Control of free arachidonic acid levels by phospholipases A2 and lysophospholipid acyltransferases

p38 mitogen-activated protein kinase interacts with vinculin at focal adhesions during fatty acid-stimulated cell adhesion

Arachidonic acid stimulates cell adhesion by activating α2β1 integrins in a process that depends on protein kinases, including p38 mitogen activated protein kinase. Here, we describe the interaction of cytoskeletal components with key signaling molecules that contribute to the spreading of, and morphological changes in, arachidonic acid-treated MDA-MB-435 human breast carcinoma cells. Arachidonic acid-treated cells showed increased attachment and spreading on collagen type IV, as measured by electric cell-substrate impedance sensing. Fatty acid-treated cells displayed short cortical actin filaments associated with an increased number of β1 integrin-containing pseudopodia, whereas untreated cells displayed elongated stress fibers and fewer clusters of β1 integrins. Confocal microscopy of arachidonic acid-treated cells showed that vinculin and phospho-p38 both appeared enriched in pseudopodia and at the tips of actin filaments, and fluorescence ratio imaging indicated the increase was specific for the phospho-(active) form of p38. Immunoprecipitates of phospho-p38 from extracts of arachidonic acid-treated cells contained vinculin, and GST-vinculin fusion proteins carrying the central region of vinculin bound phospho-p38, whereas fusion proteins expressing the terminal portions of vinculin did not. These data suggest that phospho-p38 associates with particular domains on critical focal adhesion proteins that are involved in tumor cell adhesion and spreading, and that this association can be regulated by factors in the tumor microenvironment.

Identification of acyl-CoA synthetases involved in the mammalian sphingosine 1-phosphate metabolic pathway

Sphingosine 1-phosphate (S1P) plays important roles both as a bioactive lipid molecule and an intermediate of the sphingolipid-to-glycerophospholipid metabolic pathway. To identify human acyl-CoA synthetases (ACSs) involved in S1P metabolism, we cloned all 26 human ACS genes and examined their abilities to restore deficient sphingolipid-to-glycerophospholipid metabolism in a yeast mutant lacking two ACS genes, FAA1 and FAA4. Here, in addition to the previously identified ACSL family members (ACSL1, 3, 4, 5, and 6), we found that ACSVL1, ACSVL4, and ACSBG1 also restored metabolism. All 8 ACSs were localized either exclusively or partly to the endoplasmic reticulum (ER), where S1P metabolism takes place. We previously proposed the entire S1P metabolic pathway from results obtained using yeast cells, i.e., S1P is metabolized to glycerophospholipids via trans-2-hexadecenal, trans-2-hexadecenoic acid, trans-2-hexadecenoyl-CoA, and palmitoyl-CoA. However, as S1P is not a naturally occurring long-chain base 1-phosphate in yeast, the validity of this pathway required further verification using mammalian cells. In the present study, we treated HeLa cells with the ACS inhibitor triacsin C and found that inhibition of ACSs resulted in accumulation of trans-2-hexadecenoic acid as in ACS mutant yeast. From these results, we conclude that S1P is metabolized by a common pathway in eukaryotes.

The many faces of calmodulin in cell proliferation, programmed cell death, autophagy, and cancer

Calmodulin (CaM) is a ubiquitous Ca(2+) receptor protein mediating a large number of signaling processes in all eukaryotic cells. CaM plays a central role in regulating a myriad of cellular functions via interaction with multiple target proteins. This review focuses on the action of CaM and CaM-dependent signaling systems in the control of vertebrate cell proliferation, programmed cell death and autophagy. The significance of CaM and interconnected CaM-regulated systems for the physiology of cancer cells including tumor stem cells, and processes required for tumor progression such as growth, tumor-associated angiogenesis and metastasis are highlighted. Furthermore, the potential targeting of CaM-dependent signaling processes for therapeutic use is discussed.

Quantitative metabolic profiling of lipid mediators

Lipids are heterogeneous biological molecules that possess multiple physiological roles including cell structure, homeostasis, and restoration of tissue functionality during and after inflammation. Lipid metabolism constitutes a network of pathways that are related at multiple biosynthetic hubs. Disregulation of lipid metabolism can lead to pathophysiological effects and multiple lipid mediators have been described to be involved in physiological processes, (e.g. inflammation). Accordingly, a thorough description of these pathways may shed light on putative relations in multiple complex diseases, including chronic obstructive pulmonary disease, asthma, Alzheimer's disease, multiple sclerosis, obesity, and cancer. Due to the structural complexity of lipids and the low abundance of many lipid mediators, mass spectrometry is the most commonly employed method for analysis. However, multiple challenges remain in the efforts to analyze every lipid subfamily. In this review, the biological role of sphingolipids, glycerolipids, oxylipins (e.g. eicosanoids), endocannabinoids, and N-acylethanolamines in relation to health and disease and the state-of-the-art analyses are summarized. The characterization and understanding of these pathways will increase our ability to examine for interrelations among lipid pathways and improve the knowledge of biological mechanisms in health and disease.

A phosphatidylinositol species acutely generated by activated macrophages regulates innate immune responses

Activation of macrophages with stimuli of the innate immune response results in the intense remodeling of arachidonate-containing phospholipids, leading to the mobilization of large quantities of this fatty acid for conversion into biologically active eicosanoids. As a consequence of this process, the arachidonate levels in membrane phospholipids markedly decrease. We have applied mass spectrometry-based lipid profiling to study the levels of arachidonate-containing phospholipids under inflammatory activation of macrophages. We identify an unusual inositol phospholipid molecule, PI(20:4/20:4), the levels of which do not decrease but actually increase by 300% after activation of the macrophages. PI(20:4/20:4) is formed and degraded rapidly, suggesting a role for this molecule in regulating cell signaling events. Using a metabolipidomic approach consisting in exposing the cells to deuterium-labeled arachidonate at the time they are exposed to stimuli, we show that PI(20:4/20:4) biosynthesis occurs via the sequential incorporation of arachidonate, first into the sn-2 position of a preformed phosphatidylinositol (PI) molecule, followed by the rapid introduction of a second arachidonate moiety into the sn-1 position. Generation requires the participation of cytosolic phospholipase A2α and CoA-dependent acyltransferases. PI(20:4/20:4) formation is also detected in vivo in murine peritonitis exudates. Elevating the intracellular concentration of PI(20:4/20:4) by introducing the lipid into the cells results in enhancement of the microbicidal capacity of macrophages, as measured by reactive oxygen metabolite production and lysozyme release. These findings suggest that PI(20:4/20:4) is a novel bioactive inositol phospholipid molecule that regulates innate immune responses in macrophages.

