clinical studies. Negative electrospray ionization tandem mass spectrometry of estradiol (E2) results in several product ions, including the abundant m/z 183 and m/z 169. While m/z 183 is one of the most abundant product ions used in many quantitative assays, the structure of m/z 183 has not been rigorously examined. We suggest a structure for m/z 183 and a mechanism of formation consistent with collision induced dissociation (CID) of E2 and several stable isotopes ([D4]-E2, [13C6]-E2, and [D1]-E2). An additional product ion from E2, namely m/z 169, has also been examined. MS3 experiments indicated that both m/z 183 and m/z 169 originate from only E2 [M-H]− m/z 271. These ions, m/z 183 and m/z 169, were also present in the collision induced decomposition mass spectra of other prominent estrogens, estrone (E1) and estriol (E3), indicating that these two product ions could be used to elucidate the estrogenic origin of novel metabolites. We propose two fragmentation schemes to explain the CID data and suggested a structure of m/z 183 and m/z 169 consistent with several isotopic variants and high resolution mass spectrometric measurements.
Estradiol; Estrone; Estriol; Tandem Mass Spectrometry; Product Ion Structure
The oxidative modification of polyunsaturated fatty acids which occurs through enzymatic and non-enzymatic processes is typically initiated by the attachment of molecular oxygen to an unsaturated fatty acyl chain forming a lipid hydroperoxide (LOOH). Enzymatic pathways are critical for cellular homeostasis but aberrant lipid peroxidation has been implicated in important pathologies. Analysis of primary oxidation products such as hydroperoxides has proven challenging for a variety of reasons. While negative ion electrospray ionization has been used for the specific detection of some LOOH species, hydroperoxide dehydration in the ion source has been a significant drawback. Here we describe positive ion electrospray ionization of ammoniated 13-hydroperoxy-9Z,11E-octadecadienoyl cholesterol and 9-hydroperoxy-10E,12Z-octadecadienoyl cholesterol, [M + NH4]+, following normal phase high-pressure liquid-chromatography. Dehydration in the ion source was not prevalent and the ammoniated molecular ion was the major species observed. Collisionally induced dissociation of the two positional isomers yielded unique product ion spectra resulting from carbon-carbon cleavages along their acyl chains. Further investigation of this behavior revealed that complex collision induced dissociations were initiated by scission of the hydroperoxide bond that drove subsequent acyl chain cleavages. Interestingly some of the product ions retained the ammonium nitrogen through the formation of covalent carbon-nitrogen or oxygen-nitrogen bonds. These studies were carried out using hydroperoxy-octadecadienoate cholesteryl esters as model compounds, however the observed mechanisms of [LOOH+NH4]+ ionization and dissociation are likely applicable to the analysis of other lipid hydroperoxides and may serve as the basis for selective LOOH detection as well as aid in the identification of unknown lipid hydroperoxides.
Mass spectrometric techniques have been developed to record mass spectra of biomolecules including lipids as they naturally exist within tissues and thereby permit the generation of images displaying the distribution of specific lipids in tissues, organs, and intact animals. These techniques are based on matrix-assisted laser desorption/ionization (MALDI) that requires matrix application onto the tissue surface prior to analysis. One technique of application that has recently shown significant advantages for lipid analysis is sublimation of matrix followed by vapor deposition directly onto the tissue. Explanations for enhanced sensitivity realized by sublimation/deposition related to sample temperature after a laser pulse and matrix crystal size are presented. Specific examples of sublimation/deposition in lipid imaging of various organs including brain, ocular tissue, and kidney are presented.
