Endothelin receptor antagonists inhibit antigen-induced lung inflammation in mice

Current Pharmacological Approach to ARDS: The Place of Bosentan

Acute respiratory distress syndrome is characterized by dyspnea at presentation, tachypnea on physical examination, findings of bilateral infiltration in chest radiography, refractory hypoxia, and high mortality. Although the main treatment approach is to address the underlying disease, there are also pharmacological and nonpharmacological options for supportive treatment. There is currently no pharmacological agent with proven efficacy in this syndrome, and many drugs are being studied for this purpose. One of these is the endothelin receptor antagonist bosentan.

Endothelin-1 mediates Aspergillus fumigatus-induced airway inflammation and remodelling

BACKGROUND

Asthma is a chronic inflammatory condition of the airways and patients sensitized to airborne fungi such as Aspergillus fumigatus have more severe asthma. Thickening of the bronchial subepithelial layer is a contributing factor to asthma severity for which no current treatment exists. Airway epithelium acts as an initial defence barrier to inhaled spores, orchestrating an inflammatory response and contributing to subepithelial fibrosis.

OBJECTIVE

We aimed to analyse the production of pro-fibrogenic factors by airway epithelium in response to A fumigatus, in order to propose novel anti-fibrotic strategies for fungal-induced asthma.

METHODS

We assessed the induction of key pro-fibrogenic factors, TGF-β1, TGF-β2, periostin and endothelin-1, by human airway epithelial cells and in mice exposed to A fumigatus spores or secreted fungal factors.

RESULTS

Aspergillus fumigatus specifically caused production of endothelin-1 by epithelial cells in vitro but not any of the other pro-fibrogenic factors assessed. A fumigatus also induced endothelin-1 in murine lungs, associated with extensive inflammation and airway remodelling. Using a selective endothelin-1 receptor antagonist, we demonstrated for the first time that endothelin-1 drives many features of airway remodelling and inflammation elicited by A fumigatus.

CONCLUSION

Our findings are consistent with the hypothesis that elevated endothelin-1 levels contribute to subepithelial thickening and highlight this factor as a possible therapeutic target for difficult-to-treat fungal-induced asthma.

Comparison of reducing effect on lung injury of dexamethasone and bosentan in acute lung injury: an experimental study

BACKGROUND

Different medical therapies are employed in acute lung injury (ALI) but there is still a debate about the efficacy of these drugs. Among these therapies steroids are clinically applied and bosentan is experimentally studied. The aim of this study was to evaluate the efficacy of these two drugs to treat inflammation in ALI by histopathological comparison.

METHODS

The five experimental groups (n = 5 per group) were: saline control (Group I); lipopolysaccharide (LPS) + saline (Group II); LPS + dexamethasone (Group III); LPS + 50 mg/kg bosentan (Group IV); and LPS + 100 mg/kg bosentan (Group V). Bosentan was administered orally one hour before and 12 hours after LPS treatment. Dexamethasone was administered intraperitoneally in three doses of 1 mg/kg; one dose was co-administered with LPS and the other two doses were given respectively 30 minutes before and after LPS treatment. Vasodilation-congestion, hemorrhage, polymorphonuclear leukocyte (PMN) infiltration, mononuclear leukocyte (MNL) infiltration, alveolar wall thickening, alveolar destruction/emphysematous appearance, and focal organization were the parameters used as criteria for evaluating inflammation and efficacy of treatment.

RESULTS

Compared to the LPS-only group (Group II), dexamethasone treatment (Group III) resulted in significant improvements in vasodilation-congestion, hemorrhage, PMN and MNL infiltration, alveolar wall thickening and emphysematous areas. Treatment with 50 mg/kg dose of bosentan (Group IV) also resulted in significant improvements in hemorrhage, PMN and MNL infiltration, alveolar wall thickening and alveolar destruction. Reducing lung injury and reparative effects of 100 mg/kg bosentan were significant in all parameters.

CONCLUSIONS

Bosentan is as effective as dexamethasone for treating lung injury in ALI. Bosentan at 100 mg/kg can be recommended as a first treatment choice based on its significant reducing lung injury and reparative effects.

Bosentan reduces oxidative burst in acid aspiration-induced lung injury in rats

BACKGROUND

Acid aspiration induces lung injury by causing an intense inflammatory reaction. Neutrophils are attracted by various cytokines, such as TNFbeta, and release reactive oxygen species, which then cause acute lung injury. Endothelin antagonists, such as bosentan, have been found to possess anti-inflammatory properties.

MATERIALS AND METHODS

We performed a prospective, randomised, controlled study to evaluate the effects of bosentan in a rat model of acid-induced lung injury. Sprague-Dawley rats underwent sevoflurane anaesthesia; lung injury was then induced by instillation of 1.2mL/kg, 0.1M hydrochloric acid. The lungs were ventilated for 6h and then randomised into three groups: bosentan 30mg/kg body weight, 90mg/kg body weight or sodium chloride, each applied immediately after acid aspiration via a gastric tube.

