The potential roles of leukotrienes in bronchial asthma

Exploration of benzamidochromenone derivatives with conformational restrictor as interleukin-5 inhibitors

Novel amidochromen-4-one analogs 8a-k and 9a-f were prepared and studied for their IL-5 inhibitory activity. Among the synthesized compounds, (6-benzamido-2-cyclohexyl-4-oxo-4H-chromen-3-yl)methyl acetate (8a, 95% inhibition at 30 μM, IC50=6.1 μM) exhibited potent IL-5 inhibitory activity. The conformational restrictor at position 2 like bulky cyclohexyl group is favorable for the formation of effective conformer of side chain small ester like acetoxymethyl at position 3 of these chromenone analogs 8. In addition the hydrophobic planarity of benzamido group at position 6 should be important for the potent IL-5 inhibitory activity. Since replacing acetoxymethyl moiety with hydroxymethyl group at position 3 of chromenone decreases the activity, which indicates that the location of hydrogen bonding group should be near 4 atom distances away from chromenone ring is more optimum for the activity. Therefore, these benzamidochromen-4-one analogs 8 are novel scaffold for finding potent interleukin-5 inhibitors.

Critical role of interleukin-5 in the development of a mite antigen-induced chronic bronchial asthma model

OBJECTIVE AND DESIGN

Asthma is associated with eosinophilic airway inflammation and characterized by enhanced airway sensitivity. Interleukin (IL)-5 plays an important role in the pathogenesis of asthma. The involvement of IL-5 receptor-mediated cellular signals in the pathogenesis of a mite antigen-induced chronic asthma model was investigated.

SUBJECTS

In this study, 48 female C57BL/6J (WT) mice and IL-5 receptor-deficient (IL-5RKO) mice were used.

TREATMENT

Mite antigen (50 μl) was intranasally administered 13 times to WT and IL-5RKO mice.

METHODS

Airway hypersensitivity (Mch PC200) and specific antigen exposure tests were performed, and lung tissue, bronchoalveolar lavage fluid (BALF), and blood were collected to investigate the asthma pathology and differences in the local pulmonary levels of cytokines and chemokines.

RESULTS

Airway sensitivity was enhanced and antigen-specific airway resistance was increased in WT mice. In addition, the number of eosinophils and Th2 cytokine levels in the BALF were increased. In contrast, IL-5RKO mice did not acquire the asthma pathology, such as antigen-specific airway resistance and eosinophilic airway inflammation. Mch PC200 was significantly correlated with cysteinyl leukotriene levels in WT mice.

CONCLUSION

These findings suggested that both IL-5 induced eosinophils and cysteinyl leukotrienes are involved in the pathology of this mite antigen-induced chronic asthma model.

Pharmacological modulation of the inflammatory actions of platelets

Patients with inflammatory diseases often exhibit a change in platelet function, with these alterations being clearly distinct from the well-characterized role of platelets in haemostasis and thrombosis. It has recently been revealed that platelets can behave as innate inflammatory cells in immune responses with roles in leukocyte recruitment, migration into tissues, release of cytotoxic mediators, and in tissue remodelling following injury.Platelets exhibit a wide range of receptors for mediators involved in the inflammatory pathway and the immune response (Fig. 1). These include purinergic receptors, selectins, integrins, toll-like receptors, immunoglobulins, and chemokine receptors, but the precise role platelets play in the inflammatory process is still under investigation. Nevertheless, given that many of these receptors are distinct from those involved in thrombosis and haemostasis, this raises the real possibility of targeting these receptors to regulate inflammatory diseases without compromising haemostasis.

Structural analysis of leukotriene C4 isomers using collisional activation and 157 nm photodissociation

The fragmentation of 5-hydroxy-6-glutathionyl-7,9,11,14-eicosatetraenoic acid [leukotriene C4 or LTC4 (5, 6)] and its isomeric counterpart LTC4 (14, 15) were studied by low and high-energy collisional induced dissociation (CID) and 157 nm photofragmentation. For singly charged protonated LTC4 precursors, photodissociation significantly enhances the signal intensities of informative fragment ions that are very important to distinguish the two LTC4 isomers and generates a few additional fragment ions that are not usually observed in CID experiments. The ion trap enables MSn experiments on the fragment ions generated by photodissociation. Photofragmentation is found to be suitable for the structural identification and isomeric differentiation of cysteinyl leukotrienes and is more informative than low or high-energy CID. We describe for the first time the structural characterization of the LTC4 (14, 15) isomer by mass spectrometry using CID and 157 nm light activation methods.

The cytochromes P450 (CYP) response to allergic inflammation of the lung

The expression of the mouse Cyp family and key inflammatory mediators were examined in a model of ovalbumin (OVA)-induced allergic airway disease. The expression of IL-4, IL-13 and Ccl11 increased during the acute phase of allergic inflammation and decreased with its resolution. Interestingly, the expression of Ccl20 was increased during the resolution phase. The response of the Cyp gene family to the development of allergic inflammation was differential and correlated with the evolution of the inflammatory response. During the acute inflammatory phase the mRNA levels of Cyp2e1, Cyp2f2, Cyp2j6, Cyp4b1, Cyp8a1 and Cypor were decreased while the mRNA levels of Cyp4f18, Cyp5a1 and Cyp7b1 were elevated. With resolution of the inflammation the expression patterns returned to normal. These changes suggest that the Cyp family may play a role in the allergic inflammation by modulating the metabolism of xenobiotics and endogenous compounds such as LTB4, TXA1, PGI2 and native anti-glucocorticoids.

