Analysis of choline and phosphorylcholine content in human neutrophils stimulated by f-Met-Leu-Phe and phorbol myristate acetate: contribution of phospholipase D and C

Measurement of phospholipid metabolism in intact neutrophils

Phospholipid-metabolizing enzymes are important participants in neutrophil signal transduction pathways. The methods discussed herein describe assays for assessing the activities of phospholipase A2 (PLA2), phospholipase C (PLC), phospholipase D (PLD), and phosphoinositide 3-OH-kinase in intact neutrophils. PLA2 activity is measured as the release of radiolabeled arachidonic acid. PLC activity is measured as the accumulation of inositol 1,4,5-trisphosphate (IP3), a water-soluble product, using a commercially available radioreceptor assay kit. PLD activity is measured as the appearance of its radiolabeled products, phosphatidic acid and phosphatidylethanol. PI3-K activity is measured as the appearance of its radiolabeled product, phosphatidylinositol-3,4,5-trisphosphate.

Activation of phospholipase D involved in both injury and survival in A549 alveolar epithelial cells exposed to H2O2

To determine the role of the phospholipase D (PLD) pathway in injury and survival of alveolar epithelial cells, A549 cells were exposed to H(2)O(2) (500 microM) which resulted in time-dependent injury and bi-phasic increase of PLD activity at 5 min and at 3 h, respectively. n-Butanol (0.5%) inhibited PLD activation, attenuated cell injury at 5 min of H(2)O(2) exposure, but enhanced injury at 3h of exposure. This activation was inhibited by treatment with catalase (500 units/ml). Exogenous phosphatidic acid mimicked the effects of PLD activation, and diphenyliodonium (NADPH oxidase inhibitor) reversed the decline in cell viability induced by H(2)O(2) exposure. Propranolol (phosphatidic acid phospholydrolase inhibitor) and quinacrine (phospholipase A2 inhibitor) had weak effects on H(2)O(2)-induced PLD activation but reversed H(2)O(2)-induced injury. We speculate that PLD activation at the initiation of H(2)O(2) exposure predominantly results in NAPDH oxidase activation, which mediates A549 cell injury, but turns to mediating cell survival as the H(2)O(2) attack continues, which might be mainly due to the accumulation of intracellular phosphatidic acid.

Sphingosine-1-phosphate increases human alveolar epithelial IL-8 secretion, proliferation and neutrophil chemotaxis

Sphingosine-1-phosphate (S1P) has been presented recently as a pro-inflammatory agent in the airway epithelium since S1P levels are increased in bronchoalveolar lavage fluid of human asthmatics. However, the effects of S1P over the alveolar epithelium and neutrophil interactions are poorly understood. Here, we show that S1P increased interleukin 8 (IL-8) gene expression and protein secretion and proliferation in alveolar epithelial cells A549 at physiological concentrations (1 microM). At the same time, S1P increased intracellular Ca2+ concentration (potency 17.91 microM, measured by epifluorescence microscopy), phospholipase D (PLD) activity (measured by chemiluminiscence method) and extracellular matrix-regulated kinase1/2 (ERK1/2) phosphorylation (measured by western blot) via G(i)-coupled receptor (inhibited by pertussis toxin 100 ng/ml) in A549 cells. Both, IL-8 secretion and A549 proliferation were dependent of PLD activity (inhibited by 1-butanol 0.5%), intracellular Ca2+ (inhibited by acetoxymethyl 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) 100 microM), ERK1/2 phosphorylation (inhibited by 2-[2-amino-3-methoxyphenyl]-4H-1-benzopyran-4-one (PD98059) 10 microM) and G(i)-coupled receptors (blocked by pertussis toxin 100 ng/ml). Moreover, S1P increased intercellular adhesion molecule I (ICAM-1) expression and failed in vascular cell adhesion molecule I (VCAM-1) modification (measured by flow cytometer) in A549. Indirectly, A549 supernatant fluids arising from A549-S1P 1 microM stimulation decreased L-selectin expression without CD11b/CD18 integrin modification in human neutrophils. In the same way, A549-S1P supernatant fluids increased neutrophil chemotaxis (Boyden chamber), which was inhibited by antibody against IL-8. This study demonstrates for the first time that S1P participates in the alveolar epithelial interactions in vitro.