RESULTS

After induction of acute lung inflammation, the production of reactive oxygen species by PMN following stimulation with FMLP increased significantly. Comparison of pre-treatment and post-treatment in the 90mg/kg bosentan treatment group did not show a significant increase of reactive oxygen species following stimulation with FMLP. A comparison of the absolute difference of the MESF demonstrated a significant difference between the control group and the group treated with 90mg/kg bosentan.

CONCLUSIONS

Bosentan administration at 90mg/kg body weight reduced the release of reactive oxygen species after 360min in acid aspiration-induced lung injury in rats.

Inhalation of an endothelin receptor A antagonist attenuates pulmonary inflammation in experimental acute lung injury

We recently demonstrated that inhalation of the endothelin receptor A (ETA) antagonist LU 135252 improved arterial oxygenation and reduced pulmonary artery pressure in experimental acute lung injury (ALI). In this study we analyzed potential immune modulatory effects of inhaled LU 135252 in experimental ALI. ALI was induced by repeated lung lavage in intubated (100% O2) and anesthetized piglets. Animals were randomly assigned to inhale either nebulized LU 135252 (0.3 mg.kg(-1), ALI + LU group, n = 8) or saline buffer (ALI control group, n = 16), both for 30 min. Surviving animals were sacrificed 6 h after induction of ALI, and lung tissue specimens were obtained from all animals for histology and immunhistochemistry. Induction of ALI significantly decreased arterial oxygenation in all animals. Inhalation of LU 135252 significantly reduced mortality and induced significant and sustained increase in PaO2 (316 +/- 47 mm Hg vs. control 53 +/- 3 mm Hg, p < 0.001). We measured a significant reduction in the number of pulmonary leukocyte L1 antigen-positive cells in ALI + LU animals (8% +/- 1% positive cells vs. control 12% +/- 2% positive cells, p < 0.05). The number of CD3-positive cells was not altered by treatment with LU 135252. Pulmonary tissue concentration of IL-6 was significantly suppressed by LU 135252 inhalation (4 +/- 1 pg.100 mg-1 wet weight vs. control 7 +/- 1 pg.100 mg(-1) wet weight, p < 0.05). Concentrations of TNF-alpha, IL-1beta, and ET-1 in pulmonary tissue were not influenced by inhalation of LU 135252. In conclusion, we demonstrated that inhalation of LU 135252 not only improves mortality and gas exchange, but also blunts the local immune response in experimental ALI.

Endothelin A receptor antagonist modulates lymphocyte and eosinophil infiltration, hyperreactivity and mucus in murine asthma

Levels of endothelins are particularly high in the lung, and there is evidence that these peptides are involved in asthma. Asthma is a chronic inflammatory disease associated with lymphocyte infiltration. In the present study, we used a murine model of asthma to investigate the role of endothelins in lymphocyte and eosinophil infiltration into the airway hyperreactivity and mucus secretion. Sensitized C57Bl/6 mice were treated with endothelin ETA receptor antagonist (BQ123) or endothelin ETB receptor antagonist (BQ788) 30 min before an antigen aerosol challenge. After 24 h, dose response curves to methacholine were performed in isolated lungs, FACS analysis of lymphocytes and eosinophil counts were performed in bronchoalveolar lavage fluid and mucus index was determined by histopathology. In sensitized and antigen-challenged mice there is a marked increase in the T CD4+, T CD8+, B220+, Tgammadelta+ and NK1.1+ lymphocyte subsets. Treatment with BQ123 further increased these cell populations. The number of eosinophils, airway hyperreactivity and mucus were all reduced by BQ123 treatment. The BQ 788 had no significant effect on the parameters analyzed. Treatment with BQ123 reduced the endothelin concentration in lung homogenates, suggesting that endothelins exert a positive feedback on their synthesis. We show here that in murine asthma the ETA receptor antagonist up-regulates lymphocyte infiltration and reduces eosinophils, hyperreactivity and mucus.

The role of ET(A) and ET(B) receptor antagonists in acute and allergic inflammation in mice

In this study, we investigated the effects of the selective ET(A) (BQ-123) and ET(B) (BQ-788) receptor antagonists for endothelin-1 (ET-1) against several flogistic agent-induced paw edema formation and ovalbumin-induced allergic lung inflammation in mice. The intraplantar injection of BQ-123, but not BQ-788, significantly inhibited carrageenan-, PAF-, ET-1- and bradykinin-induced paw edema formation. The obtained inhibitions (1h after the inflammatory stimulus) were 79+/-5%, 55+/-4%, 55+/-6% and 74+/-4%, respectively. In carrageenan-induced paw edema, the mean ID(50) value for BQ-123 was 0.77 (0.27-2.23)nmol/paw. The neutrophil influx induced by carrageenan or PAF was reduced by BQ-123, with inhibitions of 55+/-2% and 72+/-4%, respectively. BQ-123 also inhibited the indirect macrophage influx induced by carrageenan (55+/-6%). However, BQ-788 failed to block the cell influx caused by either of these flogistic agents. When assessed in the bronchoalveolar lavage fluid in a murine model of asthma, both BQ-123 and BQ-788 significantly inhibited ovalbumin-induced eosinophil recruitment (78+/-6% and 71+/-8%), respectively. Neither neutrophil nor mononuclear cell counts were significantly affected by these drugs. Our findings indicate that ET(A), but not ET(B), selective ET-1 antagonists are capable of preventing the acute inflammatory responses induced by carrageenan, PAF, BK and ET-1. However, both ET(A) and ET(B) receptor antagonists were found to be effective in inhibiting the allergic response in a murine model of asthma.

