Granulocyte-mediated airway edema in guinea pigs

Effect of azelastine on platelet-activating factor-induced microvascular leakage in rat airways

To determine the effect of the antiallergic drug azelastine on airway mucosal inflammation, we studied airway microvascular permeability in response to platelet-activating factor (PAF) in pathogen-free rats. Vascular permeability and neutrophil accumulation were assessed by the percent area occupied by Monastral blue-labeled blood vessels and by myeloperoxidase-containing granulocytes, respectively, in whole mounts of the trachea and main bronchus. Intravenous PAF caused dose-dependent increases in the area density of Monastral blue-labeled vessels and neutrophil influx, and the former effect was inhibited by depletion of circulating neutrophils by cyclophosphamide or treatment with the neutrophil elastase inhibitor ONO-5046. Pretreatment with azelastine inhibited PAF-induced vascular leakage without affecting neutrophil accumulation. This inhibitory effect of azelastine was not seen in neutropenic rats and ONO-5046-treated rats. PAF increased neutrophil elastase contents in bronchoalveolar lavage fluid, an effect that was inhibited by azelastine. Therefore, azelastine attenuates PAF-induced airway mucosal microvascular leakage, probably involving inhibition of the release of neutrophil elastase from activated neutrophils.

Role of platelet activating factor, leukotrienes and polymorphs in the FMLP induced increase in microvascular leakage in rabbit trachea

This study was designed to determine the time course of N-formyl-methionyl-leucyl-phenylalanine (FMLP) induced microvascular leakage in the airways of anaesthetized, tracheostomized New Zealand white rabbits. We have previously shown that FMLP increases microvascular leakage in the rabbit trachea at 30 min post challenge. A further aim was to determine the mechanisms underlying this response. Microvascular leakage was assessed using the albumin binding dye, Evans blue which was injected intravenously (50 mg/kg) immediately prior to FMLP challenge (10 mg nebulised for 2 min) or the control (dimethylsulphoxide/saline). Microvascular leakage was assessed in the trachea and bronchi at 15 min, 22.5 min, 45 min and 120 minutes with n = 6 for each group. The only significant difference between control and FMLP challenged groups was at 45 min in the bronchi (FMLP 77.6 +/- 12.2, control 33.4 +/- 5.7, P < 0.05). To determine the mechanism underlying FMLP-induced increases in microvascular leakage rabbits were treated with one of the following: (i) nitrogen mustard (1.75 mg/kg intravenously), which depletes circulating polymorphs (n = 6); (ii) the platelet activating factor (PAF) receptor antagonist WEB 2086 (10 mg/kg; n = 5); (iii) the Cys-LTR1 receptor antagonist ICI198615 (nebulised 10(-4) mol/L), or challenged with the thromboxane agonist U46619. Tracheal Evans blue concentration was assessed at 30 min after FMLP challenge and compared with the appropriate control. Treatment with WEB 2086 significantly (P < 0.05) reduced tracheal microvascular leakage (FMLP 76.3 +/- 13.1 WEB 2086/FMLP 31.4 +/- 3.7 micrograms/g trachea) as did ICI198615 (FMLP 69.8 +/- 11.5 ICI198615/FMLP 30.0 +/- 5.7). In conclusion FMLP induced an increase in tracheal microvascular leakage which was significant in the bronchi at 45 min and this increase was mediated by platelet activating factor and the sulphidopeptide leukotrienes C4 and D4.

Neutrophil chemotactic activities in bronchoalveolar lavage fluid from patients with bronchial asthma

OBJECTIVES

To elucidate the presence of neutrophil chemotactic factor (NCF) and characterize them in the bronchial trees of symptomatic patients with bronchial asthma.

METHODS

Bronchoalveolar lavage (BAL) fluids were concentrated by ultrafiltration. Differential counts of BAL cells was performed upto 500 cells on the cytocentrifuge-prepared slides. NCF activities in concentrated BAL fluids were measured by using microchemotactic chamber. These NCF activities were characterized by heat-stability, sensitivity to trysin and solubility into organic solvent.