imaging mass spectrometry; sublimation/deposition; MALDI; phosphatidylcholine; sphingolipids; brain; kidney; retina; spinal cord; human lens; glycerophospholipids
Neutral lipids are a diverse family of hydrophobic biomolecules that have important roles in cellular biochemistry of all living species but have in common the property of charge neutrality. A large component of neutral lipids are the glycerolipids composed of triacylglycerols, diacylglycerols, and monoacylglycerols that can serve as cellular energy stores as well as signaling molecules. Another abundant lipid class in many cells is the cholesterol esters that are on one hand sterols and the other fatty acyl lipids, but in either case are neutral lipids involved in cholesterol homeostasis and transport in the blood. The analysis of these molecules in the context of lipidomics remains challenging because of their charge neutrality and the complex mixtures of molecular species present in cells. Various techniques have been used to ionize these neutral lipids prior to mass spectrometric analysis including electron ionization, atmospheric chemical ionization, electrospray ionization and matrix assisted laser desorption/ionization. Various approaches to deal with the complex mixture of molecular species have been developed including shotgun lipidomics and chromatographic-based separations such as gas chromatography, reversed phase liquid chromatography, and normal phase liquid chromatography. Several applications of these approaches are discussed.
glycerolipids; electrospray ionization; electron ionization; neutral lipid; atmospheric pressure ionization; mass spectrometry; matrix assisted laser desorption/ionization; normal phase; reversed phase; triacylglycerols; diacylglycerols; cholesterol esters
The Sec14-like phosphatidylinositol transfer protein Sfh3 associates with bulk LDs in vegetative cells but targets to a neutral lipid hydrolase-rich LD pool during sporulation. Sfh3 inhibits LD utilization by a PtdIns-4-phosphate–dependent mechanism, and this inhibition prevents prospore membrane biogenesis in sporulating cells.
Lipid droplet (LD) utilization is an important cellular activity that regulates energy balance and release of lipid second messengers. Because fatty acids exhibit both beneficial and toxic properties, their release from LDs must be controlled. Here we demonstrate that yeast Sfh3, an unusual Sec14-like phosphatidylinositol transfer protein, is an LD-associated protein that inhibits lipid mobilization from these particles. We further document a complex biochemical diversification of LDs during sporulation in which Sfh3 and select other LD proteins redistribute into discrete LD subpopulations. The data show that Sfh3 modulates the efficiency with which a neutral lipid hydrolase-rich LD subclass is consumed during biogenesis of specialized membrane envelopes that package replicated haploid meiotic genomes. These results present novel insights into the interface between phosphoinositide signaling and developmental regulation of LD metabolism and unveil meiosis-specific aspects of Sfh3 (and phosphoinositide) biology that are invisible to contemporary haploid-centric cell biological, proteomic, and functional genomics approaches.
Lipids are diverse families of biomolecules that perform essential structural and signaling roles in platelets. Their formation and metabolism is tightly controlled by enzymes and signal transduction pathways, and their dysregulation leads to significant defects in platelet function and disease. Platelet activation is associated with significant changes to membrane lipids, and formation of diverse bioactive lipids that play essential roles in hemostasis. In recent years, new generation mass spectrometry analysis of lipids (termed “lipidomics”) has begun to alter our understanding of how these molecules participate in key cellular processes. While, the application of lipidomics to platelet biology is still in its infancy, seminal earlier studies have shaped our knowledge of how lipids regulate key aspects of platelet biology, including aggregation, shape change, coagulation and degranulation, as well as how lipids generated by platelets influence other cells, such as leukocytes and the vascular wall, and thus how they regulate hemostasis, vascular integrity and inflammation, as well as contribute to pathologies including arterial/deep vein thrombosis and atherosclerosis. This review will provide a brief historical perspective on the characterization of lipids in platelets, then an overview of the new generation lipidomic approaches, their recent application to platelet biology, and future perspectives for research in this area. The major platelet-regulatory lipid families, their formation, metabolism, and their role in health and disease, will be summarized.
