Asthma -- a need for a rethink?

Revisiting asthma pharmacotherapy: where do we stand and where do we want to go?

Several current guidelines/strategies outline a treatment approach to asthma, which primarily consider the goals of improving lung function and quality of life and reducing symptoms and exacerbations. They suggest a strategy of stepping up or down treatment, depending on the patient's overall current asthma symptom control and future risk of exacerbation. While this stepwise approach is undeniably practical for daily practice, it does not always address the underlying mechanisms of this heterogeneous disease. In the last decade, there have been attempts to improve the treatment of severe asthma, such as the addition of a long-acting antimuscarinic agent to the traditional inhaled corticosteroid/long-acting β2-agonist treatment and the introduction of therapies targeting key cytokines. However, despite such strategies several unmet needs in this population remain, motivating research to identify novel targets and develop improved therapeutic and/or preventative asthma treatments. Pending the availability of such therapies, it is essential to re-evaluate the current conventional "one-size-fits-all" approach to a more precise asthma management. Although challenging, identifying "treatable traits" that contribute to respiratory symptoms in individual patients with asthma may allow a more pragmatic approach to establish more personalised therapeutic goals.

Therapeutic monoclonal antibodies for respiratory diseases: Current challenges and perspectives, March 31 - April 1, 2016, Tours, France

Monoclonal antibody (mAb) therapeutics have tremendous potential to benefit patients with lung diseases, for which there remains substantial unmet medical need. To capture the current state of mAb research and development in the area of respiratory diseases, the Research Center of Respiratory Diseases (CEPR-INSERM U1100), the Laboratory of Excellence “MAbImprove,” the GDR 3260 “Antibodies and therapeutic targeting,” and the Grant Research program ARD2020 “Biotherapeutics” invited speakers from industry, academic and government organizations to present their recent research results at the Therapeutic Monoclonal Antibodies for Respiratory Diseases: Current challenges and perspectives congress held March 31 – April 1, 2016 in Tours, France.

Functional activity of peripheral blood eosinophils in allergen-induced late-phase airway inflammation in asthma patients

OBJECTIVE

We aimed to investigate peripheral blood eosinophil chemotaxis, generation of spontaneous reactive oxygen species (ROS), and apoptosis in patients with allergic asthma after bronchial allergen challenge.

MATERIAL AND METHODS

A total of 18 patients with allergic asthma (AA), 14 with allergic rhinitis (AR), and 10 healthy subjects (HS) underwent bronchial challenge with a specific allergen extract. Eosinophils from peripheral blood were isolated 24 h before as well as 7 and 24 h after bronchial allergen challenge. Chemotaxis, spontaneous ROS production in eosinophils, and apoptosis were analyzed by flow cytometry. Serum and induced sputum IL-5 levels were measured by ELISA; the cell count in sputum was analyzed by the May-Grünwald-Giemsa method.

RESULTS

Before bronchial allergen challenge, peripheral blood eosinophil chemotaxis, spontaneous ROS production was enhanced and eosinophil apoptosis was reduced in the patients with AA as compared with AR patients and HS (P < 0.05). Meanwhile, eosinophil chemotaxis and ROS generation markedly increased in the patients with AA 7 h and 24 h after challenge compared with other groups and baseline values (P < 0.05). The percentage of apoptotic eosinophils in the patients with AA decreased at 7 h as well as 24 h after challenge when compared with other groups and the baseline values (P < 0.05). There was a significant correlation between the migrated peripheral blood eosinophil count and the sputum eosinophil count (Rs = 0.89, P < 0.0001) and the sputum IL-5 level (Rs = 0.68, P = 0.002) at 24 h after bronchial challenge only in the patients with AA. Furthermore, the percentage of peripheral blood apoptotic eosinophils significantly correlated with eosinophil count in sputum (Rs = -0.53, P = 0.02), and ROS production correlated with the serum IL-5 levels (Rs = 0.71, P = 0.01).

CONCLUSION

During allergen-induced late-phase airway inflammation, peripheral blood eosinophils demonstrated further alterations of their functional activity manifested by enhanced spontaneous ROS production, increased chemotaxis, and diminished apoptosis in patients with AA.

