Cyclooxygenase isoenzyme localization and mRNA expression in rat lungs

Comparison of different detection methods in quantitative microdensitometry

Quantitative evaluation of immunohistochemical staining has become a focus of attention in research applications and in pathological diagnosis, such as Her-2/neu assessment in mammary carcinoma. Reproducibility of immunostaining techniques and microscopical evaluation are prerequisites for a standardized and reliable quantitation of immunostaining intensity. In the present study, different staining and microscopical techniques, including fluorescence microscopy, epipolarization microscopy of immunogold-silver, and absorbance microdensitometry were compared concerning suitability for quantitative evaluation. We describe a staining procedure using alkaline phosphatase-based immunohistochemistry with the substrate Vector Red and subsequent microdensitometry with a custom-designed absorbance filter. We have characterized linearity of the staining intensity in dependence of development time, antibody concentration, and section thickness by means of artificial standards consisting of agarose blocks into which immunogold- or alkaline phosphatase-conjugated antibodies were incorporated. Applicability of the different techniques was tested by anti-CD45 immunostaining of leukocytes within rat lung tissue detected by immunofluorescence, immunogold-silver epipolarization microscopy, as well as alkaline phosphatase-based Vector Red absorbance or fluorescence measurement. Excellent qualities of Vector Red for quantitative microdensitometric evaluation of staining intensity were particularly obvious for absorbance microscopy. Applicability in paraffin-embedded tissue as well as in cryosections, excellent segmentation, linearity over a wide range, light stability, and feasibility for permanent mounting and for long-term storage are the outstanding features of this technique for use in routine quantitative evaluation.

Cytokine-induced bronchoconstriction in precision-cut lung slices is dependent upon cyclooxygenase-2 and thromboxane receptor activation

Cytokines play an essential role in the regulation of inflammatory responses. The effects of cytokines on lung functions are less well known and their study in vivo is complicated by the attraction of leukocytes to the inflamed sites. Recently the model of precision-cut lung slices was developed, where viable lung slices with an intact microanatomy are taken into culture and where bronchoconstriction can be followed by observing single airways under the microscope. We used this model to study the direct effects of cytokines on airway tonus in the absence of blood-derived leukocytes. Incubation of precision-cut lung slices with a mixture of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and interferon (IFN)-gamma resulted in contraction of airways, which was accompanied by expression of cyclooxygenase (Cox)-2 and thromboxane release into the supernatant. The thromboxane receptor antagonist SQ29548 completely prevented the cytokine-induced bronchoconstriction, whereas the 5-lipoxygenase inhibitor AA681 had no effect on cytokine-induced bronchoconstriction. Preventing the expression of Cox-2 by dexamethasone or blocking Cox-2 activity with the selective Cox-2 inhibitor NS398 attenuated both thromboxane formation and bronchoconstriction. Incubation of lung slices with each of the cytokines alone caused no bronchoconstriction; in fact, IL-1 alone rather dilated the airways. However, simultaneous incubation with TNF and IL-1beta caused a bronchoconstriction that was not further enhanced by IFN-gamma. We conclude that TNF-alpha and IL-1beta synergistically cause bronchoconstriction by induction of Cox-2 and subsequent activation of the thromboxane receptor. Our study raises the possibility that TNF and IL-1 may contribute to bronchospasm during inflammatory lung diseases.

Role of PGE(2) in protease-activated receptor-1, -2 and -4 mediated relaxation in the mouse isolated trachea

