Inflammation-induced airway smooth muscle responsiveness is strain dependent in mice

Different mouse strains display different degrees of inflammation-induced airway hyperresponsiveness in vivo. It is not known whether these variations are attributable to distinct properties of the airway smooth muscle. Therefore, tracheal ring segments from C57BL/6 and BALB/c mice were exposed to three different pro-inflammatory stimuli for 4 days while maintained under tissue-culture conditions: tumour necrosis factor α (100 ng/ml), the Toll-like receptor (TLR) 3 agonist polyI:C (10 μg/ml), and the TLR4 agonist LPS (10 μg/ml). The contractile responses to carbachol, 5-hydroxytryptamine (5-HT) and bradykinin were assessed after culture. In addition, gene expression of TLR1-TLR9, pivotal inflammatory signal transduction proteins (jun-kinase, p38 and p65) and critical negative regulators of inflammation (A20, Itch, Tax1bp1 and RNF11) were studied in tracheal smooth muscle strips, fresh and following treatment for 4 days with LPS, from both strains. No differences between the strains were detected regarding the response of freshly isolated preparations to carbachol, 5-HT and bradykinin. After stimulation with pro-inflammatory mediators, contractions in response to 5-HT and bradykinin, but not to carbachol, were up-regulated. This up-regulation was markedly larger in BALB/c than in C57BL/6 segments and depended on the type of inflammatory stimulus. Expression of the genes investigated did not differ between the two strains. These findings indicate that strain differences in airway hyperresponsiveness can be linked to differences in the responsiveness of airway smooth muscle to pro-inflammatory mediators per se. The differences do not appear to be due to differential expression of TLR or common inflammatory transduction and repressor proteins.

Comparison of aerosol and intranasal challenge in a mouse model of allergic airway inflammation and hyperresponsiveness

BACKGROUND

The aim was to optimize antigen challenge for induction of airway hyperresponsiveness (AHR) and inflammation in BALB/c mice sensitized to ovalbumin (OVA). Comparisons were made between mice challenged with OVA either as an aerosol or intranasally. The protocol that induced maximal AHR in BALB/c mice was thereafter tested in C57BL/6 mice.

METHOD

Methacholine responsiveness was measured using the flexiVent® system to assess AHR. Inflammatory responses were investigated by histology and cell counts in bronchoalveolar lavage (BAL) fluid.

RESULTS

48 h after challenge with 1 or 6% OVA aerosols, there were similar increments in AHR and BAL cells, predominantly eosinophils. When comparing the effect of 1% OVA aerosol on AHR and cell infiltration at 24 and 48 h after challenge, the responses were similar. At 24 h, intranasal OVA administration (20-200 μg) caused a dose-dependent increase in AHR. BAL cells were increased by all intranasal OVA doses and to a greater extent than after 1% OVA aerosol challenge but without any dose dependency. Histological examination confirmed that there was an increase of eosinophils in lung tissue following either challenge. In C57BL/6 mice, baseline tissue elastance was the only functional outcome that was increased after intranasal OVA challenge. Even though the AHR response was negligible in C57BL/6 mice, a similar infiltration of BAL cells was observed in both strains.

CONCLUSION

Intranasal challenge was more effective than aerosol challenge at inducing both AHR and airway inflammation in BALB/c mice. Although intranasal challenge caused airway inflammation in C57BL/6 mice, this strain is not optimal for studying AHR.

Prostaglandin modulation of airway inflammation and hyperresponsiveness in mice sensitized without adjuvant

As adjuvant during sensitization may cause unspecific immune reactions, the aim of the present study was to define the role of cyclooxygenase (COX) activity on airway inflammation and airway hyperresponsiveness (AHR) in an adjuvant-free allergic mouse model. Administration of diclofenac and indomethacin (non-selective COX inhibitors), FR122047 (COX-1 inhibitor) and lumiracoxib (selective COX-2 inhibitor) enhanced AHR. Only diclofenac and lumiracoxib reduced the inflammatory cell content of bronchoalveolar lavage (BAL). Moreover, levels of prostaglandins in BAL were reduced by indomethacin and FR122047 but were unaffected by lumiracoxib. However, compared with antigen controls, none of the COX inhibitors displayed major effects on the production of cytokines, smooth muscle mass, number of goblet cells and eosinophils, or collagen deposition in the airways. These data in mice sensitized without adjuvant support the fact that COX products have a general bronchoprotective role in allergic airway inflammation. Furthermore, the data suggest that COX-1 activity predominantly generates prostanoids in BAL, whereas COX-2 activity is associated with the accumulation of inflammatory cells in BAL. This study further supports that AHR on the one hand, and the inflammatory response and generation of prostanoids on the other, are dissociated and, at least in part, uncoupled events.

Specific mediator inhibition by the NO donors SNP and NCX 2057 in the peripheral lung: implications for allergen-induced bronchoconstriction

Background

The aim of this study was to examine potential therapeutic effect of the two NO donors NCX 2057 (3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid) 4-(nitrooxy)butyl ester) and SNP (sodium nitroprusside) on the early allergic airway response in the peripheral lung.

Methods

The experiments were performed in guinea pig lung parenchyma (GPLP) derived from ovalbumin (OVA) sensitized guinea pigs. The effects of NCX 2057 and SNP were evaluated by contractile responses and mediator release during OVA challenge. The generation of nitrite and nitrate was assessed by chemiluminescence. Statistical analysis was evaluated by ANOVA.

Results

Cumulatively increasing concentrations of OVA (1–10,000 ng/ml) induced concentration-dependent contractions of the GPLP that were reduced by NCX 2057 (100 μM, p < 0.001) and SNP (100 μM, p < 0.05). Antigen-induced eicosanoid release was decreased by NCX 2057 (100 μM, p < 0.001) but not by SNP (100 μM), whereas the release of histamine was reduced by SNP (100 μM, p < 0.001) but not by NCX 2057 (100 μM). In addition, NCX 2057 (0.1–100 μM), but not SNP (0.1–100 μM), relaxed leukotriene D₄ (10 nM) precontracted GPLP (p < 0.01). The guanylyl cyclase inhibitor ODQ had no effect on the NCX 2057 mediated relaxation. SNP released significantly less nitrite than NCX 2057.

Conclusion

Although both SNP and NCX 2057 reduced the release of pro-inflammatory mediators, their profiles were distinctly different. Furthermore, NCX 2057 also induced smooth muscle dilation in the GPLP. The findings point to specific anti-inflammatory effects of different NO donors in the peripheral lung tissue.

A randomized, double-blind, placebo-controlled study of tumor necrosis factor-alpha blockade in severe persistent asthma

RATIONALE

The treatment effect of golimumab, a human monoclonal antibody against tumor necrosis factor (TNF)-alpha, in severe persistent asthma is unknown.

OBJECTIVES

To assess the safety and efficacy of golimumab in a large population of patients with uncontrolled, severe persistent asthma.

