Hydrolysis of platelet-activating factor by human serum paraoxonase.
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ABSTRACT:
SUBMITTER: Rodrigo L
PROVIDER: S-EPMC1221621 | biostudies-other | 2001 Feb
REPOSITORIES: biostudies-other
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Project description: Not available
| S-EPMC2884689 | biostudies-literature
Project description:Platelet-activating factor (PAF) is a potent, bioactive phospholipid that acts on multiple cells and tissues through its G protein-coupled receptor (GPCR). PAF is not stored but is rapidly generated via enzymatic acetylation of the precursor 1-O-hexadecyl-2-hydroxy-sn-glycero-3-phosphocholine (lysoPAF). The bioactivity of PAF is effectively and tightly regulated by PAF acetylhydrolases, which convert PAF back to lysoPAF. Previous studies report that lysoPAF is an inactive precursor and metabolite of PAF. However, lysoPAF has not been carefully studied in its own context. Here we report that lysoPAF has an opposing effect of PAF in the activation of neutrophils and platelets. Whereas PAF potentiates neutrophil NADPH oxidase activation, lysoPAF dose-dependently inhibits this function. Inhibition by lysoPAF is not affected by the use of a PAF receptor antagonist or genetic deletion of the PAF receptor gene. The mechanism of lysoPAF-mediated inhibition of neutrophils involves an elevation in the intracellular cAMP level, and pharmacological blockade of adenylyl cyclase completely reverses the inhibitory effect of lysoPAF. In addition, lysoPAF increases intracellular cAMP levels in platelets and inhibits thrombin-induced platelet aggregation, which can be reversed by inhibition of protein kinase A. These findings identify lysoPAF as a bioactive lipid with opposing functions of PAF and suggest a novel and intrinsic regulatory mechanism for balance of the potent activity of PAF.
| S-EPMC2646610 | biostudies-literature
Project description:UV radiation-induced systemic immune suppression is a major risk factor for skin cancer induction. The migration of dermal mast cells from the skin to the draining lymph nodes has a prominent role in activating systemic immune suppression. UV-induced keratinocyte-derived platelet-activating factor (PAF) activates mast cell migration, in part by upregulating the expression of CXCR4 on the surface of mast cells. Others have indicated that epigenetic mechanisms regulate CXCR4 expression; therefore, we asked whether PAF activates epigenetic mechanisms in mast cells. Human mast cells were treated with PAF, and the effect on DNA methylation and/or acetylation was measured. PAF suppressed the expression of DNA methyltransferase (DNMT) 1 and 3b. On the other hand, PAF increased p300 histone acetyltransferase expression, and the acetylation of histone H3, which coincided with a decreased expression of the histone deacetylase HDAC2. Chromatin immunoprecipitation assays indicated that PAF treatment activated the acetylation of the CXCR4 promoter. Finally, inhibiting histone acetylation blocked p300 upregulation and suppressed PAF-induced surface expression of CXCR4. Our findings suggest a novel molecular mechanism for PAF, activation of epigenetic modifications. We suggest that PAF may serve as an endogenous molecular mediator that links the environment (UV radiation) with the epigenome.
| S-EPMC4648694 | biostudies-literature
Project description:Aspirin is rapidly hydrolyzed within erythrocytes by a heterodimer of PAFAH1b2/PAFAH1b3 but also in plasma by an unidentified activity. Hydrolysis in both compartments was variable, with a 12-fold variation in plasma among 2226 Cleveland Clinic GeneBank patients. Platelet inhibition by aspirin was suppressed in plasma that rapidly hydrolyzed aspirin. Plasma aspirin hydrolysis was significantly higher in patients with coronary artery disease compared with control subjects (16.5 ± 4.4 versus 15.1 ± 3.7 nmol/ml/min; p = 3.4 × 10(-8)). A genome-wide association study of 2054 GeneBank subjects identified a single locus immediately adjacent to the BCHE (butyrylcholinesterase) gene associated with plasma aspirin hydrolytic activity (lead SNP, rs6445035; p = 9.1 × 10(-17)). However, its penetrance was low, and plasma from an individual with an inactivating mutation in BCHE still effectively hydrolyzed aspirin. A second aspirin hydrolase was identified in plasma, the purification of which showed it to be homomeric PAFAH1b2. This is distinct from the erythrocyte PAFAH1b2/PAFAH1b3 heterodimer. Inhibitors showed that both butyrylcholinesterase (BChE) and PAFAH1b2 contribute to aspirin hydrolysis in plasma, with variation primarily reflecting non-genetic variation of BChE activity. Therefore, aspirin is hydrolyzed in plasma by two enzymes, BChE and a new extracellular form of platelet-activating factor acetylhydrolase, PAFAH1b2. Hydrolytic effectiveness varies widely primarily from non-genetic variation of BChE activity that affects aspirin bioavailability in blood and the ability of aspirin to inhibit platelet aggregation.
