Platelet-activating factor in bronchoalveolar lavage from patients with sarcoidosis

An improved assay for platelet-activating factor using HPLC-tandem mass spectrometry

We describe an improved assay for platelet-activating factor (PAF; 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) using HPLC-tandem mass spectrometry (LC-MS/MS). The present method can readily detect as little as 1 pg (1.9 fmol) of PAF, a significant improvement over previously described LC-MS/MS methods, and gives a linear response up to 1,000 pg of PAF. Our method also overcomes the artifacts from isobaric lipids that have limited the usefulness of certain existing LC-MS/MS assays for PAF. In the course of these studies, we detected three novel lipid species in human neutrophils. One of the novel lipids appears to be a new molecular species of PAF, and the other two have chromatographic and mass spectrometric properties consistent with stearoyl-formyl-glycerophosphocholine and oleoyl-formyl-glycerophosphocholine. These observations identify previously unknown potential interferences in the measurement of PAF by LC-MS/MS. Moreover, our data suggest that the previously described palmitoyl-formyl-glycerophosphocholine is not unique but rather is a member of a new and poorly understood family of formylated lipids.

Selenium modulates 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) biosynthesis in bovine aortic endothelial cells

Selenium (Se) deficiency has been reported to increase platelet-activating factor (PAF) production in human endothelial cells; however, the mechanism is unclear. This study demonstrated that tumor necrosis factor-alpha (TNF-alpha) stimulated Se-deficient bovine aortic endothelial cells (BAEC) produced significantly more PAF than Se-supplemented cells. Moreover, the increase in the level of PAF was associated with enhanced activity of two anabolic enzymes in the remodeling pathway: phospholipase A2 and Lyso-PAF:acetyl-coenzyme A acetyltransferase (Lyso-PAF-AcT). In contrast, the activity of the PAF catabolic enzyme, PAF-acetylhydrolase, was not affected by Se status. Interestingly, prostacyclin, a potent vasodilator and inhibitor of platelet aggregation, inhibited the activity of Lyso-PAF-AcT and reduced the PAF production in TNF-alpha-stimulated BAEC. Therefore, we conclude that Se deficiency alters PAF production in TNF-alpha-stimulated BAEC by altering the activity of anabolic enzymes involved in the remodeling pathway partially through the inhibition of prostacyclin production.

Biochemical changes in sarcoidosis

Biochemical markers in sarcoidosis are closely related to the immunological events and the activity of inflammatory effector cells at sites of granuloma formation. The markers can be measured in serum, then reflecting whole body concentration, or in BAL fluid, then indicating activity in the lung. Only calcium and ACE serum levels have gained a proven value in the clinical field.

Enhancement of leukotriene B4 release in stimulated asthmatic neutrophils by platelet activating factor

BACKGROUND

The role of platelet activating factor (PAF) in asthma remains controversial. The priming effect of PAF on leukotriene B4 (LTB4) release, 5-lipoxygenase activity, and intracellular calcium levels in asthmatic neutrophils was examined.

METHODS

LTB4 and other lipoxygenase metabolites in neutrophils obtained from 17 asthmatic patients and 15 control subjects were measured by reverse phase-high performance liquid chromatography (RP-HPLC). Intracellular calcium levels were monitored using the fluorescent probe fura-2.

RESULTS

The mean (SD) basal LTB4, release from neutrophils was not significantly different between the two groups (0.05 (0.01) vs 0.03 (0.02) ng/10(6) cells); however, when stimulated with calcium ionophore A23187 (2.5 microM), neutrophils from asthma patients released more LTB4 than cells from control subjects (15.7 (1.2) vs 9.9 (1.6) ng/10(6) cells). Although PAF alone did not alter LTB4 release, it enhanced the response to subsequent A23187 stimulation. This effect was observed following treatment for five minutes with PAF at concentrations > 1.0 microM. The maximal effect was seen with 5.0 microM PAF + 2.5 microM A23187 (62.7 (2.2) vs 18.6 (2.3) ng/10(6) cells). Pretreatment with PAF also increased 5-lipoxygenase activity and intracellular calcium levels in neutrophils from asthmatic patients to a greater extent than in those from non-asthmatic patients.

CONCLUSIONS

These findings indicate that, in neutrophils from asthmatic patients, PAF enhances LTB4 release and increases 5-lipoxygenase activity and intracellular calcium to a greater extent than in neutrophils from non-asthmatic patients.