1. The potential mediator role of the prostanoid PGE(2) in airway smooth muscle relaxations induced by peptidic and proteolytic activators of PAR-1, PAR-2, PAR-3 and PAR-4 was investigated in carbachol-precontracted mouse isolated tracheal segments. 2. The tethered ligand domain sequences of murine PAR-1 (SFFLRN-NH(2)), PAR-2 (SLIGRL-NH(2)) and PAR-4 (GYPGKF-NH(2)), but not PAR-3 (SFNGGP-NH(2)), induced smooth muscle relaxation that was abolished by the non-selective cyclo-oxygenase (COX) inhibitor, indomethacin. The relative order for mean peak relaxation was SLIGRL-NH(2)>GYPGKF-NH(2) approximately amp; SFFLRN-NH(2)>SFNGGP-NH(2). 3. SFFLRN-NH(2), SLIGRL-NH(2) and GYPGKF-NH(2), but not SFNGGP-NH(2), induced significant PGE(2) release that was abolished by indomethacin. Like that for relaxation, the relative order for mean PGE(2) release was SLIGRL-NH(2)>GYPGKF-NH(2)>SFFLRN-NH(2)>SFNGGP-NH(2). 4. In dose-response studies, SLIGRL-NH(2) induced concentration-dependent increases in PGE(2) release (EC(50)=20.4 microM) and smooth muscle relaxation (EC(50)=15.8 microM). 5. The selective COX-2 inhibitor, nimesulide, but not the COX-1 inhibitor valeryl salicylate, significantly attenuated SLIGRL-NH(2)-induced smooth muscle relaxation and PGE(2) release. 6. Exogenously applied PGE(2) induced potent smooth muscle relaxation (EC(50)=60.3 nM) that was inhibited by the mixed DP/EP(1)/EP(2) prostanoid receptor antagonist, AH6809. SLIGRL-NH(2)-induced relaxation was also significantly inhibited by AH6809. 7. In summary, the results of this study strongly suggest that PAR-mediated relaxation in murine tracheal smooth muscle is dependent on the generation of the spasmolytic prostanoid, PGE(2). PAR-stimulated PGE(2) release appears to be generated preferentially by COX-2 rather than COX-1, and induces relaxation via activation of the EP(2) receptor.

Monocytes recruited into the alveolar air space of mice show a monocytic phenotype but upregulate CD14

The evaluation of monocytes recruited into the alveolar space under both physiological and inflammatory conditions is hampered by difficulties in discriminating these cells from resident alveolar macrophages (rAMs). Using the intravenous injected fluorescent dye PKH26, which accumulated in rAMs without labeling blood leukocytes, we developed a technique that permits the identification, isolation, and functional analysis of monocytes recruited into lung alveoli of mice. Alveolar deposition of murine JE, the homologue of human monocyte chemoattractant protein (MCP)-1 (JE/MCP-1), in mice provoked an alveolar influx of monocytes that were recovered by bronchoalveolar lavage and separated from PKH26-stained rAMs by flow cytometry. Alveolar recruited monocytes showed a blood monocytic phenotype as assessed by cell surface expression of F4/80, CD11a, CD11b, CD18, CD49d, and CD62L. In contrast, CD14 was markedly upregulated on alveolar recruited monocytes together with increased tumor necrosis factor-alpha message, discriminating this monocyte population from peripheral blood monocytes and rAMs. Thus monocytes recruited into the alveolar air space of mice in response to JE/MCP-1 keep phenotypic features of blood monocytes but upregulate CD14 and are "primed" for enhanced responsiveness to endotoxin with increased cytokine expression.

Cyclooxygenase-2 participates in the late phase of airway hyperresponsiveness after ozone exposure in guinea pigs

We examined the role of cyclooxygenase in airway hyperresponsiveness and inflammation after ozone exposure in guinea pigs using a non-selective (indomethacin) and a selective (JTE-522) cyclooxygenase-2 inhibitor. Spontaneously breathing guinea pigs were exposed to ozone (3 ppm) for 2 h after treatment with vehicle, indomethacin (10 mg/kg) or JTE-522 (10 mg/kg). Airway responsiveness to inhaled histamine (PC(200)) and bronchoalveolar lavage were assessed before, immediately and 5 h after ozone exposure. Ozone caused a significant airway hyperresponsiveness immediately after exposure, which persisted after 5 h. Neither JTE-522 nor indomethacin affected airway hyperresponsiveness immediately after ozone exposure, but significantly attenuated airway hyperresponsiveness 5 h after exposure, suggesting that cyclooxygenase-2 may participate in the late phase of airway hyperresponsiveness but not in the early phase. Ozone caused a significant increase in the concentration of prostaglandin E(2) and thromboxane B(2) in bronchoalveolar lavage fluid immediately after exposure, which decreased to the basal level 5 h after exposure. This increase in prostaglandin E(2) and thromboxane B(2) was significantly inhibited by JTE-522. An expression of cyclooxygenase-2 was detected not only after ozone exposure but also before, and there was no difference in the number of cyclooxygenase-2-positive cells at any time point. An exogenously applied thromboxane A(2) mimetic, U-46619 (10(-5) M), induced airway hyperresponsiveness 5 h after inhalation, but not immediately or 3 h after inhalation. These data suggest that cyclooxygenase-2 may be constitutively expressed before ozone exposure in guinea pig airway and may synthesize prostaglandin E(2) and thromboxane A(2) transiently under ozone stimulation and that thromboxane A(2) may, in turn, induce the late phase of airway hyperresponsiveness.

