Effects of leukotriene D on the airways in asthma

MK-571, a potent antagonist of leukotriene D4-induced bronchoconstriction in the human

MK-571 is a novel leukotriene D4/E4 (LTD4/E4) receptor antagonist. The ability of MK-571 to inhibit LTD4-induced bronchoconstriction was examined both in six healthy volunteers and in six asthmatic subjects in a double-blind, placebo-controlled, randomized crossover study design. LTD4 challenges were performed during a constant infusion with placebo or the active compound. The provocative concentration of LTD4 causing a 35% decrease in SGaw (PC35 SGaw) was 4.8 +/- 0.6 x 10(-5) M (mean +/- SEM) in healthy volunteers and 1.8 +/- 0.7 x 10(-6) M in asthmatic subjects during placebo treatment. Intravenous MK-571 (1,500, 86, or 28 mg) inhibited the LTD4-induced bronchoconstriction completely in healthy volunteers, up to an inhaled concentration of 10(-4) M LTD4. In asthmatic subjects, 28 mg MK-571 caused a significant, at least 44-fold, rightward shift of the dose-response curve to LTD4, whereas 277 mg shifted the dose-response curve at least 84-fold to the right. MK-571 is therefore a potent antagonist of LTD4-induced bronchoconstriction in both normal volunteers and asthmatic patients. MK-571 also caused a small but significant increase in baseline airway caliber in asthmatic patients, suggesting the presence of LTD4 in asthmatic airways and thus providing further support to a role for sulfidopeptide leukotrienes in the pathogenesis of asthma.

Eicosanoid release and mepyramine, LTC4 and LTD4 binding in passively sensitized human lung parenchyma in vitro

In vitro passive sensitization of human lung parenchyma with hyper-immune serum did not affect the release of prostaglandin D2 (PGD2) or leukotriene (LT)-like activity upon challenge with anti-IgE antibody with respect to control lung, despite a marked difference in IgE levels between control (C) and sensitized (S) tissue. Binding studies with [3H]LTC4, [3H]LTD4 and [3H]mepyramine (a histamine H1 antagonist) showed a statistically significant increase in the amount bound in sensitized vs control lung for [3H]mepyramine only. Contractile response to 5 x 10(-5) M histamine (H) in C and S lung parenchymal strips did not correlate with binding data. It is concluded that in vitro elevated IgE levels do not affect the interaction of sulfidopeptide leukotrienes with their putative receptors. As for the observed increase in [3H]mepyramine binding, this might not represent a true increase in histamine receptors on lung smooth muscle cells.

Mast cells and their role in urticaria

Mast cells are the primary effector cell type in urticaria and angioedema. Recognition of different types of mast cells has increased the understanding of their cell biology and may help refine the therapy of human allergic diseases. Mast cells containing chymase and tryptase (MCTC) and tryptase alone (MCT) are two distinct types distinguished on the basis of the neutral protease composition of their granules. MCT cells are distributed primarily in the lung and gastrointestinal mucosa, whereas MCTC cells lie primarily in skin and gastrointestinal submucosa. The appearance of MCT cells in intestinal tissue is T-lymphocyte dependent, whereas MCTC cells is not. The granules in unstimulated mature MCT cells typically contain complete scrolls, whereas those of MCTC cells often contain grating or lattice substructures. Major categories for the mediators of mast cells include performed mediators present in the secretory granule, newly generated lipid-derived mediators, and cytokines.

Reproducibility of leukotriene D4 inhalation challenge in asthmatics. Effect of a novel leukotriene D4/E4-antagonist (SR 2640) on leukotriene D4-induced bronchoconstriction

We have studied the reproducibility of a bronchial leukotriene (LT) provocation test in asthmatics, and the effect of prior treatment with an oral leukotriene D4/E4 antagonist (SR 2640) on LTD4-induced bronchoconstriction in nine asthmatics in a double-blind placebo-controlled randomized cross-over trial. The reproducibility of the bronchial leukotriene provocation test was high. For a specific patient, the replication variance is 0.2303, and the standard deviation is thus 0.4799, corresponding to 48%, i.e. one halving of the dose or half doubling of the dose. SR 2640 antagonised LTD4 induced bronchoconstriction causing a mean shift of 48% to the right of the dose-response curve as compared with placebo (95% confidence interval being 11-137%). This study demonstrates that bronchial LTD4 provocation test is a safe and reproducible method in asthmatics, and that the method can be used to detect LT-antagonism; furthermore that SR 2640 is a weak LTD4-antagonist in asthmatics.

Granulocyte chemotaxis in the canine trachea: inhibition by lipid mediator antagonists and systemic inhibitors