Brain natriuretic peptide protects against hyperresponsiveness of human asthmatic airway smooth muscle via an epithelial cell-dependent mechanism

Brain natriuretic peptide (BNP) relaxes airways by activating natriuretic peptide receptor-A and elevating cyclic guanosine monophosphate. BNP is more effective in passively sensitized human bronchi compared with control airways. The molecular and cellular patterns involved in this signaling are unknown. The aim of this study was to investigate the influence of BNP on airway smooth muscle (ASM) cells obtained from donors with asthma and healthy donors and to identify the mechanisms involved in BNP-mediated relaxation. The contractile response of ASM cells was microscopically assessed in vitro in the presence of 1 μM BNP or with supernatant from human bronchial epithelial (BEAS-2B) cells pretreated with 1 μM BNP. We investigated the role of muscarinic M2 receptors and inducible nitric oxide synthase (iNOS), quantified the release of acetylcholine and nitric oxide (NO), and assessed the gene/protein expression of iNOS and myosin phosphatase target subunit 1 (MYPT1). Supernatant from BEAS-2B cells treated with BNP reduced the hyperreactivity of asthmatic ASM cells by shifting the potency of histamine by 1.19-fold but had no effect in healthy ASM cells. BNP was not effective directly on ASM cells. Blocking muscarinic M2-receptors and iNOS abolished the protective role of supernatant from BEAS-2B treated with BNP. BNP stimulated the release of acetylcholine (210.7 ± 11.1%) from BEAS-2B cells that in turn increased MYPT1 and iNOS gene/protein expression and enhanced NO levels in asthmatic ASM supernatant (35.0 ± 13.0%). This study provides evidence that BNP protects against bronchial hyperresponsiveness via an interaction between respiratory epithelium and ASM in subjects with asthma.

Airway responsiveness in an allergic rabbit model

BACKGROUND

Animal models of allergy and bronchial hyperresponsiveness (BHR) are useful in researching pulmonary diseases and evaluating drug effects on the airways. Neonatally immunised rabbits exhibit several features of asthma as adults, including early and late airway responses following antigen challenge, oedema and inflammatory cell infiltration into the lung, BHR to inhaled histamine and methacholine (compared with naïve rabbits) and exacerbations of BHR following antigen challenge. Therefore this model can be used to investigate the underlying mechanisms of BHR and for the preclinical evaluation of new drugs for the treatment of asthma.

AIM

To describe the characteristics of airway responses in a rabbit model of allergic inflammation and to evaluate the relationship between skin test reactivity to antigen, airway inflammation and BHR.

METHODS

New Zealand White rabbits were neonatally immunised against Alternaria tenius. At 3 months of age, airway responsiveness was measured to aerosolised histamine, methacholine or allergen. Bronchoalveolar lavage (BAL) was performed and cell counts recorded. Direct skin tests were performed to assess skin reactivity to allergen and passive cutaneous anaphylaxis (PCA) tests were performed to determine titres of circulating IgE.

RESULTS

In a population of allergic rabbits, allergen challenge induced a significant bronchoconstriction, airway inflammation and BHR. Skin test responsiveness to allergen did not correlate with various indices of pulmonary mechanics e.g. baseline sensitivity to methacholine and histamine, or allergen-induced BHR. In contrast, skin test responsiveness did predict airway inflammation as assessed by measurements of eosinophil recruitment to the lung.

CONCLUSION

The allergic rabbit is a useful model to further our understanding of allergic diseases. Recording lung function using a minimally invasive procedure allows repeated measurements to be made in rabbits longitudinally, and each animal may thus be used as its own control. Our observations do not support the use of skin responsiveness to allergen as a predictor of airway sensitivity as we observed no correlation between skin sensitivity and airway responsiveness to inhaled histamine, methacholine or allergen. However, skin reactivity did predict airway inflammation as assessed by measurements of eosinophil recruitment to the lung. Our results also further highlight the likely dissociation between airway inflammation and BHR.

Pituitary adenylate cyclase-activating peptide receptor 1 mediates anti-inflammatory effects in allergic airway inflammation in mice

BACKGROUND

Bronchial asthma is characterized by airway inflammation and reversible obstruction. Since the gold standard of therapy, a combination of anti-inflammatory corticosteroids and bronchodilatory β(2) agonists, has recently been discussed to be related to an increased mortality, there is a need for novel therapeutic pathways.

OBJECTIVE

A new experimental concept that encompasses the vasoactive intestinal peptide/pituitary adenylate cyclase activating peptide (PACAP) family of receptors by demonstrating the anti-inflammatory effects of the PACAP receptor 1 (PAC1R) in a murine model of allergic asthma is described.

METHODS

PAC1R expression was investigated in lung tissue and isolated dendritic cells (DCs) via real-time PCR. Ovalbumin (OVA)-induced asthma models were used in PAC1R-deficient mice and BALB/c mice treated with PAC1R agonist maxadilan (MAX). Bronchoalveolar lavages have been performed and investigated at the cellular and cytokine levels. Fluorescence staining of a frozen lung section has been performed to detect eosinophil granulocytes in lung tissue. Plasma IgE levels have been quantified via the ELISA technique. Lung function was determined using head-out body plethysmography or whole-body plethysmography.

