Increased biosynthesis of platelet-activating factor in activated human eosinophils

Cytotoxicity of human eosinophil granule major basic protein to human nasal sinus mucosa in vitro

The toxic effects of the human eosinophil granule major basic protein (MBP), reduced and alkylated, were studied on human nasal mucosa in vitro. With a microscope coupled with a television monitor (magnification x 2500) and videotape recorder, we investigated the effects of MBP on the mucosa and the ciliary activity of single cells. In nasal mucosal specimens from normal individuals, MBP, 5 mumol/L and 10 mumol/L, significantly inhibited (p less than 0.01) ciliary activity by 4 and 1 hours of exposure, respectively. At these same MBP concentrations, the mucosal surface profiles were altered by 4 hours of exposure, and ciliostasis was 75% to 100% complete by 9 and 6 hours, respectively. In a mucosal specimen from a patient with nasal allergy, 1 mumol/L of MBP significantly inhibited (p less than 0.01) ciliary activity by 1 hour; alteration of the mucosal surface profile appeared by 3 hours of exposure, and ciliostasis was 75% to 100% by 13 hours. Similar alterations of the mucosal surface profile were observed with specimens from a second patient with allergies; in contrast, 1 mumol/L of MPB had no effect on specimens from a nonallergic patient. These results indicate that MBP damages human upper respiratory epithelium, causing ciliostasis and alteration of the epithelial surface at concentrations likely achieved in vivo. Furthermore, the mucosal specimens from two allergic patients were damaged by concentrations of MBP that had no effect on mucosal specimens from a normal individual.

The effect of platelet-activating factor on histamine release from rat peritoneal mast cells

The effect of platelet-activating factor (PAF) on histamine release from peritoneal mast cells of adult and young male rats was investigated. PAF alone tended to release histamine from the mast cells of adult and young rats, although very slightly. On the other hand, PAF significantly inhibited the histamine release induced by the Ca2+ ionophore A23187 in mast cells obtained from rats of either age group, but not that by compound 48/80. Such inhibition was not seen with lyso-PAF. CV-3988, a PAF antagonist, antagonized the inhibitory effect of PAF on the A23187-induced histamine release in mast cells from adult and young rats. These results suggest that PAF does not have a strong histamine-liberating action on mast cells, and that PAF inhibits the calcium influx into mast cells through the activation of PAF receptors.

What is the role of the eosinophil?

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Calcium-ionophore-induced formation of platelet-activating factor and leukotrienes by horse eosinophils: a comparative study

Horse eosinophils preincubated with 3H-labelled acetate and stimulated with the Ca2+ ionophores ionomycin or A23187 form a radioactive compound, which we have shown to be 1-O-alkyl-2-[3H]acetyl-sn-glycero-3-phosphocholine (platelet-activating factor). We could detect no 1-O-acyl-2-[3H]acetyl-glycero-3-phosphocholine in the radioactive fraction. The formation of platelet-activating factor was strongly correlated to the generation of leukotriene C4, the main arachidonate metabolite in horse eosinophils, suggesting that platelet-activating factor and leukotriene C4 have a common precursor pool (1-O-alkyl-2-arachidonyl-glycero-3-phosphocholine) and a common regulation of synthesis. Even though both ionomycin and A23187 are described as Ca2+ ionophores, they have a series of significantly different effects on the eosinophils with respect to formation of platelet-activating factor and leukotriene C4. While A23187 induces an asymptotic maximum of mediator formation at concentrations higher than 20 microM, ionomycin expressed a narrow optimum at 2 microM. The effects of exogenous pH on the release of mediators also differ strongly between the two ionophores: for A23187 the effects are the same for both mediators but when ionomycin is used as stimulant, generation of platelet-activating factor and leukotriene C4 are affected differently.

Eosinophil accumulation in pulmonary airways of guinea-pigs induced by exposure to an aerosol of platelet-activating factor: effect of anti-asthma drugs

1. Exposure of guinea-pigs to aerosols of platelet activating factor (PAF) (0.01 to 100 micrograms ml-1) induced a dose-dependent increased incidence of eosinophils in bronchoalveolar lavage fluid (BAL) at 48 h. Total leucocyte numbers and the percentages of lymphocytes and neutrophils were unchanged in BAL fluid. 2. Increased numbers of eosinophils were detected in BAL 1 h after exposure to PAF but eosinophilia was not maximal until 48 h. One week after exposure to PAF, the percentage of eosinophils in BAL was within the normal range. 3. Depletion of circulating platelets or neutrophils by intravenous injection of specific antisera did not modify accumulation of eosinophils in the airway lumen following inhalation of PAF (10 micrograms ml-1). 4. PAF-induced pulmonary airway eosinophil accumulation was inhibited by treatment with SDZ 64-412, a selective PAF-antagonist, whether the compound was administered before, or 30 min after, inhalation of PAF. 5. Pulmonary airway eosinophil accumulation due to inhaled PAF (10 micrograms ml-1) was inhibited by prior treatment with aminophylline, cromoglycate, ketotifen, dexamethasone and AH 21-132. 6. Pulmonary airway eosinophil accumulation due to inhaled PAF (10 micrograms ml-1) was not inhibited by prior treatment with indomethacin, salbutamol or mepyramine.