METHODS

From 2004 to 2006, 309 patients with severe and uncontrolled asthma, despite high-dose inhaled corticosteroids and long-acting beta(2) agonists, were randomized 1:1:1:1 to monthly subcutaneous injections of placebo or golimumab (50, 100, or 200 mg) through Week 52. Coprimary endpoints were the change from baseline through Week 24 in prebronchodilator percent-predicted FEV(1) and the number of severe asthma exacerbations through Week 24.

MEASUREMENTS AND MAIN RESULTS

No significant differences were observed for the change in percent-predicted FEV1 (least squares mean: placebo, 2.44 [95% confidence interval (CI) -0.574 to 5.461]; combined 100-mg and 200-mg, 2.91 [0.696-5.116]) or severe exacerbations (mean +/- SD: placebo, 0.5 +/- 1.07 vs. combined 100-mg and 200-mg 0.5 +/- 0.97) through week 24. Through Week 24, 2.6% of patients treated with placebo vs. 19.5% of those treated with golimumab discontinued the study agent, and 1.3% and 7.8% discontinued study participation, respectively. An unfavorable risk-benefit profile led to early discontinuation of study-agent administration after the Week-24 database lock. Through Week 76, 20.5% of patients treated with placebo and 30.3% of patients treated with golimumab experienced serious adverse events, with serious infections occurring more frequently in golimumab-treated patients. One death and all eight malignancies occurred in the active groups.

CONCLUSIONS

Overall, treatment with golimumab did not demonstrate a favorable risk-benefit profile in this study population of patients with severe persistent asthma. Clinical trial registered with www.clinicaltrials.gov (NCT00207740).

No further increase of incidence of asthma: incidence, remission and relapse of adult asthma in Sweden

BACKGROUND

Knowledge about time trends of disease patterns in society is essential for planning and prioritizing health care resources. Longitudinal population-based studies on asthma are scarce but provide an opportunity to assess incidence, remission and relapse of asthma, and their determinants, which were the objectives of the present study.

METHODS

A postal questionnaire was sent on two occasions, 1996 and 2006, to a randomly selected sample of subjects aged 20-69 years in 1996. The response rates were 72% and 83%, respectively, and in total 4479 subjects participated in both surveys. The questionnaire included questions on asthma, respiratory symptoms and possible determinants. Logistic regression was used to assess determinants.

RESULTS

Cumulative incidence of asthma was 2.4% (men 1.9%; women 2.8%, p=0.06). Family histories of asthma (OR 2.31, CI 95% 1.42-3.76), rhinitis (OR 2.25, CI 95% 1.43-3.53) and being an ex-smoker (OR 2.17, CI 95% 1.27-3.71) were determinants for incident asthma. The 10-year remission of asthma was 14.6% and inversely associated with rhinitis. Relapse was found in 38% of eligible subjects.

CONCLUSIONS

The current study with high participation rates concludes that the incidence of asthma among adults has been stable in Sweden for the past two decades. Remission was associated with mild disease at study start. Relapse in adults has rarely been reported previously and provide new insight in the course of asthma. Low remission and high relapse further support the view of asthma as a chronic disease; possibly representing fluctuations of the disease over time.

Different effects of deep inspirations on central and peripheral airways in healthy and allergen-challenged mice

BACKGROUND

Deep inspirations (DI) have bronchodilatory and bronchoprotective effects in healthy human subjects, but these effects appear to be absent in asthmatic lungs. We have characterized the effects of DI on lung mechanics during mechanical ventilation in healthy mice and in a murine model of acute and chronic airway inflammation.

METHODS

Balb/c mice were sensitized to ovalbumin (OVA) and exposed to nebulized OVA for 1 week or 12 weeks. Control mice were challenged with PBS. Mice were randomly selected to receive DI, which were given twice during the minute before assessment of lung mechanics.

RESULTS

DI protected against bronchoconstriction of central airways in healthy mice and in mice with acute airway inflammation, but not when OVA-induced chronic inflammation was present. DI reduced lung resistance induced by methacholine from 3.8 +/- 0.3 to 2.8 +/- 0.1 cmH2O.s.mL-1 in healthy mice and 5.1 +/- 0.3 to 3.5 +/- 0.3 cmH2O.s.mL-1 in acute airway inflammation (both P < 0.001). In healthy mice, DI reduced the maximum decrease in lung compliance from 15.9 +/- 1.5% to 5.6 +/- 0.6% (P < 0.0001). This protective effect was even more pronounced in mice with chronic inflammation where DI attenuated maximum decrease in compliance from 44.1 +/- 6.6% to 14.3 +/- 1.3% (P < 0.001). DI largely prevented increased peripheral tissue damping (G) and tissue elastance (H) in both healthy (G and H both P < 0.0001) and chronic allergen-treated animals (G and H both P < 0.0001).

CONCLUSION

We have tested a mouse model of potential value for defining mechanisms and sites of action of DI in healthy and asthmatic human subjects. Our current results point to potent protective effects of DI on peripheral parts of chronically inflamed murine lungs and that the presence of DI may blunt airway hyperreactivity.

Effects of selective and non-selective COX inhibitors on antigen-induced release of prostanoid mediators and bronchoconstriction in the isolated perfused and ventilated guinea pig lung

The contribution of cycloxygenase (COX)-1 and COX-2 in antigen-induced release of mediators and ensuing bronchoconstriction was investigated in the isolated perfused guinea pig lung (IPL). Antigen challenge with ovalbumin (OVA) of lungs from actively sensitised animals induced release of thromboxane (TX)A(2), prostaglandin (PG)D(2), PGF(2)(alpha), PGI(2) and PGE(2), measured in the lung effluent as immunoreactive TXB(2), PGD(2)-MOX, PGF(2)(alpha), 6-keto PGF(1)(alpha) and PGE(2), respectively. This release was abolished by the non-selective COX inhibitor flurbiprofen (10 microM). In contrast, neither the selective COX-1 inhibitor FR122047 nor the selective COX-2 inhibitor celecoxib (10 microM each) significantly inhibited the OVA-induced bronchoconstriction or release of COX products, except for PGD(2). Another non-selective COX inhibitor, diclofenac (10 microM) also significantly inhibited antigen-induced bronchoconstriction. The data suggest that both COX isoenzymes, COX-1 and COX-2 contribute to the immediate antigen-induced generation of prostanoids in IPL and that the COX-1 and COX-2 activities are not associated with different profiles of prostanoid end products.

Aggregates of ultrafine particles modulate lipid peroxidation and bacterial killing by alveolar macrophages

We hypothesized that aggregates of ultrafine carbon and washed diesel particles impair the ability of alveolar macrophages (AM) to kill bacteria and enhance the AM lipid peroxidation (LPO) of lung surfactant. Rat AM were exposed, 5h, to particles 20 microg/ml. The AM, containing carbon or washed diesel particles, were incubated 2h, with Streptococcus pneumoniae, an American Type Culture Collection (ATCC) strain or clinical isolates. Surviving bacteria were quantified. Surfactant was incubated, 5h, with carbon or washed diesel loaded AM and LPO was measured. The particle load was approximately 1 microg/10(6) AM, representing accepted exposure to ambient particles in Europe. Metal concentrations were 10 to 100 fold higher in washed diesel--than in carbon particles. There was a dose dependent increase in bacterial survival with carbon-loaded macrophages, but not with washed diesel-loaded AM. Clinical isolates had a higher survival rate with carbon-loaded macrophages than the ATCC strain. Surfactant LPO was increased with washed diesel-loaded macrophages (95%) and with carbon-loaded macrophages (55%) compared to controls. High LPO caused by washed diesel-loaded AM reflects their increased oxidative metabolism, probably caused by particle metals. The additional oxygen metabolites maintained bactericidal activity of AM, while corresponding activity was decreased in carbon-loaded AM. Altered functions of AM may explain health problems related to air pollution.