Role of arachidonic acid metabolism in Stat5 activation induced by oleic acid in MDA-MB-231 breast cancer cells

Epidemiological studies and animal models suggest an association between high levels of dietary fat intake and an increased risk of breast cancer. In breast cancer cells, the free fatty acid oleic acid (OLA) induces proliferation, migration, invasion and an increase of MMP-9 secretion. However, the role of OLA on Stat5 activation and the participation of COX-2 and LOXs activity in Stat5 activation induced by OLA remain to be investigated. We demonstrate here that stimulation of MDA-MB-231 breast cancer cells with 100 μM OLA induces Stat5 phosphorylation at Tyr-694 and an increase of Stat5-DNA complex formation. The Stat5 DNA-binding activity requires COX-2, LOXs, metalloproteinases and Src activities. In addition, OLA induces cell migration through a Stat5-dependent pathway. In summary, our findings establish that OLA induces cell migration through a Stat5-dependent pathway and that Stat5 activation requires AA metabolites in MDA-MB-231 breast cancer cells.

Aging bone marrow mesenchymal stromal cells have altered membrane glycerophospholipid composition and functionality

Human mesenchymal stem/stromal cells (hMSC) are increasingly used in advanced cellular therapies. The clinical use of hMSCs demands sequential cell expansions. As it is well established that membrane glycerophospholipids (GPL) provide precursors for signaling lipids that modulate cellular functions, we studied the effect of the donor's age and cell doublings on the GPL profile of human bone marrow MSC (hBMSC). The hBMSCs, which were harvested from five young and five old adults, showed clear compositional changes during expansion seen at the level of lipid classes, lipid species, and acyl chains. The ratio of phosphatidylinositol to phosphatidylserine increased toward the late-passage samples. Furthermore, 20:4n-6-containing species of phosphatidylcholine and phosphatidylethanolamine accumulated while the species containing monounsaturated fatty acids (FA) decreased during passaging. Additionally, in the total FA pool of the cells, 20:4n-6 increased, which happened at the expense of n-3 polyunsaturated FAs, especially 22:6n-3. The GPL and FA correlated with the decreased immunosuppressive capacity of hBMSCs during expansion. Our observations were further supported by alterations in the gene expression levels of several enzymes involved in lipid metabolism and immunomodulation. The results show that extensive expansion of hBMSCs harmfully modulates membrane GPLs, affecting lipid signaling and eventually impairing functionality.

Role of LOXs and COX-2 on FAK activation and cell migration induced by linoleic acid in MDA-MB-231 breast cancer cells

BACKGROUND

Epidemiological studies and animal models suggest a link between high levels of dietary fat intake and an increased risk of developing breast cancer. Particularly, free fatty acids (FFAs) are involved in several processes, including proliferation, migration and invasion, in breast cancer cells. Linoleic acid (LA) is a dietary n-6 polyunsaturated fatty acid that is known to induce proliferation and invasion in breast cancer cells. So far, however, the contribution of LA to focal adhesion kinase (FAK) activation and cell migration in breast cancer cells has not been studied.

RESULTS

Here, we show that LA promotes FAK and Src activation, as well as cell migration, in MDA-MB-231 breast cancer cells. FAK activation and cell migration require Src, Gi/Go, COX-2 and LOXs activities, whereas both are independent of Δ6 desaturase activity. In addition, we show that cell migration requires FAK activity, whereas FAK activation requires Src activity, thus suggesting a reciprocal catalytic activation mechanism of FAK and Src.

CONCLUSIONS

In summary, our findings show that LA induces FAK activation and cell migration in MDA-MB-231 breast cancer cells.

Simultaneous activation of p38 and JNK by arachidonic acid stimulates the cytosolic phospholipase A2-dependent synthesis of lipid droplets in human monocytes

Exposure of human peripheral blood monocytes to free arachidonic acid (AA) results in the rapid induction of lipid droplet (LD) formation by these cells. This effect appears specific for AA in that it is not mimicked by other fatty acids, whether saturated or unsaturated. LDs are formed by two different routes: (i) the direct entry of AA into triacylglycerol and (ii) activation of intracellular signaling, leading to increased triacylglycerol and cholesteryl ester formation utilizing fatty acids coming from the de novo biosynthetic route. Both routes can be dissociated by the arachidonyl-CoA synthetase inhibitor triacsin C, which prevents the former but not the latter. LD formation by AA-induced signaling predominates, accounting for 60-70% of total LD formation, and can be completely inhibited by selective inhibition of the group IVA cytosolic phospholipase A(2)α (cPLA(2)α), pointing out this enzyme as a key regulator of AA-induced signaling. LD formation in AA-treated monocytes can also be blocked by the combined inhibition of the mitogen-activated protein kinase family members p38 and JNK, which correlates with inhibition of cPLA(2)α activation by phosphorylation. Collectively, these results suggest that concomitant activation of p38 and JNK by AA cooperate to activate cPLA(2)α, which is in turn required for LD formation possibly by facilitating biogenesis of this organelle, not by regulating neutral lipid synthesis.

