Emerging lysophospholipid mediators, lysophosphatidylserine, lysophosphatidylthreonine, lysophosphatidylethanolamine and lysophosphatidylglycerol. Prostaglandins Other Lipid Mediat. 2009;89:135-139. [PMID: 19427394 DOI: 10.1016/j.prostaglandins.2009.04.009]

Meibum sphingolipid composition is altered in individuals with meibomian gland dysfunction-a side by side comparison of Meibum and Tear Sphingolipids

PURPOSE

Sphingolipids (SPL) play a role in cell signaling, inflammation, and apoptosis. The purpose of this study was to examine meibum and tear SPL composition in individuals with poor versus good meibum quality.

METHODS

Individuals were grouped by meibum quality (n = 25 with poor quality, case group and n = 25 with good quality, control group). Meibum and tears were analyzed with liquid chromatography-mass spectrometry (LC-MS) to quantify SPL classes. Semiquantitative and relative composition (mole percent) of SPL and major classes, Ceramide (Cer), Hexosyl-Ceramide (Hex-Cer), Sphingomyelin (SM), Sphingosine (Sph), and sphingosine 1-phosphate (S1P) were compared between groups.

RESULTS

Demographic characteristics were similar between the two groups. Overall, individuals with poor meibum quality had more SPL pmole in meibum and tears than controls. Relative composition analysis revealed that individuals with poor meibum quality had SPL composed of less Cer, Hex-Cer, and Sph and more SM compared to individuals with good quality meibum. This pattern was not reproduced in tears as individuals with poor meibum quality had SPL composed of a similar amount of Cer, but more Hex-Cer, Sph and SM compared to controls. In meibum, SPL pmole and relative composition most strongly correlated with MG metrics while in tears, SPL pmole and relative composition most strongly correlated with tear production. SPL in both compartments, specifically Cer pmole in meibum and S1P% in tears, correlated with DE symptoms.

CONCLUSION

SPL composition differs in meibum and tears in patients with poor vs good meibum quality. These findings may be translated into therapeutic targets for disease.

Structural and Functional Analysis of Bacterial Sulfonosphingolipids and Rosette-Inducing Factor 2 (RIF-2) by Mass Spectrometry-Guided Isolation and Total Synthesis

We have analyzed the abundance of bacterial sulfonosphingolipids, including rosette‐inducing factors (RIFs), in seven bacterial prey strains by using high‐resolution tandem mass spectrometry (HRMS²) and molecular networking (MN) within the Global Natural Product Social Molecular Networking (GNPS) web platform. Six sulfonosphingolipids resembling RIFs were isolated and their structures were elucidated based on comparative MS and NMR studies. Here, we also report the first total synthesis of two RIF‐2 diastereomers and one congener in 15 and eight synthetic steps, respectively. For the total synthesis of RIF‐2 congeners, we employed a decarboxylative cross‐coupling reaction to synthesize the necessary branched α‐hydroxy fatty acids, and the Garner‐aldehyde approach to generate the capnine base carrying three stereogenic centers. Bioactivity studies in the choanoflagellate Salpingoeca rosetta revealed that the rosette inducing activity of RIFs is inhibited dose dependently by the co‐occurring sulfonosphingolipid sulfobacins D and F and that activity of RIFs is specific for isolates obtained from Algoriphagus.

A urine and serum metabolomics study of gastroesophageal reflux disease in TCM syndrome differentiation using UPLC-Q-TOF/MS

Gastroesophageal reflux disease (GERD) is a common, chronic and complex upper gastrointestinal disease. In Traditional Chinese medicine (TCM) theory, GERD is classified into two main types: stagnant heat of liver and stomach (SHLS) and deficient cold of spleen and stomach (DCSS). The discovery and evaluation of potential biomarkers for different syndrome types of GERD may contribute to comprehend specific molecular mechanism and identify new targets for diagnosis and appropriate management. In our study, 60 subjects including 40 GERD patients (20 SHLS and 20 DCSS) and 20 healthy controls were recruited, and the serum and urine metabolic profiles from untargeted liquid chromatography coupled to mass spectrometry (LC-MS) metabolomics approach were obtained. Finally 38 biomarkers associated with disease were identified and 9 metabolic pathways were enriched. The most enriched pathways were amino acid metabolism, steroid hormone biosynthesis, glycerophospholipid metabolism, sphingolipid metabolism and TCA cycle. According to the area under curve (AUC) value, we propose a cohort of three metabolites from urine and serum samples as promising biomarkers for TCM syndrome differentiation of GERD, which are prolylhydroxyproline, glycitein-4'-O-glucuronide, capsianoside I in urine and neuAcalpha2-3Galbeta-Cer (d18:1/16:0), sphinganine, arachidonic acid in serum. The cumulative AUC value of merged biomarkers in urine and serum was 0.979 (95%CI 0.927-1) and 0.842 (95%CI 0.704-0.980), respectively. The results indicated that LC-MS based metabolomic profiling method might be an effective and promising tool on further pathogenesis discovering of GERD. The findings provided new strategy for the diagnosis of GERD TCM syndrome differentiation in clinic.

Comparative analysis of erythrocyte hemolysis, plasma parameters and metabolic features in red crucian carp (Carassius auratus red var) and triploid hybrid fish following Aeromonas hydrophila challenge

Aeromonas hydrophila can pose a great threat to survival of freshwater fish. In this study, A. hydrophila challenge could promote the erythrocyte hemolysis, increase free hemoglobin (FHB) level and generate malondialdehyde (MDA) production in plasma but decrease the levels of total antioxidant capacity (T-AOC), total superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (ALP) and lysozyme (LZM) of red crucian carp (RCC, 2 N = 100) and triploid hybrid fish (3 N fish, 3 N = 150) following A. hydrophila challenge. Elevated expression levels of heat shock protein 90 alpha (HSP90α), matrix metalloproteinase 9 (MMP-9), free fatty acid receptor 3 (FFAR3), paraoxonase 2 (PON2) and cytosolic phospholipase A2 (cPLA2) were observed in A. hydrophila-infected fish. In addition, A. hydrophila challenge could significantly increase expressions of cortisol, leucine, isoleucine, glutamate and polyunsaturated fatty acids (PUFAs) in RCC and 3 N, while glycolysis and tricarboxylic acid cycle appeared to be inactive. We identified differential fatty acid derivatives and their metabolic networks as crucial biomarkers from metabolic profiles of different ploidy cyprinid fish subjected to A. hydrophila infection. These results highlighted the comparative metabolic strategy of different ploidy cyprinid fish against bacterial infection.

Plasma characteristic metabolites of pediatric community-acquired pneumonia in traditional Chinese medicine syndrome differentiation

Community-acquired pneumonia (CAP) is the leading cause of lower respiratory tract infections in children. Heat syndrome (HS) and cold syndrome (CS) are two main syndrome types of pediatric CAP in traditional Chinese medicine (TCM). This study aimed to identify plasma metabolic profiles in pediatric CAP and to further select potential biomarkers to distinguish between HS and CS. An ultra-performance liquid chromatography coupled with linear ion trap quadrupole-orbitrap mass spectrometry method was applied to plasma samples of 296 patients and 55 healthy controls (HC). The samples were divided into the discovery group (n = 213, HS = 160, CS = 23, HC = 30) and the validation group (n = 138, HS = 93, CS = 20, HC = 25). The orthogonal partial least-squares discriminant analysis, the value of fold change, and Kruskal-Wallis test with false discovery rate correction (q-value <0.05) were applied to identify differential plasma metabolites. The area under the ROC curve (AUC) was used to evaluate the diagnostic performance of the screened metabolites. The results showed that the plasma levels of aspartic acid, phenylalanine, arginine, lysoPC20:1, lysoPE16:0, lysoPE18:0, and PE (16:0_22:6) were increased in CS compared with HC. The plasma levels of PC (18:1_18:1), PC (20:4_20:4), PE (16:0_18:2), lysoPE20:4, lysoPE18:2, and lysoPE22:6 were decreased, whereas, the plasma level of ceramide (d18:1_24:1) was increased in HS compared with HC. There were 13 differential metabolites in CS (AUC = 0.995) and 15 differential metabolites in HS (AUC = 0.954), compared with HC. A panel of seven biomarkers, including LysoPC20:1, lysoPE16:0, lysoPE18:2, lysoPE20:4, lysoPE22:6, PC (18:1_18:1), and PC (20:4_20:4) showed good discrimination between HS and CS with an AUC of 0.982. Altered plasma amino acids and lipids may provide an objective basis for TCM syndrome differentiation in pediatric CAP.