Inflammation of the airways contributes to the multicomponent disease known as asthma. The primary cells that infiltrate the airways in response to antigen exposure are PMNs and eosinophils, cells that can release cellular components, and damage the airways. We adapted a double-balloon endotracheal tube to study the cellular response to three de novo synthesized lipid mediators (LTB4, PAF-acether and 15 HETE) found in respiratory fluids following antigen exposure. In random repeat challenges in groups of 7 dogs using mongrel dogs at 240 min following exposure to 10(-6) M agonists, the PMN content of the perfused fluid was 870 +/- 240, 1632 +/- 883, 515 +/- 395, and 1575 +/- 214 cells/ml/5 high power fields for vehicle, LTB4, PAF, and 15 HETE respectively. Eosinophils that infiltrated the lumen at 240 min were 162 +/- 23, 608 +/- 287, 502 +/- 23, 115 +/- 14 cells/ml/5 HPF for vehicle, LTB4, PAF, and 15 HETE respectively. Thus LTB4 and PAF-acether significantly (p less than 0.05) increased eosinophils, and LTB4 and 15 HETE increased PMNs (p less than 0.05). After determining the agonist response for the 3 agonists we included 2 specific antagonists in the perfusate. The LTB4 antagonist U-75,302 10(-5) M, and the PAF antagonist L 652,731 10(-5) M in chambers containing LTB4 and PAF-acether respectively blocked significantly the influx of PMNs and eosinophils compared to vehicle (p less than 0.01). Methylprednisolone 5 mg/kg i.m.--18 hrs blocked eosinophilia to PAF and LTB4. Oral U-78,517F a Trolox amine lazaroid, active as an inhibitor of lipid peroxidation, 30 mg/kg--18 hrs significantly blocked eosinophilia to PAF-acether and LTB4 directed chemotaxis compared to vehicle (p less than 0.05) but not 15 HETE. Specificity was shown for each antagonist since the PAF and LTB4 antagonists did not block the opposite agonist. Use of this novel in vivo chemotaxis model allows the additional advantage of studying chemotaxis in living tissue.

Reversal and prevention of airway response to antigen challenge by the inhaled leukotriene D4 antagonist (L-648,051) in patients with atopic asthma

We examined the ability of the inhaled leukotriene D4 antagonist (L-648,051) to inhibit antigen-induced asthmatic responses. Twelve patients with stable exogenous asthma participated in two separate double-blind, placebo-controlled, cross-over trials. The ability of the antagonist to reverse or inhibit antigen-induced bronchoconstrictor response was examined; both the immediate and the late phases were studied. In the reversal study, patients inhaled 800 micrograms of L-648,051 during the immediate phase (15 min after antigen challenge) and again during in the late phase (7 h after antigen challenge). In the prevention study, the same dose (800 micrograms) of L-648,051 was inhaled before the expected immediate reaction (5 min before antigen challenge) as well as before the expected late reaction (2.5 h after antigen challenge). The LTD4 antagonist was not effective in reversing the airway response to inhaled antigen, as measured by airway resistance (Rt), forced expiratory volume in 1 s (FEV1) or forced vital capacity (FVC). When the antagonist was given prior to antigen challenge, a slight reduction in Rt was observed during the immediate phase, but not during the late phase. Some improvement in FEV1 and FVC during the immediate phase was also observed, but these changes did not reach statistical significance. These results suggest that LTD4 plays a role in the immediate phase of antigen-induced asthma.

The effect of aerosolized SK&F 104353-Z2 on the bronchoconstrictor effect of leukotriene D4 in asthmatics

Leukotriene D4 (LTD4) is a potent bronchoconstrictor and vasoactive mediator that has been implicated in the pathogenesis of bronchial asthma. We have studied the effect of SK&F 104353-Z2, a specific LTD4 antagonist, on LTD4-induced bronchoconstriction in asthmatics. A total of 12 mild asthmatics (mean baseline FEV1 +/- SEM: 85.9% +/- 2.6) received on 2 separate days, double-blind and cross-over, 800 micrograms SK&F 104353-Z2 or placebo via aerosol. After 30 min, doubling concentrations of LTD4 (0.078 to 20.1 microM in the first 4 patients and up 80.4 microM in the other patients) were inhaled with intervals of 30 min. Specific airways conductance (sGaw) and forced expiratory volume in 1 s (FEV1) were measured. On the placebo-day LTD4 inhalation caused a concentration dependent bronchoconstriction. The effect of SK&F 104353-Z2 on baseline sGaw and FEV1 could be evaluated in 10 patients. After inhalation of SK&F 104353-Z2 a small, but significant increase, in sGaw (0.107 +/- 0.013 to 0.132 +/- 0.011 cm H2O-1s-1) and FEV1 (3.39 +/- 0.23 to 3.56 +/- 0.25 liter) was observed. The effect of SK&F 104353-Z2 on the dose-response curve for LTD4 was evaluated in the six patients who inhaled concentrations of LTD4 up to 80 microM. On the active treatment day, the dose-response curve for LTD4 was significantly shifted to the right.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a novel 5-lipoxygenase inhibitor, E6080 on bronchospasm, airway cellular infiltration and leukotriene production in guinea pigs

6-Hydroxy-2-(4-sulfamoylbenzylamino)-4,5,7-trimethylbenzothiazo le hydrochloride (E6080), an orally active and selective 5-lipoxygenase inhibitor, dose-dependently inhibited the bronchospasm induced by antigen (ovalbumin) inhalation in sensitized conscious guinea pigs. The inhibitory effect of E6080 was more potent than that of a typical 5-lipoxygenase inhibitor, AA861, but less than that of a leukotriene (LT) antagonist, LY171883. When airway infiltration of neutrophils and eosinophils was measured in bronchoalveolar lavage fluid (BALF) at 6 h after antigen inhalation by passively sensitized guinea pigs, the inhibitory effect of E6080 on neutrophil infiltration was more marked than that on eosinophil infiltration. The inhibitory effect of E6080 on bronchoalveolar cellular infiltration and bronchoepithelial damage was confirmed by examination of photomicrographs of the lung. In addition to the above pharmacological effects, E6080 inhibited the increase in BALF levels of both i-LTC4 and i-LTB4. These results suggest that E6080 may prove to be effective for the treatment of asthma, in which large amounts of leukotrienes (LTs) are elaborated.

