Enzyme immunoassays of eicosanoids using acetylcholinesterase.
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Acetylcholinesterase↗
Biomedical subjects
J Maclouf
Publications and source records attributed to J Maclouf.
Enzyme immunoassays for leukotrienes C4 and E4 using acetylcholinesterase.
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Acetylcholinesterase↗
Enzyme immunoassay measurement of the urinary metabolites of thromboxane A2 and prostacyclin.
We have used a recently developed enzyme immunoassay (EIA) method for measuring urinary concentrations of TXB2, 6-keto PGF1 alpha, 2,3-dinor-TXB2, 2,3-dinor-6-keto PGF1 alpha and 11-dehydro-TXB2 using acetylcholinesterase from Electrophorus Electricus coupled to TXB2, 6-keto PGF1 alpha and 11-dehydro-TXB2. Urinary PGI2 and TXA2 breakdown products and their metabolites were extracted from 3-40 ml of urine corresponding to 100 mumoles creatinine. Measurements were performed after Sep-Pak extraction and thin layer chromatography separation in a system that allows separation between dinor- and parent derivatives. Because of the relatively high cross reactivity (10-15%) of the anti-TXB2 serum with 2,3-dinor TXB2 and the anti-6-keto PGF1 alpha serum with 2,3-dinor-6-keto PGF1 alpha, measurements were done using 3 antisera (anti-TXB2 and anti-6-keto PGF1 alpha diluted 1/50,000, anti 11-dehydro-TXB2 diluted 1/200,000). The reproducibility of the technique was assessed by measuring the same urine stored frozen in aliquots together with each series of samples (Coefficient of variation 6-12% (n = 20), depending on the compound). In addition, the use of a different solvent system for the thin layer chromatography did not affect the results although the migration of the compounds was modified significantly. Determination of the urinary excretion of TXB2 and prostacyclin metabolites in 17 healthy individuals by this method provided results in agreement with those obtained by other methodologies. In addition, comparisons made between EIA and gas chromatography/mass spectrometry analysis showed good correlation between the urinary metabolites as determined by each technique (r = 0.98).
Adult↗
Platelet-activating factor and leukotriene biosynthesis in whole blood. A model for the study of transcellular arachidonate metabolism.
As a model to perhaps better indicate potential in vivo tissue inflammatory events, the generation of leukotriene (LT)B4, 20-OH-LTB4, sulfidopeptide LT, and platelet-activating factor (PAF) from human whole blood stimulated with zymosan was compared with that produced by isolated human neutrophils suspended either in buffer or plasma. Several reports have shown that substantial LTB4 biosynthesis could be induced after addition of zymosan to whole blood, but little was known concerning the generation of other important lipid mediators, or the cellular source of these. We have shown that, in spite of some subject variation, the zymosan-induced production of 20-OH-LTB4, LTB4, and LTE4 reached maxima within 30 to 60 min with 1.1, 2.8, and 0.60 ng/10(6) neutrophils, respectively. These concentrations would be sufficient to induce significant biologic effects. Studies with isolated cell mixtures suggested that the neutrophil was the primary source of the lipid mediators or their precursors in this system, although a number of other cell types contributed as accessory cells to the final amounts and mix of mediators produced. The ratio of neutrophils to accessory cells in mixed cell experiments dramatically modified the metabolic pattern of leukotriene generation. The concentration of LTB4 was increased in the presence of RBC and that of LTE4 when platelets were present. These results suggested that cellular cooperation and transcellular biosynthesis played a key role in the overall production of eicosanoids such as LTB4 and LTC4. The concomitant synthesis of PAF in isolated cells and in whole blood was also determined as another member of the complex lipid mediator network. Maximal production of cell-associated PAF was observed within 30 min after the initiation of phagocytosis and reached levels of 3 to 5 ng PAF/10(6) neutrophils. When other cells were present in a coincubation system, the time course for production of PAF was not altered, but maximal concentration of PAF was lower, perhaps as a result of enhanced PAF metabolism. Study of eicosanoids and other lipid mediator production in mixed cell populations provides insight into those events occurring within tissues, where cross-cell signaling and transcellular biosynthesis may occur.
Arachidonic Acids↗
Transcellular sulfidopeptide leukotriene biosynthetic capacity of vascular cells.
