Platelet-activating Factor-acether Research Articles

Evidence for the involvement of a macrophage-derived chemotactic mediator in the neutrophil recruitment induced by staphylococcal enterotoxin B in mice

Staphylococcus aureus secretes enterotoxins which are superantigens and the major cause of food poisoning in man. Staphylococcal enterotoxins types A and B can induce neutrophil migration into the peritoneal cavity of mice through sensory C-fiber neuropeptides, lipoxygenase or cyclooxygenase metabolites, nitric oxide, histamine, platelet-activating factor and resident macrophages. In this work, we examined the influence of macrophage-derived products on neutrophil migration during peritonitis induced by staphylococcal enterotoxin type B (SEB) in mice. Macrophages stimulated with SEB released a thermolabile neutrophil chemotactic protein with a molecular weight of 1000–3000 (by ultrafiltration). This release was inhibited 30% by dexamethasone (an inhibitor of cytokine synthesis and phospholipase A 2 activity), but not by indomethacin (a cyclooxygenase inhibitor) or BW755C (a dual cyclo- and lipoxygenase inhibitor). Dexamethasone also inhibited (100%) the neutrophil migration induced by the chemotactic protein. Similar inhibition occurred in mice pretreated with BWA4C (lipoxygenase inhibitor; 90%), BW755C (99%), BN52021 (platelet-activating factor–acether receptor antagonist; 93%), cimetidine (histamine H 2 receptor antagonist; 76%), capsaicin (a depletor of sensory C-fiber neuropeptides; 82%) and the neurokinin-1 receptor antagonist SR140333 (71%), but not by indomethacin or the neurokinin 2 receptor antagonist SR48968. These results confirm that macrophages are involved in the neutrophil recruitment induced by SEB, and that the chemotactic protein apparently induces neutrophil migration by a mechanism mediated by platelet-activating factor, histamine H 2 receptors, lipoxygenase products and substance P.

Adenosine-induced bronchoconstriction in conscious hyperresponsive and sensitized guinea pigs.

Inhaled adenosine induces bronchoconstriction in asthmatic and allergic subjects but not in nonasthmatics. This study examined the responses of conscious guinea pigs in which antigen sensitization is induced by ovalbumin pretreatment and airway hyperresponsiveness to carbachol is induced by exposure to ozone and platelet-activating factor-acether (PAF). Airway responses to aerosol challenge with carbachol or adenosine were determined as the change in specific airway conductance (SGaw) measured by whole-body plethysmography. In untreated animals, carbachol (20 micrograms/ml, 60 s) induced a rapid fall in SGaw (peak, 18 +/- 5% at 5 min) indicative of bronchoconstriction, whereas adenosine (1 mg/ml, 60 s) caused an increase in SGaw (34 +/- 8% at 15 min). Animals pretreated with ovalbumin displayed similar responses to carbachol (14 +/- 5% at 5 min) as control animals and were therefore sensitized but not hyperresponsive. However, adenosine (1 mg/ml) caused a rapid bronchoconstriction, peaking at 20 min (25 +/- 5%). Exposure of animals to nebulized PAF-acether (10 micrograms/ml) for 60 s produced a bronchoconstriction, which peaked at 10 min (18 +/- 7%) and returned to basal levels by 60 min. Similarly, exposure to ozone (1.4 ppm) for 60 min caused bronchoconstriction (peak at 20 min, 19 +/- 6%), with recovery after 1 h. Both PAF- and ozone-exposed animals displayed significant hyperresponsiveness to carbachol administered 1 h from the end of the exposure period. The peak bronchoconstrictor responses before and after PAF exposure were 10 +/- 9 and 28 +/- 4%, and responses before and after ozone exposure were 22 +/- 5 and 61 +/- 9%.(ABSTRACT TRUNCATED AT 250 WORDS)

Eosinophil granulocyte proliferation induced by an intermediate factor generated in the pleural cavity of rats injected with platelet-activating factor-acether.

