Inflammatory mediators and cellular infiltration of the lungs in a guinea pig model of the late asthmatic reaction

Epithelium-dependent modulation of responsiveness of airways from caveolin-1 knockout mice is mediated through cyclooxygenase-2 and 5-lipoxygenase

BACKGROUND AND PURPOSE

Acute silencing of caveolin-1 (Cav-1) modulates receptor-mediated contraction of airway smooth muscle. Moreover, COX-2- and 5-lipoxygenase (5-LO)-derived prostaglandin and leukotriene biosynthesis can influence smooth muscle reactivity. COX-2 half-life can be prolonged through association with Cav-1. We suggested that lack of Cav-1 modulated levels of COX-2 which in turn modulated tracheal contraction, when arachidonic acid signalling was disturbed by inhibition of COX-2.

EXPERIMENTAL APPROACH

Using tracheal rings from Cav-1 knockout (KO) and wild-type mice (B6129SF2/J), we measured isometric contractions to methacholine and used PCR, immunoblotting and immunohistology to monitor expression of relevant proteins.

KEY RESULTS

Tracheal rings from Cav-1 KO and wild-type mice exhibited similar responses, but the COX-2 inhibitor, indomethacin, increased responses of tracheal rings from Cav-1 KO mice to methacholine. The phospholipase A₂ inhibitor, eicosatetraynoic acid, which inhibits formation of both COX-2 and 5-LO metabolites, had no effect on wild-type or Cav-1 KO tissues. Indomethacin-mediated hyperreactivity was ablated by the LTD₄ receptor antagonist (montelukast) and 5-LO inhibitor (zileuton). The potentiating effect of indomethacin on Cav-1 KO responses to methacholine was blocked by epithelial denudation. Immunoprecipitation showed that COX-2 binds Cav-1 in wild-type lungs. Immunoblotting and qPCR revealed elevated levels of COX-2 and 5-LO protein, but not COX-1, in Cav-1 KO tracheas, a feature that was prevented by removal of the epithelium.

CONCLUSION AND IMPLICATIONS

The indomethacin-induced hypercontractility observed in Cav-1 KO tracheas was linked to increased expression of COX-2 and 5-LO, which probably enhanced arachidonic acid shunting and generation of pro-contractile leukotrienes when COX-2 was inhibited.

A small molecule, orally active, alpha4beta1/alpha4beta7 dual antagonist reduces leukocyte infiltration and airway hyper-responsiveness in an experimental model of allergic asthma in Brown Norway rats

alpha(4)beta(1) and alpha(4)beta(7) integrins are preferentially expressed on eosinophils and mononuclear leukocytes and play critical roles in their recruitment to inflammatory sites. We investigated the effects of TR14035, a small molecule, alpha(4)beta(1)/alpha(4)beta(7) dual antagonist, in a rat model of allergic asthma. Actively sensitized rats were challenged with aerosol antigen or saline on day 21, and the responses evaluated 24 and 48-h later. TR14035 (3 mg kg(-1), p.o.) was given 1-h before and 4-h after antigen or saline challenge. Airway hyper-responsiveness to intravenous 5-hydroxytryptamine was suppressed in TR14035-treated rats. Eosinophil, mononuclear cell and neutrophil counts, and eosinophil peroxidase and protein content in the bronchoalveolar lavage fluid (BALF) were decreased in TR14035-treated rats. Histological study showed a marked reduction of lung inflammatory lesions by TR14035. At 24-h postchallenge, antigen-induced lung interleukin (IL)-5 mRNA upregulation was suppressed in TR14035-treated rats. By contrast, IL-4 levels in BALF were not significantly affected by TR14035 treatment. IL-4 selectively upregulates vascular cell adhesion molecule-1 (VCAM-1), which is the main endothelial ligand of alpha(4) integrins. Intravital microscopy within the rat mesenteric microcirculation showed that 24-h exposure to 1 microg per rat of IL-4 induced a significant increase in leukocyte rolling flux, adhesion and emigration. These responses were decreased by 48, 100 and 99%, respectively in animals treated with TR14035. In conclusion, TR14035, by acting on alpha(4)beta(1) and alpha(4)beta(7) integrins, is an orally active inhibitor of airway leukocyte recruitment and hyper-responsiveness in animal models with potential interest for the treatment of asthma.