RESULTS

NCF activities were significantly higher in low molecular weight (LMW)-BAL fluid fraction below 5000 dalton than those in high molecular weight (HMW)-BAL fluid fraction. The NCF activities were significantly higher in the patients with bronchial asthma when compared to those of normal subjects. The LMW-NCF and HMW-NCF activities were correlated with the percentages of neutrophils in BAL fluid in the patients with bronchial asthma. The LMW-NCF activities were extractable into ether, stable to heat and resistant to trypsin.

CONCLUSIONS

Main NCF activities in BAL fluid are suggested to be lipid substances with low molecular weight less than 5000 dalton and these substances may recruit neutrophils into the bronchial trees of patients with bronchial asthma.

Macrolide antibiotics protect against endotoxin-induced vascular leakage and neutrophil accumulation in rat trachea

We studied the effects of macrolides on lipopolysaccharide (LPS)-induced airway inflammation in the rat tracheal mucosa. Erythromycin and roxithromycin dose dependently inhibited microvascular leakage and neutrophil recruitment induced by LPS. This inhibitory action on vascular permeability was abolished by neutrophil depletion.

Clearance of 99mTc-labeled albumin from lungs in anesthetized guinea pigs

Gamma imaging was used to measure the rate of clearance of aerosolized 99mTc-human serum albumin (HSA) from the lungs of control guinea pigs and guinea pigs that received increased lung inflation or lung injury. Anesthetized guinea pigs were ventilated for 6 min with an aerosol of HSA and the radioactivity in the chest was monitored for 2 h with a gamma camera to determine whether the clearance rate would be a reliable assessment of lung epithelial permeability. Increased lung volumes were effected by application of 5 or 7 cm H2O positive end-expired pressure (5-PEEP and 7-PEEP, respectively). Lung injury was induced either by intravenous oleic acid (OA, 27-73 microliters/kg) or inhalation of nitrogen dioxide (NO2, 80-100 ppm) for 2 h. Postmortem extravascular lung water volume (EVLW) provided an assessment of the degree of lung injury. Tracer clearance rates in animals receiving 5 or 7 cm H2O PEEP were not significantly different from controls (K = 0.15 +/- 0.05 and 0.24 +/- 0.10 vs 0.12 +/- 0.03%/min, respectively, p > .05). Animals exposed to NO2 had faster tracer clearance rates (K = 0.33 +/- 0.21%/min, p < .05) and higher EVLW (5.8 +/- 3.0 vs 3.7 +/- 0.2 mL/g dry lung, p < .05) than controls. Clearance rates of HSA from the lungs of NO2-exposed guinea pigs correlated well with injury as assessed by EVLW (r = .93, p < .01). Clearance rates of HSA and EVLW in animals receiving oleic acid were significantly higher than controls and the group receiving 5 cm H2O PEEP (K = 0.58 +/- 0.41%/min, EVLW = 8.1 +/- 0.8 mL/g dry lung tissue, p < .05), but there was no correlation between these parameters in this injury model. It is concluded that imaging of the disappearance of radiolabeled HSA in the guinea pig can be a useful index of lung epithelial permeability, but this technique is limited to certain models of lung injury.

Interactions between airway epithelium and mediators of inflammation

Epithelial cells lining the respiratory airways classically are considered to be "target" cells, responding to exposure to a variety of inflammatory mediators by altering one or several of their functions, such as mucin secretion, ion transport, or ciliary beating. Specific responses of epithelial cells in vivo or in vitro to many of these inflammatory mediators are discussed. Recent studies have indicated that airway epithelial cells also can act as "effector" cells, responding to a variety of exogenous and/or endogenous stimuli by generating and releasing additional mediators of inflammation, such as eicosanoids, reactive oxygen species, and cytokines. Many of these epithelial-derived substances can diffuse away and affect neighboring cells and tissues, or can act, via autocrine or paracrine mechanisms, to affect structure and function of epithelial cells themselves. Studies dealing with airway epithelium as a source of inflammatory mediators and related compounds also are discussed.

