Modelling the asthma phenotype: impact of cigarette smoke exposure.

BACKGROUND: Asthmatics that are exposed to inhaled pollutants such as cigarette smoke (CS) have increased symptom severity. Approximately 25% of adult asthmatics are thought to be active smokers and many sufferers, especially in the third world, are exposed to high levels of inhaled pollutants. The mechanism by which CS or other airborne pollutants alter the disease phenotype and the effectiveness of treatment in asthma is not known. The aim of this study was to determine the impact of CS exposure on the phenotype and treatment sensitivity of rodent models of allergic asthma. METHODS: Models of allergic asthma were configured that mimicked aspects of the asthma phenotype and the effect of CS exposure investigated. In some experiments, treatment with gold standard asthma therapies was investigated and end-points such as airway cellular burden, late asthmatic response (LAR) and airway hyper-Reactivity (AHR) assessed. RESULTS: CS co-exposure caused an increase in the LAR but interestingly attenuated the AHR. The effectiveness of LABA, LAMA and glucocorticoid treatment on LAR appeared to be retained in the CS-exposed model system. The eosinophilia or lymphocyte burden was not altered by CS co-exposure, nor did CS appear to alter the effectiveness of glucocorticoid treatment. Steroids, however failed to reduce the neutrophilic inflammation in sensitized mice exposed to CS. CONCLUSIONS: These model data have certain parallels with clinical findings in asthmatics, where CS exposure did not impact the anti-inflammatory efficacy of steroids but attenuated AHR and enhanced symptoms such as the bronchospasm associated with the LAR. These model systems may be utilised to investigate how CS and other airborne pollutants impact the asthma phenotype; providing the opportunity to identify novel targets.

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.

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.

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.

EP4 receptor as a new target for bronchodilator therapy.

BACKGROUND: Asthma and chronic obstructive pulmonary disease are airway inflammatory diseases characterised by airflow obstruction. Currently approved bronchodilators such as long-acting ß(2) adrenoceptor agonists are the mainstay treatments but often fail to relieve symptoms of chronic obstructive pulmonary disease and severe asthma and safety concerns have been raised over long-term use. The aim of the study was to identify the receptor involved in prostaglandin E(2) (PGE(2))-induced relaxation in guinea pig, murine, monkey, rat and human airways in vitro. METHODS: Using an extensive range of pharmacological tools, the relaxant potential of PGE(2) and selective agonists for the EP(1-4) receptors in the presence and absence of selective antagonists in guinea pig, murine, monkey, rat and human isolated airways was investigated. RESULTS: In agreement with previous studies, it was found that the EP(2) receptor mediates PGE(2)-induced relaxation of guinea pig, murine and monkey trachea and that the EP(4) receptor mediates PGE(2)-induced relaxation of the rat trachea. These data have been confirmed in murine airways from EP(2) receptor-deficient mice (Ptger2). In contrast to previous publications, a role for the EP(4) receptor in relaxant responses in human airways in vitro was found. Relaxant activity of AH13205 (EP(2) agonist) was also demonstrated in guinea pig but not human airway tissue, which may explain its failure in clinical studies. CONCLUSION: Identification of the receptor mediating PGE(2)-induced relaxation represents a key step in developing a novel bronchodilator therapy. These data explain the lack of bronchodilator activity observed with selective EP(2) receptor agonists in clinical studies.

In vivo characterization of GSK256066, a high-affinity inhaled phosphodiesterase 4 inhibitor.

Oral phosphodiesterase (PDE) 4 inhibitors have demonstrated clinical efficacy in chronic obstructive pulmonary disease and asthma. Preclinical and clinical investigation of inhaled PDE4 inhibitors is ongoing. 6-({3-[(Dimethylamino)carbonyl]phenyl}sulfonyl)-8-methyl-4-{[3-methyloxy)phenyl]amino}-3-quinolinecarboxamide (GSK256066) is an exceptionally high-affinity and selective inhibitor of PDE4 designed for inhaled delivery. The aim of these studies was to investigate the potency, duration of action, and therapeutic index of GSK256066 in animal models of pulmonary inflammation. The effects of intratracheally administered GSK256066 were investigated in rat lipopolysaccharide (LPS)- and ovalbumin (OVA)-induced models of acute pulmonary inflammation. In some studies, fluticasone propionate (FP) was included as a comparator. The therapeutic index (anti-inflammatory effect versus emesis) of GSK256066 was studied in ferrets where acute pulmonary inflammation was induced with inhaled LPS. In rats, GSK256066 and FP caused significant (p < 0.05) inhibition of LPS-induced pulmonary neutrophilia. The duration of action of GSK256066 at 10 × ED(50) dose (10 µg/kg) was 12 h. GSK256066 and FP also inhibited LPS-induced increases in exhaled nitric oxide (ED(50) 35 and 92 µg/kg, respectively). In addition, GSK256066 inhibited pulmonary eosinophilia in rats exposed to OVA (ED(50) 0.4 µg/kg). In ferrets, inhaled GSK256066 inhibited LPS-induced pulmonary neutrophilia (ED(50) 18 µg/kg), and no emetic episodes were observed. Thus, GSK256066 may have an improved therapeutic index compared with oral PDE4 inhibitors, e.g., cilomilast and roflumilast. In summary, GSK256066 demonstrates potent and long-lasting anti-inflammatory effects in animal models of pulmonary inflammation and does not induce emetic episodes in ferrets. GSK256066 has potential as an inhaled therapeutic for the treatment of asthma and chronic obstructive pulmonary disease.