Increase in Cellular Lysophosphatidylserine Content Exacerbates Inflammatory Responses in LPS-Activated Microglia

Mutations in alpha/beta-hydrolase domain containing (ABHD) 12 gene, which encodes lysophosphatidylserine (LysoPS) lipase, cause the neurodegenerative disease PHARC (Polyneuropathy, Hearing loss, Ataxia, Retinitis pigmentosa, Cataract). Since ABHD12 is expressed by microglia in the central nervous system and is localized to the endoplasmic reticulum, accumulation of intracellular LysoPS by ABHD12 mutations is assumed to be one of the pathological mechanisms associated with microglial activation in PHARC. However, the role of microglia in the PHARC brain and the relationship between microglial function and cellular LysoPS content remains unclear. Therefore, we explored the influence of cellular LysoPS content in microglial inflammatory responses. We evaluated the effects of inhibitors of cellular LysoPS metabolism, KC01 and DO-264, on inflammatory responses using a lipopolysaccharide (LPS)-stimulated mouse microglial cell line, BV-2 and primary microglia. Treatment of DO-264, an inhibitor of cellular LysoPS degradation, enhanced LPS-induced phagocytosis concomitant with the increase in cellular LysoPS content in BV-2 cells. On the other hand, treatment with KC01, an agent had been developed as an inhibitor of LysoPS synthase, reduced phagocytosis without affecting cellular LysoPS content. Such effects of both inhibitors on phagocytosis were also confirmed using primary microglia. KC01 treatment decreased nitric oxide (NO) production, accompanied by a reduction in inducible NO synthase expression in BV-2 microglia. KC01 also suppressed LPS-induced generation of intracellular reactive oxygen species and cytokines such as interleukin-6. Our results suggest that increase in cellular LysoPS levels can exacerbate microglial inflammatory responses. Treatment to prevent the increase in cellular LysoPS in microglia may have therapeutic potential for PHARC.

First insights into the honey bee (Apis mellifera) brain lipidome and its neonicotinoid-induced alterations associated with reduced self-grooming behavior

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First bee brain characterization shows distinctive low plasmalogens and high alkyl-ether levels.

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PC 20:3e/15:0, PC 16:0/18:3, PA 18:0/24:1 increased by the highest dose of clothianidin.

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Levels of CL 18:3/18:1/14:0/22:6, TG 6:0/11:2/18:1 and eLPE 18:0e were linked to intense grooming.

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Membrane lipids, like PC 18:1e/20:3, ePC 8:1e/20:3, and pPE 16:1p/24:1 were up-regulated by clothianidin.

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Clothianidin exposure up-regulated genes linked to GPI-anchor biosynthesis pathway.

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Lipids can be used as biomarkers to assess the effect of neurotoxins on behaviors.

Introduction

Honey bees (Apis mellifera) play key roles in food production performing complex behaviors, like self-grooming to remove parasites. However, the lipids of their central nervous system have not been examined, even though they likely play a crucial role in the performance of cognitive process to perform intricate behaviors. Lipidomics has greatly advanced our understanding of neuropathologies in mammals and could provide the same for honey bees.

Objectives

The objectives of this study were to characterize the brain lipidome of adult honey bees and to assess the effect of clothianidin (a neurotoxic insecticide) on the brain lipid composition, gene expression, and performance of self-grooming behavior under controlled conditions (cage experiments).

Methods

After seven days of exposure to oral sublethal doses of clothianidin, the bees were assessed for self-grooming behavior; their brains were dissected to analyze the lipidome using an untargeted lipidomics approach and to perform a high throughput RNAseq analysis.

Results

Compared to all other organisms, healthy bee brain lipidomes contain unusually high levels of alkyl-ether linked (plasmanyl) phospholipids (51.42%) and low levels of plasmalogens (plasmenyl phospholipids; 3.46%). This could make it more susceptible to the effects of toxins in the environment. A positive correlation between CL 18:3/18:1/14:0/22:6, TG 6:0/11:2/18:1, LPE 18:0e and intense self-grooming was found. Sublethal doses of a neonicotinoid altered PC 20:3e/15:0, PC 16:0/18:3, PA 18:0/24:1, and TG 18:1/18:1/18/1 levels, and affected gene expression linked to GPI-anchor biosynthesis pathway and energy metabolism that may be partially responsible for the altered lipid composition.

Conclusion

This study showed that lipidomics can reveal honey bee neuropathologies associated with reduced grooming behavior due to sublethal neonicotinoid exposure. The ease of use, unusual brain lipidome as well as characterized behaviors that are affected by the environment make honey bees a promising model organism for studying the neurolipidome and associations with neurobehavioral disorders.

Two Distinct Bacterial Biofilm Components Trigger Metamorphosis in the Colonial Hydrozoan Hydractinia echinata

In marine environments, the bacterially induced metamorphosis of larvae is a widespread cross-kingdom communication phenomenon that is critical for the persistence of many marine invertebrates. However, the majority of inducing bacterial signals and underlying cellular mechanisms remain enigmatic. The marine hydroid Hydractinia echinata is a well-known model system for investigating bacterially stimulated larval metamorphosis, as larvae transform into the colonial adult stage within 24 h of signal detection. Although H. echinata has served as a cell biological model system for decades, the identity and influence of bacterial signals on the morphogenic transition remained largely unexplored. Using a bioassay-guided analysis, we first determined that specific bacterial (lyso)phospholipids, naturally present in bacterial membranes and vesicles, elicit metamorphosis in Hydractinia larvae in a dose-response manner. Lysophospholipids, as single compounds or in combination (50 μM), induced metamorphosis in up to 50% of all larvae within 48 h. Using fluorescence-labeled bacterial phospholipids, we demonstrated that phospholipids are incorporated into the larval membranes, where interactions with internal signaling cascades are proposed to occur. Second, we identified two structurally distinct exopolysaccharides of bacterial biofilms, the new Rha-Man polysaccharide from Pseudoalteromonas sp. strain P1-9 and curdlan from Alcaligenes faecalis, to induce metamorphosis in up to 75% of tested larvae. We also found that combinations of (lyso)phospholipids and curdlan induced transformation within 24 h, thereby exceeding the morphogenic activity observed for single compounds and bacterial biofilms. Our results demonstrate that two structurally distinct, bacterium-derived metabolites converge to induce high transformation rates of Hydractinia larvae and thus may help ensure optimal habitat selection. IMPORTANCE Bacterial biofilms profoundly influence the recruitment and settlement of marine invertebrates, critical steps for diverse marine processes such as the formation of coral reefs, the maintenance of marine fisheries, and the fouling of submerged surfaces. However, the complex composition of biofilms often makes the characterization of individual signals and regulatory mechanisms challenging. Developing tractable model systems to characterize these coevolved interactions is the key to understanding fundamental processes in evolutionary biology. Here, we characterized two types of bacterial signaling molecules, phospholipids and polysaccharides, that induce the morphogenic transition. We then analyzed their abundance and combinatorial activity. This study highlights the general importance of multiple bacterial signal converging activity in development-related cross-kingdom signaling and poses the question of whether complex lipids and polysaccharides are general metamorphic cues for cnidarian larvae.

Complex Alterations of Fatty Acid Metabolism and Phospholipidome Uncovered in Isolated Colon Cancer Epithelial Cells

The development of colon cancer, one of the most common malignancies, is accompanied with numerous lipid alterations. However, analyses of whole tumor samples may not always provide an accurate description of specific changes occurring directly in tumor epithelial cells. Here, we analyzed in detail the phospholipid (PL), lysophospholipid (lysoPL), and fatty acid (FA) profiles of purified EpCAM⁺ cells, isolated from tumor and adjacent non-tumor tissues of colon cancer patients. We found that a number of FAs increased significantly in isolated tumor cells, which also included a number of long polyunsaturated FAs. Higher levels of FAs were associated with increased expression of FA synthesis genes, as well as with altered expression of enzymes involved in FA elongation and desaturation, including particularly fatty acid synthase, stearoyl-CoA desaturase, fatty acid desaturase 2 and ELOVL5 fatty acid elongase 5 We identified significant changes in ratios of specific lysoPLs and corresponding PLs. A number of lysophosphatidylcholine and lysophosphatidylethanolamine species, containing long-chain and very-long chain FAs, often with high numbers of double bonds, were significantly upregulated in tumor cells. Increased de novo synthesis of very long-chain FAs, or, altered uptake or incorporation of these FAs into specific lysoPLs in tumor cells, may thus contribute to reprogramming of cellular phospholipidome and membrane alterations observed in colon cancer.