[Endothelin-1 in nasal lavage fluid of allergic rhinitis patients--new mediator of allergic rhinitis]

The nasal epithelium is considered to play an active role in the allergic inflammation through its capacity to synthesize and release a wide range of cytokines and mediators. Few studies have investigated the involvement of endothelin-1 in the pathogenesis of inflammatory diseases of the upper airways. To examine the release of endothelin-1 from nasal mucosa after allergen challenge we investigated 24 patients. 15 subjects (7 male, 8 female) allergic to birch pollen aged 37.1 +/- 4.9 years participated in the study. Nasal birch allergen provocation with following lavage was performed in all subjects. Endothelin-1 in the nasal secretion were assayed before and after challenge. Increase in concentration of endothelin-1 in nasal lavage fluid from allergic patients were significantly higher than in control group respectively from 18.33 +/- 5.47 fmol/ml to 26.41 +/- 6.92 fmol/ml versus 18.8 +/- 3.99 to 19.80 +/- 4.18 fmol/ml (p < 0.05) in controls. We conclude that endothelin-1 could be involved in the pathogenesis of seasonal allergic rhinitis.

Endothelin, PAF and thromboxane A2 in allergic pulmonary hyperreactivity in mice

The role of endothelin, PAF and thromboxane A2 in airway hyperreactivity (AHR) to carbachol induced by ovalbumin sensitization and challenge in Balb/c mice was investigated. Ovalbumin sensitization and challenge induced significant AHR to carbachol in actively sensitized and challenged mice. Treatment of these mice with the PAF antagonist CV-3988 (10 microg kg(-1), i.v.) completely abolished OVA-induced AHR to carbachol. Treatment of sensitized mice with the TxA2 antagonist L-654,664 (1 mg kg(-1), i.v.) partially blocked the induction of AHR in OVA-challenged mice. The intranasal administration of 50 pmol of the ET(A) receptor antagonist BQ-123 had no effect on the PIP but produced a significant reduction at the dose of 100 pmol. The intravenous administration of BQ-123 (100 pmol) reduced the PIP only at the highest doses of carbachol. The ET(B) receptor antagonist BQ-788 administered either via the intranasal or intravenous route had no effect on the PIP at the dose of 100 pmol. Naïve mice treated with either U-44069 (25 or 100 microg kg(-1), i.v.), endothelin-1 (100 pmol, intranasally) or the ET(B) receptor agonist IRL-1620 (100 pmol, intranasally) showed a marked increase in airway reactivity to carbachol. These results suggest an important role for endothelin, PAF and thromboxane A2 in AHR in mice actively sensitized and challenged with ovalbumin.

ETB receptor polymorphism is associated with airway obstruction

Background

Endothelin-1 (EDN1) has been involved in the development of airway obstruction and inflammation in asthma. Several polymorphisms have been identified among the genes encoding for preproET1, an inactive precursor of ET-1, and for ET_A (EDNRA) and ET_B (EDNRB), the two receptors for EDN1. In the present work, we hypothesised that molecular variation in these genes could be a major determinant of the degree of bronchial obstruction. The purpose of this study was to investigate whether the genetic polymorphisms of preproET-1, EDNRA and EDNRB genes were associated with the degree of airway obstruction, assessed by FEV₁.

Methods

Polymorphisms of preproET-1, EDNRA and EDNRB were first studied in a population of adult asthmatic patients. Results were confirmed in a large population of adults from the general population from the ECRHS II study.

Results

In our population of adult asthmatic patients, the EDNRB-30G>A (Leu277Leu) polymorphism (GG genotype) is strongly associated with a low FEV₁ and with a higher percentage of patients with FEV1 < 80% of predicted value. No relationship was found between pulmonary function and EDNRA-1363C>T (His323His) or preproET-1-595G>T (Lys198Asp) polymorphism. In the adult population from the ECRHS II, we found a similar association between GG genotype and a low FEV₁ or a higher percentage of subjects with FEV1 < 80% predicted, especially in the subgroups of asthmatics subjects (OR = 4.31 (95%CI 1.03 – 18.04)) and smokers (OR = 7.42 (95%CI 1.69 – 32.6)).

Conclusion

the EDNRB-30G>A polymorphism could be a determinant of airway obstruction in humans with predisposing factors such as tobacco smoke exposure or asthma.