Differential Muc2 and Muc5ac secretion by stimulated guinea pig tracheal epithelial cells in vitro

BACKGROUND

Mucus overproduction is a characteristic of inflammatory pulmonary diseases including asthma, chronic bronchitis, and cystic fibrosis. Expression of two mucin genes, MUC2 and MUC5AC, and their protein products (mucins), is modulated in certain disease states. Understanding the signaling mechanisms that regulate the production and secretion of these major mucus components may contribute significantly to development of effective therapies to modify their expression in inflamed airways.

METHODS

To study the differential expression of Muc2 and Muc5ac, a novel monoclonal antibody recognizing guinea pig Muc2 and a commercially-available antibody against human MUC5AC were optimized for recognition of specific guinea pig mucins by enzyme-linked immunosorbent assay (ELISA), Western blot, and immunohistochemistry (IHC). These antibodies were then used to analyze expression of Muc2 and another mucin subtype (likely Muc5ac) in guinea pig tracheal epithelial (GPTE) cells stimulated with a mixture of pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta), and interferon- gamma (IFN-gamma)].

RESULTS

The anti-Muc2 (C4) and anti-MUC5AC (45M1) monoclonal antibodies specifically recognized proteins located in Muc2-dominant small intestinal and Muc5ac-dominant stomach mucosae, respectively, in both Western and ELISA experimental protocols. IHC protocols confirmed that C4 recognizes murine small intestine mucosal proteins while 45M1 does not react. C4 and 45M1 also stained specific epithelial cells in guinea pig lung sections. In the resting state, Muc2 was recognized as a highly expressed intracellular mucin in GPTE cells in vitro. Following cytokine exposure, secretion of Muc2, but not the mucin recognized by the 45M1 antibody (likely Muc5ac), was increased from the GPTE cells, with a concomitant increase in intracellular expression of both mucins.

CONCLUSION

Given the tissue specificity in IHC and the differential hybridization to high molecular weight proteins by Western blot, we conclude that the antibodies used in this study can recognize specific mucin subtypes in guinea pig airway epithelium and in proteins from GPTE cells. In addition, Muc2 is highly expressed constitutively, modulated by inflammation, and secreted differentially (as compared to Muc5ac) in GPTE cells. This finding contrasts with expression patterns in the airway epithelium of a variety of mammalian species in which only Muc5ac predominates.

T-cell trafficking in asthma: lipid mediators grease the way

Recruitment of T cells to the airways is crucial in the pathogenesis of asthma, and it is thought to be mediated mainly by peptide chemokines. By contrast, lipid mediators such as leukotrienes and prostaglandins have classically been thought to contribute to asthma pathogenesis by other mechanisms. However, as we discuss here, the recent molecular identification of leukotriene and prostaglandin receptors, as well as the generation of mice that are genetically deficient in them, has revealed that two of these lipids - leukotriene B(4) and prostaglandin D(2) - also direct T-cell migration and seem to cooperate with chemokines in a non-redundant, sequential manner to recruit T cells to the airways in asthma.

The DP receptor, allergic inflammation and asthma

Prostaglandin (PG) D(2) is the major cyclooxygenase metabolite of arachidonic acid produced by mast cells in response to allergen in diseases, such as asthma, atopic dermatitis, allergic rhinitis and allergic conjunctivitis. However, whether PGD(2) regulates allergic process per se, and, if so, whether it facilitates or down-regulates the disease process has remained unknown. PGD(2) exerts its actions by binding to two types of specific cell surface receptor. One is DP (the PGD receptor) and the other is chemoattractant receptor-homologous molecule expressed on Th2. Between the two, the DP receptor has been better characterized since its cDNA cloning in 1994, and novel class of DP antagonists have been and are being developed. Furthermore, mice deficient in DP were generated and have been subjected to several models of allergic diseases to reveal the role of PGD(2) in allergy. In this article, we summarize these findings and provide an overview of the current status of the DP receptor research to discuss the therapeutic potential of modulating the PGD(2)-DP pathway in allergic diseases.