RESULTS

Increased PAC1R mRNA expression in lung tissue was present under inflammatory conditions. PAC1R expression was detected on DCs. In OVA-induced asthma models, which were applied to PAC1R-deficient mice (PAC1R(-/-)) and to BALB/c mice treated with the specific PAC1R agonist MAX, PAC1R deficiency resulted in inflammatory effects, while agonistic stimulation resulted in anti-inflammatory effects. No effects on lung function were detected both in the gene-depletion and in the pharmacologic studies. In summary, here, we demonstrate that anti-inflammatory effects can be achieved via PAC1R.

CONCLUSION

PAC1R agonists may represent a promising target for an anti-inflammatory therapy in airway diseases such as bronchial asthma.

Interleukin-4 as a neuromodulatory cytokine: roles and signaling in the nervous system

Although interleukin (IL)-4 is described as a prototypical anti-inflammatory cytokine, in recent years its role as a neuromodulatory cytokine has been extensively discussed. This review highlights the pivotal contributions of IL-4 during the development and normal physiology of neural cells as well as IL-4 connections with the pathophysiology of degenerative or inflammatory processes observed in the central and peripheral nervous system.

Human eosinophil adhesion and degranulation stimulated with eotaxin and RANTES in vitro: lack of interaction with nitric oxide

Background

Airway eosinophilia is considered a central event in the pathogenesis of asthma. The toxic components of eosinophils are thought to be important in inducing bronchial mucosal injury and dysfunction. Previous studies have suggested an interaction between nitric oxide (NO) and chemokines in modulating eosinophil functions, but this is still conflicting. In the present study, we have carried out functional assays (adhesion and degranulation) and flow cytometry analysis of adhesion molecules (VLA-4 and Mac-1 expression) to evaluate the interactions between NO and CC-chemokines (eotaxin and RANTES) in human eosinophils.

Methods

Eosinophils were purified using a percoll gradient followed by immunomagnetic cell separator. Cell adhesion and degranulation were evaluated by measuring eosinophil peroxidase (EPO) activity, whereas expression of Mac-1 and VLA-4 was detected using flow cytometry.

Results

At 4 h incubation, both eotaxin (100 ng/ml) and RANTES (1000 ng/ml) increased by 133% and 131% eosinophil adhesion, respectively. L-NAME alone (but not D-NAME) also increased the eosinophil adhesion, but the co-incubation of L-NAME with eotaxin or RANTES did not further affect the increased adhesion seen with chemokines alone. In addition, L-NAME alone (but not D-NAME) caused a significant cell degranulation, but it did not affect the CC-chemokine-induced cell degranulation. Incubation of eosinophils with eotaxin or RANTES, in absence or presence of L-NAME, did not affect the expression of VLA-4 and Mac-1 on eosinophil surface. Eotaxin and RANTES (100 ng/ml each) also failed to elevate the cyclic GMP levels above baseline in human eosinophils.

Conclusion

Eotaxin and RANTES increase the eosinophil adhesion to fibronectin-coated plates and promote cell degranulation by NO-independent mechanisms. The failure of CC-chemokines to affect VLA-4 and Mac-1 expression suggests that changes in integrin function (avidity or affinity) are rather involved in the enhanced adhesion.

Perinatal environmental tobacco smoke exposure alters the immune response and airway innervation in infant primates

BACKGROUND

Epidemiologic studies associate environmental tobacco smoke (ETS) exposure with childhood asthma.

OBJECTIVE

To investigate whether specific pathophysiological alterations that contribute to asthma development in human beings can be induced in infant monkeys after perinatal ETS exposure.

METHODS

Rhesus macaque fetuses/infants were exposed to ETS at 1 mg/m(3) of total suspended particulate matter from 50 days gestational age to 2.5 months postnatal age. Inflammatory and neural responses to ETS exposure were measured in the infant monkeys.

RESULTS

Perinatal ETS exposure could induce systemic and local responses, which include significant elevation of plasma levels of C5a and brain-derived neurotrophic factor, as well as significant increases in pulmonary expression of proinflammatory cytokine TNF-alpha and T(H)2 cytokine IL-5, chemokine monocyte chemoattractant protein 1, and the density of substance P-positive nerves along the bronchial epithelium. Perinatal ETS exposure also significantly increased the numbers of mast cells, eosinophils, monocytes, and lymphocytes in the lungs of infant monkeys. In addition, ex vivo measurements showed significantly increased levels of IL-4 and brain-derived neurotrophic factor in the culture supernatant of PBMCs. Interestingly, as an important component of cigarette smoke, LPS was detected in the plasma of infant monkeys subjected to perinatal exposure to ETS. In contrast, an inhibitory effect of perinatal ETS exposure was also observed, which is associated with decreased phagocytic activity of alveolar macrophages and a significantly decreased level of nerve growth factor in the bronchoalveolar lavage fluid.