Platelets; Lipidomics; Mass spectrometry
The “modern western” diet (MWD) has increased the onset and progression of chronic human diseases as qualitatively and quantitatively maladaptive dietary components give rise to obesity and destructive gene-diet interactions. There has been a three-fold increase in dietary levels of the omega-6 (n-6) 18 carbon (C18), polyunsaturated fatty acid (PUFA) linoleic acid (LA; 18:2n-6), with the addition of cooking oils and processed foods to the MWD. Intense debate has emerged regarding the impact of this increase on human health. Recent studies have uncovered population-related genetic variation in the LCPUFA biosynthetic pathway (especially within the fatty acid desaturase gene (FADS) cluster) that is associated with levels of circulating and tissue PUFAs and several biomarkers and clinical endpoints of cardiovascular disease (CVD). Importantly, populations of African descent have higher frequencies of variants associated with elevated levels of arachidonic acid (ARA), CVD biomarkers and disease endpoints. Additionally, nutrigenomic interactions between dietary n-6 PUFAs and variants in genes that encode for enzymes that mobilize and metabolize ARA to eicosanoids have been identified. These observations raise important questions of whether gene-PUFA interactions are differentially driving the risk of cardiovascular and other diseases in diverse populations, and contributing to health disparities, especially in African American populations.
polyunsaturated fatty acids; nutrition; genetic variants; fatty acid desaturase (FADS); single nucleotide polymorphisms; arachidonic acid; eicosanoids; inflammation; cardiovascular disease
The quantitative determination of 48 molecular species of regioisomeric diacylglycerols has been made in a single analysis of an extract of bone marrow derived macrophages. The analytical procedure involves solvent extraction of neutral lipids, including diacylglycerols, derivatization of free hydroxyl moieties as 2,4-difluorophenyl urethane, and analysis by normal phase liquid chromatography-tandem mass spectrometry. The derivatization step not only prevents fatty acyl group migration, thus allowing determination of both 1,2- and 1,3-diacylglycerols, but also yields species that are sensitively and uniquely determined by constant neutral loss mass spectrometry. The method also detected monoacylglycerols, which were characterized by unique retention time and collisional spectra, and were present in mouse bone marrow derived macrophage extracts.
diacylglycerol; normal phase; electrospray; diflurophenyl urethane derivative; neutral loss; lipid; monoacylglycerols; diacylglycerols
Management of lipids, particularly signaling lipids that control neuroinflammation, is crucial for the regeneration capability of a damaged nervous system. Knowledge of pro- and anti-inflammatory signals after nervous system injury is extensive, most of them being proteins acting through well-known receptors and intracellular cascades. However, the role of lipid binding extracellular proteins able to modify the fate of lipids released after injury is not well understood. Apolipoprotein D (ApoD) is an extracellular lipid binding protein of the Lipocalin family induced upon nervous system injury. Our previous study shows that axon regeneration is delayed without ApoD, and suggests its participation in early events during Wallerian degeneration. Here we demonstrate that ApoD is expressed by myelinating and non-myelinating Schwann cells and is induced early upon nerve injury. We show that ApoD, known to bind arachidonic acid (AA), also interacts with lysophosphatidylcholine (LPC) in vitro. We use an in vivo model of nerve crush injury, a nerve explant injury model, and cultured macrophages exposed to purified myelin, to uncover that: (i) ApoD regulates denervated Schwann cell-macrophage signaling, dampening MCP1- and Tnf-dependent macrophage recruitment and activation upon injury; (ii) ApoD controls the over-expression of the phagocytosis activator Galectin-3 by infiltrated macrophages; (iii) ApoD controls the basal and injury-triggered levels of LPC and AA; (iv) ApoD modifies the dynamics of myelin-macrophage interaction, favoring the initiation of phagocytosis and promoting myelin degradation. Regulation of macrophage behavior by Schwann-derived ApoD is therefore a key mechanism conditioning nerve injury resolution. These results place ApoD as a lipid binding protein controlling the signals exchanged between glia, neurons and blood-borne cells during nerve recovery after injury, and open the possibility for a therapeutic use of ApoD as a regeneration-promoting agent.