Saturated free fatty acids and association with memory formation

Polyunsaturated free fatty acids (FFAs) such as arachidonic acid, released by phospholipase activity on membrane phospholipids, have long been considered beneficial for learning and memory and are known modulators of neurotransmission and synaptic plasticity. However, the precise nature of other FFA and phospholipid changes in specific areas of the brain during learning is unknown. Here, using a targeted lipidomics approach to characterise FFAs and phospholipids across the rat brain, we demonstrated that the highest concentrations of these analytes were found in areas of the brain classically involved in fear learning and memory, such as the amygdala. Auditory fear conditioning led to an increase in saturated (particularly myristic and palmitic acids) and to a lesser extent unsaturated FFAs (predominantly arachidonic acid) in the amygdala and prefrontal cortex. Both fear conditioning and changes in FFA required activation of NMDA receptors. These results suggest a role for saturated FFAs in memory acquisition.

Decreased caveolae in AGPAT2 lacking adipocytes is independent of changes in cholesterol or sphingolipid levels: A whole cell and plasma membrane lipidomic analysis of adipogenesis

BACKGROUND

Adipocytes from lipodystrophic Agpat2^-/- mice have impaired adipogenesis and fewer caveolae. Herein, we examined whether these defects are associated with changes in lipid composition or abnormal levels of caveolae-associated proteins. Lipidome changes were quantified in differentiated Agpat2^-/- adipocytes to identify lipids with potential adipogenic roles.

METHODS

Agpat2^-/- and wild type brown preadipocytes were differentiated in vitro. Plasma membrane was purified by ultracentrifugation. Number of caveolae and caveolae-associated proteins, as well as sterol, sphingolipid, and phospholipid lipidome were determined across differentiation.

RESULTS

Differentiated Agpat2^-/- adipocytes had decreased caveolae number but conserved insulin signaling. Caveolin-1 and cavin-1 levels were equivalent between Agpat2^-/- and wild type adipocytes. No differences in PM cholesterol and sphingolipids abundance were detected between genotypes. Levels of phosphatidylserine at day 10 of differentiation were increased in Agpat2^-/- adipocytes. Wild type adipocytes had increased whole cell triglyceride, diacylglycerol, phosphatidylglycerol, phosphatidic acid, lysophosphatidylcholine, lysophosphatidylethanolamine, and trihexosyl ceramide, and decreased 24,25-dihydrolanosterol and sitosterol, as a result of adipogenic differentiation. By contrast, adipogenesis did not modify whole cell neutral lipids but increased lysophosphatidylcholine, sphingomyelin, and trihexosyl ceramide levels in Agpat2^-/- adipocytes. Unexpectedly, adipogenesis decreased PM levels of main phospholipids in both genotypes.

CONCLUSION

In Agpat2^-/- adipocytes, decreased caveolae is not associated with changes in PM cholesterol nor sphingolipid levels; however, increased PM phosphatidylserine content may be implicated. Abnormal lipid composition is associated with the adipogenic abnormalities of Agpat2 -/- adipocytes but does not prevent insulin signaling.

2-Arachidonyl-lysophosphatidylethanolamine Induces Anti-Inflammatory Effects on Macrophages and in Carrageenan-Induced Paw Edema

2-Arachidonyl-lysophosphatidylethanolamine, shortly 2-ARA-LPE, is a polyunsaturated lysophosphatidylethanolamine. 2-ARA-LPE has a very long chain arachidonic acid, formed by an ester bond at the sn-2 position. It has been reported that 2-ARA-LPE has anti-inflammatory effects in a zymosan-induced peritonitis model. However, it’s action mechanisms are poorly investigated. Recently, resolution of inflammation is considered to be an active process driven by M2 polarized macrophages. Therefore, we have investigated whether 2-ARA-LPE acts on macrophages for anti-inflammation, whether 2-ARA-LPE modulates macrophage phenotypes to reduce inflammation, and whether 2-ARA-LPE is anti-inflammatory in a carrageenan-induced paw edema model. In mouse peritoneal macrophages, 2-ARA-LPE was found to inhibit lipopolysaccharide (LPS)-induced M1 macrophage polarization, but not induce M2 polarization. 2-ARA-LPE inhibited the inductions of inducible nitric oxide synthase and cyclooxygenase-2 in mouse peritoneal macrophages at the mRNA and protein levels. Furthermore, products of the two genes, nitric oxide and prostaglandin E₂, were also inhibited by 2-ARA-LPE. However, 1-oleoyl-LPE did not show any activity on the macrophage polarization and inflammatory responses. The anti-inflammatory activity of 2-ARA-LPE was also verified in vivo in a carrageenan-induced paw edema model. 2-ARA-LPE inhibits LPS-induced M1 polarization, which contributes to anti-inflammation and suppresses the carrageenan-induced paw edema in vivo.

Untapped endocannabinoid pharmacological targets: Pipe dream or pipeline?

It has been established that the endogenous cannabinoid (endocannabinoid) system plays key modulatory roles in a wide variety of pathological conditions. The endocannabinoid system comprises both cannabinoid receptors, their endogenous ligands including 2-arachidonoylglycerol (2-AG), N-arachidonylethanolamine (anandamide, AEA), and enzymes that regulate the synthesis and degradation of endogenous ligands which include diacylglycerol lipase alpha (DAGL-α), diacylglycerol lipase beta (DAGL-β), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), α/β hydrolase domain 6 (ABHD6). As the endocannabinoid system exerts considerable involvement in the regulation of homeostasis and disease, much effort has been made towards understanding endocannabinoid-related mechanisms of action at cellular, physiological, and pathological levels as well as harnessing the various components of the endocannabinoid system to produce novel therapeutics. However, drug discovery efforts within the cannabinoid field have been slower than anticipated to reach satisfactory clinical endpoints and raises an important question into the validity of developing novel ligands that therapeutically target the endocannabinoid system. To answer this, we will first examine evidence that supports the existence of an endocannabinoid system role within inflammatory diseases, neurodegeneration, pain, substance use disorders, mood disorders, as well as metabolic diseases. Next, this review will discuss recent clinical studies, within the last 5 years, of cannabinoid compounds in context to these diseases. We will also address some of the challenges and considerations within the cannabinoid field that may be important in the advancement of therapeutics into the clinic.

Abundant oleoyl-lysophosphatidylethanolamine in brain stimulates neurite outgrowth and protects against glutamate toxicity in cultured cortical neurons

Lysophosphatidylethanolamines (LPEs) are bioactive lysophospholipids that have been suggested to play important roles in several biological processes. We performed a quantitative analysis of LPE species and showed their composition in mouse brain. We examined the roles of oleoyl-LPE (18:1 LPE), which is one of the abundant LPE species in brain. In cultured cortical neurons, application of 18:1 LPE stimulated neurite outgrowth. The effect of 18:1 LPE on neurite outgrowth was inhibited by Gq/11 inhibitor YM-254890, phospholipase C (PLC) inhibitor U73122, protein kinase C (PKC) inhibitor Go6983, or mitogen-activated protein kinase (MAPK) inhibitor U0126. Additionally, 18:1 LPE increased the phosphorylation of MAPK/extracellular signal-regulated kinase 1/2. These results suggest that the action of 18:1 LPE on neurite outgrowth is mediated by the Gq/11/PLC/PKC/MAPK pathway. Moreover, we found that application of 18:1 LPE protects neurons from glutamate-induced excitotoxicity. This effect of 18:1 LPE was suppressed by PKC inhibitor Go6983. These results suggest that 18:1 LPE protects neurons from glutamate toxicity via PKC inhibitor Go6983-sensitive PKC subtype. Collectively, our results demonstrated that 18:1 LPE stimulates neurite outgrowth and protects against glutamate toxicity in cultured cortical neurons. Our findings provide insights into the physiological or pathological roles of 18:1 LPE in the brain.

Untargeted lipidomics reveals metabolic responses to different dietary n-3 PUFA in juvenile swimming crab (Portunus trituberculatus)

While tissue fatty acid compositions reflect that of the dietary lipid source, little information is available on how dietary oils modify lipid class and molecular species profiles in hepatopancreas of crustacean. Herein, an 8-week nutritional trial and untargeted lipidomic analysis were used to investigate the impacts of dietary n-3 PUFA lipid sources including fish oil, krill oil and linseed oil on the lipidomic characteristics of hepatopancreas of swimming crab (Portunus trituberculatus). Dietary krill oil significantly increased distribution of 20:5n-3 and 22:6n-3 at sn-2 in phosphatidylcholine and phosphatidylethanolamine compared to fish oil. Fish oil intake promoted the deposition of 20:5n-3 and 22:6n-3 at sn-1,2,3 in triglyceride compared to linseed oil, which significantly increased the specific accumulation of 18:3n-3 at sn-1,3 in triglyceride and sn-2 in phosphatidylcholine and phosphatidylethanolamine. The study revealed metabolic responses to different dietary n-3 PUFA in swimming crab, which provided novel insight into the lipid nutrition of crustacean.