In previous research, we have observed that intrathoracic administration of platelet-activating factor-acether (PAF) promoted a delayed eosinophilia in the pleural cavity of rats that lasted for at least 96 h. We investigated the ability of pleural washings from rats previously injected with PAF (1 micrograms/cavity) to stimulate in vitro murine hematopoietic eosinophil proliferation. We observed that pleural fluid sustained eosinophil proliferation but not differentiation, under conditions in which PAF itself had no effect. The phenomenon lasted for 3 days and was maximal on the 1st day of culture. Treatment with neutralizing antibodies against interleukin (IL)-5, granulocyte-macrophage colony-stimulating factor (GM-CSF) or IL-3, alone or in combination, did not modify the eosinophil proliferation induced by PAF pleural fluid, suggesting that these cytokines may not be involved in the studied phenomenon. We conclude that the rat pleural fluid obtained 6 h after PAF administration induces eosinophil proliferation in vitro by a mechanism probably independent of IL-5, GM-CSF or IL-3.

CD2 triggering stimulates the formation of platelet-activating factor-acether from alkyl-arachidonoyl-glycerophosphocholine in a human CD4+ T lymphocyte clone.

A human CD4+ T lymphocyte clone synthesized platelet-activating factor (PAF) acether when stimulated via the CD2 pathway. PAF-acether was characterized by biochemical and biophysical properties and precursor-product relationships (alkyl-acyl-sn-glycero-3-phosphocholine (GPC)----alkyl-lyso-GPC (lyso-PAF)----PAF-acether) were demonstrated. The clone contained substantial amounts of alkyl-acyl-GPC. i) Hydrolysis of alkyl-acyl-GPC upon CD2 stimulation was evidenced: [3H]alkyl-lyso-GPC was formed from [3H]alkyl-acyl-GPC in [3H] alkyl-labeled cells; alkyl-lyso-GPC production was also bioassayed after CD2 triggering. ii) The rate of arachidonate transfer from diacyl-GPC to alkyl-acyl-GPC increased after CD2 stimulation of the [3H]arachidonate-labeled P28D T cells, demonstrating alkyl-lyso-GPC formation. iii) Comparison of the molecular species of the produced PAF-acether with those of arachidonate-containing alkyl-acyl-GPC raises the possibility that the produced PAF-acether is related to alkyl-arachidonoyl-GPC.

Platelet-activating factor-acether is a component of human follicular fluid

Platelet-activating factor-acether (PAF-acether) presence was investigated in 27 human follicular fluids (FFs). Aggregation of washed rabbit platelets was used to measure PAF-acether. Data were compared using Student's t-test. Follicular fluids came from the in vitro fertilization program at Antoine Béclère Hospital, and PAF-acether was assayed at Institut National de la Santé et de la Recherche Médicale, Unités 187 and 200, Clamart, France. The study concerned five infertile women 29 to 39 years of age. Ovaries were stimulated with human menopausal gonadotropin under gonadotropin-releasing hormone agonist (GnRH-a) action. The height of platelet aggregation was compared between FFs and synthetic PAF-acether. Mean FF concentration of PAF-acether was 1,367 to 3,467 pg/mL among women. Values were higher for patients in a long than in a short GnRH-a protocol (P less than 0.05). However, PAF-acether concentration was not related to fertilization rate. Platelet-activating factor-acether is possibly involved in oocyte release from the follicle, a process occulted by follicular puncture.

Eosinophil infiltration: Effects of H 1 antihistamines

This article reviews the contribution of cell-mediated inflammatory responses to the immediate immunoglobulin E—dependent allergic reaction. Apparently eosinophils play an important part in the pathogenesis of allergic reactions. Some new H 1 antihistamines may also have non-H 1-mediated antiinflammatory properties. In two double-blind, placebo-controlled, crossover studies of allergic and normal subjects, we showed that oral cetirizine, at dosages of 10 and 20 mg/day, significantly inhibited wheal-and-erythema reactions induced by grass pollen, 48/80, histamine, platelet-activating factor acether, and N-formyl-methionyl-leucyl-phenylalanine. In the first study, cutaneous eosinophil migration was significantly inhibited by cetirizine at pollen and 48/80 skin test sites (61%, p<0.01, and 53%, p< 0.01, respectively), although no change was observed at histamine sldn test sites. Inhibition of neutrophil accumulation was also observed at pollen and 48/80 sites (41%, p<0.1, and 31%, p<0.1, respectively). Monocyte accumulation was not affected by cetirizine. In the second study, cetirizine suppressed the eosinophil influx induced by pollen, platelet-activating factor, 400 ng, and platelet-activating factor, 40 ng (63%, p<0.001; 58.5%, p<0.001; and 57.8%, p<0.01, respectively), This inhibition was effective 2 hours after challenge and persisted through hours 4, 8, and 24. N-Formyl-methionyl-leucyl-phenylalanine induced a weak eosinophil accumulation that was inhibited by cetirizine.