Secretory phospholipases A2 stimulate mucus secretion, induce airway inflammation, and produce secretory hyperresponsiveness to neutrophil elastase in ferret trachea

Secretory phospholipases A(2) (sPLA(2)) are increased in the bronchoalveolar lavage fluid of patients with asthma and acute respiratory distress syndrome. Intratracheal sPLA(2) instillation induces acute lung injury in the rat and guinea pig. We hypothesized that sPLA(2) would stimulate mucus secretion in vitro and that intratracheal sPLA(2) exposure would induce mucus hypersecretion and airway inflammation in the ferret trachea in vivo. In vitro, porcine pancreatic sPLA(2) at a concentration of 0.5 or 5 U/ml significantly increased mucous glycoconjugate (MG) secretion from the excised ferret trachea. P-bromophenacylbromide (a sPLA(2) inhibitor), quercetin (a lipoxygenase inhibitor), or MK-886 (a 5-lipoxygenase inhibitor), each at 10(-4) M, significantly reduced sPLA(2)-induced MG secretion. sPLA(2)-stimulated MG secretion was decreased in Ca(2+)-free medium. In vivo, ferrets were intubated for 30 min once per day for 3 days using an ETT coated with 20 units of porcine pancreatic sPLA(2) mixed in water-soluble jelly. Constitutive MG secretion increased 1 day after sPLA(2) exposure and returned to control 5 days later. Human neutrophil elastase (HNE) at 10(-8) M increased MG secretion in the sPLA(2)-exposed trachea compared with that in the control trachea, but methacholine at 10(-7) M did not. sPLA(2)-induced secretory hyperresponsiveness continued for at least 5 days after sPLA(2) exposure ended. sPLA(2) increased tracheal inflammation, MG secretion, and secretory hyperresponsiveness to HNE probably through enzymatic action rather than by activation of its receptor.

Leukotriene D(4)-induced Rho-mediated actin reorganization in human bronchial smooth muscle cells

We investigated the role of cysteinyl leukotriene (CysLT) receptors on leukotriene D(4)-induced actin reorganization and the signaling pathways of the response in human bronchial smooth muscle cells. The effects of leukotriene D(4) on actin reorganization in human bronchial smooth muscle cells were evaluated by dual-fluorescence labeling of filamentous (F) and monomeric (G) actin with fluorescein isothiocyanate (FITC)-labeled phalloidin and Texas Red-labeled DNase I, respectively. Leukotriene D(4) (100 nM) induced actin reorganization in the presence and absence of extracellular Ca(2+). The CysLT type 1 (CysLT(1)) receptor antagonist ONO 1078 (4-oxo-8(-)[p-(4-phenylbutyloxy) benzoylamino]-2-(tetrazol-5-yl)-4H-1-benzopyran hemihydrate) inhibited leukotriene D(4)-induced actin reorganization. Pretreatment with pertussis toxin, C3 exoenzyme, or tyrosine kinase inhibitors significantly reduced leukotriene D(4)-induced actin reorganization. However, phosphatidylinositol-3-kinase and protein kinase C inhibitors had little effect on these responses. These results suggest that leukotriene D(4)-induced actin reorganization in human bronchial smooth muscle cells is extremely dependent on the CysLT(1) receptor coupled with pertussis toxin-sensitive G protein, Rho GTPases and tyrosine phosphorylation pathways.

Difference in urinary LTE4 and 11-dehydro-TXB2 excretion in asthmatic patients

Bronchoconstrictor cysteinyl leukotrienes (LT) and thromboxane (TX) A2 have been implicated in the pathogenesis of asthma. Determination of urinary leukotriene E4 (LTE4) and 11-dehydro-TXB2 levels are often used to assess cysteinyl LT and TXA2 production in humans. To define the potential role in the pathogenesis of asthma, we investigated the urinary LTE4 and 11-dehydro-TXB2 levels. LTE4 and 11-dehydro-TXB2 levels were determined using liquid chromatography/tandem mass spectrometry (LC/MS) and gas chromatography/mass spectrometry (GC/MS), respectively. Urinary LTE4 levels in asthmatic patients (192 +/- 122 pg/mg creatinine, n = 14) were significantly higher (P < 0.005) than those in healthy volunteers (55 +/- 16 pg/mg creatinine, n = 13), but no significant difference in 11-dehydro-TXB2 levels was observed. A significant inverse correlation (r = -0.821, P < 0.005) was found between urinary LTE4 levels and the forced expiratory volume in 1 s (FEV1) but no significant correlation was observed between urinary 11-dehydro-TXB2 levels and FEV1. The present findings suggest that cysteinyl LTs play a more important role in the pathogenesis of asthma than TXA2.

Airway epithelial cells, cytokines, and pollutants

The airway epithelium is a complex physicochemical barrier that plays a pivotal role in host defense. Epithelial cells have been shown to be a rich source of several classes of modulatory compounds, of which the cytokines form the largest group and possibly play the most important role in the etiology of airway disease. Evidence suggests that there are differences in the airway epithelial cells of individuals with and without respiratory disease, both with regard to (1) their capacity to express and release different types and quantities of specific cytokines and (2) their reactivity to inhaled irritants. Consequently, it is tempting to speculate that differences in epithelial cell function are an important determinant of the predisposition to respiratory disease. However, whether the differences are a result of an intrinsic defect, an acquired property due to the disease process itself, or a combination of the two, remains to be determined. In view of advances that have been made in the understanding of the putative underlying mechanisms in airway diseases, it should be possible to formulate novel therapeutic agents in the form of specific monoclonal antibodies directed against specific proinflammatory cytokines. Mills PR, Davies RJ, Devalia JL. Airway epithelial cells, cytokines, and pollutants.

