Antigen-induced mediator release in primates

A PAF receptor antagonist inhibits acute airway inflammation and late-phase responses but not chronic airway inflammation and hyperresponsiveness in a primate model of asthma

We have examined the effects of a PAF receptor antagonist, WEB 2170, on several indices of acute and chronic airway inflammation and associated changes in lung function in a primate model of allergic asthma. A single oral administration WEB 2170 provided dose related inhibition of the release of leukotriene C₄ (LTC₄) and prostaglandin D₂ (PGD₂) recovered and quantified in bronchoalveolar lavage (BAL) fluid obtained during the acute phase response to inhaled antigen. In addition, oral WEB 2170 treatment in dual responder primates blocked the acute influx of neutrophils into the airways as well as the associated late-phase airway obstruction occurring 6 h after antigen inhalation. In contrast, a multiple dosing regime with WEB 2170 (once a day for 7 consecutive days) failed to reduce the chronic airway inflammation (eosinophilic) and associated airway hyperresponsiveness to inhaled methacholine that is characteristic of dual responder monkeys. Thus, we conclude that the generation of PAF following antigen inhalation contributes to the development of lipid mediators, acute airway inflammation and associated late-phase airway obstruction in dual responder primates; however, PAF does not play a significant role in the maintenance of chronic airway inflammation and associated airway hyperresponsiveness in this primate model.

Tetrahydroquinoline derivatives as CRTH2 antagonists

A series of tetrahydroquinoline-derived inhibitors of the CRTH2 receptor was discovered by a high throughput screen. Optimization of these compounds for potency and pharmacokinetic properties led to the discovery of potent and orally bioavailable CRTH2 antagonists.

Discovery and optimization of CRTH2 and DP dual antagonists

A series of phenylacetic acid derivatives was discovered as CRTH2 antagonists. Modification of the series led to compounds that are also antagonists of DP. Since activation of CRTH2 and DP are believed to play key roles in mediating responses of asthma and other immune diseases, this series was optimized to increase the dual antagonistic activities and improve pharmacokinetic properties. These efforts led to selection of AMG 009 as a clinical candidate.

Animal models of airway inflammation and airway smooth muscle remodelling in asthma

Asthma is a complex disease that involves chronic inflammation and subsequent decline in airway function. The widespread use of animal models has greatly contributed to our understanding of the cellular and molecular pathways underlying human allergic asthma. Animal models of allergic asthma include smaller animal models which offer 'ease of use' and availability of reagents, and larger animal models that may be used to address aspects of allergic airways disease not possible in humans or smaller animal models. This review examines the application and suitability of various animal models for studying mechanisms of airway inflammation and tissue remodelling in allergic asthma, with a specific focus on airway smooth muscle.

Allergen dose dependency of the early- and late-phase cutaneous response in the cynomolgus monkey

BACKGROUND

Cutaneous administration of allergen provides a means to confirm an allergic status, investigate the pathogenesis of allergic diseases, and/or provide a mechanism to evaluate the benefit of new potential therapeutics.

OBJECTIVE

Studies were performed to characterize the allergen-induced cutaneous early- and late-phase response (EPR and LPR) in the cynomolgus monkey.

METHODS

Following intradermal injections of Ascaris suum allergen, the cutaneous weal and flare EPR was measured 15 min post-injection, and skin biopsies were collected at 8-24 h to determine the optimal time of LPR occurrence. Biopsies were analysed for epidermal and dermal inflammatory changes.

RESULTS

The EPR was dose related with a reproducible, measurable response at 1 : 10 000 and maximal at a 1 : 100 allergen dilution. In contrast, the threshold dose required for a reproducible LPR was much greater requiring a dilution of 6 : 100, suggesting independent mechanisms for the EPR and LPR. The LPR 20 h post-allergen injection induced an inflammatory response in the upper and deep dermis. The response was characterized by a moderate perivascular to diffuse inflammation consisting of mononuclear cells, neutrophils and eosinophils. Dexamethasone, while having no effect on the EPR, reduced dermal inflammation (upper dermis, P=0.004; deep dermis, P=0.03). Similarly, dermal eosinophilia was also reduced (upper dermis, P<0.001; deep dermis, P=0.02).

