Inhibition Of Platelet-activating Factor Research Articles

Reduction of stenosis-induced cyclic flow variations by inhibition of platelet-activating factor in dogs

Reduction of stenosis-induced cyclic flow variations by inhibition of platelet-activating factor in dogs

Biphenyls, a new class of compound that inhibits plateletactivating factors.

Honokiol (1), a constituent of Magnoliae cortex, and related synthetic biphenyls inhibited the platelet aggregation induced by a few aggregating agents. In particular, compounds 3, 5, and 10 had an inhibitory effect on platelet activating factor (PAF), which provides a new class of PAF inhibitor.

Effects of platelet activating factor on mouse oocyte fertilization in vitro

Platelet activating factor is rapidly gaining acceptance as a potent mediator in many reproductive processes. This study presents data that indicate a direct role of platelet activating factor in fertilization. Platelet activating factor was shown to significantly increase (p less than 0.001) the fertilization rate of mouse oocytes in vitro. Furthermore, CV3988, an inhibitor of platelet activating factor, was noted to significantly decrease in vitro fertilization rates at 10(-5) and 10(-4) mol/L concentrations.

Platelet-activating factor enhances complement-dependent phagocytosis of diamide-treated erythrocytes by human monocytes through activation of protein kinase C and phosphorylation of complement receptor type one (CR1)

Oligomerization of band 3 protein has been recently indicated as an early event in senescent or damaged red cell membrane followed by specific deposition of anti-band 3 antibodies and binding of complement C3 fragments. The band 3-anti-band 3-C3b complex is recognized by homologous monocytes, and phagocytosis ensues. This study shows that recognition of the anti-band 3-C3b complex by the monocyte C3b receptor type one (CR1) plays a crucial role in the process of removal of damaged red cells. Indeed, blocking of monocyte CR1 with an anti-CR1 monoclonal antibody abrogated phagocytosis of diamide-treated red cells. Platelet-activating factor (PAF) is a phospholipid mediator involved in inflammatory processes. Nanomolar (R)-PAF enhanced the CR1-dependent phagocytosis of diamide-treated human red cell and of sheep red cells coated with C3b, induced the fast translocation of protein kinase C to monocyte membrane compartment, and stimulated the phosphorylation of monocyte CR1. The biologically inert lyso-PAF and the enantiomer (S)-PAF were inactive. PAF receptor antagonists and inhibitors of protein kinase C blocked the enhancement of phagocytosis induced by PAF. Protein kinase C translocation, phosphorylation of CR1, and stimulation of this receptor to an active state capable of mediating phagocytosis represent a novel pathway by which PAF interferes with red cell homeostasis and possibly modulates inflammatory reactions and host mechanisms against infections.

Selective inhibition of platelet-activating factor by antiarrhythmic drugs in human platelets

Selective inhibition of platelet-activating factor by antiarrhythmic drugs in human platelets

Inhibition of [ 3H]platelet activating factor (PAF) binding by Zn 2+: A possible explanation for its specific PAF antiaggregating effects in human platelets

Zinc ions in the micromolar range exhibited a strong inhibitory activity toward platelet activating factor (PAF)-induced human washed platelet activation, if added prior to this lipid chemical mediator. The concentration of Zn 2+ required for 50% inhibition of aggregation (IC 50) was inversely proportional to the concentration of PAF present. The IC 50 values (in μ m) for Zn 2+ were 8.8 ± 3.9, 27 ± 5.8, and 34 ± 1.7 against 2, 5, and 10 n m PAF, respectively ( n = 3–6). Zn 2+ exhibited comparable inhibitory effects on [ 3H]-serotonin secretion and the IC 50 values (in μ m) were 10 ± 1.2, 18 ± 3.5, and 35 ± 0.0 against 2,5, and 10 n m PAF, respectively ( n = 3). Under the same experimental conditions, aggregation and serotonin secretion induced by ADP (5 μ m), arachidonic acid (3.3 μ m), or thrombin (0.05 U/ml) were not inhibited. Introduction of Zn 2+ within 0–2 min after PAF addition not only blocked further platelet aggregation and [ 3H]serotonin secretion but also caused reversal of aggregation. Analysis of [ 3H]PAF binding to platelets showed that Zn 2+ as well as unlabeled PAF prevented the specific binding of [ 3H]PAF. The inhibition of [ 3H]PAF specific binding was proportional to the concentration of Zn 2+ and the IC 50 value was 18 ± 2 μ m against 1 n m [ 3H]PAF ( n = 3). Other cations, such as Cd 2+, Cu 2+, and La 3+, were ineffective as inhibitors of PAF at concentrations where Zn 2+ showed its maximal effects. However, Cd 2+ and Cu 2+ at high concentrations exhibited a significant inhibition of the aggregation induced by 10 n m PAF with IC 50 values being five- and sevenfold higher, respectively, than the IC 50 for Zn 2+, and with the IC 50 values for inhibition of binding of 1 n m [ 3H]PAF being 5 and 19 times higher, respectively, than the IC 50 for Zn 2+. The specific inhibition of PAF-induced platelet activation and PAF binding to platelets suggested strongly that Zn 2+ interacted with the functional receptor site of PAF or at a contiguous site.