| S-EPMC3636881 | biostudies-literature
Project description:This data series contains spotted oligo microarray data from 10 different experiments using Agilent Rat v2 microarrays. This data is being made public in support of Fillon S et al. Journal of Immunology, (2006). Proinflammatory bacterial components are at least partially responsible for causing the clinical features of sepsis, a syndrome that causes >100,000 deaths each year in the US (1). In the case of Gram positive infection, a key bacterial element recognized by the innate immune system is the cell wall, a complex network of peptidoglycan covalently linked to teichoic acids, proteins and lipoproteins. The current model of innate immune recognition of Gram positive bacteria suggests bacterial cell wall interacts with host recognition proteins, such as toll-like receptors (TLR) and Nod proteins. We describe an additional recognition system mediated by the platelet activating factor receptor (PAFr) and directed to the pathogen associated molecular pattern (PAMP) phosphorylcholine that results in uptake of bacterial components into host cells. Intravascular choline-containing cell walls bound to endothelial cells and caused rapid lethality in wild type, Tlr2-/- and Nod2-/- mice, but not in Pafr-/- mice. Cell wall exited the vasculature into the heart and brain, accumulating within endothelial cells, cardiomyocytes and neurons in a PAFr-dependent way. Physiological consequences of the cell wall/PAFr interaction were cell specific, being noninflammatory in endothelial cells and neurons, but causing rapid loss of cardiomyocyte contractility that contributed to death. Thus, PAFr shepherds phosphorylcholine-containing bacterial components such as cell wall into host cells from where the response ranges from quiescence to severe pathophysiology. Keywords: Competitive hybridizations The ten experiments in this series comprise of four distinct experiments, two of which were performed as biological triplicates and two as biological duplicates. The table below describes the overall design in detail: File Name Experiment 16011868017643v41_GEO_format.txt RBCEC Replicate 1 16011868017644v41_GEO_format.txt RBCEC Replicate 2 251186821865v41_GEO_format.txt Neuron Replicate 1 16011868021377v41_GEO_format.txt Neuron Replicate 2 251186821690v41_GEO_format.txt CW/Lyt44 Replicate 1 251186821691v41_GEO_format.txt CW/Lyt44 Replicate 2 251186821692v41_GEO_format.txt CW/Lyt44 Replicate 1 251186821693v41_GEO_format.txt CW+TNF/Lyt44+TNF Replicate 1 251186821694v41_GEO_format.txt CW+TNF/Lyt44+TNF Replicate 2 251186829677v41_GEO_format.txt CW+TNF/Lyt44+TNF Replicate 3
2010-07-01 | E-GEOD-5545 | biostudies-arrayexpress
Project description:RationaleThe phospholipid platelet-activating factor (PAF) stimulates all cells of the innate immune system and numerous cardiovascular cells. A single enzyme (plasma PAF acetylhydrolase [PAF-AH] or lipoprotein-associated phospholipase [Lp-PL]A(2)) in plasma hydrolyzes PAF, but significant controversy exists whether its action is pro- or antiinflammatory and accordingly whether its inhibition will slow cardiovascular disease.ObjectiveWe sought to define how PAF and related short-chain oxidized phospholipids turnover in vivo and the role of PAF acetylhydrolase/Lp-PLA(2) in this process.Methods and results[(3)H-acetyl]PAF was hydrolyzed by murine or human plasma (t(1/2), 3 and 7 minutes, respectively), but injected [(3)H-acetyl]PAF disappeared from murine circulation more quickly (t(1/2), <30 seconds). [(3)H]PAF clearance was unchanged in PAF receptor(-/-) animals, or over the first 2 half-lives in PAF-AH(-/-) animals. [(3)H]PAF turnover was reduced by coinjecting excess unlabeled PAF or an oxidatively truncated phospholipid, and [(3)H]PAF clearance was slowed in hyperlipidemic apolipoprotein (apo)E(-/-) mice with excess circulating oxidatively truncated phospholipids. [(3)H]PAF, fluorescent NBD-PAF, or fluorescent oxidatively truncated phospholipid were primarily accumulated by liver and lung, and were transported into endothelium as intact phospholipids through a common mechanism involving TMEM30a.ConclusionsCirculating PAF and oxidized phospholipids are continually and rapidly cleared, and hence continually and rapidly produced. Saturable PAF receptor-independent transport, rather than just intravascular hydrolysis, controls circulating inflammatory and proapoptotic oxidized phospholipid mediators. Intravascular PAF has access to intracellular compartments. Inflammatory and proapoptotic phospholipids may accumulate in the circulation as transport is overwhelmed by substrates in hyperlipidemia.