Lipocalin; sciatic nerve; myelin phagocytosis; myelin degradation; macrophage; arachidonic acid; lysophosphatidylcholine
MALDI IMS positive ion images of rat brain show a regional distribution of phosphocholine species that is striking in the apparent distinctiveness, and reproducibility of such depictions. The interpretation of these images, specifically the relationship between MALDI IMS ion intensity and the amount of the phosphocholine (PC) species in the tissue is complicated by numerous factors such as ion suppression, ion molecule chemistry, and effects of tissue structure. This study was designed to test the hypothesis that the intensity of PC molecular species does relate to the quantity of molecules in a tissue sample. A set of comparison studies for a limited but representative selection of cell-derived PC molecular species, was carried out using LC/MS/MS to measure the amounts of these species in brain tissue extracts. There was good correlation between the MALDI IMS ion abundance of PC molecular species and the relative abundance of corresponding PC molecular species in microdissected regions analyzed by LC/MS/MS.
MALDI imaging; MALDI IMS; phospholipids; rat brain; phosphocholine; mass spectrometry; electrospray ionization
Eicosanoids are bioactive lipid mediators derived from arachidonic acid1 (AA), which is released by cytosolic phospholipase A2 (cPLA2). AA is metabolized through three major pathways, cyclooxygenase (COX), lipoxygenase (LO) and cytochrome P450, to produce a family of eicosanoids, which individually have been shown to have pro- or anti-tumorigenic activities in cancer. However, cancer progression likely depends on complex changes in multiple eicosanoids produced by cancer cells and by tumor microenvironment and a systematic examination of the spectrum of eicosanoids in cancer has not been performed. We used liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) to quantitate eicosanoids produced during lung tumor progression in an orthotopic immunocompetent mouse model of lung cancer, in which Lewis lung carcinoma (LLC) cells are injected into lungs of syngeneic mice. The presence of tumor increased products of both the cyclooxygenase and the lipoxygenase pathways in a time-dependent fashion. Comparing tumors grown in cPLA2 knockout vs wild-type mice, we demonstrated that prostaglandins (PGE2, PGD2 and PGF2a) were produced by both cancer cells and the tumor microenvironment (TME), but leukotriene (LTB4, LTC4, LTD4, LTE4) production required cPLA2 expression in the TME. Using flow cytometry, we recovered tumor-associated neutrophils and 2 types of tumor-associated macrophages from tumor-bearing lungs and we defined their distinct eicosanoid profiles by LC/MS/MS. The combination of flow cytometry and LC/MS/MS unravels the complexity of eicosanoid production in lung cancer and provides a rationale to develop therapeutic strategies that target select cell populations to inhibit specific classes of eicosanoids.
Oxidized phospholipids (oxPLs) generated nonenzymatically display pleiotropic biological actions in inflammation. Their generation by cellular cyclooxygenases (COXs) is currently unknown. To determine whether platelets generate prostaglandin (PG)-containing oxPLs, then characterize their structures and mechanisms of formation, we applied precursor scanning-tandem mass spectrometry to lipid extracts of agonist-activated human platelets. Thrombin, collagen, or ionophore activation stimulated generation of families of PGs comprising PGE2 and D2 attached to four phosphatidylethanolamine (PE) phospholipids (16:0p/, 18:1p/, 18:0p/, and 18:0a/). They formed within 2 to 5 min of activation in a calcium, phospholipase C, p38 MAP kinases, MEK1, cPLA2, and src tyrosine kinase-dependent manner (28.1 ± 2.3 pg/2 × 108 platelets). Unlike free PGs, they remained cell associated, suggesting an autocrine mode of action. Their generation was inhibited by in vivo aspirin supplementation (75 mg/day) or in vitro COX-1 blockade. Inhibitors of fatty acyl reesterification blocked generation significantly, while purified COX-1 was unable to directly oxidize PE in vitro. This indicates that they form in platelets via rapid esterification of COX-1 derived PGE2/D2 into PE. In summary, COX-1 in human platelets acutely mediates membrane phospholipid oxidation via formation of PG-esterified PLs in response to pathophysiological agonists.