Inhibitory effects of the new PAF acether antagonist WEB-2086 on pharmacologic changes induced by PAF inhalation in human beings

Recent research on asthma mediators has concentrated more and more on platelet-activating factor (PAF), which is one of the most potent bronchoconstrictors known thus far. Inhalant PAF challenge in healthy volunteers may provide a mean of testing PAF antagonists. The usefulness of the PAF provocation test in measuring the pharmacologic activity of a new PAF antagonist, WEB-2086, has been examined in 12 healthy volunteers in a double-blind, placebo-controlled, within-subject crossover study. PAF-induced immediate bronchoconstriction, slight hemodynamic changes, and PAF-related subjective side effects. Premedication with WEB-2086 (40 mg) completely prevented any increase in airway resistance after PAF inhalation, as well as development of most of the cardiovascular and side effects induced by PAF. The clear protection against PAF-induced pharmacologic effects can be explained by the specific PAF-antagonistic activity of WEB-2086. The method described in this article may be applied as a useful tool for looking at PAF-antagonistic activity in healthy volunteers.

Fibronectin Levels in Plasma after Platelet-Activating Factor Inhalation

We evaluated fibronectin levels in plasma and blood leukocyte counts after platelet-activating factor-acether (PAF) inhalation to examine whether PAF may cause pulmonary vascular injury. PAF inhalation challenges were performed on 5 normal subjects and 5 atopic asthmatics. Fibronectin levels in plasma were significantly increased at 5 min (342.5 +/- 36.9 micrograms/ml) after PAF challenge as compared with the baseline values of 277.1 +/- 33.0 micrograms/ml (p less than 0.024). Total white blood cell and neutrophil counts were significantly decreased 5 min after PAF inhalation (WBC from 5,360 +/- 460 to 4,260 +/- 380/mm3, p less than 0.028; neutrophils from 3,113 +/- 441 to 2,214 +/- 344/mm3, p less than 0.043). Our study shows that plasma fibronectin levels transiently increase and that peripheral total WBC counts decrease after PAF inhalation. Elevated fibronectin levels may provide evidence of pulmonary vascular injury due to neutrophils which might be primed and recruited to pulmonary circulation by PAF.

Selective inhibition of adrenaline-induced human platelet aggregation by the structurally related Paf antagonist Ro 19-3704.

1. Two non-lipid antagonists of platelet-activating factor acether (Paf), BN 52021 and WEB 2086, at concentrations which completely blocked Paf-induced platelet aggregation, failed to interfere with aggregation by adrenaline. In contrast, Ro 19-3704, a structurally related antagonist of Paf, inhibited concentration-dependently aggregation induced by adrenaline or by the simultaneous addition of submaximal concentrations of adrenaline and Paf. Reversal of aggregation was obtained when Ro 19-3704 was added to the platelet suspension after adrenaline. 2. Ro 19-3704 was selective for Paf and adrenaline since it failed to interfere with platelet aggregation induced by arachidonic acid or ADP. CV-3988, an antagonist of Paf structurally similar to Ro 19-3704, also inhibited adrenaline-induced aggregation. However, a morpholine analogue (MA) of Paf, which has no anti-Paf activity, failed to interfere with the aggregation induced by adrenaline. This suggests that the effect of Ro 19-3704 and CV-3988 on adrenaline is not simply due to their lipid structure. 3. Experiments on plasma membrane preparations showed that Ro 19-3704 inhibited [3H]-yohimbine binding with an inhibition constant (Ki) of 7 +/- 3 microM. In contrast, BN 52021 and MA did not interfere with [3H]-yohimbine binding. Equilibrium binding experiments showed that Ro 19-3704 increased the apparent KD of [3H]-yohimbine binding from 2.02 +/- 0.15 to 7.3 +/- 0.4 nM. The Paf antagonist Ro 19-3704 interacts specifically with the alpha 2-adrenoceptor and may thus prevent the early steps involved in the mechanism of adrenaline-induced platelet activation.