Endothelium-dependent vascular responses induced by leukotriene B4

Leukotriene B(4) (LTB(4)) is an inflammatory mediator derived from the 5-lipoxygenase pathway of arachidonic acid metabolism and has recently implicated in the pathogenesis of atherosclerosis. There are two membrane bound receptors for LTB(4): BLT(1) and BLT(2), which represent the high and low affinity receptors, respectively. BLT receptors are expressed on leukocytes, and LTB(4) is a potent chemoattractant for neutrophils, eosinophils, and T lymphocytes. Recent studies have in addition shown that LTB(4) is an indirectly acting vasoconstrictor of isolated vascular preparations. In the guinea pig aorta, the LTB(4)-induced contractions were inhibited by endothelium-denudation. In addition, pre-treatment with the NO synthase inhibitor, L-NOARG, significantly enhanced the contractions induced by LTB(4). The contractile response induced by LTB(4) in the guinea pig aorta was abolished by the selective BLT(1) receptor antagonist U75302 and the expression of BLT(1) receptor mRNA in the guinea pig aorta was established by RT-PCR. Taken together, these results suggest that LTB(4) activates BLT(1) receptors on the endothelium of the guinea pig aorta, associated with the release of both contractile factors and NO.

Pharmacological modulation of the leukotriene pathway in allergic airway disease

Leukotrienes (LTs), including cysteinyl LTs (CysLTs) and LTB(4), are potent lipid mediators that have an important pathophysiological role in asthma and allergic rhinitis. Most of the effects of CysLTs that are relevant to the pathophysiology of asthma are mediated by the activation of the CysLT(1) receptor, one of the receptor subtypes for CysLTs. LTB(4) might be functionally involved in the development of airway hyperresponsiveness, acute and severe asthma and allergic rhinitis. CysLT(1) receptor antagonists can be given as monotherapy or in addition to inhaled glucocorticoids. The potential anti-remodeling effect of CysLT(1) receptor antagonists might be relevant for preventing or reversing airway structural changes in asthmatic patients. Here, we examine the role of LTs in asthma and allergic rhinitis, and the therapeutic implications of the pharmacological modulation of the LT pathway for allergic airway disease.

The lipoxin receptor ALX: potent ligand-specific and stereoselective actions in vivo

Lipoxins (LXs) and aspirin-triggered LX (ATL) are trihydroxytetraene-containing eicosanoids generated from arachidonic acid that are distinct in structure, formation, and function from the many other proinflammatory lipid-derived mediators. These endogenous eicosanoids have now emerged as founding members of the first class of lipid/chemical mediators involved in the resolution of the inflammatory response. Lipoxin A(4) (LXA(4)), ATL, and their metabolic stable analogs elicit cellular responses and regulate leukocyte trafficking in vivo by activating the specific receptor, ALX. ALX was the first receptor cloned and identified as a G protein-coupled receptor (GPCR) for lipoxygenase-derived eicosanoids with demonstrated cell type-specific signaling pathways. ALX at the level of DNA has sequence homology to the N-formylpeptide receptor and as an orphan GPCR was initially referred to as the N-formylpeptide receptor-like 1. Although LXA(4) is the endogenous potent ligand for ALX activation, a number of peptides can also activate this receptor to stimulate calcium mobilization and chemotaxis in vitro. In contrast with LXA(4), the counterparts of many of these peptides in vivo remain to be established. The purpose of this review is to highlight the molecular characterization of the ALX receptor and provide an overview of the ALX-LXA(4) axis responsible for anti-inflammatory and proresolving signals in vivo. The information in this review provides further support for the initial nomenclature proposition for this GPCR as ALX.

Bronchial responsiveness to leukotriene D4 is resistant to inhaled fluticasone propionate

BACKGROUND

Inhaled corticosteroids are highly effective in asthma, reducing inflammatory markers and bronchial hyperresponsiveness. Cysteinyl-leukotrienes are major mediators of airway obstruction and display proinflammatory effects. Although the synthesis of leukotrienes is not affected by corticosteroid treatment, the influence of corticosteroids on the leukotriene pathway remains unresolved.

OBJECTIVE

We investigated whether or not bronchial responsiveness to leukotriene (LT) D(4) is reduced by fluticasone propionate in subjects with asthma.

METHODS

In 13 subjects with mild asthma, inhalation challenges with methacholine and LTD(4) were performed on consecutive days before and after 2 weeks of treatment with inhaled fluticasone 500 mug, twice daily, in a double-blind, randomized, placebo-controlled study with crossover design and 3 weeks of washout between periods. Exhaled nitric oxide was measured as a marker of corticosteroid responsiveness, and baseline urinary LTE(4) concentrations as an index of cysteinyl-leukotriene biosynthesis.

RESULTS

Fluticasone produced a significant decrease in methacholine responsiveness, corresponding to 2.6-fold shift in the PD(20) FEV(1), and a significant reduction in the levels of exhaled nitric oxide. By contrast, bronchial responsiveness to LTD(4) in the same subjects was unaffected by fluticasone, as were urinary LTE(4) concentrations.

CONCLUSION

These new data indicate that neither the biosynthesis nor the actions of leukotrienes appear to be sensitive to inhaled corticosteroids.

CLINICAL IMPLICATIONS

The study provides mechanistic support for the additive therapeutic efficacy of antileukotrienes and inhaled corticosteroids in asthma.

Treatment of asthma with antileukotrienes: first line or last resort therapy?

Twenty five years after the structure elucidation of slow reacting substance of anaphylaxis, antileukotrienes are established as a new therapeutic modality in asthma. The chapter reviews the biochemistry and pharmacology of leukotrienes and antileukotrienes with particular focus on the different usage of antileukotrienes for treatment of asthma and rhinitis in Europe and the US. Further research needs and new areas for leukotriene involvement in respiratory diseases are also discussed.