Role of endogenous endothelin-1 in transplant obliterative airway disease in the rat

Endothelin-1 (ET-1) expression is increased after lung transplantation in association with ischemia reperfusion injury and acute rejection. However, little is known of the role of ET-1 during the development of obliterative bronchiolitis. In this study, we investigated the biological significance of ET-1 in obliterative airway disease development using a rat tracheal allograft model. Immunoreactivity of ET-1 and its receptors ET-RA and ET-RB was increased four-fold in allografts compared with syngrafts and localized to mononuclear cells and smooth muscle cells of the myofibroproliferative lesion and airway wall, indicating that ET-1 may mediate its effects in both a paracrine and autocrine manner in smooth muscle cells. Inhibition of ET-1 action by a nonselective ET-1 receptor antagonist, bosentan, significantly decreased tracheal occlusion, which was linked to delayed epithelial necrosis, suppressed smooth muscle cell proliferation, and a marked reduction in the number of interleukin-1beta and interleukin-2 immunoreactive cells. Our findings show that endogenous ET-1 activation is associated with obliteration of the airway wall, and blocking signaling downstream of ET-1 receptors leads to attenuation of obliterative airway disease. The results suggest that ET-1 has a proproliferative and proinflammatory role in the development of obliterative bronchiolitis.

Effects of endothelin ETAreceptor antagonism on granulocyte and lymphocyte accumulation in LPS-induced inflammation

Endothelin peptides play active roles in different aspects of inflammation. This study investigates the contribution of endogenous endothelins to lipopolysaccharide (LPS) pulmonary inflammation by assessing the influence of ET(A) receptor antagonism on leukocyte accumulation, granulocyte adhesion molecule expression, and chemokine/cytokine modulation. Local pretreatment with BQ-123 or A-127722 (150 pmol), two selective and chemically unrelated endothelin ET(A) receptor antagonists, inhibits neutrophil and eosinophil accumulation in LPS-induced pleurisy at 24 h but not neutrophil migration at 4 h. The effect of endothelin antagonism on neutrophil accumulation at 24 h was concomitant with inhibition of eosinophil and CD4 and CD8 T lymphocyte influx. It is surprising that the ET(A) receptor blockade did not inhibit the accumulation of gammadelta T lymphocytes, cells that are important for granulocyte recruitment in this model. Blockade of ET(A) receptors did not influence the expression of adhesion molecules (CD11b, CD49d) on granulocytes but abrogated the increase in tumor necrosis factor alpha levels 4 h after LPS stimulation and also markedly inhibited increases in levels of interleukin-6 and keratinocyte-derived chemokine/CXC chemokine ligand 1 but not eotaxin/chemokine ligand 11. Thus, acting via ET(A) receptors, endogenous endothelins play an important role in early cytokine/chemokine production and on granulocyte and lymphocyte mobilization in LPS-induced pleurisy.

Investigation into the potential anti-inflammatory effects of endothelin antagonists in a murine model of experimental monosodium urate peritonitis

Endothelin (ET)-1 has been detected in many inflammatory pathologies, including rheumatoid arthritic patients, asthma, and ischemic-reperfusion injury. In this study, we have investigated the effect of a panel of different ET-1 antagonists displaying different selectivities for the receptors in a murine model of experimental inflammatory peritonitis. Systemic treatment of mice with the ETA antagonist C33H44N6O5, N-[N-[-N(hexahydro-1H-azepin-1-yl)carbonyl]-L-leucyl]-1-methyl-D-tryptophyl]-3-(2-pyridinyl)-D-alanine (FR139317) inhibited neutrophil accumulation. However, a greater degree of inhibition was observed with the ETB antagonist C34H51N5O7, N-cis-2,6-dimethylpiperidinocarbonyl-b-tBu-Ala-D-Trp(1-methoxycarbonyl)-D-Nle-OH (BQ-788) and the ET(A and B) antagonist C52H65N7O10, N-acetyl-alpha-[10,11-dihydro-5H-dibenzo-[a,d]cycloheptadien-5-yl]-D-Gly-Leu-Asp-lle-lle-Trp (PD145065); all these effects occurred without altering peripheral blood cell counts. Release of the CXC chemokine KC was significantly reduced by the FR139317 and PD145065 but not by BQ-788. Evaluation of the therapeutic potential of these antagonists showed that PD145065 inhibited neutrophil migration and KC release, whereas the others caused a nonsignificant reduction in these parameters. Parameters of endothelial cell activation showed that urate-stimulated interleukin-1beta release was inhibited by BQ-788 and PD145065 but not by FR139317, whereas ET-1 was only inhibited by the mixed antagonist. A different scenario was observed with respect to release of the CXC chemokine KC with FR139317 and PD145065 being effective, whereas with a marker of polymorphonuclear activation the ETA and mixed antagonist inhibited adhesion molecule expression. These data show that ET-1 antagonists elicit different mechanisms of actions in the way they display their antimigratory effects in a murine model of monosodium urate crystal peritonitis.