Inhibition of histamine, leukotriene C4/D4, and thromboxane B2 release from human leukocytes and human chopped lung mast cells by the allergic mediator release inhibitor, CI-949

The novel antiallergy compound, 5-methoxy-3-(1-methylethoxy)-1-phenyl-N-1H-tetrazol-5-yl-1H- indole-2- carboxamide, L-arginine salt (CI-949), inhibited mediator release from human basophilic leukocytes and from human chopped lung mast cells challenged with anti-IgE. In leukocytes, CI-949 was a more potent inhibitor of leukotriene C4/D4 and thromboxane B2 release (concentration of drug that inhibits mediator release by 50% [IC50] 0.5 and 0.1 mumol/L, respectively) than of histamine (IC50, 11.4 mumol/L) when anti-IgE was the challenging stimulus. In human lung, inhibition of release of all three mediators occurred at approximately equal concentrations (IC50s for histamine, 16.6 mumol/L; for leukotriene C4/D4, 7.1 mumol/L; and for thromboxane B2, 6.2 mumol/L). The inhibition of histamine release from basophils by CI-949 was further characterized using a variety of stimuli. Challenge with anti-IgE, histamine-releasing factor derived from lymphocytes, N-formyl-L-methionyl-L-leucyl-L-phenylalanine, and concanavalin A revealed potent inhibition (IC50, 10 to 15 mumol/L). CI-949 was less potent versus calcium ionophore A23187, phorbol myristate acetate (12-o-tetradecanoylphorbol-13-acetate), and C5a (IC50s, 30, 54, and 60 mumol/L, respectively). These results suggest that diverse pathways of cell activation-excitation coupling exist for different stimuli in basophils. Furthermore, the activity and potency of CI-949 in inhibiting release of histamine, leukotrienes, and thromboxane from both human basophils and mast cells suggest that the compound will be effective clinically for indications in which these mediators are implicated, including asthma and allergic rhinitis.

The pharmacology of airway hyperresponsiveness and inflammation

Hyperresponsiveness is a key abnormality in asthma and deserves recognition both in the clinical presentation of asthma and its pathogenesis. Available evidence strongly suggests that inflammatory processes are important in producing this aspect of disordered airway physiology. Pharmacologic studies have greatly increased our knowledge of mechanisms involved in hyperresponsiveness but fall short of a complete explanation of the phenomenon. It is most likely that hyperresponsiveness, as measured in the laboratory, has many different components and that any single mechanism will be an insufficient explanation.

Mucosal inflammation in asthma

Over the past decade, it has become increasingly recognized that airways inflammation is one of the major components of asthma. Until recently, measurements of bronchial responsiveness and mediators of allergic reactions were the only methods of studying pathogenetic mechanisms in asthma. With improved diagnostic procedures such as fiberoptic bronchoscopy, it has become possible to investigate these mechanisms and the resulting inflammatory changes in situ. BAL has highlighted the presence of mast cells and eosinophils and has given proof of their mediator participation in airways inflammation and hyperresponsiveness. Endobronchial biopsies have so far yielded results that are similar to those obtained from postmortem studies, although it appears that there are varying degrees of inflammation in living asthmatics. Even in mild disease, the histopathologic features of bronchial asthma are consistent with chronic inflammation. Indirect evidence obtained from allergen challenge leading to increased bronchial hyperresponsiveness during LAR, and direct evidence of inflammatory cells and their mediators in the airway mucosa and lumen after allergen challenge argue for an active role of cells in bringing about inflammatory changes. At present, however, it is not possible to relate precisely the findings obtained by bronchoscopy to the clinical presentation and progression of asthma. Cell activation with production of potent mediators of inflammation may be more relevant to inflammation than the simple presence of these cells in the airways. Almost all the inflammatory cells present in the bronchial wall and lumen have been implicated in the pathogenesis of mucosal inflammation in asthma, but with our current state of knowledge, none can be singled out as the most important contributor. The mast cell was the first to be investigated in depth, and despite the accumulation of large amounts of data concerning its ultrastructure and function, it remains uncertain to what extent this cell is involved in inflammatory responses. Thus, while its main role appears to be that of initiator of allergen-induced responses, the eosinophil has attracted more attention as a proinflammatory cell rather than as an antiinflammatory cell with a capacity to be selectively recruited from the circulation in response to IgE-dependent signals. The eosinophil secretes potent mediators that cause damage to the bronchial epithelium and lead to bronchoconstriction. The role of other cells is at present not as well defined.(ABSTRACT TRUNCATED AT 400 WORDS)

Interleukin-1 potentiates antigen-mediated arachidonic acid metabolite formation in mast cells

Mast cells were isolated from human lung tissues using density gradient centrifugation and a fluorescence-activated cell sorter. Purified cells were sensitized passively with serum from allergic patients sensitive to grass pollen and then challenged with antigen (grass pollen). When these cells were challenged with antigen, LTC4, and PGD2 (19 +/- 6, and 42 +/- 9 pmol/10(6) cells, respectively) were released during 2 hr of incubation. When mast cells were incubated with interleukin-1 (IL-1) no detectable amount of LTC4 or PGD2 was generated. However, when mast cells were challenged with antigen and IL-1, LTC4 and PGD2 were released (60 +/- 15 and 97 +/- 21 pmol/10(6), respectively) after a 2 hr incubation period. The stimulatory action of IL-1 was both time- and dose-dependent (over a 10-1000 units/ml range). In addition, greater activity was observed if IL-1 was added 5-30 min prior to the antigen. Inhibitors of arachidonic acid metabolic pathways prevented the release of LTC4 and PGD2 from mast cells activated with antigen and IL-1. This study shows that IL-1 does not stimulate arachidonic acid metabolite release by mast cells but potentiates the release induced by antigen.