Regulation of cyclooxygenase-1 and -2 expression in human nasal mucosa. Effects of cytokines and dexamethasone

BACKGROUND

Cyclooxygenase (COX) converts arachidonic acid in prostanoids. COX exists in two isoforms, COX-1 is the constitutive whereas COX-2 is the inducible isoform. The regulation of COX-1 and COX-2 expression in nasal mucosa has not been previously reported.

AIM

We studied expression and regulation by cytokines and corticosteroids of COX-1 and COX-2 in human nasal mucosa. Cultured human nasal explants from patients undergoing corrective nasal mucosal resection were examined for COX-1 and COX-2 expression by semiquantitative competitive PCR and Western blot.

METHODS

Explants were incubated with pro-(IFNgamma, IL-1beta, and TNF-alpha) and anti(IL-10) inflammatory cytokines and dexamethasone. The mechanisms which regulate COX-2 mRNA expression were studied using inhibitors of translation (Actinomycin D) and transcription (Cicloheximide).

RESULTS

The baseline expression of COX-2 mRNA was higher than COX-1 mRNA. Once in culture, there was a slight spontaneous up-regulation of COX-1 and a strong COX-2 mRNA and protein up-regulation. The incubation of nasal explants with pro-inflammatory cytokines increased the expression of COX-2 mRNA and protein, from 1 to 24 h of incubation in a dose-related manner. The regulation of these effects occurred at both transcriptional and post-transcriptional levels. Dexamethasone and IL-10 abrogated cytokine-induced COX-2 mRNA and protein expression. Pro-inflammatory cytokines, dexamethasone and IL-10 had no effect on COX-1 mRNA expression.

CONCLUSIONS

As prostanoids have important regulatory effects on the immunologically mediated inflammatory responses, our findings throw some light on the mechanisms that regulate the enzymes which produce these metabolites in the human airway.

Cyclooxygenase-2 expression in inflammatory lung lesions of nonhuman primates

Mammalian cells contain two related but unique isoforms of cyclooxygenase (COX-1 and COX-2). COX-1 is expressed constitutively in a majority of tissues and is involved in the production of prostaglandins (PGs) that modulate normal physiologic functions. COX-2 is inducible by various stimuli and is involved in the production of PGs that modulate physiologic events in development, cell growth, and inflammation. With the exception of peribronchial glands and chondrocytes of peribronchial cartilage, COX-2 is not detectable in the normal lung of nonhuman primates. We evaluated COX-2 expression by immunohistochemical methods in the inflammatory lesions of two cynomolgus monkeys (Macaca fascicularis) with acute severe pneumonia. Both monkeys exhibited acute severe bronchopneumonia; histologically, lung lesions were characterized by infiltration of large numbers of neutrophils and fewer macrophages, mild bronchial epithelial hyperplasia, and slight type-2 pneumocyte hyperplasia. In both monkeys, mild to marked COX-2 immunoreactivity was detected within the cytoplasm of macrophages, bronchial epithelial cells, type-2 pneumocytes, and endothelial cells of blood vessels. No COX-2 immunoreactivity was detectable in the neutrophils that constituted >90% of the inflammatory cells. These observations suggest that in acute inflammatory lung lesions in nonhuman primates 1) COX-2 is induced in the bronchial and alveolar epithelial cells, 2) macrophages are the primary inflammatory cells that exhibit COX-2, and 3) neutrophils do not express COX-2.