Leukotriene antagonism reduces the generation of endothelin-1 and interferon-gamma and inhibits eosinophilic airway inflammation

The cysteinyl leukotrienes (cysLTs) and the peptide hormone endothelin (ET)-1 are potent bronchoconstrictor substances, and these mediators are also claimed to be implicated in the development of eosinophilic airway inflammation. In the present study, we have investigated the effect of the cysLT1 receptor antagonist montelukaston the development of an eosinophilic airway inflammation 24 h after intratracheal Sephadex (SDX) provocation in rats. Furthermore, the effect of montelukast treatment on the generation of ET-1 and other pro-inflammatory mediators has been studied. The inflammatory response was significantly reduced in the animals receiving SDX + montelukast compared to animals receiving solely SDX, as evaluated by a decrease in bronchoalveolar lavage fluid total cell count (10.3 +/- 1.2 vs. 18.5 +/- 1.8 x 10(4) ml(-1), P<0.001), number of eosinophils (299.7 +/- 43.8 vs. 577.6 +/- 46.6 x 10(2) ml(-1), P<0.001), and lymphocytes (116.8 +/- 20 vs. 222.0 +/- 34.8 x 10(2) ml(-1), P<0.05), as well as the degree of tissue inflammation (P<0.05). Montelukast also inhibited the increase in the concentration of the pro-inflammatory mediators ET-1 (28.5 +/- 75 vs. 40.9 +/- 7.3 x pg ml(-1), P<0.05) and interferon (IFN)-gamma (4.3 +/- 2.2 vs. 15.6+/-8.7 x pg ml(-1), P<0.05), but not tumor necrosis factor-gamma or interleukin-8. In summary, treatment with the cysLT1 receptor antagonist montelukast reduced the inflammatory response during development of an eosinophilic airway inflammation, possibly by inhibiting the release of pro-inflammatory mediators like ET-1 and IFN-gamma.

An endothelin receptor antagonist, SB-217242, inhibits airway hyperresponsiveness in allergic mice

Within the airways, endothelin-1 (ET-1) can exert a range of prominent effects, including airway smooth muscle contraction, bronchial obstruction, airway wall edema, and airway remodeling. ET-1 also possesses proinflammatory properties and contributes to the late-phase response in allergic airways. However, there is no direct evidence for the contribution of endogenous ET-1 to airway hyperresponsiveness in allergic airways. Allergic inflammation induced in mice by sensitization and challenge with the house dust mite allergen Der P1 was associated with elevated levels of ET-1 within the lung, increased numbers of eosinophils within bronchoalveolar lavage fluid and tissue sections, and development of airway hyperresponsiveness to methacholine (P < 0.05, n = 6 mice per group). Treatment of allergic mice with an endothelin receptor antagonist, SB-217242 (30 mg x kg(-1) x day(-1)), during allergen challenge markedly inhibited airway eosinophilia (bronchoalveolar lavage fluid and tissue) and development of airway hyperresponsiveness. These findings provide direct evidence for a mediator role for ET-1 in development of airway hyperresponsiveness and airway eosinophilia in Der P1-sensitized mice after antigen challenge.

Modeling allergic asthma in mice: pitfalls and opportunities

Studies in murine experimental models have contributed greatly to understanding the mechanisms of allergic inflammation underlying asthma. However, models involving short-term high-level exposure of sensitized animals to antigen have significant limitations for investigating the pathogenesis of the lesions of chronic asthma. Modeling chronic asthma is problematic, because long-term antigenic challenge often triggers widespread pulmonary parenchymal inflammation or leads to eventual downregulation of inflammation and airway hyperreactivity. We have developed an improved murine model in which animals are exposed to low mass concentrations of aerosolized antigen for 6-8 wk. The mice exhibit airway-specific acute-on-chronic inflammation and changes of airway wall remodeling as seen in human asthma, together with hyperreactivity to a cholinergic agonist which can be specifically attributed to airway disease. This more realistic model of asthma offers a number of opportunities for investigation of pathogenetic mechanisms and novel therapeutic agents.

Function of the endothelinB receptor in cardiovascular physiology and pathophysiology

One of the two receptors by which the potent vasoactive effects of endothelin (ET)-1 are mediated is the ET(B) receptor (ET(BR)), which is found in several tissues, but, more importantly from a cardiovascular point of view, on the endothelial cell. The endothelial cell also has the unique capability of releasing ET-1, as well as other factors, such as the endothelial-derived relaxing factors and prostacyclin, which counteract the myotropic effects of the peptide. The secretory and contractile responses to ET-1 rely on G-protein-coupled ET(BR)s, as well as ET(A)-G-protein-coupled receptor-like proteins. The mitogenic properties of ET-1 via ET(A) receptors (ET(AR)s) coupled to mitogen-activated protein kinases and tyrosine kinases on the vascular smooth muscle may occur in conjunction with the anti-apoptotic characteristics of the endothelial ET(BR)s. Interestingly, most of the relevant antagonists and agonists for both ET(AR)s and ET(BR)s have been developed by the pharmaceutical industry. This highlights the therapeutical potential of compounds that act on ET receptors. In normal as well as in physiopathological conditions, the ET(BR) plays an important role in the control of vascular tone, and must be taken into account when using ET receptor antagonists for the treatment of cardiovascular diseases. For the management of congestive heart failure, renal failure and primary pulmonary hypertension, the most recent literature supports the use of selective ET(AR) antagonists rather than mixed antagonists of ET(AR)s and ET(BR)s. Nonetheless, validation of this view will have to await the first clinical trials comparing the actions of ET(A) to mixed ET(A)/ET(B) receptor antagonists.