Prevention of non-specific airway hyperreactivity after allergen challenge in guinea-pigs by the PAF receptor antagonist SDZ 64-412

1. Allergen challenge by aerosol in sensitized guinea-pigs elicited non-specific airway hyperreactivity assessed by reactivity to i.v. histamine or acetylcholine. Airway hyperreactivity to histamine persisted for at least 48 h and was accompanied by pulmonary eosinophilia as determined by bronchoalveolar lavage cell analysis. 2. Airway hyperreactivity was independent of vagal reflex mechanisms since it was not abrogated by bilateral vagotomy. 3. The novel platelet-activating factor (PAF) receptor antagonist SDZ 64-412 inhibited the development of airway hyperreactivity, as measured 24 h after aerosol allergen challenge, when given as a single treatment orally 2 h before allergen challenge. The PAF receptor antagonist WEB 2086 as well as methylprednisolone and ketotifen also showed efficacy in preventing development of airway hyperreactivity. 4. Neither the two PAF antagonists nor ketotifen had any effect on bronchoalveolar lavage (BAL) eosinophil numbers. Methylprednisolone was the only substance which readily prevented eosinophil recruitment in addition to airway hyperreactivity. 5. We conclude that allergen-induced airway hyperreactivity in guinea-pigs is inhibited by prophylactic anti-asthma drugs and specific PAF receptor antagonists, thus demonstrating a pivotal role of PAF in this response. There was a lack of correlation between airway hyperreactivity and the presence of BAL eosinophils.

Lipid metabolism and signal transduction in endothelial cells

Endothelial cells have the capacity to metabolize several important lipids; this includes the ability to store and then metabolize arachidonate, as well as the capacity to synthesize platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine). Arachidonate is predominantly metabolized via cyclooxygenase to PGI2 although the spectrum of prostaglandins may vary depending upon the source of the endothelial cell. Biosynthesis of eicosanoids and PAF are likely to be an important physiologic function of the endothelial cell as these potent lipids appear to have a role in maintaining vascular tone and mediating interactions of the endothelium with circulating inflammatory cells. In addition to production of eicosanoids and PAF, endothelial cells metabolize exogenous arachidonate and arachidonate metabolites and other fatty acids such as linoleate to bioactive compounds (HODEs). There is also evidence that small amounts of arachidonate are metabolized via a lipoxygenase. The physiologic significance of these minor lipid pathways is not known at this time. Production of eicosanoids and PAF is not a constitutive function of the endothelial cell. Lipid biosynthesis by endothelial cells is one component of the early activation response that occurs in response to stimulation with pro-inflammatory and vasoactive hormones or to pathologic agents such as oxidants and bacterial toxins. A central mechanism for activation of the relevant pathways is a rise in cellular calcium concentrations that can be mediated by hormone-receptor-binding or by direct permeabilization of the cell membrane to calcium (Fig. 3). Regulatory mechanisms distal to the calcium signal are unknown, but current evidence suggests that calcium directly or indirectly activates phospholipases that release arachidonate from phospholipids and hydrolyze a specific phospholipid to the immediate precursor of PAF. There is evidence that protein kinase C may, in part, regulate this process, but the role of other potential regulatory components, such as other protein kinases or G-proteins is not known. As noted above, the most direct mechanism for initiation of PAF biosynthesis and arachidonate release would be activation of a phospholipase A2 as shown in Fig. 3. Activation of other phospholipases (e.g. phospholipase C) may contribute to the total amount of arachidonate released, although the magnitude of that contribution is not yet known. In addition to generation of PAF and eicosanoids, activation of endothelial cell phospholipases generates second messengers that are important in intracellular signaling (Fig. 4). Activation of phospholipase C, in response to hormonal stimulation, generates diacylglycerol and inositol phosphates from phosphatidylinositol. Each of these is a potent intracellular second messenger.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of platelet activating factor in allergic respiratory disease

1. Platelet activating factor (PAF) is an ether-linked phospholipid capable of eliciting many of the factors of the allergic response including bronchoconstriction, mucosal oedema, eosinophil infiltration and bronchial hyperresponsiveness. 2. A wide range of selective PAF receptor antagonists have now been described which have been reported to reduce many aspects of allergen-induced inflammatory responses in experimental animals. 3. Early clinical studies have indicated that some of these drugs are also effective PAF antagonists in man, but no controlled studies have been reported using these compounds in patients with allergic asthma. 4. The gingkolide mixture BN 52063 has recently been reported to inhibit allergen-induced cutaneous inflammation in man; a response which has certain pathological similarities to allergen-induced late-onset airways obstruction in the lung. 5. Therefore, drugs antagonizing the actions of PAF may well lead to a better understanding of and may be a novel therapeutic approach for allergic respiratory disorders.