Cells in the vasculature, including polymorphonuclear leukocytes, platelets, and endothelial cells, have been shown to be jointly involved in the biosynthesis of active lipid mediators derived from arachidonic acid. Stimulation of neutrophils with the calcium ionophore A23187 as a model for cell activation results in production of leukotriene (LT)A4 with subsequent intracellular conversion into LTB4. When platelets or endothelial cells were present in the incubation system, LTC4 was produced from the neutrophil-derived LTA4. Whereas production and release of LTA4 under resting conditions in vivo might be expected to be quite low, under pathologic conditions, LTA4 production could be markedly increased. Therefore, the metabolism of exogenous LTA4 by platelets and endothelial cells was studied at a wide range of LTA4 concentrations. The production of LTC4 during coincubation of neutrophils with platelets was found to be dependent on neutrophil number ranging from 2 x 10(5) to 2 x 10(7) cells/mL. When a fixed number of neutrophils were stimulated with platelets alone or with mixtures of platelets and endothelial cells, LTC4 production was observed to be dependent on both acceptor cell types. These results suggest that mixed cell populations, which are likely to occur in vivo, may be critical determinants of the profile of eicosanoids produced in pathophysiologic circumstances. We suggest that both endothelial cells and platelets, in the presence of neutrophils, contribute large quantities of sulfidopeptide leukotrienes to inflammatory and thrombotic situations. Furthermore, platelets, because of their quantity and reactivity, may play a pivotal role in transcellular biosynthesis of eicosanoids.
Adult↗
Platelet-dependent induction and amplification of polymorphonuclear leucocyte lysosomal enzyme release.
Degranulation of human polymorphonuclear leucocytes induced by opsonized zymosan (OpZ) was studied in the presence or absence of platelets, either resting or stimulated by thrombin. Lysozyme secretion from polymorphonuclear leucocytes stimulated with OpZ increased in the presence of platelets. A further increase was observed when platelets had been stimulated with thrombin. The effect was dependent on platelet concentration (10-80 platelets/polymorphonuclear leucocytes). Resting polymorphonuclear leucocytes could be activated by platelets that had been stimulated with thrombin with an optimal effect observed at 0.1 U/ml of thrombin. Substitution of platelets with platelet-released products only resulted in significant stimulation of polymorphonuclear leucocytes at concentrations above those used in the coincubations experiments. Zymosan coated with various opsonins showed a gradient in the relative intensity of polymorphonuclear leucocytes degranulation. Platelet-dependent enhancement of polymorphonuclear leucocytes degranulation was higher with opsonins that were poorer at inducing lysosomal secretion. The role of platelets as helper cells in the activation of polymorphonuclear leucocytes appears to be dominant when polymorphonuclear leucocytes are challenged in suboptimal conditions. Positive interactions between platelets and polymorphonuclear leucocytes may be relevant in vivo at the site of inflammation where platelets could enhance effector functions of polymorphonuclear leucocytes.
Blood Platelets↗
Modulation of platelet function by SIN-1A, a metabolite of molsidomine.
Molsidomine or its active metabolite SIN-1A have antithrombotic properties in experimental models. This effect seems to be related, at least in part, to their antiplatelet activities. SIN-1A inhibited platelet adhesion to collagen, platelet aggregation, and the release reaction in in vitro experiments. SIN-1A acts as an early step of platelet activation by inhibiting calcium influx and phospholipase activity, which leads to inhibition of thromboxane formation and fibrinogen binding. Antiplatelet properties were observed after oral absorption in healthy volunteers and in patients with myocardial infarction after intravenous infusion.
Collagen↗
Platelets and endothelial cells contribute to the production of LTC4 by transcellular metabolism with neutrophils.
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Animals↗
Biochemical and morphological modifications in dexamethasone-treated mouse bone marrow-derived mast cells.