Glycerol-3-phosphate acyltransferase-2 is expressed in spermatic germ cells and incorporates arachidonic acid into triacylglycerols

BACKGROUND

De novo glycerolipid synthesis begins with the acylation of glycerol-3 phosphate catalyzed by glycerol-3-phosphate acyltransferase (GPAT). In mammals, at least four GPAT isoforms have been described, differing in their cell and tissue locations and sensitivity to sulfhydryl reagents. In this work we show that mitochondrial GPAT2 overexpression in CHO-K1 cells increased TAG content and both GPAT and AGPAT activities 2-fold with arachidonoyl-CoA as a substrate, indicating specificity for this fatty acid.

METHODS AND RESULTS

Incubation of GPAT2-transfected CHO-K1 cells with [1-(14)C]arachidonate for 3 h increased incorporation of [(14)C]arachidonate into TAG by 40%. Consistently, arachidonic acid was present in the TAG fraction of cells that overexpressed GPAT2, but not in control cells, corroborating GPAT2's role in synthesizing TAG that is rich in arachidonic acid. In rat and mouse testis, Gpat2 mRNA was expressed only in primary spermatocytes; the protein was also detected in late stages of spermatogenesis. During rat sexual maturation, both the testicular TAG content and the arachidonic acid content in the TAG fraction peaked at 30 d, matching the highest expression of Gpat2 mRNA and protein.

CONCLUSIONS

These results strongly suggest that GPAT2 expression is linked to arachidonoyl-CoA incorporation into TAG in spermatogenic germ cells.

Effect of ration size on fillet fatty acid composition, phospholipid allostasis and mRNA expression patterns of lipid regulatory genes in gilthead sea bream (Sparus aurata)

The effect of ration size on muscle fatty acid (FA) composition and mRNA expression levels of key regulatory enzymes of lipid and lipoprotein metabolism have been addressed in juveniles of gilthead sea bream fed a practical diet over the course of an 11-week trial. The experimental setup included three feeding levels: (i) full ration until visual satiety, (ii) 70 % of satiation and (iii) 70 % of satiation with the last 2 weeks at the maintenance ration. Feed restriction reduced lipid content of whole body by 30 % and that of fillet by 50 %. In this scenario, the FA composition of fillet TAG was not altered by ration size, whereas that of phospholipids was largely modified with a higher retention of arachidonic acid and DHA. The mRNA transcript levels of lysophosphatidylcholine acyltransferases, phosphatidylethanolamine N-methyltransferase and FA desaturase 2 were not regulated by ration size in the present experimental model. In contrast, mRNA levels of stearoyl-CoA desaturases were markedly down-regulated by feed restriction. An opposite trend was found for a muscle-specific lipoprotein lipase, which is exclusive of fish lineage. Several upstream regulatory transcriptions were also assessed, although nutritionally mediated changes in mRNA transcripts were almost reduced to PPARα and β, which might act in a counter-regulatory way on lipolysis and lipogenic pathways. This gene expression pattern contributes to the construction of a panel of biomarkers to direct marine fish production towards muscle lean phenotypes with increased retentions of long-chain PUFA.

MC-12, an annexin A1-based peptide, is effective in the treatment of experimental colitis

Annexin A1 (ANXA1) inhibits NF-κB, a key regulator of inflammation, the common pathophysiological mechanism of inflammatory bowel diseases (IBD). MC-12, an ANXA1-based tripeptide, suppresses NF-κB activation. Here, we determined the efficacy of MC-12 in the control of IBD. Mice with colitis induced by dextran sodium sulfate (DSS) or 2,4,6-trinitro benzene sulfonic acid (TNBS) were treated with various doses of MC-12 administered intraperitoneally, orally or intrarectally. We determined colon length and the histological score of colitis, and assayed: in colon tissue the levels of TNF-α, IFN-γ, IL-1β, IL-6 and IL-10 by RT-PCR; prostaglandin E₂ (PGE₂), cytoplasmic phospholipase A₂ (cPLA₂) and myeloperoxidase by immunoassay; and COX-2 and NF- κB by immunohistochemistry; and in serum the levels of various cytokines by immunoassay. In both models MC-12: reversed dose-dependently colonic inflammation; inhibited by up to 47% myeloperoxidase activity; had a minimal effect on cytoplasmic phospholipase A₂; reduced significantly the induced levels of TNF-α, IFN-γ, IL-1β, IL-6 and IL-10, returning them to baseline. DSS and TNBS markedly activated NF-κB in colonic epithelial cells and MC-12 decreased this effect by 85.8% and 72.5%, respectively. MC-12 had a similar effect in cultured NCM460 normal colon epithelial cells. Finally, MC-12 suppressed the induction of COX-2 expression, the level of PGE₂ in the colon and PGE₂ metabolite in serum. In conclusion, MC-12, representing a novel class of short peptide inhibitors of NF-κB, has a strong effect against colitis in two preclinical models recapitulating features of human IBD. Its mechanism of action is complex and includes pronounced inhibition of NF-κB. MC-12 merits further development as an agent for the control of IBD.

Phospholipid sources for adrenic acid mobilization in RAW 264.7 macrophages. Comparison with arachidonic acid

Cells metabolize arachidonic acid (AA) to adrenic acid (AdA) via 2-carbon elongation reactions. Like AA, AdA can be converted into multiple oxygenated metabolites, with important roles in various physiological and pathophysiological processes. However, in contrast to AA, there is virtually no information on how the cells regulate the availability of free AdA for conversion into bioactive products. We have used a comparative lipidomic approach with both gas chromatography and liquid chromatography coupled to mass spectrometry to characterize changes in the levels of AA- and AdA-containing phospholipid species in RAW 264.7 macrophage-like cells. Incubation of the cells with AA results in an extensive conversion to AdA but both fatty acids do not compete with each other for esterification into phospholipids. AdA but not AA, shows preference for incorporation into phospholipids containing stearic acid at the sn-1 position. After stimulation of the cells with zymosan, both AA and AdA are released in large quantities, albeit AA is released to a greater extent. Finally, a variety of phosphatidylcholine and phosphatidylinositol molecular species contribute to AA; however, AdA is liberated exclusively from phosphatidylcholine species. Collectively, these results identify significant differences in the cellular utilization of AA and AdA by the macrophages, suggesting non-redundant biological actions for these two fatty acids.

