Early and late bronchoconstrictions, airway hyper-reactivity, leucocyte influx and lung histamine and nitric oxide after inhaled antigen: effects of dexamethasone and rolipram

PKCε stimulation of TRPV1 orchestrates carotid body responses to asthmakines

Key points

We have previously shown that carotid body stimulation by lysophosphatidic acid elicits a reflex stimulation of vagal efferent activity sufficient to cause bronchoconstriction in asthmatic rats.

Here, we show that pathophysiological concentrations of asthma‐associated prototypical Th2 cytokines also stimulate the carotid bodies.

Stimulation of the carotid bodies by these asthmakines involves a PKCε–transient receptor potential vanilloid 1 (TRPV1) signalling mechanism likely dependent on TRPV1 S502 and T704 phosphorylation sites.

As the carotid bodies’ oxygen sensitivity is independent of PKCε–TRPV1 signalling, systemic blockade of PKCε may provide a novel therapeutic target to reduce allergen‐induced asthmatic bronchoconstriction.

Consistent with the therapeutic potential of blocking the PKCε–TRPV1 pathway, systemic delivery of a PKCε‐blocking peptide suppresses asthmatic respiratory distress in response to allergen and reduces airway hyperresponsiveness to bradykinin.

Abstract

The autonomic nervous system orchestrates organ‐specific, systemic and behavioural responses to inflammation. Recently, we demonstrated a vital role for lysophosphatidic acid in stimulating the primary autonomic oxygen chemoreceptors, the carotid bodies, in parasympathetic‐mediated asthmatic airway hyperresponsiveness. However, the cacophony of stimulatory factors and cellular mechanisms of carotid body activation are unknown. Therefore, we set out to determine the intracellular signalling involved in carotid body‐mediated sensing of asthmatic blood‐borne inflammatory mediators. We employed a range of in vitro and rat in situ preparations, site‐directed mutagenesis, patch‐clamp, nerve recordings and pharmacological inhibition to assess cellular signalling. We show that the carotid bodies are also sensitive to asthma‐associated prototypical Th2 cytokines which elicit sensory nerve excitation. This provides additional asthmatic ligands contributing to the previously established reflex arc resulting in efferent vagal activity and asthmatic bronchoconstriction. This novel sensing role for the carotid body is mediated by a PKCε‐dependent stimulation of transient receptor potential vanilloid 1 (TRPV1), likely via TRPV1 phosphorylation at sites T704 and S502. Importantly, carotid body oxygen sensing was unaffected by blocking either PKCε or TRPV1. Further, we demonstrate that systemic PKCε blockade reduces asthmatic respiratory distress in response to allergen and airway hyperresponsiveness. These discoveries support an inflammation‐dependent, oxygen‐independent function for the carotid body and suggest that targeting PKCε provides a novel therapeutic option to abate allergic airway disease without altering life‐saving autonomic hypoxic reflexes.

We have previously shown that carotid body stimulation by lysophosphatidic acid elicits a reflex stimulation of vagal efferent activity sufficient to cause bronchoconstriction in asthmatic rats.

Here, we show that pathophysiological concentrations of asthma‐associated prototypical Th2 cytokines also stimulate the carotid bodies.

Stimulation of the carotid bodies by these asthmakines involves a PKCε–transient receptor potential vanilloid 1 (TRPV1) signalling mechanism likely dependent on TRPV1 S502 and T704 phosphorylation sites.

As the carotid bodies’ oxygen sensitivity is independent of PKCε–TRPV1 signalling, systemic blockade of PKCε may provide a novel therapeutic target to reduce allergen‐induced asthmatic bronchoconstriction.

Consistent with the therapeutic potential of blocking the PKCε–TRPV1 pathway, systemic delivery of a PKCε‐blocking peptide suppresses asthmatic respiratory distress in response to allergen and reduces airway hyperresponsiveness to bradykinin.

Back to the future: re-establishing guinea pig in vivo asthma models

Research using animal models of asthma is currently dominated by mouse models. This has been driven by the comprehensive knowledge on inflammatory and immune reactions in mice, as well as tools to produce genetically modified mice. Many of the identified therapeutic targets influencing airway hyper-responsiveness and inflammation in mouse models, have however been disappointing when tested clinically in asthma. It is therefore a great need for new animal models that more closely resemble human asthma. The guinea pig has for decades been used in asthma research and a comprehensive table of different protocols for asthma models is presented. The studies have primarily been focused on the pharmacological aspects of the disease, where the guinea pig undoubtedly is superior to mice. Further reasons are the anatomical and physiological similarities between human and guinea pig airways compared with that of the mouse, especially with respect to airway branching, neurophysiology, pulmonary circulation and smooth muscle distribution, as well as mast cell localization and mediator secretion. Lack of reagents and specific molecular tools to study inflammatory and immunological reactions in the guinea pig has however greatly diminished its use in asthma research. The aim in this position paper is to review and summarize what we know about different aspects of the use of guinea pig in vivo models for asthma research. The associated aim is to highlight the unmet needs that have to be addressed in the future.

Animal Models Reflecting Chronic Obstructive Pulmonary Disease and Related Respiratory Disorders: Translating Pre-Clinical Data into Clinical Relevance

Chronic obstructive pulmonary disease (COPD) affects the lives of an ever-growing number of people worldwide. The lack of understanding surrounding the pathophysiology of the disease and its progression has led to COPD becoming the third leading cause of death worldwide. COPD is incurable, with current treatments only addressing associated symptoms and sometimes slowing its progression, thus highlighting the need to develop novel treatments. However, this has been limited by the lack of experimental standardization within the respiratory disease research area. A lack of coherent animal models that accurately represent all aspects of COPD clinical presentation makes the translation of promising in vitrodata to human clinical trials exceptionally challenging. Here, we review current knowledge within the COPD research field, with a focus on current COPD animal models. Moreover, we include a set of advantages and disadvantages for the selection of pre-clinical models for the identification of novel COPD treatments.

Review of Mouse Models Applied to the Study of Asthma

The diversity of asthma phenotypes increases its complexity. Animal models represent a useful tool to elucidate the pathophysiological mechanisms involved in both allergic and nonallergic asthma, as well as to identify potential targets for the development of new treatments. Among all available animal models, mice offer significant advantages for the study of asthma. In this chapter, the applications of mouse models to the study of asthma will be reviewed.