Leukotriene C4 in children with atopic asthma. I. Plasma levels in acute asthma

The leukotrienes C4, D4 and E4 are potent biologic mediators, and are thought to play an important role in obstructive airways disease such as asthma. In this study, plasma immunoreactive LTC4 (iLTC4) levels in asthmatic children were measured using radioimmunoassay after Sep-pak extraction in order to determine whether LTC4 is released in vivo during an asthmatic attack. In 10 non-atopic children, the mean +/- SEM of plasma iLTC4 level was 0.031 +/- 0.013 pmol/ml. Significantly higher plasma iLTC4 levels were recognized at all stages in asthmatic children, both in remission (p less than 0.01) and during an attack (p less than 0.01). PaO2 levels during an attack were significantly lower in the high iLTC4 group. In 15 asthmatic children, the plasma iLTC4 levels during an attack (0.134 +/- 0.017 pmol/ml) significantly decreased during recovery (0.078 +/- 0.012 pmol/ml) (p less than 0.05). Plasma iLTC4 levels correlated closely with lung function (p less than 0.01). The high iLTC4 levels in plasma in asthmatic children suggest a role for LTC4 in the pathophysiology of asthma.

Leukotriene C4 in children with atopic asthma. II. Plasma levels in bronchial challenge with specific allergen

Peptide leukotrienes C4, D4 and E4 are considered to be major mediators of hypersensitivity reactions. In this study, immunoreactive leukotriene C4 (iLTC4) in plasma, taken from asthmatic children who had undergone bronchial challenge with a specific allergen, was measured using radioimmunoassay in order to determine whether LTC4 is released in vivo during human allergic reactions. With regard to the bronchial challenge of 10 asthmatic children, plasma iLTC4 levels at the post-challenge stage (0.131 +/- 0.037 pmol/ml) were significantly elevated compared to the pre-challenge stage (0.065 +/- 0.016 pmol/ml) (p less than 0.01). The bronchial response was not directly related to the increased plasma iLTC4 levels, but the strength of the bronchial response did relate to the plasma iLTC4 levels at the pre-challenge (p less than 0.05) and post-challenge (p less than 0.01) states. The pre-challenge levels are relevant to bronchial reactivity, and the post-challenge levels are relevant to bronchoconstriction caused by exposure to allergens. The in vivo release of LTC4 following exposure to a specific allergen suggests that leukotrienes are important in the pathogenesis of asthma.

Urinary leukotriene E4 after antigen challenge and in acute asthma and allergic rhinitis

The leukotrienes LTC4, D4, and E4 are potent bronchoconstrictor agents and are thought to have an important role in asthma. Urinary LTE4, a stable urinary end-product of LTC4 and LTD4, was measured, by means of high-performance liquid chromatography and radioimmunoassay. LTE4 excretion followed a log-normal distribution in twenty-nine healthy controls, with a geometric mean of 23.8 (95% confidence interval 19.9-28.2) ng/mmol creatinine. Urine was collected from eight atopic subjects for 3 h after antigen inhalation and a control urine collection was made a week later at the same time of day. Urinary LTE4 was significantly higher after antigen challenge than in the control sample (153.7 [87.1-271.3] vs 23.5 [13.7-69.5] ng/mmol creatinine; p less than 0.01). Urinary LTE4 was also measured in twenty patients with severe acute asthma and nine patients with seasonal allergic rhinitis. Mean urinary LTE4 was higher in the asthmatic patients (78.3 [46.5-131.8] ng/mmol creatinine) than in normal subjects (p less than 0.01), although there was substantial overlap into the normal range. The urinary LTE4 values of the rhinitis patients were within the normal range whether or not they had symptoms. LTC4 and LTD4 were also found in bronchoalveolar lavage fluid from one of the three atopic subjects challenged with antigen before lavage, and in a single patient who underwent lavage after admission with severe acute asthma. These studies provide evidence that leukotrienes are released in vivo in man after antigen challenge and in acute asthma.

Effects of salbutamol on bronchoconstriction, bronchial hyperresponsiveness, and leucocyte responses induced by platelet activating factor in man

Platelet activating factor, a potent mediator of inflammation, causes a sustained increase in airway responsiveness to methacholine in man and has been implicated in asthma. The effect of the beta 2 agonist salbutamol (200 micrograms by inhalation) on platelet activating factor induced bronchoconstriction and airway hyperresponsiveness was studied in seven normal subjects in a double blind, crossover study. Salbutamol only partially inhibited the platelet activating factor induced fall in partial flow at 30% of vital capacity (Vp30) (mean percentage fall 47.6 (SEM 7.9); p less than 0.001), whereas it completely blocked a similar degree of bronchoconstriction induced by methacholine. Salbutamol did not prevent the accompanying transient flushing and chest irritation and did not affect the transient neutropenia (mean % fall 69.5 (13.6); p less than 0.01) or the rebound neutrophilia (mean % increase 84.7 (24.7); p less than 0.05) that followed platelet activating factor. There was an increase in the airway responsiveness to methacholine following inhalation of platelet activating factor, the maximum mean change being a three fold increase in PC40 (the provocative concentration of methacholine causing a 40% fall in Vp30) on day 3 (p less than 0.01). Salbutamol caused a significant attenuation of this response on day 3 (p less than 0.02) but had no significant effect on days 1 and 7. Thus a therapeutic dose of salbutamol caused partial inhibition of platelet activating factor induced bronchoconstriction and had a minimal effect on the increased bronchial responsiveness following platelet activating factor.