Effects of platelet-activating factor on vascular permeability and granulocyte recruitment in the rat trachea

Platelet-activating factor (PAF) is a phospholipid mediator known to produce several features of airway inflammation. We examined the effects of intravenous PAF on vascular permeability and granulocyte recruitment in the rat trachea. To assess vascular permeability, anesthetized rats were given injections of Evans blue dye (30 mg/kg, iv) and PAF (1-10 micrograms/kg, iv), and then their tracheas were removed and assayed spectrophotometrically for dye content. We found that a PAF dosage of 6 micrograms/kg increased the tracheal dye content 7-fold compared to controls. The amount of extravasated dye in the tracheas was significantly increased 1 min after PAF injection, was maximal at 5 min, and had returned to control levels by 10 min. To assess granulocyte recruitment, anesthetized rats were given an injection of PAF (6 micrograms/kg, iv), and then their tracheas were removed and stained to reveal myeloperoxidase-containing neutrophils and eosinophils. We found that the number of neutrophils in the tracheal mucosa was increased 7-fold from controls 5 min after PAF injection, but was not significantly increased 6 h later. The number of eosinophils in the tracheal mucosa was not significantly increased from controls at any time after PAF injection. We conclude that intravenous PAF causes a rapid but transient increase in vascular permeability in the rat trachea, and that intravenous PAF also causes a rapid but transient recruitment of neutrophils into the tracheal mucosa without a similar effect on eosinophils.

Pharmacologic control of plasma exudation into tracheobronchial airways

We have employed anesthetized guinea pigs to examine effects of nonsteroidal antiasthma drugs on airway plasma exudation, which is a process of potential pathogenetic importance in asthma. This study focused on exudation of plasma into the airway luman (circumventing problems with a changing blood pool in tissue samples). Topical tracheal superfusions with a neurogenic agent (capsalcin), bradykinin, and histamine increased mucosal blood flow (Laser Doppler flowmetry) and produced significant exudation of macromolecular plasma tracers (fluorescein-labeled dextran 156000 D; 131I-albumin 70,000 D). Lidocaine 3 x 10(-5) M, applied topically, inhibited capsalcin- but not bradykinin-induced plasma exudation. Intravenously administered terbutaline, enprofylline, and theophylline and topical cromoglycate dose-dependently inhibited the inflammatory stimuli-induced mucosal exudation of plasma. Cromoglycate did not alter airway blood flow, and both terbutaline and enprofylline increased the blood flow. Hence, these three types of drugs did not inhibit exudation by stopping flow. Further, both neural and non-neural exudative responses were inhibited, suggesting that the drugs may have acted directly on the permeability-regulating microvascular endothelial cells. It is proposed that antiexudative actions may contribute to the antiasthma effects of beta 2-agonists, xanthines, and cromoglycates.

Effects of single and multiple inhalations of antigen on airway responsiveness in monkeys

Airway hyperresponsiveness is an important and characteristic feature of asthma. In monkeys, we have reported that antigen (Ag) inhalation induces a prolonged airway eosinophilia, that chronic airway eosinophilia is associated with marked airway hyperresponsiveness, and that chronic Ag inhalations induce airway eosinophilia and hyperresponsiveness. In this study we have determined the effects of acute Ag inhalation(s) on airway responsiveness to obtain a protocol for the study of the mechanisms involved. Anesthetized and intubated adult male cynomolgus monkeys with a naturally occurring sensitivity to Ascaris suum extract were studied. Airway responsiveness (provocative concentration of nebulized and inhaled methacholine that induced a 100% increase in respiratory system resistance [Rrs] [PC100]; twofold decrease regarded as significant) and airway cell composition (bronchoalveolar lavage [BAL]) were determined 1 day before and 20 hours after a single inhalation of Ascaris extract, or 3 days before and 3 days after three alternate-day inhalations of Ascaris extract. The single inhalation of Ag (N = 7) caused an acute increase in Rrs (307% +/- 62%), an increase in BAL leukocytes, and a decrease in PC100 in three animals that was moderate (more than eightfold) in two animals. The mean +/- SE change in log PC100 was only -0.25 +/- 0.24. The multiple inhalations of Ag in the same animals caused acute increases in Rrs (178% +/- 48%, 380% +/- 83%, and 331% +/- 63%, respectively), an increase in BAL granulocytes, and a decrease in PC100 in six of seven animals (mean +/- SE change in log PC100 was -1.36 +/- 0.34) that was moderate in two and severe (more than 80-fold) in three animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Necrotizing tracheobronchitis (NTB) following high frequency ventilation: role of an angiotensin converting enzyme inhibitor