Gq signaling is required for allergen-induced pulmonary eosinophilia

The complexity and magnitude of interactions leading to the selective infiltration of eosinophils in response to inhaled allergens are formidable obstacles to a larger understanding of the pulmonary pathology associated with allergic asthma. This study uses knockout mice to demonstrate a novel function for the heterotrimeric G protein, G(q), in the regulation of pulmonary eosinophil recruitment. In the absence of G(q) signaling, eosinophils failed to accumulate in the lungs following allergen challenge. These studies demonstrate that the inhibition of eosinophil accumulation in the airways is attributed to the failure of hemopoietically derived cells to elaborate GM-CSF in the airways. The data suggest that activation of a G(q)-coupled receptor(s) on resident leukocytes in the lung elicits expression of GM-CSF, which, in turn, is required for allergen-induced pulmonary eosinophilia, identifying a novel pathway of eosinophil-associated effector functions leading to pulmonary pathology in diseases such as asthma.

Role of endothelin-1 in lung disease

Endothelin-1 (ET-1) is a 21 amino acid peptide with diverse biological activity that has been implicated in numerous diseases. ET-1 is a potent mitogen regulator of smooth muscle tone, and inflammatory mediator that may play a key role in diseases of the airways, pulmonary circulation, and inflammatory lung diseases, both acute and chronic. This review will focus on the biology of ET-1 and its role in lung disease.

Endothelin as a therapeutic target in the treatment of cardiovascular disease

Endothelins, a family of peptides derived from the vascular endothelium and smooth muscle cells possess vasoconstrictor and mitogenic properties. By acting predominantly in a paracrine fashion, these peptides activate specific receptors and have protean effects in normal and diseased organ systems. The wide distribution of these receptors in various tissues mediate the multiplicity of physiologic actions attributed to endothelins. Much of our understanding about endothelins has come from the development of an array of receptor-specific and mixed receptor antagonists. Based on the promising results from animal studies, active research and drug development programs are under way to investigate the clinical potential of endothelin antagonism for treatment of cardiovascular disease.

Effect of endothelin antagonism on the production of cytokines in eosinophilic airway inflammation

Endothelin (ET)-1 has been launched as an important mediator in bronchial asthma, which is an eosinophilic airway inflammation. However, the interplay between ET-1 and other proinflammatory mediators during the development of airway inflammation has not been elucidated. We wanted to study 1) whether the production of ET-1 precedes the production of other proinflammatory mediators and 2) whether ET-1 stimulates the production of these mediators within the airways. These hypotheses were studied during the development of an eosinophilic airway inflammation in rats. The increase in ET-1 mRNA level in lung tissue preceded the increase in mRNA levels of tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-8. Treatment of the animals with the ET receptor antagonist bosentan resulted in a substantial decrease in the concentrations of tumor necrosis factor-alpha, IL-4, IL-1beta, interferon-gamma, and ET-1 in bronchoalveolar lavage fluid. In conclusion, the synthesis of ET-1 as measured by increased mRNA level precedes the synthesis of other proinflammatory cytokines of importance for the development of an eosinophilic airway inflammation, and ET antagonism inhibits the production of these mediators within the airways. Whether treatment with ET antagonists will prove beneficial for patients with eosinophilic airway inflammations like bronchial asthma is not yet known.

Contribution of upregulated airway endothelin-1 expression to airway smooth muscle and epithelial cell DNA synthesis after repeated allergen exposure of sensitized Brown-Norway rats

Endothelin-1 is a potent bronchoconstrictor peptide with pro-inflammatory and growth-promoting properties. After exposure of sensitized Brown-Norway rats to six repeated ovalbumin exposures, there was an increase in pro-endothelin (ET)-1 messenger RNA compared with saline-exposed control rats 24 h after the final exposure (P < 0.01). ET-1 immunoreactivity was increased sixfold in the bronchial epithelium of the larger conducting airways in the repeated allergen-exposed rats (P < 0.001). After repeated allergen exposure, there were increased rates of DNA synthesis in the airway smooth muscle (ASM) cells (P < 0.001) and epithelial cells (P < 0. 001) compared with saline-exposed controls, as measured by bromodeoxyuridine incorporation. Treatment with a dual endothelin A and B (ET(A+B)) receptor antagonist caused a significant attenuation in both ASM (P < 0.001) and epithelial cell (P < 0.001) bromodeoxyuridine incorporation compared with the allergen-challenged and vehicle-treated group. The dual ET(A+B) antagonist attenuated eosinophil recruitment into the airways (P < 0. 05) but had no significant effect on increased bronchial reactivity to acetylcholine in allergen-exposed rats. Increased levels of ET-1 in the airways may contribute to inflammation and ASM and epithelial cell DNA synthesis after repeated allergen exposure. Such processes may underlie increased proliferation of resident cells leading to airway wall remodeling in asthmatics.