CONCLUSION

Collectively, the results indicate the dose dependency of the EPR and LPR. Furthermore, our observations indicate the value of the LPR response in the cynomolgus monkey to evaluate new therapeutics for the treatment of allergic diseases such as atopic dermatitis.

Shortening of the induction period of allergic asthma in cynomolgus monkeys by Ascaris suum and house dust mite

The development of non-human primate models of asthma requires a period of time (e.g., 0.5-1 year). To develop the models in a short period, male cynomolgus monkeys were sensitized with dinitrophenyl-Ascaris suum (DNP-As) allergen by intraperitoneal and intramuscular injection and by intratracheal inhalation. All sensitized animals developed positive intradermal skin reaction to DNP-As. Sensitization elevated allergen-specific IgE levels in serum, the number of CCR4-positive T helper lymphocytes in peripheral blood, and IL-4 and IL-5 releases from phorbol 12-myristate 13-acetate- and ionomycin-stimulated peripheral blood. In addition, allergen challenge induced increases in lung resistance, airway inflammation, and hyperresponsiveness to inhaled methacholine. Next, animals were sensitized with house dust mite extracts (HDM) under the similar procedure. In these animals sensitized with DNP-As or HDM, inhaled fluticasone propionate and oral prednisolone inhibited the allergen-induced airway hyperresponsiveness. Taken together, monkey asthma models were successfully developed by sensitization with DNP-As or HDM under a short-term protocol (within 7 weeks). These models should be useful for the evaluation of anti-inflammatory drugs for asthma treatment.

IL-13 blockade reduces lung inflammation after Ascaris suum challenge in cynomolgus monkeys

BACKGROUND

Airway inflammation is a hallmark feature of asthma and a driver of airway hyperresponsiveness. IL-13 is a key inducer of airway inflammation in rodent models of respiratory disease, but a role for IL-13 has not been demonstrated in primates.

OBJECTIVE

We sought to test the efficacy of a neutralizing antibody to human IL-13 in a cynomolgus monkey model of lung inflammation.

METHODS

Using cynomolgus monkeys (Macaca fascicularis) that are sensitized to Ascaris suum through natural exposure, we developed a reproducible model of acute airway inflammation after segmental A suum antigen challenge. This model was used to test the in vivo efficacy of mAb13.2, a mouse mAb directed against human IL-13, and IMA-638, the humanized counterpart of mAb13.2. Bronchoalveolar lavage (BAL) cells and BAL fluid were collected before and after antigen challenge and assayed for cellular content by means of differential count.

RESULTS

Total BAL cell count, eosinophil number, and neutrophil number were all reduced in animals treated with mAb13.2 or IMA-638 compared with values in control animals that were untreated, given saline, or treated with human IgG of irrelevant specificity. In addition, levels of eotaxin and RANTES in BAL fluid were reduced in anti-IL-13-treated animals compared with levels seen in control animals.

CONCLUSION

These findings support a role for IL-13 in maintaining lung inflammation in response to allergen challenge in nonhuman primates.

CLINICAL IMPLICATIONS

IL-13 neutralization with a specific antibody could be a useful therapeutic strategy for asthma.

Effects of salmeterol xinafoate and fluticasone propionate on immunological activation of human cultured mast cells

BACKGROUND

The clinical efficacy of combination therapy comprising a long acting beta(2)-agonist (LABA) and corticosteroid is widely recognized for the treatment of adult asthma. Here we examine the effect of salmeterol xinafoate (SX) and fluticasone propionate (FP) alone and in combination on the immunological activation of human cultured mast cells (HCMC)in vitro.

METHODS

HCMC were passively sensitized with IgE antibody and then activated by challenging with anti-IgE antibody. The effect of drugs on the activation of mast cells was examined by measuring the amount of released chemical mediators (histamine, leukotrienes (LT) and prostaglandin D(2) (PGD(2))) and granulocyte macrophage colony stimulating factor (GM-CSF).