Platelets in allergy. Assays and interpretation.

Since 1983, when we reported the first model of antiparasite activity by platelets, five different triggering processes have been described that induce these blood elements into the role of efficient killers of pathogens. Besides endogenous compounds, such as specific IgE antibodies, inflammatory CRP, IFNT, and a second stimulating lymphokine, provisionally termed PCIF, exogenous chemAcals have also been shown to express unexpected activating properties on uncommon platelet populations or in particular situations: aspirin and NSAID on platelets from asthmatics, and DEC on platelets from patients with filariasis. These various stimuli probably triggered thrombocytes by different pathways, but achieved a common result: the generation of cytocidal molecules. A general feature of the stimulating signals was apparently to induce cytotoxic properties without aggregation, suggesting that they triggered a platelet compartment that was not involved in classical activation by aggregating agents such as thrombine, adenosine diphosphate, or platelet-activating factor-acether. The hypothesis remains that the killing capacities of platelets were supported by specific subpopulations, either working on their own, or producing secondary mediators for the general participation of nonresponding platelet populations.

Inhibitory effect of oral cetirizine on in vivo antigen-induced histamine and PAF-acether release and eosinophil recruitment in human skin

The use of a noninvasive skin chamber technique in vivo in pollen-sensitive patients allowed us to quantify the time-course release of histamine and the recruitment of inflammatory cells (i.e., neutrophils, monocytes, and eosinophils) in skin sites challenged with pollen, histamine, and compound 48 80 . The new H I-receptor antagonist, cetirizine 2 HCl, orally administered with 10 mg once a day to pollen-sensitive patients in a double-blind, crossover study versus placebo, induced a significant decrease in the wheal-and-flare cutaneous reaction induced by intradermal injection of pollen, histamine, and compound 48 80 . It also significantly inhibited the immediate histamine release occurring in skin chambers after pollen introduction, whereas it did not significantly inhibit the late release. In patients receiving placebo, we detected platelet-activating factor—acether in media collected at the sixth hour from chambers filled with pollen. With cetirizine 2 HCl treatment, platelet-activating factor—acether was not detected in chamber media. Interestingly, cetirizine 2 HCl significantly reduced the eosinophil recruitment observed on the superficial dermis 24 hours after pollen challenge.

Skin eosinophilia in atopic patients

The responses of six atopic and six control patients to the intracutaneous administration of platelet-activating factor (PAF) acether, of the leukocyte secretagogue and chemoattractant f-methionyl-leucyl-phenylalanine (FMLP), and of allergens were studied. Immediate wheal-and-flare skin reactions to allergens and to PAF acether in atopic patients were the same, and when reactions were compared to reactions of nonatopic patients, these reactions to PAF acether and to FMLP were of equivalent intensity. Late-phase reactions were not observed macroscopically with allergen, PAF acether, or FMLP. The cellular responses, assessed by the Rebuck skin window technique, demonstrated a late (24 hours) eosinophilic response to the allergen and to both inflammatory agents, with 33% to 44% of intensively degranulated eosinophils. In comparison, very few, if there were any, eosinophils were observed in the nonatopic patients. Most infiltrated cells were neutrophils. The accumulation of eosinophils in atopic human skin indicates a potent eosinophilotactic activity restricted to the allergic patients. A similar cellular reaction has been observed in lungs from guinea pigs injected with PAF acether or with allergen, and in patients with severe asthma. The chemoattractant activity of FMLP toward eosinophils cannot be accounted for by its histamine-releasing activity and remains to be explained.

Modulation of leucocyte activation in the early phase of the rabbit burn injury

Previous studies in burned patients have shown an early enhanced polymorphonuclear leucocyte (PMN) generating capacity for superoxide radical (O 2), for the arachidonic acid (AA) lipoxygenase metabolite leukotriene B 4 (LTB 4) and for platelet activating factoracether (PAF). These findings have been confirmed on a burn injury rabbit model. As we have suggested a pivotal role for an exaggerated initial (<36–48 h) neutrophil stimulation leading to a later (72 h) immunodepression and anergy, we tried to modulate the early phase by drug therapy. A Ginkgo biloba extract (IPS200) injected i.v. in burned rabbits greatly reduced O 2 and LTB 4 generation on A23187 challenge. IPS200 includes flavonoids and other polyphenols, inhibiting either arachidonic acid metabolism or PAF receptors, and may thus exert their modulating effect on PMN function in thermal injury.