Aggregates of ultrafine particles impair phagocytosis of microorganisms by human alveolar macrophages

We investigated whether exposure of alveolar macrophages to aggregates of ultrafine carbon particles affected subsequent phagocytosis of microorganisms. Human alveolar macrophages were obtained by bronchoalveolar lavage and exposed to aggregates of ultrafine carbon particles or diesel exhaust particles (DEP) for 20 h before measurements of phagocytosis. The particle loads were estimated to be comparable to those of air pollution exposure with established health effects in humans. Phagocytotic activity was measured as attachment and ingestion of four different test particles (amorphous silica particles, yeast cells from Candida albicans, and Cryptococcus neoformans opsonized with specific IgG or fresh serum) that bind to scavenger, mannose, Fc, and complement receptors, respectively. Carbon preloading significantly impaired the attachment and ingestion process (P<0.01) for all particles, except for yeast cells from C. neoformans opsonized with specific IgG. On the average, the accumulated attachment decreased by 30% and the ingested fraction decreased by 10%. Loading of alveolar macrophages with either aggregates of ultrafine DEP or carbon particles impaired the phagocytosis of silica test particles in a similar way. Exposure of human alveolar macrophages to aggregates of carbon or DEP, in concentrations relevant to human environmental exposures, caused significant impairment of phagocytosis of silica particles and microorganisms. The inhibitory effect on particle phagocytosis mediated by four different receptors suggests that air pollution particles cause a general inhibition of macrophage phagocytosis. Such an effect may contribute to increased susceptibility to infections and, for example, result in more exacerbations of asthma and chronic obstructive pulmonary disease.

Inhibition of nitric-oxide synthase enhances antigen-induced contractions and increases release of cysteinyl-leukotrienes in guinea pig lung parenchyma: nitric oxide as a protective factor

Nitric oxide (NO) in exhaled air is a biomarker of airway inflammation. However, the role of NO in the peripheral lung is not known. The aim of this study was to determine the role of endogenous NO in antigen-induced contractions of ovalbumin (OVA)-sensitized guinea pig lung parenchyma (GPLP). The contraction in this in vitro model of the peripheral lung closely resembles the corresponding response in human airways. Cumulatively increasing concentrations (10-10,000 microg/l) of OVA induced concentration-dependent contractions of the GPLP that were enhanced by the NO synthase (NOS) inhibitors N(omega)-nitro-L-arginine (L-NOARG; 100 microM), N(omega)-monomethyl-L-arginine (100 microM), N(omega)-nitro-L-arginine methyl ester (100 microM), and N-(3-(aminomethyl)benzyl)acetamidine (1400W; 1 microM). The enhancement induced by L-NOARG was reversed by coadministration with the 5-lipoxygenase inhibitor (R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid (BAY x1005; 3 microM), whereas coadministration of L-NOARG with the cyclooxygenase inhibitor indomethacin (10 microM) did not change the effect of L-NOARG alone. L-NOARG (100 microM) did not affect the cumulative concentration-response relations for either leukotriene (LT) D4 (0.1-100 nM) or histamine (1-30 microM). The NO donor NONOate (0.001-100 microM) was ineffective in GPLP but potently relaxed precontracted guinea pig pulmonary artery. Furthermore, L-NOARG enhanced the release of LTE4 and decreased the release of prostaglandin E2 induced by OVA. In conclusion, endogenous NO exerts an inhibitory effect on antigen-induced contractions in the peripheral lung. The action of NO apparently involves inhibition of the release of mediators rather than direct relaxation of airway smooth muscle. The findings support the belief that endogenous NO has a protective anti-inflammatory effect in the airways.

Effects of 5-lipoxygenase inhibitor zileuton on airway responses to inhaled swine house dust in healthy subjects

BACKGROUND

Inhalation of swine house dust induces acute airway inflammation and increased bronchial responsiveness in healthy subjects.

OBJECTIVE

The aim of the study was to investigate whether 5-lipoxygenase products such as leukotrienes may have a role in this reaction.

METHODS

Twenty-three healthy subjects were randomised into two groups receiving treatment with either zileuton (600 mg) or placebo four times a day. After 5 days of treatment, all subjects were exposed for 3h in a swine barn. Bronchial responsiveness, exhaled nitric oxide (NO), and mediators in nasal lavage (NAL), blood and urine were measured before and after the exposure.

RESULTS

The exposure induced an increased bronchial responsiveness to methacholine in both groups with 2-3 doubling concentration steps, no significant difference between treatments. Leukotriene E(4) in urine increased significantly following exposure in the placebo group from 37.3 (29.1-45.6) (mean (95% confidence interval)) ng/mmol creatinine to 47.7 (36.3-59.0) ng/mmol creatinine (P<0.05), but not in the zileuton group. The post-exposure increase of LTB(4) levels in NAL fluid was totally abolished in the zileuton group (P<0.05 vs. the placebo). The levels of exhaled NO increased significantly (P<0.01), two-fold in both groups. The PGD(2) metabolite 9alpha, 11beta-PGF(2) increased in placebo-treated subjects (P<0.01; P<0.05 vs. zileuton), strengthening mast cell participation. Neutrophil counts and levels of IL-6 in peripheral blood increased in both groups, with a significantly larger increase in zileuton treated subjects (P<0.05 and P<0.001, respectively compared to placebo).

CONCLUSIONS

Pre-treatment with clinically recommended doses of the 5-lipoxygenase inhibitor zileuton did not affect the increase of bronchial reactivity induced by swine dust exposure. The intervention totally abolished the LTB(4) release in NAL fluid, but only partially inhibited the formation of leukotrienes as monitored by urinary levels. The enhanced increase of neutrophils and IL-6 in peripheral blood in the zileuton group, suggests that inhibition of 5-lipoxygenase may have pro-inflammatory effects.

International Union of Pharmacology XLIV. Nomenclature for the Oxoeicosanoid Receptor

Oxoeicosanoids are a family of biologically active arachidonic acid derivatives that have been intimately linked with cellular migration. These metabolites are not only potent chemotaxins but also elicit oxygen radical production as well as induce secretory events in different cells. The most potent native ligand reported is 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and the cell membrane receptor activated has now been cloned. This receptor is distinct from those receptors activated by either the prostaglandins or the leukotrienes. The purpose of this review is to briefly summarize the molecular evidence and highlight the significance of this receptor. In addition, an official nomenclature for this oxoeicosanoid receptor is proposed.

The contractile action of leukotriene B4 in the guinea-pig lung involves a vascular component

Leukotriene B4 (LTB4) is a potent leukocyte chemoattractant, acting on specific receptors, BLT receptors. The aim of this study was to examine the mechanism of action of LTB4 in the guinea-pig lung, using strips of lung parenchyma (GPLP), spirals of trachea (GPT) and bronchus (GPB) and rings of pulmonary artery (GPPA). Mechanical responses were studied in organ baths, and mediator release was assessed using enzyme immuno assay. LTB4 induced similar contractions of GPLP and GPPA, whereas LTB4 had only small contractile effects in GPT and GPB. In addition, the contractile response to LTB4 was reproduced in the human pulmonary artery. In the GPLP, the unselective BLT receptor antagonist ONO-4057 abolished the contractions induced by LTB4, whereas the selective BLT1 receptor antagonist U-75302 only partly inhibited the LTB4-induced contractions. In the GPPA, both antagonists abolished the response to LTB4. The effect of LTB4 in GPPA and GPLP was indirect and mediated by the release of thromboxane A2 and histamine, as supported by selective pharmacologic interventions and measurements of thromboxane B2 and histamine in the organ baths. In conclusion, the results indicate a new biological function of LTB4, namely to constrict isolated pulmonary arteries. Moreover, the findings suggest that the LTB4-induced contractions of GPPA were mediated by a BLT1 receptor, whereas BLT2 receptor activation accounted for a major part of the contraction of GPLP, making the latter preparation a suitable assay for BLT2 receptors. British Journal of Pharmacology (2004) 141, 449-456. doi:10.1038/sj.bjp.0705641