RESULTS

The release of each chemical mediator was inhibited by 10-9-10-8M SX but not by 10-10-10-7M FP. The production of GM-CSF was inhibited by a concentration of 10-8M in both drugs and the inhibition was augmented by combined treatment with 10-11M of each drug.

CONCLUSIONS

The immunological release of chemical mediators (histamine, LT, PGD(2)) from HCMC was inhibited by SX but not by FP. SX and FP inhibited the production of GM-CSF by HCMC and both drug showed synergistic inhibition in the production of GM-CSF.

Airway generation-specific differences in the spatial distribution of immune cells and cytokines in allergen-challenged rhesus monkeys

BACKGROUND

Accumulation of immune cell populations and their cytokine products within tracheobronchial airways contributes to the pathogenesis of allergic asthma. It has been postulated that peripheral regions of the lung play a more significant role than proximal airways with regard to inflammatory events and airflow obstruction.

OBJECTIVE

To determine whether immune cell populations and associated cytokines are uniformly distributed throughout the conducting airway tree in a non-human primate model of allergic asthma.

METHODS

We used a stereologic approach with a stratified sampling scheme to measure the volume density of immune cells within the epithelium and interstitium of trachea and 4-5 intrapulmonary airway generations from house dust mite (HDM) (Dermatophagoides farinae)-challenged adult monkeys. In conjunction with immune cell distribution profiles, mRNA levels for 21 cytokines/chemokines and three chemokine receptors were evaluated at four different airway generations from microdissected lungs.

RESULTS

In HDM-challenged monkeys, the volume of CD1a+ dendritic cells, CD4+ T helper lymphocytes, CD25+ cells, IgE+ cells, eosinophils, and proliferating cells were significantly increased within airways. All five immune cell types accumulated within airways in unique patterns of distribution, suggesting compartmentalized responses with regard to trafficking. Although cytokine mRNA levels were elevated throughout the conducting airway tree of HDM-challenged animals, the distal airways (terminal and respiratory bronchioles) exhibited the most pronounced up-regulation.

CONCLUSION

These findings demonstrate that key effector immune cell populations and cytokines associated with asthma differentially accumulate within distinct regions and compartments of tracheobronchial airways from allergen-challenged primates.

Airway closure after antigen challenge in cynomolgus monkeys: effect of the histamine H1 receptor antagonist, chlorpheniramine maleate

BACKGROUND

Airway closure is frequently observed in human asthma. However, limited information exists on the factors that cause this condition. In this study, an allergic cynomolgus monkey model was used to characterize the condition of airway closure and assess the contribution of histamine H1 receptors to this response.

METHODS

Oscillatory lung mechanics, arterial blood gases during ventilation on 100% O2 and functional residual capacity (FRC) assessed by helium dilution were measured before and then 10 min and 24 h after Ascaris aerosol challenge in 12 male Ascaris-sensitive cynomolgus monkeys. The monkeys were pretreated with intravenous saline or chlorpheniramine maleate (0.3 mg/kg) in a randomized crossover design.

RESULTS

Ascaris challenge produced a large increase in airway resistance, an increase in lung tissue damping (G) that measures ventilation inhomogeneity in the lung, a reduction in arterial oxygen tension (PaO2) during ventilation on 100% O2 and a reduction in FRC. These effects were seen 10 min after the Ascaris challenge, but by 24 h, these parameters had returned close to the baseline values. Chlorpheniramine maleate (0.3 mg/kg, i.v.) produced a 12-fold shift in the histamine bronchoconstrictor dose-response curve. Pretreatment of monkeys with chlorpheniramine maleate (0.3 mg/kg, i.v.) attenuated the increase in airway resistance induced by Ascaris challenge, but had only a small effect on the increase in G and the reductions in PaO2 and FRC after antigen.