Dose dependent effects of tadalafil and roflumilast on ovalbumin-induced airway hyperresponsiveness in guinea pigs

INTRODUCTION

Chronic obstructive diseases of airways associated with cough and/or airway smooth muscle hyperresponsiveness are usually treated with bronchodilating and anti-inflammatory drugs. Recently, selective phosphodiesterase (PDE) 4 inhibitors have been introduced into the therapy of chronic obstructive pulmonary disease. Several studies have demonstrated their ability to influence the airway reactivity and eosinophilic inflammation by increasing the intracellular cAMP concentrations also in bronchial asthma. Furthermore, the expression of PDE5 in several immune cells suggests perspectives of PDE5 inhibitors in the therapy of inflammation, as well.

PURPOSE

The aim of this study was to assess the dose-dependent effects of PDE4 and PDE5 inhibitors in allergic inflammation. Therefore, the effects of 7-days administration of PDE4 inhibitor roflumilast and PDE5 inhibitor tadalafil at two different doses in experimentally-induced allergic inflammation were evaluated.

MATERIALS AND METHODS

In the study, male adult guinea pigs were used. Control group was non-sensitized. Other animals were sensitized with ovalbumin over two weeks and thereafter treated intraperitoneally for 7 days with roflumilast or tadalafil (daily dose 0.5 mg/kg or 1.0 mg/kg b.w.), or with vehicle.

RESULTS

Both roflumilast and tadalafil reduced specific airway resistance after nebulization of histamine (marker of in vivo airway reactivity) at both doses used. The in vitro airway reactivity to cumulative doses of acetylcholine was significantly reduced for roflumilast at higher dose, predominantly in the lung tissue strips. Histamine-induced contractile responses were significantly influenced in both lung and tracheal tissue strips, predominantly at the higher doses. Tadalafil led to a decrease in contractile responses induced by both acetylcholine and histamine, with more significant effects in the lung tissue strips. These changes were associated with decreased numbers of circulating leukocytes and eosinophils and concentrations of interleukin (IL)-4, IL-5 and TNF-α in the lung homogenate.

CONCLUSIONS

The selective PDE4 and PDE5 inhibitors alleviated allergic airway inflammation, with more significant effects at the higher doses.

Route of Administration Affects Corticosteroid Sensitivity of a Combined Ovalbumin and Lipopolysaccharide Model of Asthma Exacerbation in Guinea Pigs

Lipopolysaccharide (LPS) contributes to asthma exacerbations and development of inhaled corticosteroid insensitivity. Complete resistance to systemic corticosteroids is rare, and most patients lie on a continuum of steroid responsiveness. This study aimed to examine the sensitivity of combined ovalbumin- (Ova) and LPS-induced functional and inflammatory responses to inhaled and systemic corticosteroid in conscious guinea pigs to test the hypothesis that the route of administration affects sensitivity. Guinea pigs were sensitized to Ova and challenged with inhaled Ova alone or combined with LPS. Airway function was determined by measuring specific airway conductance via whole-body plethysmography. Airway hyper-responsiveness to histamine was determined before and 24 hours post-Ova challenge. Airway inflammation and underlying mechanisms were determined from bronchoalveolar lavage cell counts and lung tissue cytokines. Vehicle or dexamethasone was administered by once-daily i.p. injection (5, 10, or 20 mg/kg) or twice-daily inhalation (4 or 20 mg/ml) for 6 days before Ova challenge or Ova with LPS. LPS exacerbated Ova-induced responses, elongating early asthmatic responses (EAR), prolonging histamine bronchoconstriction, and further elevating airway inflammation. Intraperitoneal dexamethasone (20 mg/kg) significantly reduced the elongated EAR and airway inflammation but not the increased bronchoconstriction to histamine. In contrast, inhaled dexamethasone (20 mg/ml), which inhibited responses to Ova alone, did not significantly reduce functional and inflammatory responses to combined Ova and LPS. Combined Ova and LPS–induced functional and inflammatory responses are insensitive to inhaled, but they are only partially sensitive to systemic, dexamethasone. This finding suggests that the route of corticosteroid administration may be important in determining corticosteroid sensitivity of asthmatic responses.

Effects of nebulised magnesium sulphate on inflammation and function of the guinea-pig airway

Magnesium sulphate is a potential treatment for acute severe asthma. However, the mechanisms and dose-response relationships are poorly understood. The first objective of this study was to examine whether inhaled magnesium sulphate exerts bronchodilator activity measured as bronchoprotection against histamine-induced bronchoconstriction in conscious guinea-pigs alone and combined with salbutamol. Secondly, we examined whether inhaled magnesium sulphate inhibits airways inflammation and function in models of neutrophilic and eosinophilic lung inflammation induced, respectively, by inhaled lipopolysaccharide or the inhaled antigen, ovalbumin (OVA). Airway function was measured in conscious guinea-pigs as specific airway conductance (sG_aw) by whole-body plethysmography. Anti-inflammatory activity was measured against lung inflammatory cell influx induced by OVA inhalation in OVA-sensitised animals or by lipopolysaccharide (LPS) exposure of non-sensitised animals. Airway function (sG_aw) was measured over 24h after OVA exposure. Airway hyperresponsiveness to inhaled histamine and inflammatory cells in bronchoalveolar lavage fluid were recorded 24h after OVA or LPS challenge. Histamine-induced bronchoconstriction was inhibited by inhaled magnesium sulphate or salbutamol alone and in combination, they produced synergistic bronchoprotection. LPS-induced neutrophil influx was inhibited by 6 days pretreatment with magnesium sulphate. Early and late asthmatic responses in OVA sensitised and challenged animals were attenuated by magnesium sulphate. Lung inflammatory cells were increased by OVA, macrophages being significantly reduced by magnesium sulphate. Nebulised magnesium sulphate protects against histamine-induced bronchoconstriction in conscious guinea-pigs and exerts anti-inflammatory activity against pulmonary inflammation induced by allergen (OVA) or LPS. These properties of magnesium sulphate explain its beneficial actions in acute asthma.

Anti-asthmatic property and possible mode of activity of an ethanol leaf extract of Polyscias fruticosa

CONTEXT

Polyscias fruticosa (L.) Harms (Araliaceae) is used as a traditional remedy for asthma in Ghana.

OBJECTIVE

The objective of this study is to establish the anti-asthmatic property and a possible mode of activity of an ethanol leaf extract of P. fruticosa (PFE).

MATERIALS AND METHODS

The time (min) for pre-convulsive dyspnea, and time for recovery, after sensitization with 150 μg OVA and induction of bronchospasm with 1% acetylcholine or histamine in normal, and 100, 250, and 500 mg/kg PFE-treated Dunkin Hartley guinea pigs, were recorded. Atropine (0.1 mg), mepyramine (0.1 mg), and PFE (1 mg) effect on a contractile response of 2.0 × 10(-2) μg/ml acetylcholine and 5.8 × 10(-2) μg/ml histamine on the isolated guinea pig ileum was investigated. Cytological and histological studies were conducted using guinea pig peritoneal mast cells and mesenteric cells, respectively, to establish PFE effect on compound 48/80-induced mast cell degranulation.