Interactions among three classes of mediators explain antigen-induced bronchoconstriction in the isolated perfused and ventilated guinea pig lung

Intravascular challenge of isolated perfused and ventilated guinea pig lung (IPL) from actively sensitized guinea pigs, with cumulatively increasing (10-10,000 microg) doses of ovalbumin (OVA), resulted in dose-dependent and reproducible reductions in lung conductance. The antihistamines mepyramine (1 microM) and metiamide (1 microM), the leukotriene antagonist zafirlukast (0.1 microM), or the cyclooxygenase enzyme (COX) inhibitor diclofenac (10 microM) each caused a parallel and rightward shift in the dose-response relation for OVA, providing evidence for contributions of histamine, cysteinyl-leukotrienes, and COX products to the OVA-induced bronchoconstriction in the IPL. Moreover, when all three drugs were combined there was a complete abolishment of the response to OVA. When two antagonists or inhibitors were combined, the results, however, were more complex. The 5-lipoxygenase inhibitor BAY x1005 (30 microM) and the thromboxane (TP) receptor antagonist BAY u3405 (1 microM) given as single treatment did not inhibit the response to OVA. However, combinations of different antagonists/inhibitors, including BAY x1005 and BAY u3405, caused pronounced inhibitions of the antigen responses, suggesting synergism in action. On the basis of these data it was concluded that although histamine and cysteinyl-leukotrienes mediate the major part of the bronchoconstriction, one or several prostanoids other than thromboxane contribute to the bronchoconstriction evoked by OVA. Moreover, the effect of diclofenac involved a dual action because it also made the IPL less sensitive to histamine and LTD4. The findings resemble and extend recent observations in clinical studies of patients with asthma and support the usefulness of this particular model in airway pharmacology.

Biochemical and clinical evidence that aspirin-intolerant asthmatic subjects tolerate the cyclooxygenase 2-selective analgetic drug celecoxib

BACKGROUND

Subjects with aspirin-intolerant asthma (AIA) respond with bronchoconstriction and extrapulmonary adverse reactions to conventional nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit the cyclooxygenase (COX) step in the biosynthesis of prostaglandins. Recently, 2 isotypes of COX have been identified, and COX-2-selective NSAIDs have been developed for treatment of inflammatory disorders.

OBJECTIVE

We investigated whether 33 subjects with a typical history of AIA tolerated the new COX-2-selective NSAID celecoxib.

METHODS

All subjects displayed current aspirin sensitivity in oral or inhalation challenge tests. The subjects first underwent a double-blind, randomized, cross-over, increasing-dose challenge with placebo or celecoxib (10, 30, or 100 mg in suspension) on 2 occasions 7 days apart. Thereafter, all subjects were exposed to 400 mg of celecoxib administered during an open challenge session as two 200-mg doses 2 hours apart. Lung function, clinical symptoms, and urinary excretion of leukotriene E(4) (LTE(4)) were monitored, with the latter being a sensitive biochemical marker of aspirin intolerance.

RESULTS

There were no changes in lung function or extrapulmonary symptoms during the double-blind sessions or in urinary excretion of LTE(4). Also, the highest recommended daily dose of celecoxib was well tolerated, with no symptoms, lung function changes, or alterations in urinary LTE(4) levels.

CONCLUSIONS

A group of subjects with clinically well-documented AIA tolerated acute challenge with the selective COX-2 inhibitor celecoxib. The findings indicate that the intolerance reaction in AIA is due to inhibition of COX-1. Large long-term studies of COX-2 inhibitors in AIA should be undertaken.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

Pharmacological evidence for a novel cysteinyl-leukotriene receptor subtype in human pulmonary artery smooth muscle

1. To characterize the cysteinyl-leukotriene receptors (CysLT receptors) in isolated human pulmonary arteries, ring preparations were contracted with leukotriene C(4) (LTC(4)) and leukotriene D(4) (LTD(4)) in either the absence or presence of the selective CysLT(1) receptor antagonists, ICI 198615, MK 571 or the dual CysLT(1)/CysLT(2) receptor antagonist, BAY u9773. 2. Since the contractions induced by the cysteinyl-leukotrienes (cysLTs) in intact preparations failed to attain a plateau response over the concentration range studied, the endothelium was removed and the tissue treated continuously with indomethacin (Rubbed+INDO). In these latter preparations, the pEC(50) for LTC(4) and LTD(4) were not significantly different (7.61+/-0.07, n=20 and 7.96+/-0.09, n=22, respectively). However, the LTC(4) and LTD(4) contractions were markedly potentiated when compared with data from intact tissues. 3. Leukotriene E(4) (LTE(4)) did not contract human isolated pulmonary arterial preparations. In addition, treatment of preparations with LTE(4) (1 microM; 30 min) did not modify either the LTC(4) or LTD(4) contractions. 4. Treatment of preparations with the S-conjugated glutathione (S-hexyl-GSH; 100 microM, 30 min), an inhibitor of the metabolism of LTC(4) to LTD(4), did not modify LTC(4) contractions. 5. The pEC(50) values for LTC(4) were significantly reduced by treatment of the preparations with either ICI 198615, MK 571 or BAY u9773 and the pK(B) values were: 7.20, 7.02 and 6.26, respectively. In contrast, these antagonists did not modify the LTD(4) pEC(50) values. 6. These findings suggest the presence of two CysLT receptors on human pulmonary arterial vascular smooth muscle. A CysLT(1) receptor with a low affinity for CysLT(1) antagonists and a novel CysLT receptor subtype, both responsible for vasoconstriction. Activation of this latter receptor by LTC(4) and LTD(4) induced a contractile response which was resistant to the selective CysLT(1) antagonists (ICI 198615 and MK 571) as well as the non-selective (CysLT(1)/CysLT(2)) antagonist, BAY u9773.

Influence of zafirlukast and loratadine on exercise-induced bronchoconstriction

BACKGROUND

Airway obstruction induced by physical exercise is a common feature in asthma, and conventional treatments do not offer optimal protection. There is thus a need for additional therapies for optimal control of exercise-induced bronchoconstriction (EIB).

OBJECTIVE

The influence of treatment with the antihistamine loratadine and the antileukotriene zafirlukast alone and in combination on EIB was investigated. This combination has previously shown beneficial additive effects in allergen-induced bronchoconstriction.

METHODS

In a double-blind cross-over study loratadine (10 mg twice daily) and zafirlukast (80 mg twice daily) were evaluated alone and in combination in 16 nonsmoking patients with mild asthma, previously documented EIB, and airways hyperresponsiveness to histamine.

