Acetyl-CoA:1-O-alkyl-sn-glycero-3-phosphocholine acetyltransferase (lyso-PAF AT) activity in cortical and medullary human renal tissue

Phenylmethanesulfonyl fluoride pretreatment stabilizes plasma lipidome in lipidomic and metabolomic analysis

Though it is standard practice to test the stability of analytes in the matrix for routine bioanalytical method, stability evaluation is always impractical and skipped in untargeted lipidomic and metabolomic analysis because analytes in these studies are enormous, diverse and sometimes unknown. Lipidome represents a major class of plasma metabolome and shows great potential to be diagnostic and prognostic biomarkers. However, lipidome also faces stability problems because plasma contains kinds of lipid degradation enzyme. Here, using liquid chromatography time of flight mass spectrometry based lipidomic methodology, plasma levels of various lipids including triglyceride (TG), diglyceride (DG), free fatty acid (FFA), phosphatidylethanolamine (PE) phosphatidylcholine (PC), lyso-phosphatidylcholine (LPC), lyso-phosphatidylethanolamine (LPE), and sphingomyelin (SM) were dynamically determined within 4 h at ambient temperature. In mouse and rat plasma, the levels of most TG, DG, PC and PE species significantly decreased with respect to time, whereas those of LPC, LPE and FFA significantly increased with respect to time. However, such changes did not occur in human plasma, thus indicating hepatic lipase and esterase might involve in the species-specified degradation of lipid classes in plasma. Phenylmethanesulfonyl fluoride (PMSF) pretreatment prevented such lipidome instability in mouse plasma. The results suggested the instability of plasma lipidome should be highly concerned, and the enhancement of ex vivo stability of plasma lipidome could enable more reliable clinical translation of lipidomic data for biomarker discovery.

The role of platelet-activating factor in mesangial pathophysiology

Platelet-activating factor (PAF) is a powerful proinflammatory mediator that displays an exceedingly diverse spectrum of biological effects. Importantly, PAF is shown to participate in a broad range of pathologic conditions. This review focuses on the role that PAF plays specifically in the pathophysiology of the kidney, the organ that is both a source and a target of PAF. Renal mesangial cells are responsible for glomerular PAF generation and, ultimately, are the victims of its excessive production. Mesangial pathology is widely acknowledged to reflect glomerular damage, which culminates in glomerulosclerosis and proteinuria. Therefore, modulation of mesangial cell responses would offer a pathophysiology-based therapeutic approach to prevent glomerular injury. However, the currently available therapeutic modalities do not allow for targeted intervention into these processes. A more profound understanding of the mechanisms that govern PAF metabolism and signaling in mesangial cells is important, because it could facilitate the quest for improved therapies for renal patients on the basis of PAF as a drug target.

Baseline and 6-Week follow-up levels of PAF and activity of its metabolic enzymes in patients with heart failure and healthy volunteers--a pilot study

This study aimed at evaluating the changes in platelet-activating factor (PAF) and its metabolic enzymes over a 6-week follow-up period in patients with newly diagnosed heart failure ([HF] n = 12) compared with age-, sex-, and BMI-matched apparently healthy volunteers (n = 10). The PAF, its key biosynthetic enzymes (lyso-PAF acetyltransferase [lyso-PAF-AT] and dithiothreitol [DTT]-insensitive CDP choline: 1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase [PAF-CPT]), and its catabolic isoenzymes (PAF-acetylhydrolase [PAF-AH] and lipoprotein-associated phospholipase A2 [Lp-PLA2]) were measured in serum and leukocytes of participants. At baseline, patients with HF had lower median activities of lyso-PAF-AT (P < .001) and PAF-CPT (P = .07) in parallel with PAF levels (P = .05) and higher activities of PAF-AH (P = .02) and Lp-PLA2 (P < .001) than controls. At follow-up, PAF-CPT and PAF levels marginally increased (P = .1), lyso-PAF-AT (P < .001) remained downregulated, while PAF-AH (P = .004) and Lp-PLA2 (P < .001) remained elevated compared with the controls. Newly diagnosed patients with HF under drug treatment have an affected profile of PAF biosynthetic enzymes and especially lyso-PAF-AT.