Randomized placebo-controlled study comparing a leukotriene receptor antagonist and a nasal glucocorticoid in seasonal allergic rhinitis

Allergic rhinitis is an inflammatory disorder associated with local leukotriene release during periods of symptoms. Therefore, it has been suggested that antileukotrienes may be beneficial in the treatment of this disease. Leukotriene receptor antagonists have recently become available for asthma treatment, but little is known of their effects on allergic rhinitis. We have evaluated the effects of the leukotriene receptor antagonist zafirlukast versus placebo in patients with allergic rhinitis during the grass pollen season, using the nasal glucocorticoid beclomethasone dipropionate (BDP) as a positive treatment control. Thirty-three patients with seasonal allergic rhinitis were in a double-blind, double-dummy fashion randomized to treatments with oral zafirlukast (20 mg twice a day), intranasal beclomethasone dipropionate (200 microg twice a day), or placebo. The treatment was initiated 3 wk prior to the expected beginning of the grass pollen season. Patients completed a daily symptom-score list for sneezing, rhinorrhea, nasal itch, and nasal blockage during the 50-d treatment period. Nasal biopsies for quantification of local tissue eosinophilia (immunohistochemistry; EG2) were taken 1 mo before initiation of treatment and immediately after the peak of grass pollen season. Patients receiving treatment with zafirlukast had degrees of nasal symptoms similar to those in the placebo group, whereas the BDP group had significantly less symptoms compared with both treatments (p = 0.01 and p = 0.005, respectively). The numbers of activated eosinophils in the nasal tissue increased significantly during the pollen season in both the zafirlukast and the placebo groups, but not in the BDP group. These results obtained with a limited number of patients do not support any clinical efficacy of regular treatment with an oral antileukotriene in seasonal allergic rhinitis but rather favor the use of a nasal glucocorticoid.

Neutral endopeptidase 3.4.24.11 inhibition potentiates the inhibitory effects of type-C natriuretic peptide on leukotriene D4-induced airway changes

1. Microvascular leakage, a primary feature of inflammation, is well known for worsening the asthmatic condition. Gene expression of and a specific receptor for type-C natriuretic peptide (CNP), initially considered a neuropeptide, have been detected in the human vascular wall and secretion of CNP from vascular endothelial cells has recently been demonstrated. These facts suggest the presence of a vascular natriuretic peptide system and led us to expect that CNP may act beneficially on airway microvascular leakage in asthma. In the present study, we investigated the effects of CNP against leukotriene (LT) D4-induced airway microvascular leakage and bronchoconstriction and how these effects were potentiated by thiorphan, a potent neutral endopeptidase 3.4.24.11 (NEP) inhibitor. 2. Anaesthetized male guinea-pigs, ventilated via a tracheal cannula, were placed into a plethysmograph for 10 min, in order to measure pulmonary mechanics and mean blood pressure, after challenge with 2 micrograms/kg LTD4 and then the extravasation of 20 mg/kg Evans blue dye into airway tissue was investigated to indicate and evaluate microvascular leakage. 3. Intravenous administration of CNP (100, 300 and 1000 micrograms/kg) significantly inhibited the LTD4-induced microvascular leakage and bronchoconstriction in a dose-dependent manner. These inhibitory effects were enhanced by pretreatment with 20 mg/kg thiorphan, suggesting the important role of NEP in the pulmonary metabolism of CNP. 4. We believe that these results are encouraging for the further investigation of the therapeutic applications of exogenous CNP in asthma.

Effects of LTD4 on human airway smooth muscle cell proliferation, matrix expression, and contraction In vitro: differential sensitivity to cysteinyl leukotriene receptor antagonists

The cysteinyl leukotrienes (CysLTs) mimic many of the features of asthma and are implicated in its pathophysiology. Little, however, is known about the effects of the CysLTs on airways remodeling. In this study the effects of leukotriene D4 (LTD4) on human airway smooth muscle (HASM) cell proliferation and expression of extracellular matrix proteins were investigated. LTD4 (0.1-10 microM) alone had no effect on DNA synthesis in HASM. LTD4, however, markedly augmented proliferation induced by the mitogen, epidermal growth factor (EGF, 1 ng/ml). The potentiating effect of LTD4 (1 microM) on EGF-induced DNA synthesis was abolished by pranlukast (1 microM) or pobilukast (30 microM), but unaffected by zafirlukast (1 microM). In contrast, pranlukast (pKB = 6.9), pobilukast (pKB = 7.0), and zafirlukast (pKB = 6.5) had equivalent potencies for inhibition of LTD4-induced contraction in human bronchus. LTD4 (0.1 or 10 microM) did not increase the total messenger RNA expression of the extracellular matrix proteins (pro-alpha[I] type I or alpha1[IV] type IV collagen), elastin, biglycan, decorin, and fibronectin, and did not influence tumor growth factor-beta (10 ng/ml)-induced effects on the expression of these proteins in HASM cells. These data indicate that LTD4 augments growth factor-induced HASM proliferation but does not alter the expression of various extracellular matrix components. The observed differences in sensitivity to the antagonists suggests that the former phenomenon may be mediated by a CysLT receptor distinct from that which mediates LTD4-induced HASM contraction. Collectively, these results provide preliminary evidence that CysLTs may play a role in airways remodeling in asthma.