Enhanced expression of mucin genes in a guinea pig model of allergic asthma

The ovalbumin (OVA)-sensitized guinea pig is often used as an animal model of asthma and airway hyperreactivity. A characteristic lesion of asthma is excessive production of mucin in the airways. Mechanistic studies of this lesion in guinea pigs have been limited due to lack of mucin gene probes for this species. The aim of the present study was to clone the cDNAs encoding two major airway mucins (Muc2 and Muc5ac) from the guinea pig, and investigate mucin gene expression in lungs of sensitized animals in response to antigen challenge. We isolated and sequenced two cDNA fragments coding for the sequences located within the carboxyl-terminal cysteine-rich region of guinea pig Muc2 and Muc5ac mucins. Comparison of cloned cDNAs with those from other species revealed high degrees of sequence identity and conservation of all cysteine residues in deduced primary sequences. Based on the resultant sequence information, we also designed oligonucleotide primers for specific detection of guinea-pig Muc2 and Muc5ac steady-state mRNA levels via reverse transcriptase/ polymerase chain reaction (RT-PCR). Levels of both Muc2 and Muc5ac mRNA in lungs of OVA-sensitized guinea pigs increased significantly by 30 min after an acute exposure to 0.3% OVA. In addition, levels of eotaxin mRNA also increased in these tissues, but the increases were not significant until 2 h after challenge. Correspondingly, the number of eosinophils in bronchoalveolar lavage fluid did not increase until 4 h postchallenge. Results of these studies suggest that the OVA-sensitized guinea pig responds to allergic challenge with enhanced expression of genes (e.g., eotaxin, Muc2, and Muc5ac) that likely play a role in increased airway inflammation and mucin overproduction, and enhanced mucin gene expression appears to occur before eosinophil infiltration.

Acute effects of prostaglandin D2 to induce airflow obstruction and airway microvascular leakage in guinea pigs: role of thromboxane A2 receptors

BACKGROUND

Although prostaglandin D2 (PGD2), a mast cell-derived inflammatory mediator, may trigger allergic airway inflammation, its potency and the mechanism by which it induces airway microvascular leakage, a component of airway inflammation, is not clear.

OBJECTIVE

We wanted to evaluate the relative potency of PGD2 to cause microvascular leakage as compared to airflow obstruction, because both responses were shown to occur simultaneously in allergic airway diseases such as asthma. The role of thromboxane A2 receptors (TP receptors) in inducing these airway responses was also examined.

METHODS

Anesthetized and mechanically ventilated guinea pigs were given i.v. Evans blue dye (EB dye) and, 1 min later, PGD2 (30, 100, 300 or 1,000 nmol/kg). For comparison, the effect of 150 nmol/kg histamine or 2 nmol/kg leukotriene D4 (LTD4) was also examined. Lung resistance (R(L)) was measured for 6 min (or 25 min for selected animals) and the lungs were removed to calculate the amount of extravasated EB dye into the airways as a marker of leakage. In some of the animals, specific TP receptor antagonists, S-1452 (10 microg/kg) or ONO-3708 (10 mg/kg), or a thromboxane A2 synthase inhibitor, OKY-046 (30 mg/kg), was pretreated before giving PGD2.

RESULTS

Injection of PGD2 produced an immediate and dose-dependent increase in RL (peaking within 1 min), which was significant at all doses studied. At 1,000 nmol/kg, PGD2 induced a later increase in R(L), starting at 3 min and reaching a second peak at 8 min. By contrast, only PGD2 at doses of 300 and 1,000 nmol/kg produced a significant increase in EB dye extravasation. The relative potency of 1,000 nmol/kg PGD2 to induce leakage as compared to airflow obstruction was comparable to histamine at most of airway levels, but less than LTD4. Both responses caused by PGD2 were completely abolished by S-1452 and ONO-3708, but not by OKY-046.

CONCLUSION

PGD2 may induce airway microvascular leakage by directly stimulating TP receptors without generating TXA2 in guinea pigs. Microvascular leakage may play a role in the development of allergic airway inflammation caused by PGD2.