Palmitoleate is a mitogen, formed upon stimulation with growth factors, and converted to palmitoleoyl-phosphatidylinositol

Controversial correlations between biological activity and concentration of the novel lipokine palmitoleate (9Z-hexadecenoate, 16:1) might depend on the formation of an active 16:1 metabolite. For its identification, we analyzed the glycerophospholipid composition of mouse Swiss 3T3 fibroblasts in response to 16:1 using LC-MS/MS. 16:1 was either supplemented to the cell culture medium or endogenously formed when cells were stimulated with insulin or growth factors as suggested by the enhanced mRNA expression of 16:1-biosynthetic enzymes. The proportion of 1-acyl-2-16:1-sn-phosphatidylinositol (16:1-PI) was time-dependently and specifically increased relative to other glycerophospholipids under both conditions and correlated with the proliferation of fatty acid (16:1, palmitate, oleate, or arachidonate)-supplemented cells. Accordingly, cell proliferation was impaired by blocking 16:1 biosynthesis using the selective stearoyl-CoA desaturase-1 inhibitor CAY10566 and restored by supplementation of 16:1. The accumulation of 16:1-PI occurred throughout cellular compartments and within diverse mouse cell lines (Swiss 3T3, NIH-3T3, and 3T3-L1 cells). To elucidate further whether 16:1-PI is formed through the de novo or remodeling pathway of PI biosynthesis, phosphatidate levels and lyso-PI-acyltransferase activities were analyzed as respective markers. The proportion of 16:1-phosphatidate was significantly increased by insulin and growth factors, whereas lyso-PI-acyltransferases showed negligible activity for 16:1-coenzyme A. The relevance of the de novo pathway for 16:1-PI biosynthesis is supported further by the comparable incorporation rate of deuterium-labeled 16:1 and tritium-labeled inositol into PI for growth factor-stimulated cells. In conclusion, we identified 16:1 or 16:1-PI as mitogen whose biosynthesis is induced by growth factors.

Docosahexaenoic acid-induced unfolded protein response, cell cycle arrest, and apoptosis in vascular smooth muscle cells are triggered by Ca²⁺-dependent induction of oxidative stress

Proliferation of vascular smooth muscle cells is a characteristic of pathological vascular remodeling and represents a significant therapeutic challenge in several cardiovascular diseases. Docosahexaenoic acid (DHA), a member of the n-3 polyunsaturated fatty acids, was shown to inhibit proliferation of numerous cell types, implicating several different mechanisms. In this study we examined the molecular events underlying the inhibitory effects of DHA on proliferation of primary human smooth muscle cells isolated from small pulmonary artery (hPASMCs). DHA concentration-dependently inhibited hPASMC proliferation, induced G1 cell cycle arrest, and decreased cyclin D1 protein expression. DHA activated the unfolded protein response (UPR), evidenced by increased mRNA expression of HSPA5, increased phosphorylation of eukaryotic initiation factor 2α, and splicing of X-box binding protein 1. DHA altered cellular lipid composition and led to increased reactive oxygen species (ROS) production. DHA-induced ROS were dependent on both intracellular Ca(2+) release and entry of extracellular Ca(2+). Overall cellular ROS and mitochondrial ROS were decreased by RU360, a specific inhibitor of mitochondrial Ca(2+) uptake. DHA-induced mitochondrial dysfunction was evidenced by decreased mitochondrial membrane potential and decreased cellular ATP content. DHA triggered apoptosis as found by increased numbers of cleaved caspase-3- and TUNEL-positive cells. The free radical scavenger Tempol counteracted DHA-induced ROS, cell cycle arrest, induction of UPR, and apoptosis. We conclude that Ca(2+)-dependent oxidative stress is the central and initial event responsible for induction of UPR, cell cycle arrest, and apoptosis in DHA-treated hPASMCs.

Phospholipase A2IVα regulates phagocytosis independent of its enzymatic activity

Group IVα phospholipase A(2) (PLA(2)IVα) is a lipolytic enzyme that catalyzes the hydrolysis of membrane phospholipids to generate precursors of potent inflammatory lipid mediators. Here, the role of PLA(2)IVα in Fc receptor (FcR)-mediated phagocytosis was investigated, demonstrating that PLA(2)IVα is selectively activated upon FcR-mediated phagocytosis in macrophages and that it rapidly translocates to the site of the nascent phagosome. Moreover, pharmacological inhibition of PLA(2)IVα by pyrrophenone reduces particle internalization by up to 50%. In parallel, fibroblasts from PLA(2)IVα knock-out mice overexpressing FcγRIIA and able to internalize IgG-opsonized beads show 50% lower phagocytosis, compared with wild-type cells, and transfection of PLA(2)IVα fully recovers this impaired function. Interestingly, transfection of the catalytically inactive deleted PLA(2)IVα mutant (PLA(2)IVα(1-525)) and point mutant (PLA(2)IVα-S228C) also promotes recovery of this impaired function. Finally, transfection of the PLA(2)IVα C2 domain (which is directly involved in PLA(2)IVα membrane binding), but not of PLA(2)IVα-D43N (which cannot bind to membranes), rescues FcR-mediated phagocytosis. These data unveil a new mechanism of action for PLA(2)IVα, which demonstrates that the membrane binding, and not the enzymatic activity, is required for PLA(2)IVα modulation of FcR-mediated phagocytosis.