RESULTS

PFE (100-500 mg/kg) prolonged the onset of pre-convulsive dyspnea by 76.1-180.2% (p ≤ 0.01-0.001), and decreased recovery time by 71.9-78.5% (p ≤ 0.01-0.001). It also enhanced percentage protection against histamine-induced bronchospasm by 15.8-80.1-fold (p ≤ 0.05-0.01), and decreased percentage recovery time 2.5-3.3-fold (p ≤ 0.05-0.01). PFE significantly inhibited (60.4 ± 8.3%) contractile responses of histamine and produced significant inhibition (56-79%: p ≤ 0.001) of mast cell degranulation.

CONCLUSION

PFE has anti-asthmatic, antihistaminic, and mast cell stabilization effect making it useful in traditional asthma management.

Pulmonary edema measured by MRI correlates with late-phase response to allergen challenge

PURPOSE

Asthma is associated with reversible airway obstruction, leucocyte infiltration, airways hyperresponsiveness (AHR), and airways remodeling. Fluid accumulation causes pulmonary edema contributing to airways obstruction. We examined the temporal relationship between the late asthmatic response (LAR) following allergen challenge of sensitized guinea-pigs and pulmonary edema measured by magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Ovalbumin (OVA) sensitized guinea-pigs received either a single OVA inhalation (acute) or nine OVA inhalations at 48 h intervals (chronic). Airways obstruction was measured as specific airways conductance (sG(aw)) by whole body plethysmography. AHR to inhaled histamine and bronchoalveolar lavage for leucocyte counts were measured 24 h after a single or the final chronic ovalbumin challenges. MRI was performed at intervals after OVA challenge and high-intensity edemic signals were quantified.

RESULTS

Ovalbumin caused early bronchoconstriction, followed at 7 h by an LAR and at 24 h AHR and leucocyte influx. The bright-intensity MRI edema signal, peaking at 7 h, was significantly (P < .05) greater after chronic (9.0 ± 0.7 × 10(3) mm(3)) than acute OVA (7.6 ± 0.2 × 10(3) mm(3)). Dexamethasone treatment before acute OVA abolished the AHR and LAR and significantly reduced eosinophils and the bright-intensity MRI edema from 9.1 ± 1.0 to 6.4 ± 0.3 × 10(3) mm(3).

CONCLUSION

We show a temporal relationship between edema and the LAR and their parallel reduction, along with eosinophils and AHR, by dexamethasone. This suggests a close causative association between pulmonary edema and impaired airways function.

Adjustment of sensitisation and challenge protocols restores functional and inflammatory responses to ovalbumin in guinea-pigs

Introduction

Inhalation of antigen in atopic asthma induces early (EAR) and late asthmatic responses (LARs), inflammatory cell infiltration and airways hyperresponsiveness (AHR). Previously, we have established a protocol of sensitisation and subsequent ovalbumin (Ova) inhalation challenge in guinea-pigs which induced these 4 features (Smith & Broadley, 2007). However, the responses of guinea-pigs to Ova challenge have recently declined, producing no LAR or AHR and diminished EAR and cells. By making cumulative modifications to the protocol, we sought to restore these features.

Methods

Guinea-pigs were sensitised with Ova (i.p. 100 or 150 μg) on days 1 and 5 or days 1, 4 and 7 and challenged with nebulised Ova (100 or 300 μg/ml, 1 h) on day 15. Airway function was measured in conscious guinea-pigs by whole-body plethysmography to record specific airway conductance (sGaw). Airway responsiveness to aerosolized histamine (0.3 mM) was determined before and 24 h after Ova challenge. Bronchoalveolar lavage was performed for total and differential inflammatory cell counts. Lung sections were stained for counting of eosinophils.

Results

Lack of AHR and LAR with the original protocol was confirmed. Increasing the Ova challenge concentration from 100 to 300 μg/ml restored AHR and eosinophils and increased the peak of the EAR. Increasing the number of sensitisation injections from 2 to 3 did not alter the responses. Increasing the Ova sensitisation concentration from 100 to 150 μg significantly increased total cells, particularly eosinophils. A LAR was revealed and lymphocytes and eosinophils increased when either the Al(OH)₃ concentration was increased or the duration between the final sensitisation injection and Ova challenge was extended from 15 to 21 days.

Discussion

This study has shown that declining allergic responses to Ova in guinea-pigs could be restored by increasing the sensitisation and challenge conditions. It has also demonstrated an important dissociation between EAR, LAR, AHR and inflammation.

Therapeutic potential of anti-IL-1β IgY in guinea pigs with allergic asthma induced by ovalbumin

BACKGROUND

Interleukin-1 beta (IL-1β) plays pivotal roles in the progression of allergic airway inflammation. This study aims to determine whether the blockade of IL-1β can inhibit airway inflammation in guinea pigs with allergic asthma induced by the inhalation of aerosolized ovalbumin (OVA).

METHODS

Healthy guinea pigs treated with saline were used as normal controls (group C). The guinea pigs with allergic asthma induced by the inhalation of aerosolized OVA were randomly divided into three groups: (1) the M group containing negative control animals treated with saline; (2) the Z1 group containing animals treated by the inhalation of atomized 0.1% anti-IL-1β immunoglobulin yolk (IgY); and (3) the Z2 group containing positive control animals that were treated with budesonide. The inflammatory cells in the peripheral blood (PB) and bronchoalveolar lavage fluid (BALF) were evaluated using methylene blue and eosin staining. Cytokine concentrations were measured using an enzyme-linked immunosorbent assay. Pulmonary sections were examined using hematoxylin-eosin staining.

RESULTS

Allergic inflammation and damage to the pulmonary tissues were decreased in the Z1 group compared to the M group. Eosinophils and neutrophils in the PB and BALF were significantly decreased in the Z1 group compared to the M group (P<0.05). Treatment with anti-IL-1β IgY significantly reduced the levels of IL-1β, IL-4, IL-8, IL-13, TNF-α, TGF-β1 and IgE in the BALF (P<0.05).

CONCLUSION

The inhalation of aerosolized anti-IL-1β IgY inhibits pathological responses in the pulmonary tissues of guinea pigs with allergic asthma. The inhibitory activity may be due to the decrease in the numbers of eosinophils and neutrophils and the reduced levels of inflammatory cytokines and IgE in the PB and BALF.