The mechanism of IL-5 signal transduction

Cytokines are important regulators of hematopoiesis. They exert their actions by binding to specific receptors on the cell surface. Interleukin-5 (IL-5) is a critical cytokine that regulates the growth, activation, and survival of eosinophils. Because eosinophils play a seminal role in the pathogenesis of asthma and allergic diseases, an understanding of the signal transduction mechanism of IL-5 is of paramount importance. The IL-5 receptor is a heterodimer of alpha- and beta-subunits. The alpha-subunit is specific, whereas the beta-subunit is common to IL-3, IL-5, and granulocyte/macrophage colony-stimulating factor (GM-CSF) receptors and is crucial for signal transduction. It has been shown that there are two major signaling pathways of IL-5 in eosinophils. IL-5 activates Lyn, Syk, and JAK2 and propagates signals through the Ras-MAPK and JAK-STAT pathways. Studies suggest that Lyn, Syk, and JAK2 tyrosine kinases and SHP-2 tyrosine phosphatase are important for eosinophil survival. In contrast to their survival-promoting activity, Lyn and JAK2 appear to have no role in eosinophil degranulation or expression of surface adhesion molecules. Raf-1 kinase, on the other hand, is critical for eosinophil degranulation and adhesion molecule expression. Btk is involved in IL-5 stimulation of B cell function. However, it does not appear to be important for eosinophil function. Thus a clear segregation of signaling molecules based on their functional importance is emerging. This review describes the signal transduction mechanism of the IL-3/GM-CSF/IL-5 receptor system and compares and contrasts IL-5 signaling between eosinophils and B cells.

Effects of uroguanylin and guanylin against antigen-induced bronchoconstriction and airway microvascular leakage in sensitized guinea-pigs

Uroguanylin and guanylin are isolated mainly from the gastrointestinal tract and are activators of guanylyl cyclase C receptor (GC-C), which mediates the production of intracellular cyclic guanosine 3',5'-monophosphate (cyclic GMP). The bronchodilator effects of agents that raise cyclic GMP levels, such as atrial natriuretic peptide, have been reported, and uroguanylin mRNA has recently been detected in extra-gastrointestinal tissues, including the lung, suggesting their role in pulmonary activity. In the first step of this study, we examined the relaxant effects of uroguanylin and guanylin on isolated tracheal smooth muscle of guinea-pigs, and measured tissue cyclic GMP levels by means of enzymeimmunoassay. Uroguanylin produced concentration-dependent relaxant effects on resting tone and significant elevated cyclic GMP levels. Guanylin produced the same, but less potent, effects. In this study, we first investigated the effects of uroguanylin and guanylin on antigen-induced bronchoconstriction and airway microvascular leakage in actively sensitized guinea-pigs. Anesthetized male guinea-pigs, ventilated via a tracheal cannula, were placed in a plethysmograph to measure pulmonary mechanics for 10 min after challenging with 1 mg/kg of ovalbumin. Evans blue dye was then extravasated into their airway tissues to measure microvascular leakage. Intravenous pretreatment with uroguanylin significantly inhibited ovalbumin-induced bronchoconstriction and microvascular leakage in a dose-dependent manner. These inhibitory effects were mimicked by 8-bromoguanosine 3', 5'-cyclic monophosphate. This study is the first to show that uroguanylin not only had a potent bronchodilatory effect but also inhibited microvascular leakage. These results encouraged us to continue the above experimental and clinical studies in bronchial asthma.

The effects of a novel sulphidopeptide leukotriene antagonist, BAY x7195, against elicited bronchoconstriction in the anaesthetized guinea-pig

1. The novel leukotriene antagonist Bay x7195, has been evaluated against bronchoconstriction induced by leukotriene D4 (LTD4), the thromboxane A2 (TXA2) mimetic U46619, histamine and antigen, in the guinea-pig in vivo by use of a modified Konzett-Rössler preparation. 2. LTD4, given intravenously (i.v.) at 1 or 3 microg kg(-1) in the presence of indomethacin and sotalol, caused a 50-70% maximal bronchoconstriction in most animals. 3. BAY x7195, given i.v., orally (p.o.), by aerosol or dry powder insufflation, in lactose, reduced LTD4-induced bronchoconstriction dose-dependently. The approximate ID50 values were 83 microg kg(-1), 3 mg kg(-1), 0.0003% w/v for 20 breaths and 20 microg respectively. 4. The action of BAY x7195 (10 mg kg(-1), p.o.) was long lasting, causing significant inhibition of the LTD4-induced response (88% reduction) 8 h after dosing. 5. When given intravenously, in the presence of selected antagonists, BAY x7195 caused a dose-related reduction in the antigen-induced response, with an approximate ID50 of 2 mg kg(-1). 6. At 3 mg kg(-1), i.v., a dose which abolished the response to LTD4, BAY x7195 had no effect on U46619- or histamine-induced bronchoconstriction. 7. BAY x7195 is a potent, selective and long acting antagonist of LTD4-induced bronchoconstriction, in an anaesthetized, ventilated guinea-pig model. It is therefore worthy of clinical evaluation in diseases believed to involve the sulphidopeptide leukotrienes, such as asthma.

Serum eosinophil cationic protein levels and bronchodilator responses at acute asthma exacerbation

BACKGROUND

Serum levels of eosinophil cationic protein are an indirect measure of airway inflammation in asthma. It is proposed that the extent to which broncho-constriction or airway inflammation contributes to airflow obstruction in acute asthma may determine responsiveness to bronchodilator therapy.