Effects of short chain fatty acids on effector mechanisms of neutrophils

Short chain fatty acids (SCFAs) are metabolic by products of anaerobic bacteria fermentation. These fatty acids, despite being an important fuel for colonocytes, are also modulators of leukocyte function. The aim of this study was to evaluate the effects of SCFAs (acetate, propionate, and butyrate) on function of neutrophils, and the possible mechanisms involved. Neutrophils obtained from rats by intraperitoneal lavage 4 h after injection of oyster glycogen solution (1%) were treated with non toxic concentrations of the fatty acids. After that, the following measurements were performed: phagocytosis and destruction of Candida albicans, production of ROS (O(2)(*-), H(2)O(2), and HOCl) and degranulation. Gene expression (p47(phox) and p22(phox)) and protein phosphorylation (p47(phox)) were analyzed by real time reverse transcriptase chain reaction (RT-PCR) and Western blotting, respectively. Butyrate inhibited phagocytosis and killing of C. albicans. This SCFA also had an inhibitory effect on production of O(2)(*-), H(2)O(2), and HOCl by neutrophils stimulated with PMA or fMLP. This effect of butyrate was not caused by modulation of expression of NADPH oxidase subunits (p47(phox) and p22(phox)) but it was in part due to reduced levels of p47(phox) phosphorylation and an increase in the concentration of cyclic AMP. Acetate increased the production of O(2)(*-) and H(2)O(2) in the absence of stimuli but had no effect on phagocytosis and killing of C. albicans. Propionate had no effect on the parameters studied. These results suggest that butyrate can modulate neutrophil function and thus could be important in inflammatory neutrophil-associated diseases.

CCR5 signaling through phospholipase D involves p44/42 MAP-kinases and promotes HIV-1 LTR-directed gene expression

The chemokine receptor CCR5 plays an important role as an entry gate for the human immunodeficiency virus-1 (HIV-1) and for viral postentry events. Among signal transducers used by chemoattractant receptors, the phosphatidylcholine-specific phospholipase D (PLD) produces large amounts of second messengers in most cell types. However, the relevance of PLD isoforms to CCR5 signaling and HIV-1 infection process remains unexplored. We show here that CCR5 activation by MIP-1beta in HeLa-MAGI cells triggered a rapid and substantial PLD activity, as assessed by mass choline production. This activity required the activation of ERK1/2-MAP kinases and involved both PLD1 and PLD2. MIP-1beta also promoted the activation of an HIV-1 long terminal repeat (LTR) by the transactivator Tat in HeLa P4.2 cells through a process involving ERK1/2. Expression of wild-type and catalytically inactive PLDs dramatically boosted and inhibited the LTR activation, respectively, without altering Tat expression. Wild-type and inactive PLDs also respectively potentiated and inhibited HIV-1(BAL) replication in MAGI cells. Finally, in monocytic THP-1 cells, antisense oligonucleotides to both PLDs dramatically inhibited the HIV-1 replication. Thus, PLD is activated downstream of ERK1/2 upon CCR5 activation and plays a major role in promoting HIV-1 LTR transactivation and virus replication, which may open novel perspectives to anti-HIV-1 strategies.

Measurement of phospholipid metabolism in intact neutrophils

Phospholipid metabolizing enzymes are important participants in neutrophil signal transduction pathways. The methods discussed herein describe assays for assessing the activities of phospholipase (PL)A2, PLC, PLD, and phosphoinositide 3-OH-kinase (PI3-K) in intact neutrophils. PLA2 activity is measured as the release of radiolabed arachidonic acid. PLC activity is measured as the accumulation of inositol 1,4,5-trisphosphate (IP3), a water-soluble product, using a commercially available radioreceptor assay kit. PLD activity is measured as the appearance of its radiolabeled products, phosphatidic acid and phosphatidylethanol. PI3-K activity is measured as the appearance of its radiolabeled product, phosphatidylinositol-3,4,5-trisphosphate.