CONCLUSIONS

These results demonstrate that airway closure occurs immediately after the antigen challenge in allergic cynomolgus monkeys and that histamine H1 receptors contribute very minimally to this response.

Uteroglobin represses allergen-induced inflammatory response by blocking PGD2 receptor-mediated functions

Uteroglobin (UG) is an antiinflammatory protein secreted by the epithelial lining of all organs communicating with the external environment. We reported previously that UG-knockout mice manifest exaggerated inflammatory response to allergen, characterized by increased eotaxin and Th2 cytokine gene expression, and eosinophil infiltration in the lungs. In this study, we uncovered that the airway epithelia of these mice also express high levels of cyclooxygenase (COX)-2, a key enzyme for the production of proinflammatory lipid mediators, and the bronchoalveolar lavage fluid (BALF) contain elevated levels of prostaglandin D₂. These effects are abrogated by recombinant UG treatment. Although it has been reported that prostaglandin D₂ mediates allergic inflammation via its receptor, DP, neither the molecular mechanism(s) of DP signaling nor the mechanism by which UG suppresses DP-mediated inflammatory response are clearly understood. Here we report that DP signaling is mediated via p38 mitogen–activated protein kinase, p44/42 mitogen–activated protein kinase, and protein kinase C pathways in a cell type–specific manner leading to nuclear factor–κB activation stimulating COX-2 gene expression. Further, we found that recombinant UG blocks DP-mediated nuclear factor–κB activation and suppresses COX-2 gene expression. We propose that UG is an essential component of a novel innate homeostatic mechanism in the mammalian airways to repress allergen-induced inflammatory responses.

Prostaglandin D2 reinforces Th2 type inflammatory responses of airways to low-dose antigen through bronchial expression of macrophage-derived chemokine

PGD2, a lipid mediator released from mast cells, is known to participate in allergic reactions. However, the mechanism by which PGD2 contributes to such reactions remains unclear. We established a novel experimental model of asthma that permitted direct assessment of the role of PGD2 in airway inflammation. Antigen-sensitized mice were exposed to aerosolized prostaglandin D2 (PGD2) 1 d before challenge with low-dose aerosolized antigen. Not only the numbers of eosinophils, lymphocytes, and macrophages but also the levels of IL-4 and IL-5 in bronchoalveolar lavage fluid were higher in PGD2-pretreated mice than in control mice. The expression of macrophage-derived chemokine (MDC), a chemoattractant for Th2 cells, was greater in PGD2-pretreated mice than in control. Injection of anti-MDC antibody into PGD2-pretreated mice markedly inhibited inflammatory cell infiltration as well as Th2 cyto-kine production after antigen challenge. These results indicate that PGD2 accelerates Th2 type inflammation by induction of MDC. Our results suggest that this mechanism may play a key role in the development of human asthma and that MDC might be a target molecule for therapeutic intervention.

Pronounced eosinophilic lung inflammation and Th2 cytokine release in human lipocalin-type prostaglandin D synthase transgenic mice

PGD(2) is a major lipid mediator released from mast cells, but little is known about its role in the development of allergic reactions. We used transgenic (TG) mice overexpressing human lipocalin-type PGD synthase to examine the effect of overproduction of PGD(2) in an OVA-induced murine asthma model. The sensitization of wild-type (WT) and TG mice was similar as judged by the content of OVA-specific IgE. After OVA challenge, PGD(2), but not PGE(2), substantially increased in the lungs of WT and TG mice with greater PGD(2) increment in TG mice compared with WT mice. The numbers of eosinophils and lymphocytes in the bronchoalveolar lavage (BAL) fluid were significantly greater in TG mice than in WT mice on days 1 and 3 post-OVA challenge, whereas the numbers of macrophages and neutrophils were the same in both WT and TG mice. The levels of IL-4, IL-5, and eotaxin in BAL fluid were also significantly higher in TG mice than in WT mice, although the level of IFN-gamma in the BAL fluid of TG mice was decreased compared with that in WT mice. Furthermore, lymphocytes isolated from the lungs of TG mice secreted less IFN-gamma than those from WT mice, whereas IL-4 production was unchanged between WT and TG mice. Thus, overproduction of PGD(2) caused an increase in the levels of Th2 cytokines and a chemokine, accompanied by the enhanced accumulation of eosinophils and lymphocytes in the lung. These results indicate that PGD(2) plays an important role in late phase allergic reactions in the pathophysiology of bronchial asthma.