Inhibitory effect of azelastine hydrochloride on synthesis and release of platelet activating factor from human alveolar macrophages

The effect of azelastine hydrochloride (azelastine) on synthesis and release of platelet activating factor (PAF) in alveolar macrophages obtained from asthmatic and non-asthmatic subjects was examined. Alveolar macrophages (AMs) were preincubated with or without azelastine and stimulated with f-Met-Leu-Phe (fMLP, 10 microM) for 15 min. PAF activity was detected by aggregation of washed guinea pig platelets. PAF activity released from alveolar macrophages (AMs) from asthmatics without preincubation of azelastine was 15.97 [2.17] (mean [SD], ng/10(7) cells) in supernatants and 42.52 [10.16] in cell pellets. After preincubation with 10(-8), 10(-6), and 10(-4) M of azelastine, PAF activity reduced to 10.71 [2.73] (mean [SD], ng/10(7) cells), 7.86 [0.94], and 3.52 [0.31] in the supernatants, and 35.58 [7.37], 21.57 [4.36], and 14.77 [0.99] (n = 15) in the cell pellets, respectively. PAF activity in non-asthmatic subjects without preincubation of azelastine was 8.55 [1.16] (mean [SD], ng/10(7) cells) in supernatants and 32.64 [3.37] in cell pellets. After preincubation with 10(-8), 10(-6), and 10(-4) M of azelastine, PAF activity reduced to 6.68 [0.78] (mean [SD], ng/10(7) cells), 4.47 [0.51], and 2.97 [0.36] in the supernatants, and 29.53 [3.75], 14.78 [1.95], and 6.16 [0.55] (n = 20) in the cell pellets, respectively. Our results showed that preincubation with azelastine caused a dose-dependent inhibition of intra- and extracellular PAF activity from asthmatic and non-asthmatic macrophages in the same manner.

Simultaneous determination of lysophospholipids by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatography (HPLC) procedure for the separation of choline lysophospholipids including 1-acyl-lysophosphatidylcholines and 1-O-alkyl-lysophosphatidyl- cholines, like the lysoform of the platelet activating factor (2-lysoPAF), is described. The lysophospholipids are derivatized at the sn-2 position of the hydroxyl group by 7-diethylaminocoumarin-3-carbonylazide, which converts them into the corresponding carbamoyl derivatives. The derivatized compounds were well separated by reversed-phase HPLC and quantified by fluorimetric detection. This method shows a high sensitivity and allows the separation and quantification of mixtures of lysophospholipids at picomolar level. The method was applied to assay enzyme activities, like phospholipase A2 and PAF-acetylhydrolase, on single phospholipids or their mixtures.

Determination of 1-O-acyl-2-acetyl-sn-glyceryl-3-phosphorylcholine, platelet-activating factor and related phospholipids in biological samples by high-performance liquid chromatography--tandem mass spectrometry

Combining normal-phase HPLC separation and tandem mass spectrometric detection, using an ion-spray HPLC-MS interface, a quantitative method for acyl-platelet activating factor (acyl-PAF), platelet-activating factor (PAF) and related phospholipids was developed. Mass spectra, positive ions, showed intense [M+H]+ ions; collision-induced dissociation of protonated molecular ions gave characteristic daughter ions corresponding to the polar head. Detection limits of 0.1-0.3 ng injected were obtained by multiple reaction monitoring. Samples of human endothelial cells treated with compounds modulating the levels of acyl-PAF and PAF have been analyzed by the present technique, proving that this approach is suitable for biochemical studies.

Streptokinase induces intravascular release of platelet-activating factor in patients with acute myocardial infarction and stimulates its synthesis by cultured human endothelial cells

BACKGROUND

Reocclusion of a successfully recanalized infarct-related artery may account for failure of thrombolytic therapy. Evidence suggests that the intravascular activation of platelets may limit the response to this treatment. The aim of the present study was to investigate whether platelet-activating factor (PAF), an ether lipid mediator with multiple potent biological activities, is synthesized during therapy with thrombolytic agents. Two sets of experiments were performed: (1) we extracted and quantified PAF in blood of patients with acute myocardial infarction treated or untreated with streptokinase (SK), and (2) since the endothelium/platelet interaction is thought to be at the basis of vascular reocclusion, we studied whether cultured human endothelial cells synthesize PAF after stimulation with SK or plasmin.

METHODS AND RESULTS

PAF was extracted from blood samples immediately after acidification to destroy the acid-labile PAF-acetylhydrolase in 25 patients with acute myocardial infarction treated (group A, n = 14) and untreated (group B, n = 11) with intravenous infusion of SK. PAF was detected in 10 of 14 patients of group A and none of group B. PAF began to be detectable 60 to 90 minutes after SK infusion and disappeared from the circulation within 120 to 180 minutes. Percent variation of platelet count over basal values correlated negatively with the amount of PAF present in the circulation at 90 minutes (r = -.719; P < .001) and at 120 minutes (r = -.652; P < .001). Cultured human umbilical cord vein-derived endothelial cells (ECs) synthesized PAF in a dose-dependent manner in response to SK and plasmin, with a synthesis that peaked at 15 minutes and persisted up to 30 minutes for SK and 2 hours for plasmin. PAF extracted from blood samples or from ECs was quantified by bioassay performed after purification by thin-layer chromatography and high-performance liquid chromatography (HPLC). PAF-bioactive material was characterized as PAF with physicochemical and enzymatic treatments, HPLC-tandem mass spectrometry, and specific PAF-receptor antagonists.