Human parainfluenza type 3 virus impairs the efficacy of glucocorticoids to limit allergy-induced pulmonary inflammation in guinea-pigs

Viral exacerbations of allergen-induced pulmonary inflammation in pre-clinical models reportedly reduce the efficacy of glucocorticoids to limit pulmonary inflammation and airways hyper-responsiveness to inhaled spasmogens. However, exacerbations of airway obstruction induced by allergen challenge have not yet been studied. hPIV-3 (human parainfluenza type 3 virus) inoculation of guinea-pigs increased inflammatory cell counts in BAL (bronchoalveolar lavage) fluid and caused hyper-responsiveness to inhaled histamine. Both responses were abolished by treatment with either dexamethasone (20 mg/kg of body weight, subcutaneous, once a day) or fluticasone propionate (a 0.5 mg/ml solution aerosolized and inhaled over 15 min, twice a day). In ovalbumin-sensitized guinea-pigs, allergen (ovalbumin) challenge caused two phases of airway obstruction [measured as changes in sGaw (specific airways conductance) using whole body plethysmography]: an immediate phase lasting between 4 and 6 h and a late phase at about 7 h. The late phase, airway hyper-responsiveness to histamine and inflammatory cell counts in BAL were all significantly reduced by either glucocorticoid. Inoculation of guinea-pigs sensitized to ovalbumin with hPIV-3 transformed the allergen-induced airway obstruction from two transient phases into a single sustained response lasting up to 12 h. This exacerbated airway obstruction and airway hyper-responsiveness to histamine were unaffected by treatment with either glucocorticoid whereas inflammatory cell counts in BAL were only partially inhibited. Virus- or allergen-induced pulmonary inflammation, individually, are glucocorticoid-sensitive, but in combination generate a phenotype where glucocorticoid efficacy is impaired. This suggests that during respiratory virus infection, glucocorticoids might be less effective in limiting pulmonary inflammation associated with asthma.

Inhibition of airway hyper-responsiveness by TRPV1 antagonists (SB-705498 and PF-04065463) in the unanaesthetized, ovalbumin-sensitized guinea pig

BACKGROUND AND PURPOSE Airway sensory nerves play a key role in respiratory cough, dyspnoea, airway hyper-responsiveness (AHR), all fundamental features of airway diseases [asthma and chronic obstructive pulmonary disease (COPD)]. Vagally mediated airway reflexes such as cough, bronchoconstriction and chest tightness originate from stimulation of airway sensory nerve endings. The transient receptor potential vanilloid 1 receptor (TRPV1) is present on peripheral terminals of airway sensory nerves and modulation of its activity represents a potential target for the pharmacological therapy of AHR in airway disease. EXPERIMENTAL APPROACH As guinea pig models can provide some of the essential features of asthma, including AHR, we have established the model with some classical pharmacological agents and examined the effect of the TRPV1 antagonists, SB-705498 and PF-04065463 on AHR to histamine evoked by ovalbumin (OA) in unanaesthetized sensitized guinea pigs restrained in a double chamber plethysmograph. Specific airway conductance (sGaw) derived from the airflow was calculated as a percentage of change from baseline. KEY RESULTS Cetirizine and salbutamol significantly inhibited OA-evoked bronchoconstriction [sGaw area under the curve (AUC): 70 and 78%, respectively]. Atropine, SB-705498 and PF-04065463 significantly inhibited OA-evoked AHR to histamine in unanaesthetized, OA-sensitized guinea pigs (sGaw AUC: 94%, 57% and 73%, respectively). Furthermore, this effect was not related to antagonism of histamine's activity. CONCLUSION AND IMPLICATIONS These data suggest that TRPV1 receptors located on airway sensory nerves are important in the development of AHR and that modulation of TRPV1-receptor activity represents a potential target for the pharmacological therapy of AHR in airway disease.

Heme and haemoglobin direct macrophage Mhem phenotype and counter foam cell formation in areas of intraplaque haemorrhage

PURPOSE OF REVIEW

Several studies have recently shown that haemoglobin drives a novel macrophage subset that is protected from foam cell formation.

RECENT FINDINGS

In a previously overlooked area, two centres have independently shown that heme and haemoglobin drive an atheroprotective macrophage subset. We compare and contrast the approaches and findings of the laboratories and discuss some of the underlying biology and implications, concentrating on the aspects of lipidological relevance.

SUMMARY

Treatments based on direct heme-mimetics or other agonists of this pathway have enormous potential for linked antioxidant protection via heme oxygenase 1 and reduced foam cell formation via liver X receptor, a potent combination for treating atherosclerosis.

A comparison of antiasthma drugs between acute and chronic ovalbumin-challenged guinea-pig models of asthma

Pre-clinical evaluation of asthma therapies requires animal models of chronic airways inflammation, airway hyperresponsiveness (AHR) and lung remodelling that accurately predict drug effectiveness in human asthma. However, most animal models focus on acute allergen challenges where chronic inflammation and airway remodelling are absent. Chronic allergen challenge models have been developed in mice but few studies use guinea-pigs which may be more relevant to humans. We tested the hypothesis that a chronic rather than acute pulmonary inflammation model would best predict clinical outcome for asthma treatments. Guinea-pigs sensitized with ovalbumin (OVA) received single (acute) or nine OVA inhalation challenges at 48 h intervals (chronic). Airways function was recorded as specific airways conductance (sG(aw)) in conscious animals for 12 h after OVA challenge. AHR to inhaled histamine, inflammatory cell influx and lung histology were determined 24 h after the single or 9th OVA exposure. The inhaled corticosteroid, fluticasone propionate (FP), the phosphodiesterase 4 inhibitor, roflumilast, and the inducible nitric oxide synthase (iNOS) inhibitor, GW274150, orally, were administered 24 and 0.5 h before and 6 h after the single or final chronic OVA exposure. Both models displayed early (EAR) and late (LAR) asthmatic responses to OVA challenge, as falls in sG(aw), AHR, as increased histamine-induced bronchoconstriction, and inflammatory cell influx. Tissue remodelling, seen as increased collagen and goblet cell hyperplasia, occurred after multiple OVA challenge. Treatment with FP and roflumilast inhibited the LAR, cell influx and AHR in both models, and the remodelling in the chronic model. GW274150 also inhibited the LAR, AHR and eosinophil influx in the acute model, but not, together with the remodelling, in the chronic model. In the clinical setting, inhaled corticosteroids and phosphodiesterase 4 inhibitors are relatively effective against most features of asthma whereas the iNOS inhibitor GW274150 was ineffective. Thus, while there remain certain differences between our data and clinical effectiveness of these antiasthma drugs, a chronic pulmonary inflammation guinea-pig model does appear to be a better pre-clinical predictor of potential asthma therapeutics than an acute model.