Decrease in ovarian platelet-activating factor during ovulation in the gonadotropin-primed immature rat.

Platelet-activating factor (PAF) is a biologically active phospholipid that is released locally during acute inflammatory reactions and tissue injury. Since there is evidence that the biochemical events of mammalian ovulation resemble an inflammatory reaction, the objective of this study was to determine whether ovarian levels of PAF change during ovulation. At 2-h intervals during the ovulatory process in gonadotropin-primed 25-day-old Wistar rats, the ovaries were extirpated, homogenized, and extracted for lipids. The extracts were subjected to thin-layer chromatography (TLC), and the portion of the silica gel that comigrated with PAF was re-extracted and assayed for PAF activity. The PAF was measured (in fmole equivalents of synthetic PAF) by a bioassay based on the capacity of aliquots of the extracts to release [3H]-serotonin from platelets isolated from whole blood of rabbits and prelabeled with [3H]-serotonin. The ovarian level of PAF decreased (p less than 0.01) by 36% from 6.67 +/- 0.77 to 4.27 +/- 0.45 fmoles/mg ovary by 2 h after treatment with human chorionic gonadotropin (hCG), and it declined another 14% by 4 h after hCG. The ovarian PAF remained at this reduced level for up to 24 h after hCG. The administration of indomethacin (5 mg/rat, s.c.) or epostane (5 mg/rat, s.c.) at 1 h after hCG prevented ovulation, but neither drug affected the decline in ovarian PAF. Preliminary tests showed that the lipid extracts from the ovaries also contained PAF inhibitor(s) that comigrated with PAF on the TLC plates. Similar to PAF, the lipid-soluble inhibitor(s) decreased (p less than 0.05) in the ovaries within 4 h after hCG treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of platelet activating factor does not alter myocardial stunning

Inhibition of platelet activating factor does not alter myocardial stunning

Inhibition of platelet-activating factor induced renal hemodynamic and tubular dysfunctions with L-655,240, a new thromboxane-prostaglandin endoperoxide antagonist.

The continuous infusion or bolus injection of the platelet-activating factor (PAF) is associated with profound hypotension, marked reductions of renal plasma flow, glomerular filtration, and urinary sodium excretion. All these effects are inhibited by blocking PAF receptors. To examine further the potential mediators of PAF on renal function, we utilized L-655,240 (6 mg/kg, intravenously), a thromboxane-prostaglandin endoperoxide antagonist, to study the systemic and renal response to PAF (0.8 micrograms/kg, intravenously) in the anesthetized dog, using clearance methodology. PAF decreased blood pressure from 115 +/- 7 to 54 +/- 4 mmHg (1 mmHg = 133.3 Pa), renal plasma flow from 105 +/- 6 to 74 +/- 56 mL/min, and glomerular filtration from 43 +/- 3 to 32 +/- 1 mL/min. PAF also reduced urine volume from 1.1 +/- 0.2 to 0.4 +/- 0.1 mL/min, and urinary sodium from 158 +/- 7 to 86 +/- 7 mu equiv./min. L-655,240 alone had no significant effect on blood pressure, renal plasma flow, and filtration rate, at any dose. However, the 6-mg/kg dose resulted in a slight elevation of diuresis, from 1.1 +/- 0.2 to 1.9 +/- 0.1 mL/min, and urinary sodium, from 134 +/- 13 to 212 +/- 19 mu equiv./min. All doses of L-655,240 blocked the effect of PAF on blood pressure. However, the two lower doses of this antagonist (1 and 3 mg/kg) failed to prevent the PAF-induced fall of renal plasma flow and filtration rate, and attenuated the effect on urinary sodium in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of platelet-activating factor reduces myocardial infact size: M. Maruyama, G. Vercellotti, H. Jacob, G. Gross, C. Christensen. Department of Pharmacology, Medical College of Wisconsin, Milwaukee, WI; Department of Medicine, University of Minnesota, Minneapolis, MN