Endotoxin priming of the cyclooxygenase-2-thromboxane axis in isolated rat lungs

Enhanced prostanoid generation has been implicated in vascular abnormalities occurring during endotoxemia and sepsis, and the lung is particularly prone to such events. Prostanoids are generated from arachidonic acid (AA) via cyclooxygenase (COX)-1 or -2, both isoenzymes recently demonstrated to be expressed in different lung cell types. Upregulation of COX may underlie the phenomenon that endotoxin [lipopolysaccharide (LPS)]-exposed lungs show markedly enhanced vasoconstrictor responses to secondarily applied stimuli (priming). Isolated rat lungs were perfused with a physiological salt buffer solution in the absence and presence of 1.5% rat plasma and exposed to different concentrations of LPS (1,000 or 10,000 ng/ml) during a 2-h priming period. No change in physiological variables was noted during this period, although enhanced baseline liberation of both thromboxane (Tx) A(2) and PGI(2) as well as of tumor necrosis factor (TNF)-alpha was evident compared with that in control lungs in the absence of LPS. LPS priming caused a significant elevation in AA-induced pulmonary arterial pressure, ventilation pressure, and lung weight gain. Concomitant increased levels of TxA(2) were found in the buffer perfusate. All changes were largely suppressed by three selective, structurally unrelated COX-2 inhibitors (NS-398, DUP-697, and SC-236) in both buffer- and buffer-plasma-perfused lungs. Anti-TNF-alpha neutralizing antibodies were ineffective under conditions of buffer perfusion. In the presence of plasma components, manyfold augmented TNF-alpha generation was noted, and anti-TNF-alpha antibodies significantly suppressed the increase in ventilation pressure but not in the vascular pressor response and lung edema formation. We conclude that the propensity of LPS-primed lungs to respond with enhanced vasoconstriction, edema formation, and bronchoconstriction to a secondarily applied stimulus proceeds nearly exclusively via COX-2 and increased Tx formation, with TNF-alpha generation being involved in the change in bronchomotor reactivity in the presence of plasma constituents. In context with recent immunohistological investigations, LPS-induced upregulation of the COX-2-thromboxane synthase axis in vascular and bronchial smooth muscle cells is suggested to underlie these events.

Cyclooxygenase-2 in human perinatal lung

Cyclooxygenases-1 and -2 are the key enzymes in the conversion of arachidonic acid to prostanoids. Cyclooxygenase-2 (COX-2) takes part both in inflammation and in control of cell growth. COX-2 immunohistochemistry was performed on lung tissues from autopsies, with four groups included: fetuses (n = 4, GA = 16.0 to 32.0 wk), preterm infants (n = 10, GA = 23.0 to 29.9 wk), term infants (n = 6, GA = 38.7 to 42.0 wk), and infants with bronchopulmonary dysplasia (BPD) (n = 4, GA = 28.9 to 30.7 wk). COX-2 staining occurred exclusively in the epithelial cells resembling type II pneumocytes in the alveolae, and in ciliated epithelial cells in the bronchi. In fetuses, moderate intensity alveolar staining was seen in 90-100% cells lining the alveolar epithelium. In preterm infants, high intensity alveolar staining was seen in a scattered pattern. In term infants, the alveolar staining was also scattered, but with a lower proportion of positive cells. In BPD no staining appeared in alveolar epithelial cells. The most intense bronchial staining was found in fetuses and the least intense in term infants; staining was also seen in BPD. COX-2 is present in human perinatal lung from the gestational age of 16 wk, in a changing pattern. We suggest that COX-2 may, in addition to participating in inflammation, also play a developmental role in the perinatal lung.