Airway resistance and tissue elastance from input or transfer impedance in bronchoconstricted monkeys

Ascaris suum (AS) challenge in nonhuman primates is used as an animal model of human asthma. The primary goal of this study was to determine whether the airways and respiratory tissues in monkeys that are bronchoconstricted by AS inhalation behave similarly to those in asthmatic humans. Airway resistance (Raw) and tissue elastance (Eti) were estimated from respiratory system input (Zin) or transfer (Ztr) impedance. Zin (0.4-20 Hz) and Ztr (2-128 Hz) were measured in anesthetized cynomolgus monkeys (n = 10) under baseline (BL) and post-AS challenge conditions. Our results indicate that AS challenge in monkeys produces 1) predominantly an increase in Raw and not tissue resistance, 2) airway wall shunting at higher AS doses, and 3) heterogeneous airway constriction resulting in a decrease of lung parenchyma effective compliance. We investigated whether the airway and tissue properties estimated from Zin and Ztr were similar and found that Raw estimated from Zin and Ztr were correlated [r(2) = 0.76], not significantly different at BL (13.6 +/- 1.4 and 13.1 +/- 0.9 cmH(2)O. l(-1). s(-1), respectively), but significantly different post-AS (20.5 +/- 4.5 cmH(2)O. l(-1). s(-1) and 18.5 +/- 5.2 cmH(2)O. l(-1). s(-1)). There was no correlation between Eti estimated from Zin and Ztr. The changes in lung mechanical properties in AS-bronchoconstricted monkeys are similar to those recently reported in human asthma, confirming that this is a reasonable model of human asthma.

Allergic asthma induced in rhesus monkeys by house dust mite (Dermatophagoides farinae)

To establish whether allergic asthma could be induced experimentally in a nonhuman primate using a common human allergen, three female rhesus monkeys (Macaca mulatta) were sensitized with house dust mite (Dermatophagoides farinae) allergen (HDMA) by subcutaneous injection, followed by four intranasal sensitizations, and exposure to allergen aerosol 3 hours per day, 3 days per week for up to 13 weeks. Before aerosol challenge, all three monkeys skin-tested positive for HDMA. During aerosol challenge with HDMA, sensitized monkeys exhibited cough and rapid shallow breathing and increased airway resistance, which was reversed by albuterol aerosol treatment. Compared to nonsensitized monkeys, there was a fourfold reduction in the dose of histamine aerosol necessary to produce a 150% increase in airway resistance in sensitized monkeys. After aerosol challenge, serum levels of histamine were elevated in sensitized monkeys. Sensitized monkeys exhibited increased levels of HDMA-specific IgE in serum, numbers of eosinophils and exfoliated cells within lavage, and elevated CD25 expression on circulating CD4(+) lymphocytes. Intrapulmonary bronchi of sensitized monkeys had focal mucus cell hyperplasia, interstitial infiltrates of eosinophils, and thickening of the basement membrane zone. We conclude that a model of allergic asthma can be induced in rhesus monkeys using a protocol consisting of subcutaneous injection, intranasal instillation, and aerosol challenge with HDMA.