Characterization of Fatty Acyl Modifications in Phosphatidylcholines and Lysophosphatidylcholines via Radical-Directed Dissociation

Phosphatidylcholines (PCs) are the major structural components of the plasma membrane of mammalian cells, while lysophosphatidylcholines (LPCs) are critical intermediates in lipid remodeling. Conventional tandem mass spectrometric (MSⁿ) methods via collision-induced dissociation (CID) are blind to intrachain modifications such as the location of the carbon-carbon double bond (C═C) and methyl branching point. In this study, we demonstrate that almost complete structural information can be inferred from a single MS² CID spectrum of the bicarbonate anion adducts of PC or LPC ([M + HCO₃]^-), including the identity of the headgroup, composition of fatty acyl chains, their sn-positions, the location of C═C, and the point of methyl branching in fatty acyls. We have integrated this MS² CID method onto liquid chromatography for the analysis LPCs in human plasma, revealing the existence of multiple sn-isomers, branched chain isomers, and C═C location isomers of LPC.

Bioactive Lipids in MSCs Biology: State of the Art and Role in Inflammation

Lipidomics is a lipid-targeted metabolomics approach that aims to the comprehensive analysis of lipids in biological systems in order to highlight the specific functions of lipid species in health and disease. Lipids play pivotal roles as they are major structural components of the cellular membranes and energy storage molecules but also, as most recently shown, they act as functional and regulatory components of intra- and intercellular signaling. Herein, emphasis is given to the recently highlighted roles of specific bioactive lipids species, as polyunsaturated fatty acids (PUFA)-derived mediators (generally known as eicosanoids), endocannabinoids (eCBs), and lysophospholipids (LPLs), and their involvement in the mesenchymal stem cells (MSCs)-related inflammatory scenario. Indeed, MSCs are a heterogenous population of multipotent cells that have attracted much attention for their potential in regulating inflammation, immunomodulatory capabilities, and reparative roles. The lipidomics of the inflammatory disease osteoarthritis (OA) and the influence of MSCs-derived lipids have also been addressed.

Structurally different lysophosphatidylethanolamine species stimulate neurite outgrowth in cultured cortical neurons via distinct G-protein-coupled receptors and signaling cascades

Neurite outgrowth is important in neuronal circuit formation and functions, and for regeneration of neuronal networks following trauma and disease in the brain. Thus, identification and characterization of the molecules that regulate neurite outgrowth are essential for understanding how brain circuits form and function and for the development of treatment of neurological disorders. In this study, we found that structurally different lysophosphatidylethanolamine (LPE) species, palmitoyl-LPE (16:0 LPE) and stearoyl-LPE (18:0 LPE), stimulate neurite growth in cultured cortical neurons. Interestingly, YM-254890, an inhibitor of Gq/11 protein, inhibited 16:0 LPE-stimulated neurite outgrowth but not 18:0 LPE-stimulated neurite outgrowth. In contrast, pertussis toxin, an inhibitor of Gi/Go proteins, inhibited 18:0 LPE-stimulated neurite outgrowth but not 16:0 LPE-stimulated neurite outgrowth. The effects of protein kinase C inhibitors on neurite outgrowth were also different. In addition, both 16:0 LPE and 18:0 LPE activate mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1/2, but the effect of the MAPK inhibitor differed between the 16:0 LPE- and 18:0 LPE-treated cultures. Collectively, the results suggest that the structurally different LPE species, 16:0 LPE and 18:0 LPE stimulate neurite outgrowth through distinct signaling cascades in cultured cortical neurons and that distinct G protein-coupled receptors are involved in these processes.

Lipidomic analysis of cancer cells cultivated at acidic pH reveals phospholipid fatty acids remodelling associated with transcriptional reprogramming

Cancer cells need to modulate the biosynthesis of membrane lipids and fatty acids to adapt themselves to an accelerated rate of cell division and survive into an extracellular environment characterised by a low pH. To gain insight this crucial survival process, we investigated the lipid composition of Mel 501 melanoma cells cultured at either physiological or acidic pH and observed the remodelling of phospholipids towards longer and more unsaturated acyl chains at low pH. This modification was related to changes in gene expression profile, as we observed an up-regulation of genes involved in acyl chain desaturation, elongation and transfer to phospholipids. PC3 prostate and MCF7 breast cancer cells adapted at acidic pH also demonstrated phospholipid fatty acid remodelling related to gene expression changes. Overall findings clearly indicate that low extracellular pH impresses a specific lipid signature to cells, associated with transcriptional reprogramming.

Therapeutic Potential of Porcine Liver Decomposition Product: New Insights and Perspectives for Microglia-Mediated Neuroinflammation in Neurodegenerative Diseases

It is widely accepted that microglia-mediated inflammation contributes to the progression of neurodegenerative diseases; however, the precise mechanisms through which these cells contribute remain to be elucidated. Microglia, as the primary immune effector cells of the brain, play key roles in maintaining central nervous system (CNS) homeostasis. Microglia are located throughout the brain and spinal cord and may account for up to 15% of all cells in the brain. Activated microglia express pro-inflammatory cytokines that act on the surrounding brain and spinal cord. Microglia may also play a detrimental effect on nerve cells when they gain a chronic inflammatory function and promote neuropathologies. A key feature of microglia is its rapid morphological change upon activation, characterized by the retraction of numerous fine processes and the gradual acquisition of amoeba-like shapes. These morphological changes are also accompanied by the expression and secretion of inflammatory molecules, including cytokines, chemokines, and lipid mediators that promote systemic inflammation during neurodegeneration. This may be considered a protective response intended to limit further injury and initiate repair processes. We previously reported that porcine liver decomposition product (PLDP) induces a significant increase in the Hasegawa’s Dementia Scale-Revised (HDS-R) score and the Wechsler Memory Scale (WMS) in a randomized, double-blind, placebo-controlled study in healthy humans. In addition, the oral administration of porcine liver decomposition product enhanced visual memory and delayed recall in healthy adults. We believe that PLDP is a functional food that aids cognitive function. In this review, we provide a critical assessment of recent reports of lysophospholipids derived from PLDP, a rich source of phospholipids. We also highlight some recent findings regarding bidirectional interactions between lysophospholipids and microglia and age-related neurodegenerative diseases such as dementia and Alzheimer’s disease.

Analysis of serum lysophosphatidylethanolamine levels in patients with non-alcoholic fatty liver disease by liquid chromatography-tandem mass spectrometry

Lysophosphatidylethanolamines (LysoPEs) are the partial hydrolysis products of phosphatidylethanolamine. Despite the unique in vitro bioactivities of LysoPEs, there are limited reports on the pathophysiological role of LysoPEs in the serum, due to the lack of sensitive analytical methods for determination of each molecular species in clinical samples. Herein, we developed a highly sensitive quantitative method to profile the serum LysoPE species by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with selected reaction monitoring (SRM). The internal standard (IS), chemically synthesized in-house, and the lineup of seven major LysoPE species were used in this study. The limits of detection and quantification for each LysoPE species ranged within 0.5-3.3 pmol/mL and 1.0-5.0 pmol/mL, respectively. The combined concentrations of LysoPEs in the serum from healthy subjects (n = 8) and the patients with non-alcoholic fatty liver diseases (NAFLD) including simple steatosis (SS, n = 9) and non-alcoholic steatohepatitis (NASH, n = 27) were 18.030 ± 3.832, 4.867 ± 1.852, and 5.497 ± 2.495 nmol/mL, respectively. The combined and individual concentrations of LysoPEs, except for LysoPE 18:0, significantly decreased in the patients with NAFLD compared with those for the healthy subjects. However, no significant difference was observed between the SS and NASH groups. Our proposed LC-MS/MS method is valid and has advantages of small sample volume, high sensitivity, and simultaneous absolute quantitation for multiple molecular species. This method may enable diagnostic evaluation and elucidation of the as-yet uncovered pathophysiological role of LysoPEs.