Histamine induces exocytosis and IL-6 production from human lung macrophages through interaction with H1 receptors

Increasing evidence suggests that a continuous release of histamine from mast cells occurs in the airways of asthmatic patients and that histamine may modulate functions of other inflammatory cells such as macrophages. In the present study histamine (10(-9)-10(-6) M) increased in a concentration-dependent fashion the basal release of beta-glucuronidase (EC(50) = 8.2 +/- 3.5 x 10(-9) M) and IL-6 (EC(50) = 9.3 +/- 2.9 x 10(-8) M) from human lung macrophages. Enhancement of beta-glucuronidase release induced by histamine was evident after 30 min and peaked at 90 min, whereas that of IL-6 required 2-6 h of incubation. These effects were reproduced by the H(1) agonist (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptane carboxamide but not by the H(2) agonist dimaprit. Furthermore, histamine induced a concentration-dependent increase of intracellular Ca(2+) concentrations ([Ca(2+)](i)) that followed three types of response, one characterized by a rapid increase, a second in which [Ca(2+)](i) displays a slow but progressive increase, and a third characterized by an oscillatory pattern. Histamine-induced beta-glucuronidase and IL-6 release and [Ca(2+)](i) elevation were inhibited by the selective H(1) antagonist fexofenadine (10(-7)-10(-4) M), but not by the H(2) antagonist ranitidine. Inhibition of histamine-induced beta-glucuronidase and IL-6 release by fexofenadine was concentration dependent and displayed the characteristics of a competitive antagonism (K(d) = 89 nM). These data demonstrate that histamine induces exocytosis and IL-6 production from human macrophages by activating H(1) receptor and by increasing [Ca(2+)](i) and they suggest that histamine may play a relevant role in the long-term sustainment of allergic inflammation in the airways.

Prostaglandin D2 as a mediator of allergic asthma

Allergic asthma is caused by the aberrant expansion in the lung of T helper cells that produce type 2 (TH2) cytokines and is characterized by infiltration of eosinophils and bronchial hyperreactivity. This disease is often triggered by mast cells activated by immunoglobulin E (IgE)-mediated allergic challenge. Activated mast cells release various chemical mediators, including prostaglandin D2 (PGD2), whose role in allergic asthma has now been investigated by the generation of mice deficient in the PGD receptor (DP). Sensitization and aerosol challenge of the homozygous mutant (DP-/-) mice with ovalbumin (OVA) induced increases in the serum concentration of IgE similar to those in wild-type mice subjected to this model of asthma. However, the concentrations of TH2 cytokines and the extent of lymphocyte accumulation in the lung of OVA-challenged DP-/- mice were greatly reduced compared with those in wild-type animals. Moreover, DP-/- mice showed only marginal infiltration of eosinophils and failed to develop airway hyperreactivity. Thus, PGD2 functions as a mast cell-derived mediator to trigger asthmatic responses.

Selective inflammatory response induced by intratracheal and intravenous administration of poly-L-arginine in guinea pig lungs

Major basic protein (MBP) is a cationic protein found in eosinophil granules that was postulated to participate in the pathogenesis of bronchial asthma. Recently, it has been demonstrated that MBP level in serum or bronchoalveolar lavage (BAL) fluid was correlated with bronchial hyperresponsiveness (BHR) in asthmatics. A number a studies have established that MBP actions could be mimicked by synthetic polycations as poly-L-arginine. In this study, we investigated the effects of intratracheal and intravenous administration of poly-L-arginine on lung inflammatory response development. The intratracheal injection of poly-L-arginine at the doses of 1, 10, 100 nmol/animal increased the number of eosinophils (up to 3.2 fold) and neutrophils (up to 12 fold) in BAL fluid. Eosinophil and neutrophil infiltration was reversed by 88% and 67% respectively following low molecular weight heparin treatment (500 microg/animal). The intravenous injection of increasing doses of poly-L-arginine (1, 10, 100, 500 nmol/animal) increased the number of eosinophils (up to 2.7 fold) but not neutrophil infiltration in guinea pig lungs. Eosinophil infiltration was reversed by 87% following low molecular weight heparin treatment (1.5 mg/animal). Intratracheal treatment with poly-L-arginine (100 nmol/animal) produced an important increase of beta-glucuronidase, histamine, eosinophil peroxidase (EPO) and albumin levels in BAL fluid, whereas the intravenous treatment (500 nmol/animal) did not. These results show that the route of administration of poly-L-arginine greatly influences its effect on inflammatory cell recruitment since both administration routes elicited eosinophil migration but only the intratracheal route stimulated the migration of neutrophils. Moreover, poly-L-arginine appeared to induce other inflammatory responses since it increased beta-glucuronidase, histamine, EPO and albumin levels in BAL fluid following intratracheal treatment. These results also showed that low molecular weight heparin significantly blocks the inflammatory responses elicited by poly-L-arginine.