OBJECTIVE

To test the hypothesis that subjects with acute asthma exacerbations who respond poorly to inhaled bronchodilator treatment may have more marked airway inflammation than those who respond well to identical therapy.

METHODS

Forty-eight asthmatic children who visited the emergency room due to acute exacerbations were studied. Serum levels of eosinophil cationic protein were measured at the time of acute exacerbations and of clinical remissions. At acute exacerbation, FEV1 was assessed before and after the administration of aerosolized salbutamol.

RESULTS

The mean serum level of eosinophil cationic protein at acute exacerbation (41.1 +/- 12.8 micrograms/L) was significantly higher (P < .01) than that at clinical remission (30.0 +/- 8.5 micrograms/L) in the study population. The level at acute exacerbation was even higher in group A (n = 18: postbronchodilator FEV1 < 75% predicted) than in group B (n = 30: postbronchodilator FEV1 > or = 75% predicted), whereas both groups showed similar levels at clinical remission. The level at acute exacerbation correlated positively with severity of exacerbation (r = .47, P < .01) and negatively with bronchodilator responses (r = -.56, P < .01). This negative correlation was valid among subjects with a similar degree of exacerbation.

CONCLUSION

A higher level of eosinophil cationic protein at acute asthma exacerbation was associated not only with more severe exacerbation but also with a lower degree of bronchodilator responsiveness. This suggests that degree of airway inflammation may be one determinant of degree of responsiveness to initial bronchodilator therapy at acute asthma exacerbation.

Pharmacology of leukotriene receptor antagonists. More than inhibitors of bronchoconstriction

The cysteinyl leukotrienes (LTs) are chemical mediators that are thought to contribute to the pathophysiologic condition of asthma and other inflammatory diseases. The biological effects of the cysteinyl LTs in the lung are pleiotropic, including both bronchoconstrictor and a growing list of nonbronchoconstrictor activities that extend to inflammatory cell recruitment, vascular leakage, mucus production, neuronal dysfunction, and airways remodeling. This spectrum of effects of cysteinyl LTs is consistent with an expanded view of asthma that extends beyond simply bronchoconstriction and inflammation. Consequently, the clinical efficacy of cysteinyl LT receptor antagonists (LTRAs) in asthma may be related to antagonism of more than cysteinyl LT-induced bronchoconstriction. The relationship of antagonism of the multiple effects of cysteinyl LTs by cysteinyl LTRAs to their utility in the therapy of asthma is addressed, and the preclinical and clinical pharmacology of cysteinyl LTRAs is reviewed.

Urinary leukotriene E4 in the assessment of nocturnal asthma

BACKGROUND

Urinary leukotriene E4 (LTE4) is a marker of the body's production of cysteinyl LTs, important mediators of airway inflammation. The role of the latter in nocturnal asthma is a topic of increasing interest.

OBJECTIVE

This investigation was aimed at determining whether nighttime attacks are associated with increased release of LTs, expressed by urinary LTE4, and the relationship between the two phenomena.

METHODS

Three groups were studied: group A, seven control subjects; group B, nine asthmatic patients without nocturnal attacks; and group C, nine asthmatic patients with a comparable daytime FEV1 but who were experiencing nocturnal exacerbations (morning dips in peak expiratory flow greater than 20%). Urine was collected over 24 hours in three samples (9:00 AM to 3:00 PM; 3:00 PM to 9:00 PM; and 9:00 PM to 9:00 AM). LTE4 was measured by high-performance liquid chromatography and radioimmunoassay and expressed as nanograms per millimole of creatinine.

RESULTS

No significant differences between urinary LTE4 were noticed within groups A and B. Conversely, in group C urinary LTE4 at night (geometric mean with 95% confidence interval; 35.16 with 28.77-42.85) was significantly higher than that of the other samples (respectively 23.12 with 17.78-30.06, p less than 0.05; and 25.18 with 21.03-30.13, p less than 0.02); it was also significantly higher than in all the samples of other groups. A significant (p less than 0.02) linear correlation was observed between morning dip in peak expiratory flow and the log urinary LTE4 in the nocturnal sample.

CONCLUSION

These results indicate the role of LTs in nocturnal asthma and suggest that urinary LTE4 may be a useful marker of this condition.

Reduction in leukotriene B4 generation by bronchoalveolar lavage cells in asthma

BACKGROUND

Leukotrienes are inflammatory mediators implicated in the pathogenesis of asthma. The capacity of inflammatory cells within the airways to generate leukotrienes may be altered in asthma. This hypothesis was tested using bronchoalveolar lavage (BAL) to sample cells within the airways from atopic asthmatic and normal subjects, and by measuring their capacity to generate leukotriene B4 (LTB4) and leukotriene C4 (LTC4) in response to A23187, a potent stimulus of leukotriene generation.

METHODS

Bronchoalveolar lavage was performed in 12 mild asymptomatic atopic asthmatic patients and 12 normal subjects. Mixed BAL cell aliquots (approximately 80% alveolar macrophages) were incubated with 0-20 microM A23187 for 10 minutes and with 4 microM A23187 for 0-30 minutes, and leukotrienes were measured by radioimmunoassay and high performance liquid chromatography.

RESULTS

Mixed BAL cells from asthmatic subjects generated less LTB4 than cells from normal subjects in dose response and time course experiments (area under the curve 81.5 (0.0-228.5) ng.min.10(-6) cells in asthmatic subjects and 197.9 (13.9-935.6) ng.min.10(-6) cells in normal subjects. There were no differences in LTC4 generation between BAL cells from asthmatic and normal subjects.