ATP: a mediator for HCl-induced TRPV1 activation in esophageal mucosa

In esophageal mucosa, HCl causes TRPV1-mediated release of calcitonin gene-related peptide (CGRP) and substance P (SP) from submucosal neurons and of platelet-activating factor (PAF) from epithelial cells. CGRP and SP release was unaffected by PAF antagonists but reduced by the purinergic antagonist suramin. ATP caused CGRP and SP release from esophageal mucosa, confirming a role of ATP in the release. The human esophageal epithelial cell line HET-1A was used to identify epithelial cells as the site of ATP release. HCl caused ATP release from HET-1A, which was reduced by the TRPV1 antagonist 5-iodoresiniferatoxin. Real-time PCR demonstrated the presence of mRNA for several P2X and P2Y purinergic receptors in epithelial cells. HCl also increased activity of lyso-PAF acetyl-CoA transferase (lyso-PAF AT), the enzyme responsible for production of PAF. The increase was blocked by suramin. ATP caused a similar increase, confirming ATP as a mediator for the TRPV1-induced increase in enzyme activity. Repeated exposure of HET-1A cells to HCl over 2 days caused upregulation of mRNA and protein expression for lyso-PAF AT. Suramin blocked this response. Repeated exposure to ATP caused a similar mRNA increase, confirming ATP as a mediator for upregulation of the enzyme. Thus, HCl-induced activation of TRPV1 causes ATP release from esophageal epithelial cells that causes release of CGRP and SP from esophageal submucosal neurons and activation of lyso-PAF AT, the enzyme responsible for the production of PAF in epithelial cells. Repeated application of HCl or of ATP causes upregulation of lyso-PAF AT in epithelial cells.

PAF and its metabolic enzymes in healthy volunteers: interrelations and correlations with basic characteristics

PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine), a potent inflammatory mediator, is synthesized via the remodeling and the de novo route, key enzymes of which are acetyl-CoA:lyso-PAF acetyltransferase (lyso-PAF-AT) and DTT-insensitive CDP-choline:1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase (PAF-CPT), respectively. PAF-acetylhydrolase (PAF-AH) and its extracellular isoform lipoprotein-associated phospholipase-A(2) (Lp-PLA(2)) catabolize PAF. This study evaluated PAF levels together with leukocyte PAF-CPT, lyso-PAF-AT, PAF-AH and Lp-PLA(2) activities in 106 healthy volunteers. Men had lower PAF levels and higher activity of both catabolic enzymes and lyso-PAF-AT than women (P-values <0.05). Age was inversely correlated with PAF levels in men (r=-0.279, P=0.06) and lyso-PAF-AT in women (r=-0.280, P=0.05). In contrast, Lp-PLA(2) was positively correlated with age (r=0.201, P=0.04). Moreover, PAF-CPT was positively correlated with glucose (r=0.430, P=0.002) in women. In addition, Principal Component Analysis revealed three PAF metabolic patterns: (i) increased activities of PAF-CPT and PAF-AH, (ii) increased activities of PAF-CPT and lyso-PAF-AT and (iii) increased activity of Lp-PLA(2). The present study underlines the complexity of PAF's metabolism determinants.

HCl-induced inflammatory mediators in esophageal mucosa increase migration and production of H2O2 by peripheral blood leukocytes