Inhibition of platelet-activating factor reduces myocardial infact size: M. Maruyama, G. Vercellotti, H. Jacob, G. Gross, C. Christensen. Department of Pharmacology, Medical College of Wisconsin, Milwaukee, WI; Department of Medicine, University of Minnesota, Minneapolis, MN

Selective inactivation by endogenous protein kinase C of human platelet high-affinity GTPase coupled with PAF receptors

Incubation of human platelets with protein kinase C activator 4β-phorbol-12β-myristate-13α-acetate (PMA) abolished stimulation of membrane high-affinity GTPase by platelet-activating factor (PAF). GTPase stimulation by epinephrine decreased by 30%, while the prostaglandin E 1 (PGE 1) effect was unchanged. Basal GTPase activity (22.4±1.1 pmol P i/min per mg protein) was not affected by PMA. Therefore, a study was performed of the effect of endogenous protein kinase C activation on adenylate cyclase regulation by agonists. PMA pretreatment completely suppressed PAF inhibition of basal adenylate cyclase activity but hardly influenced the inhibition by PAF of forskolin-stimulated activity. Adenylate cyclase inhibition by epinephrine in the presence of propranolol was not suppressed completely after platelet incubation with PMA. Epinephrine effects on basal and forskolin-stimulated activities decreased equally. Platelet pretreatment with PMA increased PGE 1-stimulated activity by abolishing the inhibitory effect of high GTP concentrations. These studies indicate that protein kinase C selectively inhibits PAF effects, presumably by inactivating a GTP-binding protein coupled with PAF receptors.