In situ localization and regulation of thromboxane A(2) synthase in normal and LPS-primed lungs

Thromboxane (Tx) A(2) synthase catalyzes the conversion of prostaglandin H(2) to the unstable metabolite TxA(2), which is a potent mediator of vasoconstriction and bronchoconstriction. The cellular localization of TxA(2) synthase was examined by immunohistochemistry and in situ hybridization in human and rat lung tissues. Bronchial epithelial cells, bronchial smooth muscle cells, peribronchial nerve fibers, single cells of bronchus-associated lymphoid tissue, single cells located in the alveolar septum, and alveolar macrophages exhibited positive immunostaining for TxA(2) synthase protein in lung tissue of both species. In addition, vascular smooth muscle cells of muscular and partially muscular vessels displayed strong (rat) and moderate (human) immunostaining for TxA(2) synthase. In situ hybridization performed in the rat lungs demonstrated TxA(2) synthase mRNA localization in accordance with the immunostaining pattern. Perfusing isolated rat lungs with endotoxin for 1 and 2 h resulted in a marked increase in TxA(2) synthase protein staining intensity in most cell types as measured by quantitative image analysis, whereas the in situ hybridization signal was unchanged. We conclude that the pulmonary distribution of TxA(2) synthase displays close similarity between rat and human lung tissues and matches well with the previously described immunolocalization of cyclooxygenase-1 and cyclooxygenase-2 in this tissue. Endotoxin challenge is suggested to cause a rapid upregulation of TxA(2) synthase at the posttranscriptional level. These data provide a morphological basis for the understanding of the role of TxA(2) in the regulation of lung bronchial and vascular tone and in immunologic events.

High cyclooxygenase 1 (COX-1) and cyclooxygenase 2 (COX-2) contents in mouse lung tumors

Mouse lung tumorigenesis is a convenient model for examining all stages of lung adenocarcinoma (AC) progression. Because enhanced cyclooxygenase 2 (COX-2) expression has been observed in advanced human AC, we investigated the intracellular concentrations of the two cyclooxygenases, cyclooxygenase 1 (COX-1) and COX-2, at different times after carcinogen administration to A/J mice. The concentrations of both proteins were much higher in urethane-induced adenomas and carcinomas compared with control A/J mouse lung tissue (P < 0.03 and P < 0.01 in adenomas and AC, respectively, for COX-1; P < 0.003 and P < 0.004 in adenomas and AC, respectively, for COX-2). Small benign tumors that arose spontaneously in 13-month-old mice also stained for COX-1 and COX-2, showing that this elevated enzyme content does not depend on chemical induction. COX-1 and COX-2 immunostaining was observed in normal bronchiolar and alveolar epithelia, alveolar macrophages and bronchiolar smooth muscle. This is the first report of the cellular distribution of COX-1 and COX-2 in murine lungs and the first in any species to demonstrate their co-localization. COX content in isolated bronchiolar Clara cells, a putative cell of tumor origin, was equal to that found in tumors, suggesting that the high enzyme content in neoplasms is due to their proportionally high concentration of these tumor precursor cells. Different patterns of COX-1 and COX-2 expression were observed in tumors of different growth patterns; only occasional small foci stained in solid adenomas, while most cells in papillary adenomas were immunoreactive. This staining pattern was also seen in adenocarcinomas, but some of the papillary portions also included focally stained and unstained regions. The continued expression during neoplastic progression of these specialized enzymes present in normal cells of tumor origin suggests their function in maintenance of the neoplastic state.

Rat pulmonary cyclooxygenase-2 expression in response to endotoxin challenge: differential regulation in the various types of cells in the lung