CONCLUSION

Perinatal ETS exposure can induce a T(H)2-biased inflammatory response and alter airway innervation in infant monkeys.

Allergen induces the migration of platelets to lung tissue in allergic asthma

RATIONALE

Platelets are essential for pulmonary leukocyte recruitment, airway hyperresponsiveness, and bronchial remodeling in animals with allergic inflammation and can be found in bronchoalveolar lavage of sensitized animals. No studies, however, have explored the direct migration of platelets to lungs.

OBJECTIVES

To assess whether platelets migrate into lung parenchyma in response to inhaled allergen in ovalbumin-sensitized mice; to assess the role of the FcepsilonRI receptor in this phenomenon; and to evaluate whether platelets from patients with asthma, or from sensitized mice, undergo chemotaxis in vitro in response to relevant antigens.

METHODS

Ovalbumin-sensitized wild-type (WT) mice, or FcRgamma(-/-) mice lacking the FcepsilonRIgamma, were challenged with aerosolized allergen and lungs analyzed by platelet-specific immunohistochemistry. In some experiments, mice were depleted of platelets and cross-transfused with either WT or FcRgamma(-/-) platelets to assess the role of platelet FcRgamma(-/-). Chemotaxis of platelets from patients with asthma or from sensitized mice was studied in vitro.

MEASUREMENTS AND MAIN RESULTS

Histology of lungs revealed isolated platelets, migrating out of vessels and localizing underneath the airways after allergen challenge in WT but not in FcRgamma(-/-) mice. Platelets from patients with asthma and from sensitized WT mice, but not from sensitized FcRgamma(-/-) mice, migrated in vitro toward the relevant allergen or an anti-IgE. Platelets from normal mice were found to express FcepsilonRIgamma and platelet-bound IgEs were increased in sensitized mice.

CONCLUSIONS

Platelets migrate extravascularly in response to a sensitizing allergen via a mechanism dependent on the interaction among allergen, allergen-specific IgE, and the FcepsilonRI, and this may allow them to participate directly in allergic tissue inflammation.

The role of platelets in the pathophysiology of asthma

The incidence of asthma is on the increase worldwide, yet the pathogenesis of this disease is still not fully understood. Many recent drug trials have had disappointing results, thus fuelling the need for more research to be undertaken in this area. Substantial evidence suggests an important role for platelets in various inflammatory diseases, including atherosclerosis, rheumatoid arthritis, eczema, allergic rhinitis and asthma. In asthma, platelets have been found to actively participate in most of its main features, including bronchial hyperresponsiveness, bronchoconstriction, airway inflammation and airway remodelling. It has recently become clear that platelet-release products, as well as the expression of adhesion molecules on the platelet surface and the ability to undergo chemotaxis, are all involved in these processes. This review focuses on both experimental and clinical studies available to date that have investigated the role of platelets in the pathophysiology of asthma. Taken together, the evidence points toward platelets being an attractive new target in the area of asthma research; a target with much-needed novel therapeutic potential.

Eosinophils: singularly destructive effector cells or purveyors of immunoregulation?

Eosinophils are granulocytes typically associated with immune responses to a limited number of specific insults, including helminth infection and exposure to various allergens. Moreover, the overwhelming consensus from the literature is that eosinophils evolved as uniquely destructive leukocytes with cytotoxic activities as an adaptation for host defense. However, recent studies now suggest that the parochial caricature of eosinophils as effector cells with nonspecific killing abilities that evolved as a host defense mechanism against large nonphagotizable parasites is incomplete. A new paradigm has emerged describing eosinophils as initial responders to cell death/tissue damage that are a part of remodeling/repair processes and, more importantly, significant contributors to localized innate and acquired immune responses as well as systemic adaptive immunity. Significantly, this new paradigm does not preclude roles for eosinophils in host defense leading to tissue damage but instead suggests the equal importance of eosinophil-associated regulatory mechanisms modulating local tissue immune responses. The goal of this review is to summarize the data in support of this new paradigm. In turn, we believe that this expanded role provides a probable explanation for the presence of eosinophils in diverse disease settings such as asthma, allergy, cancer, transplant rejection, gastrointestinal inflammation, and viral or helminth infection.