Cockroach allergens induce biphasic asthma-like pulmonary inflammation in outbred mice

OBJECTIVES

The aim of this study is to define the kinetics of the pulmonary inflammatory response in cockroach allergen (CRA) sensitized and challenged outbred mice.

METHODS

Asthma-like pulmonary inflammation was induced with three pulmonary exposures to CRA, without the use of adjuvants. Mice were sacrificed at multiple time points and asthma-like pulmonary inflammation quantified.

RESULTS

Several pulmonary parameters showed a pronounced biphasic inflammatory response with an early stage (1.5 hours post challenge) and late stage (24 hours). The initial phase was characterized by the production of multiple inflammatory mediators, including CXC chemokines, and the recruitment of neutrophils to the lung. The number of pulmonary eosinophils decreased in the early phase but quickly rebounded. Both the early and late phases had increases in TNF production in addition to airways hyperreactivity. The model also demonstrated early production of mucin with clearance by 12 hours followed by new accumulation of mucin in the pulmonary epithelial cells. Eotaxins within the lung peaked at about 12 hours and the numbers of eosinophils in the lung remained constant throughout the 48 hours of the study.

CONCLUSIONS

The pulmonary inflammatory parameters in response to a clinically relevant allergen define a biphasic response. These data may be used to investigate the pathogenesis of the disease and develop targeted therapies for the distinct phases.

Inhibitory effects of inhaled complex traditional Chinese medicine on early and late asthmatic responses induced by ovalbumin in sensitized guinea pigs

Background

Many formulae of traditional Chinese medicines (TCMs) have been used for antiasthma treatment dating back many centuries. There is evidence to suggest that TCMs are effective as a cure for this allergenic disease administered via gastric tubes in animal studies; however, their efficacy, safety and side effects as an asthmatic therapy are still unclear.

Methods

In this study, guinea pigs sensitized with ovalbumin (OVA) were used as an animal model for asthma challenge, and the sensitization of animals by bronchial reactivity to methacholine (Mch) and the IgE concentration in the serum after OVA challenge were estimated. Complex traditional Chinese herbs (CTCM) were administered to the animals by nebulization, and the leukocytes were evaluated from bronchoalveolar lavage fluid (BALF).

Results

The results showed that inhalation of CTCM could abolish the increased lung resistance (13-fold increase) induced by challenge with OVA in the early asthmatic response (EAR), reducing to as low as baseline (1-fold). Moreover, our results indicated higher IgE levels (range, 78-83 ng/ml) in the serum of sensitized guinea pigs than in the unsensitized controls (0.9 ± 0.256 ng/ml). In addition, increased total leukocytes and higher levels of eosinophils and neutrophils were seen 6 hours after challenge, and the increased inflammatory cells were reduced by treatment with CTCM inhalation. The interleukin-5 (IL-5) level in BALF was also reduced by CTCM.

Conclusion

Our findings indicate a novel method of administering traditional Chinese medicines for asthma treatment in an animal model that may be more effective than traditional methods.

The effect of liposome encapsulation on the pharmacokinetics of recombinant secretory leukocyte protease inhibitor (rSLPI) therapy after local delivery to a guinea pig asthma model

PURPOSE

Inhaled recombinant Secretory Leukocyte Protease Inhibitor (rSLPI) has shown potential for treatment of inflammatory lung conditions. Rapid inactivation of rSLPI by cathepsin L (Cat L) and rapid clearance from the lungs have limited clinical efficacy. Encapsulation of rSLPI within 1,2-Dioleoyl-sn-Glycero-3-[Phospho-L-Serine]:Cholesterol liposomes (DOPS-rSLPI) protects rSLPI against Cat L inactivation in vitro. We aimed to determine the effect of liposomes on rSLPI pharmacokinetics and activity in vitro and after local delivery to the airways in vivo.

METHODS

Transport of DOPS-rSLPI and free-rSLPI across a polarised air-liquid epithelial monolayer was measured. An asthma guinea pig model was administered either DOPS-rSLPI liposomes or free-rSLPI by intratracheal instillation.

RESULTS

Apparent permeability (P(app)) of free-rSLPI was significantly higher at 4.9 x 10⁻⁶ cm/s than for DOPS-rSLPI, P(app) of 2.05 x 10⁻⁷ cm/s, confirmed by in vivo studies. Plasma rSLPI concentrations were highest in free-rSLPI-treated animals compared with those treated with DOPS-rSLPI; there also appeared to be a trend for higher intracellular rSLPI content in animals dosed with DOPS-rSLPI compared to free-rSLPI. Eosinophil influx was recorded as a measure of inflammation. Pre-dosing with either free-rSLPI or DOPS-rSLPI prevented inflammatory response to antigen challenge to levels comparable to control animals.

CONCLUSION

Encapsulation of rSLPI in DOPS:Chol liposomes improves stability, reduces clearance and increases residence time in the lungs after local delivery.

Mitigation of chlorine lung injury by increasing cyclic AMP levels

Chlorine is considered a chemical threat agent to which humans may be exposed as a result of accidental or intentional release. Chlorine is highly reactive, and inhalation of the gas causes cellular damage to the respiratory tract, inflammation, pulmonary edema, and airway hyperreactivity. Drugs that increase intracellular levels of the signaling molecule cyclic AMP (cAMP) may be useful for treatment of acute lung injury through effects on alveolar fluid clearance, inflammation, and airway reactivity. This article describes mechanisms by which cAMP regulates cellular processes affecting lung injury and discusses the basis for investigating drugs that increase cAMP levels as potential treatments for chlorine-induced lung injury. The effects of beta(2)-adrenergic agonists, which stimulate cAMP synthesis, and phosphodiesterase inhibitors, which inhibit cAMP degradation, on acute lung injury are reviewed, and the relative advantages of these approaches are compared.