Exposure of esophageal mucosa to hydrochloric acid (HCl) is a crucial factor in the pathogenesis of reflux disease. We examined supernatant of HCl-exposed rabbit mucosa for inflammatory mediators enhancing migration of leukocytes and production of H(2)O(2) as an indicator of leukocyte activation. A tubular segment of rabbit esophageal mucosa was tied at both ends to form a sac, which was filled with HCl-acidified Krebs buffer at pH 5 (or plain Krebs buffer as control) and kept oxygenated at 37 degrees C. The medium around the sac (supernatant) was collected after 3 h. Rabbit peripheral blood leukocytes (PBL) were isolated, and sac supernatant was used to investigate PBL migration and H(2)O(2) production. HCl-exposed esophageal mucosa released substance P (SP), CGRP, platelet-activating factor (PAF), and IL-8 into the supernatant. PBL migration increased in response to IL-8 or to supernatant of the HCl-filled mucosal sac. Supernatant-induced PBL migration was inhibited by IL-8 antibodies and by antagonists for PAF (CV3988) or neurokinin 1 (i.e., SP), but not by a CGRP antagonist. Supernatant of the HCl-filled mucosal sac increased H(2)O(2) release by PBL that was significantly reduced by CV3988 and by a SP antagonist but was not affected by IL-8 antibodies or by a CGRP antagonist. We conclude that IL-8, PAF, and SP are important inflammatory mediators released by esophageal mucosa in response to acid that promote PBL migration. In addition, PAF and SP induce production of H(2)O(2) by PBL. These findings provide a direct link between acid exposure and recruitment and activation of immune cells in esophageal mucosa.

Signaling in TRPV1-induced platelet activating factor (PAF) in human esophageal epithelial cells

Transient receptor potential channel, vanilloid subfamily member 1 (TRPV1) receptors were identified in human esophageal squamous epithelial cell line HET-1A by RT-PCR and by Western blot. In fura-2 AM-loaded cells, the TRPV1 agonist capsaicin caused a fourfold cytosolic calcium increase, supporting a role of TRPV1 as a capsaicin-activated cation channel. Capsaicin increased production of platelet activating factor (PAF), an important inflammatory mediator that acts as a chemoattractant and activator of immune cells. The increase was reduced by the p38 MAP kinase (p38) inhibitor SB203580, by the cytosolic phospholipase A2 (cPLA(2)) inhibitor AACOCF3, and by the lyso-PAF acetyltransferase inhibitor sanguinarin, indicating that capsaicin-induced PAF production may be mediated by activation of cPLA(2), p38, and lyso-PAF acetyltransferase. To establish a sequential signaling pathway, we examined the phosphorylation of p38 and cPLA(2) by Western blot. Capsaicin induced phosphorylation of p38 and cPLA(2). Capsaicin-induced p38 phosphorylation was not affected by AACOCF3. Conversely, capsaicin-induced cPLA(2) phosphorylation was blocked by SB203580, indicating that capsaicin-induced PAF production depends on sequential activation of p38 and cPLA(2). To investigate how p38 phosphorylation may result from TRPV1-mediated calcium influx, we examined a possible role of calmodulin kinase (CaM-K). p38 phosphorylation was stimulated by the calcium ionophore A23187 and by capsaicin, and the response to both agonists was reduced by a CaM inhibitor and by CaM-KII inhibitors, indicating that calcium induced activation of CaM and CaM-KII results in P38 phosphorylation. Acetyl-CoA transferase activity increased in response to capsaicin and was inhibited by SB203580, indicating that p38 phosphorylation in turn causes activation of acetyl-CoA transferase to produce PAF. Thus epithelial cells produce PAF in response to TRPV1-mediated calcium elevation.

Platelet activating factor (PAF) and activity of its biosynthetic and catabolic enzymes in blood and leukocytes of male patients with newly diagnosed heart failure

OBJECTIVES

To evaluate platelet activating factor (PAF) levels, its metabolic enzymes activity and its associations with other inflammatory markers in heart failure (HF) patients.

DESIGN AND METHODS

PAF, and two of its key biosynthetic enzymes [lyso-PAF acetyltransferase (lyso-PAF-AT) and DTT-insensitive CDP-choline:1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase (PAF-CPT)] along with its catabolic enzymes [PAF-acetylhydrolase (PAF-AH) and lipoprotein-associated phospholipase-A(2) (Lp-PLA(2))] were measured in serum and leukocytes of twelve newly diagnosed male HF patients. Serum CRP, TNF-alpha, IL-6, sCD14 and CD40L were also determined.