Dynamics of arachidonic acid mobilization by inflammatory cells

The development of mass spectrometry-based techniques is opening new insights into the understanding of arachidonic acid (AA) metabolism. AA incorporation, remodeling and release are collectively controlled by acyltransferases, phospholipases and transacylases that exquisitely regulate the distribution of AA between the different glycerophospholipid species and its mobilization during cellular stimulation. Traditionally, studies involving phospholipid AA metabolism were conducted by using radioactive precursors and scintillation counting from thin layer chromatography separations that provided only information about lipid classes. Today, the input of lipidomic approaches offers the possibility of characterizing and quantifying specific molecular species with great accuracy and within a biological context associated to protein and/or gene expression in a temporal frame. This review summarizes recent results applying mass spectrometry-based lipidomic approaches to the identification of AA-containing glycerophospholipids, phospholipid AA remodeling and synthesis of oxygenated metabolites.

Origins of metabolic complications in obesity: ectopic fat accumulation. The importance of the qualitative aspect of lipotoxicity

PURPOSE OF REVIEW

This study highlights two aspects of the concept of lipotoxicity. First, the metabolic consequences following ectopic fat accumulation are not only determined by the amount of lipid accumulated, but also the quality of lipid species. Second, the existence of allostatic mechanisms operating at cellular and tissue levels, which counterbalance the negative effects of lipid overload.

RECENT FINDINGS

The development of lipidomics has allowed the isolation and identification of a wide range of lipid species. Some are highly reactive and capable of inducing undesirable toxic effects. Here we focus on recent information related to pathways involved in the production of these reactive lipid species, their sites of generation and tropism for specific organelles and the molecular mechanisms through which they exert toxic effects. We describe how cell membranes and the lipid species forming their bilayer constitute the main platform from which reactive lipid species are generated. We propose that strategies aimed at maintaining membrane lipid homeostasis are fundamental to preventing the initiation of metabolically relevant lipotoxicity.

SUMMARY

It is essential to understand the qualitative component of lipid species involved in cellular toxicity and the molecular mechanisms mediating these toxic effects to identify new therapeutic targets.

Ginger phenylpropanoids inhibit IL-1beta and prostanoid secretion and disrupt arachidonate-phospholipid remodeling by targeting phospholipases A2

The rhizome of ginger (Zingiber officinale) is employed in Asian traditional medicine to treat mild forms of rheumatoid arthritis and fever. We have profiled ginger constituents for robust effects on proinflammatory signaling and cytokine expression in a validated assay using human whole blood. Independent of the stimulus used (LPS, PMA, anti-CD28 Ab, anti-CD3 Ab, and thapsigargin), ginger constituents potently and specifically inhibited IL-1β expression in monocytes/macrophages. Both the calcium-independent phospholipase A(2) (iPLA(2))-triggered maturation and the cytosolic phospholipase A(2) (cPLA(2))-dependent secretion of IL-1β from isolated human monocytes were inhibited. In a fluorescence-coupled PLA(2) assay, most major ginger phenylpropanoids directly inhibited i/cPLA(2) from U937 macrophages, but not hog pancreas secretory phospholipase A(2). The effects of the ginger constituents were additive and the potency comparable to the mechanism-based inhibitor bromoenol lactone for iPLA(2) and methyl arachidonyl fluorophosphonate for cPLA(2), with 10-gingerol/-shogaol being most effective. Furthermore, a ginger extract (2 μg/ml) and 10-shogaol (2 μM) potently inhibited the release of PGE(2) and thromboxane B2 (>50%) and partially also leukotriene B(4) in LPS-stimulated macrophages. Intriguingly, the total cellular arachidonic acid was increased 2- to 3-fold in U937 cells under all experimental conditions. Our data show that the concurrent inhibition of iPLA(2) and prostanoid production causes an accumulation of free intracellular arachidonic acid by disrupting the phospholipid deacylation-reacylation cycle. The inhibition of i/cPLA(2), the resulting attenuation of IL-1β secretion, and the simultaneous inhibition of prostanoid production by common ginger phenylpropanoids uncover a new anti-inflammatory molecular mechanism of dietary ginger that may be exploited therapeutically.

Altered arachidonate distribution in macrophages from caveolin-1 null mice leading to reduced eicosanoid synthesis

In this work we have studied the effect of caveolin-1 deficiency on the mechanisms that regulate free arachidonic acid (AA) availability. The results presented here demonstrate that macrophages from caveolin-1-deficient mice exhibit elevated fatty acid incorporation and remodeling and a constitutively increased CoA-independent transacylase activity. Mass spectrometry-based lipidomic analyses reveal stable alterations in the profile of AA distribution among phospholipids, manifested by reduced levels of AA in choline glycerophospholipids but elevated levels in ethanolamine glycerophospholipids and phosphatidylinositol. Furthermore, macrophages from caveolin-1 null mice show decreased AA mobilization and prostaglandin E(2) and LTB(4) production upon cell stimulation. Collectively, these results provide insight into the role of caveolin-1 in AA homeostasis and suggest an important role for this protein in the eicosanoid biosynthetic response.

Parameters affecting the accuracy of the MALDI-TOF MS determination of the phosphatidylcholine/lysophosphatidylcholine (PC/LPC) ratio as potential marker of spermatozoa quality

Matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) is increasingly used to characterize (phospho)lipids. However, quantitative MALDI data are often questioned because ion suppression may occur if mixtures are analyzed. Therefore, relative (but no absolute) data are normally derived from the MALDI mass spectra of lipid mixtures. We are particularly interested in the phosphatidylcholine/lysophosphatidylcholine (PC/LPC) ratio because it seems to represent a suitable measure of the inflammatory activity. In this study, different parameters affecting the achievable accuracy of the MALDI-TOF MS determination of the PC/LPC ratio are compared. It will be shown that particularly the applied laser fluence as well as the used solvents influence the accuracies. Using artificial lipid mixtures it will be demonstrated that the PC/LPC ratio can be determined with an accuracy of about ±10% making the MALDI assay comparable to established methods. Finally, it will be shown that the optimized conditions are also useful to determine the PC/LPC ratios in human seminal plasma.