Endothelin-1 changes polymorphonuclear leukocytes' deformability and CD11b expression and promotes their retention in the lung

Endothelin (ET)1 influences polymorphonuclear leukocyte (PMN)- endothelial cell interactions. The aim of this study was to examine the effect of ET-1 on factors that influence PMN-endothelial interaction and retention in the lung both in vitro and in vivo. In vitro, high concentration of ET-1 (> or = 10(-8) M) rapidly increased PMN F-actin content (10(-7) M: 58 +/- 6% increase, P<0.01), whereas lower concentration of ET-1 (< or = 10(-9) M) caused a small but consistent decrease in F-actin content (10(-10) M: 6.9+/-1.5% decrease, P< 0.01). Preincubation of PMNs with the nitric oxide donor sodium nitroprusside (SNP) inhibited the F-actin content increase by 10(-7) M of ET-1 (P<0.01), and enhanced the F-actin content decrease by 10(-10) M of ET-1 (P<0.01). Preincubation of PMNs with Nomega-nitro-L-arginine methylester prevented the F-actin content decrease by 10(-10) M of ET-1. ET-1 (10(-7) M) reduced the deformability of PMNs (P<0.01), which was inhibited by preincubation of PMNs with SNP (P<0.05). ET-1 (10(-9) to 10(-7) M) increased CD11b expression of PMNs (P<0.01), which was inhibited by preincubation of PMNs with SNP. In vivo studies showed that the retention of PMNs treated with ET-1 increased from 45+/-8 to 70+/-5% compared with naive PMNs during their first pass through the lung (P<0.05). We conclude that ET-1 changes the F-actin content, the deformability, and the CD11b expression of PMNs in a dose-dependent fashion and that this leads to increased PMN sequestration in pulmonary microvessels.

Endothelin receptor blockade decreases lung water in young rats exposed to viral infection and hypoxia

Viral respiratory infections may increase the susceptibility of young animals to hypoxia-induced pulmonary edema. Because hypoxia stimulates endothelin production, we hypothesized that an increase in lung endothelin contributes to these alterations in lung water. Weanling rats were infected with Sendai virus, causing a mild respiratory infection. At day 7 after infection, animals were exposed to hypoxia (inspired O(2) fraction = 0.1) for 24 h. Exposure to virus plus hypoxia led to increases in lung water compared with control groups (P < 0.001). Lung endothelin levels were significantly higher in the virus plus hypoxia group than in control groups (P < 0.001). A second group of infected animals received bosentan, a nonselective endothelin receptor antagonist, during exposure to hypoxia. Bosentan-treated animals showed less lung water accumulation, less lung lavage fluid protein, and less perivascular fluid cuffing than untreated animals (P < 0.01). We conclude that the combination of a recent viral respiratory infection and exposure to moderate hypoxia led to increases in endothelin in the lungs of young rats and that endothelin receptor blockade ameliorates the hypoxia-induced increases in lung water found in these animals.

Sputum cellular and cytokine responses to inhaled endothelin-1 in asthma

BACKGROUND

Endothelin (ET)-1 is a 21-amino acid peptide which has potent bronchoconstrictor activity. Animal studies show elevation of ET-1 during experimental airway inflammation, and inhibition of inflammation by endothelin-antagonists, suggesting pro-inflammatory activity for ET-1.

OBJECTIVE

We wanted to assess any acute influence that bronchoconstrictor doses of inhaled ET-1 might have on cells, tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, nitrite (NO2) and albumin in induced sputum in asthma.

METHODS

Bronchial challenge was performed using nebulized ET-1 (nebulized dose range 0.96-15.36 nmol) and placebo in 10 adult asthmatic subjects in a randomized double-blind placebo-controlled cross-over study. Sputum induction was performed 30 min and 4 h after placebo or ET-1 bronchial challenge.

RESULTS

All subjects experienced dose-dependent bronchoconstriction to inhaled ET-1 with a mean (range) PC15 forced expiratory volume in 1 s (FEV1) to ET-1 of 9.45 (1.2-21.7) nmol. Comparing ET-1 with placebo inhalation, there was no change in sputum differential cell counts, TNFalpha, IL-1beta, NO2 or albumin at 30 min or 4 h after inhalation, nor was there a difference in these parameters at 4 h compared with 30 min after ET-1 inhalation. There was no fall in FEV1 at 4 h after ET-1 inhalation, suggesting that ET-1 inhalation is not associated with a late bronchoconstrictor response.

CONCLUSIONS

We conclude that inhaled ET-1 does not appear to stimulate an acute inflammatory response in asthma as assessed by differential cell count, TNFalpha, IL-1beta, NO2 and albumin concentrations in induced sputum.

Endothelins and asthma

In the decade since endothelin-1 (ET-1) and related endogenous peptides were first identified as vascular endothelium-derived spasmogens, with potential pathophysiological roles in vascular diseases, there has been a significant accumulation of evidence pointing to mediator roles in obstructive respiratory diseases such as asthma. Critical pieces of evidence for this concept include the fact that ET-1 is an extremely potent spasmogen in human and animal airway smooth muscle and that it is synthesised in and released from the bronchial epithelium. Importantly, symptomatic asthma involves a marked enhancement of these processes, whereas asthmatics treated with anti-inflammatory glucocorticoids exhibit reductions in these previously elevated indices. Despite this profile, a causal link between ET-1 and asthma has not been definitively established. This review attempts to bring together some of the evidence suggesting the potential mediator roles for ET-1 in this disease.