Emerging roles of lysophospholipids in health and disease

Lipids are abundant and play essential roles in human health and disease. The main functions of lipids are building blocks for membrane biogenesis. However, lipids are also metabolized to produce signaling molecules. Here, we discuss the emerging roles of circulating lysophospholipids. These lysophospholipids consist of lysoglycerophospholipids and lysosphingolipids. They are both present in cells at low concentration, but their concentrations in extracellular fluids are significantly higher. The biological functions of some of these lysophospholipids have been recently revealed. Remarkably, some of the lysophospholipids play pivotal signaling roles as well as being precursors for membrane biogenesis. Revealing how circulating lysophospholipids are produced, released, transported, and utilized in multi-organ systems is critical to understand their functions. The discovery of enzymes, carriers, transporters, and membrane receptors for these lysophospholipids has shed light on their physiological significance. In this review, we summarize the biological roles of these lysophospholipids via discussing about the proteins regulating their functions. We also discuss about their potential impacts to human health and diseases.

Multifactorial Analysis of Environmental Metabolomic Data in Ecotoxicology: Wild Marine Mussel Exposed to WWTP Effluent as a Case Study

Environmental metabolomics is a powerful approach to investigate the response of organisms to contaminant exposure at a molecular scale. However, metabolomic responses to realistic environmental conditions can be hindered by factors intrinsic to the environment and the organism. Hence, a well-designed experimental exposure associated with adequate statistical analysis could be helpful to better characterize and relate the observed variability to its different origins. In the current study, we applied a multifactorial experiment combined to Analysis of variance Multiblock Orthogonal Partial Least Squares (AMOPLS), to assess the metabolic response of wild marine mussels, Mytilus galloprovincialis, exposed to a wastewater treatment plant effluent, considering gender as an experimental factor. First, the total observed variability was decomposed to highlight the contribution of each effect related to the experimental factors. Both the exposure and the interaction gender × exposure had a statistically significant impact on the observed metabolic alteration. Then, these metabolic patterns were further characterized by analyzing the individual variable contributions to each effect. A main change in glycerophospholipid levels was highlighted in both males and females as a common response, possibly caused by oxidative stress, which could lead to reproductive disorders, whereas metabolic alterations in some polar lipids and kynurenine pathway were rather gender-specific. This may indicate a disturbance in the energy metabolism and immune system only in males. Finally, AMOPLS is a useful tool facilitating the interpretation of complex metabolomic data and is expected to have a broad application in the field of ecotoxicology.

Signaling lipids as diagnostic biomarkers for ocular surface cicatrizing conjunctivitis

Abstract

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

Key messages

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

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

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

Several oxylipins are identified as diagnostic biomarkers for OCP.

Phospholipases in neuronal function: A role in learning and memory?

Despite the human brain being made of nearly 60% fat, the vast majority of studies on the mechanisms of neuronal communication which underpin cognition, memory and learning, primarily focus on proteins and/or (epi)genetic mechanisms. Phospholipids are the main component of all cellular membranes and function as substrates for numerous phospholipid-modifying enzymes, including phospholipases, which release free fatty acids (FFAs) and other lipid metabolites that can alter the intrinsic properties of the membranes, recruit and activate critical proteins, and act as lipid signalling molecules. Here, we will review brain specific phospholipases, their roles in membrane remodelling, neuronal function, learning and memory, as well as their disease implications. In particular, we will highlight key roles of unsaturated FFAs, particularly arachidonic acid, in neurotransmitter release, neuroinflammation and memory. In light of recent findings, we will also discuss the emerging role of phospholipase A₁ and the creation of saturated FFAs in the brain.

Measurement of Lysophospholipid Transport Across the Membrane Using Escherichia coli Spheroplasts

In the inner membrane of Gram-negative bacteria lysophospholipid transporter (LplT) and the bifunctional acyl-acyl carrier protein (ACP) synthetase/2-acylglycerolphosphoethanolamine acyltransferase (Aas) form a glycerophospholipid remodeling system, which is capable of facilitating rapid retrograde translocation of lyso forms of phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin across the cytoplasmic membrane. This coupled remodeling enzyme tandem provides an effective method for the measurement of substrate specificity of the lipid regeneration and lysophospholipid transport per se across the membrane. This chapter describes two distinct but complementary methods for the measurement of lysophospholipid transport across membrane using Escherichia coli spheroplasts.

NLRP3 inflammasome and lipid metabolism analysis based on UPLC-Q-TOF-MS in gouty nephropathy

To determine the differences in plasma metabolism between healthy patients and patients with hyperuricaemia and gouty nephropathy, the present study identified differentially expressed metabolites associated with gouty nephropathy. Furthermore, the NLRP3 inflammasome signalling pathway in gouty nephropathy was explored, and the mechanism of hyperuricaemia-induced renal damage. Adult male patients examined between July 2016 and June 2017 were selected as the patient cohort for the present study from the Affiliated Bao'an Hospital of Shenzhen, Southern Medical University (Shenzhen, China). These patients were divided into three groups of 30 patients each: Control, hyperuricaemia and gouty nephropathy groups. The expression levels of NLRP3, ASC and caspase-1 mRNA and protein were detected in peripheral blood mononuclear cells, and the plasma levels of IL-1β and IL-18. Ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry was used to determine differential levels of metabolites between patients from different groups, in order to identify potential biomarkers. The expression of the NLRP3 inflammasome in peripheral blood mononuclear cells, and the levels of IL-1β and IL-18 in the plasma were increased in the gouty nephropathy group compared with the control and hyperuricaemia groups. In addition, 46 metabolites were identified as potential plasma metabolic biomarkers that were able to distinguish gouty nephropathy from hyperuricaemia. The majority of these metabolites were involved in lipid metabolism, in particular the activity of phospholipase A2 and β-oxidation. These data indicated that lipid metabolism and the NLRP3 inflammasome serve a pivotal role in gouty nephropathy. In addition, the results suggested that lipids may mediate the progression of gouty nephropathy through the activity of phospholipase A2, β-oxidation and activation of the NLRP3 inflammasome.

Discovery and Optimization of Selective and in Vivo Active Inhibitors of the Lysophosphatidylserine Lipase α/β-Hydrolase Domain-Containing 12 (ABHD12)

ABHD12 is a membrane-bound hydrolytic enzyme that acts on the lysophosphatidylserine (lyso-PS) and lysophosphatidylinositol (lyso-PI) classes of immunomodulatory lipids. Human and mouse genetic studies point to a key role for the ABHD12-(lyso)-PS/PI pathway in regulating (neuro)immunological functions in both the central nervous system and periphery. Selective inhibitors of ABHD12 would offer valuable pharmacological probes to complement genetic models of ABHD12-regulated (lyso)-PS/PI metabolism and signaling. Here, we provide a detailed description of the discovery and activity-based protein profiling (ABPP) guided optimization of reversible thiourea inhibitors of ABHD12 that culminated in the identification of DO264 as a potent, selective, and in vivo active ABHD12 inhibitor. We also show that DO264, but not a structurally related inactive control probe (S)-DO271, augments inflammatory cytokine production from human THP-1 macrophage cells. The in vitro and in vivo properties of DO264 designate this compound as a suitable chemical probe for studying the biological functions of ABHD12-(lyso)-PS/PI pathways.

Lysophospholipases cooperate to mediate lipid homeostasis and lysophospholipid signaling

Lysophospholipids (LysoPLs) are bioactive lipid species involved in cellular signaling processes and the regulation of cell membrane structure. LysoPLs are metabolized through the action of lysophospholipases, including lysophospholipase A1 (LYPLA1) and lysophospholipase A2 (LYPLA2). A new X-ray crystal structure of LYPLA2 compared with a previously published structure of LYPLA1 demonstrated near-identical folding of the two enzymes; however, LYPLA1 and LYPLA2 have displayed distinct substrate specificities in recombinant enzyme assays. To determine how these in vitro substrate preferences translate into a relevant cellular setting and better understand the enzymes' role in LysoPL metabolism, CRISPR-Cas9 technology was utilized to generate stable KOs of Lypla1 and/or Lypla2 in Neuro2a cells. Using these cellular models in combination with a targeted lipidomics approach, LysoPL levels were quantified and compared between cell lines to determine the effect of losing lysophospholipase activity on lipid metabolism. This work suggests that LYPLA1 and LYPLA2 are each able to account for the loss of the other to maintain lipid homeostasis in cells; however, when both are deleted, LysoPL levels are dramatically increased, causing phenotypic and morphological changes to the cells.