Addition of 1 microM dexamethasone (DM) to bone marrow-derived mast cells (BMMC) induced a time-dependent increase in cell histamine content. The latter reached a plateau of 2.5 micrograms/1 x 10(6) cells after 11 days in culture, compared with 100 ng/1 x 10(6) for untreated BMMC. Steroids, such as beta-estradiol, androsterone, and testosterone (1 microM), did not alter the histamine content of BMMC, whereas progesterone (1 microM) induced a moderate increase. Other glucocorticosteroids also enhanced histamine content, suggesting that the observed increase was specific for glucocorticosteroid. Treatment of BMMC with 1 microM DM for 14 days inhibited the Ag-induced, IgE-mediated release of histamine, beta-hexosaminidase, platelet-activating factor-acether, LTB4, and LTC4 by 65 +/- 3%, 66 +/- 1%, 93 +/- 3%, 66 +/- 2%, and 74 +/- 10%, respectively (mean +/- 1 SD, n = 3). In contrast with untreated cells which produce less than 2 ng/1 x 10(6) cells PGD2 after Ag challenge, DM-treated BMMC generated 16.8 +/- 0.3 ng/1 x 10(6) cells PGD2. Moreover, most of DM-treated BMMC became Alcian blue+/safranin+ and by ultrastructure, exhibited numerous cytoplasmic granules filled with abundant and uniform electron-dense matrix. The present results indicate that DM-treated BMMC exhibit biochemical and functional properties different from immature untreated cells, suggesting that a maturation-like process occurred in vitro during DM treatment.
Alcian Blue↗
Effect of lupus anticoagulant on antithrombogenic properties of endothelial cells--inhibition of thrombomodulin-dependent protein C activation.
We have investigated the effect of purified immunoglobulin G (IgG) on endothelial cell functions in 16 patients with lupus anticoagulant, 9 of whom had systemic lupus erythematosus (SLE). Spontaneous or thrombin-stimulated secretion of prostacyclin (PGI2) by cultured human endothelial cells from umbilical cord vein (HUVEC) was not inhibited by the patient's IgG. Nor was spontaneous release of tissue plasminogen activator (t-PA) or of its inhibitor (PAI) modified in the presence of patient's IgG. The rate of activation of purified protein C (PC) by HUVEC in the presence of thrombin was significantly lowered by patient's IgG or Fab' fragment (inhibition of 43%). Neutralization of this effect was obtained by incubation of a greater quantity of phospholipids (phosphatidylcholine, phosphatidylserine) with the patient's IgG. Activation of PC was also performed using purified rabbit thrombomodulin (TM) and a similar inhibition of the patient IgG was observed (inhibition of 48%) but the activation of Gla-domainless PC was not modified.
Animals↗
Stimulation of release of prostaglandins and thromboxanes from isolated guinea pig lung cells by bradykinin, f-Met-Leu-Phe, phorbol myristate, ionophore A23187, and leukotrienes.
Guinea pig lungs were perfused for 15 min with a solution of protease type VII (0.05 mg/ml) and dispersed to yield a suspension of morphologically intact and metabolically active lung cells (over 250 X 10(6) cells per animal). The viability of these cells assessed with the Trypan blue exclusion technique was more than 80%. Treatment of these mixed cells (1 X 10(6) cells/ml) with chemicals such as phorbol myristate acetate (1 X 10(-9) to 1 X 10(-7) M), f-Met-Leu-Phe (5 X 10(-6) to 1 X 10(-4) M), and the calcium ionophore A23187 (3.1 X 10(-7) to 2.5 X 10(-6) M), and with autacoids such as bradykinin (1 X 10(-5) to 1 X 10(-4) M), leukotriene B4 (1 X 10(-13) to 1 X 10(-7) M), and leukotriene D4 (1 X 10(-10) to 1 X 10(-7) M) stimulated to a variable degree the release of prostaglandin E2 and thromboxane B2 (measured with a novel enzyme immunoassay). It is suggested that icosanoid release from the lungs is the result of direct chemical or hormonal stimulation of the cells and not a consequence of vascular changes. Studies are in progress to purify lung cell populations and characterize the cells responsible for the release of these icosanoids.
Animals↗
Release of prostaglandin E2 and thromboxane B2 by mixed isolated human lung cells.
Human lung specimens were minced and treated for 30 min with collagenase (1 mg ml-1) and DNase (0.1 mg ml-1) to obtain a suspension of viable (approximately 80%) and metabolically active lung cells (5 x 10(6) cells per gram of tissue). Treatment of these mixed lung cells with bradykinin (1.25 x 10(-6) to 1 x 10(-5) M) and f-Met-Leu-Phe (f-MLP; 1 x 10(-8) to 5 x 10(-6) M) did not stimulate to a substantial extent the release of prostaglandins and thromboxanes (measured with novel Enzyme Immunoassays). The only concentration of PAF that stimulated significantly the release of icosanoids from lung cells was 5 x 10(-7) M. Phorbol myristate (PMA; 5 x 10(-8) to 2 x 10(-6) M) and ionophore a-21387 (2.5 x 10(-6) to 2 x 10(-5) M) strongly stimulated the release of prostaglandins and thromboxanes by dispersed human lung cells. These findings support previous observations showing that human lungs have the enzymes necessary for the synthesis and release of prostaglandins and thromboxanes but stimulation of the release of these mediators is not obtained with the hormonal stimuli that are active in guinea pigs. Studies in progress will purify the cell populations and characterize the cells responsible for the release of these icosanoids.