The purpose of this investigation was to study the effect of an angiotensin converting enzyme inhibitor (enalaprilat) on the morphologic manifestations of experimentally induced necrotizing tracheobronchitis (NTB). Twenty piglets were anesthetized before saline lung lavage. High frequency flow interrupter (HFFI) ventilation was used with a strategy known to produce NTB. Animals were randomly assigned to receive IV enalaprilat 0.1 mg/kg (ENP-Hi), enalaprilat 0.01 mg/kg (ENP-Lo), or saline (C). After 8 hours of ventilation, the piglets were sacrificed. Total airway injury scores (mean +/- S.D.) were 1.2 +/- 0.7 for ENP-Hi, 0.2 +/- 0.2 for ENP-Lo, and 21.3 +/- 16 for group C. Enalaprilat minimizes NTB lesions in neonatal piglets exposed to high frequency oscillatory ventilation. Although the origin of NTB is multifactorial, airway mucosa ischemia may play an important role. Enalaprilat may compensate for the reduction of mucosal blood flow by limiting formation of angiotensin II and/or preventing degradation of bradykinin.

Necrotizing tracheobronchitis following high frequency ventilation: effect of hydrocortisone

A piglet model of acute respiratory failure was used to determine whether necrotizing tracheobronchitis (NTB) produced during high-frequency pneumatic flow interrupter (HFFI) ventilation could be attenuated by prior administration of 2 mg/kg hydrocortisone IV. Fourteen piglets (means age 3.6 days, means wt 1.4 kg) were anesthetized and paralyzed before saline lung lavage. The animals were randomly assigned to either placebo (P) or hydrocortisone (H) group. Continuous HFFI (10 Hz) was interrupted five times per minute by a 1-second deflationary pause. All animals were kept on 1.0 FI02 with ventilators adjusted to maintain adequate arterial blood gases. Airway pressures were similar for both groups. After 8 hours of ventilation the animals were sacrificed and their lungs inflated with formalin to 40 cm H2O. Sections were obtained from trachea, carina, main stem, and peripheral bronchi. A total airway injury (TAIS) was calculated by a pathologist unaware of treatment assignment. There was a significant difference (p less than 0.01, Wilcoxon rank sum) in TAIS scores between P (means 21.3) and H (means 7.8). In five out of seven P animals and in one out of seven H animals, NTB was severe and extended to the hilar bronchi. Although NTB is multifactorial in origin, the prior use of hydrocortisone may decrease the severity and extent of lesions by modifying the inflammatory response to this specific airway injury.

Alveolar macrophages and eicosanoids but not neutrophils, mediate bronchoconstriction induced by FMLP in the guinea-pig

1. N-formyl-methionyl-leucyl-phenylalanine (FMLP), when administered by aerosol to guinea-pigs, induced a dose-dependent bronchoconstriction (BC) with no overt effect on platelet and leukocyte blood counts. Repeated administration of FMLP by aerosol was followed by desensitization. 2. Electron microscopy studies showed that administration of FMLP by aerosol is accompanied by alveolar macrophage activation, accumulation and aggregation in the alveolar lumens. Non-degranulated eosinophils were observed in the lungs and a few platelet micro-aggregates in the pulmonary microvasculature. 3. No significant accumulation of 131I-labelled albumin, 111In-labelled neutrophils or 111Inlabelled platelets was detected in the lungs after the administration of FMLP by aerosol, whereas the intravenous administration was accompanied by an increase of extravascular albumin and significant neutrophil sequestration in the lungs. 4. Aspirin administered intravenously or by aerosol reduced significantly the BC induced by an aerosol of FMLP. By contrast, intravenous indomethacin reduced only BC induced by the sub-maximal dose of FMLP as an aerosol whereas, when administered by inhalation, it inhibited BC induced by FMLP administered either intravenously or by aerosol at all the concentrations tested. 5. FMLP induced a dose-dependent contraction of the guinea-pig trachea, which was not inhibited by indomethacin. 6. The dual cyclo-oxygenase/lipoxygenase inhibitor compound BW755C suppressed the BC induced by an aerosol of FMLP at all the concentrations used, whereas the histamine H1-antagonist mepyramine was inactive. 7. Leukocyte depletion with vinblastine failed to reduce BC induced by intravenous or an aerosol of FMLP. 8. Our studies indicate that: (a) FMLP administered by aerosol induces dose-dependent BC followed by desensitization, indicating that local mechanisms account for BC; (b) BC induced by i.v. FMLP, but not by its inhalation, is accompanied by albumin extravasation and neutrophil sequestration in the lungs; (c) BC by either i.v. or an aerosol of FMLP is not due to neutrophil activation; (d) inhalation of FMLP induces BC accompanied by accumulation of activated alveolar macrophages, non-degranulated eosinophils and a few platelet microaggregates in the lung; (e) both cyclo-oxygenase and lipoxygenase metabolites are involved in the BC induced by an aerosol of FMLP.