Mechanisms for anti-inflammatory effects of 1-[15(S)-hydroxyeicosapentaenoyl] lysophosphatidylcholine, administered intraperitoneally, in zymosan A-induced peritonitis

BACKGROUND AND PURPOSE

Lysophosphatidylcholines (lysoPCs) with polyunsaturated acyl chains are known to exert anti-inflammatory actions. 15-Lipoxygeanation is crucial for anti-inflammatory action of polyunsaturated acylated lysoPCs. Here, the anti-inflammatory actions of 1-(15-hydroxyeicosapentaenoyl)-lysoPC (15-HEPE-lysoPC) and its derivatives were examined in a mechanistic analysis.

EXPERIMENTAL APPROACH

Anti-inflammatory actions of 15-HEPE-lysoPC in zymosan A-induced peritonitis of mice were examined by measuring plasma leakage and leucocyte infiltration, and determining levels of lipid mediators or cytokines.

KEY RESULTS

When each lysoPC, administered i.v., was assessed for its ability to suppress zymosan A-induced plasma leakage, 15-HEPE-lysoPC was found to be more potent than 1-(15-hydroperoxyeicosapentaenoyl)-lysoPC or 1-eicosapentaenoyl-lysoPC. Separately, i.p. administration of 15-HEPE-lysoPC markedly inhibited plasma leakage, in contrast to 15-HEPE, which had only a small effect. 15-HEPE-lysoPC also decreased leucocyte infiltration. Moreover, it reduced the formation of LTC₄ and LTB₄, 5-lipoxygenation products, as well as the levels of pro-inflammatory cytokines. The time-course study indicated that 15-HEPE-lysoPC might participate in both the early inflammatory phase and resolution phase. Additionally, 15-HEPE-lysoPC administration caused a partial suppression of LTC₄-induced plasma leakage and LTB₄-induced leucocyte infiltration. In the metabolism study, peritoneal exudate was shown to contain lysoPC-hydrolysing activity, crucial for anti-inflammatory activity, and a system capable of generating lipoxin A from 15-hydroxy eicosanoid precursor.

CONCLUSIONS AND IMPLICATIONS

15-HEPE-lysoPC, a precursor for 15-HEPE in target cells, induced anti-inflammatory actions by inhibiting the formation of pro-inflammatory leukotrienes and cytokines, and by enhancing the formation of lipoxin A. 15-HEPE-lysoPC might be one of many potent anti-inflammatory lipids in vivo.

Study of arachidonoyl specificity in two enzymes of the PI cycle

We identified a conserved pattern of residues L-X((3-4))-R-X((2))-L-X((4))-G, in which -X((n))- is n residues of any amino acid, in two enzymes acting on the polyunsaturated fatty acids, diacylglycerol kinase epsilon (DGKɛ) and phosphatidylinositol-4-phosphate-5-kinase Iα (PIP5K Iα). DGKɛ is the only one of the 10 mammalian isoforms of DGK that exhibits arachidonoyl specificity and is the only isoform with the motif mentioned above. Mutations of the essential residues in this motif result in the loss of arachidonoyl specificity. Furthermore, DGKα can be converted to an enzyme having this motif by substituting only one residue. When DGKα was mutated so that it gained the motif, the enzyme also gained some specificity for arachidonoyl-containing diacylglycerol. This motif is present also in an isoform of phosphatidylinositol-4-phosphate-5-kinase that we demonstrated had arachidonoyl specificity for its substrate. Single residue mutations within the identified motif of this isoform result in the loss of activity against an arachidonoyl substrate. The importance of acyl chain specificity for the phosphatidic acid activation of phosphatidylinositol-4-phosphate-5-kinase is also shown. We demonstrate that the acyl chain dependence of this phosphatidic acid activation is dependent on the substrate. This is the first demonstration of a motif that endows specificity for an acyl chain in enzymes DGKε and PIP5K Iα.

Role of DDR1 in the gelatinases secretion induced by native type IV collagen in MDA-MB-231 breast cancer cells

Discoidin domain receptors (DDRs) are receptor tyrosine kinases that get activated by collagens in its native triple-helical form. In mammalian cells, DDR family consists of two members, namely DDR1 and DDR2, which mediates migration and proliferation of several cell types. DDR1 is activated by native type IV collagen and overexpressed in human breast cancer. Type IV collagen is the main component of basement membrane (BM), and the ability to degrade and penetrate BM is related with an increased potential for invasion and metastasis. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that collectively are capable of degrading all components of the extracellular matrix, including the BM. In breast cancer cells, denatured type IV collagen induces MMP-9 secretion and invasion. However, the role of DDR1 in the regulation of gelatinases (MMP-2 and -9) secretion and invasion in breast cancer cells remains to be studied. We demonstrate here that native type IV collagen induces MMP-2 and -9 secretions and invasion through a DDR1 and Src-dependent pathway, together with an increase of MMP-2 and -9-cell surface levels. MMP-2 and -9 secretions require PKC kinase activity, epidermal growth factor receptor (EGFR) activation, arachidonic acid (AA) production and AA metabolites in MDA-MB-231 breast cancer cells. In summary, our data demonstrate, for the first time, that DDR1 mediates MMP-2 and -9 secretions and invasion induced by native type IV collagen in MDA-MB-231 breast cancer cells.