Determination of airway and tissue resistances after antigen and methacholine in nonhuman primates

Antigen challenge of Ascaris suum-sensitive animals has been used as a model of asthma in humans. However, no reports have separated total respiratory resistance into airway (Raw) and tissue (Rti) components. We compared input impedance (Zin) and transfer impedance (Ztr) to determine Raw and Rti in anesthetized cynomolgus monkeys under control and bronchoconstricted conditions. Zin data between 1 and 64 Hz are frequency dependent during baseline conditions, and this frequency dependence shifts in response to A. suum or methacholine. Thus it cannot be modeled with the DuBois model, and estimates of Raw and Rti cannot be determined. With Ztr, baseline data were much less variable than Zin in all monkeys. After bronchial challenge with A. suum or methacholine, the absolute amplitude of the resistive component of Ztr increased and its zero crossing shifted to higher frequencies. These data can estimate Raw and Rti with the six-element DuBois model. Therefore, in monkeys, Ztr has advantages over other measures of lung function, since it provides a methodology to separate estimates of Raw and Rti. In conclusion, Ztr shows spectral features similar to those reported in healthy and asthmatic humans.

Characterization of a primate model of asthma using anti-allergy/anti-asthma agents

The following study was performed to further characterize a primate model of asthma using classes of drugs that target allergy (pyrilamine, cetirizine), are bronchodilators for the treatment of asthma (salbutamol, salmeterol) or are anti-inflammatory (dexamethasone). These drugs were examined for their ability to inhibit acute, antigen-induced bronchoconstriction, the development of airway hyperresponsiveness (AHR) and the infiltration of leukocytes into the lungs of atopic cynomolgus monkeys (Macaca facsicularis) using a 10-day, multiple antigen (Ag) challenge protocol. All compounds except dexamethasone and cetirizine significantly (p < 0.05) reduced acute, Ag-induced bronchoconstriction (salbutamol: 74.2%, salmeterol: 52.6%%, pyrilamine: 62.4% inhibition) compared to vehicle control trials. Only dexamethasone and salmeterol prevented the development of AHR to methacholine challenge by 90.4 +/- 6.81% and 85.7 +/- 5.61% respectively. Dexamethasone significantly reduced the Ag-induced increase in BAL eosinophils by 85.9 +/- 8.53%. Cetirizine reduced the eosinophil response in 5 of 6 monkeys and salmeterol demonstrated a trend towards reduced eosinophil increases after multiple Ag challenge, but neither of these were statistically significant. These results further illustrate the utility of this model in predicting compound effects against several relevant functional endpoints that are consistent with the effects of similar classes of compounds in humans.

Adhesion molecules in lung diseases

The human body possesses highly specialized cellular defense mechanisms that, when activated pathologically, can induce a number of immunologic disorders. For a normal cellular immune response, the following conditions must be fulfilled: (1) accumulation of white blood cells, (2) their diapedesis through the vessel walls of the inflammatory area affected by an injurious agent, and (3) normal cellular effector functions in the tissue. This cascade of inflammatory processes has recently been shown to be regulated by a group of molecules that are termed adhesion molecules and consist of three subfamilies: selectins, the immunoglobulin supergene family, and integrins. The cellular functions influenced by adhesion molecules include, among others, cytotoxic T-cell responses, CD4-dependent activation of B lymphocytes by T lymphocytes, activation of granulocytes and macrophages, phagocytosis of opsonized particles by monocytes, macrophages, and granulocytes, antigen-presenting function of macrophages, their antibody-dependent cytotoxicity, initiation of a respiratory burst by white blood cells, and activation of fibroblasts. Studies performed in recent years have shown that pathogenetically relevant changes in the expression and function of adhesion molecules are involved in a variety of pulmonary diseases. These changes include the accumulation and activation of alveolar macrophages in smokers, experimentally induced bronchial hyperreactivity in bronchial asthma, accumulation of eosinophils in allergic rhinitis, bleomycin-induced pulmonary fibrosis, binding of viruses and bacteria to respiratory mucosa, and various mechanisms of acute damage to pulmonary parenchyma. Though their role in tumor development is still unclear, adhesion molecules are obviously involved in determining the route and organotropism of metastases. Further studies of the function of adhesion molecules in pulmonary diseases will contribute to our understanding of the pathomechanisms of these diseases and, through the development of specific antibodies, may provide attractive new therapeutic approaches to problems for which treatment is not yet available.