CONCLUSIONS

Generation of LTB4 by BAL cells from atopic asthmatic subjects in response to A23187 was reduced. As the alveolar macrophage is the major source of LTB4 in BAL cells, these results probably reflect reduced generation of LTB4 by alveolar macrophages from asthmatic patients. This may be a consequence of monocyte migration into the lung, or altered alveolar macrophage function in asthma, or both.

Reactive oxygen species and not lipoxygenase products are required for mouse B-lymphocyte activation and differentiation

A potential role for lipoxygenase (LO) products and reactive oxygen species (ROS) in mouse B-lymphocyte activation and differentiation was investigated. Previously published investigations with the nonspecific 5-LO (EC 1.13.11.34) and 12-LO (EC 1.13.11.31) inhibitors such as nordihydroguaiaretic acid (NDGA) and 6,7-dihydroxycoumarin (Esculetin), are misleading in that they suggest lymphocyte LO activity is required for activation and differentiation of these cells. In initial support of this concept, we report that NDGA and Esculetin completely inhibited B-lymphocyte activation mediated by either membrane immunoglobulin (mIg), or the lipopolysaccharide (LPS) receptor. NDGA and Esculetin completely inhibited cell enlargement and proliferation, exhibiting half maximal inhibitory concentrations (IC50S) of approximately 1 x 10(-6) M. In contrast, the highly specific 5-LO inhibitors BAY X 1005, MK-886 and Wy 50,295 did not inhibit cell enlargement or proliferation. Moreover, 5,8,11-eicosatriynoic acid (ETI) which inhibits 5- and 12-LO, and 5, 8, 11, 14-eicosatetraynoic acid (ETYA) which inhibits all known LOs did not affect B-lymphocyte proliferation. Interestingly, NDGA and Esculetin are antioxidants, unlike BAY X 1005, MK-886, Wy 50,295, ETI and ETYA. Our hypothesis was that the antioxidant activities of NDGA and Esculetin were reponsible for inhibiting B-lymphocyte activation and proliferation and we speculated that ROS and not LO activity was required for both processes. Additional antioxidants such as butylated hydroxy toluene, o-phenanthroline, thiourea, and alpha-tocopherol (vitamin E), also inhibited B-lymphocyte proliferation induced by either the LPS or mIg receptors. These agents exhibited IC50S of 1 x 10(-8) M, 5 x 10(-10) M, 6 x 10(-3) M and 5 x 10(-5) M, respectively. When resting B-lymphocytes were treated with a source of ROS (1 x 10(-5) M H2O2), cells enlarged in a temperature-sensitive manner, which is similar to LPS-induced enlargement. Both NDGA and Esculetin completely inhibited H2O2-induced enlargement. These results further indicate that ROS are required for B-lymphocyte activation and proliferation. Similar results were obtained for B-lymphocyte differentiation. NDGA and Esculetin completely inhibited the development of plasma cells and displayed IC50S of 5 x 10(-6) M. Conversely, BAY X 1005, MK-886, Wy 50,295, ETI, and ETYA did not block the formation of plasma cells. Therefore, ROS are also crucial for differentiation into plasma cells. These experiments are the first to directly illustrate that intracellular ROS mediate B-lymphocyte activation, proliferation and differentiation and that LO products are not required for these processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-inflammatory effects of low-dose oral theophylline in atopic asthma

Theophylline, in addition to its bronchodilator effect, may attenuate inflammation in asthma. We did a double-blind placebo-controlled study of the effect of oral theophylline on the inflammatory response of the bronchial mucosa to inhalation of allergen in 19 atopic asthmatic subjects. Bronchoscopy and bronchial biopsy were done 24 hours after allergen inhalation before and after six weeks of treatment with oral slow-release theophylline, 200 mg 12 hourly. The mean serum concentration was 36.6 mumol/L, which is below the currently-accepted therapeutic range. After treatment with theophylline there was a significant reduction in the number of EG2-positive activated eosinophils (5.9 before and 2.1 after treatment, Wilcoxon signed rank p < 0.05) and total eosinophils (16.7 before and 7.6 after treatment, p < 0.05) beneath the epithelial basement membrane. We conclude that low-dose oral theophylline attenuates airway inflammatory response to allergen inhalation in atopic asthma.

Effect of a 5-lipoxygenase inhibitor, ZM 230487, on cutaneous allergic inflammation in the guinea-pig