YM461, a PAF antagonist, blocks antigen-induced late airway responses and airway hyperresponsiveness in allergic sheep

We examined the effect of an orally active antagonist, YM461, of platelet activating factor (PAF) on antigen-induced early and late airway responses and on the development of airway hyperresponsiveness 24 h after challenge in allergic sheep. Early and late airway responses were determined by measuring specific lung resistance (SRL) before and periodically after challenge. Airway responsiveness was determined from the slopes of dose-response curves of SRL vs. increasing doses of carbachol aerosol. The sheep were challenged with Ascaris suum antigen once after vehicle treatment (control) and once 1 h after oral administration of 3 or 10 mg/kg YM461 (each trial was greater than or equal to 14 days apart). Airway responsiveness to carbachol was determined 1-3 days prior to and 24 h after antigen challenge. In control 1 and control 2 trials antigen challenge caused significant peak early (288 and 292%, respectively) and peak late (103 and 124%, respectively) increases over baseline in SRL. SRL returned to baseline 24 h after challenge but the sheep developed airway hyperresponsiveness as indicated by the 2.6-fold increases in the slopes of the carbachol dose-response curves in the control trials. YM461, 3 and 10 mg/kg p.o., significantly inhibited the late responses (66 and 82%, respectively) and blocked the development of airway hyperresponsiveness at 24 h. The early responses were not significantly reduced in either trial. These results suggest that PAF contributes to the antigen-induced late airway responses and associated airway hyperresponsiveness in allergic sheep.

Bronchial hyperresponsiveness in asthmatic children. Correlation with macrophages and eosinophils in broncholavage fluid

Bronchial responsiveness assessed by histamine bronchial challenge testing in 22 children with chronic stable asthma was compared with the number of inflammatory cells per milliliter of broncholavage fluid obtained by fiberoptic bronchoscopy. Hyperresponsiveness was closely correlated with increased counts of eosinophils and macrophages and with the ratio of eosinophils to macrophages. There was no correlation of neutrophil or lymphocyte counts with bronchial hyperresponsiveness and none of the cell types was correlated with airway obstruction. Our findings support the hypotheses that macrophages may be important in the development of bronchial hyperresponsiveness in children with asthma and that they may modulate bronchial responsiveness both directly and by recruitment of eosinophils.

Platelet-activating factor causes goblet cell depletion in the conjunctiva

Platelet-activating factor (PAF) (1-O-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) produced dose-dependent depletion of the goblet cell population associated with the conjunctival epithelium. Reductions in goblet cell numbers did not correspond to leukocyte infiltration and were consistent with a direct effect of PAF. In contrast, LTD4 and LTE4 did not affect the goblet cell population although they caused massive eosinophil infiltration into the conjunctival epithelium. Histamine also produced conjunctival goblet cell depletion, but this appeared secondary to eosinophil degranulation and resultant epithelial desquamation. In addition to goblet cell expulsion, PAF produced an increase in conjunctival microvascular permeability over an identical dose-range. PAF-induced leukocyte emigration was small or absent and comprised a neutrophil infiltrate which exhibited no clear dose-dependent relationship. Lyso-PAF produced effects only at the highest dose employed where pathological changes and a distinct increase in conjunctival microvascular permeability were evident. Lyso-PAF- and PAF-induced increases in conjunctival microvascular permeability were virtually abolished by the PAF antagonist CV-6209. The pronounced inhibitory activity of CV-6209 suggests that high doses of lyso-PAF may either weakly stimulate conjunctival PAF receptors or that there may be sufficient conversion of lyso-PAF to biologically active levels of PAF.

Regulation of Fc epsilon receptor 2 (CD23) expression on a human eosinophilic cell line EoL3 and a human monocytic cell line U937 by transforming growth factor beta

Regulation of low-affinity receptors for IgE (Fc epsilon R2/CD23) on a human eosinophilic cell line EoL3 and a human monocytic cell line U937 was studied using an anti-Fc,R2/CD23 monoclonal antibody H107 by flow cytometry. While platelet-activating factor, interleukin 4, and interferon gamma significantly augmented Fc epsilon R2/CD23 expression on both cell lines, transforming growth factor beta (TGF beta) inhibited both the basal level of Fc epsilon R2/CD23 expression and the enhanced Fc epsilon R2/CD23 expression induced by these reagents in dose- and time-dependent manners. However, TGF beta did not significantly suppress the high basal level of Fc epsilon R2/CD23 expression on RPMI 8866 cells. These results suggest that Fc epsilon R2/CD23 expression on EoL3 and U937 cells is regulated by various cytokines and growth factors, and that TGF beta plays an important regulatory role in IgE-mediated immune responses.