GSK256066, an exceptionally high-affinity and selective inhibitor of phosphodiesterase 4 suitable for administration by inhalation: in vitro, kinetic, and in vivo characterization.

Oral phosphodiesterase (PDE) 4 inhibitors such as roflumilast have established the potential of PDE4 inhibition for the treatment of respiratory diseases. However, PDE4 inhibitor efficacy is limited by mechanism-related side effects such as emesis and nausea. Delivering the inhibitor by the inhaled route may improve therapeutic index, and we describe 6-({3-[(dimethylamino)carbonyl]phenyl}sulfonyl)-8-methyl-4-{[3-methyloxy) phenyl]amino}-3-quinolinecarboxamide (GSK256066), an exceptionally high-affinity inhibitor of PDE4 designed for inhaled administration. GSK256066 is a slow and tight binding inhibitor of PDE4B (apparent IC(50) 3.2 pM; steady-state IC(50) <0.5 pM), which is more potent than any previously documented compound, for example, roflumilast (IC(50) 390 pM), tofimilast (IC(50) 1.6 nM), and cilomilast (IC(50) 74 nM). Consistent with this, GSK256066 inhibited tumor necrosis factor α production by lipopolysaccharide (LPS)-stimulated human peripheral blood monocytes with 0.01 nM IC(50) (compared with IC(50) values of 5, 22, and 389 nM for roflumilast, tofimilast, and cilomilast, respectively) and by LPS-stimulated whole blood with 126 pM IC(50). GSK256066 was highly selective for PDE4 (>380,000-fold versus PDE1, PDE2, PDE3, PDE5, and PDE6 and >2500-fold against PDE7), inhibited PDE4 isoforms A-D with equal affinity, and had a substantial high-affinity rolipram binding site ratio (>17). When administered intratracheally to rats, GSK256066 inhibited LPS-induced pulmonary neutrophilia with ED(50) values of 1.1 µg/kg (aqueous suspension) and 2.9 µg/kg (dry powder formulation) and was more potent than an aqueous suspension of the corticosteroid fluticasone propionate (ED(50) 9.3 µg/kg). Thus, GSK256066 has been demonstrated to have exceptional potency in vitro and in vivo and is being clinically investigated as a treatment for chronic obstructive pulmonary disease.

The identification of a novel phosphodiesterase 4 inhibitor, 1-ethyl-5-{5-[(4-methyl-1-piperazinyl)methyl]-1,3,4-oxadiazol-2-yl}-N-(tetrahydro-2H-pyran-4-yl)-1H-pyrazolo[3,4-b]pyridin-4-amine (EPPA-1), with improved therapeutic index using pica feeding in rats as a measure of emetogenicity.

Clinical utility of phosphodiesterase 4 (PDE4) inhibitors as anti-inflammatory agents has, to date, been limited by adverse effects including nausea and emesis, making accurate assessment of emetic versus anti-inflammatory potencies critical to the development of inhibitors with improved therapeutic indices. In the present study we determined the in vitro and in vivo anti-inflammatory potencies of the first-generation PDE4 inhibitor, rolipram, the second-generation inhibitors, roflumilast and cilomilast, and a novel third generation inhibitor, 1-ethyl-5-{5-[(4-methyl-1-piperazinyl)methyl]-1,3,4-oxadiazol-2-yl}-N-(tetrahydro-2H-pyran-4-yl)-1H-pyrazolo[3,4-b]pyridin-4-amine (EPPA-1). The rank-order potency against lipopolysaccharide (LPS)-induced tumor necrosis factor-alpha production by human peripheral blood mononuclear cells was roflumilast (IC(50) = 5 nM) > EPPA-1 (38) > rolipram (269) > cilomilast (389), and against LPS-induced pulmonary neutrophilia in the rat was EPPA-1 (D(50) = 0.042 mg/kg) > roflumilast (0.24) > rolipram (3.34) > cilomilast (4.54). Pica, the consumption of non-nutritive substances in response to gastrointestinal stress, was used as a surrogate measure for emesis, giving a rank-order potency of rolipram (D(50) = 0.495 mg/kg) > roflumilast (1.6) > cilomilast (6.4) > EPPA-1 (24.3). The low and high emetogenic activities of EPPA-1 and rolipram, respectively, detected in the pica model were confirmed in a second surrogate model of emesis, reversal of alpha(2)-adrenoceptor-mediated anesthesia in the mouse. The rank order of therapeutic indices derived in the rat [(pica D(50))/(neutrophilia D(50))] was EPPA-1 (578) > roflumilast (6.4) > cilomilast (1.4) > rolipram (0.15), consistent with the rank order derived in the ferret [(emesis D(50))/(neutrophilia D(50))]. These data validate rat pica feeding as a surrogate for PDE4 inhibitor-induced emesis in higher species, and identify EPPA-1 as a novel PDE4 inhibitor with an improved therapeutic index.