1. Leukotrienes have potent biological effects in vitro and in vivo and are found in tissue and in biological fluids in various pathological conditions including allergic diseases. Leukotriene B4 (LTB4) is a potent stimulus for eosinophil accumulation and activation and there is much interest in determining its importance in mediating the accumulation of eosinophils at sites of allergic inflammation in vivo. In this study, we investigated the effects of a potent 5-lipoxygenase inhibitor, ZM 230487, on the accumulation of eosinophils and on local oedema formation in cutaneous inflammation in the guinea-pig. 2. The i.d. injection of increasing concentrations of arachidonic acid (AA) led to a dose-dependent accumulation of 111In-eosinophils but oedema formation was only significant at the top dose of AA tested (3 x 10(-8) mol per site). Co-injection of ZM 230487 with AA inhibited 111In-eosinophil accumulation up to 99% but the small oedema response to AA was only partially inhibited. AA-induced oedema formation was only effectively inhibited when a combination of a PAF antagonist, an antihistamine and ZM 230487 was used. 3. Local administration of the cyclo-oxygenase inhibitor, ibuprofen, partially inhibited AA-induced oedema formation suggesting that vasodilator prostaglandins may be released following i.d. injection of AA. AA-induced 111In-eosinophil accumulation was also partially inhibited by ibuprofen. 4. PAF-induced 111In-eosinophil accumulation was partially suppressed by local administration of ZM 230487. In contrast, LTB4-induced 111In-eosinophil accumulation was enhanced by ZM 230487. These data suggest that locally-released leukotrienes may modulate mediator-induced eosinophil accumulation. ZM 230487 had no effect on PAF- or LTB4-induced oedema formation. 5. ZM230487 significantly inhibited the accumulation of 111 In-eosinophils, but did not affect local oedema formation, in a passive cutaneous anaphylaxis (PCA) reaction. However, the PAF antagonist WEB 2086 either alone or in combination with ZM 230487 had no effect on "'In-eosinophil accumulation or oedema formation in the PCA reaction.6. In conclusion, it appears that a product of 5-lipoxygenase, probably LTB4, is important for the accumulation of "'In-eosinophils, but not local oedema formation, in the PCA reaction in guinea-pigskin. These data support a major role for LTB4 in allergic inflammation in the guinea-pig and make this animal (and the PCA model) suitable for studying the effects of inhibitors of leukotriene synthesis or action in vivo.

Leukotriene and thromboxane antagonists

It has been suggested that arachidonate metabolites, leukotrienes, and thromboxane may play important roles in the pathogenesis of bronchial asthma. Biologic activities of these mediators are much more potent than those of histamine and acetylcholine on a molar basis in inducing bronchoconstriction, increase in microvascular permeability, formation of mucosal edema, and mucus secretion, which are characteristic features of bronchial asthma. Furthermore, recent studies have demonstrated the presence of these mediators in plasma, BALF, and urine in asthmatic patients after allergen challenge. Therefore, the regulation of the activities of these mediators may provide a novel therapeutic approach for the treatment of bronchial asthma. A large number of 5-lipoxygenase inhibitors, peptide leukotriene antagonists, thromboxane synthase inhibitors, and thromboxane antagonists have been actively developed by the pharmaceutical industry, and there are increasing findings to demonstrate a clinical efficacy by these compounds. Among them, a thromboxane synthase inhibitor, OKY-046, first became available as an antiasthmatic agent in Japan. This is a significant step in the management of bronchial asthma. Preclinical and clinical results have suggested that these inhibitors and antagonists may be capable of inhibiting airway obstruction with airway inflammation and bronchial hyperresponsiveness, which are important characteristics of bronchial asthma. Further results from clinical studies with newly developed leukotriene and thromboxane antagonists are eagerly awaited.

Tumour necrosis factor-alpha and leukotriene E4 production in wheezy infants

It is not clear why certain infants wheeze during viral upper respiratory tract infections (URTIs) but it is possible that they have a tendency to mount an exaggerated inflammatory response leading to production of mediators that induce airway narrowing. We studied nasal tumour necrosis factor-alpha (TNF alpha) and urinary leukotriene E4 (LTE4) production during infection and after recovery in 31 wheezy infants (median age 6.2 months). Urinary LTE4 production was not altered during wheezy episodes or URTIs. However, the concentration of TNF alpha in nasal lining fluid (NLF) was significantly increased during acute episodes of wheeze compared to recovery (median [interquartile range] of 293 [42-1753] vs 0 [0-203] pg/ml NLF). TNF alpha was detectable more often and in higher concentration when wheezing was due to respiratory syncytial virus. TNF alpha was also present in 7/30 asymptomatic wheezy infants who had recovered from infection (> 100 pg/ml NLF) and in 4/7 non-wheezy siblings during URTIs (> 200 pg/ml NLF). This suggests that upregulation of TNF alpha production is not the only factor that makes some infants wheeze.

Leukotrienes as a target in asthma therapy

Asthma is a chronic inflammatory condition characterised by bronchial hyper-responsiveness and reversible airways obstruction. Research has demonstrated that these effects are mediated by a wide range of compounds. In the last decade leukotrienes have been identified as products of arachidonic acid metabolism. Their effects mimic the pathological changes seen in asthma both in vitro and in vivo. Further research has demonstrated increased production of leukotrienes both during episodes of asthma and in patients with stable asthma. The demonstration that leukotrienes have proinflammatory biological properties relevant to the pathogenesis of asthma has stimulated the development of many potential therapeutic compounds to block these actions. Early studies in laboratory-induced asthma in human volunteers have shown the efficacy of some of these compounds. They have been shown to attenuate the bronchoconstriction caused by allergen challenge, exercise, aspirin and exposure to cold air. Most encouraging of all have been recent placebo-controlled studies in clinical asthma where significant improvements in terms of spirometry, symptoms and beta 2-agonist use have been demonstrated. Leukotriene receptor antagonists and synthesis inhibitors are the first mediator antagonists to have been shown to be effective in treating clinical asthma and as such represent one of the most interesting new classes of antiasthma drugs in development at present.

5-lipoxygenase-activating protein is an arachidonate binding protein

5-Lipoxygenase-activating protein (FLAP) is an 18-kDa integral membrane protein which is essential for cellular leukotriene (LT) synthesis, and is the target of LT biosynthesis inhibitors. However, the mechanism by which FLAP activates 5-LO has not been determined. We have expressed high levels of human FLAP in Spodoptera frugiperda (Sf9) insect cells infected with recombinant baculovirus, and used this system to demonstrate that FLAP specifically binds [125I]L-739,059, a novel photoaffinity analog of arachidonic acid. This binding is inhibited by both arachidonic acid and MK-886, an LT biosynthesis inhibitor which specifically interacts with FLAP. These studies suggest that FLAP may activate 5-LO by specifically binding arachidonic acid and transferring this substrate to the enzyme.