Tumor necrosis factor stimulates human neutrophils to release leukotriene B4 and platelet-activating factor. Induction of phospholipase A2 and acetyl-CoA:1-alkyl-sn-glycero-3-phosphocholine O2-acetyltransferase activity and inhibition by antiproteinase

Tumor necrosis factor stimulates polymorphonuclearneutrophils to synthesize leukotriene B4 and platelet-activating factor (PAF), but alpha 1-proteinase inhibitor and alpha 1-antichymotrypsin block this response. However, proteinases such as elastase and cathepsin G induce preferentially synthesis of PAF. An acetyltransferase required, together with phospholipase A2, in the remodeling pathway of PAF synthesis is activated in polymorphonuclearneutrophils stimulated by tumor necrosis factor and elastase. In contrast, 1-oleyl-2-acetylglycerol, a protein kinase C activator, promotes PAF formation by the de novo biosynthetic pathway without activating the acetyltransferase. Staurosporine, an inhibitor of protein kinase C, blocks PAF production apparently by inhibiting phospholipase A2. This suggests that diacylglycerols are involved in activating both pathway of PAF synthesis.

Evidence for eosinophil degranulation with deposition of granule major basic protein in solar urticaria

Multiple sequential biopsy specimens of wheals elicited by a solar simulator in four patients with severe solar urticaria were studied with the use of indirect immunofluorescence for eosinophil granule major basic protein. Examination of control biopsy specimens from normal, unstimulated skin did not show eosinophils or major basic protein deposition. Five minutes after solar simulation, eosinophils were observed in vessels in the dermis, and 2 hours later there was marked tissue eosinophilia. Extracellular major basic protein was extensively deposited in the dermis at 2 and 24 hours, suggesting eosinophil degranulation. Thus evolution of the solar urticaria wheal is accompanied by infiltration of eosinophils and neutrophils and by tissue deposition of the eosinophil major basic protein, suggesting eosinophil degranulation.

New concepts in the pathogenesis of bronchial hyperresponsiveness and asthma

Recent studies have suggested that inflammation may play an important role in the characteristic bronchial hyperresponsiveness and symptoms of chronic asthma. The mechanisms by which inflammatory cells, mediators, and nerves interact to produce the features of asthma are still uncertain, however. Although mast cells play an important role in the immediate response to allergen (and probably exercise), pharmacologic evidence argues against a critical role in the late response or bronchial hyperresponsiveness in which other cells, such as macrophages and eosinophils, may play a more important role. Many mediators have been implicated in asthma, but only PAF causes a prolonged increase in bronchial responsiveness. PAF attracts eosinophils into tissues and potently activates these cells, which may lead to epithelial damage, a key feature of asthmatic airways. PAF is also a potent inducer of microvascular leakage in airways, which may result in submucosal edema and plasma exudation into the airway lumen in the future. PAF antagonists will reveal whether PAF plays an important role in the eosinophilic inflammation of asthma. Neural mechanisms may also make an important contribution. Inflammatory mediators may influence neurotransmitter release from airway nerves, and neurotransmitters may be proinflammatory. Neural control is complex and cholinergic, adrenergic, and NANC mechanisms may contribute to bronchial hyperresponsiveness. Many neuropeptides, which may be the transmitters of NANC nerves, have been identified in airways. Neuropeptides in airway sensory nerves, such as substance P, have potent proinflammatory effects and, if these are released by an axon reflex, may amplify the inflammatory response in asthma. Since asthma may be chronic eosinophilic bronchitis, it is logical that the primary treatment should involve drugs that suppress this inflammatory response. At present, corticosteroids appear to be the most effective therapy; they have potent effects against eosinophils and macrophages (but not on mast cells) and reduce bronchial hyperresponsiveness and symptoms. By contrast, bronchodilators, such as beta-agonists, although they reduce symptoms, do not reduce the chronic inflammatory response or bronchial hyperresponsiveness and may mask the underlying inflammation. New therapies should be directed toward controlling eosinophil infiltration and activation in airways.

Differential sensitivities of purified human eosinophils and neutrophils to defined chemotaxins

Functions of eosinophils and neutrophils isolated from normal human blood were determined by measuring chemotactic migration and release of beta-glucuronidase. Four well-characterized chemotaxins, the complement fragment C5a, formyl-methionyl-leucyl-phenylalanine (FMLP), platelet-activating factor (PAF), and leukotriene B4 (LTB4) were used as stimuli. Neutrophils showed remarkable chemotactic responses to all four chemotaxins. In contrast, eosinophils showed a significant chemotactic response to C5a and PAF, but only weak responses to FMLP and LTB4. Using these chemotaxins we found the following order of chemotactic potency (maximal number of migrated cells): C5a = LTB4 greater than FMLP greater than PAF for neutrophils and PAF = C5a greater than LTB4 = FMLP for eosinophils. Neutrophils elicited a significant beta-glucuronidase release when stimulated by C5a and FMLP, whereas only small amounts were released with PAF and LTB4. On the other hand, an amount of beta-glucuronidase released from eosinophils comparable to that from neutrophils was elicited only with C5a. FMLP, LTB4, and PAF caused the release of small percentages of beta-glucuronidase. The important cellular functions of eosinophils and neutrophils, chemotaxis and enzyme release, are thought to be controlled by differential responsiveness to stimuli.