Dietary arachidonate differentially alters desaturase-elongase pathway flux and gene expression in liver and intestine of suckling pigs

Because dietary arachidonate (ARA) and its eicosanoid derivatives are major regulators of intestinal homeostasis and repair following injury, we evaluated the effects of dietary ARA on desaturation and elongation of (13)C-18:2(n-6) and mRNA abundance of Δ-6-desaturase (FADS2), elongase (ELOVL5), and Δ-5-desaturase (FADS1) in liver and intestine. Day-old pigs (n = 96) were fed milk-based formula containing 0, 0.5, 2.5, or 5% ARA or 5% eicosapentaenoic acid of total fatty acids for 4, 8, and 16 d. In liver, the desaturation rate [nmol/(g tissue⋅h)] of (13)C-18:2(n-6) to (13)C-18:3(n-6) decreased 56% between 4 and 16 d but was not affected by diet. Whereas accumulation in (13)C-20:3(n-6) also decreased with age by 67%, it increased linearly with increasing dietary ARA (P < 0.06). In comparison, intestinal flux was ~50% less than liver flux and was unaffected by age, but desaturation to (13)C-18:3(n-6) increased linearly (by 57%) in pigs fed ARA diets (P < 0.001), equaling the rate observed in sow-fed controls. In both liver and intestine, alternate elongation to (13)C-20:2(n-6) (via Δ-8-desaturase) was markedly elevated in pigs fed the 0% ARA diet compared with all other dietary treatments (P < 0.01). Transcript abundance of FADS2, ELOVL5, and FADS1 was not affected in liver by diet (P > 0.05) but decreased precipitously between birth and d 4 (~70%; P < 0.05). In contrast, intestinal abundance of FADS2 and FADS1 increased 60% from d 4 to 16. In conclusion, dietary ARA regulated the desaturase-elongase pathway in a tissue-specific manner. In liver, ARA had modest effects on (n-6) fatty acid flux, and intestinal FADS2 activity and mRNA increased. Additionally, hepatic flux decreased with postnatal age, whereas intestinal flux did not change.

CD36 protein is involved in store-operated calcium flux, phospholipase A2 activation, and production of prostaglandin E2

The scavenger receptor FAT/CD36 contributes to the inflammation associated with diabetes, atherosclerosis, thrombosis, and Alzheimer disease. Underlying mechanisms include CD36 promotion of oxidative stress and its signaling to stress kinases. Here we document an additional mechanism for the role of CD36 in inflammation. CD36 regulates membrane calcium influx in response to endoplasmic reticulum (ER) stress, release of arachidonic acid (AA) from cellular membranes by cytoplasmic phospholipase A(2)α (cPLA(2)α) and contributes to the generation of proinflammatory eicosanoids. CHO cells stably expressing human CD36 released severalfold more AA and prostaglandin E(2) (PGE(2)), a major product of AA metabolism by cyclooxygenases, in response to thapsigargin-induced ER stress as compared with control cells. Calcium influx after ER calcium release resulted in phosphorylation of cPLA(2) and its translocation to membranes in a CD36-dependent manner. Peritoneal macrophages from CD36(-/-) mice exhibited diminished calcium transients and reduced AA release after thapsigargin or UTP treatment with decreased ERK1/2 and cPLA(2) phosphorylation. However, PGE(2) production was unexpectedly enhanced in CD36(-/-) macrophages, which probably resulted from a large induction of cyclooxygenase 2 mRNA and protein. The data demonstrate participation of CD36 in membrane calcium influx in response to ER stress or purinergic receptor stimulation resulting in AA liberation for PGE(2) formation. Collectively, these results identify a mechanism contributing to the pleiotropic proinflammatory effects of CD36 and suggest that its targeted inhibition may reduce the acute inflammatory response.

Analysis of bioactive eicosanoids in equine plasma by stable isotope dilution reversed-phase liquid chromatography/multiple reaction monitoring mass spectrometry

Oxidative metabolites of arachidonic acid (AA) are implicated in inflammation. Thus, we evaluated cycloxygenases (COXs) and lipoxygenases (LOs) mediated metabolism of AA to eicosanoids in equine plasma. Eicosanoids were extracted from plasma by two liquid-liquid extraction (LLE) steps; first was by chloroform/isopropanol and second by methyl-tert-butyl ether. For identification and quantification of 25 eicosanoids, a highly specific, selective and sensitive stable isotope dilution liquid chromatography (LC) multiple reaction monitoring (MRM) mass spectrometric (MS) method was developed. To avoid artifact formation of eicosanoids, deferoxamine was added to plasma to chelate residual transition metal ions. The calibration curve showed excellent linearity within 0.1 to 10 ng/mL. Slopes of the calibration curves generated by adding known quantities of eicosanoids in plasma were higher than those prepared in methanol/mobile phase A. Addition of deferoxamine decreased the slope of calibration curves generated using plasma. Limit of detection (LOD) was 1-10 pg on-column for 25 different eicosanoids. Inter-day accuracy was 86-111%, whereas intra-day accuracy was from 88-110%, and precision did not exceed 15% for all quality control (QC) samples. To evaluate the formation of eicosanoids, AA was exogenously added or endogenous AA was released from esterified lipids by calcium ionophore (CI) A23187 treatment of equine whole blood. Pre-treatment of equine whole blood with dexamethasone (DEX) significantly inhibited AA or CI A23187- mediated formation of eicosanoids. The validated method is now employed in studies undertaken to better understand the mechanism of action and pharmacokinetics/pharmacodynamics of eicosanoids after administration of glucocorticoids to horses. This method is reliably reproducible.

The metabolic cascade leading to eicosanoid precursors--desaturases, elongases, and phospholipases A2--is altered in Zucker fatty rats

Metabolic syndrome characterized by insulin resistance and obesity is accompanied by severe lipid metabolism perturbations and chronic low-grade inflammation. However, many unresolved questions remained regarding the regulation that underlie dyslipidemia, particularly the regulation of the metabolic cascade (synthesis and release) leading to eicosanoid precursors release. This study was undertaken to investigate the regulation of desaturases/elongases and phospholipases A(2) during the establishment of metabolic syndrome. Our results showed that delta-6 desaturase as well as elongase-6 expressions were upregulated in 3-month-old Zucker fatty rats as compared to lean littermates, independently of SREBP-1c activation. We also demonstrated for the first time an increase of liver group VII phospholipase A(2) gene expression in the obese animals together with a strong specific inhibition of type IVA and VIA phospholipases A(2). These results suggest that the regulation of unsaturated fatty acids biosynthesis and signalling cascade could contribute to the development of liver lipid dysregulation related to metabolic syndrome and may be considered as new potential targets in such pathological conditions.