Bradykinin↗
Prostaglandin D2 generation in mouse bone marrow-derived mast cells exposed to dexamethasone is associated with endogenous peroxidase activity.
The appearance of fixative-sensitive peroxidase activity in the nuclear envelope and endoplasmic reticulum of bone marrow-derived mast cells (BMMC) cultured in the presence of 1 microM dexamethasone (DM) for up to 14 days and its relationship with immunologic release of prostaglandin D2 (PGD2) by these cells were studied. Endogenous peroxidase activity, previously shown as a marker of arachidonic acid metabolism in various cell types, was visualized by cell incubation in 3,3' diaminobenzidine-containing solution before glutaraldehyde fixation. PGD2 release was induced by passive sensitization of BMMC with an optimal dose of monoclonal IgE and subsequent challenge with specific a antigen. We found that 4-week-old BMMC, used as the starting population of the present study, exhibited immature morphologic features, did not present peroxidase activity when cytochemically processed, and released minute amounts of PGD2 in response to IgE-dependent stimulation. When such BMMC were exposed to DM during 24 hours, they showed aldehyde-inhibited peroxidase activity in the perinuclear envelope and a few endoplasmic reticulum segments. As compared with untreated cells, 24-hour DM-exposed BMMC released higher amounts of PGD2 upon immunologic stimulation. After an additional 14-day period of DM exposure, an intense peroxidase activity was detected in the perinuclear envelope and the endoplasmic reticulum of BMMC, which, under immunologic stimulation, released as much as 42.4 +/- 14.7 ng of PGD2/1 x 10(6) cells. Aminotriazole (20 and 50 mM) extinguished both peroxidase activity and PGD2 release from BMMC whereas indomethacin (1 microM) suppressed PGD2 production, but did not alter endogenous peroxidase activity. Previous cell fixation with glutaraldehyde totally inhibited endogenous peroxidase reaction in DM-exposed BMMC. Moreover, 14-day DM-exposed BMMC exhibited morphologic characteristics of mature mast cells and possessed alcian blue+/safranin+ granules. Therefore, the present data suggest that appearance of peroxidase activity in the nuclear envelope and the endoplasmic reticulum of DM-exposed BMMC is associated with the ability of the cells to synthetize PGD2 and appears as a cytochemical marker of the in vitro maturation of mouse bone marrow-derived mast cells.
Aldehydes↗
Mechanisms of the mAb ALB6(CD9) induced human platelet activation: comparison with thrombin.
A CD9 monoclonal antibody described to aggregate human platelets was studied on different platelet functions in order to determine its mechanism of action. After a lag phase of 35 sec the mAb ALB6 induced a transient decrease in 32P-polyphosphoinositides, synthesis of 32P-phosphatidate (PA), phosphorylation of myosin light chain (P20) and of 43 KDa protein (P43) and the release reaction. Final biological and metabolic effects of ALB6 thus appear similar to that of thrombin but three differences bring additional information: (i) the lag phase, (ii) the kinetic of ALB6-induced release is identical for all granules whereas the release of dense granules is faster when induced by thrombin. (iii) no external Ca++ is required for ALB6 induced-activation.
Antibodies, Monoclonal↗
Radioimmunoassay of 11-dehydrothromboxane B2 in human plasma and urine.
Because of the discrepancy between the capacity of platelets to synthesize thromboxane B2 ex vivo and the actual synthetic rate in vivo, measurement of thromboxane B2 in plasma is highly influenced by sampling-related artifacts. We have developed and validated a radioimmunoassay for a major enzymatic derivative of thromboxane B2 with an extended plasma half-life, i.e., 11-dehydrothromboxane B2. The binding of the tracer is displaced by as low as 1 pg/ml of the homologous ligand, with a high degree of specificity for the open ring structure as well as for the omega side-chain. This method can detect changes in the plasma concentration and urinary excretion of 11-dehydrothromboxane B2 associated with stimulated short-term increases of thromboxane B2 secretion in the human circulation.