Release of PAF-acether and eicosanoids from guinea-pig alveolar macrophages by FMLP: effect of cyclo-oxygenase and lipoxygenase inhibition

Adherent guinea-pig alveolar macrophages stimulated in vitro with FMLP (1 microM) for 5-60 min released PAF-acether, TXB2 and LTB4, with maximal levels being achieved after a 5 min incubation. The levels of eicosanoids were maintained during the 60 min incubation period, whereas the levels of PAF-acether decreased and were no longer detectable after 60 min incubation. Indomethacin (1 microM) completely suppressed the release of TXB2 stimulated by FMLP (1 microM for 5 min) whilst potentiating the release of LTB4. The selective 5-lipoxygenase inhibitor, BW A137C (1 microM), abolished the stimulated release of LTB4 without affecting the release of TXB2. BW755C (1-20 microM) caused a dose-related inhibition of TXB2 release but did not affect LTB4 release, while none of the drugs studied affected the release of PAF-acether. These results indicate that the FMLP-induced release of PAF-acether from guinea-pig alveolar macrophages is not susceptible to modulation by selective inhibition of lipoxygenase or cyclo-oxygenase and is therefore not secondary to the synthesis of LTB4 or TXB2.

Our changing understanding of asthma

It is now becoming clear that asthma is a chronic inflammatory disease, involving many interacting cells. These cells release a wide variety of inflammatory mediators that activate several target cells in the airway, resulting in bronchoconstriction, microvascular leakage and oedema, mucus hypersecretion and stimulation of neural reflexes. Recent evidence suggests that mast cells do not have a key role in either the late response or in bronchial hyper-responsiveness, though they may be involved in immediate responses to allergens. The possible role of other inflammatory cells and the many different mediators which have been implicated in asthma are discussed. Microvascular leakage and the role of neural mechanisms are also examined. It seems probable that there are several different types of asthma, involving different mechanisms, which may respond to different forms of therapy, but more research is needed.

Therapy of chronic idiopathic urticaria with nifedipine: demonstration of beneficial effect in a double-blinded, placebo-controlled, crossover trial

The efficacy of nifedipine, a calcium channel antagonist, in the treatment of chronic idiopathic urticaria, was evaluated in a double-blinded, placebo-controlled, crossover trial. Ten patients with chronic urticaria refractory to maximally tolerated doses of H1 and H2 antihistamines and in whom extensive evaluation failed to identify a cause for their urticaria were entered into the study. Patients continued with their prestudy antihistamine regimens. A study drug dosage was titrated in each patient and maintained throughout the trial. Patients were treated with placebo or nifedipine for 4 weeks and then crossed over to the other medication for 4 weeks. One patient withdrew because of unrelated medical illness, two patients withdrew after crossover to placebo because of intolerable urticaria, and seven patients completed the study. A beneficial effect of nifedipine was clearly demonstrated. Hive count, hive index, and itch index were all significantly improved at the end of 4 weeks of nifedipine treatment (p = 0.023, 0.003, and 0.003, respectively) but not placebo treatment (p = 0.194, 0.664, and 0.944, respectively). Additionally, end point hive index and itch index scores with nifedipine compared to corresponding placebo scores were significantly improved (p = 0.010 and 0.008, respectively). Nifedipine was well tolerated. Thus, when nifedipine is used as an adjunct to antihistamines, it appears to be a safe, efficacious drug for the treatment of chronic idiopathic urticaria.

Late appearance of phospholipid platelet-activating factor and leukotriene B4 in human skin after repeated antigen challenge

Inflammatory mediators were assessed in supernatants of chamber fluids from eight ragweed- or grass-sensitive subjects during antigen-induced cutaneous inflammatory responses. Platelet activating factor (PAF) accumulated at concentrations of 1 pm to 90 mumol/L in six of eight subjects beginning at 3 hours and continuing for 9 hours after antigen challenge. Leukotriene B4 (LTB4) was detectable at cutaneous sites of antigen challenge in five of five subjects throughout the 9-hour period at levels from 1 to 36 nmol, a range of 38% to 80% of which were omega-oxidation metabolites. Histamine levels peaked in the first hour at 106 +/- 18 ng/ml and decreased to a plateau of 11 to 13 ng/ml at 3 to 9 hours after antigen challenge. No PAF and only very low levels of LTB4 (0.1 to 1.3 nmol) and of histamine (less than 2 ng/ml) were detected at buffer-control sites during the 9 hours of study. Continuous antigen exposure thus results in the persistent release of histamine and LTB4 and the late appearance of PAF, all of which may contribute to the chronicity of allergic disorders and may have a bearing on the IgE-mediated, late-phase cutaneous response.