Bradykinin-induced lung inflammation and bronchoconstriction: role in parainfluenze-3 virus-induced inflammation and airway hyperreactivity

Inhaled bradykinin causes bronchoconstriction in asthmatic subjects but not nonasthmatics. To date, animal studies with inhaled bradykinin have been performed only in anesthetized guinea pigs and rats, where it causes bronchoconstriction through sensory nerve pathways. In the present study, airway function was recorded in conscious guinea pigs by whole-body plethysmography. Inhaled bradykinin (1 mM, 20 s) caused bronchoconstriction and influx of inflammatory cells to the lungs, but only when the enzymatic breakdown of bradykinin by angiotensin-converting enzyme and neutral endopeptidase was inhibited by captopril (1 mg/kg i.p.) and phosphoramidon (10 mM, 20-min inhalation), respectively. The bronchoconstriction and cell influx were antagonized by the B(2) kinin receptor antagonist 4-(S)-amino-5-(4-{4-[2,4-dichloro-3-(2,4-dimethyl-8-quinolyloxymethyl)phenylsulfonamido]-tetrahydro-2H-4-pyranylcarbonyl}piperazino)-5-oxopentyl](trimethyl)ammonium chloride hydrochloride (MEN16132) when given by inhalation (1 and 10 μM, 20 min) and are therefore mediated via B(2) kinin receptors. However, neither intraperitioneal MEN16132 nor the peptide B(2) antagonist icatibant, by inhalation, antagonized these bradykinin responses. Sensitization of guinea pigs with ovalbumin was not sufficient to induce airway hyperreactivity (AHR) to the bronchoconstriction by inhaled bradykinin. However, ovalbumin challenge of sensitized guinea pigs caused AHR to bradykinin and histamine. Infection of guinea pigs by nasal instillation of parainfluenza-3 virus produced AHR to inhaled histamine and lung influx of inflammatory cells. These responses were attenuated by the bradykinin B(2) receptor antagonist MEN16132 and H-(4-chloro)DPhe-2'(1-naphthylalanine)-(3-aminopropyl)guanidine (VA999024), an inhibitor of tissue kallikrein, the enzyme responsible for lung synthesis of bradykinin. These results suggest that bradykinin is involved in virus-induced inflammatory cell influx and AHR.

Antiasthmatic action of dibenzylbutyrolactone lignans from fruits of Forsythia viridissima on asthmatic responses to ovalbumin challenge in conscious guinea-pigs

It was reported previously that dibenzylbutyrolactone lignans from Forsythia viridissima fruits, which are traditional medicines for the treatment of inflammatory diseases, have antiinflammatory effects. In this study, the effects on the immediate-phase response (IAR) and late-phase response (LAR) following aerosolized-ovalbumin challenge in ovalbumin-sensitized guinea-pigs were evaluated by measuring the specific airway resistance (sRaw), recruitment of leukocytes and chemical mediators in the bronchoalveolar lavage fluids (BALF) as well as a histopathological survey. Arctiin and matairesinol at 12.5 mg/kg significantly (p < 0.05) decreased sRaw by 51.83% and 43.15% in IAR and by 47.41% and 35.43% in LAR, respectively, whereas arctigenin at 25 mg/kg was significantly active, compared with the controls. Furthermore, arctiin and arctigenin dose-dependently inhibited histamine, and the activities of phospholipase A₂ (PLA₂) and eosinophil peroxidase (EPO) in BALF, respectively, whereas matairesinol inhibited EPO and PLA₂ at 12.5 mg/kg and histamine at 50 mg/kg, in addition, they moderately improved the infiltration of eosinophils, compared with controls. Dexamethasone, cromolyn and salbutamol significantly inhibited sRaw in both IAR and LAR, and the recruitment of leukocytes and chemical mediators, whereas salbutamol did not alter chemical mediators, in BALF. These results indicate the three lignans have antiasthmatic effects which were less active than those of the reference drugs.

Anti-asthmatic activity of phenolic compounds from the roots of Gastrodia elata Bl

We previously reported that 4-hydroxy-3-methoxybenzaldehyde has the most potent anti-inflammatory and analgesic activity of eight phenolic compounds obtained from the dried roots of Gastrodiaelata (GE) Blume (Orchidaceae); its activity may be related to inhibition of cyclooxygenase activities and oxidation. In the present study, the effects of nine phenolic compounds from GE on immediate-phase (IAR) and late-phase (LAR) asthmatic responses after aerosolized-ovalbumin (OA) challenge were evaluated by determining the specific airway resistance (sRaw) using a double-chambered plethysmograph in conscious guinea pigs with IgE-mediated asthma. Furthermore, recruitment of leukocytes, histamine release, and eosinophil peroxidase (EPO) and phospholipase A(2) (PLA(2)) activities were determined in bronchoalveolar lavage fluids (BALF) 24h after the antigen challenge. 4-Hydroxy-3-methoxybenzyl alcohol (12.5mg/kg) significantly (p<0.05) inhibited sRaw in IAR and in LAR by 51.97+/-4.96% and 39.93+/-3.46%, respectively, compared to that of the controls. Further, hydroxy-3-methoxybenzyl alcohol significantly (p<0.05) inhibited recruitment of leukocytes in accordance with amelioration of eosinophilia and neutrophilia, histamine (30.66+/-5.20%), EPO activity (21.58+/-2.02%), and specific PLA(2) activity (16.60+/-2.52%) in BALF compared with the control. In addition, bis-(4-hydroxyphenyl) methane, 4-hydroxy-3-methoxybenzoic acid, and 4-hydroxy-3-methoxybenzaldehyde (12.5mg/kg) significantly (p<0.05) inhibited sRaw, while bis-(4-hydroxyphenyl) methane, benzyl alcohol, and 4-hydroxybenzaldehyde at 12.5mg/kg significantly (p<0.05) inhibited leukocytes, histamine, EPO and PLA(2) activities in BALF compared with the controls. The phenolic glycoside, parishin had less activity compared to aglycones, 4-hydroxybenzyl compounds. These results suggest that the C(4) hydroxy and C(3) methoxy radicals in benzyl alcohols and aldehydes play important roles in mediating the anti-asthmatic activities of these compounds.

Beta-1 selective adrenergic antagonist landiolol and esmolol can be safely used in patients with airway hyperreactivity

This study was undertaken to clarify the effects of esmolol and landiolol, beta-1 selective adrenergic antagonists, on hyperreactive airways in both ovalbumin-sensitized guinea pigs and asthmatic patients. In the animal study, asthma was induced by ovalbumin. After control acetylcholine responses for total pulmonary resistance (Raw) and dynamic lung compliance (Cdyn) were obtained, the animals received propranolol, esmolol, or landiolol, and the same protocol was again performed. Sixty inpatients with coronary risk factors and asthma were enrolled in the human study. Under propofol anesthesia, the patients received saline, esmolol, or landiolol. To assess intubation-induced bronchoconstriction, the presence of wheezing was determined. The dose-response curves of Raw and Cdyn to acetylcholine were significantly elevated and declined in the ovalbumin-sensitized model compared with those in the control group. Neither esmolol nor landiolol had any effect on the acetylcholine-induced response curve in these sensitized animals. However, propranolol significantly enhanced Raw and reduced Cdyn in this model. Tracheal intubation increased the incidence of wheezing in asthmatic patients. However, there was no significant difference in the incidence of wheezing among these groups. The ultra-short-acting beta-1 selective adrenergic antagonists esmolol and landiolol can be safely used perioperatively in patients with airway hyperreactivity.