Ｃ‐反応性蛋白（ＣＲＰ）のリガンド結合性のクロマトグラフィー的検討

Human C-reactive protein (CRP), a typical acute-phase protein, increases about hundreds-fold in concentration in response to infection, inflammation or tissue injury.CRP was first described by Tillet and Francis in 1930 as a serum protein capable of precipitating pneumococcal C-polysaccharide where phosphorylcholine (PC) was identified later to be a ligand. Clinical and biological aspects, especially immunological ones, of human CRP have been studied. And some of them have been ascribed to its capacity of ligand-binding with PC calcium-dependently. While type 4 pneumococcal polysaccharide which lacks phosphate and choline has been pointed out to be able to bind human CRP in calcium-dependent manner, ligands other than PC should be considered besides PC.We find specific affinity chromatography bearing new ligand of negatively-charged aminocaproic acid which binds human CRP calcium-dependently (buffer ; 0.15 M NaCl, 0.02 M Tris, 0.01 M CaCl2, 0.01 M NaN3, pH 7.8, room temp.), being almost comparable to PC-affinity chromatography. In addition, another specific ligand of positively-charged aminohexyl-agarose is found to bind human CRP calcium-independently (buffer; 0.09 M NaCl, 0.01 M Tris, pH 7.4, room temp.) . These new ligands may provide simple model to understand human CRP.1) Tillet, W.S., Francis, T. Jr.: Serological reactions in pneumonia with a non-protein somatic fraction of pneumococcus. J. Exp. Med. 52: 561-571, 1930.2) Volanakis, J.E., Kaplan, M.H.: Specificity of C-reactive protein for choline phosphate residues of pneumococcal C-polysaccharide. Proc. Soc. Exp. Biol. Med. 136: 612-614, 1971.3) Kaplan, M.H., Volanakis, J.E.: Interaction of C-reactive protein complexes with the complement system. I. Consumption of human complement associated with the reaction of C-reactive protein with pneumococcal C-polysaccharide and with the choline phosphatides, lecithin and sphingomyelin. J. Immunol. 112: 2135-2147, 1974.4) Heidelberger, M., Gotschlich, E. C., Higginbotham, J.D.: Inhibition experiments with pneumococcal C and depyruvylated type-IV polysaccharides. Carbohyd. Res. 22: 1-4, 1972.5) Richards, R.L., Gewurz, H., Osmand, A.P., Alving, C.R.: Interactions of C-reactive protein and complement with liposomes. Proc. Natl. Acad. Sci. USA 74: 5672-5676, 1977.6) Volanakis, J.E., Wirtz, K.W.A.: Interaction of C-reactive protein with artificial phosphatidylcholine bilayers. Nature 281: 155-157, 1979.7) Narkates, A.J., Volanakis, J.E.: C-reactive protein binding specificities : Artificial and natural phospholipid bilayers. Ann. N.Y. Acad. Sci. 389: 172-182, 1982.8) Kushner, I., Kaplan, M.H.: Studies of acute phase protein. I. An immunohistochemical method for the localization of Cx-reactive protein in rabbits. Association with necrosis in local inflammatory lesions. J. Exp. Med. 114: 961-973, 1961.9) Kushner, I., Rakita, L., Kaplan, M.H.: Studies of acute-phase protein. II. Localization of Cx-reactive protein in heart in induced myocardial infarction in rabbits. J. Clin. Invest. 42: 286-292, 1963.10) Shephard, E.G., Van Helden, PD., Strauss, M., Bohm, L., De Beer, F.C.: Functional effects of CRP binding to nuclei. Immunol. 58: 489-494, 1986.11) Whisler, R.L., Newhouse, Y.G., Mortensen, R.F.: C-reactive protein reduces the promotion of human B-cell colony formation by autoreactive T4 cells and T-cell proliferation during the autologous mixed-lymphocyte reaction. Cell Immunol. 102: 287-298, 1986.12) Kilpatrick, J.M., Virella, G.: Inhibition of platelet-activating factor by rabbit C-reactive protein. Clin. Immunol. Immunophathol. 37: 276-281, 1985.13) Tatsumi, N., Hashimoto, K., Okuda, K., Kyougoku, T.: Neutrophil chemiluminescence induced by platelet activating factor and suppressed by C-reactive protein. Clin. Chim. Acta 172: 85-92, 1988.

Inhibition of platelet-activating factor (PAF)-induced chemotaxis and PAF binding to human eosinophils and neutrophils by the specific ginkgolide-derived PAF antagonist, BN 52021

We have investigated the effects of BN 52021 (a specific PAF antagonist derived from Ginkgo biloba) on PAF-induced human eosinophil and neutrophil chemotaxis. In response to an optimal concentration of PAF (10 −6 mol/L), the drug was significantly more potent ( p < 0.001) in inhibiting eosinophil as compared to neutrophil locomotion. These inhibitory effects were observed in a dose-dependent manner with a concentration of drug required to produce 50% inhibition of 7.0 (±2.2) × 10 −6 mol/L and 2.3 (±0.2) × 10 −5 mol/L for eosinophils and neutrophils, respectively. Sodium cromoglycate, nedocromil sodium, salbutamol, and dexamethasone (preincubated with cells up to 6 hours) had no effect over a wide dose range (10 −3 to 10 −9 mol/L). BN 52021 was significantly more effective in inhibiting chemotaxis when the cells were preincubated with the compound for up to 1 hour before commencement of the locomotion assay, whereas washing the cells completely abolished this effect. Inhibition by BN 52021 was specific for PAF in that it had no effect on chemotaxis induced by either leukotriene B 4, N-formyl-methionyl-leucyl-phenylalanine, or a purified human mononuclear cell-derived neutrophil chemotactic factor. BN 52021 also inhibited the specific binding of [ 3H]-PAF (10 −8 mol/L) to eosinophils and neutrophils in a concentration-dependent fashion with a concentration of drug required to produce 50% inhibition of 1.5 (± 0.3) × 10 −6 mol/L and 9.1 (±2.5) × 10 −7 mol/L, respectively. These results suggest that BN 52021 has potential as an anti-inflammatory agent in conditions associated with PAF-induced accumulation of neutrophils and eosinophils.