Adult↗
Hermansky-Pudlak platelets: further studies on release reaction and protein phosphorylations.
Platelets from a patient with the Hermansky-Pudlak syndrome were studied. These platelets had decreased amounts of serotonin and adenine nucleotides, and a decreased number of mepacrine-labeled dense bodies. beta-Thromboglobulin and acid hydrolases contained in alpha-granules and lysosomes respectively were present in normal amount. Platelets in platelet-rich plasma did not respond to collagen, but arachidonic acid and ionophore A 23187 induced normal aggregation and normal thromboxane (TX) synthesis. Alpha-granule release was found impaired and remained subnormal even with high doses of inducers. In response to thrombin aggregation, release and TX synthesis of isolated metrizamide gradient platelets were found at lower than normal levels. Phosphorylation of P20 and P43 proteins was normal. Only a combination of ADP plus thrombin could restore a normal aggregation, with normal alpha-granule and lysosome release and normal TX synthesis. These results indicated that in the absence of dense bodies: the release of other granules is impaired; the TX synthesis is delayed except when induced by arachidonic acid and A 23187 ionophore; the absence of dense bodies could be compensated for by the addition of ADP which restores the impaired release reaction and TX formation; and P20 and P43 polypeptides were phosphorylated as rapidly as those in normal platelets.
Adenine Nucleotides↗
Conversion of arachidonic acid into 12-oxo derivatives in human platelets. A pathway possibly involving the heme-catalysed transformation of 12-hydroperoxy-eicosatetraenoic acid.
Analysis of arachidonic acid metabolites in human platelets by reverse-phase HPLC with radioactivity and UV detection revealed, besides Thromboxane B2 (TXB2), 12-hydroxy-heptadecatrienoic acid (HHT) and 12-hydroxy-eicosatetraenoic acid (12-HETE) previously described, two peaks of unidentified material absorbing at 280 nm. This material was purified by straight-phase HPLC and characterized by UV spectroscopy and gas chromatography-mass spectrometry. Three carbonyl compounds were identified: 12-keto-5,8,10,14-eicosatetraenoic acid and two geometric isomers of 12-oxo-5,8,10-dodecatrienoic acid. In a 5 min incubation at 37 degrees C in the presence of 9 microM arachidonic acid, the yield was of 0.5 to 1% of added arachidonic acid for the ketonic compound and of 4 to 7% for the sum of the two isomeric fatty acid aldehydes in comparison to 10 to 13% and 25 to 28% for TXB2 and 12-HETE, respectively. Because the three compounds carry a carbonyl group at position 12, their relationship with the 12-lipoxygenase pathway was investigated. It was found that the three compounds were formed when 12-hydroperoxy-eicosatetraenoic acid (12-HPETE) was incubated with intact or heat denaturated platelets or hemoproteins, strongly suggesting that these carbonyl compounds are products of a heme-catalysed transformation of 12-HPETE.
Arachidonic Acid↗
Signal transduction in normal and pathological thrombin-stimulated human platelets.
Human blood platelets stimulated by thrombin undergo very rapid morphological changes, the most characteristic of which are pseudopod formation and granule centralization. These early changes in shape are accompanied by a transient decrease (30%) in phosphatidyl inositol 4,5-bisphosphate (PIP2) which occurs in the first 10 s after thrombin addition. Transient decreases in phosphatidyl inositol 4-phosphate (PIP) and phosphatidyl inositol (PI) occur later (20-30 s). These events lead to the formation of inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DG) and hence phosphatidate (PA). Two polypeptides are phosphorylated during the same time span: the myosin light chain (P20) and a 43 kDa protein (P43). Concomitant with these molecular changes, platelet 'release reaction' occurs, i.e., liberation of the different granule constituents into the external medium: the earliest concerns dense bodies which liberate adenine nucleotides, calcium and serotonin; alpha-granules then liberate adhesive and specific proteins and are followed by lysosomes which liberate hydrolases. Pathological platelets from patients with inherited disorders, presenting well-characterized and specific defects of either the platelet membrane (GT) or storage granules (GPS and HPS), have also been studied. The results obtained lead to the following conclusions: (1) the transducing system is normal in platelets unable to aggregate; (2) phosphorylation of P20 and P43 proteins can be complete with impaired release; and (3) when platelets lack alpha-granules the transducing system as well as the release of other granule populations are impaired. These results evidence the relationship between the absence of intraplatelet components and metabolic events.
Blood Platelet Disorders↗