Human mast cell chymase induces the accumulation of neutrophils, eosinophils and other inflammatory cells in vivo

The roles of chymase in acute allergic responses are not clear, despite the relative abundance of this serine proteinase in the secretory granules of human mast cells. We have isolated chymase to high purity from human skin tissue by heparin-agarose affinity chromatography and Sephacryl S-200 gel filtration procedures, and have investigated the ability of human mast cell chymase to stimulate cell accumulation following injection into laboratory animals. Injection of chymase provoked marked neutrophilia and eosinophilia in the skin of Dunkin Hartley guinea-pigs. Compared with saline injected control animals, there were some 60 fold more neutrophils and 12 fold more eosinophils present at the injection site. Following injection of chymase into the peritoneum of BALB/c mice, there were up to 700 fold more neutrophils. 21 fold more eosinophils, 19 fold more lymphocytes and 7 fold more macrophages recovered than from saline injected controls at 16 h. Doses of chymase as low as 5 ng (1.7 x 10(-13) mole) stimulated an inflammatory infiltrate, and significant neutrophilia was elicited within 3 h. The chymase induced cell accumulation in both the guinea-pig and mouse models was dependent on an intact catalytic site, being reduced by co-injection of proteinase inhibitors or heat inactivation of the enzyme. Co-injection of histamine or heparin significantly reduced the chymase induced neutrophil accumulation, whereas neither histamine nor heparin by themselves had any effect on the accumulation of nucleated cells. No synergistic or antagonist interactions between chymase and tryptase were observed when these two major mast cell proteinases were co-injected into the mouse peritoneum. Our findings suggest that chymase may provide an potent stimulus for inflammatory cell recruitment following mast cell activation.

Roles of adhesion molecules ICAM-1 and alpha4 integrin in antigen-induced changes in microvascular permeability associated with lung inflammation in sensitized brown Norway rats

Increased microvascular permeability and mucosal edema are pathological features of airway inflammation in asthma. In this study, we investigated the characteristics of the edema response occurring in a model of antigen-induced lung inflammation in sensitized brown Norway rats and examined the effects of monoclonal antibodies (mAbs) to adhesion molecules on this response. Ovalbumin (OA) challenge-induced increases in lung permeability were determined by the leakage of 125I-labeled bovine serum albumin (BSA) into the extravascular tissues of the lungs 24 h after challenge in animals intravenously injected (prechallenge) with this tracer. Inflammatory cell infiltration into the alveolar space was determined by bronchoalveolar lavage (BAL). Mean extravascular plasma volume in the lung increased 233% as compared with control (P < 0.005) at 24 h and increased to 517% by 72 h. The 24-h edema response was completely inhibited by two oral doses (0.1 mg/kg) of dexamethasone 1 h before, and 7 h after, challenge. Intraperitoneal administration of the anti-rat ICAM-1 mAb 1A29, or anti-rat alpha4 integrin mAb TA-2 (2 mg/kg at 12 and 1 h before, and 7 h after, antigen challenge), significantly suppressed eosinophil infiltration into the alveolar space without inhibiting the enhanced microvascular leakage and lung edema. Determination of plasma antibody concentrations by ELISA of mouse IgG1 indicated that sufficient concentrations of the appropriate mAb were present to block alpha4- or ICAM-1-dependent adhesion. The results suggest that increases in microvascular permeability and plasma leakage occurred independently of eosinophil accumulation.