Guinea-pig lung adenylyl and guanylyl cyclase and PDE activities associated with airway hyper- and hypo-reactivity following LPS inhalation.

The relationships between changes in in vivo airway reactivity and levels cyclicAMP and cyclicGMP were determined in guinea-pig lungs after exposure to inhaled lipopolysaccharide (LPS). After LPS (30 microg.ml(-1), 1 h), guinea-pigs displayed in vivo airway hyperreactivity (AHR) at 1 h and hyporeactivity (AHOR) at 48 h, to inhaled (20 s) histamine (1 or 3 mM, respectively). Isoprenaline-stimulated cAMP or SNAP-stimulated cGMP were determined in the lungs isolated from guinea-pigs exposed to LPS inhalation to determine whether there was a relationship between AHR or AHOR and adenylyl/guanylyl cyclase and phosphodiesterase (PDE) activities. Assays were performed in the absence and presence of the non-selective PDE inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Levels of cAMP and cGMP in its presence indicated adenylyl and guanylyl cyclase activities, respectively. The difference between cAMP and cGMP levels, in the absence and presence of IBMX, reflected relevant PDE activity. In vivo AHR was associated with increased PDE activity towards cAMP and cGMP (67 and 278%, respectively) and also increased adenylyl (47%) and guanylyl (210%) cyclase activities. In vivo AHOR at 48 h after LPS inhalation was also associated with raised cyclase activity (p < 0.05), whereas relevant PDE activity declined by 79 and 68%, compared with 48 h after vehicle. Although net stimulated cGMP levels increased during AHR and AHOR and net stimulated cAMP increased during AHOR, our index of PDE activity increased during AHR and decreased during AHOR. These results therefore support the rationale for the use of PDE-inhibitors in the treatment of respiratory diseases associated with AHR.

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, 1h) 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 (0.3mM) was determined before and 24h 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.

At last, a truly selective EP2 receptor antagonist.

Ever since the discovery of prostaglandin E(2)(PGE(2)), this lipid mediator has been the focus of intense research. The diverse biological effects of PGE(2) are due, at least in part, to the existence of four distinct receptors (EP(1-4)). This can complicate the analysis of the biological effects produced by PGE2. While there are currently selective pharmacological tools to explore the roles of the EP(1,3,4) receptors in cellular and tissue responses, analysis of EP(2) receptor-induced responses has been hampered by the lack of a selective EP(2) receptor antagonist. The recent publication in this journal by af Forselles et al. suggests that such a tool compound is now available. In their manuscript, the authors describe a series of experiments that show PF-04418948 to be a potent and selective EP(2) receptor antagonist. The discovery of this tool compound will interest many scientists and through collaborations with Pfizer they may have access to PF-04418948 to facilitate further investigation of the biology of this fascinating lipid mediator.

Mouse models of allergic asthma: acute and chronic allergen challenge.

Asthma is defined as a chronic inflammatory disease of the airways; however, the underlying physiological and immunological processes are not fully understood. Animal models have been used to elucidate asthma pathophysiology, and to identify and evaluate novel therapeutic targets. Several recent review articles (Epstein, 2004; Lloyd, 2007; Boyce and Austen, 2005; Zosky and Sly, 2007) have discussed the potential value of these models. Allergen challenge models reproduce many features of clinical asthma and have been widely used by investigators; however, the majority involve acute allergen challenge procedures. It is recognised that asthma is a chronic inflammatory disease resulting from continued or intermittent allergen exposure, usually via inhalation, and there has been a recent focus on developing chronic allergen exposure models, predominantly in mice. Here, we review the acute and chronic exposure mouse models, and consider their potential role and impact in the field of asthma research.