| S-EPMC3057131 | biostudies-literature
Project description:Receptor signaling is integral for adhesion, emigration, phagocytosis, and reactive oxygen species production in polymorphonuclear neutrophils (PMNs). Priming is an important part of PMN emigration, but it can also lead to PMN-mediated organ injury in the host. Platelet-activating factor (PAF) primes PMNs through activation of a specific G protein-coupled receptor. We hypothesize that PAF priming of PMNs requires clathrin-mediated endocytosis (CME) of the PAF receptor (PAFr), and, therefore, amantadine, known to inhibit CME, significantly antagonizes PAF signaling. PMNs were isolated by standard techniques to >98% purity and tested for viability. Amantadine (1 mM) significantly inhibited the PAF-mediated changes in the cellular distribution of clathrin and the physical colocalization [fluorescence resonance energy transfer positive (FRET+)] of early endosome antigen-1 and Rab5a, known components of CME and similar to hypertonic saline, a known inhibitor of CME. Furthermore, amantadine had no effect on the PAF-induced cytosolic calcium flux; however, phosphorylation of p38 MAPK was significantly decreased. Amantadine inhibited PAF-mediated changes in PMN physiology, including priming of the NADPH oxidase and shape change with lesser inhibition of increases in CD11b surface expression and elastase release. Furthermore, rimantadine, an amantadine analog, was a more potent inhibitor of PAF priming of the N-formyl-methionyl-leucyl-phenylalanine-activated oxidase. PAF priming of PMNs requires clathrin-mediated endocytosis that is inhibited when PMNs are pretreated with either amantadine or rimantadine. Thus, amantadine and rimantadine have the potential to ameliorate PMN-mediated tissue damage in humans.
| S-EPMC2770739 | biostudies-literature
Project description:This data series contains spotted oligo microarray data from 10 different experiments using Agilent Rat v2 microarrays. This data is being made public in support of Fillon S et al. Journal of Immunology, (2006). Proinflammatory bacterial components are at least partially responsible for causing the clinical features of sepsis, a syndrome that causes >100,000 deaths each year in the US (1). In the case of Gram positive infection, a key bacterial element recognized by the innate immune system is the cell wall, a complex network of peptidoglycan covalently linked to teichoic acids, proteins and lipoproteins. The current model of innate immune recognition of Gram positive bacteria suggests bacterial cell wall interacts with host recognition proteins, such as toll-like receptors (TLR) and Nod proteins. We describe an additional recognition system mediated by the platelet activating factor receptor (PAFr) and directed to the pathogen associated molecular pattern (PAMP) phosphorylcholine that results in uptake of bacterial components into host cells. Intravascular choline-containing cell walls bound to endothelial cells and caused rapid lethality in wild type, Tlr2-/- and Nod2-/- mice, but not in Pafr-/- mice. Cell wall exited the vasculature into the heart and brain, accumulating within endothelial cells, cardiomyocytes and neurons in a PAFr-dependent way. Physiological consequences of the cell wall/PAFr interaction were cell specific, being noninflammatory in endothelial cells and neurons, but causing rapid loss of cardiomyocyte contractility that contributed to death. Thus, PAFr shepherds phosphorylcholine-containing bacterial components such as cell wall into host cells from where the response ranges from quiescence to severe pathophysiology. Keywords: Competitive hybridizations
2006-08-17 | GSE5545 | GEO
Project description:Platelet-activating factor stimulates phosphatidylinositol turnover in human platelets as indicated by [32P]phosphatidate accumulation in platelets pre-labelled with [32P]Pi, and by [3H]phosphatidate accumulation and [3H]phosphatidylinositol loss in platelets pre-labelled with [3H]arachidonate. These effects of platelet-activating factor are direct and are independent of the production and/or release of endogenous platelet agonists such as ADP, 5-hydroxytryptamine and thromboxane A2.
| S-EPMC1152064 | biostudies-other
Project description:Pulmonary hemorrhage has been recognized as a major, often lethal, manifestation of severe leptospirosis albeit the pathogenesis remains unclear. The Leptospira interrogans virulent serogroup Icterohaemorrhagiae serovar Lai encodes a protein (LA2144), which exhibited the platelet-activating factor acetylhydrolase (PAF-AH) activity in vitro similar to that of human serum with respect to its substrate affinity and specificity and thus designated L-PAF-AH. On the other hand, the primary amino acid sequence of L-PAF-AH is homologous to the alpha1-subunit of the bovine brain PAF-AH isoform I. The L-PAF-AH was proven to be an intracellular protein, which was encoded unanimously and expressed similarly in either pathogenic or saprophytic leptospires. Mongolian gerbil is an appropriate experimental model to study the PAF-AH level in serum with its basal activity level comparable to that of human while elevated directly associated with the course of pulmonary hemorrhage during severe leptospirosis. Mortality occurred around the peak of pulmonary hemorrhage, along with the transition of the PAF-AH activity level in serum, from the increasing phase to the final decreasing phase. Limited clinical data indicated that the serum activity of PAF-AH was likely to be elevated in the patients infected by L. interrogans serogroup Icterohaemorrhagiae, but not in those infected by other less severe serogroups. Although L-PAF-AH might be released into the micro-environment via cell lysis, its PAF-AH activity apparently contributed little to this elevation. Therefore, the change of PAF-AH in serum not only may be influential for pulmonary hemorrhage, but also seems suitable for disease monitoring to ensure prompt clinical treatment, which is critical for reducing the mortality of severe leptospirosis.
| S-EPMC2615213 | biostudies-literature