Oxidized phospholipids; atherosclerosis; PGE2/D2-PEs
Recently, a derivative of phosphatidylethanolamine (PE), namely the 4-(dimethylamino)benzoic acid derivative has been developed with various isotope labeled variants that provided a universal precursor ion scan for diacyl, ether, and plasmalogen PE lipids that can not be accomplished otherwise. This derivative was further investigated as a means to facilitate characterization of various oxidized phosphatidylethanolamine lipids by collision activation. Phospholipids derived from RAW 264.7 cells were treated with a free radical generating system to generate a complex mixture of oxidized and nonoxidized lipids that were separated by reversed phase HPLC and detected using a precursors of m/z 191 scan for the d0-DMABA labeled control sample and a precursors of m/z 197 scan for the d6-DMABA labeled oxidized sample. Collisional activation of the corresponding [M-H]− ions permitted the identification of several chained shortened ω-aldehydes, as well as direct oxygen addition products including isoprostane PE and monohydroxy PE oxidized phospholipids that were not easily detected without the use of the DMABA derivatives. The stable isotope labeled derivatives permitted assessment of relative quantitative changes in oxidized lipids based upon ion abundance.
electrospray; tandem mass spectrometry; lipid oxidation; derivatization
Inflammation and macrophage foam cells are characteristic features of atherosclerotic lesions, but the mechanisms linking cholesterol accumulation to inflammation and LXR-dependent response pathways are poorly understood. To investigate this relationship, we utilized lipidomic and transcriptomic methods to evaluate the effect of diet and LDL receptor genotype on macrophage foam cell formation within the peritoneal cavities of mice. Foam cell formation was associated with significant changes in hundreds of lipid species and unexpected suppression, rather than activation, of inflammatory gene expression. We provide evidence that regulated accumulation of desmosterol underlies many of the homeostatic responses observed in macrophage foam cells, including activation of LXR target genes, inhibition of SREBP target genes, selective reprogramming of fatty acid metabolism and suppression of inflammatory response genes. These observations suggest that macrophage activation in atherosclerotic lesions results from extrinsic, pro-inflammatory signals generated within the artery wall that suppress homeostatic and anti-inflammatory functions of desmosterol.
As a field, lipidomics is in its infancy, yet it has already begun to influence lipid biochemistry in myriad ways. As with other omic technologies, the field is driven by advances in analytical chemistry, particularly by mass spectrometry. At the heart of a renaissance in lipid biochemistry, systems biology is being used to define the cellular lipome, build a comprehensive picture of metabolic interconnections, discover new molecular species and determine how lipids modulate biological functions.
Ozone is a common environmental toxicant to which individuals are exposed to on a daily basis. While biochemical endpoints such as increased mortality, decrements in pulmonary function and initiation of inflammatory processes are known, little is actually understood regarding the chemical mechanisms underlying changes in pulmonary health, especially for low concentrations of ozone. This study was undertaken to investigate ozone induced oxidation of endogenous lipids that are potentially exposed to environmental ozone within lung, specifically focusing on plasmalogen glycerophospholipids present in pulmonary surfactant. Sensitive liquid chromatography-mass spectrometry methods were developed to follow oxidation of diacyl and plasmalogen phosphatidylethanolamine (PE) phospholipids, and to identify and quantitate products generated by ozonolysis. Using a unilamellar vesicle system containing a 1:1 molar mixture of 1-O-octadec-1’-enyl-2-octadecenoyl-PE and 1,2-dihexadecanoyl-PC, these studies revealed the vinyl ether bond of plasmalogens was oxidized preferentially at low concentrations of ozone (100 ppb), when compared to olefinic bond oxidation on ω-9 of the fatty acyl chain in the same phospholipids. Major phospholipid products generated were identified as 1-formyl-2-octadecenoyl-PE and 1-hydroxy-2-octadecenoyl-PE. Heptadecanal and heptadecanoic acid production was also quantitated using gas chromatography-mass spectrometry and production was consistent with oxidation of the vinyl ether, at low concentrations of ozone. Analysis of murine lung surfactant from C57Bl/6 mice revealed several plasmalogen PE lipid species, encompassing ~38% of total PE species. Upon exposure of ozone (0 ppb, 100 ppb) to murine surfactant, plasmalogen PE molecular species preferentially reacted, as compared to diacyl PE molecular species. Lysophospholipids, pentadecanal, and nonanal were found to be the primary products of surfactant ozone oxidation.