Effect of antiasthma drugs on microvascular leakage in guinea pig airways

We have studied the effect of intravenous epinephrine, albuterol, verapamil, and aminophylline on airway microvascular leakage in guinea pigs. Microvascular leakage was induced by platelet-activating factor (PAF; 50 ng/kg intravenously), which acts directly on venular endothelial cells, and measured by quantifying extravasation of Evans blue (EB) dye. Epinephrine (20 micrograms/kg) inhibited PAF-induced changes in dye leakage in larynx and main bronchi; at 80 and 160 micrograms/kg, significant inhibition was observed in all airways studied. This effect was reversed by phentolamine (2.5 mg/kg) or prazosin (100 micrograms/kg). By contrast, albuterol (20 to 320 micrograms/kg) and aminophylline (12.5 to 50 mg/kg) failed to inhibit dye leakage at any dose studied. Verapamil inhibited PAF-increased leakage in larynx, main bronchi, and intrapulmonary airways at the lowest dose tested (125 micrograms/kg), although inhibition was not dose dependent. These results suggest that the antiedema effect of epinephrine may be due to vasoconstriction rather than to a direct effect on endothelial cell contractility and that neither beta-agonists nor theophylline have an inhibitory effect. The inhibitory effect of epinephrine on airway microvascular leakage may have therapeutic implications for asthma.

Mechanisms of acute increases in airway responsiveness caused by environmental chemicals

Inhalation of inhaled environmental chemicals has long been recognized as a cause of acute increases in airway responsiveness. Extensive studies of the mechanisms of action of two of these chemicals, ozone and toluene diisocyanate, have been conducted during the past decade. The results of these studies suggest that acute airway inflammation plays an important role in the effect of inhaled chemicals but that the specific aspects of the inflammatory response that lead to the development of airway hyperresponsiveness are different for different stimuli and among different mammalian species. These observations suggest that in vivo airway hyperresponsiveness can arise via several different mechanisms and is thus not likely to reflect a single underlying defect.

Tachykinins mediate the acute increase in airway responsiveness caused by toluene diisocyanate in guinea pigs

Exposing guinea pigs to toluene diisocyanate (TDI) causes an acute increase in airway responsiveness to inhaled acetylcholine. The mechanism of this increase in airway responsiveness is unknown. Capsaicin-sensitive afferent nerves and the tachykinins they release upon activation are important in controlling bronchomotor tone in guinea pigs. To determine whether tachykinins are important in TDI-induced airway hyperresponsiveness, we studied the effects of tachykinin depletion, using capsaicin, and competitive tachykinin antagonism, using (D-Arg1, D-Pro2, D-Trp7.9, Leu11) substance P, on TDI-induced airway hyperresponsiveness. In 9 of 9 untreated animals, TDI exposure caused a large and significant increase in airway responsiveness to acetylcholine. The mean concentration of acetylcholine required to decrease specific airway conductance by 50% below baseline (the PD50) was 1.51% before TDI exposure and 0.17% after TDI exposure (p less than 0.0005). Capsaicin treatment had no effect on the PD50 but prevented the TDI-induced increase in airway responsiveness in 10 of 12 animals. (The PD50 was 1.03% before TDI and 1.27% after TDI exposure.) Treatment with the tachykinin antagonist (D-Arg1, D-Pro2, D-Trp7.9, Leu11) substance P also abolished the TDI-induced increase in airway responsiveness in all 5 animals treated. Although TDI exposure also causes airway edema, the effect of capsaicin treatment on TDI-induced airway hyperresponsiveness did not result from prevention of airway edema. TDI exposure caused a marked increase in tracheal extravasation of intravenously administered Evans blue dye that was not prevented by capsaicin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)