RESULTS

PAF ranged from 0.03 to 5.6 pmol/mL. Median lyso-PAF-AT, PAF-CPT, PAF-AH and Lp-PLA(2) activities were 4.1, 68.42, 644.44 pmol/min/mg protein and 51.42 pmol/min/microL correspondingly. Lyso-PAF-AT and PAF-CPT activities positively correlated with CRP, IL-6 and with each other, whereas PAF-CPT activity correlated with sCD14 and CD40L (P<0.05).

CONCLUSIONS

PAF's biosynthetic enzyme activities correlated with inflammatory and immunologic molecules, which are activated in HF. Our study indicates a potential role of PAF in HF patients.

Characterization of the de novo biosynthetic enzyme of platelet activating factor, DDT-insensitive cholinephosphotransferase, of human mesangial cells

Platelet activating factor (PAF), a potent inflammatory mediator, is implicated in several proinflammatory/inflammatory diseases such as glomerulonephritis, glomerulosclerosis, atherosclerosis, cancer, allergy, and diabetes. PAF can be produced by several renal cells under appropriate stimuli and it is thought to be implicated in renal diseases. The aim of this study is the characterization of DTT-insensitive cholinephosphotransferase (PAF-CPT) of human mesangial cell (HMC), the main regulatory enzyme of PAF de novo biosynthetic pathway. Microsomal fractions of mesangial cells were isolated and enzymatic activity and kinetic parameters were determined by TLC and in vitro biological test in rabbit washed platelets. The effect of bovine serum albumin (BSA), dithiothreitol (DTT), divalent cations (Mg2+ and Ca2+), EDTA, and various chemicals on the activity of PAF-CPT of HMC was also studied. Moreover, preliminary in vitro tests have been performed with several anti-inflammatory factors such as drugs (simvastatin, IFNa, rupatadine, tinzaparin, and salicylic acid) and bioactive compounds of Mediterranean diet (resveratrol and lipids of olive oil, olive pomace, sea bass "Dicentrarchus labrax," and gilthead sea bream "Sparus aurata"). The results indicated that the above compounds can influence PAF-CPT activity of HMC.

Characterization of acetyl-CoA: lyso-PAF acetyltransferase of human mesangial cells

Platelet activating factor (PAF) is a potent inflammatory mediator produced by various renal cells and it is implicated in renal pathology. The aim of this study is the characterization of remodeling lyso-PAF acetyltransferase, which is activated under inflammatory conditions, in human mesangial cell. Total membranes of mesangial cells were isolated and enzymatic activity and kinetic parameters were determined by trichloroacetic acid precipitation method. The effect of BSA, divalent cations, EDTA, and various chemicals on the activity of lyso-PAF acetyltransferase was also studied. Various detergents were also tested for the solubilization of the enzyme and only glycerol did not affect its activity. Partial purification of solubilized enzyme preparations of human kidney tissue and mesangial cells was performed on anion exchange column chromatography and native-PAGE electrophoresis and two active fractions were detected.

Application of a TCA-precipitation method for the determination of 1-alkyl-sn-glycero-3-phosphate: Acetyl-CoA acetyltransferase in human renal tissue

The activity of 1-alkyl-sn-glycero-3-phosphate:Acetyl-CoA acetyltransferase, which catalyses the first step of the de novo biosynthesis of PAF, was determined and characterised in cortical and medullary human renal tissues. A novel thin-layer chromatographic system as well as a trichloroacetic acid precipitation method, were utilised in order to determine the enzyme's activity. The acetyltransferase activity was associated with the membranous fractions of the renal tissue, it showed an optimum pH of 8.4 and it had a bell-shaped dependence on BSA concentration. One or more disulphide bonds were necessary for the action of acetyltransferase while the enzyme seemed to be independent from divalent cations. Two assay products were extracted from the incubation mixture namely alkylacetylphosphatidic acid, produced by the acetylating action of the acetyltransferase on alkyllyso-phosphatidic acid and alkylacetyl-glycerol, which is produced by the action of a phosphohydrolase on alkylacetylphosphatidic acid. The presence of NaF in the assay mixture resulted to a decreased degradation of alkylacetylphosphatidic acid, as well as to an increased overall product formation. Cortical and medullary acetyltransferases share similar biochemical properties and there is no statistical difference between the two activities.