Mass Spectrometry; Plasmalogen; Phosphatidylethanolamine; Ozone; Lipid; Surfactant; sn-1 lyso PE
Fatty Acid Synthase (FASN, FAS; EC 220.127.116.11) is the sole mammalian enzyme to synthesize fatty acids de novo from acetyl and malonyl coenzyme A esters. A new method is described that directly quantifies uniformly labeled [13C]16-palmitate by tracing [13C]2-acetyl-CoA and [13C]3-malonyl-CoA using an in vitro FASN assay. This method used GC-MS to detect [13C]16-palmitate carboxylate anions (m/z 271) of pentafluorobenzyl derivatives and was highly sensitive at femtomole quantities. Uniformly incorporated [13C]16-palmitate was the primary product of both recombinant and crude tissue lysate FASN. Quantification of FASN protein within crude tissue lysates assured equal FASN amounts, preserved steady state kinetics, and enabled calculation of FASN specific activity. FASN activity determined by [13C]16-palmitate synthesis was consistent with values obtained from NADPH oxidation assays. Analysis of FASN activity from tissue extracts was not hampered by contaminating enzymes or pre-existing fatty acids. Crude mammary gland and liver lysates had significantly different activities at 82 and 65 nmoles minute−1 mg−1 respectively, suggesting tissue specific activity levels differ in a manner unrelated to FASN amount. GC-MS quantification of [13C]16-palmitate synthesis permits sensitive evaluation of FASN activity from tissues of varied physiologic states, and of purified FASN activity in the presence of modifying proteins, enzymes, or drugs.
Fatty Acid Synthase Activity; GC-Mass Spectrometry; Mammary Gland/Liver Lysates; [13C]-substrate incorporation; [13C]16-Palmitic Acid
Bacteria isolated from marine sponges, including the Silicibacter-Ruegeria (SR) subgroup of the Roseobacter clade, produce N-acylhomoserine lactone (AHL) quorum sensing signal molecules. This study is the first detailed analysis of AHL quorum sensing in sponge-associated bacteria, specifically Ruegeria sp. KLH11, from the sponge Mycale laxissima. Two pairs of luxR and luxI homologues and one solo luxI homologue were identified and designated ssaRI, ssbRI, and sscI (sponge-associated symbiont locus A, B, and C, luxRI or luxI homologue). SsaI produced predominantly long-chain 3-oxo-AHLs and both SsbI and SscI specified 3-OH-AHLs. Addition of exogenous AHLs to KLH11 increased the expression of ssaI but not ssaR, ssbI or ssbR, and genetic analyses revealed a complex interconnected arrangement between SsaRI and SsbRI systems. Interestingly, flagellar motility was abolished in the ssaI and ssaR mutants, with the flagellar biosynthesis genes under strict SsaRI control, and active motility only at high culture density. Conversely, ssaI and ssaR mutants formed more robust biofilms than wild type KLH11. AHLs and transcript of the ssaI gene were detected in M. laxissima extracts suggesting that AHL signaling contributes to the decision between motility and sessility and that it also may facilitate acclimation to different environments including the sponge host.