CONCLUSIONS

The observation that PAF was detectable in the blood of patients of group A only after treatment with SK and was not detectable in patients with a comparable infarct not treated with SK (group B) suggested that SK stimulates the synthesis of this mediator either directly or via plasmin generation. Indeed, cultured human ECs synthesize PAF after stimulation with both SK and plasmin. PAF production by ECs may promote platelet activation and interaction of these cells as well as of circulating leukocytes with endothelium. These events may limit the beneficial effects of thrombolytic therapy.

Development of a high-performance liquid chromatographic-mass spectrometric technique, with an ionspray interface, for the determination of platelet-activating factor (PAF) and lyso-PAF in biological samples

An HPLC-mass spectrometric technique with an ionspray interface was developed for the determination of platelet-activating factor (PAF) and PAF-related compounds in biological samples. HPLC separations were performed using a reversed-phase column. The mass spectra showed intense [M + H]+ ions. Collision-induced dissociation of protonated molecular ions gave characteristic daughter ions corresponding to the phosphorylcholine group. By selective-ion monitoring, a detection limit of 0.3 ng was obtained for all molecules; by multiple reaction monitoring, the same sensitivity was achieved for PAF whereas for lyso-PAF the limit was 3 ng. Finally, PAF was comparatively determined by bioassay and HPLC-MS after extraction from the cell pellets and the supernatants of human polymorphonuclear neutrophils unstimulated or stimulated with opsonized zymosan. The good correlation observed between these techniques indicated the reliability of HPLC-MS for biochemical studies on PAF and PAF-related molecules.

Outer-membrane porins from gram-negative bacteria stimulate platelet-activating-factor biosynthesis by cultured human endothelial cells

Porins are a family of hydrophobic proteins located in the outer membrane of the cell wall in Gram-negative bacteria. The effect of porins on the biosynthesis of platelet-activating factor (PAF) by cultured human umbilical-cord-vein-derived endothelial cells (HUVEC) was investigated. The results demonstrate that porins were able to induce a dose-dependent synthesis of PAF in HUVEC. PAF, synthesized after stimulation with porins, was mainly cell associated and the synthesis peaked at 15 min, decreasing rapidly thereafter. Experiments with radiolabeled precursors demonstrated that PAF, a 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine, was synthesized via the remodeling pathway involving the acetylation of 1-O-alkyl-2-lyso-sn-glyceryl-3-phosphorylcholine (2-lysoPAF) generated from 1-O-alkyl-2-acyl-sn-glyceryl-3-phosphorylcholine by phospholipase-A2 activity. The activation of phospholipase A2 in HUVEC stimulated by porins was detected by observing the mobilization of [14C]arachidonic acid. In addition, the activity of acetyl-CoA:1-alkyl-sn-glycero-3-phosphorylcholine 2-O-acetyltransferase was transiently increased in porin-stimulated HUVEC and, after incubation with [3H]CoASAc or [3H]acetate, the [3H]acetyl group was incorporated into newly synthesized PAF. Porins, by forming transmembrane channels, induced a sustained influx of extracellular 45Ca2+ into the cytosol. The activation of PAF synthesis by porins depended on this influx rather than on intracellular calcium mobilization, since PAF synthesis did not occur in the absence of extracellular Ca2+.

Porins and lipopolysaccharide stimulate platelet activating factor synthesis by human mesangial cells

Porins, a family of hydrophobic proteins located in the outer membrane of the cell wall of gram-negative bacteria and lipopolysaccharide (LPS), were shown to stimulate the synthesis of platelet activating factor (PAF), a phospholipid mediator of inflammation and endotoxic shock, by cultured human glomerular mesangial cells (MC). The synthesis of PAF induced by porins was rapid (peak at 20 min) and independent either from contamination by LPS or from generation of an endotoxin-induced cytokine such as tumor necrosis factor (TNF) since it was not prevented by cycloheximide, an inhibitor of protein synthesis or anti-TNF blocking antibodies. LPS also stimulated PAF synthesis by MC. However, the kinetic of PAF synthesis induced by LPS was biphasic with an early and transient peak at 10 minutes and a second and sustained peak at three to six hours. This second peak required an intact protein synthesis and was prevented by anti-TNF antibodies, suggesting the dependency on LPS-induced synthesis of TNF. Experiments with labeled precursors demonstrated that in MC, either after stimulation with porins or LPS, PAF was synthesized via the remodeling pathway that involves acetylation of 1-0-alkyl-sn-glyceryl-3-phosphorylcholine (2-lyso-PAF) generated from 1-0-alkyl-2-acyl-sn-glyceryl-3-phosphorylcholine by phospholipase A2 (PLA2) activity. Porins and LPS, indeed, induced PLA2-dependent mobilization of [14C]-arachidonic acid that was inhibited by p-bromodiphenacylbromide (PBDB). PBDB, an inhibitor of PLA2, also blocked PAF synthesis by preventing the mobilization of 2-lyso-PAF, the substrate for PAF-specific acetyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)