Production of extracellular lysophosphatidic acid in the regulation of adipocyte functions and liver fibrosis

Lysophosphatidic acid (LPA), a glycerophospholipid, consists of a glycerol backbone connected to a phosphate head group and an acyl chain linked to sn-1 or sn-2 position. In the circulation, LPA is in sub-millimolar range and mainly derived from hydrolysis of lysophosphatidylcholine, a process mediated by lysophospholipase D activity in proteins such as autotaxin (ATX). Intracellular and extracellular LPAs act as bioactive lipid mediators with diverse functions in almost every mammalian cell type. The binding of LPA to its receptors LPA_1-6 activates multiple cellular processes such as migration, proliferation and survival. The production of LPA and activation of LPA receptor signaling pathways in the events of physiology and pathophysiology have attracted the interest of researchers. Results from studies using transgenic and gene knockout animals with alterations of ATX and LPA receptors genes, have revealed the roles of LPA signaling pathways in metabolic active tissues and organs. The present review was aimed to summarize recent progresses in the studies of extracellular and intracellular LPA production pathways. This includes the functional, structural and biochemical properties of ATX and LPA receptors. The potential roles of LPA production and LPA receptor signaling pathways in obesity, insulin resistance and liver fibrosis are also discussed.

cPLA2 and desaturases underlie the tau hyperphosphorylation offset induced by BACE knock-down in neuronal primary cultures

Inflammation has been suggested to play early and perhaps causative roles in Alzheimer's disease (AD) pathogenesis possibly in part by the overactivation of the aspartic acid protease named β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1), which is responsible for the β-amyloid cascade. We have described that BACE1 is involved in the lysophosphatidylethanolamine (LPE) (18:1/20:4/22:6) upregulation associated with tauopathy and inflammation signaling (cPLA2/arachidonic acid/COX2) in a triple transgenic model of Alzheimer's disease, where BACE1 silencing reversed the imbalanced profile and produced cognitive function improvement. In this study, we analyze the role of cPLA2 and desaturases (SCD1, FAD6) in the BACE1 knockdown-induced protective action under a glutamate excitotoxicity model. Glutamate (125 μM) produced hyperphosphorylation of tau in cortical primary cultures along with increased apoptotic nuclei, LDH release, and cPLA2 expression, which were all reversed by BACE1-KD. This beneficial effect was reinforced by the silencing of cPLA2 but attenuated by the reduction in SCD1 and partially attenuated by the reduction in FAD6. Inversely, overexpression SCD1 and FAD6 recovered the neuroprotective effect produced by BACE1-KD, which was not achieved by the overexpression of each desaturase alone. These findings suggest that the hyperphosphorylation of tau and the creation of a pro-inflammatory cell environment are blocked in a desaturase-dependent manner by targeting BACE1.

Examining the effect of regioisomerism on the physico-chemical properties of lysophosphatidylethanolamine-containing liposomes using fluoro probes

Lysophospholipids (LysoPLs) receive steadily increasing attention in the area of lipid chemistry and biology. However, the physico-chemical properties of individual LysoPL regioisomers have not yet been investigated. Herein, we report the synthesis of fluoro analogues of lysophosphatidylethanolamines (LPEs) and examine the physico-chemical properties of the LPE regioisomers using chemically synthesized fluoro probes.

Lysophosphatidylserine receptor P2Y10: A G protein-coupled receptor that mediates eosinophil degranulation

BACKGROUND

P2Y10, along with GPR34 and GPR174, is a G protein-coupled receptor that is activated by an endogenous lipid mediator lysophosphatidylserine (LysoPS). Its expression pattern and its function are completely unknown. We have previously shown that P2Y10 is one of the highly up-regulated genes at the late differentiation stage during in vitro eosinophilopoiesis.

OBJECTIVE

We explored the expression and functions of P2Y10 in human cord blood (CB)-derived and peripheral blood (PB) eosinophils.

METHODS

Real-time PCR, FACS, Western blot, ELISA, and chemotaxis assays were performed to determine the expression and function of P2Y10.

RESULTS

As CB cells differentiated towards eosinophils, P2Y10 mRNA and protein were abundantly expressed. P2Y10 was the most highly expressed in the granulocytes from PB, to a lesser extent in monocytes, and least in lymphocytes. Further fractionation of granulocytes revealed that eosinophils express P2Y10 much more strongly than do neutrophils. PB eosinophils solely expressed P2Y10 among the three LysoPS receptors, while PB neutrophils expressed the three at comparable levels. LysoPS activated both CB and PB eosinophils to induce a robust ERK phosphorylation. Importantly, LysoPS was capable of triggering degranulation of ECP in PB eosinophils. This response was significantly reduced by pharmacological inhibitors of TNF-alpha-converting enzyme (TACE), epidermal growth factor receptor (EGFR), and ERK1/2, which were known to be required in P2Y10-mediated signalling pathways. However, LysoPS had no effect on chemotaxis, differentiation, or eosinophil survival.

CONCLUSIONS AND CLINICAL RELEVANCE

LysoPS provokes eosinophil degranulation through P2Y10. Therefore, P2Y10 is a potential therapeutic target to control eosinophil-associated diseases.

Association between serum autotaxin or phosphatidylserine-specific phospholipase A1 levels and melanoma

Autotaxin (ATX), a producing enzyme for lysophosphatidic acids, was first identified from the medium of a melanoma cell line and has been considered to be one of the candidate targets to treat melanoma; however, the association between serum ATX and melanoma in human subjects has not been elucidated. Along with ATX, phosphatidylserine-specific phospholipase A1 (PS-PLA₁ ) is a producing enzyme for lysophosphatidylserine, a similar glycero-lysophospholipid mediator to lysophosphatidic acids. In the present study, we aimed to investigate the association between serum ATX or PS-PLA₁ levels and melanoma. We measured the serum levels of ATX, ATX isoforms and PS-PLA₁ in subjects with melanoma (n = 57) and healthy subjects (n = 58). We further investigated the existence of trends according to the clinical stages of melanoma. We observed that serum total ATX and classical ATX levels were significant higher and serum novel ATX levels tended to be higher in male subjects with melanoma, while no significant difference was observed between the two groups in female subjects. The trend test revealed that the serum total ATX and ATX isoforms were significantly associated with the clinical stages of female subjects with melanoma. Regarding PS-PLA₁ , serum PS-PLA₁ levels were significantly higher in the melanoma subjects and associated with the clinical stages. The present study is the first study which revealed the association between ATX or PS-PLA₁ and melanoma, suggesting the possible involvement of ATX/lysophosphatidic acids or PS-PLA₁ /lysophosphatidylserine axis in the pathogenesis of melanoma.

Bioactive Lipids and Chronic Inflammation: Managing the Fire Within

Inflammation is an immune response that works as a contained fire that is pre-emptively sparked as a defensive process during infections or upon any kind of tissue insult, and that is spontaneously extinguished after elimination or termination of the damage. However, persistent and uncontrolled immune reactions act as a wildfire that promote chronic inflammation, unresolved tissue damage and, eventually, chronic diseases. A wide network of soluble mediators, among which endogenous bioactive lipids, governs all immune processes. They are secreted by basically all cells involved in inflammatory processes and constitute the crucial infrastructure that triggers, coordinates and confines inflammatory mechanisms. However, these molecules are also deeply involved in the detrimental transition from acute to chronic inflammation, be it for persistent or excessive action of pro-inflammatory lipids or for the impairment of the functions carried out by resolving ones. As a matter of fact, bioactive lipids have been linked, to date, to several chronic diseases, including rheumatoid arthritis, atherosclerosis, diabetes, cancer, inflammatory bowel disease, systemic lupus erythematosus, and multiple sclerosis. This review summarizes current knowledge on the involvement of the main classes of endogenous bioactive lipids—namely classical eicosanoids, pro-resolving lipid mediators, lysoglycerophospholipids/sphingolipids, and endocannabinoids—in the cellular and molecular mechanisms that lead to the pathogenesis of chronic disorders.

Effect of lysophosphatidylglycerol on intracellular free Ca2+ concentration in A10 vascular smooth muscle cells

Although plasma levels of lysophosphatidylglycerol (LPG) are increased in hypertension, its role in the pathogenesis of vascular defects is not clear. In view of the importance of Ca²⁺ overload in causing vascular smooth muscle (VSM) dysfunction, the action of LPG on [Ca²⁺]_i in cultured A10 VSM cell line was examined by using Fura 2-AM acetoxymethyl ester technique. LPG was found to induce a concentration-dependent increase in [Ca²⁺]_i in VSM cells. This change was dependent both on the extracellular and intracellular Ca²⁺ sources, as it was reduced by 30% by EGTA, an extracellular Ca²⁺ chelator, and 70% by thapsigargin, a sarcoplasmic reticulum (SR) Ca²⁺-pump inhibitor. However the increase in [Ca²⁺]_i due to LPG was not altered by caffeine or ryanodine, which affect Ca²⁺-release through the ryanodine receptors in the SR. On the other hand, LPG-induced change in [Ca²⁺]_i was suppressed by 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate, a phospholipase C (PLC) inhibitor, as well as by xestospongin and 2-aminoethoxydiphenyl borate, two inositol trisphosphate (IP3) receptor inhibitors in the SR. These observations support the view that LPG-induced increase in [Ca²⁺]_i in VSM cells is mainly a result of Ca²⁺ release from Ca²⁺ pool in the SR through PLC/IP3-sensitive signal transduction mechanism. Furthermore, it is suggested that the elevated level of LPG may induce intracellular Ca²⁺ overload and thus play a critical role in the development of vascular abnormalities.