The role of platelet activating factor in allergic inflammation

It is becoming increasingly apparent that platelet activating factor (PAF) is an important mediator in allergic disease. It is synthesized by a variety of cells including those which are thought to participate in the inflammatory process. In turn, PAF may stimulate these cells which further propagates the inflammatory process. Furthermore, PAF can mimic most of the characteristics which are relevant in allergic inflammation and PAF can produce effects comparable to that produced by antigen in animal models of allergic inflammation and in man. Other evidence to support the involvement of PAF in allergic disease has also arisen with the advent of PAF antagonists. Many PAF-induced responses can be attenuated by these agents and many antigen-induced responses in both animal models and in man can also be attenuated by PAF antagonists. This review attempts to summarize the results from studies which have investigated the role of PAF in allergic inflammation and the effects of PAF antagonists against both PAF and allergic-induced responses.

Involvement of platelet-activating factor (PAF) in endotoxin-induced intestinal motor disturbances in rats

Intestinal myoelectrical activity was investigated in conscious fasted rats chronically implanted with Nichrome electrodes in the duodeno-jejunum. Motility of the small intestine was characterized by the presence of migrating myoelectric complex (MMC) occurring regularly at 16.2 +/- 5.8 minute intervals. Intravenous administration of endotoxin (E. coli S.0111:B4) at a dose of 50 micrograms/kg increased the interval between MMC to 112.6 +/- 26.8 min, the duration of these effects being dose-related between 10 to 100 micrograms/kg. Such a typical myoelectrical alteration, corresponding to rapidly propagated groups of spike bursts, was mimicked by the IP administration of PAF at doses of 10 to 50 micrograms/kg. Previous administration of BN 52021, a specific PAF antagonist at a dose of 50 mg/kg abolished the motor alterations induced by IP injection of PAF (25 micrograms/kg) and significantly (p less than 0.01) reduced by 61.2% those induced by IV endotoxin (50 micrograms/kg). Indomethacin (10 mg/kg IP) as well as SC 19220 (5 mg/kg IV), a PGE2 antagonist, injected prior to endotoxin (50 micrograms/kg IV) or PAF (25 micrograms/kg IP) also reduced significantly (p less than 0.01) the duration of MMC inhibition. It is concluded that endogenous release of PAF is partly responsible for the intestinal motor alterations induced by endotoxin; these effects, strongly reduced after treatment with BN 52021, are also mediated through the release of prostaglandins.

Allergy or inflammation? From neuropeptide stimulation of human skin mast cells to studies on the mechanism of the late asthmatic response

This short review examines two examples of studies into the mechanisms of allergic responses which have particular relevance to inflammation research. The first is the ability of human skin mast cells, but not those derived from lung, adenoids, tonsils or intestine, to release histamine in response to stimulation by neuropeptides including substance P, vasoactive intestinal polypeptide (VIP) and somatostatin. The neuropeptide activation site does not appear to be a classical tachykinin receptor but rather a binding site of low affinity and low specificity capable of interacting with neuropeptides and compounds with similar physicochemical characteristics. In contrast to IgE-dependent activation, neuropeptide stimulation of skin mast cells induces a rapid release of histamine with minimal generation of PGD2 and LTC4. This pseudo-allergic reaction is thought to underlie the weal and flare response in the skin and may have a role in urticaria. The second example describes studies to elucidate the mechanisms of the late asthmatic response by use of a guinea-pig model. As in man, both early and late phase responses in the guinea-pig are inhibited by sodium cromoglycate whereas only the early response is inhibited by the beta-adrenoceptor stimulant drug salbutamol. Examination of bronchoalveolar fluid has shown a temporal relationship between an airways neutrophilia and the late response. However, pharmacological manipulation and the use of an anti-neutrophil serum has shown that these events are not interdependent. The role of the airways eosinophilia requires further investigation.

A novel bioaction of PAF: induction of microbicidal activity in guinea pig bone marrow cells

When guinea pig bone marrow cells were incubated in the presence of 10(-8) to 10(-6) M platelet activating factor (PAF) for 24 to 72 hr, microbicidal activity against Candida parapsilosis of cells was augmented. This augmentation was inhibited by PAF-specific antagonists, CV6209 or FR900452. PAF-specific binding sites with a high affinity were found on guinea pig bone marrow cells. Carrageenan or 2-chloroadenosine, reagents known to be preferentially cytotoxic to macrophages, abolished the microbicidal activity of PAF-treated bone marrow cells. Macrophages prepared from the peritoneal cavity, however, acquired no appreciable microbicidal action by treatment with PAF. These observations suggest that PAF may affect a class of guinea pig bone marrow cells through binding to receptors specific to PAF, resulting in activation and/or induction of differentiation of monocyte-macrophage lineage cells.