The effects of inhaled leukotriene E4 on the airway responsiveness to histamine in subjects with asthma and normal subjects

Eight subjects with asthma inhaled on separate occasions leukotriene E4 (LTE4) (6.1 nmol, geometric mean), methacholine, and diluent, which produced an average 41.0%, 37.0%, and 3.3% decrease in specific airway conductance (SGaw), respectively. When the SGaw had recovered to baseline levels at 60 minutes after challenge, the provocative dose of inhaled histamine that produced a 35% decrease in SGaw (PD35) was determined. The histamine PD35 observed after inhalation of LTE4 was 0.46 mumol, and this was significantly less than the histamine PD35 observed after inhalation of methacholine (0.88 mumol; p less than 10(-4) and diluent (0.97 mumol; p less than 10(-5). Histamine responsiveness was also enhanced by a fiftyfold lower dose of LTE4 (p = 0.005), and the enhancement was less than that elicited by the higher dose of LTE4 in the same individuals (p = 0.02). The changes in histamine PD35 during a 1-week period after LTE4 and methacholine challenges were compared in four subjects with asthma. There was a time-dependent enhancement in histamine responsiveness that reached a maximal of 3.5-fold at 7 hours after LTE4. The enhancement had disappeared by 1 week. Similar changes were not observed after methacholine challenge, which elicited the same degree of bronchoconstriction as LTE4. Inhalation of LTE4 in five normal subjects that produced a mean 37.6% decrease in SGaw did not change histamine responsiveness for up to 7 hours. These findings suggest that LTE4 may play a role in the perpetuation of nonspecific airway hyperresponsiveness in bronchial asthma.

Endogenous regulation of bronchomotor tone

Airway smooth muscle responses are elicited in a complex manner through a large variety of endogenous mediators. Mediators augment or inhibit bronchomotor tone at a variety of sites through numerous different mechanisms. Interactions occur among mediators and nerves, muscle, and circulating blood elements or respiratory mast cells. Airway smooth muscle tone further is regulated by postsynaptic mediator-mediator interactions. Substances may circulate through the blood from distal sites to reach their target organ, as with epinephrine in its effects on airway smooth muscle, or may be secreted directly onto airway smooth muscle, as with the secretory products of respiratory mast cells. Recent observations have indicated that some mediators elicit airway contraction at least in part by activating efferent parasympathetic nerves and/or platelets. Direct secretion of minute quantities of mediators from adjacent epithelium or from infiltrating leukocytes may be an essential component of airway hyperreactivity. Complex interactions between the complement and kallikrein cascades have been cited as possible mechanisms of airway hyperresponsiveness. Ultimately, bronchomotor tone is mediated postsynaptically by the availability of calcium to the contractile apparatus of the smooth muscle cell. A role for the phosphoinositide system in membrane transduction and for cyclic adenosine monophosphate in regulating calcium distribution for smooth muscle contraction has been implicated. Mediator-mediator interactions distal to the synaptic cleft have been shown to augment both force and duration of airway smooth muscle contraction in a synergistic fashion. The stimuli eliciting mediator and neurotransmitter secretion, their physiologic significance, and the homeostatic infrastructure of these interactions are areas of promising investigation that require further definition.

Characterization of leukotriene C4 synthetase in mouse peritoneal exudate cells

Cell lysates of mouse peritoneal macrophages, in the presence of reduced glutathione, converted leukotriene LTA4 to LTC4, and neither LTD4 nor LTE4 was detected. Therefore, like cultured rat basophilic leukemia cells (RBL cells), the peritoneal macrophage contains LTC4 synthetase and appears to contain little, if any, gamma-glutamyl transpeptidase. When LTA4 was added to subcellular fractions of mouse macrophage lysate, the highest specific activity of LTC4 synthetase (nmol LTC4/mg protein per 10 min) was associated with the particulate or membrane fractions (i.e., 10(4) and 10(5) X g pellets). The 10(5) X g supernatant contains approx. 1% of the specific activity and 6% of the total LTC4 synthetase activity compared with that of the 10(5) X g pellet. Conversely, the 10(5) X g supernatant had four-times more specific activity and 19-times more total GSH S-transferase activity than did the 10(5) X g pellet when evaluated using 1-chloro-2,4-dinitrobenzene (DNCB) as the substrate. LTA4 was converted to LTC4 by the membrane enzyme LTC4 synthetase in a dose-dependent manner at low LTA4 concentrations (3-50 microM) and reached a plateau of approx. 30 microM LTA4 using the macrophage 10(5) X g pellet as an enzyme source. The apparent Km value of LTC4 synthetase for LTA4 was estimated to be 5 microM based on Lineweaver-Burk plots. Enzyme in the 10(5) X g supernatant produced negligible quantities of LTC4 (1% or less of the particulate fractions) over a wide range of LTA4 concentrations. However, an enzyme in the 10(5) X g supernatant fraction presumed to be GSH S-transferase effectively catalyzes the conjugation of glutathione (GSH) with the aromatic compound DNCB. The apparent Km value of GSH S-transferase for DNCB was estimated to be 1.0-1.5 mM. On the other hand, enzyme from the membrane fraction (i.e., 10(5) X g pellet) catalyzed this reaction at a negligible rate over a wide range of DNCB concentrations. The apparent Km value of LTC4 synthetase for GSH was estimated to be 0.36 mM and the corresponding Km value estimated for the glutathione S-transferase was 0.25-0.76 mM. These values indicate similar kinetics for GSH utilization by both enzymes. These Km values are also significantly lower than the intracellular GSH levels of 2 to 5 mM. Therefore, it is suggested that the substrate limiting LTC4 synthetase activity is LTA4 and not GSH. Our results indicate that LTC4 synthetase from mouse peritoneal macrophages is a particulate or membrane-bound enzyme, as was reported by Bach et al.(ABSTRACT TRUNCATED AT 400 WORDS)