Probing the Hydrophobic Binding Pocket of G-Protein-Coupled Lysophosphatidylserine Receptor GPR34/LPS1 by Docking-Aided Structure-Activity Analysis

The ligands of certain G-protein-coupled receptors (GPCRs) have been identified as endogenous lipids, such as lysophosphatidylserine (LysoPS). Here, we analyzed the molecular basis of the structure-activity relationship of ligands of GPR34, one of the LysoPS receptor subtypes, focusing on recognition of the long-chain fatty acid moiety by the hydrophobic pocket. By introducing benzene ring(s) into the fatty acid moiety of 2-deoxy-LysoPS, we explored the binding site's preference for the hydrophobic shape. A tribenzene-containing fatty acid surrogate with modifications of the terminal aromatic moiety showed potent agonistic activity toward GPR34. Computational docking of these derivatives with a homology modeling/molecular dynamics-based virtual binding site of GPR34 indicated that a kink in the benzene-based lipid surrogates matches the L-shaped hydrophobic pocket of GPR34. A tetrabenzene-based lipid analogue bearing a bulky tert-butyl group at the 4-position of the terminal benzene ring exhibited potent GPR34 agonistic activity, validating the present hydrophobic binding pocket model.

Lysophosphatidylcholine elicits intracellular calcium signaling in a GPR55-dependent manner

The GPR55 signaling is fertile ground for drug discovery, however despite considerable research progress during the past 10 years, many open questions remain. The GPR55 pharmacology remains controversial, as many ligands have been reported with inconsistent results. Here, we show that various molecular species of lysophosphatidylcholine (LPC) elicit intracellular Ca²⁺ mobilization in GPR55-expressing PC-3 human prostate carcinoma cells. The response was even stronger than [Ca²⁺]_i flux evoked by endogenous (OEA) and synthetic (Abn-CBD) agonists. Treatment with GPR55 antagonists CID16020046 and ML193 as well as the lipid raft disrupter methyl-β-cyclodextrin strongly blunted LPC-induced calcium signal. Additionally, molecular modeling analysis revealed that LPC 16:0 and LPC 18:1 interact stronger with the receptor than to OEA. Identified electrostatic interactions between GPR55 residues and the ligands overlap with the binding site identified previously for lysophosphatidylinositol. Therefore, we prove that LPC is another GPR55-sensitive ligand. This finding is relevant in understanding lysophospolipids-mediated signaling and opens new avenues to develop therapeutic approach based on GPR55 targeting.

G protein-coupled receptor 34 in ovarian granulosa cells of cattle: changes during follicular development and potential functional implications

Abundance of G protein-coupled receptor 34 (GPR34) mRNA is greater in granulosa cells (GCs) of cystic vs normal follicles of cattle. The present experiments were designed to determine if GPR34 mRNA in granulosa cell [GC] changes during selection and growth of dominant follicles in cattle as well as to investigate the hormonal regulation of GPR34 mRNA in bovine GC in vitro. In Exp. 1, estrous cycles of nonlactating cows were synchronized and then ovariectomized on either day 3-4 or 5-6 after ovulation. GPR34 mRNA abundance in GC was 2.8- to 3.8-fold greater (P < 0.05) in small (1-5 mm) and large (≥8 mm) estrogen-inactive dominant follicles than in large estrogen-active follicles. Also, GPR34 mRNA tended to be greater (P < 0.10) in F2 than F1 follicles on day 3-4 postovulation. In Exp. 2-7, ovaries were collected at an abattoir and GC were isolated and treated in vitro. Expression of GPR34 was increased (P < 0.05) 2.2-fold by IGF1. Tumor necrosis factor (TNF)-α decreased (P < 0.05) the IGF1-induced GPR34 mRNA abundance in small-follicle GC, whereas IGF1 decreased (P < 0.05) GPR34 expression by 45% in large-follicle GC. Treatment of small-follicle GC with either IL-2, prostaglandin E2 or angiogenin decreased (P < 0.05) GPR34 expression, whereas FSH, cortisol, wingless 3A, or hedgehog proteins did not affect (P > 0.10) GPR34 expression. In Exp. 6 and 7, 2 presumed ligands of GPR34, L-a-lysophosphatidylserine (LPPS) and LPP-ethanolamine, increased (P < 0.05) GC numbers and estradiol production by 2-fold or more in small-follicle GC, and this response was only observed in IGF1-treated GC. In conclusion, GPR34 is a developmentally and hormonally regulated gene in GC, and its presumed ligands enhance IGF1-induced proliferation and steroidogenesis of bovine GC.

Calcium Signaling of Lysophosphatidylethanolamine through LPA1 in Human SH-SY5Y Neuroblastoma Cells

Lysophosphatidylethanolamine (LPE), a lyso-type metabolite of phosphatidylethanolamine, has been reported to be an intercellular signaling molecule. LPE mobilizes intracellular Ca²⁺ through G-protein-coupled receptor (GPCR) in some cells types. However, GPCRs for lysophosphatidic acid (LPA) were not implicated in the LPE-mediated activities in LPA GPCR overexpression systems or in SK-OV3 ovarian cancer cells. In the present study, in human SH-SY5Y neuroblastoma cells, experiments with LPA₁ antagonists showed LPE induced intracellular Ca²⁺ increases in an LPA₁ GPCR-dependent manner. Furthermore, LPE increased intracellular Ca²⁺ through pertussis-sensitive G proteins, edelfosine-sensitive-phospholipase C, 2-APB-sensitive IP₃ receptors, Ca²⁺ release from intracellular Ca²⁺ stores, and subsequent Ca²⁺ influx across plasma membranes, and LPA acted on LPA₁ and LPA₂ receptors to induce Ca²⁺ response in a 2-APB-sensitive and insensitive manner. These findings suggest novel involvements for LPE and LPA in calcium signaling in human SH-SY5Y neuroblastoma cells.

Analysis of glycero-lysophospholipids in gastric cancerous ascites

Lysophosphatidic acid (LysoPA) has been proposed to be involved in the pathogenesis of various cancers. Moreover, glycero-lysophospholipids (glycero-LysoPLs) other than LysoPA are now emerging as novel lipid mediators. Therefore, we aimed to elucidate the possible involvement of glycero-LysoPLs in the pathogenesis of gastric cancer by measuring glycero-LysoPLs, autotaxin (ATX), and phosphatidylserine-specific phospholipase A1 (PS-PLA₁) in ascites obtained from patients with gastric cancer and those with cirrhosis (as a control). We observed that after adjustments according to the albumin levels, the lysophosphatidylserine (LysoPS) and lysophosphatidylglycerol (LysoPG) levels were significantly higher, while the LysoPA and ATX levels were lower, in the ascites from patients with gastric cancer. We also found that multiple regression analyses revealed that ATX was selected as a significant explanatory factor for all the detectable LysoPA species only in the cirrhosis group and that a significant positive correlation was observed between LysoPS and PS-PLA₁ only in the gastric cancer group. In conclusion, the LysoPA levels might be determined largely by LysoPC and LysoPI (possible precursors) and the PS-PLA₁-mediated pathway might be involved in the production of LysoPS in gastric cancer. Glycero-LysoPLs other than LysoPA might also be involved in the pathogenesis of cancer directly or through being converted into LysoPA.