RESULTS

The mean +/- SE maximum decrease in FEV1 after a standardized exercise provocation was 21.6% +/- 3% after placebo, 22.8% +/- 3% after loratadine, 13.9% +/- 2% after zafirlukast (P <.05 vs placebo), and 10.3% +/- 2% after the combination of loratadine and zafirlukast (P <.05 vs placebo). Expressed as the area under the FEV1 percentage change versus time curve, the mean protection produced by zafirlukast and the combination of zafirlukast and loratadine was 57% and 65%, respectively, whereas loratadine alone had no significant protective effect. There was also no significant difference between the effect of zafirlukast alone or in combination with loratadine.

CONCLUSION

The study confirmed the beneficial effect of a leukotriene receptor antagonist in EIB but failed to obtain evidence that H1-receptor antagonism alone or together with the cysteinyl-leukotriene 1 receptor antagonist zafirlukast offers a protective effect.

Improvement of aspirin-intolerant asthma by montelukast, a leukotriene antagonist: a randomized, double-blind, placebo-controlled trial

Leukotriene antagonists block the proinflammatory actions of leukotrienes (LT) and have been introduced as new treatments for asthma. Conventional therapy with glucocorticosteroids does not inhibit the biosynthesis of leukotrienes. We therefore tested whether addition of the leukotriene receptor antagonist montelukast was of therapeutic benefit in a group of aspirin-intolerant patients with asthma of whom 90% already were treated with moderate to high doses of glucocorticosteroids. Under double-blind conditions, 80 aspirin-intolerant patients with asthma were randomized to receive 4 wk oral treatment of either 10 mg of montelukast or placebo once daily at bedtime. Pulmonary function was measured as forced expiratory volume in 1 s (FEV(1)) once a week in the clinic and daily as morning and evening peak expiratory flow rate (PEFR). Asthma symptoms and use of rescue bronchodilator were also recorded daily. Asthma specific quality of life (QoL) was assessed before and after the treatments. The group receiving montelukast showed a remarkable improvement of their asthma, whereas the group given placebo showed no change. Thus, from equal baseline values, the mean difference between the groups over the 4-wk treatment period was 10.2% for FEV(1) and 28.0 L for morning PEFR (p for both < 0.001). The improved pulmonary function in the group receiving montelukast occurred at the same time as 27% less bronchodilator was used (p < 0.05), and it was associated with fewer asthma symptoms than in the group given placebo, including 1.3 nights more of sleep per week and 54% fewer asthma exacerbations (p < 0.05). There was also an improvement in asthma-specific QoL (p < 0.05). The therapeutic response to montelukast was consistent across patients with different baseline characteristics and did not correlate with baseline urinary LTE(4). Addition of a leukotriene receptor antagonist such as montelukast improves asthma in aspirin-intolerant patients over and above what can be achieved by glucocorticosteroids.

An alternative pathway for metabolism of leukotriene D(4): effects on contractions to cysteinyl-leukotrienes in the guinea-pig trachea

Contractions of guinea-pig tracheal preparations to cysteinyl-leukotrienes (LTC(4), LTD(4) and LTE(4)) were characterized in organ baths, and cysteinyl-leukotriene metabolism was studied using radiolabelled agonists and RP-HPLC separation. In the presence of S-hexyl GSH (100 microM) the metabolism of [(3)H]-LTC(4) into [(3)H]-LTD(4) was inhibited and the LTC(4)-induced contractions were resistant to CysLT(1) receptor antagonism but inhibited by the dual CysLT(1)/CysLT(2) receptor antagonist BAY u9773 (0.3 - 3 microM) with a pA(2)-value of 6.8+/-0.2. In the presence of L-cysteine (5 mM), the metabolism of [(3)H]-LTD(4) into [(3)H]-LTE(4) was inhibited and the LTD(4)-induced contractions were inhibited by the CysLT(1) receptor antagonist ICI 198,615 (1 - 10 nM) with a pA(2)-value of 9.3+/-0.2. However, at higher concentrations of ICI 198,615 (30 - 300 nM) a residual contraction to LTD(4) was unmasked, and this response was inhibited by BAY u9773 (1 - 3 microM). In the presence of the combination of S-hexyl GSH with L-cysteine, the LTD(4)-induced contractions displayed the characteristics of the LTC(4) contractile responses, i.e. resistant to CysLT(1) receptor antagonism, increased maximal contractions and slower time-course. This qualitative change of the LTD(4)-induced contraction was also observed in the presence of S-decyl GSH (100 microM), GSH (10 mM) and GSSG (10 mM). S-hexyl GSH, S-decyl GSH, GSH and GSSG all stimulated a formation of [(3)H]-LTC(4) from [(3)H]-LTD(4). In conclusion, GSH and GSH-related compounds changed the pharmacology of the LTD(4)-induced contractions by stimulating the conversion of LTD(4) into LTC(4). Moreover, the results indicate that, in addition to the metabolism of LTC(4) into LTD(4) and LTE(4), also the formation of LTC(4) from LTD(4) may regulate cysteinyl-leukotriene function.

Pulmonary gas exchange and sputum cellular responses to inhaled leukotriene D(4) in asthma

Inhalational challenges with inflammatory mediators may provoke lung function disturbances similar to those shown in spontaneous acute asthma. Cysteinyl leukotrienes (CysLTs) have recently been established as mediators of bronchoconstriction in asthma but their effects on pulmonary gas exchange in asthma have not been assessed. We therefore investigated the effects of leukotriene D(4) (LTD(4)) challenge resulting in a significant decrease in FEV(1) (mean +/- SE, by 32 +/- 3%) in 13 nonsmoking, mild asthmatics. Respiratory system resistance (Rrs), and respiratory and inert gases were measured before and immediately after, and at 15 and 45 min after challenge. After bronchoprovocation, Rrs increased (by 106 +/- 12%), Pa(O(2)) decreased (by 25 +/- 4 mm Hg), and ventilation-perfusion distributions moderately to severely deteriorated, as shown by increases in the dispersions of pulmonary blood flow (Log SDQ, by 59 +/- 12%) and alveolar ventilation (Log SDV, by 65 +/- 20%) (p < 0.05 each). Sputum eosinophils (p < 0.05) and urinary LTE(4) (p < 0.005) increased after challenge. Despite the lack of mathematical correlations between spirometric and Rrs changes and gas exchange indices, the pattern of improvement of the functional variables after challenge ran in parallel. These findings support the evidence that CysLTs, in addition to being potent bronchoconstrictors, also provoke profound disturbances of pulmonary gas exchange in asthma.