Release of leukotrienes in patients with bronchial asthma

To investigate whether leukotrienes (LTs) are released into the bronchial fluid of patients with symptomatic asthma, bronchial lavage was carried out in 17 patients with mild to severe asthma and nine healthy subjects without asthma. LTE4 was detected in 15 of the 17 patients with asthma with reverse-phase high-performance liquid chromatography. The identify of LTE4 was confirmed by ultraviolet spectrometry and by positive ion fast atom-bombardment mass spectrometry. LTD4 was found in two patients and 20-OH-LTB4 in 12 patients. No LTs were detectable in the lavage fluid from any of the healthy subjects without asthma. The finding of LTs in bronchial lavage fluid from the patients with asthma despite bronchodilator and/or corticosteroid therapy suggests that these compounds may be important in asthma. However, the presence of significant quantities of LTE4 in patients with mild asthma requiring only intermittent bronchodilator therapy for control and the lack of correlation between LTE4 and pulmonary function also suggests that other factors may be important in determining the net end organ response. The present study points to the importance of studying the whole spectrum of mediators that are released. Analysis of bronchial lavage fluid may be useful in determining the relative role of these mediators and the effect of pharmacologic intervention.

Effect of azelastine on bronchoconstriction induced by histamine and leukotriene C4 in patients with extrinsic asthma

Azelastine, a new oral agent with antiallergic and antihistamine properties, has been shown to inhibit the effect of histamine and leukotriene (LT) in vitro, though not a specific leukotriene receptor antagonist. The effect of both a single dose (8.8 mg) and 14 days' treatment (8.8 mg twice daily) with azelastine on bronchoconstriction induced by LTC4 and histamine has been examined in 10 patients with mild asthma in a placebo controlled, double blind, crossover study. LTC4 and histamine were inhaled in doubling concentrations from a dosimeter and the results expressed as the cumulative dose (PD) producing a 20% fall in FEV1 (PD20FEV1) and 35% fall in specific airways conductance (PD35sGaw). The single dose of azelastine produced a significantly greater FEV1 and sGaw values than placebo at 3 hours, but this bronchodilator effect was not present after 14 days of treatment. Azelastine was an effective H1 antagonist; after a single dose and 14 days' treatment with placebo the geometric mean PD20FEV1 histamine values (mumol) were 0.52 (95% confidence interval 0.14-1.83) and 0.54 (0.12-2.38), compared with 22.9 (11.5-38.3) and 15.2 (6.47-35.6) after azelastine (p less than 0.01 for both). LTC4 was on average 1000 times more potent than histamine in inducing bronchoconstriction. Azelastine did not inhibit the effect of inhaled LTC4; the geometric mean PD20FEV1 LTC4 (nmol) after a single dose and 14 days' treatment was 0.60 and 0.59 with placebo compared with 0.65 and 0.75 with azelastine. The PD35sGaw LTC4 was also unchanged at 0.66 and 0.73 for placebo compared with 0.83 and 0.74 for azelastine. Thus prolonged blockade of H1 receptors did not attenuate the response to LTC4, suggesting that histamine and LTC4 act on bronchial smooth muscle through different receptors. Four patients complained of drowsiness while taking azelastine but only one who was taking placebo and three patients complained of a bitter, metallic taste while taking azelastine.

In vivo and in vitro human airway responsiveness to leukotriene D4 in patients without asthma

We have examined the in vivo airway responsiveness to leukotriene (LT) D4 in 11 patients without asthma who were to undergo thoracotomy and compared this responsiveness with in vitro sensitivity and in vitro contractility of bronchial smooth muscle to LTD4. In vivo responses were measured by the provocation concentration producing a 10% fall in FEV1, a 30% fall in partial flow rate at 30% of total lung capacity from a partial forced expiratory maneuver, and a 35% fall in specific airway conductance. In vitro sensitivity was measured as the concentration of LTD4 producing a 50% of maximum contraction and maximum-induced tension. The smooth muscle content of the bronchial strip was estimated microscopically, and the absolute quantity of muscle strip was compared with the maximum tension generated by that bronchial smooth muscle sample. In vivo results varied over 2 log units, and in vitro sensitivity, over 1 log unit. The absolute amount of smooth muscle present in bronchial strips correlated with maximal LTD4-induced tension. There was no relationship between in vivo responsiveness and in vitro sensitivity nor between in vivo responsiveness and maximum tension generated, even when this was corrected for the proportion of smooth muscle present in each bronchial strip. These results suggest that in vivo airway responsiveness to LTD4 is not determined by airway smooth muscle sensitivity or its ability to generate tension alone. Other factors must be influencing the response of the airway to LTD4. Nevertheless, the finding of a positive correlation between the absolute amount of smooth muscle present in bronchial strips and maximal LTD4-induced tension suggests that hypertrophy and/or hyperplasia of airway smooth muscle may contribute to in vivo airway hyperresponsiveness.