PAF increases vascular permeability in selected tissues: effect of BN-52021 and L-655,240

The effect of the potent inflammatory mediator, platelet activating factor (PAF) was studied on the vascular permeability of selected rat tissues using the extravasation of Evans blue dye (EB) as a marker. EB (20 mg/kg) was injected in the caudal vein together with increasing doses of PAF (0.1, 1.0 and 5.0 micrograms/kg). The animals were killed and the dye was extracted in selected organs using formamide (4 ml/g wet weight tissues) and the content was expressed as EB micrograms/g dry weight. Extravasation of EB varied markedly from one tissue to another and increased as a function of time (from 0 to 60 min). PAF (5.0 micrograms/kg) increased the pancreas and duodenum vascular permeability by 15 and 5 fold respectively. At the doses of 0.1 and 1.0 microgram/kg, PAF induced a slight increase (P less than 0.01) of the vascular permeability of the heart 5 min after the injection. The PAF antagonist BN-52021 (2 and 10 mg/kg) produced a dose-dependent inhibition of the PAF effects on the pancreas, heart and duodenum. Maximum inhibition (approximately 100%) was achieved at the dose of 10 mg/kg. This antagonist given in the absence or the presence of PAF reduced the lung plasma extravasation below control levels. A thromboxane antagonist, L-655,240 (1.0 and 5.0 mg/kg) also inhibited PAF-induced increases in vascular permeability in heart, duodenum and pancreas. It also reduced below control levels the EB extravasation in kidneys, spleen and lungs. Maximum inhibition (50% for the duodenum, and 40% for the pancreas) was achieved at the dose of 5.0 mg/kg.

Role of platelet-activating factor in ulcerative colitis. Enhanced production during active disease and inhibition by sulfasalazine and prednisolone

Platelet-activating factor is released from inflammatory cells. It activates neutrophils, releases secondary messengers, and mediates mucosal ulceration and ischemia in the rat. We assessed its possible role in the pathogenesis of ulcerative colitis. Colonic biopsy specimens from patients with active ulcerative colitis and controls were incubated for 4 h in Tyrode's buffer in the presence or absence of 0.2 microM calcium ionophore (A23187) or 50 microliter of antihuman immunoglobulin E. Platelet-activating factor was determined in the tissue by aggregation assay after extraction with 80% ethanol and was confirmed by thin-layer chromatography and its inactivation by phospholipases. Platelet-activating factor was not detected in normal mucosa. Only A23187 and antihuman immunoglobulin E stimulated its activity: mean +/- SE, 43.2 +/- 8.6 and 33.0 +/- 6.1 pg/10 mg wet wt, respectively. In active ulcerative colitis basal platelet-activating factor activity was 8.9 +/- 3.5 pg/10 mg wet wt. A23187 and antihuman immunoglobulin E induced significantly higher stimulation of platelet-activating factor synthesis when compared with their effects on normal mucosa: 200 +/- 28 and 70 +/- 8.3 pg/10 mg wet wt, respectively. The enhanced stimulation induced by A23187 was dose-dependently inhibited by salazopyrine, 5-amino-salicylic acid, and prednisolone, but not by sulfapyridine. It is thus suggested that platelet-activating factor may be involved in the pathogenesis of the inflammatory response in ulcerative colitis and that its inhibition by steroids, 5-aminosalicylic acid, and salazopyrine may be an additional mechanism to explain their therapeutic effects.

Phospholipid analysis of human eosinophils: high levels of alkylacylglycerophosphocholine (PAF precursor)

The phospholipid composition and fatty acid profiles of human eosinophils were studied. Extremely high levels of ether phospholipids were found in this type of cell, such as alkylacylglycerophosphocholine (GPC) and alkenylacylglycerophosphoethanolamine (GPE); these two ether phospholipids accounted for about three-fourths of the choline and ethanolamine glycerophospholipids (CGP and EGP), respectively. Fatty acid analyses revealed that very large portions of arachidonic acid (20:4) were esterified to alkylacyl-GPC (92.0% in CGP) and alkenylacyl-GPE (86.6% in EGP), respectively. While high amounts of alkylacyl-GPC and the abundance of 20:4 in this ether phospholipid have been observed in other types of blood cells of various animals, these percentages for human eosinophils are the highest among such cells. These results suggest that alkyl and alkenyl ether phospholipids play essential roles in human eosinophils in various physiological and pathological conditions.