Health effects of diesel exhaust emissions

Epidemiological studies have demonstrated an association between different levels of air pollution and various health outcomes including mortality, exacerbation of asthma, chronic bronchitis, respiratory tract infections, ischaemic heart disease and stroke. Of the motor vehicle generated air pollutants, diesel exhaust particles account for a highly significant percentage of the particles emitted in many towns and cities. This review is therefore focused on the health effects of diesel exhaust, and especially the particular matter components. Acute effects of diesel exhaust exposure include irritation of the nose and eyes, lung function changes, respiratory changes, headache, fatigue and nausea. Chronic exposures are associated with cough, sputum production and lung function decrements. In addition to symptoms, exposure studies in healthy humans have documented a number of profound inflammatory changes in the airways, notably, before changes in pulmonary function can be detected. It is likely that such effects may be even more detrimental in asthmatics and other subjects with compromised pulmonary function. There are also observations supporting the hypothesis that diesel exhaust is one important factor contributing to the allergy pandemic. For example, in many experimental systems, diesel exhaust particles can be shown to act as adjuvants to allergen and hence increase the sensitization response. Much of the research on adverse effects of diesel exhaust, both in vivo and in vitro, has however been conducted in animals. Questions remain concerning the relevance of exposure levels and whether findings in such models can be extrapolated into humans. It is therefore imperative to further assess acute and chronic effects of diesel exhaust in mechanistic studies with careful consideration of exposure levels. Whenever possible and ethically justified, studies should be carried out in humans.

Benefits of high altitude allergen avoidance in atopic adolescents with moderate to severe asthma, over and above treatment with high dose inhaled steroids

Some patients with severe asthma cannot be controlled with high doses of inhaled steroids (ICS), which may be related to ongoing environmental allergen exposure. We investigated whether 10 weeks of high altitude allergen avoidance leads to sustained benefits regarding clinical and inflammatory markers of disease control in adolescents with persistent asthma despite treatment with high dose ICS. Eighteen atopic asthmatic adolescents (12-18 yr, 500-2000 microg ICS daily) with established house dust mite allergy, participated in a parallel-group study. Quality of life (PAQL), lung function, bronchial hyperresponsiveness (BHR) to adenosine and histamine, induced sputum and urine samples were collected repeatedly from 10 patients during a 10-week admission period to the Swiss Alps (alt. 1560 m) and at 6 weeks after return to sea level. Results were compared with those in eight patients, studied in their home environment at sea level for a similar time period. Throughout the study, asthma medication remained unchanged in both groups. During admission to high altitude, PAQL, lung function, BHR to adenosine and histamine, and urinary levels of eosinophil protein X (U-EPX), leukotriene E4 (U-LTE4) and 9alpha11beta prostaglandin F2 (U-9alpha11beta PGF2) improved significantly (P < 0.05), with a similar tendency for sputum eosinophils (P < 0.07). Furthermore, the changes in PAQL and BHR to adenosine and histamine were greater in the altitude than in the control group (P < 0.05). At 6 weeks after renewed allergen exposure at sea level, the improvements in PAQL (P < 0.05), BHR to adenosine (P < 0.07) and histamine (P < 0.05), as well as U-EPX (P < 0.05) and U-LTE4 (P < 0.05) were maintained. A short period of high altitude allergen avoidance, on top of regular treatment with ICS and long-acting beta2-agonists, results in improvement of asthma, as assessed by clinical and inflammatory markers of disease severity. These findings indicate that short-term, rigorous allergen avoidance can improve the long-term control of severe asthma over and above what can be achieved even by high doses of inhaled steroids.

Analyses of prostaglandin D2 metabolites in urine: comparison between enzyme immunoassay and negative ion chemical ionisation gas chromatography-mass spectrometry

Measurements of the prostaglandin (PGD2) metabolite 9 alpha, 11 beta-PGF2 in unextracted urine performed by enzyme immunoassay (EIA) were compared with values obtained by negative chemical ionisation gas chromatography-mass spectrometry (NCI GC-MS). Values determined by NCI GC-MS were in the same range but consistently lower than those obtained by EIA, suggesting that other endogenous compounds could be contributing to the immunoreactivity. Isoprostanes were generated by autoxidation of arachidonic acid and the 9 alpha, 11 beta-PGF2 antibody demonstrated less than 0.7% crossreactivity to the mix, making it unlikely that isoprostanes in urine interfere with quantification of 9 alpha, 11 beta-PGF2 by EIA. This was further supported by the 70% reduction in immunoreactive material measured in urine after three days treatment in a healthy volunteer with the cyclooxygenase inhibitor ibuprofen. Purification of urine samples by reverse phase high-performance liquid chromatography (HPLC) revealed the presence of two immunoreactive compounds in addition to 9 alpha, 11 beta-PGF2. The compounds were identified as dinor compounds by NCI GC-MS. One of the compounds was identical to 9 alpha, 11 beta-2,3-dinor-PGF2 which was generated by beta-oxidation of 9 alpha, 11 beta-PGF2 and identified by electron impact (EI)-GC-MS. In conclusion, urinary 9 alpha, 11 beta-PGF2 concentrations measured by EIA represent the sum of 9 alpha, 11 beta-PGF2 and two isomers of its dinor metabolite. Thus, the direct EIA is fast, sensitive and sufficiently specific to monitor activation of the PGD2 pathway, thereby providing a valuable clinical tool to assess the status of mast cell activation in vivo.

Asthma and leukotrienes: antileukotrienes as novel anti-asthmatic drugs

Antileukotriene drugs inhibit the formation or action of leukotrienes, which are potent lipid mediators generated from arachidonic acid in lung tissue and inflammatory cells. The leukotrienes were discovered in basic studies of arachidonic acid metabolism in leucocytes 20 years ago and were found to display a number of biological activities which may contribute to airway obstruction. Clinical studies with antileukotriene drugs have indeed demonstrated that leukotrienes are significant mediators of airway obstruction evoked by many common trigger factors in asthma. Moreover, treatment trials have established that this new class of drugs has beneficial anti-asthmatic properties, and several antileukotrienes have recently been introduced as new therapy of asthma. This communication presents an overview of the biosynthesis of leukotrienes, their biological effects and clinical effects of antileukotrienes in the treatment of asthama.

Markers of inflammation and bronchial reactivity in children with asthma, exposed to animal dander in school dust

Several studies have confirmed the presence of animal dander allergens in school dust but the effect of this indirect animal exposure on health has not been evaluated. In this study we investigated bronchial reactivity and markers of eosinophil activity and inflammation during two separate weeks of school in 10 children with mild asthma and a positive skin prick test to cat and dog. At the beginning and the end of the first week the children underwent bronchial challenges with methacholine, and at the beginning and the end of the second week they underwent nasal lavages (NAL) and induced sputum samplings. Blood and urine samples for analysis of inflammatory markers were obtained before and after both school weeks. Peak expiratory flow (PEF) and symptoms of asthma and allergy were recorded daily, and spirometry was performed on each visit. The exposure to animal dander allergens was estimated from dust samples obtained in the subjects' schools and homes. Bronchial sensitivity to methacholine increased in the week when this was measured. The proportion of eosinophils in peripheral blood, and urinary eosinophil protein X (EPX), decreased in both weeks. There was a trend towards an increase of eosinophil peroxidase (EPO) and myeloperoxidase (MPO) in sputum in the week when these proteins were measured. The concentrations of cat (Fel d1) and dog (Can f1) allergens were higher in dust collected in schools than in homes. Our results show that in children with mild asthma and animal dander allergy, there is a significantly increased bronchial sensitivity to methacholine after one school week. There is also a significant decrease in the number of circulating eosinophils and a trend towards an increase of sputum EPO, which could correlate with the early phase of eosinophil recruitment to the lungs. These effects may be related to the continuous exposure to animal allergens in school dust.