Arachidonic acid metabolism in alveolar macrophages. A comparison of cells from healthy subjects, allergic asthmatics, and chronic bronchitis patients

Arachidonic acid (AA) metabolism was studied in preparations of purified human alveolar macrophages (AM) from healthy subjects (HS = 5), allergic asthmatics (ABA = 9) and chronic bronchitis patients (CB = 7). AM incubated for 6 to 24 h in the presence of labeled AA and for an additional 5 h without labeled AA, released cyclooxygenase and lipoxygenase products into the medium. The study of the metabolites showed that the most abundant sulfidopeptide-leukotriene, was LTD4 as analyzed by TLC and identified by reversed phase HPLC. The release of LTD4 was time-dependent but it was shown to be significantly higher (p less than 0.01) in AM from ABA or CB than in those from HS. TLC analysis of radioactivity distributed between the different lipid classes at 24 h revealed more labeling in AM phospholipids from ABA and CB than in those from HS, and was reflected in phosphatidylethanolamine and phosphatidylinositol species. After 5 h without labeled AA the distribution was marked, by different in triglycerides, with a greater proportion of radioactivity in the control cells than in the pathological macrophages. Thus, the pathological lung state is an important factor affecting the release of LTD4 and the distribution of AA into cellular phospholipids. The differences observed between HS and ABA or CB phospholipid distribution suggests the existence of 2 different sources of AA release, one for inflammatory macrophages and another for quiescent cells.

Nebulization and selective deposition of LTD4 in human lungs

The process of nebulization and deposition of LTD4 was studied in detail. The concentration of LTD4 in a saline solution decreased by approximately 90% after 2 min of nebulization in a DeVilbiss 35B ultrasonic nebulizer. This decrease was prevented by diluting LTD4 in a phosphate buffer, pH 7.4. Nebulization of tritiated LTD4 in this phosphate buffer did not cause any appreciable deterioration of the leukotriene, as demonstrated by an unchanged ratio between radioactivity and LTD4 concentration in the test solution before and after nebulization as well as in the condensed aerosol. The aerosol generated by the DeVilbiss 35B ultrasonic nebulizer was shown to generate particles with a mass median diameter of 1.3 microns (dry particle size). Interposition of a settling bag reduced the amount of large particles, reducing the mass median diameter to 0.84 microns (dry particle size). Nine healthy volunteers were challenged on separate days with 40 nmol LTD4 or 100 mumol histamine, and the changes in FEV1 and partial flow volume curves initiated at 50% of vital capacity (Vmax30) were measured. A relative diffuse deposition pattern was ensured by inhalation via a settling bag. These results were compared to challenges with a relatively central deposition pattern as ensured by inhalation directly from the nebulizer with brisk inhalation maneuvers. The diffuse deposition pattern caused minimal changes in FEV1 but pronounced effect in Vmax30. The effects of LTD4 and histamine on FEV1 and Vmax30 changed in parallel when the deposition of the mediators was changed to a more central pattern. This indicates that the two mediators do not differ with respect to any selective effects on different parts of the airways.

Critical considerations in the development of an assay for sulfidopeptide leukotrienes in plasma

A sensitive and specific assay has been developed for measurement of total sulfidopeptide leukotrienes (LT) in plasma. LTC4 and LTD4 in plasma are converted to LTE4 which is then extracted by C18 Sep-Pak binding and elution. Total LTE4 is resolved by reverse phase high performance liquid chromatography (RP-HPLC) and quantitated by radioimmunoassay (RIA). A [3H]LTE4 internal standard is added to the starting plasma sample to allow overall recovery to be calculated and to define the fractions from RP-HPLC to be assayed for LTE4-like immunoreactivity. The correlation between the measured increase in LTE4 concentration after addition of incremental amounts of LTC4 and LTE4 to plasma was 0.989 and 0.978, respectively, with slopes of 1.05 and 1.11. Addition of 51 pg/ml LTE4 to 5 ml plasma was detectable; the measured increase was 48 +/- 12 pg/ml (mean +/- SE, n = 7). The intra-assay coefficient of variation for 341 pg/ml of added LTC4 was 3.2% (n = 6). Sulfidopeptide leukotrienes could not be detected in blood samples taken from 12 normal volunteers in whom the theoretical detection limit, calculated from the sensitivity of the RIA, the overall recovery of LTE4, and the volume of plasma extracted, was 83 +/- 4 pg LTE4/ml plasma (0.19 +/- 0.01 pmol sulfidopeptide leukotriene/ml plasma; mean +/- SE).

The role of arachidonic acid metabolites in local and systemic inflammatory processes

Leukotrienes are synthesised from arachidonic acid via the 5-lipoxygenase pathway in neutrophils, eosinophils, monocytes/macrophages, basophils and certain mast cell populations. Their synthesis is closely regulated by several known factors and the cells which contain 5-lipoxygenase do not all possess the capability to synthesise all of the leukotrienes. Neutrophils produce leukotriene B4, which attracts other neutrophils, whereas the leukotriene C4, produced by eosinophils, increases the contractile activity of smooth muscle. Monocytes/macrophages are able to produce both of these leukotrienes. Receptor sites for leukotriene B4 have been identified on monocytes and neutrophils and receptors for leukotriene D4, a cleavage product of leukotriene C4, have been defined in pulmonary tissue. In animals, sulphidopeptide leukotrienes have been shown to cause potent vasoconstriction resulting in increased blood pressure and increased vascular permeability leading to hypovolaemia. These leukotrienes also depress renal (in animals) and pulmonary (in animals and humans) function, the latter probably as a result of effects on peripheral rather than central airways. In patients with mild asthma, however, there is no differential activity of this type. The sulphidopeptide leukotrienes caused wheal and flare when administered intradermally in healthy volunteers, which was of considerably longer duration than that induced by prostaglandin D2. Conversely, leukotriene B4 caused accumulation of neutrophils in the absence of wheal and flare. Studies into the effects of dietary fish oil showed that 2 constituents, docosahexanoic acid and eicosapentaenoic acid (EPA), inhibit the conversion of arachidonic acid by cyclo-oxygenase, but not by 5-lipoxygenase. Furthermore, 5-lipoxygenase converts EPA to a pentene series of leukotrienes and the sulphidopeptide derivatives possess similar activity to their tetrameric counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of prostaglandin D2 into human airways during acute antigen challenge