A PAF-acether antagonist (N 48740 RP/Rhône-Poulenc) and laser-induced thrombi in rat mesenteric vessels.

N 48740 RP, a pyrrolo(1,2-c)thiazole derivative and platelet-activating factor inhibitor, was tested in a thrombosis model, in which thrombi are produced in small rat mesenteric vessels. A phase contrast system, based on a Leitz Orthoplan microscope, was used to visualize thrombus formation. Vascular lesions were produced with a Coherent CR-2 supergraphite ion laser (argon laser) in vessels of 25-35 microns diameter. The results show a dose-dependent (5-20 mg/kg i.v.) antithrombotic effect of N 48740 RP which reaches its maximum between 30 min and 2 h after the injection and slowly decreases during the following 24-48 h.

A platelet-activating factor antagonist inhibits interleukin 1-induced inflammation

Treatment with a platelet-activating factor receptor antagonist, SRI 63-441, inhibited interleukin 1-induced increases in vascular permeability and leukocyte infiltration in the rabbit eye following the intravitreal injection of human interleukin 1-alpha. Treatment with the prostaglandinsynthetase inhibitor, flurbiprofen, or the corticosteroid, prednisolone, resulted in comparable attenuation of the increase in vascular permeability. In contrast to the effect of flurbiprofen, SRI 63-441 did not reduce interleukin 1-induced increases in prostaglandin E 2 levels. Combined treatment with the platelet-activating factor antagonist and inhibitors of prostaglandin synthesis nearly prevented interleukin 1-induced increases in vascular permeability or cellular infiltration. These findings suggest a role for platelet-activating factor in interleukin 1-induced inflammation. Platelet-activating factor and prostaglandins may act synergistically as mediators of interleukin 1-induced vascular permeability.

Platelet-Activating Factor Primes Neutrophil Responses to Agonists: Role in Promoting Neutrophil-Mediated Endothelial Damage

During inflammation polymorphonuclear cells (PMNs) are exposed to agonistic stimuli including activated complement, kallikrein, arachidonic acid metabolites, monokines, and platelet-activating factor (PAF). We report that PAF not only directly activates PMNs but in miniscule quantities (10(-12) mol/L) "primes" them as well, that is, permits PMNs to respond to subsequent stimuli that would be otherwise ineffectual. PAF priming of responses including superoxide generation, elastase release, and aggregation is time dependent and is maximal within five minutes. PAF need not be present during the subsequent exhibition of PMN agonists, but priming is inhibited by cold and is also inhibited by the PAF receptor antagonists BN 52021, L-652, and kadsurenone. An intact PAF molecule is required because lyso-PAF and methoxy-PAF do not prime PMN responses. PAF priming is associated with both enhanced expression of the adhesive glycoprotein identified by OKM-1 antibody and an enhanced rise in intracellular calcium levels in response to the subsequent addition of agonists such as FMLP. PMNs primed with PAF and stimulated with either F-Met-Leu-Phe or phorbol esters are more effective in lysing and detaching cultured human endothelial cells--damage that can also be inhibited by the PAF antagonists. Because PAF is synthesized and exhibited on surfaces of endothelial cells perturbed by coagulation, we suggest that this lipid may potentiate otherwise trivial activators of marginated PMNs so that they become damaging to the PAF-synthesizing endothelium itself. If so, our studies suggest a possible therapeutic role for PAF inhibitors in excessive inflammatory states.