Antagonism of the prostaglandin D2 receptor CRTH2 attenuates asthma pathology in mouse eosinophilic airway inflammation

Background

Mast cell-derived prostaglandin D₂ (PGD₂), may contribute to eosinophilic inflammation and mucus production in allergic asthma. Chemoattractant receptor homologous molecule expressed on TH₂ cells (CRTH2), a high affinity receptor for prostaglandin D₂, mediates trafficking of TH₂-cells, mast cells, and eosinophils to inflammatory sites, and has recently attracted interest as target for treatment of allergic airway diseases. The present study involving mice explores the specificity of CRTH2 antagonism of TM30089, which is structurally closely related to the dual TP/CRTH2 antagonist ramatroban, and compares the ability of ramatroban and TM30089 to inhibit asthma-like pathology.

Methods

Affinity for and antagonistic potency of TM30089 on many mouse receptors including thromboxane A₂ receptor mTP, CRTH2 receptor, and selected anaphylatoxin and chemokines receptors were determined in recombinant expression systems in vitro. In vivo effects of TM30089 and ramatroban on tissue eosinophilia and mucus cell histopathology were examined in a mouse asthma model.

Results

TM30089, displayed high selectivity for and antagonistic potency on mouse CRTH2 but lacked affinity to TP and many other receptors including the related anaphylatoxin C3a and C5a receptors, selected chemokine receptors and the cyclooxygenase isoforms 1 and 2 which are all recognized players in allergic diseases. Furthermore, TM30089 and ramatroban, the latter used as a reference herein, similarly inhibited asthma pathology in vivo by reducing peribronchial eosinophilia and mucus cell hyperplasia.

Conclusion

This is the first report to demonstrate anti-allergic efficacy in vivo of a highly selective small molecule CRTH2 antagonist. Our data suggest that CRTH2 antagonism alone is effective in mouse allergic airway inflammation even to the extent that this mechanism can explain the efficacy of ramatroban.

Beta2-agonists and bronchial hyperresponsiveness

Bronchial hyperresponsiveness (BHR) is a characteristic feature of asthma, and individuals with this disease respond to a range of physiological and chemical insults that are otherwise innocuous to healthy subjects, suggesting that the mechanisms underlying this phenomenon are characteristic of the asthma phenotype. BHR can be increased following exposure to environmental allergens in suitably sensitized individuals, pollutants, and certain viruses and can also be exacerbated by exposure to certain drugs, including nonsteroidal anti-inflammatory agents and beta-blockers. Although beta2-agonists administered acutely remain the treatment for the symptoms of asthma, paradoxically, regular treatment with these drugs can result in an increase in BHR, and this has been suggested to contribute to the increase in asthma morbidity and mortality that has been reported by numerous investigators. This article highlights our current understanding of this phenomenon and examines the potential mechanisms responsible for this effect.

Mechanism of adenosine-induced airways obstruction in allergic guinea pigs

Inhaled adenosine induces airway obstruction in asthmatic but not healthy subjects, a phenomenon that is also observed in various animal species when they are immunised to a relevant antigen, but which does not occur in naïve animals. The purpose of this study was to investigate the mechanisms of airway responsiveness to adenosine receptor agonists in anaesthetised allergic guinea pigs. Inhaled adenosine 5'-monophosphate (AMP), the A1-selective adenosine receptor agonist N6-cyclopentyladenosine (CPA) and ovalbumin all caused airway obstruction in allergic guinea pigs, but not naïve animals, as assessed by changes in total lung resistance. In contrast, the A(2a)-selective (CGS 21680; 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxoamido adenosine) and A3-selective (IB-MECA; 1-deoxy-1-[6-[[3-iodophenyl)-methyl]amino]-9H-purin-9-yl]-N-methyl-beta-D-ribofuranuronamide) adenosine receptor agonists failed to elicit airway obstruction in passively sensitised guinea pigs. Airway obstruction induced by AMP or CPA was not inhibited by the H1 receptor antagonist, mepyramine (1 mg kg(-1)) in passively sensitised guinea-pigs. In contrast, airway obstruction to ovalbumin was significantly inhibited by this antagonist. Airway obstruction induced by AMP and CPA was significantly inhibited in sensitised animals chronically treated with capsaicin. In contrast, airway obstruction to ovalbumin was not inhibited by this treatment. Airway obstruction induced by AMP, CPA and ovalbumin was significantly inhibited following bilateral vagotomy or pharmacological treatment with atropine (2 mg kg(-1)). Airway obstruction to CPA was inhibited by the adenosine A1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX: 0.1-1 mg kg(-1)). In contrast, airway obstruction to ovalbumin was not inhibited by this treatment. These observations provide evidence indicating that AMP and CPA may induce airway obstruction in sensitised guinea pigs by a mechanism unrelated to histamine release from mast cells, but is mediated via an adenosine A1-receptor-dependent mechanism. The inhibition of AMP- and CPA-induced airway obstruction by atropine, capsaicin and bilateral vagotomy suggests a neuronal-dependent mechanism with the particular involvement of capsaicin-sensitive nerves.