Leukotriene C4 is a tight-binding inhibitor of microsomal glutathione transferase-1. Effects of leukotriene pathway modifiers

Microsomal glutathione transferase-1 (MGST-1) is an abundant protein that catalyzes the conjugation of electrophilic compounds with glutathione, as well as the reduction of lipid hydroperoxides. Here we report that leukotriene C4 is a potent inhibitor of MGST-1. Leukotriene C4 was found to be a tight-binding inhibitor, with a Ki of 5.4 nM for the unactivated enzyme, and 9.2 nM for the N-ethylmaleimide activated enzyme. This is the first tight-binding inhibitor characterized for this enzyme. Leukotriene C4 was competitive with respect to glutathione and non-competitive toward the second substrate, CDNB. Analysis of stoichiometry supports binding of one molecule of inhibitor per homotrimer. Leukotrienes A4, D4, and E4 were much weaker inhibitors of the purified enzyme (by at least 3 orders of magnitude). Leukotriene C4 analogues, which have been developed as antagonists of leukotriene receptors, were found to display varying degrees of inhibition of MGST-1. In particular, the cysteinyl-leukotriene analogues SKF 104,353, ONO-1078, and BAYu9773 were strong inhibitors (IC50 values: 0.13, 3. 7, and 7.6 microM, respectively). In view of the partial structural similarity between MGST-1, leukotriene C4 synthase, and 5-lipoxygenase activating protein (FLAP), it was of interest that leukotriene C4 synthesis inhibitors (which antagonize FLAP) also displayed significant inhibition (e.g. IC50 for BAYx1005 was 58 microM). In contrast, selective 5-lipoxygenase inhibitors such as zileuton only marginally inhibited activity at high concentrations (500 microM). Our discovery that leukotriene C4 and drugs developed based on its structure are potent inhibitors of MGST-1 raises the possibility that MGST-1 influences the cellular processing of leukotrienes. These findings may also have implications for the effects and side-effects of drugs developed to manipulate leukotrienes.

Lipid mediator pathways in the lung: leukotrienes as a new target for the treatment of asthma

This article summarizes recent evidence supporting that antileukotriene drugs represent a new treatment of asthma which may be particularly effective when combined with drugs that have complementary effects on airway obstruction and inflammation. Firstly, it has been documented that glucocorticosteroids do not inhibit in vivo production of leukotrienes in asthmatics. In line with such findings, addition of antileukotriene drugs to a group of aspirin-intolerant asthmatics maintained on conventional therapy was found to result in an improvement of the asthma over and above the effect of the baseline treatment with inhaled and/or oral glucocorticosteroids. Likewise, in a 6-week trial in a group of severe asthmatics, the asthma deterioration caused by a reduction of the dose of inhaled steroids by half, was prevented by addition of a leukotriene antagonist to the lowered dose of glucocorticosteroids. Current evidence therefore supports that antileukotriene drugs treat components of the pathophysiology which are left unaffected by treatment with glucocorticosteroid. Secondly, in experimental studies as well as in a recent allergen bronchoprovocation study in asthmatics, it has been found that the combination of antihistaminics with antileukotriene drugs will result in a profound inhibition of both the early and the late phase of allergen-induced airway obstruction. It is hypothesized that such a combination may be useful against bronchoconstriction induced by other asthma trigger factors as well as in the treatment of asthma and rhinitits.

Agonist and antagonist activities of the leukotriene analogue BAY u9773 in guinea pig lung parenchyma

BAY u9773(6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11( Z),14(Z)-eicosatetraenoic acid) is a leukotriene E4 analogue used to define 'atypical' receptors for cysteinyl-leukotrienes. The aims of this study were first to characterise the intrinsic properties of BAY u9773 in guinea-pig lung parenchyma in vitro and second to study the influence of BAY u9773 on the concentration-response relation for leukotriene D4 in the same preparation. BAY u9773 in itself caused a concentration-dependent contraction, which was not inhibited by the cyclooxygenase inhibitor indomethacin nor by the 5-lipoxygenase inhibitor zileuton (N-(1-benzo-(12)-thien-2-ylethyl)-N-hydroxyurea). The CysLT1 receptor antagonist ICI 198,615 [(1-((2-methoxy-4-(((phenylsulfonyl)amino) carbonyl)phenyl)methyl)-1H-indazol-6-yl)carbamic acid cyclopentyl ester] alone blocked the contractile response to BAY u9773 1 microM, whereas a combination of the TP receptor antagonist BAY u3405 ((3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbaz olepropanoic acid) and ICI 198,615 was required to block the contraction induced by BAY u9773 10 microM. Together the findings suggest that BAY u9773 acted as a CysLT1 receptor agonist and in the higher concentration also as a TP receptor agonist. The CysLT1 receptor antagonist ICI 198,615 partly inhibited the contractile response to leukotriene D4. Pretreatment with BAY u9773 or leukotriene D4, caused concentration-dependent rightward displacement of the concentration-response curve for leukotriene D4. The inhibition by BAY u9773 was partial, and not greater than that produced by ICI 198,615. Combination of BAY u9773 and ICI 198,615 did not produce additive inhibition, suggesting that the major part of the leukotriene D4 induced contraction in guinea pig lung parenchyma is mediated by a CysLT receptor with properties distinct from those of previously described CysLT1 and CysLT2 receptors.

Evidence for mast cell activation during exercise-induced bronchoconstriction

Controversy remains about the causative mediators in the bronchoconstrictive response to exercise in asthma. This study examined whether mast cell activation is a feature of exercise-induced bronchoconstriction by measuring urinary metabolites of mast cell mediators. Twelve nonsmoking subjects with mild asthma and a history of exercise-induced bronchoconstriction exercised on a stationary bicycle ergometer for 5 min at 80% maximum work load. Pulmonary function was monitored and urine was collected before and 30 and 90 min after the provocation. The urinary concentrations of the mast cell markers 9alpha,11beta-prostaglandin (PG)F2 and Ntau-methylhistamine, as well as leukotriene E4 (LTE4) were determined by immunoassay. Seven of the 12 subjects (responders) experienced bronchoconstriction (>15% fall in the forced expiratory volume in one second) following exercise, whereas the pulmonary function of the remaining five subjects (nonresponders) remained stable. The urinary excretion (mean+/-SE) of 9alpha,11beta-PGF2 in the responders increased significantly compared with the nonresponders at 30 (77.1+/-14.4 versus 37.2+/-5.6; p<0.05) and 90 min (79.3+/-8.6 versus 40.4+/-8.5, p<0.05) after exercise challenge. The urinary excretion of Ntau-methylhistamine and LTE4 was not significantly different between the two groups at 30 or 90 min after exercise. The findings represent the first documentation of increased urinary levels of 9alpha,11beta-prostaglandin F2 in adults following exercise challenge and provides clear evidence for mast cell activation during exercise-induced bronchoconstriction in asthmatics.