Assessment of the in vivo biochemical efficacy of orally active leukotriene biosynthesis inhibitors

In man, the therapeutic effectiveness of specific inhibitors of leukotriene (LT) biosynthesis against allergen-induced bronchoconstriction appears to be related to the in vivo biochemical efficacy of these compounds, as measured by inhibition of whole blood LTB4 generation (upon A23187 stimulus) and, particularly, urinary LTE4 excretion. Accordingly, we have assessed the ability of two clinically documented LT biosynthesis inhibitors, zileuton and MK-886, and the structurally novel 5-lipoxygenase activating protein antagonist, MK-0591, to inhibit the production of these inflammatory arachidonic acid metabolites in laboratory dogs. Zileuton (2 mg/kg) was extremely bioavailable in dogs (> 10 microM plasma concentrations), and inhibited the A23187-induced ex vivo production of LTB4 by venous blood by > 90%, in concordance with its potency in canine blood in vitro (IC50 = 1.1 microM). Despite this degree of inhibition in whole blood, urinary LTE4 excretion was reduced by only 52%, a profile of activity similar to that seen in clinical studies. MK-886 was less well absorbed, with plasma concentrations of 3 microM being achieved only at 25 mg/kg. These levels resulted in < 45% inhibition of LTB4 production, but a significant (p < 0.05) 47% inhibition of urinary LTE4 excretion. MK-0591 was similarly bioavailable (compared with MK-886), but 10-fold more active in vivo as a 2 mg/kg dose resulted in 41-62% inhibition of urinary LTE4 excretion (p < 0.05 vs controls; n = 4, 28). Significant inhibition of ex vivo LTB4 synthesis was also observed at this dose (49%), in accord with peak plasma concentrations of 0.5 microM and an in vitro potency of 0.2-0.4 microM (IC50) in whole blood from these animals. At higher dose (10 mg/kg), MK-0591 inhibited LTE4 excretion by 69%, with 88% inhibition of the LT biosynthetic capacity of whole blood. These data demonstrate that the biochemical efficacy of structurally diverse leukotriene biosynthesis inhibitors can be assessed in vivo in normal laboratory dogs. Such measurements, combined with bioavailability data from other species, may be useful for predicting biochemical activity in man.

The role of 5-lipoxygenase products in preclinical models of asthma

BACKGROUND

The action of 5-lipoxygenase on arachidonic acid generates potent inflammatory mediators that may contribute to the pathophysiology of asthma.

METHODS

Using the potent and selective 5-lipoxygenase inhibitor BI-L-239, we have examined the role of 5-lipoxygenase products in three animal models of asthma.

RESULTS

In vitro BI-L-239 inhibited 5-lipoxygenase product generation from human lung mast cells, alveolar macrophages, and peripheral blood leukocytes with a concentration that would provide 50% inhibition values of 28 to 340 nmol/L. A 36-fold selectivity for immunoreactive leukotriene C4 versus immunoreactive prostaglandin D2 inhibition was demonstrated in mast cells. In anesthetized cynomolgus monkeys, inhaled BI-L-239 provided dose-dependent inhibition of the inhaled Ascaris-induced immunoreactive leukotriene C4 release (maximum, 73%; bronchoalveolar lavage [BAL], 20 minutes), late-phase bronchoconstriction (maximum, 41%; +6 to 8 hours), and neutrophil infiltration (maximum, 63%; BAL, +8 hours). In conscious sheep, inhaled BI-L-239 provided dose-dependent inhibition of the inhaled Ascaris-induced late-phase bronchoconstriction (maximum, 66%; +6 to 8 hours) and increase in airway responsiveness (maximum, 82%; carbachol, +24 hours). The acute bronchoconstriction was shortened, and neutrophil infiltration diminished (maximum, 61%; BAL, +8 hours) in this model. Finally in conscious actively sensitized guinea pigs pretreated with pyrilamine and indomethacin, inhaled BI-L-239 attenuated acute bronchoconstriction (maximum, 80%; +5 to 15 minutes), leukocyte infiltration (58%; BAL, +3 days) and increase in airway responsiveness (100%; methacholine, +3 days) induced by three alternate-day ovalbumin inhalations.