Anti-inflammatory effect of amurensin H on asthma-like reaction induced by allergen in sensitized mice

AIM

To explore the anti-inflammatory effects of amurensin H on asthma-like reaction induced by allergen in sensitized mice.

METHODS

BALB/c mice were sensitized by ovalbumin (OVA, ip) on d 0 and d 14 and challenged with 1% OVA on d 18 to 22. Mice developed airway eosinophilia, mucus hypersecretion, and elevation in cytokine levels. Mice were administered amurensin H orally at the doses of 49, 70, or 100 mg/kg once every day from d 15 to the last day. Bronchoalveolar lavage fluid (BALF) were collected at 24 h and 48 h after the last OVA challenge. Levels of tumor necrosis factor-alpha (TNF-alpha), interleukin 4 (IL-4), interleukin 5 (IL-5), and interleukin 13 (IL-13) in BALF were measured using ELISA method. Differential cell counts of macrophages, lymphocytes, neutrophils and eosinophils were performed in 200 cells per slide (one slide per animal). Lung tissue sections of 6-mum thickness were stained with Mayer's hematoxylin and eosin for assessment of cell infiltration, mucus production, and tissue damage.

RESULTS

Oral administration of amurensin H significantly inhibited OVA-induced increases in total cell counts, eosinophil counts, and TNF- alpha, IL-4, IL-5 and IL-13 levels in BALF. In addition, amuresin H dramatically decreased OVA-induced lung tissue damage and mucus production.

CONCLUSION

Amurensin H may have therapeutic potential for the treatment of allergic airway inflammation.

Suppressive effect of verproside isolated from Pseudolysimachion longifolium on airway inflammation in a mouse model of allergic asthma

Allergic inflammation of the airways has a critical role in asthma development. We investigated a suppressive effect of verproside (3,4-dihydroxy catalpol) isolated from the extract of Pseudolysimachion longifolium on asthmatic parameters--such as immunoglobulin E (IgE) level, cytokine release, eosinophilia, airway hyperresponsiveness and mucus hypersecretion--in an OVA-sensitized/challenged mouse model. Verproside significantly inhibited the increase of total IgE and the cytokines IL-4 and IL-13 in plasma and bronchoalveolar lavage fluid, and also effectively suppressed airway hyperresponsiveness, eosinophilia and mucus hypersecretion in OVA-induced asthmatic mice. The efficacy of verproside was comparable to montelukast, an anti-asthmatic drug that is currently available. These results suggest that verproside could be a major marker in herbal medicines that are used for asthma treatment, and could also act as a lead for anti-asthmatic drugs.

Novel concepts of neuropeptide-based drug therapy: vasoactive intestinal polypeptide and its receptors

Chronic inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD) are major contributors to the global burden of disease. Although inflammatory cells play the central role in the pathogenesis of the diseases, recent observations indicate that also resident respiratory cells represent important targets for pulmonary drug development. Especially targeting airway neuromediators offers a possible mechanism by which respiratory diseases may be treated in the future. Among numerous peptide mediators such as tachykinins, calcitonin gene-related peptide, neurotrophins or opioids, vasoactive intestinal polypeptide (VIP) is one of the most abundant molecules found in the respiratory tract. In human airways, it influences many respiratory functions via the receptors VPAC1, VPAC2 and PAC1. VIP-expressing nerve fibers are present in the tracheobronchial smooth muscle layer, submucosal glands and in the walls of pulmonary and bronchial arteries and veins. Next to its strong bronchodilator effects, VIP potently relaxes pulmonary vessels, and plays a pivotal role in the mediation of immune mechanisms. A therapy utilizing the respiratory effects of VIP would offer potential benefits in the treatment of obstructive and inflammatory diseases and long acting VIP-based synthetic non-peptide compounds may represent a novel target for drug development.