Among the many possible mediators of the early asthmatic response, prostaglandin D2, a bronchoconstrictor, is the principal cyclooxygenase metabolite of arachidonic acid that is released upon the activation of mast cells and is also synthesized by human alveolar macrophages. We performed bronchoalveolar lavage in five patients with chronic stable asthma, before and up to nine minutes after local provocative challenge with Dermatophagoides pteronyssinus. The lavage fluid was analyzed for products of arachidonic acid metabolism. Prostaglandin D2 levels in all five patients rose an average of 150-fold, from less than 8 to 332 +/- 114 pg per milliliter (mean +/- SEM; P less than 0.050), after local instillation of the antigen. Levels of 15-hydroxyeicosatetraenoic acid, which may also have a role in the pulmonary allergic response, were detectable in lavage fluid before challenge and increased after provocation with the antigen in four of the five patients. The activity of beta-glucuronidase, an enzyme released by macrophages and mast cells upon stimulation, tended to increase in the lavage fluid after provocation in all patients. These studies provide evidence that the release of prostaglandin D2 into the airways is an early event after the instillation of D. pteronyssinus in patients who are sensitive to this antigen.

Airway responsiveness to leukotrienes C4 and D4 and to methacholine in patients with asthma and normal controls

Leukotrienes C4 and D4 may serve as chemical mediators in asthma. Although patients with asthma are known to be hyperresponsive to the bronchoconstrictive effects of histamine and methacholine, whether the same is true for the leukotrienes is controversial. We compared the airway responses to methacholine and to leukotrienes C4 and D4 in 12 asthmatic patients and 6 controls. We found that the patients were more responsive to the leukotrienes than the controls, and we observed a linear correlation between airway response to methacholine and that to leukotriene C4 (r = 0.68, P less than 0.01) and D4 (r = 0.79, P less than 0.001). However, relative to the airway response to methacholine, the response to the leukotrienes was much greater in the controls than in the patients. Furthermore, the asthmatic subjects who were most responsive to methacholine had the lowest relative airway response to both leukotrienes. Thus, the patients with the greatest airway responsiveness to methacholine paradoxically showed the lowest relative airway response to the leukotrienes. In contrast, this difference in relative airway responses has not been observed between methacholine and other bronchoconstrictor mediators, such as histamine. Although no adequate explanation for these observations has yet emerged, our data suggest that leukotrienes C4 and D4 are unique bronchoconstrictors with a possible role in the pathogenesis of asthma.

Ionophore-dependent generation of eicosanoids in human dispersed lung cells. Modulation by 6,9-deepoxy-6,9-(phenylimino)-delta 6,8-prostaglandin I1 (U-60,257)

6,9-Deepoxy-6-9-(phenylimino)-delta 6,8-prostaglandin I1, a prostacyclin analogue reported to inhibit sulphidopeptide leukotriene formation in animals, was evaluated for its pharmacological activity against eicosanoid and histamine release from human dispersed lung cells (HDLC). In the absence of drug, challenge of HDLC with A23187 (2.5 microM) increased immunoreactive eicosanoid generation by factors of 7.6 for prostaglandin (PG) D2, 9.1 for TXB2, 3.2 for PGF2 alpha, 2.0 for 5-HETE, 6.3 for LTC4, in association with a twofold increase in histamine release. When exogenous [14C]-arachidonic acid was added to HDLC simultaneously with A23187 challenge, radiolabelled eicosanoids were recovered in the supernatant, but on separating the products by radio-thin layer chromatography the proportions of individual eicosanoids were not significantly different from unchallenged cells. With endogenous arachidonate, U-60,257 was a potent inhibitor of i-LTC4 generation at 1 microM, but between 3 and 300 microM there was a concentration-related reversal of this inhibition. The effects of U-60,257 on the metabolism of exogenous [14C]-arachidonic acid were also studied. Under these circumstances the drug was a potent inhibitor of both 5-HETE and 5,12-diHETE formation, without significantly affecting the formation of other mono-HETES. In agreement with previous endogenous substrate experiments there was a concentration-dependent inhibition of TxB2 formation from exogenous arachidonic acid. These findings highlight the complex pharmacological actions of U-60,257 which appear dependent on the source of arachidonic acid substrate.

Leukotriene-associated toxic oxygen metabolites induce airway hyperreactivity

The effect of toxic oxygen metabolite scavengers was examined in a guinea pig trachealis model of leukotriene (LTD4)-induced synergism upon histamine contractures. Under both physiologic (2.5 mM) and low (OmM) extracellular calcium conditions, LTD4 (10(-7) to 10(-9) M) potentiated histamine isometric tension responses. This LTD4-induced histamine hyperresponse was inhibited by pretreatment with superoxide dismutase. Inhibition of LTD4 receptor binding by FPL 55712 (10(-5) M) also aborted this interaction. Actual trachealis superoxide anion (O2-) generation by LTD4 was observed with a maximal release of 15 nM O2-/CPK unit X 10(-2) over 60 min. Phorbol myristate acetate (PMA) also generated O2- in this preparation. Trachealis muscle hyperreactivity to histamine induced by 10(-8) M LTD4 assayed in OmM (Ca++)E was not induced by PMA. It is concluded that exogenous LTD4 activates toxic oxygen metabolites which interact to induce an acquired hyperreactivity to agonist histamine in trachealis smooth muscle.