A role of p44/42 mitogen‐activated protein kinases in formylpeptide receptor‐mediated phospholipase D activity and oxidant production

Phosphatidylcholine-specific phospholipase D (PLD) is a major cellular source of phosphatidic acid and choline, which regulate various physiopathological processes. PLD activation mediated by chemoattractants involves protein phosphorylation. This study provides pharmacological and biochemical evidence of a major role of p44/42 MAP kinases (ERK1/2) in PLD activation induced by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP). ERK1/2 inhibition by the MEK1/2 antagonist U0126 in neutrophilic HL-60 cells or HEK 293T cells stably expressing fMLP receptors abolished fMLP-mediated PLD activity. Conversely, a constitutively activated MEK1 mutant expressed in HEK 293T cells potentiated fMLP-induced PLD activity. Expression of inactive PLD mutants showed that PLD2, but not PLD1, contributed to fMLP-mediated PLD activity. PLD2 co-immunoprecipitated with ERK1/2 and became phosphorylated on MAP kinase consensus sites in fMLP-stimulated cells. In cell-free systems, ERK2 gave rise to strong ATP-dependent PLD activity and directly phosphorylated PLD2 that generated two phosphopeptides only after tryptic digestion. Finally, pharmacological inhibition of ERK activation and the inhibition of PLD expression by antisense oligonucleotides in HL-60 cells suggest that the ERK/PLD2 pathway contributes to fMLP-mediated oxidant production. In conclusion, the fMLP-mediated PLD activity is regulated by ERK1/2, involving a predominant contribution of PLD2. The ERK/PLD2 coupling may provide potential pharmacological targets to control PLD-associated cellular dysfunctions.

Sensitization of human neutrophil defense activities through activation of platelet-activating factor receptors by ginkgolide B, a bioactive component of the Ginkgo biloba extract EGB 761

Ginkgolide B (GKB, BN 52021) was described as a platelet-activating factor (Paf) receptor antagonist. However, it is not known whether all GKB biological effects are mediated through Paf receptor antagonism only. To gain insight into the drug mode of action, we investigated here the effects of GKB per se on functional and signaling activities in human polymorphonuclear leukocytes (PMN). Treatment of PMN with GKB (0.5-12 microM) stimulates a rapid and weak production of reactive oxygen species determined by chemiluminescence. ROS production required the activation of protein kinase C (PKC), tyrosine kinases and p38 mitogen-activated protein kinase as indicated by inhibitory effects of, respectively, GF 109203X (IC(50) of 0.5 microM), genistein (IC(50) of 0.5 microM) and SB 203580 (IC(50) of 0.2 microM) or SB 202190 (IC(50) of 1.1 microM). GKB stimulated a Pertussis toxin-sensitive PLD activity assessed by the formation of tritiated phosphatidic acid and choline. By contrast, GKB did prevent the Paf-mediated PLD activity and CL response (IC(50) of 2 microM). Interestingly, both GKB and Paf-induced CL response were prevented by selective Paf antagonists such as CV 6209 or WEB 2086 indicating that GKB may directly activate Paf receptors. Finally, GKB potentiated the CL response induced by fMet-Leu-Phe and zymosan. These results show that GKB is the first partial agonist of the Paf receptor described so far capable of priming the polymorphonuclear leukocyte function.

Detection of individual phospholipids in lipid mixtures by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: phosphatidylcholine prevents the detection of further species

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is an established tool for the analysis of proteins, whereas it gained by far less interest in the field of lipid analysis. This method works well with phospholipids as well as organic cell extracts and provides high sensitivity and reproducibility. The aim of the present paper is to extend our previous studies to the analysis of lysophospholipids and phospholipid mixtures. To study the suitability of MALDI-TOF mass spectrometry for the analysis of lysophospholipids, different phospholipids like phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, and phosphatidylinositol as well as their mixtures were digested with phospholipase A(2). Positive and negative ion mass spectra of all phospholipids before and after digestion were recorded. In all these cases, the molecular ions of the expected digestion products could be detected and only a very small extent of further fragmentation was observed. On the other hand, spectra of phospholipid mixtures containing phosphatidylcholine were strongly dominated by phosphatidylcholine and lysophosphatidylcholine signals, which prevented the detection of further phospholipids even if those lipids were present in comparable amounts. This is of paramount interest for the analysis of tissue and cell extracts.

Evaluation of neutrophil structure and function by electron microscopy: cytochemical studies

Methods for studying human neutrophils at the ultrastructural level by enzyme cytochemistry and immunocytochemistry are presented. The focus of these methods is on the analysis of the alkaline phosphatase-positive secretory organelle of these cells. These methods provide unique information which, when coupled with biochemical studies, provide for the most complete analysis of neutrophil structure and function.