Prostaglandin involvement in lung C-fiber activation by substance P in guinea pigs

Airway hyperresponsiveness is a cardinal feature of asthma. Lung C-fiber activation induces central and local defense reflexes that may contribute to airway hyperresponsiveness. Initial studies show that substance P (SP) activates C fibers even though it is produced and released by these same C fibers. SP may induce release of other endogenous mediators. Bradykinin (BK) is an endogenous mediator that activates C fibers. The hypothesis was tested that SP activates C fibers via BK release. Guinea pigs were anesthetized, and C-fiber activity (FA), pulmonary insufflation pressure (PIP), heart rate, and arterial blood pressure were monitored before and after intravenous injection of capsaicin (Cap), SP, and BK. Identical agonist challenges were repeated after infusion of an antagonist cocktail of des-Arg9-[Leu8]-BK (10(-3) M, B1 antagonist), and HOE-140 (10(-4) M, B2 antagonist). After antagonist administration, BK increased neither PIP nor FA. Increases in neither PIP nor FA were attenuated after Cap or SP challenge. In a second series of experiments, Cap and SP were injected before and after infusion of indomethacin (1 mg/kg iv) to determine whether either agent activates C fibers through release of arachidonic acid metabolites. Indomethacin administration decreased the effect of SP challenge on FA but not PIP. The effect of Cap on FA or PIP was not altered by indomethacin. In subsequent experiments, C fibers were activated by prostaglandin E2 and F2alpha. Therefore, exogenously applied SP stimulates an indomethacin-sensitive pathway leading to C-fiber activation.

Immunohistochemical localization of vanilloid receptor subtype 1 (TRPV1) in the guinea pig respiratory system

Transient receptor potential vanilloid-1 (TRPV1) containing nerves are implicated in cough and bronchoconstriction although the significance of their documentation on non-neuronal cells is unclear. We have investigated the anatomical distribution and location of TRPV1 in an animal species often utilized in models of cough and airway inflammation. The distribution and localization of TRPV1 immunoreactivity in the lung was studied using confocal microscopy. Double labelling were carried out using the panaxonal marker, protein gene product 9.5 (PGP) and the neuropeptide substance P. TRPV1 was localized to fine axons within the epithelium of the trachea, however this represented only a fraction of the total axonal innervation of the epithelium. TRPV1 immunoreactive axons were also found in and around subepithelial regions of the airways, including smooth muscle and blood vessels and within the lower airways, found in the vicinity of bronchi and bronchioles, and in and around alveolar tissue. TRPV1 in the epithelium of the trachea was co-localized with substance P containing axons, although TRPV1 immunoreactive neuropeptide negative axons were also discernible. We found evidence for TRPV1 localization to axons throughout the respiratory tract. The distribution was heterogeneous and represented a fraction of the total neuronal innervation of the airways. No TRPV1 was found localized to airway epithelial cells. TRPV1 was often co-localized with the sensory neuropeptide substance P but there was evidence of TRPV1 positive neurones that did not express substance P. This suggests a role for TRPV1 in the airway that is independent of sensory neuropeptides.

Effect of a plant histaminase on asthmalike reaction induced by inhaled antigen in sensitized guinea pig

This study evaluates the effects of a copper amine oxidase (histaminase) purified from the pea seedling as a free or immobilized enzyme on asthmalike reactions to inhaled antigen in actively sensitized guinea pig in vivo. Male albino guinea pigs, sensitized with ovalbumin, were challenged with the antigen given by aerosol; free histaminase or CNBr-Sepharose immobilized histaminase was given intraperitoneally (20 microg, 3 or 24 h before antigen challenge) or by aerosol (4 microg, 30 min before or during ovalbumin aerosol). The following parameters were examined: latency time for the onset of respiratory abnormalities, cough severity score, and occurrence and duration of dyspnea. We also evaluated lung histopathology, mast cell degranulation, and lung myeloperoxidase and malonydialdehyde levels. Histaminase significantly reduced the severity of cough and the occurrence of dyspnea and delayed the onset of respiratory abnormalities. Both enzymes prevented bronchial constriction, pulmonary air space inflation, leukocyte infiltration (evaluated as myeloperoxidase activity), and lipoperoxidation of cell membranes (evaluated as malonyldialdehyde production). No relevant differences in pharmacological potency were noted between free or immobilized enzyme. This study provides evidence that histaminase counteracts acute allergic asthmalike reaction in actively sensitized guinea pigs, raising the possibility of new therapeutic strategies for allergic asthma in humans.