The effects of N-3 polyunsaturated fatty acids on the generation of platelet-activating factor-acether by human monocytes.

Human leukocytes generate platelet-activating factor (PAF-acether), a lipid mediator of inflammation, from membrane alkyl phospholipids through the release of arachidonic acid or other fatty acids at the 2-position and subsequent acetylation. Because it was previously demonstrated that fish oil fatty acids suppress human leukocyte arachidonic acid release and metabolism, separate experiments were conducted to investigate the effects of dietary fish oil supplementation and in vitro incubation with fish oil fatty acids on calcium ionophore-stimulated PAF-acether generation in human monocytes. In subjects on their regular diets, a 4-hr incubation of monocyte monolayers with an optimally effective concentration of arachidonic acid of 1 micrograms/ml resulted in a 64% increase of calcium ionophore-induced net PAF-acether generation from 7.75 +/- 0.78 ng/10(6) cells for untreated monolayers to 12.70 +/- 1.21 ng/10(6) cells (mean +/- SEM). Treatment of monolayers with eicosapentaenoic acid (EPA) at the optimal concentration of 1 micrograms/ml decreased net PAF-acether generation by 28%. However, treatment of monocyte monolayers with docosahexaenoic acid did not appreciably affect net PAF-acether generation. The changes in PAF-acether release with each fatty acid added in vitro paralleled those in total PAF-acether generation; the percentage PAF-acether release remained unaffected. Three weeks of dietary supplementation with 18 g MaxEPA daily, providing 3.2 g EPA did not affect the PAF-acether generation of calcium ionophore-stimulated human monocyte monolayers. However, 6 weeks of dietary supplementation resulted in a 47% decrease of net total PAF-acether generation and a concomitant 59% decline in net PAF-acether release; the percentage release of PAF-acether was not affected. Thus, whether added to the diet or introduced in vitro, fish oil-derived fatty acids suppress PAF-acether generation by human monocyte monolayers.

Platelet-activating factor acether (PAF-acether) involvement in acute inflammatory and pain processes.

PAF-acether is a potent aggregating agent released by various cells involved in acute inflammatory process. In this paper, exogenous PAF-acether has been investigated for its ability to generate signs of inflammation (edema measured by plethysmometry) and hyperalgesia (Randall-Sellito test) by standard subplantar injection in the rat paw. From 0.005 microgram. PAF-acether induced significant edema of the paw, maximal 1 hour after injection; it was dose-dependent from 0.1 to 5 microgram. Significant dose-dependent hyperalgesia occurred from 1.25 microgram; it reached a plateau from 2 to 4 hours after injection. Both phenomena were long-lasting (greater than 6 h). PAF-acether was 1.5 to 10 times stronger than PGI2 and PGE2 in inducing edema, pain, and in increasing vascular permeability. We investigated the interaction of miscellaneous drugs with the edema and the hyperalgesia caused by 2.5 microgram of PAF-acether. Non-steroidal anti-inflammatory (NSAI) drugs exerted only moderate effects on the edema without affecting hyperalgesia. Edema was highly reduced by various agents: prednisolone, L-cysteine, anti-calcic drugs, theophylline, PGI2, salbutamol, clonidine. All of them, except clonidine, and in contrast to NSAI drugs, were more potent on PAF-acether edema than on kaolin edema; a possible link between these agents is their ability to increase cyclic AMP levels in the cells and consequently to reduce lysosomal enzyme release. PAF-acether itself, injected intra-peritoneally, inhibited PAF-acether edema without preventing pain, at doses inactive on arterial pressure and hematocrit, but inducing marked gastric mucosal damage. Among the drugs tested, including analgesics, only PGI2 and imidazole improved PAF-induced hyperalgesia, showing a dissociation between edema and hyperalgesia not only in their induction (doses of PAF required, time course of the phenomena), but in the drugs able to antagonize their development too.