Quercetin inhalation inhibits the asthmatic responses by exposure to aerosolized-ovalbumin in conscious guinea-pigs

Effects of quercetin inhalation on immediate (IAR), late-phase (LAR) and late late-phase (LLAR) asthmatic responses by exposure to aerosolized-ovalbumin (AOA) (2w/v% in saline, inhalation for 3 min) were studied in conscious guinea-pigs sensitized with AOA. We measured specific airway resistance (sRaw), and recruitment of leukocytes, histamine and protein contents and phospholipase A2 (PLA2) activity in bronchoalveolar lavage fluid (BALF). Effects of quercetin (10 mg/mL, inhalation for 2 min) compared with cromolyn sodium, salbutamol, and dexamethasone inhalations, respectively. Quercetin inhalation decreased sRaw by 57.15 +/- 3.82% in IAR, 57.72 +/- 7.28% in LAR, and 55.20 +/- 5.69% in LLAR compared with AOA-inhaled control. Salbutamol inhalation (5 mg/mL) significantly inhibited sRaw in IAR, but inhalations of cromolyn sodium (10 mg/mL) and dexamethasone (5 mg/mL) significantly inhibited sRaw in IAR, LAR and LLAR, respectively. Inhibitory activity of quercetin inhalation on sRaw was similar to effect of its oral administration (10 mg/kg) in asthmatic responses. Quercetin (10 mg/mL, inhalation for 2 min) significantly decreased histamine and protein contents, PLA2 activity, and recruitments of leukocytes in BALF and also improved slightly infiltration of eosinophils and neutrophils in histopathological survey. Its anti-asthmatic activity was similar to cromolyn sodium and dexamethasone.

Anti-asthmatic action of quercetin and rutin in conscious guinea-pigs challenged with aerosolized ovalbumin

The effects of quercetin and rutin on the asthmatic responses were studied in ovalbumin (OA)-sensitized conscious guinea pigs challenged with aerosolized-OA. We measured the specific airway resistance (sRaw) in the double-chambered plethysmograph during the immediate-phase response (IAR) and late-phase response (LAR) at 3 approximately 10 min and 24 hr after OA challenge, respectively. We counted leukocytes in bronchoalveolar lavage fluid (BALF) using Wright's stain, as well as in lung tissue fixed with 10% formalin and stained with H & E stain. Quercetin and rutin (7.5 mg/kg, p.o.) significantly and dose-dependently inhibited both sRaw on IAR (31.60 and 26.44%) and LAR (29.87 and 28.69%) but with less efficacy than dexamethasone (3 mg/kg) and salbutamol (0.3 mg/kg), which inhibited IAR by 36.71 and 69.45%, and LAR by 67.23 and 0%, respectively, Quercetin and rutin (15 mg/kg) also inhibited production of histamine, PLA2, and EPO, and recruitment of leukocytes, particularly neutrophils and eosinophils, during LAR. respectively. Dexamethasone (3 mg/kg) also significantly reduced the recruitment of neutrophils, eosinophils, and lymphocytes in BALF, and salbutamol (0.3 mg/kg) reduced neutrophils and eosinophils with lower activity than dexamethasone. These results indicate that quercetin and rutin may be useful in the treatment of IAR and LAR in asthma via inhibition of histamine release, PLA2, and EPO, and reduced recruitment of neutrophils and eosinophils into the lung.

Establishing the phenotype in novel acute and chronic murine models of allergic asthma

Allergic asthma is a chronic disease of the airways, with superimposed acute inflammatory episodes which correspond to exacerbations of asthma. Two novel models of allergic asthma have been developed in mice receiving the same allergen sensitisation, but with acute or chronic allergen exposures, the latter to mimic the human situation more closely. Ovalbumin-sensitised mice were challenged by ovalbumin inhalation twice on the same day for the acute model, and 18 times over a period of 6 weeks for the chronic model. Lung function was monitored in conscious, unrestrained mice immediately after the last challenge for up to 12 h. Airway responsiveness to inhaled methacholine and serum antibody levels were determined 24 h after challenge. Bronchoalveolar inflammatory cell recruitment was determined at 2 or 24 h. Acute and chronically treated mice had similar early and late asthmatic responses peaking at 2 h and 7-8 h, respectively. IgE and IgG antibody levels, compared with naïve mice, and eosinophil infiltration, compared with naïve and saline challenge, were elevated. Airway hyperresponsiveness to methacholine was observed 24 h after challenge in both models. The acute model had higher levels of eosinophilia, whereas the chronic model showed hyperresponsiveness to lower doses of methacholine and had higher levels of total IgE and ovalbumin-specific IgG antibodies. Both novel murine models of allergic asthma bear a close resemblance to human asthma, each offering particular advantages for studying the mechanisms underlying asthma and for evaluating existing and novel therapeutic agents.

Using guinea pigs in studies relevant to asthma and COPD

The guinea pig has been the most commonly used small animal species in preclinical studies related to asthma and COPD. The primary advantages of the guinea pig are the similar potencies and efficacies of agonists and antagonists in human and guinea pig airways and the many similarities in physiological processes, especially airway autonomic control and the response to allergen. The primary disadvantages to using guinea pigs are the lack of transgenic methods, limited numbers of guinea pig strains for comparative studies and a prominent axon reflex that is unlikely to be present in human airways. These attributes and various models developed in guinea pigs are discussed.

Inhibitory effects of the alpha-2 adrenergic agonists clonidine and dexmedetomidine on enhanced airway tone in ovalbumin-sensitized guinea pigs

BACKGROUND AND OBJECTIVE

The alpha-2 adrenergic agonists clonidine and dexmedetomidine are used as an antihypertensive and a sedative, respectively. The aim of this study was to determine the effects of these agonists on ovalbumin-sensitized airway tone in guinea pigs.

METHODS

The animals were divided into two groups: control and sensitized. The sensitized group received ovalbumin intraperitoneally and was boosted by exposure to aerosolized ovalbumin. The effects of the alpha-2 agonists were investigated by measuring (1) total lung resistance and (2) smooth muscle tension using a tracheal ring preparation.

RESULTS

In the control group, acetylcholine significantly increased total lung resistance in a dose-dependent manner. In the sensitized animals, total lung resistance was significantly higher (by 95%) at 6 mug kg-1 acetylcholine than that in the control group. Both clonidine and dexmedetomidine had a slight but significant inhibitory effect on the response curve of lung resistance at higher concentrations of carbachol, a potent muscarinic receptor agonist. Similar to the data obtained in the control group, both clonidine and dexmedetomidine significantly decreased total lung resistance and the inhibitory effects of these alpha-2 agonists on lung resistance were significantly distinguishable. Similar direct inhibitory effects of the alpha-2 agonists on carbachol-induced muscle contraction were observed in both the control and sensitized groups, the inhibitory effects in the sensitized group being significantly greater.