Inhibition of airway inflammation by amino-terminally modified RANTES/CC chemokine ligand 5 analogues is not mediated through CCR3

Chemokines play a key role in the recruitment of activated CD4(+) T cells and eosinophils into the lungs in animal models of airway inflammation. Inhibition of inflammation by N-terminally modified chemokines is well-documented in several models but is often reported with limited dose regimens. We have evaluated the effects of doses ranging from 10 ng to 100 micro g of two CC chemokine receptor antagonists, Met-RANTES/CC chemokine ligand 5 (CCL5) and aminooxypentane-RANTES/CCL5, in preventing inflammation in the OVA-sensitized murine model of human asthma. In the human system, aminooxypentane-RANTES/CCL5 is a full agonist of CCR5, but in the murine system neither variant is able to induce cellular recruitment. Both antagonists showed an inverse bell-shaped inhibition of cellular infiltration into the airways and mucus production in the lungs following allergen provocation. The loss of inhibition at higher doses did not appear to be due to partial agonist activity because neither variant showed activity in recruiting cells into the peritoneal cavity at these doses. Surprisingly, neither was able to bind to the major CCR expressed on eosinophils, CCR3. However, significant inhibition of eosinophil recruitment was observed. Both analogues retained high affinity binding for murine CCR1 and murine CCR5. Their ability to antagonize CCR1 and CCR5 but not CCR3 was confirmed by their ability to prevent RANTES/CCL5 and macrophage inflammatory protein-1beta/CCL4 recruitment in vitro and in vivo, while they had no effect on that induced by eotaxin/CCL11. These results suggest that CCR1 and/or CCR5 may be potential targets for asthma therapy.

Anandamide and vanilloid TRPV1 receptors

A large body of evidence now exists to substantiate that the endocannabinoid, anandamide, activates TRPV1 receptors. It is a low intrinsic efficacy TRPV1 agonist that behaves as a partial agonist in tissues with a low receptor reserve, while in tissues with high receptor reserve and in circumstances associated with certain disease states, it behaves as a full agonist. The efficacy of anandamide as a TRPV1 agonist is influenced by a succession of factors including receptor reserve, phosphorylation, metabolism and uptake, CB1 receptor activation, voltage, temperature, pH and bovine serum albumin. There are indications that the endocannabinoid system may play a role in the modulation of TRPV1 receptor activation. The activation of TRPV1 receptors by anandamide has potential implications in the treatment of inflammatory, respiratory and cardiovascular disorders. The relative importance of anandamide as a physiological and/or pathophysiological TRPV1 receptor agonist in comparison to other potential candidates has yet to be revealed.

Platelets are necessary for airway wall remodeling in a murine model of chronic allergic inflammation

Asthma is associated with airway remodeling. Evidence of platelet recruitment to the lungs of asthmatics after allergen exposure suggests platelets participate in various aspects of asthma; although their importance is unknown in the context of airway remodeling, their involvement in atherosclerosis is established. Studies from our laboratory have shown a requirement for platelets in pulmonary leukocyte recruitment in a murine model of allergic lung inflammation. Presently, the effects of platelet depletion and corticosteroid administration on airway remodeling and lung function were examined. Ovalbumin (OVA)-sensitized mice, exposed to aerosolized OVA for 8 weeks, demonstrated epithelial and smooth muscle thickening, and subepithelial reticular fiber deposition in the distal airways. The depletion of platelets via an immunologic (antiplatelet antisera) or nonimmunologic (busulfan) method, markedly reduced airway remodeling. In contrast, dexamethasone administration did not affect epithelial thickening or subepithelial fibrosis, despite significantly inhibiting leukocyte recruitment. Thus, pathways leading to certain aspects of airway remodeling may not depend on leukocyte recruitment, whereas platelet activation is obligatory. OVA-sensitized mice exhibited airway hyperresponsiveness (AHR) compared with sham-sensitized mice following chronic OVA exposure. Neither platelet depletion nor dexamethasone administration inhibited chronic AHR; thus, mechanisms other than inflammation and airway remodeling may be involved in the pathogenesis of chronic AHR.

A comparison of the pharmacological modulation of hyperalgesia and bronchial hyperresponsiveness

It has been proposed that there may be similarities in the mechanisms contributing toward hyperalgesia/allodynia observed in various clinical pain syndromes and bronchial hyperresponsiveness (BHR) in asthma. Both features are characterized by an increase in responsivity to various stimuli. In the case of pain, these include increase in responsiveness to mechanical and thermal stimuli whilst asthmatics bronchoconstrict in response to substances that are otherwise innocuous. A variety of mediators can induce hyperalgesia and pain when injected into the skin and these same mediators are also released during an inflammatory insult in the airways and in many cases can induce hyperresponsiveness experimentally. In this review, a comparison of the pharmacological modulation of afferent activity in hyperalgesia and in BHR will be made to ascertain whether any commonality exists between the treatment of these two disease states.