Cyclooxygenase (Cox), the key enzyme of prostanoid synthesis, consists of the two isoforms Cox-1 and Cox-2, both recently noted to be constitutively expressed in rat lungs with a distinct profile of cellular distribution. The responsiveness of pulmonary Cox-1 and Cox-2 expression to intravascular endotoxin lipopolysaccharide (LPS) administration was investigated in isolated, ventilated rat lungs, buffer-perfused with or without admixture of rat plasma. Immunohistochemical staining intensity was measured by a previously described method of silver enhancement and epipolarization image analysis. Both the Cox-1 mRNA, quantified in the whole lung homogenate, and the cellular localization of Cox-1 were unchanged in response to LPS. In contrast, time- and dose-dependent up-regulation of Cox-2 mRNA (lung homogenate) occurred, and differential LPS reactivity at the cellular level was observed. Up-regulation of Cox-2 in cell types expressing this enzyme already under baseline conditions was noted in bronchial epithelial cells, bronchial and vascular smooth muscle cells, cells within the BALT and myocytes of the large hilar veins. De novo induction of Cox-2 occurred in endothelial cells and the majority of alveolar macrophages. Down-regulation of Cox-2 was observed in perivascular and peribronchial macrophage-like cells. Moreover, differential impact of plasma components was noted: for the large majority of cells, CD14 surface expression correlated with Cox-2 responsiveness to LPS independent of plasma, whereas the presence of plasma components was a prerequisite for the LPS response in CD14-negative cells. LPS did not provoke physiological changes in the perfused lungs, but markedly enhanced baseline prostanoid generation. We conclude that LPS-induced Cox-2 regulation occurs in a complex, cell-specific manner, which may be relevant for pathogenetic sequelae in septic lung injury and acute respiratory failure.

Increased expression of cyclooxygenase-2 protein in rat lung tumors induced by N-nitrosobis(2-hydroxypropyl)amine

Expression of cyclooxygenase (COX)-2 protein in preneoplastic and neoplastic lung lesions induced by the administration of 2000 ppm of N-nitrosobis(2-hydroxypropyl)amine (BHP) in the drinking water to Wistar male rats, was examined immunohistochemically. The majority of alveolar/bronchiolar adenomas (ADs) and all adenocarcinomas (ADCs) examined, stained positive or strongly positive for COX-2. In contrast, only a minority of alveolar/bronchiolar hyperplasias demonstrated immunoreactivity and half of the squamous cell carcinomas examined, were only weakly positive. Western blotting analysis also revealed expression of COX-2 protein in the resected ADs and ADCs. These results clearly indicate up-regulated expression of COX-2 in lung neoplastic lesions, particularly ADs and ADCs, induced by BHP in rats.

Prostaglandin H synthase 2 expression in airway cells from patients with asthma and chronic obstructive pulmonary disease

Products of the prostaglandin H synthase (PGHS) metabolic pathway are thought to play a role in the pathogenesis of asthma. We determined the level of expression of the constitutive (PGHS-1) and inducible (PGHS-2) isoforms of the enzyme in induced sputum and bronchial biopsies of patients with asthma, patients with chronic obstructive pulmonary disease (COPD), and unaffected control subjects by immunocyto- and immunohistochemistry. Immunoreactivity for PGHS-2 was significantly greater in the induced sputum of patients with asthma and patients with COPD compared with unaffected control subjects. The level of PGHS-2 was greater in asthma than in COPD. Immunoreactivity for PGHS-1 increased in cells in the induced sputum of patients with asthma and patients with COPD compared with that of unaffected control subjects. Immunostained cells included macrophages, eosinophils, and neutrophils. Greater PGHS-2 immunoreactivity was seen in the submucosal inflammatory infiltrate and in the airway epithelium of patients with asthma compared with unaffected control subjects. In summary, we demonstrate an induction of PGHS-2 in asthma, suggesting increased formation of prostanoids, which may contribute to the inflammatory process.

Basic biology and clinical application of specific cyclooxygenase-2 inhibitors

In summary, COX-2 is a highly regulated gene product that catalyzes the local production of PGs in pathologic and physiologic situations (Figure 1). It is clear that COX-2 is the isoform responsible for production of the PGs that mediate inflammation, pain, and fever. However, the role for COX-2 in normal physiology is still being defined. Specific COX-2 inhibitors represent a significant conceptual advance in therapy for patients with arthritis. Although there is no expectation of superior efficacy, clinical trials suggest that efficacy will be comparable with that of nonselective NSAIDs. Clinical trials demonstrate the potential for clinically meaningful reductions in the incidence of the most serious GI complications found with nonselective NSAIDs, i.e., ulcer, perforation, and GI bleeding. Over the next several years, treatment of large numbers of patients with specific COX-2 inhibitors will help to define the biology of COX-2. The magnitude of this advance in the therapy of rheumatic diseases is yet to be accurately determined, but the development of specific COX-2 inhibitors may afford significant new treatment options for many patients.