Interleukin-8 receptor modulates IgE production and B-cell expansion and trafficking in allergen-induced pulmonary inflammation

We examined the role of the interleukin-8 (IL-8) receptor in a murine model of allergen-induced pulmonary inflammation using mice with a targeted deletion of the murine IL-8 receptor homologue (IL-8r-/-). Wild-type (Wt) and IL-8r-/- mice were systemically immunized to ovalbumin (OVA) and were exposed with either single or multiple challenge of aerosolized phosphate-buffered saline (OVA/PBS) or OVA (OVA/OVA). Analysis of cells recovered from bronchoalveolar lavage (BAL) revealed a diminished recruitment of neutrophils to the airway lumen after single challenge in IL-8r-/- mice compared with Wt mice, whereas multiply challenged IL-8r-/- mice had increased B cells and fewer neutrophils compared with Wt mice. Both Wt and IL-8r-/- OVA/OVA mice recruited similar numbers of eosinophils to the BAL fluid and exhibited comparable degrees of pulmonary inflammation histologically. Both total and OVA-specific IgE levels were greater in multiply challenged IL-8r-/- OVA/OVA mice than in Wt mice. Both the IL-8r-/- OVA/OVA and OVA/PBS mice were significantly less responsive to methacholine than their respective Wt groups, but both Wt and IL-8r mice showed similar degrees of enhancement after multiple allergen challenge. The data demonstrate that the IL-8r modulates IgE production, airway responsiveness, and the composition of the cells (B cells and neutrophils) recruited to the airway lumen in response to antigen.

Endothelin receptor distribution and function in the airways

1. Within the lung, endothelin (ET)-1 is synthesized and released by airway epithelial and vascular endothelial cells, as well as by inflammatory cells, such as macrophages. Following release, ET-1 can modulate the activities of a wide range of different cell types within the lung through the stimulation of specific endothelin ETA and ETB receptors. The present review focuses on recent advances in our understanding of the distribution and function of endothelin receptors within the airway wall and peripheral lung and, where possible, particular attention is given to studies using human cells, tissues and subjects. 2. The highest densities of endothelin receptors within the lung appear to be associated with airway smooth muscle and the alveolar septae. The relative proportions of ETA and ETB receptors present within these tissues display marked interspecies differences, although ETB receptors predominate at both sites in human lung. 3. The effects induced by ET-1 within the lung include contraction and proliferation of airway smooth muscle, facilitation of cholinergic neurotransmission, mucous gland hypersecretion, microvascular leakage and inflammatory cell influx and activation. There is also evidence that a proportion of ETB receptors in the pulmonary microvasculature act as clearance receptors for endothelin-1. 4. Evidence to date suggests that changes in the endothelin content within the airway wall, conceivably associated with lung pathology, are likely to have profound effects on the function of many cells within the lung.

Putative mediator role of endothelin-1 in asthma and other lung diseases

1. There is an increasing amount of research to implicate endothelin (ET)-1, a member of a family of 21 amino acid peptides, as a potentially important mediator in pulmonary diseases, in particular asthma and pulmonary hypertension. Thus, ET-1 fits several of the standard criteria that need to be fulfilled for a pathophysiologically relevant substance. 2. Endothelin-1 is present in abundance in human lung: the major loci for ET-1 are the epithelium, endothelium, endocrine cells and inflammatory cells. Furthermore, the receptors that mediate the biological effects of ET-1, the ETA and ETB receptor subtypes, are found in human lung, predominantly in airway smooth muscle, and vascular smooth muscle and, to a lesser extent, nerves. There is no change in the relative proportions of ETA and ETB receptors in asthmatic versus non-asthmatic bronchial smooth muscle and peripheral lung. 3. Several studies have shown that ET-1 mimics several of the features of asthma (including bronchospasm, airway remodelling, inflammatory cell recruitment and activation, oedema, mucus secretion, airway hyperreactivity and dysfunction in neuronal inputs); however, some other reports are at odds with these findings. 4. Endothelin-1 mimics the two classical features of pulmonary hypertension (pulmonary vascular constriction and remodelling), which is often a serious complication of chronic obstructive pulmonary disease. 5. Intranasal ET-1 produces several of the symptoms of allergic rhinitis. 6. There are several reports of increased levels and/or expression of ET in patients with many pulmonary disorders, in particular asthma or pulmonary hypertension, with some evidence of a correlation between ET amounts and disease severity; however, other studies do not confirm these observations. 7. Despite these intriguing data in support of a pathophysiological role of ET-1 in lung disease, the definitive test and most difficult criteria to fulfil, the clinical evaluation of ET receptor antagonists or ET synthesis inhibitors, has still to be conducted. Only after these pivotal data are available will we be able to determine definitively whether ET-1 is a pathophysiologically important mediator in lung diseases or merely an interesting peptide with several effects in the pulmonary system.