Different origins of lysophospholipid mediators between coronary and peripheral arteries in acute coronary syndrome

Lysophosphatidic acids (LysoPAs) and lysophosphatidylserine (LysoPS) are emerging lipid mediators proposed to be involved in the pathogenesis of acute coronary syndrome (ACS). In this study, we attempted to elucidate how LysoPA and LysoPS become elevated in ACS using human blood samples collected simultaneously from culprit coronary arteries and peripheral arteries in ACS subjects. We found that: 1) the plasma LysoPA, LysoPS, and lysophosphatidylglycerol levels were not different, while the lysophosphatidylcholine (LysoPC), lysophosphatidylinositol, and lysophosphatidylethanolamine (LysoPE) levels were significantly lower in the culprit coronary arteries; 2) the serum autotaxin (ATX) level was lower and the serum phosphatidylserine-specific phospholipase A₁ (PS-PLA₁) level was higher in the culprit coronary arteries; 3) the LysoPE and ATX levels were significant explanatory factors for the mainly elevated species of LysoPA, except for 22:6 LysoPA, in the peripheral arteries, while the LysoPC and LysoPE levels, but not the ATX level, were explanatory factors in the culprit coronary arteries; and 4) 18:0 and 18:1 LysoPS were significantly correlated with PS-PLA₁ only in the culprit coronary arteries. In conclusion, the origins of LysoPA and LysoPS might differ between culprit coronary arteries and peripheral arteries, and substrates for ATX, such as LysoPC and LysoPE, might be important for the generation of LysoPA in ACS.

BACE1 RNAi Restores the Composition of Phosphatidylethanolamine-Derivates Related to Memory Improvement in Aged 3xTg-AD Mice

β-amyloid (Aβ) is produced by the β-secretase 1 (BACE1)-mediated enzymatic cleavage of the amyloid precursor protein through the amyloidogenic pathway, making BACE1 a therapeutic target against Alzheimer’s disease (AD). Alterations in lipid metabolism are a risk factor for AD by an unknown mechanism. The objective of this study was to determine the effect of RNA interference against BACE1 (shBACEmiR) on the phospholipid profile in hippocampal CA1 area in aged 3xTg-AD mice after 6 and 12 months of treatment compared to aged PS1KI mice. The shBACEmiR treatment induced cognitive function recovery and restored mainly the fatty acid composition of lysophosphatidylethanolamine and etherphosphatidylethanolamine, reduced the cPLA2’s phosphorylation, down-regulated the levels of arachidonic acid and COX2 in the hippocampi of 3xTg-AD mice. Together, our findings suggest, for the first time, that BACE1 silencing restores phospholipids composition which could favor the recovery of cellular homeostasis and cognitive function in the hippocampus of triple transgenic AD mice.

Changeover from signalling to energy-provisioning lipids during transition from colostrum to mature milk in the giant panda (Ailuropoda melanoleuca)

Among the large placental mammals, ursids give birth to the most altricial neonates with the lowest neonatal:maternal body mass ratios. This is particularly exemplified by giant pandas. To examine whether there is compensation for the provision of developmentally important nutrients that other species groups may provide in utero, we examined changes in the lipids of colostrum and milk with time after birth in giant pandas. Lipids that are developmental signals or signal precursors, and those that are fundamental to nervous system construction, such as docosahexaenoic acid (DHA) and phosphatidylserines, appear early and then fall dramatically in concentration to a baseline at 20–30 days. The dynamics of lysophosphatidic acid and eicosanoids display similar patterns, but with progressive differences between mothers. Triglycerides occur at relatively low levels initially and increase in concentration until a plateau is reached at about 30 days. These patterns indicate an early provision of signalling lipids and their precursors, particularly lipids crucial to brain, retinal and central nervous system development, followed by a changeover to lipids for energy metabolism. Thus, in giant pandas, and possibly in all bears, lactation is adapted to provisioning a highly altricial neonate to a degree that suggests equivalence to an extension of gestation.

Comprehensive Plasma Metabolomic Analyses of Atherosclerotic Progression Reveal Alterations in Glycerophospholipid and Sphingolipid Metabolism in Apolipoprotein E-deficient Mice

Atherosclerosis is the major underlying cause of most cardiovascular diseases. Despite recent advances, the molecular mechanisms underlying the pathophysiology of atherogenesis are not clear. In this study, comprehensive plasma metabolomics were used to investigate early-stage atherosclerotic development and progression in chow-fed apolipoprotein E-deficient mice at 5, 10 and 15 weeks of age. Comprehensive plasma metabolomic profiles, based on 4365 detected metabolite features, differentiate atherosclerosis-prone from atherosclerosis-resistant models. Metabolites in the sphingomyelin pathway were significantly altered prior to detectable lesion formation and at all subsequent time-points. The cytidine diphosphate-diacylglycerol pathway was up-regulated during stage I of atherosclerosis, while metabolites in the phosphatidylethanolamine and glycosphingolipid pathways were augmented in mice with stage II lesions. These pathways, involving glycerophospholipid and sphingolipid metabolism, were also significantly affected during the course of atherosclerotic progression. Our findings suggest that distinct plasma metabolomic profiles can differentiate the different stages of atherosclerotic progression. This study reveals that alteration of specific, previously unreported pathways of glycerophospholipid and sphingolipid metabolism are associated with atherosclerosis. The clear difference in the level of several metabolites supports the use of plasma lipid profiling as a diagnostic tool of atherogenesis.

The chemical synthesis and preliminary biological studies of phosphodiester and phosphorothioate analogues of 2-methoxy-lysophosphatidylethanolamine

The chemical synthesis of phosphorothioate/phosphodiester analogues of 2-methoxy-lysophosphatidylethanolamine has been described. For the preparation of phosphorothioate derivatives oxathiaphospholane approach has been employed. The phosphodiester compounds were prepared by OXONE® oxidation of corresponding phosphorothioates. Each lysophospholipid analogue was synthesized as a series of four compounds, bearing different fatty acid residues both saturated (14:0, 16:0, 18:0) and unsaturated (18:1). The methylation of glycerol 2-hydroxyl function was applied in order to increase the stability of prepared analogues by preventing 1→2 acyl migration. The cytotoxicity of newly synthesized 2-methoxy-lysophosphatidylethanolamine derivatives was evaluated with resazurin-based method in prostate cancer PC3 cell line. The highest reduction of cell viability was noted for LPE analogues containing myristoyl acyl chain.

Lipid metabolites as potential diagnostic and prognostic biomarkers for acute community acquired pneumonia

Early diagnosis of acute community-acquired pneumonia (CAP) is important in patient triage and treatment decisions. To identify biomarkers that distinguish patients with CAP from non-CAP controls, we conducted an untargeted global metabolome analysis for plasma samples from 142 patients with CAP (CAP cases) and 97 without CAP (non-CAP controls). Thirteen lipid metabolites could discriminate between CAP cases and non-CAP controls with area-under-the-receiver-operating-characteristic curve of >0.8 (P ≤ 10⁻⁹). The levels of glycosphingolipids, sphingomyelins, lysophosphatidylcholines and L-palmitoylcarnitine were higher, while the levels of lysophosphatidylethanolamines were lower in the CAP cases than those in non-CAP controls. All 13 metabolites could distinguish CAP cases from the non-infection, extrapulmonary infection and non-CAP respiratory tract infection subgroups. The levels of trihexosylceramide (d18:1/16:0) were higher, while the levels of lysophosphatidylethanolamines were lower, in the fatal than those of non-fatal CAP cases. Our findings suggest that lipid metabolites are potential diagnostic and prognostic biomarkers for CAP.

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Thirteen lipid metabolites could discriminate CAP cases from non-CAP controls.

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The levels of 2 lipid metabolites differ between fatal and non-fatal CAP cases.

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Lipid metabolites are potential diagnostic and prognostic biomarkers for CAP.

β-Secretase 1's Targeting Reduces Hyperphosphorilated Tau, Implying Autophagy Actors in 3xTg-AD Mice

β-site APP cleaving enzyme 1 (BACE1) initiates APP cleavage, which has been reported to be an inducer of tau pathology by altering proteasome functions in Alzheimer’s disease (AD). However, the exact relationship between BACE1 and PHF (Paired Helical Filaments) formation is not clear. In this study, we confirm that BACE1 and Hsc70 are upregulated in the brains of AD patients, and we demonstrate that both proteins show enhanced expression in lipid rafts from AD-affected triple transgenic mouse brains. BACE1 targeting increased Hsc70 levels in the membrane and cytoplasm fractions and downregulated Hsp90 and CHIP in the nucleus in the hippocampi of 3xTg-AD mice. However, these observations occurred in a proteasome-independent manner in vitro. The BACE1miR-induced reduction of soluble hyperphosphorylated tau was associated with a decrease in MAPK activity. However, the BACE1 RNAi-mediated reduction of hyperphosphorylated tau was only blocked by 3-MA (3-methyladenine) in vitro, and it resulted in the increase of Hsc70 and LAMP2 in lipid rafts from hippocampi of 3xTg-AD mice, and upregulation of survival and homeostasis signaling. In summary, our findings suggest that BACE1 silencing neuroprotects reducing soluble hyperphosphorylated tau, modulating certain autophagy-related proteins in aged 3xTg-AD mice.