Inflammatory mechanisms and nocturnal asthma

The results of recent research strongly suggest that airway inflammation, which may increase at night as a result of circadian troughs in blood epinephrine and cortisol concentrations, underlies the bronchial hyperresponsiveness that is almost certainly a major contributor to the pathogenesis of nocturnal asthma. This article reviews what is known about the nature and complex interactions of the inflammatory cells and mediators that may be involved in asthma, with particular emphasis on nocturnal asthma. The roles of platelet-activating factor antagonists, corticosteroids, and theophylline in suppressing this response also are discussed.

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 H1-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.

Hypereosinophilic syndrome human eosinophil degranulation induced by soluble and particulate stimuli

Eosinophil degranulation induced by the calcium ionophore A23187 and opsonized zymosan particles was examined ultrastructurally in peripheral blood cells obtained from patients with the hypereosinophilic syndrome. Unstimulated hypereosinophilic syndrome eosinophils contained altered, vacuolated cytoplasmic granules and large cytoplasmic crystalloid structures not seen in normal cells. By morphometric analysis of transmission electron micrographs, the hypereosinophilic syndrome eosinophils contained a larger percentage of smaller sized cytoplasmic granules than normal cells. The hypereosinophilic syndrome eosinophils, however, were capable of undergoing noncytotoxic degranulation after stimulation with either A23187 or opsonized zymosan. Hypereosinophilic syndrome eosinophil degranulation was characterized by fusion of the perigranular membranes of adjacent cytoplasmic granules and vesiculation of the fused granules. Granule contents were released intracellularly into vacuoles after ionophore stimulation and into phagosomes containing the ingested zymosan particles. Noncytotoxic extracellular release of eosinophil peroxidase (EPO) was also observed after cell stimulation by either A23187 or zymosan. The capacity of hypereosinophilic syndrome eosinophils to degranulate after appropriate stimulation with release of toxic granule constituents such as EPO and other basic proteins may be important in the tissue injury observed in this syndrome.

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.

The effect of the selective PAF antagonist BN 52021 on PAF- and antigen-induced bronchial hyper-reactivity and eosinophil accumulation

Sensitised guinea-pigs were exposed to an aerosol of ovalbumin (100-500 micrograms/ml) and normal animals were exposed to an aerosol of platelet activating factor (PAF) (250-1000 micrograms/ml). Twenty-four hours later, bronchial reactivity was assessed by measurement of air overflow in response to i.v. histamine or acetylcholine using the Konsett-Rossler technique. Additionally, bronchoalveolar lavage was performed by washing the lungs with 10 ml of 0.9% saline and differential counts obtained to assess the ability of PAF and antigen to elicit pulmonary inflammatory cell recruitment. Both PAF and antigen exposure produced a dose-related increase in bronchial reactivity, while treatment with the vehicle (either 0.25% bovine serum albumin or 0.9% saline) had no effect on airway responsiveness. Furthermore, both PAF and antigen exposure produced a selective accumulation of eosinophils into the airways. There was no significant change in the number of neutrophils, macrophages or lymphocytes. The selective PAF antagonist BN52021 inhibited both the development of bronchial hyper-reactivity and the eosinophil influx into the airways induced by PAF or antigen exposure. These observations suggest that PAF has a central role to play in the antigen induced eosinophil accumulation and subsequent bronchial hyper-reactivity.

Development of a prolonged eosinophil-rich inflammatory leukocyte infiltration in the guinea-pig asthmatic response to ovalbumin inhalation

Considerable attention has recently focused on the role of inflammation in the pathophysiology of asthma, with special emphasis on "late-phase" bronchoconstriction and increased airway hyperreactivity after antigen challenge in sensitized subjects. The present report describes the histopathologic changes in guinea-pig lung and trachea at various time intervals after ovalbumin inhalation in nonsensitized (control) and sensitized animals. Bronchoalveolar lavage (BAL) was also used to assess the accompanying accumulation of intraluminal leukocytes. A distinct leukocyte margination, consisting of neutrophils and eosinophils, was observed in the peribronchial vasculature as early as 8 min postchallenge in sensitized guinea pigs. At 6 h, the eosinophils predominated and migrated to the peribronchiolar smooth muscle layer. Between 6 h and 18 h, eosinophils were seen in tracts between the smooth muscle cell layers, accumulating in large numbers in the bronchial mucosal epithelium. This pattern persisted for at least 7 days postchallenge during which eosinophils remained the dominant cell type present. Peribronchiolar accumulation of neutrophils and mononuclear cells was minimal at all time points studied. Intraluminal mucus eosinophilia developed between 18 h and 7 days. A similar pattern of eosinophil infiltration was observed in the tracheal epithelium. Control, nonsensitized, guinea-pig lungs showed minor changes with little or no eosinophil infiltration at any time after antigen challenge. These findings correlated well with the BAL study in which sensitized guinea pigs exhibited a marked delayed increase in eosinophil counts between 18 h and 7 days compared with that in nonsensitized animals.(ABSTRACT TRUNCATED AT 250 WORDS)