Pharmacologic modulation of antigen-induced pulmonary responses in the perfused guinea pig lung

The effect of various enzyme inhibitors and receptor antagonists on antigen (ovalbumin)-induced changes in pulmonary hemodynamics (arterial pressure, capillary pressure, and arterial and venous resistance), fluid filtration, and airway reactivity were monitored for 60 min in recirculating Ringer's-perfused, actively sensitized lungs. Bolus ovalbumin (30 micrograms) injection into the pulmonary artery produced initial (3 min postovalbumin) increases in pulmonary arterial pressure of 68 +/- 9% above baseline, which were followed by secondary increases (143 +/- 45% above baseline) at 30 min postovalbumin. Ovalbumin challenge also caused initial increases in pulmonary capillary pressure, arterial resistance, and venous resistance within 3 min after administration (100 +/- 34%, 51 +/- 10%, and 221 +/- 77% above baseline, respectively), which were further elevated at the end of the 60-min experimental period (292 +/- 74%, 66 +/- 29%, and 559 +/- 61% above baseline, respectively). Ovalbumin-induced increases in intratracheal pressure (771 +/- 142% above baseline) peaked at 3 min postchallenge and gradually returned towards baseline. Ovalbumin-induced changes in lung weight increased gradually over the perfusion period (3.5 +/- 1.0 g above baseline at 60 min postovalbumin). Antigen-induced changes in pulmonary arterial pressure, intratracheal pressure, and lung weight were abolished by pretreatment with the histamine1-receptor antagonist, pyrilamine (1 microM). The cyclooxygenase inhibitor, indomethacin (1 microM), potentiated antigen-induced secondary increases in pulmonary arterial pressure, intratracheal pressure, and lung weight.(ABSTRACT TRUNCATED AT 250 WORDS)

Asthma pathogenesis and the implications for therapy in children

Gaining greater insight into the pathogenesis of asthma has redefined the approach to treatment of children with asthma. Clearly, the Expert Panel of the National Heart, Lung, and Blood Institute National Education Program has played a major role in taking the message to a wide audience of health care providers. Although only early trends are evident at this point in time, within several years therapeutic trends underway currently will be more commonplace, and we may observe how asthma continues to impact society and our health care system. The approach to therapy will continue to evolve and most likely be controversial for years to come.

Contributory role of lung pleura to release of anaphylactic mediators from guinea pig lung in response to ovalbumin or A23187

Previous findings revealed greater contractile responses of guinea pig lung pleural surface strips to antigen or A23187 challenge than denuded lung parenchymal strips (lung strip devoid of any pleura). Moreover, we have identified a high density of mast cells distributed throughout the lung pleura. The present study examined mediators released from guinea pig lung pleural surface and denuded lung parenchyma fragments in response to immunologic challenge with ovalbumin (OA) or non-immunologic challenge with the ionophore A23187. Histamine levels were measured radioenzymatically; leukotrienes (LTs), prostaglandins (PGs) and thromboxane B2 (TXB2), a stable metabolite of thromboxane A2 (TXA2), were quantitated using an enzyme immunoassay. Histamine release reached a maximal level 3-5 min after OA challenge, whereas A23187-induced histamine release increased gradually in a time-dependent manner. Similar kinetics were observed in the release of LTs, PGs and TXA2. Pleural surface released a substantially (P < 0.05) greater amount of histamine to both challenges than denuded parenchyma. Moreover, histamine content in pleural surface was significantly (P < 0.05) higher than in denuded parenchyma. Pleural surface also released considerably (P < 0.05) more LTB4, LTC4, and LTE4 in response to OA and A23187 than denuded parenchyma. In contrast, pleural surface and denuded parenchyma released equivalent amounts of PGD2, PGE2, PGF2 alpha, and TXA2 in response to both challenges. The rank order of leukotriene release was LTC4 > LTE4 > LTB4, whereas that of prostanoid release was TXA2 >> PGD2 > or = PGF2 alpha >> PGE2. We conclude that pleural surface is the major source of histamine and leukotrienes released from guinea pig lung in vitro in response to OA and A23187, whereas both pleural surface and denuded parenchyma participate to the same extent in prostaglandin and TXA2 production after such challenges.

Inhaled budesonide regimen enhances serotonin- and arachidonic acid-induced platelet aggregation

The influence of inhaled budesonide regimen (400 micrograms x 2 for 7 days), on agonist-induced platelet aggregation and secretion, was investigated in 18 volunteers. Platelet activation induced by serotonin and arachidonic acid was significantly enhanced after budesonide, as demonstrated by an increase in aggregation velocity (Vmax) and amplitude (Amax), and in arachidonic acid-induced ATP-secretion. We found no change in platelet aggregation induced by ADP, epinephrine, and A23187. With the exception of epinephrine-induced platelet aggregation, which was inhibited by 10(-5)-10(-4) M budesonide, in vitro studies revealed no influence of 10 min budesonide preincubation (10(-9)-10(-4) M) on agonist-induced platelet activation, suggesting that the ex vivo enhancement of platelet function was mediated by secondary corticosteroid mechanisms. A tentative explanation of the increased arachidonic acid-induced platelet activation, may be a budesonide-induced stimulation of cyclooxygenase. The enhanced serotonin-induced platelet aggregation may be a reflection of exogenous corticosteroid stimulation of the 5-HT2-receptor.