Platelet-activating factor primes neutrophil responses to agonists: role in promoting neutrophil-mediated endothelial damage

During inflammation polymorphonuclear cells (PMNs) are exposed to agonistic stimuli including activated complement, kallikrein, arachidonic acid metabolites, monokines, and platelet-activating factor (PAF). We report that PAF not only directly activates PMNs but in miniscule quantities (10(-12) mol/L) “primes” them as well, that is, permits PMNs to respond to subsequent stimuli that would be otherwise ineffectual. PAF priming of responses including superoxide generation, elastase release, and aggregation is time dependent and is maximal within five minutes. PAF need not be present during the subsequent exhibition of PMN agonists, but priming is inhibited by cold and is also inhibited by the PAF receptor antagonists BN 52021, L-652, and kadsurenone. An intact PAF molecule is required because lyso-PAF and methoxy-PAF do not prime PMN responses. PAF priming is associated with both enhanced expression of the adhesive glycoprotein identified by OKM- 1 antibody and an enhanced rise in intracellular calcium levels in response to the subsequent addition of agonists such as FMLP. PMNs primed with PAF and stimulated with either F-Met-Leu-Phe or phorbol esters are more effective in lysing and detaching cultured human endothelial cells--damage that can also be inhibited by the PAF antagonists. Because PAF is synthesized and exhibited on surfaces of endothelial cells perturbed by coagulation, we suggest that this lipid may potentiate otherwise trivial activators of marginated PMNs so that they become damaging to the PAF-synthesizing endothelium itself. If so, our studies suggest a possible therapeutic role for PAF inhibitors in excessive inflammatory states.

Lipoxygenase metabolites as mediators of platelet activating factor-induced increased airways responsiveness to histamine in the guinea-pig.

Inhibitors of platelet activating factor (PAF) and leukotriene synthesis or action are of interest as potential anti-asthmatic drugs. The present study outlines evidence suggesting an interaction between PAF and lipoxygenase products mediating increased airways responsiveness to histamine in vivo.

On the use of unsymmetrically substituted furans in the furan-carbonyl photocycloaddition reaction: Synthesis of a kadsurenone-ginkgolide hybrid

The Paterno-Buchi cycloaddition of aldehydes to silyl and stannyl substituted furans has been investigated. An application of this method to a short synthesis of a hybrid of two inhibitors of platelet activating factor (paf) receptor binding is described.

Protein kinase C activity appears to be required for the synthesis of platelet-activating factor and leukotriene B4 by human neutrophils.

Human neutrophils synthesize platelet-activating factor (PAF) and leukotriene B4 (LTB4) when stimulated with the Ca2+ ionophore A23187. These processes are enhanced to a variable extent by phorbol 12-myristate 13-acetate (PMA), a direct activator of protein kinase C. The long chain amines sphingosine, stearylamine (Hannun, Y.A., Loomis, C.R., Merrill, A.H., Jr., and Bell, R.M. (1986) J. Biol. Chem. 261, 12604-12609), and palmitoylcarnitine competitively inhibit activation of purified protein kinase C in vitro and inhibit protein kinase C-mediated activation of the respiratory burst in human neutrophils (Wilson, E., Olcott, M.C., Bell, R.M., Merrill, A.H., Jr., and Lambeth, J.D. (1986) J. Biol. Chem. 261, 12616-12623). These amines were found to inhibit A23187-induced PAF and LTB4 synthesis. Inhibition of PAF and LTB4 synthesis occurred in parallel; half-maximal inhibition by sphingosine occurred at 7 microM, with complete inhibition at 15 microM. PMA by itself did not induce the synthesis of PAF or LTB4, although it did enhance PAF and LTB4 synthesis at suboptimal concentrations of A23187. PMA reversed long chain amine inhibition of PAF and LTB4 accumulation. Reversal of the inhibition of PAF and LTB4 accumulation occurred in parallel, was concentration-dependent, and was complete by approximately 3 x 10(-8) M PMA. The inactive 4 alpha-phorbol didecanoate ester did not reverse inhibition at these concentrations. Sphingosine completely prevented the A23187-induced release of [3H]arachidonate and its various metabolites from [3H]arachidonate-labeled cells. PMA, but not 4 alpha-phorbol didecanoate, restored arachidonate release and its metabolism. Therefore, while activation of protein kinase C is not sufficient to induce PAF and LTB4 synthesis, its action appears to be required to couple a rise in intracellular Ca2+ to their synthesis. This coupling occurs at the level of the initial reaction in the production of lipid mediators, a phospholipase A2-like activity that mobilizes the two substrates 1-O-alkyl-sn-glycero-3-phosphocholine and arachidonic acid from complex lipids.