quorum sensing; acyl-homoserine lactones; LuxI-LuxR type regulation; sponge symbionts; motility; biofilm
The role of Group IVA cytosolic phospholipase A2 (cPLA2α)
activation in regulating macrophage transcriptional responses to
albicans infection was investigated.
cPLA2α releases arachidonic acid for the production of
eicosanoids. In mouse resident peritoneal macrophages, prostacyclin,
prostaglandin E2 and leukotriene C4 were produced within
minutes of C.
albicans addition before cyclooxygenase 2
expression. The production of TNFα was lower in C.
than cPLA2α-/- macrophages due to an autocrine effect of
prostaglandins that increased cAMP to a greater extent in
cPLA2α+/+ than cPLA2α-/-
macrophages. For global insight, differential gene expression in
cPLA2α+/+ and cPLA2α-/-
macrophages (3 h) was compared by microarray. cPLA2α+/+
macrophages expressed 86 genes at lower levels and 181 genes at higher levels
than cPLA2α-/- macrophages (≥2-fold, p<0.05). Several
pro-inflammatory genes were expressed at lower levels (Tnfα,
Cx3cl1, Cd40, Ccl5,
Csf1, Edn1, CxCr7, Irf1,
Irf4, Akna, Ifnγ, several IFNγ-inducible
GTPases). Genes that dampen inflammation (Socs3,
Il10, Crem, Stat3,
Thbd, Thbs1, Abca1) and
genes involved in host defense (Gja1, Csf3,
Trem1, Hdc) were expressed at higher
levels in cPLA2α+/+ macrophages. Representative genes
expressed lower in cPLA2α+/+ macrophages (Tnfα,
Csf1) were increased by treatment with a prostacyclin receptor
antagonist and protein kinase A inhibitor, whereas genes expressed at higher
levels (Crem, Nr4a2, Il10,
Csf3) were suppressed. The results suggest that
albicans stimulates an autocrine loop in
macrophages involving cPLA2α, cyclooxygenase 1-derived prostaglandins
and increased cAMP that globally effects expression of genes involved in host
defense and inflammation.
Mechanisms by which mesenchymal-derived tissue lineages participate in amplifying and perpetuating synovial inflammation in arthritis have been relatively underinvestigated and are therefore poorly understood. Elucidating these processes is likely to provide new insights into the pathogenesis of multiple diseases. Leukotriene B4 (LTB4) is a potent proinflammatory lipid mediator that initiates and amplifies synovial inflammation in the K/BxN model of arthritis. We sought to elucidate mechanisms by which mesenchymal-derived fibroblast-like synoviocytes (FLSs) perpetuate synovial inflammation. We focused on the abilities of FLSs to contribute to LTB4 synthesis and to respond to LTB4 within the joint. Using a series of bone marrow chimeras generated from 5-lipoxygenase–/– and leukotriene A4 (LTA4) hydrolase–/– mice, we demonstrate that FLSs generate sufficient levels of LTB4 production through transcellular metabolism in K/BxN serum-induced arthritis to drive inflammatory arthritis. FLSs—which comprise the predominant lineage populating the synovial lining—are competent to metabolize exogenous LTA4 into LTB4 ex vivo. Stimulation of FLSs with TNF increased their capacity to generate LTB4 3-fold without inducing the expression of LTA4 hydrolase protein. Moreover, LTB4 (acting via LTB4 receptor 1) was found to modulate the migratory and invasive activity of FLSs in vitro and also promote joint erosion by pannus tissue in vivo. Our results identify novel roles for FLSs and LTB4 in joints, placing LTB4 regulation of FLS biology at the center of a previously unrecognized amplification loop for synovial inflammation and tissue pathology.