CONCLUSION

Both clonidine and dexmedetomidine can relax the airway even in the hyper-reactive state.

Optimisation of the sensitisation conditions for an ovalbumin challenge model of asthma

Antigen inhalation in patients with atopic asthma results in an early asthmatic response (EAR), accompanied by a late asthmatic response (LAR) in 60% of patients, airway hyperresponsiveness (AHR) and inflammatory cell infiltration to the lungs. An ideal animal model of asthma should, therefore, provide at least these 4 features consistently and reproducibly. The aim of this study was to optimise the ovalbumin (OA) sensitisation conditions, for achieving EAR, LAR, AHR and cell influx, in a guinea-pig model of asthma. Animals were sensitised with 10 micro g or 100 micro g OA, as either a single or booster (day 1 and day 5) injection. Airway responses to inhaled OA (10 micro g, 1 h) of actively sensitised, conscious guinea pigs were determined by whole body plethysmography as the change in specific airways conductance (sG(aw)) over a 12 h period and at 24 h. Bronchoconstriction by inhaled histamine (1 mM) was used to investigate AHR, and inflammatory cell influx was determined by bronchoalveolar lavage (BAL), both at 24 h post-challenge. A single sensitisation with 10 micro g OA did not reveal an EAR, LAR or AHR following exposure to OA. However, total and differential cell counts (eosinophils and macrophages) were significantly greater 24 h post-challenge, when compared to saline-challenged sensitised animals. The addition of a booster injection of 10 micro g revealed an EAR, but no LAR or AHR after ovalbumin inhalation. However, there was a significant cell influx. Sensitisation with 100 micro g OA (single and booster injections) revealed all four parameters of the asthmatic response (EAR, LAR, AHR and cell influx). The incorporation of the booster sensitisation injection resulted in a prolongation of the LAR, and the AHR was more pronounced and cell influx increased significantly, when compared to all other sensitisation protocols. Thus, sensitisation with 100 micro g OA (with a booster injection) can reveal an EAR, LAR, AHR and cell influx following inhalation exposure to OA (10 micro g). Cellular infiltration to the lung may be a poor marker of the asthmatic response, as a threshold level of cell influx (eosinophils) appears to be required in order to elicit the LAR and AHR. There was an association between the LAR and AHR.

Beta-adrenoceptor responses of the airways: for better or worse?

Beta2-adrenoceptor agonists are the first-line treatment of asthma and chronic obstructive pulmonary disease (COPD), in which a short-acting beta2-adrenoceptor agonist is used as required for relief of bronchoconstriction. A long-acting beta2-adrenoceptor agonist may be added to an inhaled corticosteroid as step 3 in the management of chronic asthma. Long-acting beta2-adrenoceptor agonists may also be added in treatment of COPD. This review examines the beneficial and detrimental effects of beta2-adrenoceptor agonists. The beneficial effects of beta2-adrenoceptor agonists are mainly derived from their bronchodilator activity which relieves the bronchiolar narrowing and improves air flow. The potential anti-inflammatory actions of stabilizing mast cell degranulation and release of inflammatory and bronchoconstrictor mediators, is considered. Other potential beneficial responses include improvements in mucociliary clearance and inhibition of extravasation of plasma proteins that is involved in oedema formation in asthma. The side effects of beta2-adrenoceptor agonists are primarily related to beta2-adrenoceptor-mediated responses at sites outside the airways. Of major concern has been the development of tolerance and this is discussed in relation to incidence of increased morbidity and mortality to asthma over the past three decades. A clinical aspect of beta2-adrenoceptor pharmacology in recent years has been the recognition of genetic polymorphism of the receptor and how this affects responses to and tolerance to beta2-adrenoceptor agonists. A controversial feature of beta2-adrenoceptor agonists is their stereoisomerism and whether the inactive (S)-isomer of salbutamol had detrimental actions in the commercially used racemate. The consensus is that despite these adverse properties, beta2-adrenoceptor agonist remains the most useful pharmacological agents in the management of asthma and COPD.

Early- and late-phase bronchoconstriction, airway hyper-reactivity and cell influx into the lungs, after 5'-adenosine monophosphate inhalation: comparison with ovalbumin

BACKGROUND

Antigen inhalation in atopic asthmatic patients results in an early asthmatic response (EAR), accompanied by a late asthmatic response (LAR) in 60% of patients. Inhaled 5'-adenosine monophosphate (5'-AMP) causes immediate bronchoconstriction in asthmatics but not in normal subjects.

OBJECTIVES

The aims of this study were to investigate whether 5'-AMP can produce a LAR, airway hyper-reactivity (AHR) and cell influx to the lungs, in a sensitized guinea-pig model of asthma, and to compare with the profile of activity after ovalbumin (OVA) inhalation.

METHODS

Airway responses to inhaled OVA (10 microg/mL) and 5'-AMP (3 and 300 mm) of actively sensitized, conscious guinea-pigs were determined by whole body plethysmography as the change in specific airway conductance (sGaw). Inhaled histamine (1 mm) was used to investigate AHR, and cell influx was determined by bronchoalveolar lavage (BAL).

RESULTS

Exposure to OVA revealed an EAR, and LAR at 6 h post-challenge. AHR to histamine occurred 24 h after challenge together with a significant increase in total and differential (eosinophils and macrophages) cell counts. Low dose 5'-AMP (3 mm) produced an EAR, LAR at 6 h after challenge, and AHR to histamine 12 h post-challenge. No AHR occurred 24 h after inhalation. Total and macrophage cell counts were increased significantly 6, 12 and 24 h after exposure. Bronchodilatation followed high dose 5'-AMP (300 mm), followed by a LAR at 6 h. AHR to histamine occurred 12 h after challenge, but not at 24 h. A significant increase in total and differential (eosinophils and macrophages) cell counts occurred 6, 12 and 24 h post-exposure. No changes were observed in non-sensitized guinea-pigs.

CONCLUSION

OVA challenge revealed an EAR, LAR, cell influx and AHR in a guinea-pig model of asthma. This study demonstrated for the first time that a LAR and AHR to histamine can be revealed following 5'-AMP inhalation, in sensitized but not unsensitized guinea-pigs. Cell influx at 6, 12 and 24 h post-challenge suggests that it may be associated with the LAR and AHR.