Influence of cellular arachidonic acid levels on phospholipid remodeling and CoA-independent transacylase activity in human monocytes and U937 cells

The availability of free arachidonic acid (AA) constitutes a limiting step in the synthesis of biologically active eicosanoids. Free AA levels in cells are regulated by a deacylation/reacylation cycle of membrane phospholipids, the so-called Lands cycle, as well as by further remodeling reactions catalyzed by CoA-independent transacylase. In this work, we have comparatively investigated the process of AA incorporation into and remodeling between the various phospholipid classes of human monocytes and monocyte-like U937 cells. AA incorporation into phospholipids was similar in both cell types, but a marked difference in the rate of remodeling was appreciated. U937 cells remodeled AA at a much faster rate than human monocytes. This difference was found not to be related to the differentiation state of the U937 cells, but rather to the low levels of esterified arachidonate found in U937 cells compared to human monocytes. Incubating the U937 cells in AA-rich media increased the cellular content of this fatty acid and led to a substantial decrease of the rate of phospholipid AA remodeling, which was due to reduced CoA-independent transacylase activity. Collectively, these findings provide the first evidence that cellular AA levels determine the amount of CoA-independent transacylase activity expressed by cells and provide support to the notion that CoA-IT is a major regulator of AA metabolism in human monocytes.

Role of cytochrome P450 enzymes in the bioactivation of polyunsaturated fatty acids

Cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA), such as epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid, serve as second messengers of various hormones and growth factors and play pivotal roles in the regulation of vascular, renal and cardiac function. As discussed in the present review, virtually all of the major AA metabolizing CYP isoforms accept a variety of other polyunsaturated fatty acids (PUFA), including linoleic, eicosapentaenoic (EPA) and docosahexaenoic acids (DHA), as efficient alternative substrates. The metabolites of these alternative PUFAs also elicit profound biological effects. The CYP enzymes respond to alterations in the chain-length and double bond structure of their substrates with remarkable changes in the regio- and stereoselectivity of product formation. The omega-3 double bond that distinguishes EPA and DHA from their omega-6 counterparts provides a preferred epoxidation site for CYP1A, CYP2C, CYP2J and CYP2E subfamily members. CYP4A enzymes that predominantly function as AA ω-hydroxylases show largely increased (ω-1)-hydroxylase activities towards EPA and DHA. Taken together, these findings indicate that CYP-dependent signaling pathways are highly susceptible to changes in the relative bioavailability of the different PUFAs and may provide novel insight into the complex mechanisms that link essential dietary fatty acids to the development of cardiovascular disease.

Markers of monocyte activation revealed by lipidomic profiling of arachidonic acid-containing phospholipids

Stimulated human monocytes undergo an intense trafficking of arachidonic acid (AA) among glycerophospholipidclasses. Using HPLC coupled to electrospray ionization mass spectrometry, we have characterized changes in the levels of AA-containing phospholipid species in human monocytes. In resting cells, AA was found esterified into various molecular species of phosphatidylinositol (PI), choline glycerophospholipids (PCs), and ethanolamine glycerophospholipids (PEs). All major AA-containing PC and PI molecular species decreased in zymosan-stimulated cells; however, no PE molecular species was found to decrease. In contrast, the levels of three AA-containing species increased in zymosan-activated cells compared with resting cells: 1,2-diarachidonyl-glycero-3-phosphoinositol [PI(20:4/20:4)]; 1,2-diarachidonyl-glycero-3-phosphocholine [PC(20:4/20:4)]; and 1-palmitoleoyl-2-arachidonyl-glycero-3-phosphoethanolamine [PE(16:1/20:4)]. PI(20:4/20:4) and PC(20:4/20:4), but not PE(16:1/20:4), also significantly increased when platelet-activating factor or PMA were used instead of zymosan to stimulate the monocytes. Analysis of the pathways involved in the synthesis of these three lipids suggest that PI(20:4/20:4) and PC(20:4/20:4) were produced in a deacylation/reacylation pathway via acyl-CoA synthetase-dependent reactions, whereas PE(16:1/20:4) was generated via a CoA-independent transacylation reaction. Collectively, our results define the increases in PI(20:4/20:4) and PC(20:4/20:4) as lipid metabolic markers of human monocyte activation and establish lipidomics as a powerful tool for cell typing under various experimental conditions.

Signaling role for lysophosphatidylcholine acyltransferase 3 in receptor-regulated arachidonic acid reacylation reactions in human monocytes

Cellular availability of free arachidonic acid (AA) is an important step in the production of pro- and anti-inflammatory eicosanoids. Control of free AA levels in cells is carried out by the action of phospholipase A2s and lysophospholipid acyltransferases, which are responsible for the reactions of deacylation and incorporation of AA from and into the sn-2 position of phospholipids, respectively. In this work, we have examined the pathways for AA incorporation into phospholipids in human monocytes stimulated by zymosan. Our data show that stimulated cells exhibit an enhanced incorporation of AA into phospholipids that is not secondary to an increased availability of lysophospholipid acceptors due to phospholipase A2 activation but rather reflects the receptor-regulated nature of the AA reacylation pathway. In vitro activity measurements indicate that the receptor-sensitive step of the AA reacylation pathway is the acyltransferase using lysophosphatidylcholine (lysoPC) as acceptor, and inhibition of the enzyme lysoPC acyltransferase 3 by specific small interfering RNA results in inhibition of the stimulated incorporation of AA into phospholipids. Collectively, these results define lysoPC acyltransferase 3 as a novel-signal-regulated enzyme that is centrally implicated in limiting free AA levels in activated cells.