Phospholipid-esterified oxylipins are newly described families of bioactive lipids generated by lipoxygenases in immune cells. Until now, assays for their quantitation were not well developed or widely available. Here, we describe a mass spectrometric protocol that enables accurate measurement of several, in particular hydro(pero)xyeicosatetraenoic acids (H(p)ETEs), hydroxyoctadecadienoic acids (HODEs), hydroxydocosahexaenoic acids (HDOHEs) and keto-eicosatetraenoic acids (KETEs), attached to either phosphatidylethanolamine (PE) or phosphatidylcholine (PC). Lipids are isolated from cells or tissue using a liquid phase organic extraction, then analyzed by HPLC-tandem mass spectrometry (LC/MS/MS) in multiple reaction monitoring (MRM) mode. The protocol can simultaneously monitor up to 23 different species. Generation of standards takes 2 days approximately. Following this, extraction of 30 samples takes approximately 3 hrs, with LC/MS/MS run time of 50 min per sample.
Lipid biochemistry; eicosanoid; phospholipid; mass spectrometry; macrophage; neutrophil; platelet
Cardiolipin (CL) is a tetra-acyl phospholipid that provides structural and functional support to several proteins in the inner mitochondrial membrane. The majority of CL in the healthy mammalian heart contains four linoleic acid acyl chains (L4CL). A selective loss of L4CL is associated with mitochondrial dysfunction and heart failure in humans and animal models. We examined whether supplementing the diet with linoleic acid would preserve cardiac L4CL and attenuate mitochondrial dysfunction and contractile failure in rats with hypertensive heart failure.
Methods and results
Male spontaneously hypertensive heart failure rats (21 months of age) were administered diets supplemented with high-linoleate safflower oil (HLSO) or lard (10% w/w; 28% kilocalorie fat) or without supplemental fat (control) for 4 weeks. HLSO preserved L4CL and total CL to 90% of non-failing levels (vs. 61–75% in control and lard groups), and attenuated 17–22% decreases in state 3 mitochondrial respiration observed in the control and lard groups (P < 0.05). Left ventricular fractional shortening was significantly higher in HLSO vs. control (33 ± 2 vs. 29 ± 2%, P < 0.05), while plasma insulin levels were lower (5.4 ± 1.1 vs. 9.1 ± 2.3 ng/mL; P < 0.05), with no significant effect of lard supplementation. HLSO also increased serum concentrations of several eicosanoid species compared with control and lard diets, but had no effect on plasma glucose or blood pressure.
Moderate consumption of HLSO preserves CL and mitochondrial function in the failing heart and may be a useful adjuvant therapy for this condition.
Heart failure; Polyunsaturated fatty acids; Cardiolipin; Mitochondria; Hypertension
The cellular and biochemical mechanisms leading to acute lung injury and subsequent multiple organ failure are only partially understood. In order to study the potential role of eicosanoids, particularly leukotrienes, as possible mediators of acute lung injury, we used a murine experimental model of acute lung injury induced by hemorrhagic shock after blood removal via cardiac puncture. Neutrophil sequestration as shown by immunofluorescence, and protein leakage into the alveolar space, were measured as markers of injury. We used liquid chromatography coupled to tandem mass spectrometry to unequivocally identify several eicosanoids in the bronchoalveolar lavage fluid of experimental animals. MK886, a specific inhibitor of the 5-lipoxygenase pathway, as well as transgenic mice deficient in 5-lipoxygenase, were used to determine the role of this enzymatic pathway in this model. Leukotriene B4 and leukotriene C4 were consistently elevated in shock-treated mice compared to sham-treated mice. MK886 attenuated neutrophil infiltration and protein extravasation induced by hemorrhagic shock. 5-lipoxygenase-deficient mice showed reduced neutrophil infiltration and protein extravasation after shock treatment, indicating greatly reduced lung injury. These results support the hypothesis that 5-lipoxygenase, most likely through the generation of leukotrienes, plays an important role in the pathogenesis of acute lung injury induced by hemorrhagic shock in mice. This pathway could represent a new target for pharmacological intervention to reduce lung damage following severe primary injury.
multiple organ failure; eicosanoids; leukotrienes; mass spectrometry; inflammation; pharmacological inhibition; transgenic mice