CONCLUSIONS

In conclusion, results in these three animal models indicate that 5-lipoxygenase products may be major contributors to the bronchoconstriction (especially late phase), leukocyte infiltration, and airway hyperresponsiveness that characterize asthma.

Effect of BI-L-239, A-64077 and MK-886 on leukotriene B4 synthesis by chopped guinea pig lung and on antigen-induced tracheal contraction in vitro

The 5-lipoxygenase (5-LO) inhibitors BI-L-239 and A-64077 were compared with the 5-LO translocation inhibitor MK-886 for the ability to inhibit leukotriene B4 (LTB4) biosynthesis by chopped (1 mm3) guinea pig lung. LTB4 synthesis by ovalbumin-sensitized chopped lung tissue was determined after stimulation with either calcium ionophore (A23187) or antigen. With A23187 stimulation, MK-886 was more potent (IC50 = 0.39 +/- 0.23 microM, mean +/- SEM, p < 0.01) than BI-L-239 (IC50 = 2.48 +/- 0.46 microM) or A-64077 (IC50 = 4.68 +/- 0.70 microM) and BI-L-239 was more potent than A64077 (p < 0.02). Thus, the order of potency was MK-886 > BI-L-239 > A-64077 for inhibition of calcium ionophore-induced LTB4 generation. There was no significant differences in potency of the compounds in chopped lung stimulated with antigen: IC50 for LTB4 synthesis by A-64077 = 3.31 +/- 1.70 microM, for BI-L-239 = 9.06 +/- 4.94 microM, and for MK-886 = 13.33 +/- 7.91 microM. The ability of these compounds to inhibit contraction of tracheal tissue from actively sensitized guinea pigs in response to antigen was also determined in the presence of indomethacin (15 micrograms/ml), mepyramine, and atropine (5 micrograms each/ml). Both 5-LO inhibitors inhibited antigen-induced contraction, with IC50 values for BI-L-239 and A-64077 of 1.58 and 4.35 microM respectively. MK-886 was ineffective at inhibiting antigen-induced tracheal contraction in vitro at concentrations up to 30 microM. In summary, these compounds inhibit antigen-induced and A23187-induced leukotriene biosynthesis in guinea pig tissue. These 5-LO inhibitors were similarly effective at inhibiting antigen-induced tracheal contraction where MK-886 was ineffective.

The role of intercellular adhesion molecule-1 in chronic airway inflammation

We have examined the role of intercellular adhesion molecule-1 (ICAM-1) in chronic airway inflammation and airway hyperresponsiveness in a primate model of asthma. Airway cellular composition was assessed by bronchoalveolar lavage (BAL) and airway responsiveness was measured as the bronchoconstrictor response to inhaled methacholine. In animals with chronic airway inflammation (increased BAL eosinophils) and sustained airway hyperresponsiveness, a 7 day dosing scheme with a murine anti-human ICAM-1 monoclonal antibody (R6.5, 2 mg/kg/day; i.v.) did not reduce the existing airway inflammation or airway hyperresponsiveness. In contrast, a similar dosing scheme with dexamethasone (0.2 mg/kg/day, i.m.) was found to significantly reduce both the airway eosinophilia and hyperresponsiveness. However, one week after cessation of dexamethasone treatment, the airway inflammation and hyperresponsiveness returned to pre-treatment levels. In further experiments where animals were first treated with dexamethasone (7 days) followed by a 7 day treatment with R6.5, the reoccurrence of airway inflammation and subsequent increase in airway responsiveness was prevented. We conclude that the efficacy of ICAM-1 is primarily associated with inhibition of the influx of inflammatory cells into the airways and subsequent reduction in airway responsiveness. These data suggest that in lungs with pre-existing inflammation the modulation of ICAM-1 following treatment with glucocorticoids may be a novel and more selective long-term treatment for control of the chronic airway inflammation and hyperresponsiveness associated with bronchial asthma.